Discovery of the beta-form crystal structure in electrospun nanofibers of bio-based poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] and its implication on properties

NASA Astrophysics Data System (ADS)

Gong, Liang

Bacterially produced poly[(R)-3-hydroxybutyrate-co-(R)-3-hydroxyhexanoate] (PHBHx) is a new type of bioplastic which not only inherits the excellent biodegradability and biocompatibility of its parent homopolymer, polyhydroxybutyrate (PHB), but also overcomes PHB’s brittleness and stiffness with the incorporation of 3-hydroxyhexanoate (Hx) comonomer units with medium-chain-length (mcl) side chains. The tough and ductile PHBHx, with a much lower crystallinity and melting temperature, is well-suited for many practical applications. Efforts have been made to broaden the application range of PHBHx by introducing the beta-form crystalline structure, where the molecular chains adopt a planar zig-zag conformation. However, it is extremely difficult to produce this beta-form in PHBHx due to its much lower crystallinity and much more flexible molecular chains. In this study, we report an approach using the technique of electrospinning. The strain-induced metastable β-form crystalline structure was successfully introduced in PHBHx by collecting the macroscopically aligned electrospun PHBHx nanofibers across the air gap on a piece of aluminum foil and on the tapered edge of a high-speed rotary disk. The presence of the β-form crystal structure in electrospun fiber mats was confirmed by wide-angle X-ray diffraction (WAXD) and Fourier transform infrared spectroscopy (FTIR), with molecular orientation of the polymer chains along the fiber axis revealed by polarized FTIR. Selected area electron diffraction (SAED) and AFM-IR were utilized to investigate the morphological and structural details of individual PHBHx nanofibers. The results demonstrated a coexistence of the thermodynamically stable α-form crystalline structure, where molecular chains adopt a left-handed 21 helical conformation, and the β-form in single fibers. The molecular orientation level and the relative amounts of the two crystalline polymorphs were found to be highly dependent on fiber collection methods and fiber diameter. Moreover, the α and β-form were revealed to be spatially distributed as a core-shell structure consisting of an α-form-rich core and a β-form-rich shell, with the thickness of the shell remaining constant despite the variation of fiber diameter. According to these observations, a possible mechanism for the generation of the β-form was proposed. The effects of electrospinning parameters on the formation of the beta-form were systematically investigated. The results indicated that more β-crystals can be produced when 1) a higher fiber take-up is used, so that the polymer chains are further stretched before fiber solidification; 2) an optimal solution concentration is chosen, so that a balance between polymer chain deformation and relaxation is maintained throughout the whole electrospinning process; and 3) a more volatile solvent is used, so that more planar zig-zag chains are kinetically frozen in the fibers without being converted to the helical conformation as the fibers solidify. These experimental results indicate that the β-content in PHBHx nanofibers can be easily regulated by modifying the electrospinning conditions. Finally, the influence of the presence of the β-form on the piezoelectric response of the electrospun PHBHx nanofibers was studied. It was observed that the fibers containing the β-form exhibited an obvious piezoelectric response to the applied pressure, possibly due to the planar zig-zag conformation of the chains which gives rise to a significant dipole moment change when subjected to mechanical deformation. In addition, the sensitivity of the piezoelectric PHBHx nanofibers to mechanical pressure was measured to be 7.46 mV/kPa. These preliminary investigations indicate that the piezoelectric performance of PHBHx can be largely improved by increasing the concentration of the piezoelectric-active β-form crystalline structure. The piezoelectric PHBHx distinguishes itself from all the other piezoelectric polymers with its excellent biodegradability and biocompatibility, environmental-friendliness and most importantly, low manufacturing cost. It is a promising piezoelectric polymer which can be applied in advanced areas including portable/foldable electronic devices, artificial electronic skins and implantable sensors.

Raman scattering and X-ray powder diffraction studies of hydrate layered perovskites: dirubidium aquapentafluoromanganate(III) and dipotassium aquapentafluoroferrate(III)

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

Galicka, Karolina; Slodczyk, Aneta; Ratuszna, Alicja

2004-06-08

The structural and vibrational properties of above mentioned crystals were determined using X-ray powder diffraction and Raman scattering experiments. At room temperature hydrate layered perovskites: Rb{sub 2}MnF{sub 5}{center_dot}H{sub 2}O and K{sub 2}FeF{sub 5}{center_dot}H{sub 2}O exhibit orthorhombic--Cmcm (D{sub 2h}{sup 17}) and monoclinic--C2/c (C{sub 2h}{sup 6}) symmetry. Their structure is built up of MnF{sub 6} or FeF{sub 5}{center_dot}H{sub 2}O octahedra forming trans-linked zig-zag chains or hydrogen bonded zig-zag chains along the major crystallographic direction [0 0 1], respectively. To confirm crystal structures and to describe lattice dynamics of these compounds the vibrational normal modes (in {gamma} point of first Brillouin zone) weremore » calculated on the base of the group theory analysis and compared with the spectra obtained from Raman scattering experiments. A relatively good reliability was obtained for both X-ray powder diffraction and Raman scattering.« less

2-({4-[4-(1H-Benzimidazol-2-yl)phen­yl]-1H-1,2,3-triazol-1-yl}meth­oxy)ethanol

PubMed Central

Ouahrouch, Abdelaaziz; Taourirte, Moha; Lazrek, Hassan B.; Bats, Jan W.; Engels, Joachim W.

2012-01-01

In the title molecule, C18H17N5O2, the dihedral angle between the benzene plane and the benzimidazole plane is 19.8 (1)° and the angle between the benzene plane and the triazole plane is 16.7 (1)°. In the crystal, mol­ecules are connected by O—H⋯N hydrogen bonds, forming zigzag chains along the c-axis direction. The chains are connected by bifurcated N—H⋯(N,N) hydrogen bonds into layers parallel to (100). These layers are connected along the a-axis direction by weak C—H⋯O contacts, forming a three-dimensional network. PMID:22719663

Imidazolium 3-nitro­benzoate

PubMed Central

Hou, Guang-Yang; Zhou, Li-Na; Yin, Qiu-Xiang; Su, Wei-Yi; Mao, Hui-Lin

2009-01-01

In the title compound, C3H5N2 +·C7H4NO4 −, the benzene ring forms a dihedral angle of 40.60 (5)° with the imidizolium ring. The nitro­benzoate anion is approximately planar: the benzene ring makes dihedral angles of 3.8 (3) and 3.2 (1)° with the nitro and carboxyl­ate groups, respectively. In the crystal structure, the cations and anions are linked by inter­molecular N—H⋯O hydrogen bonds, forming a zigzag chain along the b axis. PMID:21583857

Systematic study of aggregation structure and thermal behavior of a series of unique H-shape alkane molecules.

PubMed

Yamamoto, Hiroko; Tashiro, Kohji; Nemoto, Norio; Motoyama, Yukihiro; Takahashi, Yoshiaki

2011-08-11

The H-shape alkanes of various arm lengths have been synthesized successfully through the Grignard reaction. The detailed investigation of these novel compounds may allow us to widen the topological chemistry field furthermore. The molecular form and molecular packing structure in the crystal lattice have been revealed successfully on the basis of X-ray structure analysis as well as the analysis of Raman longitudinal acoustic modes (LAM) sensitive to the alkyl zigzag chain segments. The molecular conformation in the crystal lattice is deformed markedly from the originally imagined H-shape. In the cases of C3HOH to C6HOH, for example, the molecules are packed in a complicated manner and the OH···O hydrogen bonds govern the whole intermolecular interactions mainly. Since the alkyl segmental length is not very long, the conformational change is not very drastic, i.e., the small configurational entropy. Synergic effect of the hydrogen bonds and the small configurational entropy gives the higher melting point as known from the thermal data. On the other hand, in the cases of C10HOH and C12HOH, one of the long alkyl chain arms is found to be bent by 90° so that all of the alky chain segments of planar-zigzag conformation can be packed as closely as possible, and the intermolecular OH···O hydrogen bonds are also formed effectively without any mistake. As a result, the contribution of nonbonded intra- and intermolecular van der Waals interactions between the trans-zigzag alkyl chain segments become major, and the coupling of this enthalpy effect with the larger configurational entropy effect of the molecular shape results in the decrement of the melting point which approaches gradually that of longer n-alkane compound. In this way a sensitive balance between the nonbonded van der Waals interactions, the OH···O hydrogen bonds, as well as the configurational entropy effect gives the characteristic thermal behavior of the H-shape compounds. The thus-newly synthesized H-shape alkane compounds should give us new insight into the packing topology of complicated molecules, leading to the development of new functionality unexpected for normal linear alkane compounds. © 2011 American Chemical Society

Raman spectroscopic study of the conformation of dicarboxylic acid salts in aqueous solutions

NASA Astrophysics Data System (ADS)

Fukushima, Kunio; Watanabe, Toshiaki; Umemura, Matome

1986-08-01

It is already known that the molecules of long chain monocarboxylic acid salts have a tendency to form micelles in aqueous solutions, the molecular chain taking the all- trans zigzag structure. However it is considered difficult for dicarboxylic acid salts to adopt the same structure as the monocarboxylic acid salts as they have two carboxyl groups, one on each end of the molecular chain. Therefore, a special structure is expected to exist for dicarboxylic acid salts in aqueous solution. In order to examine this, Raman spectra of suberic acid salt and azelaic acid salt in aqueous solution were measured and the normal vibrational calculation carried out, showing that dicarboxylic acid salts have a helical structure in aqueous solution.

Evidence for SrHo2O4 and SrDy2O4 as model J1-J2 zigzag chain materials

NASA Astrophysics Data System (ADS)

Fennell, A.; Pomjakushin, V. Y.; Uldry, A.; Delley, B.; Prévost, B.; Désilets-Benoit, A.; Bianchi, A. D.; Bewley, R. I.; Hansen, B. R.; Klimczuk, T.; Cava, R. J.; Kenzelmann, M.

2014-06-01

Neutron diffraction and inelastic spectroscopy is used to characterize the magnetic Hamiltonian of SrHo2O4 and SrDy2O4. Through a detailed computation of the crystal-field levels we find site-dependent anisotropic single-ion magnetism in both materials, and diffraction measurements show the presence of strong one-dimensional spin correlations. Our measurements indicate that competing interactions of the zigzag chain, combined with frustrated interchain interactions, play a crucial role in stabilizing spin-liquid type correlations in this series.

Spin-polarized currents generated by magnetic Fe atomic chains.

PubMed

Lin, Zheng-Zhe; Chen, Xi

2014-06-13

Fe-based devices are widely used in spintronics because of high spin-polarization and magnetism. In this work, freestanding Fe atomic chains, the thinnest wires, were used to generate spin-polarized currents due to the spin-polarized energy bands. By ab initio calculations, the zigzag structure was found to be more stable than the wide-angle zigzag structure and had a higher ratio of spin-up and spin-down currents. By our theoretical prediction, Fe atomic chains have a sufficiently long thermal lifetime only at T ≦̸ 150 K, while C atomic chains are very stable even at T = 1000 K. This means that the spintronic devices based on Fe chains could work only at low temperatures. A system constructed by a short Fe chain sandwiched between two graphene electrodes could be used as a spin-polarized current generator, while a C chain could not be used in this way. The present work may be instructive and meaningful to further practical applications based on recent technical developments on the preparation of metal atomic chains (Proc. Natl. Acad. Sci. USA 107 9055 (2010)).

Antiferromagnetic S=1/2 spin chain driven by p-orbital ordering in CsO2.

PubMed

Riyadi, Syarif; Zhang, Baomin; de Groot, Robert A; Caretta, Antonio; van Loosdrecht, Paul H M; Palstra, Thomas T M; Blake, Graeme R

2012-05-25

We demonstrate, using a combination of experiment and density functional theory, that orbital ordering drives the formation of a one-dimensional (1D) S=1/2 antiferromagnetic spin chain in the 3D rocksalt structure of cesium superoxide (CsO2). The magnetic superoxide anion (O2(-)) exhibits degeneracy of its 2p-derived molecular orbitals, which is lifted by a structural distortion on cooling. A spin chain is then formed by zigzag ordering of the half-filled superoxide orbitals, promoting a superexchange pathway mediated by the p(z) orbitals of Cs(+) along only one crystal direction. This scenario is analogous to the 3d-orbital-driven spin chain found in the perovskite KCuF3 and is the first example of an inorganic quantum spin system with unpaired p electrons.

Fabricating and Controlling Silicon Zigzag Nanowires by Diffusion-Controlled Metal-Assisted Chemical Etching Method.

PubMed

Chen, Yun; Zhang, Cheng; Li, Liyi; Tuan, Chia-Chi; Wu, Fan; Chen, Xin; Gao, Jian; Ding, Yong; Wong, Ching-Ping

2017-07-12

Silicon (Si) zigzag nanowires (NWs) have a great potential in many applications because of its high surface/volume ratio. However, fabricating Si zigzag NWs has been challenging. In this work, a diffusion-controlled metal-assisted chemical etching method is developed to fabricate Si zigzag NWs. By tailoring the composition of etchant to change its diffusivity, etching direction, and etching time, various zigzag NWs can be easily fabricated. In addition, it is also found that a critical length of NW (>1 μm) is needed to form zigzag nanowires. Also, the amplitude of zigzag increases as the location approaches the center of the substrate and the length of zigzag nanowire increases. It is also demonstrated that such zigzag NWs can help the silicon substrate for self-cleaning and antireflection. This method may provide a feasible and economical way to fabricate zigzag NWs and novel structures for broad applications.

Platinum atomic wire encapsulated in gold nanotubes: A first principle study

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

Nigam, Sandeep, E-mail: snigam@barc.gov.in; Majumder, Chiranjib; Sahoo, Suman K.

2014-04-24

The nanotubes of gold incorporated with platinum atomic wire have been investigated by means of firstprinciples density functional theory with plane wave pseudopotential approximation. The structure with zig-zag chain of Pt atoms in side gold is found to be 0.73 eV lower in energy in comparison to straight chain of platinum atoms. The Fermi level of the composite tube was consisting of d-orbitals of Pt atoms. Further interaction of oxygen with these tubes reveals that while tube with zig-zag Pt prefers dissociative adsorption of oxygen molecule, the gold tube with linear Pt wire favors molecular adsorption.

Spin-liquid ground state in the frustrated J 1 - J 2 zigzag chain system BaTb 2 O 4

DOE PAGES

Aczel, A. A.; Li, L.; Garlea, V. O.; ...

2015-07-13

We have investigated polycrystalline samples of the zigzag chain system BaTb 2O 4 with magnetic susceptibility, heat capacity, neutron powder diffraction, and muon spin relaxation measurements. No magnetic transitions are observed in the bulk measurements, while neutron diffraction reveals low-temperature, short-range, intrachain magnetic correlations between Tb 3+ ions. Muon spin relaxation measurements indicate that these correlations are dynamic, as the technique detects no signatures of static magnetism down to 0.095 K. Altogether these findings provide strong evidence for a spin liquid ground state in BaTb 2O 4.

1-Allyl-3-chloro-5-nitro-1H-indazole

PubMed Central

Chicha, Hakima; Rakib, El Mostapha; Spinelli, Domenico; Saadi, Mohamed; El Ammari, Lahcen

2013-01-01

In the title compound, C10H8ClN3O2, the indazole ring system makes a dihedral angle of 7.9 (3)° with the plane through the nitro group. The allyl group is rotated out of the plane of the indazole ring system [N—N—C—C torsion angle = 104.28 (19)°]. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds, forming zigzag chains propagating along the b-axis direction. PMID:24427047

1-Allyl-3-chloro-5-nitro-1H-indazole.

PubMed

Chicha, Hakima; Rakib, El Mostapha; Spinelli, Domenico; Saadi, Mohamed; El Ammari, Lahcen

2013-01-01

In the title compound, C10H8ClN3O2, the indazole ring system makes a dihedral angle of 7.9 (3)° with the plane through the nitro group. The allyl group is rotated out of the plane of the indazole ring system [N-N-C-C torsion angle = 104.28 (19)°]. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds, forming zigzag chains propagating along the b-axis direction.

Confinement and Structural Changes in Vertically Aligned Dust Structures

NASA Astrophysics Data System (ADS)

Hyde, Truell

2013-10-01

In physics, confinement is known to influence collective system behavior. Examples include coulomb crystal variants such as those formed from ions or dust particles (classical), electrons in quantum dots (quantum) and the structural changes observed in vertically aligned dust particle systems formed within a glass box placed on the lower electrode of a Gaseous Electronics Conference (GEC) rf reference cell. Recent experimental studies have expanded the above to include the biological domain by showing that the stability and dynamics of proteins confined through encapsulation and enzyme molecules placed in inorganic cavities such as those found in biosensors are also directly influenced by their confinement. In this paper, the self-assembly and subsequent collective behavior of structures formed from n, charged dust particles interacting with one another and located within a glass box placed on the lower, powered electrode of a GEC rf reference cell is discussed. Self-organized formation of vertically aligned one-dimensional chains, two-dimensional zigzag structures, and three-dimensional helical structures of triangular, quadrangular, pentagonal, hexagonal, and heptagonal symmetries are shown to occur. System evolution is shown to progress from one-dimensional chain structures, through a zigzag transition to a two-dimensional, spindle like structures, and then to various three-dimensional, helical structures exhibiting various symmetries. Stable configurations are shown to be strongly dependent upon system confinement. The critical conditions for structural transitions as well as the basic symmetry exhibited by the one-, two-, and three-dimensional structures that subsequently develop will be shown to be in good agreement with molecular dynamics simulations.

Redetermination of the borax structure from laboratory X-ray data at 145 K

PubMed Central

Gainsford, Graeme J.; Kemmitt, Tim; Higham, Caleb

2008-01-01

The title compound, sodium tetraborate decahydrate (mineral name: borax), Na2[B4O5(OH)4]·8H2O, has been studied previously using X-ray [Morimoto (1956). Miner. J. 2, 1–18] and neutron [Levy & Lisensky (1978). Acta Cryst. B34, 3502–3510] diffraction data. The structure contains tetra­borate anions [B4O5(OH)4]2− with twofold rotation symmetry, which form hydrogen-bonded chains, and [Na(H2O)6] octa­hedra that form zigzag chains [Na(H2O)4/2(H2O)2/1]. The O—H bond distances obtained from the present redetermination at 145 K are shorter than those in the neutron study by an average of 0.127 (19) Å. PMID:21202161

New members of the A{sub 2}M′M{sub 2}{sup ″} structure family (A=Ca, Sr, Yb, La; M′=In,Sn,Pb; M″=Si,Ge)

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

Jehle, Michael; Dürr, Ines; Fink, Saskia

The new mixed tetrelides Sr{sub 2}PbGe{sub 2} and Yb{sub 2}SnGe{sub 2}, several mixed Ca/Sr (A{sup II}) germanides A{sub 2}{sup II}(Sn,Pb)Ge{sub 2} and two polymorphs of La{sub 2}InSi{sub 2} represent new members of the general structure family of ternary alkaline-earth/lanthanoid main group silicides/germanides A{sub 2}M′M{sub 2}{sup ″}(M′=In,Sn,Pb;M″=Si,Ge). All compounds were synthesized from melts of the elements and their crystal structures have been determined by means of single crystal X-ray diffraction. Sr{sub 2}PbGe{sub 2} (Cmmm, a=402.36(11), b=1542.3(4), c=463.27(10) pm) crystallizes with the Mn{sub 2}AlB{sub 2}-type structure. In exhibiting infinite planar Ge zig-zag chains, it represents one border of the compound series. Themore » other borderline case, where only [Ge{sub 2}] dumbbells are left as Ge building units, is represented by the Ca/Yb tin germanides Ca{sub 2}SnGe{sub 2} and Yb{sub 2}SnGe{sub 2} (Mo{sub 2}FeB{sub 2}-type; P4/mbm, a=748.58(13)/740.27(7), c=445.59(8)/435.26(5) pm). In between these two border structures compounds with variable Si/Ge chain lengths could be obtained by varying the averaged size of the A{sup II} cations: Ca{sub 0.45}Sr{sub 1.55}PbGe{sub 2} (new structure type; Pbam, a=791.64(5), b=2311.2(2), c=458.53(3) pm) contains planar six-membered chain segments [Ge{sub 6}]. Tetrameric pieces [Ge{sub 4}] are the conspicuous structure elements in Ca{sub 1.16}Sr{sub 0.84}SnGe{sub 2} and La{sub 2}InSi{sub 2} (La{sub 2}InNi{sub 2}-type; Pbam, a=781.01(2)/762.01(13), b=1477.95(3)/1494.38(6), c=457.004(9)/442.1(3) pm). The tetragonal form of ’La{sub 2}InSi{sub 2}{sup ′} (exact composition: La{sub 2}In{sub 1.07}Si{sub 1.93}, P4/mbm, a=1309.11(12), c=443.32(4) pm) also crystallizes in a new structure type, containing only [Si{sub 3}] trimers as cutouts of the planar chains. In all structures the Si/Ge zig-zag chains/chain segments are connected by In/Sn/Pb atoms to form planar M layers, which are separated by pure A layers. Band structure calculations within the FP-LAPW DFT approach together with the Zintl formalism, extended by the presence of hypervalent bonding of the heavier M′ elements, give insight into the chemical bonding of this series of p-block metallides. An analysis of the band structure for the border phases Sr{sub 2}PbGe{sub 2} and Ca{sub 2}SnGe{sub 2} shows the considerable π bonding contributions within the Ge building units, which also become apparent from the short Ge–Ge bond lengths. - Graphical abstract: Example of one of the mixed metallides A{sub 2}(In/Sn/Pb)(Si/Ge){sub 2} with planar Si/Ge zig-zag chain segments of variable lengths. - Highlights: • Mixed metallides A{sub 2}(In/Sn/Pb)(Si/Ge){sub 2} were prepared for A=Ca, Sr, Yb, La. • The structures exhibit planar Si/Ge zig-zag chain segments of variable lengths. • In, Sn and Pb atoms are connecting the Si/Ge anions to planar nets. • Atomic size effects are investigated by the synthesis of mixed Ca/Sr germanides. • Bandstructure calculations indicate Si/Ge–Si/Ge π bonding contributions.« less

3,3-Dimethyl-1-[5-(1H-1,2,4-triazol-1-yl­meth­yl)-1,3,4-thia­diazol-2-ylsulfan­yl]butan-2-one

PubMed Central

Wei, Qing-Li; He, Fu-Jin; Li, Fang; Bi, Sai

2008-01-01

In the mol­ecule of the title compound, C11H15N5OS2, the thia­diazole and triazole rings are not coplanar, the dihedral angle formed by their mean planes being 59.9 (2)°. The exocyclic S atom, and the methyl­ene, carbonyl, tert-butyl and one methyl carbon form an approximately planar zigzag chain, which makes a dihedral angle of 74.6 (1)° with the thia­diazole ring. PMID:21201440

All-zigzag graphene nanoribbons for planar interconnect application

NASA Astrophysics Data System (ADS)

Chen, Po-An; Chiang, Meng-Hsueh; Hsu, Wei-Chou

2017-07-01

A feasible "lightning-shaped" zigzag graphene nanoribbon (ZGNR) structure for planar interconnects is proposed. Based on the density functional theory and non-equilibrium Green's function, the electron transport properties are evaluated. The lightning-shaped structure increases significantly the conductance of the graphene interconnect with an odd number of zigzag chains. This proposed technique can effectively utilize the linear I-V characteristic of asymmetric ZGNRs for interconnect application. Variability study accounting for width/length variation and the edge effect is also included. The transmission spectra, transmission eigenstates, and transmission pathways are analyzed to gain the physical insights. This lightning-shaped ZGNR enables all 2D material-based devices and circuits on flexible and transparent substrates.

Crystal structure of (E)-2-hy-droxy-4'-meth-oxy-aza-stilbene.

PubMed

Chantrapromma, Suchada; Kaewmanee, Narissara; Boonnak, Nawong; Chantrapromma, Kan; Ghabbour, Hazem A; Fun, Hoong-Kun

2015-06-01

The title aza-stilbene derivative, C14H13NO2 {systematic name: (E)-2-[(4-meth-oxy-benzyl-idene)amino]-phenol}, is a product of the condensation reaction between 4-meth-oxy-benzaldehyde and 2-amino-phenol. The mol-ecule adopts an E conformation with respect to the azomethine C=N bond and is almost planar, the dihedral angle between the two substituted benzene rings being 3.29 (4)°. The meth-oxy group is coplanar with the benzene ring to which it is attached, the Cmeth-yl-O-C-C torsion angle being -1.14 (12)°. There is an intra-molecular O-H⋯N hydrogen bond generating an S(5) ring motif. In the crystal, mol-ecules are linked via C-H⋯O hydrogen bonds, forming zigzag chains along [10-1]. The chains are linked via C-H⋯π inter-actions, forming a three-dimensional structure.

Photo-oxidative doping in π-conjugated zig-zag chain of carbon atoms with sulfur-functional group

NASA Astrophysics Data System (ADS)

Ikeura-Sekiguchi, Hiromi; Sekiguchi, Tetsuhiro

2017-12-01

Photo-oxidative doping processes were studied for the trans-polyacetylene backbone with the -SCH3 side group as a chemically representative of the precisely controlled S-functionalized zig-zag graphene nanoribbon edge. Sulfur K-edge X-ray absorption near edge structure (XANES) spectroscopy indicates that photochemical reaction of S-CH3 with atmospheric O2 forms selectively oxidized products such as -S(O)CH3 and -SO3- bound to the polyacetylene (PA) backbone. Using the correlation between the oxidation states of sulfur and the XANES peak positions, the partial charge distribution of CH3Sδ+-PAδ- has been estimated. Such positively charged sulfur atoms can attract higher electronegative oxygen atoms and expect to enhance the photooxidization capabilities. The formation of the -SO3- side group is evidently responsible for hole doping into the PA backbone. The results can provide some strategy for area-selective and controllable doping processes of atomic-scale molecular systems with the assistance of UV light.

Crystal structure of catena-poly[N,N,N′,N′-tetra­methyl­guanidinium [(chlorido­cadmate)-di-μ-chlorido

PubMed Central

Ndiaye, Mamadou; Samb, Abdoulaye; Diop, Libasse; Maris, Thierry

2016-01-01

In the structure of the title salt, {(C5H14N3)[CdCl3]}n, the CdII atom of the complex anion is five-coordinated by one terminal and four bridging Cl atoms. The corresponding coordination polyhedron is a distorted trigonal bipyramid, with Cd—Cl distances in the range 2.4829 (4)–2.6402 (4) Å. The bipyramids are condensed into a polyanionic zigzag chain extending parallel to [101]. The tetra­methyl­guanidinium cations are situated between the polyanionic chains and are linked to them through N—H⋯Cl hydrogen bonds, forming a layered network parallel to (010). PMID:26870572

Crystal structure of 3-({[(morpholin-4-yl)carbono-thio-yl]sulfan-yl}acet-yl)phenyl benzoate.

PubMed

Ambekar, Sachin P; Mahesh Kumar, K; Shirahatti, Arun Kumar M; Kotresh, O; Anil Kumar, G N

2014-11-01

In the title compound, C20H19NO4S2, the morpholine ring adopts the expected chair conformation. The central phenyl ring makes dihedral angles of 67.97 (4) and 7.74 (3)°, respectively, with the benzoate phenyl ring and the morpholine mean plane. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds, forming zigzag chains along the b-axis direction. C-H⋯π inter-actions link centrosymmetrically related mol-ecules, reinforcing the three-dimensional structure.

Optimization of the nanotwin-induced zigzag surface of copper by electromigration

NASA Astrophysics Data System (ADS)

Chen, Hsin-Ping; Huang, Chun-Wei; Wang, Chun-Wen; Wu, Wen-Wei; Liao, Chien-Neng; Chen, Lih-Juann; Tu, King-Ning

2016-01-01

By adding nanotwins to Cu, the surface electromigration (EM) slows down. The atomic mobility of the surface step-edges is retarded by the triple points where a twin meets a free surface to form a zigzag-type surface. We observed that EM can alter the zigzag surface structure to optimize the reduction of EM, according to Le Chatelier's principle. Statistically, the optimal alternation is to change an arbitrary (111)/(hkl) zigzag pair to a pair having a very low index (hkl) plane, especially the (200) plane. Using in situ ultrahigh vacuum and high-resolution transmission electron microscopy, we examined the effects of different zigzag surfaces on the rate of EM. The calculated rate of surface EM can be decreased by a factor of ten.By adding nanotwins to Cu, the surface electromigration (EM) slows down. The atomic mobility of the surface step-edges is retarded by the triple points where a twin meets a free surface to form a zigzag-type surface. We observed that EM can alter the zigzag surface structure to optimize the reduction of EM, according to Le Chatelier's principle. Statistically, the optimal alternation is to change an arbitrary (111)/(hkl) zigzag pair to a pair having a very low index (hkl) plane, especially the (200) plane. Using in situ ultrahigh vacuum and high-resolution transmission electron microscopy, we examined the effects of different zigzag surfaces on the rate of EM. The calculated rate of surface EM can be decreased by a factor of ten. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr05418d

On the difference between the pyroxenes LiFeSi2O6 and LiFeGe2O6 in their magnetic structures and spin orientations

NASA Astrophysics Data System (ADS)

Lee, Changhoon; Hong, Jisook; Shim, Ji Hoon; Whangbo, Myung-Hwan

2014-03-01

The clinopyroxenes LiFeSi2O6 and LiFeGe2O6, crystallizing in a monoclinic space group P21/c, are isostructural and isoelectronic Their crystal structures are made up of zigzag chains of edge-sharing FeO6 octahedra containing high-spin Fe3 + ions, which run along the c direction. Despite this structural similarity, the two have quite different magnetic structures and spin orientations. In LiFeSi2O6 the Fe spins have a ferromagnetic coupling within the zigzag chains along c and such FM chains have an antiferromagnetic coupling along a. In contrast, in LiFeGe2O6, the spins have an AFM coupling within the zigzag chains along c and such FM chains have an ↑ ↑ ↓ ↓ coupling along a. In addition, the spin orientation is parallel to c in LiFeSi2O6, but is perpendicular to c in LiFeGe2O6. To explain these differences in the magnetic structure and spin orientation, we evaluated the spin exchange parameters by performing energy mapping analysis based on LDA +U and GGA +U calculations and also by evaluating the magnetocrystalline anisotropy energies in terms of GGA +U +SOC and LDA +U +SOC calculations. Our study show that the magnetic structures and spin orientations of LiFeSi2O6 and LiFeGe2O6 are better described by LDA +U and LDA +U +SOC calculations. This research was supported by Basic Science Research Program through the National Research Foundation of Korea(NRF) funded by the Ministry of Education(2013R1A1A2060341).

Electronic transport across a junction between armchair graphene nanotube and zigzag nanoribbon. Transmission in an armchair nanotube without a zigzag half-line of dimers

NASA Astrophysics Data System (ADS)

Sharma, Basant Lal

2018-05-01

Based on the well known nearest-neighbor tight-binding approximation for graphene, an exact expression for the electronic conductance across a zigzag nanoribbon/armchair nanotube junction is presented for non-interacting electrons. The junction results from the removal of a half-row of zigzag dimers in armchair nanotube, or equivalently by partial rolling of zigzag nanoribbon and insertion of a half-row of zigzag dimers in between. From the former point of view, a discrete form of Dirichlet condition is imposed on a zigzag half-line of dimers assuming the vanishing of wave function outside the physical structure. A closed form expression is provided for the reflection and transmission moduli for the outgoing wave modes for each given electronic wave mode incident from either side of the junction. It is demonstrated that such a contact junction between the nanotube and nanoribbon exhibits negligible backscattering, and the transmission has been found to be nearly ballistic. In contrast to the previously reported studies for partially unzipped carbon nanotubes (CNTs), using the same tight binding model, it is found that due to the "defect" there is certain amount of mixing between the electronic wave modes with even and odd reflection symmetries. But the junction remains a perfect valley filter for CNTs at certain energy ranges. Applications aside from the electronic case, include wave propagation in quasi-one-dimensional honeycomb structures of graphene-like constitution. The paper includes several numerical calculations, analytical derivations, and graphical results, which complement the provision of succinct closed form expressions.

Adsorption and oligomerization of 1,3-phenylene diisocyanide on Au(111)

DOE PAGES

Kestell, John; Walker, Joshua; Bai, Yun; ...

2016-04-18

The adsorption and self-assembly of 1,3-phenylene diisocyanide (1,3-PDI) are studied on Au(111) using reflection–adsorption infrared spectroscopy (RAIRS), scanning tunneling microscopy (STM), and temperature-programmed desorption (TPD) supplemented by density functional theory (DFT) calculations and the results compared with the structures formed from 1,4-PDI where it assembled to form –(Au–PDI)– oligomer chains that incorporate gold adatoms. The infrared spectra display a single isocyanide feature consistent with the isocyanide binding to gold adatoms, while DFT calculations confirm that isocyanide binding to gold adatoms is more energetically favorable than binding to the surface. STM images show that 1,3-PDI forms zigzag chains containing hairpin bendsmore » that cause the chains to double back on each other, consistent with the 120° angle between the isocyanide groups. Hexagonal structural motifs are also observed that are proposed to be due to the self-assembly of three isocyanides as well as small structures that are assigned to 1,3-PDI dimers. Furthermore, the results suggest that the formation of gold-containing oligomers from isocyanide-containing molecules is a general phenomenon.« less

How cellulose stretches: synergism between covalent and hydrogen bonding.

PubMed

Altaner, Clemens M; Thomas, Lynne H; Fernandes, Anwesha N; Jarvis, Michael C

2014-03-10

Cellulose is the most familiar and most abundant strong biopolymer, but the reasons for its outstanding mechanical performance are not well understood. Each glucose unit in a cellulose chain is joined to the next by a covalent C-O-C linkage flanked by two hydrogen bonds. This geometry suggests some form of cooperativity between covalent and hydrogen bonding. Using infrared spectroscopy and X-ray diffraction, we show that mechanical tension straightens out the zigzag conformation of the cellulose chain, with each glucose unit pivoting around a fulcrum at either end. Straightening the chain leads to a small increase in its length and is resisted by one of the flanking hydrogen bonds. This constitutes a simple form of molecular leverage with the covalent structure providing the fulcrum and gives the hydrogen bond an unexpectedly amplified effect on the tensile stiffness of the chain. The principle of molecular leverage can be directly applied to certain other carbohydrate polymers, including the animal polysaccharide chitin. Related but more complex effects are possible in some proteins and nucleic acids. The stiffening of cellulose by this mechanism is, however, in complete contrast to the way in which hydrogen bonding provides toughness combined with extensibility in protein materials like spider silk.

Crystal structure of 2-oxopyrrolidin-3-yl 4-(2-phenyl-diazen-1-yl)benzoate.

PubMed

Elkin, Igor; Maris, Thierry; Melkoumov, Alexandre; Hildgen, Patrice; Banquy, Xavier; Leclair, Grégoire; Barrett, Christopher

2018-04-01

In the title compound, C 17 H 15 N 3 O 3 , the plane of the pyrrolidone ring is inclined at an angle of 59.791 (2)° to that of the azo-benzene segment, which adopts a configuration close to planar. In the crystal, mol-ecules are oriented pairwise by (2-oxopyrrolidin-3-yl)-oxy moieties at an angle of 76.257 (3)°, linked by hydrogen bonds and π-stacking inter-actions, forming zigzag supra-molecular chains parallel to [010] further linked via additional C-H⋯π inter-actions.

Crystal structure of 3-({[(morpholin-4-yl)carbono­thio­yl]sulfan­yl}acet­yl)phenyl benzoate

PubMed Central

Ambekar, Sachin P.; Mahesh Kumar, K.; Shirahatti, Arun Kumar M.; Kotresh, O.; Anil Kumar, G. N.

2014-01-01

In the title compound, C20H19NO4S2, the morpholine ring adopts the expected chair conformation. The central phenyl ring makes dihedral angles of 67.97 (4) and 7.74 (3)°, respectively, with the benzoate phenyl ring and the morpholine mean plane. In the crystal, mol­ecules are linked by C—H⋯O hydrogen bonds, forming zigzag chains along the b-axis direction. C—H⋯π inter­actions link centrosymmetrically related mol­ecules, reinforcing the three-dimensional structure. PMID:25484757

Au-induced deep groove nanowire structure on the Ge(001) surface: DFT calculations

NASA Astrophysics Data System (ADS)

Tsay, Shiow-Fon

2016-09-01

The atomic geometry, stability, and electronic properties of self-organized Au induced nanowires on the Ge(001) surface are investigated based on the density-functional theory in GGA and the stoichiometry of Au. A giant Ge zigzag chain structure is suggested for 0.75 ML Au coverage, which displays c(8 × 2) deep groove zigzag nanowire structure simulated STM images. The top layer Ge and Au atomic disorder introduces the chevron units into the zigzag nanowire structure STM image as per the experimental observations. The zigzag Ge nanowire exhibits a semi-metallic characteristic, and the electric transport occurs in between the Ge zigzag nanowire and the subsurface. The system exhibits obvious electronic correlations among the Ge nanowire, the nano-facet Au trimers and the deeper layer Ge atoms, that play an important role in the electronic structure. At surface Brillouin zone boundaries, an anisotropic two-dimensional upward parabolic surface-state band is consistent with the ARPES spectra reported by Nakatsuji et al. [Phys. Rev. B 80, 081406(R) (2009); Phys. Rev. B 84, 115411 (2011)]; this electronic structure is different from the quasi-one-dimensional energy trough reported by Schäfer et al. [Phys. Rev. Lett. 101, 236802 (2008); Phys. Rev. B 83, 121411(R) (2011)].

Band-selective filter in a zigzag graphene nanoribbon.

PubMed

Nakabayashi, Jun; Yamamoto, Daisuke; Kurihara, Susumu

2009-02-13

Electric transport of a zigzag graphene nanoribbon through a steplike potential and a barrier potential is investigated by using the recursive Green's function method. In the case of the steplike potential, we demonstrate numerically that scattering processes obey a selection rule for the band indices when the number of zigzag chains is even; the electrons belonging to the "even" ("odd") bands are scattered only into the even (odd) bands so that the parity of the wave functions is preserved. In the case of the barrier potential, by tuning the barrier height to be an appropriate value, we show that it can work as the "band-selective filter", which transmits electrons selectively with respect to the indices of the bands to which the incident electrons belong. Finally, we suggest that this selection rule can be observed in the conductance by applying two barrier potentials.

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

NASA Astrophysics Data System (ADS)

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

2017-09-01

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

Two halide-containing cesium manganese vanadates: synthesis, characterization, and magnetic properties

DOE PAGES

Smith Pellizzeri, Tiffany M.; McGuire, Michael A.; McMillen, Colin D.; ...

2018-01-24

In this study, two new halide-containing cesium manganese vanadates have been synthesized by a high-temperature (580 °C) hydrothermal synthetic method from aqueous brine solutions. One compound, Cs 3Mn(VO 3) 4Cl, (1) was prepared using a mixed cesium hydroxide/chloride mineralizer, and crystallizes in the polar noncentrosymmetric space group Cmm2, with a = 16.7820(8) Å, b = 8.4765(4) Å, c = 5.7867(3) Å. This structure is built from sinusoidal zig-zag (VO 3) n chains that run along the b-axis and are coordinated to Mn 2+ containing (MnO 4Cl) square-pyramidal units that are linked together to form layers. The cesium cations reside betweenmore » the layers, but also coordinate to the chloride ion, forming a cesium chloride chain that also propagates along the b-axis. The other compound, Cs 2Mn(VO 3) 3F, (2) crystallizes in space group Pbca with a = 7.4286(2) Å, b = 15.0175(5) Å, c = 19.6957(7) Å, and was prepared using a cesium fluoride mineralizer. The structure is comprised of corner sharing octahedral Mn 2+ chains, with trans fluoride ligands acting as bridging units, whose ends are capped by (VO 3) n vanadate chains to form slabs. The cesium atoms reside between the manganese vanadate layers, and also play an integral part in the structure, forming a cesium fluoride chain that runs along the b-axis. Both compounds were characterized by single-crystal X-ray diffraction, powder X-ray diffraction, and single-crystal Raman spectroscopy. Additionally, the magnetic properties of 2 were investigated. Lastly, above 50 K, it displays behavior typical of a low dimensional system with antiferromagnetic interactions, as to be expected for linear chains of manganese(II) within the crystal structure.« less

Solvent induced synthesis, structure and properties of coordination polymers based on 5-hydroxyisophthalic acid as linker and 1,10-phenanthroline as auxiliary ligand

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

Kariem, Mukaddus; Yawer, Mohd; Sheikh, Haq Nawaz, E-mail: hnsheikh@rediffmail.com

2015-11-15

Three new coordination polymers [Mn(hip)(phen) (H{sub 2}O)]{sub n} (1), [Co(hip)(phen) (H{sub 2}O)]{sub n} (2), and [Cd(hip) (phen) (H{sub 2}O)]{sub n} (3) (H{sub 2}hip=5-hydroxyisophthalic acid; phen=1,10-phenanthroline) have been synthesized by solvo-hydrothermal method using diethyl formamide-water (DEF-H{sub 2}O) as solvent system. Single-crystal X-ray diffraction analysis reveals that all three coordination polymers 1, 2 and 3 crystallize in monoclinic space group P2/n. Metal ions are inter-connected by hydroxyisophthalate anions forming zig-zag 1D chain. 1D chains are further inter-connected by hydrogen bonding and π–π stacking interactions leading to 3D supramolecular architecture. Hydrogen-bonding and π–π stacking provide thermal stability to polymers. Compounds 1 and 2more » are paramagnetic at room temperature and variable temperature magnetic moment measurements revealed weak ferromagnetic interactions between metal ions at low temperature. Compound 3 exhibits excellent photoluminescence with large Stokes shift. - Graphical abstract: 1D helical chains of coordination polymers were synthesized by solvo-hydrothermal reaction of 5-hydroxyisopthalic acid and 1,10-phenanthroline with MnCl{sub 2}·4H{sub 2}O / CoCl{sub 2}·6H{sub 2}O / Cd(NO{sub 3}){sub 2}·6H{sub 2}O. - Highlights: • Solvent induced synthesis of three coordination polymers with 1D zig-zag structure. • Crystal structures of coordination polymers are reported and discussed. • 1,10-Phenanthroline influences magnetic and luminescent properties of polymers. • Coordination polymer of Cd is luminescent exhibiting large Stokes shift.« less

Spin-polarized electron transport in hybrid graphene-BN nanoribbons

NASA Astrophysics Data System (ADS)

Gao, Song; Lu, Wei; Zheng, Guo-Hui; Jia, Yalei; Ke, San-Huang

2017-05-01

The experimental realization of hybrid graphene and h-BN provides a new way to modify the electronic and transport properties of graphene-based materials. In this work, we investigate the spin-polarized electron transport in hybrid graphene-BN zigzag nanoribbons by performing first-principles nonequilibrium Green’s function method calculations. A 100% spin-polarized electron transport in a large energy window around the Fermi level is found and this behavior is independent of the ribbon width as long as there contain 3 zigzag carbon chains. This behavior may be useful in making perfect spin filters.

Modeling Bi-induced changes in the electronic structure of GaAs1-xBix alloys

NASA Astrophysics Data System (ADS)

Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.

2013-12-01

We suggested recently [V. Virkkala , Phys. Rev. BPRBMDO1098-012110.1103/PhysRevB.88.035204 88, 035204 (2013)] that the band-gap narrowing in dilute GaAs1-xNx alloys can be explained to result from the broadening of the localized N states due to the N-N interaction along the zigzag chains in the <110> directions. In that study our tight-binding modeling based on first-principles density-functional calculations took into account the random distribution of N atoms in a natural way. In this work we extend our modeling to GaAs1-xBix alloys. Our results indicate that Bi states mix with host material states. However, the states near the valence-band edge agglomerate along the zigzag chains originating from individual Bi atoms. This leads to Bi-Bi interactions in a random alloy broadening these states in energy and causing the band-gap narrowing.

Solution‐crystallization and related phenomena in 9,9‐dialkyl‐fluorene polymers. II. Influence of side‐chain structure

PubMed Central

Perevedentsev, Aleksandr; Stavrinou, Paul N.; Smith, Paul

2015-01-01

ABSTRACT Solution‐crystallization is studied for two polyfluorene polymers possessing different side‐chain structures. Thermal analysis and temperature‐dependent optical spectroscopy are used to clarify the nature of the crystallization process, while X‐ray diffraction and scanning electron microscopy reveal important differences in the resulting microstructures. It is shown that the planar‐zigzag chain conformation termed the β‐phase, which is observed for certain linear‐side‐chain polyfluorenes, is necessary for the formation of so‐called polymer‐solvent compounds for these polymers. Introduction of alternating fluorene repeat units with branched side‐chains prevents formation of the β‐phase conformation and results in non‐solvated, i.e. melt‐crystallization‐type, polymer crystals. Unlike non‐solvated polymer crystals, for which the chain conformation is stabilized by its incorporation into a crystalline lattice, the β‐phase conformation is stabilized by complexation with solvent molecules and, therefore, its formation does not require specific inter‐chain interactions. The presented results clarify the fundamental differences between the β‐phase and other conformational/crystalline forms of polyfluorenes. © 2015 The Authors. Journal of Polymer Science Part B: Polymer Physics published by Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2015, 53, 1492–1506 PMID:27546983

Quasi-particle energies and optical excitations of hydrogenated and fluorinated germanene.

PubMed

Shu, Huabing; Li, Yunhai; Wang, Shudong; Wang, Jinlan

2015-02-14

Using density functional theory, the G0W0 method and Bethe-Salpeter equation calculations, we systematically explore the structural, electronic and optical properties of hydrogenated and fluorinated germanene. The hydrogenated/fluorinated germanene tends to form chair and zigzag-line configurations and its electronic and optical properties show close geometry dependence. The chair hydrogenated/fluorinated and zigzag-line fluorinated germanene are direct band-gap semiconductors, while the zigzag-line hydrogenated germanene owns an indirect band-gap. Moreover, the quasi-particle corrections are significant and strong excitonic effects with large exciton binding energies are observed. Moreover, the zigzag-line hydrogenated/fluorinated germanene shows highly anisotropic optical responses, which may be used as a good optical linear polarizer.

Co-assembly of Zn(SPh){sub 2} and organic linkers into helical and zig-zag polymer chains

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

Liu Yi; Yu Lingmin; Loo, Say Chye Joachim

2012-07-15

Two novel one-dimensional coordination polymers, single helicate [Zn(SPh){sub 2}(TPyTA)(EG)]{sub n} (EG=ethylene glycol) (1) and zig-zag structure [Zn(SPh){sub 2}(BPyVB)]{sub n} (2), were synthesized under solvothermal conditions at 150 Degree-Sign C or room temperature by the co-assembly of Zn(SPh){sub 2} and organic linkers such as 2,4,6-tri(4-pyridyl)-1,3,5-triazine (TPyTA) and 1,3-bis(trans-4-pyridylvinyl)benzene (BPyVB). X-ray crystallography study reveals that both polymers 1 and 2 crystallize in space group P2{sub 1}/c of the monoclinic system. The solid-state UV-vis absorption spectra show that 1 and 2 have maxium absorption onsets at 400 nm and 420 nm, respectively. TGA analysis indicates that 1 and 2 are stable up tomore » 110 Degree-Sign C and 210 Degree-Sign C. - Graphical abstract: Two novel one-dimensional coordination polymers, single helicate [Zn(SPh){sub 2}(TPyTA)(EG)]{sub n} (1) and zig-zag structure [Zn(SPh){sub 2}(BPyVB)]{sub n} (2), were synthesized. Solid-state UV-vis absorptions show that 1 and 2 have maxium absorption onsets at 400 nm and 420 nm, respectively. TGA analysis indicates that 1 and 2 are stable up to 110 Degree-Sign C and 210 Degree-Sign C. Highlights: Black-Right-Pointing-Pointer Two novel one-dimensional coordination polymers have been synthesized. Black-Right-Pointing-Pointer TPyTA results in helical structures in 1 while BPyVB leads to zig-zag chains in 2. Black-Right-Pointing-Pointer Solid-state UV-vis absorption spectra and TGA analysis of the title polymers were studied.« less

Sequential cooling insert for turbine stator vane

DOEpatents

Jones, Russell B.; Krueger, Judson J.; Plank, William L.

2014-04-01

A sequential impingement cooling insert for a turbine stator vane that forms a double impingement for the pressure and suction sides of the vane or a triple impingement. The insert is formed from a sheet metal formed in a zigzag shape that forms a series of alternating impingement cooling channels with return air channels, where pressure side and suction side impingement cooling plates are secured over the zigzag shaped main piece. Another embodiment includes the insert formed from one or two blocks of material in which the impingement channels and return air channels are machined into each block.

Sequential cooling insert for turbine stator vane

DOEpatents

Jones, Russel B; Krueger, Judson J; Plank, William L

2014-11-04

A sequential impingement cooling insert for a turbine stator vane that forms a double impingement for the pressure and suction sides of the vane or a triple impingement. The insert is formed from a sheet metal formed in a zigzag shape that forms a series of alternating impingement cooling channels with return air channels, where pressure side and suction side impingement cooling plates are secured over the zigzag shaped main piece. Another embodiment includes the insert formed from one or two blocks of material in which the impingement channels and return air channels are machined into each block.

A Two-Dimensional 'Zigzag' Silica Polymorph on a Metal Support.

PubMed

Kuhness, David; Yang, Hyun Jin; Klemm, Hagen W; Prieto, Mauricio; Peschel, Gina; Fuhrich, Alexander; Menzel, Dietrich; Schmidt, Thomas; Yu, Xin; Shaikhutdinov, Shamil; Lewandowski, Adrian; Heyde, Markus; Kelemen, Anna; Włodarczyk, Radosław; Usvyat, Denis; Schütz, Martin; Sauer, Joachim; Freund, Hans-Joachim

2018-05-16

We present a new polymorph of the two-dimensional (2D) silica film with a characteristic 'zigzag' line structure and a rectangular unit cell which forms on a Ru(0001) metal substrate. This new silica polymorph may allow for important insights into growth modes and transformations of 2D silica films as a model system for the study of glass transitions. Based on scanning tunneling microscopy, low energy electron diffraction, infrared reflection absorption spectroscopy, and X-ray photoelectron spectroscopy measurements on the one hand, and density functional theory calculations on the other, a structural model for the 'zigzag' polymorph is proposed. In comparison to established monolayer and bilayer silica, this 'zigzag' structure system has intermediate characteristics in terms of coupling to the substrate and stoichiometry. The silica 'zigzag' phase is transformed upon reoxidation at higher annealing temperature into a SiO 2 silica bilayer film which is chemically decoupled from the substrate.

Crystal Structure of 17α-Dihydroequilin, C18H22O2, from Synchrotron Powder Diffraction Data and Density Functional Theory

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

Kaduk, James; Gindhart, Amy; Blanton, Thomas

The crystal structure of 17α-dihydroequilin has been solved and refined using synchrotron X-ray powder diffraction data, and optimized using density functional techniques. 17α-dihydroequilin crystallizes in space group P212121 (#19) with a = 6.76849(1) Å, b = 8.96849(1) Å, c = 23.39031(5) Å, V = 1419.915(3) Å3, and Z = 4. Both hydroxyl groups form hydrogen bonds to each other, resulting in zig-zag chains along the b-axis. The powder diffraction pattern has been submitted to ICDD for inclusion in the Powder Diffraction File™ as the entry 00-066-1608.

Cocrystallization of adamantane-1,3-dicarboxylic acid and 4,4'-bipyridine.

PubMed

Pan, Yue; Li, Kunhao; Bi, Wenhua; Li, Jing

2008-02-01

The cocrystallization of adamantane-1,3-dicarboxylic acid (adc) and 4,4'-bipyridine (4,4'-bpy) yields a unique 1:1 cocrystal, C(12)H(16)O(4).C(10)H(8)N(2), in the C2/c space group, with half of each molecule in the asymmetric unit. The mid-point of the central C-C bond of the 4,4'-bpy molecule rests on a center of inversion, while the adc molecule straddles a twofold rotation axis that passes through two of the adamantyl C atoms. The constituents of this cocrystal are joined by hydrogen bonds, the stronger of which are O-H...N hydrogen bonds [O...N = 2.6801 (17) A] and the weaker of which are C-H...O hydrogen bonds [C...O = 3.367 (2) A]. Alternate adc and 4,4'-bpy molecules engage in these hydrogen bonds to form zigzag chains. In turn, these chains are linked through pi-pi interactions along the c axis to generate two-dimensional layers. These layers are neatly packed into a stable crystalline three-dimensional form via weak C-H...O hydrogen bonds [C...O = 3.2744 (19) A] and van der Waals attractions.

Oxygen and sulfur adsorption on vicinal surfaces of copper and silver: Preferred adsorption sites

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

Liu, Da-Jiang; Thiel, Patricia A.

We present an extensive density functional theory (DFT) study of adsorption site energetics for oxygen and sulfur adsorbed on two vicinal surfaces of Cu and Ag, with the goal of identifying the most stable adsorption site(s), identifying trends and common themes, and comparing with experimental work in the literature where possible. We also present benchmark calculations for adsorption on the flat (111) and (100) surfaces. The first vicinal surface is the (211), and results are similar for both metals. Here, we find that the step-doubling reconstruction is favored with both adsorbates and is driven by the creation of a specialmore » stable fourfold hollow (4fh) site at the reconstructed step. Zig-zag chain structures consisting of X–M–X units (X = chalcogen, M = metal) at the step edge are considered, in which the special 4fh site is partially occupied. The zig-zag configuration is energetically competitive for oxygen but not sulfur. DFT results for oxygen agree with experiment in terms of the stability of the reconstruction, but contradict the original site assignment. The second vicinal surface is the (410), where again results are similar for both metals. For oxygen, DFT predicts that step sites are filled preferentially even at lowest coverage, followed by terrace sites, consistent with the experiment. For sulfur, in contrast, DFT predicts that terrace sites fill first. Oxygen forms O–M–O rows on the top edge of the step, where it occupies incomplete 4fh sites. This resolves an experimental ambiguity in the site assignment. Finally, for both the (211) and (410) surfaces, the interaction energy that stabilizes the X–M–X chain or row correlates with the linearity of the X–M–X unit, which may explain key differences between oxygen and sulfur.« less

Oxygen and sulfur adsorption on vicinal surfaces of copper and silver: Preferred adsorption sites

DOE PAGES

Liu, Da-Jiang; Thiel, Patricia A.

2018-03-28

We present an extensive density functional theory (DFT) study of adsorption site energetics for oxygen and sulfur adsorbed on two vicinal surfaces of Cu and Ag, with the goal of identifying the most stable adsorption site(s), identifying trends and common themes, and comparing with experimental work in the literature where possible. We also present benchmark calculations for adsorption on the flat (111) and (100) surfaces. The first vicinal surface is the (211), and results are similar for both metals. Here, we find that the step-doubling reconstruction is favored with both adsorbates and is driven by the creation of a specialmore » stable fourfold hollow (4fh) site at the reconstructed step. Zig-zag chain structures consisting of X–M–X units (X = chalcogen, M = metal) at the step edge are considered, in which the special 4fh site is partially occupied. The zig-zag configuration is energetically competitive for oxygen but not sulfur. DFT results for oxygen agree with experiment in terms of the stability of the reconstruction, but contradict the original site assignment. The second vicinal surface is the (410), where again results are similar for both metals. For oxygen, DFT predicts that step sites are filled preferentially even at lowest coverage, followed by terrace sites, consistent with the experiment. For sulfur, in contrast, DFT predicts that terrace sites fill first. Oxygen forms O–M–O rows on the top edge of the step, where it occupies incomplete 4fh sites. This resolves an experimental ambiguity in the site assignment. Finally, for both the (211) and (410) surfaces, the interaction energy that stabilizes the X–M–X chain or row correlates with the linearity of the X–M–X unit, which may explain key differences between oxygen and sulfur.« less

Monohalogenated ferrocenes C5H5FeC5H4 X (X = Cl, Br and I) and a second polymorph of C5H5FeC5H4I

PubMed Central

Romanov, Alexander S.; Mulroy, Joseph M.; Khrustalev, Victor N.; Antipin, Mikhail Yu.; Timofeeva, Tatiana V.

2009-01-01

The structures of the three title monosubstituted ferrocenes, namely 1-chloro­ferrocene, [Fe(C5H5)(C5H4Cl)], (I), 1-bromo­ferrocene, [Fe(C5H5)(C5H4Br)], (II), and 1-iodo­ferrocene, [Fe(C5H5)(C5H4I)], (III), were determined at 100 K. The chloro- and bromo­ferrocenes are isomorphous crystals. The new triclinic polymorph [space group P , Z = 4, T = 100 K, V = 943.8 (4) Å3] of iodo­ferrocene, (III), and the previously reported monoclinic polymorph of (III) [Laus, Wurst & Schottenberger (2005 ▶). Z. Kristallogr. New Cryst. Struct. 220, 229–230; space group Pc, Z = 4, T = 100 K, V = 924.9 Å3] were obtained by crystallization from ethanolic solutions at 253 and 303 K, respectively. All four phases contain two independent mol­ecules in the unit cell. The relative orientations of the cyclo­penta­dienyl (Cp) rings are eclipsed and staggered in the independent mol­ecules of (I) and (II), while (III) demonstrates only an eclipsed conformation. The triclinic and monoclinic polymorphs of (III) contain nonbonded inter­molecular I⋯I contacts, causing different packing modes. In the triclinic form of (III), the mol­ecules are arranged in zigzag tetra­mers, while in the monoclinic form the mol­ecules are arranged in zigzag chains along the a axis. Crystallographic data for (III), along with the computed lattice energies of the two polymorphs, suggest that the monoclinic form is more stable. PMID:19893225

3-Benzyl­sulfanyl-1H-1,2,4-triazol-5-amine

PubMed Central

Zhang, Shuai; Liu, Pei-Jiang; Ma, Dong-Sheng; Hou, Guang-Feng

2012-01-01

In the title mol­ecule, C9H10N4S, the dihedral angle between the benzene and triazole rings is 81.05 (5)°. In the crystal, N—H⋯N hydrogen bonds link the mol­ecules into infinite zigzag chains along [010]. PMID:22259582

Unconventional quantum antiferromagnetism with a fourfold symmetry breaking in a spin-1/2 Ising-Heisenberg pentagonal chain

NASA Astrophysics Data System (ADS)

Karľová, Katarína; Strečka, Jozef; Lyra, Marcelo L.

2018-03-01

The spin-1/2 Ising-Heisenberg pentagonal chain is investigated with use of the star-triangle transformation, which establishes a rigorous mapping equivalence with the effective spin-1/2 Ising zigzag ladder. The investigated model has a rich ground-state phase diagram including two spectacular quantum antiferromagnetic ground states with a fourfold broken symmetry. It is demonstrated that these long-period quantum ground states arise due to a competition between the effective next-nearest-neighbor and nearest-neighbor interactions of the corresponding spin-1/2 Ising zigzag ladder. The concurrence is used to quantify the bipartite entanglement between the nearest-neighbor Heisenberg spin pairs, which are quantum-mechanically entangled in two quantum ground states with or without spontaneously broken symmetry. The pair correlation functions between the nearest-neighbor Heisenberg spins as well as the next-nearest-neighbor and nearest-neighbor Ising spins were investigated with the aim to bring insight into how a relevant short-range order manifests itself at low enough temperatures. It is shown that the specific heat displays temperature dependencies with either one or two separate round maxima.

Influence of particle arrangement on the permittivity of an elastomeric composite

NASA Astrophysics Data System (ADS)

Tsai, Peiying J.; Nayak, Suchitra; Ghosh, Suvojit; Puri, Ishwar K.

2017-01-01

Elastomers are used as dielectric layers contained between the parallel conductive plates of capacitors. The introduction of filler particles into an elastomer changes its permittivity ɛ. When particle organization in a composite is intentionally varied, this alters its capacitance. Using numerical simulations, we examine how conductive particle chains introduced into polydimethylsiloxane (PDMS) alter ɛ. The effects of filler volume fraction ψ, interparticle d and interchain spacing a, zigzag angle θ between adjacent particles and overall chain orientation, particle size r, and clearance h between particles and the conductive plates are characterized. When filler particles are organized into chainlike structures rather than being just randomly distributed in the elastomer matrix, ɛ increases by as much as 85%. When particles are organized into chainlike forms, ɛ increases with increasing ψ and a, but decreases with increasing d and θ. A composite containing smaller particles has a higher ɛ when ψ <9 % while larger particles provide greater enhancement when ψ is larger than that value. To enhance ɛ, adjacent particles must be interconnected and the overall chain direction should be oriented perpendicular to the conductive plates. These results are useful for additive manufacturing on electrical applications of elastomeric composites.

Anisotropic Etching of Hexagonal Boron Nitride and Graphene: Question of Edge Terminations.

PubMed

Stehle, Yijing Y; Sang, Xiahan; Unocic, Raymond R; Voylov, Dmitry; Jackson, Roderick K; Smirnov, Sergei; Vlassiouk, Ivan

2017-12-13

Chemical vapor deposition (CVD) has been established as the most effective way to grow large area two-dimensional materials. Direct study of the etching process can reveal subtleties of this competing with the growth reaction and thus provide the necessary details of the overall growth mechanism. Here we investigate hydrogen-induced etching of hBN and graphene and compare the results with the classical kinetic Wulff construction model. Formation of the anisotropically etched holes in the center of hBN and graphene single crystals was observed along with the changes in the crystals' circumference. We show that the edges of triangular holes in hBN crystals formed at regular etching conditions are parallel to B-terminated zigzags, opposite to the N-terminated zigzag edges of hBN triangular crystals. The morphology of the etched hBN holes is affected by a disbalance of the B/N ratio upon etching and can be shifted toward the anticipated from the Wulff model N-terminated zigzag by etching in a nitrogen buffer gas instead of a typical argon. For graphene, etched hexagonal holes are terminated by zigzag, while the crystal circumference is gradually changing from a pure zigzag to a slanted angle resulting in dodecagons.

(C6H13N)2BiI5: A One-Dimensional Lead-Free Perovskite-Derivative Photoconductive Light Absorber.

PubMed

Zhang, Weichuan; Tao, Kewen; Ji, Chengmin; Sun, Zhihua; Han, Shiguo; Zhang, Jing; Wu, Zhenyue; Luo, Junhua

2018-04-16

Lead-free organic-inorganic hybrid perovskites have recently attracted intense interest as environmentally friendly, low-cost, chemically stable light absorbers. Here, we reported a new one-dimensional (1D) zigzag chainlike light-absorbing hybrid material of (C 6 H 13 N) 2 BiI 5 , in which the corner-sharing octahedral bismuth halide chains are surrounded by organic cations of tetramethylpiperidinium. This unique zigzag 1D hybrid perovskite-derivative material shows a narrow direct band gap of 2.02 eV and long-lived photoluminescence, which is encouraging for optoelectronic applications. Importantly, it behaves as a typical semiconducting material and displays obvious photoresponse in the visible-light range. This work opens a potential pathway for the further application of 1D lead-free hybrids.

Identification and correction of road courses by merging successive segments and using improved attributes

NASA Astrophysics Data System (ADS)

Bulatov, Dimitri; Häufel, Gisela; Pohl, Melanie

2016-10-01

Both in military and civil applications, there is an urgent need for a highly up-to-date road data, which should be ideally semantically structured (into main roads, walking paths, escape ways, etc.) with application-driven attributes, such as road width, road type, surface condition and many others. A vectorization algorithm processing aerial images recently acquired yields an up-to-date road vector data, which are, however, often represented by wriggly, noisy polylines without semantics. The reasons for zigzagged street courses are insufficiencies in the intermediate results of sensor data processing (orthophotos, elevation maps) and occlusions caused by trees, buildings, and others. In the current contribution, an improved computation of geometric attributes will be explained which makes a difference between straight and circular (or elliptic) polylines. Using improved attributes, the candidates for polylines having identical course and sharing a junction are determined. From such candidates, we form chains of polylines. These chains correspond better to the intuitive perception of the term street than the previously used road polylines, because, even after being interrupted by narrower side roads, a chain maintains its label. The generalization of chains with simultaneously adjusting positions of junctions is evidently performed. We apply a generalization with the purpose-based modification of a well-known polyline simplification algorithm once chain-wise and once polyline-wise in order to show - by means of qualitative results - the advantages of the chain-wise generalization.

New members of the A2 M ‧ M2″ structure family (A=Ca, Sr, Yb, La; M ‧ = In , Sn , Pb; M ″ = Si , Ge)

NASA Astrophysics Data System (ADS)

Jehle, Michael; Dürr, Ines; Fink, Saskia; Lang, Britta; Langenmaier, Michael; Steckhan, Julia; Röhr, Caroline

2015-01-01

The new mixed tetrelides Sr2PbGe2 and Yb2SnGe2, several mixed Ca/Sr (AII) germanides A2II (Sn, Pb)Ge2 and two polymorphs of La2 InSi2 represent new members of the general structure family of ternary alkaline-earth/lanthanoid main group silicides/germanides A2 M ‧ M2″ (M ‧ = In , Sn , Pb ; M ″ = Si , Ge). All compounds were synthesized from melts of the elements and their crystal structures have been determined by means of single crystal X-ray diffraction. Sr2PbGe2 (Cmmm, a=402.36(11), b=1542.3(4), c=463.27(10) pm) crystallizes with the Mn2AlB2 -type structure. In exhibiting infinite planar Ge zig-zag chains, it represents one border of the compound series. The other borderline case, where only [Ge2 ] dumbbells are left as Ge building units, is represented by the Ca/Yb tin germanides Ca2SnGe2 and Yb2SnGe2 (Mo2FeB2 -type; P4/mbm, a=748.58(13)/740.27(7), c=445.59(8)/435.26(5) pm). In between these two border structures compounds with variable Si/Ge chain lengths could be obtained by varying the averaged size of the AII cations: Ca0.45Sr1.55PbGe2 (new structure type; Pbam, a=791.64(5), b=2311.2(2), c=458.53(3) pm) contains planar six-membered chain segments [Ge6 ]. Tetrameric pieces [Ge4 ] are the conspicuous structure elements in Ca1.16Sr0.84SnGe2 and La2 InSi2 (La2InNi2 -type; Pbam, a=781.01(2)/762.01(13), b=1477.95(3)/1494.38(6), c=457.004(9)/442.1(3) pm). The tetragonal form of 'La2 In Si2‧ (exact composition: La2In1.07Si1.93, P4/mbm, a=1309.11(12), c=443.32(4) pm) also crystallizes in a new structure type, containing only [Si3 ] trimers as cutouts of the planar chains. In all structures the Si/Ge zig-zag chains/chain segments are connected by In/Sn/Pb atoms to form planar M layers, which are separated by pure A layers. Band structure calculations within the FP-LAPW DFT approach together with the Zintl formalism, extended by the presence of hypervalent bonding of the heavier M ‧ elements, give insight into the chemical bonding of this series of p-block metallides. An analysis of the band structure for the border phases Sr2PbGe2 and Ca2SnGe2 shows the considerable π bonding contributions within the Ge building units, which also become apparent from the short Ge-Ge bond lengths.

An Implementation of RC4+ Algorithm and Zig-zag Algorithm in a Super Encryption Scheme for Text Security

NASA Astrophysics Data System (ADS)

Budiman, M. A.; Amalia; Chayanie, N. I.

2018-03-01

Cryptography is the art and science of using mathematical methods to preserve message security. There are two types of cryptography, namely classical and modern cryptography. Nowadays, most people would rather use modern cryptography than classical cryptography because it is harder to break than the classical one. One of classical algorithm is the Zig-zag algorithm that uses the transposition technique: the original message is unreadable unless the person has the key to decrypt the message. To improve the security, the Zig-zag Cipher is combined with RC4+ Cipher which is one of the symmetric key algorithms in the form of stream cipher. The two algorithms are combined to make a super-encryption. By combining these two algorithms, the message will be harder to break by a cryptanalyst. The result showed that complexity of the combined algorithm is θ(n2 ), while the complexity of Zig-zag Cipher and RC4+ Cipher are θ(n2 ) and θ(n), respectively.

Structural study of quasi-one-dimensional vanadium pyroxene LiVSi{sub 2}O{sub 6} single crystals

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

Ishii, Yuto; Matsushita, Yoshitaka; Oda, Migaku

Single crystals of quasi-one-dimensional vanadium pyroxene LiVSi{sub 2}O{sub 6} were synthesized and the crystal structures at 293 K and 113 K were studied using X-ray diffraction experiments. We found a structural phase transition from the room-temperature crystal structure with space group C2/c to a low-temperature structure with space group P2{sub 1}/c, resulting from a rotational displacement of SiO{sub 4} tetrahedra. The temperature dependence of magnetic susceptibility shows a broad maximum around 116 K, suggesting an opening of the Haldane gap expected for one-dimensional antiferromagnets with S=1. However, an antiferromagnetic long-range order was developed below 24 K, probably caused by amore » weak inter-chain magnetic coupling in the compound. - Graphical abstract: Low temperature crystal structure of LiVSi{sub 2}O{sub 6} and an orbital arrangement within the V-O zig-zag chain along the c-axis. - Highlights: • A low temperature structure of LiVSi{sub 2}O{sub 6} was determined by single crystal X-ray diffraction measurements. • The origin of the structural transition is a rotational displacement of SiO{sub 4} tetrahedra. • The uniform orbital overlap in the V-O zigzag chain makes the system a quasi one-dimensional antiferromagnet.« less

Pb4(OH)4(BrO3)3(NO3): An Example of SHG Crystal in Metal Bromates Containing π-Conjugated Planar Triangle.

PubMed

Kong, Fang; Hu, Chun-Li; Liang, Ming-Li; Mao, Jiang-Gao

2016-01-19

The first example of SHG crystal in the metal bromates containing π-conjugated planar triangle systems, namely, Pb4(OH)4(BrO3)3(NO3), was successfully synthesized via the hydrothermal method. Furthermore, a single crystal of centrosymmetric Pb8O(OH)6(BrO3)6(NO3)2·H2O was also obtained. Both compounds contain similar [Pb4(OH)4] cubane-like tetranuclear clusters, but they display different one-dimensional (1D) chain structures. Pb4(OH)4(BrO3)3(NO3) features a zigzag [Pb4(OH)4(BrO3)3](+) 1D chain, while Pb8O(OH)6(BrO3)6(NO3)2·H2O is composed of two different orthogonal chains: the linear [Pb4(OH)4(BrO3)2](2+) 1D chain along the b-axis and the zigzag [Pb4O2(OH)2(BrO3)4](2-) 1D chain along the a-axis. The NO3 planar triangles of the compounds are all isolated and located in the spaces of the structures. Pb4(OH)4(BrO3)3(NO3) exhibits the first example of SHG crystal in the metal bromates with π-conjugated planar triangle. The second-harmonic generation (SHG) efficiency of Pb4(OH)4(BrO3)3(NO3) is approximately equal to that of KDP and it is phase-matchable. Dipole moment and theory calculations indicate that BrO3, NO3, and PbO4 groups are the origin of its SHG efficiency, although some of the contributions cancel each other out.

Delicate crystal structure changes govern the magnetic properties of 1D coordination polymers based on 3d metal carboxylates.

PubMed

Gavrilenko, Konstantin S; Cador, Olivier; Bernot, Kevin; Rosa, Patrick; Sessoli, Roberta; Golhen, Stéphane; Pavlishchuk, Vitaly V; Ouahab, Lahcène

2008-01-01

Homo- and heterometallic 1D coordination polymers of transition metals (Co II, Mn II, Zn II) have been synthesized by an in-situ ligand generation route. Carboxylato-based complexes [Co(PhCOO)2]n (1 a, 1 b), [Co(p-MePhCOO)2]n (2), [ZnMn(PhCOO)4]n (3), and [CoZn(PhCOO)4]n (4) (PhCOOH=benzoic acid, p-MePhCOOH=p-methylbenzoic acid) have been characterized by chemical analysis, single-crystal X-ray diffraction, and magnetization measurements. The new complexes 2 and 3 crystallize in orthorhombic space groups Pnab and Pcab respectively. Their crystal structures consist of zigzag chains, with alternating M(II) centers in octahedral and tetrahedral positions, which are similar to those of 1 a and 1 b. Compound 4 crystallizes in monoclinic space group P2 1/c and comprises zigzag chains of M II ions in a tetrahedral coordination environment. Magnetic investigations reveal the existence of antiferromagnetic interactions between magnetic centers in the heterometallic complexes 3 and 4, while ferromagnetic interactions operate in homometallic compounds (1 a, 1 b, and 2). Compound 1 b orders ferromagnetically at TC=3.7 K whereas 1 a does not show any magnetic ordering down to 330 mK and displays typical single-chain magnet (SCM) behavior with slowing down of magnetization relaxation below 0.6 K. Single-crystal measurements reveal that the system is easily magnetized in the chain direction for 1 a whereas the chain direction coincides with the hard magnetic axis in 1 b. Despite important similarities, small differences in the molecular and crystal structures of these two compounds lead to this dramatic change in properties.

Quantum phase transitions in effective spin-ladder models for graphene zigzag nanoribbons

NASA Astrophysics Data System (ADS)

Koop, Cornelie; Wessel, Stefan

2017-10-01

We examine the magnetic correlations in quantum spin models that were derived recently as effective low-energy theories for electronic correlation effects on the edge states of graphene nanoribbons. For this purpose, we employ quantum Monte Carlo simulations to access the large-distance properties, accounting for quantum fluctuations beyond mean-field-theory approaches to edge magnetism. For certain chiral nanoribbons, antiferromagnetic interedge couplings were previously found to induce a gapped quantum disordered ground state of the effective spin model. We find that the extended nature of the intraedge couplings in the effective spin model for zigzag nanoribbons leads to a quantum phase transition at a large, finite value of the interedge coupling. This quantum critical point separates the quantum disordered region from a gapless phase of stable edge magnetism at weak intraedge coupling, which includes the ground states of spin-ladder models for wide zigzag nanoribbons. To study the quantum critical behavior, the effective spin model can be related to a model of two antiferromagnetically coupled Haldane-Shastry spin-half chains with long-ranged ferromagnetic intrachain couplings. The results for the critical exponents are compared also to several recent renormalization-group calculations for related long-ranged interacting quantum systems.

Negative differential resistance and rectification effects in zigzag graphene nanoribbon heterojunctions: Induced by edge oxidation and symmetry concept

NASA Astrophysics Data System (ADS)

Nazirfakhr, Maryam; Shahhoseini, Ali

2018-03-01

By applying non-equilibrium Green's functions (NEGF) in combination with tight-binding (TB) model, we investigate and compare the electronic transport properties of H-terminated zigzag graphene nanoribbon (H/ZGNR) and O-terminated ZGNR/H-terminated ZGNR (O/ZGNR-H/ZGNR) heterostructure under finite bias. Moreover, the effect of width and symmetry on the electronic transport properties of both models is also considered. The results reveal that asymmetric H/ZGNRs have linear I-V characteristics in whole bias range, but symmetric H-ZGNRs show negative differential resistance (NDR) behavior which is inversely proportional to the width of the H/ZGNR. It is also shown that the I-V characteristic of O/ZGNR-H/ZGNR heterostructure shows a rectification effect, whether the geometrical structure is symmetric or asymmetric. The fewer the number of zigzag chains, the bigger the rectification ratio. It should be mentioned that, the rectification ratios of symmetric heterostructures are much bigger than asymmetric one. Transmission spectrum, density of states (DOS), molecular projected self-consistent Hamiltonian (MPSH) and molecular eigenstates are analyzed subsequently to understand the electronic transport properties of these ZGNR devices. Our findings could be used in developing nanoscale rectifiers and NDR devices.

Determination of graphene's edge energy using hexagonal graphene quantum dots and PM7 method.

PubMed

Vorontsov, Alexander V; Tretyakov, Evgeny V

2018-05-18

Graphene quantum dots (GQDs) are important for a variety of applications and designs, and the shapes of GQDs rely on the energy of their boundaries. Presently, many methods have been developed for the preparation of GQDs with the required boundaries, shapes and edge terminations. However, research on the properties of GQDs and their applications is limited due to the unavailability of these compounds in pure form. In the present computational study, the standard enthalpy of formation, the standard enthalpy of formation of edges and the standard enthalpy of hydrogenation are studied for hexagonal GQDs with purely zigzag and armchair edges in non-passivated and H-passivated forms using the semiempirical quantum chemistry method pm7. The standard enthalpy of formation of the edge is found to remain constant for GQDs studied in the range of 1 to 6 nm, and the enthalpies of edge C atoms are 32.4 and 35.5 kcal mol-1 for armchair and zigzag edges, respectively. In contrast to some literature data, the standard enthalpy of formation of hydrogenated edges is far from zero, and the values are 7.3 and 8.0 kcal mol-1 C for armchair and zigzag edges, respectively. The standard enthalpy of hydrogenation is found to be -10.2 and -9.72 eV nm-1 for the armchair and zigzag edges, respectively.

(E)-4-{[(Pyridin-4-yl­methyl­idene)amino]­meth­yl}benzoic acid

PubMed Central

Han, Sun Hwa; Lee, Soon W.

2012-01-01

The title mol­ecule, C14H12N2O2, exhibits a V-shaped conformation with a dihedral angle of 59.69 (3)° between the benzene and pyridine rings. In the crystal, O—H⋯N hydrogen bonds link the mol­ecules into zigzag chains along [010]. PMID:22346932

Anisotropic Etching of Hexagonal Boron Nitride and Graphene: Question of Edge Terminations

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

Stehle, Yijing Y.; Sang, Xiahan; Unocic, Raymond R.

Here, chemical vapor deposition (CVD) has been established as the most effective way to grow large area two-dimensional materials. Direct study of the etching process can reveal subtleties of this competing with the growth reaction and thus provide the necessary details of the overall growth mechanism. Here we investigate hydrogen-induced etching of hBN and graphene and compare the results with the classical kinetic Wulff construction model. Formation of the anisotropically etched holes in the center of hBN and graphene single crystals was observed along with the changes in the crystals' circumference. We show that the edges of triangular holes inmore » hBN crystals formed at regular etching conditions are parallel to B-terminated zigzags, opposite to the N-terminated zigzag edges of hBN triangular crystals. The morphology of the etched hBN holes is affected by a disbalance of the B/N ratio upon etching and can be shifted toward the anticipated from the Wulff model N-terminated zigzag by etching in a nitrogen buffer gas instead of a typical argon. For graphene, etched hexagonal holes are terminated by zigzag, while the crystal circumference is gradually changing from a pure zigzag to a slanted angle resulting in dodecagons.« less

Anisotropic Etching of Hexagonal Boron Nitride and Graphene: Question of Edge Terminations

DOE PAGES

Stehle, Yijing Y.; Sang, Xiahan; Unocic, Raymond R.; ...

2017-11-14

Here, chemical vapor deposition (CVD) has been established as the most effective way to grow large area two-dimensional materials. Direct study of the etching process can reveal subtleties of this competing with the growth reaction and thus provide the necessary details of the overall growth mechanism. Here we investigate hydrogen-induced etching of hBN and graphene and compare the results with the classical kinetic Wulff construction model. Formation of the anisotropically etched holes in the center of hBN and graphene single crystals was observed along with the changes in the crystals' circumference. We show that the edges of triangular holes inmore » hBN crystals formed at regular etching conditions are parallel to B-terminated zigzags, opposite to the N-terminated zigzag edges of hBN triangular crystals. The morphology of the etched hBN holes is affected by a disbalance of the B/N ratio upon etching and can be shifted toward the anticipated from the Wulff model N-terminated zigzag by etching in a nitrogen buffer gas instead of a typical argon. For graphene, etched hexagonal holes are terminated by zigzag, while the crystal circumference is gradually changing from a pure zigzag to a slanted angle resulting in dodecagons.« less

Solvent induced synthesis, structure and properties of coordination polymers based on 5-hydroxyisophthalic acid as linker and 1,10-phenanthroline as auxiliary ligand

NASA Astrophysics Data System (ADS)

Kariem, Mukaddus; Yawer, Mohd; Sheikh, Haq Nawaz

2015-11-01

Three new coordination polymers [Mn(hip)(phen) (H2O)]n (1), [Co(hip)(phen) (H2O)]n (2), and [Cd(hip) (phen) (H2O)]n (3) (H2hip=5-hydroxyisophthalic acid; phen=1,10-phenanthroline) have been synthesized by solvo-hydrothermal method using diethyl formamide-water (DEF-H2O) as solvent system. Single-crystal X-ray diffraction analysis reveals that all three coordination polymers 1, 2 and 3 crystallize in monoclinic space group P2/n. Metal ions are inter-connected by hydroxyisophthalate anions forming zig-zag 1D chain. 1D chains are further inter-connected by hydrogen bonding and π-π stacking interactions leading to 3D supramolecular architecture. Hydrogen-bonding and π-π stacking provide thermal stability to polymers. Compounds 1 and 2 are paramagnetic at room temperature and variable temperature magnetic moment measurements revealed weak ferromagnetic interactions between metal ions at low temperature. Compound 3 exhibits excellent photoluminescence with large Stokes shift.

Electroosmotic flow mixing in zigzag microchannels.

PubMed

Chen, Jia-Kun; Yang, Ruey-Jen

2007-03-01

In this study we performed numerical and experimental investigations into the mixing of EOFs in zigzag microchannels with two different corner geometries, namely sharp corners and flat corners. In the zigzag microchannel with sharp corners, the flow travels more rapidly near the inner wall of the corner than near the outer wall as a result of the higher electric potential drop. The resulting velocity gradient induces a racetrack effect, which enhances diffusion within the fluid and hence improves the mixing performance. The simulation results reveal that the mixing index is approximately 88.83%. However, the sharp-corner geometry causes residual liquid or bubbles to become trapped in the channel at the point where the flow is almost stationary, when the channel is in the process of cleaning. Accordingly, a zigzag microchannel with flat-corner geometry is developed. The flat-corner geometry forms a convergent-divergent type nozzle which not only enhances the mixing performance in the channel, but also prevents the accumulation of residual liquid or bubbles. Scaling analysis reveals that this corner geometry leads to an effective increase in the mixing length. The experimental results reveal that the mixing index is increased to 94.30% in the flat-corner zigzag channel. Hence, the results demonstrate that the mixing index of the flat-corner zigzag channel is better than that of the conventional sharp-corner microchannel. Finally, the results of Taguchi analysis indicate that the attainable mixing index is determined primarily by the number of corners in the microchannel and by the flow passing height at each corner.

2D-1D structural phase transformation of Co(II) 3,5-pyridinedicarboxylate frameworks with chromotropism.

PubMed

Cheansirisomboon, Achareeya; Pakawatchai, Chaveng; Youngme, Sujittra

2012-09-21

Two new metal-organic frameworks [Co(pydc)(H(2)O)(2)](n) (1) and [Co(pydc)(H(2)O)(4)](n)(H(2)O)(n) (2), (pydc = 3,5-pyridinedicarboxylate) have been synthesized by a diffusion method and characterized by single-crystal X-ray diffraction. The structure of 1 reveals an infinite 2D layer with honeycomb-like cavities in which each pydc ligand bridges three Co(II) ions. The adjacent 2D layers are orderly packed in an ABAB-type array via intermolecular interactions of the combined π-π stacking and hydrogen bonds to form a 3D supramolecular architecture. Interestingly, compound 1 exhibits a water induced crystal-to-amorphous transformation with chromotropism confirmed by spectroscopic techniques, elemental analysis, TGA and XRPD. When this amorphous phase (1A) was exposed to water vapor, it was readily converted into the second crystalline phase 1B with a color change. Moreover, a reversible process between 1A and 1B was performed. In the case of compound 2, pydc acts as didentate bridging ligand connecting two Co(II) ions, leading to a 1D zig-zag chain. Guest water molecules fill the gaps in between chains and form hydrogen bonds with the host chains stabilizing the 3D network of 2. Additionally, compound 2 also exhibits a water induced crystal-to-amorphous transformation with chromotropism and the reversible process was also performed between the dehydrated (2A) and rehydrated (2') forms. Surprisingly, the IR and UV-vis spectra, elemental analysis, TGA curve and XRPD pattern of the rehydrated second phase 1B are found to be identical to that of 2 and 2', these results confirm that 2, 2' and 1B are the same compound.

Helical structures in vertically aligned dust particle chains in a complex plasma

NASA Astrophysics Data System (ADS)

Hyde, Truell W.; Kong, Jie; Matthews, Lorin S.

2013-05-01

Self-assembly of structures from vertically aligned, charged dust particle bundles within a glass box placed on the lower, powered electrode of a Gaseous Electronics Conference rf reference cell were produced and examined experimentally. Self-organized formation of one-dimensional vertical chains, two-dimensional zigzag structures, and three-dimensional helical structures of triangular, quadrangular, pentagonal, hexagonal, and heptagonal symmetries are shown to occur. System evolution is shown to progress from a one-dimensional chain structure, through a zigzag transition to a two-dimensional, spindlelike structure, and then to various three-dimensional, helical structures exhibiting multiple symmetries. Stable configurations are found to be dependent upon the system confinement, γ2=ω0h/ω0v2 (where ω0h,v are the horizontal and vertical dust resonance frequencies), the total number of particles within a bundle, and the rf power. For clusters having fixed numbers of particles, the rf power at which structural phase transitions occur is repeatable and exhibits no observable hysteresis. The critical conditions for these structural phase transitions as well as the basic symmetry exhibited by the one-, two-, and three-dimensional structures that subsequently develop are in good agreement with the theoretically predicted configurations of minimum energy determined employing molecular dynamics simulations for charged dust particles confined in a prolate, spheroidal potential as presented theoretically by Kamimura and Ishihara [Kamimura and Ishihara, Phys. Rev. EPLEEE81063-651X10.1103/PhysRevE.85.016406 85, 016406 (2012)].

Multimode Bose-Hubbard model for quantum dipolar gases in confined geometries

NASA Astrophysics Data System (ADS)

Cartarius, Florian; Minguzzi, Anna; Morigi, Giovanna

2017-06-01

We theoretically consider ultracold polar molecules in a wave guide. The particles are bosons: They experience a periodic potential due to an optical lattice oriented along the wave guide and are polarized by an electric field orthogonal to the guide axis. The array is mechanically unstable by opening the transverse confinement in the direction orthogonal to the polarizing electric field and can undergo a transition to a double-chain (zigzag) structure. For this geometry we derive a multimode generalized Bose-Hubbard model for determining the quantum phases of the gas at the mechanical instability, taking into account the quantum fluctuations in all directions of space. Our model limits the dimension of the numerically relevant Hilbert subspace by means of an appropriate decomposition of the field operator, which is obtained from a field theoretical model of the linear-zigzag instability. We determine the phase diagrams of small systems using exact diagonalization and find that, even for tight transverse confinement, the aspect ratio between the two transverse trap frequencies controls not only the classical but also the quantum properties of the ground state in a nontrivial way. Convergence tests at the linear-zigzag instability demonstrate that our multimode generalized Bose-Hubbard model can catch the essential features of the quantum phases of dipolar gases in confined geometries with a limited computational effort.

Heterometal silver/copper(I) modulated thermochromism of two isostructural iodoplumbates

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

Li, Honghong; Yu, Tanlai; An, Li

2015-01-15

Two isostructrual heterometallic iodoplumbates [Y(DMF){sub 8}]{sub 2n}[Pb{sub 7}M{sub 2}I{sub 22}]{sub n} [M=Cu(1), Ag(2)] have been prepared. Chargely balanced by [Y(DMF){sub 8}]{sup 3+}, [Pb{sub 7}M{sub 2}I{sub 22}]{sub n}{sup 6n−} displays a 1D zigzag chain constructed from MI{sub 4} tetrahedron and Pb{sub 7}I{sub 24} unit similar to a fragment of commonly observed (PbI{sub 3}){sub n}{sup n−} chain. Their band gaps (Eg) can be estimated as 2.66 and 2.72 eV, revealing potential semiconducting properties. Interestingly, thermochromism exhibits different response to the temperature for two compounds, which is verified by the diffuse-reflectance UV–visible spectra and crystallographic data at different temperatures. Moreover, this phenomenon ismore » attributed to the difference of heterometal Ag and Cu(I). - Graphical abstract: Two isostructrual heterometallic iodoplumbates [Y(DMF){sub 8}]{sub 2n}[Pb{sub 7}M{sub 2}I{sub 22}]{sub n} [M=Cu(1),Ag(2)] have been prepared. [Pb{sub 7}M{sub 2}I{sub 22}]{sub n}{sup 6n−} displays a 1D zigzag chain constructed from MI{sub 4} tetrahedron and Pb{sub 7}I{sub 24} unit similar to a fragment of commonly observed (PbI{sub 3}){sub n}{sup n−} chain. Interestingly, the thermochromism for two compounds exhibits different response to the temperature, which is attributed to the difference of heterometal Ag and Cu. - Highlights: • Two isostructrual heterometallic iodoplumbates have been prepared. • Single-crystal-X-ray diffraction data were collected at different temperatures. • Spectroscopic characterization showed semiconducting and thermochromic properties. • The difference of thermochromic properties for two compounds was studied.« less

Encapsulation and Polymerization of White Phosphorus Inside Single-Wall Carbon Nanotubes.

PubMed

Hart, Martin; White, Edward R; Chen, Ji; McGilvery, Catriona M; Pickard, Chris J; Michaelides, Angelos; Sella, Andrea; Shaffer, Milo S P; Salzmann, Christoph G

2017-07-03

Elemental phosphorus displays an impressive number of allotropes with highly diverse chemical and physical properties. White phosphorus has now been filled into single-wall carbon nanotubes (SWCNTs) from the liquid and thereby stabilized against the highly exothermic reaction with atmospheric oxygen. The encapsulated tetraphosphorus molecules were visualized with transmission electron microscopy, but found to convert readily into chain structures inside the SWCNT "nanoreactors". The energies of the possible chain structures were determined computationally, highlighting a delicate balance between the extent of polymerization and the SWCNT diameter. Experimentally, a single-stranded zig-zag chain of phosphorus atoms was observed, which is the lowest energy structure at small confinement diameters. These one-dimensional chains provide a glimpse into the very first steps of the transformation from white to red phosphorus. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Comparison of noncovalent interactions of zigzag and armchair carbon nanotubes with heterocyclic and aromatic compounds: Imidazole and benzene, imidazophenazines, and tetracene

NASA Astrophysics Data System (ADS)

Zarudnev, Eugene S.; Stepanian, Stepan G.; Adamowicz, Ludwik; Leontiev, Victor S.; Karachevtsev, Victor A.

2017-02-01

We study non-covalent functionalization of SWCNT by linear heterocyclic compounds such as imidazophenazine (F1) and its derivatives (F2-F4). MP2 and DFT/M05-2X quantum-chemical methods are used to determine the structures and the interaction energies of complexes formed by F1-F4 with the zigzag(10,10) and armchair(6,6) nanotubes. The calculations show that for small diameter nanotubes the binding energies with zigzag nanotubes are stronger than with armchair nanotubes. But above the diameter of 1.4 nm the interaction energies for the armchair nanotubes become larger than for the zigzag nanotubes. Experimental measurements demonstrates that the ratio of the integral intensity of the resonance Raman bands assigned to the RBM modes of semiconducting nanotubes to the integral intensity of the metallic nanotubes increases for supernatant of SWCNT:F4 (1,2,3-triazole-[4,5-d]-phenazine) hybrids solved in 1-Methyl-2-pyrrolidone as compared to this ratio in sediment samples. It demonstrates that the linear heterocyclic compounds can be used for separating SWCNTs with different electron-conduction types.

Na Diffusion in Quasi One-Dimensional Ion Conductor NaMn2O4 Observed by μ+SR

NASA Astrophysics Data System (ADS)

Umegaki, Izumi; Nozaki, Hiroshi; Harada, Masashi; Månsson, Martin; Sakurai, Hiroya; Kawasaki, Ikuto; Watanabe, Isao; Sugiyama, Jun

A quasi one-dimensional (1D) compound, NaMn2O4, in which Mn2O4 zigzag chains form a 1D channel along the b-axis and Na ions locate at the center of the channel, is thought to be a good Na ionic conductor. In order to study Na-ion diffusion, we have measured μ+SR spectra using a powder sample in the temperature range between 100 and 500 K. A diffusive behavior was clearly observed above 325 K. Assuming a thermal activate process for jump diffusion of Na-ion between two nearest neighboring sites, a self diffusion coefficient of Na ion (DNa) and its activation energy (Ea) were estimated as DNa = (3.1 ± 0.2) × 10 - 11 cm2/s at 350 K and Ea = 180(9) meV.

Reversible conformational transition gives rise to 'zig-zag' temperature dependence of the rate constant of irreversible thermoinactivation of enzymes.

PubMed

Levitsky VYu; Melik-Nubarov, N S; Siksnis, V A; Grinberg VYa; Burova, T V; Levashov, A V; Mozhaev, V V

1994-01-15

We have obtained unusual 'zig-zag' temperature dependencies of the rate constant of irreversible thermoinactivation (k(in)) of enzymes (alpha-chymotrypsin, covalently modified alpha-chymotrypsin, and ribonuclease) in a plot of log k(in) versus reciprocal temperature (Arrhenius plot). These dependencies are characterized by the presence of both ascending and descending linear portions which have positive and negative values of the effective activation energy (Ea), respectively. A kinetic scheme has been suggested that fits best for a description of these zig-zag dependencies. A key element of this scheme is the temperature-dependent reversible conformational transition of enzyme from the 'low-temperature' native state to a 'high-temperature' denatured form; the latter form is significantly more stable against irreversible thermoinactivation than the native enzyme. A possible explanation for a difference in thermal stabilities is that low-temperature and high-temperature forms are inactivated according to different mechanisms. Existence of the suggested conformational transition was proved by the methods of fluorescence spectroscopy and differential scanning calorimetry. The values of delta H and delta S for this transition, determined from calorimetric experiments, are highly positive; this fact underlies a conclusion that this heat-induced transition is caused by an unfolding of the protein molecule. Surprisingly, in the unfolded high-temperature conformation, alpha-chymotrypsin has a pronounced proteolytic activity, although this activity is much smaller than that of the native enzyme.

Modulating the spin transport behaviors in ZBNCNRs by edge hydrogenation and position of BN chain

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

Ouyang, Jun; Long, Mengqiu, E-mail: mqlong@csu.edu.cn, E-mail: ygao@csu.edu.cn; Zhang, Dan

2016-03-15

Using the density functional theory and the nonequilibrium Green’s function method, we study the spin transport behaviors in zigzag boron-nitrogen-carbon nanoribbons (ZBNCNRs) by modulating the edge hydrogenation and the position of B-N nanoribbons (BNNRs) chain. The different edge hydrogenations of the ZBNCNRs and the different position relationships of the BNNRs have been considered systematically. Our results show that the metallic, semimetallic and semiconductive properties of the ZBNCNRs can be modulated by the different edge hydrogenations and different position relationships of BN chains. And our proposaled ZBNCNRs devices act as perfect spin-filters with nearly 100% spin polarization. These effects would havemore » potential applications for boron-nitrogen-carbon-based nanomaterials in spintronics nano-devices.« less

Effect of Chain Conformation on the Single-Molecule Melting Force in Polymer Single Crystals: Steered Molecular Dynamics Simulations Study.

PubMed

Feng, Wei; Wang, Zhigang; Zhang, Wenke

2017-02-28

Understanding the relationship between polymer chain conformation as well as the chain composition within the single crystal and the mechanical properties of the corresponding single polymer chain will facilitate the rational design of high performance polymer materials. Here three model systems of polymer single crystals, namely poly(ethylene oxide) (PEO), polyethylene (PE), and nylon-66 (PA66) have been chosen to study the effects of chain conformation, helical (PEO) versus planar zigzag conformation (PE, PA66), and chain composition (PE versus PA66) on the mechanical properties of a single polymer chain. To do that, steered molecular dynamics simulations were performed on those polymer single crystals by pulling individual polymer chains out of the crystals. Our results show that the patterns of force-extension curve as well as the chain moving mode are closely related to the conformation of the polymer chain in the single crystal. In addition, hydrogen bonds can enhance greatly the force required to stretch the polymer chain out of the single crystal. The dynamic breaking and reformation of multivalent hydrogen bonds have been observed for the first time in PA66 at the single molecule level.

Absence of long-range order in the frustrated magnet SrDy2O4 due to trapped defects from a dimensionality crossover

NASA Astrophysics Data System (ADS)

Gauthier, N.; Fennell, A.; Prévost, B.; Uldry, A.-C.; Delley, B.; Sibille, R.; Désilets-Benoit, A.; Dabkowska, H. A.; Nilsen, G. J.; Regnault, L.-P.; White, J. S.; Niedermayer, C.; Pomjakushin, V.; Bianchi, A. D.; Kenzelmann, M.

2017-04-01

Magnetic frustration and low dimensionality can prevent long-range magnetic order and lead to exotic correlated ground states. SrDy2O4 consists of magnetic Dy3 + ions forming magnetically frustrated zigzag chains along the c axis and shows no long-range order to temperatures as low as T =60 mK. We carried out neutron scattering and ac magnetic susceptibility measurements using powder and single crystals of SrDy2O4 . Diffuse neutron scattering indicates strong one-dimensional (1D) magnetic correlations along the chain direction that can be qualitatively accounted for by the axial next-nearest-neighbor Ising model with nearest-neighbor and next-nearest-neighbor exchange J1=0.3 meV and J2=0.2 meV, respectively. Three-dimensional (3D) correlations become important below T*≈0.7 K. At T =60 mK, the short-range correlations are characterized by a putative propagation vector k1 /2=(0 ,1/2 ,1/2 ) . We argue that the absence of long-range order arises from the presence of slowly decaying 1D domain walls that are trapped due to 3D correlations. This stabilizes a low-temperature phase without long-range magnetic order, but with well-ordered chain segments separated by slowly moving domain walls.

Capacity improvement of the carbon-based electrochemical capacitor by zigzag-edge introduced graphene

NASA Astrophysics Data System (ADS)

Tamura, Naoki; Tomai, Takaaki; Oka, Nobuto; Honma, Itaru

2018-01-01

The electrochemical properties of graphene edge has been attracted much attention. Especially, zigzag edge has high electrochemical activity because neutral radical exits on edge. However, due to a lack of efficient production method for zigzag graphene, the electrochemical properties of zigzag edge have not been experimentally demonstrated and the capacitance enhancement of carbonaceous materials in energy storage devices by the control in their edge states is still challenge. In this study, we fabricated zigzag-edge-rich graphene by a one-step method combining graphene exfoliation in supercritical fluid and anisotropic etching by catalytic nanoparticles. This efficient production of zigzag-edge-rich graphene allows us to investigate the electrochemical activity of zigzag edge. By cyclic voltammetry, we revealed the zigzag edge-introduced graphene exhibited unique redox reaction in aqueous acid solution. Moreover, by the calculation on the density function theory (DFT), this unique redox potential for zigzag edge-introduced graphene can be attributed to the proton-insertion/-extraction reactions at the zigzag edge. This finding indicates that the graphene edge modification can contribute to the further increase in the capacitance of the carbon-based electrochemical capacitor.

Spin Bose-metal phase in a spin- (1)/(2) model with ring exchange on a two-leg triangular strip

NASA Astrophysics Data System (ADS)

Sheng, D. N.; Motrunich, Olexei I.; Fisher, Matthew P. A.

2009-05-01

Recent experiments on triangular lattice organic Mott insulators have found evidence for a two-dimensional (2D) spin liquid in close proximity to the metal-insulator transition. A Gutzwiller wave function study of the triangular lattice Heisenberg model with a four-spin ring exchange term appropriate in this regime has found that the projected spinon Fermi sea state has a low variational energy. This wave function, together with a slave particle-gauge theory analysis, suggests that this putative spin liquid possesses spin correlations that are singular along surfaces in momentum space, i.e., “Bose surfaces.” Signatures of this state, which we will refer to as a “spin Bose metal” (SBM), are expected to manifest in quasi-one-dimensional (quasi-1D) ladder systems: the discrete transverse momenta cut through the 2D Bose surface leading to a distinct pattern of 1D gapless modes. Here, we search for a quasi-1D descendant of the triangular lattice SBM state by exploring the Heisenberg plus ring model on a two-leg triangular strip (zigzag chain). Using density matrix renormalization group (DMRG) supplemented by variational wave functions and a bosonization analysis, we map out the full phase diagram. In the absence of ring exchange the model is equivalent to the J1-J2 Heisenberg chain, and we find the expected Bethe-chain and dimerized phases. Remarkably, moderate ring exchange reveals a new gapless phase over a large swath of the phase diagram. Spin and dimer correlations possess singular wave vectors at particular “Bose points” (remnants of the 2D Bose surface) and allow us to identify this phase as the hoped for quasi-1D descendant of the triangular lattice SBM state. We use bosonization to derive a low-energy effective theory for the zigzag spin Bose metal and find three gapless modes and one Luttinger parameter controlling all power law correlations. Potential instabilities out of the zigzag SBM give rise to other interesting phases such as a period-3 valence bond solid or a period-4 chirality order, which we discover in the DMRG. Another interesting instability is into a spin Bose-metal phase with partial ferromagnetism (spin polarization of one spinon band), which we also find numerically using the DMRG.

A distributed parameter electromechanical model for bimorph piezoelectric energy harvesters based on the refined zigzag theory

NASA Astrophysics Data System (ADS)

Chen, Chung-De

2018-04-01

In this paper, a distributed parameter electromechanical model for bimorph piezoelectric energy harvesters based on the refined zigzag theory (RZT) is developed. In this model, the zigzag function is incorporated into the axial displacement, and the zigzag distribution of the displacement between the adjacent layers of the bimorph structure can be considered. The governing equations, including three equations of motions and one equation of circuit, are derived using Hamilton’s principle. The natural frequency, its corresponding modal function and the steady state response of the base excitation motion are given in exact forms. The presented results are benchmarked with the finite element method and two beam theories, the first-order shear deformation theory and the classical beam theory. Comparing examples shows that the RZT provides predictions of output voltage and generated power at high accuracy, especially for the case of a soft middle layer. Variation of the parameters, such as the beam thickness, excitation frequencies and the external electrical loads, is investigated and its effects on the performance of the energy harvesters are studied by using the RZT developed in this paper. Based on this refined theory, analysts and engineers can capture more details on the electromechanical behavior of piezoelectric harvesters.

Simulation of Cell Patterning Triggered by Cell Death and Differential Adhesion in Drosophila Wing.

PubMed

Nagai, Tatsuzo; Honda, Hisao; Takemura, Masahiko

2018-02-27

The Drosophila wing exhibits a well-ordered cell pattern, especially along the posterior margin, where hair cells are arranged in a zigzag pattern in the lateral view. Based on an experimental result observed during metamorphosis of Drosophila, we considered that a pattern of initial cells autonomously develops to the zigzag pattern through cell differentiation, intercellular communication, and cell death (apoptosis) and performed computer simulations of a cell-based model of vertex dynamics for tissues. The model describes the epithelial tissue as a monolayer cell sheet of polyhedral cells. Their vertices move according to equations of motion, minimizing the sum total of the interfacial and elastic energies of cells. The interfacial energy densities between cells are introduced consistently with an ideal zigzag cell pattern, extracted from the experimental result. The apoptosis of cells is modeled by gradually reducing their equilibrium volume to zero and by assuming that the hair cells prohibit neighboring cells from undergoing apoptosis. Based on experimental observations, we also assumed wing elongation along the proximal-distal axis. Starting with an initial cell pattern similar to the micrograph experimentally obtained just before apoptosis, we carried out the simulations according to the model mentioned above and successfully reproduced the ideal zigzag cell pattern. This elucidates a physical mechanism of patterning triggered by cell apoptosis theoretically and exemplifies, to our knowledge, a new framework to study apoptosis-induced patterning. We conclude that the zigzag cell pattern is formed by an autonomous communicative process among the participant cells. Copyright © 2018 Biophysical Society. All rights reserved.

Negative differential resistance in oxidized zigzag graphene nanoribbons.

PubMed

Wang, Min; Li, Chang Ming

2011-01-28

A theoretical study of zigzag graphene nanoribbons (ZGNRs) with an epoxy-pair chain (ZGO) is performed. The electronic transport properties are mainly evaluated by non-equilibrium Green's functions using the TRANSIESTA package. The results indicate that the graphene oxide can have a negative differential resistance (NDR) phenomenon, supported by bias-dependent transmission curves of different spin orientations. Applying non-zero bias voltages makes the density of states (DOS) of the right electrodes shift down. Due to an energy gap between the LUMO and LUMO+1 in ZGOs, with a certain bias, the conduction band of the right electrode cannot match the LUMO of the scattering region, then NDR occurs. With a larger bias, NDR ends when the second conduction band of the right electrode's DOS covers the LUMO of the scattering region. Since most of proposed ZGO systems possess such a gap between the LUMO and LUMO+1, NDR can be widely observed and this discovery may provide great potential applications in NDR-based nanoelectronics by using modified graphene materials.

Dual-channel current valve in a three terminal zigzag graphene nanoribbon junction

NASA Astrophysics Data System (ADS)

Zhang, L.

2017-02-01

We theoretically propose a dual-channel current valve based on a three terminal zigzag graphene nanoribbon (ZGNR) junction driven by three asymmetric time-dependent pumping potentials. By means of the Keldysh Green’s function method, we show that two asymmetric charge currents can be pumped in the different left-right terminals of the device at a zero bias, which mainly stems from the single photon-assisted pumping approximation and the valley valve effect in a ZGNR p-n junction. The ON and OFF states of pumped charge currents are crucially dependent on the even-odd chain widths of the three electrodes, the pumping frequency, the lattice potential and the Fermi level. Two-tunneling spin valves are also considered to spatially separate and detect 100% polarized spin currents owing to the combined spin pump effect and the valley selective transport in a three terminal ZGNR ferromagnetic junction. Our investigations might be helpful to control the spatial and spin degrees of freedom of electrons in graphene pumping devices.

Electronic and transport properties of 1D aluminum at atomic scale

NASA Astrophysics Data System (ADS)

Bhuyan, Prabal Dev; Gupta, Sanjeev K.; Sonvane, Yogesh; Kumar, Ashok

2018-04-01

In this paper, we have studied the structural, electronic and transport properties of 1D carbyne like chain and ribbon like zigzag structures of aluminum (Al) nanowire. The ribbon with width of 4.79Å (2R) and 7.01Å (3R) shows better room temperature conductivity i.e. 3.50×1019 (Ω m s)-1 and 3.91×1019 (Ω m s)-1 respectively. We have observed that Al chain conducts better than Al ribbon; however the conductivity for the ribbon can be enhanced by increasing the width. On the other hand, higher thermal conductivity has been found to possess Al ribbon (3R) structure.

Studies of mixed-chain diacyl phosphatidylcholines with highly asymmetric acyl chains: a Fourier transform infrared spectroscopic study of interfacial hydration and hydrocarbon chain packing in the mixed interdigitated gel phase.

PubMed Central

Lewis, R N; McElhaney, R N

1993-01-01

The mixed interdigitated gel phases of unlabeled, specifically 13C = O-labeled, and specifically chain-perdeuterated samples of 1-O-eicosanoyl, 2-O-lauroyl phosphatidylcholine and 1-O-decanoyl, 2-O-docosanoyl phosphatidylcholine were studied by infrared spectroscopy. Our results suggest that at the liquid-crystalline/gel phase transition temperatures of these lipids, there is a greater redistribution in the populations of free and hydrogen-bonded ester carbonyl groups than is commonly observed with symmetric chain n-saturated diacyl phosphatidylcholines. The formation of the mixed interdigitated gel phase coincides with the appearance of a marked asymmetry in the contours of the C = O stretching band, a process which becomes more pronounced as the temperature is reduced. This asymmetry is ascribed to the emergence of a predominant lipid population consisting of free sn1- and hydrogen-bonded (hydrated) sn2-ester carbonyl groups. This suggests that the region of the mixed interdigitated bilayer polar/apolar interface near to the sn1-ester carbonyl group is less hydrated than is the case with the noninterdigitated gel-phase bilayers formed by normal symmetric chain phosphatidylcholines. In the methylene deformation region of the spectrum, the unlabeled lipids exhibit a pronounced splitting of the CH2 scissoring bands. This splitting is significantly attenuated when the short chains are perdeuterated and collapses completely upon perdeuteration of the long chains, irrespective of whether the long (or short) chains are esterified to the sn1 or sn2 positions of the glycerol backbone. These results are consistent with a global hydrocarbon chain packing motif in which the zigzag planes of the hydrocarbon chains are perpendicular to each other and the sites occupied by long chains are twice as numerous as those occupied by short chains. The experimental support for this chain-packing motif enabled more detailed considerations of the possible ways in which these lipid molecules are assembled in the mixed interdigitated gel phase. Generally, our results are compatible with a previously proposed model in which the mixed interdigitated gel phase is an assembly of repeat units which consists of two phosphatidylcholine molecules forming a triple-chain structure with the long chains traversing the bilayer and with the methyl termini of the shorter chains opposed at the bilayer center. Our data also suggest that the packing format which is most consistent with our results and previously published work is one in which the hydrocarbon chains of each repeat unit are parallel to each other with the repeat units themselves being perpendicularly packed. PMID:8298016

Optofluidic Modulation of Self-Associated Nanostructural Units Forming Planar Bragg Microcavities.

PubMed

Oliva-Ramirez, Manuel; Barranco, Angel; Löffler, Markus; Yubero, Francisco; González-Elipe, Agustin R

2016-01-26

Bragg microcavities (BMs) formed by the successive stacking of nanocolumnar porous SiO2 and TiO2 layers with slanted, zigzag, chiral, and vertical configurations are prepared by physical vapor deposition at oblique angles while azimuthally varying the substrate orientation during the multilayer growth. The slanted and zigzag BMs act as wavelength-selective optical retarders when they are illuminated with linearly polarized light, while no polarization dependence is observed for the chiral and vertical cavities. This distinct optical behavior is attributed to a self-nanostructuration mechanism involving a fence-bundling association of nanocolumns as observed by focused ion beam scanning electron microscopy in the slanted and zigzag microcavities. The outstanding retarder response of the optically active BMs can be effectively modulated by dynamic infiltration of nano- and mesopores with liquids of different refraction indices acting as a switch of the polarization behavior. The unprecedented polarization and tunable optofluidic properties of these nanostructured photonic systems have been successfully simulated with a simple model that assumes a certain birefringence for the individual stacked layers and accounts for the light interference phenomena developed in the BMs. The possibilities of this type of self-arranged nanostructured and optically active BMs for liquid sensing and monitoring applications are discussed.

Dispersion relations for circular single and double dusty plasma chains

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

Tkachenko, D. V.; Misko, V. R.; Sheridan, T. E.

2011-10-15

We derive dispersion relations for a system of identical particles confined in a two-dimensional annular harmonic well and which interact through a Yukawa potential, e.g., a dusty plasma ring. When the particles are in a single chain (i.e., a one-dimensional ring), we find a longitudinal acoustic mode and a transverse optical mode which show approximate agreement with the dispersion relation for a straight configuration for large radii of the ring. When the radius decreases, the dispersion relations modify: there appears an anticrossing of the modes near the crossing point resulting in a frequency gap between the lower and upper branchesmore » of the modified dispersion relations. For the double chain (i.e., a two-dimensional zigzag configuration), the dispersion relation has four branches: longitudinal acoustic and optical and transverse acoustic and optical.« less

Dispersion relations for circular single and double dusty plasma chains

NASA Astrophysics Data System (ADS)

Tkachenko, D. V.; Sheridan, T. E.; Misko, V. R.

2011-10-01

We derive dispersion relations for a system of identical particles confined in a two-dimensional annular harmonic well and which interact through a Yukawa potential, e.g., a dusty plasma ring. When the particles are in a single chain (i.e., a one-dimensional ring), we find a longitudinal acoustic mode and a transverse optical mode which show approximate agreement with the dispersion relation for a straight configuration for large radii of the ring. When the radius decreases, the dispersion relations modify: there appears an anticrossing of the modes near the crossing point resulting in a frequency gap between the lower and upper branches of the modified dispersion relations. For the double chain (i.e., a two-dimensional zigzag configuration), the dispersion relation has four branches: longitudinal acoustic and optical and transverse acoustic and optical.

(E)-3-Methyl-2,6-di­phenyl­piperidin-4-one O-(3-methyl­benzo­yl)oxime

PubMed Central

Kathiravan, V.; Krishnan, K. Gokula; Mohandas, T.; Thanikachalam, V.; Sakthivel, P.

2014-01-01

In the title compound, C26H26N2O2, the piperidine ring exhibits a chair conformation. The phenyl rings are attached to the central heterocycle in an equatorial position. The dihedral angle between the planes of the phenyl rings is 57.58 (8)°. In the crystal, C—H⋯O inter­actions connect the mol­ecules into zigzag chains along [001]. PMID:25249925

Crystal structure of carnidazole form II from synchrotron X-ray powder diffraction: structural comparison with form I, the hydrated form and the low energy conformations in vacuo.

PubMed

de Armas, Héctor Novoa; Peeters, Oswald M; Blaton, Norbert; Van den Mooter, Guy; De Ridder, Dirk J A; Schenk, Henk

2006-10-01

The crystal structure of carnidazole form II, O-methyl [2-(2-methyl-5-nitro-1H-imidazole-1-yl)ethyl]thiocarbamate, has been determined using synchrotron X-ray powder diffraction in combination with simulated annealing and whole profile pattern matching, and refined by the Rietveld method. For structure solution, 12 degrees of freedom were defined: one motion group and six torsions. Form II crystallizes in space group P2(1)/n, Z=4, with unit cell parameters after Rietveld refinement: a=13.915(4), b=8.095(2), c=10.649(3) A, beta=110.83(1) degrees, and V=1121.1(5) A3. The two polymorphic forms, as well as the hydrate, crystallize in the monoclinic space group P2(1)/n having four molecules in the cell. In form II, the molecules are held together by forming two infinite zig-zag chains via hydrogen bonds of the type N--H...N, the same pattern as in form I. A conformational study of carnidazole, at semiempirical PM3 level, was performed using stochastic approaches based on modification of the flexible torsion angles. The values of the torsion angles for the molecules of the two polymorphic forms and the hydrate of carnidazole are compared to those obtained from the conformational search. Form I and form II are enantiotropic polymorphic pairs this agrees with the fact that the two forms are conformational polymorphs. Copyright (c) 2006 Wiley-Liss, Inc. and the American Pharmacists Association

Tuning conductivity in boron nanowire by edge geometry

NASA Astrophysics Data System (ADS)

Bhuyan, Prabal Dev; Gupta, Sanjeev K.; Sonvane, Yogesh; Gajjar, P. N.

2018-04-01

In present study, we have investigated electronic and temperature dependent transport properties of carbyne like linear chain and ribbon like zigzag structures of Boron (B) nanowire. The linear chain structure showed higher electric and thermal conductivity, as it is sp-hybridized, than its counterpart ribbon (R) structure. However the conductivity of ribbon structure increases with increases in width due to edge geometry effect. The ribbon (3R) structure showed high electric and thermal conductivity of 8.0×1019 1/Ω m s and 0.59×1015 W/ m K respectively. Interestingly we have observed that B linear chain showed higher thermal conductivity of 0.23×1015 W/ m K than its ribbon R and 2R structure above 600K. Because of high Seebeck co-efficient of boron chain and ribbon (R) structures at low temperature, they could find applications in thermoelectric sensors. Our results show that tuning conductivity property of boron nanowire could be of great interest in research for future electric connector in nanodevices.

High performance current and spin diode of atomic carbon chain between transversely symmetric ribbon electrodes.

PubMed

Dong, Yao-Jun; Wang, Xue-Feng; Yang, Shuo-Wang; Wu, Xue-Mei

2014-08-21

We demonstrate that giant current and high spin rectification ratios can be achieved in atomic carbon chain devices connected between two symmetric ferromagnetic zigzag-graphene-nanoribbon electrodes. The spin dependent transport simulation is carried out by density functional theory combined with the non-equilibrium Green's function method. It is found that the transverse symmetries of the electronic wave functions in the nanoribbons and the carbon chain are critical to the spin transport modes. In the parallel magnetization configuration of two electrodes, pure spin current is observed in both linear and nonlinear regions. However, in the antiparallel configuration, the spin-up (down) current is prohibited under the positive (negative) voltage bias, which results in a spin rectification ratio of order 10(4). When edge carbon atoms are substituted with boron atoms to suppress the edge magnetization in one of the electrodes, we obtain a diode with current rectification ratio over 10(6).

High performance current and spin diode of atomic carbon chain between transversely symmetric ribbon electrodes

PubMed Central

Dong, Yao-Jun; Wang, Xue-Feng; Yang, Shuo-Wang; Wu, Xue-Mei

2014-01-01

We demonstrate that giant current and high spin rectification ratios can be achieved in atomic carbon chain devices connected between two symmetric ferromagnetic zigzag-graphene-nanoribbon electrodes. The spin dependent transport simulation is carried out by density functional theory combined with the non-equilibrium Green's function method. It is found that the transverse symmetries of the electronic wave functions in the nanoribbons and the carbon chain are critical to the spin transport modes. In the parallel magnetization configuration of two electrodes, pure spin current is observed in both linear and nonlinear regions. However, in the antiparallel configuration, the spin-up (down) current is prohibited under the positive (negative) voltage bias, which results in a spin rectification ratio of order 104. When edge carbon atoms are substituted with boron atoms to suppress the edge magnetization in one of the electrodes, we obtain a diode with current rectification ratio over 106. PMID:25142376

A threefold interpenetrated two-dimensional zinc(II) supramolecular architecture based on 3-nitrobenzoic acid and 4,4'-bipyridine.

PubMed

Tang, Long; Wang, Ji-Jiang; Fu, Feng; Wang, Sheng-Wen; Liu, Qi-Rui

2016-02-01

With regard to crystal engineering, building block or modular assembly methodologies have shown great success in the design and construction of metal-organic coordination polymers. The critical factor for the construction of coordination polymers is the rational choice of the organic building blocks and the metal centre. The reaction of Zn(OAc)2·2H2O (OAc is acetate) with 3-nitrobenzoic acid (HNBA) and 4,4'-bipyridine (4,4'-bipy) under hydrothermal conditions produced a two-dimensional zinc(II) supramolecular architecture, catena-poly[[bis(3-nitrobenzoato-κ(2)O,O')zinc(II)]-μ-4,4'-bipyridine-κ(2)N:N'], [Zn(C7H4NO4)2(C10H8N2)]n or [Zn(NBA)2(4,4'-bipy)]n, which was characterized by elemental analysis, IR spectroscopy, thermogravimetric analysis and single-crystal X-ray diffraction analysis. The Zn(II) ions are connected by the 4,4'-bipy ligands to form a one-dimensional zigzag chain and the chains are decorated with anionic NBA ligands which interact further through aromatic π-π stacking interactions, expanding the structure into a threefold interpenetrated two-dimensional supramolecular architecture. The solid-state fluorescence analysis indicates a slight blue shift compared with pure 4,4'-bipyridine and HNBA.

Structure and optical properties of several organic-inorganic hybrids containing corner-sharing chains of bismuth iodide octahedra.

PubMed

Mitzi, D B; Brock, P

2001-04-23

Two organic-inorganic bismuth iodides of the form (H3N-R-NH3)BiI5 are reported, each containing long and relatively flexible organic groups, R. The norganic framework in each case consists of distorted BiI6 octahedra sharing cis vertexes to form zigzag chains. Crystals of (H3NC18H24S2NH3)BiI5 were grown from a slowly cooled ethylene glycol/2-butanol solution containing bismuth(III) iodide and AETH.2HI, where AETH = 1,6-bis[5'-(2' '-aminoethyl)-2'-thienyl]hexane. The new compound, (H2AETH)BiI5, adopts an orthorhombic (Aba2) cell with the lattice parameters a = 20.427(3) A, b = 35.078(5) A, c = 8.559(1) A, and Z = 8. The structure consists of corrugated layers of BiI5(2-) chains, with Bi-I bond lengths ranging from 2.942(3) to 3.233(3) A, separated by layers of the organic (H2AETH)(2+) cations. Crystals of the analogous (H3NC12H24NH3)BiI5 compound were also prepared from a concentrated aqueous hydriodic acid solution containing bismuth(III) iodide and the 1,12-dodecanediamine (DDDA) salt, DDDA.2HI. (H2DDDA)BiI5 crystallizes in an orthorhombic (Ibam) cell with a = 17.226(2) A, b = 34.277(4) A, c = 8.654(1) A, and Z = 8. The Bi-I bonds range in length from 2.929(1) to 3.271(1) A. While the inorganic chain structure is nearly identical for the two title compounds, as well as for the previously reported (H3NC6H12NH3)BiI5 [i.e., (H2DAH)BiI5] structure, the packing of the chains is strongly influenced by the choice of organic cation. Optical absorption spectra for thermally ablated thin films of the three organic-inorganic hybrids containing BiI5(2-) chains are reported as a function of temperature (25-290 K). The dominant long-wavelength feature in each case is attributed to an exciton band, which is apparent at room temperature and, despite the similar inorganic chain structure, varies in position from 491 to 541 nm (at 25 K).

The opposite induced magnetic moment in narrow zigzag graphene nanoribbons

NASA Astrophysics Data System (ADS)

Liu, Hong; Hu, Bian; Liu, Na

2016-11-01

Based on the analysis of band structure and edge states on zigzag graphene nanoribbons (ZGNRs), we can study theoretically the origination of two minimal quantum conductance. At the two energy points - 0.20 eV and 0.15 eV corresponding to the two dips of quantum conductance, the spin-polarized quantum conductance is about 45%. Furthermore, the two types of edge-localized carriers in the opposite transport directions along the two opposite edge sides form the quantum internal loop current, which can generate one big magnetic moment. At these two energy points - 0.17 eV and 0.15 eV the two induced magnetic moments are in opposite signals.

Ethyl 2-[(carbamoyl-amino)-imino]-propano-ate hemihydrate.

PubMed

Corrêa, Charlane C; Graúdo, José Eugênio J C; de Oliveira, Luiz Fernando C; de Almeida, Mauro V; Diniz, Renata

2011-08-01

The title compound, C(6)H(11)N(3)O(3)·0.5H(2)O, has two independent mol-ecules and one mol-ecule of water in the asymmetric unit. The crystal packing is stabilized by inter-molecular N-H⋯N, O-H⋯O, N-H⋯O and C-H⋯O hydrogen bonds. These inter-actions form a two-dimensional array in the ab plane with a zigzag motif which has an angle close to 35° between the zigzag planes. The hydrogen bonding can be best described using the graph-set notation as N(1) = C(10)R(2) (2)(10)R(2) (2)(8) and N(2) = R(6) (4)(20)R(2) (2)(8).

Improved Photo-Detection Using Zigzag TiO2 Nanostructures as an Active Medium.

PubMed

Tiwari, A K; Mondal, A; Mahajan, B K; Choudhuri, B; Goswami, T; Sarkar, M B; Chakrabartty, S; Ngangbam, C; Saha, S

2015-07-01

Zigzag TiO2 nanostructures were fabricated using oblique angle deposition technique. The field emission gun-scanning electron microscope (FEG-SEM) image shows that the TiO2 zigzag nanostructures were ~500 nm in length. Averagely two times enhanced UV-Vis absorption was recorded for zigzag structure compared to perpendicular TiO2 nanowires. The main band transition was observed at ~3.4 eV. The zigzag TiO2 exhibited high turn on voltage (+11 V) than that of nanowire (+2 V) detector under dark which were reduced to +0.2 V and +1.0 V under white light illumination, respectively. A maximum ~6 fold photo-responsivity was observed for the zigzag TiO2 compared with nanowire device at + 1.0 V applied potential. The maximum photo-responsivity of 0.36 A/W at 370 nm was measured for the zigzag TiO2 detector. The TiO2 zigzag detector showed slow response with rise time of 10.2 s and fall time of 10.3 s respectively. The UV (370 nm) to visible (450 nm) wavelength rejection ratio of photo-responsivity was recorded ~4 times for the detector.

The impact of inversion and mirror reflection symmetry on Raman scattering of T'transition metal dichalcogenides

NASA Astrophysics Data System (ADS)

Yan, Jun; Chen, Shao-Yu; Naylor, Carl; Goldstein, Thomas; Johnson, Charlie; Venkataraman, Dhandapani; Ramasubramaniam, Ashwin

Distorted octahedral (T') transition metal dichalcogenides (TMDCs) are topologically interesting material systems. Inversion-symmetry-broken bulk T'-TMDCs are predicted to be type II Weyl semimetals and inversion-symmetric monolayer (1L) T'-TMDCs are shown to be 2D topological insulators. In this talk, I will show that both the inversion symmetry and the mirror symmetry are important for understanding the lattice dynamics and Raman scattering of T'-TMDCs. The mirror plane that is perpendicular to the zigzag transition metal atomic chain classifies lattice vibrations into z-modes and m-modes where ` z' stands for zigzag and ` m' stands for mirror. Raman active z- and m- modes can be experimentally determined with light-polarization and crystal angle-resolved Raman tensor analysis. We report observation of all 9 even-parity zone-center phonons in 1L-T'-MoTe2. In bulk T'-MoTe2, we monitor inversion symmetry breaking with the shear lattice vibrations, which is important for supporting Weyl fermions. This work is supported by the Armstrong Fund for Science and NSF EFRI 2DARE EFMA-1542879.

FAST TRACK COMMUNICATION: Preferential functionalization on zigzag graphene nanoribbons: first-principles calculations

NASA Astrophysics Data System (ADS)

Lee, Hoonkyung

2010-09-01

We investigate the functionalization of functional groups to graphene nanoribbons with zigzag and armchair edges using first-principles calculations. We find that the formation energy for the configuration of the functional groups functionalized to the zigzag edge is ~ 0.2 eV per functional group lower than that to the armchair edge. The formation energy difference arises from a structural deformation on the armchair edge by the functionalization whereas there is no structural deformation on the zigzag edge. Selective functionalization on the zigzag edge takes place at a condition of the temperature and the pressure of ~ 25 °C and 10 - 5 atm. Our findings show that selective functionalization can offer the opportunity for an approach to the separation of zigzag graphene nanoribbons with their solubility change.

Direction-dependent waist-shift-difference of Gaussian beam in a multiple-pass zigzag slab amplifier and geometrical optics compensation method.

PubMed

Li, Zhaoyang; Kurita, Takashi; Miyanaga, Noriaki

2017-10-20

Zigzag and non-zigzag beam waist shifts in a multiple-pass zigzag slab amplifier are investigated based on the propagation of a Gaussian beam. Different incident angles in the zigzag and non-zigzag planes would introduce a direction-dependent waist-shift-difference, which distorts the beam quality in both the near- and far-fields. The theoretical model and analytical expressions of this phenomenon are presented, and intensity distributions in the two orthogonal planes are simulated and compared. A geometrical optics compensation method by a beam with 90° rotation is proposed, which not only could correct the direction-dependent waist-shift-difference but also possibly average the traditional thermally induced wavefront-distortion-difference between the horizontal and vertical beam directions.

Crystal structures of 5-amino-N-phenyl-3H-1,2,4-di-thia-zol-3-iminium chloride and 5-amino-N-(4-chloro-phen-yl)-3H-1,2,4-di-thia-zol-3-iminium chloride monohydrate.

PubMed

Yeo, Chien Ing; Tan, Yee Seng; Tiekink, Edward R T

2015-10-01

The crystal and mol-ecular structures of the title salt, C8H8N3S2 (+)·Cl(-), (I), and salt hydrate, C8H7ClN3S2 (+)·Cl(-)·H2O, (II), are described. The heterocyclic ring in (I) is statistically planar and forms a dihedral angle of 9.05 (12)° with the pendant phenyl ring. The comparable angle in (II) is 15.60 (12)°, indicating a greater twist in this cation. An evaluation of the bond lengths in the H2N-C-N-C-N sequence of each cation indicates significant delocalization of π-electron density over these atoms. The common feature of the crystal packing in (I) and (II) is the formation of charge-assisted amino-N-H⋯Cl(-) hydrogen bonds, leading to helical chains in (I) and zigzag chains in (II). In (I), these are linked by chains mediated by charge-assisted iminium-N(+)-H⋯Cl(-) hydrogen bonds into a three-dimensional architecture. In (II), the chains are linked into a layer by charge-assisted water-O-H⋯Cl(-) and water-O-H⋯O(water) hydrogen bonds with charge-assisted iminium-N(+)-H⋯O(water) hydrogen bonds providing the connections between the layers to generate the three-dimensional packing. In (II), the chloride anion and water mol-ecules are resolved into two proximate sites with the major component being present with a site occupancy factor of 0.9327 (18).

A computational NMR study on zigzag aluminum nitride nanotubes

NASA Astrophysics Data System (ADS)

Bodaghi, Ali; Mirzaei, Mahmoud; Seif, Ahmad; Giahi, Masoud

2008-12-01

A computational nuclear magnetic resonance (NMR) study is performed to investigate the electronic structure properties of the single-walled zigzag aluminum nitride nanotubes (AlNNTs). The chemical-shielding (CS) tensors are calculated at the sites of Al-27 and N-15 nuclei in three structural forms of AlNNT including H-saturated, Al-terminated, and N-terminated ones. The structural forms are firstly optimized and then the calculated CS tensors in the optimized structures are converted to chemical-shielding isotropic (CSI) and chemical-shielding anisotropic (CSA) parameters. The calculated parameters reveal that various Al-27 and N-15 nuclei are divided into some layers with equivalent electrostatic properties; furthermore, Al and N can act as Lewis base and acid, respectively. In the Al-terminated and N-terminated forms of AlNNT, in which one mouth of the nanotube is terminated by aluminum and nitrogen nuclei, respectively, just the CS tensors of the nearest nuclei to the mouth of the nanotube are significantly changed due to removal of saturating hydrogen atoms. Density functional theory (DFT) calculations are performed using GAUSSIAN 98 package of program.

New oxyfluorotellurates(IV): MTeO3F (M = FeIII, GaIII and CrIII).

PubMed

Laval, Jean Paul; Jennene Boukharrata, Nefla; Thomas, Philippe

2008-02-01

The crystal structures of the new isomorphous compounds iron(III) oxyfluorotellurate(IV), FeTeO(3)F, gallium(III) oxyfluorotellurate(IV), GaTeO(3)F, and chromium(III) oxyfluorotellurate(IV), CrTeO(3)F, consist of zigzag chains of MO(4)F(2) distorted octahedra alternately sharing O-O and F-F edges and connected via TeO(3) trigonal pyramids. A full O/F anionic ordering is observed and the electronic lone pair of the Te(IV) cation is stereochemically active.

Thiocyanate-Ligated Heterobimetallic {PtM} Lantern Complexes Including a Ferromagnetically Coupled 1D Coordination Polymer.

PubMed

Guillet, Jesse L; Bhowmick, Indrani; Shores, Matthew P; Daley, Christopher J A; Gembicky, Milan; Golen, James A; Rheingold, Arnold L; Doerrer, Linda H

2016-08-15

A series of heterobimetallic lantern complexes with the central unit {PtM(SAc)4(NCS)} have been prepared and thoroughly characterized. The {Na(15C5)}[PtM(SAc)4(NCS)] series, 1 (Co), 2 (Ni), 3 (Zn), are discrete compounds in the solid state, whereas the {Na(12C4)2)}[PtM(SAc)4(NCS)] series, 4 (Co), 5 (Ni), 6 (Zn), and 7 (Mn), are ion-separated species. Compound 7 is the first {PtMn} lantern of any bridging ligand (carboxylate, amide, etc.). Monomeric 1-7 have M(2+), necessitating counter cations that have been prepared as {(15C5)Na}(+) and {(12C4)2Na}(+) variants, none of which form extended structures. In contrast, neutral [PtCr(tba)4(NCS)]∞ 8 forms a coordination polymer of {PtCr}(+) units linked by (NCS)(-) in a zigzag chain. All eight compounds have been thoroughly characterized and analyzed in comparison to a previously reported family of compounds. Crystal structures are presented for compounds 1-6 and 8, and solution magnetic susceptibility measurements are presented for compounds 1, 2, 4, 5, and 7. Further structural analysis of dimerized {PtM} units reinforces the empirical observation that greater charge density along the Pt-M vector leads to more Pt···Pt interactions in the solid state. Four structural classes, one new, of {MPt}···{PtM} units are presented. Solid state magnetic characterization of 8 reveals a ferromagnetic interaction in the {PtCr(NCS)} chain between the Cr centers of J/kB = 1.7(4) K.

Thermoelectric Properties of Novel One-dimensional and Two-dimensional Systems Based on MoS2 Nanoribbons and Sheets

NASA Astrophysics Data System (ADS)

Arab, Abbas

Atomically thin materials such as hexagonal boron nitride (h-BN) and transition metal dichalcogenides (TMDCs) have attracted a lot of interest since the discovery of Graphene. Potential use of Graphene in semiconductor industry has been hindered by the fact that graphene is a semi metal with zero band gap. The difficulties in engineering band gap in graphene turn the focus light to inherent semiconducting two-dimensional (2D) materials; TMDCs. Bulk of TMDCs are formed by layers vertically stacked and weakly bonded together via weak van der Waals interactions. These weak interlayer forces make it possible to obtain monolayer by using scotch tape exfoliation or lithium-ion intercalation. Among the semiconducting members of TMDCs, MoS 2 is the most appealing candidate, partly due to its thermal stability and also for its natural abundance. Intensive study of electronic properties of MoS2 has revealed the desirable band gap (1.2 eV), good carrier xmobility (which is close to those of silicon thin films and graphene nanoribbons), thermal stability and a surface free from dangling bonds make it a perfect candidate for electronic and opto-electronic applications. Despite the fact that MoS2 has a high Seebeck coefficient, its thermoelectric properties have not studied as well as it should be. In this work, we have studied thermoelectric properties of monolayer and fewlayer MoS2 sheets in both armchair and zigzag orientations and also of monolayer MoS2 armchair nanoribbons. Density functional theory (DFT) using non-equilibrium Green's function (NEGF) method in ballistic transport regime of Landauer-Buttiker formulation in linear transport approximation has been implemented to calculate the transmission spectra and consequently electronic transport coefficients. Phonon transmission spectra are calculated based on parameterization of Stillinger-Weber potential. Thermoelectric figure of merit, ZT, is calculated using these electronic and phonon transmission spectra. In the case of MoS2 sheets, thermoelectric properties of monolayer, bilayer, trilayer and quadlayer in armchair and zigzag directions have been studied. Our results show that as number of layers increase from monolayer to quadlayer, both transmission spectrum and phonon thermal conductance increase. In addition, strong electronic and thermal anisotropy is found between zigzag and armchair orientations. Transmission coefficient and phonon thermal conductance of zigzag orientation is higher than those of armchair with the same number of layers. Electrical conductance and phonon thermal conductance are competing forces in achieving a high thermoelectric figure of merit. Advantage of having a higher electrical conductance in zigzag orientation has been nullified by having a higher phonon thermal conductance. In fact, our results show higher thermoelectric xifigure of merit for armchair oriented than zigzag oriented sheets. Also as number of layer decreases from quadlayer to monolayer, we are witnessing a higher thermoelectric figure of merit for both armchair and zigzag oriented sheets. Hence, the highest achieved thermoelectric figure of merit was obtained by monolayer armchair MoS2 sheet for both p-type and n-type semiconducting behavior. In case of MoS2 armchair nanoribbons, effect of several factors has been studied; width of nanoribbon, Sulfur vacancy and edge roughness. The electronic properties of nanoribbons are dominated by the presence of edge states that are dependent on the number of zigzag chains across the nanoribbon. In addition, it is found that the phonon thermal conductance of monolayer MoS2 armchair nanoribbon is smaller compared to MoS2 monolayer armchair sheet. This outcome can be explained by phonon edge scattering. The effect of this phonon edge scattering is more pronounced in narrower nanoribbons compared to wide ones which leads to higher thermoelectric figure of merit for narrow nanoribbons. The effect of edge roughness and sulfur vacancy on thermoelectric behavior of MoS2 nanoribbons is also studied. Our result shows that edge roughness decreased the thermoelectric figure of merit compared to those of a perfect nanoribbon as its impact on electrical conductance is more severe than on phonon thermal conductance. Sulfur vacancy, however, improved thermoelectric figure of merit of MoS2 nanoribbons. It has been shown that thermoelectric figure of merit as high as 4 and 3 at T = 500K can be achieved n-doped and p-doped MoS2 nanoribbons. The ability of getting a high thermoelectric figure of merit for both n-type and p-type behavior from the same material will be a huge boost to thermoelectric industry if realized.

The ground state of two-dimensional silicon

NASA Astrophysics Data System (ADS)

Borlido, Pedro; Rödl, Claudia; Marques, Miguel A. L.; Botti, Silvana

2018-07-01

We perform ab initio structure-prediction calculations of the low-energy crystal structures of two-dimensional silicon. Besides the well-known silicene and a few other allotropes proposed earlier in the literature, we discover a wealth of new phases with interesting properties. In particular, we find that the ground state of two-dimensional silicon is an unreported structure formed by a honeycomb lattice with dumbbell atoms arranged in a zigzag pattern. This material, that we call zigzag dumbbell silicene, is 218 meV/atom more stable than silicene and displays a quasi-direct band gap of around 1.11 eV, with a very dispersive electron band. These properties should make it easier to synthesize than silicene and interesting for a wealth of opto-electronic applications.

Optical Properties of a Single Carbon Chain-Doped Silicene Nanoribbon

NASA Astrophysics Data System (ADS)

Lu, Dao-Bang; Song, Yu-Ling; Huang, Xiao-yu; Wang, Chong

2018-05-01

Using first-principles spin polarization density function theory calculations, we have studied the electronic and optical properties of zigzag-edge silicene nanoribbons (ZSiNRs) doped with a single carbon chain. Because of the doped carbon chain, there are several defect states in the band structures of ZSiNRs across the Fermi level, and the ferromagnetic ground state is metallic. The dielectric functions in all three dimensions are completely different from each other, and thus the system exhibits strong optical anisotropism. The carbon chain influenced the dielectric functions most at low energy. The first peak in the E//x direction of the dielectric spectrum exhibits a significant blueshift, and its value has changed as well. The main absorption wavelength depends on the polarization direction of the incident light, but occurs within the UV region for all polarization directions. The peaks of the energy loss spectra correspond to the trailing edges in the reflectivity spectrum, and the highest peak corresponds to a plasmon frequency. Our results could be useful for investigating nanodevices based on silicene nanoribbons.

Variable Asymmetric Chains in Transition Metal Oxyfluorides: Structure-Second-Harmonic-Generation Property Relationships.

PubMed

Ahmed, Belal; Jo, Hongil; Oh, Seung-Jin; Ok, Kang Min

2018-05-15

Four novel transition metal oxyfluorides, [Zn(pz) 3 ][MoO 2 F 4 ]·0.1H 2 O (1), [Zn(pz) 2 F 2 ][Zn(pz) 3 ] 2 [WO 2 F 4 ] 2 (2), [Cd(pz) 4 ][Cd(pz) 4 (H 2 O)][MoO 2 F 4 ] 2 ·0.625H 2 O (3), and [Zn(mpz) 3 ] 2 [MoO 2 F 4 ] 2 (4) (pz = pyrazole; mpz = 3-methyl pyrazole) have been synthesized. Compounds 1 and 4 contain helical chains. Compound 2 accommodates zigzag chains, and compound 3 has quasi-one-dimensional linear chains. The variable chain structures are found to be attributable to the different structure-directing anionic groups and hydrogen bonding interactions. Compound 4 crystallized in the noncentrosymmetric (NCS) polar space group, Pna2 1 , is nonphase-matchable (Type I), and reveals a moderate second-harmonic-generation (SHG) efficiency (10 × α-SiO 2 ). The observed SHG efficiency of compound 4 is due to the small net polarization occurring from the arrangement of ZnN 3 F 2 trigonal bipyramids. Spectroscopic and thermal characterizations along with calculations for the title materials are reported.

Unraveling metamaterial properties in zigzag-base folded sheets.

PubMed

Eidini, Maryam; Paulino, Glaucio H

2015-09-01

Creating complex spatial objects from a flat sheet of material using origami folding techniques has attracted attention in science and engineering. In the present work, we use the geometric properties of partially folded zigzag strips to better describe the kinematics of known zigzag/herringbone-base folded sheet metamaterials such as Miura-ori. Inspired by the kinematics of a one-degree of freedom zigzag strip, we introduce a class of cellular folded mechanical metamaterials comprising different scales of zigzag strips. This class of patterns combines origami folding techniques with kirigami. Using analytical and numerical models, we study the key mechanical properties of the folded materials. We show that our class of patterns, by expanding on the design space of Miura-ori, is appropriate for a wide range of applications from mechanical metamaterials to deployable structures at small and large scales. We further show that, depending on the geometry, these materials exhibit either negative or positive in-plane Poisson's ratios. By introducing a class of zigzag-base materials in the current study, we unify the concept of in-plane Poisson's ratio for similar materials in the literature and extend it to the class of zigzag-base folded sheet materials.

Effectiveness of zigzag Incision and 1.5-Layer method for frontotemporal craniotomy

PubMed Central

Minami, Noriaki; Kimura, Toshikazu; Kohmura, Eiji

2014-01-01

Background: In this era of minimally invasive treatment, it is important to make operative scars as inconspicuous as possible, and there is a great deal of room for improvement in daily practice. Zigzag incision with coronal incision has been described mainly in the field of plastic surgery, and its applicability for skin incision in general neurosurgery has not been reported. Methods: Zigzag incision with 1.5-layer method was applied to 14 patients with unruptured cerebral aneurysm between April 2011 and August 2012. A questionnaire survey was administered among patients with unruptured aneurysm using SF-36v2 since April 2010. The results were compared between patients with zigzag incision and a previous cohort with traditional incision. Results: There were no cases of complications associated with the operative wound. In the questionnaire survey, all parameters tended to be better in the patients with zigzag incision, and role social component score (RCS) was significantly higher in the zigzag group than in the traditional incision group (P =0.0436). Conclusion: Zigzag incision using the 1.5-layer method with frontotemporal craniotomy seems to represent an improvement over the conventional curvilinear incision with regard to cosmetic outcome and RCS. PMID:24991472

Chemical scissors cut phosphorene and their novel electronic properties

NASA Astrophysics Data System (ADS)

Peng, Xihong; Wei, Qun

2015-03-01

Phosphorene, a recently fabricated two-dimensional puckered honeycomb structure of black phosphorus, showed promising properties for applications in nano-electronics. In this work, we report a chemical scissors effect on phosphorene, using first principles density-functional methods. It was found that chemical species, such as H, OH, F, and Cl, can act as scissors to cut phosphorene. Phosphorus nanochains and nanoribbons can be obtained using such chemical scissors. The scissors effect results from the strong bonding between the chemical species and phosphorus atoms. Other species such as O, S and Se fail to cut phosphorene due to their weak bonding with phosphorus. The electronic structures of the produced P-chains reveal that the hydrogenated P-chain is an insulator; however, the pristine P-chain is a one-dimensional Dirac material, in which the charge carriers are massless fermions travelling at an effective speed of light approximately 8x105 m/s. The obtained zigzag phosphorene nanoribbons show either metallic or semiconducting behaviors, depending on the treatment of the edge phosphorus atoms.

Chemical scissors cut phosphorene nanostructures

NASA Astrophysics Data System (ADS)

Peng, Xihong; Wei, Qun

2014-12-01

Phosphorene, a recently fabricated two-dimensional puckered honeycomb structure of phosphorus, showed promising properties for applications in nano-electronics. In this work, we report a chemical scissors effect on phosphorene, using first-principles method. It was found that chemical species, such as H, OH, F, and Cl, can act as scissors to cut phosphorene. Phosphorus nanochains and nanoribbons can be obtained. The scissors effect results from the strong bonding between the chemical species and phosphorus atoms. Other species such as O, S and Se fail to cut phosphorene nanostructures due to their weak bonding with phosphorus. The electronic structures of the produced P-chains reveal that the hydrogenated chain is an insulator while the pristine chain is a one-dimensional Dirac material, in which the charge carriers are massless fermions travelling at an effective speed of light ˜8 × 105 m s-1. The obtained zigzag phosphorene nanoribbons show either metallic or semiconducting behaviors, depending on the treatment of the edge phosphorus atoms.

Phase stability and large in-plane resistivity anisotropy in the 112-type iron-based superconductor Ca 1 - x La x FeAs 2

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

Kang, Chang-Jong; Birol, Turan; Kotliar, Gabriel

The recently discovered high-T c superconductor Ca 1-xLa xFeAs 2 is a unique compound not just because of its low-symmetry crystal structure but also because of its electronic structure, which hosts Dirac-like metallic bands resulting from (spacer) zigzag As chains. We present a comprehensive first-principles theoretical study of the electronic and crystal structures of Ca 1-xLa xFeAs 2. After discussing the connection between the crystal structure of the 112 family, which Ca 1-xLa xFeAs 2 is a member of, with the other known structures of Fe pnictide superconductors, we check the thermodynamic phase stability of CaFeAs 2, and similar hyphotheticalmore » compounds SrFeAs 2 and BaFeAs 2 which, we find, are slightly higher in energy. We calculate the optical conductivity of Ca 1-xLa xFeAs 2 using the DFT+DMFT method and predict a large in-plane resistivity anisotropy in the normal phase, which does not originate from electronic nematicity, but is enhanced by the electronic correlations. In particular, we predict a 0.34 eV peak in the yy component of the optical conductivity of the 30% La-doped compound, which corresponds to coherent interband transitions within a fast-dispersing band arising from the zigzag As chains, which are unique to this compound. We also study the Landau free energy for Ca 1-xLa xFeAs 2 including the order parameter relevant for the nematic transition and find that the free energy does not have any extra terms that could induce ferro-orbital order. This explains why the presence of As chains does not broaden the nematic transition in Ca 1-xLa xFeAs 2.« less

Phase stability and large in-plane resistivity anisotropy in the 112-type iron-based superconductor Ca 1 - x La x FeAs 2

DOE PAGES

Kang, Chang-Jong; Birol, Turan; Kotliar, Gabriel

2017-01-17

The recently discovered high-T c superconductor Ca 1-xLa xFeAs 2 is a unique compound not just because of its low-symmetry crystal structure but also because of its electronic structure, which hosts Dirac-like metallic bands resulting from (spacer) zigzag As chains. We present a comprehensive first-principles theoretical study of the electronic and crystal structures of Ca 1-xLa xFeAs 2. After discussing the connection between the crystal structure of the 112 family, which Ca 1-xLa xFeAs 2 is a member of, with the other known structures of Fe pnictide superconductors, we check the thermodynamic phase stability of CaFeAs 2, and similar hyphotheticalmore » compounds SrFeAs 2 and BaFeAs 2 which, we find, are slightly higher in energy. We calculate the optical conductivity of Ca 1-xLa xFeAs 2 using the DFT+DMFT method and predict a large in-plane resistivity anisotropy in the normal phase, which does not originate from electronic nematicity, but is enhanced by the electronic correlations. In particular, we predict a 0.34 eV peak in the yy component of the optical conductivity of the 30% La-doped compound, which corresponds to coherent interband transitions within a fast-dispersing band arising from the zigzag As chains, which are unique to this compound. We also study the Landau free energy for Ca 1-xLa xFeAs 2 including the order parameter relevant for the nematic transition and find that the free energy does not have any extra terms that could induce ferro-orbital order. This explains why the presence of As chains does not broaden the nematic transition in Ca 1-xLa xFeAs 2.« less

Refined Zigzag Theory for Homogeneous, Laminated Composite, and Sandwich Plates: A Homogeneous Limit Methodology for Zigzag Function Selection

NASA Technical Reports Server (NTRS)

Tessler, Alexander; DiSciuva, Marco; Gherlone, marco

2010-01-01

The Refined Zigzag Theory (RZT) for homogeneous, laminated composite, and sandwich plates is presented from a multi-scale formalism starting with the inplane displacement field expressed as a superposition of coarse and fine contributions. The coarse kinematic field is that of first-order shear-deformation theory, whereas the fine kinematic field has a piecewise-linear zigzag distribution through the thickness. The condition of limiting homogeneity of transverse-shear properties is proposed and yields four distinct sets of zigzag functions. By examining elastostatic solutions for highly heterogeneous sandwich plates, the best-performing zigzag functions are identified. The RZT predictive capabilities to model homogeneous and highly heterogeneous sandwich plates are critically assessed, demonstrating its superior efficiency, accuracy ; and a wide range of applicability. The present theory, which is derived from the virtual work principle, is well-suited for developing computationally efficient CO-continuous finite elements, and is thus appropriate for the analysis and design of high-performance load-bearing aerospace structures.

Patterns of hydrogen bonding involving thiourea in the series of thioureaṡtrans-1,2-bispyridyl ethylene cocrystals - A comparative study

NASA Astrophysics Data System (ADS)

Kole, Goutam Kumar; Kumar, Mukesh

2018-07-01

Thiourea is known to act as a template to preorganise a series of trans-1,2-bispyridyl ethylenes (bpe), where the thiourea molecules present in an infinite zigzag chain with R22(8) graph set (the β-tape) which offers three different types of hydrogen bonding [J. Am. Chem. Soc. 132 (2010) 13434]. This article reports a new cocrystal of thiourea with 3,4‧-bpe and acts as a 'missing link' in the series. In this cocrystal, thiourea present in an infinite corrugated chain with R21(6) graph set, a rarely observed thiourea synthon i.e. α-tape. A comparative study has been discussed which demonstrates various types of hydrogen bonding that exist in the series and their impact on the parallel stacking of the pyridyl based olefins.

Catalytic behavior of ‘Pt-atomic chain encapsulated gold nanotube’: A density functional study

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

Nigam, Sandeep, E-mail: snigam@barc.gov.in; Majumder, Chiranjib

2016-05-23

With an aim to design novel material and explore its catalytic performance towards CO oxidation, Pt atomic chain was introduced inside gold nanotube (Au-NT). Theoretical calculations at the level of first principles formalism was carried out to investigate the atomic and electronic properties of the composite. Geometrically Pt atoms prefer to align in zig-zag fashion. Significant electronic charge transfer from inside Pt atoms to the outer wall Au atoms is observed. Interaction of O{sub 2} with Au-NT wall follows by injection of additional electronic charge in the anti-bonding orbital of oxygen molecule leading to activation of the O-O bond. Furthermore » interaction of CO molecule with the activated oxygen molecule leads to spontaneous oxidation reaction and formation of CO{sub 2}.« less

Ethyl 2-[(carbamoyl­amino)­imino]­propano­ate hemihydrate

PubMed Central

Corrêa, Charlane C.; Graúdo, José Eugênio J. C.; de Oliveira, Luiz Fernando C.; de Almeida, Mauro V.; Diniz, Renata

2011-01-01

The title compound, C6H11N3O3·0.5H2O, has two independent mol­ecules and one mol­ecule of water in the asymmetric unit. The crystal packing is stabilized by inter­molecular N—H⋯N, O—H⋯O, N—H⋯O and C—H⋯O hydrogen bonds. These inter­actions form a two-dimensional array in the ab plane with a zigzag motif which has an angle close to 35° between the zigzag planes. The hydrogen bonding can be best described using the graph-set notation as N 1 = C(10)R 2 2(10)R 2 2(8) and N 2 = R 6 4(20)R 2 2(8). PMID:22090934

Frustrated quantum magnetism in the Kondo lattice on the zigzag ladder

NASA Astrophysics Data System (ADS)

Peschke, Matthias; Rausch, Roman; Potthoff, Michael

2018-03-01

The interplay between the Kondo effect, indirect magnetic interaction, and geometrical frustration is studied in the Kondo lattice on the one-dimensional zigzag ladder. Using the density-matrix renormalization group, the ground-state and various short- and long-range spin- and density-correlation functions are calculated for the model at half filling as a function of the antiferromagnetic Kondo interaction down to J =0.3 t , where t is the nearest-neighbor hopping on the zigzag ladder. Geometrical frustration is shown to lead to at least two critical points: Starting from the strong-J limit, where almost local Kondo screening dominates and where the system is a nonmagnetic Kondo insulator, antiferromagnetic correlations between nearest-neighbor and next-nearest-neighbor local spins become stronger and stronger, until at Jcdim≈0.89 t frustration is alleviated by a spontaneous breaking of translational symmetry and a corresponding transition to a dimerized state. This is characterized by antiferromagnetic correlations along the legs and by alternating antiferro- and ferromagnetic correlations on the rungs of the ladder. A mechanism of partial Kondo screening that has been suggested for the Kondo lattice on the two-dimensional triangular lattice is not realized in the one-dimensional case. Furthermore, within the symmetry-broken dimerized state, there is a magnetic transition to a 90∘ quantum spin spiral with quasi-long-range order at Jcmag≈0.84 t . The quantum-critical point is characterized by a closure of the spin gap (with decreasing J ) and a divergence of the spin-correlation length and of the spin-structure factor S (q ) at wave vector q =π /2 . This is opposed to the model on the one-dimensional bipartite chain, which is known to have a finite spin gap for all J >0 at half filling.

Drawing dependent structures, mechanical properties and cyclization behaviors of polyacrylonitrile and polyacrylonitrile/carbon nanotube composite fibers prepared by plasticized spinning.

PubMed

Li, Xiang; Qin, Aiwen; Zhao, Xinzhen; Liu, Dapeng; Wang, Haiye; He, Chunju

2015-09-14

Drawing to change the structural properties and cyclization behaviors of the polyacrylonitrile (PAN) chains in crystalline and amorphous regions is carried out on PAN and PAN/carbon nanotube (CNT) composite fibers. Various characterization methods including Fourier transform infrared spectroscopy, differential scanning calorimetry, X-ray diffraction and thermal gravimetric analysis are used to monitor the structural evolution and cyclization behaviors of the fibers. With an increase of the draw ratio during the plasticized spinning process, the structural parameters of the fibers, i.e. crystallinity and planar zigzag conformation, are decreased at first, and then increased, which are associated with the heat exchange rate and the oriented-crystallization rate. A possible mechanism for plasticized spinning is proposed to explain the changing trends of crystallinity and planar zigzag conformation. PAN and PAN/CNT fibers exhibit various cyclization behaviors induced by drawing, e.g., the initiation temperature for the cyclization (Ti) of PAN fibers is increased with increasing draw ratio, while Ti of PAN/CNT fibers is decreased. Drawing also facilitates cyclization and lowers the percentage of β-amino nitrile for PAN/CNT fibers during the stabilization.

Adiabatic quantum pump in a zigzag graphene nanoribbon junction

NASA Astrophysics Data System (ADS)

Zhang, Lin

2015-11-01

The adiabatic electron transport is theoretically studied in a zigzag graphene nanoribbon (ZGNR) junction with two time-dependent pumping electric fields. By modeling a ZGNR p-n junction and applying the Keldysh Green’s function method, we find that a pumped charge current is flowing in the device at a zero external bias, which mainly comes from the photon-assisted tunneling process and the valley selection rule in an even-chain ZGNR junction. The pumped charge current and its ON and OFF states can be efficiently modulated by changing the system parameters such as the pumping frequency, the pumping phase difference, and the Fermi level. A ferromagnetic ZGNR device is also studied to generate a pure spin current and a fully polarized spin current due to the combined spin pump effect and the valley valve effect. Our finding might pave the way to manipulate the degree of freedom of electrons in a graphene-based electronic device. Project supported by the National Natural Science Foundation of China (Grant No. 110704033), the Natural Science Foundation of Jiangsu Province, China (Grant No. BK2010416), and the Natural Science Foundation for Colleges and Universities in Jiangsu Province, China (Grant No. 13KJB140005).

Giant rectification in graphene nanoflake molecular devices with asymmetric graphene nanoribbon electrodes

NASA Astrophysics Data System (ADS)

Ji, Xiao-Li; Xie, Zhen; Zuo, Xi; Zhang, Guang-Ping; Li, Zong-Liang; Wang, Chuan-Kui

2016-09-01

By applying density functional theory based nonequilibrium Green's function method, we theoretically investigate the electron transport properties of a zigzag-edged trigonal graphene nanoflake (ZTGNF) sandwiched between two asymmetric zigzag graphene nanoribbon (zGNR) and armchair graphene nanoribbon (aGNR) electrodes with carbon atomic chains (CACs) as the anchoring groups. Significant rectifying effects have been observed for these molecular devices in low bias voltage regions. Interestingly, the rectifying performance of molecular devices can be optimized by changing the width of the aGNR electrode and the number of anchoring CACs. Especially, the molecular device displays giant rectification ratios up to the order of 104 when two CACs are used as the anchoring group between the ZTGNF and the right aGNR electrode. Further analysis indicates that the asymmetric shift of the perturbed molecular energy levels and the spatial parity of the electron wavefunctions in the electrodes around the Fermi level play key roles in determining the rectification performance. And the spatial distributions of tunneling electron wavefunctions under negative bias voltages can be modified to be very localized by changing the number of anchoring CACs, which is found to be the origin of the giant rectification ratios.

Coupling of Armchair and Zigzag Tubes to a Free Electron Metal

NASA Technical Reports Server (NTRS)

Anantram, M. P.; Biegel, Bryan (Technical Monitor)

2001-01-01

The effect of nanotube chirality is of prime importance in determining its electronic properties. We address the issue of how chirality affects the coupling of a nanotube to metal contacts. We model coupling of armchair and zigzag nanotubes to metal contacts, in both the side- and end-contacted geometries. In the side-contacted geometry, the coupling of armchair and metallic-zigzag nanotubes to a free electron metal are significantly different. Namely, it is possible to drive a larger current through a metallic-zigzag nanotube. The predicted difference holds good when both (a) the entire circumference and (b) only a finite sector of the nanotube makes contact to the metal electrode. It might be possible to observe the predicted difference between armchair and zigzag nanotubes using gold contacts.

Multiple pathways in pressure-induced phase transition of coesite

NASA Astrophysics Data System (ADS)

Liu, Wei; Wu, Xuebang; Liang, Yunfeng; Liu, Changsong; Miranda, Caetano R.; Scandolo, Sandro

2017-12-01

High-pressure single-crystal X-ray diffraction method with precise control of hydrostatic conditions, typically with helium or neon as the pressure-transmitting medium, has significantly changed our view on what happens with low-density silica phases under pressure. Coesite is a prototype material for pressure-induced amorphization. However, it was found to transform into a high-pressure octahedral (HPO) phase, or coesite-II and coesite-III. Given that the pressure is believed to be hydrostatic in two recent experiments, the different transformation pathways are striking. Based on molecular dynamic simulations with an ab initio parameterized potential, we reproduced all of the above experiments in three transformation pathways, including the one leading to an HPO phase. This octahedral phase has an oxygen hcp sublattice featuring 2 × 2 zigzag octahedral edge-sharing chains, however with some broken points (i.e., point defects). It transforms into α-PbO2 phase when it is relaxed under further compression. We show that the HPO phase forms through a continuous rearrangement of the oxygen sublattice toward hcp arrangement. The high-pressure amorphous phases can be described by an fcc and hcp sublattice mixture.

Syntheses, structures and properties of four 3D microporous lanthanide coordination polymers based on 3,5-pyrazoledicarboxylate and oxalate ligands

NASA Astrophysics Data System (ADS)

Song, Juan; Wang, Ji-Jiang; Hu, Huai-Ming; Wu, Qing-Ran; Xie, Juan; Dong, Fa-Xin; Yang, Meng-Lin; Xue, Gang-Lin

2014-04-01

Four three-dimensional lanthanide coordination polymers with reversible structural interconversions, [Ln2(Hpdc)2(C2O4)(H2O)4]n·2nH2O [Ln=Sm (1), Eu (2), Tb (3) and Dy (4)], have been synthesized by hydrothermal reactions of lanthanide nitrates with 3,5-pyrazoledicarboxylic (H3pdc) and oxalic acids. It is noteworthy that there is an in situ reaction in 1, in which H3pdc was decomposed into (ox)2- with Cu(II)-Sm(III) synergistic effect under hydrothermal conditions. These compounds are isostructural and crystallized in the monoclinic P21/c space group. The Ln(III) ions are eight-coordinated with dodecahedron coordination geometry. These polyhedra are linked by oxalate groups to form 1D zigzag chain, which are further connected by 3,5-pyrazoledicarboxylate to extend similar 3D frameworks with channels along c-axis in 1-4. These coordination polymers display the characteristic emission bands of the Ln(III) ions in the solid state and possess good thermal stabilities.

Nonequilibrium quantum thermodynamics in Coulomb crystals

NASA Astrophysics Data System (ADS)

Cosco, F.; Borrelli, M.; Silvi, P.; Maniscalco, S.; De Chiara, G.

2017-06-01

We present an in-depth study of the nonequilibrium statistics of the irreversible work produced during sudden quenches in proximity to the structural linear-zigzag transition of ion Coulomb crystals in 1+1 dimensions. By employing both an analytical approach based on a harmonic expansion and numerical simulations, we show the divergence of the average irreversible work in proximity to the transition. We show that the nonanalytic behavior of the work fluctuations can be characterized in terms of the critical exponents of the quantum Ising chain. Due to the technological advancements in trapped-ion experiments, our results can be readily verified.

The increase in conductance of a gold single atom chain during elastic elongation

NASA Astrophysics Data System (ADS)

Tavazza, F.; Barzilai, S.; Smith, D. T.; Levine, L. E.

2013-02-01

The conductance of monoatomic gold wires has been studied using ab initio calculations and the transmission was found to vary with the elastic strain. Counter-intuitively, the conductance was found to increase for the initial stages of the elongation, where the structure has a zigzag shape and the bond angles increase from ≈140° toward ≈160°. After a certain elongation limit, where the angles are relatively high, the bond length elongation associated with a Peierls distortion reverses this trend and the conductance decreases. These simulations are in good agreement with previously unexplained experimental results.

Mesoscale Modeling of Chromatin Folding

NASA Astrophysics Data System (ADS)

Schlick, Tamar

2009-03-01

Eukaryotic chromatin is the fundamental protein/nucleic acid unit that stores the genetic material. Understanding how chromatin fibers fold and unfold in physiological conditions is important for interpreting fundamental biological processes like DNA replication and transcription regulation. Using a mesoscopic model of oligonucleosome chains and tailored sampling protocols, we elucidate the energetics of oligonucleosome folding/unfolding and the role of each histone tail, linker histones, and divalent ions in regulating chromatin structure. The resulting compact topologies reconcile features of the zigzag model with straight linker DNAs with the solenoid model with bent linker DNAs for optimal fiber organization and reveal dynamic and energetic aspects involved.

A GEM readout with radial zigzag strips and linear charge-sharing response

DOE PAGES

Zhang, Aiwu; Hohlmann, Marcus; Azmoun, Babak; ...

2018-01-10

Here, we study the position sensitivity of radial zigzag strips intended to read out large GEM detectors for tracking at future experiments. Zigzag strips can cover a readout area with fewer strips than regular straight strips while maintaining good spatial resolution. Consequently, they can reduce the number of required electronic channels and related cost for large-area GEM detector systems. A non-linear relation between incident particle position and hit position measured from charge sharing among zigzag strips was observed in a previous study. We significantly reduce this non-linearity by improving the interleaving of adjacent physical zigzag strips. Zigzag readout structures aremore » implemented on PCBs and on a flexible foil and are tested using a 10 cm × 10 cm triple-GEM detector scanned with a strongly collimated X-ray gun on a 2D motorized stage. Lastly, angular resolutions of 60–84 μrad are achieved with a 1.37 mrad angular strip pitch at a radius of 784 mm. On a linear scale this corresponds to resolutions below 100 μm.« less

A GEM readout with radial zigzag strips and linear charge-sharing response

NASA Astrophysics Data System (ADS)

Zhang, Aiwu; Hohlmann, Marcus; Azmoun, Babak; Purschke, Martin L.; Woody, Craig

2018-04-01

We study the position sensitivity of radial zigzag strips intended to read out large GEM detectors for tracking at future experiments. Zigzag strips can cover a readout area with fewer strips than regular straight strips while maintaining good spatial resolution. Consequently, they can reduce the number of required electronic channels and related cost for large-area GEM detector systems. A non-linear relation between incident particle position and hit position measured from charge sharing among zigzag strips was observed in a previous study. We significantly reduce this non-linearity by improving the interleaving of adjacent physical zigzag strips. Zigzag readout structures are implemented on PCBs and on a flexible foil and are tested using a 10 cm × 10 cm triple-GEM detector scanned with a strongly collimated X-ray gun on a 2D motorized stage. Angular resolutions of 60-84 μrad are achieved with a 1.37 mrad angular strip pitch at a radius of 784 mm. On a linear scale this corresponds to resolutions below 100 μm.

A new model for the surface arrangement of myosin molecules in tarantula thick filaments.

PubMed

Offer, G; Knight, P J; Burgess, S A; Alamo, L; Padrón, R

2000-04-28

Three-dimensional reconstructions of the negatively stained thick filaments of tarantula muscle with a resolution of 50 A have previously suggested that the helical tracks of myosin heads are zigzagged, short diagonal ridges being connected by nearly axial links. However, surface views of lower contour levels reveal an additional J-shaped feature approximately the size and shape of a myosin head. We have modelled the surface array of myosin heads on the filaments using as a building block a model of a two-headed regulated myosin molecule in which the regulatory light chains of the two heads together form a compact head-tail junction. Four parameters defining the radius, orientation and rotation of each myosin molecule were varied. In addition, the heads were allowed independently to bend in a plane perpendicular to the coiled-coil tail at three sites, and to tilt with respect to the tail and to twist at one of these sites. After low-pass filtering, models were aligned with the reconstruction, scored by cross-correlation and refined by simulated annealing. Comparison of the geometry of the reconstruction and the distance between domains in the myosin molecule narrowed the choice of models to two main classes. A good match to the reconstruction was obtained with a model in which each ridge is formed from the motor domain of a head pointing to the bare zone together with the head-tail junction of a neighbouring molecule. The heads pointing to the Z-disc intermittently occupy the J-position. Each motor domain interacts with the essential and regulatory light chains of the neighbouring heads. A near-radial spoke in the reconstruction connecting the backbone to one end of the ridge can be identified as the start of the coiled-coil tail. Copyright 2000 Academic Press.

Patterning monolayer graphene with zigzag edges on hexagonal boron nitride by anisotropic etching

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

Wang, Guole; Wu, Shuang; Zhang, Tingting

2016-08-01

Graphene nanostructures are potential building blocks for nanoelectronic and spintronic devices. However, the production of monolayer graphene nanostructures with well-defined zigzag edges remains a challenge. In this paper, we report the patterning of monolayer graphene nanostructures with zigzag edges on hexagonal boron nitride (h-BN) substrates by an anisotropic etching technique. We found that hydrogen plasma etching of monolayer graphene on h-BN is highly anisotropic due to the inert and ultra-flat nature of the h-BN surface, resulting in zigzag edge formation. The as-fabricated zigzag-edged monolayer graphene nanoribbons (Z-GNRs) with widths below 30 nm show high carrier mobility and width-dependent energy gaps atmore » liquid helium temperature. These high quality Z-GNRs are thus ideal structures for exploring their valleytronic or spintronic properties.« less

Bridging the gap between atomic microstructure and electronic properties of alloys: The case of (In,Ga)N

NASA Astrophysics Data System (ADS)

Chan, J. A.; Liu, J. Z.; Zunger, Alex

2010-07-01

The atomic microstructure of alloys is rarely perfectly random, instead exhibiting differently shaped precipitates, clusters, zigzag chains, etc. While it is expected that such microstructural features will affect the electronic structures (carrier localization and band gaps), theoretical studies have, until now, been restricted to investigate either perfectly random or artificial “guessed” microstructural features. In this paper, we simulate the alloy microstructures in thermodynamic equilibrium using the static Monte Carlo method and study their electronic structures explicitly using a pseudopotential supercell approach. In this way, we can bridge atomic microstructures with their electronic properties. We derive the atomic microstructures of InGaN using (i) density-functional theory total energies of ˜50 ordered structures to construct a (ii) multibody cluster expansion, including strain effects to which we have applied (iii) static Monte Carlo simulations of systems consisting of over 27000 atoms to determine the equilibrium atomic microstructures. We study two types of alloy thermodynamic behavior: (a) under lattice incoherent conditions, the formation enthalpies are positive and thus the alloy system phase-separates below the miscibility-gap temperature TMG , (b) under lattice coherent conditions, the formation enthalpies can be negative and thus the alloy system exhibits ordering tendency. The microstructure is analyzed in terms of structural motifs (e.g., zigzag chains and InnGa4-nN tetrahedral clusters). The corresponding electronic structure, calculated with the empirical pseudopotentials method, is analyzed in terms of band-edge energies and wave-function localization. We find that the disordered alloys have no electronic localization but significant hole localization, while below the miscibility gap under the incoherent conditions, In-rich precipitates lead to strong electron and hole localization and a reduction in the band gap.

Immobilization of paracetamol and benzocaine pro-drug derivatives as long-range self-organized monolayers on graphite.

PubMed

Popoff, Alexandre; Fichou, Denis

2008-05-01

We show here by means of scanning tunneling microscopy (STM) at the liquid/solid interface that paracetamol and benzocaine molecules bearing a long aliphatic chain can be immobilized on highly oriented pyrolitic graphite (HOPG) as perfectly ordered two-dimensional domains extending over several hundreds of nanometers. In both cases, high-resolution STM images reveal that compounds 1 and 2 self-assemble into parallel lamellae having a head-to-head arrangement. The paracetamol heads of 1 are in a zigzag position with entangled n-dodecyloxy side chains while benzocaine heads of compound 2 are perfectly aligned as a double row and have their palmitic side chains on either sides of the head alignment. We attribute the very long-range ordering of these two pro-drug derivatives on HOPG to the combined effects of intermolecular H-bonding on one side and Van der Waals interactions between aliphatic side chains and graphite on the other side. The 2D immobilization of pro-drug derivatives via a non-destructive physisorption mechanism could prove to be useful for applications such as drug delivery if it can be realized on a biocompatible substrate.

Structure and thermodynamic properties of (C5H12N)CuBr3: a new weakly coupled antiferromagnetic spin-1/2 chain complex lying in the 1D-3D dimensional cross-over regime.

PubMed

Pan, Bingying; Wang, Yang; Zhang, Lijuan; Li, Shiyan

2014-04-07

Single crystals of a metal organic complex (C5H12N)CuBr3 (C5H12N = piperidinium, pipH for short) have been synthesized, and the structure was determined by single-crystal X-ray diffraction. (pipH)CuBr3 crystallizes in the monoclinic group C2/c. Edging-sharing CuBr5 units link to form zigzag chains along the c axis, and the neighboring Cu(II) ions with spin-1/2 are bridged by bibromide ions. Magnetic susceptibility data down to 1.8 K can be well fitted by the Bonner-Fisher formula for the antiferromagnetic spin-1/2 chain, giving the intrachain magnetic coupling constant J ≈ -17 K. At zero field, (pipH)CuBr3 shows three-dimensional (3D) order below TN = 1.68 K. Calculated by the mean-field theory, the interchain coupling constant J' = -0.91 K is obtained and the ordered magnetic moment m0 is about 0.23 μB. This value of m0 makes (pipH)CuBr3 a rare compound suitable to study the 1D-3D dimensional cross-over problem in magnetism, since both 3D order and one-dimensional (1D) quantum fluctuations are prominent. In addition, specific heat measurements reveal two successive magnetic transitions with lowering temperature when external field μ0H ≥ 3 T is applied along the a' axis. The μ0H-T phase diagram of (pipH)CuBr3 is roughly constructed.

Assembly and property research on seven 0D-3D complexes derived from imidazole dicarboxylate and 1,2-bi(pyridin-4-yl)ethene

NASA Astrophysics Data System (ADS)

Mu, Bao; Li, Qian; Lv, Lei; Yang, Dan-Dan; Wang, Qing; Huang, Ru-Dan

2015-03-01

The hydrothermal reaction of transition metals, 1H-imidazole-4,5-dicarboxylic acid (H3ImDC) and 1,2-bi(pyridin-4-yl)ethene (bpe) affords a series of new complexes, namely, [Mn(HImDC)(bpe)(H2O)] (1), [M(H2ImDC)2(H2O)2]·(bpe) (M=Fe(2), Co(3), Zn(4), Cd(6)), [Zn3(ImDC)2(bpe)(H2O)]·3H2O (5) and [Cd(H2ImDC)(bpe)] (7), which are characterized by elemental analyses, IR, TG, XRPD and single crystal X-ray diffraction. Complex 1 exhibits a one dimensional (1D) zigzag chain with two types of irregular rings, and the 1D chains are linked to form a three dimensional (3D) supramolecular framework by the hydrogen bonding interactions (O-H•••O and O-H•••N). Complexes 2-4 and 6 are isomorphous, and they display the mononuclear structures. In these complexes, the O-H•••O and O-H•••N hydrogen bonds play an important role in sustaining the whole 3D supramolecular frameworks. Complex 5 shows a (3,3)-connected 3D framework with (103) topology, and the lattice water molecules as guest molecules exist in the 3D framework. Complex 7 is a wave-like two dimensional (2D) structure, in which the adjacent 1D chains point at the opposite directions. Moreover, the fluorescent properties of complexes 1-7 and the magnetic property of 1 have been investigated. The water vapor adsorption for complex 5 has been researched at 298 K.

Crystal structure of 2-meth-oxy-2-[(4-meth-oxy-phen-yl)sulfan-yl]-1-phenyl-ethanone.

PubMed

Caracelli, Ignez; Olivato, Paulo R; Traesel, Henrique J; Valença, Jéssica; Rodrigues, Daniel N S; Tiekink, Edward R T

2015-09-01

In the title β-thio-carbonyl compound, C16H16O3S, the adjacent meth-oxy and carbonyl O atoms are synperiplanar [the O-C-C-O torsion angle is 19.8 (4)°] and are separated by 2.582 (3) Å. The dihedral angle between the rings is 40.11 (16)°, and the meth-oxy group is coplanar with the benzene ring to which it is connected [the C-C-O-C torsion angle is 179.1 (3)°]. The most notable feature of the crystal packing is the formation of methine and methyl C-H⋯O(carbon-yl) inter-actions that lead to a supra-molecular chain with a zigzag topology along the c axis. Chains pack with no specific inter-molecular inter-actions between them.

Spin-filtering and giant magnetoresistance effects in polyacetylene-based molecular devices

NASA Astrophysics Data System (ADS)

Chen, Tong; Yan, Shenlang; Xu, Liang; Liu, Desheng; Li, Quan; Wang, Lingling; Long, Mengqiu

2017-07-01

Using the non-equilibrium Green's function formalism in combination with density functional theory, we performed ab initio calculations of spin-dependent electron transport in molecular devices consisting of a polyacetylene (CnHn+1) chain vertically attached to a carbon chain sandwiched between two semi-infinite zigzag-edged graphene nanoribbon electrodes. Spin-charge transport in the device could be modulated to different magnetic configurations by an external magnetic field. The results showed that single spin conduction could be obtained. Specifically, the proposed CnHn+1 devices exhibited several interesting effects, including (dual) spin filtering, spin negative differential resistance, odd-even oscillation, and magnetoresistance (MR). Marked spin polarization with a filtering efficiency of up to 100% over a large bias range was found, and the highest MR ratio for the CnHn+1 junctions reached 4.6 × 104. In addition, the physical mechanisms for these phenomena were also revealed.

Magnetotransport Properties of Graphene Nanoribbons with Zigzag Edges

NASA Astrophysics Data System (ADS)

Wu, Shuang; Liu, Bing; Shen, Cheng; Li, Si; Huang, Xiaochun; Lu, Xiaobo; Chen, Peng; Wang, Guole; Wang, Duoming; Liao, Mengzhou; Zhang, Jing; Zhang, Tingting; Wang, Shuopei; Yang, Wei; Yang, Rong; Shi, Dongxia; Watanabe, Kenji; Taniguchi, Takashi; Yao, Yugui; Wang, Weihua; Zhang, Guangyu

2018-05-01

The determination of the electronic structure by edge geometry is unique to graphene. In theory, an evanescent nonchiral edge state is predicted at the zigzag edges of graphene. Up to now, the approach used to study zigzag-edged graphene has mostly been limited to scanning tunneling microscopy. The transport properties have not been revealed. Recent advances in hydrogen plasma-assisted "top-down" fabrication of zigzag-edged graphene nanoribbons (Z-GNRs) have allowed us to investigate edge-related transport properties. In this Letter, we report the magnetotransport properties of Z-GNRs down to ˜70 nm wide on an h -BN substrate. In the quantum Hall effect regime, a prominent conductance peak is observed at Landau ν =0 , which is absent in GNRs with nonzigzag edges. The conductance peak persists under perpendicular magnetic fields and low temperatures. At a zero magnetic field, a nonlocal voltage signal, evidenced by edge conduction, is detected. These prominent transport features are closely related to the observable density of states at the hydrogen-etched zigzag edge of graphene probed by scanning tunneling spectroscopy, which qualitatively matches the theoretically predicted electronic structure for zigzag-edged graphene. Our study gives important insights for the design of new edge-related electronic devices.

Stability, diffusion and interactions of nonlinear excitations in a many body system

NASA Astrophysics Data System (ADS)

Coste, Christophe; Jean, Michel Saint; Dessup, Tommy

2017-04-01

When repelling particles are confined in a quasi-one-dimensional trap by a transverse potential, a configurational phase transition happens. All particles are aligned along the trap axis at large confinement, but below a critical transverse confinement they adopt a staggered row configuration (zigzag phase). This zigzag transition is a subcritical pitchfork bifurcation in extended systems and in systems with cyclic boundary conditions in the longitudinal direction. Among many evidences, phase coexistence is exhibited by localized nonlinear patterns made of a zigzag phase embedded in otherwise aligned particles. We give the normal form at the bifurcation and we show that these patterns can be described as solitary wave envelopes that we call bubbles. They are stable in a large temperature range and can diffuse as quasi-particles, with a diffusion coefficient that may be deduced from the normal form. The potential energy of a bubble is found to be lower than that of the homogeneous bifurcated phase, which explains their stability. We observe also metastable states, that are pairs of solitary wave envelopes which spontaneously evolve toward a stable single bubble. We evidence a strong effect of the discreteness of the underlying particles system and introduce the concept of topological frustration of a bubble pair. A configuration is frustrated when the particles between the two bubbles are not organized in a modulated staggered row. For a nonfrustrated (NF) bubble pair configuration, the bubbles interaction is attractive so that the bubbles come closer and eventually merge as a single bubble. In contrast, the bubbles interaction is found to be repulsive for a frustrated (F) configuration. We describe a model of interacting solitary wave that provides all qualitative characteristics of the interaction force: it is attractive for NF-systems, repulsive for F-systems, and decreases exponentially with the bubbles distance.

Synthesis, characterization and crystal structure of a 1D thiocyanato bridged [Cu(en)2Zn(NCS)4]ṡH2O. Comparison of the three structures with the same [Cu(en)2Zn(NCS)4] unit - different in structural terms

NASA Astrophysics Data System (ADS)

Wrzeszcz, Grzegorz; Muzioł, Tadeusz M.; Tereba, Natalia

2015-03-01

In this paper we report the synthesis method and the structure of a one-dimensional thiocyanato bridged heterometallic compound, [Cu(en)2Zn(NCS)4]ṡH2O (1). Moreover, we compare the structure of (1) with the previously described structures of [Cu(en)2Zn(NCS)4]ṡ0.5H2O (2) and [Cu(en)2Zn(NCS)4]ṡCH3CN (3) Pryma et al. (2003) [7]. The compound (1) has been characterized by thermal decomposition, IR, Vis and EPR spectra, and magnetic studies. Structure has been determined by X-ray analysis. Described coordination polymer crystallizes in the orthorhombic Cmcm space group with a = 12.414(2), b = 10.3276(14), c = 14.967(2) Å, α = β = γ = 90°, V = 1918.8(5) Å3 and Z = 4. Each distorted tetrahedral zinc(II) centre (with N-bonded NCS-) links two tetragonally distorted octahedral copper(II) centres by two end-to-end thiocyanato bridges and vice versa forming a zigzag type of CuZn chain. The structures of (1), (2) and (3) differ in crystallographic system, space group and/or CuZn chain type as well as in details. Variable temperature magnetic susceptibility measurements show very weak antiferromagnetic interactions between the paramagnetic copper(II) ions for compound (1).

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

Yin, Fei; Chen, Jing; Liang, Yongfeng

Two coordination polymers [Co(dnbab){sub 2}(bimb)](H{sub 2}O){sub 4} (1) and [Zn(dnbab){sub 2}(bimb)](H{sub 2}O){sub 5} (2) (Hdnbab=4-[(3,5-dinitrobenzoyl)amino]benzoic acid, bimb=1,4-bis(1-imidazolyl) benzene) have been solvothermally synthesized. Their structures have been determined by single-crystal X-ray diffraction analyses and further characterized by powder X-ray diffraction (PXRD) and thermogravimetric (TG) analyses. Complexes 1 and 2 are isostructures and each displays an one-dimensional (1D) zigzag chain, which further forms a 3D supramolecular architecture with 1-D channels via inter-chain π–π interactions and hydrogen bonds. Moreover, the magnetic properties of 1 and fluorescent properties of 2 have been investigated. - Graphical abstract: Two coordination supramolecular frameworks [Co(dnbab){sub 2}(bimb)](H{sub 2}O){sub 4}(1)more » and [Zn(dnbab){sub 2}(bimb)](H{sub 2}O){sub 5}(2) (Hdnbab=4-[(3,5-dinitrobenzoyl)amino]benzoic acid, bimb=1,4-bis(1-imidazolyl) benzene) have been synthesized and characterized by X-ray single-crystal diffraction. Their thermal, magnetic and fluorescent properties have also been studied. - Highlights: • Two isomorphic Co(II)/Zn(II) complexes with the mixed-ligands have been synthesized. • Hydrogen bonds and π–π stacking interactions directed the final 3-D architecture assembly. • Both Co(II) and Zn(II) complexes show good thermal stability. • Co complex exhibits antiferromagnetic interaction. • The fluorescent property of Zn(II) complex has been investigated in the solid state.« less

Lanthanide-based coordination polymers assembled by a flexible multidentate linker: design, structure, photophysical properties, and dynamic solid-state behavior.

PubMed

Marchal, Claire; Filinchuk, Yaroslav; Chen, Xiao-Yan; Imbert, Daniel; Mazzanti, Marinella

2009-01-01

Four picolinate building blocks were implemented into the multidentate linker N,N',N'-tetrakis[(6-carboxypyridin-2-yl)methyl]butylenediamine (H(4)tpabn) with a linear flexible spacer to promote the assembly of lanthanide-based 1D coordination polymers. The role of the linker in directing the geometry of the final assembly is evidenced by the different results obtained in the presence of Htpabn(3-) and tpabn(4-) ions. The tpabn(4-) ion leads to the desired 1D polymer {[Nd(tpabn)]H(3)O x 6 H(2)O}(infinity) (12). The Htpabn(3-) ion leads to the assembly of Tb(III) and Er(III) ions into 1D zigzag chains of the general formula {[M(Htpabn)] x xH(2)O}(infinity) (M = Tb, x = 14 (1); M = Tb, x = 8 (11); M = Er, x = 14 (2); M = Er, x = 5.5 (4)), a 2D network is formed by the Eu(III) ion (i.e., {[Eu(Htpabn)] x 10 H(2)O}(infinity) (7)), and both supramolecular isomers (1D and 2D) are obtained by the Tb(III) ion. The high flexibility of the polymeric chains results in a dynamic behavior with a solvent-induced reversible structural transition. The Tb(III)- and Eu(III)-containing polymers display high-luminescence quantum yields (38 and 18%, respectively). A sizeable near-IR luminescence emission is observed for the Er(III)- and Nd(III)-containing polymers when lattice water molecules are removed.

Study on zigzag maneuver characteristics of V-U very large crude oil (VLCC) tankers

NASA Astrophysics Data System (ADS)

Jaswar, Maimun, A.; Wahid, M. A.; Priyanto, A.; Zamani, Pauzi, Saman

2012-06-01

The Department of Marine Technology at the Faculty of Mechanical Engineering, University Teknologi Malaysia has recently developed an Ship Maneuverability tool which intends to upgrade student's level understanding the application of fluid dynamic on interaction between hull, propeller, and rudder during maneuvering. This paper discusses zigzag maneuver for conventional Very Large Crude Oil (VLCC) ships with the same principal dimensions but different stern flame shape. 10/10 zigzag maneuver characteristics of U and V types of VLCC ships are investigated. Simulation results for U-type show a good agreement with the experimental data, but V-type not good agreement with experimental one. Further study on zigzag maneuver characteristics are required.

Catalyst-free growth of Al-doped SnO2 zigzag-nanobelts for low ppm detection of organic vapours

NASA Astrophysics Data System (ADS)

Sinha, Sudip Kumar; Ghosh, Saptarshi

2016-10-01

In this effort, we report on development of specific sensors dedicated for detection of two of these volatiles, namely ethanol and acetone, below the prescribed statutory limits. Single crystalline Al-doped SnO2 zigzag nanobelt structures were deposited on Si substrate by a catalyst-free thermal evaporation method. The Al-doped SnO2 zigzag nanostructures exhibit high sensitivity and repeatability together with coveted features like fast response and excellent stability. Structural attributes involving the crystal quality and morphology of Al-doped SnO2 zigzag nanobelts were analyzed using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy and transmission electron microscopy. The microscopic images revealed formation of randomly oriented 'zigzag-like' nanobelts with characteristic width between 60 nm and 200 nm and length of 50-300 μm. The Al-doping was observed to have a discerning effect in enhancing the sensitivity in comparison to the pristine nanowires by creating excess oxygen vacancies in the crystal lattice, confirmed through XPS and PL spectra.

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

Zhang, Aiwu; Hohlmann, Marcus; Azmoun, Babak

Here, we study the position sensitivity of radial zigzag strips intended to read out large GEM detectors for tracking at future experiments. Zigzag strips can cover a readout area with fewer strips than regular straight strips while maintaining good spatial resolution. Consequently, they can reduce the number of required electronic channels and related cost for large-area GEM detector systems. A non-linear relation between incident particle position and hit position measured from charge sharing among zigzag strips was observed in a previous study. We significantly reduce this non-linearity by improving the interleaving of adjacent physical zigzag strips. Zigzag readout structures aremore » implemented on PCBs and on a flexible foil and are tested using a 10 cm × 10 cm triple-GEM detector scanned with a strongly collimated X-ray gun on a 2D motorized stage. Lastly, angular resolutions of 60–84 μrad are achieved with a 1.37 mrad angular strip pitch at a radius of 784 mm. On a linear scale this corresponds to resolutions below 100 μm.« less

Structural study of gold clusters.

PubMed

Xiao, Li; Tollberg, Bethany; Hu, Xiankui; Wang, Lichang

2006-03-21

Density functional theory (DFT) calculations were carried out to study gold clusters of up to 55 atoms. Between the linear and zigzag monoatomic Au nanowires, the zigzag nanowires were found to be more stable. Furthermore, the linear Au nanowires of up to 2 nm are formed by slightly stretched Au dimers. These suggest that a substantial Peierls distortion exists in those structures. Planar geometries of Au clusters were found to be the global minima till the cluster size of 13. A quantitative correlation is provided between various properties of Au clusters and the structure and size. The relative stability of selected clusters was also estimated by the Sutton-Chen potential, and the result disagrees with that obtained from the DFT calculations. This suggests that a modification of the Sutton-Chen potential has to be made, such as obtaining new parameters, in order to use it to search the global minima for bigger Au clusters.

Structural and Electronic Properties of α2-Graphyne Nanotubes: A Density Functional Theory Study

NASA Astrophysics Data System (ADS)

Majidi, Roya

2018-02-01

Another form of carbon-based two-dimensional material in the graphene family, named the α2-graphyne sheet, was predicted very recently. The α2-graphyne sheet was created by doubling each acetylenic linker in an α-graphyne sheet. It exhibited semimetallic Dirac point features similar to graphene and α-graphyne sheets. In the present work, single -walled carbon nanotubes based on an α2-graphyne sheet was introduced. The structural and electronic properties of these nanotubes were studied using density functional theory. It was found that armchair α2-graphyne nanotubes showed metallic behavior, while zigzag α2-graphyne nanotubes were found to have semiconducting or metallic properties depending on tube size. The energy band gap of zigzag α2-graphyne nanotubes decreased with increasing tube diameter. The results indicated that the α2-graphyne sheet and its nanotubes can be proper materials for future nanoelectronics.

Syntheses, structures, electrochemistry and catalytic oxidation degradation of organic dyes of two new coordination polymers derived from Cu(II) and Mn(II) and 1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene

NASA Astrophysics Data System (ADS)

Song, Ming; Mu, Bao; Huang, Ru-Dan

2017-02-01

Two new coordination polymers (CPs), namely, [Cu2(ttbz)(H2btc)2(OH)]n (1) and [Mn(ttbz)2(H2O)2]n (2) (Httbz =1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene, H3btc =1,3,5-benzenetricarboxylic acid), have been hydrothermally synthesized and structurally characterized. Complex 1 exhibits a (3,5,5,5)-connected 2D layer with a Schläfli symbol of {3·42}{3·440.520.63}{320.440.520.62}{320.440.530.6}, in which the ttbz- ligand can be described as μ5-bridge, linking Cu(II) ions into a 2D layer and H2btc- ions play a supporting role in complex 1. The ttbz- ligand in complex 2 represents the bridging coordination mode, connecting two Mn(II) ions to form the infinite 1D zigzag chains, respectively, which are further connected by two different types of hydrogen bonds to form a 3D supramolecular. Furthermore, catalytic oxidation activities toward organic dyes and electrochemical behaviors of the title complexes have been investigated at room temperature in aqueous solutions, indicating these complexes may be applicable to color removal in a textile wastewater stream and practical applications in areas of electrocatalytic reduction toward nitrite, respectively.

Synthesis and characterization of two new zinc(II) coordination polymers with bidentate flexible ligands: Formation of a 2D structure with (44.62)-sql topology

NASA Astrophysics Data System (ADS)

Lalegani, Arash; Khaledi Sardashti, Mohammad; Gajda, Roman; Woźniak, Krzysztof

2017-12-01

Zinc(II) coordination polymers [Zn(bip)2(NCS)2]n (1) and [Zn(μ-bbd)(N3)2]n (2) were synthesized by using the neutral flexible bidentate N-donor ligands 1,4-bis(3,5-dimethylpyrazolyl)butane (bbd) and 1,3-bis(imidazolyl)propane (bip), mono-anionic NCS- or N3-ligand and zinc(II) chloride salts. The results of the X-ray analyses demonstrate that in the structure of 1, the zinc(II) ion is located on an inversion center and exhibits an ZnN6 octahedral arrangement while, in the structure of 2, the zinc(II) ion adopts an ZnN4 tetrahedral geometry. In the polymer 1, the NCS groups are terminally N-bonded to the metal center and the each bip with anti-gauche conformation acts as bridging connecting four zinc(II) ions to form a two-dimensional network with a sql [point symbol (44.62)] topology while, in the polymer 1, the N3 groups are terminally bonded to the metal center and each bbd with anti-anti-anti conformation acts as bridging ligand connecting two zinc(II) ions to form a one-dimensional zig-zag chain. Coordination compounds 1 and 2 have been characterized by infrared spectroscopy, elemental analyses and single-crystal X-ray diffraction. Thermal analyses of polymers were also presented.

Synthesis and structural characterization of dinuclear Cd2+, Hg2+ and Fe2+ complexes with neutral bi and tetradentate flexible pyrazole-based ligands

NASA Astrophysics Data System (ADS)

Beheshti, Azizolla; Lalegani, Arash; Behvandi, Fatemeh; Safaeiyan, Forough; Sarkarzadeh, Afsoon; Bruno, Giuseppe; Amiri Rudbari, Hadi

2015-02-01

Four new complexes of [Hg2Cl4(bpp)]n (1), [Hg2Cl4(tdmpp)] (2), [Cd2I4(tdmpp)] (3) and [Fe2Cl4(tdmpp)] (4) were prepared by using the neutral N-donor ligands 1,3-bis(3,5-dimethyl-1-pyrazolyl)propane (bpp) and 1,1,3,3-tetrakis(3,5-dimethyl-1-pyrazolyl)propane (tdmpp) with different flexibility and appropriate metal salts of Cd(II), Hg(II) and Fe(II) ions. These compounds were characterized by the infrared spectroscopy, elemental analysis and X-ray crystallography. Flexible ligands and non-covalent Csbnd H⋯Cl hydrogen bonds play a major role in the crystal packing of compounds 1, 2 and 4. In the two-dimensional non-covalent structure of 1, there are two distinctly different coordination modes for the mercury atoms. One mercury atom has pseudo-trigonal bipyramidal geometry and the other adopts a distorted tetrahedral environment. In the dinuclear structures of 2 and 4 the neutral molecules are linked together by the Csbnd H⋯Cl hydrogen bonds, forming an infinite one-dimensional zigzag chain structure. Compounds 2-4 are isostructural with each other.

Multiple pathways in pressure-induced phase transition of coesite

PubMed Central

Liu, Wei; Wu, Xuebang; Liu, Changsong; Miranda, Caetano R.; Scandolo, Sandro

2017-01-01

High-pressure single-crystal X-ray diffraction method with precise control of hydrostatic conditions, typically with helium or neon as the pressure-transmitting medium, has significantly changed our view on what happens with low-density silica phases under pressure. Coesite is a prototype material for pressure-induced amorphization. However, it was found to transform into a high-pressure octahedral (HPO) phase, or coesite-II and coesite-III. Given that the pressure is believed to be hydrostatic in two recent experiments, the different transformation pathways are striking. Based on molecular dynamic simulations with an ab initio parameterized potential, we reproduced all of the above experiments in three transformation pathways, including the one leading to an HPO phase. This octahedral phase has an oxygen hcp sublattice featuring 2 × 2 zigzag octahedral edge-sharing chains, however with some broken points (i.e., point defects). It transforms into α-PbO2 phase when it is relaxed under further compression. We show that the HPO phase forms through a continuous rearrangement of the oxygen sublattice toward hcp arrangement. The high-pressure amorphous phases can be described by an fcc and hcp sublattice mixture. PMID:29162690

3-D Stall Cell Inducement Using Static Trips on a NACA0015 Airfoil

NASA Astrophysics Data System (ADS)

Dell'Orso, Haley; Amitay, Michael

2015-11-01

Stall cells typically occur at high angles of attack and moderate to high Reynolds numbers (105 to 106) , which are applicable to High Altitude Long Endurance (HALE) vehicles. Under certain conditions stall cells can form abruptly and have a severe and detrimental impact on flight. In order to better understand this phenomenon, stall cell formation is studied using oil flow visualization and SPIV on a NACA0015 airfoil with AR = 2.67. It was shown that there is a critical Reynolds number above which stall cells begin to form, and that Recrit varies with angle of attack. Zig-zag tape and balsa wood trips were used to induce stall cells at lower Reynolds numbers than they would otherwise be present. This will aid in understanding the formation mechanism of these cells. It was also demonstrated that, in the case of full span trips, stall cells are induced by the 3-D nature of zig-zag trips and did not appear when balsa wood trips were used. This suggests that the formation of the stall cell might be due to 3-D disturbances that are naturally present in a flow field. AFOSR Grant Number FA9550-13-1-0059.

A Refined Zigzag Beam Theory for Composite and Sandwich Beams

NASA Technical Reports Server (NTRS)

Tessler, Alexander; Sciuva, Marco Di; Gherlone, Marco

2009-01-01

A new refined theory for laminated composite and sandwich beams that contains the kinematics of the Timoshenko Beam Theory as a proper baseline subset is presented. This variationally consistent theory is derived from the virtual work principle and employs a novel piecewise linear zigzag function that provides a more realistic representation of the deformation states of transverse-shear flexible beams than other similar theories. This new zigzag function is unique in that it vanishes at the top and bottom bounding surfaces of a beam. The formulation does not enforce continuity of the transverse shear stress across the beam s cross-section, yet is robust. Two major shortcomings that are inherent in the previous zigzag theories, shear-force inconsistency and difficulties in simulating clamped boundary conditions, and that have greatly limited the utility of these previous theories are discussed in detail. An approach that has successfully resolved these shortcomings is presented herein. Exact solutions for simply supported and cantilevered beams subjected to static loads are derived and the improved modelling capability of the new zigzag beam theory is demonstrated. In particular, extensive results for thick beams with highly heterogeneous material lay-ups are discussed and compared with corresponding results obtained from elasticity solutions, two other zigzag theories, and high-fidelity finite element analyses. Comparisons with the baseline Timoshenko Beam Theory are also presented. The comparisons clearly show the improved accuracy of the new, refined zigzag theory presented herein over similar existing theories. This new theory can be readily extended to plate and shell structures, and should be useful for obtaining relatively low-cost, accurate estimates of structural response needed to design an important class of high-performance aerospace structures.

Role of route previewing strategies on climbing fluency and exploratory movements.

PubMed

Seifert, Ludovic; Cordier, Romain; Orth, Dominic; Courtine, Yoan; Croft, James L

2017-01-01

This study examined the role of route previewing strategies on climbing fluency and on exploratory movements of the limbs, in order to understand whether previewing helps people to perceive and to realize affordances. Eight inexperienced and ten experienced climbers previewed a 10 m high route of 5b difficulty on French scale, then climbed it with a top-rope as fluently as possible. Gaze behavior was collected from an eye tracking system during the preview and allowed us to determine the number of times they scanned the route, and which of four route previewing strategies (fragmentary, ascending, zigzagging, and sequence-of-blocks) they used. Five inertial measurement units (IMU) (3D accelerometer, 3D gyroscope, 3D magnetometer) were attached to the hip, both feet, and forearms to analyze the vertical acceleration and direction of each limb and hip during the ascent. We were able to detect movement and immobility phases of each IMU using segmentation and classification processes. Depending on whether the limbs and/or hip were moving, five states of behavior were detected: immobility, postural regulation, hold exploration, hold change, and hold traction. Using cluster analysis we identified four clusters of gaze behavior during route previewing depending on route preview duration, number of scan paths, fixations duration, ascending, zigzagging, and sequence-of-blocks strategies. The number of scan paths was positively correlated with relative duration of exploration and negatively correlated with relative duration of hold changes during the ascent. Additionally, a high relative duration of sequence-of-blocks strategy and zigzagging strategy were associated with a high relative duration of immobility during the ascent. Route previewing might help to pick up functional information about reachable, graspable, and usable holds, in order to chain movements together and to find the route. In other words, route previewing might contribute to perceiving and realizing nested affordances.

Application of the Refined Zigzag Theory to the Modeling of Delaminations in Laminated Composites

NASA Technical Reports Server (NTRS)

Groh, Rainer M. J.; Weaver, Paul M.; Tessler, Alexander

2015-01-01

The Refined Zigzag Theory is applied to the modeling of delaminations in laminated composites. The commonly used cohesive zone approach is adapted for use within a continuum mechanics model, and then used to predict the onset and propagation of delamination in five cross-ply composite beams. The resin-rich area between individual composite plies is modeled explicitly using thin, discrete layers with isotropic material properties. A damage model is applied to these resin-rich layers to enable tracking of delamination propagation. The displacement jump across the damaged interfacial resin layer is captured using the zigzag function of the Refined Zigzag Theory. The overall model predicts the initiation of delamination to within 8% compared to experimental results and the load drop after propagation is represented accurately.

4,4′-[4,4′-Sulfonyl­bis­(p-phenyl­ene­oxy)]dibutanoic acid

PubMed Central

Fu, Chun-Yan; Liu, Yong-Hui; Zhou, Zhong-Liu; Tang, Hong

2011-01-01

In the title compound, C20H22O8S, the dihedral angle between the two benzene rings is 81.6 (3)°. The benzene-connected portions of the alk­oxy substituents are almost coplanar with their respective rings [C—C—O—C torsion angles of 174.77 (17) and −178.5 (4)°]. One of the butanoic acid groups is disordered over two conformations with a site-occupancy ratio 0.719 (6):0.281 (6). In the crystal, pairs of O—H⋯O hydrogen bonds link the mol­ecules into infinite zigzag chains along [130]. PMID:21754375

Bridging cobalt-calixarene subunits into a Co8 entity or a chain with 4,4‧-bipyridyl

NASA Astrophysics Data System (ADS)

Liu, Wei; Liu, Mei; Du, Shangchao; Li, Yafeng; Liao, Wuping

2014-02-01

Two novel calixarene-based compounds, {[Co4Cl(TC4A)(HCOO)3]2(4,4‧-bpy)2} (CIAC-206) and {[Co3(H2O)(SC4A-SO2)(HCOO)2]2(4,4‧-bpy)}n (CIAC-207) (H4TC4A = p-tert-butylthiacalix[4]arene, SC4A-SO2 = p-tert-butylsulfonylcalix[4]arene, 4,4‧-bpy = 4,4‧-bipyridyl) were synthesized under solvothermal conditions, and characterized by single crystal X-ray diffraction analysis, TG-DSC analysis, elemental analysis and IR spectroscopy. These two structures are featured with isolated Z-shaped Co8 entities containing two Co4-TC4A subunits bridged by two parallel 4,4‧-bpy (CIAC-206) and some zigzag chains with [Co3-SC4A-SO2]2 dimers bridged by single 4,4‧-bpy (CIAC-207), respectively. In order to evaluate their properties, the N2 sorption behavior and magnetic property were examined.

Ammonium iron(III) phosphate(V) fluoride, (NH4)0.5[(NH4)0.375K0.125]FePO4F, with ammonium partially substituted by potassium

PubMed Central

Wang, Lei; Zhou, Yan; Huang, Ya-Xi; Mi, Jin-Xiao

2009-01-01

The title compound, ammonium potassium iron(III) phosphate fluoride, (NH4)0.875K0.125FePO4F, is built from zigzag chains ∞ 1{[FeO4F2]7−}, with Fe3+ in a distorted octahedral coordination, extending along both the [011] and [01] directions. These chains are made up of alternating trans-[FeO4F2] and cis-[FeO4F2] octa­hedra via shared F-atom corners, and are linked by PO4 tetra­hedra, resulting in an open-framework structure with channels along the [010] and [100] directions. There are two crystallographically independent ammonium sites: one in the [010] channels and the other, partially substituted by K+ ions, in the [100] channels. The ammonium in the [010] channels is fixed to the framework via eight hydrogen bonds (six N—H⋯O and two N—H⋯F). PMID:21581466

Dynamical ion transfer between coupled Coulomb crystals in a double-well potential.

PubMed

Klumpp, Andrea; Zampetaki, Alexandra; Schmelcher, Peter

2017-09-01

We investigate the nonequilibrium dynamics of coupled Coulomb crystals of different sizes trapped in a double well potential. The dynamics is induced by an instantaneous quench of the potential barrier separating the two crystals. Due to the intra- and intercrystal Coulomb interactions and the asymmetric population of the potential wells, we observe a complex reordering of ions within the two crystals as well as ion transfer processes from one well to the other. The study and analysis of the latter processes constitutes the main focus of this work. In particular, we examine the dependence of the observed ion transfers on the quench amplitude performing an analysis for different crystalline configurations ranging from one-dimensional ion chains via two-dimensional zigzag chains and ring structures to three-dimensional spherical structures. Such an analysis provides us with the means to extract the general principles governing the ion transfer dynamics and we gain some insight on the structural disorder caused by the quench of the barrier height.

All-carbon sp-sp2 hybrid structures: Geometrical properties, current rectification, and current amplification

PubMed Central

Zhang, Zhenhua; Zhang, Junjun; Kwong, Gordon; Li, Ji; Fan, Zhiqiang; Deng, Xiaoqing; Tang, Guiping

2013-01-01

All-carbon sp-sp2 hybrid structures comprised of a zigzag-edged trigonal graphene (ZTG)and carbon chains are proposed and constructed as nanojunctions. It has been found that such simple hybrid structures possess very intriguing propertiesapp:addword:intriguing. The high-performance rectifying behaviors similar to macroscopic p-n junction diodes, such as a nearly linear positive-bias I-V curve (metallic behavior), a very small leakage current under negative bias (insulating behavior), a rather low threshold voltage, and a large bias region contributed to a rectification, can be predicted. And also, a transistor can be built by such a hybrid structure, which can show an extremely high current amplification. This is because a sp-hybrid carbon chain has a special electronic structure which can limit the electronic resonant tunneling of the ZTG to a unique and favorable situation. These results suggest that these hybrid structures might promise importantly potential applications for developing nano-scale integrated circuits. PMID:23999318

Structure-directing weak phosphoryl XH...O=P (X = C, N) hydrogen bonds in cyclic oxazaphospholidines and oxazaphosphinanes.

PubMed

van der Lee, A; Rolland, M; Marat, X; Virieux, D; Volle, J N; Pirat, J L

2008-04-01

The structures of six cyclic oxazaphospholidines and three cyclic oxazaphosphinanes have been determined and their supramolecular structures have been compared. The molecules differ with respect to the functional groups attached to the central five- or six-membered rings, but have one phosphoryl group in common. The predominant feature in the supramolecular structures is the existence of relatively weak intermolecular phosphoryl XH...O=P (X = C, N) hydrogen bonds, creating in nearly all cases linear zigzag or double molecular chains. The molecular chains are in general linked to each other via very weak CH...pi or usual hydrogen-bond interactions. A survey of the Cambridge Structural Database on similar XH...O=P interactions shows a very large flexibility of the XH...O angle, which is in agreement with the DFT calculation reported elsewhere. The strength of the XH...O=P interaction can therefore be considered as relatively weak to moderately strong, and is expected to play at least a role in the formation of secondary substructures.

Sample Archaeological Survey of Public Use Areas, Milford Lake, Kansas

DTIC Science & Technology

1982-09-01

6,000 B.C. Llano -(Clovis projectile points) Lindenmeier - (Folsom projectile points) Plano -(Plainview, Angostora, Hell Gap, Scotts- bluff, etc...plain, flaring or S-form rims, shell tempered, plain surfaced pottery with low rolled rims 0 and incised alternating hatched triangles on the...tempered pottery with a marked collar rim incised with zig-zags, herringbone and hatched alternating triangles; unnotched triangular arrow points; French

Modification of the band offset in boronitrene

NASA Astrophysics Data System (ADS)

Obodo, K. O.; Andrew, R. C.; Chetty, N.

2011-10-01

Using density functional methods within the generalized gradient approximation implemented in the Quantum Espresso codes, we modify the band offset in a single layer of boronitrene by substituting a double line of carbon atoms. This effectively introduces a line of dipoles at the interface. We considered various junctions of this system within the zigzag and armchair orientations. Our results show that the “zigzag-short” structure is energetically most stable, with a formation energy of 0.502 eV and with a band offset of 1.51 eV. The “zigzag-long” structure has a band offset of 1.99 eV. The armchair structures are nonpolar, while the zigzag-single structures show a charge accumulation for the C-substituted B and charge depletion for the C-substituted N at the junction. Consequently there is no shifting of the bands.

Bis(N'-{(E)-[(2E)-1,3-di-phenyl-prop-2-en-1-yl-idene]amino}-N-ethyl-carbamimido-thio-ato-κ2N',S)zinc(II): crystal structure and Hirshfeld surface analysis.

PubMed

Tan, Ming Yueh; Crouse, Karen A; Ravoof, Thahira B S A; Jotani, Mukesh M; Tiekink, Edward R T

2017-07-01

The title Zn II complex, [Zn(C 18 H 18 N 3 S) 2 ], (I), features two independent but chemically equivalent mol-ecules in the asymmetric unit. In each, the thio-semicarbazonate monoanion coordinates the Zn II atom via the thiol-ate-S and imine-N atoms, with the resulting N 2 S 2 donor set defining a distorted tetra-hedral geometry. The five-membered ZnSCN 2 chelate rings adopt distinct conformations in each independent mol-ecule, i.e. one ring is almost planar while the other is twisted about the Zn-S bond. In the crystal, the two mol-ecules comprising the asymmetric unit are linked by amine-N-H⋯N(imine) and amine-N-H⋯S(thiol-ate) hydrogen bonds via an eight-membered heterosynthon, {⋯HNCN⋯HNCS}. The dimeric aggregates are further consolidated by benzene-C-H⋯S(thiol-ate) inter-actions and are linked into a zigzag supra-molecular chain along the c axis via amine-N-H⋯S(thiol-ate) hydrogen bonds. The chains are connected into a three-dimensional architecture via phenyl-C-H⋯π(phen-yl) and π-π inter-actions, the latter occurring between chelate and phenyl rings [inter-centroid separation = 3.6873 (11) Å]. The analysis of the Hirshfeld surfaces calculated for (I) emphasizes the different inter-actions formed by the independent mol-ecules in the crystal and the impact of the π-π inter-actions between chelate and phenyl rings.

Highly Efficient Carbon Dioxide Hydrogenation to Methanol Catalyzed by Zigzag Platinum-Cobalt Nanowires.

PubMed

Bai, Shuxing; Shao, Qi; Feng, Yonggang; Bu, Lingzheng; Huang, Xiaoqing

2017-06-01

Carbon dioxide (CO 2 ) hydrogenation is an effective strategy for CO 2 utilization, while unsatisfied conversion efficiencies remain great challenges. It is reported herein that zigzag Pt-Co nanowires (NWs) with Pt-rich surfaces and abundant steps/edges can perform as highly active and stable CO 2 hydrogenation catalysts. It is found that tuning the Pt/Co ratio of the Pt-Co NWs, solvents, and catalyst supports could well optimize the CO 2 hydrogenation to methanol (CH 3 OH) with the Pt 4 Co NWs/C exhibiting the best performance, outperforming all the previous catalysts. They are also very durable with limited activity decays after six catalytic cycles. The diffuse reflectance infrared Fourier transform spectroscopy result of CO 2 adsorption shows that the Pt 4 Co NWs/C undergoes the adsorption/activation of CO 2 by forming appropriate carboxylate intermediates, and thus enhancing the CH 3 OH production. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Correlation between micrometer-scale ripple alignment and atomic-scale crystallographic orientation of monolayer graphene.

PubMed

Choi, Jin Sik; Chang, Young Jun; Woo, Sungjong; Son, Young-Woo; Park, Yeonggu; Lee, Mi Jung; Byun, Ik-Su; Kim, Jin-Soo; Choi, Choon-Gi; Bostwick, Aaron; Rotenberg, Eli; Park, Bae Ho

2014-12-01

Deformation normal to the surface is intrinsic in two-dimensional materials due to phononic thermal fluctuations at finite temperatures. Graphene's negative thermal expansion coefficient is generally explained by such an intrinsic property. Recently, friction measurements on graphene exfoliated on a silicon oxide surface revealed an anomalous anisotropy whose origin was believed to be the formation of ripple domains. Here, we uncover the atomistic origin of the observed friction domains using a cantilever torsion microscopy in conjunction with angle-resolved photoemission spectroscopy. We experimentally demonstrate that ripples on graphene are formed along the zigzag direction of the hexagonal lattice. The formation of zigzag directional ripple is consistent with our theoretical model that takes account of the atomic-scale bending stiffness of carbon-carbon bonds and the interaction of graphene with the substrate. The correlation between micrometer-scale ripple alignment and atomic-scale arrangement of exfoliated monolayer graphene is first discovered and suggests a practical tool for measuring lattice orientation of graphene.

Six uranyl-organic frameworks with naphthalene-dicarboxylic acid and bipyridyl-based spacers: syntheses, structures, and properties.

PubMed

Xu, Wei; Ren, Ya-Nan; Xie, Miao; Zhou, Lin-Xia; Zheng, Yue-Qing

2018-03-28

A new series of uranium coordination polymers have been hydrothermally synthesized by using 1,4-naphthalene dicarboxylic acid (H 2 NDC), namely, (H 3 O) 2 [(UO 2 ) 2 (NDC) 3 ]·H 2 O (1), (H 2 -bpp)[(UO 2 ) 2 (NDC) 3 ]·EtOH·5H 2 O (2), (H 2 -bpe) 2/2 [(UO 2 ) 2 (NDC) 3 ]·EtOH (3), (H 2 -bpp)[(UO 2 ) 2 (NDC) 3 ]·5H 2 O (4), (H 2 -bpp)[(UO 2 )(HNDC)(NDC)] 2 ·2H 2 O (5), and (H 2 -bpy)[(UO 2 )(NDC) 2 ] (6) [bpp = 1,3-di(4-pyridyl) propane, bpe = 4,4'-vinylenedipyridine, bpy = 4,4'-bipyridine]. Single-crystal X-ray diffraction demonstrates that complex 1 represents the uranyl-organic polycatenated framework derived from a simple two-dimensional honeycomb grid network structure via a H 2 NDC linker. Complexes 2-4 contain the dinuclear motifs of the two UO 7 pentagonal and one UO 8 hexagonal bipyramids which are linked by NDC 2- anions creating a (UO 2 ) 4 (NDC) 2 unit, and further extend to a 2D layer through NDC 2- anions. Complex 5 displays a 1D zigzag double chain structure, in which the carboxylate groups of the NDC 2- anions adopt a chelate mode and further extends to a 2D framework via hydrogen bonds. The 1D structure of complex 6 is similar to the zigzag chain of complex 5. In addition, powder X-ray diffraction, elemental analysis, IR, thermal stability and luminescence properties of all complexes have also been investigated in this paper. The photocatalytic properties of the six complexes for the degradation of tetracycline hydrochloride (TC) under UV irradiation have been examined. Moreover, density functional theory (DFT) calculations were carried out to explore the electronic structural and bonding properties of the uranyl complexes 1-6.

Relationship between morphological change and crystalline phase transitions of polyethylene-poly(ethylene oxide) diblock copolymers, revealed by the temperature-dependent synchrotron WAXD/SAXS and infrared/Raman spectral measurements.

PubMed

Weiyu, Cao; Tashiro, Kohji; Hanesaka, Makoto; Takeda, Shinichi; Masunaga, Hiroyasu; Sasaki, Sono; Takata, Masaki

2009-02-26

The phase transition behaviors of low-molecular-weight polyethylene-poly(ethylene oxide) (PE-b-PEO) diblock copolymers with the monomeric units of PE/PEO = 17/40 and 39/86 have been successfully investigated through the temperature-dependent measurements of wide-angle X-ray diffraction (WAXD), small-angle X-ray scattering (SAXS), infrared and Raman spectra, as well as thermal analysis. These diblock copolymers had been believed to show only order-to-disorder transition of lamellar morphology in a wide temperature region, but it has been found here for the first time that this copolymer clearly exhibits the three stages of transitions among lamella, gyroid, cylinder, and spherical phases in the heating and cooling processes. The WAXD and IR/Raman spectral measurements allowed us to relate these morphological changes to the microscopic changes in the aggregation states of PEO and PE segments. In the low-temperature region the PEO segments form the monoclinic crystal of (7/2) helical chain conformation and the PE segments of planar-zigzag form take the orthorhombic crystalline phase. These crystalline lamellae of PEO and PE segments are alternately stacked with the long period of 165 Angstroms. In a higher temperature region, where the PEO crystalline parts are on the way of melting but the PE parts are still in the orthorhombic phase, the gyroid morphology is detected in the SAXS data. By heating further, the gyroid morphology changes to the hexagonally packed cylindrical morphology, where the orthorhombic phase of PE segments is gradually disordered because of thermally activated molecular motion and finally transforms to the pseudohexagonal or rotator phase. Once the PE segments are perfectly melted, the higher-order structure changes from the cylinder to the spherical morphology. These morphological transitions might relate to the thermally activated motions of two short chain segments of the diblock copolymer, although the details of the transition mechanism are unclear at the present stage.

Cristobalite X-I: A bridge between low and high density silica polymorphs

NASA Astrophysics Data System (ADS)

Shelton, H.; Tiange, B.; Zurek, E.; Smith, J.; Dera, P.

2017-12-01

SiO2 is one of the most common compounds found on Earth. Despite its chemical simplicity, and because of its crystal chemical characteristics, SiO2 exhibits a complex phase diagram. SiO2 has a wide variety of thermodynamically stable crystalline phases, as well as numerous metastable crystalline and amorphous polymorphs. Many of the phase transition sequences that produce metastable phases of SiO2 are strongly path-dependent, where the rate of change controls the transition just as much as the final conditions. The elusive metastable polymorphs of SiO2 may provide a better understanding of the factors controlling its densification. On compression of α-cristobalite (the high temperature tetrahedral phase of SiO2) to pressures above 12 GPa, a new polymorph known as cristobalite X-I forms. Existence of cristobalite X-I has been known for several decades, however, consensus regarding the exact atomic arrangement has not yet been reached. The X-I phase constitutes an important step in the silica densification process, separating low-density tetrahedral framework structures from high-density octahedral polymorphs. It is unique in being the only non-quenchable high-density SiO2 phase, which reverts back to the tetrahedral low-density form on decompression at ambient temperature. Our new single crystal synchrotron X-ray diffraction experiments, with quasihydrostatic neon as the pressure medium, revealed the structure of this enigmatic phase to consist of octahedral silicate chains with 4-60°-2 zigzag chain geometry. This geometry has not been considered before, but is closely related to post-quartz, stishovite and seifertite. Density functional theory calculations support this observation, confirming the dynamic stability of the X-I arrangement and reasonably reproducing the pressure at which the transformation takes place. The enthalpy of cristobalite X-I is higher than stishovite and seifertite, but it is favored as a high-pressure successor of cristobalite due to a unique transformation pathway.

A new security solution to JPEG using hyper-chaotic system and modified zigzag scan coding

NASA Astrophysics Data System (ADS)

Ji, Xiao-yong; Bai, Sen; Guo, Yu; Guo, Hui

2015-05-01

Though JPEG is an excellent compression standard of images, it does not provide any security performance. Thus, a security solution to JPEG was proposed in Zhang et al. (2014). But there are some flaws in Zhang's scheme and in this paper we propose a new scheme based on discrete hyper-chaotic system and modified zigzag scan coding. By shuffling the identifiers of zigzag scan encoded sequence with hyper-chaotic sequence and accurately encrypting the certain coefficients which have little relationship with the correlation of the plain image in zigzag scan encoded domain, we achieve high compression performance and robust security simultaneously. Meanwhile we present and analyze the flaws in Zhang's scheme through theoretical analysis and experimental verification, and give the comparisons between our scheme and Zhang's. Simulation results verify that our method has better performance in security and efficiency.

Iris Segmentation and Normalization Algorithm Based on Zigzag Collarette

NASA Astrophysics Data System (ADS)

Rizky Faundra, M.; Ratna Sulistyaningrum, Dwi

2017-01-01

In this paper, we proposed iris segmentation and normalization algorithm based on the zigzag collarette. First of all, iris images are processed by using Canny Edge Detection to detect pupil edge, then finding the center and the radius of the pupil with the Hough Transform Circle. Next, isolate important part in iris based zigzag collarette area. Finally, Daugman Rubber Sheet Model applied to get the fixed dimensions or normalization iris by transforming cartesian into polar format and thresholding technique to remove eyelid and eyelash. This experiment will be conducted with a grayscale eye image data taken from a database of iris-Chinese Academy of Sciences Institute of Automation (CASIA). Data iris taken is the data reliable and widely used to study the iris biometrics. The result show that specific threshold level is 0.3 have better accuracy than other, so the present algorithm can be used to segmentation and normalization zigzag collarette with accuracy is 98.88%

Mechanical properties of graphene nanoribbons under uniaxial tensile strain

NASA Astrophysics Data System (ADS)

Yoneyama, Kazufumi; Yamanaka, Ayaka; Okada, Susumu

2018-03-01

Based on the density functional theory with the generalized gradient approximation, we investigated the mechanical properties of graphene nanoribbons in terms of their edge shape under a uniaxial tensile strain. The nanoribbons with armchair and zigzag edges retain their structure under a large tensile strain, while the nanoribbons with chiral edges are fragile against the tensile strain compared with those with armchair and zigzag edges. The fracture started at the cove region, which corresponds to the border between the zigzag and armchair edges for the nanoribbons with chiral edges. For the nanoribbons with armchair edges, the fracture started at one of the cove regions at the edges. In contrast, the fracture started at the inner region of the nanoribbons with zigzag edges. The bond elongation under the tensile strain depends on the mutual arrangement of covalent bonds with respect to the strain direction.

On the polymorphism of benzocaine; a low-temperature structural phase transition for form (II).

PubMed

Chan, Eric J; Rae, A David; Welberry, T Richard

2009-08-01

A low-temperature structural phase transition has been observed for form (II) of benzocaine (BZC). Lowering the temperature doubles the b-axis repeat and changes the space group from P2(1)2(1)2(1) to P112(1) with gamma now 99.37 degrees. The structure is twinned, the twin rule corresponding to a 2(1) screw rotation parallel to a. The phase transition is associated with a sequential displacement parallel to a of zigzag bi-layers of ribbons perpendicular to b*. No similar phase transition was observed for form (I) and this was attributed to the different packing symmetries of the two room-temperature polymorphic forms.

Aposematism and crypsis are not enough to explain dorsal polymorphism in the Iberian adder

NASA Astrophysics Data System (ADS)

Martínez-Freiría, Fernando; Pérez i de Lanuza, Guillem; Pimenta, António A.; Pinto, Tiago; Santos, Xavier

2017-11-01

Aposematic organisms can show phenotypic variability across their distributional ranges. The ecological advantages of this variability have been scarcely studied in vipers. We explored this issue in Vipera seoanei, a species that exhibits five geographically structured dorsal colour phenotypes across Northern Iberia: two zigzag patterned (Classic and Cantabrica), one dorsal-strip patterned (Bilineata), one even grey (Uniform), and one melanistic (Melanistic). We compared predation rates (raptors and mammals) on plasticine models resembling each colour phenotype in three localities. Visual modelling techniques were used to infer detectability (i.e. conspicuousness) of each model type for visually guided predators (i.e. diurnal raptors). We hypothesize that predation rates will be lower for the two zigzag models (aposematism hypothesis) and that models with higher detectability would show higher predation rates (detectability hypothesis). Classic and Bilineata models were the most conspicuous, while Cantabrica and Uniform were the less. Melanistic presented an intermediate conspicuousness. Predation rate was low (3.24% of models) although there was variation in attack frequency among models. Zigzag models were scarcely predated supporting the aposematic role of the zigzag pattern in European vipers to reduce predation (aposematism hypothesis). From the non-zigzag models, high predation occurred on Bilineata and Melanistic models, and low on Uniform models, partially supporting our detectability hypothesis. These results suggest particular evolutionary advantages for non-zigzag phenotypes such as better performance of Melanistic phenotypes in cold environments or better crypsis of Uniform phenotypes. Polymorphism in V. seoanei may respond to a complex number of forces acting differentially across an environmental gradient.

Synthesis and characterization of new fluoride-containing manganese vanadates A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F

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

Sanjeewa, Liurukara D.; McGuire, Michael A.; Smith Pellizzeri, Tiffany M.

2016-09-15

Large single crystals of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO{sub 4}F{sub 2} building blocks. The A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed of zigzag chains ofmore » edge-sharing MnO{sub 4}F{sub 2} units running along the a-axis, and interconnected through V{sub 2}O{sub 7} pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn{sup 2+} indicated that Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} is antiferromagnetic with a Neél temperature, T{sub N}=~3 K and a Weiss constant, θ, of −11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}. Mn{sub 2}(VO{sub 4})F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn{sup 2+}. These interpenetrating chains are additionally connected through isolated VO{sub 4} tetrahedra to form the condensed structure. - Graphical abstract: New vanadate fluorides A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} (A=Rb, Cs) and Mn{sub 2}(VO{sub 4})F have been synthesized hydrothermally. Upon cooling, the one-dimensional Mn(II) substructure results in antiferromagnetic ordering. Display Omitted - Highlights: • Single crystals of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2}, (A=Rb, Cs) and Mn{sub 2}VO{sub 4}F were grown hydrothermally. • The use of fluoride mineralizers in the synthesis led to the formation of new compounds without OH{sup −} groups. • The structure of A{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} features zigzag chains of MnO{sub 4}F{sub 2} units. • Cs{sub 2}Mn{sub 2}V{sub 2}O{sub 7}F{sub 2} exhibits antiferromagnetic ordering with a Neel temperature of ~3 K. • Mn{sub 2}VO{sub 4}F possesses a condensed framework structure with disordered fluorine atoms.« less

New metal-organic complexes based on bis(tetrazole) ligands: Synthesis, structures and properties

NASA Astrophysics Data System (ADS)

Du, Ceng-Ceng; Fan, Jian-Zhong; Wang, Xin-Fang; Zhou, Sheng-Bin; Wang, Duo-Zhi

2017-04-01

In this paper, a series of new complexes, [Zn2(HL1)2(H2O)4]·H2O (1), [Co2(HL1)2]·TEA (2), [Co3(HL1)2(H2L1)2(H2O)4]n (3), [Cu(HL1)(H2O)2]n (4), {[Cu5(HL2)2(OH)4(ClO4)2]·4H2O}n (5) and [Cu2(L3)]n (6) were successfully prepared by utilizing three bis(tetrazole) ligands [bis-(1H-tetrazol-5-ylmethyl)-amine (H3L1), bis-(1H-tetrazol-5-ylethyl)-amine (H3L2) and 1,5-bis(5-tetrazolo)-3-thiapentane (H2L3)], all of which have been characterized by elemental analyses, FT-IR spectroscopy, powder X-ray diffraction (PXRD), thermogravimetric analyses as well as single-crystal X-ray diffraction analyses showing different dimensionalities (0D, 1D and 3D). Complexes 1 and 2 are 0D structures, 1 shows a dinuclear structure, 2 displays two crystallographically different mononuclear structures, 1 and 2 are further assembled to form 3D supramolecular framework and 2D supramolecular network by hydrogen-bonding interactions, respectively. Complexes 3, 4 and 5 are 1D structures, 3 features a mononuclear unit and a 1D chain, which are arranged into 3D supramolecular architecture by hydrogen-bonding interactions, 4 presents a zigzag chain, 5 shows an infinite chain structure constructed from pentanuclear Cu(II) subunits and ClO4- anions. Complex 6 exhibits a 3D coordination framework based on cyclic [Cu4(L3)2] dimmer subunits as nodes possessing an 8-connected network topology with the point symbol {424·64}. Further, semiconductor behaviors, the solid-state luminescent properties of the complexes 1-3 and 6 were measured and studied seriously at room temperature.

Electrocatalytic properties of three new POMs-based inorganic–organic frameworks with flexible zwitterionic dicarboxylate ligands

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

Ren, Yanli; Li, Ling; Mu, Bao

2017-05-15

Three POMs–based inorganic–organic frameworks, namely, [Cu{sub 2}(L){sub 2}(SiW{sub 12}O{sub 40})(H{sub 2}O){sub 2}]·6H{sub 2}O (1), [Co{sub 2}(L){sub 2}(SiW{sub 12}O{sub 40})(H{sub 2}O){sub 8}]·8H{sub 2}O (2) and [Ni{sub 2}(L){sub 2}(SiW{sub 12}O{sub 40})(H{sub 2}O){sub 8}]·6H{sub 2}O (3), (L=1,1′-(1,4-phenylene-bis(methylene))-bis(pyridine-3-carboxylic acid)), have been synthesized and characterized by elemental analyses, IR, XRPD, TG, and single crystal X-ray diffraction. Compound 1 contains 1D double chains decorated by (Cu{sub 2}(L){sub 4}(H{sub 2}O){sub 2}) units and the 1D chains and POMs are stacked to yield 2D frameworks. Compound 2 displays a 2D network constructed from 1D zigzag chains and POMs arranged in ABAB mode. Compound 3 consists of big squaremore » girds and the POMs are dispersed in the middle of the two adjacent girds, forming 2D networks. Compounds 1–3 all show structural integrity in aqueous solutions at different pH values and in common organic solvents. Additionally, the fluorescence and electrochemical properties of compounds 1–3 are also investigated. Compounds 1–3 exhibit good electrocatalytic activities for the reduction of NaNO{sub 2} and H{sub 2}O{sub 2}. - Highlights: • Compound 1–3 all contain different 1D chains. The noncovalent interaction of metal–organic moieties from compounds 1–3 and POMs to construct three new host–guest supramolecular compounds. • Compounds 1–3 show good electrocatalytic activities towards the reduction of NaNO{sub 2} and H{sub 2}O{sub 2}. • Compounds 1–3 all show structural integrity in aqueous solutions at different pH values and in common organic solvents. • Compounds 1–3 may be promising luminescent materials due to their luminescent properties.« less

Crystal structures and magnetic properties of chiral heterobimetallic chains based on the dicyanoruthenate building block.

PubMed

Ru, Jing; Gao, Feng; Yao, Min-Xia; Wu, Tao; Zuo, Jing-Lin

2014-12-28

By the reaction of chiral Mn(III) Schiff-base complexes with the dicyanoruthenate building block, [Ru(salen)(CN)2](-) (salen(2-) = N,N'-ethylenebis(salicylideneimine) dianion), two couples of enantiomerically pure chiral cyano-bridged heterobimetallic one-dimensional (1D) chain complexes, [Mn((R,R)-salcy)Ru(salen)(CN)2]n (1-(RR)) and [Mn((S,S)-salcy)Ru(salen)(CN)2]n (1-(SS)) (Salcy = N,N'-(1,2-cyclohexanediylethylene)bis(salicylideneiminato) dianion), [Mn((R,R)-salphen)Ru(salen)(CN)2]n (2-(RR)) and [Mn((S,S)-salphen)Ru(salen)(CN)2]n (2-(SS)) (salphen = N,N'-(1,2-diphenylethylene)bis(salicylideneiminato) dianion), were synthesized and structurally characterized. Circular dichroism (CD) and vibrational circular dichroism (VCD) spectra confirm the enantiomeric nature of the optically active complexes. Structural analyses reveal the formation of neutral cyano-bridged zigzag single chains in 1-(RR) and 1-(SS), and double chains in 2-(RR) and 2-(SS). Magnetic studies show that antiferromagnetic coupling is operative between Ru(III) and Mn(III) centers bridged by cyanide. Compounds 1-(RR) and 1-(SS) show metamagnetic behavior with a critical field of about 7.2 kOe at 1.9 K resulting from the intermolecular π∙∙∙π interactions. Additionally, magnetostructural correlation for some typical cyano-bridged heterobimetallic Ru(III)-Mn(III) compounds is discussed.

In pursuit of barrierless transition metal dichalcogenides lateral heterojunctions

NASA Astrophysics Data System (ADS)

Aierken, Yierpan; Sevik, Cem; Gülseren, Oğuz; Peeters, François M.; Çakır, Deniz

2018-07-01

There is an increasing need to understand interfaces between two-dimensional materials to realize an energy efficient boundary with low contact resistance and small heat dissipation. In this respect, we investigated the impact of charge and substitutional atom doping on the electronic transport properties of the hybrid metallic-semiconducting lateral junctions, formed between metallic (1T and 1T d ) and semiconducting (1H) phases of MoS2 by means of first-principles and non-equilibrium Green function formalism based calculations. Our results clearly revealed the strong influence of the type of interface and crystallographic orientation of the metallic phase on the transport properties of these systems. The Schottky barrier height, which is the dominant mechanism for contact resistance, was found to be as large as 0.63 eV and 1.19 eV for holes and electrons, respectively. We found that armchair interfaces are more conductive as compared to zigzag termination due to the presence of the metallic Mo zigzag chains that are directed along the transport direction. In order to manipulate these barrier heights we investigated the influence of electron doping of the metallic part (i.e. 1T d -MoS2). We observed that the Fermi level of the hybrid system moves towards the conduction band of semiconducting 1H-MoS2 due to filling of 4d-orbital of metallic MoS2, and thus the Schottky barrier for electrons decreases considerably. Besides electron doping, we also investigated the effect of substitutional doping of metallic MoS2 by replacing Mo atoms with either Re or Ta. Due to its valency, Re (Ta) behaves as a donor (acceptor) and reduces the Schottky barrier for electrons (holes). Since Re and Ta based transition metal dichalcogenides crystallize in either the 1T d or 1T phase, substitutional doping with these atom favors the stabilization of the 1T d phase of MoS2. Co-doping of hybrid structure results in an electronic structure, which facilities easy dissociation of excitons created in the 1H part.

In pursuit of barrierless transition metal dichalcogenides lateral heterojunctions.

PubMed

Aierken, Yierpan; Sevik, Cem; Gülseren, Oğuz; Peeters, François M; Çakır, Deniz

2018-07-20

There is an increasing need to understand interfaces between two-dimensional materials to realize an energy efficient boundary with low contact resistance and small heat dissipation. In this respect, we investigated the impact of charge and substitutional atom doping on the electronic transport properties of the hybrid metallic-semiconducting lateral junctions, formed between metallic (1T and 1T d ) and semiconducting (1H) phases of MoS 2 by means of first-principles and non-equilibrium Green function formalism based calculations. Our results clearly revealed the strong influence of the type of interface and crystallographic orientation of the metallic phase on the transport properties of these systems. The Schottky barrier height, which is the dominant mechanism for contact resistance, was found to be as large as 0.63 eV and 1.19 eV for holes and electrons, respectively. We found that armchair interfaces are more conductive as compared to zigzag termination due to the presence of the metallic Mo zigzag chains that are directed along the transport direction. In order to manipulate these barrier heights we investigated the influence of electron doping of the metallic part (i.e. 1T d -MoS 2 ). We observed that the Fermi level of the hybrid system moves towards the conduction band of semiconducting 1H-MoS 2 due to filling of 4d-orbital of metallic MoS 2 , and thus the Schottky barrier for electrons decreases considerably. Besides electron doping, we also investigated the effect of substitutional doping of metallic MoS 2 by replacing Mo atoms with either Re or Ta. Due to its valency, Re (Ta) behaves as a donor (acceptor) and reduces the Schottky barrier for electrons (holes). Since Re and Ta based transition metal dichalcogenides crystallize in either the 1T d or 1T phase, substitutional doping with these atom favors the stabilization of the 1T d phase of MoS 2 . Co-doping of hybrid structure results in an electronic structure, which facilities easy dissociation of excitons created in the 1H part.

Pillared graphene on the basis of zigzag carbon nanotubes for adsorption in medicine: mechanical properties

NASA Astrophysics Data System (ADS)

Kolesnikova, Anna S.; Mazepa, Margarita M.

2018-02-01

In nowadays the nanoscale materials are actively used in medicine, based on the properties of adsorption. One of the main problems of this field of medicine is the increase in specific surface of sorbent. We proposed to use carbon composites consisting of an extended in its directions graphene sheet with attached to it by chemical bonds zigzag carbon nanotubes (CNT). This paper presents the results of a theoretical study of the mechanical properties of graphene based on the CNT zigzag depending on the geometric dimensions of the composite (length and diameter of CNTs).

Fabrication and Optimal Design of Biodegradable Polymeric Stents for Aneurysms Treatments

PubMed Central

Han, Xue; Wu, Xia; Kelly, Michael; Chen, Xiongbiao

2017-01-01

An aneurysm is a balloon-like bulge in the wall of blood vessels, occurring in major arteries of the heart and brain. Biodegradable polymeric stent-assisted coiling is expected to be the ideal treatment of wide-neck complex aneurysms. This paper presents the development of methods to fabricate and optimally design biodegradable polymeric stents for aneurysms treatment. Firstly, a dispensing-based rapid prototyping (DBRP) system was developed to fabricate coil and zigzag structures of biodegradable polymeric stents. Then, compression testing was carried out to characterize the radial deformation of the stents fabricated with the coil or zigzag structure. The results illustrated the stent with a zigzag structure has a stronger radial stiffness than the one with a coil structure. On this basis, the stent with a zigzag structure was chosen for the development of a finite element model for simulating the real compression tests. The result showed the finite element model of biodegradable polymeric stents is acceptable within a range of radial deformation around 20%. Furthermore, the optimization of the zigzag structure was performed with ANSYS DesignXplorer, and the results indicated that the total deformation could be decreased by 35.7% by optimizing the structure parameters, which would represent a significant advance of the radial stiffness of biodegradable polymeric stents. PMID:28264515

Synthesis and characterization of silver nanowires with zigzag morphology in N, N-dimethylformamide

NASA Astrophysics Data System (ADS)

He, Xin; Zhao, Xiujian; Chen, Yunxia; Feng, Jinyang; Sun, Zhenya

2007-08-01

Zigzag silver nanowires with a uniform diameter of 20±5 nm were prepared by reducing silver nitrate (AgNO 3) with N, N-dimethylformamide (DMF) in the presence of tetrabutyl titanate (TBT) and acetylacetone (AcAc) at 373 K for 18 h. X-ray and selected area electron diffraction (XRD and SAED) patterns reveal that the prepared product is made of pure silver with face centered cubic structure. Transmission electron microscopy (TEM) investigations suggest that the amount of silver nanowires is enhanced with increase in reaction time, and the end-to-end assemblies of silver nanorods are observed during the reaction process. After 18 h reaction, silver nanowires with zigzag morphology are obtained. In this paper, a possible growth process of silver nanowires with this interesting shape is described. Silver nanoparticles with small sizes were obtained by reducing Ag + ions with DMF, providing seeds for homogeneous growth of silver nanorods. With the extending reaction time, the synthesized silver nanorods were connected in an end-to-end manner, and the interface between the connections of two nanorods gradually disappeared. The final product shows zigzag morphology with various angles. The angles between two connecting straight parts of zigzag nanowires exhibit an alterable range of 74-151°. These silver nanowires show tremendous potential applications in future nanoscale electronic circuits.

The Effect of Acceleration Sprint and Zig-zag Drill Combination to Increase Students’ Speed and Agility

NASA Astrophysics Data System (ADS)

Bana, O.; Mintarto, E.; Kusnanik, N. W.

2018-01-01

The purpose of this research is to analyze the following factors: (1) how far the effect of exercise acceleration sprint on the speed and agility (2) how much influence the zig-zag drill combination to the speed and agility (3) and is there any difference between the effects of exercise acceleration sprint and practice zig-zag drill combination of the speed and agility. This research is quantitative with quasi-experimental approach. The design of this study is matching only design.This study was conducted on 33 male students who take part in extracurricular and divided into 3 groups with 11 students in each group. Group 1 was given training of acceleration sprint, group 2 was given zig-zag training combination drills of conventional and exercises for group 3, for 8 weeks. The data collection was using sprint 30 meter to test the speed and agility t-test to test agility. Data were analyzed using t-test and analysis of variance. The conclusion of the research is (1) there is a significant effect of exercise acceleration sprint for the speed and agility, (2) there is a significant influence combination zig-zag drills, on speed and agility (3) and exercise acceleration sprint have more effect on the speed and agility.

K2Ho(PO4)(WO4)

PubMed Central

Terebilenko, Katherina V.; Zatovsky, Igor V.; Baumer, Vyacheslav N.; Slobodyanik, Nikolay S.; Shishkin, Oleg V.

2008-01-01

A new compound, dipotassium holmium(III) phosphate(V) tungstate(VI), K2Ho(PO4)(WO4), has been obtained during investigation of the K2O–P2O5–WO3–HoF3 phase system using the flux technique. The compound is isotypic with K2Bi(PO4)(WO4). Its framework structure consists of flat ∞ 2[HoPO4] layers parallel to (100) that are made up of ∞ 1[HoO8] zigzag chains inter­linked via slightly distorted PO4 tetra­hedra. WO4 tetra­hedra are attached above and below these layers, leaving space for the K+ counter-cations. The HoO8, PO4 and WO4 units exhibit 2 symmetry. PMID:21580811

Origin of band gap bowing in dilute GaAs1-xNx and GaP1-xNx alloys: A real-space view

NASA Astrophysics Data System (ADS)

Virkkala, Ville; Havu, Ville; Tuomisto, Filip; Puska, Martti J.

2013-07-01

The origin of the band gap bowing in dilute nitrogen doped gallium based III-V semiconductors is largely debated. In this paper we show the dilute GaAs1-xNx and GaP1-xNx as representative examples that the nitrogen-induced states close to the conduction band minimum propagate along the zigzag chains on the {110} planes. Thereby states originating from different N atoms interact with each other resulting in broadening of the nitrogen-induced states which narrows the band gap. Our modeling based on ab initio theoretical calculations explains the experimentally observed N concentration dependent band gap narrowing both qualitatively and quantitatively.

Quality evaluation of extracted ion chromatograms and chromatographic peaks in liquid chromatography/mass spectrometry-based metabolomics data

PubMed Central

2014-01-01

Background Extracted ion chromatogram (EIC) extraction and chromatographic peak detection are two important processing procedures in liquid chromatography/mass spectrometry (LC/MS)-based metabolomics data analysis. Most commonly, the LC/MS technique employs electrospray ionization as the ionization method. The EICs from LC/MS data are often noisy and contain high background signals. Furthermore, the chromatographic peak quality varies with respect to its location in the chromatogram and most peaks have zigzag shapes. Therefore, there is a critical need to develop effective metrics for quality evaluation of EICs and chromatographic peaks in LC/MS based metabolomics data analysis. Results We investigated a comprehensive set of potential quality evaluation metrics for extracted EICs and detected chromatographic peaks. Specifically, for EIC quality evaluation, we analyzed the mass chromatographic quality index (MCQ index) and propose a novel quality evaluation metric, the EIC-related global zigzag index, which is based on an EIC's first order derivatives. For chromatographic peak quality evaluation, we analyzed and compared six metrics: sharpness, Gaussian similarity, signal-to-noise ratio, peak significance level, triangle peak area similarity ratio and the local peak-related local zigzag index. Conclusions Although the MCQ index is suited for selecting and aligning analyte components, it cannot fairly evaluate EICs with high background signals or those containing only a single peak. Our proposed EIC related global zigzag index is robust enough to evaluate EIC qualities in both scenarios. Of the six peak quality evaluation metrics, the sharpness, peak significance level, and zigzag index outperform the others due to the zigzag nature of LC/MS chromatographic peaks. Furthermore, using several peak quality metrics in combination is more efficient than individual metrics in peak quality evaluation. PMID:25350128

Quality evaluation of extracted ion chromatograms and chromatographic peaks in liquid chromatography/mass spectrometry-based metabolomics data.

PubMed

Zhang, Wenchao; Zhao, Patrick X

2014-01-01

Extracted ion chromatogram (EIC) extraction and chromatographic peak detection are two important processing procedures in liquid chromatography/mass spectrometry (LC/MS)-based metabolomics data analysis. Most commonly, the LC/MS technique employs electrospray ionization as the ionization method. The EICs from LC/MS data are often noisy and contain high background signals. Furthermore, the chromatographic peak quality varies with respect to its location in the chromatogram and most peaks have zigzag shapes. Therefore, there is a critical need to develop effective metrics for quality evaluation of EICs and chromatographic peaks in LC/MS based metabolomics data analysis. We investigated a comprehensive set of potential quality evaluation metrics for extracted EICs and detected chromatographic peaks. Specifically, for EIC quality evaluation, we analyzed the mass chromatographic quality index (MCQ index) and propose a novel quality evaluation metric, the EIC-related global zigzag index, which is based on an EIC's first order derivatives. For chromatographic peak quality evaluation, we analyzed and compared six metrics: sharpness, Gaussian similarity, signal-to-noise ratio, peak significance level, triangle peak area similarity ratio and the local peak-related local zigzag index. Although the MCQ index is suited for selecting and aligning analyte components, it cannot fairly evaluate EICs with high background signals or those containing only a single peak. Our proposed EIC related global zigzag index is robust enough to evaluate EIC qualities in both scenarios. Of the six peak quality evaluation metrics, the sharpness, peak significance level, and zigzag index outperform the others due to the zigzag nature of LC/MS chromatographic peaks. Furthermore, using several peak quality metrics in combination is more efficient than individual metrics in peak quality evaluation.

A series of silver(I) coordination polymers with saccarinate and flexible aliphatic diamines

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

Yeşilel, Okan Zafer, E-mail: yesilel@ogu.edu.tr; Karamahmut, Bingül; Semerci, Fatih

A series of Ag(I) complexes with aliphatic diamines having a different chain length (NH{sub 2}-(CH{sub 2}){sub n}-NH{sub 2}, n=4–9), with the formulas, [Ag(μ-sac)(μ-db){sub 0.5}]{sub n} (1), ([Ag{sub 4}(sac){sub 4}(μ-dp){sub 2}]·4H{sub 2}O){sub n} (2){sub ,} ([Ag{sub 2}(sac){sub 2}(μ-dz)]·2H{sub 2}O){sub n} (3), ([Ag{sub 2}(sac){sub 2}(μ-dh)]·H{sub 2}O){sub n} (4), ([Ag{sub 2}(sac){sub 2}(μ-do)]·H{sub 2}O){sub n} (5a), [Ag{sub 2}(sac){sub 2}(μ-do){sub 2}] (5b) and [Ag{sub 4}(sac){sub 4}(μ-dn){sub 2}]·2H{sub 2}O (6), where sac=saccharinate, db=1,4-diaminobutane, dp=1,5-diaminopentane, dz=1,6-diaminohexane, dh=1,7-diaminoheptane, do=1,8-diaminooctane and dn=1,9-diaminononane, were synthesized and characterized by elemental analysis, infrared spectra and single-crystal X-ray diffraction analysis. In 1, the sac ligand bridges adjacent Ag(I) ions through the nitrogen andmore » carbonyl oxygen atoms to form eight-membered bimetallic rings with the Ag···Ag distance being 3.897 Å, which are linked by db ligands to give a 1D zigzag chain. The complexes 2–5a consist of a one-dimensional (1D) linear cationic chains and discrete mononuclear anions. The discreet complex units are further connected by ligand unsupported argentophilic interactions. In 6, the dn ligands bridge adjacent silver centers to form 24-membered macrometallacyclic rings, which are further connected to the anionic [Ag(sac){sub 2}]{sup -} units by argentophilic Ag1···Ag2 interactions to form a tetranuclear structure. The adjacent dinuclear units are further linked together through ligand-unsupported argentophilic Ag···Ag (3.207(1) Å) interactions, generating a one-dimensional linear chain. The most striking feature of complexes is the presence of the rare intermolecular C-H···Ag interactions. In 5b, the do ligand bridges two Ag(I) ions to form a dinuclear with a 22-membered macrometallacyclic ring. Furthermore, biological activities, luminescence properties and thermal analysis (TG/DTA) of the complexes were investigated. - Graphical abstract: In this study, six new silver coordination compounds were synthesized by using saccharinate and flexible aliphatic diamine derivatives. All the compounds were characterized by elemental analysis, IR and single-crystal X-ray analysis. TG/DTA. Furthermore, biological activities, luminescence properties and thermal analysis (TG/DTA) of the complexes have been investigated. Complexes 1–5a and 6 were synthesized with the same reactant ratio and room temperature by using a mixture of AgNO{sub 3}, sac and different length diamine derivatives. The complex 5b is also synthesized was similar to that of 1 at 80 °C. In the complexes, the diamine derivatives ligands show bis(bridging) coordination mode. The sac ligand exhibits a µ-bridging coordination mode in 1 and N-donor monodentate coordination mode in 2–6. Complexes 1–5 exhibit 1D chain structure while complex 6 are tetranuclear structure. In the crystal packing of complexes, 3D supramolecular frameworks are formed via C-H···Ag, Ag···π and Ag···Ag interactions.« less

Synthesis, crystal structure, and vibrational spectroscopic and UV-visible studies of Cs{sub 2}MnP{sub 2}O{sub 7}

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

Kaoua, Saida; Krimi, Saida; Pechev, Stanislav

2013-02-15

A new member of the A{sub 2}MP{sub 2}O{sub 7} diphosphate family, Cs{sub 2}MnP{sub 2}O{sub 7}, has been synthesized and structurally characterized. The crystal structure was determined by single crystal X-Ray diffraction. Cs{sub 2}MnP{sub 2}O{sub 7} crystallizes in the orthorhombic system, space group Pnma ( Music-Sharp-Sign 62), with the unit cell parameters a=16.3398(3), b=5.3872(1), c=9.8872(2) A, Z=4 and V=870.33(3) A{sup 3}. The structure parameters were refined to a final R{sub 1}/wR{sub 2}=0.0194/0.0441 for 1650 observed reflections. The 2D framework of Cs{sub 2}MnP{sub 2}O{sub 7} structure consists of P{sub 2}O{sub 7} and MnO{sub 5} units. The corner-shared MnO{sub 5} and P{sub 2}O{submore » 7} units are alternately arranged along the b axis to form [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains. These chains are interconnected by an oxygen atom to form sheets parallel to the (b, c) plane. The cesium atoms are located between the sheets in 9- and 10-fold coordinated sites. The infrared and Raman vibrational spectra have been investigated. A factor group analysis leads to the determination of internal modes of (P{sub 2}O{sub 7}) groups. UV-visible spectrum consists of weak bands, between 340 and 700 nm, assigned to the forbidden d-d transitions of Mn{sup 2+} ion, and of a strong band around 250 nm, attributed to the O--Mn charge transfer. - Graphical abstract: Structure of Cs{sub 2}MnP{sub 2}O{sub 7}: The 2D structure of Cs{sub 2}MnP{sub 2}O{sub 7} is built from P{sub 2}O{sub 7} diphosphate groups and MnO{sub 5} square pyramids which share corners and form [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains along b axis. These chains are interconnected by an oxygen atom to form wavy (MnP{sub 2}O{sub 7}){sup 2-} sheets parallel to the (b, c) plane. The cesium ions are located between these sheets in the inter-layers space, in zigzag positions. Highlights: Black-Right-Pointing-Pointer A new diphosphate, Cs{sub 2}MnP{sub 2}O{sub 7}, has been synthesized and structurally characterized. Black-Right-Pointing-Pointer The structure consists of a 2D framework built up from (MnP{sub 2}O{sub 7}) sheets. Black-Right-Pointing-Pointer The sheets consist of [(MnO)P{sub 2}O{sub 7}]{sub {infinity}} chains formed by P{sub 2}O{sub 7} units and MnO{sub 5} square pyramids. Black-Right-Pointing-Pointer A factor group analysis leads to the determination of internal modes of (P{sub 2}O{sub 7}) groups. Black-Right-Pointing-Pointer UV-visible spectrum consists bands assigned to d-d transitions of Mn{sup 2+} ion and to O--Mn CT.« less

A one-dimensional statistical mechanics model for nucleosome positioning on genomic DNA.

PubMed

Tesoro, S; Ali, I; Morozov, A N; Sulaiman, N; Marenduzzo, D

2016-02-12

The first level of folding of DNA in eukaryotes is provided by the so-called '10 nm chromatin fibre', where DNA wraps around histone proteins (∼10 nm in size) to form nucleosomes, which go on to create a zig-zagging bead-on-a-string structure. In this work we present a one-dimensional statistical mechanics model to study nucleosome positioning within one such 10 nm fibre. We focus on the case of genomic sheep DNA, and we start from effective potentials valid at infinite dilution and determined from high-resolution in vitro salt dialysis experiments. We study positioning within a polynucleosome chain, and compare the results for genomic DNA to that obtained in the simplest case of homogeneous DNA, where the problem can be mapped to a Tonks gas. First, we consider the simple, analytically solvable, case where nucleosomes are assumed to be point-like. Then, we perform numerical simulations to gauge the effect of their finite size on the nucleosomal distribution probabilities. Finally we compare nucleosome distributions and simulated nuclease digestion patterns for the two cases (homogeneous and sheep DNA), thereby providing testable predictions of the effect of sequence on experimentally observable quantities in experiments on polynucleosome chromatin fibres reconstituted in vitro.

Structural diversity and electronic properties in potassium silicides

NASA Astrophysics Data System (ADS)

Hao, Chun-Mei; Li, Yunguo; Huang, Hong-Mei; Li, Yan-Ling

2018-05-01

Stable potassium silicides in the complete compositional landscape were systematically explored up to 30 GPa using the variable-composition evolutionary structure prediction method. The results show that K4Si, K3Si, K5Si2, K2Si, K3Si2, KSi, KSi2, KSi3, and K8Si46 have their stability fields in the phase diagram. The spatial dimensional diversity of polymerized silicon atoms (0D "isolated" anion, dimer, Si4 group, 1D zigzag chain, 2D layer, and 3D network) under the potassium sublattice was uncovered as silicon content increases. Especially, the 2D layered silicon presents interestingly a variety of shapes, such as the "4 + 6" ring, "4 + 8"ring, and 8-membered ring. K-Si bonding exhibits a mixed covalency and ionicity, while Si-Si bonding is always of covalent character. Semiconductivity or metallicity mainly depends on the form of sublattices and K:Si ratio, which allows us to find more semiconductors in the Si-rich side when closed-shell K cations are encompassed by polymerized Si. The semiconducting silicides present strong absorption in the infrared and visible light range. These findings open up the avenue for experimental synthesis of alkali metal-IVA compounds and potential applications as battery electrode materials or photoelectric materials.

First principles absorption spectra of Cu{sub n} (n = 2 - 20) clusters.

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

Baishya, K.; Idrobo, J. C.; Ogut, S.

2011-06-17

Optical absorption spectra for the computed ground state structures of copper clusters (Cu{sub n}, n = 2-20) are investigated from first principles using time-dependent density functional theory in the adiabatic local density approximation (TDLDA). The results are compared with available experimental data, existing calculations, and with results from our previous computations on silver and gold clusters. The main effects of d electrons on the absorption spectra, quenching the oscillator strengths, and getting directly involved in low-energy excitations increase in going from Ag{sub n} to Au{sub n} to Cu{sub n} due to the increase in the hybridization of the occupied, yetmore » shallow, d orbitals and the partially occupied s orbitals. We predict that while Cu nanoparticles of spherical or moderately ellipsoidal shape do not exhibit Mie (surface plasmon) resonances, unlike the case for Ag and Au, extremely prolate or oblate Cu nanoparticles with eccentricities near unity should give rise to Mie resonances in the lower end of the visible range and in the infrared. This tunable resonance predicted by the classical Mie-Gans theory is reproduced with remarkable accuracy by our TDLDA computations on hypothetical Cu clusters in the form of zigzag chains with as few as 6 to 20 atoms.« less

Electronic transport in disordered MoS2 nanoribbons

NASA Astrophysics Data System (ADS)

Ridolfi, Emilia; Lima, Leandro R. F.; Mucciolo, Eduardo R.; Lewenkopf, Caio H.

2017-01-01

We study the electronic structure and transport properties of zigzag and armchair monolayer molybdenum disulfide nanoribbons using an 11-band tight-binding model that accurately reproduces the material's bulk band structure near the band gap. We study the electronic properties of pristine zigzag and armchair nanoribbons, paying particular attention to the edges states that appear within the MoS2 bulk gap. By analyzing both their orbital composition and their local density of states, we find that in zigzag-terminated nanoribbons these states can be localized at a single edge for certain energies independent of the nanoribbon width. We also study the effects of disorder in these systems using the recursive Green's function technique. We show that for the zigzag nanoribbons, the conductance due to the edge states is strongly suppressed by short-range disorder such as vacancies. In contrast, the local density of states still shows edge localization. We also show that long-range disorder has a small effect on the transport properties of nanoribbons within the bulk gap energy window.

Refined Zigzag Theory for Laminated Composite and Sandwich Plates

NASA Technical Reports Server (NTRS)

Tessler, Alexander; DiSciuva, Marco; Gherlone, Marco

2009-01-01

A refined zigzag theory is presented for laminated-composite and sandwich plates that includes the kinematics of first-order shear deformation theory as its baseline. The theory is variationally consistent and is derived from the virtual work principle. Novel piecewise-linear zigzag functions that provide a more realistic representation of the deformation states of transverse-shear-flexible plates than other similar theories are used. The formulation does not enforce full continuity of the transverse shear stresses across the plate s thickness, yet is robust. Transverse-shear correction factors are not required to yield accurate results. The theory is devoid of the shortcomings inherent in the previous zigzag theories including shear-force inconsistency and difficulties in simulating clamped boundary conditions, which have greatly limited the accuracy of these theories. This new theory requires only C(sup 0)-continuous kinematic approximations and is perfectly suited for developing computationally efficient finite elements. The theory should be useful for obtaining relatively efficient, accurate estimates of structural response needed to design high-performance load-bearing aerospace structures.

Coordinating compass-based and nest-based flight directions during bumblebee learning and return flights.

PubMed

Collett, Thomas S; de Ibarra, Natalie Hempel; Riabinina, Olena; Philippides, Andrew

2013-03-15

Bumblebees tend to face their nest over a limited range of compass directions when learning the nest's location on departure and finding it on their approach after foraging. They thus obtain similar views of the nest and its surroundings on their learning and return flights. How do bees coordinate their flights relative to nest-based and compass-based reference frames to get such similar views? We show, first, that learning and return flights contain straight segments that are directed along particular compass bearings, which are independent of the orientation of a bee's body. Bees are thus free within limits to adjust their viewing direction relative to the nest, without disturbing flight direction. Second, we examine the coordination of nest-based and compass-based control during likely information gathering segments of these flights: loops during learning flights and zigzags on return flights. We find that bees tend to start a loop or zigzag when flying within a restricted range of compass directions and to fly towards the nest and face it after a fixed change in compass direction, without continuous interactions between their nest-based and compass-based directions of flight. A preferred trajectory of compass-based flight over the course of a motif, combined with the tendency of the bees to keep their body oriented towards the nest automatically narrows the range of compass directions over which bees view the nest. Additionally, the absence of interactions between the two reference frames allows loops and zigzags to have a stereotyped form that can generate informative visual feedback.

The structures and electronic properties of zigzag silicene nanoribbons with periodically embedded with four- and eight-membered rings

NASA Astrophysics Data System (ADS)

Tan, Guiping; Lu, Junzhe; Zhu, Hengjiang; Li, Fangfang; Ma, Miaomiao; Wang, Xiaoning

2018-07-01

Using density functional theory (DFT), we have studied the structure of a zigzag silicene nanoribbons (SiNRs) with periodically embedded with four- and eight-membered rings, and studied their electronic properties by calculating its band structures and density of states (DOS). The results showed that the zigzag SiNRs have a sp2 hybridization, in addition, the band gap gradually decreased with the increase of the width by layer, and gradually changed from semiconductor properties to metal properties. The existence of vacancy defects increased the band gap and energies, but their positions could not change the structure and the electronic properties.

Compressive buckling of black phosphorene nanotubes: an atomistic study

NASA Astrophysics Data System (ADS)

Nguyen, Van-Trang; Le, Minh-Quy

2018-04-01

We investigate through molecular dynamics finite element method with Stillinger-Weber potential the uniaxial compression of armchair and zigzag black phosphorene nanotubes. We focus especially on the effects of the tube’s diameter with fixed length-diameter ratio, effects of the tube’s length for a pair of armchair and zigzag tubes of equal diameters, and effects of the tube’s diameter with fixed lengths. Their Young’s modulus, critical compressive stress and critical compressive strain are studied and discussed for these 3 case studies. Compressive buckling was clearly observed in the armchair nanotubes. Local bond breaking near the boundary occurred in the zigzag ones under compression.

Electronic structure and electric polarity of edge-functionalized graphene nanoribbons

NASA Astrophysics Data System (ADS)

Taira, Remi; Yamanaka, Ayaka; Okada, Susumu

2017-08-01

On the basis of the density functional theory combined with the effective screening medium method, we studied the electronic structure of graphene nanoribbons with zigzag edges, which are terminated by functional groups. The work function of the nanoribbons is sensitive to the functional groups. The edge state inherent in the zigzag edges is robust against edge functionalization. OH termination causes the injection of electrons into the nearly free electron states situated alongside the nanoribbons, resulting in the formation of free electron channels outside the nanoribbons. We also demonstrated that the polarity of zigzag graphene nanoribbons is controllable by the asymmetrical functionalization of their edges.

In Situ Nondestructive Analysis of Kalanchoe pinnata Leaf Surface Structure by Polarization-Modulation Infrared Reflection-Absorption Spectroscopy.

PubMed

Hama, Tetsuya; Kouchi, Akira; Watanabe, Naoki; Enami, Shinichi; Shimoaka, Takafumi; Hasegawa, Takeshi

2017-12-14

The outermost surface of the leaves of land plants is covered with a lipid membrane called the cuticle that protects against various stress factors. Probing the molecular-level structure of the intact cuticle is highly desirable for understanding its multifunctional properties. We report the in situ characterization of the surface structure of Kalanchoe pinnata leaves using polarization-modulation infrared reflection-absorption spectroscopy (PM-IRRAS). Without sample pretreatment, PM-IRRAS measures the IR spectra of the leaf cuticle of a potted K. pinnata plant. The peak position of the CH 2 -related modes shows that the cuticular waxes on the leaf surface are mainly crystalline, and the alkyl chains are highly packed in an all-trans zigzag conformation. The surface selection rule of PM-IRRAS revealed the average orientation of the cuticular molecules, as indicated by the positive and negative signals of the IR peaks. This unique property of PM-IRRAS revealed that the alkyl chains of the waxes and the main chains of polysaccharides are oriented almost perpendicular to the leaf surface. The nondestructive, background-free, and environmental gas-free nature of PM-IRRAS allows the structure and chemistry of the leaf cuticle to be studied directly in its native environment.

Lithium amide (LiNH2) under pressure.

PubMed

Prasad, Dasari L V K; Ashcroft, N W; Hoffmann, Roald

2012-10-11

Static high pressure lithium amide (LiNH(2)) crystal structures are predicted using evolutionary structure search methodologies and intuitive approaches. In the process, we explore the relationship of the structure and properties of solid LiNH(2) to its molecular monomer and dimer, as well as its valence-isoelectronic crystalline phases of methane, water, and ammonia all under pressure. A NaNH(2) (Fddd) structure type is found to be competitive for the ground state of LiNH(2) above 6 GPa with the P = 1 atm I4[overline] phase. Three novel phases emerge at 11 (P4[overline]2(1)m), 13 (P4(2)/ncm), and 46 GPa (P2(1)2(1)2(1)), still containing molecular amide anions, which begin to form N-H···N hydrogen bonds. The P2(1)2(1)2(1) phase remains stable over a wide pressure range. This phase and another Pmc2(1) structure found at 280 GPa have infinite ···(H)N···H···N(H)···H polymeric zigzag chains comprising symmetric N···H···N hydrogen bonds with one NH bond kept out of the chain, an interesting general feature found in many of our high pressure (>280 GPa) LiNH(2) structures, with analogies in high pressure H(2)O-ices. All the predicted low enthalpy LiNH(2) phases are calculated to be enthalpically stable with respect to their elements but resist metallization with increasing pressure up to several TPa. The possibility of Li sublattice melting in the intermediate pressure range structures is raised.

Crystal structure, spectral and thermal properties of 1,2-bis[2-(4,4,4-trifluoro-1-hydroxy-3-oxobut-1-enyl)phenoxy]-ethane and luminescent properties of its complexes with Al(III) and Eu(III)

NASA Astrophysics Data System (ADS)

Khamidullina, Liliya A.; Obydennov, Konstantin L.; Slepukhin, Pavel A.; Puzyrev, Igor S.

2016-12-01

Describing the crystal structure, packing, FT-IR, UV-Vis and NMR spectra and thermal properties of new polydentate O-ligand based on aryl-β-diketone moieties connected by ethylene glycol spacer is the subject of this article. The results of IR, UV-Vis and 1H NMR spectroscopy as well X-ray crystallography of 1,2-bis[2-(4,4,4-trifluoro-1-hydroxy-3-oxobut-1-enyl)phenoxy]-ethane (BTFPE) indicate that the compound exists in solution and in solid as enol. The crystal structure analysis shows that BTFPE has C2/c group of the monoclinic system. Typical S(6) intramolecular hydrogen bond occurs in each 1,3-diketo moiety. This bond is asymmetric and the H atom is closest to the O atom adjacent to the phenyl ring. The packing of the crystal is sustained by numerous Csbnd H⋯O, Osbnd H⋯F, Csbnd H⋯F interactions. In the crystal, supramolecular zig-zag chains are formed along the c-axis. Short contacts interconnect the molecules into a two-dimensional layered structure wherein each molecule is node between chains. According to the thermal investigation this compound is stable up to 200 °C in air atmosphere, above this temperature it decomposes. Photoluminescent properties of aluminum(III) and europium(III) complexes of BTFPE were evaluated in chloroform solution and in the solid state. Aluminum complex of BTFPE shows blue luminescence with maximum at 445 nm. Europium complex exhibits intense red color luminescence at 613 nm from central Eu(III) ion through the excitation of the ligand.

Lanthanide coordination polymers: Synthesis, diverse structure and luminescence properties

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

Song, Xue-Qin, E-mail: songxq@mail.lzjtu.cn; Lei, Yao-Kun; Wang, Xiao-Run

2014-10-15

The new semirigid exo-bidentate ligand incorporating furfurysalicylamide terminal groups, namely, 1,4-bis([(2′-furfurylaminoformyl)phenoxyl]methyl)-2,5-bismethylbenzene (L) was synthesized and used as building blocks for constructing lanthanide coordination polymers with luminescent properties. The series of lanthanide nitrate complexes have been characterized by elemental analysis, IR spectroscopy, and X-ray diffraction analysis. The semirigid ligand L, as a bridging ligand, reacts with lanthanide nitrates forming three distinct structure types: chiral noninterpenetrated two-dimensional (2D) honeycomblike (6,3) (hcb, Schläfli symbol 6{sup 3}, vertex symbol 6 6 6) topological network as type I, 1D zigzag chain as type II and 1D trapezoid ladder-like chain as type III. The structural diversitiesmore » indicate that lanthanide contraction effect played significant roles in the structural self-assembled process. The luminescent properties of Eu{sup III}, Tb{sup III} and Dy{sup III} complexes are discussed in detail. Due to the good match between the lowest triplet state of the ligand and the resonant energy level of the lanthanide ion, the lanthanide ions in Eu{sup III}, Tb{sup III} and Dy{sup III} complexes can be efficiently sensitized by the ligand. - Graphical abstract: We present herein six lanthanide coordination polymers of a new semirigid exo-bidentate ligand which not only display diverse structures but also possess strong luminescence properties. - Highlights: • We present lanthanide coordination polymers of a new semirigid exo-bidentate ligand. • The lanthanide coordination polymers exhibit diverse structures. • The luminescent properties of Tb{sup III}, Eu{sup III} and Dy{sup III} complexes are discussed in detail.« less

Metal-organic framework assembled from erbium and a tetrapodal polyphosphonic acid organic linker.

PubMed

Mendes, Ricardo F; Firmino, Ana D G; Tomé, João P C; Almeida Paz, Filipe A

2018-06-01

A three-dimensional metal-organic framework (MOF), poly[[μ 6 -5'-pentahydrogen [1,1'-biphenyl]-3,3',5,5'-tetrayltetrakis(phosphonato)]erbium(III)] 2.5-hydrate], formulated as [Er(C 12 H 11 O 12 P 4 )]·2.5H 2 O or [Er(H 5 btp)]·2.5H 2 O (I) and isotypical with a Y 3+ -based MOF reported previously by our research group [Firmino et al. (2017b). Inorg. Chem. 56, 1193-1208], was constructed based solely on Er 3+ and on the polyphosphonic organic linker [1,1'-biphenyl]-3,3',5,5'-tetrakis(phosphonic acid) (H 8 btp). The present work describes our efforts to introduce lanthanide cations into the flexible network, demonstrating that, on the one hand, the compound can be obtained using three distinct experimental methods, i.e. hydro(solvo)thermal (Hy), microwave-assisted (MW) and one-pot (Op), and, on the other hand, that crystallite size can be approximately fine-tuned according to the method employed. MOF I contains hexacoordinated Er 3+ cations which are distributed in a zigzag inorganic chain running parallel to the [100] direction of the unit cell. The chains are, in turn, bridged by the anionic organic linker to form a three-dimensional 6,6-connected binodal network. This connectivity leads to the existence of one-dimensional channels (also running parallel to the [100] direction) filled with disordered and partially occupied water molecules of crystalization which are engaged in O-H...O hydrogen-bonding interactions with the [Er(H 5 btp)] framework. Additional weak π-π interactions [intercentroid distance = 3.957 (7) Å] exist between aromatic rings, which help to maintain the structural integrity of the network.

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

Marana, Naiara L.; Albuquerque, Anderson R.; La Porta, Felipe A.

Periodic density functional theory calculations with the B3LYP hybrid functional and all-electron Gaussian basis set were performed to simulate the structural and electronic properties as well as the strain and formation energies of single-walled ZnO nanotubes (SWZnONTs) and Carbon nanotubes (SWCNTs) with different chiralities as functions of their diameters. For all SWZnONTs, the band gap, strain energy, and formation energy converge to ~4.5 eV, 0.0 eV/atom, and 0.40 eV/atom, respectively. This result suggests that the nanotubes are formed more easily from the surface than from the bulk. For SWCNTs, the strain energy is always positive, while the formation energy ismore » negative for armchair and zigzag nanotubes, therefore suggesting that these types of nanotubes can be preferentially formed from the bulk. The electronic properties of SWCNTs depend on the chirality; all armchair nanotubes are metallic, while zigzag and chiral nanotubes can be metallic or semiconducting, depending on the n and m vectors. - Graphical abstract: DFT/B3LYP were performed to simulate the structural and electronic properties as well as the strain and formation energies of SWZnONTs and SWCNTs with different chiralities as functions of their diameters. - Highlights: • The energies of SWZnONTs converge for chirality with diameters up 20 Å. • SWCNTs electronic properties depend on the chirality. • The properties of SWZnONTs are very similar to those of monolayer surface.« less

Magnonic quantum spin Hall state in the zigzag and stripe phases of the antiferromagnetic honeycomb lattice

NASA Astrophysics Data System (ADS)

Lee, Ki Hoon; Chung, Suk Bum; Park, Kisoo; Park, Je-Geun

2018-05-01

We investigated the topological property of magnon bands in the collinear magnetic orders of zigzag and stripe phases for the antiferromagnetic honeycomb lattice and identified Berry curvature and symmetry constraints on the magnon band structure. Different symmetries of both zigzag and stripe phases lead to different topological properties, in particular, the magnon bands of the stripe phase being disentangled with a finite Dzyaloshinskii-Moriya (DM) term with nonzero spin Chern number. This is corroborated by calculating the spin Nernst effect. Our study establishes the existence of a nontrivial magnon band topology for all observed collinear antiferromagnetic honeycomb lattices in the presence of the DM term.

Thermodynamics and vibrational study of hydrogenated carbon nanotubes: A DFT study

NASA Astrophysics Data System (ADS)

Khalil, Rana M. Arif; Hussain, Fayyaz; Rana, Anwar Manzoor; Imran, Muhammad

2018-02-01

Thermodynamic stability of the hydrogenated carbon nanotubes has been explored in the chemisorption limit. Statistical physics and density functional theory calculations have been used to predict hydrogen release temperatures at standard pressure in zigzag and armchair carbon nanotubes. It is found that hydrogen release temperatures decrease with increase in diameters of hydrogenated zigzag carbon nanotubes (CNTs) but opposite trend is noted in armchair CNTs at standard pressure of 1 bar. The smaller diameter hydrogenated zigzag CNTs have large values of hydrogen release temperature due to the stability of Csbnd H bonds. The vibrational density of states for hydrogenated carbon nanotubes have been calculated to confirm the Csbnd H stretching mode caused by sp3 hybridization.

A New, Simple and Versatile Strategy for the Synthesis of Short Segments of Zigzag-Type Carbon Nanotubes.

PubMed

André, Etienne; Boutonnet, Baptiste; Charles, Pauline; Martini, Cyril; Aguiar-Hualde, Juan-Manuel; Latil, Sylvain; Guérineau, Vincent; Hammad, Karim; Ray, Priyanka; Guillot, Régis; Huc, Vincent

2016-02-24

Short segments of zigzag single-walled carbon nanotubes (SWCNTs) were obtained from a calixarene scaffold by using a completely new, simple and expedited strategy that allowed fine-tuning of their diameters. This new approach also allows for functionalised short segments of zigzag SWCNTs to be obtained; a prerequisite towards their lengthening. These new SWCNT short segments/calixarene composites show interesting behaviour in solution. DFT analysis of these new compounds also suggests interesting photophysical behaviour. Along with the synthesis of various SWCNTs segments, this approach also constitutes a powerful tool for the construction of new, radially oriented π systems. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Zigzagging causility model of EPR correlations and on the interpretation of quantum mechanics

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

de Beauregard, O.C.

1988-09-01

Being formalized inside the S-matrix scheme, the zigzagging causility model of EPR correlations has full Lorentz and CPT invariance. EPR correlations, proper or reversed, and Wheeler's smoky dragon metaphor are respectively pictured in a spacetime or in the momentum-energy space, as V-shaped, anti LAMBDA-shaped, or C-shaped ABC zigzags, with a summation at B over virtual states absolute value B>=*. The reversibility = * implies that causality is CPT-invariant, or arrowless, at the microlevel. Arrowed causality is a macroscopic emergence, corollary to wave retardation and probability increase. Factlike irreversibility states repression, not suppression, of blind statistical retrodiction- that is, of finalmore » cause.« less

A new heterometallic hybrid based on polymeric iodoplumbate and lanthanide metal-carboxylic coordination polycation

NASA Astrophysics Data System (ADS)

Gong, An-Weng; Wu, Hong-Yan; Lian, Zhao-Xun; Dong, Hai-Jun; Li, Hao-Hong; Chen, Zhi-Rong

2013-03-01

A 3-D supramolecular hybrid {[La(EPC)3(H2O)3]2(Pb6I18)}n (EPC+ = N-ethyl-pyridium-4-carboxylate) (1) has been structurally determined, which assume significance for its incorporating lanthanide metal-carboxylic coordination polycation into polymeric iodoplumbate to get heterometallics. 1 consists of 1-D (PbI)n6n- zigzag-like anion chains with lanthanide metalcarboxylic [La(EPC)3(HO)3]n3n+ polycations, which arrange in a criss-cross configuration. C-H⋯I and C-H⋯O hydrogen bonds among inorganic anions and polycations contribute to the formation of a 3-D supramolecular framework. Moreover, the framework displays an absorption edge at 2.46 eV which is comparable to PbI2's absorption edge.

Zirconium tetrachloride revisited

DOE PAGES

Borjas Nevarez, Rosendo; Balasekaran, Samundeeswari Mariappan; Kim, Eunja; ...

2018-02-19

We present that zirconium tetrachloride, ZrCl 4, is a strategic material with wide-ranging applications. Until now, only one crystallographic study on ZrCl 4has been reported [Krebs (1970).Z. Anorg. Allg. Chem.378, 263–272] and that was more than 40 years ago. The compound used for the previous determination was prepared from ZrO 2 and Cl 2–CCl 4, and single-crystal X-ray diffraction (SCXRD) studies on ZrCl 4 obtained from Zr metal have not yet been reported. In this context, we prepared ZrCl 4 from the reaction of Zr metal and Cl 2 gas in a sealed tube and investigated its structure at 100,more » 150, 200, 250, and 300 K. At 300 K, the SCXRD analysis indicates that ZrCl 4 crystallizes in the orthorhombic space group Pca2 1 [a= 6.262 (9),b= 7.402 (11),c= 12.039 (17) Å, andV= 558.0 (14) Å 3] and consists of infinite zigzag chains of edge-sharing ZrCl 6 octahedra. This chain motif is similar to that observed previously in ZrCl 4, but the structural parameters and space group differ. Finally, in the temperature range 100–300 K, no phase transformation was identified, while elongation of intra-chain Zr...Zr [3.950 (1) Å at 100 K and 3.968 (5) Å at 300 K] and inter-chain Cl...Cl [3.630 (3) Å at 100 K and 3.687 (9) Å at 300 K] distances occurred.« less

Charged magnetic domain walls as observed in nanostructured thin films: dependence on both film thickness and anisotropy.

PubMed

Favieres, C; Vergara, J; Madurga, V

2013-02-13

The magnetic domain configurations of soft magnetic, nanostructured, pulsed laser-deposited Co films were investigated. Their dependence on both the thickness t (20 nm ≤ t ≤ 200 nm) and the anisotropy was studied. Charged zigzag walls, with a characteristic saw-tooth vertex angle θ, were observed. θ changed with t from θ ≈ 17° to ≈25°, presenting an intermediate sharp maximum that has not been described before. The reduced length of the zigzag walls also exhibited a peak at t ≈ 70 nm. The relationship between the total reduced length and the density energy of the magnetic wall allowed us to establish a change from a Néel-type to a Bloch-type core of the zigzag walls at this thickness, t ≈ 70 nm. We also accounted for the magnetic energy arising from the surface roughness of the thinner films after imaging the film surface morphologies. Moreover, this distinctive behaviour of the zigzag walls of these low-anisotropy films was compared to that of high-anisotropy films.

Refinement of Timoshenko Beam Theory for Composite and Sandwich Beams Using Zigzag Kinematics

NASA Technical Reports Server (NTRS)

Tessler, Alexander; DiSciuva, Marco; Gherlone, Marco

2007-01-01

A new refined theory for laminated-composite and sandwich beams that contains the kinematics of the Timoshenko Beam Theory as a proper baseline subset is presented. This variationally consistent theory is derived from the virtual work principle and employs a novel piecewise linear zigzag function that provides a more realistic representation of the deformation states of transverse shear flexible beams than other similar theories. This new zigzag function is unique in that it vanishes at the top and bottom bounding surfaces of a beam. The formulation does not enforce continuity of the transverse shear stress across the beam s cross-section, yet is robust. Two major shortcomings that are inherent in the previous zigzag theories, shear-force inconsistency and difficulties in simulating clamped boundary conditions, and that have greatly limited the utility of these previous theories are discussed in detail. An approach that has successfully resolved these shortcomings is presented herein. This new theory can be readily extended to plate and shell structures, and should be useful for obtaining accurate estimates of structural response of laminated composites.

Magnetic and crystal structures of the honeycomb lattice Na2IrO3 and single layer Sr2IrO4

NASA Astrophysics Data System (ADS)

Ye, Feng

2013-03-01

5 d based iridates have recently attracted great attention due to the large spin-orbit coupling (SOC). It is now recognized that the SOC that competes with other relevant energies, particularly the on-site Coulomb interaction U, and have driven novel electronic and magnetic phases. Combining single crystal neutron and x-ray diffractions, we have investigated the magnetic and crystal structures of the honeycomb lattice Na2IrO3. The system orders magnetically below 18.1 K with Ir4+ ions forming zigzag spin chains within the layered honeycomb network with ordered moment of 0.22 μB /Ir site. Such a configuration sharply contrasts the Neel or stripe states proposed in the Kitaev-Heisenberg model. The structure refinement reveals that the Ir atoms form nearly ideal 2D honeycomb lattice while the IrO6 octahedra experience a trigonal distortion that is critical to the ground state. The results of this study provide much-needed experimental insights into the magnetic and crystal structure crucial to the understanding of the exotic magnetic order and possible topological characteristics in the 5 d-electron based honeycomb lattice. Neutron diffraction experiments are also performed to investigate the magnetic and crystal structure of the single layer iridate Sr2IrO4, where new structural information and spin order are obtained that is not available from previous neutron powder diffraction measurement. This work was sponsored in part by the Scientific User Facilities Division, Office of Basic Energy Sciences, US Department of Energy.

Polypyrrole polyvinylidene difluoride composite stripe and zigzag actuators for use in facial robotics

NASA Astrophysics Data System (ADS)

Tadesse, Yonas; Priya, Shashank; Ramannair Chenthamarakshan, C.; de Tacconi, Norma R.; Rajeshwar, Krishnan

2008-04-01

Composite stripe and zigzag actuators consisting of a sandwich polypyrrole (PPy)/polyvinylidene difluoride (PVDF)/PPy structure were synthesized using potentiodynamic film growth on gold electrodes. The synthesis was done from an aqueous solution containing tetrabutylammonium perchlorate and pyrrole by polymerization at room temperature. The actuator displacement was modeled using finite element simulations. For depositing thin PPy films and thereby minimizing the response time, experimental optimization of the deposition conditions was performed. The number of current-potential (potentiodynamic) growth cycles and the thickness of the deposited PPy film were highly correlated in the initial stages of polymer film growth. The actuation response measurements indicate that the zigzag shaped actuators provide promising properties to develop artificial muscle.

Which nanowire couples better electrically to a metal contact: Armchair or zigzag nanotube?

NASA Technical Reports Server (NTRS)

Anantram, M. P.; Biegel, Bryan (Technical Monitor)

2001-01-01

The fundamental question of how chirality affects tile electronic coupling of a nanotube to metal contacts is important for tile application of nanotubes as nanowires. We show that metallic-zigzag nanotubes are superior to armchair nanotubes as nanowires, by modeling the metal-nanotube interface. More specifically, we show that as a function of coupling strength, the total electron transmission of armchair nanotubes increases and tends to be pinned close to unity for a metal with Fermi wave vector close to that of gold. In contrast, the transmission probability of zigzag nanotubes increases to the maximum possible value of two. The origin of these effects lies in the details of the wave function, which is explained.

LCD real-time mask technique for fabrication of arbitrarily shaped microstructure

NASA Astrophysics Data System (ADS)

Peng, Qinjun; Guo, Yongkang; Chen, Bo; Du, Jinglei; Xiang, Jinshan; Cui, Zheng

2002-04-01

A new technique to fabricate arbitrarily shaped microstructures by using LCD (liquid crystal display) real- time mask is reported in this paper. Its principle and design method are explained. Based on partial coherent imaging theory, the process to fabricate micro-axicon array and zigzag grating has been simulated. The experiment using a color LCD as real-time mask has been set up. Micro-axicon array and zigzag grating has been fabricated by the LCD real-time mask technique. The 3D surface relief structures were made on pan chromatic silver-halide sensitized gelatin (Kodak-131) with trypsinase etching. The pitch size of zigzag grating is 46.26micrometers . The caliber of axicon is 118.7micrometers , and the etching depth is 1.332micrometers .

Nematic liquid crystals on sinusoidal channels: the zigzag instability.

PubMed

Silvestre, Nuno M; Romero-Enrique, Jose M; Telo da Gama, Margarida M

2017-01-11

Substrates which are chemically or topographically patterned induce a variety of liquid crystal textures. The response of the liquid crystal to competing surface orientations, typical of patterned substrates, is determined by the anisotropy of the elastic constants and the interplay of the relevant lengths scales, such as the correlation length and the surface geometrical parameters. Transitions between different textures, usually with different symmetries, may occur under a wide range of conditions. We use the Landau-de Gennes free energy to investigate the texture of nematics in sinusoidal channels with parallel anchoring bounded by nematic-air interfaces that favour perpendicular (hometropic) anchoring. In micron size channels 5CB was observed to exhibit a non-trivial texture characterized by a disclination line, within the channel, which is broken into a zigzag pattern. Our calculations reveal that when the elastic anisotropy of the nematic does not favour twist distortions the defect is a straight disclination line that runs along the channel, which breaks into a zigzag pattern with a characteristic period, when the twist elastic constant becomes sufficiently small when compared to the splay and bend constants. The transition occurs through a twist instability that drives the defect line to rotate from its original position. The interplay between the energetically favourable twist distortions that induce the defect rotation and the liquid crystal anchoring at the surfaces leads to the zigzag pattern. We investigate in detail the dependence of the periodicity of the zigzag pattern on the geometrical parameters of the sinusoidal channels, which in line with the experimental results is found to be non-linear.

Magneto-structural correlation in a series of bimetallic alternating chain complexes of [CrIIIL(CN)4]n[MnIII(salpn)]n.nsolvents (L=2,2'-bipy or 9,10-phen, salpn=substituted salicyldehyde, solvents=water and methanol).

PubMed

Pan, Feng; Wang, Zhe-Ming; Gao, Song

2007-11-26

Five chain compounds based on the building block of [Cr(L)(CN)4]- (L=2,2'-bipy, 1-4; L=9,10-phen, 5) and [Mn(salpn)]+ (salpn=substituted salicyldehyde-type Schiff base in Scheme 1) have been prepared and characterized structurally and magnetically. The four compounds (1-4) consisting of [Cr(bipy)(CN)4]- units possess straight bimetallic chains as the [Cr(bpy)(CN)4]- unit links the two neighbor [Mn(salpn)]+ units with the two trans-cyanide ligands, while in 5 the chain is zigzag because the [Cr(phen)(CN)4]- unit connects the [Mn(salpn)]+ units with its two cis-cyanide ligands. The bond angles of Mn-N-C-Cr are adjusted by different coligands of salpn and bipy/phen. The chains are stacking via mainly the aromatic pi-pi-type interactions. All compounds show 3D antiferromagnetic ordering with Néel temperatures ranging from 3.7 to 8.1 K, and they are metamagnets displaying antiferromagnetic to ferrimagnetic transition at critical fields of 4.0-13.1 kOe at 1.9 K. This is due to weak interchain antiferromagnetic interactions between the ferrimagnetic bimetallic chains in the materials. The intrachain couplings (J, in cm(-1)) in the materials, between cyanide-bridged CrIII and MnIII ions, from -1.84 to -5.35 cm(-1), follow a linear relationship (J=-33+0.18alpha) to the Mn-N-C angles (alpha, in deg). In addition, the weak interchain antiferromagnetic interactions and critical fields for antiferromagnetic-ferrimagnetic transition are closely related to some of their structural factors, which were studied very superficially only referring to the separations of nearest chains in each material.

Zigzag spin structure in layered honeycomb L i3N i2Sb O6 : A combined diffraction and antiferromagnetic resonance study

NASA Astrophysics Data System (ADS)

Kurbakov, A. I.; Korshunov, A. N.; Podchezertsev, S. Yu.; Malyshev, A. L.; Evstigneeva, M. A.; Damay, F.; Park, J.; Koo, C.; Klingeler, R.; Zvereva, E. A.; Nalbandyan, V. B.

2017-07-01

The magnetic structure of L i3N i2Sb O6 has been determined by low-temperature neutron diffraction, and the crystal structure has been refined by a combination of synchrotron and neutron powder diffraction. The monoclinic (C 2 /m ) symmetry, assigned previously to this pseudohexagonal layered structure, has been unambiguously proven by peak splitting in the synchrotron diffraction pattern. The structure is based on essentially hexagonal honeycomb-ordered N i2Sb O6 layers alternating with L i3 layers, all cations and anions being in an octahedral environment. The compound orders antiferromagnetically below TN=15 K , with the magnetic supercell being a 2 a ×2 b multiple of the crystal cell. The magnetic structure within the honeycomb layer consists of zigzag ferromagnetic spin chains coupled antiferromagnetically. The ordered magnetic moment amounts to 1.62 (2 ) μB/Ni , which is slightly lower than the full theoretical value. Upon cooling below TN, the spins tilt from the c axis, with a maximum tilting angle of 15 .6∘ at T =1.5 K . Our data imply non-negligible ferromagnetic interactions between the honeycomb layers. The observed antiferromagnetic resonance modes are in agreement with the two-sublattice model derived from the neutron data. Orthorhombic anisotropy shows up in zero-field splitting of Δ =198 ±4 and 218 ±4 GHz . Above TN, the electron spin resonance data imply short-range antiferromagnetic order up to about 80 K.

High power tube solid-state laser with zigzag propagation of pump and laser beam

NASA Astrophysics Data System (ADS)

Savich, Michael

2015-02-01

A novel resonator and pumping design with zigzag propagation of pumping and laser beams permits to design an improved tube Solid State Laser (SSL), solving the problem of short absorption path to produce a high power laser beam (100 - 1000kW). The novel design provides an amplifier module and laser oscillator. The tube-shaped SSL includes a gain element fiber-optically coupled to a pumping source. The fiber optic coupling facilitates light entry at compound Brewster's angle of incidence into the laser gain element and uses internal reflection to follow a "zigzag" path in a generally spiral direction along the length of the tube. Optics are arranged for zigzag propagation of the laser beam, while the cryogenic cooling system is traditional. The novel method of lasing uses advantages of cylindrical geometry to reach the high volume of gain medium with compactness and structural rigidity, attain high pump density and uniformity, and reach a low threshold without excessive increase of the temperature of the crystal. The design minimizes thermal lensing and stress effects, and provides high gain amplification, high power extraction from lasing medium, high pumping and lasing efficiency and a high beam quality.

Low resistivity of graphene nanoribbons with zigzag-dominated edge fabricated by hydrogen plasma etching combined with Zn/HCl pretreatment

NASA Astrophysics Data System (ADS)

Liu, Fengkui; Li, Qi; Wang, Rubing; Xu, Jianbao; Hu, Junxiong; Li, Weiwei; Guo, Yufen; Qian, Yuting; Deng, Wei; Ullah, Zaka; Zeng, Zhongming; Sun, Mengtao; Liu, Liwei

2017-11-01

Graphene nanoribbons (GNRs) have attracted intensive research interest owing to their potential applications in high performance graphene-based electronics. However, the deterioration of electrical performance caused by edge disorder is still an important obstacle to the applications. Here, we report the fabrication of low resistivity GNRs with a zigzag-dominated edge through hydrogen plasma etching combined with the Zn/HCl pretreatment method. This method is based on the anisotropic etching properties of hydrogen plasma in the vicinity of defects created by sputtering zinc (Zn) onto planar graphene. The polarized Raman spectra measurement of GNRs exhibits highly polarization dependence, which reveals the appearance of the zigzag-dominated edge. The as-prepared GNRs exhibit high carrier mobility (˜1332.4 cm2 v-1 s-1) and low resistivity (˜0.7 kΩ) at room temperature. Particularly, the GNRs can carry large current density (5.02 × 108 A cm-2) at high voltage (20.0 V) in the air atmosphere. Our study develops a controllable method to fabricate zigzag edge dominated GNRs for promising applications in transistors, sensors, nanoelectronics, and interconnects.

Superconductivity of Ca2 InN with a layered structure embedding an anionic indium chain array

NASA Astrophysics Data System (ADS)

Jeong, Sehoon; Matsuishi, Satoru; Lee, Kimoon; Toda, Yoshitake; Wng Kim, Sung; Hosono, Hideo

2014-05-01

We report the emergence of superconductivity in Ca2InN consisting of a two-dimensional (2D) array of zigzag indium chains embedded between Ca2N layers. A sudden drop of resistivity and a specific heat (Cp) jump attributed to the superconducting transition were observed at 0.6 K. The Sommerfeld coefficient γ = 4.24 mJ mol-1K-2 and Debye temperature ΘD = 322 K were determined from the Cp of the normal conducting state and the superconducting volume fraction was estimated to be ˜80% from the Cp jump, assuming a BCS-type weak coupling. Density functional theory calculations demonstrated that the electronic bands near the Fermi level (EF) are mainly derived from In 5p orbitals with π and σ bonding states and the Fermi surface is composed of cylindrical parts, corresponding to the quasi-2D electronic state of the In-chain array. By integrating the projected density of states of the In-p component up to EF, a valence electron population of ˜1.6 electrons/In was calculated, indicating that partially anionic state of In. The In 3d binding energies observed in Ca2InN by x-ray photoemission spectroscopy were negatively shifted from that in In metal. The superconductivity of Ca2InN is associated with the p-p bonding states of the anionic In layer.

Design of new anti-Alzheimer drugs: ring-expansion synthesis and synchrotron X-ray diffraction study of dimethyl 4-ethyl-11-fluoro-1,4,5,6,7,8-hexa­hydro­azonino[5,6-b]indole-2,3-di­carboxyl­ate

PubMed Central

Toze, Flavien A. A.; Listratova, Anna V.; Voskressensky, Leonid G.; Chernikova, Natalia Yu.; Lobanov, Nikolai N.; Bilyachenko, Alexey N.

2018-01-01

The title compound, C20H23FN2O4, is the product of a ring-expansion reaction from a seven-membered fluorinated hexa­hydro­azepine to a nine-membered azonine. The nine-membered azonine ring of the mol­ecule adopts a chair–boat conformation. The C=C and C—N bond lengths [1.366 (3) and 1.407 (3) Å, respectively] indicate the presence of conjugation within the enamine CH2—C=C—N—CH2 fragment. The substituent planes at the C=C double bond of this fragment are twisted by 16.0 (3)° as a result of steric effects. The amine N(Et) N atom has a trigonal–pyramidal configuration (sum of the bond angles = 346.3°). The inter­planar angle between the two carboxyl­ate substituents is 60.39 (8)°. In the crystal, mol­ecules form zigzag chains along [010] by inter­molecular N—H⋯O hydrogen-bonding inter­actions, which are further packed in stacks toward [100]. The title azonino­indole might be considered as a candidate for the design of new Alzheimer drugs. PMID:29765710

Six complexes based on bis(imidazole/benzimidazole-1-yl)pyridazine ligands: Syntheses, structures and properties

NASA Astrophysics Data System (ADS)

Wang, Xin-Fang; Du, Ceng-Ceng; Zhou, Sheng-Bin; Wang, Duo-Zhi

2017-01-01

Herein we reported six new Ni(II)/Cu(II)/Zn(II) complexes, namely, [Ni(L1)4(OH)2] (1), [Cu(L1)4(OH)2] (2), [Cu(L1)2(SiF6)]n (3), {[Cu(L2)(HCOO)2]·H2O·CH3OH}n (4), [Ni(L2)2(NO3)2]n (5) and {[Zn(L2)Cl2]·DMF}n (6) (L1 = 3,6-bis(imidazole-1-yl)pyridazine, L2 = 3,6-bis(benzimidazole-1-yl)pyridazine), which were characterized by single-crystal X-ray diffraction, elemental analysis, IR, PXRD. These complexes have been successfully constructed under interface diffusion process, heating reflux or hydrothermal conditions. The structures of 1 and 2 are mononuclear complexes. Complex 3 exhibits a 6-connected 3D topology network with the Schläfli symbol of (412·63). In complex 4, two Cu(II) were connected through two HCOO- anions to form dinuclear structure unit, which is arranged into a 1D ladder-like structure by μ2-L2 ligands. Complexes 5 and 6 are 1D zigzag chains connected by L2 ligands, but the Ni(II) ion is six-coordinated in 5 and the Zn(II) ion is four-coordinated in 6. Moreover, the solid-state luminescence property and UV-vis diffuse reflection spectrum of complex 6 have been investigated and discussed.

Physics of knuckleballs

NASA Astrophysics Data System (ADS)

Darbois Texier, Baptiste; Cohen, Caroline; Quéré, David; Clanet, Christophe

2016-07-01

Zigzag paths in sports ball trajectories are exceptional events. They have been reported in baseball (from where the word knuckleball comes from), in volleyball and in soccer. Such trajectories are associated with intermittent breaking of the lateral symmetry in the surrounding flow. The different scenarios proposed in the literature (such as the effect of seams in baseball) are first discussed and compared to existing data. We then perform experiments on zigzag trajectories and propose a new explanation based on unsteady lift forces. In a second step, we exploit wind tunnel measurements of these unsteady lift forces to solve the equations of motion for various sports and deduce the characteristics of the zigzags, pointing out the role of the drag crisis. Finally, the conditions for the observation of such trajectories in sports are discussed.

Enhancement of thermoelectric figure of merit in zigzag graphene nanoribbons with periodic edge vacancies

NASA Astrophysics Data System (ADS)

Kolesnikov, D. V.; Sadykova, O. G.; Osipov, V. A.

2017-06-01

The influence of periodic edge vacancies and antidot arrays on the thermoelectric properties of zigzag graphene nanoribbons (ZGNRs) are investigated. Using Green’s function method, the tight-binding approximation for the electron Hamiltonian and the 4th nearest neighbor approximation for the phonon dynamical matrix, we calculate the Seebeck coefficient and the thermoelectric figure of merit. It is found that, at a certain periodic arrangement of vacancies on both edges of zigzag nanoribbon, a finite band gap opens and almost twofold degenerate energy levels appear. As a result, a marked increase in the Seebeck coefficient takes place. It is shown that an additional enhancement of the thermoelectric figure of merit can be achieved by a combination of periodic edge defects with an antidot array.

Small influence of magnetic ordering on lattice dynamics in TaFe 1.25 Te 3

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

Opačić, M.; Lazarević, N.; Tanasković, D.

2017-11-16

Raman scattering spectra of zigzag spin chain TaFe 1.25Te 3 single crystal are presented in a temperature range from 80 to 300 K. Nine Raman active modes of A g and B g symmetry are clearly observed and assigned by probing different scattering channels, which is confirmed by lattice dynamics calculations. Temperature dependence of the Raman modes linewidth is mainly governed by the lattice anharmonicity. The only deviation from the conventional behavior is observed for A g symmetry modes in a vicinity of the magnetic phase transition at T N ≈ 200 K. This implies that the electron-phonon interaction weaklymore » changes with temperature and magnetic ordering, whereas small changes in the spectra near the critical temperature can be ascribed to spin fluctuations.« less

Synthesis and characterization of new fluoride-containing manganese vanadates A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F

NASA Astrophysics Data System (ADS)

Sanjeewa, Liurukara D.; McGuire, Michael A.; Smith Pellizzeri, Tiffany M.; McMillen, Colin D.; Ovidiu Garlea, V.; Willett, Daniel; Chumanov, George; Kolis, Joseph W.

2016-09-01

Large single crystals of A2Mn2V2O7F2 (A=Rb, Cs) and Mn2VO4F were grown using a high-temperature (~600 °C) hydrothermal technique. Single crystal X-ray diffraction and powder X-ray diffraction were utilized to characterize the structures, which both possess MnO4F2 building blocks. The A2Mn2V2O7F2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb2Mn2V2O7F2: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs2Mn2V2O7F2: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed of zigzag chains of edge-sharing MnO4F2 units running along the a-axis, and interconnected through V2O7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn2+ indicated that Cs2Mn2V2O7F2 is antiferromagnetic with a Neél temperature, TN=~3 K and a Weiss constant, θ, of -11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V-O vibrational modes in Cs2Mn2V2O7F2. Mn2(VO4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn2+. These interpenetrating chains are additionally connected through isolated VO4 tetrahedra to form the condensed structure.

Synthesis and characterization of new fluoride-containing manganese vanadates A 2Mn 2V 2O 7F 2 (A=Rb, Cs) and Mn 2VO 4F

DOE PAGES

Sanjeewa, Liurukara D.; McGuire, Michael A.; Smith Pellizzeri, Tiffany M.; ...

2016-05-10

In large single crystals of A 2Mn 2V 2O 7F 2 (A=Rb, Cs) and Mn 2VO 4F were grown using a high-temperature (~600 °C) hydrothermal technique. We utilized single crystal X-ray diffraction and powder X-ray diffraction in order to characterize the structures, which both possess MnO 4F 2 building blocks. The A 2Mn 2V 2O 7F 2 series crystallizes as a new structure type in space group Pbcn (No. 60), Z=4 (Rb 2Mn 2V 2O 7F 2: a=7.4389(17) Å, b=11.574(3) Å, c=10.914(2) Å; Cs 2Mn 2V 2O 7F 2: a=7.5615(15) Å, b=11.745(2) Å, c=11.127(2) Å). The structure is composed ofmore » zigzag chains of edge-sharing MnO 4F 2 units running along the a-axis, and interconnected through V 2O 7 pyrovanadate groups. Temperature dependent magnetic susceptibility measurements on this interesting one-dimensional structural feature based on Mn 2+ indicated that Cs 2Mn 2V 2O 7F 2 is antiferromagnetic with a Neél temperature, TN=~3 K and a Weiss constant, θ, of -11.7(1) K. Raman and infrared spectra were also analyzed to identify the fundamental V–O vibrational modes in Cs 2Mn 2V 2O 7F 2. Mn 2(VO 4)F crystalizes in the monoclinic space group of C2/c (no. 15), Z=8 with unit cell parameters of a=13.559(2) Å, b=6.8036(7) Å, c=10.1408(13) Å and β=116.16(3)°. The structure is associated with those of triplite and wagnerite. Dynamic fluorine disorder gives rise to complex alternating chains of five-and six-coordinate Mn 2+. Our interpenetrating chains are additionally connected through isolated VO 4 tetrahedra to form the condensed structure.« less

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

Chang, Y.L.; Chen, P.Y.; Tsai, Y.T.

The crystallography of lenticular martensite, which formed in coarse austenite grains (size about 80 μm) after subzero treatment at − 196 °C (liquid nitrogen) for different holding times, was investigated using electron backscatter diffraction (EBSD). For the sample treated with 15 min of isothermal holding, more than 50 martensite plates (with a thickness of larger than 1 μm) that formed within a coarse austenite grain were employed to obtain the pole figures. The pole figures clearly indicated that the individual plate of lenticular martensite approximately adopted the Kurdjumov–Sachs (K–S) orientation relationship with respect to the austenite matrix. For the samplemore » treated with 30 s of isothermal holding, a few martensite plates that formed in variant pairings in a coarse austenite grain were analyzed. The results showed that zigzag couplings (including spear couplings), the major product of plate martensite, had an absolute dominance of a specific variant pair (V1/V17). The orientation gradient within a lenticular martensite plate was also measured using convergent beam electron diffraction (CBED). The evidence strongly suggests that the spread in diffracted intensity within pole figures is related to the misorientation gradient within the lenticular martensite plate. - Highlights: • The orientation relationship between lenticular martensite and austenite was investigated by pole figures via Electron Backscatter Diffraction (EBSD). • The initial stage of lenticular martensite formation was investigated, excluding interference from hard impingement. • In addition to EBSD, convergent beam electron diffraction (CBED) was used to measure the misorientation angle from the midrib to the untwinned region in lenticular martensite plate. • Zigzag couplings (including spear couplings), the major product of plate martensite, had an absolute dominance of a specific variant pair (V1/V17).« less

Electronic Structures of Silicene Nanoribbons: Two-Edge-Chemistry Modification and First-Principles Study.

PubMed

Yao, Yin; Liu, Anping; Bai, Jianhui; Zhang, Xuanmei; Wang, Rui

2016-12-01

In this paper, we investigate the structural and electronic properties of zigzag silicene nanoribbons (ZSiNRs) with edge-chemistry modified by H, F, OH, and O, using the ab initio density functional theory method and local spin-density approximation. Three kinds of spin polarized configurations are considered: nonspin polarization (NM), ferromagnetic spin coupling for all electrons (FM), ferromagnetic ordering along each edge, and antiparallel spin orientation between the two edges (AFM). The H, F, and OH groups modified 8-ZSiNRs have the AFM ground state. The directly edge oxidized (O1) ZSiNRs yield the same energy and band structure for NM, FM, and AFM configurations, owning to the same s p (2) hybridization. And replacing the Si atoms on the two edges with O atoms (O2) yields FM ground state. The edge-chemistry-modified ZSiNRs all exhibit metallic band structures. And the modifications introduce special edge state strongly localized at the Si atoms in the edge, except for the O1 form. The modification of the zigzag edges of silicene nanoribbons is a key issue to apply the silicene into the field effect transistors (FETs) and gives more necessity to better understand the experimental findings.

Silicene nanoribbon as a new DNA sequencing device

NASA Astrophysics Data System (ADS)

Alesheikh, Sara; Shahtahmassebi, Nasser; Roknabadi, Mahmood Rezaee; Pilevar Shahri, Raheleh

2018-02-01

The importance of applying DNA sequencing in different fields, results in looking for fast and cheap methods. Nanotechnology helps this development by introducing nanostructures used for DNA sequencing. In this work we study the interaction between zigzag silicene nanoribbon and DNA nucleobases using DFT and non equilibrium Green's function approach, to investigate the possibility of using zigzag silicene nanoribbons as a biosensor for DNA sequencing.

Intrinsic anharmonic effects on the phonon frequencies and effective spin-spin interactions in a quantum simulator made from trapped ions in a linear Paul trap

NASA Astrophysics Data System (ADS)

McAneny, M.; Freericks, J. K.

2014-11-01

The Coulomb repulsion between ions in a linear Paul trap gives rise to anharmonic terms in the potential energy when expanded about the equilibrium positions. We examine the effect of these anharmonic terms on the accuracy of a quantum simulator made from trapped ions. To be concrete, we consider a linear chain of Yb171+ ions stabilized close to the zigzag transition. We find that for typical experimental temperatures, frequencies change by no more than a factor of 0.01 % due to the anharmonic couplings. Furthermore, shifts in the effective spin-spin interactions (driven by a spin-dependent optical dipole force) are also, in general, less than 0.01 % for detunings to the blue of the transverse center-of-mass frequency. However, detuning the spin interactions near other frequencies can lead to non-negligible anharmonic contributions to the effective spin-spin interactions. We also examine an odd behavior exhibited by the harmonic spin-spin interactions for a range of intermediate detunings, where nearest-neighbor spins with a larger spatial separation on the ion chain interact more strongly than nearest neighbors with a smaller spatial separation.

Empirical potential influence and effect of temperature on the mechanical properties of pristine and defective hexagonal boron nitride

NASA Astrophysics Data System (ADS)

Thomas, Siby; Ajith, K. M.; Valsakumar, M. C.

2017-06-01

The major objective of this work is to present results of a classical molecular dynamics study to investigate the effect of changing the cut-off distance in the empirical potential on the stress-strain relation and also the temperature dependent Young’s modulus of pristine and defective hexagonal boron nitride. As the temperature increases, the computed Young’s modulus shows a significant decrease along both the armchair and zigzag directions. The computed Young’s modulus shows a trend in keeping with the structural anisotropy of h-BN. The variation of Young’s modulus with system size is elucidated. The observed mechanical strength of h-BN is significantly affected by the vacancy and Stone-Wales type defects. The computed room temperature Young’s modulus of pristine h-BN is 755 GPa and 769 GPa respectively along the armchair and zigzag directions. The decrease of Young’s modulus with increase in temperature has been analyzed and the results show that the system with zigzag edge shows a higher value of Young’s modulus in comparison to that with armchair edge. As the temperature increases, the computed stiffness decreases and the system with zigzag edge possesses a higher value of stiffness as compared to the armchair counterpart and this behaviour is consistent with the variation of Young’s modulus. The defect analysis shows that presence of vacancy type defects leads to a higher Young’s modulus, in the studied range with different percentage of defect concentration, in comparison with Stone-Wales defect. The variations in the peak position of the computed radial distribution function reveals the changes in the structural features of systems with zigzag and armchair edges in the presence of applied stress.

Transport gap engineering by contact geometry in graphene nanoribbons: Experimental and theoretical studies on artificial materials

NASA Astrophysics Data System (ADS)

Stegmann, Thomas; Franco-Villafañe, John A.; Kuhl, Ulrich; Mortessagne, Fabrice; Seligman, Thomas H.

2017-01-01

Electron transport in small graphene nanoribbons is studied by microwave emulation experiments and tight-binding calculations. In particular, it is investigated under which conditions a transport gap can be observed. Our experiments provide evidence that armchair ribbons of width 3 m +2 with integer m are metallic and otherwise semiconducting, whereas zigzag ribbons are metallic independent of their width. The contact geometry, defining to which atoms at the ribbon edges the source and drain leads are attached, has strong effects on the transport. If leads are attached only to the inner atoms of zigzag edges, broad transport gaps can be observed in all armchair ribbons as well as in rhomboid-shaped zigzag ribbons. All experimental results agree qualitatively with tight-binding calculations using the nonequilibrium Green's function method.

Investigating the edge state of graphene nanoribbons by a chemical approach: Synthesis and magnetic properties of zigzag-edged nanographene molecules

NASA Astrophysics Data System (ADS)

Konishi, Akihito; Hirao, Yasukazu; Kurata, Hiroyuki; Kubo, Takashi

2013-12-01

The edge state, which is a peculiar magnetic state in zigzag-edged graphene nanoribbons (GNRs) originating from an electron-electron correlation in an edge-localized π-state, has promising applications for magnetic and spintronics devices and has attracted much attention of physicists, chemists, and engineers. For deeper understanding the edge state, precise fabrication of edge structures in GNRs has been highly demanded. We focus on [a.b]periacene, which are polycyclic aromatic hydrocarbons (PAHs) that have zigzag and armchair edges on molecular periphery, as a model compound for the understanding and actually prepare and characterize them. This review summarizes our recent studies on the origin of the edge state by investigating [a.b]periacene in terms of the relationship between the molecular structure and spin-localizing character.

Shape-dependent electronic properties of blue phosphorene nano-flakes

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

Bhatia, Pradeep; Swaroop, Ram; Kumar, Ashok, E-mail: ashok@cup.ac.in

In recent year’s considerable attention has been given to the first principles method for modifying and controlling electronic properties of nano-materials. We performed DFT-based calculations on the electronic properties of zigzag-edged nano-flakes of blue phosphorene with three possible shapes namely rectangular, triangular and hexagonal. We observed that HOMO-LUMO gap of zigzag phosphorene nano-flakes with different shapes is ∼2.9 eV with H-passivations and ∼0.7 – 1.2 eV in pristine cases. Electronic properties of blue phosphorene nano-flakes show the strong dependence on their shape. We observed that distributions of molecular orbitals were strongly affected by the different shapes. Zigzag edged considered nanostructuresmore » are non-magnetic and semiconducting in nature. The shape dependent electronic properties may find applications in tunable nano-electronics.« less

The neurobiological basis of orientation in insects: insights from the silkmoth mating dance.

PubMed

Namiki, Shigehiro; Kanzaki, Ryohei

2016-06-01

Counterturning is a common movement pattern during orientation behavior in insects. Once male moths sense sex pheromones and then lose the input, they demonstrate zigzag movements, alternating between left and right turns, to increase the probability to contact with the pheromone plume. We summarize the anatomy and function of the neural circuit involved in pheromone orientation in the silkmoth. A neural circuit, the lateral accessory lobe (LAL), serves a role as the circuit module for zigzag movements and controls this operation using a flip-flop neural switch. Circuit design of the LAL is well conserved across species. We hypothesize that this zigzag module is utilized in a wide range of insect behavior. We introduce two examples of the potential use: orientation flight and the waggle dance in bees. Copyright © 2016 Elsevier Inc. All rights reserved.

Phonon stiffen and soften at zigzag- and armchair-dominated edges of exfoliated bilayer graphene ribbon presented by Raman spectra

NASA Astrophysics Data System (ADS)

Xia, Minggang; Zhou, Xiaohua; Xin, Duqiang; Xu, Qiang

2018-01-01

The Raman spectra at the edge of the exfoliated bilayer graphene ribbon (GR) were investigated in detail. Results show that both G and 2D phonons stiffen (wave number increases) at zigzag-dominated edge, while they soften at armchair-dominated edge compared with those at the middle position in the GR. Furthermore, the full widths at half maximum intensity of both G and 2D Raman peaks narrow at the zigzag-dominated edge, while they broaden at the armchair-dominated edge. The stiffness and softness are attributed to the C-C bonds at the edge. For zigzag-dominated edge, the stiffness may originate in the increase of the force constant induced by the shrinking of C-C bond. For armchair-dominated edge, the softness may be due to the decrease of the force constant induced by the unsaturated hanging bonds at edge, which is different from Kohn anomaly and charge doping. The analysis is in agreement well with others calculation results about C-C bonds and the edge energy. These results may be useful to understand physical properties at the bilayer graphene edge and for applications in the device by taking advantage of the edge states in bilayer graphene.

Large-Scale Molecular Simulations on the Mechanical Response and Failure Behavior of a defective Graphene: Cases of 5-8-5 Defects

NASA Astrophysics Data System (ADS)

Wang, Shuaiwei; Yang, Baocheng; Yuan, Jinyun; Si, Yubing; Chen, Houyang

2015-10-01

Understanding the effect of defects on mechanical responses and failure behaviors of a graphene membrane is important for its applications. As examples, in this paper, a family of graphene with various 5-8-5 defects are designed and their mechanical responses are investigated by employing molecular dynamics simulations. The dependence of fracture strength and strain as well as Young’s moduli on the nearest neighbor distance and defect types is examined. By introducing the 5-8-5 defects into graphene, the fracture strength and strain become smaller. However, the Young’s moduli of DL (Linear arrangement of repeat unit 5-8-5 defect along zigzag-direction of graphene), DS (a Slope angle between repeat unit 5-8-5 defect and zigzag direction of graphene) and DZ (Zigzag-like 5-8-5 defects) defects in the zigzag direction become larger than those in the pristine graphene in the same direction. A maximum increase of 11.8% of Young’s modulus is obtained. Furthermore, the brittle cracking mechanism is proposed for the graphene with 5-8-5 defects. The present work may provide insights in controlling the mechanical properties by preparing defects in the graphene, and give a full picture for the applications of graphene with defects in flexible electronics and nanodevices.

Thermally induced spin-dependent current based on Zigzag Germanene Nanoribbons

NASA Astrophysics Data System (ADS)

Majidi, Danial; Faez, Rahim

2017-02-01

In this paper, using first principle calculation and non-equilibrium Green's function, the thermally induced spin current in Hydrogen terminated Zigzag-edge Germanene Nanoribbon (ZGeNR-H) is investigated. In this model, because of the difference between the source and the drain temperature of ZGeNR device, the spin up and spin down currents flow in the opposite direction with two different threshold temperatures (Tth). Hence, a pure spin polarized current which belongs to spin down is obtained. It is shown that, for temperatures above the threshold temperature spin down current increases with the increasing temperature up to 75 K and then decreases. But spin up current rises steadily and in the high temperature we can obtain polarized spin up current. In addition, we show an acceptable spin current around the room temperature for ZGeNR. The transmission peaks in ZGeNR which are closer to the Fermi level rather than Zigzag Graphene Nanoribbon (ZGNRS) which causes ZGeNR to have spin current at higher temperatures. Finally, it is indicated that by tuning the back gate voltage, the spin current can be completely modulated and polarized. Simulation results verify the Zigzag Germanene Nanoribbon as a promising candidate for spin caloritronics devices, which can be applied in future low power consumption technology.

First principles study on the electronic structures and transport properties of armchair/zigzag edge hybridized graphene nanoribbons

NASA Astrophysics Data System (ADS)

Yi, Xiuying; Long, Mengqiu; Liu, Anhua; Li, Mingjun; Xu, Hui

2018-05-01

Graphene nanoribbons (GNRs) can be mainly classified into armchair graphene nanoribbons (aGNRs) and zigzag graphene nanoribbons (zGNRs) by different edge chiral directions. In this work, by introducing Stone-Wales defects on the edges of the V-shaped aGNRs, we propose a kind of armchair/zigzag edge hybridized GNRs (a/zHGNRs) and using the density functional theory and the nonequilibrium Green's function method, the band structures and electronic transport properties of the a/zHGNRs have been calculated. Our results show that an indirect bandgap appears in the band structures of the a/zHGNRs, which is very different from the direct bandgap of aGNRs and gapless of zGNRs. We also find that the valance band is mainly derived from the armchair partial atoms on the hybridized edge, while the conduction band comes mainly from the zigzag partial atoms of the hybridized edge. Meanwhile, the bandgap also oscillates with a period of three when the ribbon width increases. In addition, our quantum transport calculations show that there is a remarkable transition between the semiconductor and the metal with different ribbon widths in the a/zHGNRs devices, and the corresponding physical analysis is given.

A structural and electronic comparison of armchair and zigzag epitaxial graphene sidewall nanoribbons

NASA Astrophysics Data System (ADS)

Nevius, Meredith; Wang, F.; Palacio, I.; Celis, A.; Tejeda, A.; Taleb-Ibrahimi, A.; de Heer, W.; Berger, C.; Conrad, E.

2014-03-01

Graphene grown on sidewalls of trenches etched in SiC shows particular promise as a candidate for post-Si CMOS electronics because of its ballistic transport, exceptional mobilities, low intrinsic doping, and the opening of a large band gap. However, before definitive progress can be made toward epitaxial graphene-based transistors, we must fully understand the nuances of graphene ribbon growth on different SiC facets. We have now confirmed that sidewall ribbons grown in graphene's two primary crystallographic directions (``armchair'' and ``zigzag'') differ greatly in both structure and electronic band-structure. We present data from both geometries obtained using low-energy electron microscopy (LEEM), low-energy electron diffraction (LEED), angle-resolved photoemission spectroscopy (ARPES), photoemission electron microscopy (PEEM), micro-ARPES and dark-field micro-ARPES. We demonstrate that while graphene grows on stable facets of trenches oriented for armchair edge growth, trenches oriented for zigzag edge growth prefer narrow ribbons of graphene on the (0001) surface near the trench edge. The structure of these zigzag edge graphene ribbons is complex and paramount to understanding their transport. This work was supported by the NSF under grants DMR-1005880 and DMR-0820382, the W. M. Keck Foundation and the Partner University Fund from the Embassy of France

Fabrication of Defect-Free Ferroelectric Liquid Crystal Displays Using Photoalignment and Their Electrooptic Performance

NASA Astrophysics Data System (ADS)

Kurihara, Ryuji; Furue, Hirokazu; Takahashi, Taiju; Yamashita, Tomo-o; Xu, Jun; Kobayashi, Shunsuke

2001-07-01

A photoalignment technique has been utilized for fabricating zigzag-defect-free ferroelectric liquid crystal displays (FLCDs) using polyimide RN-1199, -1286, -1266 (Nissan Chem. Ind.) and adopting oblique irradiation of unpolarized UV light. A rubbing technique was also utilized for comparison. It is shown that among these polyimide materials, RN-1199 is the best for fabricating defect-free cells with C-1 uniform states, but RN-1286 requires low energy to produce a photoaligned FLC phase. We have conducted an analytical investigation to clarify the conditions for obtaining zigzag-defect-free C-1 states, and it is theoretically shown that zigzag-defect-free C-1 state is obtained using a low azimuthal anchoring energy at a low pretilt angle, while a zigzag-defect-free C-2 state is obtained by increasing azimuthal anchoring energy above a critical value, also at a low pretilt angle. The estimated critical value of the azimuthal anchoring energy at which a transition from the C-1 state to the C-2 state occurs is 3×10-6 J/m2 for the FLC material FELIX M4654/100 (Clariant) used in this research; this value is shown to fall in a favorable range which is measured in an independent experiment.

Negative differential resistance and bias-modulated metal-to-insulator transition in zigzag C2N-h2D nanoribbon

NASA Astrophysics Data System (ADS)

He, Jing-Jing; Guo, Yan-Dong; Yan, Xiao-Hong

2017-04-01

Motivated by the fabrication of layered two-dimensional material C2N-h2D [Nat. Commun. 6, 6486 (2015)], we cut the single-layer C2N-h2D into a zigzag nanoribbon and perform a theoretical study. The results indicate that the band structure changes from semiconducting to metallic and a negative differential resistance effect occurs in the I-V curve. Interestingly, the current can be reduced to zero and this insulator-like state can be maintained as the bias increases. We find this unique property is originated from a peculiar band morphology, with only two subbands appearing around the Fermi level while others being far away. Furthermore the width and symmetry of the zigzag C2N-h2D nanoribbon can be used to tune the transport properties, such as cut-off bias and the maximum current. We also explore the electron transport property of an aperiodic model composed of two nanoribbons with different widths and obtain the same conclusion. This mechanism can be extended to other systems, e.g., hybrid BCN nanoribbons. Our discoveries suggest that the zigzag C2N-h2D nanoribbon has great potential in nanoelectronics applications.

Anisotropic thermoelectric behavior in armchair and zigzag mono- and fewlayer MoS2 in thermoelectric generator applications

PubMed Central

Arab, Abbas; Li, Qiliang

2015-01-01

In this work, we have studied thermoelectric properties of monolayer and fewlayer MoS2 in both armchair and zigzag orientations. Density functional theory (DFT) using non-equilibrium Green’s function (NEGF) method has been implemented to calculate the transmission spectra of mono- and fewlayer MoS2 in armchair and zigzag directions. Phonon transmission spectra are calculated based on parameterization of Stillinger-Weber potential. Thermoelectric figure of merit, ZT, is calculated using these electronic and phonon transmission spectra. In general, a thermoelectric generator is composed of thermocouples made of both n-type and p-type legs. Based on our calculations, monolayer MoS2 in armchair orientation is found to have the highest ZT value for both p-type and n-type legs compared to all other armchair and zigzag structures. We have proposed a thermoelectric generator based on monolayer MoS2 in armchair orientation. Moreover, we have studied the effect of various dopant species on thermoelectric current of our proposed generator. Further, we have compared output current of our proposed generator with those of Silicon thin films. Results indicate that thermoelectric current of MoS2 armchair monolayer is several orders of magnitude higher than that of Silicon thin films. PMID:26333948

Anisotropic thermoelectric behavior in armchair and zigzag mono- and fewlayer MoS2 in thermoelectric generator applications.

PubMed

Arab, Abbas; Li, Qiliang

2015-09-03

In this work, we have studied thermoelectric properties of monolayer and fewlayer MoS2 in both armchair and zigzag orientations. Density functional theory (DFT) using non-equilibrium Green's function (NEGF) method has been implemented to calculate the transmission spectra of mono- and fewlayer MoS2 in armchair and zigzag directions. Phonon transmission spectra are calculated based on parameterization of Stillinger-Weber potential. Thermoelectric figure of merit, ZT, is calculated using these electronic and phonon transmission spectra. In general, a thermoelectric generator is composed of thermocouples made of both n-type and p-type legs. Based on our calculations, monolayer MoS2 in armchair orientation is found to have the highest ZT value for both p-type and n-type legs compared to all other armchair and zigzag structures. We have proposed a thermoelectric generator based on monolayer MoS2 in armchair orientation. Moreover, we have studied the effect of various dopant species on thermoelectric current of our proposed generator. Further, we have compared output current of our proposed generator with those of Silicon thin films. Results indicate that thermoelectric current of MoS2 armchair monolayer is several orders of magnitude higher than that of Silicon thin films.

TeX4 (X = F, Cl, Br) as Lewis acids--complexes with soft thio- and seleno-ether ligands.

PubMed

Hector, Andrew L; Jolleys, Andrew; Levason, William; Reid, Gillian

2012-08-28

TeF(4) reacts with OPR(3) (R = Me or Ph) in anhydrous CH(2)Cl(2) to give the colourless, square based pyramidal 1 : 1 complexes [TeF(4)(OPR(3))] only, in which the OPR(3) is coordinated basally in the solid state, (R = Me: d(Te-O) = 2.122(2) Å; R = Ph: d(Te-O) = 2.1849(14) Å). Variable temperature (19)F{(1)H}, (31)P{(1)H} and (125)Te{(1)H} NMR spectroscopic studies strongly suggest this is the low temperature structure in solution, although the systems are dynamic. The much softer donor ligands SMe(2) and SeMe(2) show a lower affinity for TeF(4), although unstable, yellow products with spectroscopic features consistent with [TeF(4)(EMe(2))] are obtained by the reaction of TeF(4) in neat SMe(2) or via reaction in CH(2)Cl(2) with SeMe(2). TeX(4) (X = F, Cl or Br) causes oxidation and halogenation of TeMe(2) to form X(2)TeMe(2). The Br(2)TeMe(2) hydrolyses in trace moisture to form [BrMe(2)Te-O-TeMe(2)Br], the crystal structure of which has been determined. TeX(4) (X = Cl or Br) react with the selenoethers SeMe(2), MeSe(CH(2))(3)SeMe or o-C(6)H(4)(SeMe)(2) (X = Cl) in anhydrous CH(2)Cl(2) to give the distorted octahedral monomers trans-[TeX(4)(SeMe(2))(2)], cis-[TeX(4){MeSe(CH(2))(3)SeMe}] and cis-[TeCl(4){o-C(6)H(4)(SeMe)(2)}], which have been characterised by IR, Raman and multinuclear NMR ((1)H, (77)Se{(1)H} and (125)Te{(1)H}) spectroscopy, and via X-ray structure determinations of representative examples. Tetrahydrothiophene (tht) can form both 1 : 1 and 1 : 2 Te : L complexes. For X = Br, the former has been shown to be a Br-bridged dimer, [Br(3)(tht)Te(μ-Br)(2)TeBr(3)(tht)], by crystallography with the tht ligands anti, whereas the latter are trans-octahedral monomers. Like its selenoether analogue, MeS(CH(2))(3)SMe forms distorted octahedral cis-chelates, [TeX(4){MeS(CH(2))(3)SMe}], whereas the more rigid o-C(6)H(4)(SMe)(2) unexpectedly forms a zig-zag chain polymer in the solid state, [TeCl(4){o-C(6)H(4)(SMe)(2)}](n), in which the dithioether adopts an extremely unusual bridging mode. This is in contrast to the chelating monomer, cis-[TeCl(4){o-C(6)H(4)(SeMe)(2)}], formed with the analogous selenoether and may be attributed to small differences in the ligand chelate bite angles. The wider bite angle xylyl-linked bidentates, o-C(6)H(4)(CH(2)EMe(2))(2) behave differently; the thioether forms cis-chelated [TeX(4){o-C(6)H(4)(CH(2)SMe)(2)}] confirmed crystallographically, whereas the selenoether undergoes C-Se cleavage and rearrangement on treatment with TeX(4), forming the cyclic selenonium salts, [C(9)H(11)Se](2)[TeX(6)]. The tetrathiamacrocycle, [14]aneS(4) (1,4,8,11-tetrathiacyclotetradecane), does not react cleanly with TeCl(4), but forms the very poorly soluble [TeCl(4)([14]aneS(4))](n), shown by crystallography to be a zig-zag polymer with exo-coordinated [14]aneS(4) units linked via alternate S atoms to a cis-TeCl(4) unit. Trends in the (125)Te{(1)H} NMR shifts for this series of Te(IV) halides chalcogenoether complexes are discussed.

Electro-optical properties of zigzag and armchair boron nitride nanotubes under a transverse electric field: Tight binding calculations

NASA Astrophysics Data System (ADS)

Chegel, Raad; Behzad, Somayeh

2012-02-01

The electro-optical properties of zigzag and armchair BNNTs in a uniform transverse electric field are investigated within tight binding approximation. It is found that the electric field modifies the band structure and splits band degeneracy where these effects reflect in the DOS and JDOS spectra. A decrease in the band gap, as a function of the electric field, is observed. This gap reduction increases with the diameter and it is independent of chirality. An analytic function to estimate the electric field needed for band gap closing is proposed which is in good agreement with DFT results. In additional, we show that the larger diameter tubes are more sensitive than small ones. Number and position of peaks in DOS and JDOS spectra for armchair and zigzag tubes with similar radius are dependent on electric field strength.

Experimental study and modeling of atomic-scale friction in zigzag and armchair lattice orientations of MoS2.

PubMed

Li, Meng; Shi, Jialin; Liu, Lianqing; Yu, Peng; Xi, Ning; Wang, Yuechao

2016-01-01

Physical properties of two-dimensional materials, such as graphene, black phosphorus, molybdenum disulfide (MoS 2 ) and tungsten disulfide, exhibit significant dependence on their lattice orientations, especially for zigzag and armchair lattice orientations. Understanding of the atomic probe motion on surfaces with different orientations helps in the study of anisotropic materials. Unfortunately, there is no comprehensive model that can describe the probe motion mechanism. In this paper, we report a tribological study of MoS 2 in zigzag and armchair orientations. We observed a characteristic power spectrum and friction force values. To explain our results, we developed a modified, two-dimensional, stick-slip Tomlinson model that allows simulation of the probe motion on MoS 2 surfaces by combining the motion in the Mo layer and S layer. Our model fits well with the experimental data and provides a theoretical basis for tribological studies of two-dimensional materials.

Study of structural and optical properties of ZnS zigzag nanostructured thin films

NASA Astrophysics Data System (ADS)

Rahchamani, Seyyed Zabihollah; Rezagholipour Dizaji, Hamid; Ehsani, Mohammad Hossein

2015-11-01

Zinc sulfide (ZnS) nanostructured thin films of different thicknesses with zigzag shapes have been deposited on glass substrates by glancing angle deposition (GLAD) technique. Employing a homemade accessory attached to the substrate holder enabled the authors to control the substrate temperature and substrate angle. The prepared samples were subjected to X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM) and UV-VIS. spectroscopy techniques. The structural studies revealed that the film deposited at room temperature crystallized in cubic structure. The FESEM images of the samples confirmed the formation of zigzag nano-columnar shape with mean diameter about 60-80 nm. By using the data obtained from optical studies, the real part of the refractive index (n), the absorption coefficient (α) and the band gap (Eg) of the samples were calculated. The results show that the refractive indices of the prepared films are very sensitive to deposition conditions.

Sensory Organ Like Response of Zigzag Edge Graphene Nanoribbons

NASA Astrophysics Data System (ADS)

Shenoy, Vijay; Bhowmick, Somnath

2011-03-01

Using a continuum Dirac theory, we study the density and spin response of zigzag edge terminated graphene ribbons subjected to edge potentials and Zeeman fields. Our analytical calculations of the density and spin responses of the closed system (fixed particle number) to the static edge fields, show a highly nonlinear Weber-Fechner type behavior where the response depends logarithmically on the edge potential. The dependence of the response on the size of the system (e.g.~width of a nanoribbon) is also uncovered. Zigzag edge graphene nanoribbons, therefore, provide a realization of response of organs such as the eye and ear that obey Weber-Fechner law. We validate our analytical results with tight binding calculations. These results are crucial in understanding important effects of electron-electron interactions in graphene nanoribbons such as edge magnetism etc., and also suggest possibilities for device applications of graphene nanoribbons. Work supported by DST, India through MONAMI and Ramanujan grants.

Superconducting high-pressure phases composed of hydrogen and iodine

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

Shamp, Andrew; Zurek, Eva

2015-09-25

Evolutionary structure searches predict three new phases of iodine polyhydrides stable under pressure. Insulating P 1-H 5I, consisting of zigzag chains of (HI) δ+ and H 2 molecules, is stable between 30-90 GPa. Cmcm-H 2I and P6/mmm-H 4I are found on the 100, 150 and 200 GPa convex hulls. These two phases are good metals, even at 1 atm, because they consist of monoatomic lattices of iodine. At 100 GPa the superconducting transition temperature, T c, of H 2I and H 4I are estimated to be 7.8 and 17.5 K, respectively. Lastly, the increase in T c relative tomore » elemental iodine results from a larger ω log from the light mass of hydrogen, and an enhanced from modes containing H/I and H/H vibrations.« less

Naphtho[1,2-b:5,6-b']dithiophene-Based Conjugated Polymers for Fullerene-Free Inverted Polymer Solar Cells.

PubMed

Jiang, Zhaoyan; Li, Huan; Wang, Zhen; Zhang, Jianqi; Zhang, Yajie; Lu, Kun; Wei, Zhixiang

2018-03-23

Three novel copolymers based on zigzag naphthodithiophene (zNDT) with different aromatic rings as π bridges and different core side substitutions are designed and synthesized (PzNDT-T-1,3-bis(4-(2-ethylhexyl)-thiophen-2-yl)-5,7-bis(2-ethylhexyl)benzo[1,2-c:4,5-c']-dithiophene-4,8-dione (BDD), PzNDT-TT-BDD, and PzNDTP-T-BDD, respectively). The 2D conjugation structure and molecular planarity of the polymers can be effectively altered through the modification of conjugated side chains and π-bridges. These alterations contribute to the variation in energy levels, light absorption capacity, and morphology compatibility of the polymers. When blended with the nonfullerene acceptor (2,2'-[(4,4,9,9-tetrahexyl-4,9-dihydro-sindaceno[1,2-b:5,6-b']dithiophene-2,7-diyl)bis[methylidyne(3-oxo-1H-indene-2,1(3H)-diylidene)

Field dependence of the magnetic correlations of the frustrated magnet SrDy 2 O 4

DOE PAGES

Gauthier, N.; Fennell, A.; Prévost, B.; ...

2017-05-30

Tmore » he frustrated magnet SrDy 2 O 4 exhibits a field-induced phase with a magnetization plateau at 1 / 3 of the saturation value for magnetic fields applied along the b axis. We report here a neutron scattering study of the nature and symmetry of the magnetic order in this field-induced phase. Below ≈ 0.5 K, there are strong hysteretic effects, and the order is short- or long-ranged for zero-field and field cooling, respectively. We find that the long-range ordered magnetic structure within the zigzag chains is identical to that expected for the one-dimensional axial next-nearest neighbor Ising (ANNNI) model in longitudinal fields. he long-range ordered structure in field contrasts with the short-range order found at zero field, and is most likely reached through enhanced quantum fluctuations with increasing fields.« less

Solitary Magnons in the S=5/2 Antiferromagnet CaFe_{2}O_{4}.

PubMed

Stock, C; Rodriguez, E E; Lee, N; Green, M A; Demmel, F; Ewings, R A; Fouquet, P; Laver, M; Niedermayer, Ch; Su, Y; Nemkovski, K; Rodriguez-Rivera, J A; Cheong, S-W

2016-07-01

CaFe_{2}O_{4} is a S=5/2 anisotropic antiferromagnet based upon zig-zag chains having two competing magnetic structures, denoted as the A (↑↑↓↓) and B (↑↓↑↓) phases, which differ by the c-axis stacking of ferromagnetic stripes. We apply neutron scattering to demonstrate that the competing A and B phase order parameters result in magnetic antiphase boundaries along c which freeze on the time scale of ∼1  ns at the onset of magnetic order at 200 K. Using high resolution neutron spectroscopy, we find quantized spin wave levels and measure 9 such excitations localized in regions ∼1-2 c-axis lattice constants in size. We discuss these in the context of solitary magnons predicted to exist in anisotropic systems. The magnetic anisotropy affords both competing A+B orders as well as localization of spin excitations in a classical magnet.

Solitary Magnons in the S =5/2 Antiferromagnet CaFe2O4

NASA Astrophysics Data System (ADS)

Stock, C.; Rodriguez, E. E.; Lee, N.; Green, M. A.; Demmel, F.; Ewings, R. A.; Fouquet, P.; Laver, M.; Niedermayer, Ch.; Su, Y.; Nemkovski, K.; Rodriguez-Rivera, J. A.; Cheong, S.-W.

2016-07-01

CaFe2O4 is a S =5/2 anisotropic antiferromagnet based upon zig-zag chains having two competing magnetic structures, denoted as the A (↑↑↓↓) and B (↑↓↑↓) phases, which differ by the c -axis stacking of ferromagnetic stripes. We apply neutron scattering to demonstrate that the competing A and B phase order parameters result in magnetic antiphase boundaries along c which freeze on the time scale of ˜1 ns at the onset of magnetic order at 200 K. Using high resolution neutron spectroscopy, we find quantized spin wave levels and measure 9 such excitations localized in regions ˜1 - 2 c -axis lattice constants in size. We discuss these in the context of solitary magnons predicted to exist in anisotropic systems. The magnetic anisotropy affords both competing A +B orders as well as localization of spin excitations in a classical magnet.

Field dependence of the magnetic correlations of the frustrated magnet SrDy2O4

NASA Astrophysics Data System (ADS)

Gauthier, N.; Fennell, A.; Prévost, B.; Désilets-Benoit, A.; Dabkowska, H. A.; Zaharko, O.; Frontzek, M.; Sibille, R.; Bianchi, A. D.; Kenzelmann, M.

2017-05-01

The frustrated magnet SrDy2O4 exhibits a field-induced phase with a magnetization plateau at 1 /3 of the saturation value for magnetic fields applied along the b axis. We report here a neutron scattering study of the nature and symmetry of the magnetic order in this field-induced phase. Below T ≈0.5 K, there are strong hysteretic effects, and the order is short- or long-ranged for zero-field and field cooling, respectively. We find that the long-range ordered magnetic structure within the zigzag chains is identical to that expected for the one-dimensional axial next-nearest neighbor Ising (ANNNI) model in longitudinal fields. The long-range ordered structure in field contrasts with the short-range order found at zero field, and is probably reached through enhanced quantum fluctuations with increasing fields.

Low Melt Viscosity Resins for Resin Transfer Molding

NASA Technical Reports Server (NTRS)

Harris, Frank W.

2002-01-01

In recent years, resin transfer molding (RTM) has become one of the methods of choice for high performance composites. Its cost effectiveness and ease of fabrication are major advantages of RTM. RTM process usually requires resins with very low melt viscosity (less than 10 Poise). The optimum RTM resins also need to display high thennal-oxidative stability, high glass transition temperature (T(sub g)), and good toughness. The traditional PMR-type polyimides (e.g. PMR-15) do not fit this requirement, because the viscosities are too high and the nadic endcap cures too fast. High T(sub g), low-melt viscosity resins are highly desirable for aerospace applications and NASA s Reusable Launch Vehicle (RLV) program. The objective of this work is to prepare low-melt viscosity polyimide resins for RTM or resin film infusion (RFI) processes. The approach involves the synthesis of phenylethynyl-terminated imide oligomers. These materials have been designed to minimize their melt viscosity so that they can be readily processed. During the cure, the oligomers undergo both chain extension and crosslinking via the thermal polymerization of the phenylethynyl groups. The Phenylethynyl endcap is preferred over the nadic group due to its high curing temperature, which provides broader processing windows. This work involved the synthesis and polymerization of oligomers containing zig-zag backbones and twisted biphenyl structures. Some A-B type precursors which possessed both nitro and anhydride functionality, or both nitro and amine functionality, were also synthesized in order to obtain the well defined oligomers. The resulting zig-zag structured oligomers were then end-capped with 4-phenylethynylphthalic anhydride (PEPA) for further cure. The properties of these novel imide oligomers are evaluated.

Cyanide-bridged Fe(III)-Mn(III) bimetallic complexes with dimeric and chain structures constructed from a newly made mer-Fe tricyanide: structures and magnetic properties.

PubMed

Kim, Jae Il; Kwak, Hyun Young; Yoon, Jung Hee; Ryu, Dae Won; Yoo, In Young; Yang, Namgeun; Cho, Beong Ki; Park, Je-Geun; Lee, Hyosug; Hong, Chang Seop

2009-04-06

Four cyanide-linked Fe(III)-Mn(III) complexes were prepared by reacting Mn Schiff bases with a new molecular precursor (PPh(4))[Fe(qcq)(CN)(3)] [1; qcq = 8-(2-quinolinecarboxamido)quinoline anion]. They include a dimeric molecule, [Fe(qcq)(CN)(3)][Mn(3-MeOsalen)(H(2)O)] x 2 H(2)O [2 x 2 H(2)O; 3-MeOsalen = N,N'-ethylenebis(3-methoxysalicylideneiminato) dianion], and three 1D zigzag chains, [Fe(qcq)(CN)(3)][Mn(5-Clsalen)] x 3 H(2)O [3 x 2 MeOH; 5-Clsalen = N,N'-ethylenebis(5-chlorosalicylideneiminato) dianion], [Fe(qcq)(CN)(3)][Mn(5-Brsalen)] x 2 MeOH [4 x 2 MeOH; 5-Brsalen = N,N'-ethylenebis(5-bromosalicylideneiminato) dianion], and Fe(qcq)(CN)(3)][Mn(salen)].MeCN x H(2)O [5 x MeCN; salen = N,N'-ethylenebis(salicylideneiminato) dianion]. The complexes consist of extensive hydrogen bonding and pi-pi stacking interactions, generating multidimensional structures. Magnetic studies demonstrate that antiferromagnetic couplings are operative between Fe(III) and Mn(III) centers bridged by cyanide ligands. On the basis of an infinite chain model, magnetic coupling parameters of 2-5 range from -9.3 to -14.1 cm(-1). A long-range order is observed at 2.3 K for 3 and 2.2 K for 4, while compound 5 shows spin glass behavior possibly coupled with magnetic ordering.

Switching single chain magnet behavior via photoinduced bidirectional metal-to-metal charge transfer† †Electronic supplementary information (ESI) available: Synthesis and physical measurement details. Crystal data in CIF format and additional figures (Fig. S1–S15). CCDC 1528877. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c7sc03401f

PubMed Central

Jiang, Wenjing; Jiao, Chengqi; Meng, Yinshan; Zhao, Liang; Liu, Qiang

2017-01-01

The preparation of single-chain magnets (SCMs) with photo-switchable bistable states is essential for the development of high-density photo-recording devices. However, the reversible switching of the SCM behavior upon light irradiation is a formidable challenge. Here we report a well-isolated double zigzag chain {[Fe(bpy)(CN)4]2[Co(phpy)2]}·2H2O (bpy = 2,2′-bipyridine, phpy = 4-phenylpyridine), which exhibits reversible redox reactions with interconversion between FeIIILS(μ-CN)CoIIHS(μ-NC)FeIIILS (LS = low-spin, HS = high-spin) and FeIIILS(μ-CN)CoIIILS(μ-NC)FeIILS linkages under alternating irradiation with 808 and 532 nm lasers. The bidirectional photo-induced metal-to-metal charge transfer results in significant changes of anisotropy and intrachain magnetic interactions, reversibly switching the SCM behavior. The on-switching SCM behavior driven by light irradiation at 808 nm could be reversibly switched off by irradiation at 532 nm. The results provide an additional and independent way to control the bistable states of SCMs by switching in the 0 → 1 → 0 sequence, with potential applications in high density storage and molecular switches. PMID:29629126

Electron doping effects on the electrical conductivity of zigzag carbon nanotubes and corresponding unzipped armchair graphene nanoribbons

NASA Astrophysics Data System (ADS)

Mousavi, Hamze; Jalilvand, Samira; Kurdestany, Jamshid Moradi; Grabowski, Marek

2017-10-01

The Kubo formula is used to extract the electrical conductivity (EC) of different diameters of doped zigzag carbon nanotubes and their corresponding unzipped armchair graphene nanoribbons, as a function of temperature and chemical potential, within the tight-binding Hamiltonian model and Green's functions approach. The results reveal more sensitivity to temperature for semiconducting systems in addition to a decrease in EC of all systems with increasing cross-sections.

Designing of spin-filtering devices in zigzag graphene nanoribbons heterojunctions by asymmetric hydrogenation and B-N doping

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

Zhang, Dan; Zhang, Xiaojiao; Ouyang, Fangping

2015-01-07

Using nonequilibrium Green's function in combination with the spin-polarized density functional theory, the spin-dependent transport properties of boron and nitrogen doped zigzag graphene nanoribbons (ZGNRs) heterojunctions with single or double edge-saturated hydrogen have been investigated. Our results show that the perfect spin-filtering effect (100%), rectifying behavior and negative differential resistance can be realized in the ZGNRs-based systems. And the corresponding physical analysis has been given.

Nonlinear modeling of crystal system transition of black phosphorus using continuum-DFT model.

PubMed

Setoodeh, A R; Farahmand, H

2018-01-24

In this paper, the nonlinear behavior of black phosphorus crystals is investigated in tandem with dispersion-corrected density functional theory (DFT-D) analysis under uniaxial loadings. From the identified anisotropic behavior of black phosphorus due to its morphological anisotropy, a hyperelastic anisotropic (HA) model named continuum-DFT is established to predict the nonlinear behavior of the material. In this respect, uniaxial Cauchy stresses are employed on both the DFT-D and HA models along the zig-zag and armchair directions. Simultaneously, the transition of the crystal system is recognized at about 4.5 GPa of the applied uniaxial tensile stress along the zig-zag direction on the DFT-D simulation in the nonlinear region. In order to develop the nonlinear continuum model, unknown constants are surveyed with the optimized least square technique. In this regard, the continuum model is obtained to reproduce the Cauchy stress-stretch and density of strain-stretch results of the DFT-D simulation. Consequently, the modified HA model is introduced to characterize the nonlinear behavior of black phosphorus along the zig-zag direction. More importantly, the specific transition of the crystal system is successfully predicted in the new modified continuum-DFT model. The results reveal that the multiscale continuum-DFT model is well defined to replicate the nonlinear behavior of black phosphorus along the zig-zag and armchair directions.

Analytic and Computational Perspectives of Multi-Scale Theory for Homogeneous, Laminated Composite, and Sandwich Beams and Plates

NASA Technical Reports Server (NTRS)

Tessler, Alexander; Gherlone, Marco; Versino, Daniele; DiSciuva, Marco

2012-01-01

This paper reviews the theoretical foundation and computational mechanics aspects of the recently developed shear-deformation theory, called the Refined Zigzag Theory (RZT). The theory is based on a multi-scale formalism in which an equivalent single-layer plate theory is refined with a robust set of zigzag local layer displacements that are free of the usual deficiencies found in common plate theories with zigzag kinematics. In the RZT, first-order shear-deformation plate theory is used as the equivalent single-layer plate theory, which represents the overall response characteristics. Local piecewise-linear zigzag displacements are used to provide corrections to these overall response characteristics that are associated with the plate heterogeneity and the relative stiffnesses of the layers. The theory does not rely on shear correction factors and is equally accurate for homogeneous, laminated composite, and sandwich beams and plates. Regardless of the number of material layers, the theory maintains only seven kinematic unknowns that describe the membrane, bending, and transverse shear plate-deformation modes. Derived from the virtual work principle, RZT is well-suited for developing computationally efficient, C(sup 0)-continuous finite elements; formulations of several RZT-based elements are highlighted. The theory and its finite element approximations thus provide a unified and reliable computational platform for the analysis and design of high-performance load-bearing aerospace structures.

Defect induced plasticity and failure mechanism of boron nitride nanotubes under tension

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

Anoop Krishnan, N. M., E-mail: anoopnm@civil.iisc.ernet.in; Ghosh, Debraj

2014-07-28

The effects of Stone-Wales (SW) and vacancy defects on the failure behavior of boron nitride nanotubes (BNNTs) under tension are investigated using molecular dynamics simulations. The Tersoff-Brenner potential is used to model the atomic interaction and the temperature is maintained close to 300 K. The effect of a SW defect is studied by determining the failure strength and failure mechanism of nanotubes with different radii. In the case of a vacancy defect, the effect of an N-vacancy and a B-vacancy is studied separately. Nanotubes with different chiralities but similar diameter is considered first to evaluate the chirality dependence. The variation ofmore » failure strength with the radius is then studied by considering nanotubes of different diameters but same chirality. It is observed that the armchair BNNTs are extremely sensitive to defects, whereas the zigzag configurations are the least sensitive. In the case of pristine BNNTs, both armchair and zigzag nanotubes undergo brittle failure, whereas in the case of defective BNNTs, only the zigzag ones undergo brittle failure. An interesting defect induced plastic behavior is observed in defective armchair BNNTs. For this nanotube, the presence of a defect triggers mechanical relaxation by bond breaking along the closest zigzag helical path, with the defect as the nucleus. This mechanism results in a plastic failure.« less

Analytic and Computational Perspectives of Multi-Scale Theory for Homogeneous, Laminated Composite, and Sandwich Beams and Plates

NASA Technical Reports Server (NTRS)

Tessler, Alexander; Gherlone, Marco; Versino, Daniele; Di Sciuva, Marco

2012-01-01

This paper reviews the theoretical foundation and computational mechanics aspects of the recently developed shear-deformation theory, called the Refined Zigzag Theory (RZT). The theory is based on a multi-scale formalism in which an equivalent single-layer plate theory is refined with a robust set of zigzag local layer displacements that are free of the usual deficiencies found in common plate theories with zigzag kinematics. In the RZT, first-order shear-deformation plate theory is used as the equivalent single-layer plate theory, which represents the overall response characteristics. Local piecewise-linear zigzag displacements are used to provide corrections to these overall response characteristics that are associated with the plate heterogeneity and the relative stiffnesses of the layers. The theory does not rely on shear correction factors and is equally accurate for homogeneous, laminated composite, and sandwich beams and plates. Regardless of the number of material layers, the theory maintains only seven kinematic unknowns that describe the membrane, bending, and transverse shear plate-deformation modes. Derived from the virtual work principle, RZT is well-suited for developing computationally efficient, C0-continuous finite elements; formulations of several RZT-based elements are highlighted. The theory and its finite elements provide a unified and reliable computational platform for the analysis and design of high-performance load-bearing aerospace structures.

Theoretical prediction of high carrier mobility in single-walled black phosphorus nanotubes

NASA Astrophysics Data System (ADS)

Li, Q. F.; Wang, H. F.; Yang, C. H.; Li, Q. Q.; Rao, W. F.

2018-05-01

One-dimensional semiconductors are promising materials for high-performance nanoscale devices. Using the first-principles calculations combined with deformation potential approximation, we study the electronic structures and carrier transport properties of black phosphorus nanotubes (BPNTs). It is found that both armchair and zigzag BPNTs with diameter 13.5-18.5 Å are direct bandgap semiconductors. At a similar diameter, the carrier mobility of zigzag BPNT is one order of magnitude larger than that of armchair BPNT. For armchair BPNTs, the electron mobility is about 90.70-155.33 cm2 V-1 s-1 at room temperature, which is about three times of its hole counterpart. For zigzag BPNTs, the maximum mobility can reach 2.87 ×103 cm2 V-1 s-1. Furthermore, the electronic properties can be effectively tuned by the strain. For zigzag (0,13) nanotube, there is a direct-to-indirect band gap transition at a tensile strain of about 6%. Moreover, the electron mobility is boosted sharply by one order of magnitude by applying the compressive or tensile strain. The electron mobility increases to 14.05 ×103 cm2 V-1 s-1 at a tensile strain of 9%. Our calculations highlight the tunable electronic properties and superior carrier mobility of BPNTs that are promising for interesting applications in future nano-electronic devices.

Quantitative and qualitative characterization of zigzag spatiotemporal chaos in a system of amplitude equations for nematic electroconvection.

PubMed

Oprea, Iuliana; Triandaf, Ioana; Dangelmayr, Gerhard; Schwartz, Ira B

2007-06-01

It has been suggested by experimentalists that a weakly nonlinear analysis of the recently introduced equations of motion for the nematic electroconvection by M. Treiber and L. Kramer [Phys. Rev. E 58, 1973 (1998)] has the potential to reproduce the dynamics of the zigzag-type extended spatiotemporal chaos and localized solutions observed near onset in experiments [M. Dennin, D. S. Cannell, and G. Ahlers, Phys. Rev. E 57, 638 (1998); J. T. Gleeson (private communication)]. In this paper, we study a complex spatiotemporal pattern, identified as spatiotemporal chaos, that bifurcates at the onset from a spatially uniform solution of a system of globally coupled complex Ginzburg-Landau equations governing the weakly nonlinear evolution of four traveling wave envelopes. The Ginzburg-Landau system can be derived directly from the weak electrolyte model for electroconvection in nematic liquid crystals when the primary instability is a Hopf bifurcation to oblique traveling rolls. The chaotic nature of the pattern and the resemblance to the observed experimental spatiotemporal chaos in the electroconvection of nematic liquid crystals are confirmed through a combination of techniques including the Karhunen-Loeve decomposition, time-series analysis of the amplitudes of the dominant modes, statistical descriptions, and normal form theory, showing good agreement between theory and experiments.

Investigation of the charge-orbital ordering mechanism in single-layered Pr0.5Ca1.5MnO4

NASA Astrophysics Data System (ADS)

Rangkuti, C. N.; Majidi, M. A.

2018-04-01

Motivated by the experimental study of half-doped single-layered Pr0.5Ca1.5MnO4 showing charge, orbital, and spin orderings [1], we propose a model to theoretically study the system to explain such ordering phenomena. The ground state electron configuration reveals that the charges form a checkerboard pattern with alternating Mn3+/Mn4+ sites, while the orbitals are aligned in zigzag chains [1, 2]. We calculate the ground state energy of this system to find the most preferable configuration by comparing three types of configurations (charge-unordered, charge-ordered, and charge-orbital-ordered states). The calculations are based on a tight-binding model representing effective electron hoppings among Mn ions in MnO2-plane. We take into account the horizontally- and vertically-oriented orbital and spin degrees of freedom at Mn sites. We assume that the hopping integral values depend on the relative orientation between the corresponding orbitals of adjacent Mn ions. The interaction terms we incorporate into our effective Hamiltonian include inter-orbital, intra-orbital Hubbard repulsions, and Jahn-Teller distortion [2]. We absorb the exchange interaction between spins into local self-energy that we calculate within dynamical mean field algorithm [2]. Within our model we show a circumstance in which the charge-orbital ordered configuration has the lowest energy, consistent with the ground state ordering revealed by the experimental data.

Geometry, bonding and magnetism in planar triangulene graphene molecules with D3h symmetry: Zigzag Cm∗∗2+4m+1H3m+3 (m = 2, …, 15)

NASA Astrophysics Data System (ADS)

Philpott, Michael R.; Cimpoesu, Fanica; Kawazoe, Yoshiyuki

2008-12-01

Ab initio plane wave based all valence electron DFT calculations with geometry optimization are reported for the electronic structure of planar zigzag edged triangular shaped graphene molecules CH where the zigzag ring number m = 2, …, 15. The largest molecule C 286H 48 has a 3.8 nm side length and retains D3h symmetric geometry. The zone in the middle of the molecules, where the geometry and electronic properties resemble infinite single sheet graphite (graphene), expands with increasing ring number m, driving deviations in geometry, charge and spin to the perimeter. If a molecule is viewed as a set of nested triangular rings of carbon, then the zone where the lattice resembles an infinite sheet of graphene with CC = 142 pm, extends to the middle of the penultimate ring. The radial bonds joining the perimeter carbon atoms to the interior are long CC = 144 pm, except near the three apexes where the bonds are shorter. Isometric surfaces of the total charge density show that the two bonds joined at the apex have the highest valence charge. The perimeter CC bonds establish a simple pattern as the zigzag number increases, which shares some features with the zigzag edges in the D2h linear acenes C 4m+2H 2m+4 and the D6h hexangulenes CH6m but not the D6h symmetric annulenes (CH). The two CC bonds forming each apex are short (≈139 pm), next comes one long bond CC ≈ 142 pm and a middle region where all the CC bonds have length ≈141 pm. The homo-lumo gap declines from 0.53 eV at m = 2 to approximately 0.29 V at m = 15, the latter being larger than found for linear or hexagonal shaped graphenes with comparable edge lengths. Across the molecule the charge on the carbon atoms undergoes a small oscillation following the bipartite lattice. The magnitude of the charge in the same nested triangle decreases monotonically with the distance of the row from the center of the molecule. These systems are predicted to have spin polarized ground states with S = ½( m - 1), in accord with the theorems of Lieb for a bipartite lattice with unequal numbers of sub-lattice carbon atoms. The magnitude of the spin on the atoms increases monotonically from the center to the edges, this effect being greatest on the majority A-sub lattice atoms. The spins are delocalized, not confined to specific atoms as might result in geometries stabilized by islands of aromatic resonance. In the largest systems the magnetic non-bonding levels (NBL) occur as a narrowly distributed set of homos close to the Fermi level, separated from the lower lying valence bond manifold by a gap of about 1 eV. The NBL are a set of disjoint radical orbitals having charge only on atoms belonging to the A-lattice and this charge is concentrated on the perimeter and penultimate row atoms.

D4Z - a new renumbering for iterative solution of ground-water flow and solute- transport equations

USGS Publications Warehouse

Kipp, K.L.; Russell, T.F.; Otto, J.S.

1992-01-01

D4 zig-zag (D4Z) is a new renumbering scheme for producing a reduced matrix to be solved by an incomplete LU preconditioned, restarted conjugate-gradient iterative solver. By renumbering alternate diagonals in a zig-zag fashion, a very low sensitivity of convergence rate to renumbering direction is obtained. For two demonstration problems involving groundwater flow and solute transport, iteration counts are related to condition numbers and spectra of the reduced matrices.

Atomistic full-quantum transport model for zigzag graphene nanoribbon-based structures: Complex energy-band method

NASA Astrophysics Data System (ADS)

Chen, Chun-Nan; Luo, Win-Jet; Shyu, Feng-Lin; Chung, Hsien-Ching; Lin, Chiun-Yan; Wu, Jhao-Ying

2018-01-01

Using a non-equilibrium Green’s function framework in combination with the complex energy-band method, an atomistic full-quantum model for solving quantum transport problems for a zigzag-edge graphene nanoribbon (zGNR) structure is proposed. For transport calculations, the mathematical expressions from the theory for zGNR-based device structures are derived in detail. The transport properties of zGNR-based devices are calculated and studied in detail using the proposed method.

Shape and edge dependent electronic and magnetic properties of silicene nano-flakes

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

Mohan, Brij, E-mail: brijmohanhpu@yahoo.com; Pooja,; Ahluwalia, P. K.

2015-06-24

We performed first-principle study of the geometric, electronic and magnetic properties of arm-chair and zigzag edge silicene nano-flakes of triangular and hexagonal shapes. Electronic properties of silicene nano-flakes show strong dependence on their edge structure and shape. The considered nanostructures shows energy gap ranging ∼ 0.4 – 1.0 eV. Zigzag edged triangular nano-flake is magnetic and semiconducting in nature with 4.0 µ{sub B} magnetic moment and ∼ 0.4 eV energy gap.

Real-time gray-scale photolithography for fabrication of continuous microstructure

NASA Astrophysics Data System (ADS)

Peng, Qinjun; Guo, Yongkang; Liu, Shijie; Cui, Zheng

2002-10-01

A novel real-time gray-scale photolithography technique for the fabrication of continuous microstructures that uses a LCD panel as a real-time gray-scale mask is presented. The principle of design of the technique is explained, and computer simulation results based on partially coherent imaging theory are given for the patterning of a microlens array and a zigzag grating. An experiment is set up, and a microlens array and a zigzag grating on panchromatic silver halide sensitized gelatin with trypsinase etching are obtained.

Proceedings of the Antenna Applications Symposium Held at Monticello, Illinois on 21-23 September 1983. Volume 1.

DTIC Science & Technology

1984-03-01

are the zig-zag [12] and the yagi. A zig-zag antenna is the two-dimensional equivalent of a helix . It may be printed unto a supporting substrate and...In the last decade the advances have been subtle, but none-the-less important in optimizing performance of broadband systems. This paper describes some...geometry commonly used is the planar spiral/ helix antenna. Figure 4 shows a single-mode 2 inch diameter spiral/ helix antenna designed to operate

Anomalous Insulator-Metal Transition in Boron Nitride-Graphene Hybrid Atomic Layers

DTIC Science & Technology

2012-08-13

REPORT Anomalous insulator-metal transition in boron nitride-graphene hybrid atomic layers 14 . ABSTRACT 16. SECURITY CLASSIFICATION OF: The study of...from the DFT calculation. The calculated transmission through a N terminated zigzag edged h-BN nanodomain embedded in graphene is shown in Fig. 14 , with...Energy ε − ε F (eV) 0 0.5 1 1.5 2 Tr an sm is si on FIG. 14 . (Color online) Transmission through a N terminated zigzag edged h-BN nanodomain embedded in

STM/STS investigation of edge structure in epitaxial graphene

NASA Astrophysics Data System (ADS)

Ridene, M.; Girard, J. C.; Travers, L.; David, C.; Ouerghi, A.

2012-08-01

In this paper, we have used low temperature scanning tunneling microscopy and spectroscopy (LT-STM/STS) to study zigzag or armchair edges of epitaxial graphene on 6H-SiC (0001). The monolayer carbon structures exhibit occasionally one-dimensional ridge (1D) in close vicinity to step edge. This ridge exhibits different edges orientations in armchair-zigzag transition which give rise to different local density of states (LDOS) along this 1D structure. This ridge formation is likely explained by residual compressive in-plane stresses.

Zigzag laser with reduced optical distortion

DOEpatents

Albrecht, G.F.; Comaskey, B.; Sutton, S.B.

1994-04-19

The architecture of the present invention has been driven by the need to solve the beam quality problems inherent in Brewster's angle tipped slab lasers. The entrance and exit faces of a solid state slab laser are cut perpendicular with respect to the pump face, thus intrinsically eliminating distortion caused by the unpumped Brewster's angled faces. For a given zigzag angle, the residual distortions inherent in the remaining unpumped or lightly pumped ends may be reduced further by tailoring the pump intensity at these ends. 11 figures.

Zigzag laser with reduced optical distortion

DOEpatents

Albrecht, Georg F.; Comaskey, Brian; Sutton, Steven B.

1994-01-01

The architecture of the present invention has been driven by the need to solve the beam quality problems inherent in Brewster's angle tipped slab lasers. The entrance and exit faces of a solid state slab laser are cut perpendicular with respect to the pump face, thus intrinsically eliminating distortion caused by the unpumped Brewster's angled faces. For a given zigzag angle, the residual distortions inherent in the remaining unpumped or lightly pumped ends may be reduced further by tailoring the pump intensity at these ends.

The relation between ferroelasticity and superconductivity

NASA Technical Reports Server (NTRS)

Molak, A.; Manka, R.

1991-01-01

The high-temperature superconductivity is explained widely by the layered crystal structure. The one- and two-dimensional subsystems and their interaction are investigated here. It is assumed that the high-T(sub c) superconductivity takes place in the two-dimensional subsystem and the increase of the phase transition temperature from 60 K up to 90 K is the consequence of turning on the influence of one-dimensional chains. The interaction between the two subsystems is transferred along the c axis by the phonons of breathing mode, which causes the hybridization of the electronic bonds between these subsystems. The experimental works indicate that the existence of both the chains Cu(1)-O and their interaction with the superconducting plane of Cu(2)-O modify the temperature of the transition to the superconducting state. It is seen from the neutron scattering data that the rates of the interatomic distance dependencies on temperature are changed around 240 K and 90 K. The 'zig-zag' order in Cu(1)-O chains has been postulated but, on the other hand, the vibrations with a large amplitude only were reported. The bi-stabilized situation of the oxygen ions can be caused by the change of distance between these ions and the Ba ions. It leads to the appearance of a two-well potential. Its parameters depend on temperature and the dynamics of the oxygen ions' movement. They can induce the antipolar order, which can be, however, more or less chaotic. The investigation of the ferroelastic properties of Y-Ba-Cu-O samples lead to the conclusion that they are related to jumps of ions inside the given chain and not to a diffusion between different sites in the ab plane. Researchers deduce, thus, that the fluctuating oxygen ions from these chains create dipoles in the ab plane. They can be described with the pseudo-spin formalism (- Pauli matrices). The system can be described with the Ising model. The pseudo-spins interact with phonons and influence the superconductivity in the second subsystem.

The relation between ferroelasticity and superconductivity

NASA Technical Reports Server (NTRS)

Molak, A.; Manka, R.

1990-01-01

The high-temperature superconductivity is explained widely by the layered crystal structure. The one- and two-dimensional subsystems and their interaction are investigated here. It is assumed that the high-T(sub c) superconductivity takes place in the two-dimensional subsystem and the increase of the phase transition temperature from 60 K up to 90 K is the consequence of turning on the influence of one-dimensional chains. The interaction between the two subsystems is transferred along the c axis by the phonons of breathing mode, which causes the hybridization of the electronic bonds between these subsystems. The experimental works indicate that the existence of both the chains Cu(1)-O and their interaction with the superconducting plane of Cu(2)-O modify the temperature of the transition to the superconducting state. It is seen from the neutron scattering data that the rates of the interatomic distance dependencies on temperature are changed around 140 K and 90 K. The 'zig-zag' order in Cu(1)-O chains has been postulated but, on the other hand, the vibrations with a large amplitude only were reported. The bi-stabilized situation of the oxygen ions can be caused by the change of distance between these ions and the Ba ions. It leads to the appearance of a two-well potential. Its parameters depend on temperature and the dynamics of the oxygen ions' movement. They can induce the antipolar order, which can be, however, more or less chaotic. The investigation of the ferroelastic properties of Y-Ba-Cu-O samples lead to the conclusion that they are related to jumps of ions inside the given chain and not to a diffusion between different sites in the ab plane. Researchers deduce thus that the fluctuating oxygen ions from these chains create dipoles in the ab plane. They can be described with the pseudo-spin formalism/ - Pauli matrices/. The system can be described with the Ising model. The pseudo-spins interact with phonons and influence the superconductivity in the second subsystem.

Experimental study and modeling of atomic-scale friction in zigzag and armchair lattice orientations of MoS2

PubMed Central

Li, Meng; Shi, Jialin; Liu, Lianqing; Yu, Peng; Xi, Ning; Wang, Yuechao

2016-01-01

Abstract Physical properties of two-dimensional materials, such as graphene, black phosphorus, molybdenum disulfide (MoS2) and tungsten disulfide, exhibit significant dependence on their lattice orientations, especially for zigzag and armchair lattice orientations. Understanding of the atomic probe motion on surfaces with different orientations helps in the study of anisotropic materials. Unfortunately, there is no comprehensive model that can describe the probe motion mechanism. In this paper, we report a tribological study of MoS2 in zigzag and armchair orientations. We observed a characteristic power spectrum and friction force values. To explain our results, we developed a modified, two-dimensional, stick-slip Tomlinson model that allows simulation of the probe motion on MoS2 surfaces by combining the motion in the Mo layer and S layer. Our model fits well with the experimental data and provides a theoretical basis for tribological studies of two-dimensional materials. PMID:27877869

Effects of electric and magnetic fields on the electronic properties of zigzag carbon and boron nitride nanotubes

NASA Astrophysics Data System (ADS)

Chegel, Raad; Behzad, Somayeh; Ahmadi, Eghbal

2012-04-01

We have investigated the electronic properties of zigzag CNTs and BNNTs under the external transverse electric field and axial magnetic field, using tight binding approximation. It was found that after switching on the electric and magnetic fields, the band modification such as distortion of the degeneracy, change in energy dispersion, subband spacing and band gap size reduction occurs. The band gap of zigzag BNNTs decreases linearly with increasing the electric field strength but the band gap variation for CNTs increases first and later decreases (Metallic) or first hold constant and then decreases (semiconductor). For type (II) CNTs, at a weak magnetic field, by increasing the electric field strength, the band gap remains constant first and then decreases and in a stronger magnetic field the band gap reduction becomes parabolic. For type (III) CNTs, in any magnetic field, the band gap increases slowly until reaches a maximum value and then decreases linearly. Unlike to CNTs, the magnetic field has less effects on the BNNTs band gap variation.

Formation of Stone-Wales edge: Multistep reconstruction and growth mechanisms of zigzag nanographene.

PubMed

Dang, Jing-Shuang; Wang, Wei-Wei; Zheng, Jia-Jia; Nagase, Shigeru; Zhao, Xiang

2017-10-05

Although the existence of Stone-Wales (5-7) defect at graphene edge has been clarified experimentally, theoretical study on the formation mechanism is still imperfect. In particular, the regioselectivity of multistep reactions at edge (self-reconstruction and growth with foreign carbon feedstock) is essential to understand the kinetic behavior of reactive boundaries but investigations are still lacking. Herein, by using finite-sized models, multistep reconstructions and carbon dimer additions of a bared zigzag edge are introduced using density functional theory calculations. The zigzag to 5-7 transformation is proved as a site-selective process to generate alternating 5-7 pairs sequentially and the first step with largest barrier is suggested as the rate-determining step. Conversely, successive C 2 insertions on the active edge are calculated to elucidate the formation of 5-7 edge during graphene growth. A metastable intermediate with a triple sequentially fused pentagon fragment is proved as the key structure for 5-7 edge formation. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

Atom-Dependent Edge-Enhanced Second-Harmonic Generation on MoS2 Monolayers.

PubMed

Lin, Kuang-I; Ho, Yen-Hung; Liu, Shu-Bai; Ciou, Jian-Jhih; Huang, Bo-Ting; Chen, Christopher; Chang, Han-Ching; Tu, Chien-Liang; Chen, Chang-Hsiao

2018-02-14

Edge morphology and lattice orientation of single-crystal molybdenum disulfide (MoS 2 ) monolayers, a transition metal dichalcogenide (TMD), possessing a triangular shape with different edges grown by chemical vapor deposition are characterized by atomic force microscopy and transmission electron microscopy. Multiphoton laser scanning microscopy is utilized to study one-dimensional atomic edges of MoS 2 monolayers with localized midgap electronic states, which result in greatly enhanced optical second-harmonic generation (SHG). Microscopic S-zigzag edge and S-Mo Klein edge (bare Mo atoms protruding from a S-zigzag edge) terminations and the edge-atom dependent resonance energies can therefore be deduced based on SHG images. Theoretical calculations based on density functional theory clearly explain the lower energy of the S-zigzag edge states compared to the corresponding S-Mo Klein edge states. Characterization of the atomic-scale variation of edge-enhanced SHG is a step forward in this full-optical and high-yield technique of atomic-layer TMDs.

Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes: A comparative study

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

Singh, Ram Sevak, E-mail: singh915@gmail.com

2015-11-15

Influence of oxygen impurity on electronic properties of carbon and boron nitride nanotubes (CNTs and BNNTs) is systematically studied using first principle calculations based on density functional theory. Energy band structures and density of states of optimized zigzag (5, 0), armchair (3, 3), and chiral (4, 2) structures of CNT and BNNT are calculated. Oxygen doping in zigzag CNT exhibits a reduction in metallicity with opening of band gap in near-infrared region while metallicity is enhanced in armchair and chiral CNTs. Unlike oxygen-doped CNTs, energy bands are drastically modulated in oxygen-doped zigzag and armchair BNNTs, showing the nanotubes to havemore » metallic behaviour. Furthermore, oxygen impurity in chiral BNNT induces narrowing of band gap, indicating a gradual modification of electronic band structure. This study underscores the understanding of different electronic properties induced in CNTs and BNNTs under oxygen doping, and has potential in fabrication of various nanoelectronic devices.« less

Bandgaps and directional propagation of elastic waves in 2D square zigzag lattice structures

NASA Astrophysics Data System (ADS)

Wang, Yan-Feng; Wang, Yue-Sheng; Zhang, Chuanzeng

2014-12-01

In this paper we propose various types of two-dimensional (2D) square zigzag lattice structures, and we study their bandgaps and directional propagation of elastic waves. The band structures and the transmission spectra of the systems are calculated by using the finite element method. The effects of the geometry parameters of the 2D-zigzag lattices on the bandgaps are investigated and discussed. The mechanism of the bandgap generation is analyzed by studying the vibration modes at the bandgap edges. Multiple wide complete bandgaps are found in a wide porosity range owing to the separation of the degeneracy by introducing bending arms. The bandgaps are sensitive to the geometry parameters of the systems. The deformed displacement fields of the transient response of finite structures subjected to time-harmonic loads are presented to show the directional wave propagation. The research in this paper is relevant to the practical design of cellular structures with enhanced vibro-acoustics performance.

Transverse single-file diffusion and enhanced longitudinal diffusion near a subcritical bifurcation

NASA Astrophysics Data System (ADS)

Dessup, Tommy; Coste, Christophe; Saint Jean, Michel

2018-05-01

A quasi-one-dimensional system of repelling particles undergoes a configurational phase transition when the transverse confining potential decreases. Below a threshold, it becomes energetically favorable for the system to adopt one of two staggered raw patterns, symmetric with respect to the system axis. This transition is a subcritical pitchfork bifurcation for short range interactions. As a consequence, the homogeneous zigzag pattern is unstable in a finite zigzag amplitude range [hC 1,hC 2] . We exhibit strong qualitative effects of the subcriticality on the thermal motions of the particles. When the zigzag amplitude is close enough to the limits hC 1 and hC 2, a transverse vibrational soft mode occurs which induces a strongly subdiffusive behavior of the transverse fluctuations, similar to single-file diffusion. On the contrary, the longitudinal fluctuations are enhanced, with a diffusion coefficient which is more than doubled. Conversely, a simple measurement of the thermal fluctuations allows a precise determination of the bifurcation thresholds.

Effect of uniaxial stress on the electrochemical properties of graphene with point defects

NASA Astrophysics Data System (ADS)

Szroeder, Paweł; Sagalianov, Igor Yu.; Radchenko, Taras M.; Tatarenko, Valentyn A.; Prylutskyy, Yuriy I.; Strupiński, Włodzimierz

2018-06-01

We report a calculational study of electron states and the resulting electrochemical properties of uniaxially strained graphene with point defects. For this study the reduction of ferricyanide to ferrocyanide serves as a benchmark electrochemical reaction. We find that the heterogeneous electron transfer activity of the perfect graphene electrode rises under uniaxial strain. However, evolution of the cathodic reaction rate depends on the direction of strain. For moderate lattice deformations, the zigzag strain improves electrochemical performance better than the armchair strain. Standard rate constant increases by 50% at the zigzag strain of 10%. Vacancies, covalently bonded moieties, charged adatoms and substitutional impurities in the zigzag strained graphene induce changes in the shape of the curve of the cathodic reaction rate. However, this changes do not translate into the electrocatalytic activity. Vacancies and covalently bonded moieties at concentration of 0.1% do not affect the electrochemical performance. Charged adatoms and substitutional impurities give a slight increase in the standard rate constant by, respectively, 2.2% and 3.4%.

Two-dimensional arsenic monolayer sheet predicted from first-principles

NASA Astrophysics Data System (ADS)

Pu, Chun-Ying; Ye, Xiao-Tao; Jiang, Hua-Long; Zhang, Fei-Wu; Lu, Zhi-Wen; He, Jun-Bao; Zhou, Da-Wei

2015-03-01

Using first-principles calculations, we investigate the two-dimensional arsenic nanosheet isolated from bulk gray arsenic. Its dynamical stability is confirmed by phonon calculations and molecular dynamics analyzing. The arsenic sheet is an indirect band gap semiconductor with a band gap of 2.21 eV in the hybrid HSE06 functional calculations. The valence band maximum (VBM) and the conduction band minimum (CBM) are mainly occupied by the 4p orbitals of arsenic atoms, which is consistent with the partial charge densities of VBM and CBM. The charge density of the VBM G point has the character of a π bond, which originates from p orbitals. Furthermore, tensile and compressive strains are applied in the armchair and zigzag directions, related to the tensile deformations of zigzag and armchair nanotubes, respectively. We find that the ultimate strain in zigzag deformation is 0.13, smaller than 0.18 of armchair deformation. The limit compressive stresses of single-layer arsenic along armchair and zigzag directions are -4.83 GPa and -4.76 GPa with corresponding strains of -0.15 and -0.14, respectively. Projected supported by the Henan Joint Funds of the National Natural Science Foundation of China (Grant Nos. U1304612 and U1404608), the National Natural Science Foundation of China (Grant Nos. 51374132 and 11404175), the Special Fund for Theoretical Physics of China (Grant No. 11247222), and Nanyang Normal University Science Foundation, China (Grant Nos. ZX2012018 and ZX2013019).

Intermolecular C-H···O, Cl···Cl and π-π interactions in the 2-dichloromethyl derivative of vitamin K3.

PubMed

Soave, Raffaella; Colombo, Pietro

2013-12-15

The title 1,4-naphthoquinone, 2-dichloromethyl-3-methyl-1,4-dihydronaphthalene-1,4-dione, C12H8Cl2O2, is a chlorinated derivative of vitamin K3, which is a synthetic compound also known as menadione. Molecules of (I) are planar and lie on a crystallographic mirror plane (Z' = 0.5) in the space group Pnma. They are connected to each other by C-H···O hydrogen bonds, forming two-dimensional layers parallel to the ac plane. In addition, Cl···Cl and π-π interactions link adjacent molecules in different layers, thus forming zigzag ribbons along the b axis, such that a three-dimensional architecture is generated.

Shale oil recovery process

DOEpatents

Zerga, Daniel P.

1980-01-01

A process of producing within a subterranean oil shale deposit a retort chamber containing permeable fragmented material wherein a series of explosive charges are emplaced in the deposit in a particular configuration comprising an initiating round which functions to produce an upward flexure of the overburden and to initiate fragmentation of the oil shale within the area of the retort chamber to be formed, the initiating round being followed in a predetermined time sequence by retreating lines of emplaced charges developing further fragmentation within the retort zone and continued lateral upward flexure of the overburden. The initiating round is characterized by a plurality of 5-spot patterns and the retreating lines of charges are positioned and fired along zigzag lines generally forming retreating rows of W's. Particular time delays in the firing of successive charges are disclosed.

Assembly and property research on seven 0D–3D complexes derived from imidazole dicarboxylate and 1,2-bi(pyridin-4-yl)ethene

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

Mu, Bao; Li, Qian; Lv, Lei

2015-03-15

The hydrothermal reaction of transition metals, 1H-imidazole-4,5-dicarboxylic acid (H{sub 3}ImDC) and 1,2-bi(pyridin-4-yl)ethene (bpe) affords a series of new complexes, namely, [Mn(HImDC)(bpe)(H{sub 2}O)] (1), [M(H{sub 2}ImDC){sub 2}(H{sub 2}O){sub 2}]·(bpe) (M=Fe(2), Co(3), Zn(4), Cd(6)), [Zn{sub 3}(ImDC){sub 2}(bpe)(H{sub 2}O)]·3H{sub 2}O (5) and [Cd(H{sub 2}ImDC)(bpe)] (7), which are characterized by elemental analyses, IR, TG, XRPD and single crystal X-ray diffraction. Complex 1 exhibits a one dimensional (1D) zigzag chain with two types of irregular rings, and the 1D chains are linked to form a three dimensional (3D) supramolecular framework by the hydrogen bonding interactions (O–H∙∙∙O and O–H∙∙∙N). Complexes 2–4 and 6 are isomorphous, andmore » they display the mononuclear structures. In these complexes, the O–H∙∙∙O and O–H∙∙∙N hydrogen bonds play an important role in sustaining the whole 3D supramolecular frameworks. Complex 5 shows a (3,3)-connected 3D framework with (10{sup 3}) topology, and the lattice water molecules as guest molecules exist in the 3D framework. Complex 7 is a wave-like two dimensional (2D) structure, in which the adjacent 1D chains point at the opposite directions. Moreover, the fluorescent properties of complexes 1–7 and the magnetic property of 1 have been investigated. The water vapor adsorption for complex 5 has been researched at 298 K. - Graphical abstract: Seven new complexes based on different structural characteristics have been hydrothermally synthesized by the mixed ligands. The fluorescent properties, the magnetic property and the water vapor adsorption have been investigated. - Highlights: • The semi-rigid ligand with C=C bonds and imidazole dicarboxylates with some advantages have been used. • A series of new complexes with different structural characteristics have been discussed in detail. • The fluorescent properties, the magnetic property and the water vapor adsorption have been investigated.« less

Patterning nanowire and micro-nanoparticle array on micropillar-structured surface: Experiment and modeling.

PubMed

Lin, Chung Hsun; Guan, Jingjiao; Chau, Shiu Wu; Chen, Shia Chung; Lee, L James

2010-08-04

DNA molecules in a solution can be immobilized and stretched into a highly ordered array on a solid surface containing micropillars by molecular combing technique. However, the mechanism of this process is not well understood. In this study, we demonstrated the generation of DNA nanostrand array with linear, zigzag, and fork-zigzag patterns and the microfluidic processes are modeled based on a deforming body-fitted grid approach. The simulation results provide insights for explaining the stretching, immobilizing, and patterning of DNA molecules observed in the experiments.

Method and apparatus for reducing the harmonic currents in alternating-current distribution networks

DOEpatents

Beverly, Leon H.; Hance, Richard D.; Kristalinski, Alexandr L.; Visser, Age T.

1996-01-01

An improved apparatus and method reduce the harmonic content of AC line and neutral line currents in polyphase AC source distribution networks. The apparatus and method employ a polyphase Zig-Zag transformer connected between the AC source distribution network and a load. The apparatus and method also employs a mechanism for increasing the source neutral impedance of the AC source distribution network. This mechanism can consist of a choke installed in the neutral line between the AC source and the Zig-Zag transformer.

Method and apparatus for reducing the harmonic currents in alternating-current distribution networks

DOEpatents

Beverly, L.H.; Hance, R.D.; Kristalinski, A.L.; Visser, A.T.

1996-11-19

An improved apparatus and method reduce the harmonic content of AC line and neutral line currents in polyphase AC source distribution networks. The apparatus and method employ a polyphase Zig-Zag transformer connected between the AC source distribution network and a load. The apparatus and method also employs a mechanism for increasing the source neutral impedance of the AC source distribution network. This mechanism can consist of a choke installed in the neutral line between the AC source and the Zig-Zag transformer. 23 figs.

Focusing and directional beaming effects of airborne sound through a planar lens with zigzag slits

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

Tang, Kun; Qiu, Chunyin, E-mail: cyqiu@whu.edu.cn; Lu, Jiuyang

2015-01-14

Based on the Huygens-Fresnel principle, we design a planar lens to efficiently realize the interconversion between the point-like sound source and Gaussian beam in ambient air. The lens is constructed by a planar plate perforated elaborately with a nonuniform array of zigzag slits, where the slit exits act as subwavelength-sized secondary sources carrying desired sound responses. The experiments operated at audible regime agree well with the theoretical predictions. This compact device could be useful in daily life applications, such as for medical and detection purposes.

Idiosyncratic Findings in Trichoscopy of Tinea Capitis: Comma, Zigzag Hairs, Corkscrew, and Morse Code-like Hair

PubMed Central

Elghblawi, Ebtisam

2016-01-01

Dermoscopy is a method of growing significance in the diagnoses of dermatological pigmented skin diseases. However, in my case, mycology culture was negative and successful treatment was given on the basis of trichoscopy and wood lamp examination. I hereby describe a young boy with tinea capitis, multiple “comma hairs” and “zigzag hair” and a subtle additional feature “Morse code-like hair” when intensification was applied. Dermatoscopic aspects found skin Type 2 in a child of as a distinctive dermoscopic finding. PMID:28442876

Idiosyncratic Findings in Trichoscopy of Tinea Capitis: Comma, Zigzag Hairs, Corkscrew, and Morse Code-like Hair.

PubMed

Elghblawi, Ebtisam

2016-01-01

Dermoscopy is a method of growing significance in the diagnoses of dermatological pigmented skin diseases. However, in my case, mycology culture was negative and successful treatment was given on the basis of trichoscopy and wood lamp examination. I hereby describe a young boy with tinea capitis, multiple "comma hairs" and "zigzag hair" and a subtle additional feature "Morse code-like hair" when intensification was applied. Dermatoscopic aspects found skin Type 2 in a child of as a distinctive dermoscopic finding.

Effect of edge defects on band structure of zigzag graphene nanoribbons

NASA Astrophysics Data System (ADS)

Wadhwa, Payal; Kumar, Shailesh; Dhilip Kumar, T. J.; Shukla, Alok; Kumar, Rakesh

2018-04-01

In this article, we report band structure studies of zigzag graphene nanoribbons (ZGNRs) on introducing defects (sp3 hybridized carbon atoms) in different concentrations at edges by varying the ratio of sp3 to sp2 hybridized carbon atoms. On the basis of theoretical analyses, bandgap values of ZGNRs are found to be strongly dependent on the relative arrangement of sp3 to sp2 hybridized carbon atoms at the edges for a defect concentration; so the findings would greatly help in understanding the bandgap of nanoribbons for their electronic applications.

Size effect on the magnetic and electronic properties of the monolayer lateral hetero-junction WS2-MoS2 nanoribbon

NASA Astrophysics Data System (ADS)

Wen, Yan-Ni; Xia, Ming-Gang; Zhang, Sheng-Li

2016-05-01

By using the VASP, we studied the magnetic and electronic properties of the monolayer lateral hetero-junction WS2-MoS2-nanoribbons (WS2-MoS2-NRs). Our results show that the NRs' edge chirality and width affect significantly its magnetic and electronic properties. The monolayer lateral hetero-junction ZZ-WS2-MoS2-NRs(ZZ: zigzag) exhibitmetallic behavior and have considerable magnetic moment. Their magnetic moments decrease in the order of Nz = 2, 6 and 4 (the width of NRs). While, the magnetic moment decreases with the increased rz (the number of the Mo-S chains, rz ≠ 0 and rz ≠ Nz) at the same width Nz. The NA-AC-WS2-NR (AC: armchair) and NA-AC-WS2-MoS2-NR-1 (the number of the Mo-S chain is 1) show metallic behavior when NA = 3 (the width of NRs). The other monolayer lateral hetero-junction AC-WS2-MoS2-NRs remain the nonmagnetic and semiconductingbehavior as bulk. But they are indirect band-gap except for the NA = 3, rA = 2 (the number of the Mo-S chains) and NA = 7, rA = 0 when NA < 9. However they are direct band-gap when NA ≥ 9. Their lowest and highest band gaps are 0.150 eV and 0.581 eV, respectively. These unique magnetic and electronic properties will provide guidanceon the WS2-MoS2 hetero-junction application in nanodevice.

Geometry of the neoproterozoic and paleozoic rift margin of western Laurentia: Implications for mineral deposit settings

USGS Publications Warehouse

Lund, K.

2008-01-01

The U.S. and Canadian Cordilleran miogeocline evolved during several phases of Cryogenian-Devonian intracontinental rifting that formed the western mangin of Laurentia. Recent field and dating studies across central Idaho and northern Nevada result in identification of two segments of the rift margin. Resulting interpretations of rift geometry in the northern U.S. Cordillera are compatible with interpretations of northwest- striking asymmetric extensional segments subdivided by northeast-striking transform and transfer segments. The new interpretation permits integration of miogeoclinal segments along the length of the western North American Cordillera. For the U.S. Cordillera, miogeoclinal segments include the St. Mary-Moyie transform, eastern Washington- eastern Idaho upper-plate margin, Snake River transfer, Nevada-Utah lower-plate margin, and Mina transfer. The rift is orthogonal to most older basement domains, but the location of the transform-transfer zones suggests control of them by basement domain boundaries. The zigzag geometry of reentrants and promontories along the rift is paralleled by salients and recesses in younger thrust belts and by segmentation of younger extensional domains. Likewise, transform transfer zones localized subsequent transcurrent structures and igneous activity. Sediment-hosted mineral deposits trace the same zigzag geometry along the margin. Sedimentary exhalative (sedex) Zn-Pb-Ag ??Au and barite mineral deposits formed in continental-slope rocks during the Late Devonian-Mississippian and to a lesser degree, during the Cambrian-Early Ordovician. Such deposits formed during episodes of renewed extension along miogeoclinal segments. Carbonate-hosted Mississippi Valley- type (MVT) Zn-Pb deposits formed in structurally reactivated continental shelf rocks during the Late Devonian-Mississippian and Mesozoic due to reactivation of preexisting structures. The distribution and abundance of sedex and MVT deposits are controlled by the polarity and kinematics of the rift segment. Locally, discrete mineral belts parallel secondary structures such as rotated crustal blocks at depth that produced sedimentary subbasins and conduits for hydrothermal fluids. Where the miogeocline was overprinted by Mesozoic and Cenozoic deformation and magmatism, igneous rock-related mineral deposits are common. ??2008 Geological Society of America.

From Kondo to local singlet state in graphene nanoribbons with magnetic impurities

NASA Astrophysics Data System (ADS)

Diniz, G. S.; Luiz, G. I.; Latgé, A.; Vernek, E.

2018-03-01

A detailed analysis of the Kondo effect of a magnetic impurity in a zigzag graphene nanoribbon is addressed. An adatom is coupled to the graphene nanoribbon via a hybridization amplitude Γimp in a hollow- or top-site configuration. In addition, the adatom is also weakly coupled to a metallic scanning tunnel microscope (STM) tip by a hybridization function Γtip that provides a Kondo screening of its magnetic moment. The entire system is described by an Anderson-like Hamiltonian whose low-temperature physics is accessed by employing the numerical renormalization-group approach, which allows us to obtain the thermodynamic properties used to compute the Kondo temperature of the system. We find two screening regimes when the adatom is close to the edge of the zigzag graphene nanoribbon: (1) a weak-coupling regime (Γimp≪Γtip ), in which the edge states produce an enhancement of the Kondo temperature TK, and (2) a strong-coupling regime (Γimp≫Γtip ), in which a local singlet is formed, to the detriment of the Kondo screening by the STM tip. These two regimes can be clearly distinguished by the dependence of their characteristic temperature T* on the coupling between the adatom and the carbon sites of the graphene nanoribbon Vimp. We observe that in the weak-coupling regime T* increases exponentially with Vimp2. Differently, in the strong-coupling regime, T* increases linearly with Vimp2.

Afocal three-mirror anastigmat with zigzag optical axis for widened field of view and enlarged aperture

NASA Astrophysics Data System (ADS)

Li, Qi; Han, Lin; Jin, Yangming; Shen, Weimin

2016-10-01

In order to improve the detection accuracy and range of new generation of Forward Looking Infra-Red (FLIR) system for distant targets, its optical system, which usually consists of a fore afocal telescope and rear imaging lenses, is required to has wide spectral range, large entrance pupil aperture, and wide field of view (FOV). In this paper, a new afocal Three-Mirror Anastigmat (TMA) with widened field of view and high demagnification is suggested. Its mechanical structure remains coaxial, but it has zigzag optical axis through properly and slightly decentering and tilting of the three mirrors to avoid its secondary obscuration due to the third mirror as FOV increase. Compared with conventional off-axis TMA, the suggested zigzag-axis TMA is compact, easy-alignment and low-cost. The design method and optimum result of the suggested afocal TMA is presented. Its initial structural parameters are determined with its first-order relationship and primary aberration theory. Slight and proper decentration and tilt of each mirror is leaded in optimization so that its coaxial mechanical structure is held but attainable FOV and demagnification are respectively as wide and as high as possible. As an example, a 5.5-demagnification zigzag-axis afocal TMA with a wavelength range, an entrance pupil diameter, and FOV respectively from 3μm to 12μm, of 320mm, and 2×3.2 degrees and with a real exit pupil, is designed. Its imaging quality is diffraction limited. It is suitable for fore afocal telescope of the so-called third generation FLIR.

Optimal design of wavy microchannel and comparison of heat transfer characteristics with zigzag and straight geometries

NASA Astrophysics Data System (ADS)

Parlak, Zekeriya

2018-05-01

Design concept of microchannel heat exchangers is going to plan with new flow microchannel configuration to reduce the pressure drop and improve heat transfer performance. The study aims to find optimum microchannel design providing the best performance of flow and heat transfer characterization in a heat sink. Therefore, three different types of microchannels in which water is used, straight, wavy and zigzag have been studied. The optimization operation has been performed to find optimum geometry with ANSYS's Response Surface Optimization Tool. Primarily, CFD analysis has been performed by parameterizing a wavy microchannel geometry. Optimum wavy microchannel design has been obtained by the response surface created for the range of velocity from 0.5 to 5, the range of amplitude from 0.06 to 0.3, the range of microchannel height from 0.1 to 0.2, the range of microchannel width from 0.1 to 0.2 and range of sinusoidal wave length from 0.25 to 2.0. All simulations have been performed in the laminar regime for Reynolds number ranging from 100 to 900. Results showed that the Reynolds number range corresponding to the industrial pressure drop limits is between 100 and 400. Nu values obtained in this range for optimum wavy geometry were found at a rate of 10% higher than those of the zigzag channel and 40% higher than those of the straight channels. In addition, when the pressure values of the straight channel did not exceed 10 kPa, the inlet pressure data calculated for zigzag and wavy channel data almost coincided with each other.

Optimal packing size of non-ligated CdSe nanoclusters for microstructure synthesis

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

Tefera, Anteneh G.; Mochena, Mogus D.; Johnson, Elijah

2014-09-14

Structural and electrostatic properties of nanoclusters of CdSe of diameter 1–2 nm are studied with first principle calculations to determine the optimal size for synthesizing microstructures. Based on robustness of the core structure, i.e., the retention of tetrahedral geometry, hexagonal ring structure, and overall wu{sup ¨}rtzite structure to surface relaxations, we conclude that nanoclusters of ~2 nm diameter are the best candidates to form a dense microstructure with minimal interstitial space. Se-terminated surfaces retain a zigzag structure as Se atoms are pulled out and Cd atoms are pulled in due to relaxation, therefore, are best suited for inter-nanocluster formations.

Optical design of a street lamp based on dual-module chip-on-board LED arrays.

PubMed

Ge, Aiming; Cai, Jinlin; Chen, Dehua; Shu, Hongyun; Qiu, Peng; Wang, Junwei; Zhu, Ling

2014-09-01

We design and propose a compact street lamp based on dual-module chip-on-board LED. The street lamp is composed of six faceted reflectors. It can direct the luminous flux and form uniform illumination on the target area, and it effectively reduces power consumption. We have conducted both simulations and prototype measurements. The test results show good optical performance in that the uniformity of luminance reaches 0.58 for LED lamp zigzag arrangements and 0.60 for LED lamp double-side arrangements. The average luminance can fulfill the requirements in Chinese road lighting Standard CJJ45-2006.

Optical absorption of zigzag single walled boron nitride nanotubes in axial magnetic field

NASA Astrophysics Data System (ADS)

Chegel, Raad; Behzad, Somayeh

2013-11-01

We have investigated the effect of axial magnetic field on the band structure, dipole matrix elements and absorption spectrum in different energy ranges, using tight binding approximation. It is found that magnetic field breaks the degeneracy in the band structure and creates new allowed transitions in the dipole matrix which leads to creation of new peaks in the absorption spectrum. It is found that, unlike to CNTs which show metallic-semiconductor transition, the BNNTs remain semiconductor in any magnetic field strength. By calculation the diameter dependence of peak positions, we found that the positions of three first peaks in the lower energy region (E <5.3 eV) are proportional to n-2. In the middle energy region (7 < E < 7.5 eV) all (n, 0) zigzag BNNTs, with even and odd nanotube index, have two distinct peaks in the absence of magnetic field which these peaks may be used to identify zigzag BNNTs from other tube chiralities. For odd (even) tubes, in the middle energy region, applying the magnetic field leads to splitting of these two peaks into three (five) distinct peaks.

Modelling of single walled carbon nanotube cylindrical structures with finite element method simulations

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

Günay, E.

In this study, the modulus of elasticity and shear modulus values of single-walled carbon nanotubes SWCNTs were modelled by using both finite element method and the Matlab code. Initially, cylindrical armchair and zigzag single walled 3D space frames were demonstrated as carbon nanostructures. Thereafter, macro programs were written by the Matlab code producing the space truss for zigzag and armchair models. 3D space frames were introduced to the ANSYS software and then tension, compression and additionally torsion tests were performed on zigzag and armchair carbon nanotubes with BEAM4 element in obtaining the exact values of elastic and shear modulus values.more » In this study, two different boundary conditions were tested and especially used in torsion loading. The equivalent shear modulus data was found by averaging the corresponding values obtained from ten different nodal points on the nanotube path. Finally, in this study it was determined that the elastic constant values showed proportional changes by increasing the carbon nanotube diameters up to a certain level but beyond this level these values remained stable.« less

Valley dependent transport in graphene L junction

NASA Astrophysics Data System (ADS)

Chan, K. S.

2018-05-01

We studied the valley dependent transport in graphene L junctions connecting an armchair lead and a zigzag lead. The junction can be used in valleytronic devices and circuits. Electrons injected from the armchair lead into the junction is not valley polarized, but they can become valley polarized in the zigzag lead. There are Fermi energies, where the current in the zigzag lead is highly valley polarized and the junction is an efficient generator of valley polarized current. The features of the valley polarized current depend sensitively on the widths of the two leads, as well as the number of dimers in the armchair lead, because this number has a sensitive effect on the band structure of the armchair lead. When an external potential is applied to the junction, the energy range with high valley polarization is enlarged enhancing its function as a generator of highly valley polarized current. The scaling behavior found in other graphene devices is also found in L junctions, which means that the results presented here can be extended to junctions with larger dimensions after appropriate scaling of the energy.

Buckling-dependent switching behaviours in shifted bilayer germanene nanoribbons: A computational study

NASA Astrophysics Data System (ADS)

Arjmand, T.; Tagani, M. Bagheri; Soleimani, H. Rahimpour

2018-01-01

Bilayer germanene nanoribbons are investigated in different stacks like buckled and flat armchair and buckled zigzag germanene nanoribbons by performing theoretical calculations using the nonequilibrium Greens function method combined with density functional theory. In these bilayer types, the current oscillates with change of interlayer distances or intra-layer overlaps and is dependent on the type of the bilayer. Band gap of AA-stacked of shifted flat bilayer armchair germanene nanoribbon oscillates by change of interlayer distance which is in contrast to buckled bilayer armchair germanene nanoribbon. So, results show the buckling makes system tend to be a semiconductor with wide band gap. Therefore, AA-stacked of shifted flat bilayer armchair germanene nanoribbon has properties between zigzag and armchair edges, the higher current under bias voltages similar to zigzag edge and also oscillations in current like buckled armchair edges. Also, it is found that HOMO-LUMO band gap strongly affects oscillation in currents and their I-V characteristic. This kind of junction improves the switching properties at low voltages around the band gap.

Charge transport in doped zigzag phosphorene nanoribbons

NASA Astrophysics Data System (ADS)

Nourbakhsh, Zahra; Asgari, Reza

2018-06-01

The effects of lattice distortion and chemical disorder on charge transport properties of two-terminal zigzag phosphorene nanoribbons (zPNRs), which shows resonant tunneling behavior under an electrical applied bias, are studied. Our comprehensive study is based on ab initio quantum transport calculations on the basis of the Landauer theory. We use nitrogen and silicon substitutional dopant atoms, and employ different physical quantities such as the I -V curve, voltage drop behavior, transmission spectrum, transmission pathway, and atomic current to explore the transport mechanism of zPNR devices under a bias voltage. The calculated transmission pathways show the transition from a ballistic transport regime to a diffusive and in some particular cases to localized transport regimes. Current flowing via the chemical bonds and hopping are monitored; however, the conductance originates mainly from the charge traveling through the chemical bonds in the vicinity of the zigzag edges. Our results show that in the doped systems, the device conductance decreases and the negative differential resistance characteristic becomes weak or is eliminated. Besides, the conductance in a pure zPNR system is almost independent of the ribbon width.

Bandgaps and directional properties of two-dimensional square beam-like zigzag lattices

NASA Astrophysics Data System (ADS)

Wang, Yan-Feng; Wang, Yue-Sheng; Zhang, Chuanzeng

2014-12-01

In this paper we propose four kinds of two-dimensional square beam-like zigzag lattice structures and study their bandgaps and directional propagation of elastic waves. The band structures are calculated by using the finite element method. Both the in-plane and out-of-plane waves are investigated simultaneously via the three-dimensional Euler beam elements. The mechanism of the bandgap generation is analyzed by studying the vibration modes at the bandgap edges. The effects of the geometry parameters of the xy- and z-zigzag lattices on the bandgaps are investigated and discussed. Multiple complete bandgaps are found owing to the separation of the degeneracy by introducing bending arms. The bandgaps are sensitive to the geometry parameters of the periodic systems. The deformed displacement fields of the harmonic responses of a finite lattice structure subjected to harmonic loads at different positions are illustrated to show the directional wave propagation. An extension of the proposed concept to the hexagonal lattices is also presented. The research work in this paper is relevant to the practical design of cellular structures with enhanced vibro-acoustics performance.

Graphene nanoribbons production from flat carbon nanotubes

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

Melo, W. S.; Guerini, S.; Diniz, E. M., E-mail: eduardo.diniz@ufma.br

2015-11-14

Graphene nanoribbons are of great interest for pure and applied sciences due to their unique properties which depend on the nanoribbon edges, as, for example, energy gap and antiferromagnetic coupling. Nevertheless, the synthesis of nanoribbons with well-defined edges remains a challenge. To collaborate with this subject, here we propose a new route for the production of graphene nanoribbons from flat carbon nanotubes filled with a one-dimensional chain of Fe atoms by first principles calculations based on density functional theory. Our results show that Fe-filled flat carbon nanotubes are energetically more stable than non flattened geometries. Also we find that bymore » hydrogenation or oxygenation of the most curved region of the Fe-filled flat armchair carbon nanotube, it occurred a spontaneous production of zigzag graphene nanoribbons which have metallic or semiconducting behavior depending on the edge and size of the graphene nanoribbon. Such findings can be used to create a new method of synthesis of regular-edge carbon nanoribbons.« less

Manganese mono-boride, an inexpensive room temperature ferromagnetic hard material

PubMed Central

Ma, Shuailing; Bao, Kuo; Tao, Qiang; Zhu, Pinwen; Ma, Teng; Liu, Bo; Liu, Yazhou; Cui, Tian

2017-01-01

We synthesized orthorhombic FeB-type MnB (space group: Pnma) with high pressure and high temperature method. MnB is a promising soft magnetic material, which is ferromagnetic with Curie temperature as high as 546.3 K, and high magnetization value up to 155.5 emu/g, and comparatively low coercive field. The strong room temperature ferromagnetic properties stem from the positive exchange-correlation between manganese atoms and the large number of unpaired Mn 3d electrons. The asymptotic Vickers hardness (AVH) is 15.7 GPa which is far higher than that of traditional ferromagnetic materials. The high hardness is ascribed to the zigzag boron chains running through manganese lattice, as unraveled by X-ray photoelectron spectroscopy result and first principle calculations. This exploration opens a new class of materials with the integration of superior mechanical properties, lower cost, electrical conductivity, and fantastic soft magnetic properties which will be significant for scientific research and industrial application as advanced structural and functional materials. PMID:28262805

Syntheses, structures and luminescence of three copper(I) cyanide coordination polymers based on trigonal 1,3,5-tris(1H-imidazol-1-yl)benzene ligand

NASA Astrophysics Data System (ADS)

Shao, Min; Li, Ming-Xing; Lu, Li-Ruo; Zhang, Heng-Hua

2016-09-01

Three Cu(I)-cyanide coordination polymers based on trigonal 1,3,5-tris(1H-imidazol-1-yl)benzene (tib) ligand, namely [Cu3(CN)3(tib)]n (1), [Cu4(CN)4(tib)]n (2), and [Cu2(CN)2(tib)]n (3), have been prepared and characterized by elemental analysis, IR, PXRD, thermogravimetry and single-crystal X-ray diffraction analysis. Complex 1 displays a 3D metal-organic framework with nanosized pores. Complex 2 is a 3D coordination polymer assembled by three μ2-cyanides and a μ3-cyanide with a very short Cu(I)···Cu(I) metal bond(2.5206 Å). Complex 3 is a 2D coordination polymer constructing from 1D Cu(I)-cyanide zigzag chain and bidentate tib spacer. Three Cu(I) complexes are thermally stable up to 250-350 °C. Complexes 1-3 show similar orange emission band at 602 nm originating from LMCT mechanism.

Neutron Spin Resonance in the 112-Type Iron-Based Superconductor

NASA Astrophysics Data System (ADS)

Xie, Tao; Gong, Dongliang; Ghosh, Haranath; Ghosh, Abyay; Soda, Minoru; Masuda, Takatsugu; Itoh, Shinichi; Bourdarot, Frédéric; Regnault, Louis-Pierre; Danilkin, Sergey; Li, Shiliang; Luo, Huiqian

2018-03-01

We use inelastic neutron scattering to study the low-energy spin excitations of the 112-type iron pnictide Ca0.82La0.18Fe0.96Ni0.04As2 with bulk superconductivity below Tc=22 K . A two-dimensional spin resonance mode is found around E =11 meV , where the resonance energy is almost temperature independent and linearly scales with Tc along with other iron-based superconductors. Polarized neutron analysis reveals the resonance is nearly isotropic in spin space without any L modulations. Because of the unique monoclinic structure with additional zigzag arsenic chains, the As 4 p orbitals contribute to a three-dimensional hole pocket around the Γ point and an extra electron pocket at the X point. Our results suggest that the energy and momentum distribution of the spin resonance does not directly respond to the kz dependence of the fermiology, and the spin resonance intrinsically is a spin-1 mode from singlet-triplet excitations of the Cooper pairs in the case of weak spin-orbital coupling.

An Analysis of Conceptual Flow Patterns and Structures in the Physics Classroom

NASA Astrophysics Data System (ADS)

Eshach, Haim

2010-03-01

The aim of the current research is to characterize the conceptual flow processes occurring in whole-class dialogic discussions with a high level of interanimation; in the present case, of a high-school class learning about image creation on plane mirrors. Using detailed chains of interaction and conceptual flow discourse maps-both developed for the purpose of this research-the classroom discourse, audio-taped and transcribed verbatim, was analyzed and three discussion structures were revealed: accumulation around budding foci concepts, zigzag between foci concepts, and concept tower. These structures as well as two additional factors, suggest the Two-Space Model of the whole class discussion proposed in the present article. The two additional factors are: (1) the teacher intervention; and (2) the conceptual barriers observed among the students, namely, materialistic thinking, and the tendency to attribute "unique characteristics" to optical devices. This model might help teachers to prepare and conduct efficient whole-class discussions which accord with the social constructivist perspective of learning.

Efficient and Highly Selective Solvent-Free Oxidation of Primary Alcohols to Aldehydes Using Bucky Nanodiamond.

PubMed

Lin, Yangming; Wu, Kuang-Hsu Tim; Yu, Linhui; Heumann, Saskia; Su, Dang Sheng

2017-09-11

Selective oxidation of alcohols to aldehydes is widely applicable to the synthesis of various green chemicals. The poor chemoselectivity for complicated primary aldehydes over state-of-the-art metal-free or metal-based catalysts represents a major obstacle for industrial application. Bucky nanodiamond is a potential green catalyst that exhibits excellent chemoselectivity and cycling stability for the selective oxidation of primary alcohols in diverse structures (22 examples, including aromatic, substituted aromatic, unsaturated, heterocyclic, and linear chain alcohols) to their corresponding aldehydes. The results are comparable to reported transition-metal catalysts including conventional Pt/C and Ru/C catalysts for certain substrates under solvent-free conditions. The possible activation process of the oxidant and substrates by the surface oxygen groups and defect species are revealed with model catalysts, ex situ electrochemical measurements, and ex situ attenuated total reflectance. The zigzag edges of sp 2 carbon planes are shown to play a key role in these reactions. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

High energy, high average power solid state green or UV laser

DOEpatents

Hackel, Lloyd A.; Norton, Mary; Dane, C. Brent

2004-03-02

A system for producing a green or UV output beam for illuminating a large area with relatively high beam fluence. A Nd:glass laser produces a near-infrared output by means of an oscillator that generates a high quality but low power output and then multi-pass through and amplification in a zig-zag slab amplifier and wavefront correction in a phase conjugator at the midway point of the multi-pass amplification. The green or UV output is generated by means of conversion crystals that follow final propagation through the zig-zag slab amplifier.

Oxygen vacancy effect on dielectric and hysteretic properties of zigzag ferroelectric iron dioxide nanoribbon

NASA Astrophysics Data System (ADS)

Zriouel, S.; Taychour, B.; Yahyaoui, F. El; Drissi, L. B.

2017-07-01

Zigzag FeO2 nanoribbon defected by the removal of oxygen atoms is simulated using Monte Carlo simulations. All possible arrangements of positions and number of oxygen vacancy are investigated. Temperature dependence of polarization, dielectric susceptibility, internal energy, specific heat and dielectric hysteresis loops are all studied. Results show the presence of second order phase transition and Q - type behavior. Dielectric properties dependence on ribbon's edge, positions and number of oxygen vacancy are discussed in detail. Moreover, single and square hysteresis loops are observed whatever the number of oxygen vacancy in the system.

Concentration-dependent multiple chirality transition in halogen-bond-driven 2D self-assembly process

NASA Astrophysics Data System (ADS)

Miao, Xinrui; Li, Jinxing; Zha, Bao; Miao, Kai; Dong, Meiqiu; Wu, Juntian; Deng, Wenli

2018-03-01

The concentration-dependent self-assembly of iodine substituted thienophenanthrene derivative (5,10-DITD) is investigated at the 1-octanic acid/graphite interface using scanning tunneling microscopy. Three kinds of chiral arrangement and transition of 2D molecular assembly mainly driven by halogen bonding is clearly revealed. At high concentration the molecules self-assembled into a honeycomb-like chiral network. Except for the interchain van der Waals forces, this pattern is stabilized by intermolecular continuous Cdbnd O⋯I⋯S halogen bonds in each zigzag line. At moderate concentration, a chiral kite-like nanoarchitecture are observed, in which the Cdbnd O⋯I⋯S and I⋯Odbnd C halogen bonds, along with the molecule-solvent Cdbnd O⋯I⋯H halogen bonds are the dominated forces to determine the structural formation. At low concentration, the molecules form a chiral cyclic network resulting from the solvent coadsorption mainly by molecule-molecule Cdbnd O⋯I⋯S halogen bonds and molecule-solvent Cdbnd O⋯I⋯H halogen bonds. The density of molecular packing becomes lower with the decreasing of the solution concentration. The solution-concentration dependent self-assembly of thienophenanthrene derivative with iodine and ester chain moieties reveals that the type of intermolecular halogen bond and the number of the co-adsorbing 1-octanic acids by molecule-solvent Cdbnd O⋯I⋯H halogen bonds determine the formation and transformation of chirality. This research emphasizes the role of different types of halogen (I) bonds in the controllable supramolecular structures and provides an approach for the fabrication of chirality.

High-field magnetization and magnetic phase diagram of α -Cu2V2O7

NASA Astrophysics Data System (ADS)

Gitgeatpong, G.; Suewattana, M.; Zhang, Shiwei; Miyake, A.; Tokunaga, M.; Chanlert, P.; Kurita, N.; Tanaka, H.; Sato, T. J.; Zhao, Y.; Matan, K.

2017-06-01

High-field magnetization of the spin-1 /2 antiferromagnet α -Cu2V2O7 was measured in pulsed magnetic fields of up to 56 T in order to study its magnetic phase diagram. When the field was applied along the easy axis (the a axis), two distinct transitions were observed at Hc 1=6.5 T and Hc 2=18.0 T. The former is a spin-flop transition typical for a collinear antiferromagnet and the latter is believed to be a spin-flip transition of canted moments. The canted moments, which are induced by the Dzyaloshinskii-Moriya interactions, anti-align for Hc 1

Syntheses and crystal structures of "unligated" copper(I) and copper(II) trifluoroacetates.

PubMed

Cotton, F A; Dikarev, E V; Petrukhina, M A

2000-12-25

Two extremely unstable copper trifluoroacetates with no exogenous ligands, namely, Cu(O2CCF3) (1) and Cu(O2CCF3)2 (2), are prepared for the first time and obtained in crystalline form by deposition from the vapor phase. Their structures are determined by X-ray crystallography. The crystallographic parameters are as follows: for 1, monoclinic space group P2(1)/c, with a = 9.7937(6) A, b = 15.322(1) A, c = 12.002(1) A, beta = 106.493(9) degrees, and Z = 4; for 2, orthorhombic space group Pcca, with a = 16.911(1) A, b = 10.5063(9) A, c = 9.0357(6) A, and Z = 4. Both structures are unique among other CuI and CuII carboxylates, as well as among metal carboxylates in general. Compound 1 consists of a planar rhombus of four copper atoms with sides of 2.719(1)-2.833(1) A and trifluoroacetate ligands bridging the pairs of adjacent metal atoms alternately above and below the plane. The tetrameric units are further aggregated in a polymeric zigzag ribbon [Cu4(O2CCF3)4]infinity by virtue of intermolecular Cu...O contacts. The structure of 2 is built on cis bis-bridged dimers in which every metal atom is also connected with two copper atoms of the neighboring units. The stacking planes in this extended chain are almost perpendicular to one another. The Cu...Cu distance inside the dimer is 3.086(2) A, indicating a nonbonding interaction.

Highly selective and sensitive detection of metal ions and nitroaromatic compounds by an anionic europium(iii) coordination polymer.

PubMed

Feyisa Bogale, Raji; Ye, Junwei; Sun, Yuan; Sun, Tongxin; Zhang, Siqi; Rauf, Abdul; Hang, Cheng; Tian, Peng; Ning, Guiling

2016-07-05

A luminescent Eu(iii)-based coordination polymer, {[Eu(H2O)5(BTEC)][H(C5H6N2)]·3H2O} () has been synthesized under hydrothermal conditions using 1,2,4,5-benzenetetracarboxylic acid (H4BTEC) as a linker. Compound possesses an anionic zig-zag chain constructed from the BTEC ligands and [EuO4(H2O)5] nodes. The protonated 4-aminopyridine groups as guests are located between chains. exhibits the characteristic sharp emission bands of Eu(3+) at 578, 593, 615, 652 and 693 nm upon excitation at 290 nm. The strong emission of could be quenched effectively by trace amounts of Fe(3+) ions even in the presence of other metal ions including Al(3+), Ca(2+), Cd(2+), Co(2+), Cr(3+), Cu(2+), Fe(2+), K(+), Mg(2+), Mn(2+), Pd(2+) and Zn(2+). Similarly, also exhibits superior selectivity and sensitivity towards 4-nitrophenol (4-NP) compared with other competing interfering analytes, such as 2,4,6-trinitrophenol, 2,6-dinitrotolune, 4-nitrotoluene, nitrobenzene, 1,3-dinitrobenzene, o-xylene, nitromethane, nitropropane, phenol, 4-bromophenol and bromobenzene, through a fluorescence quenching mechanism. The possible fluorescence quenching mechanisms are discussed. Moreover, could be used as a visual fluorescent test paper for selectively detecting trace amounts of Fe(3+) and 4-NP.

Substrate and chain length dependencies of the thermal behavior of [CF3(CF2)m(CH2)nCOO]2Cd single monolayers investigated by infrared reflection absorption spectroscopy

NASA Astrophysics Data System (ADS)

Ren, Yanzhi; Asanuma, Morito; Iimura, Ken-ichi; Kato, Teiji

2001-01-01

Temperature-variable grazing incidence reflection absorption (GIR) spectra were recorded for the single monolayer of [CF3(CF2)m(CH2)nCOO)]2Cd [(m,n)=(7,10), (7,16), (7,22), (5,22), and (3,22)], transferred from aqueous Cd2+ subphase to gold- and aluminum-evaporated glass substrates. The spectra reveal that these monolayers have better thermal stability on Al substrates than on Au. An "interaction band" is identified at 1484˜1480 cm-1, due to the νs(COO-) mode of carboxylate headgroups in ionic bonding with the Al surface. It is found that both the van der Waals interaction between the trans zig-zag hydrocarbon chains and the overlapping interaction between the fluorocarbon helixes are responsible for the systematic variation of the monolayer thermal behavior with (m,n). The thermal behavior of a single monolayer of cadmium stearate, serving as a model system, has been investigated to further confirm the spectral interpretation about the partially fluorinated monolayer. In addition, temperature-dependent friction measurements show that the single monolayers of (m,n)=(7,16), (7,22), (5,22), and (3,22) are potential molecular lubricants that can be used in the range of 25˜140 °C.

Photoconductivity in the chalcohalide semiconductor, SbSeI: a new candidate for hard radiation detection.

PubMed

Wibowo, Arief C; Malliakas, Christos D; Liu, Zhifu; Peters, John A; Sebastian, Maria; Chung, Duck Young; Wessels, Bruce W; Kanatzidis, Mercouri G

2013-06-17

We investigated an antimony chalcohalide compound, SbSeI, as a potential semiconductor material for X-ray and γ-ray detection. SbSeI has a wide band gap of 1.70 eV with a density of 5.80 g/cm(3), and it crystallizes in the orthorhombic Pnma space group with a one-dimensional chain structure comprised of infinite zigzag chains of dimers [Sb2Se4I8]n running along the crystallographic b axis. In this study, we investigate conditions for vertical Bridgman crystal growth using combinations of the peak temperature and temperature gradients as well as translation rate set in a three-zone furnace. SbSeI samples grown at 495 °C peak temperature and 19 °C/cm temperature gradient with 2.5 mm/h translation rate produced a single phase of columnar needlelike crystals aligned along the translational direction of the growth. The ingot sample exhibited an n-type semiconductor with resistivity of ∼10(8) Ω·cm. Photoconductivity measurements on these specimens allowed us to determine mobility-lifetime (μτ) products for electron and hole carriers that were found to be of similar order of magnitude (∼10(-4) cm(2)/V). Further, the SbSeI ingot with well-aligned, one-dimensional columnar needlelike crystals shows an appreciable response of Ag Kα X-ray.

Batagayite, CaZn2(Zn,Cu)6(PO4)4(PO3OH)3·12H2O, a new phosphate mineral from Këster tin deposit (Yakutia, Russia): occurrence and crystal structure

NASA Astrophysics Data System (ADS)

Yakovenchuk, Victor N.; Pakhomovsky, Yakov A.; Konopleva, Nataliya G.; Panikorovskii, Taras L.; Bazai, Ayya; Mikhailova, Julia A.; Bocharov, Vladimir N.; Ivanyuk, Gregory Yu.; Krivovichev, Sergey V.

2017-12-01

Batagayite, CaZn2(Zn,Cu)6(PO4)4(PO3OH)3·12H2O, is a new secondary phosphate mineral from the Këster deposit, Arga-Ynnykh-Khai massif, NE Yakutia, Russia. It is monoclinic, P21, a = 8.4264(4), b = 12.8309(6), c = 14.6928(9) Å, β = 98.514(6)o, V = 1571.05(15) Å3 and Z = 2 (from single-crystal X-ray diffraction data). Batagayite crystals are blades up to 2 mm long, flattened on {001} and elongated on [100]; blades often grow in radial aggregates. Associated minerals are arsenolite, native copper, epifanovite, fluorapatite, libethenite, Na-analogue of batagayite, pseudomalachite, quartz, sampleite, tobermorite, and Mg-analogue of hopeite. The streak is white and the luster is vitreous. The mineral is brittle and has a perfect cleavage on {001}, no parting was observed. The Mohs hardness is 3. Density, determined by the float-sink method in Clerici solution, is 2.90(3) g/cm3, and the calculated density is 3.02 g/cm3 (using the empirical formula and single-crystal unit-cell parameters). Batagayite is biaxial, optically negative, α = 1.566 ± 0.002, β = 1.572 ± 0.002, γ = 1.573 ± 0.002 at 589 nm. 2V meas. = 40(5)°, 2V calc = 44.3°. Optical orientation: Z is perpendicular to (001), further details unclear. No dispersion or pleochroism were observed. The mean chemical composition determined by electron microprobe is: Na2O 0.31, MgO 1.39, Al2O3 0.55, SiO2 0.48, P2O5 34.37, K2O 0.17, CaO 2.76, MnO 1.03, CuO 5.80, ZnO 35.62, CdO 0.24 wt%. The H2O content estimated from the crystal-structure refinement is 16.83 wt%, giving a total of 99.55 wt%. The empirical formula calculated on the basis of P + Si = 7 is (Zn6.22Cu1.04Ca0.70Mg0.49Mn0.21Al0.15Na0.14K0.05Cd0.03)Σ9.03(P6.89Si0.11)Σ7.00O24.91(OH)3.09·12.10H2O. The mineral easily dissolves in 10% room-temperature HCl. The eight diagnostic lines in the X-ray powder-diffraction pattern are (I-d[Å]-hkl): 100-14.59-001, 25-6.34-012, 11-6.02-111, 37-4.864-003, 13-4.766-112, 20-3.102-1 \\overline {2} \\overline {4} , 11-2.678-2 \\overline {3} \\overline {3} , 16-2.411-044. The crystal structure of batagayite was solved by direct methods and refined to R 1 = 0.069 for 3847 independent reflections with F o > 4σ(F o). It is based upon complex heteropolyhedral [M 8(PO4)4(PO3OH)3(H2O)9]2- layers parallel to the (001) plane. The layer can be considered as consisting of three sublayers, one A and two B. The central A layer has the composition [M 4(PO4)4(H2O)4]4- and consists of the zigzag chains of edge-sharing (MO6) octahedra running parallel to the a axis and linked into layers by sharing peripheral O atoms. The (PO4) tetrahedra are attached above and below the holes created by the linkage of zigzag octahedral chains. The B sublayer consists of chains of (ZnO4) and (PO3OH) tetrahedra. The interlayer space is occupied by the Ca2+ cations and H2O molecules. Batagayite is a secondary low-temperature mineral formed as a result of alteration of primary minerals such as native copper and fluorapatite. On the basis of its structural complexity calculated as 1058.257 bits/cell (taking into account contributions from H atoms), batagayite should be considered as a very complex mineral. The high complexity of batagayite is due to its high hydration state and the modular character of its structure, which contains both octahedral-tetrahedral layers and tetrahedral chains.

Exploration and exploitation of homologous series of bis(acrylamido)alkanes containing pyridyl and phenyl groups: β-sheet versus two-dimensional layers in solid-state photochemical [2 + 2] reactions.

PubMed

Garai, Mousumi; Biradha, Kumar

2015-09-01

The homologous series of phenyl and pyridyl substituted bis(acrylamido)alkanes have been synthesized with the aim of systematic analysis of their crystal structures and their solid-state [2 + 2] reactivities. The changes in the crystal structures with respect to a small change in the molecular structure, that is by varying alkyl spacers between acrylamides and/or by varying the end groups (phenyl, 2-pyridyl, 3-pyridyl, 4-pyridyl) on the C-terminal of the amide, were analyzed in terms of hydrogen-bonding interference (N-H⋯Npy versus N-H⋯O=C) and network geometries. In this series, a greater tendency towards the formation of N-H⋯O hydrogen bonds (β-sheets and two-dimensional networks) over N-H⋯N hydrogen bonds was observed. Among all the structures seven structures were found to have the required alignments of double bonds for the [2 + 2] reaction such that the formations of single dimer, double dimer and polymer are facilitated. However, only four structures were found to exhibit such a solid-state [2 + 2] reaction to form a single dimer and polymers. The two-dimensional hydrogen-bonding layer via N-H⋯O hydrogen bonds was found to promote solid-state [2 + 2] photo-polymerization in a single-crystal-to-single-crystal manner. Such two-dimensional layers were encountered only when the spacer between acryl amide moieties is butyl. Only four out of the 16 derivatives were found to form hydrates, two each from 2-pyridyl and 4-pyridyl derivatives. The water molecules in these structures govern the hydrogen-bonding networks by the formation of an octameric water cluster and one-dimensional zigzag water chains. The trends in the melting points and densities were also analyzed.

M(II)-dipyridylamide-based coordination frameworks (M=Mn, Co, Ni): Structural transformation

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

Tzeng, Biing-Chiau; Selvam, TamilSelvi; Tsai, Miao-Hsin

2016-11-15

A series of 1-D double-zigzag (([M(papx){sub 2}(H{sub 2}O){sub 2}](ClO{sub 4}){sub 2}){sub n}; M=Mn, x=s (1), x=o (3); M=Co, x=s (4), x=o (5); M=Ni, x=s (6), x=o (7)) and 2-D polyrotaxane ([Mn(paps){sub 2}(ClO{sub 4}){sub 2}]{sub n} (2)) frameworks were synthesized by reactions of M(ClO{sub 4}){sub 2} (M=Mn, Co, and Ni) with papx (paps, N,N’-bis(pyridylcarbonyl)-4,4’-diaminodiphenylthioether; papo, N,N’-bis(pyridylcarbonyl)-4,4’-diaminodiphenyl ether), which have been isolated and structurally characterized by X-ray diffraction. Based on powder X-ray diffraction (PXRD) experiments, heating the double-zigzag frameworks underwent structural transformation to give the respective polyrotaxane ones. Moreover, grinding the solid samples of the respective polyrotaxanes in the presence of moisturemore » also resulted in the total conversion to the original double-zigzag frameworks. In this study, we have successfully extended studies to Mn{sup II}, Co{sup II}, and Ni{sup II} frameworks from the previous Zn{sup II}, Cd{sup II}, and Cu{sup II} ones, and interestingly such structural transformation is able to be proven experimentally by powder and single-crystal X-ray diffraction studies as well. - Graphical abstract: 1-D double-zigzag and 2-D polyrotaxane frameworks of M(II)-papx (x=s, o; M=Mn, Co, Ni) frameworks can be interconverted by heating and grinding in the presence of moiture, and such structural transformation has be proven experimentally by powder and single-crystal X-ray diffraction studies.« less

Dimension changing phase transitions in instanton crystals

NASA Astrophysics Data System (ADS)

Kaplunovsky, Vadim; Sonnenschein, Jacob

2014-04-01

We investigate lattices of instantons and the dimension-changing transitions between them. Our ultimate goal is the 3D → 4D transition, which is holographically dual to the phase transition between the baryonic and the quarkyonic phases of cold nuclear matter. However, in this paper (just as in [1]) we focus on lower dimensions — the 1D lattice of instantons in a harmonic potential V ∝ , and the zigzag-shaped lattice as a first stage of the 1D → 2D transition. We prove that in the low- and moderate-density regimes, interactions between the instantons are dominated by two-body forces. This drastically simplifies finding the ground state of the instantons' orientations, so we made a numeric scan of the whole orientation space instead of assuming any particular ansatz. We find that depending on the M 2 /M 3 /M 4 ratios, the ground state of instanton orientations can follow a wide variety of patterns. For the straight 1D lattices, we found orientations periodically running over elements of a , Klein, prismatic, or dihedral subgroup of the , as well as irrational but link-periodic patterns. For the zigzag-shaped lattices, we detected 4 distinct orientation phases — the anti-ferromagnet, another abelian phase, and two non-abelian phases. Allowing the zigzag amplitude to vary as a function of increasing compression force, we obtained the phase diagrams for the straight and zigzag-shaped lattices in the (force , M 3 /M 4), (chemical potential , M 3 /M 4), and (density , M 3 /M 4) planes. Some of the transitions between these phases are second-order while others are first-order. Our techniques can be applied to other types of non-abelian crystals.

Interlaminar Stresses by Refined Beam Theories and the Sinc Method Based on Interpolation of Highest Derivative

NASA Technical Reports Server (NTRS)

Slemp, Wesley C. H.; Kapania, Rakesh K.; Tessler, Alexander

2010-01-01

Computation of interlaminar stresses from the higher-order shear and normal deformable beam theory and the refined zigzag theory was performed using the Sinc method based on Interpolation of Highest Derivative. The Sinc method based on Interpolation of Highest Derivative was proposed as an efficient method for determining through-the-thickness variations of interlaminar stresses from one- and two-dimensional analysis by integration of the equilibrium equations of three-dimensional elasticity. However, the use of traditional equivalent single layer theories often results in inaccuracies near the boundaries and when the lamina have extremely large differences in material properties. Interlaminar stresses in symmetric cross-ply laminated beams were obtained by solving the higher-order shear and normal deformable beam theory and the refined zigzag theory with the Sinc method based on Interpolation of Highest Derivative. Interlaminar stresses and bending stresses from the present approach were compared with a detailed finite element solution obtained by ABAQUS/Standard. The results illustrate the ease with which the Sinc method based on Interpolation of Highest Derivative can be used to obtain the through-the-thickness distributions of interlaminar stresses from the beam theories. Moreover, the results indicate that the refined zigzag theory is a substantial improvement over the Timoshenko beam theory due to the piecewise continuous displacement field which more accurately represents interlaminar discontinuities in the strain field. The higher-order shear and normal deformable beam theory more accurately captures the interlaminar stresses at the ends of the beam because it allows transverse normal strain. However, the continuous nature of the displacement field requires a large number of monomial terms before the interlaminar stresses are computed as accurately as the refined zigzag theory.

Spin-1/2 Heisenberg antiferromagnet on an anisotropic triangular lattice

NASA Astrophysics Data System (ADS)

Starykh, Oleg

2007-03-01

The Triangular lattice spin-1/2 Heisenberg AntiFerromagnet (TAF) is a prototypical model of frustrated quantum magnetism. While it is believed to exhibit long-range order in the isotropic limit, changes such as spatial anisotropy can alter the delicate balance amongst competing ground states. I will describe the static and dynamic properties of the spatially anisotropic TAF, with inter-chain diagonal exchange J' much weaker than the intrachain exchange J. Treating J' as a perturbation of decoupled Heisenberg spin-1/2 chains, I find that the ground state is spontaneously dimerized in a four-fold degenerate zig-zag pattern. This dimerization instability is driven by quantum fluctuations, which are dramatically enhanced here by the frustrated nature of inter-chain exchange. A magnetic field partially relieves frustration, by canting the spins along the field direction, and causes a quantum phase transition into a magnetically-ordered spin-density-wave phase. This is followed by cone and, finally, fully polarized (saturated) phases, as a function of increasing magnetic field. I show that many of these features are in fact observed in experiments on the celebrated material Cs2CuCl4 (J'/J =1/3). I will also discuss the significant modification of the phase diagram by symmetry-breaking anisotropic Dzyaloshinskii-Moriya (DM) interactions, present in this interesting magnet. In addition to static and thermodynamic properties, the proposed ``one-dimensional'' approach offers a compelling explanation of the unusual experimentally measured dynamical structure factor of Cs2CuCl4 in terms of descendants of one-dimensional spinons. Quite generally, I find characteristic features of a momentum-dependent spinon bound state and a dispersing incoherent excitation in the structure factor, in agreement with experiments.

Structural phase transition of magnetic [Ni(dmit)2]- salts induced by supramolecular cation structures of (M+)([12]crown-4)2.

PubMed

Akutagawa, Tomoyuki; Motokizawa, Takeshi; Matsuura, Kazumasa; Nishihara, Sadafumi; Noro, Shin-ichiro; Nakamura, Takayoshi

2006-03-30

Sandwich-type supramolecular cation structures of (M(+))([12]crown-4)(2) complexes (M(+) = Li(+), Na(+), K(+), and Rb(+)) were introduced as countercations to the [Ni(dmit)(2)](-) anion, which bears an S = (1)/(2) spin, to form novel magnetic crystals (dmit(2-) = 2-thione-1,3-dithiole-4,5-dithiolate). The zigzag arrangement of Li(+)([12]crown-4)(2) cations in Li(+)([12]crown-4)(2)[Ni(dmit)(2)](-) salt induced weak intermolecular interactions of [Ni(dmit)(2)](-) dimers, whose magnetic spins were isolated from each other. The molecular arrangements of cations and anions in M(+)([12]crown-4)(2)[Ni(dmit)(2)](-) salts (M(+) = Na(+), K(+), and Rb(+)) were isostructural to each other. In the case of Na(+)([12]crown-4)(2)[Ni(dmit)(2)](-), the space group C2/m changed to C2/c with a lowering in temperature from 298 to 100 K. This structural change occurred at 222.5 K as a first-order phase transition. The space group C2/m (T = 298 K) in the salt K(+)([12]crown-4)(2)[Ni(dmit)(2)](-) also changed to C2/c (T = 100 K), which transition occurred at 270 K. Crystal structural analyses at 298 and 100 K revealed changes in both supramolecular cation conformation and [Ni(dmit)(2)](-) anion arrangements. The transition from C2/m to C2/c crystals generated a dipole moment in the Na(+)([12]crown-4)(2) and K(+)([12]crown-4)(2) structures, which were reconstructed to cancel the net dipole moment of the C2/c crystals. These cation transformations led to changes in intermolecular interactions between the [Ni(dmit)(2)](-) anions via structural rearrangements. The crystal structure of C2/c was stabilized in Rb(+)([12]crown-4)(2)[Ni(dmit)(2)](-) at 298 K. The [Ni(dmit)(2)](-) configuration in these salts with the C2/c space group was a one-dimensional uniform chain, which showed the temperature-dependent magnetic susceptibility of a one-dimensional linear Heisenberg antiferromagnetic chain.

Synthesis, structural analysis, and magnetic properties of ethylmalonate-manganese(II) complexes.

PubMed

Déniz, Mariadel; Pasán, Jorge; Ferrando-Soria, Jesús; Fabelo, Oscar; Cañadillas-Delgado, Laura; Yuste, Consuelo; Julve, Miguel; Cano, Joan; Ruiz-Pérez, Catalina

2011-11-07

Five manganese(II) complexes of formulas [Mn(2)(Etmal)(2)(H(2)O)(2)(L)](n) (1-4) and {[Mn(Etmal)(2)(H(2)O)][Mn(H(2)O)(4)]}(n) (5) with H(2)Etmal = ethylmalonic acid (1-5) and L = 1,2-bis(4-pyridyl)ethane (bpa) (1), 4,4'-azobispyridine (azpy) (2), 4,4'-bipyridyl (4,4'-bpy) (3), and 1,2-bis(4-pyridyl)ethylene (bpe) (4) were synthesized and structurally characterized by single crystal X-ray diffraction. Their thermal behavior and variable-temperature magnetic properties were also investigated. The structure of the compounds 1-4 consists of corrugated layers of aquamanganese(II) units with intralayer carboxylate-ethylmalonate bridges in the anti-syn (equatorial-equatorial) coordination mode which are linked through bis-monodentate bpa (1), azpy (2), 4,4'-bpy (3), and bpe (4) ligands to build up a three-dimensional (3D) framework. The structure of compound 5 is made up by zigzag chains of manganese(II) ions with a regular alternation of [Mn(H(2)O)(4)](2+) and chiral (either Δ or λ enantiomeric forms) [Mn(Etmal)(2)(H(2)O)](2-) units within each chain. In contrast to the bidentate/bis-monodentate coordination mode of the Etmal ligand in 1-4, it adopts the bidentate/monodentate coordination mode in 5 with the bridging carboxylate-ethylmalonate also exhibiting the anti-syn conformation but connecting one equatorial and an axial position from adjacent metal centers. The manganese-manganese separation through the carboxylate-ethylmalonate bridge in 1-5 vary in the range 5.3167(4)-5.5336(7) Å. These values are much shorter than those across the extended bis-monodentate N-donors in 1-4 with longest/shortest values of 11.682(3) (3)/13.9745(9) Å (4). Compounds 1-5 exhibit an overall antiferromagnetic behavior, where the exchange pathway is provided by the carboxylate-ethylmalonate bridge. Monte Carlo simulations based on the classical spin approach (1-5) were used to successfully reproduce the magnetic data of 1-5. © 2011 American Chemical Society

Decay and the double-decay properties of edge bands of phosphorene ribbons

NASA Astrophysics Data System (ADS)

Yang, M.; Duan, H.-J.; Wang, R.-Q.

2015-11-01

Phosphorene (a monolayer of black phosphorus) recently spurred much attention due to its potential for application. We notice there are two types of zigzag edge and two types of armchair edge for phosphorene lattice. We study the winding number of various types of edge of phosphorene ribbons and conclude that, besides on the typical zigzag edge, the flat zero-energy edge band can be found in the ribbon of another nontypical armchair edge. The localization of these edge bands is investigated analytically. We find every single edge state of the atypical armchair edge decays to the bulk at two different decay rates.

The structure of 110 tilt boundaries in large area solar silicon

NASA Technical Reports Server (NTRS)

Ast, D. G.; Cunningham, B.; Vaudin, M.

1982-01-01

The models of Hornstra and their connection to the repeating group description of grain boundaries (7-10) are discussed. A model for the Sigma = 27 boundary containing a zig-zag arrangement of dislocations is constructed and it is shown that zig-zag models can account for the contrast features observed in high resolution transmission electron micrographs of second and third order twin boundaries in silicon. The boundaries discussed are symmetric with a 110 tilt axis and a (110) boundary plane in the median lattice (the median plane). The median lattice is identical in structure and halfway in orientation between the crystal lattices either side of the boundary.

Automatic low-order aberrations compensator for a conduction-cooled end-pumped solid-state zigzag slab laser

NASA Astrophysics Data System (ADS)

Yu, Xin; Dong, Lizhi; Lai, Boheng; Yang, Ping; Wang, Shuai; Wang, Xun; Liu, Yong; Tang, Guomao; Xu, Bing

2017-11-01

In order to solve the problem of large low-order aberrations with solid-state zigzag slab lasers, an automatic compensator has been developed in this paper. In this compensator, three lenses are mounted on a motorized rail, whose positions can be obtained using ray tracing method based on the beam parameters detected by a wave-front sensor. The initial peak to valley (PV) values of the wave-front range up to several tens of microns. Both simulated and experimental results show that the PV values of the wave-front can be reduced to around 1 . 6 μm with the proposed automatic compensator.

Plasmonic eigenmodes in individual and bow-tie graphene nanotriangles

NASA Astrophysics Data System (ADS)

Wang, Weihua; Christensen, Thomas; Jauho, Antti-Pekka; Thygesen, Kristian S.; Wubs, Martijn; Mortensen, N. Asger

2015-04-01

In classical electrodynamics, nanostructured graphene is commonly modeled by the computationally demanding problem of a three-dimensional conducting film of atomic-scale thickness. Here, we propose an efficient alternative two-dimensional electrostatic approach where all calculation procedures are restricted to the graphene sheet. Furthermore, to explore possible quantum effects, we perform tight-binding calculations, adopting a random-phase approximation. We investigate multiple plasmon modes in 20 nm equilateral triangles of graphene, treating the optical response classically as well as quantum mechanically. Compared to the classical plasmonic spectrum which is ``blind'' to the edge termination, we find that the quantum plasmon frequencies exhibit blueshifts in the case of armchair edge termination of the underlying atomic lattice, while redshifts are found for zigzag edges. Furthermore, we find spectral features in the zigzag case which are associated with electronic edge states not present for armchair termination. Merging pairs of triangles into dimers, plasmon hybridization leads to energy splitting that appears strongest in classical calculations while splitting is lower for armchair edges and even more reduced for zigzag edges. Our various results illustrate a surprising phenomenon: Even 20 nm large graphene structures clearly exhibit quantum plasmonic features due to atomic-scale details in the edge termination.

Thermal Lens Measurement in Diode-Pumped Nd:YAG Zig-Zag Slab

NASA Technical Reports Server (NTRS)

Smoak, M. C.; Kay, R. B.; Coyle, D. B.; Hopf, D.

1998-01-01

A major advantage that solid state zig-zag slab lasers have over conventional rod-based designs is that a much weaker thermal lens is produced in the slab when side-pumped with Quasi-CW laser diode arrays, particularly if the pump radiation is kept well away from the Brewster-cut ends. This paper reports on a rather strong thermal lens produced when diode pump radiation is collimated into a narrow portion of the zig-zag slab. The collimation of multi-bar pump packages to increase brightness and improve overlap is a direct consequence of designs which seek to maximize performance and efficiency. Our slab design employed a 8.1 cm x 2.5 mm x 5 mm slab with opposing Brewster end faces. It was pumped through the 2.5 mm direction by seven laser diode array packages, each housing four 6OW diode bars, 1 cm in width. The pump face, anti-reflection (AR) coated at 809 nm, was 6.8 cm in width and the 8.1 cm opposing side, high-reflection (HR) coated at 809 nm, reflected the unabsorbed pump beam for a second pass through the slab.

Optical absorption of zigzag single walled boron nitride nanotubes

NASA Astrophysics Data System (ADS)

Moradian, Rostam; Chegel, Raad; Behzad, Somayeh

2010-11-01

In a realistic three-dimensional model, optical matrix element and linear optical absorption of zigzag single walled boron nitride nanotubes (BNNTs) in the tight binding approximation are studied. In terms of absolute value of dipole matrix elements of the first three direct transitions at kz=0, we divided the zigzag BNNTs into three groups and investigated their optical absorption spectrum in energy ranges E<5, 77.5 eV. We found that in lower energies, E<5 eV, all groups show different behaviors while in the higher energies, 77.5 eV, their behaviors depend on their even or odd nanotube index. We also found that in the energy range 7

Four highly pseudosymmetric and/or twinned structures of d(CGCGCG) 2 extend the repertoire of crystal structures of Z-DNA

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

Luo, Zhipu; Dauter, Zbigniew; Gilski, Miroslaw

DNA oligomer duplexes containing alternating cytosines and guanines in their sequences tend to form left-handed helices of the Z-DNA type, with the sugar and phosphate backbone in a zigzag conformation and a helical repeat of two successive nucleotides. Z-DNA duplexes usually crystallize as hexagonally arranged parallel helical tubes, with various relative orientations and translation of neighboring duplexes. Four novel high-resolution crystal structures of d(CGCGCG) 2duplexes are described here. They are characterized by a high degree of pseudosymmetry and/or twinning, with three or four independent duplexes differently oriented in a monoclinicP2 1lattice of hexagonal metric. The various twinning criteria give somewhatmore » conflicting indications in these complicated cases of crystal pathology. The details of molecular packing in these crystal structures are compared with other known crystal forms of Z-DNA.« less

Structures of the Kplus and NH4 Forms of Linde J

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

R Broach; R Kirchner

2011-12-31

The aluminosilicate zeolite Linde J has a unique topology. The structures of the K{sup +} and NH{sub 4}{sup +} forms of Linde J ([X{sub 2}(H{sub 2}O)][Si{sub 2}Al{sub 2}O{sub 8}] where X = K or NH{sub 4}) are identical except for slight cell size and positional differences due to NH{sub 4}{sup +} being larger than K{sup +} cations. The space group is P2{sub 1}2{sub 1}2{sub 1}. Cell dimensions are: K{sup +} Linde J, a = 9.4577(2) {angstrom}, b = 9.5573(2) {angstrom}, c = 9.9429(2) {angstrom}; NH{sub 4}{sup +} Linde J, a = 9.6324(4) {angstrom}, b = 9.6423(3) {angstrom}, c = 10.0230(3)more » {angstrom}. Zigzag 8-ring channels intersect giving a 2-D pore system.« less

Droplet size distributions in waveplate demisters using optical techniques

NASA Astrophysics Data System (ADS)

Layton, J. S.; Zaidi, Sohail H.; Altunbas, Ayse; Walters, J. K.; Azzopardi, B. J.

1997-11-01

Droplet separators or demisters are extensively used in the chemical industry. The effectiveness of many demisters is decisively affected by droplet sizes. As the misty gas passes through the demister, the liquid droplets impinge on the walls and form a liquid film. A part of this film can be re-entrained by the gas flow in the form of larger droplets. These droplets can escape the demister, affecting its efficiency. The measurement of drop size distributions inside the zigzag passages of the demister can provide useful information about the complex flow phenomena occurring within the demister. In the present work, a wave plate demister of the industrial dimensional specifications has been chosen to investigate the drop size distributions at various flow conditions. The laser diffraction technique has been employed for this purpose. This paper describes the suitability of the technique and presents some laser results to describe the effect of changing flow conditions inside and outside the demister.

Control of the conformations of ion Coulomb crystals in a Penning trap

PubMed Central

Mavadia, Sandeep; Goodwin, Joseph F.; Stutter, Graham; Bharadia, Shailen; Crick, Daniel R.; Segal, Daniel M.; Thompson, Richard C.

2013-01-01

Laser-cooled atomic ions form ordered structures in radiofrequency ion traps and in Penning traps. Here we demonstrate in a Penning trap the creation and manipulation of a wide variety of ion Coulomb crystals formed from small numbers of ions. The configuration can be changed from a linear string, through intermediate geometries, to a planar structure. The transition from a linear string to a zigzag geometry is observed for the first time in a Penning trap. The conformations of the crystals are set by the applied trap potential and the laser parameters, and agree with simulations. These simulations indicate that the rotation frequency of a small crystal is mainly determined by the laser parameters, independent of the number of ions and the axial confinement strength. This system has potential applications for quantum simulation, quantum information processing and tests of fundamental physics models from quantum field theory to cosmology. PMID:24096901

Quantum chemistry study on the open end of single-walled carbon nanotubes

NASA Astrophysics Data System (ADS)

Hou, Shimin; Shen, Ziyong; Zhao, Xingyu; Xue, Zengquan

2003-05-01

Geometrical and electronic structures of open-ended single-walled carbon nanotubes (SWCNTs) are calculated using density functional theory (DFT) with hybrid functional (B3LYP) approximation. Due to different distances between carbon atoms along the edge, reconstruction occurs at the open end of the (4,4) armchair SWCNT, i.e., triple bonds are formed in the carbon atom pairs at the mouth; however, for the (6,0) zigzag SWCNT, electrons in dangling bonds still remain at 'no-bonding' states. The ionization potential (IP) of both (4,4) and (6,0) SWCNTs is increased by their negative intrinsic dipole moments, and localized electronic states existed at both of their open ends.

Coulomb double helical structure

NASA Astrophysics Data System (ADS)

Kamimura, Tetsuo; Ishihara, Osamu

2012-01-01

Structures of Coulomb clusters formed by dust particles in a plasma are studied by numerical simulation. Our study reveals the presence of various types of self-organized structures of a cluster confined in a prolate spheroidal electrostatic potential. The stable configurations depend on a prolateness parameter for the confining potential as well as on the number of dust particles in a cluster. One-dimensional string, two-dimensional zigzag structure and three-dimensional double helical structure are found as a result of the transition controlled by the prolateness parameter. The formation of stable double helical structures resulted from the transition associated with the instability of angular perturbations on double strings. Analytical perturbation study supports the findings of numerical simulations.

RECOMBINATION OF ANTIBODY POLYPEPTIDE CHAINS IN THE PRESENCE OF ANTIGEN

PubMed Central

Metzger, Henry; Mannik, Mart

1964-01-01

Conditions were developed by which the separated H and L chains of gamma2 globulins recombined to form four-chained molecules in good yields. In the absence of antigen, anti-2,4-dinitrophenyl (anti-DNP) H chains randomly reassociated with a mixture of antibody and non-specific gamma2 globulin L chains. In the presence of a specific hapten, however, the antibody H chains preferentially interacted with the anti-DNP L chains. Antibody H chain-antibody L chain recombinants formed in the presence of hapten were more active than the corresponding recombinants formed in the absence of hapten. Speculations are made regarding the possible mechanisms and biological significance of these effects. PMID:14247718

Investigation of supramolecular synthons and structural characterisation of aminopyridine-carboxylic acid derivatives

PubMed Central

2014-01-01

Background Co-crystal is a structurally homogeneous crystalline material that contains two or more neutral building blocks that are present in definite stoichiometric amounts. The main advantage of co-crystals is their ability to generate a variety of solid forms of a drug that have distinct physicochemical properties from the solid co-crystal components. In the present investigation, five co-crystals containing 2-amino-6-chloropyridine (AMPY) moiety were synthesized and characterized. Results The crystal structure of 2-amino-6-chloropyridine (AMPY) (I), and the robustness of pyridine-acid supramolecular synthon were discussed in four stoichiometry co-crystals of AMPY…BA (II), AMPY…2ABA (III), AMPY…3CLBA (IV) and AMPY…4NBA (V). The abbreviated designations used are benzoic acid (BA), 2-aminobenzoic acid (2ABA), 3-chlorobenzoic acid (3CLBA) and 4-nitrobenzoic acid (4NBA). All the crystalline materials have been characterized by 1HNMR, 13CNMR, IR, photoluminescence, TEM analysis and X-ray diffraction. The supramolecular assembly of each co-crystal is analyzed and discussed. Conclusions Extensive N---H · · · N/N---H · · · O/O---H · · · N hydrogen bonds are found in (I-V), featuring different supramolecular synthons. In the crystal structure, for compound (I), the 2-amino-6-chloropyridine molecules are linked together into centrosymmetric dimers by hydrogen bonds to form homosynthon, whereas for compounds (II-V), the carboxylic group of the respective acids (benzoic acid, 2-aminobenzoic acid, 3-chlorobenzoic acid and 4-nitrobenzoic acid) interacts with pyridine molecule in a linear fashion through a pair of N---H · · · O and O---H · · · N hydrogen bonds, generating cyclic hydrogen-bonded motifs with the graph-set notation R 2 2 8 , to form heterosynthon. In compound (II), another intermolecular N---H · · · O hydrogen bonds further link these heterosynthons into zig-zag chains. Whereas in compounds (IV) and (V), these heterosynthons are centrosymmetrically paired via N---H · · · O hydrogen bonds and each forms a complementary DADA [D = donor and A = acceptor] array of quadruple hydrogen bonds, with graph-set notation R238, R228 and R238. PMID:24887234

Investigation of supramolecular synthons and structural characterisation of aminopyridine-carboxylic acid derivatives.

PubMed

Hemamalini, Madhukar; Loh, Wan-Sin; Quah, Ching Kheng; Fun, Hoong-Kun

2014-01-01

Co-crystal is a structurally homogeneous crystalline material that contains two or more neutral building blocks that are present in definite stoichiometric amounts. The main advantage of co-crystals is their ability to generate a variety of solid forms of a drug that have distinct physicochemical properties from the solid co-crystal components. In the present investigation, five co-crystals containing 2-amino-6-chloropyridine (AMPY) moiety were synthesized and characterized. The crystal structure of 2-amino-6-chloropyridine (AMPY) (I), and the robustness of pyridine-acid supramolecular synthon were discussed in four stoichiometry co-crystals of AMPY…BA (II), AMPY…2ABA (III), AMPY…3CLBA (IV) and AMPY…4NBA (V). The abbreviated designations used are benzoic acid (BA), 2-aminobenzoic acid (2ABA), 3-chlorobenzoic acid (3CLBA) and 4-nitrobenzoic acid (4NBA). All the crystalline materials have been characterized by (1)HNMR, (13)CNMR, IR, photoluminescence, TEM analysis and X-ray diffraction. The supramolecular assembly of each co-crystal is analyzed and discussed. Extensive N---H · · · N/N---H · · · O/O---H · · · N hydrogen bonds are found in (I-V), featuring different supramolecular synthons. In the crystal structure, for compound (I), the 2-amino-6-chloropyridine molecules are linked together into centrosymmetric dimers by hydrogen bonds to form homosynthon, whereas for compounds (II-V), the carboxylic group of the respective acids (benzoic acid, 2-aminobenzoic acid, 3-chlorobenzoic acid and 4-nitrobenzoic acid) interacts with pyridine molecule in a linear fashion through a pair of N---H · · · O and O---H · · · N hydrogen bonds, generating cyclic hydrogen-bonded motifs with the graph-set notation [Formula: see text] , to form heterosynthon. In compound (II), another intermolecular N---H · · · O hydrogen bonds further link these heterosynthons into zig-zag chains. Whereas in compounds (IV) and (V), these heterosynthons are centrosymmetrically paired via N---H · · · O hydrogen bonds and each forms a complementary DADA [D = donor and A = acceptor] array of quadruple hydrogen bonds, with graph-set notation [Formula: see text], [Formula: see text] and [Formula: see text].

All-wurtzite ZnO/ZnSe hetero-nanohelix: formation, mechanics and luminescence

NASA Astrophysics Data System (ADS)

Sun, Luwei; Ye, Zhizhen; He, Haiping

2015-04-01

A unique all-wurtzite ZnO/ZnSe hetero-nanohelix is formed via growing wurtzite ZnSe nanoteeth on ZnO nanobelts through a one step thermal evaporation method. The microstructure and growth mechanism of the hetero-nanohelix are investigated in detail. The formation of metastable wurtzite ZnSe is attributed to the wurtzite ZnO template. Mechanical forces, thermal expansion and polar plane in hexagonal crystals are suggested to contribute to the bending of the nanohelix. A boomerang-like structural block is proposed to assemble the zigzag ZnO nanobelts. The incorporation of Se into ZnO results in a strong orange emission. The heterostructure of the ZnO/ZnSe nanohelix is confirmed by elemental mapping and luminescence imaging. The fabrication of such a hetero-nanohelix may provide insights into the growth mechanism of the rich family of ZnO-based nanostructures.A unique all-wurtzite ZnO/ZnSe hetero-nanohelix is formed via growing wurtzite ZnSe nanoteeth on ZnO nanobelts through a one step thermal evaporation method. The microstructure and growth mechanism of the hetero-nanohelix are investigated in detail. The formation of metastable wurtzite ZnSe is attributed to the wurtzite ZnO template. Mechanical forces, thermal expansion and polar plane in hexagonal crystals are suggested to contribute to the bending of the nanohelix. A boomerang-like structural block is proposed to assemble the zigzag ZnO nanobelts. The incorporation of Se into ZnO results in a strong orange emission. The heterostructure of the ZnO/ZnSe nanohelix is confirmed by elemental mapping and luminescence imaging. The fabrication of such a hetero-nanohelix may provide insights into the growth mechanism of the rich family of ZnO-based nanostructures. Electronic supplementary information (ESI) available: HRTEM image, EDS elemental mapping, XRD data, and calculation of bending mechanics. See DOI: 10.1039/c5nr00567a

Increased Chain Length Promotes Pneumococcal Adherence and Colonization

PubMed Central

Rodriguez, Jesse L.; Dalia, Ankur B.

2012-01-01

Streptococcus pneumoniae is a mucosal pathogen that grows in chains of variable lengths. Short-chain forms are less likely to activate complement, and as a consequence they evade opsonophagocytic clearance more effectively during invasive disease. When grown in human nasal airway surface fluid, pneumococci exhibited both short- and long-chain forms. Here, we determined whether longer chains provide an advantage during colonization when the organism is attached to the epithelial surface. Chain-forming mutants and the parental strain grown under conditions to promote chain formation showed increased adherence to human epithelial cells (A549 cells) in vitro. Additionally, adherence to A549 cells selected for longer chains within the wild-type strain. In vivo in a murine model of colonization, chain-forming mutants outcompeted the parental strain. Together, our results demonstrate that morphological heterogeneity in the pneumococcus may promote colonization of the upper respiratory tract by enhancing the ability of the organism to bind to the epithelial surface. PMID:22825449

Yb:YAG master oscillator power amplifier for remote wind sensing.

PubMed

Sridharan, A K; Saraf, S; Byer, R L

2007-10-20

We have demonstrated key advances towards a solid-state laser amplifier at 1.03 microm for global remote wind sensing. We designed end-pumped zig-zag slab amplifiers to achieve high gain. We overcame parasitic oscillation limitations using claddings on the slab's total internal reflection (TIR) and edge surfaces to confine the pump and signal light by TIR and allow leakage of amplified spontaneous emission rays that do not meet the TIR condition. This enables e3, e5, and e8 single-, double-, and quadruple-pass small-signal amplifier gain, respectively. The stored energy density is 15.6 J/cm3, a record for a laser-diode end-pumped Yb:YAG zig-zag slab amplifier.

Communication: electronic band gaps of semiconducting zig-zag carbon nanotubes from many-body perturbation theory calculations.

PubMed

Umari, P; Petrenko, O; Taioli, S; De Souza, M M

2012-05-14

Electronic band gaps for optically allowed transitions are calculated for a series of semiconducting single-walled zig-zag carbon nanotubes of increasing diameter within the many-body perturbation theory GW method. The dependence of the evaluated gaps with respect to tube diameters is then compared with those found from previous experimental data for optical gaps combined with theoretical estimations of exciton binding energies. We find that our GW gaps confirm the behavior inferred from experiment. The relationship between the electronic gap and the diameter extrapolated from the GW values is also in excellent agreement with a direct measurement recently performed through scanning tunneling spectroscopy.

Effect of edge modification on the zigzag BC2N nanoribbons

NASA Astrophysics Data System (ADS)

Xiao, Xiang; Li, Hong; Tie, Jun; Lu, Jing

2016-08-01

We use first principles calculations to investigate the effects of edge modification with nonmetal species on zigzag-edged BC2N nanoribbons (ZBC2NNRs). These ZBC2NNRs show either semiconducting or metallic behaviors depending on the edge modifications and ribbon widths. We find that the O-modification induces a ferromagnetic ground state with a metallic behavior for all the ribbon widths investigated. And when the ribbon width is more than 3.32 nm (NZ ⩾ 16), an antiferromagnetic ground state with a half-metallic behavior is realized in the H-passivated ZBC2NNRs. These versatile electronic properties render the ZBC2NNRs a promising candidate material in nanoelectronics and nanospintronics.

Electronic structure and optical properties of boron nitride nanotube bundles from first principles

NASA Astrophysics Data System (ADS)

Behzad, Somayeh

2015-06-01

The electronic and optical properties of bundled armchair and zigzag boron nitride nanotubes (BNNTs) are investigated by using density functional theory. Owing to the inter-tube coupling, the dispersions along the tube axis and in the plane perpendicular to the tube axis of BNNT bundles are significantly varied, which are characterized by the decrease of band gap, the splitting of the doubly degenerated states, the expansions of valence and conduction bands. The calculated dielectric functions of the armchair and zigzag bundles are similar to that of the isolated tubes, except for the appearance of broadened peaks, small shifts of peak positions about 0.1 eV and increasing of peak intensities.

Armchair and zigzag nanoribbons of gold and silver: A DFT study

NASA Astrophysics Data System (ADS)

Kapoor, Pooja; Sharma, Munish; Kumar, Ashok; Ahluwalia, P. K.

2018-04-01

This paper presents the results from a DFT-based computational study of structural and electronic properties of zigzag and armchair edge shaped nanoribbons of gold and silver in hexagonal phase. The cohesive energy of the considered nanoribbons are found to be more than the corresponding 2D counterpart, thereby, suggesting Au and Ag nanoribbons to be more stable in 1D as compared to 2D. All nanoribbons are found to be metallic with a modulation in quantum ballistic conductance with length and edge type of the nanoribbon. Au nanoribbons are found to have higher conductance than Ag nanoribbon. There is increase in conductance with increase in length of nanoribbon.

Two-dimensional thermography image retrieval from zig-zag scanned data with TZ-SCAN

NASA Astrophysics Data System (ADS)

Okumura, Hiroshi; Yamasaki, Ryohei; Arai, Kohei

2008-10-01

TZ-SCAN is a simple and low cost thermal imaging device which consists of a single point radiation thermometer on a tripod with a pan-tilt rotator, a DC motor controller board with a USB interface, and a laptop computer for rotator control, data acquisition, and data processing. TZ-SCAN acquires a series of zig-zag scanned data and stores the data as CSV file. A 2-D thermal distribution image can be retrieved by using the second quefrency peak calculated from TZ-SCAN data. An experiment is conducted to confirm the validity of the thermal retrieval algorithm. The experimental result shows efficient accuracy for 2-D thermal distribution image retrieval.

Energetics and formation mechanism of borders between hexagonal boron nitride and graphene

NASA Astrophysics Data System (ADS)

Sawahata, Hisaki; Yamanaka, Ayaka; Maruyama, Mina; Okada, Susumu

2018-06-01

We studied the energetics of two-dimensional heterostructures consisting of hexagonal boron nitride (h-BN) and graphene with respect to the border structure and heterobond species using density functional theory. A BC heterobond is energetically preferable at the border between h-BN and graphene. We also found that the polarization at the zigzag border increases the total energy of the heterostructures. Competition between the bond formation energy and the polarization energy leads to chiral borders at which BC heterobonds are dominant. By taking the formation process of the heterostructures into account, the zigzag border with BC heterobonds is found to be preferentially synthesized from graphene edges under hydrogen-rich conditions.

The deflection of carbon composite carbon nanotube / graphene using molecular dynamics simulation

NASA Astrophysics Data System (ADS)

Kolesnikova, A. S.; Kirillova, I. V.; Kossovich, L. U.

2018-02-01

For the first time, the dependence of the bending force on the transverse displacement of atoms in the center of the composite material consisting of graphene and parallel oriented zigzag nanotubes was studied. Mathematical modeling of the action of the needle of the atomic force microscope was carried out using the single-layer armchair carbon nanotube. Armchair nanotubes are convenient for using them as a needle of an atomic force microscope, because their edges are not sharpened (unlike zigzag tubes). Consequently, armchair nanotubes will cause minimal damage upon contact with the investigation object. The geometric parameters of the composite was revealed under the action of the bending force of 6μN.

Study on the Electronic Transport Properties of Zigzag GaN Nanotubes

NASA Astrophysics Data System (ADS)

Li, Enling; Wang, Xiqiang; Hou, Liping; Zhao, Danna; Dai, Yuanbin; Wang, Xuewen

2011-02-01

The electronic transport properties of zigzag GaN nanotubes (n, 0) (4 <= n <= 9) have been calculated using the density functional theory and non-equilibrium Green's functions method. Firstly, the density functional theory (DFT) is used to optimize and calculate the electronic structure of GaNNTs (n, 0) (4<=n<=9). Secondly, DFT and non-equilibrium Green function (NEGF) method are also used to predict the electronic transport properties of GaNNTs two-probe system. The results showed: there is a corresponding relation between the electronic transport properties and the valley of state density of each GaNNT. In addition, the volt-ampere curve of GaNNT is approximately linear.

Direct-current nanogenerator driven by ultrasonic waves.

PubMed

Wang, Xudong; Song, Jinhui; Liu, Jin; Wang, Zhong Lin

2007-04-06

We have developed a nanowire nanogenerator that is driven by an ultrasonic wave to produce continuous direct-current output. The nanogenerator was fabricated with vertically aligned zinc oxide nanowire arrays that were placed beneath a zigzag metal electrode with a small gap. The wave drives the electrode up and down to bend and/or vibrate the nanowires. A piezoelectric-semiconducting coupling process converts mechanical energy into electricity. The zigzag electrode acts as an array of parallel integrated metal tips that simultaneously and continuously create, collect, and output electricity from all of the nanowires. The approach presents an adaptable, mobile, and cost-effective technology for harvesting energy from the environment, and it offers a potential solution for powering nanodevices and nanosystems.

Pressure-induced stable BeN4 as a high-energy density material

NASA Astrophysics Data System (ADS)

Zhang, Shoutao; Zhao, Ziyuan; Liu, Lulu; Yang, Guochun

2017-10-01

Polynitrogens are the ideal rocket fuels or propellants. Due to strong triple N≡N bond in N2, the direct polymerization of nitrogen is rather difficult (i.e. extreme high temperature and high pressure). However, the use of nitrides as precursors or the reaction of N2 with other elements has been proved to be an effective way to obtain polynitrogens. Here, with assistance of the advanced first-principles swarm-intelligence structure searches, we found that P 1 bar -BeN4, containing infinite zigzag-like polymeric nitrogen chains, can be synthesized by compressing the mixture of Be3N2 and N2 at 25.4 GPa, which is greatly lower than 110 GPa for synthesizing cubic gauche nitrogen and other polynitrogen compounds (e.g. bulk CNO at 52 GPa and SN4 at 49 GPa). Its structural stability can be attributed to the coexistence of ionic Be-N and covalent N-N bonds. Intriguingly, this phase has high kinetic stability and remains metastable at ambient pressure. The exceptional properties, including high energy density (3.60 kJ g-1), high nitrogen content (86.1%), high dynamical stability, and low polymerization pressure, make P 1 bar -structured BeN4 a promising high energy material. Infinite nitrogen chains in P 1 bar -BeN4 transform to N10 rings network in P21/c phase at 115.1 GPa. P 1 bar -BeN4 is metallic, while P21/c-BeN4 is an insulator.

Metallic Borides, La 2 Re 3 B 7 and La 3 Re 2 B 5 , Featuring Extensive Boron–Boron Bonding

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

Bugaris, Daniel E.; Malliakas, Christos D.; Chung, Duck Young

We synthesized La 2Re 3B 7 and La 3Re 2B 5 in single-crystalline form from a molten La/Ni eutectic at 1000°C, in the first example of the flux crystal growth of ternary rare-earth rhenium borides. Both compounds crystallize in their own orthorhombic structure types, with La 2Re 3B 7 (space group Pcca) having lattice parameters a = 7.657(2) Å, b = 6.755(1) Å, and c = 11.617(2) Å, and La 3Re 2B 5 (space group Pmma) having lattice parameters a = 10.809(2) Å, b = 5.287(1) Å, and c = 5.747(1) Å. Furthermore, the compounds possess three-dimensional framework structures thatmore » are built up from rhenium boride polyhedra and boron-boron bonding. La 3Re 2B 5 features fairly common B 2 dumbbells, whereas La 2Re 3B 7 has unique one-dimensional subunits composed of alternating triangular B3 and trans-B4 zigzag chain fragments. Also observed in La 3Re 2B 5 is an unusual coordination of B by an octahedron of La atoms. Electronic band structure calculations predict that La 2Re 3B 7 is a semimetal, which is observed in the electrical resistivity data as measured on single crystals, with behavior obeying the Bloch-Grüneisen model and a room-temperature resistivity ρ300K of ~ 375 μΩ cm. The electronic band structure calculations also suggest that La 3Re 2B 5 is a regular metal.« less

Ordering of calcium and vacancies in calcium catapleiite CaZr[Si{sub 3}O{sub 9}] • 2H{sub 2}O

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

Aksenov, S. M., E-mail: aks.crys@gmail.com; Portnov, A. M.; Chukanov, N. V.

A sample of holotypic calcium catapleiite from the Burpala alkaline massif (Northern Baikal, Russia) is studied by single crystal X-ray analysis at 120 K and IR spectroscopy. The empirical formula of calcium catapleiite is Ca{sub 0.97}Na{sub 0.02}Zr{sub 1.01}Si{sub 3}O{sub 9} • 2H{sub 2}O (Z = 4). The X-ray diffraction study confirms the orthorhombic unit cell with the following parameters: a = 7.406(1), b = 12.687(1), and c = 10.112(1) Å; V = 950.1(2) Å{sup 3}; space group Pbnn. The crystal structure is refined in the anisotropic approximation of atomic displacement parameters using 1177 reflections with I > 2σ(I) to themore » final R = 2.91%. The structure of calcium catapleiite under study is based on the microporous heteropolyhedral framework formed by ZrO{sub 6} octahedra and threemembered silicon–oxygen rings [Si{sub 3}O{sub 9}]. It is on the whole analogous to the structures of the samples studied earlier, but differs from them by a high degree of ordering of calcium and vacancies at extraframework positions. The distribution of calcium over Ca1 and Ca2 positions in the calcium catapleiite structure leads to the formation of zigzag chains of the …Ca1–Zr–Ca1–Zr… and …Ca2–h–Ca2–□… types. Low occupancy of the Ca2 position and its alternation with the vacancy are prerequisites for potential Ca{sup 2+} cationic conduction.« less

Metallic Borides, La 2 Re 3 B 7 and La 3 Re 2 B 5 , Featuring Extensive Boron–Boron Bonding

DOE PAGES

Bugaris, Daniel E.; Malliakas, Christos D.; Chung, Duck Young; ...

2016-01-26

We synthesized La 2Re 3B 7 and La 3Re 2B 5 in single-crystalline form from a molten La/Ni eutectic at 1000°C, in the first example of the flux crystal growth of ternary rare-earth rhenium borides. Both compounds crystallize in their own orthorhombic structure types, with La 2Re 3B 7 (space group Pcca) having lattice parameters a = 7.657(2) Å, b = 6.755(1) Å, and c = 11.617(2) Å, and La 3Re 2B 5 (space group Pmma) having lattice parameters a = 10.809(2) Å, b = 5.287(1) Å, and c = 5.747(1) Å. Furthermore, the compounds possess three-dimensional framework structures thatmore » are built up from rhenium boride polyhedra and boron-boron bonding. La 3Re 2B 5 features fairly common B 2 dumbbells, whereas La 2Re 3B 7 has unique one-dimensional subunits composed of alternating triangular B3 and trans-B4 zigzag chain fragments. Also observed in La 3Re 2B 5 is an unusual coordination of B by an octahedron of La atoms. Electronic band structure calculations predict that La 2Re 3B 7 is a semimetal, which is observed in the electrical resistivity data as measured on single crystals, with behavior obeying the Bloch-Grüneisen model and a room-temperature resistivity ρ300K of ~ 375 μΩ cm. The electronic band structure calculations also suggest that La 3Re 2B 5 is a regular metal.« less

Pinning in high performance MgB2 thin films and bulks: Role of Mg-B-O nano-scale inhomogeneities

NASA Astrophysics Data System (ADS)

Prikhna, Tatiana; Shapovalov, Andrey; Eisterer, Michael; Shaternik, Vladimir; Goldacker, Wilfried; Weber, Harald W.; Moshchil, Viktor; Kozyrev, Artem; Sverdun, Vladimir; Boutko, Viktor; Grechnev, Gennadiy; Gusev, Alexandr; Kovylaev, Valeriy; Shaternik, Anton

2017-02-01

The comparison of nano-crystalline MgB2 oxygen-containing thin film (140 nm) and highly dense bulk materials showed that the critical current density, Jc, depends on the distribution of Mg-B-O nano-scale inhomogeneities. It has been shown that MgB2 bulks with high Jc in low (∼106 A/cm2 in 0-1 T at 10 K) and medium magnetic fields contain MgB0.6-0.8O0.8-0.9 nano-inclusions, where δTc or a combined δTc (dominant) / δl pinning mechanism prevails, while in bulk MgB2 with high Jc in high magnetic fields (Birr(18.5 K) = 15 T, Bc2(0 K) = 42.1 T) MgB1.2-2.7O1.8-2.5 nano-layers are present and δl pinning prevails. The structure of oxygen-containing films with high Jc in low and high magnetic fields (Jc (0 Т) = 1.8 × 107 А/сm2 and Jc (5 Т) = 2 × 106 А/сm2 at 10 К) contains very fine oxygen-enriched Mg-B-O inhomogeneities and δl pinning is realized. The results of DOS calculations in MgB2-xOx cells for x = 0, 0.125, 0.25, 0.5, 1 demonstrate that all compounds are conductors with metal-like behaviour. In the case of ordered oxygen substitution for boron the binding energy, Eb, does not increase sufficiently as compared with that for MgB2, while when oxygen atoms form zigzag chains the calculated Eb is even lower (Eb = -1.15712 Ry).

Molecular dynamics simulation of a nanofluidic energy absorption system: effects of the chiral vector of carbon nanotubes.

PubMed

Ganjiani, Sayed Hossein; Hossein Nezhad, Alireza

2018-02-14

A Nanofluidic Energy Absorption System (NEAS) is a novel nanofluidic system with a small volume and weight. In this system, the input mechanical energy is converted to surface tension energy during liquid infiltration in the nanotube. The NEAS is made of a mixture of nanoporous material particles in a functional liquid. In this work, the effects of the chiral vector of a carbon nanotube (CNT) on the performance characteristics of the NEAS are investigated by using molecular dynamics simulation. For this purpose, six CNTs with different diameters for each type of armchair, zigzag and chiral, and several chiral CNTs with different chiral vectors (different values of indices (m,n)) are selected and studied. The results show that in the chiral CNTs, the contact angle shows the hydrophobicity of the CNT, and infiltration pressure is reduced by increasing the values of m and n (increasing the CNT diameter). Contact angle and infiltration pressure are decreased by almost 1.4% and 9% at all diameters, as the type of CNT is changed from chiral to zigzag and then to armchair. Absorbed energy density and efficiency are also decreased by increasing m and n and by changing the type of CNT from chiral to zigzag and then to armchair.

The Effects of Graphene Stacking on the Performance of Methane Sensor: A First-Principles Study on the Adsorption, Band Gap and Doping of Graphene

PubMed Central

Yang, Daoguo; Zhang, Guoqi; Chen, Liangbiao; Liu, Dongjing; Cai, Miao; Fan, Xuejun

2018-01-01

The effects of graphene stacking are investigated by comparing the results of methane adsorption energy, electronic performance, and the doping feasibility of five dopants (i.e., B, N, Al, Si, and P) via first-principles theory. Both zigzag and armchair graphenes are considered. It is found that the zigzag graphene with Bernal stacking has the largest adsorption energy on methane, while the armchair graphene with Order stacking is opposite. In addition, both the Order and Bernal stacked graphenes possess a positive linear relationship between adsorption energy and layer number. Furthermore, they always have larger adsorption energy in zigzag graphene. For electronic properties, the results show that the stacking effects on band gap are significant, but it does not cause big changes to band structure and density of states. In the comparison of distance, the average interlamellar spacing of the Order stacked graphene is the largest. Moreover, the adsorption effect is the result of the interactions between graphene and methane combined with the change of graphene’s structure. Lastly, the armchair graphene with Order stacking possesses the lowest formation energy in these five dopants. It could be the best choice for doping to improve the methane adsorption. PMID:29389860

The Effects of Graphene Stacking on the Performance of Methane Sensor: A First-Principles Study on the Adsorption, Band Gap and Doping of Graphene.

PubMed

Yang, Ning; Yang, Daoguo; Zhang, Guoqi; Chen, Liangbiao; Liu, Dongjing; Cai, Miao; Fan, Xuejun

2018-02-01

The effects of graphene stacking are investigated by comparing the results of methane adsorption energy, electronic performance, and the doping feasibility of five dopants (i.e., B, N, Al, Si, and P) via first-principles theory. Both zigzag and armchair graphenes are considered. It is found that the zigzag graphene with Bernal stacking has the largest adsorption energy on methane, while the armchair graphene with Order stacking is opposite. In addition, both the Order and Bernal stacked graphenes possess a positive linear relationship between adsorption energy and layer number. Furthermore, they always have larger adsorption energy in zigzag graphene. For electronic properties, the results show that the stacking effects on band gap are significant, but it does not cause big changes to band structure and density of states. In the comparison of distance, the average interlamellar spacing of the Order stacked graphene is the largest. Moreover, the adsorption effect is the result of the interactions between graphene and methane combined with the change of graphene's structure. Lastly, the armchair graphene with Order stacking possesses the lowest formation energy in these five dopants. It could be the best choice for doping to improve the methane adsorption.

Electromechanical and Photoluminescence Properties of Al-doped ZnO Nanorods Applied in Piezoelectric Nanogenerators

NASA Astrophysics Data System (ADS)

Chang, Wen-Yang; Fang, Te-Hua; Tsai, Ju-Hsuan

2015-02-01

A piezoelectric nanogenerator based on Al-doped ZnO (AZO) nanorods with a V-zigzag layer is investigated at a low temperature. The growth temperature, growth time, growth concentration, photoluminescence (PL) spectrum, and AZO epitaxial growth on the ITO glass substrate using aqueous solution are reported and the associated electromechanical and PL properties are discussed. In general, the properties of piezoelectric nanogenerators and their functionality at ultralow temperatures (near liquid helium temperature) are important for applications in extreme environments. A V-zigzag layer is used to enhance the bending and compression deformation of the piezoelectric nanogenerator. The electromechanical properties of AZO nanorods are tested using an ultrasonic wave generator. Results show that the percent transmittance decreases with increasing growth time and growth temperature. The intensities of the PL spectrum and the (002) peak orientation increases with increasing growth temperature. AZO at a low growth temperature of 90 C has good piezoelectric harvesting efficiency when the piezoelectric nanogenerator has a zigzag structure. The average current, voltage, and power density of the piezoelectric harvesting are 0.76 A, 1.35 mV, and 1.026 nW/mm, respectively. These results confirm the feasibility of growing AZO at low temperature. AZO nanorods have potential for energy harvester applications.

A structural insight into mechanical strength of graphene-like carbon and carbon nitride networks

NASA Astrophysics Data System (ADS)

Rahaman, Obaidur; Mortazavi, Bohayra; Dianat, Arezoo; Cuniberti, Gianaurelio; Rabczuk, Timon

2017-02-01

Graphene, one of the strongest materials ever discovered, triggered the exploration of many 2D materials in the last decade. However, the successful synthesis of a stable nanomaterial requires a rudimentary understanding of the relationship between its structure and strength. In the present study, we investigate the mechanical properties of eight different carbon-based 2D nanomaterials by performing extensive density functional theory calculations. The considered structures were just recently either experimentally synthesized or theoretically predicted. The corresponding stress-strain curves and elastic moduli are reported. They can be useful in training force field parameters for large scale simulations. A comparative analysis of these results revealed a direct relationship between atomic density per area and elastic modulus. Furthermore, for the networks that have an armchair and a zigzag orientation, we observed that they were more stretchable in the zigzag direction than the armchair direction. A critical analysis of the angular distributions and radial distribution functions suggested that it could be due to the higher ability of the networks to suppress the elongations of the bonds in the zigzag direction by deforming the bond angles. The structural interpretations provided in this work not only improve the general understanding of a 2D material’s strength but also enables us to rationally design them for higher qualities.

Spin density waves predicted in zigzag puckered phosphorene, arsenene and antimonene nanoribbons

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

Wu, Xiaohua; Zhang, Xiaoli; Wang, Xianlong

2016-04-15

The pursuit of controlled magnetism in semiconductors has been a persisting goal in condensed matter physics. Recently, Vene (phosphorene, arsenene and antimonene) has been predicted as a new class of 2D-semiconductor with suitable band gap and high carrier mobility. In this work, we investigate the edge magnetism in zigzag puckered Vene nanoribbons (ZVNRs) based on the density functional theory. The band structures of ZVNRs show half-filled bands crossing the Fermi level at the midpoint of reciprocal lattice vectors, indicating a strong Peierls instability. To remove this instability, we consider two different mechanisms, namely, spin density wave (SDW) caused by electron-electronmore » interaction and charge density wave (CDW) caused by electron-phonon coupling. We have found that an antiferromagnetic Mott-insulating state defined by SDW is the ground state of ZVNRs. In particular, SDW in ZVNRs displays several surprising characteristics:1) comparing with other nanoribbon systems, their magnetic moments are antiparallelly arranged at each zigzag edge and almost independent on the width of nanoribbons; 2) comparing with other SDW systems, its magnetic moments and band gap of SDW are unexpectedly large, indicating a higher SDW transition temperature in ZVNRs; 3) SDW can be effectively modified by strains and charge doping, which indicates that ZVNRs have bright prospects in nanoelectronic device.« less

Synthesis and characterization of a new family of alkylammonium-chromium phosphates with worm-like morphology

NASA Astrophysics Data System (ADS)

Amghouz, Zakariae; Espina, Aránzazu; García, José R.

2015-01-01

A series of layered alkylammonium-chromium phosphates, formulated as [CnH2n+1NH3]Cr(OH)PO4 (n=2-6), has been synthesized under hydrothermal conditions. The interlayer spacing, increasing linearly with the increase of alkyl-chain length from 13.61 Å (n=2) to 21.20 Å (n=6), is occupied by a double sheet of packed amine molecules with a tilt angle of ca. 51° respect to the inorganic sheet. The powders are constituted by circular plates (diameter=0.5-3 μm, thickness= 50 nm) with central holes when n=4-6, stacked in axial direction showing worm-like morphologies. The presence of holes, and some corrugated and zig-zag fashions observed on the edge of thin circular plates are the most probable ways for the reduction of the steric tensions between organic and inorganic portions in these hybrid materials. The thermal and thermo-oxidative stability of selected compounds have been studied, including the determination of activation energy data for the decomposition processes.

Two novel transition metal-organic frameworks based on 1,3,5-benzenetricarboxylate ligand: Syntheses, structures and thermal properties

NASA Astrophysics Data System (ADS)

Fu, Ying; Li, Guobao; Liao, Fuhui; Xiong, Ming; Lin, Jianhua

2011-10-01

Two novel transition metal-organic frameworks, [Zn 6(OH) 3(BTC) 3(H 2O) 3]ṡ7H 2O ( 1) and [Cd(BTC)(H 2O)]ṡ[HIM] ( 2) (H 3BTC = 1,3,5-benzenetricarboxylic acid), have been synthesized under hydrothermal conditions and characterized by single crystal and variable temperature powder X-ray diffraction (VTPXRD), IR spectroscopy, elemental analyses, ICP measurements, and coupled TG-MS analyses. Compound 1 crystallizes in the trigonal space group R3 c, and could be described as a 3D porous network consisting of (Zn 2O 8) n zigzag chains and bridging BTC ligands with 1D channels along c axis. Compound 2 crystallizes in the monoclinic space group P2 1/ c, and exhibits a 2D framework made up of CdO 6 octahedra and BTC ligands parallel the bc plane. TG-MS and VTPXRD studies reveal that 1 is stable up to 320 °C under air, and 2 stable up to 220 °C.

Two novel copper(II) complexes constructed from dicarboxylate ligands with different spacer lengths and 2-phenylimidazo[4,5- f]1,10-phenanthroline (PIP): Synthesis, structures and properties

NASA Astrophysics Data System (ADS)

Wang, X.-L.; Chen, Yongqiang; Liu, Guocheng; Lin, Hongyan; Zhang, Jinxia

2009-09-01

Two novel metal-organic coordination polymers [Cu(PIP)(bpea)(H 2O)]·H 2O ( 1) and [Cu(PIP)(1,4-bdc)] ( 2) have been obtained from hydrothermal reaction of copper(II) with the mixed ligands [biphenylethene-4,4'-dicarboxylic acid (bpea) for 1, benzene-1,4-dicarboxylic acid (1,4-H 2bdc) for 2, and 2-phenylimidazo[4,5- f]1,10-phenanthroline (PIP)]. Both complexes have been structurally characterized by elemental analyses, IR and single-crystal X-ray diffraction analyses. Structural analyses reveal that complex 1 possesses infinite one-dimensional zigzag chain, 2 exhibits a two-dimensional (4,4) network, both of which are extended into three-dimensional supramolecular network by weak interactions. The different structures of the title complexes illustrate the influence of the flexibility (the spacer length of carboxyl groups and the structural rigidity of the spacer) of organic dicarboxylate ligands on the formation of such coordination architectures. Moreover, the thermal properties and the voltammetric behavior of complexes 1 and 2 have been reported.

Neutron Spin Resonance in the 112-Type Iron-Based Superconductor.

PubMed

Xie, Tao; Gong, Dongliang; Ghosh, Haranath; Ghosh, Abyay; Soda, Minoru; Masuda, Takatsugu; Itoh, Shinichi; Bourdarot, Frédéric; Regnault, Louis-Pierre; Danilkin, Sergey; Li, Shiliang; Luo, Huiqian

2018-03-30

We use inelastic neutron scattering to study the low-energy spin excitations of the 112-type iron pnictide Ca_{0.82}La_{0.18}Fe_{0.96}Ni_{0.04}As_{2} with bulk superconductivity below T_{c}=22  K. A two-dimensional spin resonance mode is found around E=11  meV, where the resonance energy is almost temperature independent and linearly scales with T_{c} along with other iron-based superconductors. Polarized neutron analysis reveals the resonance is nearly isotropic in spin space without any L modulations. Because of the unique monoclinic structure with additional zigzag arsenic chains, the As 4p orbitals contribute to a three-dimensional hole pocket around the Γ point and an extra electron pocket at the X point. Our results suggest that the energy and momentum distribution of the spin resonance does not directly respond to the k_{z} dependence of the fermiology, and the spin resonance intrinsically is a spin-1 mode from singlet-triplet excitations of the Cooper pairs in the case of weak spin-orbital coupling.

Relationship Between Change of Direction, Speed and Power in Male and Female National Olympic Team Handball Athletes.

PubMed

Pereira, Lucas A; Nimphius, Sophia; Kobal, Ronaldo; Kitamura, Katia; Turisco, Luiz A L; Orsi, Rita C; Cal Abad, César Cs; Loturco, Irineu

2018-02-22

The aims of this study were to (1) assess the relationship between selected speed-power related abilities (determined by 20-m sprint, unloaded countermovement and squat jumps [CMJ and SJ] and loaded jump squat [JS]) and performance in two distinct change of direction (COD) protocols (Zigzag and T-Test), and (2) determine the magnitude of difference between female and male Brazilian National Olympic Team handball athletes. Fifteen male and twenty-three female elite handball athletes volunteered to perform the following assessments: SJ and CMJ; Zigzag and T-Test; 20-m sprint with 5-, 10-, and 20-m splits, and mean propulsive power (MPP) in JS. Pearson product moment correlation (P< 0.05) was performed to determine the relationship between the COD tests (Zigzag and T-test) and speed-power measures (sprint, SJ, CMJ and JS). The differences between male and female performances were determined using the magnitude-based inference. Moderate to very large significant correlations were observed between both COD tests and the speed-power abilities. Further, male athletes demonstrated likely to almost certainly higher performances than female athletes in all assessed variables. The results of the current study suggest that different speed-power qualities are strongly correlated to the performance obtained in various COD assessments (r values varying from 0.38 to 0.84 and from 0.34 to 0.84 for correlations between speed and power tests with Zigzag and T-Test, respectively). However, the level of these associations can vary greatly, according to the mechanical demands of each respective COD task. Whilst COD tests may be difficult to implement during competitive seasons, due to the strong correlations presented herein, the regular use of vertical jump tests with these athletes seems to be an effective and applied alternative. Furthermore, it might be inferred that the proper development of loaded and unloaded jump abilities has potential for improving the physical qualities related to COD performance in handball athletes.

Villification of the gut

NASA Astrophysics Data System (ADS)

Tallinen, Tuomas; Shyer, Amy E.; Tabin, Clifford J.; Mahadevan, L.

2014-03-01

The villi of the human and chick gut are formed in similar stepwise progressions, wherein the mesenchyme and attached epithelium first fold into longitudinal ridges, then a zigzag pattern, and lastly individual villi. We combine biological manipulations and quantitative modeling to show that these steps of villification depend on the sequential differentiation of the distinct smooth muscle layers of the gut, which restrict the expansion of the growing endoderm and mesenchyme, generating compressive stresses that lead to their buckling and folding. Our computational model incorporates measured elastic properties and growth rates in the developing gut, recapitulating the morphological patterns seen during villification in a variety of species. Our study provides a mechanical basis for the genesis of these epithelial protrusions that are essential for providing sufficient surface area for nutrient absorption.

Attraction between pancake vortices and vortex molecule formation in the crossing lattices in thin films of layered superconductors

NASA Astrophysics Data System (ADS)

Samokhvalov, A. V.; Mel'nikov, A. S.; Buzdin, A. I.

2012-05-01

We study the intervortex interaction in thin films of layered superconductors for the magnetic field tilted with respect to the c axis. In such a case, the crossing lattice of Abrikosov vortices (AVs) and Josephson vortices appears. The interaction between pancake vortices, forming the AVs, with Josephson ones, produces the zigzag deformation of the AV line. This deformation induces a long-range attraction between Abrikosov vortices and, in thin films, it competes with another long-range interaction, i.e., with Pearl's repulsion. This interplay results in the formation of clusters of Abrikosov vortices, which can be considered as vortex molecules. The number of vortices in such clusters depends on field tilting angle and film thickness.

Chlorine effect on the formation of carbon nanofibers.

PubMed

Lin, Wang-Hua; Takahashi, Yusuke; Li, Yuan-Yao; Sakoda, Akiyoshi

2012-12-01

Platelet graphite nanofibers (GNFs) and turbostratic carbon nanofibers (CNFs) are synthesized by the thermal evaporation and decomposition of a polymer-based mixture at 700 degrees C using Ni as a catalyst. The mixture consists of poly(ethylene glycol) (PEG), serving as the carbon source, and hydrochloric acid solution (HCl(aq)), serving as the promoter/additive for the growth of CNFs. High-purity zigzag-shaped platelet GNFs form with 10 wt% HCl(aq) as an additive in the PEG. The diameters of the platelet GNFs are in the range of 40-60 nm, with lengths of a few micrometers. High-resolution transmission electron microscopy images indicate a high degree of graphitization and well ordered graphene layers along the fiber axis. In contrast, high-purity turbostratic CNFs form with 20 wt% HCl(aq) in the PEG. The diameter and length of the turbostratic CNFs are 20-40 nm and a few micrometers, respectively. The participation of HCl in the thermal process leads to the formation of Ni-Cl compounds. The amount of chlorine affects the shape of the Ni catalyst, which determines the type of CNF formed.

Imaging electron flow from collimating contacts in graphene

NASA Astrophysics Data System (ADS)

Bhandari, S.; Lee, G. H.; Watanabe, K.; Taniguchi, T.; Kim, P.; Westervelt, R. M.

2018-04-01

The ballistic motion of electrons in graphene opens exciting opportunities for electron-optic devices based on collimated electron beams. We form a collimating contact in a hBN-encapsulated graphene hall bar by adding zigzag contacts on either side of an electron emitter that absorb stray electrons; collimation can be turned off by floating the zig-zag contacts. The electron beam is imaged using a liquid-He cooled scanning gate microscope (SGM). The tip deflects electrons as they pass from the collimating contact to a receiving contact on the opposite side of the channel, and an image of electron flow can be made by displaying the change in transmission as the tip is raster scanned across the sample. The angular half width Δθ of the electron beam is found by applying a perpendicular magnetic field B that bends electron paths into cyclotron orbits. The images reveal that the electron flow from the collimating contact drops quickly at B  =  0.05 T when the electron orbits miss the receiving contact. The flow for the non-collimating case persists longer, up to B  =  0.19 T, due to the broader range of entry angles. Ray-tracing simulations agree well with the experimental images. By fitting the fields B at which the magnitude of electron flow drops in the experimental SGM images, we find Δθ  =  9° for electron flow from the collimating contact, compared with Δθ  =  54° for the non-collimating case.

Aspects of electron transport in zigzag graphene nanoribbons

NASA Astrophysics Data System (ADS)

Bhalla, Pankaj; Pratap, Surender

2018-05-01

In this paper, we investigate the aspects of electron transport in the zigzag graphene nanoribbons (ZGNRs) using the nonequilibrium Green’s function (NEGF) formalism. The latter is an esoteric tool in mesoscopic physics. It is used to perform an analysis of ZGNRs by considering potential well. Within this potential, the dependence of transmission coefficient, local density of states (LDOS) and electron transport properties on number of atoms per unit cell is discussed. It is observed that there is an increment in electron and thermal conductance with increasing number of atoms. In addition to these properties, the dependence of same is also studied in figure of merit. The results infer that the contribution of electrons to enhance the figure of merit is important above the crossover temperature.

Car-Parrinello molecular dynamics study of the melting behaviors of n-atom (n = 6, 10) graphene quantum dots

NASA Astrophysics Data System (ADS)

Shekaari, Ashkan; Abolhassani, Mohammad Reza

2017-06-01

First-principles molecular dynamics has been applied to inquire into the melting behaviors of n-atom (n = 6, 10) graphene quantum dots (GQD6 and zigzag GQD10) within the temperature range of T = 0-500 K. The temperature dependence of the geometry of each quantum dot is thoroughly evaluated via calculating the related shape deformation parameters and the eigenvalues of the quadrupole tensors. Examining the variations of some phase-transition indicators such as root-mean-square bond length fluctuations and mean square displacements broadly proposes the value of Tm = 70 K for the melting point of GQD6 while a continuous, two-stage phase transition has been concluded for zigzag GQD10.

Novel Design for Centrifugal Countercurrent Chromatography: II. Studies on Novel Geometries of Zigzag Toroidal Tubing

PubMed Central

Yang, Yi; Aisa, Haji Akber; Ito, Yoichiro

2009-01-01

The toroidal column using a zigzag pattern has been improved in both retention of the stationary phase and peak resolution. To further improve the retention of stationary phase and peak resolution, a series of novel geometric designs of tubing (plain, mid-clamping, flattened and flat-twisted tubing) was evaluated their performance in CCC. The results showed that the tubing which was flattened vertically against centrifugal force (vert-flattened tubing) produced the best peak resolution among them. Using vert-flattened tubing a series of experiments was performed to study the effects of column capacity and sample size. The results indicated that a 0.25 ml capacity column is ideal for analysis of small amount samples. PMID:20454530

Time-dependent density-functional theory simulation of local currents in pristine and single-defect zigzag graphene nanoribbons

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

He, Shenglai, E-mail: shenglai.he@vanderbilt.edu; Russakoff, Arthur; Li, Yonghui

2016-07-21

The spatial current distribution in H-terminated zigzag graphene nanoribbons (ZGNRs) under electrical bias is investigated using time-dependent density-functional theory solved on a real-space grid. A projected complex absorbing potential is used to minimize the effect of reflection at simulation cell boundary. The calculations show that the current flows mainly along the edge atoms in the hydrogen terminated pristine ZGNRs. When a vacancy is introduced to the ZGNRs, loop currents emerge at the ribbon edge due to electrons hopping between carbon atoms of the same sublattice. The loop currents hinder the flow of the edge current, explaining the poor electric conductancemore » observed in recent experiments.« less

Development of thermally controlled HALNA DPSSL for inertial fusion energy

NASA Astrophysics Data System (ADS)

Matsumoto, Osamu; Yasuhara, Ryo; Kurita, Takashi; Ikegawa, Tadashi; Sekine, Takashi; Kawashima, Toshiyuki; Kawanaka, Junji; Norimatsu, Takayoshi; Miyanaga, Noriaki; Izawa, Yasukazu; Nakatsuka, Masahiro; Miyamoto, Masahiro; Kan, Hirofumi; Furukawa, Hiroyuki; Motokoshi, Shinji

2006-02-01

We have been developing a high average-power laser system for science and industry applications that can generate an output of 20 J per pulse at 10-Hz operation. Water-cooled Nd:glass zig-zag slab is pumped with 803-nm AlGaAs laser-diode modules. To efficiently extract energy from the laser medium, the laser beam alternately passes through dual zig-zag slab amplifier modules. Twin LD modules equipped on each slab amplifier module pump the laser medium with a peak power density of 2.5 kW/cm2. In high power laser system, thermal load in the laser medium causes serious thermal effects. We arranged cladding glasses on the top and bottom of the laser slab to reduce thermal effects.

Effects of edge magnetism on the Kohn anomalies of zigzag graphene nanoribbons.

PubMed

Culchac, F J; Capaz, Rodrigo B

2016-02-12

The effects of edge magnetism on the Kohn anomaly (KA) of the G-band phonons of zigzag graphene nanoribbons (ZGNRs) are studied using a combination of the tight-binding and mean-field Hubbard models. We show that the opening of an energy gap, induced by magnetic ordering, significantly changes the KA effects, particularly for narrow ribbons in which the gap is larger than the phonon energy. Therefore, the G-band phonon frequency and lifetime are altered for a magnetically-ordered edge state with respect to an unpolarized edge state. The effects of temperature, ZGNR width, doping and transverse electric fields are systematically investigated. We propose using this effect to probe the magnetic order of edge states in graphene nanoribbons using Raman spectroscopy.

Eccentric mastectomy and zigzag periareolar incision for gynecomastia.

PubMed

Tu, Lung-Chen; Tung, Kwang-Yi; Chen, Heng-Chang; Huang, Wen-Chen; Hsiao, Hung-Tao

2009-07-01

Gynecomastia is enlargement of the male breast caused by gland proliferation. Surgery is performed for symptom relief or for cosmetic reasons. The authors used a modified operative procedure, then evaluated the results and safety. Between 2001 and 2005, 22 men (median age, 26 years; range, 13-63 years) with gynecomastia underwent surgery. The operative procedure included a zigzag periareolar skin incision, eccentric subcutaneous mastectomy, and liposuction, with postoperative compression. All the patients were satisfied with the results of the surgery, which produced a chest contour resembling a normal male chest rather than simply a smaller breast. The only complication was a hematoma. One patient was found to have breast cancer. The normal male chest contour can be restored by the described method of eccentric subcutaneous mastectomy.

Nanocarbon: Defect Architectures and Properties

NASA Astrophysics Data System (ADS)

Vuong, Amanda

The allotropes of carbon make its solid phases amongst the most diverse of any element. It can occur naturally as graphite and diamond, which have very different properties that make them suitable for a wide range of technological and commercial purposes. Recent developments in synthetic carbon include Highly Oriented Pyrolytic Graphite (HOPG) and nano-carbons, such as fullerenes, nanotubes and graphene. The main industrial application of bulk graphite is as an electrode material in steel production, but in purified nuclear graphite form, it is also used as a moderator in Advanced Gas-cooled Reactors across the United Kingdom. Both graphene and graphite are damaged over time when subjected to bombardment by electrons, neutrons or ions, and these have a wide range of effects on their physical and electrical properties, depending on the radiation flux and temperature. This research focuses on intrinsic defects in graphene and dimensional change in nuclear graphite. The method used here is computational chemistry, which complements physical experiments. Techniques used comprise of density functional theory (DFT) and molecular dynamics (MD), which are discussed in chapter 2 and chapter 3, respectively. The succeeding chapters describe the results of simulations performed to model defects in graphene and graphite. Chapter 4 presents the results of ab initio DFT calculations performed to investigate vacancy complexes that are formed in AA stacked bilayer graphene. In AB stacking, carbon atoms surrounding the lattice vacancies can form interlayer structures with sp2 bonding that are lower in energy compared to in-plane reconstructions. From the investigation of AA stacking, sp2 interlayer bonding of adjacent multivacancy defects in registry creates a type of stable sp2 bonded wormhole between the layers. Also, a new class of mezzanine structure characterised by sp3 interlayer bonding, resembling a prismatic vacancy loop has also been identified. The mezzanine, which is a V6 hexavacancy variant, where six sp3 carbon atoms sit midway between two carbon layers and bond to both, is substantially more stable than any other vacancy aggregate in AA stacked layers. Chapter 5 presents the results of ab initio DFT calculations performed to investigate the wormhole and mezzanine defect that were identified in chapter 4 and the ramp defect discovered by Trevethan et al.. DFT calculations were performed on these defects in twisted bilayer graphene. From the investigation of vacancy complexes in twisted bilayer graphene, it is found that vacancy complexes are unstable in the twisted region and are more favourable in formation energy when the stacking arrangement is close to AA or AB stacking. It has also been discovered that the ramp defect is more stable in the twisted bilayer graphene compared to the mezzanine defect. Chapter 6 presents the results of ab initio DFT calculations performed to investigate a form of extending defect, prismatic edge dislocation. Suarez-Martinez et al.'s research suggest the armchair core is disconnected from any other layer, whilst the zigzag core is connected. In the investigation here, the curvature of the mezzanine defect allows it to swing between the armchair, zigzag and Klein in the AA stacking. For the AB stacking configuration, the armchair and zigzag core are connected from any other layer. Chapter 7 present results of MD simulations using the adaptive intermolecular reactive empirical bond order (AIREBO) potential to investigate the dimensional change of graphite due to the formation of vacancies present in a single crystal. It has been identified that there is an expansion along the c-axis, whilst a contraction along the a- and b- axes due to the coalescence of vacancy forming in-plane and between the layers. The results here are in good agreement with experimental studies of low temperature irradiation. The final chapter gives conclusions to this work.

The structure and organization of lanceolate mechanosensory complexes at mouse hair follicles

PubMed Central

Li, Lishi; Ginty, David D

2014-01-01

In mouse hairy skin, lanceolate complexes associated with three types of hair follicles, guard, awl/auchene and zigzag, serve as mechanosensory end organs. These structures are formed by unique combinations of low-threshold mechanoreceptors (LTMRs), Aβ RA-LTMRs, Aδ-LTMRs, and C-LTMRs, and their associated terminal Schwann cells (TSCs). In this study, we investigated the organization, ultrastructure, and maintenance of longitudinal lanceolate complexes at each hair follicle subtype. We found that TSC processes at hair follicles are tiled and that individual TSCs host axonal endings of more than one LTMR subtype. Electron microscopic analyses revealed unique ultrastructural features of lanceolate complexes that are proposed to underlie mechanotransduction. Moreover, Schwann cell ablation leads to loss of LTMR terminals at hair follicles while, in contrast, TSCs remain associated with hair follicles following skin denervation in adult mice and, remarkably, become re-associated with newly formed axons, indicating a TSC-dependence of lanceolate complex maintenance and regeneration in adults. DOI: http://dx.doi.org/10.7554/eLife.01901.001 PMID:24569481

The structure and organization of lanceolate mechanosensory complexes at mouse hair follicles.

PubMed

Li, Lishi; Ginty, David D

2014-02-25

In mouse hairy skin, lanceolate complexes associated with three types of hair follicles, guard, awl/auchene and zigzag, serve as mechanosensory end organs. These structures are formed by unique combinations of low-threshold mechanoreceptors (LTMRs), Aβ RA-LTMRs, Aδ-LTMRs, and C-LTMRs, and their associated terminal Schwann cells (TSCs). In this study, we investigated the organization, ultrastructure, and maintenance of longitudinal lanceolate complexes at each hair follicle subtype. We found that TSC processes at hair follicles are tiled and that individual TSCs host axonal endings of more than one LTMR subtype. Electron microscopic analyses revealed unique ultrastructural features of lanceolate complexes that are proposed to underlie mechanotransduction. Moreover, Schwann cell ablation leads to loss of LTMR terminals at hair follicles while, in contrast, TSCs remain associated with hair follicles following skin denervation in adult mice and, remarkably, become re-associated with newly formed axons, indicating a TSC-dependence of lanceolate complex maintenance and regeneration in adults. DOI: http://dx.doi.org/10.7554/eLife.01901.001.

Immobilization of Alkali Metal Fluorides via Recrystallization in a Cationic Lamellar Material, [Th(MoO4)(H2O)4Cl]Cl·H2O.

PubMed

Lin, Jian; Bao, Hongliang; Qie, Meiying; Silver, Mark A; Yue, Zenghui; Li, Xiaoyun; Zhu, Lin; Wang, Xiaomei; Zhang, Linjuan; Wang, Jian-Qiang

2018-06-05

Searching for cationic extended materials with a capacity for anion exchange resulted in a unique thorium molybdate chloride (TMC) with the formula of [Th(MoO 4 )(H 2 O) 4 Cl]Cl·H 2 O. The structure of TMC is composed of zigzagging cationic layers [Th(MoO 4 )(H 2 O) 4 Cl] + with Cl - as interlamellar charge-balancing anions. Instead of performing ion exchange, alkali thorium fluorides were formed after soaking TMC in AF (A = Na, K, and Cs) solutions. The mechanism of AF immobilization is elucidated by the combination of SEM-EDS, PXRD, FTIR, and EXAFS spectroscopy. It was observed that four water molecules coordinating with the Th 4+ center in TMC are vulnerable to competition with F - , due to the formation of more favorable Th-F bonds compared to Th-OH 2 . This leads to a single crystal-to-polycrystalline transformation via a pathway of recrystallization to form alkali thorium fluorides.

A series of divalent metal coordination polymers based on isomeric tetracarboxylic acids: synthesis, structures and magnetic properties.

PubMed

Han, Min-Le; Duan, Ya-Ping; Li, Dong-Sheng; Xu, Guo-Wang; Wu, Ya-Pan; Zhao, Jun

2014-12-14

Five new coordination polymers, namely, [Mn(2,2′-bipy)(H2O)2(H2L1)]n (1), {[Co(btb)(H2O)2(H2L1)]·0.5H2O}n (2), [Co(bib)(H2O)2(H2L1)]n (3), [Ni2(bpm)(H2O)3(L2)]n (4), and {[Co2(H2O)3(OH)(HL2)]·H2O}n (5), (H4L1 = 1,1′:2′,1′′-terphenyl-4,4′,4′′,5′-tetracarboxylic acid, H4L2 = 1,1′:2′,1′′-terphenyl-3,3′′,4′,5′-tetracarboxylic acid, 2,2′-bipy = 2,2′-bipyridine, btb = 1,4-bis(1,2,4-triazol-1-yl)butane, bib = 1,4-bis(imidazol-1-yl)butane, bpm = bis(4-pyridyl)amine), have been obtained under hydrothermal conditions. Complex 1 exhibits a 3D supramolecular framework based on 1D chains. Both complexes 2 and 3 are 3D supramolecular frameworks constructed from 1D zig-zag chains. Complex 4 features a 3D tetra-nodal (3,4,4,5)-connected architecture containing 1D μ-COO bridged chains with (5(2)·6(2)·7.9)(5(2)·6(4)·7(3)·8)2(5(2)·6)2(6(3)·7(2)·9) topology. Complex 5 shows a 3D penta-nodal (3,4,4,6,6)-connected net containing 1D μ-OH/μ-COO bridged chains and mononuclear Co(II) nodes with a (4(2)·6(3)·8)(4(3))2(4(4)·6(2))2(4(4)·6(6)·8(5))2(4(4)·6(7)·8(4)) topology. Variable-temperature magnetic susceptibility measurements reveal that complexes 2 and 3 show antiferromagnetic interactions between the adjacent Co(II) ions, whereas 4 is a ferromagnetic system.

Bumblebee calligraphy: the design and control of flight motifs in the learning and return flights of Bombus terrestris.

PubMed

Philippides, Andrew; de Ibarra, Natalie Hempel; Riabinina, Olena; Collett, Thomas S

2013-03-15

Many wasps and bees learn the position of their nest relative to nearby visual features during elaborate 'learning' flights that they perform on leaving the nest. Return flights to the nest are thought to be patterned so that insects can reach their nest by matching their current view to views of their surroundings stored during learning flights. To understand how ground-nesting bumblebees might implement such a matching process, we have video-recorded the bees' learning and return flights and analysed the similarities and differences between the principal motifs of their flights. Loops that take bees away from and bring them back towards the nest are common during learning flights and less so in return flights. Zigzags are more prominent on return flights. Both motifs tend to be nest based. Bees often both fly towards and face the nest in the middle of loops and at the turns of zigzags. Before and after flight direction and body orientation are aligned, the two diverge from each other so that the nest is held within the bees' fronto-lateral visual field while flight direction relative to the nest can fluctuate more widely. These and other parallels between loops and zigzags suggest that they are stable variations of an underlying pattern, which enable bees to store and reacquire similar nest-focused views during learning and return flights.

Geometric effects on mixing performance in a novel passive micromixer with trapezoidal-zigzag channels

NASA Astrophysics Data System (ADS)

Le The, Hai; Ta, Bao Quoc; Le Thanh, Hoa; Dong, Tao; Nguyen Thoi, Trung; Karlsen, Frank

2015-09-01

A novel passive micromixer, called a trapezoidal-zigzag micromixer (TZM), is reported. A TZM is composed of trapezoidal channels in a zigzag and split-recombine arrangement that enables multiple mixing mechanisms, including splitting-recombining, twisting, transversal flows, vortices, and chaotic advection. The effects of geometric parameters of the TZM on mixing performance are systematically investigated by the Taguchi method and numerical simulations in COMSOL Multiphysics. The number of mixing units, the slope angle of the trapezoidal channel, the height of the constriction element, and the width ratio between the middle-trapezoidal channel and the side-trapezoidal channel are the four parameters under study. The mixing performance of the TZM is investigated at three different Reynolds number (Re) values of 0.5, 5, and 50. The results showed that a TZM with six mixing units, a trapezoidal slope angle of 75°, a constricting height of 100 µm, and a width ratio of 0.5 has the highest mixing efficiency. This optimal TZM has a mixing efficiency greater than 85% for Re values from 0.1 to 80. In particular, for Re  ⩽  0.9 and Re  ⩾  20, the mixing efficiency of the optimal TZM is greater than 90%. The proposed TZM has a higher mixing efficiency and a smaller footprint than previously reported micromixers.

Shear Strength of Square Graphene Nanoribbons beyond Wrinkling

NASA Astrophysics Data System (ADS)

Ragab, Tarek; Basaran, Cemal

2018-04-01

Atomistic modeling of armchair and zigzag graphene nanoribbons (GNRs) has been performed to investigate the post-wrinkling behavior under in-plane (x-y) shear deformation. Simulations were performed at 300 K for square GNRs with size ranging from 2.5 nm to 20 nm. Shear stresses led only to diagonal tension, and wrinkling was not accompanied by any diagonal compressive force. Once the diagonal tension reached its ultimate elastic level, three major stress-relaxing phenomena were observed. The type of stress-relaxing phenomenon involved greatly affected the mechanical behavior in terms of the slope of the stress-strain diagram beyond the elastic range. The results showed that the average slope of the stress-strain relation beyond the ultimate elastic stress decreased with the increase of the GNR size. Moreover, the slope of the shear stress-strain curve beyond the ultimate elastic stress was always greater for armchair than for zigzag GNRs. GNRs can sustain very high plastic shear strains beyond 100% before failure. The ultimate elastic stress can range from 20 GPa to 50 GPa, occurring at shear strain ranging from 52% to 19%. The ultimate elastic stress and strain were inversely proportional to the size of the GNR with a power factor ranging from 0.261 for armchair GNRs to 0.354 for zigzag GNRs due to the decrease in the effective width for diagonal tension.

Modeling Ballistic Current Flow in Carbon Nanotube Wires

NASA Technical Reports Server (NTRS)

Anantram, M. P.; Biegel, Bryan (Technical Monitor)

2001-01-01

Experiments have shown carbon nanotubes (CNT) to be almost perfect conductors at small applied biases. The features of the CNT band structure, large velocity of the crossing subbands and the small number of modes that an electron close to the band center / Fermi energy can scatter into, are the reasons for the near perfect small bias conductance. We show that the CNT band structure does not help at large applied biases - electrons injected into the non crossing subbands can either be Bragg reflected or undergo Zener-type tunneling. This limits the current carrying capacity of CNT. We point out that the current carrying capacity of semiconductor quantum wires in the ballistic limit is different, owing to its band structure. The second aspect addressed is the relationship of nanotube chirality in determining the physics of metal-nanotube coupling. We show that a metallic-zigzag nanotube couples better than an armchair nanotube to a metal contact. This arises because in the case of armchair nanotubes, while the pi band couples well, the pi* band does not couple well to the metal. In the case of zigzag nanotube both crossing modes couple reasonably well to the metal. Many factors such as the role of curvature, strain and defects will play a role in determining the suitability of nanotubes as nanowires. From the limited view point of metal-nanotube coupling, we feel that metallic-zigzag nanotubes are preferable to armchair nanotubes.

A comment on "The interaction of X2 (X = F, Cl, and Br) with active sites of graphite" [Xu et al., Chem. Phys. Lett., 418, 413 (2006)

NASA Astrophysics Data System (ADS)

Lechner, Christoph; Baranek, Philippe; Vach, Holger

2018-04-01

In their article, Xu et al. (2006) present the adsorption energies for the chemisorption of the three halogens F2 , Cl2 , and Br2 on the active sites of graphite. The three investigated systems are the three most stable surfaces, (0 0 1), (1 0 0), and (1 1 0); the latter two are also called zigzag and armchair surface, respectively. Due to some inconsistencies in their article, we re-evaluated the results of Xu et al. in order to investigate the impact on the adsorption energies of the halogens. For the (0 0 1) surface, our results agree with Xu et al. However, for the other two surfaces we find major differences. Contrary to Xu et al., we find that the halogens adsorb the strongest on the zigzag surface. The second strongest adsorption is found on the armchair surface for the symmetric configurations, the third strongest for the asymmetric configurations. Several reasons are given which explain this discrepancy. The most striking source of error in the work of Xu et al. is due to the fact that they did not choose the correct spin multiplicities for the model systems which means that they performed the calculations in excited states. This leads to errors between 50 and 600% for the zigzag surface and 3-42% for the armchair surface.

New understanding of photocatalytic properties of zigzag and armchair g-C3N4 nanotubes from electronic structures and carrier effective mass

NASA Astrophysics Data System (ADS)

Liu, Jianjun; Cheng, Bei

2018-02-01

Low-dimensional g-C3N4 nanostructures own distinct electronic structure and remarkable photocatalytic properties, hence their wide application in the photocatalysis field. However, the correlations of structures and photoinduced carrier migrations with the photocatalytic properties of g-C3N4 nanostructures remain unclear. In this study, the geometrical and electronic structures and the photocatalytic properties of zigzag (n, 0) and armchair (n, n) g-C3N4 nanotubes (n = 6, 9, 12) were systematically investigated using hybrid DFT. Results indicated that the differences in geometrical structures of g-C3N4 nanotubes changed the band gaps and effective mass of carriers. Accordingly, the photocatalytic properties of g-C3N4 nanotubes also changed. Notably, the change trends of band gaps and the effective mass of the electrons and holes were the opposite for zigzag (n, 0) and armchair (n, n) g-C3N4 nanotubes. The absolute band edge potential of (n, 0) and (n, n) g-C3N4 nanotubes can split water for hydrogen production. These theoretical results revealed the correlations of structures and carrier effective mass with the photocatalytic properties of g-C3N4 nanotubes, and provided significant guidance for designing low-dimensional g-C3N4 nanostructures.

Shear Strength of Square Graphene Nanoribbons beyond Wrinkling

NASA Astrophysics Data System (ADS)

Ragab, Tarek; Basaran, Cemal

2018-07-01

Atomistic modeling of armchair and zigzag graphene nanoribbons (GNRs) has been performed to investigate the post-wrinkling behavior under in-plane ( x- y) shear deformation. Simulations were performed at 300 K for square GNRs with size ranging from 2.5 nm to 20 nm. Shear stresses led only to diagonal tension, and wrinkling was not accompanied by any diagonal compressive force. Once the diagonal tension reached its ultimate elastic level, three major stress-relaxing phenomena were observed. The type of stress-relaxing phenomenon involved greatly affected the mechanical behavior in terms of the slope of the stress-strain diagram beyond the elastic range. The results showed that the average slope of the stress-strain relation beyond the ultimate elastic stress decreased with the increase of the GNR size. Moreover, the slope of the shear stress-strain curve beyond the ultimate elastic stress was always greater for armchair than for zigzag GNRs. GNRs can sustain very high plastic shear strains beyond 100% before failure. The ultimate elastic stress can range from 20 GPa to 50 GPa, occurring at shear strain ranging from 52% to 19%. The ultimate elastic stress and strain were inversely proportional to the size of the GNR with a power factor ranging from 0.261 for armchair GNRs to 0.354 for zigzag GNRs due to the decrease in the effective width for diagonal tension.

Syntheses and characterizations of secondary Pb-O bonding supported Pb(II)-sulfonate complexes

NASA Astrophysics Data System (ADS)

Huang, Guo-Zhen; Zou, Xin; Zhu, Zhi-Biao; Deng, Zhao-Peng; Huo, Li-Hua; Gao, Shan

2018-06-01

The reaction of Pb(II) salts and mono- or disulfonates leads to the formation of eight new Pb(II)-mono/disulfonate complexes, [Pb(L1)(H2O)]2 (1), [Pb4(L2)2(AcO)2]n·5nH2O (2), [Pb(L3)(H2O)]2 (3), [Pb(HL4)(H2O)2]n·nH2O (4), [Pb(HL5)(H2O)2]n·2nH2O (5), [Pb(H2L6)(H2O)]n·nDMF·2nH2O (6), [Pb2(H3L7)4(H2O)6]·2H2O (7) and [Pb(H2L7)(H2O)]n·nH2O (8) (H2L1= 2-hydroxy-5-methyl-benzenesulfonic acid, H3L2= 2-hydroxyl-5-methyl- 1,3-benzenedisulfonic acid, H2L3= 2-hydroxy-5-nitro-benzenesulfonic acid, H3L4= 2-hydroxyl-5-bromo-1,3- benzenedisulfonic acid, H3L5= 2-hydroxyl-5-carboxyl-benzenesulfonic acid, H4L6= 2,5-dihydroxyl-3-carboxyl- benzenesulfonic acid, H4L7= 2,4-dihydroxyl-5-carboxyl-benzenesulfonic acid, DMF = N,N'-dimethyl-formamide, AcO- = acetate), which have been characterized by elemental analysis, IR, TG, PL, powder and single-crystal X-ray diffraction. In view of the primary Pb-O bonds, these eight complexes exhibit diverse dinuclear (1, 3 and 7), helical chain (4), wave-like chain (5), linear chain (6), zigzag chain (8) and layer structure (2), in which the Pb(II) cations present different hemi-directed geometries. Taking the secondary Pb-O bonds into account, chain structure for complex 7, layer motifs for complexes 1 and 3-6, as well as 3-D framework for complex 8 are observed with Pb(II) cations showing more intricate holo-directed geometries. The various coordination modes of these seven different mono/disulfonate anions are responsible for the formation of these multiple structures. Furthermore, the introduction of hydroxyl and carboxyl groups increases the coordination ability of sulfonate to the p-block metal cation. Luminescent analyses indicate that complex 7 presents purple emission at 395 nm at room temperature.

5. Within building #5, the forming of chain from wire, ...

Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

5. Within building #5, the forming of chain from wire, as well as other operations, was powered by such belt-driven wheels and shafts. - American Chain & Cable Company, East Princess Street (400 Block), York, York County, PA

Functionalization and migration of bromine adatoms on zigzag graphene nanoribbons: A first-principles study

NASA Astrophysics Data System (ADS)

Jaiswal, Neeraj K.; Kumar, Amit; Patel, Chandrabhan

2018-05-01

Tailoring the electronic band gap of graphene nanoribbons (GNR) through edge functionalization and understanding the adsorption of guest adatoms on GNR is crucial for realization of upcoming organic devices. In the present work, we have investigated the structural stability and electronic property of bromine (Br) termination at the edges of zigzag GNR (ZGNR). The migration pathways of Br adatom on ZGNR have also been discussed along four different diffusion paths. It is revealed that Br termination induces metallicity in ZGNR and caused upward shifting of Fermi level. Further, the migration is predicted to take place preferable along the ribbon edges whereas across the ribbon width, migration is least probable to take place due to sufficiently higher migration barrier of ˜160 meV.

Effects of inter-tube coupling on the electro-optical properties of silicon carbide nanotube bundles studied by density functional theory

NASA Astrophysics Data System (ADS)

Behzad, Somayeh

2015-09-01

The electronic and optical properties of bundled armchair and zigzag silicon carbide nanotubes (SiCNTs) are investigated by using density functional theory. The effects of inter-tube coupling on the electronic dispersions of SiCNT bundles are demonstrated. It was found that the band structure of (6, 0) SiCNT bundle shows metallic feature. The calculated dielectric functions of the armchair and zigzag bundles are similar to that of the isolated tubes, except for the appearance of broadened peaks, small shifts of peak positions about 0.1 eV and increasing of peak intensities. For (6, 0) SiCNT with smaller radius, by considering interband and interaband transitions, the band structure coupling causes an extra peak at low energies.

MOUNT HOOD WILDERNESS AND ADJACENT AREAS, OREGON.

USGS Publications Warehouse

Keith, T.E.C.; Causey, J.D.

1984-01-01

A mineral survey of the Mount Hood Wilderness, Oregon, was conducted. Geochemical data indicate two areas of substantiated mineral-resource potential containing weak epithermal mineralization: an area of the north side of Zigzag Mountain where vein-type lead-zinc-silver deposits occur and an area of the south side of Zigzag Mountain, where the upper part of a quartz diorite pluton has propylitic alteration associated with mineralization of copper, gold, silver, lead, and zinc in discontinuous veins. Geothermal-resource potential for low- to intermediate-temperature (less than 248 degree F) hot-water systems in the wilderness is probable in these areas. Part of the wilderness is classified as a Known Geothermal Resource Area (KGRA), which is considered to have probable geothermal-resource potential, and two parts of the wilderness have been included in geothermal lease areas.

Width-Tuned Magnetic Order Oscillation on Zigzag Edges of Honeycomb Nanoribbons.

PubMed

Chen, Wen-Chao; Zhou, Yuan; Yu, Shun-Li; Yin, Wei-Guo; Gong, Chang-De

2017-07-12

Quantum confinement and interference often generate exotic properties in nanostructures. One recent highlight is the experimental indication of a magnetic phase transition in zigzag-edged graphene nanoribbons at the critical ribbon width of about 7 nm [ Magda , G. Z. et al. Nature 2014 , 514 , 608 ]. Here we show theoretically that with further increase in the ribbon width, the magnetic correlation of the two edges can exhibit an intriguing oscillatory behavior between antiferromagnetic and ferromagnetic, driven by acquiring the positive coherence between the two edges to lower the free energy. The oscillation effect is readily tunable in applied magnetic fields. These novel properties suggest new experimental manifestation of the edge magnetic orders in graphene nanoribbons and enhance the hopes of graphene-like spintronic nanodevices functioning at room temperature.

Dense zig-zag microstructures in YSZ thin films by pulsed laser deposition

NASA Astrophysics Data System (ADS)

Stender, Dieter; Schäuble, Nina; Weidenkaff, Anke; Montagne, Alex; Ghisleni, Rudy; Michler, Johann; Schneider, Christof W.; Wokaun, Alexander; Lippert, Thomas

2015-01-01

The very brittle oxygen ion conductor yttria stabilized zirconia (YSZ) is a typical solid electrolyte for miniaturized thin film fuel cells. In order to decrease the fuel cell operating temperature, the thickness of yttria stabilized zirconia thin films is reduced. Often, these thin membranes suffer from mechanical failure and gas permeability. To improve these mechanical issues, a glancing angle deposition approach is used to grow yttria stabilized zirconia thin films with tilted columnar structures. Changes of the material flux direction during the deposition result in a dense, zigzag-like structure with columnar crystallites. This structure reduces the elastic modulus of these membranes as compared to columnar yttria stabilized zirconia thin films as monitored by nano-indentation which makes them more adaptable to applied stress.

The spin-dependent electronic transport properties of M(dcdmp)2 (M = Cu, Au, Co, Ni) molecular devices based on zigzag graphene nanoribbon electrodes

NASA Astrophysics Data System (ADS)

Li, Dongde; Wu, Di; Zhang, Xiaojiao; Zeng, Bowen; Li, Mingjun; Duan, Haiming; Yang, Bingchu; Long, Mengqiu

2018-05-01

The spin-dependent electronic transport properties of M(dcdmp)2 (M = Cu, Au, Co, Ni; dcdmp = 2,3-dicyano-5,6-dimercaptopyrazyne) molecular devices based on zigzag graphene nanoribbon (ZGNR) electrodes were investigated by density functional theory combined nonequilibrium Green's function method (DFT-NEGF). Our results show that the spin-dependent transport properties of the M(dcdmp)2 molecular devices can be controlled by the spin configurations of the ZGNR electrodes, and the central 3d-transition metal atom can introduce a larger magnetism than that of the nonferrous metal one. Moreover, the perfect spin filtering effect, negative differential resistance, rectifying effect and magnetic resistance phenomena can be observed in our proposed M(dcdmp)2 molecular devices.

Transforming graphene nanoribbons into nanotubes by use of point defects.

PubMed

Sgouros, A; Sigalas, M M; Papagelis, K; Kalosakas, G

2014-03-26

Using molecular dynamics simulations with semi-empirical potentials, we demonstrate a method to fabricate carbon nanotubes (CNTs) from graphene nanoribbons (GNRs), by periodically inserting appropriate structural defects into the GNR crystal structure. We have found that various defect types initiate the bending of GNRs and eventually lead to the formation of CNTs. All kinds of carbon nanotubes (armchair, zigzag, chiral) can be produced with this method. The structural characteristics of the resulting CNTs, and the dependence on the different type and distribution of the defects, were examined. The smallest (largest) CNT obtained had a diameter of ∼ 5 Å (∼ 39 Å). Proper manipulation of ribbon edges controls the chirality of the CNTs formed. Finally, the effect of randomly distributed defects on the ability of GNRs to transform into CNTs is considered.

Water vascular system architecture in an Ordovician ophiuroid.

PubMed

Clark, Elizabeth G; Bhullar, Bhart-Anjan S; Darroch, Simon A F; Briggs, Derek E G

2017-12-01

Understanding the water vascular system (WVS) in early fossil echinoderms is critical to elucidating the evolution of this system in extant forms. Here we present the first report of the internal morphology of the water vascular system of a stem ophiuroid. The radial canals are internal to the arm, but protected dorsally by a plate separate to the ambulacrals. The canals zig-zag with no evidence of constrictions, corresponding to sphincters, which control pairs of tube feet in extant ophiuroids. The morphology suggests that the unpaired tube feet must have operated individually, and relied on the elasticity of the radial canals, lateral valves and tube foot musculature alone for extension and retraction. This arrangement differs radically from that in extant ophiuroids, revealing a previously unknown Palaeozoic configuration. © 2017 The Author(s).

Modulation of the electronic property of phosphorene by wrinkle and vertical electric field

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

Li, Yan; Wei, Zhongming, E-mail: zmwei@semi.ac.cn; Li, Jingbo, E-mail: jbli@semi.ac.cn

2015-09-14

The electronic properties of wrinkled phosphorene and its response to charge injection and external vertical electric field have been studied using first-principles calculations. It is found that small-size wrinkle systems have lower energy than wrinkle-free monolayer, suggesting that free-standing phosphorene spontaneously forms small protrusion on its nanosheet. The ratio of wrinkle height to curvature radius increases with enlarging height, indicating a promotion of field enhancement factor. Furthermore, the injected charges mostly distribute at peak and valley. Direct-to-indirect band-gap transition has been found for zigzag wrinkle with height of 14.81 Å. The band gaps of wrinkled nanosheets decrease almost linearly with increasingmore » field, which is caused by charge separation of valence band maximum and conduction band minimum.« less

Crystal and molecular structure of Sr{sub 2}(Edta) . 5H{sub 2}O, Sr{sub 2}(H{sub 2}Edta)(HCO{sub 3}){sub 2} . 4H{sub 2}O, and Sr{sub 2}(H{sub 2}Edta)Cl{sub 2} . 5H{sub 2}O strontium ethylenediaminetetraacetates

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

Polyakova, I. N., E-mail: polyakova@igic.ras.ru; Poznyak, A. L.; Sergienko, V. S.

2009-03-15

Three Sr{sup 2+} compounds with the Edta{sup 4-} and H{sub 2}Edta{sup 2-} ligands-Sr{sub 2}(Edta) . 5H{sub 2}O (I), Sr{sub 2}(H{sub 2}Edta)(HCO{sub 3}){sub 2} . 4H{sub 2}O (II), and Sr{sub 2}(H{sub 2}Edta)Cl{sub 2} . 5H{sub 2}O (III)-are synthesized, and their crystal structures are studied. In I, the Sr(1) atom is coordinated by the hexadentate Edta{sup 4-} ligand following the 2N + 4O pattern and by two O atoms of the neighboring ligands, which affords the formation of zigzag chains. The Sr(2) atom forms bonds with O atoms of five water molecules and attaches itself to a chain via bonds with threemore » O atoms of the Edta{sup 4-} ligands. The Sr(1)-O and Sr(2)-O bond lengths fall in the ranges 2.520(2)-2.656(3) and 2.527(3)-2.683(2) A, respectively. The Sr(1)-N bonds are 2.702(3) and 2.743(3) A long. In II and III, the H{sub 2}Edta{sup 2-} anions have a centrosymmetric structure with the trans configuration of the planar ethylenediamine fragment. The N atoms are blocked by acid protons. In II, the environment of the Sr atom is formed by six O atoms of three H{sub 2}Edta ligands, two O atoms of water molecules, and an O atom of the bicarbonate ion, which is disordered over two positions. In III, the environment of the Sr atom includes six O atoms of four H{sub 2}Edta{sup 2-} ligands and three O atoms of water molecules. The coordination number of the Sr atoms is equal to 8 + 1. In II and III, the main bonds fall in the ranges 2.534(3)-2.732(2) and 2.482(2)-2.746(3) A, whereas the ninth bond is elongated to 2.937(3) and 3.055(3) A, respectively. In II, all the structural elements are linked into wavy layers. The O-H-O interactions contribute to the stabilization of the layer and link neighboring layers. In III, hydrated Sr{sup 2+} cations and H{sub 2}Edta{sup -} anions form a three-dimensional [Sr{sub 2}(H{sub 2}Edta)(H{sub 2}O){sub 3}]{sub n}{sup 2n+} framework. The Cl{sup -} anions are fixed in channels of the framework by hydrogen bonds with four water molecules. In II and III, the N-H groups form four-center N-H-O{sub 3} hydrogen bonds, which include one intermolecular and two intramolecular components. PACS numbers: 61.66.Hq.« less

Cobalt(II) complexes with bis(N-imidazolyl/benzimidazolyl) pyridazine: Structures, photoluminescent and photocatalytic properties

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

Li, Jin-Ping; Fan, Jian-Zhong; Wang, Duo-Zhi, E-mail: wangdz@xju.edu.cn

2016-07-15

Six new Co{sup II} complexes [Co(L{sup 1}){sub 4}(OH){sub 2}] (1), {[Co(L"1)(H_2O)_4]·2ClO_4}{sub ∞} (2), {[Co(L"1)(H_2O)_4]·SiF_6}{sub ∞} (3), {[Co(L"1)_3]·2ClO_4}{sub ∞} (4), [Co(L{sup 2})Cl{sub 2}]{sub ∞} (5) and {[Co(L"2)_2]·SiF_6}{sub ∞} (6) [L{sup 1}=3,6-bis(N-imidazolyl) pyridazine, L{sup 2}=3,6-bis (N-benzimidazolyl) pyridazine] have been synthesized and characterized by elemental analysis, IR spectra and single crystal X-ray diffraction. Complex 1 has a mononuclear structure, while complexes 2 and 3 have 1-D chain structures. Considering the Co{sup II} centers were linked by the L{sup 1} ligands, the 3-D framework of complex 4 can be rationalized to be a {4^12.6^3} 6-c topological net with the stoichiometry uninodal net. 5 revealsmore » a coordination 1-D zigzag chain structure consisting of a neutral chain [Co(L{sup 2})Cl{sub 2}]{sub n} with the Co{sup II} centers. Complex 6 has a rhombohedral grid with a (4, 4) topology. The TGA property, fluorescent property and photocatalytic activity of complexes 1–6 have been investigated and discussed. - Graphical abstract: Six Co{sup II} complexes of bis(N-imidazolyl/benzimidazolyl)pyridazine were synthesized and structurally characterized. The fluorescence properties and photocatalytic activity for dye degradation under UV light of all complexes have been investigated and discussed. Display Omitted - Highlights: • Six new Co{sup II} complexes with bis(N-imidazolyl/benzimidazolyl) pyridazine. • Structural analysis of all complexes. • Fluorescent property of all complexes. • Photocatalytic activity for dye degradation under UV light of all complexes.« less

Energy levels of double triangular graphene quantum dots

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

Liang, F. X.; Jiang, Z. T., E-mail: ztjiang616@hotmail.com; Zhang, H. Y.

2014-09-28

We investigate theoretically the energy levels of the coupled double triangular graphene quantum dots (GQDs) based on the tight-binding Hamiltonian model. The double GQDs including the ZZ-type, ZA-type, and AA-type GQDs with the two GQDs having the zigzag or armchair boundaries can be coupled together via different interdot connections, such as the direct coupling, the chains of benzene rings, and those of carbon atoms. It is shown that the energy spectrum of the coupled double GQDs is the amalgamation of those spectra of the corresponding two isolated GQDs with the modification triggered by the interdot connections. The interdot connection ismore » inclined to lift up the degeneracies of the energy levels in different degree, and as the connection changes from the direct coupling to the long chains, the removal of energy degeneracies is suppressed in ZZ-type and AA-type double GQDs, which indicates that the two coupled GQDs are inclined to become decoupled. Then we consider the influences on the spectra of the coupled double GQDs induced by the electric fields applied on the GQDs or the connection, which manifests as the global spectrum redistribution or the local energy level shift. Finally, we study the symmetrical and asymmetrical energy spectra of the double GQDs caused by the substrates supporting the two GQDs, clearly demonstrating how the substrates affect the double GQDs' spectrum. This research elucidates the energy spectra of the coupled double GQDs, as well as the mechanics of manipulating them by the electric field and the substrates, which would be a significant reference for designing GQD-based devices.« less

Syntheses, structures, electrochemistry and catalytic oxidation degradation of organic dyes of two new coordination polymers derived from Cu(II) and Mn(II) and 1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene

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

Song, Ming; Mu, Bao; Huang, Ru-Dan, E-mail: huangrd@bit.edu.cn

Two new coordination polymers (CPs), namely, [Cu{sub 2}(ttbz)(H{sub 2}btc){sub 2}(OH)]{sub n} (1) and [Mn(ttbz){sub 2}(H{sub 2}O){sub 2}]{sub n} (2) (Httbz =1-(tetrazo-5-yl)-4-(triazo-1-yl)benzene, H{sub 3}btc =1,3,5-benzenetricarboxylic acid), have been hydrothermally synthesized and structurally characterized. Complex 1 exhibits a (3,5,5,5)-connected 2D layer with a Schläfli symbol of (3·4{sup 2})(3·4{sup 4}0.5{sup 2}0.6{sup 3})(3{sup 2}0.4{sup 4}0.5{sup 2}0.6{sup 2})(3{sup 2}0.4{sup 4}0.5{sup 3}0.6), in which the ttbz{sup -} ligand can be described as μ{sub 5}-bridge, linking Cu(II) ions into a 2D layer and H{sub 2}btc{sup -} ions play a supporting role in complex 1. The ttbz{sup -} ligand in complex 2 represents the bridging coordination mode, connectingmore » two Mn(II) ions to form the infinite 1D zigzag chains, respectively, which are further connected by two different types of hydrogen bonds to form a 3D supramolecular. Furthermore, catalytic oxidation activities toward organic dyes and electrochemical behaviors of the title complexes have been investigated at room temperature in aqueous solutions, indicating these complexes may be applicable to color removal in a textile wastewater stream and practical applications in areas of electrocatalytic reduction toward nitrite, respectively. - Graphical abstract: Two new coordination polymers based on different structural characteristics have been hydrothermally synthesized by the mixed ligands. The catalytic oxidation activities toward organic dyes and electrochemical behaviors of the title complexes have been investigated. - Highlights: • The organic ligand containing the tetrazolyl group and triazolyl group with some advantages has been used. • Two new coordination polymers with different structural characteristics has been discussed in detail. • Catalytic oxidation activities toward organic dyes and electrochemical behaviors of the title complexes have been investigated.« less

Evaluation of beam wobbling methods for heavy-ion radiotherapy.

PubMed

Yonai, Shunsuke; Kanematsu, Nobuyuki; Komori, Masataka; Kanai, Tatsuaki; Takei, Yuka; Takahashi, Osamu; Isobe, Yoshiharu; Tashiro, Mutsumi; Koikegami, Hajime; Tomita, Hideki

2008-03-01

The National Institute of Radiological Sciences (NIRS) has extensively studied carbon-ion radiotherapy at the Heavy-Ion Medical Accelerator in Chiba (HIMAC) with some positive outcomes, and has established its efficacy. Therefore, efforts to distribute the therapy to the general public should be made, for which it is essential to enable direct application of clinical and technological experiences obtained at NIRS. For widespread use, it is very important to reduce the cost through facility downsizing with minimal acceleration energy to deliver the HIMAC-equivalent clinical beams. For the beam delivery system, the requirement of miniaturization is translated to reduction in length while maintaining the clinically available field size and penetration range for range-modulated uniform broad beams of regular fields that are either circular or square for simplicity. In this paper, we evaluate the various wobbling methods including original improvements, especially for application to the compact facilities through the experimental and computational studies. The single-ring wobbling method used at HIMAC is the best one including a lot of experience at HIMAC but the residual range is a fatal problem in the case of a compact facility. On the other hand, uniform wobbling methods such as the spiral and zigzag wobbling methods are effective and suitable for a compact facility. Furthermore, these methods can be applied for treatment with passive range modulation including respiratory gated irradiation. In theory, the choice between the spiral and zigzag wobbling methods depends on the shape of the required irradiation field. However, we found that it is better to use the zigzag wobbling method with transformation of the wobbling pattern even when a circular uniform irradiation field is required, because it is difficult to maintain the stability of the wobbler magnet due to the rapid change of the wobbler current in the spiral wobbling method. The regulated wobbling method, which is our improvement, can well expand the uniform irradiation field and lead to reducing the power requirement of the wobbler magnets. Our evaluations showed that the regulated zigzag wobbling method is the most suitable method for use in currently designed compact carbon-therapy facilities.

Paths and wakes of deformable nearly spheroidal rising bubbles close to the transition to path instability

NASA Astrophysics Data System (ADS)

Cano-Lozano, José Carlos; Martínez-Bazán, Carlos; Magnaudet, Jacques; Tchoufag, Joël

2016-09-01

We report on a series of results provided by three-dimensional numerical simulations of nearly spheroidal bubbles freely rising and deforming in a still liquid in the regime close to the transition to path instability. These results improve upon those of recent computational studies [Cano-Lozano et al., Int. J. Multiphase Flow 51, 11 (2013), 10.1016/j.ijmultiphaseflow.2012.11.005; Phys. Fluids 28, 014102 (2016), 10.1063/1.4939703] in which the neutral curve associated with this transition was obtained by considering realistic but frozen bubble shapes. Depending on the dimensionless parameters that characterize the system, various paths geometries are observed by letting an initially spherical bubble starting from rest rise under the effect of buoyancy and adjust its shape to the surrounding flow. These include the well-documented rectilinear axisymmetric, planar zigzagging, and spiraling (or helical) regimes. A flattened spiraling regime that most often eventually turns into either a planar zigzagging or a helical regime is also frequently observed. Finally, a chaotic regime in which the bubble experiences small horizontal displacements (typically one order of magnitude smaller than in the other regimes) is found to take place in a region of the parameter space where no standing eddy exists at the back of the bubble. The discovery of this regime provides evidence that path instability does not always result from a wake instability as previously believed. In each regime, we examine the characteristics of the path, bubble shape, and vortical structure in the wake, as well as their couplings. In particular, we observe that, depending on the fluctuations of the rise velocity, two different vortex shedding modes exist in the zigzagging regime, confirming earlier findings with falling spheres. The simulations also reveal that significant bubble deformations may take place along zigzagging or spiraling paths and that, under certain circumstances, they dramatically alter the wake structure. The instability thresholds that can be inferred from the computations compare favorably with experimental data provided by various sets of recent experiments guaranteeing that the bubble surface is free of surfactants.

Molecule-assisted ferromagnetic atomic chain formation

NASA Astrophysics Data System (ADS)

Kumar, Manohar; Sethu, Kiran Kumar Vidya; van Ruitenbeek, Jan M.

2015-06-01

One dimensional systems strongly enhance the quantum character of electron transport. Such systems can be realized in 5 d transition metals Au, Pt, and Ir, in the form of suspended monatomic chains between bulk leads. Atomic chains between ferromagnetic leads would open up many perspectives in the context of spin-dependent transport and spintronics, but the evidence suggests that for pure metals only the mentioned three 5 d metals are susceptible to chain formation. It has been argued that the stability of atomic chains made up from ferromagnetic metals is compromised by the same exchange interaction that produces the local moments. Here we demonstrate that magnetic atomic chains can be induced to form in break junctions under the influence of light molecules. Explicitly, we find deuterium assisted chain formation in the 3 d ferromagnetic transition metals Fe and Ni. Chain lengths up to eight atoms are formed upon stretching the ferromagnetic atomic contact in deuterium atmosphere at cryogenic temperatures. From differential conductance spectra vibronic states of D2 can be identified, confirming the presence of deuterium in the atomic chains. Shot noise spectroscopy indicates the presence of weakly spin polarized transmission channels.

Reading the Rover Tracks

NASA Image and Video Library

2012-08-29

The straight lines in Curiosity zigzag track marks are Morse code for JPL. The footprint is an important reference mark that the rover can use to drive more precisely via a system called visual odometry.

Iodine binding to explore the conformational state of internal chains of amylopectin.

PubMed

Shen, Xinyu; Bertoft, Eric; Zhang, Genyi; Hamaker, Bruce R

2013-10-15

Previous studies have found that the proportion of long chains of amylopectin correlates to its functional and nutritional properties. As a possible explanation of this correlation, the iodine binding property of amylopectin internal chains was investigated as an indirect evidence of their ability to form helices for intra- or inter-molecular interactions. Waxy and amylose-extender waxy corn starches were hydrolyzed by β-amylase for varying periods of time to incrementally remove the external chains, and the absorbance and the wavelength of maximum absorbance of iodine binding were examined. Experimental results suggest that iodine can bind with both external and internal chains; a significant amount of absorption comes from the latter, as stepwise removal of external chains only somewhat reduced absorption. Internal amylopectin chains, thus, were concluded to likely pre-exist in helical form, as opposed to a conformational change into helices facilitating iodine binding in the absence of external chains. Such internal chain helical structures possibly drive intermolecular interactions that would explain why amylopectin with high proportion of internal chains form harder gels, create pastes less prone to shear breakdown, and are more slowly digesting. Copyright © 2013 Elsevier Ltd. All rights reserved.

DISTINCT ANTIBODY SPECIES: STRUCTURAL DIFFERENCES CREATING THERAPEUTIC OPPORTUNITIES

PubMed Central

Muyldermans, Serge; Smider, Vaughn V.

2016-01-01

Antibodies have been a remarkably successful class of molecules for binding a large number of antigens in therapeutic, diagnostic, and research applications. Typical antibodies derived from mouse or human sources use the surface formed by complementarity determining regions (CDRs) on the variable regions of the heavy chain/light chain heterodimer, which typically forms a relatively flat binding surface. Alternative species, particularly camelids and bovines, provide a unique paradigm for antigen recognition through novel domains which form the antigen binding paratope. For camelids, heavy chain antibodies bind antigen with only a single heavy chain variable region, in the absence of light chains. In bovines, ultralong CDR-H3 regions form an independently folding minidomain, which protrudes from the surface of the antibody and is diverse in both its sequence and disulfide patterns. The atypical paratopes of camelids and bovines potentially provide the ability to interact with different epitopes, particularly recessed or concave surfaces, compared to traditional antibodies. PMID:26922135

Device and method to relieve cordelle action in a chain driven pump

DOEpatents

Dysarz, Edward D.

1994-01-01

A cordelle action relief apparatus or device for use in sucker rod pumps in a petroleum or water well. The device is incorporated in a chain driven pump to prevent the chain from forming a bow or archlike configuration as the chain rolls off of the sprocket and down into the well. When the chain is allowed to form this bow or arch it could damage the well and well casing. The device includes a first rod on the side of the chain and a second rod on the second side of the chain that will allow the rollers of the chain to roll on the rod and further prevent the chain from bowing or arching and will further allow the rollers on the chain to roll on the rods which will further prevent damage to the well casing, the well, and the chain.

Suspended chains damp wind-induced oscillations of tall flexible structures

NASA Technical Reports Server (NTRS)

Reed, W. H., III

1968-01-01

Hanging-chain system, which is a form of impact damper, suppresses wind-induced bending oscillations of tall cylindrical antenna masts. A cluster of chains enclosed in a neoprene shroud is suspended inside the tip of the antenna mast, forming a simple method of damping structural vibrations.

Identification of pristine and defective graphene nanoribbons by phonon signatures in the electron transport characteristics

NASA Astrophysics Data System (ADS)

Christensen, Rasmus B.; Frederiksen, Thomas; Brandbyge, Mads

2015-02-01

Inspired by recent experiments where electron transport was measured across graphene nanoribbons (GNRs) suspended between a metal surface and the tip of a scanning tunneling microscope [Koch et al., Nat. Nanotechnol. 7, 713 (2012), 10.1038/nnano.2012.169], we present detailed first-principles simulations of inelastic electron tunneling spectroscopy (IETS) of long pristine and defective armchair and zigzag nanoribbons under a range of charge carrier conditions. For the armchair ribbons we find two robust IETS signals around 169 and 196 mV corresponding to the D and G modes of Raman spectroscopy as well as additional fingerprints due to various types of defects in the edge passivation. For the zigzag ribbons we show that the spin state strongly influences the spectrum and thus propose IETS as an indirect proof of spin polarization.

Energetics and electronic properties of Pt wires of different topologies on monolayer MoSe{sub 2}

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

Jamdagni, Pooja, E-mail: j.poojaa1228@gmail.com; Ahluwalia, P. K.; Kumar, Ashok

2016-05-23

The energetics and electronic properties of different topology of Pt wires including linear, zigzag and ladder structures on MoSe{sub 2} monolayer have been investigated in the framework of density functional theory (DFT). The predicted order of stability of Pt wire on MoSe{sub 2} monolayer is found to be: linear > ladder > zigzag. Pt wires induce states near the Fermi level of MoSe{sub 2} that results into metallic characteristics of Pt-wire/MoSe{sub 2} assembled system. Valence band charge density signifies most of the contribution from Pt atoms near the Fermi energy of assembled wire/MoSe{sub 2} system. These findings are expected tomore » be important for the fabrication of devices based on MoSe{sub 2} layers for flexible nanoelectronics.« less

Electrostatic Manipulation of Graphene On Graphite

NASA Astrophysics Data System (ADS)

Untiedt, Carlos; Rubio-Verdu, Carmen; Saenz-Arce, Giovanni; Martinez-Asencio, Jesús; Milan, David C.; Moaied, Mohamed; Palacios, Juan J.; Caturla, Maria Jose

2015-03-01

Here we report the use of a Scanning Tunneling Microscope (STM) under ambient and vacuum conditions to study the controlled exfoliation of the last layer of a graphite surface when an electrostatic force is applied from a STM tip. In this work we have focused on the study of two parameters: the applied voltage needed to compensate the graphite interlayer attractive force and the one needed to break atomic bonds to produce folded structures. Additionally, we have studied the influence of edge structure in the breaking geometry. Independently of the edge orientation the graphite layer is found to tear through the zig-zag direction and the lifled layer shows a zig-zag folding direction. Molecular Dinamics simulations and DFT calculations have been performed to understand our results, showing a strong correlation with the experiments. Comunidad Valenciana through Prometeo project.

Modulational Instability and Quantum Discrete Breather States of Cold Bosonic Atoms in a Zig-Zag Optical Lattice

NASA Astrophysics Data System (ADS)

Chang, Xia; Xie, Jiayu; Wu, Tianle; Tang, Bing

2018-07-01

A theoretical study on modulational instability and quantum discrete breather states in a system of cold bosonic atoms in zig-zag optical lattices is presented in this work. The time-dependent Hartree approximation is employed to deal with the multiple body problem. By means of a linear stability analysis, we analytically study the modulational instability, and estimate existence conditions of the bright stationary localized solutions for different values of the second-neighbor hopping constant. On the other hand, we get analytical bright stationary localized solutions, and analyze the influence of the second-neighbor hopping on their existence conditions. The predictions of the modulational instability analysis are shown to be reliable. Using these stationary localized single-boson wave functions, the quantum breather states corresponding to the system with different types of nonlinearities are constructed.

Width-Tuned Magnetic Order Oscillation on Zigzag Edges of Honeycomb Nanoribbons

DOE PAGES

Chen, Wen-Chao; Zhou, Yuan; Yu, Shun-Li; ...

2017-06-24

Quantum confinement and interference often generate exotic properties in nanostructures. One recent highlight is the experimental indication of a magnetic phase transition in zigzag-edged graphene nanoribbons at the critical ribbon width of about 7 nm [Magda, G. Z. et al. Nature 2014, 514, 608]. Here in this work, we show theoretically that with further increase in the ribbon width, the magnetic correlation of the two edges can exhibit an intriguing oscillatory behavior between antiferromagnetic and ferromagnetic, driven by acquiring the positive coherence between the two edges to lower the free energy. The oscillation effect is readily tunable in applied magneticmore » fields. In conclusion, these novel properties suggest new experimental manifestation of the edge magnetic orders in graphene nanoribbons and enhance the hopes of graphene-like spintronic nanodevices functioning at room temperature.« less

Cubic Zig-Zag Enrichment of the Classical Kirchhoff Kinematics for Laminated and Sandwich Plates

NASA Technical Reports Server (NTRS)

Nemeth, Michael P.

2012-01-01

A detailed anaylsis and examples are presented that show how to enrich the kinematics of classical Kirchhoff plate theory by appending them with a set of continuous piecewise-cubic functions. This analysis is used to obtain functions that contain the effects of laminate heterogeneity and asymmetry on the variations of the inplane displacements and transverse shearing stresses, for use with a {3, 0} plate theory in which these distributions are specified apriori. The functions used for the enrichment are based on the improved zig-zag plate theory presented recently by Tessler, Di Scuva, and Gherlone. With the approach presented herein, the inplane displacements are represented by a set of continuous piecewise-cubic functions, and the transverse shearing stresses and strains are represented by a set of piecewise-quadratic functions that are discontinuous at the ply interfaces.

Unique Zigzag-Shaped Buckling Zn2C Monolayer with Strain-Tunable Band Gap and Negative Poisson Ratio.

PubMed

Meng, Lingbiao; Zhang, Yingjuan; Zhou, Minjie; Zhang, Jicheng; Zhou, Xiuwen; Ni, Shuang; Wu, Weidong

2018-02-19

Designing new materials with reduced dimensionality and distinguished properties has continuously attracted intense interest for materials innovation. Here we report a novel two-dimensional (2D) Zn 2 C monolayer nanomaterial with exceptional structure and properties by means of first-principles calculations. This new Zn 2 C monolayer is composed of quasi-tetrahedral tetracoordinate carbon and quasi-linear bicoordinate zinc, featuring a peculiar zigzag-shaped buckling configuration. The unique coordinate topology endows this natural 2D semiconducting monolayer with strongly strain tunable band gap and unusual negative Poisson ratios. The monolayer has good dynamic and thermal stabilities and is also the lowest-energy structure of 2D space indicated by the particle-swarm optimization (PSO) method, implying its synthetic feasibility. With these intriguing properties the material may find applications in nanoelectronics and micromechanics.

Application of silicon zig-zag wall arrays for anodes of Li-ion batteries

NASA Astrophysics Data System (ADS)

Li, G. V.; Rumyantsev, A. M.; Levitskii, V. S.; Beregulin, E. V.; Zhdanov, V. V.; Terukov, E. I.; Astrova, E. V.

2016-01-01

Cyclic tests of anodes based on zigzag wall arrays fabricated by the electrochemical etching and post-anodization treatment of silicon have been performed. Compared with anodes based on nanowires and planar thin films, these structures have several advantages. An ex situ analysis of the morphology and structural transformations in a material subjected to cyclic lithiation was conducted by electron microscopy and micro-Raman spectroscopy. The effect of geometrical parameters and a cycling mode on the degradation rate was studied. It is shown that a significant rise in the cycle life of the anode can be obtained by the restriction of the inserted amount of lithium. The anode, subjected to galvanostatic cycling at a rate C/2.8 at a limited charge capacity of 1000 mA · h g-1, demonstrates no degradation after 1200 cycles.

Narrow-linewidth, quasi-continuous-wave ASE source based on a multiple-pass Nd:YAG zigzag slab amplifier configuration.

PubMed

Chen, Xiaoming; Lu, Yanhua; Hu, Hao; Tong, Lixin; Zhang, Lei; Yu, Yi; Wang, Juntao; Ren, Huaijin; Xu, Liu

2018-03-05

We present investigations into a narrow-linewidth, quasi-continuous-wave pulsed all-solid-state amplified spontaneous emission (ASE) source by use of a novel multiple-pass zigzag slab amplifier. The SE fluorescence emitted from a Nd:YAG slab active medium acts as the seed and is amplified back and forth 8 times through the same slab. Thanks to the angular multiplexing nature of the zigzag slab, high-intensity 1064-nm ASE output can be produced without unwanted self-lasing in this configuration. Experimentally, the output energy, optical conversion efficiency, pulse dynamics, spectral property, and beam quality of the ASE source are studied when the Nd:YAG slab end-pumped by two high-brightness laser diode arrays. The maximum single pulse energy of 347 mJ is generated with an optical efficiency of ~5.9% and a beam quality of 3.5/17 in the thickness/width direction of the slab. As expected, smooth pulses without relaxing spikes and continuous spectra are achieved. Moreover, the spectral width of the ASE source narrows versus the pump energy, getting a 3-dB linewidth of as narrow as 20 pm (i.e. 5.3 GHz). Via the sum frequency generation, high-intensity, smooth-pulse, and narrow-linewidth ASE sources are preferred for solving the major problem of saturation of the mesospheric sodium atoms and can create a much brighter sodium guide star to meet the needs of adaptive imaging applications in astronomy.

Comparison of surface abrasion produced on the enamel surface by a standard dentifrice using three different toothbrush bristle designs: A profilometric in vitro study

PubMed Central

Kumar, Sandeep; Kumari, Minal; Acharya, Shashidhar; Prasad, Ram

2014-01-01

Aim: The aim was to assess, in vitro, the effect on surface abrasivity of enamel surface caused by three different types (flat trim, zig-zag, bi-level) of toothbrush bristle design. Materials and Methods: Twenty-four freshly extracted, sound, human incisor teeth were collected for this study. The enamel slab was prepared, which were mounted, on separate acrylic bases followed by subjected to profilometric analysis. The surface roughness was measured using the profilometer. The specimen were divided into three groups, each group containing eight mounted specimens, wherein, Group 1 specimens were brushed with flat trim toothbrush; Group 2 brushed with zig-zag and Group 3 with bi-level bristle design. A commercially available dentifrice was used throughout the study. A single specimen was brushed for 2 times daily for 2 min period for 1 week using a customized brushing apparatus. The pre- and post-roughness value change were analyzed and recorded. Statistical test: Kruskal–Wallis test and Mann–Whitney U-test. Result: The results showed that surface abrasion was produced on each specimen, in all the three groups, which were subjected to brushing cycle. However, the bi-level bristle design (350% increase in roughness, P = 0.021) and zig-zag bristle design (160% increase in roughness, P = 0.050) showed significantly higher surface abrasion when compared with flat trim bristle design toothbrush. Conclusion: Flat trim toothbrush bristle produces least surface abrasion and is relatively safe for use. PMID:25125852

Surface-micromachined chain for use in microelectromechanical structures

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

Vernon, Sr., George E.

2001-01-01

A surface-micromachined chain and a microelectromechanical (MEM) structure incorporating such a chain are disclosed. The surface-micromachined chain can be fabricated in place on a substrate (e.g. a silicon substrate) by depositing and patterning a plurality of alternating layers of a chain-forming material (e.g. polycrystalline silicon) and a sacrificial material (e.g. silicon dioxide or a silicate glass). The sacrificial material is then removed by etching to release the chain for movement. The chain has applications for forming various types of MEM devices which include a microengine (e.g. an electrostatic motor) connected to rotate a drive sprocket, with the surface-micromachined chain beingmore » connected between the drive sprocket and one or more driven sprockets.« less

Molecular dynamics simulation of water in and around carbon nanotubes: A coarse-grained description

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

Pantawane, Sanwardhini; Choudhury, Niharendu, E-mail: nihcho@barc.gov.in

2016-05-23

In the present study, we intend to investigate behaviour of water in and around hydrophobic open ended carbon nanotubes (CNTs) using a coarse-grained, core-softened model potential for water. The model potential considered here for water has recently been shown to successfully reproduce dynamic, thermodynamic and structural anomalies of water. The epitome of the study is to understand the incarceration of this coarse-grained water in a single-file carbon nanotube. In order to examine the effect of fluid-water van der Waals interaction on the structure of fluid in and around the nanotube, we have simulated three different CNT-water systems with varying degreemore » of solute-water dispersion interaction. The analyses of the radial one-particle density profiles reveal varying degree of permeation and wetting of the CNT interior depending on the degree of fluid-solute attractive van der Waals interaction. A peak in the radial density profile slightly off the nanotube axis signifies a zigzag chain of water molecule around the CNT axis. The average numbers of water molecules inside the CNT have been shown to increase with the increase in fluid-water attractive dispersion interaction.« less

Crystal structure of N-de­acetyl­lappa­coni­tine

PubMed Central

Shi, Xin-Wei; Lu, Qiang-Qiang; Zhou, Jun-Hui; Cui, Xin-Ai

2015-01-01

The title compound, C30H42N2O7 [systematic name: (1S,4S,5S,7S,8S,9S,10S,11S,13R,14S,16S,17R)-20-ethyl-4,8,9-trihy­droxy-1,14,16-tri­meth­oxy­aconitan-4-yl 2-amino­benzoate], isolated from roots of Aconitum sinomontanum Nakai, is a typical aconitane-type C19-diterpenoid alkaloid, which crystallizes with two independent mol­ecules in the asymmetric unit. The conformations of the two independent mol­ecules are closely similar. Each mol­ecule comprises four six-membered rings (A, B, D and E) including one six-membered N-containing heterocyclic ring (E), and two five-membered rings (C and F). Rings A, B and E adopt chair conformations, while ring D displays a boat conformation. Five-membered rings C and F exhibit envelope conformations. IntramolecularN—H⋯O hydrogen bonds between the amino group and carbonyl O atom help to stabilize molecular structure. In the crystal, O—H⋯O hydrogen bonds link the mol­ecules into zigzag chains propagating in [010]. PMID:26396805

Three coordination polymers constructed from 5-(4-(tetrazol-5-yl)phenyl)isophthalic acid: Synthesis, crystal structure and properties

NASA Astrophysics Data System (ADS)

Zhai, Dandan; Sun, Wujuan; Fan, Fei; Liao, Xuzhao; Chen, Sanping; Yang, Xuwu

2017-04-01

Three new coordination polymers, namely, {[Co2(TPA)(μ3-O)3]·0.5DMA}n (1), {[Co(H2TPA)(bibp)(H2O)3]·H2O}n (2) and {[Cd3(TPA)2(phen)4]·4H2O}n (3), (H3TPA = 5-(4-(tetrazol-5-yl)phenyl)isophthalic acid, bibp = 4,4'-bis(imidazolyl)biphenyl, phen = 1,10-phenanthroline and DMA = N,N-dimethylacetamide), have been synthesized under solvothermal conditions and structurally characterized by elemental analysis, IR spectroscopy, powder X-ray diffraction (PXRD) and single-crystal X-ray diffraction analysis. Polymer 1 exhibits a three-dimensional (3D) structure constructed from 5-connected secondary building units (SBUs) [Co3(μ3-O)] and 3-connected H3TPA ligands. Polymer 2 has a 1D zigzag polymer chain connected by H3TPA and bibp ligands. Polymer 3 features an unusual 3D framework with a (3,4,2)-connected {4; 6;8}{4; 62;83} topology. Moreover, the thermal stabilities of 1-3 and photoluminescence properties of 3 have been investigated. Magnetic susceptibility measurements indicate that polymers 1-2 display antiferromagnetic exchange properties.

Optical properties of silicene, Si/Ag(111), and Si/Ag(110)

NASA Astrophysics Data System (ADS)

Hogan, C.; Pulci, O.; Gori, P.; Bechstedt, F.; Martin, D. S.; Barritt, E. E.; Curcella, A.; Prevot, G.; Borensztein, Y.

2018-05-01

We present a state-of-the-art study of the optical properties of free-standing silicene and of single-layer Si one- and two-dimensional (1D and 2D) nanostructures supported on Ag(110) and Ag(111) substrates. Ab initio simulations of reflectance anisotropy spectroscopy (RAS) and surface differential reflectivity spectroscopy (SDRS) applied to the clean Ag surface and Si/Ag interfaces are compared with new measurements. For Si/Ag(110), we confirm a pentagonal nanoribbon geometry, strongly bonded to the substrate, and rule out competing zigzag chain and silicenelike models. For Si/Ag(111), we reproduce the main experimental features and isolate the optical signal of the epitaxial silicene overlayer. The absorption spectrum of a silicene sheet computed including excitonic and local field effects is found to be quite similar to that calculated within an independent particle approximation and shows strong modifications when adsorbed on a Ag substrate. Important details of the computational approach are examined and the origins of the RAS and SDRS signals are explained in terms of the interface and substrate response functions. Our study does not find any evidence for Si adlayers that retain the properties of freestanding silicene.

Self-assembly of a nanotube from a black phosphorus nanoribbon on a string of fullerenes at low temperature.

PubMed

Cai, Kun; Shi, Jiao; Liu, Ling-Nan; Qin, Qing-Hua

2017-09-13

A string of fullerenes is used for generating a nanotube by self-assembly of a black phosphorus (BP) nanoribbon at a temperature of 8 K. Among the fullerenes in the string, there are at least two fixed fullerenes placed along the edge of the BP ribbon for keeping its configuration stability during winding. By way of molecular dynamics simulations, it is found that successful generation of a BP nanotube depends on the bending stiffness of the ribbon and the attraction between the fullerenes and the ribbon. When the attraction is strong enough, the two edges (along the zigzag direction) of the BP ribbon will be able to bond covalently to form a nanotube. By the molecular dynamics approach, the maximum width of the BP ribbon capable of forming a nanotube with a perfect length is investigated in three typical models. The maximum width of the BP ribbon becomes larger with the string containing more fullerenes. This finding reveals a way to control the width of the BP ribbon which forms a nanotube. It provides guidance for fabricating a BP nanotube with a specified length, the same as to the width of the ribbon.

Bethe vectors for XXX-spin chain

NASA Astrophysics Data System (ADS)

Burdík, Čestmír; Fuksa, Jan; Isaev, Alexei

2014-11-01

The paper deals with algebraic Bethe ansatz for XXX-spin chain. Generators of Yang-Baxter algebra are expressed in basis of free fermions and used to calculate explicit form of Bethe vectors. Their relation to N-component models is used to prove conjecture about their form in general. Some remarks on inhomogeneous XXX-spin chain are included.

Polyethylene composites containing a phase change material having a C14 straight chain hydrocarbon

DOEpatents

Salyer, Ival O.

1987-01-01

A composite useful in thermal energy storage, said composite being formed of a polyethylene matrix having a straight chain alkyl hydrocarbon incorporated therein, said polyethylene being crosslinked to such a degree that said polyethylene matrix is form stable and said polyethylene matrix is capable of absorbing at least 10% by weight of said straight chain alkyl hydrocarbon; the composite is useful in forming pellets or sheets having thermal energy storage characteristics.

Translational vibrations between chains of hydrogen-bonded molecules in solid-state aspirin form I

NASA Astrophysics Data System (ADS)

Takahashi, Masae; Ishikawa, Yoichi

2013-06-01

We perform dispersion-corrected first-principles calculations, and far-infrared (terahertz) spectroscopic experiments at 4 K, to examine translational vibrations between chains of hydrogen-bonded molecules in solid-state aspirin form I. The calculated frequencies and relative intensities reproduce the observed spectrum to accuracy of 11 cm-1 or less. The stronger one of the two peaks assigned to the translational mode includes the stretching vibration of the weak hydrogen bond between the acetyl groups of a neighboring one-dimensional chain. The calculation of aspirin form II performed for comparison gives the stretching vibration of the weak hydrogen bond in one-dimensional chain.

Simultaneous covalent and noncovalent hybrid polymerizations

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

Yu, Z.; Tantakitti, F.; Yu, T.

Covalent and supramolecular polymers are two distinct forms of soft matter, composed of long chains of covalently and noncovalently linked structural units, respectively. We report a hybrid system formed by simultaneous covalent and supramolecular polymerizations of monomers. The process yields cylindrical fibers of uniform diameter that contain covalent and supramolecular compartments, a morphology not observed when the two polymers are formed independently. The covalent polymer has a rigid aromatic imine backbone with helicoidal conformation, and its alkylated peptide side chains are structurally identical to the monomer molecules of supramolecular polymers. In the hybrid system, covalent chains grow to higher averagemore » molar mass relative to chains formed via the same polymerization in the absence of a supramolecular compartment. The supramolecular compartments can be reversibly removed and re-formed to reconstitute the hybrid structure, suggesting soft materials with novel delivery or repair functions.« less

NHEXAS PHASE I MARYLAND STUDY--STANDARD OPERATING PROCEDURE FOR CHAIN-OF-CUSTODY AND SAMPLE TRACKING (G04)

EPA Science Inventory

The purpose of the SOP is to establish the normal procedures for ensuring data chain-of-custody and data tracking. The chain-of-custody form included in this SOP is the standard form to be used for all data collected in the field. Keywords: samples; custody; records.

The Nat...

First-principles investigation on structural and electronic properties of antimonene nanoribbons and nanotubes

NASA Astrophysics Data System (ADS)

Nagarajan, V.; Chandiramouli, R.

2018-03-01

The electronic properties of antimonene nanotubes and nanoribbons hydrogenated along the zigzag and armchair borders are investigated with the help of density functional theory (DFT) method. The structural stability of antimonene nanostructures is confirmed with the formation energy. The electronic properties of hydrogenated zigzag and armchair antimonene nanostructures are studied in terms of highest occupied molecular orbital (HOMO) & lowest unoccupied molecular orbital (LUMO) gap and density of states (DOS) spectrum. Moreover, due to the influence of buckled orientation, hydrogen passivation and width of antimonene nanostructures, the HOMO-LUMO gap widens in the range of 0.15-0.41 eV. The findings of the present study confirm that the electronic properties of antimonene nanostructures can be tailored with the influence of width, orientation of the edges, passivation with hydrogen and morphology of antimonene nanostructures (nanoribbons, nanotubes), which can be used as chemical sensor and for spintronic devices.

Ab-initio study of structural, electronic, and transport properties of zigzag GaP nanotubes.

PubMed

Srivastava, Anurag; Jain, Sumit Kumar; Khare, Purnima Swarup

2014-03-01

Stability and electronic properties of zigzag (3 ≤ n ≤ 16) gallium phosphide nanotubes (GaP NTs) have been analyzed by employing a systematic ab-intio approach based on density functional theory using generalized gradient approximation with revised Perdew Burke Ernzerhoff type parameterization. Diameter dependence of bond length, buckling, binding energy, and band gap has been investigated and the analysis shows that the bond length and buckling decreases with increasing diameter of the tube, highest binding energy of (16, 0) confirms this as the most stable amongst all the NTs taken into consideration. The present GaP NTs shows direct band gap and it increases with diameter of the tubes. Using a two probe model for (4, 0) NT the I-V relationship shows an exponential increase in current on applying bias voltage beyond 1.73 volt.

Tailoring graphene magnetism by zigzag triangular holes: A first-principles thermodynamics study

DOE PAGES

Khan, Muhammad Ejaz; Zhang, P.; Sun, Yi -Yang; ...

2016-03-30

In this study, we discuss the thermodynamic stability and magnetic property of zigzag triangular holes (ZTHs) in graphene based on the results of first-principles density functional theory calculations. We find that ZTHs with hydrogen-passivated edges in mixed sp 2/sp 3 configurations (z 211) could be readily available at experimental thermodynamic conditions, but ZTHs with 100% sp 2 hydrogen-passivation (z 1) could be limitedly available at high temperature and ultra-high vacuum conditions. Graphene magnetization near the ZTHs strongly depends on the type and the size of the triangles. While metallic z 1 ZTHs exhibit characteristic edge magnetism due to the same-sublatticemore » engineering, semiconducting z 211 ZTHs do show characteristic corner magnetism when the size is small < 2 nm. Our findings could be useful for experimentally tailoring metal-free carbon magnetism by simply fabricating triangular holes in graphene.« less

Hetonic quartets in a two-layer quasi-geostrophic flow: V-states and stability

NASA Astrophysics Data System (ADS)

Reinaud, J. N.; Sokolovskiy, M. A.; Carton, X.

2018-05-01

We investigate families of finite core vortex quartets in mutual equilibrium in a two-layer quasi-geostrophic flow. The finite core solutions stem from known solutions for discrete (singular) vortex quartets. Two vortices lie in the top layer and two vortices lie in the bottom layer. Two vortices have a positive potential vorticity anomaly, while the two others have negative potential vorticity anomaly. The vortex configurations are therefore related to the baroclinic dipoles known in the literature as hetons. Two main branches of solutions exist depending on the arrangement of the vortices: the translating zigzag-shaped hetonic quartets and the rotating zigzag-shaped hetonic quartets. By addressing their linear stability, we show that while the rotating quartets can be unstable over a large range of the parameter space, most translating quartets are stable. This has implications on the longevity of such vortex equilibria in the oceans.

Effects of an electric field on the electronic and optical properties of zigzag boron nitride nanotubes

NASA Astrophysics Data System (ADS)

Chegel, Raad; Behzad, Somayeh

2011-02-01

We have investigated the electro-optical properties of zigzag BNNTs, under an external electric field, using the tight binding approximation. It is found that an electric field modifies the band structure and splits the band degeneracy. Also the large electric strength leads to coupling the neighbor subbands which these effects reflect in the DOS and JDOS spectrum. It has been shown that, unlike CNTs, the band gap of BNNTs can be reduced linearly by applying a transverse external electric field. Also we show that the larger diameter tubes are more sensitive than small ones. The semiconducting metallic transition can be achieved through increasing the applied fields. The number and position of peaks in the JDOS spectrum are dependent on electric field strength. It is found that at a high electric field, the two lowest subbands are oscillatory with multiple nodes at the Fermi level.

Correlated states in β-Li 2IrO 3 driven by applied magnetic fields

DOE PAGES

Ruiz, Alejandro; Frano, Alex; Breznay, Nicholas P.; ...

2017-10-16

Magnetic honeycomb iridates are thought to show strongly spin-anisotropic exchange interactions which, when highly frustrated, lead to an exotic state of matter known as the Kitaev quantum spin liquid. However, in all known examples these materials magnetically order at finite temperatures, the scale of which may imply weak frustration. Here we show that the application of a relatively small magnetic field drives the three-dimensional magnet β-Li 2IrO 3 from its incommensurate ground state into a quantum correlated paramagnet. Interestingly, this paramagnetic state admixes a zig-zag spin mode analogous to the zig-zag order seen in other Mott-Kitaev compounds. The rapid onsetmore » of the field-induced correlated state implies the exchange interactions are delicately balanced, leading to strong frustration and a near degeneracy of different ground states.« less

Prediction of Composite Laminate Strength Properties Using a Refined Zigzag Plate Element

NASA Technical Reports Server (NTRS)

Barut, Atila; Madenci, Erdogan; Tessler, Alexander

2013-01-01

This study presents an approach that uses the refined zigzag element, RZE(exp2,2) in conjunction with progressive failure criteria to predict the ultimate strength of composite laminates based on only ply-level strength properties. The methodology involves four major steps: (1) Determination of accurate stress and strain fields under complex loading conditions using RZE(exp2,2)-based finite element analysis, (2) Determination of failure locations and failure modes using the commonly accepted Hashin's failure criteria, (3) Recursive degradation of the material stiffness, and (4) Non-linear incremental finite element analysis to obtain stress redistribution until global failure. The validity of this approach is established by considering the published test data and predictions for (1) strength of laminates under various off-axis loading, (2) strength of laminates with a hole under compression, and (3) strength of laminates with a hole under tension.

Spin Transport in Electric-Barrier-Modulated Ferromagnetic/Normal/Ferromagnetic Monolayer Zigzag MoS2 Nanoribbon Junction

NASA Astrophysics Data System (ADS)

Xia, Y.-Y.; Yuan, R.-Y.; Yang, Q.-J.; Sun, Q.; Zheng, J.; Guo, Y.

In this paper, with the three-band tight-binding model and non-equilibrium Green’s function technique, we investigate spin transport in electric-barrier-modulated Ferromagnetic/Normal/Ferromagnetic (F/N/F) monolayer (ML) zigzag MoS2 nanoribbon junction. The results demonstrate that once the double electric barriers structure emerges, the oscillations of spin conductances become violent, especially for spin-down conductance, the numbers of resonant peaks increase obviously, thus we can obtain 100% spin polarization in the low energy region. It is also found that with the intensity of the exchange field enhancement, the resonant peaks of spin-up and spin-down conductances move in the opposite direction in a certain energy region. As a consequence, the spin-down conductance can be filtered out completely. The findings here indicate that the present structure may be considered as a good candidate for spin filter.

Zigzagging Across Pluto

NASA Image and Video Library

2015-12-16

This high-resolution swat of Pluto sweeps over the cratered plains at the west of the New Horizons' encounter hemisphere and across numerous prominent faults, skimming the eastern margin of the dark, forbidding region informally known as Cthulhu Regio, and finally passing over the mysterious, possibly cryovolcanic edifice Wright Mons, before reaching the terminator or day-night line. Among the many notable details shown are the overlapping and infilling relationships between units of the relatively smooth, bright volatile ices from Sputnik Planum (at the edge of the mosaic) and the dark edge or "shore" of Cthulhu. The pictures in this mosaic were taken by the Long Range Reconnaissance Imager (LORRI) in "ride-along" mode with the LEISA spectrometer, which accounts for the 'zigzag' or step pattern. Taken shortly before New Horizons' July 14 closest approach to Pluto, details as small as 500 yards (500 meters) can be seen. http://photojournal.jpl.nasa.gov/catalog/PIA20286

Magnetic ground state of the layered honeycomb compound Na2Co2TeO6

NASA Astrophysics Data System (ADS)

Bera, A. K.; Yusuf, S. M.

2018-04-01

The magnetic correlations in the 2D layered honeycomb compound Na2Co2TeO6 has been investigated. The temperature dependent susceptibility curve reveals a transition to the magnetically ordered state at TN ˜ 25 K. The temperature dependent neutron diffraction study confirms an antiferromagnetic ordering below TN. The magnetic ground state is determined to be a zigzag antiferromagnet that appears due to competing exchange interactions beyond nearest neighbors. The moments align along the crystallographic b axis with reduced ordered magnetic moment values of 2.72(2) μB/Co2+ and 2.52(3) μB/Co2+ for two Co sites, respectively. In comparison to the theoretical phase diagram the determined zigzag antiferromagnetic ground state suggests that the compound Na2Co2TeO6 is situated in the proximity to the quantum spin liquid state in the phase diagram.

Tailoring graphene magnetism by zigzag triangular holes: A first-principles thermodynamics study

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

Khan, Muhammad Ejaz; Zhang, P.; Kim, Yong-Hyun, E-mail: yong.hyun.kim@kaist.ac.kr

We discuss the thermodynamic stability and magnetic property of zigzag triangular holes (ZTHs) in graphene based on the results of first-principles density functional theory calculations. We find that ZTHs with hydrogen-passivated edges in mixed sp{sup 2}/sp{sup 3} configurations (z{sub 211}) could be readily available at experimental thermodynamic conditions, but ZTHs with 100% sp{sup 2} hydrogen-passivation (z{sub 1}) could be limitedly available at high temperature and ultra-high vacuum conditions. Graphene magnetization near the ZTHs strongly depends on the type and the size of the triangles. While metallic z{sub 1} ZTHs exhibit characteristic edge magnetism due to the same-sublattice engineering, semiconducting z{submore » 211} ZTHs do show characteristic corner magnetism when the size is small <2 nm. Our findings could be useful for experimentally tailoring metal-free carbon magnetism by simply fabricating triangular holes in graphene.« less

Electronic structure and transport properties of zigzag MoS2 nanoribbons

NASA Astrophysics Data System (ADS)

Sharma, Uma Shankar; Shah, Rashmi; Mishra, Pankaj Kumar

2018-05-01

In present study, electronic and transport properties of the 8zigzag MoS2 nanoribbons (8ZMoS2NRs) are investigated using ab-initio density functional theory [DFT]. The calculations were performed using nonequilibrium Green's function (NEGF) formalism based on DFT as implemented in the TranSiesta code. Results show that the defect can introduces few extra states into the energy gap, which lead nanoribbons to reveal a metallic characteristic. The voltage-current (VI) graph of 8ZMoS2NRs show a threshold current increases after introducing Mo defect in the devices. when introducing a Mo vacancy under low biases, the current will be suppressed—whereas under high biases, the current through the defected 8ZMoS2NRs will increases rapidly, due to the other channel being opened, that make possibility of 8ZMoS2NRs application in electronic devices such as voltage regulation.

A first-principles study of electronic properties of H and F-terminated zigzag BNC nanoribbons

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

Alaal, Naresh; Department of Physics, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India.; Department of Materials Engineering, Monash University, Clayton, Victoria -3800, Australia.

2016-05-06

Nanoribbons are quasi one-dimensional structures which have interesting electronic properties on the basis of their edge geometries, and width. We studied the electronic properties of hydrogen and fluorine-terminated zigzag BNC nanoribbons (BNCNRs) using a first-principles based density functional theory approach. We considered BNCNRs that were composed of an equal number of C-C and B-N dimers; one of the edges ends with an N atom and opposite edge ends with a C atom. These two edge atoms are passivated by H or F atoms. Our results suggest that hydrogen-terminated BNCNRs (H-BNCNRs) and flourine-terminated BNCNRs (F-BNCNRs) have different electronic properties. H-BNCNRs exhibitmore » intrinsic half-metallic behavior while F-BNCNRs are indirect band gap semiconductors. Chemical functionalization of BNCNRs with H and F atoms show that BNCNRs have a diverse range of electronic properties.« less

Non-equilibrium tunneling in zigzag graphene nanoribbon break-junction results in spin filtering

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

Jiang, Liming; Department of Electrical and Electronic Engineering, The University of Melbourne, Parkville 3010; National ICT Australia, The University of Melbourne, Parkville 3010

Spintronic devices promise new faster and lower energy-consumption electronic systems. Graphene, a versatile material and candidate for next generation electronics, is known to possess interesting spintronic properties. In this paper, by utilizing density functional theory and non-equilibrium green function formalism, we show that Fano resonance can be generated by introducing a break junction in a zigzag graphene nanoribbon (ZGNR). Using this effect, we propose a new spin filtering device that can be used for spin injection. Our theoretical results indicate that the proposed device could achieve high spin filtering efficiency (over 90%) at practical fabrication geometries. Furthermore, our results indicatemore » that the ZGNR break junction lattice configuration can dramatically affect spin filtering efficiency and thus needs to be considered when fabricating real devices. Our device can be fabricated on top of spin transport channel and provides good integration between spin injection and spin transport.« less

Interaction of multiarmed spirals in bistable media.

PubMed

He, Ya-feng; Ai, Bao-quan; Liu, Fu-cheng

2013-05-01

We study the interaction of both dense and sparse multiarmed spirals in bistable media modeled by equations of the FitzHugh-Nagumo type. A dense one-armed spiral is characterized by its fixed tip. For dense multiarmed spirals, when the initial distance between tips is less than a critical value, the arms collide, connect, and disconnect continuously as the spirals rotate. The continuous reconstruction between the front and the back drives the tips to corotate along a rough circle and to meander zigzaggedly. The rotation frequency of tip, the frequency of zigzagged displacement, the frequency of spiral, the oscillation frequency of media, and the number of arms satisfy certain relations as long as the control parameters of the model are fixed. When the initial distance between tips is larger than the critical value, the behaviors of individual arms within either dense or sparse multiarmed spirals are identical to that of corresponding one-armed spirals.

Multicomponent Pt-Based Zigzag Nanowires as Selectivity Controllers for Selective Hydrogenation Reactions.

PubMed

Bai, Shuxing; Bu, Lingzheng; Shao, Qi; Zhu, Xing; Huang, Xiaoqing

2018-06-22

The selective hydrogenation of α, β-unsaturated aldehyde is an extremely important transformation, while developing efficient catalysts with desirable selectivity to highly value-added products is challenging, mainly due to the coexistence of two conjugated unsaturated functional groups. Herein, we report that a series of Pt-based zigzag nanowires (ZNWs) can be adopted as selectivity controllers for α, β-unsaturated aldehyde hydrogenation, where the excellent unsaturated alcohol (UOL) selectivity (>95%) and high saturated aldehyde (SA) selectivity (>94%) are achieved on PtFe ZNWs and PtFeNi ZNWs+AlCl 3 , respectively. The excellent UOL selectivity of PtFe ZNWs is attributed to the lower electron density of the surface Pt atoms, while the high SA selectivity of PtFeNi ZNWs+AlCl 3 is due to synergy between PtFeNi ZNWs and AlCl 3 , highlighting the importance of Pt-based NWs with precisely controlled surface and composition for catalysis and beyond.

Unusual polarity-dependent patterns in a bent-core nematic liquid crystal under low-frequency ac field.

PubMed

Xiang, Ying; Zhou, Meng-jie; Xu, Ming-Ya; Salamon, Péter; Éber, Nándor; Buka, Ágnes

2015-04-01

Electric-field-induced patterns of diverse morphology have been observed over a wide frequency range in a recently synthesized bent-core nematic (BCN) liquid crystal. At low frequencies (up to ∼25 Hz), the BCN exhibited unusual polarity-dependent patterns. When the amplitude of the ac field was enhanced, these two time-asymmetrical patterns turned into time-symmetrical prewavylike stripes. At ac frequencies in the middle-frequency range (∼50-3000 Hz), zigzag patterns were detected whose obliqueness varied with the frequency. Finally, if the frequency was increased above 3 kHz, the zigzag pattern was replaced by another, prewavylike pattern, whose threshold voltage depended on the frequency; however, the wave vector did not. For a more complete characterization, material parameters such as elastic constants, dielectric permittivities, and the anisotropy of the diamagnetic susceptibility were also determined.

Thermodynamics and kinetics of graphene chemistry: a graphene hydrogenation prototype study.

PubMed

Pham, Buu Q; Gordon, Mark S

2016-12-07

The thermodynamic and kinetic controls of graphene chemistry are studied computationally using a graphene hydrogenation reaction and polyaromatic hydrocarbons to represent the graphene surface. Hydrogen atoms are concertedly chemisorped onto the surface of graphene models of different shapes (i.e., all-zigzag, all-armchair, zigzag-armchair mixed edges) and sizes (i.e., from 16-42 carbon atoms). The second-order Z-averaged perturbation theory (ZAPT2) method combined with Pople double and triple zeta basis sets are used for all calculations. It is found that both the net enthalpy change and the barrier height of graphene hydrogenation at graphene edges are lower than at their interior surfaces. While the thermodynamic product distribution is mainly determined by the remaining π-islands of functionalized graphenes (Phys. Chem. Chem. Phys., 2013, 15, 3725-3735), the kinetics of the reaction is primarily correlated with the localization of the electrostatic potential of the graphene surface.

Role of impurities on the optical properties of rectangular graphene flakes

NASA Astrophysics Data System (ADS)

Sadeq, Z. S.; Muniz, Rodrigo A.; Sipe, J. E.

2018-01-01

We study rectangular graphene flakes using mean field states as the basis for a configuration interaction calculation, which allows us to analyze the low lying electronic excited states including electron correlations beyond the mean field level. We find that the lowest energy transition is polarized along the long axis of the flake, but the charge distributions involved in these transitions are invariably localized on the zigzag edges. We also investigate the impact of both short and long range impurity potentials on the optical properties of these systems. We predict that even a weak impurity localized at a zigzag edge of the flake can have a significant—and often dramatic—effect on its optical properties. This is in contrast to impurities localized at armchair edges or central regions of the flake, for which we predict almost no change to the optical properties of the flake even with strong impurity potentials.

A Three-Dimensional Capsule-Like Carbon Nanocage as a Novel Segment Model of Capped Zigzag [12,0] Carbon Nanotubes: Synthesis, Characterization, and Complexation with C70.

PubMed

Du, Pingwu

2018-05-17

Herein we report the synthesis, photophysical, and supramolecular properties of a novel three-dimensional capsule-like hexa-peri-hexabenzocoronene (HBC)-containing carbon nanocage, tripodal-[2]HBC, which represents the first synthetic model of the capped zigzag [12,0] carbon nanotubes (CNTs). Tripodal-[2]HBC was achieved by rationally designed palladium-catalyzed coupling of triborylhexabenzocoronene and L-shaped cyclohexane units, followed by nickel-mediated C-Br/C-Br coupling and the subsequent aromatization of the cyclohexane moieties. The physical properties of tripodal-[2]HBC and its supramolecular host-guest interaction with C70 were further studied by UV-vis and fluorescence spectroscopy. Theoretical calculations reveal that the strain energy of tripodal-[2]HBC is as high as 55.2 kcal mol-1. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Negative differential resistance and magnetoresistance in zigzag borophene nanoribbons

NASA Astrophysics Data System (ADS)

Liu, Jiayi; Wu, Jiaxin; Chen, Changpeng; Han, Lu; Zhu, Ziqing; Wu, Jinping

2018-02-01

Since borophene has been grown experimentally, its extraordinary characteristics have attracted more and more attentions. In this paper, we construct pristine zigzag-edged borophene nanoribbons (ZBNRs) of different widths to study the transport properties, using the first-principles calculations. The differences of the quantum transport properties are discussed, where even-N ZBNRs and odd-N ZBNRs have different current-voltage relationships. Especially, the negative differential resistance (NDR) can be observed within certain bias range in 5-ZBNR and 7-ZBNR, while 6-ZBNR behaves like a metal whose current rises with the increase of the voltage. Moreover, borophene nanoribbon shows interesting magnetic transport properties. The spin-filtering effect can be revealed when the two electrodes have opposite magnetization directions. Besides, the magnetoresistance effect appears to exist in even-N ZBNRs and the maximum value can reach 70%. The mechanisms of these phenomena are proposed in detail.

On prototypical wave transmission across a junction of waveguides with honeycomb structure

NASA Astrophysics Data System (ADS)

Sharma, Basant Lal

2018-02-01

An exact expression for the scattering matrix associated with a junction generated by partial unzipping along the zigzag direction of armchair tubes is presented. The assumed simple, but representative, model, for scalar wave transmission can be interpreted in terms of the transport of the out-of-plane phonons in the ribbon-side vis-a-vis the radial phonons in the tubular-side of junction, based on the nearest-neighbor interactions between lattice sites. The exact solution for the `bondlength' in `broken' versus intact bonds can be constructed via a standard application of the Wiener-Hopf technique. The amplitude distribution of outgoing phonons, far away from the junction on either side of it, is obtained in closed form by the mode-matching method; eventually, this leads to the provision of the scattering matrix. As the main result of the paper, a succinct and closed form expression for the accompanying reflection and transmission coefficients is provided along with a detailed derivation using the Chebyshev polynomials. Applications of the analysis presented in this paper include linear wave transmission in nanotubes, nanoribbons, and monolayers of honeycomb lattices containing carbon-like units.

Reactive Searching and Infotaxis in Odor Source Localization

PubMed Central

Voges, Nicole; Chaffiol, Antoine; Lucas, Philippe; Martinez, Dominique

2014-01-01

Male moths aiming to locate pheromone-releasing females rely on stimulus-adapted search maneuvers complicated by a discontinuous distribution of pheromone patches. They alternate sequences of upwind surge when perceiving the pheromone and cross- or downwind casting when the odor is lost. We compare four search strategies: three reactive versus one cognitive. The former consist of pre-programmed movement sequences triggered by pheromone detections while the latter uses Bayesian inference to build spatial probability maps. Based on the analysis of triphasic responses of antennal lobe neurons (On, inhibition, Off), we propose three reactive strategies. One combines upwind surge (representing the On response to a pheromone detection) and spiral casting, only. The other two additionally include crosswind (zigzag) casting representing the Off phase. As cognitive strategy we use the infotaxis algorithm which was developed for searching in a turbulent medium. Detection events in the electroantennogram of a moth attached to a robot indirectly control this cyborg, depending on the strategy in use. The recorded trajectories are analyzed with regard to success rates, efficiency, and other features. In addition, we qualitatively compare our robotic trajectories to behavioral search paths. Reactive searching is more efficient (yielding shorter trajectories) for higher pheromone doses whereas cognitive searching works better for lower doses. With respect to our experimental conditions (2 m from starting position to pheromone source), reactive searching with crosswind zigzag yields the shortest trajectories (for comparable success rates). Assuming that the neuronal Off response represents a short-term memory, zigzagging is an efficient movement to relocate a recently lost pheromone plume. Accordingly, such reactive strategies offer an interesting alternative to complex cognitive searching. PMID:25330317

Reactive searching and infotaxis in odor source localization.

PubMed

Voges, Nicole; Chaffiol, Antoine; Lucas, Philippe; Martinez, Dominique

2014-10-01

Male moths aiming to locate pheromone-releasing females rely on stimulus-adapted search maneuvers complicated by a discontinuous distribution of pheromone patches. They alternate sequences of upwind surge when perceiving the pheromone and cross- or downwind casting when the odor is lost. We compare four search strategies: three reactive versus one cognitive. The former consist of pre-programmed movement sequences triggered by pheromone detections while the latter uses Bayesian inference to build spatial probability maps. Based on the analysis of triphasic responses of antennal lobe neurons (On, inhibition, Off), we propose three reactive strategies. One combines upwind surge (representing the On response to a pheromone detection) and spiral casting, only. The other two additionally include crosswind (zigzag) casting representing the Off phase. As cognitive strategy we use the infotaxis algorithm which was developed for searching in a turbulent medium. Detection events in the electroantennogram of a moth attached to a robot indirectly control this cyborg, depending on the strategy in use. The recorded trajectories are analyzed with regard to success rates, efficiency, and other features. In addition, we qualitatively compare our robotic trajectories to behavioral search paths. Reactive searching is more efficient (yielding shorter trajectories) for higher pheromone doses whereas cognitive searching works better for lower doses. With respect to our experimental conditions (2 m from starting position to pheromone source), reactive searching with crosswind zigzag yields the shortest trajectories (for comparable success rates). Assuming that the neuronal Off response represents a short-term memory, zigzagging is an efficient movement to relocate a recently lost pheromone plume. Accordingly, such reactive strategies offer an interesting alternative to complex cognitive searching.

Rectification of light refraction in curved waveguide arrays.

PubMed

Longhi, Stefano

2009-02-15

An "optical ratchet" for discretized light in photonic lattices, which enables observing rectification of light refraction at any input beam conditions, is theoretically presented, and a possible experimental implementation based on periodically curved zigzag waveguide arrays is proposed.

Spheres settling in an Oldroyd-B fluid

NASA Astrophysics Data System (ADS)

Pan, Tsorng-Whay; Glowinski, Roland

2017-11-01

In this talk we present a numerical study of the dynamics of balls settling in a vertical channel with a square cross-section filled with an Oldroyd-B fluid. For the case of two balls, two typical kinds of particle dynamics are obtained: (i) periodic interaction between two balls and (ii) the formation of a vertical chain of two balls. For the periodic interaction of two balls occurred at lower values of the elasticity number, two balls draft, kiss and break away periodically and the chain is not formed due to not strong enough elastic force. For slightly higher values of the elasticity number, two balls draft, kiss and break away a couple times first and then form a chain. Such chain finally becomes a vertical one after the oscillation damps out. For higher values of the elasticity number, two balls draft, kiss and form a vertical chain right away. The formation of three ball chain can be obtained at higher values of the elasticity number. This work was supported by NSF (Grant DMS-1418308).

Syntheses, structures and properties of four 3D microporous lanthanide coordination polymers based on 3,5-pyrazoledicarboxylate and oxalate ligands

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

Song, Juan; Wang, Ji-Jiang; Hu, Huai-Ming, E-mail: ChemHu1@NWU.EDU.CN

2014-04-01

Four three-dimensional lanthanide coordination polymers with reversible structural interconversions, [Ln{sub 2}(Hpdc){sub 2}(C{sub 2}O{sub 4})(H{sub 2}O){sub 4}]{sub n}·2nH{sub 2}O [Ln=Sm (1), Eu (2), Tb (3) and Dy (4)], have been synthesized by hydrothermal reactions of lanthanide nitrates with 3,5-pyrazoledicarboxylic (H{sub 3}pdc) and oxalic acids. It is noteworthy that there is an in situ reaction in 1, in which H{sub 3}pdc was decomposed into (ox){sup 2−} with Cu(II)–Sm(III) synergistic effect under hydrothermal conditions. These compounds are isostructural and crystallized in the monoclinic P2{sub 1}/c space group. The Ln(III) ions are eight-coordinated with dodecahedron coordination geometry. These polyhedra are linked by oxalate groupsmore » to form 1D zigzag chain, which are further connected by 3,5-pyrazoledicarboxylate to extend similar 3D frameworks with channels along c-axis in 1–4. These coordination polymers display the characteristic emission bands of the Ln(III) ions in the solid state and possess good thermal stabilities. - Graphical abstract: Four 3D microporous lanthanide coordination polymers with reversible structural interconversion have been synthesized. They exhibit characteristic emission bands of the lanthanide ions and possess great thermal stability. - Highlights: • Four lanthanide coordination polymers have been hydrothermal synthesized. • There is an in situ reaction in 1 in which H{sub 3}pdc was decomposed into (ox){sup 2−} with the Cu(II)–Sm(III) synergistic effect under hydrothermal conditions. • TGA and XRD studies reveal that upon hydration–dehydration, compounds 1–4 undergo a reversible structural interconversion process through a cooling-heating cycle. • Compounds 1–4 exhibit characteristic lanthanide-centered luminescence.« less

Gold deposited on a Ge(0 0 1) surface: DFT calculations

NASA Astrophysics Data System (ADS)

Tsay, Shiow-Fon

2016-11-01

The atomic geometry, stability and electronic properties of self-organized Au induced nanowires on a Ge(0 0 1) surface are investigated based on the density-functional theory in the generalized gradient approximation and the stoichiometry of Au. According to the formation energy and the simulated STM image, the Ge atoms substituted by the Au atoms have been confirmed as occurring at a Au coverage lower than 0.25 Ml. The STM image with single and double dimer vacancies looks like the Au atoms have penetrated the subsurface. The energetically favorable dimer-row arrayed structures at 0.50 Ml and 0.75 Ml Au coverages have a 4  ×  1, 4  ×  2 or c(8  ×  2) transition symmetry, which comprise a flat Au-Au homodimer row and an alternating various buckling phase Ge-Ge or Au-Ge dimer row. The c(8  ×  2) zigzag-shaped protruding chains of shallow-groove STM images are highly consistent with the observations, but a long-range order dimer-row arrayed structure formation requires sufficient mobile energy to complete mass transport of the substituted Ge atoms in order to avoid the re-adsorption of these atoms; otherwise a deep-groove structure reconstruction is sequentially formed. A quasi-1D electron-like energy trough aligns in the direction perpendicular to the nanowire of the dimer-row arrayed structure in the c(8  ×  2) phase on a 0.75 Ml Au/Ge(0 0 1) surface, which is contributed by the Au-Ge dimer rows and the subsurface Ge atoms below them. The bottom energy of the energy trough is consistent with angle-resolved photo-emission spectroscopy studies (Schäfer et al 2008 Phys. Rev. Lett. 101 236802, Meyer et al 2011 Phys. Rev. B 83 121411(R)).

Molecular-specific urokinase antibodies

NASA Technical Reports Server (NTRS)

Atassi, M. Zouhair (Inventor); Morrison, Dennis R. (Inventor)

2009-01-01

Antibodies have been developed against the different molecular forms of urokinase using synthetic peptides as immunogens. The peptides were synthesized specifically to represent those regions of the urokinase molecules which are exposed in the three-dimensional configuration of the molecule and are uniquely homologous to urokinase. Antibodies are directed against the lysine 158-isoleucine 159 peptide bond which is cleaved during activation from the single-chain (ScuPA) form to the bioactive double chain (54 KDa and 33 KDa) forms of urokinase and against the lysine 135 lysine 136 bond that is cleaved in the process of removing the alpha-chain from the 54 KDa form to produce the 33 KDa form of urokinase. These antibodies enable the direct measurement of the different molecular forms of urokinase from small samples of conditioned medium harvested from cell cultures.

Immunoglobulin light chains, glycosaminoglycans and amyloid.

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

Stevens, F. J.; Kisilevsky, R.; Biosciences Division

2000-03-01

Immunoglobulin light chains are the precursor proteins for fibrils that are formed during primary amyloidosis and in amyloidosis associated with multiple myeloma. As found for the approximately 20 currently described forms of focal, localized, or systemic amyloidoses, light chain-related fibrils extracted from physiological deposits are invariably associated with glycosaminoglycans, predominantly heparan sulfate. Other amyloid-related proteins are either structurally normal, such as g2-microglobulin and islet amyloid polypeptide, fragments of normal proteins such as serum amyloid A protein or the precursor protein of the g peptide involved in Alzheimer's disease, or are inherited forms of single amino acid variants of a normalmore » protein such as found in the familial forms of amyloid associated with transthyretin. In contrast, the primary structures of light chains involved in fibril formation exhibit extensive mutational diversity rendering some proteins highly amyloidogenic and others non-pathological. The interactions between light chains and glycosaminoglycans are also affected by amino acid variation and may influence the clinical course of disease by enhancing fibril stability and contributing to resistance to protease degradation. Relatively little is currently known about the mechanisms by which glycosaminoglycans interact with light chains and light-chain fibrils. It is probable that future studies of this uniquely diverse family of proteins will continue o shed light on the processes of amyloidosis, and contribute as well to a greater understanding of the normal physiological roles of glycosaminoglycans.« less