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Sample records for helical zincii-lanthanideiii trinuclear

  1. Half-lives of trinuclear molecules

    Science.gov (United States)

    Carstoiu, F.; Bulboacă, I.; Săndulescu, A.; Greiner, W.

    2000-04-01

    Recent discoveries of 10Be and 12C accompanied cold fission in the spontaneous fission of 252Cf lead to the surprising result that long living trinuclear molecules may exists. For the description of the dynamics and decay of such molecules, we used a coplanar three body cluster model (two deformed fragments and an α particle) with a three body potential computed by a double folding potential generated by M3Y effective interaction. A repulsive compression term was included. The computed α ternary cold fission yields are in agreement with the experiment. The energy and angular distributions of the three clusters at infinity and the half-lives are strongly dependent of the initial positions of the α particle relative to the two fragments and of mass asymmetry of the fragments. The evaluated lifetimes of such trinuclear molecules are quite large, of the order of one second.

  2. Helicity scalings

    Energy Technology Data Exchange (ETDEWEB)

    Plunian, F [ISTerre, CNRS, Universite Joseph Fourier, Grenoble (France); Lessinnes, T; Carati, D [Physique Statistique et Plasmas, Universite Libre de Bruxelles (Belgium); Stepanov, R, E-mail: Franck.Plunian@ujf-grenoble.fr [Institute of Continuous Media Mechanics of the Russian Academy of Science, Perm (Russian Federation)

    2011-12-22

    Using a helical shell model of turbulence, Chen et al. (2003) showed that both helicity and energy dissipate at the Kolmogorov scale, independently from any helicity input. This is in contradiction with a previous paper by Ditlevsen and Giuliani (2001) in which, using a GOY shell model of turbulence, they found that helicity dissipates at a scale larger than the Kolmogorov scale, and does depend on the helicity input. In a recent paper by Lessinnes et al. (2011), we showed that this discrepancy is due to the fact that in the GOY shell model only one helical mode (+ or -) is present at each scale instead of both modes in the helical shell model. Then, using the GOY model, the near cancellation of the helicity flux between the + and - modes cannot occur at small scales, as it should be in true turbulence. We review the main results with a focus on the numerical procedure needed to obtain accurate statistics.

  3. Homochiral [2]Catenane and Bis[2]catenane from Alleno-Acetylenic Helicates - A Highly Selective Narcissistic Self-Sorting Process.

    Science.gov (United States)

    Gidron, Ori; Jirásek, Michael; Trapp, Nils; Ebert, Marc-Olivier; Zhang, Xiangyang; Diederich, François

    2015-10-07

    Homochiral strands of alternating alleno-acetylenes and phenanthroline ligands (P)-1 and (P2)-2, as well as their corresponding enantiomers, selectively assemble with the addition of silver(I) salt to yield dinuclear and trinuclear double helicates, respectively. Upon increasing the solvent polarity, the dinuclear and trinuclear helicates interlock to form a [2]catenane and bis[2]catenane, bearing 14 chirality elements, respectively. The solid-state structure of the [2]catenane reveals a nearly perfect fit of the interlocked strands, and the ECD spectra show a significant amplification of the chiroptical properties upon catenation, indicating stabilization of the helical secondary structure. Highly selective narcissistic self-sorting was demonstrated for a racemic mixture consisting of both short and long alleno-acetylenic strands, highlighting their potential for the preparation of linear catenanes of higher order.

  4. On the Half-Lives of Trinuclear Molecules

    Science.gov (United States)

    Săndulescu, A.; Carstoiu, F.; Bulboacă, I.; Greiner, W.

    2001-10-01

    Recent discoveries of 10Be and 12C accompanied cold fission in the spontaneous fission of 252Cf lead to the surprising result that long living trinuclear molecules may exists. For the description of the dynamics and decay of such molecules, we used a coplanar three body cluster model (two deformed fragments and an α particle) with a three body potential computed by a double folding potential generated by M3Y effective interaction. A repulsive compression term was included. The computed α ternary cold fission yields are in agreement with the experiment. The energy and angular distributions of the three clusters at infinity and the half lives are strongly dependent of the initial positions of the α particle relative to the two fragments and of mass asymmetry of the fragments. The evaluated lifetimes of such trinuclear molecules are quite large of the order of one second.

  5. Two new coordination polymers, a trinuclear metal complex and their interconversion depending on the solvent.

    Science.gov (United States)

    Koike, Shiori; Hirakawa, Takeshi; Yamanishi, Katsunori; Kondo, Mitsuru

    2014-09-14

    Two new 1-D coordination polymers and a discrete trinuclear complex with a double-ring framework were synthesized and structurally characterized. The unique irreversible conversion from one of the 1-D coordination polymers to the trinuclear complex by contact with MeCN is described.

  6. Mononuclear, trinuclear, and hetero-trinuclear supramolecular complexes containing a new tri-sulfonate ligand and cobalt(II)/copper(II)-(1, 10-phenanthroline)(2) building blocks

    NARCIS (Netherlands)

    Yu, Yunfang; Wei, Yongqin; Broer, Ria; Sa, Rongjian; Wu, Kechen

    2008-01-01

    Novel mononuclear, trinuclear, and hetero-trinuclear supermolecular complexes, [Co(phen)(2)(H2O)(HTST)] center dot 2H(2)O (1), [CO3(phen)(6) (H2O)(2)(TST)(2)]center dot 7H(2)O (2), and [CO2Cu(phen)(6)(H2O)(2)(TST)(2)]center dot 10H(2)O (3), have been synthesized by the reactions of a new tri-sulfona

  7. Effect of hydrogen atoms on the structures of trinuclear metal carbonyl clusters: trinuclear manganese carbonyl hydrides.

    Science.gov (United States)

    Liu, Xian-mei; Wang, Chao-yang; Li, Qian-shu; Xie, Yaoming; King, R Bruce; Schaefer, Henry F

    2009-05-18

    The structures of the trinuclear manganese carbonyl hydrides H(3)Mn(3)(CO)(n) (n = 12, 11, 10, 9) have been investigated by density functional theory (DFT). Optimization of H(3)Mn(3)(CO)(12) gives the experimentally known structure in which all carbonyl groups are terminal and each edge of a central Mn(3) equilateral triangle is bridged by a single hydrogen atom. This structure establishes the canonical distance 3.11 A for the Mn-Mn single bond satisfying the 18-electron rule. The central triangular (mu-H)(3)Mn(3) unit is retained in the lowest energy structure of H(3)Mn(3)(CO)(11), which may thus be derived from the H(3)Mn(3)(CO)(12) structure by removal of a carbonyl group with concurrent conversion of one of the remaining carbonyl groups into a semibridging carbonyl group to fill the resulting hole. The potential energy surface of H(3)Mn(3)(CO)(10) is relatively complicated with six singlet and five triplet structures. One of the lower energy H(3)Mn(3)(CO)(10) structures has one of the hydrogen atoms bridging the entire Mn(3) triangle and the other two hydrogen atoms bridging Mn-Mn edges. This H(3)Mn(3)(CO)(10) structure achieves the favored 18-electron configuration with a very short MnMn triple bond of 2.36 A. The other low energy H(3)Mn(3)(CO)(10) structure retains the (mu-H)(3)Mn(3) core of H(3)Mn(3)(CO)(12) but has a unique six-electron donor eta(2)-mu(3) carbonyl group bridging the entire Mn(3) triangle similar to the unique carbonyl group in the known compound Cp(3)Nb(3)(CO)(6)(eta(2)-mu(3)-CO). For H(3)Mn(3)(CO)(9) a structure with a central (mu(3)-H)(2)Mn(3) trigonal bipyramid lies >20 kcal/mol below any of the other structures. Triplet structures were found for the unsaturated H(3)Mn(3)(CO)(n) (n = 11, 10, 9) systems but at significantly higher energies than the lowest lying singlet structures.

  8. Helical filaments

    Energy Technology Data Exchange (ETDEWEB)

    Barbieri, Nicholas; Lim, Khan; Durand, Magali; Baudelet, Matthieu; Richardson, Martin [Townes Laser Institute, CREOL—The College of Optics and Photonics, University of Central Florida, Orlando, Florida 32816 (United States); Hosseinimakarem, Zahra; Johnson, Eric [Micro-Photonics Laboratory – Center for Optical Material Science, Clemson, Anderson, South Carolina 29634 (United States)

    2014-06-30

    The shaping of laser-induced filamenting plasma channels into helical structures by guiding the process with a non-diffracting beam is demonstrated. This was achieved using a Bessel beam superposition to control the phase of an ultrafast laser beam possessing intensities sufficient to induce Kerr effect driven non-linear self-focusing. Several experimental methods were used to characterize the resulting beams and confirm the observed structures are laser air filaments.

  9. Linear trinuclear cobalt(II) single molecule magnet.

    Science.gov (United States)

    Zhang, Yuan-Zhu; Brown, Andrew J; Meng, Yin-Shan; Sun, Hao-Ling; Gao, Song

    2015-02-14

    The introduction of NaBPh(4) into a methanolic solution of CoCl(2)·(6)H(2)O and 2-[(pyridine-2-ylimine)-methyl]phenol (Hpymp) afforded {[Co(II)(3)(pymp)(4)(MeOH)(2)][BPh(4)](2)}·(2)MeOH (1) with a centro-symmetrically linear trinuclear structure. Magnetic analysis of 1 exhibited significant intracluster ferromagnetic exchange (2.4 cm(-1)) and slow relaxation of magnetization in both zero and non-zero static fields below 5 K, giving the first [Co(II)(3)] single molecule magnet with an effective energy barrier of 17.2(3) cm(-1) under a 500 Oe dc field.

  10. Dinitrogen cleavage and hydrogenation by a trinuclear titanium polyhydride complex.

    Science.gov (United States)

    Shima, Takanori; Hu, Shaowei; Luo, Gen; Kang, Xiaohui; Luo, Yi; Hou, Zhaomin

    2013-06-28

    Both the Haber-Bosch and biological ammonia syntheses are thought to rely on the cooperation of multiple metals in breaking the strong N≡N triple bond and forming an N-H bond. This has spurred investigations of the reactivity of molecular multimetallic hydrides with dinitrogen. We report here the reaction of a trinuclear titanium polyhydride complex with dinitrogen, which induces dinitrogen cleavage and partial hydrogenation at ambient temperature and pressure. By (1)H and (15)N nuclear magnetic resonance, x-ray crystallographic, and computational studies of some key reaction steps and products, we have determined that the dinitrogen (N2) reduction proceeds sequentially through scission of a N2 molecule bonded to three Ti atoms in a μ-η(1):η(2):η(2)-end-on-side-on fashion to give a μ2-N/μ3-N dinitrido species, followed by intramolecular hydrogen migration from Ti to the μ2-N nitrido unit.

  11. Currents for Arbitrary Helicity

    CERN Document Server

    Dragon, Norbert

    2016-01-01

    Using Mackey's classification of unitary representations of the Poincar\\'e group on massles states of arbitrary helicity we disprove the claim that states with helicity |h|>=1 cannot couple to a conserved current by constructing such a current.

  12. Synthesis and spectroscopic behavior of highly luminescent trinuclear europium complexes with tris-β-diketone ligand

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Dunjia, E-mail: dunjiawang@163.com; Pi, Yan; Liu, Hua; Wei, Xianhong; Hu, Yanjun; Zheng, Jing

    2014-11-15

    Highlights: • Synthesis of the tris-β-diketone ligand and its trinuclear europium complexes. • Photoluminescence behavior of trinuclear europium complexes. • Analysis of the Judd–Ofelt intensity parameters (Ω{sub t}), lifetime (τ) and quantum yield (η). - Abstract: A new tris-β-diketone ligand, 2-[4,6-bis-(1-benzoyl-2-oxo-2-phenyl-ethyl)-[1,3,5]triazin-2-yl] -1,3-diphenyl-propane-1,3-dione (H{sub 3}L), and its trinuclear europium complexes, Eu{sub 3}(DBM){sub 6}L (C1), Eu{sub 3}(DBM){sub 6}(Bipy){sub 3}L (C2) and Eu{sub 3}(DBM){sub 6}(Phen){sub 3}L (C3) were synthesized and their spectroscopic behaviors were studied by FT-IR, {sup 1}H NMR, UV–vis and photoluminescence spectroscopic techniques. These europium complexes exhibited the characteristic emission bands that arise from the {sup 5}D{sub 0} → {sup 7}F{sub J} (J = 0–4) transitions of the europium ion in solid state. The Ω{sub 2} and Ω{sub 4} intensity parameters, lifetime (τ) and luminescence quantum yield (η) were calculated according to the emission spectra and luminescence decay curves in solid state. The results indicated that these trinuclear europium complexes displayed a longer lifetime (τ) and higher luminescence quantum efficiency (η), especially complexes C2 (τ = 0.820 ms, η = 46.5%) and C3 (τ = 0.804 ms, η = 47.4%), which due to the effect of two additional europium ion lumophors and the introduction of the third ligands, Bipy or Phen in trinuclear complexes. Their Ω{sub 2} values demonstrated that the europium ion in these complexes is in a highly polarizable chemical environment.

  13. Shearing Wind Helicity and Thermal Wind Helicity

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Helicity is defined as H=V.ω, where V and ω are the velocity and vorticity vectors, respectively.Many works have pointed out that the larger the helicity is, the longer the life cycle of the weather system is. However, the direct relationship of the helicity to the evolution of the weather system is not quite clear. In this paper, the concept of helicity is generalized as shearing wind helicity (SWH). Dynamically,it is found that the average SWH is directly related to the increase of the average cyclonic rotation of the weather system. Physically, it is also pointed out that the SWH, as a matter of fact, is the sum of the torsion terms and the divergence term in the vorticity equation. Thermal wind helicity (TWH), as a derivative of SWH, is also discussed here because it links the temperature field and the vertical wind field. These two quantities may be effective for diagnosing a weather system. This paper applies these two quantities in cylindrical coordinates to study the development of Hurricane Andrew to validate their practical use. Through analyzing the hurricane, it is found that TWH can well describe the characteristics of the hurricane such as the strong convection and release of latent heat. SWH is not only a good quantity for diagnosing the weather system, but also an effective one for diagnosing the development of the hurricane.

  14. Incorporation of trinuclear lanthanide(III) hydroxo bridged clusters in macrocyclic frameworks.

    Science.gov (United States)

    Kobyłka, Michał J; Ślepokura, Katarzyna; Acebrón Rodicio, Maria; Paluch, Marta; Lisowski, Jerzy

    2013-11-18

    A cluster of lanthanide(III) or yttrium(III) ions, Ln3(μ3-OH)2, (Ln(III) = Nd(III), Sm(III), Eu(III), Gd(III), Tb(III), Dy(III), Yb(III), or Y(III)) can be bound in the center of a chiral macrocyclic amines H3L1(R), H3L1(S), and H3L2(S) obtained in a reduction of a 3 + 3 condensation product of (1R,2R)- or (1S,2S)-1,2-diaminocyclohexane and 2,6-diformyl-4-methylphenol or 2,6-diformyl-4-tertbutylphenol. X-ray crystal structures of the Nd(III), Sm(III), Gd(III), Dy(III), and Y(III) complexes reveal trinuclear complexes with Ln(III) ions bridged by the phenolate oxygen atoms of the macrocycle as well as by μ3-hydroxo bridges. In the case of the Nd(III) ion, another complex form can be obtained, whose X-ray crystal structure reveals two trinuclear macrocyclic units additionally bridged by hydroxide anions, corresponding to a [Ln3(μ3-OH)]2(μ2-OH)2 cluster encapsulated by two macrocycles. The formation of trinuclear complexes is confirmed additionally by (1)H NMR, electrospray ionization mass spectrometry (ESI MS), and elemental analyses. Titrations of free macrocycles with Sm(III) or Y(III) salts and KOH also indicate that a trinuclear complex is formed in solution. On the other hand, analogous titrations with La(III) salt indicate that this kind of complex is not formed even with the excess of La(III) salt. The magnetic data for the trinuclear Gd(III) indicate weak antiferromagnetic coupling (J = -0.17 cm(-1)) between the Gd(III) ions. For the trinuclear Dy(III) and Tb(III) complexes the χ(M)T vs T plots indicate a more complicated dependence, resulting from the combination of thermal depopulation of mJ sublevels, magnetic anisotropy, and possibly weak antiferromagnetic and ferromagnetic interactions.

  15. A trinuclear ruthenium complex as a highly efficient molecular catalyst for water oxidation.

    Science.gov (United States)

    Zhang, L L; Gao, Y; Liu, Z; Ding, X; Yu, Z; Sun, L C

    2016-03-01

    A trinuclear ruthenium complex, 3, was designed and synthesized with the ligand 2,2'-bipyridine-6,6'-dicarboxylic acid (bda) and we found that this complex could function as a highly efficient molecular catalyst for water oxidation in homogeneous systems. This trinuclear molecular water oxidation catalyst, 3, displayed much higher efficiencies in terms of turnover numbers and initial oxygen evolution rate than its counterparts, a binuclear catalyst, 2, and a mononuclear catalyst, 1, in both chemically driven and photochemically driven water oxidation based on either the whole catalytic molecules or just the active Ru centers. The reasons for the superior performance of catalyst 3 were discussed and we believe that multiple Ru centers in a single molecule are indeed beneficial for increasing the probability of the formation of O-O bonds through an intramolecular radical coupling pathway.

  16. Single molecule magnet behaviour in a rare trinuclear {Cr(III)Dy} methoxo-bridged complex.

    Science.gov (United States)

    Car, Pierre-Emmanuel; Favre, Annaïck; Caneschi, Andrea; Sessoli, Roberta

    2015-09-28

    The reaction of the chromium(iii) chloride tetrahydrofuran complex with the dipivaloylmethane ligand, the lanthanide alcoholic salt DyCl3·CH3OH and the 1,1,1-tris(hydroxymethyl)-ethane ligand resulted in the formation of a new trinuclear chromium-dysprosium complex. Magnetic investigations revealed that the new 3d-4f complex exhibits single molecule magnet behaviour.

  17. Helical surface structures

    CERN Document Server

    Brandenburg, A; Brandenburg, Axel; Blackman, Eric G.

    2002-01-01

    Over the past few years there has been growing interest in helical magnetic field structures seen at the solar surface, in coronal mass ejections, as well as in the solar wind. Although there is a great deal of randomness in the data, on average the extended structures are mostly left-handed on the northern hemisphere and right-handed on the southern. Surface field structures are also classified as dextral (= right bearing) and sinistral (= left bearing) occurring preferentially in the northern and southern hemispheres respectively. Of particular interest here is a quantitative measurement of the associated emergence rates of helical structures, which translate to magnetic helicity fluxes. In this review, we give a brief survey of what has been found so far and what is expected based on models. Particular emphasis is put on the scale dependence of the associated fields and an attempt is made to estimate the helicity flux of the mean field vs. fluctuating field.

  18. Helical superconducting black holes.

    Science.gov (United States)

    Donos, Aristomenis; Gauntlett, Jerome P

    2012-05-25

    We construct novel static, asymptotically five-dimensional anti-de Sitter black hole solutions with Bianchi type-VII(0) symmetry that are holographically dual to superconducting phases in four spacetime dimensions with a helical p-wave order. We calculate the precise temperature dependence of the pitch of the helical order. At zero temperature the black holes have a vanishing entropy and approach domain wall solutions that reveal homogenous, nonisotropic dual ground states with an emergent scaling symmetry.

  19. Trinuclear Cu(Ⅱ) and Zn(Ⅱ) complexes bridged by μ3-carbonato anion

    Institute of Scientific and Technical Information of China (English)

    阎世平; 崔建中; 刘欣; 程鹏; 廖代正; 姜宗慧; 王耕霖; 王宏根; 姚心侃

    1999-01-01

    The trinuclear Cu(Ⅱ) and Zn(Ⅱ) complexes [(CuTPA)3(μ3-CO3)] (ClO4)4(1) and [(ZnTPA)3(μ3-CO3)] (ClO4)4 (2) (TPA=tri(pyridylmethyl) amine) have been synthesized. X-ray structure analysis of the two complexes proves that CO32- anion has an unusual triply bridging ligand, bridging three CuTPA and ZnTPA units respectively, and assembles new trinuclear complexes. The CO32- comes from atmospheric CO2. The structure of each trinuclear unit consists of three copper or zinc atoms in a five-coordinate triangular bipyramidal environment. The [(CuTPA)3 (μ3-CO3)] (ClO4)4 compound shows a very weak antiferromagnetic coupling.

  20. Sulfate-bridged dimeric trinuclear copper(II–pyrazolate complex with three different terminal ligands

    Directory of Open Access Journals (Sweden)

    Gellert Mezei

    2016-08-01

    Full Text Available The reaction of CuSO4·5H2O, 4-chloropyrazole (4-Cl-pzH and triethylamine (Et3N in dimethylformamide (DMF produced crystals of diaquahexakis(μ-4-chloropyrazolato-κ2N:N′bis(N,N-dimethylformamidedi-μ3-hydroxido-bis(μ4-sulfato-κ4O:O′:O′′:O′′hexacopper(II N,N-dimethylformamide tetrasolvate dihydrate, [Cu3(OH(SO4(C3H2ClN23(C3H7NO(H2O]2·4C3H7NO·2H2O. The centrosymmetric dimeric molecule consists of two trinuclear copper–pyrazolate units bridged by two sulfate ions. The title compound provides the first example of a trinuclear copper–pyrazolate complex with three different terminal ligands on the Cu atoms, and also the first example of such complex with a strongly binding basal sulfate ion. Within each trinuclear unit, the CuII atoms are bridged by μ-pyrazolate groups and a central μ3-OH group, and are coordinated by terminal sulfate, H2O and DMF ligands, respectively. Moreover, the sulfate O atoms coordinate at the apical position to the Cu atoms of the symmetry-related unit, providing square–pyramidal coordination geometry around each copper cation. The metal complex and solvent molecules are involved in O—H...O hydrogen bonds, leading to a two-dimensional network parallel to (10-1.

  1. Sulfate-bridged dimeric trinuclear copper(II)-pyrazolate complex with three different terminal ligands.

    Science.gov (United States)

    Mezei, Gellert

    2016-08-01

    The reaction of CuSO4·5H2O, 4-chloro-pyrazole (4-Cl-pzH) and tri-ethyl-amine (Et3N) in di-methyl-formamide (DMF) produced crystals of di-aqua-hexa-kis-(μ-4-chloro-pyrazolato-κ(2) N:N')bis-(N,N-di-methyl-formamide)di-μ3-hydroxido-bis-(μ4-sulfato-κ(4) O:O':O'':O'')hexa-copper(II) N,N-di-methyl-formamide tetra-solvate dihydrate, [Cu3(OH)(SO4)(C3H2ClN2)3(C3H7NO)(H2O)]2·4C3H7NO·2H2O. The centrosymmetric dimeric molecule consists of two trinuclear copper-pyrazolate units bridged by two sulfate ions. The title compound provides the first example of a trinuclear copper-pyrazolate complex with three different terminal ligands on the Cu atoms, and also the first example of such complex with a strongly binding basal sulfate ion. Within each trinuclear unit, the Cu(II) atoms are bridged by μ-pyrazolate groups and a central μ3-OH group, and are coordinated by terminal sulfate, H2O and DMF ligands, respectively. Moreover, the sulfate O atoms coordinate at the apical position to the Cu atoms of the symmetry-related unit, providing square-pyramidal coordination geometry around each copper cation. The metal complex and solvent mol-ecules are involved in O-H⋯O hydrogen bonds, leading to a two-dimensional network parallel to (10-1).

  2. Helicity, Reconnection, and Dynamo Effects

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Hantao

    1998-11-01

    The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo effects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly affects the reconnection rate, as well as the shape of the diffusion region. Conversely, magnetic reconnection events also strongly affect the global helicity, resulting in efficient helicity cancellation (but not dissipation) during counter-helicity reconnection and a finite helicity increase or decrease (but less efficiently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo effects. The turbulent electromotive force along the mean magnetic field (alpha-effect), due to either electrostatic turbulence or the electron diamagnetic effect, transports mean-field helicity across space without dissipation. This has been supported by direct measurements of helicity flux in a laboratory plasma. When the dynamo effect is driven by electromagnetic turbulence, helicity in the turbulent field is converted to mean-field helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery effect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation.

  3. Mathisson's helical motions demystified

    CERN Document Server

    Costa, L Filipe O; Zilhão, Miguel

    2012-01-01

    The motion of spinning test particles in general relativity is described by Mathisson-Papapetrou-Dixon equations, which are undetermined up to a spin supplementary condition, the latter being today still an open question. The Mathisson-Pirani (MP) condition is known to lead to rather mysterious helical motions which have been deemed unphysical, and for this reason discarded. We show that these assessments are unfounded and originate from a subtle (but crucial) misconception. We discuss the kinematical explanation of the helical motions, and dynamically interpret them through the concept of hidden momentum, which has an electromagnetic analogue. We also show that, contrary to previous claims, the frequency of the helical motions coincides exactly with the zitterbewegung frequency of the Dirac equation for the electron.

  4. Helical plasma thruster

    Energy Technology Data Exchange (ETDEWEB)

    Beklemishev, A. D., E-mail: bekl@bk.ru [Budker Institute of Nuclear Physics SB RAS, Novosibirsk (Russian Federation)

    2015-10-15

    A new scheme of plasma thruster is proposed. It is based on axial acceleration of rotating magnetized plasmas in magnetic field with helical corrugation. The idea is that the propellant ionization zone can be placed into the local magnetic well, so that initially the ions are trapped. The E × B rotation is provided by an applied radial electric field that makes the setup similar to a magnetron discharge. Then, from the rotating plasma viewpoint, the magnetic wells of the helically corrugated field look like axially moving mirror traps. Specific shaping of the corrugation can allow continuous acceleration of trapped plasma ions along the magnetic field by diamagnetic forces. The accelerated propellant is expelled through the expanding field of magnetic nozzle. By features of the acceleration principle, the helical plasma thruster may operate at high energy densities but requires a rather high axial magnetic field, which places it in the same class as the VASIMR{sup ®} rocket engine.

  5. Low-valent iron: an Fe(I) ate compound as a building block for a linear trinuclear Fe cluster

    NARCIS (Netherlands)

    Lichtenberg, C.; Viciu, L.; Vogt, M.; Rodríguez-Lugo, R.E.; Adelhardt, M.; Sutter, J.; Khusniyarov, M.M.; Meyer, K.; de Bruin, B.; Bill, E.; Grützmacher, H.

    2015-01-01

    A low-valent trinuclear iron complex with an unusual linear Fe(I)-Fe(II)-Fe(I) unit is presented. It is accessed in a rational approach using a salt metathesis reaction between a new anionic Fe(I) containing heterocycle and FeCl2. Its electronic structure was studied by single crystal XRD analysis,

  6. Changes in magnetic properties from solid state to solution in a trinuclear linear copper(II) complex

    NARCIS (Netherlands)

    Koval, I.A.; Akhideno, H.; Tanase, S.; Belle, C.; Duboc, C.; Saint-Aman, E.; Gamez, P.; Tooke, D.M.; Spek, A.L.; Pierre, J.-L.; Reedijk, J.

    2007-01-01

    A linear trinuclear copper(II) complex containing phenoxido- and alkoxido-bridges between the metal centers has been isolated and structurally characterized. The complex cation consists of a linear array of three copper ions, assembled by means of two doubly deprotonated ligands. The octahedral coor

  7. Flat Helical Nanosieves

    CERN Document Server

    Mei, Shengtao; Hussain, Sajid; Huang, Kun; Ling, Xiaohui; Siew, Shawn Yohanes; Liu, Hong; Teng, Jinghua; Danner, Aaron; Qiu, Cheng-Wei

    2016-01-01

    Compact and miniaturized devices with flexible functionalities are always highly demanded in optical integrated systems. Plasmonic nanosieve has been successfully harnessed as an ultrathin flat platform for complex manipulation of light, including holography, vortex generation and non-linear processes. Compared with most of reported single-functional devices, multi-functional nanosieves might find more complex and novel applications across nano-photonics, optics and nanotechnology. Here, we experimentally demonstrate a promising roadmap for nanosieve-based helical devices, which achieves full manipulations of optical vortices, including its generation, hybridization, spatial multiplexing, focusing and non-diffraction propagation etc., by controlling the geometric phase of spin light via over 121 thousands of spatially-rotated nano-sieves. Thanks to such spin-conversion nanosieve helical elements, it is no longer necessary to employ the conventional two-beam interferometric measurement to characterize optical ...

  8. Helices and vector bundles

    CERN Document Server

    Rudakov, A N

    1990-01-01

    This volume is devoted to the use of helices as a method for studying exceptional vector bundles, an important and natural concept in algebraic geometry. The work arises out of a series of seminars organised in Moscow by A. N. Rudakov. The first article sets up the general machinery, and later ones explore its use in various contexts. As to be expected, the approach is concrete; the theory is considered for quadrics, ruled surfaces, K3 surfaces and P3(C).

  9. Nonlinear helical MHD instability

    Energy Technology Data Exchange (ETDEWEB)

    Zueva, N.M.; Solov' ev, L.S.

    1977-07-01

    An examination is made of the boundary problem on the development of MHD instability in a toroidal plasma. Two types of local helical instability are noted - Alfven and thermal, and the corresponding criteria of instability are cited. An evaluation is made of the maximum attainable kinetic energy, limited by the degree to which the law of conservation is fulfilled. An examination is made of a precise solution to a kinematic problem on the helical evolution of a cylindrical magnetic configuration at a given velocity distribution in a plasma. A numerical computation of the development of MHD instability in a plasma cylinder by a computerized solution of MHD equations is made where the process's helical symmetry is conserved. The development of instability is of a resonance nature. The instability involves the entire cross section of the plasma and leads to an inside-out reversal of the magnetic surfaces when there is a maximum unstable equilibrium configuration in the nonlinear stage. The examined instability in the tore is apparently stabilized by a magnetic hole when certain limitations are placed on the distribution of flows in the plasma. 29 references, 8 figures.

  10. Chemical bonding and aromaticity in trinuclear transition-metal halide clusters.

    Science.gov (United States)

    Weck, Philippe F; Sergeeva, Alina P; Kim, Eunja; Boldyrev, Alexander I; Czerwinski, Kenneth R

    2011-02-07

    Trinuclear transition-metal complexes such as Re(3)X(9) (X = Cl, Br, I), with their uniquely featured structure among metal halides, have posed intriguing questions related to multicenter electron delocalization for several decades. Here we report a comprehensive study of the technetium halide clusters [Tc(3)(μ-X)(3)X(6)](0/1-/2-) (X = F, Cl, Br, I), isomorphous with their rhenium congeners, predicted from density functional theory calculations. The chemical bonding and aromaticity in these clusters are analyzed using the recently developed adaptive natural density partitioning method, which indicates that only [Tc(3)X(9)](2-) clusters exhibit aromatic character, stemming from a d-orbital-based π bond delocalized over the three metal centers. We also show that standard methods founded on the nucleus-independent chemical shift concept incorrectly predict the neutral Tc(3)X(9) clusters to be aromatic.

  11. Crystal structure and solid-state properties of discrete hexa cationic trinuclear zinc triazole cluster

    Indian Academy of Sciences (India)

    Chatla Naga Babu; Paladugu Suresh; Arruri Sathyanarayana; Prasenjit Das; Ganesan Prabusankar

    2015-08-01

    A linear trinuclear cluster of the type [{Zn3 (HTrz)6 (H2O)6}6+ (NO$_{3}^{−}$)6 (H2O)] (ZnT) has been synthesized by one-pot reaction between 1,2,4-triazole and Zn(NO3).6H2O. Molecule consists of three Zn2+ ions linearly connected by 1,2,4-triazole with tri-fold symmetry. The coordination geometry around the zinc centre is octahedral with zinc-zinc separation of 3.810 Å. The coordination environment of central Zn2+ ion is satisfied by nitrogen atoms of six 1,2,4-triazoles, while the geometry of terminal Zn2+ ions is fulfilled by nitrogen atoms of three 1,2,4-triazoles and three water molecules. The thermal and absorption properties of ZnT have been reported for the first time.

  12. NITRATE-SELECTIVE ELECTRODES BASED ON THE TRINUCLEAR CHROMIUM(III PIVALATES

    Directory of Open Access Journals (Sweden)

    Mihail Revenco

    2008-06-01

    Full Text Available The paper describes the analytical potentialities of the trinuclear chromium(III complexes as potentiometric ionophores for the construction of electrodes sensitive to the presence of nitrate anion. The electroactive material containing 4,4’-bipyridil was synthesized in situ. The membrane was prepared using dioctylphthalate as a solvent mediator and poly (vinyl chloride as a polymeric matrix. The electrodes presented a slope of 56 mV/decade, a low limit of detection (3,2.10-6 mol/l, an adequate lifetime (4 months, and suitable selectivity characteristics when compared with other nitrate electrodes. The good parameters of this electrode made possible its application to the determination of nitrate in different types of fertilizers.

  13. The metamorphosis of heterometallic trinuclear antiferromagnetic complexes into nano-sized superparamagnetic spinels.

    Science.gov (United States)

    Vasylenko, Inna V; Gavrylenko, Konstiantyn S; Il'yin, Vladimir G; Golub, Vladimir; Goloverda, Galina; Kolesnichenko, Vladimir; Addison, Anthony W; Pavlishchuk, Vitaly V

    2010-05-15

    Thermal decomposition of the trinuclear heterometallic oxoacetates [Fe(2)M(μ(3)-O)(CH(3)COO)(6)(H(2)O)(3)] has been used as a single-precursor method for synthesis of the spinel-structured ternary oxides MFe(2)O(4) (M = Mn(II), Co(II), and Ni(II)). This facile process occurring at 320 °C results in the formation of nanocrystalline, (7-20 nm) highly pure stoichiometric ferrites in quantitative yield. The magnetic properties of these nanoparticulate ferrites were studied in the 10-300 K temperature range, revealing superparamagnetic behaviour for the Ni and Mn particles and ferromagnetic behavior for the Co ones at room temperature. Their blocking temperatures follow the order: CoFe(2)O(4) > MnFe(2)O(4) > NiFe(2)O(4).

  14. Site-selective detection of vibrational modes of an iron atom in a trinuclear complex

    Energy Technology Data Exchange (ETDEWEB)

    Faus, Isabelle, E-mail: faus@rhrk.uni-kl.de; Rackwitz, Sergej; Wolny, Juliusz A. [University of Kaiserslautern, Department of Physics (Germany); Banerjee, Atanu; Kelm, Harald; Krüger, Hans-Jörg [University of Kaiserslautern, Department of Chemistry (Germany); Schlage, Kai; Wille, Hans-Christian [DESY, PETRA III, P01 (Germany); Schünemann, Volker [University of Kaiserslautern, Department of Physics (Germany)

    2016-12-15

    Nuclear inelastic scattering (NIS) experiments on the trinuclear complex [{sup 57}Fe{L-N_4(CH_2Fc)_2} (CH{sub 3}CN){sub 2}](ClO{sub 4}){sub 2} have been performed. The octahedral iron ion in the complex was labelled with {sup 57}Fe and thereby exclusively the vibrational modes of this iron ion have been detected with NIS. The analysis of nuclear forward scattering (NFS) data yields a ferrous low-spin state for the {sup 57}Fe labelled iron ion. The simulation of the partial density of states (pDOS) for the octahedral low-spin iron(II) ion of the complex by density functional theory (DFT) calculations is in excellent agreement with the experimental pDOS of the complex determined from the NIS data obtained at 80 K. Thereby it was possible to assign almost each of the experimentally observed NIS bands to the corresponding molecular vibrational modes.

  15. Dynamics of the tri-nuclear system at spontaneous fission of $^{252}$Cf

    CERN Document Server

    Tashkhodjaev, R B; Alpomeshev, E Kh

    2016-01-01

    To describe of dynamics of ternary fission of $^{252}$Cf an equation of motion of the tri-nuclear system is calculated. The fission of the $^{70}$Ni+$^{50}$Ca+$^{132}$Sn channel was chosen as one of the more probable channels of true ternary fission of $^{252}$Cf. The collinearity of ternary fission has been checked by analyzing results of the equation of motion. The results show that if initially all nuclei are placed collinearly (potential energy of this position is the smallest) and the component of the middle fragment's initial velocity which is perpendicular to this line, is zero then ternary fission is collinear, otherwise the non collinear ternary fission takes place.

  16. Helical CT for lumbosacral spinal

    Energy Technology Data Exchange (ETDEWEB)

    Tatsuno, Satoshi; Fukuda, Kunihiko [Jikei Univ., Tokyo (Japan). School of Medicine

    1996-10-01

    The aim of this study was to investigate the efficacy of helical CT for lumbosacral pathology. We performed helical CT with multiplanar reconstruction, including the formation of oblique transaxial and coronal images, in 62 patients with various lumboscral disorders, including 32 non-enhanced CT and 36 CT after myelography. We correlated the appearance of the stenotic spinal canal and neoplastic disease with the findings on MRI obtained at nearly the same time. We obtained helical CT images in all cases in about 30 seconds. The diagnostic ability of helical CT was roughly equal to that of MRI in patients with spondylosis deformans, spondylolisthesis and herniated nucleus pulposus. There was no significant difference in diagnostic value for degenerative lumbosacral disease with canal and foraminal stenosis between non-enhanced and post-myelography helical CT. However, non-enhanced helical CT could not clearly demonstrate neoplastic disease because of the poor contrast resolution. Helical CT was useful in evaluating degenerative disorder and its diagnostic value was nearly equal to that of MRI. We considered that helical CT may be suitable for the assessment of patients with severe lumbago owing to the markedly shortened examination time. However, if helical CT is used as a screening method for lumbosacral disease, one must be careful of its limitations, for example, poor detectability of neoplastic disease, vascular anomalies and so on. (author)

  17. Helicity Transfer in Turbulent Models

    CERN Document Server

    Biferale, L; Toschi, F

    1998-01-01

    Helicity transfer in a shell model of turbulence is investigated. We show that a Reynolds-independent helicity flux is present in the model when the large scale forcing breaks inversion symmetry. The equivalent in Shell Models of the ``2/15 law'', obtained from helicity conservation in Navier-Stokes eqs., is derived and tested. The odd part of helicity flux statistic is found to be dominated by a few very intense events. In a particular model, we calculate analytically leading and sub-leading contribution to the scaling of triple velocity correlation.

  18. Employing Helicity Amplitudes for Resummation

    NARCIS (Netherlands)

    Moult, I.; Stewart, I.W.; Tackmann, F.J.; Waalewijn, W.J.

    2015-01-01

    Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are dire

  19. Quark Helicity and Transversity Distributions

    CERN Document Server

    Hwang, Dae Sung

    2016-01-01

    The quark transversity distribution inside nucleon is less understood than the quark unpolarized and helicity distributions inside nucleon. In particular, it is important to know clearly why the quark helicity and transversity distributions are different. We investigate the origin of their discrepancy.

  20. Magnetic design constraints of helical solenoids

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, M. L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Krave, S. T. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Tompkins, J. C. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Yonehara, K. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Flanagan, G. [Muons Inc., Batavia, IL (United States); Kahn, S. A. [Muons Inc., Batavia, IL (United States); Melconian, K. [Texas A & M Univ., College Station, TX (United States)

    2015-01-30

    Helical solenoids have been proposed as an option for a Helical Cooling Channel for muons in a proposed Muon Collider. Helical solenoids can provide the required three main field components: solenoidal, helical dipole, and a helical gradient. In general terms, the last two are a function of many geometric parameters: coil aperture, coil radial and longitudinal dimensions, helix period and orbit radius. In this paper, we present design studies of a Helical Solenoid, addressing the geometric tunability limits and auxiliary correction system.

  1. The Advanced Helical Generator

    Energy Technology Data Exchange (ETDEWEB)

    Reisman, D B; Javedani, J B; Ellsworth, G F; Kuklo, R M; Goerz, D A; White, A D; Tallerico, L J; Gidding, D A; Murphy, M J; Chase, J B

    2009-10-26

    A high explosive pulsed power (HEPP) generator called the Advanced Helical Generator (AHG) has been designed, built, and successfully tested. The AHG incorporates design principles of voltage and current management to obtain a high current and energy gain. Its design was facilitated by the use of modern modeling tools as well as high precision manufacture. The result was a first-shot success. The AHG delivered 16 Mega-Amperes of current and 11 Mega-Joules of energy to a quasi-static 80 nH inductive load. A current gain of 154 times was obtained with a peak exponential rise time of 20 {micro}s. We will describe in detail the design and testing of the AHG.

  2. Helicity dependent parton distributions

    CERN Document Server

    Scopetta, Sergio; 10.4249/scholarpedia.10226

    2011-01-01

    The helicity dependent parton distributions describe the number density of partons with given longitudinal momentum x and given polarization in a hadron polarized longitudinally with respect to its motion. After the discovery, more than 70 years ago, that the proton is not elementary, the observation of Bjorken scaling in the late 1960s lead to the idea of hadrons containing almost pointlike constituents, the partons. Since then, Deep Inelastic Scattering (DIS) has played a crucial role in our understanding of hadron structure. Through DIS experiments it has been possible to link the partons to the quarks, and to unveil the presence of other pointlike constituents, the gluons, which lead into a dynamical theory of quarks and gluons - quantum chromodynamics (QCD). Polarized DIS, i.e. the collision of a longitudinally polarized lepton beam on a polarized target (either longitudinally or transversely polarized), provides a complementary information regarding the structure of the nucleon. Whereas ordinary DIS pro...

  3. Coordination geometry around copper in a Schiff-base trinuclear copper complex using EXAFS spectroscopy

    Science.gov (United States)

    Gaur, Abhijeet; Shrivastava, B. D.; Gaur, D. C.; Prasad, J.; Srivastava, K.; Jha, S. N.; Bhattacharyya, D.; Poswal, A.

    2012-05-01

    In the present investigation, we have studied extended X-ray absorption fine structure (EXAFS) spectra of a trinuclear Schiff-base copper complex tetraaqua-di-μ3-(N-salicylidene-DL-glutamato)-tricopper(II)heptahydrate, [Cu3(C12H10NO5)2 (H2O)4]. 7H2O, in which three metal sites are present. One metal site is square-pyramidal (4+1) and other two similar metal sites are tetragonally distorted octahedral (4+2). EXAFS has been recorded at the K-edge of copper in the complex at the dispersive EXAFS beamline at 2 GeV Indus-2 synchrotron source at RRCAT, Indore, India. The analysis of EXAFS spectra of multinuclear metal complexes pose some problems due to the presence of many absorbing atoms, even when the absorbing atoms may be of the same element. Hence, using the available crystal structure of the complex, theoretical models have been generated for the different copper sites separately, which are then fitted to the experimental EXAFS data. The two coordination geometries around the copper sites have been determined. The contributions of the different copper sites to the experimental spectrum have been estimated. The structural parameters, which include bond-lengths, coordination numbers and thermal disorders, for the two types of copper sites have been reported. Further, copper has been found to be in +2 oxidation state at these metal sites.

  4. Magneto-structural correlations in trinuclear Cu(II) complexes: a density functional study

    CERN Document Server

    Rodríguez-Forteá, A; Alvarez, S; Centre-De Recera-En-Quimica-Teorica; Alemany, P A; Centre-De Recera-En-Quimica-Teorica

    2003-01-01

    Density functional theoretical methods have been used to study magneto-structural correlations for linear trinuclear hydroxo-bridged copper(II) complexes. The nearest-neighbor exchange coupling constant shows very similar trends to those found earlier for dinuclear compounds for which the Cu-O-Cu angle and the out of plane displacement of the hydrogen atoms at the bridge are the two key structural factors that determine the nature of their magnetic behavior. Changes in these two parameters can induce variations of over 1000 cm sup - sup 1 in the value of the nearest-neighbor coupling constant. On the contrary, coupling between next-nearest neighbors is found to be practically independent of structural changes with a value for the coupling constant of about -60 cm sup - sup 1. The magnitude calculated for this coupling constant indicates that considering its value to be negligible, as usually done in experimental studies, can lead to considerable errors, especially for compounds in which the nearest-neighbor c...

  5. Di- and Trinuclear Mixed-Valence Copper Amidinate Complexes from Reduction of Iodine.

    Science.gov (United States)

    Lane, Andrew C; Barnes, Charles L; Antholine, William E; Wang, Denan; Fiedler, Adam T; Walensky, Justin R

    2015-09-08

    Molecular examples of mixed-valence copper complexes through chemical oxidation are rare but invoked in the mechanism of substrate activation, especially oxygen, in copper-containing enzymes. To examine the cooperative chemistry between two metals in close proximity to each other we began studying the reactivity of a dinuclear Cu(I) amidinate complex. The reaction of [(2,6-Me2C6H3N)2C(H)]2Cu2, 1, with I2 in tetrahydrofuran (THF), CH3CN, and toluene affords three new mixed-valence copper complexes [(2,6-Me2C6H3N)2C(H)]2Cu2(μ2-I3)(THF)2, 2, [(2,6-Me2C6H3N)2C(H)]2Cu2(μ2-I) (NCMe)2, 3, and [(2,6-Me2C6H3N)2C(H)]3Cu3(μ3-I)2, 4, respectively. The first two compounds were characterized by UV-vis and electron paramagnetic resonance spectroscopies, and their molecular structure was determined by X-ray crystallography. Both di- and trinuclear mixed-valence intermediates were characterized for the reaction of compound 1 to compound 4, and the molecular structure of 4 was determined by X-ray crystallography. The electronic structure of each of these complexes was also investigated using density functional theory.

  6. Heterometallic Trinuclear Carbonyl Sulfido Clusters and the Tetranuclear Intermediate via Electrophilic Addition-Elimination Reaction

    Institute of Scientific and Technical Information of China (English)

    孙文华; 杨世琰; 汪汉卿; 周全福; 郁开北

    1994-01-01

    The reaction of HFe2Co(CO)9(μ3-S)with(η5-C5H4CH3)Mo(CO)3CI has been carried outin refluxing tetrahydrofuran(THF)to give out heterometallic trinuclear clusters(η5-C5H4CH3)MoFeCo-(CO)8(μ3-S)and(η5-C5H4CH3)2Mo2Fe(CO)7(μ3-S)by electrophilic addition-elimination reaction.Howev-er,(η5-C5H4CH3)Fe(CO)2Cl reacted with HFe2Co(CO)9(μ3-S)at room temperature to yield a tetranuclearcluster(η5-C5H4CH3)Fe3Co(CO)11(μ4-S).The μ4-S cluster could be used as an intermediate in confirmationof the mechanism of the electrophilic addition-elimination reaction.The syntheses,characterizations andX-ray crystal structures of these clusters are reported herein as well as the discussion on the reaction mecha-nism.

  7. A monofunctional trinuclear platinum complex with steric hindrance demonstrates strong cytotoxicity against tumor cells.

    Science.gov (United States)

    Wu, Shangnong; Wang, Xiaoyong; He, Yafeng; Zhu, Zhenzhu; Zhu, Chengcheng; Guo, Zijian

    2014-10-01

    Polynuclear platinum complexes constitute a special class of hopeful antitumor agents. In this study, a Y-type monofunctional trinuclear platinum complex (MTPC) with 1,3,5-tris(pyridin-2-ylmethoxy)benzene, ammine and chloride as ligands was synthesized and characterized by (1)H NMR and electrospray ionization mass spectrometry (ESI-MS). The DNA binding mode of MTPC was investigated using circular dichroism spectroscopy and gel electrophoresis, and the reactivity of MTPC towards glutathione was studied by (1)H NMR and ESI-MS. The results show that MTPC can affect the conformation of calf-thymus DNA (CT-DNA) significantly and tends to form 1,4-GG rather than 1,2-GG intrastrand crosslinks, which are different from the instance of cisplatin. MTPC reacts with glutathione quite slowly in comparison with cisplatin because of the steric hindrance. The cytotoxicity of MTPC was tested on the human breast cancer cell line MCF-7, the human non-small-cell lung cancer cell line A549, and the human ovarian cancer cell line Skov-3 by the MTT [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide] assay. MTPC is more potent than or comparable to cisplatin. The cellular inhibition mode of MTPC was examined by flow cytometry using MCF-7 cells. MTPC arrests the cell cycle mainly in G2 or M phase, while cisplatin arrests the cell cycle in S phase. Similar to cisplatin, MTPC kills the cells predominantly through an apoptotic pathway.

  8. Noncovalent interactions between a trinuclear monofunctional platinum complex and human serum albumin.

    Science.gov (United States)

    Wang, Yanqing; Wang, Xiaoyong; Wang, Jing; Zhao, Yongmei; He, Weijiang; Guo, Zijian

    2011-12-19

    Interactions between platinum complexes and human serum albumin (HSA) play crucial roles in the metabolism, distribution, and efficacy of platinum-based anticancer drugs. Polynuclear monofunctional platinum(II) complexes represent a new class of anticancer agents that display distinct molecular characters of pharmacological action from those of cisplatin. In this study, the interaction between a trinuclear monofunctional platinum(II) complex, [Pt(3)LCl(3)](ClO(4))(3) (L = N,N,N',N',N",N"-hexakis(2-pyridylmethyl)-1,3,5-tris(aminomethyl)benzene) (1), and HSA was investigated using ultraviolet-visible spectroscopy, Fourier transform infrared spectroscopy, circular dichroism spectroscopy, fluorescence spectroscopy, molecular docking, and inductively coupled plasma mass spectrometry. The spectroscopic and thermodynamic data show that the interaction is a spontaneous process with the estimated enthalpy and entropy changes being 14.6 kJ mol(-1) and 145.5 J mol(-1) K(-1), respectively. The reactive sites of HSA to complex 1 mainly locate within its hydrophobic cavity in domain II. Noncovalent actions such as π-π stacking and hydrophobic bonding are the primary contributors to the interaction between HSA and complex 1, which is different from the scenario for cisplatin in similar conditions. The results suggest that the connection between complex 1 and HSA is reversible, and therefore the cytotoxic activity of the complex could be preserved during blood circulation.

  9. Turbulent Dynamos and Magnetic Helicity

    Energy Technology Data Exchange (ETDEWEB)

    Ji, Hantao

    1999-04-01

    It is shown that the turbulent dynamo alpha-effect converts magnetic helicity from the turbulent field to the mean field when the turbulence is electromagnetic while the magnetic helicity of the mean-field is transported across space when the turbulence is elcetrostatic or due to the elcetron diamagnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity expect for a battery effect which vanishes in the limit of magnetohydrodynamics. Implications for astrophysical situations, especially for the solar dynamo, are discussed.

  10. SPring-8 twin helical undulator.

    Science.gov (United States)

    Hara, T; Tanaka, T; Tanabe, T; Maréchal, X M; Kumagai, K; Kitamura, H

    1998-05-01

    There are several ways of producing circularly polarized light, such as using asymmetric devices, crossed undulators etc. The SPring-8 helical undulator introduces a simple way of producing both horizontal and vertical fields in one undulator. All the magnet arrays are arranged above and below the plane of the electron orbit, so there is no limitation of access from the sides of the undulator. For the SPring-8 BL25SU, two helical undulators will be installed in tandem, and the helicity of the polarization can be switched at up to 10 Hz using five kicker magnets.

  11. Decay of helical and non-helical magnetic knots

    CERN Document Server

    Candelaresi, Simon

    2011-01-01

    We present calculations of the relaxation of magnetic field structures that have the shape of particular knots and links. A set of helical magnetic flux configurations is considered, which we call $n$-foil knots of which the trefoil knot is the most primitive member. We also consider two non-helical knots, namely the Borromean rings as well as a single interlocked flux rope that also serves as the logo of the Inter-University Centre for Astronomy and Astrophysics in Pune, India. The field decay characteristics of both configurations is investigated and compared with previous calculations of helical and non-helical triple ring configurations. For the $n$-foil knots the decay is described by power laws that range form $t^{-2/3}$ to $t^{-1/3}$, which can be as slow as the $t^{-1/3}$ behavior for helical triple-ring structures that was seen in earlier work. The two non-helical configurations decay like $t^{-1}$, which is somewhat slower than the previously obtained $t^{-3/2}$ behavior in the decay of interlocked ...

  12. Magnetic Helicity and Planetary Dynamos

    Science.gov (United States)

    Shebalin, John V.

    2012-01-01

    A model planetary dynamo based on the Boussinesq approximation along with homogeneous boundary conditions is considered. A statistical theory describing a large-scale MHD dynamo is found, in which magnetic helicity is the critical parameter

  13. Asymmetric catalysis with helical polymers

    NARCIS (Netherlands)

    Megens, Rik P.; Roelfes, Gerard

    Inspired by nature, the use of helical biopolymer catalysts has emerged over the last years as a new approach to asymmetric catalysis. In this Concept article the various approaches and designs and their application in asymmetric catalysis will be discussed.

  14. Asymmetric catalysis with helical polymers

    NARCIS (Netherlands)

    Megens, Rik P.; Roelfes, Gerard

    2011-01-01

    Inspired by nature, the use of helical biopolymer catalysts has emerged over the last years as a new approach to asymmetric catalysis. In this Concept article the various approaches and designs and their application in asymmetric catalysis will be discussed.

  15. Modeling helicity dissipation-rate equation

    CERN Document Server

    Yokoi, Nobumitsu

    2016-01-01

    Transport equation of the dissipation rate of turbulent helicity is derived with the aid of a statistical analytical closure theory of inhomogeneous turbulence. It is shown that an assumption on the helicity scaling with an algebraic relationship between the helicity and its dissipation rate leads to the transport equation of the turbulent helicity dissipation rate without resorting to a heuristic modeling.

  16. Cyclic Trinuclear Gold(I) Clusters with N,N and Unusual C,C Mixed-Ligand Bridges.

    Science.gov (United States)

    Melgarejo, Doris Y; Chiarella, Gina M; Fackler, John P

    2016-11-21

    Three crystalline trinuclear gold(I) clusters, [Au3f2y] (1), [Au3fy2] (2), and [Au3y3] (3), where f = N,N'-bis(2,6-dimethylphenyl)methanimidamidate and y = dimethylendiphenylphosphinate, exhibit bridges from the N,N-formamidinate and/or from the ylide anion ligand whose P-methylene groups chelate in an unusual fashion, where the chelate CPC unit is perpendicular to the trigonal plane of the metal atoms. Assemblies 1 and 2 are the first gold(I) trinuclear clusters featuring mixed-ligand bridges from different N,N and C,C donors; 3 is a previously unknown homoleptic ylide anion cyclic trinuclear assembly. Formamidinate bridges in 1 and 2 connect gold(I) atoms at aurophilic distances of 3.084(2) and 3.0543(4) Å, whereas an out-of-plane (perpendicular) P-ylide anion bite produces Au(I)-Au(I) distances of as large as 3.900(2) Å in 3. The crystal space groups for 1 and 2 are triclinic P1̅ and that for 3 is monoclinic P21/c, with Z = 2 for 1 and 2 and Z = 4 for 3. Compounds are synthesized under Schlenk conditions at -20 °C in toluene by reacting the proper ratios of the gold(I) formamidinate [Au2f2] with the phosphorus ylide [Hy] under basic conditions (KOH), followed by extraction with ether. This synthesis also produces a dinuclear cation, [Au2f(Hy)2](+), previously reported by our group. A neutral mixed-ligand dinuclear complex, [Au2fy], was not observed. Under UV light, 1 and 2 display a bright-green luminescence at room temperature and in frozen methyltetrahydrofuran solutions under liquid nitrogen, with microsecond lifetimes. All three complexes 1-3 are characterized by their X-ray crystal structures, (1)H NMR, IR, UV-visible, and luminescence spectroscopies, and elemental analysis.

  17. The next large helical devices

    Science.gov (United States)

    Iiyoshi, Atsuo; Yamazaki, Kozo

    1995-06-01

    Helical systems have the strong advantage of inherent steady-state operation for fusion reactors. Two large helical devices with fully superconducting coil systems are presently under design and construction. One is the LHD (Large Helical Device) [Fusion Technol. 17, 169 (1990)] with major radius=3.9 m and magnetic field=3-4 T, that is under construction during 1990-1997 at NIFS (National Institute for Fusion Science), Nagoya/Toki, Japan; it features continuous helical coils and a clean helical divertor focusing on edge configuration optimization. The other one in the W7-X (Wendelstein 7-X) [in Plasma Physics and Controlled Fusion Nuclear Research, 1990, (International Atomic Energy Agency, Vienna, 1991), Vol. 3, p. 525] with major radius=5.5 m and magnetic field=3 T, that is under review at IPP (Max-Planck Institute for Plasma Physics), Garching, Germany; it has adopted a modular coil system after elaborate optimization studies. These two programs are complementary in promoting world helical fusion research and in extending the understanding of toroidal plasmas through comparisons with large tokamaks.

  18. omega-Helices in proteins.

    Science.gov (United States)

    Enkhbayar, Purevjav; Boldgiv, Bazartseren; Matsushima, Norio

    2010-05-01

    A modification of the alpha-helix, termed the omega-helix, has four residues in one turn of a helix. We searched the omega-helix in proteins by the HELFIT program which determines the helical parameters-pitch, residues per turn, radius, and handedness-and p = rmsd/(N - 1)(1/2) estimating helical regularity, where "rmsd" is the root mean square deviation from the best fit helix and "N" is helix length. A total of 1,496 regular alpha-helices 6-9 residues long with p < or = 0.10 A were identified from 866 protein chains. The statistical analysis provides a strong evidence that the frequency distribution of helices versus n indicates the bimodality of typical alpha-helix and omega-helix. Sixty-two right handed omega-helices identified (7.2% of proteins) show non-planarity of the peptide groups. There is amino acid preference of Asp and Cys. These observations and analyses insist that the omega-helices occur really in proteins.

  19. Employing Helicity Amplitudes for Resummation

    CERN Document Server

    Moult, Ian; Tackmann, Frank J; Waalewijn, Wouter J

    2015-01-01

    Many state-of-the-art QCD calculations for multileg processes use helicity amplitudes as their fundamental ingredients. We construct a simple and easy-to-use helicity operator basis in soft-collinear effective theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are directly given in terms of color-ordered helicity amplitudes. Using this basis allows one to seamlessly combine fixed-order helicity amplitudes at any order they are known with a resummation of higher-order logarithmic corrections. In particular, the virtual loop amplitudes can be employed in factorization theorems to make predictions for exclusive jet cross sections without the use of numerical subtraction schemes to handle real-virtual infrared cancellations. We also discuss matching onto SCET in renormalization schemes with helicities in $4$- and $d$-dimensions. To demonstrate that our helicity operator basis is easy to use, we provide an explicit construction of the operator basis, as well as results for the hard m...

  20. Trinuclear lanthanide complexes of a compartmental ligand N, N'-bis(2-pyridinyl)-2,6-pyridinedicarboxamide: A spectroscopic investigation

    Science.gov (United States)

    Gudasi, Kalagouda B.; Shenoy, Rashmi V.; Vadavi, Ramesh S.; Patil, Siddappa A.

    2006-11-01

    Trinuclear lanthanide complexes of the formula [Ln 3(PPDA)(NO 3) 6(H 2O) 2]·NO 3·2H 2O where Ln = La(III), Pr(III), Sm(III), Nd(III), Eu(III) Gd(III) Tb(III), Dy(III) and Y(III); H 2PPDA = N, N'-bis(2-pyridinyl)-2,6-pyridinedicarboxamide, have been isolated. The complexes were characterized by elemental analyses, conductivity measurements, magnetic susceptibility measurements and spectral (IR, NMR, UV-vis, fluorescence, FAB and EPR) and thermal studies.

  1. Halogen-bonded network of trinuclear copper(II 4-iodopyrazolate complexes formed by mutual breakdown of chloroform and nanojars

    Directory of Open Access Journals (Sweden)

    Stuart A. Surmann

    2016-11-01

    Full Text Available Crystals of bis(tetrabutylammonium di-μ3-chlorido-tris(μ2-4-iodopyrazolato-κ2N:N′tris[chloridocuprate(II] 1,4-dioxane hemisolvate, (C16H36N2[Cu3(C3H2IN23Cl5]·0.5C4H8O or (Bu4N2[CuII3(μ3-Cl2(μ-4-I-pz3Cl3]·0.5C4H8O, were obtained by evaporating a solution of (Bu4N2[{CuII(μ-OH(μ-4-I-pz}nCO3] (n = 27–31 nanojars in chloroform/1,4-dioxane. The decomposition of chloroform in the presence of oxygen and moisture provides HCl, which leads to the breakdown of nanojars to the title trinuclear copper(II pyrazolate complex, and possibly CuII ions and free 4-iodopyrazole. CuII ions, in turn, act as catalyst for the accelerated decomposition of chloroform, ultimately leading to the complete breakdown of nanojars. The crystal structure presented here provides the first structural description of a trinuclear copper(II pyrazolate complex with iodine-substituted pyrazoles. In contrast to related trinuclear complexes based on differently substituted 4-R-pyrazoles (R = H, Cl, Br, Me, the [Cu3(μ-4-I-pz3Cl3] core in the title complex is nearly planar. This difference is likely a result of the presence of the iodine substituent, which provides a unique, novel feature in copper pyrazolate chemistry. Thus, the iodine atoms form halogen bonds with the terminal chlorido ligands of the surrounding complexes [mean length of I...Cl contacts = 3.48 (1 Å], leading to an extended two-dimensional, halogen-bonded network along (-110. The cavities within this framework are filled by centrosymmetric 1,4-dioxane solvent molecules, which create further bridges via C—H...Cl hydrogen bonds with terminal chlorido ligands of the trinuclear complex not involved in halogen bonding.

  2. Characterization of a trinuclear ruthenium species in catalytic water oxidation by Ru(bda)(pic)2 in neutral media.

    Science.gov (United States)

    Zhang, Biaobiao; Li, Fei; Zhang, Rong; Ma, Chengbing; Chen, Lin; Sun, Licheng

    2016-06-30

    A Ru(III)-O-Ru(IV)-O-Ru(III) type trinuclear species was crystallographically characterized in water oxidation by Ru(bda)(pic)2 (H2bda = 2,2'-bipyridine-6,6'-dicarboxylic acid; pic = 4-picoline) under neutral conditions. The formation of a ruthenium trimer due to the reaction of Ru(IV)[double bond, length as m-dash]O with Ru(II)-OH2 was fully confirmed by chemical, electrochemical and photochemical methods. Since the oxidation of the trimer was proposed to lead to catalyst decomposition, the photocatalytic water oxidation activity was rationally improved by the suppression of the formation of the trimer.

  3. Reversible Redox Activity in Multicomponent Metal-Organic Frameworks Constructed from Trinuclear Copper Pyrazolate Building Blocks.

    Science.gov (United States)

    Tu, Binbin; Pang, Qingqing; Xu, Huoshu; Li, Xiaomin; Wang, Yulin; Ma, Zhen; Weng, Linhong; Li, Qiaowei

    2017-06-14

    Inorganic functionalization of metal-organic frameworks (MOFs), such as incorporation of multiple inorganic building blocks with distinct metals into one structure and further modulation of the metal charges, endows the porous materials with significant properties toward their applications in catalysis. In this work, by an exploration of the role of 4-pyrazolecarboxylic acid (H2PyC) in the formation of trinuclear copper pyrazolate as a metalloligand in situ, four new MOFs with multiple components in order were constructed through one-pot synthesis. This metalloligand strategy provides multicomponent MOFs with new topologies (tub for FDM-4 and tap for FDM-5) and is also compatible with a second organic linker for cooperative construction of complex MOFs (1,4-benzenedicarboxylic acid for FDM-6 and 2,6-naphthalenedicarboxylic acid for FDM-7). The component multiplicity of these MOFs originates from PyC's ability to separate Cu and Zn on the basis of their differentiated binding affinities toward pyrazolate and carboxylate. These MOFs feature reversible and facile redox transformations between Cu(I)3(PyC)3 and Cu(II)3(μ-OH)(PyC)3(OH)3 without altering the connecting geometries of the units, thus further contributing to the significant catalytic activities in the oxidation of CO and aromatic alcohols and the decomposition of H2O2. This study on programming multiple inorganic components into one framework and modulating their electronic structures is an example of functionalizing the inorganic units of MOFs with a high degree of control.

  4. Mononuclear, Dinuclear, and Trinuclear Iron Complexes Featuring a New Monoanionic SNS Thiolate Ligand.

    Science.gov (United States)

    Das, Uttam K; Daifuku, Stephanie L; Gorelsky, Serge I; Korobkov, Ilia; Neidig, Michael L; Le Roy, Jennifer J; Murugesu, Muralee; Baker, R Tom

    2016-01-19

    The new tridentate ligand, S(Me)N(H)S = 2-(2-methylthiophenyl)benzothiazolidine, prepared in a single step from commercial precursors in excellent yield, undergoes ring-opening on treatment with Fe(OTf)2 in the presence of base affording a trinuclear iron complex, [Fe3(μ2-S(Me)NS(-))4](OTf)2 (1) which is fully characterized by structural and spectroscopic methods. X-ray structural data reveal that 1 contains four S(Me)NS(-) ligands meridionally bound to two pseudooctahedral iron centers each bridged by two thiolates to a distorted tetrahedral central iron. The combined spectroscopic (UV-vis, Mössbauer, NMR), magnetic (solution and solid state), and computational (DFT) studies indicate that 1 includes a central, high-spin Fe(II) (S = 2) with two low-spin (S = 0) peripheral Fe(II) centers. Complex 1 reacts with excess PMePh2, CNxylyl (2,6-dimethylphenyl isocyanide), and P(OMe)3 in CH3CN to form diamagnetic, thiolate-bridged, dinuclear Fe(II) complexes {[Fe(μ-S(Me)NS(-))L2]2}(OTf)2 (2-4). These complexes are characterized by elemental analysis; (1)H NMR, IR, UV-vis, and Mössbauer spectroscopy; and single crystal X-ray diffraction. Interestingly, addition of excess P(OMe)3 to complex 1 in CH2Cl2 produces primarily the diamagnetic, mononuclear Fe(II) complex, {Fe(S(Me)NS(-))[P(OMe)3]3}(OTf) (5).

  5. Synthesis and spectral characterization of trinuclear, oxo-centered, carboxylate-bridged, mixed-valence iron complexes with Schiff bases.

    Science.gov (United States)

    Singh, Atresh Kumar; Singh, Alok Kumar

    2012-10-01

    Some novel trinuclear, oxo-centered, carboxylate-bridged, mixed-valence iron complexes of the general formula [Fe(3)O(OOCR)(3)(SB)(3)L(3)] (where R=C(13)H(27), C(15)H(31) or C(17)H(35,) HSB=Schiff bases and L=Ethanol) have been synthesized by the stepwise substitutions of acetate ions from μ(3)-oxo-hexa(acetato)tri(aqua)iron(II)diiron(III), first with straight chain carboxylic acids and then with Schiff bases. The complexes were characterized by elemental analyses, molecular weight determinations and spectral (electronic, infrared, FAB mass, Mössbauer and powder XRD) studies. Molar conductance measurements indicated the complexes to be non-electrolytes in nitrobenzene. Bridging nature of carboxylate and Schiff base anions in the complexes was established by their infrared spectra. Mössbauer spectroscopic studies indicated two quadrupole-split doublets due to Fe(II) and Fe(III) ions at 80, 200 and 295K, confirming the complexes are mixed-valence species. This was also supported by the observed electronic spectra of the complexes. Magnetic susceptibility measurements displayed octahedral geometry around iron in mixed-valence state and a net antiferromagnetic exchange coupling via μ-oxo atom. Trinuclear nature of the complexes was confirmed by their molecular weight determination and FAB mass spectra. A plausible structure for these complexes has been established on the basis of spectral and magnetic moment data.

  6. Unprecedented trinuclear Ag(I) complex with 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine as an efficient catalyst for the aziridination of olefins.

    Science.gov (United States)

    Safin, Damir A; Pialat, Amélie; Korobkov, Ilia; Murugesu, Muralee

    2015-04-13

    An unprecedented trinuclear heteroleptic Ag(I) complex was isolated using a stable multidentate 2,4,6-tris(2-pyrimidyl)-1,3,5-triazine (TPymT) ligand. The obtained compound is an efficient catalyst for the direct aziridination of terminal olefins.

  7. Coupling of metal-based light-harvesting antennas and electron-donor subunits: Trinuclear Ruthenium(II) complexes containing tetrathiafulvalene-substituted polypyridine ligands

    DEFF Research Database (Denmark)

    Campagna, Sebastiano; Serroni, Scolastica; Puntoriero, Fausto

    2002-01-01

    Three new tetrathiafulvalene-substituted 2,2'-bipyridine ligands, cis-bpy-TTF1, trans-bpy-TTF1, and cis-bpy-TTF2 have been prepared and characterized. X-ray analysis of trans-bpy-TTF1, is also reported. Such ligands have been used to prepare two new trinuclear Ru-II complexes, namely, [{(bpy)(2)R...

  8. Synthesis and X-ray crystal structure of a novel organometallic (µ(3)-oxido)(µ(3)-imido) trinuclear iridium complex

    DEFF Research Database (Denmark)

    Schau-Magnussen, Magnus; Malcho, Phillip; Herbst, Konrad

    2011-01-01

    Reaction of the organometallic aqua ion [Cp*Ir(H(2)O)(3)](2+) with tert-butyl(trimethylsilyl)amine in acetone yielded a novel trinuclear (µ(3)-oxido)(µ(3)-imido)pentamethylcyclopentadienyliridium(iii) complex, [(Cp*Ir)(3)(O)(N(t)Bu)](2+). Single crystal structure analyses show the complex can...

  9. Generalized helicity and Beltrami fields

    Energy Technology Data Exchange (ETDEWEB)

    Buniy, Roman V., E-mail: roman.buniy@gmail.com [Schmid College of Science, Chapman University, Orange, CA 92866 (United States); Isaac Newton Institute, University of Cambridge, Cambridge, CB3 0EH (United Kingdom); Kephart, Thomas W., E-mail: tom.kephart@gmail.com [Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235 (United States); Isaac Newton Institute, University of Cambridge, Cambridge, CB3 0EH (United Kingdom)

    2014-05-15

    We propose covariant and non-abelian generalizations of the magnetic helicity and Beltrami equation. The gauge invariance, variational principle, conserved current, energy–momentum tensor and choice of boundary conditions elucidate the subject. In particular, we prove that any extremal of the Yang–Mills action functional 1/4 ∫{sub Ω}trF{sub μν}F{sup μν}d{sup 4}x subject to the local constraint ε{sup μναβ}trF{sub μν}F{sub αβ}=0 satisfies the covariant non-abelian Beltrami equation. -- Highlights: •We introduce the covariant non-abelian helicity and Beltrami equation. •The Yang–Mills action and instanton term constraint lead to the Beltrami equation. •Solutions of the Beltrami equation conserve helicity.

  10. Brownian motion of helical flagella.

    Science.gov (United States)

    Hoshikawa, H; Saito, N

    1979-07-01

    We develops a theory of the Brownian motion of a rigid helical object such as bacterial flagella. The statistical properties of the random forces acting on the helical object are discussed and the coefficients of the correlations of the random forces are determined. The averages , and are also calculated where z and theta are the position along and angle around the helix axis respectively. Although the theory is limited to short time interval, direct comparison with experiment is possible by using the recently developed cinematography technique.

  11. Optical and Infrared Helical Metamaterials

    Directory of Open Access Journals (Sweden)

    Kaschke Johannes

    2016-09-01

    Full Text Available By tailoring metamaterials with chiral unit cells, giant optical activity and strong circular dichroism have been achieved successfully over the past decade. Metamaterials based on arrays of metal helices have revolutionized the field of chiral metamaterials, because of their capability of exhibiting these pronounced chiro-optical effects over previously unmatched bandwidths. More recently, a large number of new metamaterial designs based on metal helices have been introduced with either optimized optical performance or other chiro-optical properties for novel applications.

  12. A hypothesis on neutrino helicity

    CERN Document Server

    Sahin, I

    2016-01-01

    It is firmly established by experimental results that neutrinos are almost 100\\% longitudinally polarized and left-handed. It is also confirmed by neutrino oscillation experiments that neutrinos have tiny but non-zero masses. Since the helicity is not a Lorentz invariant quantity for massive particles, neutrinos can not be strictly left-handed. On the other hand, it is generally assumed that ultrarelativistic massive fermions can be described well enough by the Weyl equations. We discuss the validity of this assumption and propose a new hypothesis according to which neutrinos can be described by pure helicity states although they are not massless.

  13. Magnetic Helicity Injection in Solar Active Regions

    Institute of Scientific and Technical Information of China (English)

    Hong-Qi Zhang

    2006-01-01

    We present the evolution of magnetic field and its relationship with magnetic (current) helicity in solar active regions from a series of photospheric vector magnetograms obtained by Huairou Solar Observing Station, longitudinal magnetograms by MDI of SOHO and white light images of TRACE. The photospheric current helicity density is a quantity reflecting the local twisted magnetic field and is related to the remaining magnetic helicity in the photosphere, even if the mean current helicity density brings the general chiral property in a layer of solar active regions. As new magnetic flux emerges in active regions, changes of photospheric current helicity density with the injection of magnetic helicity into the corona from the subatmosphere can be detected, including changes in sign caused by the injection of magnetic helicity of opposite sign. Because the injection rate of magnetic helicity and photospheric current helicity density have different means in the solar atmosphere,the injected magnetic helicity is probably not proportional to the current helicity density remaining in the photosphere. The evidence is that rotation of sunspots does not synchronize exactly with the twist of photospheric transverse magnetic field in some active regions (such as, delta active regions). They represent different aspects of magnetic chirality. A combined analysis of the observational magnetic helicity parameters actually provides a relative complete picture of magnetic helicity and its transfer in the solar atmosphere.

  14. Trinuclear nickel coordination complexes of phenanthrene-9,10-dione dioxime

    Directory of Open Access Journals (Sweden)

    Owen M. Williams

    2016-04-01

    Full Text Available A trinuclear nickel complex of phenanthrene-9,10-dione dioxime (H2pqd, namely bis[μ2-9,10-bis(oxidoiminophenanthrene]bis[μ2-10-(oxidoiminophenanthrene-9-one oxime](phenanthrene-9,10-dione dioximetrinickel(II toluene disolvate, [Ni3(C14H8N2O22(C14H9N2O22(C14H10N2O2]·2C7H8, has been isolated and its crystal structure determined. This complex features three independent NiII atoms that are arranged in a triangular fashion along with five supporting ligands. There are two square-planar NiII atoms and a third pseudo-octahedral NiII atom. While the square-planar NiII atoms are stacked, there are no ligand bridges between them. Each square-planar NiII atom, however, bridges with the pseudo-octahedral NiII atom through Ni—N—O—Ni and Ni—O—Ni bonds. A fluoridoboration reaction of the proton-bridged species gave the analogous complex bis(μ2-bis{[10-(oxidoimino-9,10-dihydrophenanthren-9-ylidene]amino}difluoridoborato(phenanthrene-9,10-dione dioximetrinickel(II dichloromethane trisolvate, [Ni3(C28H16BF2N4O24(C14H10N2O2]·3CH2Cl2, which shows the same binding structure, but features a widened Ni—Ni interaction between the square-planar NiII atoms. The proton-bridged complex completes the macrocyclic coordination around the square-planar NiII atoms by means of an O—H...O hydrogen bond. Both compounds feature O—H...N hydrogen bonds between the oxime and the N atoms attached to square-planar nickel atom. The nickel units show no direct interaction with their nearest neighbors in the extended lattice. Two π-stacking interactions between adjacent molecules are found: one with a centroid–centroid distance of 3.886 (2 Å and the other with a centroid–centroid distance of 4.256 (3 Å. In the latter case, although not aromatic, the distance to the centroid of the central phenanthrene ring is shorter, with a distance of 3.528 (3 Å. Toluene molecules occupy the solvent channels that are oriented along the c axis. In the

  15. The Transport of Relative Canonical Helicity

    CERN Document Server

    You, Setthivoine

    2012-01-01

    The evolution of relative canonical helicity is examined in the two-fluid magnetohydrodynamic formalism. Canonical helicity is defined here as the helicity of the plasma species' canonical momentum. The species' canonical helicity are coupled together and can be converted from one into the other while the total gauge-invariant relative canonical helicity remains globally invariant. The conversion is driven by enthalpy differences at a surface common to ion and electron canonical flux tubes. The model provides an explanation for why the threshold for bifurcation in counter-helicity merging depends on the size parameter. The size parameter determines whether magnetic helicity annihilation channels enthalpy into the magnetic flux tube or into the vorticity flow tube components of the canonical flux tube. The transport of relative canonical helicity constrains the interaction between plasma flows and magnetic fields, and provides a more general framework for driving flows and currents from enthalpy or inductive b...

  16. Applications of 2D helical vortex dynamics

    DEFF Research Database (Denmark)

    Okulov, Valery; Sørensen, Jens Nørkær

    2010-01-01

    In the paper, we show how the assumption of helical symmetry in the context of 2D helical vortices can be exploited to analyse and to model various cases of rotating flows. From theory, examples of three basic applications of 2D dynamics of helical vortices embedded in flows with helical symmetry...... of the vorticity field are addressed. These included some of the problems related to vortex breakdown, instability of far wakes behind rotors and vortex theory of ideal rotors....

  17. Influence of Magnetic Helicity in MHD

    CERN Document Server

    Candelaresi, Simon; Brandenburg, Axel

    2010-01-01

    Observations have shown that the Sun's magnetic field has helical structures. The helicity content in magnetic field configurations is a crucial constraint on the dynamical evolution of the system. Since helicity is connected with the number of links we investigate configurations with interlocked magnetic flux rings and one with unlinked rings. It turns out that it is not the linking of the tubes which affects the magnetic field decay, but the content of magnetic helicity.

  18. On the triple correlations in helical turbulence

    CERN Document Server

    Chkhetiani, O

    1997-01-01

    The evolution of correlation characteristics in homogeneous helical turbulence is considered. Additional K'arm'an-Howarth type equations, describing the evolution of the mixed correlation tensor of the velocity and vorticity are obtained. In the helical scaling region, the solution of obtained equation gives the exact relation between antisymmetric component of a rank-three tensor and the average dissipation of helicity. This relation is a helical analogue of Kolmogorov's known 4/5 law.

  19. Hybrid helical snakes and rotators for RHIC

    Energy Technology Data Exchange (ETDEWEB)

    Courant, E.D.

    1995-06-13

    The spin rotators and Siberian snakes presently envisaged for RHIC utilize helical dipole magnets. The snakes and the rotators each consist of four helices, each with a full twist (360{degrees}) of the field. Here we investigate an alternate layout, namely combinations of helical and pure bending magnet, and show that this may have advantages.

  20. Enantiomeric differentiation by synthetic helical polymers.

    Science.gov (United States)

    Yashima, Eiji; Iida, Hiroki; Okamoto, Yoshio

    2013-01-01

    Recent advances in the synthesis of helical polymers and their applications as chiral materials, in particular chiral stationary phases (CSPs), for high-performance liquid chromatography (HPLC) are reviewed with an emphasis on the key role of the helical conformations with one-handedness for the prominent chiral recognition of enantiomers. The historical background of artificial optically active helical polymers is also briefly described.

  1. Influence of a thermochromic anion on the spin crossover of iron(II) trinuclear complexes probed by Moessbauer spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Robert, Francois; Naik, Anil D; Garcia, Yann, E-mail: yann.garcia@uclouvain.b [Institut de la Matiere Condensee et des Nanosciences, Universite Catholique de Louvain, Place L. Pasteur 1, 1348 Louvain-la-Neuve (Belgium)

    2010-03-01

    The insertion of thermochromic anions (1 and 2) into triazole based iron(II) trinuclear spin crossover complexes [Fe{sup II}{sub 3}(hyetrz){sub 6}(H{sub 2}O){sub 6}](1 or 2){sub 4}Cl{sub 2} paves the way to a large panel of multifunctional materials. In addition to a gradual thermo-induced spin conversion of the central metal ion on cooling below room temperature, an unexpected split of the Moessbauer signal of the external iron(II) ions as well as pronounced relaxation phenomenon for the central HS iron(II) ion was discovered. This phenomenon is suggested to be induced by the tautomeric equilibrium between enol and keto forms of the anion.

  2. Performance tests on helical Savonius rotors

    Energy Technology Data Exchange (ETDEWEB)

    Kamoji, M.A.; Kedare, S.B. [Department of Energy Science and Engineering, Indian Institute of Technology, Bombay (India); Prabhu, S.V. [Department of Mechanical Engineering, Indian Institute of Technology, Bombay (India)

    2009-03-15

    Conventional Savonius rotors have high coefficient of static torque at certain rotor angles and a negative coefficient of static torque from 135 to 165 and from 315 to 345 in one cycle of 360 . In order to decrease this variation in static torque from 0 to 360 , a helical Savonius rotor with a twist of 90 is proposed. In this study, tests on helical Savonius rotors are conducted in an open jet wind tunnel. Coefficient of static torque, coefficient of torque and coefficient of power for each helical Savonius rotor are measured. The performance of helical rotor with shaft between the end plates and helical rotor without shaft between the end plates at different overlap ratios namely 0.0, 0.1 and 0.16 is compared. Helical Savonius rotor without shaft is also compared with the performance of the conventional Savonius rotor. The results indicate that all the helical Savonius rotors have positive coefficient of static torque at all the rotor angles. The helical rotors with shaft have lower coefficient of power than the helical rotors without shaft. Helical rotor without shaft at an overlap ratio of 0.0 and an aspect ratio of 0.88 is found to have almost the same coefficient of power when compared with the conventional Savonius rotor. Correlation for coefficient of torque and power is developed for helical Savonius rotor for a range of Reynolds numbers studied. (author)

  3. Predictive supracolloidal helices from patchy particles

    Science.gov (United States)

    Guo, Ruohai; Mao, Jian; Xie, Xu-Ming; Yan, Li-Tang

    2014-11-01

    A priori prediction of supracolloidal architectures from nanoparticle and colloidal assembly is a challenging goal in materials chemistry and physics. Despite intense research in this area, much less has been known about the predictive science of supracolloidal helices from designed building blocks. Therefore, developing conceptually new rules to construct supracolloidal architectures with predictive helicity is becoming an important and urgent task of great scientific interest. Here, inspired by biological helices, we show that the rational design of patchy arrangement and interaction can drive patchy particles to self-assemble into biomolecular mimetic supracolloidal helices. We further derive a facile design rule for encoding the target supracolloidal helices, thus opening the doors to the predictive science of these supracolloidal architectures. It is also found that kinetics and reaction pathway during the formation of supracolloidal helices offer a unique way to study supramolecular polymerization, and that well-controlled supracolloidal helices can exhibit tailorable circular dichroism effects at visible wavelengths.

  4. A helical scintillating fiber hodoscope

    CERN Document Server

    Altmeier, M; Bisplinghoff, J; Bissel, T; Bollmann, R; Busch, M; Büsser, K; Colberg, T; Demiroers, L; Diehl, O; Dohrmann, F; Engelhardt, H P; Eversheim, P D; Felden, O; Gebel, R; Glende, M; Greiff, J; Gross, A; Gross-Hardt, R; Hinterberger, F; Jahn, R; Jeske, M; Jonas, E; Krause, H; Lahr, U; Langkau, R; Lindemann, T; Lindlein, J; Maier, R; Maschuw, R; Mayer-Kuckuck, T; Meinerzhagen, A; Naehle, O; Pfuff, M; Prasuhn, D; Rohdjess, H; Rosendaal, D; Von Rossen, P; Sanz, B; Schirm, N; Schulz-Rojahn, M; Schwarz, V; Scobel, W; Thomas, S; Trelle, H J; Weise, E; Wellinghausen, A; Wiedmann, W; Woller, K; Ziegler, R

    1999-01-01

    A novel scintillating fiber hodoscope in helically cylindric geometry has been developed for detection of low multiplicity events of fast protons and other light charged particles in the internal target experiment EDDA at the Cooler Synchrotron COSY. The hodoscope consists of 640 scintillating fibers (2.5 mm diameter), arranged in four layers surrounding the COSY beam pipe. The fibers are helically wound in opposing directions and read out individually using 16-channel photomultipliers connected to a modified commercial encoding system. The detector covers an angular range of 9 deg. <= THETA<=72 deg. and 0 deg. <=phi (cursive,open) Greek<=360 deg. in the lab frame. The detector length is 590 mm, the inner diameter 161 mm. Geometry and granularity of the hodoscope afford a position resolution of about 1.3 mm. The detector design took into consideration a maximum of reliability and a minimum of maintenance. An LED array may be used for monitoring purposes. (author)

  5. A helical scintillating fiber hodoscope

    Energy Technology Data Exchange (ETDEWEB)

    Altmeier, M.; Bauer, F.; Bisplinghoff, J.; Bissel, T.; Bollmann, R.; Busch, M.; Buesser, K.; Colberg, T.; Demiroers, L.; Diehl, O.; Dohrmann, F.; Engelhardt, H.P.; Eversheim, P.D.; Felden, O.; Gebel, R.; Glende, M.; Greiff, J.; Gross, A.; Gross-Hardt, R.; Hinterberger, F.; Jahn, R.; Jeske, M.; Jonas, E.; Krause, H.; Lahr, U.; Langkau, R.; Lindemann, T.; Lindlein, J.; Maier, R.; Maschuw, R.; Mayer-Kuckuck, T.; Meinerzhagen, A.; Naehle, O.; Pfuff, M.; Prasuhn, D.; Rohdjess, H.; Rosendaal, D.; Rossen, P. von; Sanz, B.; Schirm, N.; Schulz-Rojahn, M.; Schwarz, V.; Scobel, W.; Thomas, S.; Trelle, H.J.; Weise, E.; Wellinghausen, A.; Wiedmann, W.; Woller, K.; Ziegler, R

    1999-07-21

    A novel scintillating fiber hodoscope in helically cylindric geometry has been developed for detection of low multiplicity events of fast protons and other light charged particles in the internal target experiment EDDA at the Cooler Synchrotron COSY. The hodoscope consists of 640 scintillating fibers (2.5 mm diameter), arranged in four layers surrounding the COSY beam pipe. The fibers are helically wound in opposing directions and read out individually using 16-channel photomultipliers connected to a modified commercial encoding system. The detector covers an angular range of 9 deg. {<=}{theta}{<=}72 deg. and 0 deg. {<=}phi (cursive,open) Greek{<=}360 deg. in the lab frame. The detector length is 590 mm, the inner diameter 161 mm. Geometry and granularity of the hodoscope afford a position resolution of about 1.3 mm. The detector design took into consideration a maximum of reliability and a minimum of maintenance. An LED array may be used for monitoring purposes. (author)

  6. Adjustable phase planar helical undulator

    Science.gov (United States)

    Carr, Roger G.; Lidia, Steve

    1993-11-01

    We present here the design description of a new type of planar helical undulator, which we are constructing for the SPEAR storage ring at the Stanford Synchrotron Radiation Laboratory. It comprises four rows of pure permanent magnet blocks, one row in each quadrant about the axis defined by the electron beam. Rows may be translated longitudinally with respect to each other to change the helicity of the magnetic field they create at the position of the beam. They may also be translated longitudinally to vary the energy of the x-rays emitted, unlike designs where this function is performed by varying the gap between the rows. This work includes numerical calculations of the fields, electron trajectories, and x-ray spectra, including off-axis effects.

  7. An experimental superconducting helical undulator

    Energy Technology Data Exchange (ETDEWEB)

    Caspi, S.; Taylor, C. [Lawrence Berkeley Lab., CA (United States)

    1995-12-31

    Improvements in the technology of superconducting magnets for high energy physics and recent advancements in SC materials with the artificial pinning centers (APC){sup 2}, have made a bifilar helical SC device an attractive candidate for a single-pass free electron laser (FEL){sup 3}. Initial studies have suggested that a 6.5 mm inner diameter helical device, with a 27 mm period, can generate a central field of 2-2.5 Tesla. Additional studies have also suggested that with a stored energy of 300 J/m, such a device can be made self-protecting in the event of a quench. However, since the most critical area associated with high current density SC magnets is connected with quenching and training, a short experimental device will have to be built and tested. In this paper we discuss technical issues relevant to the construction of such a device, including a conceptual design, fields, and forces.

  8. Emulsification-Induced Homohelicity in Racemic Helical Polymer for Preparing Optically Active Helical Polymer Nanoparticles.

    Science.gov (United States)

    Zhao, Biao; Deng, Jinrui; Deng, Jianping

    2016-04-01

    Optically active nano- and microparticles have constituted a significant category of advanced functional materials. However, constructing optically active particles derived from synthetic helical polymers still remains as a big challenge. In the present study, it is attempted to induce a racemic helical polymer (containing right- and left-handed helices in equal amount) to prefer one predominant helicity in aqueous media by using emulsifier in the presence of chiral additive (emulsification process). Excitingly, the emulsification process promotes the racemic helical polymer to unify the helicity and directly provides optically active nanoparticles constructed by chirally helical polymer. A possible mechanism is proposed to explain the emulsification-induced homohelicity effect. The present study establishes a novel strategy for preparing chirally helical polymer-derived optically active nanoparticles based on racemic helical polymers.

  9. Helical Antimicrobial Sulfono- {gamma} -AApeptides

    Energy Technology Data Exchange (ETDEWEB)

    Li, Yaqiong; Wu, Haifan; Teng, Peng; Bai, Ge; Lin, Xiaoyang; Zuo, Xiaobing; Cao, Chuanhai; Cai, Jianfeng

    2015-06-11

    Host-defense peptides (HDPs) such as magainin 2 have emerged as potential therapeutic agents combating antibiotic resistance. Inspired by their structures and mechanism of action, herein we report the fi rst example of antimicrobial helical sulfono- γ - AApeptide foldamers. The lead molecule displays broad-spectrum and potent antimicrobial activity against multi-drug-resistant Gram- positive and Gram-negative bacterial pathogens. Time-kill studies and fl uorescence microscopy suggest that sulfono- γ -AApeptides eradicate bacteria by taking a mode of action analogous to that of HDPs. Clear structure - function relationships exist in the studied sequences. Longer sequences, presumably adopting more-de fi ned helical structures, are more potent than shorter ones. Interestingly, the sequence with less helical propensity in solution could be more selective than the stronger helix-forming sequences. Moreover, this class of antimicrobial agents are resistant to proteolytic degradation. These results may lead to the development of a new class of antimicrobial foldamers combating emerging antibiotic-resistant pathogens.

  10. Helically twisted photonic crystal fibres.

    Science.gov (United States)

    Russell, P St J; Beravat, R; Wong, G K L

    2017-02-28

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic 'space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of 'numerical experiments' based on finite-element solutions of Maxwell's equations in a helicoidal frame.This article is part of the themed issue 'Optical orbital angular momentum'. © 2017 The Authors.

  11. Helically twisted photonic crystal fibres

    Science.gov (United States)

    Russell, P. St. J.; Beravat, R.; Wong, G. K. L.

    2017-02-01

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic `space', cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of `numerical experiments' based on finite-element solutions of Maxwell's equations in a helicoidal frame. This article is part of the themed issue 'Optical orbital angular momentum'.

  12. Helically twisted photonic crystal fibres

    Science.gov (United States)

    Beravat, R.; Wong, G. K. L.

    2017-01-01

    Recent theoretical and experimental work on helically twisted photonic crystal fibres (PCFs) is reviewed. Helical Bloch theory is introduced, including a new formalism based on the tight-binding approximation. It is used to explore and explain a variety of unusual effects that appear in a range of different twisted PCFs, including fibres with a single core and fibres with N cores arranged in a ring around the fibre axis. We discuss a new kind of birefringence that causes the propagation constants of left- and right-spinning optical vortices to be non-degenerate for the same order of orbital angular momentum (OAM). Topological effects, arising from the twisted periodic ‘space’, cause light to spiral around the fibre axis, with fascinating consequences, including the appearance of dips in the transmission spectrum and low loss guidance in coreless PCF. Discussing twisted fibres with a single off-axis core, we report that optical activity in a PCF is opposite in sign to that seen in a step-index fibre. Fabrication techniques are briefly described and emerging applications reviewed. The analytical results of helical Bloch theory are verified by an extensive series of ‘numerical experiments’ based on finite-element solutions of Maxwell's equations in a helicoidal frame. This article is part of the themed issue ‘Optical orbital angular momentum’. PMID:28069771

  13. Synthesis, structure and magnetic properties of 5-(4-Sulfophenylazo) salicylate-bridged 1D coordination polymers containing linear trinuclear metal clusters

    Science.gov (United States)

    Liu, Hong; Song, Li-jun; Ju, Zhan-feng; Li, Wei; Zhang, Jie

    2008-03-01

    Three new trinuclear metal complexes with an azobenzene-containing ligand [M 3(Sasa) 2(Py) 2(H 2O) 8] (Na 2HSasa = 5-(4-Sulfophenylazo) salicylic acid disodium salt; Py = pyridine; M = Cu, Co, Zn), are synthesized through the interface diffusion and structurally characterized by single crystal X-ray diffraction, XRPD analysis and spectral methods. The metal ions in distorted octahedral coordination environments are connected by Sasa ligands to form 1D coordination polymer chain containing the linear trinuclear units with single syn-anti carboxylate bridges. The extensive hydrogen bonding interactions hold these chains together into 3D supramolecular network. Weak antiferromagnetic interactions between adjacent metal ions with J = -1.85 cm -1 and J = -2.81 cm -1 dominate the magnetic properties of Cu(II) and Co(II) complexes, separately.

  14. Helical Aharonov-Casher edge states

    OpenAIRE

    Heremans, J. J.; Xu, L. L.

    2010-01-01

    It is shown that an Aharonov-Casher vector potential in a two-dimensional geometry can lead to helical edge states. The Aharonov-Casher vector potential is the electromagnetic dual of the magnetic vector potential, and leads to traveling states at the sample edge in analogy to the integer quantum Hall effect. The helical edge states are predicted to appear in a narrow channel geometry with parabolic or sufficiently symmetric confinement potential. The implications of the helical Aharonov-Cash...

  15. Employing Helicity Amplitudes for Resummation in SCET

    CERN Document Server

    Moult, Ian; Tackmann, Frank J; Waalewijn, Wouter J

    2016-01-01

    Helicity amplitudes are the fundamental ingredients of many QCD calculations for multi-leg processes. We describe how these can seamlessly be combined with resummation in Soft-Collinear Effective Theory (SCET), by constructing a helicity operator basis for which the Wilson coefficients are directly given in terms of color-ordered helicity amplitudes. This basis is crossing symmetric and has simple transformation properties under discrete symmetries.

  16. Revisiting fermion helicity flip in Podolsky's Electromagnetism

    CERN Document Server

    Sales, Jorge Henrique; Thibes, Ronaldo

    2016-01-01

    The spin projection of a massive particle onto its direction of motion is called helicity (or "handedness"). It can therefore be positive or negative. When a particle's helicity changes from positive to negative (or vice-versa) due to its interaction with other particles or fields, we say there is a helicity flip. In this work we show that such helicity flip can be seen for an electron of $20 MeV$ of energy interacting with a charged scalar meson through the exchange of a virtual photon. This photon {\\it does not} necessarily need to be Podolsky's proposed photon; in fact, it is independent of it.

  17. Higher helicity invariants and solar dynamo

    Science.gov (United States)

    Sokolov, D. D.; Illarionov, E. A.; Akhmet'ev, P. M.

    2017-01-01

    Modern models of nonlinear dynamo saturation in celestial bodies (specifically, on the Sun) are largely based on the consideration of the balance of magnetic helicity. This physical variable has also a topological meaning: it is associated with the linking coefficient of magnetic tubes. In addition to magnetic helicity, magnetohydrodynamics has a number of topological integrals of motion (the so-called higher helicity moments). We have compared these invariants with magnetic helicity properties and concluded that they can hardly serve as nonlinear constraints on dynamo action.

  18. Structure, adsorption and magnetic properties of chiral metal-organic frameworks bearing linear trinuclear secondary building blocks.

    Science.gov (United States)

    Chen, Zilu; Liu, Xianlin; Zhang, Chuanbing; Zhang, Zhong; Liang, Fupei

    2011-03-07

    The reactions of new chiral organic ligands trimesoyltri(L-alanine) (L-TMTAH(3)) or trimesoyltri(D-alanine) (D-TMTAH(3)) with transition metal salts in the presence of an ancillary ligand of 4,4'-bipyridine gave two pairs of three dimensional frameworks [Co(3)(L-TMTA)(2)(4,4'-bpy)(4)]·28H(2)O (1), [Co(3)(D-TMTA)(2)(4,4'-bpy)(4)]·28H(2)O (2) [Ni(3)(L-TMTA)(2)(4,4'-bpy)(4)]·2C(2)H(5)OH·14H(2)O (3) and [Ni(3)(D-TMTA)(2)(4,4'-bpy)(4)]·2C(2)H(5)OH·14H(2)O (4). These compounds were characterized by elemental analysis, IR, and X-ray powder diffraction analysis and the structures of 1-3 were determined from X-ray single crystal diffraction analysis. Complexes 1-4 feature linear trinuclear secondary building blocks [M(3)(COO)(4)](2+) formed via the connection of three metal ions by four carboxylato groups from four TMTA(3-) ligands. Every adjacent two linear trinuclear secondary building blocks are linked by one and three 4,4'-bipyridine molecules along the a and c axis, respectively, to form two-dimensional sheets, which are further connected by TMTA(3-) ligands to construct a porous three dimensional framework with one-dimensional channels. Compound 3 was taken as an example to investigate the adsorption properties of compounds 1-4. It revealed a saturated hydrogen uptake of 216.6 cm(3) g(-1) (2.0 wt%) at 11.1 atm measured at 77 K, a maximum CO(2) uptake of 119.4 cm(3) g(-1) (23.5 wt%) at 19.5 atm measured at 298 K and a saturated CH(4) uptake of 77.8 cm(3) g(-1) (5.6 wt%) at 27.1 atm measured at 298 K. The magnetic studies of complexes 1 and 3 indicate the presence of antiferromagnetic interactions between the metal ions in the two compounds.

  19. Dinuclear and Trinuclear Nickel Complexes as Effective Catalysts for Alternating Copolymerization on Carbon Dioxide and Cyclohexene Oxide.

    Science.gov (United States)

    Tsai, Chen-Yen; Cheng, Fu-Yin; Lu, Kuan-Yeh; Wu, Jung-Tsu; Huang, Bor-Hunn; Chen, Wei-An; Lin, Chu-Chieh; Ko, Bao-Tsan

    2016-08-15

    A series of novel nickel complexes 1-9 supported by NNO-tridentate Schiff-base derivatives have been synthesized and characterized. Treatment of the pro-ligands [L(1)-H = 2,4-di-tert-butyl-6-(((2-(dimethylamino)ethyl)imino)methyl)phenol, L(2)-H = 2-(((2-(dimethylamino)ethyl)imino)methyl)-4,6-bis(2-phenylpropan-2-yl)phenol, L(3)-H = 2-(((2-(dimethylamino)ethyl)imino)methyl)phenol] with Ni(OAc)2·4H2O in refluxing ethanol afforded mono- or bimetallic nickel complexes {[(L(1))Ni(OAc)] (1); (L(2))Ni(OAc)] (2); (L(3))2Ni2(OAc)2(H2O)] (3)}. Alcohol-solvated trimetallic nickel acetate complexes {[(L(3))2Ni3(OAc)4(MeOH)2] (4); (L(3))2Ni3(OAc)4(EtOH)2] (5)} could be generated from the reaction of L(3)-H and anhydrous nickel(II) acetate with a ratio of 2:3 in refluxing anhydrous MeOH or EtOH. The reaction of nickel acetate tetrahydrate and L(4)-H to L(6)-H [L(4)-H = 2-(((2-(dimethylamino)ethyl)imino)methyl)-5-methoxyphenol, L(5)-H = 2-(((2-(dimethylamino)ethyl)imino)methyl)-4-methoxy-phenol, L(6)-H = 2-(((2-(dimethylamino)ethyl)imino)(phenyl)methyl)phenol] produced, respectively, the alcohol-free trinuclear nickel complexes {[(L(4))2Ni3(OAc)4] (7); [(L(5))2Ni3(OAc)4] (8); [(L(6))2Ni3(OAc)4] (9)} with the same ratio in refluxing EtOH under the atmospheric environment. Interestingly, recrystallization of [(L(3))2Ni3(OAc)4(MeOH)] (4) or [(L(3))2Ni3(OAc)4(EtOH)] (5) in the mixed solvent of CH2Cl2/hexane gives [(L(3))2Ni3(OAc)4] (6), which is isostructural with analogues 7-9. All bi- and trimetallic nickel complexes exhibit efficient activity and good selectivity for copolymerization of CO2 with cyclohexene oxide, resulting in copolymers with a high alternating microstructure possessing ≥99% carbonate-linkage content. This is the first example to apply well-defined trinuclear nickel complexes as efficient catalysts for the production of perfectly alternating poly(cyclohexene carbonate).

  20. Increased toxicity of a trinuclear Pt-compound in a human squamous carcinoma cell line by polyamine depletion

    Directory of Open Access Journals (Sweden)

    Kjellström Johan

    2012-05-01

    Full Text Available Abstract Background Mononuclear platinum anticancer agents hold a pivotal place in the treatment of many forms of cancers, however, there is a potential to improve response to evade resistance development and toxic side effects. BBR3464 is a promising trinuclear platinum anticancer agent, which is a polyamine mimic. The aim was to investigate the influence of polyamine pool reduction on the cytotoxic effects of the trinuclear platinum complex BBR3464 and cisplatin. Polyamine pool reduction was achieved by treating cells with either the polyamine biosynthesis inhibitor α-difluoromethylornithine (DFMO or the polyamine analogue N1,N11-diethylnorspermine (DENSPM. Methods A human squamous cell carcinoma cell line, LU-HNSCC-4, established from a primary head and neck tumour was used to evaluate cellular effects of each drug alone or combinations thereof. High-performance liquid-chromatography was used to quantify intracellular polyamine contents. Inductively coupled mass spectroscopy was used to quantify intracellular platinum uptake. Cells were exposed to DFMO or DENSPM during 48 h at concentrations ranging from 0 to 5 mM or 0 to 10 μM, respectively. Thereafter, non-treated and treated cells were exposed to cisplatin or BBR3464 during 1 h at concentrations ranging from 0 to 100 μM. A 96-well assay was used to determine cytotoxicity after five days after treatment. Results The cytotoxic effect of BBR3464 on LU-HNSCC-4 cells was increased after cells were pre-treated with DENSPM or DFMO, and the interaction was found to be synergistic. In contrast, the interaction between cisplatin and DFMO or DENSPM was near-additive to antagonistic. The intracellular levels of the polyamines putrescine and spermidine were decreased after treatment with DFMO, and treatment with DENSPM resulted in an increase in putrescine level and concomitant decrease in spermidine and spermine levels. The uptake of BBR3464 was significantly increased after pre

  1. Helical coil thermal hydraulic model

    Science.gov (United States)

    Caramello, M.; Bertani, C.; De Salve, M.; Panella, B.

    2014-11-01

    A model has been developed in Matlab environment for the thermal hydraulic analysis of helical coil and shell steam generators. The model considers the internal flow inside one helix and its associated control volume of water on the external side, both characterized by their inlet thermodynamic conditions and the characteristic geometry data. The model evaluates the behaviour of the thermal-hydraulic parameters of the two fluids, such as temperature, pressure, heat transfer coefficients, flow quality, void fraction and heat flux. The evaluation of the heat transfer coefficients as well as the pressure drops has been performed by means of the most validated literature correlations. The model has been applied to one of the steam generators of the IRIS modular reactor and a comparison has been performed with the RELAP5/Mod.3.3 code applied to an inclined straight pipe that has the same length and the same elevation change between inlet and outlet of the real helix. The predictions of the developed model and RELAP5/Mod.3.3 code are in fairly good agreement before the dryout region, while the dryout front inside the helical pipes is predicted at a lower distance from inlet by the model.

  2. Segregation of helicity in inertial wave packets

    Science.gov (United States)

    Ranjan, A.

    2017-03-01

    Inertial waves are known to exist in the Earth's rapidly rotating outer core and could be important for the dynamo generation. It is well known that a monochromatic inertial plane wave traveling parallel to the rotation axis (along positive z ) has negative helicity while the wave traveling antiparallel (negative z ) has positive helicity. Such a helicity segregation, north and south of the equator, is necessary for the α2-dynamo model based on inertial waves [Davidson, Geophys. J. Int. 198, 1832 (2014), 10.1093/gji/ggu220] to work. The core is likely to contain a myriad of inertial waves of different wave numbers and frequencies. In this study, we investigate whether this characteristic of helicity segregation also holds for an inertial wave packet comprising waves with the same sign of Cg ,z, the z component of group velocity. We first derive the polarization relations for inertial waves and subsequently derive the resultant helicity in wave packets forming as a result of superposition of two or more waves. We find that the helicity segregation does hold for an inertial wave packet unless the wave numbers of the constituent waves are widely separated. In the latter case, regions of opposite color helicity do appear, but the mean helicity retains the expected sign. An illustration of this observation is provided by (a) calculating the resultant helicity for a wave packet formed by superposition of four upward-propagating inertial waves with different wave vectors and (b) conducting the direct numerical simulation of a Gaussian eddy under rapid rotation. Last, the possible effects of other forces such as the viscous dissipation, the Lorentz force, buoyancy stratification, and nonlinearity on helicity are investigated and discussed. The helical structure of the wave packet is likely to remain unaffected by dissipation or the magnetic field, but can be modified by the presence of linearly stable stratification and nonlinearity.

  3. Magnetic Helicity and the Solar Dynamo

    Science.gov (United States)

    Canfield, Richard C.

    1997-01-01

    The objective of this investigation is to open a new window into the solar dynamo, convection, and magnetic reconnection through measurement of the helicity density of magnetic fields in the photosphere and tracing of large-scale patterns of magnetic helicity in the corona.

  4. The AGS synchrotron with four helical magnets

    Energy Technology Data Exchange (ETDEWEB)

    Tsoupas N.; Huang, H.; Roser, T.; MacKay, W.W.; Trbojevic, D.

    2012-05-20

    The idea of using two partial helical magnets was applied successfully to the AGS synchrotron to preserve the proton beam polarization. In this paper we explore in details the idea of using four helical magnets placed symmetrically in the AGS ring. The placement of four helical magnets in the AGS ring provides many advantages over the present setup of the AGS which uses two partial helical magnets. First, the symmetric placement of the four helical magnets allows for a better control of the AGS optics with reduced values of the beta functions especially near beam injection, second, the vertical spin direction during beam injection and extraction is closer to vertical, and third, it provides for a larger 'spin tune gap', which allows the vertical and horizontal tunes to be placed, and prevent the horizontal and vertical intrinsic spin resonances of the AGS to occur during the acceleration cycle. Although the same spin gap can be obtained with a single or two partial helices, the required high field strength of a single helix makes its use impractical, and that of the double helix rather difficult. In this paper we will provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and compare these results with the present setup of the AGS that uses two partial helical magnets.

  5. Helical Magnetic Fields in AGN Jets

    Indian Academy of Sciences (India)

    Y. J. Chen; G.-Y. Zhao; Z.-Q. Shen

    2014-09-01

    We establish a simple model to describe the helical magnetic fields in AGN jets projected on the sky plane and the line-of-sight. This kind of profile has been detected in the polarimetric VLBI observation of many blazar objects, suggesting the existence of helical magnetic fields in these sources.

  6. Synthesis, structural characterization and biological activity of a trinuclear zinc(II) complex: DNA interaction study and antimicrobial activity

    Indian Academy of Sciences (India)

    Bhaskar Biswas; Niranjan Kole; Moumita Patra; Shampa Dutta; Mousumi Ganguly

    2013-11-01

    A trinuclear zinc(II) complex [Zn3L2(-O2CCH3)2(H2O)2]·H2O·2CH3OH (1) was synthesized from an in situ reaction between zinc acetate and a Schiff base ligand (H2L = 2-((2-hydroxyphenylimino) methyl)-6-methoxyphenol). The ligand was prepared by (1:1) condensation of ortho-vanillin and ortho-aminophenol. The ligand and zinc(II) complex were characterized by elemental analysis, Fourier Transform Infrared (FTIR), 1H-Nuclear Magnetic Resonance (NMR), UV-Vis spectroscopy, Powder X-ray Diffraction (PXRD) and thermogravimetric analysis. 1 crystallizes in P-1 space group with = 11.9241(3) Å, = 12.19746 Å, = 20.47784 Å with unit cell volume is 2674.440 (Å)3. Binding property of the complex with calf thymus DNA (CT-DNA) has been investigated using absorption and emission studies. Thermal melting and viscosity experiments were further performed to determine the mode of binding of 1 with CT-DNA. Spectroscopic and viscosity investigations revealed an intercalative binding mode of 1 with CT-DNA. The ligand and its zinc complex were screened for their biological activity against bacterial species and fungi. Activity data show that the metal complex has more antibacterial and antifungal activity than the parent Schiff base ligand and against those bacterial or fungi species.

  7. Synthesis and characterization of oxo-bridged, trinuclear, six-coordinate mixed-carboxylato complexes of chromium (III)

    Science.gov (United States)

    Baranwal, B. P.; Fatma, Talat

    2005-08-01

    Mixed-carboxylato β-diketonato complexes of chromium (III) (R=C13H27, C15H31 or C17H35 and L=CH3OH) [Cr3O(OOCR)3(dike)3L3]+ have been synthesized by enforced substitution reactions of [Cr3O(OOCCH3)7(H2O)] first with straight chain fatty acids (myristic, palmitic or stearic acid) and then with β-diketones (Hβ-dike) like acetylacetone(Hacac) or benzoylacetone(Hbzac) in toluene under reflux. These are new type of oxo-bridged chromium(III) complexes in which one ligand is a fatty acid while the other one is a β-diketone. The complexes were characterized by elemental analyses, spectral (infrared, electronic, FAB mass and powder XRD) studies, molar conductance and magnetic susceptibility measurements. Bridging coordination modes for both carboxylate and β-diketonate anions were indicated by presence of νasym(Cr3O) vibrations in the infrared spectra. Trinuclear nature of the complexes and their structural features have been discussed on the basis of physicochemical studies.

  8. DNA interstrand cross-links of an antitumor trinuclear platinum(II) complex: thermodynamic analysis and chemical probing.

    Science.gov (United States)

    Malina, Jaroslav; Farrell, Nicholas P; Brabec, Viktor

    2011-06-06

    The trinuclear platinum compound [{trans-PtCl(NH(3))(2)}(2)(μ-trans-Pt(NH(3))(2){NH(2)(CH(2))(6)NH(2)}(2))](4+) (BBR3464) belongs to the polynuclear class of platinum-based anticancer agents. These agents form in DNA long-range (Pt,Pt) interstrand cross-links, whose role in the antitumor effects of BBR3464 predominates. Our results show for the first time that the interstrand cross-links formed by BBR3464 between two guanine bases in opposite strands separated by two base pairs (1,4-interstrand cross-links) exist as two distinct conformers, which are not interconvertible, not only if these cross-links are formed in the 5'-5', but also in the less-usual 3'-3' direction. Analysis of the conformers by differential scanning calorimetry, chemical probes of DNA conformation, and minor groove binder Hoechst 33258 demonstrate that each of the four conformers affects DNA in a distinctly different way and adopts a different conformation. The results also support the thesis that the molecule of antitumor BBR3464 when forming DNA interstrand cross-links may adopt different global structures, including different configurations of the linker chain of BBR3464 in the minor groove of DNA. Our findings suggest that the multiple DNA interstrand cross-links available to BBR3464 may all contribute substantially to its cytotoxicity.

  9. Helical chirality induction of expanded porphyrin analogues

    Indian Academy of Sciences (India)

    Jun-Ichiro Setsune

    2012-11-01

    Expanded porphyrin analogues with unique figure-eight conformation were prepared by way of useful pyrrole intermediates such as bis(azafulvene)s and 2-borylpyrrole. Supramolecular chirogenesis of cyclooctapyrrole O1 with 32-cycloconjugation was successfully applied to determine absolute configuration of chiral carboxylic acids. Dinuclear CuII complex of cyclooctapyrrole O2 with interrupted -conjugation was resolved by HPLC into enantiomers and their helical handedness was determined by theoretical simulation of their CD spectral pattern. Enantioselective induction of helicity in the metal helicate formation in the presence of a chiral promoter was demonstrated by using ()-(+)-1-(1-phenyl)ethylamine that favoured , helicity. Dinuclear CoII complexes of cyclotetrapyrroletetrapyridine O3 were found to be substitution labile and pick up amino acid anions in water. Those amino acid complexes of O3Co2 were rendered to adopt a particular unidirectional helical conformation preferentially depending on the ligated amino acid anion.

  10. Solubilization and fractionation of paired helical filaments.

    Science.gov (United States)

    González, P J; Correas, I; Avila, J

    1992-09-01

    Paired helical filaments isolated from brains of two different patients with Alzheimer's disease were extensively treated with the ionic detergent, sodium dodecyl sulphate. Filaments were solubilized at different extents, depending on the brain examined, thus suggesting the existence of two types of paired helical filaments: sodium dodecyl sulphate-soluble and insoluble filaments. In the first case, the number of structures resembling paired helical filaments greatly decreased after the detergent treatment, as observed by electron microscopy. Simultaneously, a decrease in the amount of sedimentable protein was also observed upon centrifugation of the sodium dodecyl sulfate-treated paired helical filaments. A sodium dodecyl sulphate-soluble fraction was isolated as a supernatant after low-speed centrifugation of the sodium dodecyl sulphate-treated paired helical filaments. The addition of the non-ionic detergent Nonidet-P40 to this fraction resulted in the formation of paired helical filament-like structures. When the sodium dodecyl sulphate-soluble fraction was further fractionated by high-speed centrifugation, three subfractions were observed: a supernatant, a pellet and a thin layer between these two subfractions. No paired helical filaments were observed in any of these subfractions, even after addition of Nonidet P-40. However, when they were mixed back together, the treatment with Nonidet P-40 resulted in the visualization of paired helical filament-like structures. These results suggest that at least two different components are needed for the reconstitution of paired helical filaments as determined by electron microscopy. The method described here may allow the study of the components involved in the formation of paired helical filaments and the identification of possible factors capable of blocking this process.

  11. Cationic Nitrogen Doped Helical Nanographenes.

    Science.gov (United States)

    Xu, Kun; Feng, Xinliang; Berger, Reinhard; Popov, Alexey A; Weigand, Jan J; Vincon, Ilka; Machata, Peter; Hennersdorf, Felix; Zhou, Youjia; Fu, Yubin

    2017-09-13

    Herein, we report on the synthesis of a series of novel cationic nitrogen doped nanographenes (CNDN) by rhodium catalyzed annulation reactions. This powerful method allows for the synthesis of cationic nanographenes with non-planar, axial chiral geometries. Single-crystal X-ray analysis reveals helical and cove-edged structures. Compared to their all-carbon analogues, the CNDN exhibit energetically lower lying frontier orbitals with a reduced optical energy gap and an electron accepting behavior. All derivatives show quasi reversible reductions in cyclic voltammetry. Depending on the number of nitrogen dopant, in situ spectroelectrochemistry proves the formation of neutral radicals (one nitrogen dopant) or radical cations (two nitrogen dopants) upon reduction. The developed synthetic protocol paves the way for the design and synthesis of expanded nanographenes or even graphene nanoribbons containing cationic nitrogen doping. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Formation of helical ion chains

    CERN Document Server

    Nigmatullin, Ramil; De Chiara, Gabriele; Morigi, Giovanna; Plenio, Martin B; Retzker, Alex

    2011-01-01

    We study the nonequilibrium dynamics of the linear to zigzag structural phase transition exhibited by an ion chain confined in a trap with periodic boundary conditions. The transition is driven by reducing the transverse confinement at a finite quench rate, which can be accurately controlled. This results in the formation of zigzag domains oriented along different transverse planes. The twists between different domains can be stabilized by the topology of the trap and under laser cooling the system relaxes to a helical chain with possibly nonzero winding number. Molecular dynamics simulations are used to obtain a large sample of possible trajectories for different quench rates. The scaling of the average winding number with different quench rates is compared to the prediction of the Kibble-Zurek theory, and a good quantitative agreement is found.

  13. Best packing of identical helices

    Science.gov (United States)

    Huh, Youngsik; Hong, Kyungpyo; Kim, Hyoungjun; No, Sungjong; Oh, Seungsang

    2016-10-01

    In this paper we prove the unique existence of a ropelength-minimizing conformation of the θ-spun double helix in a mathematically rigorous way, and find the minimal ropelength {{{Rop}}}* (θ )=-\\tfrac{8π }{t} where t is the unique solution in [-θ ,0] of the equation 2-2\\cos (t+θ )={t}2. Using this result, the pitch angles of the standard, triple and quadruple helices are around 39.3771^\\circ , 42.8354^\\circ and 43.8351^\\circ , respectively, which are almost identical with the approximated pitch angles of the zero-twist structures previously known by Olsen and Bohr. We also find the ropelength of the standard N-helix.

  14. Magnetic Helicity in a Cyclic Convective Dynamo

    Science.gov (United States)

    Miesch, Mark S.; Zhang, Mei; Augustson, Kyle C.

    2016-05-01

    Magnetic helicity is a fundamental agent for magnetic self-organization in magnetohydrodynamic (MHD) dynamos. As a conserved quantity in ideal MHD, it establishes a strict topological coupling between large and small-scale magnetic fields. The generation of magnetic fields on scales larger than the velocity field is linked to an upscale transfer of magnetic helicity, either locally in spectral space as in the inverse cascade of magnetic helicity in MHD turbulence or non-locally, as in the turbulent alpha-effect of mean-field dynamo theory. Thus, understanding the generation, transport, and dissipation of magnetic helicity is an essential prerequisite to understanding manifestations of magnetic self-organization in the solar dynamo, including sunspots, the prominent dipole and quadrupole moments, and the 22-year magnetic activity cycle. We investigate the role of magnetic helicity in a convective dynamo model that exhibits regular magnetic cycles. The cycle is marked by coherent bands of toroidal field that persist within the convection zone and that are antisymmetric about the equator. When these toriodal bands interact across the equator, it initiates a global restructuring of the magnetic topology that contributes to the reversal of the dipole moment. Thus, the polar field reversals are preceeded by a brief reversal of the subsurface magnetic helicity. There is some evidence that the Sun may exhibit a similar magnetic helicity reversal prior to its polar field reversals.

  15. Optical and magneto-optical properties of spin coated films of novel trinuclear bis(oxamato) and bis(oxamidato) type complexes

    Science.gov (United States)

    Abdulmalic, Mohammad A.; Fronk, Michael; Bräuer, Björn; Zahn, Dietrich R. T.; Salvan, Georgeta; Eya‧ane Meva, Francois; Rüffer, Tobias

    2016-12-01

    This work reports the first example of the spectroscopic measurements of the Magneto-Optical Kerr Effect (MOKE) of films being composed of trinuclear transition metal complexes on a non-transparent substrate at room temperature. The thin films of the tailor-made trinuclear bis(oxamidato) type complex 5 ([Cu3(opbonPr2)(tmcd)2(NO3)2], opbonPr2 = o-phenylenebis(N'-npropyloxamido, tmcd=trans-(1 R,2 R)-N,N,N‧,N‧-tetramethyl-cyclohexanediamine) and of the bis(oxamato) type complexes 11 ([Cu2Ni(opbaCF3)(pmdta)2(NO3)2], opbaCF3 = 4-trifluoromethyl-o-phenylenebis(oxamato), pmdta = N,N,N,‧N″,N″-pentamethyldiethylenetriamine) and 12 ([Cu3(opba)(bppe)2(NO3)2] (opba = o-phenylenebis(oxamato), bppe = S-N,N-bis(2-picolyl)-1-phenylethylamine) were fabricated by spin-coating and their thicknesses in the range between 0.5 μm and 2 μm was determined by spectroscopic ellipsometry. Based on the spectroscopic ellipsometry results it was also possible to determine the optical constants of the film and compare them with the absorption of the complexes in solution in order to confirm the complex integrity after the film deposition. The fabrication of high-quality films which exhibit Kerr rotation up to 0.2 mrad (11.5 mdeg) was only possible due to tailor-made synthesis, which allows circumventing intermolecular interactions of the trinuclear complexes during the film formation.

  16. Single Band Helical Antenna in Axial Mode

    Directory of Open Access Journals (Sweden)

    Parminder Singh

    2012-11-01

    Full Text Available Helical antennas have been widely used in a various useful applications, due to their low weight and low profile conformability, easy and cheap realization.Radiation properties of this antenna are examined both theoretically and experimentally. In this paper, an attempt has been made to investigate new helical antenna structure for Applications. CST MWS Software is used for the simulation and design calculations of the helical antennas. The axial ratio, return loss, VSWR, Directivity, gain, radiation pattern is evaluated. Using CST MWS simulation software proposed antenna is designed/simulated and optimized. The antenna exhibits a single band from 0 GHz to 3 GHz for GPS and several satellite applications

  17. Analysis on two novel spherical helical antennas

    Institute of Scientific and Technical Information of China (English)

    Hou ZHANG; Yingzeng YIN; Dongyu XIA

    2009-01-01

    Two novel spherical helical antennas are designed by projecting the planar equiangular spiral antenna onto hemisphere and partial sphere surfaces.Their radiation properties are analyzed by the moment method with curved basis and test function,and the curves of the voltage standing wave ratio (VSWR),gain,polarization and pattern that change with frequency are also given,respectively.It can be seen that the circular polarization band of the novel hemispherical helical antenna is broader.The gain curve of the partial spherical helical antenna is flatter and the structure is simpler.

  18. Investigation of backfire monofilar helical antenna

    DEFF Research Database (Denmark)

    Smith, Thomas Gunst; Larsen, Niels Vesterdal; Gothelf, Ulrich Vesterager

    2011-01-01

    This paper presents a numerical investigation of the electromagnetic properties of the backfire monofilar helical antenna. The current distribution along the helical conductor, the input impedance, and the front-to-back ratio are calculated and analyzed for the backfire operation of the antenna....... A parametric study of the helical geometry and the resulting antenna characteristics will be described and discussed. The currents and fields are calculated using the simulation software AWAS based on the Method of Moments with a wire representation of the ground plane....

  19. Synthesis and SMM behaviour of trinuclear versus dinuclear 3d-5f uranyl(v)-cobalt(ii) cation-cation complexes.

    Science.gov (United States)

    Chatelain, Lucile; Tuna, Floriana; Pécaut, Jacques; Mazzanti, Marinella

    2017-01-17

    Trinuclear versus dinuclear heterodimetallic U(V)O2(+)Co(2+) complexes were selectively assembled via a cation-cation interaction by tuning the ligand. The trimeric complex 2, with a linear [Co-O[double bond, length as m-dash]U[double bond, length as m-dash]O-Co] core, exhibits magnetic exchange and slow relaxation with a reversal barrier of 30.5 ± 0.9 K providing the first example of a U-Co exchange-coupled SMM.

  20. Optical and magneto-optical properties of spin coated films of novel trinuclear bis(oxamato) and bis(oxamidato) type complexes

    Energy Technology Data Exchange (ETDEWEB)

    Abdulmalic, Mohammad A. [Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Chemie, Straße der Nationen 62, D-09111 Chemnitz (Germany); Fronk, Michael [Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Physik, Reichenhainer Straße 70, D-09107 Chemnitz (Germany); Bräuer, Björn [Stanford Institute of Materials and Energy Science, Stanford University, Stanford, CA 94025 (United States); Zahn, Dietrich R.T. [Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Physik, Reichenhainer Straße 70, D-09107 Chemnitz (Germany); Salvan, Georgeta, E-mail: salvan@physik.tu-chemnitz.de [Technische Universität Chemnitz, Fakultät für Naturwissenschaften, Institut für Physik, Reichenhainer Straße 70, D-09107 Chemnitz (Germany); Eya' ane Meva, Francois [Department of Pharmaceutical Sciences, Faculty of Medicine and Pharmaceutical Sciences, University of Douala, BP 2701 (Cameroon); and others

    2016-12-01

    This work reports the first example of the spectroscopic measurements of the Magneto-Optical Kerr Effect (MOKE) of films being composed of trinuclear transition metal complexes on a non-transparent substrate at room temperature. The thin films of the tailor-made trinuclear bis(oxamidato) type complex 5 ([Cu{sub 3}(opbo{sup n}Pr{sub 2})(tmcd){sub 2}(NO{sub 3}){sub 2}], opbo{sup n}Pr{sub 2} = o-phenylenebis(N’-{sup n}propyloxamido, tmcd=trans-(1 R,2 R)-N,N,N′,N′-tetramethyl-cyclohexanediamine) and of the bis(oxamato) type complexes 11 ([Cu{sub 2}Ni(opbaCF{sub 3})(pmdta){sub 2}(NO{sub 3}){sub 2}], opbaCF{sub 3} = 4-trifluoromethyl-o-phenylenebis(oxamato), pmdta = N,N,N,′N″,N″-pentamethyldiethylenetriamine) and 12 ([Cu{sub 3}(opba)(bppe){sub 2}(NO{sub 3}){sub 2}] (opba = o-phenylenebis(oxamato), bppe = S-N,N-bis(2-picolyl)−1-phenylethylamine) were fabricated by spin-coating and their thicknesses in the range between 0.5 µm and 2 µm was determined by spectroscopic ellipsometry. Based on the spectroscopic ellipsometry results it was also possible to determine the optical constants of the film and compare them with the absorption of the complexes in solution in order to confirm the complex integrity after the film deposition. The fabrication of high-quality films which exhibit Kerr rotation up to 0.2 mrad (11.5 mdeg) was only possible due to tailor-made synthesis, which allows circumventing intermolecular interactions of the trinuclear complexes during the film formation. - Highlights: • Tailor-made trinuclear bis(oxamidato) and bis(oxamato) type complexes were synthesized. • Thin films (between 0.5 µm and 2 µm) were fabricated by spin-coating. • The film optical constants indicate the complex integrity after the deposition. • Film quality enabled first spectroscopic MOKE measurements of multi-nuclear complexes. • Magneto-optical Kerr rotation up to 11.5 mdeg was observed at RT (in 1.7 T).

  1. Shielding requirements in helical tomotherapy

    Science.gov (United States)

    Baechler, S.; Bochud, F. O.; Verellen, D.; Moeckli, R.

    2007-08-01

    Helical tomotherapy is a relatively new intensity-modulated radiation therapy (IMRT) treatment for which room shielding has to be reassessed for the following reasons. The beam-on-time needed to deliver a given target dose is increased and leads to a weekly workload of typically one order of magnitude higher than that for conventional radiation therapy. The special configuration of tomotherapy units does not allow the use of standard shielding calculation methods. A conventional linear accelerator must be shielded for primary, leakage and scatter photon radiations. For tomotherapy, primary radiation is no longer the main shielding issue since a beam stop is mounted on the gantry directly opposite the source. On the other hand, due to the longer irradiation time, the accelerator head leakage becomes a major concern. An analytical model based on geometric considerations has been developed to determine leakage radiation levels throughout the room for continuous gantry rotation. Compared to leakage radiation, scatter radiation is a minor contribution. Since tomotherapy units operate at a nominal energy of 6 MV, neutron production is negligible. This work proposes a synthetic and conservative model for calculating shielding requirements for the Hi-Art II TomoTherapy unit. Finally, the required concrete shielding thickness is given for different positions of interest.

  2. Motion of a helical vortex

    CERN Document Server

    Fuentes, Oscar Velasco

    2015-01-01

    We study the motion of a single helical vortex in an unbounded, inviscid, incompressible fluid. The vortex is an infinite tube whose centerline is a helix and whose cross section is a circle of small radius (compared to the radius of curvature) where the vorticity is uniform and parallel to the centerline. Ever since Joukowsky (1912) deduced that this vortex translates and rotates steadily without change of form, numerous attempts have been made to compute these self-induced velocities. Here we use Hardin's (1982) solution for the velocity field to find new expressions for the vortex's linear and angular velocities. Our results, verified by numerically computing the Helmholtz integral and the Rosenhead-Moore approximation to the Biot-Savart law, are more accurate than previous results over the whole range of values of the vortex pitch and cross-section. We then use the new formulas to study the advection of passive particles near the vortex; we find that the vortex's motion and capacity to transport fluid dep...

  3. Helical Two-Revolutional Cyclical Surface

    Directory of Open Access Journals (Sweden)

    Tatiana Olejníková

    2009-12-01

    Full Text Available Paper presents a family of helical two-revolutional cyclical surfaces, which arecreated by movement of the circle alongside the helical cycloidal curve, where circle islocated in the curve normal plane and its centre is on this curve. Helical cycloidal curvecan be created by simultaneous revolution of a point about two different axes 3o, 2o and byscrewing about axis 1o in the space. Form of the helical cycloidal curve and also of thehelical two-revolutional cyclical surface is dependent on the relative position of the threeaxes of revolutions, on multiples of angular velocities and orientations of separaterevolutions. Analytic representation, classification of surfaces and some of their geometricproperties are derived.

  4. Helicity at Photospheric and Chromospheric Heights

    CERN Document Server

    Tiwari, S K; Sankarasubramanian, K

    2009-01-01

    In the solar atmosphere the twist parameter $\\alpha$ has the same sign as magnetic helicity. It has been observed using photospheric vector magnetograms that negative/positive helicity is dominant in the northern/southern hemisphere of the Sun. Chromospheric features show dextral/sinistral dominance in the northern/southern hemisphere and sigmoids observed in X-rays also have a dominant sense of reverse-S/forward-S in the northern/southern hemisphere. It is of interest whether individual features have one-to-one correspondence in terms of helicity at different atmospheric heights. We use UBF \\Halpha images from the Dunn Solar Telescope (DST) and other \\Halpha data from Udaipur Solar Observatory and Big Bear Solar Observatory. Near-simultaneous vector magnetograms from the DST are used to establish one-to-one correspondence of helicity at photospheric and chromospheric heights. We plan to extend this investigation with more data including coronal intensities.

  5. Spin versus helicity in processes involving transversity

    CERN Document Server

    Mekhfi, Mustapha

    2011-01-01

    We construct the spin formalism in order to deal in a direct and natural way with processes involving transversity which are now of increasing popularity. The helicity formalism which is more appropriate for collision processes of definite helicity has been so far used also to manage processes with transversity, but at the price of computing numerous helicity amplitudes generally involving unnecessary kinematical variables.In a second step we work out the correspondence between both formalisms and retrieve in another way all results of the helicity formalism but in simpler forms.We then compute certain processes for comparison.A special process:the quark dipole magnetic moment is shown to be exclusively treated within the spin formalism as it is directly related to the transverse spin of the quark inside the baryon.

  6. Magnetic Helicity Conservation and Astrophysical Dynamos

    CERN Document Server

    Vishniac, E T; Vishniac, Ethan T.; Cho, Jungyeon

    2000-01-01

    We construct a magnetic helicity conserving dynamo theory which incorporates a calculated magnetic helicity current. In this model the fluid helicity plays a small role in large scale magnetic field generation. Instead, the dynamo process is dominated by a new quantity, derived from asymmetries in the second derivative of the velocity correlation function, closely related to the `twist and fold' dynamo model. The turbulent damping term is, as expected, almost unchanged. Numerical simulations with a spatially constant fluid helicity and vanishing resistivity are not expected to generate large scale fields in equipartition with the turbulent energy density. In fact, there seems to be little prospect for driving a fast dynamo in a closed box containing homogeneous turbulence. On the other hand, there is an efficient analog to the $\\alpha-\\Omega$ dynamo. Systems whose turbulence is driven by some anisotropic local instability in shearing flow, like real stars and accretion disks, and some computer simulations, ma...

  7. Synthesis and structure of neutral double helicate

    Institute of Scientific and Technical Information of China (English)

    SU, Xun-Cheng; ZHOU, Zhi-Fen; ZHU, Shou-Rong; CHEN, Yun-Ti; LENG, Xue-Bing; WENG, Lin-Hong; LIN, Hua-Kuan

    2000-01-01

    A new approach to geaerating supramolecular architectures, based on easy-to-prepare sehiff base ligands, is described to gether with its application to the self-assembly of supramolecu lar neutral double helicates.

  8. Mechanical resonances of helically coiled carbon nanowires

    National Research Council Canada - National Science Library

    Saini, D; Behlow, H; Podila, R; Dickel, D; Pillai, B; Skove, M J; Serkiz, S M; Rao, A M

    2014-01-01

    ...) mainly due to their geometrical complexity. The advent of helically coiled micro/nanoscale structures in nano-robotics, nano-inductors, and impact protection coatings has necessitated the development of new methodologies for determining...

  9. Microfluidic Lithography of Bioinspired Helical Micromotors.

    Science.gov (United States)

    Yu, Yunru; Shang, Luoran; Gao, Wei; Zhao, Ze; Wang, Huan; Zhao, Yuanjin

    2017-07-29

    Considerable efforts have been devoted to developing artificial micro/nanomotors that can convert energy into movement. A flow lithography integrated microfluidic spinning and spiraling system is developed for the continuous generation of bioinspired helical micromotors. Because the generation processes could be precisely tuned by adjusting the flow rates and the illuminating frequency, the length, diameter, and pitch of the helical micromotors were highly controllable. Benefiting from the fast online gelation and polymerization, the resultant helical micromotors could be imparted with Janus, triplex, and core-shell cross-sectional structures that have never been achieved by other methods. Owing to the spatially controlled encapsulation of functional nanoparticles in the microstructures, the helical micromotors can perform locomotion not only by magnetically actuated rotation or corkscrew motion but also through chemically powered catalytic reaction. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. Helical magnetized wiggler for synchrotron radiation laser

    CERN Document Server

    Wang Mei; Hirshfield, J L

    1999-01-01

    A helical magnetized iron wiggler has been built for a novel infrared synchrotron radiation laser (SRL) experiment. The wiggler consists of four periods of helical iron structure immersed in a solenoid field. This wiggler is to impart transverse velocity to a prebunched 6 MeV electron beam, and thus to obtain a desired high orbit pitch ratio for the SRL. Field tapering at beam entrance is considered and tested on a similar wiggler. Analytic and simulated characteristics of wigglers of this type are discussed and the performance of the fabricated wigglers is demonstrated experimentally. A 4.7 kG peak field was measured for a 6.4 mm air gap and a 5.4 cm wiggler period at a 20 kG solenoid field. The measured helical fields compare favorably with the analytical solution. This type of helical iron wigglers has the potential to be scaled to small periods with strong field amplitude.

  11. STUDY ON A NOVEL ELLIPSOIDAL HELICAL ANTENNA

    Institute of Scientific and Technical Information of China (English)

    Xia Dongyu; Zhang Hou; Wang Chong; Zhang Qianyue

    2007-01-01

    A novel ellipsoidal helical antenna is proposed and studied in this letter.As a special instance,the hemispherical helical antennas are analyzed firstly,which indicates that the characteristics of a two-arm unit are better than that of a single-arm unit.Based on this,the ellipsoidal helical antenna,formed by changing the axial direction's dimension of the two-arm hemispherical helical antenna,is analyzed by the moment method with curved basic and testing function.The effects to VSWR (Voltage Standing Wave Ratio),gain,polarization and patterns by the axial direction's dimensions are investigated.The study results provide dependable gist to the choice of antenna format according to the practical requirements.

  12. Kinematic dynamo induced by helical waves

    OpenAIRE

    Wei, Xing

    2014-01-01

    We investigate numerically the kinematic dynamo induced by the superposition of two helical waves in a periodic box as a simplified model to understand the dynamo action in astronomical bodies. The effects of magnetic Reynolds number, wavenumber and wave frequency on the dynamo action are studied. It is found that this helical-wave dynamo is a slow dynamo. There exists an optimal wavenumber for the dynamo growth rate. A lower wave frequency facilitates the dynamo action and the oscillations o...

  13. Cosmological Magnetic Fields from Primordial Helical Seeds

    CERN Document Server

    Sigl, G

    2002-01-01

    Most early Universe scenarios predict negligible magnetic fields on cosmological scales if they are unprocessed during subsequent expansion of the Universe. We present a new numerical treatment of the evolution of primordial fields and apply it to weakly helical seeds as they occur in certain early Universe scenarios. We find that initial helicities not much larger than the baryon to photon number can lead to fields of about 10^{-13} Gauss with coherence scales slightly below a kilo-parsec today.

  14. Duality and helicity: A symplectic viewpoint

    Science.gov (United States)

    Elbistan, M.; Duval, C.; Horváthy, P. A.; Zhang, P.-M.

    2016-10-01

    The theorem which says that helicity is the conserved quantity associated with the duality symmetry of the vacuum Maxwell equations is proved by viewing electromagnetism as an infinite dimensional symplectic system. In fact, it is shown that helicity is the moment map of duality acting as an SO (2) group of canonical transformations on the symplectic space of all solutions of the vacuum Maxwell equations.

  15. Intrahepatic arterioportal shunt: helical CT findings

    Energy Technology Data Exchange (ETDEWEB)

    Quiroga, S.; Sebastia, M.C.; Moreiras, M.; Pallisa, E.; Rius, J.M.; Alvarez-Castells, A. [I. D. I. Hospital General i Universitari Vall d`Hebron, Barcelona (Spain). Servei de Radiodiagnostic

    1999-08-01

    The purpose of this study was to characterize the appearance of intrahepatic arterioportal shunts (APS) on two-phase helical CT, with emphasis on the importance of the hepatic arterial-dominant phase (HAP) to demonstrate perfusion disorders. We review eight cases of APS diagnosed by helical CT in our institution from January 1996 to March 1997 and describe the CT findings that established diagnosis. Five of them were confirmed by angiography. In seven (87.5 %) cases of APS we found early enhancement of the peripheral portal branches during the HAP of helical CT, whereas the superior mesenteric and splenic veins remained unenhanced. In five (62.5 %) cases of APS, transient, peripheral, triangular parenchymal enhancement was depicted during the HAP of helical CT; in four of these cases there was associated early enhancement of the portal branches. Helical CT can show perfusion alterations that might remain undiagnosed with conventional CT. An understanding of the hemodynamic changes that occur in APS can help in the interpretation of focal transient hepatic parenchymal enhancement and to differentiate APS from hypervascular tumors. We believe that the helical CT findings described herein are characteristic enough to suggest the diagnosis of APS. (orig.) With 3 figs., 1 tab., 16 refs.

  16. The AGS with four helical magnets

    Energy Technology Data Exchange (ETDEWEB)

    Tsoupas, N.; Huang, H.; MacKay, W.W.; Roser, T.; Trbojevic, D.

    2010-02-25

    The idea of using multiple partial helical magnets was applied successfully to the AGS synchrotron, to preserve the proton beam polarization. In this paper we explore in details the idea of using four helical magnets placed symmetrically in the AGS ring. This modification provides many advantages over the present setup of the AGS that uses two partial helical magnets. First, it provides a larger 'spin tune gap' for the placement of the vertical betatron tune of the AGS during acceleration, second, the vertical spin direction during the beam injection and extraction is closer to vertical, third, the symmetric placement of the snakes allows for a better control of the AGS optics, and for reduced values of the beta and eta functions, especially near injection, fourth, the optical properties of the helical magnets also favor the placement of the horizontal betatron tune in the 'spin tune gap', thus eliminating the horizontal spin resonances. In this paper we provide results on the spin tune and on the optics of the AGS with four partial helical magnets, and we compare these results with the present setup of the AGS that uses two partial helical magnets.

  17. Alternative Methods for Field Corrections in Helical Solenoids

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, M. L. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Krave, S. T. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Tompkins, J. C. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Yonehara, K. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Flanagan, G. [Muons Inc., Batavia, IL (United States); Kahn, S. A. [Muons Inc., Batavia, IL (United States); Melconian, K. [Texas A & M Univ., College Station, TX (United States)

    2015-05-01

    Helical cooling channels have been proposed for highly efficient 6D muon cooling. Helical solenoids produce solenoidal, helical dipole, and helical gradient field components. Previous studies explored the geometric tunability limits on these main field components. In this paper we present two alternative correction schemes, tilting the solenoids and the addition of helical lines, to reduce the required strength of the anti-solenoid and add an additional tuning knob.

  18. Long Lived Photo-induced Charge Separation in a Trinuclear Iron-{mu}3-oxo-based Metal-Organic Framework

    Energy Technology Data Exchange (ETDEWEB)

    Hanna, Lauren; Kucheryavy, Pavel; Liu, Cunming; Zhang, Xiaoyi; Lockard, Jenny V.

    2017-06-29

    The presence of long-lived charge-separated excited states in metal-organic frameworks (MOFs) can enhance their photocatalytic activity by decreasing the probability that photogenerated electrons and holes recombine before accessing adsorbed reactants. Detecting these charge separated states via optical transient absorption, however, can be challenging when they lack definitive optical signatures. Here, we investigate the long-lived excited state of a MOF with such vague optical properties, MIL-100(Fe), comprised of Fe3-μ3-oxo clusters and trimesic acid linkers using Fe K-edge X-ray transient absorption (XTA) spectroscopy, to unambiguously determine its ligand-to-metal charge transfer character. Spectra measured at time delays up to 3.6 μs confirm the long lived nature of the charge separated excited state. Several trinuclear iron μ3- oxo carboxylate complexes, which model the trinuclear cores of the MOF structure, are measured for comparison using both steady state XAS and XTA to further support this assignment and corresponding decay time. The MOF is prepared as a colloidal nanoparticle suspension for these measurements so both its fabrication and particle size analysis are presented, as well.

  19. Preparation, X-ray Structures, Spectroscopic, and Redox Properties of Di- and Trinuclear Iron-Zirconium and Iron-Hafnium Porphyrinoclathrochelates.

    Science.gov (United States)

    Dudkin, Semyon V; Erickson, Nathan R; Vologzhanina, Anna V; Novikov, Valentin V; Rhoda, Hannah M; Holstrom, Cole D; Zatsikha, Yuriy V; Yusubov, Mekhman S; Voloshin, Yan Z; Nemykin, Victor N

    2016-11-21

    The first hybrid di- and trinuclear iron(II)-zirconium(IV) and iron(II)-hafnium(IV) macrobicyclic complexes with one or two apical 5,10,15,20-tetraphenylporphyrin fragments were obtained using transmetalation reaction between n-butylboron-triethylantimony-capped or bis(triethylantimony)-capped iron(II) clathrochelate precursors and dichlorozirconium(IV)- or dichlorohafnium(IV)-5,10,15,20-tetraphenylporphyrins under mild conditions. New di- and trinuclear porphyrinoclathrochelates of general formula FeNx3((Bn-Bu)(MTPP)) and FeNx3(MTPP)2 [M = Zr, Hf; TPP = 5,10,15,20-tetraporphyrinato(2-); Nx = nioximo(2-)] were characterized by one-dimensional ((1)H and (13)C{(1)H}) and two-dimensional (COSY and HSQC) NMR, high-resolution electrospray ionization mass spectrometry, UV-visible, and magnetic circular dichroism spectra, single-crystal X-ray diffraction experiments, as well as elemental analyses. Redox properties of all complexes were probed using electrochemical and spectroelectrochemical approaches. Electrochemical and spectroelectrochemical data suggestive of a very weak, if any, long-range electronic coupling between two porphyrin π-systems in FeNx3(MTPP)2 complexes. Density functional theory and time-dependent density functional theory calculations were used to correlate spectroscopic signatures and redox properties of new compounds with their electronic structures.

  20. Synthesis, crystal structure and spectral properties of a supramolecular trinuclear nickel(II) complex with 5-methoxy-4'-bromo-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol.

    Science.gov (United States)

    Dong, Wen-Kui; Du, Wei; Zhang, Xin-Ying; Li, Gang; Dong, Xiu-Yan

    2014-11-11

    A novel trinuclear Ni(II) complex [{NiL(n-PrOH)(μ-OAc)}2Ni]·n-PrOH·H2O with an asymmetric Salamo-type ligand, 5-methoxy-4'-bromo-2,2'-[ethylenedioxybis(nitrilomethylidyne)]diphenol (H2L), has been synthesized and characterized by elemental analyses, IR, UV/Vis and fluorescence spectra and molar conductance measurement. The crystal structure of the Ni(II) complex has been determined by single-crystal X-ray diffraction. Two acetate groups coordinating to three Ni(II) ions through NiOCONi bridges and four μ-phenoxo oxygen atoms from two [NiL(n-PrOH)] units also coordinating to Ni(II) ions. In the Ni(II) complex, two n-propanol molecules are coordinated to the two terminal Ni(II) ions having slightly distorted octahedral coordination geometries and form a trinuclear structure, There are also one non-coordinated n-propanol and one non-coordinated water molecule. In the crystal structure, the Ni(II) complex is linked by intermolecular hydrogen bonds into an infinite 1D supramolecular chain-like structure.

  1. A computational study of structural and magnetic properties of bi- and trinuclear Cu(II) complexes with extremely long Cu-Cu distances

    Science.gov (United States)

    Baryshnikov, Gleb V.; Minaev, Boris F.; Baryshnikova, Alina T.; Ågren, Hans

    2017-07-01

    Three recently synthesized copper(II) complexes with aroylhydrazones of trifluoroacetic and benzenecarboxylic acids (Dalton Trans., 2013, 42, 16878) have been computationally investigated by density functional theory within the broken symmetry approximation accounting for empirical dispersion corrections. A topological analysis of electron density distributions has been carried out using Bader's ;quantum theory of atoms in molecules; formalism. The calculated values of spin-spin exchange for the studied dinuclear complexes indicate a very weak ferromagnetic coupling of the unpaired electrons in good agreement with experimental data. At the same time, the trinuclear copper(II) complex possesses a low-spin doublet ground state with one ferromagnetic and two antiferromagnetic spin projections between the triangular-positioned Cu2+ ions. The estimated values of the coupling constants for the spin-spin exchange in this trinuclear complex are in a good agreement with experimental observations. The calculations support a mechanism of exchange coupling through the aromatic links in these strongly spin-separated systems.

  2. Rational design of azide-bridged bimetallic complexes. Crystal structure and magnetic properties of Fe(III)MFe(III) (M = Ni(II) and Cu(II)) trinuclear species.

    Science.gov (United States)

    Colacio, Enrique; Costes, Jean-Pierre; Domínguez-Vera, José M; Maimoun, Ikram Ben; Suárez-Varela, José

    2005-01-28

    The first examples of azide-bridged bimetallic trinuclear complexes ([M(cyclam)][FeL(N3)(mu1,5-N3)]2) (H2L = 4,5-dichloro-1,2-bis(pyridine-2-carboxamido) benzene) have been structurally and magnetically characterized.

  3. Hydrogels of Superlong Helices to Synthesize Hybrid Ag-Helical Nanomaterials.

    Science.gov (United States)

    Li, Guihua; Wang, Yitong; Wang, Ling; Song, Aixin; Hao, Jingcheng

    2016-11-22

    The gelation behavior of mixtures of sodium deoxycholate (NaDC) and glutathione (GSH) in water is investigated. The system exhibits a structural transition of self-assembled hydrogels from nanofibers to nanohelix structures, and then to helical ribbons with increasing GSH concentration. Superlong helical nanofibers with left- and right-handed orientations are produced by tuning the concentration of GSH at a fixed concentration of NaDC. Random coil and β-sheet structures are significant for the formation of the helical structures, and are indicated by circular dichroism (CD) and Fourier transform infrared (FT-IR) spectra. The mechanical strength of the "weak" hydrogels is enhanced by the introduction of appropriate suitable amount of AgNO3. Furthermore, the controlled growth of Ag nanoparticles at spatially arranged locations along the nanohelices (hybrid Ag-helical nanomaterial) is readily achieved by UV reduction of Ag (I) ions on the supramolecular helical templates.

  4. Fabrication and experimentation of FRP helical spring

    Science.gov (United States)

    Ekanthappa, J.; Shiva Shankar, G. S.; Amith, B. M.; Gagan, M.

    2016-09-01

    In present scenario, the automobile industry sector is showing increased interest in reducing the unsprung weight of the automobile & hence increasing the fuel Efficiency. One of the feasible sub systems of a vehicle where weight reduction may be attempted is vehicle- suspension system. Usage of composite material is a proven way to lower the component weight without any compromise in strength. The composite materials are having high specific strength, more elastic strain energy storage capacity in comparison with those of steel. Therefore, helical coil spring made of steel is replaceable by composite cylindrical helical coil spring. This research aims at preparing a re-usable mandrel (mould) of Mild steel, developing a setup for fabrication, fabrication of FRP helical spring using continuous glass fibers and Epoxy Resin (Polymer). Experimentation has been conducted on fabricated FRP helical spring to determine its strength parameters & for failure analysis. It is found that spring stiffness (K) of Glass/Epoxy helical-spring is greater than steel-coil spring with reduced weight.

  5. Unusually Stable Helical Coil Allotrope of Phosphorus.

    Science.gov (United States)

    Liu, Dan; Guan, Jie; Jiang, Jingwei; Tománek, David

    2016-12-14

    We have identified an unusually stable helical coil allotrope of phosphorus. Our ab initio density functional theory calculations indicate that the uncoiled, isolated straight one-dimensional chain is equally stable as a monolayer of black phosphorus dubbed phosphorene. The coiling tendency and the attraction between adjacent coil segments add an extra stabilization energy of ∼12 meV/atom to the coil allotrope, similar in value to the ∼16 meV/atom interlayer attraction in bulk black phosphorus. Thus, the helical coil structure is essentially as stable as black phosphorus, the most stable phosphorus allotrope known to date. With an optimum radius of 2.4 nm, the helical coil of phosphorus may fit well and even form inside wide carbon nanotubes.

  6. FLUID FLOW IN ROTATING HELICAL SQUARE DUCTS

    Institute of Scientific and Technical Information of China (English)

    Chen Hua-jun; Zhang Ben-zhao; Zhang Jin-suo

    2003-01-01

    A numerical study is made for a fully developed laminar flow in rotating helical pipes.Due to the rotation, the Coriolis force can also contribute to the secondary flow.The interaction between rotation, torsion, and curvature complicates the flow characteristics.The effects of rotation and torsion on the flow transitions are studied in details.The results show that there are obvious differences between the flow in rotating ducts and in helical ducts without rotation.Certain hitherto unknown flow patterns are found.The effects of rotation and torsion on the friction factor are also examined.Present results show the characteristics of the fluid flow in rotating helical square ducts.

  7. Manipulation of wavefront using helical metamaterials.

    Science.gov (United States)

    Yang, Zhenyu; Wang, Zhaokun; Tao, Huan; Zhao, Ming

    2016-08-01

    Helical metamaterials, a kind of 3-dimensional structure, has relatively strong coupling effect among the helical nano-wires. Therefore, it is expected to be a good candidate for generating phase shift and controlling wavefront with high efficiency. In this paper, using the finite-difference time-domain (FDTD) method, we studied the phase shift properties in the helical metamaterials. It is found that the phase shift occurs for both transmitted and reflected light waves. And the maximum of reflection coefficients can reach over 60%. In addition, the phase shift (φ) is dispersionless in the range of 600 nm to 860 nm, that is, it is only dominated by the initial angle (θ) of the helix. The relationship between them is φ = ± 2θ. Using Jones calculus we give a further explanation for these properties. Finally, by arranging the helixes in an array with a constant phase gradient, the phenomenon of anomalous refraction was also observed in a broad wavelength range.

  8. Nondispersive optical activity of meshed helical metamaterials.

    Science.gov (United States)

    Park, Hyun Sung; Kim, Teun-Teun; Kim, Hyeon-Don; Kim, Kyungjin; Min, Bumki

    2014-11-17

    Extreme optical properties can be realized by the strong resonant response of metamaterials consisting of subwavelength-scale metallic resonators. However, highly dispersive optical properties resulting from strong resonances have impeded the broadband operation required for frequency-independent optical components or devices. Here we demonstrate that strong, flat broadband optical activity with high transparency can be obtained with meshed helical metamaterials in which metallic helical structures are networked and arranged to have fourfold rotational symmetry around the propagation axis. This nondispersive optical activity originates from the Drude-like response as well as the fourfold rotational symmetry of the meshed helical metamaterials. The theoretical concept is validated in a microwave experiment in which flat broadband optical activity with a designed magnitude of 45° per layer of metamaterial is measured. The broadband capabilities of chiral metamaterials may provide opportunities in the design of various broadband optical systems and applications.

  9. Large-scale dynamics of magnetic helicity

    Science.gov (United States)

    Linkmann, Moritz; Dallas, Vassilios

    2016-11-01

    In this paper we investigate the dynamics of magnetic helicity in magnetohydrodynamic (MHD) turbulent flows focusing at scales larger than the forcing scale. Our results show a nonlocal inverse cascade of magnetic helicity, which occurs directly from the forcing scale into the largest scales of the magnetic field. We also observe that no magnetic helicity and no energy is transferred to an intermediate range of scales sufficiently smaller than the container size and larger than the forcing scale. Thus, the statistical properties of this range of scales, which increases with scale separation, is shown to be described to a large extent by the zero flux solutions of the absolute statistical equilibrium theory exhibited by the truncated ideal MHD equations.

  10. A helically distorted MHD flux rope model

    Science.gov (United States)

    Theobald, Michael L.; Montgomery, David

    1990-01-01

    A flux rope model is proposed which has a variable degree of helical distortion from axisymmetry. The basis for this suggestion is a series of numerical and analytical investigations of magnetohydrodynamic states which result when an axial electric current is directed down on dc magnetic field. The helically distorted states involve a flow velocity and seem to be favored because of their lower rate of energy dissipation. Emphasis is on the magnetometer and particle energy analyzer traces that might be characteristic of such flux ropes. It is shown that even a fractionally small helical distortion may considerably alter the traces in minimum-variance coordinates. In short, what may be fairly common MHD processes can render a flux rope almost unrecognizable under standard diagnostics, even if the departures from axisymmetry are not great.

  11. Turbulent dynamo with advective magnetic helicity flux

    CERN Document Server

    Del Sordo, Fabio; Brandenburg, Axel

    2012-01-01

    Many astrophysical bodies harbor magnetic fields that are thought to be sustained by dynamo processes. However, it has been argued that the production of large-scale magnetic fields by a mean-field dynamo is strongly suppressed at large magnetic Reynolds numbers owing to the conservation of magnetic helicity. This phenomenon is known as catastrophic quenching. Advection of magnetic field toward the outer boundaries and away from the dynamo is expected to alleviate such quenching. Examples are stellar and galactic winds. Such advection might be able to overcome the constraint imposed by the conservation of magnetic helicity, transporting a fraction of it outside the domain in which the dynamo operates. We study how the dynamo process is affected by advection. In particular, we study the relative roles played by advective and diffusive fluxes of magnetic helicity. We do this by performing direct numerical simulations of a turbulent dynamo of alpha^2 type driven by forced turbulence in a Cartesian domain in the ...

  12. Metallofoldamers supramolecular architectures from helicates to biomimetics

    CERN Document Server

    Maayan, Galia

    2013-01-01

    Metallofoldamers are oligomers that fold into three-dimensional structures in a controlled manner upon coordination with metal ions. Molecules in this class have shown an impressive ability to form single-handed helical structures and other three-dimensional architectures. Several metallofoldamers have been applied as sensors due to their selective folding when binding to a specific metal ion, while others show promise for applications as responsive materials on the basis of their ability to fold and unfold upon changes in the oxidation state of the coordinated metal ion, and as novel catalysts. Metallofoldamers: From Helicates to Biomimetic Architectures describes the variety of interactions between oligomers and metal species, with a focus on non-natural synthetic molecules. Topics covered include: the major classes of foldamers and their folding driving force metalloproteins and metalloenzymes helicates: self-assembly, structure and applications abiotic metallo-DNA metallo-PNA and iDNA metallopeptides inte...

  13. The helical structure of DNA facilitates binding

    Science.gov (United States)

    Berg, Otto G.; Mahmutovic, Anel; Marklund, Emil; Elf, Johan

    2016-09-01

    The helical structure of DNA imposes constraints on the rate of diffusion-limited protein binding. Here we solve the reaction-diffusion equations for DNA-like geometries and extend with simulations when necessary. We find that the helical structure can make binding to the DNA more than twice as fast compared to a case where DNA would be reactive only along one side. We also find that this rate advantage remains when the contributions from steric constraints and rotational diffusion of the DNA-binding protein are included. Furthermore, we find that the association rate is insensitive to changes in the steric constraints on the DNA in the helix geometry, while it is much more dependent on the steric constraints on the DNA-binding protein. We conclude that the helical structure of DNA facilitates the nonspecific binding of transcription factors and structural DNA-binding proteins in general.

  14. Demonstration of steady inductive helicity injection

    Science.gov (United States)

    Sieck, P. E.; Jarboe, T. R.; Izzo, V. A.; Hamp, W. T.; Nelson, B. A.; O'Neill, R. G.; Redd, A. J.; Smith, R. J.

    2006-02-01

    Initial results demonstrating the concept of constant inductive helicity injection are presented. Constant helicity injection is achieved using two oscillating inductive helicity injectors, with the goal of producing a bow tie spheromak. Each injector is a 180° segment of a reverse field pinch and they are driven 90° out of phase. Approximately 5 MW of power is injected during the 6 ms pulse, and the input power has been maintained at a fairly constant value by directly fuelling the injectors with neutral gas. Motivation for the experiment is given, including beta-limit calculations for the bow tie spheromak. Fuelling the injectors with neutral gas during the discharge is shown to produce injector parameters that are more constant in time. A series of discharges with increasing power input shows a promising increase in toroidal current. Unique construction techniques of the experiment are also described.

  15. Current helicity and electromotive force of magnetoconvection influenced by helical background fields

    CERN Document Server

    Ruediger, Guenther

    2016-01-01

    Motivated by the empirical finding that the known hemispheric rules for the current helicity at the solar surface are not strict, the excitation of small-scale current helicity by the influence of a large-scale helical magnetic background fields on nonrotating magnetoconvection is demonstrated. It is shown within a quasilinear analytic theory of driven turbulence and by nonlinear simulations of magnetoconvection that the resulting small-scale current helicity has the same sign as the large-scale current helicity while the ratio of both pseudo-scalars is of the order of the magnetic Reynolds number of the convection. The same models do not provide finite values of the small-scale kinetic helicity. On the other hand, a turbulence-induced electromotive force is produced including the diamagnetic pumping term as well as the eddy diffusivity but no alpha effect. It is thus argued that the relations by Pouquet & Patterson (1978) and Keinigs (1983) for the simultaneous existence of small-scale current helicity a...

  16. Statistical mechanics of double-helical polymers.

    Science.gov (United States)

    De Col, Alvise; Liverpool, Tanniemola B

    2004-06-01

    We introduce a simple geometric model for a double-stranded and double-helical polymer. We study the statistical mechanics of such polymers using both analytical techniques and simulations. Our model has a single energy scale which determines both the bending and twisting rigidity of the polymer. The helix melts at a particular temperature T(c) below which the chain has a helical structure and above which this structure is disordered. Under extension we find that for small forces, the behavior is very similar to wormlike chain behavior but becomes very different at higher forces.

  17. Helicity and nuclear $\\beta$ decay correlations

    CERN Document Server

    Hong, Ran; García, Alejandro

    2016-01-01

    We present simple derivations of nuclear $\\beta$-decay correlations with an emphasis on the special role of helicity. This provides a good opportunity to teach students about helicity and chirality in particle physics through exercises using simple aspects of quantum mechanics. In addition, this paper serves as an introduction to nuclear $\\beta$-decay correlations from both a theoretical and experimental vantage. This article can be used to introduce students to ongoing experiments searching for hints of new physics in the low-energy precision frontier.

  18. Helicity and nuclear β decay correlations

    Science.gov (United States)

    Hong, Ran; Sternberg, Matthew G.; Garcia, Alejandro

    2017-01-01

    We present simple derivations of nuclear β-decay correlations with an emphasis on the special role of helicity. This topic provides a good opportunity to teach students about helicity and chirality in particle physics with exercises that use simple aspects of quantum mechanics. In addition, this paper serves as an introduction to nuclear β-decay correlations from both a theoretical and experimental perspective. This article can be used to introduce students to ongoing experiments searching for hints of new physics in the low-energy precision frontier.

  19. Helicity separation in Heavy-Ion Collisions

    CERN Document Server

    Baznat, Mircea; Sorin, Alexander; Teryaev, Oleg

    2013-01-01

    We study the P-odd effects related to the vorticity of the medium formed in noncentral heavy ion collisions. Using the kinetic Quark-Gluon Strings Model we perform the numerical simulations of the vorticity and hydrodynamical helicity for the various atomic numbers, energies and centralities. We observed the vortical structures typically occupying the relatively small fraction of the fireball volume. In the course of numerical simulations the noticeable hydrodanamical helicity was observed manifesting the specific mirror behaviour with respect to the reaction plane. The effect is maximal at the NICA and FAIR energy range.

  20. Conversion from mutual helicity to self-helicity observed with IRIS

    Science.gov (United States)

    Li, L. P.; Peter, H.; Chen, F.; Zhang, J.

    2014-10-01

    Context. In the upper atmosphere of the Sun observations show convincing evidence for crossing and twisted structures, which are interpreted as mutual helicity and self-helicity. Aims: We use observations with the new Interface Region Imaging Spectrograph (IRIS) to show the conversion of mutual helicity into self-helicity in coronal structures on the Sun. Methods: Using far UV spectra and slit-jaw images from IRIS and coronal images and magnetograms from SDO, we investigated the evolution of two crossing loops in an active region, in particular, the properties of the Si IV line profile in cool loops. Results: In the early stage two cool loops cross each other and accordingly have mutual helicity. The Doppler shifts in the loops indicate that they wind around each other. As a consequence, near the crossing point of the loops (interchange) reconnection sets in, which heats the plasma. This is consistent with the observed increase of the line width and of the appearance of the loops at higher temperatures. After this interaction, the two new loops run in parallel, and in one of them shows a clear spectral tilt of the Si IV line profile. This is indicative of a helical (twisting) motion, which is the same as to say that the loop has self-helicity. Conclusions: The high spatial and spectral resolution of IRIS allowed us to see the conversion of mutual helicity to self-helicity in the (interchange) reconnection of two loops. This is observational evidence for earlier theoretical speculations. Movie associated with Fig. 1 and Appendix A are available in electronic form at http://www.aanda.org

  1. Eikonal slant helices and eikonal Darboux helices in 3-dimensional pseudo-Riemannian manifolds

    OpenAIRE

    Önder, Mehmet; Ziplar, Evren

    2013-01-01

    In this study, we give definitions and characterizations of eikonal slant helices, eikonal Darboux helices and non-normed eikonal Darboux helices in 3-dimensional pseudo- Riemannian manifold M . We show that every eikonal slant helix is also an eikonal Darboux helix for timelike and spacelike curves. Furthermore, we obtain that if the non-null curve a is a non-normed eikonal Darboux helix, then a is an eikonal slant helix if and only if 2 2 e 3k +e1t = constant, where k and t are curvature an...

  2. Energy and helicity budgets of solar quiet regions

    CERN Document Server

    Tziotziou, K; Georgoulis, M K; Kontogiannis, I

    2014-01-01

    We investigate the free magnetic energy and relative magnetic helicity budgets of solar quiet regions. Using a novel non-linear force-free method requiring single solar vector magnetograms we calculate the instantaneous free magnetic energy and relative magnetic helicity budgets in 55 quiet-Sun vector magnetograms. As in a previous work on active regions, we construct here for the first time the (free) energy-(relative) helicity diagram of quiet-Sun regions. We find that quiet-Sun regions have no dominant sense of helicity and show monotonic correlations a) between free magnetic energy/relative helicity and magnetic network area and, consequently, b) between free magnetic energy and helicity. Free magnetic energy budgets of quiet-Sun regions represent a rather continuous extension of respective active-region budgets towards lower values, but the corresponding helicity transition is discontinuous due to the incoherence of the helicity sense contrary to active regions. We further estimate the instantaneous free...

  3. Helical mode interactions and spectral transfer processes in magnetohydrodynamic turbulence

    CERN Document Server

    Linkmann, Moritz F; McKay, Mairi E; Jäger, Julia

    2015-01-01

    Spectral transfer processes in magnetohydrodynamic (MHD) turbulence are investigated analytically by decomposition of the velocity and magnetic fields in Fourier space into helical modes. Steady solutions of the dynamical system which governs the evolution of the helical modes are determined, and a stability analysis of these solutions is carried out. The interpretation of the analysis is that unstable solutions lead to energy transfer between the interacting modes while stable solutions do not. From this, a dependence of possible interscale energy and helicity transfers on the helicities of the interacting modes is derived. As expected from the inverse cascade of magnetic helicity in 3D MHD turbulence, mode interactions with like helicities lead to transfer of energy and magnetic helicity to smaller wavenumbers. However, some interactions of modes with unlike helicities also contribute to an inverse energy transfer. As such, an inverse energy cascade for nonhelical magnetic fields is shown to be possible. Fu...

  4. Two new coordination polymers with flexible alicyclic carboxylate and bipyridyl co-ligands bearing trinuclear [Ni3(COO)6] SBUs: Synthesis, crystal structures, and magnetic properties

    Science.gov (United States)

    Zhu, Xian-Dong; Li, Yong; Gao, Jian-Gang; Wang, Fen-Hua; Li, Qing-Hai; Yang, Hong-Xun; Chen, Lei

    2017-02-01

    Two new coordination polymers generally formulated as [Ni3(Hchda)2(chda)2(bpy)2(H2O)2]n (1) and [Ni3(Hchda)2(chda)2(bpp)2(H2O)2]n (2) [H2chda = 1,1'-cyclohexanediacetic acid, bpy = 4,4'-bipyridine and bpp = 1,3-bis(4-pyridyl)propane], have been successfully assembled through mixed-ligands synthetic strategy with flexible alicyclic carboxylate and bipyridyl ligands. There structures feature trinuclear nickel secondary building units connected via the bridging bipyridyl spacers to form two-dimensional (4,4) grid layer. The nature of the different N-donor auxiliary ligands leads to the discrepancy in supramolecular structure of the two compounds. Magnetic studies indicate the ferromagnetic intra-complex magnetic interaction in the molecule for 1 and 2.

  5. A trinuclear Mo-Fe-Mo cluster compound [ Et4N] {[Me2dtcMoO(μ-S) 2] 2Fe} containing dialkyldithiocarbamate ligand

    Institute of Scientific and Technical Information of China (English)

    ZHANG, Yan-Shi; LIU, Qiu-Tian; ZHU, Hong-Ping; CHEN, Yi-Hui; CHEN, Chang-Neng

    2000-01-01

    A trinuclear linear Mo-Fe-Mo dialkyldithiocarbamate complex [Et4N] {[Me2dtcMoO(μ-S)2]2Fe} has been obtained and structurally characterized, which contains two Me2dtcMoO(μ-S)2 units coordinated to a central tetrahedral Fe atom. A comparison of the structural parameters indicates the metal oxidation states of 2Mo(v) + Fe(Ⅲ). The 1H NMR shows chemical shifts of Me2dtc ligands at δ 10.14 and δ 9.40 with the intensity ratio of 1:1. The cyclic voltammogram displays a reversiible couple at - 1.41 V/- 1.36 V responsible for 1-/2-anions of the complex and an irreversible oxidation at 0.5 V,which seems to show the apparent lack of stability for its neutral species (Me2dtcMoOS2)2Fe.

  6. Tuning the photoluminescence of condensed-phase cyclic trinuclear Au(I) complexes through control of their aggregated structures by external stimuli

    Science.gov (United States)

    Fujisawa, Kaori; Yamada, Shigeyuki; Yanagi, Yukihiro; Yoshioka, Yasunori; Kiyohara, Ayumi; Tsutsumi, Osamu

    2015-01-01

    A series of new cyclic trinuclear Au(I) complexes with alkoxy side chains of various lengths were synthesized as photoluminescence materials. None of the complexes emitted luminescence in solution; however, some showed photoluminescence in the crystalline phase. Single crystal X-ray structural analyses revealed that an intermolecular interaction between two Au atoms (aurophilic interaction) existed only in the emissive complexes, which formed molecular aggregates in the crystal. Because isolated molecules show no luminescence in the present system, we conclude that only molecules aggregated via aurophilic interactions can luminesce. We demonstrated that luminescence properties, such as colour and intensity, were very sensitive to the aggregated structure of the molecules. We also found that such luminescence properties can be controlled by a change in the aggregated structure induced by external stimuli, such as heat, solvent, and mechanical stress. PMID:25879782

  7. Synthesis, Characterization and DFT-Based Investigation of a Novel Trinuclear Singly-Chloro-Bridged Copper(II)-1-Vinylimidazole Complex.

    Science.gov (United States)

    Yolcu, Zuhal; Demir, Serkan; Andaç, Ömer; Büyükgüngör, Orhan

    2016-01-01

    A novel trinuclear copper(II) complex [Cu3(μ-Cl)2Cl4(1-Vim)6] with monodentate 1-vinylimidazole (1-Vim) and chloro ligands has been prepared and experimentally characterized by elemental analysis, thermogravimetry (TGA, DTG, DTA), X-ray single crystal diffractometry, TOF-MS and FT-IR spectroscopies. The electronic and structural properties of the complex were further investigated by DFT/TD-DFT methods. Density functional hybrid method (B3LYP) was applied throughout the calculations. The calculated UV-Vis results based on TD-DFT approach were simulated and compared with experimental spectrum. Based on the data obtained, DFT calculations have been found in reasonable accordance with experimental data.

  8. Tuning the photoluminescence of condensed-phase cyclic trinuclear Au(I) complexes through control of their aggregated structures by external stimuli

    Science.gov (United States)

    Fujisawa, Kaori; Yamada, Shigeyuki; Yanagi, Yukihiro; Yoshioka, Yasunori; Kiyohara, Ayumi; Tsutsumi, Osamu

    2015-03-01

    A series of new cyclic trinuclear Au(I) complexes with alkoxy side chains of various lengths were synthesized as photoluminescence materials. None of the complexes emitted luminescence in solution; however, some showed photoluminescence in the crystalline phase. Single crystal X-ray structural analyses revealed that an intermolecular interaction between two Au atoms (aurophilic interaction) existed only in the emissive complexes, which formed molecular aggregates in the crystal. Because isolated molecules show no luminescence in the present system, we conclude that only molecules aggregated via aurophilic interactions can luminesce. We demonstrated that luminescence properties, such as colour and intensity, were very sensitive to the aggregated structure of the molecules. We also found that such luminescence properties can be controlled by a change in the aggregated structure induced by external stimuli, such as heat, solvent, and mechanical stress.

  9. An Extended Chain and Trinuclear Complexes Based on Pt(II)-M (M = Tl(I), Pb(II)) Bonds: Contrasting Photophysical Behavior.

    Science.gov (United States)

    Forniés, Juan; Giménez, Nora; Ibáñez, Susana; Lalinde, Elena; Martín, Antonio; Moreno, M Teresa

    2015-05-04

    The syntheses and structural characterizations of a Pt-Tl chain [{Pt(bzq)(C6F5)2}Tl(Me2CO)]n 1 and two trinuclear Pt2M clusters (NBu4)[{Pt(bzq)(C6F5)2}2Tl] 2 and [{Pt(bzq)(C6F5)2}2Pb] 3 (bzq = 7,8-benzoquinolinyl), stabilized by donor-acceptor Pt → M bonds, are reported. The one-dimensional heterometallic chain 1 is formed by alternate "Pt(bzq)(C6F5)2" and "Tl(Me2CO)" fragments, with Pt-Tl bond separations in the range of 2.961(1)-3.067(1) Å. The isoelectronic trinuclear complexes 2 (which crystallizes in three forms, namely, 2a, 2b, and 2c) and 3 present a sandwich structure in which the Tl(I) or Pb(II) is located between two "Pt(bzq)(C6F5)2" subunits. NMR studies suggest equilibria in solution implying cleavage and reformation of Pt-M bonds. The lowest-lying absorption band in the UV-vis spectra in CH2Cl2 and tetrahydrofuran (THF) of 1, associated with (1)MLCT/(1)L'LCT (1)[5dπ(Pt) → π*(bzq)]/(1)[(C6F5) → bzq], displays a blue shift in relation to the precursor, suggesting the cleavage of the chain maintaining bimetallic Pt-Tl fragments in solution, also supported by NMR spectroscopy. In 2 and 3, it shows a blue shift in THF and a red shift in CH2Cl2, supporting a more extensive cleavage of the Pt-M bonds in THF solutions than in CH2Cl2, where the trinuclear entities are predominant. The Pt-Tl chain 1 displays in solid state a bright orange-red emission ascribed to (3)MM'CT (M' = Tl). It exhibits remarkable and fast reversible vapochromic and vapoluminescent response to donor vapors (THF and Et2O), related to the coordination/decoordination of the guest molecule to the Tl(I) ion, and mechanochromic behavior, associated with the shortening of the intermetallic Pt-Tl separations in the chain induced by grinding. In frozen solutions (THF, acetone, and CH2Cl2) 1 shows interesting luminescence thermochromism with emissions strongly dependent on the solvent, concentration, and excitation wavelengths. The Pt2Tl complex 2 shows an emission close to 1, ascribed to

  10. Theoretical study on magneto-structural correlation of trinuclear copper (II) complex with the hydroxo bridge and bidentate syn-syn carboxylate group

    Institute of Scientific and Technical Information of China (English)

    QI Zhongnan; WU Jian; LIU Chengbu; WANG Ruoxi; SUN Youmin

    2006-01-01

    The theoretical study on magneto- structural correlation in linear trinuclear Cu (II) complex bridged by hydroxo group and bidentate formato group has been performed using the broken symmetry approach with the framework of density functional theory (DFT-BS). The magnetic coupling constant for the model complex is 70.97 cm-1, comparable with the experimentally measured J value (77 cm-1). The calculated results show that the magnetic coupling interaction firstly slightly increases with the changes of the coordination environment around the terminal Cu atoms from a distorted square pyramid to a trigonal bi-pyramid, and decreases subsequently. In the course of changes, the sign of J value shifts from positive to negative. The magnetic coupling interaction is sensitive to coordination environment of the terminal Cu. The calculated results also reveal that the ferromagnetic coupling arises from the countercomplementarity of the hydroxo and formato bridges. Molecular orbital analysis validates the conclusion.

  11. Synthesis of stabilized alpha-helical peptides.

    Science.gov (United States)

    Bernal, Federico; Katz, Samuel G

    2014-01-01

    Stabilized alpha-helical (SAH) peptides are valuable laboratory tools to explore important protein-protein interactions. Whereas most peptides lose their secondary structure when isolated from the host protein, stapled peptides incorporate an all-hydrocarbon "staple" that reinforces their natural alpha-helical structure. Thus, stapled peptides retain their functional ability to bind their native protein targets and serve multiple experimental uses. First, they are useful for structural studies such as NMR or crystal structures that map and better define binding sites. Second, they can be used to identify small molecules that specifically target that interaction site. Third, stapled peptides can be used to test the importance of specific amino acid residues or posttranslational modifications to the binding. Fourth, they can serve as structurally competent bait to identify novel binding partners to specific alpha-helical motifs. In addition to markedly improved alpha-helicity, stapled peptides also display resistance to protease cleavage and enhanced cell permeability. Most importantly, they are useful for intracellular experiments that explore the functional consequences of blocking particular protein interactions. Because of their remarkable stability, stapled peptides can be applied to whole-animal, in vivo studies. Here we describe a protocol for the synthesis of a peptide that incorporates an all-hydrocarbon "staple" employing a ring-closing olefin metathesis reaction. With proper optimization, stapled peptides can be a fundamental, accurate laboratory tool in the modern chemical biologist's armory.

  12. LAMINAR FLUID FLOW IN HELICAL ELLIPTICAL PIPE

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    In this paper, using an orthogonal curvilinear coordinate system and solving the complete N-S equations, we analyzed the flow in a helical elliptical duct by the perturbation method. The first-order solutions of the stream function Ψ, axial velocity w and the velocity of secondary flow (u, v) were obtained. The effects of torsion, curvature and the axial pressure gradient on the secondary flow were discussed in detail. The study indicates that the torsion has first-order effect on the secondary flow in a helical elliptical pipe, the secondary flow is dominated by torsion when the axial pressure gradient is small and for increasing gradient the secondary flow is eventually dominated by the effect due to curvature. The fact that the torsion has no effect on fluid flow in a helical pipe with a circular cross section was also confirmed. The most important conclusion is that the flow in a helical elliptical pipe to the first-order can be obtained as a combination of the flow in a toroidal pipe and the flow in a twisted pipe.

  13. On statistical equilibrium in helical fluid flows

    Directory of Open Access Journals (Sweden)

    M. V. Kurgansky

    2006-01-01

    Full Text Available The statistical mechanics of 3-D helical flows is re-examined for a continuum truncated at a top wavenumber. Based on the principle of equipartition of the flow enstrophy between helical modes, the emerging (i energy spectrum law '–2' and (ii formal mathematical analogy between the helicity and the thermodynamic entropy are discussed. It is noted that the '–2' scaling law is consistent with both spectral equilibrium and spectral cascade paradigms. In an attempt to apply the obtained results to a turbulent flow regime within the Earth's outer liquid core, where the net helicity of a turbulent flow component is presumably explained by Earth's rotation, it has been noticed that it is the energy spectral law '–1', but not '–2', which is likely realized there and within the logarithmic accuracy corresponds to the case of the velocity structure function [u(l]2 independency on the spatial scale l, the latter is consistent with observations. It is argued that the '–1' scaling law can also be interpreted in terms of the spectral equilibrium and it is emphasized that the causes of the likely dominance of the spectral law '–1' over the spectral law '–2' in this geophysical application deserve further investigation and clarification.

  14. Coulomb drag between helical Luttinger liquids

    Science.gov (United States)

    Kainaris, N.; Gornyi, I. V.; Levchenko, A.; Polyakov, D. G.

    2017-01-01

    We theoretically study Coulomb drag between two helical edges with broken spin-rotational symmetry, such as would occur in two capacitively coupled quantum spin Hall insulators. For the helical edges, Coulomb drag is particularly interesting because it specifically probes the inelastic interactions that break the conductance quantization for a single edge. Using the kinetic equation formalism, supplemented by bosonization, we find that the drag resistivity ρD exhibits a nonmonotonic dependence on the temperature T . In the limit of low T ,ρD vanishes with decreasing T as a power law if intraedge interactions are not too strong. This is in stark contrast to Coulomb drag in conventional quantum wires, where ρD diverges at T →0 irrespective of the strength of repulsive interactions. Another unusual property of Coulomb drag between the helical edges concerns higher T for which, unlike in the Luttinger liquid model, drag is mediated by plasmons. The special type of plasmon-mediated drag can be viewed as a distinguishing feature of the helical liquid—because it requires peculiar umklapp scattering only available in the presence of a Dirac point in the electron spectrum.

  15. Helical Gears Modified To Decrease Transmission Errors

    Science.gov (United States)

    Handschuh, R. F.; Coy, J. J.; Litvin, F. L.; Zhang, J.

    1993-01-01

    Tooth surfaces of helical gears modified, according to proposed design concept, to make gears more tolerant of misalignments and to improve distribution of contact stresses. Results in smaller transmission errors, with concomitant decreases in vibrations and noise and, possibly, increases in service lives.

  16. Helical Ordering in Chiral Block Copolymers

    Science.gov (United States)

    Zhao, Wei; Hong, Sung Woo; Chen, Dian; Grason, Gregory; Russell, Thomas

    2012-02-01

    Introducing molecular chirality into the segments of block copolymers can influence the nature of the resultant morphology. Such an effect was found for poly(styrene-b-L-lactide) (PS-b-PLLA) diblock copolymers where hexagonally packed PLLA helical microdomains (H* phase) form in a PS matrix. However, molecular ordering of PLLA within the helical microdomains and the transfer of chirality from the segmental level to the mesoscale is still not well understood. We developed a field theoretic model to describe the interactions between segments of chiral blocks, which have the tendency to form a ``cholesteric'' texture. Based on the model, we calculated the bulk morphologies of chiral AB diblock copolymers using self-consistent field theory (SCFT). Experiments show that the H* phase only forms when microphase separation between PS and PLLA block happens first and crystallization of PLLA block is suppressed or happens within confined microdomain. Hence, crystalline ordering is not necessary for H* phase formation. The SCFT offers the chance to explore the range of thermodynamic stability of helical structures in the phase diagram of chiral block copolymer melts, by tuning parameters not only like the block segregation strength and composition, but also new parameters such as the ratio between preferred helical pitch to the radius of gyration and the Frank elastic constant for inter-segment distortions.

  17. Magnetic stripes and skyrmions with helicity reversals.

    Science.gov (United States)

    Yu, Xiuzhen; Mostovoy, Maxim; Tokunaga, Yusuke; Zhang, Weizhu; Kimoto, Koji; Matsui, Yoshio; Kaneko, Yoshio; Nagaosa, Naoto; Tokura, Yoshinori

    2012-06-05

    It was recently realized that topological spin textures do not merely have mathematical beauty but can also give rise to unique functionalities of magnetic materials. An example is the skyrmion--a nano-sized bundle of noncoplanar spins--that by virtue of its nontrivial topology acts as a flux of magnetic field on spin-polarized electrons. Lorentz transmission electron microscopy recently emerged as a powerful tool for direct visualization of skyrmions in noncentrosymmetric helimagnets. Topologically, skyrmions are equivalent to magnetic bubbles (cylindrical domains) in ferromagnetic thin films, which were extensively explored in the 1970s for data storage applications. In this study we use Lorentz microscopy to image magnetic domain patterns in the prototypical magnetic oxide-M-type hexaferrite with a hint of scandium. Surprisingly, we find that the magnetic bubbles and stripes in the hexaferrite have a much more complex structure than the skyrmions and spirals in helimagnets, which we associate with the new degree of freedom--helicity (or vector spin chirality) describing the direction of spin rotation across the domain walls. We observe numerous random reversals of helicity in the stripe domain state. Random helicity of cylindrical domain walls coexists with the positional order of magnetic bubbles in a triangular lattice. Most unexpectedly, we observe regular helicity reversals inside skyrmions with an unusual multiple-ring structure.

  18. Muon Beam Helical Cooling Channel Design

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Rolland; Ankenbrandt, Charles; Flanagan, G; Kazakevich, G M; Marhauser, Frank; Neubauer, Michael; Roberts, T; Yoshikawa, C; Derbenev, Yaroslav; Morozov, Vasiliy; Kashikhin, V S; Lopes, Mattlock; Tollestrup, A; Yonehara, Katsuya; Zloblin, A

    2013-06-01

    The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet.

  19. Artificial, parallel, left-handed DNA helices.

    Science.gov (United States)

    Tian, Cheng; Zhang, Chuan; Li, Xiang; Li, Yingmei; Wang, Guansong; Mao, Chengde

    2012-12-19

    This communication reports an engineered DNA architecture. It contains multiple domains of half-turn-long, standard B-DNA duplexes. While each helical domain is right-handed and its two component strands are antiparallel, the global architecture is left-handed and the two component DNA strands are oriented parallel to each other.

  20. Review of the helicity formalism; Revision del formalismo de helicidad

    Energy Technology Data Exchange (ETDEWEB)

    Barreiro, F.; Cerrada, M.; Fernandez, E.

    1972-07-01

    Our purpose in these notes has been to present a brief and general review of the helicity formalism. We begin by discussing Lorentz invariance, spin and helicity ideas, in section 1 . In section 2 we deal with the construction of relativistic states and scattering amplitudes in the helicity basis and we study their transformation properties under discrete symmetries. Finally we present some more sophisticated topics like kinematical singularities of helicity amplitudes, kinematical constraints and crossing relations 3, 4, 5 respectively. (Author) 8 refs.

  1. From a Dy(III) single molecule magnet (SMM) to a ferromagnetic [Mn(II)Dy(III)Mn(II)] trinuclear complex.

    Science.gov (United States)

    Bhunia, Asamanjoy; Gamer, Michael T; Ungur, Liviu; Chibotaru, Liviu F; Powell, Annie K; Lan, Yanhua; Roesky, Peter W; Menges, Fabian; Riehn, Christoph; Niedner-Schatteburg, Gereon

    2012-09-17

    The Schiff base compound 2,2'-{[(2-aminoethyl)imino]bis[2,1-ethanediyl-nitriloethylidyne]}bis-2-hydroxy-benzoic acid (H(4)L) as a proligand was prepared in situ. This proligand has three potential coordination pockets which make it possible to accommodate from one to three metal ions allowing for the possible formation of mono-, di-, and trinuclear complexes. Reaction of in situ prepared H(4)L with Dy(NO(3))(3)·5H(2)O resulted in the formation of a mononuclear complex [Dy(H(3)L)(2)](NO(3))·(EtOH)·8(H(2)O) (1), which shows SMM behavior. In contrast, reaction of in situ prepared H(4)L with Mn(ClO(4))(2)·6H(2)O and Dy(NO(3))(3)·5H(2)O in the presence of a base resulted in a trinuclear mixed 3d-4f complex (NHEt(3))(2)[Dy{Mn(L)}(2)](ClO(4))·2(H(2)O) (2). At low temperatures, compound 2 is a weak ferromagnet. Thus, the SMM behavior of compound 1 can be switched off by incorporating two Mn(II) ions in close proximity either side of the Dy(III). This quenching behavior is ascribed to the presence of the weak ferromagnetic interactions between the Mn(II) and Dy(III) ions, which at T > 2 K act as a fluctuating field causing the reversal of magnetization on the dysprosium ion. Mass spectrometric ion signals related to compounds 1 and 2 were both detected in positive and negative ion modes via electrospray ionization mass spectrometry. Hydrogen/deuterium exchange (HDX) reactions with ND(3) were performed in a FT-ICR Penning-trap mass spectrometer.

  2. Structural, vibrational, and electronic properties of an uncoordinated pseudoephedrine derivative and its mononuclear and trinuclear copper(II)-coordinated compounds: A combined theoretical and experimental study

    Science.gov (United States)

    Valencia, Israel; Ávila-Torres, Yenny; Barba-Behrens, Norah; Garzón, Ignacio L.

    2014-11-01

    Multicopper oxidases are fundamental in a variety of biological processes in bacteria, fungi and vertebrates. The catalytic center in these enzymes is formed basically by three copper ions, bridged by oxygen bonds. In order to get insights into the reactivity of these complex systems, biomimetic compounds are usually synthesized. Accordingly, in this work, we studied structural, vibrational, and electronic properties of an uncoordinated pseudoephedrine derivative, as well as its corresponding mononuclear and trinuclear copper(II)-coordinated complexes by means of density functional theory. The calculations are compared with experimental results using measurements of the infrared spectra. It is obtained that the molecular configuration of the pseudoephedrine amino-alcohol derivative is stabilized by hydrogen bonding Osbnd H⋯N and by Csbnd H⋯π interactions that are not present in the mononuclear and trinuclear compounds. The coordination compounds show octahedral and square pyramid geometries, respectively, which are slightly distorted by Jahn-Teller effects. The analysis of their theoretical and experimental IR spectra reveals signals related with hydrogen bonding as well as metal-ligand vibrational modes. Regarding the electronic structure, the density of states was calculated in order to analyze the atomic orbital contributions present in these compounds. This analysis would provide useful insights about the optical behavior, for example, in the visible region of the spectrum of the coordinated compounds. At these energies, the optical absorption would be influenced by the orbital interaction of the Cu2+d orbitals with sp ones of the ligand, reflecting a decrease of the HOMO-LUMO gap of the organic ligand due to the presence of the copper(II) ions.

  3. Synthesis of a new N-substituted bis-benzimidazolyl diamide ligand and its trinuclear copper(II) complex: structural and fluorescence studies.

    Science.gov (United States)

    Mahiya, Kuldeep; Mathur, Pavan

    2013-09-01

    The synthesis of a new N-substituted fluorescent probe based on a bis-benzimidazole diamide N(2),N(2')-bis[(1-(4-methylbenzyl)-benzimidazol-2-yl)methyl]biphenyl-2,2'-dicarboxamide (L1) with a biphenyl spacer group and its trinuclear copper(II) complex [Cu3(L1)3Cl3]·3Cl·3H2O] has been described. X-ray studies shows that the trinuclear complex crystallizes as [{Cu3(L1)3Cl3}2·6Cl·13CH3CN·2H2O] in triclinic space group P-1 with two independent molecules in the asymmetric unit. Each copper(II) adopts a distorted penta-coordinated geometry in each unit. The fluorescence spectra of L1 in methanol show an emission band centered at 300 nm. This band arises due to benzimidazolyl moiety in the ligating system. The diamide L1 in the presence of Fe(3+) show the simultaneous 'quenching' of (300nm) and 'enhancement' of (375 nm) emission band. The new emission band at 375 nm is attributed to intra ligand π-π(*) transition of the biphenyl moiety. While Cu(2+) and Ag(+) show only the quenching of the 300 nm band. No such behavior was observed with other metal ions like Ni(2+), Co(2+), Mn(2+), Mg(2+), Zn(2+) and Pb(2+). The quenching constant with Fe(3+), Ag(+) and Cu(2+) are calculated by the Stern-Volmer plots.

  4. Helicity of Solar Active Regions from a Dynamo Model

    Indian Academy of Sciences (India)

    Piyali Chatterjee

    2006-06-01

    We calculate helicities of solar active regions based on the idea that poloidal flux lines get wrapped around a toroidal flux tube rising through the convection zone, thereby giving rise to the helicity. We use our solar dynamo model based on the Babcock–Leighton -effect to study how helicity varies with latitude and time.

  5. Sign of helicity in the alpha-Omega geodynamo

    CERN Document Server

    Wei, Xing

    2010-01-01

    In this paper we investigate the sign of helicity in the alpha-Omega dynamo and point out that the alpha effect in the geodynamo is induced by helical wave but not helical flow as in the solar dynamo. We then postulate the mechanisms of the Earth's magnetic tilt angle, westward drift and dipole reversals.

  6. Field-theoretic calculation of kinetic helicity flux

    Indian Academy of Sciences (India)

    V Avinash; Mahendra K Verma; Amar K Chandra

    2006-02-01

    In this paper we apply perturbative field-theoretic technique to helical turbulence. In the inertial range the kinetic helicity flux is found to be constant and forward. The universal constant H appearing in the spectrum of kinetic helicity was found to be 2.47.

  7. The Effects of Spatial Smoothing on Solar Magnetic Helicity and the Hemispheric Helicity Sign Rule

    Science.gov (United States)

    Koch Ocker, Stella; Petrie, Gordon

    2016-05-01

    The hemispheric sign rule for solar magnetic helicity, which states that negative/positive helicity occurs preferentially in the northern/southern hemisphere, provides clues to the causes of twisted, flaring magnetic fields. However, previous studies on the hemisphere rule may have been significantly affected by seeing from atmospheric turbulent motions. Using Hinode/SOT-SP data spanning from 2006 to 2012, we studied the effects of two important data processing steps that imitate the effects of atmospheric seeing: noise reduction by ignoring pixel values that are weaker than the estimated noise threshold, and Gaussian spatial smoothing. We applied these processing techniques to the helicity distribution maps for active regions NOAA 11158 and NOAA 11243, along with the average helicities of 36 active regions, in order to imitate and understand the effects of seeing from atmospheric turbulence. We found that rather than changing trends in the helicity distributions, Gaussian smoothing and noise reduction enhanced existing trends by pushing outliers towards the mean or removing them altogether. We also found that, when separated for weak and strong magnetic fields, the average helicities of the 36 active regions conformed to the hemisphere rule for weak field helicities and breached the rule for strong field helicities. In general, we found that data processing did not affect whether the hemisphere rule held for data taken from space-based instruments, and thus that seeing from atmospheric turbulence did not significantly affect previous studies' ground-based results on the hemisphere rule. This work was carried out through the National Solar Observatory Research Experiences for Undergraduates (REU) Program, which is funded by the National Science Foundation (NSF). The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the NSF.

  8. What Helicity Can Tell Us about Solar Magnetic Fields

    Indian Academy of Sciences (India)

    Alexei A. Pevtsov

    2008-03-01

    Concept of magnetic/current helicity was introduced to solar physics about 15 years ago. Earlier studies led to discovery of such fundamental properties as hemispheric helicity rule, and role of helicity in magnetic reconnection and solar eruptions. Later, the concept was successfully applied in studies of different solar processes from solar dynamo to flare and CME phenomena. Although no silver bullet, helicity has proven to be a very useful “tool” in answering many still-puzzling questions about origin and evolution of solar magnetic fields. I present an overview of some helicity studies and briefly analyze their findings.

  9. Time-Mean Helicity Distribution in Turbulent Swirling Jets

    Directory of Open Access Journals (Sweden)

    V. Tesař

    2005-01-01

    Full Text Available Helicity offers an alternative approach to investigations of the structure of turbulent flows. Knowledge of the spatial distribution of the time-mean component of helicity is the starting point. Yet very little is known even about basic cases in which Helicity plays important role, such as the case of a swirling jet. This is the subject of the present investigations, based mainly on numerical flowfield computations. The region of significantly large time-mean helicity density is found only in a rather small region reaching to several nozzle diameters downstream from the exit. The most important result is the similarity of the helicity density profiles. 

  10. Ion temperature gradient modes in toroidal helical systems

    Energy Technology Data Exchange (ETDEWEB)

    Kuroda, T. [Graduate University for Advanced Studies, Toki, Gifu (Japan); Sugama, H.; Kanno, R.; Okamoto, M.

    2000-04-01

    Linear properties of ion temperature gradient (ITG) modes in helical systems are studied. The real frequency, growth rate, and eigenfunction are obtained for both stable and unstable cases by solving a kinetic integral equation with proper analytic continuation performed in the complex frequency plane. Based on the model magnetic configuration for toroidal helical systems like the Large Helical Device (LHD), dependences of the ITG mode properties on various plasma equilibrium parameters are investigated. Particularly, relative effects of {nabla}B-curvature drifts driven by the toroidicity and by the helical ripples are examined in order to compare the ITG modes in helical systems with those in tokamaks. (author)

  11. Helical localized wave solutions of the scalar wave equation.

    Science.gov (United States)

    Overfelt, P L

    2001-08-01

    A right-handed helical nonorthogonal coordinate system is used to determine helical localized wave solutions of the homogeneous scalar wave equation. Introducing the characteristic variables in the helical system, i.e., u = zeta - ct and v = zeta + ct, where zeta is the coordinate along the helical axis, we can use the bidirectional traveling plane wave representation and obtain sets of elementary bidirectional helical solutions to the wave equation. Not only are these sets bidirectional, i.e., based on a product of plane waves, but they may also be broken up into right-handed and left-handed solutions. The elementary helical solutions may in turn be used to create general superpositions, both Fourier and bidirectional, from which new solutions to the wave equation may be synthesized. These new solutions, based on the helical bidirectional superposition, are members of the class of localized waves. Examples of these new solutions are a helical fundamental Gaussian focus wave mode, a helical Bessel-Gauss pulse, and a helical acoustic directed energy pulse train. Some of these solutions have the interesting feature that their shape and localization properties depend not only on the wave number governing propagation along the longitudinal axis but also on the normalized helical pitch.

  12. Magnetic helicity balance in the Sustained Spheromak Plasma Experiment

    Science.gov (United States)

    Stallard, B. W.; Hooper, E. B.; Woodruff, S.; Bulmer, R. H.; Hill, D. N.; McLean, H. S.; Wood, R. D.

    2003-07-01

    The magnetic helicity balance between the helicity input injected by a magnetized coaxial gun, the rate-of-change in plasma helicity content, and helicity dissipation in electrode sheaths and Ohmic losses have been examined in the Sustained Spheromak Plasma Experiment (SSPX) [E. B. Hooper, L. D. Pearlstein, and R. H. Bulmer, Nucl. Fusion 39, 863 (1999)]. Helicity is treated as a flux function in the mean-field approximation, allowing separation of helicity drive and losses between closed and open field volumes. For nearly sustained spheromak plasmas with low fluctuations, helicity balance analysis implies a decreasing transport of helicity from the gun input into the spheromak core at higher spheromak electron temperature. Long pulse discharges with continuously increasing helicity and larger fluctuations show higher helicity coupling from the edge to the spheromak core. The magnitude of the sheath voltage drop, inferred from cathode heating and a current threshold dependence of the gun voltage, shows that sheath losses are important and reduce the helicity injection efficiency in SSPX.

  13. Large-scale flow generation by inhomogeneous helicity

    CERN Document Server

    Yokoi, Nobumitsu

    2015-01-01

    The effect of kinetic helicity (velocity--vorticity correlation) on turbulent momentum transport is investigated. The turbulent kinetic helicity (pseudoscalar) enters into the Reynolds stress (mirrorsymmetric tensor) expression in the form of a helicity gradient as the coupling coefficient for the mean vorticity and/or the angular velocity (axial vector), which suggests the possibility of mean-flow generation in the presence of inhomogeneous helicity. This inhomogeneous helicity effect, which was previously confirmed at the level of a turbulence- or closure-model simulation, is examined with the aid of direct numerical simulations of rotating turbulence with non-uniform helicity sustained by an external forcing. The numerical simulations show that the spatial distribution of the Reynolds stress is in agreement with the helicity-related term coupled with the angular velocity, and that a large-scale flow is generated in the direction of angular velocity. Such a large-scale flow is not induced in the case of hom...

  14. Autonomously folded α-helical lockers promote RNAi*

    Science.gov (United States)

    Guyader, Christian P. E.; Lamarre, Baptiste; De Santis, Emiliana; Noble, James E.; Slater, Nigel K.; Ryadnov, Maxim G.

    2016-01-01

    RNAi is an indispensable research tool with a substantial therapeutic potential. However, the complete transition of the approach to an applied capability remains hampered due to poorly understood relationships between siRNA delivery and gene suppression. Here we propose that interfacial tertiary contacts between α-helices can regulate siRNA cytoplasmic delivery and RNAi. We introduce a rationale of helical amphipathic lockers that differentiates autonomously folded helices, which promote gene silencing, from helices folded with siRNA, which do not. Each of the helical designs can deliver siRNA into cells via energy-dependent endocytosis, while only autonomously folded helices with pre-locked hydrophobic interfaces were able to promote statistically appreciable gene silencing. We propose that it is the amphipathic locking of interfacing helices prior to binding to siRNA that enables RNAi. The rationale offers structurally balanced amphipathic scaffolds to advance the exploitation of functional RNAi. PMID:27721465

  15. Autonomously folded α-helical lockers promote RNAi.

    Science.gov (United States)

    Guyader, Christian P E; Lamarre, Baptiste; De Santis, Emiliana; Noble, James E; Slater, Nigel K; Ryadnov, Maxim G

    2016-10-10

    RNAi is an indispensable research tool with a substantial therapeutic potential. However, the complete transition of the approach to an applied capability remains hampered due to poorly understood relationships between siRNA delivery and gene suppression. Here we propose that interfacial tertiary contacts between α-helices can regulate siRNA cytoplasmic delivery and RNAi. We introduce a rationale of helical amphipathic lockers that differentiates autonomously folded helices, which promote gene silencing, from helices folded with siRNA, which do not. Each of the helical designs can deliver siRNA into cells via energy-dependent endocytosis, while only autonomously folded helices with pre-locked hydrophobic interfaces were able to promote statistically appreciable gene silencing. We propose that it is the amphipathic locking of interfacing helices prior to binding to siRNA that enables RNAi. The rationale offers structurally balanced amphipathic scaffolds to advance the exploitation of functional RNAi.

  16. Autonomously folded α-helical lockers promote RNAi*

    Science.gov (United States)

    Guyader, Christian P. E.; Lamarre, Baptiste; de Santis, Emiliana; Noble, James E.; Slater, Nigel K.; Ryadnov, Maxim G.

    2016-10-01

    RNAi is an indispensable research tool with a substantial therapeutic potential. However, the complete transition of the approach to an applied capability remains hampered due to poorly understood relationships between siRNA delivery and gene suppression. Here we propose that interfacial tertiary contacts between α-helices can regulate siRNA cytoplasmic delivery and RNAi. We introduce a rationale of helical amphipathic lockers that differentiates autonomously folded helices, which promote gene silencing, from helices folded with siRNA, which do not. Each of the helical designs can deliver siRNA into cells via energy-dependent endocytosis, while only autonomously folded helices with pre-locked hydrophobic interfaces were able to promote statistically appreciable gene silencing. We propose that it is the amphipathic locking of interfacing helices prior to binding to siRNA that enables RNAi. The rationale offers structurally balanced amphipathic scaffolds to advance the exploitation of functional RNAi.

  17. Helicity, Topology and Kelvin Waves in reconnecting quantum knots

    CERN Document Server

    di Leoni, P Clark; Brachet, M E

    2016-01-01

    Helicity is a topological invariant that measures the linkage and knottedness of lines, tubes and ribbons. As such, it has found myriads of applications in astrophysics and solar physics, in fluid dynamics, in atmospheric sciences, and in biology. In quantum flows, where topology-changing reconnection events are a staple, helicity appears as a key quantity to study. However, the usual definition of helicity is not well posed in quantum vortices, and its computation based on counting links and crossings of vortex lines can be downright impossible to apply in complex and turbulent scenarios. We present a new definition of helicity which overcomes these problems. With it, we show that only certain reconnection events conserve helicity. In other cases helicity can change abruptly during reconnection. Furthermore, we show that these events can also excite Kelvin waves, which slowly deplete helicity as they interact nonlinearly, thus linking the theory of vortex knots with observations of quantum turbulence.

  18. Evolution of field line helicity during magnetic reconnection

    CERN Document Server

    Russell, Alexander J B; Hornig, Gunnar; Wilmot-Smith, Antonia L

    2015-01-01

    We investigate the evolution of field line helicity for non-zero magnetic fields that connect two boundaries, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field topology and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a topologically complex magnetic field, the evolution of field line helicity is dominated by a work-like term ...

  19. Stabilization of helical macromolecular phases by confined bending

    CERN Document Server

    Williams, Matthew J

    2015-01-01

    By means of extensive replica-exchange simulations of generic coarse-grained models for helical polymers, we systematically investigate the structural transitions into all possible helical phases for flexible and semiflexible elastic polymers with self-interaction under the influence of torsion barriers. The competing interactions lead to a variety of conformational phases including disordered helical arrangements, single helices, and ordered, tertiary helix bundles. Most remarkably, we find that a bending restraint entails a clear separation and stabilization of the helical phases. This aids in understanding why semiflexible polymers such as double-stranded DNA tend to form pronounced helical structures and proteins often exhibit an abundance of helical structures, such as helix bundles, within their tertiary structure.

  20. Helicity dynamics in stratified turbulence in the absence of forcing

    CERN Document Server

    Rorai, C; Pouquet, A; Mininni, P D

    2012-01-01

    A numerical study of decaying stably-stratified flows is performed. Relatively high stratification and moderate Reynolds numbers are considered, and a particular emphasis is placed on the role of helicity (velocity-vorticity correlations). The problem is tackled by integrating the Boussinesq equations in a periodic cubical domain using different initial conditions: a non-helical Taylor-Green (TG) flow, a fully helical Beltrami (ABC) flow, and random flows with a tunable helicity. We show that for stratified ABC flows helicity undergoes a substantially slower decay than for unstratified ABC flows. This fact is likely associated to the combined effect of stratification and large scale coherent structures. Indeed, when the latter are missing, as in random flows, helicity is rapidly destroyed by the onset of gravitational waves. A type of large-scale dissipative "cyclostrophic" balance can be invoked to explain this behavior. When helicity survives in the system it strongly affects the temporal energy decay and t...

  1. Iterative assembly of helical proteins by optimal hydrophobic packing.

    Science.gov (United States)

    Wu, G Albert; Coutsias, Evangelos A; Dill, Ken A

    2008-08-06

    We present a method for the computer-based iterative assembly of native-like tertiary structures of helical proteins from alpha-helical fragments. For any pair of helices, our method, called MATCHSTIX, first generates an ensemble of possible relative orientations of the helices with various ways to form hydrophobic contacts between them. Those conformations having steric clashes, or a large radius of gyration of hydrophobic residues, or with helices too far separated to be connected by the intervening linking region, are discarded. Then, we attempt to connect the two helical fragments by using a robotics-based loop-closure algorithm. When loop closure is feasible, the algorithm generates an ensemble of viable interconnecting loops. After energy minimization and clustering, we use a representative set of conformations for further assembly with the remaining helices, adding one helix at a time. To efficiently sample the conformational space, the order of assembly generally proceeds from the pair of helices connected by the shortest loop, followed by joining one of its adjacent helices, always proceeding with the shorter connecting loop. We tested MATCHSTIX on 28 helical proteins each containing up to 5 helices and found it to heavily sample native-like conformations. The average rmsd of the best conformations for the 17 helix-bundle proteins that have 2 or 3 helices is less than 2 A; errors increase somewhat for proteins containing more helices. Native-like states are even more densely sampled when disulfide bonds are known and imposed as restraints. We conclude that, at least for helical proteins, if the secondary structures are known, this rapid rigid-body maximization of hydrophobic interactions can lead to small ensembles of highly native-like structures. It may be useful for protein structure prediction.

  2. Vacuum systems for the ILC helical undulator

    CERN Document Server

    Malyshev, O B; Clarke, J A; Bailey, I R; Dainton, J B; Malysheva, L I; Barber, D P; Cooke, P; Baynham, E; Bradshaw, T; Brummitt, A; Carr, S; Ivanyushenkov, Y; Rochford, J; Moortgat-Pick, G A

    2007-01-01

    The International Linear Collider (ILC) positron source uses a helical undulator to generate polarized photons of ∼10MeV∼10MeV at the first harmonic. Unlike many undulators used in synchrotron radiation sources, the ILC helical undulator vacuum chamber will be bombarded by photons, generated by the undulator, with energies mostly below that of the first harmonic. Achieving the vacuum specification of ∼100nTorr∼100nTorr in a narrow chamber of 4–6mm4–6mm inner diameter, with a long length of 100–200m100–200m, makes the design of the vacuum system challenging. This article describes the vacuum specifications and calculations of the flux and energy of photons irradiating the undulator vacuum chamber and considers possible vacuum system design solutions for two cases: cryogenic and room temperature.

  3. Weaving knotted vector fields with tunable helicity

    CERN Document Server

    Kedia, Hridesh; Dennis, Mark R; Irvine, William T M

    2016-01-01

    We present a general construction of divergence-free knotted vector fields from complex scalar fields, whose closed field lines encode many kinds of knots and links, including torus knots, their cables, the figure-8 knot and its generalizations. As finite-energy physical fields they represent initial states for fields such as the magnetic field in a plasma, or the vorticity field in a fluid. We give a systematic procedure for calculating the vector potential, starting from complex scalar functions with knotted zero filaments, thus enabling an explicit computation of the helicity of these knotted fields. The construction can be used to generate isolated knotted flux tubes, filled by knots encoded in the lines of the vector field. Lastly we give examples of manifestly knotted vector fields with vanishing helicity. Our results provide building blocks for analytical models and simulations alike.

  4. Broadband optical isolator based on helical metamaterials.

    Science.gov (United States)

    Cao, Hu; Yang, ZhenYu; Zhao, Ming; Wu, Lin; Zhang, Peng

    2015-05-01

    Based on helical metamaterials, a new broadband optical isolator with a triple-helix structure is proposed in this paper. The right-handed circularly polarized light can transmit through the isolator with its polarization unchanged. The reverse propagating light, which is caused by the reflection of the latter optical devices, is converted into left-handed circularly polarized light that is suppressed by the proposed isolator because of absorption. Our design has some unprecedented advantages such as broad frequency ranges and a compact structure; moreover, neither polarizers nor adscititious magnetic fields are required. Properties of the isolator are investigated using the finite-difference time-domain method, and this phenomenon is studied by the mechanism of helical antenna theory.

  5. Electronic structure calculations on helical conducting polymers.

    Science.gov (United States)

    Ripoll, Juan D; Serna, Andrei; Guerra, Doris; Restrepo, Albeiro

    2010-10-21

    We present a study of the electronic structure and derived properties of polyfurane (PFu), polypyrrol (PPy), and polythiophene (PTh). Two spatial arrangements are considered: trans chain (tc-PFu, tc-PPy, tc-PTh) and cis α-helical (α-PFu, α-PPy, α-PTh). Even at the small sizes considered here, helical conformations appear to be stable. Band gaps of pure, undoped oligomers fall into the semiconductor range. Density of states (DOS) analysis suggest dense valence and conduction bands. Bond length alternation analysis predicts almost complete delocalization of the π clouds in all spatial arrangements. Doping with electron donors or electron-withdrawing impurities reduces all band gaps close to the metallic regime in addition to increasing the DOS for the valence and conduction bands.

  6. Helicity of the toroidal vortex with swirl

    CERN Document Server

    Bannikova, Elena Yu; Poslavsky, Sergey A

    2016-01-01

    On the basis of solutions of the Bragg-Hawthorne equations we discuss the helicity of thin toroidal vortices with the swirl - the orbital motion along the torus diretrix. It is shown that relationship of the helicity with circulations along the small and large linked circles - directrix and generatrix of the torus - depends on distribution of the azimuthal velocity in the core of the swirling vortex ring. In the case of non-homogeneous swirl this relationship differs from the well-known Moffat relationship - the doubled product of such circulations multiplied by the number of links. The results can be applied to vortices in planetary atmospheres and to vortex movements in the vicinity of active galactic nuclei.

  7. Driving Solar Eruptions via Helicity Condensation

    Science.gov (United States)

    Dahlin, Joel Timothy; Antiochos, Spiro K.; DeVore, C. Richard

    2017-08-01

    One of the important questions in solar physics is, “How does the Sun store and release energy in coronal mass ejections"? Key to answering this question is understanding how the sun (a) stores magnetic energy in the form of a solar filament and (b) suddenly releases this energy as a coronal mass ejection. An important model for the energy release is the ‘magnetic breakout’ - a positive-feedback mechanism between filament ejection and magnetic reconnection. Recent theory and numerical calculations have demonstrated that helicity injected into the corona via photospheric driving can accumulate in the form of a filament channel of strongly sheared magnetic fields that can provide the free energy for a coronal mass ejection. We present preliminary calculations that, for the first time, incorporate helicity injection in a breakout topology to model a fully self-consistent eruption, from filament formation to ejection.

  8. Weyl spinors and the helicity formalism

    CERN Document Server

    Diaz-Cruz, J Lorenzo; Meza-Aldama, O; Perez, Jonathan Reyes

    2015-01-01

    In this work we give a review of the original formulation of the relativistic wave equation for particles with spin one-half. Traditionally \\`a la Dirac, it's proposed that the ``square root'' of the Klein-Gordon (K-G) equation involves a 4 component (Dirac) spinor and in the non-relativistic limit it can be written as 2 equations for two 2 component spinors. On the other hand, there exists Weyl's formalism, in which one works from the beginning with 2 component Weyl spinors, which are the fundamental objects of the helicity formalism. In this work we rederive Weyl's equations directly, starting from K-G equation. We also obtain the electromagnetic interaction through minimal coupling and we get the interaction with the magnetic moment. As an example of the use of that formalism, we calculate Compton scattering using the helicity methods.

  9. Helical apodizers for tunable hyper Gaussian masks

    Science.gov (United States)

    Ojeda-Castañeda, J.; Ledesma, Sergio; Gómez-Sarabia, Cristina M.

    2013-09-01

    We discuss an optical method for controlling the half-width of Gaussian like transmittance windows, by using a pair of absorption masks that have both radial and helical amplitude variations. For describing the radial part of the proposed masks, we employ amplitude transmittance profiles of the form T(ρ) = exp(- ρ s ). For s = 2, one has an amplitude transmittance that is proportional to a Gaussian function. A sub Gaussian mask is defined by a value of s 2, one has super Gaussian masks. Our discussion considers that any of these radially varying masks has also helical modulations. We show that by using a suitable pair of this type of masks, one can control the halfwidth of Gaussian like windows.

  10. Instabilities of a rotating helical rod

    Science.gov (United States)

    Park, Yunyoung; Ko, William; Kim, Yongsam; Lim, Sookkyung

    2016-11-01

    Bacteria such as Escherichia coli and Vibrio alginolyticus have helical flagellar filament. By rotating a motor, which is located at the bottom end of the flagellar filament embedded in the cell body, CCW or CW, they swim forward or backward. We model a left-handed helix by the Kirchhoff rod theory and use regularized Stokes formulation to study an interaction between the surrounding fluid and the flagellar filament. We perform numerical studies focusing on relations between physical parameters and critical angular frequency of the motor, which separates overwhiring from twirling. We are also interested in the buckling instability of the hook, which is very flexible elastic rod. By measuring buckling angle, which is an angle between rotational axis and helical axis, we observe the effects of physical parameters on buckling of the hook.

  11. Helical propulsion in shear-thinning fluids

    CERN Document Server

    Gomez, Saul; Lauga, Eric; Zenit, Roberto

    2016-01-01

    Swimming microorganisms often have to propel in complex, non-Newtonian fluids. We carry out experiments with self-propelling helical swimmers driven by an externally rotating magnetic field in shear-thinning, inelastic fluids. Similarly to swimming in a Newtonian fluid, we obtain for each fluid a locomotion speed which scales linearly with the rotation frequency of the swimmer, but with a prefactor which depends on the power index of the fluid. The fluid is seen to always increase the swimming speed of the helix, up to 50% faster and thus the strongest of such type reported to date. The maximum relative increase for a fluid power index of around 0.6. Using simple scalings, we argue that the speed increase is not due to the local decrease of the flow viscosity around the helical filament but hypothesise instead that it originates from confinement-like effect due to viscosity stratification around the swimmer.

  12. Helical Muon Beam Cooling Channel Engineering Design

    Energy Technology Data Exchange (ETDEWEB)

    Kashikhin, V.S.; Lopes, M.L.; Romanov, G.V.; Tartaglia, M.A.; Yonehara, K.; Yu, M.; Zlobin, A.V.; /Fermilab; Flanagan, G.; Johnson, R.P.; Kazakevich, G.M.; Marhauser, F.; /MUONS Inc., Batavia

    2012-05-01

    The Helical Cooling Channel (HCC), a novel technique for six-dimensional (6D) ionization cooling of muon beams, has shown considerable promise based on analytic and simulation studies. However, the implementation of this revolutionary method of muon cooling requires new techniques for the integration of hydrogen-pressurized, high-power RF cavities into the low-temperature superconducting magnets of the HCC. We present the progress toward a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb{sub 3}Sn based HCC test section. We include discussions on the pressure and thermal barriers needed within the cryostat to maintain operation of the magnet at 4.2 K while operating the RF and energy absorber at a higher temperature. Additionally, we include progress on the Nb{sub 3}Sn helical solenoid design.

  13. Synthesis and characterization of dopamine substitue tripodal trinuclear [(salen/salophen/salpropen)M] (Mdbnd Cr(III), Mn(III), Fe(III) ions) capped s-triazine complexes: Investigation of their thermal and magnetic properties

    Science.gov (United States)

    Uysal, Şaban; Koç, Ziya Erdem

    2016-04-01

    In this work, we aimed to synthesize and characterize a novel tridirectional ligand including three catechol groups and its novel tridirectional-trinuclear triazine core complexes. For this purpose, we used melamine (2,4,6-triamino-1,3,5-triazine) (MA) as starting material. 2,4,6-tris(4-carboxybenzimino)-1,3,5-triazine (II) was synthesized by the reaction of an equivalent melamine (I) and three equivalent 4-carboxybenzaldehyde. 4,4‧,4″-((1E,1‧E,1″E)-((1,3,5-triazine-2,4,6-triyl)tris(azanylylidene))tris(methanylylidene))tris(N-(3,4-dihydroxyphenethyl)benzamide) L (IV) was synthesized by the reaction of one equivalent (II) and three equivalent dopamine (3,4-dihydroxyphenethylamine) (DA) by using two different methods. (II, III, IV) and nine novel trinuclear Cr(III), Mn(III) and Fe(III) complexes of (IV) were characterized by means of elemental analyses, 1H NMR, FT-IR spectrometry, LC-MS (ESI+) and thermal analyses. The metal ratios of the prepared complexes were performed using Atomic Absorption Spectrophotometry (AAS). We also synthesized novel tridirectional-trinuclear systems and investigated their effects on magnetic behaviors of [salen, salophen, salpropen Cr(III)/Mn(III)/Fe(III)] capped complexes. The complexes were determined to be low-spin distorted octahedral Mn(III) and Fe(III), and distorted octahedral Cr(III) all bridged by catechol group.

  14. Field of a helical Siberian Snake

    Energy Technology Data Exchange (ETDEWEB)

    Luccio, A. [Brookhaven National Lab., Upton, NY (United States)

    1995-02-01

    To preserve the spin polarization of a beam of high energy protons in a circular accelerator, magnets with periodic magnetic field, called Siberian Snakes are being used. Recently, it was proposed to build Siberian Snakes with superconducting helical dipoles. In a helical, or twisted dipole, the magnetic field is perpendicular to the axis of the helix and rotates around it as one proceeds along the magnet. In an engineering study of a 4 Tesla helical snake, the coil geometry is derived, by twisting, from the geometry of a cosine superconducting dipole. While waiting for magnetic measurement data on such a prototype, an analytical expression for the field of the helice is important, to calculate the particle trajectories and the spin precession in the helix. This model will also allow to determine the optical characteristics of the snake, as an insertion in the lattice of the accelerator. In particular, one can calculate the integrated multipoles through the magnet and the equivalent transfer matrix. An expression for the field in the helix body, i.e., excluding the fringe field was given in a classical paper. An alternate expression can be found by elaborating on the treatment of the field of a transverse wiggler obtained under the rather general conditions that the variables are separable. This expression exactly satisfies Maxwell`s div and curl equations for a stationary field, {del} {center_dot} B = 0, {del} x B = 0. This approach is useful in that it will allow one to use much of the work already done on the problem of inserting wigglers and undulators in the lattice of a circular accelerator.

  15. Automatic generation of tree level helicity amplitudes

    CERN Document Server

    Stelzer, T

    1994-01-01

    The program MadGraph is presented which automatically generates postscript Feynman diagrams and Fortran code to calculate arbitrary tree level helicity amplitudes by calling HELAS[1] subroutines. The program is written in Fortran and is available in Unix and VMS versions. MadGraph currently includes standard model interactions of QCD and QFD, but is easily modified to include additional models such as supersymmetry.

  16. Droplets climbing a rotating helical fiber

    CERN Document Server

    Texier, Baptiste Darbois

    2015-01-01

    A liquid droplet is placed on a rotating helical fiber. We find that the droplet may slide down, attach or climb up the fiber. We inspect experimentally the domain of existence of these three behaviors as a function of the geometrical characteristics of the fiber, its angle relatively to the horizontal, the wetting properties of the fluid and the rotating speed of the helix. A theoretical model is proposed in order to capture the boundaries of the experimental phase diagram.

  17. Helicity formalism for spin-2 particles

    Energy Technology Data Exchange (ETDEWEB)

    Gleisberg, Tanju [Institut fuer Theoretische Physik, TU Dresden, D-01062 Dresden (Germany); Physics Department, University of Florida, Gainesville, FL 32611 (United States); Krauss, Frank [Theory Division, CERN, CH-1211 Geneva 23 (Switzerland); Matchev, Konstantin T. [Physics Department, University of Florida, Gainesville, FL 32611 (United States) and LEPP, Cornell University, Ithaca, NY 14853 (United States)]. E-mail: matchev@mail.lns.cornell.edu; Schaelicke, Andreas [Institut fuer Theoretische Physik, TU Dresden, D-01062 Dresden (Germany); Schumann, Steffen [Institut fuer Theoretische Physik, TU Dresden, D-01062 Dresden (Germany); Soff, Gerhard [Institut fuer theoretische Physik, TU Dresden, D-01062 Dresden (Germany)

    2003-09-01

    We develop the helicity formalism for spin-2 particles and apply it to the case of gravity in flat extra dimensions. We then implement the large extra dimensions scenario of Arkani-Hamed, Dimopoulos and Dvali in the program AMEGIC++, allowing for an easy calculation of arbitrary processes involving the emission or exchange of gravitons. We complete the set of Feynman rules derived by Han, Lykken and Zhang, and perform several consistency checks of our implementation. (author)

  18. Physics of collapses in toroidal helical plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Kimitaka [National Inst. for Fusion Science, Toki, Gifu (Japan); Itoh, Sanae; Fukuyama, Atsushi; Yagi, Masatoshi

    1998-12-31

    Theoretical model for the collapse events in toroidal helical plasmas with magnetic hill is presented. There exists a turbulent-turbulent transition at a critical pressure gradient, leading to a sudden increase of the anomalous transport. When the magnetic shear is low, the nonlinear excitation of the global mode is possible. This model explains an abrupt growth of the perturbations, i.e., the trigger phenomena. Achievable limit of the plasma beta value is discussed. (author)

  19. Propulsion by Helical Strips in Circular Channels

    Science.gov (United States)

    Yesilyurt, Serhat; Demir, Ebru

    2016-11-01

    Progress in manufacturing techniques avails the production of artificial micro swimmers (AMS) in various shapes and sizes. There are numerous studies on the generation of efficient locomotion by means of helical tails with circular cross-sections. This work focuses on locomotion with helical strips in circular channels. A CFD model is used to analyze the effects of geometric parameters and the radius of the channel on swimming velocity of infinite helical-strips in circular channels. Results show that there is an optimum wavelength that depends on thickness to channel radius ratio, suggesting that these parameters need to be optimized simultaneously. With constant torque, thinner strips swim faster, whereas under constant angular velocity application, thicker strips (in radial direction) prevail. As width approaches the wavelength, velocity decreases under both conditions, unless a magnetically coated tail is simulated, for which width has an optimum value. Increasing channel radius to helix amplitude ratio increases the velocity up to a maximum and after a slight drop, saturation occurs as bulk swimming conditions are approached.

  20. Mechanical Resonances of Helically Coiled Carbon Nanowires

    Science.gov (United States)

    Saini, D.; Behlow, H.; Podila, R.; Dickel, D.; Pillai, B.; Skove, M. J.; Serkiz, S. M.; Rao, A. M.

    2014-07-01

    Despite their wide spread applications, the mechanical behavior of helically coiled structures has evaded an accurate understanding at any length scale (nano to macro) mainly due to their geometrical complexity. The advent of helically coiled micro/nanoscale structures in nano-robotics, nano-inductors, and impact protection coatings has necessitated the development of new methodologies for determining their shear and tensile properties. Accordingly, we developed a synergistic protocol which (i) integrates analytical, numerical (i.e., finite element using COMSOL®) and experimental (harmonic detection of resonance; HDR) methods to obtain an empirically validated closed form expression for the shear modulus and resonance frequency of a singly clamped helically coiled carbon nanowire (HCNW), and (ii) circumvents the need for solving 12th order differential equations. From the experimental standpoint, a visual detection of resonances (using in situ scanning electron microscopy) combined with HDR revealed intriguing non-planar resonance modes at much lower driving forces relative to those needed for linear carbon nanotube cantilevers. Interestingly, despite the presence of mechanical and geometrical nonlinearities in the HCNW resonance behavior the ratio of the first two transverse modes f2/f1 was found to be similar to the ratio predicted by the Euler-Bernoulli theorem for linear cantilevers.

  1. Superconducting Helical Snake Magnet for the AGS

    CERN Document Server

    Willen, Erich; Escallier, John; Ganetis, George; Ghosh, Arup; Gupta, Ramesh C; Harrison, Michael; Jain, Animesh K; Luccio, Alfredo U; MacKay, William W; Marone, Andrew; Muratore, Joseph F; Okamura, Masahiro; Plate, Stephen R; Roser, Thomas; Tsoupas, Nicholaos; Wanderer, Peter

    2005-01-01

    A superconducting helical magnet has been built for polarized proton acceleration in the Brookhaven AGS. This "partial Snake" magnet will help to reduce the loss of polarization of the beam due to machine resonances. It is a 3 T magnet some 1940 mm in magnetic length in which the dipole field rotates with a pitch of 0.2053 degrees/mm for 1154 mm in the center and a pitch of 0.3920 degrees/mm for 393 mm in each end. The coil cross-section is made of two slotted cylinders containing superconductor. In order to minimize residual offsets and deflections of the beam on its orbit through the Snake, a careful balancing of the coil parameters was necessary. In addition to the main helical coils, a solenoid winding was built on the cold bore tube inside the main coils to compensate for the axial component of the field that is experienced by the beam when it is off-axis in this helical magnet. Also, two dipole corrector magnets were placed on the same tube with the solenoid. A low heat leak cryostat was built so that t...

  2. SUPERCONDUCTING HELICAL SNAKE MAGNET FOR THE AGS.

    Energy Technology Data Exchange (ETDEWEB)

    WILLEN, E.; ANERELLA, M.; ESCALLIER, G.; GANETIS, G.; GHOSH, A.; GUPTA, R.; HARRISON, M.; JAIN, A.; LUCCIO, A.; MACKAY, W.; MARONE, A.; MURATORE, J.; PLATE, S.; ET AL.

    2005-05-16

    A superconducting helical magnet has been built for polarized proton acceleration in the Brookhaven AGS. This ''partial Snake'' magnet will help to reduce the loss of polarization of the beam due to machine resonances. It is a 3 T magnet some 1940 mm in magnetic length in which the dipole field rotates with a pitch of 0.2053 degrees/mm for 1154 mm in the center and a pitch of 0.3920 degrees/mm for 393 mm in each end. The coil cross-section is made of two slotted cylinders containing superconductor. In order to minimize residual offsets and deflections of the beam on its orbit through the Snake, a careful balancing of the coil parameters was necessary. In addition to the main helical coils, a solenoid winding was built on the cold bore tube inside the main coils to compensate for the axial component of the field that is experienced by the beam when it is off-axis in this helical magnet. Also, two dipole corrector magnets were placed on the same tube with the solenoid. A low heat leak cryostat was built so that the magnet can operate in the AGS cooled by several cryocoolers. The design, construction and performance of this unique magnet will be summarized.

  3. Galactic dynamos supported by magnetic helicity fluxes

    CERN Document Server

    Sur, S; Subramanian, K; Sur, Sharanya; Shukurov, Anvar; Subramanian, Kandaswamy

    2006-01-01

    We present a simple semi-analytical model of nonlinear, mean-field galactic dynamos and use it to study the effects of various magnetic helicity fluxes. The dynamo equations are reduced using the `no-$z$' approximation to a nonlinear system of ordinary differential equations in time; we demonstrate that the model reproduces accurately earlier results, including those where nonlinear behaviour is driven by a magnetic helicity flux. We discuss the implications and interplay of two types of magnetic helicity flux, one produced by advection (e.g., due to the galactic fountain or wind) and the other, arising from anisotropy of turbulence as suggested by Vishniac & Cho(2001). We argue that the latter is significant if the galactic differential rotation is strong enough: in our model, for $\\Rw\\la-10$ in terms of the corresponding turbulent magnetic Reynolds number. We confirm that the intensity of gas outflow from the galactic disc optimal for the dynamo action is close to that expected for normal spiral galaxie...

  4. Buckling transition in long α-helices

    Energy Technology Data Exchange (ETDEWEB)

    Palenčár, Peter; Bleha, Tomáš, E-mail: bleha@savba.sk [Polymer Institute, Slovak Academy of Sciences, 845 41 Bratislava (Slovakia)

    2014-11-07

    The treatment of bending and buckling of stiff biopolymer filaments by the popular worm-like chain model does not provide adequate understanding of these processes at the microscopic level. Thus, we have used the atomistic molecular-dynamic simulations and the Amber03 force field to examine the compression buckling of α-helix (AH) filaments at room temperature. It was found that the buckling instability occurs in AHs at the critical force f{sub c} in the range of tens of pN depending on the AH length. The decrease of the force f{sub c} with the contour length follows the prediction of the classic thin rod theory. At the force f{sub c} the helical filament undergoes the swift and irreversible transition from the smoothly bent structure to the buckled one. A sharp kink in the AH contour arises at the transition, accompanied by the disruption of the hydrogen bonds in its vicinity. The kink defect brings in an effective softening of the AH molecule at buckling. Nonbonded interactions between helical branches drive the rearrangement of a kinked AH into the ultimate buckled structure of a compact helical hairpin described earlier in the literature.

  5. Differential geometry of proteins. Helical approximations.

    Science.gov (United States)

    Louie, A H; Somorjai, R L

    1983-07-25

    We regard a protein molecule as a geometric object, and in a first approximation represent it as a regular parametrized space curve passing through its alpha-carbon atoms (the backbone). In an earlier paper we argued that the regular patterns of secondary structures of proteins (morphons) correspond to geodesics on minimal surfaces. In this paper we discuss methods of recognizing these morphons on space curves that represent the protein backbone conformation. The mathematical tool we employ is the differential geometry of curves and surfaces. We introduce a natural approximation of backbone space curves in terms of helical approximating elements and present a computer algorithm to implement the approximation. Simple recognition criteria are given for the various morphons of proteins. These are incorporated into our helical approximation algorithm, together with more non-local criteria for the recognition of beta-sheet topologies. The method and the algorithm are illustrated with several examples of representative proteins. Generalizations of the helical approximation method are considered and their possible implications for protein energetics are sketched.

  6. Helical CT in acute lower gastrointestinal bleeding

    Energy Technology Data Exchange (ETDEWEB)

    Ernst, Olivier; Leroy, Christophe; Sergent, Geraldine [Department of Radiology, Hopital Huriez, 1 rue Polonovski, 59037 Lille (France); Bulois, Philippe; Saint-Drenant, Sophie; Paris, Jean-Claude [Department of Gastroenterology, Hopital Huriez, 1 rue Polonovski, 59037 Lille (France)

    2003-01-01

    The purpose of this study was to assess the usefulness of helical CT in depicting the location of acute lower gastrointestinal bleeding. A three-phase helical CT of the abdomen was performed in 24 patients referred for acute lower gastrointestinal bleeding. The diagnosis of the bleeding site was established by CT when there was at least one of the following criteria: spontaneous hyperdensity of the peribowel fat; contrast enhancement of the bowel wall; vascular extravasation of the contrast medium; thickening of the bowel wall; polyp or tumor; or vascular dilation. Diverticula alone were not enough to locate the bleeding site. The results of CT were compared with the diagnosis obtained by colonoscopy, enteroscopy, or surgery. A definite diagnosis was made in 19 patients. The bleeding site was located in the small bowel in 5 patients and the colon in 14 patients. The CT correctly located 4 small bowel hemorrhages and 11 colonic hemorrhages. Diagnosis of the primary lesion responsible for the bleeding was made in 10 patients. Our results suggest that helical CT could be a good diagnostic tool in acute lower gastrointestinal bleeding to help the physician to diagnose the bleeding site. (orig.)

  7. NUMERICAL INVESTIGATION FOR THE HEAT TRANSFER ENHANCEMENT IN HELICAL CONE COILS OVER ORDINARY HELICAL COILS

    Directory of Open Access Journals (Sweden)

    M. M. ABO ELAZM

    2013-02-01

    Full Text Available This numerical research is introducing the concept of helical cone coils and their enhanced heat transfer characteristics compared to the ordinary helical coils. Helical and spiral coils are known to have better heat and mass transfer than straight tubes, which is attributed to the generation of a vortex at the helical coil known as Dean Vortex. The Dean number which is a dimensionless number used to describe the Dean vortex is a function of Reynolds number and the square root of the curvature ratio, so varying the curvature ratio for the same coil would vary the Dean number. Two scenarios were adopted to study the effect of changing the taper angle (curvature ratio on the heat transfer characteristics of the coil; the commercial software FLUENT was used in the investigation. It was found that Nusselt number increased with increasing the taper angle. A MATLAB code was built based on empirical correlation of Manlapaz and Churchill for ordinary helical coils to calculate the Nusselt number at each coil turn, and then calculate the average Nusselt number for the entire coil turns, the CFD simulation results were found acceptable when compared with the MATLAB results.

  8. Helicity and alpha-effect by current-driven instabilities of helical magnetic fields

    CERN Document Server

    Gellert, M; Hollerbach, R

    2011-01-01

    Helical magnetic background fields with adjustable pitch angle are imposed on a conducting fluid in a differentially rotating cylindrical container. The small-scale kinetic and current helicities are calculated for various field geometries, and shown to have the opposite sign as the helicity of the large-scale field. These helicities and also the corresponding $\\alpha$-effect scale with the current helicity of the background field. The $\\alpha$-tensor is highly anisotropic as the components $\\alpha_{\\phi\\phi}$ and $\\alpha_{zz}$ have opposite signs. The amplitudes of the azimuthal $\\alpha$-effect computed with the cylindrical 3D MHD code are so small that the operation of an $\\alpha\\Omega$ dynamo on the basis of the current-driven, kink-type instabilities of toroidal fields is highly questionable. In any case the low value of the $\\alpha$-effect would lead to very long growth times of a dynamo in the radiation zone of the Sun and early-type stars of the order of mega-years.

  9. The Effects of Spatial Smoothing on Solar Magnetic Helicity Parameters and the Hemispheric Helicity Sign Rule

    Science.gov (United States)

    Koch Ocker, Stella; Petrie, Gordon

    2016-12-01

    The hemispheric preference for negative/positive helicity to occur in the northern/southern solar hemisphere provides clues to the causes of twisted, flaring magnetic fields. Previous studies on the hemisphere rule may have been affected by seeing from atmospheric turbulence. Using Hinode/SOT-SP data spanning 2006-2013, we studied the effects of two spatial smoothing tests that imitate atmospheric seeing: noise reduction by ignoring pixel values weaker than the estimated noise threshold, and Gaussian spatial smoothing. We studied in detail the effects of atmospheric seeing on the helicity distributions across various field strengths for active regions (ARs) NOAA 11158 and NOAA 11243, in addition to studying the average helicities of 179 ARs with and without smoothing. We found that, rather than changing trends in the helicity distributions, spatial smoothing modified existing trends by reducing random noise and by regressing outliers toward the mean, or removing them altogether. Furthermore, the average helicity parameter values of the 179 ARs did not conform to the hemisphere rule: independent of smoothing, the weak-vertical-field values tended to be negative in both hemispheres, and the strong-vertical-field values tended to be positive, especially in the south. We conclude that spatial smoothing does not significantly affect the overall statistics for space-based data, and thus seeing from atmospheric turbulence seems not to have significantly affected previous studies’ ground-based results on the hemisphere rule.

  10. Cryo-EM Structure Determination Using Segmented Helical Image Reconstruction.

    Science.gov (United States)

    Fromm, S A; Sachse, C

    2016-01-01

    Treating helices as single-particle-like segments followed by helical image reconstruction has become the method of choice for high-resolution structure determination of well-ordered helical viruses as well as flexible filaments. In this review, we will illustrate how the combination of latest hardware developments with optimized image processing routines have led to a series of near-atomic resolution structures of helical assemblies. Originally, the treatment of helices as a sequence of segments followed by Fourier-Bessel reconstruction revealed the potential to determine near-atomic resolution structures from helical specimens. In the meantime, real-space image processing of helices in a stack of single particles was developed and enabled the structure determination of specimens that resisted classical Fourier helical reconstruction and also facilitated high-resolution structure determination. Despite the progress in real-space analysis, the combination of Fourier and real-space processing is still commonly used to better estimate the symmetry parameters as the imposition of the correct helical symmetry is essential for high-resolution structure determination. Recent hardware advancement by the introduction of direct electron detectors has significantly enhanced the image quality and together with improved image processing procedures has made segmented helical reconstruction a very productive cryo-EM structure determination method.

  11. Helical muon beam cooling channel engineering design

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Rolland [Muons, Inc., Batavia, IL (United States)

    2015-08-07

    The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb3Sn based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb3Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb3Sn solenoid as originally planned. Instead, a complementary project was approved by the DOE

  12. Helical muon beam cooling channel engineering design

    Energy Technology Data Exchange (ETDEWEB)

    Johnson, Rolland [Muons, Inc., Batavia, IL (United States)

    2015-08-07

    The Helical Cooling Channel (HCC) achieves effective ionization cooling of the six-dimensional (6d) phase space of a muon beam by means of a series of 21st century inventions. In the HCC, hydrogen-pressurized RF cavities enable high RF gradients in strong external magnetic fields. The theory of the HCC, which requires a magnetic field with solenoid, helical dipole, and helical quadrupole components, demonstrates that dispersion in the gaseous hydrogen energy absorber provides effective emittance exchange to enable longitudinal ionization cooling. The 10-year development of a practical implementation of a muon-beam cooling device has involved a series of technical innovations and experiments that imply that an HCC of less than 300 m length can cool the 6d emittance of a muon beam by six orders of magnitude. We describe the design and construction plans for a prototype HCC module based on oxygen-doped hydrogen-pressurized RF cavities that are loaded with dielectric, fed by magnetrons, and operate in a superconducting helical solenoid magnet. The first phase of this project saw the development of a conceptual design for the integration of 805 MHz RF cavities into a 10 T Nb3Sn-based HS test section. Two very novel ideas are required to realize the design. The first idea is the use of dielectric inserts in the RF cavities to make them smaller for a given frequency so that the cavities and associated plumbing easily fit inside the magnet cryostat. Calculations indicate that heat loads will be tolerable, while RF breakdown of the dielectric inserts will be suppressed by the pressurized hydrogen gas. The second new idea is the use of a multi-layer Nb3Sn helical solenoid. The technology demonstrations for the two aforementioned key components of a 10T, 805 MHz HCC were begun in this project. The work load in the Fermilab Technical Division made it difficult to test a multi-layer Nb3Sn solenoid as originally planned. Instead, a complementary

  13. Helical electron-beam microbunching by harmonic coupling in a helical undulator.

    Science.gov (United States)

    Hemsing, E; Musumeci, P; Reiche, S; Tikhoplav, R; Marinelli, A; Rosenzweig, J B; Gover, A

    2009-05-01

    Microbunching of a relativistic electron beam into a helix is examined analytically and in simulation. Helical microbunching is shown to occur naturally when an e beam interacts resonantly at the harmonics of the combined field of a helical magnetic undulator and an axisymmetric input laser beam. This type of interaction is proposed as a method to generate a strongly prebunched e beam for coherent emission of light with orbital angular momentum at virtually any wavelength. The results from the linear microbunching theory show excellent agreement with three-dimensional numerical simulations.

  14. Eikonal Slant Helices and Eikonal Darboux Helices In 3-Dimensional Riemannian Manifolds

    OpenAIRE

    Önder, Mehmet; Ziplar, Evren; Kaya, Onur

    2013-01-01

    In this study, we give definitions and characterizations of eikonal slant helix curves, eikonal Darboux helices and non-normed eikonal Darboux helices in three dimensional Riemannian manifold 3 M . We show that every eikonal slant helix is also an eikonal Darboux helix. Furthermore, we obtain that if the curve a is a non-normed eikonal Darboux helix, then a is an eikonal slant helix if and only if k 2 +t 2 = constant, where k and t are curvature and torsion of a, respectively.

  15. Coordination chemistry strategies for dynamic helicates: time-programmable chirality switching with labile and inert metal helicates.

    Science.gov (United States)

    Miyake, Hiroyuki; Tsukube, Hiroshi

    2012-11-01

    'Chirality switching' is one of the most important chemical processes controlling many biological systems. DNAs and proteins often work as time-programmed functional helices, in which specific external stimuli alter the helical direction and tune the time scale of subsequent events. Although a variety of organic foldamers and their hybrids with natural helices have been developed, we highlight coordination chemistry strategies for development of structurally and functionally defined metal helicates. These metal helicates have characteristic coordination geometries, redox reactivities and spectroscopic/magnetic properties as well as complex chiralities. Several kinds of inert metal helicates maintain rigid helical structures and their stereoisomers are separable by optical resolution techniques, while labile metal helicates offer dynamic inversion of their helical structures via non-covalent interactions with external chemical signals. The latter particularly have dynamically ordered helical structures, which are controlled by the combinations of metal centres and chiral ligands. They further function as time-programmable switches of chirality-derived dynamic rotations, translations, stretching and shape flipping, which are useful applications in nanoscience and related technology.

  16. Trinuclear complexes of palladium(ii) with chalcogenated N-heterocyclic carbenes: catalysis of selective nitrile-primary amide interconversion and Sonogashira coupling.

    Science.gov (United States)

    Dubey, Pooja; Gupta, Sonu; Singh, Ajai K

    2017-09-22

    3-Methyl-1-(2-(phenylthio/seleno)ethyl)-1H-benzo[d]imidazol-3-ium iodide (L1/L2), a precursor of sulfated/selenated N-heterocyclic carbene, was synthesized by the reaction of benzimidazole with 1,2-dichloroethane followed by treatment with PhS/SeNa and MeI. The reaction of L1/L2 with Ag2O followed by treatment with [Pd(CH3CN)2Cl2] (metal to ligand ratio 3 : 2), i.e. transmetallation, resulted in trinuclear palladium(ii) complexes [Pd3(L1/L2-HI)2(CH3CN)Cl6] (1-2). The complexes were characterized with (1)H, (13)C{(1)H} and (77)Se{(1)H} NMR (2 only), elemental analyses, HR-MS and single-crystal X-ray diffraction. The geometry of three Pd atoms in each complex is nearly square planar. The Pd-S/Se, Pd-C, Pd-N and Pd-Cl bond distances (Å) in 1/2 are 2.3179(19)/2.4312(10), 1.968(7)/1.952(4), 2.073(8)/2.079(4) and 2.2784(19)-2.298(2)/2.292(2)-2.3003(15), respectively. In both the complexes, all Cl are trans to each other. For the central Pd atom, two benzimidazole rings are also trans to each other. The C-HCl non-covalent interactions result in a three-dimensional network. The moisture and air insensitive trinuclear Pd(ii) complexes 1 and 2 are thermally stable and efficient as a catalyst for nitrile-amide interconversion and amine-free Sonogashira C-C coupling (in the presence of CuI). The optimum temperature is 80 °C for the interconversion and 110 °C for the coupling. The catalytic protocols are applicable to both aliphatic and aromatic amides/nitriles. The optimum catalyst loading is 1 mol% for the C-C coupling and 0.5 to 1 mol% for the interconversion. K2CO3 as a base gives the best result for Sonogashira C-C coupling. In the conversion of nitriles to amides, the formation of an acid was not detected. After using once, 1/2 can carry out the conversion of ten fresh lots of nitriles to amides with almost the same efficiency. The real catalytic species for the interconversion and coupling appear to be based on Pd(ii) and Pd(0), respectively.

  17. A Helical Polymer with a Cooperative Response to Chiral Information

    Science.gov (United States)

    Green, Mark M.; Peterson, Norman C.; Sato, Takahiro; Teramoto, Akio; Cook, Robert; Lifson, Shneior

    1995-06-01

    Polyisocyanates, long studied as theoretical models for wormlike chains in dilute solution and liquid crystals, differ from their biological helical analogs in the absence of a predetermined helical sense. These polymers have an unusual sensitivity to chiral effects that arises from a structure in which alternating right- and left-handed long helical blocks are separated by infrequent and mobile helical reversals. Statistical thermodynamic methods yield an exact description of the polymer and the cooperative nature of its chiral properties. Minute energies that favor one of the helical senses drive easily measurable conformational changes, even though such energies may be extremely difficult to calculate from structural theory. In addition, the chiral nature of the polymer can be used to test theoretical ideas concerned with cholesteric liquid crystals, one of which solves the problem of assigning the helical sense.

  18. Hydrodynamic Helical Orientations of Nanofibers in a Vortex

    Directory of Open Access Journals (Sweden)

    Akihiko Tsuda

    2014-05-01

    Full Text Available In this review article, I report our recent studies on spectroscopic visualizations of macroscopic helical alignments of nanofibers in vortex flows. Our designed supramolecular nanofibers, formed through self-assemblies of dye molecules, helically align in torsional flows of a vortex generated by mechanical rotary stirring of the sample solutions. The nanofiber, formed through bundling of linear supramolecular polymers, aligns equally in right- and left-handed vortex flows. However, in contrast, a one-handedly twisted nanofiber, formed through helical bundling of the supramolecular polymers, shows unequal helical alignments in these torsional flows. When the helical handedness of the nanofiber matches that of the vortex flow, the nanofiber aligns more efficiently in the flowing fluid. Such phenomena are observed not only with the artificial helical supramolecular nanofibers but also with biological nanofibers such as double-stranded DNA.

  19. System assessment of helical reactors in comparison with tokamaks

    Energy Technology Data Exchange (ETDEWEB)

    Yamazaki, K.; Imagawa, S.; Muroga, T.; Sagara, A.; Okamura, S.

    2002-10-01

    A comparative assessment of tokamak and helical reactors has been performed using equivalent physics/engineering model and common costing model. Higher-temperature plasma operation is required in tokamak reactors to increase bootstrap current fraction and to reduce current-drive (CD) power. In helical systems, lower-temperature operation is feasible and desirable to reduce helical ripple transport. The capital cost of helical reactor is rather high, however, the cost of electricity (COE) is almost same as that of tokamak reactor because of smaller re-circulation power (no CD power) and less-frequent blanket replacement (lower neutron wall loading). The standard LHD-type helical reactor with 5% beta value is economically equivalent to the standard tokamak with 3% beta. The COE of lower-aspect ratio helical reactor is on the same level of high-{beta}{sub N} tokamak reactors. (author)

  20. Magnetoelectric-field helicities and reactive power flows

    CERN Document Server

    Kamenetskii, E O; Shavit, R

    2015-01-01

    The dual symmetry between the electric and magnetic fields underlies Maxwell's electrodynamics. Due to this symmetry one can describe topological properties of an electromagnetic field in free space and obtain the conservation law of optical (electromagnetic) helicity. What kind of the field helicity one can expect to see when the electromagnetic-field symmetry is broken? The near fields originated from small ferrite particles with magnetic dipolar mode (MDM) oscillations are the fields with the electric and magnetic components, but with broken dual (electric-magnetic) symmetry. These fields, called magnetoelectric (ME) fields, have topological properties different from such properties of electromagnetic fields. The helicity states of ME fields are topologically protected quantum like states. In this paper, we study the helicity properties of ME fields. We analyze conservation laws of the ME-field helicity and show that the helicity density is related to an imaginary part of the complex power flow density. We...

  1. Dispersion phenomena in helical flow in a concentric annulus.

    Science.gov (United States)

    Song, Young Seok; Brenner, Howard

    2009-12-14

    We examined dispersion phenomena of solutes in helical flow in a concentric annulus through a multiscale approach. The helical flow was developed by the combination of the Poiseuille flow and Couette flow. Here, we present an analytic model that can address the multidimensional Taylor dispersion in the helical flow under a lateral field of thermophoresis (or thermal diffusion) in the gapwise direction. Macroscopic parameters including the average solute velocity and dispersivity were analyzed using relevant microscopic physicochemical properties. The mathematically obtained results were validated by the numerical simulation carried out in this study. The findings show that macrotransport processes are robust and straightforward to handle multidimensional dispersion phenomena of solutes in helical flow. This study is expected to provide a theoretical platform for applications of helical flow such as tube exchangers, oil drilling, and multidimensional field flow fractionations (e.g., helical flow field flow fractionation).

  2. Role of Cross Helicity in Cascade Processes of MHD turbulence

    CERN Document Server

    Mizeva, Irina; Frick, Peter; 10.1134/S1028335809020128

    2009-01-01

    The purpose of this work is to investigate the spectral properties of the developed isotropic (non-Alfven) MHD turbulence stationary excited by an external force, which injects the cross helicity into the flow simultaneously with the energy. It is shown that the cross helicity blocks the spectral energy transfer in MHD turbulence and results in energy accumulation in the system. This accumulation proceeds until the vortex intensification compensates the decreasing efficiency of nonlinear interactions. The formula for estimating the average turbulence energy is obtained for the set ratio between the injected helicity and energy. It is remarkable that the turbulence accumulates the injected cross helicity at its low rate injection -- the integral correlation coefficient significantly exceeds the ratio between the injected helicity and the energy. It is shown that the spectrum slope gradually increases from "5/3" to "2" with the cross helicity level.

  3. Stochastic Particle Acceleration by Helical Turbulence in Solar Flares

    CERN Document Server

    Fleishman, Gregory D

    2012-01-01

    Flaring release of magnetic energy in solar corona is only possible if the magnetic field deviates from a potential one. We show that the linear MHD modes excited on top of the non-potential magnetic field possess a nonzero kinetic helicity. Accordingly, this necessarily results in a noticeable kinetic helicity of the turbulence, composed of these linear modes with various scales and random phases, generated at the flare site by the primary energy release, which may be important for many applications. In particular, a nonzero turbulence helicity has a potentially strong effect on the particle acceleration because the helical component of the turbulence induces a mean regular large-scale (DC) electric field capable of directly accelerating the charged particles in addition to the commonly considered stochastic turbulent electric field. In this paper, we derive the kinetic helicity density of the linear MHD modes excited on top of a twisted large-scale magnetic field, estimate the corresponding turbulence helic...

  4. Ureterolithiasis: classical and atypical findings on unenhanced helical computed tomography.

    Science.gov (United States)

    Vaswani, Kuldeep K; El-Dieb, Adam; Vitellas, Kenneth M; Bennett, William F; Bova, James G

    2002-03-01

    Evaluation of patients with acute flank pain using helical computed tomography (CT) is a well-accepted, rapid, and safe procedure in the emergency setting. Various primary and secondary signs are described in the literature for evaluation of these patients. Our purpose is to demonstrate both the classical findings associated with ureteral calculi on unenhanced helical CT and atypical findings and potential pitfalls. We also provide readers with a systematic approach to interpreting unenhanced helical CT scans performed for acute flank pain.

  5. Helical relativistic electron beam and THz radiation

    CERN Document Server

    Son, S

    2011-01-01

    A THz laser generation utilizing a helical relativistic electron beam propagating through a strong magnetic field is discussed. The initial amplification rate in this scheme is much stronger than that in the conventional free electron laser. A magnetic field of the order of Tesla can yield a radiation in the range of 0.5 to 3 THz, corresponding to the total energy of mJ and the duration of tens of pico-second, or the temporal power of the order of GW.

  6. Holographic Metals and Insulators with Helical Symmetry

    CERN Document Server

    Donos, Aristomenis; Kiritsis, Elias

    2014-01-01

    Homogeneous, zero temperature scaling solutions with Bianchi VII spatial geometry are constructed in Einstein-Maxwell-Dilaton theory. They correspond to quantum critical saddle points with helical symmetry at finite density. Assuming $AdS_{5}$ UV asymptotics, the small frequency/(temperature) dependence of the AC/(DC) electric conductivity along the director of the helix are computed. A large class of insulating and conducting anisotropic phases is found, as well as isotropic, metallic phases. Conduction can be dominated by dissipation due to weak breaking of translation symmetry or by a quantum critical current.

  7. Preferential sampling of helicity by isotropic helicoids

    CERN Document Server

    Gustavsson, Kristian

    2016-01-01

    We present a theoretical and numerical study on the motion of isotropic helicoids in complex flows. These are particles whose motion is invariant under rotations but not under mirror reflections of the particle. This is the simplest, yet unexplored, extension of the much studied case of small spherical particles. We show that heavy isotropic helicoids, due to the coupling between translational and rotational degrees of freedom, preferentially sample different helical regions in laminar or chaotic advecting flows. This opens the way to control and engineer particles able to track complex flow structures with potential applications to microfluidics and turbulence.

  8. Insertion of helical Siberian snakes in RHIC

    Energy Technology Data Exchange (ETDEWEB)

    Luccio, A.; Pilat, F.

    1995-05-01

    Spin rotators and Siberian snakes for RHIC can be built using 4 helical magnets obtained, by twisting, from the cosine dipoles. The authors found that the fringe fields are important. In the calculations they have used a plausible model for the fringe. However, only magnetic measurements on the prototypes presently being built will allow a final optimization. The linear coupling at injection, {Delta}Q{sub min} < 10{sup {minus}2}, is well within the range of the RHIC decoupling system. At storage, the coupling introduced by the devices ({Delta}Q{sub min} < 10{sup {minus}4}) is negligible.

  9. Four-fold way to helicity

    CERN Document Server

    Elbistan, M; Zhang, P -M

    2016-01-01

    Bialynicki-Birula's "photon wave equation", derived from a Dirac/Weyl-type action principle, is symmetric w.r.t. duality transformations, but the associated Noether quantity vanishes. Replacing fields by potentials in the definition and using instead a Klein-Gordon-type action allows us to recover the previously proposed conserved "double-Chern-Simons" expression of helicity. A similar argument applied to the original Bialynicki-Birula setting yields Lipkin's "zilch". The Dirac/Weyl-type approach, applied to our potential-modified theory, yields again zero conserved charge. Our results are consistent with the theorem of Weinberg and Witten.

  10. Numerical studies of helical CMF generators

    Energy Technology Data Exchange (ETDEWEB)

    Freeman, J.R.; McGlaun, J.M.; Thompson, S.L.; Cnare, E.C.

    1979-01-01

    The COMAG-III code has been used to model the dynamic behavior of a small CMF generator having a helical coil. The results have been compared with experiments which employed light pipe diagnostics of the explosive timing together with flash radiography to time correlate the mechanical behavior with the previously reported electrical output. The code has also been used to study and compare the importance of various loss mechanisms in these generators including ohmic heating and the flux lost be the switching action of the armature. A parameter study in which the injection current was varied is described. The possible importance of electrical breakdown is also discussed.

  11. Electric field domain interface in helical systems

    Energy Technology Data Exchange (ETDEWEB)

    Itoh, Kimitaka; Sanuki, Heiji; Toda, Shinichiro; Yokoyama, Masayuki [National Inst. for Fusion Science, Toki, Gifu (Japan); Itoh, Sanae-I.; Yagi, Masatoshi [Kyushu Univ., Research Institute for Applied Mechanics, Kasuga, Fukuoka (Japan); Fukuyama, Atsushi [Kyoto Univ., Department of Nuclear Engineering, Kyoto (Japan)

    2001-07-01

    The electric field bifurcation in helical plasmas under the condition of continuous fluxes is investigated. The stationary solution of the transport equation, together with charge neutrality condition, is investigated. It is shown that the anomalous flux plays an important role in determining multiple electric field solutions. The transition to the branch with a strong positive electric field occurs when the heat flux exceeds a critical value. Condition for the presence of transition is obtained. The radial structure of the electric field domain interface is obtained. The condition that the suppression of turbulence is expected to occur is discussed. Comparison with experimental observation is briefly mentioned. (author)

  12. Superposition of helical beams by using a Michelson interferometer.

    Science.gov (United States)

    Gao, Chunqing; Qi, Xiaoqing; Liu, Yidong; Weber, Horst

    2010-01-04

    Orbital angular momentum (OAM) of a helical beam is of great interests in the high density optical communication due to its infinite number of eigen-states. In this paper, an experimental setup is realized to the information encoding and decoding on the OAM eigen-states. A hologram designed by the iterative method is used to generate the helical beams, and a Michelson interferometer with two Porro prisms is used for the superposition of two helical beams. The experimental results of the collinear superposition of helical beams and their OAM eigen-states detection are presented.

  13. The global distribution of magnetic helicity in the solar corona

    Science.gov (United States)

    Yeates, A. R.; Hornig, G.

    2016-10-01

    By defining an appropriate field line helicity, we apply the powerful concept of magnetic helicity to the problem of global magnetic field evolution in the Sun's corona. As an ideal-magnetohydrodynamic invariant, the field line helicity is a meaningful measure of how magnetic helicity is distributed within the coronal volume. It may be interpreted, for each magnetic field line, as a magnetic flux linking with that field line. Using magneto-frictional simulations, we investigate how field line helicity evolves in the non-potential corona as a result of shearing by large-scale motions on the solar surface. On open magnetic field lines, the helicity injected by the Sun is largely output to the solar wind, provided that the coronal relaxation is sufficiently fast. But on closed magnetic field lines, helicity is able to build up. We find that the field line helicity is non-uniformly distributed, and is highly concentrated in twisted magnetic flux ropes. Eruption of these flux ropes is shown to lead to sudden bursts of helicity output, in contrast to the steady flux along the open magnetic field lines. Movies are available at http://www.aanda.org

  14. Geometric nonlinearity and mechanical anisotropy in strained helical nanoribbons

    Science.gov (United States)

    Chen, Z.

    2014-07-01

    Fabrication and synthesis of helical nanoribbons have received increasing attention because of the broad applications of helical nanostructures in nano-elecromechanical/micro-electromechanical systems (NEMS/MEMS), sensors, active materials, drug delivery, etc. In this paper, I study the mechanical principles used in designing strained helical nanoribbons, and propose the use of a full three-dimensional finite element method to simulate the coexistence of both left- and right-handed segments in the same strained nanoribbon. This work can both help understand the large deformation behaviours of such nanostructures and assist in the design of helical nanostructures for engineering applications.

  15. Inhomogeneous helicity effect in the solar angular-momentum transport

    Science.gov (United States)

    Yokoi, Nobumitsu

    2017-04-01

    Coupled with mean absolute vorticity Ω∗ (rotation and mean relative vorticity), inhomogeneous turbulent helicity is expected to contribute to the generation of global flow structure against the linear and angular momentum mixing due to turbulent or eddy viscosity. This inhomogeneous helicity effect was originally derived in Yokoi & Yoshizawa (1993) [1], and recently has been validated by direct numerical simulations (DNSs) of rotating helical turbulence [2]. Turbulence effect enters the mean-vorticity equation through the turbulent vortexmotive force ⟨u'×ω'⟩ [u': velocity fluctuation, ω'(= ∇× u'): vorticity fluctuation], which is the vorticity counterpart of the electromotive force ⟨u'× b'⟩ (b': magnetic fluctuation) in the mean magnetic-field induction. The mean velocity induction δU is proportional to the vortexmotive force. According to the theoretical result [1,2], it is expressed as δU = -νT∇×Ω∗-ηT(∇2H)Ω∗, where ηT is the transport coefficient, H = ⟨u'ṡω'⟩ the turbulent helicity, and Ω∗ the mean absolute vorticity. The first term corresponds to the enhanced diffusion due to turbulent viscosity νT. The second term expresses the large-scale flow generation due to inhomogeneous helicity. Since helicity is self-generated in rotating stratified turbulence [3], an inhomogeneous helicity distribution is expected to exist in the solar convection zone. A rising flow with expansion near the surface of the Sun generates a strongly negative helicity there [4]. This spatial distribution of helicity would lead to a positive Laplacian of turbulent helicity (∇2H > 0) in the subsurface layer of the Sun. In the combination with the large-scale vorticity associated with the meridional circulation, the inhomogeneous helicity effect works for accelerating the mean velocity in the azimuthal direction. The relevance of this inhomogeneous helicity effect in the solar convection zone is discussed further. References [1] Yokoi, N. and

  16. Interferometric measurement of the helical mode of a single photon

    Energy Technology Data Exchange (ETDEWEB)

    Galvez, E J; Coyle, L E; Johnson, E; Reschovsky, B J, E-mail: egalvez@colgate.edu [Department of Physics and Astronomy, Colgate University, 13 Oak Drive, Hamilton, NY 13346 (United States)

    2011-05-15

    We present measurements of the helical mode of single photons and do so by sending heralded photons through a Mach-Zehnder interferometer that prepares the light in a helical mode with topological charge one, and interferes it with itself in the fundamental non-helical mode. Masks placed after the interferometer were used to diagnose the amplitude and phase of the mode of the light. Auxiliary measurements verified that the light was in a non-classical state. The results are in good agreement with theory. The experiments demonstrate in a direct way that single photons carry the entire spatial helical-mode information.

  17. Alteration of helical vortex core without change in flow topology

    DEFF Research Database (Denmark)

    Velte, Clara Marika; Okulov, Valery; Hansen, Martin Otto Laver

    2011-01-01

    The abrupt expansion of the slender vortex core with changes in flow topology is commonly known as vortex breakdown. We present new experimental observations of an alteration of the helical vortex core in wall bounded turbulent flow with abrupt growth in core size, but without change in flow...... topology. The helical symmetry as such is preserved, although the characteristic parameters of helical symmetry of the vortex core transfer from a smooth linear variation to a different trend under the influence of a non-uniform pressure gradient, causing an increase in helical pitch without changing its...

  18. Helicity conservation under quantum reconnection of vortex rings

    CERN Document Server

    Zuccher, Simone

    2016-01-01

    Here we show that under quantum reconnection, simulated by using the three-dimensional Gross- Pitaevskii equation, self-helicity of a system of two interacting vortex rings remains conserved. By resolving the fine structure of the vortex cores, we demonstrate that total length of the vortex system reaches a maximum at the reconnection time, while both writhe helicity and twist helicity remain separately unchanged throughout the process. Self-helicity is computed by two independent methods, and topological information is based on the extraction and analysis of geometric quantities such as writhe, total torsion and intrinsic twist of the reconnecting vortex rings.

  19. Passive scalars: mixing, diffusion and intermittency in helical and non-helical rotating turbulence

    CERN Document Server

    Imazio, P Rodriguez

    2015-01-01

    We use direct numerical simulations to compute structure functions, scaling exponents, probability density functions and turbulent transport coefficients of passive scalars in turbulent rotating helical and non-helical flows. We show that helicity affects the inertial range scaling of the velocity and of the passive scalar when rotation is present, with a spectral law consistent with $\\sim k_{\\perp}^{-1.4}$ for the passive scalar variance spectrum. This scaling law is consistent with the phenomenological argument presented in \\cite{imazio2011} for rotating non-helical flows, wich states that if energy follows a $E(k)\\sim k^{-n}$ law, then the passive scalar variance follows a law $V(k) \\sim k^{-n_{\\theta}}$ with $n_{\\theta}=(5-n)/2$. With the second order scaling exponent obtained from this law, and using the Kraichnan model, we obtain anomalous scaling exponents for the passive scalar that are in good agreement with the numerical results. Intermittency of the passive scalar is found to be stronger than in th...

  20. Electronic transport in single-helical protein molecules: Effects of multiple charge conduction pathways and helical symmetry

    Energy Technology Data Exchange (ETDEWEB)

    Kundu, Sourav, E-mail: sourav.kunduphy@gmail.com; Karmakar, S.N.

    2016-07-15

    We propose a tight-binding model to investigate electronic transport properties of single helical protein molecules incorporating both the helical symmetry and the possibility of multiple charge transfer pathways. Our study reveals that due to existence of both the multiple charge transfer pathways and helical symmetry, the transport properties are quite rigid under influence of environmental fluctuations which indicates that these biomolecules can serve as better alternatives in nanoelectronic devices than its other biological counterparts e.g., single-stranded DNA.

  1. Left- and right-handed alpha-helical turns in homo- and hetero-chiral helical scaffolds.

    Science.gov (United States)

    Shepherd, Nicholas E; Hoang, Huy N; Abbenante, Giovanni; Fairlie, David P

    2009-11-04

    Proteins typically consist of right-handed alpha helices, whereas left-handed alpha helices are rare in nature. Peptides of 20 amino acids or less corresponding to protein helices do not form thermodynamically stable alpha helices in water away from protein environments. The smallest known water-stable right- (alpha(R)) and left- (alpha(L)) handed alpha helices are reported, each stabilized in cyclic pentapeptide units containing all L- or all D-amino acids. Homochiral decapeptides comprising two identical cyclic pentapeptides (alpha(R)alpha(R) or alpha(L)alpha(L)) are continuous alpha-helical structures that are extremely stable to denaturants, degradative proteases, serum, and additives like TFE, acid, and base. Heterochiral decapeptides comprising two different cyclic pentapeptides (alpha(L)alpha(R) or alpha(R)alpha(L)) maintain the respective helical handedness of each monocyclic helical turn component but adopt extended or bent helical structures depending on the solvent environment. Adding TFE to their aqueous solutions caused a change to bent helical structures with slightly distorted N-terminal alpha(R) or alpha(L)-helical turns terminated by a Schellman-like motif adjacent to the C-terminal alpha(L) or alpha(R)-turn. This hinge-like switching between structures in response to an external cue suggests possible uses in larger structures to generate smart materials. The library of left- and right-handed 1-3 turn alpha-helical compounds reported herein project their amino acid side chains into very different regions of 3D space, constituting a unique and potentially valuable class of novel scaffolds.

  2. Electronic transport in single-helical protein molecules: Effects of multiple charge conduction pathways and helical symmetry

    Science.gov (United States)

    Kundu, Sourav; Karmakar, S. N.

    2016-07-01

    We propose a tight-binding model to investigate electronic transport properties of single helical protein molecules incorporating both the helical symmetry and the possibility of multiple charge transfer pathways. Our study reveals that due to existence of both the multiple charge transfer pathways and helical symmetry, the transport properties are quite rigid under influence of environmental fluctuations which indicates that these biomolecules can serve as better alternatives in nanoelectronic devices than its other biological counterparts e.g., single-stranded DNA.

  3. Bi- and trinuclear copper(I) complexes of 1,2,3-triazole-tethered NHC ligands: synthesis, structure, and catalytic properties

    Science.gov (United States)

    Du, Jiehao; Huang, Jingjing; Xia, Huan; Yang, Ling; Xu, Weilin

    2016-01-01

    Summary A series of copper complexes (3–6) stabilized by 1,2,3-triazole-tethered N-heterocyclic carbene ligands have been prepared via simple reaction of imidazolium salts with copper powder in good yields. The structures of bi- and trinuclear copper complexes were fully characterized by NMR, elemental analysis (EA), and X-ray crystallography. In particular, [Cu2(L2)2](PF6)2 (3) and [Cu2(L3)2](PF6)2 (4) were dinuclear copper complexes. Complexes [Cu3(L4)2](PF6)3 (5) and [Cu3(L5)2](PF6)3 (6) consist of a triangular Cu3 core. These structures vary depending on the imidazolium backbone and N substituents. The copper–NHC complexes tested are highly active for the Cu-catalyzed azide–alkyne cycloaddition (CuAAC) reaction in an air atmosphere at room temperature in a CH3CN solution. Complex 4 is the most efficient catalyst among these polynuclear complexes in an air atmosphere at room temperature. PMID:27340477

  4. A Zinc(Ⅱ) Coordination Polymer Possessing a Linear Trinuclear Building Block[Zn3(CO2)6N2

    Institute of Scientific and Technical Information of China (English)

    JIANG Ya-Qi; LI Fang-Fang; XIE Zhao-Xiong

    2008-01-01

    A new coordination polymer[Zn3(bpda)3(bpy)]1(H2bpda=2,2'-biphenyldicarboxylic acid,bpy=4,4'-bipyridien)has been hydrothermally synthesized and characterized by single-crystal X-ray diffraction analysis,elemental analysis,TG analysis and IR spectrum.1 Crystallizes in cubic crystal system,space group Ia-3,with a=20.9687(9) A,V=9219.7(3)A3,Z=8,and R (Ⅰ>2σ(Ⅰ))=0.0431.Complex 1 is a three-dimensional framework involving a new building block,linear trinuclear {Zn3(CO2)6N2} cluster.In the structure,each bpda coordinates to four zinc atoms via its two bridging bidentate carboxylate groups.To the best of our knowledge,1 implies a new coordination mode of 2,2'-biphenyldicarboxylic acid. The solid state fluorescent spectra show a strong emission peak at 451 nm(λex=341 nm).

  5. N-donor co-ligands driven two new Co(II)- coordination polymers with bi- and trinuclear units: Crystal structures, and magnetic properties

    Science.gov (United States)

    Zhou, Zhi-Hang; Han, Min-Le; Wu, Ya-Pan; Dong, Wen-Wen; Li, Dong-Sheng; Lu, Jack Y.

    2016-10-01

    Two new Co(II) coordination polymers(CPs), namely [Co2(bpe)2(Hbppc)]n (1) and [Co3(μ3-OH)(bppc)(bpm)(H2O)]·3H2O (2) (H5bppc=biphenyl-2,4,6,3‧,5‧-pentacarboxylic acid, bpe=1,2-bis(4-pyridyl)ethene, bpm=bis(4-pyridyl)amine), have been obtained and characterized by elemental analysis, single-crystal X-ray diffraction, powder X-ray diffraction (PXRD), IR spectra and thermogravimetric analysis (TGA). 1 shows a binodal (4,6)-connected fsc net with a (44·610·8)(44·62) topology, while 2 shows a binodal (5,7)-connected 3D network based on trinuclear [Co3(μ3-OH)]5+ units with unusual (3.46.52.6)(32.46.57.65.7) topology. Variable-temperature magnetic susceptibility measurements reveals that complex 1 shows ferromagnetic interactions between the adjacent Co(II) ions, whereas 2 is a antiferromagnetic system.

  6. First principle simulation of the temperature dependent magnetic circular dichroism of a trinuclear copper complex in the presence of zero field splitting.

    Science.gov (United States)

    Zhekova, Hristina R; Seth, Michael; Ziegler, Tom

    2011-09-22

    We present a test of a recently developed density functional theory (DFT) based methodology for the calculation of magnetic circular dichroism (MCD) spectra in the presence of zero-field splitting (ZFS). The absorption and MCD spectra of the trinuclear copper complex μ(3)O ([Cu(3)(L)(μ(3)-O)](4+)), which models the native intermediate produced in the catalytic cycle of the multicopper oxidases, have been simulated from first principle within the framework of adiabatic time dependent density functional theory. The effects of the ZFS of the quartet (4)A(2) ground state on the theoretical MCD spectrum of μ(3)O have been analyzed. The simulated spectra are consistent with the experimental ones. The theoretical assignments of the MCD spectra are based on direct simulation as well as a detailed analysis of the molecular orbitals in μ(3)O. Some of the assignments differ from those given in previous studies. The ZFS effects in the presence of a strong external magnetic field (7 T) prove negligible. The change of the sign of the ZFS changes systematically the intensity of the MCD bands of the z-polarized excitations. The effect of the ZFS on the x,y-polarized excitations is not uniform.

  7. Bi- and trinuclear copper(I complexes of 1,2,3-triazole-tethered NHC ligands: synthesis, structure, and catalytic properties

    Directory of Open Access Journals (Sweden)

    Shaojin Gu

    2016-05-01

    Full Text Available A series of copper complexes (3–6 stabilized by 1,2,3-triazole-tethered N-heterocyclic carbene ligands have been prepared via simple reaction of imidazolium salts with copper powder in good yields. The structures of bi- and trinuclear copper complexes were fully characterized by NMR, elemental analysis (EA, and X-ray crystallography. In particular, [Cu2(L22](PF62 (3 and [Cu2(L32](PF62 (4 were dinuclear copper complexes. Complexes [Cu3(L42](PF63 (5 and [Cu3(L52](PF63 (6 consist of a triangular Cu3 core. These structures vary depending on the imidazolium backbone and N substituents. The copper–NHC complexes tested are highly active for the Cu-catalyzed azide–alkyne cycloaddition (CuAAC reaction in an air atmosphere at room temperature in a CH3CN solution. Complex 4 is the most efficient catalyst among these polynuclear complexes in an air atmosphere at room temperature.

  8. Electron spin-lattice and spin-spin relaxation study of a trinuclear iron(III) complex and its relevance in quantum computing.

    Science.gov (United States)

    Mitrikas, George; Sanakis, Yiannis; Raptopoulou, Catherine P; Kordas, George; Papavassiliou, Georgios

    2008-02-01

    Electron spins of molecular magnets are promising candidates for large scale quantum information processing because they exhibit a large number of low-lying excited states. In this paper X-band pulse electron paramagnetic resonance spectroscopy is used to determine the intrinsic relaxation times T1 and T2 of a molecular magnet with an S = 1/2 ground state, namely the neutral trinuclear oxo-centered iron (III) complex, [Fe3(micro3-O)(O2CPh)5(salox)(EtOH)(EtOH)(H2O)]. The temperature dependence of the spin-lattice relaxation time T1 between 4.5 and 11 K shows that the Orbach relaxation process is dominant with the first excited state lying 57 cm(-1) above the ground state, whereas the phase memory time T(M) is of the order of 2.6 micros and exhibits a modest temperature dependence. These results together with previous magnetic measurements give further insight into the magnetic properties of the complex. The coherent manipulation of the electron spins is also examined by means of transient nutation experiments.

  9. Study on dioxygen reduction by mutational modifications of the hydrogen bond network leading from bulk water to the trinuclear copper center in bilirubin oxidase

    Energy Technology Data Exchange (ETDEWEB)

    Morishita, Hirotoshi; Kurita, Daisuke; Kataoka, Kunishige; Sakurai, Takeshi, E-mail: tsakurai@se.kanazawa-u.ac.jp

    2014-07-18

    Highlights: • Proton transport pathway in bilirubin oxidase was mutated. • Two intermediates in the dioxygen reduction steps were trapped and characterized. • A specific glutamate for dioxygen reduction by multicopper oxidases was identified. - Abstract: The hydrogen bond network leading from bulk water to the trinuclear copper center in bilirubin oxidase is constructed with Glu463 and water molecules to transport protons for the four-electron reduction of dioxygen. Substitutions of Glu463 with Gln or Ala were attributed to virtually complete loss or significant reduction in enzymatic activities due to an inhibition of the proton transfer steps to dioxygen. The single turnover reaction of the Glu463Gln mutant afforded the highly magnetically interacted intermediate II (native intermediate) with a broad g = 1.96 electron paramagnetic resonance signal detectable at cryogenic temperatures. Reactions of the double mutants, Cys457Ser/Glu463Gln and Cys457Ser/Glu463Ala afforded the intermediate I (peroxide intermediate) because the type I copper center to donate the fourth electron to dioxygen was vacant in addition to the interference of proton transport due to the mutation at Glu463. The intermediate I gave no electron paramagnetic resonance signal, but the type II copper signal became detectable with the decay of the intermediate I. Structural and functional similarities between multicopper oxidases are discussed based on the present mutation at Glu463 in bilirubin oxidase.

  10. Quantification of a Helical Origami Fold

    Science.gov (United States)

    Dai, Eric; Han, Xiaomin; Chen, Zi

    2015-03-01

    Origami, the Japanese art of paper folding, is traditionally viewed as an amusing pastime and medium of artistic expression. However, in recent years, origami has served as a source of inspiration for innovations in science and engineering. Here, we present the geometric and mechanical properties of a twisting origami fold. The origami structure created by the fold exhibits several interesting properties, including rigid foldibility, local bistability and finely tunable helical coiling, with control over pitch, radius and handedness of the helix. In addition, the pattern generated by the fold closely mimics the twist buckling patterns shown by thin materials, for example, a mobius strip. We use six parameters of the twisting origami pattern to generate a fully tunable graphical model of the fold. Finally, we present a mathematical model of the local bistability of the twisting origami fold. Our study elucidates the mechanisms behind the helical coiling and local bistability of the twisting origami fold, with potential applications in robotics and deployable structures. Acknowledgment to Branco Weiss Fellowship for funding.

  11. Jet dynamics. Recollimation shocks and helical patterns

    CERN Document Server

    Perucho, M

    2013-01-01

    The dynamics and stability of extragalactic jets may be strongly influenced by small (and probable) differences in pressure between the jet and the ambient and within the jet itself. The former give rise to expansion and recollimation of the jet. This occurs in the form of conical shocks, or Mach disks, if the pressure difference is large enough. Pressure asymmetries within the jet may trigger the development of helical patterns via coupling to kink current-driven instability, or to helical Kelvin-Helmholtz instability, depending on the physical conditions in the jet. I summarize here the evidence collected during the last years on the presence of recollimation shocks and waves in jets. In the jet of CTA 102 evidence has been found for (traveling)shock-(standing)shock interaction in the core-region (0.1 mas from the core), using information from the light-curve of the source combined with VLBI data. The conclusions derived have been confirmed by numerical simulations combined with emission calculations that h...

  12. Cosmic Acceleration and the Helicity-0 Graviton

    CERN Document Server

    de Rham, Claudia; Heisenberg, Lavinia; Pirtskhalava, David

    2010-01-01

    We explore cosmology in the decoupling limit of a non-linear covariant extension of Fierz-Pauli massive gravity obtained recently in arXiv:1007.0443. In this limit the theory is a scalar-tensor model of a unique form defined by symmetries. We find that it admits a self-accelerated solution, with the Hubble parameter set by the graviton mass. The negative pressure causing the acceleration is due to a condensate of the helicity-0 component of the massive graviton, and the background evolution, in the approximation used, is indistinguishable from the \\Lambda CDM model. Fluctuations about the self-accelerated background are stable for a certain range of parameters involved. Most surprisingly, the fluctuation of the helicity-0 field above its background decouples from an arbitrary source in the linearized theory. We also show how massive gravity can remarkably screen an arbitrarily large cosmological constant in the decoupling limit, while evading issues with ghosts. The obtained static solution is stable against ...

  13. Cosmic acceleration and the helicity-0 graviton

    Science.gov (United States)

    de Rham, Claudia; Gabadadze, Gregory; Heisenberg, Lavinia; Pirtskhalava, David

    2011-05-01

    We explore cosmology in the decoupling limit of a nonlinear covariant extension of Fierz-Pauli massive gravity obtained recently in arXiv:1007.0443. In this limit the theory is a scalar-tensor model of a unique form defined by symmetries. We find that it admits a self-accelerated solution, with the Hubble parameter set by the graviton mass. The negative pressure causing the acceleration is due to a condensate of the helicity-0 component of the massive graviton, and the background evolution, in the approximation used, is indistinguishable from the ΛCDM model. Fluctuations about the self-accelerated background are stable for a certain range of parameters involved. Most surprisingly, the fluctuation of the helicity-0 field above its background decouples from an arbitrary source in the linearized theory. We also show how massive gravity can remarkably screen an arbitrarily large cosmological constant in the decoupling limit, while evading issues with ghosts. The obtained static solution is stable against small perturbations, suggesting that the degravitation of the vacuum energy is possible in the full theory. Interestingly, however, this mechanism postpones the Vainshtein effect to shorter distance scales. Hence, fifth force measurements severely constrain the value of the cosmological constant that can be neutralized, making this scheme phenomenologically not viable for solving the old cosmological constant problem. We briefly speculate on a possible way out of this issue.

  14. Microwave Studies of Perfluoropentane and its Helicity

    Science.gov (United States)

    Fournier, Joseph A.; Bohn, Robert K.; Montgomery, John A.; , Jr.

    2009-06-01

    Unlike hydrocarbons, fluorocarbons are helical in their all-trans most stable conformations. A definitive experimental determination of the helical angle has not been accomplished because single crystal X-ray studies are not available due to the lack of suitable crystallization solvents, but a value of 17^° from exactly trans is generally accepted from X-ray fiber studies. Using a pulsed-jet Fourier Transform microwave spectrometer, we have observed and assigned the rotational spectra of the lowest energy all-anti C_2 symmetry form of perfluoro-n-pentane and all three of its ^{13}C isotopomers. A, B, and C values of the parent species are 990.6394(4) MHz, 314.00020(14) MHz, and 304.37034(14) MHz, respectively. A range of effective r_0 structures incorporating various model constraints are consistent with about 16^° torsion and a Kraitchman analysis of the parent and ^{13}C species gives 13.3^°. Ab initio calculations are consistent with the experimental results.

  15. spinney: A Form library for helicity spinors

    Science.gov (United States)

    Cullen, G.; Koch-Janusz, M.; Reiter, T.

    2011-11-01

    In this work, the library spinney is presented, which provides an implementation of helicity spinors and related algorithms for the symbolical manipulation program Form. The package is well suited for symbolic amplitude calculations both in traditional, Feynman diagram based approaches and unitarity-based techniques. Program summaryProgram title: spinney Catalogue identifier: AEJQ_v1_0 Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEJQ_v1_0.html Program obtainable from: CPC Program Library, Queen's University, Belfast, N. Ireland Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html No. of lines in distributed program, including test data, etc.: 21 128 No. of bytes in distributed program, including test data, etc.: 377 589 Distribution format: tar.gz Programming language: Form Computer: Any supporting the Form language Operating system: Any supporting the Form language Classification: 4.4, 5, 11.1 Nature of problem: Implementation of the spinor-helicity formalism Solution method: Form implementation Running time: From actual calculations of all six-point one-loop diagrams of the process gg→qq¯qq bounds of 50 ms

  16. Measurements of Magnetic Helicity within Two Interacting Flux Ropes

    Science.gov (United States)

    Dehaas, Timothy; Gekelman, Walter

    2016-10-01

    Magnetic helicity (HM) has become a useful tool in the exploration of astrophysical plasmas. Its conservation in the MHD limit (and even some fluid approaches) constrains the global behavior of large plasma structures. One such astrophysical structure is a magnetic flux rope: a rope-like, current-carrying plasma embedded in an external magnetic field. Bundles of these ropes are commonly observed extending from the solar surface and can be found in the near-earth environment. In this well-diagnosed experiment (3D measurements of ne, Te, Vp, B, J, E, uflow) , two magnetic flux ropes were generated in the Large Plasma Device at UCLA. These ropes were driven kink-unstable, commencing complex motion. As they interact, helicity conservation is broken in regions of reconnection, turbulence, and instabilities. The changes in helicity can be visualized as 1) the transport of helicity (ϕB +E × A) and 2) the dissipation of the helicity (-2EB). Magnetic helicity is observed to have a negative sign and its counterpart, cross helicity, a positive one. These qualities oscillate 8% peak-to-peak. As the ropes move and the topology of the field lines change, a quasi-separatrix layer (QSL) is formed. The volume averaged HM and the largest value of Q both oscillate but not in phase. In addition to magnetic helicity, similar quantities such as self-helicity, mutual-helicity, vorticity, and canonical helicity are derived and will be presented. This work is supported by LANL-UC research Grant and done at the Basic Plasma Science Facility, which is funded by DOE and NSF.

  17. Design of aromatic helical polymers for STM visualization: imaging of single and double helices with a pattern of π-π stacking.

    Science.gov (United States)

    Zhu, Junyan; Dong, Zeyuan; Lei, Shengbin; Cao, Lili; Yang, Bing; Li, Wenfang; Zhang, Yuanchao; Liu, Junqiu; Shen, Jiacong

    2015-03-02

    From scanning tunneling microscopy (STM) images of rationally designed helical polymers with a pattern of π-π stacking, we successfully identified the single- and double-helical superstructures. The STM images of the helical structures revealed the smallest helical architecture (diameter ca. 1.3 nm) that has been seen so far. Furthermore, the interconversion of single and double helices was further underpinned by experimental analyses. Significantly, the formation of double helices induced different supramolecular chirality to that observed for the single helices.

  18. Experimental investigation of solar powered diaphragm and helical pumps

    Science.gov (United States)

    For several years, many types of solar powered water pumping systems were evaluated, and in this paper, diaphragm and helical solar photovoltaic (PV) powered water pumping systems are discussed. Data were collected on diaphragm and helical pumps which were powered by different solar PV arrays at mul...

  19. Experimental Evidence of Helical Flow in Porous Media

    DEFF Research Database (Denmark)

    Ye, Yu; Chiogna, Gabriele; Cirpka, Olaf A.;

    2015-01-01

    Helical flow leads to deformation of solute plumes and enhances transverse mixing in porous media. We present experiments in which macroscopic helical flow is created by arranging different materials to obtain an anisotropic macroscopic permeability tensor with spatially variable orientation...... mixers, but in porous media....

  20. Downstream Evolution of Longitudinal Embedded Vortices with Helical Structure

    DEFF Research Database (Denmark)

    Velte, Clara Marika; Okulov, Valery; Hansen, Martin Otto Laver

    2009-01-01

    In the present work the downstream development of device induced vortices with helical symmetry embedded in wall bounded flow on a bump is studied with the aid of Stereoscopic Particle Image Velocimetry (SPIV). The downstream evolution of characteristic parameters of helical vortices is studied...

  1. Micro helical polymeric structures produced by variable voltage direct electrospinning

    NARCIS (Netherlands)

    Shariatpanahi, S.P.; Iraji zad, A.; Abdollahzadeh, I.; Shirsavar, R.; Bonn, D.; Ejtehadi, R.

    2011-01-01

    Direct near field electrospinning is used to produce very long helical polystyrene microfibers in water. The pitch length of helices can be controlled by changing the applied voltage, allowing the production of both microsprings and microchannels. Using a novel high frequency variable voltage electr

  2. Fermion helicity flip in higher-derivative electromagnetism

    Energy Technology Data Exchange (ETDEWEB)

    Accioly, A.J. [Instituto de Fisica Teorica (IFT), Sao Paulo, SP (Brazil); Mukai, H. [Universidade Estadual de Maringa, PR (Brazil). Dept. de Fisica

    1996-10-01

    It is shown that massive fermions have their helicity flipped on account of their interaction with an electromagnetic field described by Podolsky`s generalized electrodynamics. Massless fermions, in turn, seem to be unaffected by the electromagnetic field as far as their helicity is concerned. (author).

  3. Helical channel design and technology for cooling of muon beams

    CERN Document Server

    Yonehara, K; Johnson, R P

    2012-01-01

    Novel magnetic helical channel designs for capture and cooling of bright muon beams are being developed using numerical simulations based on new inventions such as helical solenoid (HS) magnets and hydrogen-pressurized RF (HPRF) cavities. We are close to the factor of a million six-dimensional phase space (6D) reduction needed for muon colliders. Recent experimental and simulation results are presented.

  4. Optical asymmetry of helical media with a gradient of parameters

    CERN Document Server

    Eritsyan, H S

    2002-01-01

    The propagation of electromagnetic waves in isotropic gyrotropic media and helical media in the presence of gradients of optical parameters is considered. It is shown that in helical media effects of asymmetry analogous to effects of irreversibility of waves can be observed.

  5. Water tuned the helical nanostructures and supramolecular chirality in organogels.

    Science.gov (United States)

    Liu, Changxia; Jin, Qingxian; Lv, Kai; Zhang, Li; Liu, Minghua

    2014-04-11

    Water was found to tune the self-assembled nanostructures of a cationic amphiphile in organic solvents from nanofibers to helical tapes, helical tubes and chiral nanotwists with various pitch lengths depending on water content. Inversion of CD spectra was observed in the water-triggered polar and non-polar solvent gels.

  6. The global distribution of magnetic helicity in the solar corona

    CERN Document Server

    Yeates, A R

    2016-01-01

    By defining an appropriate field line helicity, we apply the powerful concept of magnetic helicity to the problem of global magnetic field evolution in the Sun's corona. As an ideal-magnetohydrodynamic invariant, the field line helicity is a meaningful measure of how magnetic helicity is distributed within the coronal volume. It may be interpreted, for each magnetic field line, as a magnetic flux linking with that field line. Using magneto-frictional simulations, we investigate how field line helicity evolves in the non-potential corona as a result of shearing by large-scale motions on the solar surface. On open magnetic field lines, the helicity injected by the Sun is largely output to the solar wind, provided that the coronal relaxation is sufficiently fast. But on closed magnetic field lines, helicity is able to build up. We find that the field line helicity is non-uniformly distributed, and is highly concentrated in twisted magnetic flux ropes. Eruption of these flux ropes is shown to lead to sudden burst...

  7. Numerical Simulations of Helicity Condensation in the Solar Corona

    Science.gov (United States)

    Zhao, L.; DeVore, C. R.; Antiochos, S. K.; Zurbuchen, T. H.

    2015-01-01

    The helicity condensation model has been proposed by Antiochos (2013) to explain the observed smoothness of coronal loops and the observed buildup of magnetic shear at filament channels. The basic hypothesis of the model is that magnetic reconnection in the corona causes the magnetic stress injected by photospheric motions to collect only at those special locations where prominences form. In this work we present the first detailed quantitative MHD simulations of the reconnection evolution proposed by the helicity condensation model. We use the well-known ansatz of modeling the closed corona as an initially uniform field between two horizontal photospheric plates. The system is driven by applying photospheric rotational flows that inject magnetic helicity into the system. The flows are confined to a finite region on the photosphere so as to mimic the finite flux system of, for example, a bipolar active region. The calculations demonstrate that, contrary to common belief, coronal loops having opposite helicity do not reconnect, whereas loops having the same sense of helicity do reconnect. Furthermore, we find that for a given amount of helicity injected into the corona, the evolution of the magnetic shear is insensitive to whether the pattern of driving photospheric motions is fixed or quasi-random. In all cases, the shear propagates via reconnection to the boundary of the flow region while the total magnetic helicity is conserved, as predicted by the model. We discuss the implications of our results for solar observations and for future, more realistic simulations of the helicity condensation process.

  8. Generation of Subwavelength Plasmonic Nanovortices via Helically Corrugated Metallic Nanowires

    CERN Document Server

    Huang, Changming; Oladipo, Abiola O; Panoiu, Nicolae C; Ye, Fangwei

    2015-01-01

    We demonstrate that plasmonic helical gratings consisting of metallic nanowires imprinted with helical grooves or ridges can be used efficiently to generate plasmonic vortices with radius much smaller than the operating wavelength. In our proposed approach, these helical surface gratings are designed so that plasmon modes with different azimuthal quantum numbers (topological charge) are phase-matched, thus allowing one to generate optical plasmonic vortices with arbitrary topological charge. The general principles for designing plasmonic helical gratings that facilitate efficient generation of such plasmonic vortices are derived and their applicability to the conversion of plasmonic vortices with zero angular momentum into plasmonic vortices with arbitrary angular momentum is illustrated in several particular cases. Our analysis, based both on the exact solutions for the electromagnetic field propagating in the helical plasmonic grating and a coupled-mode theory, suggests that even in the presence of metal lo...

  9. Magnetic helicity in stellar dynamos new numerical experiments

    CERN Document Server

    Brandenburg, A; Subramanian, K

    2002-01-01

    The theory of large scale dynamos is reviewed with particular emphasis on the problem of magnetic helicity conservation in the presence of closed and open boundaries. It is concluded that in solar and stellar large scale dynamos the production and destruction of magnetic helicity during one cycle may still be accomplished by ordinary Spitzer resistivity. This is mainly because of geometric effects causing significant magnetic helicity cancellation on each hemisphere, but also partly because the generation of toroidal field by shear does not involve the production of magnetic helicity. A number of alternatives are discussed and dismissed. These include open boundaries which lead to preferential loss of large scale magnetic helicity together with large scale magnetic fields. It is also shown that artificially induced losses of small scale field do not accelerate the production of large scale (poloidal) field. In fact, resistively limited evolution towards saturation is also found at intermediate scales before t...

  10. Hierarchical Helical Order in the Twisted Growth of Plant Organs

    Science.gov (United States)

    Wada, Hirofumi

    2012-09-01

    The molecular and cellular basis of left-right asymmetry in plant morphogenesis is a fundamental issue in biology. A rapidly elongating root or hypocotyl of twisting mutants of Arabidopsis thaliana exhibits a helical growth with a handedness opposite to that of the underlying cortical microtubule arrays in epidermal cells. However, how such a hierarchical helical order emerges is currently unknown. We propose a model for investigating macroscopic chiral asymmetry in Arabidopsis mutants. Our elastic model suggests that the helical pattern observed is a direct consequence of the simultaneous presence of anisotropic growth and tilting of cortical microtubule arrays. We predict that the root helical pitch angle is a function of the microtubule helical angle and elastic moduli of the tissues. The proposed model is versatile and is potentially important for other biological systems ranging from protein fibrous structures to tree trunks.

  11. Stimuli-Directed Helical Chirality Inversion and Bio-Applications

    Directory of Open Access Journals (Sweden)

    Ziyu Lv

    2016-08-01

    Full Text Available Helical structure is a sophisticated ubiquitous motif found in nature, in artificial polymers, and in supramolecular assemblies from microscopic to macroscopic points of view. Significant progress has been made in the synthesis and structural elucidation of helical polymers, nevertheless, a new direction for helical polymeric materials, is how to design smart systems with controllable helical chirality, and further use them to develop chiral functional materials and promote their applications in biology, biochemistry, medicine, and nanotechnology fields. This review summarizes the recent progress in the development of high-performance systems with tunable helical chirality on receiving external stimuli and discusses advances in their applications as drug delivery vesicles, sensors, molecular switches, and liquid crystals. Challenges and opportunities in this emerging area are also presented in the conclusion.

  12. Chiral Exact Relations for Helicities in Hall Magnetohydrodynamic Turbulence

    CERN Document Server

    Banerjee, Supratik

    2016-01-01

    Besides total energy, three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses two inviscid invariants which are the magnetic helicity and the generalized helicity. New exact relations are derived for homogeneous (non-isotropic) stationary Hall MHD turbulence (and also for its inertialess electron MHD limit) with non-zero helicities and in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e. the scalar product of two different increments. It provides, therefore, a direct measurement of the dissipation rates for the corresponding invariant flux. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations while the magnetic helicity cascade is linked to the right polarized fluctuations.

  13. On Helical Projection and Its Application in Screw Modeling

    Directory of Open Access Journals (Sweden)

    Riliang Liu

    2014-04-01

    Full Text Available As helical surfaces, in their many and varied forms, are finding more and more applications in engineering, new approaches to their efficient design and manufacture are desired. To that end, the helical projection method that uses curvilinear projection lines to map a space object to a plane is examined in this paper, focusing on its mathematical model and characteristics in terms of graphical representation of helical objects. A number of interesting projective properties are identified in regard to straight lines, curves, and planes, and then the method is further investigated with respect to screws. The result shows that the helical projection of a cylindrical screw turns out to be a Jordan curve, which is determined by the screw's axial profile and number of flights. Based on the projection theory, a practical approach to the modeling of screws and helical surfaces is proposed and illustrated with examples, and its possible application in screw manufacturing is discussed.

  14. Chiral exact relations for helicities in Hall magnetohydrodynamic turbulence.

    Science.gov (United States)

    Banerjee, Supratik; Galtier, Sébastien

    2016-03-01

    Besides total energy, three-dimensional incompressible Hall magnetohydrodynamics (MHD) possesses two inviscid invariants, which are the magnetic helicity and the generalized helicity. Exact relations are derived for homogeneous (nonisotropic) stationary Hall MHD turbulence (and also for its inertialess electron MHD limit) with nonzero helicities and in the asymptotic limit of large Reynolds numbers. The universal laws are written only in terms of mixed second-order structure functions, i.e., the scalar product of two different increments. It provides, therefore, a direct measurement of the dissipation rates for the corresponding invariant flux. This study shows that the generalized helicity cascade is strongly linked to the left polarized fluctuations, while the magnetic helicity cascade is linked to the right polarized fluctuations.

  15. Broadband circularly polarizing dichroism with high efficient plasmonic helical surface.

    Science.gov (United States)

    Hu, Jingpei; Zhao, Xiaonan; Li, Ruibin; Zhu, Aijiao; Chen, Linghua; Lin, Yu; Cao, Bing; Zhu, Xiaojun; Wang, Chinhua

    2016-05-16

    We propose and experimentally demonstrate a broadband and high efficient circularly polarizing dichroism using a simple single-cycle and single-helical plasmonic surface array arranged in square lattice. Two types of helical surface structures (partially or completely covered with a gold film) are investigated. It is shown that the circular polarization dichroism in the mid-IR range (3µm - 5µm) can reach 80% (when the surface is partially covered with gold) or 65% (when the surface is completely covered with gold) with a single-cycle and single-helical surface. Experimental fabrications of the proposed helical plasmonic surface are implemented with direct 3D laser writing followed by electron beam evaporation deposition of gold. The experimental evaluations of the circular polarization dichroism are in excellent agreement with the simulation. The proposed helical surface structure is of advantages of easy-fabrication, high-dichroism and scalable to other frequencies as a high efficient broadband circular polarizer.

  16. Radiation Field of a Square, Helical Beam Antenna

    DEFF Research Database (Denmark)

    Knudsen, Hans Lottrup

    1952-01-01

    ' approximate calculation of the field from a circular, helical antenna by replacing this antenna with an ``equivalent'' square helix. This investigation is carried out by means of a numerical example. The investigation shows that Kraus' approximate method of calculation yields results in fair agreement......Rigorous formulas have been derived for the field from a square, helical antenna with a uniformly progressing current wave of constant amplitude. These formulas that have the advantage of great simplicity are of direct use for helical antennas in the meter band, where for practical reasons only...... square helices are used. Further, in connection with corresponding rigorous formulas for the field from a circular, helical antenna with a uniformly progressing current wave of constant amplitude the present formulas may be used for an investigation of the magnitude of the error introduced in Kraus...

  17. A survey of left-handed helices in protein structures.

    Science.gov (United States)

    Novotny, Marian; Kleywegt, Gerard J

    2005-03-25

    All naturally occurring amino acids with the exception of glycine contain one or more chiral carbon atoms and can therefore occur in two different configurations, L (levo, left-handed) and D (dextro, right-handed). Proteins are almost exclusively built from L-amino acids. The stereochemical bias of nature is further reflected at the secondary structure level where right-handed helices are strongly preferred over left-handed helices. The handedness of helices has not received much attention in the past and is often overlooked during the analysis, description and deposition of experimentally solved protein structures. Therefore, an extensive survey of left-handed helices in the Protein Data Bank (PDB) was undertaken to analyse their frequency of occurrence, length, amino acid composition, conservation and possible structural or functional role. All left-handed helices (of four or more residues) in a non-redundant subset of the PDB, were identified using hydrogen-bonding analysis, comparison of related structures, and experimental electron density assessment to filter out likely spurious and artefactual hits. This analysis yielded 31 verified left-handed helices in a set of 7284 proteins. The phi angles of the residues in the left-handed helices lie between 30 degrees and 130 degrees and the psi angles lie between -50 degrees and 100 degrees . Most of the helices are short (four residues) and for 87% of them, it was possible to determine that they are important for the stability of the protein, for ligand binding, or as part of the active site. This suggests that, even though left-handed helices are rare, when they do occur, they are structurally or functionally significant. Four secondary structure assignment programs were tested for their ability to identify the handedness of the helices. Of these programs, only DSSP correctly assigns the handedness.

  18. The Writhe of Helical Structures in the Solar Corona

    Science.gov (United States)

    Toeroek, T.; Berger, M. A.; Kliem, B.

    2010-01-01

    Context. Helicity is a fundamental property of magnetic fields, conserved in ideal MHD. In flux rope topology, it consists of twist and writhe helicity. Despite the common occurrence of helical structures in the solar atmosphere, little is known about how their shape relates to the writhe, which fraction of helicity is contained in writhe, and how much helicity is exchanged between twist and writhe when they erupt. Aims. Here we perform a quantitative investigation of these questions relevant for coronal flux ropes. Methods. The decomposition of the writhe of a curve into local and nonlocal components greatly facilitates its computation. We use it to study the relation between writhe and projected S shape of helical curves and to measure writhe and twist in numerical simulations of flux rope instabilities. The results are discussed with regard to filament eruptions and coronal mass ejections (CMEs). Results. (1) We demonstrate that the relation between writhe and projected S shape is not unique in principle, but that the ambiguity does not affect low-lying structures, thus supporting the established empirical rule which associates stable forward (reverse) S shaped structures low in the corona with positive (negative) helicity. (2) Kink-unstable erupting flux ropes are found to transform a far smaller fraction of their twist helicity into writhe helicity than often assumed. (3) Confined flux rope eruptions tend to show stronger writhe at low heights than ejective eruptions (CMEs). This argues against suggestions that the writhing facilitates the rise of the rope through the overlying field. (4) Erupting filaments which are S shaped already before the eruption and keep the sign of their axis writhe (which is expected if field of one chirality dominates the source volume of the eruption), must reverse their S shape in the course of the rise. Implications for the occurrence of the helical kink instability in such events are discussed.

  19. Winding light beams along elliptical helical trajectories

    CERN Document Server

    Wen, Yuanhui; Zhang, Yanfeng; Chen, Hui; Yu, Siyuan

    2016-01-01

    Conventional caustic methods in real or Fourier space produced accelerating optical beams only with convex trajectories. We develop a superposition caustic method capable of winding light beams along non-convex trajectories. We ascertain this method by constructing a one-dimensional (1D) accelerating beam moving along a sinusoidal trajectory, and subsequently extending to two-dimensional (2D) accelerating beams along arbitrarily elliptical helical trajectories. We experimentally implement the method with a compact and robust integrated optics approach by fabricating micro-optical structures on quartz glass plates to perform the spatial phase and amplitude modulation to the incident light, generating beam trajectories highly consistent with prediction. The theoretical and implementation methods can in principle be extended to the construction of accelerating beams with a wide variety of non-convex trajectories, thereby opening up a new route of manipulating light beams for fundamental research and practical ap...

  20. Helical spin rotators and snakes for RHIC

    Energy Technology Data Exchange (ETDEWEB)

    Ptitsin, V.I.; Shatunov, Yu.M. [Budker Inst. of Nuclear Physics, Novosibirsk (Russian Federation); Peggs, S. [Brookhaven National Lab., Upton, NY (United States)

    1995-05-01

    The RHIC collider, now under construction at BNL, will have the possibility of polarized proton-proton collisions up to a beam energy of 250 Gev. Polarized proton beams of such high energy can be only obtained with the use of siberian snakes, a special kind of spin rotator that rotates the particle spin by 180{degree} around an axis lying in the horizontal plane. Siberian snakes help to preserve the beam polarization while numerous spin depolarizing resonances are crossed, during acceleration. In order to collide longitudinally polarized beams, it is also planned to install spin rotators around two interaction regions. This paper discusses snake and spin rotator designs based on sequences of four helical magnets. The schemes that were chosen to be applied at RHIC are presented.

  1. Cool and hot flux ropes, their helicity

    Science.gov (United States)

    Nindos, Alexander

    2016-07-01

    We will review recent indirect and direct evidence for the existence of magnetic flux ropes in the solar atmosphere. Magnetic flux ropes may appear as S-shaped or reverse S-shaped (sigmoidal) structures in regions that are likely to erupt, and may also show in nonlinear force-free field extrapolations that use data from photospheric vector magnetograms as boundary condition. The availability of high sensitivity data recorded with unprecedented spatial and temporal resolution in hot EUV wavelengths by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) has revealed the existence of coherent structures identified as hot flux ropes. In this presentation, we will review the properties of both cool and hot flux ropes with an emphasis on the frequency of their occurrence in large flares and on their magnetic helicity content.

  2. Landau Theory of Helical Fermi Liquids.

    Science.gov (United States)

    Lundgren, Rex; Maciejko, Joseph

    2015-08-07

    We construct a phenomenological Landau theory for the two-dimensional helical Fermi liquid found on the surface of a three-dimensional time-reversal invariant topological insulator. In the presence of rotation symmetry, interactions between quasiparticles are described by ten independent Landau parameters per angular momentum channel, by contrast with the two (symmetric and antisymmetric) Landau parameters for a conventional spin-degenerate Fermi liquid. We project quasiparticle states onto the Fermi surface and obtain an effectively spinless, projected Landau theory with a single projected Landau parameter per angular momentum channel that captures the spin-momentum locking or nontrivial Berry phase of the Fermi surface. As a result of this nontrivial Berry phase, projection to the Fermi surface can increase or lower the angular momentum of the quasiparticle interactions. We derive equilibrium properties, criteria for Fermi surface instabilities, and collective mode dispersions in terms of the projected Landau parameters. We briefly discuss experimental means of measuring projected Landau parameters.

  3. Spherical Helices for Resonant Wireless Power Transfer

    Directory of Open Access Journals (Sweden)

    Maja Škiljo

    2013-01-01

    Full Text Available The capabilities of electrically small spherical helical antennas for wireless power transmission at small and moderate distances are analyzed. Influence of design on antenna radiation resistance, efficiency, and mode ratio is examined. These are the factors that, according to the theoretical considerations depicted herein, govern the maximum transfer performances. Various designs and configurations are considered for the purpose, with accent on small-size receivers suitable for implementation in powering common-sized gadgets. It is shown that spherical helix design is easily manipulated to achieve a reduced antenna size. Good radiation characteristics and impedance match are maintained by multiple-arm folded antenna design and by adjusting the separation between the arms.

  4. Helical Locomotion in a Granular Medium

    Science.gov (United States)

    Darbois Texier, Baptiste; Ibarra, Alejandro; Melo, Francisco

    2017-08-01

    The physical mechanisms that bring about the propulsion of a rotating helix in a granular medium are considered. A propulsive motion along the axis of the rotating helix is induced by both symmetry breaking due to the helical shape, and the anisotropic frictional forces undergone by all segments of the helix in the medium. Helix dynamics is studied as a function of helix rotation speed and its geometrical parameters. The effect of the granular pressure and the applied external load were also investigated. A theoretical model is developed based on the anisotropic frictional force experienced by a slender body moving in a granular material, to account for the translation speed of the helix. A good agreement with experimental data is obtained, which allows for predicting the helix design to propel optimally within granular media. These results pave the way for the development of an efficient sand robot operating according to this mode of locomotion.

  5. Stable helical solitons in optical media

    Indian Academy of Sciences (India)

    Boris Malomed; G D Peng; P L Chu; Isaac Towers; Alexander V Buryak; Rowland A Sammut

    2001-11-01

    We present a review of new results which suggest the existence of fully stable spinning solitons (self-supporting localised objects with an internal vorticity) in optical fibres with self-focusing Kerr (cubic) nonlinearity, and in bulk media featuring a combination of the cubic self-defocusing and quadratic nonlinearities. Their distinctive difference from other optical solitons with an internal vorticity, which were recently studied in various optical media, theoretically and also experimentally, is that all the spinning solitons considered thus far have been found to be unstable against azimuthal perturbations. In the first part of the paper, we consider solitons in a nonlinear optical fibre in a region of parameters where the fibre carries exactly two distinct modes, viz., the fundamental one and the first-order helical mode. From the viewpoint of application to communication systems, this opens the way to doubling the number of channels carried by a fibre. Besides that, these solitons are objects of fundamental interest. To fully examine their stability, it is crucially important to consider collisions between them, and their collisions with fundamental solitons, in (ordinary or hollow) optical fibres. We introduce a system of coupled nonlinear Schrödinger equations for the fundamental and helical modes with nonstandard values of the cross-phase-modulation coupling constants, and show, in analytical and numerical forms, results of collisions between solitons carried by the two modes. In the second part of the paper, we demonstrate that the interaction of the fundamental beam with its second harmonic in bulk media, in the presence of self-defocusing Kerr nonlinearity, gives rise to the first ever example of completely stable spatial ring-shaped solitons with intrinsic vorticity. The stability is demonstrated both by direct simulations and by analysis of linearized equations.

  6. Syntheses, structures, properties and DFT study of hybrid inorganic-organic architectures constructed from trinuclear lanthanide frameworks and Keggin-type polyoxometalates.

    Science.gov (United States)

    Mirzaei, Masoud; Eshtiagh-Hosseini, Hossein; Lotfian, Nahid; Salimi, Alireza; Bauzá, Antonio; Van Deun, Rik; Decadt, Roel; Barceló-Oliver, Miquel; Frontera, Antonio

    2014-01-28

    In this paper we report the synthesis and X-ray characterization of four novel hybrid inorganic-organic assemblies generated from H4SiW12O40 as Keggin-type polyoxometalates (POM) and, in three of them, a trinuclear lanthanide cluster of type {Na(H2O)3[Ln(HCAM)(H2O)3]3}(4+) is formed, where Ln metal is La in compound 1, Ce in compound 2, and Eu in compound 3 (H3CAM = chelidamic acid or 2,6-dicarboxy-4-hydroxypyridine). These compounds represent the first POM-based inorganic-organic assemblies using chelidamic acid as an organic ligand. The thermal stability of the organic ligand is crucial, since pyridine-2,6-bis(monothiocarboxylate) instead of chelidamic acid is used (compound 4) under the same synthesis conditions, the decomposition of the ligand to pyridine was observed leading to the formation of colorless crystals of a pseudo hybrid inorganic-organic assembly. In compound 4 the hybrid inorganic-organic assembly is not formed and the organic part simply consists of four molecules of protonated pyridine acting as counterions of the [SiW12O40](4-) counterpart. The luminescent properties of compounds and have been investigated and their solid state architectures have been analyzed. Whereas compound only shows ligand emission, the Eu(3+) emission in compound 3 is discussed in detail. We have found that unprecedented anion-π interactions between the POM, which is a tetra-anion, and the aromatic rings play a crucial role in the crystal packing formation. To the best of our knowledge, this is the first report that describes and analyzes this interaction in Keggin-type POM based inorganic-organic frameworks. The energetic features of these interactions in the solid state have been analyzed using DFT calculations in some model systems predicted by us.

  7. Phage Selection of Chemically Stabilized α-Helical Peptide Ligands.

    Science.gov (United States)

    Diderich, Philippe; Bertoldo, Davide; Dessen, Pierre; Khan, Maola M; Pizzitola, Irene; Held, Werner; Huelsken, Joerg; Heinis, Christian

    2016-05-20

    Short α-helical peptides stabilized by linkages between constituent amino acids offer an attractive format for ligand development. In recent years, a range of excellent ligands based on stabilized α-helices were generated by rational design using α-helical peptides of natural proteins as templates. Herein, we developed a method to engineer chemically stabilized α-helical ligands in a combinatorial fashion. In brief, peptides containing cysteines in position i and i + 4 are genetically encoded by phage display, the cysteines are modified with chemical bridges to impose α-helical conformations, and binders are isolated by affinity selection. We applied the strategy to affinity mature an α-helical peptide binding β-catenin. We succeeded in developing ligands with Kd's as low as 5.2 nM, having >200-fold improved affinity. The strategy is generally applicable for affinity maturation of any α-helical peptide. Compared to hydrocarbon stapled peptides, the herein evolved thioether-bridged peptide ligands can be synthesized more easily, as no unnatural amino acids are required and the cyclization reaction is more efficient and yields no stereoisomers. A further advantage of the thioether-bridged peptide ligands is that they can be expressed recombinantly as fusion proteins.

  8. Helicity, topology, and Kelvin waves in reconnecting quantum knots

    Science.gov (United States)

    Clark di Leoni, P.; Mininni, P. D.; Brachet, M. E.

    2016-10-01

    Helicity is a topological invariant that measures the linkage and knottedness of lines, tubes, and ribbons. As such, it has found myriads of applications in astrophysics, fluid dynamics, atmospheric sciences, and biology. In quantum flows, where topology-changing reconnection events are a staple, helicity appears as a key quantity to study. However, the usual definition of helicity is not well posed in quantum vortices, and its computation based on counting links and crossings of centerline vorticity can be downright impossible to apply in complex and turbulent scenarios. We present a definition of helicity which overcomes these problems and which gives the expected result in the large-scale limit. With it, we show that certain reconnection events can excite Kelvin waves and other complex motions of the centerline vorticity, which slowly deplete helicity as they interact nonlinearly, thus linking the theory of vortex knots with observations of quantum fluids. This process also results in the depletion of helicity in a fully turbulent quantum flow, in a way reminiscent of the decay of helicity in classical fluids.

  9. Magnetic Helicities and Dynamo Action in Magneto-rotational Turbulence

    Science.gov (United States)

    Bodo, G.; Cattaneo, F.; Mignone, A.; Rossi, P.

    2017-07-01

    We examine the relationship between magnetic flux generation, taken as an indicator of large-scale dynamo action, and magnetic helicity, computed as an integral over the dynamo volume, in a simple dynamo. We consider dynamo action driven by magneto-rotational turbulence (MRT) within the shearing-box approximation. We consider magnetically open boundary conditions that allow a flux of helicity in or out of the computational domain. We circumvent the problem of the lack of gauge invariance in open domains by choosing a particular gauge—the winding gauge—that provides a natural interpretation in terms of the average winding number of pairwise field lines. We use this gauge precisely to define and measure the helicity and the helicity flux for several realizations of dynamo action. We find in these cases that the system as a whole does not break reflectional symmetry and that the total helicity remains small even in cases when substantial magnetic flux is generated. We find no particular connection between the generation of magnetic flux and the helicity or the helicity flux through the boundaries. We suggest that this result may be due to the essentially nonlinear nature of the dynamo processes in MRT.

  10. Helicity and its role in the varieties of magnetohydrodynamic turbulence

    Science.gov (United States)

    Montgomery, David C.; Bates, Jason W.

    Magnetic helicity has appeared as an important but slippery quantity in the theory of magnetohydrodynamic (MHD) turbulence in two contexts: (1) as a slowly-decaying ideal invariant that can control to some extent the formation of a "relaxed" MHD state—one far from thermal equilibrium—in laboratory confinement devices such as the toroidal pinch; and (2) as a potentially inversely-cascadable global quantity in driven, homogeneous MHD turbulence. In the former case, the origin of helicity is straightforwardly clear: electric current is forced to flow along a dc magnetic field, generating poloidal magnetic flux and causing the magnetic field lines to kink up, helically. In the latter, helicity's origins and physical interpretation are more obscure, sometimes having to do with mechanically driven helical motions which supposedly generate magnetic helicity that, however, no longer has any obvious "linked flux" interpretation. In both cases, its usefulness and even its definition sometimes depend sensitively on boundary conditions in a way that, say, those for energy do not. We will examine what the utility of the concept of magnetic helicity has so far been shown to be in discussing turbulent MHD, and comment on some of the ways it differs from other global ideal invariants that have been discussed, such as kinetic energy in 2D Navier-Stokes flows, and mean-square magnetic vector potential in 2D MHD. Attention will be devoted to the evidence for variational principles such as "maximal helicity," or "minimum energy," conjectured to predict various relaxation processes and late-time laminar states in evolving MHD situations. What is believed to be an important distinction between applications of the principles to decaying and driven situations will be stressed. Our discussion will be confined to the cases of small but non-zero transport coefficients, and will not deal with any possible role of helicity in ideal MHD.

  11. Multipinhole SPECT helical scan parameters and imaging volume

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Rutao, E-mail: rutaoyao@buffalo.edu; Deng, Xiao [Department of Nuclear Medicine, State University of New York at Buffalo, Buffalo, New York 14214 (United States); Wei, Qingyang; Dai, Tiantian; Ma, Tianyu [Department of Engineering Physics, Tsinghua University, Beijing 100084 (China); Lecomte, Roger [Department of Nuclear Medicine and Radiobiology, Sherbrooke Molecular Imaging Center, Université de Sherbrooke, Sherbrooke, Quebec J1H 5N4 (Canada)

    2015-11-15

    Purpose: The authors developed SPECT imaging capability on an animal PET scanner using a multiple-pinhole collimator and step-and-shoot helical data acquisition protocols. The objective of this work was to determine the preferred helical scan parameters, i.e., the angular and axial step sizes, and the imaging volume, that provide optimal imaging performance. Methods: The authors studied nine helical scan protocols formed by permuting three rotational and three axial step sizes. These step sizes were chosen around the reference values analytically calculated from the estimated spatial resolution of the SPECT system and the Nyquist sampling theorem. The nine helical protocols were evaluated by two figures-of-merit: the sampling completeness percentage (SCP) and the root-mean-square (RMS) resolution. SCP was an analytically calculated numerical index based on projection sampling. RMS resolution was derived from the reconstructed images of a sphere-grid phantom. Results: The RMS resolution results show that (1) the start and end pinhole planes of the helical scheme determine the axial extent of the effective field of view (EFOV), and (2) the diameter of the transverse EFOV is adequately calculated from the geometry of the pinhole opening, since the peripheral region beyond EFOV would introduce projection multiplexing and consequent effects. The RMS resolution results of the nine helical scan schemes show optimal resolution is achieved when the axial step size is the half, and the angular step size is about twice the corresponding values derived from the Nyquist theorem. The SCP results agree in general with that of RMS resolution but are less critical in assessing the effects of helical parameters and EFOV. Conclusions: The authors quantitatively validated the effective FOV of multiple pinhole helical scan protocols and proposed a simple method to calculate optimal helical scan parameters.

  12. Galactic dynamo and helicity losses through fountain flow

    CERN Document Server

    Shukurov, A; Subramanian, K; Brandenburg, A; Shukurov, Anvar; Sokoloff, Dmitry; Subramanian, Kandaswamy; Brandenburg, Axel

    2006-01-01

    Nonlinear behaviour of galactic dynamos is studied, allowing for magnetic helicity removal by the galactic fountain flow. A suitable advection speed is estimated, and a one-dimensional mean-field dynamo model with dynamic alpha-effect is explored. It is shown that the galactic fountain flow is efficient in removing magnetic helicity from galactic discs. This alleviates the constraint on the galactic mean-field dynamo resulting from magnetic helicity conservation and thereby allows the mean magnetic field to saturate at a strength comparable to equipartition with the turbulent kinetic energy.

  13. Corner junction as a probe of helical edge states.

    Science.gov (United States)

    Hou, Chang-Yu; Kim, Eun-Ah; Chamon, Claudio

    2009-02-20

    We propose and analyze interedge tunneling in a quantum spin Hall corner junction as a means to probe the helical nature of the edge states. We show that electron-electron interactions in the one-dimensional helical edge states result in Luttinger parameters for spin and charge that are intertwined, and thus rather different from those for a quantum wire with spin rotation invariance. Consequently, we find that the four-terminal conductance in a corner junction has a distinctive form that could be used as evidence for the helical nature of the edge states.

  14. Combining Fixed-Order Helicity Amplitudes With Resummation Using SCET

    CERN Document Server

    Stewart, Iain W; Waalewijn, Wouter J

    2012-01-01

    We discuss how to construct a simple and easy-to-use helicity operator basis in Soft-Collinear Effective Theory (SCET), for which the hard Wilson coefficients from matching QCD onto SCET are directly given in terms of the color-ordered QCD helicity amplitudes. This provides an interface to seamlessly combine fixed-order helicity amplitudes, which are the basic building blocks of state-of-the-art next-to-leading order calculations for multileg processes, with a resummation of higher-order logarithmic corrections using SCET.

  15. Magnetic Helical Micro- and Nanorobots: Toward Their Biomedical Applications

    Directory of Open Access Journals (Sweden)

    Famin Qiu

    2015-03-01

    Full Text Available Magnetic helical micro- and nanorobots can perform 3D navigation in various liquids with a sub-micrometer precision under low-strength rotating magnetic fields (<10 mT. Since magnetic fields with low strengths are harmless to cells and tissues, magnetic helical micro/nanorobots are promising tools for biomedical applications, such as minimally invasive surgery, cell manipulation and analysis, and targeted therapy. This review provides general information on magnetic helical micro/nanorobots, including their fabrication, motion control, and further functionalization for biomedical applications.

  16. Numerical studies on divertor plasmas in helical systems

    Energy Technology Data Exchange (ETDEWEB)

    Ueda, Noriaki (Mitsubishi Atomic Power Industries, Inc., Tokyo (Japan)); Itoh, Kimitaka; Itoh, Sanae

    1989-12-01

    Scrape-off layer and divertor plasmas in helical systems are studied by using the two-dimensional (2D) numerical simulation code. Unified edge divertor analysis code (UEDA code) is applied to the straight helical model of torsatron/helical heliotron configurations. 2D profiles of plasma parameter, neutrals and impurities are obtained. Erosion rate and neutral back flow rate to the core plasma are also evaluated. Various shapes of the buffle plate are examined from the view point of the establishment of 'dense-cold divertor plasma' by which we can avoid the damage of the target plate. (author).

  17. XPS study of the electron structure of heterometallic trinuclear complexes Fe{sub 2}M(μ{sub 3}-O)(μ-Piv){sub 6}(HPiv){sub 3} (M=Mn, Co, Ni)

    Energy Technology Data Exchange (ETDEWEB)

    Ivanova, T.M. [Kurnakov Institute of General and Inorganic Chemistry of RAS, Moscow (Russian Federation); Kochur, A.G., E-mail: agk@rgups.ru [Rostov State Transport University, Rostov-na-Donu (Russian Federation); Maslakov, K.I. [Lomonosov Moskow State University, Moscow (Russian Federation); Kiskin, M.A. [Kurnakov Institute of General and Inorganic Chemistry of RAS, Moscow (Russian Federation); Savilov, S.V.; Lunin, V.V. [Lomonosov Moskow State University, Moscow (Russian Federation); Novotortsev, V.M.; Eremenko, I.L. [Kurnakov Institute of General and Inorganic Chemistry of RAS, Moscow (Russian Federation)

    2015-11-15

    Highlights: • Electron structure of pivalate trinuclear heterometallic complexes is studied by XPS. • C1s-, O1s-, M2p, and M3s-spectra are measured (M=Fe, Mn, Co, Ni). • Redistribution of electron density upon complex formation is studied. - Abstract: Electron structure of pivalate heterometallic trinuclear complexes with a triangular structure and varying ligands environment is studied by the XPS method. An effect of substitution of one of the Fe atoms by M=Mn, Co, Ni on Fe2p and M2p spectra is studied. Redistribution of electron density in an OCO group upon formation of complexes and introduction of donor ligands is discovered. Correlation of the characteristics of photoelectron spectra with the variation of ligands environment is studied. The complexes are assigned to high-spin ones with Fe in oxidation state III, and M, II. A relation is established between Fe2p-spectra characteristics and electron affinity of M ions.

  18. Spin Helicity in Chiral Lanthanide Chains.

    Science.gov (United States)

    Mihalcea, Ionut; Perfetti, Mauro; Pineider, Francesco; Tesi, Lorenzo; Mereacre, Valeriu; Wilhelm, Fabrice; Rogalev, Andrei; Anson, Christopher E; Powell, Annie K; Sessoli, Roberta

    2016-10-17

    We report here the determination of the helical spin structure of three Ln-based chiral chains of the formula [Ln(Hnic)(nic)2(NO3)]n (Hnic = nicotinic acid; Ln = Tb, Dy, and Er) by means of cantilever torque magnetometry. While the Dy and Er derivatives are strongly axial (easy-axis and easy-plane anisotropy, respectively), the Tb derivative is characterized by a remarkable rhombicity. In agreement with these findings, alternating-current susceptibility reveals slow magnetic relaxation only in the Dy derivative. Dilution of Dy(III) ions in the diamagnetic Y-based analogue shows that the weak ferromagnetic intrachain interactions do not contribute significantly to the energy barrier for the reversal of magnetization, which is better described as a single-ion process. Single crystals of the two enantiomers of the Dy derivative have also been investigated using hard X-ray synchrotron radiation at the L-edge of the metal revealing optical activity although with negligible involvement of the 4f electrons of the Dy(III) ion.

  19. Large-scale instabilities of helical flows

    CERN Document Server

    Cameron, Alexandre; Brachet, Marc-Étienne

    2016-01-01

    Large-scale hydrodynamic instabilities of periodic helical flows are investigated using $3$D Floquet numerical computations. A minimal three-modes analytical model that reproduce and explains some of the full Floquet results is derived. The growth-rate $\\sigma$ of the most unstable modes (at small scale, low Reynolds number $Re$ and small wavenumber $q$) is found to scale differently in the presence or absence of anisotropic kinetic alpha (\\AKA{}) effect. When an $AKA$ effect is present the scaling $\\sigma \\propto q\\; Re\\,$ predicted by the $AKA$ effect theory [U. Frisch, Z. S. She, and P. L. Sulem, Physica D: Nonlinear Phenomena 28, 382 (1987)] is recovered for $Re\\ll 1$ as expected (with most of the energy of the unstable mode concentrated in the large scales). However, as $Re$ increases, the growth-rate is found to saturate and most of the energy is found at small scales. In the absence of \\AKA{} effect, it is found that flows can still have large-scale instabilities, but with a negative eddy-viscosity sca...

  20. Helical Screw Expander Evaluation Project. Final report

    Energy Technology Data Exchange (ETDEWEB)

    McKay, R.

    1982-03-01

    A functional 1-MW geothermal electric power plant that featured a helical screw expander was produced and then tested in Utah in 1978 to 1979 with a demonstrated average performance of approximately 45% machine efficiency over a wide range of test conditions in noncondensing operation on two-phase geothermal fluids. The Project also produced a computer-equipped data system, an instrumentation and control van, and a 1000-kW variable load bank, all integrated into a test array designed for operation at a variety of remote test sites. Additional testing was performed in Mexico in 1980 under a cooperative test program using the same test array, and machine efficiency was measured at 62% maximum with the rotors partially coated with scale, compared with approximately 54% maximum in Utah with uncoated rotors, confirming the importance of scale deposits within the machine on performance. Data are presented for the Utah testing and for the noncondensing phases of the testing in Mexico. Test time logged was 437 hours during the Utah tests and 1101 hours during the Mexico tests.

  1. Helical path separation for guided wave tomography

    Energy Technology Data Exchange (ETDEWEB)

    Huthwaite, P.; Seher, M. [Department of Mechanical Engineering, Imperial College, London, SW7 2AZ (United Kingdom)

    2015-03-31

    The pipe wall loss caused by corrosion can be quantified across an area by transmitting guided Lamb waves through the region and measuring the resulting signals. Typically the dispersive relationship for these waves, resulting in the wave velocity being a function of thickness, is exploited which enables the wall thickness to be determined from a velocity reconstruction. The accuracy and quality of this reconstruction is commonly limited by the angle of view available from the transducer arrays. These arrays are often attached as a pair of ring arrays either side of the inspected region, and due to the cyclic nature of the pipe, waves are able to travel in an inifinite number of helical paths between any two transducers. The first arrivals can be separated relatively easily by time gating, but by using just these components the angle of view is strongly restricted. To improve the viewing angle, it is necessary to separate the wavepackets. This paper provides an outline of a separation approach: initially the waves are backpropagated to their source to align the different signals, then a filtering technique is applied to select the desired components. The technique is applied to experimental data and demonstrated to robustly separate the signals.

  2. Towards online patient imaging during helical radiotherapy.

    Science.gov (United States)

    Yu, L; Poole, C M; Lancaster, C M; Sylvander, S R

    2015-03-01

    Exit-detector data from helical radiation therapy have been studied extensively for delivery verification and dose reconstruction. Since the same radiation source is used for both imaging and treatment, this work investigates the possibility of utilising exit-detector raw data for imaging purposes. This gives rise to potential clinical applications such as retrospective daily setup verification and inter-fractional setup error detection. The exit-detector raw data were acquired and independently analysed using Python programming language. The raw data were extracted from the treatment machine's onboard computer, and converted into 2D array files. The contours of objects (phantom or patient) were acquired by applying a logarithmic function to the ratio of two sinograms, one with the object in the beam and one without. The setup variation between any two treatment deliveries can be detected by applying the same function to their corresponding exit-detector sinograms. The contour of the object was well defined by the secondary radiation from the treatment beam and validated with the imaging beam, although no internal structures were discernible due to the interference from the primary radiation. The sensitivity of the setup variation detection was down to 2 mm, which was mainly limited by the resolution of the exit-detector itself. The exit-detector data from treatment procedures contain valuable photon exit fluence maps which can be utilised for contour definition and verification of patient alignment without reconstruction.

  3. ECE Measurements of Helical Plasmas in LHD

    Science.gov (United States)

    Nagayama, Y.; Inagaki, S.; Ito, Y.; Kawahata, K.; Sasao, H.; de Vries, P.

    1999-11-01

    This paper presents ECE measurements on LHD, which is the l=2, n=10 heriotron with the major radius of 3.8 m, with the averaged minor radius of 60 cm and with the helical field of up to 3 T. The ECE is collected from both inner and outer sides, since the magnetic field has a peaked profile. ECE is detcted with Michelson, GPC and 70 GHz and 140 GHz radiometers. The LHD plasma is generated using ECH of up to 1 MW and is heated using NBI of up to 8 GW. Notch filters reduce the ECH leakage. The polarization of ECE is theoretically and experimentally investigated in the heriotoron system, where the field angle rotates -30 to 30^o. The polarization follows as the field angle changes. Since the density profile is flat, ECE is cut off in the edge region in the high density LHD plasma. An interesting observation is the breathing phenomena, which is as follows: the electron temperature and other plasma parameters oscillate with frequency of 0.5-1Hz like a sine-wave when the NBI power is about 1 MW.

  4. Next-to-Maximal Helicity Violating Amplitudes in Gauge Theory

    CERN Document Server

    Kosower, D A

    2004-01-01

    Using the novel diagrammatic rules recently proposed by Cachazo, Svrcek, and Witten, I give a compact, manifestly Lorentz-invariant form for tree-level gauge-theory amplitudes with three opposite helicities.

  5. A Improved Method of Measurement Helicity Value of Neutrino

    Institute of Scientific and Technical Information of China (English)

    Ye Zipiao

    2000-01-01

    The Goldhaber's experimental result is analyzed in this paper. The improved method of measureing helicity value of the neutrino put forward here can greatly enhance the accuracy of measurement result and evidently reduce the experimental error.

  6. Magnetic Helicity and Large Scale Magnetic Fields: A Primer

    CERN Document Server

    Blackman, Eric G

    2014-01-01

    Magnetic fields of laboratory, planetary, stellar, and galactic plasmas commonly exhibit significant order on large temporal or spatial scales compared to the otherwise random motions within the hosting system. Such ordered fields can be measured in the case of planets, stars, and galaxies, or inferred indirectly by the action of their dynamical influence, such as jets. Whether large scale fields are amplified in situ or a remnant from previous stages of an object's history is often debated for objects without a definitive magnetic activity cycle. Magnetic helicity, a measure of twist and linkage of magnetic field lines, is a unifying tool for understanding large scale field evolution for both mechanisms of origin. Its importance stems from its two basic properties: (1) magnetic helicity is typically better conserved than magnetic energy; and (2) the magnetic energy associated with a fixed amount of magnetic helicity is minimized when the system relaxes this helical structure to the largest scale available. H...

  7. Role of helicities for the dynamics of turbulent magnetic fields

    CERN Document Server

    Mueller, Wollf-Christian

    2013-01-01

    Investigations of the inverse cascade of magnetic helicity are conducted with pseudospectral, three-dimensional direct numerical simulations of forced and decaying incompressible magnetohydrodynamic turbulence. The high-resolution simulations which allow for the necessary scale-separation show that the observed self-similar scaling behavior of magnetic helicity and related quantities can only be understood by taking the full nonlinear interplay of velocity and magnetic fluctuations into account. With the help of the eddy-damped quasi-normal Markovian approximation a probably universal relation between kinetic and magnetic helicities is derived that closely resembles the extended definition of the prominent dynamo pseudoscalar $\\alpha$. This unexpected similarity suggests an additional nonlinear quenching mechanism of the current-helicity contribution to $\\alpha$.

  8. Perfect spin filtering effect in ultrasmall helical zigzag graphene nanoribbons

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Zi-Yue, E-mail: zzy8423@jiangnan.edu.cn

    2017-02-05

    The spin-polarized transport properties of helical zigzag graphene nanoribbons (ZGNRs) are investigated by first-principles calculations. It is found that although all helical ZGNRs have similar density of states and edge states, they show obviously different transport characteristics depending on the curling manners. ZGNRs curled along zigzag orientation exhibit perfect spin filtering effect with a large spin-split gap near the Fermi level, while ZGNRs curled along armchair orientation behave as conventional conductors for both two spin channels. The spin filtering effect will be weakened with the increase of either ribbon width or curling diameter. The results suggest that ultrasmall helical ZGNRs have important potential applications in spintronics and flexible electronics. - Highlights: • Perfect spin filtering effect has been found in helical ZGNRs. • The effect strongly depends on the curling manners of ZGNRs. • Different transport properties do not induced by distinct electronic properties. • The effect may be weakened with increasing either ribbon width or curling diameter.

  9. Amphipathic Alpha-Helical Peptide Compositions as Antiviral Agents

    Science.gov (United States)

    Glenn, Jeffrey (Inventor); Cho, Nam-Joon (Inventor); Frank, Curtis W. (Inventor); Cheong, Kwang Ho (Inventor)

    2014-01-01

    The invention features methods and compositions that exploit the ability of amphipathic alpha-helical (AH) peptides to cause disruption of lipid-containing vesicles, such as enveloped viruses, in a size-dependent manner.

  10. Coronal Magnetic Flux Rope Equilibria and Magnetic Helicity

    Institute of Scientific and Technical Information of China (English)

    2001-01-01

    Using a 2.5-dimensional (2.5-D) ideal MHD model, this paper ana lyzes the equilibrium properties of coronal magnetic flux ropes in a bipolar ambient magnetic field. It is found that the geometrical features of the magnetic flux rope,including the height of the rope axis, the half-width of the rope, and the length of the vertical current sheet below the rope, are determined by a single magnetic parameter, the magnetic helicity, which is the sum of the self-helicity of the rope and the mutual helicity between the rope field and the ambient magnetic field. All the geometrical parameters increase monotonically with increasing magnetic helicity.The implication of this result in solar active phenomena is briefly discussed.

  11. Microfabricated, 94 GHz, 25 W, Helical Traveling Wave Tube Project

    Data.gov (United States)

    National Aeronautics and Space Administration — Teraphysics Corporation completed the Phase I objectives for the electrical design of a 94 GHz, 26 W TWT with 53% overall efficiency, including the helical circuit...

  12. Design study of a normal conducting helical snake for AGS

    CERN Document Server

    Takano, Junpei; Okamura, Masahiro; Roser, Thomas; MacKay, William W; Luccio, Alfredo U; Takano, Koji

    2004-01-01

    A new normal conducting snake magnet is being fabricated for the Alternate Gradient Synchrotron (AGS) at Brookhaven National Laboratory (BNL). In the Relativistic Heavy Ion Collider (RHIC) project, a superconducting type helical dipole magnets had been developed and it performed successfully in high-energy polarized proton acceleration. The new AGS helical snake has the same basic magnetic structure but is more complicated. To achieve no beam shift and no beam deflection in one magnetic device, helical pitches and rotating angles were carefully calculated. Compared to a superconducting magnet, a normal warm magnet must have a large cross- sectional area of conductors which make it difficult to design a magnet with large helical pitch. We developed a modified window frame structure to accommodate the large number of conductors. Its three dimensional magnetic field was simulated by using OPERA3D/TOSCA. 3 Refs.

  13. Heat and mass transfer characteristics of a small helical absorber

    Energy Technology Data Exchange (ETDEWEB)

    Yoon, Jung-In [College of Engineering, School of Mechanical Engineering, Pukyong National University, San 100, Yongdang-dong, Nam-gu, Pusan 608-739 (Korea, Republic of); Kwon, Oh-Kyung [KITECH, 35-3 Hongchon-ri, Ipjang-meon, Chonan, Chungnam 330-825 (Korea, Republic of); Bansal, P.K. [Department of Mechanical Engineering, The University of Auckland, Private bag 92019, Auckland (New Zealand); Moon, Choon-Geun; Lee, Ho-Saeng [Department of Refrigeration and Air-conditioning Engineering, Graduate School, Pukyong National University, San 100, Yongdang-dong, Nam-gu, Pusan 608-739 (Korea, Republic of)

    2006-02-01

    This paper presents experimental results of heat and mass transfer investigation of the falling film absorber (with strong lithium bromide solution) for a small household absorption chiller/heater. Various components (e.g. low temperature generator, absorber and evaporator) were arranged concentrically in cylindrical form such that the helical-arrangement of the heat exchangers allowed the system to be more compact than the conventional system. Measurements from the helical absorber were compared with data from the literature. The comparison revealed that the heat and mass transfer performance of the helical absorber tube is similar to the existing tube bundle absorber. As a result, the proposed helical absorber shows a good potential due its reduced size and weight for the future designs of small capacity absorption chillers/heaters. (author)

  14. Supramolecular helices: chirality transfer from conjugated molecules to structures.

    Science.gov (United States)

    Yang, Yang; Zhang, Yajie; Wei, Zhixiang

    2013-11-13

    Different scales of chirality endow a material with many excellent properties and potential applications. In this review, using π-conjugated molecules as functional building blocks, recent progress on supramolecular helices inspired by biological helicity is summarized. First, induced chirality on conjugated polymers and small molecules is introduced. Molecular chirality can be amplified to nanostructures, superstructures, and even macroscopic structures by a self-assembly process. Then, the principles for tuning the helicity of supramolecular chirality, as well as formation of helical heterojunctions, are summarized. Finally, the potential applications of chiral structures in chiral sensing and organic electronic devices are critically reviewed. Due to recent progress in chiral structures, an interdisciplinary area called "chiral electronics" is expected to gain wide popularity in the near future.

  15. Extragalactic jets with helical magnetic fields: relativistic MHD simulations

    CERN Document Server

    Keppens, R; van der Holst, B; Casse, F

    2008-01-01

    Extragalactic jets are inferred to harbor dynamically important, organized magnetic fields which presumably aid in the collimation of the relativistic jet flows. We here explore by means of grid-adaptive, high resolution numerical simulations the morphology of AGN jets pervaded by helical field and flow topologies. We concentrate on morphological features of the bow shock and the jet beam behind the Mach disk, for various jet Lorentz factors and magnetic field helicities. We investigate the influence of helical magnetic fields on jet beam propagation in overdense external medium. We use the AMRVAC code, employing a novel hybrid block-based AMR strategy, to compute ideal plasma dynamics in special relativity. The helicity of the beam magnetic field is effectively transported down the beam, with compression zones in between diagonal internal cross-shocks showing stronger toroidal field regions. In comparison with equivalent low-relativistic jets which get surrounded by cocoons with vortical backflows filled by ...

  16. Direct numerical simulations of helical dynamo action: MHD and beyond

    Directory of Open Access Journals (Sweden)

    D. O. Gómez

    2004-01-01

    Full Text Available Magnetohydrodynamic dynamo action is often invoked to explain the existence of magnetic fields in several astronomical objects. In this work, we present direct numerical simulations of MHD helical dynamos, to study the exponential growth and saturation of magnetic fields. Simulations are made within the framework of incompressible flows and using periodic boundary conditions. The statistical properties of the flow are studied, and it is found that its helicity displays strong spatial fluctuations. Regions with large kinetic helicity are also strongly concentrated in space, forming elongated structures. In dynamo simulations using these flows, we found that the growth rate and the saturation level of magnetic energy and magnetic helicity reach an asymptotic value as the Reynolds number is increased. Finally, extensions of the MHD theory to include kinetic effects relevant in astrophysical environments are discussed.

  17. Design activities on helical DEMO reactor FFHR-d1

    Energy Technology Data Exchange (ETDEWEB)

    Sagara, A., E-mail: sagara.akio@LHD.nifs.ac.jp [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Goto, T.; Miyazawa, J.; Yanagi, N.; Tanaka, T.; Tamura, H.; Sakamoto, R.; Tanaka, M.; Tsumori, K. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan); Mitarai, O. [Tokai University, 9-1-1 Toroku, Kumamoto 862-8652 (Japan); Imagawa, S.; Muroga, T. [National Institute for Fusion Science, Toki, Gifu 509-5292 (Japan)

    2012-08-15

    Highlights: Black-Right-Pointing-Pointer Conceptual design studies of the helical DEMO reactor FFHR-d1 have been conducted. Black-Right-Pointing-Pointer Design window analyses with core plasma and engineering designs have been carried out. Black-Right-Pointing-Pointer R and Ds on blanket, magnet, tritium control, fuelling and heating systems are discussed. - Abstract: Based on high-density and high-temperature plasma experiments in the large helical device (LHD), conceptual design studies of the LHD-type helical DEMO reactor FFHR-d1 have been conducted by integrating wide-ranged R and D activities on core plasmas and reactor technologies through cooperative researches under the fusion engineering research project, which has been launched newly in NIFS. Current activities for the FFHR-d1 in this project are presented on design window analyses with designs on core plasma, neutronics for liquid blankets, continuous helical magnets, pellet fueling, tritium systems and plasma heating devices.

  18. Scaling laws in decaying helical 3D magnetohydrodynamic turbulence

    CERN Document Server

    Christensson, M; Brandenburg, A; Christensson, Mattias; Hindmarsh, Mark; Brandenburg, Axel

    2002-01-01

    We study the evolution of growth and decay laws for the magnetic field coherence length xi, energy E_M and magnetic helicity H in freely decaying 3D MHD turbulence. We show that with certain assumptions, self-similarity of the magnetic power spectrum alone implies that xi ~ t^{1/2}. This in turn implies that magnetic helicity decays as H ~ t^{-2s}, where s=(xi_diff/xi_H)^2, in terms of xi_diff, the diffusion length scale, and xi_H, a length scale defined from the helicity power spectrum. The relative magnetic helicity remains constant, implying that the magnetic energy decays as E_M ~ t^{-0.5-2s}. At late times s is constant and inversely proportional to the magnetic Reynolds number Re_M.

  19. Conservation of writhe helicity under anti-parallel reconnection

    CERN Document Server

    Laing, Christian E; Sumners, De Witt L

    2014-01-01

    Reconnection is a fundamental event in many areas of science, from the interaction of vortices in classical and quantum fluids, and magnetic flux tubes in magnetohydrodynamics and plasma physics, to the recombination in polymer physics and DNA biology. By using fundamental results in topological fluid mechanics, the helicity of a flux tube can be calculated in terms of writhe and twist contributions. Here we show that the writhe is conserved under anti-parallel reconnection. Hence, for a pair of interacting flux tubes of equal flux, if the twist of the reconnected tube is the sum of the original twists of the interacting tubes, then helicity is conserved during reconnection. Thus, any deviation from helicity conservation is entirely due to the intrinsic twist inserted or deleted locally at the reconnection site. This result has important implications for helicity and energy considerations in various physical contexts.

  20. Experimental evaluation of helically coiled tube flocculators for ...

    African Journals Online (AJOL)

    Experimental evaluation of helically coiled tube flocculators for turbidity removal ... clarification system, while varying hydraulic and geometrical parameters in HCTs. ... of baffled tank processing times) were observed for high efficiency process ...

  1. Comparison between helical computed tomography angiography and intraoperative findings

    Directory of Open Access Journals (Sweden)

    Abijit Shetty

    2014-01-01

    Conclusions: Helical CT is important in delineating the arterial, venous, and ureteral anatomy and can show the important incidental findings. Left renal donors and males have more variations in their renal anatomy. Technically challenging laparoscopic nephrectomy on the multiple-vessel-side donor is possible with the aid of helical CT. The importance of the CT in evaluating donor renal anatomy for a technically challenging laparoscopic donor nephrectomy is commendable.

  2. Thermal metal-insulator transition in a helical topological superconductor

    OpenAIRE

    Fulga, I. C.; Akhmerov, A. R.; Tworzydło, J.; Béri, B.; Beenakker, C. W. J.

    2012-01-01

    Two-dimensional superconductors with time-reversal symmetry have a Z_2 topological invariant, that distinguishes phases with and without helical Majorana edge states. We study the topological phase transition in a class-DIII network model, and show that it is associated with a metal-insulator transition for the thermal conductance of the helical superconductor. The localization length diverges at the transition with critical exponent nu approx 2.0, about twice the known value in a chiral supe...

  3. Scale Dependence of Magnetic Helicity in the Solar Wind

    Science.gov (United States)

    Brandenburg, Axel; Subramanian, Kandaswamy; Balogh, Andre; Goldstein, Melvyn L.

    2011-01-01

    We determine the magnetic helicity, along with the magnetic energy, at high latitudes using data from the Ulysses mission. The data set spans the time period from 1993 to 1996. The basic assumption of the analysis is that the solar wind is homogeneous. Because the solar wind speed is high, we follow the approach first pioneered by Matthaeus et al. by which, under the assumption of spatial homogeneity, one can use Fourier transforms of the magnetic field time series to construct one-dimensional spectra of the magnetic energy and magnetic helicity under the assumption that the Taylor frozen-in-flow hypothesis is valid. That is a well-satisfied assumption for the data used in this study. The magnetic helicity derives from the skew-symmetric terms of the three-dimensional magnetic correlation tensor, while the symmetric terms of the tensor are used to determine the magnetic energy spectrum. Our results show a sign change of magnetic helicity at wavenumber k approximately equal to 2AU(sup -1) (or frequency nu approximately equal to 2 microHz) at distances below 2.8AU and at k approximately equal to 30AU(sup -1) (or nu approximately equal to 25 microHz) at larger distances. At small scales the magnetic helicity is positive at northern heliographic latitudes and negative at southern latitudes. The positive magnetic helicity at small scales is argued to be the result of turbulent diffusion reversing the sign relative to what is seen at small scales at the solar surface. Furthermore, the magnetic helicity declines toward solar minimum in 1996. The magnetic helicity flux integrated separately over one hemisphere amounts to about 10(sup 45) Mx(sup 2) cycle(sup -1) at large scales and to a three times lower value at smaller scales.

  4. First Helical Structure in the Nano-world

    Institute of Scientific and Technical Information of China (English)

    2005-01-01

    @@ Although a commonplace structure in nature, the helix remains a mystery to scientific researchers. In biology,the structure is important as DNA is helical and so does the substructure of many proteins. Since its discovery more than 50 years ago, the double helix has offered an important approach to interpret and make use of bio-organic structures. Yet, it is seldom to see a helical structure formed by inorganic crystalstate materials.

  5. Tree-level split helicity amplitudes in ambitwistor space

    Science.gov (United States)

    Chen, Bin; Wu, Jun-Bao

    2009-12-01

    We study all tree-level split helicity gluon amplitudes by using the recently proposed Britto-Cachazo-Feng-Witten recursion relation and Hodges diagrams in ambitwistor space. We pick out the contributing diagrams and find that all of them can be divided into triangles in a suitable way. We give the explicit expressions for all of these amplitudes. As an example, we reproduce the six-gluon split next-to-maximally-helicity-violating amplitudes in momentum space.

  6. On the Modelling of Spur and Helical Gear Dynamic Behaviour

    OpenAIRE

    Philippe, Velex

    2012-01-01

    This chapter is aimed at introducing the fundamentals of spur and helical gear dynamics. Using three-dimensional lumped models and a thin-slice approach for mesh elasticity, the general equations of motion for single-stage spur or helical gears are presented. Some particular cases including the classic one degree-of-freedom model are examined in order to introduce and illustrate the basic phenomena. The interest of the concept of transmission errors is analysed and a number of practical consi...

  7. Spinning swimming of Volvox by tangential helical wave

    CERN Document Server

    Felderhof, B U

    2016-01-01

    The swimming of a sphere by means of tangential helical waves running along its surface is studied on the basis of the Stokes equations. Two types of tangential waves are found. The first of these is associated with a pressure disturbance and leads to a higher rate of net rotation than the second one for the same power. It is suggested that the helical waves are relevant for the rotational swimming of Volvox.

  8. Krypton on graphite and the striped helical Potts model

    Science.gov (United States)

    Halpin-Healy, Timothy; Kardar, Mehran

    1985-02-01

    A generalization of the helical Potts model, with two species of domain wall due to explicit triaxial helical symmetry breaking, is studied via position-space renormalization-group methods and is discovered to exhibit striped, as well as hexagonal, phases. The disordering transition of the commensurate ferromagnetic phase belongs to the symmetric Potts universality class. No evidence is found for a chiral melting transition. Commensurate-incommensurate phase diagrams for oversaturated krypton on graphite are constructed.

  9. Tailoring chiro-optical effects by helical nanowire arrangement.

    Science.gov (United States)

    Esposito, Marco; Tasco, Vittorianna; Todisco, Francesco; Benedetti, Alessio; Tarantini, Iolena; Cuscunà, Massimo; Dominici, Lorenzo; De Giorgi, Milena; Passaseo, Adriana

    2015-11-21

    In this work, we experimentally investigate the chiro-optical properties of 3D metallic helical systems at optical frequencies. Both single and triple-nanowire geometries have been studied. In particular, we found that in single-helical nanostructures, the enhancement of chiro-optical effects achievable by geometrical design is limited, especially with respect to the operation wavelength and the circular polarization conversion purity. Conversely, in the triple-helical nanowire configuration, the dominant interaction is the coupling among the intertwined coaxial helices which is driven by a symmetric spatial arrangement. Consequently, a general improvement in the g-factor, extinction ratio and signal-to-noise-ratio is achieved in a broad spectral range. Moreover, while in single-helical nanowires a mixed linear and circular birefringence results in an optical activity strongly dependent on the sample orientation and wavelength, in the triple-helical nanowire configuration, the obtained purely circular birefringence leads to a large optical activity up to 8°, independent of the sample angle, and extending in a broad band of 500 nm in the visible range. These results demonstrate a strong correlation between the configurational internal interactions and the chiral feature designation, which can be effectively exploited for nanoscale chiral device engineering.

  10. Magnetic helicity and energy spectra of a solar active region

    CERN Document Server

    Zhang, Hongqi; Sokoloff, D D

    2013-01-01

    We compute magnetic helicity and energy spectra of the solar active region NOAA 11158 during 11-15 February 2011 at 20 degr southern heliographic latitude using observational photospheric vector magnetograms. We adopt the isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field. The sign of magnetic helicity turns out to be predominantly positive at all wavenumbers. This sign is consistent with what is theoretically expected for the southern hemisphere. The relative magnetic helicity is around 8% and strongest at intermediate wavenumbers of k ~ 0.4 Mm^{-1}, corresponding to a scale of 2 pi/k ~ 16 Mm. The same sign and a somewhat smaller value is also found for the relative current helicity evaluated in real space based on the vertical components of magnetic field and current density. The current helicity spectrum is estimated from the magnetic helicity spectrum and its modulus shows a k^{-5/3} spectrum at large wavenumbers. A similar power law is also obtained for...

  11. Helical dipole partial Siberian snake for the AGS

    Energy Technology Data Exchange (ETDEWEB)

    Takano, J [RIKEN, Saitama, (Japan); Ahrens, L A [Brookhaven National Laboratory, Upton, NY 11973 (United States); Alforque, R [Brookhaven National Laboratory, Upton, NY 11973 (United States); Bai, M [Brookhaven National Laboratory, Upton, NY 11973 (United States); Brown, K [Brookhaven National Laboratory, Upton, NY 11973 (United States); Courant, E D [Brookhaven National Laboratory, Upton, NY 11973 (United States); Ganetis, G [Brookhaven National Laboratory, Upton, NY 11973 (United States); Gardner, C J [Brookhaven National Laboratory, Upton, NY 11973 (United States); Glenn, J W [Brookhaven National Laboratory, Upton, NY 11973 (United States); Hattori, T [Tokyo Institute of Technology, Tokyo, (Japan); Huang, H [Brookhaven National Laboratory, Upton, NY 11973 (United States); Jain, A [Brookhaven National Laboratory, Upton, NY 11973 (United States); Luccio, A U [Brookhaven National Laboratory, Upton, NY 11973 (United States); MacKay, W W [Brookhaven National Laboratory, Upton, NY 11973 (United States); Okamura, M [Brookhaven National Laboratory, Upton, NY 11973 (United States); Roser, T [Brookhaven National Laboratory, Upton, NY 11973 (United States); Tsoupas, N [Brookhaven National Laboratory, Upton, NY 11973 (United States); Tepikian, S [Brookhaven National Laboratory, Upton, NY 11973 (United States); Tuozzolo, J [Brookhaven National Laboratory, Upton, NY 11973 (United States); Wood, J [Brookhaven National Laboratory, Upton, NY 11973 (United States); Zelenski, A [Brookhaven National Laboratory, Upton, NY 11973 (United States); Zeno, K [Brookhaven National Laboratory, Upton, NY 11973 (United States)

    2006-11-15

    Overcoming depolarization resonances in medium class synchrotrons (3 to 50 GeV) is one of the key issues in accelerating a highly polarized proton beam up to very high energies. Since such synchrotrons, including the Alternating Gradient Synchrotron (AGS) and the J-PARC Main Ring, generally do not have sufficiently long straight sections to accommodate full Siberian snakes with reasonable beam excursions, the practical solution is to use partial Siberian snakes that rotate the particle spin about a horizontal axis by a fraction of 180 degrees. For the AGS, we designed and installed a new partial Siberian snake consisting of a helical dipole magnet with a double pitch structure. The helical structure reduced the amount of transverse coupling as compared to that achieved by the previous solenoidal partial snake. This coupling led to partial depolarization at certain energies from horizontal betatron oscillations. The helical magnetic field in the snake magnet was calculated using a 3D magnetic field code TOSCA, and was optimized by segmenting the helical pitch and varying the lengths of the segments. Fabrication errors were checked and verified to be within required tolerances. Finally, the transverse field was measured by rotating harmonic coils. After installation, we achieved a 37.5% improvement in polarization - from 40% with the old solenoid to 55% with the new helical snake, thereby demonstrating that the helical partial snake is an effective device to suppress depolarization resonances in medium-sized synchrotrons.

  12. Helical dipole partial Siberian snake for the AGS

    Science.gov (United States)

    Takano, J.; Ahrens, L. A.; Alforque, R.; Bai, M.; Brown, K.; Courant, E. D.; Ganetis, G.; Gardner, C. J.; Glenn, J. W.; Hattori, T.; Huang, H.; Jain, A.; Luccio, A. U.; MacKay, W. W.; Okamura, M.; Roser, T.; Tsoupas, N.; Tepikian, S.; Tuozzolo, J.; Wood, J.; Zelenski, A.; Zeno, K.

    2006-11-01

    Overcoming depolarization resonances in medium class synchrotrons (3 to 50 GeV) is one of the key issues in accelerating a highly polarized proton beam up to very high energies. Since such synchrotrons, including the Alternating Gradient Synchrotron (AGS) and the J-PARC Main Ring, generally do not have sufficiently long straight sections to accommodate full Siberian snakes with reasonable beam excursions, the practical solution is to use partial Siberian snakes that rotate the particle spin about a horizontal axis by a fraction of 180 degrees. For the AGS, we designed and installed a new partial Siberian snake consisting of a helical dipole magnet with a double pitch structure. The helical structure reduced the amount of transverse coupling as compared to that achieved by the previous solenoidal partial snake. This coupling led to partial depolarization at certain energies from horizontal betatron oscillations. The helical magnetic field in the snake magnet was calculated using a 3D magnetic field code TOSCA, and was optimized by segmenting the helical pitch and varying the lengths of the segments. Fabrication errors were checked and verified to be within required tolerances. Finally, the transverse field was measured by rotating harmonic coils. After installation, we achieved a 37.5% improvement in polarization - from 40% with the old solenoid to 55% with the new helical snake, thereby demonstrating that the helical partial snake is an effective device to suppress depolarization resonances in medium-sized synchrotrons.

  13. Biomimetic Hierarchical Assembly of Helical Supraparticles from Chiral Nanoparticles.

    Science.gov (United States)

    Zhou, Yunlong; Marson, Ryan L; van Anders, Greg; Zhu, Jian; Ma, Guanxiang; Ercius, Peter; Sun, Kai; Yeom, Bongjun; Glotzer, Sharon C; Kotov, Nicholas A

    2016-03-22

    Chiroptical materials found in butterflies, beetles, stomatopod crustaceans, and other creatures are attributed to biocomposites with helical motifs and multiscale hierarchical organization. These structurally sophisticated materials self-assemble from primitive nanoscale building blocks, a process that is simpler and more energy efficient than many top-down methods currently used to produce similarly sized three-dimensional materials. Here, we report that molecular-scale chirality of a CdTe nanoparticle surface can be translated to nanoscale helical assemblies, leading to chiroptical activity in the visible electromagnetic range. Chiral CdTe nanoparticles coated with cysteine self-organize around Te cores to produce helical supraparticles. D-/L-Form of the amino acid determines the dominant left/right helicity of the supraparticles. Coarse-grained molecular dynamics simulations with a helical pair-potential confirm the assembly mechanism and the origin of its enantioselectivity, providing a framework for engineering three-dimensional chiral materials by self-assembly. The helical supraparticles further self-organize into lamellar crystals with liquid crystalline order, demonstrating the possibility of hierarchical organization and with multiple structural motifs and length scales determined by molecular-scale asymmetry of nanoparticle interactions.

  14. Helical Birods: An Elastic Model of Helically Wound Double-Stranded Rods

    KAUST Repository

    Prior, Christopher

    2014-03-11

    © 2014, Springer Science+Business Media Dordrecht. We consider a geometrically accurate model for a helically wound rope constructed from two intertwined elastic rods. The line of contact has an arbitrary smooth shape which is obtained under the action of an arbitrary set of applied forces and moments. We discuss the general form the theory should take along with an insight into the necessary geometric or constitutive laws which must be detailed in order for the system to be complete. This includes a number of contact laws for the interaction of the two rods, in order to fit various relevant physical scenarios. This discussion also extends to the boundary and how this composite system can be acted upon by a single moment and force pair. A second strand of inquiry concerns the linear response of an initially helical rope to an arbitrary set of forces and moments. In particular we show that if the rope has the dimensions assumed of a rod in the Kirchhoff rod theory then it can be accurately treated as an isotropic inextensible elastic rod. An important consideration in this demonstration is the possible effect of varying the geometric boundary constraints; it is shown the effect of this choice becomes negligible in this limit in which the rope has dimensions similar to those of a Kirchhoff rod. Finally we derive the bending and twisting coefficients of this effective rod.

  15. Structural insights for designed alanine-rich helices: Comparing NMR helicity measures and conformational ensembles from molecular dynamics simulation

    Science.gov (United States)

    Song, Kun; Stewart, James M.; Fesinmeyer, R. Matthew

    2013-01-01

    The temperature dependence of helical propensities for the peptides Ac-ZGG-(KAAAA)3X-NH2 (Z = Y or G, X = A, K, and d-Arg) were studied both experimentally and by molecular dynamics simulations. Good agreement is observed in both the absolute helical propensities as well as relative helical content along the sequence; the global minimum on the calculated free energy landscape corresponds to a single α-helical conformation running from K4 – A18 with some terminal fraying, particularly at the C-terminus. Energy component analysis shows that the single helix state has favorable intramolecular electrostatic energy due to hydrogen bonds, and that less-favorable two-helix globular states have favorable solvation energy. The central lysine residues do not appear to increase helicity; however, both experimental and simulation studies show increasing helicity in the series X = Ala → Lys → d-Arg. This C-capping preference was also experimentally confirmed in Ac-(KAAAA)3X-GY-NH2 and (KAAAA)3X-GY-NH2 sequences. The roles of the C-capping groups, and of lysines throughout the sequence, in the MD-derived ensembles are analyzed in detail. PMID:18428207

  16. Structure and Dynamics of a Trinuclear Gadolinium(III) Complex: The Effect of Intramolecular Electron Spin Relaxation on Its Proton Relaxivity(1).

    Science.gov (United States)

    Tóth É, Éva; Helm, Lothar; Merbach, André E.; Hedinger, Roman; Hegetschweiler, Kaspar; Jánossy, András

    1998-08-10

    The trinuclear [Gd(3)(H(-)(3)taci)(2)(H(2)O)(6)](3+) complex has been characterized in aqueous solution as a model compound from the point of view of MRI: the parameters that affect proton relaxivity have been determined in a combined variable temperature, pressure, and multiple-field (17)O NMR, EPR, and NMRD study. The solution structure of the complex was found to be the same as in solid state: the total coordination number of the lanthanide(III) ion is 8 with two inner-sphere water molecules. EPR measurements proved a strong intramolecular dipole-dipole interaction between Gd(III) electron spins. This mechanism dominates electron spin relaxation at high magnetic fields (B > 5 T). Its proportion to the overall relaxation decreases with decreasing magnetic field and becomes a minor term at fields used in MRI. Consequently, it cannot increase the electronic relaxation rates to such an extent that they limit proton relaxivity. [Gd(3)(H(-)(3)taci)(2)(H(2)O)(6)](3+) undergoes a relatively slow water exchange (k(ex)(298) = (1.1 +/- 0.2) x 10(7) s(-1)) compared to the Gd(III) aqua ion, while the mechanism is much more associatively activated as shown by the activation volume (DeltaV () = (-12.7 +/- 1.5) cm(3) mol(-)(1)). The lower exchange rate, as compared to [Gd(H(2)O)(8)](3+) and [Gd(PDTA)(H(2)O)(2)](-), can be explained with the higher rigidity of the [Gd(3)(H(-)(3)taci)(2)(H(2)O)(6)](3+) which considerably slows down the transition from the eight-coordinate reactant to the nine-coordinate transition state. The unexpectedly low rotational correlation time of the complex is interpreted in terms of a spherical structure with a large hydrophobic surface avoiding the formation of a substantial hydration sphere around [Gd(3)(H(-)(3)taci)(2)(H(2)O)(6)](3+).

  17. Magnetic ordering in two molecule-based (10,3)-a nets prepared from a copper(II) trinuclear secondary building unit.

    Science.gov (United States)

    Gil-Hernández, Beatriz; Gili, Pedro; Vieth, Jana K; Janiak, Christoph; Sanchiz, Joaquín

    2010-08-16

    Two new molecule-based materials of formulas 3D-{[K(H(2)O)(6)](0.5)[K(18-crown-6)](0.5)[MnCu(3)(Hmesox)(3)].5.25H(2)O} (1) and 3D-{(Ph(4)P)(2)[MnCu(3)(Hmesox)(3)Cl].3.5H(2)O} (2) have been prepared from a tricopper(II) secondary building unit (SBU), [Cu(3)(Hmesox)(3)](3-) (H(4)mesox = mesoxalic acid, 2-dihydroxymalonic acid). Compound 1 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of potassium cations and the 18-crown-6 ether, whereas compound 2 is obtained by means of the reaction of the SBU with manganese(II) acetate in the presence of Ph(4)PCl. The [MnCu(3)(Hmesox)(3)](-) and [MnCu(3)(Hmesox)(3)Cl](2-) moieties in compounds 1 and 2, respectively, yield chiral 3-connected three-dimensional (3D) anionic (10,3)-a (srs, SrSi(2)) nets. In the cubic and centrosymmetric structures (Pa3) of 1, two inversion-symmetry-related anion nets interpenetrate to a racemic structure. The Ph(4)P(+) cations in 2 are organized in a supramolecular (10,3)-a net through the 6-fold phenyl embrace. In 2, both the cationic and anionic nets are homochiral and enantiopure with opposite handedness and form interpenetrating supramolecular and covalent (10,3)-a nets in the noncentrosymmetric Sohncke space group P 2(1)2(1)2(1). Both compounds display ferrimagnetic interaction with long-range magnetic ordering below 2.5 and 15.2 K for 1 and 2, respectively. A dehydrated phase of 2 exhibits a T(c) of 21.8 K. The saturation of magnetization, M(S), indicates two different ground states, S = (1)/(2) and (3)/(2), for the tricopper(II) units in 1 and 2, respectively. The different spin states of the tricopper(II) unit in 1 and 2 has been explained by means of a density functional theory (DFT) study performed in the [Cu(3)(Hmesox)(3)](3-) and [Cu(3)(Hmesox)(3)Cl](4-) fragments, for 1 and 2, respectively. A further DFT study has allowed one to analyze the structural parameters that lead to the different spin ground states for the trinuclear units in both

  18. ‘Ionic crystals’ consisting of trinuclear macrocations and polyoxometalate anions exhibiting single crystal to single crystal transformation: breathing of crystals

    Indian Academy of Sciences (India)

    T ARUMUGANATHAN; ASHA SIDDIKHA; SAMAR K DAS

    2017-08-01

    Ion pairing of trinuclear macrocation cluster (known as basic carboxylate), [M ₃ (μ ₃-O) (ClCH ₂COO) ₆ (H ₂O) ₃] ¹⁺ and a Keggin type polyoxometalate cluster anion [SiW ₁₂O₄₀] ⁴⁻ is stabilized with a number of crystal water molecules in composite type compounds [M ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄[SiW ₁₂O₄₀] ·xH ₂O · 2ClCH ₂COOH [M = Fe ³⁺, x = 18(1); M = Cr ³⁺x = 14(2)]. When the crystals of 1 are heated at 85◦C and 135◦C for 3.5 hours in an open atmospheric condition, it goes to [Fe ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW ₁₂O₄₀] ·10H ₂O ·2ClCH ₂COOH (dehydrated 1-85o ≡ 1'), and [Fe ₃ (μ ₃-O) (ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW ₁₂O₄₀] · 8H ₂O · 2ClCH ₂COOH (dehydrated 1-135o ≡ 1'') respectively with the loss of considerable amount of lattice water molecules retaining their single crystallinity. On the other hand, the single crystals of compound 2, upon heating at 85◦C or 135◦C for 3.5 hours, undergo ‘crystal-to-crystal transformation’ to the single crystals of [Cr ₃ (μ ₃-O)(ClCH ₂COO) ₆ (H ₂O) ₃] ₄ [SiW₁₂O₄₀]·8H₂O·2ClCH ₂COOH (dehydrated 2 ≡ 2'). Crystal structure analyses show that the parent compounds 1 and 2 undergo molecular rearrangement (molecular motion in the solid state) in respective dehydrated compounds. Remarkably, these dehydrated crystals (1', 1'' and 2'), upon exposure to water vapor at an ambient condition, regenerate the crystals of parent compounds 1 and 2, respectively

  19. A benzene-core trinuclear GdIII complex: towards the optimization of relaxivity for MRI contrast agent applications at high magnetic field.

    Science.gov (United States)

    Livramento, João Bruno; Helm, Lothar; Sour, Angélique; O'Neil, Conlin; Merbach, André E; Tóth, Eva

    2008-03-07

    A novel ligand, H(12)L, based on a trimethylbenzene core bearing three methylenediethylenetriamine-N,N,N'',N''-tetraacetate moieties (-CH(2)DTTA(4-)) for Gd(3+) chelation has been synthesized, and its trinuclear Gd(3+) complex [Gd(3)L(H(2)O)(6)](3-) investigated with respect to MRI contrast agent applications. A multiple-field, variable-temperature (17)O NMR and proton relaxivity study on [Gd(3)L(H(2)O)(6)](3-) yielded the parameters characterizing water exchange and rotational dynamics. On the basis of the (17)O chemical shifts, bishydration of Gd(3+) could be evidenced. The water exchange rate, k(ex)(298)=9.0+/-3.0 s(-1) is around twice as high as k(ex)(298) of the commercial [Gd(DTPA)(H(2)O)](2-) and comparable to those on analogous Gd(3+)-DTTA chelates. Despite the relatively small size of the complex, the rotational dynamics had to be described with the Lipari-Szabo approach, by separating global and local motions. The difference between the local and global rotational correlation times, tau(lO)(298)=170+/-10 ps and tau(gO)(298)=540+/-100 ps respectively, shows that [Gd(3)L(H(2)O)(6)](3-) is not fully rigid; its flexibility originates from the CH(2) linker between the benzene core and the poly(amino carboxylate) moiety. As a consequence of the two inner-sphere water molecules per Gd(3+), their close to optimal exchange rate and the appropriate size and limited flexibility of the molecule, [Gd(3)L(H(2)O)(6)](3-) has remarkable proton relaxivities when compared with commercial contrast agents, particularly at high magnetic fields (r(1)=21.6, 17.0 and 10.7 mM(-1)s(-1) at 60, 200 and 400 MHz respectively, at 25 degrees C; r(1) is the paramagnetic enhancement of the longitudinal water proton relaxation rate, referred to 1 mM concentration of Gd(3+)).

  20. The Role of Magnetic Helicity in Structuring the Solar Corona

    Science.gov (United States)

    Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

    2017-01-01

    Two of the most widely observed and striking features of the Sun's magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure—filament channels—is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.

  1. The Role of Magnetic Helicity in Structuring the Solar Corona

    Science.gov (United States)

    Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

    2017-01-01

    Two of the most widely observed and striking features of the Suns magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure filament channels is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.

  2. Enhancing the magnetic coupling of oxalato-bridged Re(IV)2M(II) (M=Mn, Co, Ni, and Cu) trinuclear complexes via peripheral halide ligand effects.

    Science.gov (United States)

    Martínez-Lillo, José; Mastropietro, Teresa F; De Munno, Giovanni; Lloret, Francesc; Julve, Miguel; Faus, Juan

    2011-06-20

    Four heterotrinuclear Re(IV)(2)M(II) compounds of general formula (NBu(4))(2)[{Re(IV)Br(4)(μ-ox)}(2)M(II)(Him)(2)] [NBu(4)(+) = tetra-n-butylammonium cation, ox = oxalate, Him = imidazole; M = Mn (1), Co (2), Ni (3), and Cu (4)] have been synthesized by using the novel mononuclear complex [Re(IV)Br(4)(ox)](2-) as a ligand toward divalent first-row transition metal ions in the presence of imidazole. Compounds 1-4 are isostructural complexes whose structure contains discrete trinuclear [{Re(IV)Br(4)(μ-ox)}(2)M(II)(Him)(2)](2-) anions and bulky NBu(4)(+) cations. The Re and M atoms are six-coordinated: four peripheral bromo and two oxalate-oxygens (at Re), and two cis-coordinated imidazole molecules and four oxygen atoms from two oxalate ligands (at M), build distorted octahedral surroundings. Two peripheral [ReBr(4)(ox)](2-) units act as bidentate ligands through the oxalate group toward the central [M(II)(Him)(2)] fragment affording the trinuclear entities. The values of the intramolecular Re···M separation are 5.62(1) (1), 5.51(1) (2), 5.46(1) (3), and 5.55(1) Å (4). Magnetic susceptibility measurements on polycrystalline samples of 1-4 in the temperature range of 1.9-300 K show the occurrence of intramolecular antiferro- [J = -1.1 cm(-1) (1)] and ferromagnetic interactions [J = +3.9 (2), +19.7 (3), and +14.4 cm(-1) (4)], the Hamiltonian being defined as Ĥ = -J [Ŝ(M)(Ŝ(Re1) + Ŝ(Re2))]. The larger spin delocalization on the oxalato bridge in 1-4 when compared to the trinuclear Re(IV)(2)M(II) complexes with chloro instead of bromo as peripheral ligands (1'-4') accounts for the strengthening of the magnetic interactions in 1-4 [J = -0.35 (1'), +14.2 (3'), and +7.7 cm(-1) (4')]. An incipient frequency dependence of the out-of-phase ac signals of 3 at very low temperatures is reminiscent of a system with slow relaxation of the magnetization, a phenomenon characteristic of single-molecule magnet behavior.

  3. 3D Framework and Intense Photoluminescence of a Novel Trinuclear Cadmium(Ⅱ) Complex with Mixed Ligands%三维混配型三核镉(Ⅱ)配合物的合成及荧光性质

    Institute of Scientific and Technical Information of China (English)

    王娟; 苏进雄; 唐霞; 王应席; 程时远

    2011-01-01

    水热合成法合成了新颖的三核超分子配合物[Cd3(PDA)3(2,2'bipy)3(H2O)2]·2H2O(1)(H2PDA=pyridine-2,6-dicarboxylic acid),并进行了元素分析、红外、热重、荧光及单晶衍射测试.该化合物属单斜晶系,P21/n空间群,晶胞参数分别为:a=2.12281(14)nm,b=1.00609(7)nm,c=2.83064(19)nm,β=108.9370(10)°.中心原子配位数为7,羧基以双齿形式将Cd1、Cd2、Cd3桥联组成三核配合物.分子间氢键与π-π堆积构筑成三维超分子结构.荧光分析表明该配合物在室温下发出强烈的蓝色荧光,具有潜在的应用价值.%A novel trinuclear cadmium(Ⅱ) supramolecular complex [Cd3(PDA)3(2,2'-bipy)3(H2O)2]· 2H2O (1) (H2PDA=pyridine-2,6-dicarboxylic acid) has been prepared under hydrothermal condition and characterized by elemental analysis, IR, TG, fluorescence spectrum and single-crystal X-ray diffraction. The complex crystallizes in monoclinic system, space group P21/n with a=2.122 81(14) nm, b=1.006 09(7) nm, c=2.830 64(19) nm, β=108.937 0(10)°. The structure of the complex consists of trinuclear units with all metal centers being seven-coordinated. Cdl, Cd2 and Cd3 atoms are bridged by three carboxylate groups in dimonodentate fashion to give a trinuclear molecular building block [Cd3N9(CO2R)6]. Intermolecular hydrogen-bond interactions and face-to-face π-π stacking interactions lead the complex to a 3D supramolecular architecture. Fluorescent analyses show that the complex exhibits intense blue photoluminescence at room temperature and may be potential candidate for photoactive material.

  4. Spatially fractionated radiotherapy (GRID) using helical tomotherapy.

    Science.gov (United States)

    Zhang, Xin; Penagaricano, Jose; Yan, Yulong; Liang, Xiaoying; Morrill, Steven; Griffin, Robert J; Corry, Peter; Ratanatharathorn, Vaneerat

    2016-01-08

    Spatially fractionated radiotherapy (GRID) was designed to treat large tumors while sparing skin, and it is usually delivered with a linear accelerator using a commercially available block or multileaf collimator (LINAC-GRID). For deep-seated (skin to tumor distance (> 8 cm)) tumors, it is always a challenge to achieve adequate tumor dose coverage. A novel method to perform GRID treatment using helical tomotherapy (HT-GRID) was developed at our institution. Our approach allows treating patients by generating a patient-specific virtual GRID block (software-generated) and using IMRT technique to optimize the treatment plan. Here, we report our initial clinical experience using HT-GRID, and dosimetric comparison results between HT-GRID and LINAC-GRID. This study evaluates 10 previously treated patients who had deep-seated bulky tumors with complex geometries. Five of these patients were treated with HT-GRID and replanned with LINAC-GRID for comparison. Similarly, five other patients were treated with LINAC-GRID and replanned with HT-GRID for comparison. The prescription was set such that the maximum dose to the GTV is 20 Gy in a single fraction. Dosimetric parameters compared included: mean GTV dose (DGTV mean), GTV dose inhomogeneity (valley-to-peak dose ratio (VPR)), normal tissue doses (DNmean), and other organs-at-risk (OARs) doses. In addition, equivalent uniform doses (EUD) for both GTV and normal tissue were evaluated. In summary, HT-GRID technique is patient-specific, and allows adjustment of the GRID pattern to match different tumor sizes and shapes when they are deep-seated and cannot be adequately treated with LINAC-GRID. HT-GRID delivers a higher DGTV mean, EUD, and VPR compared to LINAC-GRID. HT-GRID delivers a higher DNmean and lower EUD for normal tissue compared to LINAC-GRID. HT-GRID plans also have more options for tumors with complex anatomical relationships between the GTV and the avoidance OARs (abutment or close proximity).

  5. Dynamo effect in a driven helical flow.

    Science.gov (United States)

    Feudel, F; Gellert, M; Rüdiger, S; Witt, A; Seehafer, N

    2003-10-01

    The Roberts flow, a helical flow in the form of convectionlike rolls, is known to be capable of both kinematic and nonlinear dynamo action. We study the Roberts dynamo with particular attention being paid to the spatial structure of the generated magnetic field and its back-reaction on the flow. The dynamo bifurcation is decisively determined by the symmetry group of the problem, which is given by a subgroup of discrete transformations and a continuous translational invariance of the flow. In the bifurcation the continuous symmetry is broken while the discrete subgroup symmetry completely survives. Its actions help in understanding the spatial structures of the magnetic field and of the modified flow. In accordance with experimental observations, the magnetic field component perpendicular to the originally invariant direction is much stronger than the component in this direction. Furthermore, the magnetic field is largely concentrated in layers separating the convectionlike rolls of the flow and containing, in particular, its stagnation points, which are isolated for the modified flow while they are line filling for the original Roberts flow. The magnetic field is strongest near beta-type stagnation points, with a two-dimensional unstable and a one-dimensional stable manifold, and is weak near alpha-type stagnation points, with a two-dimensional stable and a one-dimensional unstable manifold. This contrasts with the usual picture that dynamo action is promoted at the alpha points and impeded at the beta points. Both the creation of isolated stagnation points and the concentration of strong fields at the beta points may be understood as a result of the way in which the Roberts dynamo saturates. It is also found that, while the original Roberts flow is regular, the modified flow is chaotic in the layers between the convectionlike rolls where the magnetic field is concentrated. This chaoticity, which results from the back-reaction of the magnetic field on the flow

  6. Stable double helical iodine chains inside single-walled carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Zhen [College of Science, Liaoning University of Technology, Jinzhou, Liaoning, 121001 (China); Liu, Chun-Jian [College of Mathematics and Physics, Bohai University, Jinzhou, Liaoning, 121000 (China); Lv, Hang [Institute of New Energy, Bohai University, Jinzhou, Liaoning, 121000 (China); Liu, Bing-Bing, E-mail: liubb@jlu.edu.cn [State Key Laboratory of Superhard Materials, Jilin University, Changchun, 130012 (China)

    2016-08-12

    The helicity of stable double helical iodine chains inside single-walled carbon nanotubes (SWCNTs) is studied by calculating the systematic interaction energy. Our results present clear images of stable double helical structures inside SWCNTs. The optimum helical radius and helical angle increase and decrease with increasing diameter, respectively. The tube's diameter plays a leading role in the helicity of encapsulated structures, while the tube's chirality may induce different metastable structures. This study indicates that the observed double helical iodine chains in experiments are not necessarily the optimum structures, but may also be metastable structures. - Highlights: • The stable double helical iodine chain inside single-walled carbon nanotubes is proposed. • The influence of tube's diameter and chirality on the stability of encapsulated iodine chains is studied. • The metastable double helical structures may be co-existence with the stable structure but not in the same tubes.

  7. JOINT INVERSE CASCADE OF MAGNETIC ENERGY AND MAGNETIC HELICITY IN MHD TURBULENCE

    Energy Technology Data Exchange (ETDEWEB)

    Stepanov, R.; Frick, P.; Mizeva, I. [Institute of Continuous Media Mechanics, Korolyov str. 1, 614013 Perm (Russian Federation)

    2015-01-10

    We show that oppositely directed fluxes of energy and magnetic helicity coexist in the inertial range in fully developed magnetohydrodynamic (MHD) turbulence with small-scale sources of magnetic helicity. Using a helical shell model of MHD turbulence, we study the high Reynolds number MHD turbulence for helicity injection at a scale that is much smaller than the scale of energy injection. In a short range of scales larger than the forcing scale of magnetic helicity, a bottleneck-like effect appears, which results in a local reduction of the spectral slope. The slope changes in a domain with a high level of relative magnetic helicity, which determines that part of the magnetic energy is related to the helical modes at a given scale. If the relative helicity approaches unity, the spectral slope tends to –3/2. We show that this energy pileup is caused by an inverse cascade of magnetic energy associated with the magnetic helicity. This negative energy flux is the contribution of the pure magnetic-to-magnetic energy transfer, which vanishes in the non-helical limit. In the context of astrophysical dynamos, our results indicate that a large-scale dynamo can be affected by the magnetic helicity generated at small scales. The kinetic helicity, in particular, is not involved in the process at all. An interesting finding is that an inverse cascade of magnetic energy can be provided by a small-scale source of magnetic helicity fluctuations without a mean injection of magnetic helicity.

  8. Double Helical Gear Performance Results in High Speed Gear Trains

    Science.gov (United States)

    Handschuh, Robert F.; Ehinger, Ryan; Sinusas, Eric; Kilmain, Charles

    2010-01-01

    The operation of high speed gearing systems in the transmissions of tiltrotor aircraft has an effect on overall propulsion system efficiency. Recent work has focused on many aspects of high-speed helical gear trains as would be used in tiltrotor aircraft such as operational characteristics, comparison of analytical predictions to experimental data and the affect of superfinishing on transmission performance. Baseline tests of an aerospace quality system have been conducted in the NASA Glenn High-Speed Helical Gear Train Test Facility and have been described in earlier studies. These earlier tests had utilized single helical gears. The results that will be described in this study are those attained using double helical gears. This type of gear mesh can be configured in this facility to either pump the air-oil environment from the center gap between the meshing gears to the outside of tooth ends or in the reverse direction. Tests were conducted with both inward and outward air-oil pumping directions. Results are compared to the earlier baseline results of single helical gears.

  9. Efficacy of cholangiography under helical computed tomography for laparoscopic cholecystectomy

    Energy Technology Data Exchange (ETDEWEB)

    Takeuchi, Motoya; Hishiyama, Houhei [Asahikawa Red Cross Hospital, Hokkaido (Japan); Kondo, Satoshi; Katoh, Hiroyuki [Hokkaido Univ., Sapporo (Japan). Graduate School of Medicine

    2002-05-01

    Although laparoscopic cholecystectomy (LC) is known to be safe, the optimal imaging technique for examining the common bile duct and cystic duct prior to laparoscopic intervention remains controversial. The objective of this study was to evaluate the efficacy of cholangiography under helical computed tomography (helical CT cholangiography) for LC. We studied 53 consecutive patients who underwent LC carried out by the same surgeon. The data of 23 of these patients who had undergone LC before the introduction of helical CT were used as the reference standard. Among the 53 patients, 28 were prospectively randomized for preoperative biliary tract evaluation with versus without helical CT cholangiography, into a CT/+ group (n=13) and a CT/- group (n=15), respectively. Two patients were excluded from the study preoperatively. There were no significant differences in age or laboratory findings, including liver function tests or the serum amylase level before or after surgery, between the two groups. In the CT/- group, endoscopic retrograde cholangiography-related pancreatitis developed in one patient, and one patient required conversion to open surgery. In contrast, in the CT/+ group, there were no preoperative complications and no patient required conversion to open surgery. The mean operative time was significantly shorter in the CT/+ group than in the CT/- group (P=0.0137). These findings provide evidence to support the advantages of helical CT cholangiography in relation to operative time, conversion, and procedure-related preoperative complications. (author)

  10. Controlling skyrmion helicity via engineered Dzyaloshinskii-Moriya interactions

    Science.gov (United States)

    Díaz, Sebastián A.; Troncoso, Roberto E.

    2016-10-01

    Single magnetic skyrmion dynamics in chiral magnets with a spatially inhomogeneous Dzyaloshinskii-Moriya interaction (DMI) is considered. Based on the relation between DMI coupling and skyrmion helicity, it is argued that the latter must be included as an extra degree of freedom in the dynamics of skyrmions. An effective description of the skyrmion dynamics for an arbitrary inhomogeneous DMI coupling is obtained through the collective coordinates method. The resulting generalized Thiele equation is a dynamical system for the center of mass position and helicity of the skyrmion. It is found that the dissipative tensor and hence the Hall angle become helicity dependent. The skyrmion position and helicity dynamics are fully characterized by our model in two particular examples of engineered DMI coupling: half-planes with opposite-sign DMI and linearly varying DMI. In light of the experiment of Shibata et al (2013 Nat. Nanotechnol. 8 723) on the magnitude and sign of the DMI, our results constitute the first step toward a more complete understanding of the skyrmion helicity as a new degree of freedom that could be harnessed in future high-density magnetic storage and logic devices.

  11. Energy fluxes in helical magnetohydrodynamics and dynamo action

    Indian Academy of Sciences (India)

    Mahendra K Verma

    2003-10-01

    Renormalized viscosity, renormalized resistivity, and various energy fluxes are calculated for helical magnetohydrodynamics using perturbative field theory. The calculation is of first-order in perturbation. Kinetic and magnetic helicities do not affect the renormalized parameters, but they induce an inverse cascade of magnetic energy. The sources for the large-scale magnetic field have been shown to be (1) energy flux from large-scale velocity field to large-scale magnetic field arising due to non-helical interactions and (2) inverse energy flux of magnetic energy caused by helical interactions. Based on our flux results, a primitive model for galactic dynamo has been constructed. Our calculations yield dynamo time-scale for a typical galaxy to be of the order of 108 years. Our field-theoretic calculations also reveal that the flux of magnetic helicity is backward, consistent with the earlier observations based on absolute equilibrium theory.

  12. Helical crystallization on lipid nanotubes: streptavidin as a model protein.

    Science.gov (United States)

    Dang, Thanh X; Farah, Sammy J; Gast, Alice; Robertson, Channing; Carragher, Bridget; Egelman, Edward; Wilson-Kubalek, Elizabeth M

    2005-04-01

    In this study, we use streptavidin (SA) as a model system to study helical protein array formation on lipid nanotubes, an alternative to 2D studies on lipid monolayers. We demonstrate that wild-type and a mutant form of SA form helical arrays on biotinylated lipid nanotubes. 3D maps from helical arrays of wild-type and mutant SA were reconstructed using two different approaches: Fourier-Bessel methods and an iterative single particle algorithm. The maps show that wild-type and mutant streptavidin molecules order differently. The molecular packing arrangements of SA on the surface of the lipid nanotubes differ from previously reported lattice packing of SA on biotinylated monolayers. Helical crystallization on lipid nanotubes presents an alternative platform to explore fundamentals of protein ordering, intermolecular protein interaction and phase behavior. We demonstrate that lipid nanotubes offer a robust and reproducible substrate for forming helical protein arrays which present a means for studying protein structure and structure-function relationships.

  13. Helical computed tomography in the assessment of abdominal aortic pathology

    Energy Technology Data Exchange (ETDEWEB)

    Vicaretti, M.; Young, N.; Jenkins, J.; Fletcher, J. [Westmead Hospital, Westmead, NSW (Australia)

    1997-05-01

    A pilot study was undertaken to evaluate the role of helical computed tomography in the assessment of abdominal aortic pathology. A total of 17 patients underwent intra-arterial digital subtraction angiography (IADSA) and helical computed tomography, with eight patients undergoing subsequent operative intervention. A comparison of radiological findings between IADSA and helical computed tomography (CT) was made and, where applicable, a comparison was made with operative findings. Pathology included abdominal aortic aneurysm (AAA) (n=12), thoraco abdominal aneurysm (n=2) and dissection (n=1), graft distension following AAA repair (n=1) and plaque haemorrhage in the distal aorta following percutaneous transluminal angioplasty (PTA) of the iliac artery (n=1). Planned operative management as based on pre-operative helical CT imaging findings, in particular with reference to the type of graft used (straight or bifurcated) was not changed at operation. Our findings on helical CT in regards to AAA, thoraco-abdominal aneurysm and dissection correlated well with angiography and surgery findings. (authors). 26 refs., 2 tabs., 5 figs.

  14. Peptide tessellation yields micrometre-scale collagen triple helices

    Science.gov (United States)

    Tanrikulu, I. Caglar; Forticaux, Audrey; Jin, Song; Raines, Ronald T.

    2016-11-01

    Sticky-ended DNA duplexes can associate spontaneously into long double helices; however, such self-assembly is much less developed with proteins. Collagen is the most prevalent component of the extracellular matrix and a common clinical biomaterial. As for natural DNA, the ~103-residue triple helices (~300 nm) of natural collagen are recalcitrant to chemical synthesis. Here we show how the self-assembly of short collagen-mimetic peptides (CMPs) can enable the fabrication of synthetic collagen triple helices that are nearly a micrometre in length. Inspired by the mathematics of tessellations, we derive rules for the design of single CMPs that self-assemble into long triple helices with perfect symmetry. Sticky ends thus created are uniform across the assembly and drive its growth. Enacting this design yields individual triple helices that, in length, match or exceed those in natural collagen and are remarkably thermostable, despite the absence of higher-order association. The symmetric assembly of CMPs provides an enabling platform for the development of advanced materials for medicine and nanotechnology.

  15. The Role of Magnetic Helicity in Structuring the Solar Corona

    CERN Document Server

    Knizhnik, Kalman J; DeVore, C Richard

    2016-01-01

    Two of the most widely observed and yet most puzzling features of the Sun's magnetic field are coronal loops that are smooth and laminar and prominences/filaments that are strongly sheared. These two features would seem to be quite unrelated in that the loops are near their minimum-energy current-free state, whereas filaments are regions of high magnetic stress and intense electric currents. We argue that, in fact, these two features are inextricably linked in that both are due to a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a \\citet{Parker72} corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: 1) in agreement with the helicity condensation model of \\citet{Antiochos13}, the inverse cascade of helicity by magnetic reconnection results in the formation of prom...

  16. Two-scale analysis of solar magnetic helicity

    CERN Document Server

    Brandenburg, Axel; Singh, Nishant K

    2016-01-01

    We develop a two-scale formalism to determine global magnetic helicity spectra in systems where the local magnetic helicity has opposite signs on both sides of the equator, giving rise to cancelation with conventional methods. We verify this approach using first synthetic one-dimensional magnetic field and then two-dimensional slices from a three-dimensional alpha effect-type dynamo-generated magnetic field with forced turbulence of opposite helicity above and below the midplane of the domain. We then apply this formalism to global solar synoptic vector magnetograms. To improve the statistics, data from three consecutive Carrington rotations (2161--2163) are combined into a single map. We find that the spectral magnetic helicity representative of the northern hemisphere is negative at all wavenumbers and peaks at ~0.06 Mm^{-1} (scales around 100 Mm). There is no evidence of bihelical magnetic fields that are found in three-dimensional turbulence simulations of helicity-driven alpha effect-type turbulent dynam...

  17. Microscopic Processes in Global Relativistic Jets Containing Helical Magnetic Fields

    Directory of Open Access Journals (Sweden)

    Ken-Ichi Nishikawa

    2016-09-01

    Full Text Available In the study of relativistic jets one of the key open questions is their interaction with the environment on the microscopic level. Here, we study the initial evolution of both electron–proton ( e − – p + and electron–positron ( e ± relativistic jets containing helical magnetic fields, focusing on their interaction with an ambient plasma. We have performed simulations of “global” jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI and the Mushroom instability (MI. In our initial simulation study these kinetic instabilities are suppressed and new types of instabilities can grow. In the e − – p + jet simulation a recollimation-like instability occurs and jet electrons are strongly perturbed. In the e ± jet simulation a recollimation-like instability occurs at early times followed by a kinetic instability and the general structure is similar to a simulation without helical magnetic field. Simulations using much larger systems are required in order to thoroughly follow the evolution of global jets containing helical magnetic fields.

  18. Package of double helical bromine chains inside single-walled carbon nanotubes

    Science.gov (United States)

    Yao, Zhen; Liu, Chun Jian; Lv, Hang; Yang, Xi Bao

    2016-10-01

    The helicity of stable double helical bromine chains inside single-walled carbon nanotubes (SWCNTs) was studied through the calculation of systematic interaction energy, using the van der Waals interaction potential. The results presented clear images of stable double helical structures inside SWCNTs. The optimal helical radius and helical angle of chain structure increase and decrease, respectively, with the increase of tube radius. The detailed analysis indicated that some metastable structures in SWCNTs may also co-exist with the optimal structures, but not within the same tubes. In addition, a detailed simulation of X-ray diffraction patterns was performed for the obtained optimal helical structures.

  19. Significance of bending restraints for the stability of helical polymer conformations

    Science.gov (United States)

    Williams, Matthew J.; Bachmann, Michael

    2016-06-01

    We performed parallel-tempering Monte Carlo simulations to investigate the formation and stability of helical tertiary structures for flexible and semiflexible polymers, employing a generic coarse-grained model. Structural conformations exhibit helical order with tertiary ordering into single helices, multiple helical segments organized into bundles, and disorganized helical arrangements. For both bending-restrained semiflexible and bending-unrestrained flexible helical polymers, the stability of the structural phases is discussed systematically by means of hyperphase diagrams parametrized by suitable order parameters, temperature, and torsion strength. This exploration lends insight into the restricted flexibility of biological polymers such as double-stranded DNA and proteins.

  20. Significance of bending restraints for the stability of helical polymer conformations.

    Science.gov (United States)

    Williams, Matthew J; Bachmann, Michael

    2016-06-01

    We performed parallel-tempering Monte Carlo simulations to investigate the formation and stability of helical tertiary structures for flexible and semiflexible polymers, employing a generic coarse-grained model. Structural conformations exhibit helical order with tertiary ordering into single helices, multiple helical segments organized into bundles, and disorganized helical arrangements. For both bending-restrained semiflexible and bending-unrestrained flexible helical polymers, the stability of the structural phases is discussed systematically by means of hyperphase diagrams parametrized by suitable order parameters, temperature, and torsion strength. This exploration lends insight into the restricted flexibility of biological polymers such as double-stranded DNA and proteins.

  1. A Combined Study of Photospheric Magnetic and Current Helicities and Subsurface Kinetic Helicities of Solar Active Regions during 2006-2013

    CERN Document Server

    Seligman, Darryl; Komm, Rudi

    2014-01-01

    We compare the average photospheric current helicity $H_c$, photospheric twist parameter $\\alpha$ (a well-known proxy for the full relative magnetic helicity), and subsurface kinetic helicity $H_k$ for 194 active regions observed between 2006-2013. We use 2440 Hinode photospheric vector magnetograms, and the corresponding subsurface fluid velocity data derived from GONG (2006-2012) and HMI (2010-2013) Dopplergrams. We find a significant hemispheric bias in all three parameters. The subsurface kinetic helicity is preferentially positive in the southern hemisphere and negative in the northern hemisphere. The photospheric current helicity and the $\\alpha$ parameter have the same bias for strong fields ($|B|>1000$ G) and no significant bias for weak fields (100 G $<|B|<500$ G). We find no significant region-by-region correlation between the subsurface kinetic helicity and either the strong-field current helicity or $\\alpha$. Subsurface fluid motions of a given handedness correspond to photospheric helicitie...

  2. Investigation of helical flow by using tracer technique

    Directory of Open Access Journals (Sweden)

    Hacıyakupoğlu S.

    2013-05-01

    Full Text Available The flow through coiled tubes is, in practice, important for pipe systems, heat exchangers, chemical reactors, mixers of different gas components, etc., and is physically interesting because of the peculiar characteristics caused by the centrifugal force. Therefore, it is not so easy to observe flow parameters in the helical pipe experimentally. Tracer techniques are being increasingly used to determine characteristics such as volume flow rate, residence time, dispersion and mixing process in industry. In this study, the flow in the helical pipe was obtained in the laboratory and investigated by using the tracer technique. The experimental system including the helical pipe was set up in the laboratory. In the experiments methylene-blue (C16H17N3S has been used as the tracer. The experiments were successfully performed with different flow rates and their results were evaluated with the flow parameters.

  3. Fabrication of a magnetic helical mesostructured silica rod

    Science.gov (United States)

    Zhang, Lei; Zhang Qiao, Shi; Cheng, Lina; Yan, Zifeng; Qing Lu, Gao Max

    2008-10-01

    We report a one-step synthesis of magnetic helical mesostructured silica (MHMS) by self-assembly of an achiral surfactant, magnetic nanocrystals with stearic acid ligands and silicate. This core-shell structured material consists of an Fe3O4 superparamagnetic nanocrystal core and a highly ordered periodic helical mesoporous silica shell. We propose that the formation of the helical structure is induced by the interaction between the surfactant and dissociated stearic acid ligands. The MHMS obtained possesses superparamagnetism, uniform mesostructure, narrow pore size distribution, high surface area, and large pore volume. Furthermore, the drug release process is demonstrated using aspirin as a drug model and MHMS as a drug carrier in a sodium phosphate buffer solution.

  4. Initial transient process in a simple helical flux compression generator

    Institute of Scientific and Technical Information of China (English)

    Yang Xian-Jun

    2006-01-01

    An analytical scheme on the initial transient process in a simple helical flux compression generator, which includes the distributions of both the magnetic field in the hollow of an armature and the conducting current density in the stator, is developed by means of a diffusion equation. A relationship between frequency of the conducting current, root of the characteristic function of Bessel equation and decay time in the armature is given. The skin depth in the helical stator is calculated and is compared with the approximate one which is widely used in the calculation of magnetic diffusion. Our analytical results are helpful to understanding the mechanism of the loss of magnetic flux in both the armature and stator and to suggesting an optimal design for improving performance of the helical flux compression generator.

  5. Kelvin Waves and Dynamic Knots on Perturbative Helical Vortex Lines

    CERN Document Server

    Kou, Su-Peng

    2016-01-01

    Vortex lines are one-dimensional extended objects in three-dimensional superfluids. Vortex lines have many interesting properties, including Kelvin waves, exotic statistics, and possible entanglement. In this paper, an emergent "quantum world" is explored by projecting helical vortex lines. A one-dimensional quantum Fermionic model is developed to effectively describe the local fluctuations of helical vortex lines. The elementary excitations are knots with half winding-number that obey emergent quantum mechanics. The Biot-Savart equation, and its Kelvin wave solutions on helical vortex lines become Schrodinger equation, and the wave functions of probability waves for finding knots, respectively. This work shows an alternative approach to simulating quantum many-body physics based on classical systems.

  6. Helical Nanomachines for Fast Mechanical Mapping of Heterogeneous Environments

    CERN Document Server

    Ghosh, Arijit

    2016-01-01

    Artificial micro and nano machines have been envisioned and demonstrated as potential candidates for variety of applications, ranging from targeted drug or gene delivery, cell manipulation, environmental sensing and many more. Here, we demonstrate the application of helical nanomachines that can measure and map the local rheological properties of a complex heterogeneous environment. The position of the helical nanomachine was controlled precisely using magnetic fields, while the instantaneous orientation provided an estimation of the viscosity of the surrounding medium with high spatial and temporal accuracy. Apart from providing viscosity estimates in purely viscous and viscoelastic media with shear rate independent viscosity (Boger fluids), their motion was also found to be extremely sensitive to fluid elasticity. Taken together we report a promising new technique of mapping the rheological properties of a complex fluidic environment by helical nanomachines with high spatial and temporal resolutions, a func...

  7. Stability of helical tip vortices in a rotor far wake

    DEFF Research Database (Denmark)

    Okulov, Valery; Sørensen, Jens Nørkær

    2007-01-01

    , corresponding to Rankine, Gaussian and Scully vortices, at radial extents ranging from the core radius of a tip vortex to several rotor radii. The analysis shows that the stability of tip vortices largely depends on the radial extent of the hub vorticity as well as on the type of vorticity distribution. As part......As a means of analysing the stability of the wake behind a multi-bladed rotor the stability of a multiplicity of helical vortices embedded in an assigned flow field is addressed. In the model the tip vortices in the far wake are approximated by infinitely long helical vortices with constant pitch...... and radius. The work is a further development of a model developed in Okulov (J. Fluid Mech., vol. 521, p. 319) in which the linear stability of N equally azimuthally spaced helical vortices was considered. In the present work the analysis is extended to include an assigned vorticity field due to root...

  8. Comparison of Helical tomotherapy and Cyberknife in Spine Radiosurgery

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Young Nam; Yoon, Se Chul; Chi, Byung Ok; Jng, Hong Suk; Sohn, Suk Hyun [Seoul ST.Mary' s Hospital, The Catholic University of Korea, Seoul (Korea, Republic of); Jung, Gee Young; Shin, Heon Ju; Choi, Ilbong; Gea, Cheol Seong [Incheon ST.Mary' s Hospital, The Catholic University of Korea, Seoul (Korea, Republic of); Kim, Hee Jong [Dept. of Radiation Oncology, Yonsei University, Seoul (Korea, Republic of)

    2011-04-15

    The purpose of this study is planning comparison of helicaltomotherapy and Cyber knife in spine radiosurgery. Spine radiosurgery is an alternative to invasive spine surgery. The tomotherapy is megavoltage CT(MVCT) based image guided helical IMRT delivery system. The cyberknife using robotic arm and image guided based fiducial marker killo voltage X-ray image. The helical tomotherapy is modulated by a 64-multileaf collimator that has paired, pneumatically driven, 6.25-mm-wide leaves calculated to open or close at approximately every 7 .deg. of LINAC rotation, or 51 times per gantry rotation. But cyber knife use 100 or more than bean path. Although, cord maximum dose in CKP is lower than HTP, target homogeneity in HTP is better than CKP. Target coverage is 85% in CKP, 92% in HTP. It was benefit of helical radiation therapy. Tomotheapy and cyberknife are useful equipment to spine radiosurgery.

  9. Helicity statistics in homogeneous and isotropic turbulence and turbulence models

    CERN Document Server

    Sahoo, Ganapati; Biferale, Luca

    2016-01-01

    We study the statistical properties of helicity in direct numerical simulations of fully developed homogeneous and isotropic turbulence and in a class of turbulence shell models. We consider correlation functions based on combinations of vorticity and velocity increments that are not invariant under mirror symmetry. We also study the scaling properties of high-order structure functions based on the moments of the velocity increments projected on a subset of modes with either positive or negative helicity (chirality). We show that mirror symmetry is recovered at small-scales, i.e. chiral terms are always subleading and they are well captured by a dimensional argument plus a small anomalous correction. We confirm these findings with numerical study of helical shell models at high Reynolds numbers.

  10. The large-scale dynamics of magnetic helicity

    CERN Document Server

    Linkmann, Moritz

    2016-01-01

    In this Letter we investigate the dynamics of magnetic helicity in magnetohydrodynamic (MHD) turbulent flows focusing at scales larger than the forcing scale. Our results show a non-local inverse cascade of magnetic helicity, which occurs directly from the forcing scale into the largest scales of the magnetic fields. We also observe that no magnetic helicity and no energy is transferred to an intermediate range of scales sufficiently smaller than the container size and larger than the forcing scale. Thus, the statistical properties of this range of scales, which increases with scale separation, is shown to be described to a large extent by the zero-flux solutions of the absolute statistical equilibrium theory exhibited by the truncated ideal MHD equations.

  11. Analysis of heat and mass transfer on helical absorber

    Energy Technology Data Exchange (ETDEWEB)

    Kwon, O.K.; Kim, S.C.; Yun, J.H. [Korea Institute of Industrial Technology, Chonan (Korea); Lim, J.K.; Yoon, J.I. [Pukyong National University, Pusan (Korea)

    2000-11-01

    The absorption of vapor involves simultaneous heat and mass transfer in the vapor/liquid system. In this paper, a numerical study for vapor absorption process into LiBr-H{sub 2}O solution film flowing over helical absorber has been carried out. Axisymmetric cylindrical coordinate system was adopted to model the helical tube and the transport equations were solved by the finite volume method. The effects of operating conditions, such as the cooling water temperature, the system pressure, the film Reynolds number and the solution inlet concentration have been investigated in view of the absorption mass flux and the total absorption rate. The results for the temperature and concentration profiles, as well as the local absorption mass flux at the helical absorber are presented. It is shown that solution inlet concentration affected other than operation conditions for a mass flux. (author). 10 refs., 14 figs., 2 tabs.

  12. Simulation of a Helical Channel using GEANT4

    Energy Technology Data Exchange (ETDEWEB)

    Elvira, V. D. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lebrun, P. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Spentzouris, P. [Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States)

    2001-02-01

    We present a simulation of a 72 m long cooling channel proposed by V. Balbekov based on the helical cooling concept developed by Ya. Derbenev. LiH wedge absorbers provide the energy loss mechanism and 201 MHz cavities are used for re-acceleration. They are placed inside a main solenoidal field to focus the beam. A helical field with an amplitude of 0.3 T and a period of 1.8 m provides momentum dispersion for emittance exchange.The simulation is performed using GEANT4. The total fractional transmission is 0.85, and the transverse, longitudinal, and 3-D cooling factors are 3.75, 2.27, and 14.61, respectively. Some version of this helical channel could eventually be used to replace the first section of the double flip channel to keep the longitudinal emittance under control and increase transmission. Although this is an interesting option, the technical challenges are still significant.

  13. Helicity statistics in homogeneous and isotropic turbulence and turbulence models

    Science.gov (United States)

    Sahoo, Ganapati; De Pietro, Massimo; Biferale, Luca

    2017-02-01

    We study the statistical properties of helicity in direct numerical simulations of fully developed homogeneous and isotropic turbulence and in a class of turbulence shell models. We consider correlation functions based on combinations of vorticity and velocity increments that are not invariant under mirror symmetry. We also study the scaling properties of high-order structure functions based on the moments of the velocity increments projected on a subset of modes with either positive or negative helicity (chirality). We show that mirror symmetry is recovered at small scales, i.e., chiral terms are subleading and they are well captured by a dimensional argument plus anomalous corrections. These findings are also supported by a high Reynolds numbers study of helical shell models with the same chiral symmetry of Navier-Stokes equations.

  14. Virtual CT laparoscopic imaging using intravenous cholangiography with helical CT

    Energy Technology Data Exchange (ETDEWEB)

    Uchida, Masafumi; Ishibashi, Masatoshi; Nishimura, Hiroshi; Hayabuchi, Naofumi [Kurume Univ., Fukuoka (Japan). School of Medicine

    2000-08-01

    Laparoscopic cholecystectomy is a reatively new technology that allows for minimally invasive treatment of cholelithiasis. The purpose of this paper is to demonstrate the feasibility of virtual laparoscopic imaging using helical CT cholangiography with volume rendering technique. We used the technique with ten patients with suspected gallbladder abnormalities. Our imaging sets produced high quality 3D images with excellent visualization in 70% (7/10) of all cases. Virtual laparoscopic imaging was also compared with other imaging techniques and imaging using helical scans can proved useful in preoperative imaging. Furthermore, virtual laparoscopic imaging using helical scans can in surgical planning and serve as a visual aid in discussions between radiologists, surgeons, and patients. (author)

  15. Dual electromagnetism: Helicity, spin, momentum, and angular momentum

    CERN Document Server

    Bliokh, Konstantin Y; Nori, Franco

    2012-01-01

    The dual symmetry between electric and magnetic fields is an important intrinsic property of Maxwell equations in free space. This symmetry underlies the conservation of optical helicity (chirality). However, the standard field-theory formulation of electromagnetism lacks helicity conservation because the field Lagrangian is not dual symmetric. To resolve this discrepancy between the symmetries of the Lagrangian and Maxwell equations, we put forward a dual-symmetric Lagrangian formulation of electromagnetism. This preserves the form of Maxwell equations, all fundamental conservation laws of standard electromagnetism, but recovers the helicity conservation as one of the Noether currents. Moreover, we show that the dual-symmetric electromagnetism naturally yields a meaningful separation of the spin and orbital degrees of freedom of light, in complete agreement with other recent results.

  16. Tunneling into and between helical edge states: Fermionic approach

    Science.gov (United States)

    Aristov, D. N.; Niyazov, R. A.

    2016-07-01

    We study the four-terminal junction of spinless Luttinger liquid wires, which describes either a corner junction of two helical edge states of topological insulators or the tunneling from the spinful wire into the helical edge state. We use the fermionic representation and the scattering state formalism, in order to compute the renormalization group (RG) equations for the linear response conductances. We establish our approach by considering a junction between two possibly nonequivalent helical edge states and find an agreement with the earlier analysis of this situation. Tunneling from the tip of the spinful wire to the edge state is further analyzed which requires some modification of our formalism. In the latter case we demonstrate (i) the existence of both fixed lines and conventional fixed points of RG equations, and (ii) certain proportionality relations holding for conductances during renormalization. The scaling exponents and phase portraits are obtained in all cases.

  17. Design principles for Bernal spirals and helices with tunable pitch.

    Science.gov (United States)

    Fejer, Szilard N; Chakrabarti, Dwaipayan; Kusumaatmaja, Halim; Wales, David J

    2014-08-21

    Using the framework of potential energy landscape theory, we describe two in silico designs for self-assembling helical colloidal superstructures based upon dipolar dumbbells and Janus-type building blocks, respectively. Helical superstructures with controllable pitch length are obtained using external magnetic field driven assembly of asymmetric dumbbells involving screened electrostatic as well as magnetic dipolar interactions. The pitch of the helix is tuned by modulating the Debye screening length over an experimentally accessible range. The second design is based on building blocks composed of rigidly linked spheres with short-range anisotropic interactions, which are predicted to self-assemble into Bernal spirals. These spirals are quite flexible, and longer helices undergo rearrangements via cooperative, hinge-like moves, in agreement with experiment.

  18. A Novel Method for Sampling Alpha-Helical Protein Backbones

    Science.gov (United States)

    Fain, Boris; Levitt, Michael

    2001-01-01

    We present a novel technique of sampling the configurations of helical proteins. Assuming knowledge of native secondary structure, we employ assembly rules gathered from a database of existing structures to enumerate the geometrically possible 3-D arrangements of the constituent helices. We produce a library of possible folds for 25 helical protein cores. In each case the method finds significant numbers of conformations close to the native structure. In addition we assign coordinates to all atoms for 4 of the 25 proteins. In the context of database driven exhaustive enumeration our method performs extremely well, yielding significant percentages of structures (0.02%--82%) within 6A of the native structure. The method's speed and efficiency make it a valuable contribution towards the goal of predicting protein structure.

  19. Cooperative polymerization of α-helices induced by macromolecular architecture

    Science.gov (United States)

    Baumgartner, Ryan; Fu, Hailin; Song, Ziyuan; Lin, Yao; Cheng, Jianjun

    2017-07-01

    Catalysis observed in enzymatic processes and protein polymerizations often relies on the use of supramolecular interactions and the organization of functional elements in order to gain control over the spatial and temporal elements of fundamental cellular processes. Harnessing these cooperative interactions to catalyse reactions in synthetic systems, however, remains challenging due to the difficulty in creating structurally controlled macromolecules. Here, we report a polypeptide-based macromolecule with spatially organized α-helices that can catalyse its own formation. The system consists of a linear polymeric scaffold containing a high density of initiating groups from which polypeptides are grown, forming a brush polymer. The folding of polypeptide side chains into α-helices dramatically enhances the polymerization rate due to cooperative interactions of macrodipoles between neighbouring α-helices. The parameters that affect the rate are elucidated by a two-stage kinetic model using principles from nucleation-controlled protein polymerizations; the key difference being the irreversible nature of this polymerization.

  20. Microscopic Processes in Global Relativistic Jets Containing Helical Magnetic Fields

    CERN Document Server

    Nishikawa, Ken-Ichi; Niemiec, Jacek; Kobzar, Oleh; Pohl, Martin; Gomez, Jose L; Dutan, Ioana; Pe'er, Asaf; Frederiksen, Jacob Trier; Nordlund, AAke; Meli, Athina; Sol, Helene; Hardee, Philip E; Hartmann, Dieter H

    2016-01-01

    In the study of relativistic jets one of the key open questions is their interaction with the environment on the microscopic level. Here, we study the initial evolution of both electron$-$proton ($e^{-}-p^{+}$) and electron$-$positron ($e^{\\pm}$) relativistic jets containing helical magnetic fields, focusing on their interaction with an ambient plasma. We have performed simulations of "global" jets containing helical magnetic fields in order to examine how helical magnetic fields affect kinetic instabilities such as the Weibel instability, the kinetic Kelvin-Helmholtz instability (kKHI) and the Mushroom instability (MI). In our initial simulation study these kinetic instabilities are suppressed and new types of instabilities can grow. In the $e^{-}-p^{+}$ jet simulation a recollimation-like instability occurs and jet electrons are strongly perturbed. In the $e^{\\pm}$ jet simulation a recollimation-like instability occurs at early times followed by a kinetic instability and the general structure is similar to ...

  1. Perfect spin filtering effect in ultrasmall helical zigzag graphene nanoribbons

    Science.gov (United States)

    Zhang, Zi-Yue

    2017-02-01

    The spin-polarized transport properties of helical zigzag graphene nanoribbons (ZGNRs) are investigated by first-principles calculations. It is found that although all helical ZGNRs have similar density of states and edge states, they show obviously different transport characteristics depending on the curling manners. ZGNRs curled along zigzag orientation exhibit perfect spin filtering effect with a large spin-split gap near the Fermi level, while ZGNRs curled along armchair orientation behave as conventional conductors for both two spin channels. The spin filtering effect will be weakened with the increase of either ribbon width or curling diameter. The results suggest that ultrasmall helical ZGNRs have important potential applications in spintronics and flexible electronics.

  2. Structural mechanics and helical geometry of thin elastic composites.

    Science.gov (United States)

    Wada, Hirofumi

    2016-09-21

    Helices are ubiquitous in nature, and helical shape transition is often observed in residually stressed bodies, such as composites, wherein materials with different mechanical properties are glued firmly together to form a whole body. Inspired by a variety of biological examples, the basic physical mechanism responsible for the emergence of twisting and bending in such thin composite structures has been extensively studied. Here, we propose a simplified analytical model wherein a slender membrane tube undergoes a helical transition driven by the contraction of an elastic ribbon bound to the membrane surface. We analytically predict the curvature and twist of an emergent helix as functions of differential strains and elastic moduli, which are confirmed by our numerical simulations. Our results may help understand shapes observed in different biological systems, such as spiral bacteria, and could be applied to novel designs of soft machines and robots.

  3. Valence-delocalization of the mixed-valence oxo-centered trinuclear iron propionates [Fe{2/III}FeIIO(C2H5CO2)6(py)3] npy; n=0, 1.5

    Science.gov (United States)

    Nakamoto, Tadahiro; Katada, Motomi; Kawata, Satoshi; Kitagawa, Susumu; Sano, Hirotoshi; Konno, Michiko

    1994-12-01

    Mixed-valence trinuclear iron propionates [Fe{2/III}FeIIO(C2H5CO2)6(py)3]npy, where n=0, 1.5, were synthesized and the structure of the pyridine-solvated complex was determined by single-crystal X-ray diffraction. Mössbauer spectra of the solvated propionate complex showed a temperature-dependent mixed-valence state related to phase transitions, reaching an almost delocalized valence state at room temperature. On the other hand, the non-solvated propionate showed a remarkable change of the spectral shape related to a phase transition, remaining in a localized valence state at higher temperatures up to room temperature.

  4. mer-[Fe(pcq)(CN)3]-: a novel cyanide-containing building block and its application to assembling cyanide-bridged trinuclear FeIII2MnII complexes [pcq- = 8-(pyridine-2-carboxamido)quinoline anion].

    Science.gov (United States)

    Ni, Zhong-Hai; Kou, Hui-Zhong; Zhang, Li-Fang; Ni, Wei-Wei; Jiang, Yun-Bo; Cui, Ai-Li; Ribas, Joan; Sato, Osamu

    2005-12-26

    A new cyanide-containing building block K[Fe(pcq)(CN)(3)] [1; pcq(-) = 8-(pyridine-2-carboxamido)quinoline anion] containing a low-spin Fe(III) center with three cyanide groups in a meridional arrangement has been successfully designed and synthesized. Three cyanide-bridged trinuclear Fe(III)(2)Mn(II) complexes, [Fe(pcq)(CN)(3)](2)[Mn(CH(3)OH)(2)(H(2)O)(2)].2H(2)O (2), [Fe(pcq)(CN)(3)](2)[Mn(bipy)(2)].CH(3)OH.2H(2)O (3), and [Fe(pcq)(CN)(3)](2)[Mn(phen)(2)].CH(3)OH.2H(2)O (4), have been synthesized and structurally characterized. The magnetic susceptibilities of the three heterometallic complexes have been investigated.

  5. Synthesis, Crystal Structure and Fluorescence Property of a Five- and Six-coordinated Trinuclear Zinc(II) Complex:{[ZnL(OAc)]2Zn}·CH3COCH3

    Institute of Scientific and Technical Information of China (English)

    DONG,Wen-Kui; ZHANG,Yan-Ping; ZHAO,Chun-Yu; TANG,Xiao-Lu; L(U),Zhong-Wu; ZOU,Zheng

    2008-01-01

    A novel linear trinuclear zinc(II) complex, {[ZnL(OAc)]2Zn}·CH3COCH3 (H2L: ethylenedioxybis(5-bromo-2-hydroxybenzylideneamino)), has been synthesized and structurally characterized. X-ray crystal structure of the complex reveals that three zinc(II) ions are coordinated by two tetradentate L2- units and two acetate ions acting as bridging groups. The coordination geometry around the terminal Zn(1) or Zn(1)#1 atom approaches a distorted square pyramid. The coordination sphere of the central Zn(2) atom constitutes a slightly distorted octahedral geometry. The blue-green emission from the zinc(II) complex can be observed, where the maximum emission wavelength is at 464 nm.

  6. Variation in the helical structure of native collagen.

    Directory of Open Access Journals (Sweden)

    Joseph P R O Orgel

    Full Text Available The structure of collagen has been a matter of curiosity, investigation, and debate for the better part of a century. There has been a particularly productive period recently, during which much progress has been made in better describing all aspects of collagen structure. However, there remain some questions regarding its helical symmetry and its persistence within the triple-helix. Previous considerations of this symmetry have sometimes confused the picture by not fully recognizing that collagen structure is a highly complex and large hierarchical entity, and this affects and is effected by the super-coiled molecules that make it. Nevertheless, the symmetry question is not trite, but of some significance as it relates to extracellular matrix organization and cellular integration. The correlation between helical structure in the context of the molecular packing arrangement determines which parts of the amino acid sequence of the collagen fibril are buried or accessible to the extracellular matrix or the cell. In this study, we concentrate primarily on the triple-helical structure of fibrillar collagens I and II, the two most predominant types. By comparing X-ray diffraction data collected from type I and type II containing tissues, we point to evidence for a range of triple-helical symmetries being extant in the molecules native environment. The possible significance of helical instability, local helix dissociation and molecular packing of the triple-helices is discussed in the context of collagen's supramolecular organization, all of which must affect the symmetry of the collagen triple-helix.

  7. Differential Geometric Analysis of Alterations in MH α-Helices

    Science.gov (United States)

    Hischenhuber, Birgit; Havlicek, Hans; Todoric, Jelena; Höllrigl-Binder, Sonja; Schreiner, Wolfgang; Knapp, Bernhard

    2013-01-01

    Antigen presenting cells present processed peptides via their major histocompatibility (MH) complex to the T cell receptors (TRs) of T cells. If a peptide is immunogenic, a signaling cascade can be triggered within the T cell. However, the binding of different peptides and/or different TRs to MH is also known to influence the spatial arrangement of the MH α-helices which could itself be an additional level of T cell regulation. In this study, we introduce a new methodology based on differential geometric parameters to describe MH deformations in a detailed and comparable way. For this purpose, we represent MH α-helices by curves. On the basis of these curves, we calculate in a first step the curvature and torsion to describe each α-helix independently. In a second step, we calculate the distribution parameter and the conical curvature of the ruled surface to describe the relative orientation of the two α-helices. On the basis of four different test sets, we show how these differential geometric parameters can be used to describe changes in the spatial arrangement of the MH α-helices for different biological challenges. In the first test set, we illustrate on the basis of all available crystal structures for (TR)/pMH complexes how the binding of TRs influences the MH helices. In the second test set, we show a cross evaluation of different MH alleles with the same peptide and the same MH allele with different peptides. In the third test set, we present the spatial effects of different TRs on the same peptide/MH complex. In the fourth test set, we illustrate how a severe conformational change in an α-helix can be described quantitatively. Taken together, we provide a novel structural methodology to numerically describe subtle and severe alterations in MH α-helices for a broad range of applications. © 2013 Wiley Periodicals, Inc. PMID:23703160

  8. A trinuclear palladium(II) complex containing N,S-coordinating 2-(benzylsulfanyl)anilinide and 1,3-benzothiazole-2-thiolate ligands with a central square-planar PdN4 motif.

    Science.gov (United States)

    Cross, Edward D; MacDonald, Kristen L; McDonald, Robert; Bierenstiel, Matthias

    2014-01-01

    The reaction of dichlorido(cod)palladium(II) (cod = 1,5-cyclooctadiene) with 2-(benzylsulfanyl)aniline followed by heating in N,N-dimethylformamide (DMF) produces the linear trinuclear Pd3 complex bis(μ2-1,3-benzothiazole-2-thiolato)bis[μ2-2-(benzylsulfanyl)anilinido]dichloridotripalladium(II) N,N-dimethylformamide disolvate, [Pd3(C7H4NS2)2(C13H12NS)2Cl2]·2C3H7NO. The molecule has -1 symmetry and a Pd...Pd separation of 3.2012 (4) Å. The outer Pd(II) atoms have a square-planar geometry formed by an N,S-chelating 2-(benzylsulfanyl)anilinide ligand, a chloride ligand and the thiolate S atom of a bridging 1,3-benzothiazole-2-thiolate ligand, while the central Pd(II) core shows an all N-coordinated square-planar geometry. The geometry is perfectly planar within the PdN4 core and the N-Pd-N bond angles differ significantly [84.72 (15)° for the N atoms of ligands coordinated to the same outer Pd atom and 95.28 (15)° for the N atoms of ligands coordinated to different outer Pd atoms]. This trinuclear Pd3 complex is the first example of one in which 1,3-benzothiazole-2-thiolate ligands are only N-coordinated to one Pd centre. The 1,3-benzothiazole-2-thiolate ligands were formed in situ from 2-(benzylsulfanyl)aniline.

  9. Helical Growth of Ultrathin Gold-Copper Nanowires.

    Science.gov (United States)

    Mendoza-Cruz, Rubén; Bazán-Díaz, Lourdes; Velázquez-Salazar, J Jesús; Plascencia-Villa, Germán; Bahena-Uribe, Daniel; Reyes-Gasga, José; Romeu, David; Guisbiers, Grégory; Herrera-Becerra, Raúl; José-Yacamán, Miguel

    2016-03-09

    In this work, we report the synthesis and detailed structural characterization of novel helical gold-copper nanowires. The nanowires possess the Boerdijk-Coxeter-Bernal structure, based on the pile up of octahedral, icosahedral, and/or decahedral seeds. They are self-assembled into a coiled manner as individual wires or into a parallel-ordering way as groups of wires. The helical nanowires are ultrathin with a diameter of less than 10 nm and variable length of several micrometers, presenting a high density of twin boundaries and stacking faults. To the best of our knowledge, such gold-copper nanowires have never been reported previously.

  10. Helicity Selection Rules and Non-Interference for BSM Amplitudes

    CERN Document Server

    Azatov, Aleksandr; Machado, Camila S.; Riva, Francesco

    2016-01-01

    Precision studies of scattering processes at colliders provide powerful indirect constraints on new physics. We study the helicity structure of scattering amplitudes in the SM and in the context of an effective Lagrangian description of BSM dynamics. Our analysis reveals a novel set of helicity selection rules according to which, in the majority of 2 to 2 scattering processes at high energy, the SM and the leading BSM effects do not interfere. In such situations, the naive expectation that dimension-6 operators represent the leading BSM contribution is compromised, as corrections from dimension-8 operators can become equally (if not more) important well within the validity of the effective field theory approach.

  11. A Highly Adjustable Helical Beam: Design and Propagation Characteristic

    CERN Document Server

    Wen, Yuanhui; Yu, Siyuan

    2016-01-01

    Light fields with extraordinary propagation behaviours such as nondiffracting and self-bending are useful in optical delivery for energy, information, and even objects. A kind of helical beams is constructed here based on the caustic method. With appropriate design, the main lobe of these helical beams can be both well-confined and almost nondiffracting while moving along a helix with its radius, period, the number of rotations and main lobes highly adjustable. In addition, the main lobe contains almost half of the optical power and the peak intensity fluctuates below 15% during propagation. These promising characteristics may enable a variety of potential applications based on these beams.

  12. Small-$x$ asymptotics of the quark helicity distribution

    CERN Document Server

    Kovchegov, Yuri V; Sievert, Matthew D

    2016-01-01

    We construct a numerical solution of the small-$x$ evolution equations recently derived in \\cite{Kovchegov:2015pbl} for the (anti)quark helicity TMDs and PDFs as well as the $g_1$ structure function. We focus on the case of large $N_c$ where one finds a closed set of equations. Employing the extracted intercept, we are able to predict directly from theory the behavior of the helicity PDFs at small $x$, which should have important phenomenological consequences. We also give an estimate of how much of the proton's spin may be at small $x$ and what impact this has on the so-called "spin crisis."

  13. Fiber-guided modes conversion using superposed helical gratings

    Science.gov (United States)

    Ma, Yancheng; Fang, Liang; Wu, Guoan

    2017-03-01

    Optical fibers can support various modal forms, including vector modes, linear polarization (LP) modes, and orbital angular momentum (OAM) modes, etc. The modal correlation among these modes is investigated via Jones matrix, associated with polarization and helical phase corresponding to spin angular momentum (SAM) and OAM of light, respectively. We can generate different modal forms by adopting superposed helical gratings (SHGs) with opposite helix orientations. Detailed analysis and discussion on mode conversion is given as for mode coupling in optical fibers with both low and high contrast index, respectively. Our study may deepen the understanding for various fiber-guided modes and mode conversion among them via fiber gratings.

  14. Staged retroauricular flap for helical reconstruction after Mohs micrographic surgery*

    Science.gov (United States)

    Cerci, Felipe Bochnia

    2016-01-01

    Staged retroauricular flap is a great option for full-thickness defects along the helical rim and antihelix. Donor site consists of the posterior ear, postauricular sulcus and mastoid area. The advantages of this flap include hidden donor scar, donor tissue similarity and rich vascularity. We present a case of collision tumor on the left helix treated with Mohs micrographic surgery and the resulting full-thickness defect repaired with a staged retroauricular flap. This flap is an effective technique for full-thickness helical defect repair with relatively little operative morbidity. High esthetic and functional results may be obtained restoring the ear size and shape.

  15. Ion temperature gradient turbulence in helical and axisymmetric RFP plasmas

    CERN Document Server

    Predebon, I

    2015-01-01

    Turbulence induced by the ion temperature gradient (ITG) is investigated in the helical and axisymmetric plasma states of a reversed field pinch device by means of gyrokinetic calculations. The two magnetic configurations are systematically compared, both linearly and nonlinearly, in order to evaluate the impact of the geometry on the instability and its ensuing transport, as well as on the production of zonal flows. Despite its enhanced confinement, the high-current helical state demonstrates a lower ITG stability threshold compared to the axisymmetric state, and ITG turbulence is expected to become an important contributor to the total heat transport.

  16. Synthesis, model and stability of helically coiled carbon nanotubes

    DEFF Research Database (Denmark)

    Fejes, Dora; Raffai, Manuella; Hernadi, Klara

    2013-01-01

    Structural model of helically coiled carbon nanotubes is proposed. It is constructed by means of topological coordinate method. Relaxation and cohesive energy calculation are performed by molecular mechanics, using second-generation bond order potential for hydrocarbons introduced by D. W. Brenner....... Our experiments focused on the production and development of catalysts for the synthesis of helically coiled CNTs (carbon nanotubes). The catalysts were tested in the decomposition of acetylene by CCVD (Catalytic Chemical Vapor Deposition) method. The carbon deposit was imaged by TEM (Transmission...

  17. Frequency characteristics of tapered backfire helical antenna with loaded termination

    Science.gov (United States)

    Nakano, H.; Iio, S.; Yamauchi, J.

    1984-06-01

    Effects of loaded termination on a tapered backfire bifilar helical antenna are numerically and experimentally investigated over a wide frequency range of ratio 1:1.7. With the help of the scalar potential for a lumped resistance at the arm end, the current distribution along the helical wire is determined. It is found that nearly constant input impedance, high front-to-back ratio and low axial ratio are realised. The inherent absolute gain is not significantly deteriorated in spite of the use of a terminal resistor. The existence of the phase centre is also demonstrated, and the phase centre location is presented as a function of frequency.

  18. Interpolating Helicity Spinors Between the Instant Form and the Light-front Form

    CERN Document Server

    Li, Ziyue; Ji, Chueng-Ryong

    2015-01-01

    We discuss the helicity spinors interpolating between the instant form dynamics (IFD) and the front form dynamics, or the light-front dynamics (LFD), and present the interpolating helicity amplitudes as well as their squares for the scattering of two fermions, and the annihilation of fermion and anti-fermion. We parametrize the interpolation between the two dynamics, IFD and LFD, by an interpolation angle and derive not only the generalized helicity spinors in the $(0,J)\\oplus(J,0)$ chiral representation that links naturally the two typical IFD vs. LFD helicity spinors but also the generalized Melosh transformation that relates these generalized helicity spinors to the usual Dirac spinors. Analyzing the directions of the particle momentum and spin with the variation of the interpolation angle, we inspect the whole landscape of the generalized helicity intermediating between the usual Jacob-Wick helicity in the IFD and the light-front helicity in the LFD. Our analysis clarifies the characteristic difference of...

  19. A Combined Study of Photospheric Magnetic and Current Helicities and Subsurface Kinetic Helicities of Solar Active Regions during 2006-2013

    Science.gov (United States)

    Seligman, D.; Petrie, G. J. D.; Komm, R.

    2014-11-01

    We compare the average photospheric current helicity Hc , photospheric twist parameter α (a well-known proxy for the full relative magnetic helicity), and subsurface kinetic helicity Hk for 194 active regions observed between 2006-2013. We use 2440 Hinode photospheric vector magnetograms, and the corresponding subsurface fluid velocity data derived from GONG (2006-2012) and Helioseismic and Magnetic Imager (2010-2013) dopplergrams. We find a significant hemispheric bias in all three parameters. The subsurface kinetic helicity is preferentially positive in the southern hemisphere and negative in the northern hemisphere. The photospheric current helicity and the α parameter have the same bias for strong fields (|B| > 1000 G) and no significant bias for weak fields (100 G <|B| < 500 G). We find no significant region-by-region correlation between the subsurface kinetic helicity and either the strong-field current helicity or α. Subsurface fluid motions of a given handedness correspond to photospheric helicities of both signs in approximately equal numbers. However, common variations appear in annual averages of these quantities over all regions. Furthermore, in a subset of 77 regions, we find significant correlations between the temporal profiles of the subsurface and photospheric helicities. In these cases, the sign of the linear correlation coefficient matches the sign relationship between the helicities, indicating that the photospheric magnetic field twist is sensitive to the twisting motions below the surface.

  20. A combined study of photospheric magnetic and current helicities and subsurface kinetic helicities of solar active regions during 2006-2013

    Energy Technology Data Exchange (ETDEWEB)

    Seligman, D. [National Solar Observatory REU Program, University of Pennsylvania (United States); Petrie, G. J. D.; Komm, R. [National Solar Observatory, Tucson, AZ 85719 (United States)

    2014-11-10

    We compare the average photospheric current helicity H{sub c} , photospheric twist parameter α (a well-known proxy for the full relative magnetic helicity), and subsurface kinetic helicity H{sub k} for 194 active regions observed between 2006-2013. We use 2440 Hinode photospheric vector magnetograms, and the corresponding subsurface fluid velocity data derived from GONG (2006-2012) and Helioseismic and Magnetic Imager (2010-2013) dopplergrams. We find a significant hemispheric bias in all three parameters. The subsurface kinetic helicity is preferentially positive in the southern hemisphere and negative in the northern hemisphere. The photospheric current helicity and the α parameter have the same bias for strong fields (|B| > 1000 G) and no significant bias for weak fields (100 G <|B| < 500 G). We find no significant region-by-region correlation between the subsurface kinetic helicity and either the strong-field current helicity or α. Subsurface fluid motions of a given handedness correspond to photospheric helicities of both signs in approximately equal numbers. However, common variations appear in annual averages of these quantities over all regions. Furthermore, in a subset of 77 regions, we find significant correlations between the temporal profiles of the subsurface and photospheric helicities. In these cases, the sign of the linear correlation coefficient matches the sign relationship between the helicities, indicating that the photospheric magnetic field twist is sensitive to the twisting motions below the surface.

  1. Global Analysis of Helicity PDFs: past - present - future

    Energy Technology Data Exchange (ETDEWEB)

    de Florian, D.; Stratmann, M.; Sassot, R.; Vogelsang, W.

    2011-04-11

    We discuss the current status of the DSSV global analysis of helicity-dependent parton densities. A comparison with recent semi-inclusive DIS data from COMPASS is presented, and constraints on the polarized strangeness density are examined in some detail.

  2. Performance of Upgraded Cooling System for Lhd Helical Coils

    Science.gov (United States)

    Hamaguchi, S.; Imagawa, S.; Obana, T.; Yanagi, N.; Moriuchi, S.; Sekiguchi, H.; Oba, K.; Mito, T.; Motojima, O.; Okamura, T.; Semba, T.; Yoshinaga, S.; Wakisaka, H.

    2008-03-01

    Helical coils of the Large Helical Device (LHD) are large scale superconducting magnets for heliotron plasma experiments. The helical coils had been cooled by saturated helium at 4.4 K, 120 kPa until 2005. An upgrade of the cooling system was carried out in 2006 in order to improve the cryogenic stability of the helical coils and then it has been possible to supply the coils with subcooled helium at 3.2 K, 120 kPa. A designed mass flow of the supplied subcooled helium is 50 g/s. The subcooled helium is generated at a heat exchanger in a saturated helium bath. A series of two centrifugal cold compressors with gas foil bearing is utilized to lower the helium pressure in the bath. The supplied helium temperature is regulated by rotational speed of the cold compressors and power of a heater in the bath. The mass flow of the supplied helium is also controlled manually by a supply valve and its surplus is evaporated by ten heaters at the outlet above the coils. In the present study, the performance of the cooling system has been investigated and a stable operating method has also developed. As the result, it was confirmed that the performance of the upgraded cooling system satisfies the requirements.

  3. Heat exchanger with helical bundles of finned tubes

    Energy Technology Data Exchange (ETDEWEB)

    Eyking, H.J.

    1975-01-23

    The invention applies to a heat exchanger with helical bundles of tubes consisting of finned tubes separated by spacers. The spacers are designed as closed holding cylinders with holding devices for the tube bundles, each ot which surrounds a bundle of tubes. This construction serves to simplify the production process and to enable the use of the heat exchanger at higher loads.

  4. Variation in the Helical Structure of Native Collagen

    Science.gov (United States)

    2014-02-24

    Hongo C, Noguchi K (2006) Helical twists of collagen model peptides. Biopolymers 84: 421–432. 39. Kramer R, Bella J, Mayville P, Brodsky B, Berman H...Iguchi M, Noguchi K (2006) Revision of collagen molecular structure. Biopolymers 84: 181–191. 43. Shoulders MD, Raines RT (2009) Collagen structure

  5. Phylogeny and evolution of class-I helical cytokines

    NARCIS (Netherlands)

    Huising, M.O.; Kruiswijk, C.P.; Flik, G.

    2006-01-01

    The class-1 helical cytokines constitute a large group of signalling molecules that play key roles in a plethora of physiological processes including host defence, inuinine regulation, somatic growth, reproduction, food intake and energy metabolism, regulation of neural growth and many more. Despite

  6. Phylogeny and evolution of class-I helical cytokines

    NARCIS (Netherlands)

    Huising, M.O.; Kruiswijk, C.P.; Flik, G.

    2006-01-01

    The class-I helical cytokines constitute a large group of signalling molecules that play key roles in a plethora of physiological processes including host defence, immune regulation, somatic growth, reproduction, food intake and energy metabolism, regulation of neural growth and many more. Despite l

  7. Locally Enhanced and Tunable Optical Chirality in Helical Metamaterials

    CERN Document Server

    Gutsche, Philipp; Burger, Sven

    2016-01-01

    We report on a numerical study of optical chirality. Intertwined gold helices illuminated with plane waves concentrate right and left circularly polarized electromagnetic field energy to sub-wavelength regions. These spots of enhanced chirality can be smoothly shifted in position and magnitude by varying illumination parameters, allowing for the control of light-matter interactions on a nanometer scale.

  8. Helicity and internal twist within the vortex filament model

    CERN Document Server

    Hietala, N; Salman, H

    2016-01-01

    For ideal fluids, besides energy, kinetic helicity is the only other known quadratic invariant of the Euler equations besides energy and is understood to be inherently linked to the degree of knotting of vortex lines within the fluid. For vortices arising in superfluid $^4$He, the vorticity is concentrated along vortex filaments. In this setting, helicity would be expected to acquire its simplest form. However, the lack of a core structure for vortex filaments appears to result in a helicity that does not retain its key attribute as a quadratic invariant. By defining the spanwise vector to coincide with the Seifert framing, we are able to introduce twist and henceforth recover the key properties of helicity. Through a detailed analysis of the velocity field induced in the vicinity of the superfluid vortices we are able to express our choice of the spanwise vector in terms of the tangential component of velocity along the filament. Since adding an arbitrary tangential velocity does not alter the configuration ...

  9. Helical Feed Milling with MQL for Boring of Aluminum Alloy

    Science.gov (United States)

    Sasahara, Hiroyuki; Kawasaki, Makoto; Tsutsumi, Masaomi

    MQL is applied to the helical feed milling hole-making process of aluminum alloy. It is difficult to drill on aluminum alloy without cutting fluid because the adhesion to the tool leads to a chip jam, the tool breakage or low accuracy. By employing the helical feed milling, cutting temperature will decrease, each chip length will become short and a chip jam in a hole will be avoided, because the intermittent cutting is realized. As a result of employing the helical feed milling with MQL, it was shown that the shape error is decreased, a burr formation is decreased, machining temperature becomes low and the cutting force becomes small comparing with drilling process. Shape error by helical feed milling with MQL is comparable with that with flood coolant. In this case, small mist particle counts under 5μm, which affects working environment, are almost constant if the spindle speed varies. Scattered mist particle counts are less when MQL is employed over 20000 min-1 spindle speed comparing with the flood coolant.

  10. Helical Phase Inflation and Monodromy in Supergravity Theory

    Directory of Open Access Journals (Sweden)

    Tianjun Li

    2015-01-01

    Full Text Available We study helical phase inflation which realizes “monodromy inflation” in supergravity theory. In the model, inflation is driven by the phase component of a complex field whose potential possesses helicoid structure. We construct phase monodromy based on explicitly breaking global U(1 symmetry in the superpotential. By integrating out heavy fields, the phase monodromy from single complex scalar field is realized and the model fulfills natural inflation. The phase-axion alignment is achieved from explicitly symmetry breaking and gives super-Planckian phase decay constant. The F-term scalar potential provides strong field stabilization for all the scalars except inflaton, which is protected by the approximate global U(1 symmetry. Besides, we show that helical phase inflation can be naturally realized in no-scale supergravity with SU(2,1/SU(2×U(1 symmetry since the supergravity setup needed for phase monodromy is automatically provided in the no-scale Kähler potential. We also demonstrate that helical phase inflation can be reduced to another well-known supergravity inflation model with shift symmetry. Helical phase inflation is free from the UV-sensitivity problem although there is super-Planckian field excursion, and it suggests that inflation can be effectively studied based on supersymmetric field theory while a UV-completed framework is not prerequisite.

  11. Conservation of helical bundle structure between the exocyst subunits.

    Directory of Open Access Journals (Sweden)

    Nicole J Croteau

    Full Text Available BACKGROUND: The exocyst is a large hetero-octomeric protein complex required for regulating the targeting and fusion of secretory vesicles to the plasma membrane in eukaryotic cells. Although the sequence identity between the eight different exocyst subunits is less than 10%, structures of domains of four of the subunits revealed a similar helical bundle topology. Characterization of several of these subunits has been hindered by lack of soluble protein for biochemical and structural studies. METHODOLOGY/PRINCIPAL FINDINGS: Using advanced hidden Markov models combined with secondary structure predictions, we detect significant sequence similarity between each of the exocyst subunits, indicating that they all contain helical bundle structures. We corroborate these remote homology predictions by identifying and purifying a predicted domain of yeast Sec10p, a previously insoluble exocyst subunit. This domain is soluble and folded with approximately 60% alpha-helicity, in agreement with our predictions, and capable of interacting with several known Sec10p binding partners. CONCLUSIONS/SIGNIFICANCE: Although all eight of the exocyst subunits had been suggested to be composed of similar helical bundles, this has now been validated by our hidden Markov model structure predictions. In addition, these predictions identified protein domains within the exocyst subunits, resulting in creation and characterization of a soluble, folded domain of Sec10p.

  12. Chiral Charge Erasure via Thermal Fluctuations of Magnetic Helicity

    CERN Document Server

    Long, Andrew J

    2016-01-01

    We consider a relativistic plasma of fermions coupled to an Abelian gauge field and carrying a chiral charge asymmetry, which might arise in the early Universe through baryogenesis. It is known that on large length scales, $\\lambda \\gtrsim 1/(\\alpha \\mu_5)$, the chiral anomaly opens an instability toward the erasure of chiral charge and growth of magnetic helicity. Here the chemical potential $\\mu_{5}$ parametrizes the chiral asymmetry and $\\alpha$ is the fine-structure constant. We study the process of chiral charge erasure through the thermal fluctuations of magnetic helicity and contrast with the well-studied phenomenon of Chern-Simons number diffusion. Through the fluctuation-dissipation theorem we estimate the amplitude and time scale of helicity fluctuations on the length scale $\\lambda$, finding $\\delta \\mathcal{H} \\sim \\lambda T$ and $\\tau \\sim \\alpha \\lambda^3 T^2$ for a relativistic plasma at temperature $T$. We argue that the presence of a chiral asymmetry allows the helicity to grow diffusively fo...

  13. Instability of helical tip vortices in rotor wakes

    DEFF Research Database (Denmark)

    Sørensen, Jens Nørkær

    2011-01-01

    The conditions for the appearance of instabilities in systems of helical vortices constitute an intriguing problem that still remains partly unsolved. The experimental study of Felli, Camussi & Di Felice (J. Fluid Mech., this issue, vol. 682, 2011, pp. 5-53) has shed new light on some of the basi...

  14. Stokesian swimming of a sphere by radial helical surface wave

    CERN Document Server

    Felderhof, B U

    2016-01-01

    The swimming of a sphere by means of radial helical surface waves is studied on the basis of the Stokes equations. Explicit expressions are derived for the matrices characterizing the mean translational and rotational swimming velocities and the mean rate of dissipation to second order in the wave amplitude.

  15. Effects of parameters on rotational fine blanking of helical gears

    Institute of Scientific and Technical Information of China (English)

    杨珊; 宋燕利; 张梅

    2014-01-01

    The application of fine blanking to the manufacturing of helical gears directly from a strip has been restricted due to the traditional linear cutting stroke of the punch and die. In this work, rotational fine blanking which combined the linear and rotational motion of punch and counterpunch was applied for the forming of helical gears. A three-dimensional (3D) rigid-plastic finite element model was developed on the DEFORM-3D platform. By finite element simulation and analysis, the influences of key parameters on the punch load and cut surface were investigated. It is shown that:1) with increasing the counterforce or helical angle, the punch load and the depth of die roll increase;2) with increasing blank holder force, the punch load increases while the depth of die roll decreases;3) V-ring indenter facilitates an improvement in the quality. The results of this research reveal the deformation mechanism of rotational fine blanking of helical gears, and provide valuable guidelines for further experimental studies.

  16. Topology of magnetic helicity of torsioned filaments in Hall plasmas

    CERN Document Server

    de Andrade, L C Garcia

    2007-01-01

    A solution of magnetic Hall equations for plasma filaments in the Coulomb gauge is obtained in the non-holonomic frame. Some physical features of the solution include, the non-conservation of the magnetic helicity and the decay of the magnetic field in the filaments. From the mathematical point of view,the presence of Frenet torsion in the filament is actually shown to be fundamental for the breaking of conservation of magnetic helicity in the case of helicoidal filaments. Since the magnetic helicity is not conserved even in the Coulomb gauge, and the magnetic field decays, one can say that the dynamo action fails. Actually the presence of torsion enhances the breaking of magnetic field helicity conservation. A similar formula of the one obtained here without considering the Hall effect has been obtained by Moffatt and Ricca (PRSA-1992) in the case of holonomic filaments. It is shown that unknotted magnetic filaments may place a lower bound on the magnetic energy. Discussions on the writhe number are also dis...

  17. Helical metallic micro- and nanostructures: fabrication and application

    Science.gov (United States)

    Liu, Lichun; Zhang, Liqiu; Kim, Sang Min; Park, Sungho

    2014-07-01

    Metal elements occupy more than 70% of the positions in the periodic table, and their use has accelerated human civilization due to their invaluable chemical and physical characteristics. With the rapid development of metals, various structures of microscopic metal particles have been fabricated and investigated as functional materials in scientific research and practical applications. The phrase `structure determines properties' has been widely acknowledged as a golden rule in chemistry and materials science, especially when the size of small particles is in the micro- or nanoscale dimension. Helical metallic micro- and nanostructures with complex shapes have recently emerged and may be used for various useful applications such as photonics, sensors, actuators, micro-/nanorobotics, and micro-/nanoelectronics, based on their unique mechanical, electrical, and electromagnetic properties. This review paper specifically focuses on the fabrication and application of helical metallic structures with a size ranging from the micro- to nanoscale. The unusual spatial distribution of active atoms in helical metallic micro- and nanostructures and their helical morphology could offer new opportunities for applications beyond those of other conventional metallic and nonmetallic micro- and nanostructures.

  18. Generation of hypermagnetic helicity and leptogenesis in the early Universe

    Science.gov (United States)

    Semikoz, V. B.; Smirnov, A. Yu.; Sokoloff, D. D.

    2016-05-01

    We study hypermagnetic helicity and lepton asymmetry evolution in the plasma of the early Universe before the electroweak phase transition accounting for chirality flip processes via inverse Higgs decays and sphaleron transitions which violate the left lepton number and wash out the baryon asymmetry of the Universe (BAU). In the scenario where the right electron asymmetry supports the BAU alone through the conservation law B /3 -Le R=const at temperatures T >TRL≃10 TeV , the following Universe cooling leads to the production of a nonzero left lepton (electrons and neutrinos) asymmetry. This is due to the Higgs decays becoming faster when entering the equilibrium at T =TRL, with the Universe expansion, ΓRL˜T >H ˜T2 , resulting in the parallel evolution of the right and left electron asymmetries at T helicity evolution proceeds in a self-consistent way with the lepton asymmetry growth. The role of sphaleron transitions in decreasing the left lepton number turns out to be negligible in a given scenario. The hypermagnetic helicity plays a key role in lepto-/baryogenesis in our scenario, and the more hypermagnetic field gets closer to the maximum helical one the faster the BAU grows to the observable value, Bobs˜1 0-10 .

  19. Mechanics of tunable helices and geometric frustration in biomimetic seashells

    Science.gov (United States)

    Guo, Qiaohang; Chen, Zi; Li, Wei; Dai, Pinqiang; Ren, Kun; Lin, Junjie; Taber, Larry A.; Chen, Wenzhe

    2014-03-01

    Helical structures are ubiquitous in nature and engineering, ranging from DNA molecules to plant tendrils, from sea snail shells to nanoribbons. While the helical shapes in natural and engineered systems often exhibit nearly uniform radius and pitch, helical shell structures with changing radius and pitch, such as seashells and some plant tendrils, add to the variety of this family of aesthetic beauty. Here we develop a comprehensive theoretical framework for tunable helical morphologies, and report the first biomimetic seashell-like structure resulting from mechanics of geometric frustration. In previous studies, the total potential energy is everywhere minimized when the system achieves equilibrium. In this work, however, the local energy minimization cannot be realized because of the geometric incompatibility, and hence the whole system deforms into a shape with a global energy minimum whereby the energy in each segment may not necessarily be locally optimized. This novel approach can be applied to develop materials and devices of tunable geometries with a range of applications in nano/biotechnology.

  20. Conductance through a helical state in an Indium antimonide nanowire.

    Science.gov (United States)

    Kammhuber, J; Cassidy, M C; Pei, F; Nowak, M P; Vuik, A; Gül, Ö; Car, D; Plissard, S R; Bakkers, E P A M; Wimmer, M; Kouwenhoven, L P

    2017-09-07

    The motion of an electron and its spin are generally not coupled. However in a one-dimensional material with strong spin-orbit interaction (SOI) a helical state may emerge at finite magnetic fields, where electrons of opposite spin will have opposite momentum. The existence of this helical state has applications for spin filtering and cooper pair splitter devices and is an essential ingredient for realizing topologically protected quantum computing using Majorana zero modes. Here, we report measurements of a quantum point contact in an indium antimonide nanowire. At magnetic fields exceeding 3 T, the 2 e (2)/h conductance plateau shows a re-entrant feature toward 1 e (2)/h which increases linearly in width with magnetic field. Rotating the magnetic field clearly attributes this experimental signature to SOI and by comparing our observations with a numerical model we extract a spin-orbit energy of approximately 6.5 meV, which is stronger than the spin-orbit energy obtained by other methods.Indium antimonide nanowires have large spin-orbit coupling, which can give rise to helical states that are an important part of proposals for topological quantum computing. Here the authors measure conductance through the helical states and extract a larger spin-orbit energy than obtained before.

  1. Scale-invariant helical magnetic fields and the duration of inflation

    CERN Document Server

    Kahniashvili, Tina; Durrer, Ruth; Tevzadze, Alexander G; Yin, Winston

    2016-01-01

    In this paper we study a (nearly) scale-invariant helical magnetic field generated during inflation. We show that, if the helicity of such fields is measured, it can be used to determine the beginning of inflation. Upper bounds can be used to derive constraints on the minimal duration of inflation if one assumes that the magnetic fields generated during inflation are helical.

  2. In situ control of polymer helicity with a non-covalently bound photoresponsive molecular motor dopant.

    Science.gov (United States)

    van Leeuwen, Thomas; Heideman, G Henrieke; Zhao, Depeng; Wezenberg, Sander J; Feringa, Ben L

    2017-06-13

    The transfer of chirality from a molecular motor to a dynamic helical polymer via ionic interactions was investigated. A dopant with photoswitchable chirality was able to induce a preferred helicity in a poly(phenylacetylene) polymer and the helicity is inverted upon irradiation. The findings described herein will advance the development of functional and responsive polymeric systems.

  3. Collagenolytic Matrix Metalloproteinase Activities toward Peptomeric Triple-Helical Substrates.

    Science.gov (United States)

    Stawikowski, Maciej J; Stawikowska, Roma; Fields, Gregg B

    2015-05-19

    Although collagenolytic matrix metalloproteinases (MMPs) possess common domain organizations, there are subtle differences in their processing of collagenous triple-helical substrates. In this study, we have incorporated peptoid residues into collagen model triple-helical peptides and examined MMP activities toward these peptomeric chimeras. Several different peptoid residues were incorporated into triple-helical substrates at subsites P3, P1, P1', and P10' individually or in combination, and the effects of the peptoid residues were evaluated on the activities of full-length MMP-1, MMP-8, MMP-13, and MMP-14/MT1-MMP. Most peptomers showed little discrimination between MMPs. However, a peptomer containing N-methyl Gly (sarcosine) in the P1' subsite and N-isobutyl Gly (NLeu) in the P10' subsite was hydrolyzed efficiently only by MMP-13 [nomenclature relative to the α1(I)772-786 sequence]. Cleavage site analysis showed hydrolysis at the Gly-Gln bond, indicating a shifted binding of the triple helix compared to the parent sequence. Favorable hydrolysis by MMP-13 was not due to sequence specificity or instability of the substrate triple helix but rather was based on the specific interactions of the P7' peptoid residue with the MMP-13 hemopexin-like domain. A fluorescence resonance energy transfer triple-helical peptomer was constructed and found to be readily processed by MMP-13, not cleaved by MMP-1 and MMP-8, and weakly hydrolyzed by MT1-MMP. The influence of the triple-helical structure containing peptoid residues on the interaction between MMP subsites and individual substrate residues may provide additional information about the mechanism of collagenolysis, the understanding of collagen specificity, and the design of selective MMP probes.

  4. Fluid-magnetic helicity in axisymmetric stationary relativistic magnetohydrodynamics

    Science.gov (United States)

    Prasad, G.

    2017-10-01

    The present work is intended to gain a fruitful insight into the understanding of the formations of magneto-vortex configurations and their role in the physical processes of mutual exchange of energies associated with fluid's motion and the magnetic fields in an axisymmetric stationary hydromagnetic system subject to strong gravitational field (e.g., neutron star/magnetar). It is found that the vorticity flux vector field associated with vorticity 2-form is a linear combination of fluid's vorticity vector and of magnetic vorticity vector. The vorticity flux vector obeys Helmholtz's flux conservation. The energy equation associated with the vorticity flux vector field is deduced. It is shown that the mechanical rotation of vorticity flux surfaces contributes to the formation of vorticity flux vector field. The dynamo action for the generation of toroidal components of vorticity flux vector field is described in the presence of meridional circulations. It is shown that the stretching of twisting magnetic lines due to differential rotation leads to the breakdown of gravitational isorotation in the absence of meridional circulations. An explicit expression consists of rotation of vorticity flux surface, energy and angular momentum per baryon for the fluid-magnetic helicity current vector is obtained. The conservation of fluid-magnetic helicity is demonstrated. It is found that the fluid-magnetic helicity displays the energy spectrum arising due to the interaction between the mechanical rotation of vorticity flux surfaces and the fluid's motion obeying Euler's equations. The dissipation of a linear combination of modified fluid helicity and magnetic twist is shown to occur due to coupled effect of frame dragging and meridional circulation. It is found that the growing twist of magnetic lines causes the dissipation of modified fluid helicity in the absence of meridional circulations.

  5. Plasma transport simulation modeling for helical confinement systems

    Energy Technology Data Exchange (ETDEWEB)

    Yamazaki, K.; Amano, T.

    1991-08-01

    New empirical and theoretical transport models for helical confinement systems are developed based on the neoclassical transport theory including the effect of radial electric field and multi-helicity magnetic components, and the drift wave turbulence transport for electrostatic and electromagnetic modes, or the anomalous semi-empirical transport. These electron thermal diffusivities are compared with CHS (Compact Helical System) experimental data, which indicates that the central transport coefficient of the ECH plasma agrees with the neoclassical axi-symmetric value and the transport outside the half radius is anomalous. On the other hand, the transport of NBI-heated plasmas is anomalous in the whole plasma region. This anomaly is not explained by the electrostatic drift wave turbulence models in these flat-density-profile discharges. For the detailed prediction of plasma parameters in LHD (Large Helical Device), 3-D(dimensional) equilibrium/1-D transport simulations including empirical or drift wave turbulence models are carried out, which suggests that the global confinement time of LHD is determined mainly by the electron anomalous transport near the plasma edge region rather than the helical ripple transport in the core region. Even if the ripple loss can be eliminated, the increase of the global confinement is 10%. However, the rise in the central ion temperature is more than 20%. If the anomalous loss can be reduced to the half level of the present scaling, like so-called `H-mode` of the tokamak discharge, the neoclassical ripple loss through the ion channel becomes important even in the plasma core. The 5% radial inward shift of the plasma column with respect to the major radius is effective for improving plasma confinement and raising more than 50% of the fusion product by reducing this neoclassical asymmetric ion transport loss and increasing 10% in the plasma radius. (author).

  6. Effects of magnetic and kinetic helicities on the growth of magnetic fields in laminar and turbulent flows by helical-Fourier decomposition

    CERN Document Server

    Linkmann, Moritz; McKay, Mairi; Berera, Arjun; Biferale, Luca

    2016-01-01

    We present a numerical and analytical study of incompressible homogeneous conducting fluids using a Fourier-helical representation. We analytically study both small- and large-scale dynamo properties, as well as the inverse cascade of magnetic helicity, in the most general minimal subset of interacting velocity and magnetic fields on a closed Fourier triad. We mainly focus on the dependency of magnetic field growth as a function of the distribution of kinetic and magnetic helicities among the three interacting wavenumbers. By combining direct numerical simulations of the full magnetohydrodynamics (MHD) equations with the Fourier-helical decomposition we numerically confirm that in the kinematic dynamo regime the system develops a large-scale magnetic helicity with opposite sign compared to the small-scale kinetic helicity, a sort of triad-by-triad $\\alpha$-effect in Fourier space. Concerning the small-scale perturbations, we predict theoretically and confirm numerically that the largest instability is achived...

  7. Effects of magnetic and kinetic helicities on the growth of magnetic fields in laminar and turbulent flows by helical-Fourier decomposition

    Science.gov (United States)

    Linkmann, Moritz; Sahoo, Ganapati; McKay, Mairi; Berera, Arjun; Biferale, Luca

    2016-11-01

    We perform an analytical and numerical study of incompressible homogeneous conducting fluids by Fourier-helical decomposition of the equations of magnetohydrodynamics (MHD) and a subsequent reduction of the number of degrees of freedom. From the stability properties of the most general subset of interacting velocity and magnetic fields on a closed Fourier triad, we make predictions on the large-scale magnetic-field growth depending on the distribution of magnetic and kinetic helicities among the three wavenumbers. In the kinematic dynamo regime we predict the formation of a large-scale magnetic component with a magnetic helicity of opposite sign with respect to the kinetic helicity, a sort of triadic-by-triad α-effect in Fourier space, while in presence of strong small-scale magnetic helicity we predict an inverse cascade of magnetic helicity. We confirm these predictions through a series of Direct Numerical Simulations, either seeding different magnetic helical components in a strongly helical flow (turbulent/laminar) or directly injecting helical magnetic fluctuations at small scales. Our results show that important dynamical features of MHD flows can be predicted from an analytically tractable dynamical system derived directly from the MHD equations. ERC ADG NewTURB 2013.

  8. The generic geometry of helices and their close-packed structures

    DEFF Research Database (Denmark)

    Olsen, Kasper; Bohr, Jakob

    2010-01-01

    The formation of helices is an ubiquitous phenomenon for molecular structures whether they are biological, organic, or inorganic, in nature. Helical structures have geometrical constraints analogous to close packing of three-dimensional crystal structures. For helical packing the geometrical cons....... For double helices comparisons are made to the A,B, and Z forms of DNA. The helical geometry of the A form is nearly close-packed. The packing density for the B and Z form are found to be approximately equal to each other....

  9. A designed protein with packing between left-handed and right-handed helices.

    Science.gov (United States)

    Sia, S K; Kim, P S

    2001-07-31

    A common motif in protein structures is the assembly of alpha-helices. Natural alpha-helical assemblies, such as helical bundles and coiled coils, consist of multiple right-handed alpha-helices. Here we design a protein complex containing both left-handed and right-handed helices, with peptides of D- and L-amino acids, respectively. The two peptides, D-Acid and L-Base, feature hydrophobic heptad repeats and are designed to pack against each other in a "knobs-into-holes" manner. In solution, the peptides form a stable, helical heterotetramer with tight packing in the most solvent-protected core. This motif may be useful for designing protease-resistant, helical D-peptide ligands against biological protein targets.

  10. Successive Injection of Opposite Magnetic Helicity in Solar Active Region NOAA 11928

    CERN Document Server

    Vemareddy, P

    2016-01-01

    Understanding the nature and evolution of the photospheric helicity flux transfer is a key to reveal the role of magnetic helicity in coronal dynamics of solar active regions. Using SDO/HMI photospheric vector magnetograms and the derived flow velocity field, we computed boundary driven helicity flux with a 12 minute cadence during the emergence of AR 11928. Accounting the foot point connectivity defined by non-linear force-free magnetic extrapolations, we derived and analyzed the corrected distribution of helicity flux maps. The photospheric helicity flux injection is found to changes sign during the steady emergence of the AR. This reversal is confirmed with the evolution of the photospheric electric currents and with the coronal connectivity as observed in EUV wavelengths with SDO/AIA. During about the three first days of emergence, the AR coronal helicity is positive while later on the field configuration is close to a potential field. As theoretically expected, the magnetic helicity cancelation is associ...

  11. Helicity conservation in topology-changing reconnections: the flow of linking and coiling across scales

    CERN Document Server

    Scheeler, Martin W; Proment, Davide; Kindlmann, Gordon L; Irvine, William T M

    2014-01-01

    The conjecture that knottedness is a fundamental conserved physical quantity has a long history in fluid mechanics. In ideal flows, the conservation of helicity arises because the topology of vortex lines is invariant. In real flows (including superfluids), the large scale topology of vortex tubes changes through 'reconnection' events, so helicity can only be conserved by transferring to different spatial scales. By measuring the behavior of vortex knots and links in viscous fluid experiments and quantum fluid simulations, we identify a mechanism for helicity scale transfer through reconnections, allowing helicity to be conserved even when the topology is not. We also describe a new method for quantifying helicity across scales, and discuss the transfer of helicity to sub-core local twisting where it may ultimately be dissipated. Remarkably, we find that topology-changing reconnections proceed in a manner than tends to conserve helicity, suggesting that it plays a fundamental role in real fluids, from turbule...

  12. The Conservation of Helicity in Hurricane Andrew (1992) and the Formation of the Spiral Rainband

    Institute of Scientific and Technical Information of China (English)

    徐亚梅; 伍荣生

    2003-01-01

    The characteristics of helicity in a hurricane are presented by calculating the MM5 model output in addition to theoretical analysis. It is found that helicity in a hurricane mainly depends on its horizontal component, whose magnitude is about 100 to 1000 times larger than its vertical component. It is also found that helicity is approximately conserved in the hurricane. Since the fluid has the intention to adjust the wind shear to satisfy the conservation of helicity, the horizontal vorticity is even larger than the vertical vorticity, and the three-dimensional vortices slant to the horizontal plane except in the inner eye. There are significant horizontal vortices and inhomogeneous helical flows in the hurricane. The formation of the spiral rainband is discussed by using the law of horizontal helical flows. It is closely related to the horizontal strong vortices and inhomogeneous helical flows.

  13. Self-assembly of double helical nanostructures inside carbon nanotubes.

    Science.gov (United States)

    Lv, Cheng; Xue, Qingzhong; Shan, Meixia; Jing, Nuannuan; Ling, Cuicui; Zhou, Xiaoyan; Jiao, Zhiyong; Xing, Wei; Yan, Zifeng

    2013-05-21

    We use molecular dynamics (MD) simulations to show that a DNA-like double helix of two poly(acetylene) (PA) chains can form inside single-walled carbon nanotubes (SWNTs). The computational results indicate that SWNTs can activate and guide the self-assembly of polymer chains, allowing them to adopt a helical configuration in a SWNT through the combined action of the van der Waals potential well and the π-π stacking interaction between the polymer and the inner surface of SWNTs. Meanwhile both the SWNT size and polymer chain stiffness determine the outcome of the nanostructure. Furthermore, we also found that water clusters encourage the self-assembly of PA helical structures in the tube. This molecular model may lead to a better understanding of the formation of a double helix biological molecule inside SWNTs. Alternatively, it could form the basis of a novel nanoscale material by utilizing the 'empty' spaces of SWNTs.

  14. Helical tractor beam: analytical solution of Rayleigh particle dynamics.

    Science.gov (United States)

    Carretero, Luis; Acebal, Pablo; Garcia, Celia; Blaya, Salvador

    2015-08-10

    We analyze particle dynamics in an optical force field generated by helical tractor beams obtained by the interference of a cylindrical beam with a topological charge and a co-propagating temporally de-phased plane wave. We show that, for standard experimental conditions, it is possible to obtain analytical solutions for the trajectories of particles in such force field by using of some approximations. These solutions show that, in contrast to other tractor beams described before, the intensity becomes a key parameter for the control of particle trajectories. Therefore, by tuning the intensity value the particle can describe helical trajectories upstream and downstream, a circular trajectory in a fixed plane, or a linear displacement in the propagation direction. The approximated analytical solutions show good agreement to the corresponding numerical solutions of the exact dynamical differential equations.

  15. Nucleon Helicity and Transversity Parton Distributions from Lattice QCD

    CERN Document Server

    Chen, Jiunn-Wei; Ji, Xiangdong; Lin, Huey-Wen; Zhang, Jian-Hui

    2016-01-01

    We present the first lattice-QCD calculation of the isovector polarized parton distribution functions (both helicity and transversity) using the large-momentum effective field theory (LaMET) approach for direct Bjorken-$x$ dependence. We first review the detailed steps of the procedure in the unpolarized case, then generalize to the helicity and transversity cases. We also derive a new mass-correction formulation for all three cases. We then compare the effects of each finite-momentum correction using lattice data calculated at $M_\\pi\\approx 310$ MeV. Finally, we discuss the implications of these results for the poorly known antiquark structure and predict the sea-flavor asymmetry in the transversely polarized nucleon.

  16. Glomus tumor of the gastric body:helical CT findings

    Institute of Scientific and Technical Information of China (English)

    HU Xiao-yun; HU Chun-hong; FANG Xiang-ming; ZHANG Tong-hua

    2007-01-01

    @@ Glomus tumors, also known as glomangiomas, are rare and originate in the neuromyoarterial glomus, a normal arteriovenous shunt which is abundantly supplied with nerve fibers and fulfills a temperature-regulating function. The classic location of glomus tumor is the subungual region, but the tumor can occur elsewhere in the skin, soft tissues, nerves, stomach, nasal cavity, and trachea.1 In the gastrointestinal (GI) tract the tumor occurs more often in the stomach than other parts, and typically occurs as a solitary submucosal nodule in the antrum.2 We reported a case of glomus tumor originating from the greater curvature of stomach which was studied with contrast-enhanced helical computed tomography (CT) and described the characteristic helical CT findings of the rare lesion.

  17. Small-x Asymptotics of the Quark Helicity Distribution.

    Science.gov (United States)

    Kovchegov, Yuri V; Pitonyak, Daniel; Sievert, Matthew D

    2017-02-03

    We construct a numerical solution of the small-x evolution equations derived in our recent work [J. High Energy Phys. 01 (2016) 072.JHEPFG1029-847910.1007/JHEP01(2016)072] for the (anti)quark transverse momentum dependent helicity TMDs and parton distribution functions (PDFs) as well as the g_{1} structure function. We focus on the case of large N_{c}, where one finds a closed set of equations. Employing the extracted intercept, we are able to predict directly from theory the behavior of the quark helicity PDFs at small x, which should have important phenomenological consequences. We also give an estimate of how much of the proton's spin carried by the quarks may be at small x and what impact this has on the spin puzzle.

  18. Symmetry analysis of transport properties in helical superconductor junctions

    Science.gov (United States)

    Cheng, Qiang; Zhang, Yinhan; Zhang, Kunhua; Jin, Biao; Zhang, Changlian

    2017-03-01

    We study the discrete symmetries satisfied by helical p-wave superconductors with the d-vectors {{k}x}\\hat{x}+/- {{k}y}\\hat{y} or {{k}y}\\hat{x}+/- {{k}x}\\hat{y} and the transformations brought by symmetry operations to ferromagnet and spin-singlet superconductors, which show intimate associations with the transport properties in heterojunctions, including helical superconductors. In particular, the partial symmetries of the Hamiltonian under spin-rotation and gauge-rotation operations are responsible for the novel invariances of the conductance in tunnel junctions and the new selection rules for the lowest current and peculiar phase diagrams in Josephson junctions, which were reported recently. The symmetries of constructed free energies for Josephson junctions are also analyzed, and are consistent with the results from the Hamiltonian.

  19. The inverse cascade of magnetic helicity in magnetohydrodynamic turbulence

    CERN Document Server

    Müller, Wolf-Christian; Busse, Angela

    2012-01-01

    The nonlinear dynamics of magnetic helicity, $H^M$, which is responsible for large-scale magnetic structure formation in electrically conducting turbulent media is investigated in forced and decaying three-dimensional magnetohydrodynamic turbulence. This is done with the help of high resolution direct numerical simulations and statistical closure theory. The numerically observed spectral scaling of $H^M$ is at variance with earlier work using a statistical closure model [Pouquet et al., J. Fluid Mech. \\textbf{77} 321 (1976)]. By revisiting this theory a universal dynamical balance relation is found that includes effects of kinetic helicity, as well as kinetic and magnetic energy on the inverse cascade of $H^M$ and explains the above-mentioned discrepancy. Considering the result in the context of mean-field dynamo theory suggests a nonlinear modification of the $\\alpha$-dynamo effect important in the context of magnetic field excitation in turbulent plasmas.

  20. Helicity selection rules and noninterference for BSM amplitudes

    Science.gov (United States)

    Azatov, Aleksandr; Contino, Roberto; Machado, Camila S.; Riva, Francesco

    2017-03-01

    Precision studies of scattering processes at colliders provide powerful indirect constraints on new physics. We study the helicity structure of scattering amplitudes in the standard model (SM) and in the context of an effective Lagrangian description of beyond-the-SM (BSM) dynamics. Our analysis reveals a novel set of helicity selection rules according to which, in the majority of 2 →2 scattering processes at high energy, the SM and the leading BSM effects do not interfere. In such situations, the naive expectation that dimension-6 operators represent the leading BSM contribution is compromised, as corrections from dimension-8 operators can become equally (if not more) important well within the validity of the effective field theory approach.

  1. Helical Dipole Magnets for Polarized Protons in RHIC

    Science.gov (United States)

    Syphers, M.; Courant, E.; Fischer, W.; Luccio, A.; Mariam, F.; Peggs, S.; Pilat, F.; Roser, T.; Tepikian, S.; Tsoupas, N.; Willen, E.; Katayama, T.; Hatanaka, K.; Kawaguchi, T.; Okamura, M.; Tominaka, T.; Wu, H.; Ptitsin, V.; Shatunov, Y.

    1997-05-01

    The Brookhaven Relativistic Heavy Ion Collider (RHIC) will be able to support experiments using polarized proton beams. Siberian Snakes are used to maintain polarization in this high energy superconducting collider. To make efficient use of available space while taking advantage of high field superconducting magnets, 4 Tesla helical dipole magnets will be used. These magnets generate a central dipole field in which the field direction rotates through 360^circ about the longitudinal axis over the length of the device. An arrangement of four such magnets can produce the desired change in the spin direction while keeping the proton orbit outside of the ``Snake'' unaltered. Similar magnet arrangements will be used to produce longitudinal polarization at the two major interaction points in RHIC. The basic requirements and layout of these magnets are described, as well as tolerances on field quality and integrated field strengths. First results of tests of prototype helical magnets will be discussed.

  2. Inverse cascade of magnetic helicity in magnetohydrodynamic turbulence.

    Science.gov (United States)

    Müller, Wolf-Christian; Malapaka, Shiva Kumar; Busse, Angela

    2012-01-01

    The nonlinear dynamics of magnetic helicity HM, which is responsible for large-scale magnetic structure formation in electrically conducting turbulent media, is investigated in forced and decaying three-dimensional magnetohydrodynamic turbulence. This is done with the help of high-resolution direct numerical simulations and statistical closure theory. The numerically observed spectral scaling of HM is at variance with earlier work using a statistical closure model [Pouquet et al., J. Fluid Mech. 77, 321 (1976)]. By revisiting this theory, a universal dynamical balance relation is found that includes the effects of kinetic helicity as well as kinetic and magnetic energies on the inverse cascade of HM and explains the above-mentioned discrepancy. Consideration of the result in the context of mean-field dynamo theory suggests a nonlinear modification of the α-dynamo effect, which is important in the context of magnetic-field excitation in turbulent plasmas.

  3. Propulsion by a Helical Flagellum in a Capillary Tube

    CERN Document Server

    Liu, Bin; Powers, Thomas R

    2014-01-01

    We study the microscale propulsion of a rotating helical filament confined by a cylindrical tube, using a boundary-element method for Stokes flow that accounts for helical symmetry. We determine the effect of confinement on swimming speed and power consumption. Except for a small range of tube radii at the tightest confinements, the swimming speed at fixed rotation rate increases monotonically as the confinement becomes tighter. At fixed torque, the swimming speed and power consumption depend only on the geometry of the filament centerline, except at the smallest pitch angles for which the filament thickness plays a role. We find that the `normal' geometry of \\textit{Escherichia coli} flagella is optimized for swimming efficiency, independent of the degree of confinement. The efficiency peaks when the arc length of the helix within a pitch matches the circumference of the cylindrical wall. We also show that a swimming helix in a tube induces a net flow of fluid along the tube.

  4. Equilibrium reconstruction for Single Helical Axis reversed field pinch plasmas

    CERN Document Server

    Martines, Emilio; Momo, Barbara; Terranova, David; Zanca, Paolo; Alfier, Alberto; Bonomo, Federica; Canton, Alessandra; Fassina, Alessandro; Franz, Paolo; Innocente, Paolo

    2011-01-01

    Single Helical Axis (SHAx) configurations are emerging as the natural state for high current reversed field pinch (RFP) plasmas. These states feature the presence of transport barriers in the core plasma. Here we present a method for computing the equilibrium magnetic surfaces for these states in the force-free approximation, which has been implemented in the SHEq code. The method is based on the superposition of a zeroth order axisymmetric equilibrium and of a first order helical perturbation computed according to Newcomb's equation supplemented with edge magnetic field measurements. The mapping of the measured electron temperature profiles, soft X-ray emission and interferometric density measurements on the computed magnetic surfaces demonstrates the quality of the equilibrium reconstruction. The procedure for computing flux surface averages is illustrated, and applied to the evaluation of the thermal conductivity profile. The consistency of the evaluated equilibria with Ohm's law is also discussed.

  5. Equilibrium reconstruction for single helical axis reversed field pinch plasmas

    Energy Technology Data Exchange (ETDEWEB)

    Martines, E; Lorenzini, R; Momo, B; Terranova, D; Zanca, P; Alfier, A; Bonomo, F; Canton, A; Fassina, A; Franz, P; Innocente, P, E-mail: emilio.martines@igi.cnr.it [Consorzio RFX, Associazione Euratom-ENEA sulla Fusione, corso Stati Uniti 4, 35127 Padova (Italy)

    2011-03-15

    Single helical axis configurations are emerging as the natural state for high-current reversed field pinch plasmas. These states feature the presence of transport barriers in the core plasma. Here we present a method for computing the equilibrium magnetic surfaces for these states in the force-free approximation, which has been implemented in the SHEq code. The method is based on the superposition of a zeroth-order axisymmetric equilibrium and of a first-order helical perturbation computed according to Newcomb's equation supplemented with edge magnetic field measurements. The mapping of the measured electron temperature profiles, soft x-ray emission and interferometric density measurements on the computed magnetic surfaces demonstrates the quality of the equilibrium reconstruction. The procedure for computing flux surface averages is illustrated, and applied to the evaluation of the thermal conductivity profile. The consistency of the evaluated equilibria with Ohm's law is also discussed.

  6. Geodesics on Surfaces with Helical Symmetry: Cavatappi Geometry

    CERN Document Server

    Jantzen, Robert T

    2013-01-01

    A 3-parameter family of helical tubular surfaces obtained by screw revolving a circle provides a useful pedagogical example of how to study geodesics on a surface that admits a 1-parameter symmetry group, but is not as simple as a surface of revolution like the torus which it contains as a special case. It serves as a simple example of helically symmetric surfaces which are the generalizations of surfaces of revolution in which an initial plane curve is screw-revolved around an axis in its plane. The physics description of geodesic motion on these surfaces requires a slightly more involved effective potential approach than the torus case due to the nonorthogonal coordinate grid necessary to describe this problem. Amazingly this discussion allows one to very nicely describe the geodesics of the surface of the more complicated ridged cavatappi pasta.

  7. Helical Kink Instability in a Confined Solar Eruption

    CERN Document Server

    Hassanin, Alshaimaa

    2016-01-01

    A model for strongly writhing confined solar eruptions suggests an origin in the helical kink instability of a coronal flux rope which remains stable against the torus instability. This model is tested against the well observed filament eruption on 2002 May 27 in a parametric MHD simulation study which comprises all phases of the event. Good agreement with the essential observed properties is obtained. These include the confinement, terminal height, writhing, distortion, and dissolution of the filament, and the flare loops. The agreement is robust against variations in a representative range of parameter space. Careful comparisons with the observation data constrain the ratio of the external toroidal and poloidal field components to $B_\\mathrm{et}/B_\\mathrm{ep}\\approx1$ and the initial flux rope twist to $\\Phi\\approx4\\pi$. Different from ejective eruptions, two distinct phases of strong magnetic reconnection can occur. First, the erupting flux is cut by reconnection with overlying flux in the helical current ...

  8. Nonmodal analysis of helical and azimuthal magnetorotational instabilities

    CERN Document Server

    Mamatsashvili, G

    2016-01-01

    The helical and the azimuthal magnetorotational instabilities operate in rotating magnetized flows with relatively steep negative or extremely steep positive shear. The corresponding lower and upper Liu limits of the shear, which determine the threshold of modal growth of these instabilities, are continuously connected when some axial electrical current is allowed to pass through the rotating fluid. We investigate the nonmodal dynamics of these instabilities arising from the nonnormality of shear flow in the local approximation, generalizing the results of the modal approach. It is demonstrated that moderate transient/nonmodal amplification of both types of magnetorotational instability occurs within the Liu limits, where the system is stable according to modal analysis. We show that for the helical magnetorotational instability this magnetohydrodynamic behavior is closely connected with the nonmodal growth of the underlying purely hydrodynamic problem.

  9. Fiber optic stress-independent helical torsion sensor.

    Science.gov (United States)

    Fernandes, Luís A; Grenier, Jason R; Aitchison, J Stewart; Herman, Peter R

    2015-02-15

    Femtosecond laser-fabricated waveguides have been formed into helical paths throughout the cladding of single-mode optical fibers to demonstrate a strain-independent fiber torsion sensor. A comparison between a Bragg grating sensor and a Mach-Zehnder based on helical waveguides (HWs) showed a much weaker twist sensitivity of 1.5 pm/(rad/m) for the grating in contrast with a value of 261 pm/(rad/m) for the interferometer. The HW geometry provided an unambiguous determination of the rotational direction of the twist while facilitating a convenient and efficient means for optical coupling into the single-mode core of the fiber. The flexible three-dimensional writing by the femtosecond laser fabrication method enabled the direct inscription of compact and robust optical cladding devices without the need for combining or splicing multiple-fiber segments.

  10. On the modelling of spur and helical gear dynamic behaviour

    CERN Document Server

    Velex, Philippe

    2012-01-01

    This chapter is aimed at introducing the fundamentals of spur and helical gear dynamics. Using three-dimensional lumped models and a thin-slice approach for mesh elasticity, the general equations of motion for single-stage spur or helical gears are presented. Some particular cases including the classic one degree-of-freedom model are examined in order to introduce and illustrate the basic phenomena. The interest of the concept of transmission errors is analysed and a number of practical considerations are deduced. Emphasis is deliberately placed on analytical results which, although approximate, allow a clearer understanding of gear dynamics than that provided by extensive numerical simulations. Some extensions towards continuous models are presented.

  11. Hot electron stabilization of a helically symmetric plasma

    Energy Technology Data Exchange (ETDEWEB)

    Miller, R.L.

    1986-04-01

    Furth and Boozer (private communication; Proceedings of the Advanced Bumpy Torus Concepts Workshop, CONF-830758, Oak Ridge National Laboratory, Oak Ridge, Tennessee, 1983, p. 161) have suggested the use of relativistic electrons to achieve the second stability regime in a helical axis stellarator (Heliac). The hot electrons would only be required until the background plasma reached the second stability regime; the heating power maintaining the hot electron layer would then be turned off. The basic correctness of Furth and Boozer's suggestion is confirmed numerically by a localized stability analysis of helically symmetric plasma equilibria, with anisotropic pressure profiles. Stability is evaluated using the localized interchange criterion in which the hot electrons, because of their large drift speeds, are treated as rigid. A hot electron pressure profile is exhibited; it provides a stable path to the second stability regime for the background plasma.

  12. Magnetic Helicity Reversals in a Cyclic Convective Dynamo

    CERN Document Server

    Miesch, Mark S; Augustson, Kyle C

    2016-01-01

    We investigate the role of magnetic helicity in promoting cyclic magnetic activity in a global, 3D, magnetohydrodynamic (MHD) simulation of a convective dynamo. This simulation is characterized by coherent bands of toroidal field that exist within the convection zone, with opposite polarities in the northern and southern hemispheres. Throughout most of the cycle, the magnetic helicity in these bands is negative in the northern hemisphere and positive in the southern hemisphere. However, during the declining phase of each cycle, this hemispheric rule reverses. We attribute this to a global restructuring of the magnetic topology that is induced by the interaction of the bands across the equator. This band interaction appears to be ultimately responsible for, or at least associated with, the decay and subsequent reversal of both the toroidal bands and the polar fields. We briefly discuss the implications of these results within the context of solar observations, which also show some potential evidence for toroid...

  13. Analysis of Eyring-Powell Fluid in Helical Screw Rheometer

    Directory of Open Access Journals (Sweden)

    A. M. Siddiqui

    2014-01-01

    Full Text Available This paper aims to study the flow of an incompressible, isothermal Eyring-Powell fluid in a helical screw rheometer. The complicated geometry of the helical screw rheometer is simplified by “unwrapping or flattening” the channel, lands, and the outside rotating barrel, assuming the width of the channel is larger as compared to the depth. The developed second order nonlinear differential equations are solved by using Adomian decomposition method. Analytical expressions are obtained for the velocity profiles, shear stresses, shear at wall, force exerted on fluid, volume flow rates, and average velocity. The effect of non-Newtonian parameters, pressure gradients, and flight angle on the velocity profiles is noticed with the help of graphical representation. The observation confirmed the vital role of involved parameters during the extrusion process.

  14. Analysis of Eyring-Powell fluid in helical screw rheometer.

    Science.gov (United States)

    Siddiqui, A M; Haroon, T; Zeb, M

    2014-01-01

    This paper aims to study the flow of an incompressible, isothermal Eyring-Powell fluid in a helical screw rheometer. The complicated geometry of the helical screw rheometer is simplified by "unwrapping or flattening" the channel, lands, and the outside rotating barrel, assuming the width of the channel is larger as compared to the depth. The developed second order nonlinear differential equations are solved by using Adomian decomposition method. Analytical expressions are obtained for the velocity profiles, shear stresses, shear at wall, force exerted on fluid, volume flow rates, and average velocity. The effect of non-Newtonian parameters, pressure gradients, and flight angle on the velocity profiles is noticed with the help of graphical representation. The observation confirmed the vital role of involved parameters during the extrusion process.

  15. On helical behavior of turbulence in the ship wake

    Institute of Scientific and Technical Information of China (English)

    GOLBRAIKH Ephim; EIDELMAN Alexander; SOLOVIEV Alex

    2013-01-01

    Turbulent ship wake conservation at a long distance is among unsolved problems at present.It is well known that far wakes have a vortical structure and slowly expand with distance.As was obtained by Dubrovin et al.,slow expansion of the wake may be related to the distribution of turbulent viscosity in it.In our work we study the effect of helicity in the wake on the behavior of turbulent viscosity.Taking into account the helical nature of the wake,we can clarify the difference between turbulence inside and outside the wake on the one hand and slowing down of its expansion with time on the other hand.

  16. Accurate analysis of arbitrarily-shaped helical groove waveguide

    Institute of Scientific and Technical Information of China (English)

    Liu Hong-Tao; Wei Yan-Yu; Gong Yu-Bin; Yue Ling-Na; Wang Wen-Xiang

    2006-01-01

    This paper presents a theory on accurately analysing the dispersion relation and the interaction impedance of electromagnetic waves propagating through a helical groove waveguide with arbitrary groove shape, in which the complex groove profile is synthesized by a series of rectangular steps. By introducing the influence of high-order evanescent modes on the connection of any two neighbouring steps by an equivalent susceptance under a modified admittance matching condition, the assumption of the neglecting discontinuity capacitance in previously published analysis is avoided, and the accurate dispersion equation is obtained by means of a combination of field-matching method and admittancematching technique. The validity of this theory is proved by comparison between the measurements and the numerical calculations for two kinds of helical groove waveguides with different groove shapes.

  17. Improving heat transfer in stirred tanks cooled by helical coils

    Directory of Open Access Journals (Sweden)

    S.M.C.P. Pedrosa

    2003-06-01

    Full Text Available Stirred Tank Reactors are extensively used in chemical industries. When they are used for highly exothermic reactions, jackets or coils are employed for heat removal. Internal coils can be either helical or axial and they considerably affect the flow inside the reactor because they impose an additional resistance to flow circulation. The aim of this work is to show that the design of vessels cooled by helical coils can be further improved. The design of these reactors follows very much the geometry proposed by Oldshue and Gretton (1954, and some minor modifications in the coil arrangements are likely to improve internal circulation inside these vessels mainly in the region between coils and wall of the vessel. Results show a gain in performance when small alterations are made specially in the shape of the coil arrangement.

  18. Helicity coherence in binary neutron star mergers and nonlinear feedback

    Science.gov (United States)

    Chatelain, Amélie; Volpe, Cristina

    2017-02-01

    Neutrino flavor conversion studies based on astrophysical environments usually implement neutrino mixings, neutrino interactions with matter, and neutrino self-interactions. In anisotropic media, the most general mean-field treatment includes neutrino mass contributions as well, which introduce a coupling between neutrinos and antineutrinos termed helicity or spin coherence. We discuss resonance conditions for helicity coherence for Dirac and Majorana neutrinos. We explore the role of these mean-field contributions on flavor evolution in the context of a binary neutron star merger remnant. We find that resonance conditions can be satisfied in neutron star merger scenarios while adiabaticity is not sufficient for efficient flavor conversion. We analyze our numerical findings by discussing general conditions to have multiple Mikheyev-Smirnov-Wolfenstein-like resonances, in the presence of nonlinear feedback, in astrophysical environments.

  19. Helical flow in RFX-mod tokamak plasmas

    Science.gov (United States)

    Piron, L.; Zaniol, B.; Bonfiglio, D.; Carraro, L.; Kirk, A.; Marrelli, L.; Martin, R.; Piron, C.; Piovesan, P.; Zuin, M.

    2017-05-01

    This work presents the first evidence of helical flow in RFX-mod q(a)  Jardin et al 2015 Phys. Rev. Lett. 115 215001). Among them, the 3D fully non-linear PIXIE3D has been used to calculate synthetic flow measurements, using a 2D flow modelling code. Inputs to the code are the PIXIE3D flow maps, the ion emission profiles as calculated by a 1D collisional radiative impurity transport code (Carraro et al 2000 Plasma Phys. Control. Fusion 42 731) and a synthetic diagnostic with the same geometry installed in RFX-mod. Good agreement between the synthetic and the experimental flow behaviour has been obtained, confirming that the flow oscillations observed with the associated convective cells are a signature of helical flow.

  20. A 3D printed helical antenna with integrated lens

    KAUST Repository

    Farooqui, Muhammad Fahad

    2015-10-26

    A novel antenna configuration comprising a helical antenna with an integrated lens is demonstrated in this work. The antenna is manufactured by a unique combination of 3D printing of plastic material (ABS) and inkjet printing of silver nano-particle based metallic ink. The integration of lens enhances the gain by around 7 dB giving a peak gain of about 16.4 dBi at 9.4 GHz. The helical antenna operates in the end-fire mode and radiates a left-hand circularly polarized (LHCP) pattern. The 3-dB axial ratio (AR) bandwidth of the antenna with lens is 3.2 %. Due to integration of lens and fully printed processing, this antenna configuration offers high gain performance and requires low cost for manufacturing.

  1. The helical flow pump with a hydrodynamic levitation impeller.

    Science.gov (United States)

    Abe, Yusuke; Ishii, Kohei; Isoyama, Takashi; Saito, Itsuro; Inoue, Yusuke; Ono, Toshiya; Nakagawa, Hidemoto; Nakano, Emiko; Fukazawa, Kyoko; Ishihara, Kazuhiko; Fukunaga, Kazuyoshi; Ono, Minoru; Imachi, Kou

    2012-12-01

    The helical flow pump (HFP) is a novel rotary blood pump invented for developing a total artificial heart (TAH). The HFP with a hydrodynamic levitation impeller, which consists of a multi-vane impeller involving rotor magnets, stator coils at the core position, and double helical-volute pump housing, was developed. Between the stator and impeller, a hydrodynamic bearing is formed. Since the helical volutes are formed at both sides of the impeller, blood flows with a helical flow pattern inside the pump. The developed HFP showed maximum output of 19 l/min against 100 mmHg of pressure head and 11 % maximum efficiency. The profile of the H-Q (pressure head vs. flow) curve was similar to that of the undulation pump. Hydrodynamic levitation of the impeller was possible with higher than 1,000 rpm rotation speed. The normalized index of the hemolysis ratio of the HFP to centrifugal pump (BPX-80) was from 2.61 to 8.07 depending on the design of the bearing. The HFP was implanted in two goats with a left ventricular bypass method. After surgery, hemolysis occurred in both goats. The hemolysis ceased on postoperative days 14 and 9, respectively. In the first experiment, no thrombus was found in the pump after 203 days of pumping. In the second experiment, a white thrombus was found in the pump after 23 days of pumping. While further research and development are necessary, we are expecting to develop an excellent TAH with the HFP.

  2. Chiral charge erasure via thermal fluctuations of magnetic helicity

    Energy Technology Data Exchange (ETDEWEB)

    Long, Andrew J. [Kavli Institute for Cosmological Physics, University of Chicago,Chicago, Illinois 60637 (United States); Sabancilar, Eray [Institut de Théorie des Phénoménes Physiques, Ecole Polytechnique Fédérale de Lausanne,CH-1015 Lausanne (Switzerland)

    2016-05-11

    We consider a relativistic plasma of fermions coupled to an Abelian gauge field and carrying a chiral charge asymmetry, which might arise in the early Universe through baryogenesis. It is known that on large length scales, λ≳1/(αμ{sub 5}), the chiral anomaly opens an instability toward the erasure of chiral charge and growth of magnetic helicity. Here the chemical potential μ{sub 5} parametrizes the chiral asymmetry and α is the fine-structure constant. We study the process of chiral charge erasure through the thermal fluctuations of magnetic helicity and contrast with the well-studied phenomenon of Chern-Simons number diffusion. Through the fluctuation-dissipation theorem we estimate the amplitude and time scale of helicity fluctuations on the length scale λ, finding δ H∼λT and τ∼αλ{sup 3}T{sup 2} for a relativistic plasma at temperature T. We argue that the presence of a chiral asymmetry allows the helicity to grow diffusively for a time t∼T{sup 3}/(α{sup 5}μ{sub 5}{sup 4}) until it reaches an equilibrium value H∼μ{sub 5}T{sup 2}/α, and the chiral asymmetry is partially erased. If the chiral asymmetry is small, μ{sub 5}

  3. Inherent helicity in an extended tris-bipyridyl molecular cage

    Energy Technology Data Exchange (ETDEWEB)

    Perkins, D.; Lindoy, L.; Meehan, G.; Turner, P. (University of Sydney)

    2010-11-16

    A new molecular cage incorporating three bipyridyl units has been synthesised by a conventional multi-step procedure as well as, much more efficiently, by a Ni(II) template procedure; an X-ray structure of the nickel complex shows that it adopts an exo configuration of each of the bridgehead nitrogen lone pairs, the central metal ion acts to promote a triple helical twist that extends {approx}22 {angstrom} along the axial length of the molecule.

  4. Stabilization of helical magnetic structures in thin multilayers

    OpenAIRE

    Dzemiantsova, L. V.; Meier, G.; R. Röhlsberger

    2014-01-01

    Based on micromagnetic simulations, we report on a novel helical magnetic structure in a soft magnetic film that is sandwiched between and exchange-coupled to two hard magnetic layers. Confined between antiparallel hard magnetic moments, a helix with a turn of 180$^{\\circ}$ is stable without the presence of an external magnetic field. The magnetic stability is determined by the energy minimization and is a result of an internal field created by exchange interaction and anisotropy. Since the i...

  5. Dispersion of helically corrugated waveguides: Analytical, numerical, and experimental study

    Science.gov (United States)

    Burt, G.; Samsonov, S. V.; Ronald, K.; Denisov, G. G.; Young, A. R.; Bratman, V. L.; Phelps, A. D.; Cross, A. W.; Konoplev, I. V.; He, W.; Thomson, J.; Whyte, C. G.

    2004-10-01

    Helically corrugated waveguides have recently been studied for use in various applications such as interaction regions in gyrotron traveling-wave tubes and gyrotron backward-wave oscillators and as a dispersive medium for passive microwave pulse compression. The paper presents a summary of various methods that can be used for analysis of the wave dispersion of such waveguides. The results obtained from an analytical approach, simulations with the three-dimensional numerical code MAGIC, and cold microwave measurements are analyzed and compared.

  6. Is gadolinium a helical antiferromagnet or a collinear ferromagnet?

    Indian Academy of Sciences (India)

    S N Kaul

    2003-03-01

    Controversial issues concerning the nature of magnetic ordering in gadolinium are briefly reviewed. The recent experimental results are shown to resolve most of such issues in that they rule out the possibility of a helical spin structure in Gd and clearly bring out the role of long-range dipolar interactions in stabilising collinear ferromagnetic order for temperatures between the spin-reorientation temperature and the Curie point.

  7. Ideal, best packing, and energy minimizing double helices

    CERN Document Server

    O'Hara, Jun

    2011-01-01

    We study optimal double helices with straight axes (or the fattest tubes around them) computationally using three kinds of functionals; ideal ones using ropelength, best volume packing ones, and energy minimizers using two one-parameter families of interaction energies between two strands of types $r^{-\\alpha}$ and $\\frac1r\\exp(-kr)$. We compare the numerical results with experimental data of DNA.

  8. Lanthanide bimetallic helicates for in vitro imaging and sensing.

    Science.gov (United States)

    Bünzli, Jean-Claude G; Chauvin, Anne-Sophie; Vandevyver, Caroline D B; Bo, Song; Comby, Steve

    2008-01-01

    As the need for targeting luminescent biolabels increases, for mapping selected analytes, imaging of cells and organs, and tracking in cellulo processes, lanthanide bimetallic helicates are emerging as versatile bioprobes. The wrapping of three ligand strands around two metallic centers by self-assembly affords robust molecular edifices with tunable chemical and photophysical properties. In addition, heterometallic helical chelates can be assembled leading to bioprobes with inherent chiral properties. In this paper, we review the literature demonstrating that neutral [Ln(2)(L(CX))(3)] (x=1-3) helicates represent a viable alternative to existing chelating agents for bio-analyses, while featuring specific enhanced properties. These bimetallic chelates self-assemble in water, and at physiological pH the 2:3 (Ln:L(CX)) complex is by far the dominant species, conditional stability constants logbeta(23) being in the range 23-30. The metal ions are 9-coordinate and lie in sites with slightly distorted D(3) symmetry. Efficient protection from water interaction by the tightly wrapped ligand strands results in sizeable photophysical properties, with quantum yields up to 24% for Eu(III) and 11% for Tb(III), while the luminescence of several other visible and/or near-infrared emitting Ln(III) ions is also sensitized. Noncytotoxicity for all the helicates is established for several living cell lines including HeLa, HaCat, MCF-7, 5D10, and Jurkat. We present new data pertaining to the live cell imaging ability of [Eu(2)(L(C1))(3)] and compare the three systems with x=1-3 with respect to thermodynamic stability, photophysics, cell-permeation ability, and targeting capability for sensing in cellulo processes. Prospects of derivatization for characterizing specific biological interactions are discussed.

  9. Light scattering measurements supporting helical structures for chromatin in solution.

    Science.gov (United States)

    Campbell, A M; Cotter, R I; Pardon, J F

    1978-05-01

    Laser light scattering measurements have been made on a series of polynucleosomes containing from 50 to 150 nucleosomes. Radii of gyration have been determined as a function of polynucleosome length for different ionic strength solutions. The results suggest that at low ionic strength the chromatin adopts a loosely helical structure rather than a random coil. The helix becomes more regular on increasing the ionic strength, the dimension resembling those proposed by Finch and Klug for their solenoid model.

  10. Fast Theoretical Simulation for Design of Helical Flux Compression Generators

    Institute of Scientific and Technical Information of China (English)

    YANG Xian-Jun; DONG Zhi-Wei

    2006-01-01

    A theoretical scheme is derived to achieve the numerical simulation of helical flux compression generator (HFCG) design, by which not only any physical approximation is not made, but also numerical simulation can be fast obtained. In particular, an analytic formula to calculate the inductance is deduced, which is extremely close to the experimental results. The physical process of relevant interesting physical quantity, such as inductance, enlarging current, and magnetic flux density, can be calculated to compare with the experimentally quantitative results.

  11. New Classes of Quasi-helically Symmetric Stellarators

    Energy Technology Data Exchange (ETDEWEB)

    L.P. Ku and A.H. Boozer

    2010-08-09

    New classes of quasi-helically symmetric stellarators with aspect ratios ≤ 10 have been found which are stable to the perturbation of magnetohydrodynamic modes at plasma pressures of practical interest. These configurations have large rotational transform and good quality of flux surfaces. Characteristics of some selected examples are discussed in detail. The feasibility of using modular coils for these stellarators has been investigated. It is shown that practical designs for modular coils can be achieved.

  12. Precise Determination of the Helical Repeat of Tobacco Mosaic Virus

    Energy Technology Data Exchange (ETDEWEB)

    Kendall, A.; McDonald, M.; Stubbs, G.

    2009-06-01

    Tobacco mosaic virus (TMV) is widely used as a distance standard in electron microscopy, fiber diffraction, and other imaging techniques. The dimension used as a reference is the pitch of the viral helix, 23 {angstrom}. This distance, however, has never been measured with any great degree of precision. The helical pitch of TMV has been determined to be 22.92 {+-}0.03 {angstrom} by X-ray fiber diffraction methods using highly collimated synchrotron radiation.

  13. Transmembrane helices in "classical" nuclear reproductive steroid receptors: a perspective.

    Science.gov (United States)

    Morrill, Gene A; Kostellow, Adele B; Gupta, Raj K

    2015-01-01

    Steroid receptors of the nuclear receptor superfamily are proposed to be either: 1) located in the cytosol and moved to the cell nucleus upon activation, 2) tethered to the inside of the plasma membrane, or 3) retained in the nucleus until free steroid hormone enters and activates specific receptors. Using computational methods to analyze peptide receptor topology, we find that the "classical" nuclear receptors for progesterone (PRB/PGR), androgen (ARB/AR) and estrogen (ER1/ESR1) contain two transmembrane helices (TMH) within their ligand-binding domains (LBD).The MEMSAT-SVM algorithm indicates that ARB and ER2 (but not PRB or ER1) contain a pore-lining (channel-forming) region which may merge with other pore-lining regions to form a membrane channel. ER2 lacks a TMH, but contains a single pore-lining region. The MemBrain algorithm predicts that PRB, ARB and ER1 each contain one TMH plus a half TMH separated by 51 amino acids.ER2 contains two half helices. The TM-2 helices of ARB, ER1 and ER2 each contain 9-13 amino acid motifs reported to translocate the receptor to the plasma membrane, as well as cysteine palmitoylation sites. PoreWalker analysis of X-ray crystallographic data identifies a pore or channel within the LBDs of ARB and ER1 and predicts that 70 and 72 residues are pore-lining residues, respectively. The data suggest that (except for ER2), cytosolic receptors become anchored to the plasma membrane following synthesis. Half-helices and pore-lining regions in turn form functional ion channels and/or facilitate passive steroid uptake into the cell. In perspective, steroid-dependent insertion of "classical" receptors containing pore-lining regions into the plasma membrane may regulate permeability to ions such as Ca(2+), Na(+) or K(+), as well as facilitate steroid translocation into the nucleus.

  14. MHD and Reconnection Activity During Local Helicity Injection

    Science.gov (United States)

    Barr, J. L.; Bongard, M. W.; Burke, M. G.; Fonck, R. J.; Reusch, J. A.; Richner, N. J.

    2016-10-01

    Scaling local helicity injection (LHI) to larger devices requires a validated, predictive model of its current drive mechanism. NIMROD simulations predict the injected helical current streams persist in the edge and periodically reconnect to form axisymmetric current rings that travel into the bulk plasma to grow Ip and poloidal flux. In simulation, these events result in discrete bursts of Alfvénic-frequency MHD activity and jumps in Ip of order ΔIp Iinj , in qualitative agreement with large n = 1 activity found in experiment. Fast imaging prior to tokamak formation supports the instability of, and apparent reconnection between, adjacent helical streams. The bursts exhibit toroidal amplitude asymmetries consistent with a kink structure singly line-tied to the injectors. Internal measurements localize this activity to the injector radial location. Pairwise correlations of poloidal Mirnov coil amplitude and phase match expectations of an edge-localized current stream carrying Iinj. Prior to tokamak formation, reconnection from both adjacent helical windings and co-injected current streams are shown to strongly heat impurity ions. After tokamak formation, strong anomalous ion heating in the plasma edge is attributed to continuous reconnection between colinear streams. The n = 1 bursts occur less frequently as Ip rises, likely caused by increased stream stability as Bv rises and qedge drops. This evidence supports the general NIMROD model of LHI, confirms the persistence and role of the edge current streams, and motivates experiments at higher Iinj and BT. Supported by US DOE Grants DE-FG02-96ER54375, DE-SC0006928.

  15. Chiral charge erasure via thermal fluctuations of magnetic helicity

    Science.gov (United States)

    Long, Andrew J.; Sabancilar, Eray

    2016-05-01

    We consider a relativistic plasma of fermions coupled to an Abelian gauge field and carrying a chiral charge asymmetry, which might arise in the early Universe through baryogenesis. It is known that on large length scales, λ gtrsim 1/(αμ5), the chiral anomaly opens an instability toward the erasure of chiral charge and growth of magnetic helicity. Here the chemical potential μ5 parametrizes the chiral asymmetry and α is the fine-structure constant. We study the process of chiral charge erasure through the thermal fluctuations of magnetic helicity and contrast with the well-studied phenomenon of Chern-Simons number diffusion. Through the fluctuation-dissipation theorem we estimate the amplitude and time scale of helicity fluctuations on the length scale λ, finding δScript H ~ λT and τ ~ αλ3T2 for a relativistic plasma at temperature T. We argue that the presence of a chiral asymmetry allows the helicity to grow diffusively for a time t ~ T3/(α5μ54) until it reaches an equilibrium value Script H ~ μ5T2/α, and the chiral asymmetry is partially erased. If the chiral asymmetry is small, μ5 < T/α, this avenue for chiral charge erasure is found to be slower than the chiral magnetic effect for which t ~ T/(α3μ52). This mechanism for chiral charge erasure can be important for the hypercharge sector of the Standard Model as well as extensions including U(1) gauge interactions, such as asymmetric dark matter models.

  16. Studi Eksperimental Perancangan Turbin Air Terapung Tipe Helical Blade

    OpenAIRE

    Muhammad, Andi Haris; Had, Abdul Latief; Terti, Wayan

    2016-01-01

    This research describes the design of floating helical water turbine for electric power generation in free flow and low head water operation. The design involves the use of strips attached to the blades of turbine. The efficiency of turbine (??) investigation was carried out using empirical formulas. The rotation of turbine (n) of the calculation with variation strips angles (450, 900, and 1350) were obtained through captive model tests carried out in towing tank. The result indicated the eff...

  17. The worldline approach to helicity flip in plane waves

    CERN Document Server

    Ilderton, Anton

    2016-01-01

    We apply worldline methods to the study of vacuum polarisation effects in plane wave backgrounds, in both scalar and spinor QED. We calculate helicity-flip probabilities to one loop order and treated exactly in the background field, and provide a toolkit of methods for use in investigations of higher-order processes. We also discuss the connections between the worldline, S-matrix, and lightfront approaches to vacuum polarisation effects.

  18. Weak Boson Production Amplitude Zeros; Equalities of the Helicity Amplitudes

    CERN Document Server

    Mamedov, F

    2002-01-01

    We investigate the radiation amplitude zeros exhibited by many Standard Model amplitudes for triple weak gauge boson production processes. We show that $WZ\\gamma$ production amplitudes have especially rich structure in terms of zeros, these amplitudes have zeros originating from several different sources. It is also shown that TYPE I current null zone is the special case of the equality of the specific helicity amplitudes.

  19. Rashba Torque Driven Domain Wall Motion in Magnetic Helices.

    Science.gov (United States)

    Pylypovskyi, Oleksandr V; Sheka, Denis D; Kravchuk, Volodymyr P; Yershov, Kostiantyn V; Makarov, Denys; Gaididei, Yuri

    2016-01-01

    Manipulation of the domain wall propagation in magnetic wires is a key practical task for a number of devices including racetrack memory and magnetic logic. Recently, curvilinear effects emerged as an efficient mean to impact substantially the statics and dynamics of magnetic textures. Here, we demonstrate that the curvilinear form of the exchange interaction of a magnetic helix results in an effective anisotropy term and Dzyaloshinskii-Moriya interaction with a complete set of Lifshitz invariants for a one-dimensional system. In contrast to their planar counterparts, the geometrically induced modifications of the static magnetic texture of the domain walls in magnetic helices offer unconventional means to control the wall dynamics relying on spin-orbit Rashba torque. The chiral symmetry breaking due to the Dzyaloshinskii-Moriya interaction leads to the opposite directions of the domain wall motion in left- or right-handed helices. Furthermore, for the magnetic helices, the emergent effective anisotropy term and Dzyaloshinskii-Moriya interaction can be attributed to the clear geometrical parameters like curvature and torsion offering intuitive understanding of the complex curvilinear effects in magnetism.

  20. Evidence of Magnetic Helicity in Emerging Flux and Associated Flare

    CERN Document Server

    Chandra, R; Aulanier, G; Malherbe, J M

    2009-01-01

    The aim of this paper is to look at the magnetic helicity structure of an emerging active region and show that both emergence and flaring signatures are consistent with a same sign for magnetic helicity. We present a multi-wavelength analysis of an M1.6 flare occurring in the active region NOAA 10365 on 27 May, 2003, in which a large new bipole emerges in a decaying active region. The diverging flow pattern and the "tongue" shape of the magnetic field in the photosphere with elongated polarities are highly suggestive of the emergence of a twisted flux tube. The orientation of these tongues indicates the emergence of a flux tube with a right hand twist, i.e. positive magnetic helicity. The flare signatures in the chromosphere are ribbons observed in H-alpha by the MSDP spectrograph in the Meudon solar tower and in 1600 A by TRACE. These ribbons have a `J' shape and are shifted along the inversion line. The pattern of these ribbons suggests that the flare was triggered by magnetic reconnection at coronal height...