Multilattice sampling strategies for region of interest dynamic MRI.

PubMed

Rilling, Gabriel; Tao, Yuehui; Marshall, Ian; Davies, Mike E

2013-08-01

A multilattice sampling approach is proposed for dynamic MRI with Cartesian trajectories. It relies on the use of sampling patterns composed of several different lattices and exploits an image model where only some parts of the image are dynamic, whereas the rest is assumed static. Given the parameters of such an image model, the methodology followed for the design of a multilattice sampling pattern adapted to the model is described. The multi-lattice approach is compared to single-lattice sampling, as used by traditional acceleration methods such as UNFOLD (UNaliasing by Fourier-Encoding the Overlaps using the temporal Dimension) or k-t BLAST, and random sampling used by modern compressed sensing-based methods. On the considered image model, it allows more flexibility and higher accelerations than lattice sampling and better performance than random sampling. The method is illustrated on a phase-contrast carotid blood velocity mapping MR experiment. Combining the multilattice approach with the KEYHOLE technique allows up to 12× acceleration factors. Simulation and in vivo undersampling results validate the method. Compared to lattice and random sampling, multilattice sampling provides significant gains at high acceleration factors. © 2012 Wiley Periodicals, Inc.

Progress in lattice gauge theory

DOE Office of Scientific and Technical Information (OSTI.GOV)

Creutz, M.

1983-01-01

These lectures first provide an overview of the current status of lattice gauge theory calculations. They then review some technical points on group integration, gauge fixing, and order parameters. Various Monte Carlo algorithms are discussed. Finally, alternatives to the Wilson action are considered in the context of universality for the continuum limit. 41 references.

Progressive slowing down of spin fluctuations in underdoped LaFeAsO1-xFx

NASA Astrophysics Data System (ADS)

Hammerath, F.; Gräfe, U.; Kühne, T.; Kühne, H.; Kuhns, P. L.; Reyes, A. P.; Lang, G.; Wurmehl, S.; Büchner, B.; Carretta, P.; Grafe, H.-J.

2013-09-01

The evolution of low-energy spin dynamics in the iron-based superconductor LaFeAsO1-xFx was studied over a broad doping, temperature, and magnetic field range (x= 0-0.15, T≤ 480 K, μ0H≤ 30 T) by means of 75As nuclear magnetic resonance. An enhanced spin-lattice relaxation rate divided by temperature (T1T)-1 in underdoped superconducting samples (x= 0.045, 0.05, and 0.075) suggests the presence of antiferromagnetic spin fluctuations, which are strongly reduced in optimally doped (x=0.10) and completely absent in overdoped (x=0.15) samples. In contrast to previous analysis, Curie-Weiss fits are shown to be insufficient to describe the data over the whole temperature range. Instead, a Bloembergen-Purcell-Pound (BPP) model is used to describe the occurrence of a peak in (T1T)-1 clearly above the superconducting transition, reflecting a progressive slowing down of the spin fluctuations down to the superconducting phase transition.

Progress towards an electron electric dipole moment search in Europium-Barium Titanates

NASA Astrophysics Data System (ADS)

Eckel, Stephen; Sushkov, Alexander; Lamoreaux, Steven

2012-06-01

We report on recent progress on a search for the electron's electric dipole moment (eEDM) using solid- state Eu0.5Ba0.5TiO3. This material has many desirable properties including ferroelectricity below 200 K and paramagnetism above 1.8 K. When the sample has a non-zero electric polarization, the seven unpaired 4f electrons of the Eu^2+ ions in the lattice feel a large effective electric field of order 10 MV/cm in the direction of the polarization. This causes the electron spins to align with the electric polarization and generate a magnetization, which is measured using DC SQUID magnetometers. We will detail measurements of systematic effects along with recent results toward a measurement of the eEDM.

Progress Report for the Joint Services Electronic Program for the Period April 1, 1989 through March 31, 1990 (Coordinated Science Laboratory, University of Illinois at Urbana-Champaign)

DTIC Science & Technology

1990-06-30

since the projected ion range is of the order of lattice constants. Thus, we have extended our thermal-dopant incorporation model and have developed...bombardment results in residual lattice damage, which degrades electrical and optical properties. Obviously, at sufficiently high acceleration energies...understand the details of collisional lattice dynamics and ion-induced defect for- mation and annihilation. In addition, the simulations are providing, for

Lattice QCD and the unitarity triangle

DOE Office of Scientific and Technical Information (OSTI.GOV)

Andreas S Kronfeld

2001-12-03

Theoretical and computational advances in lattice calculations are reviewed, with focus on examples relevant to the unitarity triangle of the CKM matrix. Recent progress in semi-leptonic form factors for B {yields} {pi}/v and B {yields} D*lv, as well as the parameter {zeta} in B{sup 0}-{bar B}{sup 0} mixing, are highlighted.

BSM Kaon Mixing at the Physical Point

NASA Astrophysics Data System (ADS)

Boyle, Peter; Garron, Nicolas; Kettle, Julia; Khamseh, Ava; Tsang, Justus Tobias

2018-03-01

We present a progress update on the RBC-UKQCD calculation of beyond the standard model (BSM) kaon mixing matrix elements at the physical point. Simulations are performed using 2+1 flavour domain wall lattice QCD with the Iwasaki gauge action at 3 lattice spacings and with pion masses ranging from 430 MeV to the physical pion mass.

Multicanonical hybrid Monte Carlo algorithm: Boosting simulations of compact QED

NASA Astrophysics Data System (ADS)

Arnold, G.; Schilling, K.; Lippert, Th.

1999-03-01

We demonstrate that substantial progress can be achieved in the study of the phase structure of four-dimensional compact QED by a joint use of hybrid Monte Carlo and multicanonical algorithms through an efficient parallel implementation. This is borne out by the observation of considerable speedup of tunnelling between the metastable states, close to the phase transition, on the Wilson line. We estimate that the creation of adequate samples (with order 100 flip-flops) becomes a matter of half a year's run time at 2 Gflops sustained performance for lattices of size up to 244.

The Abelian Higgs model on Optical Lattice?

NASA Astrophysics Data System (ADS)

Meurice, Yannick; Tsai, Shan-Wen; Bazavov, Alexei; Zhang, Jin

2015-03-01

We study the Lattice Gauge Theory of the U(1)-Higgs model in 1+1 dimensions in the strongly coupled regime. We discuss the plaquette corrections to the effective theory where link variables are integrated out. We discuss matching with the second-order perturbation theory effective Hamiltonian for various Bose-Hubbard models. This correspondence can be exploited for building a lattice gauge theory simulator on optical lattices. We propose to implement the quantum rotors which appear in the Hamiltonian formulation using Bose mixtures or p-orbitals. Recent progress on magnetic effects in 2+1 dimensions will be discussed. Supported by the Army Research Office of the Department of Defense under Award Number W911NF-13-1-0119.

Visual sensitivity to spatially sampled modulation in human observers

NASA Technical Reports Server (NTRS)

Mulligan, Jeffrey B.; Macleod, Donald I. A.

1991-01-01

Thresholds were measured for detecting spatial luminance modulation in regular lattices of visually discrete dots. Thresholds for modulation of a lattice are generally higher than the corresponding threshold for modulation of a continuous field, and the size of the threshold elevation, which depends on the spacing of the lattice elements, can be as large as a one log unit. The largest threshold elevations are seen when the sample spacing is 12 min arc or greater. Theories based on response compression cannot explain the further observation that the threshold elevations due to spatial sampling are also dependent on modulation frequency: the greatest elevations occur with higher modulation frequencies. The idea that this is due to masking of the modulation frequency by the spatial frequencies in the sampling lattice is considered.

Structural and Morphological Evaluation of Nano-Sized MoSi2 Powder Produced by Mechanical Milling

NASA Astrophysics Data System (ADS)

Sameezadeh, Mahmood; Farhangi, Hassan; Emamy, Masoud

Nano-sized intermetallic powders have received great attention owing to their property advantages over conventional micro-sized counterparts. In the present study nano-sized MoSi2 powder has been produced successfully from commercially available MoSi2 (3 μm) by a mechanical milling process carried out for a period of 100 hours. The effects of milling time on size and morphology of the powders were studied by SEM and TEM and image analyzing system. The results indicate that the as-received micrometric powder with a wide size distribution of irregular shaped morphology changes to a narrow size distribution of nearly equiaxed particles with the progress of attrition milling up to 100 h, reaching an average particle size of 71 nm. Structural evolution of milled samples was characterized by XRD to determine the crystallite size and lattice microstrain using Williamson-Hall method. According to the results, the crystallite size of the powders decreases continuously down to 23 nm with increasing milling time up to 100 h and this size refinement is more rapid at the early stages of the milling process. On the other hand, the lattice strain increases considerably with milling up to 65 h and further milling causes no significant changes of lattice strain.

Mesoscopic structural phase progression in photo-excited VO 2 revealed by time-resolved x-ray diffraction microscopy

DOE PAGES

Zhu, Yi; Cai, Zhonghou; Chen, Pice; ...

2016-02-26

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase seperated regions. The ability to simultanousely track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of- the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO 2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation ismore » initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO 2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, which is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO 2. Lastly, the direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.« less

Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy

NASA Astrophysics Data System (ADS)

Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J.; Jung, Il Woong; Walko, Donald A.; Dufresne, Eric M.; Jeong, Jaewoo; Samant, Mahesh G.; Parkin, Stuart S. P.; Freeland, John W.; Evans, Paul G.; Wen, Haidan

2016-02-01

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

Mesoscopic structural phase progression in photo-excited VO2 revealed by time-resolved x-ray diffraction microscopy.

PubMed

Zhu, Yi; Cai, Zhonghou; Chen, Pice; Zhang, Qingteng; Highland, Matthew J; Jung, Il Woong; Walko, Donald A; Dufresne, Eric M; Jeong, Jaewoo; Samant, Mahesh G; Parkin, Stuart S P; Freeland, John W; Evans, Paul G; Wen, Haidan

2016-02-26

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase separated regions. The ability to simultaneously track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of-the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation is initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, and is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO2. The direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.

Progression in structural, magnetic and electrical properties of La-doped group IV elements

NASA Astrophysics Data System (ADS)

Deepapriya, S.; Annie Vinosha, P.; Rodney, John D.; Jerome Das, S.

2018-04-01

Progression of group IV elements such as zinc ferrite (ZnFe2O4), cobalt ferrite (CoFe2O4) was synthesized by doping lanthanum (La), via adopting a facile co-precipitation method. Doping hefty rare earth ion in spinel structure can amend to the physical properties of the lattice, which can be used in the enhancement of magnetic and electrical properties of the as-synthesized nanomaterial, it is vital to metamorphose and optimize its micro structural and magnetic features. The structural properties of the samples was analysed by powder X-ray diffraction (XRD), Fourier transform infrared (FTIR), Transmission electron microscopy (TEM) and UV-visible spectral analysis (UV-vis) reveals the optical property and optical band gap. The magnetic properties were evaluated using a vibrating sample magnetometer (VSM), the presence of functional group was confirmed by FTIR. XRD analyses elucidates that the synthesized samples zinc and cobalt had a spinel structure. From TEM analyses the morphology and diameter of the particle was observed. The substituted rare earth ions in Zinc ferrite inhibit the grain growth of the materials in an efficient manner compared with that of the Cobalt ferrite.

An orthogonal oriented quadrature hexagonal image pyramid

NASA Technical Reports Server (NTRS)

Watson, Andrew B.; Ahumada, Albert J., Jr.

1987-01-01

An image pyramid has been developed with basis functions that are orthogonal, self-similar, and localized in space, spatial frequency, orientation, and phase. The pyramid operates on a hexagonal sample lattice. The set of seven basis functions consist of three even high-pass kernels, three odd high-pass kernels, and one low-pass kernel. The three even kernels are identified when rotated by 60 or 120 deg, and likewise for the odd. The seven basis functions occupy a point and a hexagon of six nearest neighbors on a hexagonal sample lattice. At the lowest level of the pyramid, the input lattice is the image sample lattice. At each higher level, the input lattice is provided by the low-pass coefficients computed at the previous level. At each level, the output is subsampled in such a way as to yield a new hexagonal lattice with a spacing sq rt 7 larger than the previous level, so that the number of coefficients is reduced by a factor of 7 at each level. The relationship between this image code and the processing architecture of the primate visual cortex is discussed.

Physics of higher orbital bands in optical lattices: a review.

PubMed

Li, Xiaopeng; Liu, W Vincent

2016-11-01

The orbital degree of freedom plays a fundamental role in understanding the unconventional properties in solid state materials. Experimental progress in quantum atomic gases has demonstrated that high orbitals in optical lattices can be used to construct quantum emulators of exotic models beyond natural crystals, where novel many-body states such as complex Bose-Einstein condensates and topological semimetals emerge. A brief introduction of orbital degrees of freedom in optical lattices is given and a summary of exotic orbital models and resulting many-body phases is provided. Experimental consequences of the novel phases are also discussed.

Temperature dependence of helium-implantation-induced lattice swelling in polycrystalline tungsten: X-ray micro-diffraction and Eigenstrain modelling

DOE PAGES

de Broglie, I.; Beck, C. E.; Liu, W.; ...

2015-05-30

Using synchrotron X-ray micro-diffraction and Eigenstrain analysis the distribution of lattice swelling near grain boundaries in helium-implanted polycrystalline tungsten is quantified. Samples heat-treated at up to 1473 K after implantation show less uniform lattice swelling that varies significantly from grain to grain compared to as-implanted samples. An increase in lattice swelling is found in the vicinity of some grain boundaries, even at depths beyond the implanted layer. As a result, these findings are discussed in terms of the evolution of helium-ion-implantation-induced defects.

Temperature dependence of helium-implantation-induced lattice swelling in polycrystalline tungsten: X-ray micro-diffraction and Eigenstrain modelling

DOE Office of Scientific and Technical Information (OSTI.GOV)

de Broglie, I.; Beck, C. E.; Liu, W.

Using synchrotron X-ray micro-diffraction and Eigenstrain analysis the distribution of lattice swelling near grain boundaries in helium-implanted polycrystalline tungsten is quantified. Samples heat-treated at up to 1473 K after implantation show less uniform lattice swelling that varies significantly from grain to grain compared to as-implanted samples. An increase in lattice swelling is found in the vicinity of some grain boundaries, even at depths beyond the implanted layer. As a result, these findings are discussed in terms of the evolution of helium-ion-implantation-induced defects.

Quasi interpolation with Voronoi splines.

PubMed

Mirzargar, Mahsa; Entezari, Alireza

2011-12-01

We present a quasi interpolation framework that attains the optimal approximation-order of Voronoi splines for reconstruction of volumetric data sampled on general lattices. The quasi interpolation framework of Voronoi splines provides an unbiased reconstruction method across various lattices. Therefore this framework allows us to analyze and contrast the sampling-theoretic performance of general lattices, using signal reconstruction, in an unbiased manner. Our quasi interpolation methodology is implemented as an efficient FIR filter that can be applied online or as a preprocessing step. We present visual and numerical experiments that demonstrate the improved accuracy of reconstruction across lattices, using the quasi interpolation framework. © 2011 IEEE

Coherent X-Ray Diffraction Imaging and Characterization of Strain in Silicon-on-Insulator Nanostructures

PubMed Central

Xiong, Gang; Moutanabbir, Oussama; Reiche, Manfred; Harder, Ross; Robinson, Ian

2014-01-01

Coherent X-ray diffraction imaging (CDI) has emerged in the last decade as a promising high resolution lens-less imaging approach for the characterization of various samples. It has made significant technical progress through developments in source, algorithm and imaging methodologies thus enabling important scientific breakthroughs in a broad range of disciplines. In this report, we will introduce the principles of forward scattering CDI and Bragg geometry CDI (BCDI), with an emphasis on the latter. BCDI exploits the ultra-high sensitivity of the diffraction pattern to the distortions of crystalline lattice. Its ability of imaging strain on the nanometer scale in three dimensions is highly novel. We will present the latest progress on the application of BCDI in investigating the strain relaxation behavior in nanoscale patterned strained silicon-on-insulator (sSOI) materials, aiming to understand and engineer strain for the design and implementation of new generation semiconductor devices. PMID:24955950

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhu, Yi; Cai, Zhonghou; Chen, Pice

Dynamical phase separation during a solid-solid phase transition poses a challenge for understanding the fundamental processes in correlated materials. Critical information underlying a phase transition, such as localized phase competition, is difficult to reveal by measurements that are spatially averaged over many phase seperated regions. The ability to simultanousely track the spatial and temporal evolution of such systems is essential to understanding mesoscopic processes during a phase transition. Using state-of- the-art time-resolved hard x-ray diffraction microscopy, we directly visualize the structural phase progression in a VO 2 film upon photoexcitation. Following a homogenous in-plane optical excitation, the phase transformation ismore » initiated at discrete sites and completed by the growth of one lattice structure into the other, instead of a simultaneous isotropic lattice symmetry change. The time-dependent x-ray diffraction spatial maps show that the in-plane phase progression in laser-superheated VO 2 is via a displacive lattice transformation as a result of relaxation from an excited monoclinic phase into a rutile phase. The speed of the phase front progression is quantitatively measured, which is faster than the process driven by in-plane thermal diffusion but slower than the sound speed in VO 2. Lastly, the direct visualization of localized structural changes in the time domain opens a new avenue to study mesoscopic processes in driven systems.« less

Theoretical Studies of Magnetic Systems. Final Report, August 1, 1994 - November 30, 1997

DOE R&D Accomplishments Database

Gor`kov, L. P.; Novotny, M. A.; Schrieffer, J. R.

1997-01-01

During the grant period the authors have studied five areas of research: (1) low dimensional ferrimagnets; (2) lattice effects in the mixed valence problem; (3) spin compensation in the one dimensional Kondo lattice; (4) the interaction of quasi particles in short coherence length superconductors; and (5) novel effects in angle resolved photoemission spectra from nearly antiferromagnetic materials. Progress in each area is summarized.

Lattice Boltzmann Methods to Address Fundamental Boiling and Two-Phase Problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Uddin, Rizwan

2012-01-01

This report presents the progress made during the fourth (no cost extension) year of this three-year grant aimed at the development of a consistent Lattice Boltzmann formulation for boiling and two-phase flows. During the first year, a consistent LBM formulation for the simulation of a two-phase water-steam system was developed. Results of initial model validation in a range of thermo-dynamic conditions typical for Boiling Water Reactors (BWRs) were shown. Progress was made on several fronts during the second year. Most important of these included the simulation of the coalescence of two bubbles including the surface tension effects. Work during themore » third year focused on the development of a new lattice Boltzmann model, called the artificial interface lattice Boltzmann model (AILB model) for the 3 simulation of two-phase dynamics. The model is based on the principle of free energy minimization and invokes the Gibbs-Duhem equation in the formulation of non-ideal forcing function. This was reported in detail in the last progress report. Part of the efforts during the last (no-cost extension) year were focused on developing a parallel capability for the 2D as well as for the 3D codes developed in this project. This will be reported in the final report. Here we report the work carried out on testing the AILB model for conditions including the thermal effects. A simplified thermal LB model, based on the thermal energy distribution approach, was developed. The simplifications are made after neglecting the viscous heat dissipation and the work done by pressure in the original thermal energy distribution model. Details of the model are presented here, followed by a discussion of the boundary conditions, and then results for some two-phase thermal problems.« less

Experimental evidence for the lattice instability of Bi-based superconducting systems

NASA Astrophysics Data System (ADS)

Yusheng, He; Jiong, Xiang; Hsin, Wang; Aisheng, He; Jincang, Zhang; Fanggao, Chang

1989-11-01

Ultrasonic measurements, specific heat and thermal analysis experiments, X-ray diffraction study and infrared investigation revealed that there are anomalous structural changes or lattice instabilities near 200 K in single 2212 or 2223 phase samples of Bi(Pb)-Sr-Ca-Cu-O system. Detailed study showed that anomalous changes or lattice instabilities are isothermal-like processes and have the characteristics of a structural phase transition, accompanying with increases in lattice constants. Possible mechanism for this lattice instability is discussed.

Glancing-incidence focussed ion beam milling: A coherent X-ray diffraction study of 3D nano-scale lattice strains and crystal defects

DOE PAGES

Hofmann, Felix; Harder, Ross J.; Liu, Wenjun; ...

2018-05-11

Here, this study presents a detailed examination of the lattice distortions introduced by glancing incidence Focussed Ion Beam (FIB) milling. Using non-destructive multi-reflection Bragg coherent X-ray diffraction we probe damage formation in an initially pristine gold micro-crystal following several stages of FIB milling. These experiments allow access to the full lattice strain tensor in the micro-crystal with ~25 nm 3D spatial resolution, enabling a nano-scale analysis of residual lattice strains and defects formed. Our results show that 30 keV glancing incidence milling produces fewer large defects than normal incidence milling at the same energy. However the resulting residual lattice strainsmore » have similar magnitude and extend up to ~50 nm into the sample. At the edges of the milled surface, where the ion-beam tails impact the sample at near-normal incidence, large dislocation loops with a range of Burgers vectors are formed. Further glancing incidence FIB polishing with 5 keV ion energy removes these dislocation loops and reduces the lattice strains caused by higher energy FIB milling. However, even at the lower ion energy, damage-induced lattice strains are present within a ~20 nm thick surface layer. These results highlight the need for careful consideration and management of FIB damage. They also show that low-energy FIB-milling is an effective tool for removing FIB-milling induced lattice strains. This is important for the preparation of micro-mechanical test specimens and strain microscopy samples.« less

Glancing-incidence focussed ion beam milling: A coherent X-ray diffraction study of 3D nano-scale lattice strains and crystal defects

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hofmann, Felix; Harder, Ross J.; Liu, Wenjun

Here, this study presents a detailed examination of the lattice distortions introduced by glancing incidence Focussed Ion Beam (FIB) milling. Using non-destructive multi-reflection Bragg coherent X-ray diffraction we probe damage formation in an initially pristine gold micro-crystal following several stages of FIB milling. These experiments allow access to the full lattice strain tensor in the micro-crystal with ~25 nm 3D spatial resolution, enabling a nano-scale analysis of residual lattice strains and defects formed. Our results show that 30 keV glancing incidence milling produces fewer large defects than normal incidence milling at the same energy. However the resulting residual lattice strainsmore » have similar magnitude and extend up to ~50 nm into the sample. At the edges of the milled surface, where the ion-beam tails impact the sample at near-normal incidence, large dislocation loops with a range of Burgers vectors are formed. Further glancing incidence FIB polishing with 5 keV ion energy removes these dislocation loops and reduces the lattice strains caused by higher energy FIB milling. However, even at the lower ion energy, damage-induced lattice strains are present within a ~20 nm thick surface layer. These results highlight the need for careful consideration and management of FIB damage. They also show that low-energy FIB-milling is an effective tool for removing FIB-milling induced lattice strains. This is important for the preparation of micro-mechanical test specimens and strain microscopy samples.« less

Reorientations, relaxations, metastabilities, and multidomains of skyrmion lattices

NASA Astrophysics Data System (ADS)

Bannenberg, L. J.; Qian, F.; Dalgliesh, R. M.; Martin, N.; Chaboussant, G.; Schmidt, M.; Schlagel, D. L.; Lograsso, T. A.; Wilhelm, H.; Pappas, C.

2017-11-01

Magnetic skyrmions are nanosized topologically protected spin textures with particlelike properties. They can form lattices perpendicular to the magnetic field, and the orientation of these skyrmion lattices with respect to the crystallographic lattice is governed by spin-orbit coupling. By performing small-angle neutron scattering measurements, we investigate the coupling between the crystallographic and skyrmion lattices in both Cu2OSeO3 and the archetype chiral magnet MnSi. The results reveal that the orientation of the skyrmion lattice is primarily determined by the magnetic field direction with respect to the crystallographic lattice. In addition, it is also influenced by the magnetic history of the sample, which can induce metastable lattices. Kinetic measurements show that these metastable skyrmion lattices may or may not relax to their equilibrium positions under macroscopic relaxation times. Furthermore, multidomain lattices may form when two or more equivalent crystallographic directions are favored by spin-orbit coupling and oriented perpendicular to the magnetic field.

Lattice QCD and heavy ion collisions: a review of recent progress.

PubMed

Ratti, Claudia

2018-04-04

In the last few years, numerical simulations of QCD on the lattice have reached a new level of accuracy. A wide range of thermodynamic quantities is now available in the continuum limit and for physical quark masses. This allows a comparison with measurements from heavy ion collisions for the first time. Furthermore, calculations of dynamical quantities are also becoming available. The combined effort from first principles and experiment allows us to gain an unprecedented understanding of the properties of quark-gluon plasma. I will review the state-of-the-art results from lattice simulations and connect them to the experimental information from RHIC and the LHC. © 2018 IOP Publishing Ltd.

Lattice dynamics and thermoelectric properties of nanocrystalline silicon-germanium alloys: Lattice dynamics and thermoelectric properties of nc Si-Ge alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Claudio, Tania; Stein, Niklas; Petermann, Nils

2015-10-26

The lattice dynamics and thermoelectric properties of sintered phosphorus-doped nanostructured silicon–germanium alloys obtained by gas-phase synthesis were studied. Measurements of the density of phonon states by inelastic neutron scattering were combined with measurements of the elastic constants and the low-temperature heat capacity. A strong influence of nanostructuring and alloying on the lattice dynamics was observed. The thermoelectric transport properties of samples with different doping as well as samples sintered at different temperature were characterized between room temperature and 1000°C. A peak figure of merit zT=0.88 at 900°C is observed and is comparatively insensitive to the aforementioned parameter variations.

The irreversibility line of magnetically grain-aligned Hg-1212 sample - Evidences of flux line lattice melting

NASA Astrophysics Data System (ADS)

de Andrade, R., Jr.; Lanfredi, A. J. C.; Ortiz, W. A.; Leite, E. R.

1997-08-01

The irreversibility line (IL) of a magnetically grain-aligned HgBa2CaCu2O6+δ (Hg-1212) sample was determined from magnetization measurements, with the magnetic fieldH parallel to the samplec-axis. The grain-aligned sample was made by mixing powdered polycrystalline samples with epoxy resin, cured under 94 KOe at room temperature. For fields below 10 kOe the Il is well fitted by a model of flux line lattice melting due to thermal fluctuations. For higher fields the IL behavior changes to an exponential growth of Hirr with 1/T. This change is related to a corresponding alteration in the character of the vortex fluctuations leading to the melting of the flux line lattice.

Decay constants $$f_B$$ and $$f_{B_s}$$ and quark masses $$m_b$$ and $$m_c$$ from HISQ simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Komijani, J.; et al.

2016-11-22

We present a progress report on our calculation of the decay constantsmore » $$f_B$$ and $$f_{B_s}$$ from lattice-QCD simulations with highly-improved staggered quarks. Simulations are carried out with several heavy valence-quark masses on $(2+1+1)$-flavor ensembles that include charm sea quarks. We include data at six lattice spacings and several light sea-quark masses, including an approximately physical-mass ensemble at all but the smallest lattice spacing, 0.03 fm. This range of parameters provides excellent control of the continuum extrapolation to zero lattice spacing and of heavy-quark discretization errors. Finally, using the heavy-quark effective theory expansion we present a method of extracting from the same correlation functions the charm- and bottom-quark masses as well as some low-energy constants appearing in the heavy-quark expansion.« less

Constructing a neutron star from the lattice in G2-QCD

NASA Astrophysics Data System (ADS)

Hajizadeh, Ouraman; Maas, Axel

2017-10-01

The inner structure of neutron stars is still an open question. One obstacle is the infamous sign problem of lattice QCD, which bars access to the high-density equation of state. A possibility to make progress and understand the qualitative impact of gauge interactions on the neutron star structure is to study a modified version of QCD without the sign problem. In the modification studied here the gauge group of QCD is replaced by the exceptional Lie group G_2 , which keeps neutrons in the spectrum. Using an equation of state from lattice calculations only we determine the mass-radius-relation for a neutron star using the Tolman-Oppenheimer-Volkoff equation. This allows us to understand the challenges and approximations currently necessary to use lattice data for this purpose. We discuss in detail the particular uncertainties and systematic problems of this approach.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bannenberg, L. J.; Qian, F.; Dalgliesh, R. M.

Magnetic skyrmions are nanosized topologically protected spin textures with particlelike properties. They can form lattices perpendicular to the magnetic field, and the orientation of these skyrmion lattices with respect to the crystallographic lattice is governed by spin-orbit coupling. By performing small-angle neutron scattering measurements, we investigate the coupling between the crystallographic and skyrmion lattices in both Cu 2OSeO 3 and the archetype chiral magnet MnSi. The results reveal that the orientation of the skyrmion lattice is primarily determined by the magnetic field direction with respect to the crystallographic lattice. In addition, it is also influenced by the magnetic history ofmore » the sample, which can induce metastable lattices. Kinetic measurements show that these metastable skyrmion lattices may or may not relax to their equilibrium positions under macroscopic relaxation times. Moreover, multidomain lattices may form when two or more equivalent crystallographic directions are favored by spin-orbit coupling and oriented perpendicular to the magnetic field.« less

Structural effects due to the incorporation of Ar atoms in the lattice of ZrO 2 thin films prepared by ion beam assisted deposition

NASA Astrophysics Data System (ADS)

Holgado, J. P.; Escobar Galindo, R.; van Veen, A.; Schut, H.; de Hosson, J. Th. M.; González-Elipe, A. R.

2002-09-01

Two sets of ZrO 2 thin films have been prepared at room temperature by ion beam induced chemical vapour deposition and subsequently annealed up to 1323 K. The two sets of samples have been prepared by using either O 2+ or mixtures of (O 2++Ar +) ions for the decomposition of a volatile metallorganic precursor of zirconium. The structure and microstructure of these two sets of samples have been determined by means of X-ray diffraction, Fourier transform infrared spectroscopy and positron beam analysis (PBA). The samples were very compact and dense and had a very low-surface roughness. After annealing in air at T⩾573 K both sets of films were transparent and showed similar refraction indexes. For the (O 2++Ar +)-ZrO 2 thin films it is shown by X-ray photoelectron spectroscopy and Rutherford back scattering that a certain amount of incorporated Ar (5-6 at.%) remains incorporated within the oxide lattice. No changes were detected in the amount of incorporated Ar even after annealing at T=773 K. For higher annealing temperatures ( T>1073 K), the amount of Ar starts to decrease, and at T=1223 K only residual amounts of Ar (<0.4%) remain within the lattice. It has been found that as far as Ar atoms remain incorporated within the ZrO 2 network, the (O 2+-Ar +)-ZrO 2 films present a cubic/tetragonal phase. When the amount of "embedded" Ar decreases, the crystalline phase reverts to monoclinic, the majority phase observed for the (O 2+)-ZrO 2 films after any annealing treatments. The microstructure of the films after different annealing treatments has been investigated by PBA. The presence of Ar ions and the initial amorphous state of the layers were detected by this technique. An increase of the open volume was observed after annealing up to 773 K in both sets of samples. For higher annealing temperatures the samples showed a progressive crystallisation resulting in a decrease of the open volume. During this sintering the samples without embedded Ar present a higher concentration of open volume defects. After the release of Ar occurs ( T⩾1223 K) both samples approach to a similar defect free state. The incorporation of Ar within the ZrO 2 thin film structure, is proposed as the main factor contributing to the stabilisation of the cubic/tetragonal phase of ZrO 2 at room temperature.

Is there lattice contraction in multicomponent metal oxides? Case study for GdVO4:Eu3+ nanoparticles.

PubMed

Yang, Liusai; Li, Liping; Zhao, Minglei; Fu, Chaochao; Li, Guangshe

2013-08-02

Metal oxide nanomaterials have been found to have great potential for diverse applications due to their unique relationships between structure and properties. Lattice expansion as particle size reduces was previously considered to be general for metal oxide nanomaterials. It is now a great challenge to see if lattice contraction could be induced by the size effect for metal oxide nanomaterials. ABO4 metal oxides (e.g., CaWO4, GdVO4, and CdWO4) are some of the most important functional materials with many applications, while such oxides at the nanoscale are never reported to show a lattice contraction. This work presents a first report on the variation from lattice expansion to lattice contraction by tuning the microstructures of GdVO4:Eu(3+) nanocrystals. A hydrothermal method was adopted to synthesize GdVO4:Eu(3+) nanocrystals, and then these nanoparticles were calcined at 600 ° C in air. It is found that particle size reduction led to a lattice contraction for the calcined samples, which is in contrast to the lattice expansion observed for the hydrothermally synthesized counterparts or many other metal oxide nanomaterials. In addition, the lattice symmetry of the calcined samples remained almost a constant. The results indicate that the negative surface stress was eliminated by calcination treatment, leading to a homogeneous compression process in the lattice structure of the calcined GdVO4:Eu(3+) nanocrystals. Furthermore, Eu(3+) was taken as a structural probe and a luminescence center to study the local environments pertinent to these structural changes and to optimize the photoluminescence performance.

Interaction of multiferroic properties and interfaces in hexagonal LuMnO3 ceramics

NASA Astrophysics Data System (ADS)

Baghizadeh, A.; Vieira, J. M.; Stroppa, D. G.; Mirzadeh Vaghefi, P.; Graça, M. P.; Amaral, J. S.; Willinger, M.-G.; Amaral, V. S.

2017-02-01

A study on the underlying interaction mechanisms between lattice constants, magnetic and dielectric properties with inhomogeneities or internal interfaces in hexagonal, off-stoichiometric LuMnO3 oxide is presented. By increasing Mn content the a-axis constant and volume of the unit cell, the antiferromagnetic (AFM) Néel temperature, T N, and frustration factor of the frustrated Mn3+ trimmers in basal plane show decreasing trends. It was found that increasing the annealing time improves the properties of the lattices and progressively eliminates secondary phases for compositions within the solid solution stability limits. A magnetic contribution below T N is observed for all samples. Two regimes of magnetization below and above 45 K were observed in the AFM state. The magnetic contribution below T N is assigned to either the secondary phase or internal interfaces like ferroelectric (FE) domain walls. Magneto-dielectric coupling at T N is preserved in off-stoichiometric ceramics. The presence of a low temperature anomaly of the dielectric constant is correlated to the composition of the solid solution in off-stoichiometric ceramics. Large FE domains are observed in piezoresponse force microscopy (PFM) images of doped and un-doped ceramics, whereas atomic structure analysis indicates the parallel formation of nano-sized FE domains. A combination of measured properties and microscopy images of micron- and nano-sized domains ascertain the role of lattice distortion and stability of solid solution on multiferroic properties.

Characterization of a water-solid interaction in a partially ordered system.

PubMed

Chakravarty, Paroma; Lubach, Joseph W

2013-11-04

GNE068-PC, a developmental compound, was previously characterized to be mesomorphous, i.e. having long-range order associated with significant local molecular disorder (Chakravarty et. al., Mol. Pharmaceutics, accepted). The compound was exposed to moisture under different relative humidity conditions ranging from 11% to 60% RH at room temperature (RT) for 7 days, and the resultant product phases were characterized. The partially ordered sample progressively lost crystallinity (long-range order) and birefringence (orientational order) upon exposure to increasing RH conditions, leading to the formation of a completely disordered amorphous phase at 60% RH (RT). Long-range positional order was irrecoverable even after moisture removal from the sample exposed to 60% RH. This was attributed to replacement of residual ethyl acetate by water, the former being critical for maintenance of long-range order in the material. In addition, water sorption appeared to irreversibly alter the molecular orientation, thereby affecting sample birefringence. Solid-state NMR revealed increases in (1)H and (13)C spin-lattice relaxation times (T1) going from the mesomorphous phase to the fully amorphous phase. This was indicative of reduction in lattice mobility, likely due to the decreased motion of the aromatic portions of the molecule, in particular C17, which showed the most dramatic increase in (13)C T1. This is likely due to decrease in available free volume upon water sorption. Drying of the hydrated disordered phase showed somewhat greater mobility than the hydrated phase, likely due to increased relative free volume through removal of water. A water-solid interaction therefore irreversibly changed the solid-state makeup of GNE068-PC.

News and views in discontinuous phase transitions

NASA Astrophysics Data System (ADS)

Nagler, Jan

2014-03-01

Recent progress in the theory of discontinuous percolation allow us to better understand the the sudden emergence of large-scale connectedness both in networked systems and on the lattice. We analytically study mechanisms for the amplification of critical fluctuations at the phase transition point, non-self-averaging and power law fluctuations. A single event analysis allow to establish criteria for discontinuous percolation transitions, even on the high-dimensional lattice. Some applications such as salad bowl percolation, and inverse fragmentation are discussed.

Wiener-matrix image restoration beyond the sampling passband

NASA Technical Reports Server (NTRS)

Rahman, Zia-Ur; Alter-Gartenberg, Rachel; Fales, Carl L.; Huck, Friedrich O.

1991-01-01

A finer-than-sampling-lattice resolution image can be obtained using multiresponse image gathering and Wiener-matrix restoration. The multiresponse image gathering weighs the within-passband and aliased signal components differently, allowing the Wiener-matrix restoration filter to unscramble these signal components and restore spatial frequencies beyond the sampling passband of the photodetector array. A multiresponse images can be reassembled into a single minimum mean square error image with a resolution that is sq rt A times finer than the photodetector-array sampling lattice.

Coherent X-ray diffraction imaging and characterization of strain in silicon-on-insulator nanostructures

DOE PAGES

Xiong, Gang; Moutanabbir, Oussama; Reiche, Manfred; ...

2014-12-06

Coherent X-ray diffraction imaging (CDI) has emerged in the last decade as a promising high resolution lens-less imaging approach for the characterization of various samples. It has made significant technical progress through developments in source, algorithm and imaging methodologies thus enabling important scientific breakthroughs in a broad range of disciplines. In this report, we will introduce the principles of forward scattering CDI and Bragg geometry CDI (BCDI), with an emphasis on the latter. BCDI exploits the ultra-high sensitivity of the diffraction pattern to the distortions of crystalline lattice. Its ability of imaging strain on the nanometer scale in three dimensionsmore » is highly novel. In this study, we will present the latest progress on the application of BCDI in investigating the strain relaxation behavior in nanoscale patterned strained silicon-on-insulator (sSOI) materials, aiming to understand and engineer strain for the design and implementation of new generation semiconductor devices.« less

Coherent X-ray diffraction imaging and characterization of strain in silicon-on-insulator nanostructures.

PubMed

Xiong, Gang; Moutanabbir, Oussama; Reiche, Manfred; Harder, Ross; Robinson, Ian

2014-12-10

Coherent X-ray diffraction imaging (CDI) has emerged in the last decade as a promising high resolution lens-less imaging approach for the characterization of various samples. It has made significant technical progress through developments in source, algorithm and imaging methodologies thus enabling important scientific breakthroughs in a broad range of disciplines. In this report, we will introduce the principles of forward scattering CDI and Bragg geometry CDI (BCDI), with an emphasis on the latter. BCDI exploits the ultra-high sensitivity of the diffraction pattern to the distortions of crystalline lattice. Its ability of imaging strain on the nanometer scale in three dimensions is highly novel. We will present the latest progress on the application of BCDI in investigating the strain relaxation behavior in nanoscale patterned strained silicon-on-insulator (sSOI) materials, aiming to understand and engineer strain for the design and implementation of new generation semiconductor devices. © 2014 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Studies on Amorphizing Silicon Using Silicon Ion Implantation.

DTIC Science & Technology

1985-04-01

for removal from their lattice site, relax or recombine with their original or other vacant lattice site. This effect is also temperature sensitive...The results should be comparable since the samples were oriented to appear like a random lattice target to the incoming ion beam. At the Avionics...times greater than 10- seconds after the impinging ion has come to Il rest. Thus any displaced atoms which relax back onto a lattice site or are able

Reorientations, relaxations, metastabilities, and multidomains of skyrmion lattices

DOE PAGES

Bannenberg, L. J.; Qian, F.; Dalgliesh, R. M.; ...

2017-11-13

Magnetic skyrmions are nanosized topologically protected spin textures with particlelike properties. They can form lattices perpendicular to the magnetic field, and the orientation of these skyrmion lattices with respect to the crystallographic lattice is governed by spin-orbit coupling. By performing small-angle neutron scattering measurements, we investigate the coupling between the crystallographic and skyrmion lattices in both Cu 2OSeO 3 and the archetype chiral magnet MnSi. The results reveal that the orientation of the skyrmion lattice is primarily determined by the magnetic field direction with respect to the crystallographic lattice. In addition, it is also influenced by the magnetic history ofmore » the sample, which can induce metastable lattices. Kinetic measurements show that these metastable skyrmion lattices may or may not relax to their equilibrium positions under macroscopic relaxation times. Moreover, multidomain lattices may form when two or more equivalent crystallographic directions are favored by spin-orbit coupling and oriented perpendicular to the magnetic field.« less

Influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures and lattice defects accumulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sedao, Xxx; Garrelie, Florence, E-mail: florence.garrelie@univ-st-etienne.fr; Colombier, Jean-Philippe

2014-04-28

The influence of crystal orientation on the formation of femtosecond laser-induced periodic surface structures (LIPSS) has been investigated on a polycrystalline nickel sample. Electron Backscatter Diffraction characterization has been exploited to provide structural information within the laser spot on irradiated samples to determine the dependence of LIPSS formation and lattice defects (stacking faults, twins, dislocations) upon the crystal orientation. Significant differences are observed at low-to-medium number of laser pulses, outstandingly for (111)-oriented surface which favors lattice defects formation rather than LIPSS formation.

High Curie temperature Bi(1.85)Mn(0.15)Te3 nanoplates.

PubMed

Cheng, Lina; Chen, Zhi-Gang; Ma, Song; Zhang, Zhi-dong; Wang, Yong; Xu, Hong-Yi; Yang, Lei; Han, Guang; Jack, Kevin; Lu, Gaoqing Max; Zou, Jin

2012-11-21

Bi(1.85)Mn(0.15)Te(3) hexagonal nanoplates with a width of ~200 nm and a thickness of ~20 nm were synthesized using a solvothermal method. According to the structural characterization and compositional analysis, the Mn(2+) and Mn(3+) ions were found to substitute Bi(3+) ions in the lattice. High-level Mn doping induces significant lattice distortion and decreases the crystal lattice by 1.07% in the a axis and 3.18% in the c axis. A high ferromagnetic state with a Curie temperature of ~45 K is observed in these nanoplates due to Mn(2+) and Mn(3+) ion doping, which is a significant progress in the field of electronics and spintronics.

Manufacturing and Characterization of 18Ni Marage 300 Lattice Components by Selective Laser Melting.

PubMed

Contuzzi, Nicola; Campanelli, Sabina L; Casavola, Caterina; Lamberti, Luciano

2013-08-13

The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The paper investigates the suitability of Selective Laser Melting for manufacturing steel cellular lattice structures with characteristic dimensions in the micrometer range. Alternative lattice topologies including reinforcing bars in the vertical direction also are considered. The selected lattice structure topology is shown to be superior over other lattice structure designs considered in literature. Compression tests are carried out in order to evaluate mechanical strength of lattice strut specimens made via SLM. Compressive behavior of samples also is simulated by finite element analysis and numerical results are compared with experimental data in order to assess the constitutive behavior of the lattice structure designs considered in this study. Experimental data show that it is possible to build samples of relative density in the 0.2456-0.4367 range. Compressive strength changes almost linearly with respect to relative density, which in turns depends linearly on the number of vertical reinforces. Specific strength increases with cell and strut edge size. Numerical simulations confirm the plastic nature of the instability phenomena that leads the cellular structures to collapse under compression loading.

The optical gap in VO2 insulating phases is dominated by Coulomb repulsion

NASA Astrophysics Data System (ADS)

Hendriks, Christopher; Walter, Eric; Krakauer, Henry; Huffman, Tyler; Qazilbash, Mumtaz

Under doping, tensile strain or heating, vanadium dioxide (VO2) transforms from an insulating monoclinic (M1) to a metallic rutile (R) phase, progressing through intermediate insulating triclinic (T) and magnetic (M2) phases. Broadband optical spectroscopy data have been obtained on the T and M2 phases in the same sample. While only half the V atoms are dimerized in M2 compared to M1 and T, the measured optical gap is essentially unaltered by the first-order structural phase transition between them. Moreover, the optical interband features in the T and M2 phases are remarkably similar to those previously observed in the well-studied M1 phase. This shows that the electronic structure is insensitive to the lattice structure. Our ab-initio HSE optical conductivity calculations on the insulating phases of VO2 are in excellent agreement with the experimental measurements. We will discuss the choice of α, the fraction of exact exchange. As the energy gap is insensitive to the different lattice structures of the three insulating phases, we rule out Peierls effects as the dominant contributor to the opening of the gap. Rather, the energy gap arises from intra-atomic Coulomb correlations. Supported by ONR.

Characterization of zirconium carbides using electron microscopy, optical anisotropy, Auger depth profiles, X-ray diffraction, and electron density calculated by charge flipping method

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chinthaka Silva, G.W., E-mail: chinthaka.silva@gmail.com; Kercher, Andrew A., E-mail: rokparent@comcast.net; Hunn, John D., E-mail: hunnjd@ornl.gov

2012-10-15

Samples with five different zirconium carbide compositions (C/Zr molar ratio=0.84, 0.89, 0.95, 1.05, and 1.17) have been fabricated and studied using a variety of experimental techniques. Each sample was zone refined to ensure that the end product was polycrystalline with a grain size of 10-100 {mu}m. It was found that the lattice parameter was largest for the x=0.89 composition and smallest for the x=1.17 total C/Zr composition, but was not linear; this nonlinearity is possibly explained using electron densities calculated using charge flipping technique. Among the five samples, the unit cell of the ZrC{sub 0.89} sample showed the highest electronmore » density, corresponding to the highest carbon incorporation and the largest lattice parameter. The ZrC{sub 0.84} sample showed the lowest carbon incorporation, resulting in a larger number of carbon vacancies and resultant strain. Samples with larger carbon ratios (x=0.95, 1.05, and 1.17) showed a slight decrease in lattice parameter, due to a decrease in electron density. Optical anisotropy measurements suggest that these three samples contained significant amounts of a graphitic carbon phase, not bonded to the Zr atoms. - Graphical abstract: Characterization of zirconium carbides using electron microscopy, optical anisotropy, Auger depth profiles, X-ray diffraction, and electron density calculated by the charge flipping method. Highlights: Black-Right-Pointing-Pointer The lattice parameter variation: ZrC{sub 0.89}>ZrC{sub 0.84}>ZrC{sub 0.95}>ZrC{sub 1.05}>ZrC{sub 1.17}. Black-Right-Pointing-Pointer Surface oxygen with no correlation to the lattice parameter variation. Black-Right-Pointing-Pointer ZrC{sub 0.89} had highest electron densities correspond to highest carbon incorporation. Black-Right-Pointing-Pointer Second highest lattice parameter in ZrC{sub 0.84} due to strain. Black-Right-Pointing-Pointer Unit cell electron density order: ZrC{sub 0.95}>ZrC{sub 1.05}>ZrC{sub 1.17}.« less

Is there lattice contraction in multicomponent metal oxides? Case study for GdVO4:Eu3+ nanoparticles

NASA Astrophysics Data System (ADS)

Yang, Liusai; Li, Liping; Zhao, Minglei; Fu, Chaochao; Li, Guangshe

2013-08-01

Metal oxide nanomaterials have been found to have great potential for diverse applications due to their unique relationships between structure and properties. Lattice expansion as particle size reduces was previously considered to be general for metal oxide nanomaterials. It is now a great challenge to see if lattice contraction could be induced by the size effect for metal oxide nanomaterials. ABO4 metal oxides (e.g., CaWO4, GdVO4, and CdWO4) are some of the most important functional materials with many applications, while such oxides at the nanoscale are never reported to show a lattice contraction. This work presents a first report on the variation from lattice expansion to lattice contraction by tuning the microstructures of GdVO4:Eu3+ nanocrystals. A hydrothermal method was adopted to synthesize GdVO4:Eu3+ nanocrystals, and then these nanoparticles were calcined at 600 ° C in air. It is found that particle size reduction led to a lattice contraction for the calcined samples, which is in contrast to the lattice expansion observed for the hydrothermally synthesized counterparts or many other metal oxide nanomaterials. In addition, the lattice symmetry of the calcined samples remained almost a constant. The results indicate that the negative surface stress was eliminated by calcination treatment, leading to a homogeneous compression process in the lattice structure of the calcined GdVO4:Eu3+ nanocrystals. Furthermore, Eu3+ was taken as a structural probe and a luminescence center to study the local environments pertinent to these structural changes and to optimize the photoluminescence performance.

The Effect of Crystallite Size and Texture on the Strength of MgGeO3 Post-Perovskite

NASA Astrophysics Data System (ADS)

Miyagi, Lowell

2011-06-01

In-situ radial synchrotron x-ray diffraction is used to measure lattice strain and lattice preferred orientation (texture) in MgGeO3 post-perovskite synthesized and deformed in the diamond anvil cell up to 135 GPa. Lattice strains are used to calculate differential stress supported by the sample and can provide a lower bounds estimate on yield strength. MgGeO3 post-perovskite synthesized from the enstatite phase exhibits a weak transformation texture of (100) planes at high angles to the direction of compression. In a sample with larger crystallites, pressure increase and deformation results in (001) lattice planes orienting nearly perpendicular to compression, consistent with dominant (001) slip. In another sample with smaller crystallites it is difficult to induce texture change, and differential stress is higher than in the sample with larger crystallites. When MgGeO3 post-perovskite is synthesized from the perovskite phase a different transformation texture of (001) planes at high angles to compression is observed. This sample is able to support large differential stress as the direction perpendicular to the (001) plane is a plastically hard orientation for MgGeO3 post-perovskite. This work was supported by the Carnegie DOE Alliance Center and a Bateman fellowship at Yale University.

Efficient LBM visual simulation on face-centered cubic lattices.

PubMed

Petkov, Kaloian; Qiu, Feng; Fan, Zhe; Kaufman, Arie E; Mueller, Klaus

2009-01-01

The Lattice Boltzmann method (LBM) for visual simulation of fluid flow generally employs cubic Cartesian (CC) lattices such as the D3Q13 and D3Q19 lattices for the particle transport. However, the CC lattices lead to suboptimal representation of the simulation space. We introduce the face-centered cubic (FCC) lattice, fD3Q13, for LBM simulations. Compared to the CC lattices, the fD3Q13 lattice creates a more isotropic sampling of the simulation domain and its single lattice speed (i.e., link length) simplifies the computations and data storage. Furthermore, the fD3Q13 lattice can be decomposed into two independent interleaved lattices, one of which can be discarded, which doubles the simulation speed. The resulting LBM simulation can be efficiently mapped to the GPU, further increasing the computational performance. We show the numerical advantages of the FCC lattice on channeled flow in 2D and the flow-past-a-sphere benchmark in 3D. In both cases, the comparison is against the corresponding CC lattices using the analytical solutions for the systems as well as velocity field visualizations. We also demonstrate the performance advantages of the fD3Q13 lattice for interactive simulation and rendering of hot smoke in an urban environment using thermal LBM.

An NMR thermometer for cryogenic magic-angle spinning NMR: The spin-lattice relaxation of 127I in cesium iodide

NASA Astrophysics Data System (ADS)

Sarkar, Riddhiman; Concistrè, Maria; Johannessen, Ole G.; Beckett, Peter; Denning, Mark; Carravetta, Marina; al-Mosawi, Maitham; Beduz, Carlo; Yang, Yifeng; Levitt, Malcolm H.

2011-10-01

The accurate temperature measurement of solid samples under magic-angle spinning (MAS) is difficult in the cryogenic regime. It has been demonstrated by Thurber et al. (J. Magn. Reson., 196 (2009) 84-87) [10] that the temperature dependent spin-lattice relaxation time constant of 79Br in KBr powder can be useful for measuring sample temperature under MAS over a wide temperature range (20-296 K). However the value of T1 exceeds 3 min at temperatures below 20 K, which is inconveniently long. In this communication, we show that the spin-lattice relaxation time constant of 127I in CsI powder can be used to accurately measure sample temperature under MAS within a reasonable experimental time down to 10 K.

A Fermi-degenerate three-dimentional optical lattice clock

NASA Astrophysics Data System (ADS)

Goban, Akihisa; Campbell, Sara; Hutson, Ross; Marti, G. Edward; Sonderhouse, Lindsay; Robinson, John; Zhang, Wei; Ye, Jun

2017-04-01

The pursuit of better atomic clocks has advanced many research areas, providing better quantum state control, tighter limits on fundamental constant variation, and improved tests of relativity. Recent progress in optical lattice clock to the accuracy of 2E-18 has benefited from the understanding of atomic interactions. Also the precision of clock spectroscopy has been applied to explore many-body interactions including SU(N) symmetry. In our previous 1D optical lattice, atomic interactions cause suppression and broadening of the atomic resonance, limiting the clock stability. To overcome this limitation, we demonstrate a scalable solution that takes advantage of the high density of a degenerate Fermi gas in a three-dimensional optical lattice to protect against on-site interaction shifts. Using an ultrastable laser, we achieve an unprecedented level of atom-light coherence, reaching a spectroscopic quality factor 5.2E15. We investigate clock systematics unique to this design; on-site interactions are resolved so that their contribution to clock shifts is orders of magnitude suppressed compared to the 1D optical lattice experiments. Also, we measure the combined scalar and tensor magic wavelengths for state-independent trapping along all three lattice axes. We acknowledge support from NIST, DARPA and the NSF JILA Physics Frontier Center.

Structural Changes in PEO-PPO-PEO Gels Induced by Methylparaben and Dexamethasone Observed Using Time-Resolved SAXS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meznarich, Norman A.K.; Juggernauth, K Anne; Batzli, Kiersten M

2011-11-17

Aqueous solutions of polyoxyethylene-polyoxypropylene-polyoxyethylene (PEO-PPO-PEO) triblock copolymers (commercially available as Pluronic surfactants) micellize and structurally arrange into cubic quasicrystalline lattices as their temperature is raised. This structural evolution is seen macroscopically as a gelation, and the presence of these ordered phases can be controlled through both polymer concentration and temperature. The presence of added solutes within the dispersions can also affect the onset and kinetics of structure formation. Here we investigate the structures formed in Pluronic F127 solutions ranging from 20 to 30% with two pharmaceutical additives [methylparaben (MP) and dexamethasone (DX)] using small-angle X-ray scattering (SAXS). We observe bothmore » the progressive evolution and breakdown of these structures as the temperature is increased from 0 to 80 °C. Additionally, we conducted time-resolved SAXS measurements to elucidate the kinetics of the structural evolution. On the basis of the evolution of scattering peaks as the samples were being heated, we suggest that added MP changes the nucleation behavior of fcc phases within the sample from a heterogeneous process to a more homogeneous distribution of nucleated species. MP and DX also stabilize the micelle lattices, allowing them to persevere at higher temperatures. We observed the unusual result that the presence of DX caused the primary peaks of the structure factor to be suppressed, while preserving the higher order peaks. The primary peaks reappeared at the highest temperatures tested.« less

Phase Transformation and Lattice Parameter Changes of Non-trivalent Rare Earth-Doped YSZ as a Function of Temperature

NASA Astrophysics Data System (ADS)

Jiang, Shengli; Huang, Xiao; He, Zhang; Buyers, Andrew

2018-01-01

To examine the effect of doping/co-doping on high-temperature phase compositions of YSZ, stand-alone YSZ and CeO2 and Nb2O5 co-doped YSZ samples were prepared using mechanical alloy and high-temperature sintering. XRD analysis was performed on these samples from room temperature to 1100 °C. The results show that the structure for the co-doped samples tends to be thermally stable when the test temperature is higher than a critical value. Monoclinic phase was dominant in Nb2O5 co-doped YSZ at temperatures lower than 600 °C, while for the YSZ and CeO2 co-doped YSZ, cubic/tetragonal phase was dominant in the whole test temperature range. The lattice parameters for all the samples increase with increasing test temperature generally. The lattice parameters for the two non-trivalent rare earth oxides co-doped YSZ show that the lattice parameter a for the cubic phase of the Ce4+ co-doped YSZ is consistently greater than that of 7YSZ which is related to the presence of larger radius of Ce4+ in the matrix. The lattice parameters a, b, c for the monoclinic phase of Ce4+ co-doped YSZ are much closer to each other than that of the Nb5+ co-doped YSZ, indicating the former has better tendency to form cubic/tetragonal phase, which is desired for vast engineering applications.

Phase Transformation and Lattice Parameter Changes of Non-trivalent Rare Earth-Doped YSZ as a Function of Temperature

NASA Astrophysics Data System (ADS)

Jiang, Shengli; Huang, Xiao; He, Zhang; Buyers, Andrew

2018-05-01

To examine the effect of doping/co-doping on high-temperature phase compositions of YSZ, stand-alone YSZ and CeO2 and Nb2O5 co-doped YSZ samples were prepared using mechanical alloy and high-temperature sintering. XRD analysis was performed on these samples from room temperature to 1100 °C. The results show that the structure for the co-doped samples tends to be thermally stable when the test temperature is higher than a critical value. Monoclinic phase was dominant in Nb2O5 co-doped YSZ at temperatures lower than 600 °C, while for the YSZ and CeO2 co-doped YSZ, cubic/tetragonal phase was dominant in the whole test temperature range. The lattice parameters for all the samples increase with increasing test temperature generally. The lattice parameters for the two non-trivalent rare earth oxides co-doped YSZ show that the lattice parameter a for the cubic phase of the Ce4+ co-doped YSZ is consistently greater than that of 7YSZ which is related to the presence of larger radius of Ce4+ in the matrix. The lattice parameters a, b, c for the monoclinic phase of Ce4+ co-doped YSZ are much closer to each other than that of the Nb5+ co-doped YSZ, indicating the former has better tendency to form cubic/tetragonal phase, which is desired for vast engineering applications.

Progress report on the k{sub infinity} measurements of HTGR type lattices with the oscillation technique at zero reactivity; Rapport d'advancement sur les mesures de K {sub infinite} des reseaux du type HTGR avec la technique de l'oscillateur a'reactivite' nulle (in French)

DOE Office of Scientific and Technical Information (OSTI.GOV)

NONE

1971-01-15

The principles of measuring k {sub infinity} for a HTGR lattice using the oscillation technique with zero reactivity were already presented at the ''9th reactor physics meeting of countries participating in the Dragon project''. A brief summary of the essential characteristics of the experiment is followed by a status report on present work.

Optical evaluation of the wave filtering properties of graded undulated lattices

NASA Astrophysics Data System (ADS)

Trainiti, G.; Rimoli, J. J.; Ruzzene, M.

2018-03-01

We investigate and experimentally demonstrate the elastic wave filtering properties of graded undulated lattices. Square reticulates composed of curved beams are characterized by graded mechanical properties which result from the spatial modulation of the curvature parameter. Among such properties, the progressive formation of frequency bandgaps leads to strong wave attenuation over a broad frequency range. The experimental investigation of wave transmission and the detection of full wavefields effectively illustrate this behavior. Transmission measurements are conducted using a scanning laser Doppler vibrometer, while a dedicated digital image correlation procedure is implemented to capture in-plane wave motion at selected frequencies. The presented results illustrate the broadband attenuation characteristics resulting from spatial grading of the lattice curvature, whose in-depth investigation is enabled by the presented experimental procedures.

Exploring Flavor Physics with Lattice QCD

NASA Astrophysics Data System (ADS)

Du, Daping; Fermilab/MILC Collaborations Collaboration

2016-03-01

The Standard Model has been a very good description of the subatomic particle physics. In the search for physics beyond the Standard Model in the context of flavor physics, it is important to sharpen our probes using some gold-plated processes (such as B rare decays), which requires the knowledge of the input parameters, such as the Cabibbo-Kobayashi-Maskawa (CKM) matrix elements and other nonperturbative quantities, with sufficient precision. Lattice QCD is so far the only first-principle method which could compute these quantities with competitive and systematically improvable precision using the state of the art simulation techniques. I will discuss the recent progress of lattice QCD calculations on some of these nonpurturbative quantities and their applications in flavor physics. I will also discuss the implications and future perspectives of these calculations in flavor physics.

Processing of IN-718 Lattice Block Castings

NASA Technical Reports Server (NTRS)

Hebsur, Mohan G.

2002-01-01

Recently a low cost casting method known as lattice block casting has been developed by JAM Corporation, Wilmington, Massachusetts for engineering materials such as aluminum and stainless steels that has shown to provide very high stiffness and strength with only a fraction of density of the alloy. NASA Glenn Research Center has initiated research to investigate lattice block castings of high temperature Ni-base superalloys such as the model system Inconel-718 (IN-718) for lightweight nozzle applications. Although difficulties were encountered throughout the manufacturing process , a successful investment casting procedure was eventually developed. Wax formulation and pattern assembly, shell mold processing, and counter gravity casting techniques were developed. Ten IN-718 lattice block castings (each measuring 15-cm wide by 30-cm long by 1.2-cm thick) have been successfully produced by Hitchiner Gas Turbine Division, Milford, New Hampshire, using their patented counter gravity casting techniques. Details of the processing and resulting microstructures are discussed in this paper. Post casting processing and evaluation of system specific mechanical properties of these specimens are in progress.

Manufacturing and Characterization of 18Ni Marage 300 Lattice Components by Selective Laser Melting

PubMed Central

Contuzzi, Nicola; Campanelli, Sabina L.; Casavola, Caterina; Lamberti, Luciano

2013-01-01

The spreading use of cellular structures brings the need to speed up manufacturing processes without deteriorating mechanical properties. By using Selective Laser Melting (SLM) to produce cellular structures, the designer has total freedom in defining part geometry and manufacturing is simplified. The paper investigates the suitability of Selective Laser Melting for manufacturing steel cellular lattice structures with characteristic dimensions in the micrometer range. Alternative lattice topologies including reinforcing bars in the vertical direction also are considered. The selected lattice structure topology is shown to be superior over other lattice structure designs considered in literature. Compression tests are carried out in order to evaluate mechanical strength of lattice strut specimens made via SLM. Compressive behavior of samples also is simulated by finite element analysis and numerical results are compared with experimental data in order to assess the constitutive behavior of the lattice structure designs considered in this study. Experimental data show that it is possible to build samples of relative density in the 0.2456–0.4367 range. Compressive strength changes almost linearly with respect to relative density, which in turns depends linearly on the number of vertical reinforces. Specific strength increases with cell and strut edge size. Numerical simulations confirm the plastic nature of the instability phenomena that leads the cellular structures to collapse under compression loading. PMID:28811445

Measurement of sample temperatures under magic-angle spinning from the chemical shift and spin-lattice relaxation rate of 79Br in KBr powder

PubMed Central

Thurber, Kent R.; Tycko, Robert

2009-01-01

Accurate determination of sample temperatures in solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) can be problematic, particularly because frictional heating and heating by radio-frequency irradiation can make the internal sample temperature significantly different from the temperature outside the MAS rotor. This paper demonstrates the use of 79Br chemical shifts and spin-lattice relaxation rates in KBr powder as temperature-dependent parameters for the determination of internal sample temperatures. Advantages of this method include high signal-to-noise, proximity of the 79Br NMR frequency to that of 13C, applicability from 20 K to 320 K or higher, and simultaneity with adjustment of the MAS axis direction. We show that spin-lattice relaxation in KBr is driven by a quadrupolar mechanism. We demonstrate a simple approach to including KBr powder in hydrated samples, such as biological membrane samples, hydrated amyloid fibrils, and hydrated microcrystalline proteins, that allows direct assessment of the effects of frictional and radio-frequency heating under experimentally relevant conditions. PMID:18930418

Measurement of sample temperatures under magic-angle spinning from the chemical shift and spin-lattice relaxation rate of 79Br in KBr powder.

PubMed

Thurber, Kent R; Tycko, Robert

2009-01-01

Accurate determination of sample temperatures in solid state nuclear magnetic resonance (NMR) with magic-angle spinning (MAS) can be problematic, particularly because frictional heating and heating by radio-frequency irradiation can make the internal sample temperature significantly different from the temperature outside the MAS rotor. This paper demonstrates the use of (79)Br chemical shifts and spin-lattice relaxation rates in KBr powder as temperature-dependent parameters for the determination of internal sample temperatures. Advantages of this method include high signal-to-noise, proximity of the (79)Br NMR frequency to that of (13)C, applicability from 20 K to 320 K or higher, and simultaneity with adjustment of the MAS axis direction. We show that spin-lattice relaxation in KBr is driven by a quadrupolar mechanism. We demonstrate a simple approach to including KBr powder in hydrated samples, such as biological membrane samples, hydrated amyloid fibrils, and hydrated microcrystalline proteins, that allows direct assessment of the effects of frictional and radio-frequency heating under experimentally relevant conditions.

Three-Dimensional Cellular Structures Enhanced By Shape Memory Alloys

NASA Technical Reports Server (NTRS)

Nathal, Michael V.; Krause, David L.; Wilmoth, Nathan G.; Bednarcyk, Brett A.; Baker, Eric H.

2014-01-01

This research effort explored lightweight structural concepts married with advanced smart materials to achieve a wide variety of benefits in airframe and engine components. Lattice block structures were cast from an aerospace structural titanium alloy Ti-6Al-4V and a NiTi shape memory alloy (SMA), and preliminary properties have been measured. A finite element-based modeling approach that can rapidly and accurately capture the deformation response of lattice architectures was developed. The Ti-6-4 and SMA material behavior was calibrated via experimental tests of ligaments machined from the lattice. Benchmark testing of complete lattice structures verified the main aspects of the model as well as demonstrated the advantages of the lattice structure. Shape memory behavior of a sample machined from a lattice block was also demonstrated.

X-Ray diffraction on large single crystals using a powder diffractometer

DOE PAGES

Jesche, A.; Fix, M.; Kreyssig, A.; ...

2016-06-16

Information on the lattice parameter of single crystals with known crystallographic structure allows for estimations of sample quality and composition. In many cases it is sufficient to determine one lattice parameter or the lattice spacing along a certain, high- symmetry direction, e.g. in order to determine the composition in a substitution series by taking advantage of Vegard’s rule. Here we present a guide to accurate measurements of single crystals with dimensions ranging from 200 μm up to several millimeter using a standard powder diffractometer in Bragg-Brentano geometry. The correction of the error introduced by the sample height and the optimizationmore » of the alignment are discussed in detail. Finally, in particular for single crystals with a plate-like habit, the described procedure allows for measurement of the lattice spacings normal to the plates with high accuracy on a timescale of minutes.« less

Precipitation Mechanisms in Aluminum-Lithium Alloys.

DTIC Science & Technology

1983-09-01

the theoretical lattice sites. Figure 38. Illustration of two growing 6’ precipitates. * Figure 39. Illustration of a precipitate formed by the...encounter of two precipitates, forming an antiphase domain boundary (APB). Figure 40. Lattice image of one 6’ precipitate showing the 4o04A repeat distance... lattice images were formed on selected samples to determine the nature of the 6’ precipitates. Particle sizes were determined by hand measuring individual

Irradiation effects and micro-structural changes in large grain uranium dioxide fuel investigated by micro-beam X-ray diffraction

NASA Astrophysics Data System (ADS)

Mieszczynski, C.; Kuri, G.; Degueldre, C.; Martin, M.; Bertsch, J.; Borca, C. N.; Grolimund, D.; Delafoy, Ch.; Simoni, E.

2014-01-01

Microstructural changes in a set of commercial grade UO2 fuel samples have been investigated using synchrotron based micro-focused X-ray fluorescence (μ-XRF) and X-ray diffraction (μ-XRD) techniques. The results are associated with conventional UO2 materials and relatively larger grain chromia-doped UO2 fuels, irradiated in a commercial light water reactor plant (average burn-up: 40 MW d kg-1). The lattice parameters of UO2 in fresh and irradiated specimens have been measured and compared with theoretical predictions. In the pristine state, the doped fuel has a somewhat smaller lattice parameter than the standard UO2 as a result of chromia doping. Increase in micro-strain and lattice parameter in irradiated materials is highlighted. All irradiated samples behave in a similar manner with UO2 lattice expansion occurring upon irradiation, where any Cr induced effect seems insignificant and accumulated lattice defects prevail. Elastic strain energy densities in the irradiated fuels are also evaluated based on the UO2 crystal lattice strain and non-uniform strain. The μ-XRD patterns further allow the evaluation of the crystalline domain size and sub-grain formation at different locations of the irradiated UO2 pellets.

Progress Toward an Neutral Yb Frequency Standard

NASA Astrophysics Data System (ADS)

Cramer, Claire; Hong, Tao; Nagourney, Warren; Fortson, Norval

2004-05-01

We report recent progress toward a direct observation of the ^1S_0^ -- ^3P0 clock transition at 578 nm in atomic Yb and review the experimental path to an optical frequency standard based on neutral Yb confined in a Stark-free optical lattice. Lamb-Dicke confinement in an optical lattice at the ``magic wavelength'' (λ _M) at which ground and excited state light shifts cancel will free the spectrum from Doppler and recoil shifts, providing an optimal environment for a clock consisting of an ensemble of cold, trapped atoms. In^171Yb the ^3P0 level has a hfs induced lifetime of 21 s. With this isotope in a Stark-free lattice at λ M ng 750 nm, perturbations to the clock energy levels can be held below the mHz level, providing an accuracy of a few parts in 10^18[1]. To observe the clock transition we use a shelving scheme that creates a leak in a MOT on the ^1S_0^ -- ^1P1 transition. A laser resonant with the clock transition drives atoms into the ^3P0 state, in which they can escape the MOT, leading to an observable decrease in MOT fluorescence. [1] S. Porsev and A. Derevianko, to be published in PRA

An Assessment of Subsurface Residual Stress Analysis in SLM Ti-6Al-4V

PubMed Central

Mishurova, Tatiana; Cabeza, Sandra; Artzt, Katia; Haubrich, Jan; Klaus, Manuela; Genzel, Christoph; Requena, Guillermo; Bruno, Giovanni

2017-01-01

Ti-6Al-4V bridges were additively fabricated by selective laser melting (SLM) under different scanning speed conditions, to compare the effect of process energy density on the residual stress state. Subsurface lattice strain characterization was conducted by means of synchrotron diffraction in energy dispersive mode. High tensile strain gradients were found at the frontal surface for samples in an as-built condition. The geometry of the samples promotes increasing strains towards the pillar of the bridges. We observed that the higher the laser energy density during fabrication, the lower the lattice strains. A relief of lattice strains takes place after heat treatment. PMID:28772706

Lattice dynamics and thermoelectric properties of nanocrystalline silicon-germanium alloys

DOE PAGES

Claudio, Tania; Stein, Niklas; Peterman, Nils; ...

2015-10-26

The lattice dynamics and thermoelectric properties of sintered phosphorus-doped nanostructured silicon- germanium alloys obtained by gas-phase synthesis were studied. Measurements of the density of phonon states by inelastic neutron scattering were combined with measurements of the elastic constants and the low- temperature heat capacity. A strong influence of nanostructuring and alloying on the lattice dynamics was observed. The thermoelectric transport properties of samples with different doping as well as samples sintered at different temperature were characterized between room temperature and 1000C. A peak figure of merit zT = 0:88 at 900C is observed and comparatively insensitive to the aforementioned param-more » eter variations.« less

Unbiased Sampling of Globular Lattice Proteins in Three Dimensions

NASA Astrophysics Data System (ADS)

Jacobsen, Jesper Lykke

2008-03-01

We present a Monte Carlo method that allows efficient and unbiased sampling of Hamiltonian walks on a cubic lattice. Such walks are self-avoiding and visit each lattice site exactly once. They are often used as simple models of globular proteins, upon adding suitable local interactions. Our algorithm can easily be equipped with such interactions, but we study here mainly the flexible homopolymer case where each conformation is generated with uniform probability. We argue that the algorithm is ergodic and has dynamical exponent z=0. We then use it to study polymers of size up to 643=262144 monomers. Results are presented for the effective interaction between end points, and the interaction with the boundaries of the system.

The VIS-AD data model: Integrating metadata and polymorphic display with a scientific programming language

NASA Technical Reports Server (NTRS)

Hibbard, William L.; Dyer, Charles R.; Paul, Brian E.

1994-01-01

The VIS-AD data model integrates metadata about the precision of values, including missing data indicators and the way that arrays sample continuous functions, with the data objects of a scientific programming language. The data objects of this data model form a lattice, ordered by the precision with which they approximate mathematical objects. We define a similar lattice of displays and study visualization processes as functions from data lattices to display lattices. Such functions can be applied to visualize data objects of all data types and are thus polymorphic.

Effect of elastic collisions and electronic excitation on lattice structure of NiTi bulk intermetallic compound irradiated with energetic ions

NASA Astrophysics Data System (ADS)

Ochi, M.; Kojima, H.; Hori, F.; Kaneno, Y.; Semboshi, S.; Saitoh, Y.; Okamoto, Y.; Ishikawa, N.; Iwase, A.

2018-07-01

NiTi bulk intermetallic compound with the B19‧ structure was irradiated with 1 MeV He, 5 MeV Al, 16 MeV Au and 200 MeV Xe ions, and the change in lattice structure near the surface by the ion bombardment was investigated by using the grazing incidence X-ray diffraction (GIXD) and the extended X-ray absorption fine structure (EXAFS). The lattice structure transformation by the irradiation strongly depends on ion species and/or energies. For the 1 MeV He irradiation, the lattice structure changed from B19‧ to the A2 structure, but did not show an amorphization even after the high fluence irradiation. For the 5 MeV Al irradiation, the samples are partially amorphized. For the 16 MeV Au irradiation, the lattice structure of the NiTi samples changed nearly completely from the B19‧ structure to the amorphous state via the A2 structure. The value of dpa (displacement per atom) which is needed for the amorphization is, however, much smaller than the case of the Al ion irradiation. For the 200 MeV Xe ion irradiation, the lattice structure completely changed to the A2 structure even by a small ion fluence. The dependence of the lattice structure transformation on elastic collisions (dpa), the spectrum of the primary knock-on (PKA) atoms and the density of energy deposited through electronic excitation was discussed.

Flavor-singlet baryons in the graded symmetry approach to partially quenched QCD

NASA Astrophysics Data System (ADS)

Hall, Jonathan M. M.; Leinweber, Derek B.

2016-11-01

Progress in the calculation of the electromagnetic properties of baryon excitations in lattice QCD presents new challenges in the determination of sea-quark loop contributions to matrix elements. A reliable estimation of the sea-quark loop contributions represents a pressing issue in the accurate comparison of lattice QCD results with experiment. In this article, an extension of the graded symmetry approach to partially quenched QCD is presented, which builds on previous theory by explicitly including flavor-singlet baryons in its construction. The formalism takes into account the interactions among both octet and singlet baryons, octet mesons, and their ghost counterparts; the latter enables the isolation of the quark-flow disconnected sea-quark loop contributions. The introduction of flavor-singlet states enables systematic studies of the internal structure of Λ -baryon excitations in lattice QCD, including the topical Λ (1405 ).

Nanoscale microstructure effects on hydrogen behavior in rapidly solidified aluminum alloys

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tashlykova-Bushkevich, Iya I.

2015-12-31

The present work summarizes recent progress in the investigation of nanoscale microstructure effects on hydrogen behavior in rapidly solidified aluminum alloys foils produced at exceptionally high cooling rates. We focus here on the potential of modification of hydrogen desorption kinetics in respect to weak and strong trapping sites that could serve as hydrogen sinks in Al materials. It is shown that it is important to elucidate the surface microstructure of the Al alloy foils at the submicrometer scale because rapidly solidified microstructural features affect hydrogen trapping at nanostructured defects. We discuss the profound influence of solute atoms on hydrogen−lattice defectmore » interactions in the alloys. with emphasis on role of vacancies in hydrogen evolution; both rapidly solidified pure Al and conventionally processed aluminum samples are considered.« less

Quantum simulation of strongly correlated condensed matter systems

NASA Astrophysics Data System (ADS)

Hofstetter, W.; Qin, T.

2018-04-01

We review recent experimental and theoretical progress in realizing and simulating many-body phases of ultracold atoms in optical lattices, which gives access to analog quantum simulations of fundamental model Hamiltonians for strongly correlated condensed matter systems, such as the Hubbard model. After a general introduction to quantum gases in optical lattices, their preparation and cooling, and measurement techniques for relevant observables, we focus on several examples, where quantum simulations of this type have been performed successfully during the past years: Mott-insulator states, itinerant quantum magnetism, disorder-induced localization and its interplay with interactions, and topological quantum states in synthetic gauge fields.

Nuclear physics from Lattice QCD

NASA Astrophysics Data System (ADS)

Shanahan, Phiala

2017-09-01

I will discuss the current state and future scope of numerical Lattice Quantum Chromodynamics (LQCD) calculations of nuclear matrix elements. The goal of the program is to provide direct QCD calculations of nuclear observables relevant to experimental programs, including double-beta decay matrix elements, nuclear corrections to axial matrix elements relevant to long-baseline neutrino experiments and nuclear sigma terms needed for theory predictions of dark matter cross-sections at underground detectors. I will discuss the progress and challenges on these fronts, and also address recent work constraining a gluonic analogue of the EMC effect, which will be measurable at a future electron-ion collider.

Stress Induced Charge-Ordering Process in LiMn 2O 4

DOE PAGES

Chen, Yan; Yu, Dunji; An, Ke

2016-07-25

In this letter we report the stress-induced Mn charge-ordering process in the LiMn 2O 4 spinel, evidenced by the lattice strain evolutions due to the Jahn–Teller effects. In situ neutron diffraction reveals the initial stage of this process at low stress, indicating the eg electron localization at the preferential Mn sites during the early phase transition as an underlying charge-ordering mechanism in the charge-frustrated LiMn 2O 4. The initial stage of this transition exhibits as a progressive lattice and charge evolution, without showing a first-order behavior.

Neutron diffraction study of the in situ oxidation of UO(2).

PubMed

Desgranges, Lionel; Baldinozzi, Gianguido; Rousseau, Gurvan; Nièpce, Jean-Claude; Calvarin, Gilbert

2009-08-17

This paper discusses uranium oxide crystal structure modifications that are observed during the low-temperature oxidation which transforms UO(2) into U(3)O(8). The symmetries and the structural parameters of UO(2), beta-U(4)O(9), beta-U(3)O(7), and U(3)O(8) were determined by refining neutron diffraction patterns on pure single-phase samples. Neutron diffraction patterns were also collected during the in situ oxidation of powder samples at 483 K. The lattice parameters and relative ratios of the four pure phases were measured during the progression of the isothermal oxidation. The transformation of UO(2) into U(3)O(8) involves a complex modification of the oxygen sublattice and the onset of complex superstructures for U(4)O(9) and U(3)O(7), associated with regular stacks of complex defects known as cuboctahedra, which consist of 13 oxygen atoms. The kinetics of the oxidation process are discussed on the basis of the results of the structural analysis.

Phase separation and large deviations of lattice active matter

NASA Astrophysics Data System (ADS)

Whitelam, Stephen; Klymko, Katherine; Mandal, Dibyendu

2018-04-01

Off-lattice active Brownian particles form clusters and undergo phase separation even in the absence of attractions or velocity-alignment mechanisms. Arguments that explain this phenomenon appeal only to the ability of particles to move persistently in a direction that fluctuates, but existing lattice models of hard particles that account for this behavior do not exhibit phase separation. Here we present a lattice model of active matter that exhibits motility-induced phase separation in the absence of velocity alignment. Using direct and rare-event sampling of dynamical trajectories, we show that clustering and phase separation are accompanied by pronounced fluctuations of static and dynamic order parameters. This model provides a complement to off-lattice models for the study of motility-induced phase separation.

Differentially Constrained Motion Planning with State Lattice Motion Primitives

DTIC Science & Technology

2012-02-01

datapoint distribution in such histograms to a scalar may be used . One example is Kullback - Leibler divergence; an even simpler method is a sum of ...the Coupled Layer Architecture for Robotic Autonomy (CLARAty) system at the Jet Propulsion Laboratory. This al- lowed us to test the application of ... good fit to extend the tree or the graph towards a random sample. However, by virtue of the regular structure of the state samples, lattice

Three-dimensional magnetophotonic crystals based on artificial opals

NASA Astrophysics Data System (ADS)

Baryshev, A. V.; Kodama, T.; Nishimura, K.; Uchida, H.; Inoue, M.

2004-06-01

We fabricated and experimentally investigated three-dimensional magnetophotonic crystals (3D MPCs) based on artificial opals. Opal samples with three-dimensional dielectric lattices were impregnated with different types of magnetic material. Magnetic and structural properties of 3D MPCs were studied by field emission scanning electron microscopy, x-ray diffraction analysis, and vibrating sample magnetometer. We have shown that magnetic materials synthesized in voids of opal lattices and the composites obtained have typical magnetic properties.

Modeling the self-assembly of ordered nanoporous materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Monson, Peter; Auerbach, Scott

This report describes progress on a collaborative project on the multiscale modeling of the assembly processes in the synthesis of nanoporous materials. Such materials are of enormous importance in modern technology with application in the chemical process industries, biomedicine and biotechnology as well as microelectronics. The project focuses on two important classes of materials: i) microporous crystalline materials, such as zeolites, and ii) ordered mesoporous materials. In the first case the pores are part of the crystalline structure, while in the second the structures are amorphous on the atomistic length scale but where surfactant templating gives rise to order onmore » the length scale of 2 - 20 nm. We have developed a modeling framework that encompasses both these kinds of materials. Our models focus on the assembly of corner sharing silica tetrahedra in the presence of structure directing agents. We emphasize a balance between sufficient realism in the models and computational tractibility given the complex many-body phenomena. We use both on-lattice and off-lattice models and the primary computational tools are Monte Carlo simulations with sampling techniques and ensembles appropriate to specific situations. Our modeling approach is the first to capture silica polymerization, nanopore crystallization, and mesopore formation through computer-simulated self assembly.« less

Effect of Nd Doping on Dielectric and Impedance Properties of PZT Nanoceramics

NASA Astrophysics Data System (ADS)

Kour, P.; Pradhan, S. K.; Kumar, Pawan; Sinha, S. K.; Kar, Manoranjan

2018-02-01

Neodymium-doped lead zirconate tianate, i.e. Pb1-x Nd x Zr0.52Ti0.48O3 (PNZT) ceramics, with x = 0-10 mol.% has been prepared by the sol-gel process. X-ray diffraction pattern at room temperature shows the pyrochlore free phase for all samples. The structural analysis suggests the coexistence of both rhombohedral (R3m space group) and tetragonal (P4 mm space group) crystal symmetries. Scanning electron micrographs of the samples show uniform distribution of grain and grain boundaries. Dielectric constant increases with the increase in neodymium concentration in the crystal lattice. Degree of diffuse phase transition increases with the increase in Nd3+ concentration in the sample. Nd3+ incorporation into the lead zirconatetitanate (PZT) lattice enhances the spreading factor. Interaction between neighbouring dipoles decreases with the increase of Nd3+ in PZT lattice. The conduction mechanism of the sample can be attributed to the overlapping large polar tunnelling. Second-order dielectric phase transition has been observed at the Curie temperature. The electrical properties of the sample can be explained by considering grain and grain boundaries contributions. All the samples show the poly-dispersive non-Debye type relaxation.

Parton distributions and lattice QCD calculations: A community white paper

NASA Astrophysics Data System (ADS)

Lin, Huey-Wen; Nocera, Emanuele R.; Olness, Fred; Orginos, Kostas; Rojo, Juan; Accardi, Alberto; Alexandrou, Constantia; Bacchetta, Alessandro; Bozzi, Giuseppe; Chen, Jiunn-Wei; Collins, Sara; Cooper-Sarkar, Amanda; Constantinou, Martha; Del Debbio, Luigi; Engelhardt, Michael; Green, Jeremy; Gupta, Rajan; Harland-Lang, Lucian A.; Ishikawa, Tomomi; Kusina, Aleksander; Liu, Keh-Fei; Liuti, Simonetta; Monahan, Christopher; Nadolsky, Pavel; Qiu, Jian-Wei; Schienbein, Ingo; Schierholz, Gerrit; Thorne, Robert S.; Vogelsang, Werner; Wittig, Hartmut; Yuan, C.-P.; Zanotti, James

2018-05-01

In the framework of quantum chromodynamics (QCD), parton distribution functions (PDFs) quantify how the momentum and spin of a hadron are divided among its quark and gluon constituents. Two main approaches exist to determine PDFs. The first approach, based on QCD factorization theorems, realizes a QCD analysis of a suitable set of hard-scattering measurements, often using a variety of hadronic observables. The second approach, based on first-principle operator definitions of PDFs, uses lattice QCD to compute directly some PDF-related quantities, such as their moments. Motivated by recent progress in both approaches, in this document we present an overview of lattice-QCD and global-analysis techniques used to determine unpolarized and polarized proton PDFs and their moments. We provide benchmark numbers to validate present and future lattice-QCD calculations and we illustrate how they could be used to reduce the PDF uncertainties in current unpolarized and polarized global analyses. This document represents a first step towards establishing a common language between the two communities, to foster dialogue and to further improve our knowledge of PDFs.

Role of the Euclidean signature in lattice calculations of quasidistributions and other nonlocal matrix elements

NASA Astrophysics Data System (ADS)

Briceño, Raúl A.; Hansen, Maxwell T.; Monahan, Christopher J.

2017-07-01

Lattice quantum chromodynamics (QCD) provides the only known systematic, nonperturbative method for first-principles calculations of nucleon structure. However, for quantities such as light-front parton distribution functions (PDFs) and generalized parton distributions (GPDs), the restriction to Euclidean time prevents direct calculation of the desired observable. Recently, progress has been made in relating these quantities to matrix elements of spatially nonlocal, zero-time operators, referred to as quasidistributions. Still, even for these time-independent matrix elements, potential subtleties have been identified in the role of the Euclidean signature. In this work, we investigate the analytic behavior of spatially nonlocal correlation functions and demonstrate that the matrix elements obtained from Euclidean lattice QCD are identical to those obtained using the Lehmann-Symanzik-Zimmermann reduction formula in Minkowski space. After arguing the equivalence on general grounds, we also show that it holds in a perturbative calculation, where special care is needed to identify the lattice prediction. Finally we present a proof of the uniqueness of the matrix elements obtained from Minkowski and Euclidean correlation functions to all order in perturbation theory.

Crystallographic Lattice Boltzmann Method

PubMed Central

Namburi, Manjusha; Krithivasan, Siddharth; Ansumali, Santosh

2016-01-01

Current approaches to Direct Numerical Simulation (DNS) are computationally quite expensive for most realistic scientific and engineering applications of Fluid Dynamics such as automobiles or atmospheric flows. The Lattice Boltzmann Method (LBM), with its simplified kinetic descriptions, has emerged as an important tool for simulating hydrodynamics. In a heterogeneous computing environment, it is often preferred due to its flexibility and better parallel scaling. However, direct simulation of realistic applications, without the use of turbulence models, remains a distant dream even with highly efficient methods such as LBM. In LBM, a fictitious lattice with suitable isotropy in the velocity space is considered to recover Navier-Stokes hydrodynamics in macroscopic limit. The same lattice is mapped onto a cartesian grid for spatial discretization of the kinetic equation. In this paper, we present an inverted argument of the LBM, by making spatial discretization as the central theme. We argue that the optimal spatial discretization for LBM is a Body Centered Cubic (BCC) arrangement of grid points. We illustrate an order-of-magnitude gain in efficiency for LBM and thus a significant progress towards feasibility of DNS for realistic flows. PMID:27251098

Parton distributions and lattice QCD calculations: A community white paper

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Huey-Wen; Nocera, Emanuele R.; Olness, Fred

In the framework of quantum chromodynamics (QCD), parton distribution functions (PDFs) quantify how the momentum and spin of a hadron are divided among its quark and gluon constituents. Two main approaches exist to determine PDFs. The first approach, based on QCD factorization theorems, realizes a QCD analysis of a suitable set of hard-scattering measurements, often using a variety of hadronic observables. The second approach, based on first-principle operator definitions of PDFs, uses lattice QCD to compute directly some PDF-related quantities, such as their moments. Motivated by recent progress in both approaches, in this paper we present an overview of lattice-QCDmore » and global-analysis techniques used to determine unpolarized and polarized proton PDFs and their moments. We provide benchmark numbers to validate present and future lattice-QCD calculations and we illustrate how they could be used to reduce the PDF uncertainties in current unpolarized and polarized global analyses. Finally, this document represents a first step towards establishing a common language between the two communities, to foster dialogue and to further improve our knowledge of PDFs.« less

Role of the Euclidean signature in lattice calculations of quasidistributions and other nonlocal matrix elements

DOE PAGES

Briceno, Raul A.; Hansen, Maxwell T.; Monahan, Christopher J.

2017-07-11

Lattice quantum chromodynamics (QCD) provides the only known systematic, nonperturbative method for first-principles calculations of nucleon structure. However, for quantities such as light-front parton distribution functions (PDFs) and generalized parton distributions (GPDs), the restriction to Euclidean time prevents direct calculation of the desired observable. Recently, progress has been made in relating these quantities to matrix elements of spatially nonlocal, zero-time operators, referred to as quasidistributions. Still, even for these time-independent matrix elements, potential subtleties have been identified in the role of the Euclidean signature. In this work, we investigate the analytic behavior of spatially nonlocal correlation functions and demonstrate thatmore » the matrix elements obtained from Euclidean lattice QCD are identical to those obtained using the Lehmann-Symanzik-Zimmermann reduction formula in Minkowski space. After arguing the equivalence on general grounds, we also show that it holds in a perturbative calculation, where special care is needed to identify the lattice prediction. Lastly, we present a proof of the uniqueness of the matrix elements obtained from Minkowski and Euclidean correlation functions to all order in perturbation theory.« less

Lattice QCD results on soft and hard probes of strongly interacting matter

NASA Astrophysics Data System (ADS)

Kaczmarek, Olaf

2017-11-01

We present recent results from lattice QCD relevant for the study of strongly interacting matter as it is produced in heavy ion collision experiments. The equation of state at non-vanishing density from a Taylor expansion up to 6th order will be discussed for a strangeness neutral system and using the expansion coefficients of the series limits on the critical point are estimated. Chemical freeze-out temperatures from the STAR and ALICE Collaborations will be compared to lines of constant physics calculated from the Taylor expansion of QCD bulk thermodynamic quantities. We show that qualitative features of the √{sNN} dependence of skewness and kurtosis ratios of net proton-number fluctuations measured by the STAR Collaboration can be understood from QCD results for cumulants of conserved baryon-number fluctuations. As an example for recent progress towards the determination of spectral and transport properties of the QGP from lattice QCD, we will present constraints on the thermal photon rate determined from a spectral reconstruction of continuum extrapolated lattice correlation functions in combination with input from most recent perturbative calculations.

Modulation of spin dynamics via voltage control of spin-lattice coupling in multiferroics

DOE PAGES

Zhu, Mingmin; Zhou, Ziyao; Peng, Bin; ...

2017-02-03

Our work aims at magnonics manipulation by the magnetoelectric coupling effect and is motivated by the most recent progresses in both magnonics (spin dynamics) and multiferroics fields. Here, voltage control of magnonics, particularly the surface spin waves, is achieved in La 0.7Sr 0.3MnO 3/0.7Pb(Mg 1/3Nb 2/3)O 3-0.3PbTiO 3 multiferroic heterostructures. With the electron spin resonance method, a large 135 Oe shift of surface spin wave resonance (≈7 times greater than conventional voltage-induced ferromagnetic resonance shift of 20 Oe) is determined. A model of the spin-lattice coupling effect, i.e., varying exchange stiffness due to voltage-induced anisotropic lattice changes, has been establishedmore » to explain experiment results with good agreement. In addition, an “on” and “off” spin wave state switch near the critical angle upon applying a voltage is created. The modulation of spin dynamics by spin-lattice coupling effect provides a platform for realizing energy-efficient, tunable magnonics devices.« less

Parton distributions and lattice QCD calculations: A community white paper

DOE PAGES

Lin, Huey-Wen; Nocera, Emanuele R.; Olness, Fred; ...

2018-01-31

In the framework of quantum chromodynamics (QCD), parton distribution functions (PDFs) quantify how the momentum and spin of a hadron are divided among its quark and gluon constituents. Two main approaches exist to determine PDFs. The first approach, based on QCD factorization theorems, realizes a QCD analysis of a suitable set of hard-scattering measurements, often using a variety of hadronic observables. The second approach, based on first-principle operator definitions of PDFs, uses lattice QCD to compute directly some PDF-related quantities, such as their moments. Motivated by recent progress in both approaches, in this paper we present an overview of lattice-QCDmore » and global-analysis techniques used to determine unpolarized and polarized proton PDFs and their moments. We provide benchmark numbers to validate present and future lattice-QCD calculations and we illustrate how they could be used to reduce the PDF uncertainties in current unpolarized and polarized global analyses. Finally, this document represents a first step towards establishing a common language between the two communities, to foster dialogue and to further improve our knowledge of PDFs.« less

Hadron mass and decays constant predictions of the valence approximation to lattice QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weingarten, D.

1993-05-01

A key goal of the lattice formulation of QCD is to reproduce the masses and decay constants of the low-lying baryons and mesons. Lattice QCD mass and decay constant predictions for the real world are supposed to be obtained from masses and decay constants calculated with finite lattice spacing and finite lattice volume by taking the limits of zero spacing and infinite volume. In addition, since the algorithms used for hadron mass and decay constant calculations become progressively slower for small quark masses, results are presently found with quark masses much larger than the expected values of the up andmore » down quark masses. Predictions for the properties of hadrons containing up and down quarks then require a further extrapolation to small quark masses. The author reports here mass and decay constant predictions combining all three extrapolations for Wilson quarks in the valence (quenched) approximation. This approximation may be viewed as replacing the momentum and frequency dependent color dielectric constant arising from quark-antiquark vacuum polarization with its zero-momentum, zero-frequency limit. These calculations used approximately one year of machine time on the GF11 parallel computer running at a sustained rate of between 5 and 7 Gflops.« less

Optical ferris wheel for ultracold atoms

NASA Astrophysics Data System (ADS)

Franke-Arnold, S.; Leach, J.; Padgett, M. J.; Lembessis, V. E.; Ellinas, D.; Wright, A. J.; Girkin, J. M.; Ohberg, P.; Arnold, A. S.

2007-07-01

We propose a versatile optical ring lattice suitable for trapping cold and quantum degenerate atomic samples. We demonstrate the realisation of intensity patterns from pairs of Laguerre-Gauss (exp(iℓө) modes with different ℓ indices. These patterns can be rotated by introducing a frequency shift between the modes. We can generate bright ring lattices for trapping atoms in red-detuned light, and dark ring lattices suitable for trapping atoms with minimal heating in the optical vortices of blue-detuned light. The lattice sites can be joined to form a uniform ring trap, making it ideal for studying persistent currents and the Mott insulator transition in a ring geometry.

The behavior of commensurate-incommensurate transitions using the phase field crystal model

NASA Astrophysics Data System (ADS)

Zhang, Tinghui; Lu, Yanli; Chen, Zheng

2018-02-01

We study the behavior of the commensurate-incommensurate (CI) transitions by using a phase field crystal model. The model is capable of modeling both elastic and plastic deformation and can simulate the evolution of the microstructure of the material at the atomic scale and the diffusive time scale, such as for adsorbed monolayer. Specifically, we study the behavior of the CI transitions as a function of lattice mismatch and the amplitude of substrate pinning potential. The behavior of CI phase transitions is revealed with the increase of the amplitude of pinning potential in some certain lattice mismatches. We find that for the negative lattice mismatch absorbed monolayer undergoes division, reorganization and displacement as increasing the amplitude of substrate pinning potential. In addition, for the positive mismatch absorbed monolayer undergoes a progress of phase transformation after a complete grain is split. Our results accord with simulations for atomic models of absorbed monolayer on a substrate surface.

X-ray investigations related to the shock history of the Shergotty achondrite

NASA Technical Reports Server (NTRS)

Horz, F.; Hanss, R.; Serna, C.

1986-01-01

The shock stress suffered by naturally shocked materials from the Shergotty achondrite was studied using X-ray diffraction techniques and experimentally shocked augite and enstatite as standards. The Shergotty pyroxenes revealed the formation of continuous diffraction rings, line broadening, preferred orientation of small scale diffraction domains, and other evidence of substantial lattice disorders. As disclosed by the application of Debye-Scherrer techniques, they are hybrids between single crystals and fine-grained random powders. The pyroxene lattice is very resistant to shock damage on smaller scales. While measurable lattice disaggregation and progressive fragmentation occur below 25 GPa, little additional damage is suffered from application of pressures between 30 to 60 GPa, making pressure calibration of naturally shocked pyroxenes via X-ray methods difficult. Powder diffractometer scans on pure maskelynite fractions of Shergotty revealed small amounts of still coherently diffracting plagioclase, which may contribute to the high refractive indices of the diaplectic feldspar glasses of Shergotty.

Phonon triggered rhombohedral lattice distortion in vanadium at high pressure

DOE PAGES

Antonangeli, Daniele; Farber, Daniel L.; Bosak, Alexei; ...

2016-08-19

In spite of the simple body-centered-cubic crystal structure, the elements of group V, vanadium, niobium and tantalum, show strong interactions between the electronic properties and lattice dynamics. Further, these interactions can be tuned by external parameters, such as pressure and temperature. We used inelastic x-ray scattering to probe the phonon dispersion of single-crystalline vanadium as a function of pressure to 45 GPa. Our measurements show an anomalous high-pressure behavior of the transverse acoustic mode along the (100) direction and a softening of the elastic modulus C44 that triggers a rhombohedral lattice distortion occurring between 34 and 39 GPa. Lastly, ourmore » results provide the missing experimental confirmation of the theoretically predicted shear instability arising from the progressive intra-band nesting of the Fermi surface with increasing pressure, a scenario common to all transition metals of group V.« less

Giant photostriction in organic–inorganic lead halide perovskites

PubMed Central

Zhou, Yang; You, Lu; Wang, Shiwei; Ku, Zhiliang; Fan, Hongjin; Schmidt, Daniel; Rusydi, Andrivo; Chang, Lei; Wang, Le; Ren, Peng; Chen, Liufang; Yuan, Guoliang; Chen, Lang; Wang, Junling

2016-01-01

Among the many materials investigated for next-generation photovoltaic cells, organic–inorganic lead halide perovskites have demonstrated great potential thanks to their high power conversion efficiency and solution processability. Within a short period of about 5 years, the efficiency of solar cells based on these materials has increased dramatically from 3.8 to over 20%. Despite the tremendous progress in device performance, much less is known about the underlying photophysics involving charge–orbital–lattice interactions and the role of the organic molecules in this hybrid material remains poorly understood. Here, we report a giant photostrictive response, that is, light-induced lattice change, of >1,200 p.p.m. in methylammonium lead iodide, which could be the key to understand its superior optical properties. The strong photon-lattice coupling also opens up the possibility of employing these materials in wireless opto-mechanical devices. PMID:27044485

Symmetry-protected gapless Z2 spin liquids

NASA Astrophysics Data System (ADS)

Lu, Yuan-Ming

2018-03-01

Despite rapid progress in understanding gapped topological states, much less is known about gapless topological phases of matter, especially in strongly correlated electrons. In this work, we discuss a large class of robust gapless quantum spin liquids in frustrated magnets made of half-integer spins, which are described by gapless fermionic spinons coupled to dynamical Z2 gauge fields. Requiring U(1 ) spin conservation, time-reversal, and certain space-group symmetries, we show that certain spinon symmetry fractionalization class necessarily leads to a gapless spectrum. These gapless excitations are stable against any perturbations, as long as the required symmetries are preserved. Applying these gapless criteria to spin-1/2 systems on square, triangular, and kagome lattices, we show that all gapped symmetric Z2 spin liquids in Abrikosov-fermion representation can also be realized in Schwinger-boson representation. This leads to 64 gapped Z2 spin liquids on square lattice, and 8 gapped states on both kagome and triangular lattices.

Exact Calculation of the Thermodynamics of Biomacromolecules on Cubic Recursive Lattice.

NASA Astrophysics Data System (ADS)

Huang, Ran

The thermodynamics of biomacromolecules featured as foldable polymer with inner-linkage of hydrogen bonds, e. g. protein, RNA and DNA, play an impressive role in either physical, biological, and polymer sciences. By treating the foldable chains to be the two-tolerate self-avoiding trails (2T polymer), abstract lattice modeling of these complex polymer systems to approach their thermodynamics and subsequent bio-functional properties have been developed for decades. Among these works, the calculations modeled on Bethe and Husimi lattice have shown the excellence of being exactly solvable. Our project extended this effort into the 3D situation, i.e. the cubic recursive lattice. The preliminary exploration basically confirmed others' previous findings on the planar structure, that we have three phases in the grand-canonical phase diagram, with a 1st order transition between non-polymerized and polymer phases, and a 2nd order transition between two distinguishable polymer phases. However the hydrogen bond energy J, stacking energy ɛ, and chain rigidity energy H play more vigorous effects on the thermal behaviors, and this is hypothesized to be due to the larger number of possible configurations provided by the complicated 3D model. By the so far progress, the calculation of biomacromolecules may be applied onto more complex recursive lattices, such as the inhomogeneous lattice to describe the cross-dimensional situations, and beside the thermal properties of the 2T polymers, we may infer some interesting insights of the mysterious folding problem itself. National Natural Science Foundation of China.

Dual tunneling-unit scanning tunneling microscope for length measurement based on crystalline lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, H.; Higuchi, T.; Nishioki, N.

1997-01-01

A dual tunneling-unit scanning tunneling microscope (DTU STM) was developed for nm order length measurement with wide scan range. The crystalline lattice of highly oriented pyrolitic graphite (HOPG) was used as reference scale. A reference unit was set up on top of a test unit. The reference sample holder and the probe tip of test unit were attached to one single XY scanner on either surface, while the test sample holder was open. This enables simultaneous acquisition of wide images of HOPG and test sample. The length in test sample image was measured by counting the number of HOPG lattices.more » An inchworm actuator and an impact drive mechanism were introduced to roughly position probe tips. The XY scanner was designed to be elastic to eliminate image distortion. Some comparison experiments using two HOPG chips were carried out in air. The DTU STM is confirmed to be a stable and more powerful device for length measurement which has nanometer accuracy when covering a wide scan range up to several micrometers, and is capable of measuring comparatively large and heavy samples. {copyright} {ital 1997 American Vacuum Society.}« less

The recombination velocity at III-V compound heterojunctions with applications to Al (x) Ga(1-x)As-GaAs(1-y)Sb(y)

NASA Technical Reports Server (NTRS)

Kim, J. S.

1978-01-01

Interface recombination velocity in AlxGa1-xAs-GaAs and A10.85 Ga0.15As-GaAs1-ySby heterojunction systems was studied as a function of lattice mismatch. The results are applied to the design of highly efficient III-V heterojunction solar cells. A horizontal liquid-phase epitaxial growth system was used to prepare p-p-p and p-p-n double heterojunction test samples with specified values of x and y. Samples were grown at each composition, with different GaAs and GaAsSb layer thicknesses. A method was developed to obtain the lattice mismatch and lattice constants in mixed single crystals grown on (100) and (111)B oriented GaAs substrates.

PROGRESS ON THE STUDY OF THE URANIUM-ALUMINUM-IRON CONSTITUTION DIAGRAM FOR THE PERIOD APRIL 1-AUGUST 31, 1963

DOE Office of Scientific and Technical Information (OSTI.GOV)

Russell, R.B.

Progress is reported of a research program on deterinining the U--Al-- Fe constitution diagram up to approximates 1000 ppm each of Al and Fe. Results are reported of metallographic examinations of U--Al, U--Fe, and U--Al--Fe alloys, and tentative phase diagrams are given for all three systems. Lattice parameters and electrical resistances were measured in an effort to determine the solid solubilities of Al and Fe in U. (D.L.C.)

Gibbs sampling on large lattice with GMRF

NASA Astrophysics Data System (ADS)

Marcotte, Denis; Allard, Denis

2018-02-01

Gibbs sampling is routinely used to sample truncated Gaussian distributions. These distributions naturally occur when associating latent Gaussian fields to category fields obtained by discrete simulation methods like multipoint, sequential indicator simulation and object-based simulation. The latent Gaussians are often used in data assimilation and history matching algorithms. When the Gibbs sampling is applied on a large lattice, the computing cost can become prohibitive. The usual practice of using local neighborhoods is unsatisfying as it can diverge and it does not reproduce exactly the desired covariance. A better approach is to use Gaussian Markov Random Fields (GMRF) which enables to compute the conditional distributions at any point without having to compute and invert the full covariance matrix. As the GMRF is locally defined, it allows simultaneous updating of all points that do not share neighbors (coding sets). We propose a new simultaneous Gibbs updating strategy on coding sets that can be efficiently computed by convolution and applied with an acceptance/rejection method in the truncated case. We study empirically the speed of convergence, the effect of choice of boundary conditions, of the correlation range and of GMRF smoothness. We show that the convergence is slower in the Gaussian case on the torus than for the finite case studied in the literature. However, in the truncated Gaussian case, we show that short scale correlation is quickly restored and the conditioning categories at each lattice point imprint the long scale correlation. Hence our approach enables to realistically apply Gibbs sampling on large 2D or 3D lattice with the desired GMRF covariance.

Ising lattices with +/-J second-nearest-neighbor interactions

NASA Astrophysics Data System (ADS)

Ramírez-Pastor, A. J.; Nieto, F.; Vogel, E. E.

1997-06-01

Second-nearest-neighbor interactions are added to the usual nearest-neighbor Ising Hamiltonian for square lattices in different ways. The starting point is a square lattice where half the nearest-neighbor interactions are ferromagnetic and the other half of the bonds are antiferromagnetic. Then, second-nearest-neighbor interactions can also be assigned randomly or in a variety of causal manners determined by the nearest-neighbor interactions. In the present paper we consider three causal and three random ways of assigning second-nearest-neighbor exchange interactions. Several ground-state properties are then calculated for each of these lattices:energy per bond ɛg, site correlation parameter pg, maximal magnetization μg, and fraction of unfrustrated bonds hg. A set of 500 samples is considered for each size N (number of spins) and array (way of distributing the N spins). The properties of the original lattices with only nearest-neighbor interactions are already known, which allows realizing the effect of the additional interactions. We also include cubic lattices to discuss the distinction between coordination number and dimensionality. Comparison with results for triangular and honeycomb lattices is done at specific points.

Scattering processes and resonances from lattice QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Briceno, Raul A.; Dudek, Jozef J.; Young, Ross D.

The vast majority of hadrons observed in nature are not stable under the strong interaction; rather they are resonances whose existence is deduced from enhancements in the energy dependence of scattering amplitudes. The study of hadron resonances offers a window into the workings of quantum chromodynamics (QCD) in the low-energy nonperturbative region, and in addition many probes of the limits of the electroweak sector of the standard model consider processes which feature hadron resonances. From a theoretical standpoint, this is a challenging field: the same dynamics that binds quarks and gluons into hadron resonances also controls their decay into lightermore » hadrons, so a complete approach to QCD is required. Presently, lattice QCD is the only available tool that provides the required nonperturbative evaluation of hadron observables. This paper reviews progress in the study of few-hadron reactions in which resonances and bound states appear using lattice QCD techniques. The leading approach is described that takes advantage of the periodic finite spatial volume used in lattice QCD calculations to extract scattering amplitudes from the discrete spectrum of QCD eigenstates in a box. An explanation is given of how from explicit lattice QCD calculations one can rigorously garner information about a variety of resonance properties, including their masses, widths, decay couplings, and form factors. Finally, the challenges which currently limit the field are discussed along with the steps being taken to resolve them.« less

Scattering processes and resonances from lattice QCD

NASA Astrophysics Data System (ADS)

Briceño, Raúl A.; Dudek, Jozef J.; Young, Ross D.

2018-04-01

The vast majority of hadrons observed in nature are not stable under the strong interaction; rather they are resonances whose existence is deduced from enhancements in the energy dependence of scattering amplitudes. The study of hadron resonances offers a window into the workings of quantum chromodynamics (QCD) in the low-energy nonperturbative region, and in addition many probes of the limits of the electroweak sector of the standard model consider processes which feature hadron resonances. From a theoretical standpoint, this is a challenging field: the same dynamics that binds quarks and gluons into hadron resonances also controls their decay into lighter hadrons, so a complete approach to QCD is required. Presently, lattice QCD is the only available tool that provides the required nonperturbative evaluation of hadron observables. This article reviews progress in the study of few-hadron reactions in which resonances and bound states appear using lattice QCD techniques. The leading approach is described that takes advantage of the periodic finite spatial volume used in lattice QCD calculations to extract scattering amplitudes from the discrete spectrum of QCD eigenstates in a box. An explanation is given of how from explicit lattice QCD calculations one can rigorously garner information about a variety of resonance properties, including their masses, widths, decay couplings, and form factors. The challenges which currently limit the field are discussed along with the steps being taken to resolve them.

Scattering processes and resonances from lattice QCD

DOE PAGES

Briceno, Raul A.; Dudek, Jozef J.; Young, Ross D.

2018-04-18

The vast majority of hadrons observed in nature are not stable under the strong interaction; rather they are resonances whose existence is deduced from enhancements in the energy dependence of scattering amplitudes. The study of hadron resonances offers a window into the workings of quantum chromodynamics (QCD) in the low-energy nonperturbative region, and in addition many probes of the limits of the electroweak sector of the standard model consider processes which feature hadron resonances. From a theoretical standpoint, this is a challenging field: the same dynamics that binds quarks and gluons into hadron resonances also controls their decay into lightermore » hadrons, so a complete approach to QCD is required. Presently, lattice QCD is the only available tool that provides the required nonperturbative evaluation of hadron observables. This paper reviews progress in the study of few-hadron reactions in which resonances and bound states appear using lattice QCD techniques. The leading approach is described that takes advantage of the periodic finite spatial volume used in lattice QCD calculations to extract scattering amplitudes from the discrete spectrum of QCD eigenstates in a box. An explanation is given of how from explicit lattice QCD calculations one can rigorously garner information about a variety of resonance properties, including their masses, widths, decay couplings, and form factors. Finally, the challenges which currently limit the field are discussed along with the steps being taken to resolve them.« less

Nuclear reaction analysis of Ge ion-implanted ZnO bulk single crystals: The evaluation of the displacement in oxygen lattices

NASA Astrophysics Data System (ADS)

Kamioka, K.; Oga, T.; Izawa, Y.; Kuriyama, K.; Kushida, K.; Kinomura, A.

2014-08-01

The displacement of oxygen lattices in Ge ion-implanted ZnO bulk single crystals is studied by nuclear reaction analysis (NAR), photoluminescence (PL), and Van der Pauw methods. The Ge ion-implantation (net concentration: 2.6 × 1020 cm-3) into ZnO is performed using a multiple-step energy. The high resistivity of ∼103 Ω cm in un-implanted samples remarkably decreased to ∼10-2 Ω cm after implanting Ge-ion and annealing subsequently. NRA measurements of as-implanted and annealed samples suggest the existence of the lattice displacement of O atoms acting as acceptor defects. As O related defects still remain after annealing, these defects are not attributed to the origin of the low resistivity in 800 and 1000 °C annealed ZnO.

Bose-Einstein condensate in an optical lattice with Raman-assisted two-dimensional spin-orbit coupling

NASA Astrophysics Data System (ADS)

Pan, Jian-Song; Zhang, Wei; Yi, Wei; Guo, Guang-Can

2016-10-01

In a recent experiment (Z. Wu, L. Zhang, W. Sun, X.-T. Xu, B.-Z. Wang, S.-C. Ji, Y. Deng, S. Chen, X.-J. Liu, and J.-W. Pan, arXiv:1511.08170 [cond-mat.quant-gas]), a Raman-assisted two-dimensional spin-orbit coupling has been realized for a Bose-Einstein condensate in an optical lattice potential. In light of this exciting progress, we study in detail key properties of the system. As the Raman lasers inevitably couple atoms to high-lying bands, the behaviors of the system in both the single- and many-particle sectors are significantly affected. In particular, the high-band effects enhance the plane-wave phase and lead to the emergence of "roton" gaps at low Zeeman fields. Furthermore, we identify high-band-induced topological phase boundaries in both the single-particle and the quasiparticle spectra. We then derive an effective two-band model, which captures the high-band physics in the experimentally relevant regime. Our results not only offer valuable insights into the two-dimensional lattice spin-orbit coupling, but also provide a systematic formalism to model high-band effects in lattice systems with Raman-assisted spin-orbit couplings.

Self-assembled DNA Structures for Nanoconstruction

NASA Astrophysics Data System (ADS)

Yan, Hao; Yin, Peng; Park, Sung Ha; Li, Hanying; Feng, Liping; Guan, Xiaoju; Liu, Dage; Reif, John H.; LaBean, Thomas H.

2004-09-01

In recent years, a number of research groups have begun developing nanofabrication methods based on DNA self-assembly. Here we review our recent experimental progress to utilize novel DNA nanostructures for self-assembly as well as for templates in the fabrication of functional nano-patterned materials. We have prototyped a new DNA nanostructure known as a cross structure. This nanostructure has a 4-fold symmetry which promotes its self-assembly into tetragonal 2D lattices. We have utilized the tetragonal 2D lattices as templates for highly conductive metallic nanowires and periodic 2D protein nano-arrays. We have constructed and characterized a DNA nanotube, a new self-assembling superstructure composed of DNA tiles. We have also demonstrated an aperiodic DNA lattice composed of DNA tiles assembled around a long scaffold strand; the system translates information encoded in the scaffold strand into a specific and reprogrammable barcode pattern. We have achieved metallic nanoparticle linear arrays templated on self-assembled 1D DNA arrays. We have designed and demonstrated a 2-state DNA lattice, which displays expand/contract motion switched by DNA nanoactuators. We have also achieved an autonomous DNA motor executing unidirectional motion along a linear DNA track.

Magnetic field-induced changes of lattice parameters and thermal expansion behavior of the CoMnSi compound

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kou, R. H.; Gao, J.; Wang, G.

2016-02-01

The crystal structure of the CoMnSi compound during zero-field cooling and field cooling from room temperature down to 200 K was studied using the synchrotron radiation X-ray diffraction technique. The results show that the lattice parameters and thermal expansion behavior of the sample are changed by the applied magnetic fields. The lattice contracts along the a axis, but expands along the b and c axes. Due to enlarged and anisotropic changes under a magnetic field of 6 T, the lattice shows an invar-like behavior along all three axes. Critical interatomic distances and bond angles also show large changes under themore » influence of such a high magnetic field. These magnetic field-induced changes of the lattice are discussed with respect to their contributions to the large magnetocaloric effect of the CoMnSi compound.« less

Intergranular stress study of TC11 titanium alloy after laser shock peening by synchrotron-based high-energy X-ray diffraction

NASA Astrophysics Data System (ADS)

Su, R.; Li, L.; Wang, Y. D.; Nie, Z. H.; Ren, Y.; Zhou, X.; Wang, J.

2018-05-01

The distribution of residual lattice strain as a function of depth were carefully investigated by synchrotron-based high energy X-ray diffraction (HEXRD) in TC11 titanium alloy after laser shock peening (LSP). The results presented big compressive residual lattice strains at surface and subsurface, then tensile residual lattice strains in deeper region, and finally close to zero lattice strains in further deep interior with no plastic deformation thereafter. These evolutions in residual lattice strains were attributed to the balance of direct load effect from laser shock wave and the derivative restriction force effect from surrounding material. Significant intergranular stress was evidenced in the processed sample. The intergranular stress exhibited the largest value at surface, and rapidly decreased with depth increase. The magnitude of intergranular stress was proportional to the severity of the plastic deformation caused by LSP. Two shocks generated larger intergranular stress than one shock.

Density functional calculation of activation energies for lattice and grain boundary diffusion in alumina

NASA Astrophysics Data System (ADS)

Lei, Yinkai; Gong, Yu; Duan, Zhiyao; Wang, Guofeng

2013-06-01

To acquire knowledge on the lattice and grain boundary diffusion processes in alumina, we have determined the activation energies of elementary O and Al diffusive jumps in the bulk crystal, Σ3(0001) grain boundaries, and Σ3(101¯0) grain boundaries of α-Al2O3 using the first-principles density functional theory method. Specifically, we calculated the activation energies for four elementary jumps of both O and Al lattice diffusion in alumina. It was predicted that the activation energy of O lattice diffusion varied from 3.58 to 5.03 eV, while the activation energy of Al lattice diffusion ranged from 1.80 to 3.17 eV. As compared with experimental measurements, the theoretical predictions of the activation energy for lattice diffusion were lower and thus implied that there might be other high-energy diffusive jumps in the experimental alumina samples. Moreover, our results suggested that the Al lattice diffusion was faster than the O lattice diffusion in alumina, in agreement with experiment observations. Furthermore, it was found from our calculations for α-Al2O3 that the activation energies of O and Al grain boundary diffusion in the high-energy Σ3(0001) grain boundaries were significantly lower than those of the lattice diffusion. In contrast, the activation energies of O and Al grain boundary diffusion in the low-energy Σ3(101¯0) grain boundaries could be even higher than those of the lattice diffusion.

Prediction of protein loop conformations using multiscale modeling methods with physical energy scoring functions.

PubMed

Olson, Mark A; Feig, Michael; Brooks, Charles L

2008-04-15

This article examines ab initio methods for the prediction of protein loops by a computational strategy of multiscale conformational sampling and physical energy scoring functions. Our approach consists of initial sampling of loop conformations from lattice-based low-resolution models followed by refinement using all-atom simulations. To allow enhanced conformational sampling, the replica exchange method was implemented. Physical energy functions based on CHARMM19 and CHARMM22 parameterizations with generalized Born (GB) solvent models were applied in scoring loop conformations extracted from the lattice simulations and, in the case of all-atom simulations, the ensemble of conformations were generated and scored with these models. Predictions are reported for 25 loop segments, each eight residues long and taken from a diverse set of 22 protein structures. We find that the simulations generally sampled conformations with low global root-mean-square-deviation (RMSD) for loop backbone coordinates from the known structures, whereas clustering conformations in RMSD space and scoring detected less favorable loop structures. Specifically, the lattice simulations sampled basins that exhibited an average global RMSD of 2.21 +/- 1.42 A, whereas clustering and scoring the loop conformations determined an RMSD of 3.72 +/- 1.91 A. Using CHARMM19/GB to refine the lattice conformations improved the sampling RMSD to 1.57 +/- 0.98 A and detection to 2.58 +/- 1.48 A. We found that further improvement could be gained from extending the upper temperature in the all-atom refinement from 400 to 800 K, where the results typically yield a reduction of approximately 1 A or greater in the RMSD of the detected loop. Overall, CHARMM19 with a simple pairwise GB solvent model is more efficient at sampling low-RMSD loop basins than CHARMM22 with a higher-resolution modified analytical GB model; however, the latter simulation method provides a more accurate description of the all-atom energy surface, yet demands a much greater computational cost. (c) 2007 Wiley Periodicals, Inc.

Radiation-Induced Changes in Quartz, A Mineral Analog of Nuclear Power Plant Concrete Aggregates.

PubMed

Silva, Chinthaka M; Rosseel, Thomas M; Kirkegaard, Marie C

2018-03-19

Quartz single-crystal samples consisting of α-quartz crystal structure were neutron irradiated to fluences of 5 × 10 18 , 4 × 10 19 , and 2 × 10 20 n/cm 2 (E > 0.1 MeV) at two temperatures (52 and 95 °C). The changes in the α-quartz phase as a function of these two conditions (temperature and fluence) were studied using X-ray powder diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM), and the results acquired using these complementary techniques are presented in a single place for the first time. XRD studies showed that the lattice parameters of α-quartz increased with increasing neutron flux. The lattice growth was larger for the samples that were neutron irradiated at 52 °C than at 95 °C. Moreover, an amorphous content was determined in the quartz samples neutron irradiated at 4 × 10 19 n/cm 2 , with the greater amount being in the 52 °C irradiated sample. Complete amorphization of quartz was observed at a fluence of 2 × 10 20 n/cm 2 (E > 0.1 MeV) using XRD and confirmed by TEM characterization and Raman spectroscopic studies. The cause for α-quartz lattice expansion and sample amorphization was also explored using XRD and Raman spectroscopic studies.

Growth and characterization of AlInAsSb layers lattice-matched to GaSb

NASA Astrophysics Data System (ADS)

Tournet, J.; Rouillard, Y.; Tournié, E.

2017-11-01

We report on the growth by solid-source MBE of random-alloy AlxIn1-xAsySb1-y layers lattice-matched to (0 0 1)-GaSb substrates, with xAl ∈ [0.25; 0.75]. The samples quality and morphology were characterized by X-ray diffraction, Nomarski microscopy and atomic force microscopy. Layers grown at 400 °C demonstrated smooth surfaces and no sign of phase decomposition. Samples with xAl ≤ 0.60 demonstrated photoluminescence (PL) at 300 K whereas samples with higher Al content only demonstrated PL at low temperature. Samples grown at 430 °C, in contrast, exhibited PL at low temperature only, whatever their composition. Inferred bandgap energies corroborate the estimation of a non-null quaternary bowing parameter made by Donati, Kaspi and Malloy in Journal of Applied Physics 94 (2003) 5814. Upon annealing, the PL peak energies increased, getting even closer to the theoretical values. These results are in agreement with recently published results on digital AlInAsSb alloys. Our work, which reports the first evidence for PL emission from random-alloy AlInAsSb layers lattice-matched to GaSb, opens the way to their use in optoelectronic devices.

Lattice based Kinetic Monte Carlo Simulations of a complex chemical reaction network

NASA Astrophysics Data System (ADS)

Danielson, Thomas; Savara, Aditya; Hin, Celine

Lattice Kinetic Monte Carlo (KMC) simulations offer a powerful alternative to using ordinary differential equations for the simulation of complex chemical reaction networks. Lattice KMC provides the ability to account for local spatial configurations of species in the reaction network, resulting in a more detailed description of the reaction pathway. In KMC simulations with a large number of reactions, the range of transition probabilities can span many orders of magnitude, creating subsets of processes that occur more frequently or more rarely. Consequently, processes that have a high probability of occurring may be selected repeatedly without actually progressing the system (i.e. the forward and reverse process for the same reaction). In order to avoid the repeated occurrence of fast frivolous processes, it is necessary to throttle the transition probabilities in such a way that avoids altering the overall selectivity. Likewise, as the reaction progresses, new frequently occurring species and reactions may be introduced, making a dynamic throttling algorithm a necessity. We present a dynamic steady-state detection scheme with the goal of accurately throttling rate constants in order to optimize the KMC run time without compromising the selectivity of the reaction network. The algorithm has been applied to a large catalytic chemical reaction network, specifically that of methanol oxidative dehydrogenation, as well as additional pathways on CeO2(111) resulting in formaldehyde, CO, methanol, CO2, H2 and H2O as gas products.

Classical Magnetic Frustration

NASA Astrophysics Data System (ADS)

Tsao, Eugene; Henriksen, Erik

We report on studies of classical magnetic frustration, inspired by Mellado et al., by studying an ensemble of freely rotating magnets, made of 1'' rare-earth bar magnets press-fit into polypropylene spheres floating on air bearings. The magnets can be arranged in any configuration to study frustration in 1, 2, or 3 dimensions. For instance, arranged in a Kagome lattice the magnets show an absence of high-energy in-in-in and out-out-out states; the presence of multiple ground states is indicative of macroscopic frustration. We also observe classical ``magnon'' transport in a one-dimensional chain. We will report on progress made in exploring the behavior of these magnets in triangular, Kagome, and honeycomb lattice configurations.

Negative and Zero Thermal Expansion NiTi Superelastic Shape Memory Alloy by Microstructure Engineering

NASA Astrophysics Data System (ADS)

Sun, Qingping; Yu, Chao; Kang, Guozheng

2018-03-01

We report recent progress in tailoring the thermal expansion (TE) of nanocrystalline (NC) NiTi by microstructure hierarchical design and control without composition change. Fabrication and characterization methods are outlined and preliminary results of both experiment and mechanism-based modeling are presented to understand and get insight into the unusual TE phenomena. The important roles of the intrinsic thermal expansion anisotropy of B19' lattice and the suppression of phase transition by the extrinsic fabricated microstructure (cold rolling and annealing, grain size, defects, textures and volume fractions of nanoscaled B2 and B19' lattices) in the overall macroscopic TE behaviors of the superelastic NC NiTi polycrystal SMAs are emphasized.

Mesoscopic modeling of multi-physicochemical transport phenomena in porous media

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kang, Qinjin; Wang, Moran; Mukherjee, Partha P

2009-01-01

We present our recent progress on mesoscopic modeling of multi-physicochemical transport phenomena in porous media based on the lattice Boltzmann method. Simulation examples include injection of CO{sub 2} saturated brine into a limestone rock, two-phase behavior and flooding phenomena in polymer electrolyte fuel cells, and electroosmosis in homogeneously charged porous media. It is shown that the lattice Boltzmann method can account for multiple, coupled physicochemical processes in these systems and can shed some light on the underlying physics occuning at the fundamental scale. Therefore, it can be a potential powerful numerical tool to analyze multi-physicochemical processes in various energy, earth,more » and environmental systems.« less

Comparison of competing segmentation standards for X-ray computed topographic imaging using Lattice Boltzmann techniques

NASA Astrophysics Data System (ADS)

Larsen, J. D.; Schaap, M. G.

2013-12-01

Recent advances in computing technology and experimental techniques have made it possible to observe and characterize fluid dynamics at the micro-scale. Many computational methods exist that can adequately simulate fluid flow in porous media. Lattice Boltzmann methods provide the distinct advantage of tracking particles at the microscopic level and returning macroscopic observations. While experimental methods can accurately measure macroscopic fluid dynamics, computational efforts can be used to predict and gain insight into fluid dynamics by utilizing thin sections or computed micro-tomography (CMT) images of core sections. Although substantial effort have been made to advance non-invasive imaging methods such as CMT, fluid dynamics simulations, and microscale analysis, a true three dimensional image segmentation technique has not been developed until recently. Many competing segmentation techniques are utilized in industry and research settings with varying results. In this study lattice Boltzmann method is used to simulate stokes flow in a macroporous soil column. Two dimensional CMT images were used to reconstruct a three dimensional representation of the original sample. Six competing segmentation standards were used to binarize the CMT volumes which provide distinction between solid phase and pore space. The permeability of the reconstructed samples was calculated, with Darcy's Law, from lattice Boltzmann simulations of fluid flow in the samples. We compare simulated permeability from differing segmentation algorithms to experimental findings.

Lattice-based model of ductal carcinoma in situ suggests rules for breast cancer progression to an invasive state.

PubMed

Boghaert, Eline; Radisky, Derek C; Nelson, Celeste M

2014-12-01

Ductal carcinoma in situ (DCIS) is a heterogeneous group of non-invasive lesions of the breast that result from abnormal proliferation of mammary epithelial cells. Pathologists characterize DCIS by four tissue morphologies (micropapillary, cribriform, solid, and comedo), but the underlying mechanisms that distinguish the development and progression of these morphologies are not well understood. Here we explored the conditions leading to the emergence of the different morphologies of DCIS using a two-dimensional multi-cell lattice-based model that incorporates cell proliferation, apoptosis, necrosis, adhesion, and contractility. We found that the relative rates of cell proliferation and apoptosis governed which of the four morphologies emerged. High proliferation and low apoptosis favored the emergence of solid and comedo morphologies. In contrast, low proliferation and high apoptosis led to the micropapillary morphology, whereas high proliferation and high apoptosis led to the cribriform morphology. The natural progression between morphologies cannot be investigated in vivo since lesions are usually surgically removed upon detection; however, our model suggests probable transitions between these morphologies during breast cancer progression. Importantly, cribriform and comedo appear to be the ultimate morphologies of DCIS. Motivated by previous experimental studies demonstrating that tumor cells behave differently depending on where they are located within the mammary duct in vivo or in engineered tissues, we examined the effects of tissue geometry on the progression of DCIS. In agreement with our previous experimental work, we found that cells are more likely to invade from the end of ducts and that this preferential invasion is regulated by cell adhesion and contractility. This model provides additional insight into tumor cell behavior and allows the exploration of phenotypic transitions not easily monitored in vivo.

Decoupling the Lattice Distortion and Charge Doping Effects on the Phase Transition Behavior of VO2 by Titanium (Ti4+) Doping

PubMed Central

Wu, Yanfei; Fan, Lele; Liu, Qinghua; Chen, Shi; Huang, Weifeng; Chen, Feihu; Liao, Guangming; Zou, Chongwen; Wu, Ziyu

2015-01-01

The mechanism for regulating the critical temperature (TC) of metal-insulator transition (MIT) in ions-doped VO2 systems is still a matter of debate, in particular, the unclear roles of lattice distortion and charge doping effects. To rule out the charge doping effect on the regulation of TC, we investigated Ti4+-doped VO2 (TixV1-xO2) system. It was observed that the TC of TixV1-xO2 samples first slightly decreased and then increased with increasing Ti concentration. X-ray absorption fine structure (XAFS) spectroscopy was used to explore the electronic states and local lattice structures around both Ti and V atoms in TixV1-xO2 samples. Our results revealed the local structure evolution from the initial anatase to the rutile-like structure around the Ti dopants. Furthermore, the host monoclinic VO2 lattice, specifically, the VO6 octahedra would be subtly distorted by Ti doping. The distortion of VO6 octahedra and the variation of TC showed almost the similar trend, confirming the direct effect of local structural perturbations on the phase transition behavior. By comparing other ion-doping systems, we point out that the charge doping is more effective than the lattice distortion in modulating the MIT behavior of VO2 materials. PMID:25950809

Effect of lattice strain on structural and magnetic properties of Ca substituted barium hexaferrite

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Supriya, Sweety; Pandey, Rabichandra; Pradhan, Lagen Kumar; Singh, Rakesh Kumar; Kar, Manoranjan

2018-07-01

The calcium (Ca2+) substituted M-type barium hexaferrite (Ba1-xCaxFe12O19) for Ca2+ (x = 0.00, 0.025, 0.050, 0.075, 0.100, 0.150, and 0.200) have been synthesized by the citrate sol-gel method. The X-ray diffraction (XRD) patterns with Rietveld refinement reveal the formation of hexagonal crystal structure with P63/mmc space group. The lattice parameters a = b and c decrease, whereas lattice strain found to increase with the increase in Ca concentration in the samples. The analysis of Raman spectra well supports the XRD patterns analysis. The average particle size is obtained from the FE-SEM (Field Emission Scanning Electron Microscopy) micrographs and these are similar to that of crystallite size obtained from the XRD pattern analysis. The saturation magnetization and magnetocrystalline anisotropy have been obtained by employing the "Law of Approach (LA) to Saturation magnetization" technique at room temperature. The saturation magnetization and magnetocrystalline anisotropy constant are maximum for 5% Ca substitution in barium hexaferrite. It could be due to lattice strain mediated magnetism. However, these magnetic properties decrease for more than the 5% Ca substitution in barium hexaferrite. It could be due to decrease of magnetic exchange interaction (Fe-O-Fe) in the sample. A correlation between magnetic interaction and lattice strain has been observed in Ca2+ substituted M-type barium hexaferrite.

Synthesis and magnetic properties of Zr doped ZnO Nanoparticles.

PubMed

Zhang, Jing; Gao, Daqiang; Yang, Guijin; Zhang, Jinlin; Shi, Zhenhua; Zhang, Zhaohui; Zhu, Zhonghua; Xue, Desheng

2011-11-10

Zr doped ZnO nanoparticles are prepared by the sol-gel method with post-annealing. X-ray diffraction results show that all samples are the typical hexagonal wurtzite structure without any other new phase, as well as the Zr atoms have successfully entered into the ZnO lattices instead of forming other lattices. Magnetic measurements indicate that all the doping samples show room temperature ferromagnetism and the pure ZnO is paramagneism. The results of Raman and X-ray photoelectron spectroscopy indicate that there are a lot of oxygen vacancies in the samples by doping element of Zr. It is considered that the observed ferromagnetism is related to the doping induced oxygen vacancies.

NMR spin-lattice relaxation time T1 of thin films obtained by magnetic resonance force microscopy

NASA Astrophysics Data System (ADS)

Saun, Seung-Bo; Won, Soonho; Kwon, Sungmin; Lee, Soonchil

2015-05-01

We obtained the NMR spectrum and the spin-lattice relaxation time (T1) for thin film samples by magnetic resonance force microscopy (MRFM). The samples were CaF2 thin films which were 50 nm and 150 nm thick. T1 was measured at 18 K using a cyclic adiabatic inversion method at a fixed frequency. A comparison of the bulk and two thin films showed that T1 becomes shorter as the film thickness decreases. To make the comparison as accurate as possible, all three samples were loaded onto different beams of a multi-cantilever array and measured in the same experimental environment.

Equilibration dynamics of a many-body quantum system across the superfluid to Mott insulator phase transition

NASA Astrophysics Data System (ADS)

Mullers, Andreas; Baals, Christian; Santra, Bodhaditya; Labouvie, Ralf; Mertz, Thomas; Dhar, Arya; Vasic, Ivana; Cichy, Agnieszka; Hofstetter, Walter; Ott, Herwig

2017-04-01

We report on the center-of-mass motion of ultracold 87Rb atoms on displacing an underlying potential. The atoms are adiabatically loaded into an optical lattice superimposed onto an optical dipole trap. The CO2 laser beam forming the dipole trap is then shifted by 1 μm which forces the system out of equilibrium. The subsequent motion of the atoms center-of mass is imaged with a scanning electron microscope for various depths of the optical lattice spanning the superfluid to Mott-insulator phase transition. The observed dynamics range from fast oscillations in the superfluid regime to a steady exponential movement towards the new equilibrium position for higher lattice depths. By piecewise analysis of the system, we can also identify a thermal phase at the edges which moves with velocities in between those of the superfluid and the insulating phase. We will present the experiment and the results of theoretical modelling currently in progress.

Chiral sp-orbital paired superfluid of fermionic atoms in a 2D spin-dependent optical lattice

NASA Astrophysics Data System (ADS)

Liu, Bo; Li, Xiaopeng; Wu, Biao; Liu, W. Vincent

2014-03-01

Recent progress in realizing synthetic quantum orbital materials in chequerboard and hexagonal optical lattices opens an avenue towards exploiting unconventional quantum states, advancing our understanding of correlated quantum matter. Here, we unveil a chiral sp -orbital paired superfluid state for an interacting two-component Fermi gas in a 2D spin-dependent optical lattice. Surprisingly, this novel state is found to exist in a wide regime of experimentally tunable interaction strengths. The coexistence of this chiral superfluid and the ferro-orbital order is reminiscent of that of magnetism and superconductivity which is a long-standing issue in condensed matter physics. The topological properties are demonstrated by the existence of gapless chiral fermions in the presence of domain wall defects, reminiscent of quantum Hall edge states. Such properties can be measured by radio frequency spectroscopy in cold atomic experiments. Work supported in part by U.S. ARO, AFOSR, and DARPA-OLE-ARO, Kaufman Foundation, and NSF of China.

Progress towards measuring the Rydberg Constant Using Circular Rydberg Atoms in an Intensity-Modulated Optical Lattice

NASA Astrophysics Data System (ADS)

Ramos, Andira; Moore, Kaitlin; Raithel, Georg

2015-05-01

Recent significant disagreement with the previously established size of the proton demonstrates a need to reconsider the current value of the Rydberg constant, the effects of the nuclear charge distribution and QED in hydrogen-like atoms. An experiment is in progress to obtain a measurement of the Rydberg constant by studying circular Rydberg atoms, which exhibit very small QED shifts and electron wavefunctions which do not overlap with the nucleus. Cold Rydberg atoms are trapped using a ponderomotive potential. To drive the transitions, a novel type of spectroscopy is used which utilizes an optical-lattice field that is intensity-modulated at the frequencies of atomic transitions. The method is free of typical spectroscopic selection rules and has been shown to drive transitions up to fifth order. Combined with optical Rydberg-atom trapping, the method enables the measurement of narrow, sub-THz transitions between long-lived circular Rydberg levels. Energy shifts affecting this precision measurement will also be discussed. This work is suported by NSF, NIST and NASA grants.

High precision optical spectroscopy and quantum state selected photodissociation of ultracold 88Sr2 molecules in an optical lattice

NASA Astrophysics Data System (ADS)

McDonald, Mickey

2017-04-01

Over the past several decades, rapid progress has been made toward the accurate characterization and control of atoms, epitomized by the ever-increasing accuracy and precision of optical atomic lattice clocks. Extending this progress to molecules will have exciting implications for chemistry, condensed matter physics, and precision tests of physics beyond the Standard Model. My thesis describes work performed over the past six years to establish the state of the art in manipulation and quantum control of ultracold molecules. We describe a thorough set of measurements characterizing the rovibrational structure of weakly bound 88Sr2 molecules from several different perspectives, including determinations of binding energies; linear, quadratic, and higher order Zeeman shifts; transition strengths between bound states; and lifetimes of narrow subradiant states. Finally, we discuss measurements of photofragment angular distributions produced by photodissociation of molecules in single quantum states, leading to an exploration of quantum-state-resolved ultracold chemistry. The images of exploding photofragments produced in these studies exhibit dramatic interference effects and strongly violate semiclassical predictions, instead requiring a fully quantum mechanical description.

Recent progress in MBE grown HgCdTe materials and devices at UWA

NASA Astrophysics Data System (ADS)

Gu, R.; Lei, W.; Antoszewski, J.; Madni, I.; Umana-Menbreno, G.; Faraone, L.

2016-05-01

HgCdTe has dominated the high performance end of the IR detector market for decades. At present, the fabrication costs of HgCdTe based advanced infrared devices is relatively high, due to the low yield associated with lattice matched CdZnTe substrates and a complicated cooling system. One approach to ease this problem is to use a cost effective alternative substrate, such as Si or GaAs. Recently, GaSb has emerged as a new alternative with better lattice matching. In addition, implementation of MBE-grown unipolar n-type/barrier/n-type detector structures in the HgCdTe material system has been recently proposed and studied intensively to enhance the detector operating temperature. The unipolar nBn photodetector structure can be used to substantially reduce dark current and noise without impeding photocurrent flow. In this paper, recent progress in MBE growth of HgCdTe infrared material at the University of Western Australia (UWA) is reported, including MBE growth of HgCdTe on GaSb alternative substrates and growth of HgCdTe nBn structures.

Statistics of lattice animals

NASA Astrophysics Data System (ADS)

Hsu, Hsiao-Ping; Nadler, Walder; Grassberger, Peter

2005-07-01

The scaling behavior of randomly branched polymers in a good solvent is studied in two to nine dimensions, modeled by lattice animals on simple hypercubic lattices. For the simulations, we use a biased sequential sampling algorithm with re-sampling, similar to the pruned-enriched Rosenbluth method (PERM) used extensively for linear polymers. We obtain high statistics of animals with up to several thousand sites in all dimension 2⩽d⩽9. The partition sum (number of different animals) and gyration radii are estimated. In all dimensions we verify the Parisi-Sourlas prediction, and we verify all exactly known critical exponents in dimensions 2, 3, 4, and ⩾8. In addition, we present the hitherto most precise estimates for growth constants in d⩾3. For clusters with one site attached to an attractive surface, we verify the superuniversality of the cross-over exponent at the adsorption transition predicted by Janssen and Lyssy.

Transition from two-dimensional photonic crystals to dielectric metasurfaces in the optical diffraction with a fine structure

PubMed Central

Rybin, Mikhail V.; Samusev, Kirill B.; Lukashenko, Stanislav Yu.; Kivshar, Yuri S.; Limonov, Mikhail F.

2016-01-01

We study experimentally a fine structure of the optical Laue diffraction from two-dimensional periodic photonic lattices. The periodic photonic lattices with the C4v square symmetry, orthogonal C2v symmetry, and hexagonal C6v symmetry are composed of submicron dielectric elements fabricated by the direct laser writing technique. We observe surprisingly strong optical diffraction from a finite number of elements that provides an excellent tool to determine not only the symmetry but also exact number of particles in the finite-length structure and the sample shape. Using different samples with orthogonal C2v symmetry and varying the lattice spacing, we observe experimentally a transition between the regime of multi-order diffraction, being typical for photonic crystals to the regime where only the zero-order diffraction can be observed, being is a clear fingerprint of dielectric metasurfaces characterized by effective parameters. PMID:27491952

Ballistic magnetotransport in a suspended two-dimensional electron gas with periodic antidot lattices

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhdanov, E. Yu., E-mail: zhdanov@isp.nsc.ru; Pogosov, A. G.; Budantsev, M. V.

2017-01-15

The magnetoresistance of suspended semiconductor nanostructures with a two-dimensional electron gas structured by periodic square antidot lattices is studied. It is shown that the ballistic regime of electron transport is retained after detaching the sample from the substrate. Direct comparative analysis of commensurability oscillations of magnetoresistance and their temperature dependences in samples before and after suspension is performed. It is found that the temperature dependences are almost identical for non-suspended and suspended samples, whereas significant differences are observed in the nonlinear regime, caused by direct current passage. Commensurability oscillations in the suspended samples are more stable with respect to exposuremore » to direct current, which can be presumably explained by electron–electron interaction enhancement after detaching nanostructures from the high-permittivity substrate.« less

Ultrafast lattice dynamics of single crystal and polycrystalline gold nanofilms☆

NASA Astrophysics Data System (ADS)

Hu, Jianbo; Karam, Tony E.; Blake, Geoffrey A.; Zewail, Ahmed H.

2017-09-01

Ultrafast electron diffraction is employed to spatiotemporally visualize the lattice dynamics of 11 nm-thick single-crystal and 2 nm-thick polycrystalline gold nanofilms. Surprisingly, the electron-phonon coupling rates derived from two temperature simulations of the data reveal a faster interaction between electrons and the lattice in the case of the single-crystal sample. We interpret this unexpected behavior as arising from quantum confinement of the electrons in the 2 nm-thick gold nanofilm, as supported by absorption spectra, an effect that counteracts the expected increase in the electron scattering off surfaces and grain boundaries in the polycrystalline materials.

Detector shape in hexagonal sampling grids

NASA Astrophysics Data System (ADS)

Baronti, Stefano; Capanni, Annalisa; Romoli, Andrea; Santurri, Leonardo; Vitulli, Raffaele

2001-12-01

Recent improvements in CCD technology make hexagonal sampling attractive for practical applications and bring a new interest on this topic. In the following the performances of hexagonal sampling are analyzed under general assumptions and compared with the performances of conventional rectangular sampling. This analysis will take into account both the lattice form (squared, rectangular, hexagonal, and regular hexagonal), and the pixel shape. The analyzed hexagonal grid will not based a-priori on a regular hexagon tessellation, i.e., no constraints will be made on the ratio between the sampling frequencies in the two spatial directions. By assuming an elliptic support for the spectrum of the signal being sampled, sampling conditions will be expressed for a generic hexagonal sampling grid, and a comaprison with the well-known sampling conditions for a comparable rectangular lattice will be performed. Further, by considering for sake of clarity a spectrum with a circular support, the comparison will be performed under the assumption of same number of pixels for unity of surface, and the particular case of regular hexagonal sampling grid will also be considered. Regular hexagonal lattice with regular hexagonal sensitivity shape of the detector elements will result as the best trade-off between the proposed sampling requirement. Concerning the detector shape, the hexagonal is more advantageous than the rectangular. To show that a figure of merit is defined which takes into account that the MTF (modulation transfer function) of a hexagonal detector is not separable, conversely from that of a rectangular detector. As a final result, octagonal shape detectors are compared to those with rectangular and hexagonal shape in the two hypotheses of equal and ideal fill factor, respectively.

Versatile strain-tuning of modulated long-period magnetic structures

DOE PAGES

Fobes, D. M.; Luo, Yongkang; León-Brito, N.; ...

2017-05-10

In this paper, we report a detailed small-angle neutron scattering (SANS) study of the skyrmion lattice phase of MnSi under compressive and tensile strain. In particular, we demonstrate that tensile strain applied to the skyrmion lattice plane, perpendicular to the magnetic field, acts to destabilize the skyrmion lattice phase. Finally, this experiment was enabled by our development of a versatile strain cell, unique in its ability to select the application of either tensile or compressive strain in-situ by using two independent helium-actuated copper pressure transducers, whose design has been optimized for magnetic SANS on modulated long-period magnetic structures and vortexmore » lattices, and is compact enough to fit in common sample environments such as cryostats and superconducting magnets.« less

Americium alloys with gold and copper

NASA Astrophysics Data System (ADS)

Radchenko, V. M.; Ryabinin, M. A.; Chernakova, T. A.; Tomilin, S. V.

2010-03-01

Presented are results of the production and X-ray examination of micro-samples of americium-241 compounds with gold and copper produced by high-temperature condensation of metal americium vapor onto corresponding substrates. No mutual solubility of the investigated system components was revealed at room temperature. The following three intermetallic compounds were revealed in the Am-Au system: Au6Am with tetragonal lattice of the Au6Sm structural type, AuAm with orthorhombic lattice of the CuCe structural type and AuAm with cubic lattice. The Am-Cu system showed the intermetallic compound Cu5Am (Cu7Am) with a hexagonal lattice of the Cu5Ca(Cu7Tb) structure type. An effect of the 241Am nuclide alpha-activity on the crystal structure of the produced intermetallide was studied.

Alkali metal intercalated fullerene-like MS(2) (M = W, Mo) nanoparticles and their properties.

PubMed

Zak, Alla; Feldman, Yishay; Lyakhovitskaya, Vera; Leitus, Gregory; Popovitz-Biro, Ronit; Wachtel, Ellen; Cohen, Hagai; Reich, Shimon; Tenne, Reshef

2002-05-01

Layered metal disulfides-MS(2) (M = Mo, W) in the form of fullerene-like nanoparticles and in the form of platelets (crystallites of the 2H polytype) have been intercalated by exposure to alkali metal (potassium and sodium) vapor using a two-zone transport method. The composition of the intercalated systems was established using X-ray energy dispersive spectrometer and X-ray photoelectron spectroscopy (XPS). The alkali metal concentration in the host lattice was found to depend on the kind of sample and the experimental conditions. Furthermore, an inhomogeneity of the intercalated samples was observed. The product consisted of both nonintercalated and intercalated phases. X-ray diffraction analysis and transmission electron microscopy of the samples, which were not exposed to the ambient atmosphere, showed that they suffered little change in their lattice parameters. On the other hand, after exposure to ambient atmosphere, substantial increase in the interplanar spacing (3-5 A) was observed for the intercalated phases. Insertion of one to two water molecules per intercalated metal atom was suggested as a possible explanation for this large expansion along the c-axis. Deintercalation of the hydrated alkali atoms and restacking of the MS(2) layers was observed in all the samples after prolonged exposure to the atmosphere. Electric field induced deintercalation of the alkali metal atoms from the host lattice was also observed by means of the XPS technique. Magnetic moment measurements for all the samples indicate a diamagnetic to paramagnetic transition after intercalation. Measurements of the transport properties reveal a semiconductor to metal transition for the heavily K intercalated 2H-MoS(2). Other samples show several orders of magnitude decrease in resistivity and two- to five-fold decrease in activation energies upon intercalation. These modifications are believed to occur via charge transfer from the alkali metal to the conduction band of the host lattice. Recovery of the pristine compound properties (diamagnetism and semiconductivity) was observed as a result of deintercalation.

Adaptive two-regime method: Application to front propagation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Robinson, Martin, E-mail: martin.robinson@maths.ox.ac.uk; Erban, Radek, E-mail: erban@maths.ox.ac.uk; Flegg, Mark, E-mail: mark.flegg@monash.edu

2014-03-28

The Adaptive Two-Regime Method (ATRM) is developed for hybrid (multiscale) stochastic simulation of reaction-diffusion problems. It efficiently couples detailed Brownian dynamics simulations with coarser lattice-based models. The ATRM is a generalization of the previously developed Two-Regime Method [Flegg et al., J. R. Soc., Interface 9, 859 (2012)] to multiscale problems which require a dynamic selection of regions where detailed Brownian dynamics simulation is used. Typical applications include a front propagation or spatio-temporal oscillations. In this paper, the ATRM is used for an in-depth study of front propagation in a stochastic reaction-diffusion system which has its mean-field model given in termsmore » of the Fisher equation [R. Fisher, Ann. Eugen. 7, 355 (1937)]. It exhibits a travelling reaction front which is sensitive to stochastic fluctuations at the leading edge of the wavefront. Previous studies into stochastic effects on the Fisher wave propagation speed have focused on lattice-based models, but there has been limited progress using off-lattice (Brownian dynamics) models, which suffer due to their high computational cost, particularly at the high molecular numbers that are necessary to approach the Fisher mean-field model. By modelling only the wavefront itself with the off-lattice model, it is shown that the ATRM leads to the same Fisher wave results as purely off-lattice models, but at a fraction of the computational cost. The error analysis of the ATRM is also presented for a morphogen gradient model.« less

Nonequilibrium electron and lattice dynamics of strongly correlated Bi2Sr2CaCu2O8+δ single crystals

PubMed Central

Li, Renkai; Gu, Genda; Avigo, Isabella; Dürr, Hermann A.; Johnson, Peter D.; Wang, Xijie

2018-01-01

The interplay between the electronic and lattice degrees of freedom in nonequilibrium states of strongly correlated systems has been debated for decades. Although progress has been made in establishing a hierarchy of electronic interactions with the use of time-resolved techniques, the role of the phonons often remains in dispute, a situation highlighting the need for tools that directly probe the lattice. We present the first combined megaelectron volt ultrafast electron diffraction and time- and angle-resolved photoemission spectroscopy study of optimally doped Bi2Sr2CaCu2O8+δ. Quantitative analysis of the lattice and electron subsystems’ dynamics provides a unified picture of nonequilibrium electron-phonon interactions in the cuprates beyond the N-temperature model. The work provides new insights on the specific phonon branches involved in the nonequilibrium heat dissipation from the high-energy Cu–O bond stretching “hot” phonons to the lowest-energy acoustic phonons with correlated atomic motion along the <110> crystal directions and their characteristic time scales. It reveals a highly nonthermal phonon population during the first several picoseconds after the photoexcitation. The approach, taking advantage of the distinct nature of electrons and photons as probes, is applicable for studying energy relaxation in other strongly correlated electron systems. PMID:29719862

Finite-volume and partial quenching effects in the magnetic polarizability of the neutron

NASA Astrophysics Data System (ADS)

Hall, J. M. M.; Leinweber, D. B.; Young, R. D.

2014-03-01

There has been much progress in the experimental measurement of the electric and magnetic polarizabilities of the nucleon. Similarly, lattice QCD simulations have recently produced dynamical QCD results for the magnetic polarizability of the neutron approaching the chiral regime. In order to compare the lattice simulations with experiment, calculation of partial quenching and finite-volume effects is required prior to an extrapolation in quark mass to the physical point. These dependencies are described using chiral effective field theory. Corrections to the partial quenching effects associated with the sea-quark-loop electric charges are estimated by modeling corrections to the pion cloud. These are compared to the uncorrected lattice results. In addition, the behavior of the finite-volume corrections as a function of pion mass is explored. Box sizes of approximately 7 fm are required to achieve a result within 5% of the infinite-volume result at the physical pion mass. A variety of extrapolations are shown at different box sizes, providing a benchmark to guide future lattice QCD calculations of the magnetic polarizabilities. A relatively precise value for the physical magnetic polarizability of the neutron is presented, βn=1.93(11)stat(11)sys×10-4 fm3, which is in agreement with current experimental results.

Simulation of Electromigration Based on Resistor Networks

NASA Astrophysics Data System (ADS)

Patrinos, Anthony John

A two dimensional computer simulation of electromigration based on resistor networks was designed and implemented. The model utilizes a realistic grain structure generated by the Monte Carlo method and takes specific account of the local effects through which electromigration damage progresses. The dynamic evolution of the simulated thin film is governed by the local current and temperature distributions. The current distribution is calculated by superimposing a two dimensional electrical network on the lattice whose nodes correspond to the particles in the lattice and the branches to interparticle bonds. Current is assumed to flow from site to site via nearest neighbor bonds. The current distribution problem is solved by applying Kirchhoff's rules on the resulting electrical network. The calculation of the temperature distribution in the lattice proceeds by discretizing the partial differential equation for heat conduction, with appropriate material parameters chosen for the lattice and its defects. SEReNe (for Simulation of Electromigration using Resistor Networks) was tested by applying it to common situations arising in experiments with real films with satisfactory results. Specifically, the model successfully reproduces the expected grain size, line width and bamboo effects, the lognormal failure time distribution and the relationship between current density exponent and current density. It has also been modified to simulate temperature ramp experiments but with mixed, in this case, results.

Radiation-Induced Changes in Quartz, A Mineral Analog of Nuclear Power Plant Concrete Aggregates

DOE Office of Scientific and Technical Information (OSTI.GOV)

Silva, Chinthaka M.; Rosseel, Thomas M.; Kirkegaard, Marie C.

Quartz single-crystal samples consisting of α-quartz crystal structure were neutron irradiated to fluences of 5 × 10 18, 4 × 10 19, and 2 × 10 20 n/cm 2 (E > 0.1 MeV) at two temperatures (52 and 95 °C). The changes in the α-quartz phase as a function of these two conditions (temperature and fluence) were studied using X-ray powder diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM), and the results acquired using these complementary techniques are presented in a single place for the first time. XRD studies showed that the lattice parameters of α-quartz increased with increasingmore » neutron flux. The lattice growth was larger for the samples that were neutron irradiated at 52 °C than at 95 °C. Moreover, an amorphous content was determined in the quartz samples neutron irradiated at 4 × 10 19 n/cm 2, with the greater amount being in the 52 °C irradiated sample. Complete amorphization of quartz was observed at a fluence of 2 × 10 20 n/cm 2 (E > 0.1 MeV) using XRD and confirmed by TEM characterization and Raman spectroscopic studies. In conclusion, the cause for α-quartz lattice expansion and sample amorphization was also explored using XRD and Raman spectroscopic studies.« less

Radiation-Induced Changes in Quartz, A Mineral Analog of Nuclear Power Plant Concrete Aggregates

DOE PAGES

Silva, Chinthaka M.; Rosseel, Thomas M.; Kirkegaard, Marie C.

2018-03-07

Quartz single-crystal samples consisting of α-quartz crystal structure were neutron irradiated to fluences of 5 × 10 18, 4 × 10 19, and 2 × 10 20 n/cm 2 (E > 0.1 MeV) at two temperatures (52 and 95 °C). The changes in the α-quartz phase as a function of these two conditions (temperature and fluence) were studied using X-ray powder diffraction (XRD), Raman spectroscopy, and transmission electron microscopy (TEM), and the results acquired using these complementary techniques are presented in a single place for the first time. XRD studies showed that the lattice parameters of α-quartz increased with increasingmore » neutron flux. The lattice growth was larger for the samples that were neutron irradiated at 52 °C than at 95 °C. Moreover, an amorphous content was determined in the quartz samples neutron irradiated at 4 × 10 19 n/cm 2, with the greater amount being in the 52 °C irradiated sample. Complete amorphization of quartz was observed at a fluence of 2 × 10 20 n/cm 2 (E > 0.1 MeV) using XRD and confirmed by TEM characterization and Raman spectroscopic studies. In conclusion, the cause for α-quartz lattice expansion and sample amorphization was also explored using XRD and Raman spectroscopic studies.« less

Solubility and partitioning of Ar in anorthite, diopside, forsterite, spinel, and synthetic basaltic liquids

NASA Technical Reports Server (NTRS)

Broadhurst, C. Leigh; Drake, Michael J.; Hagee, Bryan E.; Bernatowicz, Thomas J.

1990-01-01

The solubility and partitioning of Ar in natural anorthite, diopside, forsterite, spinel, and synthetic iron-free basaltic melts was investigated using a new technique that obviates the postquenching phase separation. It was found that the solubility of Ar in the minerals was surprisingly high. Moreover, the solubility of Ar in different samples of a particular mineral run in the same experiment varied more than the solubility in the same sample run in different experiments, suggesting that noble gases are held in lattice vacancy defects. Moreover, the results of TEM imaging revealed no anomalous microstructures, while EXAFS studies of some samples showed that Kr has no preferred site in the lattices, supporting the defect siting conclusion.

Depth Profiling of SiC Lattice Damage Using Micro-Raman Spectroscopy

DTIC Science & Technology

2002-01-01

can significantly change the electric behavior. Techniques like Positron Annihilation Spectroscopy [5,6] and Rutherford Backscattering/Channeling... Semiconductor Materials for Optoelectronic Applications Symposium held in Boston, Massachusetts on November 26-29, 2001. To order the complete compilation... Spectroscopy DISTRIBUTION: Approved for public release, distribution unlimited This paper is part of the following report: TITLE: Progress in

Lattice Calculations and the Muon Anomalous Magnetic Moment

NASA Astrophysics Data System (ADS)

Marinković, Marina Krstić

2017-07-01

Anomalous magnetic moment of the muon, a_{μ }=(g_{μ }-2)/2, is one of the most precisely measured quantities in particle physics and it provides a stringent test of the Standard Model. The planned improvements of the experimental precision at Fermilab and at J-PARC propel further reduction of the theoretical uncertainty of a_{μ }. The hope is that the efforts on both sides will help resolve the current discrepancy between the experimental measurement of a_{μ } and its theoretical prediction, and potentially gain insight into new physics. The dominant sources of the uncertainty in the theoretical prediction of a_{μ } are the errors of the hadronic contributions. I will discuss recent progress on determination of hadronic contributions to a_{μ } from lattice calculations.

An approach to spin-resolved molecular gas microscopy

NASA Astrophysics Data System (ADS)

Covey, Jacob P.; De Marco, Luigi; Acevedo, Óscar L.; Rey, Ana Maria; Ye, Jun

2018-04-01

Ultracold polar molecules are an ideal platform for studying many-body physics with long-range dipolar interactions. Experiments in this field have progressed enormously, and several groups are pursuing advanced apparatus for manipulation of molecules with electric fields as well as single-atom-resolved in situ detection. Such detection has become ubiquitous for atoms in optical lattices and tweezer arrays, but has yet to be demonstrated for ultracold polar molecules. Here we present a proposal for the implementation of site-resolved microscopy for polar molecules, and specifically discuss a technique for spin-resolved molecular detection. We use numerical simulation of spin dynamics of lattice-confined polar molecules to show how such a scheme would be of utility in a spin-diffusion experiment.

Evaluation of permeability and non-Darcy flow in vuggy macroporous limestone aquifer samples with lattice Boltzmann methods

USGS Publications Warehouse

Sukop, Michael C.; Huang, Haibo; Alvarez, Pedro F.; Variano, Evan A.; Cunningham, Kevin J.

2013-01-01

Lattice Boltzmann flow simulations provide a physics-based means of estimating intrinsic permeability from pore structure and accounting for inertial flow that leads to departures from Darcy's law. Simulations were used to compute intrinsic permeability where standard measurement methods may fail and to provide better understanding of departures from Darcy's law under field conditions. Simulations also investigated resolution issues. Computed tomography (CT) images were acquired at 0.8 mm interscan spacing for seven samples characterized by centimeter-scale biogenic vuggy macroporosity from the extremely transmissive sole-source carbonate karst Biscayne aquifer in southeastern Florida. Samples were as large as 0.3 m in length; 7–9 cm-scale-length subsamples were used for lattice Boltzmann computations. Macroporosity of the subsamples was as high as 81%. Matrix porosity was ignored in the simulations. Non-Darcy behavior led to a twofold reduction in apparent hydraulic conductivity as an applied hydraulic gradient increased to levels observed at regional scale within the Biscayne aquifer; larger reductions are expected under higher gradients near wells and canals. Thus, inertial flows and departures from Darcy's law may occur under field conditions. Changes in apparent hydraulic conductivity with changes in head gradient computed with the lattice Boltzmann model closely fit the Darcy-Forchheimer equation allowing estimation of the Forchheimer parameter. CT-scan resolution appeared adequate to capture intrinsic permeability; however, departures from Darcy behavior were less detectable as resolution coarsened.

Improved texture measurement during deformation of polycrystalline olivine at high pressure

NASA Astrophysics Data System (ADS)

Dixon, N. A.; Durham, W. B.; Kohlstedt, D. L.; Hunt, S. A.

2014-12-01

Unresolved issues in geodynamics demand a better understanding of the bulk mechanical properties of mantle minerals, and also careful analysis of the complex lattice-scale physics behind these properties. Instead of probing the mechanical properties of a material by testing the relationship between "bulk" stress and strain rate in a sample at a variety of conditions (varying P, T, water content, and other environmental variables), synchrotron x-ray diffraction now allows us to observe, in situ, the active deformation physics in much greater detail. This includes in situ monitoring of plastic anisotropy and local stress heterogeneity, grain size, the development of lattice-preferred orientation (LPO), and even the partitioning of stress between multiple phases in the same polycrystalline sample. Here, we present results obtained with the use of the MTEX toolbox for Matlab and energy-dispersive x-ray diffraction, showing the in situ development of LPO in deforming dry San Carlos olivine samples, at pressures from 2-7 GPa. These measurements hint at the active dislocation mechanisms for these conditions. The ability generate a broad range of mantle conditions in the D-DIA, while precisely measuring the structure and conditions within our sample at the grain and lattice scale, demonstrates the promising future of deformation experiments as a means to understanding the evolution of the deep Earth.

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

NASA Astrophysics Data System (ADS)

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.

Impact of Heterogeneity and Lattice Bond Strength on DNA Triangle Crystal Growth.

PubMed

Stahl, Evi; Praetorius, Florian; de Oliveira Mann, Carina C; Hopfner, Karl-Peter; Dietz, Hendrik

2016-09-07

One key goal of DNA nanotechnology is the bottom-up construction of macroscopic crystalline materials. Beyond applications in fields such as photonics or plasmonics, DNA-based crystal matrices could possibly facilitate the diffraction-based structural analysis of guest molecules. Seeman and co-workers reported in 2009 the first designed crystal matrices based on a 38 kDa DNA triangle that was composed of seven chains. The crystal lattice was stabilized, unprecedentedly, by Watson-Crick base pairing. However, 3D crystallization of larger designed DNA objects that include more chains such as DNA origami remains an unsolved problem. Larger objects would offer more degrees of freedom and design options with respect to tailoring lattice geometry and for positioning other objects within a crystal lattice. The greater rigidity of multilayer DNA origami could also positively influence the diffractive properties of crystals composed of such particles. Here, we rationally explore the role of heterogeneity and Watson-Crick interaction strengths in crystal growth using 40 variants of the original DNA triangle as model multichain objects. Crystal growth of the triangle was remarkably robust despite massive chemical, geometrical, and thermodynamical sample heterogeneity that we introduced, but the crystal growth sensitively depended on the sequences of base pairs next to the Watson-Crick sticky ends of the triangle. Our results point to weak lattice interactions and high concentrations as decisive factors for achieving productive crystallization, while sample heterogeneity and impurities played a minor role.

Optimum inhomogeneity of local lattice distortions in La2CuO4+y

PubMed Central

Poccia, Nicola; Ricci, Alessandro; Campi, Gaetano; Fratini, Michela; Puri, Alessandro; Gioacchino, Daniele Di; Marcelli, Augusto; Reynolds, Michael; Burghammer, Manfred; Saini, Naurang Lal; Aeppli, Gabriel; Bianconi, Antonio

2012-01-01

Electronic functionalities in materials from silicon to transition metal oxides are, to a large extent, controlled by defects and their relative arrangement. Outstanding examples are the oxides of copper, where defect order is correlated with their high superconducting transition temperatures. The oxygen defect order can be highly inhomogeneous, even in optimal superconducting samples, which raises the question of the nature of the sample regions where the order does not exist but which nonetheless form the “glue” binding the ordered regions together. Here we use scanning X-ray microdiffraction (with a beam 300 nm in diameter) to show that for La2CuO4+y, the glue regions contain incommensurate modulated local lattice distortions, whose spatial extent is most pronounced for the best superconducting samples. For an underdoped single crystal with mobile oxygen interstitials in the spacer La2O2+y layers intercalated between the CuO2 layers, the incommensurate modulated local lattice distortions form droplets anticorrelated with the ordered oxygen interstitials, and whose spatial extent is most pronounced for the best superconducting samples. In this simplest of high temperature superconductors, there are therefore not one, but two networks of ordered defects which can be tuned to achieve optimal superconductivity. For a given stoichiometry, the highest transition temperature is obtained when both the ordered oxygen and lattice defects form fractal patterns, as opposed to appearing in isolated spots. We speculate that the relationship between material complexity and superconducting transition temperature Tc is actually underpinned by a fundamental relation between Tc and the distribution of ordered defect networks supported by the materials. PMID:22961255

An analysis of the nucleon spectrum from lattice partially-quenched QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

W. Armour; Allton, C. R.; Leinweber, Derek B.

2010-09-01

The chiral extrapolation of the nucleon mass, Mn, is investigated using data coming from 2-flavour partially-quenched lattice simulations. The leading one-loop corrections to the nucleon mass are derived for partially-quenched QCD. A large sample of lattice results from the CP-PACS Collaboration is analysed, with explicit corrections for finite lattice spacing artifacts. The extrapolation is studied using finite range regularised chiral perturbation theory. The analysis also provides a quantitative estimate of the leading finite volume corrections. It is found that the discretisation, finite-volume and partial quenching effects can all be very well described in this framework, producing an extrapolated value ofmore » Mn in agreement with experiment. This procedure is also compared with extrapolations based on polynomial forms, where the results are less encouraging.« less

Sznajd Opinion Dynamics with Global and Local Neighborhood

NASA Astrophysics Data System (ADS)

Schulze, Christian

In this modification of the Sznajd consensus model on the square lattice, two people of arbitrary distance who agree in their opinions convince their nearest neighbors of this opinion. Similarly to the mean field theory of Slanina and Lavicka, the times needed to reach consensus are distributed exponentially and are quite small. The width of the phase transition vanishes reciprocally to the linear lattice dimension. Advertising has effects independent of the system size. For more than two opinions, three opinions reach a consensus in roughly half of the samples, and four only rarely and only for small lattices. Up to 109 agents were simulated.

Bold Diagrammatic Monte Carlo for Fermionic and Fermionized Systems

NASA Astrophysics Data System (ADS)

Svistunov, Boris

2013-03-01

In three different fermionic cases--repulsive Hubbard model, resonant fermions, and fermionized spins-1/2 (on triangular lattice)--we observe the phenomenon of sign blessing: Feynman diagrammatic series features finite convergence radius despite factorial growth of the number of diagrams with diagram order. Bold diagrammatic Monte Carlo technique allows us to sample millions of skeleton Feynman diagrams. With the universal fermionization trick we can fermionize essentially any (bosonic, spin, mixed, etc.) lattice system. The combination of fermionization and Bold diagrammatic Monte Carlo yields a universal first-principle approach to strongly correlated lattice systems, provided the sign blessing is a generic fermionic phenomenon. Supported by NSF and DARPA

Lattice Independent Component Analysis for Mobile Robot Localization

NASA Astrophysics Data System (ADS)

Villaverde, Ivan; Fernandez-Gauna, Borja; Zulueta, Ekaitz

This paper introduces an approach to appearance based mobile robot localization using Lattice Independent Component Analysis (LICA). The Endmember Induction Heuristic Algorithm (EIHA) is used to select a set of Strong Lattice Independent (SLI) vectors, which can be assumed to be Affine Independent, and therefore candidates to be the endmembers of the data. Selected endmembers are used to compute the linear unmixing of the robot's acquired images. The resulting mixing coefficients are used as feature vectors for view recognition through classification. We show on a sample path experiment that our approach can recognise the localization of the robot and we compare the results with the Independent Component Analysis (ICA).

In situ neutron diffraction study of micromechanical interactions and phase transformation in Ni-Mn-Ga alloy under uniaxial and hydrostatic stress.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Peng, R. L.; Wang, Y. D.; Nie, Z. H.

2008-01-01

This paper deals with the experimental study of stress-induced phase transformation in a polycrystalline Ni-Mn-Ga alloy under uniaxial compression and its powder under hydrostatic compression. In situ neutron diffraction experiments were employed to follow changes in the structure and lattice strains caused by the applied stresses. Large lattice strains that are dependent on the lattice planes or grain orientations were observed in the parent Heusler phase for both the bulk material and the powder sample. The development of such anisotropic strains and the influence of external load conditions are discussed in the paper.

Solid-State Division progress report for period ending March 31, 1983

DOE Office of Scientific and Technical Information (OSTI.GOV)

Green, P.H.; Watson, D.M.

1983-09-01

Progress and activities are reported on: theoretical solid-state physics (surfaces; electronic, vibrational, and magnetic properties; particle-solid interactions; laser annealing), surface and near-surface properties of solids (surface, plasma-material interactions, ion implantation and ion-beam mixing, pulsed-laser and thermal processing), defects in solids (radiation effects, fracture, impurities and defects, semiconductor physics and photovoltaic conversion), transport properties of solids (fast-ion conductors, superconductivity, mass and charge transport in materials), neutron scattering (small-angle scattering, lattice dynamics, magnetic properties, structure and instrumentation), and preparation and characterization of research materials (growth and preparative methods, nuclear waste forms, special materials). (DLC)

The effects of annealing temperature on the in-field Jc and surface pinning in silicone oil doped MgB2 bulks and wires

NASA Astrophysics Data System (ADS)

Hossain, M. S. A.; Motaman, A.; Çiçek, Ö.; Ağıl, H.; Ertekin, E.; Gencer, A.; Wang, X. L.; Dou, S. X.

2012-12-01

The effects of sintering temperature on the lattice parameters, full width at half maximum (FWHM), strain, critical temperature (Tc), critical current density (Jc), irreversibility field (Hirr), upper critical field (Hc2), and resistivity (ρ) of 10 wt.% silicone oil doped MgB2 bulk and wire samples are investigated in state of the art by this article. The a-lattice parameter of the silicone oil doped samples which were sintered at different temperatures was drastically reduced from 3.0864 Å to 3.0745 Å, compared to the un-doped samples, which indicates the substitution of the carbon (C) into the boron sites. It was found that sintered samples at the low temperature of 600 °C shows more lattice distortion by more C-substitution and higher strain, lower Tc, higher impurity scattering, and enhancement of both magnetic Jc and Hc2, compared to those sintered samples at high temperatures. The flux pinning mechanism has been analyzed based on the extended normalized pinning force density fp = Fp/Fp,max scaled with b = B/Bmax. Results show that surface pinning is the dominant pinning mechanism for the doped sample sintered at the low temperature of 600 °C, while point pinning is dominant for the un-doped sample. The powder in tube (PIT) MgB2 wire was also fabricated by using of this liquid doping and found that both transport Jc and n-factor increased which proves this cheap and abundant silicone oil doping can be a good candidate for industrial application.

All optical detection of picosecond spin-wave dynamics in 2D annular antidot lattice

NASA Astrophysics Data System (ADS)

Porwal, Nikita; Mondal, Sucheta; Choudhury, Samiran; De, Anulekha; Sinha, Jaivardhan; Barman, Anjan; Datta, Prasanta Kumar

2018-02-01

Novel magnetic structures with precisely controlled dimensions and shapes at the nanoscale have potential applications in spin logic, spintronics and other spin-based communication devices. We report the fabrication of 2D bi-structure magnonic crystal in the form of embedded nanodots in a periodic Ni80Fe20 antidot lattice structure (annular antidot) by focused ion-beam lithography. The spin-wave spectra of the annular antidot sample, studied for the first time by a time-resolved magneto-optic Kerr effect microscopy show a remarkable variation with bias field, which is important for the above device applications. The optically induced spin-wave spectra show multiple modes in the frequency range 14.7 GHz-3.5 GHz due to collective interactions between the dots and antidots as well as the annular elements within the whole array. Numerical simulations qualitatively reproduce the experimental results, and simulated mode profiles reveal the spatial distribution of the spin-wave modes and internal magnetic fields responsible for these observations. It is observed that the internal field strength increases by about 200 Oe inside each dot embedded within the hole of annular antidot lattice as compared to pure antidot lattice and pure dot lattice. The stray field for the annular antidot lattice is found to be significant (0.8 kOe) as opposed to the negligible values of the same for the pure dot lattice and pure antidot lattice. Our findings open up new possibilities for development of novel artificial crystals.

Measurement of spin-lattice relaxation times and concentrations in systems with chemical exchange using the one-pulse sequence: breakdown of the Ernst model for partial saturation in nuclear magnetic resonance spectroscopy.

PubMed

Spencer, R G; Fishbein, K W

2000-01-01

A fundamental problem in Fourier transform NMR spectroscopy is the calculation of observed resonance amplitudes for a repetitively pulsed sample, as first analyzed by Ernst and Anderson in 1966. Applications include determination of spin-lattice relaxation times (T(1)'s) by progressive saturation and correction for partial saturation in order to determine the concentrations of the chemical constituents of a spectrum. Accordingly, the Ernst and Anderson formalism has been used in innumerable studies of chemical and, more recently, physiological systems. However, that formalism implicitly assumes that no chemical exchange occurs. Here, we present an analysis of N sites in an arbitrary chemical exchange network, explicitly focusing on the intermediate exchange rate regime in which the spin-lattice relaxation rates and the chemical exchange rates are comparable in magnitude. As a special case of particular importance, detailed results are provided for a system with three sites undergoing mutual exchange. Specific properties of the N-site network are then detailed. We find that (i) the Ernst and Anderson analysis describing the response of a system to repetitive pulsing is inapplicable to systems with chemical exchange and can result in large errors in T(1) and concentration measurements; (ii) T(1)'s for systems with arbitrary exchange networks may still be correctly determined from a one-pulse experiment using the Ernst formula, provided that a short interpulse delay time and a large flip angle are used; (iii) chemical concentrations for exchanging systems may be correctly determined from a one-pulse experiment either by using a short interpulse delay time with a large flip angle, as for measuring T(1)'s, and correcting for partial saturation by use of the Ernst formula, or directly by using a long interpulse delay time to avoid saturation; (iv) there is a significant signal-to-noise penalty for performing one-pulse experiments under conditions which permit accurate measurements of T(1)'s and chemical concentrations. The present results are analogous to but are much more general than those that we have previously derived for systems with two exchanging sites. These considerations have implications for the design and interpretation of one-pulse experiments for all systems exhibiting chemical exchange in the intermediate exchange regime, including virtually all physiologic samples.

Impact of crystalline defects and size on X-ray line broadening: A phenomenological approach for tetragonal SnO{sub 2} nanocrystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Muhammed Shafi, P.; Chandra Bose, A., E-mail: acbose@nitt.edu

2015-05-15

Nanocrystalline tin oxide (SnO{sub 2}) powders with different grain size were prepared by chemical precipitation method. The reaction was carried out by varying the period of hydrolysis and the as-prepared samples were annealed at different temperatures. The samples were characterized using X-ray powder diffractometer and transmission electron microscopy. The microstrain and crystallite size were calculated for all the samples by using Williamson-Hall (W-H) models namely, isotropic strain model (ISM), anisotropic strain model (ASM) and uniform deformation energy density model (UDEDM). The morphology and particle size were determined using TEM micrographs. The directional dependant young’s modulus was modified as an equationmore » relating elastic compliances (s{sub ij}) and Miller indices of the lattice plane (hkl) for tetragonal crystal system and also the equation for elastic compliance in terms of stiffness constants was derived. The changes in crystallite size and microstrain due to lattice defects were observed while varying the hydrolysis time and the annealing temperature. The dependence of crystallite size on lattice strain was studied. The results were correlated with the available studies on electrical properties using impedance spectroscopy.« less

Control and distribution of uranium in coral reefs during diagenesis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gvirtzman, G.; Friedman, G.M.; Miller, D.S.

1973-12-01

The concentration of about 2 ppM of uranium in the aragonitic skeletons of modern scleractinian corals which we studied is a constant value, regardless of occurrence, anatomy, or taxonomy. The presence of cement of aragonite or high- magnesian calcite usually raises the concentration of bulk samples to about 3 ppM. Modern corals may contain up to 50% of cementing minerals. Organisms, such as corals and coralline algae, while secreting their skeleton, discriminate against the uptake of uranium, whereas the uptake of uranium by mineral cements is less restrained. Aragonite cement contains about 3.6 ppM and highmagnesian calcite cement 2.6 ppMmore » uranium. During leaching by freshwater, the aragonite of the skeletons of corals dissolves out. This creates hollow molds which fill with drusy low-magnesian calcite. In emergent reefs from the shores of the Red Sea which display the ellects of progressive diagenesis this calcite is enriched in uranium (3.9 ppM) beyond that found in marine cements. Second-generation calcite, which fills original voids in the corals from the emergent reefs, contains a lower level of uranium concent ration (1.3 ppM). The level of concentration of uranium in low-magnesian calcite of diagenetically altered corals is a function of the availability of uranium in meteoric waters. In aragonite as well as in high- and low-magnesian calcite uranium replaces calcium or occupies lattice vacancies in the crystal lattice. (auth)« less

Hybrid Systems: Cold Atoms Coupled to Micro Mechanical Oscillators =

NASA Astrophysics Data System (ADS)

Montoya Monge, Cris A.

Micro mechanical oscillators can serve as probes in precision measurements, as transducers to mediate photon-phonon interactions, and when functionalized with magnetic material, as tools to manipulate spins in quantum systems. This dissertation includes two projects where the interactions between cold atoms and mechanical oscillators are studied. In one of the experiments, we have manipulated the Zeeman state of magnetically trapped Rubidium atoms with a magnetic micro cantilever. The results show a spatially localized effect produced by the cantilever that agrees with Landau-Zener theory. In the future, such a scalable system with highly localized interactions and the potential for single-spin sensitivity could be useful for applications in quantum information science or quantum simulation. In a second experiment, work is in progress to couple a sample of optically trapped Rubidium atoms to a levitated nanosphere via an optical lattice. This coupling enables the cooling of the center-of-mass motion of the nanosphere by laser cooling the atoms. In this system, the atoms are trapped in the optical lattice while the sphere is levitated in a separate vacuum chamber by a single-beam optical tweezer. Theoretical analysis of such a system has determined that cooling the center-of-mass motion of the sphere to its quantum ground state is possible, even when starting at room temperature, due to the excellent environmental decoupling achievable in this setup. Nanospheres cooled to the quantum regime can provide new tests of quantum behavior at mesoscopic scales and have novel applications in precision sensing.

Susceptibility of the Ising Model on a Kagomé Lattice by Using Wang-Landau Sampling

NASA Astrophysics Data System (ADS)

Kim, Seung-Yeon; Kwak, Wooseop

2018-03-01

The susceptibility of the Ising model on a kagomé lattice has never been obtained. We investigate the properties of the kagomé-lattice Ising model by using the Wang-Landau sampling method. We estimate both the magnetic scaling exponent yh = 1.90(1) and the thermal scaling exponent yt = 1.04(2) only from the susceptibility. From the estimated values of yh and yt, we obtain all the critical exponents, the specific-heat critical exponent α = 0.08(4), the spontaneous-magnetization critical exponent β = 0.10(1), the susceptibility critical exponent γ = 1.73(5), the isothermalmagnetization critical exponent δ = 16(4), the correlation-length critical exponent ν = 0.96(2), and the correlation-function critical exponent η = 0.20(4), without using any other thermodynamic function, such as the specific heat, magnetization, correlation length, and correlation function. One should note that the evaluation of all the critical exponents only from information on the susceptibility is an innovative approach.

Computer program documentation for a subcritical wing design code using higher order far-field drag minimization

NASA Technical Reports Server (NTRS)

Kuhlman, J. M.; Shu, J. Y.

1981-01-01

A subsonic, linearized aerodynamic theory, wing design program for one or two planforms was developed which uses a vortex lattice near field model and a higher order panel method in the far field. The theoretical development of the wake model and its implementation in the vortex lattice design code are summarized and sample results are given. Detailed program usage instructions, sample input and output data, and a program listing are presented in the Appendixes. The far field wake model assumes a wake vortex sheet whose strength varies piecewise linearly in the spanwise direction. From this model analytical expressions for lift coefficient, induced drag coefficient, pitching moment coefficient, and bending moment coefficient were developed. From these relationships a direct optimization scheme is used to determine the optimum wake vorticity distribution for minimum induced drag, subject to constraints on lift, and pitching or bending moment. Integration spanwise yields the bound circulation, which is interpolated in the near field vortex lattice to obtain the design camber surface(s).

Coarse-Grained Lattice Model Simulations of Sequence-Structure Fitness of a Ribosome-Inactivating Protein

DTIC Science & Technology

2007-11-05

limits of what is considered practical when applying all-atom molecular - dynamics simulation methods. Lattice models provide computationally robust...of expectation values from the density of states. All-atom molecular - dynamics simulations provide the most rigorous sampling method to generate con... molecular - dynamics simulations of protein folding,6–9 reported studies of computing a heat capacity or other calorimetric observables have been limited to

Si Lattice, Avogadro Constant, and X- and Gamma-Ray Measurements: Contributions by R.D. Deslattes

NASA Astrophysics Data System (ADS)

Kessler, Jr.

2002-04-01

The achievement of x-ray interferometry in 1965 opened the possibility of more accurately measuring the lattice spacing of a diffraction crystal on a scale directly tied to the SI system of units. The road from the possible to reality required moving objects and measuring translations with sub-atomic accuracy. The improved crystal lattice spacing determinations had a significant impact on two fundamental measurement areas: 1) the amount of substance (the mole and the associated Avogadro Constant), and 2) short wavelengths (the x- and gamma-ray regions). Progress in both areas required additional metrological advances: density and isotopic abundance measurements are needed for the Avogadro constant and small angle measurements are required for the determination of short wavelengths. The x- and gamma-ray measurements have led to more accurate wavelength standards and neutron binding energy measurements that connect gamma-ray measurements to precision atomic mass measurements, particularly the neutron mass. Richard D. Deslattes devoted much of his scientific career to this measurement program. His outstanding contributions and insights will be reviewed.

Impact of growth rate on graphene lattice-defect formation within a single crystalline domain.

PubMed

Chin, Hao-Ting; Lee, Jian-Jhang; Hofmann, Mario; Hsieh, Ya-Ping

2018-03-06

Chemical vapor deposition (CVD) is promising for the large scale production of graphene and other two-dimensional materials. Optimization of the CVD process for enhancing their quality is a focus of ongoing effort and significant progress has been made in decreasing the defectiveness associated with grain boundaries and nucleation spots. However, little is known about the quality and origin of structural defects in the outgrowing lattice which are present even in single-crystalline material and represent the limit of current optimization efforts. We here investigate the formation kinetics of such defects by controlling graphene's growth rate over a wide range using nanoscale confinements. Statistical analysis of Raman spectroscopic results shows a clear trend between growth rate and defectiveness that is in quantitative agreement with a model where defects are healed preferentially at the growth front. Our results suggest that low growth rates are required to avoid the freezing of lattice defects and form high quality material. This conclusion is confirmed by a fourfold enhancement in graphene's carrier mobility upon optimization of the growth rate.

Developmental Arrest and Mouse Antral Not-Surrounded Nucleolus Oocytes1

PubMed Central

Monti, Manuela; Zanoni, Mario; Calligaro, Alberto; Ko, Minoru S.H.; Mauri, Pierluigi; Redi, Carlo Alberto

2013-01-01

ABSTRACT The antral compartment in the ovary consists of two populations of oocytes that differ by their ability to resume meiosis and to develop to the blastocyst stage. For reasons still not entirely clear, antral oocytes termed surrounded nucleolus (SN; 70% of the population of antral oocytes) develop to the blastocyst stage, whereas those called not-surrounded nucleolus (NSN) arrest at two cells. We profiled transcriptomic, proteomic, and morphological characteristics of antral oocytes and observed that NSN oocyte arrest is associated with lack of cytoplasmic lattices coincident with reduced expression of MATER and ribosomal proteins. Cytoplasmic lattices have been shown to store maternally derived mRNA and ribosomes in mammalian oocytes and embryos, and MATER has been shown to be required for cytoplasmic lattice formation. Thus, we isolated antral oocytes from a Matertm/tm mouse and we observed that 84% of oocytes are of the NSN type. Our results provide the first molecular evidence to account for inability of NSN-derived embryos to progress beyond the two-cell stage; these results may be relevant to naturally occurring preimplantation embryo demise in mammals. PMID:23136301

DOE Office of Scientific and Technical Information (OSTI.GOV)

Briceno, Raul A.; Hansen, Maxwell T.; Monahan, Christopher J.

Lattice quantum chromodynamics (QCD) provides the only known systematic, nonperturbative method for first-principles calculations of nucleon structure. However, for quantities such as light-front parton distribution functions (PDFs) and generalized parton distributions (GPDs), the restriction to Euclidean time prevents direct calculation of the desired observable. Recently, progress has been made in relating these quantities to matrix elements of spatially nonlocal, zero-time operators, referred to as quasidistributions. Still, even for these time-independent matrix elements, potential subtleties have been identified in the role of the Euclidean signature. In this work, we investigate the analytic behavior of spatially nonlocal correlation functions and demonstrate thatmore » the matrix elements obtained from Euclidean lattice QCD are identical to those obtained using the Lehmann-Symanzik-Zimmermann reduction formula in Minkowski space. After arguing the equivalence on general grounds, we also show that it holds in a perturbative calculation, where special care is needed to identify the lattice prediction. Lastly, we present a proof of the uniqueness of the matrix elements obtained from Minkowski and Euclidean correlation functions to all order in perturbation theory.« less

Improper ferroelectric polarization in a perovskite driven by intersite charge transfer and ordering

NASA Astrophysics Data System (ADS)

Chen, Wei-Tin; Wang, Chin-Wei; Wu, Hung-Cheng; Chou, Fang-Cheng; Yang, Hung-Duen; Simonov, Arkadiy; Senn, M. S.

2018-04-01

It is of great interest to design and make materials in which ferroelectric polarization is coupled to other order parameters such as lattice, magnetic, and electronic instabilities. Such materials will be invaluable in next-generation data storage devices. Recently, remarkable progress has been made in understanding improper ferroelectric coupling mechanisms that arise from lattice and magnetic instabilities. However, although theoretically predicted, a compact lattice coupling between electronic and ferroelectric (polar) instabilities has yet to be realized. Here we report detailed crystallographic studies of a perovskite HgAMn3A'Mn4BO12 that is found to exhibit a polar ground state on account of such couplings that arise from charge and orbital ordering on both the A'- and B-sites, which are themselves driven by a highly unusual MnA '-MnB intersite charge transfer. The inherent coupling of polar, charge, orbital, and hence magnetic degrees of freedom make this a system of great fundamental interest, and demonstrating ferroelectric switching in this and a host of recently reported hybrid improper ferroelectrics remains a substantial challenge.

Further Applications of a Crystal Lattice Disintegration Criterion to Predict Shock-Induced Reactive Conditions in Solid Materials.

DTIC Science & Technology

1991-07-01

515-568. 6. Billingsley, J. P., and Oliver, J. M., "The Relevance of the De Broglie Relation to the Hugo - niot Elastic Limit (HEL) of Shock Loaded...Soloukin, Progress in Astronautics and Aeronautics, Vol. 94, 1984, Martin Summerfield, Ed-in-chief, pp. 405-415. 66. Trevino , S. F. and Tsai, D. H

Recent progress in Lagrangian field theory and applications. Proceedings of the colloquium held at Marseille, France, June 24--28, 1974

DOE Office of Scientific and Technical Information (OSTI.GOV)

Korthals-Altes, C.P.; de Rafael, E.; Stora, R.

1975-07-01

This Colloquium was devoted to recent developments in the study of Lagrangian models of quantum field theory: renormalized pertubation theories; supergauge fields; asymptotic freedom and infrared slavery in gauge field models involving quarks; gauge fields on lattices; and theory of critical exponents. Papers were abstracted separately for the database.

13C and 1H NMR (Nuclear Magnetic Resonance) studies of solid polyolefines

NASA Technical Reports Server (NTRS)

Cudby, M. E. A.; Harris, R. K.; Metcalfe, K.; Packer, K. J.; Smith, P. W. R.

1983-01-01

The basis of H-1 and C-13 high-resolution NMR investigations of solid polymers is outlined. The C-13 NMR spectra of solid syndiotactic and isotactic polypropene are discussed and their interpretation in terms of conformation and chain-packing effects are reviewed. The effects of decreasing temperature on the C-13 high-resolution spectrum of an annealed sample of isotactic polypropene is described and interpreted in terms of the crystal structure. The question of the proportion of the sample giving rise to C-13 signals is addressed and some results reported. The main cause for observing only part of the total sample is shown to be the H-1 rotating frame spin-lattice relaxation behavior. The H-1 spin-lattice relaxation and spectral characteristics of a number of polyolefin samples are summarized and the role of spin-diffusion discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Corredor, L.T.; Programa de Pós-Graduação em Ciências de Materiais-CCEN, Universidade Federal de Pernambuco, 50670-901 Recife, PE; Grupo de Física de Nuevos Materiales, Departamento de Física, Universidad Nacional de Colombia, Bogotá D.C.

Highlights: • We investigated the effect of the dilution of magnetic Ru sub-lattice of RuSr{sub 2}GdCu{sub 2}O{sub 8}. • We synthesized the doped compound Rui{sub x}Re{sub x}Sr{sub 2}GdCu{sub 2}O{sub y}, for 3%, 6%, 9% and 12% Re. • Re would affect the electron coupling: just 3 and 6% samples were superconductor. • Superconductivity emergence strongly affects magnetic properties of 3 and 6% samples. • A weak ferromagnetic component is consistent with a globally antiferromagnetic system. - Abstract: Despite the discovery of new superconductors classes, high-Tc oxides continue to be a current topic, because of their complex phase diagrams and doping-dependantmore » effects (allowing one to investigate the interaction between orbitals), as well as structural properties such as lattice distortion and charge ordering, among many others. Ruthenocuprates are magnetic superconductors in which the magnetic transition temperature is much higher than the critical superconducting temperature, making them unique compounds. With the aim of investigating the dilution of the magnetic Ru sub-lattice, we proposed the synthesis of the Ru{sub 1−x}Re{sub x}Sr{sub 2}GdCu{sub 2}O{sub y} ruthenocuprate-type family, adapting the known two-step process (double perovskite + CuO) by directly doping the double perovskite, thus obtaining the perovskite compound Sr{sub 2}GdRu{sub 1−x}Re{sub x}O{sub y}, which represents a new synthesis process to the best of our knowledge. Our samples were structurally characterized through X-ray diffraction, and the patterns were analysed via Rietveld refinement. A complete magnetic characterization as a function of temperature and applied field, as well as transport measurements were carried out. We discuss our results in the light of the two-lattice model for ruthenocuprates, and a relation between RuO{sub 2} (magnetic) and CuO{sub 2} (superconductor) sub-lattices can clearly be observed.« less

Effect of texture on rheological properties: the case of ɛ-Fe (Invited)

NASA Astrophysics Data System (ADS)

Merkel, S.; Gruson, M.; Tomé, C. N.; Nishiyama, N.; Wang, Y.

2009-12-01

Lattice preferred orientations (LPO) are known to affect the physical properties of materials. However, in most high pressure deformation experiments, LPO are ignored when interpreting the measured stress-strain curves. In addition, stress measurements in those experiments are complicated by the effect of plastic deformation on the measured lattice strains(1). Here, we present a new interpretation of the results obtained on hcp-iron at up to 19 GPa and 600 K in the deformation-DIA(2). In those experiments, five independent stress-strain curves were obtained on axial shortening with a ductile behavior of the sample for all. Stress were studied using results of monochromatic X-ray diffraction and the elastic theory of lattice strains(3). However, measured stresses were inconsistent with a change of behavior after 4% axial strain, particularly for strains measured on the 0002 line. We use elasto-plastic self consistent modeling(1) to show that this change of behavior is due to the evolution of LPO in the sample. With compression, 10-10 planes in hcp-iron align parallel to the compression direction and this affects the rheological behavior of the sample, which can not be summarized in a simple average law. We will also discuss the implication of those results for the extraction of polycrystalline rheological properties for materials with non-random lattice preferred orientations and how this could affect our understanding of the Earth deep interior. 1- S. Merkel, C.N. Tomé, H.-R Wenk, A modeling analysis of the influence of plasticity on high pressure deformation of hcp-Co, Phys. Rev. B, 79, 064110 (2009) 2- N. Nishiyama, Y. Wang, M. L. Rivers, S. R. Sutton, D. Cookson, Rheology of e-iron up to 19 GPa and 600 K in the D-DIA, Geophys. Res. Lett., 34, L23304 (2007) 3- A. K. Singh, C. Balasingh, H. K. Mao, R. J. Hemley, J. Shu, Analysis of lattice strains measured under non-hydrostatic pressure, J. Appl. Phys., 83, 7567-7575 (1998)

Enhanced nickelidation rate in silicon nanowires with interfacial lattice disorder

NASA Astrophysics Data System (ADS)

Hashimoto, Shuichiro; Yokogawa, Ryo; Oba, Shunsuke; Asada, Shuhei; Xu, Taiyu; Tomita, Motohiro; Ogura, Atsushi; Matsukawa, Takashi; Masahara, Meishoku; Watanabe, Takanobu

2017-10-01

We demonstrate that the nickelidation (nickel silicidation) reaction rate of silicon nanowires (SiNWs) surrounded by a thermally grown silicon dioxide (SiO2) film is enhanced by post-oxidation annealing (POA). The SiNWs are fabricated by electron beam lithography, and some of the SiNWs are subjected to the POA process. The nickelidation reaction rate of the SiNWs is enhanced in the samples subjected to the POA treatment. Ultraviolet Raman spectroscopy measurements reveal that POA enhances compressive strain and lattice disorder in the SiNWs. By considering these experimental results in conjunction with our molecular dynamics simulation analysis, we conclude that the oxide-induced lattice disorder is the dominant origin of the increase in the nickelidation rate in smaller width SiNWs. This study sheds light on the pivotal role of lattice disorders in controlling metallic contact formation in SiNW devices.

Conditions of excitation and sensitivity of diffractively-coupled surface lattice resonances over plasmonic nanoparticle arrays in ATR geometry

NASA Astrophysics Data System (ADS)

Danilov, Artem; Tselikov, Gleb; Wu, Fan; Kravets, Vasyl G.; Ozerov, Igor; Bedu, Frederic; Grigorenko, Alexander N.; Kabashin, Andrei V.

2018-02-01

We investigate conditions of excitation and properties of Plasmonic Surface Lattice Resonances (PSLR) over glass substrate-supported Au nanoparticle dimers ( 100-200 nm) arranged in a periodic metamaterial lattice, in Attenuated Total Reflection (ATR) optical excitation geometry, and assess their sensitivities to variations of refractive index (RI) of the adjacent sample dielectric medium. We show that spectral sensitivity of PSLR to RI variations is determined by the lattice periodicity ( 320 nm per RIU change in our case), while ultranarrow resonance lineshapes (down to a few nm full-widthat-half-maximum) provide very high figure-of-merit values evidencing the possibility of ultrasensitive biosensing measurements. Combining advantages of nanoscale architectures, including a strong concentration of electric field, the possibility of manipulation at the nanoscale etc, and high phase and spectral sensitivities, PSLRs promise a drastic advancement of current state-of-the-art plasmonic biosensing technology.

Development of a new lattice physics code robin for PWR application

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, S.; Chen, G.

2013-07-01

This paper presents a description of methodologies and preliminary verification results of a new lattice physics code ROBIN, being developed for PWR application at Shanghai NuStar Nuclear Power Technology Co., Ltd. The methods used in ROBIN to fulfill various tasks of lattice physics analysis are an integration of historical methods and new methods that came into being very recently. Not only these methods like equivalence theory for resonance treatment and method of characteristics for neutron transport calculation are adopted, as they are applied in many of today's production-level LWR lattice codes, but also very useful new methods like the enhancedmore » neutron current method for Dancoff correction in large and complicated geometry and the log linear rate constant power depletion method for Gd-bearing fuel are implemented in the code. A small sample of verification results are provided to illustrate the type of accuracy achievable using ROBIN. It is demonstrated that ROBIN is capable of satisfying most of the needs for PWR lattice analysis and has the potential to become a production quality code in the future. (authors)« less

Formability and thermal stability of phase in (Fe1-y Coy)-(B, C, N) films

NASA Astrophysics Data System (ADS)

Sunaga, K.; Kadowaki, S.; Tsunoda, M.; Takahashi, M.

2004-06-01

In order to find a way to obtain stable -Fe16X2 phase, the formability and thermal stability of (bct) phase were discussed. According to a rigid sphere model, we concluded that the less formability of B for the phase is due to its large atomic radius. We elucidated the difference of thermal stability of -Fe-X, taking into account their decomposition process. While, the decomposition of -Fe-N progresses only by the migration of N, without changing the bone structure of Fe lattice, the additional energy is needed to break the original α-Fe lattice in the cases of α-Fe-B and α-Fe-C. Therefore thermal stability of α-Fe-B and α-Fe-C is higher than that of α-Fe-N.

Mossbauer effect in dilute iron alloys

NASA Technical Reports Server (NTRS)

Singh, J. J.

1975-01-01

The effects of variable concentration, x, of Aluminum, Germanium, and Lanthanum atoms in Iron lattice on various Mossbauer parameters was studied. Dilute binary alloys of (Fe-Al), (Fe-Ge), (Fe-Al) containing up to x = 2 a/o of the dilute constituent were prepared in the form of ingots and rolled to a thickness of 0.001 in. Mossbauer spectra of these targets were then studied in transmission geometry to measure changes in the hyperfine field, peak widths isomer shifts as well as the ratio of the intensities of peaks (1,6) to the intensities of peaks (2,5). It was shown that the concept of effective hyperfine structure field in very dilute alloys provides a useful means of studying the effects of progressively increasing the solute concentration on host lattice properties.

Evaluation of stress in high pressure radial diffraction: application to hcp Co

NASA Astrophysics Data System (ADS)

Merkel, S.; Tome, C.; Wenk, H.

2007-12-01

Understanding the coupling between elastic and plastic behaviour in hcp Co plastically deformed is important as it can serve as a starting model for improving our understanding of hcp-Fe, the main constituent of the Earth's inner core. For many years, the radial diffraction technique has been used to study mechanical properties under pressure. In those experiments, a polycrystalline sample is plastically deformed between two diamond anvils and lattice spacings are measured using diffraction, with the incoming x-ray beam perpendicular to the compression direction. From the variations of the d-spacings with the diffraction angle, we deduce information on the hydrostatic and deviatoric stress in the sample, while the variations of diffraction intensities provide information on the lattice preferred orientations within the polycrystal. Theories have been developed to relate the observed lattice strains to elastic moduli and stress within the sample (1). However, those models do not account for the effect of plastic deformation and, as a consequence, stress determinations can be inconsistent between lattice planes. In particular, experiments on cobalt have shown that plasticity effects on lattice strains were particularly large in hcp metals (2). This implies that the elastic moduli previously measured for hcp-iron using this technique are not directly related to single-crystal elastic moduli(3). Addressing this problem requires us to consider plastic relaxation, in addition to elastic effects. This can be done using polycrystal elasto-plastic models, which account for slip activity and the threshold stresses associated with their activation. Here, we present new results on modeling radial diffraction experiments using an elasto-plastic self-consistent (EPSC) model and show how the model can be used to interpret radial diffraction data on hcp-Co. More important, we also show how this can be used to derive information about the active slip systems and their critical stress of activation. (1) A.K. Singh, C. Balasingh, Mao, R.J. Hemley & J. Shu, Analysis of lattice strains measured under non- hydrostatic pressure, J. Appl. Phys., 1998, 83, 7567-7575 (2) S. Merkel, N. Miyajima, D. Antonangeli, G. Fiquet & T. Yagi, Lattice preferred orientation and stress in polycrystalline hcp-Co plastically deformed under high pressure, J. Appl. Phys., 2006, 100, 023510 (3) D. Antonangeli, S. Merkel & D. L. Farber, Elastic anisotropy in hcp metals at high pressure and the sound wave anisotropy of the Earth's inner core, Geophys. Res. Lett., 2006, 33, L24303

Bold Diagrammatic Monte Carlo Method Applied to Fermionized Frustrated Spins

NASA Astrophysics Data System (ADS)

Kulagin, S. A.; Prokof'ev, N.; Starykh, O. A.; Svistunov, B.; Varney, C. N.

2013-02-01

We demonstrate, by considering the triangular lattice spin-1/2 Heisenberg model, that Monte Carlo sampling of skeleton Feynman diagrams within the fermionization framework offers a universal first-principles tool for strongly correlated lattice quantum systems. We observe the fermionic sign blessing—cancellation of higher order diagrams leading to a finite convergence radius of the series. We calculate the magnetic susceptibility of the triangular-lattice quantum antiferromagnet in the correlated paramagnet regime and reveal a surprisingly accurate microscopic correspondence with its classical counterpart at all accessible temperatures. The extrapolation of the observed relation to zero temperature suggests the absence of the magnetic order in the ground state. We critically examine the implications of this unusual scenario.

Coupling XRD, EXAFS, and 13C NMR to study the effect of the carbon stoichiometry on the local structure of UC(1±x).

PubMed

Carvajal Nuñez, U; Martel, L; Prieur, D; Lopez Honorato, E; Eloirdi, R; Farnan, I; Vitova, T; Somers, J

2013-10-07

A series of uranium carbide samples, prepared by arc melting with a C/U ratio ranging from 0.96 to 1.04, has been studied by X-ray diffraction (XRD), (13)C nuclear magnetic resonance (NMR), and extended X-ray absorption fine structure (EXAFS). XRD determines phase uniqueness and the increase of the lattice parameter versus the carbon content. In contrast, (13)C NMR detects the different carbon environments in the lattice and in this study, clearly identifies the presence of discrete peaks for carbon in the octahedral lattice site in UC and an additional peak associated with excess carbon in hyperstoichiometric samples. Two peaks associated with different levels of carbon deficiency are detected for all hypostoichiometric compositions. More than one carbon environment is always detected by (13)C NMR. This exemplifies the difficulty in obtaining a perfect stoichiometric uranium monocarbide UC(1.00). The (13)C MAS spectra of uranium carbides exhibit the effects resulting from the carbon content on both the broadening of the peaks and on the Knight shift. An abrupt spectral change occurs between hypo- and hyperstoichiometric samples. The results obtained by EXAFS highlight subtle differences between the different stoichiometries, and in the hyperstoichiometric samples, the EXAFS results are consistent with the excess carbon atoms being in the tetrahedral interstitial position.

On the Progress of Scanning Transmission Electron Microscopy (STEM) Imaging in a Scanning Electron Microscope.

PubMed

Sun, Cheng; Müller, Erich; Meffert, Matthias; Gerthsen, Dagmar

2018-04-01

Transmission electron microscopy (TEM) with low-energy electrons has been recognized as an important addition to the family of electron microscopies as it may avoid knock-on damage and increase the contrast of weakly scattering objects. Scanning electron microscopes (SEMs) are well suited for low-energy electron microscopy with maximum electron energies of 30 keV, but they are mainly used for topography imaging of bulk samples. Implementation of a scanning transmission electron microscopy (STEM) detector and a charge-coupled-device camera for the acquisition of on-axis transmission electron diffraction (TED) patterns, in combination with recent resolution improvements, make SEMs highly interesting for structure analysis of some electron-transparent specimens which are traditionally investigated by TEM. A new aspect is correlative SEM, STEM, and TED imaging from the same specimen region in a SEM which leads to a wealth of information. Simultaneous image acquisition gives information on surface topography, inner structure including crystal defects and qualitative material contrast. Lattice-fringe resolution is obtained in bright-field STEM imaging. The benefits of correlative SEM/STEM/TED imaging in a SEM are exemplified by structure analyses from representative sample classes such as nanoparticulates and bulk materials.

Nonequilibrium electron and lattice dynamics of strongly correlated Bi 2Sr 2CaCu 2O 8+δ single crystals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Konstantinova, Tatiana; Rameau, Jonathan D.; Reid, Alexander H.

Here, the interplay between the electronic and lattice degrees of freedom in nonequilibrium states of strongly correlated systems has been debated for decades. Although progress has been made in establishing a hierarchy of electronic interactions with the use of time-resolved techniques, the role of the phonons often remains in dispute, a situation highlighting the need for tools that directly probe the lattice. We present the first combined megaelectron volt ultrafast electron diffraction and time- and angle-resolved photoemission spectroscopy study of optimally doped Bi 2Sr 2CaCu 2O 8+δ. Quantitative analysis of the lattice and electron subsystems’ dynamics provides a unified picturemore » of nonequilibrium electron-phonon interactions in the cuprates beyond the N-temperature model. The work provides new insights on the specific phonon branches involved in the nonequilibrium heat dissipation from the high-energy Cu–O bond stretching “hot” phonons to the lowest-energy acoustic phonons with correlated atomic motion along the <110> crystal directions and their characteristic time scales. It reveals a highly nonthermal phonon population during the first several picoseconds after the photoexcitation. The approach, taking advantage of the distinct nature of electrons and photons as probes, is applicable for studying energy relaxation in other strongly correlated electron systems.« less

Nonequilibrium electron and lattice dynamics of strongly correlated Bi 2Sr 2CaCu 2O 8+δ single crystals

DOE PAGES

Konstantinova, Tatiana; Rameau, Jonathan D.; Reid, Alexander H.; ...

2018-04-27

Here, the interplay between the electronic and lattice degrees of freedom in nonequilibrium states of strongly correlated systems has been debated for decades. Although progress has been made in establishing a hierarchy of electronic interactions with the use of time-resolved techniques, the role of the phonons often remains in dispute, a situation highlighting the need for tools that directly probe the lattice. We present the first combined megaelectron volt ultrafast electron diffraction and time- and angle-resolved photoemission spectroscopy study of optimally doped Bi 2Sr 2CaCu 2O 8+δ. Quantitative analysis of the lattice and electron subsystems’ dynamics provides a unified picturemore » of nonequilibrium electron-phonon interactions in the cuprates beyond the N-temperature model. The work provides new insights on the specific phonon branches involved in the nonequilibrium heat dissipation from the high-energy Cu–O bond stretching “hot” phonons to the lowest-energy acoustic phonons with correlated atomic motion along the <110> crystal directions and their characteristic time scales. It reveals a highly nonthermal phonon population during the first several picoseconds after the photoexcitation. The approach, taking advantage of the distinct nature of electrons and photons as probes, is applicable for studying energy relaxation in other strongly correlated electron systems.« less

Reduced Iron Sulfide Systems for Removal of Heavy Metal Ions from Groundwater

DTIC Science & Technology

2009-07-01

be gleaned from higher magnification of these samples. Each set of lattice fringes represents a single crystal of mackinawite (Ohfuji and Ricard...diffractograms, the diffraction peaks are broad and weak, indicating a poor degree of crystallization or a small crystallite size. For the non-magnetic...the lattice spacings of synthetic mackinawite in this study are shorter. The 3-day aging in this study resulted in a higher degree of crystallization

Mapping local deformation behavior in single cell metal lattice structures

DOE Office of Scientific and Technical Information (OSTI.GOV)

Carlton, Holly D.; Lind, Jonathan; Messner, Mark C.

The deformation behavior of metal lattice structures is extremely complex and challenging to predict, especially since strain is not uniformly distributed throughout the structure. Understanding and predicting the failure behavior for these types of light-weighting structures is of great interest due to the excellent scaling of stiffness- and strength-to weight ratios they display. Therefore, there is a need to perform simplified experiments that probe unit cell mechanisms. This study reports on high resolution mapping of the heterogeneous structural response of single unit cells to the macro-scale loading condition. Two types of structures, known to show different stress-strain responses, were evaluatedmore » using synchrotron radiation micro-tomography while performing in-situ uniaxial compression tests to capture the local micro-strain deformation. These structures included the octet-truss, a stretch-dominated lattice, and the rhombic-dodecahedron, a bend-dominated lattice. The tomographic analysis showed that the stretch- and bend-dominated lattices exhibit different failure mechanisms and that the defects built into the structure cause a heterogeneous localized deformation response. Also shown here is a change in failure mode for stretch-dominated lattices, where there appears to be a transition from buckling to plastic yielding for samples with a relative density between 10 and 20%. In conclusion, the experimental results were also used to inform computational studies designed to predict the mesoscale deformation behavior of lattice structures. Here an equivalent continuum model and a finite element model were used to predict both local strain fields and mechanical behavior of lattices with different topologies.« less

Mapping local deformation behavior in single cell metal lattice structures

DOE PAGES

Carlton, Holly D.; Lind, Jonathan; Messner, Mark C.; ...

2017-02-08

The deformation behavior of metal lattice structures is extremely complex and challenging to predict, especially since strain is not uniformly distributed throughout the structure. Understanding and predicting the failure behavior for these types of light-weighting structures is of great interest due to the excellent scaling of stiffness- and strength-to weight ratios they display. Therefore, there is a need to perform simplified experiments that probe unit cell mechanisms. This study reports on high resolution mapping of the heterogeneous structural response of single unit cells to the macro-scale loading condition. Two types of structures, known to show different stress-strain responses, were evaluatedmore » using synchrotron radiation micro-tomography while performing in-situ uniaxial compression tests to capture the local micro-strain deformation. These structures included the octet-truss, a stretch-dominated lattice, and the rhombic-dodecahedron, a bend-dominated lattice. The tomographic analysis showed that the stretch- and bend-dominated lattices exhibit different failure mechanisms and that the defects built into the structure cause a heterogeneous localized deformation response. Also shown here is a change in failure mode for stretch-dominated lattices, where there appears to be a transition from buckling to plastic yielding for samples with a relative density between 10 and 20%. In conclusion, the experimental results were also used to inform computational studies designed to predict the mesoscale deformation behavior of lattice structures. Here an equivalent continuum model and a finite element model were used to predict both local strain fields and mechanical behavior of lattices with different topologies.« less

Some New/Old Approaches to QCD

DOE R&D Accomplishments Database

Gross, D. J.

1992-11-01

In this lecture I shall discuss some recent attempts to revive some old ideas to address the problem of solving QCD. I believe that it is timely to return to this problem which has been woefully neglected for the last decade. QCD is a permanent part of the theoretical landscape and eventually we will have to develop analytic tools for dealing with the theory in the infra-red. Lattice techniques are useful but they have not yet lived up to their promise. Even if one manages to derive the hadronic spectrum numerically, to an accuracy of 10% or even 1%, we will not be truly satisfied unless we have some analytic understanding of the results. Also, lattice Monte-Carlo methods can only be used to answer a small set of questions. Many issues of great conceptual and practical interest-in particular the calculation of scattering amplitudes, are thus far beyond lattice control. Any progress in controlling QCD in an explicit analytic, fashion would be of great conceptual value. It would also be of great practical aid to experimentalists, who must use rather ad-hoc and primitive models of QCD scattering amplitudes to estimate the backgrounds to interesting new physics. I will discuss an attempt to derive a string representation of QCD and a revival of the large N approach to QCD. Both of these ideas have a long history, many theorist-years have been devoted to their pursuit-so far with little success. I believe that it is time to try again. In part this is because of the progress in the last few years in string theory. Our increased understanding of string theory should make the attempt to discover a stringy representation of QCD easier, and the methods explored in matrix models might be employed to study the large N limit of QCD.

Chiral Dynamics 2006

NASA Astrophysics Data System (ADS)

Ahmed, Mohammad W.; Gao, Haiyan; Weller, Henry R.; Holstein, Barry

2007-10-01

pt. A. Plenary session. Opening remarks: experimental tests of chiral symmetry breaking / A. M. Bernstein. [Double pie symbols] scattering / H. Leutwyler. Chiral effective field theory in a [Triangle]-resonance region / V. Pascalutsa. Some recent developments in chiral perturbation theory / Ulf-G. Mei ner. Chiral extrapolation and nucleon structure from the lattice / R.D. Young. Recent results from HAPPEX / R. Michaels. Chiral symmetries and low energy searches for new physics / M.J. Ramsey-Musolf. Kaon physics: recent experimental progress / M. Moulson. Status of the Cabibbo angle / V. Cirigliano. Lattice QCD and nucleon spin structure / J.W. Negele. Spin sum rules and polarizabilities: results from Jefferson lab / J-P Chen. Compton scattering and nucleon polarisabilities / Judith A. McGovern. Virtual compton scattering at MIT-bates / R. Miskimen. Physics results from the BLAST detector at the BATES accelerator / R.P. Redwine. The [Pie sympbol]NN system, recent progress / C. Hanhart. Application of chiral nuclear forces to light nuclei / A. Nogga. New results on few-body experiments at low energy / Y. Nagai. Few-body lattice calculations / M.J. Savage. Research opportunities at the upgraded HI?S facility / H.R. Weller -- pt. B. Goldstone boson dynamics. Working group summary: Goldstone Boson dynamics / G. Colangelo and S. Giovannella. Recent results on radiative Kaon decays from NA48 and NA48/2 / S.G. López. Cusps in K-->3 [Pie symbol] decays / B. Kubis. Recent KTeV results on radiative Kaon decays / M.C. Ronquest. The [Double pie symbols] scattering amplitude / J.R. Peláez. Determination of the Regge parameters in the [Double pie symbols] scattering amplitude / I. Caprini. e+e- Hadronic cross section measurement at DA[symbol]NE with the KLOE detector / P. Beltrame. Measurement of the form factors of e+e- -->2([Pie symbol]+[Pie symbol]-), pp and the resonant parameters of the heavy charmonia at BES / H. Hu. Measurement of e+e- multihadronic cross section below 4.5 GeV with BABAR / A. Denig. The pion vector form-factor and (g-2)u / C. Smith. Partially quenched CHPT results to two loops / J. Bijnens. Pion-pion scattering with mixed action lattice QCD / P.F. Bedaque. Meson systems with Ginsparg-Wilson valence quarks / A. Walker-Loud. Low energy constants from the MILC collaboration / C. Bernard. Finite volume effects: lattice meets CHPT / G. Schierholz. Lattice QCD simulations with two light dynamical (Wilson) quarks / L. Giusti. Do we understand the low-energy constant L8? / M. Golterman. Quark mass dependence of LECs in the two-flavour sector / M. Schmid. Progress report on the [Pie symbol]0 Lifetime experiment (PRIMEX) at Jlab / D.E. McNulty. Determination of the charged pion polarizabilities / L.V. Fil'kov. Proposed measurement of electroproduction of [Pie symbol]0 near threshold using a large acceptance spectrometer / R.A. Lindgren. The [Pie symbol] meson in [Pie symbol]K scattering / B. Moussallam. Strangeness -1 Meson-Baryon scattering S-wave / J.A. Oller. Results on light mesons decays and dynamics at KLOE / M. Martini. Studies of decays of [symbol] and [symbol] mesons with WASA detector / A. Kupsc. Heavy Quark-Diquark symmetry and X PT for doubly heavy baryons / T. Mehen. HHChPT applied to the charmed-strange parity partners/ R.P. Springer. Study of pion structure through precise measurements of the [Pie symbol]+ --> e+[symbol] decay / D. Pocanic. Exceptional and non-exceptional contributions to the radiative [Pie symbol] decay / V. Mateu. Leading chiral logarithms from unitarity, analyticity and the Roy equations / A. Fuhrer. All orders symmetric subtraction of the nonlinear sigma model in D=4 / A. Quadri -- pt. C. Chiral dynamics in few-nucleon systems. Working group summary: chiral dynamics in few-nucleon systems / H.W Hammer, N. Kalantar-Nayestanaki, and D.R. Phillips. Power counting in nuclear chiral effective field theory / U. van Kolck. On the consistency of Weinberg's power counting / U-G Mei ner. Renormalization of singular potentials and power counting / M.P. Valderrrama. The challenge of calculating Baryon-Baryon scattering from lattice QCD / S.R. Beane. Precise absolute np scattering cross section and the charged [Pie symbol] NN coupling constant / S. E. Vigdor. Probing hadronic parity violation using few nucleon systems / S.A. Page. Extracting the neutron-neutron scattering length from neutron-deuteron breakup / C.R. Howell. Extraction of [equationl] from [Pie symbol]-d --> [equation] / A. Grudestig. The three- and four-body system with large scattering length / L. Platter. 3N and 4N systems and the Ay puzzle / T. Clegg. Recent progress in nuclear lattice simulations with effective field theory / D. Lee. Few-body studies at KVI / J.G. Messchendorp. Results of three nucleon experiments from RIKEN / K. Sekiguchi. A new opportunity to measure the total photoabsorption cross section of helium / P. T. Debevec. Three-body photodisintegration of 3He with double polarizations / X. Zong. Large two-pion exchange contributions to the pp --> pp[Pie symbol]0 reaction / F. Myhrer. Towards a systematic theory of nuclear forces / E. Epelbaum. Ab initio calculations of eletromagnetic reactions in light nuclei / W. Leidemann. Electron scattering from a polarized deuterium target at BLAST / R. Fatemi. Neutron-neutron scattering length from the reaction [equation] / V. Lensky. Renormalization group analysis of nuclear current operators / S.X. Nakamura. Recent results and future plans at MAX-LAB / K.G. Fissum. Nucleon polarizabilities from deutron compton scattering, and its lessons for chiral power counting / H. W. Grie hammer. Compton scattering on HE-3 / D. Choudhury -- pt. D. Hadron structure and Meson-Baryon interactions. Summary of the working group on Hadron structure and Meson-Baryon interactions / G. Feldman and T.R. Hemmert. Finite volume effects: lattice meets CHPT / G. Schierholz. Lattice discretization errors in chiral effective field theories / B.C. Tiburzi. SU(3)-breaking effects in hyperon semileptonic decays from lattice QCD / S. Simula. Uncertainty bands for chiral extrapolations / B.U. Musch. Update of the nucleon electromagnetic form factors / C. B. Crawford. N and N to ? transition from factors from lattice QCD / C. Alexandrou. The [equation] transition at low Q2 and the pionic contribution / S. Stave. Strange Quark CoNtributions to the form factors of the nucleon / F. Benmokhtar. Dynamical polarizabilities of the nucleon / B. Pasquini. Hadron magnetic moments and polarizabilities in lattice QCD / F.X. Lee. Spin-dependent compton scattering from 3He and the neutron spin polarizabilities / H. Gao. Chiral dynamics from Dyson-Schwinger equations / C.D. Roberts. Radiative neutron [Beta symbol]-decay in effective field theory / S. Gardner. Comparison between different renormalization schemes for co-variant BChPT / T.A. Gail. Non-perturbative study of the light pseudoscalar masses in chiral dynamics / José Antonio Oller. Masses and widths of hadrons in nuclear matter / M. Kotulla. Chiral effective field theory at finite density / R.J. Furnstahl. The K-nuclear interaction: a search fro deeply bound K-nuclear clusters / P. Camerini. Moments of GPDs from lattice QCD / D.G. Richards. Generalized parton distributions in effective field theory / J.W. Chen. Near-threshold pion production: experimental update / M.W. Ahmed. Pion photoproduction near threshold theory update / L. Tiator.

Doping behavior of iodine in Hg/0.8/Cd/0.2/Te

NASA Technical Reports Server (NTRS)

Vydyanath, H. R.; Kroger, F. A.

1982-01-01

The defect state prevailing in iodine doped single-crystal samples of Hg0.8Cd0.2Te, annealed at 450-600 C in Hg vapor, has been deduced from Hall effect measurements on samples cooled to 77 K from the annealing temperature. Results are found to be similar to those previously obtained for iodine doped CdS, i.e. iodine acts as a single donor occupying Te lattice sites with a fraction paired with the native acceptor defects. The concentration of iodine on tellurium lattice sites increases with the partial pressure of Hg, whereas that of the pair species increases as the partial pressure of Hg decreases.

Progress on the Design of the Storage Ring Vacuum System for the Advanced Photon Source Upgrade Project

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stillwell, B.; Billett, B.; Brajuskovic, B.

2017-06-20

Recent work on the design of the storage ring vacuum system for the Advanced Photon Source Upgrade project (APS-U) includes: revising the vacuum system design to accommodate a new lattice with reverse bend magnets, modifying the designs of vacuum chambers in the FODO sections for more intense incident synchrotron radiation power, modifying the design of rf-shielding bellows liners for better performance and reliability, modifying photon absorber designs to make better use of available space, and integrated planning of components needed in the injection, extraction and rf cavity straight sections. An overview of progress in these areas is presented.

Mechanical parameters of strontium doped hydroxyapatite sintered using microwave and conventional methods.

PubMed

Curran, Declan J; Fleming, Thomas J; Towler, Mark R; Hampshire, Stuart

2011-11-01

The effects of ion substitution in hydroxyapatite (HA) on crystal structure and lattice stability is investigated in the green state and post sintering. The effects of ion incorporation on the biaxial flexural strength and hardness are also investigated. Sintering is carried out at 1200 °C using comparative conventional and microwave regimes. Post sintering, the effects of ion incorporation manifest as an increase in the lattice d-spacings and a reduction of the crystallite size. Some HA decomposition occurs with β-TCP stabilisation in conventional sintering (CS), but this phase is destabilised during microwave sintering (MS), generating α-TCP. Conventional sintering (CS) allows higher densification in the undoped samples. Overall, for the Sr-doped compositions, the MS samples retain higher amounts of HA and experience higher density levels compared to the CS samples. Published by Elsevier Ltd.

Narrow Line Cooling of 88Sr Atoms in the Magneto-optical Trap for Precision Frequency Standard

NASA Astrophysics Data System (ADS)

Strelkin, S. A.; Galyshev, A. A.; Berdasov, O. I.; Gribov, A. Yu.; Sutyrin, D. V.; Khabarova, K. Yu.; Kolachevsky, N. N.; Slyusarev, S. N.

We report on our progress toward the realization of a Strontium optical lattice clock, which is under development at VNIIFTRI as a part of GLONASS program. We've prepared the narrow line width laser system for secondary cooling of 88Sr atoms which allows us to reach atom cloud temperature below 3 μK after second cooling stage.

Phase-Pure and Multiphase Ceramic Waste Forms: Microstructure Evolution and Cesium Immobilization

NASA Astrophysics Data System (ADS)

Tumurugoti, Priyatham

Efforts of this thesis are directed towards developing ceramic waste forms as a potential replacement for the conventional glass waste forms for the safe immobilization and disposal of nuclear wastes from the legacy weapons programs as well as commercial power production. The body of this work consists of two equal parts with first focused on multiphase waste form containing hollandite as major phase and the later, on single-phase hollandites for Cs incorporation. Part I: Multiphase waste forms:. Hollandite-rich multiphase waste form compositions processed by melt-solidification and spark plasma sintering (SPS) were characterized, compared, and validated for nuclear waste incorporation. Phase identification by X-ray diffraction (XRD) and electron back-scattered diffraction (EBSD) confirm hollandite as the major phase present in these samples along with perovskite, pyrochlore and zirconolite. Distribution of select elements observed by wavelength dispersive spectroscopy (WDS) maps indicate that Cs forms a secondary phase during SPS processing, which is considered undesirable. On the other hand Cs partitioned into hollandite phase in melt-processed samples. Further analysis of hollandite structure in melt-processed composition, by selected area electron diffraction (SAED), reveals ordered arrangement of tunnel ions (Ba/Cs) and vacancies, suggesting efficient Cs incorporation into the lattice. Following the microstructural analysis, the crystallization behavior of the multiphase composition during melt-processing was studied. The phase assemblage and evolution of hollandite, zirconolite, pyrochlore, and perovskite type structures during melt processing were studied using thermal analysis, in-situ XRD, and scanning electron microscopy (SEM). Samples prepared by melting followed by annealing and quenching were analyzed to determine and measure the progression of the phase assemblage. Samples were melted at 1500°C and heat-treated at crystallization temperatures of 1285°C and 1325°C corresponding to exothermic events identified from differential scanning calorimetry (DSC) measurements. Results indicate that the selected multiphase composition partially melts at 1500°C with hollandite coexisting as crystalline phase. Perovskite and zirconolite phases crystallized from the residual melt at temperatures below 1350°C. Depending on their respective thermal histories, different quenched samples were found to have different phase assemblages including phases such as perovskite, zirconolite and TiO2. Part II: Single phase waste forms. Hollandites with compositions Ba1.15-xCs2xCr 2.3Ti5.7O16 have been identified as promising lattices to host Cs. Series of compositions with 0 ≤ x ≤ 1.15 were prepared by sol-gel synthesis, characterized, and analyzed for Cs retention properties. Phase-pure hollandites adopting monoclinic symmetry (I2/m) were observed to form in the compositional range 0 ≤ x ≤ 0.4. Structural models for the compositions: x = 0, 0.15, and 0.25, were developed from Rietveld analysis of powder XRD and neutron diffraction data. Refined anisotropic displacement parameters (beta ij) for Ba and Cs ions in the hollandite tunnels indicate local disorder of Ba/Cs along the tunnel direction. In addition, weak super lattice reflections have also been observed in XRD patterns. Our data suggests the presence of supercell structures with ordered tunnel cations for the phase-pure hollandites studied. Finally, the performance of phase-pure hollandites have been evaluated qualitatively by chemical durability testing and ion-irradiation experiments. Elemental analysis of the leachants after 7-day leach tests show that Cs and Cr were extracted from the lattice together. No direct correlation between structural parameters or Cs content was observed. The simulated light-ion (He2+) and heavy-ion (Kr3+) irradiation experiments reveal that all the hollandite compositions studied undergo amorphization during alpha-decay events, and the extent of it increases with the Cs content. In summary, the present work validates melt-processing as an effective method to prepare multiphase waste forms with the desired phase assemblage. Ba1.15-xCs2xCr2.3Ti5.7O16 hollandite has been identified as an effective ceramic host for Cs immobilization and appropriate structural models for hollandites with different Cs levels have been developed. The structural information may be used to study or simulate the lattice-environment interaction.

Oxygen content tailored magnetic and electronic properties in cobaltite double perovskite thin films

DOE Office of Scientific and Technical Information (OSTI.GOV)

Harrell, Zach John; Enriquez, Erik M.; Chen, Aiping

Oxygen content in transition metal oxides is one of the most important parameters to control for the desired physical properties. Recently, we have systematically studied the oxygen content and property relationship of the double perovskite PrBaCo 2O 5.5+δ (PBCO) thin films deposited on the LaAlO 3 substrates. The oxygen content in the films was varied by in-situ annealing in a nitrogen, oxygen, or ozone environment. Associated with the oxygen content, the out-of-plane lattice parameter progressively decreases with increasing oxygen content in the films. The saturated magnetization shows a drastic increase and resistivity is significantly reduced in the ozone annealed samples,more » indicating the strong coupling between physical properties and oxygen content. Furthermore, these results demonstrate that the magnetic properties of PBCO films are highly dependent on the oxygen contents, or the film with higher oxygen uptake has the largest magnetization.« less

Raman and electronic transport characterization of few- and single-layer-thick α-RuCl3

NASA Astrophysics Data System (ADS)

Zhou, Boyi; Henriksen, Erik

The layered magnetic semiconductor α-RuCl3, having a honeycomb lattice of spin-1/2 moments, has been identified as a potential candidate material to realize the Kitaev quantum spin liquid. In particular, bulk RuCl3 crystals have been studied and found to be on the cusp of manifesting QSL behavior. As the QSL is primarily a two-dimensional phenomenon, and since the layers of RuCl3 are weakly coupled, we propose to create and study a 2D spin-1/2 honeycomb system by isolating single sheets. Here we report the exfoliation of RuCl3 down to few- and single-layer-thick samples, which we characterize by Raman spectroscopy and atomic force microscopy at room temperature. We will also report our progress on measurements of basic electronic transport properties in the 2D RuCl3 system by controlling the chemical potential via gating in a field-effect configuration.

Oxygen content tailored magnetic and electronic properties in cobaltite double perovskite thin films

DOE PAGES

Harrell, Zach John; Enriquez, Erik M.; Chen, Aiping; ...

2017-02-27

Oxygen content in transition metal oxides is one of the most important parameters to control for the desired physical properties. Recently, we have systematically studied the oxygen content and property relationship of the double perovskite PrBaCo 2O 5.5+δ (PBCO) thin films deposited on the LaAlO 3 substrates. The oxygen content in the films was varied by in-situ annealing in a nitrogen, oxygen, or ozone environment. Associated with the oxygen content, the out-of-plane lattice parameter progressively decreases with increasing oxygen content in the films. The saturated magnetization shows a drastic increase and resistivity is significantly reduced in the ozone annealed samples,more » indicating the strong coupling between physical properties and oxygen content. Furthermore, these results demonstrate that the magnetic properties of PBCO films are highly dependent on the oxygen contents, or the film with higher oxygen uptake has the largest magnetization.« less

Preparation of fine single crystals of magnetic superconductor RuSr2GdCu2O8-δ by partial melting

NASA Astrophysics Data System (ADS)

Yamaki, Kazuhiro; Bamba, Yoshihiro; Irie, Akinobu

2018-03-01

In this study, fine uniform RuSr2GdCu2O8-δ (RuGd-1212) single crystals have been successfully prepared by partial melting. Synthesis temperature could be lowered to a value not exceeding the decomposition temperature of RuGd-1212 using the Sr-Gd-Cu-O flux. The crystals grown by alumina boats are cubic, which coincides with the result of a previous study of RuGd-1212 single crystals using platinum crucibles. The single crystals were up to 15 × 15 × 15 µm3 in size and their lattice constants were consistent with those of polycrystalline samples reported previously. Although the present size of single crystals is not sufficient for measurements, the partial melting technique will be beneficial for future progress of research using RuGd-1212 single crystals. Appropriate nominal composition, sintering atmosphere, and temperature are essential factors for growing RuGd-1212 single crystals.

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

PubMed

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.

Structural phase transition of as-synthesized Sr-Mn nanoferrites by annealing temperature

NASA Astrophysics Data System (ADS)

Amer, M. A.; Meaz, T. M.; Attalah, S. S.; Ghoneim, A. I.

2015-11-01

The Sr0.2Mn0.8Fe2O4 nanoparticle ferrites were synthesized by the co-precipitation method and annealed at different temperatures T. XRD, TEM, FT-IR, VSM and Mössbauer techniques were used to characterize the samples. This study proved that the structural phase of nanoferrites was transformed from cubic spinel for T≤500 °C to Z-type hexagonal for T≥700 °C. The structural transformation was attributed to Jahn-Teller effect of the Mn3+ ions and/or atomic disorder existed in the crystal lattice. The obtained spectra and parameters for the samples were affected by the transformation process. The lattice constant a showed a splitting to a and c for T>500 °C. The lattice constant c, grain and crystallite size R, strain, octahedral B-site band position and force constant, Debye temperature, coercivity Hc, remnant magnetization, squareness and magnetic moment, spontaneous magnetization and hyperfine magnetic fields showed increase against T. The lattice constant a, distortion and dislocation parameters, specific surface area, tetrahedral A-site band position and force constant, threshold frequency, Young's and bulk moduli, saturation magnetization Ms, area ratio of B-/A-sites, A-site line width were decreased with T. Experimental and theoretical densities, porosity, Poison ratio, stiffness constants, rigidity modulus, B-site line width and spontaneous magnetization showed dependence on T, whereas Ms and Hc proved dependence on R.

Low-temperature thermoelectric, galvanomagnetic, and thermodynamic properties of the type-I clathrate Ba8AuxSi46-x

NASA Astrophysics Data System (ADS)

Aydemir, U.; Candolfi, C.; Ormeci, A.; Oztan, Y.; Baitinger, M.; Oeschler, N.; Steglich, F.; Grin, Yu.

2011-11-01

Polycrystalline samples of the clathrate Ba8AuxSi46-x were synthesized for 0.2 ⩽ x ⩽ 10. The homogeneity range of the type-I clathrate phase was determined to be 3.63 ⩽ x ⩽ 6.10 after annealing at 900 °C, while a lower Au concentration (x ≈ 2.2) was obtained by steel-quenching. Quasisingle phase materials were obtained for 4.10 ⩽ x ⩽ 6.10. In this composition range, thermoelectric properties, including electrical resistivity, thermopower, and thermal conductivity, were investigated between 2 and 350 K. These experiments were complemented by low-temperature specific heat and Hall-effect measurements (2-300 K). First-principles calculations were carried out to determine the evolution of the electronic structure as a function of x. Both theoretical and experimental results evidence a progressive evolution, with the Au content, from a metallic-like behavior towards a highly doped semiconducting state which develops around x = 5.43. At this concentration, a crossover from n- to p-type conduction occurs, suggesting that the present system satisfies the Zintl-Klemm concept, which predicts a transition at x = 5.33. This crossover is traced by Hall-effect data indicating a dominant electronlike response for x ⩽ 5.43, which turns into a holelike signal at higher x values. Analysis of the data based on a single-parabolic-band model under the assumption of a single scattering mechanism of the charge carriers proved to adequately describe the transport properties in the compositional range investigated. Interestingly, the temperature dependence of the lattice thermal conductivity is strongly influenced by the Au concentration: the typical behavior of crystalline insulators in the n-type compounds evolves into a glasslike dependence in the p-type samples. The series Ba8AuxSi46-x thus provides an excellent testing ground for the interplay between crystal structure, electronic properties, and lattice thermal conductivity in type-I clathrates.

Matrix metalloproteinase inhibition reduces contraction by dupuytren fibroblasts.

PubMed

Townley, William A; Cambrey, Alison D; Khaw, Peng T; Grobbelaar, Adriaan O

2008-11-01

Dupuytren's disease is a common fibroproliferative condition of the hand characterized by fibrotic lesions (nodules and cords), leading to disability through progressive digital contracture. Although the etiology of the disease is poorly understood, recent evidence suggests that abnormal matrix metalloproteinase (MMP) activity may play a role in cell-mediated collagen contraction and tissue scarring. The aim of this study was to investigate the efficacy of ilomastat, a broad-spectrum MMP inhibitor, in an in vitro model of Dupuytren fibroblast-mediated contraction. Nodule-derived and cord-derived fibroblasts were isolated from Dupuytren patients; carpal ligament-derived fibroblasts acted as control. Stress-release fibroblast-populated collagen lattices (FPCLs) were used as a model of contraction. FPCLs were allowed to develop mechanical stress (48 hours) during treatment with ilomastat (0-100 micromol/L), released, and allowed to contract over a 48-hour period. Contraction was estimated by measuring lattice area compared with untreated cells or treatment with a control peptide. MMP-1, MMP-2, and MT1-MMP levels were assessed by zymography, Western blotting, and enzyme-linked immunosorbent assay. Nodule-derived fibroblasts contracted lattices (69% +/- 2) to a greater extent than did cord-derived (55% +/- 3) or carpal ligament-derived (55% +/- 1) fibroblasts. Exposure to ilomastat led to significant inhibition of lattice contraction by all fibroblasts, although a reduction in lattice contraction by nodule-derived fibroblasts was most prominent (84% +/- 8). In addition, treatment with ilomastat led to a concomitant suppression of MMP-1 and MMP-2 activity, whereas MT1-MMP activity was found to be upregulated. Our results demonstrate that inhibition of MMP activity results in a reduction in extracellular matrix contraction by Dupuytren fibroblasts and suggest that MMP activity may be a critical target in preventing recurrent contracture caused by this disease.

Altered myofilament structure and function in dogs with Duchenne muscular dystrophy cardiomyopathy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ait Mou, Younss; Lacampagne, Alain; Irving, Thomas

Aim Duchenne Muscular Dystrophy (DMD) is associated with progressive depressed left ventricular (LV) function. However, DMD effects on myofilament structure and function are poorly understood. Golden Retriever Muscular Dystrophy (GRMD) is a dog model of DMD recapitulating the human form of DMD. Objective The objective of this study is to evaluate myofilament structure and function alterations in GRMD model with spontaneous cardiac failure. Methods and results We have employed synchrotron X-rays diffraction to evaluate myofilament lattice spacing at various sarcomere lengths (SL) on permeabilized LV myocardium. We found a negative correlation between SL and lattice spacing in both sub-epicardium (EPI)more » and sub-endocardium (ENDO) LV layers in control dog hearts. In the ENDO of GRMD hearts this correlation is steeper due to higher lattice spacing at short SL (1.9 μm). Furthermore, cross-bridge cycling indexed by the kinetics of tension redevelopment (ktr) was faster in ENDO GRMD myofilaments at short SL. We measured post-translational modifications of key regulatory contractile proteins. S-glutathionylation of cardiac Myosin Binding Protein-C (cMyBP-C) was unchanged and PKA dependent phosphorylation of the cMyBP-C was significantly reduced in GRMD ENDO tissue and more modestly in EPI tissue. Conclusions We found a gradient of contractility in control dogs' myocardium that spreads across the LV wall, negatively correlated with myofilament lattice spacing. Chronic stress induced by dystrophin deficiency leads to heart failure that is tightly associated with regional structural changes indexed by increased myofilament lattice spacing, reduced phosphorylation of regulatory proteins and altered myofilament contractile properties in GRMD dogs.« less

How Single-site Mutation Affects HP Lattice Proteins

NASA Astrophysics Data System (ADS)

Shi, Guangjie; Landau, David P.; Vogel, Thomas; Wüst, Thomas; Li, Ying Wai

2014-03-01

We developed a heuristic method based on Wang-Landauand multicanonical sampling for determining the ground-state degeneracy of HP lattice proteins . Our algorithm allowed the most precise estimations of the (sometimes substantial) ground-state degeneracies of some widely studied HP sequences. We investigated the effects of single-site mutation on specific long HP lattice proteins comprehensively, including structural changes in ground-states, changes of ground-state degeneracy and thermodynamic properties of the systems. Both extremely sensitive and insensitive cases have been observed; consequently, properties such as specific heat, tortuosities etc. may be either largely unaffected or may change significantly due to mutation. More interestingly, mutation can even induce a lower ground-state energy in a few cases. Supported by NSF.

First Monte Carlo Global Analysis of Nucleon Transversity with Lattice QCD Constraints

DOE PAGES

Lin, Huey-Wen; Melnitchouk, Wally; Prokudin, Alexei; ...

2018-04-11

We report on the first global QCD analysis of the quark transversity distributions in the nucleon from semi-inclusive deep-inelastic scattering (SIDIS), using a new Monte Carlo method based on nested sampling and constraints on the isovector tensor chargemore » $$g_T$$ from lattice QCD. A simultaneous fit to the available SIDIS Collins asymmetry data is compatible with $$g_T$$ values extracted from a comprehensive reanalysis of existing lattice simulations, in contrast to previous analyses, which found significantly smaller $$g_T$$ values. The contributions to the nucleon tensor charge from $u$ and $d$ quarks are found to be $$\\delta u = 0.3(2)$$ and $$\\delta d = -0.7(2)$$ at a scale $Q^2 = 2$ GeV$^2$.« less

First Monte Carlo Global Analysis of Nucleon Transversity with Lattice QCD Constraints

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lin, Huey-Wen; Melnitchouk, Wally; Prokudin, Alexei

We report on the first global QCD analysis of the quark transversity distributions in the nucleon from semi-inclusive deep-inelastic scattering (SIDIS), using a new Monte Carlo method based on nested sampling and constraints on the isovector tensor chargemore » $$g_T$$ from lattice QCD. A simultaneous fit to the available SIDIS Collins asymmetry data is compatible with $$g_T$$ values extracted from a comprehensive reanalysis of existing lattice simulations, in contrast to previous analyses, which found significantly smaller $$g_T$$ values. The contributions to the nucleon tensor charge from $u$ and $d$ quarks are found to be $$\\delta u = 0.3(2)$$ and $$\\delta d = -0.7(2)$$ at a scale $Q^2 = 2$ GeV$^2$.« less

Favoured local structures in liquids and solids: a 3D lattice model.

PubMed

Ronceray, Pierre; Harrowell, Peter

2015-05-07

We investigate the connection between the geometry of Favoured Local Structures (FLS) in liquids and the associated liquid and solid properties. We introduce a lattice spin model - the FLS model on a face-centered cubic lattice - where this geometry can be arbitrarily chosen among a discrete set of 115 possible FLS. We find crystalline groundstates for all choices of a single FLS. Sampling all possible FLS's, we identify the following trends: (i) low symmetry FLS's produce larger crystal unit cells but not necessarily higher energy groundstates, (ii) chiral FLS's exhibit peculiarly poor packing properties, (iii) accumulation of FLS's in supercooled liquids is linked to large crystal unit cells, and (iv) low symmetry FLS's tend to find metastable structures on cooling.

First Monte Carlo Global Analysis of Nucleon Transversity with Lattice QCD Constraints.

PubMed

Lin, H-W; Melnitchouk, W; Prokudin, A; Sato, N; Shows, H

2018-04-13

We report on the first global QCD analysis of the quark transversity distributions in the nucleon from semi-inclusive deep-inelastic scattering (SIDIS), using a new Monte Carlo method based on nested sampling and constraints on the isovector tensor charge g_{T} from lattice QCD. A simultaneous fit to the available SIDIS Collins asymmetry data is compatible with g_{T} values extracted from a comprehensive reanalysis of existing lattice simulations, in contrast to previous analyses, which found significantly smaller g_{T} values. The contributions to the nucleon tensor charge from u and d quarks are found to be δu=0.3(2) and δd=-0.7(2) at a scale Q^{2}=2  GeV^{2}.

First Monte Carlo Global Analysis of Nucleon Transversity with Lattice QCD Constraints

NASA Astrophysics Data System (ADS)

Lin, H.-W.; Melnitchouk, W.; Prokudin, A.; Sato, N.; Shows, H.; Jefferson Lab Angular Momentum JAM Collaboration

2018-04-01

We report on the first global QCD analysis of the quark transversity distributions in the nucleon from semi-inclusive deep-inelastic scattering (SIDIS), using a new Monte Carlo method based on nested sampling and constraints on the isovector tensor charge gT from lattice QCD. A simultaneous fit to the available SIDIS Collins asymmetry data is compatible with gT values extracted from a comprehensive reanalysis of existing lattice simulations, in contrast to previous analyses, which found significantly smaller gT values. The contributions to the nucleon tensor charge from u and d quarks are found to be δ u =0.3 (2 ) and δ d =-0.7 (2 ) at a scale Q2=2 GeV2.

Monitoring a simple hydrolysis process in an organic solid by observing methyl group rotation.

PubMed

Beckmann, Peter A; Bohen, Joseph M; Ford, Jamie; Malachowski, William P; Mallory, Clelia W; Mallory, Frank B; McGhie, Andrew R; Rheingold, Arnold L; Sloan, Gilbert J; Szewczyk, Steven T; Wang, Xianlong; Wheeler, Kraig A

2017-09-01

We report a variety of experiments and calculations and their interpretations regarding methyl group (CH 3 ) rotation in samples of pure 3-methylglutaric anhydride (1), pure 3-methylglutaric acid (2), and samples where the anhydride is slowly absorbing water from the air and converting to the acid [C 6 H 8 O 3 (1) + H 2 O → C 6 H 10 O 4 (2)]. The techniques are solid state 1 H nuclear magnetic resonance (NMR) spin-lattice relaxation, single-crystal X-ray diffraction, electronic structure calculations in both isolated molecules and in clusters of molecules that mimic the crystal structure, field emission scanning electron microscopy, differential scanning calorimetry, and high resolution 1 H NMR spectroscopy. The solid state 1 H spin-lattice relaxation experiments allow us to observe the temperature dependence of the parameters that characterize methyl group rotation in both compounds and in mixtures of the two compounds. In the mixtures, both types of methyl groups (that is, molecules of 1 and 2) can be observed independently and simultaneously at low temperatures because the solid state 1 H spin-lattice relaxation is appropriately described by a double exponential. We have followed the conversion 1 → 2 over periods of two years. The solid state 1 H spin-lattice relaxation experiments in pure samples of 1 and 2 indicate that there is a distribution of NMR activation energies for methyl group rotation in 1 but not in 2 and we are able to explain this in terms of the particle sizes seen in the field emission scanning electron microscopy images. Copyright © 2017 Elsevier Inc. All rights reserved.

Simulations of lattice animals and trees

NASA Astrophysics Data System (ADS)

Hsu, Hsiao-Ping; Nadler, Walter; Grassberger, Peter

2005-01-01

The scaling behaviour of randomly branched polymers in a good solvent is studied in two to nine dimensions, using as microscopic models lattice animals and lattice trees on simple hypercubic lattices. As a stochastic sampling method we use a biased sequential sampling algorithm with re-sampling, similar to the pruned-enriched Rosenbluth method (PERM) used extensively for linear polymers. Essentially we start simulating percolation clusters (either site or bond), re-weigh them according to the animal (tree) ensemble, and prune or branch the further growth according to a heuristic fitness function. In contrast to previous applications of PERM, this fitness function is not the weight with which the actual configuration would contribute to the partition sum, but is closely related to it. We obtain high statistics of animals with up to several thousand sites in all dimension 2 <= d <= 9. In addition to the partition sum (number of different animals) we estimate gyration radii and numbers of perimeter sites. In all dimensions we verify the Parisi-Sourlas prediction, and we verify all exactly known critical exponents in dimensions 2, 3, 4 and >=8. In addition, we present the hitherto most precise estimates for growth constants in d >= 3. For clusters with one site attached to an attractive surface, we verify for d >= 3 the superuniversality of the cross-over exponent phgr at the adsorption transition predicted by Janssen and Lyssy, but not for d = 2. There, we find phgr = 0.480(4) instead of the conjectured phgr = 1/2. Finally, we discuss the collapse of animals and trees, arguing that our present version of the algorithm is also efficient for some of the models studied in this context, but showing that it is not very efficient for the 'classical' model for collapsing animals.

Tiny twists in time; exploring angular resolution of in situ EBSD orientation microstructures in solar system zircon

NASA Astrophysics Data System (ADS)

Moser, D. E.

2012-12-01

Kikuchi discovered electron diffraction in samples of calcite in the 1920's, and orientation of lattice planes by Electron Backscatter Diffraction (EBSD) is now routinely measured by automated camera systems at a spatial resolution of tens of nanometers using Field Emission Gun SEM. The current methodology is proving particularly powerful when measuring lattice orientation microstructure in U-Pb geochronology minerals such as zircon and baddeleyite that have experienced high temperature deformation or shock metamorphism. These are among the oldest preserved mineral phases in inner solar system materials, and we have been applying EBSD to rare samples of the Early Earth and grains from extraterrestrial environments such as the Moon and Mars. In these cases the EBSD orientation data are useful for identifying high diffusivity pathways that may have afforded isotopic and trace element disturbance, microstructural proxies for shock metamorphic pressures, as well as resolving glide plane systems in ductile zircon and shear twin mechanisms. Blanket estimates of angular resolution for automated EBSD misorientation measurements are often in the range of 0.5 degrees. In some cases strain giving rise to only a few degrees of lattice misorientation has facilitated 100% Pb-loss. In some cases, however, there is a spatial correlation between trace element or cathodoluminescence zoning in zircon and what appears to be low magnitudes misorientation close to the limits of resolution. Given the proven value of performing EBSD analysis on geochronology minerals, a more thorough exploration of the precision and accuracy of EBSD lattice misorientation measurements is warranted. In this talk the relative weighting of the factors that limit EBSD angular resolution will be investigated, focusing on U-Pb dating minerals such as zircon. These factors include; sample surface preparation, phase symmetry, pseudo-symmetry effects, degree of crystallinity, Kikuchi band contrast and indexing, solid solution effects on unit cell, dimension camera calibration and camera-sample distance, beam conditions and focussing, and general microscope operating conditions (e.g. high vacuum vs. variable pressure). An assessment of potential zircon EBSD reference materials and sample preparation protocols will be presented, along with case studies of zircon orientation microstructures from meteorites and terrestrial craters representative of different strain and thermal environments in the inner solar system.BSD lattice misorientation maps of a) crystal-plastically deformed and partly recrystallized zircon, after Rayner et al. (in prep.), and b) shock-metamorphosed lunar zircon (Darling et al., in prep.).

Thermal stability of the Mobil Five type metallosilicate molecular sieves-An in situ high temperature X-ray diffraction study

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bhange, D.S.; Ramaswamy, Veda

2007-05-03

We have carried out in situ high temperature X-ray diffraction (HTXRD) studies of silicalite-1 (S-1) and metallosilicate molecular sieves containing iron, titanium and zirconium having Mobil Five (MFI) structure (iron silicalite-1 (FeS-1), titanium silicalite-1 (TS-1) and zirconium silicalite-1 (ZrS-1), respectively) in order to study the thermal stability of these materials. Isomorphous substitution of Si{sup 4+} by metal atoms is confirmed by the expansion of unit cell volume by X-ray diffraction (XRD) and the presence of Si-O-M stretching band at {approx}960 cm{sup -1} by Fourier transform infrared (FTIR) spectroscopy. Appearance of cristobalite phase is seen at 1023 and 1173 K inmore » S-1 and FeS-1 samples. While the samples S-1 and FeS-1 decompose completely to cristobalite at 1173 and 1323 K, respectively, the other two samples are thermally stable upto 1623 K. This transformation is irreversible. Although all materials show a negative lattice thermal expansion, their lattice thermal expansion coefficients vary. The thermal expansion behavior in all samples is anisotropic with relative strength of contraction along 'a' axes is more than along 'b' and 'c' axes in S-1, TS-1, ZrS-1 and vice versa in FeS-1. Lattice thermal expansion coefficients ({alpha} {sub v}) in the temperature range 298-1023 K were -6.75 x 10{sup -6} K{sup -1} for S-1, -12.91 x 10{sup -6} K{sup -1} for FeS-1, -16.02 x 10{sup -6} K{sup -1} for TS-1 and -17.92 x 10{sup -6} K{sup -1} for ZrS-1. The highest lattice thermal expansion coefficients ({alpha} {sub v}) obtained were -11.53 x 10{sup -6} K{sup -1} for FeS-1 in temperature range 298-1173 K, -20.86 x 10{sup -6} K{sup -1} for TS-1 and -25.54 x 10{sup -6} K{sup -1} for ZrS-1, respectively, in the temperature range 298-1623 K. Tetravalent cation substitution for Si{sup 4+} in the lattice leads to a high thermal stability as compared to substitution by trivalent cations.« less

Lattice QCD Calculations in Nuclear Physics towards the Exascale

NASA Astrophysics Data System (ADS)

Joo, Balint

2017-01-01

The combination of algorithmic advances and new highly parallel computing architectures are enabling lattice QCD calculations to tackle ever more complex problems in nuclear physics. In this talk I will review some computational challenges that are encountered in large scale cold nuclear physics campaigns such as those in hadron spectroscopy calculations. I will discuss progress in addressing these with algorithmic improvements such as multi-grid solvers and software for recent hardware architectures such as GPUs and Intel Xeon Phi, Knights Landing. Finally, I will highlight some current topics for research and development as we head towards the Exascale era This material is funded by the U.S. Department of Energy, Office Of Science, Offices of Nuclear Physics, High Energy Physics and Advanced Scientific Computing Research, as well as the Office of Nuclear Physics under contract DE-AC05-06OR23177.

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

PubMed

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.

Bose-Einstein condensation in chains with power-law hoppings: Exact mapping on the critical behavior in d-dimensional regular lattices.

PubMed

Dias, W S; Bertrand, D; Lyra, M L

2017-06-01

Recent experimental progress on the realization of quantum systems with highly controllable long-range interactions has impelled the study of quantum phase transitions in low-dimensional systems with power-law couplings. Long-range couplings mimic higher-dimensional effects in several physical contexts. Here, we provide the exact relation between the spectral dimension d at the band bottom and the exponent α that tunes the range of power-law hoppings of a one-dimensional ideal lattice Bose gas. We also develop a finite-size scaling analysis to obtain some relevant critical exponents and the critical temperature of the BEC transition. In particular, an irrelevant dangerous scaling field has to be taken into account when the hopping range is sufficiently large to make the effective dimensionality d>4.

Bose-Einstein condensation in chains with power-law hoppings: Exact mapping on the critical behavior in d -dimensional regular lattices

NASA Astrophysics Data System (ADS)

Dias, W. S.; Bertrand, D.; Lyra, M. L.

2017-06-01

Recent experimental progress on the realization of quantum systems with highly controllable long-range interactions has impelled the study of quantum phase transitions in low-dimensional systems with power-law couplings. Long-range couplings mimic higher-dimensional effects in several physical contexts. Here, we provide the exact relation between the spectral dimension d at the band bottom and the exponent α that tunes the range of power-law hoppings of a one-dimensional ideal lattice Bose gas. We also develop a finite-size scaling analysis to obtain some relevant critical exponents and the critical temperature of the BEC transition. In particular, an irrelevant dangerous scaling field has to be taken into account when the hopping range is sufficiently large to make the effective dimensionality d >4 .

Development of a force sensor using atom interferometry to constrain theories on dark matter and dark energy

NASA Astrophysics Data System (ADS)

Schlupf, Chandler; Niederriter, Robert; Bohr, Eliot; Khamis, Sami; Park, Youna; Szwed, Erik; Hamilton, Paul

2017-04-01

Atom interferometry has been used in many precision measurements such as Newton's gravitational constant, the fine structure constant, and tests of the equivalence principle. We will perform atom interferometry in an optical lattice to measure the force felt by an atom due to a test mass in search of new forces suggested by dark matter and dark energy theories. We will be developing a new apparatus using laser-cooled ytterbium to continuously measure this force by observing their Bloch oscillations. Interfering atoms in an optical lattice allows continuous measurements in a small volume over a long period of time, enabling our device to be sensitive to time-varying forces while minimizing vibrational noise. We present the details of this experiment and the progress on it thus far.

All-electrical detection of spin dynamics in magnetic antidot lattices by the inverse spin Hall effect

DOE PAGES

Jungfleisch, Matthias B.; Zhang, Wei; Ding, Junjia; ...

2016-02-03

The understanding of spin dynamics in laterally confined structures on sub-micron length scales has become a significant aspect of the development of novel magnetic storage technologies. Numerous ferromagnetic resonance measurements, optical characterization by Kerr microscopy and Brillouin light scattering spectroscopy and x-ray studies were carried out to detect the dynamics in patterned magnetic antidot lattices. Here, we investigate Oersted-field driven spin dynamics in rectangular Ni80Fe20/Pt antidot lattices with different lattice parameters by electrical means. When the system is driven to resonance, a dc voltage across the length of the sample is detected that changes its sign upon field reversal, whichmore » is in agreement with a rectification mechanism based on the inverse spin Hall effect. Furthermore, we show that the voltage output scales linearly with the applied microwave drive in the investigated range of powers. Lastly, our findings have direct implications on the development of engineered magnonics applications and devices.« less

Quality Assurance of NCI Thesaurus by Mining Structural-Lexical Patterns

PubMed Central

Abeysinghe, Rashmie; Brooks, Michael A.; Talbert, Jeffery; Licong, Cui

2017-01-01

Quality assurance of biomedical terminologies such as the National Cancer Institute (NCI) Thesaurus is an essential part of the terminology management lifecycle. We investigate a structural-lexical approach based on non-lattice subgraphs to automatically identify missing hierarchical relations and missing concepts in the NCI Thesaurus. We mine six structural-lexical patterns exhibiting in non-lattice subgraphs: containment, union, intersection, union-intersection, inference-contradiction, and inference union. Each pattern indicates a potential specific type of error and suggests a potential type of remediation. We found 809 non-lattice subgraphs with these patterns in the NCI Thesaurus (version 16.12d). Domain experts evaluated a random sample of 50 small non-lattice subgraphs, of which 33 were confirmed to contain errors and make correct suggestions (33/50 = 66%). Of the 25 evaluated subgraphs revealing multiple patterns, 22 were verified correct (22/25 = 88%). This shows the effectiveness of our structurallexical-pattern-based approach in detecting errors and suggesting remediations in the NCI Thesaurus. PMID:29854100

Algebraic signal processing theory: 2-D spatial hexagonal lattice.

PubMed

Pünschel, Markus; Rötteler, Martin

2007-06-01

We develop the framework for signal processing on a spatial, or undirected, 2-D hexagonal lattice for both an infinite and a finite array of signal samples. This framework includes the proper notions of z-transform, boundary conditions, filtering or convolution, spectrum, frequency response, and Fourier transform. In the finite case, the Fourier transform is called discrete triangle transform. Like the hexagonal lattice, this transform is nonseparable. The derivation of the framework makes it a natural extension of the algebraic signal processing theory that we recently introduced. Namely, we construct the proper signal models, given by polynomial algebras, bottom-up from a suitable definition of hexagonal space shifts using a procedure provided by the algebraic theory. These signal models, in turn, then provide all the basic signal processing concepts. The framework developed in this paper is related to Mersereau's early work on hexagonal lattices in the same way as the discrete cosine and sine transforms are related to the discrete Fourier transform-a fact that will be made rigorous in this paper.

Characterization of dipole defects in MgAl2O4 spinel

NASA Astrophysics Data System (ADS)

Carvalhaes, R. P. M.; da Rocha, M. S. F.; de Souza, S. S.; Blak, A. R.

2005-01-01

Dipole defects in gamma-irradiated and thermal treated MgAl2O4 samples have been studied through thermally stimulated depolarisation currents(TSDC) technique and computer modelling methods. The presence of TSDC bands varies from sample to sample and some crystals do not present any band. The origin of these bands has been investigated in several different samples. In the spectra of spinels showing TSDC peaks, three bands at 130K, 160K and 320K are observed. The peaks at 130K and 160K have been attributed to dipole defects. After 1200kGy of gamma irradiation the broad band at 320K dislocates to 290K and increases ten times. Pulsed thermal treatments between 350K and 470K produce a progressive reduction of the peak area and a shift in the peak position back to 320K. A detailed analysis of the curve indicates the possibility of a superposition of peaks. Gamma irradiation restores the 320K TSDC peak. Taking into account optical absorption(OA) and electron paramagnetic resonance(EPR) results, the thermal reduction of the 320K TSDC band was attributed to V-type centres as a result of hole trapping at tetrahedral and octahedral cation vacancies. Computer modelling methods, based on lattice energy and defect minimisation, were applied to identify dipole defects that occur in these crystals. The calculations were made in normal and inverse spinel structures, doped with Cr, Co, Mn and Fe in order to justify the presence of dipole bands.

Design of a One-Dimensional Sextupole Using Semi-Analytic Methods

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gupta, L.; Nagaitsev, S.; Baturin, S. S.

Sextupole magnets provide position-dependent momentum kicks and are tuned to provide the correct kicks to parti- cles within a small acceptance region in phase space. Sextupoles are useful and even necessary in circular accelerators for chromaticity corrections. They are routinely used in most rings, i.e. CESR. Although sextupole magnets are necessary for particle energy corrections, they also have undesirable effects on dynamic aperture, especially because of their non- linear coupling term in the momentum kick. Studies of integrable systems suggest that there is an analytic way to create transport lattices with specific transfer matrices that limit the momentum kick tomore » one dimension. A one-dimension sex- tupole is needed for chromaticity corrections: a horizontal sextupole for horizontal bending magnets. We know how to make a “composite” horizontal sextupole using regular 2D sextupoles and linear transfer matrices in an ideal thin-lens approximation. Thus, one could create an accelerator lattice using linear elements, in series with sextupole magnets to create a “1D sextupole”. This paper describes progress to- wards realizing a realistic focusing lattice resulting in a 1D sextupole.« less

SciDAC-3: Searching for Physics Beyond the Standard Model, University of Arizona component, Year 2 progress report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Toussaint, Doug

2014-03-21

The Arizona component of the SciDAC-3 Lattice Gauge Theory program consisted of partial support for a postdoctoral position. In the original budget this covered three fourths of a postdoc, but the University of Arizona changed its ERE rate for postdoctoral positions from 4.3% to 21%, so the support level was closer to two-thirds of a postdoc. The grant covered the work of postdoc Thomas Primer. Dr. Primer's first task was an urgent one, although it was not forseen in our proposed work. It turned out that on the large lattices used in some of our current computations the gauge fixingmore » code was not working as expected, and this revealed itself in inconsistent results in the correlators needed to compute the semileptonic form factors for K and D decays. Dr. Primer participated in the effort to understand this problem and to modify our codes to deal with the large lattices we are now generating (as large as 144 3 x 288). Corrected code was incorporated in our standard codes, and workarounds that allow us to use the correlators already computed with the unexpected gauge fixing were been implemented.« less

Toward a nanoscience emulator with two dimensional atomic gases

NASA Astrophysics Data System (ADS)

Wang, Ping; Ma, Q.; Dutta, S.; Chen, Yong P.

2009-05-01

We report our experimental progress in constructing a cold atom apparatus for emulating phenomena in nanoscience using low dimensional atom gases. Our first experiments will be performed with a 2D ^87Rb Bose-Einstein condensate created in an optical lattice. Our compact vacuum system consists of two AR-coated glass cells --- a low vacuum magneto-optical trap (MOT) chamber and a high vacuum ``science chamber'', connected by a 15cm-long tube for differential pumping. We have used elliptically shaped cooling laser beams and magnet field coils to realize an elongated MOT in the first chamber, and transferred the atoms to a second MOT in the science chamber by a push laser beam. In the science chamber, a 50W, 1550nm single frequency erbium fiber laser is used to produce an optical dipole trap and optical lattice.In addition, controllable disorder can be introduced with laser speckle and inter-atomic interactions can be tuned by atomic density or Feshbach resonance. We plan to explore important phenomena in nanoscience, such as 2D disorder-induced conductor-insulator transition, quantum Hall effect and graphene-like physics in such a tunable 2D atomic gas in optical lattices.

Two-dimensional triangular lattice and its application to lithium-intercalated layered compounds

NASA Astrophysics Data System (ADS)

Decerqueira, R. O.

1982-08-01

Good rechargeable batteries are being searched for use in electric vehicles and in energy storage during off-peak consumption periods and from solar sources. The interest in lithium intercalation compounds has been recently enhanced by the search for such batteries. The process of intercalation of lithium in several transition metal dichalcogenides can provide an emf of several volts. The progress achieved in the last decade in the investigation of these intercalates has been facilitated by the availability of the dichalcogenides as single crystals and by their chemical stability. The transition-metal dichalcogenides and their Li-intercalates are studied, with emphasis on the Li/su xTa/sub yTi/sub l-y/S2 series. The interactions between the Li atoms and the applicability of a lattice gas model to the problem of ordering of these atoms is discussed. A formulation is presented of the cluster-variation aproximation to the lattice gas problem. The single-site and the nearest-neighbor triangle basic clusters are considered as models for Li/sub x TiS2. Also a theory is presented for the effects of a random distribution of different species of host atoms, as in Ta/sub y/Ti/sub l-y/S2.

Global QCD Analysis of the Nucleon Tensor Charge with Lattice QCD Constraints

NASA Astrophysics Data System (ADS)

Shows, Harvey, III; Melnitchouk, Wally; Sato, Nobuo

2017-09-01

By studying the parton distribution functions (PDFs) of a nucleon, we probe the partonic scale of nature, exploring what it means to be a nucleon. In this study, we are interested in the transversity PDF-the least studied of the three collinear PDFs. By conducting a global analysis on experimental data from semi-inclusive deep inelastic scattering (SIDIS), as well as single-inclusive e+e- annihilation (SIA), we extract the fit parameters needed to describe the transverse moment dependent (TMD) transversity PDF, as well as the Collins fragmentation function. Once the collinear transversity PDF is obtained by integrating the extracted TMD PDF, we wish to resolve discrepancies between lattice QCD calculations and phenomenological extractions of the tensor charge from data. Here we show our results for the transversity distribution and tensor charge. Using our method of iterative Monte Carlo, we now have a more robust understanding of the transversity PDF. With these results we are able to progress in our understanding of TMD PDFs, as well as testify to the efficacy of current lattice QCD calculations. This work is made possible through support from NSF award 1659177 to Old Dominion University.

Colloquium: Herbertsmithite and the search for the quantum spin liquid

DOE PAGES

Norman, M. R.

2016-12-02

Quantum spin liquids form a novel class of matter where, despite the existence of strong exchange interactions, spins do not order down to the lowest measured temperature. Typically, these occur in lattices that act to frustrate the appearance of magnetism. In two dimensions, the classic example is the kagome lattice composed of corner sharing triangles. There are a variety of minerals whose transition metal ions form such a lattice. Hence, a number of them have been studied and were then subsequently synthesized in order to obtain more pristine samples. Of particular note was the report in 2005 by Dan Nocera'smore » group of the synthesis of herbertsmithite, composed of a lattice of copper ions sitting on a kagome lattice, which indeed does not order down to the lowest measured temperature despite the existence of a large exchange interaction of 17 meV. Over the past decade, this material has been extensively studied, yielding a number of intriguing surprises that have in turn motivated a resurgence of interest in the theoretical study of the spin 1/2 Heisenberg model on a kagome lattice. In this paper, this Colloquium reviews these developments and then discusses potential future directions, both experimental and theoretical, as well as the challenge of doping these materials with the hope that this could lead to the discovery of novel topological and superconducting phases.« less

In situ neutron diffraction in quantifying deformation behaviors of nano-sized carbide strengthened UFG ferritic steel

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, J. W.; Shen, Y. F.; Zhang, C. S.

Here, the microstructures and mechanical properties of a low-alloy medium-carbon steel with a duplex microstructure composed of nanoscale spheroidized carbides in ultrafine-grained (UFG) ferritic steel are examined. The average grain size of the studied steel is ~ 430 nm, and these grains coexist with numerous carbides. Neutron diffraction reveals that the intensity of (011) and (022) peaks for the UFG sample is significantly enhanced, suggesting that the (011)//RD texture is a result of the warm rolling process. The lattice parameter of UFG steel is smaller than that of a martensitic steel (M steel) counterpart, indicating a lower carbon concentration inmore » the lattice. The estimated dislocation densities for M steel and UFG steel are 2.59 × 10 14 cm –2 and 1.76 × 10 12 cm –2, respectively. The UFG steel reveals a nearly isotropic lattice strain response under initial tension from 0 to 450 MPa, where the lattice strains of the (110), (002), and (112) planes are identical. The increase of lattice strain of the (110) plane becomes smaller than that of the (002) and (112) planes as the stress exceeds 450 MPa, suggesting that the nanosized carbides contribute to the hardening ability by promoting the accumulation of geometrically necessary dislocations around the particles, and the (110) lattice becomes harder compared to the other two planes.« less

In situ neutron diffraction in quantifying deformation behaviors of nano-sized carbide strengthened UFG ferritic steel

DOE PAGES

Liang, J. W.; Shen, Y. F.; Zhang, C. S.; ...

2018-04-25

Here, the microstructures and mechanical properties of a low-alloy medium-carbon steel with a duplex microstructure composed of nanoscale spheroidized carbides in ultrafine-grained (UFG) ferritic steel are examined. The average grain size of the studied steel is ~ 430 nm, and these grains coexist with numerous carbides. Neutron diffraction reveals that the intensity of (011) and (022) peaks for the UFG sample is significantly enhanced, suggesting that the (011)//RD texture is a result of the warm rolling process. The lattice parameter of UFG steel is smaller than that of a martensitic steel (M steel) counterpart, indicating a lower carbon concentration inmore » the lattice. The estimated dislocation densities for M steel and UFG steel are 2.59 × 10 14 cm –2 and 1.76 × 10 12 cm –2, respectively. The UFG steel reveals a nearly isotropic lattice strain response under initial tension from 0 to 450 MPa, where the lattice strains of the (110), (002), and (112) planes are identical. The increase of lattice strain of the (110) plane becomes smaller than that of the (002) and (112) planes as the stress exceeds 450 MPa, suggesting that the nanosized carbides contribute to the hardening ability by promoting the accumulation of geometrically necessary dislocations around the particles, and the (110) lattice becomes harder compared to the other two planes.« less

Structural, Optical and Magnetic Properties of Ni-Zn Ferrite Nanoparticles Prepared by a Microwave Assisted Combustion Method.

PubMed

Vijaya, J Judith; Bououdina, M

2016-01-01

Ni-doped ZnFe₂O₄(Ni(x)Zn₁₋xFe₂O₄; x = 0.0 to 0.5) nanoparticles were synthesized by a simple microwave combustion method. The X-ray diffraction confirms the presence of cubic spinel ZnFe₂O₄for all compositions. The lattice parameter decreases with an increase in Ni content resulting in the reduction of lattice strain. High resolution scanning electron microscope images revealed that the as-prepared samples are crystalline with particle size distribution in 40-50 nm range. Optical properties were determined by UV-Visible diffuse reflectance and photoluminescence spectroscopy respectively. The saturation magnetization (Ms) shows the super paramagnetic nature of the sample for x = 0.0-0.2, whereas for x = 0.3-0.5, it shows ferromagnetic nature. The Ms value is 1.638 emu/g for pure ZnFe₂O₄ sample and it increases with increase in Ni content.

Study on Over-Sampling for Imager

NASA Technical Reports Server (NTRS)

Kigawa, Seiichiro; Sullivan, Pamela C.

1998-01-01

This report describes the potential improvement of the effective ground resolution of MTSAT (Multi-functional Transport Satellite) Imager. The IFOV (Instantaneous Field of View) of MTSAT Imager is 4 km for infrared and 1 km visible. A combination of some images acquired by the MTSAT Imager could generate 2 km-latticed infrared images. Furthermore, it is possible to generate an effective 2 km IFOV image by the enhancement of the 2 km-latticed image using Digital Signal Processing. This report also mentions the on-orbit demonstration of this concept.

Characterization of the Microstructure of the Compositionally Complex Alloy Al1Mo0.5Nb1Ta0.5Ti1Zr1 (Postprint)

DTIC Science & Technology

2016-05-01

limited to X-ray diffraction ( XRD ) and scanning electron microscopy (SEM). The alloy was reported to contain two bcc phases with similar lattice...it appears that the interface between the two phases is fairly coherent. Interestingly, the XRD study described in [8] suggested that there were two...line-scan shown in (h). 3 Distribution A. Approved for public reledifference in lattice parameter measurements realized in bulk samples ( XRD ) vs

Validation of a Crystal Plasticity Model Using High Energy Diffraction Microscopy

NASA Technical Reports Server (NTRS)

Beaudoin, A. J.; Obstalecki, M.; Storer, R.; Tayon, W.; Mach, J.; Kenesei, P.; Lienert, U.

2012-01-01

High energy diffraction microscopy is used to measure the crystallographic orientation and evolution of lattice strain in an Al Li alloy. The relative spatial arrangement of the several pancake-shaped grains in a tensile sample is determined through in situ and ex situ techniques. A model for crystal plasticity with continuity of lattice spin is posed, where grains are represented by layers in a finite element mesh following the arrangement indicated by experiment. Comparison is drawn between experiment and simulation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Frølich, S.; Leemreize, H.; Jakus, A.

A model sample consisting of two different hydroxyapatite (hAp) powders was used as a bone phantom to investigate the extent to which X-ray diffraction tomography could map differences in hAp lattice constants and crystallite size. The diffraction data were collected at beamline 1-ID, the Advanced Photon Source, using monochromatic 65 keV X-radiation, a 25 × 25 µm pinhole beam and translation/rotation data collection. The diffraction pattern was reconstructed for each volume element (voxel) in the sample, and Rietveld refinement was used to determine the hAp lattice constants. The crystallite size for each voxel was also determined from the 00.2 hApmore » diffraction peak width. The results clearly show that differences between hAp powders could be measured with diffraction tomography.« less

Observation of FeGe skyrmions by electron phase microscopy with hole-free phase plate

NASA Astrophysics Data System (ADS)

Kotani, Atsuhiro; Harada, Ken; Malac, Marek; Salomons, Mark; Hayashida, Misa; Mori, Shigeo

2018-05-01

We report application of hole-free phase plate (HFPP) to imaging of magnetic skyrmion lattices. Using HFPP imaging, we observed skyrmions in FeGe, and succeeded in obtaining phase contrast images that reflect the sample magnetization distribution. According to the Aharonov-Bohm effect, the electron phase is shifted by the magnetic flux due to sample magnetization. The differential processing of the intensity in a HFPP image allows us to successfully reconstruct the magnetization map of the skyrmion lattice. Furthermore, the calculated phase shift due to the magnetization of the thin film was consistent with that measured by electron holography experiment, which demonstrates that HFPP imaging can be utilized for analysis of magnetic fields and electrostatic potential distribution at the nanoscale.

Nuclear Physics Review

DOE Office of Scientific and Technical Information (OSTI.GOV)

Walker-Loud, Andre

2014-11-01

Anchoring low-energy nuclear physics to the fundamental theory of strong interactions remains an outstanding challenge. I review the current progress and challenges of the endeavor to use lattice QCD to bridge this connection. This is a particularly exciting time for this line of research as demonstrated by the spike in the number of different collaborative efforts focussed on this problem and presented at this conference. I first digress and discuss the 2013 Ken Wilson Award.

Plasmonic Surface Lattice Resonances: A Review of Properties and Applications.

PubMed

Kravets, V G; Kabashin, A V; Barnes, W L; Grigorenko, A N

2018-06-27

When metal nanoparticles are arranged in an ordered array, they may scatter light to produce diffracted waves. If one of the diffracted waves then propagates in the plane of the array, it may couple the localized plasmon resonances associated with individual nanoparticles together, leading to an exciting phenomenon, the drastic narrowing of plasmon resonances, down to 1-2 nm in spectral width. This presents a dramatic improvement compared to a typical single particle resonance line width of >80 nm. The very high quality factors of these diffractively coupled plasmon resonances, often referred to as plasmonic surface lattice resonances, and related effects have made this topic a very active and exciting field for fundamental research, and increasingly, these resonances have been investigated for their potential in the development of practical devices for communications, optoelectronics, photovoltaics, data storage, biosensing, and other applications. In the present review article, we describe the basic physical principles and properties of plasmonic surface lattice resonances: the width and quality of the resonances, singularities of the light phase, electric field enhancement, etc. We pay special attention to the conditions of their excitation in different experimental architectures by considering the following: in-plane and out-of-plane polarizations of the incident light, symmetric and asymmetric optical (refractive index) environments, the presence of substrate conductivity, and the presence of an active or magnetic medium. Finally, we review recent progress in applications of plasmonic surface lattice resonances in various fields.

Microstructure characterization and phase transformation kinetic study of ball-milled m-ZrO 2-30 mol% a-TiO 2 mixture by Rietveld method

NASA Astrophysics Data System (ADS)

Pradhan, S. K.; Dutta, H.

2005-05-01

High-energy ball milling of monoclinic ZrO 2-30 mol% anatase TiO 2 mixture at different durations results in the formation of m-ZrO 2-a-TiO 2 solid solution from which the nucleation of nanocrystalline cubic (c) ZrO 2 polymorphic phase sets in. Post-annealing of 12 h ball-milled sample at different elevated temperatures for 1 h results in almost complete formation of c-ZrO 2 phase. Microstructure of the unmilled, all the ball milled and annealed samples has been characterized by Rietveld's X-ray powder structure refinement method. Particle size, rms lattice strain, change in lattice parameters and phase content of individual phases have been estimated from Rietveld analysis, and are utilized to interpret the results. In course of milling, (1 1 1) of cubic lattice became parallel to ( 1bar 1 1) plane of monoclinic lattice due to the orientation effect and cubic phase may have been formed on the (0 0 1) of the m-ZrO 2-a-TiO 2 solid solution lattice. A comparative study of microstructure and phase transformation kinetics of ZrO 2-10, 20 and 30 mol% a-TiO 2 ball-milled and post-annealed samples reveals that rate of phase transformation m→c-ZrO 2 increases with increasing a-TiO 2 concentration and ∼30 mol% of nanocrystalline c-ZrO 2 phase can be obtained within 4 h of milling time in the presence of 30 mol% of a-TiO 2. The post-annealing treatment at 773, 873 and 973 K for 1 h duration each reveals that rate of c-ZrO 2 formation with increasing temperature is retarded with increasing a-TiO 2 concentration but the amount of c-ZrO 2 becomes almost equal (∼95 mol%) at 973 K. It suggests that almost fully stabilized nanocrystalline c-ZrO 2 can be formed by adding a tetravalent solute to m-ZrO 2.

Silicon carbide - Progress in crystal growth

NASA Technical Reports Server (NTRS)

Powell, J. Anthony

1987-01-01

Recent progress in the development of two processes for producing large-area high-quality single crystals of SiC is described: (1) a modified Lely process for the growth of the alpha polytypes (e.g., 6H SiC) initially developed by Tairov and Tsvetkov (1978, 1981) and Ziegler et al. (1983), and (2) a process for the epitaxial growth of the beta polytype on single-crystal silicon or other substrates. Growth of large-area cubic SiC on Si is described together with growth of defect-free beta-SiC films on alpha-6H SiC crystals and TiC lattice. Semiconducting qualities of silicon carbide crystals grown by various techniques are discussed.

Effects of Rapid Solidification on Phase Formation and Microstructure Evolution of AgSbTe₂-Based Thermoelectric Compounds.

PubMed

Castellero, Alberto; Fiore, Gianluca; Evenstein, Eliran; Baricco, Marcello; Amouyal, Yaron

2017-03-01

We report on rapid solidification of an Ag(16.7)Sb(30.0)Te(53.3) compound using planar flow casting to stabilize the δ-AgSbTe₂ single phase and avoid precipitation of the interconnected Sb₂Te₃ phase, which leads to deterioration of thermoelectric properties. Rapidly solidified samples are in form of flakes with different thickness (60–400 μm). Precipitation of Sb2Te₃ phase is fully inhibited in thin flakes (thickness below 100 μm), which consist of an homogeneous δ-AgSbTe₂ matrix, whereas isolated Sb₂Te₃ precipitates, dispersed throughout the δ-AgSbTe₂ matrix, were found in thick flakes (thickness above 100 μm). The lattice parameter of the δ-AgSbTe₂ phase progressively increases with the cooling rate, indicating progressive supersaturation of the matrix for high degree of supercooling. Bulk specimens were prepared by hot pressing of the rapidly solidified flakes to evaluate thermoelectric properties. After sintering of the rapidly solidified flakes, the differential scanning calorimetry (DSC) traces indicates partial decomposition of the non equilibrium δ-AgSbTe₂ into the stable phases. Measurements of the thermoelectric transport properties indicate the positive effects of rapid solidification on thermal conductivity and Seebeck coefficient and its negative effect on electrical conductivity, suggesting an operative way to improve thermoelectric performance.

Three-dimensional artificial spin ice in nanostructured Co on an inverse opal-like lattice

NASA Astrophysics Data System (ADS)

Mistonov, A. A.; Grigoryeva, N. A.; Chumakova, A. V.; Eckerlebe, H.; Sapoletova, N. A.; Napolskii, K. S.; Eliseev, A. A.; Menzel, D.; Grigoriev, S. V.

2013-06-01

The evolution of the magnetic structure for an inverse opal-like structure under an applied magnetic field is studied by small-angle neutron scattering. The samples were produced by filling the voids of an artificial opal film with Co. It is shown that the local configuration of magnetization is inhomogeneous over the basic element of the inverse opal-like lattice structure (IOLS) but follows its periodicity. Applying the “ice-rule” concept to the structure, we describe the local magnetization of this ferromagnetic three-dimensional lattice. We have developed a model of the remagnetization process predicting the occurrence of an unusual perpendicular component of the magnetization in the IOLS which is defined only by the direction and strength of the applied magnetic field.

[Spectroscopic studies on transition metal ions in colored diamonds].

PubMed

Meng, Yu-Fei; Peng, Ming-Sheng

2004-07-01

Transition metals like nickel, cobalt and iron have been often used as solvent catalysts in high pressure high temperature (HPHT) synthesis of diamond, and nickel and cobalt ions have been found in diamond lattice. Available studies indicated that nickel and cobalt ions could enter the lattice as interstitial or substitutional impurities and form complexes with nitrogen. Polarized microscopy, SEM-EDS, EPR, PL and FTIR have been used in this study to investigate six fancy color natural and synthetic diamonds in order to determine the spectroscopic characteristics and the existing forms of transition metal ions in colored diamond lattice. Cobalt-related optical centers were first found in natural chameleon diamonds, and some new nickel and cobalt-related optical and EPR centers have also been detected in these diamond samples.

Structural analysis and characterization of synthesized ordered mesoporous silicate (MCM-41) using small angle X-rays scattering and complementary techniques

NASA Astrophysics Data System (ADS)

Akinlalu, Ademola V.

Mesoporous silicate have widespread potential applications, such as drug delivery, supports for catalysis, selective adsorption and host to guest molecules. Most important in the area of scientific research and industrial applications is their demand due to its extremely high surface areas (> 800m 2g-1) and larger pores with well defined structures. Mesoporous silicate (MCM-41) samples were prepared by hydrothermal method under various chemo-physical conditions and various experimental methods such as small angle X-rays scattering (SAXS), Nitrogen adsorption-desorption analysis at 77 K, Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were employed to investigate the changes in the structural morphology and subtle lattice parameter changes. With regards to the subtle changes in the structural characteristics of the synthesized mesoporous silicate, we seek to understand the electron density function changes as the synthesis parameter are varied from low molar concentration of ATAB/Si to higher concentration, the system becoming more acidity due to increase in the hydrolysis time of pH regulator as a result of increased production of ethanol and acetic acid and the changes due to extended reaction time. This Ph.D. research tries to understand the influence of various parameters like surfactant-Si molar ratio, reaction time, and the hydrolysis of the pH regulator on the orderliness/disorderliness of the lattice order, lattice spacing and electron density function. The stages during synthesis are carefully selected to better understand where the greater influence on the overall structural morphology exist so as to be able to ne tune this parameter for any desired specification and application. The SAXS measurement were conducted on a HECUS S3-Micro X-ray system at Rensselaer Polytechnic Institute, Troy, NY. while the data evaluation and visualization were carried in 3DView 4.2 and EasySWAXS software. The electron density functions were generated with a proprietary software called edens. In this dissertation, the following observations have been revealed resulting from SAXS measurement. 1. As one increases the hydrolysis duration of ethyl acetate, a gradual collapse of the lattice spacing of the mesoporous silcate MCM-41 is observed. We found from SAXS that there is a slight right shift of the spectra toward the higher q-values indicating that we are gradually losing orderliness in the lattice spacing and hexagonal structure of the mesoporous silica. Also, the intensity of the peak of second and third peaks are diminutive when compared to sample with shorter hydrolysis time. 2. A comparison of the SAXS spectra for the different molar concentration sample reveals that the 0:5M samples shows a deteriorating structural characteristics as compared to the 0:25 and 0:75M samples respectively and a clear decrease in the (100) reflection planes. Also noticed is the slight rightward shift in the overall spectrum prole. This observation suggest that further analysis is needed so as to better understand the result. 3. We establish that during MCM-41 synthesis, longer reaction time is needed to produce quality sample with well defined structurally characteristic for its intended application because according to spectrum for the sample with a longer reaction time (aging), a shift towards the lower q-values indicates that a sample with a larger lattice parameter and wall thickness but the intensities of its peak are diminishing when compared to the other of relatively shorter reaction time. Other complementary techniques were used to corroborated the result obtained from SAXS. Nitrogen adsorption-desorption analysis at 77K was used to generate the isotherms while B.E.T method was used in conjunction with the isotherms to obtained the very important surface area information. SEM provide a visual structural morphology of the samples and FTIR gave the fingerprint detail of the bonds and vibration types between particle present.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pavlou, A. T.; Betzler, B. R.; Burke, T. P.

Uncertainties in the composition and fabrication of fuel compacts for the Fort St. Vrain (FSV) high temperature gas reactor have been studied by performing eigenvalue sensitivity studies that represent the key uncertainties for the FSV neutronic analysis. The uncertainties for the TRISO fuel kernels were addressed by developing a suite of models for an 'average' FSV fuel compact that models the fuel as (1) a mixture of two different TRISO fuel particles representing fissile and fertile kernels, (2) a mixture of four different TRISO fuel particles representing small and large fissile kernels and small and large fertile kernels and (3)more » a stochastic mixture of the four types of fuel particles where every kernel has its diameter sampled from a continuous probability density function. All of the discrete diameter and continuous diameter fuel models were constrained to have the same fuel loadings and packing fractions. For the non-stochastic discrete diameter cases, the MCNP compact model arranged the TRISO fuel particles on a hexagonal honeycomb lattice. This lattice-based fuel compact was compared to a stochastic compact where the locations (and kernel diameters for the continuous diameter cases) of the fuel particles were randomly sampled. Partial core configurations were modeled by stacking compacts into fuel columns containing graphite. The differences in eigenvalues between the lattice-based and stochastic models were small but the runtime of the lattice-based fuel model was roughly 20 times shorter than with the stochastic-based fuel model. (authors)« less

Pulsed Laser Techniques to Determine Lattice and Radiative Thermal Conductivity of Deep Planetary Materials at Extreme Pressure-Temperature Conditions

NASA Astrophysics Data System (ADS)

Lobanov, S.; Goncharov, A. F.; Holtgrewe, N.; Konopkova, Z.; McWilliams, R. S.

2017-12-01

Thermal conductivity of deep planetary materials determines the planetary heat transport mode and properties (e.g. magnetic field) and can be used to decipher the planetary thermal history. Due to the lack of direct measurements of the lattice and radiative conductivity of the relevant materials at the planetary conditions, the current geodynamical models use theoretical calculations and extrapolations of the available experimental data. Here we describe our pulsed laser techniques that enable direct measurements of the lattice and radiative lattice conductivity of the Earth's mantle and core materials and also of noble gases and simple molecules present in the interiors of giant planets (e.g. hydrogen). Flash heating laser techniques working in a pump-probe mode that include time resolved two-side radiative and thermoreflection temperature probes employ various laser and photo-detector configurations, which provide a measure of the thermal fluxes propagating through the samples confined in the diamond anvil cell cavity. A supercontinuum ultra-bright broadband laser source empower accurate measurements of the optical properties of planetary materials used to extract the radiative conductivity. Finite element calculations serve to extract the temperature and pressure dependent thermal conductivity and temperature gradients across the sample. We report thermal conductivity measurements of the Earth's minerals (postperovskite, bridgmanite, ferropericlase) and their assemblies (pyrolite) and core materials (Fe and alloys with Si and O) at the realistic deep Earth's pressure temperature conditions. We thank J.-F.Lin, M. Murakami, J. Badro for contributing to this work.

Simultaneous effect of crystal lattice and non magnetic substitution on magnetic properties of barium hexaferrite

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Supriya, Sweety; Pradhan, Lagen Kumar; Pandey, Rabichandra; Kar, Manoranjan

2018-05-01

The aluminium doped barium hexaferrite BaFe12-xAlxO19 with x =0.0, 1.0, 2.0, 4.0 and 6.0 have been synthesized by the sol-gel method to modify the magnetic properties for technological applications. The crystal structure and phase purity of all the samples have been explored by employing the X-ray diffraction (XRD) technique. It confirms that the sample is nanocrystalline, hexagonal symmetry and all the intense peaks could be indexed to the P63/mmc space group. The obtained lattice parameters from the XRD analysis decrease with the increase in Al3+ content in the samples. The microstructural morphology and particle sizes of all samples were studied by using the Field Emission Scanning Electron Microscopy (FESEM-Hitachi-S4800) technique. The magnetic hysteresis (M-H) loops measurement has been carried out at room temperature by employing the vibrating sample magnetometer (VSM) over a field range of +20 kOe to -20 kOe. The magnetic hysteresis (M-H) loops revealed the ferromagnetic (hard magnetic materials) nature of the samples and, analyzed by using the Law of Approach to Saturation.

Fuzzy and rough formal concept analysis: a survey

NASA Astrophysics Data System (ADS)

Poelmans, Jonas; Ignatov, Dmitry I.; Kuznetsov, Sergei O.; Dedene, Guido

2014-02-01

Formal Concept Analysis (FCA) is a mathematical technique that has been extensively applied to Boolean data in knowledge discovery, information retrieval, web mining, etc. applications. During the past years, the research on extending FCA theory to cope with imprecise and incomplete information made significant progress. In this paper, we give a systematic overview of the more than 120 papers published between 2003 and 2011 on FCA with fuzzy attributes and rough FCA. We applied traditional FCA as a text-mining instrument to 1072 papers mentioning FCA in the abstract. These papers were formatted in pdf files and using a thesaurus with terms referring to research topics, we transformed them into concept lattices. These lattices were used to analyze and explore the most prominent research topics within the FCA with fuzzy attributes and rough FCA research communities. FCA turned out to be an ideal metatechnique for representing large volumes of unstructured texts.

Hierarchical Architecturing for Layered Thermoelectric Sulfides and Chalcogenides.

PubMed

Jood, Priyanka; Ohta, Michihiro

2015-03-16

Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS₂-based layered sulfides, misfit layered sulfides, homologous chalcogenides, accordion-like layered Sn chalcogenides, and thermoelectric minerals. CS₂ sulfurization is an appropriate method for preparing sulfide thermoelectric materials. At the atomic scale, the intercalation of guest atoms/layers into host crystal layers, crystal-structural evolution enabled by the homologous series, and low-energy atomic vibration effectively scatter phonons, resulting in a reduced lattice thermal conductivity. At the nanoscale, stacking faults further reduce the lattice thermal conductivity. At the microscale, the highly oriented microtexture allows high carrier mobility in the in-plane direction, leading to a high thermoelectric power factor.

Influence of point defects on the thermal conductivity in FeSi

NASA Astrophysics Data System (ADS)

Stern, Robin; Wang, Tao; Carrete, Jesús; Mingo, Natalio; Madsen, Georg K. H.

2018-05-01

The unique transport properties of B20 FeSi have been investigated for decades. The progress in theoretical calculations allows the explanation and prediction of more and more of such properties. In this paper we investigate the lattice thermal conductivity of FeSi. Calculation for pristine FeSi severely overestimates the lattice thermal conductivity compared to experiment. We point out that the defect concentration can be considerably larger than indicated by the Hall coefficient. The defect formation energies are calculated and it is found that a substantial amount of iron vacancies can form at thermal equilibrium. These will lead to an increased phonon scattering. To explain the thermal conductivity of FeSi, we consider phonon-phonon, isotope, and phonon-defect scattering to assess possible scattering mechanisms. The calculated thermal conductivities indicate that phonon-defect scattering is important in order to explain the reported experimental values.

Imaging of nonlocal hot-electron energy dissipation via shot noise.

PubMed

Weng, Qianchun; Komiyama, Susumu; Yang, Le; An, Zhenghua; Chen, Pingping; Biehs, Svend-Age; Kajihara, Yusuke; Lu, Wei

2018-05-18

In modern microelectronic devices, hot electrons accelerate, scatter, and dissipate energy in nanoscale dimensions. Despite recent progress in nanothermometry, direct real-space mapping of hot-electron energy dissipation is challenging because existing techniques are restricted to probing the lattice rather than the electrons. We realize electronic nanothermometry by measuring local current fluctuations, or shot noise, associated with ultrafast hot-electron kinetic processes (~21 terahertz). Exploiting a scanning and contact-free tungsten tip as a local noise probe, we directly visualize hot-electron distributions before their thermal equilibration with the host gallium arsenide/aluminium gallium arsenide crystal lattice. With nanoconstriction devices, we reveal unexpected nonlocal energy dissipation at room temperature, which is reminiscent of ballistic transport of low-temperature quantum conductors. Copyright © 2018 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.

A principle of economy predicts the functional architecture of grid cells.

PubMed

Wei, Xue-Xin; Prentice, Jason; Balasubramanian, Vijay

2015-09-03

Grid cells in the brain respond when an animal occupies a periodic lattice of 'grid fields' during navigation. Grids are organized in modules with different periodicity. We propose that the grid system implements a hierarchical code for space that economizes the number of neurons required to encode location with a given resolution across a range equal to the largest period. This theory predicts that (i) grid fields should lie on a triangular lattice, (ii) grid scales should follow a geometric progression, (iii) the ratio between adjacent grid scales should be √e for idealized neurons, and lie between 1.4 and 1.7 for realistic neurons, (iv) the scale ratio should vary modestly within and between animals. These results explain the measured grid structure in rodents. We also predict optimal organization in one and three dimensions, the number of modules, and, with added assumptions, the ratio between grid periods and field widths.

Assessment of current state of the art in modeling techniques and analysis methods for large space structures

NASA Technical Reports Server (NTRS)

Noor, A. K.

1983-01-01

Advances in continuum modeling, progress in reduction methods, and analysis and modeling needs for large space structures are covered with specific attention given to repetitive lattice trusses. As far as continuum modeling is concerned, an effective and verified analysis capability exists for linear thermoelastic stress, birfurcation buckling, and free vibration problems of repetitive lattices. However, application of continuum modeling to nonlinear analysis needs more development. Reduction methods are very effective for bifurcation buckling and static (steady-state) nonlinear analysis. However, more work is needed to realize their full potential for nonlinear dynamic and time-dependent problems. As far as analysis and modeling needs are concerned, three areas are identified: loads determination, modeling and nonclassical behavior characteristics, and computational algorithms. The impact of new advances in computer hardware, software, integrated analysis, CAD/CAM stems, and materials technology is also discussed.

Lattice QCD input for nuclear structure and reactions

NASA Astrophysics Data System (ADS)

Davoudi, Zohreh

2018-03-01

Explorations of the properties of light nuclear systems beyond their lowestlying spectra have begun with Lattice Quantum Chromodynamics. While progress has been made in the past year in pursuing calculations with physical quark masses, studies of the simplest nuclear matrix elements and nuclear reactions at heavier quark masses have been conducted, and several interesting results have been obtained. A community effort has been devoted to investigate the impact of such Quantum Chromodynamics input on the nuclear many-body calculations. Systems involving hyperons and their interactions have been the focus of intense investigations in the field, with new results and deeper insights emerging. While the validity of some of the previous multi-nucleon studies has been questioned during the past year, controversy remains as whether such concerns are relevant to a given result. In an effort to summarize the newest developments in the field, this talk will touch on most of these topics.

Application of microdynamics and lattice mechanics to problems in plastic flow and fracture. Final report, 1 April 1973--31 March 1978

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bilello, J C; Liu, J M

Progress in an investigation of the application of microdynamics and lattice mechanics to the problems in plastic flow and fracture is described. The research program consisted of both theoretical formulations and experimental measurements of a number of intrinsic material parameters in bcc metals and alloys including surface energy, phonon-dispersion curves for dislocated solids, dislocation-point defect interaction energy, slip initiation and microplastic flow behavior. The study has resulted in an improved understanding in the relationship among the experimentally determined fracture surface energy, the intrinsic cohesive energy between atomic planes, and the plastic deformation associated with the initial stages of crack propagation.more » The values of intrinsic surface energy of tungsten, molybdenum, niobium and niobium-molybdenum alloys, deduced from the measurements, serve as a starting point from which fracture toughness of these materials in engineering service may be intelligently discussed.« less

The role of ion irradiation in activating silent Raman modes via tuning in plasmonic behaviour and surface disorder of Au/ZnO/Pt NFG system

NASA Astrophysics Data System (ADS)

Singh, Udai B.; Gautam, Subodh K.; Kumar, Sunil; Ojha, Sunil; Ghosh, Santanu; Singh, Fouran

2017-09-01

The perceptible progression of Raman modes of zinc oxide (ZnO) is studied in nanostructures film gap (Au (10 nm)/ZnO (70 nm)/Pt (50 nm)) system with 1.2 MeV Xe ion irradiation. Unattainable silent Raman modes of ZnO turn out to be strongly visible after ion irradiation. The creation of ion-beam-induced lattice disorder, defects, and impurities in a ZnO layer leads to breakdown the translational crystal symmetry that results in the origin of silent modes. The formation of hot-spots in the ZnO layer of the NFG system also supports the enhancement of the intensity of Raman modes. Overall results are attributed to combined effects of lattice disorder, defects, and impurities along with plasmonic effect and explained in the framework of elastic-thermal-spike formation.

Numerical Study of Single Bubble Growth on and Departure from a Horizontal Superheated Wall by Three-dimensional Lattice Boltzmann Method

NASA Astrophysics Data System (ADS)

Feng, Yuan; Li, Hui-Xiong; Guo, Kai-Kai; Zhao, Jian-Fu; Wang, Tai

2018-05-01

A three-dimensional hybrid lattice Boltzmann method was used to simulate the progress of a single bubble's growth and departure from a horizontal superheated wall. The evolutionary process of the bubble shapes and also the temperature fields during pool nucleate boiling were obtained and the influence of the gravitational acceleration on the bubble departure diameter (BDD), the bubble release frequency (BRF) and the heat flux on the superheated wall was analyzed. The simulation results obtained by the present three-dimensional numerical studies demonstrate that the BDD is proportional to g^{-0.301}, the BRF is proportional to g^{-0.58}, and the averaged wall heat flux is proportional to g^{0.201}, where g is the gravitational acceleration. These results are in good agreement with the common-used experimental correlations, indicating the rationality of the present numerical model and results.

Hierarchical Architecturing for Layered Thermoelectric Sulfides and Chalcogenides

PubMed Central

Jood, Priyanka; Ohta, Michihiro

2015-01-01

Sulfides are promising candidates for environment-friendly and cost-effective thermoelectric materials. In this article, we review the recent progress in all-length-scale hierarchical architecturing for sulfides and chalcogenides, highlighting the key strategies used to enhance their thermoelectric performance. We primarily focus on TiS2-based layered sulfides, misfit layered sulfides, homologous chalcogenides, accordion-like layered Sn chalcogenides, and thermoelectric minerals. CS2 sulfurization is an appropriate method for preparing sulfide thermoelectric materials. At the atomic scale, the intercalation of guest atoms/layers into host crystal layers, crystal-structural evolution enabled by the homologous series, and low-energy atomic vibration effectively scatter phonons, resulting in a reduced lattice thermal conductivity. At the nanoscale, stacking faults further reduce the lattice thermal conductivity. At the microscale, the highly oriented microtexture allows high carrier mobility in the in-plane direction, leading to a high thermoelectric power factor. PMID:28787992

Aeroelastic Scaling of a Joined Wing Aircraft Concept

DTIC Science & Technology

2010-01-11

waxed and then peel ply is laid down, next the layers of fabric are laid down (outermost first) with an outer layer of light glass scrim used as the...A parametric model is developed using Phoenix Integration’s Model Center Software (MC). This model includes the vortex lattice software, AVL that...piece of real-time footage taken from the on-board, gimbaled camera. 2009 Progress Report 27 Figure 35 – initial Autonomous Flight After

Ultra-narrow surface lattice resonances in plasmonic metamaterial arrays for biosensing applications.

PubMed

Danilov, Artem; Tselikov, Gleb; Wu, Fan; Kravets, Vasyl G; Ozerov, Igor; Bedu, Frederic; Grigorenko, Alexander N; Kabashin, Andrei V

2018-05-01

When excited over a periodic metamaterial lattice of gold nanoparticles (~ 100nm), localized plasmon resonances (LPR) can be coupled by a diffraction wave propagating along the array plane, which leads to a drastic narrowing of plasmon resonance lineshapes (down to a few nm full-width-at-half-maximum) and the generation of singularities of phase of reflected light. These phenomena look very promising for the improvement of performance of plasmonic biosensors, but conditions of implementation of such diffractively coupled plasmonic resonances, also referred to as plasmonic surface lattice resonances (PSLR), are not always compatible with biosensing arrangement implying the placement of the nanoparticles between a glass substrate and a sample medium (air, water). Here, we consider conditions of excitation and properties of PSLR over arrays of glass substrate-supported single and double Au nanoparticles (~ 100-200nm), arranged in a periodic metamaterial lattice, in direct and Attenuated Total Reflection (ATR) geometries, and assess their sensitivities to variations of refractive index (RI) of the adjacent sample dielectric medium. First, we identify medium (PSLR air , PSLR wat for air and water, respectively) and substrate (PSLR sub ) modes corresponding to the coupling of individual plasmon oscillations at medium- and substrate-related diffraction cut-off edges. We show that spectral sensitivity of medium modes to RI variations is determined by the lattice periodicity in both direct and ATR geometries (~ 320nm per RIU change in our case), while substrate mode demonstrates much lower sensitivity. We also show that phase sensitivity of PSLR can exceed 10 5 degrees of phase shift per RIU change and thus outperform the relevant parameter for all other plasmonic sensor counterparts. We finally demonstrate the applicability of surface lattice resonances in plasmonic metamaterial arrays to biosensing using standard streptavidin-biotin affinity model. Combining advantages of nanoscale architectures, including drastic concentration of electric field, possibility of manipulation at the nanoscale etc, and high phase and spectral sensitivities, PSLRs promise the advancement of current state-of-the-art plasmonic biosensing technology toward single molecule label-free detection. Copyright © 2017 Elsevier B.V. All rights reserved.

Cd ion implantation in AlN

NASA Astrophysics Data System (ADS)

Miranda, S. M. C.; Franco, N.; Alves, E.; Lorenz, K.

2012-10-01

AlN thin films were implanted with cadmium, to fluences of 1 × 1013 and 8 × 1014 at/cm2. The implanted samples were annealed at 950 °C under flowing nitrogen. Although implantation damage in AlN is known to be extremely stable the crystal could be fully recovered at low fluences. At high fluences the implantation damage was only partially removed. Implantation defects cause an expansion of the c-lattice parameter. For the high fluence sample the lattice site location of the ions was studied by Rutherford Backscattering/Channelling Spectrometry. Cd ions are found to be incorporated in substitutional Al sites in the crystal and no significant diffusion is seen upon thermal annealing. The observed high solubility limit and site stability are prerequisite for using Cd as p-type dopant in AlN.

Ab initio computational study on the lattice thermal conductivity of Zintl clathrates [Si19P4] Cl4 and Na4[Al4Si19

NASA Astrophysics Data System (ADS)

Härkönen, Ville J.; Karttunen, Antti J.

2016-08-01

The lattice thermal conductivity of silicon clathrate framework Si23 and two Zintl clathrates, [Si19P4] Cl4 and Na4[Al4Si19] , is investigated by using an iterative solution of the linearized Boltzmann transport equation in conjunction with ab initio lattice dynamical techniques. At 300 K, the lattice thermal conductivities for Si23, [Si19P4] Cl4 , and Na4[Al4Si19] were found to be 43 W/(m K), 25 W/(m K), and 2 W/(m K), respectively. In the case of Na4[Al4Si19] , the order-of-magnitude reduction in the lattice thermal conductivity was found to be mostly due to relaxation times and group velocities differing from Si23 and [Si19P4] Cl4 . The difference in the relaxation times and group velocities arises primarily due to the phonon spectrum at low frequencies, resulting eventually from the differences in the second-order interatomic force constants (IFCs). The obtained third-order IFCs were rather similar for all materials considered here. The present findings are similar to those obtained earlier for some skutterudites. The predicted lattice thermal conductivity of Na4[Al4Si19] is in line with the experimentally measured thermal conductivity of recently synthesized type-I Zintl clathrate Na8[Al8Si38] (polycrystalline samples).

Percolation of light through whispering gallery modes in 3D lattices of coupled microspheres.

PubMed

Astratov, Vasily N; Ashili, Shashanka P

2007-12-10

Using techniques of flow-assisted self-assembly we synthesized three-dimensional (3D) lattices of dye-doped fluorescent (FL) 5 mum polystyrene spheres with 3% size dispersion with well controlled thickness from one monolayer up to 43 monolayers. In FL transmission spectra of such lattices we observed signatures of coupling between multiple spheres with nearly resonant whispering gallery modes (WGMs). These include (i) splitting of the WGM-related peaks with the magnitude 4.0-5.3 nm at the average wavelength 535 nm, (ii) pump dependence of FL transmission showing that the splitting is seen only above the threshold for lasing WGMs, and (iii) anomalously high transmission at the WGM peak wavelengths compared to the background for samples with thickness around 25 mum. We propose a qualitative interpretation of the observed WGM transport based on an analogy with percolation theory where the sites of the lattice (spheres) are connected with optical "bonds" which are present with probability depending on the spheres' size dispersion. We predict that the WGM percolation threshold should be achievable in close packed 3D lattices formed by cavities with ~10(3) quality factors of WGMs and with ~1% size dispersion. Such systems can be used for developing next generation of resonant sensors and arrayed-resonator light emitting devices.

Optical Measurement of In-plane Waves in Mechanical Metamaterials Through Digital Image Correlation

NASA Astrophysics Data System (ADS)

Schaeffer, Marshall; Trainiti, Giuseppe; Ruzzene, Massimo

2017-02-01

We report on a Digital Image Correlation-based technique for the detection of in-plane elastic waves propagating in structural lattices. The experimental characterization of wave motion in lattice structures is currently of great interest due its relevance to the design of novel mechanical metamaterials with unique/unusual properties such as strongly directional behaviour, negative refractive indexes and topologically protected wave motion. Assessment of these functionalities often requires the detection of highly spatially resolved in-plane wavefields, which for reticulated or porous structural assemblies is an open challenge. A Digital Image Correlation approach is implemented that tracks small displacements of the lattice nodes by centring image subsets about the lattice intersections. A high speed camera records the motion of the points by properly interleaving subse- quent frames thus artificially enhancing the available sampling rate. This, along with an imaging stitching procedure, enables the capturing of a field of view that is sufficiently large for subsequent processing. The transient response is recorded in the form of the full wavefields, which are processed to unveil features of wave motion in a hexagonal lattice. Time snapshots and frequency contours in the spatial Fourier domain are compared with numerical predictions to illustrate the accuracy of the recorded wavefields.

Statistical uncertainty analysis applied to the DRAGONv4 code lattice calculations and based on JENDL-4 covariance data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hernandez-Solis, A.; Demaziere, C.; Ekberg, C.

2012-07-01

In this paper, multi-group microscopic cross-section uncertainty is propagated through the DRAGON (Version 4) lattice code, in order to perform uncertainty analysis on k{infinity} and 2-group homogenized macroscopic cross-sections predictions. A statistical methodology is employed for such purposes, where cross-sections of certain isotopes of various elements belonging to the 172 groups DRAGLIB library format, are considered as normal random variables. This library is based on JENDL-4 data, because JENDL-4 contains the largest amount of isotopic covariance matrixes among the different major nuclear data libraries. The aim is to propagate multi-group nuclide uncertainty by running the DRAGONv4 code 500 times, andmore » to assess the output uncertainty of a test case corresponding to a 17 x 17 PWR fuel assembly segment without poison. The chosen sampling strategy for the current study is Latin Hypercube Sampling (LHS). The quasi-random LHS allows a much better coverage of the input uncertainties than simple random sampling (SRS) because it densely stratifies across the range of each input probability distribution. Output uncertainty assessment is based on the tolerance limits concept, where the sample formed by the code calculations infers to cover 95% of the output population with at least a 95% of confidence. This analysis is the first attempt to propagate parameter uncertainties of modern multi-group libraries, which are used to feed advanced lattice codes that perform state of the art resonant self-shielding calculations such as DRAGONv4. (authors)« less

Direct observation of vast off-stoichiometric defects in single crystalline SnSe

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wu, Di; Wu, Lijun; He, Dongsheng

Single crystalline tin selenide (SnSe) recently emerged as a very promising thermoelectric material for waste heat harvesting and thermoelectric cooling, due to its record high figure of merit ZT in mediate temperature range. The most striking feature of SnSe lies in its extremely low lattice thermal conductivity as ascribed to the anisotropic and highly distorted Sn-Se bonds as well as the giant bond anharmonicity by previous studies, yet no theoretical models so far can give a quantitative explanation to such low a lattice thermal conductivity. Here, we presented direct observation of an astonishingly vast number of off-stoichiometric Sn vacancies andmore » Se interstitials, using sophisticated aberration corrected scanning transmission electron microscope; and credited the previously reported ultralow thermal conductivity of the SnSe single crystalline samples partly to their off-stoichiometric feature. In order to further validate the conclusion, we also synthesized stoichiometric SnSe single crystalline samples, and illustrated that the lattice thermal conductivity is deed much higher as compared with the off-stoichiometric single crystals. Finally, the scattering efficiency of individual point defect on heat-carrying phonons was then discussed in the state-of-art Debye-Callaway model.« less

Nanocrystalline silicon: Lattice dynamics and enhanced thermoelectric properties

DOE PAGES

Claudio, Tania; Stein, Niklas; Stroppa, Daniel G.; ...

2014-12-21

In this study, silicon has several advantages when compared to other thermoelectric materials, but until recently it was not used for thermoelectric applications due to its high thermal conductivity, 156 W K -1 m -1 at room temperature. Nanostructuration as means to decrease thermal transport through enhanced phonon scattering has been a subject of many studies. In this work we have evaluated the effects of nanostructuration on the lattice dynamics of bulk nanocrystalline doped silicon. The samples were prepared by gas phase synthesis, followed by current and pressure assisted sintering. The heat capacity, density of phonons states, and elastic constantsmore » were measured, which all reveal a significant, ≈25%, reduction in the speed of sound. The samples present a significantly decreased lattice thermal conductivity, ≈25 W K -1 m -1, which, combined with a very high carrier mobility, results in a dimensionless figure of merit with a competitive value that peaks at ZT ≈ 0.57 at 973 °C. Due to its easily scalable and extremely low-cost production process, nanocrystalline Si prepared by gas phase synthesis followed by sintering could become the material of choice for high temperature thermoelectric generators.« less

Direct observation of vast off-stoichiometric defects in single crystalline SnSe

DOE PAGES

Wu, Di; Wu, Lijun; He, Dongsheng; ...

2017-04-06

Single crystalline tin selenide (SnSe) recently emerged as a very promising thermoelectric material for waste heat harvesting and thermoelectric cooling, due to its record high figure of merit ZT in mediate temperature range. The most striking feature of SnSe lies in its extremely low lattice thermal conductivity as ascribed to the anisotropic and highly distorted Sn-Se bonds as well as the giant bond anharmonicity by previous studies, yet no theoretical models so far can give a quantitative explanation to such low a lattice thermal conductivity. Here, we presented direct observation of an astonishingly vast number of off-stoichiometric Sn vacancies andmore » Se interstitials, using sophisticated aberration corrected scanning transmission electron microscope; and credited the previously reported ultralow thermal conductivity of the SnSe single crystalline samples partly to their off-stoichiometric feature. In order to further validate the conclusion, we also synthesized stoichiometric SnSe single crystalline samples, and illustrated that the lattice thermal conductivity is deed much higher as compared with the off-stoichiometric single crystals. Finally, the scattering efficiency of individual point defect on heat-carrying phonons was then discussed in the state-of-art Debye-Callaway model.« less

On the synthesis, structural, optical and magnetic properties of nano-size Zn-MgO

NASA Astrophysics Data System (ADS)

Varshney, Dinesh; Dwivedi, Sonam

2015-09-01

Chemical co-precipitation method is employed to synthesize ZnO, MgO and Zn0.5Mg0.5O nanoparticles. X-ray diffraction (XRD) pattern infers that the sample of ZnO is in single-phase wurtzite structure (hexagonal phase, P63mc), MgO crystallizes in cubic Fd3m space group and Zn0.5Mg0.5O represents mixed nature of ZnO and MgO lattices. MgO nanocrystals band around 1078 cm-1 is ascribed to the TO-LO surface phonon modes in MgO lattice. In case of Zn0.5Mg0.5O lattice illustrating two bands at 436 and 1087 cm-1. FTIR spectra clearly show the broad band within 450-600 cm-1 is associated with the special vibration of magnesium oxide. FT-IR spectrum of Zn0.5Mg0.5O represents the combined bands of both ZnO-MgO oxides. Further the optical study obtained value of MgO (4.08 eV) is much lower than the corresponding bulk value (7.08 eV). All samples show diamagnetic nature at room temperature.

Effect of Zn doping on structural, optical and thermal properties of CeO2 nanoparticles

NASA Astrophysics Data System (ADS)

Ramasamy, V.; Vijayalakshmi, G.

2015-09-01

The undoped and Zn doped CeO2 nanoparticles were synthesized by chemical precipitation method at room temperature. The undoped and Zn doped CeO2 nanoparticles have been characterized by X-ray powder diffraction (XRD), Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), ultraviolet visible and photoluminescence (PL) spectroscopy, Fourier transform infrared spectroscopy (FTIR) and thermogravimetry and differential thermal analysis (TG-DTA). The cubic fluorite structures of the CeO2 nanoparticles were determined by XRD. The influence of particle size on structural parameters such as lattice parameter (a), inter planar distance (d), dislocation density (δ), microstrain (ε), lattice strain (η) and texture co-efficient (TC) were also determined. The lattice strains were determined by Williamson-Hall plot method. The effect of Zn doping with shifting of the bands were observed by UV-Vis spectroscopy and also their optical band gap were determined. The emission spectra and energy band diagram of the undoped and Zn doped samples were derived from PL spectroscopy. The structural bond vibrations of undoped and Zn doped CeO2 nanoparticles were analyzed by FTIR spectroscopy. The thermal property (weight loss and decomposition) of the sample is observed by TG-DTA curve.

Mechanism of γ-irradiation induced phase transformations in nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jagadeesha Angadi, V.; Anupama, A.V.; Choudhary, Harish K.

The structural, infrared absorption and magnetic property transformations in nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} samples irradiated with different doses (0, 15, 25 and 50 kGy) of γ-irradiation were investigated in this work and a mechanism of phase transformation/decomposition is provided based on the metastable nature of the Mn-atoms in the spinel lattice. The nano-powder sample was prepared by solution combustion route and the pellets of the sample were exposed to γ-radiation. Up to a dose of 25 kGy of γ-radiation, the sample retained the single phase cubic spinel (Fd-3m) structure, but the disorder in the sample increased. On irradiatingmore » the sample with 50 kGy γ-radiation, the spinel phase decomposed into new stable phases such as α-Fe{sub 2}O{sub 3} and ZnFe{sub 2}O{sub 4} phases along with amorphous MnO phase, leading to a change in the surface morphology of the sample. Along with the structural transformations the magnetic properties deteriorated due to breakage of the ferrimagnetic order with higher doses of γ-irradiation. Our results are important for the understanding of the stability, durability and performance of the Mn-Zn ferrite based devices used in space applications. - Graphical abstract: The nanocrystalline Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramic sample transforms to crystalline α-Fe{sub 2}O{sub 3} and ZnFe{sub 2}O{sub 4} phases (and amorphous MnO phase) at a γ-irradiation dose of 50 kGy, as MnO goes out of the spinel lattice. The high energy γ-irradiation causes structural damage to the nanomaterials leading to change in morphology of the sample as seen in the SEM images. - Highlights: • Mn atoms are more unstable in the Mn-Zn ferrite spinel lattice than Zn-atoms. • Displacement of Mn atoms by γ-radiation from the lattice renders phase transformation. • In Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4}, Mn-ferrite cell transforms to crystalline α-Fe{sub 2}O{sub 3} and amorphous MnO. • The stable ZnFe{sub 2}O{sub 4} phase retains its structure even after 50 KGy γ-irradiation. • The γ-irradiation degrades the magnetic properties of Mn{sub 0.5}Zn{sub 0.5}Fe{sub 2}O{sub 4} ceramics.« less

Subsurface bending and reorientation of tilted vortex lattices in bulk isotropic superconductors due to Coulomb-like repulsion at the surface

DOE Office of Scientific and Technical Information (OSTI.GOV)

Herrera, E.; Guillamón, I.; Galvis, J. A.

Here, we study vortex lattices (VLs) in superconducting weak-pinning platelet-like single crystals of β–Bi 2Pd in tilted magnetic fields with a scanning tunneling microscope. We show that vortices exit the sample perpendicular to the surface and are thus bent beneath the surface. The structure and orientation of the tilted VLs in the bulk are, for large tilt angles, strongly affected by Coulomb-type intervortex repulsion at the surface due to stray magnetic fields.

Subsurface bending and reorientation of tilted vortex lattices in bulk isotropic superconductors due to Coulomb-like repulsion at the surface

DOE PAGES

Herrera, E.; Guillamón, I.; Galvis, J. A.; ...

2017-11-03

Here, we study vortex lattices (VLs) in superconducting weak-pinning platelet-like single crystals of β–Bi 2Pd in tilted magnetic fields with a scanning tunneling microscope. We show that vortices exit the sample perpendicular to the surface and are thus bent beneath the surface. The structure and orientation of the tilted VLs in the bulk are, for large tilt angles, strongly affected by Coulomb-type intervortex repulsion at the surface due to stray magnetic fields.

A microstructural lattice model for strain oriented problems: A combined Monte Carlo finite element technique

NASA Technical Reports Server (NTRS)

Gayda, J.; Srolovitz, D. J.

1987-01-01

A specialized, microstructural lattice model, termed MCFET for combined Monte Carlo Finite Element Technique, was developed which simulates microstructural evolution in material systems where modulated phases occur and the directionality of the modulation is influenced by internal and external stresses. In this approach, the microstructure is discretized onto a fine lattice. Each element in the lattice is labelled in accordance with its microstructural identity. Diffusion of material at elevated temperatures is simulated by allowing exchanges of neighboring elements if the exchange lowers the total energy of the system. A Monte Carlo approach is used to select the exchange site while the change in energy associated with stress fields is computed using a finite element technique. The MCFET analysis was validated by comparing this approach with a closed form, analytical method for stress assisted, shape changes of a single particle in an infinite matrix. Sample MCFET analytical for multiparticle problems were also run and in general the resulting microstructural changes associated with the application of an external stress are similar to that observed in Ni-Al-Cr alloys at elevated temperature.

Effects of Stiffness on Low Energy States in a Lattice Protein Model for Crambin

NASA Astrophysics Data System (ADS)

Farris, Alfred C. K.; Shi, Guangjie; Wüst, Thomas; Landau, David P.

2018-04-01

Many studies inspired by the HP lattice protein model have helped to confirm the importance of the hydrophobic “driving force” during folding. Unfortunately, the high level of coarse-graining inherent to this model leads to significant limitations; results from proteins studied under the framework of the HP model fail to reproduce many, sometimes significant, details of the folding process, and the obtained ground states are usually highly degenerate. We propose simple modifications to the original HP model, with the goal of reducing degeneracy and gaining insight into how other interaction parameters influence the folding, while retaining the computational simplicity of lattice models. Namely, we introduce a “neutral” monomer (0) to further divide the hydrophobicity scale and an energetic penalty for “bends” in the protein to account for rigidity. Using replica-exchange Wang-Landau (REWL) sampling and suitable Monte Carlo trial moves, we obtain a unique (non-degenerate) ground state for the new lattice mapping of Crambin (a small, 46 amino acid plant protein), and investigate the effects of stiffness on the folding and the low energy structures.

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

NASA Astrophysics Data System (ADS)

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.

Size dependence of 13C nuclear spin-lattice relaxation in micro- and nanodiamonds

NASA Astrophysics Data System (ADS)

Panich, A. M.; Sergeev, N. A.; Shames, A. I.; Osipov, V. Yu; Boudou, J.-P.; Goren, S. D.

2015-02-01

Size dependence of physical properties of nanodiamond particles is of crucial importance for various applications in which defect density and location as well as relaxation processes play a significant role. In this work, the impact of defects induced by milling of micron-sized synthetic diamonds was studied by magnetic resonance techniques as a function of the particle size. EPR and 13C NMR studies of highly purified commercial synthetic micro- and nanodiamonds were done for various fractions separated by sizes. Noticeable acceleration of 13C nuclear spin-lattice relaxation with decreasing particle size was found. We showed that this effect is caused by the contribution to relaxation coming from the surface paramagnetic centers induced by sample milling. The developed theory of the spin-lattice relaxation for such a case shows good compliance with the experiment.

The effect of doping on global lattice properties of magnetite Fe{sub 3-x}Me{sub x}O{sub 4} (Me=Zn, Ti and Al)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kakol, Z.; Owoc, D.; Przewoznik, J.

2012-08-15

X-ray powder diffraction was measured in Fe{sub 3-x}Me{sub x}O{sub 4} (Me=Zn, Ti, Al; x<0.065), in T range 70-300 K to see the effect of different doping on global lattice properties. The experimental results have shown that some lattice properties (e.g., the cell volume) are dopand specific. This can be attributed to the difference in preferential sites occupation by dopants. As confirmed by EXAFS, Zn enters tetrahedral, while Ti octahedral lattice sites, differently affecting crucial octahedral iron positions in the spinel lattice. However, despite this fact, it was found that T dependence of both monoclinic angle and lattice parameters is universalmore » for studied samples above and below the Verwey transition temperature T{sub V}. So, not the iron atoms in octahedral positions individually, but interactions between them are responsible for the Verwey transition character change with doping. - Graphical abstract: A low temperature magnetite cell volume vs. dopants content. Apparently, Zn, Ti and Al atoms have different effect on the global lattice properties at individual temperatures. However, the Verwey transition reacts to dopants in a similar manner, despite the different way the octahedral iron positions are affected. Highlights: Black-Right-Pointing-Pointer We measure powder diffraction and EXAFS on Fe{sub 3-x}Me{sub x}O{sub 4}, Me=Zn, Ti, Al (x<0.065), in T range 70-300 K. Black-Right-Pointing-Pointer XRD: atom-type independent changes of lattice parameters with T. Black-Right-Pointing-Pointer EXAFS: Zn replaces Fe on tetrahedral positions, Ti on octahedral positions. Black-Right-Pointing-Pointer Thus, some secondary interactions between ordering orbitals, not the primary one driving the Verwey transition, control the transition order.« less

Mapping the spatial and temporal progression of human dental enamel biomineralization using synchrotron X-ray diffraction.

PubMed

Simmons, Lisa M; Montgomery, Janet; Beaumont, Julia; Davis, Graham R; Al-Jawad, Maisoon

2013-11-01

The complex biological, physicochemical process of human dental enamel formation begins in utero and for most teeth takes several years to complete. Lost enamel tissue cannot regenerate, therefore a better understanding of the spatial and temporal progression of mineralization of this tissue is needed in order to design improved in vivo mineral growth processes for regenerative dentistry and allow the possibility to grow a synthetic whole or partial tooth. Human dental enamel samples across a range of developmental stages available through archaeological collections have been used to explore the spatial and temporal progression of enamel biomineralization. Position sensitive synchrotron X-ray diffraction was used to quantify spatial and temporal variations in crystallite organization, lattice parameters and crystallite thickness at three different stages in enamel maturation. In addition X-ray microtomography was used to study mineral content distributions. An inverse correlation was found between the spatial variation in mineral content and the distribution of crystallite organization and thickness as a function of time during enamel maturation. Combined X-ray microtomography and synchrotron X-ray diffraction results show that as enamel matures the mineral content increases and the mineral density distribution becomes more homogeneous. Starting concurrently but proceeding at a slower rate, the enamel crystallites become more oriented and larger; and the crystallite organization becomes spatially more complex and heterogeneous. During the mineralization of human dental enamel, the rate of mineral formation and mineral organization are not identical. Whilst the processes start simultaneously, full mineral content is achieved earlier, and crystallite organization is slower and continues for longer. These findings provide detailed insights into mineral development in human dental enamel which can inform synthetic biomimetic approaches for the benefit of clinical dentistry. Copyright © 2013 Elsevier Ltd. All rights reserved.

Investigation of magnetic ordering and cation distribution in the spinel ferrites CrxFe3-xO4 (0.0≤x≤1.0)

NASA Astrophysics Data System (ADS)

Tang, G. D.; Han, Q. J.; Xu, J.; Ji, D. H.; Qi, W. H.; Li, Z. Z.; Shang, Z. F.; Zhang, X. Y.

2014-04-01

Ferrite powder samples of CrxFe3-xO4 (0.0≤x≤1.0) were prepared by chemical co-precipitation, and calcined in a tube furnace with argon-flow at 1723 K for 2 h. X-ray diffraction patterns indicated that all the samples had an (A)[B]2O4 single phase cubic spinel structure with a Fd3barm space group. Magnetic measurements indicated that the magnetization of the samples decreased with the Cr doping level. A new model for the magnetic ordering in these samples was employed to explain the dependence of the magnetization and cation distribution on the Cr doping level; namely, taking into consideration constraints arising from Hund's rules and from the spin direction of the itinerant 3d electrons, the directions of the Cr2+ and Cr3+ cation magnetic moments were taken to lie antiparallel to the moments of the Fe cations within the same sub-lattice (A or B sub-lattice).

Influence of persistent exchangeable oxygen on biogenic silica δ18O in deep sea cores

NASA Astrophysics Data System (ADS)

Menicucci, A. J.; Spero, H. J.

2016-12-01

The removal of exchangeable oxygen from biogenic opal prior to IRMS analysis is critical during sample preparation. Exchangeable oxygen is found in the form of hydroxyl and between defects within the amorphous silicate lattice structure. Typical analytical procedures utilize a variety of dehydroxylation methods to eliminate this exchangeable oxygen, including vacuum dehydroxylation and prefluorination. Such methods are generally considered sufficient for elimination of non-lattice bound oxygen that would obfuscate environmental oxygen isotopic signals contained within the silicate tetrahedra. δ18O data that are then empirically calibrated against modern hydrographic data, and applied down core in paleoceanographic applications. We have conducted a suite of experiments on purified marine opal samples using the new microfluorination method (Menicucci et al., 2013). Our data demonstrate that the amount of exchangeable oxygen in biogenic opal decreases as sample age/depth in core increases. These changes are not accounted for by current researchers. Further, our experimental data indicate that vacuum dehydroxylation does not eliminate all exchangeable oxygen, even after hydroxyl is undetectable. We have conducted experiments to quantify the amount of time necessary to ensure vacuum dehydroxylation has eliminated exchangeable oxygen so that opal samples are stable prior to δ18Odiatom analysis. Our experiments suggest that previously generated opal δ18O data may contain a variable down-core offset due to the presence of exchangeable, non-lattice bound oxygen sources. Our experiments indicate that diatom silica requires dehydroxylation for ≥ 44 hours at 1060oC to quantitatively remove all non-lattice bound oxygen. Further, this variable amount of exchangeable oxygen may be responsible for some of the disagreement between existing empirical calibrations based on core-top diatom frustule remains. Analysis of δ18Odiatom values after this long vacuum dehydroxylation time is necessary for quantitative comparisons of stable isotopic values across geologic time periods. Menicucci, A. J., et al. (2013). "Oxygen isotope analyses of biogenic opal and quartz using a novel microfluorination technique." Rapid Communications in Mass Spectrometry 27(16): 1873-1881

Study on the site preference of Ca in superconducting oxides Bi{sub 2}Sr{sub 2−x}Ca{sub x}CuO{sub 6+δ} (0.1 ≤ x ≤ 1.0)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, B.Z.; Zhou, S.L.; Wang, H.

2014-01-15

A series of compound with the nominal composition of Bi{sub 2}Sr{sub 2−x}Ca{sub x}CuO{sub 6+δ} (x = 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0) were synthesized by the sol–gel method. Constituent phases and crystal structure of samples were analyzed by X-ray diffraction. It can be found that the Ca-doped Bi-2201 system was composed of Bi-2201 phase containing Ca and a small quantity of Bi{sub 16}(Sr,Ca){sub 14}O{sub 38}. For Bi-2201 unit cell containing Ca, chemical component and site preference of Ca atoms were characterized systematically by transmission electron microscopy. With the introduction of Ca atoms, Sr-sites have been occupiedmore » partially by Ca{sup 2+} in Bi-2201 unit cell, which leads to a decrease in the lattice parameters c and b of the Bi-2201 phase when the Ca-content x is below 0.6. Two types of new orthorhombic lattices are formed in the substitution. One is a lattice with space group Pma2 as the two nearest neighbor Sr-sites in the same Sr–O layer are occupied by Ca{sup 2+}. Its lattice parameters can be characterized as a = 5.402 Å, b = 5.313 Å and c = 24.272 Å, respectively. When two nearest Sr ions of the second neighboring Sr–O layers are replaced by Ca{sup 2+} ions, the lattice with the space group Pmn2{sub 1} can be formed. Its lattice parameters are close to that of the previous. The modulation vector is lying in the a*–c* plane in the two new orthorhombic lattices (Pma2 and Pmn2{sub 1}). Bi/Ca-2201 lattice (with Ca) and Bi-2201 lattice (without Ca) coexist in the same Bi{sub 2}Sr{sub 2−x}Ca{sub x}CuO{sub 6}+{sub δ} grain, which can be described as an intergrowth structure.« less

Large-Eddy/Lattice Boltzmann Simulations of Micro-blowing Strategies for Subsonic and Supersonic Drag Control

NASA Technical Reports Server (NTRS)

Menon, Suresh

2003-01-01

This report summarizes the progress made in the first 8 to 9 months of this research. The Lattice Boltzmann Equation (LBE) methodology for Large-eddy Simulations (LES) of microblowing has been validated using a jet-in-crossflow test configuration. In this study, the flow intake is also simulated to allow the interaction to occur naturally. The Lattice Boltzmann Equation Large-eddy Simulations (LBELES) approach is capable of capturing not only the flow features associated with the flow, such as hairpin vortices and recirculation behind the jet, but also is able to show better agreement with experiments when compared to previous RANS predictions. The LBELES is shown to be computationally very efficient and therefore, a viable method for simulating the injection process. Two strategies have been developed to simulate multi-hole injection process as in the experiment. In order to allow natural interaction between the injected fluid and the primary stream, the flow intakes for all the holes have to be simulated. The LBE method is computationally efficient but is still 3D in nature and therefore, there may be some computational penalty. In order to study a large number or holes, a new 1D subgrid model has been developed that will simulate a reduced form of the Navier-Stokes equation in these holes.

Mobile spin impurity in an optical lattice

NASA Astrophysics Data System (ADS)

Duncan, C. W.; Bellotti, F. F.; Öhberg, P.; Zinner, N. T.; Valiente, M.

2017-07-01

We investigate the Fermi polaron problem in a spin-1/2 Fermi gas in an optical lattice for the limit of both strong repulsive contact interactions and one dimension. In this limit, a polaronic-like behaviour is not expected, and the physics is that of a magnon or impurity. While the charge degrees of freedom of the system are frozen, the resulting tight-binding Hamiltonian for the impurity’s spin exhibits an intriguing structure that strongly depends on the filling factor of the lattice potential. This filling dependency also transfers to the nature of the interactions for the case of two magnons and the important spin balanced case. At low filling, and up until near unit filling, the single impurity Hamiltonian faithfully reproduces a single-band, quasi-homogeneous tight-binding problem. As the filling is increased and the second band of the single particle spectrum of the periodic potential is progressively filled, the impurity Hamiltonian, at low energies, describes a single particle trapped in a multi-well potential. Interestingly, once the first two bands are fully filled, the impurity Hamiltonian is a near-perfect realisation of the Su-Schrieffer-Heeger model. Our studies, which go well beyond the single-band approximation, that is, the Hubbard model, pave the way for the realisation of interacting one-dimensional models of condensed matter physics.

Molecular mechanism of melting of a helical polymer crystal: Role of conformational order, packing and mobility of polymers

NASA Astrophysics Data System (ADS)

Cheerla, Ramesh; Krishnan, Marimuthu

2018-03-01

The molecular mechanism of melting of a superheated helical polymer crystal has been investigated using isothermal-isobaric molecular dynamics simulation that allows anisotropic deformation of the crystal lattice. A detailed microscopic analysis of the onset and progression of melting and accompanying changes in the polymer conformational order, translational, and orientation order of the solid along the melting pathway is presented. Upon gradual heating from room temperature to beyond the melting point at ambient pressure, the crystal exhibits signatures of premelting well below the solid-to-liquid melting transition at the melting point. The melting transition is manifested by abrupt changes in the crystal volume, lattice energy, polymer conformation, and dynamical properties. In the premelting stage, the crystal lattice structure and backbone orientation of the polymer chains are retained but with the onset of weakening of long-range helical order and interchain packing of polymers perpendicular to the fibre axis of the crystal. The premelting also marks the onset of conformational defects and anisotropic solid-state diffusion of polymers along the fibre axis. The present study underscores the importance of the interplay between intermolecular packing, interactions, and conformational dynamics at the atomic level in determining the macroscopic melting behavior of polymer crystals.

Solid State Division progress report, September 30, 1981

DOE Office of Scientific and Technical Information (OSTI.GOV)

Not Available

1982-04-01

Progress made during the 19 months from March 1, 1980, through September 30, 1981, is reported in the following areas: theoretical solid state physics (surfaces, electronic and magnetic properties, particle-solid interactions, and laser annealing); surface and near-surface properties of solids (plasma materials interactions, ion-solid interactions, pulsed laser annealing, and semiconductor physics and photovoltaic conversion); defects in solids (radiation effects, fracture, and defects and impurities in insulating crystals); transport properties of solids (fast-ion conductors, superconductivity, and physical properties of insulating materials); neutron scattering (small-angle scattering, lattice dynamics, and magnetic properties); crystal growth and characterization (nuclear waste forms, ferroelectric mateirals, high-temperature materials,more » and special materials); and isotope research materials. Publications and papers are listed. (WHK)« less

Bubble Formation and Lattice Parameter Changes Resulting from He Irradiation of Defect-Fluorite Gd2Zr2O7

DOE Office of Scientific and Technical Information (OSTI.GOV)

Taylor, Caitlin A.; Patel, Maulik K.; Aguiar, Jeffery A.

2016-08-15

Pyrochlores have long been considered as potential candidates for advanced ceramic waste-forms for the immobilization of radioactive waste nuclides. This work provides evidence that Gd2Zr2O7, often considered the most radiation tolerant pyrochlore, could be susceptible to radiation damage in the form of bubble nucleation at the highest He doses expected over geological time. Ion irradiations were utilized to experimentally simulate the radiation damage and He accumulation produced by ..alpha..-decay. Samples were pre-damaged using 7 MeV Au3+ to induce the pyrochlore to defect-fluorite phase transformation, which would occur due to ..alpha..-recoil damage within several hundred years of storage in a Gd2Zr2O7more » waste-form. These samples were then implanted to various He concentrations in order to study the long-term effects of He accumulation. Helium bubbles 1-3 nm in diameter were observed in TEM at a concentration of 4.6 at.% He. Some bubbles remained isolated, while others formed chains 10-30 nm in length parallel to the surface. GIXRD measurements showed lattice swelling after irradiating pristine Gd2Zr2O7 with 7 MeV Au3+ to a fluence of 2.2 x 1015 Au/cm2. An increase in lattice swelling was also measured after 2.2 x 1015 Au/cm2 + 2 x 1015 He/cm2 and 2.2 x 1015 Au/cm2 + 2 x 1016 He/cm2. A decrease in lattice swelling was measured after irradiation with 2.2 x 1015 Au/cm2 + 2 x 1017 He/cm2, the fluence where bubbles and bubble chains were observed in TEM. Bubble chains are thought to form in order to reduce lattice strain normal to the surface, which is produced by the Au and He irradiation damage.« less

Crystallographic and magnetic properties of the spinel-type ferrites ZnxCo1-xFe2O4 (0.0 ≤ x ≤ 0.75)

NASA Astrophysics Data System (ADS)

Azad, A. K.; Zakaria, A. K. M.; Jewel, Md. Yusuf; Khan, Abu Saeed; Yunus, S. M.; Kamal, I.; Datta, T. K.; Eriksson, S.-G.

2015-05-01

Ultrahigh frequencies (UHF) have applications in signal and power electronics to minimize product sizes, increase production quantity and lower manufacturing cost. In the UHF range of 300 MHz to 3 GHz, ferrimagnetic iron oxides (ferrites) are especially useful because they combine the properties of a magnetic material with that of an electrical insulator. Ferrites have much higher electrical resistivity than metallic ferromagnetic materials, resulting in minimization of the eddy current losses, and total penetration of the electromagnetic (EM) field. Hence ferrites are frequently applied as circuit elements, magnetic storage media like read/write heads, phase shifters and Faraday rotators. The electromagnetic properties of ferrites are affected by operating conditions such as field strength, temperature and frequency. The spinel system ZnxCo1-xFe2O4 (x=0.0, 0.25, 0.50 and 0.75) has been prepared by the standard solid state sintering method. X-ray and neutron powder diffraction measurements were performed at room temperature. Neutron diffraction data analysis confirms the cubic symmetry corresponding to the space group Fd3m. The distribution of three cations Zn2+, Co2+ and Fe3+ over the spinel lattice and other crystallographic parameters like lattice constant, oxygen position parameter, overall temperature factor and occupancies of different ions in different lattice sites for the samples have been determined from the analysis of neutron diffraction data. The lattice constant increases with increasing Zn content in the system. The magnetic structure was found to be ferrimagnetic for the samples with x≤0.50. Magnetization measurements show that with the increase of Zn content in the system the value of saturation magnetization first increases and then decreases. The variation of the magnetic moment with Zn substitution has been discussed in terms of the distribution of magnetic and non-magnetic ions over the A and B sub-lattices and their exchange coupling.

Defect chemistry and characterization of (Hg, Cd)Te

NASA Technical Reports Server (NTRS)

Vydyanath, H. R.

1981-01-01

Single crystal samples of phosphorus doped Hg sub 0.8 Cd sub 0.2 Te were anneald at temperatures varying from 450 C to 600 C in various Hg atmospheres. The samples were quenched to room temperature from the annealing temperatures. Hall effect and mobility measurements were performed at 77 K on all these samples. The results indicate the crystals to be p type for a total phosphorus concentration of 10 to the 19th power/cu cm in all the samples. The hole concentration at 77 K increases with increasing Hg pressures at 450 C and 500 C contrary to the observation in undoped crystals. Also, at low Hg pressures the concentration of holes in the phosphorus doped crystals is lower than in the undoped crystals. The hole concentration in all the samples is lower than the intrinsic carrier concentration at the annealing temperatures. The hole mobility in the doped crystals is similar to that in the undoped crystals. A defect model according to which phosphorus behaves as a single acceptor interstitially, occupying Te lattice sites while it acts as a single donor occupying Hg lattice sites was established. Equilibrum constants established for the incorporation of all the phosphorus species explain the experimental results

Preparation and characterization of Pt loaded WO3 films suitable for gas sensing applications

NASA Astrophysics Data System (ADS)

Jolly Bose, R.; Illyasukutty, Navas; Tan, K. S.; Rawat, R. S.; Vadakke Matham, Murukesan; Kohler, Heinz; Mahadevan Pillai, V. P.

2018-05-01

This paper presents the preparation of nanostructured platinum (Pt) loaded tungsten oxide (WO3) thin films by radio frequency (RF) magnetron sputtering technique. Even though, Pt loading does not produce any phase change in WO3 lattice, it deteriorates the crystalline quality and induces defects on WO3 films. The Pt loading in WO3 has profound impact on structural and optical properties of the films by which the particle size, lattice strain and optical band gap energy are reduced. Nanoporous film with reduced particle size is obtained for 5 wt% Pt loaded WO3 sample which is crucial for gas sensors. Hence the sensing response of 5 wt% Pt loaded sample is tested towards carbon monoxide (CO) gas along with pure WO3 sample. The sensing response of Pt loaded sample is nearly 15 times higher than pure WO3 sample in non-humid ambience at an operating temperature 200 °C. This indicates the suitability of the prepared films for gas sensors. The sensing response of pure WO3 film depends on the humidity while the Pt loaded WO3 film shows stable response in both humid and non-humid ambiences.

Effects of ultraviolet light on B-doped CdS thin films prepared by spray pyrolysis method using perfume atomizer

NASA Astrophysics Data System (ADS)

Novruzov, V. D.; Keskenler, E. F.; Tomakin, M.; Kahraman, S.; Gorur, O.

2013-09-01

Boron doped CdS thin films were deposited by spray pyrolysis method using perfume atomizer. The effects of ultraviolet light on the structural, optical and electrical properties of B-doped CdS thin films were investigated as a function of dopant concentration (B/Cd). X-ray diffraction studies showed that all samples were polycrystalline nature with hexagonal structure. It was determined that the preferred orientation of non-illuminated samples changes from (1 0 1) to (0 0 2) with B concentration. The c lattice constant of films decreases from 6.810 Å to 6.661 Å with boron doping. The XRD peak intensity increased with the illumination for almost all the samples. The lattice parameters of B-doped samples remained nearly constant after illumination. It was found that the optical transmittance, photoluminescence spectra, resistivity and carrier concentration of the B-doped samples are stable after the illumination with UV light. Also the effects of UV light on B-doped CdS/Cu2S solar cell were investigated and it was determined that photoelectrical parameters of B-doped solar cell were more durable against the UV light.

Residual stresses in continuous graphite fiber Al metal matrix composites

NASA Technical Reports Server (NTRS)

Park, Hun Sub; Zong, Gui Sheng; Marcus, Harris L.

1988-01-01

The residual stresses in graphite fiber reinforced aluminum (Gr/Al) composites with various thermal histories are measured using X-ray diffraction (XRD) methods. The XRD stress analysis is based on the determination of lattice strains by precise measurements of the interplanar spacings in different directions of the sample. The sample is a plate consisting of two-ply P 100 Gr/Al 6061 precursor wires and Al 6061 overlayers. Prior to XRD measurement, the 6061 overlayers are electrochemically removed. In order to calibrate the relationship between stress magnitude and lattice spacing shift, samples of Al 6061 are loaded at varying stress levels in a three-point bend fixture, while the stresses are simultaneously determined by XRD and surface-attached strain gages. The stresses determined by XRD closely match those determined by the strain gages. Using these calibrations, the longitudinal residual stresses of P 100 Gr/Al 6061 composites are measured for various heat treatments, and the results are presented.

Fragile magnetic order in the honeycomb lattice Iridate Na2IrO3 revealed by magnetic impurity doping

NASA Astrophysics Data System (ADS)

Mehlawat, Kavita; Sharma, G.; Singh, Yogesh

2015-10-01

We report the structure, magnetic, and thermal property measurements on single-crystalline and polycrystalline samples of the Ru-substituted honeycomb lattice iridate Na2Ir1 -xRuxO3 (x =0 ,0.05 ,0.1 ,0.15 ,0.2 ,0.3 ,0.5 ) . The evolution of magnetism in Na2Ir1 -xRuxO3 has been studied using dc and ac magnetic susceptibilities and heat-capacity measurements. The parent compound Na2IrO3 is a spin-orbit-driven Mott insulator with magnetic order of reduced moments below TN=15 K . In the Ru-substituted samples the antiferromagnetic long-range state is replaced by a spin-glass-like state even for the smallest substitution suggesting that the magnetic order in Na2IrO3 is extremely fragile. We argue that these behaviors indicate the importance of nearest-neighbor magnetic exchange in the parent Na2IrO3 . Additionally, all samples show insulating electrical transport.

The partial substitution of copper with nickel oxide on the Structural and electrical properties of HgBa2 Ca2 Cu3xNix O8+δ superconducting compound

NASA Astrophysics Data System (ADS)

Jasim, K. A.; Mohammed, L. A.

2018-05-01

The present study the partial substitution of copper with nickel on of HgBa2Ca2Cu3xNix O8+δ superconducting compound where x=002040608. Samples were prepared by solid state reaction method with sintering temperature 850C0 for 24h. By using x-ray powder diffraction the structure of the samples were studied. The XRD analyses showed the structures of polycrystalline with tetragonal diagram with majority 1223 phase and the change of the nickel concentrations produce a change in lattice parameters of the lattice a b and c axis c/a density of mass ρm and volume fraction Vphase. Four probe apparatus was used to test the electrical resistivity to defined the critical temperature at zero resistivity Tc offset Optimum Tc offset was found from HgBa2Ca2Cu24Ni06O8+δ sample with transition temperature its equal to 137K.

Effect of Spark Plasma Sintering on the Structure and Properties of Ti1−xZrxNiSn Half-Heusler Alloys

PubMed Central

Downie, Ruth A.; Popuri, Srinivas R.; Ning, Huanpo; Reece, Mike J.; Bos, Jan-Willem G.

2014-01-01

XNiSn (X = Ti, Zr and Hf) half-Heusler alloys have promising thermoelectric properties and are attracting enormous interest for use in waste heat recovery. In particular, multiphase behaviour has been linked to reduced lattice thermal conductivities, which enables improved energy conversion efficiencies. This manuscript describes the impact of spark plasma sintering (SPS) on the phase distributions and thermoelectric properties of Ti0.5Zr0.5NiSn based half-Heuslers. Rietveld analysis reveals small changes in composition, while measurement of the Seebeck coefficient and electrical resistivities reveals that all SPS treated samples are electron doped compared to the as-prepared samples. The lattice thermal conductivities fall between 4 W·m−1·K−1 at 350 K and 3 W·m−1·K−1 at 740 K. A maximum ZT = 0.7 at 740 K is observed in a sample with nominal Ti0.5Zr0.5NiSn composition. PMID:28788234

Cation distribution of Ni-Zn-Mn ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Parvatheeswara Rao, B.; Dhanalakshmi, B.; Ramesh, S.; Subba Rao, P. S. V.

2018-06-01

Mn substituted Ni-Zn ferrite nanoparticles, Ni0.4Zn0.6-xMnxFe2O4 (x = 0.00-0.25 in steps of 0.05), using metal nitrates were prepared by sol-gel autocombustion in citric acid matrix. The samples were examined by X-ray diffraction and vibrating sample magnetometer techniques. Rietveld structural refinements using the XRD data were performed on the samples to consolidate various structural parameters like phase (spinel), crystallite size (24.86-37.43 nm), lattice constant (8.3764-8.4089 Å) etc and also to determine cation distributions based on profile matching and integrated intensity ratios. Saturation magnetization values (37.18-68.40 emu/g) were extracted from the measured M-H loops of these nanoparticles to estimate their magnetic moments. Experimental and calculated magnetic moments and lattice constants were used to confirm the derived cation distributions from Rietveld analysis. The results of these ferrite nanoparticles are discussed in terms of the compositional modifications, particle sizes and the corresponding cation distributions as a result of Mn substitutions.

Milestone report on MD potential development for uranium silicide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Jianguo; Zhang, Yongfeng; Hales, Jason Dean

2016-03-01

This report summarizes the progress on the interatomic potential development of triuranium-disilicide (U 3Si 2) for molecular dynamics (MD) simulations. The development is based on the Tersoff type potentials for single element U and Si. The Si potential is taken from the literature and a Tersoff type U potential is developed in this project. With the primary focus on the U 3Si 2 phase, some other U-Si systems such as U 3Si are also included as a test of the transferability of the potentials for binary U-Si phases. Based on the potentials for unary U and Si, two sets ofmore » parameters for the binary U-Si system are developed using the Tersoff mixing rules and the cross-term fitting, respectively. The cross-term potential is found to give better results on the enthalpy of formation, lattice constants and elastic constants than those produced by the Tersoff mixing potential, with the reference data taken from either experiments or density functional theory (DFT) calculations. In particular, the results on the formation enthalpy and lattice constants for the U 3Si 2 phase and lattice constants for the high temperature U 3Si (h-U 3Si) phase generated by the cross-term potential agree well with experimental data. Reasonable agreements are also reached on the elastic constants of U 3Si 2, on the formation enthalpy for the low temperature U 3Si (m-U 3Si) and h-U 3Si phases, and on the lattice constants of m-U 3Si phase. All these phases are predicted to be mechanically stable. The unary U potential is tested for three metallic U phases (α, β, γ). The potential is found capable to predict the cohesive energies well against experimental data for all three phases. It matches reasonably with previous experiments on the lattice constants and elastic constants of αU.« less

Enhancement of the in-field Jc of MgB2 via SiCl4 doping

NASA Astrophysics Data System (ADS)

Wang, Xiao-Lin; Dou, S. X.; Hossain, M. S. A.; Cheng, Z. X.; Liao, X. Z.; Ghorbani, S. R.; Yao, Q. W.; Kim, J. H.; Silver, T.

2010-06-01

We present the following results. (1) We introduce a doping source for MgB2 , liquid SiCl4 , which is free of C, to significantly enhance the irreversibility field (Hirr) , the upper critical field (Hc2) , and the critical current density (Jc) with a little reduction in the critical temperature (Tc) . (2) Although Si can not be incorporated into the crystal lattice, a significant reduction in the a -axis lattice parameter was found, to the same extent as for carbon doping. (3) Based on the first-principles calculation, it is found that it is reliable to estimate the C concentration just from the reduction in the a -lattice parameter for C-doped MgB2 polycrystalline samples that are prepared at high sintering temperatures, but not for those prepared at low sintering temperatures. Strain effects and magnesium deficiency might be reasons for the a -lattice reduction in non-C or some of the C-added MgB2 samples. (4) The SiCl4 -doped MgB2 shows much higher Jc with superior field dependence above 20 K compared to undoped MgB2 and MgB2 doped with various carbon sources. (5) We introduce a parameter, RHH (Hc2/Hirr) , which can clearly reflect the degree of flux-pinning enhancement, providing us with guidance for further enhancing Jc . (6) It was found that spatial variation in the charge-carrier mean free path is responsible for the flux-pinning mechanism in the SiCl4 treated MgB2 with large in-field Jc .

Synergistic Strategy to Enhance the Thermoelectric Properties of CoSbS1-xSex Compounds via Solid Solution.

PubMed

Yao, Wei; Yang, Dingfeng; Yan, Yanci; Peng, Kunling; Zhan, Heng; Liu, Anping; Lu, Xu; Wang, Guoyu; Zhou, Xiaoyuan

2017-03-29

High thermal conductivity of CoSbS-based limited its own prospect application in thermoelectric energy conversion. Solid solution is an effective approach to optimize the performance of thermoelectric materials with high lattice thermal conductivity because of the enhanced phonons scattering from disorder atoms. In this paper, we have synthesized and measured the thermoelectric properties of solid solution CoSbS 1-x Se x (x = 0, 0.05, 0.10, 0.15, 0.20, 0.30) series samples. The collaborative optimization (enhancing the power factors and reducing the thermal conductivities) to add zT values were realized via substitution of S atoms with the isoelectronic Se atoms in the matrix. Meanwhile, the lowest room temperature lattice thermal conductivity in CoSbS-based materials is obtained (4.72 W m -1 K -1 ) at present. Benefiting from the results of synergistic strategy, a zT of 0.35 was achieved at 923 K for sample CoSbS 0.85 Se 0.15 , a 59% improvement as compared with that of the pristine CoSbS. Band calculation demonstrated that CoSbS 0.85 Se 0.15 present a similar band dispersion with CoSbS. The mechanism of point defect scattering for reducing the lattice thermal conductivity at room temperature, was also analyzed by the Callaway model. The contributions to decrease the room temperature lattice thermal conductivity from the mass and the strain fluctuation in the crystal are comparable. These results can also be extended to other high-efficiency thermoelectric materials with stiff bond and smaller Gruneisen parameters.

Quantification of oil and water in preserved reservoir rock by NMR spectroscopy and imaging.

PubMed

Davies, S; Hardwick, A; Roberts, D; Spowage, K; Packer, K J

1994-01-01

Reservoir rock analysis by proton NMR requires separation of the response into brine and crude oil components. Tests on preserved core from a North Sea chalk reservoir show that spin-lattice relaxation time distributions can be used to distinguish the two fluids. NMR estimates of oil and water saturations for 1.5" diameter core examined in a 10 MHz Bruker Minispec spectrometer closely match fluid contents determined by distillation. The spin-lattice relaxation contrast mechanism developed for core samples can be applied in the quantitative analysis of NMR images. The relaxation data are compared with data from chemical shift imaging on the same core sample. The results indicate that it will be possible to monitor changes in fluid distributions, in this and similar systems, under dynamic conditions such as in a waterflood.

Isotope effects associated with tunneling and double proton transfer in the hydrogen bonds of benzoic acid

NASA Astrophysics Data System (ADS)

Xue, Q.; Horsewill, A. J.; Johnson, M. R.; Trommsdorff, H. P.

2004-06-01

The isotope effects associated with double proton transfer in the hydrogen bonds of benzoic acid (BA) dimers have been measured using field-cycling 1H NMR relaxometry and quasielastic neutron scattering. By studying mixed isotope (hydrogen and deuterium) samples, the dynamics of three isotopologues, BA-HH, BA-HD, and BA-DD, have been investigated. Low temperature measurements provide accurate measurements of the incoherent tunneling rate, k0. This parameter scales accurately with the mass number, m, according to the formula k0=(E/m)e-F√m providing conclusive evidence that the proton transfer process is a strongly correlated motion of two hydrons. Furthermore, we conclude that the tunneling pathway is the same for the three isotopologue species. Measurements at higher temperatures illuminate the through barrier processes that are mediated via intermediate or excited vibrational states. In parallel with the investigation of proton transfer dynamics, the theoretical and experimental aspects of studying spin-lattice relaxation in single crystals of mixed isotope samples are investigated in depth. Heteronuclear dipolar interactions between 1H and 2H isotopes contribute significantly to the overall proton spin-lattice relaxation and it is shown that these must be modeled correctly to obtain accurate values for the proton transfer rates. Since the sample used in the NMR measurements was a single crystal, full account of the orientation dependence of the spin-lattice relaxation with respect to the applied B field was incorporated into the data analysis.

FROM FOLDING THEORIES TO FOLDING PROTEINS: A Review and Assessment of Simulation Studies of Protein Folding and Unfolding

NASA Astrophysics Data System (ADS)

Shea, Joan-Emma; Brooks, Charles L., III

2001-10-01

Beginning with simplified lattice and continuum "minimalist" models and progressing to detailed atomic models, simulation studies have augmented and directed development of the modern landscape perspective of protein folding. In this review we discuss aspects of detailed atomic simulation methods applied to studies of protein folding free energy surfaces, using biased-sampling free energy methods and temperature-induced protein unfolding. We review studies from each on systems of particular experimental interest and assess the strengths and weaknesses of each approach in the context of "exact" results for both free energies and kinetics of a minimalist model for a beta-barrel protein. We illustrate in detail how each approach is implemented and discuss analysis methods that have been developed as components of these studies. We describe key insights into the relationship between protein topology and the folding mechanism emerging from folding free energy surface calculations. We further describe the determination of detailed "pathways" and models of folding transition states that have resulted from unfolding studies. Our assessment of the two methods suggests that both can provide, often complementary, details of folding mechanism and thermodynamics, but this success relies on (a) adequate sampling of diverse conformational regions for the biased-sampling free energy approach and (b) many trajectories at multiple temperatures for unfolding studies. Furthermore, we find that temperature-induced unfolding provides representatives of folding trajectories only when the topology and sequence (energy) provide a relatively funneled landscape and "off-pathway" intermediates do not exist.

Effect of Ce-substitution on structural, morphological, magnetic and DC electrical resistivity of Co-ferrite materials

NASA Astrophysics Data System (ADS)

Mammo, Tulu Wegayehu; Murali, N.; Sileshi, Yonatan Mulushoa; Arunamani, T.

2018-02-01

Partially substituted spinel structured CoFe2-xCexO4 (x = 0, 0.03, 0.06, and 0.09) samples have been synthesized using the sol-gel autocombustion route. Stoichiometric amounts of metal nitrates and citric acid were mixed in double distilled water to get homogeneously mixed solutions which were then heated to burn and result in samples for the next two-step annealing procedures. Structural and phase characterization using powder X-ray diffraction (XRD) has been carried out; and a pure spinel structured samples with lattice parameters increasing with the increase of Ce concentration levels have been obtained. The lattice parameters were calculated to be in the range of 8.42774-8.4744 Å. Field emission scanning electron microscopy (FESEM) microstructure characterizations revealed clear grain structures of the so synthesized samples with grain sizes decreasing with Ce. Fourier transform Infrared (FT-IR) characterization measured in the wave number ranges of 400-4000 cm-1 showed the cation vibrations and stretching at characteristic frequency of 668-418 cm-1. The DC resistivity measurements confirmed a decrease in the resistivity of the samples with the increase of Ce concentration and with the increase of temperature in all of the samples synthesized. Room temperature vibrating sample magnetometer measurement revealed the magnetic properties of the samples with decreasing magnetic parameters as Ce concentration increases.

Assessment of microcrystal quality by transmission electron microscopy for efficient serial femtosecond crystallography.

PubMed

Barnes, Christopher O; Kovaleva, Elena G; Fu, Xiaofeng; Stevenson, Hilary P; Brewster, Aaron S; DePonte, Daniel P; Baxter, Elizabeth L; Cohen, Aina E; Calero, Guillermo

2016-07-15

Serial femtosecond crystallography (SFX) employing high-intensity X-ray free-electron laser (XFEL) sources has enabled structural studies on microcrystalline protein samples at non-cryogenic temperatures. However, the identification and optimization of conditions that produce well diffracting microcrystals remains an experimental challenge. Here, we report parallel SFX and transmission electron microscopy (TEM) experiments using fragmented microcrystals of wild type (WT) homoprotocatechuate 2,3-dioxygenase (HPCD) and an active site variant (H200Q). Despite identical crystallization conditions and morphology, as well as similar crystal size and density, the indexing efficiency of the diffraction data collected using the H200Q variant sample was over 7-fold higher compared to the diffraction results obtained using the WT sample. TEM analysis revealed an abundance of protein aggregates, crystal conglomerates and a smaller population of highly ordered lattices in the WT sample as compared to the H200Q variant sample. While not reported herein, the 1.75 Å resolution structure of the H200Q variant was determined from ∼16 min of beam time, demonstrating the utility of TEM analysis in evaluating sample monodispersity and lattice quality, parameters critical to the efficiency of SFX experiments. Copyright © 2016 Elsevier Inc. All rights reserved.

Phase separation and defect formation in stable, metastable, and unstable GaInAsSb alloys for infrared applications

NASA Astrophysics Data System (ADS)

Yildirim, Asli

GaInAsSb is a promising material for mid-infrared devices such as lasers and detectors because it is a direct band gap material with large radiative coefficient and a cut-off wavelength that can be varied across the mid-infrared (from 1.7 to 4.9 mum) while remaining lattice matched to GaSb. On the other hand, the potential of the alloy is hampered by predicted ranges of concentration where the constituents of the alloy become immiscible when the crystal is grown near thermodynamic equilibrium at typical growth temperatures. There have been efforts to extend the wavelength of GaInAsSb alloys through such techniques as digital alloy growth and non-equilibrium growth, but most of the compositional range has for a long time been inaccessible due to immiscibility challenges. Theoretical studies also supported the existence of thermodynamic immiscibility gaps for non-equilibrium growth conditions. Lower growth temperatures lead to shorther adatom diffusion length. While a shorter adatom diffusion length suppresses phase separation, too short an adatom length is associated with increased defect formation and eventually loss of crystallinity. On the other hand, hotter growth temperatures move epitaxial growth closer to thermodynamic equilib- rium conditions, and will eventually cause phase separation to occur. In this study thick 2 um; bulk GaInAsSb layers lattice-matched to GaSb substrates were grown across the entire (lattice-matched) compositional range at low growth temperatures (450° C), including the immiscibility region, when grown under non-equilibrium conditions with MBE. High quality epitaxial layers were grown for all compositions, as evidenced by smooth morphology (atomic force microscopy), high structural quality (X-ray diffraction), low alloy fluctuactions (electron dispersive spectroscopy in cross sectioned samples), and bright room temperature photoluminescence. Because initial theoretical efforts have suggessted that lattice strain can influence layer stability, we have studied effects of strain on alloy stability. Unstable and metastable alloys were grown hot enough for the onset of phase separation, then progressively strained and characterized. We show that strain is effective in suppressing phase separation. Finally, we performed time-resolved carrier lifetime measurements for InAsSb alloy with low concentrations of Ga to investigate the role of Ga in influencing nonradiative carrier recombination. There have been studies on non-Ga containing antimonide structures (InAsSb, InAs/InAsSb) that show long carrier lifetimes, which suggest that Ga plays a role in reducing carrier lifetime, because Ga-containing structures such as InAs/GaSb superlattices have much shorter carrier lifetimes. Ga may reduce carrier lifetime through native defects that increase background carrier concentration, or that create mid-gap electronic states. Here, a series of GaInAsSb alloys were grown with low to zero Ga concentration. No difference in carrier lifetime was observed between Ga and Ga-free structures, and minority carrier lifetimes > 600 ns were observed. Additional work remains to be done to obtain background carrier densities in the samples with Hall measurements.

Simulating anomalous transport and multiphase segregation in porous media with the Lattice Boltzmann Method

NASA Astrophysics Data System (ADS)

Matin, Rastin; Hernandez, Anier; Misztal, Marek; Mathiesen, Joachim

2015-04-01

Many hydrodynamic phenomena ranging from flows at micron scale in porous media, large Reynolds numbers flows, non-Newtonian and multiphase flows have been simulated on computers using the lattice Boltzmann (LB) method. By solving the Lattice Boltzmann Equation on unstructured meshes in three dimensions, we have developed methods to efficiently model the fluid flow in real rock samples. We use this model to study the spatio-temporal statistics of the velocity field inside three-dimensional real geometries and investigate its relation to the, in general, anomalous transport of passive tracers for a wide range of Peclet and Reynolds numbers. We extend this model by free-energy based method, which allows us to simulate binary systems with large-density ratios in a thermodynamically consistent way and track the interface explicitly. In this presentation we will present our recent results on both anomalous transport and multiphase segregation.

Optical increase of photo-integrated micro- and nano-periodic susceptibility lattices

NASA Astrophysics Data System (ADS)

Smirnov, Vitaly A.; Vostrikova, Liubov I.

2015-03-01

It is demonstrated that the nonlinear photo-integrated micro- and nano-periodic second-order susceptibility lattices with very small amplitudes which were preliminarily recorded using bi-chromatic powerful laser light in amorphous glass materials can be increased up to some orders of magnitude under the action of a simple coherent monochromatic radiation. The optical increase of the small lattices takes place independent of the polarization and direction of propagation of the optical amplifying radiation and is achieved at various wavelengths. The observed phenomenon is not be explained only by nonlinear wave interaction in medium and also may be related to the microscopic asymmetry processes of the optical transitions between local centers in an isotropic medium that leads to the appearance and growth of the all-optically induced small micro- and nano-periodic electrical charges separations inside the sample. Possible mechanisms that may be responsible for the observed effects in the studied phosphate glasses are discussed.

Realization of Rectangular Artificial Spin Ice and Direct Observation of High Energy Topology.

PubMed

Ribeiro, I R B; Nascimento, F S; Ferreira, S O; Moura-Melo, W A; Costa, C A R; Borme, J; Freitas, P P; Wysin, G M; de Araujo, C I L; Pereira, A R

2017-10-25

In this work, we have constructed and experimentally investigated frustrated arrays of dipoles forming two-dimensional artificial spin ices with different lattice parameters (rectangular arrays with horizontal and vertical lattice spacings denoted by a and b respectively). Arrays with three different aspect ratios γ = a/b = [Formula: see text], [Formula: see text] and [Formula: see text] are studied. Theoretical calculations of low-energy demagnetized configurations for these same parameters are also presented. Experimental data for demagnetized samples confirm most of the theoretical results. However, the highest energy topology (doubly-charged monopoles) does not emerge in our theoretical model, while they are seen in experiments for large enough γ. Our results also insinuate that the string tension connecting two magnetic monopoles in a pair vanishes in rectangular lattices with a critical ratio γ = γ c  = [Formula: see text], supporting previous theoretical predictions.

Elasticity and magnetocaloric effect in MnFe 4Si 3

DOE PAGES

Herlitschke, Marcus; Klobes, B.; Sergueev, I.; ...

2016-03-16

The room temperature magnetocaloric material MnFe 4Si 3 was investigated with nuclear inelastic scattering (NIS) and resonant ultrasound spectroscopy (RUS) at different temperatures and applied magnetic fields in order to assess the infuence of the magnetic transition and the magnetocaloric effect on the lattice dynamics. The NIS data give access to phonons with energies above 3 meV, whereas RUS probes the elasticity of the material in the MHz frequency range and thus low energy, ~5 neV, phonon modes. A significant infuence of the magnetic transition on the lattice dynamics is observed only in the low energy region. Here, MnFe 4Simore » 3 and other compounds in the Mn 5-xFe xSi 3 series were also investigated with vibrating sample magnetometry, resistivity measurements and Moessbauer spectroscopy in order to study the magnetic transitions and to complement the obtained results on the lattice dynamics.« less

Prediction of sound absorption in rigid porous media with the lattice Boltzmann method

NASA Astrophysics Data System (ADS)

da Silva, Andrey Ricardo; Mareze, Paulo; Brandão, Eric

2016-02-01

In this work, sound absorption phenomena associated with the viscous shear stress within rigid porous media is investigated with a simple isothermal lattice Boltzmann BGK model. Simulations are conducted for different macroscopic material properties such as sample thickness and porosity and the results are compared with the exact analytical solution for materials with slit-like structure in terms of acoustic impedance and sound absorption coefficient. The numerical results agree very well with the exact solution, particularly for the sound absorption coefficient. The small deviations found in the low frequency limit for the real part of the acoustic impedance are attributed to the ratio between the thicknesses of the slit and the viscous boundary layer. The results suggest that the lattice Boltzmann method can be a very compelling numerical tool for simulating viscous sound absorption phenomena in the time domain, particularly due to its computational simplicity when compared to traditional continuum based techniques.

Dependence of the propagators on the sampling of Gribov copies inside the first Gribov region of Landau gauge

NASA Astrophysics Data System (ADS)

Maas, Axel

2017-12-01

Beyond perturbation theory the number of gauge copies drastically increases due to the Gribov-Singer ambiguity. Any way of treating them defines, in principle, a new, non-perturbative gauge, and the gauge-dependent correlation functions can vary between them. Herein various such gauges will be constructed as completions of the Landau gauge inside the first Gribov region. The dependence of the propagators and the running coupling on these gauges will be studied for SU(2) Yang-Mills theory in two, three, and four dimensions using lattice gauge theory, and for a wide range of lattice parameters. While the gluon propagator is rather insensitive to the choice, the ghost propagator and the running coupling show a stronger dependence. It is also found that the influence of lattice artifacts is larger than in minimal Landau gauge.

Non-classical photon correlation in a two-dimensional photonic lattice.

PubMed

Gao, Jun; Qiao, Lu-Feng; Lin, Xiao-Feng; Jiao, Zhi-Qiang; Feng, Zhen; Zhou, Zheng; Gao, Zhen-Wei; Xu, Xiao-Yun; Chen, Yuan; Tang, Hao; Jin, Xian-Min

2016-06-13

Quantum interference and quantum correlation, as two main features of quantum optics, play an essential role in quantum information applications, such as multi-particle quantum walk and boson sampling. While many experimental demonstrations have been done in one-dimensional waveguide arrays, it remains unexplored in higher dimensions due to tight requirement of manipulating and detecting photons in large-scale. Here, we experimentally observe non-classical correlation of two identical photons in a fully coupled two-dimensional structure, i.e. photonic lattice manufactured by three-dimensional femtosecond laser writing. Photon interference consists of 36 Hong-Ou-Mandel interference and 9 bunching. The overlap between measured and simulated distribution is up to 0.890 ± 0.001. Clear photon correlation is observed in the two-dimensional photonic lattice. Combining with controllably engineered disorder, our results open new perspectives towards large-scale implementation of quantum simulation on integrated photonic chips.

Exchange-mediated spin-lattice relaxation of Fe3+ ions in borate glasses.

PubMed

Misra, Sushil K; Pilbrow, John R

2007-03-01

Spin-lattice relaxation times (T1) of two borate glasses doped with different concentrations of Fe2O3 were measured using the Electron Spin-Echo (ESE) technique at X-band (9.630 GHz) in the temperature range 2-6K. In comparison with a previous investigation of Fe3+-doped silicate glasses, the relaxation rates were comparable and differed by no more than a factor of two. The data presented here extend those previously reported for borate glasses in the 10-250K range but measured using the amplitude-modulation technique. The T1 values were found to depend on temperature (T) as T(n) with n approximately 1 for the 1% and 0.1% Fe2O3-doped glass samples. These results are consistent with spin-lattice relaxation as effected by exchange interaction of a Fe3+ spin exchange-coupled to another Fe3+ spin in an amorphous material.

Study of the second magnetization peak and the pinning behaviour in Ba(Fe0.935Co0.065)2As2 pnictide superconductor

NASA Astrophysics Data System (ADS)

Sundar, Shyam; Mosqueira, J.; Alvarenga, A. D.; Sóñora, D.; Sefat, A. S.; Salem-Sugui, S., Jr.

2017-12-01

Isothermal magnetic field dependence of magnetization and magnetic relaxation measurements were performed for the H\\parallel {{c}} axis on a single crystal of Ba(Fe0.935 Co0.065)2As2 pnictide superconductor having T c = 21.7 K. The second magnetization peak (SMP) for each isothermal M(H) was observed in a wide temperature range from T c to the lowest temperature of measurement (2 K). The magnetic field dependence of relaxation rate R(H), showed a peak (H spt) between H on (onset of SMP in M(H)) and H p (peak field of SMP in M(H)), which is likely to be related to a vortex-lattice structural phase transition, as suggested in the literature for a similar sample. In addition, the magnetic relaxation measured for magnetic fields near H spt showed some noise, which might be the signature of the structural phase transition of the vortex lattice. Analysis of the magnetic relaxation data using Maley’s criterion and the collective pinning theory suggested that the SMP in the sample was due to the collective (elastic) to plastic creep crossover, which was also accompanied by a rhombic to square vortex lattice phase transition. Analysis of the pinning force density suggested a single dominating pinning mechanism in the sample, which did not showing the usual δ {l} and δ {T}{{c}} nature of pinning. The critical current density (J c), estimated using the Bean critical state model, was found to be 5 × 105 A cm- 2 at 2 K in the zero magnetic field limit. Surprisingly, the maximum of the pinning force density was not responsible for the maximum value of the critical current density in the sample.

Excited-State Effective Masses in Lattice QCD

DOE Office of Scientific and Technical Information (OSTI.GOV)

George Fleming, Saul Cohen, Huey-Wen Lin

2009-10-01

We apply black-box methods, i.e. where the performance of the method does not depend upon initial guesses, to extract excited-state energies from Euclidean-time hadron correlation functions. In particular, we extend the widely used effective-mass method to incorporate multiple correlation functions and produce effective mass estimates for multiple excited states. In general, these excited-state effective masses will be determined by finding the roots of some polynomial. We demonstrate the method using sample lattice data to determine excited-state energies of the nucleon and compare the results to other energy-level finding techniques.

Experimental evidence for a transverse magnetization of the Abrikosov lattice in anisotropic superconductors

NASA Technical Reports Server (NTRS)

Farrel, D. E.; Williams, C. M.; Wolf, S. A.; Bansal, N. P.; Kogan, V. G.

1988-01-01

The torque on a superconductor in a magnetic field H has been thought to be dominated by trapped flux or sample shape effects, but it has recently been suggested that an anisotropic type-II material should experience an intrinsic torque for H(c1) much less than H, which in turn is less than H(c2). The predicted phenomenon results from transverse magnetization of the Abrikosov lattice. Measurements are presented on copper-oxide superconductors which delineate the experimental regime in which extrinsic effects are negligible and confirm the existence of the predicted intrinsic torque.

Neutron powder diffraction studies as a function of temperature of structure II hydrate formed from propane

USGS Publications Warehouse

Rawn, C.J.; Rondinone, A.J.; Chakoumakos, B.C.; Circone, S.; Stern, L.A.; Kirby, S.H.; Ishii, Y.

2003-01-01

Neutron powder diffraction data confirm that hydrate samples synthesized with propane crystallize as structure type II hydrate. The structure has been modeled using rigid-body constraints to describe C3H8 molecules located in the eight larger polyhedral cavities of a deuterated host lattice. Data were collected at 12, 40, 100, 130, 160, 190, 220, and 250 K and used to calculate the thermal expansivity from the temperature dependence of the lattice parameters. The data collected allowed for full structural refinement of atomic coordinates and the atomic-displacement parameters.

Phase Transitions in a Model of Y-Molecules Abstract

NASA Astrophysics Data System (ADS)

Holz, Danielle; Ruth, Donovan; Toral, Raul; Gunton, James

Immunoglobulin is a Y-shaped molecule that functions as an antibody to neutralize pathogens. In special cases where there is a high concentration of immunoglobulin molecules, self-aggregation can occur and the molecules undergo phase transitions. This prevents the molecules from completing their function. We used a simplified model of 2-Dimensional Y-molecules with three identical arms on a triangular lattice with 2-dimensional Grand Canonical Ensemble. The molecules were permitted to be placed, removed, rotated or moved on the lattice. Once phase coexistence was found, we used histogram reweighting and multicanonical sampling to calculate our phase diagram.

Evaluation of Low Melting Halide Systems for Battery Applications.

DTIC Science & Technology

1983-04-01

prominent peak at 95 cm-1 . The spectrum of the other sample exhibits 124 -4 ,4 -4 -44 .. t - CD - 0o - N. 0 uN C)(j QCD oca CD u C 125. the same peaks... lattice with 6-fold coordination about in this region can be drawn. However. his isotherms have aluminum and melts at 192.4 ’C with a AH° of 35.3 kJ the...temperature in the composition of SbC.AICI is favored by the relatively large direction of increasing aluminum bromide content. just as lattice energy of

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jena, Puru; Kandalam, Anil K.; Christian, Theresa M.

Gallium phosphide bismide (GaP1-xBix) epilayers with bismuth fractions from 0.9% to 3.2%, as calculated from lattice parameter measurements, were studied with Rutherford backscattering spectrometry (RBS) to directly measure bismuth incorporation. The total bismuth fractions found by RBS were higher than expected from the lattice parameter calculations. Furthermore, in one analyzed sample grown by molecular beam epitaxy at 300 degrees C, 55% of incorporated bismuth was found to occupy interstitial sites. We discuss implications of this high interstitial incorporation fraction and its possible relationship to x-ray diffraction and photoluminescence measurements of GaP0.99Bi0.01.

Thermoelectric Properties and Hall Effect of Bi2Te3-xSex Polycrystalline Materials Prepared by a Hot Press Method

NASA Astrophysics Data System (ADS)

Yashima, Isamu; Watanave, Hiroshi; Ogisu, Takayasu; Tsukuda, Ryouma; Sato, Susumu

1998-05-01

Bi2Te3-xSex (0≦x<1) polycrystalline solids are prepared by a hot press method and their thermoelectric properties are studied. The samples show the maximum value of Z = 2.3×10-3 K-1 at x=0.22. The lattice thermal conductivity is smaller than that of a single crystal. The lattice constant and power factor decrease upon increasing the selenium substitution while thermal conductivity decreases for x values up to 0.33 and becomes constant for x values greater than 0.33.

InP and InGaAs Submicron Gate Microwave Power Transistors for 20 GHz Applications

DTIC Science & Technology

1991-06-01

APLIC ( ATIO NS I:F ( 6 AUTHORiSI VI )N4Wh 7 ERFORMLNG ORGANIZATION NAME(IS) AND ADORE SCISI S Naval Ocean Systems Center San DiegEE, CA 92152-5300(0 9...electronic material for high frequency applications. In0 .5 3Ga. 4 7 As lattice matched to semi-insulating (SI) InP has higher low field mobility , peak...lattice parameter was < ±5 x 10- 4 . The InGaAs mobility at 300 K was 5500 cm 2/V sec. For the device fabrication, the samples were initially cleaned

i-anvils : in situ measurements of pressure, temperature and conductivity in diamond anvil cells

NASA Astrophysics Data System (ADS)

Munsch, P.; Bureau, H.; Kubsky, S.; Meijer, J.; Datchi, F.; Ninet, S.; Estève, I.

2011-12-01

The precise determination of the pressure and temperature conditions during diamond anvils cells (DAC) experiments is of primary importance. Such determinations are critical more especially for the fields corresponding to "low pressures" (<4 GPa) and moderate temperature (600-1500°C). Determining the electrical properties of mantle minerals is also a condition to understand the physics of the Deep Earth. This has to be done in situ at pressures and temperatures relevant for the interior of the Earth. i-anvils allow in situ pressure (P) and temperature (T) measurements in experiments using a DAC. Boron and carbon micro-structures are implanted in the diamond anvil lattice a few micrometers below the surface, the sensors are located a few μm below the center of the diamond culet (sample chamber position). When conductive electrodes are implanted at the position of the sample chamber on the culet of the anvil, instead of P,T sensors, they allow in situ measurements of electrical properties of the loaded sample at high P,T conditions in a DAC. The principle consists of applying an electrical potential across the structures through external contacts placed on the slopes of the anvil. The resistivity of these structures is sensitive to pressure and temperature applied in the sample chamber. The electrical transport properties of the sample can be measured the same way when electrodes have been implanted on the culet. Here we will present our last progresses, more especially using the focus ion beam (FIB) technology to perform contacts and electrodes. Progresses about the i-anvils connexions with the electronic devices will also be shown. We will present the last P and T sensors calibrations. Furnaces are also introduced through Boron implantation into the anvils, allowing the possibility to reach intermediate temperatures between externally heated DAC (up to 1100°C) and laser heated DAC (from 1500°C to a few thousands). Preliminary tests and the interest of such devices will be discussed at the meeting. A new diamond anvil cell has been especially designed for this purpose. This DAC allows in situ spectroscopies and X-Ray characterisation of geological fluids in their equilibrium conditions in the crust and in the upper mantle. Preliminary results will be presented.

Superconductivity in the lanthanum-yttrium-manganese alloy system

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stierman, R.J.

An empirical approach involving lattice instabilities was investigated in the search for new superconducting materials. Pseudo-lanthanide compounds using La and Y were prepared for the system La/sub 1-x/Y/sub x/Mn/sub 2/ by arc melting and subsequent heat treatment. Low temperature magnetic susceptibility and low temperature heat capacity measurements were made. The unit cell lattice parameters were determined from x-ray powder patterns taken on most samples and metallographic examination was carried out on selected samples. Alloys with low La concentrations (x greater than or equal to 0.6) showed RMn/sub 2/ in the cubic C15 Laves phase as the major component with secondmore » phase material present. The magnetic susceptibility and x-ray data indicated a superconducting phase which seemed to be the RMn/sub 2/ phase, but heat capacity measurements showed the second phase material was the superconductor, while the RMn/sub 2/ was not. Failure to form compounds with higher La content was experienced and may be due to the lattice instability expected at x = 0.56. This indicates that perhaps more stingent conditions are required to form pseudo-lanthanide compounds than were previously considered. More systems should be investigated to see if this is true, and to determine the possibilities of this approach.« less

Mesoscopic Vortex–Meissner currents in ring ladders

NASA Astrophysics Data System (ADS)

Haug, Tobias; Amico, Luigi; Dumke, Rainer; Kwek, Leong-Chuan

2018-07-01

Recent experimental progress have revealed Meissner and Vortex phases in low-dimensional ultracold atoms systems. Atomtronic setups can realize ring ladders, while explicitly taking the finite size of the system into account. This enables the engineering of quantized chiral currents and phase slips in between them. We find that the mesoscopic scale modifies the current. Full control of the lattice configuration reveals a reentrant behavior of Vortex and Meissner phases. Our approach allows a feasible diagnostic of the currents’ configuration through time-of-flight measurements.

Synthesis and polymorphic control for visible light active titania nanoparticles

NASA Astrophysics Data System (ADS)

Kaewgun, Sujaree

Titania (TiO2) is useful for many applications in photocatalysis, antimicrobials, pigment, deodorization, and decomposition of harmful organics and undesirable compounds in the air and waste water under UV irradiation. Among the three phases of TiO2, Rutile, Anatase, and Brookite, studies have been more focused on the anatase and rutile phases. Pure brookite is the most difficult phase to prepare, even under hydrothermal conditions. Predominantly brookite phase TiO2 nanoparticles were prepared by the Water-based Ambient Condition Sol (WACS) process in our laboratory. The objectives of this research were to enhance visible light active (VLA) photocatalytic properties of polymorphic brookite TiO2 by minimizing the lattice defects and narrowing band gap of titania by nitrogen and/or carbon chromophone, and to investigate the deactivation, reusability, and regeneration of the VLA titania in order to design better titania catalysts for organic compound degradation applications. In order to study the influence of hydroxyl content on photocatalytic activities (PCAs) of polymorphic titania nanoparticles, the WACS samples were post-treated by a Solvent-based Ambient Condition Sol (SACS) process in sec-butanol (sec-BuOH). All samples were characterized for phase composition, surface area, hydroxyl contamination, and particle morphology by x-ray diffraction, N2 physisorption, FT-IR, solid state 1H NMR and scanning electron microscopy, and then compared to a commercial titania, Degussa P25. Evaluation of methyl orange (MO) degradation under UV irradiation results showed that the lower lattice hydroxyl content in SACS titania enhanced the PCA. As-prepared titania and SACS samples, which have similar surface areas and crystallinity, were compared in order to prove that the superior PCA came from the reduction in the lattice hydroxyl content. To enhance PCA and VLA properties of WACS, an alternative high boiling point polar solvent, N-methylpyrrolidone (NMP), was utilized in the SACS process at a higher treatment temperature to modify polymorphic titania nanoparticles. This SACS sample was called "SACS-NMP". SACS, using NMP as the solvent, could also extract lattice hydroxyls, and decorate nitrogen on the titania surface. The PCA of SACS-NMP was superior to that of SACS-sec-BuOH. Nitrogen incorporation of SACS-NMP titania was investigated by CHN analysis and x-ray photoelectron spectroscopy (XPS). VL absorbance for all samples was characterized by UV-Vis absorption spectrophotometry. PCA of MO degradation under UV and VL showed that SACS-NMP is a powerful treatment to enhance PCA by minimizing lattice hydroxyls and doping the titania surface with nitrogen. The effect of calcination conditions on SACS-NMP samples was also studied. The calcination conditions, especially the temperature and calcination atmosphere, have an influence on the BET surface area, crystallite size, titania phase content, and PCA under VL irradiation. SACS-NMP samples calcined in air at 200°C for 2 hours showed the best VL activated photocatalytic performance in this research. Additionally, the SACS-NMP sample exhibited superior VL properties to several available reference anatase titania samples. This could be explained as the effective charge separation by the intercrystalline electron transport from brookite to anatase grains complemented by strong VL absorption by the nitrogen species in NMP. The deactivation and regeneration of the VLA titania were investigated and compared to a commercial titania, Kronos VLP7000. PCA of the titania under VL for MO decolorization gradually decreased with increasing testing time and the number of runs. The cause of the deactivation was identified as the deposition of the decomposed MO or the carbonaceous deposit. Among the possible regeneration procedures for used SACS-NMP samples, methanol washing was shown to be the most effective up to ˜80% of the PCA recovery. Accordingly, the SACS-NMP samples could not be completely recovered since a regeneration process would possibly remove some of nitrogen species responsible for the VL properties.

Lattice distortion mechanism study of TiO2 nanoparticles during photocatalysis degradation and reactivation

NASA Astrophysics Data System (ADS)

Wu, Wenhui; Xue, Xudong; Jiang, Xudong; Zhang, Yupeng; Wu, Yichu; Pan, Chunxu

2015-05-01

In this paper, the photocatalytic process of TiO2 (P25) is directly characterized by using a positron annihilation lifetime spectroscopy (PALS), high-resolution transmission electron microscopy (HRTEM), Photoluminescence spectroscopy (PL) and UV Raman spectroscopy (Raman). The experimental results reveal that: 1) From PALS measurements, because τ1 and τ2 values and their intensity (I1 and I2) assigned to the different size and amounts of defects, respectively, their variations indicate the formation of different types and amounts of defects during the absorption and degradation. 2) HRTEM observations show that the lattice images become partly blurring when the methylene blue is fully degradated, and clear again after exposed in the air for 30 days. According to the results, we propose a mechanism that the lattice distortion induces the defects as electron capture sites and provides energy for improving photocatalytic process. Meanwhile, the lattice distortion relaxation after exposing in the air for 30 days perfectly explains the gradual deactivation of TiO2, because the smaller vacancy defects grow and agglomerate through the several photocatalytic processes. The instrumental PL and Raman are also used to analyze the samples and approved the results of PALS and HRTEM.

Effect of a Nitrogen Impurity on the Fundamental Raman Band of Diamond Single Crystals

NASA Astrophysics Data System (ADS)

Gusakov, G. A.; Samtsov, M. P.; Voropay, E. S.

2018-05-01

The effect of nitrogen defects in natural and synthetic diamond single crystals on the position and half-width of the fundamental Raman band was investigated. Samples containing the main types of nitrogen lattice defects at impurity contents of 1-1500 ppm were studied. The parameters of the Stokes and anti-Stokes components in Raman spectra of crystals situated in a cell with distilled water to minimize the influence of heating by the exciting laser radiation were analyzed to determine the effect of a nitrogen impurity in the diamond crystal lattice. It was shown that an increase of impurity atoms in the crystals in the studied concentration range resulted in broadening of the Raman band from 1.61 to 2.85 cm-1 and shifting of the maximum to lower frequency from 1332.65 to 1332.3 cm-1. The observed effect was directly proportional to the impurity concentration and depended on the form of the impurity incorporated into the diamond lattice. It was found that the changes in the position and half-width of the fundamental Raman band for diamond were consistent with the magnitude of crystal lattice distortions due to the presence of impurity defects and obeyed the Gruneisen law.

Capability of X-ray diffraction for the study of microstructure of metastable thin films

PubMed Central

Rafaja, David; Wüstefeld, Christina; Dopita, Milan; Motylenko, Mykhaylo; Baehtz, Carsten

2014-01-01

Metastable phases are often used to design materials with outstanding properties, which cannot be achieved with thermodynamically stable compounds. In many cases, the metastable phases are employed as precursors for controlled formation of nanocomposites. This contribution shows how the microstructure of crystalline metastable phases and the formation of nanocomposites can be concluded from X-ray diffraction experiments by taking advantage of the high sensitivity of X-ray diffraction to macroscopic and microscopic lattice deformations and to the dependence of the lattice deformations on the crystallographic direction. The lattice deformations were determined from the positions and from the widths of the diffraction lines, the dependence of the lattice deformations on the crystallographic direction from the anisotropy of the line shift and the line broadening. As an example of the metastable system, the supersaturated solid solution of titanium nitride and aluminium nitride was investigated, which was prepared in the form of thin films by using cathodic arc evaporation of titanium and aluminium in a nitrogen atmosphere. The microstructure of the (Ti,Al)N samples under study was tailored by modifying the [Al]/[Ti] ratio in the thin films and the surface mobility of the deposited species. PMID:25485125

The relation between lattice parameters and very low twinning stress in Ni50Mn25+x Ga25-x magnetic shape memory alloys

NASA Astrophysics Data System (ADS)

Straka, L.; Drahokoupil, J.; Pacherová, O.; Fabiánová, K.; Kopecký, V.; Seiner, H.; Hänninen, H.; Heczko, O.

2016-02-01

In search of the origins of the extraordinary low twinning stress of Ni-Mn-Ga 10M martensite, we studied the temperature induced changes in lattice parameters of Ni50Mn25+x Ga25-x (x = 2.7-3.9) single crystal samples and compared them with twinning stress dependences. The alloys exhibited transformation to five-layered (10M) martensite structure (cubic to monoclinic) between 297 to 328 K and exhibited the magnetic shape memory effect in martensite. The structural changes were monitored using x-ray diffraction in the temperature range 200-343 K. The 10M structure was approximated by monoclinic lattice, a = b > c, γ > 90° with the coordinates derived from the cubic unit cell of the parent L21 phase. The lattice parameters γ and c/a correlate well with the universal linear increase of twinning stress of type 1 twins with decreasing temperature. On the contrary, the twinning stress is not affected by differences between a and b and thus a/b twins seem to play no role in a - c twin boundary motion resulting in magnetically induced reorientation.

Iodine doping effects on the lattice thermal conductivity of oxidized polyacetylene nanofibers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bi, Kedong, E-mail: lishi@mail.utexas.edu, E-mail: kedongbi@seu.edu.cn; Department of Mechanical Engineering, University of Texas at Austin, Austin, Texas 78712; Weathers, Annie

2013-11-21

Thermal transport in oxidized polyacetylene (PA) nanofibers with diameters in the range between 74 and 126 nm is measured with the use of a suspended micro heater device. With the error due to both radiation and contact thermal resistance corrected via a differential measurement procedure, the obtained thermal conductivity of oxidized PA nanofibers varies in the range between 0.84 and 1.24 W m{sup −1} K{sup −1} near room temperature, and decreases by 40%–70% after iodine doping. It is also found that the thermal conductivity of oxidized PA nanofibers increases with temperature between 100 and 350 K. Because of exposure to oxygen during sample preparation, themore » PA nanofibers are oxidized to be electrically insulating before and after iodine doping. The measurement results reveal that iodine doping can result in enhanced lattice disorder and reduced lattice thermal conductivity of PA nanofibers. If the oxidation issue can be addressed via further research to increase the electrical conductivity via doping, the observed suppressed lattice thermal conductivity in doped polymer nanofibers can be useful for the development of such conducting polymer nanostructures for thermoelectric energy conversion.« less

Quantification of Honeycomb Number-Type Stacking Faults: Application to Na 3Ni 2BiO 6 Cathodes for Na-Ion Batteries

DOE PAGES

Liu, Jue; Yin, Liang; Wu, Lijun; ...

2016-08-17

Here, ordered and disordered samples of honeycomb-lattice Na 3Ni 2BiO 6 were investigated as cathodes for Na-ion batteries, and it was determined that the ordered sample exhibits better electrochemical performance, with a specific capacity of 104 mA h/g delivered at plateaus of 3.5 and 3.2 V (vs Na +/Na) with minimal capacity fade during extended cycling. Advanced imaging and diffraction investigations showed that the primary difference between the ordered and disordered samples is the amount of number-type stacking faults associated with the three possible centering choices for each honeycomb layer. A labeling scheme for assigning the number position of honeycombmore » layers is described, and it is shown that the translational shift vectors between layers provide the simplest method for classifying different repeat patterns. We demonstrate that the number position of honeycomb layers can be directly determined in high-angle annular dark-field scanning transmission electron microscopy (STEM-HAADF) imaging studies. By the use of fault models derived from STEM studies, it is shown that both the sharp, symmetric subcell peaks and the broad, asymmetric superstructure peaks in powder diffraction patterns can be quantitatively modeled. About 20% of the layers in the ordered monoclinic sample are faulted in a nonrandom manner, while the disordered sample stacking is not fully random but instead contains about 4% monoclinic order. Furthermore, it is shown that the ordered sample has a series of higher-order superstructure peaks associated with 6-, 9-, 12-, and 15-layer periods whose existence is transiently driven by the presence of long-range strain that is an inherent consequence of the synthesis mechanism revealed through the present diffraction and imaging studies. This strain is closely associated with a monoclinic shear that can be directly calculated from cell lattice parameters and is strongly correlated with the degree of ordering in the samples. The present results are broadly applicable to other honeycomb-lattice systems, including Li 2MnO 3 and related Li-excess cathode compositions.« less

Quantification of Honeycomb Number-Type Stacking Faults: Application to Na 3Ni 2BiO 6 Cathodes for Na-Ion Batteries

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Jue; Yin, Liang; Wu, Lijun

Here, ordered and disordered samples of honeycomb-lattice Na 3Ni 2BiO 6 were investigated as cathodes for Na-ion batteries, and it was determined that the ordered sample exhibits better electrochemical performance, with a specific capacity of 104 mA h/g delivered at plateaus of 3.5 and 3.2 V (vs Na +/Na) with minimal capacity fade during extended cycling. Advanced imaging and diffraction investigations showed that the primary difference between the ordered and disordered samples is the amount of number-type stacking faults associated with the three possible centering choices for each honeycomb layer. A labeling scheme for assigning the number position of honeycombmore » layers is described, and it is shown that the translational shift vectors between layers provide the simplest method for classifying different repeat patterns. We demonstrate that the number position of honeycomb layers can be directly determined in high-angle annular dark-field scanning transmission electron microscopy (STEM-HAADF) imaging studies. By the use of fault models derived from STEM studies, it is shown that both the sharp, symmetric subcell peaks and the broad, asymmetric superstructure peaks in powder diffraction patterns can be quantitatively modeled. About 20% of the layers in the ordered monoclinic sample are faulted in a nonrandom manner, while the disordered sample stacking is not fully random but instead contains about 4% monoclinic order. Furthermore, it is shown that the ordered sample has a series of higher-order superstructure peaks associated with 6-, 9-, 12-, and 15-layer periods whose existence is transiently driven by the presence of long-range strain that is an inherent consequence of the synthesis mechanism revealed through the present diffraction and imaging studies. This strain is closely associated with a monoclinic shear that can be directly calculated from cell lattice parameters and is strongly correlated with the degree of ordering in the samples. The present results are broadly applicable to other honeycomb-lattice systems, including Li 2MnO 3 and related Li-excess cathode compositions.« less

Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for Photovoltaics

DOE PAGES

Prasanna, Rohit; Gold-Parker, Aryeh; Leijtens, Tomas; ...

2017-07-13

Tin and lead iodide perovskite semiconductors of the composition AMX 3, where M is a metal and X is a halide, are leading candidates for high efficiency low cost tandem photovoltaics, in part because they have band gaps that can be tuned over a wide range by compositional substitution. We experimentally identify two competing mechanisms through which the A-site cation influences the band gap of 3D metal halide perovskites. Using a smaller A-site cation can distort the perovskite lattice in two distinct ways: by tilting the MX 6 octahedra or by simply contracting the lattice isotropically. The former effect tendsmore » to raise the band gap, while the latter tends to decrease it. Lead iodide perovskites show an increase in band gap upon partial substitution of the larger formamidinium with the smaller cesium, due to octahedral tilting. Perovskites based on tin, which is slightly smaller than lead, show the opposite trend: they show no octahedral tilting upon Cs-substitution but only a contraction of the lattice, leading to progressive reduction of the band gap. We outline a strategy to systematically tune the band gap and valence and conduction band positions of metal halide perovskites through control of the cation composition. Using this strategy, we demonstrate solar cells that harvest light in the infrared up to 1040 nm, reaching a stabilized power conversion efficiency of 17.8%, showing promise for improvements of the bottom cell of all-perovskite tandem solar cells. In conclusion, the mechanisms of cation-based band gap tuning we describe are broadly applicable to 3D metal halide perovskites and will be useful in further development of perovskite semiconductors for optoelectronic applications.« less

Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for Photovoltaics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prasanna, Rohit; Gold-Parker, Aryeh; Leijtens, Tomas

Tin and lead iodide perovskite semiconductors of the composition AMX 3, where M is a metal and X is a halide, are leading candidates for high efficiency low cost tandem photovoltaics, in part because they have band gaps that can be tuned over a wide range by compositional substitution. We experimentally identify two competing mechanisms through which the A-site cation influences the band gap of 3D metal halide perovskites. Using a smaller A-site cation can distort the perovskite lattice in two distinct ways: by tilting the MX 6 octahedra or by simply contracting the lattice isotropically. The former effect tendsmore » to raise the band gap, while the latter tends to decrease it. Lead iodide perovskites show an increase in band gap upon partial substitution of the larger formamidinium with the smaller cesium, due to octahedral tilting. Perovskites based on tin, which is slightly smaller than lead, show the opposite trend: they show no octahedral tilting upon Cs-substitution but only a contraction of the lattice, leading to progressive reduction of the band gap. We outline a strategy to systematically tune the band gap and valence and conduction band positions of metal halide perovskites through control of the cation composition. Using this strategy, we demonstrate solar cells that harvest light in the infrared up to 1040 nm, reaching a stabilized power conversion efficiency of 17.8%, showing promise for improvements of the bottom cell of all-perovskite tandem solar cells. In conclusion, the mechanisms of cation-based band gap tuning we describe are broadly applicable to 3D metal halide perovskites and will be useful in further development of perovskite semiconductors for optoelectronic applications.« less

Band Gap Tuning via Lattice Contraction and Octahedral Tilting in Perovskite Materials for Photovoltaics.

PubMed

Prasanna, Rohit; Gold-Parker, Aryeh; Leijtens, Tomas; Conings, Bert; Babayigit, Aslihan; Boyen, Hans-Gerd; Toney, Michael F; McGehee, Michael D

2017-08-16

Tin and lead iodide perovskite semiconductors of the composition AMX 3 , where M is a metal and X is a halide, are leading candidates for high efficiency low cost tandem photovoltaics, in part because they have band gaps that can be tuned over a wide range by compositional substitution. We experimentally identify two competing mechanisms through which the A-site cation influences the band gap of 3D metal halide perovskites. Using a smaller A-site cation can distort the perovskite lattice in two distinct ways: by tilting the MX 6 octahedra or by simply contracting the lattice isotropically. The former effect tends to raise the band gap, while the latter tends to decrease it. Lead iodide perovskites show an increase in band gap upon partial substitution of the larger formamidinium with the smaller cesium, due to octahedral tilting. Perovskites based on tin, which is slightly smaller than lead, show the opposite trend: they show no octahedral tilting upon Cs-substitution but only a contraction of the lattice, leading to progressive reduction of the band gap. We outline a strategy to systematically tune the band gap and valence and conduction band positions of metal halide perovskites through control of the cation composition. Using this strategy, we demonstrate solar cells that harvest light in the infrared up to 1040 nm, reaching a stabilized power conversion efficiency of 17.8%, showing promise for improvements of the bottom cell of all-perovskite tandem solar cells. The mechanisms of cation-based band gap tuning we describe are broadly applicable to 3D metal halide perovskites and will be useful in further development of perovskite semiconductors for optoelectronic applications.

Synthesis and magnetic behaviour of Mn:ZnO nanocrystalline powders.

PubMed

Sagar, R Vidya; Buddhudu, S

2010-04-01

This paper reports on the magnetic properties of Mn:ZnO nanoparticles. XRD profiles have shown that the undertaken materials are in wurtzite structures. The crystallite size of the sample has been examined using TEM for one sample. In order to verify the lattice site occupancy and also valence state of the manganese ion, EPR spectral measurements have also been carried out for these samples. The magnetic properties of the samples have been investigated on a Vibrating Sample Magnetometer (VSM). Copyright 2009 Elsevier B.V. All rights reserved.

Setup for in situ x-ray diffraction study of swift heavy ion irradiated materials.

PubMed

Kulriya, P K; Singh, F; Tripathi, A; Ahuja, R; Kothari, A; Dutt, R N; Mishra, Y K; Kumar, Amit; Avasthi, D K

2007-11-01

An in situ x-ray diffraction (XRD) setup is designed and installed in the materials science beam line of the Pelletron accelerator at the Inter-University Accelerator Centre for in situ studies of phase change in swift heavy ion irradiated materials. A high vacuum chamber with suitable windows for incident and diffracted X-rays is integrated with the goniometer and the beamline. Indigenously made liquid nitrogen (LN2) temperature sample cooling unit is installed. The snapshots of growth of particles with fluence of 90 MeV Ni ions were recorded using in situ XRD experiment, illustrating the potential of this in situ facility. A thin film of C60 was used to test the sample cooling unit. It shows that the phase of the C60 film transforms from a cubic lattice (at room temperature) to a fcc lattice at around T=255 K.

Heavy doping of CdTe single crystals by Cr ion implantation

NASA Astrophysics Data System (ADS)

Popovych, Volodymyr D.; Böttger, Roman; Heller, Rene; Zhou, Shengqiang; Bester, Mariusz; Cieniek, Bogumil; Mroczka, Robert; Lopucki, Rafal; Sagan, Piotr; Kuzma, Marian

2018-03-01

Implantation of bulk CdTe single crystals with high fluences of 500 keV Cr+ ions was performed to achieve Cr concentration above the equilibrium solubility limit of this element in CdTe lattice. The structure and composition of the implanted samples were studied using secondary ion mass spectrometry (SIMS), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, X-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) to characterize the incorporation of chromium into the host lattice and to investigate irradiation-induced damage build-up. It was found that out-diffusion of Cr atoms and sputtering of the targets alter the depth distribution and limit concentration of the projectile ions in the as-implanted samples. Appearance of crystallographically oriented, metallic α-Cr nanoparticles inside CdTe matrix was found after implantation, as well as a strong disorder at the depth far beyond the projected range of the implanted ions.

Lattice modification in KTiOPO4 by hydrogen and helium sequentially implantation in submicrometer depth

NASA Astrophysics Data System (ADS)

Ma, Changdong; Lu, Fei; Xu, Bo; Fan, Ranran

2016-05-01

We investigated lattice modification and its physical mechanism in H and He co-implanted, z-cut potassium titanyl phosphate (KTiOPO4). The samples were implanted with 110 keV H and 190 keV He, both to a fluence of 4 × 1016 cm-2, at room temperature. Rutherford backscattering/channeling, high-resolution x-ray diffraction, and transmission electron microscopy were used to examine the implantation-induced structural changes and strain. Experimental and simulated x-ray diffraction results show that the strain in the implanted KTiOPO4 crystal is caused by interstitial atoms. The strain and stress are anisotropic and depend on the crystal's orientation. Transmission electron microscopy studies indicate that ion implantation produces many dislocations in the as-implanted samples. Annealing can induce ion aggregation to form nanobubbles, but plastic deformation and ion out-diffusion prevent the KTiOPO4 surface from blistering.

Synthesis and magnetic properties of NiFe2-xSmxO4 nanopowder

NASA Astrophysics Data System (ADS)

Hassanzadeh-Tabrizi, S. A.; Behbahanian, Shahrzad; Amighian, Jamshid

2016-07-01

NiFe2-xSmxO4 (x=0.00, 0.05, 0.10 and 0.15) nanopowders were synthesized via a sol-gel combustion route. The structural studies were carried out by X-ray diffractometer, Fourier transform infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The XRD results confirmed the formation of single-phase spinel cubic structure. The crystallite size decreased with an increase of samarium ion concentration, while lattice parameter and lattice strain increased with samarium substitution. TEM micrographs showed that agglomerated nanoparticles with particle sizes ranging from 35 to 90 nm were obtained. The magnetic studies were carried out using vibrating sample magnetometer. Magnetic measurements revealed that the saturation magnetization (Ms) of NiFe2-xSmxO4 nanoparticles decreases with increasing Sm3+substitution. The reduction of saturation magnetization is attributed to the dilution of the magnetic interaction. The coercivity (Hc) of samples increases by adding samarium.

Cu-doped Cd1- x Zn x S alloy: synthesis and structural investigations

NASA Astrophysics Data System (ADS)

Yadav, Indu; Ahlawat, Dharamvir Singh; Ahlawat, Rachna

2016-03-01

Copper doped Cd1- x Zn x S ( x ≤ 1) quantum dots have been synthesized using chemical co-precipitation method. Structural investigation of the synthesized nanomaterials has been carried out by powder XRD method. The XRD results have confirmed that as-prepared Cu-doped Cd1- x Zn x S quantum dots have hexagonal structure. The average nanocrystallite size was estimated in the range 2-12 nm using Debye-Scherrer formula. The lattice constants, lattice plane, d-spacing, unit cell volume, Lorentz factor and dislocation density were also calculated from XRD data. The change in particle size was observed with the change in Zn concentration. Furthermore, FTIR spectra of the prepared samples were observed for identification of COO- and O-H functional groups. The TEM study has also reported the same size range of nanoparticles. The increase in agglomeration has been observed with the increase in Zn concentration in the prepared samples.

Reduced photoconductivity observed by time-resolved terahertz spectroscopy in metal nanofilms with and without adhesion layers

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alberding, Brian G.; Heilweil, Edwin J., E-mail: edwin.heilweil@nist.gov; Kushto, Gary P.

2016-05-30

Non-contact, optical time-resolved terahertz spectroscopy has been used to study the transient photoconductivity of nanometer-scale metallic films deposited on the fused quartz substrates. Samples of 8 nm thick gold or titanium show an instrument-limited (ca. 0.5 ps) decrease in conductivity following photoexcitation due to electron-phonon coupling and subsequent increased lattice temperatures which increases charge carrier scattering. In contrast, for samples of 8 nm gold with a 4 nm adhesion layer of titanium or chromium, a ca. 70 ps rise time for the lattice temperature increase is observed. These results establish the increased transient terahertz transmission sign change of metallic compared to semiconductor materials.more » The results also suggest nanoscale gold films that utilize an adhesion material do not consist of distinct layers.« less

Markov chain sampling of the O(n) loop models on the infinite plane

NASA Astrophysics Data System (ADS)

Herdeiro, Victor

2017-07-01

A numerical method was recently proposed in Herdeiro and Doyon [Phys. Rev. E 94, 043322 (2016), 10.1103/PhysRevE.94.043322] showing a precise sampling of the infinite plane two-dimensional critical Ising model for finite lattice subsections. The present note extends the method to a larger class of models, namely the O(n) loop gas models for n ∈(1 ,2 ] . We argue that even though the Gibbs measure is nonlocal, it is factorizable on finite subsections when sufficient information on the loops touching the boundaries is stored. Our results attempt to show that provided an efficient Markov chain mixing algorithm and an improved discrete lattice dilation procedure the planar limit of the O(n) models can be numerically studied with efficiency similar to the Ising case. This confirms that scale invariance is the only requirement for the present numerical method to work.

Efficient field-theoretic simulation of polymer solutions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Villet, Michael C.; Fredrickson, Glenn H., E-mail: ghf@mrl.ucsb.edu; Department of Materials, University of California, Santa Barbara, California 93106

2014-12-14

We present several developments that facilitate the efficient field-theoretic simulation of polymers by complex Langevin sampling. A regularization scheme using finite Gaussian excluded volume interactions is used to derive a polymer solution model that appears free of ultraviolet divergences and hence is well-suited for lattice-discretized field theoretic simulation. We show that such models can exhibit ultraviolet sensitivity, a numerical pathology that dramatically increases sampling error in the continuum lattice limit, and further show that this pathology can be eliminated by appropriate model reformulation by variable transformation. We present an exponential time differencing algorithm for integrating complex Langevin equations for fieldmore » theoretic simulation, and show that the algorithm exhibits excellent accuracy and stability properties for our regularized polymer model. These developments collectively enable substantially more efficient field-theoretic simulation of polymers, and illustrate the importance of simultaneously addressing analytical and numerical pathologies when implementing such computations.« less

Setup for in situ x-ray diffraction study of swift heavy ion irradiated materials

NASA Astrophysics Data System (ADS)

Kulriya, P. K.; Singh, F.; Tripathi, A.; Ahuja, R.; Kothari, A.; Dutt, R. N.; Mishra, Y. K.; Kumar, Amit; Avasthi, D. K.

2007-11-01

An in situ x-ray diffraction (XRD) setup is designed and installed in the materials science beam line of the Pelletron accelerator at the Inter-University Accelerator Centre for in situ studies of phase change in swift heavy ion irradiated materials. A high vacuum chamber with suitable windows for incident and diffracted X-rays is integrated with the goniometer and the beamline. Indigenously made liquid nitrogen (LN2) temperature sample cooling unit is installed. The snapshots of growth of particles with fluence of 90MeV Ni ions were recorded using in situ XRD experiment, illustrating the potential of this in situ facility. A thin film of C60 was used to test the sample cooling unit. It shows that the phase of the C60 film transforms from a cubic lattice (at room temperature) to a fcc lattice at around T =255K.

Mechanism of oil bank formation, coalescence in porous media and emulsion and foam stability. Quarterly research progress report, July 1, 1984-September 30, 1984

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wasan, D.T.

The relative permeability model for two phase flow in porous media (Wasan 1983; Ramakrishnan and Wasan 1984) provides the necessary fractional flow curves at a given capillary number. These curves can be utilized in modeling both enhanced secondary and tertiary recovery processes. Important parameters in the fractional flow curves of our relative permeability model are the residual wetting and nonwetting phase saturations in a low capillary number flooding process. To understand, what constitutes the residual saturations, this quarter we have studied the displacement of one incompressible fluid by another in a porous medium using the network representation. The Bernoulli percolationmore » model for an infinite lattice graph is utilized in the interpretation of the capillary behavior of the medium, which ultimately determines residual saturations. The calculated capillary pressure-saturation relationship using Bethe lattice results agrees qualitatively with experimental data. 4 references, 2 figures.« less

Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd3Al5O12)

PubMed Central

Li, Ji-Guang; Sakka, Yoshio

2015-01-01

This review article summarizes the recent achievements in stabilization of the metastable lattice of gadolinium aluminate garnet (Gd3Al5O12, GAG) and the related developments of advanced optical materials, including down-conversion phosphors, up-conversion phosphors, transparent ceramics, and single crystals. Whenever possible, the materials are compared with their better known YAG and LuAG counterparts to demonstrate the merits of the GAG host. It is shown that novel emission features and significantly improved luminescence can be attained for a number of phosphor systems with the more covalent GAG lattice and the efficient energy transfer from Gd3+ to the activator. Ce3+ doped GAG-based single crystals and transparent ceramics are also shown to simultaneously possess the advantages of high theoretical density, fast scintillation decay, and high light yields, and hold great potential as scintillators for a wide range of applications. The unresolved issues are also pointed out. PMID:27877750

Forming a three-dimensional porous organic network via solid-state explosion of organic single crystals.

PubMed

Bae, Seo-Yoon; Kim, Dongwook; Shin, Dongbin; Mahmood, Javeed; Jeon, In-Yup; Jung, Sun-Min; Shin, Sun-Hee; Kim, Seok-Jin; Park, Noejung; Lah, Myoung Soo; Baek, Jong-Beom

2017-11-17

Solid-state reaction of organic molecules holds a considerable advantage over liquid-phase processes in the manufacturing industry. However, the research progress in exploring this benefit is largely staggering, which leaves few liquid-phase systems to work with. Here, we show a synthetic protocol for the formation of a three-dimensional porous organic network via solid-state explosion of organic single crystals. The explosive reaction is realized by the Bergman reaction (cycloaromatization) of three enediyne groups on 2,3,6,7,14,15-hexaethynyl-9,10-dihydro-9,10-[1,2]benzenoanthracene. The origin of the explosion is systematically studied using single-crystal X-ray diffraction and differential scanning calorimetry, along with high-speed camera and density functional theory calculations. The results suggest that the solid-state explosion is triggered by an abrupt change in lattice energy induced by release of primer molecules in the 2,3,6,7,14,15-hexaethynyl-9,10-dihydro-9,10-[1,2]benzenoanthracene crystal lattice.

From Lattice Boltzmann to hydrodynamics in dissipative relativistic fluids

NASA Astrophysics Data System (ADS)

Gabbana, Alessandro; Mendoza, Miller; Succi, Sauro; Tripiccione, Raffaele

2017-11-01

Relativistic fluid dynamics is currently applied to several fields of modern physics, covering many physical scales, from astrophysics, to atomic scales (e.g. in the study of effective 2D systems such as graphene) and further down to subnuclear scales (e.g. quark-gluon plasmas). This talk focuses on recent progress in the largely debated connection between kinetic transport coefficients and macroscopic hydrodynamic parameters in dissipative relativistic fluid dynamics. We use a new relativistic Lattice Boltzmann method (RLBM), able to handle from ultra-relativistic to almost non-relativistic flows, and obtain strong evidence that the Chapman-Enskog expansion provides the correct pathway from kinetic theory to hydrodynamics. This analysis confirms recently obtained theoretical results, which can be used to obtain accurate calibrations for RLBM methods applied to realistic physics systems in the relativistic regime. Using this calibration methodology, RLBM methods are able to deliver improved physical accuracy in the simulation of the physical systems described above. European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie Grant Agreement No. 642069.

Analysis of the Casson and Carreau-Yasuda non-Newtonian blood models in steady and oscillatory flows using the lattice Boltzmann method

NASA Astrophysics Data System (ADS)

Boyd, Joshua; Buick, James M.; Green, Simon

2007-09-01

The lattice Boltzmann method is modified to allow the simulation of non-Newtonian shear-dependent viscosity models. Casson and Carreau-Yasuda non-Newtonian blood viscosity models are implemented and are used to compare two-dimensional Newtonian and non-Newtonian flows in the context of simple steady flow and oscillatory flow in straight and curved pipe geometries. It is found that compared to analogous Newtonian flows, both the Casson and Carreau-Yasuda flows exhibit significant differences in the steady flow situation. In the straight pipe oscillatory flows, both models exhibit differences in velocity and shear, with the largest differences occurring at low Reynolds and Womersley numbers. Larger differences occur for the Casson model. In the curved pipe Carreau-Yasuda model, moderate differences are observed in the velocities in the central regions of the geometries, and the largest shear rate differences are observed near the geometry walls. These differences may be important for the study of atherosclerotic progression.

3D printed hierarchical honeycombs with shape integrity under large compressive deformations

DOE PAGES

Chen, Yanyu; Li, Tiantian; Jia, Zian; ...

2017-10-12

Here, we describe the in-plane compressive performance of a new type of hierarchical cellular structure created by replacing cell walls in regular honeycombs with triangular lattice configurations. The fabrication of this relatively complex material architecture with size features spanning from micrometer to centimeter is facilitated by the availability of commercial 3D printers. We apply to these hierarchical honeycombs a thermal treatment that facilitates the shape preservation and structural integrity of the structures under large compressive loading. The proposed hierarchical honeycombs exhibit a progressive failure mode, along with improved stiffness and energy absorption under uniaxial compression. High energy dissipation and shapemore » integrity at large imposed strains (up to 60%) have also been observed in these hierarchical honeycombs under cyclic loading. Experimental and numerical studies suggest that these anomalous mechanical behaviors are attributed to the introduction of a structural hierarchy, intrinsically controlled by the cell wall slenderness of the triangular lattice and by the shape memory effect induced by the thermal and mechanical compressive treatment.« less

Effects of laser immunotherapy on tumor microenvironment

NASA Astrophysics Data System (ADS)

Acquaviva, Joseph T.; Wood, Ethan W.; Hasanjee, Aamr; Chen, Wei R.; Vaughan, Melville B.

2014-02-01

The microenvironments of tumors are involved in a complex and reciprocal dialog with surrounding cancer cells. Any novel treatment must consider the impact of the therapy on the microenvironment. Recently, clinical trials with laser immunotherapy (LIT) have proven to effectively treat patients with late-stage, metastatic breast cancer and melanoma. LIT is the synergistic combination of phototherapy (laser irradiation) and immunological stimulation. One prominent cell type found in the tumor stroma is the fibroblast. Fibroblast cells can secrete different growth factors and extracellular matrix modifying molecules. Furthermore, fibroblast cells found in the tumor stroma often express alpha smooth muscle actin. These particular fibroblasts are coined cancer-associated fibroblast cells (CAFs). CAFs are known to facilitate the malignant progression of tumors. A collagen lattice assay with human fibroblast cells is used to elucidate the effects LIT has on the microenvironment of tumors. Changes in the contraction of the lattice, the differentiation of the fibroblast cells, as well as the proliferation of the fibroblast cells will be determined.

A principle of economy predicts the functional architecture of grid cells

PubMed Central

Wei, Xue-Xin; Prentice, Jason; Balasubramanian, Vijay

2015-01-01

Grid cells in the brain respond when an animal occupies a periodic lattice of ‘grid fields’ during navigation. Grids are organized in modules with different periodicity. We propose that the grid system implements a hierarchical code for space that economizes the number of neurons required to encode location with a given resolution across a range equal to the largest period. This theory predicts that (i) grid fields should lie on a triangular lattice, (ii) grid scales should follow a geometric progression, (iii) the ratio between adjacent grid scales should be √e for idealized neurons, and lie between 1.4 and 1.7 for realistic neurons, (iv) the scale ratio should vary modestly within and between animals. These results explain the measured grid structure in rodents. We also predict optimal organization in one and three dimensions, the number of modules, and, with added assumptions, the ratio between grid periods and field widths. DOI: http://dx.doi.org/10.7554/eLife.08362.001 PMID:26335200

Bandgap engineering in semiconductor alloy nanomaterials with widely tunable compositions

NASA Astrophysics Data System (ADS)

Ning, Cun-Zheng; Dou, Letian; Yang, Peidong

2017-12-01

Over the past decade, tremendous progress has been achieved in the development of nanoscale semiconductor materials with a wide range of bandgaps by alloying different individual semiconductors. These materials include traditional II-VI and III-V semiconductors and their alloys, inorganic and hybrid perovskites, and the newly emerging 2D materials. One important common feature of these materials is that their nanoscale dimensions result in a large tolerance to lattice mismatches within a monolithic structure of varying composition or between the substrate and target material, which enables us to achieve almost arbitrary control of the variation of the alloy composition. As a result, the bandgaps of these alloys can be widely tuned without the detrimental defects that are often unavoidable in bulk materials, which have a much more limited tolerance to lattice mismatches. This class of nanomaterials could have a far-reaching impact on a wide range of photonic applications, including tunable lasers, solid-state lighting, artificial photosynthesis and new solar cells.

3D printed hierarchical honeycombs with shape integrity under large compressive deformations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Yanyu; Li, Tiantian; Jia, Zian

Here, we describe the in-plane compressive performance of a new type of hierarchical cellular structure created by replacing cell walls in regular honeycombs with triangular lattice configurations. The fabrication of this relatively complex material architecture with size features spanning from micrometer to centimeter is facilitated by the availability of commercial 3D printers. We apply to these hierarchical honeycombs a thermal treatment that facilitates the shape preservation and structural integrity of the structures under large compressive loading. The proposed hierarchical honeycombs exhibit a progressive failure mode, along with improved stiffness and energy absorption under uniaxial compression. High energy dissipation and shapemore » integrity at large imposed strains (up to 60%) have also been observed in these hierarchical honeycombs under cyclic loading. Experimental and numerical studies suggest that these anomalous mechanical behaviors are attributed to the introduction of a structural hierarchy, intrinsically controlled by the cell wall slenderness of the triangular lattice and by the shape memory effect induced by the thermal and mechanical compressive treatment.« less

Experimental investigation of the ordering pathway in a Ni-33 at.%Cr alloy

DOE PAGES

Gwalani, B.; Alam, T.; Miller, C.; ...

2016-06-17

The present study involves a detailed experimental investigation of the concurrent compositional clustering and long-range ordering tendencies in a Ni-33 at.%Cr alloy, carried out by coupling synchrotron-based X-ray diffraction (XRD), transmission electron microscopy (TEM), and atom probe tomography (APT). Synchrotron-based XRD results clearly exhibited progressively increasing lattice contraction in the matrix with increasing isothermal aging time, at 475 degrees C, eventually leading to the development of long-range ordering (LRO) of the Pt2Mo-type. Detailed TEM and APT investigations revealed that this LRO in the matrix is manifested in the form of nanometer-scale ordered domains, and the spatial distribution, size, morphology andmore » compositional evolution of these domains have been carefully investigated. Here, the APT results also revealed the early stages of compositional clustering prior to the onset of long-range ordering in this alloy and such compositional clustering can potentially be correlated to the lattice contraction and previously proposed short-range ordering tendencies.« less

Synthesis of ktenasite, a double hydroxide of zinc and copper, and its intercalation reaction

NASA Astrophysics Data System (ADS)

Xue, Mei; Chitrakar, Ramesh; Sakane, Kohji; Ooi, Kenta; Kobayashi, Shoichi; Ohnishi, Masayuki; Doi, Akira

2004-04-01

Ktenasite was synthesized by the simple method of mixing ZnO powder with CuSO 4 solution at room temperature. The X-ray diffraction pattern of synthesized ktenasite was very similar to that of mineral ktenasite. The lattice parameters were determined as a=0.559, b=0.616, c=2.374 nm and β=95.63°, which agreed comparatively well with those for mineral ktenasite. The synthesized ktenasite consisted of thin rectangular particles ranging in size from 2 to 4 μm in length. TEM observation suggested the formation of a super lattice structure in the a-axis direction and significant crystal growth in the b-axis direction. The intercalation reaction of sodium dodecyl sulfate (NaDS) with ktenasite showed that the intercalation took place accompanied by the expansion of basal spacing from 1.17 to 2.70 nm. The reaction progressed by the SO 42-/DS - anion exchange mechanism with the dissolution of interlayer [Zn(H 2O) 6]SO 4 salt.

Soliton motion in a parametrically ac-driven damped Toda lattice

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rasmussen, K.O.; Malomed, B.A.; Bishop, A.R.

We demonstrate that a staggered parametric ac driving term can support stable progressive motion of a soliton in a Toda lattice with friction, while an unstaggered driving force cannot. A physical context of the model is that of a chain of anharmonically coupled particles adsorbed on a solid surface of a finite size. The ac driving force is generated by a standing acoustic wave excited on the surface. Simulations demonstrate that the state left behind the moving soliton, with the particles shifted from their equilibrium positions, gradually relaxes back to the equilibrium state that existed before the passage of themore » soliton. The perturbation theory predicts that the ac-driven soliton exists if the amplitude of the drive exceeds a certain threshold. The analytical prediction for the threshold is in reasonable agreement with that found numerically. Collisions between two counterpropagating solitons is also simulated, demonstrating that the collisions are, effectively, fully elastic. {copyright} {ital 1998} {ital The American Physical Society}« less

Recent progress in advanced optical materials based on gadolinium aluminate garnet (Gd3Al5O12)

NASA Astrophysics Data System (ADS)

Li, Ji-Guang; Sakka, Yoshio

2015-02-01

This review article summarizes the recent achievements in stabilization of the metastable lattice of gadolinium aluminate garnet (Gd3Al5O12, GAG) and the related developments of advanced optical materials, including down-conversion phosphors, up-conversion phosphors, transparent ceramics, and single crystals. Whenever possible, the materials are compared with their better known YAG and LuAG counterparts to demonstrate the merits of the GAG host. It is shown that novel emission features and significantly improved luminescence can be attained for a number of phosphor systems with the more covalent GAG lattice and the efficient energy transfer from Gd3+ to the activator. Ce3+ doped GAG-based single crystals and transparent ceramics are also shown to simultaneously possess the advantages of high theoretical density, fast scintillation decay, and high light yields, and hold great potential as scintillators for a wide range of applications. The unresolved issues are also pointed out.

Structural Benchmark Testing of Superalloy Lattice Block Subelements Completed

NASA Technical Reports Server (NTRS)

2004-01-01

Superalloy lattice block panels, which are produced directly by investment casting, are composed of thin ligaments arranged in three-dimensional triangulated trusslike structures (see the preceding figure). Optionally, solid panel face sheets can be formed integrally during casting. In either form, lattice block panels can easily be produced with weights less than 25 percent of the mass of a solid panel. Inconel 718 (IN 718) and MarM-247 superalloy lattice block panels have been developed under NASA's Ultra-Efficient Engine Technology Project and Higher Operating Temperature Propulsion Components Project to take advantage of the superalloys' high strength and elevated temperature capability with the inherent light weight and high stiffness of the lattice architecture (ref. 1). These characteristics are important in the future development of turbine engine components. Casting quality and structural efficiency were evaluated experimentally using small beam specimens machined from the cast and heat treated 140- by 300- by 11-mm panels. The matrix of specimens included samples of each superalloy in both open-celled and single-face-sheet configurations, machined from longitudinal, transverse, and diagonal panel orientations. Thirty-five beam subelements were tested in Glenn's Life Prediction Branch's material test machine at room temperature and 650 C under both static (see the following photograph) and cyclic load conditions. Surprisingly, test results exceeded initial linear elastic analytical predictions. This was likely a result of the formation of plastic hinges and redundancies inherent in lattice block geometry, which was not considered in the finite element models. The value of a single face sheet was demonstrated by increased bending moment capacity, where the face sheet simultaneously increased the gross section modulus and braced the compression ligaments against early buckling as seen in open-cell specimens. Preexisting flaws in specimens were not a discriminator in flexural, shear, or stiffness measurements, again because of redundant load paths available in the lattice block structure. Early test results are available in references 2 and 3; more complete analyses are scheduled for publication in 2004.

Phase stability and lattice thermal conductivity reduction in CoSb{sub 3} skutterudites, doped with chalcogen atoms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Battabyal, M., E-mail: manjusha.battabyal@project.arci.res.in; Priyadarshini, B.; Gopalan, R.

We report a significant reduction in the lattice thermal conductivity of the CoSb{sub 3} skuttertudites, doped with chalcogen atoms. Te/Se chalcogen atoms doped CoSb{sub 3} skutterudite samples (Te{sub 0.1}Co{sub 4}Sb{sub 12}, Se{sub 0.1}Co{sub 4}Sb{sub 12}, Te{sub 0.05}Se{sub 0.05}Co{sub 4}Sb{sub 12}) are processed by ball milling and spark plasma sintering. X-ray diffraction data combined with energy dispersive X-ray spectra indicate the doping of Te/Se chalcogen atoms in the skutterudite. The temperature dependent X-ray diffraction confirms the stability of the Te/Se doped CoSb{sub 3} skutterudite phase and absence of any secondary phase in the temperature range starting from 300 K to 773more » K. The Raman spectroscopy reveals that different chalcogen dopant atoms cause different resonant optical vibrational modes between the dopant atom and the host CoSb{sub 3} skutterudite lattice. These optical vibrational modes do scatter heat carrying acoustic phonons in a different spectral range. It was found that among the Te/Se chalcogen atoms, Te atoms alter the host CoSb{sub 3} skutterudite lattice vibrations to a larger extent than Se atoms, and can potentially scatter more Sb related acoustic phonons. The Debye model of lattice thermal conductivity confirms that the resonant phonon scattering has important contributions to the reduction of lattice thermal conductivity in CoSb{sub 3} skutterudites doped with Te/Se chalcogen atoms. Lattice thermal conductivity ∼ 0.9 W/mK at 773 K is achieved in Te{sub 0.1}Co{sub 4}Sb{sub 12} skutterudites, which is the lowest value reported so far in CoSb{sub 3} skutterudites, doped with single Te chalcogen atom.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Pengfei; Nie, Anmin; Zheng, Jianming

Voltage and capacity fading of layer structured lithium and manganese rich (LMR) transition metal oxide is directly related to the structural and composition evolution of the material during the cycling of the battery. However, understanding such evolution at atomic level remains elusive. Based on atomic level structural imaging, elemental mapping of the pristine and cycled samples and density functional theory calculations, it is found that accompanying the hoping of Li ions is the simultaneous migration of Ni ions towards the surface from the bulk lattice, leading to the gradual depletion of Ni in the bulk lattice and thickening of amore » Ni enriched surface reconstruction layer (SRL). Furthermore, Ni and Mn also exhibit concentration partitions within the thin layer of SRL in the cycled samples where Ni is almost depleted at the very surface of the SRL, indicating the preferential dissolution of Ni ions in the electrolyte. Accompanying the elemental composition evolution, significant structural evolution is also observed and identified as a sequential phase transition of C2/m →I41→Spinel. For the first time, it is found that the surface facet terminated with pure cation is more stable than that with a mixture of cation and anion. These findings firmly established how the elemental species in the lattice of LMR cathode transfer from the bulk lattice to surface layer and further into the electrolyte, clarifying the long standing confusion and debate on the structure and chemistry of the surface layer and their correlation with the voltage fading and capacity decaying of LMR cathode. Therefore, this work provides critical insights for designing of cathode materials with both high capacity and voltage stability during cycling.« less

Imaging system design for improved information capacity

NASA Technical Reports Server (NTRS)

Fales, C. L.; Huck, F. O.; Samms, R. W.

1984-01-01

Shannon's theory of information for communication channels is used to assess the performance of line-scan and sensor-array imaging systems and to optimize the design trade-offs involving sensitivity, spatial response, and sampling intervals. Formulations and computational evaluations account for spatial responses typical of line-scan and sensor-array mechanisms, lens diffraction and transmittance shading, defocus blur, and square and hexagonal sampling lattices.

Nano crystalline Bi2(VO5) phases in lithium bismuth borate glasses containing mixed vanadium-nickel oxides

NASA Astrophysics Data System (ADS)

Yadav, Arti; Khasa, S.; Dahiya, M. S.; Agarwal, A.

2016-05-01

Glass composition 7V2O5.23Li2O.20Bi2O3.50B2O3 and x(2NiO.V2O5).(30-x)Li2O.20Bi2O3.50B2O3, x=0, 2, 5, 7 and 10, were produced by conventional melt quenching technique. The quenched amorphous glass samples were annealed at temperatures 400°C and 500°C for 6 hours. The Bi2(VO5) crystallite were grown in all prepared glass matrix. Tn vanadium lithium bismuth borate glass (annealed), the some phrase of V2O5-crystal were observed along with the nano crystalline Bi2(VO5) phase. The sharp peaks in FTTR spectra of all annealed compositions were also compatible with the XRD diffraction peaks of the system under investigation. Average crystalline size (D) of the Bi2(VO5) nano-crystallite was ~30nm for samples annealed at 400°C and ~42nm for samples annealed at 500°C. Lattice parameter and the lattice strain for all the samples was also calculated corresponding to the (113) plane of Bi2(VO5) crystallite.

Dynamic Structural Changes of SiO₂ Supported Pt-Ni Bimetallic Catalysts over Redox Treatments Revealed by NMR and EPR

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Suochang; Walter, Eric D.; Zhao, Zhenchao

2015-08-18

SiO 2 supported Pt-Ni bimetallic catalysts with different nickel loadings were prepared and their structural changes after redox treatments were studied by XRD, NMR, and EPR. It is found that the paramagnetic Ni species are mainly located on the surface of silica lattice. The relaxation of detected 29Si nuclei in our samples is mainly governed by a spin-diffusion mechanism. The paramagnetic effects are reflected in the spin-lattice relaxation of Q 4 species, with the oxidized samples presenting faster relaxation rates than the corresponding reduced ones. Meanwhile the Q 3 species, which are in close contact with the paramagnetic nickel ions,more » are “spectrally invisible”. In reducing atmosphere Ni gradually diffuses into Pt NPs to form PtNi alloys. While under oxidization treatment, the alloyed Ni atoms migrate outward from the core of Pt NPs and are oxidized. The main EPR spectrum results from reduced nickel species, and the reduced samples show stronger EPR signal than the corresponding oxidized ones. However, in the reduced samples, the superparamagnetic or ferromagnetic metallic Ni particles were inside the PtNi NPs, making their influence on the 29Si relaxation in the SiO 2 support weaker than the oxidized samples.« less

Low field magnetocaloric effect in bulk and ribbon alloy La(Fe0.88Si0.12)13

NASA Astrophysics Data System (ADS)

Vuong, Van-Hiep; Do-Thi, Kim-Anh; Nguyen, Duy-Thien; Nguyen, Quang-Hoa; Hoang, Nam-Nhat

2018-03-01

Low-field magnetocaloric effect occurred in itinerant metamagnetic materials is at core for magnetic cooling application. This works reports the magnetocaloric responses obtained at 1.35 T for the silicon-doped iron-based binary alloy La(Fe0.88Si0.12)13 in the bulk and ribbon form. Both samples possess a same symmetry but with different crystallite sizes and lattice parameters. The ribbon sample shows a larger maximum entropy change (nearly 8.5 times larger) and a higher Curie temperature (5 K higher) in comparison with that of the bulk sample. The obtained relative cooling power for the ribbon is also larger and very promising for application (RCP = 153 J/kg versus 25.2 J/kg for the bulk). The origin of the effect observed is assigned to the occurrence of negative magnetovolume effect in the ribbon structure with limit crystallization, caused by rapid cooling process at the preparation, which induced smaller crystallite size and large lattice constant at the overall weaker local crystal field.

2.7 MeV Ar11+ ion irradiation induced structural evolution in Lu2(Ti2-xLux)O7-x/2 pyrochlores

NASA Astrophysics Data System (ADS)

Yang, D. Y.; Liu, C. G.; Zhang, K. Q.; Xia, Y.; Chen, L. J.; Liu, H.; Li, Y. H.

2015-11-01

This paper aims to study the radiation effects of nonstoichiometric pyrochlore series Lu2(Ti2-xLux)O7-x/2 (x = 0-0.667). Polycrystalline Lu2(Ti2-xLux)O7-x/2 samples were irradiated with 2.7 MeV Ar11+ ions up to a fluence of 8 × 1014 ions/cm2. The irradiated samples were characterized using grazing incidence X-ray diffraction technique. The results reveal that Lu2(Ti2-xLux)O7-x/2 samples undergo significant amorphization and lattice swelling upon irradiation. Specifically, the amorphization process is predominantly driven by ballistic nuclear energy deposition of Ar11+ ions at this energy regime, which can be well described by a direct-impact/defect-stimulated model. Both the amorphization fraction and the relative variation of lattice parameter decrease with increasing x, showing a strong dependence on the chemical composition. The results are then discussed in the framework of the structural disorder and recovery ability from damage, applying an atomic layer model.

Al3+ ions dependent structural and magnetic properties of Co-Ni nano-alloys.

PubMed

Kadam, R H; Alone, Suresh T; Gaikwad, Anil S; Birajdar, A P; Shirsath, Sagar E

2014-06-01

Ferrite samples with a chemical formula Co0.5Ni0.5Al(x)Fe(2-x)O4 (where x = 0.0, 0.25, 0.5, 0.75 and 1.0) were synthesized by sol-gel auto-combustion method. The synthesized samples were annealed at 600 degrees C for 4 h. An analysis of X-ray diffraction (XRD) patterns reveals the formation of single phase cubic spinel structure. The lattice parameter decreased linearly with the increasing Al content x. Nano size of the powders were confirmed by the transmission electron micrographs (TEM). Particle size, bulk density decreased whereas specific surface area and porosity of the samples increased with the Al substitution. Cation distribution of constituent ions shows linear dependence of Al substitution. Based on the cation distribution obtained from XRD data, structural parameters such as lattice parameters, ionic radii of available sites and the oxygen parameter 'u' is calculated. Saturation magnetization (M(s)), magneton number (n(B)) and coercivity (H(c)) decreased with the Al substitution. Possible explanation for the observed structural and magnetic behavior with various Al content are discussed.

Simultaneous X-ray and neutron diffraction Rietveld refinements of nanophase iron substituted hydroxyapatite

NASA Astrophysics Data System (ADS)

Kyriacou, Andreas

The effect of Fe substitution on the crystal structure of hydroxyapatite (HAp) is studied by applying simultaneous Rietveld refinements of powder x-ray and neutron diffraction patterns. Fe is one of the trace elements replacing Ca in HAp, which is the major mineral phase in bones and teeth. The morphology and magnetic properties of the Fe-HAp system are also studied by transmission electron microscopy and magnetization measurements. Samples of Ca(5-x)Fex(PO4)3OH with 0 ≤ x ≤ 0.3 were prepared. Single phase HAp was identified in x-ray diffraction patterns (XRD) of samples with x < 0.1 inferring that the solubility limits are less than 0.1. Hematite (alpha-Fe2O3) is identified as a secondary phase for higher Fe content. The refined parameters show that Fe is incorporated in the HAp structure by replacing Ca in the two crystallographic sites with a preference at the Ca2 site. This preference explains the small effect of the Fe substitution on the lattice constants of HAp. The overall decrease of the lattice constants is explained by the ionic size difference of Ca and Fe. The increasing trend of the a-lattice constant with x in the Fe substituted samples is attributed to a lattice relaxation caused by the substitution of the 4- and 6-fold Fe at the 7- and 9-fold Ca1 and Ca2 sites. This Ca local geometry reduction is indicated by a slight increase of the Ca1-O3 and Ca2-O1 bond lengths. Above the solubility limit x = 0.05, the Fe is partitioned in and out of the HAp structure with increasing nominal Fe content x. The excess Fe is oxidized to hematite. The TEM analysis and magnetic measurements support the results of the simultaneous Rietveld refinements. The TEM images show no significant effect on the morphology and size of the HAp particles upon Fe incorporation. The particles are either spheres or short rods of dimensions 20--60 nm. Hematite particles are imaged in the samples with x exceeding the solubility limit. These particles are spheres, about 15 nm in diameter and are more resistant to electron beam damage. Magnetic measurements reveal a transition of the diamagnetic pure HAp to paramagnetic Fe substituted HAp.

Microwave (EPR) measurements of the penetration depth measurements of high-Tc superconductors

NASA Technical Reports Server (NTRS)

Dalal, N. S.; Rakvin, B.; Mahl, T. A.; Bhalla, A. S.; Sheng, Z. Z.

1991-01-01

The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T sub c superconductors. The method uses the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T sub c is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, neutron scattering, and magnetic susceptibility.

An EPR methodology for measuring the London penetration depth for the ceramic superconductors

NASA Technical Reports Server (NTRS)

Rakvin, B.; Mahl, T. A.; Dalal, N. S.

1990-01-01

The use is discussed of electron paramagnetic resonance (EPR) as a quick and easily accessible method for measuring the London penetration depth, lambda for the high T(sub c) superconductors. The method utilizes the broadening of the EPR signal, due to the emergence of the magnetic flux lattice, of a free radical adsorbed on the surface of the sample. The second moment, of the EPR signal below T(sub c) is fitted to the Brandt equation for a simple triangular lattice. The precision of this method compares quite favorably with those of the more standard methods such as micro sup(+)SR, Neutron scattering, and magnetic susceptibility.

Green synthesis of Si-incorporated hydroxyapatite using sodium metasilicate as silicon precursor and in vitro antibiotic release studies.

PubMed

Abinaya Sindu, P; Kolanthai, Elayaraja; Suganthi, R V; Thanigai Arul, K; Manikandan, E; Catalani, Luiz H; Narayana Kalkura, S

2017-10-01

The aim of the current study is to synthesize nanosized silicon incorporated HAp (Si-HAP) using sodium metasilicate as the silicon source. The sol-gel derived samples were further subjected to microwave irradiation. Incorporation of Si into HAp did not alter the HAp phase, as confirmed by the X-ray diffraction analysis (XRD). Moreover, variation in the lattice parameters of the Si-incorporated HAp indicates that Si is substituted into the HAp lattice. The decrease in the intensity of the peaks attributed to hydroxyl groups, which appeared in the FTIR and Raman spectra of Si-HAp, further confirms the Si substitution in HAp lattices. The silicon incorporation enhanced the nanorods length by 70%, when compared to that of pure HAp. Microwave irradiation improved the crystallinity of Si-HAp when compared to as-synthesized Si-HAp samples. As-synthesized Si-incorporated HAp sample showed an intense blue emission under UV excitation. Microwave irradiation reduced the intensity of blue emission and exhibited red shift due to the reduction of defects in the Si-HAp crystal. The morphological change from rod to spherical and ribbon-like forms was observed with an increase in silicon content. Further, Si-HAp exhibited better bioactivity and low dissolution rate. Initially there was a burst release of amoxicillin from all the samples, subsequently it followed a sustained release. The microwave-irradiated HAp showed extended period of sustained release than that of as-synthesized HAp and Si-HAp. Similarly, the microwave-irradiated Si-incorporated samples exhibited prolonged drug release, as compared to that of the as-synthesized samples. Hence, Si-HAp is rapidly synthesized by a simple and cost effective method without inducing any additional phases, as compared to the conventional sintering process. This study provides a new insight into the rapid green synthesis of Si-HAp. Si-HAp could emerge as a promising material for the bone tissue replacement and as a drug delivery system. Copyright © 2017 Elsevier B.V. All rights reserved.

Ferromagnetic Potts models with multisite interaction

NASA Astrophysics Data System (ADS)

Schreiber, Nir; Cohen, Reuven; Haber, Simi

2018-03-01

We study the q -state Potts model with four-site interaction on a square lattice. Based on the asymptotic behavior of lattice animals, it is argued that when q ≤4 the system exhibits a second-order phase transition and when q >4 the transition is first order. The q =4 model is borderline. We find 1 /lnq to be an upper bound on Tc, the exact critical temperature. Using a low-temperature expansion, we show that 1 /(θ lnq ) , where θ >1 is a q -dependent geometrical term, is an improved upper bound on Tc. In fact, our findings support Tc=1 /(θ lnq ) . This expression is used to estimate the finite correlation length in first-order transition systems. These results can be extended to other lattices. Our theoretical predictions are confirmed numerically by an extensive study of the four-site interaction model using the Wang-Landau entropic sampling method for q =3 ,4 ,5 . In particular, the q =4 model shows an ambiguous finite-size pseudocritical behavior.

Tunable Quantum Spin Liquidity in the 1 /6 th-Filled Breathing Kagome Lattice

NASA Astrophysics Data System (ADS)

Akbari-Sharbaf, A.; Sinclair, R.; Verrier, A.; Ziat, D.; Zhou, H. D.; Sun, X. F.; Quilliam, J. A.

2018-06-01

We present measurements on a series of materials, Li2 In1 -xScx Mo3 O8 , that can be described as a 1 /6 th-filled breathing kagome lattice. Substituting Sc for In generates chemical pressure which alters the breathing parameter nonmonotonically. Muon spin rotation experiments show that this chemical pressure tunes the system from antiferromagnetic long range order to a quantum spin liquid phase. A strong correlation with the breathing parameter implies that it is the dominant parameter controlling the level of magnetic frustration, with increased kagome symmetry generating the quantum spin liquid phase. Magnetic susceptibility measurements suggest that this is related to distinct types of charge order induced by changes in lattice symmetry, in line with the theory of Chen et al. [Phys. Rev. B 93, 245134 (2016), 10.1103/PhysRevB.93.245134]. The specific heat for samples at intermediate Sc concentration, which have the minimum breathing parameter, show consistency with the predicted U (1 ) quantum spin liquid.

Universal properties of knotted polymer rings.

PubMed

Baiesi, M; Orlandini, E

2012-09-01

By performing Monte Carlo sampling of N-steps self-avoiding polygons embedded on different Bravais lattices we explore the robustness of universality in the entropic, metric, and geometrical properties of knotted polymer rings. In particular, by simulating polygons with N up to 10(5) we furnish a sharp estimate of the asymptotic values of the knot probability ratios and show their independence on the lattice type. This universal feature was previously suggested, although with different estimates of the asymptotic values. In addition, we show that the scaling behavior of the mean-squared radius of gyration of polygons depends on their knot type only through its correction to scaling. Finally, as a measure of the geometrical self-entanglement of the self-avoiding polygons we consider the standard deviation of the writhe distribution and estimate its power-law behavior in the large N limit. The estimates of the power exponent do depend neither on the lattice nor on the knot type, strongly supporting an extension of the universality property to some features of the geometrical entanglement.

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

NASA Astrophysics Data System (ADS)

Sivakami, R.; Dhanuskodi, S.; Karvembu, R.

2016-01-01

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 3.55 eV. BET measurements show a high specific surface area (SSA) of 118-133 m2/g and pore diameter (10-25 nm) 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.

Bohman-Frieze-Wormald model on the lattice, yielding a discontinuous percolation transition

NASA Astrophysics Data System (ADS)

Schrenk, K. J.; Felder, A.; Deflorin, S.; Araújo, N. A. M.; D'Souza, R. M.; Herrmann, H. J.

2012-03-01

The BFW model introduced by Bohman, Frieze, and Wormald [Random Struct. Algorithms1042-983210.1002/rsa.20038, 25, 432 (2004)], and recently investigated in the framework of discontinuous percolation by Chen and D'Souza [Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.106.115701 106, 115701 (2011)], is studied on the square and simple-cubic lattices. In two and three dimensions, we find numerical evidence for a strongly discontinuous transition. In two dimensions, the clusters at the threshold are compact with a fractal surface of fractal dimension df=1.49±0.02. On the simple-cubic lattice, distinct jumps in the size of the largest cluster are observed. We proceed to analyze the tree-like version of the model, where only merging bonds are sampled, for dimension two to seven. The transition is again discontinuous in any considered dimension. Finally, the dependence of the cluster-size distribution at the threshold on the spatial dimension is also investigated.

Gamma-irradiation effect on a commercial composite anticorrosive pigment and acidity-to-alkalinity conversion

NASA Astrophysics Data System (ADS)

Song, Weiqiang; Niu, Kaihui; Wu, Longchao

2016-05-01

A commercial composite anticorrosive pigment based on aluminum dihydrogen tripolyphosphate was studied after exposure to gamma irradiation (Co60, 0, 20, 50, 100 and 150 kGy) using FTIR, XRD, TGA and acid-base titration technologies. Although the FTIR spectra showed that the effect of the irradiation on functional groups in the pigments was not obvious, the decrease in the crystal lattice parameters of the irradiated pigments was observed in the XRD spectra compared to the non-irradiated sample. But the extent of the lattice parameter decrease monotonically with the increase of absorbed dose from 20 to 150 kGy, which was attributed to the decomposition of water and the simultaneous occurrence of lattice damage when the pigments were exposed to gamma rays. Of particular significance was the displayed basicity of the aqueous solutions of the irradiated pigments compared to the acidity of the solution of the non-irradiated pigment, which was attributed to the decomposition of P-OH groups (combined water).

Electric transport through circular graphene quantum dots: Presence of disorder

NASA Astrophysics Data System (ADS)

Pal, G.; Apel, W.; Schweitzer, L.

2011-08-01

The electronic states of an electrostatically confined cylindrical graphene quantum dot and the electric transport through this device are studied theoretically within the continuum Dirac-equation approximation and compared with numerical results obtained from a tight-binding lattice description. A spectral gap, which may originate from strain effects, additional adsorbed atoms, or substrate-induced sublattice-symmetry breaking, allows for bound and scattering states. As long as the diameter of the dot is much larger than the lattice constant, the results of the continuum and the lattice model are in very good agreement. We also investigate the influence of a sloping dot-potential step, of on-site disorder along the sample edges, of uncorrelated short-range disorder potentials in the bulk, and of random magnetic fluxes that mimic ripple disorder. The quantum dot's spectral and transport properties depend crucially on the specific type of disorder. In general, the peaks in the density of bound states are broadened but remain sharp only in the case of edge disorder.

A scanning tunneling microscope for a dilution refrigerator.

PubMed

Marz, M; Goll, G; Löhneysen, H v

2010-04-01

We present the main features of a home-built scanning tunneling microscope that has been attached to the mixing chamber of a dilution refrigerator. It allows scanning tunneling microscopy and spectroscopy measurements down to the base temperature of the cryostat, T approximately 30 mK, and in applied magnetic fields up to 13 T. The topography of both highly ordered pyrolytic graphite and the dichalcogenide superconductor NbSe(2) has been imaged with atomic resolution down to T approximately 50 mK as determined from a resistance thermometer adjacent to the sample. As a test for a successful operation in magnetic fields, the flux-line lattice of superconducting NbSe(2) in low magnetic fields has been studied. The lattice constant of the Abrikosov lattice shows the expected field dependence proportional to 1/square root of B and measurements in the scanning tunneling spectroscopy mode clearly show the superconductive density of states with Andreev bound states in the vortex core.

Structural analysis of as-deposited and annealed low-temperature gallium arsenide

NASA Astrophysics Data System (ADS)

Matyi, R. J.; Melloch, M. R.; Woodall, J. M.

1993-04-01

The structure of GaAs grown at low substrate temperatures (LT-GaAs) by molecular beam epitaxy has been studied using high resolution X-ray diffraction methods. Double crystal rocking curves from the as-deposited LT-GaAs show well defined interference fringes, indicating a high level of structural perfection. Triple crystal diffraction analysis of the as-deposited sample showed significantly less diffuse scattering near the LT-GaAs 004 reciprocal lattice point compared with the substrate 004 reciprocal lattice point, suggesting that despite the incorporation of approximately 1% excess arsenic, the epitaxial layer had superior crystalline perfection than did the GaAs substrate. Triple crystal scans of annealed LT-GaAs showed an increase in the integrated diffuse intensity by approximately a factor of three as the anneal temperature was increased from 700 to 900°C. Analogous to the effects of SiO2 precipitates in annealed Czochralski silicon, the diffuse intensity is attributed to distortions in the epitaxial LT-GaAs lattice by arsenic precipitates.

Enhanced thermoelectric property of oxygen deficient nickel doped SnO2 for high temperature application

NASA Astrophysics Data System (ADS)

Paulson, Anju; Sabeer, N. A. Muhammad; Pradyumnan, P. P.

2018-04-01

Motivated by the detailed investigation on the thermoelectric performance of oxide materials our work concentrated on the influence of acceptor dopants and defect density in the lattice plane for the enhancement of thermoelectric power. The series of Sn1‑x Nix O2 (0.01 ≤ x ≤ 0.05) compositions were prepared by solid state reaction mechanism and found that 3 atomic percentage Ni doped SnO2 can be considered as a good candidate due to its promising electrical and transport properties. Defect lattices were introduced in the sample and the deviation from oxygen stochiometry was ensured using photoluminescence measurement. High power factor was obtained for the 3 atomic percentage nickel doped SnO2 due to the effective number of charge carrier concentration and the depletion of oxygen rich layers. Defect centered and acceptor doped SnO2 lattice opens a new door for energy harvesting at higher temperatures.

Nonlinear stochastic interacting dynamics and complexity of financial gasket fractal-like lattice percolation

NASA Astrophysics Data System (ADS)

Zhang, Wei; Wang, Jun

2018-05-01

A novel nonlinear stochastic interacting price dynamics is proposed and investigated by the bond percolation on Sierpinski gasket fractal-like lattice, aim to make a new approach to reproduce and study the complexity dynamics of real security markets. Fractal-like lattices correspond to finite graphs with vertices and edges, which are similar to fractals, and Sierpinski gasket is a well-known example of fractals. Fractional ordinal array entropy and fractional ordinal array complexity are introduced to analyze the complexity behaviors of financial signals. To deeper comprehend the fluctuation characteristics of the stochastic price evolution, the complexity analysis of random logarithmic returns and volatility are preformed, including power-law distribution, fractional sample entropy and fractional ordinal array complexity. For further verifying the rationality and validity of the developed stochastic price evolution, the actual security market dataset are also studied with the same statistical methods for comparison. The empirical results show that this stochastic price dynamics can reconstruct complexity behaviors of the actual security markets to some extent.

Defect chemistry and characterization of Hg sub 1x Cd sub x Te

NASA Technical Reports Server (NTRS)

Vydyanath, H. R.

1982-01-01

Single crystal samples of undoped and doped Hg sub 1-x Cd sub x Te were annealed at varying temperatures and partial pressures of Hg. Hall effect and mobility measurements were carried out on these samples after quenching to room temperature. Based on the variation of the carrier concentration and the carrier mobility as a function of the partial pressure of Hg temperature, and dopant concentration, defect models were established for the doped and the undoped crystals. These models indicate that the native acceptor defects in both Hg0.8Cd0.2Te and Hg0.6Cd0.4Te doubly ionized and the native donor defects are negligible in concentration, implying that p to n conversion in these alloys occurs due only to residual donors. Incorporation mechanism of copper, indium, iodine, and phosphorus were investigated. A large concentration of indium is found to be paired with the native acceptor defects. Results on crystals doped with phosphorus indicate that phosphorus behaves amphoterically, acting as a donor on Hg lattice sites and as an acceptor intersitially on Te lattice sites. A majority of the phosphorus is found to be present as neutral species formed from the pairing reaction between phosphorus on Hg lattice sites and phosphorus in interstitial sites. Equilibrium constants for the intrinsic excitation reaction, as well as for the incorporation of the different dopants and the native acceptor defects were established.

Transient NOE enhancement in solid-state MAS NMR of mobile systems

NASA Astrophysics Data System (ADS)

Cui, Jiangyu; Li, Jun; Peng, Xinhua; Fu, Riqiang

2017-11-01

It has been known that the heteronuclear cross-relaxation affects the dilute S spin magnetization along the longitudinal direction, causing an overshoot phenomenon for those mobile systems in spin-lattice relaxation rate measurements. Here, we analyze the Solomon equations for an I-S system and derive the transient cross relaxation effect as to when an overshoot phenomenon would take place and what the maximum enhancement could be at the time of the overshoot. In order to utilize such a transient nuclear Overhauser effect (NOE), we first time apply it to dynamic solid samples by inverting the 1H magnetization prior to the excitation of the S spin. It is found that the overshoot depends on the ratio of the I and S spin-lattice relaxation rates, i.e. RSS /RII . When RSS /RII ≫ 1 , the maximum enhancement factor for transient NOE could be larger than that obtained in steady-state NOE experiments. Furthermore, transient NOE appears to be more efficient in terms of sensitivity enhancement of dilute spins in solid-state NMR of mobile systems than the traditional cross polarization scheme whose efficiency is greatly compromised by molecular mobility. A sample of natural abundance L-isoleucine amino acid, in which the spin-lattice relaxation rates for the four methyl carbons are different, has been used to demonstrate sensitivity enhancement factors under various experimental schemes.

Quantitative x-ray diffraction analysis of bimodal damage distributions in Tm implanted Al0.15Ga0.85N

NASA Astrophysics Data System (ADS)

Magalhães, S.; Fialho, M.; Peres, M.; Lorenz, K.; Alves, E.

2016-04-01

In this work radial symmetric x-ray diffraction scans of Al0.15Ga0.85N thin films implanted with Tm ions were measured to determine the lattice deformation and crystal quality as functions of depth. The alloys were implanted with 300 keV Tm with 10° off-set to the sample normal to avoid channelling, with fluences varying between 1013 Tm cm-2 and 5  ×  1015 Tm cm-2. Simulations of the radial 2θ-ω scans were performed under the frame of the dynamical theory of x-ray diffraction assuming Gaussian distributions of the lattice strain induced by implantation defects. The structure factor of the individual layers is multiplied by a static Debye-Waller factor in order to take into account the effect of lattice disorder due to implantation. For higher fluences two asymmetric Gaussians are required to describe well the experimental diffractograms, although a single asymmetric Gaussian profile for the deformation is found in the sample implanted with 1013 Tm cm-2. After thermal treatment at 1200 °C, the crystal quality partially recovers as seen in a reduction of the amplitude of the deformation maximum as well as the total thickness of the deformed layer. Furthermore, no evidence of changes with respect to the virgin crystal mosaicity is found after implantation and annealing.

Monte Carlo simulations of backscattering process in dislocation-containing SrTiO3 single crystal

NASA Astrophysics Data System (ADS)

Jozwik, P.; Sathish, N.; Nowicki, L.; Jagielski, J.; Turos, A.; Kovarik, L.; Arey, B.

2014-05-01

Studies of defects formation in crystals are of obvious importance in electronics, nuclear engineering and other disciplines where materials are exposed to different forms of irradiation. Rutherford Backscattering/Channeling (RBS/C) and Monte Carlo (MC) simulations are the most convenient tool for this purpose, as they allow one to determine several features of lattice defects: their type, concentration and damage accumulation kinetic. On the other hand various irradiation conditions can be efficiently modeled by ion irradiation method without leading to the radioactivity of the sample. Combination of ion irradiation with channeling experiment and MC simulations appears thus as a most versatile method in studies of radiation damage in materials. The paper presents the results on such a study performed on SrTiO3 (STO) single crystals irradiated with 320 keV Ar ions. The samples were analyzed also by using HRTEM as a complementary method which enables the measurement of geometrical parameters of crystal lattice deformation in the vicinity of dislocations. Once the parameters and their variations within the distance of several lattice constants from the dislocation core are known, they may be used in MC simulations for the quantitative determination of dislocation depth distribution profiles. The final outcome of the deconvolution procedure are cross-sections values calculated for two types of defects observed (RDA and dislocations).

Parasol cell mosaics are unlikely to drive the formation of structured orientation maps in primary visual cortex.

PubMed

Hore, Victoria R A; Troy, John B; Eglen, Stephen J

2012-11-01

The receptive fields of on- and off-center parasol cell mosaics independently tile the retina to ensure efficient sampling of visual space. A recent theoretical model represented the on- and off-center mosaics by noisy hexagonal lattices of slightly different density. When the two lattices are overlaid, long-range Moiré interference patterns are generated. These Moiré interference patterns have been suggested to drive the formation of highly structured orientation maps in visual cortex. Here, we show that noisy hexagonal lattices do not capture the spatial statistics of parasol cell mosaics. An alternative model based upon local exclusion zones, termed as the pairwise interaction point process (PIPP) model, generates patterns that are statistically indistinguishable from parasol cell mosaics. A key difference between the PIPP model and the hexagonal lattice model is that the PIPP model does not generate Moiré interference patterns, and hence stimulated orientation maps do not show any hexagonal structure. Finally, we estimate the spatial extent of spatial correlations in parasol cell mosaics to be only 200-350 μm, far less than that required to generate Moiré interference. We conclude that parasol cell mosaics are too disordered to drive the formation of highly structured orientation maps in visual cortex.

Validity of Vegard’s rule for Al1-xInxN (0.08  <  x  <  0.28) thin films grown on GaN templates

NASA Astrophysics Data System (ADS)

Magalhães, S.; Franco, N.; Watson, I. M.; Martin, R. W.; O'Donnell, K. P.; Schenk, H. P. D.; Tang, F.; Sadler, T. C.; Kappers, M. J.; Oliver, R. A.; Monteiro, T.; Martin, T. L.; Bagot, P. A. J.; Moody, M. P.; Alves, E.; Lorenz, K.

2017-05-01

In this work, comparative x-ray diffraction (XRD) and Rutherford backscattering spectrometry (RBS) measurements allow a comprehensive characterization of Al1-xInxN thin films grown on GaN. Within the limits of experimental accuracy, and in the compositional range 0.08  <  x  <  0.28, the lattice parameters of the alloys generally obey Vegard’s rule, varying linearly with the InN fraction. Results are also consistent with the small deviation from linear behaviour suggested by Darakchieva et al (2008 Appl. Phys. Lett. 93 261908). However, unintentional incorporation of Ga, revealed by atom probe tomography (APT) at levels below the detection limit for RBS, may also affect the lattice parameters. Furthermore, in certain samples the compositions determined by XRD and RBS differ significantly. This fact, which was interpreted in earlier publications as an indication of a deviation from Vegard’s rule, may rather be ascribed to the influence of defects or impurities on the lattice parameters of the alloy. The wide-ranging set of Al1-xInxN films studied allowed furthermore a detailed investigation of the composition leading to lattice-matching of Al1-xInxN/GaN bilayers.

Mechanical topological insulator in zero dimensions

NASA Astrophysics Data System (ADS)

Lera, Natalia; Alvarez, J. V.

2018-04-01

We study linear vibrational modes in finite isostatic Maxwell lattices, mechanical systems where the number of degrees of freedom matches the number of constraints. Recent progress in topological mechanics exploits the nontrivial topology of BDI class Hamiltonians in one dimenson and arising topological floppy modes at the edges. A finite frame, or zero-dimensional system, also exhibits a nonzero topological index according to the classification table. We construct mechanical insulating models in zero dimensions that complete the BDI classification in the available real space dimensions. We compute and interpret its nontrivial invariant Z2.

Wave Propagation and Dynamics of Lattice Structures.

DTIC Science & Technology

1984-05-01

Progress in Solid Mechanics, North Holand Publishing Company, Amsterdam, 1960. [7) Y. K. Linn, and T. J. McDaniel, ’n)amics of Beam Type Periodic...deformation. -99- APPENDIX F FREQUENCY RESPONSE AND IMPULSE RESPONSE FUNCTIONS FOR LONGITUDINAL VIBRATION IN AN ELASTIC ROD Figure F1 shows the elastic rod to b...6 (F38) Rearranging eqn. (F38), .HE(w) = e’ 4e~3 ~e e 2 e1" +e " 6 e r (F39) Mlultiplying eqn. ( F1 =39) by 6Ŕ 6- and aragn te - . e 6 -e _ aix

Direct Compositional Characterization of (U,Th)O2 Powders, Microspheres, and Pellets Using TXRF.

PubMed

Dhara, Sangita; Prabhat, Parimal; Misra, N L

2015-10-20

A total reflection X-ray fluorescence (TXRF) analysis method for direct compositional characterization of sintered and green (U,Th)O2 samples in different forms (e.g., pellets, powders, and microspheres) without sample dissolution has been developed for the first time. The methodology involves transfer of only a few nanograms of the sample on the TXRF sample support by gently rubbing the samples on supports or taking their tiny uniform slurry in collodion on the sample support, drying them to make thin film, and measuring the TXRF spectra of the specimens thus prepared. This approach minimizes the matrix effects. Uranium determinations from the TXRF spectra of such specimens were made with respect to thorium, considering it as an internal standard. Samples having uranium atom percent (at%) from 0 to 100 in (U,Th)O2 were analyzed for uranium in comparison to thorium. The results showed an average precision of 2.6% (RSD, 2σ, n = 8). The TXRF-determined results deviated from expected values within 5%. The TXRF results were compared with those of biamperometry with good agreement. The lattice parameters of the solid solutions were calculated using their XRD patterns. A good correlation between lattice parameters and TXRF-determined U at% and between TXRF-determined U at% and expected U at%, calculated on the basis of preparation of (U,Th)O2 solid solutions, was obtained. The developed method is capable of analyzing (U,Th)O2 samples directly with almost negligible sample preparation and is well suited for radioactive samples. The present study suggests that this method can be extended for the determination of U,Th and Pu in other nuclear fuel materials (e.g., nitrides, carbides, etc.) in the form of pellets, powders, and microspheres after suitable modifications in sample handling procedure.

On Traveling Waves in Lattices: The Case of Riccati Lattices

NASA Astrophysics Data System (ADS)

Dimitrova, Zlatinka

2012-09-01

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

Response of dupuytren fibroblasts to different oxygen environments.

PubMed

Türker, Tolga; Murphy, Erin; Kaufman, Christina L; Kutz, Joseph E; Meister, Edward A; Hoying, James B

2013-12-01

It is thought that local ischemia and oxygen radicals are responsible for fibroblast-to-myofibroblast cell transformation and proliferation. We hypothesized that hypoxia could differentially activate the contractility of fibroblasts from normal human palmar fascia and from fibroblasts-myofibroblasts of Dupuytren cords. Normal palmar fascia from 5 patients with carpal tunnel syndrome and Dupuytren cords from 5 patients were harvested. Cells were cultured from all tissue samples, and collagen lattices were prepared containing these cells. Oxygen treatment subgroups were created and incubated under hypoxic (1% O(2), 5% CO(2), and 94% N(2)), normoxic (21% O(2), 5% CO(2), and 74% N(2)), and hyperoxic (100% oxygen using 2.4 atm pressure twice a day for 7 d) conditions. After 7 days, each subgroup was photographed, and lattices were released from dishes. Postrelease photographs were taken immediately, 5 minutes after release, and after 1 hour. Areas of the lattices at each time point were calculated using MetaMorph software. Actin staining and live/dead cell analysis was performed. Linear repeated measures analysis of variance was used for data analysis given that contraction levels were measured over 3 distinct time points. We found a statistically significant difference between normal samples and Dupuytren samples in mean contraction levels over time. There was no statistically significant difference between tissue groups over the 3 time periods based on the oxygen treatment received. Our results showed a greater degree of contractility in Dupuytren disease cells than normal fibroblasts. However, the contraction in either group was not affected by oxygen level. Future in vivo research is needed to better understand the nature of pathophysiology of Dupuytren disease. Copyright © 2013 American Society for Surgery of the Hand. Published by Elsevier Inc. All rights reserved.

Thermoelectric Properties of Sr-Filled Ge-Based Type I Single-Crystal Clathrate Grown by Sn-Flux Method

NASA Astrophysics Data System (ADS)

Deng, Shuping; Liu, Hongxia; Li, Decong; Wang, Jinsong; Cheng, Feng; Shen, Lanxian; Deng, Shukang

2017-05-01

Single-crystal samples of Sr-filled Ge-based type I clathrate have been prepared by the Sn-flux method, and their thermoelectric properties investigated. The obtained samples exhibited n-type conduction with carrier concentration varying from 2.8 × 1019/cm3 to 6.8 × 1019/cm3 as the carrier mobility changed from 23.9 cm2/V-s to 15.1 cm2/V-s at room temperature. Structural analysis indicated that all samples were type I clathrate in space group pm\\bar{it{3}}n . The total content of group IV (Ge + Sn) atoms in the crystalline structure increased with increasing x value (where x defines the atomic ratio of starting elements, Sr:Ga:Ge:Sn = 8:16: x:20), reaching a maximum value of 31.76 at.% for the sample with x = 30; consequently, the lattice parameters increased. The melting points for all samples were approximately 1012 K, being considerably lower than that of single-crystal Sr8Ga16Ge30 prepared by other methods. The electrical conductivity increased while the absolute value of α increased gradually with increasing temperature; the maximum value of α reached 193 μV/K at 750 K for the sample with x = 24. The sample with x = 30 exhibited lower lattice thermal conductivity of 0.80 W/m-K. As a result, among all the Sn-flux samples, single-crystal Sr7.92Ga15.04Sn0.35Ge30.69 had the largest ZT value of 1.0 at about 750 K.

X-ray phase Identification of Chocolate is Possible

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guthrie,S.; Mazzanti, G.; Idziak, S.

2005-01-01

When examining chocolate samples by means of X-ray diffraction, it has become common practice for any sugar to be removed through repeated rinsing in cold water. While necessary in some cases, we show that it is possible to determine the phase of certain dark chocolate samples without sugar removal, through examination of distinctive X-ray diffraction peaks corresponding to lattice spacings of 3.98 and 3.70 Angstroms.

Structural differences between single crystal and polycrystalline UBe 13

DOE Office of Scientific and Technical Information (OSTI.GOV)

Volz, Heather Michelle; Vogel, Sven C.; Smith, Alice Iulia

Here, we report on observations of structural and chemical differences between samples of UBe 13 that were synthesised using two different methods. Unexplained discrepancies in properties between samples with differing synthesis had previously been found in this heavy fermion superconductor. A polycrystalline UBe13 sample was made by arc-melting the constituents. Single crystals were grown using an aluminium flux and had a consistently slightly larger lattice parameter than the polycrystals, which merited further study. Neutron diffraction data were collected at the Lujan Center at LANSCE on the HIPPO diffractometer. Aluminium was detected by inductively coupled plasma mass spectrometry (ICP-MS) in themore » flux-grown single crystal (0.803 wt%), and small amounts (~0.2 wt%) of thorium were detected in the UBe 13 polycrystalline sample. In order to probe the implications of the presence of Al, calculations by spin-polarised DFT-GGA+U show that the incorporation of Al onto the 96i site (the lowest symmetry site in the structure) is energetically more favourable than on other sites. In general, the trends calculated by DFT for bond lengths and lattice parameter increases are consistent with bond lengths experimentally observed by neutron diffraction, but specific percentage changes with aluminium incorporation may be obscured by the unexpected thorium in the polycrystalline sample. The aggregate of our initial observations suggests that incorporation of aluminium from the flux into single crystal UBe 13 is significant.« less

Structural differences between single crystal and polycrystalline UBe 13

DOE PAGES

Volz, Heather Michelle; Vogel, Sven C.; Smith, Alice Iulia; ...

2018-05-16

Here, we report on observations of structural and chemical differences between samples of UBe 13 that were synthesised using two different methods. Unexplained discrepancies in properties between samples with differing synthesis had previously been found in this heavy fermion superconductor. A polycrystalline UBe13 sample was made by arc-melting the constituents. Single crystals were grown using an aluminium flux and had a consistently slightly larger lattice parameter than the polycrystals, which merited further study. Neutron diffraction data were collected at the Lujan Center at LANSCE on the HIPPO diffractometer. Aluminium was detected by inductively coupled plasma mass spectrometry (ICP-MS) in themore » flux-grown single crystal (0.803 wt%), and small amounts (~0.2 wt%) of thorium were detected in the UBe 13 polycrystalline sample. In order to probe the implications of the presence of Al, calculations by spin-polarised DFT-GGA+U show that the incorporation of Al onto the 96i site (the lowest symmetry site in the structure) is energetically more favourable than on other sites. In general, the trends calculated by DFT for bond lengths and lattice parameter increases are consistent with bond lengths experimentally observed by neutron diffraction, but specific percentage changes with aluminium incorporation may be obscured by the unexpected thorium in the polycrystalline sample. The aggregate of our initial observations suggests that incorporation of aluminium from the flux into single crystal UBe 13 is significant.« less

Nuclear magnetic resonance studies of DNP-ready trehalose obtained by solid state mechanochemical amorphization

NASA Astrophysics Data System (ADS)

Filibian, M.; Elisei, E.; Colombo Serra, S.; Rosso, A.; Tedoldi, F.; Cesàro, A.; Carretta, P.

$^1$H nuclear spin-lattice relaxation and Dynamic Nuclear Polarization (DNP) have been studied in amorphous samples of trehalose sugar doped with TEMPO radicals by means of mechanical milling, in the 1.6 K $\\div$ 4.2 K temperature range. The radical concentration was varied between 0.34 and 0.81 $\\%$. The highest polarization of 15 \\% at 1.6 K, observed in the sample with concentration $0.50 \\%$, is of the same order of magnitude of that reported in standard frozen solutions with TEMPO. The temperature and concentration dependence of the spin-lattice relaxation rate $1/T_{\\text{1}}$, dominated by the coupling with the electron spins, were found to follow power laws with an exponent close to $3$ in all samples. The observed proportionality between $1/T_{\\text{1}}$ and the polarization rate $1/T_{\\text{pol}}$, with a coefficient related to the electron polarization, is consistent with the presence of Thermal Mixing (TM) and a good contact between the nuclear and the electron spins. At high electron concentration additional relaxation channels causing a decrease in the nuclear polarization must be considered. These results provide further support for a more extensive use of amorphous DNP-ready samples, obtained by means of comilling, in dissolution DNP experiments and possibly for $\\textit{in vivo}$ metabolic imaging.

Nuclear magnetic resonance studies of DNP-ready trehalose obtained by solid state mechanochemical amorphization.

PubMed

Filibian, M; Elisei, E; Colombo Serra, S; Rosso, A; Tedoldi, F; Cesàro, A; Carretta, P

2016-06-22

(1)H nuclear spin-lattice relaxation and Dynamic Nuclear Polarization (DNP) have been studied in amorphous samples of trehalose sugar doped with TEMPO radicals by means of mechanical milling, in the 1.6-4.2 K temperature range. The radical concentration was varied between 0.34 and 0.81%. The highest polarization of 15% at 1.6 K, observed in the sample with concentration 0.50%, is of the same order of magnitude of that reported in standard frozen solutions with TEMPO. The temperature and concentration dependence of the spin-lattice relaxation rate 1/T1, dominated by the coupling with the electron spins, were found to follow power laws with an exponent close to 3 in all samples. The observed proportionality between 1/T1 and the polarization rate 1/Tpol, with a coefficient related to the electron polarization, is consistent with the presence of Thermal Mixing (TM) and a good contact between the nuclear and the electron spins. At high electron concentration additional relaxation channels causing a decrease in the nuclear polarization must be considered. These results provide further support for a more extensive use of amorphous DNP-ready samples, obtained by means of comilling, in dissolution DNP experiments and possibly for in vivo metabolic imaging.

Electronic structure and chemical bonding in La1-x Sr x MnO3 perovskite ceramics

NASA Astrophysics Data System (ADS)

Thenmozhi, N.; Sasikumar, S.; Sonai, S.; Saravanan, R.

2017-04-01

This study reports on the synthesis of La1-x Sr x MnO3 (x  =  0.3, 0.4 and 0.5) manganites by high temperature solid state reaction method using lanthanum oxide, strontium carbonate and manganese oxide as starting materials. The synthesized samples were characterized by XRD, UV-vis, SEM/EDS and VSM. Structural characterization shows that all the prepared samples have the perovskite rhombohedral structure. Influence of Sr doping on electron density distributions in the lattice structure of LaMnO3 were analyzed through maximum entropy method (MEM). Cell parameters are found to be decreasing with the addition of Sr content. The qualitative and quantitative analysis by MEM reveals that, incorporation of Sr into LaMnO3 lattice enhances the ionic nature between La and O ions and decreases the covalent nature between Mn and O ions. Optical band gap values are determined from the UV-visible absorption spectra. Particles with polygonal form are observed from the SEM micrographs. The elemental compositions of the synthesized samples are confirmed by EDS. The magnetic properties studied from the M-H plot taken at room temperature indicated that, the prepared samples are exhibited ferromagnetic behavior.

Effects of lattice morphology upon reaction dynamics in matrix-isolated systems

NASA Astrophysics Data System (ADS)

Raff, Lionel M.

1992-11-01

The dynamics of the cis-d2-ethylene+F2 addition reaction and the subsequent reaction dynamics of the products isolated in vapor-deposited Ar matrices at 12 K are investigated using trajectory methods that incorporate nonstatistical sampling to enhance the reaction probabilities. The matrix-isolated cis-d2-ethylene+F2 system is generated using a combination of Monte Carlo, damped trajectory, and volume contraction methods. Transport effects of the bulk are simulated using the velocity reset procedure developed by Riley et al. [J. Chem. Phys. 88, 5934 (1988)]. The potential-energy hypersurface is the same as that employed in our previous investigations of the matrix-isolated, decomposition dynamics of 1,2-difluoroethane-d4 and the bimolecular cis-d2-ethylene+F2 system in face-centered-cubic (fcc) matrices [J. Chem. Phys. 93, 3160 (1990); 95, 8901 (1991)]. It is found that matrices generated by these methods are amorphous with numerous vacancies and other imperfections. On the average, there are approximately three vacancies about each lattice atom compared to the fcc crystal. The calculated lattice density is about 82% that for a bulk fcc Ar solid. Computed radial distribution functions resemble those expected for a liquid which exhibits some short-range order. The imperfections of the lattice remain even after substantial annealing at 50 K. The calculated energy relaxation rate to the lattice phonon modes in these amorphous matrices is about a factor of 4 less than that for a close-packed fcc lattice. The 1,2-difluoroethane product is formed primarily via an αβ-addition process, as is the case for fcc matrices. However, the prominence of this pathway is greatly reduced. The major process leading to a fluoroethylene elimination product in amorphous matrices involves an atomic addition mechanism. Such a reaction path accounts for 94% of the elimination reactions. The probability of internal rotation about the C■C double bond in the fluoroethylene product is increased fivefold over that for fcc lattices. The calculated stabilization/elimination product ratio, the cis/trans ratios of fluoroethylene products, and the HF/DF elimination ratio are all found to be in fair to good accord with the reported experimental data. It is concluded that accurate simulation of matrix-isolation experiments requires a matrix model that properly represents the lattice structure present in the experiments.

Understanding lattice defects to influence ferromagnetic order of ZnO nanoparticles by Ni, Cu, Ce ions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Verma, Kuldeep Chand, E-mail: dkuldeep.physics@gmail.com; Kotnala, R.K., E-mail: rkkotnala@gmail.com

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+},more » 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 interactions with cluster and spin-glass type growth. - Highlights: • Lattice defects/vacancies attributed high T{sub c} –ferromagnetism. • Transition metal and rare earth ions deform the wurtzite ZnO lattice to induce defects. • Oxygen vacancies are more favorable than Zn with Ni, Cu, Ce into ZnO. • Defects assisted long-range ferromagnetism of doped ZnO include cluster and spin-glass growth.« less

Effect of single-site mutations on hydrophobic-polar lattice proteins

NASA Astrophysics Data System (ADS)

Shi, Guangjie; Vogel, Thomas; Wüst, Thomas; Li, Ying Wai; Landau, David P.

2014-09-01

We developed a heuristic method for determining the ground-state degeneracy of hydrophobic-polar (HP) lattice proteins, based on Wang-Landau and multicanonical sampling. It is applied during comprehensive studies of single-site mutations in specific HP proteins with different sequences. The effects in which we are interested include structural changes in ground states, changes of ground-state energy, degeneracy, and thermodynamic properties of the system. With respect to mutations, both extremely sensitive and insensitive positions in the HP sequence have been found. That is, ground-state energies and degeneracies, as well as other thermodynamic and structural quantities, may be either largely unaffected or may change significantly due to mutation.

Flux lattice imaging of a patterned niobium thin film

NASA Astrophysics Data System (ADS)

Roseman, M.; Grütter, P.; Badía, A.; Metlushko, V.

2001-06-01

Using our cryogenic magnetic force microscope, we have investigated a superconducting Nb thin film, 100 nm in thickness with Tc˜6.5 K. The film is patterned with a square array (1 μm×1 μm) of antidots, which serve as artificial pinning centers for magnetic flux. We have observed flux lattice matching as a function of applied magnetic field and temperature, for field strengths up to the third matching field, with evidence of flux dragging by the tip around the antidots. Force gradient distance curves acquired at temperatures about Tc clearly demonstrate an observable Meissner force between tip and sample, and allow for an estimation of the magnetic screening penetration depth.

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

NASA Astrophysics Data System (ADS)

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.; Higginbotham, A.; Lazicki, A.; Lee, H. J.; Nagler, B.; Park, H.-S.; Remington, B. A.; Rudd, R. E.; Sliwa, M.; Suggit, M.; Swift, D.; Tavella, F.; Zepeda-Ruiz, L.; Wark, J. S.

2017-10-01

Pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation is challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. The techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.

We report that pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation ismore » challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. Lastly, the techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.« less

In situ X-ray diffraction measurement of shock-wave-driven twinning and lattice dynamics

DOE PAGES

Wehrenberg, C. E.; McGonegle, D.; Bolme, C.; ...

2017-10-25

We report that pressure-driven shock waves in solid materials can cause extreme damage and deformation. Understanding this deformation and the associated defects that are created in the material is crucial in the study of a wide range of phenomena, including planetary formation and asteroid impact sites, the formation of interstellar dust clouds, ballistic penetrators, spacecraft shielding and ductility in high-performance ceramics. At the lattice level, the basic mechanisms of plastic deformation are twinning (whereby crystallites with a mirror-image lattice form) and slip (whereby lattice dislocations are generated and move), but determining which of these mechanisms is active during deformation ismore » challenging. Experiments that characterized lattice defects have typically examined the microstructure of samples after deformation, and so are complicated by post-shock annealing and reverberations. In addition, measurements have been limited to relatively modest pressures (less than 100 gigapascals). In situ X-ray diffraction experiments can provide insights into the dynamic behaviour of materials, but have only recently been applied to plasticity during shock compression and have yet to provide detailed insight into competing deformation mechanisms. Here we present X-ray diffraction experiments with femtosecond resolution that capture in situ, lattice-level information on the microstructural processes that drive shock-wave-driven deformation. To demonstrate this method we shock-compress the body-centred-cubic material tantalum—an important material for high-energy-density physics owing to its high shock impedance and high X-ray opacity. Tantalum is also a material for which previous shock compression simulations and experiments have provided conflicting information about the dominant deformation mechanism. Our experiments reveal twinning and related lattice rotation occurring on the timescale of tens of picoseconds. In addition, despite the common association between twinning and strong shocks, we find a transition from twinning to dislocation-slip-dominated plasticity at high pressure (more than 150 gigapascals), a regime that recovery experiments cannot accurately access. Lastly, the techniques demonstrated here will be useful for studying shock waves and other high-strain-rate phenomena, as well as a broad range of processes induced by plasticity.« less

Sampling algorithms for validation of supervised learning models for Ising-like systems

NASA Astrophysics Data System (ADS)

Portman, Nataliya; Tamblyn, Isaac

2017-12-01

In this paper, we build and explore supervised learning models of ferromagnetic system behavior, using Monte-Carlo sampling of the spin configuration space generated by the 2D Ising model. Given the enormous size of the space of all possible Ising model realizations, the question arises as to how to choose a reasonable number of samples that will form physically meaningful and non-intersecting training and testing datasets. Here, we propose a sampling technique called ;ID-MH; that uses the Metropolis-Hastings algorithm creating Markov process across energy levels within the predefined configuration subspace. We show that application of this method retains phase transitions in both training and testing datasets and serves the purpose of validation of a machine learning algorithm. For larger lattice dimensions, ID-MH is not feasible as it requires knowledge of the complete configuration space. As such, we develop a new ;block-ID; sampling strategy: it decomposes the given structure into square blocks with lattice dimension N ≤ 5 and uses ID-MH sampling of candidate blocks. Further comparison of the performance of commonly used machine learning methods such as random forests, decision trees, k nearest neighbors and artificial neural networks shows that the PCA-based Decision Tree regressor is the most accurate predictor of magnetizations of the Ising model. For energies, however, the accuracy of prediction is not satisfactory, highlighting the need to consider more algorithmically complex methods (e.g., deep learning).

Determining the strengths of HCP slip systems using harmonic analyses of lattice strain distributions

DOE PAGES

Dawson, Paul R.; Boyce, Donald E.; Park, Jun-Sang; ...

2017-10-15

A robust methodology is presented to extract slip system strengths from lattice strain distributions for polycrystalline samples obtained from high-energy x-ray diffraction (HEXD) experiments with in situ loading. The methodology consists of matching the evolution of coefficients of a harmonic expansion of the distributions from simulation to the coefficients derived from measurements. Simulation results are generated via finite element simulations of virtual polycrystals that are subjected to the loading history applied in the HEXD experiments. Advantages of the methodology include: (1) its ability to utilize extensive data sets generated by HEXD experiments; (2) its ability to capture trends in distributionsmore » that may be noisy (both measured and simulated); and (3) its sensitivity to the ratios of the family strengths. The approach is used to evaluate the slip system strengths of Ti-6Al-4V using samples having relatively equiaxed grains. These strength estimates are compared to values in the literature.« less

Defect chemistry and characterization Hg(1-x)Cd(x)Te

NASA Technical Reports Server (NTRS)

Vydyanath, H. R.; Donovan, J. C.

1981-01-01

Iodine doped single crystal samples of mercury cadmium telluride were annealed at temperatures varying from 450 C to 600 C in Hg vapor and quenched to room temperature. Hall effect measurements at 77 K on the crystals cooled to room temperature indicate the samples to be n-type after anneals at high Hg pressures whereas they turn p-type after anneals at low Hg pressures; the electron concentration increases with increase in Hg pressure. The results are explained on the basis that the crystals are saturated with (Hg,Cd)I2, with a fraction of the iodine being present as donor occupying tellurium lattice sites and a fraction being present as acceptors resulting from the iodine on tellurium lattice sites pairing with the doubly ionized native acceptor defects. The solubility of the donor species increases with increase in Hg pressure, whereas that of the acceptor species increases with decrease in Hg pressure. Equilibrium constants for the incorporation of the iodine species as well as the pairing reaction were established.

Hydrotalcite-derived cobalt-aluminum mixed oxide catalysts for toluene combustion

NASA Astrophysics Data System (ADS)

Białas, Anna; Mazur, Michal; Natkański, Piotr; Dudek, Barbara; Kozak, Marek; Wach, Anna; Kuśtrowski, Piotr

2016-01-01

Hydrotalcite-like compounds (HTlcs) containing cobalt and aluminum (intended Co/Al molar ratio = 3.0) were coprecipitated at 30, 50 and 70 °C. Their crystallinity, which was confirmed by powder X-ray diffraction, increased with the precipitation temperature. Furthermore, HTlcs with various cobalt contents were prepared at 70 °C. Thermogravimetric analysis showed that HTlcs were transformed into stable oxides at 550 °C. The decrease in the crystallite size of the formed spinels with the increase in the precipitation temperature was observed. Low temperature sorption of nitrogen revealed meso-macroporous nature of the oxides with extended interparticle porosity. Aluminum segregated on the samples surface, which contained various amounts of lattice and adsorbed/electrophilic oxygen as detected by X-ray electron spectroscopy. The high ratio of lattice to adsorbed/electrophilic oxygen found for the sample with Co/Al = 3:1 caused that it turned out to be the most efficient catalyst in the total oxidation of toluene (50% conversion at 257 °C).

Classification of trivial spin-1 tensor network states on a square lattice

NASA Astrophysics Data System (ADS)

Lee, Hyunyong; Han, Jung Hoon

2016-09-01

Classification of possible quantum spin liquid (QSL) states of interacting spin-1/2's in two dimensions has been a fascinating topic of condensed matter for decades, resulting in enormous progress in our understanding of low-dimensional quantum matter. By contrast, relatively little work exists on the identification, let alone classification, of QSL phases for spin-1 systems in dimensions higher than one. Employing the powerful ideas of tensor network theory and its classification, we develop general methods for writing QSL wave functions of spin-1 respecting all the lattice symmetries, spin rotation, and time reversal with trivial gauge structure on the square lattice. We find 25 distinct classes characterized by five binary quantum numbers. Several explicit constructions of such wave functions are given for bond dimensions D ranging from two to four, along with thorough numerical analyses to identify their physical characters. Both gapless and gapped states are found. The topological entanglement entropy of the gapped states is close to zero, indicative of topologically trivial states. In D =4 , several different tensors can be linearly combined to produce a family of states within the same symmetry class. A rich "phase diagram" can be worked out among the phases of these tensors, as well as the phase transitions among them. Among the states we identified in this putative phase diagram is the plaquette-ordered phase, gapped resonating valence bond phase, and a critical phase. A continuous transition separates the plaquette-ordered phase from the resonating valence bond phase.

Investigation of Some Potent Medicinal Plants of N.E.INDIA with Respect to Thermophysical, Chromatographic and Crystallographic Properties

NASA Astrophysics Data System (ADS)

Bora, M. N.; Kalita, Mahendra

2010-06-01

North East India is readily available of various kinds of medicinal plants. A lot of studies on thermophysical properties of plant leaves, fluids, stems and roots had already been made[3,4,8]. In the present studies of thermophysical properties, chromatographic and crystallographic properties of specific medicinal plant leaves (Azadirechta indica)A, (Vinca rosea)B, (Clerodrendrum colebrookianum)C, (Osimum sanctum)D and fruits (Chisocheton paniculatus) E, and (Cudrania javanensis) F have been made plant based drugs for curing for different chronic diseases. The thermophysical properties of these leaves and fruits have been studies with XRD, XRF, TG, DTG, DTA, and DSC thermograms. From weight loss(%), time and temperature variations, the Activation Energies of these medicinal plant samples have been computed. The thermal stability is found more for the fruits samples than that of the leave samples. Thermal behaviours of all six samples have shown hygroscopic behaviour. The results TG, DTG and DTA thermograms confirmed that all samples show similar dehydration and decomposition reactions and hydrophilic nature. Both chromatographic techniques thin layer (TLC) and Column chromatography have been used for separation of components of the mixtures of samples. From these methods of the fruit sample E a pure crystalline white solids have been identified and confirm them as (MK 01) α-isomer. Our interest to study the molecular and crystal structure of the sample E. The single crystal of (MK 01) is found to be orthorhombic cell with lattice parameters a = 10ṡ699(3)Å b = 15ṡ5100(4)Å c = 16ṡ626(4)Å α = 90° β = 90° γ = 90° with space group P212121 Again from fruit sample F a light yellow solid is isolated and on crystallization give crystalline solid MN-01 and MN-02 and it is confirmed that these two compounds are unsaturated isoflavonoids. The single crystal of MN-01 has been found monoclinic with lattice parameters a = 6.2374(11)Å, b = 8.4243(11)Å, c = 21.181(4)Å, α = 96.083(13)°, β = 95.602(10)° and γ = 107.419(7)° with Space group P-1. Again single crystal MN-02 has been found monoclinic with lattice parameters being a = 25.2732 Å, b = 7.4414 Å, c = 22.3113 Å, α = 90°, β = 93.063°, γ = 90°, with space group C2/c.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ahmed, Asar; Gajbhiye, Namdeo S., E-mail: nsg@iitk.ac.i

Cuprous oxide (Cu{sub 2}O) flower-like nanostructures doped with various metal ions i.e. Fe, Co, Ni and Mn have been synthesized by an organic phase solution method. The powder X-ray diffraction study clearly reveals them as single phase simple cubic cuprite lattice. Study of their magnetic properties have shown that these doped samples are ferromagnetic in nature; however, no such property was observed for the undoped Cu{sub 2}O sample. The magnitude of the ferromagnetic behavior was found to be dependent on the dopant metal ions amount, which increased consistently with its increase. As total magnetic moment contribution of the doped metalmore » ions calculated was insignificant, it is believed to have originated from the induced magnetic moments at cation deficiency sites in the material, created possibly due to the disturbance of the crystal lattice by the dopant ions. The existence of the defects has been supported by photoluminescence spectra of the doped samples. -- Graphical abstract: Room temperature ferromagnetic behavior was observed in the Cu{sub 2}O nanoflowers doped with Fe, Co, Ni and Mn ions. Cation deficiencies formed due to dopant ions were possibly responsible for ferromagnetism. Display Omitted« less

In Situ X-ray Diffraction Studies of Li(sub x)Mn(sub 2)O(sub 4) Cathode Materials by Synchrotron X-ray Radiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, X. Q.; Sun, X.; Lee, S. J.

In Situ x-ray diffraction studies on Li{sub x}Mn{sub 2}O{sub 4} spinel cathode materials during charge-discharge cycles were carried out by using a synchrotron as x-ray source. Lithium rich (x = 1.03-1.06) spinel materials obtained from two different sources were studied. Three cubic phases with different lattice constants were observed during charge-discharge cycles in all the samples when a Sufficiently low charge-discharge rate (C/10) was used. There are two regions of two-phase coexistence between these three phases, indicating that both phase transitions are first order. The separation of the Bragg peaks representing these three phases varies from sample to sample andmore » also depends on the charge-discharge rate. These results show that the de-intercalation of lithium in lithium-rich spinel cathode materials proceeds through a series of phase transitions from a lithium-rich phase to a lithium-poor phase and finally to a {lambda}-MnO{sub 2} like cubic phase, rather than through a continuous lattice constant contraction in a single phase.« less

A novel fabrication methodology for sulfur-doped ZnO nanorods as an active photoanode for improved water oxidation in visible-light regime

NASA Astrophysics Data System (ADS)

Khan, A.; Ahmed, M. I.; Adam, A.; Azad, A.-M.; Qamar, M.

2017-02-01

Incorporation of foreign moiety in the lattice of semiconductors significantly alters their optoelectronic behavior and opens a plethora of new applications. In this paper, we report the synthesis of sulfur-doped zinc oxide (S-doped ZnO) nanorods by reacting ZnO nanorods with diammonium sulfide in vapor phase. Microscopic investigation revealed that the morphological features, such as, the length (2-4 μm) and width (100-250 nm) of the original hexagonal ZnO nanorods remained intact post-sulfidation. X-ray photoelectron spectroscopy analysis of the sulfide sample confirmed the incorporation of sulfur into ZnO lattice. The optical measurements suggested the extension of absorption threshold into visible region upon sulfidation. Photoelectrochemical (PEC) activities of pure and S-doped ZnO nanorods were compared for water oxidation in visible light (λ > 420 nm), which showed several-fold increment in the performance of S-doped ZnO sample; the observed amelioration in the PEC activity was rationalized in terms of preferred visible light absorption and low resistance of sulfide sample, as evidenced by optical and electrochemical impedance spectroscopy.

Heterogeneous Ice Nucleation: Interplay of Surface Properties and Their Impact on Water Orientations.

PubMed

Glatz, Brittany; Sarupria, Sapna

2018-01-23

Ice is ubiquitous in nature, and heterogeneous ice nucleation is the most common pathway of ice formation. How surface properties affect the propensity to observe ice nucleation on that surface remains an open question. We present results of molecular dynamics studies of heterogeneous ice nucleation on model surfaces. The models surfaces considered emulate the chemistry of kaolinite, an abundant component of mineral dust. We investigate the interplay of surface lattice and hydrogen bonding properties in affecting ice nucleation. We find that lattice matching and hydrogen bonding are necessary but not sufficient conditions for observing ice nucleation at these surfaces. We correlate this behavior to the orientations sampled by the metastable supercooled water in contact with the surfaces. We find that ice is observed in cases where water molecules not only sample orientations favorable for bilayer formation but also do not sample unfavorable orientations. This distribution depends on both surface-water and water-water interactions and can change with subtle modifications to the surface properties. Our results provide insights into the diverse behavior of ice nucleation observed at different surfaces and highlight the complexity in elucidating heterogeneous ice nucleation.

Thermoelectric study of Ag doped SnSe-Sb2Se3 based alloy

NASA Astrophysics Data System (ADS)

Das, Anish; Talukdar, M.; Kumar, Aparabal; Sarkar, Kalyan Jyoti; Dhama, P.; Banerji, P.

2018-05-01

In this article we have synthesized p-type alloy of SnSe and Sb2Se3 (10 atomic %) to study the thermoelectric transport properties. The alloy was prepared by melt grown technique followed by spark plasma sintering and latter doped with 2 atomic % Ag to compensate the carrier density in order to achieve higher electrical conductivity (σ). Out of these, the doped sample resulted in the maximum figure of merit, ZT˜0.7 at 773 K due to the existence of the secondary phase AgSbSe2 and reduced lattice thermal conductivity (0.61 W m-1 K-1 at 300 K). The fitted lattice thermal conductivity shows that point defect and Umklapp scattering are the primary process of phonon scattering for all the samples whereas the fitted mobility data confirms acoustic phonon scattering along with point defect and grain boundary scattering to be the main carrier scattering mechanism. More over room temperature carrier density and electrical conductivity are found to increase for the doped sample which further corroborate (90%)SnSe-(10%)Sb2Se3:2%Ag to be a potential candidate for highly efficient thermoelectric materials.

High-energy transmission Laue micro-beam X-ray diffraction: a probe for intra-granular lattice orientation and elastic strain in thicker samples.

PubMed

Hofmann, Felix; Song, Xu; Abbey, Brian; Jun, Tea-Sung; Korsunsky, Alexander M

2012-05-01

An understanding of the mechanical response of modern engineering alloys to complex loading conditions is essential for the design of load-bearing components in high-performance safety-critical aerospace applications. A detailed knowledge of how material behaviour is modified by fatigue and the ability to predict failure reliably are vital for enhanced component performance. Unlike macroscopic bulk properties (e.g. stiffness, yield stress, etc.) that depend on the average behaviour of many grains, material failure is governed by `weakest link'-type mechanisms. It is strongly dependent on the anisotropic single-crystal elastic-plastic behaviour, local morphology and microstructure, and grain-to-grain interactions. For the development and validation of models that capture these complex phenomena, the ability to probe deformation behaviour at the micro-scale is key. The diffraction of highly penetrating synchrotron X-rays is well suited to this purpose and micro-beam Laue diffraction is a particularly powerful tool that has emerged in recent years. Typically it uses photon energies of 5-25 keV, limiting penetration into the material, so that only thin samples or near-surface regions can be studied. In this paper the development of high-energy transmission Laue (HETL) micro-beam X-ray diffraction is described, extending the micro-beam Laue technique to significantly higher photon energies (50-150 keV). It allows the probing of thicker sample sections, with the potential for grain-level characterization of real engineering components. The new HETL technique is used to study the deformation behaviour of individual grains in a large-grained polycrystalline nickel sample during in situ tensile loading. Refinement of the Laue diffraction patterns yields lattice orientations and qualitative information about elastic strains. After deformation, bands of high lattice misorientation can be identified in the sample. Orientation spread within individual scattering volumes is studied using a pattern-matching approach. The results highlight the inability of a simple Schmid-factor model to capture the behaviour of individual grains and illustrate the need for complementary mechanical modelling.

Composite Interval Mapping Based on Lattice Design for Error Control May Increase Power of Quantitative Trait Locus Detection.

PubMed

He, Jianbo; Li, Jijie; Huang, Zhongwen; Zhao, Tuanjie; Xing, Guangnan; Gai, Junyi; Guan, Rongzhan

2015-01-01

Experimental error control is very important in quantitative trait locus (QTL) mapping. Although numerous statistical methods have been developed for QTL mapping, a QTL detection model based on an appropriate experimental design that emphasizes error control has not been developed. Lattice design is very suitable for experiments with large sample sizes, which is usually required for accurate mapping of quantitative traits. However, the lack of a QTL mapping method based on lattice design dictates that the arithmetic mean or adjusted mean of each line of observations in the lattice design had to be used as a response variable, resulting in low QTL detection power. As an improvement, we developed a QTL mapping method termed composite interval mapping based on lattice design (CIMLD). In the lattice design, experimental errors are decomposed into random errors and block-within-replication errors. Four levels of block-within-replication errors were simulated to show the power of QTL detection under different error controls. The simulation results showed that the arithmetic mean method, which is equivalent to a method under random complete block design (RCBD), was very sensitive to the size of the block variance and with the increase of block variance, the power of QTL detection decreased from 51.3% to 9.4%. In contrast to the RCBD method, the power of CIMLD and the adjusted mean method did not change for different block variances. The CIMLD method showed 1.2- to 7.6-fold higher power of QTL detection than the arithmetic or adjusted mean methods. Our proposed method was applied to real soybean (Glycine max) data as an example and 10 QTLs for biomass were identified that explained 65.87% of the phenotypic variation, while only three and two QTLs were identified by arithmetic and adjusted mean methods, respectively.

Lattice Thermal Conductivity of Ultra High Temperature Ceramics (UHTC) ZrB2 and HfB2 from Atomistic Simulations

NASA Technical Reports Server (NTRS)

Lawson, John W.; Daw, Murray S.; Bauschlicher, Charles W.

2012-01-01

Ultra high temperature ceramics (UHTC) including ZrB2 and HfB2 have a number of properties that make them attractive for applications in extreme environments. One such property is their high thermal conductivity. Computational modeling of these materials will facilitate understanding of fundamental mechanisms, elucidate structure-property relationships, and ultimately accelerate the materials design cycle. Progress in computational modeling of UHTCs however has been limited in part due to the absence of suitable interatomic potentials. Recently, we developed Tersoff style parameterizations of such potentials for both ZrB2 and HfB2 appropriate for atomistic simulations. As an application, Green-Kubo molecular dynamics simulations were performed to evaluate the lattice thermal conductivity for single crystals of ZrB2 and HfB2. The atomic mass difference in these binary compounds leads to oscillations in the time correlation function of the heat current, in contrast to the more typical monotonic decay seen in monoatomic materials such as Silicon, for example. Results at room temperature and at elevated temperatures will be reported.

Lattice Thermal Conductivity from Atomistic Simulations: ZrB2 and HfB2

NASA Technical Reports Server (NTRS)

Lawson, John W.; Daw, Murray S.; Bauschlicher, Charles W.

2012-01-01

Ultra high temperature ceramics (UHTC) including ZrB2 and HfB2 have a number of properties that make them attractive for applications in extreme environments. One such property is their high thermal conductivity. Computational modeling of these materials will facilitate understanding of fundamental mechanisms, elucidate structure-property relationships, and ultimately accelerate the materials design cycle. Progress in computational modeling of UHTCs however has been limited in part due to the absence of suitable interatomic potentials. Recently, we developed Tersoff style parameterizations of such potentials for both ZrB2 and HfB2 appropriate for atomistic simulations. As an application, Green-Kubo molecular dynamics simulations were performed to evaluate the lattice thermal conductivity for single crystals of ZrB2 and HfB2. The atomic mass difference in these binary compounds leads to oscillations in the time correlation function of the heat current, in contrast to the more typical monotonic decay seen in monoatomic materials such as Silicon, for example. Results at room temperature and at elevated temperatures will be reported.

Proceedings of RIKEN BNL Research Center Workshop: The Approach to Equilibrium in Strongly Interacting Matter. Volume 118

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liao, J.; Venugopalan, R.; Berges, J.

The RIKEN BNL Research Center (RBRC) was established in April 1997 at Brookhaven National Laboratory*. It is funded by the ''Rikagaku Kenkyusho'' (RIKEN, The Institute of Physical and Chemical Research) of Japan and the U. S. Department of Energy’s Office of Science. The RBRC is dedicated to the study of strong interactions, including spin physics, lattice QCD, and RHIC physics through the nurturing of a new generation of young physicists. The RBRC has theory, lattice gauge computing and experimental components. It is presently exploring the possibility of an astrophysics component being added to the program. The purpose of this Workshopmore » is to critically review the recent progress on the theory and phenomenology of early time dynamics in relativistic heavy ion collisions from RHIC to LHC energies, to examine the various approaches on thermalization and existing issues, and to formulate new research efforts for the future. Topics slated to be covered include Experimental evidence for equilibration/isotropization, comparison of various approaches, dependence on the initial conditions and couplings, and turbulent cascades and Bose-Einstein condensation.« less

Construction of a Quantum Matter Synthesizer

NASA Astrophysics Data System (ADS)

Trisnadi, Jonathan; McDonald, Mickey; Chin, Cheng

2017-04-01

We report progress on the construction of a new platform to manipulate ultracold atoms. The ``Quantum Matter Synthesizer (QMS)'' will have the capability of deterministically preparing large 2D arrays of atoms with single site addressability. Cesium atoms are first transferred into a science cell (specially textured to reduce reflectance to 0.1% across a wide range of wavelengths and incident angles) via a moving 1D lattice, where they are loaded into a magic-wavelength, far-detuned 2D optical lattice. Two NA=0.8 microscope objectives surround the science cell from above and below. The lower objective will be used to project an array of optical tweezers created via a digital micromirror device (DMD) onto the atom-trapping plane, which will be used to rearrange atoms into a desired configuration after first taking a site-resolved fluorescence image of the initial atomic distribution with the upper objective. We provide updates on our magnetic-optical trap and Raman-sideband cooling performance, characterization of the resolution of our microscope objectives, and stability tests for the objective mounting structure.

Dissipative preparation of antiferromagnetic order in the Fermi-Hubbard model

NASA Astrophysics Data System (ADS)

Kaczmarczyk, J.; Weimer, H.; Lemeshko, M.

2016-09-01

The Fermi-Hubbard model is one of the key models of condensed matter physics, which holds a potential for explaining the mystery of high-temperature superconductivity. Recent progress in ultracold atoms in optical lattices has paved the way to studying the model’s phase diagram using the tools of quantum simulation, which emerged as a promising alternative to the numerical calculations plagued by the infamous sign problem. However, the temperatures achieved using elaborate laser cooling protocols so far have been too high to show the appearance of antiferromagnetic (AF) and superconducting quantum phases directly. In this work, we demonstrate that using the machinery of dissipative quantum state engineering, one can observe the emergence of the AF order in the Fermi-Hubbard model with fermions in optical lattices. The core of the approach is to add incoherent laser scattering in such a way that the AF state emerges as the dark state of the driven-dissipative dynamics. The proposed controlled dissipation channels described in this work are straightforward to add to already existing experimental setups.

Covariant information-density cutoff in curved space-time.

PubMed

Kempf, Achim

2004-06-04

In information theory, the link between continuous information and discrete information is established through well-known sampling theorems. Sampling theory explains, for example, how frequency-filtered music signals are reconstructible perfectly from discrete samples. In this Letter, sampling theory is generalized to pseudo-Riemannian manifolds. This provides a new set of mathematical tools for the study of space-time at the Planck scale: theories formulated on a differentiable space-time manifold can be equivalent to lattice theories. There is a close connection to generalized uncertainty relations which have appeared in string theory and other studies of quantum gravity.

Generation of complementary sampled phase-only holograms.

PubMed

Tsang, P W M; Chow, Y T; Poon, T-C

2016-10-03

If an image is uniformly down-sampled into a sparse form and converted into a hologram, the phase component alone will be adequate to reconstruct the image. However, the appearance of the reconstructed image is degraded with numerous empty holes. In this paper, we present a low complexity and non-iterative solution to this problem. Briefly, two phase-only holograms are generated for an image, each based on a different down-sampling lattice. Subsequently, the holograms are displayed alternately at high frame rate. The reconstructed images of the 2 holograms will appear to be a single, densely sampled image with enhance visual quality.

Structural elucidation and magnetic behavior evaluation of Cu-Cr doped BaCo-X hexagonal ferrites

NASA Astrophysics Data System (ADS)

Azhar Khan, Muhammad; Hussain, Farhat; Rashid, Muhammad; Mahmood, Asif; Ramay, Shahid M.; Majeed, Abdul

2018-04-01

Ba2-xCuxCo2CryFe28-yO46 (x = 0.0, 0.1, 0.2, 0.3, 0.4, y = 0.0, 0.2, 0.4, 0.6, 0.8) X-type hexagonal ferrites were synthesized via micro-emulsion route. The techniques which were applied to characterize the prepared samples are as follows: X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), Dielectric measurements and vibrating sample magnetometer (VSM). The structural parameters i.e. lattice constant (a, c), cell volume (V), X-ray density, bulk density and crystallite size of all the prepared samples were obtained using XRD analysis. The lattice parameters 'a' and 'c' increase from 5.875 Å to 5.934 Å and 83.367 Å to 83.990 Å respectively. The crystallite size of investigated samples lies in the range of 28-32 nm. The magnetic properties of all samples have been calculated by vibrating sample magnetometer (VSM) analysis. The increase in coercivity (Hc) was observed with the increase of doping contents. It was observed that the coercivity (Hc) of all prepared samples is inversely related to the crystalline size which reflects that all materials are super-paramagnetic. The dielectric parameters i.e. dielectric constant, dielectric loss, tangent loss etc were obtained in the frequency range of 1 MHz-3 GHz and followed the Maxwell-Wagner's model. The significant variation the dielectric parameters are observed with increasing frequency. The maximum Q value is obtained at ∼2 GHz due to which these materials are used for high frequency multilayer chip inductors.

Modeling Interfacial Thermal Boundary Conductance of Engineered Interfaces

DTIC Science & Technology

2014-08-31

melting / recrystallization of the subsurface Ag/Cu interface. Observed the formation of a novel, lattice-mismatched interfacial microstruc- ture...calculations were converged within 1 × 10−4 Ryd with respect to wave function cutoff energy, energy density cutoff, and k- point sampling. The A-EAM

Ultratrace analysis of transuranic actinides by laser-induced fluorescence

DOEpatents

Miller, S.M.

1983-10-31

Ultratrace quantities of transuranic actinides are detected indirectly by their effect on the fluorescent emissions of a preselected fluorescent species. Transuranic actinides in a sample are coprecipitated with a host lattice material containing at least one preselected fluorescent species. The actinide either quenches or enhances the laser-induced fluorescence of the preselected fluorescent species. The degree of enhancement or quenching is quantitatively related to the concentration of actinide in the sample.

Extreme conditions magnetostriction study of the Shastry-Sutherland sample SCBO

NASA Astrophysics Data System (ADS)

Grockowiak, Audrey; Wehinger, BjöRn; Coniglio, William; Ruegg, Chistian; Tozer, Stanley; National High Magnetic Field Laboratory Team; Paul Scherrer Institute Collaboration

The Shasty-Sutherland model, which consists of a set of spin 1/2 dimers on a 2D square lattice, is simple and soluble but captures a central theme of condensed matter physics by sitting precariously on the quantum edge between isolated, gapped excitations and collective, ordered ground states. This model is realized in SrCu2(BO3)2. Recent x-ray diffraction data revealed a direct correlation of the lattice with magnetic susceptibility measurements at low temperatures. The variation of the lattice parameters with temperature is thus directly linked to the spin response of the system. Indeed, scattering intensities from the spin waves, measured by inelastic neutron scattering experiments, decay accordingly. The magnetic correlations can thus be monitored by the lattice parameters and are thus sensitive to magnetostriction. Ambient pressure magnetostriction up to 100.7 T show clear signatures related to the magnetization plateaus at 30, 40 and 80T. Together with total energy calculations these studies revealed a strong magneto elastic coupling driven by the super exchange angle CuOCu. Applying hydrostatic external pressure results in continuous and discontinuous quantum phase transitions. Zero field high pressure neutron spectroscopy measurements have revealed so far three phases : spin dimer from 0 to 2GPa, antiferromagnetic from 4 to 6 GPa, and a 4-spin plaquette singlet state was recently identified in the 2 to 4GPa region. We report here on high pressure (up to 2GPa), high magnetic field (up to 65T) and 3He temperature magnetostriction experiments, using FBGs. Fiber Bragg Grating (FBG) Dilatometry permits to measure the magnetostriction of a sample in function of the response of an optical fiber to applied strain. This work was performed at the NHMFL, supported by the NSF Cooperative Agreement No. DMR-1157490 and the State of Florida, and the DOE NNSA DE-NA0001979 Grant.

One-Pot Polyol Synthesis of Pt/CeO2 and Au/CeO2 Nanopowders as Catalysts for CO Oxidation.

PubMed

Pilger, Frank; Testino, Andrea; Lucchini, Mattia Alberto; Kambolis, Anastasios; Tarik, Mohammed; El Kazzi, Mario; Arroyo, Yadira; Rossell, Marta D; Ludwig, Christian

2015-05-01

The facile one-pot synthesis of CeO2-based catalysts has been developed to prepare a relatively large amount of nanopowders with relevant catalytic activity towards CO oxidation. The method consists of a two-steps process carried out in ethylene glycol: in the first step, 5 nm well-crystallized pure CeO2 is prepared. In a subsequent second step, a salt of a noble metal is added to the CeO2 suspension and the deposition of the noble metal on the nanocrystalline CeO2 is induced by heating. Two catalysts were prepared: Pt/CeO2 and Au/CeO2. The as-prepared catalysts, the thermally treated catalysts, as well as the pure CeO2, are characterized by XRD, TGA, XPS, FTIR, HR-TEM, STEM, particle size distribution, and N2-physisorption. In spite of the identical preparation protocol, Au and Pt behave in a completely different way: Au forms rather large particles, most of them with triangular shape, easily identifiable and dispersed in the CeO2 matrix. In contrast, Pt was not identified as isolated particles. The high resolution X-ray diffraction carried out on the Pt/CeO2 thermally treated sample (500 degrees C for 1 h) shows a significant CeO2 lattice shrinkage, which can be interpreted as an at least partial incorporation of Pt into the CeO2 crystal lattice. Moreover, only Pt2+ and Pt4+ species were identified by XPS. In literature, the incorporation of Pt into the CeO2 lattice is supported by first-principle calculations and experimentally demonstrated only by combustion synthesis methods. To the best of our knowledge this is the first report where ionically dispersed Pt into the CeO2 lattice is obtained via a liquid synthesis method. The thermally treated Pt/CeO2 sample revealed good activity with 50% CO conversion at almost room temperature.

A hetero-homogeneous investigation of chemical bath deposited Ga-doped ZnO nanorods

NASA Astrophysics Data System (ADS)

Rakhsha, Amir Hosein; Abdizadeh, Hossein; Pourshaban, Erfan; Golobostanfard, Mohammad Reza

2018-01-01

One-dimensional nanostructures of zinc oxide (ZnO) have been in the center of attention, mostly for electronic applications due to their distinctive properties such as high electron mobility (100 cm2V-1s-1) and crystallinity. Thanks to its high density of vacancies and interstitial sites, wurtzite lattice of ZnO is a suitable host for gallium (Ga) as a dopant element. Herein, ZnO nanorod arrays (NRAs) are synthesized by a low-temperature chemical bath deposition (CBD) method with various concentrations of gallium nitrate hydrate as a dopant precursor. Structural and morphological analyses confirm that optimum properties of gallium-doped ZnO (GZO) are obtained at 1% (Ga to Zn molar ratio). Owing to the replacement of smaller Ga3+ ions with Zn2+ ions in the GZO structure, a slight shift of (002) peak to higher angles could be observed in XRD pattern of GZO NRAs. The scanning electron microscope images demonstrate a proliferation in the ZnO NRAs length from 650 nm for undoped ZnO (UZO) to 1200 nm for GZO-1%. However, increasing the dopant concentration above 2.5% results in formation of homogeneous zinc gallium oxide in the bulk solution, which is a sign of inefficient process of doping in GZO NRAs. Furthermore, photoluminescence spectroscopy is used to characterize the band-gap variation of the samples, which demonstrates a small red-shift in the UV emission peak and a decrease in visible emission peak intensity with introducing Ga in ZnO lattice. Lower resistivity for GZO-1% (1.1 MΩ) sample compared to UZO (1.4 MΩ) is recorded, which is compelling evidence for the presence of Ga3+ in ZnO lattice. The results suggest that incorporating Ga into ZnO lattice using CBD method is an easy and effective technique to improve the electrical properties of ZnO NRAs that is an essential factor for a broad range of devices.

Congressing kinetochores progressively load Ska complexes to prevent force-dependent detachment

PubMed Central

Auckland, Philip; Clarke, Nicholas I.

2017-01-01

Kinetochores mediate chromosome congression by either sliding along the lattice of spindle microtubules or forming end-on attachments to their depolymerizing plus-ends. By following the fates of individual kinetochores as they congress in live cells, we reveal that the Ska complex is required for a distinct substep of the depolymerization-coupled pulling mechanism. Ska depletion increases the frequency of naturally occurring, force-dependent P kinetochore detachment events, while being dispensable for the initial biorientation and movement of chromosomes. In unperturbed cells, these release events are followed by reattachment and successful congression, whereas in Ska-depleted cells, detached kinetochores remain in a futile reattachment/detachment cycle that prevents congression. We further find that Ska is progressively loaded onto bioriented kinetochore pairs as they congress. We thus propose a model in which kinetochores mature through Ska complex recruitment and that this is required for improved load-bearing capacity and silencing of the spindle assembly checkpoint. PMID:28495837

Magnetic anisotropy of some phyllosilicates

NASA Astrophysics Data System (ADS)

Borradaile, Graham J.; Werner, Tomasz

1994-08-01

Magnetic susceptibility, anisotropy of susceptibility and hysteresis of single microcrystals of chlorite, biotite, phlogopite, muscovite, zinnwaldite and fuchsite were measured in low and high magnetic fields with an alternating gradient force magnetometer (Micromag). Their properties are sufficient to account for the low field susceptibility (AMS) of most micaceous rocks. Nearly all samples show some ferromagnetic contribution at low fields due to inclusions of pseudosingle domain and multidomain magnetite. The paramagnetic contribution isolated at high fields usually exceeds the ferromagnetic contribution. The paramagnetic susceptibility is intrinsic to the silicate lattice and agrees with values predicted from chemical composition within the limits of error. The minimum susceptibility is nearly parallel to c, another axis is parallel to b and the third susceptibility (usually the maximum) is close to a. The paramagnetic susceptibility has a disk-shaped magnitude ellipsoid with strong anisotropy ( P' < 2). The ferromagnetic contributions at low fields have more variably shaped ellipsoids with greater eccentricity ( P' < 5). The silicate lattice does not constrain their orientation. Our technique cannot determine the principal axes of the ferromagnetic component. However, its principal values usually correspond with the paramagnetic principal susceptibilities in order of magnitude. Thus, the combined paramagnetic-ferromagnetic anisotropy recognised in routine studies of AMS should faithfully represent the petrofabric of most micaceous rocks. Nevertheless, nearly 10% of our samples have incompatible anisotropy ellipsoids for the silicate host and magnetite inclusions. These yield a net inverse AMS that does not correctly represent the orientation of the silicate lattice. Therefore, some caution is necessary in petrofabric-AMS studies of micaceous rocks.

Neutron diffraction and thermoelectric properties of indium filled In x Co 4 Sb 12 ( x=0.05, 0.2) and indium cerium filled Ce 0.05 In 0.1 Co 4 Sb 12 skutterudites: Neutron diffraction and thermoelectric properties of In/Ce skutterudites

DOE PAGES

Sesselmann, Andreas; Klobes, Benedikt; Dasgupta, Titas; ...

2015-09-25

The thermoelectric properties on polycrystalline single (In) and double filled (Ce, In) skutterudites are characterized between 300 and 700 K. Powder neutron diffraction measurements of the skutterudite compositions In xCo 4Sb 12 (x= 0.05, 0.2) and Ce 0.05In 0.1Co 4Sb 12 as a function of temperature (12- 300 K) were carried out, which gives more insight into the structural data of single and double-filled skutterudites. Our results show that due to the annealing treatment, a Sb deficiency is detectable and thus verifies defects at the Sb lattice site of the skutterudite. Furthermore, we show by electron microprobe analysis that amore » considerable amount of indium is lost during synthesis and post-processing for the single indium filled samples, but not for the double cerium and indium skutterudite sample. The double-filled skutterudite is superior to the single-filled skutterudite composition due to a higher charge carrier density, a comparable lattice thermal resistivity, and a higher density of states effective mass in our experiment. Finally, we obtained a significantly higher Einstein temperature for the double-filled skutterudite composition in comparison to the single-filled species, which reflects the high sensitivity due to filling of the void lattice position within the skutterudite crystal.« less

High pressure study of a highly energetic nitrogen-rich carbon nitride, cyanuric triazide

DOE Office of Scientific and Technical Information (OSTI.GOV)

Laniel, Dominique; Desgreniers, Serge; Downie, Laura E.

Cyanuric triazide (CTA), a nitrogen-rich energetic material, was compressed in a diamond anvil cell up to 63.2 GPa. Samples were characterized by x-ray diffraction, Raman, and infrared spectroscopy. A phase transition occurring between 29.8 and 30.7 GPa was found by all three techniques. The bulk modulus and its pressure derivative of the low pressure phase were determined by fitting the 300 K isothermal compression data to the Birch-Murnaghan equation of state. Due to the strong photosensitivity of CTA, synchrotron generated x-rays and visible laser radiation both lead to the progressive conversion of CTA into a two dimensional amorphous C=N network,more » starting from 9.2 GPa. As a result of the conversion, increasingly weak and broad x-ray diffraction lines were recorded from crystalline CTA as a function of pressure. Hence, a definite structure could not be obtained for the high pressure phase of CTA. Results from infrared spectroscopy carried out to 40.5 GPa suggest the high pressure formation of a lattice built of tri-tetrazole molecular units. The decompression study showed stability of the high pressure phase down to 13.9 GPa. Finally, two CTA samples, one loaded with neon and the other with nitrogen, used as pressure transmitting media, were laser-heated to approximately 1100 K and 1500 K while compressed at 37.7 GPa and 42.0 GPa, respectively. In both cases CTA decomposed resulting in amorphous compounds, as recovered at ambient conditions.« less

Size-induced variations in bulk/surface structures and their impact on photoluminescence properties of GdVO4:Eu3+ nanoparticles.

PubMed

Yang, Liusai; Li, Liping; Zhao, Minglei; Li, Guangshe

2012-07-28

This work explores the size-induced lattice modification and its relevance to photoluminescence properties of tetragonal zircon-type GdVO(4):Eu(3+) nanostructures. GdVO(4):Eu(3+) nanoparticles with crystallite sizes ranging from 14.4 to 24.7 nm were synthesized by a hydrothermal method using sodium citrate as a capping agent. Regardless of the reaction temperatures, all samples retained an ellipsoidal-like morphology. Nevertheless, as the crystallite size reduces, there appears a tensile strain and lattice distortion, which is accompanied by a lattice expansion and a decreased symmetry of structural units. These lattice modifications could be associated with the changes in the interior chemical bonding due to the interactions of surface defect dipoles that have imposed an increased negative pressure with crystallite size reduction. Furthermore, crystallite size reduction also led to a significant increase in the amounts of surface hydroxyl groups and citric species, as well as the concentration of the surface Eu(3+) ions. When Eu(3+) was taken as a structural probe, it was found that the asymmetric ratio (I(02)/I(01)) of Eu(3+) gradually declined to show a remarkable decrease in color chromaticity as crystallite size reduces, which could be interpreted as due to the change of local environments of Eu(3+) ions from the interior to the surface of the nanoparticles.

Doping effects on structural and magnetic properties of Heusler alloys Fe2Cr1-xCoxSi

NASA Astrophysics Data System (ADS)

Liu, Yifan; Ren, Lizhu; Zheng, Yuhong; He, Shikun; Liu, Yang; Yang, Ping; Yang, Hyunsoo; Teo, Kie Leong

2018-05-01

In this work, 30nm Fe2Cr1-xCoxSi (FCCS) magnetic films were deposited on Cr buffered MgO (100) substrates by sputtering. Fe2Cr0.5Co0.5Si exhibits the largest magnetization and optimal ordered L21 cubic structure at in-situ annealing temperature (Tia) of 450°C. The Co composition dependence of crystalline structures, surface morphology, defects, lattice distortions and their correlation with the magnetic properties are analyzed in detail. The Co-doped samples show in-plane M-H loops with magnetic squareness ratio of 1 and increasing anisotropy energy density with Co composition. Appropriate Co doping composition promotes L21 phase but higher Co composition converts L21 to B2 phase. Doping effect and lattice mismatch both are proved to increase the defect density. In addition, distortions of the FCCS lattice are found to be approximately linear with Co composition. The largest lattice distortion (c/a) is 0.969 for Fe2Cr0.25Co0.75Si and the smallest is 0.983 for Fe2CrSi. Our analyses suggest that these tetragonal distortions mainly induced by an elastic stress from Cr buffer account for the large in-plane anisotropy energy. This work paves the way for further tailoring the magnetic and structural properties of quaternary Heusler alloys.

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

NASA Astrophysics Data System (ADS)

Johns, Steve; Shin, Wontak; Kane, Joshua J.; Windes, William E.; Ubic, Rick; Karthik, Chinnathambi

2018-07-01

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. To ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ∼60 μm. Discs 3 mm in diameter were then oxidized at temperatures between 575 °C and 625 °C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575 °C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Johns, Steve; Shin, Wontak; Kane, Joshua J.

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. Thus,tomore » ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ~60μm. Discs 3mm in diameter were then oxidized at temperatures between 575°C and 625°C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575°C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.« less

Chip-based microtrap arrays for cold polar molecules

NASA Astrophysics Data System (ADS)

Hou, Shunyong; Wei, Bin; Deng, Lianzhong; Yin, Jianping

2017-12-01

Compared to the atomic chip, which has been a powerful platform to perform an astonishing range of applications from rapid Bose-Einstein condensate (BEC) production to the atomic clock, the molecular chip is only in its infant stages. Recently a one-dimensional electric lattice was demonstrated to trap polar molecules on a chip. This excellent work opens up the way to building a molecular chip laboratory. Here we propose a two-dimensional (2D) electric lattice on a chip with concise and robust structure, which is formed by arrays of squared gold wires. Arrays of microtraps that originate in the microsize electrodes offer a steep gradient and thus allow for confining both light and heavy polar molecules. Theoretical analysis and numerical calculations are performed using two types of sample molecules, N D3 and SrF, to justify the possibility of our proposal. The height of the minima of the potential wells is about 10 μm above the surface of the chip and can be easily adjusted in a wide range by changing the voltages applied on the electrodes. These microtraps offer intriguing perspectives for investigating cold molecules in periodic potentials, such as quantum computing science, low-dimensional physics, and some other possible applications amenable to magnetic or optical lattice. The 2D adjustable electric lattice is expected to act as a building block for a future gas-phase molecular chip laboratory.

Nuclear data uncertainty propagation by the XSUSA method in the HELIOS2 lattice code

NASA Astrophysics Data System (ADS)

Wemple, Charles; Zwermann, Winfried

2017-09-01

Uncertainty quantification has been extensively applied to nuclear criticality analyses for many years and has recently begun to be applied to depletion calculations. However, regulatory bodies worldwide are trending toward requiring such analyses for reactor fuel cycle calculations, which also requires uncertainty propagation for isotopics and nuclear reaction rates. XSUSA is a proven methodology for cross section uncertainty propagation based on random sampling of the nuclear data according to covariance data in multi-group representation; HELIOS2 is a lattice code widely used for commercial and research reactor fuel cycle calculations. This work describes a technique to automatically propagate the nuclear data uncertainties via the XSUSA approach through fuel lattice calculations in HELIOS2. Application of the XSUSA methodology in HELIOS2 presented some unusual challenges because of the highly-processed multi-group cross section data used in commercial lattice codes. Currently, uncertainties based on the SCALE 6.1 covariance data file are being used, but the implementation can be adapted to other covariance data in multi-group structure. Pin-cell and assembly depletion calculations, based on models described in the UAM-LWR Phase I and II benchmarks, are performed and uncertainties in multiplication factor, reaction rates, isotope concentrations, and delayed-neutron data are calculated. With this extension, it will be possible for HELIOS2 users to propagate nuclear data uncertainties directly from the microscopic cross sections to subsequent core simulations.

A new oxidation based technique for artifact free TEM specimen preparation of nuclear graphite

DOE PAGES

Johns, Steve; Shin, Wontak; Kane, Joshua J.; ...

2018-04-03

Graphite is a key component in designs of current and future nuclear reactors whose in-service lifetimes are dependent upon the mechanical performance of the graphite. Irradiation damage from fast neutrons creates lattice defects which have a dynamic effect on the microstructure and mechanical properties of graphite. Transmission electron microscopy (TEM) can offer real-time monitoring of the dynamic atomic-level response of graphite subjected to irradiation; however, conventional TEM specimen-preparation techniques, such as argon ion milling itself, damage the graphite specimen and introduce lattice defects. It is impossible to distinguish these defects from the ones created by electron or neutron irradiation. Thus,tomore » ensure that TEM specimens are artifact-free, a new oxidation-based technique has been developed. Bulk nuclear grades of graphite (IG-110 and NBG-18) and highly oriented pyrolytic graphite (HOPG) were initially mechanically thinned to ~60μm. Discs 3mm in diameter were then oxidized at temperatures between 575°C and 625°C in oxidizing gasses using a new jet-polisher-like set-up in order to achieve optimal oxidation conditions to create self-supporting electron-transparent TEM specimens. The quality of these oxidized specimens were established using optical and electron microscopy. Samples oxidized at 575°C exhibited large areas of electron transparency and the corresponding lattice imaging showed no apparent damage to the graphite lattice.« less

Microstructural analysis in the depth direction of a heteroepitaxial AlN thick film grown on a trench-patterned template by nanobeam X-ray diffraction

NASA Astrophysics Data System (ADS)

Shida, K.; Takeuchi, S.; Tohei, T.; Miyake, H.; Hiramatsu, K.; Sumitani, K.; Imai, Y.; Kimura, S.; Sakai, A.

2018-04-01

This work quantitatively assessed the three-dimensional distribution of crystal lattice distortions in an epitaxial AlN thick film grown on a trench-patterned template, using nanobeam X-ray diffraction. Position-dependent ω-2θ-φ mapping clearly demonstrated local tilting, spacing and twisting of lattice planes as well as fluctuations in these phenomena on a sub-micrometer scale comparable to the pitch of the trench-and-terrace patterning. Analysis of the crystal lattice distortion in the depth direction was performed using a newly developed method in which the X-ray nanobeam diffracted from the sample surface to specific depths can be selectively detected by employing a Pt wire profiler. This technique generated depth-resolved ω-2θ-φ maps confirming that fluctuations in lattice plane tilting and spacing greatly depend on the dislocation distribution and the history of the AlN epitaxial growth on the trench-patterned structure. It was also found that both fluctuations were reduced on approaching the AlN surface and, in particular, were sharply reduced at specific depths in the terrace regions. These sharp reductions are attributed to the formation of sacrificial zones with degraded crystal quality around the trenches and possibly lead to raising the crystal quality near the surface of the AlN film.

A Mechanical Lattice Aid for Crystallography Teaching.

ERIC Educational Resources Information Center

Amezcua-Lopez, J.; Cordero-Borboa, A. E.

1988-01-01

Introduces a 3-dimensional mechanical lattice with adjustable telescoping mechanisms. Discusses the crystalline state, the 14 Bravais lattices, operational principles of the mechanical lattice, construction methods, and demonstrations in classroom. Provides lattice diagrams, schemes of the lattice, and various pictures of the lattice. (YP)

High-resolution three-dimensional structural microscopy by single-angle Bragg ptychography

DOE PAGES

Hruszkewycz, S. O.; Allain, M.; Holt, M. V.; ...

2016-11-21

Coherent X-ray microscopy by phase retrieval of Bragg diffraction intensities enables lattice distortions within a crystal to be imaged at nanometre-scale spatial resolutions in three dimensions. While this capability can be used to resolve structure–property relationships at the nanoscale under working conditions, strict data measurement requirements can limit the application of current approaches. Here, in this work, we introduce an efficient method of imaging three-dimensional (3D) nanoscale lattice behaviour and strain fields in crystalline materials with a methodology that we call 3D Bragg projection ptychography (3DBPP). This method enables 3D image reconstruction of a crystal volume from a series ofmore » two-dimensional X-ray Bragg coherent intensity diffraction patterns measured at a single incident beam angle. Structural information about the sample is encoded along two reciprocal-space directions normal to the Bragg diffracted exit beam, and along the third dimension in real space by the scanning beam. Finally, we present our approach with an analytical derivation, a numerical demonstration, and an experimental reconstruction of lattice distortions in a component of a nanoelectronic prototype device.« less

Micro-beam Laue alignment of multi-reflection Bragg coherent diffraction imaging measurements

DOE PAGES

Hofmann, Felix; Phillips, Nicholas W.; Harder, Ross J.; ...

2017-08-08

Multi-reflection Bragg coherent diffraction imaging has the potential to allow three-dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here, in this paper, a different approach is demonstrated, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focusedmore » ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Lastly, our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples.« less

Epitaxial growth and magnetic properties of Fe4-xMnxN thin films grown on MgO(0 0 1) substrates by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Anzai, Akihito; Takata, Fumiya; Gushi, Toshiki; Toko, Kaoru; Suemasu, Takashi

2018-05-01

Epitaxial Fe4-xMnxN (x = 0, 1, 2, 3, and 4) thin films were successfully grown on MgO(0 0 1) single-crystal substrates by molecular beam epitaxy, and their crystalline qualities and magnetic properties were investigated. It was found that the lattice constants of Fe4-xMnxN obtained from X-ray diffraction measurement increased with the Mn content. The ratio of the perpendicular lattice constant c to the in-plane lattice constant a of Fe4-xMnxN was found to be about 0.99 at x ⩾ 2. The magnetic properties evaluated using a vibrating sample magnetometer at room temperature revealed that all of the Fe4-xMnxN films exhibited ferromagnetic behavior regardless of the value of x. In addition, the saturation magnetization decreased non-linearly as the Mn content increased. Finally, FeMn3N and Mn4N exhibited perpendicular anisotropy and their uniaxial magnetic anisotropy energies were 2.2 × 105 and 7.5 × 105 erg/cm3, respectively.

Micro-beam Laue alignment of multi-reflection Bragg coherent diffraction imaging measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hofmann, Felix; Phillips, Nicholas W.; Harder, Ross J.

Multi-reflection Bragg coherent diffraction imaging has the potential to allow three-dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here, in this paper, a different approach is demonstrated, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focusedmore » ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Lastly, our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples.« less

Low-frequency zone boundary phonons in Li doped ZnO ceramics

NASA Astrophysics Data System (ADS)

Yadav, Harish Kumar; Sreenivas, K.; Gupta, Vinay; Katiyar, R. S.

2008-09-01

Room temperature Raman spectra of Li doped ZnO (Zn1-xLixO) ceramics with varying Li concentrations (x =0.0, 0.05, 0.10, and 0.15) are investigated in this study. Four peaks were identified at 96.6, 127, 157, and 194 cm-1 in the Li doped samples. The peaks at 127, 157, and 194 cm-1 are assigned to zone boundary phonons in ZnO [J. M. Calleja and M. Cardona, Phys. Rev. B 16, 3753 (1977)], and appear due to disorder in ZnO lattice with Li incorporation. Lithium, owing to its smaller radius, adjusts itself anywhere in the ZnO lattice and breaks the crystal translational symmetry to a large extent, compared to other dopants. Disorder in the lattice is seen to be finely modulated with varying Li content. The peak at 96.6 cm-1 is hypothesized to be a projection of the vibrational motion of Li atoms at lower frequencies, which contributes in a major fashion at higher frequencies, due to its lighter mass than Zn or O atoms.

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

PubMed

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.

Micro-beam Laue alignment of multi-reflection Bragg coherent diffraction imaging measurements.

PubMed

Hofmann, Felix; Phillips, Nicholas W; Harder, Ross J; Liu, Wenjun; Clark, Jesse N; Robinson, Ian K; Abbey, Brian

2017-09-01

Multi-reflection Bragg coherent diffraction imaging has the potential to allow three-dimensional (3D) resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here a different approach is demonstrated, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focused ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples.

Micro-beam Laue Alignment of Multi-Reflection Bragg Coherent Diffraction Imaging Measurements

PubMed Central

Hofmann, Felix; Phillips, Nicholas W.; Harder, Ross J.; Liu, Wenjun; Clark, Jesse N.; Robinson, Ian K.; Abbey, Brian

2017-01-01

Multi-reflection Bragg coherent diffraction imaging has the potential to allow 3D resolved measurements of the full lattice strain tensor in specific micro-crystals. Until now such measurements were hampered by the need for laborious, time-intensive alignment procedures. Here we demonstrate a different approach, using micro-beam Laue X-ray diffraction to first determine the lattice orientation of the micro-crystal. This information is then used to rapidly align coherent diffraction measurements of three or more reflections from the crystal. Based on these, 3D strain and stress fields in the crystal are successfully determined. This approach is demonstrated on a focussed ion beam milled micro-crystal from which six reflections could be measured. Since information from more than three independent reflections is available, the reliability of the phases retrieved from the coherent diffraction data can be assessed. Our results show that rapid, reliable 3D coherent diffraction measurements of the full lattice strain tensor in specific micro-crystals are now feasible and can be successfully carried out even in heavily distorted samples. PMID:28862628

Application of powder X-ray diffraction in studying the compaction behavior of bulk pharmaceutical powders.

PubMed

Bandyopadhyay, Rebanta; Selbo, Jon; Amidon, Gregory E; Hawley, Michael

2005-11-01

This study investigates the effects of crystal lattice deformation on the powder X-ray diffraction (PXRD) patterns of compressed polycrystalline specimen (compacts/tablets) made from molecular, crystalline powders. The displacement of molecules and the corresponding adjustment of interplanar distances (d-spacings) between diffracting planes of PNU-288034 and PNU-177553, which have crystal habits with a high aspect ratio favoring preferred orientation during tableting, are demonstrated by shifts in the diffracted peak positions. The direction of shift in diffracted peak positions suggests a reduction of interplanar d-spacing in the crystals of PNU-288034 and PNU-177553 following compaction. There is also a general reduction of peak intensities following compression at the different compressive loads. The lattice strain representing the reduction in d-spacing is proportional to the original d-spacing of the uncompressed sample suggesting that, as with systems that obey a simple Hooke's law relationship, the further apart the planes of atoms/molecules within the lattice are, the easier it is for them to approach each other under compressive stresses. For a third model compound comprising more equant-shaped crystals of PNU-141659, the shift in diffracted peak positions are consistent with an expansion of lattice spacing after compression. This apparent anomaly is supported by the PXRD studies of the bulk powder consisting of fractured crystals where also, the shift in peak position suggests expansion of the lattice planes. Thus the crystals of PNU-141659 may be fracturing under the compressive loads used to produce the compacts. Additional studies are underway to relate the PXRD observations with the bulk tableting properties of these model compounds.

Vortex Matter in Highly Strained Nb_{75}Zr_{25}: Analogy with Viscous Flow of Disordered Solids

NASA Astrophysics Data System (ADS)

Chandra, Jagdish; Manekar, Meghmalhar; Sharma, V. K.; Mondal, Puspen; Tiwari, Pragya; Roy, S. B.

2017-01-01

We present the results of magnetization and magneto-transport measurements in the superconducting state of an as-cast Nb_{75}Zr_{25} alloy. We also report the microstructure of our sample at various length scales by using optical, scanning electron and transmission electron microscopies. The information of microstructure is used to understand the flux pinning properties in the superconducting state within the framework of collective pinning. The magneto-transport measurements show a non-Arrhenius behaviour of the temperature- and field-dependent resistivity across the resistive transition and is understood in terms of a model for viscous flow of disordered solids which is popularly known as the `shoving model'. The activation energy for flux flow is assumed to be mainly the elastic energy stored in the flux-line lattice. The scaling of pinning force density indicates the presence of two pinning mechanisms of different origins. The elastic constants of the flux-line lattice are used to estimate the length scale of vortex lattice movement, or the volume displaced by the flux-line lattice. It appears that the vortex lattice displacement estimated from elastic energy considerations is of the same order of magnitude as that of the flux bundle hopping length during flux flow. Our results could provide possible directions for establishing a framework where vortex matter and glass-forming liquids or amorphous solids can be treated in a similar manner for understanding the phenomenon of viscous flow in disordered solids or more generally the pinning and depinning properties of elastic manifolds in random media. It is likely that the vortex molasses scenario is more suited to explain the vortex dynamics in conventional low-T_C superconductors.

Ex-Situ Synthesis of Polyvinyl alcohol(PVA)-coated Fe3O4 Nanoparticles by Coprecipitation-Ultrasonication Method

NASA Astrophysics Data System (ADS)

Riva'i, Imam; Oktavia Wulandari, Ika; Sulistyarti, Hermin; Sabarudin, Akhmad

2018-01-01

In this study, the synthesis of Fe3O4 nanoparticles was done with surface modification using PVA with coprecipitation-ultrasonication method. Time variations and PVA concentrations were added to determine the effect on crystallite size and lattice parameters on the synthesis of Fe3O4-PVA nanoparticles. Fe3O4 characterization was done using X-Ray Diffraction (XRD) and Fourier Transform Infrared Spectroscopy (FTIR) instruments. FTIR was employed to determine PVA coating on the surface of Fe3O4 nanoparticles. The crystallite size and lattice parameters were analyzed using XRD. From the FTIR data, it is known that the interaction between PVA and Fe3O4 nanoparticles is characterized by Fe-O-C group at 1100 cm-1 region which is characteristic of Fe3O4-PVA nanoparticles, C-H groups of PVA in the range of 2950 cm-1 wave number, C-C of PVA regions of wave number 1405 cm-1, Fe3O4 and Fe3O4-PVA samples are in the range of 565 cm-1. In addition, the variation of ultrasonication time and the addition of PVA concentration have an effect on the crystallite size change and the lattice parameter observed from the XRD data. The use of ultrasonication time will affect the size of the crystallite become smaller and the grating lattice parameters obtained are wider. The effect of addition of PVA showed that higher concentration of PVA resulted in smaller crystallite size and larger lattice parameters. These results indicated that ultrasonication time and addition of PVA concentration greatly affect the characteristics of nanoparticles.

A hexagonal orthogonal-oriented pyramid as a model of image representation in visual cortex

NASA Technical Reports Server (NTRS)

Watson, Andrew B.; Ahumada, Albert J., Jr.

1989-01-01

Retinal ganglion cells represent the visual image with a spatial code, in which each cell conveys information about a small region in the image. In contrast, cells of the primary visual cortex use a hybrid space-frequency code in which each cell conveys information about a region that is local in space, spatial frequency, and orientation. A mathematical model for this transformation is described. The hexagonal orthogonal-oriented quadrature pyramid (HOP) transform, which operates on a hexagonal input lattice, uses basis functions that are orthogonal, self-similar, and localized in space, spatial frequency, orientation, and phase. The basis functions, which are generated from seven basic types through a recursive process, form an image code of the pyramid type. The seven basis functions, six bandpass and one low-pass, occupy a point and a hexagon of six nearest neighbors on a hexagonal lattice. The six bandpass basis functions consist of three with even symmetry, and three with odd symmetry. At the lowest level, the inputs are image samples. At each higher level, the input lattice is provided by the low-pass coefficients computed at the previous level. At each level, the output is subsampled in such a way as to yield a new hexagonal lattice with a spacing square root of 7 larger than the previous level, so that the number of coefficients is reduced by a factor of seven at each level. In the biological model, the input lattice is the retinal ganglion cell array. The resulting scheme provides a compact, efficient code of the image and generates receptive fields that resemble those of the primary visual cortex.

Effect of Mutations on HP Lattice Proteins

NASA Astrophysics Data System (ADS)

Shi, Guangjie; Vogel, Thomas; Landau, David; Li, Ying; Wüst, Thomas

2013-03-01

Using Wang-Landau sampling with approriate trial moves[2], we investigate the effect of different types of mutations on lattice proteins in the HP model. While exact studies have been carried out for short HP proteins[3], the systems we investigate are of much larger size and hence not accessible for exact enumerations. Based on the estimated density of states, we systematically analyse the changes in structure and degeneracy of ground states of particular proteins and measure thermodynamic quantities like the stability of ground states and the specific heat, for example. Both, neutral mutations, which do not change the structure and stability of ground states, as well as critical mutations, which do change the thermodynamic behavior qualitatively, have been observed. Research supported by NSF

Measurement of O and Ti atom displacements in TiO 2 during flash sintering experiments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yoon, Bola; Yadav, Devinder; Raj, Rishi

In-situ flash experiments on rutile TiO 2 were performed at the synchrotron at the Brookhaven National Laboratory. Pair distribution function analysis of total X-ray scattering measurements yielded mean-square atomic displacements of oxygen and titanium atoms during the progression of the 3 stages of flash. The displacements are measured to be far greater for oxygen atoms than for titanium atoms. Thus, these large displacements may signal an “elastic softening” of the lattice, which, recently, has been predicted as a precursor to the onset of flash.

Measurement of O and Ti atom displacements in TiO 2 during flash sintering experiments

DOE PAGES

Yoon, Bola; Yadav, Devinder; Raj, Rishi; ...

2017-12-29

In-situ flash experiments on rutile TiO 2 were performed at the synchrotron at the Brookhaven National Laboratory. Pair distribution function analysis of total X-ray scattering measurements yielded mean-square atomic displacements of oxygen and titanium atoms during the progression of the 3 stages of flash. The displacements are measured to be far greater for oxygen atoms than for titanium atoms. Thus, these large displacements may signal an “elastic softening” of the lattice, which, recently, has been predicted as a precursor to the onset of flash.

CUDA programs for the GPU computing of the Swendsen-Wang multi-cluster spin flip algorithm: 2D and 3D Ising, Potts, and XY models

NASA Astrophysics Data System (ADS)

Komura, Yukihiro; Okabe, Yutaka

2014-03-01

We present sample CUDA programs for the GPU computing of the Swendsen-Wang multi-cluster spin flip algorithm. We deal with the classical spin models; the Ising model, the q-state Potts model, and the classical XY model. As for the lattice, both the 2D (square) lattice and the 3D (simple cubic) lattice are treated. We already reported the idea of the GPU implementation for 2D models (Komura and Okabe, 2012). We here explain the details of sample programs, and discuss the performance of the present GPU implementation for the 3D Ising and XY models. We also show the calculated results of the moment ratio for these models, and discuss phase transitions. Catalogue identifier: AERM_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AERM_v1_0.html Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 5632 No. of bytes in distributed program, including test data, etc.: 14688 Distribution format: tar.gz Programming language: C, CUDA. Computer: System with an NVIDIA CUDA enabled GPU. Operating system: System with an NVIDIA CUDA enabled GPU. Classification: 23. External routines: NVIDIA CUDA Toolkit 3.0 or newer Nature of problem: Monte Carlo simulation of classical spin systems. Ising, q-state Potts model, and the classical XY model are treated for both two-dimensional and three-dimensional lattices. Solution method: GPU-based Swendsen-Wang multi-cluster spin flip Monte Carlo method. The CUDA implementation for the cluster-labeling is based on the work by Hawick et al. [1] and that by Kalentev et al. [2]. Restrictions: The system size is limited depending on the memory of a GPU. Running time: For the parameters used in the sample programs, it takes about a minute for each program. Of course, it depends on the system size, the number of Monte Carlo steps, etc. References: [1] K.A. Hawick, A. Leist, and D. P. Playne, Parallel Computing 36 (2010) 655-678 [2] O. Kalentev, A. Rai, S. Kemnitzb, and R. Schneider, J. Parallel Distrib. Comput. 71 (2011) 615-620

Structural, optical and dielectric studies of Er substituted zinc ferrite nanospheres

NASA Astrophysics Data System (ADS)

Shoba, M.; Kaleemulla, S.

2017-12-01

The cationic distributions among tetrahedral and octahedral sites in spinel ferrites have a profound influence on their properties. Many studies were reported with various transition metal (TM) and rare earth (RE) cations distribution. We report the synthesis, structural, morphology, lattice vibrational, optical and dielectric properties of heavy RE cation (Er) substituted ZnFe2O4 as a function of different experimental parameters. The coprecipitated and calcined ZnFe2-xErxO4 (x = 0, 0.2, 0.4, 0.6 & 0.8) compounds crystallizes in cubic spinel structure and show narrow particle size distribution due to surfactant PEG. Particle size reduces (27-16 nm) with enhance of Er concentration (x = 0 to 0.8) in the compounds. The EDAX spectra of the samples incorporation Er3+ ions into the lattice and the cubic lattice parameter enhances with Er3+ concentration. The lattice vibrational spectra reveal that the particles surface were free from surfactant PEG. Optical excitation studies show that energy band gap (Eg) of compounds reduces (1.85-2.00 eV) with enhance of Er concentration. The temperature, as well as frequency dependent dielectric constant (εrʹ) of ZnFe2-xErxO4, shows enhanced εrʹ with Er concentration up to x = 0.4 and then reduces with further enhancing of Er concentration. The dielectric loss factor (εrʹʹ) show similar variation with Er concentration. Further, both εrʹ and εrʹʹ were reduced with enhancing of field frequency. In addition, both εrʹ and εrʹʹ were enhanced with temperature and showed exponential change at low frequencies and high temperature and is attributed magnetic transition at around 525 K. The interface polarization mechanism is the predominant one in the present samples. The ac impedance spectra show two semicircles and each semicircle results from dielectric relaxation due to either particle (grain) or particles interface (grain boundary) polarization. The ac impedance reduces with enhancing of temperature. From the above studies, it is concluded that ZnFe1.6Er0.4O4 composition was best for high εrʹ and εrʹʹ values at low frequencies. All samples could be used in high-frequency application.

Recent progress in the imaging of soil processes at the microscopic scale, and a look ahead

NASA Astrophysics Data System (ADS)

Garnier, Patricia; Baveye, Philippe C.; Pot, Valérie; Monga, Olivier; Portell, Xavier

2016-04-01

Over the last few years, tremendous progress has been achieved in the visualization of soil structures at the microscopic scale. Computed tomography, based on synchrotron X-ray beams or table-top equipment, allows the visualization of pore geometry at micrometric resolution. Chemical and microbiological information obtainable in 2D cuts through soils can now be interpolated, with the support of CT-data, to produce 3-dimensional maps. In parallel with these analytical advances, significant progress has also been achieved in the computer simulation and visualization of a range of physical, chemical, and microbiological processes taking place in soil pores. In terms of water distribution and transport in soils, for example, the use of Lattice-Boltzmann models as well as models based on geometric primitives has been shown recently to reproduce very faithfully observations made with synchrotron X-ray tomography. Coupling of these models with fungal and bacterial growth models allows the description of a range of microbiologically-mediated processes of great importance at the moment, for example in terms of carbon sequestration. In this talk, we shall review progress achieved to date in this field, indicate where questions remain unanswered, and point out areas where further advances are expected in the next few years.

Reactivity-worth estimates of the OSMOSE samples in the MINERVE reactor R1-MOX, R2-UO2 and MORGANE/R configurations.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhong, Z.; Klann, R. T.; Nuclear Engineering Division

2007-08-03

An initial series of calculations of the reactivity-worth of the OSMOSE samples in the MINERVE reactor with the R2-UO2 and MORGANE/R core configuration were completed. The calculation model was generated using the lattice physics code DRAGON. In addition, an initial comparison of calculated values to experimental measurements was performed based on preliminary results for the R1-MOX configuration.

A Solid-State NMR Study of Selenium Substitution into Nanocrystalline Hydroxyapatite

PubMed Central

Kolmas, Joanna; Kuras, Marzena; Oledzka, Ewa; Sobczak, Marcin

2015-01-01

The substitution of selenium oxyanions in the hydroxyapatite structure was examined using multinuclear solid-state resonance spectroscopy (ssNMR). The study was supported by powder X-ray diffractometry (PXRD) and wavelength dispersion X-ray fluorescence (WD-XRF). Samples of pure hydroxyapatite (HA300) and selenate (HA300-1.2SeO4) or selenite (HA300-1.2SeO3) substituted hydroxyapatites were synthesized using the standard wet method and heated at 300 °C to remove loosely bonded water. PXRD data showed that all samples are single-phase, nanocrystalline hydroxyapatite. The incorporation of selenite and selenate ions affected the lattice constants. In selenium-containing samples the concentration of Se was very similar and amounted to 9.55% and 9.64%, for HA300-1.2SeO4 and HA300-1.2SeO3, respectively. PXRD and ssNMR data showed that the selenite doping significantly decreases the crystallite size and crystallinity degree. 31P and 1H NMR experiments demonstrated the developed surface hydrated layer in all samples, especially in HA300-1.2SeO3. 1H NMR studies showed the dehydroxylation of HA during the selenium oxyanions substitution and the existence of hydrogen bonding in structural hydroxyl group channels. 1H→77Se cross polarization NMR experiments indicated that selenites and selenates are located in the crystal lattice and on the crystal surface. PMID:25997001

The interaction of Ag with Bi-Pb-Sr-Ca-Cu-O superconductor

NASA Astrophysics Data System (ADS)

Dou, S. X.; Song, K. H.; Liu, H. K.; Sorrell, C. C.; Apperley, M. H.; Gouch, A. J.; Savvides, N.; Hensley, D. W.

1989-10-01

Bi-Pb-Sr-Ca-Cu-O superconductor compounds have been doped with up to 30 wt% Ag, sintered under variable oxygen partial pressure, and characterised in terms of the electrical and crystallographic behaviour. In contrast to previous reports that claim that Ag is the only metal non-poisoning to the superconductivity of Bi-Sr-Ca-Cu-O (BSCCO), it has been found that Ag additions to Bi-Pb-Sr-Ca-Cu-O depress Tc and Jc drastically and cause a large decrease in lattice parameters when samples are treated in air or pure oxygen. However, the lattice parameters, Tc and Jc remain unaffected by Ag additions when samples are heat treated in 0.030-0.067 atm oxygen. It is clear that the Ag reacts with and destabilises the superconducting phase when the samples are treated in air or pure oxygen while, when the samples are heat treated in low oxygen partial pressures, the Ag remains as an isolated inert metal phase that improves the weak links between the grains. This discovery clearly shows the feasibility of Ag-clad superconductor wire. For Ag-clad superconductor tape of 0.1 mm 2 cross sectional area heat treated in air, Jc was measured to be 54 A/cm 2. The same specimen sintered in 0.067 atm oxygen showed that the Jc increased to 2078 A/cm 2.

Colossal magnetoresistance in amino-functionalized graphene quantum dots at room temperature: manifestation of weak anti-localization and doorway to spintronics

NASA Astrophysics Data System (ADS)

Roy, Rajarshi; Thapa, Ranjit; Kumar, Gundam Sandeep; Mazumder, Nilesh; Sen, Dipayan; Sinthika, S.; Das, Nirmalya S.; Chattopadhyay, Kalyan K.

2016-04-01

In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (~1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for future graphene quantum dot based spintronic applications.In this work, we have demonstrated the signatures of localized surface distortions and disorders in functionalized graphene quantum dots (fGQD) and consequences in magneto-transport under weak field regime (~1 Tesla) at room temperature. Observed positive colossal magnetoresistance (MR) and its suppression is primarily explained by weak anti-localization phenomenon where competitive valley (inter and intra) dependent scattering takes place at room temperature under low magnetic field; analogous to low mobility disordered graphene samples. Furthermore, using ab-initio analysis we show that sub-lattice sensitive spin-polarized ground state exists in the GQD as a result of pz orbital asymmetry in GQD carbon atoms with amino functional groups. This spin polarized ground state is believed to help the weak anti-localization dependent magneto transport by generating more disorder and strain in a GQD lattice under applied magnetic field and lays the premise for future graphene quantum dot based spintronic applications. Electronic supplementary information (ESI) available: UV-Vis spectrum of synthesized fGQDs, reconstructed false color surface topographic images from a high-resolution fGQD TEM lattice; Raman spectra with corresponding Breit-Wigner-Fano (BWF) line fitting of `G band' before and after the application of sTMF, spin density distribution (SDD) with different shapes of a functionalized graphene quantum dot, SDD of the main simulated fGQD model obtained using different exchange correlation functional (PW91, RBPE and LDA). Models of (a) two NH2 molecules adsorbed on a graphene sheet (periodic structure), (b) representing corresponding SPDOS are also provided. Charge density distribution (CDD) with two-dimensional side view contour plots of adsorbed -NH2 and O&z.dbd;C-NH2 on GQD lattice and SPDOS of a main fGQD model with 0.2% strain. See DOI: 10.1039/c5nr09292b

Integer lattice gas with Monte Carlo collision operator recovers the lattice Boltzmann method with Poisson-distributed fluctuations

NASA Astrophysics Data System (ADS)

Blommel, Thomas; Wagner, Alexander J.

2018-02-01

We examine a new kind of lattice gas that closely resembles modern lattice Boltzmann methods. This new kind of lattice gas, which we call a Monte Carlo lattice gas, has interesting properties that shed light on the origin of the multirelaxation time collision operator, and it derives the equilibrium distribution for an entropic lattice Boltzmann. Furthermore these lattice gas methods have Galilean invariant fluctuations given by a Poisson statistics, giving further insight into the properties that we should expect for fluctuating lattice Boltzmann methods.

Study of defects and vacancies in structural properties of Mn, co-doped oxides: ZnO

NASA Astrophysics Data System (ADS)

Kumar, Harish; Kaushik, A.; Alvi, P. A.; Dalela, B.; Dalela, S.

2018-05-01

The paper deals with the Structural properties on Mn, Co doped oxides ZnO samples using XRD, Positron Annihilation Lifetime (PAL) Spectra and Raman Spectra. The Mn, Co doped ZnO samples crystallize in a wurtzite structure without any impurity phases in XRD Spectra. The defect state of these samples has been investigated by using positron annihilation lifetime (PAL) spectroscopy technique in which all the relevant lifetime parameters are measured for all the spectra. The results are explained in the direction of doping concentration in these samples in terms of defects structure on Zn lattice site VZn and oxygen defects Vo.