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Sample records for atomic quasicrystal structure

  1. Quasicrystals

    International Nuclear Information System (INIS)

    Bratkovskij, A.M.; Danilov, Yu.A.; Kuznetsov, G.I.

    1989-01-01

    New field of condensed state physics which deals with study of quasiperiodical solids (quasicrystals) is presented in the review. Preparation techniques for quasicrystals, models of their atomic structure (for Al-TM, TM-transition metal and Al with sp-metals type quasicrystals) and different structure-sensitive techniques of investigation are considered. Elastic and thermodynamic features of quasicrystals, electron properties, lattice dynamics, transfer phenomena, phase transformations and stability are described. Essential attention is paid to the description of quasiperiodical system geometry: decompositions, packing, grids, quasilattices and inlay. Phenomenological description of quasicrystals using Landau functional is given, problem concerning stability in corresponding models is discussed and main correlations for quasicrystal spectrum, structure factor are given

  2. Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal

    Directory of Open Access Journals (Sweden)

    Tsunetomo Yamada

    2016-07-01

    Full Text Available The detailed atomic structure of the binary icosahedral (i ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP, both resulting from a close-packing of a large (Sc and a small (Zn atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K2/K1 = −0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason Debye–Waller factor, which explains the vanishing of `high-Qperp' reflections.

  3. Atomic structure and phason modes of the Sc–Zn icosahedral quasicrystal

    Science.gov (United States)

    Yamada, Tsunetomo; Takakura, Hiroyuki; Euchner, Holger; Pay Gómez, Cesar; Bosak, Alexei; Fertey, Pierre; de Boissieu, Marc

    2016-01-01

    The detailed atomic structure of the binary icosahedral (i) ScZn7.33 quasicrystal has been investigated by means of high-resolution synchrotron single-crystal X-ray diffraction and absolute scale measurements of diffuse scattering. The average atomic structure has been solved using the measured Bragg intensity data based on a six-dimensional model that is isostructural to the i-YbCd5.7 one. The structure is described with a quasiperiodic packing of large Tsai-type rhombic triacontahedron clusters and double Friauf polyhedra (DFP), both resulting from a close-packing of a large (Sc) and a small (Zn) atom. The difference in chemical composition between i-ScZn7.33 and i-YbCd5.7 was found to lie in the icosahedron shell and the DFP where in i-ScZn7.33 chemical disorder occurs on the large atom sites, which induces a significant distortion to the structure units. The intensity in reciprocal space displays a substantial amount of diffuse scattering with anisotropic distribution, located around the strong Bragg peaks, that can be fully interpreted as resulting from phason fluctuations, with a ratio of the phason elastic constants K 2/K 1 = −0.53, i.e. close to a threefold instability limit. This induces a relatively large perpendicular (or phason) Debye–Waller factor, which explains the vanishing of ‘high-Q perp’ reflections. PMID:27437112

  4. Atomic structure of nanoscale quasicrystal-forming Zr-noble metal binary metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Saida, J., E-mail: jsaida@cir.tohoku.ac.jp [Center for Interdisciplinary Research, Tohoku University, Aramaki Aoba, Aoba-ku, Sendai 980-8578 (Japan); Itoh, K. [Graduate School of Education, Okayama University, Tsushimanaka, Kita-ku, Okayama 700-8530 (Japan); Sanada, T. [Research Department, Nissan ARC Ltd., Natsushima, Yokosuka 237-0061 (Japan); Sato, S. [Institute for Materials Research, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577 (Japan); Imafuku, M. [Faculty of Engineering, Tokyo City University, Setagaya-ku, Tokyo 158-8557 (Japan); Ohnuma, M. [National Institute of Materials Science (NIMS), Sengen, Tsukuba, Ibaraki 305-0047 (Japan); Inoue, A. [WPI-AIMR, Tohoku University, Katahira, Aoba-ku, Sendai 980-8577 (Japan)

    2011-06-15

    Research highlights: > Zr{sub 70}Pd{sub 30} and Zr{sub 80}Pt{sub 20} are the quasicrystal (QC)-forming glassy alloys. > The QC phase precipitates by a cooperative motion of atoms or clusters. > Relatively perfect icosahedrons frequently exist around Zr in Zr{sub 70}Pd{sub 30}, however, distorted icosahedral-like clusters are formed around Zr and Pt in Zr{sub 80}Pt{sub 20}. > The QC phase formation originates from a different mechanism in the two alloys. - Abstract: We report the results of the local structural evaluation and mechanism of QC formation in the Zr{sub 70}Pd{sub 30} and Zr{sub 80}Pt{sub 20} glassy alloys. Voronoi analysis indicates the difference of local environment between two alloys. The perfect icosahedron frequently exists around Zr atom and major polyhedra have prism-like structure around Pd in Zr{sub 70}Pd{sub 30}. In contrast, icosahedral-like distorted polyhedra formation is favorable around Pt as well as Zr in Zr{sub 80}Pt{sub 20}. It is therefore, concluded that the quasicrystallization originates from the medium-range order based on the Zr-centered perfect icosahedron and the Pd-centered prism-like ones remain during the QC phase formation in Zr{sub 70}Pd{sub 30}. Icosahedral-like local structure around Zr and Pt might contribute together to the nucleation of QC phase in Zr{sub 80}Pt{sub 20}. This feature with a different mechanism of QC formation in the two alloys may correlate to the difference of solute concentration and the structure of stable crystalline phase after the decomposition of QC phase.

  5. Crystallography of quasicrystals concepts, methods and structures

    CERN Document Server

    Walter, Steurer

    2009-01-01

    From tilings to quasicrystal structures and from surfaces to the n-dimensional approach, this book gives a full, self-contained in-depth description of the crystallography of quasicrystals. It aims not only at conveying the concepts and a precise picture of the structures of quasicrystals, butit also enables the interested reader to enter the field of quasicrystal structure analysis. Going beyond metallic quasicrystals, it also describes the new, dynamically growing field of photonic quasicrystals. The readership will be graduate students and researchers in crystallography, solid-state physics, materials science, solid- state chemistry and applied mathematics.

  6. Quasicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Steurer, W. [ETH Zurich, Lab. of Crystallography, Zurich (Switzerland)

    1996-11-01

    Quasicrystals are new materials with strictly defined quasiperiodic atomic long-range order. One of their most striking features is their scaling symmetry (self-similarity) in direct and reciprocal space. The quasiperiodic order gives rise to a new type of low-energy excitations, the so-called phason modes which are related to well-defined atomic jumps. The open problems connected with the research on quasicrystals and the role of neutron scattering in their solution is discussed. (author) 13 figs., 24 refs.

  7. Quasicrystals

    International Nuclear Information System (INIS)

    Steurer, W.

    1996-01-01

    Quasicrystals are new materials with strictly defined quasiperiodic atomic long-range order. One of their most striking features is their scaling symmetry (self-similarity) in direct and reciprocal space. The quasiperiodic order gives rise to a new type of low-energy excitations, the so-called phason modes which are related to well-defined atomic jumps. The open problems connected with the research on quasicrystals and the role of neutron scattering in their solution is discussed. (author) 13 figs., 24 refs

  8. Atomic clusters and atomic surfaces in icosahedral quasicrystals.

    Science.gov (United States)

    Quiquandon, Marianne; Portier, Richard; Gratias, Denis

    2014-05-01

    This paper presents the basic tools commonly used to describe the atomic structures of quasicrystals with a specific focus on the icosahedral phases. After a brief recall of the main properties of quasiperiodic objects, two simple physical rules are discussed that lead one to eventually obtain a surprisingly small number of atomic structures as ideal quasiperiodic models for real quasicrystals. This is due to the fact that the atomic surfaces (ASs) used to describe all known icosahedral phases are located on high-symmetry special points in six-dimensional space. The first rule is maximizing the density using simple polyhedral ASs that leads to two possible sets of ASs according to the value of the six-dimensional lattice parameter A between 0.63 and 0.79 nm. The second rule is maximizing the number of complete orbits of high symmetry to construct as large as possible atomic clusters similar to those observed in complex intermetallic structures and approximant phases. The practical use of these two rules together is demonstrated on two typical examples of icosahedral phases, i-AlMnSi and i-CdRE (RE = Gd, Ho, Tm).

  9. Long range ordered magnetic and atomic structures of the quasicrystal approximant in the Tb-Au-Si system

    Czech Academy of Sciences Publication Activity Database

    Gebresenbut, G.; Andersson, M. S.; Beran, Přemysl; Manuel, P.; Nordblad, P.; Sahlberg, M.; Gomez, C. P.

    2014-01-01

    Roč. 26, č. 32 (2014), s. 322202 ISSN 0953-8984 R&D Projects: GA MŠk(XE) LM2011019 EU Projects: European Commission(XE) 283883 - NMI3-II Institutional support: RVO:61389005 Keywords : magnetic property * magnetic structure refinement * approximants of quasicrystals Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.346, year: 2014

  10. The local atomic quasicrystal structure of the icosahedral Mg25Y11Zn64 alloy

    Science.gov (United States)

    Brühne, S.; Uhrig, E.; Gross, C.; Assmus, W.; Masadeh, A. S.; Billinge, S. J. L.

    2005-03-01

    A local and medium range atomic structure model for the face centred icosahedral (fci) Mg25Y11Zn64 alloy has been established in a sphere of r = 27 Å. The model was refined by least squares techniques using the atomic pair distribution (PDF) function obtained from synchrotron powder diffraction. Three hierarchies of the atomic arrangement can be found: (i) five types of local coordination polyhedra for the single atoms, four of which are of Frank-Kasper type. In turn, they (ii) form a three-shell (Bergman) cluster containing 104 atoms, which is condensed sharing its outer shell with its neighbouring clusters, and (iii) a cluster connecting scheme corresponding to a three-dimensional tiling leaving space for a few glue atoms. Inside adjacent clusters, Y8 cubes are tilted with respect to each other and thus allow for overall icosahedral symmetry. It is shown that the title compound is essentially isomorphic to its holmium analogue. Therefore, fci-Mg-Y-Zn can be seen as the representative structure type for the other rare earth analogues fci-Mg-Zn-RE (RE = Dy, Er, Ho, Tb) reported in the literature.

  11. The local atomic quasicrystal structure of the icosahedral Mg25Y11Zn64 alloy

    International Nuclear Information System (INIS)

    Bruehne, S; Uhrig, E; Gross, C; Assmus, W; Masadeh, A S; Billinge, S J L

    2005-01-01

    A local and medium range atomic structure model for the face centred icosahedral (fci) Mg 25 Y 11 Zn 64 alloy has been established in a sphere of r = 27 A. The model was refined by least squares techniques using the atomic pair distribution (PDF) function obtained from synchrotron powder diffraction. Three hierarchies of the atomic arrangement can be found: (i) five types of local coordination polyhedra for the single atoms, four of which are of Frank-Kasper type. In turn, they (ii) form a three-shell (Bergman) cluster containing 104 atoms, which is condensed sharing its outer shell with its neighbouring clusters, and (iii) a cluster connecting scheme corresponding to a three-dimensional tiling leaving space for a few glue atoms. Inside adjacent clusters, Y 8 cubes are tilted with respect to each other and thus allow for overall icosahedral symmetry. It is shown that the title compound is essentially isomorphic to its holmium analogue. Therefore, fci-Mg-Y-Zn can be seen as the representative structure type for the other rare earth analogues fci-Mg-Zn-RE (RE = Dy, Er, Ho, Tb) reported in the literature

  12. Quantum Simulation of a 2D Quasicrystal with Cold Atoms

    Directory of Open Access Journals (Sweden)

    Nicolas Macé

    2016-09-01

    Full Text Available We describe a way to obtain a two-dimensional quasiperiodic tiling with eight-fold symmetry using cold atoms. One can obtain a series of such optical tilings, related by scale transformations, for a series of specific values of the chemical potential of the atoms. A theoretical model for the optical system is described and compared with that of the well-known cut-and-project method for the Ammann–Beenker tiling. The relation between the two tilings is discussed. This type of cold atom structure should allow the simulation of several important lattice models for interacting quantum particles and spins in quasicrystals.

  13. Atomic scale structure of the 5-fold surface of an AlPdMn quasicrystal: A quantitative X-Ray photoelectron diffraction analysis

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Jin-Cheng; Huan, C.H.A.; Wee, A.T.S.; Van Hove, M.A.; Fadley, C.S.; Shi, F.J.; Rotenberg, E.; Barman, S.R.; Paggel, J.J.; Horn, K.; Ebert, Ph.; Urban, K.

    2004-02-11

    The atomic scale structure of the 5-fold symmetric surface of an AlPdMn quasicrystal is investigated quantitatively by comparing x-ray photoelectron diffraction (XPD) simulations to experiment. The observed 5-fold symmetry of the diffraction patterns indicates that the surface is quasicrystalline with no hint of a reconstruction from the bulk structure. In analyzing the experimental data, many possible bulk terminations have been tested. Those few that fit best to the data have in common that they contain an Al-rich surface layer followed by a dense mixed Al/Pd/Mn layer. These best terminations, while not identical to each other, are suggested to form terraces coexisting on a real surface. Structural relaxations of the quasicrystal surface are also analyzed: mixing several best-fit terminations gives average best-fit interlayer spacing changes of Dd12 = -0.057 Angstrom, Dd24 = +0.159 Angstrom. These results are in good agreement with a prior structure determination by LEED on a sample that was prepared in a different manner.

  14. Study of atomic jumps in quasi-crystals

    International Nuclear Information System (INIS)

    Lyonnard, S.

    1997-01-01

    The terminology phason used in quasicrystals to refer to atomic jumps. The study of the hopping process is important for the understanding of many basic issues in quasi-crystallography: structure, stability, diffusion, phase transitions between quasicrystals and approximants, mechanical properties. Quasi-elastic neutron scattering allows to find the characteristics of each elementary jump: chemical species involves, relaxation times, activation energies, jump distances and orientations. We performed a series of experiments in the perfect icosahedral phases AlFeCu and AlMnPd, on both powders and single domain samples, using time-of-flight, backscattering and triple axis spectrometers. We evidenced the existence of very fast phason hopping, and studied about ten different atomic jumps. An unusual temperature dependence has been found systematically: each process is assisted by a thermally activated mechanism. The assistance process has to be determined case by case, but the more plausible explanation invokes assistance by phonons or phason clouds. Moreover, the dependence of the quasi elastic signal as a function of the momentum transfer shows that the jumps are local and do not give rise to any long-range diffusion. Phason hopping mainly corresponds to the atom moving forwards and backwards between two energetically equivalent sites. Finally, we have been able to show that the jumps occur along the various quasi-crystalline symmetry axes. (author)

  15. Quasicrystals: Atomic coverings and windows are dual projects

    OpenAIRE

    Kramer, Peter

    1999-01-01

    In the window approach to quasicrystals, the atomic position space E_parallel is embedded into a space E^n = E_parallel + E_perp. Windows are attached to points of a lattice Lambda \\in E^n. For standard 5fold and icosahedral tiling models, the windows are perpendicular projections of dual Voronoi and Delone cells from Lambda. Their cuts by the position space E_parallel mark tiles and atomic positions. In the alternative covering approach, the position space is covered by overlapping copies of...

  16. Nonlinear photonic quasicrystals

    International Nuclear Information System (INIS)

    Freedman, B.; Bartal, G.; Segev, M.; Lifshitz, R.; Christodoulides, D.; Fleischer, J.

    2005-01-01

    Full Text:Quasicrystals are structures with long-range order and no periodicity, whose unique structural and physical properties have intrigued scientists ever since their discovery and initial theoretical analysis more than two decades ago. The lack of periodicity excludes the use of well-established theoretical and experimental tools for the analysis of quasicrystals, including such notions as the Brillouin zone and Bloch theorem. Instead, the quasiperiodic atomic arrangement gives rise to unique properties such as a hierarchy of effective Brillouin (or Jones) zones, yielding a fractal-like band structure, and the existence of unique phason degrees of freedom. Generally, in atomic quasicrystals it is very difficult to directly observe the evolution of electronic wave-packets propagating through the structure, or the dynamics of the structure itself. Photonic quasicrystals, on the other hand, are macroscopic objects and hence their internal wave dynamics can be locally excited and directly imaged. Here, we employ optical induction to create 2D photonic quasicrystals, and explore wave transport phenomena in quasicrystals in ways that were impossible until now. We demonstrate linear tunneling-transport of light initiated at different crystal sites, and observe the formation of lattice solitons when the light is made sufficiently intense. We experiment with dynamical photonic quasicrystals, in which crystal sites interact with one another, and directly observe dislocation dynamics: creation, healing, and local structural rearrangement due to phason flips. Our experiments show that photonic quasicrystals are an excellent model system through which one can study the universal features of wave dynamics in quasiperiodic structures, that should apply not only to photonics, but also to other systems such as matter waves in quasiperiodic traps, generic pattern-forming systems as in parametrically-excited surface waves, liquid quasicrystals, as well as the more familiar

  17. An Exact Method to Determine the Photonic Resonances of Quasicrystals Based on Discrete Fourier Harmonics of Higher-Dimensional Atomic Surfaces

    Directory of Open Access Journals (Sweden)

    Farhad A. Namin

    2016-08-01

    Full Text Available A rigorous method for obtaining the diffraction patterns of quasicrystals is presented. Diffraction patterns are an essential analytical tool in the study of quasicrystals, since they can be used to determine their photonic resonances. Previous methods for approximating the diffraction patterns of quasicrystals have relied on evaluating the Fourier transform of finite-sized super-lattices. Our approach, on the other hand, is exact in the sense that it is based on a technique that embeds quasicrystals into higher dimensional periodic hyper-lattices, thereby completely capturing the properties of the infinite structure. The periodicity of the unit cell in the higher dimensional space can be exploited to obtain the Fourier series expansion in closed-form of the corresponding atomic surfaces. The utility of the method is demonstrated by applying it to one-dimensional Fibonacci and two-dimensional Penrose quasicrystals. The results are verified by comparing them to those obtained by using the conventional super-lattice method. It is shown that the conventional super-cell approach can lead to inaccurate results due to the continuous nature of the Fourier transform, since quasicrystals have a discrete spectrum, whereas the approach introduced in this paper generates discrete Fourier harmonics. Furthermore, the conventional approach requires very large super-cells and high-resolution sampling of the reciprocal space in order to produce accurate results leading to a very large computational burden, whereas the proposed method generates accurate results with a relatively small number of terms. Finally, we propose how this approach can be generalized from the vertex model, which assumes identical particles at all vertices, to a more realistic case where the quasicrystal is composed of different atoms.

  18. Vacancies and atomic processes in intermetallics - From crystals to quasicrystals and bulk metallic glasses

    Energy Technology Data Exchange (ETDEWEB)

    Schaefer, Hans-Eckhardt [Institute of Theoretical and Applied Physics, Stuttgart University, Pfaffenwaldring 57, 70569 Stuttgart (Germany); Baier, Falko [Voith Turbo Comp., Alexanderstr. 2, 89552 Heidenheim (Germany); Mueller, Markus A. [GFT Technologies A. G., Filderhauptstr. 142, 70599 Stuttgart (Germany); Reichle, Klaus J. [Philipp-Matthaeus-Hahn School, Jakob-Beutter-Str. 15, 72336 Balingen (Germany); Reimann, Klaus [NXP Semiconductors, Central Research and Development, High Tech Campus 4, 5656 AE Eindhoven (Netherlands); Rempel, Andrey A. [Institute of Solid State Chemistry, Russian Academy of Sciences, Ul. Pervomaiskaya 91, 620041 Ekaterinburg (Russian Federation); Sato, Kiminori [Tokyo Gakugei University, Nukuikita 4-1-1, Koganei, Tokyo 184-8501 (Japan); Ye, Feng [State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing, 30 Xue Yuan Road, Beijing 100083 (China); Zhang, Xiangyi [Yanshan University, Qinhuangdao 066004 (China); Sprengel, Wolfgang [Institute of Materials Physics, Graz University of Technology, Petersgasse 16, 8010 Graz (Austria)

    2011-10-15

    A review is given on atomic vacancies in intermetallic compounds. The intermetallic compounds cover crystalline, quasicrystalline, and bulk metallic glass (BMG) structures. Vacancies can be specifically characterized by their positron lifetimes, by the coincident measurement of the Doppler broadening of the two quanta emitted by positron-electron annihilation, or by time-differential dilatometry. By these techniques, high concentrations and low mobilities of thermal vacancies were found in open-structured B2 intermetallics such as FeAl or NiAl, whereas the concentrations of vacancies are low and their mobilities high in close-packed structure as, e.g., L1{sub 2}-Ni{sub 3}Al. The activation volumes of vacancy formation and migration are determined by high-pressure experiments. The favorable sublattice for vacancy formation is found to be the majority sublattice in Fe{sub 61}Al{sub 39} and in MoSi{sub 2}. In the icosahedral quasicrystal Al{sub 70}Pd{sub 21}Mn{sub 9} the thermal vacancy concentration is low, whereas in the BMG Zr{sub 57}Cu{sub 15.4}Ni{sub 12.6}Nb{sub 3}Al{sub 10} thermal vacancies are found in high concentrations with low mobilities. This may determine the basic mechanisms of the glass transition. Making use of the experimentally determined vacancy data, the main features of atomic diffusion studies in crystalline intermetallics, in quasicrystals, and in BMGs can be understood. Manfred Faehnle and his group have substantially contributed to the theoretical understanding of vacancies and diffusion mechanisms in intermetallics. (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  19. The local atomic quasicrystal structure of the icosahedral Mg{sub 25}Y{sub 11}Zn{sub 64} alloy

    Energy Technology Data Exchange (ETDEWEB)

    Bruehne, S [Physikalisches Institut, Johann Wolfgang Goethe-Universitaet, Robert-Mayer-Strasse 2-4, D-60054 Frankfurt (Germany); Uhrig, E [Physikalisches Institut, Johann Wolfgang Goethe-Universitaet, Robert-Mayer-Strasse 2-4, D-60054 Frankfurt (Germany); Gross, C [Physikalisches Institut, Johann Wolfgang Goethe-Universitaet, Robert-Mayer-Strasse 2-4, D-60054 Frankfurt (Germany); Assmus, W [Physikalisches Institut, Johann Wolfgang Goethe-Universitaet, Robert-Mayer-Strasse 2-4, D-60054 Frankfurt (Germany); Masadeh, A S [Department of Physics and Astronomy and Center for Fundamental Materials Research, Michigan State University, East Lansing, MI 48824-1116 (United States); Billinge, S J L [Department of Physics and Astronomy and Center for Fundamental Materials Research, Michigan State University, East Lansing, MI 48824-1116 (United States)

    2005-03-16

    A local and medium range atomic structure model for the face centred icosahedral (fci) Mg{sub 25}Y{sub 11}Zn{sub 64} alloy has been established in a sphere of r = 27 A. The model was refined by least squares techniques using the atomic pair distribution (PDF) function obtained from synchrotron powder diffraction. Three hierarchies of the atomic arrangement can be found: (i) five types of local coordination polyhedra for the single atoms, four of which are of Frank-Kasper type. In turn, they (ii) form a three-shell (Bergman) cluster containing 104 atoms, which is condensed sharing its outer shell with its neighbouring clusters, and (iii) a cluster connecting scheme corresponding to a three-dimensional tiling leaving space for a few glue atoms. Inside adjacent clusters, Y{sub 8} cubes are tilted with respect to each other and thus allow for overall icosahedral symmetry. It is shown that the title compound is essentially isomorphic to its holmium analogue. Therefore, fci-Mg-Y-Zn can be seen as the representative structure type for the other rare earth analogues fci-Mg-Zn-RE (RE = Dy, Er, Ho, Tb) reported in the literature.

  20. Structural stability of binary CdCa quasicrystal under high pressure

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Gerward, Leif; Olsen, J. S.

    2001-01-01

    The structural stability of a binary CdCa quasicrystal with a primitive icosahedral structure has been investigated by in situ high-pressure x-ray powder diffraction at an ambient temperature using synchrotron radiation. It is demonstrated that the icosahedral quasicrystalline structure of the sa......The structural stability of a binary CdCa quasicrystal with a primitive icosahedral structure has been investigated by in situ high-pressure x-ray powder diffraction at an ambient temperature using synchrotron radiation. It is demonstrated that the icosahedral quasicrystalline structure...... elasticity in the stable binary icosahedral CdCa quasicrystals....

  1. Study of atomic jumps in quasi-crystals; Etude des sauts atomiques dans les quasi-cristaux

    Energy Technology Data Exchange (ETDEWEB)

    Lyonnard, S

    1997-05-07

    The terminology phason used in quasicrystals to refer to atomic jumps. The study of the hopping process is important for the understanding of many basic issues in quasi-crystallography: structure, stability, diffusion, phase transitions between quasicrystals and approximants, mechanical properties. Quasi-elastic neutron scattering allows to find the characteristics of each elementary jump: chemical species involves, relaxation times, activation energies, jump distances and orientations. We performed a series of experiments in the perfect icosahedral phases AlFeCu and AlMnPd, on both powders and single domain samples, using time-of-flight, backscattering and triple axis spectrometers. We evidenced the existence of very fast phason hopping, and studied about ten different atomic jumps. An unusual temperature dependence has been found systematically: each process is assisted by a thermally activated mechanism. The assistance process has to be determined case by case, but the more plausible explanation invokes assistance by phonons or phason clouds. Moreover, the dependence of the quasi elastic signal as a function of the momentum transfer shows that the jumps are local and do not give rise to any long-range diffusion. Phason hopping mainly corresponds to the atom moving forwards and backwards between two energetically equivalent sites. Finally, we have been able to show that the jumps occur along the various quasi-crystalline symmetry axes. (author) 91 refs.

  2. Time Crystal Platform: From Quasicrystal Structures in Time to Systems with Exotic Interactions

    Science.gov (United States)

    Giergiel, Krzysztof; Miroszewski, Artur; Sacha, Krzysztof

    2018-04-01

    Time crystals are quantum many-body systems that, due to interactions between particles, are able to spontaneously self-organize their motion in a periodic way in time by analogy with the formation of crystalline structures in space in condensed matter physics. In solid state physics properties of space crystals are often investigated with the help of external potentials that are spatially periodic and reflect various crystalline structures. A similar approach can be applied for time crystals, as periodically driven systems constitute counterparts of spatially periodic systems, but in the time domain. Here we show that condensed matter problems ranging from single particles in potentials of quasicrystal structure to many-body systems with exotic long-range interactions can be realized in the time domain with an appropriate periodic driving. Moreover, it is possible to create molecules where atoms are bound together due to destructive interference if the atomic scattering length is modulated in time.

  3. Quasi-crystal structures with neutron diffraction

    International Nuclear Information System (INIS)

    Janot, C.

    1992-01-01

    Long-range order in materials can be aperiodic. This paper reports on quasi-periodic lattices that are mathematically derived from cross sections of objects that are periodically arranged in a higher dimensional space. Experimental investigations of these structures require the specification of more parameters than for classical crystallography. Neutron diffraction, with the special technique of contrast variation, allows a reasonable approach to this problem

  4. Atomic-partial vibrational density of states of i-AlCuFe quasicrystals

    CERN Document Server

    Parshin, P P; Brand, R A; Dianoux, A J; Calvayrac, Y

    2002-01-01

    We present new results on the separation of the atomic-partial vibrational density of states for the ternary quasicrystal i-Al sub 6 sub 2 Cu sub 2 sub 5 sub . sub 5 Fe sub 1 sub 2 sub . sub 5. The decomposition into three atomic-partial functions, Al-, Cu- and Fe-g(E), has been performed self-consistently with the calculation of the multi-phonon contributions. The results show the surprising result that both Cu- and Fe-g(E) are strongly peaked. The low-energy regions of Al- and Cu-g(E) show strong deviations from Debye behaviour due to the presence of non-propagating low-energy vibrational states. (orig.)

  5. Measuring the Thermophysical and Structural Properties of Glass-Forming and Quasicrystal-Forming Liquids

    Science.gov (United States)

    Hyers, Robert W.; Bradshaw, Richard C.; Rogers, Jan R.; Gangopadhyay, Anup K.; Kelton, Ken F.

    2006-01-01

    The thermophysical properties of glass-forming and quasicrystal-forming alloys show many interesting features in the undercooled liquid range. Some of the features in the thermophysical property curves are expected to reflect changes in the structure and coordination of the liquid. These measurements require containerless processing such as electrostatic levitation to access the undercooled liquid regime. An overview of the state of the art in measuring the thermophysical properties and structure of undercooled liquid glass-forming and quasicrystal-forming alloys will be presented, along with the status of current measurements.

  6. Atomic model of anti-phase boundaries in a face-centred icosahedral Zn-Mg-Dy quasicrystal

    CERN Document Server

    Wang Jian Bo; Wang Ren Hui

    2003-01-01

    An atomic model in the physical space for an anti-phase boundary (APB) in the ordered face-centred icosahedral Zn-Mg-Dy quasicrystal phase is presented, based on a six-dimensional model suggested by Ishimasa and Shimizu (2000 Mater. Sci. Eng. A 294-296 232, Ishimasa 2001 private communication). The physical space atomic positions of the defected structure were used for the calculation of the corresponding exit-plane wavefunction and high-resolution transmission electron microscopy images. The analysis of the defect by inverse Fourier transformation reveals that when superstructure reflection spots are used for back-transformation, then at the APB, bright lattice fringes are found to turn into dark ones, and vice versa. When fundamental reflections are used, the APB is not visible. This phenomenon is the same as the corresponding experimental study recently published by Heggen et al(2001a Phys. Rev. B 64 014202). Based on this atomic model it is found that the APB perpendicular to a fivefold axis A5 (APB-A5) i...

  7. Image Sampling with Quasicrystals

    Directory of Open Access Journals (Sweden)

    Mark Grundland

    2009-07-01

    Full Text Available We investigate the use of quasicrystals in image sampling. Quasicrystals produce space-filling, non-periodic point sets that are uniformly discrete and relatively dense, thereby ensuring the sample sites are evenly spread out throughout the sampled image. Their self-similar structure can be attractive for creating sampling patterns endowed with a decorative symmetry. We present a brief general overview of the algebraic theory of cut-and-project quasicrystals based on the geometry of the golden ratio. To assess the practical utility of quasicrystal sampling, we evaluate the visual effects of a variety of non-adaptive image sampling strategies on photorealistic image reconstruction and non-photorealistic image rendering used in multiresolution image representations. For computer visualization of point sets used in image sampling, we introduce a mosaic rendering technique.

  8. Syntheses, structure determination, magnetic and thermoelectric properties of quasicrystal approximants in RE-Au-SM systems (RE = Gd, Tb and Yb and SM = Si, Ge)

    OpenAIRE

    Gebresenbut, Girma Hailu

    2014-01-01

    In this study, new compositions of Tsai-type 1/1 quasicrystal approximants Gd(14)Au(70)Si(16), Gd(14)Au(67)Ge(19), Tb(14)Au(70)Si(16) and Yb(16)Au(65)Ge(19)are synthesized using both self-flux and arc-melting-annealing techniques. Both syntheses routes resulted single phase samples. The crystal structures of the compounds are determined by collecting single crystal X-ray and/or powder X-ray and powder neutron diffraction intensities.  The atomic structure refinements indicated that the compou...

  9. Three-Dimensional Modeling of Quasicrystal Structures from X-ray Diffraction: An Icosahedral Al-Cu-Fe Alloy.

    Science.gov (United States)

    Hong, Seung-Tae

    2017-07-03

    Quasicrystals (QCs) are well-ordered but aperiodic crystals with classically forbidden symmetries (such as 5-fold). High-dimensional (HD) crystallography is a standard method to locate atom positions explicitly. However, in practice, it is still challenging because of its complexity. Here, we report a new simple approach to three-dimensional (3D) atomic modeling derived from X-ray diffraction data, and apply it to the icosahedral QC Al 0.63 Cu 0.25 Fe 0.12 . Electron density maps were calculated directly from 3D diffraction data indexed with noninteger (fractional) numbers as measured, with proper phases; each of 2 5 = 32 possible phase assignments for the five strongest reflections was used for Fourier synthesis. This resulted in an initial phasing model based on chemically sensible electron density maps. The following procedure was exactly the same as that used to determine ordinary crystal structures, except that fractional indices were assigned to the reciprocal vectors relative to the three orthogonal 2-fold axes in icosahedral (I h ) symmetry to which the observed diffraction data conformed. Finally, ∼30 000 atoms were located within a sphere of a ∼48 Å radius. Structural motifs or basic repeating units with a hierarchical nature can be found. Isolated icosahedral clusters are surrounded by a concentric dodecahedron, beyond which there is a concentric truncated icosahedron. These are strikingly similar to those obtained via HD crystallography, but show very clear real-space relationships between the clusters.

  10. Atomic structure of a decagonal Al-Pd-Mn phase

    Science.gov (United States)

    Mihalkovič, Marek; Roth, Johannes; Trebin, Hans-Rainer

    2017-12-01

    We present a detailed structure solution for the 16 -Å decagonal quasicrystal in the Al-Pd-Mn system by means of cluster decoration and ab initio energy minimization. It is based on structure models of the ɛ and other approximant phases. The ɛ phases can be represented as subsets of a hexagon-boat-star (HBS) tiling. The decagonal phase comprises further HBS tiles. We have constructed several fictitious HBS approximants and optimized their structures individually. All tiles are decorated by two types of atomic clusters: the pseudo-Mackay icosahedron (PMI) and the large bicapped pentagonal prism (LBPP). It turns out that, whereas the PMI clusters can be kept essentially unchanged, the LBPP clusters must be adjusted in occupancy with Al atoms depending on their positions in the various tiles. In this way we obtain cluster decorations for all tiles of the decagonal quasicrystal. The calculations were confirmed by evaluation of an effective tile Hamiltonian.

  11. Beyond quasicrystals

    International Nuclear Information System (INIS)

    Axel, F.; Gratias, D.

    1995-01-01

    This book is the collection of most of the written versions of the courses given at the Winter School Beyond Quasicrystals. The first part is devoted more specifically to quasicrystals. These materials were the common starting point of most of the audience and present a first concrete example of a non-trivial geometric order. We chose to focus on a new fundamental aspects of quasicrystals related to hidden symmetries in solids which are not easily found in standard textbooks on the topic. The second part deals with deterministic aperiodic order beyond quasi periodicity. Deterministic sequences are a major example of quasicrystal generalization. Different properties are presented here from basics with possible relationships to diffusion. Their Fourier transformations are discussed in great details based on the general notions of measures and substitution dynamical systems. Their entropies are presented and discussed and their algebraic properties. Realizations in physics of such deterministic aperiodic sequences are at present of two kinds: Schroedinger type equations having such a deterministic sequence for a potential; multilayers systems which are now being studied mostly by diffraction analysts. Finally an introductory course with basics for multifractal analysis is given. (authors). 984 refs., 140 figs., 6 tabs

  12. Splitting rules for the electronic spectra of two-dimensional Fibonacci-class quasicrystals with one kind of atom and two bond lengths

    Science.gov (United States)

    Yang, Xiangbo; Xing, Da

    2002-04-01

    On the basis of the substitution rules for a one-dimensional Fibonacci-class chain, we construct two-dimensional Fibonacci-class quasicrystals with one kind of atom and two bond lengths. In the framework of the single-electron tight-binding nearest-interaction transfer model, we study the splitting rules of the electronic energy spectra for two-dimensional Fibonacci-class quasicrystals by means of a decomposition-decimation method based on a renormalization-group technique, and we also calculate the electronic energy spectra numerically. It is found that there exist only three kinds of clusters-n×n, n×(n+1), and (n+1)×(n+1)-for all classes of two-dimensional quasilattices, and that the electronic energy bands split as Ym-n-l. The general formula of the number for energy levels is obtained. We discover that there is a kind of so-called Fibonacci-class-number set for the parameters used to describe the energy-level number, and we obtain the set formulas. The experienced formula are sought out. The analytical results are confirmed by numerical simulations.

  13. Splitting rules for the 2nd hierarchy structure of the electronic spectra of 2D FC(n) quasicrystals

    Science.gov (United States)

    Li, Feng; Yang, Xiangbo

    2004-06-01

    On the basis of our former work and by means of the decomposition-decimation method, we study the splitting rules for the second hierarchy of the electronic energy spectra for two-dimensional Fibonacci-class quasicrystals with one kind of atom and two bond lengths. It is found that every line of the sub-spectra for n x n and ( n + 1) x ( n + 1) clusters of FC(n) (n ≥ 2) splits according to the type Y‘( n-1)-2-1 and type Y n-2-1 respectively. The one for n x ( n + 1) clusters of FC(n) consists of three sub-subbands when n le 2, and five sub-subbranches when n ge 3. The general formulae of the number of energy levels for the spectra of the second hierarchy are obtained. The analytical results are confirmed by numerical simulations.

  14. An accurate and efficient analytical method for 1D hexagonal quasicrystal coating based on Green's function

    Science.gov (United States)

    Hou, Peng-Fei; Chen, Bing-Jie; Zhang, Yang

    2017-08-01

    As a solid material between the crystal and the amorphous, the study on quasicrystals has become an important branch of condensed matter physics. Due to the special arrangement of atoms, quasicrystals own some desirable properties, such as low friction coefficient, low adhesion, high wear resistance and low porosity. Thus, quasicrystals are expected to be applied to the coating surfaces for engines, solar cells, nuclear fuel containers and heat converters. However, when the quasicrystals are used as coating material, it is very hard to simulate the coupling fields by the finite elements numerical methods because of its thin thickness and extreme stress gradient. This is the main reason why the structure of quasicrystal coating cannot be calculated accurately and stably by various numerical platform. A general solution method which can be used to solve this contact problem for a 1D hexagonal quasicrystal coating perfectly bonded to a transversely isotropic semi-infinite substrate under the point force is presented in this paper. The solutions of the Green's function under the distributed load can be obtained through the superposition principle. The simulation results show that this method is correct and effective, which has high calculation accuracy and fast convergence speed. The phonon-phason coupling field and elastic field in the coating and semi-infinite substrate will be derived based on the axisymmetric general solution, and the complicated coupling field of quasicrystals in coating contact space is explicitly presented in terms of elementary functions. In addition, the relationship between the coating thickness or external force and the stress component is also obtained to solve practical problems in engineering applications. The solutions presented not only bear theoretical merits, but also can serve as benchmarks to clarify various approximate methods.

  15. Simulation of the diffraction pattern of one dimensional quasicrystal ...

    African Journals Online (AJOL)

    The effects of the variation of atomic spacing ratio of a one dimensional quasicrystal material are investigated. The work involves the use of the solid state simulation code, Laue written by Silsbee and Drager. We are able to observe the general features of the diffraction pattern by a quasicrystal. In addition, it has been found ...

  16. Teach us atom structure

    Energy Technology Data Exchange (ETDEWEB)

    Lim, Suh Yeon

    2006-08-15

    This book is written to teach atom structure in very easy way. It is divided into nine chapters, which indicates what is the components of matter? when we divide matter continuously, it becomes atom, what did atom look like? particles comprised of matter is not only atom, discover of particles comprised of atom, symbol of element, various radiation, form alchemy to nuclear transmutation, shape of atom is evolving. It also has various pictures in each chapters to explain easily.

  17. On the stable Mg-Zn-Y quasicrystals

    Science.gov (United States)

    Luo, Z. P.; Sui, H. X.; Zhang, S. Q.

    1996-07-01

    By the conventional air-cooled casting method, bulk ingots with a large fraction of stable Mg-Zn-Y icosahedral quasicrystals, both simple and face-centered, were obtained. The quasicrystal structures were directly confirmed by high-resolution electron microscopy (HREM) observations. The electron diffraction patterns from the quasicrystals were studied by computer simulations. A coexisting crys-talline phase of the quasicrystals was identified as the Mg7Zn3 phase, which was proved to be the (1/1) approximant of the quasicrystals. The quasicrystals were stable during a continuous heating process. However, at high temperature, oxidation occurred, and thus, Y2O3 and MgO products were formed. Oxidation at high temperatures is characteristic for the Mg-Zn-Y alloys and differs from Al-base alloys.

  18. Disorder-Enhanced Transport in Photonic Quasicrystals

    Science.gov (United States)

    Levi, Liad; Rechtsman, Mikael; Freedman, Barak; Schwartz, Tal; Manela, Ofer; Segev, Mordechai

    2011-06-01

    Quasicrystals are aperiodic structures with rotational symmetries forbidden to conventional periodic crystals; examples of quasicrystals can be found in aluminum alloys, polymers, and even ancient Islamic art. Here, we present direct experimental observation of disorder-enhanced wave transport in quasicrystals, which contrasts directly with the characteristic suppression of transport by disorder. Our experiments are carried out in photonic quasicrystals, where we find that increasing disorder leads to enhanced expansion of the beam propagating through the medium. By further increasing the disorder, we observe that the beam progresses through a regime of diffusive-like transport until it finally transitions to Anderson localization and the suppression of transport. We study this fundamental phenomenon and elucidate its origins by relating it to the basic properties of quasicrystalline media in the presence of disorder.

  19. Scanning Tunneling Microscopy Studies of Surface Structures of Icosahedral Al-Cu-Fe Quasicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Cai, Tanhong [Iowa State Univ., Ames, IA (United States)

    2001-01-01

    Three papers are included in this dissertation. The first paper: ''Structural aspects of the fivefold quasicrystalline Al-Cu-Fe surface from STM and dynamical LEED studies'', is in press with ''Surface Science''. The second paper: ''An STM study of the atomic structure of the icosahedral Al-Cu-Fe fivefold surface'' is submitted to ''Physical Review B, Rapid Communication''. The third paper: ''Pseudomorphic starfish: arrangement of extrinsic metal atoms on a quasicrystalline substrate'' is submitted to ''Nature''. Following the third paper are general conclusions and appendices that document the published paper ''Structural aspects of the three-fold surface of icosahedral Al-Pd-Mn'' (appearing in volume 461, issue 1-3 of ''Surface Science'' on page L521-L527, 2000), the design as well as the specifications of the aluminum evaporator used in the aluminum deposition study in this dissertation, an extended discussion of the aluminum deposition on the quasicrystalline surface, and the STM database.

  20. Manganese adlayers on i-Al-Pd-Mn quasicrystal: growth and electronic structure.

    Science.gov (United States)

    Shukla, A K; Dhaka, R S; D'Souza, S W; Maniraj, M; Barman, S R; Horn, K; Ebert, Ph; Urban, K; Wu, D; Lograsso, T A

    2009-10-07

    Pseudomorphic growth of thin elemental metal films is often observed on a variety of crystalline solids. On quasicrystalline surfaces with their complex structure and the absence of translational periodicity, the situation is different since elemental metals do not exhibit quasicrystalline order, and hence the specific interaction between overlayer and substrate is decisive. Here we study the growth of manganese films on an icosahedral i-Al-Pd-Mn alloy with a view to establishing the growth mode and electronic structure. Although we observe an exponential intensity variation of the adlayer and substrate related x-ray photoemission spectroscopy (XPS) peaks, low energy electron diffraction (LEED) shows that Mn adlayers do not exhibit quasicrystallinity. The detailed structure of the Mn 2p core level line reveals considerable electronic structure differences between the quasicrystalline and elemental metal environment. Evidence of a substantial local magnetic moment on the Mn atoms in the overlayer (about 2.8  µ(B)) is obtained from the Mn 3s exchange splitting.

  1. Sampling on Quasicrystals

    OpenAIRE

    Grepstad, Sigrid

    2011-01-01

    We prove that quasicrystals are universal sets of stable sampling in any dimension. Necessary and sufficient density conditions for stable sampling and interpolation sets in one dimension are studied in detail.

  2. Superfluid-Quasicrystal in a Bose-Einstein Condensate

    Science.gov (United States)

    Hou, Junpeng; Hu, Haiping; Sun, Kuei; Zhang, Chuanwei

    2018-02-01

    A quasicrystal is a class of ordered structures defying conventional classification of solid crystals and may carry classically forbidden (e.g., fivefold) rotational symmetries. In view of long-sought supersolids, a natural question is whether a superfluid can spontaneously form quasicrystalline order that is not possessed by the underlying Hamiltonian, forming "superfluid-quasicrystals." Here we show that a superfluid-quasicrystal stripe state with the minimal fivefold rotational symmetry can be realized as the ground state of a Bose-Einstein condensate within a practical experimental scheme. There exists a rich phase diagram consisting of various superfluid-quasicrystal, supersolid, and plane-wave phases. Our scheme can be generalized for generating other higher-order (e.g., sevenfold) quasicrystal states, and provides a platform for investigating such new exotic quantum matter.

  3. Photonic crystals, amorphous materials, and quasicrystals.

    Science.gov (United States)

    Edagawa, Keiichi

    2014-06-01

    Photonic crystals consist of artificial periodic structures of dielectrics, which have attracted much attention because of their wide range of potential applications in the field of optics. We may also fabricate artificial amorphous or quasicrystalline structures of dielectrics, i.e. photonic amorphous materials or photonic quasicrystals. So far, both theoretical and experimental studies have been conducted to reveal the characteristic features of their optical properties, as compared with those of conventional photonic crystals. In this article, we review these studies and discuss various aspects of photonic amorphous materials and photonic quasicrystals, including photonic band gap formation, light propagation properties, and characteristic photonic states.

  4. Quasicrystal Approximants in the RE-Au-SM systems (RE = Gd, Tb, Ho, Yb; SM = Si, Ge) : Syntheses, structures and properties

    OpenAIRE

    Gebresenbut, Girma Hailu

    2016-01-01

    In this study, new Tsai-type 1/1 quasicrystal approximants (ACs) in the RE-Au-SM systems (RE = Gd, Tb, Ho, Yb; SM = Si, Ge) were synthesized using high temperature synthesis techniques such as self-flux, arc-melting-annealing and novel arc-melting-self-flux methods. The syntheses not only provided appropriate samples for the intended structural and physical property measurements but could also be adapted to other systems, especially where crystal growth is a challenge. The newly developed arc...

  5. Thermodynamic properties of Al-Mn, Al-Cu, and Al-Fe-Cu melts and their relations to liquid and quasicrystal structure

    International Nuclear Information System (INIS)

    Zaitsev, A I; Zaitseva, N E; Shimko, R Yu; Arutyunyan, N A; Dunaev, S F; Kraposhin, V S; Lam, Ha Thanh

    2008-01-01

    Thermodynamic properties of molten Al-Mn, Al-Cu and Al-Fe-Cu alloys in a wide temperature range of 1123-1878 K and the whole range of concentrations have been studied using the integral effusion method and Knudsen mass spectrometry. Thermodynamic functions of melts were described by the associated solution model. The possibility of icosahedral quasicrystal (i-QC) precipitation from liquid Al-Mn and Al-Cu-Fe alloys was found to be a consequence of the existence in liquid associates (clusters). A geometric model is suggested for the structure of associates in liquid

  6. Surfaces of Intermetallics: Quasicrystals and Beyond

    Energy Technology Data Exchange (ETDEWEB)

    Yuen, Chad [Iowa State Univ., Ames, IA (United States)

    2012-01-01

    The goal of this work is to characterize surfaces of intermetallics, including quasicrystals. In this work, surface characterization is primarily focused on composition and structure using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) performed under ultrahigh vacuum (UHV) conditions.

  7. Atomic Structure Theory Lectures on Atomic Physics

    CERN Document Server

    Johnson, Walter R

    2007-01-01

    Atomic Structure Theory is a textbook for students with a background in quantum mechanics. The text is designed to give hands-on experience with atomic structure calculations. Material covered includes angular momentum methods, the central field Schrödinger and Dirac equations, Hartree-Fock and Dirac-Hartree-Fock equations, multiplet structure, hyperfine structure, the isotope shift, dipole and multipole transitions, basic many-body perturbation theory, configuration interaction, and correlation corrections to matrix elements. Numerical methods for solving the Schrödinger and Dirac eigenvalue problems and the (Dirac)-Hartree-Fock equations are given as well. B-spline basis sets are used to carry out sums arising in higher-order many-body calculations. Illustrative problems are provided, together with solutions. FORTRAN programs implementing the numerical methods in the text are included.

  8. Levitated crystals and quasicrystals of metamaterials

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Zhehui [Los Alamos National Laboratory; Morris, Christopher [Los Alamos National Laboratory; Goree, John A [Dept Phys and Astron., University of Iowa

    2012-07-25

    New scientific and technological opportunities exist by marrying dusty plasma research with metamaterials. Specifically, by balancing control and self-assembly, certain laboratory plasmas can become a generic levitation platform for novel structure formation and nanomaterial synthesis. We propose to experimentally investigate two dimensional (2D) and three dimensional (3D) levitated structures of metamaterials and their properties. Such structures can self assemble in laboratory plasmas, similar to levitated dust crystals which were discovered in the mid 1990's. Laboratory plasma platform for metamaterial formation eliminates substrates upon which most metamaterials have to be supported. Three types of experiments, with similar setups, are discussed here. Levitated crystal structures of metamaterials using anisotropic microparticles are the most basic of the three. The second experiment examines whether quasicrystals of metamaterials are possible. Quasicrystals, discovered in the 1980's, possess so-called forbidden symmetries according to the conventional crystallography. The proposed experiment could answer many fundamental questions about structural, thermal and dynamical properties of quasicrystals. And finally, how to use nanoparticle coated microparticles to synthesize very long carbon nanotubes is also described. All of the experiments can fit inside a standard International Space Station locker with dimensions of 8-inch x 17-inch X 18-inch. Microgravity environment is deemed essential in particular for large 3D structures and very long carbon nanotube synthesis.

  9. The Anisotropic Glassy Properties of Decagonal Quasicrystals

    Directory of Open Access Journals (Sweden)

    Dragoş-Victor Anghel

    2013-01-01

    Full Text Available We use an extended version of the standard tunneling model to explain the anisotropic sound absorption in decagonal quasicrystals. The glassy properties are determined by an ensemble of two level systems (TLSs, arbitrarily oriented. The TLS is characterized by a 3 × 3 symmetric tensor, [T], which couples to the strain field, [S], through a 3 × 3 × 3 × 3 tensor of coupling constants, [R]. The structure of [R] reflects the symmetry of the quasicrystal. We also analyze the probability distributions of the elements of [T] in this particular model for a better understanding of the characteristics of “isotropic” and “anisotropic” distributions of the ensemble of TLSs. We observe that the distribution of the elements is neither simple nor intuitive and therefore it is difficult to guess it a priory, using qualitative arguments based on the symmetry properties.

  10. Fine Structure of Diffuse Scattering Rings in Al-Li-Cu Quasicrystal: A Comparative X-ray and Electron Diffraction Study

    Science.gov (United States)

    Donnadieu, P.; Dénoyer, F.

    1996-11-01

    A comparative X-ray and electron diffraction study has been performed on Al-Li-Cu icosahedral quasicrystal in order to investigate the diffuse scattering rings revealed by a previous work. Electron diffraction confirms the existence of rings but shows that the rings have a fine structure. The diffuse aspect on the X-ray diffraction patterns is then due to an averaging effect. Recent simulations based on the model of canonical cells related to the icosahedral packing give diffractions patterns in agreement with this fine structure effect. Nous comparons les diagrammes de diffraction des rayon-X et des électrons obtenus sur les mêmes échantillons du quasicristal icosaèdrique Al-Li-Cu. Notre but est d'étudier les anneaux de diffusion diffuse mis en évidence par un travail précédent. Les diagrammes de diffraction électronique confirment la présence des anneaux mais ils montrent aussi que ces anneaux possèdent une structure fine. L'aspect diffus des anneaux révélés par la diffraction des rayons X est dû à un effet de moyenne. Des simulations récentes basées sur la décomposition en cellules canoniques de l'empilement icosaédrique produisent des diagrammes de diffraction en accord avec ces effects de structure fine.

  11. Positron annihilation studies of icosahedral quasicrystals and their approximants in the Al-Cu-Ru-(Si) alloy systems

    International Nuclear Information System (INIS)

    Uchiyama, H; Takahashi, T; Arinuma, K; Sato, K; Kanazawa, I; Hamada, E; Suzuki, T; Kirihara, K; Kimura, K

    2004-01-01

    The positron lifetimes for the icosahedral quasicrystal Al 62.4 Cu 25.4 Ru 12.2 and its cubic approximants (1/ 1-Al 58 Cu 31.5 Ru 10.5 , 1/ 1-Al 68 Cu 7 Ru 17 Si 8 , and 1/0-Al 55 Cu 15 Ru 20 Si 10 ), two-detector coincident Doppler broadening for the icosahedral quasicrystal Al 62.4 Cu 25.4 Ru 12.2 and its 1/ 1-Al 68 Cu 7 Ru 17 Si 8 cubic approximant, and the Doppler broadening obtained by making use of a slow positron beam for the 1/ 1-Al 58 Cu 31.5 Ru 10.5 cubic approximant have been measured. Structurally intrinsic trapping sites giving rise to saturation trapping were detected by lifetime measurements. The chemical environments of the trapping sites in the icosahedral quasicrystal Al 62.4 Cu 25.4 Ru 12.2 and the 1/ 1-Al 68 Cu 7 Ru 17 Si 8 cubic approximant were determined by coincident Doppler broadening techniques to be dominantly surrounded by Al atoms. The positron diffusion length in the 1/ 1-Al 58 Cu 31.5 Ru 10.5 cubic approximant derived from the measured S parameter measured by means of a slow positron beam was ∼ 180 A, which is clearly too short, probably due to the high concentration of trapping sites as described above. The atomic structures of the icosahedral quasicrystal Al 62.4 Cu 25.4 Ru 12.2 and its variety of approximants are discussed and compared to the present proposed model

  12. Finite size specimens with cracks of icosahedral Al—Pd—Mn quasicrystals

    International Nuclear Information System (INIS)

    Yang Lian-Zhi; Gao Yang; Andreas Ricoeur; He Fan-Min

    2014-01-01

    Icosahedral quasicrystals are the most important and thermodynamically stable in all about 200 kinds of quasicrystals currently observed. Beyond the scope of classical elasticity, apart from a phonon displacement field, there is a phason displacement field in the elasticity of the quasicrystal, which induces an important effect on the mechanical properties of the material and makes an analytical solution difficult to obtain. In this paper, a finite element algorithm for the static elasticity of icosahedral quasicrystals is developed by transforming the elastic boundary value problem of the icosahedral quasicrystals into an equivalent variational problem. Analytical and numerical solutions for an icosahedral Al—Pd—Mn quasicrystal cuboid subjected to a uniaxial tension with different phonon—phason coupling parameters are given to verify the validity of the numerical approach. A comparison between the analytical and numerical solutions of the specimen demonstrates the accuracy and efficiency of the present algorithm. Finally, in order to reveal the fracture behavior of the icosahedral Al—Pd—Mn quasicrystal, a cracked specimen with a finite size of matter is investigated, both with and without phonon—phason coupling. Meanwhile, the geometry factors are calculated, including the stress intensity factor and the crack opening displacement for the finite-size specimen. Computational results reveal the importance of phonon—phason coupling effect on the icosahedral Al—Pd—Mn quasicrystal. Furthermore, the finite element procedure can be used to solve more complicated boundary value problems. (condensed matter: structural, mechanical, and thermal properties)

  13. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    International Nuclear Information System (INIS)

    Lowe, M.; McGrath, R.; Sharma, H. R.; Yadav, T. P.; Fournée, V.; Ledieu, J.

    2015-01-01

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe 3 O 4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol

  14. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    Science.gov (United States)

    Lowe, M.; Yadav, T. P.; Fournée, V.; Ledieu, J.; McGrath, R.; Sharma, H. R.

    2015-03-01

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe3O4 rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol.

  15. Influence of leaching on surface composition, microstructure, and valence band of single grain icosahedral Al-Cu-Fe quasicrystal

    Energy Technology Data Exchange (ETDEWEB)

    Lowe, M.; McGrath, R.; Sharma, H. R. [Surface Science Research Centre and The Department of Physics, The University of Liverpool, Liverpool L69 3BX (United Kingdom); Yadav, T. P. [Hydrogen Energy Centre, Department of Physics, Banaras Hindu University, Varanasi 221005 (India); Fournée, V.; Ledieu, J. [Institut Jean Lamour (UMR7198 CNRS-Université de Lorraine), Parc de Saurupt, 54011 Nancy Cedex (France)

    2015-03-07

    The use of quasicrystals as precursors to catalysts for the steam reforming of methanol is potentially one of the most important applications of these new materials. To develop application as a technology requires a detailed understanding of the microscopic behavior of the catalyst. Here, we report the effect of leaching treatments on the surface microstructure, chemical composition, and valence band of the icosahedral (i-) Al-Cu-Fe quasicrystal in an attempt to prepare a model catalyst. The high symmetry fivefold surface of a single grain i-Al-Cu-Fe quasicrystal was leached with NaOH solution for varying times, and the resulting surface was characterized by x-ray photoelectron spectroscopy (XPS), ultraviolet photoelectron spectroscopy (UPS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). The leaching treatments preferentially remove Al producing a capping layer consisting of Fe and Cu oxides. The subsurface layer contains elemental Fe and Cu in addition to the oxides. The quasicrystalline bulk structure beneath remains unchanged. The subsurface gradually becomes Fe{sub 3}O{sub 4} rich with increasing leaching time. The surface after leaching exhibits micron sized dodecahedral cavities due to preferential leaching along the fivefold axis. Nanoparticles of the transition metals and their oxides are precipitated on the surface after leaching. The size of the nanoparticles is estimated by high resolution transmission microscopy to be 5-20 nm, which is in agreement with the AFM results. Selected area electron diffraction (SAED) confirms the crystalline nature of the nanoparticles. SAED further reveals the formation of an interface between the high atomic density lattice planes of nanoparticles and the quasicrystal. These results provide an important insight into the preparation of model catalysts of nanoparticles for steam reforming of methanol.

  16. Large sonic band gaps in 12-fold quasicrystals

    Science.gov (United States)

    Lai, Yun; Zhang, Xiangdong; Zhang, Zhao-Qing

    2002-05-01

    The sonic band-gap structures of 12-fold symmetry quasicrystals consisting of rigid cylinders in air are investigated by using the multiple scattering method. Large full gaps are found in this system owing to its high symmetry. At filling fractions between 0.2 and 0.4, this 12-fold square-triangle tiling is much better for the realization of sonic band gaps than the square or triangular lattice. This makes the 12-fold quasicrystal a promising structure for acoustic-wave band-gap materials.

  17. Defects in Static Elasticity of Quasicrystals

    Directory of Open Access Journals (Sweden)

    Qin Xu

    2017-12-01

    Full Text Available A review on mathematical elasticity of quasicrystals is given. In this review, the focus is on various defects of quasicrystals. Dislocation and crack are two classes of typical topological defects, while their existence has great influence on the mechanical behavior of quasicrystals. The analytic and numerical solutions of dislocations and crack in quasicrystals are the core of the static and dynamic elasticity theory, and this paper gives a comprehensive review on the solutions for dislocations and crack with different configurations in different various important quasicrystalline systems. We review some results in linear elasticity of quasicrystals, referring to different boundary value problems. We also add some new achievements.

  18. Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals

    Directory of Open Access Journals (Sweden)

    Xiaogang Liang

    2016-06-01

    Full Text Available The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure. The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti > (Cu, Fe, Co, Ni, Mg, Ag > (Pb, Au, Pd, Pt, Rh, Ir, which correspond to the predicted formation ability of the quasicrystals. Thedifferences of the sequences can be explained by analyzing the parameters of the Gupta-type many-body inter-atomic potentials.

  19. Dynamic stabilities of icosahedral-like clusters and their ability to form quasicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Liang, Xiaogang; Hamid, Ilyar; Duan, Haiming, E-mail: dhm@xju.edu.cn [College of Physics Science and Technology. Xinjiang University, Urumqi 830046 (China)

    2016-06-15

    The dynamic stabilities of the icosahedral-like clusters containing up to 2200 atoms are investigated for 15 metal elements. The clusters originate from five different initial structures (icosahedron, truncated decahedron, octahedron, closed-shell fragment of an HCP structure, and non-closed-shell fragment of an HCP structure). The obtained order of the dynamic stabilities of the icosahedral-like clusters can be assigned to three groups, from stronger to weaker, according to the size ranges involved: (Zr, Al, Ti) > (Cu, Fe, Co, Ni, Mg, Ag) > (Pb, Au, Pd, Pt, Rh, Ir), which correspond to the predicted formation ability of the quasicrystals. The differences of the sequences can be explained by analyzing the parameters of the Gupta-type many-body inter-atomic potentials.

  20. Light transport through the bandedge states of Fibonacci quasicrystals

    NARCIS (Netherlands)

    Dal Negro, Luca; Oton, Claudio J.; Gaburro, Zeno; Pavesi, Lorenzo; Johnson, Patrick; Lagendijk, Aart; Righini, Roberto; Colocci, Marcello; Wiersma, Diederik S.

    2003-01-01

    The propagation of light in nonperiodic quasicrystals is studied by ultrashort pulse interferometry. Samples consist of multilayer dielectric structures of the Fibonacci type and are realized from porous silicon. We observe mode beating and strong pulse stretching in the light transport through

  1. Atomic structure in black hole

    International Nuclear Information System (INIS)

    Nagatani, Yukinori

    2006-01-01

    We propose that any black hole has atomic structure in its inside and has no horizon as a model of black holes. Our proposal is founded on a mean field approximation of gravity. The structure of our model consists of a (charged) singularity at the center and quantum fluctuations of fields around the singularity, namely, it is quite similar to that of atoms. Any properties of black holes, e.g. entropy, can be explained by the model. The model naturally quantizes black holes. In particular, we find the minimum black hole, whose structure is similar to that of the hydrogen atom and whose Schwarzschild radius is approximately 1.1287 times the Planck length. Our approach is conceptually similar to Bohr's model of the atomic structure, and the concept of the minimum Schwarzschild radius is similar to that of the Bohr radius. The model predicts that black holes carry baryon number, and the baryon number is rapidly violated. This baryon number violation can be used as verification of the model. (author)

  2. BOOK REVIEW: Computational Atomic Structure

    Science.gov (United States)

    Post, Douglass E.

    1998-02-01

    The primary purpose of `Computational Atomic Structure' is to give a potential user of the Multi-Configuration Hartree-Fock (MCHF) Atomic Structure Package an outline of the physics and computational methods in the package, guidance on how to use the package, and information on how to interpret and use the computational results. The book is successful in all three aspects. In addition, the book provides a good overview and review of the physics of atomic structure that would be useful to the plasma physicist interested in refreshing his knowledge of atomic structure and quantum mechanics. While most of the subjects are covered in greater detail in other sources, the book is reasonably self-contained, and, in most cases, the reader can understand the basic material without recourse to other sources. The MCHF package is the standard package for computing atomic structure and wavefunctions for single or multielectron ions and atoms. It is available from a number of ftp sites. When the code was originally written in FORTRAN 77, it could only be run on large mainframes. With the advances in computer technology, the suite of codes can now be compiled and run on present day workstations and personal computers and is thus available for use by any physicist, even those with extremely modest computing resources. Sample calculations in interactive mode are included in the book to illustrate the input needed for the code, what types of results and information the code can produce, and whether the user has installed the code correctly. The user can also specify the calculational level, from simple Hartree-Fock to multiconfiguration Hartree-Fock. The MCHF method begins by finding approximate wavefunctions for the bound states of an atomic system. This involves minimizing the energy of the bound state using a variational technique. Once the wavefunctions have been determined, other atomic properties, such as the transition rates, can be determined. The book begins with an

  3. NMR and NQR study of the electronic and structural properties of Al-Cu-Fe and Al-Cu-Ru quasicrystals

    International Nuclear Information System (INIS)

    Shastri, A.; Borsa, F.; Torgeson, D.R.; Shield, J.E.; Goldman, A.I.

    1994-01-01

    27 Al and 63,65 Cu NMR is reported for powdered stable Al-Cu-Fe and Al-Cu-Ru icosahedral quasicrystals and crystalline approximants, and for an Al-Pd-Mn single-grain quasicrystal. 27 Al NQR spectra at 4.2 K were observed in Al-Cu-Fe and Al-Cu-Ru samples. From quadrupole-perturbed NMR spectra at different magnetic fields, and from zero-field NQR spectra, a wide distribution of local electric-field gradient (EFG) tensor components and principal-axis-system orientations was found at the Al site. A model EFG calculation based on a 1/1 Al-Cu-Fe approximant successfully explained the observed NQR spectra. The average local gradient is largely determined by the p-electron wave function at the Al site, while the width of the distribution is due to EFG lattice contribution. Comparison of 63 Cu and 27 Al NMR shows the EFG distribution at the two sites is similar, but the electronic contribution to the EFG is considerably smaller at the Cu site, in agreement with a more s-type wave function of the conduction electrons. Overall spread of EFG values is well reproduced by calculation based on the approximant. However, the experimental spectra indicate a much larger number of nonequivalent sites when compared with the simulated NQR spectra based on the 1/1 approximant. The short-range, local chemical order is well represented by the approximant, but differences in coordination must be included at intermediate range in the quasicrystal. Measured 27 Al Knight shift, magnetic susceptibility, and nuclear spin-lattice relaxation time as a function of temperature indicate reduced density of states at the Fermi level by a factor of 7 or 8 from the value in Al metal, consistent with the notion of a pseudogap for these quasicrystals. No differences in measured parameters were detected as a function of composition of the quasicrystalline alloys

  4. Can atom-surface potential measurements test atomic structure models?

    Science.gov (United States)

    Lonij, Vincent P A; Klauss, Catherine E; Holmgren, William F; Cronin, Alexander D

    2011-06-30

    van der Waals (vdW) atom-surface potentials can be excellent benchmarks for atomic structure calculations. This is especially true if measurements are made with two different types of atoms interacting with the same surface sample. Here we show theoretically how ratios of vdW potential strengths (e.g., C₃(K)/C₃(Na)) depend sensitively on the properties of each atom, yet these ratios are relatively insensitive to properties of the surface. We discuss how C₃ ratios depend on atomic core electrons by using a two-oscillator model to represent the contribution from atomic valence electrons and core electrons separately. We explain why certain pairs of atoms are preferable to study for future experimental tests of atomic structure calculations. A well chosen pair of atoms (e.g., K and Na) will have a C₃ ratio that is insensitive to the permittivity of the surface, whereas a poorly chosen pair (e.g., K and He) will have a ratio of C₃ values that depends more strongly on the permittivity of the surface.

  5. Electronic structure interpolation via atomic orbitals

    Energy Technology Data Exchange (ETDEWEB)

    Chen Mohan; Guo, G-C; He Lixin, E-mail: helx@ustc.edu.cn [Key Laboratory of Quantum Information, University of Science and Technology of China, Hefei, 230026 (China)

    2011-08-17

    We present an efficient scheme for accurate electronic structure interpolation based on systematically improvable optimized atomic orbitals. The atomic orbitals are generated by minimizing the spillage value between the atomic basis calculations and the converged plane wave basis calculations on some coarse k-point grid. They are then used to calculate the band structure of the full Brillouin zone using the linear combination of atomic orbitals algorithms. We find that usually 16-25 orbitals per atom can give an accuracy of about 10 meV compared to the full ab initio calculations, and the accuracy can be systematically improved by using more atomic orbitals. The scheme is easy to implement and robust, and works equally well for metallic systems and systems with complicated band structures. Furthermore, the atomic orbitals have much better transferability than Shirley's basis and Wannier functions, which is very useful for perturbation calculations.

  6. A study of a stable Al-Cu-Fe quasicrystal in solid and liquid state

    International Nuclear Information System (INIS)

    Chen Lifan; Chen Xishen

    1992-01-01

    A stable Al 65 Cu 20 Fe 15 quasicrystal with an icosahedral structure is studied in solid and liquid state. It is found that the icosahedral phase in Al 65 Cu 20 Fe 15 alloy does not grow directly from the pure liquid state, but rather forms between monoclinic Al 13 Fe 4 and residual liquid state at 865degC. The melting point of the Al 65 Cu 20 Fe 15 icosahedral quasicrystal occurs at 865degC and that of the Al 65 Cu 20 Fe 15 alloy occurs at 1008degC. Moreover, the monoclinic Al 13 Fe 4 is transformed into the icosahedral phase easily at the temperature of 845degC. The icosahedral quasicrystal in Al 65 Cu 20 Fe 15 alloy has a high thermal stability even at 950degC. Above 950degC, the icosahedral structure tends to an amorphous structure. (orig.)

  7. Root lattices and quasicrystals

    Science.gov (United States)

    Baake, M.; Joseph, D.; Kramer, P.; Schlottmann, M.

    1990-10-01

    It is shown that root lattices and their reciprocals might serve as the right pool for the construction of quasicrystalline structure models. All noncrystallographic symmetries observed so far are covered in minimal embedding with maximal symmetry.

  8. Fabrication of ten-fold photonic quasicrystalline structures

    Directory of Open Access Journals (Sweden)

    XiaoHong Sun

    2015-05-01

    Full Text Available Compared to periodic crystals, quasicrystals have higher point group symmetry and are more favorable in achieving complete band-gaps. In this report, a top-cut prism interferometer is designed to fabricate ten-fold photonic quasicrystalline structures. By optimizing the exposing conditions and material characteristics, appropriate quasicrystals have been obtained in the SU8 photoresist films. Atomic Force Microscopy and laser diffraction are used to characterize the fabricated structures. The measurement results show the consistence between the theoretical design and experiments. This will provide guidance for the large-area and fast production of ten-fold quasicrystalline structures with high quality.

  9. Studying the properties of photonic quasi-crystals by the scaling convergence method

    International Nuclear Information System (INIS)

    Ho, I-Lin; Ng, Ming-Yaw; Mai, Chien Chin; Ko, Peng Yu; Chang, Yia-Chung

    2013-01-01

    This work introduces the iterative scaling (or inflation) method to systematically approach and analyse the infinite structure of quasi-crystals. The resulting structures preserve local geometric orderings in order to prevent artificial disclination across the boundaries of super-cells, with realistic quasi-crystals coming out under high iteration (infinite super-cell). The method provides an easy way for decorations of quasi-crystalline lattices, and for compact reliefs with a quasi-periodic arrangement to underlying applications. Numerical examples for in-plane and off-plane properties of square-triangle quasi-crystals show fast convergence during iteratively geometric scaling, revealing characteristics that do not appear on regular crystals. (paper)

  10. Catalytic mechanism of LENR in quasicrystals based on localized anharmonic vibrations and phasons

    OpenAIRE

    Dubinko, Volodymyr; Laptev, Denis; Irwin, Klee

    2016-01-01

    Quasicrystals (QCs) are a novel form of matter, which are neither crystalline nor amorphous. Among many surprising properties of QCs is their high catalytic activity. We propose a mechanism explaining this peculiarity based on unusual dynamics of atoms at special sites in QCs, namely, localized anharmonic vibrations (LAVs) and phasons. In the former case, one deals with a large amplitude (~ fractions of an angstrom) time-periodic oscillations of a small group of atoms around their stable posi...

  11. Dislocation-free growth of quasicrystals from two seeds due to additional phasonic degrees of freedom

    Science.gov (United States)

    Schmiedeberg, M.; Achim, C. V.; Hielscher, J.; Kapfer, S. C.; Löwen, H.

    2017-07-01

    We explore the growth of two-dimensional quasicrystals, i.e., aperiodic structures that possess long-range order, from two seeds at various distances and with different orientations by using dynamical phase-field crystal calculations. We compare the results to the growth of periodic crystals from two seeds. There, a domain border consisting of dislocations is observed in case of large distances between the seed and large angles between their orientation. Furthermore, a domain border is found if the seeds are placed at a distance that does not fit to the periodic lattice. In the case of the growth of quasicrystals, we only observe domain borders for large distances and different orientations. Note that all distances do inherently not match to a perfect domain wall-free quasicrystalline structure. Nevertheless, we find dislocation-free growth for all seeds at a small enough distance and for all seeds that approximately have the same orientation. In periodic structures, the stress that occurs due to incommensurate distances between the seeds results in phononic strain fields or, in the case of too large stresses, in dislocations. In contrast, in quasicrystals an additional phasonic strain field can occur and suppress dislocations. Phasons are additional degrees of freedom that are unique to quasicrystals. As a consequence, the additional phasonic strain field helps to distribute the stress and facilitates the growth of dislocation-free quasicrystals from multiple seeds. In contrast, in the periodic case the growth from multiple seeds most likely leads to a structure with multiple domains. Our work lays the theoretical foundations for growing perfect quasicrystals from different seeds and is therefore relevant for many applications.

  12. Quasicrystals in Medieval Islamic Architecture

    Science.gov (United States)

    Lu, Peter

    2009-03-01

    The conventional view holds that girih (geometric star-and-polygon) patterns in medieval Islamic architecture were conceived by their designers as a network of zigzagging lines, and drafted directly with a straightedge and a compass. I discuss our recent findings that, by 1200 A. D., a conceptual breakthrough occurred in which girih patterns were reconceived as tessellations of a special set of equilateral polygons (girih tiles) decorated with lines. These girih tiles enabled the creation of increasingly complex periodic girih patterns, and by the 15th century, the tessellation approach was combined with self-similar transformations to construct nearly-perfect quasicrystalline patterns. These patterns have remarkable properties; they do not repeat periodically, and have special symmetry---and were not understood in the West until the 1970s. I will discuss some of the properties of Islamic quasicrystalline tilings, and their relation to the Penrose tiling, perhaps the best known quasicrystal pattern.

  13. Anti-plane problem analysis for icosahedral quasicrystals under shear loadings

    International Nuclear Information System (INIS)

    Li Wu; Chai Yu-Zhen

    2014-01-01

    The present paper is concerned with the longitudinal shear elasticity of three-dimensional icosahedral quasicrystals. By virtue of the Dugdale hypothesis along with the method of complex potential theory, it involves two defect problems of the icosahedral quasicrystals. The first one is the calculation of stress intensity factors and the size of the cohesive force zone in a half-infinite crack. Meanwhile, the crack tip tearing displacements can be exactly derived. The other is the demonstration of the generalized stress intensity factors induced by a sharp V-notch as an extension of a crack. The generalized E-integral around the notch tip gives the energy release rate when the V-notch degenerates into a crack. Apart from their own usefulness in carrying out some simplified crack analyses, the results obtained in this work can particularly serve as a basis for fracture mechanics of anti-plane defect problems of icosahedral quasicrystals. (condensed matter: structural, mechanical, and thermal properties)

  14. A crystal-chemical model of atomic interactions. Pt. 6

    International Nuclear Information System (INIS)

    Aslanov, L.A.; Markov, V.T.

    1992-01-01

    Commonly occurring structures are considered from the point of view of a crystal-chemical model of atomic interactions. It is shown that these structures sometimes contain coordination polyhedra distinct from Platonic, Archimedean and Zalgaller's polyhedra. These polyhedra have two or more groups of atoms into which all the vertices of the coordination polyhedron can be divided and which differ in distance from the central atom. The reasons for such polyhedra are considered. The crystal structure of NiTi 2 is analyzed and the causes of the quasicrystal state are revealed. (orig.)

  15. Formation of quasicrystals in Zr46.8Ti8.2Cu7.5Ni10Be27.5 bulk glass

    DEFF Research Database (Denmark)

    Wanderka, N.; Macht, M. P.; Siedel, M.

    2000-01-01

    The formation of the quasicrystalline phase is observed as a first step of crystallization during isothermal annealing of the Zr46.7Ti8.3Cu7.5Ni10Be27.5 bulk glass. The structure of the quasicrystals and the sequence of phase formation have been investigated by x-ray powder diffraction...... and transmission electron microscopy. The structure of the quasicrystals is determined to be primitive icosahedral with a quasilattice constant of 4.779 Angstrom. The quasicrystals decompose into several intermetallic compounds after prolonged annealing at lower temperatures or in a short time period (less than 5...

  16. Methods for Calculating Empires in Quasicrystals

    Directory of Open Access Journals (Sweden)

    Fang Fang

    2017-10-01

    Full Text Available This paper reviews the empire problem for quasiperiodic tilings and the existing methods for generating the empires of the vertex configurations in quasicrystals, while introducing a new and more efficient method based on the cut-and-project technique. Using Penrose tiling as an example, this method finds the forced tiles with the restrictions in the high dimensional lattice (the mother lattice that can be cut-and-projected into the lower dimensional quasicrystal. We compare our method to the two existing methods, namely one method that uses the algorithm of the Fibonacci chain to force the Ammann bars in order to find the forced tiles of an empire and the method that follows the work of N.G. de Bruijn on constructing a Penrose tiling as the dual to a pentagrid. This new method is not only conceptually simple and clear, but it also allows us to calculate the empires of the vertex configurations in a defected quasicrystal by reversing the configuration of the quasicrystal to its higher dimensional lattice, where we then apply the restrictions. These advantages may provide a key guiding principle for phason dynamics and an important tool for self error-correction in quasicrystal growth.

  17. Generalized dynamics of moving dislocations in quasicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Agiasofitou, Eleni; Lazar, Markus [Emmy Noether Research Group, Department of Physics, Darmstadt University of Technology, Hochschulstrasse 6, D-64289 Darmstadt (Germany); Kirchner, Helmut, E-mail: agiasofitou@mechanik.tu-darmstadt.d, E-mail: lazar@mechanik.tu-darmstadt.d, E-mail: kirchnerhok@hotmail.co [INM-Leibniz Institute for New Materials, Campus D22, D-66123 Saarbruecken (Germany)

    2010-12-15

    A theoretical framework for dislocation dynamics in quasicrystals is provided according to the continuum theory of dislocations. Firstly, we present the fundamental theory for moving dislocations in quasicrystals giving the dislocation density tensors and introducing the dislocation current tensors for the phonon and phason fields, including the Bianchi identities. Next, we give the equations of motion for the incompatible elastodynamics as well as for the incompatible elasto-hydrodynamics of quasicrystals. We continue with the derivation of the balance law of pseudomomentum thereby obtaining the generalized forms of the Eshelby stress tensor, the pseudomomentum vector, the dynamical Peach-Koehler force density and the Cherepanov force density for quasicrystals. The form of the dynamical Peach-Koehler force for a straight dislocation is obtained as well. Moreover, we deduce the balance law of energy that gives rise to the generalized forms of the field intensity vector and the elastic power density of quasicrystals. The above balance laws are produced for both models. The differences between the two models and their consequences are revealed. The influences of the phason fields as well as of the dynamical terms are also discussed.

  18. Acoustic and electronic properties of one-dimensional quasicrystals

    International Nuclear Information System (INIS)

    Nori, F.; Rodriguez, J.P.

    1986-01-01

    We study the acoustic and electronic properties of one-dimensional quasicrystals. Both numerical (nonperturbative) and analytical (perturbative) results are shown. The phonon and electronic spectra exhibit a self-similar hierarchy of gaps and many localized states in the gaps. We study quasiperiodic structures with any number of layers and several types of boundary conditions. We discuss the connection between our phonon model and recent experiments on quasiperiodic GaAs-AlAs superlattices. We predict the existence of many gap states localized at the surfaces

  19. Semiclassical dynamics, Berry curvature, and spiral holonomy in optical quasicrystals

    Science.gov (United States)

    Spurrier, Stephen; Cooper, Nigel R.

    2018-04-01

    We describe the theory of the dynamics of atoms in two-dimensional quasicrystalline optical lattices. We focus on a regime of shallow lattice depths under which the applied force can cause Landau-Zener tunneling past a dense hierarchy of gaps in the quasiperiodic energy spectrum. We derive conditions on the external force that allow for a "semiadiabatic" regime in which semiclassical equations of motion can apply, leading to Bloch oscillations between the edges of a pseudo-Brillouin-zone. We verify this semiclassical theory by comparing to the results of an exact numerical solution. Interesting features appear in the semiclassical dynamics for the quasicrystal for a particle driven in a cyclic trajectory around the corner of the pseudo-Brillouin-zone: The particle fails to return to its initial state, providing a realization of a "spiral holonomy" in the dynamics. We show that there can appear anomalous velocity contributions, associated with nonzero Berry curvature. We relate these to the Berry phase associated with the spiral holonomy, and show how the Berry curvature can be accessed from the semiclassical dynamics. Finally, by identifying the pseudo-Brillouin-zone as a higher genus surface, we show that the Chern number classification for periodic systems can be extended to a quasicrystal, thereby determining a topological index for the system.

  20. Relativistic collisions of structured atomic particles

    International Nuclear Information System (INIS)

    Voitkiv, A.; Ullrich, J.

    2008-01-01

    The book reviews the progress achieved over the last decade in the study of collisions between an ion and an atom in which both the atomic particles carry electrons and can undergo transitions between their internal states - including continua. It presents the detailed considerations of different theoretical approaches, that can be used to describe collisions of structured atomic particles for the very broad interval of impact energies ranging from 0.5-1 MeV/u till extreme relativistic energies where the collision velocity very closely approaches the speed of light. (orig.)

  1. Quasicrystals the state of the art

    CERN Document Server

    Di Vincenzo, D P

    1991-01-01

    This review volume provides the most up-to-date and authoritative description of research on icosahedral solids, which has advanced rapidly since the discovery of these unique materials in 1984. The present book, intended as a companion volume to the reprint volume on The Physics of Quasicrystals edited by P Steinhardt and S Ostlund, will be invaluable to graduate students and workers in the field as a comprehensive reference. Scientists in related fields can use it as a readable introduction to the important current problems in quasicrystals. The chapters have been written by many of the most

  2. Semiempirical studies of atomic structure

    International Nuclear Information System (INIS)

    Curtis, L.J.

    1992-01-01

    The energy level structure, transition probabilities, and general spectroscopic properties of highly ionized many-electron systems are studied through the combined use of sensitive semiempirical data systematizations, selected precision experimental measurements, and specialized theoretical computations. Measurements are made primarily through the use of fast ion beam excitation methods, which are combined with available data from laser-and tokamak-produced plasmas, astrophysical sources, and conventional light sources. The experimental studies are strengthened through large-scale ab initio calculations. Typical examples are the following: lifetime measurements in the neon isoelectronic sequence; multiplexed decay curve measurements of Li-like Si XII; and isoelectronic specification of intershell resonance and intercombination decay rates using measured transition probabilities and spectroscopically determined singlet-mixing amplitudes

  3. Orthorhombic rational approximants for decagonal quasicrystals

    Indian Academy of Sciences (India)

    Unknown

    An important exercise in the study of rational approximants is to derive their metric, especially in relation to the corresponding quasicrystal or the underlying clusters. Kuo's model has ..... the smaller diagonal of the fat rhombus in the Penrose tiling. This length scale is obtained by a section along a1 in the Penrose tiling and ...

  4. Photonic quasicrystals for application in WDM systems

    DEFF Research Database (Denmark)

    Romero-Vivas, J.; Chigrin, D. N.; Lavrinenko, Andrei

    2005-01-01

    Photonic quasicrystals can possess an isotropic (complete) photonic bandgap even in the case of low refractive indices of the constitutive materials, which makes them atrractive optical materials with important technological applications. In this work, several aspects related to the design of wav...

  5. Grain boundary atomic structure and properties

    Czech Academy of Sciences Publication Activity Database

    Paidar, Václav

    2002-01-01

    Roč. 8, - (2002), s. 24-30 ISSN 1335-1532 R&D Projects: GA ČR GA202/02/0916 Institutional research plan: CEZ:AV0Z1010914 Keywords : atomic structures * grain boundary properties * phase transformations Subject RIV: BM - Solid Matter Physics ; Magnetism

  6. Niels Bohr and the Atomic Structure

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 18; Issue 10. Niels Bohr and the Atomic Structure. M Durga Prasad. General Article Volume 18 Issue 10 October 2013 pp 897-904. Fulltext. Click here to view fulltext PDF. Permanent link: http://www.ias.ac.in/article/fulltext/reso/018/10/0897-0904 ...

  7. Atomic Reference Data for Electronic Structure Calculations

    CERN Document Server

    Kotochigova, S; Shirley, E L

    We have generated data for atomic electronic structure calculations, to provide a standard reference for results of specified accuracy under commonly used approximations. Results are presented here for total energies and orbital energy eigenvalues for all atoms from H to U, at microHartree accuracy in the total energy, as computed in the local-density approximation (LDA) the local-spin-density approximation (LSD); the relativistic local-density approximation (RLDA); and scalar-relativistic local-density approximation (ScRLDA).

  8. Structure and properties of atomic nanoclusters

    CERN Document Server

    Alonso, Julio A

    2005-01-01

    Atomic clusters are the bridge between molecules and the bulk matter. Following two key experiments - the observation of electronic shells in metallic clusters and the discovery of the C60 fullerence - the field of atomic clusters has experienced a rapid growth, and is now considered a mature field. The electrons of the cluster are confined to a small volume, hence, quantum effects are manifested on many properties of the clusters. Another interesting feature is that the properties often change in a non-smooth way as the number of atoms in the cluster increases. This book provides an updated overview of the field, and presents a detailed description of the structure and electronic properties of different types of clusters: Van der Waals clusters, metallic clusters, clusters of ionic materials and network clusters. The assembling of clusters is also considered, since specially stable clusters are expected to play a role in the future design and synthesis of new materials.

  9. On the low-temperature specific heat of icosahedral and decagonal quasicrystals

    International Nuclear Information System (INIS)

    Chernikov, M.A.

    2005-01-01

    Calorimetric experiments on icosahedral (Al-Re-Pd, Al-Mn-Pd) and decagonal (Al-Cu-Co, Al-Ni-Co) quasicrystals are described. For quasicrystals of both classes, the coefficient γ of the linear term to the specific heat falls into the range of 0.1-0.6 mJ/g-atom K 2 indicating a low density of energy states at Fermi level. For icosahedral Al-Mn-Pd, the cubic-in-temperature term to the specific heat is distinctly larger than the estimated contribution of long-wave acoustic excitations. On the contrary, the magnitude of the cubic-in-temperature term to the specific heat of decagonal Al-Ni-Co is in agreement,within the experimental accuracy, with the Debye acoustic contribution from the results of low-temperature measurements of the elastic modules [ru

  10. An Atomic Data and Analysis Structure

    International Nuclear Information System (INIS)

    Summers, Hugh P.

    2000-01-01

    The Atomic Data and Analysis Structure (ADAS) Project is a shared activity of a world-wide consortium of fusion and astrophysical laboratories directed at developing and maintaining a common approach to analysing and modelling the radiating properties of plasmas. The origin and objectives of ADAS and the organization of its codes and data collections outlined. Current special projects in the ADAS Project work-plans are listed and an illustration given of ADAS at work. (author)

  11. Phonons in models for icosahedral quasicrystals : low frequency behaviour and inelastic scattering properties

    Science.gov (United States)

    Los, J.; Janssen, T.; Gähler, F.

    1993-06-01

    A detailed study of the low frequency behaviour of the phonon spectrum for 3-dimensional tiling models of icosahedral quasicrystals is presented, in commensurate approximations with up to 10 336 atoms per unit cell. The scaling behaviour of the lowest phonon branches shows that the widths of the gaps relative to the bandwidths vanish in the low frequency limit. The density of states at low frequencies is calculated by Brillouin zone integration, using either local linear or local quadratic interpolation of the branch surface. For perfect approximants it appears that there is a deviation from the normal ω^2-behaviour already at relatively low frequencies, in the form of pseudogaps. Also randomized approximants are considered, and it turns out that the pseudogaps in the density of states are flattened by randomization. When approaching the quasiperiodic limit, the dispersion of the acoustic branches becomes more and more isotropic, and the two transversal sound velocities tend to the same value. The dynamical structure factor is determined for several approximants, and it is shown that the linearity and the isotropy of the dispersion are extended far beyond the range of the acoustic branches inside the Brillouin zone. A sharply peaked response is observed at low frequencies, and broadening at higher frequencies. To obtain these results, an efficient algorithm based on Lanczos tridiagonalisation is used.

  12. Lekhnitskii's formalism of one-dimensional quasicrystals and its ...

    Indian Academy of Sciences (India)

    To illustrate its utility, the generalized Lekhnitskii's formal- ism is used to analyse the coupled phonon and phason fields in an infinite quasicrystal medium con- taining an elliptic rigid inclusion. Keywords. Generalized Lekhnitskii's formalism; one-dimensional quasicrystals; plane problems; elliptic inclusion. PACS Nos 61.44.

  13. Thin Films of Quasicrystals: Optical, Electronic, and Mechanical Properties

    Science.gov (United States)

    Symko, Orest G.

    1998-03-01

    In order to extend some of the unusual properties of quasicrystals toward practical applications and to study fundamental aspects of these properties, we have developed a technology for the deposition of high quality thin films of quasicrystals on a variety of substrates. Mechanical support for the thin films is provided by the substrate as bulk quasicrystals are brittle. We have applied the thin films to studies of their optical, electrical, and mechanical properties as well as to coatings of biomedical devices. An important characteristic of a quasicrystal is its pseudogap in the electronic density of states; it is determined directly from optical transmission measurements. Optical and mechanical characteristics of the thin films provide strong support for the cluster nature of quasicrystals and emphasize their importance for coatings. When used in biomedical devices, thin film quasicrystalline coatings show remarkable strength, low friction, and non-stick behavior. This work was in collaboration with W. Park, E. Abdel-Rahman, and T. Klein.

  14. Atoms

    International Nuclear Information System (INIS)

    Fuchs, Alain; Villani, Cedric; Guthleben, Denis; Leduc, Michele; Brenner, Anastasios; Pouthas, Joel; Perrin, Jean

    2014-01-01

    Completed by recent contributions on various topics (atoms and the Brownian motion, the career of Jean Perrin, the evolution of atomic physics since Jean Perrin, relationship between scientific atomism and philosophical atomism), this book is a reprint of a book published at the beginning of the twentieth century in which the author addressed the relationship between atomic theory and chemistry (molecules, atoms, the Avogadro hypothesis, molecule structures, solutes, upper limits of molecular quantities), molecular agitation (molecule velocity, molecule rotation or vibration, molecular free range), the Brownian motion and emulsions (history and general features, statistical equilibrium of emulsions), the laws of the Brownian motion (Einstein's theory, experimental control), fluctuations (the theory of Smoluchowski), light and quanta (black body, extension of quantum theory), the electricity atom, the atom genesis and destruction (transmutations, atom counting)

  15. Propagator theory of atomic and molecular structure

    International Nuclear Information System (INIS)

    Oehrn, Y.

    1976-01-01

    It is not at all obvious which methods of use in quantum chemistry can be characterized as being without wavefunctions. There are, however, a number of methods that purpose to calculate atomic and molecular electronic structure and properties without the explicit use of many-electron wavefunctions. Fully realizing the arbitrariness of any classification of such methods as well as the absence of sharp boundaries between any choice of groups, the author separates the three kinds of approaches: (i) Local Density Energy Functional Methods, (ii) Density Matrix Methods, (iii) Propagator or Green's Function Methods. (Auth.)

  16. High-pressure x-ray diffraction of icosahedral Zr-Al-Ni-Cu-Ag quasicrystals

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Saksl, Karel; Rasmussen, Helge Kildahl

    2001-01-01

    The effect of pressure on the structural stability of icosahedral Zr-Al-Ni-Cu-Ag quasicrystals forming from a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass with a supercooled liquid region of 44 K has been investigated by in situ high-pressure angle-dispersive x-ray powder diffraction at ambient temperat......The effect of pressure on the structural stability of icosahedral Zr-Al-Ni-Cu-Ag quasicrystals forming from a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass with a supercooled liquid region of 44 K has been investigated by in situ high-pressure angle-dispersive x-ray powder diffraction at ambient...

  17. Symmetry-Induced Light Confinement in a Photonic Quasicrystal-Based Mirrorless Cavity

    Directory of Open Access Journals (Sweden)

    Gianluigi Zito

    2016-09-01

    Full Text Available We numerically investigate the electromagnetic field localization in a two-dimensional photonic quasicrystal generated with a holographic tiling. We demonstrate that light confinement can be induced into an air mirrorless cavity by the inherent symmetry of the spatial distribution of the dielectric scatterers forming the side walls of the open cavity. Furthermore, the propagation direction can be controlled by suitable designs of the structure. This opens up new avenues for designing photonic materials and devices.

  18. Self-consistent calculation of atomic structure for mixture

    International Nuclear Information System (INIS)

    Meng Xujun; Bai Yun; Sun Yongsheng; Zhang Jinglin; Zong Xiaoping

    2000-01-01

    Based on relativistic Hartree-Fock-Slater self-consistent average atomic model, atomic structure for mixture is studied by summing up component volumes in mixture. Algorithmic procedure for solving both the group of Thomas-Fermi equations and the self-consistent atomic structure is presented in detail, and, some numerical results are discussed

  19. On-line system for investigation of atomic structure

    International Nuclear Information System (INIS)

    Amus'ya, M.Ya.; Chernysheva, L.V.

    1983-01-01

    A description of the on-line ATOM system is presented that enables to investigate the structure of atomic electron shells and their interactions with different scattering particles-electrons, positronse photons, mesons - with the use of computerized numerical solutions. The problem is stated along with mathematical description of atomic properties including theoretical and numerical models for each investigated physical process. The ATOM system structure is considered. The Hartree-Fock method is used to determine the wave functions of the ground and excited atomic states. The programs are written in the ALGOL langauge. Different atomic characteristics were possible to be calculated for the first time with an accuracy exceeding an experimental one

  20. On the origin of the giant magnetic moment of the Al-Mn quasicrystals

    Directory of Open Access Journals (Sweden)

    Bocharov P.V.

    2011-05-01

    Full Text Available Ab initio calculations of magnetic moments for icosahedral clusters contained in crystal structures Al10Mn3, Al5Co2, Al17Mn4 (Al13Cr4Si4-type fulfilled in the framework of Density Functional Theory. The AlMn cluster having the trigonal D3h symmetry with the triangle of Mn ions in the interior has the moment being equal to three magnetic moments of a single manganese ion (4.4 μB, the moment of the tetrahedral Td cluster with the Mn tetrahedron in the interior is equal approximately to twelve magnetic moments of the single manganese ion (15.5 μB. The magnetic moment of icosahedral Al-Co clusters having the same configuration is equal to zero. The magnetic moments of the rod assembled from the icosahedral clusters with the sequence Td D3h - Td was found to be 20.5 μB. This value permits to explain the giant magnetic moment of icosahedral and decagonal Al-Mn quasicrystals and gives the indirect evidence to the hierarchical model of the quasicrystals structure proposed by the authors recently. An arrangement of magnetic moment carriers in the interior of the aluminum shell of icosahedral clusters permits to suggest the interaction between contacting manganese ions as the main origin of the giant magnetic moment of the Al-Mn quasicrystals.

  1. Photonic crystal and photonic quasicrystal patterned in PDMS surfaces and their effect on LED radiation properties

    Energy Technology Data Exchange (ETDEWEB)

    Suslik, Lubos [Dept. of Physics, Faculty of Electrical Engineering, University of Zilina, Univerzitna 1, 010 26, Zilina (Slovakia); Pudis, Dusan, E-mail: pudis@fyzika.uniza.sk [Dept. of Physics, Faculty of Electrical Engineering, University of Zilina, Univerzitna 1, 010 26, Zilina (Slovakia); Goraus, Matej [Dept. of Physics, Faculty of Electrical Engineering, University of Zilina, Univerzitna 1, 010 26, Zilina (Slovakia); Nolte, Rainer [Fakultät für Maschinenbau FG Lichttechnik Ilmenau University of Technology, Ilmenau (Germany); Kovac, Jaroslav [Inst. of Electronics and Photonics, Slovak University of Technology, Ilkovicova 3, 812 19, Bratislava (Slovakia); Durisova, Jana; Gaso, Peter [Dept. of Physics, Faculty of Electrical Engineering, University of Zilina, Univerzitna 1, 010 26, Zilina (Slovakia); Hronec, Pavol [Inst. of Electronics and Photonics, Slovak University of Technology, Ilkovicova 3, 812 19, Bratislava (Slovakia); Schaaf, Peter [Chair Materials for Electronics, Institute of Materials Engineering and Institute of Micro- and Nanotechnologies MacroNano, TU Ilmenau, Gustav-Kirchhoff-Str. 5, 98693 Ilmenau (Germany)

    2017-02-15

    Graphical abstract: Photonic quasicrystal patterned in the surface of polydimethylsiloxane membrane (left) and radiation pattern of light emitting diode with patterned membrane applied in the surface (right). - Highlights: • We presented fabrication technique of PDMS membranes with patterned surface by photonic crystal (PhC) and photonic quasi-crystal (PQC). • Presented technique is effective for preparation PhC and PQC PDMS membranes easily implementing in the LED chip. • From the goniophotometer measurements, the membranes document effective angular emission due to the diffraction on patterned surfaces. • 12 fold symmetry PQC structure shows homogeneous radiation pattern, while the 2 fold symmetry of square PhC shows evident diffraction lobes. - Abstract: We present results of fabrication and implementation of thin polydimethylsiloxane (PDMS) membranes with patterned surface for the light emitting diode (LED). PDMS membranes were patterned by using the interference lithography in combination with embossing technique. Two-dimensional photonic crystal and photonic quasicrystal structures with different period were patterned in the surface of thin PDMS membranes with depth up to 550 nm. Patterned PDMS membranes placed on the LED chip effectively diffracted light and increased angular emission of LED radiation pattern. We presented effective technique for fabrication of patterned PDMS membranes, which could modify the emission properties of optoelectronic devices and can be applied directly on surface LEDs and small optical devices.

  2. Influence of the atomic structure on the quantum state of sputtered Ir atoms

    International Nuclear Information System (INIS)

    Bastiaansen, J.; Philipsen, V.; Lievens, P.; Silverans, R.E.; Vandeweert, E.

    2004-01-01

    The probability of the ejection of a neutral atom in a specific quantum state after keV-ion beam sputtering is often interpreted in terms of the interaction between the atomic states of the escaping atom and the electronic states of the solid. In this work, we examined this interplay in the sputtering of iridium as this element has--unlike the elements employed in previous investigations--a complex atomic structure due to strong configuration interactions. Double-resonant two-photon laser ionization is used to probe the sputtered Ir atoms yielding information about the probability for an ejected atom to populate a specific atomic state and its escape velocity. The qualitative features of the corresponding population partition and state-selective velocity distributions show the influence of the excitation energy and the electronic structure of the different atomic states. A comparison is made between the experimental data and predictions from the resonant electron transfer description

  3. Electronic equipment for atomic nucleus structure studying

    International Nuclear Information System (INIS)

    Brudanin, V.B.; Vasilev, D.; Vylov, Ts.; Zhuravlev, N.I.; Salamatin, A.V.; Sidorov, V.T.; Sinaev, A.N.; Churin, I.N.

    1985-01-01

    The CAMAC electronic equipment used in data acquisition systems for spectrometers intended for investigation of the structure of an atomic nucleus is considered. Specific features of electronic units forming a part of spectrometers for determination of neutrino helicity and three-dimensional amplitude-time measurements as well as electrostatic beta-spectrometer are discussed. Parameters of the MAK-1, the MAK-2 and the MAK-3 multichannel amplitude analyzers developed specially for these spectrometers are given. Accumulation of data coming from analog-to-digital converters and output of recorded spectra on the screens of displays is realized without use of the crate dataway that permits to avoid time losses and to place several analyzers in a crate. Observation of spectra is realized simultaneously with their registration

  4. Watching Atoms Work: Nanocluster Structure and Dynamics.

    Science.gov (United States)

    Pennycook, Stephen J; Zhou, Wu; Pantelides, Sokrates T

    2015-10-27

    In the space of little more than a decade, the resolution of the electron microscope has improved to provide clear views of the atomic world. Not only can atomic arrangements be imaged, but with a little gentle provocation from the electron beam, atoms can be energized and their dynamics can also be revealed. In this issue of ACS Nano, Chen et al. image Si atoms growing under the beam into cubic crystalline arrangements.

  5. Inner Space: The Structure of the Atom

    Energy Technology Data Exchange (ETDEWEB)

    Glasstone, Samuel

    1972-01-01

    The atom is now regarded as the smallest possible particle of an element that retains the identity of that element. The atoms of an element determine the characteristics of that particular element. One of the purposes of this booklet is to explain how the atoms of various elements differ from one another.

  6. Structurally uniform and atomically precise carbon nanostructures

    Science.gov (United States)

    Segawa, Yasutomo; Ito, Hideto; Itami, Kenichiro

    2016-01-01

    Nanometre-sized carbon materials consisting of benzene units oriented in unique geometric patterns, hereafter named nanocarbons, conduct electricity, absorb and emit light, and exhibit interesting magnetic properties. Spherical fullerene C60, cylindrical carbon nanotubes and sheet-like graphene are representative forms of nanocarbons, and theoretical simulations have predicted several exotic 3D nanocarbon structures. At present, synthetic routes to nanocarbons mainly lead to mixtures of molecules with a range of different structures and properties, which cannot be easily separated or refined into pure forms. Some researchers believe that it is impossible to synthesize these materials in a precise manner. Obtaining ‘pure’ nanocarbons is a great challenge in the field of nanocarbon science, and the construction of structurally uniform nanocarbons, ideally as single molecules, is crucial for the development of functional materials in nanotechnology, electronics, optics and biomedical applications. This Review highlights the organic chemistry approach — more specifically, bottom-up construction with atomic precision — that is currently the most promising strategy towards this end.

  7. Mathematical theory of elasticity of quasicrystals and its applications

    CERN Document Server

    Fan, Tianyou

    2011-01-01

    This book presents a clear-cut, strict and systematic mathematical overview of the continuum mechanics of novel materials, condensed matter physics and partial differential equations, and explores the mathematical theory of elasticity of quasicrystals.

  8. Lekhnitskii's formalism of one-dimensional quasicrystals and its ...

    Indian Academy of Sciences (India)

    dimensional quasicrystals and its application. YANG GAO. College of Science, China Agricultural ... integration of the expressions for deformations and application of the anisotropic constitutive law and the ..... von Humboldt Foundation in Germany.

  9. Atomic probes of surface structure and dynamics

    International Nuclear Information System (INIS)

    Heller, E.J.; Jonsson, H.

    1992-01-01

    Progress for the period Sept. 15, 1992 to Sept. 14, 1993 is discussed. Semiclassical methods that will allow much faster and more accurate three-dimensional atom--surface scattering calculations, both elastic and inelastic, are being developed. The scattering of He atoms from buckyballs is being investigated as a test problem. Somewhat more detail is given on studies of He atom scattering from defective Pt surfaces. Molecular dynamics simulations of He + and Ar + ion sputtering of Pt surfaces are also being done. He atom scattering from Xe overlayers on metal surfaces and the thermalized dissociation of H 2 on Cu(110) are being studied. (R.W.R.) 64 refs

  10. Big Atoms for Small Children: Building Atomic Models from Common Materials to Better Visualize and Conceptualize Atomic Structure

    Science.gov (United States)

    Cipolla, Laura; Ferrari, Lia A.

    2016-01-01

    A hands-on approach to introduce the chemical elements and the atomic structure to elementary/middle school students is described. The proposed classroom activity presents Bohr models of atoms using common and inexpensive materials, such as nested plastic balls, colored modeling clay, and small-sized pasta (or small plastic beads).

  11. Atomic structure holography using thermal neutrons

    International Nuclear Information System (INIS)

    Sur, B.; Rogge, R.B.; Hammond, R.P.; Anghel, V.N.P.; Katsaras, J.

    2001-01-01

    The idea of atomic-resolution holography has its roots in the X-ray work of Bragg and in Gabor's electron interference microscope. Gabor's lensless microscope was not realized in his time, but over the past twelve years there has been a steady increase in the number of reports on atomic-resolution holography. All of this work involves the use of electrons or hard X-rays to produce the hologram. Neutrons are often unique among scattering probes in their interaction with materials: for example, the relative visibility of hydrogen and its isotopes is a great advantage in the study of polymers and biologically relevant materials. Recent work proposed that atomic-resolution holography could be achieved with thermal neutrons. Here we use monochromatic thermal neutrons, adopting the inside-source concept of Szoke, to image planes of oxygen atoms located above and below a single hydrogen atom in the oxide mineral Simpsonite. (author)

  12. Generalized Quasiperiodic Structures

    Science.gov (United States)

    Steurer, Walter; Deloudi, Sofia

    This chapter is dedicated to the discussion of soft polymeric quasicrystals, which show dodecagonal symmetry, as well as photonic and phononic quasicrystals. On the example of transmission spectra, the characteristic features of one-, two- and three-dimensional phononic quasicrystals are illustrated. The high-symmetry of particular quasicrystals makes omnidirectional band-gaps possible even in low-contrast materials. The structures used for that purpose are the Fibonacci sequence, the octagonal tiling and the Ammann tiling. The consequences of soft and hard contrast as well as the role of resonant and Bragg scattering are discussed.

  13. Atomic structure and physical properties of liquid Pb Bi alloys

    Science.gov (United States)

    Kaban, I.; Hoyer, W.; Plevachuk, Yu; Sklyarchuk, V.

    2004-09-01

    The atomic structure and physical properties (dynamic viscosity, electrical conductivity, and thermopower) of liquid Pb-Bi alloys have been investigated in a wide temperature range. Gradual and reversible changes of the physical properties during heating and cooling of the Pb-Bi liquid alloys have been observed. No drastic structural transformations or atomic rearrangement with temperature variation have been found.

  14. Determination of atomic cluster structure with cluster fusion algorithm

    DEFF Research Database (Denmark)

    Obolensky, Oleg I.; Solov'yov, Ilia; Solov'yov, Andrey V.

    2005-01-01

    We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters.......We report an efficient scheme of global optimization, called cluster fusion algorithm, which has proved its reliability and high efficiency in determination of the structure of various atomic clusters....

  15. 8x8 and 10x10 Hyperspace Representations of SU(3) and 10-fold Point-Symmetry Group of Quasicrystals

    Science.gov (United States)

    Animalu, Alexander

    2012-02-01

    In order to further elucidate the unexpected 10-fold point-symmetry group structure of quasi-crystals for which the 2011 Nobel Prize in chemistry was awarded to Daniel Shechtman, we explore a correspondence principle between the number of (projective) geometric elements (points[vertices] + lines[edges] + planes[faces]) of primitive cells of periodic or quasi-periodic arrangement of hard or deformable spheres in 3-dimensional space of crystallography and elements of quantum field theory of particle physics [points ( particles, lines ( particles, planes ( currents] and hence construct 8x8 =64 = 28+36 = 26 + 38, and 10x10 =100= 64 + 36 = 74 + 26 hyperspace representations of the SU(3) symmetry of elementary particle physics and quasicrystals of condensed matter (solid state) physics respectively, As a result, we predict the Cabibbo-like angles in leptonic decay of hadrons in elementary-particle physics and the observed 10-fold symmetric diffraction pattern of quasi-crystals.

  16. Atomic correlations in non-periodic matter

    International Nuclear Information System (INIS)

    Egami, T.

    1990-01-01

    Recent advances in the methods of structural analysis, in particular the use of particle accelerators to produce pulsed neutrons and synchrotron radiation, have greatly improved our ability to describe the atomic structure of non-periodic matter quantitatively using the atomic pair distribution analysis, or the real-space method of powder diffraction. The method can now be applied to crystalline or nearly crystalline solids as well to describe deviations from perfect periodicity with a sufficient accuracy. We discuss the fundamental issues pertaining to the use of this technique, and review some of the recent results obtained by this method in the fields of high-T c oxide superconductors, quasicrystals and metallic glasses. (author) 76 refs

  17. Another 2-dimensional oxide quasicrystal: Strontium titanate on Pt(111)

    Energy Technology Data Exchange (ETDEWEB)

    Schenk, Sebastian; Hammer, Rene; Schumann, Florian; Foerster, Stefan; Meinel, Klaus [Institute of Physics, Martin-Luther-Universitaet Halle-Wittenberg, Halle (Germany); Widdra, Wolf [Institute of Physics, Martin-Luther-Universitaet Halle-Wittenberg, Halle (Germany); Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany)

    2016-07-01

    Recently the formation of a BaTiO{sub 3}-derived 2-dimensional oxide quasicrystal (OQC) with 12-fold diffraction symmetry has been discovered on Pt(111) substrates [1]. Following an analogous preparation procedure, we show that SrTiO{sub 3} on Pt(111) develops an OQC as well. First, a closed SrTiO{sub 3} film on Pt(111) has been prepared using MBE. The stoichiometry and structure of the film has been analyzed by means of AES and SPA-LEED. Annealing the film in an O{sub 2} atmosphere yields the formation of 3-dimensional SrTiO{sub 3} islands with bare Pt(111) in between. Annealing in UHV causes a rewetting on the Pt(111) via surface diffusion of SrTiO{sub 3} from the islands. SPA-LEED and STM reveal that at temperatures around 700 C an OQC is formed in the rewetting layer. The SrTiO{sub 3} derived OQC is composed by quadratic, triangular, and rhombic elements of equal side length of about 0.6 nm. They form an aperiodic structure, which displays a well-ordered 12-fold diffraction pattern. Our results suggest that OQC formation is a general process of oxide perovskites on suitable substrates.

  18. Visualization of atomic structure using AFM: theoretical description

    OpenAIRE

    Gallyamov, M. O.; Yaminsky, I. V.

    2011-01-01

    We suggest simple model of image formation in atomic force microscope (AFM) taking into account contact deformations of probe and sample during scanning. The model explains the possibility of AFM visualization of regular atomic or molecular structure when probe-sample contact area is greater than an area per atom or molecule in surface lattice. (This is usually the case when lattice to be studied has subnanometer unit cell parameters and AFM investigations are carried out in air in contact mo...

  19. Niels Bohr and the Atomic Structure

    Indian Academy of Sciences (India)

    IAS Admin

    the electrons such as optical spectroscopy or chemical reactivity. This picture of the .... body of uncorrelated data, and thus could get to the heart of the problem. Second, he appreciated the distinction between atomic processes and the nuclear processes. .... theory needed new concepts and mathematical tools, but classical.

  20. Niels Bohr and the Atomic Structure

    Indian Academy of Sciences (India)

    IAS Admin

    that succeeded in explaining the spectral features of hydrogen atom. In the process, he incorporated some non-classical features such as discrete energy levels for the bound electrons, and quantization of their angular ... element in the periodic table is determined by the nuclear charge. The particle has a mass of four ...

  1. Structures of 38-atom gold-platinum nanoalloy clusters

    Energy Technology Data Exchange (ETDEWEB)

    Ong, Yee Pin; Yoon, Tiem Leong [School of Physics, Universiti Sains Malaysia, 11800 USM, Penang (Malaysia); Lim, Thong Leng [Faculty of Engineering and Technology, Multimedia University, Melaka Campus, 75450 Melaka (Malaysia)

    2015-04-24

    Bimetallic nanoclusters, such as gold-platinum nanoclusters, are nanomaterials promising wide range of applications. We perform a numerical study of 38-atom gold-platinum nanoalloy clusters, Au{sub n}Pt{sub 38−n} (0 ≤ n ≤ 38), to elucidate the geometrical structures of these clusters. The lowest-energy structures of these bimetallic nanoclusters at the semi-empirical level are obtained via a global-minimum search algorithm known as parallel tempering multi-canonical basin hopping plus genetic algorithm (PTMBHGA), in which empirical Gupta many-body potential is used to describe the inter-atomic interactions among the constituent atoms. The structures of gold-platinum nanoalloy clusters are predicted to be core-shell segregated nanoclusters. Gold atoms are observed to preferentially occupy the surface of the clusters, while platinum atoms tend to occupy the core due to the slightly smaller atomic radius of platinum as compared to gold’s. The evolution of the geometrical structure of 38-atom Au-Pt clusters displays striking similarity with that of 38-atom Au-Cu nanoalloy clusters as reported in the literature.

  2. Atomic structure of highly-charged ions. Final report

    International Nuclear Information System (INIS)

    Livingston, A. Eugene

    2002-01-01

    Atomic properties of multiply charged ions have been investigated using excitation of energetic heavy ion beams. Spectroscopy of excited atomic transitions has been applied from the visible to the extreme ultraviolet wavelength regions to provide accurate atomic structure and transition rate data in selected highly ionized atoms. High-resolution position-sensitive photon detection has been introduced for measurements in the ultraviolet region. The detailed structures of Rydberg states in highly charged beryllium-like ions have been measured as a test of long-range electron-ion interactions. The measurements are supported by multiconfiguration Dirac-Fock calculations and by many-body perturbation theory. The high-angular-momentum Rydberg transitions may be used to establish reference wavelengths and improve the accuracy of ionization energies in highly charged systems. Precision wavelength measurements in highly charged few-electron ions have been performed to test the most accurate relativistic atomic structure calculations for prominent low-lying excited states. Lifetime measurements for allowed and forbidden transitions in highly charged few-electron ions have been made to test theoretical transition matrix elements for simple atomic systems. Precision lifetime measurements in laser-excited alkali atoms have been initiated to establish the accuracy of relativistic atomic many-body theory in many-electron systems

  3. Mathematical theory of elasticity of quasicrystals and its applications

    CERN Document Server

    Fan, Tian-You

    2016-01-01

    This interdisciplinary work on condensed matter physics, the continuum mechanics of novel materials, and partial differential equations, discusses the mathematical theory of elasticity and hydrodynamics of quasicrystals, as well as its applications. By establishing new partial differential equations of higher order and their solutions under complicated boundary value and initial value conditions, the theories developed here dramatically simplify the solution of complex elasticity problems. Comprehensive and detailed mathematical derivations guide readers through the work. By combining theoretical analysis and experimental data, mathematical studies and practical applications, readers will gain a systematic, comprehensive and in-depth understanding of condensed matter physics, new continuum mechanics and applied mathematics. This new edition covers the latest developments in quasicrystal studies. In particular, it pays special attention to the hydrodynamics, soft-matter quasicrystals, and the Poisson bracket m...

  4. Acousto-optic interactions for terahertz waves using phoxonic quasicrystals

    Science.gov (United States)

    Wang, Zhong; Yu, Tianbao; Wang, Tongbiao; Liu, Wenxing; Liu, Nianhua; Liao, Qinghua

    2018-03-01

    Phoxonic quasicrystals possess abundant localized modes and low-index-contrast bandgaps, thus showing much advantage over periodic counterparts. We calculated the modulation of photonic modes for terahertz waves by phononic modes in defect-free phoxonic quasicrystals (FDQs) and quasicrystals having center point defects (PDQs). Both the moving interface (MI) and photoelastic effects are considered in acousto-optic coupling. Terahertz modes can be efficiently modified by acoustic modes due to the simultaneous confinement of electromagnetic and elastic fields both inside and outside the bandgaps. The acousto-optic coupling strength depends on the selection of the acoustic and terahertz defect modes. The predominant coupling mechanism is determined by the overlapping between the terahertz and acoustic modes in PDQs, while the MI effect becomes predominant in FDQs. Our results are important for terahertz wave modulation with ultra-small footprint size.

  5. Update on nuclear structure effects in light muonic atoms

    Energy Technology Data Exchange (ETDEWEB)

    Hernandez, Oscar Javier, E-mail: javierh@triumf.ca; Dinur, Nir Nevo; Ji, Chen; Bacca, Sonia [TRIUMF (Canada); Barnea, Nir [The Hebrew University, Racah Institute of Physics (Israel)

    2016-12-15

    We present calculations of the nuclear structure corrections to the Lamb shift in light muonic atoms, using state-of-the-art nuclear potentials. We outline updated results on finite nucleon size contributions.

  6. Insights into plant consciousness from neuroscience, physics and mathematics: a role for quasicrystals?

    Science.gov (United States)

    Gardiner, John

    2012-09-01

    There is considerable debate over whether plants are conscious and this, indeed, is an important question. Here I look at developments in neuroscience, physics and mathematics that may impact on this question. Two major concomitants of consciousness in animals are microtubule function and electrical gamma wave synchrony. Both these factors may also play a role in plant consciousness. I show that plants possess aperiodic quasicrystal structures composed of ribosomes that may enable quantum computing, which has been suggested to lie at the core of animal consciousness. Finally I look at whether a microtubule fractal suggests that electric current plays a part in conventional neurocomputing processes in plants.

  7. Modeling of the atomic and electronic structures of interfaces

    International Nuclear Information System (INIS)

    Sutton, A.P.

    1988-01-01

    Recent tight binding and Car-Parrinello simulations of grain boundaries in semiconductors are reviewed. A critique is given of some models of embrittlement that are based on electronic structure considerations. The structural unit model of grain boundary structure is critically assessed using some results for mixed tilt and twist grain boundaries. A new method of characterizing interfacial structure in terms of bond angle distribution functions is described. A new formulation of thermodynamic properties of interfaces is presented which focusses on the local atomic environment. Effective, temperature dependent N-body atomic interactions are derived for studying grain boundary structure at elevated temperature

  8. Protein crystal structure analysis using synchrotron radiation at atomic resolution

    International Nuclear Information System (INIS)

    Nonaka, Takamasa

    1999-01-01

    We can now obtain a detailed picture of protein, allowing the identification of individual atoms, by interpreting the diffraction of X-rays from a protein crystal at atomic resolution, 1.2 A or better. As of this writing, about 45 unique protein structures beyond 1.2 A resolution have been deposited in the Protein Data Bank. This review provides a simplified overview of how protein crystallographers use such diffraction data to solve, refine, and validate protein structures. (author)

  9. Fractal spectra in generalized Fibonacci one-dimensional magnonic quasicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Costa, C.H.O. [Departamento de Fisica Teorica e Experimental, Universidade Federal do Rio grande do Norte, 59072-970 Natal-RN (Brazil); Vasconcelos, M.S., E-mail: manoelvasconcelos@yahoo.com.br [Escola de Ciencias e Tecnologia, Universidade Federal do Rio grande do Norte, 59072-970 Natal-RN (Brazil); Barbosa, P.H.R.; Barbosa Filho, F.F. [Departamento de Fisica, Universidade Federal do Piaui, 64049-550 Teresina-Pi (Brazil)

    2012-07-15

    In this work we carry out a theoretical analysis of the spectra of magnons in quasiperiodic magnonic crystals arranged in accordance with generalized Fibonacci sequences in the exchange regime, by using a model based on a transfer-matrix method together random-phase approximation (RPA). The generalized Fibonacci sequences are characterized by an irrational parameter {sigma}(p,q), which rules the physical properties of the system. We discussed the magnonic fractal spectra for first three generalizations, i.e., silver, bronze and nickel mean. By varying the generation number, we have found that the fragmentation process of allowed bands makes possible the emergence of new allowed magnonic bulk bands in spectra regions that were magnonic band gaps before, such as which occurs in doped semiconductor devices. This interesting property arises in one-dimensional magnonic quasicrystals fabricated in accordance to quasiperiodic sequences, without the need to introduce some deferent atomic layer or defect in the system. We also make a qualitative and quantitative investigations on these magnonic spectra by analyzing the distribution and magnitude of allowed bulk bands in function of the generalized Fibonacci number F{sub n} and as well as how they scale as a function of the number of generations of the sequences, respectively. - Highlights: Black-Right-Pointing-Pointer Quasiperiodic magnonic crystals are arranged in accordance with the generalized Fibonacci sequence. Black-Right-Pointing-Pointer Heisenberg model in exchange regime is applied. Black-Right-Pointing-Pointer We use a theoretical model based on a transfer-matrix method together random-phase approximation. Black-Right-Pointing-Pointer Fractal spectra are characterized. Black-Right-Pointing-Pointer We analyze the distribution of allowed bulk bands in function of the generalized Fibonacci number.

  10. Magnetic moments and non-Fermi-liquid behavior in quasicrystals

    Science.gov (United States)

    Andrade, Eric

    Motivated by the intrinsic non-Fermi-liquid behavior observed in the heavy-fermion quasicrystal Au51Al34Yb15, we study the low-temperature behavior of dilute magnetic impurities placed in metallic quasicrystals. We find that a large fraction of the magnetic moments are not quenched down to very low temperatures, leading to a power-law distribution of Kondo temperatures, accompanied by a non-Fermi-liquid behavior, in a remarkable similarity to the Kondo-disorder scenario found in disordered heavy-fermion metals. This work was supported by FAPESP (Brazil) Grant No. 2013/00681-8.

  11. DFT computations of the lattice constant, stable atomic structure and ...

    African Journals Online (AJOL)

    This paper presents the most stable atomic structure and lattice constant of Fullerenes (C60). FHI-aims DFT code was used to predict the stable structure and the computational lattice constant of C60. These were compared with known experimental structures and lattice constants of C60. The results obtained showed that ...

  12. Understanding Atomic Structure: Is There a More Direct and Compelling Connection between Atomic Line Spectra and the Quantization of an Atom's Energy?

    Science.gov (United States)

    Rittenhouse, Robert C.

    2015-01-01

    The "atoms first" philosophy, adopted by a growing number of General Chemistry textbook authors, places greater emphasis on atomic structure as a key to a deeper understanding of the field of chemistry. A pivotal concept needed to understand the behavior of atoms is the restriction of an atom's energy to specific allowed values. However,…

  13. Effects of spherical quasi-crystal on microstructure and mechanical properties of ZA155 high zinc magnesium alloy

    Directory of Open Access Journals (Sweden)

    Zhang Jinshan

    2010-05-01

    Full Text Available Effects of spherical quasi-crystal contained in Mg-Zn-Y-Mn master alloy on the microstructure and as-cast mechanical properties of ZA155 high zinc magnesium alloy have been investigated by means of optical microscopy, XRD, SEM, EDS, tensile test, impact test and hardness test. Experimental results show that the addition of spherical quasi-crystal contained in the Mg-Zn-Y-Mn master alloy into the ZA155 high zinc magnesium alloy resulted in grain refinement of the matrix, changing the morphologies of φ-Al2Mg5Zn2 phase and τ-Mg32(Al, Zn49 phase from continuous net-like structures to discontinuous strip-like structure and blocky one, respectively. In the present research, the best comprehensive mechanical properties of reinforced ZA155 high zinc magnesium alloy has been obtained when 5.0wt% spherical quasi-crystal was introduced from the Mg-Zn-Y-Mn master alloy into the target alloy system. In such case, the room-temperature tensile strength reached 207 MPa, about 23% higher than that of the base alloy; the impact toughness peaked at 5.5 J/cm2, about 40% higher than that of the base alloy; and the elevated-temperature tensile strength reached 203 MPa, indicating improved heat resistance.

  14. Unraveling the atomic structure of ultrafine iron clusters

    KAUST Repository

    Wang, Hongtao

    2012-12-18

    Unraveling the atomic structures of ultrafine iron clusters is critical to understanding their size-dependent catalytic effects and electronic properties. Here, we describe the stable close-packed structure of ultrafine Fe clusters for the first time, thanks to the superior properties of graphene, including the monolayer thickness, chemical inertness, mechanical strength, electrical and thermal conductivity. These clusters prefer to take regular planar shapes with morphology changes by local atomic shuffling, as suggested by the early hypothesis of solid-solid transformation. Our observations differ from observations from earlier experimental study and theoretical model, such as icosahedron, decahedron or cuboctahedron. No interaction was observed between Fe atoms or clusters and pristine graphene. However, preferential carving, as observed by other research groups, can be realized only when Fe clusters are embedded in graphene. The techniques introduced here will be of use in investigations of other clusters or even single atoms or molecules.

  15. Contact mechanics, friction and adhesion with application to quasicrystals

    DEFF Research Database (Denmark)

    Persson, Bo; Carbone, Giuseppe; Samoilov, Vladimir N.

    2015-01-01

    We discuss the origin of friction and adhesion between hard solids such as quasicrystals. We emphasize the fundamental role of surface roughness in many contact mechanics problems, in particular for friction and adhesion between solid bodies. The most important property of rough surfaces...

  16. Lekhnitskii's formalism of one-dimensional quasicrystals and its ...

    Indian Academy of Sciences (India)

    ... of the expressions for deformations and application of the anisotropic constitutive law and the compatibility of displacements. To illustrate its utility, the generalized lekhnitskii's formalism is used to analyse the coupled phonon and phason fields in an infinite quasicrystal medium containing an elliptic rigid inclusion.

  17. Direct experimental determination of the atomic structure at internal interfaces

    Energy Technology Data Exchange (ETDEWEB)

    Browning, N.D. [Oak Ridge National Lab., TN (United States)]|[Illinois Univ., Chicago, IL (United States); Pennycook, S.J. [Oak Ridge National Lab., TN (United States)

    1995-07-01

    A crucial first step in understanding the effect that internal interfaces have on the properties of materials is the ability to determine the atomic structure at the interface. As interfaces can contain atomic disorder, dislocations, segregated impurities and interphases, sensitivity to all of these features is essential for complete experimental characterization. By combining Z-contrast imaging and electron energy loss spectroscopy (EELS) in a dedicated scanning transmission electron microscope (STEM), the ability to probe the structure, bonding and composition at interfaces with the necessary atomic resolution has been obtained. Experimental conditions can be controlled to provide, simultaneously, both incoherent imaging and spectroscopy. This enables interface structures observed in the image to be interpreted intuitively and the bonding in a specified atomic column to be probed directly by EELS. The bonding and structure information can then be correlated using bond-valence sum analysis to produce structural models. This technique is demonstrated for 25{degrees}, 36{degrees} and 67{degrees} symmetric and 45{degrees} and 25{degrees} asymmetric [001] tilt grain boundaries in SrTiO{sub 3} The structures of both types of boundary were found to contain partially occupied columns in the boundary plane. From these experimental results, a series of structural units were identified which could be combined, using continuity of gain boundary structure principles, to construct all [001] tilt boundaries in SrTiO{sub 3}. Using these models, the ability of this technique to address the issues of vacancies and dopant segregation at grain boundaries in electroceramics is discussed.

  18. ISOTROPIC INELASTIC COLLISIONS IN A MULTITERM ATOM WITH HYPERFINE STRUCTURE

    Energy Technology Data Exchange (ETDEWEB)

    Belluzzi, Luca [Istituto Ricerche Solari Locarno, CH-6605 Locarno Monti (Switzerland); Landi Degl’Innocenti, Egidio [Dipartimento di Fisica e Astronomia, Università di Firenze, I-50125 Firenze (Italy); Bueno, Javier Trujillo [Instituto de Astrofísica de Canarias, E-38205 La Laguna, Tenerife (Spain)

    2015-10-10

    A correct modeling of the scattering polarization profiles observed in some spectral lines of diagnostic interest, the sodium doublet being one of the most important examples, requires taking hyperfine structure (HFS) and quantum interference between different J-levels into account. An atomic model suitable for taking these physical ingredients into account is the so-called multiterm atom with HFS. In this work, we introduce and study the transfer and relaxation rates due to isotropic inelastic collisions with electrons, which enter the statistical equilibrium equations (SEE) for the atomic density matrix of this atomic model. Under the hypothesis that the electron–atom interaction is described by a dipolar operator, we provide useful relations between the rates describing the transfer and relaxation of quantum interference between different levels (whose numerical values are in most cases unknown) and the usual rates for the atomic level populations, for which experimental data and/or approximate theoretical expressions are generally available. For the particular case of a two-term atom with HFS, we present an analytical solution of the SEE for the spherical statistical tensors of the upper term, including both radiative and collisional processes, and we derive the expression of the emission coefficient in the four Stokes parameters. Finally, an illustrative application to the Na i D{sub 1} and D{sub 2} lines is presented.

  19. Solitonic fullerene structures in light atomic nuclei.

    Science.gov (United States)

    Battye, R A; Sutcliffe, P M

    2001-04-30

    The Skyrme model is a classical field theory which has topological soliton solutions. These solitons are candidates for describing nuclei, with an identification between the numbers of solitons and nucleons. We have computed numerically, using two different minimization algorithms, minimum energy configurations for up to 22 solitons. We find, remarkably, that the solutions for seven or more solitons have nucleon density isosurfaces in the form of polyhedra made of hexagons and pentagons. Precisely these structures arise, though at the much larger molecular scale, in the chemistry of carbon shells, where they are known as fullerenes.

  20. Structural atlas of dynein motors at atomic resolution.

    Science.gov (United States)

    Toda, Akiyuki; Tanaka, Hideaki; Kurisu, Genji

    2018-02-24

    Dynein motors are biologically important bio-nanomachines, and many atomic resolution structures of cytoplasmic dynein components from different organisms have been analyzed by X-ray crystallography, cryo-EM, and NMR spectroscopy. This review provides a historical perspective of structural studies of cytoplasmic and axonemal dynein including accessory proteins. We describe representative structural studies of every component of dynein and summarize them as a structural atlas that classifies the cytoplasmic and axonemal dyneins. Based on our review of all dynein structures in the Protein Data Bank, we raise two important points for understanding the two types of dynein motor and discuss the potential prospects of future structural studies.

  1. Atomic-level Analysis of Membrane Protein Structure

    OpenAIRE

    Hendrickson, Wayne A.

    2016-01-01

    Membrane proteins are substantially more challenging than natively soluble proteins as subjects for structural analysis. Thus, membrane proteins are greatly under-represented in structural databases. Recently, as a consequence of focused attention by consortium efforts and advances in methodology, the pace has accelerated for atomic-level structure determination of membrane proteins. Enabling advances have come in methods for protein production, for crystallographic analysis, and for cryo-EM ...

  2. Theoretical atomic physics code development I: CATS: Cowan Atomic Structure Code

    International Nuclear Information System (INIS)

    Abdallah, J. Jr.; Clark, R.E.H.; Cowan, R.D.

    1988-12-01

    An adaptation of R.D. Cowan's Atomic Structure program, CATS, has been developed as part of the Theoretical Atomic Physics (TAPS) code development effort at Los Alamos. CATS has been designed to be easy to run and to produce data files that can interface with other programs easily. The CATS produced data files currently include wave functions, energy levels, oscillator strengths, plane-wave-Born electron-ion collision strengths, photoionization cross sections, and a variety of other quantities. This paper describes the use of CATS. 10 refs

  3. Atomic parity nonconservation: Electroweak parameters and nuclear structure

    International Nuclear Information System (INIS)

    Pollock, S.J.; Fortson, E.N.; Wilets, L.

    1992-01-01

    There have been suggestions to measure atomic parity nonconservation (PNC) along an isotopic chain, by taking ratios of observables in order to cancel complicated atomic-structure effects. Precise atomic PNC measurements could make a significant contribution to tests of the standard model at the level of one-loop radiative corrections. However, the results also depend upon certain features of nuclear structure, such as the spatial distribution of neutrons in the nucleus. To examine the sensitivity to nuclear structure, we consider the case of Pb isotopes using various recent relativistic and nonrelativistic nuclear model calculations. Contributions from nucleon internal weak structure are included, but found to be fairly negligible. The spread among present models in predicted sizes of nuclear-structure effects may preclude using Pb isotope ratios to test the standard model at better than a 1% level, unless there are adequate independent tests of the nuclear models by various alternative strong and electroweak nuclear probes. On the other hand, sufficiently accurate atomic PNC experiments would provide a unique method to measure neutron distributions in heavy nuclei

  4. Polymorphism of dislocation core structures at the atomic scale.

    Science.gov (United States)

    Wang, Zhongchang; Saito, Mitsuhiro; McKenna, Keith P; Ikuhara, Yuichi

    2014-01-01

    Dislocation defects together with their associated strain fields and segregated impurities are of considerable significance in many areas of materials science. However, their atomic-scale structures have remained extremely challenging to resolve, limiting our understanding of these ubiquitous defects. Here, by developing a complex modelling approach in combination with bicrystal experiments and systematic atomic-resolution imaging, we are now able to pinpoint individual dislocation cores at the atomic scale, leading to the discovery that even simple magnesium oxide can exhibit polymorphism of core structures for a given dislocation species. These polymorphic cores are associated with local variations in strain fields, segregation of defects, and electronic states, adding a new dimension to understanding the properties of dislocations in real materials. The findings advance our fundamental understanding of basic behaviours of dislocations and demonstrate that quantitative prediction and characterization of dislocations in real materials is possible.

  5. Atomic structure of graphene supported heterogeneous model catalysts

    International Nuclear Information System (INIS)

    Franz, Dirk

    2017-04-01

    Graphene on Ir(111) forms a moire structure with well defined nucleation centres. Therefore it can be utilized to create hexagonal metal cluster lattices with outstanding structural quality. At diffraction experiments these 2D surface lattices cause a coherent superposition of the moire cell structure factor, so that the measured signal intensity scales with the square of coherently scattering unit cells. This artificial signal enhancement enables the opportunity for X-ray diffraction to determine the atomic structure of small nano-objects, which are hardly accessible with any experimental technique. The uniform environment of every metal cluster makes the described metal cluster lattices on graphene/Ir(111) an attractive model system for the investigation of catalytic, magnetic and quantum size properties of ultra-small nano-objects. In this context the use of x-rays provides a maximum of flexibility concerning the possible sample environments (vacuum, selected gases, liquids, sample temperature) and allows in-situ/operando measurements. In the framework of the present thesis the structure of different metal clusters grown by physical vapor deposition in an UHV environment and after gas exposure have been investigated. On the one hand the obtained results will explore many aspects of the atomic structure of these small metal clusters and on the other hand the presented results will proof the capabilities of the described technique (SXRD on cluster lattices). For iridium, platinum, iridium/palladium and platinum/rhodium the growth on graphene/Ir(111) of epitaxial, crystalline clusters with an ordered hexagonal lattice arrangement has been confirmed using SXRD. The clusters nucleate at the hcp sites of the moire cell and bind via rehybridization of the carbon atoms (sp 2 → sp 3 ) to the Ir(111) substrate. This causes small displacements of the substrate atoms, which is revealed by the diffraction experiments. All metal clusters exhibit a fcc structure, whereupon

  6. A narrowband filter based on 2D 8-fold photonic quasicrystal

    Science.gov (United States)

    Ren, Jie; Sun, XiaoHong; Wang, Shuai

    2018-04-01

    In this paper, a novel structure of narrowband filter based on 2D 8-fold photonic quasicrystal (PQC) is proposed and investigated. The structure size is 8 μm × 8 μm, which promises its applications in optical integrated circuits and communication devices. Finite Element Method (FEM) has been employed to investigate the band gap of the filter. The resonance wavelength, transmission coefficient and 3 dB bandwidth are analyzed by varying the parameters of the structure. By optimizing the parameters of the filter, two design formulas of resonance wavelength are obtained. Also, for its better linearity of the resonance, the structure with line-defect has also seen a large uptake in sensor design.

  7. Formation of Al70Cu20Fe10 icosahedral quasicrystal by mechanically alloyed method

    International Nuclear Information System (INIS)

    Yin Shilong; Bian Qing; Qian Liying; Zhang Aimei

    2007-01-01

    The structural evolutions of the mechanically alloyed ternary Al 70 Cu 20 Fe 10 powders with the milling time and the annealing treatment have been studied by X-ray diffraction (XRD), transmission electronic microscopy (TEM) and X-ray absorption fine-structure spectroscopy (XAFS) techniques. Results show that an Al 2 Cu compound forms with short-time milling, while a Cu 9 Al 4 compound forms with long-time milling. Fe can react with Al-Cu alloy by annealing treatment. Al 7 Cu 2 Fe compound with tetragonal structure or Al (Cu, Fe) solid solution with cubic structure may form at lower temperature, while a quasicrystal phase of Al 65 Cu 20 Fe 15 alloy may form at higher temperature

  8. Crystal structures and atomic model of NADPH oxidase

    NARCIS (Netherlands)

    Magnani, Francesca; Nenci, Simone; Fananas, Elisa Millana; Ceccon, Marta; Romero, Elvira; Fraaije, Marco W.; Mattevi, Andrea

    2017-01-01

    NADPH oxidases (NOXs) are the only enzymes exclusively dedicated to reactive oxygen species (ROS) generation. Dysregulation of these polytopic membrane proteins impacts the redox signaling cascades that control cell proliferation and death. We describe the atomic crystal structures of the catalytic

  9. Atomic scale structures of interfaces between kaolinite edges and water

    NARCIS (Netherlands)

    Liu, X.; Lu, X.; Wang, R.; Meijer, E.J.; Zhou, H.; He, H.

    2012-01-01

    This paper reports the atomic scale structures of kaolinite edge surfaces in contact with water. The commonly occurring edge surfaces are investigated (i.e. (0 1 0) and (1 1 0)) by using first principles molecular dynamics (FPMD) technique. For (1 1 0)-type edge surface, there are two different

  10. Pattern recognition approach to quantify the atomic structure of graphene

    DEFF Research Database (Denmark)

    Kling, Jens; Vestergaard, Jacob Schack; Dahl, Anders Bjorholm

    2014-01-01

    We report a pattern recognition approach to detect the atomic structure in high-resolution transmission electron microscopy images of graphene. The approach provides quantitative information such as carbon-carbon bond lengths and bond length variations on a global and local scale alike. © 2014...

  11. Classroom: inexpensive models for teaching atomic structure and ...

    African Journals Online (AJOL)

    Classroom: inexpensive models for teaching atomic structure and compounds at junior secondary school level of education. WHK Hordzi, BA Mensah. Abstract. No Abstract. Global Journal of Educational Research Vol. 2(1&2) 2003: 33-40. Full Text: EMAIL FREE FULL TEXT EMAIL FREE FULL TEXT · DOWNLOAD FULL ...

  12. Nanoscale Structuring of Surfaces by Using Atomic Layer Deposition.

    Science.gov (United States)

    Sobel, Nicolas; Hess, Christian

    2015-12-07

    Controlled structuring of surfaces is interesting for a wide variety of areas, including microelectronic device fabrication, optical devices, bio(sensing), (electro-, photo)catalysis, batteries, solar cells, fuel cells, and sorption. A unique feature of atomic layer deposition (ALD) is the possibility to form conformal uniform coatings on arbitrarily shaped materials with controlled atomic-scale thickness. In this Minireview, we discuss the potential of ALD for the nanoscale structuring of surfaces, highlighting its versatile application to structuring both planar substrates and powder materials. Recent progress in the application of ALD to porous substrates has even made the nanoscale structuring of high-surface-area materials now feasible, thereby enabling novel applications, such as those in the fields of catalysis and alternative energy. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  13. Surface structure investigations using noncontact atomic force microscopy

    International Nuclear Information System (INIS)

    Kolodziej, J.J.; Such, B.; Goryl, M.; Krok, F.; Piatkowski, P.; Szymonski, M.

    2006-01-01

    Surfaces of several A III B V compound semiconductors (InSb, GaAs, InP, InAs) of the (0 0 1) orientation have been studied with noncontact atomic force microscopy (NC-AFM). Obtained atomically resolved patterns have been compared with structural models available in the literature. It is shown that NC-AFM is an efficient tool for imaging complex surface structures in real space. It is also demonstrated that the recent structural models of III-V compound surfaces provide a sound base for interpretation of majority of features present in recorded patterns. However, there are also many new findings revealed by the NC-AFM method that is still new experimental technique in the context of surface structure determination

  14. Toward the Atomic Structure of PrPSc.

    Science.gov (United States)

    Rodriguez, Jose A; Jiang, Lin; Eisenberg, David S

    2017-09-01

    In this review, we detail our current knowledge of PrP Sc structure on the basis of structural and computational studies. We discuss the progress toward an atomic resolution description of PrP Sc and results from the broader field of amyloid studies that may further inform our knowledge of this structure. Moreover, we summarize work that investigates the role of PrP Sc structure in its toxicity, transmissibility, and species specificity. We look forward to an atomic model of PrP Sc , which is expected to bring diagnostics and/or therapeutics to the field of prion disease. Copyright © 2017 Cold Spring Harbor Laboratory Press; all rights reserved.

  15. Diffraction pattern of modulated structures described by Bessel functions

    Science.gov (United States)

    Wolny, Janusz; Buganski, Ireneusz; Strzalka, Radoslaw

    2016-05-01

    We performed detailed analysis of 1D modulated structure (MS) with harmonic modulation within the statistical approach. By applying two-mode Fourier transform, we were able to derive analytically the structure factor for MS with single harmonic modulation component. We confirmed in a very smooth way that ordinary Bessel functions of the first kind define envelopes tuning the intensities of the diffraction peaks. This applies not only to main reflections of the diffraction pattern but also to all satellites. In the second part, we discussed in details the similarities between harmonically modulated structures with multiple modulations and 1D model quasicrystal. The Fourier expansion of the nodes' positions in the Fibonacci chain gives direct numerical definition of the atomic arrangement in MS. In that sense, we can define 1D quasicrystal as a MS with infinite number of harmonic modulations. We prove that characteristic measures (like v(u) relation typical for statistical approach and diffraction pattern) calculated for MS asymptotically approach their counterparts for 1D quasicrystal as large enough number of modulation terms is taken into account.

  16. Atomic structure of As25Si40Te35 glass

    Science.gov (United States)

    Kaban, I.; Gruner, S.; Jóvári, P.; Kehr, M.; Hoyer, W.; Delaplane, R. G.; Popescu, M.

    2007-08-01

    Glassy As25Si40Te35 has been studied by x-ray and neutron diffraction as well as x-ray absorption spectroscopy (EXAFS) at As and Te K-edges. Simultaneous modelling of the four independent measurements by means of the reverse Monte Carlo (RMC) simulation technique allowed the separation of partial pair distribution functions and estimation of the corresponding coordination numbers. It is shown that the atomic structure of As25Si40Te35 glass can be presented as a three-dimensional network of twofold coordinated Te, threefold coordinated As and fourfold coordinated Si atoms.

  17. Atomic physics. Introduction to quantum physics and structure of the atomic system. 2. ed.

    International Nuclear Information System (INIS)

    Cagnac, Bernard; Pebay-Peyroula, J.-C.

    1975-01-01

    This lecture is intended for providing experimental foundations to the basic principles of quantum mechanics, from descriptions of some characteristic experiments which emphasize the limitations of the classical theory. The basic laws that govern the internal structure of atomic systems are exposed (waves and photons, the planetary model and principal quantum number, and the spatial classification of kinetic momenta and magnetic moments). Experimental studies presently in progress are reviewed and their aims are outlined [fr

  18. New State of Matter: Heavy Fermion Systems, Quantum Spin Liquids, Quasicrystals, Cold Gases, and High-Temperature Superconductors

    Science.gov (United States)

    Shaginyan, V. R.; Stephanovich, V. A.; Msezane, A. Z.; Schuck, P.; Clark, J. W.; Amusia, M. Ya.; Japaridze, G. S.; Popov, K. G.; Kirichenko, E. V.

    2017-12-01

    We report on a new state of matter manifested by strongly correlated Fermi systems including various heavy fermion (HF) metals, two-dimensional quantum liquids such as ^3He films, certain quasicrystals, and systems behaving as quantum spin liquids. Generically, these systems can be viewed as HF systems or HF compounds, in that they exhibit typical behavior of HF metals. At zero temperature, such systems can experience a so-called fermion condensation quantum phase transition (FCQPT). Combining analytical considerations with arguments based entirely on experimental grounds, we argue and demonstrate that the class of HF systems is characterized by universal scaling behavior of their thermodynamic, transport, and relaxation properties. That is, the quantum physics of different HF compounds is found to be universal, emerging irrespective of the individual details of their symmetries, interactions, and microscopic structure. This observed universal behavior reveals the existence of a new state of matter manifest in HF compounds. We propose a simple, realistic model to study the appearance of flat bands in two-dimensional ensembles of ultracold fermionic atoms, interacting with coherent resonant light. It is shown that signatures of these flat bands may be found in peculiarities in their thermodynamic and spectroscopic properties. We also show that the FCQPT, in generating flat bands and altering Fermi surface topology, is an essential progenitor of the exotic behavior of the overdoped high-temperature superconductors represented by La_{2-x}SrxxCuO_4, whose superconductivity differs from that predicted by the classical Bardeen-Cooper-Schrieffer theory. The theoretical results presented are in good agreement with recent experimental observations, closing the colossal gap between these empirical findings and Bardeen-Cooper-Schrieffer-like theories.

  19. Scanning tuneeling microscopy studies of fivefold surfaces of icosahedral Al-Pd-Mn quasicrystals and of thin silver films on those surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Unal, Baris [Iowa State Univ., Ames, IA (United States)

    2008-01-01

    The present work in this dissertation mainly focuses on the clean fivefold surfaces of i-Al-Pd-Mn quasicrystals as well as the nucleation and growth of Ag films on these surfaces. In addition, Ag film growth on NiAl(110) has been explored in the frame of this dissertation. First, we have investigated the equilibration of a fivefold surface of icosahedral Al-Pd-Mn quasicrystal at 900-915 K and 925-950 K, using Omicron variable temperature scanning tunneling microscope (STM). Annealing at low temperatures resulted in many voids on some terraces while the others were almost void-free. After annealing at 925-950K, void-rich terraces became much rarer. Our STM images suggest that through growth and coalescence of the voids, a different termination becomes exposed on host terraces. All of these observations in our study indicate that even after the quasicrystalline terrace-step structure appears, it evolves with time and temperature. More specifically, based on the STM observations, we conclude that during the annealing a wide range of energetically similar layers nucleate as surface terminations, however, with increasing temperature (and time) this distribution gets narrower via elimination of the metastable void-rich terraces. Next, we have examined the bulk structural models of icosahedral Al-Pd-Mn quasicrystal in terms of the densities, compositions and interplanar spacings for the fivefold planes that might represent physical surface terminations. In our analyses, we mainly have focused on four deterministic models which have no partial or mixed occupancy but we have made some comparisons with an undeterministic model. We have compared the models with each other and also with the available experimental data including STM, LEED-IV, XPD and LEIS. In all deterministic models, there are two different families of layers (a pair of planes), and the nondeterministic model contains similar group of planes. These two families differ in terms of the chemical decoration of

  20. Atom by atom: HRTEM insights into inorganic nanotubes and fullerene-like structures.

    Science.gov (United States)

    Bar Sadan, Maya; Houben, Lothar; Enyashin, Andrey N; Seifert, Gotthard; Tenne, Reshef

    2008-10-14

    The characterization of nanostructures down to the atomic scale is essential to understand some physical properties. Such a characterization is possible today using direct imaging methods such as aberration-corrected high-resolution transmission electron microscopy (HRTEM), when iteratively backed by advanced modeling produced by theoretical structure calculations and image calculations. Aberration-corrected HRTEM is therefore extremely useful for investigating low-dimensional structures, such as inorganic fullerene-like particles and inorganic nanotubes. The atomic arrangement in these nanostructures can lead to new insights into the growth mechanism or physical properties, where imminent commercial applications are unfolding. This article will focus on two structures that are symmetric and reproducible. The first structure that will be dealt with is the smallest stable symmetric closed-cage structure in the inorganic system, a MoS(2) nanooctahedron. It is investigated by means of aberration-corrected microscopy which allowed validating the suggested DFTB-MD model. It will be shown that structures diverging from the energetically most stable structures are present in the laser ablated soot and that the alignment of the different shells is parallel, unlike the bulk material where the alignment is antiparallel. These findings correspond well with the high-energy synthetic route and they provide more insight into the growth mechanism. The second structure studied is WS(2) nanotubes, which have already been shown to have a unique structure with very desirable mechanical properties. The joint HRTEM study combined with modeling reveals new information regarding the chirality of the different shells and provides a better understanding of their growth mechanism.

  1. Modeling Protein Structure at Near Atomic Resolutions With Gorgon

    Science.gov (United States)

    Baker, Matthew L.; Abeysinghe, Sasakthi S.; Schuh, Stephen; Coleman, Ross A.; Abrams, Austin; Marsh, Michael P.; Hryc, Corey F.; Ruths, Troy; Chiu, Wah; Ju, Tao

    2011-01-01

    Electron cryo-microscopy (cryo-EM) has played an increasingly important role in elucidating the structure and function of macromolecular assemblies in near native solution conditions. Typically, however, only non-atomic resolution reconstructions have been obtained for these large complexes, necessitating computational tools for integrating and extracting structural details. With recent advances in cryo-EM, maps at near-atomic resolutions have been achieved for several macromolecular assemblies from which models have been manually constructed. In this work, we describe a new interactive modeling toolkit called Gorgon targeted at intermediate to near-atomic resolution density maps (10-3.5 Å), particularly from cryo-EM. Gorgon's de novo modeling procedure couples sequence-based secondary structure prediction with feature detection and geometric modeling techniques to generate initial protein backbone models. Beyond model building, Gorgon is an extensible interactive visualization platform with a variety of computational tools for annotating a wide variety of 3D volumes. Examples from cryo-EM maps of Rotavirus and Rice Dwarf Virus are used to demonstrate its applicability to modeling protein structure. PMID:21296162

  2. Atomic Structure Control of Silica Thin Films on Pt(111)

    KAUST Repository

    Crampton, Andrew S

    2015-05-27

    Metal oxide thin films grown on metal single crystals are commonly used to model heterogeneous catalyst supports. The structure and properties of thin silicon dioxide films grown on metal single crystals have only recently been thoroughly characterized and their spectral properties well established. We report the successful growth of a three- dimensional, vitreous silicon dioxide thin film on the Pt(111) surface and reproduce the closed bilayer structure previously reported. The confirmation of the three dimensional nature of the film is unequivocally shown by the infrared absorption band at 1252 cm−1. Temperature programmed desorption was used to show that this three-dimensional thin film covers the Pt(111) surface to such an extent that its application as a catalyst support for clusters/nanoparticles is possible. The growth of a three-dimensional film was seen to be directly correlated with the amount of oxygen present on the surface after the silicon evaporation process. This excess of oxygen is tentatively attributed to atomic oxygen being generated in the evaporator. The identification of atomic oxygen as a necessary building block for the formation of a three-dimensional thin film opens up new possibilities for thin film growth on metal supports, whereby simply changing the type of oxygen enables thin films with different atomic structures to be synthesized. This is a novel approach to tune the synthesis parameters of thin films to grow a specific structure and expands the options for modeling common amorphous silica supports under ultra high vacuum conditions.

  3. NATO Advanced Research Workshop on Incommensurate Crystals, Liquid Crystals, and Quasi-Crystals

    CERN Document Server

    Clark, N

    1988-01-01

    In this NATO-sponsored Advanced Research Workshop we succeeded in bringing together approximately forty scientists working in the three main areas of structurally incommensurate materials: incommensurate crystals (primarily ferroelectric insulators), incommensurate liquid crystals, and metallic quasi-crystals. Although these three classes of materials are quite distinct, the commonality of the physics of the origin and descrip­ tion of these incommensurate structures is striking and evident in these proceedings. A measure of the success of this conference was the degree to which interaction among the three subgroups occurred; this was facili­ tated by approximately equal amounts of theory and experiment in the papers presented. We thank the University of Colorado for providing pleasant housing and conference facilities at a modest cost, and we are especially grate­ ful to Ann Underwood, who retyped all the manuscripts into camera-ready form. J. F. Scott Boulder, Colorado N. A. Clark v CONTENTS PART I: INCO...

  4. Development of atomic spectroscopy technologies - Hyperfine structure of 2 period atoms using optogalvanic effects

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, Nam Ic [Hankuk University of foreign studies, Seoul (Korea)

    2000-03-01

    The source of anomalous broad linewidth of 3{sup 3}P{sub 1},{sub 2},{sub 3}-3{sup 3}D{sub 2},{sub 3},4(3s') transition was explained. The broad optogalvanic spectrum was consisted of two gaussian peaks of different linewidths, and they are separated by 250 MHz. The Narrow peak, which has linewidth of room temperature, is from oxygen atoms already separated, and the shifted broad peak, which has linewidth corresponding to a temperature of 9000 K, is from weakly bound molecular ions. Obtained hyperfine spectrum of fluorine atom at the expected frequency, was too weak to analyze hyperfine structure constants. Microwave discharge might be necessary for higher density of excited state. 16 refs., 11 figs. (Author)

  5. Structural and chemical characterization of complex nanomaterials at atomic resolution

    Science.gov (United States)

    Sanchez, Sergio I.

    Catalytic and energetic nanomaterials are analyzed chemically and structurally in atomistic detail. Examination of the prototypical industrial catalyst Pt catalysts supported on gamma-Al2O3 using X-ray absorption spectroscopy (XAS) and scanning transmission electron microscopy (STEM) revealed non-bulk-like behavior. Anomalous, temperature-dependent structural dynamics were characterized in the form of negative thermal expansion (NTE) and abnormal levels of disorder. To examine a less complex system, electrocatalytically-active, core-shell nanostructures assembled from Pt and Pd were synthesized and subsequently examined using spherical aberration-corrected STEM (Cs-STEM) and high-energy X-ray diffraction (XRD). Atomically resolved micrographs provide significant insight into the differences in crystallinity and metal-atom bonding between Pt and Pd. The apparent structural dichotomy between Pt and Pd was extended to studying the differences in nanostructure between other third row fcc transition metals (3M -- Ir, Pt, and Au) and their second row counterparts (2M -- Rh, Pd, and Ag). With the use of Cs-STEM and atomic pair distribution function (PDF) measurements it was determined that the Au, Pt and Ir nanocrystals were more crystalline than their Ag, Pd and Rh analogues and that the 3M series was capable of imparting its crystal structure onto the atoms from the 2M series. Lastly, we looked at highly-reactive Al crystals and their successive passivation by secondary transition metals (Cu, Ni, Ag, Pd, Au and Pt). Rather than affording a uniform, monolayer coverage, C s-STEM, XRD and energy dispersive X-ray spectroscopy revealed unalloyed, particulate deposits of the secondary metal on the Al.

  6. Atomic structure calculations of Mo XV-XL

    International Nuclear Information System (INIS)

    Kubo, Hirotaka; Sugie, Tatsuo; Shiho, Makoto; Suzuki, Yasuo; Ishii, Keishi; Maeda, Hikosuke.

    1986-06-01

    Energy levels and oscillator strengths were calculated for Mo XV - Mo XL. The computer program for atomic structure calculation, developed by Dr. Robert D. Cowan, Los Alamos National Laboratory, was used in the present work. The scaled energy parameters were empirically determined from the observed spectral data. We present wavelengths and transition probabilities of Mo XV-XL. Energy levels and spectral patterns are presented in figures that are useful for the identification of spectral lines. (author)

  7. Green's functions of one-dimensional quasicrystal bi-material with piezoelectric effect

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Liangliang [College of Engineering, China Agricultural University, Beijing 100083 (China); Sinomatech Wind Power Blade Co., Ltd, Beijing 100092 (China); Wu, Di [College of Engineering, China Agricultural University, Beijing 100083 (China); Xu, Wenshuai [College of Science, China Agricultural University, Beijing 100083 (China); Yang, Lianzhi [Civil and Environmental Engineering School, University of Science and Technology Beijing, Beijing 100083 (China); Ricoeur, Andreas; Wang, Zhibin [Institute of Mechanics, University of Kassel, 34125 Kassel (Germany); Gao, Yang, E-mail: gaoyangg@gmail.com [College of Science, China Agricultural University, Beijing 100083 (China)

    2016-09-16

    Based on the Stroh formalism of one-dimensional quasicrystals with piezoelectric effect, the problems of an infinite plane composed of two different quasicrystal half-planes are taken into account. The solutions of the internal and interfacial Green's functions of quasicrystal bi-material are obtained. Moreover, numerical examples are analyzed for a quasicrystal bi-material subjected to line forces or line dislocations, showing the contour maps of the coupled fields. The impacts of changing material constants on the coupled field components are investigated. - Highlights: • Green's functions of 1D piezoelectric quasicrystal bi-material are studied. • The coupled fields subjected to line forces or line dislocations are obtained. • Mechanical behavior under the effect of different material constants is researched.

  8. Efficient evaluation of atom tunneling combined with electronic structure calculations.

    Science.gov (United States)

    Ásgeirsson, Vilhjálmur; Arnaldsson, Andri; Jónsson, Hannes

    2018-03-14

    Methodology for finding optimal tunneling paths and evaluating tunneling rates for atomic rearrangements is described. First, an optimal JWKB tunneling path for a system with fixed energy is obtained using a line integral extension of the nudged elastic band method. Then, a calculation of the dynamics along the path is used to determine the temperature at which it corresponds to an optimal Feynman path for thermally activated tunneling (instanton) and a harmonic approximation is used to estimate the transition rate. The method is illustrated with calculations for a modified two-dimensional Müller-Brown surface but is efficient enough to be used in combination with electronic structure calculations of the energy and atomic forces in systems containing many atoms. An example is presented where tunneling is the dominant mechanism well above room temperature as an H 3 BNH 3 molecule dissociates to form H 2 . Also, a solid-state example is presented where density functional theory calculations of H atom tunneling in a Ta crystal give close agreement with experimental measurements on hydrogen diffusion over a wide range in temperature.

  9. Efficient evaluation of atom tunneling combined with electronic structure calculations

    Science.gov (United States)

    Ásgeirsson, Vilhjálmur; Arnaldsson, Andri; Jónsson, Hannes

    2018-03-01

    Methodology for finding optimal tunneling paths and evaluating tunneling rates for atomic rearrangements is described. First, an optimal JWKB tunneling path for a system with fixed energy is obtained using a line integral extension of the nudged elastic band method. Then, a calculation of the dynamics along the path is used to determine the temperature at which it corresponds to an optimal Feynman path for thermally activated tunneling (instanton) and a harmonic approximation is used to estimate the transition rate. The method is illustrated with calculations for a modified two-dimensional Müller-Brown surface but is efficient enough to be used in combination with electronic structure calculations of the energy and atomic forces in systems containing many atoms. An example is presented where tunneling is the dominant mechanism well above room temperature as an H3BNH3 molecule dissociates to form H2. Also, a solid-state example is presented where density functional theory calculations of H atom tunneling in a Ta crystal give close agreement with experimental measurements on hydrogen diffusion over a wide range in temperature.

  10. Atomic and electronic structures of novel silicon surface structures

    Energy Technology Data Exchange (ETDEWEB)

    Terry, J.H. Jr.

    1997-03-01

    The modification of silicon surfaces is presently of great interest to the semiconductor device community. Three distinct areas are the subject of inquiry: first, modification of the silicon electronic structure; second, passivation of the silicon surface; and third, functionalization of the silicon surface. It is believed that surface modification of these types will lead to useful electronic devices by pairing these modified surfaces with traditional silicon device technology. Therefore, silicon wafers with modified electronic structure (light-emitting porous silicon), passivated surfaces (H-Si(111), Cl-Si(111), Alkyl-Si(111)), and functionalized surfaces (Alkyl-Si(111)) have been studied in order to determine the fundamental properties of surface geometry and electronic structure using synchrotron radiation-based techniques.

  11. On atom-bond connectivity molecule structure descriptors

    Directory of Open Access Journals (Sweden)

    Furtula Boris

    2016-01-01

    Full Text Available The atom-bond connectivity index (ABC is a degree-based molecular structure descriptor with well-documented chemical applications. In 2010 a distance-based new variant of this index (ABCGG has been proposed. Until now, the relation between ABC and ABCGG has not been analyzed. In this paper, we establish the basic characteristics of this relation. In particular, ABC and ABCGG are not correlated and both cases ABC > ABCGG and ABC < ABCGG may occur in the case of (structurally similar molecules. However, in the case of benzenoid hydrocarbons, ABC always exceeds ABCGG. [Projekat Ministarstva nauke Republike Srbije, br. 174033

  12. Self-generation of dissipative solitons in magnonic quasicrystal active ring resonator

    Energy Technology Data Exchange (ETDEWEB)

    Grishin, S. V., E-mail: grishfam@sgu.ru; Beginin, E. N.; Morozova, M. A.; Sharaevskii, Yu. P. [Laboratory “Metamaterials,” Saratov State University, Saratov 410012 (Russian Federation); Nikitov, S. A. [Laboratory “Metamaterials,” Saratov State University, Saratov 410012 (Russian Federation); Kotel' nikov Institute of Radioengineering and Electronics, Russian Academy of Science, Moscow 125009 (Russian Federation)

    2014-02-07

    Self-generation of dissipative solitons in the magnonic quasicrystal (MQC) active ring resonator is studied theoretically and experimentally. The developed magnonic crystal has quasiperiodic Fibonacci type structure. Frequency selectivity of the MQC together with the parametric three-wave decay of magnetostatic surface spin wave (MSSW) leads to the dissipative soliton self-generation. The transfer matrix method is used to describe MQC transmission responses. Besides, the model of MQC active ring resonator is suggested. The model includes three coupled differential equations describing the parametric decay of MSSW and two differential equations of linear oscillators describing the frequency selectivity of MQC. Numerical simulation results of dissipative soliton self-generation are in a fair agreement with experimental data.

  13. Atomic structure of graphene supported heterogeneous model catalysts

    Energy Technology Data Exchange (ETDEWEB)

    Franz, Dirk

    2017-04-15

    Graphene on Ir(111) forms a moire structure with well defined nucleation centres. Therefore it can be utilized to create hexagonal metal cluster lattices with outstanding structural quality. At diffraction experiments these 2D surface lattices cause a coherent superposition of the moire cell structure factor, so that the measured signal intensity scales with the square of coherently scattering unit cells. This artificial signal enhancement enables the opportunity for X-ray diffraction to determine the atomic structure of small nano-objects, which are hardly accessible with any experimental technique. The uniform environment of every metal cluster makes the described metal cluster lattices on graphene/Ir(111) an attractive model system for the investigation of catalytic, magnetic and quantum size properties of ultra-small nano-objects. In this context the use of x-rays provides a maximum of flexibility concerning the possible sample environments (vacuum, selected gases, liquids, sample temperature) and allows in-situ/operando measurements. In the framework of the present thesis the structure of different metal clusters grown by physical vapor deposition in an UHV environment and after gas exposure have been investigated. On the one hand the obtained results will explore many aspects of the atomic structure of these small metal clusters and on the other hand the presented results will proof the capabilities of the described technique (SXRD on cluster lattices). For iridium, platinum, iridium/palladium and platinum/rhodium the growth on graphene/Ir(111) of epitaxial, crystalline clusters with an ordered hexagonal lattice arrangement has been confirmed using SXRD. The clusters nucleate at the hcp sites of the moire cell and bind via rehybridization of the carbon atoms (sp{sup 2} → sp{sup 3}) to the Ir(111) substrate. This causes small displacements of the substrate atoms, which is revealed by the diffraction experiments. All metal clusters exhibit a fcc structure

  14. Atomic Structure of Au−Pd Bimetallic Alloyed Nanoparticles

    KAUST Repository

    Ding, Yong

    2010-09-08

    Using a two-step seed-mediated growth method, we synthesized bimetallic nanoparticles (NPs) having a gold octahedron core and a palladium epitaxial shell with controlled Pd-shell thickness. The mismatch-release mechanism between the Au core and Pd shell of the NPs was systematically investigated by high-resolution transmission electron microscopy. In the NPs coated with a single atomic layer of Pd, the strain between the surface Pd layer and the Au core is released by Shockley partial dislocations (SPDs) accompanied by the formation of stacking faults. For NPs coated with more Pd (>2 nm), the stacking faults still exist, but no SPDs are found. This may be due to the diffusion of Au atoms into the Pd shell layers to eliminate the SPDs. At the same time, a long-range ordered L11 AuPd alloy phase has been identified in the interface area, supporting the assumption of the diffusion of Au into Pd to release the interface mismatch. With increasing numbers of Pd shell layers, the shape of the Au-Pd NP changes, step by step, from truncated-octahedral to cubic. After the bimetallic NPs were annealed at 523 K for 10 min, the SPDs at the surface of the NPs coated with a single atomic layer of Pd disappeared due to diffusion of the Au atoms into the surface layer, while the stacking faults and the L11 Au-Pd alloyed structure remained. When the annealing temperature was increased to 800 K, electron diffraction patterns and diffraction contrast images revealed that the NPs became a uniform Au-Pd alloy, and most of the stacking faults disappeared as a result of the annealing. Even so, some clues still support the existence of the L11 phase, which suggests that the L11 phase is a stable, long-range ordered structure in Au-Pd bimetallic NPs. © 2010 American Chemical Society.

  15. In situ transmission electron microscopy investigation of quasicrystal-crystal transformations in Mg–Zn–Y alloys

    Energy Technology Data Exchange (ETDEWEB)

    Liu, J.F.; Yang, Z.Q., E-mail: yangzq34@yahoo.com; Ye, H.Q.

    2015-02-05

    Highlights: • Quasicrystal-to-crystal transformation sequence in Mg–Zn–Y alloys was determined. • H phase Zn{sub 3}MgY and W phase Zn{sub 3}Mg{sub 3}Y{sub 2} nucleated on icosahedral quasicrystal Zn{sub 6}Mg{sub 3}Y. • Growth of both H and W phase is controlled by diffusion. • The close relationship between building units plays a key role in the transformation. - Abstract: Evolution of icosahedral quasicrystals (IQC) in Mg–Zn–Y alloys during annealing was investigated by in situ transmission electron microscopy (TEM), in combination with differential thermal analysis and X-ray diffraction. In bulk samples, the IQC phase transformed to face-centered cubic phase W and hexagonal phase H at 720 K and 727 K, respectively. In TEM samples, IQC started to transform to W at 673 K and H at 688 K during heating, and H transformed to W at 623 K on cooling. Quantitative analysis of the in situ transformation process reveals that growth of both H and W is controlled by diffusion, agreeing with the Avrami’s model. The transformed products have specific orientation relationships with the parent phases: 3-fold{sub IQC}//[0 0 0 1]{sub H}//[1 1 1]{sub W} and 2-fold{sub IQC}//112{sup ¯}0]{sub H}//[01{sup ¯}1]{sub W}. The specific orientation relationships are attributed to close structural correlation among icosahedron, distorted icosahedron and cuboctahedron in IQC, H and W phases. The close structure relationship among IQC, H and W phases on the unit-cell level plays an important role in the phase transformations.

  16. Third sound in one and two dimensional modulated structures

    International Nuclear Information System (INIS)

    Komuro, T.; Kawashima, H., Shirahama, K.; Kono, K.

    1996-01-01

    An experimental technique is developed to study acoustic transmission in one and two dimensional modulated structures by employing third sound of a superfluid helium film. In particular, the Penrose lattice, which is a two dimensional quasiperiodic structure, is studied. In two dimensions, the scattering of third sound is weaker than in one dimension. Nevertheless, the authors find that the transmission spectrum in the Penrose lattice, which is a two dimensional prototype of the quasicrystal, is observable if the helium film thickness is chosen around 5 atomic layers. The transmission spectra in the Penrose lattice are explained in terms of dynamical theory of diffraction

  17. Structure formation in atom lithography using geometric collimation

    NARCIS (Netherlands)

    Meijer, T.; Beardmore, J.P.; Fabrie, C.G.C.H.M.; van Lieshout, J.P.; Notermans, R.P.M.J.W.; Sang, R.T.; Vredenbregt, E.J.D.; Van Leeuwen, K.A.H.

    2011-01-01

    Atom lithography uses standing wave light fields as arrays of lenses to focus neutral atom beams into line patterns on a substrate. Laser cooled atom beams are commonly used, but an atom beam source with a small opening placed at a large distance from a substrate creates atom beams which are locally

  18. Variable temperature investigation of the atomic structure of gold nanoparticles

    International Nuclear Information System (INIS)

    Young, N P; Kirkland, A I; Huis, M A van; Zandbergen, H W; Xu, H

    2010-01-01

    The characterisation of nanoparticle structures is the first step towards understanding and optimising their utility in important technological applications such as catalysis. Using newly developed in-situ transmission electron microscopy (TEM) specimen holders, the temperature dependent atomic structure of gold nanoparticles in the size range 5-12 nm has been investigated. In this size interval, the decahedral morphology has been identified as the most favourable structure at or above room temperature, while particle surface roughening becomes evident above 600 0 C. An icosahedral transition has also been identified at low temperature in particles under 9 nm in diameter. These experimental results are consistent with recently published temperature dependent equilibrium phase maps for gold nanoparticles.

  19. Ordering of carbon atoms in boron carbide structure

    Energy Technology Data Exchange (ETDEWEB)

    Ponomarev, V. I., E-mail: i2212@yandex.ru; Kovalev, I. D.; Konovalikhin, S. V.; Vershinnikov, V. I. [Russian Academy of Sciences, Institute of Structural Macrokinetics and Materials Science (Russian Federation)

    2013-05-15

    Boron carbide crystals have been obtained in the entire compositional range according to the phase diagram by self-propagating high-temperature synthesis (SHS). Based on the results of X-ray diffraction investigations, the samples were characterized by the unit-cell metric and reflection half-width in the entire range of carbon concentrations. A significant spread in the boron carbide unit-cell parameters for the same carbon content is found in the data in the literature; this spread contradicts the structural concepts for covalent compounds. The SHS samples have not revealed any significant spread in the unit-cell parameters. Structural analysis suggests that the spread of parameters in the literary data is related to the unique process of ordering of carbon atoms in the boron carbide structure.

  20. Atomic structures of icosahedral phases of type F and dislocations

    International Nuclear Information System (INIS)

    Beauchesne, Jean-Tristan

    2008-01-01

    The object of this thesis is the study of atomic structures of icosahedral phases of type F and their dislocations. In this study, we have first built a prototypical structure that describes the already known F type icosahedral phases. In order to check it we synthesized some of the new compositions predicted by this model. This synthesis led to the discovery of two new quasi-periodical phases of the stoichiometry Al66,08Cu21,35Mn8,29Fe4,28. One of these phases is icosahedral (metastable) of type F and the other one is decagonal (stable). A F-IQC phase is present on these compounds that have a different composition with respect to the ones already studied for the system (Al,Pd,Fe). Globally, these experimental results on new icosahedral phases allowed to prove the viability of the model: on the three samples of new composition, two of them have shown the existence of icosahedral phases of type F and the third one has given a decagonal phase, in relation of canonical orientation with the icosahedral metastable phase (10-fold axis parallel with 5-fold axis). Using this reliable model, we have been able to introduce dislocations. We could thus provide the geometry of dislocations (outside the dislocation core) at atomic scale for F-IQC phases. On this structure we have also identified the distributions of phasons and given some elements of answer for the global dislocations moves. (author) [fr

  1. Muonic radioactive atoms a unique probe for nuclear structure

    CERN Document Server

    Nilsson, Thomas; Kolbe, E; Langanke, K; Martínez-Pinedo, G; Riisager, Karsten

    2004-01-01

    Muonic atoms have been a source of high-precision experimental nuclear structure data for decades, through muonic X-rays that yield information on nuclear charge distributions. The intense driver beams for production of radioactive beams in so-called second generation facilities will simultaneously be capable of producing unprecedented amounts of low-energy muons. This paper concerns some of the potential synergies of combining muons with radioactive nuclei as one possible new tool to be used at future RIB facilities. As a case study, muonic capture rates into highly excited states in /sup 78/Ni have been calculated.

  2. Generalized dynamics of soft-matter quasicrystals mathematical models and solutions

    CERN Document Server

    Fan, Tian-You

    2017-01-01

    The book systematically introduces the mathematical models and solutions of generalized hydrodynamics of soft-matter quasicrystals (SMQ). It provides methods for solving the initial-boundary value problems in these systems. The solutions obtained demonstrate the distribution, deformation and motion of the soft-matter quasicrystals, and determine the stress, velocity and displacement fields. The interactions between phonons, phasons and fluid phonons are discussed in some fundamental materials samples. Mathematical solutions for solid and soft-matter quasicrystals are compared, to help readers to better understand the featured properties of SMQ.

  3. Atomic structure of amorphous shear bands in boron carbide.

    Science.gov (United States)

    Reddy, K Madhav; Liu, P; Hirata, A; Fujita, T; Chen, M W

    2013-01-01

    Amorphous shear bands are the main deformation and failure mode of super-hard boron carbide subjected to shock loading and high pressures at room temperature. Nevertheless, the formation mechanisms of the amorphous shear bands remain a long-standing scientific curiosity mainly because of the lack of experimental structure information of the disordered shear bands, comprising light elements of carbon and boron only. Here we report the atomic structure of the amorphous shear bands in boron carbide characterized by state-of-the-art aberration-corrected transmission electron microscopy. Distorted icosahedra, displaced from the crystalline matrix, were observed in nano-sized amorphous bands that produce dislocation-like local shear strains. These experimental results provide direct experimental evidence that the formation of amorphous shear bands in boron carbide results from the disassembly of the icosahedra, driven by shear stresses.

  4. NMR and NQR study of the thermodynamically stable quasicrystals

    Energy Technology Data Exchange (ETDEWEB)

    Shastri, Ananda [Iowa State Univ., Ames, IA (United States)

    1995-02-10

    27Al and 61,65Cu NMR measurements are reported for powder samples of stable AlCuFe and AlCuRu icosahedral quasicrystals and their crystalline approximants, and for a AlPdMn single grain quasicrystal. Furthermore, 27Al NQR spectra at 4.2 K have been observed in the AlCuFe and AlCuRu samples. From the quadrupole perturbed NMR spectra at different magnetic fields, and from the zero field NQR spectra, a wide distribution of local electric field gradient (EFG) tensor components and principal axis system orientations was found at the Al site. A model EFG calculation based on a 1/1 AlCuFe approximant was successful in explaining the observed NQR spectra. It is concluded that the average local gradient is largely determined by the p-electron wave function at the Al site, while the width of the distribution is due to the lattice contribution to the EFG. Comparison of 63Cu NMR with 27Al NMR shows that the EFG distribution at the two sites is similar, but that the electronic contribution to the EFG is considerably smaller at the Cu site, in agreement with a more s-type wave function of the conduction electrons.

  5. Atomic structures - an investigation into the vortex theory of atoms in the light of twentieth century knowledge

    International Nuclear Information System (INIS)

    Newman, J.A.

    1981-01-01

    Atomic structures are considered using the basic assumption that the Universe is composed of a basic fluid and that the only feasible structure which is capable of continuous existence is the ethereal vortex, similar in general structure to the atmospheric vortex. An appraisal is made of this approach under the headings; introduction, the basic theory, particles and waves, internal structure of electrons, electronic orbits and crystallography, valency, electrical, spin and mass effects, nuclear structure, fundamental particles, and commentary and summary. (U.K.)

  6. Electronic Structure of Helium Atom in a Quantum Dot

    Science.gov (United States)

    Saha, Jayanta K.; Bhattacharyya, S.; Mukherjee, T. K.

    2016-03-01

    Bound and resonance states of helium atom have been investigated inside a quantum dot by using explicitly correlated Hylleraas type basis set within the framework of stabilization method. To be specific, precise energy eigenvalues of bound 1sns (1Se) (n = 1-6) states and the resonance parameters i.e. positions and widths of 1Se states due to 2sns (n = 2-5) and 2pnp (n = 2-5) configurations of confined helium below N = 2 ionization threshold of He+ have been estimated. The two-parameter (Depth and Width) finite oscillator potential is used to represent the confining potential due to the quantum dot. It has been explicitly demonstrated that the electronic structural properties become sensitive functions of the dot size. It is observed from the calculations of ionization potential that the stability of an impurity ion within a quantum dot may be manipulated by varying the confinement parameters. A possibility of controlling the autoionization lifetime of doubly excited states of two-electron ions by tuning the width of the quantum cavity is also discussed here. TKM Gratefully Acknowledges Financial Support under Grant No. 37(3)/14/27/2014-BRNS from the Department of Atomic Energy, BRNS, Government of India. SB Acknowledges Financial Support under Grant No. PSW-160/14-15(ERO) from University Grants Commission, Government of India

  7. Michael Faraday and the concept of atomic structure

    International Nuclear Information System (INIS)

    Pocock, R.F.

    1991-01-01

    Written to commemorate the bicentenary of Faraday's birth, this article surveys his influence on atomic theory during the 19th and early 20th centuries. It identifies which developments were derived from projects which he had started; it shows that his ideas and methods determined the direction of researches which he had not himself initiated. The account is in the form of a chronological narrative. This is based entirely on published sources, and the treatment is non-mathematical. In consequence it contains no new factual data. The presentation of Faraday's work in this particular context is, however, original. Although not covering studies of the nucleus - which were mostly later than the period considered -this article describes the origins of modern theories of atomic structure reasonably completely. It is a useful overview for engineers unfamiliar with details of the history of physics. In addition, it is a case-study of the persistence of scientific ideas in researches occupying a century or more. (author)

  8. Fracture analysis of one-dimensional hexagonal quasicrystals: Researches of a finite dimension rectangular plate by boundary collocation method

    Energy Technology Data Exchange (ETDEWEB)

    Jiaxing, Cheng; Dongfa, Sheng [Southwest Forestry University, Yunnan (China)

    2017-05-15

    As an important supplement and development to crystallography, the applications about quasicrystal materials have played a core role in many fields, such as manufacturing and the space industry. Due to the sensitivity of quasicrystals to defects, the research on the fracture problem of quasicrystals has attracted a great deal of attention. We present a boundary collocation method to research fracture problems for a finite dimension rectangular one-dimensional hexagonal quasicrystal plate. Because mode I and mode II problems for one- dimensional hexagonal quasicrystals are like that for the classical elastic materials, only the anti-plane problem is discussed in this paper. The correctness of the present numerical method is verified through a comparison of the present results and the existing results. And then, the size effects on stress field, stress intensity factor and energy release rate are discussed in detail. The obtained results can provide valuable references for the fracture behavior of quasicrystals.

  9. The atomic and electronic structure of amorphous silicon nitride

    CERN Document Server

    Alvarez, F

    2002-01-01

    Using a novel approach to the ab initio generation of random networks we constructed two nearly stoichiometric samples of amorphous silicon nitride with the same content x= 1.29. The two 64-atom periodically-continued cubic diamond-like cells contain 28 silicons and 36 nitrogens randomly substituted, and were amorphized with a 6 f s time step by heating them to just below their melting temperature with a Harris-functional based, molecular dynamics code in the LDA approximation. The averaged total radial distribution function (RDF) obtained is compared with some existing Tersoff-like potential simulations and with experiment; ours agree with experiment. All the partial radial features are calculated and the composition of the second peak also agrees with experiment. The electronic structure is calculated and the optical gaps obtained using both a HOMO-LUMO approach and the Tauc-like procedure developed recently that gives reasonable gaps. (Author)

  10. Atomic and electronic structure of surfaces theoretical foundations

    CERN Document Server

    Lannoo, Michel

    1991-01-01

    Surfaces and interfaces play an increasingly important role in today's solid state devices. In this book the reader is introduced, in a didactic manner, to the essential theoretical aspects of the atomic and electronic structure of surfaces and interfaces. The book does not pretend to give a complete overview of contemporary problems and methods. Instead, the authors strive to provide simple but qualitatively useful arguments that apply to a wide variety of cases. The emphasis of the book is on semiconductor surfaces and interfaces but it also includes a thorough treatment of transition metals, a general discussion of phonon dispersion curves, and examples of large computational calculations. The exercises accompanying every chapter will be of great benefit to the student.

  11. Superplastic behavior in Mg-Zn-Y alloy with dispersed quasicrystal phase particles

    Energy Technology Data Exchange (ETDEWEB)

    Somekawa, Hidetoshi; Singh, Alok; Mukai, Toshiji [Structural Metals Center, National Institute for Materials Science, Tsukuba, Ibaraki (Japan)

    2009-10-15

    An Mg-Zn-Y alloy with a dispersion of quasicrystal phase particles showed low-temperature superplastic behavior, and the dominant deformation process was grain boundary sliding. Observations of the deformed microstructure showed that the quasicrystal phase particles were an obstacle to dislocation movements; the kinetics of the superplastic behavior were lower than those of a conventional magnesium alloy. This alloy also demonstrated a high possibility for secondary forming - i.e., superplastic forging. (Abstract Copyright [2009], Wiley Periodicals, Inc.)

  12. Depth sectioning combined with atom-counting in HAADF STEM to retrieve the 3D atomic structure

    Energy Technology Data Exchange (ETDEWEB)

    Alania, M.; Altantzis, T.; De Backer, A.; Lobato, I.; Bals, S.; Van Aert, S., E-mail: sandra.vanaert@uantwerpen.be

    2017-06-15

    Aberration correction in scanning transmission electron microscopy (STEM) has greatly improved the lateral and depth resolution. When using depth sectioning, a technique during which a series of images is recorded at different defocus values, single impurity atoms can be visualised in three dimensions. In this paper, we investigate new possibilities emerging when combining depth sectioning and precise atom-counting in order to reconstruct nanosized particles in three dimensions. Although the depth resolution does not allow one to precisely locate each atom within an atomic column, it will be shown that the depth location of an atomic column as a whole can be measured precisely. In this manner, the morphology of a nanoparticle can be reconstructed in three dimensions. This will be demonstrated using simulations and experimental data of a gold nanorod. - Highlights: • Depth sectioning in HAADF STEM is combined with atom-counting. • This can be used to retrieve the 3D atomic structure. • The theoretical precision with atoms can be located is investigated. • An algorithm is introduced to reconstruct the morphology of a nanoparticle. • The method is applied to reconstruct a gold nanorod.

  13. Iron phosphate glasses: Bulk properties and atomic scale structure

    Energy Technology Data Exchange (ETDEWEB)

    Joseph, Kitheri; Stennett, Martin C.; Hyatt, Neil C.; Asuvathraman, R.; Dube, Charu L.; Gandy, Amy S.; Govindan Kutty, K. V.; Jolley, Kenny; Vasudeva Rao, P. R.; Smith, Roger

    2017-10-01

    Bulk properties such as glass transition temperature, density and thermal expansion of iron phosphate glass compositions, with replacement of Cs by Ba, are investigated as a surrogate for the transmutation of 137Cs to 137Ba, relevant to the immobilisation of Cs in glass. These studies are required to establish the appropriate incorporation rate of 137Cs in iron phosphate glass. Density and glass transition temperature increases with the addition of BaO indicating the shrinkage and reticulation of the iron phosphate glass network. The average thermal expansion coefficient reduces from 19.8 × 10-6 K-1 to 13.4 × 10-6 K-1, when 25 wt. % of Cs2O was replaced by 25 wt. % of BaO in caesium loaded iron phosphate glass. In addition to the above bulk properties, the role of Ba as a network modifier in the structure of iron phosphate glass is examined using various spectroscopic techniques. The FeII content and average coordination number of iron in the glass network was estimated using Mössbauer spectroscopy. The FeII content in the un-doped iron phosphate glass and barium doped iron phosphate glasses was 20, 21 and 22 ± 1% respectively and the average Fe coordination varied from 5.3 ± 0.2 to 5.7 ± 0.2 with increasing Ba content. The atomic scale structure was further probed by Fe K-edge X-ray absorption spectroscopy. The average coordination number provided by extended X-ray absorption fine structure spectroscopy and X-ray absorption near edge structure was in good agreement with that given by the Mössbauer data.

  14. Crystal structures and atomic model of NADPH oxidase.

    Science.gov (United States)

    Magnani, Francesca; Nenci, Simone; Millana Fananas, Elisa; Ceccon, Marta; Romero, Elvira; Fraaije, Marco W; Mattevi, Andrea

    2017-06-27

    NADPH oxidases (NOXs) are the only enzymes exclusively dedicated to reactive oxygen species (ROS) generation. Dysregulation of these polytopic membrane proteins impacts the redox signaling cascades that control cell proliferation and death. We describe the atomic crystal structures of the catalytic flavin adenine dinucleotide (FAD)- and heme-binding domains of Cylindrospermum stagnale NOX5. The two domains form the core subunit that is common to all seven members of the NOX family. The domain structures were then docked in silico to provide a generic model for the NOX family. A linear arrangement of cofactors (NADPH, FAD, and two membrane-embedded heme moieties) injects electrons from the intracellular side across the membrane to a specific oxygen-binding cavity on the extracytoplasmic side. The overall spatial organization of critical interactions is revealed between the intracellular loops on the transmembrane domain and the NADPH-oxidizing dehydrogenase domain. In particular, the C terminus functions as a toggle switch, which affects access of the NADPH substrate to the enzyme. The essence of this mechanistic model is that the regulatory cues conformationally gate NADPH-binding, implicitly providing a handle for activating/deactivating the very first step in the redox chain. Such insight provides a framework to the discovery of much needed drugs that selectively target the distinct members of the NOX family and interfere with ROS signaling.

  15. Rotational Spectrum and Carbon Atom Structure of Dihydroartemisinic Acid

    Science.gov (United States)

    Evangelisti, Luca; Seifert, Nathan A.; Spada, Lorenzo; Pate, Brooks

    2016-06-01

    Dihydroartemisinic acid (DHAA, C15H24O2, five chiral centers) is a precursor in proposed low-cost synthetic routes to the antimalarial drug artemisinin. In one reaction process being considered in pharmaceutical production, DHAA is formed from an enantiopure sample of artemisinic acid through hydrogenation of the alkene. This reaction needs to properly set the stereochemistry of the asymmetric carbon for the synthesis to produce artemisinin. A recrystallization process can purify the diastereomer mixture of the hydrogenation reaction if the unwanted epimer is produced in less than 10% abundance. There is a need in the process analytical chemistry to rapidly (less than 1 min) measure the diastereomer excess and current solutions, such a HPLC, lack the needed measurement speed. The rotational spectrum of DHAA has been measured at 300:1 signal-to-noise ratio in a chirped-pulsed Fourier transform microwave spectrometer operating from 2-8 GHz using simple heating of the compound. The 13C isotope analysis provides a carbon atom structure that confirms the diastereomer. This structure is in excellent agreement with quantum chemistry calculations at the B2PLYPD3/ 6-311++G** level of theory. The DHAA spectrum is expected to be fully resolved from the unwanted diastereomer raising the potential for fast diastereomer excess measurement by rotational spectroscopy in the pharmaceutical production process.

  16. Less singular quasicrystals: The case of low codimensions

    Science.gov (United States)

    Jagannathan, A.

    2001-10-01

    We consider a set of tilings proposed recently as d-dimensional generalizations of the Fibonacci chain, by Vidal and Mosseri. These tilings have a particularly simple theoretical description, making them appealing candidates for analytical solutions for electronic properties. Given their self-similar geometry, one could expect that the tight-binding spectra of these tilings might possess the characteristically singular features of well-known quasiperiodic systems such as the Penrose or the octagonal tilings. We show here, by a numerical study of statistical properties of the tight-binding spectra that these tilings fall rather in an intermediate category between the crystal and the quasicrystal, i.e., in a class of almost integrable models. This is certainly a consequence of the low codimension of the tilings.

  17. Frustration and thermalization in an artificial magnetic quasicrystal

    Science.gov (United States)

    Shi, Dong; Budrikis, Zoe; Stein, Aaron; Morley, Sophie A.; Olmsted, Peter D.; Burnell, Gavin; Marrows, Christopher H.

    2017-12-01

    Artificial frustrated systems offer a playground to study the emergent properties of interacting systems. Most work to date has been on spatially periodic systems, known as artificial spin ices when the interacting elements are magnetic. Here we have studied artificial magnetic quasicrystals based on quasiperiodic Penrose tiling patterns of interacting nanomagnets. We construct a low-energy configuration from a step-by-step approach that we propose as a ground state. Topologically induced emergent frustration means that this configuration cannot be constructed from vertices in their ground states. It has two parts, a quasi-one-dimensional `skeleton' that spans the entire pattern and is capable of long-range order, surrounding `flippable' clusters of macrospins that lead to macroscopic degeneracy. Magnetic force microscopy imaging of Penrose tiling arrays revealed superdomains that are larger for more strongly coupled arrays, especially after annealing the array above its blocking temperature.

  18. Influence of initial microstructure of aluminium alloy charge after its melting on the hard metal inherited structure

    Directory of Open Access Journals (Sweden)

    Г. О. Іванов

    2016-07-01

    Full Text Available Metal properties heredity in the chain- initial hard state > liquid state > final solidified state has always been interesting for metallurgists. It is known that after the primary melting of charge there occurs microheterogenеous non-equilibrium melt with crystal-like groups of atoms and disordered area in it. With increase in temperature the melt approaches the equilibrium microhomogeneous state. The aim of this work is to study the charge microstructure influence on melt fluidity in the light of quasi-crystal model of liquid structure. Influence of isothermal heating on fluidity of aluminium melt, smelted from fine-grained and coarse-grained charge has been investigated. It has been stated that for coarse-grained metal additional melting of crystallization «genes» takes place in 1,4-quick time, as compared to fine-grained. The coefficients of exponential function for our experimental data have been calculated. It has been stated that the exponent depends on the charge microstructure, and multiplier depends on the soaking temperature. On the basis of A. Einstein equation for the calculation of liquid viscosity from the known fraction of admixtures and clean liquid viscosity an analogical equation for fluidity and calculation of quasi-crystals volume share in the melt have been derived. It has been found that the charge grain size affects the speed of quasi-crystals additional melting in the melt. The reference amount of quasi-crystals at the initial moment of large- and fine-grained charge melting has been calculated from our metallographic, experimental and estimated data

  19. Atomic structure of As2S3-Ag chalcogenide glasses

    Science.gov (United States)

    Kaban, I.; Jóvári, P.; Wagner, T.; Frumar, M.; Stehlik, S.; Bartos, M.; Hoyer, W.; Beuneu, B.; Webb, M. A.

    2009-09-01

    (As0.4S0.6)100-xAgx glasses (x = 0, 4, 8, 12 at.%) have been studied with high-energy x-ray diffraction, neutron diffraction and extended x-ray absorption spectroscopy at As and Ag K-edges. The experimental data were modelled simultaneously with the reverse Monte Carlo simulation method. Analysis of the partial pair correlation functions and coordination numbers extracted from the model atomic configurations revealed that silver preferentially bonds to sulfur in the As2S3-Ag ternary glasses, which results in the formation of homoatomic As-As bonds. Upon the addition of Ag, a small proportion of Ag-As bonds (NAgAs≈0.3) are formed in all three ternary compositions, while the direct Ag-Ag bonds (NAgAg≈ 0.4) appear only in the glass with the highest Ag content (12 at.%). Similar to the g- As2S3 binary, the mean coordination number of arsenic is close to three, and that of sulfur is close to two, in the As2S3-Ag ternary glasses. The first sharp diffraction peak on the total structure factors of As2S3 binary and (As0.4S0.6)100-xAgx ternary glasses is related to the As-As and As-S correlations.

  20. Atomic structure of intracellular amorphous calcium phosphate deposits.

    Science.gov (United States)

    Betts, F; Blumenthal, N C; Posner, A S; Becker, G L; Lehninger, A L

    1975-06-01

    The radial distribution function calculated from x-ray diffraction of mineralized cytoplasmic structures isolated from the hepatopancreas of the blue crab (Callinectes sapidus) is very similar to that previously found for synthetic amorphous calcium phosphate. Both types of mineral apparently have only short-range atomic order, represented as a neutral ion cluster of about 10 A in longest dimension, whose probable composition is expressed by the formula Ca9(PO4)6. The minor differences observed are attributed to the presence in the biological mineral of significant amounts of Mg-2+ and ATP. Synthetic amorphous calcium phosphate in contact with a solution containing an amount of ATP equivalent to that of the biological mineral failed to undergo conversion to the thermodynamically more stable hydroxyapatite. The amorphous calcium phosphate of the cytoplasmic mineral granules is similarly stable, and does not undergo conversion to hydroxyapatite, presumably owing to the presence of ATP and Mg-2+, known in inhibitors of the conversion process. The physiological implications of mineral deposits consisting of stabilized calcium phosphate ion clusters are discussed.

  1. A new program for calculating matrix elements in atomic structure

    International Nuclear Information System (INIS)

    The solution of many problems concerning the electronic structure of atoms requires the evaluation of the matrix elements of the Hamiltonian operator, including the electrostatic interaction. These matrix elements may be expressed as weighted sums of radial integrals. The program we describe in this paper evaluates the coefficients of the Slater integrals and, if these are given, computes all the matrix elements for a given set of configurations. This program has nearly the same purposes as Hibbert's program and is also based on the Racach techniques. The main difference between this algorithm and the cited one is the method used to calculate the recoupling coefficients. While Hibbert's programs use Burke's algorithm to calculate these coefficients, in our program they are computed using the graphical techniques developed by Jucys et al. According to this method, that we describe in another paper the formulae needed to calculate the recoupling coefficients are previously derived and simplified (as a first step of the program). The use of this method may considerably reduce the running time, specially in the case of large configuration interaction matrices. (orig.)

  2. Direct nuclear reactions and the structure of atomic nuclei

    International Nuclear Information System (INIS)

    Osterfeld, F.

    1985-01-01

    The present thesis deals with two different aspects of direct nuclear reactions, namely on the one hand with the microscopic calculation of the imaginary optical potential for the elastic nucleon-nucleus scattering as well as on the other hand with the microscopic analysis of giant magnetic resonances in atomic nuclei which are excited by (p,n) charge-exchange reactions. In the first part of the thesis the imaginary part of the optical potential for the elastic proton- and neutron-nucleus scattering is microscopically calculated in the framework of the so called nuclear-structure approximation to the optical potential. The calculations are performed in the Feshbach formalism in second-order perturbation theory corresponding to an effective projectile-target-nucleon interaction. In the second part of this thesis in the framework of microscopic nuclear models a complete analysis of different A(p,n)B charge-exchange reactions at high incident energies 160 MeV 90 Zr(p,n) reaction three collective spin-isospin resonances could be uniquely identified. (orig./HSI) [de

  3. Atomic structure calculations using the relativistic random phase approximation

    International Nuclear Information System (INIS)

    Cheng, K.T.; Johnson, W.R.

    1981-01-01

    A brief review is given for the relativistic random phase approximation (RRPA) applied to atomic transition problems. Selected examples of RRPA calculations on discrete excitations and photoionization are given to illustrate the need of relativistic many-body theories in dealing with atomic processes where both relativity and correlation are important

  4. Ab initio calculations and modelling of atomic cluster structure

    DEFF Research Database (Denmark)

    Solov'yov, Ilia; Lyalin, Andrey G.; Solov'yov, Andrey V.

    2004-01-01

    framework for modelling the fusion process of noble gas clusters is presented. We report the striking correspondence of the peaks in the experimentally measured abundance mass spectra with the peaks in the size-dependence of the second derivative of the binding energy per atom calculated for the chain...... of the noble gas clusters up to 150 atoms....

  5. The cytotoxicity of organobismuth compounds with certain molecular structures can be diminished by replacing the bismuth atom with an antimony atom in the molecules.

    Science.gov (United States)

    Kohri, Kumiko; Yoshida, Eiko; Yasuike, Shuji; Fujie, Tomoya; Yamamoto, Chika; Kaji, Toshiyuki

    2015-06-01

    Organic-inorganic hybrid molecules, which are composed of an organic structure and metal(s), are indispensable for synthetic chemical reactions; however, their toxicity has been incompletely understood. In the present study, we discovered two cytotoxic organobismuth compounds whose cytotoxicity diminished upon replacement of the intramolecular bismuth atom with an antimony atom. The intracellular accumulation of the organobismuth compounds was much higher than that of the organoantimony compounds with the corresponding organic structures. We also showed that both the organic structure and bismuth atom are required for certain organobismuth compounds to exert their cytotoxic effect, suggesting that the cytotoxicity of such a compound is a result of an interaction between the organic structure and the bismuth atom. The present data suggest that organobismuth compounds with certain molecular structures exhibit cytotoxicity via an interaction between the molecular structure and the bismuth atom, and this cytotoxicity can be diminished by replacing the bismuth atom with an antimony atom, resulting in lower intracellular accumulation.

  6. Atomic structure and surface defects at mineral-water interfaces probed by in situ atomic force microscopy

    NARCIS (Netherlands)

    Sîretanu, Igor; van den Ende, Henricus T.M.; Mugele, Friedrich Gunther

    2016-01-01

    Atomic scale details of surface structure play a crucial role for solid–liquid interfaces. While macroscopic characterization techniques provide averaged information about bulk and interfaces, high resolution real space imaging reveals unique insights into the role of defects that are believed to

  7. Atomic structure of machined semiconducting chips: An x-ray absorption spectroscopy study

    Energy Technology Data Exchange (ETDEWEB)

    Paesler, M.; Sayers, D.

    1988-12-01

    X-ray absorption spectroscopy (XAS) has been used to examine the atomic structure of chips of germanium that were produced by single point diamond machining. It is demonstrated that although the local (nearest neighbor) atomic structure is experimentally quite similar to that of single crystal specimens information from more distant atoms indicates the presence of considerable stress. An outline of the technique is given and the strength of XAS in studying the machining process is demonstrated.

  8. Local Structures of High-Entropy Alloys (HEAs) on Atomic Scales: An Overview

    Science.gov (United States)

    Diao, Haoyan; Santodonato, Louis J.; Tang, Zhi; Egami, Takeshi; Liaw, Peter K.

    2015-08-01

    The high-entropy alloys, containing several elements mixed in equimolar or near-equimolar ratios, have shown exceptional engineering properties. Local structures on the atomic level are essential to understand the mechanical behaviors and related mechanisms. In this article, the local structure and stress on the atomic level are reviewed by the pair-distribution function of neutron-diffraction data, ab-initio molecular dynamics simulations, and the atomic probe microscopy.

  9. Atomic spectral-product representations of molecular electronic structure: metric matrices and atomic-product composition of molecular eigenfunctions.

    Science.gov (United States)

    Ben-Nun, M; Mills, J D; Hinde, R J; Winstead, C L; Boatz, J A; Gallup, G A; Langhoff, P W

    2009-07-02

    Recent progress is reported in development of ab initio computational methods for the electronic structures of molecules employing the many-electron eigenstates of constituent atoms in spectral-product forms. The approach provides a universal atomic-product description of the electronic structure of matter as an alternative to more commonly employed valence-bond- or molecular-orbital-based representations. The Hamiltonian matrix in this representation is seen to comprise a sum over atomic energies and a pairwise sum over Coulombic interaction terms that depend only on the separations of the individual atomic pairs. Overall electron antisymmetry can be enforced by unitary transformation when appropriate, rather than as a possibly encumbering or unnecessary global constraint. The matrix representative of the antisymmetrizer in the spectral-product basis, which is equivalent to the metric matrix of the corresponding explicitly antisymmetric basis, provides the required transformation to antisymmetric or linearly independent states after Hamiltonian evaluation. Particular attention is focused in the present report on properties of the metric matrix and on the atomic-product compositions of molecular eigenstates as described in the spectral-product representations. Illustrative calculations are reported for simple but prototypically important diatomic (H(2), CH) and triatomic (H(3), CH(2)) molecules employing algorithms and computer codes devised recently for this purpose. This particular implementation of the approach combines Slater-orbital-based one- and two-electron integral evaluations, valence-bond constructions of standard tableau functions and matrices, and transformations to atomic eigenstate-product representations. The calculated metric matrices and corresponding potential energy surfaces obtained in this way elucidate a number of aspects of the spectral-product development, including the nature of closure in the representation, the general redundancy or

  10. Polarization-gradient laser cooling as a way to create strongly localized structures for atom lithography

    International Nuclear Information System (INIS)

    Prudnikov, O. N.; Taichenachev, A. V.; Tumaikin, A. M.; Yudin, V. I.

    2007-01-01

    Generally, conditions for deep sub-Doppler laser cooling do not match conditions for strong atomic localization, that takes place in a deeper optical potential and leads to higher temperature. Moreover, for a given detuning in a deep optical potential the secular approximation, which is frequently used for a quantum description of laser cooling, fails. Here we investigate the atomic localization in optical potential, using a full quantum approach for atomic density matrix beyond the secular approximation. It is shown that laser cooling in a deep optical potential, created by a light field with polarization gradients, can be used as an alternative method for the formation of high contrast spatially localized structures of atoms for the purposes of atom lithography and atomic nanofabrication. Finally, we analyze possible limits for the width and contrast of localized atomic structures that can be reached in this type of light mask

  11. Formation and structural phase transition in Co atomic chains on a Cu(775) surface

    International Nuclear Information System (INIS)

    Syromyatnikov, A. G.; Kabanov, N. S.; Saletsky, A. M.; Klavsyuk, A. L.

    2017-01-01

    The formation of Co atomic chains on a Cu(775) surface is investigated by the kinetic Monte Carlo method. It is found that the length of Co atomic chains formed as a result of self-organization during epitaxial growth is a random quantity and its mean value depends on the parameters of the experiment. The existence of two structural phases in atomic chains is detected using the density functional theory. In the first phase, the separations between an atom and its two nearest neighbors in a chain are 0.230 and 0.280 nm. In the second phase, an atomic chain has identical atomic spacings of 0.255 nm. It is shown that the temperature of the structural phase transition depends on the length of the atomic chain.

  12. Gyration-radius dynamics in structural transitions of atomic clusters

    Science.gov (United States)

    Yanao, Tomohiro; Koon, Wang S.; Marsden, Jerrold E.; Kevrekidis, Ioannis G.

    2007-03-01

    This paper is concerned with the structural transition dynamics of the six-atom Morse cluster with zero total angular momentum, which serves as an illustrative example of the general reaction dynamics of isolated polyatomic molecules. It develops a methodology that highlights the interplay between the effects of the potential energy topography and those of the intrinsic geometry of the molecular internal space. The method focuses on the dynamics of three coarse variables, the molecular gyration radii. By using the framework of geometric mechanics and hyperspherical coordinates, the internal motions of a molecule are described in terms of these three gyration radii and hyperangular modes. The gyration radii serve as slow collective variables, while the remaining hyperangular modes serve as rapidly oscillating "bath" modes. Internal equations of motion reveal that the gyration radii are subject to two different kinds of forces: One is the ordinary force that originates from the potential energy function of the system, while the other is an internal centrifugal force. The latter originates from the dynamical coupling of the gyration radii with the hyperangular modes. The effects of these two forces often counteract each other: The potential force generally works to keep the internal mass distribution of the system compact and symmetric, while the internal centrifugal force works to inflate and elongate it. Averaged fields of these two forces are calculated numerically along a reaction path for the structural transition of the molecule in the three-dimensional space of gyration radii. By integrating the sum of these two force fields along the reaction path, an effective energy curve is deduced, which quantifies the gross work necessary for the system to change its mass distribution along the reaction path. This effective energy curve elucidates the energy-dependent switching of the structural preference between symmetric and asymmetric conformations. The present

  13. Bloch oscillations of ultracold atoms and measurement of the fine structure constant; Oscillations de Bloch d'atomes ultrafroids et mesure de la constante de structure fine

    Energy Technology Data Exchange (ETDEWEB)

    Clade, P

    2005-10-15

    From a measurement of the recoil velocity of an atom absorbing a photon, it is possible to deduce a determination of the ratio h/m between the Planck constant and the mass of the atoms and then to deduce a value of the fine structure constant alpha. To do this measurement, we use the technique of Bloch oscillations, which allows us to transfer a large number of recoils to atoms. A velocity sensor, based on velocity selective Raman transition, enables us to measure the momentum transferred to the atoms. A measurement with a statistical uncertainty of 4.4 10{sup -9}, in conjunction with a careful study of systematic effects (5 10{sup -9}), has led us to a determination of alpha with an uncertainty of 6.7 10{sup -9}: {alpha}{sup -1}(Rb) = 137.03599878 (91). This uncertainty is similar to the uncertainty of the best determinations of alpha based on atom interferometry. (author)

  14. Intracluster atomic and electronic structural heterogeneities in supported nanoscale metal catalysts

    NARCIS (Netherlands)

    Elsen, A.; Jung, U.; Vila, F.; Li, Y.; Safonova, O.V.; Thomas, R.; Tromp, M.; Rehr, J.J.; Nuzzo, R.G.; Frenkel, A.I.

    2015-01-01

    This work reveals and quantifies the inherent intracluster heterogeneity in the atomic structure and charge distribution present in supported metal catalysts. The results demonstrate that these distributions are pronounced and strongly coupled to both structural and dynamic perturbations. They also

  15. Structure of the electron momentum density of atomic systems

    Energy Technology Data Exchange (ETDEWEB)

    Romera, E.; Dehesa, J.S. [Granada Univ. (Spain). Dept. de Fisica Moderna; Koga, T. [Department of Applied Chemistry, Muroran Institute of Technology, Muroran, Hokkaido 050 (Japan)

    1997-12-01

    The present paper addresses the controversial problem on the nonmonotonic behavior of the spherically-averaged momentum density {gamma}(p) observed previously for some ground-state atoms based on the Roothaan-Hartree-Fock (RHF) wave functions of Clementi and Roetti. Highly accurate RHF wave functions of Koga et al. are used to study the existence of extrema in the momentum density {gamma}(p) of all the neutral atoms from hydrogen to xenon. Three groups of atoms are clearly identified according to the nonmonotonicity parameter {mu}, whose value is either equal to, larger, or smaller than unity. Additionally, it is found that the function p{sup -{alpha}} {gamma}(p) is (i) monotonically decreasing from the origin for {alpha}{>=}0.75, (ii) convex for {alpha}{>=}1.35, and (iii) logarithmically convex for {alpha}{>=}3.64 for all the neutral atoms with nuclear charges Z = 1-54. Finally, these monotonicity properties are applied to derive simple yet general inequalities which involve three momentum moments left angle p{sup t} right angle. These inequalities not only generalize similar inequalities reported so far but also allow us to correlate some fundamental atomic quantities, such as the electron-electron repulsion energy and the peak height of Compton profile, in a simple manner. (orig.) 40 refs.

  16. Elastic limit at macroscopic deformation of icosahedral Al-Pd-Mn single quasicrystals

    International Nuclear Information System (INIS)

    Ledig, L.; Bartsch, M.; Messerschmidt, U.

    2006-01-01

    Al 70.5 Pd 21 Mn 8.5 single quasicrystals were plastically deformed between 482 and 821 deg. C. The strain rate sensitivity of the flow stress was measured by stress relaxation tests. At several temperatures, the dislocation structures were imaged by diffraction contrast in a high-voltage electron microscope for determining the dislocation densities. At all temperatures, the plastic deformation starts with a range of very high work-hardening. The transition point between almost elastic and elastic-plastic deformation is called the elastic limit. At low temperatures, the deformation was stopped at about 1.5 GPa to prevent fracture. Above about 580 deg. C, the stress-strain curves bend down and show a yield point effect followed by a range of almost steady state deformation. At low temperatures, the elastic limit is much lower than the steady state flow stress or the maximum stresses reached without fracture. The activation parameters are different for the elastic limit, the range of high work-hardening and steady state deformation. The flow stresses are interpreted by the stress necessary to move individual dislocations and the athermal component due to the elastic interaction between dislocations. At low temperatures, a further component is necessary to explain the very high flow stresses reached by work-hardening

  17. Growth and decay of a two-dimensional oxide quasicrystal: High-temperature in situ microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Foerster, Stefan [Physik-Institut, Universitaet Zuerich (Switzerland); Institute of Physics, Martin-Luther-Universitaet Halle-Wittenberg, Halle (Germany); Flege, Jan Ingo; Falta, Jens [Institute of Solid State Physics, University of Bremen (Germany); MAPEX Center for Materials and Processes, University of Bremen (Germany); Zollner, Eva Maria; Schumann, Florian Otto; Hammer, Rene; Bayat, Alireza; Schindler, Karl-Michael [Institute of Physics, Martin-Luther-Universitaet Halle-Wittenberg, Halle (Germany); Widdra, Wolf [Institute of Physics, Martin-Luther-Universitaet Halle-Wittenberg, Halle (Germany); Max-Planck-Institut fuer Mikrostrukturphysik, Halle (Germany)

    2017-01-15

    The recently discovered two-dimensional oxide quasicrystal (OQC) derived from BaTiO{sub 3} on Pt(111) is the first material in which a spontaneous formation of an aperiodic structure at the interface to a periodic support has been observed. Herein, we report in situ low-energy electron microscopy (LEEM) studies on the fundamental processes involved in the OQC growth. The OQC formation proceeds in two steps via of an amorphous two-dimensional wetting layer. At 1170 K the long-range aperiodic order of the OQC develops. Annealing in O{sub 2} induces the reverse process, the conversion of the OQC into BaTiO{sub 3} islands and bare Pt(111), which has been monitored by in situ LEEM. A quantitative analysis of the temporal decay of the OQC shows that oxygen adsorption on bare Pt patches is the rate limiting step of this dewetting process. (copyright 2016 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  18. Electrical and Magnetic Properties of Quasicrystal Approximants RCd6 (R: Rare Earth)

    Science.gov (United States)

    Mori, Akinobu; Ota, Hisashi; Yoshiuchi, Shingo; Iwakawa, Ken; Taga, Yuki; Hirose, Yusuke; Takeuchi, Tetsuya; Yamamoto, Etsuji; Haga, Yoshinori; Honda, Fuminori; Settai, Rikio; Ōnuki, Yoshichika

    2012-02-01

    We measured the electrical resistivity, magnetic susceptibility, magnetization, and specific heat of the quasicrystal approximants RCd6 (R: rare earth, Y--Lu) with a body-centered cubic (bcc) crystal structure. Single crystals were grown by the Cd-self flux method and annealing method. We confirmed that the structural order--disorder transition is realized at about 160 K when the lattice constant a is larger than 15.481 Å in YCd6, namely, for R = Pr, Nd, Sm, Gd, Tb, Dy, and Yb. At lower temperatures, RCd6 compounds, except non-4f reference compounds YCd6 and LuCd6, and a divalent compound YbCd6, are found to order antiferromagnetically. We clarified that the structural order--disorder transition has a great influence on the magnetic ordering and transport properties. The Néel temperature of RCd6 (R: Nd, Sm, Tb, and Dy) with the structural order--disorder transition is appreciably higher than the de Gennes scaling normalized by the Néel temperature of GdCd6, while the the Néel temperature of RCd6 (R: Ho, Er, and Tm) without the structural transition approximately follows the de Gennes scaling. Moreover, the electrical resistivity of RCd6 with the structural transition decreases monotonically below the Néel temperature, while it increases below the Néel temperature and a large residual resistivity remains at low temperatures in RCd6 without the structural transition. The contribution of an Einstein oscillator to the phonon specific heat is also discussed in YCd6 and LuCd6.

  19. Electronic and atomic disorder in icosahedral AlPdRe

    International Nuclear Information System (INIS)

    Rapp, Oe; Karkin, A A; Goshchitskii, B N; Voronin, V I; Srinivas, V; Poon, S J

    2008-01-01

    Relations between electronic and atomic disorder of i-AlPdRe have been investigated by studies of neutron irradiated and annealed samples. The advantage with this technique is that a single sample can be monitored over a significant range of varying electronic properties, without concern for any influence of varying impurities. X-ray diffraction, the electrical resistivity and its temperature dependence, and the magnetoresistance are studied. The results show that annealings of an irradiated sample lead to improvement of the atomic order, as reflected in increased intensities of the x-ray diffraction peaks, while electronic properties change in the direction of increasing electronic disorder towards a metal-insulator transition. The observed relation in quasicrystals that improved atomic structure is associated with stronger anomalies in transport properties is thus also seen in i-AlPdRe. In particular, the variation of the diffusion constant in the region of small values of the resistivity is found to be similar for annealed polygrain samples and for single grain samples with varying Pd concentration, as evaluated from literature data, indicating a similar development of electronic disorder in both sets of samples. However, the problem remains as to why the resistivity is small in single grain samples which are atomically well-ordered. The possibility of a strong sensitivity to concentration differences is pointed out

  20. Structure and transport properties of atomic chains and molecules

    DEFF Research Database (Denmark)

    Strange, Mikkel

    2008-01-01

    of atomically thin, suspended chains containing silver and oxygen atoms in an alternating sequence has been studied. The conductances of the chains exhibit weak even-odd oscillations around an anomalously low value of 0.1G0 (G0 = 2e2/h) in agreement with experiments [1] in the long chain limit. These unusual...... conductance properties are explained in terms of a resonating-chain model, which takes the reflection probability and phase-shift of a single bulk-chain interface as the only input. The stability of silver-oxygen chains was studied with a thermodynamic model. This model has been developed in this work...... to describe tip-suspended atomically thin chains between macroscopic size electrodes. It has been tested with the use of DFT calculations on metal chains for which good agreement with experiments was obtained. To ensure the correctness of the DFT based transport calculations presented here, and in more...

  1. Femtosecond structural dynamics on the atomic length scale

    International Nuclear Information System (INIS)

    Zhang, Dongfang

    2014-03-01

    This thesis reports on the development and application of two different but complementary ultrafast electron diffraction setups built at the Max Planck Research Department for Structural Dynamics. One is an ultra-compact femtosecond electron diffraction (FED) setup (Egun300), which is currently operational (with a maximum electron energy of 150 keV) and provides ultrashort (∝300 fs) and bright (∝10 e/μm 2 ) electron bunches. The other one, named as Relativistic Electron Gun for Atomic Exploration (REGAE) is a radio frequency driven 2 to 5 MeV FED setup built in collaboration with different groups from DESY. REGAE was developed as a facility that will provide high quality diffraction with sufficient coherence to even address structural protein dynamics and with electron pulses as short as 20 fs (FWHM). As one of the first students in Prof. R.J. Dwayne Miller's group, I led the femtosecond (fs) laser sub-group at REGAE being responsible for the construction of different key optical elements required to drive both of aforementioned FED systems. A third harmonic generation (THG) and a nonlinear optical parametric amplifier (NOPA) have been used for the photo-generation of ultrashort electron bursts as well as sample laser excitation. Different diagnostic tools have been constructed to monitor the performance of the fs optical system. A fast autocorrelator was developed to provide on the fly pulse duration correction. A transient-grating frequency-resolved optical gating (TG-FROG) was built to obtain detail information about the characteristics of fs optical pulse, i.e. phase and amplitude of its spectral components. In addition to these optical setups, I developed a fs optical pump-probe system, which supports broadband probe pulses. This setup was successfully applied to investigate the semiconductor-to-metal photoinduced phase transition in VO 2 and the ultrafast photo-reduction mechanism of graphene oxide. In regard to FED setups, I have been deeply involved in

  2. Femtosecond structural dynamics on the atomic length scale

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Dongfang

    2014-03-15

    This thesis reports on the development and application of two different but complementary ultrafast electron diffraction setups built at the Max Planck Research Department for Structural Dynamics. One is an ultra-compact femtosecond electron diffraction (FED) setup (Egun300), which is currently operational (with a maximum electron energy of 150 keV) and provides ultrashort (∝300 fs) and bright (∝10 e/μm{sup 2}) electron bunches. The other one, named as Relativistic Electron Gun for Atomic Exploration (REGAE) is a radio frequency driven 2 to 5 MeV FED setup built in collaboration with different groups from DESY. REGAE was developed as a facility that will provide high quality diffraction with sufficient coherence to even address structural protein dynamics and with electron pulses as short as 20 fs (FWHM). As one of the first students in Prof. R.J. Dwayne Miller's group, I led the femtosecond (fs) laser sub-group at REGAE being responsible for the construction of different key optical elements required to drive both of aforementioned FED systems. A third harmonic generation (THG) and a nonlinear optical parametric amplifier (NOPA) have been used for the photo-generation of ultrashort electron bursts as well as sample laser excitation. Different diagnostic tools have been constructed to monitor the performance of the fs optical system. A fast autocorrelator was developed to provide on the fly pulse duration correction. A transient-grating frequency-resolved optical gating (TG-FROG) was built to obtain detail information about the characteristics of fs optical pulse, i.e. phase and amplitude of its spectral components. In addition to these optical setups, I developed a fs optical pump-probe system, which supports broadband probe pulses. This setup was successfully applied to investigate the semiconductor-to-metal photoinduced phase transition in VO{sub 2} and the ultrafast photo-reduction mechanism of graphene oxide. In regard to FED setups, I have been

  3. Tamm-plasmon polaritons in one-dimensional photonic quasi-crystals.

    Science.gov (United States)

    Shukla, Mukesh Kumar; Das, Ritwick

    2018-02-01

    We present an investigation to ascertain the existence of Tamm-plasmon-polariton-like modes in one-dimensional (1D) quasi-periodic photonic systems. Photonic bandgap formation in quasi-crystals is essentially a consequence of long-range periodicity exhibited by multilayers and, thus, it can be explained using the dispersion relation in the Brillouin zone. Defining a "Zak"-like topological phase in 1D quasi-crystals, we propose a recipe to ascertain the existence of Tamm-like photonic surface modes in a metal-terminated quasi-crystal lattice. Additionally, we also explore the conditions of efficient excitation of such surface modes along with their dispersion characteristics.

  4. Anti-plane problem analysis for icosahedral quasicrystals under shear loadings

    Science.gov (United States)

    Li, Wu; Chai, Yu-Zhen

    2014-11-01

    The present paper is concerned with the longitudinal shear elasticity of three-dimensional icosahedral quasicrystals. By virtue of the Dugdale hypothesis along with the method of complex potential theory, it involves two defect problems of the icosahedral quasicrystals. The first one is the calculation of stress intensity factors and the size of the cohesive force zone in a half-infinite crack. Meanwhile, the crack tip tearing displacements can be exactly derived. The other is the demonstration of the generalized stress intensity factors induced by a sharp V-notch as an extension of a crack. The generalized E-integral around the notch tip gives the energy release rate when the V-notch degenerates into a crack. Apart from their own usefulness in carrying out some simplified crack analyses, the results obtained in this work can particularly serve as a basis for fracture mechanics of anti-plane defect problems of icosahedral quasicrystals.

  5. A Hartree-Fock program for atomic structure calculations

    International Nuclear Information System (INIS)

    Mitroy, J.

    1999-01-01

    The Hartree-Fock equations for a general open shell atom are described. The matrix equations that result when the single particle orbitals are written in terms of a linear combination of analytic basis functions are derived. Attention is paid to the complexities that occur when open shells are present. The specifics of a working FORTRAN program which is available for public use are described. The program has the flexibility to handle either Slater-type orbitals or Gaussian-type orbitals. It can be obtained over the internet at http://lacebark.ntu.edu.au/j_mitroy/research/atomic.htm Copyright (1999) CSIRO Australia

  6. The Atom in a Molecule: Implications for Molecular Structure and Properties

    Science.gov (United States)

    2016-05-23

    Briefing Charts 3. DATES COVERED (From - To) 01 February 2016 – 23 May 2016 4. TITLE AND SUBTITLE The atom in a molecule: Implications for molecular...For presentation at American Physical Society - Division of Atomic , Molecular, and Optical Physics (May 2016) PA Case Number: #16075; Clearance Date...10 Energy (eV) R C--H (au) R C--H(au) The Atom in a Molecule: Implications for Molecular Structures and Properties P. W. Langhoff, Chemistry

  7. Atomic-level structure and structure-property relationship in metallic glass

    Science.gov (United States)

    Cheng, Yongqiang

    One of the key tasks in material science is to understand the structure and structure-property relationship. The recently emerging bulk metallic glasses (BMGs) have demonstrated unique properties, especially intriguing mechanical properties such as their high strength and high propensity to localize deformation in shear bands. However, a comprehensive understanding of the structure of BMGs has been hindered by the complexity of these amorphous materials. Even more challenging is the structure-property correlation, which has been well established in crystals but has been seriously lacking for BMGs. This thesis presents a systematic study of the atomic-level structures of two representative BMGs, Cu-Zr and Cu-Zr-Al. The interpenetrating Cu-centered icosahedral clusters have been identified to be the primary structural feature. The fraction of icosahedra increases with increasing Cu or Al contents, and with decreasing cooling rate. The effect of Al in improving the icosahedral order is two-fold: the geometric effect due to the atomic-size mismatch and the chemical effect originated from the Cu-Al bond shortening. The resolved structure is used to study the structure-property relationship. The full icosahedra are found to be responsible for the dynamical slowdown of the supercooled liquid, which underlies the non-Arrhenius behavior, and explains the composition dependence of glass transition temperature, glass forming ability, and the room temperature strength. By simulated deformation, the initiation of plasticity and tendency for strain localization are also investigated. The full icosahedra are found to be the most rigid and resistant cluster with solid-like character, while the unstable clusters with liquid-like character serve as the fertile sites for initiating shear transformations. In addition, the elastic moduli are calculated and analyzed, and the origins of the different configurational dependence of shear modulus (G) and bulk modulus ( B) are explained. The

  8. Thermal stability of Al-Cu-Fe quasicrystals prepared by SHS method

    Directory of Open Access Journals (Sweden)

    Pavel Novak

    2013-02-01

    Full Text Available Quasicrystal-containing materials are usually prepared by rapid solidification of the melt (e.g. by melt spinning or mechanical alloying. In this work, the method using exothermic reactions between compressed metallic powders called SHS (Self-propagating High-temperature Synthesis was tested. The microstructure and phase composition of the product was described in dependence on cooling regime from the reaction temperature. Thermal stability of prepared Al-Cu-Fe quasicrystals was studied by annealing at the temperatures of 300 and 500 °C.

  9. THERMAL STABILITY OF Al-Cu-Fe QUASICRYSTALS PREPARED BY SHS METHOD

    Directory of Open Access Journals (Sweden)

    Pavel Novák

    2013-04-01

    Full Text Available Quasicrystal-containing materials are usually prepared by rapid solidification of the melt (e.g. by melt spinning or mechanical alloying. In this work, the method using exothermic reactions between compressed metallic powders called SHS (Self-propagating High-temperature Synthesis was tested. The microstructure and phase composition of the product was described in dependence on cooling regime from the reaction temperature. Thermal stability of prepared Al-Cu-Fe quasicrystals was studied by annealing at the temperatures of 300 and 500 °C.

  10. Identifying Atomic Structure as a Threshold Concept: Student Mental Models and Troublesomeness

    Science.gov (United States)

    Park, Eun Jung; Light, Gregory

    2009-01-01

    Atomic theory or the nature of matter is a principal concept in science and science education. This has, however, been complicated by the difficulty students have in learning the concept and the subsequent construction of many alternative models. To understand better the conceptual barriers to learning atomic structure, this study explores the…

  11. Electronic and atomic structures of liquid tellurium containing alkali elements

    International Nuclear Information System (INIS)

    Kawakita, Yukinobu; Yao, Makoto; Endo, Hirohisa.

    1997-01-01

    The measurements of electrical conductivity σ, density, EXAFS and neutron scattering were carried out for liquid K-Te and Rb-Te mixtures. The conductivity σ decreases rapidly with alkali concentration and a metal-semiconductor transition occurs at about 10 at.% alkali. It is found that the compositional variation of σ is nearly independent of the alkali species. The Te-Te bond length deduced from EXAFS and neutron scattering measurements is 2.8 A and changes little with alkali concentrations. The average distances from K and Rb atom to Te atoms are 3.6 A and 3.8 A, respectively. Two kinds of relaxation processes are observed in quasielastic neutron scattering for K 20 Te 80 . Upon the addition of alkali the interaction between the neighbouring Te chains, which is responsible for the metallic conduction, weaken considerably. (author)

  12. Local atomic structure in (Zr1-xUx)N

    International Nuclear Information System (INIS)

    Walter, M.; Somers, J.; Fernandez-Carretero, A.; Rothe, J.

    2008-01-01

    (Zr 1-x U x )N solid solutions were prepared for EXAFS measurements by a sol-gel route combined with infiltration and carbothermic reduction. The lattice parameter and the more distant coordination shells (Me 2 and Me 3 ) around the Zr and U atoms follow the Vegard law. In the first coordination shell, the U-N distance also follows the Vegard law. Though the Zr-N bond distance increases with the lattice expansion caused by increasing U content, it remains constant at 232-235 pm in U-rich (Zr 1-x U x )N (x > 0.6). The measurements indicate that U accommodates the lattice contraction with increasing Zr content, whereas Zr is able to expand its Zr-N bond only at lower U content. In the composition range of transmutation fuels, (Zr 1-x U x )N is homogeneous at the local atomic scale

  13. Construction of the energy matrix for complex atoms. Part VIII: Hyperfine structure HPC calculations for terbium atom

    Science.gov (United States)

    Elantkowska, Magdalena; Ruczkowski, Jarosław; Sikorski, Andrzej; Dembczyński, Jerzy

    2017-11-01

    A parametric analysis of the hyperfine structure (hfs) for the even parity configurations of atomic terbium (Tb I) is presented in this work. We introduce the complete set of 4fN-core states in our high-performance computing (HPC) calculations. For calculations of the huge hyperfine structure matrix, requiring approximately 5000 hours when run on a single CPU, we propose the methods utilizing a personal computer cluster or, alternatively a cluster of Microsoft Azure virtual machines (VM). These methods give a factor 12 performance boost, enabling the calculations to complete in an acceptable time.

  14. On the way to unveiling the atomic structure of superheavy elements

    Science.gov (United States)

    Laatiaoui, Mustapha

    2016-12-01

    Optical spectroscopy of the transfermium elements (atomic number Z > 100) is nowadays one of the most fascinating and simultaneously challenging tasks in atomic physics. On the one hand, key atomic and even nuclear ground-state properties may be obtained by studying the spectral lines of these heaviest elements. On the other hand, these elements have to be produced "online" by heavy-ion induced fusion-evaporation reactions yielding rates on the order of a few atoms per second at most, which renders their optical spectroscopy extremely difficult. Only recently, a first foray of laser spectroscopy into this heaviest element region was reported. Several atomic transitions in the element nobelium (Z = 102) were observed and characterized, using an ultra-sensitive and highly efficient resonance ionization technique. The findings confirm the predictions and additionally provide a benchmark for theoretical modelling. The work represents an important stepping stone towards experimental studies of the atomic structure of superheavy elements.

  15. On the way to unveiling the atomic structure of superheavy elements

    Directory of Open Access Journals (Sweden)

    Laatiaoui Mustapha

    2016-01-01

    Full Text Available Optical spectroscopy of the transfermium elements (atomic number Z > 100 is nowadays one of the most fascinating and simultaneously challenging tasks in atomic physics. On the one hand, key atomic and even nuclear ground-state properties may be obtained by studying the spectral lines of these heaviest elements. On the other hand, these elements have to be produced “online” by heavy-ion induced fusion-evaporation reactions yielding rates on the order of a few atoms per second at most, which renders their optical spectroscopy extremely difficult. Only recently, a first foray of laser spectroscopy into this heaviest element region was reported. Several atomic transitions in the element nobelium (Z = 102 were observed and characterized, using an ultra-sensitive and highly efficient resonance ionization technique. The findings confirm the predictions and additionally provide a benchmark for theoretical modelling. The work represents an important stepping stone towards experimental studies of the atomic structure of superheavy elements.

  16. Semiempirical Studies of Atomic Structure. Final Report for July 1, 2000 - June 30, 2003

    Energy Technology Data Exchange (ETDEWEB)

    Curtis, L. J.

    2004-05-01

    This project has developed a comprehensive and reliable base of accurate atomic structure data for complex many-electron systems. This has been achieved through the use of sensitive data-based parametric systematizations, precise experimental measurements, and supporting theoretical computations. The atomic properties studies involved primary data (wavelengths, frequency intervals, lifetimes, relative intensities, production rates, etc.) and derived structural parameters (energy levels, ionization potentials, line strengths, electric polarizabilities, branching fractions, excitation functions, etc).

  17. Computer Simulation of Atoms Nuclei Structure Using Information Coefficients of Proportionality

    OpenAIRE

    Labushev, Mikhail M.

    2012-01-01

    The latest research of the proportionality of atomic weights of chemical elements made it possible to obtain 3 x 3 matrices for the calculation of information coefficients of proportionality Ip that can be used for 3D modeling of the structure of atom nucleus. The results of computer simulation show high potential of nucleus structure research for the characterization of their chemical and physical properties.

  18. Atomic structure and vibrational properties of icosahedral B$_4$C boron carbide

    OpenAIRE

    Lazzari, R.; Vast, N.; Besson, J. M.; Baroni, S.; Corso, A. Dal

    1999-01-01

    The atomic structure of icosahedral B$_4$C boron carbide is determined by comparing existing infra-red absorption and Raman diffusion measurements with the predictions of accurate {\\it ab initio} lattice-dynamical calculations performed for different structural models. This allows us to unambiguously determine the location of the carbon atom within the boron icosahedron, a task presently beyond X-ray and neutron diffraction ability. By examining the inter- and intra-icosahedral contributions ...

  19. Structure and hydrogen storage properties of the hexagonal Laves phase Sc(Al1−xNix)2

    International Nuclear Information System (INIS)

    Sahlberg, Martin; Ångström, Jonas; Zlotea, Claudia; Beran, Premysl; Latroche, Michel; Pay Gómez, Cesar

    2012-01-01

    The crystal structures of hydrogenated and unhydrogenated Sc(Al 1−x Ni x ) 2 Laves phases have been studied by combining several diffraction techniques and it is shown that hydrogen is situated interstitially in the A 2 B 2 -sites, which have the maximum number of scandium neighbours. The hydrogen absorption/desorption behaviour has also been investigated. It is shown that a solid solution of hydrogen forms in the mother compound. The hydrogen storage capacity exceeds 1.7 H/f.u. at 374 K, and the activation energy of hydrogen desorption was determined to 4.6 kJ/mol H 2 . It is shown that these compounds share the same local coordination as Frank–Kasper-type approximants and quasicrystals, which opens up the possibility of finding many new hydride phases with these types of crystal structures. - Graphical abstract: The structure of ScNiAlDx, Sc atoms are shown in purple and Ni/Al atoms in blue and the iso-surfaces of deuterium in yellow. Revealed from refinements of neutron powder diffraction data. Highlights: ► The crystal structure of ScNiAl and ScNiAlDx is reported. ► We show the hydrogen storage properties of Sc(Al 1−x Ni x ) 2 . ► We discuss the possibility to store hydrogen in quasicrystals.

  20. Atomic Structure of Highly Strained BiFeO3 Thin Films

    Energy Technology Data Exchange (ETDEWEB)

    Rossell, M.D. [Lawrence Berkeley National Laboratory (LBNL); Erni, R. [Lawrence Berkeley National Laboratory (LBNL); Prange, Micah P [ORNL; Idrobo Tapia, Juan C [ORNL; Luo, Weidong [ORNL; Zeches, R J [University of California, Berkeley; Pantelides, Sokrates T [ORNL; Ramesh, R [Lawrence Berkeley National Laboratory (LBNL)

    2012-01-01

    We determine the atomic structure of the pseudotetragonal T phase and the pseudorhombohedral R phase in highly strained multiferroic BiFeO3 thin films by using a combination of atomic-resolution scanning transmission electron microscopy and electron energy-loss spectroscopy. The coordination of the Fe atoms and their displacement relative to the O and Bi positions are assessed by direct imaging. These observations allow us to interpret the electronic structure data derived from electron energy-loss spectroscopy and provide evidence for the giant spontaneous polarization in strained BiFeO3 thin films.

  1. Pushing the frontiers of atomic models for protein tertiary structure ...

    Indian Academy of Sciences (India)

    Abstract. Protein folding, considered to be the holy grail of molecular biology, remains intractable even after six decades since the report of the first crystal structure. Over 70,000 X-ray and NMR structures are now available in protein structural repositories and no physico-chemical solution is in sight. Molecular simulation.

  2. Atomic Resolution Imaging of Nanoscale Structural Ordering in a Complex Metal Oxide Catalyst

    KAUST Repository

    Zhu, Yihan

    2012-08-28

    The determination of the atomic structure of a functional material is crucial to understanding its "structure-to-property" relationship (e.g., the active sites in a catalyst), which is however challenging if the structure possesses complex inhomogeneities. Here, we report an atomic structure study of an important MoVTeO complex metal oxide catalyst that is potentially useful for the industrially relevant propane-based BP/SOHIO process. We combined aberration-corrected scanning transmission electron microscopy with synchrotron powder X-ray crystallography to explore the structure at both nanoscopic and macroscopic scales. At the nanoscopic scale, this material exhibits structural and compositional order within nanosized "domains", while the domains show disordered distribution at the macroscopic scale. We proposed that the intradomain compositional ordering and the interdomain electric dipolar interaction synergistically induce the displacement of Te atoms in the Mo-V-O channels, which determines the geometry of the multifunctional metal oxo-active sites.

  3. Effects of Al addition on atomic structure of Cu-Zr metallic glass

    Science.gov (United States)

    Li, Feng; Zhang, Huajian; Liu, Xiongjun; Dong, Yuecheng; Yu, Chunyan; Lu, Zhaoping

    2018-02-01

    The atomic structures of Cu52Zr48 and Cu45Zr48Al7 metallic glasses (MGs) have been studied by molecular dynamic simulations. The results reveal that the molar volume of the Cu45Zr48Al7 MG is smaller than that of the Cu52Zr48 MG, although the size of the Al atom is larger than that of the Cu atom, implying an enhanced atomic packing density achieved by introducing Al into the ternary MG. Bond shortening in unlike atomic pairs Zr-Al and Cu-Al is observed in the Cu45Zr48Al7 MG, which is attributed to strong interactions between Al and (Zr, Cu) atoms. Meanwhile, the atomic packing efficiency is enhanced by the minor addition of Al. Compared with the Cu52Zr48 binary MG, the potential energy of the ternary MG decreases and the glass transition temperature increases. Structural analyses indicate that more Cu- and Al-centered full icosahedral clusters emerge in the Cu45Zr48Al7 MG as some Cu atoms are substituted by Al. Furthermore, the addition of Al leads to more icosahedral medium-range orders in the ternary MG. The increase of full icosahedral clusters and the enhancement of the packing density are responsible for the improved glass-forming ability of Cu45Zr48Al7.

  4. Atomic structure of self-organizing iridium induced nanowires on Ge(001)

    Energy Technology Data Exchange (ETDEWEB)

    Kabanov, N.S., E-mail: n.kabanov@utwente.nl [Faculty of Physics, Moscow State University, 119991 (Russian Federation); Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P. O. Box 217, Enschede 7500 AE (Netherlands); Heimbuch, R.; Zandvliet, H.J.W. [Physics of Interfaces and Nanomaterials, MESA+ Institute for Nanotechnology, University of Twente, P. O. Box 217, Enschede 7500 AE (Netherlands); Saletsky, A.M.; Klavsyuk, A.L. [Faculty of Physics, Moscow State University, 119991 (Russian Federation)

    2017-05-15

    Highlights: • Ir/Ge(001) structure has been studied with DFT calculations and scanning tunneling microscopy. • Ir/Ge(001) nanowires are composed of Ge atoms and Ir atoms are located in subsurface positions. • The regions in the vicinity of the nanowires are very dynamic, even at temperatures as low as 77 K. - Abstract: The atomic structure of self-organizing iridium (Ir) induced nanowires on Ge(001) is studied by density functional theory (DFT) calculations and variable-temperature scanning tunneling microscopy. The Ir induced nanowires are aligned in a direction perpendicular to the Ge(001) substrate dimer rows, have a width of two atoms and are completely kink-less. Density functional theory calculations show that the Ir atoms prefer to dive into the Ge(001) substrate and push up the neighboring Ge substrate atoms. The nanowires are composed of Ge atoms and not Ir atoms as previously assumed. The regions in the vicinity of the nanowires are very dynamic, even at temperatures as low as 77 K. Time-resolved scanning tunneling microscopy measurements reveal that this dynamics is caused by buckled Ge substrate dimers that flip back and forth between their two buckled configurations.

  5. Atomic structure and dynamics properties of Cu50Zr50 films

    Science.gov (United States)

    Chen, Heng; Qu, Bingyan; Li, Dongdong; Zhou, Rulong; Zhang, Bo

    2018-01-01

    In this paper, the structural and dynamic properties of Cu50Zr50 films are investigated by molecular dynamics simulations. Our results show that the dynamics of the surface atoms are much faster than those of the bulk. Especially, the diffusion coefficient of the surface atoms is about forty times larger than that of the bulk at 600 K, which qualitatively agrees with the experimental results. Meanwhile, we find that the population of the icosahedral (-like) clusters in the surface region is obviously higher than that of the bulk, which prevents the surface from crystallization. A new method to determine the string-like collective atomic motion is introduced in the paper, and it suggests a possible connection between the glass formation ability and collective atomic motion. By using the method, the effects of surface on collective motion are illustrated. Our results show that the string-like collective atomic motion of surface atoms is weakened while that of the interior atoms is strengthened. The studies clearly explain the effects of surface on the structural and dynamic properties of Cu50Zr50 films from the atomic scale.

  6. Atomic structure governed diversity of exchange-driven spin helices in Fe nanoislands: Experiment and theory

    Science.gov (United States)

    Fischer, Jeison A.; Sandratskii, Leonid M.; Phark, Soo-hyon; Sander, Dirk; Parkin, Stuart

    2017-10-01

    We combine spin-polarized scanning tunneling microscopy (SP-STM) and first-principles calculations to demonstrate the control of the wavelength of helical spin textures in Fe nanoislands by varying their atomic structure. We make use of the complexity of submonolayer growth of Fe on Cu(111) to prepare nanoislands characterized by different thickness and in-plane atomic structure. SP-STM results reveal that the magnetic states of different nanoislands are spin helices. The wavelength of the spin helices varies strongly. Calculations performed for Fe films with different thickness and in-plane atomic structure explain the strong variation of the wavelength by a subtle balance in the competition between ferromagnetic and antiferromagnetic exchange interactions. We identify the crucial role of the effectively enhanced weak antiferromagnetic exchange interactions between distant atoms.

  7. Development of thermally-sprayed Al-Cu-Fe-Cr quasicrystal coating

    Science.gov (United States)

    Setiamarga, Budi Hartono

    A class of quasicrystal alloys that has drawn a lot of attention is aluminum based quasicrystal alloys because they are hard, light weight, wear resistant, and have a non-stick property. Quasicrystalline materials in the form of coatings produced by thermal spray techniques have been developed to utilize their properties. The goal of this research has been to develop the knowledge necessary to produce good thermally sprayed Al-Cu-Fe-Cr quasicrystal coatings. Boron has been found to improve ductility, reduce porosity and increase hardness when added to other thermally sprayed powders, therefore, as part of this research, quasicrystal coatings containing boron will also be produced and evaluated. The first phase of this research utilized a fine QC-1 quasicrystal powder of Alsb{70.5}Cusb{10.1}Fesb{8.8}Crsb{10.6}. The addition of boron was done using mechanical mixing. The addition of boron in fused QC-1 powders shows that boron can reduce porosity and increase hardness. Due to difficulties with thermal spraying the fine QC-1 powder and evaporation of aluminum, a coarser QC-2 powder with similar composition to QC-1 powder was produced. QC-2 and boron modified QC-2 coatings have similar hardness and levels of porosity, around 11%, although boron modified QC-2 coatings proved to be more wear resistant than plain QC-2 coatings. Both coatings demonstrated a weak coating-substrate interface bonding. Laser heat treatment was used to reduce the porosity and strengthen the coating-substrate interface bonding. Laser treatment of QC-2 quasicrystal coatings resulted in harder and lower porosity coatings with better coating-substrate interface bonding. Unfortunately, hot-cracks in the coatings were also produced. Hot-cracks are undesireable because they decrease the coating's corrosion resistance. Thermal spraying using High Velocity Oxygen Fuel (HVOF) technique was done. It was used on QC-2 powder and QC-3 powder of composition Alsb{68.6}Cusb{10.8}Fesb{8.9}Crsb{9.7}Bsb{2.0}. This

  8. Direct Determination of Atomic Structure and Magnetic Coupling of Magnetite Twin Boundaries.

    Science.gov (United States)

    Chen, Chunlin; Li, Hongping; Seki, Takehito; Yin, Deqiang; Sanchez-Santolino, Gabriel; Inoue, Kazutoshi; Shibata, Naoya; Ikuhara, Yuichi

    2018-03-27

    Clarifying how the atomic structure of interfaces/boundaries in materials affects the magnetic coupling nature across them is of significant academic value and will facilitate the development of state-of-the-art magnetic devices. Here, by combining atomic-resolution transmission electron microscopy, atomistic spin-polarized first-principles calculations, and differential phase contrast imaging, we conduct a systematic investigation of the atomic and electronic structures of individual Fe 3 O 4 twin boundaries (TBs) and determine their concomitant magnetic couplings. We demonstrate that the magnetic coupling across the Fe 3 O 4 TBs can be either antiferromagnetic or ferromagnetic, which directly depends on the TB atomic core structures and resultant electronic structures within a few atomic layers. Revealing the one-to-one correspondence between local atomic structures and magnetic properties of individual grain boundaries will shed light on in-depth understanding of many interesting magnetic behaviors of widely used polycrystalline magnetic materials, which will surely promote the development of advanced magnetic materials and devices.

  9. Energy losses at collisions of relativistic structural heavy ions with atoms

    International Nuclear Information System (INIS)

    Matveev, V.I.; Gusarevich, E.S.

    2001-01-01

    One elaborated nonperturbation theory of energy losses at collisions of structural highly-charged heavy ions moving with relativistic speed. Ions containing partially populated electron shells are taken to be structural ions. The elaborated theory considers ion as an extended structural particle which size is equal to that of electronic shells. Paper contains the results of calculations of the efficient breaking at collision of a relativistic highly-charged ions with hydrogen atom derived for three domains of collision parameter values corresponding to low, average and high parameters of collision. The derived results are generalized for the case of collisions of relativistic structural heavy ions with compound atoms [ru

  10. The role and structure of the Atomic Energy Control Board

    International Nuclear Information System (INIS)

    Hamel, P.E.

    1981-04-01

    The Atomic Energy Control Board is responsible for the control and supervision of the application and use of nuclear materials and the operation of nuclear facilities to ensure that the health and safety of people are protected and that the nuclear materials and equipment are used only in accordance with the government non-proliferation policy. Requirements for control and supervision are made into regulations subject to approval by the Governor in Council. They are applied through a comprehensive licensing system. The interpretation and implementation of the regulations are contained in a series of regulatory documents published from time to time by the Board. The functional organization of staff that assist the Board for the administration, the assessment and issuance of licenses, compliance and inspection, as well as for the management of the regulatory research program is described. (author) [fr

  11. Atomic structure of Fe thin-films on Cu(0 0 1) studied with stereoscopic photography

    International Nuclear Information System (INIS)

    Hattori, Azusa N.; Fujikado, M.; Uchida, T.; Okamoto, S.; Fukumoto, K.; Guo, F.Z.; Matsui, F.; Nakatani, K.; Matsushita, T.; Hattori, K.; Daimon, H.

    2004-01-01

    The complex magnetic properties of Fe films epitaxially grown on Cu(0 0 1) have been discussed in relation to their atomic structure. We have studied the Fe films on Cu(0 0 1) by a new direct method for three-dimensional (3D) atomic structure analysis, so-called 'stereoscopic photography'. The forward-focusing peaks in the photoelectron angular distribution pattern excited by the circularly polarized light rotate around the light axis in either clockwise or counterclockwise direction depending on the light helicity. By using a display-type spherical mirror analyzer for this phenomenon, we can obtain stereoscopic photographs of atomic structure. The photographs revealed that the iron structure changes from bcc to fcc and almost bcc structure with increasing iron film thickness

  12. Atomic structure of large angle grain boundaries determined by quantitative X-ray diffraction techniques

    International Nuclear Information System (INIS)

    Fitzsimmons, M.R.; Sass, S.L.

    1988-01-01

    Quantitative X-ray diffraction techniques have been used to determine the atomic structure of the Σ = 5 and 13 [001] twist boundaries in Au with a resolution of 0.09 Angstrom or better. The reciprocal lattices of these boundaries were mapped out using synchrotron radiation. The atomic structures were obtained by testing model structures against the intensity observations with a chi square analysis. The boundary structure were modeled using polyhedra, including octahedra, special configurations of tetrahedra and Archimedian anti-prisms, interwoven together by the boundary symmetry. The results of this work point to the possibility of obtaining general rules for grain boundary structure based on X-ray diffraction observations that give the atomic positions with high resolution

  13. Pre-service physics teachers' ideas on size, visibility and structure of the atom

    Energy Technology Data Exchange (ETDEWEB)

    Uenlue, Pervin, E-mail: pgunes@gazi.edu.t [Gazi University Education Faculty, K-314 06500 Ankara (Turkey)

    2010-07-15

    Understanding the atom gives the opportunity to both understand and conceptually unify the various domains of science, such as physics, chemistry, biology, astronomy and geology. Among these disciplines, physics teachers are expected to be particularly well educated in this topic. It is important that pre-service physics teachers know what sort of theories regarding the atom they will bring into their own classrooms. Six tasks were developed, comprising size, visibility and structure of the atom. These tasks carried out by pre-service physics teachers were examined by content analysis and six categories were determined. These are size, visibility, subatomic particles, atom models, electron orbit and electron features. Pre-service physics teachers' ideas about the atom were clarified under these categories.

  14. Bloch oscillations of ultracold atoms and measurement of the fine structure constant

    International Nuclear Information System (INIS)

    Clade, P.

    2005-10-01

    From a measurement of the recoil velocity of an atom absorbing a photon, it is possible to deduce a determination of the ratio h/m between the Planck constant and the mass of the atoms and then to deduce a value of the fine structure constant alpha. To do this measurement, we use the technique of Bloch oscillations, which allows us to transfer a large number of recoils to atoms. A velocity sensor, based on velocity selective Raman transition, enables us to measure the momentum transferred to the atoms. A measurement with a statistical uncertainty of 4.4 10 -9 , in conjunction with a careful study of systematic effects (5 10 -9 ), has led us to a determination of alpha with an uncertainty of 6.7 10 -9 : α -1 (Rb) = 137.03599878 (91). This uncertainty is similar to the uncertainty of the best determinations of alpha based on atom interferometry. (author)

  15. Atomic Properties from Electronic Structure: X ^1Σ^+ CaF^+

    Science.gov (United States)

    Coy, Stephen; Grimes, David; Barnum, Timothy J.; Field, Robert W.; Wong, Bryan M.

    2017-06-01

    Purpose: Compare methods of obtaining atoms-in-molecules properties from electronic structure calculations and spectroscopy. Spectroscopic connection: Rydberg penetrating states and shape resonances see the atoms, non-penetrating states see molecules. Clusters see both. Scope: Ca and F in CaF+, and by extension, Ca and F in other bonded and non-bonded environments. Converting molecular properties to atomic models: Two point-localized models, dipole induction model with integer ionic charges, Hirshfeld local multipole model. Data used: CCSD and CCSD(T) ab-initio calculations, Experimental values of Q_1^2 - eQ_2, and of dipole polarizability. Result: Hirshfeld model connects long range multipole potential to atomic properties, and matches multipoles. Traditional dipole induction matches calc'd Q_1, Q_2, expt'l Q_1^2-eQ_2, sensible atomic polarizabilities.

  16. Atomic structure and chemistry of human serum albumin

    Science.gov (United States)

    He, Xiao M.; Carter, Daniel C.

    1992-01-01

    The three-dimensional structure of human serum albumin has been determined crystallographically to a resolution of 2.8 A. It comprises three homologous domains that assemble to form a heart-shaped molecule. Each domain is a product of two subdomains that possess common structural motifs. The principal regions of ligand binding to human serum albumin are located in hydrophobic cavities in subdomains IIA and ILIA, which exhibit similar chemistry. The structure explains numerous physical phenomena and should provide insight into future pharmacokinetic and genetically engineered therapeutic applications of serum albumin.

  17. Structure and hydrogen storage properties of the hexagonal Laves phase Sc(Al{sub 1-x}Ni{sub x}){sub 2}

    Energy Technology Data Exchange (ETDEWEB)

    Sahlberg, Martin, E-mail: Martin.sahlberg@kemi.uu.se [Department of Chemistry, The Angstroem Laboratory, Uppsala University, Box 538, SE-751 21 Uppsala (Sweden); Angstroem, Jonas, E-mail: jonas.angstrom@kemi.uu.se [Department of Chemistry, The Angstroem Laboratory, Uppsala University, Box 538, SE-751 21 Uppsala (Sweden); Zlotea, Claudia, E-mail: claudia.zlotea@icmpe.cnrs.fr [Chimie Metallurgique des Terres Rares, Institut de Chimie et des Materiaux de Paris Est, UMR 7182, CNRS, 2-8 rue Henri Dunant, 94320 Thiais Cedex (France); Beran, Premysl, E-mail: pberan@ujf.cas.cz [Nuclear Physics Institute, Academy of Sciences of the Czech Republic, 25068 Rez (Czech Republic); Latroche, Michel, E-mail: michel.latroche@glvt-cnrs.fr [Chimie Metallurgique des Terres Rares, Institut de Chimie et des Materiaux de Paris Est, UMR 7182, CNRS, 2-8 rue Henri Dunant, 94320 Thiais Cedex (France); Pay Gomez, Cesar, E-mail: Cesar.paygomez@kemi.uu.se [Department of Chemistry, The Angstroem Laboratory, Uppsala University, Box 538, SE-751 21 Uppsala (Sweden)

    2012-12-15

    The crystal structures of hydrogenated and unhydrogenated Sc(Al{sub 1-x}Ni{sub x}){sub 2} Laves phases have been studied by combining several diffraction techniques and it is shown that hydrogen is situated interstitially in the A{sub 2}B{sub 2}-sites, which have the maximum number of scandium neighbours. The hydrogen absorption/desorption behaviour has also been investigated. It is shown that a solid solution of hydrogen forms in the mother compound. The hydrogen storage capacity exceeds 1.7 H/f.u. at 374 K, and the activation energy of hydrogen desorption was determined to 4.6 kJ/mol H{sub 2}. It is shown that these compounds share the same local coordination as Frank-Kasper-type approximants and quasicrystals, which opens up the possibility of finding many new hydride phases with these types of crystal structures. - Graphical abstract: The structure of ScNiAlDx, Sc atoms are shown in purple and Ni/Al atoms in blue and the iso-surfaces of deuterium in yellow. Revealed from refinements of neutron powder diffraction data. Highlights: Black-Right-Pointing-Pointer The crystal structure of ScNiAl and ScNiAlDx is reported. Black-Right-Pointing-Pointer We show the hydrogen storage properties of Sc(Al{sub 1-x}Ni{sub x}){sub 2}. Black-Right-Pointing-Pointer We discuss the possibility to store hydrogen in quasicrystals.

  18. Green's functions for infinite bi-material planes of cubic quasicrystals with imperfect interface

    Energy Technology Data Exchange (ETDEWEB)

    Gao Yang, E-mail: gaoyangg@gmail.co [Institute of Mechanics, University of Kassel, Kassel D-34125 (Germany); Ricoeur, Andreas [Institute of Mechanics, University of Kassel, Kassel D-34125 (Germany)

    2010-09-20

    The problem of an infinite plane which is composed of two half-planes with different cubic quasicrystal materials subjected to line phonon and phason forces is investigated. By virtue of the general solution of cubic quasicrystals, a series of displacement functions is adopted to obtain Green's functions in the closed form. For the bonding along the bi-material interface three different models account for different coupling conditions.

  19. The structure of filled skutterudites and the local vibration behavior of the filling atom

    Energy Technology Data Exchange (ETDEWEB)

    Zhou, Xiaojuan [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Dongguan Institute of Neutron Science, Dongguan 523808 (China); University of Chinese Academy of Sciences, Beijing 100049 (China); Zong, Peng-an [State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084 (China); Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Chen, Xihong [Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai 200050 (China); Tao, Juzhou, E-mail: taoj@ihep.ac.cn [Institute of High Energy Physics, Chinese Academy of Sciences, Beijing 100049 (China); Dongguan Institute of Neutron Science, Dongguan 523808 (China); Lin, He, E-mail: linhe@sinap.ac.cn [Shanghai Institute of Applied Physics, Chinese Academy of Science, Shanghai 201204 (China)

    2017-02-15

    Both of atomic pair distribution function (PDF) and extended x-ray absorption fine structure (EXAFS) experiments have been carried out on unfilled and Yb-filled skutterudites Yb{sub x}Co{sub 4}Sb{sub 12} (x=0, 0.15, 0.2 and 0.25) samples. The structure refinements on PDF data confirm the large amplitude vibration of Yb atom and the dependence of Yb vibration amplitude on the filling content. Temperature dependent EXAFS experiment on filled skutterudites have been carried out at Yb L{sub Ⅲ}-edge in order to explore the local vibration behavior of filled atom. EXAFS experiments show that the Einstein temperature of the filled atom is very low (70.9 K) which agrees with the rattling behavior.

  20. Enrichment of true positives from structural alerts through the use of novel atomic fragment based descriptors

    DEFF Research Database (Denmark)

    Long, A.; Rydberg, Patrik

    2013-01-01

    To enhance the discrimination rate for methods applying structural alerts and biotransformation rules in the prediction of toxicity and drug metabolism we have developed a set of novel fragment based atomic descriptors. These atomic descriptors encode the properties of the fragments separating...... an atom from the closest end of a branch or the molecule. The end of a branch and the end of a molecule, as well as the selection of the fragments, are made by an algorithm that uses only the distance matrix of the molecule. The novel descriptors are applied to a small set of biotransformation rules...

  1. Atomic oxygen fine-structure splittings with tunable far-infrared spectroscopy

    Science.gov (United States)

    Zink, Lyndon R.; Evenson, Kenneth M.; Matsushima, Fusakazu; Nelis, Thomas; Robinson, Ruth L.

    1991-01-01

    Fine-structure splittings of atomic oxygen (O-16) in the ground state have been accurately measured using a tunable far-infrared spectrometer. The 3P0-3pl splitting is 2,060,069.09 (10) MHz, and the 3Pl-3P2 splitting is 4,744,777.49 (16) MHz. These frequencies are important for measuring atomic oxygen concentration in earth's atmosphere and the interstellar medium.

  2. Critical Assessment of Theoretical Calculations of Atomic Structure and Transition Probabilities: An Experimenter’s View

    Directory of Open Access Journals (Sweden)

    Elmar Träbert

    2014-03-01

    Full Text Available The interpretation of atomic observations by theory and the testing of computational predictions by experiment are interactive processes. It is necessary to gain experience with “the other side” before claims of achievement can be validated and judged. The discussion covers some general problems in the field as well as many specific examples, mostly organized by isoelectronic sequence, of what level of accuracy recently has been reached or which atomic structure or level lifetime problem needs more attention.

  3. BNC nanoshells: a novel structure for atomic storage

    Science.gov (United States)

    Silva, F. W. N.; Cruz-Silva, E.; Terrones, M.; Terrones, H.; Barros, E. B.

    2017-11-01

    Quantum molecular dynamics (QMD) and density functional theory are employed in this work in order to study the structural and electronic properties of carbon, boron nitride or hybrid BNC nanoshells. The studied nanoshells can be formed by stacking two zigzag graphene nanoribbons, two zigzag boron nitride nanoribbons or one zigzag graphene nanoribbon on a boron nitride nanoribbon. In all cases only one of the edges of the ribbon is passivated, while the other one is left unpassivated. Our QMD results show that these nanoribbons collapse just a few femtoseconds after the beginning of the simulation, forming a coalesced structure in the shape of a shell. Our band structure calculations revealed that this structures may be metallic or semiconductor, depending on its stoichiometry. Furthermore, a spin splitting for energies near the Fermi level is predicted for both the pure carbon and the hybrid BNC-nanoshell systems. We further show that when a transverse electric field is applied to these systems, the nanoshell structure tends to open up. This effect can lead to the application of these nanoshells for molecular storage. As a proof of concept, We investigate this storage effect for the H2 molecule.

  4. Effect of Mg-Zn-Nd spherical quasi-crystals on microstructure and mechanical properties of ZK60 alloy

    Directory of Open Access Journals (Sweden)

    Zhang Jinshan

    2011-08-01

    Full Text Available To improve the strength, toughness, heat-resistance and deformability of magnesium alloy, the microstructure and mechanical properties of ZK60 alloy strengthened by Mg-Zn-Nd spherical quasi-crystal phase (I-phase particles were investigated. Mg40Zn55Nd5 (I-phase particles in addition to α-Mg, MgZn phase and MgZn2 phases can be obtained in ZK60-based composites under normal casting condition by the addition of quasi-crystal containing Mg-Zn-Nd master alloy. The experimental results show that the introduction of Mg-Zn-Nd spherical quasi-crystal phase into ZK60 alloy makes a great contribution to the refinement of the matrix microstructures and the improvement of mechanical properties. While adding Mg-Zn-Nd spherical quasi-crystal master alloy of 4.0wt.%, the ultimate tensile strength and yield strength of ZK60-based composite at ambient temperature reach their peak values of 256.7 MPa and 150.4 MPa, which were about 17.8% and 24.1% higher respectively than those of the ZK60 alloy. The improved mechanical properties are mainly attributed to the pinning effect of the quasi-crystal particles (I-phase at the grain boundaries. This research results provide a new way for strengthening and toughening of magnesium alloys as well as a new application of Mg-based spherical quasi-crystals.

  5. Chemical Structure and Properties: A Modified Atoms-First, One-Semester Introductory Chemistry Course

    Science.gov (United States)

    Schaller, Chris P.; Graham, Kate J.; Johnson, Brian J.; Jakubowski, Henry V.; McKenna, Anna G.; McIntee, Edward J.; Jones, T. Nicholas; Fazal, M. A.; Peterson, Alicia A.

    2015-01-01

    A one-semester, introductory chemistry course is described that develops a primarily qualitative understanding of structure-property relationships. Starting from an atoms-first approach, the course examines the properties and three-dimensional structure of metallic and ionic solids before expanding into a thorough investigation of molecules. In…

  6. Atomic and electronic structure of MoS2 nanoparticles

    DEFF Research Database (Denmark)

    Bollinger, Mikkel; Jacobsen, Karsten Wedel; Nørskov, Jens Kehlet

    2003-01-01

    Using density-functional theory (DFT) we present a detailed theoretical study of MoS2 nanoparticles. We focus on the edge structures, and a number of different edge terminations are investigated. Several, but not all, of these configurations have one-dimensional metallic states localized at the e......Using density-functional theory (DFT) we present a detailed theoretical study of MoS2 nanoparticles. We focus on the edge structures, and a number of different edge terminations are investigated. Several, but not all, of these configurations have one-dimensional metallic states localized...

  7. Halo-like structures studied by atomic force microscopy

    DEFF Research Database (Denmark)

    Sørensen, Alexis Hammer; Kyhle, Anders; Hansen, L. Theil

    1997-01-01

    Nanometer-sized clusters of copper have been produced in a hollow cathode sputtering source and deposited on SiOx. Halo-like structures consisting of micrometer sized protrusions in the solicon oxide surface surrounded by thin rings of smaller particles are observed. The area in between seems...... to be depleted of particles. We propose that the halo-like structures are a result of electrostatic forces acting between the incoming charged clusters and charged regions on the surface. A simple computer simulation supports this suggestion....

  8. Size effect on atomic structure in low-dimensional Cu-Zr amorphous systems.

    Science.gov (United States)

    Zhang, W B; Liu, J; Lu, S H; Zhang, H; Wang, H; Wang, X D; Cao, Q P; Zhang, D X; Jiang, J Z

    2017-08-04

    The size effect on atomic structure of a Cu 64 Zr 36 amorphous system, including zero-dimensional small-size amorphous particles (SSAPs) and two-dimensional small-size amorphous films (SSAFs) together with bulk sample was investigated by molecular dynamics simulations. We revealed that sample size strongly affects local atomic structure in both Cu 64 Zr 36 SSAPs and SSAFs, which are composed of core and shell (surface) components. Compared with core component, the shell component of SSAPs has lower average coordination number and average bond length, higher degree of ordering, and lower packing density due to the segregation of Cu atoms on the shell of Cu 64 Zr 36 SSAPs. These atomic structure differences in SSAPs with various sizes result in different glass transition temperatures, in which the glass transition temperature for the shell component is found to be 577 K, which is much lower than 910 K for the core component. We further extended the size effect on the structure and glasses transition temperature to Cu 64 Zr 36 SSAFs, and revealed that the T g decreases when SSAFs becomes thinner due to the following factors: different dynamic motion (mean square displacement), different density of core and surface and Cu segregation on the surface of SSAFs. The obtained results here are different from the results for the size effect on atomic structure of nanometer-sized crystalline metallic alloys.

  9. Study of the Adsorption of Atoms and Molecules on Silicon Surfaces Crystallographics and Electronic Structure

    CERN Document Server

    Bengio, S

    2003-01-01

    This thesis work has been concerned with adsorption properties of silicon surfaces.The atomic and electronic structure of molecules and atoms adsorbed on Si has been investigated by means of photoemission experiments combined with synchrotron radiation.The quantitative atomic structure determination was held applying the photoelectron diffraction technique.This technique is sensible to the local structure of a reference atomic specie and has elemental and chemical-state specificity.This approach has been applied to three quite different systems with different degrees of complexity, Sb/Si(111) sq root 3x sq root 3R30 sup 0 , H sub 2 O/Si(100)2x1 and NH sub 3 /Si(111)7x7.Our results show that Sb which forms a ( sq root 3 sq root 3)R30 sup 0 phase produces a bulklike-terminated Si(111)1x1 substrate free of stacking faults.Regarding the atomic structure of its interface, this study strongly favours the T4-site milkstool model over the H3 one.An important aspect regarding the H sub 2 O/Si(100)(2x1) system was esta...

  10. Imaging the atomic structure and local chemistry of platelets in natural type Ia diamond.

    Science.gov (United States)

    Olivier, E J; Neethling, J H; Kroon, R E; Naidoo, S R; Allen, C S; Sawada, H; van Aken, P A; Kirkland, A I

    2018-03-01

    In the past decades, many efforts have been devoted to characterizing {001} platelet defects in type Ia diamond. It is known that N is concentrated at the defect core. However, an accurate description of the atomic structure of the defect and the role that N plays in it is still unknown. Here, by using aberration-corrected transmission electron microscopy and electron energy-loss spectroscopy we have determined the atomic arrangement within platelet defects in a natural type Ia diamond and matched it to a prevalent theoretical model. The platelet has an anisotropic atomic structure with a zigzag ordering of defect pairs along the defect line. The electron energy-loss near-edge fine structure of both carbon K- and nitrogen K-edges obtained from the platelet core is consistent with a trigonal bonding arrangement at interstitial sites. The experimental observations support an interstitial aggregate mode of formation for platelet defects in natural diamond.

  11. Large scale structural optimization of trimetallic Cu-Au-Pt clusters up to 147 atoms

    Science.gov (United States)

    Wu, Genhua; Sun, Yan; Wu, Xia; Chen, Run; Wang, Yan

    2017-10-01

    The stable structures of Cu-Au-Pt clusters up to 147 atoms are optimized by using an improved adaptive immune optimization algorithm (AIOA-IC method), in which several motifs, such as decahedron, icosahedron, face centered cubic, sixfold pancake, and Leary tetrahedron, are randomly selected as the inner cores of the starting structures. The structures of Cu8AunPt30-n (n = 1-29), Cu8AunPt47-n (n = 1-46), and partial 75-, 79-, 100-, and 147-atom clusters are analyzed. Cu12Au93Pt42 cluster has onion-like Mackay icosahedral motif. The segregation phenomena of Cu, Au and Pt in clusters are explained by the atomic radius, surface energy, and cohesive energy.

  12. Mossbauer analysis of the atomic and magnetic structure of alloys

    CERN Document Server

    Ovchinnikov, VV

    2007-01-01

    The monograph indicates the key problems that have to be solved for the further development of the Mössbauer methods for analysis of the nuclear and magnetic structure of alloys, and offer solution variants for some of these problems based on the generalised results of a wide range of theoretical and experimental investigations,including original work by the author of the book and his colleagues. Contents 1. Description of the nature of the Mössbauer effect 2. Interpretation of the ossbauer spectra of alloys 3.Electrical and magnetics hyperfine interactions of resonant nuclei in metals and

  13. The development of high-resolution spectroscopic methods and their use in atomic structure studies

    International Nuclear Information System (INIS)

    Poulsen, O.

    1984-01-01

    This thesis discusses work performed during the last nine years in the field of atomic spectroscopy. Several high-resolution techniques, ranging from quantum beats, level crossings, rf-laser double resonances to nonlinear field atom interactions, have been employed. In particular, these methods have been adopted and developed to deal with fast accelerated atomic or ionic beams, allowing studies of problems in atomic-structure theory. Fine- and hyperfine-structure determinations in the He I and Li I isoelectronic sequences, in 51 V I, and in 235 U I, II have permitted a detailed comparison with ab initio calculations, demonstrating the change in problems when going towards heavier elements or higher ionization stage. The last part of the thesis is concerned with the fundamental question of obtaining very high optical resolution in the interaction between a fast accelerated atom or ion beam and a laser field, this problem being the core in the continuing development of atomic spectroscopy necessary to challenge the more precise and sophisticated theories advanced. (Auth.)

  14. Atomic structure of icosahedral B4C boron carbide from a first principles analysis of NMR spectra.

    Science.gov (United States)

    Mauri, F; Vast, N; Pickard, C J

    2001-08-20

    Density functional theory is demonstrated to reproduce the 13C and 11B NMR chemical shifts of icosahedral boron carbides with sufficient accuracy to extract previously unresolved structural information from experimental NMR spectra. B4C can be viewed as an arrangement of 3-atom linear chains and 12-atom icosahedra. According to our results, all the chains have a CBC structure. Most of the icosahedra have a B11C structure with the C atom placed in a polar site, and a few percent have a B (12) structure or a B10C2 structure with the two C atoms placed in two antipodal polar sites.

  15. Atomic structures and covalent-to-metallic transition of lead clusters Pbn (n=2-22)

    International Nuclear Information System (INIS)

    Wang Baolin; Zhao Jijun; Chen Xiaoshuang; Shi Daning; Wang Guanghou

    2005-01-01

    The lowest-energy structures and electronic properties of the lead clusters are studied by density-functional-theory calculations with Becke-Lee-Yang-Parr gradient correction. The lowest-energy structures of Pb n (n=2-22) clusters are determined from a number of structural isomers, which are generated from empirical genetic algorithm simulations. The competition between atom-centered compact structures and layered stacking structures leads to the alternative appearance of the two types of structures as global minimum. The size evolution of geometric and electronic properties from covalent bonding towards bulk metallic behavior in Pb clusters is discussed

  16. Electrode structure of a compact microwave driven capacitively coupled atomic beam source

    Science.gov (United States)

    Shimabukuro, Yuji; Takahashi, Hidenori; Wada, Motoi

    2018-01-01

    A compact magnetic field free atomic beam source was designed, assembled and tested the performance to produce hydrogen and nitrogen atoms. A forced air-cooled solid-state microwave power supply at 2.45 GHz frequency drives the source up to 100 W through a coaxial transmission cable coupled to a triple stub tuner for realizing a proper matching condition to the discharge load. The discharge structure of the source affected the range of operation pressure, and the pressure was reduced by four orders of magnitude through improving the electrode geometry to enhance the local electric field intensity. Optical emission spectra of the produced plasmas indicate production of hydrogen and nitrogen atoms, while the flux intensity of excited nitrogen atoms monitored by a surface ionization type detector showed the signal level close to a source developed for molecular beam epitaxy applications with 500 W RF power.

  17. Interaction and dynamics of add-atoms with 2-dimensional structures

    CERN Multimedia

    The interaction and dynamics of add-atoms with graphene, graphene-derivate structures and, later, MoSi$_2$, two-dimensional – single and few – atomic layers will be studied with the Perturbed Angular Correlation – PAC – technique. Graphene is also envisaged as new platform for growing semiconductor nanostructure devices, such as quantum dots and as a particularly powerful catalyst. Understanding nucleation of nanostructures and clusters on graphene and related phases in wet conditions as they are used in chemical methods in research and industry require complementary studies. These systems will therefore be studied systematically using radioactive probe atoms attaching via a transfer media (e.g., water in catalysis process) or being deposited with soft-landing techniques under vacuum and UHV conditions, as put in place at the ASPIC setup at ISOLDE. The hyperfine fields obtained under different environments are expected to reveal basic information on the rich atomic and physical mechanisms associated w...

  18. On the atomic structure of Zr60Cu20Fe20 metallic glass

    Science.gov (United States)

    Kaban, I.; Jóvári, P.; Stoica, M.; Mattern, N.; Eckert, J.; Hoyer, W.; Beuneu, B.

    2010-10-01

    The structure of Zr60Cu20Fe20 metallic glass has been studied with high-energy x-ray diffraction, neutron diffraction and extended x-ray absorption spectroscopy and modelled with the reverse Monte Carlo simulation technique. It is found that Cu and Fe atoms prefer Zr as a nearest neighbour. The mean interatomic distance between Cu/Fe and Zr atoms in the glass is remarkably shorter than the sum of the respective atomic radii. The coordination numbers for Cu/Fe-Cu/Fe pairs are very close to each other, suggesting a regular distribution of Cu and Fe atoms in the Zr60Cu20Fe20 metallic glass.

  19. Dye-sensitized solar cells: Atomic scale investigation of interface structure and dynamics

    International Nuclear Information System (INIS)

    Ma Wei; Zhang Fan; Meng Sheng

    2014-01-01

    Recent progress in dye-sensitized solar cells (DSC) research is reviewed, focusing on atomic-scale investigations of the interface electronic structures and dynamical processes, including the structure of dye adsorption onto TiO 2 , ultrafast electron injection, hot-electron injection, multiple-exciton generation, and electron—hole recombination. Advanced experimental techniques and theoretical approaches are briefly summarized, and then progressive achievements in photovoltaic device optimization based on insights from atomic scale investigations are introduced. Finally, some challenges and opportunities for further improvement of dye solar cells are presented. (invited review — international conference on nanoscience and technology, china 2013)

  20. Structure of ordered polyelectrolyte films from atomic-force microscopy and X-ray reflectivity data

    International Nuclear Information System (INIS)

    Belyaev, V.V.; Tolstikhina, A.L.; Stepina, N.D.; Kayushina, R.L.

    1998-01-01

    The possible application of atomic-force microscopy and X-ray reflectometry methods to structural studies of polyelectrolyte films obtained due to alternating adsorption of oppositely charged polyanion [sodium polysterenesulfonate (PSS)] and polycation [poly(allylamine) hydrochloride (PAA)] layers on solid substrates has been considered. The atomic-force microscopy study has revealed the characteristic features of the surface topography of samples consisting of different numbers of polyelectrolyte layers deposited from solutions characterized by different ionic strength values. It is shown that the shape of the reflectivity curves obtained from thin polyelectrolyte films depends on their surface structure

  1. Extended x-ray absorption fine structure studies of the atomic structure of nanoparticles in different metallic matrices.

    Science.gov (United States)

    Baker, S H; Roy, M; Gurman, S J; Binns, C

    2009-05-06

    It has been appreciated for some time that the novel properties of particles in the size range 1-10 nm are potentially exploitable in a range of applications. In order to ultimately produce commercial devices containing nanosized particles, it is necessary to develop controllable means of incorporating them into macroscopic samples. One way of doing this is to embed the nanoparticles in a matrix of a different material, by co-deposition for example, to form a nanocomposite film. The atomic structure of the embedded particles can be strongly influenced by the matrix. Since some of the key properties of materials, including magnetism, strongly depend on atomic structure, the ability to determine atomic structure in embedded nanoparticles is very important. This review focuses on nanoparticles, in particular magnetic nanoparticles, embedded in different metal matrices. Extended x-ray absorption fine structure (EXAFS) provides an excellent means of probing atomic structure in nanocomposite materials, and an overview of this technique is given. Its application in probing catalytic metal clusters is described briefly, before giving an account of the use of EXAFS in determining atomic structure in magnetic nanocomposite films. In particular, we focus on cluster-assembled films comprised of Fe and Co nanosized particles embedded in various metal matrices, and show how the crystal structure of the particles can be changed by appropriate choice of the matrix material. The work discussed here demonstrates that combining the results of structural and magnetic measurements, as well as theoretical calculations, can play a significant part in tailoring the properties of new magnetic cluster-assembled materials.

  2. Atomic disorder and amorphization of B2-structure CoZr by ball milling

    International Nuclear Information System (INIS)

    Zhou, G.F.; Bakker, H.

    1996-01-01

    For a considerable number of intermetallic compounds it has been found that ball milling introduces atomic (chemical) disorder. Disorder due to milling was demonstrated by x-ray diffraction in AlRu, crystallizing in the B2 structure (ordered b.c.c.) by a decrease of the intensity of superlattice reflections relative to fundamental reflections. The same technique was used to investigate disordering by milling in Ni 3 Al, crystallizing in the L1 2 structure (ordered f.c.c.). In both cases the disorder is anti-site disorder of both components, i.e. both atomic species substitute on the wrong sublattices. Besides x-ray diffraction measurements of magnetic properties turned out to be useful in monitoring structural changes due to milling. The change in the superconducting transition temperature, measured by magnetic a.c. susceptibility, was used to demonstrate atomic disordering by milling in Nb 3 Sn and Nb 3 Au. The type of disorder turned out to be anti-site disorder. Such a type of disorder occurs in the same materials also at high temperatures or after irradiation by neutrons. The disordering was accompanied by an increase of the lattice parameter. An increase in high-field magnetization accompanied by a decrease of the lattice parameter during milling was found in B2 CoGa and B2 CoAl. In principle in the completely ordered state both compounds are non-magnetic, because the CO atoms are shielded from one another by Ga and Al atoms, respectively. However, when a Co atom is transferred to the wrong sublattice, it is surrounded by Co atoms as nearest neighbors and bears a magnetic moment. This explains the strong increase of the magnetization due to milling

  3. Compound semiconductor alloys: From atomic-scale structure to bandgap bowing

    Science.gov (United States)

    Schnohr, C. S.

    2015-09-01

    Compound semiconductor alloys such as InxGa1-xAs, GaAsxP1-x, or CuInxGa1-xSe2 are increasingly employed in numerous electronic, optoelectronic, and photonic devices due to the possibility of tuning their properties over a wide parameter range simply by adjusting the alloy composition. Interestingly, the material properties are also determined by the atomic-scale structure of the alloys on the subnanometer scale. These local atomic arrangements exhibit a striking deviation from the average crystallographic structure featuring different element-specific bond lengths, pronounced bond angle relaxation and severe atomic displacements. The latter, in particular, have a strong influence on the bandgap energy and give rise to a significant contribution to the experimentally observed bandgap bowing. This article therefore reviews experimental and theoretical studies of the atomic-scale structure of III-V and II-VI zincblende alloys and I-III-VI2 chalcopyrite alloys and explains the characteristic findings in terms of bond length and bond angle relaxation. Different approaches to describe and predict the bandgap bowing are presented and the correlation with local structural parameters is discussed in detail. The article further highlights both similarities and differences between the cubic zincblende alloys and the more complex chalcopyrite alloys and demonstrates that similar effects can also be expected for other tetrahedrally coordinated semiconductors of the adamantine structural family.

  4. Non-Fermi-Liquid Behavior in Metallic Quasicrystals with Local Magnetic Moments

    Science.gov (United States)

    Andrade, Eric C.; Jagannathan, Anuradha; Miranda, Eduardo; Vojta, Matthias; Dobrosavljević, Vladimir

    2015-07-01

    Motivated by the intrinsic non-Fermi-liquid behavior observed in the heavy-fermion quasicrystal Au51Al34Yb15 , we study the low-temperature behavior of dilute magnetic impurities placed in metallic quasicrystals. We find that a large fraction of the magnetic moments are not quenched down to very low temperatures T , leading to a power-law distribution of Kondo temperatures P (TK)˜TKα -1, with a nonuniversal exponent α , in a remarkable similarity to the Kondo-disorder scenario found in disordered heavy-fermion metals. For α <1 , the resulting singular P (TK) induces non-Fermi-liquid behavior with diverging thermodynamic responses as T →0 .

  5. Topological Control on the Structural Relaxation of Atomic Networks under Stress

    Science.gov (United States)

    Bauchy, Mathieu; Wang, Mengyi; Yu, Yingtian; Wang, Bu; Krishnan, N. M. Anoop; Masoero, Enrico; Ulm, Franz-Joseph; Pellenq, Roland

    2017-07-01

    Upon loading, atomic networks can feature delayed irreversible relaxation. However, the effect of composition and structure on relaxation remains poorly understood. Herein, relying on accelerated molecular dynamics simulations and topological constraint theory, we investigate the relationship between atomic topology and stress-induced structural relaxation, by taking the example of creep deformations in calcium silicate hydrates (C - S - H ), the binding phase of concrete. Under constant shear stress, C - S - H is found to feature delayed logarithmic shear deformations. We demonstrate that the propensity for relaxation is minimum for isostatic atomic networks, which are characterized by the simultaneous absence of floppy internal modes of relaxation and eigenstress. This suggests that topological nanoengineering could lead to the discovery of nonaging materials.

  6. On the effect of atomic structure on the deactivation of catalytic gold nanoparticles

    International Nuclear Information System (INIS)

    Walsh, M J; Gai, P L; Boyes, E D

    2012-01-01

    Here we present atomic scale studies into the nature of both the internal structure and external surfaces of catalytic Au nanoparticles using aberration corrected in-situ electron microscopy. The activity of catalytic nanoparticles is thought to be highly sensitive to the particles' structure, meaning typical local atomic rearrangements are likely to significantly affect the overall performance of the catalyst. As-deposited Au nanoparticles are found to exhibit a variety of morphologies, with many being internally strained or highly stepped at the surface. Upon heating, surface atoms are observed to minimise the particles' surface energy by restructuring towards planar (111) facets, resulting in the removal of low co-ordinated sites thought to be crucial in catalysis by Au nanoparticles. These results suggest the process of surface energy minimisation made possible by heating may lead to a loss of active sites and consequently contribute to the deactivation of the catalyst.

  7. Putting structure into context: fitting of atomic models into electron microscopic and electron tomographic reconstructions.

    Science.gov (United States)

    Volkmann, Niels

    2012-02-01

    A complete understanding of complex dynamic cellular processes such as cell migration or cell adhesion requires the integration of atomic level structural information into the larger cellular context. While direct atomic-level information at the cellular level remains inaccessible, electron microscopy, electron tomography and their associated computational image processing approaches have now matured to a point where sub-cellular structures can be imaged in three dimensions at the nanometer scale. Atomic-resolution information obtained by other means can be combined with this data to obtain three-dimensional models of large macromolecular assemblies in their cellular context. This article summarizes some recent advances in this field. Copyright © 2011 Elsevier Ltd. All rights reserved.

  8. Antiferromagnetic correlations in icosahedral R-Mg-Zn quasicrystals (R rare earth)

    Energy Technology Data Exchange (ETDEWEB)

    Charrier, B.; Schmitt, D. [Centre National de la Recherche Scientifique (CNRS), 38 - Grenoble (France); Ouladdiaf, B. [Institut Max von Laue - Paul Langevin (ILL), 38 - Grenoble (France)

    1997-04-01

    Powder neutron-diffraction experiments performed on R-Mg-Zn quasicrystals have shown for the first time the existence of magnetic ordering of the rare earth in these systems at low temperature (T{sub c} {<=} 6.5 K depending on the rare earth). Both narrow and broad magnetic diffraction peaks have been observed showing the presence of two different scales of magnetic correlations. (author). 3 refs.

  9. Using a matter wave model to study the structure of the electron inside an atom

    Science.gov (United States)

    Chang, Donald

    In Bohr's atomic model, the atom was conceptually modeled as a miniature solar system. With the development of the Schrödinger equation, the wave function of the electron inside an atom becomes much better known. But the electron is still regarded as a pointed object; according to the Copenhagen Interpretation, the wave function is thought to describe only the probability of finding the electron. Such an interpretation, however, has raised some conceptual questions. For example, how can a point-like electron form a chemical bond between neighboring atoms? In an attempt to overcome this difficulty, we use a matter wave theory to model the structure of an electron inside the atom. This model is inspired by noticing the similarity between a free electron and a photon; both particles behave like a corpuscular object as well as a physical wave. Thus, we hypothesize that, like the photon, an electron is an excitation wave of a real physical field. Based on this hypothesis, we have derived a basic wave equation for the free electron. We show that, in the presence of an electrical potential, this basic wave equation can lead to the Schrödinger equation. This work implies that the solution of the Schrödinger equation actually represents the physical waves of the electron. Thus, the electron inside the atom should behave more like a topologically distributive wave than a pointed object. In this presentation, we will discuss the advantages and limitations of this model.

  10. Electronic structure of graphene nanoribbons doped with nitrogen atoms: a theoretical insight.

    Science.gov (United States)

    Torres, A E; Fomine, S

    2015-04-28

    The electronic structure of graphene nanoribbons doped with a graphitic type of nitrogen atoms has been studied using B3LYP, B2PLYP and CAS methods. In all but one case the restricted B3LYP solutions were unstable and the CAS calculations provided evidence for the multiconfigurational nature of the ground state with contributions from two dominant configurations. The relative stability of the doped nanoribbons depends mostly on the mutual position of the dopant atoms and notably less on the position of nitrogen atoms within the nanoribbon. N-graphitic doping affects cationic states much more than anionic ones due the participation of the nitrogen atoms in the stabilization of the positive charge, resulting in a drop in ionization energies (IPs) for N-graphitic doped systems. Nitrogen atoms do not participate in the negative charge stabilization of anionic species and, therefore, the doping does not affect the electron affinities (EAs). The unrestricted B3LYP method is the method of choice for the calculation of IPs and EAs. Restricted B3LYP and B2PLYP produces unreliable results for both IPs and EAs while CAS strongly underestimates the electron affinities. This is also true for the reorganization energies where restricted B3LYP produces qualitatively incorrect results. Doping changes the reorganization energy of the nanoribbons; the hole reorganization energy is generally higher than the corresponding electron reorganization energy due to the participation of nitrogen atoms in the stabilization of the positive charge.

  11. Classification of Voronoi and Delone tiles of quasicrystals: III. Decagonal acceptance window of any size

    International Nuclear Information System (INIS)

    Masakova, Z; Patera, J; Zich, J

    2005-01-01

    This paper is the last of a series of three articles presenting a classification of Vornoi and Delone tilings determined by point sets Σ(Ω) ('quasicrystals'), built by the standard projection of the root lattice of type A 4 to a two-dimensional plane spanned by the roots of the Coxeter group H 2 (dihedral group of order 10). The acceptance window Ω for Σ(Ω) in the present paper is a regular decagon of any radius 0 k , τ = 1/2(1+√5) and k element of Z. The number of Voronoi tiles in different quasicrystal tilings varies between 3 and 12. Similarly, the number of Delone tiles is varying between 4 and 6. There are 7 VT sets of the 'generic' type and 7 of the 'singular' type. The latter occur for seven precise values of the radius of the acceptance window. Quasicrystals with acceptance windows with radii in between these values have constant VT sets, only the relative densities and arrangement of the tiles in the tilings change. Similarly, we distinguish singular and generic sets DT of Delone tiles

  12. Quantitative characterization of the atomic-scale structure of oxyhydroxides in rusts formed on steel surfaces

    International Nuclear Information System (INIS)

    Saito, M.; Suzuki, S.; Kimura, M.; Suzuki, T.; Kihira, H.; Waseda, Y.

    2005-01-01

    Quantitative X-ray structural analysis coupled with anomalous X-ray scattering has been used for characterizing the atomic-scale structure of rust formed on steel surfaces. Samples were prepared from rust layers formed on the surfaces of two commercial steels. X-ray scattered intensity profiles of the two samples showed that the rusts consisted mainly of two types of ferric oxyhydroxide, α-FeOOH and γ-FeOOH. The amounts of these rust components and the realistic atomic arrangements in the components were estimated by fitting both the ordinary and the environmental interference functions with a model structure calculated using the reverse Monte Carlo simulation technique. The two rust components were found to be the network structure formed by FeO 6 octahedral units, the network structure itself deviating from the ideal case. The present results also suggest that the structural analysis method using anomalous X-ray scattering and the reverse Monte Carlo technique is very successful in determining the atomic-scale structure of rusts formed on the steel surfaces

  13. Do General Physics Textbooks Discuss Scientists' Ideas about Atomic Structure? A Case in Korea

    Science.gov (United States)

    Niaz, Mansoor; Kwon, Sangwoon; Kim, Nahyun; Lee, Gyoungho

    2013-01-01

    Research in science education has recognized the importance of teaching atomic structure within a history and philosophy of science perspective. The objective of this study is to evaluate general physics textbooks published in Korea based on the eight criteria developed in previous research. The result of this study shows that Korean general…

  14. Studying the Consistency between and within the Student Mental Models for Atomic Structure

    Science.gov (United States)

    Zarkadis, Nikolaos; Papageorgiou, George; Stamovlasis, Dimitrios

    2017-01-01

    Science education research has revealed a number of student mental models for atomic structure, among which, the one based on Bohr's model seems to be the most dominant. The aim of the current study is to investigate the coherence of these models when students apply them for the explanation of a variety of situations. For this purpose, a set of…

  15. Supporting Students in Learning with Multiple Representation to Improve Student Mental Models on Atomic Structure Concepts

    Science.gov (United States)

    Sunyono; Yuanita, L.; Ibrahim, M.

    2015-01-01

    The aim of this research is identify the effectiveness of a multiple representation-based learning model, which builds a mental model within the concept of atomic structure. The research sample of 108 students in 3 classes is obtained randomly from among students of Mathematics and Science Education Studies using a stratified random sampling…

  16. Physico-Chemical and Structural Interpretation of Discrete Derivative Indices on N-Tuples Atoms

    Science.gov (United States)

    Martínez-Santiago, Oscar; Marrero-Ponce, Yovani; Barigye, Stephen J.; Le Thi Thu, Huong; Torres, F. Javier; Zambrano, Cesar H.; Muñiz Olite, Jorge L.; Cruz-Monteagudo, Maykel; Vivas-Reyes, Ricardo; Vázquez Infante, Liliana; Artiles Martínez, Luis M.

    2016-01-01

    This report examines the interpretation of the Graph Derivative Indices (GDIs) from three different perspectives (i.e., in structural, steric and electronic terms). It is found that the individual vertex frequencies may be expressed in terms of the geometrical and electronic reactivity of the atoms and bonds, respectively. On the other hand, it is demonstrated that the GDIs are sensitive to progressive structural modifications in terms of: size, ramifications, electronic richness, conjugation effects and molecular symmetry. Moreover, it is observed that the GDIs quantify the interaction capacity among molecules and codify information on the activation entropy. A structure property relationship study reveals that there exists a direct correspondence between the individual frequencies of atoms and Hückel’s Free Valence, as well as between the atomic GDIs and the chemical shift in NMR, which collectively validates the theory that these indices codify steric and electronic information of the atoms in a molecule. Taking in consideration the regularity and coherence found in experiments performed with the GDIs, it is possible to say that GDIs possess plausible interpretation in structural and physicochemical terms. PMID:27240357

  17. Atomic and electronic structures of I-V-VI2 ternary chalcogenides

    Directory of Open Access Journals (Sweden)

    Khang Hoang

    2016-03-01

    Full Text Available Atomic and electronic structures of I-V-VI2 (I = Na, K, Ag, Cu, Au; V = As, Sb, Bi; VI = S, Se, Te are studied using first-principles hybrid density functional calculations. We find that the strong hybridization between the trivalent cation (As, Sb, and Bi p states and the divalent anion (S, Se, and Te p states tends to introduce electronic states in the band gap or pseudogap region and drive the systems toward metallicity. The atomic ordering on the cation sublattice of the ternary chalcogenides, therefore, has a strong impact on the energetics and the electronic structure in the neighborhood of the Fermi level as it determines if a certain atomic configuration is favorable to the highly directional cation p–anion p interaction. Besides these p states, the s state (in the case of Na and K or the s and d states (Ag, Cu, and Au can also play an important role in the band-gap formation. Our study suggests how to manipulate the electronic structure of these ternary compounds such that they show desired features for different applications by modifying their atomic structure and/or by changing their constituent element(s.

  18. Structural and electronic properties of isovalent boron atoms in GaAs

    Science.gov (United States)

    Krammel, C. M.; Nattermann, L.; Sterzer, E.; Volz, K.; Koenraad, P. M.

    2018-04-01

    Boron containing GaAs, which is grown by metal organic vapour phase epitaxy, is studied at the atomic level by cross-sectional scanning tunneling microscopy (X-STM) and spectroscopy (STS). In topographic X-STM images, three classes of B related features are identified, which are attributed to individual B atoms on substitutional Ga sites down to the second layer below the natural {110} cleavage planes. The X-STM contrast of B atoms below the surface reflects primarily the structural modification of the GaAs matrix by the small B atoms. However, B atoms in the cleavage plane have in contrast to conventional isovalent impurities, such as Al and In, a strong influence on the local electronic structure similar to donors or acceptors. STS measurements show that B in the GaAs {110} surfaces gives rise to a localized state short below the conduction band (CB) edge while in bulk GaAs, the B impurity state is resonant with the CB. The analysis of BxGa1-xAs/GaAs quantum wells reveals a good crystal quality and shows that the incorporation of B atoms in GaAs can be controlled along the [001] growth direction at the atomic level. Surprisingly, the formation of the first and fourth nearest neighbor B pairs, which are oriented along the directions, is strongly suppressed at a B concentration of 1% while the third nearest neighbor B pairs are found more than twice as often than expected for a completely spatially random pattern.

  19. Pressler's Quantumization of the Atom and The Left-handed Electron's Internal Structure

    Science.gov (United States)

    Pressler, David E.

    2000-03-01

    A new theory of superconductivity will be presented. In addition, I will reveal the answer to one of the most intriguing questions in science since the elusive electron particle was discovered by J. J. Thomson: Exactly what is the electron particle and why does it exhibit both particle and wave characteristics. Specifically, how does the electron exhibit an intrinsic magnetic field and, inside the atom, how does it exhibit angular momentum. I will describe, in detail, particle pair production. The fundamental physical theoretical parameters, the physical mass and charge, of all elementary particles is introduced. The fundamental neutron particle’s internal structure is also illustrated. The electron radius is estimated to eight significant figures. I will present a novel theory concerning atomic structure, the position and nature of the electron inside the atom, and the nature of bonding, i.e., the covalent bond is described in terms of the interactions of atomic magnetic fields. Precise bond angles and distances of the molecule are considered. This new concept is consistent with experimental evidence and adheres strictly to the valence-shell electron-pair repulsion (VSEPR) model presently used in chemistry. I will explain the atomic model concept as being a true harmonic oscillator; periodic motion of the electron at resonant frequency produces radiation at discrete frequencies or line spectra because the electron is under the action of two restoring forces.

  20. Asymptotic Structure in the Classically Forbidden Region of the Hooke's Atoms

    International Nuclear Information System (INIS)

    Wang Xuemei

    2013-01-01

    The two-electron Hooke's atom — a quantum mechanical system with two electrons bound in a harmonic potential — is well known for its exact analytical properties at certain oscillator strengths. The Hooke's atoms with more than two electrons offer more scope for valuable practical applications. In this work, we study the asymptotic structure of these Hooke's atoms in the classically forbidden region. The leading-order term of the long-range expression for the KS exchange-correlation potential v xc (r) is shown to be −1/r. The second and third higher order terms are also exactly obtained. Various components of v xc (r) are also studied. It is shown that the leading term of O(1/r) in v xc (r) is due to the pure Pauli correlation, while the leading contribution of the Coulomb correlation is of O(1/r 3 ). Neither of them makes contribution to the term of O(1/r 2 ), which is shown to be solely due to the kinetic correlation effect. Results for the two-electron Hooke's atom were obtained before in the literature. Our results reduce to those of the two-electron Hooke's atom as a special case. (condensed matter: electronic structure, electrical, magnetic, and optical properties)

  1. Direct evidence of atomic-scale structural fluctuations in catalyst nanoparticles.

    Science.gov (United States)

    Lin, Pin Ann; Gomez-Ballesteros, Jose L; Burgos, Juan C; Balbuena, Perla B; Natarajan, Bharath; Sharma, Renu

    2017-05-01

    Rational catalyst design requires an atomic scale mechanistic understanding of the chemical pathways involved in the catalytic process. A heterogeneous catalyst typically works by adsorbing reactants onto its surface, where the energies for specific bonds to dissociate and/or combine with other species (to form desired intermediate or final products) are lower. Here, using the catalytic growth of single-walled carbon nanotubes (SWCNTs) as a prototype reaction, we show that the chemical pathway may in-fact involve the entire catalyst particle, and can proceed via the fluctuations in the formation and decomposition of metastable phases in the particle interior. We record in situ and at atomic resolution, the dynamic phase transformations occurring in a Cobalt catalyst nanoparticle during SWCNT growth, using a state-of-the-art environmental transmission electron microscope (ETEM). The fluctuations in catalyst carbon content are quantified by the automated, atomic-scale structural analysis of the time-resolved ETEM images and correlated with the SWCNT growth rate. We find the fluctuations in the carbon concentration in the catalyst nanoparticle and the fluctuations in nanotube growth rates to be of complementary character. These findings are successfully explained by reactive molecular dynamics (RMD) simulations that track the spatial and temporal evolution of the distribution of carbon atoms within and on the surface of the catalyst particle. We anticipate that our approach combining real-time, atomic-resolution image analysis and molecular dynamics simulations will facilitate catalyst design, improving reaction efficiencies and selectivity towards the growth of desired structure.

  2. The structural and electronic properties of metal atoms adsorbed on graphene

    Science.gov (United States)

    Liu, Wenjiang; Zhang, Cheng; Deng, Mingsen; Cai, Shaohong

    2017-09-01

    Based on density functional theory (DFT), we studied the structural and electronic properties of seven different metal atoms adsorbed on graphene (M + graphene). The geometries, adsorption energies, density of states (DOS), band structures, electronic dipole moment, magnetic moment and work function (WF) of M + graphene were calculated. The adsorption energies ΔE indicated that Li, Na, K, Ca and Fe adsorbed on graphene were tending to form stable structures. However, diffusion would occur on Cu and Ag adsorbed on graphene. In addition, the electronic structure near the Fermi level of graphene was significantly affected by Fe (Cu and Ag), compared with Li (Na, K and Ca). The electronic dipole moment and magnetic moment of M + graphene were sensitive to the adsorbed metal atoms. Moreover, we found electropositive (electronegative) adsorption can decrease (increase) the WF of the surface. Specially, the WF of Ag + graphene and Fe + graphene would increase because surface dipole moment make a contribution to electron.

  3. Higher order structure of short immunostimulatory oligonucleotides studied by atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Klein, Dionne C.G., E-mail: dionne.c.g.klein@ntnu.no [Department of Physics, Norwegian University of Science and Technology, N-7491, Trondheim (Norway); Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, N-7489, Trondheim (Norway); Latz, Eicke [Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, N-7489, Trondheim (Norway); Division of Infectious Diseases and Immunology, University of Massachusetts Medical School, 364 Plantation Street, Worcester, MA 01605 (United States); Institute of Innate Immunity, University Hospitals, University of Bonn, Sigmund-Freud-Str. 25, 53127 Bonn (Germany); Espevik, Terje [Department of Cancer Research and Molecular Medicine, Norwegian University of Science and Technology, N-7489, Trondheim (Norway); Stokke, Bjorn T. [Department of Physics, Norwegian University of Science and Technology, N-7491, Trondheim (Norway)

    2010-05-15

    Immunostimulatory CpG-DNA activates the innate immune system by binding to Toll-like receptor 9. Structurally different CpG-containing oligonucleotides trigger a different type of immune response while activating the same receptor. We therefore investigated the higher order structure of two different classes of immunostimulatory CpG-DNA. Class A, which contains a partly self-complementary sequence and poly-G ends, forms duplexes and nanoparticles in salt solution, while class B, which does not contain these features and is purely linear, does not form a duplex or nanoparticles. Results obtained here by high-resolution atomic force microscopy of classes A and B CpG-DNA, reflect these differences in secondary structure. Detailed structural analysis of the atomic force microscopy topographs is presented for two different sample preparation methods.

  4. Segregation and temperature effect on the atomic structure of Bi30Ga70 liquid alloy

    Science.gov (United States)

    Sbihi, D. Es; Grosdidier, B.; Kaban, I.; Gruner, S.; Hoyer, W.; Gasser, J.-G.

    2009-06-01

    We investigate the structure of liquid monotectic alloy Bi30Ga70 above and below the critical point. The three-dimensional structure at 265 °C is modelled by means of the reverse Monte Carlo simulation technique using neutron and x-ray diffraction experimental data. It is shown that atomic segregation on the short-range scale exists in the liquid Bi30Ga70 slightly above the critical temperature (TC = 262 °C). We present also the structure factors of Bi30Ga70 liquid alloy under the critical point at 240 and 230 °C obtained with neutron diffraction to highlight the temperature effect in the atomic structure.

  5. Evolution of local atomic structure during solidification of Al2Au liquid: An ab initio study

    Energy Technology Data Exchange (ETDEWEB)

    Xiong, L H; Lou, H B; Wang, X D; Debela, T T; Cao, Q P; Zhang, D X; Wang, S Y; Wang, C Z; Jiang, J Z

    2014-04-01

    The local atomic structure evolution in Al2Au alloy during solidification from 2000 K to 400 K was studied by ab initio molecular dynamics simulations and analyzed using the structure factor, pair correlation functions, bond angle distributions, the Honeycutt-Anderson (HA) index and Voronoi tessellation methods. It was found that the icosahedral-like clusters are negligible in the Al2Au stable liquid and supercooled liquid states, and the most abundant clusters are those having HA indices of 131 and 120 or Voronoi indices of < 0,4,4,0 >, < 0,3, 6,0 > and < 0,4,4,2 > with coordination numbers of 8, 9 and 10, respectively. These clusters are similar to the local atomic structures in the CaF2-type Al2Au crystal, revealing the existence of structure heredity between liquid and crystalline phase in Al2Au alloy. (C) 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.

  6. Neutron diffraction studies of atomic structures of amorphous Fe-Ge and Ni-Ge alloys

    International Nuclear Information System (INIS)

    Yamada, Kazuyoshi; Endoh, Yasuo; Ishikawa, Yoshikazu; Watanabe, Noboru.

    1980-01-01

    The structures of Ge rich amorphous Fe-Ge and Ni-Ge alloys were studied by pulsed neutron total scattering. The partial structure factors of S sub(GeGe)(Q), S sub(NiGe)(Q) and S sub(NiNi)(Q) were determined successfully by using Ni 60 isotope for the Ni-Ge alloys. The Ge atoms in the 10 at% Ni-Ge amorphous alloy were found to construct a similar atomic structure as that of the amorphous Ge, while the intermediate short range order configuration between the tetrahedral random network (TRN) and the dense random packing (DRP) structure was found for the 30 at% Ni-Ge alloy. The Ge-Ge pair correlation for this intermediate short range order could well be reproduced by the modified Ge II microcrystalline model. (author)

  7. Chemical structure of descriptors with an active hydrogen atom in certain bioregulators.

    Science.gov (United States)

    Kurchii, B A

    1996-01-01

    The chemical structure of descriptors (D) for some plant growth regulators (PGR), herbicides, pesticides and drugs is described. The presence of an active hydrogen atom in molecules is an essential factor determining biological activity of chemicals. The results obtained from the study of dependence existing between the structure of a certain substance and its biological activity may be used in designing of novel compounds which possess in biological activity.

  8. Matrix Methods for Solving Hartree-Fock Equations in Atomic Structure Calculations and Line Broadening

    Directory of Open Access Journals (Sweden)

    Thomas Gomez

    2018-04-01

    Full Text Available Atomic structure of N-electron atoms is often determined by solving the Hartree-Fock equations, which are a set of integro-differential equations. The integral part of the Hartree-Fock equations treats electron exchange, but the Hartree-Fock equations are not often treated as an integro-differential equation. The exchange term is often approximated as an inhomogeneous or an effective potential so that the Hartree-Fock equations become a set of ordinary differential equations (which can be solved using the usual shooting methods. Because the Hartree-Fock equations are an iterative-refinement method, the inhomogeneous term relies on the previous guess of the wavefunction. In addition, there are numerical complications associated with solving inhomogeneous differential equations. This work uses matrix methods to solve the Hartree-Fock equations as an integro-differential equation. It is well known that a derivative operator can be expressed as a matrix made of finite-difference coefficients; energy eigenvalues and eigenvectors can be obtained by using linear-algebra packages. The integral (exchange part of the Hartree-Fock equation can be approximated as a sum and written as a matrix. The Hartree-Fock equations can be solved as a matrix that is the sum of the differential and integral matrices. We compare calculations using this method against experiment and standard atomic structure calculations. This matrix method can also be used to solve for free-electron wavefunctions, thus improving how the atoms and free electrons interact. This technique is important for spectral line broadening in two ways: it improves the atomic structure calculations, and it improves the motion of the plasma electrons that collide with the atom.

  9. Nanoscale structure and atomic disorder in the iron-based chalcogenides

    Directory of Open Access Journals (Sweden)

    Naurang Lal Saini

    2013-01-01

    Full Text Available The multiband iron-based superconductors have layered structure with a phase diagram characterized by a complex interplay of charge, spin and lattice excitations, with nanoscale atomic structure playing a key role in their fundamental electronic properties. In this paper, we briefly review nanoscale structure and atomic disorder in iron-based chalcogenide superconductors. We focus on the Fe(Se,S1−xTex (11-type and K0.8Fe1.6Se2 (122-type systems, discussing their local structure obtained by extended x-ray absorption fine structure. Local structure studies on the Fe(Se,S1−xTex system reveal clear nanoscale phase separation characterized by coexisting components of different atomic configurations, similar to the case of random alloys. In fact, the Fe–Se/S and Fe–Te distances in the ternary Fe(Se,S1−xTex are found to be closer to the respective distances in the binary FeSe/FeS and FeTe systems, showing significant divergence of the local structure from the average one. The observed features are characteristic of ternary random alloys, indicating breaking of the local symmetry in these materials. On the other hand, K0.8Fe1.6Se2 is known for phase separation in an iron-vacancy ordered phase and an in-plane compressed lattice phase. The local structure of these 122-type chalcogenides shows that this system is characterized by a large local disorder. Indeed, the experiments suggest a nanoscale glassy phase in K0.8Fe1.6Se2, with the superconductivity being similar to the granular materials. While the 11-type structure has no spacer layer, the 122-type structure contains intercalated atoms unlike the 1111-type REFeAsO (RE = rare earth oxypnictides, having well-defined REO spacer layers. It is clear that the interlayer atomic correlations in these iron-based superconducting structures play an important role in structural stability as well as superconductivity and magnetism.

  10. Atomic-scale structure of single-layer MoS2 nanoclusters

    DEFF Research Database (Denmark)

    Helveg, S.; Lauritsen, J. V.; Lægsgaard, E.

    2000-01-01

    We have studied using scanning tunneling microscopy (STM) the atomic-scale realm of molybdenum disulfide (MoS2) nanoclusters, which are of interest as a model system in hydrodesulfurization catalysis. The STM gives the first real space images of the shape and edge structure of single-layer MoS2 n...... nanoparticles synthesized on Au(lll), and establishes a new picture of the active edge sires of the nanoclusters. The results demonstrate a way to get detailed atomic-scale information on catalysts in general....

  11. Site specific incorporation of heavy atom-containing unnatural amino acids into proteins for structure determination

    Science.gov (United States)

    Xie, Jianming [San Diego, CA; Wang, Lei [San Diego, CA; Wu, Ning [Boston, MA; Schultz, Peter G [La Jolla, CA

    2008-07-15

    Translation systems and other compositions including orthogonal aminoacyl tRNA-synthetases that preferentially charge an orthogonal tRNA with an iodinated or brominated amino acid are provided. Nucleic acids encoding such synthetases are also described, as are methods and kits for producing proteins including heavy atom-containing amino acids, e.g., brominated or iodinated amino acids. Methods of determining the structure of a protein, e.g., a protein into which a heavy atom has been site-specifically incorporated through use of an orthogonal tRNA/aminoacyl tRNA-synthetase pair, are also described.

  12. Local atomic and crystal structure rearrangement during the martensitic transformation in Ti50Ni25Cu25 shape memory alloy

    International Nuclear Information System (INIS)

    Menushenkov, Alexey; Grishina, Olga; Shelyakov, Alexander; Yaroslavtsev, Alexander; Zubavichus, Yan; Veligzhanin, Alexey; Bednarcik, Jozef; Chernikov, Roman; Sitnikov, Nikolay

    2014-01-01

    Highlights: • Local crystalline structure of TiNiCu SMA is investigated using EXAFS. • Peculiarities of Ni and Cu local environment are found. • Ti atoms show greater mobility relative to Ni atoms. • Ni local environment change is significant for shape memory effect. -- Abstract: The changes of crystal structure and local crystalline environment of Ti, Ni and Cu atoms in Ti 50 Ni 25 Cu 25 shape memory alloy are investigated using X-ray diffraction and extended X-ray absorption fine structure spectroscopy (EXAFS) in temperature range of martensite transformation. The analysis of the EXAFS-spectra shows that the bonds involving Ni atoms have the highest degree of disorder and the change in the local environment around Ni atoms is significant for the occurrence of the shape memory effect, while Cu atoms occupy the normal positions in the crystallographic structure and have the lowest displacement amplitude leading to the stabilization of both phases

  13. Rapid increase of near atomic resolution virus capsid structures determined by cryo-electron microscopy.

    Science.gov (United States)

    Ho, Phuong T; Reddy, Vijay S

    2018-01-01

    The recent technological advances in electron microscopes, detectors, as well as image processing and reconstruction software have brought single particle cryo-electron microscopy (cryo-EM) into prominence for determining structures of bio-molecules at near atomic resolution. This has been particularly true for virus capsids, ribosomes, and other large assemblies, which have been the ideal specimens for structural studies by cryo-EM approaches. An analysis of time series metadata of virus structures on the methods of structure determination, resolution of the structures, and size of the virus particles revealed a rapid increase in the virus structures determined by cryo-EM at near atomic resolution since 2010. In addition, the data highlight the median resolution (∼3.0 Å) and size (∼310.0 Å in diameter) of the virus particles determined by X-ray crystallography while no such limits exist for cryo-EM structures, which have a median diameter of 508 Å. Notably, cryo-EM virus structures in the last four years have a median resolution of 3.9 Å. Taken together with minimal sample requirements, not needing diffraction quality crystals, and being able to achieve similar resolutions of the crystal structures makes cryo-EM the method of choice for current and future virus capsid structure determinations. Copyright © 2017 Elsevier Inc. All rights reserved.

  14. Atomic structure of a metal-supported two-dimensional germania film

    Science.gov (United States)

    Lewandowski, Adrián Leandro; Schlexer, Philomena; Büchner, Christin; Davis, Earl M.; Burrall, Hannah; Burson, Kristen M.; Schneider, Wolf-Dieter; Heyde, Markus; Pacchioni, Gianfranco; Freund, Hans-Joachim

    2018-03-01

    The growth and microscopic characterization of two-dimensional germania films is presented. Germanium oxide monolayer films were grown on Ru(0001) by physical vapor deposition and subsequent annealing in oxygen. We obtain a comprehensive image of the germania film structure by combining intensity-voltage low-energy electron diffraction (I/V-LEED) and ab initio density functional theory (DFT) analysis with atomic-resolution scanning tunneling microscopy (STM) imaging. For benchmarking purposes, the bare Ru(0001) substrate and the (2 ×2 )3 O covered Ru(0001) were analyzed with I/V-LEED with respect to previous reports. STM topographic images of the germania film reveal a hexagonal network where the oxygen and germanium atom positions appear in different imaging contrasts. For quantitative LEED, the best agreement has been achieved with DFT structures where the germanium atoms are located preferentially on the top and fcc hollow sites of the Ru(0001) substrate. Moreover, in these atomically flat germania films, local site geometries, i.e., tetrahedral building blocks, ring structures, and domain boundaries, have been identified, indicating possible pathways towards two-dimensional amorphous networks.

  15. Atomic structure and edge magnetism in MoS(2+x) parallelogram shaped platelets.

    Science.gov (United States)

    Karthikeyan, J; Kumar, Vijay; Murugan, P

    2013-08-21

    The structural, electronic, and magnetic properties of MoS(2+x) parallelogram shaped platelets having m and n Mo atoms on the adjoining edges have been studied using first principles calculations and by varying m and n from 1 to 6. These platelets have 100% S coverage on two adjoining edges while 50% S coverage on the other two edges. The structural stability of the platelets increases with size but the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap in general decreases. There is a triangular metallic corner at the intersection of 100% S covered edges of the platelets when m = n. On the other hand magnetism is observed on the 50% S covered edges of the platelets for the sizes greater than that of the (3,4) platelet. The magnetic moments mainly arise from the undercoordinated S(2c) atoms at the 50% S covered edges rather than from Mo atoms. The criteria for the existence of the magnetic moments on S(2c) atoms are suggested and the electronic structure of the platelets on the edges as well as inside is discussed.

  16. Novel low-dose imaging technique for characterizing atomic structures through scanning transmission electron microscope

    Science.gov (United States)

    Su, Chia-Ping; Syu, Wei-Jhe; Hsiao, Chien-Nan; Lai, Ping-Shan; Chen, Chien-Chun

    2017-08-01

    To investigate dislocations or heterostructures across interfaces is now of great interest to condensed matter and materials scientists. With the advances in aberration-corrected electron optics, the scanning transmission electron microscope has demonstrated its excellent capability of characterizing atomic structures within nanomaterials, and well-resolved atomic-resolution images can be obtained through long-exposure data acquisition. However, the sample drifting, carbon contamination, and radiation damage hinder further analysis, such as deriving three-dimensional (3D) structures from a series of images. In this study, a method for obtaining atomic-resolution images with significantly reduced exposure time was developed, using which an original high-resolution image with approximately one tenth the electron dose can be obtained by combining a fast-scan high-magnification image and a slow-scan low-magnification image. The feasibility of obtaining 3D atomic structures using the proposed approach was demonstrated through multislice simulation. Finally, the feasibility and accuracy of image restoration were experimentally verified. This general method cannot only apply to electron microscopy but also benefit to image radiation-sensitive materials using various light sources.

  17. Atomic structures of a monolayer of AlAs, GaAs, and InAs on Si(111)

    International Nuclear Information System (INIS)

    Lee, Geunjung; Yoon, Younggui

    2010-01-01

    We study atomic structures of a monolayer of AlAs, GaAs, and InAs on a Si(111) substrate from first-principles. The surface with the stacking sequence of ...SiSiMAsSiAs is energetically more stable than the surface with the stacking sequence of ...SiSiSiAsMAs, where M is Al, Ga, or In. The atomic structure of the three top layers of the low-energy surfaces are quite robust, irrespective of M, and the atomic structure of the AlAsSiAs terminated surface and that of the GaAsSiAs terminated surface are very similar. For the high-energy AsMAs terminated surfaces, the broken local tetrahedral symmetry plays an important role in the atomic structures. The calculated atomic structures of InAs on the Si(111) substrate depart most from the structure of crystalline Si.

  18. Insights into the Electronic Structure of Ozone and Sulfur Dioxide from Generalized Valence Bond Theory: Addition of Hydrogen Atoms.

    Science.gov (United States)

    Lindquist, Beth A; Takeshita, Tyler Y; Dunning, Thom H

    2016-05-05

    Ozone (O3) and sulfur dioxide (SO2) are valence isoelectronic species, yet their properties and reactivities differ dramatically. In particular, O3 is highly reactive, whereas SO2 is chemically relatively stable. In this paper, we investigate serial addition of hydrogen atoms to both the terminal atoms of O3 and SO2 and to the central atom of these species. It is well-known that the terminal atoms of O3 are much more amenable to bond formation than those of SO2. We show that the differences in the electronic structure of the π systems in the parent triatomic species account for the differences in the addition of hydrogen atoms to the terminal atoms of O3 and SO2. Further, we find that the π system in SO2, which is a recoupled pair bond dyad, facilitates the addition of hydrogen atoms to the sulfur atom, resulting in stable HSO2 and H2SO2 species.

  19. Atomic structure of the SbCu surface alloy: A surface X-ray diffraction study

    DEFF Research Database (Denmark)

    Meunier, I.; Gay, J.M.; Lapena, L.

    1999-01-01

    The dissolution at 400 degrees C of an antimony layer deposited at room temperature on a Cu(111) substrate leads to a surface alloy with a p(root 3x root 3)R 30 degrees x 30 degrees superstructure and a Sb composition of 1/3.We present here a structural study of this Sb-Cu compound by surface X......-ray diffraction (SXRD). The best agreement is obtained for a Cu,Sb surface layer with Sb atoms substituting 1/3 of the Cu atoms, over an essentially unperturbed Cu(111) plane. The largest relaxation is undergone by the Sb atoms which rise by 0.32+0.02 Angstrom over the mean plane of its Cu neighbours....... No substantial in-plane relaxations were observed. (C) 1999 Elsevier Science B.V. All rights reserved....

  20. Mechanical deformation of atomic-scale metallic contacts: Structure and mechanisms

    DEFF Research Database (Denmark)

    Sørensen, Mads Reinholdt; Brandbyge, Mads; Jacobsen, Karsten Wedel

    1998-01-01

    electronic conductance. Various defects such as intersecting stacking faults, local disorder, and vacancies are created during the deformation. Disordered regions act as weak spots that reduce the strength of the contacts. The disorder tends to anneal out again during the subsequent atomic rearrangements......We have simulated the mechanical deformation of atomic-scale metallic contacts under tensile strain using molecular dynamics and effective medium theory potentials. The evolution of the structure of the contacts and the underlying deformation mechanisms are described along with the calculated...... that the results measured in a nanocontact experiment depend significantly on the elastic stiffness of the experimental apparatus. For a soft setup, some of the atomic rearrangements might not be detected, whereas others are amplified....

  1. Fine- and hyperfine structure investigations of the even-parity configuration system of the atomic holmium

    Science.gov (United States)

    Stefanska, D.; Ruczkowski, J.; Elantkowska, M.; Furmann, B.

    2018-04-01

    In this work new experimental results concerning the hyperfine structure (hfs) for the even-parity level system of the holmium atom (Ho I) were obtained; additionally, hfs data obtained recently as a by-product in investigations of the odd-parity level system were summarized. In the present work the values of the magnetic dipole and the electric quadrupole hfs constants A and B were determined for 24 even-parity levels, for 14 of them for the first time. On the basis of these results, as well as on available literature data, a parametric study of the fine structure and the hyperfine structure for the even-parity configurations of atomic holmium was performed. A multi-configuration fit of 7 configurations was carried out, taking into account second-order of the perturbation theory. For unknown electronic levels predicted values of the level energies and hfs constants are given, which can facilitate further experimental investigations.

  2. Local Atomic Structure and Discommensurations in the Charge Density Wave of CeTe3

    International Nuclear Information System (INIS)

    Kim, H.J.; Tomic, A.T.; Tessmer, S.H.; Billinge, S.J.L.; Malliakas, C.D.; Kanatzidis, M.G.

    2006-01-01

    The local structure of CeTe 3 in the incommensurate charge density wave (IC-CDW) state has been obtained using atomic pair distribution function analysis of x-ray diffraction data. Local atomic distortions in the Te nets due to the CDW are larger than observed crystallographically, resulting in distinct short and long Te-Te bonds. Observation of different distortion amplitudes in the local and average structures is explained by the discommensurated nature of the CDW, since the pair distribution function is sensitive to the local displacements within the commensurate regions, whereas the crystallographic result averages over many discommensurated domains. The result is supported by STM data. This is the first quantitative local structural study within the commensurate domains in an IC-CDW system

  3. Temperature effects on the atomic structure and kinetics in single crystal electrochemistry

    Energy Technology Data Exchange (ETDEWEB)

    Gründer, Yvonne; Markovic, Nenad M.; Thompson, Paul; Lucas, Christopher A.

    2015-01-01

    The influence of temperature on the atomic structure at the electrochemical interface has been studied using in-situ surface x-ray scattering (SXS) during the formation of metal monolayers on a Au(111) electrode. For the surface reconstruction of Au(111), higher temperatures increase the mobility of surface atoms in the unreconstructed phase which then determines the surface ordering during the formation of the reconstruction. For the underpotential deposition (UPD) systems, the surface diffusion of the depositing metal adatoms is significantly reduced at low temperatures which results in the frustration of ordered structures in the case of Cu UPD, occurring on a Br-modified surface, and in the formation of a disordered Ag monolayer during Ag UPD. The results indicate that temperature changes affect the mass transport and diffusion of metal adatoms on the electrode surface. This demonstrates the importance of including temperature as a variable in studying surface structure and reactions at the electrochemical interface.

  4. Atom exchange between aqueous Fe(II) and structural Fe in clay minerals.

    Science.gov (United States)

    Neumann, Anke; Wu, Lingling; Li, Weiqiang; Beard, Brian L; Johnson, Clark M; Rosso, Kevin M; Frierdich, Andrew J; Scherer, Michelle M

    2015-03-03

    Due to their stability toward reductive dissolution, Fe-bearing clay minerals are viewed as a renewable source of Fe redox activity in diverse environments. Recent findings of interfacial electron transfer between aqueous Fe(II) and structural Fe in clay minerals and electron conduction in octahedral sheets of nontronite, however, raise the question whether Fe interaction with clay minerals is more dynamic than previously thought. Here, we use an enriched isotope tracer approach to simultaneously trace Fe atom movement from the aqueous phase to the solid ((57)Fe) and from the solid into the aqueous phase ((56)Fe). Over 6 months, we observed a significant decrease in aqueous (57)Fe isotope fraction, with a fast initial decrease which slowed after 3 days and stabilized after about 50 days. For the aqueous (56)Fe isotope fraction, we observed a similar but opposite trend, indicating that Fe atom movement had occurred in both directions: from the aqueous phase into the solid and from the solid into aqueous phase. We calculated that 5-20% of structural Fe in clay minerals NAu-1, NAu-2, and SWa-1 exchanged with aqueous Fe(II), which significantly exceeds the Fe atom layer exposed directly to solution. Calculations based on electron-hopping rates in nontronite suggest that the bulk conduction mechanism previously demonstrated for hematite1 and suggested as an explanation for the significant Fe atom exchange observed in goethite2 may be a plausible mechanism for Fe atom exchange in Fe-bearing clay minerals. Our finding of 5-20% Fe atom exchange in clay minerals indicates that we need to rethink how Fe mobility affects the macroscopic properties of Fe-bearing phyllosilicates and its role in Fe biogeochemical cycling, as well as its use in a variety of engineered applications, such as landfill liners and nuclear repositories.

  5. Study of the Adsorption of Atoms and Molecules on Silicon Surfaces: Crystallographics and Electronic Structure

    International Nuclear Information System (INIS)

    Bengio, Silvina

    2003-01-01

    This thesis work has been concerned with adsorption properties of silicon surfaces.The atomic and electronic structure of molecules and atoms adsorbed on Si has been investigated by means of photoemission experiments combined with synchrotron radiation.The quantitative atomic structure determination was held applying the photoelectron diffraction technique.This technique is sensible to the local structure of a reference atomic specie and has elemental and chemical-state specificity.This approach has been applied to three quite different systems with different degrees of complexity, Sb/Si(111) √3x √3R30 0 , H 2 O/Si(100)2x1 and NH 3 /Si(111)7x7.Our results show that Sb which forms a ( √3√3)R30 0 phase produces a bulklike-terminated Si(111)1x1 substrate free of stacking faults.Regarding the atomic structure of its interface, this study strongly favours the T4-site milkstool model over the H3 one.An important aspect regarding the H 2 O/Si(100)(2x1) system was establishing the limits of precision with which one can determine not only the location of the adsorbed hydroxyl (OH) species, but also the extent to which this adsorption modifes the asymmetric dimers of the clean surface to which it is bonded.On the Si(111)(7x7) surface the problem is particularly complex because there are several different potentially active sites for NH3 adsorption and fragmentation.The application of the PhD method, however, has shown that the majority of the N atoms are on so-called 'rest atom' sites when deposited at RT.This is consistent with the N in the NH2 chemical state.This investigation represents the first quantitative structural study of any molecular adsorbate on the complex Si(111)(7x7) surface.This atomic structures determination shows the PhD is a powerful tool for the atomic structure determination.The molecular systems interacting with the active sites of the substrate fragments producing a short-range order surface.This long-range disorder is produced by the

  6. Accelerating Atomic Orbital-based Electronic Structure Calculation via Pole Expansion plus Selected Inversion

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Lin; Chen, Mohan; Yang, Chao; He, Lixin

    2012-02-10

    We describe how to apply the recently developed pole expansion plus selected inversion (PEpSI) technique to Kohn-Sham density function theory (DFT) electronic structure calculations that are based on atomic orbital discretization. We give analytic expressions for evaluating charge density, total energy, Helmholtz free energy and atomic forces without using the eigenvalues and eigenvectors of the Kohn-Sham Hamiltonian. We also show how to update the chemical potential without using Kohn-Sham eigenvalues. The advantage of using PEpSI is that it has a much lower computational complexity than that associated with the matrix diagonalization procedure. We demonstrate the performance gain by comparing the timing of PEpSI with that of diagonalization on insulating and metallic nanotubes. For these quasi-1D systems, the complexity of PEpSI is linear with respect to the number of atoms. This linear scaling can be observed in our computational experiments when the number of atoms in a nanotube is larger than a few hundreds. Both the wall clock time and the memory requirement of PEpSI is modest. This makes it even possible to perform Kohn-Sham DFT calculations for 10,000-atom nanotubes on a single processor. We also show that the use of PEpSI does not lead to loss of accuracy required in a practical DFT calculation.

  7. Dislocations in AlGaN: Core Structure, Atom Segregation, and Optical Properties.

    Science.gov (United States)

    Massabuau, Fabien C-P; Rhode, Sneha L; Horton, Matthew K; O'Hanlon, Thomas J; Kovács, András; Zielinski, Marcin S; Kappers, Menno J; Dunin-Borkowski, Rafal E; Humphreys, Colin J; Oliver, Rachel A

    2017-08-09

    We conducted a comprehensive investigation of dislocations in Al 0.46 Ga 0.54 N. Using aberration-corrected scanning transmission electron microscopy and energy dispersive X-ray spectroscopy, the atomic structure and atom distribution at the dislocation core have been examined. We report that the core configuration of dislocations in AlGaN is consistent with that of other materials in the III-Nitride system. However, we observed that the dissociation of mixed-type dislocations is impeded by alloying GaN with AlN, which is confirmed by our experimental observation of Ga and Al atom segregation in the tensile and compressive parts of the dislocations, respectively. Investigation of the optical properties of the dislocations shows that the atom segregation at dislocations has no significant effect on the intensity recorded by cathodoluminescence in the vicinity of the dislocations. These results are in contrast with the case of dislocations in In 0.09 Ga 0.91 N where segregation of In and Ga atoms also occurs but results in carrier localization limiting non-radiative recombination at the dislocation. This study therefore sheds light on why InGaN-based devices are generally more resilient to dislocations than their AlGaN-based counterparts.

  8. Highly-nonlinear polarization-maintaining As2Se3-based photonic quasi-crystal fiber for supercontinuum generation

    Science.gov (United States)

    Zhao, Tongtong; Lian, Zhenggang; Benson, Trevor; Wang, Xin; Zhang, Wan; Lou, Shuqin

    2017-11-01

    We propose an As2Se3-based photonic quasi-crystal fiber (PQF) with high nonlinearity and birefringence. By optimizing the structure parameters, a nonlinear coefficient up to 2079 W-1km-1 can be achieved at the wavelength of 2 μm; the birefringence reaches up to the order of 10-2 due to the introduction of large circular air holes in the cladding. Using an optical pulse with a peak power of 6 kW, a pulse width of 150 fs, and a central wavelength of 2.94 μm as the pump pulse, a mid-infrared polarized supercontinuum is obtained by using a 15 mm long PQF. The spectral width for x- and y-polarizations covers 1 μm-10.2 μm and 1 μm-12.5 μm, respectively. The polarization state can be well maintained when the incident angle of the input pulse changes within ±2°. The proposed PQF, with high nonlinear coefficient and birefringence, has potential applications in mid-infrared polarization-maintaining supercontinuum generation.

  9. Local atomic structure of Zr-Cu and Zr-Cu-Al amorphous alloys investigated by EXAFS method

    International Nuclear Information System (INIS)

    Antonowicz, J.; Pietnoczka, A.; Zalewski, W.; Bacewicz, R.; Stoica, M.; Georgarakis, K.; Yavari, A.R.

    2011-01-01

    Research highlights: → Coordination number, interatomic distances and mean square atomic displacement in Zr-Cu and Zr-Cu-Al glasses. → Icosahedral symmetry in local atomic structure. → Deviation from random mixing behavior resulting from Al addition. - Abstract: We report on extended X-ray absorption fine structure (EXAFS) study of rapidly quenched Zr-Cu and Zr-Cu-Al glassy alloys. The local atomic order around Zr and Cu atoms was investigated. From the EXAFS data fitting the values of coordination number, interatomic distances and mean square atomic displacement were obtained for wide range of compositions. It was found that icosahedral symmetry rather than that of corresponding crystalline analogs dominates in the local atomic structure of Zr-Cu and Zr-Cu-Al amorphous alloys. Judging from bonding preferences we conclude that addition of Al as an alloying element results in considerable deviation from random mixing behavior observed in binary Zr-Cu alloys.

  10. Prediction of atomic structure from sequence for double helical DNA oligomers.

    Science.gov (United States)

    Farwer, Jochen; Packer, Martin J; Hunter, Christopher A

    2006-01-01

    DNA can adopt different conformations depending on the base sequence, solvent, electrolyte composition and concentration, pH, temperature, and interaction with proteins. Here we present a model for calculating the three-dimensional atomic structure of double-stranded DNA oligomers. A theoretical energy function is used for calculating the interactions within the base steps and an empirical backbone function is used to restrict the conformational space accessible to the bases and to account for the conformational coupling of neighboring steps in a sequence. Conformational searching on large structures or a large number of structures is possible, because each base step can be described by just two primary degrees of freedom (slide and shift). A genetic algorithm is used to search for low-energy structures in slide-shift space, and this allows very rapid optimization of DNA oligomers. The other base step parameters have been previously optimized for all possible slide-shift sequence combinations, and a heuristic algorithm is used to add the atomic details of the backbone conformation in the final step of the calculation. The structures obtained by this method are very similar to the corresponding X-ray crystal structures observed experimentally. The average RMSD is 2.24 Angstroms for a set of 20 oligomer structures. For 15 of these sequences, the X-ray crystal structure is the global energy minimum. The other 5 are bistable sequences that have B-form global energy minima but crystallize as A-DNA. Copyright 2005 Wiley Periodicals, Inc.

  11. On the atomic structure of liquid Ni-Si alloys: a neutron diffraction study

    Science.gov (United States)

    Gruner, S.; Marczinke, J.; Hennet, L.; Hoyer, W.; Cuello, G. J.

    2009-09-01

    The atomic structure of the liquid NiSi and NiSi2 alloys is investigated by means of neutron diffraction experiments with isotopic substitution. From experimental data-sets obtained using four Ni isotopes, partial structure factors and pair correlation functions are obtained by applying a reverse Monte Carlo modelling approach. Both alloys were found to exhibit a strong tendency to hetero-coordination within the first coordination shell. In particular, covalent Si-Si bonds with somewhat greater distances seem to influence the structure of the liquid NiSi alloy.

  12. Optically excited structural transition in atomic wires on surfaces at the quantum limit

    Science.gov (United States)

    Frigge, T.; Hafke, B.; Witte, T.; Krenzer, B.; Streubühr, C.; Samad Syed, A.; Mikšić Trontl, V.; Avigo, I.; Zhou, P.; Ligges, M.; von der Linde, D.; Bovensiepen, U.; Horn-von Hoegen, M.; Wippermann, S.; Lücke, A.; Sanna, S.; Gerstmann, U.; Schmidt, W. G.

    2017-03-01

    Transient control over the atomic potential-energy landscapes of solids could lead to new states of matter and to quantum control of nuclear motion on the timescale of lattice vibrations. Recently developed ultrafast time-resolved diffraction techniques combine ultrafast temporal manipulation with atomic-scale spatial resolution and femtosecond temporal resolution. These advances have enabled investigations of photo-induced structural changes in bulk solids that often occur on timescales as short as a few hundred femtoseconds. In contrast, experiments at surfaces and on single atomic layers such as graphene report timescales of structural changes that are orders of magnitude longer. This raises the question of whether the structural response of low-dimensional materials to femtosecond laser excitation is, in general, limited. Here we show that a photo-induced transition from the low- to high-symmetry state of a charge density wave in atomic indium (In) wires supported by a silicon (Si) surface takes place within 350 femtoseconds. The optical excitation breaks and creates In-In bonds, leading to the non-thermal excitation of soft phonon modes, and drives the structural transition in the limit of critically damped nuclear motion through coupling of these soft phonon modes to a manifold of surface and interface phonons that arise from the symmetry breaking at the silicon surface. This finding demonstrates that carefully tuned electronic excitations can create non-equilibrium potential energy surfaces that drive structural dynamics at interfaces in the quantum limit (that is, in a regime in which the nuclear motion is directed and deterministic). This technique could potentially be used to tune the dynamic response of a solid to optical excitation, and has widespread potential application, for example in ultrafast detectors.

  13. Protein structure prediction by all-atom free-energy refinement

    Science.gov (United States)

    Verma, Abhinav; Wenzel, Wolfgang

    2007-01-01

    Background The reliable prediction of protein tertiary structure from the amino acid sequence remains challenging even for small proteins. We have developed an all-atom free-energy protein forcefield (PFF01) that we could use to fold several small proteins from completely extended conformations. Because the computational cost of de-novo folding studies rises steeply with system size, this approach is unsuitable for structure prediction purposes. We therefore investigate here a low-cost free-energy relaxation protocol for protein structure prediction that combines heuristic methods for model generation with all-atom free-energy relaxation in PFF01. Results We use PFF01 to rank and cluster the conformations for 32 proteins generated by ROSETTA. For 22/10 high-quality/low quality decoy sets we select near-native conformations with an average Cα root mean square deviation of 3.03 Å/6.04 Å. The protocol incorporates an inherent reliability indicator that succeeds for 78% of the decoy sets. In over 90% of these cases near-native conformations are selected from the decoy set. This success rate is rationalized by the quality of the decoys and the selectivity of the PFF01 forcefield, which ranks near-native conformations an average 3.06 standard deviations below that of the relaxed decoys (Z-score). Conclusion All-atom free-energy relaxation with PFF01 emerges as a powerful low-cost approach toward generic de-novo protein structure prediction. The approach can be applied to large all-atom decoy sets of any origin and requires no preexisting structural information to identify the native conformation. The study provides evidence that a large class of proteins may be foldable by PFF01. PMID:17371594

  14. Improving the Physical Realism and Structural Accuracy of Protein Models by a Two-Step Atomic-Level Energy Minimization

    Science.gov (United States)

    Xu, Dong; Zhang, Yang

    2011-01-01

    Most protein structural prediction algorithms assemble structures as reduced models that represent amino acids by a reduced number of atoms to speed up the conformational search. Building accurate full-atom models from these reduced models is a necessary step toward a detailed function analysis. However, it is difficult to ensure that the atomic models retain the desired global topology while maintaining a sound local atomic geometry because the reduced models often have unphysical local distortions. To address this issue, we developed a new program, called ModRefiner, to construct and refine protein structures from Cα traces based on a two-step, atomic-level energy minimization. The main-chain structures are first constructed from initial Cα traces and the side-chain rotamers are then refined together with the backbone atoms with the use of a composite physics- and knowledge-based force field. We tested the method by performing an atomic structure refinement of 261 proteins with the initial models constructed from both ab initio and template-based structure assemblies. Compared with other state-of-art programs, ModRefiner shows improvements in both global and local structures, which have more accurate side-chain positions, better hydrogen-bonding networks, and fewer atomic overlaps. ModRefiner is freely available at http://zhanglab.ccmb.med.umich.edu/ModRefiner. PMID:22098752

  15. Improving the physical realism and structural accuracy of protein models by a two-step atomic-level energy minimization.

    Science.gov (United States)

    Xu, Dong; Zhang, Yang

    2011-11-16

    Most protein structural prediction algorithms assemble structures as reduced models that represent amino acids by a reduced number of atoms to speed up the conformational search. Building accurate full-atom models from these reduced models is a necessary step toward a detailed function analysis. However, it is difficult to ensure that the atomic models retain the desired global topology while maintaining a sound local atomic geometry because the reduced models often have unphysical local distortions. To address this issue, we developed a new program, called ModRefiner, to construct and refine protein structures from Cα traces based on a two-step, atomic-level energy minimization. The main-chain structures are first constructed from initial Cα traces and the side-chain rotamers are then refined together with the backbone atoms with the use of a composite physics- and knowledge-based force field. We tested the method by performing an atomic structure refinement of 261 proteins with the initial models constructed from both ab initio and template-based structure assemblies. Compared with other state-of-art programs, ModRefiner shows improvements in both global and local structures, which have more accurate side-chain positions, better hydrogen-bonding networks, and fewer atomic overlaps. ModRefiner is freely available at http://zhanglab.ccmb.med.umich.edu/ModRefiner. Copyright © 2011 Biophysical Society. Published by Elsevier Inc. All rights reserved.

  16. Atomic Structures of Minor Proteins VI and VII in the Human Adenovirus.

    Science.gov (United States)

    Dai, Xinghong; Wu, Lily; Sun, Ren; Zhou, Z Hong

    2017-10-04

    Human adenoviruses (Ad) are dsDNA viruses associated with infectious diseases, yet better known as tools for gene delivery and oncolytic anti-cancer therapy. Atomic structures of Ad provide the basis for the development of antivirals and for engineering efforts towards more effective applications. Since 2010, atomic models of human Ad5 have been independently derived from photographic film cryoEM and X-ray crystallography, but discrepancies exist concerning the assignment of cement proteins IIIa, VIII and IX. To clarify these discrepancies, here we have employed the technology of direct electron-counting to obtain a cryoEM structure of human Ad5 at 3.2 Å resolution. Our improved structure unambiguously confirmed our previous cryoEM models of proteins IIIa, VIII and IX and explained the likely cause of conflict in the crystallography models. The improved structure also allows the identification of three new components in the cavities of hexons - the cleaved N-terminus of precursor protein VI (pVIn), the cleaved N-terminus of precursor protein VII (pVIIn2), and mature protein VI. The binding of pVIIn2--by extension that of genome-condensing pVII--to hexons is consistent with the previously proposed dsDNA genome-capsid co-assembly for adenoviruses, which resembles that of ssRNA viruses but differs from the well-established mechanism of pumping dsDNA into a preformed protein capsid, as exemplified by tailed bacteriophages and herpesviruses. IMPORTANCE Adenovirus is a double-edged sword to humans - as a widespread pathogen and a bioengineering tool for anti-cancer and gene therapy. Atomic structure of the virus provides the basis for antiviral and application developments, but conflicting atomic models from conventional/film cryoEM and X-ray crystallography for important cement proteins IIIa, VIII, and IX have caused confusion. Using the cutting-edge cryoEM technology with electron counting, we improved the structure of human adenovirus type 5 and confirmed our

  17. Charge transfer driven surface segregation of gold atoms in 13-atom Au-Ag nanoalloys and its relevance to their structural, optical and electronic properties

    International Nuclear Information System (INIS)

    Chen Fuyi; Johnston, Roy L.

    2008-01-01

    The structural, optical and electronic properties of 13-atom Ag-Au nanoalloys are determined by a combination of global optimization using semi-empirical potentials and density functional theory calculations. A family of Au surface-segregated structures are found for core-shell Ag n Au 13-n (n = 1, 2, 3, 5, 7, 8, 9, 12) and hollow Ag n Au 13-n (n = 4, 6, 10, 11) clusters, whose stability is enhanced by directional charge transfer. The atomic ordering in core-shell structures is related to the electric dipole moment and odd-numbered surface Au-atom clusters have high moments. Their ferroelectric and ferromagnetic properties provide a potential approach for tailoring their surface plasmonic modes

  18. Electronic Structure Changes Due to Crystal Phase Switching at the Atomic Scale Limit.

    Science.gov (United States)

    Knutsson, Johan Valentin; Lehmann, Sebastian; Hjort, Martin; Lundgren, Edvin; Dick, Kimberly A; Timm, Rainer; Mikkelsen, Anders

    2017-10-24

    The perfect switching between crystal phases with different electronic structure in III-V nanowires allows for the design of superstructures with quantum wells only a single atomic layer wide. However, it has only been indirectly inferred how the electronic structure will vary down to the smallest possible crystal segments. We use low-temperature scanning tunneling microscopy and spectroscopy to directly probe the electronic structure of Zinc blende (Zb) segments in Wurtzite (Wz) InAs nanowires with atomic-scale precision. We find that the major features in the band structure change abruptly down to a single atomic layer level. Distinct Zb electronic structure signatures are observed on both the conduction and valence band sides for the smallest possible Zb segment: a single InAs bilayer. We find evidence of confined states in the region of both single and double bilayer Zb segments indicative of the formation of crystal segment quantum wells due to the smaller band gap of Zb as compared to Wz. In contrast to the internal electronic structure of the nanowire, surface states located in the band gap were found to be only weakly influenced by the presence of the smallest Zb segments. Our findings directly demonstrate the feasibility of crystal phase switching for the ultimate limit of atomistic band structure engineering of quantum confined structures. Further, it indicates that band gap values obtained for the bulk are reasonable to use even for the smallest crystal segments. However, we also find that the suppression of surface and interface states could be necessary in the use of this effect for engineering of future electronic devices.

  19. Knowledge-based instantiation of full atomic detail into coarse-grain RNA 3D structural models.

    Science.gov (United States)

    Jonikas, Magdalena A; Radmer, Randall J; Altman, Russ B

    2009-12-15

    The recent development of methods for modeling RNA 3D structures using coarse-grain approaches creates a need to bridge low- and high-resolution modeling methods. Although they contain topological information, coarse-grain models lack atomic detail, which limits their utility for some applications. We have developed a method for adding full atomic detail to coarse-grain models of RNA 3D structures. Our method [Coarse to Atomic (C2A)] uses geometries observed in known RNA crystal structures. Our method rebuilds full atomic detail from ideal coarse-grain backbones taken from crystal structures to within 1.87-3.31 A RMSD of the full atomic crystal structure. When starting from coarse-grain models generated by the modeling tool NAST, our method builds full atomic structures that are within 1.00 A RMSD of the starting structure. The resulting full atomic structures can be used as starting points for higher resolution modeling, thus bridging high- and low-resolution approaches to modeling RNA 3D structure. Code for the C2A method, as well as the examples discussed in this article, are freely available at www.simtk.org/home/c2a. russ.altman@stanford.edu

  20. Molecular dynamics simulation of chemical sputtering of hydrogen atom on layer structured graphite

    International Nuclear Information System (INIS)

    Ito, A.; Wang, Y.; Irle, S.; Morokuma, K.; Nakamura, H.

    2008-10-01

    Chemical sputtering of hydrogen atom on graphite was simulated using molecular dynamics. Especially, the layer structure of the graphite was maintained by interlayer intermolecular interaction. Three kinds of graphite surfaces, flat (0 0 0 1) surface, armchair (1 1 2-bar 0) surface and zigzag (1 0 1-bar 0) surface, are dealt with as targets of hydrogen atom bombardment. In the case of the flat surface, graphene layers were peeled off one by one and yielded molecules had chain structures. On the other hand, C 2 H 2 and H 2 are dominant yielded molecules on the armchair and zigzag surfaces, respectively. In addition, the interaction of a single hydrogen isotope on a single graphene is investigated. Adsorption, reflection and penetration rates are obtained as functions of incident energy and explain hydrogen retention on layered graphite. (author)

  1. Small angle neutron and X-ray studies of carbon structures with metal atoms

    Science.gov (United States)

    Lebedev, V. T.; Szhogina, A. A.; Bairamukov, V. Yu

    2017-05-01

    Encapsulation of metal atoms inside carbon single-wall cages or within multi-layer cells has been realized using molecular precursors and high temperature processes transforming them into desirable structures. Endohedral fullerenols Fe@C60(OH)X with 3d-metal (iron) have been studied by SANS in aqueous solutions where they form stable globular clusters with radii R C ∼ 10-12 nm and aggregation numbers N C ∼ 104. This self-assembly is a crucial feature of paramagnetic fullerenols as perspective contrast agents for Magneto-Resonance Imaging in medicine. Cellular carbon-metal structures have been created by the pyrolysis of diphthalocyanines of lanthanides and actinides. It was established that these ultra porous matrices consist of globular cells of molecular precursor size (∼ 1 nm) which are aggregated into superstructures. This provides retain of metal atoms inside matrices which may serve for safety storage of spent fuel of nuclear power plants.

  2. Microtraps for neutral atoms using superconducting structures in the critical state

    International Nuclear Information System (INIS)

    Emmert, A.; Brune, M.; Raimond, J.-M.; Nogues, G.; Lupascu, A.; Haroche, S.

    2009-01-01

    Recently demonstrated superconducting atom chips provide a platform for trapping atoms and coupling them to solid-state quantum systems. Controlling these devices requires a full understanding of the supercurrent distribution in the trapping structures. For type-II superconductors, this distribution is hysteretic in the critical state due to the partial penetration of the magnetic field in the thin superconducting film through pinned vortices. We report here an experimental observation of this memory effect. Our results are in good agreement with the predictions of the Bean model of the critical state without adjustable parameters. The memory effect allows to write and store permanent currents in micron-sized superconducting structures and paves the way toward engineered trapping potentials.

  3. Small angle neutron and X-ray studies of carbon structures with metal atoms

    International Nuclear Information System (INIS)

    Lebedev, V T; Szhogina, A A; Yu Bairamukov, V

    2017-01-01

    Encapsulation of metal atoms inside carbon single-wall cages or within multi-layer cells has been realized using molecular precursors and high temperature processes transforming them into desirable structures. Endohedral fullerenols Fe@C 60 (OH) X with 3d-metal (iron) have been studied by SANS in aqueous solutions where they form stable globular clusters with radii R C ∼ 10-12 nm and aggregation numbers N C ∼ 10 4 . This self-assembly is a crucial feature of paramagnetic fullerenols as perspective contrast agents for Magneto-Resonance Imaging in medicine. Cellular carbon-metal structures have been created by the pyrolysis of diphthalocyanines of lanthanides and actinides. It was established that these ultra porous matrices consist of globular cells of molecular precursor size (∼ 1 nm) which are aggregated into superstructures. This provides retain of metal atoms inside matrices which may serve for safety storage of spent fuel of nuclear power plants. (paper)

  4. Electronic structure engineering in silicene via atom substitution and a new two-dimensional Dirac structure Si3C

    Science.gov (United States)

    Yin, Na; Dai, Ying; Wei, Wei; Huang, Baibiao

    2018-04-01

    A lot of efforts have been made towards the band gap opening in two-dimensional silicene, the silicon version of graphene. In the present work, the electronic structures of single atom doped (B, N, Al and P) and codoped (B/N and Al/P) silicene monolayers are systematically examined on the base of density functional electronic calculations. Our results demonstrate that single atom doping can realize electron or hole doping in the silicene; while codoping, due to the syergistic effects, results in finite band gap in silicene at the Dirac point without significantly degrading the electronic properties. In addition, the characteristic of band gap shows dependence on the doping concentration. Importantly, we predict a new two-dimensional Dirac structure, the graphene-like Si3C, which also shows linear band dispersion relation around the Fermi level. Our results demonstrates an important perspective to engineer the electronic and optical properties of silicene.

  5. A robust and general Schrödinger and Dirac solver for atomic structure calculations

    Czech Academy of Sciences Publication Activity Database

    Čertík, O.; Pask, J.E.; Vackář, Jiří

    2013-01-01

    Roč. 184, č. 7 (2013), s. 1777-1791 ISSN 0010-4655 R&D Projects: GA MŠk(CZ) LC06040; GA ČR GA101/09/1630 Institutional support: RVO:68378271 Keywords : atom * electronic structure * Dirac equation * density-functional theory Subject RIV: BE - Theoretical Physics Impact factor: 2.407, year: 2013 http://www.sciencedirect.com/science/article/pii/S0010465513000714

  6. Understanding the proton radius puzzle: Nuclear structure effects in light muonic atoms

    Directory of Open Access Journals (Sweden)

    Ji Chen

    2016-01-01

    Full Text Available We present calculations of nuclear structure effects to the Lamb shift in light muonic atoms. We adopt a modern ab-initio approach by combining state-of-the-art nuclear potentials with the hyperspherical harmonics method. Our calculations are instrumental to the determination of nuclear charge radii in the Lamb shift measurements, which will shed light on the proton radius puzzle.

  7. Atomic dopants involved in the structural evolution of thermally graphitized graphene.

    Science.gov (United States)

    Yoon, Yeoheung; Seo, Sohyeon; Kim, Giyoun; Lee, Hyoyoung

    2012-10-15

    Thermally doped nitrogen atoms on the sp(2)-carbon network of reduced graphene oxide (rGO) enhance its electrical conductivity. Atomic structural information of thermally annealed graphene oxide (GO) provides an understanding on how the heteroatomic doping could affect electronic property of rGO. Herein, the spectroscopic and microscopic variations during thermal graphitization from 573 to 1,373 K are reported in two different rGO sheets, prepared by thermal annealing of GO (rGO(therm)) and post-thermal annealing of chemically nitrogen-doped rGO (post-therm-rGO(N(2)H(4))). The spectroscopic transitions of rGO(N(2)H(4)) in thermal annealing ultimately showed new oxygen-functional groups, such as cyclic edge ethers and new graphitized nitrogen atoms at 1,373 K. During the graphitization process, the microscopic evolution resolved by scanning tunneling microscopy (STM) produced more wrinkled surface morphology with graphitized nanocrystalline domains due to atomic doping of nitrogen on a post-therm-rGO(N(2)H(4)) sheet. As a result, the post-therm-rGO(N(2)H(4))-containing nitrogen showed a less defected sp(2)-carbon network, resulting in enhanced conductivity, whereas the rGO(therm) sheet containing no nitrogen had large topological defects on the basal plane of the sp(2)-carbon network. Thus, our investigation of the structural evolution of original wrinkles on a GO sheet incorporated into the graphitized N-doped rGO helps to explain how the atomic doping can enhance the electrical conductivity. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. SGO: A fast engine for ab initio atomic structure global optimization by differential evolution

    Science.gov (United States)

    Chen, Zhanghui; Jia, Weile; Jiang, Xiangwei; Li, Shu-Shen; Wang, Lin-Wang

    2017-10-01

    As the high throughout calculations and material genome approaches become more and more popular in material science, the search for optimal ways to predict atomic global minimum structure is a high research priority. This paper presents a fast method for global search of atomic structures at ab initio level. The structures global optimization (SGO) engine consists of a high-efficiency differential evolution algorithm, accelerated local relaxation methods and a plane-wave density functional theory code running on GPU machines. The purpose is to show what can be achieved by combining the superior algorithms at the different levels of the searching scheme. SGO can search the global-minimum configurations of crystals, two-dimensional materials and quantum clusters without prior symmetry restriction in a relatively short time (half or several hours for systems with less than 25 atoms), thus making such a task a routine calculation. Comparisons with other existing methods such as minima hopping and genetic algorithm are provided. One motivation of our study is to investigate the properties of magnetic systems in different phases. The SGO engine is capable of surveying the local minima surrounding the global minimum, which provides the information for the overall energy landscape of a given system. Using this capability we have found several new configurations for testing systems, explored their energy landscape, and demonstrated that the magnetic moment of metal clusters fluctuates strongly in different local minima.

  9. The Relationship Between Atomic Structure and Strain Distribution of Misfit Dislocation Cores at Cubic Heteroepitaxial Interfaces.

    Science.gov (United States)

    Wen, Cai

    2017-06-01

    The atomic reconstruction of a misfit dislocation (MD) core causes change in the strain distribution around the core. Several MD cores at the AlSb/GaAs (001) cubic zincblende interface, including a symmetrical glide set Lomer dislocation (LD), a left-displaced glide set LD, a glide set LD with an atomic step, a symmetrical shuffle set LD, and a 60° dislocation pair, were studied using simulated projected potential and aberration-corrected transmission electron microscope images. Image deconvolution was also used to restore structure images from nonoptimum-defocus images. The corresponding biaxial strain maps, ε xx (in-plane) and ε yy (out-of-plane), were obtained by geometric phase analysis using the GaAs substrate as the reference lattice. The results show that atomic structure characteristics of MD cores can be revealed by the strain maps. The strain maps should be measured from optimum-defocus images or restored structure images. Furthermore, the ε xx strain map has been found more accurate than the ε yy strain map for MD cores, and the specimen thickness should be below the critical thickness due to the influence of dynamical scattering.

  10. Structure stability and magnetism in graphene impurity complexes with embedded V and Nb atoms

    Energy Technology Data Exchange (ETDEWEB)

    Thakur, Jyoti [Department of Physics, University College, Kurukshetra University, Kurukshetra 136119, Haryana (India); Kashyap, Manish K., E-mail: manishdft@gmail.com [Department of Physics, Kurukshetra University, Kurukshetra 136119, Haryana (India); Ames Laboratory, U.S. Department of Energy, Iowa State University, Ames, IA 50011-3020 (United States); Taya, Ankur; Rani, Priti [Department of Physics, Kurukshetra University, Kurukshetra 136119, Haryana (India); Saini, Hardev S. [Department of Physics, Guru Jambheshwar University of Science & Technology, Hisar 125001, Haryana (India); Reshak, A.H. [New Technologies – Research Centre, University of West Bohemia, Univerzitni 8, 306 14 Pilsen (Czech Republic); School of Material Engineering, University Malaysia Perlis, 01007 Kangar, Perlis (Malaysia)

    2017-07-01

    Highlights: • V/Nb embedding in graphene containing monovacancies/divacancies is presented. • Spin polarization near/equal to 100% ensures use of studied nanosystems in spin filter devices. • Bandstructures are analyzed to identify shifting of Dirac cone of graphene. - Abstract: The appearance of vacancy defects could produce appropriate magnetic moment in graphene and the sensitivity to absorb atoms/molecules also increases with this. In this direction, a DFT study of embedding V and Nb atom in graphene containing monovacancies (MV) and divacancies (DV) is reported. Complete/almost complete spin polarization is detected for V/Nb embedding. The origin of magnetism has been identified via interaction of 3d-states of embedded atom with C-p states present in the vicinity of embedded site. The band structures have been analyzed to counter the observed semiconducting nature of graphene in minority spin on embedding V/Nb atom. The isosurface analysis also confirms the induced magnetism of present nanosystems. The present results reveal that these nanosystems have the potential for futuristic applications like spintronics and energy resources.

  11. Likelihood of atom–atom contacts in crystal structures of halogenated organic compounds

    Directory of Open Access Journals (Sweden)

    Christian Jelsch

    2015-05-01

    Full Text Available The likelihood of occurrence of intermolecular contacts in crystals of halogenated organic compounds has been analysed statistically using tools based on the Hirshfeld surface. Several families of small halogenated molecules (containing organic F, Cl, Br or I atoms were analysed, based on chemical composition and aromatic or aliphatic character. The behaviour of crystal contacts was also probed for molecules containing O or N. So-called halogen bonding (a halogen making short interactions with O or N, or a π interaction with C is generally disfavoured, except when H is scarce on the molecular surface. Similarly, halogen...halogen contacts are more rare than expected, except for molecules that are poor in H. In general, the H atom is found to be the preferred partner of organic halogen atoms in crystal structures. On the other hand, C...C interactions in parallel π-stacking have a high propensity to occur in halogenated aromatic molecules. The behaviour of the four different halogen species (F, Cl, Br, I is compared in several chemical composition contexts. The analysis tool can be refined by distinguishing several types for a given chemical species, such as H atoms bound to O or C. Such distinction shows, for instance, that C—H...Cl and O—H...O are the preferred interactions in compounds containing both O and Cl.

  12. Universal structure conversion method for organic molecules: From atomic connectivity to three-dimensional geometry

    International Nuclear Information System (INIS)

    Kim, Yeon Joon; Kim, Woo Youn

    2015-01-01

    We present a powerful method for the conversion of molecular structures from atomic connectivity to bond orders to three-dimensional (3D) geometries. There are a number of bond orders and 3D geometries corresponding to a given atomic connectivity. To uniquely determine an energetically more favorable one among them, we use general chemical rules without invoking any empirical parameter, which makes our method valid for any organic molecule. Specifically, we first assign a proper bond order to each atomic pair in the atomic connectivity so as to maximize their sum and the result is converted to a SMILES notation using graph theory. The corresponding 3D geometry is then obtained using force field or ab initio calculations. This method successfully reproduced the bond order matrices and 3D geometries of 10 000 molecules randomly sampled from the PubChem database with high success rates of near 100% except a few exceptional cases. As an application, we demonstrate that it can be used to search for molecular isomers efficiently

  13. Fine-structure transitions of interstellar atomic sulfur and silicon induced by collisions with helium.

    Science.gov (United States)

    Lique, F; Kłos, J; Le Picard, S D

    2018-02-21

    Atomic sulfur and silicon are important constituents of the interstellar matter and are both used as tracers of the physical conditions in interstellar shocks and outflows. We present an investigation of the spin-orbit (de-)excitation of S( 3 P) and Si( 3 P) atoms induced by collisions with helium with the aim to improve the determination of atomic sulfur and silicon abundances in the interstellar medium from S and Si emission spectra. Quantum-mechanical calculations have been performed in order to determine rate coefficients for the fine-structure transitions in the 5-1000 K temperature range. The scattering calculations are based on new highly correlated ab initio potentials. The theoretical results show that the (de-)excitation of Si is much faster than that of S. The rate coefficients deduced from this study are in good agreement with previous experimental and theoretical findings despite some deviations at low temperatures. From the computation of critical densities defined as the ratios between Einstein coefficients and the sum of the relevant collisional de-excitation rate coefficients, we show that local thermodynamic equilibrium conditions are not fulfilled for analyzing S and Si emission spectra observed in the interstellar medium. Hence, the present rate coefficients will be extremely useful for the accurate determination of interstellar atomic sulfur and silicon abundances.

  14. Formulation of probabilistic models of protein structure in atomic detail using the reference ratio method

    DEFF Research Database (Denmark)

    Valentin, Jan B.; Andreetta, Christian; Boomsma, Wouter

    2014-01-01

    We propose a method to formulate probabilistic models of protein structure in atomic detail, for a given amino acid sequence, based on Bayesian principles, while retaining a close link to physics. We start from two previously developed probabilistic models of protein structure on a local length...... the parameters of the nonlocal model from the native structure without loss of generality. The local and nonlocal models are combined using the reference ratio method, which is a well-justified probabilistic construction. For evaluation, we use the resulting joint models to predict the structure of four proteins....... The results indicate that the proposed method and the probabilistic models show considerable promise for probabilistic protein structure prediction and related applications. © 2013 Wiley Periodicals, Inc....

  15. Atom-by-atom assembly

    International Nuclear Information System (INIS)

    Hla, Saw Wai

    2014-01-01

    Atomic manipulation using a scanning tunneling microscope (STM) tip enables the construction of quantum structures on an atom-by-atom basis, as well as the investigation of the electronic and dynamical properties of individual atoms on a one-atom-at-a-time basis. An STM is not only an instrument that is used to ‘see’ individual atoms by means of imaging, but is also a tool that is used to ‘touch’ and ‘take’ the atoms, or to ‘hear’ their movements. Therefore, the STM can be considered as the ‘eyes’, ‘hands’ and ‘ears’ of the scientists, connecting our macroscopic world to the exciting atomic world. In this article, various STM atom manipulation schemes and their example applications are described. The future directions of atomic level assembly on surfaces using scanning probe tips are also discussed. (review article)

  16. Chain-Branching Control of the Atomic Structure of Alkanethiol-Based Gold–Sulfur Interfaces

    DEFF Research Database (Denmark)

    Wang, Yun; Chi, Qijin; Zhang, Jingdong

    2011-01-01

    Density functional theory structure calculations at 0 K and simulations at 300 K of observed high-resolution in situ scanning tunneling microscopy (STM) images reveal three different atomic-interface structures for the self-assembled monolayers (SAMs) of three isomeric butanethiols on Au(111......): direct binding to the Au(111) surface without pitting, binding to adatoms above a regular surface with extensive pitting, and binding to adatoms with local surface vacancies and some pitting. Thermal motions are shown to produce some observed STM features, with a very tight energy balance controlling...

  17. ZnO: Hydroquinone superlattice structures fabricated by atomic/molecular layer deposition

    International Nuclear Information System (INIS)

    Tynell, Tommi; Karppinen, Maarit

    2014-01-01

    Here we employ atomic layer deposition in combination with molecular layer deposition to deposit crystalline thin films of ZnO interspersed with single layers of hydroquinone in an effort to create hybrid inorganic–organic superlattice structures. The ratio of the ZnO and hydroquinone deposition cycles is varied between 199:1 and 1:1, and the structure of the resultant thin films is verified with X-ray diffraction and reflectivity techniques. Clear evidence of the formation of a superlattice-type structure is observed in the X-ray reflectivity patterns and the presence of organic bonds in the films corresponding to the structure of hydroquinone is confirmed with Fourier transform infrared spectroscopy measurements. We anticipate that hybrid superlattice structures such as the ones described in this work have the potential to be of great importance for future applications where the precise control of different inorganic and organic layers in hybrid superlattice materials is required. - Highlights: • Inorganic–organic superlattices can be made by atomic/molecular layer deposition. • This is demonstrated here for ZnO and hydroquinone (HQ). • The ratio of the ZnO and HQ layers is varied between 199:1 and 14:1. • The resultant thin films are crystalline

  18. Near-atomic structure of Japanese encephalitis virus reveals critical determinants of virulence and stability.

    Science.gov (United States)

    Wang, Xiangxi; Li, Shi-Hua; Zhu, Ling; Nian, Qing-Gong; Yuan, Shuai; Gao, Qiang; Hu, Zhongyu; Ye, Qing; Li, Xiao-Feng; Xie, Dong-Yang; Shaw, Neil; Wang, Junzhi; Walter, Thomas S; Huiskonen, Juha T; Fry, Elizabeth E; Qin, Cheng-Feng; Stuart, David I; Rao, Zihe

    2017-04-26

    Although several different flaviviruses may cause encephalitis, Japanese encephalitis virus is the most significant, being responsible for thousands of deaths each year in Asia. The structural and molecular basis of this encephalitis is not fully understood. Here, we report the cryo-electron microscopy structure of mature Japanese encephalitis virus at near-atomic resolution, which reveals an unusual "hole" on the surface, surrounded by five encephalitic-specific motifs implicated in receptor binding. Glu138 of E, which is highly conserved in encephalitic flaviviruses, maps onto one of these motifs and is essential for binding to neuroblastoma cells, with the E138K mutation abrogating the neurovirulence and neuroinvasiveness of Japanese encephalitis virus in mice. We also identify structural elements modulating viral stability, notably Gln264 of E, which, when replaced by His264 strengthens a hydrogen-bonding network, leading to a more stable virus. These studies unveil determinants of neurovirulence and stability in Japanese encephalitis virus, opening up new avenues for therapeutic interventions against neurotropic flaviviruses.Japanese encephalitis virus (JEV) is a Flavivirus responsible for thousands of deaths every year for which there are no specific anti-virals. Here, Wang et al. report the cryo-EM structure of mature JEV at near-atomic resolution and identify structural elements that modulate stability and virulence.

  19. Non-Markovian decay of a three-level cascade atom in a structured reservoir

    International Nuclear Information System (INIS)

    Dalton, B.J.; Garraway, B.M.

    2003-01-01

    The dynamics of a three-level atom in a cascade (or ladder) configuration with both transitions coupled to a single structured reservoir of quantized electromagnetic field modes is treated using Laplace transform methods applied to the coupled amplitude equations. In this system two-photon excitation of the reservoir occurs, and both sequences for emitting the two photons are allowed and included in the theory. An integral equation is found to govern the complex amplitudes of interest. It is shown that the dynamics of the atomic system is completely determined in terms of reservoir structure functions, which are products of the mode density with the coupling constant squared. This dependence on reservoir structure functions rather than on the mode density or coupling constants alone, shows that it may be possible to extend pseudomode theory to treat multiphoton excitation of a structured reservoir--pseudomodes being introduced in one-one correspondence with the poles of reservoir structure functions in the complex frequency plane. A general numerical method for solving the integral equations based on discretizing frequency space, and applicable to different structured reservoirs such as high-Q cavities and photonic band-gap systems, is presented. An application to a high-Q-cavity case with identical Lorentzian reservoir structure functions is made, and the non-Markovian decay of the excited state shown. A formal solution to the integral equations in terms of right and left eigenfunctions of a non-Hermitian kernel is also given. The dynamics of the cascade atom, with the two transitions coupled to two separate structured reservoirs of quantized electromagnetic field modes, is treated similarly to the single structured reservoir situation. Again the dynamics only depends on reservoir structure functions. As only one sequence of emitting the two photons now occurs, the integral equation for the amplitudes can be solved analytically. The non-Markovian decay of the

  20. Fine- and hyperfine structure investigations of even configuration system of atomic terbium

    Science.gov (United States)

    Stefanska, D.; Elantkowska, M.; Ruczkowski, J.; Furmann, B.

    2017-03-01

    In this work a parametric study of the fine structure (fs) and the hyperfine structure (hfs) for the even-parity configurations of atomic terbium (Tb I) is presented, based in considerable part on the new experimental results. Measurements on 134 spectral lines were performed by laser induced fluorescence (LIF) in a hollow cathode discharge lamp; on this basis, the hyperfine structure constants A and B were determined for 52 even-parity levels belonging to the configurations 4f85d6s2, 4f85d26s or 4f96s6p; in all the cases those levels were involved in the transitions investigated as the lower levels. For 40 levels the hfs was examined for the first time, and for the remaining 12 levels the new measurements supplement our earlier results. As a by-product, also preliminary values of the hfs constants for 84 odd-parity levels were determined (the investigations of the odd-parity levels system in the terbium atom are still in progress). This huge amount of new experimental data, supplemented by our earlier published results, were considered for the fine and hyperfine structure analysis. A multi-configuration fit of 7 configurations was performed, taking into account second-order of perturbation theory, including the effects of closed shell-open shell excitations. Predicted values of the level energies, as well as of magnetic dipole and electric quadrupole hyperfine structure constants A and B, are quoted in cases when no experimental values are available. By combining our experimental data with our own semi-empirical procedure it was possible to identify correctly the lower and upper level of the line 544.1440 nm measured by Childs with the use of the atomic-beam laser-rf double-resonance technique (Childs, J Opt Soc Am B 9;1992:191-6).

  1. Structure and transport at grain boundaries in polycrystalline olivine: An atomic-scale perspective

    Science.gov (United States)

    Mantisi, Boris; Sator, Nicolas; Guillot, Bertrand

    2017-12-01

    Structure and transport properties at grain boundaries in polycrystalline olivine have been investigated at the atomic scale by molecular dynamics simulation (MD) using an empirical ionocovalent interaction potential. On the time scale of the simulation (a few tens of nanoseconds for a system size of ∼650,000 atoms) grain boundaries and grain interior were identified by mapping the atomic displacements along the simulation run. In the investigated temperature range (1300-1700 K) the mean thickness of the grain boundary phase is evaluated between 0.5 and 2 nm, a value which depends on temperature and grain size. The structure of the grain boundary phase is found to be disordered (amorphous-like) and is different from the one exhibited by the supercooled liquid. The self-diffusion coefficients of major elements in the intergranular region range from ∼10-13 to 10-10 m2/s between 1300 and 1700 K (with DSigb viscosity has been evaluated from the Green-Kubo relation expressing the viscosity as function of the stress tensor time correlation function. In spite of a slow convergence of the calculation by MD, the grain boundary viscosity was estimated about ∼105 Pa s at 1500 K, a value in agreement with high-temperature viscoelastic relaxation data. An interesting information gained from MD is that sliding at grain boundaries is essentially controlled by the internal friction between the intergranular phase and the grain edges.

  2. A real-time all-atom structural search engine for proteins.

    Science.gov (United States)

    Gonzalez, Gabriel; Hannigan, Brett; DeGrado, William F

    2014-07-01

    Protein designers use a wide variety of software tools for de novo design, yet their repertoire still lacks a fast and interactive all-atom search engine. To solve this, we have built the Suns program: a real-time, atomic search engine integrated into the PyMOL molecular visualization system. Users build atomic-level structural search queries within PyMOL and receive a stream of search results aligned to their query within a few seconds. This instant feedback cycle enables a new "designability"-inspired approach to protein design where the designer searches for and interactively incorporates native-like fragments from proven protein structures. We demonstrate the use of Suns to interactively build protein motifs, tertiary interactions, and to identify scaffolds compatible with hot-spot residues. The official web site and installer are located at http://www.degradolab.org/suns/ and the source code is hosted at https://github.com/godotgildor/Suns (PyMOL plugin, BSD license), https://github.com/Gabriel439/suns-cmd (command line client, BSD license), and https://github.com/Gabriel439/suns-search (search engine server, GPLv2 license).

  3. Atomic scale imaging of structural changes in solid electrolyte lanthanum lithium niobate upon annealing

    International Nuclear Information System (INIS)

    Hu, Xiaobing; Fisher, Craig A.J.; Kobayashi, Shunsuke; Ikuhara, Yumi H.; Fujiwara, Yasuyuki; Hoshikawa, Keigo; Moriwake, Hiroki; Kohama, Keiichi; Iba, Hideki; Ikuhara, Yuichi

    2017-01-01

    La (1-x)/3 Li x NbO 3 (LLNbO) is a promising electrolyte material for solid-state lithium-ion batteries because it is stable in contact with Li metal and contains a high concentration of intrinsic Li-ion vacancies. One strategy for improving its ionic conductivity and making it more competitive with other solid-state Li-ion electrolytes is to disorder the Li-ion vacancies by appropriate post-synthesis heat treatment, e.g., annealing. In this study, we examine the effects of annealing on single crystals of LLNbO with Li contents x = 0.07 and 0.13 based on simultaneous atomic resolution high angle annular dark field and annular bright field imaging methods using state-of-the-art aberration corrected scanning transmission electron microscopes. It is found that La modulation within A1 layers of the cation-deficient layered perovskite structure becomes more diffuse after annealing. In addition, some La atoms move to A-site positions and O4 window positions in the nominally vacant A2 layer, while O atom columns in this layer become rumpled in the [001] p direction, indicating that the NbO 6 octahedra are more heavily distorted after annealing. The observed crystal structure differences between as-prepared and annealed single crystals explain the drop in Li-ion conductivities of LLNbO single crystals after heat treatment.

  4. Dynamic and structural studies of molecular or atomic systems through the generation of high order harmonics

    International Nuclear Information System (INIS)

    Higuet, J.

    2010-10-01

    High harmonic generation is a well known phenomenon explained by a three step model: because of the high intensity field generated by an ultrashort laser pulse, an atom or a molecule can be tunnel ionized. The ejected electron is then accelerated by the intense electric field, and eventually can recombine on its parent ion, leading to the emission of a XUV photon. Because of the generating process in itself, this light source is a promising candidate to probe the electronic structure of atoms and molecules, with an atto-second/sub-nanometer potential resolution (1 as=10 -18 s). In this work, we have studied the sensitivity of the emitted light (in terms of amplitude, but also phase and polarization) towards the electronic structure of the generating medium. We have first worked on atomic medium, then on molecules (N 2 , CO 2 , O 2 ). Comparing the experimental results with numerical simulations shows the necessity to model finely the generation process and to go beyond commonly used approximations. We have also shown the possibility to perform high harmonic spectroscopy in order to measure dynamics of complex molecules, such as Nitrogen Dioxide (NO 2 ). This technic has obtained complementary results compared to classical spectroscopy and has revealed dynamics of the electronic wave packet along a conical intersection. In this experiment, we have adapted conventional optical spectroscopy technic to the XUV spectral area, which significantly improved the signal over noise ratio. (author)

  5. Wigner’s phase-space function and atomic structure: II. Ground states for closed-shell atoms

    DEFF Research Database (Denmark)

    Springborg, Michael; Dahl, Jens Peder

    1987-01-01

    We present formulas for reduced Wigner phase-space functions for atoms, with an emphasis on the first-order spinless Wigner function. This function can be written as the sum of separate contributions from single orbitals (the natural orbitals). This allows a detailed study of the function. Here we...... display and analyze the function for the closed-shell atoms helium, beryllium, neon, argon, and zinc in the Hartree-Fock approximation. The quantum-mechanical exact results are compared with those obtained with the approximate Thomas-Fermi description of electron densities in phase space....

  6. Revealing the correlation between real-space structure and chiral magnetic order at the atomic scale

    Science.gov (United States)

    Hauptmann, Nadine; Dupé, Melanie; Hung, Tzu-Chao; Lemmens, Alexander K.; Wegner, Daniel; Dupé, Bertrand; Khajetoorians, Alexander A.

    2018-03-01

    We image simultaneously the geometric, the electronic, and the magnetic structures of a buckled iron bilayer film that exhibits chiral magnetic order. We achieve this by combining spin-polarized scanning tunneling microscopy and magnetic exchange force microscopy (SPEX) to independently characterize the geometric as well as the electronic and magnetic structures of nonflat surfaces. This new SPEX imaging technique reveals the geometric height corrugation of the reconstruction lines resulting from strong strain relaxation in the bilayer, enabling the decomposition of the real-space from the electronic structure at the atomic level and the correlation with the resultant spin-spiral ground state. By additionally utilizing adatom manipulation, we reveal the chiral magnetic ground state of portions of the unit cell that were not previously imaged with spin-polarized scanning tunneling microscopy alone. Using density functional theory, we investigate the structural and electronic properties of the reconstructed bilayer and identify the favorable stoichiometry regime in agreement with our experimental result.

  7. The evolution of structural and chemical heterogeneity during rapid solidification at gas atomization

    Science.gov (United States)

    Golod, V. M.; Sufiiarov, V. Sh

    2017-04-01

    Gas atomization is a high-performance process for manufacturing superfine metal powders. Formation of the powder particles takes place primarily through the fragmentation of alloy melt flow with high-pressure inert gas, which leads to the formation of non-uniform sized micron-scale particles and subsequent their rapid solidification due to heat exchange with gas environment. The article presents results of computer modeling of crystallization process, simulation and experimental studies of the cellular-dendrite structure formation and microsegregation in different size particles. It presents results of adaptation of the approach for local nonequilibrium solidification to conditions of crystallization at gas atomization, detected border values of the particle size at which it is possible a manifestation of diffusionless crystallization.

  8. Electronic and atomic structure of the AlnHn+2 clusters

    DEFF Research Database (Denmark)

    Martinez, Jose Ignacio; Alonso, J.A.

    2008-01-01

    The electronic and atomic structure of the family of hydrogenated Al clusters AlnHn+2 with n=4-11 has been studied using the density functional theory with the generalized gradient approximation (GGA) for exchange and correlation. All these clusters have substantial gaps between the highest...... a polyhedron of n vertices and n H atoms form strong H-Al terminal bonds; one pair of electrons is involved in each of those bonds. The remaining n+1 electron pairs form a delocalized cloud over the surface of the Al cage. The clusters fulfilling the Wade-Mingos rule have wider HOMO-LUMO gaps...... and are chemically more stable. The trends in the gap have some reflections in the form of the photoabsorption spectra, calculated in the framework of time-dependent density functional theory using the GGA single-particle energies and orbitals and a local density approximation exchange-correlation kernel....

  9. Atomic-accuracy prediction of protein loop structures through an RNA-inspired Ansatz.

    Directory of Open Access Journals (Sweden)

    Rhiju Das

    Full Text Available Consistently predicting biopolymer structure at atomic resolution from sequence alone remains a difficult problem, even for small sub-segments of large proteins. Such loop prediction challenges, which arise frequently in comparative modeling and protein design, can become intractable as loop lengths exceed 10 residues and if surrounding side-chain conformations are erased. Current approaches, such as the protein local optimization protocol or kinematic inversion closure (KIC Monte Carlo, involve stages that coarse-grain proteins, simplifying modeling but precluding a systematic search of all-atom configurations. This article introduces an alternative modeling strategy based on a 'stepwise ansatz', recently developed for RNA modeling, which posits that any realistic all-atom molecular conformation can be built up by residue-by-residue stepwise enumeration. When harnessed to a dynamic-programming-like recursion in the Rosetta framework, the resulting stepwise assembly (SWA protocol enables enumerative sampling of a 12 residue loop at a significant but achievable cost of thousands of CPU-hours. In a previously established benchmark, SWA recovers crystallographic conformations with sub-Angstrom accuracy for 19 of 20 loops, compared to 14 of 20 by KIC modeling with a comparable expenditure of computational power. Furthermore, SWA gives high accuracy results on an additional set of 15 loops highlighted in the biological literature for their irregularity or unusual length. Successes include cis-Pro touch turns, loops that pass through tunnels of other side-chains, and loops of lengths up to 24 residues. Remaining problem cases are traced to inaccuracies in the Rosetta all-atom energy function. In five additional blind tests, SWA achieves sub-Angstrom accuracy models, including the first such success in a protein/RNA binding interface, the YbxF/kink-turn interaction in the fourth 'RNA-puzzle' competition. These results establish all-atom enumeration as

  10. Adhesion and Atomic Structures of Gold on Ceria Nanostructures:The Role of Surface Structure and Oxidation State of Ceria Supports

    Energy Technology Data Exchange (ETDEWEB)

    Lin, Yuyuan [Northwestern University, Evanston; Wu, Zili [ORNL; Wen, Jianguo [Argonne National Laboratory (ANL); Poeppelmeier, Kenneth R [Northwestern University, Evanston; Marks, Laurence D [Northwestern University, Evanston

    2015-01-01

    Recent advances in heterogeneous catalysis have demonstrated that oxides supports with the same material but different shapes can result in metal catalysts with distinct catalytic properties. The shape-dependent catalysis was not well-understood owing to the lack of direct visualization of the atomic structures at metal-oxide interface. Herein, we utilized aberration-corrected electron microscopy and revealed the atomic structures of gold particles deposited on ceria nanocubes and nanorods with {100} or {111} facets exposed. For the ceria nanocube support, gold nanoparticles have extended atom layers at the metal-support interface. In contrast, regular gold nanoparticles and rafts are present on the ceria nanorod support. After hours of water gas shift reaction, the extended gold atom layers and rafts vanish, which is associated with the decrease of the catalytic activities. By understanding the atomic structures of the support surfaces, metal-support interfaces, and morphologies of the gold particles, a direct structure-property relationship is established.

  11. Quantitative structure determination of nanostructured materials using the atomic pair distribution function analysis

    Science.gov (United States)

    Masadeh, Ahmad Salah

    The employed experimental method in this Ph.D. dissertation research is the atomic pair distribution function (PDF) technique specializing in high real space resolution local structure determination. The PDF is obtained via Fourier transform from powder total scattering data including the important local structural information in the diffuse scattering intensities underneath, and in-between, the Bragg peaks. Having long been used to study liquids and amorphous materials, the PDF technique has been recently successfully applied to highly crystalline materials owing to the advances in modern X-ray and neutron sources and computing power. The conventional XRD experiments probe for the presence of periodic structure which are reflected in the Bragg peaks. Local structural deviations or disorder mainly affect the diffuse scattering background. In order to have information about both long-range order and local structure disorder, a technique that takes both Bragg and diffuse scattering need to be used, such as the atomic pair distribution function (PDF) technique. This Ph.D. work introduces a PDF based methodology to quantitatively study nanostructure materials in general. The introduced methodology have been applied to a size-dependent structural study on CdSe nanoparticles (NPs). Quantitative structural information about structure, crystallinity level, core size, NP size, and inhomogeneous internal strain in the studied NPs have been obtained. This method is generally applicable to the characterization of the nano-scale solid, many of which may exhibit complex disorder and strain. The introduced methodology have been also applied on technologically important system, ultra-small CdSe NPs.

  12. Structural, atomic Hirschfeld surface, magnetic and magnetocaloric properties of SmNi{sub 5} compound

    Energy Technology Data Exchange (ETDEWEB)

    Nouri, K., E-mail: nouri@icmpe.cnrs.fr [C.M.T.R, I.C.M.P.E, CNRS, Université Paris Est Créteil, UMR 7182, 2-8 rue Henri Dunant, F-94320 Thiais (France); Laboratoire des Sciences des Matériaux et de l' Environnement, Faculté des Sciences de Sfax- Université de Sfax, BP 1171, Sfax, 3018 (Tunisia); Jemmali, M. [Laboratoire des Sciences des Matériaux et de l' Environnement, Faculté des Sciences de Sfax- Université de Sfax, BP 1171, Sfax, 3018 (Tunisia); Chemistry Departement, College of Science and Arts at Ar-Rass, Qassim University, P.O. Box53 (Saudi Arabia); Walha, S. [Laboratoire des Sciences des Matériaux et de l' Environnement, Faculté des Sciences de Sfax- Université de Sfax, BP 1171, Sfax, 3018 (Tunisia); Zehani, K. [C.M.T.R, I.C.M.P.E, CNRS, Université Paris Est Créteil, UMR 7182, 2-8 rue Henri Dunant, F-94320 Thiais (France); Ben Salah, A. [Laboratoire des Sciences des Matériaux et de l' Environnement, Faculté des Sciences de Sfax- Université de Sfax, BP 1171, Sfax, 3018 (Tunisia); Bessais, L. [C.M.T.R, I.C.M.P.E, CNRS, Université Paris Est Créteil, UMR 7182, 2-8 rue Henri Dunant, F-94320 Thiais (France)

    2016-07-05

    The SmNi{sub 5} intermetallic compound has been investigated by arc-melting. Powder X-ray diffraction analysis and Rietveld refinement revealed that the sample crystallized in the hexagonal CaCu{sub 5}-type structure P6/mmm space group with the following lattice parameters: a = 4.9203 (1) Å, c = 3.9662 (1) Å. These lattice parameters for the compound are in good agreement with previous theoretical result and experimental data. The EDX analysis has been performed to confirm the composition of this compound. The chemical bonding in SmNi{sub 5} was analyzed using atomic Hirshfeld surfaces, and this analysis supports the presence of the structural elements and the coordination of Sm (1a), Ni (2c) and Ni (3 g). This study indicates the different types of interatomic interactions between the Sm and Ni atoms and the weak interactions between Sm–Sm atoms were also observed along the c axis. The magnetic properties and magnetocaloric effect (MCE) have been established by the magnetization and isothermal magnetization of different temperature measurements. The magnetization curve as a function of temperature shows a magnetic transition from ferromagnetic to paramagnetic state at the Curie temperature T{sub C} = 29 K. We have studied the MCE phenomena in the vicinity of magnetic phase transitions in terms of magnetic entropy change. The temperature dependence of the magnetization, the magnetic entropy changeΔS{sub M}, as well as the relative cooling power around the second-order magnetic transition and the Arrott plots for the alloys are reported. - Highlights: • The SmNi{sub 5} intermetallic compound has been investigated by arc-melting. • The chemical bonding in SmNi{sub 5} was analyzed using atomic Hirshfeld surfaces. • The second order magnetocaloric material SmNi{sub 5} is investigated.

  13. Morphology and atomic-scale structure of single-layer WS2 nanoclusters.

    Science.gov (United States)

    Füchtbauer, Henrik G; Tuxen, Anders K; Moses, Poul G; Topsøe, Henrik; Besenbacher, Flemming; Lauritsen, Jeppe V

    2013-10-14

    Two-dimensional sheets of transition metal (Mo and W) sulfides are attracting strong attention due to the unique electronic and optical properties associated with the material in its single-layer form. The single-layer MoS2 and WS2 are already in widespread commercial use in catalytic applications as both hydrotreating and hydrocracking catalysts. Consequently, characterization of the morphology and atomic structure of such particles is of utmost importance for the understanding of the catalytic active phase. However, in comparison with the related MoS2 system only little is known about the fundamental properties of single-layer WS2 (tungstenite). Here, we use an interplay of atom-resolved Scanning Tunneling Microscopy (STM) studies of Au(111)-supported WS2 nanoparticles and calculated edge structures using Density Functional Theory (DFT) to reveal the equilibrium morphology and prevalent edge structures of single-layer WS2. The STM results reveal that the single layer S-W-S sheets adopt a triangular equilibrium shape under the sulfiding conditions of the synthesis, with fully sulfided edges. The predominant edge structures are determined to be the (101[combining macron]0) W-edge, but for the smallest nanoclusters also the (1[combining macron]010) S-edges become important. DFT calculations are used to construct phase diagrams of the WS2 edges, and describe their sulfur and hydrogen coordination under different conditions, and in this way shed light on the catalytic role of WS2 edges.

  14. Doppler-free spectroscopy of the atomic rubidium fine structure using ultrafast spatial coherent control method

    Science.gov (United States)

    Kim, Minhyuk; Kim, Kyungtae; Lee, Woojun; Kim, Hyosub; Ahn, Jaewook

    2017-04-01

    Spectral programming solutions for the ultrafast spatial coherent control (USCC) method to resolve the fine-structure energy levels of atomic rubidium are reported. In USCC, a pair of counter-propagating ultrashort laser pulses are programmed to make a two-photon excitation pattern specific to particular transition pathways and atom species, thus allowing the involved transitions resolvable in space simultaneously. With a proper spectral phase and amplitude modulation, USCC has been also demonstrated for the systems with many intermediate energy levels. Pushing the limit of system complexity even further, we show here an experimental demonstration of the rubidium fine-structure excitation pattern resolvable by USCC. The spectral programming solution for the given USCC is achieved by combining a double-V-shape spectral phase function and a set of phase steps, where the former distinguishes the fine structure and the latter prevents resonant transitions. The experimental results will be presented along with its application in conjunction with the Doppler-free frequency-comb spectroscopy for rubidium hyperfine structure measurements. Samsung Science and Technology Foundation [SSTFBA1301-12].

  15. Atomic Structure of Salutaridine Reductase from the Opium Poppy (Papaver somniferum)

    Energy Technology Data Exchange (ETDEWEB)

    Higashi, Yasuhiro; Kutchan, Toni M.; Smith, Thomas J. (Danforth)

    2011-11-18

    The opium poppy (Papaver somniferum L.) is one of the oldest known medicinal plants. In the biosynthetic pathway for morphine and codeine, salutaridine is reduced to salutaridinol by salutaridine reductase (SalR; EC 1.1.1.248) using NADPH as coenzyme. Here, we report the atomic structure of SalR to a resolution of {approx}1.9 {angstrom} in the presence of NADPH. The core structure is highly homologous to other members of the short chain dehydrogenase/reductase family. The major difference is that the nicotinamide moiety and the substrate-binding pocket are covered by a loop (residues 265-279), on top of which lies a large 'flap'-like domain (residues 105-140). This configuration appears to be a combination of the two common structural themes found in other members of the short chain dehydrogenase/reductase family. Previous modeling studies suggested that substrate inhibition is due to mutually exclusive productive and nonproductive modes of substrate binding in the active site. This model was tested via site-directed mutagenesis, and a number of these mutations abrogated substrate inhibition. However, the atomic structure of SalR shows that these mutated residues are instead distributed over a wide area of the enzyme, and many are not in the active site. To explain how residues distal to the active site might affect catalysis, a model is presented whereby SalR may undergo significant conformational changes during catalytic turnover.

  16. Salient design features of secondary containment structure of Narora Atomic Power Project

    International Nuclear Information System (INIS)

    Rahalkar, B.D.

    1975-01-01

    Design of the secondary containment structure for Narora Atomic Power Project is an improvement over the two earlier structures at of Rajasthan and Kalpakkam wherein Candu-type of reactors are involved. The major improvements envisaged are : to limit the leakage through the double containment envelope to 0.1% of volume of the building per day as against 0.1% per hour achieved for earlier stations; to separate heavy water atmosphere from that of light water for effective heavy water recovery; and better man-rem budgetting by limiting inner containment structure upto boiler room floor level and making boiler room area accessible during normal operation for servicing of light water system equipment. Narora Atomic Power Station is located in the Indo-Gangetic alluvial plains in seismically active zone IV. Comprehensive soil investigation, including dynamic properties of soil is required to be undertaken as the foundation level of the containment structure is 17 M below the ground level. The salient results of this investigation relevant to the foundations as well as type of foundation proposed are presented in brief. Double containment concept similar to that adopted for Kalpakkam station is provided for this station also. However, necessary changes in design to withstand large earthquake forces are required to be made. These design problems are discussed in brief. (author)

  17. Near-atomic structural model for bacterial DNA replication initiation complex and its functional insights.

    Science.gov (United States)

    Shimizu, Masahiro; Noguchi, Yasunori; Sakiyama, Yukari; Kawakami, Hironori; Katayama, Tsutomu; Takada, Shoji

    2016-12-13

    Upon DNA replication initiation in Escherichia coli, the initiator protein DnaA forms higher-order complexes with the chromosomal origin oriC and a DNA-bending protein IHF. Although tertiary structures of DnaA and IHF have previously been elucidated, dynamic structures of oriC-DnaA-IHF complexes remain unknown. Here, combining computer simulations with biochemical assays, we obtained models at almost-atomic resolution for the central part of the oriC-DnaA-IHF complex. This complex can be divided into three subcomplexes; the left and right subcomplexes include pentameric DnaA bound in a head-to-tail manner and the middle subcomplex contains only a single DnaA. In the left and right subcomplexes, DnaA ATPases associated with various cellular activities (AAA+) domain III formed helices with specific structural differences in interdomain orientations, provoking a bend in the bound DNA. In the left subcomplex a continuous DnaA chain exists, including insertion of IHF into the DNA looping, consistent with the DNA unwinding function of the complex. The intervening spaces in those subcomplexes are crucial for DNA unwinding and loading of DnaB helicases. Taken together, this model provides a reasonable near-atomic level structural solution of the initiation complex, including the dynamic conformations and spatial arrangements of DnaA subcomplexes.

  18. Ab initio random structure search for 13-atom clusters of fcc elements

    International Nuclear Information System (INIS)

    Chou, J P; Hsing, C R; Wei, C M; Cheng, C; Chang, C M

    2013-01-01

    The 13-atom metal clusters of fcc elements (Al, Rh, Ir, Ni, Pd, Pt, Cu, Ag, Au) were studied by density functional theory calculations. The global minima were searched for by the ab initio random structure searching method. In addition to some new lowest-energy structures for Pd 13 and Au 13 , we found that the effective coordination numbers of the lowest-energy clusters would increase with the ratio of the dimer-to-bulk bond length. This correlation, together with the electronic structures of the lowest-energy clusters, divides the 13-atom clusters of these fcc elements into two groups (except for Au 13 , which prefers a two-dimensional structure due to the relativistic effect). Compact-like clusters that are composed exclusively of triangular motifs are preferred for elements without d-electrons (Al) or with (nearly) filled d-band electrons (Ni, Pd, Cu, Ag). Non-compact clusters composed mainly of square motifs connected by some triangular motifs (Rh, Ir, Pt) are favored for elements with unfilled d-band electrons. (paper)

  19. Atomic structure of the adsorption of transition metals on silicon surfaces

    International Nuclear Information System (INIS)

    Cocoletzi, G.H.; Takeuchi, N.

    2007-01-01

    Full text: Solid state devices are useful for their high sensitivity in a small volume. Applications of such devices as dose materials include semi-conducting dose-rate, and dose-reading measuring devices. Transition metals (TM) have electronic and atomic properties similar to those of rare earth elements when they are adsorbed on silicon surfaces. The interfaces of transition metals silicides with Si (111) have very small lattice mismatches, sharp interfaces, and low Schottky barrier, making them ideal in electronic devices, such as infrared detectors and rectifying contacts. In this work we shall describe our first principles total energy calculations to investigate structural properties of bulk ScSi and YSi, the two dimensional arrangement of ScSi 2 and YSi 2 on the Si(111) surface, and the growth of a few layers of ScSi 1.7 and YSi 1.7 on the Si(111) surface. Our calculated bulk structural parameters are in excellent agreement with experimental values. It will be shown that one monolayer of a TM on Si( l l 1) yields a two dimensional phase with (lxl) periodicity consisting of a layer of TM atoms on T4 sites and a Si bilayer on top. This double layer of Si atoms is very close to ideal Si(111)-(1x1) surface, but rotated 180 with respect to the rest of the crystal. More layers of TM silicide epitaxially grown on Si(l 11) result in a hexagonal structure similar to bulk ScSi2 and YSi2: graphite-like Si planes (with vacancies) intercalated with TM planes, and forming a (√3x√3) arrangement with a ScSi 1.7 and YSi 1.7 stoichiometry. The top Si layer does not contain vacancies and it does not present a graphite-like structure, but forms a bilayer arrangement as in bulk Si. (Author)

  20. Distinct atomic structures of the Ni-Nb metallic glasses formed by ion beam mixing

    International Nuclear Information System (INIS)

    Tai, K. P.; Wang, L. T.; Liu, B. X.

    2007-01-01

    Four Ni-Nb metallic glasses are obtained by ion beam mixing and their compositions are measured to be Ni 77 Nb 23 , Ni 55 Nb 45 , Ni 31 Nb 69 , and Ni 15 Nb 85 , respectively, suggesting that a composition range of 23-85 at. % of Nb is favored for metallic glass formation in the Ni-Nb system. Interestingly, diffraction analyses show that the structure of the Nb-based Ni 31 Nb 69 metallic glass is distinctly different from the structure of the Nb-based Ni 15 Nb 85 metallic glass, as the respective amorphous halos are located at 2θ≅38 and 39 deg. To explore an atomic scale description of the Ni-Nb metallic glasses, an n-body Ni-Nb potential is first constructed with an aid of the ab initio calculations and then applied to perform the molecular dynamics simulation. Simulation results determine not only the intrinsic glass forming range of the Ni-Nb system to be within 20-85 at. % of Nb, but also the exact atomic positions in the Ni-Nb metallic glasses. Through a statistical analysis of the determined atomic positions, a new dominant local packing unit is found in the Ni 15 Nb 85 metallic glass, i.e., an icositetrahedron with a coordination number to be around 14, while in Ni 31 Nb 69 metallic glasses, the dominant local packing unit is an icosahedron with a coordination number to be around 12, which has been reported for the other metallic glasses. In fact, with increasing the irradiation dose, the Ni 31 Nb 69 metallic glasses are formed through an intermediate state of face-centered-cubic-solid solution, whereas the Ni 15 Nb 85 metallic glass is through an intermediate state of body-centered-cubic-solid solution, suggesting that the structures of the constituent metals play an important role in governing the structural characteristics of the resultant metallic glasses

  1. Atomic structure of the adsorption of transition metals on silicon surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Cocoletzi, G.H. [IF-BUAP, 72000 Puebla (Mexico); Takeuchi, N. [CCMC-UNAM, Ensenada, BCN (Mexico)

    2007-07-01

    Full text: Solid state devices are useful for their high sensitivity in a small volume. Applications of such devices as dose materials include semi-conducting dose-rate, and dose-reading measuring devices. Transition metals (TM) have electronic and atomic properties similar to those of rare earth elements when they are adsorbed on silicon surfaces. The interfaces of transition metals silicides with Si (111) have very small lattice mismatches, sharp interfaces, and low Schottky barrier, making them ideal in electronic devices, such as infrared detectors and rectifying contacts. In this work we shall describe our first principles total energy calculations to investigate structural properties of bulk ScSi and YSi, the two dimensional arrangement of ScSi{sub 2} and YSi{sub 2} on the Si(111) surface, and the growth of a few layers of ScSi{sub 1.7} and YSi{sub 1.7} on the Si(111) surface. Our calculated bulk structural parameters are in excellent agreement with experimental values. It will be shown that one monolayer of a TM on Si( l l 1) yields a two dimensional phase with (lxl) periodicity consisting of a layer of TM atoms on T4 sites and a Si bilayer on top. This double layer of Si atoms is very close to ideal Si(111)-(1x1) surface, but rotated 180 with respect to the rest of the crystal. More layers of TM silicide epitaxially grown on Si(l 11) result in a hexagonal structure similar to bulk ScSi2 and YSi2: graphite-like Si planes (with vacancies) intercalated with TM planes, and forming a ({radical}3x{radical}3) arrangement with a ScSi{sub 1.7} and YSi{sub 1.7} stoichiometry. The top Si layer does not contain vacancies and it does not present a graphite-like structure, but forms a bilayer arrangement as in bulk Si. (Author)

  2. Quasi-crystalline geometry for architectural structures

    DEFF Research Database (Denmark)

    Weizierl, Barbara; Wester, Ture

    2001-01-01

    Artikel på CD-Rom 8 sider. The quasi-crystal (QC) type of material was discovered in 1983 by Dan Schechtman from Technion, Haifa. This new crystalline structure of material broke totally with the traditional conception of crystals and geometry introducing non-periodic close packing of cells...... with fivefold symmetry in 3D space. The quasi-crystal geometry can be constructed from two different cubic cells with identical rhombic facets, where the relation between the diagonals is the golden section. All cells have identical rhombic faces, identical edges and identical icosahedral/dedecahedral nodes....... The purpose of the paper is to investigate some possibilities for the application of Quasi-Crystal geometry for structures in architecture. The basis for the investigations is A: to use the Golden Cubes (the two different hexahedra consisting of rhombic facets where the length of the diagonals has the Golden...

  3. The hydrogen-atom environment of the ether oxygen atom in crystal structures of some representative muscarinic agonists

    Science.gov (United States)

    Kroon, J.; Scherrenberg, R. L.; Kooijman, H.; Kanters, J. A.

    1990-06-01

    The hypothesis that the ether oxygen atom in muscarinic agonists acts as a hydrogen-bond acceptor is supported by evidence from crystallographic data. The same evidence suggests that in such interactions N +CH⋯O bonds donated by the ligand to the receptor may be involved.

  4. MolProbity: all-atom structure validation for macromolecular crystallography

    International Nuclear Information System (INIS)

    Chen, Vincent B.; Arendall, W. Bryan III; Headd, Jeffrey J.; Keedy, Daniel A.; Immormino, Robert M.; Kapral, Gary J.; Murray, Laura W.; Richardson, Jane S.; Richardson, David C.

    2010-01-01

    MolProbity structure validation will diagnose most local errors in macromolecular crystal structures and help to guide their correction. MolProbity is a structure-validation web service that provides broad-spectrum solidly based evaluation of model quality at both the global and local levels for both proteins and nucleic acids. It relies heavily on the power and sensitivity provided by optimized hydrogen placement and all-atom contact analysis, complemented by updated versions of covalent-geometry and torsion-angle criteria. Some of the local corrections can be performed automatically in MolProbity and all of the diagnostics are presented in chart and graphical forms that help guide manual rebuilding. X-ray crystallography provides a wealth of biologically important molecular data in the form of atomic three-dimensional structures of proteins, nucleic acids and increasingly large complexes in multiple forms and states. Advances in automation, in everything from crystallization to data collection to phasing to model building to refinement, have made solving a structure using crystallography easier than ever. However, despite these improvements, local errors that can affect biological interpretation are widespread at low resolution and even high-resolution structures nearly all contain at least a few local errors such as Ramachandran outliers, flipped branched protein side chains and incorrect sugar puckers. It is critical both for the crystallographer and for the end user that there are easy and reliable methods to diagnose and correct these sorts of errors in structures. MolProbity is the authors’ contribution to helping solve this problem and this article reviews its general capabilities, reports on recent enhancements and usage, and presents evidence that the resulting improvements are now beneficially affecting the global database

  5. An All-Atom Force Field for Tertiary Structure Prediction of Helical Proteins

    Science.gov (United States)

    Herges, T.; Wenzel, W.

    2004-01-01

    We have developed an all-atom free-energy force field (PFF01) for protein tertiary structure prediction. PFF01 is based on physical interactions and was parameterized using experimental structures of a family of proteins believed to span a wide variety of possible folds. It contains empirical, although sequence-independent terms for hydrogen bonding. Its solvent-accessible surface area solvent model was first fit to transfer energies of small peptides. The parameters of the solvent model were then further optimized to stabilize the native structure of a single protein, the autonomously folding villin headpiece, against competing low-energy decoys. Here we validate the force field for five nonhomologous helical proteins with 20–60 amino acids. For each protein, decoys with 2–3 Å backbone root mean-square deviation and correct experimental Cβ–Cβ distance constraints emerge as those with the lowest energy. PMID:15507688

  6. An atomic model of HIV-1 capsid-SP1 reveals structures regulating assembly and maturation.

    Science.gov (United States)

    Schur, Florian K M; Obr, Martin; Hagen, Wim J H; Wan, William; Jakobi, Arjen J; Kirkpatrick, Joanna M; Sachse, Carsten; Kräusslich, Hans-Georg; Briggs, John A G

    2016-07-29

    Immature HIV-1 assembles at and buds from the plasma membrane before proteolytic cleavage of the viral Gag polyprotein induces structural maturation. Maturation can be blocked by maturation inhibitors (MIs), thereby abolishing infectivity. The CA (capsid) and SP1 (spacer peptide 1) region of Gag is the key regulator of assembly and maturation and is the target of MIs. We applied optimized cryo-electron tomography and subtomogram averaging to resolve this region within assembled immature HIV-1 particles at 3.9 angstrom resolution and built an atomic model. The structure reveals a network of intra- and intermolecular interactions mediating immature HIV-1 assembly. The proteolytic cleavage site between CA and SP1 is inaccessible to protease. We suggest that MIs prevent CA-SP1 cleavage by stabilizing the structure, and MI resistance develops by destabilizing CA-SP1. Copyright © 2016, American Association for the Advancement of Science.

  7. Structural properties of transition metal-Sin (n=14-16) atomic clusters

    International Nuclear Information System (INIS)

    Radny, M.W.; Kumar, V.; Kawazoe, Y.

    2003-01-01

    Full text: Structure has a central role in cluster science and is a prerequisite for elucidating many of the properties of clusters. As a consequence, much experimental and theoretical effort has been expended in order to characterize cluster structures. In this paper we demonstrate that the most energetically stable M-Si n clusters (n = 12, 14, 15, and 16) for Group IV elements are conformally limited to the so-called Frank-Kasper (FK) 14, 15 and 16 structures. By exploring the FK configuration space we have also found that the rearrangement of a M-Si FK-type cluster - by attachment of additional Si atoms - transforms the cluster to another FK-type cluster. The latter shows the preferential growth mode for the M-Si n clusters and indicates on the strong magic behaviour of the FK cluster topologies

  8. The multi-scattering-Xα method for analysis of the electronic structure of atomic clusters

    International Nuclear Information System (INIS)

    Bahurmuz, A.A.; Woo, C.H.

    1984-12-01

    A computer program, MSXALPHA, has been developed to carry out a quantum-mechanical analysis of the electronic structure of molecules and atomic clusters using the Multi-Scattering-Xα (MSXα) method. The MSXALPHA program is based on a code obtained from the University of Alberta; several improvements and new features were incorporated to increase generality and efficiency. The major ones are: (1) minimization of core memory usage, (2) reduction of execution time, (3) introduction of a dynamic core allocation scheme for a large number of arrays, (4) incorporation of an atomic program to generate numerical orbitals used to construct the initial molecular potential, and (5) inclusion of a routine to evaluate total energy. This report is divided into three parts. The first discusses the theory of the MSXα method. The second gives a detailed description of the program, MSXALPHA. The third discusses the results of calculations carried out for the methane molecule (CH 4 ) and a four-atom zirconium cluster (Zr 4 )

  9. Impacts of the 2010 Amazon drought on forest structure and function using CAO AToMS

    Science.gov (United States)

    Asner, G. P.; Martin, R. E.; Knapp, D. E.; Kennedy-Bowdoin, T.; Kellner, J.

    2012-12-01

    The 2010 Amazon mega-drought is thought to have had a widespread impact on forest condition, including tree mortality. However, no large-scale, high-resolution information exists on changes in forest structure, function, turnover or other processes in response to the drought. With the possibility of increasing drought frequency in the Amazon basin, it is now critical that we develop repeat, large-area studies to assess impacts and recovery. Using the Carnegie Airborne Observatory Airborne Taxonomic Mapping System (AToMS), we assessed the impacts of the 2010 drought by repeat flying of approximately 500,000 hectares of lowland humid tropical forest in the Peru Amazon. The CAO AToMS Visible-to-Near-Infrared (VNIR) and Visible-to-Shortwave-Infrared (VSWIR) imaging spectrometers recorded changes in forest canopy spectral, chemical and physiological state from 2009 to 2011. Areas of greatest functional change were observed near the Peru-Brazil border in areas under heavy forest use for selective logging. The CAO AToMS waveform Light Detection and Ranging (LiDAR) instruments measured highest rates of treefall and canopy gap formation in areas subjected to combined drought and logging, and on low fertility soils. The results provide the first spatially-explicit, large-scale and ecologically detailed information on the response of Amazonian forests to drought.

  10. Atomic structure calculations and identification of EUV and SXR spectral lines in Sr XXX

    Science.gov (United States)

    Goyal, Arun; Khatri, Indu; Aggarwal, Sunny; Singh, A. K.; Mohan, Man

    2015-08-01

    We report an extensive theoretical study of atomic data for Sr XXX in a wide range with L-shell electron excitations to the M-shell. We have calculated energy levels, wave-function compositions and lifetimes for lowest 113 fine structure levels and wavelengths of an extreme Ultraviolet (EUV) and soft X-ray (SXR) transitions. We have employed multi-configuration Dirac Fock method (MCDF) approach within the framework of Dirac-Coulomb Hamiltonian including quantum electrodynamics (QED) and Breit corrections. We have also presented the radiative data for electric and magnetic dipole (E1, M1) and quadrupole (E2, M2) transitions from the ground state. We have made comparisons with available energy levels compiled by NIST and achieve good agreement. But due to inadequate data in the literature, analogous relativistic distorted wave calculations have also been performed using flexible atomic code (FAC) to assess the reliability and accuracy of our results. Additionally, we have provided new atomic data for Sr XXX which is not published elsewhere in the literature and we believe that our results may be beneficial in fusion plasma research and astrophysical investigations and applications.

  11. Atomic and electronic structures of a-SiC:H from tight-binding molecular dynamics

    CERN Document Server

    Ivashchenko, V I; Shevchenko, V I; Ivashchenko, L A; Rusakov, G V

    2003-01-01

    The atomic and electronic properties of amorphous unhydrogenated (a-SiC) and hydrogenated (a-SiC:H) silicon carbides are studied using an sp sup 3 s sup * tight-binding force model with molecular dynamics simulations. The parameters of a repulsive pairwise potential are determined from ab initio pseudopotential calculations. Both carbides are generated from dilute vapours condensed from high temperature, with post-annealing at low temperature for a-SiC:H. A plausible model for the inter-atomic correlations and electronic states in a-SiC:H is suggested. According to this model, the formation of the amorphous network is weakly sensitive to the presence of hydrogen. Hydrogen passivates effectively only the weak bonds of threefold-coordinated atoms. Chemical ordering is very much affected by the cooling rate and the structure of the high-temperature vapour. The as-computed characteristics are in rather good agreement with the results for a-SiC and a-Si:H from ab initio calculations.

  12. Structural evolution and atomic dynamics in Ni-Nb metallic glasses: A molecular dynamics study

    Science.gov (United States)

    Xu, T. D.; Wang, X. D.; Zhang, H.; Cao, Q. P.; Zhang, D. X.; Jiang, J. Z.

    2017-10-01

    The composition and temperature dependence of static and dynamic structures in NixNb1-x (x = 50-70 at. %) were systematically studied using molecular dynamics with a new-released semi-empirical embedded atom method potential by Mendelev. The calculated pair correlation functions and the structure factor match well with the experimental data, demonstrating the reliability of the potential within relatively wide composition and temperature ranges. The local atomic structures were then characterized by bond angle distributions and Voronoi tessellation methods, demonstrating that the icosahedral ⟨0,0,12,0⟩ is only a small fraction in the liquid state but increases significantly during cooling and becomes dominant at 300 K. The most abundant clusters are identified as ⟨0,0,12,0⟩ and distorted icosahedron ⟨0,2,8,2⟩. The large fraction of these two clusters hints that the relatively good glass forming ability is near the eutectic point. Unlike Cu-Zr alloys, both the self-diffusion coefficient and shear viscosity are insensitive to compositions upon cooling in Ni-Nb alloys. The breakdown of the Stokes-Einstein relation happens at around 1.6Tg (Tg: glass transition temperature). In the amorphous state, the solid and liquid-like atoms can be distinguished based on the Debye-Waller factor ⟨u2⟩. The insensitivity of the dynamic properties of Ni-Nb alloys to compositions may result from the relatively simple solidification process in the phase diagram, in which only one eutectic point exists in the studied composition range.

  13. Atomic layer deposition TiO2 coated porous silicon surface: Structural characterization and morphological features

    International Nuclear Information System (INIS)

    Iatsunskyi, Igor; Jancelewicz, Mariusz; Nowaczyk, Grzegorz; Kempiński, Mateusz; Peplińska, Barbara; Jarek, Marcin; Załęski, Karol; Jurga, Stefan; Smyntyna, Valentyn

    2015-01-01

    TiO 2 thin films were grown on highly-doped p-Si (100) macro- and mesoporous structures by atomic layer deposition (ALD) using TiCl 4 and deionized water as precursors at 300 °C. The crystalline structure, chemical composition, and morphology of the deposited films and initial silicon nanostructures were investigated by scanning electron microscopy, transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, micro-Raman spectroscopy and X-ray diffraction (XRD). The mean size of TiO 2 crystallites was determined by TEM, XRD and Raman spectroscopy. It was shown that the mean crystallite size and the crystallinity of the TiO 2 are influenced dramatically by the morphology of the porous silicon, with the mesoporous silicon resulting in a much finer grain size and amorphous structure than the macroporous silicon having a partially crystal anatase phase. A simple model of the ALD layer growth inside the pores was presented. - Highlights: • The morphology and chemical composition of TiO 2 and porous Si were established. • The approximate size of TiO 2 nanocrystals was estimated. • The model of the atomic layer deposition coating in the porous Si was presented

  14. Influence of the atomic structure of crystal surfaces on the surface diffusion in medium temperature range

    International Nuclear Information System (INIS)

    Cousty, J.P.

    1981-12-01

    In this work, we have studied the influence of atomic structure of crystal surface on surface self-diffusion in the medium temperature range. Two ways are followed. First, we have measured, using a radiotracer method, the self-diffusion coefficient at 820 K (0.6 T melting) on copper surfaces both the structure and the cleanliness of which were stable during the experiment. We have shown that the interaction between mobile surface defects and steps can be studied through measurements of the anisotropy of surface self diffusion. Second, the behavior of an adatom and a surface vacancy is simulated via a molecular dynamics method, on several surfaces of a Lennard Jones crystal. An inventory of possible migration mechanisms of these surface defects has been drawn between 0.35 and 0.45 Tsub(m). The results obtained with both the methods point out the influence of the surface atomic structure in surface self-diffusion in the medium temperature range [fr

  15. Cosmic history and a candidate parent asteroid for the quasicrystal-bearing meteorite Khatyrka

    Science.gov (United States)

    Meier, Matthias M. M.; Bindi, Luca; Heck, Philipp R.; Neander, April I.; Spring, Nicole H.; Riebe, My E. I.; Maden, Colin; Baur, Heinrich; Steinhardt, Paul J.; Wieler, Rainer; Busemann, Henner

    2018-05-01

    The unique CV-type meteorite Khatyrka is the only natural sample in which "quasicrystals" and associated crystalline Cu, Al-alloys, including khatyrkite and cupalite, have been found. They are suspected to have formed in the early Solar System. To better understand the origin of these exotic phases, and the relationship of Khatyrka to other CV chondrites, we have measured He and Ne in six individual, ∼40-μm-sized olivine grains from Khatyrka. We find a cosmic-ray exposure age of about 2-4 Ma (if the meteoroid was <3 m in diameter, more if it was larger). The U, Th-He ages of the olivine grains suggest that Khatyrka experienced a relatively recent (<600 Ma) shock event, which created pressure and temperature conditions sufficient to form both the quasicrystals and the high-pressure phases found in the meteorite. We propose that the parent body of Khatyrka is the large K-type asteroid 89 Julia, based on its peculiar, but matching reflectance spectrum, evidence for an impact/shock event within the last few 100 Ma (which formed the Julia family), and its location close to strong orbital resonances, so that the Khatyrka meteoroid could plausibly have reached Earth within its rather short cosmic-ray exposure age.

  16. Origin of quantum criticality in Yb-Al-Au approximant crystal and quasicrystal

    International Nuclear Information System (INIS)

    Watanabe, Shinji; Miyake, Kazumasa

    2016-01-01

    To get insight into the mechanism of emergence of unconventional quantum criticality observed in quasicrystal Yb 15 Al 34 Au 51 , the approximant crystal Yb 14 Al 35 Au 51 is analyzed theoretically. By constructing a minimal model for the approximant crystal, the heavy quasiparticle band is shown to emerge near the Fermi level because of strong correlation of 4f electrons at Yb. We find that charge-transfer mode between 4f electron at Yb on the 3rd shell and 3p electron at Al on the 4th shell in Tsai-type cluster is considerably enhanced with almost flat momentum dependence. The mode-coupling theory shows that magnetic as well as valence susceptibility exhibits χ ∼ T -0.5 for zero-field limit and is expressed as a single scaling function of the ratio of temperature to magnetic field T/B over four decades even in the approximant crystal when some condition is satisfied by varying parameters, e.g., by applying pressure. The key origin is clarified to be due to strong locality of the critical Yb-valence fluctuation and small Brillouin zone reflecting the large unit cell, giving rise to the extremely-small characteristic energy scale. This also gives a natural explanation for the quantum criticality in the quasicrystal corresponding to the infinite limit of the unit-cell size. (author)

  17. Geometry induced sequence of nanoscale Frank–Kasper and quasicrystal mesophases in giant surfactants

    Energy Technology Data Exchange (ETDEWEB)

    Yue, Kan; Huang, Mingjun; Marson, Ryan L.; He, Jinlin; Huang, Jiahao; Zhou, Zhe; Wang, Jing; Liu, Chang; Yan, Xuesheng; Wu, Kan; Guo, Zaihong; Liu, Hao; Zhang, Wei; Ni, Peihong; Wesdemiotis, Chrys; Zhang, Wen-Bin; Glotzer, Sharon C.; Cheng, Stephen Z.D. (Akron); (Soochow); (Michigan)

    2016-11-28

    Frank–Kasper (F-K) and quasicrystal phases were originally identified in metal alloys and only sporadically reported in soft materials. These unconventional sphere-packing schemes open up possibilities to design materials with different properties. The challenge in soft materials is how to correlate complex phases built from spheres with the tunable parameters of chemical composition and molecular architecture. Here, we report a complete sequence of various highly ordered mesophases by the self-assembly of specifically designed and synthesized giant surfactants, which are conjugates of hydrophilic polyhedral oligomeric silsesquioxane cages tethered with hydrophobic polystyrene tails. We show that the occurrence of these mesophases results from nanophase separation between the heads and tails and thus is critically dependent on molecular geometry. Variations in molecular geometry achieved by changing the number of tails from one to four not only shift compositional phase boundaries but also stabilize F-K and quasicrystal phases in regions where simple phases of spheroidal micelles are typically observed. These complex self-assembled nanostructures have been identified by combining X-ray scattering techniques and real-space electron microscopy images. Brownian dynamics simulations based on a simplified molecular model confirm the architecture-induced sequence of phases. Our results demonstrate the critical role of molecular architecture in dictating the formation of supramolecular crystals with “soft” spheroidal motifs and provide guidelines to the design of unconventional self-assembled nanostructures.

  18. Atomic structure calculation of energy levels and oscillator strengths in Ti ion, 2

    International Nuclear Information System (INIS)

    Ishii, Keishi

    1983-10-01

    Energy levels and oscillator strengths are calculated for 3s-3p and 3p-3d transition arrays in Ti X, isoelectronic to Al I. The energy levels are obtained by the Slater-Condon theory of atomic structure, including explicitly the strong configuration interactions. The results are presented both in numerical tables and in diagrams. In the tables, the observed data are included for comparison, where available. The calculated weighted oscillator strengths (gf-value) are also displayed in figures, where the weighted oscillator strengths are plotted as a function of wavelength. (author)

  19. On-the-Fly Machine Learning of Atomic Potential in Density Functional Theory Structure Optimization

    Science.gov (United States)

    Jacobsen, T. L.; Jørgensen, M. S.; Hammer, B.

    2018-01-01

    Machine learning (ML) is used to derive local stability information for density functional theory calculations of systems in relation to the recently discovered SnO2 (110 )-(4 ×1 ) reconstruction. The ML model is trained on (structure, total energy) relations collected during global minimum energy search runs with an evolutionary algorithm (EA). While being built, the ML model is used to guide the EA, thereby speeding up the overall rate by which the EA succeeds. Inspection of the local atomic potentials emerging from the model further shows chemically intuitive patterns.

  20. The first multiplication atom-bond connectivity index of molecular structures in drugs.

    Science.gov (United States)

    Gao, Wei; Wang, Yiqiao; Wang, Weifan; Shi, Li

    2017-05-01

    In the field of medicine, there are a large number of new drugs synthesis every year. Before entering the clinical stage, it needs a lot of work on drug testing of the various properties. Due to the lack of a large number of laboratory technician, laboratory equipment and reagents, the drug testing of many biochemical properties are not completed. Theoretical medicine provides a theoretical way for medical researchers to obtain the pharmaceutical properties of compounds by calculation tricks. In this paper, the first multiplication atom-bond connectivity index of several common drugs structure are studied, and the accurate expressions are determined. These theoretical conclusions provide practical guiding significance for pharmaceutical engineering.

  1. Atomic structure calculation of energy levels and oscillator strenghts in Fe ion, 1

    International Nuclear Information System (INIS)

    Ishii, Keishi; Kubo, Hirotaka; Ozawa, Kunio.

    1984-01-01

    Energy levels and oscillator strengths were calculated for 3s-3p and 3p-3d transition arrays in Fe XV, isoelectronic to Mg I. The energy levels are obtained by the Slater-Condon theory of atomic structure, including explicitly the strong configuration interactions. The calculated wavelengths are presented for electric dipole transition with gf>= 0.0001. The calculated energy levels are given in diagrams, too. The theoretical spectra are also shown in graphical representation, where the gf is plotted as a function of the wavelength. The results are compared with experimental data, where available. (author)

  2. Comparing two iteration algorithms of Broyden electron density mixing through an atomic electronic structure computation

    International Nuclear Information System (INIS)

    Zhang Man-Hong

    2016-01-01

    By performing the electronic structure computation of a Si atom, we compare two iteration algorithms of Broyden electron density mixing in the literature. One was proposed by Johnson and implemented in the well-known VASP code. The other was given by Eyert. We solve the Kohn-Sham equation by using a conventional outward/inward integration of the differential equation and then connect two parts of solutions at the classical turning points, which is different from the method of the matrix eigenvalue solution as used in the VASP code. Compared to Johnson’s algorithm, the one proposed by Eyert needs fewer total iteration numbers. (paper)

  3. Tuning the electronic structure of graphene through alkali metal and halogen atom intercalation

    Science.gov (United States)

    Ahmad, Sohail; Miró, Pere; Audiffred, Martha; Heine, Thomas

    2018-04-01

    The deposition, intercalation and co-intercalation of heavy alkali metals and light halogens atoms in graphene mono- and bilayers have been studied using first principles density-functional calculations. Both the deposition and the intercalation of alkali metals gives rise to n-type doping due to the formation of M+-C- pairs. The co-intercalation of a 1:1 ratio of alkali metals and halogens derives into the formation of ionic pairs among the intercalated species, unaltering the electronic structure of the layered material.

  4. Exploring the atomic structure of 1.8nm monolayer-protected gold clusters with aberration-corrected STEM.

    Science.gov (United States)

    Liu, Jian; Jian, Nan; Ornelas, Isabel; Pattison, Alexander J; Lahtinen, Tanja; Salorinne, Kirsi; Häkkinen, Hannu; Palmer, Richard E

    2017-05-01

    Monolayer-protected (MP) Au clusters present attractive quantum systems with a range of potential applications e.g. in catalysis. Knowledge of the atomic structure is needed to obtain a full understanding of their intriguing physical and chemical properties. Here we employed aberration-corrected scanning transmission electron microscopy (ac-STEM), combined with multislice simulations, to make a round-robin investigation of the atomic structure of chemically synthesised clusters with nominal composition Au 144 (SCH 2 CH 2 Ph) 60 provided by two different research groups. The MP Au clusters were "weighed" by the atom counting method, based on their integrated intensities in the high angle annular dark field (HAADF) regime and calibrated exponent of the Z dependence. For atomic structure analysis, we compared experimental images of hundreds of clusters, with atomic resolution, against a variety of structural models. Across the size range 123-151 atoms, only 3% of clusters matched the theoretically predicted Au 144 (SR) 60 structure, while a large proportion of the clusters were amorphous (i.e. did not match any model structure). However, a distinct ring-dot feature, characteristic of local icosahedral symmetry, was observed in about 20% of the clusters. Copyright © 2017. Published by Elsevier B.V.

  5. Formulation of probabilistic models of protein structure in atomic detail using the reference ratio method.

    Science.gov (United States)

    Valentin, Jan B; Andreetta, Christian; Boomsma, Wouter; Bottaro, Sandro; Ferkinghoff-Borg, Jesper; Frellsen, Jes; Mardia, Kanti V; Tian, Pengfei; Hamelryck, Thomas

    2014-02-01

    We propose a method to formulate probabilistic models of protein structure in atomic detail, for a given amino acid sequence, based on Bayesian principles, while retaining a close link to physics. We start from two previously developed probabilistic models of protein structure on a local length scale, which concern the dihedral angles in main chain and side chains, respectively. Conceptually, this constitutes a probabilistic and continuous alternative to the use of discrete fragment and rotamer libraries. The local model is combined with a nonlocal model that involves a small number of energy terms according to a physical force field, and some information on the overall secondary structure content. In this initial study we focus on the formulation of the joint model and the evaluation of the use of an energy vector as a descriptor of a protein's nonlocal structure; hence, we derive the parameters of the nonlocal model from the native structure without loss of generality. The local and nonlocal models are combined using the reference ratio method, which is a well-justified probabilistic construction. For evaluation, we use the resulting joint models to predict the structure of four proteins. The results indicate that the proposed method and the probabilistic models show considerable promise for probabilistic protein structure prediction and related applications. Copyright © 2013 Wiley Periodicals, Inc.

  6. The Expanded FindCore Method for Identification of a Core Atom Set for Assessment of Protein Structure Prediction

    Science.gov (United States)

    Snyder, David A.; Grullon, Jennifer; Huang, Yuanpeng J.; Tejero, Roberto; Montelione, Gaetano T.

    2014-01-01

    Maximizing the scientific impact of NMR-based structure determination requires robust and statistically sound methods for assessing the precision of NMR-derived structures. In particular, a method to define a core atom set for calculating superimpositions and validating structure predictions is critical to the use of NMR-derived structures as targets in the CASP competition. FindCore (D.A. Snyder and G.T. Montelione PROTEINS 2005;59:673–686) is a superimposition independent method for identifying a core atom set, and partitioning that set into domains. However, as FindCore optimizes superimposition by sensitively excluding not-well-defined atoms, the FindCore core may not comprise all atoms suitable for use in certain applications of NMR structures, including the CASP assessment process. Adapting the FindCore approach to assess predicted models against experimental NMR structures in CASP10 required modification of the FindCore method. This paper describes conventions and a standard protocol to calculate an “Expanded FindCore” atom set suitable for validation and application in biological and biophysical contexts. A key application of the Expanded FindCore method is to identify a core set of atoms in the experimental NMR structure for which it makes sense to validate predicted protein structure models. We demonstrate the application of this Expanded FindCore method in characterizing well-defined regions of 18 NMR-derived CASP10 target structures. The Expanded FindCore protocol defines “expanded core atom sets” that match an expert’s intuition of which parts of the structure are sufficiently well-defined to use in assessing CASP model predictions. We also illustrate the impact of this analysis on the CASP GDT assessment scores. PMID:24327305

  7. Exploring the atomic structure of 1.8 nm monolayer-protected gold clusters with aberration-corrected STEM

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Jian; Jian, Nan; Ornelas, Isabel; Pattison, Alexander J. [Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom); Lahtinen, Tanja; Salorinne, Kirsi [Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä (Finland); Häkkinen, Hannu [Department of Chemistry, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä (Finland); Department of Physics, Nanoscience Center, University of Jyväskylä, FI-40014 Jyväskylä (Finland); Palmer, Richard E., E-mail: richardepalmerwork@yahoo.com [Nanoscale Physics Research Laboratory, School of Physics and Astronomy, University of Birmingham, Birmingham B15 2TT (United Kingdom)

    2017-05-15

    Monolayer-protected (MP) Au clusters present attractive quantum systems with a range of potential applications e.g. in catalysis. Knowledge of the atomic structure is needed to obtain a full understanding of their intriguing physical and chemical properties. Here we employed aberration-corrected scanning transmission electron microscopy (ac-STEM), combined with multislice simulations, to make a round-robin investigation of the atomic structure of chemically synthesised clusters with nominal composition Au{sub 144}(SCH{sub 2}CH{sub 2}Ph){sub 60} provided by two different research groups. The MP Au clusters were “weighed” by the atom counting method, based on their integrated intensities in the high angle annular dark field (HAADF) regime and calibrated exponent of the Z dependence. For atomic structure analysis, we compared experimental images of hundreds of clusters, with atomic resolution, against a variety of structural models. Across the size range 123–151 atoms, only 3% of clusters matched the theoretically predicted Au{sub 144}(SR){sub 60} structure, while a large proportion of the clusters were amorphous (i.e. did not match any model structure). However, a distinct ring-dot feature, characteristic of local icosahedral symmetry, was observed in about 20% of the clusters. - Highlights: • Chemically synthesised gold clusters were “weighed” by atom counting to get true size. • Image simulations show a few percent of clusters have the predicted atomic structure. • But a specific ring-dot feature indicates local icosahedral order in many clusters.

  8. Formation of quasicrystals and amorphous-to-quasicrystalline phase transformation kinetics in Zr65Al7.5Ni10Cu7.5Ag10 metallic glass under pressure

    DEFF Research Database (Denmark)

    Jiang, Jianzhong; Zhuang, Yanxin; Rasmussen, Helge Kildahl

    2001-01-01

    The effect of pressure on the formation of quasicrystals and the amorphous-to-quasicrystalline phase transformation kinetics in the supercooled liquid region for a Zr65Al7.5Ni10Cu7.5Ag10 metallic glass have been investigated by in situ high-pressure and high-temperature nonisothermal and isothermal...... and growth models together with the Johnson-Mehl-Avrami model. The Avrami exponent was found to be near I at all four temperatures, also indicating that atomic diffusion might involve in the amorphous-to-quasicrystalline phase transformation for the Zr65Cu7.5Al7.5Ni10Ag10 metallic glass. It is found...

  9. Atomic structure calculations and identification of EUV and SXR spectral lines in Sr XXX

    International Nuclear Information System (INIS)

    Goyal, Arun; Khatri, Indu; Aggarwal, Sunny; Singh, A.K.; Mohan, Man

    2015-01-01

    We report an extensive theoretical study of atomic data for Sr XXX in a wide range with L-shell electron excitations to the M-shell. We have calculated energy levels, wave-function compositions and lifetimes for lowest 113 fine structure levels and wavelengths of an extreme Ultraviolet (EUV) and soft X-ray (SXR) transitions. We have employed multi-configuration Dirac Fock method (MCDF) approach within the framework of Dirac–Coulomb Hamiltonian including quantum electrodynamics (QED) and Breit corrections. We have also presented the radiative data for electric and magnetic dipole (E1, M1) and quadrupole (E2, M2) transitions from the ground state. We have made comparisons with available energy levels compiled by NIST and achieve good agreement. But due to inadequate data in the literature, analogous relativistic distorted wave calculations have also been performed using flexible atomic code (FAC) to assess the reliability and accuracy of our results. Additionally, we have provided new atomic data for Sr XXX which is not published elsewhere in the literature and we believe that our results may be beneficial in fusion plasma research and astrophysical investigations and applications. - Highlights: • 113 Lowest levels for Sr XXX are calculated. • Extreme Ultraviolet (EUV) and soft-X ray (SXR) spectral lines are identified. • Wavelengths of EUV and SXR spectral lines are reported. • E1, E2, M1 and M2 transition rates, oscillator strengths and lines strengths for lowest 113 levels are presented. • Lifetimes for lowest 113 fine structure levels are provided

  10. Electrical activation and local structure of Se atoms in ion-implanted indium phosphide

    International Nuclear Information System (INIS)

    Yu, K.M.; Chan, N.; Hsu, L.

    1996-01-01

    The solid phase regrowth, dopant activation, and local environments of Se-implanted InP are investigated with ion-beam techniques and extended x-ray-absorption fine structure spectroscopy. We find that the local Se endash In structure is already established in the as-implanted amorphous InP although the Se atoms have a lower average coordination number (∼3.5) and no long-range order. After high-temperature rapid thermal annealing (950 degree C, 5 s), the amorphous InP regrows, becoming a single crystal with the Se atoms bonded to four In neighbors; however, only ∼50% of the Se becomes electrically active. Part of the Se precipitates in the form of an In endash Se phase, another part is compensated by defects which are not totally removed by annealing. The Se emdash In bond distance for a Se on a P site is 4.5% longer than the matrix In emdash P bond length, introducing large strains in the crystal. The solid solubility of Se in InP is estimated from our results to be ≅8.7x10 19 /cm 3 while the electron concentration saturates at 5.4x10 19 /cm 3 . Se atoms in InP regrown at lower temperatures in a furnace are only ∼7% electrically active and are found to have different local environments (higher coordination number and shorter bond distance) than those in the InP perfectly regrown at higher temperature. copyright 1996 American Institute of Physics

  11. Atomic physics

    CERN Document Server

    Born, Max

    1969-01-01

    The Nobel Laureate's brilliant exposition of the kinetic theory of gases, elementary particles, the nuclear atom, wave-corpuscles, atomic structure and spectral lines, electron spin and Pauli's principle, quantum statistics, molecular structure and nuclear physics. Over 40 appendices, a bibliography, numerous figures and graphs.

  12. GRASP92: a package for large-scale relativistic atomic structure calculations

    Science.gov (United States)

    Parpia, F. A.; Froese Fischer, C.; Grant, I. P.

    2006-12-01

    of CSFs sharing the same quantum numbers is determined using the configuration-interaction (CI) procedure that results upon varying the expansion coefficients to determine the extremum of a variational functional. Radial functions may be determined by numerically solving the multiconfiguration Dirac-Fock (MCDF) equations that result upon varying the orbital radial functions or some subset thereof so as to obtain an extremum of the variational functional. Radial wavefunctions may also be determined using a screened hydrogenic or Thomas-Fermi model, although these schemes generally provide initial estimates for MCDF self-consistent-field (SCF) calculations. Transition properties for pairs of ASFs are computed from matrix elements of multipole operators of the electromagnetic field. All matrix elements of CSFs are evaluated using the Racah algebra. Reasons for the new version: During recent studies using the general relativistic atomic structure package (GRASP92), several errors were found, some of which might have been present already in the earlier GRASP92 version (program ABJN_v1_0, Comput. Phys. Comm. 55 (1989) 425). These errors were reported and discussed by Froese Fischer, Gaigalas, and Ralchenko in a separate publication [C. Froese Fischer, G. Gaigalas, Y. Ralchenko, Comput. Phys. Comm. 175 (2006) 738-744. [7

  13. Structure investigation of ultra-small CdSe nanoparticles using the atomic PDF

    Science.gov (United States)

    Masadeh, Ahmad S.; Billinge, Simon J. L.; Bozin, Emil S.; McBride, James R.; Rosenthal, Sandra J.

    2011-03-01

    The size-dependent structure of CdSe nanoparticles, with diameter ranging from 1.5 to 3.6 nm, has been studied using the atomic pair distribution function (PDF) method. The samples are prepared by the methods of Peng et al, with modifications. The structure of the smallest stable size, (~ 1.5 nm), have been found to posses locally distorted wurtzite structure, with no clear evidence of a heavily disordered surface region. The PDF data of the smallest particle show an extra structural peak appears around r = 3.5 A indicates there is structure modification happened in this sample. This peak start appearing the nanoparticles PDF data gradually as nanoparticle size decreases. The structural parameters are reported quantitatively. We measure a size-dependent strain on the Cd-Se bond which reaches 1.0% at the smallest particle size. The size of the well-ordered core extracted directly from the data agrees with the size determined from other methods.

  14. Probing atomic structure in magnetic core/shell nanoparticles using synchrotron radiation.

    Science.gov (United States)

    Baker, S H; Roy, M; Thornton, S C; Qureshi, M; Binns, C

    2010-09-29

    Core/shell Fe/Cu and Fe/Au nanoparticles were prepared directly by deposition from the gas phase. A detailed study of the atomic structure in both the cores and shells of the nanoparticles was undertaken by means of extended absorption fine structure (EXAFS) measurements. For Fe/Cu nanoparticles, a Cu shell ∼ 20 monolayers thick appears similar in structure to bulk Cu and is sufficient to cause the structure in the Fe core to switch from body centred cubic (bcc; as in bulk Fe) to face centred cubic. This is not the case for thinner Cu shells, 1-2 monolayers in thickness, in which there is a considerable contraction in nearest-neighbour interatomic distance as the shell structure changes to bcc. In Fe/Au nanoparticles, the crystal structure in the Fe core remains bcc for all Au thicknesses although there is some stretching of the lattice. In thin Au shells ∼ 2 monolayers thick, there is strong contraction in interatomic distances. There does not appear to be significant alloying at the Fe/Au interface.

  15. Atomic and electronic structure transformations of silver nanoparticles under rapid cooling conditions

    Science.gov (United States)

    Lobato, I.; Rojas, J.; Landauro, C. V.; Torres, J.

    2009-02-01

    The structural evolution and dynamics of silver nanodrops Ag2869 (4.4 nm in diameter) under rapid cooling conditions have been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modelled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique are used to reveal the structural transition in the process of solidification. It is shown that Ag nanoparticles evolve into different nanostructures under different cooling processes. At a cooling rate of 1.5625 × 1013 K s-1 the nanoparticles preserve an amorphous-like structure containing a large amount of 1551 and 1541 pairs which correspond to icosahedral symmetry. For a lower cooling rate (1.5625 × 1012 K s-1), the nanoparticles transform into a crystal-like structure consisting mainly of 1421 and 1422 pairs which correspond to the face centred cubic and hexagonal close packed structures, respectively. The variations of the electronic density of states for the differently cooled nanoparticles are small, but in correspondence with the structural changes.

  16. Atomic and electronic structure transformations of silver nanoparticles under rapid cooling conditions

    International Nuclear Information System (INIS)

    Lobato, I; Rojas, J; Landauro, C V; Torres, J

    2009-01-01

    The structural evolution and dynamics of silver nanodrops Ag 2869 (4.4 nm in diameter) under rapid cooling conditions have been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modelled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique are used to reveal the structural transition in the process of solidification. It is shown that Ag nanoparticles evolve into different nanostructures under different cooling processes. At a cooling rate of 1.5625 x 10 13 K s -1 the nanoparticles preserve an amorphous-like structure containing a large amount of 1551 and 1541 pairs which correspond to icosahedral symmetry. For a lower cooling rate (1.5625 x 10 12 K s -1 ), the nanoparticles transform into a crystal-like structure consisting mainly of 1421 and 1422 pairs which correspond to the face centred cubic and hexagonal close packed structures, respectively. The variations of the electronic density of states for the differently cooled nanoparticles are small, but in correspondence with the structural changes.

  17. Atomic and electronic structure transformations of silver nanoparticles under rapid cooling conditions

    Energy Technology Data Exchange (ETDEWEB)

    Lobato, I; Rojas, J [Instituto Peruano de EnergIa Nuclear, Avenida Canada 1470, Lima 41 (Peru); Landauro, C V; Torres, J [Facultad de Ciencias Fisicas, Universidad Nacional Mayor de San Marcos, P.O. box 14-0149, Lima 14 (Peru)], E-mail: jrojast@unmsm.edu.pe

    2009-02-04

    The structural evolution and dynamics of silver nanodrops Ag{sub 2869} (4.4 nm in diameter) under rapid cooling conditions have been studied by means of molecular dynamics simulations and electronic density of state calculations. The interaction of silver atoms is modelled by a tight-binding semiempirical interatomic potential proposed by Cleri and Rosato. The pair correlation functions and the pair analysis technique are used to reveal the structural transition in the process of solidification. It is shown that Ag nanoparticles evolve into different nanostructures under different cooling processes. At a cooling rate of 1.5625 x 10{sup 13} K s{sup -1} the nanoparticles preserve an amorphous-like structure containing a large amount of 1551 and 1541 pairs which correspond to icosahedral symmetry. For a lower cooling rate (1.5625 x 10{sup 12} K s{sup -1}), the nanoparticles transform into a crystal-like structure consisting mainly of 1421 and 1422 pairs which correspond to the face centred cubic and hexagonal close packed structures, respectively. The variations of the electronic density of states for the differently cooled nanoparticles are small, but in correspondence with the structural changes.

  18. Optical properties and band structure of atomically thin MoS2

    Science.gov (United States)

    Shan, Jie; Mak, Kin Fai; Lee, Changgu; Hone, James; Heinz, Tony

    2010-03-01

    Atomically thin layers of materials can be expected to exhibit distinct electronic structure and novel properties compared to their bulk counterparts. Layered compounds, for which stable atomically thin samples can be produced, are ideal candidates for such studies. Graphene, a monolayer slice of the graphite crystal, is an illustrative example of both the stability and of the interest and importance of such materials. Here we report a study of thin layers of MoS2, a hexagonal layered bulk semiconductor with an indirect band gap of 1.3 eV. MoS2 samples with layer thickness N down to a monolayer were obtained by mechanical exfoliation. We observed an enhancement of the luminescence quantum yield by more than a factor of 100 in monolayer MoS2 compared to the bulk material. The combination of absorption, photoluminescence, and photoconductivity measurements indicates that a transition to a direct-gap material occurs in the limit of the single MoS2 layer. This result is supported by an earlier first-principles calculation [J. Phys. Chem. C 2007, 111, 16192]. Further, by varying the thickness of the samples, we were able to probe the evolution of the electronic structure for N = 1 -- 6 layers.

  19. Paramyxovirus membrane fusion: Lessons from the F and HN atomic structures

    International Nuclear Information System (INIS)

    Lamb, Robert A.; Paterson, Reay G.; Jardetzky, Theodore S.

    2006-01-01

    Paramyxoviruses enter cells by fusion of their lipid envelope with the target cell plasma membrane. Fusion of the viral membrane with the plasma membrane allows entry of the viral genome into the cytoplasm. For paramyxoviruses, membrane fusion occurs at neutral pH, but the trigger mechanism that controls the viral entry machinery such that it occurs at the right time and in the right place remains to be elucidated. Two viral glycoproteins are key to the infection process-an attachment protein that varies among different paramyxoviruses and the fusion (F) protein, which is found in all paramyxoviruses. For many of the paramyxoviruses (parainfluenza viruses 1-5, mumps virus, Newcastle disease virus and others), the attachment protein is the hemagglutinin/neuraminidase (HN) protein. In the last 5 years, atomic structures of paramyxovirus F and HN proteins have been reported. The knowledge gained from these structures towards understanding the mechanism of viral membrane fusion is described

  20. Atomic resolution of structural changes in elastic crystals of copper(II) acetylacetonate

    Science.gov (United States)

    Worthy, Anna; Grosjean, Arnaud; Pfrunder, Michael C.; Xu, Yanan; Yan, Cheng; Edwards, Grant; Clegg, Jack K.; McMurtrie, John C.

    2018-01-01

    Single crystals are typically brittle, inelastic materials. Such mechanical responses limit their use in practical applications, particularly in flexible electronics and optical devices. Here we describe single crystals of a well-known coordination compound—copper(II) acetylacetonate—that are flexible enough to be reversibly tied into a knot. Mechanical measurements indicate that the crystals exhibit an elasticity similar to that of soft materials such as nylon, and thus display properties normally associated with both hard and soft matter. Using microfocused synchrotron radiation, we mapped the changes in crystal structure that occur on bending, and determined the mechanism that allows this flexibility with atomic precision. We show that, under strain, the molecules in the crystal reversibly rotate, and thus reorganize to allow the mechanical compression and expansion required for elasticity and still maintain the integrity of the crystal structure.

  1. Rationalizing the role of structural motif and underlying electronic structure in the finite temperature behavior of atomic clusters

    International Nuclear Information System (INIS)

    Susan, Anju; Joshi, Kavita

    2014-01-01

    Melting in finite size systems is an interesting but complex phenomenon. Many factors affect melting and owing to their interdependencies it is a challenging task to rationalize their roles in the phase transition. In this work, we demonstrate how structural motif of the ground state influences melting transition in small clusters. Here, we report a case with clusters of aluminum and gallium having same number of atoms, valence electrons, and similar structural motif of the ground state but drastically different melting temperatures. We have employed Born-Oppenheimer molecular dynamics to simulate the solid-like to liquid-like transition in these clusters. Our simulations have reproduced the experimental trends fairly well. Further, the detailed analysis of isomers has brought out the role of the ground state structure and underlying electronic structure in the finite temperature behavior of these clusters. For both clusters, isomers accessible before cluster melts have striking similarities and does have strong influence of the structural motif of the ground state. Further, the shape of the heat capacity curve is similar in both the cases but the transition is more spread over for Al 36 which is consistent with the observed isomerization pattern. Our simulations also suggest a way to characterize transition region on the basis of accessibility of the ground state at a specific temperature

  2. Quasi-crystalline geometry for architectural structures

    DEFF Research Database (Denmark)

    Wester, Ture; Weinzieri, Barbara

    The quasi-crystal (QC) type of material was discovered in 1983 by Dan Schechtman from Technion, Haifa. This new crystalline structure of material broke totally with the traditional conception of crystals and geometry introducing non-periodic close packing of cells with fivefold symmetry in 3D space....... The quasi-crystal geometry can be constructed from two different cubic cells with identical rhombic facets, where the relation between the diagonals is the golden section. All cells have identical rhombic faces, identical edges and identical icosahedral/dodecahedral nodes....

  3. Quasi-crystalline geometry for architectural structures

    DEFF Research Database (Denmark)

    Weizierl, Barbara; Wester, Ture

    2001-01-01

    with fivefold symmetry in 3D space. The quasi-crystal geometry can be constructed from two different cubic cells with identical rhombic facets, where the relation between the diagonals is the golden section. All cells have identical rhombic faces, identical edges and identical icosahedral/dedecahedral nodes....... The purpose of the paper is to investigate some possibilities for the application of Quasi-Crystal geometry for structures in architecture. The basis for the investigations is A: to use the Golden Cubes (the two different hexahedra consisting of rhombic facets where the length of the diagonals has the Golden...

  4. All-Atom Four-Body Knowledge-Based Statistical Potentials to Distinguish Native Protein Structures from Nonnative Folds

    Directory of Open Access Journals (Sweden)

    Majid Masso

    2017-01-01

    Full Text Available Recent advances in understanding protein folding have benefitted from coarse-grained representations of protein structures. Empirical energy functions derived from these techniques occasionally succeed in distinguishing native structures from their corresponding ensembles of nonnative folds or decoys which display varying degrees of structural dissimilarity to the native proteins. Here we utilized atomic coordinates of single protein chains, comprising a large diverse training set, to develop and evaluate twelve all-atom four-body statistical potentials obtained by exploring alternative values for a pair of inherent parameters. Delaunay tessellation was performed on the atomic coordinates of each protein to objectively identify all quadruplets of interacting atoms, and atomic potentials were generated via statistical analysis of the data and implementation of the inverted Boltzmann principle. Our potentials were evaluated using benchmarking datasets from Decoys-‘R’-Us, and comparisons were made with twelve other physics- and knowledge-based potentials. Ranking 3rd, our best potential tied CHARMM19 and surpassed AMBER force field potentials. We illustrate how a generalized version of our potential can be used to empirically calculate binding energies for target-ligand complexes, using HIV-1 protease-inhibitor complexes for a practical application. The combined results suggest an accurate and efficient atomic four-body statistical potential for protein structure prediction and assessment.

  5. Structural characterization of Pt-Pd and Pd-Pt core-shell nanoclusters at atomic resolution.

    Science.gov (United States)

    Sanchez, Sergio I; Small, Matthew W; Zuo, Jian-min; Nuzzo, Ralph G

    2009-06-24

    We describe the results of a study at atomic resolution of the structures exhibited by polymer-capped monometallic and bimetallic Pt and Pd nanoclusters--models for nanoscale material electrocatalysts--as carried out using an aberration-corrected scanning transmission electron microscope (STEM). The coupling of sub-nanometer resolution with Z-contrast measurements provides unprecedented insights into the atomic structures and relative elemental speciation of Pt and Pd within these clusters. The work further defines the nature of deeply quenched states that prevent facile conversions of core-shell motifs to equilibrium alloys and the nature of nonidealities such as twinning (icosahedral cores) and atomic segregation that these structures can embed. The nature of the facet structure present in these model systems is revealed by theory directed modeling in which experimental intensity profiles obtained in Z-contrast measurements at atomic resolution are compared to simulated intensity profiles using theoretically predicted cluster geometries. These comparisons show close correspondences between experiment and model and highlight striking structural complexities in these systems that are compositionally sensitive and subject to amplification by subsequent cluster growth processes. The work demonstrates an empowering competency in nanomaterials research for STEM measurements carried out using aberration corrected microscopes, approaches that hold considerable promise for characterizing the structure of these and other important catalytic materials systems at the atomic scale.

  6. Simulation of the Atomic and Electronic Structure of Oxygen Vacancies and Polyvacancies in ZrO2

    Science.gov (United States)

    Perevalov, T. V.

    2018-03-01

    Cubic, tetragonal, and monoclinic phases of zirconium oxide with oxygen vacancies and polyvacancies are studied by quantum chemical modeling of the atomic and electronic structure. It is demonstrated that an oxygen vacancy in ZrO2 may act as both an electron trap and a hole one. An electron added to the ZrO2 structure with an oxygen vacancy is distributed between two neighboring Zr atoms and is a bonding orbital by nature. It is advantageous for each subsequent O vacancy to form close to the already existing ones; notably, one Zr atom has no more than two removed O atoms related to it. Defect levels from oxygen polyvacancies are distributed in the bandgap with preferential localization in the vicinity of the oxygen monovacancy level.

  7. Mechanical properties and electronic structure of edge-doped graphene nanoribbons with F, O, and Cl atoms.

    Science.gov (United States)

    Piriz, Sebastián; Fernández-Werner, Luciana; Pardo, Helena; Jasen, Paula; Faccio, Ricardo; Mombrú, Álvaro W

    2017-08-16

    In this study, we present the structural, electronic, and mechanical properties of edge-doped zigzag graphene nanoribbons (ZGNRs) doped with fluorine, oxygen, and chlorine atoms. To the best of our knowledge, to date, no experimental results concerning the mechanical properties of graphene-derived nanoribbons have been reported in the literature. Simulations indicate that Cl- and F-doped ZGNRs present an equivalent 2-dimensional Young's modulus E 2D , which seems to be higher than those of graphene and H-doped ZGNRs. This is a consequence of the electronic structure of the system, particularly originating from strong interactions between the dopant atoms localized at the edges. The interaction between dopant atoms located at the edges is higher for Cl and lower for F and O atoms. This is the origin of the observed trend, in which E > E > E for all the analyzed ZGNRs.

  8. Fluorescence detection of white-beam X-ray absorption anisotropy: towards element-sensitive projections of local atomic structure

    Science.gov (United States)

    Korecki, P.; Tolkiehn, M.; Dąbrowski, K. M.; Novikov, D. V.

    2011-01-01

    Projections of the atomic structure around Nb atoms in a LiNbO3 single crystal were obtained from a white-beam X-ray absorption anisotropy (XAA) pattern detected using Nb K fluorescence. This kind of anisotropy results from the interference of X-rays inside a sample and, owing to the short coherence length of a white beam, is visible only at small angles around interatomic directions. Consequently, the main features of the recorded XAA corresponded to distorted real-space projections of dense-packed atomic planes and atomic rows. A quantitative analysis of XAA was carried out using a wavelet transform and allowed well resolved projections of Nb atoms to be obtained up to distances of 10 Å. The signal of nearest O atoms was detected indirectly by a comparison with model calculations. The measurement of white-beam XAA using characteristic radiation indicates the possibility of obtaining element-sensitive projections of the local atomic structure in more complex samples. PMID:21997909

  9. Investigation of the structure change of atomic shells due to uranium ionization by the Dirac-Fock-Slater method

    International Nuclear Information System (INIS)

    Shchornak, G.

    1979-01-01

    The influence of outer vacancies in the atomic shells of uranium on the atomic shell structure is claculated by the Dirac-Fock-Slater method. It is found out that the energy of the X-ray transitions increases due to the detachment of the electrons with the lowest binding energies. The electron detachment from the subshells of the 4f level gives rise to negative energy shifts of the X-ray transitions.(author)

  10. Research Investigation Directed Toward Extending the Useful Range of the Electromagnetic Spectrum. [atomic spectra and electronic structure of alkali metals

    Science.gov (United States)

    Hartmann, S. R.; Happer, W.

    1974-01-01

    The report discusses completed and proposed research in atomic and molecular physics conducted at the Columbia Radiation Laboratory from July 1972 to June 1973. Central topics described include the atomic spectra and electronic structure of alkali metals and helium, molecular microwave spectroscopy, the resonance physics of photon echoes in some solid state systems (including Raman echoes, superradiance, and two photon absorption), and liquid helium superfluidity.

  11. Atomic PDF study of size and structure of CdSe nanoparticles

    Science.gov (United States)

    Masadeh, A. S.; Paglia, G.; Bozin, E. S.; Billinge, S. J. L.; Karkamkar, A.; Kanatzidis, M. G.

    2006-03-01

    The atomic pair distribution function (PDF) is used to address the size and structure of series of CdSe nanoparticles prepared by the method of distribution focusing [1]. Due to their limiting structure coherence conventional crystallographic methods, such as Rietveld can't be used to assess quantitative size or structural information. Total scattering techniques, such PDF have been successfully applied recently on some similar systems [2, 3]. The PDF includes both Bragg and diffuse scattering and provides quantitative information about the local structure of the materials at different length scales. We report on results of the PDF analysis of synchrotron x-ray diffraction on series of CdSe nanoparticles, data were collected using the rapid acquisition PDF (RA-PDF) technique [4]. [1] X. G. Peng, J. Wickham, A. P. Alivisatos, J. Am. Chem. Soc. 1998, 120, 5343-5344 [2] B. Gilbert, F. Huang,^ H. Zhang,^ G. A. Waychunas,^ J. F. Banfield. Science, 305, 651-654 (2004). [3] R. B. Neder, V. I. Korsunskiy, J. Phys: Condens. Matter 17, 125-134 (2005) [4] P. J. Chupas, X. Qiu, J. C. Hanson, P. L. Lee, C. P. Grey and S. J. L. Billinge. J. Appl. Crystallogr. 36, 1342-1347 (2003).

  12. The asymmetrical structure of Golgi apparatus membranes revealed by in situ atomic force microscope.

    Directory of Open Access Journals (Sweden)

    Haijiao Xu

    Full Text Available The Golgi apparatus has attracted intense attentions due to its fascinating morphology and vital role as the pivot of cellular secretory pathway since its discovery. However, its complex structure at the molecular level remains elusive due to limited approaches. In this study, the structure of Golgi apparatus, including the Golgi stack, cisternal structure, relevant tubules and vesicles, were directly visualized by high-resolution atomic force microscope. We imaged both sides of Golgi apparatus membranes and revealed that the outer leaflet of Golgi membranes is relatively smooth while the inner membrane leaflet is rough and covered by dense proteins. With the treatment of methyl-β-cyclodextrin and Triton X-100, we confirmed the existence of lipid rafts in Golgi apparatus membrane, which are mostly in the size of 20 nm -200 nm and appear irregular in shape. Our results may be of significance to reveal the structure-function relationship of the Golgi complex and pave the way for visualizing the endomembrane system in mammalian cells at the molecular level.

  13. A theoretical inquiry into the question of W and Ta (100) atomic structures

    International Nuclear Information System (INIS)

    Treglia, G.; Spanjaard, D.

    1983-01-01

    In spite of the very large number of experiments (LEED, AES, UPS, MeV He + scattering, work function, FIM) carried out on W (100), no structural model consistent with all the data has been proposed yet: in particular, the question of the reconstruction thermally induced when the sample is cooled below room temperature remains a puzzling problem. Furthermore, from a theoretical point of view, no definitive answer has been given. Actually, either the mechanism invoked for the reconstruction is too weak, or some contributions are omitted or calculated without sufficient care. The surface energy of W (100) is computed taking into account the band term treated in the tight binding approximation, a pairwise repulsive potential of the Born-Mayer type and the electronic correlation contribution obtained from a perturbation treatment of the Hubbard model in the band limit. This energy is then fully minimised with respect to all coordinates of surface atoms, keeping all atoms neutral for any displace,ment. It is found that the unreconstructed surface is the most stable at T = 0 K and discuss this unexpected result. A similar calculation for Ta (100) leads to opposite conclusions. (author)

  14. The atomic structure of the Si(111) (2 root 3x2 root 3)R30 degrees-Sn reconstruction

    DEFF Research Database (Denmark)

    Levermann, A.H.; Howes, P.B.; Edwards, K.A.

    1996-01-01

    We have studied the atomic structure of the (2 root 3x2 root)R30 degrees reconstruction induced by adsorption of about 1.1 monolayers of Sn on Si(lll) using surface X-ray diffraction (SXRD) and scanning tunnelling microscopy (STM). The experimentally obtained structure factors in SXRD...

  15. Molecular dynamic simulation of the atomic structure of aluminum solid–liquid interfaces

    International Nuclear Information System (INIS)

    Men, H; Fan, Z

    2014-01-01

    In this paper, molecular dynamic (MD) simulation was used to investigate the equilibrium atomic arrangement at aluminum solid–liquid (S/L) interfaces with {111}, {110} and {100} orientations. The simulation results reveal that the aluminum S/L interfaces are diffuse for all the orientations, and extend up to 7 atomic layers. Within the diffuse interfaces there exists substantial atomic ordering, which is manifested by atomic layering perpendicular to the interface and in-plane atomic ordering parallel to the interface. Atomic layering can be quantified by the atomic density profile (ρ(z)) while the in-plane atomic ordering can be described by the in-plane ordering parameter (S(z)). The detailed MD simulation suggests that atomic layering at the interface always occurs within 7 atomic layers independent of the interface orientation while the in-plane ordering is highly dependent on the interface orientations, with the {111} interface being less diffuse than the {100} and {110} interfaces. This study demonstrates clearly that the physical origin of the diffuse interface is atomic layering and in-plane atomic ordering at the S/L interfaces. It is suggested that the difference in atomic layering and in-plane ordering at the S/L interface with different orientations is responsible for the observed growth anisotropy. (papers)

  16. Specific heat properties of electrons in generalized Fibonacci quasicrystals

    Science.gov (United States)

    Mauriz, P. W.; Vasconcelos, M. S.; Albuquerque, E. L.

    2003-11-01

    The purpose of this paper is to investigate the specific heat properties of electrons in one-dimensional quasiperiodic potentials, arranged in accordance with the generalized Fibonacci sequence. The electronic energy spectra are calculated using the one-dimensional Schrödinger equation in a tight-binding approximation. Both analytical and numerical results on the temperature dependence of the electron's specific heat associated with their multiscale fractal energy spectra are presented. We compare our numerical results with those found for the ordinary Fibonacci structure. A rich and varied behavior is found for the specific heat oscillations when T→0, with interesting physical consequences.

  17. An atomic-force-microscopy study of the structure of surface layers of intact fibroblasts

    Science.gov (United States)

    Khalisov, M. M.; Ankudinov, A. V.; Penniyaynen, V. A.; Nyapshaev, I. A.; Kipenko, A. V.; Timoshchuk, K. I.; Podzorova, S. A.; Krylov, B. V.

    2017-02-01

    Intact embryonic fibroblasts on a collagen-treated substrate have been studied by atomic-force microscopy (AFM) using probes of two types: (i) standard probes with tip curvature radii of 2-10 nm and (ii) special probes with a calibrated 325-nm SiO2 ball radius at the tip apex. It is established that, irrespective of probe type, the average maximum fibroblast height is on a level of 1.7 μm and the average stiffness of the probe-cell contact amounts to 16.5 mN/m. The obtained AFM data reveal a peculiarity of the fibroblast structure, whereby its external layers move as a rigid shell relative to the interior and can be pressed inside to a depth dependent on the load only.

  18. Atomic and electronic structure of clusters from car-Parrinello method

    International Nuclear Information System (INIS)

    Kumar, V.

    1994-06-01

    With the development of ab-initio molecular dynamics method, it has now become possible to study the static and dynamical properties of clusters containing up to a few tens of atoms. Here I present a review of the method within the framework of the density functional theory and pseudopotential approach to represent the electron-ion interaction and discuss some of its applications to clusters. Particular attention is focussed on the structure and bonding properties of clusters as a function of their size. Applications to clusters of alkali metals and Al, non-metal - metal transition in divalent metal clusters, molecular clusters of carbon and Sb are discussed in detail. Some results are also presented on mixed clusters. (author). 121 refs, 24 ifigs

  19. Hyperfine structure of the odd parity level system in the terbium atom

    International Nuclear Information System (INIS)

    Stefanska, D; Furmann, B

    2017-01-01

    Within this work new experimental results concerning the hyperfine structure ( hfs ) in the terbium atom are presented, concerning the odd parity levels system, hitherto only scarcely investigated (apart from the ground term). hfs constants A and B for 113 levels were determined for the first time, and for another 16 levels, which already occurred in our earlier works, supplementary results were obtained; additionally, our earlier results for 93 levels were compiled. The hfs of the odd parity levels was investigated using the method of laser induced fluorescence in a hollow cathode discharge. The hfs of 165 spectral lines, where the levels in question were involved as the upper levels, was recorded. Literature values of hfs constants of the even-parity lower levels (including our own earlier results) greatly facilitated the present data evaluation. (paper)

  20. Plane problems of cubic quasicrystal media with an elliptic hole or a crack

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Yang, E-mail: gaoyangg@gmail.com [Institute of Mechanics, University of Kassel, Kassel 34125 (Germany); Ricoeur, Andreas [Institute of Mechanics, University of Kassel, Kassel 34125 (Germany); Zhang, Liangliang [College of Science, China Agricultural University, Beijing 100083 (China)

    2011-07-11

    Based on the complex potential method, plane problems of cubic quasicrystal media containing an elliptic hole subjected to uniform remote loadings are solved. The explicit solutions for the coupled fields are given in the closed form. Degenerating the elliptic hole into a crack, the asymptotic distribution of the phonon and phason stress fields near the crack tip exhibits inverse square root singularities. Explicit expressions for the stress intensity factors, crack opening displacements and strain energy release rate are also presented. -- Highlights: → Lekhnitskii's formalism is extended to cubic QC solids. → The plane problem of an elliptic hole or crack is investigated. → Analytical expressions for both entire and asymptotic fields are determined. → The stress intensity factors are independent of material constants. → The coupled field strongly affects the configuration and strain energy of the crack.

  1. Liquid refractive index sensor based on a 2D 10-fold photonic quasicrystal

    Science.gov (United States)

    Wang, Shuai; Sun, XiaoHong; Wang, Cong; Peng, Gangding; Qi, Yongle; Wang, XiShi

    2017-09-01

    A liquid refractive index sensor is designed and optimized by using silicon-rods based on a 10-fold photonic quasicrystal without defects. The resonant mode with high Q value is chosen as the sensing wavelength in the transmission spectrum. By changing the radius of the silicon pillars, the sensor size and the refractive index of the background media, different types of sensors are designed and investigated. On the other hand, the performance of the sensor is investigated including the measurement range, sensitivity, etc. In the detection limit of spectral instruments, 0.02 nm, the sensing accuracy is 10-4 refractive index unit with a figure of merit of 1478. The measurement range is from 1.2731 to 1.4185. This will provide a new method for the design and fabrication of lab-on-chip, microfluidic optical elements and integrated optical circuits.

  2. MolProbity: More and better reference data for improved all-atom structure validation.

    Science.gov (United States)

    Williams, Christopher J; Headd, Jeffrey J; Moriarty, Nigel W; Prisant, Michael G; Videau, Lizbeth L; Deis, Lindsay N; Verma, Vishal; Keedy, Daniel A; Hintze, Bradley J; Chen, Vincent B; Jain, Swati; Lewis, Steven M; Arendall, W Bryan; Snoeyink, Jack; Adams, Paul D; Lovell, Simon C; Richardson, Jane S; Richardson, David C

    2018-01-01

    This paper describes the current update on macromolecular model validation services that are provided at the MolProbity website, emphasizing changes and additions since the previous review in 2010. There have been many infrastructure improvements, including rewrite of previous Java utilities to now use existing or newly written Python utilities in the open-source CCTBX portion of the Phenix software system. This improves long-term maintainability and enhances the thorough integration of MolProbity-style validation within Phenix. There is now a complete MolProbity mirror site at http://molprobity.manchester.ac.uk. GitHub serves our open-source code, reference datasets, and the resulting multi-dimensional distributions that define most validation criteria. Coordinate output after Asn/Gln/His "flip" correction is now more idealized, since the post-refinement step has apparently often been skipped in the past. Two distinct sets of heavy-atom-to-hydrogen distances and accompanying van der Waals radii have been researched and improved in accuracy, one for the electron-cloud-center positions suitable for X-ray crystallography and one for nuclear positions. New validations include messages at input about problem-causing format irregularities, updates of Ramachandran and rotamer criteria from the million quality-filtered residues in a new reference dataset, the CaBLAM Cα-CO virtual-angle analysis of backbone and secondary structure for cryoEM or low-resolution X-ray, and flagging of the very rare cis-nonProline and twisted peptides which have recently been greatly overused. Due to wide application of MolProbity validation and corrections by the research community, in Phenix, and at the worldwide Protein Data Bank, newly deposited structures have continued to improve greatly as measured by MolProbity's unique all-atom clashscore. © 2017 The Protein Society.

  3. The electronic structures and optical properties of light-element atom adsorbed SnSe monolayers

    Science.gov (United States)

    Cai, Xiaoyu; Luo, Jia; Zhang, Xi; Xiang, Gang

    2018-03-01

    The effect of adsorption of different light-element atoms on the electronic structures and optical properties of single-layered SnSe sheets are investigated using density-functional theory. The optimized structures of SnSe monolayers with the adatoms (H, Li, B, C, N, O and F) are calculated by full optimization method. We found that depending on the nature of the adatoms, SnSe monolayers can be designed to be either metal or semiconductor. With the decoration of H, Li, B, N or F adatoms, SnSe monolayers become metallic, either resulted from the formation of impurity bands (H, B and N) or the shifts of energy bands (Li and F). With the decoration of C or O adatoms, SnSe monolayers remain semiconducting, but the band structures change evidently, resulting in robust modulation of effective masses of charge carriers near band edges and optical absorption properties of the monolayers. Our calculated results demonstrate that the electronic and optical properties of SnSe monolayers can be tuned by adsorption of light-element adatoms which may be used in electrical and optical applications.

  4. Epitaxial B-Graphene: Large-Scale Growth and Atomic Structure.

    Science.gov (United States)

    Usachov, Dmitry Yu; Fedorov, Alexander V; Petukhov, Anatoly E; Vilkov, Oleg Yu; Rybkin, Artem G; Otrokov, Mikhail M; Arnau, Andrés; Chulkov, Evgueni V; Yashina, Lada V; Farjam, Mani; Adamchuk, Vera K; Senkovskiy, Boris V; Laubschat, Clemens; Vyalikh, Denis V

    2015-07-28

    Embedding foreign atoms or molecules in graphene has become the key approach in its functionalization and is intensively used for tuning its structural and electronic properties. Here, we present an efficient method based on chemical vapor deposition for large scale growth of boron-doped graphene (B-graphene) on Ni(111) and Co(0001) substrates using carborane molecules as the precursor. It is shown that up to 19 at. % of boron can be embedded in the graphene matrix and that a planar C-B sp(2) network is formed. It is resistant to air exposure and widely retains the electronic structure of graphene on metals. The large-scale and local structure of this material has been explored depending on boron content and substrate. By resolving individual impurities with scanning tunneling microscopy we have demonstrated the possibility for preferential substitution of carbon with boron in one of the graphene sublattices (unbalanced sublattice doping) at low doping level on the Ni(111) substrate. At high boron content the honeycomb lattice of B-graphene is strongly distorted, and therefore, it demonstrates no unballanced sublattice doping.

  5. Nanoimaging and ultra structure of Entamoeba histolytica and its pseudopods by using atomic force microscope

    Science.gov (United States)

    Joshi, Narahari V.; Medina, Honorio; Urdaneta, H.; Barboza, J.

    2000-04-01

    Nan-imaging of Entamoeba histolytica was carried out by using Atomic Force Microscope (AFM). The structure of the nucleus, endoplasm and ectoplasm were studied separately. The diameter of the nucleus in living E. histolytica was found to be of the order of 10 micrometers which is slightly higher than the earlier reported value. The presence of karysome was detected in the nucleus. Well-organized patterns of chromatoid bodies located within the endoplasm, were detected and their repetitive patterns were examined. The organized structure was also extended within the ectoplasm. The dimensions and form of the organization suggest that chromatic bodies are constituted with ribosomes ordered in the form of folded sheet. Such structures were found to be absent in non-living E. histolytica. AFM images were also captured just in the act when ameba was extending its pseudopods. Alteration in the ultrastructure caused during the process of extension was viewed. Well marked canals of width 694.05 nm. And height 211.05 nm are clearly perceptible towards the direction of the pseudopods. 3D images are presented to appreciate the height variation, which can not be achieved by conventional well-established techniques such as electron microscopy.

  6. Enhanced light output power of GaN-based vertical-injection light-emitting diodes with a 12-fold photonic quasi-crystal by nano-imprint lithography

    International Nuclear Information System (INIS)

    Huang, H W; Huang, J K; Kuo, H C; Wang, S C; Lin, C H; Lee, K Y; Yu, C C; Lee, B D; Leung, K M

    2009-01-01

    GaN-based thin-film vertical-injection light-emitting diodes (VLEDs) with a 12-fold photonic quasi-crystal (PQC) by nano-imprint lithography (NIL) are fabricated and presented. At a driving current of 20 mA and with a chip size of 350 µm × 350 µm, the light output power of our thin-film LED with a 12-fold PQC structure reaches 41 mW. This result is an enhancement of 78% when compared with the output power of a VLED without a PQC structure. In addition, the corresponding light radiation pattern shows a narrower beam shape due to the strong guided light extraction effect by the formed PQC structure in the vertical direction

  7. The role of electron localization in the atomic structure of transition-metal 13-atom clusters: the example of Co13, Rh13, and Hf13.

    Science.gov (United States)

    Piotrowski, Maurício J; Piquini, Paulo; Cândido, Ladir; Da Silva, Juarez L F

    2011-10-14

    The crystalline structure of transition-metals (TM) has been widely known for several decades, however, our knowledge on the atomic structure of TM clusters is still far from satisfactory, which compromises an atomistic understanding of the reactivity of TM clusters. For example, almost all density functional theory (DFT) calculations for TM clusters have been based on local (local density approximation--LDA) and semilocal (generalized gradient approximation--GGA) exchange-correlation functionals, however, it is well known that plain DFT fails to correct the self-interaction error, which affects the properties of several systems. To improve our basic understanding of the atomic and electronic properties of TM clusters, we report a DFT study within two nonlocal functionals, namely, the hybrid HSE (Heyd, Scuseria, and Ernzerhof) and GGA+U functionals, of the structural and electronic properties of the Co(13), Rh(13), and Hf(13) clusters. For Co(13) and Rh(13), we found that improved exchange-correlation functionals decrease the stability of open structures such as the hexagonal bilayer (HBL) and double simple-cubic (DSC) compared with the compact icosahedron (ICO) structure, however, DFT-GGA, DFT-GGA+U, and DFT-HSE yield very similar results for Hf(13). Thus, our results suggest that the DSC structure obtained by several plain DFT calculations for Rh(13) can be improved by the use of improved functionals. Using the sd hybridization analysis, we found that a strong hybridization favors compact structures, and hence, a correct description of the sd hybridization is crucial for the relative energy stability. For example, the sd hybridization decreases for HBL and DSC and increases for ICO in the case of Co(13) and Rh(13), while for Hf(13), the sd hybridization decreases for all configurations, and hence, it does not affect the relative stability among open and compact configurations.

  8. Early Atomism

    Indian Academy of Sciences (India)

    https://www.ias.ac.in/article/fulltext/reso/015/10/0905-0925. Keywords. Atomic theory; Avogadro's hypothesis; atomic weights; periodic table; valence; molecular weights; molecular formula; isomerism. Author Affiliations. S Ramasesha1. Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560 012, ...

  9. A Dugdale—Barenblatt model for a strip with a semi-infinite crack embedded in decagonal quasicrystals

    International Nuclear Information System (INIS)

    Li Wu; Xie Ling-Yun

    2013-01-01

    The present study is to determine the solution of a strip with a semi-infinite crack embedded in decagonal quasicrystals, which transforms a physically and mathematically daunting problem. Then cohesive forces are incorporated into a plastic strip in the elastic body for nonlinear deformation. By superposing the two linear elastic fields, one is evaluated with internal loadings and the other with cohesive forces, the problem is treated in Dugdale-Barenblatt manner. A simple but yet rigorous version of the complex analysis theory is employed here, which involves a conformal mapping technique. The analytical approach leads to the establishment of a few equations, which allows the exact calculation of the size of cohesive force zone and the most important physical quantity in crack theory: stress intensity factor. The analytical results of the present study may be used as the basis of fracture theory of decagonal quasicrystals

  10. A Dugdale—Barenblatt model for a strip with a semi-infinite crack embedded in decagonal quasicrystals

    Science.gov (United States)

    Li, Wu; Xie, Ling-Yun

    2013-03-01

    The present study is to determine the solution of a strip with a semi-infinite crack embedded in decagonal quasicrystals, which transforms a physically and mathematically daunting problem. Then cohesive forces are incorporated into a plastic strip in the elastic body for nonlinear deformation. By superposing the two linear elastic fields, one is evaluated with internal loadings and the other with cohesive forces, the problem is treated in Dugdale-Barenblatt manner. A simple but yet rigorous version of the complex analysis theory is employed here, which involves a conformal mapping technique. The analytical approach leads to the establishment of a few equations, which allows the exact calculation of the size of cohesive force zone and the most important physical quantity in crack theory: stress intensity factor. The analytical results of the present study may be used as the basis of fracture theory of decagonal quasicrystals.

  11. 2nd International Symposium "Atomic Cluster Collisions : Structure and Dynamics from the Nuclear to the Biological Scale"

    CERN Document Server

    Solov'yov, Andrey; ISACC 2007; Latest advances in atomic cluster collisions

    2008-01-01

    This book presents a 'snapshot' of the most recent and significant advances in the field of cluster physics. It is a comprehensive review based on contributions by the participants of the 2nd International Symposium on Atomic Cluster Collisions (ISACC 2007) held in July 19-23, 2007 at GSI, Darmstadt, Germany. The purpose of the Symposium is to promote the growth and exchange of scientific information on the structure and properties of nuclear, atomic, molecular, biological and complex cluster systems studied by means of photonic, electronic, heavy particle and atomic collisions. Particular attention is devoted to dynamic phenomena, many-body effects taking place in cluster systems of a different nature - these include problems of fusion and fission, fragmentation, collective electron excitations, phase transitions, etc.Both the experimental and theoretical aspects of cluster physics, uniquely placed between nuclear physics on the one hand and atomic, molecular and solid state physics on the other, are discuss...

  12. Is the Oxygen Atom Static or Dynamic? The Effect of Generating Animations on Students' Mental Models of Atomic Structure

    Science.gov (United States)

    Akaygun, Sevil

    2016-01-01

    Visualizing the chemical structure and dynamics of particles has been challenging for many students; therefore, various visualizations and tools have been used in chemistry education. For science educators, it has been important to understand how students visualize and represent particular phenomena--i.e., their mental models-- to design more…

  13. Alignment and geometrical effects on Stueckelberg interference structure in cross sections for inelastic collisions involving Rydberg atoms

    International Nuclear Information System (INIS)

    Saha, B.C.; Lane, N.F.

    1994-01-01

    A theoretical study of Stueckelberg interference structure in inelastic, state-changing integrated cross sections for collisions of low-Rydberg Na (n<10) atoms with ground state He atoms is reported. The dependence of the Stueckelberg interference structure on orbital geometry and alignment of the initial state is predicted. Interference oscillations are found in the cross sections for both initial ns and np states; in the latter case, the features show considerable sensitivity with respect to variations in the spatial alignment of the principal axis of the electron charge distribution at some collision velocities and near isotropy at others

  14. A method for the calculation of collision strengths for complex atomic structures based on Slater parameter optimisation

    International Nuclear Information System (INIS)

    Fawcett, B.C.; Mason, H.E.

    1989-02-01

    This report presents details of a new method to enable the computation of collision strengths for complex ions which is adapted from long established optimisation techniques previously applied to the calculation of atomic structures and oscillator strengths. The procedure involves the adjustment of Slater parameters so that they determine improved energy levels and eigenvectors. They provide a basis for collision strength calculations in ions where ab initio computations break down or result in reducible errors. This application is demonstrated through modifications of the DISTORTED WAVE collision code and SUPERSTRUCTURE atomic-structure code which interface via a transformation code JAJOM which processes their output. (author)

  15. Atomic structure and electronic properties of the SixSb100-x phase-change memory material

    DEFF Research Database (Denmark)

    Verma, Ashok K.; Modak, Paritosh; Svane, Axel

    2011-01-01

    The electronic and structural properties of SixSb100-x (x∼16) materials are investigated using first-principles molecular dynamics simulations. Crystalline-liquid-amorphous phase transitions are examined and remarkable changes in the local structure around the Si atoms are found. The average Si...... coordination number 6 (3 long + 3 short Si-Sb bonds) of the crystalline phase changes to 4 (3 long Si-Sb + 1 short Si-Si bonds) by preserving three Si-Sb bonds in both the liquid and the amorphous phases. In the amorphous phase ∼90% of the Si atoms are fourfold coordinated compared to 40% in the liquid...

  16. The Dugdale model for a semi-infinite crack in a strip of two-dimensional decagonal quasicrystals

    Science.gov (United States)

    Ling-yun, Xie; Tian-you, Fan

    2011-05-01

    The problem of a semi-infinite crack in a strip is useful in materials science and engineering. The paper proposes a Dugdale model for the configuration of two-dimensional decagonal quasicrystals. Through the complex variable method, we obtain the exact solution of the problem. The plastic zone and the crack tip opening displacement and the most important physical quantity, stress intensity factor, can be expressed in quite a simple form.

  17. Contribution to viscosity from the structural relaxation via the atomic scale Green-Kubo stress correlation function.

    Science.gov (United States)

    Levashov, V A

    2017-11-14

    We studied the connection between the structural relaxation and viscosity for a binary model of repulsive particles in the supercooled liquid regime. The used approach is based on the decomposition of the macroscopic Green-Kubo stress correlation function into the correlation functions between the atomic level stresses. Previously we used the approach to study an iron-like single component system of particles. The role of vibrational motion has been addressed through the demonstration of the relationship between viscosity and the shear waves propagating over large distances. In our previous considerations, however, we did not discuss the role of the structural relaxation. Here we suggest that the contribution to viscosity from the structural relaxation can be taken into account through the consideration of the contribution from the atomic stress auto-correlation term only. This conclusion, however, does not mean that only the auto-correlation term represents the contribution to viscosity from the structural relaxation. Previously the role of the structural relaxation for viscosity has been addressed through the considerations of the transitions between inherent structures and within the mode-coupling theory by other authors. In the present work, we study the structural relaxation through the considerations of the parent liquid and the atomic level stress correlations in it. The comparison with the results obtained on the inherent structures also is made. Our current results suggest, as our previous observations, that in the supercooled liquid regime, the vibrational contribution to viscosity extends over the times that are much larger than the Einstein's vibrational period and much larger than the times that it takes for the shear waves to propagate over the model systems. Besides addressing the atomic level shear stress correlations, we also studied correlations between the atomic level pressure elements.

  18. Formation, atomic structure, and electronic properties of GaSb quantum dots in GaAs

    Energy Technology Data Exchange (ETDEWEB)

    Timm, R.

    2007-12-14

    In this work, cross-sectional scanning tunneling microscopy and spectroscopy are used for the first time to study the shape, size, strain, chemical composition, and electronic properties of capped GaSb/GaAs QDs at the atomic scale. By evaluating such structural results on a variety of nanostructures built using different epitaxy methods and growth conditions, details on the underlying QD formation processes can be revealed. A cross-over from flat quantum wells (QWs) to optically active QDs can be observed in samples grown by metalorganic chemical vapor deposition (MOCVD) with increasing amount of GaSb, including self-assembled Sb accumulations within a still two-dimensional layer and tiny three-dimensional GaSb islands probably acting as precursor structures. The QWs consist of significantly intermixed material with stoichiometries of maximally 50% GaSb, additionally exhibiting small gaps filled with GaAs. A higher GaSb content up to nearly pure material is found in the QDs, being characterized by small sizes of up to 8 nm baselength and about 2 nm height. In spite of the intermixing, all nanostructures have rather abrupt interfaces, and no significant Sb segregation in growth direction is observed. This changes completely when molecular beam epitaxy (MBE) is used as growth method, in which case individual Sb atoms are found to be distributed over several nm above the nanostructures. Massive group-V atomic exchange processes are causing this strong inter-mixing and Sb segregation during GaAs overgrowth. In combination with the large strain inherent to GaSb/GaAs QDs, this segregation upon overgrowth is assumed to be the reason for a unique structural phenomenon: All MBE-grown QDs, independent of the amount of deposited GaSb, exhibit a ring structure, consisting of a ring body of high GaSb content and a more or less extended central gap filled with GaAs. These rings have formed in a self-assembled way even when the initial GaSb layer was overgrown considerably fast

  19. Quasi-crystalline geometry for architectural structures

    DEFF Research Database (Denmark)

    Wester, Ture; Weinzieri, Barbara

    The quasi-crystal (QC) type of material was discovered in 1983 by Dan Schechtman from Technion, Haifa. This new crystalline structure of material broke totally with the traditional conception of crystals and geometry introducing non-periodic close packing of cells with fivefold symmetry in 3D space...

  20. Characterization of iron ferromagnetism by the local atomic volume: from three-dimensional structures to isolated atoms

    Czech Academy of Sciences Publication Activity Database

    Zhang, L.; Šob, Mojmír; Wu, Z.; Zhang, Y.; Lu, G-H.

    2014-01-01

    Roč. 26, č. 8 (2014), 086002-1-086002-17 ISSN 0953-8984 R&D Projects: GA MŠk(CZ) ED1.1.00/02.0068; GA ČR(CZ) GAP108/12/0311; GA AV ČR IAA100100920 Institutional support: RVO:68081723 Keywords : electronic structure * magnetism * iron * ab initio calculations Subject RIV: BM - Solid Matter Physics ; Magnetism Impact factor: 2.346, year: 2014

  1. Groundwater Arsenic Adsorption on Granular TiO2: Integrating Atomic Structure, Filtration, and Health Impact.

    Science.gov (United States)

    Hu, Shan; Shi, Qiantao; Jing, Chuanyong

    2015-08-18

    A pressing challenge in arsenic (As) adsorptive filtration is to decipher how the As atomic surface structure obtained in the laboratory can be used to accurately predict the field filtration cycle. The motivation of this study was therefore to integrate molecular level As adsorption mechanisms and capacities to predict effluent As from granular TiO2 columns in the field as well as its health impacts. Approximately 2,955 bed volumes of groundwater with an average of 542 μg/L As were filtered before the effluent As concentration exceeded 10 μg/L, corresponding to an adsorption capacity of 1.53 mg As/g TiO2. After regeneration, the TiO2 column could treat 2,563 bed volumes of groundwater, resulting in an As load of 1.36 mg/g TiO2. Column filtration and EXAFS results showed that among coexisting ions present in groundwater, only Ca(2+), Si(OH)4, and HCO3(-) would interfere with As adsorption. The compound effects of coexisting ions and molecular level structural information were incorporated in the PHREEQC program to satisfactorily predict the As breakthrough curves. The total urinary As concentration from four volunteers of local residences, ranging from 972 to 2,080 μg/L before groundwater treatment, decreased to the range 31.7-73.3 μg/L at the end of the experimental cycle (15-33 days).

  2. Atomic structure and domain wall pinning in samarium-cobalt-based permanent magnets.

    Science.gov (United States)

    Duerrschnabel, M; Yi, M; Uestuener, K; Liesegang, M; Katter, M; Kleebe, H-J; Xu, B; Gutfleisch, O; Molina-Luna, L

    2017-07-04

    A higher saturation magnetization obtained by an increased iron content is essential for yielding larger energy products in rare-earth Sm 2 Co 17 -type pinning-controlled permanent magnets. These are of importance for high-temperature industrial applications due to their intrinsic corrosion resistance and temperature stability. Here we present model magnets with an increased iron content based on a unique nanostructure and -chemical modification route using Fe, Cu, and Zr as dopants. The iron content controls the formation of a diamond-shaped cellular structure that dominates the density and strength of the domain wall pinning sites and thus the coercivity. Using ultra-high-resolution experimental and theoretical methods, we revealed the atomic structure of the single phases present and established a direct correlation to the macroscopic magnetic properties. With further development, this knowledge can be applied to produce samarium cobalt permanent magnets with improved magnetic performance.Understanding the factors that determine the properties of permanent magnets, which play a central role in many industrial applications, can help in improving their performance. Here, the authors study how changes in the iron content affect the microstructure of samarium cobalt magnets.

  3. Structural characterization of polycarbonates for membrane applications by atomic level simulation

    Energy Technology Data Exchange (ETDEWEB)

    Gentile, F.T.; Arizzi, S.; Suter, U.W. [ETH-Zentrum, Zuerich (Switzerland). Inst. fuer Polymere; Ludovice, P.J. [Georgia Inst. of Tech., Atlanta, GA (United States). School of Chemical Engineering

    1995-12-01

    Polycarbonate polymers are desirable for use in membrane applications for separating gas mixtures due to their unique properties. Two commercially important membrane polymers, the tetramethyl (TMPC) and tetrabromo (TBPC) derivatives of Bisphenol A polycarbonate, were studied with computer simulation. The volume available to various gas diffusants in these polymers was characterized by calculating the volume of clusters of Delauney tetrahedra between the atoms of an ensemble of bulk molecular mechanics models of the polymer. The inverse of this available volume correlated with the diffusivity of various gases in these polymers. This correlation was able to qualitatively reproduce the gas diffusion consistent with the superior diffusivity and superior selectivity of TMPC and TBPC, respectively. Analysis of the structure of the two polymers suggests a more ordered packing of the TMPC chain which is consistent with the experimentally observed trend in which inhibited packing leads to increased selectivity for gas diffusion in polymers. Despite the model`s neglect of the thermal motion of the polymer, it has potential for use as a tool to suggest other perturbations in polycarbonate structure that may produce superior properties.

  4. Materials-by-design: computation, synthesis, and characterization from atoms to structures

    Science.gov (United States)

    Yeo, Jingjie; Jung, Gang Seob; Martín-Martínez, Francisco J.; Ling, Shengjie; Gu, Grace X.; Qin, Zhao; Buehler, Markus J.

    2018-05-01

    In the 50 years that succeeded Richard Feynman’s exposition of the idea that there is ‘plenty of room at the bottom’ for manipulating individual atoms for the synthesis and manufacturing processing of materials, the materials-by-design paradigm is being developed gradually through synergistic integration of experimental material synthesis and characterization with predictive computational modeling and optimization. This paper reviews how this paradigm creates the possibility to develop materials according to specific, rational designs from the molecular to the macroscopic scale. We discuss promising techniques in experimental small-scale material synthesis and large-scale fabrication methods to manipulate atomistic or macroscale structures, which can be designed by computational modeling. These include recombinant protein technology to produce peptides and proteins with tailored sequences encoded by recombinant DNA, self-assembly processes induced by conformational transition of proteins, additive manufacturing for designing complex structures, and qualitative and quantitative characterization of materials at different length scales. We describe important material characterization techniques using numerous methods of spectroscopy and microscopy. We detail numerous multi-scale computational modeling techniques that complements these experimental techniques: DFT at the atomistic scale; fully atomistic and coarse-grain molecular dynamics at the molecular to mesoscale; continuum modeling at the macroscale. Additionally, we present case studies that utilize experimental and computational approaches in an integrated manner to broaden our understanding of the properties of two-dimensional materials and materials based on silk and silk-elastin-like proteins.

  5. Chiral Nematic Structure of Cellulose Nanocrystal Suspensions and Films; Polarized Light and Atomic Force Microscopy

    Directory of Open Access Journals (Sweden)

    Derek G. Gray

    2015-11-01

    Full Text Available Cellulosic liquid crystalline solutions and suspensions form chiral nematic phases that show a rich variety of optical textures in the liquid crystalline state. These ordered structures may be preserved in solid films prepared by evaporation of solvent or suspending medium. Film formation from aqueous suspensions of cellulose nanocrystals (CNC was investigated by polarized light microscopy, optical profilometry and atomic force microscopy (AFM. An attempt is made to interpret qualitatively the observed textures in terms of the orientation of the cellulose nanocrystals in the suspensions and films, and the changes in orientation caused by the evaporative process. Mass transfer within the evaporating droplet resulted in the formation of raised rings whose magnitude depended on the degree of pinning of the receding contact line. AFM of dry films at short length scales showed a radial orientation of the CNC at the free surface of the film, along with a radial height variation with a period of approximately P/2, ascribed to the anisotropic shrinkage of the chiral nematic structure.

  6. Investigation of the atomic and electronic structures of highly ordered two-dimensional germanium on Au(111)

    Science.gov (United States)

    Wang, W.; Uhrberg, R. I. G.

    2017-12-01

    Low-energy electron diffraction (LEED), scanning tunneling microscopy (STM), and photoelectron spectroscopy have been used to study an ordered structure formed by Ge atoms deposited onto the Au(111) surface. Based on a careful analysis of STM images and LEED patterns, we propose a ( 5 0 8 -14 ) unit cell for the atomic structure of the Ge layer. Core-level data indicate that some Ge atoms diffuse into the Au(111) crystal during annealing after deposition at room temperature. This is further corroborated by angle-resolved photoelectron spectroscopy (ARPES) measured for different amounts of Ge remaining after sputtering and annealing. The results of the ARPES study clearly disprove an earlier assignment of a parabolic band, centered at normal emission, as a part of a Dirac cone of germanene.

  7. Electronic Structures Localized at the Boron Atom in Amorphous Fe-B and Fe-B-P Alloys

    Science.gov (United States)

    Yasuda, Hidehiro; Nakayama, Hiroshi; Fujita, Hiroshi

    1989-11-01

    The electronic structures localized at the B in amorphous Fe-B and Fe-B-P alloys and their crystallized alloys were studied by Auger valence electron spectroscopy and the states of solute B are discussed based on the change in the degree of covalent bonding and the charge transfer between the Fe and B atoms. In amorphous phases, the charge transfers from Fe to B above 15at%B where B atoms occupy the substitutionallike situations, and from B to Fe below 15at%B where B atoms occupy the interstitiallike situations. Magnetic properties depend on such states of solute B. In crystalline phases, covalent bonding becomes dominant because the electron excitation occurs to the B2p state. Consequently, amorphous phases are more metallic in character than crystalline phases and amorphous structures are stabilized by a mixture of more than two different bonding states.

  8. Spray structure of a pressure-swirl atomizer for combustion applications

    OpenAIRE

    Jicha Miroslav; Jedelsky Jan; Durdina Lukas

    2012-01-01

    In the present work, global as well as spatially resolved parameters of a spray produced by a pressure-swirl atomizer are obtained. Small pressure-swirl atomizer for aircraft combustion chambers was run on a newly designed test bench with Jet A-1 kerosene type aviation fuel. The atomizer was tested in four regimes based on typical operation conditions of the engine. Spray characteristics were studied using two optical measurement systems, Particle Image velocimetry (PIV) and Phase-Doppler Par...

  9. The effect of surface structure on Ag atom adsorption over CuO(111) surfaces: A first principles study

    Science.gov (United States)

    Hu, Riming; Zhou, Xiaolong; Yu, Jie

    2017-12-01

    The interactions of Ag atom with different types of CuO(111) surface, including the perfect, oxygen-vacancy and precovered oxygen surfaces, have been systematically investigated using density functional theory (DFT) calculations to examine the effect of surface structures on Ag atom adsorption. The calculated results indicate that the Cu1-Cu1 bridge site and the oxygen-vacancy site are the active centres for atomic Ag adsorption on the perfect surface and the oxygen-vacancy surface respectively, while atomic Ag preferentially adsorbs at the Op site on the precovered oxygen surface. The activity of the CuO(111) surface for atomic Ag adsorption can be improved both on the perfect and oxygen-vacancy surfaces, while the activity of the CuO(111) surface for atomic Ag adsorption will be suppressed on precovered oxygen surfaces. Furthermore, the adsorption of NO on different CuO(111) surfaces with Ag adsorption was investigated, and the calculation results show that the adsorption of NO on an Ag-loaded CuO(111) surface is greater than that on the pure CuO(111) surface.

  10. Line strengths, A-factors and absorption cross-sections for fine structure lines in multiplets and hyperfine structure components in lines in atomic spectrometry - a user's guide

    International Nuclear Information System (INIS)

    Axner, Ove; Gustafsson, Joergen; Omenetto, Nicolo; Winefordner, James D.

    2004-01-01

    This work summarizes and elucidates a number of fundamental concepts in atomic spectrometry regarding the 'strengths' of transitions between various energy levels and states in atoms. Although several of the expressions and rules for line strengths of transitions reported here can be found, in one way or another, in various books dealing with atomic structure, atomic spectrometry or quantum mechanics, the treatment in such books can be variously complex and difficult to follow for a non-experienced reader. In addition, detailed information about transition-specific 'strengths' of transitions used to be restricted to line strengths, whereas most experiments rather need transition-specific A-factors or transition-specific absorption cross-sections. This work therefore aims at pointing out the most important aspects of the concept of 'strengths' of transitions between various energy levels and states in atoms by presenting explicit expressions for not only relative and absolute line strengths but also oscillator strengths (f-values), A-factors and absorption cross-sections, for transitions between fine structure levels within a multiplet as well as for hyperfine structure components within a line (i.e. between hyperfine structure levels), including their mutual relations, in a consistent and user-friendly manner. The work also recapitulates the most important summation rules for line strengths, oscillator strengths (f-values), A-factors and absorption cross-sections for lines within multiplets and hyperfine structure components within lines. Many of the expressions are illustrated with clear and intelligible examples. For the sake of clarity and completeness, the work also comprises a short review of the nomenclature for atomic structure and transitions

  11. How in Spite of the Rhetoric, History of Chemistry Has Been Ignored in Presenting Atomic Structure in Textbooks.

    Science.gov (United States)

    Rodriguez, Maria A.; Niaz, Mansoor

    2002-01-01

    Reports on a study designed to: (a) show how the importance of the history of chemistry has been recognized in the classroom; (b) demonstrate how criteria based on history and philosophy of science can be used to evaluate the presentation of atomic structure in general chemistry textbooks; and (c) compare new (1970-1992) and old textbooks…

  12. Band structure of one-dimensional doped photonic crystal with three level atoms using the Fresnel coefficients method

    Science.gov (United States)

    Jafari, A.; Rahmat, A.; Bakkeshizadeh, S.

    2018-01-01

    We consider a one-dimensional photonic crystal (1DPC) composed of double-layered dielectrics. Electric permittivity and magnetic permeability of this crystal depends on the incident electromagnetic wave frequency. We suppose that three level atoms have been added to the second layer of each dielectric and this photonic crystal (PC) has been doped. These atoms can be added to the layer with different rates. In this paper, we have calculated and compared the band structure of the mentioned PC considering the effect of added atoms to the second layer with different rates through the Fresnel coefficients method. We find out that according to the effective medium theory, the electric permittivity of the second layer changes. Also the band structure of PC for both TE and TM polarizations changes, too. The width of bandgaps related to “zero averaged refractive index” and “Bragg” increases. Moreover, new gap branches appear in new frequencies at both TE and TM polarizations. In specific state, two branches of “zero permittivity” gap appear in the PC band structure related to TM polarization. With increasing the amount of the filling rate of total volume with three level atoms, we observe a lot of changes in the PC band structure.

  13. Effect of Programmed Instruction on Students' Attitude towards Structure of the Atom and the Periodic Table among Kenyan Secondary Schools

    Science.gov (United States)

    Wangila, M. J.; Martin, W.; Ronald, M.

    2015-01-01

    This study examined the effect of Programmed Instruction on students' attitude towards Structure of the Atom and the Periodic Table (SAPT) among mixed (co-educational) secondary schools of Butere district, Kakamega county, Kenya. The quasi-experimental research design was adopted, using the nonrandomized Solomon four-group as a model. The sample…

  14. The atomic surface structure of SrTiO3 (001) studied with synchrotron X-rays

    NARCIS (Netherlands)

    Vonk, V.; Konings, S.; van Hummel, G.J.; Harkema, Sybolt; Graafsma, H

    2005-01-01

    The atomic surface structure of single terminated SrTiO3(0 0 1) (1 × 1) is investigated employing surface X-ray diffraction. In order to obtain these surfaces a special treatment is needed consisting of chemical etching and annealing. Since this is done in an aqueous and subsequently oxygen

  15. Atomic structure of screw dislocations intersecting the Au(111) surface: A combined scanning tunneling microscopy and molecular dynamics study

    DEFF Research Database (Denmark)

    Engbæk, Jakob; Schiøtz, Jakob; Dahl-Madsen, Bjarke

    2006-01-01

    The atomic-scale structure of naturally occurring screw dislocations intersecting a Au(111) surface has been investigated both experimentally by scanning tunneling microscopy (STM) and theoretically using molecular dynamics (MD) simulations. The step profiles of 166 dislocations were measured using...

  16. A critical comparison of coarse-grained structure-based approaches and atomic models of protein folding.

    Science.gov (United States)

    Hu, Jie; Chen, Tao; Wang, Moye; Chan, Hue Sun; Zhang, Zhuqing

    2017-05-31

    Structure-based coarse-grained Gō-like models have been used extensively in deciphering protein folding mechanisms because of their simplicity and tractability. Meanwhile, explicit-solvent molecular dynamics (MD) simulations with physics-based all-atom force fields have been applied successfully to simulate folding/unfolding transitions for several small, fast-folding proteins. To explore the degree to which coarse-grained Gō-like models and their extensions to incorporate nonnative interactions are capable of producing folding processes similar to those in all-atom MD simulations, here we systematically compare the computed unfolded states, transition states, and transition paths obtained using coarse-grained models and all-atom explicit-solvent MD simulations. The conformations in the unfolded state in common Gō models are more extended, and are thus more in line with experiment, than those from all-atom MD simulations. Nevertheless, the structural features of transition states obtained by the two types of models are largely similar. In contrast, the folding transition paths are significantly more sensitive to modeling details. In particular, when common Gō-like models are augmented with nonnative interactions, the predicted dimensions of the unfolded conformations become similar to those computed using all-atom MD. With this connection, the large deviations of all-atom MD from simple diffusion theory are likely caused in part by the presence of significant nonnative effects in folding processes modelled by current atomic force fields. The ramifications of our findings to the application of coarse-grained modeling to more complex biomolecular systems are discussed.

  17. NOMAD-Ref: visualization, deformation and refinement of macromolecular structures based on all-atom normal mode analysis.

    Science.gov (United States)

    Lindahl, Erik; Azuara, Cyril; Koehl, Patrice; Delarue, Marc

    2006-07-01

    Normal mode analysis (NMA) is an efficient way to study collective motions in biomolecules that bypasses the computational costs and many limitations associated with full dynamics simulations. The NOMAD-Ref web server presented here provides tools for online calculation of the normal modes of large molecules (up to 100,000 atoms) maintaining a full all-atom representation of their structures, as well as access to a number of programs that utilize these collective motions for deformation and refinement of biomolecular structures. Applications include the generation of sets of decoys with correct stereochemistry but arbitrary large amplitude movements, the quantification of the overlap between alternative conformations of a molecule, refinement of structures against experimental data, such as X-ray diffraction structure factors or Cryo-EM maps and optimization of docked complexes by modeling receptor/ligand flexibility through normal mode motions. The server can be accessed at the URL http://lorentz.immstr.pasteur.fr/nomad-ref.php.

  18. Quantitative size-dependent structure and strain determination of CdSe nanoparticles using atomic pair distribution function analysis

    International Nuclear Information System (INIS)

    Masadeh, A. S.; Bozin, E. S.; Farrow, C. L.; Paglia, G.; Juhas, P.; Billinge, S. J. L.; Karkamkar, A.; Kanatzidis, M. G.

    2007-01-01

    The size-dependent structure of CdSe nanoparticles, with diameters ranging from 2 to 4 nm, has been studied using the atomic pair distribution function (PDF) method. The core structure of the measured CdSe nanoparticles can be described in terms of the wurtzite atomic structure with extensive stacking faults. The density of faults in the nanoparticles is ∼50%. The diameter of the core region was extracted directly from the PDF data and is in good agreement with the diameter obtained from standard characterization methods, suggesting that there is little surface amorphous region. A compressive strain was measured in the Cd-Se bond length that increases with decreasing particle size being 0.5% with respect to bulk CdSe for the 2 nm diameter particles. This study demonstrates the size-dependent quantitative structural information that can be obtained even from very small nanoparticles using the PDF approach

  19. Quantitative size-dependent structure and strain determination of CdSe nanoparticles using atomic pair distribution function analysis

    Science.gov (United States)

    Masadeh, A. S.; Božin, E. S.; Farrow, C. L.; Paglia, G.; Juhas, P.; Billinge, S. J. L.; Karkamkar, A.; Kanatzidis, M. G.

    2007-09-01

    The size-dependent structure of CdSe nanoparticles, with diameters ranging from 2to4nm , has been studied using the atomic pair distribution function (PDF) method. The core structure of the measured CdSe nanoparticles can be described in terms of the wurtzite atomic structure with extensive stacking faults. The density of faults in the nanoparticles is ˜50% . The diameter of the core region was extracted directly from the PDF data and is in good agreement with the diameter obtained from standard characterization methods, suggesting that there is little surface amorphous region. A compressive strain was measured in the Cd-Se bond length that increases with decreasing particle size being 0.5% with respect to bulk CdSe for the 2nm diameter particles. This study demonstrates the size-dependent quantitative structural information that can be obtained even from very small nanoparticles using the PDF approach.

  20. The atomic and electronic structure of nitrogen- and boron-doped phosphorene.

    Science.gov (United States)

    Boukhvalov, Danil W

    2015-10-28

    First principles modeling of nitrogen- and boron-doped phosphorene demonstrates the tendency toward the formation of highly ordered structures. Nitrogen doping leads to the formation of -N-P-P-P-N- lines. Further transformation into -P-N-P-N- lines across the chains of phosphorene occurs with increasing band gap and increasing nitrogen concentration, which coincides with the decreasing chemical activity of N-doped phosphorene. In contrast to the case of nitrogen, boron atoms prefer to form -B-B- pairs with the further formation of -P-P-B-B-P-P- patterns along the phosphorene chains. The low concentration of boron dopants converts the phosphorene from a semiconductor into a semimetal with the simultaneous enhancement of its chemical activity. Co-doping of phosphorene by both boron and nitrogen starts from the formation of -B-N- pairs, which provides flat bands and further transformation of these pairs into hexagonal BN lines and ribbons across the phosphorene chains.

  1. Determining the resolution of scanning microwave impedance microscopy using atomic-precision buried donor structures

    Science.gov (United States)

    Scrymgeour, D. A.; Baca, A.; Fishgrab, K.; Simonson, R. J.; Marshall, M.; Bussmann, E.; Nakakura, C. Y.; Anderson, M.; Misra, S.

    2017-11-01

    To quantify the resolution limits of scanning microwave impedance microscopy (sMIM), we created scanning tunneling microscope (STM)-patterned donor nanostructures in silicon composed of 10 nm lines of highly conductive silicon buried under a protective top cap of silicon, and imaged them with sMIM. This dopant pattern is an ideal test of the resolution and sensitivity of the sMIM technique, as it is made with nm-resolution and offers minimal complications from topography convolution. It has been determined that typical sMIM tips can resolve lines down to ∼80 nm spacing, while resolution is independent of tip geometry as extreme tip wear does not change the resolving power, contrary to traditional scanning capacitance microscopy (SCM). Going forward, sMIM is an ideal technique for qualifying buried patterned devices, potentially allowing for quantitative post-fabrication characterization of donor structures, which may be an important tool for the study of atomic-scale transistors and state of the art quantum computation schemes.

  2. Electronic structure calculations of atomic transport properties in uranium dioxide: influence of strong correlations

    International Nuclear Information System (INIS)

    Dorado, B.

    2010-09-01

    Uranium dioxide UO 2 is the standard nuclear fuel used in pressurized water reactors. During in-reactor operation, the fission of uranium atoms yields a wide variety of fission products (FP) which create numerous point defects while slowing down in the material. Point defects and FP govern in turn the evolution of the fuel physical properties under irradiation. In this study, we use electronic structure calculations in order to better understand the fuel behavior under irradiation. In particular, we investigate point defect behavior, as well as the stability of three volatile FP: iodine, krypton and xenon. In order to take into account the strong correlations of uranium 5f electrons in UO 2 , we use the DFT+U approximation, based on the density functional theory. This approximation, however, creates numerous metastable states which trap the system and induce discrepancies in the results reported in the literature. To solve this issue and to ensure the ground state is systematically approached as much as possible, we use a method based on electronic occupancy control of the correlated orbitals. We show that the DFT+U approximation, when used with electronic occupancy control, can describe accurately point defect and fission product behavior in UO 2 and provide quantitative information regarding point defect transport properties in the oxide fuel. (author)

  3. Hyperfine structure measurements of neutral iodine atom (127I) using Fourier Transform Spectrometry

    Science.gov (United States)

    Ashok, Chilukoti; Vishwakarma, S. R.; Bhatt, Himal; Ankush, B. K.; Deo, M. N.

    2018-01-01

    We report the hyperfine Structure (hfs) splitting observations of neutral iodine atom (II) in the 6000 - 10,000 cm-1 near infrared spectral region. The measurements were carried out using a high-resolution Fourier Transform Spectrometer (FTS), where an electrodeless discharge lamp (EDL), excited using microwaves, was employed as the light source and InGaAs as the light detector. A specially designed setup was used to lower the plasma temperature of the medium so as to reduce the Doppler width and consequently to increase the spectral resolution of hfs components. A total of 183 lines with hfs splitting have been observed, out of which hfs in 53 spectral lines are reported for the first time. On the basis of hfs analysis, we derived the magnetic dipole and electric quadrupole coupling constants, A and B respectively for 30 even and 30 odd energy levels and are compared with the values available in the literature. New hfs values for 5 even and 4 odd levels are also reported here for the first time.

  4. Surface structure of polymers and their model compounds observed by atomic force microscopy

    NARCIS (Netherlands)

    Stocker, W.; Bickmann, B.; Magonov, S.N.; Cantow, H.J.; Lotz, B.; Wittmann, J.C.; Moller, M.; Möller, M.

    1992-01-01

    Results of atomic force microscopy (AFM) of normal alkanes, polyethylene, isotactic polypropylene and of a diblock copolymer are presented. Various types of surfaces - naturally and epitaxially grown on different substrates - have been examined from hundreds of nanometers down to the atomic scale.

  5. Erosion of Carbon-based spacecraft structures in LEO by Atomic Oxygen

    DEFF Research Database (Denmark)

    Jørgensen, John Leif

    1998-01-01

    Atomic oxygen is constantly generated on the topside of the atmosphere by ionizing radiation. The ionizing solar radiation, UV and particles, will on impact dissociate molecular oxygen to atomic oxygen. However, due to the ratio between the UV and the particle flux from the sun, and due to compar...

  6. Growth mechanisms for Si epitaxy on O atomic layers: Impact of O-content and surface structure

    Energy Technology Data Exchange (ETDEWEB)

    Jayachandran, Suseendran, E-mail: suseendran.jayachandran@imec.be [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Metallurgy and Materials, Castle Arenberg 44, B-3001 Leuven (Belgium); Billen, Arne [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Chemistry, Celestijnenlaan 200F, B-3001 Leuven (Belgium); Douhard, Bastien; Conard, Thierry; Meersschaut, Johan; Moussa, Alain; Caymax, Matty; Bender, Hugo [Imec, Kapeldreef 75, 3001 Leuven (Belgium); Vandervorst, Wilfried [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Physics and Astronomy, Celestijnenlaan 200D, B-3001 Leuven (Belgium); Heyns, Marc [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Metallurgy and Materials, Castle Arenberg 44, B-3001 Leuven (Belgium); Delabie, Annelies [Imec, Kapeldreef 75, 3001 Leuven (Belgium); KU Leuven (University of Leuven), Department of Chemistry, Celestijnenlaan 200F, B-3001 Leuven (Belgium)

    2016-10-30

    Highlights: • O{sub 3} or O{sub 2} exposures on H-Si(100) result in O ALs with different surface structures. • Si-EPI on O AL using O{sub 3} process is by direct epitaxial growth mechanism. • Si-EPI on O AL using O{sub 2} process is by epitaxial lateral overgrowth mechanism. • Distortions by O AL, SiH{sub 4} flux rate and Si thickness has an impact on Si-EPI quality. - Abstract: The epitaxial growth of Si layers on Si substrates in the presence of O atoms is generally considered a challenge, as O atoms degrade the epitaxial quality by generating defects. Here, we investigate the growth mechanisms for Si epitaxy on O atomic layers (ALs) with different O-contents and structures. O ALs are deposited by ozone (O{sub 3}) or oxygen (O{sub 2}) exposure on H-terminated Si at 50 °C and 300 °C respectively. Epitaxial Si is deposited by chemical vapor deposition using silane (SiH{sub 4}) at 500 °C. After O{sub 3} exposure, the O atoms are uniformly distributed in Si-Si dimer/back bonds. This O layer still allows epitaxial seeding of Si. The epitaxial quality is enhanced by lowering the surface distortions due to O atoms and by decreasing the arrival rate of SiH{sub 4} reactants, allowing more time for surface diffusion. After O{sub 2} exposure, the O atoms are present in the form of SiO{sub x} clusters. Regions of hydrogen-terminated Si remain present between the SiO{sub x} clusters. The epitaxial seeding of Si in these structures is realized on H-Si regions, and an epitaxial layer grows by a lateral overgrowth mechanism. A breakdown in the epitaxial ordering occurs at a critical Si thickness, presumably by accumulation of surface roughness.

  7. Tailoring characteristic thermal stability of Ni-Au binary nanocrystals via structure and composition engineering: theoretical insights into structural evolution and atomic inter-diffusion

    Directory of Open Access Journals (Sweden)

    Bangquan Li

    2014-11-01

    Full Text Available We report on the structural evolution and atomic inter-diffusion characteristics of the bimetallic Ni-Au nanocrystals (NCs by molecular dynamics simulations studies. Our results reveal that the thermal stability dynamics of Ni-Au NCs strongly depends on the atomic configurations. By engineering the structural construction with Ni:Au = 1:1 atomic composition, compared with core-shell Au@Ni and alloy NCs, the melting point of core-shell Ni@Au NCs is significantly enhanced up to 1215 K. Unexpectedly, with atomic ratio of Au:Ni= 1:9, the melting process initiates from the atoms in the shell of Ni@Au and alloy NCs, while starts from the core of Au@Ni NCs. The corresponding features and evolution process of structural motifs, mixing and segregation are illustrated via a series of dynamic simulations videos. Moreover, our results revealed that the face centered cubic phase Au0.75Ni0.25 favorably stabilizes in NCs form but does not exist in the bulk counterpart, which elucidates the anomalies of previously reported experimental results on such bimetallic NCs.

  8. Atomic structure of a stable high-index Ge surface: G2(103)-(4x1)

    DEFF Research Database (Denmark)

    Seehofer, L.; Bunk, O.; Falkenberg, G.

    1997-01-01

    Based on scanning tunneling microscopy and surface X-ray diffraction, we propose a complex structural model for the Ge(103)-(4 x 1) reconstruction. Each unit cell contains two (103) double steps, which gives rise to the formation of stripes of Ge atoms oriented in the [] direction....... The stripes and the spaces between them are covered with threefold-coordinated Ge adatoms. Charge is transferred from the bulk-like edge atoms of the double steps to the adatoms. The formation of the reconstruction can be explained in terms of stress relief, charge transfer, and minimization of the dangling...

  9. Investigations of the Electronic Properties and Surface Structures of Aluminium-Rich Quasicrystalline Alloys

    Energy Technology Data Exchange (ETDEWEB)

    Barrow, Jason A. [Iowa State Univ., Ames, IA (United States)

    2003-01-01

    The work presented in this dissertation has investigated three distinct areas of interest in the field of quasicrystals: bulk structure, transport properties, and electronic structure. First, they have described the results of a study which explored the fundamental interactions between the atomic species of the icosahedral Al-Pd-Mn quasicrystal. The goal of this work was to determine whether the pseudo-MacKay or Bergman type clusters have a special stability or are merely a geometric coincidence. This was carried out by using laser vaporization to produce gas-phase metal clusters, which were analyzed using time-of-flight mass spectrometry. Both the kinetic and thermodynamic stabilities of the clusters were probed. The data indicated no special stability for either pseudo-MacKay or Bergman type clusters as isolated units. This, however, is not proof that these clusters are simply a geometric coincidence. It is possible that such clusters only have stability in the framework of the bulk matrix and do not exist as isolated units. Next, they have reported their investigations of the bulk thermal transport properties of a decagonal Al-Ni-Co two dimensional quasicrystal in the temperature range 373K-873K. The properties of a sample oriented along the periodic axis and another oriented along the aperiodic axis were measured. A high degree of anisotropy was observed between the aperiodic and periodic directions. Additionally, the properties were measured for a sample miscut to an orientation 45° off-axis. The properties of the miscut sample were shown to have good agreement with a theoretical model used to describe thermal transport in metallic single crystals. This model only considers thermal transport by a free-electron gas; therefore, agreement with experimental data suggests the validity of the Drude free-electron model for the decagonal Al-Ni-Co at these temperatures. Consequently, the observed anisotropy may be adequately described using classical transport

  10. Watching Silica's Dance: Imaging the Structure and Dynamics of the Atomic (Re-) Arrangements in 2D Glass

    Science.gov (United States)

    Muller, David

    2014-03-01

    Even though glasses are almost ubiquitous--in our windows, on our iPhones, even on our faces--they are also mysterious. Because glasses are notoriously difficult to study, basic questions like: ``How are the atoms arranged? Where and how do glasses break?'' are still under contention. We use aberration corrected transmission electron microscopy (TEM) to image the atoms in a new two-dimensional phase of silica glass - freestanding it becomes the world's thinnest pane of glass at only 3-atoms thick, and take a unique look into these questions. Using atom-by-atom imaging and spectroscopy, we are able to reconstruct the full structure and bonding of this 2D glass and identify it as a bi-tetrahedral layer of SiO2. Our images also strikingly resemble Zachariasen's original cartoon models of glasses, drawn in 1932. As such, our work realizes an 80-year-old vision for easily understandable glassy systems and introduces promising methods to test theoretical predictions against experimental data. We image atoms in the disordered solid and track their motions in response to local strain. We directly obtain ring statistics and pair distribution functions that span short-, medium-, and long-range order, and test these against long-standing theoretical predictions of glass structure and dynamics. We use the electron beam to excite atomic rearrangements, producing surprisingly rich and beautiful videos of how a glass bends and breaks, as well as the exchange of atoms at a solid/liquid interface. Detailed analyses of these videos reveal a complex dance of elastic and plastic deformations, phase transitions, and their interplay. These examples illustrate the wide-ranging and fundamental materials physics that can now be studied at atomic-resolution via transmission electron microscopy of two-dimensional glasses. Work in collaboration with: S. Kurasch, U. Kaiser, R. Hovden, Q. Mao, J. Kotakoski, J. S. Alden, A. Shekhawat, A. A. Alemi, J. P. Sethna, P. L. McEuen, A.V. Krasheninnikov

  11. Order within disorder: The atomic structure of ion-beam sputtered amorphous tantala (a-Ta2O5

    Directory of Open Access Journals (Sweden)

    Riccardo Bassiri

    2015-03-01

    Full Text Available Amorphous tantala (a-Ta2O5 is a technologically important material often used in high-performance coatings. Understanding this material at the atomic level provides a way to further improve performance. This work details extended X-ray absorption fine structure measurements of a-Ta2O5 coatings, where high-quality experimental data and theoretical fits have allowed a detailed interpretation of the nearest-neighbor distributions. It was found that the tantalum atom is surrounded by four shells of atoms in sequence; oxygen, tantalum, oxygen, and tantalum. A discussion is also included on how these models can be interpreted within the context of published crystalline Ta2O5 and other a-T2O5 studies.

  12. Modification in structure, phase transition, and magnetic property of metallic gallium driven by atom-molecule interactions.

    Science.gov (United States)

    Song, Le Xin; Chen, Jie; Zhu, Lin Hong; Xia, Juan; Yang, Jun

    2011-09-05

    The present work supports a novel paradigm in which the surface structure and stacking behavior of metallic gallium (Ga) were significantly influenced by the preparation process in the presence of organic small molecules (ethanol, acetone, dichloromethane, and diethyl ether). The extent of the effect strongly depends on the polarity of the molecules. Especially, a series of new atom-molecule aggregates consisting of metallic Ga and macrocyclic hosts (cyclodextrins, CDs) were prepared and characterized by various techniques. A comprehensive comparative analysis between free metallic Ga and the Ga samples obtained provides important and at present rare information on the modification in structure, phase transition, and magnetic property of Ga driven by atom-molecule interactions. First, there is a notable difference in microstructure and electronic structure between the different types of Ga samples. Second, differential scanning calorimetry analysis gives us a complete picture (such as the occurrence of a series of metastable phases of Ga in the presence of CDs) that has allowed us to consider that Ga atoms were protected by the shielding effect provided by the cavities of CDs. Third, the metallic Ga distributed in the aggregates exhibits very interesting magnetic property compared to free metallic Ga, such as the uniform zero-field-cooled and field-cooled magnetization processes, the enhanced responses in magnetization to temperature and applied field, and the fundamental change in shape of magnetic hysteresis loops. These significant changes in structural transformation and physical property of Ga provide a novel insight into the understanding of atom-molecule interactions between metallic atoms and organic molecules.

  13. Photoluminescence polarization anisotropy for studying long-range structural ordering within semiconductor multi-atomic alloys and organic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Prutskij, T.; Percino, J. [Instituto de Ciencias, BUAP, Privada 17 Norte, No 3417, col. San Miguel Huyeotlipan, 72050, Puebla, Pue. (Mexico); Orlova, T. [Department of Chemical and Biochemical Engineering, University of Notre Dame, Notre Dame, IN (United States); Vavilova, L. [Ioffe Physical-Technical Institute, 26 Polytekhnicheskaya, St Petersburg 194021, Russian Federation (Russian Federation)

    2013-12-04

    Long-range structural ordering within multi-component semiconductor alloys and organic crystals leads to significant optical anisotropy and, in particular, to anisotropy of the photoluminescence (PL) emission. The PL emission of ternary and quaternary semiconductor alloys is polarized if there is some amount of the atomic ordering within the crystal structure. We analyze the polarization of the PL emission from the quaternary GaInAsP semiconductor alloy grown by Liquid Phase Epitaxy (LPE) and conclude that it could be caused by low degree atomic ordering within the crystal structure together with the thermal biaxial strain due to difference between the thermal expansion coefficients of the layer and the substrate. We also study the state of polarization of the PL from organic crystals in order to identify different features of the crystal PL spectrum.

  14. Atomic resolution structure of the double mutant (K53,56M) of bovine pancreatic phospholipase A2

    International Nuclear Information System (INIS)

    Sekar, K.; Yogavel, M.; Gayathri, D.; Velmurugan, D.; Krishna, R.; Poi, M.-J.; Dauter, Z.; Dauter, M.; Tsai, M.-D.

    2005-01-01

    The atomic resolution crystal structure of the double mutant (K53,56M) of bovine pancreatic phospholipase A 2 is reported. The structure of the double mutant K53,56M has previously been refined at 1.9 Å resolution using room-temperature data. The present paper reports the crystal structure of the same mutant K53,56M refined against 1.1 Å data collected using synchrotron radiation. A total of 116 main-chain atoms from 29 residues and 44 side chains are modelled in alternate conformations. Most of the interfacial binding residues are found to be disordered and alternate conformations could be recognized. The second calcium ion-binding site residue Glu92 adopts two alternate conformations. The minor and major conformations of Glu92 correspond to the second calcium ion bound and unbound states

  15. Near-atomic resolution structures of urate oxidase complexed with its substrate and analogues: the protonation state of the ligand.

    Science.gov (United States)

    Gabison, Laure; Chiadmi, Mohamed; El Hajji, Mohamed; Castro, Bertrand; Colloc'h, Nathalie; Prangé, Thierry

    2010-06-01

    Urate oxidase (uricase; EC 1.7.3.3; UOX) from Aspergillus flavus catalyzes the oxidation of uric acid in the presence of molecular oxygen to 5-hydroxyisourate in the degradation cascade of purines; intriguingly, catalysis proceeds using neither a metal ion (Fe, Cu etc.) nor a redox cofactor. UOX is a tetrameric enzyme with four active sites located at the interface of two subunits; its structure was refined at atomic resolution (1 A) using new crystal data in the presence of xanthine and at near-atomic resolution (1.3-1.7 A) in complexes with the natural substrate (urate) and two inhibitors: 8-nitroxanthine and 8-thiouric acid. Three new features of the structural and mechanistic behaviour of the enzyme were addressed. Firstly, the high resolution of the UOX-xanthine structure allowed the solution of an old structural problem at a contact zone within the tetramer; secondly, the protonation state of the substrate was determined from both a halochromic inhibitor complex (UOX-8-nitroxanthine) and from the H-atom distribution in the active site, using the structures of the UOX-xanthine and the UOX-uric acid complexes; and thirdly, it was possible to extend the general base system, characterized by the conserved catalytic triad Thr-Lys-His, to a large water network that is able to buffer and shuttle protons back and forth between the substrate and the peroxo hole along the reaction pathway.

  16. Atom and Amine Adsorption on Flat and Stepped Gold Surfaces & Structure, Stability and Spin Ordering in Manganese Sulfide Clusters

    Science.gov (United States)

    Lewoczko, April D.

    In part I, we investigate gold catalysis in the chemistry of organonitrogen compounds. We examine the adsorption of oxygen, nitrogen and sulfur atoms on the gold (111), (100) and (211) surfaces using density functional theory (DFT). Sulfur atoms bind most strongly, followed by oxygen and nitrogen atoms with stronger adsorption for greater coordination to the surface. We see a trend of stronger adsorption to undercoordinated gold, but find it is non-universal with the adsorption strength trend: (111) > (211) > (100). We consider the diffusion of oxygen, nitrogen and sulfur adatoms and find facile long-range diffusion of oxygen atoms on the (100) surface. Lastly, we compare the adsorption of methylamine on gold to that of a selection of alkylamines, methanol and methanethiol. In each case, the ontop site is preferred with stronger adsorption at low coordinated gold. At oxygen atom coverages of 0.125 -- 0.25 ML on Au (111), we find cooperative adsorption of methylamine and oxygen atoms. Energetic costs for adsorbate tilt from the surface normal and rotation about the gold-nitrogen bond are calculated. While methylamine rotation is barrierless on the (111) and (211) surfaces, it has a low energetic barrier for the 0.125 ML and 0.25 ML O atom pre-covered Au (111) surfaces. In part II, we interpret the experimental mass spectrum of small gas phase manganese sulfide clusters using DFT and elucidate the role of ionicity and spin ordering in sizes with special stability, i.e. magic clusters. We first consider nine low lying minima (MnS)6 structures and reveal antiferromagnetic (AFM) spin ordering with a ˜0.1 eV/pair AFM energy benefit and a ˜0.1 A shrinkage of average Mn-Mn distances over clusters with ferromagnetic (FM) spin ordering. We calculate energetic barriers for interconversion between the two lowest lying (MnS)6 isomers and predict an elevated cluster melting temperature due to increased configurational entropy in a pre-melted state. Second, we demonstrate the

  17. Atomic displacements and the electronic structure of the Mo(001) surface

    International Nuclear Information System (INIS)

    Inglesfield, J.E.

    1978-01-01

    The uniform surface contraction on Mo(001) and the phase transition observed below 300 K are due to the peak in the surface density of states at the Fermi energy. This is essentially a virtual bound 4d state on the surface atoms and contraction increases its interaction with the substrate and lowers the energy. The phase transition probably consists of a sideways displacement of the atoms which introduces new Brillouin zone boundaries broadening surface resonances at the Fermi energy. (author)

  18. Quantum chemical calculation of the equilibrium structures of small metal atom clusters

    Science.gov (United States)

    Kahn, L. R.

    1982-01-01

    Metal atom clusters are studied based on the application of ab initio quantum mechanical approaches. Because these large 'molecular' systems pose special practical computational problems in the application of the quantum mechanical methods, there is a special need to find simplifying techniques that do not compromise the reliability of the calculations. Research is therefore directed towards various aspects of the implementation of the effective core potential technique for the removal of the metal atom core electrons from the calculations.

  19. Atomic-scale structure relaxation, chemistry and charge distribution of dislocation cores in SrTiO3.

    Science.gov (United States)

    Gao, Peng; Ishikawa, Ryo; Feng, Bin; Kumamoto, Akihito; Shibata, Naoya; Ikuhara, Yuichi

    2018-01-01

    By using the state-of-the-art microscopy and spectroscopy in aberration-corrected scanning transmission electron microscopes, we determine the atomic arrangements, occupancy, elemental distribution, and the electronic structures of dislocation cores in the 10° tilted SrTiO 3 bicrystal. We identify that there are two different types of oxygen deficient dislocation cores, i.e., the SrO plane terminated Sr 0.82 Ti 0.85 O 3-x (Ti 3.67+ , 0.48 ≤ x ≤ 0.91) and TiO 2 plane terminated Sr 0.63 Ti 0.90 O 3-y (Ti 3.60+ , 0.57 ≤ y ≤ 1). They have the same Burgers vector of a[100] but different atomic arrangements and chemical properties. Besides the oxygen vacancies, Sr vacancies and rocksalt-like titanium oxide reconstruction are also identified in the dislocation core with TiO 2 plane termination. Our atomic-scale study reveals the true atomic structures and chemistry of individual dislocation cores, providing useful insights into understanding the properties of dislocations and grain boundaries. Copyright © 2017 Elsevier B.V. All rights reserved.

  20. Melt holding time as an important factor on the formation of quasicrystal phase in Mg67Zn30Gd3 alloy

    Science.gov (United States)

    Zhang, Jinyang; Jia, Peng; Zhao, Degang; Zhou, Guorong; Teng, Xinying

    2018-03-01

    In the present work, the content of icosahedral quasicrystal phase (I-phase) and melt holding time shows a mono peak curve: a small amount of I-phase and lots of Mg3(Gd,Zn) phase are presented for t 21 min, and the volumetric fraction of I-phase has the maximum of 49.50% for t = 41 min. This strategy of formation of quasicrystal phase makes us realize that melt thermal treatment could significantly affect the phase types in Mgsbnd Znsbnd Gd alloy.