WorldWideScience

Sample records for stabilized anil-type nematic

  1. Stability of Disclinations in Nematic Liquid Crystals

    International Nuclear Information System (INIS)

    Wang Yusheng; Yang Guohong; Tian Lijun; Duan Yishi

    2006-01-01

    In the light of φ-mapping method and topological current theory, the stability of disclinations around a spherical particle in nematic liquid crystals is studied. We consider two different defect structures around a spherical particle: disclination ring and point defect at the north or south pole of the particle. We calculate the free energy of these different defects in the elastic theory. It is pointed out that the total Frank free energy density can be divided into two parts. One is the distorted energy density of director field around the disclinations. The other is the free energy density of disclinations themselves, which is shown to be concentrated at the defect and to be topologically quantized in the unit of (k-k 24 )π/2. It is shown that in the presence of saddle-splay elasticity a dipole (radial and hyperbolic hedgehog) configuration that accompanies a particle with strong homeotropic anchoring takes the structure of a small disclination ring, not a point defect.

  2. Curvature-driven stability of defects in nematic textures over spherical disks

    Science.gov (United States)

    Duan, Xiuqing; Yao, Zhenwei

    2017-06-01

    Stabilizing defects in liquid-crystal systems is crucial for many physical processes and applications ranging from functionalizing liquid-crystal textures to recently reported command of chaotic behaviors of active matters. In this work, we perform analytical calculations to study the curvature-driven stability mechanism of defects based on the isotropic nematic disk model that is free of any topological constraint. We show that in a growing spherical disk covering a sphere the accumulation of curvature effect can prevent typical +1 and +1/2 defects from forming boojum textures where the defects are repelled to the boundary of the disk. Our calculations reveal that the movement of the equilibrium position of the +1 defect from the boundary to the center of the spherical disk occurs in a very narrow window of the disk area, exhibiting the first-order phase-transition-like behavior. For the pair of +1/2 defects by splitting a +1 defect, we find the curvature-driven alternating repulsive and attractive interactions between the two defects. With the growth of the spherical disk these two defects tend to approach and finally recombine towards a +1 defect texture. The sensitive response of defects to curvature and the curvature-driven stability mechanism demonstrated in this work in nematic disk systems may have implications towards versatile control and engineering of liquid-crystal textures in various applications.

  3. Shape control of surface-stabilized disclination loops in nematic liquid crystals

    Science.gov (United States)

    Sunami, Kanta; Imamura, Koki; Ouchi, Tomohiro; Yoshida, Hiroyuki; Ozaki, Masanori

    2018-02-01

    Recent studies on topological defects in conventional and active nematic liquid crystals have revealed their potential as sources of advanced functionality whereby the collective behavior of the constituent molecules or cells is controlled. On the other hand, the fact that they have high energies and are metastable makes their shape control a nontrivial issue. Here, we demonstrate stabilization of arbitrary-shaped closed disclination loops with 1/2 strength floating in the bulk by designing the twist angle distribution in a liquid crystal cell. Continuous variation of the twist angle from below to above |π /2 | allows us to unambiguously position reverse twist disclinations at will. We also analyze the elastic free energy and uncover the relationship between the twist angle pattern and shrink rate of the surface-stabilized disclination loop.

  4. Electrolyte effects on the stability of nematic and lamellar lyotropic liquid crystal phases: colligative and ion-specific aspects.

    Science.gov (United States)

    Dawin, Ute C; Lagerwall, Jan P F; Giesselmann, Frank

    2009-08-20

    We investigated the electrolyte effects on the stability of nematic and lamellar lyotropic liquid crystalline (LLC) phases formed by the simple anionic surfactant cesium pentadecafluorooctanoate (CsPFO) in water. To the lyotropic guest phase, at the constant CsPFO-mass fraction of 0.55, the series of electrolytes LiCl, NaCl, KCl, CsCl, CsI, and Cs(2)SO(4), respectively, was added at concentrations ranging from 0.5 to 2.5 mol %. With increasing electrolyte concentration two substantially different effects were observed. At low concentrations all added electrolytes caused an increase of the thermal stability of the LLC phases, favoring the lamellar phase over the nematic phase. This behavior is, at least qualitatively, understood within the packing parameter model. The extent of the stabilization clearly depends on the chemical nature of the added cation. For a given cation, however, the effect is colligative, i.e., independent of the chemical nature of the added anion. At higher salt concentrations a salting-out-like phase separation was induced. This effect is clearly ion-specific as the salting-out concentration varied for each cation following the order of the Hofmeister series for cations.

  5. Pattern Formation in Active Nematics

    Science.gov (United States)

    Mishra, Prashant

    This thesis presents analytical and numerical studies of the nonequilibrium dynamics of active nematic liquid crystals. Active nematics are a new class of liquid crystals consisting of elongated rod-like units that convert energy into motion and spontaneously organize in large-scale structures with orientational order and self-sustained flows. Examples include suspensions of cytoskeletal filaments and associated motor proteins, monolayers of epithelial cells plated on a substrate, and bacteria swimming in a nematic liquid crystal. In these systems activity drives the continuous generation and annihilation of topological defects and streaming flows, resulting in spatio-temporal chaotic dynamics akin to fluid turbulence, but that occurs in a regime of flow of vanishing Reynolds number, where inertia is negligible. Quantifying the origin of this nonequilibrium dynamics has implications for understanding phenomena ranging from bacterial swarming to cytoplasmic flows in living cells. After a brief review (Chapter 2) of the properties of equilibrium or passive nematic liquid crystals, in Chapter 3 we discuss how the hydrodynamic equations of nematic liquid crystals can be modified to account for the effect of activity. We then use these equations of active nemato-hydrodynamics to characterize analytically the nonequilibrium steady states of the system and their stability. We supplement the analytical work with numerical solution of the full nonlinear equations for the active suspension and construct a phase diagram that identifies the various emergent patterns as a function of activity and nematic stiffness. In Chapter 4 we compare results obtained with two distinct hydrodynamic models that have been employed in previous studies. In both models we find that the chaotic spatio-temporal dynamics in the regime of fully developed active turbulence is controlled by a single active scale determined by the balance of active and elastic stresses. This work provides a unified

  6. Preparation and thermo-optical characteristics of a smart polymer-stabilized liquid crystal thin film based on smectic A–chiral nematic phase transition

    International Nuclear Information System (INIS)

    Sun, Jian; Wang, Huihui; Cao, Hui; Ding, Hangjun; Yang, Zhou; Yang, Huai; Wang, Ling; Xie, Hui; Luo, Xueyao; Xiao, Jiumei

    2014-01-01

    A smart polymer stabilized liquid crystal (PSLC) thin film with temperature-controllable light transmittance was prepared based on a smectic-A (SmA)–chiral nematic (N*) phase transition, and then the effect of the composition and the preparation condition of the PSLC film on its thermo-optical (T-O) characteristics has been investigated in detail. Within the temperature range of the SmA phase, the PSLC shows a strong opaque state due to the focal conic alignment of liquid crystal (LC) molecules, while the film exhibits a transparent state result from the parallel alignment of N* phase LC molecules at a higher temperature. Importantly, the PSLC films with different temperature of phase transition and contrast ratio can be prepared by changing the composition of photo-polymerizable monomer/LC/chiral dopant. According to the competition between the polymerization of the curable monomers and the diffusion of LC molecules, the ultraviolet (UV) curing surrounding temperature and the intensity of UV irradiation play a critical role in tuning the size of the polymer network meshes, which in turn influence the contrast ratio and the switching speed of the film. Our observations are expected to pave the way for preparing smart PSLC thin films for applications in areas of smart windows, thermo-detectors and other information recording devices. (paper)

  7. In Silico Measurement of Elastic Moduli of Nematic Liquid Crystals

    Science.gov (United States)

    Sidky, Hythem; de Pablo, Juan J.; Whitmer, Jonathan K.

    2018-03-01

    Experiments on confined droplets of the nematic liquid crystal 5CB have questioned long-established bounds imposed on the elastic free energy of nematic systems. This elasticity, which derives from molecular alignment within nematic systems, is quantified through a set of moduli which can be difficult to measure experimentally and, in some cases, can only be probed indirectly. This is particularly true of the surfacelike saddle-splay elastic term, for which the available experimental data indicate values on the cusp of stability, often with large uncertainties. Here, we demonstrate that all nematic elastic moduli, including the saddle-splay elastic constant k24, may be calculated directly from atomistic molecular simulations. Importantly, results obtained through in silico measurements of the 5CB elastic properties demonstrate unambiguously that saddle-splay elasticity alone is unable to describe the observed confined morphologies.

  8. The Nematic Phases of Bent-Core Liquid Crystals

    Science.gov (United States)

    Gleeson, Helen F; Kaur, Sarabjot; Görtz, Verena; Belaissaoui, Abdel; Cowling, Stephen; Goodby, John W

    2014-01-01

    Over the last ten years, the nematic phases of liquid crystals formed from bent-core structures have provoked considerable research because of their remarkable properties. This Minireview summarises some recent measurements of the physical properties of these systems, as well as describing some new data. We concentrate on oxadiazole-based materials as exemplars of this class of nematogens, but also describe some other bent-core systems. The influence of molecular structure on the stability of the nematic phase is described, together with progress in reducing the nematic transition temperatures by modifications to the molecular structure. The physical properties of bent-core nematic materials have proven difficult to study, but patterns are emerging regarding their optical and dielectric properties. Recent breakthroughs in understanding the elastic and flexoelectric behaviour are summarised. Finally, some exemplars of unusual electric field behaviour are described. PMID:24700653

  9. Fractal nematic colloids

    Science.gov (United States)

    Hashemi, S. M.; Jagodič, U.; Mozaffari, M. R.; Ejtehadi, M. R.; Muševič, I.; Ravnik, M.

    2017-01-01

    Fractals are remarkable examples of self-similarity where a structure or dynamic pattern is repeated over multiple spatial or time scales. However, little is known about how fractal stimuli such as fractal surfaces interact with their local environment if it exhibits order. Here we show geometry-induced formation of fractal defect states in Koch nematic colloids, exhibiting fractal self-similarity better than 90% over three orders of magnitude in the length scales, from micrometers to nanometres. We produce polymer Koch-shaped hollow colloidal prisms of three successive fractal iterations by direct laser writing, and characterize their coupling with the nematic by polarization microscopy and numerical modelling. Explicit generation of topological defect pairs is found, with the number of defects following exponential-law dependence and reaching few 100 already at fractal iteration four. This work demonstrates a route for generation of fractal topological defect states in responsive soft matter. PMID:28117325

  10. Depletion-induced biaxial nematic states of boardlike particles

    International Nuclear Information System (INIS)

    Belli, S; Van Roij, R; Dijkstra, M

    2012-01-01

    With the aim of investigating the stability conditions of biaxial nematic liquid crystals, we study the effect of adding a non-adsorbing ideal depletant on the phase behavior of colloidal hard boardlike particles. We take into account the presence of the depletant by introducing an effective depletion attraction between a pair of boardlike particles. At fixed depletant fugacity, the stable liquid-crystal phase is determined through a mean-field theory with restricted orientations. Interestingly, we predict that for slightly elongated boardlike particles a critical depletant density exists, where the system undergoes a direct transition from an isotropic liquid to a biaxial nematic phase. As a consequence, by tuning the depletant density, an easy experimental control parameter, one can stabilize states of high biaxial nematic order even when these states are unstable for pure systems of boardlike particles. (paper)

  11. Nematic Liquid-Crystal Colloids.

    Science.gov (United States)

    Muševič, Igor

    2017-12-25

    This article provides a concise review of a new state of colloidal matter called nematic liquid-crystal colloids. These colloids are obtained by dispersing microparticles of different shapes in a nematic liquid crystal that acts as a solvent for the dispersed particles. The microparticles induce a local deformation of the liquid crystal, which then generates topological defects and long-range forces between the neighboring particles. The colloidal forces in nematic colloids are much stronger than the forces in ordinary colloids in isotropic solvents, exceeding thousands of k B T per micrometer-sized particle. Of special interest are the topological defects in nematic colloids, which appear in many fascinating forms, such as singular points, closed loops, multitudes of interlinked and knotted loops or soliton-like structures. The richness of the topological phenomena and the possibility to design and control topological defects with laser tweezers make colloids in nematic liquid crystals an excellent playground for testing the basic theorems of topology.

  12. Density functional theory for chiral nematic liquid crystals

    NARCIS (Netherlands)

    Belli, S.; Dussi, S.|info:eu-repo/dai/nl/372628885; Dijkstra, Marjolein|info:eu-repo/dai/nl/123538807; van Roij, R.|info:eu-repo/dai/nl/152978984

    2014-01-01

    Even though chiral nematic phases were the first liquid crystals experimentally observed more than a century ago, the origin of the thermodynamic stability of cholesteric states is still unclear. In this Rapid Communication we address the problem by means of a density functional theory for the

  13. Depletion-induced biaxial nematic states of boardlike particles

    NARCIS (Netherlands)

    Belli, S; Dijkstra, M.; van Roij, R.H.H.G.

    2012-01-01

    With the aim of investigating the stability conditions of biaxial nematic liquid crystals, we study the effect of adding a non-adsorbing ideal depletant on the phase behavior of colloidal hard boardlike particles. We take into account the presence of the depletant by introducing an effective

  14. Colloidal interactions in two-dimensional nematic emulsions

    Indian Academy of Sciences (India)

    These were reported to lead to a variety of novel self-organized colloidal structures, such as linear chains [5,6], periodic lattices [7], anisotropic clusters [3], and cellular structures [8] that are stabilized, in general, by topological defects. More recently, two-dimensional (2D) inverted nematic emulsions were also stud- ied and ...

  15. Colloidal discs in nematic liquid crystals

    International Nuclear Information System (INIS)

    Silvestre, N M; Patricio, P; Tasinkevych, M; Andrienko, D; Gama, M M Telo da

    2004-01-01

    We use adaptive finite elements methods to investigate a variety of structures in inverted nematic emulsions numerically. In particular, we study dipolar and quadrupolar interactions between colloidal discs in two-dimensional nematics. The behaviour of colloidal particles near a substrate and at a nematic-isotropic interface are also considered

  16. Nematic Liquid-Crystal Colloids

    Science.gov (United States)

    Muševič, Igor

    2017-01-01

    This article provides a concise review of a new state of colloidal matter called nematic liquid-crystal colloids. These colloids are obtained by dispersing microparticles of different shapes in a nematic liquid crystal that acts as a solvent for the dispersed particles. The microparticles induce a local deformation of the liquid crystal, which then generates topological defects and long-range forces between the neighboring particles. The colloidal forces in nematic colloids are much stronger than the forces in ordinary colloids in isotropic solvents, exceeding thousands of kBT per micrometer-sized particle. Of special interest are the topological defects in nematic colloids, which appear in many fascinating forms, such as singular points, closed loops, multitudes of interlinked and knotted loops or soliton-like structures. The richness of the topological phenomena and the possibility to design and control topological defects with laser tweezers make colloids in nematic liquid crystals an excellent playground for testing the basic theorems of topology. PMID:29295574

  17. Nematic Liquid-Crystal Colloids

    Directory of Open Access Journals (Sweden)

    Igor Muševič

    2017-12-01

    Full Text Available This article provides a concise review of a new state of colloidal matter called nematic liquid-crystal colloids. These colloids are obtained by dispersing microparticles of different shapes in a nematic liquid crystal that acts as a solvent for the dispersed particles. The microparticles induce a local deformation of the liquid crystal, which then generates topological defects and long-range forces between the neighboring particles. The colloidal forces in nematic colloids are much stronger than the forces in ordinary colloids in isotropic solvents, exceeding thousands of kBT per micrometer-sized particle. Of special interest are the topological defects in nematic colloids, which appear in many fascinating forms, such as singular points, closed loops, multitudes of interlinked and knotted loops or soliton-like structures. The richness of the topological phenomena and the possibility to design and control topological defects with laser tweezers make colloids in nematic liquid crystals an excellent playground for testing the basic theorems of topology.

  18. Solid microparticles in nematic liquid crystals

    Science.gov (United States)

    Muševič, Igor

    A brief historic overview of colloidal experiments in the 1990's is given in the introduction. These experiments have later inspired research on nematic colloids, after the technique of laser tweezers manipulation of particles was introduced to this field. Basic topological properties of colloidal inclusions in the nematic liquid crystals are discussed and the nematic-mediated forces between dipolar and quadrupolar colloidal particles in bulk nematic are explained. Structural and topological properties of 2D and 3D colloidal crystals and superstructures made of colloidal particles of different size and symmetry in bulk nematic liquid crystal are described. Laser-tweezer manipulation and rewiring of topological defect loops around colloidal particles is introduced. This results in the colloidal entanglement, as well as knotting and linking of defect loops of the order parameter field. Shape and size-dependent colloidal interactions in the nematic liquid crystals are reviewed. The chapter concludes with the discussion of bulk chiral nematic and blue phase colloids.

  19. Transitions through critical temperatures in nematic liquid crystals

    KAUST Repository

    Majumdar, Apala

    2013-08-06

    We obtain estimates for critical nematic liquid crystal (LC) temperatures under the action of a slowly varying temperature-dependent control variable. We show that biaxiality has a negligible effect within our model and that these delay estimates are well described by a purely uniaxial model. The static theory predicts two critical temperatures: the supercooling temperature below which the isotropic phase loses stability and the superheating temperature above which the ordered nematic states do not exist. In contrast to the static problem, the isotropic phase exhibits a memory effect below the supercooling temperature in the dynamic framework. This delayed loss of stability is independent of the rate of change of temperature and depends purely on the initial value of the temperature. We also show how our results can be used to improve estimates for LC material constants. © 2013 American Physical Society.

  20. Modulational instability of nematic phase

    Indian Academy of Sciences (India)

    2014-02-08

    Feb 8, 2014 ... We numerically observe the effect of homogeneous magnetic field on the modulation- ally stable case ... irrespective of the magnetic field effect the uniaxial and biaxial nematic phases show modulational instability. ..... [13] J Kronjager, C Becker, P S Panahi, K Bongs and K Sengstock, Phys. Rev. Lett. 105 ...

  1. Two-Dimensional Spatial Solitons in Nematic Liquid Crystals

    International Nuclear Information System (INIS)

    Zhong Weiping; Xie Ruihua; Goong Chen; Belic, Milivoj; Yang Zhengping

    2009-01-01

    We study the propagation of spatial solitons in nematic liquid crystals, using the self-similar method. Analytical solutions in the form of self-similar solitons are obtained exactly. We confirm the stability of these solutions by direct numerical simulation, and find that the stable spatial solitons can exist in various forms, such as Gaussian solitons, radially symmetric solitons, multipole solitons, and soliton vortices.

  2. Solitary waves in nematic liquid crystals

    Science.gov (United States)

    Panayotaros, Panayotis; Marchant, T. R.

    2014-02-01

    We study soliton solutions of a two-dimensional nonlocal NLS equation of Hartree-type with a Bessel potential kernel. The equation models laser propagation in nematic liquid crystals. Motivated by the experimental observation of spatially localized beams, see Conti et al. (2003), we show existence, stability, regularity, and radial symmetry of energy minimizing soliton solutions in R2. We also give theoretical lower bounds for the L2-norm (power) of these solitons, and show that small L2-norm initial conditions lead to decaying solutions. We also present numerical computations of radial soliton solutions. These solutions exhibit the properties expected by the infinite plane theory, although we also see some finite (computational) domain effects, especially solutions with arbitrarily small power.

  3. Flexoelectricity in nematic domain walls.

    Science.gov (United States)

    Elston, Steve J

    2008-07-01

    Flexoelectric effects are studied in the domain walls of a nematic liquid crystal device showing the Freedericksz transition. Walls parallel to the alignment direction have a strong twist distortion and an electro-optic effect dominated by e1-e3 is seen. Walls perpendicular to the alignment direction have a strong splay-bend distortion and an electro-optic effect dominated by e1+e3 is seen. This allows the study of both flexoelectric coefficient combinations in a single device.

  4. Discotic nematic liquid crystals: science and technology.

    Science.gov (United States)

    Bisoyi, Hari Krishna; Kumar, Sandeep

    2010-01-01

    The nematic phase of discotic liquid crystals, although rarely observed, has made very significant progress over the past three decades since their discovery. It has made its way from a mere scientific curiosity to application in commodities. The negative birefringence films formed by polymerized nematic discotic liquid crystals have been commercialized as compensation films to enlarge the viewing angle and enhance the contrast ratio of commonly used twisted nematic liquid-crystal displays. High strength and high performance carbon fibers for industrial applications have been obtained from the carbonaceous mesophase and a liquid-crystal display device with wide and symmetrical viewing angle has been demonstrated by using discotic nematic liquid crystals. Discotic films with patterned colours have been obtained from cholesteric lyo-mesophases of discotic liquid crystals. Various molecular architectures have been designed and synthesized to exhibit the discotic nematic phase over a wide range of temperature. This critical review focuses on the synthesis and physical properties of these fascinating materials. It deals with the structure of various nematic phases, different discotic cores exhibiting the nematic phase, novel designing and transition temperature engineering principles, alignment and physical properties, and finally the application of discotic nematic LCs as the active switching component and as optical compensation films for widening the viewing angle and contrast ratio of liquid-crystal display devices (98 references).

  5. Report on twisted nematic and supertwisted nematic device characterization program

    Science.gov (United States)

    1995-01-01

    In this study we measured the optical characteristics of normally white twisted nematic (NWTN) and super twisted nematic (STN ) cells. Though no dynamic computer model was available, the static observations were compared with computer simulated behavior. The measurements were taken as a function of both viewing angle and applied voltage and included in the static case not only luminance but also contrast ratio and chromaticity . We employed the computer model Twist Cell Optics, developed at Kent State in conjunction with this study, and whose optical modeling foundation, Iike the ViDEOS program, is the 4 x 4 matrix method of Berreman. In order to resolve discrepancies between the experimental and modeled data the optical parameters of the individual cell components, where not known, were determined using refractometry, profilometry, and various forms of ellipsometry. The resulting agreement between experiment and model is quite good due primarily to a better understanding of the structure and optics of dichroic sheet polarizers. A description of the model and test cells employed are given in section 2. Section 3 contains the experimental data gathered and section 4 gives examples of the fit between model and experiment. Also included with this report are a pair of papers which resulted from the research and which detail the polarizer properties and some of the cell characterization methods.

  6. 3D structure of nematic and columnar phases of hard colloidal platelets

    Science.gov (United States)

    Reinink, A. B. G. M. Leferink op; Meijer, J. M.; Kleshchanok, D.; Byelov, D. V.; Vroege, G. J.; Petukhov, A. V.; Lekkerkerker, H. N. W.

    2011-05-01

    We present small angle x-ray scattering data of single-domain nematic and columnar liquid crystal phases in suspensions of sterically stabilized gibbsite platelets. The measurements are performed with different sample orientations to obtain information about the three-dimensional structure of the liquid crystalline phases. With the x-ray beam incident along the director of the nematic phase a strong correlation peak is observed corresponding to the side-to-side interparticle correlations, which suggests a columnar nematic structure. Upon sample rotation this side-to-side correlation peak of the nematic shifts to higher Q-values, suggesting the presence of strong fluctuations of small stacks of particles with different orientations, while the overall particle orientation is constant. In the hexagonal columnar phase, clear Bragg intercolumnar reflections are observed. Upon rotation, the Q-value of these reflections remains constant while their intensity monotonically decreases upon rotation. This indicates that the column orientation fluctuates together with the particle director in the columnar phase. This difference between the behaviour of the columnar and the nematic reflections upon sample rotation is used to assign the liquid crystal phase of a suspension consisting of larger platelets, where identification can be ambiguous due to resolution limitations.

  7. 3D structure of nematic and columnar phases of hard colloidal platelets

    Energy Technology Data Exchange (ETDEWEB)

    Op Reinink, A B G M Leferink; Meijer, J M; Kleshchanok, D; Byelov, D V; Vroege, G J; Petukhov, A V; Lekkerkerker, H N W, E-mail: A.B.G.M.LeferinkopReinink@uu.nl [Van' t Hoff Laboratory for Physical and Colloid Chemistry, Utrecht University, PO Box 80.051, 3508 TB Utrecht (Netherlands)

    2011-05-18

    We present small angle x-ray scattering data of single-domain nematic and columnar liquid crystal phases in suspensions of sterically stabilized gibbsite platelets. The measurements are performed with different sample orientations to obtain information about the three-dimensional structure of the liquid crystalline phases. With the x-ray beam incident along the director of the nematic phase a strong correlation peak is observed corresponding to the side-to-side interparticle correlations, which suggests a columnar nematic structure. Upon sample rotation this side-to-side correlation peak of the nematic shifts to higher Q-values, suggesting the presence of strong fluctuations of small stacks of particles with different orientations, while the overall particle orientation is constant. In the hexagonal columnar phase, clear Bragg intercolumnar reflections are observed. Upon rotation, the Q-value of these reflections remains constant while their intensity monotonically decreases upon rotation. This indicates that the column orientation fluctuates together with the particle director in the columnar phase. This difference between the behaviour of the columnar and the nematic reflections upon sample rotation is used to assign the liquid crystal phase of a suspension consisting of larger platelets, where identification can be ambiguous due to resolution limitations.

  8. Geometry of Thin Nematic Elastomer Sheets

    Science.gov (United States)

    Aharoni, Hillel; Sharon, Eran; Kupferman, Raz

    2014-12-01

    A thin sheet of nematic elastomer attains 3D configurations depending on the nematic director field upon heating. In this Letter, we describe the intrinsic geometry of such a sheet and derive an expression for the metric induced by general nematic director fields. Furthermore, we investigate the reverse problem of constructing a director field that induces a specified 2D geometry. We provide an explicit recipe for how to construct any surface of revolution using this method. Finally, we show that by inscribing a director field gradient across the sheet's thickness, one can obtain a nontrivial hyperbolic reference curvature tensor, which together with the prescription of a reference metric allows dictation of actual configurations for a thin sheet of nematic elastomer.

  9. Dielectric properties of liquid crystalline dimer mixtures exhibiting the nematic and twist-bend nematic phases.

    Science.gov (United States)

    Trbojevic, Nina; Read, Daniel J; Nagaraj, Mamatha

    2017-11-01

    A detailed investigation of the thermal and dielectric properties of a series of binary mixtures exhibiting the nematic (N) and twist-bend nematic (N_{TB}) liquid crystal phases is presented. The mixtures consist of an achiral, dimeric liquid crystal CB7CB, which forms the nematic and twist-bend nematic phases, and a calamitic liquid crystal 5CB, which shows the nematic phase. As the concentration of the calamitic liquid crystal is increased, the transition temperatures decrease linearly, and the width of the nematic phase increases. The enthalpies of phase transitions obtained from DSC measurements show that on increasing the concentration of 5CB in the binary mixtures, the enthalpy associated with the N-N_{TB} phase transitions reduces considerably compared to a clear first-order N-N_{TB} transition in pure CB7CB. The real and imaginary parts of the dielectric permittivity are measured as a function of frequency from 100 Hz to 2 MHz in the nematic and twist-bend nematic phases in planar and homeotropic devices. A significant decrease in the average dielectric permittivity as a function of temperature for mixtures forming the N_{TB} phase is observed. Measurements of the imaginary part of the dielectric permittivity show a relaxation peak in the measured frequency window for all of the mixtures exhibiting the N_{TB} phase. The activation energy associated with this relaxation process is calculated and is shown to remain constant irrespective of the composition of the mixtures.

  10. Nematic Equilibria on a Two-Dimensional Annulus

    KAUST Repository

    Lewis, A. H.

    2017-01-16

    We study planar nematic equilibria on a two-dimensional annulus with strong and weak tangent anchoring, in the Oseen–Frank theoretical framework. We analyze a radially invariant defect-free state and compute analytic stability criteria for this state in terms of the elastic anisotropy, annular aspect ratio, and anchoring strength. In the strong anchoring case, we define and characterize a new spiral-like equilibrium which emerges as the defect-free state loses stability. In the weak anchoring case, we compute stability diagrams that quantify the response of the defect-free state to radial and azimuthal perturbations. We study sector equilibria on sectors of an annulus, including the effects of weak anchoring and elastic anisotropy, giving novel insights into the correlation between preferred numbers of boundary defects and the geometry. We numerically demonstrate that these sector configurations can approximate experimentally observed equilibria with boundary defects.

  11. A theory for the orientational ordering in nematic liquids and for the phase diagram of the nematic-isotropic transition

    International Nuclear Information System (INIS)

    Hazoume, R.P.

    1982-10-01

    A molecular theory for the orientational distribution function f(#betta#) in the nematic phase is presented. Simple models are also derived yielding nematic order parameters in agreement with experimental data. The phase diagram of the nematic-isotropic transition is obtained by using a rigid rod model, showing that a short-range order theory does explain the structure in the nematic phase. (author)

  12. Particles with changeable topology in nematic colloids

    International Nuclear Information System (INIS)

    Ravnik, Miha; Čopar, Simon; Žumer, Slobodan

    2015-01-01

    We show that nematic colloids can serve as a highly variable and controllable platform for studying inclusions with changeable topology and their effects on the surrounding ordering fields. We explore morphing of toroidal and knotted colloidal particles into effective spheres, distinctively changing their Euler characteristic and affecting the surrounding nematic field, including topological defect structures. With toroidal particles, the inner nematic defect eventually transitions from a wide loop to a point defect (a small loop). Trefoil particles become linked with two knotted defect loops, mutually forming a three component link, that upon tightening transform into a two-component particle-defect loop link. For more detailed topological analysis, Pontryagin-Thom surfaces are calculated and visualised, indicating an interesting cascade of defect rewirings caused by the shape morphing of the knotted particles. (paper)

  13. Field Induced Memory Effects in Random Nematics

    Directory of Open Access Journals (Sweden)

    Amid Ranjkesh

    2014-01-01

    Full Text Available We studied numerically external field induced memory effects in randomly perturbed nematic liquid crystals. Random anisotropy nematic-type lattice model was used. The impurities imposing orientational disorder were randomly spatially distributed with the concentration p below the percolation threshold. Simulations were carried for finite temperatures, where we varied p, interaction strength between LC molecules, and impurities and external field B. In the {B,T} plane we determined lines separating short range—quasi long range and quasi long range—long range order. Furthermore, crossover regime separating external field and random field dominated regime was estimated. We calculated remanent nematic ordering in samples at B=0 as a function of the previously experienced external field strength B.

  14. Modeling elastic instabilities in nematic elastomers

    Science.gov (United States)

    Mbanga, Badel L.; Ye, Fangfu; Selinger, Jonathan V.; Selinger, Robin L. B.

    2010-11-01

    Liquid crystal elastomers are cross-linked polymer networks covalently bonded with liquid crystal mesogens. In the nematic phase, due to strong coupling between mechanical strain and orientational order, these materials display strain-induced instabilities associated with formation and evolution of orientational domains. Using a three-dimensional finite element elastodynamics simulation, we investigate one such instability, the onset of stripe formation in a monodomain film stretched along an axis perpendicular to the nematic director. In our simulation, we observe the formation of striped domains with alternating director rotation. This model allows us to explore the fundamental physics governing dynamic mechanical response of nematic elastomers and also provides a potentially useful computational tool for engineering device applications.

  15. Phase separation and disorder in doped nematic elastomers

    KAUST Repository

    Köpf, M. H.

    2013-10-01

    We formulate and analyse a model describing the combined effect of mechanical deformation, dynamics of the nematic order parameter, and concentration inhomogeneities in an elastomeric mixture of a mesogenic and an isotropic component. The uniform nematic state may exhibit a long-wave instability corresponding to nematic-isotropic demixing. Numerical simulations starting from either a perfectly ordered nematic state or a quenched isotropic state show that coupling between the mesogen concentration and the nematic order parameter influences the shape and orientation of the domains formed during the demixing process. © EDP Sciences/ Società Italiana di Fisica/ Springer-Verlag 2013.

  16. Direct and inverted nematic dispersions for soft matter photonics.

    Science.gov (United States)

    Muševič, I; Skarabot, M; Humar, M

    2011-07-20

    General properties and recent developments in the field of nematic colloids and emulsions are discussed. The origin and nature of pair colloidal interactions in the nematic colloids are explained and an overview of the stable colloidal 2D crystalline structures and superstructures discovered so far is given. The nature and role of topological defects in the nematic colloids is discussed, with an emphasis on recently discovered entangled colloidal structures. Applications of inverted nematic emulsions and binding force mechanisms in nematic colloids for soft matter photonic devices are discussed.

  17. Surface-polarization electrooptic effect in a nematic liquid crystal

    International Nuclear Information System (INIS)

    Lavrentovich, O.D.; Nazarenko, V.G.; Pergamenshchik, V.M.; Sergan, V.V.; Sorokin, V.M.

    1991-01-01

    A new electrooptic effect was observed experimentally in a homeotropic layer of a nematic with a positive anisotropy of the permittivity and of the electrical conductivity. This effect appeared in an external vertical static electric field and was manifested by the appearance of circular or elongated domain structures due to static distortions of the director near the anode or cathode of a cell. The polarity of the effect depended on the nature of an orienting coating. The origin of the effect was the nematic surface polarization which was sufficiently strong (∼10 -2 dyn 1/2 ) to induce an instability even under the conditions where other mechanisms (dielectric, flexoelectric, anisotropic electrohydrodynamic) impeded stability. Special attention was given to the separation of the surface polarization mechanism of the investigated effect from the flexoelectric and isotropic electrodynamic mechanisms. A hierarchy of static structures observed experimentally was clearly accounted for by a theory based on an equilibrium thermodynamic approach allowing for the anisotropic properties and for the real geometry of the system

  18. Nematic liquid crystal director structures in rectangular regions

    Science.gov (United States)

    Walton, J.; Mottram, N. J.; McKay, G.

    2018-02-01

    We consider a shallow rectangular well of nematic liquid crystal subject to weak anchoring on the sides of the well. By considering weak anchoring instead of infinitely strong anchoring, we are able to analyze nematic equilibria in the well without the need to exclude point defects at the corners, as done in previous work in the area. For relatively weak anchoring, we are able to derive analytic expressions for the director alignment angle in terms of an infinite series of modes, involving roots of a transcendental equation. The analytic forms of the director configuration are then used to calculate critical anchoring strengths at which uniform and distorted director structures exchange stability. We also consider the asymptotic behavior of the director structure and energy for very strong anchoring. We show that in both cases—for the transitions from uniform to distorted states and the limit of infinitely strong anchoring—the approximate analytic expansions agree very well with corresponding numerical calculations of the full model.

  19. Self-Assembling, Stable Photonic Bend-Gap Phases in Emulsions of Chiral Nematics with Isotropic Fluids

    Science.gov (United States)

    Huang, Chien-Yueh; Petschek, R. G.

    1998-03-01

    We investigate the possible mesophases in emulsions of chiral nematic liquid crystals with immiscible isotropic fluids and surfactants. The interactions between the orientational fields of the chiral nematics and the surfactant membranes together with the topological constraints affect stability of micellar geometries and produce a new phase diagram. We compare the free energies of various candidate phases. Appropriate, likely realizable conditions on the surfactant and the pitch of the liquid crystal result in thermodynamically stable blue-phase like phases for a relatively wide range of parameters. Processing such emulsions may result in materials with photonic band gaps.

  20. Isotropic-nematic spinodal decomposition dynamics

    NARCIS (Netherlands)

    Dhont, Jan K.G.; Briels, Willem J.

    2005-01-01

    The initial stage of isotropic-nematic spinodal demixing kinetics of suspensions of very long and thin, stiff, repulsive rods is analyzed on the basis of the N -particle Smoluchowski equation. Equations of motion for the reduced probability density function of the position and orientation of a rod

  1. Integral equation theory for nematic fluids

    Directory of Open Access Journals (Sweden)

    M.F. Holovko

    2010-01-01

    Full Text Available The traditional formalism in liquid state theory based on the calculation of the pair distribution function is generalized and reviewed for nematic fluids. The considered approach is based on the solution of orientationally inhomogeneous Ornstein-Zernike equation in combination with the Triezenberg-Zwanzig-Lovett-Mou-Buff-Wertheim equation. It is shown that such an approach correctly describes the behavior of correlation functions of anisotropic fluids connected with the presence of Goldstone modes in the ordered phase in the zero-field limit. We focus on the discussions of analytical results obtained in collaboration with T.G. Sokolovska in the framework of the mean spherical approximation for Maier-Saupe nematogenic model. The phase behavior of this model is presented. It is found that in the nematic state the harmonics of the pair distribution function connected with the correlations of the director transverse fluctuations become long-range in the zero-field limit. It is shown that such a behavior of distribution function of nematic fluid leads to dipole-like and quadrupole-like long-range asymptotes for effective interaction between colloids solved in nematic fluids, predicted before by phenomenological theories.

  2. Molecular engineering of discotic nematic liquid crystals

    Indian Academy of Sciences (India)

    Molecular engineering of discotic nematic liquid crystals. SANDEEP KUMAR. Centre for Liquid Crystal Research, P.O. Box 1329, Jalahalli, Bangalore 560 013, India. Present Address: Raman Research Institute, C.V. Raman Avenue, Bangalore 560 080, India. Abstract. Connecting two columnar phase forming discotic ...

  3. Deformable nematic droplets in a magnetic field

    NARCIS (Netherlands)

    Otten, R.H.J.; van der Schoot, P. P. A. M.

    2012-01-01

    We present a Frank-Oseen elasticity theory for the shape and structure of deformable nematic droplets with homeotropic surface anchoring in the presence of a magnetic field. Inspired by recent experimental observations, we focus on the case where the magnetic susceptibility is negative, and find

  4. Molecular engineering of discotic nematic liquid crystals

    Indian Academy of Sciences (India)

    Connecting two columnar phase forming discotic mesogens via a short rigid spacer leads to the formation of a -conjugated discotic dimer showing discotic nematic (D) phase. Attaching branched-alkyl chains directly to the core in hexaalkynylbenzene resulted in the stabilisation of D phase at ambient temperature.

  5. Hidden topological constellations and polyvalent charges in chiral nematic droplets.

    Science.gov (United States)

    Posnjak, Gregor; Čopar, Simon; Muševič, Igor

    2017-02-21

    Topology has an increasingly important role in the physics of condensed matter, quantum systems, material science, photonics and biology, with spectacular realizations of topological concepts in liquid crystals. Here we report on long-lived hidden topological states in thermally quenched, chiral nematic droplets, formed from string-like, triangular and polyhedral constellations of monovalent and polyvalent singular point defects. These topological defects are regularly packed into a spherical liquid volume and stabilized by the elastic energy barrier due to the helical structure and confinement of the liquid crystal in the micro-sphere. We observe, for the first time, topological three-dimensional point defects of the quantized hedgehog charge q=-2, -3. These higher-charge defects act as ideal polyvalent artificial atoms, binding the defects into polyhedral constellations representing topological molecules.

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

    Energy Technology Data Exchange (ETDEWEB)

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

    2017-07-15

    Here, iron telluride (FeTe) is known to display bicollinear magnetic order at low temperatures together with a monoclinic lattice distortion. Because the bicollinear order can involve two different wave vectors (π/2,π/2) and (π/2,–π/2), symmetry considerations allow for the possible stabilization of a nematic state with short-range bicollinear order coupled to monoclinic lattice distortions at a TS higher than the temperature TN where long-range bicollinear order fully develops. As a concrete example, the three-orbital spin-fermion model for iron telluride is studied with an additional coupling ˜λ12 between the monoclinic lattice strain and an orbital-nematic order parameter with B2g symmetry. Monte Carlo simulations show that with increasing ˜λ12 the first-order transition characteristic of FeTe splits and bicollinear nematicity is stabilized in a (narrow) temperature range. In this new regime, the lattice is monoclinically distorted and short-range spin and orbital order breaks rotational invariance. A discussion of possible realizations of this exotic state is provided.

  7. Splitting, linking, knotting, and solitonic escape of topological defects in nematic drops with handles.

    Science.gov (United States)

    Tasinkevych, Mykola; Campbell, Michael G; Smalyukh, Ivan I

    2014-11-18

    Topologically nontrivial field excitations, including solitonic, linked, and knotted structures, play important roles in physical systems ranging from classical fluids and liquid crystals, to electromagnetism, classic, and quantum field theories. These excitations can appear spontaneously during symmetry-breaking phase transitions. For example, in cosmological theories, cosmic strings may have formed knotted configurations influencing the Early Universe development, whereas in liquid crystals transient tangled defect lines were observed during isotropic-nematic transitions, eventually relaxing to defect-free states. Knotted and solitonic fields and defects were also obtained using optical manipulation, complex-shaped colloids, and frustrated cholesterics. Here we use confinement of nematic liquid crystal by closed surfaces with varied genus and perpendicular boundary conditions for a robust control of appearance and stability of such field excitations. Theoretical modeling and experiments reveal structure of defect lines as a function of the surface topology and material and geometric parameters, establishing a robust means of controlling solitonic, knotted, linked, and other field excitations.

  8. Thermal diode made by nematic liquid crystal

    Energy Technology Data Exchange (ETDEWEB)

    Melo, Djair, E-mail: djfmelo@gmail.com [Instituto de Física, Universidade Federal de Alagoas, Av. Lourival Melo Mota, s/n, 57072-900 Maceió, AL (Brazil); Fernandes, Ivna [Instituto de Física, Universidade Federal de Alagoas, Av. Lourival Melo Mota, s/n, 57072-900 Maceió, AL (Brazil); Moraes, Fernando [Departamento de Física, CCEN, Universidade Federal da Paraíba, Caixa Postal 5008, 58051-900, João Pessoa, PB (Brazil); Departamento de Física, Universidade Federal Rural de Pernambuco, 52171-900 Recife, PE (Brazil); Fumeron, Sébastien [Institut Jean Lamour, Université de Lorraine, BP 239, Boulevard des Aiguillettes, 54506 Vandoeuvre les Nancy (France); Pereira, Erms [Escola Politécnica de Pernambuco, Universidade de Pernambuco, Rua Benfíca, 455, Madalena, 50720-001 Recife, PE (Brazil)

    2016-09-07

    This work investigates how a thermal diode can be designed from a nematic liquid crystal confined inside a cylindrical capillary. In the case of homeotropic anchoring, a defect structure called escaped radial disclination arises. The asymmetry of such structure causes thermal rectification rates up to 3.5% at room temperature, comparable to thermal diodes made from carbon nanotubes. Sensitivity of the system with respect to the heat power supply, the geometry of the capillary tube and the molecular anchoring angle is also discussed. - Highlights: • An escaped radial disclination as a thermal diode made by a nematic liquid crystal. • Rectifying effects comparable to those caused by carbon and boron nitride nanotubes. • Thermal rectification increasing with radius and decreasing with height of the tube. • Asymmetric BCs cause rectification from the spatial asymmetry produced by the escape. • Symmetric BCs provide rectifications smaller than those yields by asymmetric BCs.

  9. Post-Tanner spreading of nematic droplets

    Energy Technology Data Exchange (ETDEWEB)

    Mechkov, S; Oshanin, G [Laboratoire de Physique Theorique de la Matiere Condensee, Universite Pierre et Marie Curie, 4 place Jussieu, 75252 Paris Cedex 5 (France); Cazabat, A M, E-mail: mechkov@lptmc.jussieu.f, E-mail: anne-marie.cazabat@lps.ens.f, E-mail: oshanin@lptmc.jussieu.f [Laboratoire de Physique Statistique, Ecole Normale Superieure, 75252 Paris Cedex 5 (France)

    2009-11-18

    The quasistationary spreading of a circular liquid drop on a solid substrate typically obeys the so-called Tanner law, with the instantaneous base radius R(t) growing with time as Rapproxt{sup 1/10}-an effect of the dominant role of capillary forces for a small-sized droplet. However, for droplets of nematic liquid crystals, a faster spreading law sets in at long times, so that Rapproxt{sup a}lpha with alpha significantly larger than the Tanner exponent 1/10. In the framework of the thin film model (or lubrication approximation), we describe this 'acceleration' as a transition to a qualitatively different spreading regime driven by a strong substrate-liquid interaction specific to nematics (antagonistic anchoring at the interfaces). The numerical solution of the thin film equation agrees well with the available experimental data for nematics, even though the non-Newtonian rheology has yet to be taken into account. Thus we complement the theory of spreading with a post-Tanner stage, noting that the spreading process can be expected to cross over from the usual capillarity-dominated stage to a regime where the whole reservoir becomes a diffusive film in the sense of Derjaguin.

  10. Post-Tanner spreading of nematic droplets

    International Nuclear Information System (INIS)

    Mechkov, S; Oshanin, G; Cazabat, A M

    2009-01-01

    The quasistationary spreading of a circular liquid drop on a solid substrate typically obeys the so-called Tanner law, with the instantaneous base radius R(t) growing with time as R∼t 1/10 -an effect of the dominant role of capillary forces for a small-sized droplet. However, for droplets of nematic liquid crystals, a faster spreading law sets in at long times, so that R∼t α with α significantly larger than the Tanner exponent 1/10. In the framework of the thin film model (or lubrication approximation), we describe this 'acceleration' as a transition to a qualitatively different spreading regime driven by a strong substrate-liquid interaction specific to nematics (antagonistic anchoring at the interfaces). The numerical solution of the thin film equation agrees well with the available experimental data for nematics, even though the non-Newtonian rheology has yet to be taken into account. Thus we complement the theory of spreading with a post-Tanner stage, noting that the spreading process can be expected to cross over from the usual capillarity-dominated stage to a regime where the whole reservoir becomes a diffusive film in the sense of Derjaguin.

  11. UV response on dielectric properties of nano nematic liquid crystal

    Directory of Open Access Journals (Sweden)

    Kamal Kumar Pandey

    2018-03-01

    Full Text Available In this work, we investigate the effect of UV light irradiation on the dielectric parameters of nematic liquid crystal (5CB and ZnO nanoparticles dispersed liquid crystal. With addition of nanoparticles in nematic LC are promising new materials for a variety of application in energy harvesting, displays and photonics including the liquid crystal laser. To realize many applications, however we optimize the properties of liquid crystal and understand how the UV light irradiation interact the nanoparticles and LC molecules in dispersed/doped LC. The dielectric permittivity and loss factor have discussed the pure nematic LC and dispersed/doped system after, during and before UV light exposure. The dielectric relaxation spectroscopy was carried out in the frequency range 100 Hz–10 MHz in the nematic mesophase range. Keywords: Dielectric permittivity, Relaxation frequency, Nematic liquid crystal, UV light irradiation

  12. A finite-density calculation of the surface tension of isotropic-nematic interfaces

    International Nuclear Information System (INIS)

    Moore, B.G.; McMullen, W.E.

    1992-01-01

    The surface tension of the isotropic-nematic interface in a fluid of intermediate-sized hard particles is studied and calculated. The transition from isotropic to nematic is fixed to occur in a continuous fashion by varying the biaxiality of the model particles. A reversal in the preferred orientation of the bulk nematic relative to the isotropic-nematic interface suggests an oblique orientation of the bulk nematic. 32 refs., 8 figs

  13. Flexoelectricity in chiral nematic liquid crystals as a driving mechanism for the twist-bend and splay-bend modulated phases.

    Science.gov (United States)

    Vaupotič, Nataša; Čepič, Mojca; Osipov, Mikhail A; Gorecka, Ewa

    2014-03-01

    We present a continuum theoretical model describing the impact of chirality on nematic systems with large flexoelectricity. As opposed to achiral materials, where only one type of the modulated structure can exist in a given material, the model predicts that chirality can stabilize several modulated phases, which have already been observed experimentally [A. Zep et al., J. Mater. Chem. C 1, 46 (2013)].

  14. Artificial web of disclination lines in nematic liquid crystals.

    Science.gov (United States)

    Wang, Mengfei; Li, Yannian; Yokoyama, Hiroshi

    2017-08-30

    Disclinations are topological singularities of molecular arrangement in liquid crystals, which typically occur when the average orientation of molecules makes a π rotation along a fictitious closed loop taken inside the liquid crystal. Depending on the sense of molecular rotation, the disclination lines are either of 1/2 or -1/2 strength. When two disclination lines with the opposite strength meet, they are annihilated without trace. It is hence generally considered difficult in the nematic phase to stabilize a condensed array of free-standing disclination lines without the aid of topological objects like colloidal inclusions. Here we show that a free-standing web of 1/2-strength twist disclination lines can be stably formed in thin liquid crystal cells by means of a judicious combination of orientationally patterned confining surfaces fabricated by the micropatterned photoalignment technique. Theoretical model indicates that disclination lines are held apart at the intersection by a repulsive force generated by the Frank elasticity.Disclination lines are topological defects in molecular orientation widely found in liquid crystals. Here Wang et al. use a surface patterning technique to produce a very stable freestanding 3D array of ½ twist disclinations, which could be exploited in a variety of nanometre scale applications.

  15. Domain Structures in Nematic Liquid Crystals on a Polycarbonate Surface

    Directory of Open Access Journals (Sweden)

    Vasily F. Shabanov

    2013-08-01

    Full Text Available Alignment of nematic liquid crystals on polycarbonate films obtained with the use of solvents with different solvations is studied. Domain structures occurring during the growth on the polymer surface against the background of the initial thread-like or schlieren texture are demonstrated. It is established by optical methods that the domains are stable formations visualizing the polymer surface structures. In nematic droplets, the temperature-induced transition from the domain structure with two extinction bands to the structure with four bands is observed. This transition is shown to be caused by reorientation of the nematic director in the liquid crystal volume from the planar alignment to the homeotropic state with the pronounced radial configuration of nematic molecules on the surface. The observed textures are compared with different combinations of the volume LC orientations and the radial distribution of the director field and the disclination lines at the polycarbonate surface.

  16. Modulation instability and solitons in two-color nematic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Horikis, Theodoros P., E-mail: horikis@uoi.gr

    2016-10-14

    The conditions under which stable evolution of two nonlinear interacting waves are derived within the context of nematic liquid crystals. Two cases are considered: plane waves and solitons. In the first case, the modulation instability analysis reveals that while the nonlocal term suppresses the growth rates, substantially, the coupled system exhibits significantly higher growth rates than its scalar counterpart. In the soliton case, the necessary conditions are derived that lead the solitons to exhibit stable, undistorted evolution, suppressing any breathing behavior and radiation, leading to soliton mutual guiding. - Highlights: • Modulation instability analysis for two-color nematic crystals. • Stable soliton propagation for two-color nematic crystals. • Conditions for stable propagation of continuous waves and solitons in two-color nematic crystals.

  17. Strong-coupling approach to nematicity in the cuprates

    Science.gov (United States)

    Orth, Peter Philipp; Jeevanesan, Bhilahari; Schmalian, Joerg; Fernandes, Rafael

    The underdoped cuprate superconductor YBa2Cu3O7-δ is known to exhibit an electronic nematic phase in proximity to antiferromagnetism. While nematicity sets in at large temperatures of T ~ 150 K, static spin density wave order only emerges at much lower temperatures. The magnetic response shows a strong in-plane anisotropy, displaying incommensurate Bragg peaks along one of the crystalline directions and a commensurate peak along the other one. Such an anisotropy persists even in the absence of long-range magnetic order at higher temperatures, marking the onset of nematic order. Here we theoretically investigate this situation using a strong-coupling method that takes into account both the localized Cu spins and the holes doped into the oxygen orbitals. We derive an effective spin Hamiltonian and show that charge fluctuations promote an enhancement of the nematic susceptibility near the antiferromagnetic transition temperature.

  18. UV response on dielectric properties of nano nematic liquid crystal

    Science.gov (United States)

    Pandey, Kamal Kumar; Tripathi, Pankaj Kumar; Misra, Abhishek Kumar; Manohar, Rajiv

    2018-03-01

    In this work, we investigate the effect of UV light irradiation on the dielectric parameters of nematic liquid crystal (5CB) and ZnO nanoparticles dispersed liquid crystal. With addition of nanoparticles in nematic LC are promising new materials for a variety of application in energy harvesting, displays and photonics including the liquid crystal laser. To realize many applications, however we optimize the properties of liquid crystal and understand how the UV light irradiation interact the nanoparticles and LC molecules in dispersed/doped LC. The dielectric permittivity and loss factor have discussed the pure nematic LC and dispersed/doped system after, during and before UV light exposure. The dielectric relaxation spectroscopy was carried out in the frequency range 100 Hz-10 MHz in the nematic mesophase range.

  19. Defects in an active nematic confined to a toroid

    Science.gov (United States)

    Ellis, Perry; Pearce, Dan; Giomi, Luca; Fernandez-Nieves, Alberto

    Active materials are driven far from the ground state by the motion of their constituent particles, thereby making them inherently non-equilibrium materials. For an active nematic, this results in a continuous creation and annihilation of +/- 1 / 2 defect pairs. Here, we confine an active nematic to the surface of a toroid and show that the topological charge of the defects couples to the Gaussian curvature of the underlying surface. However, in our experiments this defect unbinding happens on average, illustrating that despite subtle differences, the role of activity is reminiscent of the role of temperature in conventional nematics. This is confirmed by computer simulations which clearly illustrate that defect unbinding depends on activity. Overall, our results illustrate the role of confinement and curvature on the defect behavior of active nematic liquid crystals. PWE is supported by FLAMEL under Grant NSF 1258425.

  20. Adsorption phenomena and anchoring energy in nematic liquid crystals

    CERN Document Server

    Barbero, Giovanni

    2005-01-01

    Despite the large quantity of phenomenological information concerning the bulk properties of nematic phase liquid crystals, little is understood about the origin of the surface energy, particularly the surface, interfacial, and anchoring properties of liquid crystals that affect the performance of liquid crystal devices. Self-contained and unique, Adsorption Phenomena and Anchoring Energy in Nematic Liquid Crystals provides an account of new and established results spanning three decades of research into the problems of anchoring energy and adsorption phenomena in liquid crystals.The book contains a detailed discussion of the origin and possible sources of anchoring energy in nematic liquid crystals, emphasizing the dielectric contribution to the anchoring energy in particular. Beginning with fundamental surface and anchoring properties of liquid crystals and the definition of the nematic phase, the authors explain how selective ion adsorption, dielectric energy density, thickness dependence, and bias voltage...

  1. Fluid dynamics in biological active nematics

    Science.gov (United States)

    Tan, Amanda; Hirst, Linda

    We use biological materials to form a self-mixing active system that consists of microtubules driven by kinesin clusters. Microtubules are rigid biopolymers that are a part of the cytoskeleton. Kinesin motors are molecular motors that walk along microtubules to transport cellular cargo. In this system, microtubules are bundled together, and as the kinesin clusters walk along the filaments, the microtubule bundles move relative to each other. As microtubules shear against each other, they extend, bend, buckle and fracture. When confined in a 2D water-oil interface, the system becomes an active nematic that self-mixes due to the buckling and fracturing. To quantify this self-mixing, we attached beads to the microtubules, and tracked their motion. We quantify the quality of mixing using the bead trajectories. This new active material has potential applications as a self-mixing solvent. CCBM NSF-CREST, UC Merced Health Science Research Institute.

  2. Nematicity at the Hund's metal crossover in iron superconductors

    Science.gov (United States)

    Fanfarillo, L.; Giovannetti, G.; Capone, M.; Bascones, E.

    2017-04-01

    The theoretical understanding of the nematic state of iron-based superconductors and especially of FeSe is still a puzzling problem. Although a number of experiments call for a prominent role of local correlations and place iron superconductors at the entrance of a Hund's metal state, the effect of the electronic correlations on the nematic state has been theoretically poorly investigated. In this work we study the nematic phase of iron superconductors accounting for local correlations, including the effect of the Hund's coupling. We show that Hund's physics strongly affects the nematic properties of the system. It severely constrains the precise nature of the feasible orbital-ordered state and induces a differentiation in the effective masses of the z x /y z orbitals in the nematic phase. The latter effect leads to distinctive signatures in different experimental probes overlooked so far in the interpretation of experiments. As notable examples the splittings between z x and y z bands at Γ and M points are modified, with important consequences for angle-resolved photoemission spectroscopy measurements.

  3. Flexoelectricity and pattern formation in nematic liquid crystals.

    Science.gov (United States)

    Krekhov, Alexei; Pesch, Werner; Buka, Agnes

    2011-05-01

    We present in this paper a detailed analysis of the flexoelectric instability of a planar nematic layer in the presence of an alternating electric field (frequency ω), which leads to stripe patterns (flexodomains) in the plane of the layer. This equilibrium transition is governed by the free energy of the nematic, which describes the elasticity with respect to the orientational degrees of freedom supplemented by an electric part. Surprisingly the limit ω→0 is highly singular. In distinct contrast to the dc case, where the patterns are stationary and time independent, they appear at finite, small ω periodically in time as sudden bursts. Flexodomains are in competition with the intensively studied electrohydrodynamic instability in nematics, which presents a nonequilibrium dissipative transition. It will be demonstrated that ω is a very convenient control parameter to tune between flexodomains and convection patterns, which are clearly distinguished by the orientation of their stripes.

  4. Statistical mechanics of splay flexoelectricity in nematic liquid crystals.

    Science.gov (United States)

    Dhakal, Subas; Selinger, Jonathan V

    2010-03-01

    We develop a lattice model for the splay flexoelectric effect in nematic liquid crystals. In this model, each lattice site has a spin representing the local molecular orientation, and the interaction between neighboring spins represents pear-shaped molecules with shape polarity. We perform Monte Carlo simulations and mean-field calculations to find the behavior as a function of interaction parameters, temperature, and applied electric field. The resulting phase diagram has three phases: isotropic, nematic, and polar. In the nematic phase, there is a large splay flexoelectric effect, which diverges as the system approaches the transition to the polar phase. These results show that flexoelectricity can be a statistical phenomenon associated with the onset of polar order.

  5. Standard and nonstandard nematic electrohydrodynamic convection in the presence of asymmetric ac electric fields.

    Science.gov (United States)

    Low, Jonathan; Hogan, S John

    2008-10-01

    In planar nematic electrohydrodynamic convection (EHC), a microscopic liquid crystal cell is driven by a homogeneous ac electric field, which, if strong enough, causes the fluid to destabilize into a regular pattern-forming state. We consider asymmetric electric fields E(t)=E(t+T) not equal-E(t+T2) , which leads to the possibility of three different types of instabilities at onset: conductive, dielectric, and subharmonic. The first two are already well known as they are easily produced when the system is driven by symmetric electric fields; the third can only occur when the electric field symmetry is broken. We present theoretical results on EHC using linear stability analysis and Floquet theory. We consider rigid and free boundary conditions, extending the model to two Fourier modes in the vertical plane, the inclusion of flexoelectricity, and using standard (nematic electric conductivity sigma_{a}>0 and dielectric anisotorpy _{a}<0 ) and nonstandard (sigma_{a}<0) material parameters. We make full use of a three-dimensional linear model where two mutually perpendicular planar wave numbers q and p can be varied. Our results show that there is a qualitative difference between the boundary conditions used, which is also dependent on how many vertical Fourier modes were used in the model. We have obtained threshold values favoring oblique rolls in subharmonic and dielectric regimes in parameter space. For the nonstandard EHC parameter values, both conduction and subharmonic regimes disappear and only the dielectric threshold exists.

  6. Nonstandard electroconvection and flexoelectricity in nematic liquid crystals.

    Science.gov (United States)

    Krekhov, Alexei; Pesch, Werner; Eber, Nándor; Tóth-Katona, Tibor; Buka, Agnes

    2008-02-01

    For many years it has been commonly accepted that electroconvection (EC) as primary instability in nematic liquid crystals for the "classical" planar geometry requires a positive anisotropy of the electric conductivity, sigma(a), and a slightly negative dielectric anisotropy, epsilon(a). This firm belief was supported by many experimental and theoretical studies. Recent experiments, which have surprisingly revealed EC patterns at negative conduction anisotropy as well, have motivated the theoretical studies in this paper. It will be demonstrated that extending the common hydrodynamic description of nematics by the usually neglected flexoelectric effect allows for a simple explanation of EC in the "nonstandard" case sigma(a)<0 .

  7. A faster switching regime for zenithal bistable nematic displays

    International Nuclear Information System (INIS)

    Rudin, J.

    1997-01-01

    A simpler and faster switching regime for Zenithal Bistable Nematic displays is reported. A cell, based on homeotropic alignment of nematic liquid crystal over a continuous blazed monograting on one surface, can be switched using bipolar pulses an order of magnitude faster than monopolar pulses of the same voltage. We propose that this regime relies on simple dielectric coupling to drive the cell into a higher energy state with a long pulse time, and the relaxation into a lower energy state after the creation of surface defects from a shorter applied pulse. Although flexoelectric effects are observed, they do not form the basis of state selection as was proposed for the monopolar pulses

  8. Flexoelectric instability in nematic cells with weak anchoring energy

    International Nuclear Information System (INIS)

    Lelidis, I.; Barbero, G.

    2003-01-01

    We analyze the role of weak anchoring energy boundary conditions on electric field induced structural instabilities of flexoelectric origin in a finite thickness nematic cell. It is shown that stripe-like domain patterns can appear above a rather low threshold voltage V th ∼0.3 V. V th and the wave-length of the instability at the threshold vary as the square root of the cell thickness. Our analysis is valid when the extrapolation length is large with respect to the nematic slab thickness

  9. Multiscale approach to nematic liquid crystals via statistical field theory.

    Science.gov (United States)

    Lu, Bing-Sui

    2017-08-01

    We propose an approach to a multiscale problem in the theory of thermotropic uniaxial nematics based on the method of statistical field theory. This approach enables us to relate the coefficients A, B, C, L_{1}, and L_{2} of the Landau-de Gennes free energy for the isotropic-nematic phase transition to the parameters of a molecular model of uniaxial nematics, which we take to be a lattice gas model of nematogenic molecules interacting via a short-ranged potential. We obtain general constraints on the temperature and volume fraction of nematogens for the Landau-de Gennes theory to be stable against molecular orientation fluctuations at quartic order. In particular, for the case of a fully occupied lattice, we compute the values of the isotropic-nematic transition temperature and the order parameter discontinuity predicted by (i) a continuum approximation of the nearest-neighbor Lebwohl-Lasher model and (ii) a Lebwohl-Lasher-type model with a nematogenic interaction of finite range. We find that the predictions of (i) are in reasonably good agreement with known results of Monte Carlo simulation.

  10. Elastic constants of hard and soft nematic liquid crystals

    NARCIS (Netherlands)

    Tjipto-Margo, B.; Evans, G.T.; Allen, M.P.; Frenkel, D.

    1992-01-01

    The Frank elastic constants for a nematic liquid crystal have been calculated by computer simulations for a fluid of hard ellipsoids and by the Poniewierski-Stecki method for ellipsoids with and without an attractive square well. Required for the Poniewierski-Stecki method is the direct

  11. Fractional Brownian motion of director fluctuations in nematic ordering

    DEFF Research Database (Denmark)

    Zhang, Z.; Mouritsen, Ole G.; Otnes, K.

    1993-01-01

    to determine the Hurst exponent H. Theory and experiment are in good agreement. A value of H congruent-to 1 was found for the nematic phase, characterizing fractional Brownian motion, whereas H congruent-to 0.5, reflecting ordinary Brownian motion, applies in the isotropic phase. Field-induced crossover from...

  12. Nematic and Smectic Mesophases from a Novel Triphenylene ...

    African Journals Online (AJOL)

    Salisu Abdulsalam

    phenylazo)azobenzene on to the 2,3,6,7,10,11-hexahydroxytriphenylene nucleus. The presence of a nematic and smectic A mesophases was confirmed by optical textures and ..... containing both mono- and bisazobenzene mesogene: Synthesis and properties,. Macromolecules, 38: 9526-9538. Furumi S., Kidowaki M., ...

  13. Transient Splitting of Conoscopic Isogyres of a Uniaxial Nematic

    Science.gov (United States)

    Kim, Young-Ki; Senuk, Bohdan; Tortora, Luana; Sprunt, Samuel; Lehmann, Matthias; Lavrentovich, Oleg D.

    2012-02-01

    The phase identification is often based on conoscopic observations of homeotropic cells: A uniaxial nematic produces a pattern with crossed isogyres, while the biaxial nematic shows a split of isogyres. We demonstrate that the splitting of isogyres occurs even when the material remains in the uniaxial nematic phase. In particular, in the bent core material J35, splitting of isogyres is caused by change of the temperature. The effect is transient and the isogyres return to a uniaxial (crossed) configuration after a certain time that depends on sample thickness, temperature, and rate of temperature change; the time varies from a few seconds to tens of hours. The transient splitting is caused by the temperature-induced material flow that triggers a (uniaxial) director tilt in the cell. The flows and the director tilt are demonstrated by the CARS microscopy and fluorescent confocal polarizing microscopy (FCPM). This transient effect is general and can be observed even in E7 and 5CB. The effect should be considered in textural identifications of potential biaxial nematic materials.

  14. Quantum Dot Chain Assembly Mediated by Nematic Liquid Crystals

    Science.gov (United States)

    Brereton, Peter; Basu, Rajratan; Finkenstadt, Daniel

    2015-03-01

    A small quantity of CdSe quantum dots (QDs) were dispersed in a nematic liquid crystal (LC) media and the QDs were found to exhibit self-assembled asymmetric structures, most likely QD-chains. In the nematic phase the ensemble LC +QD photoluminescence (PL) exhibits an anisotropic spectral line shape, as compared to the emission of QDs doped in the isotropic phase. This indicates a nematic mediated arrangement of the QDs. A simple model is proposed to explain the asymmetric behavior of the PL band as an effective chain of radiatively coupled emitters. The effect of the liquid crystals is to provide an entropic force that attracts dots to minimize the excluded volume. The dielectric reorientation dynamics immediately following the removal of an applied field appears as a one-step exponential decay for the LC and a two-step exponential decay with a slower process for the LC +QD system. The results suggest that anisotropic chain-like QD-assemblies are formed in the nematic platform. A related study has examined PL of ferroelectric LC doped with graphene QD [Kumar, Veeresh, et al., Liquid Crystals (2014)

  15. Development of an equation of state for nematic liquid crystals

    NARCIS (Netherlands)

    Van Westen, T.

    2015-01-01

    In this thesis I aim to contribute to a molecular understanding and -description of the phase behaviour of liquid crystalline materials. In particular, I aim at the development of a molecular-based equation of state (EoS) for describing nematic (only orientationally ordered) liquid crystals (LCs)

  16. Emergence of biaxial nematic phases in solutions of semiflexible dimers

    Science.gov (United States)

    Vaghela, Arvin; Teixeira, Paulo I. C.; Terentjev, Eugene M.

    2017-10-01

    We investigate the isotropic, uniaxial nematic and biaxial nematic phases, and the transitions between them, for a model lyotropic mixture of flexible molecules consisting of two rigid rods connected by a spacer with variable bending stiffness. We apply density-functional theory within the Onsager approximation to describe strictly excluded-volume interactions in this athermal model and to self-consistently find the orientational order parameters dictated by its complex symmetry, as functions of the density. Earlier work on lyotropic ordering of rigid bent-rod molecules is reproduced and extended to show explicitly the continuous phase transition at the Landau point, at a critical bend angle of 36∘. For flexible dimers with no intrinsic biaxiality, we find that a biaxial nematic phase can nevertheless form at a sufficiently high density and low bending stiffness. For bending stiffness κ >0.86 kBT , this biaxial phase manifests as dimer bending fluctuations occurring preferentially in one plane. When the dimers are more flexible, κ the modal shape of the fluctuating dimer is a V with an acute opening angle, and one of the biaxial order parameters changes sign, indicating a rotation of the directors. These two regions are separated by a narrow strip of uniaxial nematic in the phase diagram, which we generate in terms of the spacer stiffness and particle density.

  17. History-Dependent Patterns in Randomly Perturbed Nematic Liquid Crystals

    Directory of Open Access Journals (Sweden)

    A. Ranjkesh

    2013-01-01

    Full Text Available We study the characteristics of nematic structures in a randomly perturbed nematic liquid crystal (LC phase. We focus on the impact of the samples history on the universal behavior. The obtained results are of interest for every randomly perturbed system exhibiting a continuous symmetry-breaking phase transition. A semimicroscopic lattice simulation is used where the LC molecules are treated as cylindrically symmetric, rod-like objects interacting via a Lebwohl-Lasher (LL interaction. Pure LC systems exhibit a first order phase transition into the orientationally ordered nematic phase at T=Tc on lowering the temperature T. The orientational ordering of LC molecules is perturbed by the quenched, randomly distributed rod-like impurities of concentration p. Their orientation is randomly distributed, and they are coupled with the LC molecules via an LL-type interaction. Only concentrations below the percolation threshold are considered. The key macroscopic characteristics of perturbed LC structures in the symmetry-broken nematic phase are analyzed for two qualitatively different histories at T≪Tc. We demonstrate that, for a weak enough interaction among the LC molecules and impurities, qualitatively different history-dependent states could be obtained. These states could exhibit either short-range, quasi-long-range, or even long-range order.

  18. Stabilization

    Directory of Open Access Journals (Sweden)

    Muhammad H. Al-Malack

    2016-07-01

    Full Text Available Fuel oil flyash (FFA produced in power and water desalination plants firing crude oils in the Kingdom of Saudi Arabia is being disposed in landfills, which increases the burden on the environment, therefore, FFA utilization must be encouraged. In the current research, the effect of adding FFA on the engineering properties of two indigenous soils, namely sand and marl, was investigated. FFA was added at concentrations of 5%, 10% and 15% to both soils with and without the addition of Portland cement. Mixtures of the stabilized soils were thoroughly evaluated using compaction, California Bearing Ratio (CBR, unconfined compressive strength (USC and durability tests. Results of these tests indicated that stabilized sand mixtures could not attain the ACI strength requirements. However, marl was found to satisfy the ACI strength requirement when only 5% of FFA was added together with 5% of cement. When the FFA was increased to 10% and 15%, the mixture’s strength was found to decrease to values below the ACI requirements. Results of the Toxicity Characteristics Leaching Procedure (TCLP, which was performed on samples that passed the ACI requirements, indicated that FFA must be cautiously used in soil stabilization.

  19. Flexoelectricity in chiral nematic liquid crystals as a driving mechanism for the twist-bend and splay-bend modulated phases

    Science.gov (United States)

    Vaupotič, Nataša; Čepič, Mojca; Osipov, Mikhail A.; Gorecka, Ewa

    2014-03-01

    We present a continuum theoretical model describing the impact of chirality on nematic systems with large flexoelectricity. As opposed to achiral materials, where only one type of the modulated structure can exist in a given material, the model predicts that chirality can stabilize several modulated phases, which have already been observed experimentally [A. Zep et al., J. Mater. Chem. C 1, 46 (2013), 10.1039/c2tc00163b].

  20. Electro-optical memory of a nematic liquid crystal doped by multi-walled carbon nanotubes

    Directory of Open Access Journals (Sweden)

    L. Dolgov

    2012-10-01

    Full Text Available A pronounced irreversible electro-optical response (memory effect has been recently observed for nematic liquid crystal (LC EBBA doped by multi-walled carbon nanotubes (MWCNTs near the percolation threshold of the MWCNTs (0.02÷0.05 wt. %. It is caused by irreversible homeotropic-to-planar reorientation of LC in an electric field. This feature is explained by electro-hydrodynamically stimulated dispergation of MWCNTs in LC and by the formation of a percolation MWCNT network which acts as a spatially distributed surface stabilizing the planar state of the LC. This mechanism is confirmed by the absence of memory in the EBBA/MWCNT composites, whose original structure is fixed by a polymer. The observed effect suggests new operation modes for the memory type and bistable LC devices, as well as a method for in situ dispergation of carbon nanotubes in LC cells.

  1. Statistical physics of modulated phases in nematic liquid crystals

    Science.gov (United States)

    Shamid, Shaikh M.

    Nematic liquid crystals are the state of the matter in which there is no positional order like crystals but it has orientational order of the constituent molecules. In the conventional nematics, the long axes of the rod-like molecules tend to align up or down uniformly along a director n. If the constituent molecules are chiral, they tend to form a modulated structure in one of the space dimensions. They are called the chiral nematics. If the chirality is strong enough we get the modulated structures in all three dimensions called the chiral blue phase. On the other hand, if the molecules are achiral, but an additional polar dipole is attached to the molecules, they also tend to form a modulated structure. In these types of materials we observe an important physical effect called flexoelectric effect, in which the polar order is linearly coupled to the director gradients. This dissertation work presents analytical and simulation studies of that modulated structures using the flexoelectric mechanism. Classic work by R. B. Meyer and further studies by I. Dozov predicted two possible structures, known as twist-bend and splay-bend. One of these predictions, the twist-bend phase, has recently been identified in experiments on bent-shaped liquid crystals. In this recently discovered twist-bend nematic phase the modulation is along one of the space dimensions. If this flexoelectric coupling is strong enough, in addition to twist-bend and splay-bend, here we predict the formation of polar analog of chiral blue phases (in both 2D and 3D) made of achiral polar liquid crystal materials by using Elastic continuum theory-based numerical calculations and computer simulations. This dissertation work also presents the coarse-grained theory of twist-bend phase. This theory predicts normal modes of fluctuation in both sides of nematic to twist-bend transition, which then compared with light scattering experiments. Macroscopic elastic and electric properties of twist-bend nematics

  2. Multiple Order Diffractions by laser-Injured Transient Grating in Nematic MBBA Film

    International Nuclear Information System (INIS)

    Kim, Seong Kyu; Kim, Hack Jin

    1999-01-01

    The laser-induced transient grating method is applied to study the dynamics of the nematic MBBA film. The nanosecond laser pulses of 355 nm are used to make the transient grating and the cw He-Ne laser of 633 nm is used to probe the dynamics. Strong multiple order diffractions are observed at high nematic temperatures. The reordering process induced by the phototransformed state, which is the locally melted state from the nematic sample, is attributed to the main origin of the multiple order diffractions from the nematic MBBA. The characteristics of the multiple order gratings are discussed with the grating profiles simulated from the multiple diffraction signals

  3. Analytical description of the Saturn-ring defect in nematic colloids.

    Science.gov (United States)

    Alama, Stan; Bronsard, Lia; Lamy, Xavier

    2016-01-01

    We derive an analytical formula for the Saturn-ring configuration around a small colloidal particle suspended in nematic liquid crystal. In particular we obtain an explicit expression for the ring radius and its dependence on the anchoring energy. We work within Landau-de Gennes theory: Nematic alignment is described by a tensorial order parameter. For nematic colloids this model had previously been used exclusively to perform numerical computations. Our method demonstrates that the tensorial theory can also be used to obtain analytical results, suggesting a different approach to the understanding of nematic colloidal interactions.

  4. Dynamic behavior of a nematic liquid crystal mixed with CoFe2O4 ferromagnetic nanoparticles in a magnetic field

    Directory of Open Access Journals (Sweden)

    Emil Petrescu

    2017-11-01

    Full Text Available The dynamic behavior of a mixture of 4-cyano-4′-pentylbiphenyl (5CB with 1% CoFe2O4 nanoparticles was analyzed. Experimental data indicate a high stability of the nematic director in the mixture compared to a reference 5CB sample in the magnetic field. The ferrite nanoparticles agglomerate forming long chains as observed in polarized microscopy images. These chains have a very high influence on the magneto-optic effect of the cell. When the magnetic field is applied on the mixture, the chains tend to align with the field direction but, due to their large size, they remain oriented obliquely between the support plates. Thus, the nematic molecules anchored on their surface can not reorient with the field and only a small distortion angle of the liquid crystal molecular director is observed. A comparison with a previously developed theoretical model confirms this small deviation.

  5. Quantum Hall Ferroelectrics and Nematics in Multivalley Systems

    Science.gov (United States)

    Sodemann, Inti; Zhu, Zheng; Fu, Liang

    2017-10-01

    We study broken symmetry states at integer Landau-level fillings in multivalley quantum Hall systems whose low-energy dispersions are anisotropic. When the Fermi surface of individual pockets lacks twofold rotational symmetry, like in bismuth (111) [Feldman et al. , Observation of a Nematic Quantum Hall Liquid on the Surface of Bismuth, Science 354, 316 (2016), 10.1126/science.aag1715] and in Sn1 -xPbxSe (001) [Dziawa et al., Topological Crystalline Insulator States in Pb1 -xSnxSe , Nat. Mater. 11, 1023 (2012), 10.1038/nmat3449] surfaces, interactions tend to drive the formation of quantum Hall ferroelectric states. We demonstrate that the dipole moment in these states has an intimate relation to the Fermi surface geometry of the parent metal. In quantum Hall nematic states, like those arising in AlAs quantum wells, we demonstrate the existence of unusually robust Skyrmion quasiparticles.

  6. Morphology of Colloidal Particles Dispersed in Nematic Solvent

    Science.gov (United States)

    Kumar, Anupam; Mandal, Biplab Kumar; Mishra, Pankaj

    2016-10-01

    We have studied a system of spherical colloidal particles suspended in nematic liquid crystal confined to a two-dimensional plane. The dispersed colloidal particles pervert the uniform orientation of nematic resulting in topological defects. This small change in director field induces elastic interaction in the system. Considering the system exhibiting octopolar symmetry, the interaction of the particles can be described by octopole-octopole interaction potential which on some suitable scaling has the form, βu(r) ≈ Γ/r7, where Γ is dimensionless interaction strength parameter. We have calculated the pair correlation function and radial distribution function of the system by employing Roger-Young's integral equation theory, where the mixing parameter a, is obtained by demanding the consistency in pressure via virial and compressibility routs. With the increase in interaction strength, the system is found to become more ordered.

  7. Morphology of Colloidal Particles Dispersed in Nematic Solvent

    International Nuclear Information System (INIS)

    Kumar, Anupam; Kumar Mandal, Biplab; Mishra, Pankaj

    2016-01-01

    We have studied a system of spherical colloidal particles suspended in nematic liquid crystal confined to a two-dimensional plane. The dispersed colloidal particles pervert the uniform orientation of nematic resulting in topological defects. This small change in director field induces elastic interaction in the system. Considering the system exhibiting octopolar symmetry, the interaction of the particles can be described by octopole-octopole interaction potential which on some suitable scaling has the form, βu(r) ≈ Γ/r 7 , where Γ is dimensionless interaction strength parameter. We have calculated the pair correlation function and radial distribution function of the system by employing Roger-Young's integral equation theory, where the mixing parameter a, is obtained by demanding the consistency in pressure via virial and compressibility routs. With the increase in interaction strength, the system is found to become more ordered. (paper)

  8. Nematicity, magnetism and superconductivity in FeSe

    Science.gov (United States)

    Böhmer, Anna E.; Kreisel, Andreas

    2018-01-01

    Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c, ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.

  9. Modified dynamical equation for dye doped nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Manohar, Rajiv, E-mail: rajlu1@rediffmail.co [Liquid Crystal Research Lab, Physics Department, University of Lucknow, Lucknow 226007 (India); Misra, Abhishek Kumar; Srivastava, Abhishek Kumar [Liquid Crystal Research Lab, Physics Department, University of Lucknow, Lucknow 226007 (India)

    2010-04-15

    Dye doped liquid crystals show changed dielectric properties in comparison to pure liquid crystals. These changes are strongly dependent on the concentration of dye. In the present work we have measured dielectric properties of standard nematic liquid crystals E-24 and its two guest host mixtures of different concentrations with Anthraquinone dye D5. The experimental results are fitted using linear response and in the light of this we have proposed some modifications in the dynamical equation for the nematic liquid crystals by introducing two new variables as dye concentration coefficients. The limitations of the proposed equation in high temperature range have also been discussed. With the help of the proposed dynamical equation for the guest-host liquid crystals (GHLCs) it is possible to predict the various parameters like rotational viscosity, dielectric anisotropy and relaxation time for GHLCs at other concentrations of dye in liquid crystals theoretically.

  10. Creation and manipulation of topological states in chiral nematic microspheres

    Science.gov (United States)

    Orlova, Tetiana; Aßhoff, Sarah Jane; Yamaguchi, Tadatsugu; Katsonis, Nathalie; Brasselet, Etienne

    2015-07-01

    Topology is a universal concept that is encountered in daily life and is known to determine many static and dynamical properties of matter. Taming and controlling the topology of materials therefore constitutes a contemporary interdisciplinary challenge. Building on the controllable spatial properties of soft matter appears as a relevant strategy to address the challenge, in particular, because it may lead to paradigmatic model systems that allow checking theories experimentally. Here we report experimentally on a wealth of complex free-standing metastable topological architectures at the micron scale, in frustrated chiral nematic droplets. These results support recent works predicting the formation of free-standing knotted and linked disclination structures in confined chiral nematic fluids. We also demonstrate that various kinds of external fields (thermal, electrical and optical) can be used to achieve topological remote control. All this may foster the development of new devices based on topologically structured soft media.

  11. Converse flexoelectric effect in bent-core nematic liquid crystals.

    Science.gov (United States)

    Kumar, Pramoda; Marinov, Y G; Hinov, H P; Hiremath, Uma S; Yelamaggad, C V; Krishnamurthy, K S; Petrov, A G

    2009-07-09

    We report on the converse flexoelectric effect in two bent-core nematic liquid crystals with opposite dielectric anisotropies. The results are based on electro-optic investigations of inplane field-driven distortions in homeotropic samples (the Helfrich method). They are interpreted by an extension of the Helfrich theory that takes into account the higher order distortions. The bend flexocoefficient for both the compounds is of the usual order of magnitude as in calamitics, unlike in a previously investigated bent-core nematic for which giant values of the bend flexocoefficient are reported. In order to resolve this discrepancy, we propose a molecular model with nonpolar clusters showing quadrupolar flexoelectricity. The study also includes measurements on surface polarization instabilities in the dielectrically positive material; the splay flexocoefficient thereby deduced is also of the conventional order.

  12. Giant flexoelectricity of bent-core nematic liquid crystals.

    Science.gov (United States)

    Harden, J; Mbanga, B; Eber, N; Fodor-Csorba, K; Sprunt, S; Gleeson, J T; Jákli, A

    2006-10-13

    Flexoelectricity is a coupling between orientational deformation and electric polarization. We present a direct method for measuring the flexoelectric coefficients of nematic liquid crystals (NLCs) via the electric current produced by periodic mechanical flexing of the NLC's bounding surfaces. This method is suitable for measuring the response of bent-core liquid crystals, which are expected to demonstrate a much larger flexoelectric effect than traditional, calamitic liquid crystals. Our results reveal that not only is the bend flexoelectric coefficient of bent-core NLCs gigantic (more than 3 orders of magnitude larger than in calamitics) but also it is much larger than would be expected from microscopic models based on molecular geometry. Thus, bent-core nematic materials can form the basis of a technological breakthrough for conversion between mechanical and electrical energy.

  13. Nematicity, magnetism and superconductivity in FeSe.

    Science.gov (United States)

    Böhmer, Anna E; Kreisel, Andreas

    2018-01-17

    Iron-based superconductors are well known for their complex interplay between structure, magnetism and superconductivity. FeSe offers a particularly fascinating example. This material has been intensely discussed because of its extended nematic phase, whose relationship with magnetism is not obvious. Superconductivity in FeSe is highly tunable, with the superconducting transition temperature, T c , ranging from 8 K in bulk single crystals at ambient pressure to almost 40 K under pressure or in intercalated systems, and to even higher temperatures in thin films. In this topical review, we present an overview of nematicity, magnetism and superconductivity, and discuss the interplay of these phases in FeSe. We focus on bulk FeSe and the effects of physical pressure and chemical substitutions as tuning parameters. The experimental results are discussed in the context of the well-studied iron-pnictide superconductors and interpretations from theoretical approaches are presented.

  14. Forced convection in nanoparticles doped nematics without reorientation

    International Nuclear Information System (INIS)

    Hakobyan, M.R.; Hakobyan, R.S.

    2016-01-01

    The problem of forced convection in the cell of nanoparticles doped nematic liquid crystal with both boundaries being free, plane and isotherm is discussed. These boundary conditions (offered by Rayleigh) allow to get simple and exact solution for boundary-value problem, from which its most important peculiarities can be clearly seen. Particularly, there appears a possibility to induce convection without reorientation of liquid crystal director. It was shown that nanoparticles could have significant influence on the convection

  15. Nematic biaxiality in a bent-core material

    Science.gov (United States)

    Yoon, Hyung Guen; Kang, Shin-Woong; Dong, Ronald Y.; Marini, Alberto; Suresh, Kattera A.; Srinivasarao, Mohan; Kumar, Satyendra

    2010-05-01

    The results of a recent investigation of the nematic biaxiality in a bent-core mesogen (A131) are in apparent disagreement with earlier claims. Samples of mesogen A131 used in the two studies were investigated with polarized optical microscopy, conoscopy, carbon-13 NMR, and crossover frequency measurements. The results demonstrate that textural changes associated with the growth of biaxial nematic order appear at ˜149°C . The Maltese cross observed in the conoscopic figure gradually splits into two isogyres at lower temperatures indicating phase biaxiality. Presence of the uniaxial to biaxial nematic phase transition is further confirmed by temperature trends of local order parameters based on C13 chemical shifts in NMR experiments. Frequency switching measurements also clearly reveal a transition at 149°C . Differences between the two reports appear to be related to the presence of solvent, impurities, and/or adsorbed gases in samples of A131 used in the study of Van Le [Phys. Rev. E 79, 030701 (2009)].

  16. Nematic quantum liquid crystals of bosons in frustrated lattices

    Science.gov (United States)

    Zhu, Guanyu; Koch, Jens; Martin, Ivar

    2016-04-01

    The problem of interacting bosons in frustrated lattices is an intricate one due to the absence of a unique minimum in the single-particle dispersion where macroscopic number of bosons can condense. Here, we consider a family of tight-binding models with macroscopically degenerate lowest energy bands, separated from other bands by a gap. We predict the formation of exotic states that spontaneously break rotational symmetry at relatively low filling. These states belong to three nematic phases: Wigner crystal, supersolid, and superfluid. The Wigner crystal phase is established exactly at low filling. Supersolid and superfluid phases, at larger filling, are obtained by making use of a projection onto the flat band, construction of an appropriate Wannier basis, and subsequent mean-field treatment. The nematic superfluid that we predict is uniform in real space but has an anisotropic momentum distribution, providing a novel scenario for Bose condensation with an additional nematic order. Our findings open up a promising direction of studying microscopic quantum liquid crystalline phases of bosons.

  17. Topological Nematic States and Non-Abelian Lattice Dislocations

    Directory of Open Access Journals (Sweden)

    Maissam Barkeshli

    2012-08-01

    Full Text Available An exciting new prospect in condensed matter physics is the possibility of realizing fractional quantum Hall states in simple lattice models without a large external magnetic field. A fundamental question is whether qualitatively new states can be realized on the lattice as compared with ordinary fractional quantum Hall states. Here we propose new symmetry-enriched topological states, topological nematic states, which are a dramatic consequence of the interplay between the lattice translational symmetry and topological properties of these fractional Chern insulators. The topological nematic states are realized in a partially filled flat band with a Chern number N, which can be mapped to an N-layer quantum Hall system on a regular lattice. However, in the topological nematic states the lattice dislocations can act as wormholes connecting the different layers and effectively change the topology of the space. Consequently, lattice dislocations become defects with a nontrivial quantum dimension, even when the fractional quantum Hall state being realized is, by itself, Abelian. Our proposal leads to the possibility of realizing the physics of topologically ordered states on high-genus surfaces in the lab even though the sample has only the disk geometry.

  18. Enhancement of polar anchoring strength in a graphene-nematic suspension and its effect on nematic electro-optic switching

    Science.gov (United States)

    Basu, Rajratan

    2017-07-01

    A small quantity of monolayer graphene flakes is doped in a nematic liquid crystal (LC), and the effective polar anchoring strength coefficient between the LC and the alignment substrate is found to increase by an order of magnitude. The hexagonal pattern of graphene can interact with the LC's benzene rings via π -π electron stacking, enabling the LC to anchor to the graphene surface homogeneously (i.e., planar anchoring). When the LC cell is filled with the graphene-doped LC, some graphene flakes are preferentially attached to the alignment layer and modify the substrate's anchoring property. These spontaneously deposited graphene flakes promote planar anchoring at the substrate and the polar anchoring energy at alignment layer is enhanced significantly. The enhanced anchoring energy is found to impact favorably on the electro-optic response of the LC. Additional studies reveal that the nematic electro-optic switching is significantly faster in the LC-graphene hybrid than that of the pure LC.

  19. The dependency of twist-bend nematic liquid crystals on molecular structure: a progression from dimers to trimers, oligomers and polymers.

    Science.gov (United States)

    Mandle, Richard J

    2016-09-28

    This article gives an overview on recent developments concerning the twist-bend nematic phase. The twist-bend nematic phase has been discussed as the missing link between the uniaxial nematic mesophase (N) and the helical chiral nematic phase (N*). After an introduction discussing the key physical properties of the N TB phase and the methods used to identify the twist-bend nematic mesophase this review focuses on structure property relationships and molecular features that govern the incidence of this phase.

  20. Biaxial nematic liquid crystals theory, simulation and experiment

    CERN Document Server

    Luckhurst, Geoffrey R

    2015-01-01

    Liquid Crystals are a state of matter that have properties between those of conventional liquid and those of a solid crystal. Thermotropic liquid crystals react to changes in temperature or, in some cases, pressure. The reaction of lyotropic liquid crystals, which are used in the manufacture of soaps and detergents, depends on the type of solvent they are mixed with. Since the accidental discovery of the chiral nematic (ordered) phase in 1888 many liquid crystal phases have been found, sometimes by chance and sometimes by design. The existence of one such phase was predicted by Freiser in 197

  1. Theory of nonlocal soliton interaction in nematic liquid crystals

    DEFF Research Database (Denmark)

    Rasmussen, Per Dalgaard; Bang, Ole; Krolikowski, Wieslaw

    2005-01-01

    We investigate interactions between spatial nonlocal bright solitons in nematic liquid crystals using an analytical “effective particle” approach as well as direct numerical simulations. The model predicts attraction of out-of-phase solitons and the existence of their stable bound state....... This nontrivial property is solely due to the nonlocal nature of the nonlinear response of the liquid crystals. We further predict and verify numerically the critical outwards angle and degree of nonlocality which determine the transition between attraction and repulsion of out-of-phase solitons....

  2. Millisecond time resolution neutron reflection from a nematic liquid crystal

    International Nuclear Information System (INIS)

    Dalgliesh, R.M.; Lau, Y.G.J.; Richardson, R.M.; Riley, D.J.

    2004-01-01

    The director reorientation of the liquid crystal 4,4' octyl cyanobiphenyl in the nematic phase under application of bursts of ac field have been observed using time-resolved neutron scattering in reflection geometry. The relaxation of the director has been shown to agree with existing theory, as determined by material and cell parameters. This result shows that it is possible to use neutron reflection measurements from buried interfaces to follow kinetic processes on a time scale comparable with the pulse length of the ISIS neutron source (20 ms)

  3. Effective Field Theory of Fractional Quantized Hall Nematics

    Energy Technology Data Exchange (ETDEWEB)

    Mulligan, Michael; /MIT, LNS; Nayak, Chetan; /Station Q, UCSB; Kachru, Shamit; /Stanford U., Phys. Dept. /SLAC

    2012-06-06

    We present a Landau-Ginzburg theory for a fractional quantized Hall nematic state and the transition to it from an isotropic fractional quantum Hall state. This justifies Lifshitz-Chern-Simons theory - which is shown to be its dual - on a more microscopic basis and enables us to compute a ground state wave function in the symmetry-broken phase. In such a state of matter, the Hall resistance remains quantized while the longitudinal DC resistivity due to thermally-excited quasiparticles is anisotropic. We interpret recent experiments at Landau level filling factor {nu} = 7/3 in terms of our theory.

  4. Traveling waves in twisted nematic liquid crystal cells

    International Nuclear Information System (INIS)

    Zakharov, A.V.; Vakulenko, A.A.

    2007-01-01

    We have described a novel reorientation mechanism in the form of the traveling waves, under influence of an external electric field, directed parallel to both glass plates, which occur in the twisted nematic cell (TNC). It is found that the slowest velocity of the traveling front is proportional to the field strength, and, approximately, in three times higher than the front velocity corresponding to the non-traveling solution. The value of the critical electric field E cr which may excite the traveling waves in the TNC in π times less than the value of the threshold electric field E th corresponding to the untwisted geometry

  5. Distinctive orbital anisotropy observed in the nematic state of a FeSe thin film

    International Nuclear Information System (INIS)

    Zhang, Y.; Lawrence Berkeley National Laboratory; Yi, M.; Stanford University, CA; Liu, Z.-K.

    2016-01-01

    Nematic state, where the system is translationally invariant but breaks the rotational symmetry, has drawn great attentions recently due to experimental observations of such a state in both cuprates and iron-based superconductors. The mechanism of nematicity that is likely tied to the pairing mechanism of high-T c , however, still remains controversial. Here, we studied the electronic structure of multilayer FeSe film by angle-resolved photoemission spectroscopy (ARPES). We found that the FeSe film enters the nematic state around 125 K, while the electronic signature of long range magnetic order has not been observed down to 20K indicating the non-magnetic origin of the nematicity. The band reconstruction in the nematic state is characterized by the splitting of the d xz and d yz bands. More intriguingly, such energy splitting is strong momentum dependent with the largest band splitting of ~80 meV at the zone corner. The simple on-site ferro-orbital ordering is insufficient to reproduce the nontrivial momentum dependence of the band reconstruction. Instead, our results suggest that the nearest-neighbor hopping of d xz and d yz is highly anisotropic in the nematic state, the origin of which holds the key in understanding the nematicity in iron-based superconductors.

  6. Geometry of thresholdless active flow in nematic microfluidics

    Science.gov (United States)

    Green, Richard; Toner, John; Vitelli, Vincenzo

    2017-10-01

    Active nematics are orientationally ordered but apolar fluids composed of interacting constituents individually powered by an internal source of energy. When activity exceeds a system-size-dependent threshold, spatially uniform active apolar fluids undergo a hydrodynamic instability leading to spontaneous macroscopic fluid flow. Here we show that a special class of spatially nonuniform configurations of such active apolar fluids display laminar (i.e., time-independent) flow even for arbitrarily small activity. We also show that two-dimensional active nematics confined on a surface of nonvanishing Gaussian curvature must necessarily experience a nonvanishing active force. This general conclusion follows from a key result of differential geometry: Geodesics must converge or diverge on surfaces with nonzero Gaussian curvature. We derive the conditions under which such curvature-induced active forces generate thresholdless flow for two-dimensional curved shells. We then extend our analysis to bulk systems and show how to induce thresholdless active flow by controlling the curvature of confining surfaces, external fields, or both. The resulting laminar flow fields are determined analytically in three experimentally realizable configurations that exemplify this general phenomenon: (i) toroidal shells with planar alignment, (ii) a cylinder with nonplanar boundary conditions, and (iii) a Frederiks cell that functions like a pump without moving parts. Our work suggests a robust design strategy for active microfluidic chips and could be tested with the recently discovered living liquid crystals.

  7. Nematic DNA Thermotropic Liquid Crystals with Photoresponsive Mechanical Properties.

    Science.gov (United States)

    Zhang, Lei; Maity, Sourav; Liu, Kai; Liu, Qing; Göstl, Robert; Portale, Giuseppe; Roos, Wouter H; Herrmann, Andreas

    2017-09-01

    Over the last decades, water-based lyotropic liquid crystals of nucleic acids have been extensively investigated because of their important role in biology. Alongside, solvent-free thermotropic liquid crystals (TLCs) from DNA are gaining great interest, owing to their relevance to DNA-inspired optoelectronic applications. Up to now, however, only the smectic phase of DNA TLCs has been reported. The development of new mesophases including nematic, hexagonal, and cubic structures for DNA TLCs remains a significant challenge, which thus limits their technological applications considerably. In this work, a new type of DNA TLC that is formed by electrostatic complexation of anionic oligonucleotides and cationic surfactants containing an azobenzene (AZO) moiety is demonstrated. DNA-AZO complexes form a stable nematic mesophase over a temperature range from -7 to 110 °C and retain double-stranded DNA structure at ambient temperature. Photoisomerization of the AZO moieties from the E- to the Z-form alters the stiffness of the DNA-AZO hybrid materials opening a pathway toward the development of DNA TLCs as stimuli-responsive biomaterials. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  8. Electroconvection of pure nematic liquid crystals without free charge carriers.

    Science.gov (United States)

    Lee, Kuang-Wu; Pöschel, Thorsten

    2017-11-29

    We consider electroconvection as a response of nematic liquid crystals to an external electric AC field, in the absence of free charge carriers. Previous experimental and theoretical results emphasized charge carriers as a necessary precondition of electroconvection because free-charges in the fluid can respond to an external electric field. Therefore, ionized molecules are considered as responsible for the driving of electroconvective flows. In experiments, finite conductivity is achieved by adding charge-carrying dye molecules or in non-dyed liquid crystals by impurities of the samples. The phenomenon of electroconvection is explained by the Carr-Helfrich theory, supported by numerical simulations. In the present paper, we show that electroconvection may occur also in pure nematic liquid crystals. By means of particle-based numerical simulations we found that bound charges emerge by alignment of polarized liquid crystal molecules in response to the external electric field. In our simulations we could reproduce the characteristic features of electroconvection, such as director-flow patterns, the phase-transition in the voltage-frequency diagram, and dislocation climb/glide motion, which are well known from experiments and hydrodynamic simulations under the assumption of free charge carriers.

  9. Topological Defects in a Living Nematic Ensnare Swimming Bacteria

    Directory of Open Access Journals (Sweden)

    Mikhail M. Genkin

    2017-03-01

    Full Text Available Active matter exemplified by suspensions of motile bacteria or synthetic self-propelled particles exhibits a remarkable propensity to self-organization and collective motion. The local input of energy and simple particle interactions often lead to complex emergent behavior manifested by the formation of macroscopic vortices and coherent structures with long-range order. A realization of an active system has been conceived by combining swimming bacteria and a lyotropic liquid crystal. Here, by coupling the well-established and validated model of nematic liquid crystals with the bacterial dynamics, we develop a computational model describing intricate properties of such a living nematic. In faithful agreement with the experiment, the model reproduces the onset of periodic undulation of the director and consequent proliferation of topological defects with the increase in bacterial concentration. It yields a testable prediction on the accumulation of bacteria in the cores of +1/2 topological defects and depletion of bacteria in the cores of -1/2 defects. Our dedicated experiment on motile bacteria suspended in a freestanding liquid crystalline film fully confirms this prediction. Our findings suggest novel approaches for trapping and transport of bacteria and synthetic swimmers in anisotropic liquids and extend a scope of tools to control and manipulate microscopic objects in active matter.

  10. Flexoelectricity in an oxadiazole bent-core nematic liquid crystal

    Energy Technology Data Exchange (ETDEWEB)

    Kaur, S., E-mail: Sarabjot.Kaur@manchester.ac.uk; Panov, V. P.; Gleeson, H. F. [School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom); Greco, C.; Ferrarini, A. [Department of Chemical Sciences, University of Padua, Padua I-35131 (Italy); Görtz, V. [Department of Chemistry, University of York, York YO10 5DD (United Kingdom); Department of Chemistry, University of Lancaster, Lancaster LA1 4YB (United Kingdom); Goodby, J. W. [Department of Chemistry, University of York, York YO10 5DD (United Kingdom)

    2014-12-01

    We have determined experimentally the magnitude of the difference in the splay and bend flexoelectric coefficients, |e{sub 1} − e{sub 3}|, of an oxadiazole bent-core liquid crystal by measuring the critical voltage for the formation of flexodomains together with their wave number. The coefficient |e{sub 1} − e{sub 3}| is found to be a factor of 2–3 times higher than in most conventional calamitic nematic liquid crystals, varying from 8 pCm{sup −1} to 20 pCm{sup −1} across the ∼60 K—wide nematic regime. We have also calculated the individual flexoelectric coefficients e{sub 1} and e{sub 3}, with the dipolar and quadrupolar contributions of the bent-core liquid crystal by combining density functional theory calculations with a molecular field approach and atomistic modelling. Interestingly, the magnitude of the bend flexoelectric coefficient is found to be rather small, in contrast to common expectations for bent-core molecules. The calculations are in excellent agreement with the experimental values, offering an insight into how molecular parameters contribute to the flexoelectric coefficients and illustrating a huge potential for the prediction of flexoelectric behaviour in bent-core liquid crystals.

  11. Flexoelectricity in an oxadiazole bent-core nematic liquid crystal

    International Nuclear Information System (INIS)

    Kaur, S.; Panov, V. P.; Gleeson, H. F.; Greco, C.; Ferrarini, A.; Görtz, V.; Goodby, J. W.

    2014-01-01

    We have determined experimentally the magnitude of the difference in the splay and bend flexoelectric coefficients, |e 1 − e 3 |, of an oxadiazole bent-core liquid crystal by measuring the critical voltage for the formation of flexodomains together with their wave number. The coefficient |e 1 − e 3 | is found to be a factor of 2–3 times higher than in most conventional calamitic nematic liquid crystals, varying from 8 pCm −1 to 20 pCm −1 across the ∼60 K—wide nematic regime. We have also calculated the individual flexoelectric coefficients e 1 and e 3 , with the dipolar and quadrupolar contributions of the bent-core liquid crystal by combining density functional theory calculations with a molecular field approach and atomistic modelling. Interestingly, the magnitude of the bend flexoelectric coefficient is found to be rather small, in contrast to common expectations for bent-core molecules. The calculations are in excellent agreement with the experimental values, offering an insight into how molecular parameters contribute to the flexoelectric coefficients and illustrating a huge potential for the prediction of flexoelectric behaviour in bent-core liquid crystals

  12. Laser Induced Refractive Index Change in Nematic Liquid Crystals

    Directory of Open Access Journals (Sweden)

    Crispulo Larraga

    1999-12-01

    Full Text Available We report the observation of laser induced refractive index change for a homeotropically aligned nematic liquid crystal (BDH-E7 film of 10 mm thickness. Diffraction rings were observed when an intense Ar+ ion laser hits a homeotropically aligned nematic liquid crystal at normal incidence above a threshold of 110 KW/cm2, which correspond to the threshold of the Optical Freedericksz Transition (OFT. Above the threshold, as the laser intensity was increased, the number of observed diffraction rings likewise increased. The mechanism for optical molecular reorientation has a great dependence on elastic restoring forces. By exploring the dependence of bend elastic constant, K33 with Freedericksz transition, the value of the K33 was calculated at 2.6 x 10-12 N. To investigate the behavior of Dn as a function of intensity, an experiment was performed for oblique laser incidence. It was shown that the refractive index change increased linearly from values of 0.00 1 to 0.18 at laser intensities ranging from 50 KW /cm2 to 200 KW /cm2. The Kerr coefficient n2 was calculated for various laser incidence angles.

  13. Simple theory of transitions between smectic, nematic, and isotropic phases

    Science.gov (United States)

    Emelyanenko, A. V.; Khokhlov, A. R.

    2015-05-01

    The transitions between smectic, nematic, and isotropic phases are investigated in the framework of a unified molecular-statistical approach. The new translational order parameter is different from the one introduced in K. Kobayashi [Phys. Lett. A 31, 125 (1970)] and W. L. McMillan [Phys. Rev. A 4, 1238 (1971)]. The variance of the square sine of intermolecular shift angle along the director is introduced to take self-consistently into account the most probable location of the molecules with respect to each other, which is unique for every liquid crystal (LC) material and is mainly responsible for the order parameters and phase sequences. The mean molecular field was treated in terms of only two parameters specific to any intermolecular potential of elongated molecules: (1) its global minimum position with respect to the shift of two interacting molecules along the director and (2) its inhomogeneity/anisotropy ratio. A simple molecular model is also introduced, where the global minimum position is determined by the linking groups elongation Δ/d, while the inhomogeneity/anisotropy ratio Gβ/Gγ is determined by the ratio of electrostatic and dispersion contributions. All possible phase sequences, including abrupt/continuous transformation between the smectic and nematic states and the direct smectic-isotropic phase transition, are predicted. The theoretical prediction is in a good agreement with experimental data for some simple materials correlating with our molecular model, but it is expected to be valid for any LC material.

  14. Optical security devices using nonuniform schlieren texture of UV-curable nematic liquid crystal.

    Science.gov (United States)

    Nakayama, Keizo; Ohtsubo, Junji

    2016-02-10

    We proposed and quantitatively evaluated an optical security device that provides nonuniform or random patterns of schlieren texture in nematic liquid crystal as unique identification information with a design by employing computer image processing and normalized cross correlation. Using the same photomask as the first author's university logo, the written patterns, which were composed of polymerized isotropic areas and polymerized nematic areas, were stable among different cells. Judging from the maximum correlation coefficient of 0.09, the patterns of the schlieren texture were unique in different cells. These results indicate that photocurable nematic liquid crystal materials have the potential to be applied to security devices for anticounterfeiting measures.

  15. The radial-hedgehog solution in Landau–de Gennes' theory for nematic liquid crystals

    KAUST Repository

    MAJUMDAR, APALA

    2011-09-06

    We study the radial-hedgehog solution in a three-dimensional spherical droplet, with homeotropic boundary conditions, within the Landau-de Gennes theory for nematic liquid crystals. The radial-hedgehog solution is a candidate for a global Landau-de Gennes minimiser in this model framework and is also a prototype configuration for studying isolated point defects in condensed matter physics. The static properties of the radial-hedgehog solution are governed by a non-linear singular ordinary differential equation. We study the analogies between Ginzburg-Landau vortices and the radial-hedgehog solution and demonstrate a Ginzburg-Landau limit for the Landau-de Gennes theory. We prove that the radial-hedgehog solution is not the global Landau-de Gennes minimiser for droplets of finite radius and sufficiently low temperatures and prove the stability of the radial-hedgehog solution in other parameter regimes. These results contain quantitative information about the effect of geometry and temperature on the properties of the radial-hedgehog solution and the associated biaxial instabilities. © Copyright Cambridge University Press 2011.

  16. Investigation into the temperature dependence of isotropic- nematic phase transition of Gay- Berne liquid crystals

    Directory of Open Access Journals (Sweden)

    A Avazpour

    2014-12-01

    Full Text Available Density functional approach was used to study the isotropic- nematic (I-N transition and calculate the values of freezing parameters of the Gay- Berne liquid crystal model. New direct and pair correlation functions of a molecular fluid with Gay- Berne pair potential were used. These new functions were used in density functional theory as input to calculate the isotropic- nematic transition densities for elongation at various reduced temperatures. It was observed that the isotropic- nematic transition densities increase as the temperature increases. It was found that the new direct correlation function is suitable to study the isotropic- nematic transition of Gay- Berne liquids. Comparison to other works showed qualitative agreement

  17. The symmetry of the nematic phase of a thermotropic liquid crystal: biaxial or uniaxial?

    Science.gov (United States)

    Fan, S. M.; Fletcher, I. D.; GündoAn, B.; Heaton, N. J.; Kothe, G.; Luckhurst, G. R.; Praefcke, K.

    1993-03-01

    The symmetry of the thermotropic nematic phase of 2,3,4-tri- n-hexyloxycinnamic acid is investigated using deuterium NMR spectroscopy of the nematogen selectively deuterated in the ethylenic bond. In our experiments the sample was spun about an axis orthogonal to the magnetic field in order to produce a random distribution of the director in two dimensions. The resultant NMR powder pattern is characteristic of a partially averaged quadrupolar tensor with cylindrical symmetry and hence of a uniaxial nematic phase. Simulation of the powder patterns reveals that the upper limit to the biaxiality parameter is approximately 0.1 which is in marked contrast to the large values found for lyotropic biaxial nematics. Our result is not, however, necassarily inconsistent with conoscopic measurements which indicated a small optical biaxiality for this thermotropic nematic.

  18. Magnetically driven suppression of nematic order in an iron-based superconductor.

    Science.gov (United States)

    Avci, S; Chmaissem, O; Allred, J M; Rosenkranz, S; Eremin, I; Chubukov, A V; Bugaris, D E; Chung, D Y; Kanatzidis, M G; Castellan, J-P; Schlueter, J A; Claus, H; Khalyavin, D D; Manuel, P; Daoud-Aladine, A; Osborn, R

    2014-05-22

    A theory of superconductivity in the iron-based materials requires an understanding of the phase diagram of the normal state. In these compounds, superconductivity emerges when stripe spin density wave (SDW) order is suppressed by doping, pressure or atomic disorder. This magnetic order is often pre-empted by nematic order, whose origin is yet to be resolved. One scenario is that nematic order is driven by orbital ordering of the iron 3d electrons that triggers stripe SDW order. Another is that magnetic interactions produce a spin-nematic phase, which then induces orbital order. Here we report the observation by neutron powder diffraction of an additional fourfold-symmetric phase in Ba1-xNaxFe2As2 close to the suppression of SDW order, which is consistent with the predictions of magnetically driven models of nematic order.

  19. Simulations of nematic homopolymer melts using particle-based models with interactions expressed through collective variables

    International Nuclear Information System (INIS)

    Daoulas, Kostas Ch; Rühle, Victor; Kremer, Kurt

    2012-01-01

    We develop a hybrid Monte Carlo approach for modelling nematic liquid crystals of homopolymer melts. The polymer architecture is described with a discrete worm-like chain model. A quadratic density functional accounts for the limited compressibility of the liquid, while an additional quadratic functional of the local orientation tensor of the segments captures the nematic ordering. The approach can efficiently address large systems parametrized according to volumetric and conformational properties, representative of real polymeric materials. The results of the simulations regarding the influence of the molecular weight on the isotropic-nematic transition are compared to predictions from a Landau-de Gennes free energy expansion. The formation of the nematic phase is addressed within Rouse-like dynamics, realized using the current model. (paper)

  20. Steady States and Dynamics of 2-D Nematic Polymers Driven by an Imposed Weak Shear

    National Research Council Canada - National Science Library

    Zhou, Hong; Wang, Hongyun

    2007-01-01

    ...]: in the absence of flow the isotropic-nematic phase transition occurs at U =2 where U is the normalized polymer concentration, representing the intensity of the Maier-Saupe interaction potential...

  1. Asymmetric director structures and flexoelectricity in nematic pi-cell devices

    Science.gov (United States)

    Tartan, Chloe C.; Elston, Steve J.

    2015-08-01

    The sum of the flexoelectric coefficients in a liquid crystal material has been measured in nematic pi-cell devices, based on a method that exploits the asymmetry in the director configurations of the different states in a pi-cell, the uniform surface alignment polarities, and the influence of ions. A value of |e1 + e3| = 10 pC m-1 was measured from data-theory comparisons in the standard commercial eutectic E7 nematic liquid crystal mixture.

  2. Theory of Electron Nematic Order in LaOFeAs

    Energy Technology Data Exchange (ETDEWEB)

    Fang, Chen

    2010-04-06

    We study a spin S quantum Heisenberg model on the Fe lattice of the rare-earth oxypnictide superconductors. Using both large S and large N methods, we show that this model exhibits a sequence of two phase transitions: from a high temperature symmetric phase to a narrow region of intermediate 'nematic' phase, and then to a low temperature spin ordered phase. Identifying phases by their broken symmetries, these phases correspond precisely to the sequence of structural (tetragonal to monoclinic) and magnetic transitions that have been recently revealed in neutron scattering studies of LaOFeAs. The structural transition can thus be identified with the existence of incipient ('fluctuating') magnetic order.

  3. Optical solitons in nematic liquid crystals: model with saturation effects

    Science.gov (United States)

    Borgna, Juan Pablo; Panayotaros, Panayotis; Rial, Diego; de la Vega, Constanza Sánchez F.

    2018-04-01

    We study a 2D system that couples a Schrödinger evolution equation to a nonlinear elliptic equation and models the propagation of a laser beam in a nematic liquid crystal. The nonlinear elliptic equation describes the response of the director angle to the laser beam electric field. We obtain results on well-posedness and solitary wave solutions of this system, generalizing results for a well-studied simpler system with a linear elliptic equation for the director field. The analysis of the nonlinear elliptic problem shows the existence of an isolated global branch of solutions with director angles that remain bounded for arbitrary electric field. The results on the director equation are also used to show local and global existence, as well as decay for initial conditions with sufficiently small L 2‑norm. For sufficiently large L 2‑norm we show the existence of energy minimizing optical solitons with radial, positive and monotone profiles.

  4. Soliton-like defects in nematic liquid crystal thin layers

    Energy Technology Data Exchange (ETDEWEB)

    Chuvyrov, A. N.; Krekhov, A. P.; Lebedev, Yu. A., E-mail: lebedev@anrb.ru; Timirov, Yu. I. [Russian Academy of Sciences, Institute of Molecule and Crystal Physics, Ufa Research Center (Russian Federation)

    2016-11-15

    The nonsingular soliton-like defects in plane nematic liquid crystal (NLC) layers and spherical NLC drops are experimentally detected and studied when the interaction of NLC molecules with a bounding surface is varied. The dynamics and the annihilation of nonsingular defects of opposite signs on a plane surface are investigated. Periodic transformations of the soliton-like defects in NLC drops in an electric field are detected. The theory of elasticity is used to show that the surface energy taken into account in the total free energy of NLC in the case of weak anchoring leads to the possibility of nonsingular solutions of a director equilibrium equation. The calculated pictures of director distribution in a plane NLC layer and in a spherical NLC drop characterized by weak surface anchoring agree well with the results of polarized light optical observations.

  5. Fullerene (C60) nano-colloids in nematic liquid crystal

    Science.gov (United States)

    Visco, Angelo; Sobczak, Kevin; Mahmood, Rizwan

    2015-03-01

    We report high resolution homodyne light scattering studies to probe director fluctuations in bend/splay mode in bulk nematic liquid crystal and as a function of fullerene (C60) nanoparticles concentration. The preliminary analysis shows that the relaxation time of these fluctuations is fairly constant with in the experimental uncertainty despite the constraints imposed on the director fluctuations due to the insertion of nano colloids. The relaxation time extracted from the data found to be in nano seconds range and the diffusion constant (D) found to be, D = 4.29 x 106 cm/sec. The authors acknowledge the financial support from grants office, Dean, college of Health, Environment & Science and the physics department.

  6. New theories for smectic and nematic liquid crystalline polymers

    International Nuclear Information System (INIS)

    Dowell, F.

    1987-01-01

    A summary of results from new statistical-physics theories for both backbone and side-chain liquid crystalline polymers (LCPs) and for mixtures with LCPs is presented. Thermodynamic and molecular ordering properties (including odd-even effects) have been calculated as a function of pressure, density, temperature, and molecule chemical structures (including degree of polymerization and the following properties of the chemical structures of the repeat units: lengths and shapes, intra-chain rotation energies, dipole moments, site-site polarizabilities and Lennard-Jones potentials, etc.) in nematic and multiple smectic-A LC phases and in the isotropic liquid phase. These theories can also be applied to combined LCPs. Since these theories have no ad hoc or arbitrarily adjustable parameters, these theories have been used to design new LCPs and new solvents and to predict and explain properties

  7. Hydrodynamically controlled optical propagation in a nematic fiber

    International Nuclear Information System (INIS)

    Corella-Madueno, A.; Adrian Reyes, J.

    2008-01-01

    We show that a cylindrical guide whose core is a liquid crystal (LC), having initially the escaped configuration, can be mechanically controlled. Indeed, we show how the nematic textures, distorted by a pressure gradient applied along the cylinder, are able to significantly alter the propagation of the optical fields. Above certain critical pressure, the fiber only conducts the optical beams within two coaxial but unconnected regions, where the light can propagate independently. We demonstrate this result by using two complementary formalisms. For multimodal waveguides in the small wavelength limit and by performing exact numerical calculation of the transverse magnetic (TM) modes distribution in the guide. The last calculation not only corroborates the asymptotic results of the geometrical analysis, but evinces the way in which the signals propagating in each region overlap and interact each other, when their wavelength are larger than the regions thickness

  8. Hydrodynamically controlled optical propagation in a nematic fiber

    Energy Technology Data Exchange (ETDEWEB)

    Corella-Madueno, A. [Departamento de Fisica, Universidad de Sonora, Apartado Postal 1626, Hermosillo, Sonora (Mexico); Adrian Reyes, J. [Departamento de Fisica Quimica, Instituto de Fisica, Universidad Nacional Autonoma de Mexico, Mexico D. F., Mexico C. P. 04510 (Mexico)], E-mail: adrian@fisica.unam.mx

    2008-05-01

    We show that a cylindrical guide whose core is a liquid crystal (LC), having initially the escaped configuration, can be mechanically controlled. Indeed, we show how the nematic textures, distorted by a pressure gradient applied along the cylinder, are able to significantly alter the propagation of the optical fields. Above certain critical pressure, the fiber only conducts the optical beams within two coaxial but unconnected regions, where the light can propagate independently. We demonstrate this result by using two complementary formalisms. For multimodal waveguides in the small wavelength limit and by performing exact numerical calculation of the transverse magnetic (TM) modes distribution in the guide. The last calculation not only corroborates the asymptotic results of the geometrical analysis, but evinces the way in which the signals propagating in each region overlap and interact each other, when their wavelength are larger than the regions thickness.

  9. Light-controlled topological charge in a nematic liquid crystal

    Science.gov (United States)

    Nikkhou, Maryam; Škarabot, Miha; Čopar, Simon; Ravnik, Miha; Žumer, Slobodan; Muševič, Igor

    2015-02-01

    Creating, imaging, and transforming the topological charge in a superconductor, a superfluid, a system of cold atoms, or a soft ferromagnet is a difficult--if not impossible--task because of the shortness of the length scales and lack of control. The length scale and softness of defects in liquid crystals allow the easy observation of charges, but it is difficult to control charge creation. Here we demonstrate full control over the creation, manipulation and analysis of topological charges that are pinned to a microfibre in a nematic liquid crystal. Oppositely charged pairs are created through the Kibble-Zurek mechanism by applying a laser-induced local temperature quench in the presence of symmetry-breaking boundaries. The pairs are long-lived, oppositely charged rings or points that either attract and annihilate, or form a long-lived, charge-neutral loop made of two segments with a fractional topological charge.

  10. Biaxiality in Nematic and Smectic Liquid Crystals. Final Report

    Energy Technology Data Exchange (ETDEWEB)

    Kumar, Satyendra [Kent State Univ., Kent, OH (United States); Li, Quan [Kent State Univ., Kent, OH (United States); Srinivasarao, Mohan [Georgia Inst. of Technology, Atlanta, GA (United States); Agra-Kooijman, Dena M. [Kent State Univ., Kent, OH (United States); Rey, Alejandro [McGill Univ., Montreal, QC (Canada)

    2017-01-24

    During the award period, the project team explored several phenomena in a diverse group of soft condensed matter systems. These include understanding of the structure of the newly discovered twist-bend nematic phase, solving the mystery of de Vries smectic phases, probing of interesting associations and defect structures in chromonic liquid crystalline systems, dispersions of ferroelectric nanoparticles in smectic liquid crystals, investigations of newly synthesized light sensitive and energy harvesting materials with highly desirable transport properties. Our findings are summarized in the following report followed by a list of 36 publications and 37 conference presentations. We achieved this with the support of Basic Sciences Division of the US DOE for which we are thankful.

  11. Interfacial motion in flexo- and order-electric switching between nematic filled states

    International Nuclear Information System (INIS)

    Blow, M L; Telo da Gama, M M

    2013-01-01

    We consider a nematic liquid crystal, in coexistence with its isotropic phase, in contact with a substrate patterned with rectangular grooves. In such a system the nematic phase may fill the grooves without the occurrence of complete wetting. There may exist multiple (meta)stable filled states, each characterized by the type of distortion (bend or splay) in each corner of the groove and by the shape of the nematic–isotropic interface, and additionally the plateaux that separate the grooves may be either dry or wet with a thin layer of nematic. Using numerical simulations, we analyse the dynamical response of the system to an externally-applied electric field, with the aim of identifying switching transitions between these filled states. We find that order-electric coupling between the fluid and the field provides a means of switching between states where the plateaux between grooves are dry and states where they are wetted by a nematic layer, without affecting the configuration of the nematic within the groove. We find that flexoelectric coupling may change the nematic texture in the groove, provided that the flexoelectric coupling differentiates between the types of distortion at the corners of the substrate. We identify intermediate stages of the transitions, and the role played by the motion of the nematic–isotropic interface. We determine quantitatively the field magnitudes and orientations required to effect each type of transition. (paper)

  12. Compression induced phase transition of nematic brush: A mean-field theory study.

    Science.gov (United States)

    Tang, Jiuzhou; Zhang, Xinghua; Yan, Dadong

    2015-11-28

    Responsive behavior of polymer brush to the external compression is one of the most important characters for its application. For the flexible polymer brush, in the case of low grafting density, which is widely studied by the Gaussian chain model based theory, the compression leads to a uniform deformation of the chain. However, in the case of high grafting density, the brush becomes anisotropic and the nematic phase will be formed. The normal compression tends to destroy the nematic order, which leads to a complex responsive behaviors. Under weak compression, chains in the nematic brush are buckled, and the bending energy and Onsager interaction give rise to the elasticity. Under deep compression, the responsive behaviors of the nematic polymer brush depend on the chain rigidity. For the compressed rigid polymer brush, the chains incline to re-orientate randomly to maximize the orientational entropy and its nematic order is destroyed. For the compressed flexible polymer brush, the chains incline to fold back to keep the nematic order. A buckling-folding transition takes place during the compressing process. For the compressed semiflexible brush, the chains are collectively tilted to a certain direction, which leads to the breaking of the rotational symmetry in the lateral plane. These responsive behaviors of nematic brush relate to the properties of highly frustrated worm-like chain, which is hard to be studied by the traditional self-consistent field theory due to the difficulty to solve the modified diffusion equation. To overcome this difficulty, a single chain in mean-field theory incorporating Monte Carlo simulation and mean-field theory for the worm-like chain model is developed in present work. This method shows high performance for entire region of chain rigidity in the confined condition.

  13. Effect of hockey-stick-shaped molecules on the critical behavior at the nematic to isotropic and smectic-A to nematic phase transitions in octylcyanobiphenyl.

    Science.gov (United States)

    Chakraborty, Anish; Chakraborty, Susanta; Das, Malay Kumar

    2015-03-01

    In the field of soft matter research, the characteristic behavior of both nematic-isotropic (N-I) and smectic-A nematic(Sm-A N) phase transitions has gained considerable attention due to their several attractive features. In this work, a high-resolution measurement of optical birefringence (Δn) has been performed to probe the critical behavior at the N-I and Sm-A N phase transitions in a binary system comprising the rodlike octylcyanobiphenyl and a laterally methyl substituted hockey-stick-shaped mesogen, 4-(3-n-decyloxy-2-methyl-phenyliminomethyl)phenyl 4-n-dodecyloxycinnamate. For the investigated mixtures, the critical exponent β related to the limiting behavior of the nematic order parameter close to the N-I phase transition has come out to be in good conformity with the tricritical hypothesis. Moreover, the yielded effective critical exponents (α', β', γ') characterizing the critical fluctuation near the Sm-A N phase transition have appeared to be nonuniversal in nature. With increasing hockey-stick-shaped dopant concentration, the Sm-A N phase transition demonstrates a strong tendency to be driven towards a first-order nature. Such a behavior has been accounted for by considering a modification of the effective intermolecular interactions and hence the related coupling between the nematic and smectic order parameters, caused by the introduction of the angular mesogenic molecules.

  14. Effect of hockey-stick-shaped molecules on the critical behavior at the nematic to isotropic and smectic-A to nematic phase transitions in octylcyanobiphenyl

    Science.gov (United States)

    Chakraborty, Anish; Chakraborty, Susanta; Das, Malay Kumar

    2015-03-01

    In the field of soft matter research, the characteristic behavior of both nematic-isotropic (N -I ) and smectic-A nematic (Sm -A N ) phase transitions has gained considerable attention due to their several attractive features. In this work, a high-resolution measurement of optical birefringence (Δ n ) has been performed to probe the critical behavior at the N -I and Sm -A N phase transitions in a binary system comprising the rodlike octylcyanobiphenyl and a laterally methyl substituted hockey-stick-shaped mesogen, 4-(3-n -decyloxy-2-methyl-phenyliminomethyl)phenyl 4-n -dodecyloxycinnamate. For the investigated mixtures, the critical exponent β related to the limiting behavior of the nematic order parameter close to the N -I phase transition has come out to be in good conformity with the tricritical hypothesis. Moreover, the yielded effective critical exponents (α', β', γ') characterizing the critical fluctuation near the Sm -A N phase transition have appeared to be nonuniversal in nature. With increasing hockey-stick-shaped dopant concentration, the Sm -A N phase transition demonstrates a strong tendency to be driven towards a first-order nature. Such a behavior has been accounted for by considering a modification of the effective intermolecular interactions and hence the related coupling between the nematic and smectic order parameters, caused by the introduction of the angular mesogenic molecules.

  15. Vitrified chiral-nematic liquid crystalline films for selective reflection and circular polarization

    Energy Technology Data Exchange (ETDEWEB)

    Katsis, D.; Chen, P.H.M.; Mastrangelo, J.C.; Chen, S.H. [Univ. of Rochester, NY (United States); Blanton, T.N. [Eastman Kodak Co., Rochester, NY (United States)

    1999-06-01

    Nematic and left-handed chiral-nematic liquid crystals comprising methoxybiphenylbenzoate and (S)-(-)-1-phenylethylamine pendants to a cyclohexane core were synthesized and characterized. Although pristine samples were found to be polycrystalline, thermal quenching following heating to and annealing at elevated temperatures permitted the molecular orders characteristic of liquid crystalline mesomorphism to be frozen in the glassy state. Left at room temperature for 6 months, the vitrified liquid crystalline films showed no evidence of recrystallization. An orientational order parameter of 0.65 was determined with linear dichroism of a vitrified nematic film doped with Exalite 428 at a mole fraction of 0.0025. Birefringence dispersion of a blank vitrified nematic film was determined using a phase-difference method complemented by Abbe refractometry. A series of vitrified chiral-nematic films were prepared to demonstrate selective reflection and circular polarization with a spectral region tunable from blue to the infrared region by varying the chemical composition. The experimentally measured circular polarization spectra were found to agree with the Good-Karali theory in which all four system parameters were determined a priori: optical birefringence, average refractive index, selective reflection wavelength, and film thickness.

  16. Nematic director fields and topographies of solid shells of revolution

    Science.gov (United States)

    Warner, Mark; Mostajeran, Cyrus

    2018-02-01

    We solve the forward and inverse problems associated with the transformation of flat sheets with circularly symmetric director fields to surfaces of revolution with non-trivial topography, including Gaussian curvature, without a stretch elastic cost. We deal with systems slender enough to have a small bend energy cost. Shape change is induced by light or heat causing contraction along a non-uniform director field in the plane of an initially flat nematic sheet. The forward problem is, given a director distribution, what shape is induced? Along the way, we determine the Gaussian curvature and the evolution with induced mechanical deformation of the director field and of material curves in the surface (proto-radii) that will become radii in the final surface. The inverse problem is, given a target shape, what director field does one need to specify? Analytic examples of director fields are fully calculated that will, for specific deformations, yield catenoids and paraboloids of revolution. The general prescription is given in terms of an integral equation and yields a method that is generally applicable to surfaces of revolution.

  17. Structural Transformations in Nematic Liquid Crystals with a Hybrid Orientation

    Science.gov (United States)

    Delev, V. A.; Krekhov, A. P.

    2017-12-01

    The structural transformations in a nematic liquid crystal (NLC) layer with a hybrid orientation (planar director orientation is created on one substrate and homeotropic director orientation is created on the other) are studied. In the case of a dc voltage applied to the NLC layer, the primary instability is flexoelectric. It causes the appearance of flexoelectric domains oriented along the director on the substrate with a planar orientation. When the voltage increases further, an electroconvective instability in the form of rolls moving almost normal to flexoelectric domains develops along with these domains. Thus, the following spatially periodic structures of different natures coexist in one system: equilibrium static flexoelectric deformation of a director and dissipative moving oblique electroconvection rolls. The primary instability in the case of an ac voltage is represented by electroconvection, which leads to moving oblique or normal rolls depending on the electric field frequency. Above the electroconvection threshold, a transition to moving "abnormal" rolls is detected. The wavevector of the rolls coincides with the initial director orientation on the substrate with a planar orientation, and the projection of the director at the midplane of the NLC layer on the layer plane makes a certain angle with the wavevector. The results of numerical calculations of the threshold characteristics of the primary instabilities agree well with the obtained experimental data.

  18. Snakes on a plane: modeling flexible active nematics

    Science.gov (United States)

    Selinger, Robin

    Active soft matter systems of self-propelled rod-shaped particles exhibit ordered phases and collective behavior that are remarkably different from their passive analogs. In nature, many self-propelled rod-shaped particles, such as gliding bacteria and kinesin-driven microtubules, are flexible and can bend. We model these ``living liquid crystals'' to explore their phase behavior, dynamics, and pattern formation. We model particles as short polymers via molecular dynamics with a Langevin thermostat and various types of activity, substrate, and environments. For self-propelled polar particles gliding on a solid substrate, we map out the phase diagram as a function of particle density and flexibility. We compare simulated defect structures to those observed in colonies of gliding myxobacteria; compare spooling behavior to that observed in microtubule gliding assays; and analyze emergence of nematic and polar order. Next we explore pattern formation of self-propelled polar particles under flexible encapsulation, and on substrates with non-uniform Gaussian curvature. Lastly, we impose an activity mechanism that mimics extensile shear, study flexible particles both on solid substrates and coupled to a lipid membrane, and discuss comparisons to relevant experiments. Work performed in collaboration with Michael Varga (Kent State) and Luca Giomi (Universiteit Leiden.) Work supported by NSF DMR-1409658.

  19. Isotropic–Nematic Phase Transitions in Gravitational Systems

    Energy Technology Data Exchange (ETDEWEB)

    Roupas, Zacharias; Kocsis, Bence [Institute of Physics, Eötvös University, Pázmány P. s. 1/A, Budapest, 1117 (Hungary); Tremaine, Scott [Institute for Advanced Study, Princeton, NJ 08540 (United States)

    2017-06-20

    We examine dense self-gravitating stellar systems dominated by a central potential, such as nuclear star clusters hosting a central supermassive black hole. Different dynamical properties of these systems evolve on vastly different timescales. In particular, the orbital-plane orientations are typically driven into internal thermodynamic equilibrium by vector resonant relaxation before the orbital eccentricities or semimajor axes relax. We show that the statistical mechanics of such systems exhibit a striking resemblance to liquid crystals, with analogous ordered-nematic and disordered-isotropic phases. The ordered phase consists of bodies orbiting in a disk in both directions, with the disk thickness depending on temperature, while the disordered phase corresponds to a nearly isotropic distribution of the orbit normals. We show that below a critical value of the total angular momentum, the system undergoes a first-order phase transition between the ordered and disordered phases. At a critical point, the phase transition becomes second order, while for higher angular momenta there is a smooth crossover. We also find metastable equilibria containing two identical disks with mutual inclinations between 90° and 180°.

  20. Neutron small-angle scattering by dislocations in homogeneously oriented nematic liquid crystals

    International Nuclear Information System (INIS)

    Olivei, A.

    1976-01-01

    A complete examination of the shape of the neutron-scattering cross-section curves at very small scattering vectors, of the order of 0.05 to approximately 0.1 nm -1 , has been made for homogeneously oriented nematic liquid crystals. It is shown that the shape of the scattering curves at small angles is mainly determined by the kind of dislocation configuration exhibited by homogeneously oriented nematic liquid crystals. This study will furnish a partial guide to the construction of scattering relations for any kind of possible dislocation configuration in homogeneously oriented nematic liquid crystals, e.g. for stationary straight edge dislocations, moving edge dislocations, oscillating edge dislocations, curved dislocations and dislocation networks. (Auth.)

  1. Robust short-range-ordered nematicity in FeSe evidenced by high-pressure NMR

    Science.gov (United States)

    Wang, P. S.; Zhou, P.; Sun, S. S.; Cui, Y.; Li, T. R.; Lei, Hechang; Wang, Ziqiang; Yu, Weiqiang

    2017-09-01

    We report high-pressure 77Se NMR studies on FeSe single crystals that reveal a prominent inhomogeneous NMR linewidth broadening upon cooling, with the magnetic field applied along the tetragonal [110] direction. The data indicate the existence of short-range-ordered, inhomogeneous electronic nematicity, which has surprisingly long time scales over milliseconds. The short-range order survives temperatures up to eight times the structural transition temperature, and remains robust against pressure, in contrast to the strong pressure-dependence of the orbital ordering, structural transition, and the ground state magnetism. Such an extended region of static nematicity in the (P ,T ) space of FeSe indicates an enormously large fluctuating regime, and provides fresh insights and constraints to the understanding of electronic nematicity in iron-based superconductors.

  2. Anomalous Brownian motion of colloidal particle in a nematic environment: effect of the director fluctuations

    Directory of Open Access Journals (Sweden)

    T. Turiv

    2015-06-01

    Full Text Available As recently reported [Turiv T. et al., Science, 2013, Vol. 342, 1351], fluctuations in the orientation of the liquid crystal (LC director can transfer momentum from the LC to a colloid, such that the diffusion of the colloid becomes anomalous on a short time scale. Using video microscopy and single particle tracking, we investigate random thermal motion of colloidal particles in a nematic liquid crystal for the time scales shorter than the expected time of director fluctuations. At long times, compared to the characteristic time of the nematic director relaxation we observe typical anisotropic Brownian motion with the mean square displacement (MSD linear in time τ and inversly proportional to the effective viscosity of the nematic medium. At shorter times, however, the dynamics is markedly nonlinear with MSD growing more slowly (subdiffusion or faster (superdiffusion than τ. These results are discussed in the context of coupling of colloidal particle's dynamics to the director fluctuation dynamics.

  3. Nonlinear continuous-wave optical propagation in nematic liquid crystals: Interplay between reorientational and thermal effects.

    Science.gov (United States)

    Alberucci, Alessandro; Laudyn, Urszula A; Piccardi, Armando; Kwasny, Michał; Klus, Bartlomiej; Karpierz, Mirosław A; Assanto, Gaetano

    2017-07-01

    We investigate nonlinear optical propagation of continuous-wave (CW) beams in bulk nematic liquid crystals. We thoroughly analyze the competing roles of reorientational and thermal nonlinearity with reference to self-focusing/defocusing and, eventually, the formation of nonlinear diffraction-free wavepackets, the so-called spatial optical solitons. To this extent we refer to dye-doped nematic liquid crystals in planar cells excited by a single CW beam in the highly nonlocal limit. To adjust the relative weight between the two nonlinear responses, we employ two distinct wavelengths, inside and outside the absorption band of the dye, respectively. Different concentrations of the dye are considered in order to enhance the thermal effect. The theoretical analysis is complemented by numerical simulations in the highly nonlocal approximation based on a semi-analytic approach. Theoretical results are finally compared to experimental results in the Nematic Liquid Crystals (NLC) 4-trans-4'-n-hexylcyclohexylisothiocyanatobenzene (6CHBT) doped with Sudan Blue dye.

  4. Enhanced diffraction properties of photoinduced gratings in nematic liquid crystals doped with Disperse Red 1.

    Science.gov (United States)

    Li, Hongjing; Wang, Jianhao; Wang, Changshun; Zeng, Pengfei; Pan, Yujia; Yang, Yifei

    2016-01-01

    Diffraction properties of photoinduced gratings recorded by overlapping two coherent beams at 532 nm in nematic liquid crystals doped with Disperse Red 1 were investigated with a probe beam at 632.8 nm. The grating was formed due to the alignment of dye molecules that leaded to the reorientation of the liquid crystal phase. The diffraction efficiency of the photoinduced grating was found to increase rapidly when the sample temperature was close to the clearing point in the nematic phase and a nearly 30-fold enhancement of the first-order diffraction efficiency was obtained. The pretransitional enhancement of the diffraction efficiency was discussed in terms of the reorientation of liquid crystals, optical nonlinearity effects and the onset of critical opalescence near the nematic-isotropic phase transition. Moreover, a peak shift of diffraction efficiency towards the lower temperature was observed with the increase of recording light intensity, which was attributed to laser induced photochemical disordering.

  5. Structure and Dynamics of Reentrant Nematics: Any Open Questions after Almost 40 Years?

    Directory of Open Access Journals (Sweden)

    Marco G. Mazza

    2011-08-01

    Full Text Available Liquid crystals have attracted enormous interest because of the variety of their phases and richness of their application. The interplay of general physical symmetries and specific molecular features generates a myriad of different phenomena. A surprising behavior of liquid crystals is the reentrancy of phases as temperature, pressure, or concentration are varied. Here, we review the main experimental facts and the different theoretical scenarios that have guided the understanding of bulk reentrant nematics. Recently, some computer simulations of a system confined to nanoscopic scales have found new dynamical features of the reentrant nematic phase. We discuss this prediction in relation with the available experimental evidence on reentrant nematics and with the dynamics of liquids in strongly confined environments.

  6. Electro-optic characterization of a nematic phase formed by bent core mesogens.

    Science.gov (United States)

    Tamba, M-G; Weissflog, W; Eremin, A; Heuer, J; Stannarius, R

    2007-01-01

    The purpose of this paper is the demonstration that bent core nematic phases behave quantitatively and qualitatively very different from ordinary calamitic nematics in their electro-optical characteristics. We present measurements of the elastic properties from the analysis of Brochard-Leger walls that are formed during the splay Fréedericksz transition in sandwich cells. These walls possess an unusually large shape anisotropy as compared to similar structures in calamitic nematics. The wall shapes can be explained when one assumes that the bend elastic constant K(33) is one order of magnitude larger than the twist constant K(22) of the material, supposing that flexoelectricity in the description of the elastic deformations can be neglected. Further we report periodic structures above the splay Fréedericksz transition with a wave vector perpendicular to the director easy axis. They represent either a static instability or an unconventional type of electrically driven convection.

  7. Determining the sum of flexoelectric coefficients in nematic liquid crystals by the capacitance method

    International Nuclear Information System (INIS)

    Ye Wen-Jiang; Xing Hong-Yu; Zhou Xuan; Sun Yu-Bao; Zhang Zhi-Dong; Cui Wen-Jing

    2014-01-01

    A detailed theoretical analysis of determining the sum of flexoelectric coefficients in nematic liquid crystals using the capacitance method is given. In the strong anchoring parallel aligned nematic (PAN) and hybrid aligned nematic (HAN) cells, the dependences of the capacitance on the sum of flexoelectric coefficients and the applied voltage are obtained by numerical simulations, and the distributions of the director and the electric potential for different applied voltages and flexoelectric coefficients are also given. Based on this theoretical analysis, we propose an experimental design for measuring the capacitance of a liquid crystal cell using the improved precision LCR meter E4980A (Agilent). Through comparing the experimental data with the simulated results, the sum of flexoeletric coefficients can be determined. (condensed matter: structural, mechanical, and thermal properties)

  8. Theoretical analysis of the influence of flexoelectric effect on the defect site in nematic inversion walls

    International Nuclear Information System (INIS)

    Zheng Gui-Li; Xuan Li; Zhang Hui; Ye Wen-Jiang; Zhang Zhi-Dong; Song Hong-Wei

    2016-01-01

    Based on the experimental phenomena of flexoelectric response at defect sites in nematic inversion walls conducted by Kumar et al., we gave the theoretical analysis using the Frank elastic theory. When a direct-current electric field normal to the plane of the substrate is applied to the parallel aligned nematic liquid crystal cell with weak anchoring, the rotation of ±1 defects in the narrow inversion walls can be exhibited. The free energy of liquid crystal molecules around the +1 and –1 defect sites in the nematic inversion walls under the electric field was formulated and the electric-field-driven structural changes at the defect site characterized by polar and azimuthal angles of the local director were simulated. The results reveal that the deviation of azimuthal angle induced by flexoelectric effect are consistent with the switching of extinction brushes at the +1 and −1 defects obtained in the experiment conducted by Kumar et al. (paper)

  9. Anisotropic stokes drag and dynamic lift on cylindrical colloids in a nematic liquid crystal.

    Science.gov (United States)

    Rovner, Joel B; Lapointe, Clayton P; Reich, Daniel H; Leheny, Robert L

    2010-11-26

    We have measured the Stokes drag on magnetic nanowires suspended in the nematic liquid crystal 4-cyano-4'-pentylbiphenyl (5CB). The effective drag viscosity for wires moving perpendicular to the nematic director differs from that for motion parallel to the director by factors of 0.88 to 2.4, depending on the orientation of the wires and their surface anchoring. When the force on the wires is applied at an oblique angle to the director, the wires move at an angle to the force, demonstrating the existence of a lift force on particles moving in a nematic. This dynamic lift is significantly larger for wires with homeotropic anchoring than with longitudinal anchoring in the experiments, suggesting the lift force as a mechanism for sorting particles according to their surface properties.

  10. Theory of elastic interaction between arbitrary colloidal particles in confined nematic liquid crystals.

    Science.gov (United States)

    Tovkach, O M; Chernyshuk, S B; Lev, B I

    2012-12-01

    We develop the method proposed by Chernyshuk and Lev [Phys. Rev. E 81, 041701 (2010)] for theoretical investigation of elastic interactions between colloidal particles of arbitrary shape and chirality (polar as well as azimuthal anchoring) in the confined nematic liquid crystal (NLC). General expressions for six different types of multipole elastic interactions are obtained in the confined NLC: monopole-monopole (Coulomb type), monopole-dipole, monopole-quadrupole, dipole-dipole, dipole-quadrupole, and quadrupole-quadrupole interactions. The obtained formulas remain valid in the presence of the external electric or magnetic fields. The exact equations are found for all multipole coefficients for the weak anchoring case. For the strong anchoring coupling, the connection between the symmetry of the shape or director and multipole coefficients is obtained, which enables us to predict which multipole coefficients vanish and which remain nonzero. The particles with azimuthal helicoid anchoring are considered as an example. Dipole-dipole interactions between helicoid cylinders and cones are found in the confined NLC. In addition, the banana-shaped particles in homeotropic and planar nematic cells are considered. It is found that the dipole-dipole interaction between banana-shaped particles differs greatly from the dipole-dipole interaction between the axially symmetrical particles in the nematic cell. There is a crossover from attraction to repulsion between banana particles along some directions in nematic cells. It is shown that monopoles do not "feel" the type of nematic cell: monopole-monopole interaction turns out to be the same in homeotropic and planar nematic cells and converges to the Coulomb law as thickness increases, L→∞.

  11. Elastic and viscous properties of the nematic dimer CB7CB

    Science.gov (United States)

    Babakhanova, Greta; Parsouzi, Zeinab; Paladugu, Sathyanarayana; Wang, Hao; Nastishin, Yu. A.; Shiyanovskii, Sergij V.; Sprunt, Samuel; Lavrentovich, Oleg D.

    2017-12-01

    We present a comprehensive set of measurements of optical, dielectric, diamagnetic, elastic, and viscous properties in the nematic (N) phase formed by a liquid crystalline dimer. The studied dimer, 1,7-bis-4-(4'-cyanobiphenyl) heptane (CB7CB), is composed of two rigid rodlike cyanobiphenyl segments connected by a flexible aliphatic link with seven methyl groups. CB7CB and other nematic dimers are of interest due to their tendency to adopt bent configurations and to form two states possessing a modulated nematic director structure, namely, the twist-bend nematic, NTB, and the oblique helicoidal cholesteric, C hOH , which occurs when the achiral dimer is doped with a chiral additive and exposed to an external electric or magnetic field. We characterize the material parameters as functions of temperature in the entire temperature range of the N phase, including the pretransitional regions near the N -NTB and N-to-isotropic (I) transitions. The splay constant K11 is determined by two direct and independent techniques, namely, detection of the Frederiks transition and measurement of director fluctuation amplitudes by dynamic light scattering (DLS). The bend K33 and twist K22 constants are measured by DLS. K33, being the smallest of the three constants, shows a strong nonmonotonous temperature dependence with a negative slope in both N-I and N -NTB pretransitional regions. The measured ratio K11/K22 is larger than 2 in the entire nematic temperature range. The orientational viscosities associated with splay, twist, and bend fluctuations in the N phase are comparable to those of nematics formed by rodlike molecules. All three show strong temperature dependence, increasing sharply near the N -NTB transition.

  12. Global solution to the 3D inhomogeneous nematic liquid crystal flows with variable density

    Science.gov (United States)

    Hu, Xianpeng; Liu, Qiao

    2018-04-01

    In this paper, we investigate the global existence and uniqueness of solution to the 3D inhomogeneous incompressible nematic liquid crystal flows with variable density in the framework of Besov spaces. It is proved that there exists a global and unique solution to the nematic liquid crystal flows if the initial data (ρ0 - 1 ,u0 ,n0 -e3) ∈ M (B˙p,1 3/p - 1 (R3)) × B˙p,1 3/p - 1 (R3) × B˙p,1 3/p (R3) with 1 ≤ p < 6, and satisfies

  13. Chromonic liquid crystalline nematic phase exhibited in binary mixture of two liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Govindaiah, T. N., E-mail: tngovi.phy@gmail.com; Sreepad, H. R. [Post-Graduate Department of Physics, Government College (Autonomous), Mandya-571401 (India); Sridhar, K. N.; Sridhara, G. R.; Nagaraja, N. [Government College for Boys, Kolar-563101 (India)

    2015-06-24

    A binary mixture of abietic acid and orthophosphoric acid (H{sub 3}PO{sub 4}) exhibits co-existence of biphasic region of Nematic+Isotropic (N+I), lyotropic Nematic (ND) and Smectic-G (SmG) phases. The mixture exhibits N+I, N and SmG phases at different concentrations and at different temperatures. Mixtures with all concentrations of abietic acid exhibit I→N+I→N→SmG phases sequentially when the specimen is cooled from its isotropic melt. These phases have been characterized by using differential scanning calorimetric, X-ray diffraction, and optical texture studies.

  14. Nematic liquid crystal in a cylindrical sample: Theoretical analysis of the electrical response

    Science.gov (United States)

    Gomes, O. A.; Yednak, C. A. R.; da Silva, B. V. H. V.; Teixeira-Souza, R. T.

    2018-02-01

    The electrical responses of a nematic liquid crystal sample confined between two cylindrical surfaces are investigated in the framework of elastic continuum theory. The responses are the result of the molecular reorientation induced by both the applied electric field and the cylindrical geometry of the sample. The nematic medium is considered as a parallel RC circuit since the capacitance and the resistance are under the same difference of potential. The electrical properties, including the total electric current, are determined from the molecular reorientation of the director. The elastic anisotropy has been shown to influence substantially the profile of the electrical current, capacitance, and resistance characterizing the equivalent circuit for the medium.

  15. Thermally enhanced optical nonlinearity in nematic liquid crystal close to phase transition temperature

    Science.gov (United States)

    Shih, Chia-Chi; Chen, Yu-Jen; Hung, Wen-Chi; Jiang, I.-Min; Tsai, Ming-Shan

    2010-09-01

    This study investigates the beam profile and the liquid crystal (LC) arrangement affected by an optical field on LC thin films at a temperature close to nematic-isotropic phase transition temperature ( TNI). A combined microscopic and conoscopic technique was used in experiments as a convenient way to analyze the optical nonlinearity that is associated with the molecular configuration of nematic liquid crystal (NLC). An optical field combined with thermal enhancement enhances molecular reorientation and causes additional molecular excitation along the axis of propagation of the beam. The reorientational nonlinearity yields an undulating structure with multi-foci; the length between each pair of foci increases with time, as described.

  16. Polarization resolved conoscopic patterns in nematic cells: effects induced by the incident light ellipticity

    Science.gov (United States)

    Buinyi, Igor O.; Soskin, Marat S.; Vovk, Roman G.

    2008-05-01

    Topological structure of the polarization resolved conoscopic patterns, calculated theoretically and measured experimentally for nematic liquid crystal (NLC) cells, is described in terms of polarization singularities, saddle points and bifurcation lines. The parametric dynamics of the topological network, induced by the variation of the incident light ellipticity, is analyzed for the nematic cells with uniform and non-uniform director configuration. Different stages of similar dynamics are observed for homeotropically oriented NLC cell. Non-uniform director configuration within the cell results in broken central symmentry in the arrangement of the topological network. Main features of the experimentally obtained polarization resolved conoscopic patterns are the same to the theoretically predicted ones.

  17. Laser beam propagation in nematic liquid crystals at the temperature close to the nematicisotropic critical point.

    Science.gov (United States)

    Chen, Yu-Jen; Lin, Yu-Sung; Jiang, I-Min; Tsai, Ming-Shan

    2008-03-17

    This study investigates the optical nonlinearity of beam propagation in homogeneously aligned nematic liquid crystal (NLC) cells at a temperature close to the nematic-isotropic temperature (TNI). The undulate propagation mode with convergent and divergent loops appearing alternately is reported and the thermally enhanced optical reorientation nonlinearity at the focus is described. The optically induced phase transition exists along the pump beam direction. With the application of the conscopic technique, the arrangements of LC at the focus are proposed in this study. Results of this study demonstrate that the evolution of the LC configuration was affected by the pump beam based on the analysis of conoscopic patterns.

  18. Competition of elasticity and flexoelectricity for bistable alignment of nematic liquid crystals on patterned substrates.

    Science.gov (United States)

    Atherton, T J; Adler, J H

    2012-10-01

    We show that patterned surfaces can promote bistable configurations of nematics for reasons other than the symmetry of the surface. Numerical and analytical calculations reveal that a nematic liquid crystal in contact with a striped surface is subject to the competing aligning influences of elastic anisotropy, differing energy cost of various types of deformation, and flexoelectricity, curvature-induced spontaneous polarization. These effects favor opposing ground states where the azimuthal alignment is, respectively, parallel or perpendicular to the stripes. Material parameters for which the effect might be observed lie within the range measured for bent-core nematogens.

  19. Competition of Elasticity and Flexoelectricity for bistable alignment of nematics on patterned substrates

    Science.gov (United States)

    Atherton, Timothy; Adler, James

    2013-03-01

    We show that patterned surfaces can promote bistable configurations of nematics for reasons other than the symmetry of the surface. Numerical and analytical calculations reveal that a nematic liquid crystal in contact with a striped surface is subject to the competing aligning influences of elastic anisotropy, differing energy cost of various types of deformation, and flexoelectricity, curvature-induced spontaneous polarization. These effects favor opposing ground states where the azimuthal alignment is, respectively, parallel or perpendicular to the stripes. Material parameters for which the effect might be observed lie within the range measured for bent-core nematogens.

  20. Competition of elasticity and flexoelectricity for bistable alignment of nematic liquid crystals on patterned substrates

    Science.gov (United States)

    Atherton, T. J.; Adler, J. H.

    2012-10-01

    We show that patterned surfaces can promote bistable configurations of nematics for reasons other than the symmetry of the surface. Numerical and analytical calculations reveal that a nematic liquid crystal in contact with a striped surface is subject to the competing aligning influences of elastic anisotropy, differing energy cost of various types of deformation, and flexoelectricity, curvature-induced spontaneous polarization. These effects favor opposing ground states where the azimuthal alignment is, respectively, parallel or perpendicular to the stripes. Material parameters for which the effect might be observed lie within the range measured for bent-core nematogens.

  1. Chiral nematic mesoporous films of ZrO₂:Eu³⁺: new luminescent materials.

    Science.gov (United States)

    Chu, Guang; Feng, Jing; Wang, Yu; Zhang, Xiao; Xu, Yan; Zhang, Hongjie

    2014-11-07

    Integration of luminescent rare earth ions and iridescence into a zirconium oxide photonic material is attractive for the design of new optical devices. The free-standing chiral nematic mesoporous films of ZrO2:Eu(3+) are assembled by a hard-templating approach using nanocrystalline cellulose-templated silica. The ZrO2:Eu(3+) films show tunable optical properties. The chiral nematic structured ZrO2:Eu(3+) exhibits selective suppression of the spontaneous emission of Eu(3+) and the capability to modulate the lifetime of luminescent Eu(3+).

  2. Asymmetric electrooptic response in a nematic liquid crystal

    Energy Technology Data Exchange (ETDEWEB)

    Dascalu, Constanta [Politechnica University of Bucharest, Bucharest (Romania)

    2001-06-01

    An asymmetric electrooptic response in nematic liquid crystal (LC) has been obtained. The liquid crystal hybrid cell was made by using a standard configuration. One of the ITO (Indium Tin Oxide) electrodes was covered with a surfactant, which induces a homeotropic alignment. The second of the indium tin oxide electrodes was covered by a thin layer of photopolymer, which was previously mixed with an acid, which favours a process of release of protons. Such cations are responsible of electrochemical process in the LC leading to an asymmetric electrooptic response, which depend on the polarity of the applied electric field. This fact is due to an internal field, which change the effective voltage thresholds for the reorientation of the liquid crystal. During the anodic polarization, the optical switching is inhibited because the effective field decreases below the threshold value. On contrary for the opposite polarization the effective field is enough to determine a homeotropic alignment. [Spanish] Se ha obtenido una respuesta electro-optica asimetrica en cristales liquidos neumaticos. La celula hibrida de cristal liquido fue construida utilizando una configuracion estandar. Uno de los electrodos ITO fue cubierto con una pelicula delgada de material organico para inducir una alineacion homeotropa. El otro electrodo ITO fue cubierto con una pelicula delgada de fotopolimero anteriormente mezclada con un acido para favorecer la emision de protones. Estos cationes son responsables del proceso electroquimico en LC, conduciendo a una respuesta electro-optica asimetrica que depende de la polaridad del campo electrico aplicado. Este efecto es originado por un campo interno que cambia el umbral efectivo del voltaje para la reorientacion del cristal liquido. Durante la polarizacion anodica, la conmutacion optica se inhibe debido a que el campo efectivo disminuye abajo del valor del umbral. Por el contrario, para la polarizacion opuesta el campo efectivo es suficiente para

  3. The magnetic and nematic phase diagram of Ba1-xSrxFe2-yNiyAs2

    Science.gov (United States)

    Gong, Dongliang; Li, Shiliang; SC8, National Lab for superconductivity, IOP, CAS Team

    The correlation between magnetic and nematic orders has been widely studied in iron-based superconductors. The magnetic and nematic phase transitions may be both first order as in SrFe2As2,o or both second order as in BaFe2-xNixAs2. Within spin-nematic scenario, it is possible for a system to establish the nematic phase as second order while keeping the magnetic transition first-ordered. Experimentally, it is rather hard to distinguish a second-order transition from a weakly first-order transition. Here we have systematically studied the nematic susceptibility and magnetic susceptibility in the iron-based superconductor Ba1-xSrxFe2-yNiyAs2 by elastoresistivity and magnetic susceptibility measurements, respectively. The evolutions of the nematic and magnetic transitions from first order to second order can be continuously tuned by the substitution of Sr by Ba. Our results give a phase diagram that is consistent with the spin-nematic theory. Chinese Academy of Sciences, Ministry of Science and Technology of China, e National Science Foundation of China, China Academy of Engineering Physics.

  4. Extensional rheology of entangled polystyrene solutions suggests importance of nematic interactions

    DEFF Research Database (Denmark)

    Huang, Qian; Javier Alvarez, Nicolas; Matsumiya, Yumi

    Local correlations in the orientation of neighboring molecules have been shown to exist both experimentally and theoretically for polymer melts, blends and networks. Such nematic interactions alter the stress-optic coefficient, but predict no change in the overall stress in long time scales in th...

  5. A new method for solid surface topographical studies using nematic liquid crystals

    Science.gov (United States)

    Baber, N.; Strugalski, Z.

    1984-03-01

    A new simple method has been developed to investigate the topography of a wide range of solid surfaces using nematic liquid crystals. Polarizing microscopy is employed. The usefulness of the method for detecting weak mechanical effects has been demonstrated. An application in criminology is foreseen.

  6. Molecular dynamics simulations of Gay-Berne nematic liquid crystal: Elastic properties from direct correlation functions

    International Nuclear Information System (INIS)

    Stelzer, J.; Trebin, H.R.; Longa, L.

    1994-08-01

    We report NVT and NPT molecular dynamics simulations of a Gay-Berne nematic liquid crystal using generalization of recently proposed algorithm by Toxvaerd [Phys. Rev. E47, 343, 1993]. On the basis of these simulations the Oseen-Zoher-Frank elastic constants K 11 , K 22 and K 33 as well as the surface constants K 13 and K 24 have been calculated within the framework of the direct correlation function approach of Lipkin et al. [J. Chem. Phys. 82, 472 (1985)]. The angular coefficients of the direct pair correlation function, which enter the final formulas, have been determined from the computer simulation data for the pair correlation function of the nematic by combining the Ornstein-Zernike relation and the Wienier-Hopf factorization scheme. The unoriented nematic approximation has been assumed when constructing the reference, isotropic state of Lipkin et al. By an extensive study of the model over a wide range of temperatures, densities and pressures a very detailed information has been provided about elastic behaviour of the Gay-Berne nematic. Interestingly, it is found that the results for the surface elastic constants are qualitatively different than those obtained with the help of analytical approximations for the isotropic, direct pair correlation function. For example, the values of the surface elastic constants are negative and an order of magnitude smaller than the bulk elasticity. (author). 30 refs, 9 figs

  7. Formation of nematic liquid crystals in suspensions of hard colloidal platelets

    NARCIS (Netherlands)

    Kooij, F.M. van der; Lekkerkerker, H.N.W.

    1998-01-01

    A novel model system of hard colloidal platelets was observed to phase-separate into an isotropic and a liquid crystalline phase. Polarization microscopy revealed that the liquid crystalline phase was of nematic origin. With such orientational ordering in suspensions of platelike particles already

  8. Demixing by a Nematic Mean Field: Coarse-Grained Simulations of Liquid Crystalline Polymers

    Energy Technology Data Exchange (ETDEWEB)

    Ramírez-Hernández, Abelardo; Hur, Su-Mi; Armas-Pérez, Julio; Cruz, Monica; de Pablo, Juan

    2017-03-01

    Liquid crystalline polymers exhibit a particular richness of behaviors that stems from their rigidity and their macromolecular nature. On the one hand, the orientational interaction between liquid-crystalline motifs promotes their alignment, thereby leading to the emergence of nematic phases. On the other hand, the large number of configurations associated with polymer chains favors formation of isotropic phases, with chain stiffness becoming the factor that tips the balance. In this work, a soft coarse-grained model is introduced to explore the interplay of chain stiffness, molecular weight and orientational coupling, and their role on the isotropic-nematic transition in homopolymer melts. We also study the structure of polymer mixtures composed of stiff and flexible polymeric molecules. We consider the effects of blend composition, persistence length, molecular weight and orientational coupling strength on the melt structure at the nano-and mesoscopic levels. Conditions are found where the systems separate into two phases, one isotropic and the other nematic. We confirm the existence of non-equilibrium states that exhibit sought-after percolating nematic domains, which are of interest for applications in organic photovoltaic and electronic devices.

  9. Monotonicity of a Key Function Arised in Studies of Nematic Liquid Crystal Polymers

    Directory of Open Access Journals (Sweden)

    Hongyun Wang

    2007-01-01

    Full Text Available We revisit a key function arised in studies of nematic liquid crystal polymers. Previously, it was conjectured that the function is strictly decreasing and the conjecture was numerically confirmed. Here we prove the conjecture analytically. More specifically, we write the derivative of the function into two parts and prove that each part is strictly negative.

  10. Stripes developed at the strong limit of nematicity in FeSe film

    Science.gov (United States)

    Li, Wei; Zhang, Yan; Deng, Peng; Xu, Zhilin; Mo, S.-K.; Yi, Ming; Ding, Hao; Hashimoto, M.; Moore, R. G.; Lu, D.-H.; Chen, Xi; Shen, Z.-X.; Xue, Qi-Kun

    2017-10-01

    A single monolayer of iron selenide grown on strontium titanate shows an impressive enhancement of superconductivity compared with the bulk, as well as a novel Fermi surface topology, extreme two-dimensionality, and the possibility of phonon-enhanced electron pairing. For films thicker than one unit cell, however, the electronic structure is markedly different, with a drastically suppressed superconductivity and strong nematicity appearing. The physics driving this extraordinary dichotomy of superconducting behaviour is far from clear. Here, we use low-temperature scanning tunnelling microscopy to study multilayers of iron selenide grown by molecular beam epitaxy, and find a stripe-type charge ordering instability that develops beneath the nematic state. The charge ordering is visible and pinned in the vicinity of impurities. And as it emerges in the strong limit of nematicity, it suggests that a magnetic fluctuation with a rather small wavevector may be competing with the ordinary collinear antiferromagnetic ordering in multilayer films. The existence of stripes in iron-based superconductors, which resemble the stripe order in cuprates, not only suggests that electronic anisotropy and correlation are playing an important role, but also provides a platform for probing the complex interactions between nematicity, charge ordering, magnetism and superconductivity in high-temperature superconductors.

  11. Recent developments of analysis for hydrodynamic flow of nematic liquid crystals

    Science.gov (United States)

    Lin, Fanghua; Wang, Changyou

    2014-01-01

    The study of hydrodynamics of liquid crystals leads to many fascinating mathematical problems, which has prompted various interesting works recently. This article reviews the static Oseen–Frank theory and surveys some recent progress on the existence, regularity, uniqueness and large time asymptotic of the hydrodynamic flow of nematic liquid crystals. We will also propose a few interesting questions for future investigations. PMID:25332384

  12. Optical tuning of photonic bandgaps in dye-doped nematic liquid crystal photonic crystal fibers

    DEFF Research Database (Denmark)

    Alkeskjold, Thomas Tanggaard; Bjarklev, Anders Overgaard; Hermann, David Sparre

    2005-01-01

    An all-optical modulator is demonstrated, which utilizes a pulsed 532 nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid crystal. In order to investigate the time response of the LCPBG fiber device, a low-power CW probe...

  13. Nematic ordering in a cell with modulated surface anchoring: effects of flexoelectricity.

    Science.gov (United States)

    Barbero, G; Skacej, G; Alexe-Ionescu, A L; Zumer, S

    1999-07-01

    We have analyzed molecular ordering in a nematic sample sandwiched between two parallel substrates, characterized by a periodically varying anchoring easy axis. If the periodicity lambda is smaller than the Debye screening length l(D) and the nematic material possesses flexoelectric properties, it is necessary to take into account also the electrostatic and flexoelectric contributions in the thermodynamical potential when the actual director field is determined. In this framework, for small deviations from the homeotropic alignment we have derived analytical expressions for the tilt angle (theta) and the electrical potential. To establish a connection with experimentally observable quantities, we have related the theta profile to the average and investigated its behavior for different values of lambda, the flexoelectric coefficient, and the anchoring strength w. Our results indicate that in a nematic with pronounced flexoelectric properties for small enough lambda, a kind of subsurface deformation appears, which substantially decreases . Therefore, effects of flexoelectricity cannot be neglected in treating nematic cells with modulated anchoring which allows bistable ordering.

  14. Consequences of director-density coupling theory for flexoelectricity in nematic liquid crystals

    Science.gov (United States)

    Vitoriano, Carlindo; Sátiro, Caio

    2016-02-01

    We theoretically study how the measurements of the flexoelectric coefficients in nematic liquid crystals are affected by the inclusion of the director-density coupling energy. It is shown that this investigation is quite relevant for interpreting the data of experiments.

  15. Threshold voltages and optical retardation of deformed flexoelectric nematic layers with asymmetric surface anchoring

    Science.gov (United States)

    Derfel, G.; Buczkowska, M.

    2013-06-01

    Deformations of homeotropically aligned flexoelectric nematic layers induced by dc electric fields were simulated numerically. Two different anchoring strengths on the limiting surfaces were assumed. Nematic material was characterised by negative dielectric anisotropy. Both signs of the sum of flexoelectric coefficients were taken into account. The electric properties of the layer were described in terms of a weak electrolyte model. Mobility of cations was assumed to be one order of magnitude lower than that of anions. Quasi-blocking electrode contacts were assumed. The threshold voltages for deformations were determined by means of calculations of the phase difference Φ between ordinary and extraordinary light rays passing through a layer placed between crossed polarisers. The threshold values depended on the polarity of the bias voltage U. When the threshold value was exceeded, the phase difference increased with the voltage. Two different Φ(U/Uthreshold) dependencies for the two polarities of the voltage were found for each layer if the nematic possessed the flexoelectric properties. The possibility of using this effect to detect the flexoelectricity in the nematic was explored by simulated experiments. The effectiveness of the proposed method is discussed.

  16. Nematic ordering in a cell with modulated surface anchoring: Effects of flexoelectricity

    Science.gov (United States)

    Barbero, G.; Skačej, G.; Alexe-Ionescu, A. L.; Žumer, S.

    1999-07-01

    We have analyzed molecular ordering in a nematic sample sandwiched between two parallel substrates, characterized by a periodically varying anchoring easy axis. If the periodicity λ is smaller than the Debye screening length lD and the nematic material possesses flexoelectric properties, it is necessary to take into account also the electrostatic and flexoelectric contributions in the thermodynamical potential when the actual director field is determined. In this framework, for small deviations from the homeotropic alignment we have derived analytical expressions for the tilt angle (θ) and the electrical potential. To establish a connection with experimentally observable quantities, we have related the θ profile to the average and investigated its behavior for different values of λ, the flexoelectric coefficient, and the anchoring strength w. Our results indicate that in a nematic with pronounced flexoelectric properties for small enough λ, a kind of subsurface deformation appears, which substantially decreases . Therefore, effects of flexoelectricity cannot be neglected in treating nematic cells with modulated anchoring which allows bistable ordering.

  17. Effect of ionic charge on flexoelectric deformations in planar nematic layers

    Science.gov (United States)

    Felczak, Mariola; Derfel, Grzegorz

    2004-09-01

    Elastic deformations of nematic liquid crystal layers subjected to d.c. electric field were studied numerically. Nearly planar alignment with 1° tilt angle and with finite surface anchoring strength was assumed. The flexoelectric properties of the nematic material as well as the ionic space charge were taken into account. Perfectly blocking electrodes were adopted. The director orientation, the electric potential distribution and the space charge density were calculated. The optical transmission of the layer placed between crossed polarizers was also determined. The deformations had nearly threshold character due to the low value of the surface tilt. It was found that the threshold voltage strongly depended on the parameters of the system. When the nematic was not flexoelectric, the value of the threshold voltage was independent of the ion concentration and was equal to about 1 volt. In the case of a flexoelectric nematic, the threshold as low as a few tenths of a volt occurred when the ion concentration was sufficiently high, and given sufficiently large magnitudes of the flexoelectric coefficients. These results can be explained as the effect of the inhomogeneous electric field arising in vicinity of the surfaces created by the ionic space charge redistributed by the external voltage.

  18. The elusive thermotropic biaxial nematic phase in rigid bent-core ...

    Indian Academy of Sciences (India)

    Abstract. The biaxial nematic liquid crystalline phase was predicted several decades ago. Several vigorous attempts to find it in various systems resulted in mis-identifications. The results of X-ray diffraction and optical texture studies of the phases exhibited by rigid bent-core molecules derived from 2 ...

  19. Dielectric relaxation studies in 5CB nematic liquid crystal at 9 GHz ...

    Indian Academy of Sciences (India)

    Resonance width, shift in resonance frequency, relaxation time and activation energy of 5CB nematic liquid crystal are measured using microwave cavity technique under the influence of an external magnetic field at 9 GHz and at different temperatures. The dielectric response in liquid crystal at different temperatures and ...

  20. Dielectric relaxation studies in 5CB nematic liquid crystal at 9 GHz ...

    Indian Academy of Sciences (India)

    Abstract. Resonance width, shift in resonance frequency, relaxation time and activation energy of. 5CB nematic liquid crystal are measured using microwave cavity technique under the influence of an external magnetic field at 9 GHz and at different temperatures. The dielectric response in liquid crystal at different ...

  1. Making Faces: Thin Nematic Elastomer Sheets in Theory and in Practice

    Science.gov (United States)

    Aharoni, Hillel

    Thin nematic elastomer sheets attain 3D configurations that depend on the nematic director field upon heating. Recent experiments from various groups demonstrate excellent control over the director fields embedded into such sheets, thus opening a door for achieving accurate and versatile designs of shape-shifting surfaces. In this talk we describe the intrinsic geometry of such sheets at different temperatures, depending on their preprogrammed nematic director field. We focus on investigating the inverse problem - constructing a director field that would induce a specified geometry. We provide analytical solutions for certain classes of desired geometries, and show how arbitrary geometries can be designed using approximate numerical methods. We show how further control over resultant shapes can be achieved by inscribing gradients in the director field across the sheet's thickness, thus prescribing nontrivial local curvatures. Finally, we combine these methods to create designs that are micropatterned onto a mold using photolithography, and then embedded via the mold into thin nematic elastomer sheets polymerized within it. Using this method we show success in experimentally producing flat sheets that, upon activation, take an arbitrary desired shape.

  2. Two-loop disorder effects on the nematic quantum criticality in d-wave superconductors

    International Nuclear Information System (INIS)

    Wang, Jing

    2015-01-01

    The gapless nodal fermions exhibit non-Fermi liquid behaviors at the nematic quantum critical point that is supposed to exist in some d-wave cuprate superconductors. This non-Fermi liquid state may be turned into a disorder-dominated diffusive metal if the fermions also couple to a disordered potential that generates a relevant perturbation in the sense of renormalization group theory. It is therefore necessary to examine whether a specific disorder is relevant or not. We study the interplay between critical nematic fluctuation and random chemical potential by performing renormalization group analysis. The parameter that characterizes the strength of random chemical potential is marginal at the one-loop level, but becomes marginally relevant after including the two-loop corrections. Thus even weak random chemical potential leads to diffusive motion of nodal fermions and the significantly critical behaviors of physical implications, since the strength flows eventually to large values at low energies. - Highlights: • The gapless nodal fermions exhibit non-Fermi liquid behaviors at the nematic QCP. • The strength of random chemical potential is marginal at the one-loop level. • The strength becomes marginally relevant after including the two-loop corrections. • The diffusive metallic state is induced by the marginally relevant disorder. • The behaviors of some physical observables are presented at the nematic QCP

  3. Rheological properties of a nematic cell oriented in a planar manner

    Energy Technology Data Exchange (ETDEWEB)

    Barbero, G., E-mail: giovanni.barbero@polito.i [Dipartimento di Fisica and C. N. I. S. M., Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy)] [Universite de Picardie Jules Verne, Laboratoire de Physique des Systemes Complexes, 33 rue Saint-Leu 80039, Amiens (France); Meyer, C.; Lelidis, I. [Universite de Picardie Jules Verne, Laboratoire de Physique des Systemes Complexes, 33 rue Saint-Leu 80039, Amiens (France)

    2010-05-17

    We propose a simple model to investigate the rheological properties of a nematic cell oriented in a planar manner. The storage and loss modulus are evaluated in the case of strong and weak anchoring conditions. The contribution of the surface viscosity to the rheological parameters is also considered.

  4. Magnetic and Nematic Orders of the Two-Dimensional Electron Gas at Oxide (111) Surfaces and Interfaces

    Science.gov (United States)

    Boudjada, Nazim; Wachtel, Gideon; Paramekanti, Arun

    2018-02-01

    Recent experiments have explored two-dimensional electron gases (2DEGs) at oxide (111) surfaces and interfaces, finding evidence for hexagonal symmetry breaking in SrTiO3 at low temperature. We discuss many-body instabilities of such (111) 2DEGs, incorporating multiorbital interactions in the t2 g manifold which can induce diverse magnetic and orbital orders. Such broken symmetries may partly account for the observed nematicity, cooperating or competing with phonon mechanisms. We present an effective field theory for the interplay of magnetism and nematic charge order, and discuss implications of the nematicity for transport and superconductivity in (111) 2DEGs.

  5. Modeling deformation and chaining of flexible shells in a nematic solvent with finite elements on an adaptive moving mesh

    Science.gov (United States)

    DeBenedictis, Andrew; Atherton, Timothy J.; Rodarte, Andrea L.; Hirst, Linda S.

    2018-03-01

    A micrometer-scale elastic shell immersed in a nematic liquid crystal may be deformed by the host if the cost of deformation is comparable to the cost of elastic deformation of the nematic. Moreover, such inclusions interact and form chains due to quadrupolar distortions induced in the host. A continuum theory model using finite elements is developed for this system, using mesh regularization and dynamic refinement to ensure quality of the numerical representation even for large deformations. From this model, we determine the influence of the shell elasticity, nematic elasticity, and anchoring condition on the shape of the shell and hence extract parameter values from an experimental realization. Extending the model to multibody interactions, we predict the alignment angle of the chain with respect to the host nematic as a function of aspect ratio, which is found to be in excellent agreement with experiments.

  6. The nematicity induced d-symmetry charge density wave in electron-doped iron-pnictide superconductors

    Science.gov (United States)

    Chou, Chung-Pin; Chen, Hong-Yi; Ting, C. S.

    2018-03-01

    The interplay among the nematicity, the stripe spin-density-wave (SDW) order and superconductivity in iron-pnictides is studied in a self-consistent Bogoliubov-de Gennes equations. Our calculations have shown that the nematic-order breaks the degeneracy of dxz and dyz orbitals and causes the elliptic Fermi surface near the Γ point in the normal state. In addition, the appearance of the orthorhombic magnetic fluctuations generates two uneven pairs of peaks at ( ± π, 0) and (0, ± π) in its Fourier transformation. All these are comparing favorably with experimental measurements. In the nematic phase, our results indicate that the charge density and its spatial image in the local density of states exhibit a dx2 -y2-like symmetry. Finally, the complete phase diagram is obtained and the nematic phase is found to be in a narrow region close to the SDW transition in the electron-doped iron-pnictide superconductors.

  7. Local nematic susceptibility in stressed BaFe2As2 from NMR electric field gradient measurements

    Science.gov (United States)

    Kissikov, T.; Sarkar, R.; Lawson, M.; Bush, B. T.; Timmons, E. I.; Tanatar, M. A.; Prozorov, R.; Bud'ko, S. L.; Canfield, P. C.; Fernandes, R. M.; Goh, W. F.; Pickett, W. E.; Curro, N. J.

    2017-12-01

    The electric field gradient (EFG) tensor at the 75As site couples to the orbital occupations of the As p orbitals and is a sensitive probe of local nematicity in BaFe2As2 . We use nuclear magnetic resonance to measure the nuclear quadrupolar splittings and find that the EFG asymmetry responds linearly to the presence of a strain field in the paramagnetic phase. We extract the nematic susceptibility from the slope of this linear response as a function of temperature and find that it diverges near the structural transition, in agreement with other measures of the bulk nematic susceptibility. Our work establishes an alternative method to extract the nematic susceptibility which, in contrast to transport methods, can be extended inside the superconducting state.

  8. Nematic fluctuations in iron arsenides NaFeAs and LiFeAs probed by 75As NMR

    Science.gov (United States)

    Toyoda, Masayuki; Kobayashi, Yoshiaki; Itoh, Masayuki

    2018-03-01

    75As NMR measurements have been made on single crystals to study the nematic state in the iron arsenides NaFeAs, which undergoes a structural transition from a high-temperature (high-T ) tetragonal phase to a low-T orthorhombic phase at Ts=57 K and an antiferromagnetic transition at TN=42 K, and LiFeAs having a superconducting transition at Tc=18 K. We observe the in-plane anisotropy of the electric field gradient η even in the tetragonal phase of NaFeAs and LiFeAs, showing the local breaking of tetragonal C4 symmetry. Then, η is found to obey the Curie-Weiss (CW) law as well as in Ba (Fe1-xCox) 2As2 . The good agreement between η and the nematic susceptibility obtained by electronic Raman spectroscopy indicates that η is governed by the nematic susceptibility. From comparing η in NaFeAs and LiFeAs with η in Ba (Fe1-xCox) 2As2 , we discuss the carrier-doping dependence of the nematic susceptibility. The spin contribution to nematic susceptibility is also discussed from comparing the CW terms in η with the nuclear spin-lattice relaxation rate divided by temperature 1 /T1T . Finally, we discuss the nematic transition in the paramagnetic orthorhombic phase of NaFeAs from the in-plane anisotropy of 1 /T1T .

  9. Electro-optic studies of the flexoelectric effect in chiral nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Musgrave, B

    2000-01-01

    With the advent of global telecommunications networks and the Internet, the development of portable display technology has gained a new impetus. Liquid crystal devices have played a major role in this area, most conspicuously as displays in laptop computers. To date, these liquid crystalline devices have been generally based on the rather slow ({approx} 30 ms) dielectric response of the achiral nematic liquid crystal phase, although more expensive devices based on the faster (< 100 {mu}s) ferroelectric switching of the smectic C* phase are in production. The research presented in this thesis relates to a new switching effect recently discovered in the chiral nematic phase. The flexoelectrically-driven rotation of the chiral nematic phase's optic axis is fast - of the order 10 {mu}s to lms - proportional to the applied field amplitude and completely in-plane. The optic axis has been deflected by over 30 deg. from the equilibrium position in some materials. These electro-optic properties make the 'flexoelectro-optic' effect a potential contender in the liquid crystal device market. The present thesis contains the first studies of the effect of molecular structure on flexoelectric coupling in the chiral nematic phase. Several homologous series of estradiol-cyanobiphenyl bimesogenic materials synthesized for this work have been characterized and their electro-optic properties investigated. The chiral nematic phases of these materials have unusually strong flexoelectro-optic effects and respond on a sub-millisecond timescale. The ratios of the effective flexoelectric coefficient to the mean splay-bend elastic constant, e-bar/K, in the present materials lie in the range 0.3 to 0.6 C N{sup -1} m{sup -1}, and are the highest measured to date: the highest value previously published is 0.12 C N{sup -1} m{sup -1}, measured for the commercial mixture TM216. In order to interpret the effect of the bimesogens' molecular structure, achiral nematic monomesogens

  10. Orientational behavior of a nematic liquid crystal filled with inorganic oxide nanoparticles

    International Nuclear Information System (INIS)

    Gavrilko, T.; Kovalchuk, O.; Nazarenko, V.; Hauser, A.; Kresse, H.

    2004-01-01

    We report the results of dielectric spectroscopy, Fourier transformed infrared spectroscopy (FTIR) and atomic force microscopy (AFM) studies performed on the nematic liquid crystal (LC) mixture Merck ZLI-1132 filled with TiO 2 (rutile and anatase) and SiO 2 nanoparticles. The observed static dielectric permittivities are interpreted in terms of orientation of the LC with respect to the measuring electric field. Adding of SiO 2 particles mainly induces a statistical orientation of LC molecules, whereas TiO 2 particles promote the perpendicular orientation. The dynamics of LC molecules in all systems is very similar. The reason for the slightly faster reorientation observed in the mixtures may be connected with a disturbed nematic order near the surface of solid particles

  11. Generalized nematohydrodynamic boundary conditions with application to bistable twisted nematic liquid-crystal displays

    KAUST Repository

    Fang, Angbo

    2008-12-08

    Parallel to the highly successful Ericksen-Leslie hydrodynamic theory for the bulk behavior of nematic liquid crystals (NLCs), we derive a set of coupled hydrodynamic boundary conditions to describe the NLC dynamics near NLC-solid interfaces. In our boundary conditions, translational flux (flow slippage) and rotational flux (surface director relaxation) are coupled according to the Onsager variational principle of least energy dissipation. The application of our boundary conditions to the truly bistable π -twist NLC cell reveals a complete picture of the dynamic switching processes. It is found that the thus far overlooked translation-rotation dissipative coupling at solid surfaces can accelerate surface director relaxation and enhance the flow rate. This can be utilized to improve the performance of electro-optical nematic devices by lowering the required switching voltages and reducing the switching times. © 2008 The American Physical Society.

  12. High-resolution bistable nematic liquid crystal device realized on orientational surface patterns

    International Nuclear Information System (INIS)

    Kim, Jong-Hyun; Yoneya, Makoto; Yokoyama, Hiroshi

    2003-01-01

    The four-fold symmetry of a checkerboard-like surface alignment consisted of square domains arrived at the macroscopic orientational bistability of nematic liquid crystals. Switching between the two orientations took place with an appropriate electric field. Here the threshold field of bistable switching decreased as temperature increased, and the light could heat only the selected region in the cell including a light-absorbing medium. Irradiating the laser concurrently with an electric field, we addressed a selected region in the alignment pattern without the disturbance of neighboring regions. Extending this process, we realized an extremely fine bistable device of nematic liquid crystal with a pixel size down to about 2 μm

  13. Scattering of light from small nematic spheres with radial dielectric anisotropy

    International Nuclear Information System (INIS)

    Karacali, H.; Risser, S.M.; Ferris, K.F.

    1997-01-01

    We have calculated the scattering cross sections of small anisotropic nematic droplets embedded in a polymer matrix as a function of the dielectric constants of the nematic and the polymer. We have derived the general form for the Helmholtz wave equation for a droplet which has spatially varying radial anisotropy, and have explicitly solved this equation for three distinct models of the dielectric anisotropy, including one model where the anisotropy increases linearly with droplet radius. Numerical calculations of the scattering amplitudes for droplets much smaller than the wavelength of the incident radiation show that droplets with continual variation in the dielectric anisotropy have much larger scattering amplitude than droplets with fixed anisotropy. The scattering from droplets with linearly varying anisotropy exhibits a scattering minimum for much smaller polymer dielectric constants than the other models. These results show that the scattering from small anisotropic droplets is sensitive to details of the internal structure and anisotropy of the droplet. copyright 1997 The American Physical Society

  14. Nematic fluctuations, fermiology and the pairing potential in iron-based superconductors

    Energy Technology Data Exchange (ETDEWEB)

    Kretzschmar, Florian

    2015-08-18

    The thesis comprises a systematic study on the doping, temperature and momentum dependent electron dynamics in iron-based superconductors using inelastic light scattering. The observation of Bardasis-Schrieffer modes in the excitation spectrum of superconducting Ba{sub 0.6}K{sub 0.4}Fe{sub 2}As{sub 2} is reported and the energy and symmetry dependence of the modes are analyzed. The analysis yields the identification of a strong subdominant component of the interaction potential V(k,k{sup '}). Strong nematic fluctuations are investigated in Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2}. The nature of the fluctuations and the origin of nematicity in Ba(Fe{sub 1-x}Co{sub x}){sub 2}As{sub 2} are identified.

  15. Chiral nematic self-assembly of minimally surface damaged chitin nanofibrils and its load bearing functions

    Science.gov (United States)

    Oh, Dongyeop X.; Cha, Yun Jeong; Nguyen, Hoang-Linh; Je, Hwa Heon; Jho, Yong Seok; Hwang, Dong Soo; Yoon, Dong Ki

    2016-03-01

    Chitin is one of the most abundant biomaterials in nature, with 1010 tons produced annually as hierarchically organized nanofibril fillers to reinforce the exoskeletons of arthropods. This green and cheap biomaterial has attracted great attention due to its potential application to reinforce biomedical materials. Despite that, its practical use is limited since the extraction of chitin nanofibrils requires surface modification involving harsh chemical treatments, leading to difficulties in reproducing their natural prototypal hierarchical structure, i.e. chiral nematic phase. Here, we develop a chemical etching-free approach using calcium ions, called “natural way”, to disintegrate the chitin nanofibrils while keeping the essential moiety for the self-assembly, ultimately resulting in the reproduction of chitin’s natural chiral structure in a polymeric matrix. This chiral chitin nanostructure exceptionally toughens the composite. Our resultant chiral nematic phase of chitin materials can contribute to the understanding and use of the reinforcing strategy in nature.

  16. The molecular ordering phenomenon in dye-doped nematic liquid crystals

    Energy Technology Data Exchange (ETDEWEB)

    Prakash Yadav, Satya; Pandey, Kamal Kumar; Kumar Misra, Abhishek; Kumar Tripathi, Pankaj; Manohar, Rajiv, E-mail: rajiv.manohar@gmail.com [Liquid Crystal Research Laboratory, Physics Department, University of Lucknow, Lucknow-226007 (India)

    2011-03-15

    The experimental results of this work point out the role of the guest dye molecules in the molecular ordering of nematic liquid crystals. We have discussed the changes in the energies of interactions between rod-like nematic molecules and anthraquinone dye by considering the presence of steric and dipole-dipole interactions in the dye-doped system. The concentration of the dye plays an important role in the determination of molecular ordering in such dye-doped systems. Below a certain concentration of dye (known as the critical concentration), where the interaction between the dye molecules can be neglected, the addition of dye molecules introduces some disorder into the system in the form of domain formation. Above this critical concentration, this disorder is small.

  17. Influence of flexoelectricity above the nematic Fréedericksz transition.

    Science.gov (United States)

    Brown, C V; Mottram, N J

    2003-09-01

    Continuum theory is used to demonstrate that the presence of flexoelectricity significantly alters the response to an applied voltage of a homogeneous nematic liquid crystal cell above the ac Fréedericksz threshold voltage. In such a system there is a fitting degeneracy: we obtain very good fits between theory and experimental permittivity data using any value of the sum of flexoelectric coefficients, e(11)+e(33), between 0.0 C/m and 1.5 x 10(-11) C/m. The corresponding values of the nematic bend elastic constant show an inverse parabolic relationship with e(11)+e(33), with K33 being reduced down to 90% of its value when flexoelectricity is neglected.

  18. Influences of surface and flexoelectric polarization on the effective anchoring energy in nematic liquid crystal

    International Nuclear Information System (INIS)

    Guan Rong-Hua; Ye Wen-Jiang; Xing Hong-Yu

    2015-01-01

    The physical effects on surface and flexoelectric polarization in a weak anchoring nematic liquid crystal cell are investigated systematically. We derive the analytic expressions of two effective anchoring energies for lower and upper substrates respectively as well as their effective anchoring strengths and corresponding tilt angles of effective easy direction. All of these quantities are relevant to the magnitudes of both two polarizations and the applied voltage U. Based on these expressions, the variations of effective anchoring strength and the tilt angle with the applied voltage are calculated for the fixed values of two polarizations. For an original weak anchoring hybrid aligned nematic cell, it may be equivalent to a planar cell for a small value of U and has a threshold voltage. The variation of reduced threshold voltage with reduced surface polarization strength is also calculated. The role of surface polarization is important without the adsorptive ions considered. (paper)

  19. Curvature-induced defect unbinding and dynamics in active nematic toroids

    Science.gov (United States)

    Ellis, Perry W.; Pearce, Daniel J. G.; Chang, Ya-Wen; Goldsztein, Guillermo; Giomi, Luca; Fernandez-Nieves, Alberto

    2018-01-01

    Nematic order on curved surfaces is often disrupted by the presence of topological defects, which are singular regions in which the orientational order is undefined. In the presence of force-generating active materials, these defects are able to migrate through space like swimming microorganisms. We use toroidal surfaces to show that despite their highly chaotic and non-equilibrium dynamics, pairs of defects unbind and segregate in regions of opposite Gaussian curvature. Using numerical simulations, we find that the degree of defect unbinding can be controlled by tuning the system activity, and even suppressed in strongly active systems. Furthermore, by using the defects as active microrheological tracers and quantitatively comparing our experimental and theoretical results, we are able to determine material properties of the active nematic. Our results illustrate how topology and geometry can be used to control the behaviour of active materials, and introduce a new avenue for the quantitative mechanical characterization of active fluids.

  20. Shifts and Splittings of the Hole Bands in the Nematic Phase of FeSe

    Science.gov (United States)

    Watson, Matthew D.; Haghighirad, Amir A.; Takita, Hitoshi; Mansuer, Wumiti; Iwasawa, Hideaki; Schwier, Eike F.; Ino, Akihiro; Hoesch, Moritz

    2017-05-01

    We report a high-resolution laser-based angle-resolved photoemission spectroscopy (laser-ARPES) study of single crystals of FeSe, focusing on the temperature-dependence of the hole-like bands around the Γ point. As the system cools through the tetragonal-orthorhombic "nematic" structural transition at 90 K, the splitting of the dxz/dyz bands is observed to increase by a magnitude of 13 meV. Moreover, the onset of a ˜10 meV downward shift of the dxy band is also observed at 90 K. These measurements provide clarity on the nature, magnitude and temperature-dependence of the band shifts at the Γ point in the nematic phase of FeSe.

  1. Static alignment states in a bistable azimuthal nematic device with blazed grating sidewalls

    Energy Technology Data Exchange (ETDEWEB)

    Evans, C R; Brown, C V [School of Science and Technology, Nottingham Trent University, Erasmus Darwin Building, Clifton Lane, Clifton, Nottingham, NG11 8NS (United Kingdom); Davidson, A J; Mottram, N J, E-mail: carl.brown@ntu.ac.u [Department of Mathematics and Statistics, University of Strathclyde, Livingstone Tower, 26 Richmond Street, Glasgow G1 1XH (United Kingdom)

    2010-12-15

    Bistable azimuthal alignment has been produced in channels of homogeneous nematic liquid crystal with periodic grating sidewalls. The grating morphologies included a symmetric triangular profile (blaze/pitch (b/p) = 0), an asymmetric highly blazed sawtooth profile (b/p = 0.5) and profiles with different amounts of blaze asymmetry between these two extremes. The observed optical textures and the trend in the relative frequency of occurrence of the two stable states as a function of the asymmetry were in agreement with the predictions of n-director-based Frank-Oseen nematic continuum theory. A sidewall grating morphology with an intermediate degree of blaze asymmetry, b/p = 0.3, gave the highest optical contrast between the bistable states.

  2. Calculating the dielectric anisotropy of nematic liquid crystals: a reinvestigation of the Maier–Meier theory

    International Nuclear Information System (INIS)

    Ran, Zhang; Jun, He; Zeng-Hui, Peng; Li, Xuan

    2009-01-01

    This paper investigates the average dielectric permittivity (ε-bar ) in the Maier–Meier theory for calculating the dielectric anisotropy (Δε) of nematic liquid crystals. For the reason that ε-bar of nematics has the same expression as the dielectric permittivity of the isotropic state, the Onsager equation for isotropic dielectric was used to calculate it. The computed ε-bar shows reasonable agreement with the results of the numerical methods used in the literature. Molecular parameters, such as the polarizability and its anisotropy, the dipole moment and its angle with the molecular long axis, were taken from semi-empirical quantum chemistry (MOCPAC/AM1) modeling. The calculated values of Δε according to the Maier–Meier equation are in good agreement with the experimental results for the investigated compounds having different core structures and polar substituents. (condensed matter: structure, thermal and mechanical properties)

  3. Landau–De Gennes Theory of Nematic Liquid Crystals: the Oseen–Frank Limit and Beyond

    KAUST Repository

    Majumdar, Apala

    2009-07-07

    We study global minimizers of a continuum Landau-De Gennes energy functional for nematic liquid crystals, in three-dimensional domains, subject to uniaxial boundary conditions. We analyze the physically relevant limit of small elastic constant and show that global minimizers converge strongly, in W1,2, to a global minimizer predicted by the Oseen-Frank theory for uniaxial nematic liquid crystals with constant order parameter. Moreover, the convergence is uniform in the interior of the domain, away from the singularities of the limiting Oseen-Frank global minimizer. We obtain results on the rate of convergence of the eigenvalues and the regularity of the eigenvectors of the Landau-De Gennes global minimizer. We also study the interplay between biaxiality and uniaxiality in Landau-De Gennes global energy minimizers and obtain estimates for various related quantities such as the biaxiality parameter and the size of admissible strongly biaxial regions. © Springer-Verlag (2009).

  4. Light-induced rewiring and winding of Saturn ring defects in photosensitive chiral nematic colloids.

    Science.gov (United States)

    Gvozdovskyy, I; Jampani, V S R; Skarabot, M; Muševič, I

    2013-09-01

    We study the winding and unwinding of Saturn ring defects around silica microspheres with homeotropic surface anchoring in a cholesteric liquid crystal with a variable pitch. We use mixtures of a nematic liquid crystal 5CB and various photoresponsive chiral dopants to vary the helical pitch and sense of the helical winding by illuminating the mixtures with UV or visible light. Upon illumination, we observe motion of the Grandjean-Cano disclination lines in wedge-like cells. When the line touches the colloidal particle, we observe topological reconstruction of the Grandjean-Cano line and the Saturn ring. The result of this topological reconstruction is either an increase or decrease of the degree of winding of the Saturn ring around the colloidal particle. This phenomenon is similar to topological rewiring of -1/2 disclination lines, observed recently in chiral nematic colloids.

  5. Saddle-splay screening and chiral symmetry breaking in toroidal nematics

    OpenAIRE

    Koning, Vinzenz; van Zuiden, Benjamin C.; Kamien, Randall D.; Vitelli, Vincenzo

    2013-01-01

    We present a theoretical study of director fields in toroidal geometries with degenerate planar boundary conditions. We find spontaneous chirality: despite the achiral nature of nematics the director configuration show a handedness if the toroid is thick enough. In the chiral state the director field displays a double twist, whereas in the achiral state there is only bend deformation. The critical thickness increases as the difference between the twist and saddle-splay moduli grows. A positiv...

  6. Radiative Transfer Theory and Diffusion of Light in Nematic Liquid Crystals

    OpenAIRE

    Stark, Holger

    1997-01-01

    In nematic liquid crystals light is strongly scattered from director fluctuations. We are interested in the limit where the incoming light wave is scattered many times. Then, the light transport can be described by a diffusion equation for the energy density of light with diffusion constants $D_{\\|}$ and $D_{\\perp}$, respectively, parallel and perpendicular to the director. We start from a radiative transfer theory, connect the diffusion constants to the dynamic structure factor of director f...

  7. Elasticity and Viscosity of a Lyotropic Chromonic Nematic Studied with Dynamic Light Scattering

    OpenAIRE

    Nastishin, Yu. A.; Neupane, K.; Baldwin, A. R.; Lavrentovich, O. D.; Sprunt, S.

    2008-01-01

    Using dynamic light scattering, we measure for the first time the temperature-dependent elastic moduli and associated orientational viscosity coefficients of the nematic phase in a self-assembled lyotropic chromonic liquid crystal. The bend K3 and splay K1 moduli are an order of magnitude higher than the twist K2 constant. The ratio K3/K1 shows an anomalous increase with temperature; we attribute this to the shortening of the aggregates as temperature increases. The viscosity coefficients als...

  8. Nonisothermal nematic liquid crystal flows with the Ball-Majumdar free energy

    Czech Academy of Sciences Publication Activity Database

    Feireisl, Eduard; Schimperna, G.; Rocca, E.; Zarnescu, A.

    2015-01-01

    Roč. 194, č. 5 (2015), s. 1269-1299 ISSN 0373-3114 EU Projects: European Commission(XE) 320078 - MATHEF Institutional support: RVO:67985840 Keywords : nematic liquid crystal * Ball-Majumdar free theory * nonisothermal model * existence theorem Subject RIV: BA - General Mathematics Impact factor: 0.861, year: 2015 http://link.springer.com/article/10.1007%2Fs10231-014-0419-1

  9. On the role of flexoeffect in synchronization of electroconvective roll oscillations in nematics

    International Nuclear Information System (INIS)

    Batyrshin, E. S.; Krekhov, A. P.; Scaldin, O. A.; Delev, V. A.

    2012-01-01

    We describe the dynamics of zigzag oscillations in a system of convective rolls in a nematic liquid crystal above the electroconvection threshold under the action of an ac voltage with a biased position of the mean value. It is found that an increase in the contribution from the constant component leads to a substantial increase in the spatiotemporal ordering of zigzag rolls and their synchronization with the homogeneous twist mode. The results confirm the flexoelectric mechanism of locking.

  10. Pair creation, motion, and annihilation of topological defects in two-dimensional nematic liquid crystals

    OpenAIRE

    Cortese, Dario; Eggers, Jens; Liverpool, Tanniemola

    2018-01-01

    We present a novel framework for the study of disclinations in two-dimensional active nematic liquid crystals, and topological defects in general. The order tensor formalism is used to calculate exact multi-particle solutions of the linearized static equations inside a uniformly aligned state. Topological charge conservation requires a fixed difference between the number of half charges. Starting from a set of hydrodynamic equations, we derive a low-dimensional dynamical system for the parame...

  11. Pair creation, motion, and annihilation of topological defects in 2D nematics

    OpenAIRE

    Cortese, Dario; Eggers, Jens; Liverpool, Tanniemola B.

    2017-01-01

    We present a novel framework for the study of disclinations in two-dimensional active nematic liquid crystals, and topological defects in general. The order tensor formalism is used to calculate exact multi-particle solutions of the linearized static equations inside a uniformly aligned state. Topological charge conservation requires a fixed difference between the number of half charges. Starting from a set of hydrodynamic equations, we derive a low-dimensional dynamical system for the parame...

  12. On the long-time behavior of some mathematical models for nematic liquid crystals

    Czech Academy of Sciences Publication Activity Database

    Petzeltová, Hana; Rocca, E.; Schimperna, G.

    2013-01-01

    Roč. 46, 3-4 (2013), s. 623-639 ISSN 0944-2669 R&D Projects: GA MŠk LC06052 Institutional research plan: CEZ:AV0Z10190503 Keywords : nematic liquid crystals * long-time behavior * flows Subject RIV: BA - General Mathematics Impact factor: 1.526, year: 2013 http://www.springerlink.com/content/d61u566014515884/

  13. Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching

    International Nuclear Information System (INIS)

    Tartan, Chloe C.; Salter, Patrick S.; Booth, Martin J.; Morris, Stephen M.; Elston, Steve J.

    2016-01-01

    Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10–100 μs. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phase of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.

  14. Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching

    Energy Technology Data Exchange (ETDEWEB)

    Tartan, Chloe C., E-mail: chloe.tartan@eng.ox.ac.uk, E-mail: steve.elston@eng.ox.ac.uk; Salter, Patrick S.; Booth, Martin J.; Morris, Stephen M.; Elston, Steve J., E-mail: chloe.tartan@eng.ox.ac.uk, E-mail: steve.elston@eng.ox.ac.uk [Department of Engineering Science, University of Oxford, Parks Road, Oxford OX1 3PJ (United Kingdom)

    2016-05-14

    Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10–100 μs. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phase of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.

  15. Symmetry breaking in nematic liquid crystals: analogy with cosmology and magnetism.

    Science.gov (United States)

    Repnik, R; Ranjkesh, A; Simonka, V; Ambrozic, M; Bradac, Z; Kralj, S

    2013-10-09

    Universal behavior related to continuous symmetry breaking in nematic liquid crystals is studied using Brownian molecular dynamics. A three-dimensional lattice system of rod-like objects interacting via the Lebwohl-Lasher interaction is considered. We test the applicability of predictions originally derived in cosmology and magnetism. In the first part we focus on coarsening dynamics following the temperature driven isotropic-nematic phase transition for different quench rates. The behavior in the early coarsening regime supports predictions made originally by Kibble in cosmology. For fast enough quenches, symmetry breaking and causality give rise to a dense tangle of defects. When the degree of orientational ordering is large enough, well defined protodomains characterized by a single average domain length are formed. With time subcritical domains gradually vanish and supercritical domains grow with time, exhibiting a universal scaling law. In the second part of the paper we study the impact of random-field-type disorder on a range of ordering in the (symmetry broken) nematic phase. We demonstrate that short-range order is observed even for a minute concentration of impurities, giving rise to disorder in line with the Imry-Ma theorem prediction only for the appropriate history of systems.

  16. Electro-osmosis of nematic liquid crystals under weak anchoring and second-order surface effects

    Science.gov (United States)

    Poddar, Antarip; Dhar, Jayabrata; Chakraborty, Suman

    2017-07-01

    Advent of nematic liquid crystal flows has attracted renewed attention in view of microfluidic transport phenomena. Among various transport processes, electro-osmosis stands as one of the efficient flow actuation mechanisms through narrow confinements. In the present study, we explore the electrically actuated flow of an ordered nematic fluid with ionic inclusions, taking into account the influences from surface-induced elasticity and electrical double layer (EDL) phenomena. Toward this, we devise the coupled flow governing equations from fundamental free-energy analysis, considering the contributions from first- and second-order elastic, dielectric, flexoelectric, charged surface polarization, ionic and entropic energies. The present study focuses on the influence of surface charge and elasticity effects in the resulting linear electro-osmosis through a slit-type microchannel whose surfaces are chemically treated to display a homeotropic-type weak anchoring state. An optical periodic stripe configuration of the nematic director has been observed, especially for higher electric fields, wherein the Ericksen number for the dynamic study is restricted to the order of unity. Contrary to the isotropic electrolytes, the EDL potential in this case was found to be dependent on the external field strength. Through a systematic investigation, we brought out the fact that the wavelength of the oscillating patterns is dictated mainly by the external field, while the amplitude depends on most of the physical variables ranging from the anchoring strength and the flexoelectric coefficients to the surface charge density and electrical double layer thickness.

  17. Physical properties of a bent-core nematic liquid crystal and its mixtures with calamitic molecules

    Science.gov (United States)

    Buka, Á.; Éber, N.; Fodor-Csorba, K.; Jákli, A.; Salamon, P.

    2012-10-01

    This article summarizes the results obtained by various experimental methods on the physical properties of a bent-core nematic liquid crystal 4-chloro-1,3-phenylene bis-4-[4‧-(9-decenyloxy) benzoyloxy] benzoate (ClPbis10BB). The material exhibits unusual properties in all aspects tested. Its bend flexoelectric coefficient is 1000 times larger than in calamitics; it is viscoelastic with a large, shear-rate-dependent viscosity. Its bend and twist elastic constants are abnormally low; thus the nematic phase can be rendered to be a blue fog phase with a small amount of chiral dopant. It shows very high flow birefringence and unusually small leading Landau coefficient. It has two types of isotropic phases; at lower temperature it is probably tetrahedratic that can be transferred into the nematic phase with magnetic field. ClPbis10BB has a frequency-dependent conductivity anisotropy which is characterized by a double sign inversion. It exhibits various electroconvection (EC) patterns which are currently not understood in the frame of the standard theory of EC.

  18. Bioinspired Mesoporous Chiral Nematic Graphitic Carbon Nitride Photocatalysts modulated by Polarized Light.

    Science.gov (United States)

    Lin, Wensheng; Hong, Wei; Sun, Lu; Yu, Di; Yu, Dingshan; Chen, Xudong

    2018-01-10

    Endowing materials with chirality and exploring the responses of the material under circularly polarized light (CPL) can enable further insight into the physical and chemical properties of the semiconductors to be gained, thus expanding on optoelectronic applications. Herein a bioinspired mesoporous chiral nematic graphitic carbon nitride (g-C 3 N 4 ) for efficient hydrogen evolution with polarized light modulation based on chiral nematic cellulose nanocrystal films prepared through silica templating is described. The mesoporous nematic chiral g-C 3 N 4 exhibits an ultrahigh hydrogen evolution rate of 219.9 μmol h -1 (for 20 mg catalyst), corresponding to a high enhancement factor of 55 when compared to the bulk g-C 3 N 4 under λ>420 nm irradiation. Furthermore, the chiral g-C 3 N 4 material exhibits unique photocatalytic activity modulated by CPL within the absorption region. This CPL-assisted photocatalytic regulation strategy holds great promise for a wide range of applications including optical devices, asymmetric photocatalysis, and chiral recognition/separation. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. Equilibrium state of a cylindrical particle with flat ends in nematic liquid crystals.

    Science.gov (United States)

    Hashemi, S Masoomeh; Ejtehadi, Mohammad Reza

    2015-01-01

    A continuum theory is employed to numerically study the equilibrium orientation and defect structures of a circular cylindrical particle with flat ends under a homeotropic anchoring condition in a uniform nematic medium. Different aspect ratios of this colloidal geometry from thin discotic to long rodlike shapes and several colloidal length scales ranging from mesoscale to nanoscale are investigated. We show that the equilibrium state of this colloidal geometry is sensitive to the two geometrical parameters: aspect ratio and length scale of the particle. For a large enough mesoscopic particle, there is a specific asymptotic equilibrium angle associated to each aspect ratio. Upon reducing the particle size to nanoscale, the equilibrium angle follows a descending or ascending trend in such a way that the equilibrium angle of a particle with the aspect ratio bigger than 1:1 (a discotic particle) goes to a parallel alignment with respect to the far-field nematic, whereas the equilibrium angle for a particle with the aspect ratio 1:1 and smaller (a rodlike particle) tends toward a perpendicular alignment to the uniform nematic direction. The discrepancy between the equilibrium angles of the mesoscopic and nanoscopic particles originates from the significant differences between their defect structures. The possible defect structures related to mesoscopic and nanoscopic colloidal particles of this geometry are also introduced.

  20. Periodic grating-like patterns induced by self assembly of gelator fibres in nematic gels.

    Science.gov (United States)

    Ramarao, Pratibha; Topnani, Neha Bhagwani; N, Prutha

    2018-03-15

    Periodic orientation patterns occurring in nematic gels revealed by optical and scanning electron microscopy are found to be formed by spontaneous self assembly of fibrous aggregates of a low-molecular weight organogelator in an aligned thermotropic liquid crystal (LC). The self organization into the periodic structure is also reflected in a calorimetric study which shows the occurrence of three thermoreversible states viz. isotropic liquid, nematic and nematic gel. The segregation and self assembly of the fibrous aggregates leading to the pattern formation is attributed to the highly polar LC and the hydrogen bonding between gelator molecules as shown by x-ray diffraction and vibrational spectroscopy. This study aims to investigate in detail the effect of the chemical nature and alignment of an anisotropic solvent on the morphology of the gelator fibres and the resulting gelation process. The periodic organization of the LC rich and fibre rich regions can also provide a technique of obtaining templates for positioning nanoparticle arrays in an LC matrix which can lead to novel devices. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  1. Role of Molecular Structure on X-ray Diffraction in Thermotropic Uniaxial and Biaxial Nematic Liquid Crystal Phases

    Energy Technology Data Exchange (ETDEWEB)

    Acharya, Bharat R.; Kang, Shin-Woong; Prasad, Veena; Kumar, Satyendra; (Kent); (Platypus)

    2009-08-27

    X-ray diffraction is one of the most definitive methods to determine the structure of condensed matter phases, and it has been applied to unequivocally infer the structures of conventional calamitic and lyotropic liquid crystals. With the advent of bent-core and tetrapodic mesogens and the discovery of the biaxial nematic phase in them, the experimental results require more careful interpretation and analysis. Here, we present ab-initio calculations of X-ray diffraction patterns in the isotropic, uniaxial nematic, and biaxial nematic phases of bent-core mesogens. A simple Meier-Saupe-like molecular distribution function is employed to describe both aligned and unaligned mesophases. The distribution function is decomposed into two, polar and azimuthal, distribution functions to calculate the effect of the evolution of uniaxial and biaxial nematic orientational order. The calculations provide satisfactory semiquantitative interpretations of experimental results. The calculations presented here should provide a pathway to more refined and quantitative analysis of X-ray diffraction data from the biaxial nematic phase.

  2. Fast and ultrafast all-optical control of light in nematic and smectic-A liquid crystals

    Science.gov (United States)

    Muševič, Igor; Vitek, Maruša.; Cattaneo, Laura; Savoini, Matteo; Kimel, Alexey; Rasing, Theo

    2016-03-01

    We review recent experiments on the fast and ultrafast all-optical control of light in bulk nematic and smectic-A liquid crystals. Ultrafast optical control at sub-picosecond time scalecan be achieved via the optical Kerr response of a nematic liquid crystal. We show that the refractive index changes are of the order of 10-4 in 5CB nematic liquid crystal and can be optically induced by applying 100 fs pulses of 4 mJ/cm2 fluence. We discuss stimulated emission depletion of fluorescence in a smectic-A liquid crystal and demonstrate nanosecond light control of fluorescent pulse shaping. Both methods could be applied to control light by light in future photonic devices based on liquid crystals.

  3. Electron-phonon coupling in BaFe2As2: A possible origin of nematic phase

    Science.gov (United States)

    Zhang, Anmin; Ji, Jianting; Xia, Tianlong; Zhao, Guihua; Tian, Yong; Jin, Feng; Zhang, Qingming

    2015-12-01

    Iron-based superconductors have the second-highest superconducting transition temperature next to cuprate superconductors. There are many electronic phases such as superconducting, antiferromagnetic and nematic phases, coexisting in the family of iron pnictides. The charge/spin orders are the key factors for understanding the mechanism of high-temperature superconductivity. In this paper we have performed a Raman scattering study of parent compound BaFe2As2. A relatively strong electron-phonon coupling is observed for B1g phonon mode and is weakened after the structural transition at ∼140 K. Through a careful symmetry analysis, we revealed the possibility that B1g mode can be effectively coupled with dxz and dyz orbits. The coupling can remove the degeneracy of the two orbits and further cause the fluctuations of electronic nematic phases. The study suggests that electron-phonon coupling can be a possible origin of nematic phase.

  4. Detection of a new 'nematic-like' phase in liquid crystal-amphiphile mixture by differential scanning calorimetry

    Energy Technology Data Exchange (ETDEWEB)

    Dan, Kaustabh, E-mail: kaustabhdan@gmail.com; Roy, Madhusudan, E-mail: kaustabhdan@gmail.com; Datta, Alokmay, E-mail: kaustabhdan@gmail.com [Surface Physics and Materials Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar Block, Sector 1, Kolkata-700064 (India)

    2014-04-24

    Differential Scanning Calorimetry (DSC) studies on phase transitions of the pure liquid crystalline material N-4-methoxybenzylidene-4-butylaniline (MBBA) and mixtures of MBBA and the amphiphile Stearic Acid (StA) show significant changes in the behavior of mixture from pure MBBA, as regards the nematic-isotropic (N-I) transition temperature (T{sub c}) and other thermodynamic parameters like enthalpy, specific heat and activation energy with concentration of StA. In particular, the convexity of the Arrhenius plot in pure MBBA vanishes with StA concentration pointing to the formation of a new, perhaps 'nematic-like', phase in the mixtures.

  5. Ação dos extratos de quatro plantas sobre larvas infectantes de nematódeos gastrintestinais de ovinos

    OpenAIRE

    Hassum, Izabella Cabral; Venturi, Caroline Rita; Gosmann, Grace; Deiro, Ana M. Girardi

    2013-01-01

    Introdução: a ação de extratos hidroalcoólicos de Eugenia uniflora L. (pitangueira), Mentha x piperita L. (hortelã), Myrcianthes pungens (O. Berg) D. Legrand (guabiju) e Peltophorum dubium (Spreng.) Taub. (canafístula) foi avaliada sobre o desenvolvimento de nematódeos gastrintestinais nas coproculturas de ovinos. Objetivo: avaliar a ação in vitro dos extratos vegetais sobre os nematódeos gastrintestinais de ovinos. Métodos: cada extrato foi testado em culturas triplicadas de fezes nas seguin...

  6. Critical divergence of the symmetric (A1 g) nonlinear elastoresistance near the nematic transition in an iron-based superconductor

    Science.gov (United States)

    Palmstrom, J. C.; Hristov, A. T.; Kivelson, S. A.; Chu, J.-H.; Fisher, I. R.

    2017-11-01

    We report the observation of a nonlinear elastoresistivity response for the prototypical underdoped iron pnictide Ba (Fe0.975Co0.025)2As2 . Our measurements reveal a large quadratic term in the isotropic (A1 g) electronic response that was produced by a purely shear (B2 g) strain. The divergence of this quantity upon cooling towards the structural phase transition reflects the temperature dependence of the nematic susceptibility. This observation shows that nematic fluctuations play a significant role in determining even the isotropic properties of this family of compounds.

  7. Pretransitional behaviour in the vicinity of the isotropic-nematic transition of strongly polar compounds

    International Nuclear Information System (INIS)

    Sridevi, S; Krishna Prasad, S; Shankar Rao, D S; Yelamaggad, C V

    2008-01-01

    The isotropic-nematic transition, being weakly first order, exhibits pretransitional effects signifying the appearance of the nematic-like regions in the isotropic phase. In the isotropic phase, strongly polar liquid crystals, such as the popular alkyl and alkoxy cyano biphenyl behave in a non-standard fashion: whereas far away from the transition the dielectric constant ε iso has a 1/T dependence (a feature also commonly seen in polar liquids), on approaching the nematic phase the trend reverses resulting in a maximum in ε iso , at a temperature slightly above the transition, an effect explained on the basis of short-range correlations with an antiparallel association of the neighbouring molecules. Recently, there has been a revival in studies on this behaviour to possibly associate it with the order of transition. Here we report dielectric measurements carried in the vicinity of this transition for a number of compounds having different molecular structures including a bent core system, but with a common feature that the molecules possess a strong terminal polar group, nitro in one case and cyano in the rest. Surprisingly, the convex shape of the thermal variation of ε iso was more an exception than the rule. In materials that exhibit such an anomaly we find a linear correlation between δε = (ε peak -ε IN )/ε IN and δT = T peak -T IN , where ε peak is the maximum value of the dielectric constant in the isotropic phase, ε IN the value at the transition, and T peak and T IN the corresponding temperatures.

  8. A Simple Method to Measure the Twist Elastic Constant of a Nematic Liquid Crystal

    Science.gov (United States)

    2015-01-01

    as 180° super- twisted nematic (STN) cell. Next, we assume the helical twisting power ( HTP ) of chiral dopant is also unknown, same as K22. To solve...threshold voltages of these two 180° STN cells, both K22 and HTP can be obtained simultaneously. In the whole process, there is no need to measure...Equation (1), if we sub- stitute ϕ = π and pitch length P = 1/( HTP · c) (where c is chiral concentration), then the critical voltage can be rewritten

  9. Statistical thermodynamics of long straight rigid rods on triangular lattices: nematic order and adsorption thermodynamic functions.

    Science.gov (United States)

    Matoz-Fernandez, D A; Linares, D H; Ramirez-Pastor, A J

    2012-09-04

    The statistical thermodynamics of straight rigid rods of length k on triangular lattices was developed on a generalization in the spirit of the lattice-gas model and the classical Guggenheim-DiMarzio approximation. In this scheme, the Helmholtz free energy and its derivatives were written in terms of the order parameter, δ, which characterizes the nematic phase occurring in the system at intermediate densities. Then, using the principle of minimum free energy with δ as a parameter, the main adsorption properties were calculated. Comparisons with Monte Carlo simulations and experimental data were performed in order to evaluate the outcome and limitations of the theoretical model.

  10. Electrical Properties of Zn-Phthalocyanine and Poly (3-hexylthiophene Doped Nematic Liquid Crystal

    Directory of Open Access Journals (Sweden)

    Y. Karakuş

    2011-01-01

    Full Text Available An E7 coded nematic liquid crystal was doped with zinc phthalocyanine and poly (3-hexylthiophene. A variety of properties including relaxation time, absorption coefficient, and critical frequency of this doped system were investigated using impedance spectroscopy. The doped systems displayed increased absorption coefficients in the range 0.22–0.55 and relaxation times from 5.05×10−7 s to 3.59×10−6 s with a decrease in the critical frequency from 3.54 MHz to 2.048 MHz.

  11. Electrically Rotatable Polarizer Using One-Dimensional Photonic Crystal with a Nematic Liquid Crystal Defect Layer

    Directory of Open Access Journals (Sweden)

    Ryotaro Ozaki

    2015-09-01

    Full Text Available Polarization characteristics of defect mode peaks in a one-dimensional (1D photonic crystal (PC with a nematic liquid crystal (NLC defect layer have been investigated. Two different polarized defect modes are observed in a stop band. One group of defect modes is polarized along the long molecular axis of the NLC, whereas another group is polarized along its short axis. Polarizations of the defect modes can be tuned by field-induced in-plane reorientation of the NLC in the defect layer. The polarization properties of the 1D PC with the NLC defect layer is also investigated by the finite difference time domain (FDTD simulation.

  12. Electric-field-induced local rotation of molecules in nematic-cholesteric droplets

    Science.gov (United States)

    Timirov, Yu. I.; Skaldin, O. A.; Basyrova, E. R.; Kayumov, I. R.

    2014-07-01

    The structural dynamics of nematic-cholesteric liquid crystal (LC) droplets occurring in an isotropic environment in an alternating electric field have been studied. It is established that, above a certain threshold field strength, the conoscopic pattern of a Maltese cross becomes dynamic and begins to rotate. The threshold voltage, as well as the frequency of rotation, is almost independent of the droplet diameter. This phenomenon is related to the development of a self-consistent rotation of LC molecules in the plane perpendicular to the droplet axis. It is shown that this rotation initiates the propagation of a helicoidal wave from one pole of the droplet to another.

  13. Impact of titanium dioxide nanoparticles on purification and contamination of nematic liquid crystals.

    Science.gov (United States)

    Shcherbinin, Dmitrii Pavlovich; Konshina, Elena A

    2017-01-01

    We have investigated the impact of titanium dioxide nanoparticles on the ionic contamination of liquid crystals. Nematic liquid crystals with high and low initial ionic contamination have been examined. It has been shown that titanium dioxide nanoparticles reduced the ion density of liquid crystals with high initial ionic contamination from 134.5 × 10 12 cm -3 to 63.2 × 10 12 cm -3 . In the case of liquid crystals with low initial ionic contamination, the nanoparticles led to an insignificant increase of ion density from 19.8 × 10 12 cm -3 to 25.7 × 10 12 cm -3 .

  14. Shear flow dynamics in the Beris-Edwards model of nematic liquid crystals.

    Science.gov (United States)

    Murza, Adrian C; Teruel, Antonio E; Zarnescu, Arghir D

    2018-02-01

    We consider the Beris-Edwards model describing nematic liquid crystal dynamics and restrict it to a shear flow and spatially homogeneous situation. We analyse the dynamics focusing on the effect of the flow. We show that in the co-rotational case one has gradient dynamics, up to a periodic eigenframe rotation, while in the non-co-rotational case we identify the short- and long-time regimes of the dynamics. We express these in terms of the physical variables and compare with the predictions of other models of liquid crystal dynamics.

  15. Flexoelectric-Induced Voltage Shift in Hybrid Aligned Nematic Liquid Crystal Cell

    International Nuclear Information System (INIS)

    Xing Hongyu; Xuan Li; Ye Wenjiang; Zhang Zhidong

    2011-01-01

    Flexoelectric-induced voltage shift in a weak anchoring hybrid aligned nematic liquid crystal cell is investigated theoretically. Based on the elastic theory of liquid crystal and the variation method, the equations for the bulk and the boundary of the cell are derived. By computer simulation, the dependence of the shift voltage on the sum of the flexoelectric coefficients and the anchoring energy strength is obtained. As a result, a novel method to determine the sum of the flexoelectric coefficients by measuring the shift voltage is put forward. (condensed matter: structural, mechanical, and thermal properties)

  16. Communication: Orientational structure manipulation in nematic liquid crystal droplets induced by light excitation of azodendrimer dopant

    Science.gov (United States)

    Shvetsov, Sergey A.; Emelyanenko, Alexander V.; Boiko, Natalia I.; Liu, Jui-Hsiang; Khokhlov, Alexei R.

    2017-06-01

    Reversible orientational transitions in the droplets of a nematic liquid crystal (NLC) caused by the change of boundary conditions under the low intensity diode illumination are investigated. Photosensitivity of NLC is achieved by the addition of the dendrimer compound with azobenzene terminal groups. Two types of NLC droplets in glycerol are considered: the spherical droplets in the bulk of glycerol and the droplets laid-down onto the solid substrate. In the second case, the first order phase transition is revealed. The effects described can be useful for the development of highly sensitive chemical detectors and microsized photo-tunable optical devices.

  17. Nature of the antiferromagnetic and nematic transitions in Sr1 -xBaxFe1.97Ni0.03As2

    Science.gov (United States)

    Gong, Dongliang; Liu, Zhaoyu; Gu, Yanhong; Xie, Tao; Ma, Xiaoyan; Luo, Huiqian; Yang, Yi-feng; Li, Shiliang

    2017-09-01

    We have systematically studied the antiferromagnetic and nematic transitions in Sr1 -xBaxFe1.97Ni0.03As2 by magnetic susceptibility and uniaxial-pressure resistivity measurements, respectively. The derivatives of the temperature dependence of both magnetic and nematic susceptibilities show clearly sharp peaks when the transitions are first order. Accordingly, we show that while both of the magnetic and nematic transitions change from first-order to second-order with increasing Barium doping level, there is a narrow doping range where the former becomes second order but the latter remains first order, which has never been realized before in other systems. Moreover, the antiferromagnetic and nematic transition temperatures become different and the jump of nematic susceptibility becomes small in this intermediate doping range. Our results provide key information on the interplay between magnetic and nematic transitions. Concerning the current debate on the microscopic models for nematicity in iron-based superconductors, these observations agree with the magnetic scenario for an itinerant fermionic model.

  18. Helical phase of chiral nematic liquid crystals as the Bianchi VII0 group manifold.

    Science.gov (United States)

    Gibbons, G W; Warnick, C M

    2011-09-01

    We show that the optical structure of the helical phase of a chiral nematic is naturally associated with the Bianchi VII(0) group manifold, of which we give a full account. The Joets-Ribotta metric governing propagation of the extraordinary rays is invariant under the simply transitive action of the universal cover E(2) of the three-dimensional Euclidean group of two dimensions. Thus extraordinary light rays are geodesics of a left-invariant metric on this Bianchi type VII(0) group. We are able to solve, by separation of variables, both the wave equation and the Hamilton-Jacobi equation for this metric. The former reduces to Mathieu's equation, and the latter to the quadrantal pendulum equation. We discuss Maxwell's equations for uniaxial optical materials where the configuration is invariant under a group action and develop a formalism to take advantage of these symmetries. The material is not assumed to be impedance matched, thus going beyond the usual scope of transformation optics. We show that for a chiral nematic in its helical phase Maxwell's equations reduce to a generalized Mathieu equation. Our results may also be relevant to helical phases of some magnetic materials and to light propagation in certain cosmological models.

  19. Modeling Textural Processes during Self-Assembly of Plant-Based Chiral-Nematic Liquid Crystals

    Directory of Open Access Journals (Sweden)

    Yogesh K. Murugesan

    2010-12-01

    Full Text Available Biological liquid crystalline polymers are found in cellulosic, chitin, and DNA based natural materials. Chiral nematic liquid crystalline orientational order is observed frozen-in in the solid state in plant cell walls and is known as a liquid crystal analogue characterized by a helicoidal plywood architecture. The emergence of the plywood architecture by directed chiral nematic liquid crystalline self assembly has been postulated as the mechanism that leads to optimal cellulose fibril organization. In natural systems, tissue growth and development takes place in the presence of inclusions and secondary phases leaving behind characteristic defects and textures, which provide a unique testing ground for the validity of the liquid crystal self-assembly postulate. In this work, a mathematical model, based on the Landau-de Gennes theory of liquid crystals, is used to simulate defect textures arising in the domain of self assembly, due to presence of secondary phases representing plant cells, lumens and pit canals. It is shown that the obtained defect patterns observed in some plant cell walls are those expected from a truly liquid crystalline phase. The analysis reveals the nature and magnitude of the viscoelastic material parameters that lead to observed patterns in plant-based helicoids through directed self-assembly. In addition, the results provide new guidance to develop biomimetic plywoods for structural and functional applications.

  20. Numerical simulation and optimization of triple supertwist nematic liquid crystal displays

    Science.gov (United States)

    Fogarty, John Patrick

    1998-12-01

    An optimization process was undertaken for Triple Supertwist Nematic (TSTN) subtractive color stacked liquid crystal displays. An optical model for an arbitrary liquid crystal cell has been developed. This model, which is based on the Jones matrix method for light propagation through non-depolarizing elements, has been modified to account for the high voltage behavior of Supertwist nematic devices. The model has been used to characterize and optimize liquid crystal cells for use in a subtractive color stack. The simulation has been designed with a graphical user interface to ease the optimization process. Subtractive color display systems have been studied and compared to additive color systems so as to obtain a benchmark for LCD display performance. A process for optimization of the LCD displays has been developed. Liquid crystal displays have been fabricated and characterized so that the modeled optimization could be compared with experimental measurements. The results of the comparison demonstrate that modeling using a simplified Jones calculus model is effective and efficient as compared to the two other approaches which require extensive numerical computation.

  1. Microscopic origins of anisotropic active stress in motor-driven nematic liquid crystals.

    Science.gov (United States)

    Blackwell, Robert; Sweezy-Schindler, Oliver; Baldwin, Christopher; Hough, Loren E; Glaser, Matthew A; Betterton, M D

    2016-03-14

    The cytoskeleton, despite comprising relatively few building blocks, drives an impressive variety of cellular phenomena ranging from cell division to motility. These building blocks include filaments, motor proteins, and static crosslinkers. Outside of cells, these same components can form novel materials exhibiting active flows and nonequilibrium contraction or extension. While dipolar extensile or contractile active stresses are common in nematic motor-filament systems, their microscopic origin remains unclear. Here we study a minimal physical model of filaments, crosslinking motors, and static crosslinkers to dissect the microscopic mechanisms of stress generation in a two-dimensional system of orientationally aligned rods. We demonstrate the essential role of filament steric interactions which have not previously been considered to significantly contribute to active stresses. With this insight, we are able to tune contractile or extensile behavior through the control of motor-driven filament sliding and crosslinking. This work provides a roadmap for engineering stresses in active liquid crystals. The mechanisms we study may help explain why flowing nematic motor-filament mixtures are extensile while gelled systems are contractile.

  2. Study of uniaxial nematic lyomesophases by x-ray diffraction and auxiliary techniques

    International Nuclear Information System (INIS)

    Bittencourt, D.R.S.

    1986-01-01

    The uniaxial lyotropic nematic liquid crystals made of amphiphile/water/decanol/salt have been studied. The amphiphiles sodium decyl sulphate and sodium dodecil sulphate have been used. Characterization of samples conditioned in plane and cylindrical cells has been made by orthoscopic polarized optical microscopy (OM) and X.ray diffraction (XD) by observation of orientation under surface and magnetic field effects. It was possible to determine the director orientation of uniaxial discotic (N D ) and cylindrical (N C ) samples under surface and magnetic effects by both OM and XD techniques in independent ways. The homologous amphiphilies sodium octil, decil and dodecil sulfate, in powder form, have been studied by Debye-Scherrer technique. Observed reflexions have been indexed and crystallographic parameters determined. Good agreement between calculated and measured densities has been obtained. A crysostat for temperature variation in the interval- 10 0 /60 0 has been constructed, XD diagrams has been obtained for sodium decil sulfate samples allowing determination of phase transitions of two systems. Scattering curves at room temperatures have been obtained in a small-angle X-ray diffractometer. Analysis of profiles allowed determination of short range positional order and correlation ranges. Interference function between scattering objects have been obtained using structural models for the micelles of the uniaxial nematic phases. (author) [pt

  3. Effect of confining walls on the interaction between particles in a nematic liquid crystal

    CERN Document Server

    Fukuda, J I; Yokoyama, H

    2003-01-01

    We investigate theoretically how the confining walls of a nematic cell affect the interaction of particles mediated by the elastic deformation of a nematic liquid crystal. We consider the case where strong homeotropic or planar anchoring is imposed on the flat parallel walls so that the director on the wall surfaces is fixed and uniform alignment is achieved in the bulk. This set-up is more realistic experimentally than any other previous theoretical studies concerning the elastic-deformation-mediated interactions that assume an infinite medium. When the anchoring on the particle surfaces is weak, an exact expression of the interaction between two particles can be obtained. The two-body interaction can be regarded as the interaction between one particle and an infinite array of 'mirror images' of the other particle. We also obtain the 'self-energy' of one particle, the interaction of a particle with confining walls, which is interpreted along the same way as the interaction of one particle with its mirror ima...

  4. Electro-optic studies of the flexoelectric effect in chiral nematic liquid crystals

    International Nuclear Information System (INIS)

    Musgrave, B.

    2000-01-01

    With the advent of global telecommunications networks and the Internet, the development of portable display technology has gained a new impetus. Liquid crystal devices have played a major role in this area, most conspicuously as displays in laptop computers. To date, these liquid crystalline devices have been generally based on the rather slow (∼ 30 ms) dielectric response of the achiral nematic liquid crystal phase, although more expensive devices based on the faster ( -1 m -1 , and are the highest measured to date: the highest value previously published is 0.12 C N -1 m -1 , measured for the commercial mixture TM216. In order to interpret the effect of the bimesogens' molecular structure, achiral nematic monomesogens and bimesogens have been doped with chiral additives and the resultant mixtures' flexoelectro-optic properties have been analysed. From this work it has been possible to determine that the polar cyanobiphenyl group is the key to the strong response in the estradiol-cyanobiphenyl materials. In conclusion, a recommendation is made, for the first time, for a general molecular structure likely to exhibit a strong flexoelectro-optic response: namely, bimesogenic materials composed of highly polar end groups separated by a flexible spacer. (author)

  5. Chirality transfer across length-scales in nematic liquid crystals: fundamentals and applications.

    Science.gov (United States)

    Pieraccini, Silvia; Masiero, Stefano; Ferrarini, Alberta; Piero Spada, Gian

    2011-01-01

    When a chiral dopant is dissolved in an achiral liquid crystal medium, the whole sample organizes into a helical structure with a characteristic length-scale of the order of microns. The relation between chirality at these quite different length-scales can be rationalized by a relatively simple model, which retains the relevant factors coming into play: the molecular shape of the chiral dopant, which controls the chirality of short range intermolecular interactions, and the elastic properties of the nematic environment, which control the restoring torques opposing distortion of the director. In this tutorial review the relation between molecular and phase chirality will be reviewed and several applications of the chiral doping of nematic LCs will be discussed. These range from the exploitation of the amplified molecular chirality for stereochemical purposes (e.g., the determination of the absolute configuration or the enantiomeric excess), to newer applications in physico-chemical fields. The latter take advantage of the periodicity of the chiral field, with length-scales ranging from hundreds to thousands of nanometres, which characterise the cholesteric phase.

  6. Hybrid aligned nematic based measurement of the sum (e1+e3) of the flexoelectric coefficients

    Science.gov (United States)

    Tartan, Chloe C.; Elston, Steve J.

    2015-02-01

    A new method has been established for the measurement of the sum of the flexoelectric coefficients e1+e3 in liquid crystals by exploiting the properties of highly ionic materials in order to screen out the internal bias due to the different surface alignment polarities in a Hybrid Aligned Nematic (HAN) liquid crystal device. It has been shown that responses to pulses are independent of the external offset of a signal applied to a HAN device filled with a highly ionic material. Driving the device with step changes in the offset leads to either a transient increase or transient decrease in the response, depending on the polarity of the offset, while the equilibrium response remains the same. The time constant of the transient effect is consistent with the relaxation time of the ions present in the material. Assuming these ions screen out the internal bias completely, the remaining response can be used as a measure of the flexoelectric effect. Based on this approach, a value of (10 ± 2) pC m-1 was found for the modulus of the flexoelectric sum in the standard commercial eutectic E70 nematic liquid crystal mixture.

  7. Flexoelectro-optic properties of chiral nematic liquid crystals in the uniform standing helix configuration

    Science.gov (United States)

    Castles, F.; Morris, S. M.; Coles, H. J.

    2009-09-01

    The flexoelectro-optic effect describes the rotation of the optic axis of a short-pitch chiral nematic liquid crystal under the application of an electric field. We investigate the effect in the uniform standing helix, or “Grandjean” configuration. An in-plane electric field is applied. The director profile is determined numerically using a static one-dimensional continuum model with strong surface anchoring. The Berreman method is used to solve for plane-wave solutions to Maxwell’s equations, and predict the optical properties of the resulting structure in general cases. By using a chiral nematic with short pitch between crossed polarizers an optical switch may be generated. With no applied field the configuration is nontransmissive at normal incidence, but becomes transmissive with an applied field. For this case, numerical results using the Berreman method are supplemented with an analytic theory and found to be in good agreement. The transmitted intensity as a function of tilt, the contrast ratio, and the tilt required for full intensity modulation are presented. The angular dependence of the transmission is calculated and the isocontrast curves are plotted. For typical material and cell parameters a switching speed of 0.017 ms and contrast ratio of 1500:1 at normal incidence are predicted, at a switch-on tilt of 41.5 degrees. Experimental verification of the analytic and numerical models is provided.

  8. Nematic topological superconducting phase in Nb-doped Bi2Se3

    Science.gov (United States)

    Shen, Junying; He, Wen-Yu; Yuan, Noah Fan Qi; Huang, Zengle; Cho, Chang-woo; Lee, Seng Huat; Hor, Yew San; Law, Kam Tuen; Lortz, Rolf

    2017-10-01

    A nematic topological superconductor has an order parameter symmetry, which spontaneously breaks the crystalline symmetry in its superconducting state. This state can be observed, for example, by thermodynamic or upper critical field experiments in which a magnetic field is rotated with respect to the crystalline axes. The corresponding physical quantity then directly reflects the symmetry of the order parameter. We present a study on the superconducting upper critical field of the Nb-doped topological insulator NbxBi2Se3 for various magnetic field orientations parallel and perpendicular to the basal plane of the Bi2Se3 layers. The data were obtained by two complementary experimental techniques, magnetoresistance and DC magnetization, on three different single crystalline samples of the same batch. Both methods and all samples show with perfect agreement that the in-plane upper critical fields clearly demonstrate a two-fold symmetry that breaks the three-fold crystal symmetry. The two-fold symmetry is also found in the absolute value of the magnetization of the initial zero-field-cooled branch of the hysteresis loop and in the value of the thermodynamic contribution above the irreversibility field, but also in the irreversible properties such as the value of the characteristic irreversibility field and in the width of the hysteresis loop. This provides strong experimental evidence that Nb-doped Bi2Se3 is a nematic topological superconductor similar to the Cu- and Sr-doped Bi2Se3.

  9. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    International Nuclear Information System (INIS)

    Bhargavi, R.; Nair, Geetha G.; Krishna Prasad, S.; Majumdar, R.; Bag, Braja G.

    2014-01-01

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4–5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  10. A charge transfer complex nematic liquid crystalline gel with high electrical conductivity

    Science.gov (United States)

    Bhargavi, R.; Nair, Geetha G.; Krishna Prasad, S.; Majumdar, R.; Bag, Braja G.

    2014-10-01

    We describe the rheological, dielectric and elastic properties of a nematic liquid crystal gel created using an anthrylidene derivative of arjunolic acid, a chiral triterpenoid, obtained from the extracts of the wood of Terminalia arjuna. In this novel gel, having the electron-donor and acceptor components as minority constituents, the gelation and strengthening of charge-transfer complex (CTC) formation are seen to be occurring concomitantly. In addition to being mechanically strong with a large storage modulus, the gel with the maximized CTC exhibits Frank bend elastic constant values that approach nanonewton levels. The highlight of the study is the observation of 4-5 orders of magnitude increase in electrical conductivity for this gel, a value that is higher than even in the CT complexes of 2-d ordered columnar structures. A further important advantage of the present system over the columnar complex is that the high conductivity is seen for ac probing also, and owing to the nematic nature can be switched between its anisotropic limits. Some of these features are ascribed to a specific molecular packing architecture, which reduces the trapping of the charge carriers.

  11. Nanodoping: a route for enhancing electro-optic performance of bent core nematic system

    Science.gov (United States)

    Kumar, Pradeep; Debnath, Somen; Rao, Nandiraju V. S.; Sinha, Aloka

    2018-03-01

    We report the effect of dispersion of barium titanate (BaTiO3) nanoparticles (BNPs) in a four ring bent core nematic (BCN) liquid crystal. Polarizing optical microscopy reveals the presence of a single nematic phase in pure and doped states. Polar switching has been observed in the bent core system and the value of spontaneous polarization (P s) increases with increase in doping concentration of BNPs in BCN. Dielectric study shows a lower frequency mode, which can be ascribed to the formation of cybotactic clusters. These clusters are also responsible for the observed polar switching in pure, as well as, in doped BCNs. Another higher frequency mode, observed only in pure BCN, indicates the rotation of molecules about their long molecular axis. The conductivity of doped samples is also found to decrease as compared to the pure BCN. This reduction helps in the minimization of negative effects caused by free ions in liquid crystal based devices. This study demonstrates that the interaction between BNPs and BCN molecules improves the P s, dielectric behaviour, viscosity and reduces the conductivity of pure BCN. Hence, nanodoping in a BCN is an effective method for the enhancement of electro-optic performances and will lead to the development of faster electro-optic devices.

  12. Large-Scale Patterns in a Minimal Cognitive Flocking Model: Incidental Leaders, Nematic Patterns, and Aggregates

    Science.gov (United States)

    Barberis, Lucas; Peruani, Fernando

    2016-12-01

    We study a minimal cognitive flocking model, which assumes that the moving entities navigate using the available instantaneous visual information exclusively. The model consists of active particles, with no memory, that interact by a short-ranged, position-based, attractive force, which acts inside a vision cone (VC), and lack velocity-velocity alignment. We show that this active system can exhibit—due to the VC that breaks Newton's third law—various complex, large-scale, self-organized patterns. Depending on parameter values, we observe the emergence of aggregates or millinglike patterns, the formation of moving—locally polar—files with particles at the front of these structures acting as effective leaders, and the self-organization of particles into macroscopic nematic structures leading to long-ranged nematic order. Combining simulations and nonlinear field equations, we show that position-based active models, as the one analyzed here, represent a new class of active systems fundamentally different from other active systems, including velocity-alignment-based flocking systems. The reported results are of prime importance in the study, interpretation, and modeling of collective motion patterns in living and nonliving active systems.

  13. Faster in-plane switching and reduced rotational viscosity characteristics in a graphene-nematic suspension

    Energy Technology Data Exchange (ETDEWEB)

    Basu, Rajratan, E-mail: basu@usna.edu; Kinnamon, Daniel; Skaggs, Nicole; Womack, James [Soft Matter and Nanomaterials Laboratory, Department of Physics, The United States Naval Academy, Annapolis, Maryland 21402 (United States)

    2016-05-14

    The in-plane switching (IPS) for a nematic liquid crystal (LC) was found to be considerably faster when the LC was doped with dilute concentrations of monolayer graphene flakes. Additional studies revealed that the presence of graphene reduced the rotational viscosity of the LC, permitting the nematic director to respond quicker in IPS mode on turning the electric field on. The studies were carried out with several graphene concentrations in the LC, and the experimental results coherently suggest that there exists an optimal concentration of graphene, allowing a reduction in the IPS response time and rotational viscosity in the LC. Above this optimal graphene concentration, the rotational viscosity was found to increase, and consequently, the LC no longer switched faster in IPS mode. The presence of graphene suspension was also found to decrease the LC's pretilt angle significantly due to the π-π electron stacking between the LC molecules and graphene flakes. To understand the π-π stacking interaction, the anchoring mechanism of the LC on a CVD grown monolayer graphene film on copper substrate was studied by reflected crossed polarized microscopy. Optical microphotographs revealed that the LC alignment direction depended on monolayer graphene's hexagonal crystal structure and its orientation.

  14. Helical phase of chiral nematic liquid crystals as the Bianchi VII0 group manifold

    Science.gov (United States)

    Gibbons, G. W.; Warnick, C. M.

    2011-09-01

    We show that the optical structure of the helical phase of a chiral nematic is naturally associated with the Bianchi VII0 group manifold, of which we give a full account. The Joets-Ribotta metric governing propagation of the extraordinary rays is invariant under the simply transitive action of the universal cover Ẽ(2) of the three-dimensional Euclidean group of two dimensions. Thus extraordinary light rays are geodesics of a left-invariant metric on this Bianchi type VII0 group. We are able to solve, by separation of variables, both the wave equation and the Hamilton-Jacobi equation for this metric. The former reduces to Mathieu’s equation, and the latter to the quadrantal pendulum equation. We discuss Maxwell’s equations for uniaxial optical materials where the configuration is invariant under a group action and develop a formalism to take advantage of these symmetries. The material is not assumed to be impedance matched, thus going beyond the usual scope of transformation optics. We show that for a chiral nematic in its helical phase Maxwell’s equations reduce to a generalized Mathieu equation. Our results may also be relevant to helical phases of some magnetic materials and to light propagation in certain cosmological models.

  15. Chiral Nematic Structure of Cellulose Nanocrystal Suspensions and Films; Polarized Light and Atomic Force Microscopy

    Directory of Open Access Journals (Sweden)

    Derek G. Gray

    2015-11-01

    Full Text Available Cellulosic liquid crystalline solutions and suspensions form chiral nematic phases that show a rich variety of optical textures in the liquid crystalline state. These ordered structures may be preserved in solid films prepared by evaporation of solvent or suspending medium. Film formation from aqueous suspensions of cellulose nanocrystals (CNC was investigated by polarized light microscopy, optical profilometry and atomic force microscopy (AFM. An attempt is made to interpret qualitatively the observed textures in terms of the orientation of the cellulose nanocrystals in the suspensions and films, and the changes in orientation caused by the evaporative process. Mass transfer within the evaporating droplet resulted in the formation of raised rings whose magnitude depended on the degree of pinning of the receding contact line. AFM of dry films at short length scales showed a radial orientation of the CNC at the free surface of the film, along with a radial height variation with a period of approximately P/2, ascribed to the anisotropic shrinkage of the chiral nematic structure.

  16. Aggregation, percolation and phase transitions in nematic liquid crystal EBBA doped with carbon nanotubes

    Science.gov (United States)

    Goncharuk, A. I.; Lebovka, N. I.; Lisetski, L. N.; Minenko, S. S.

    2009-08-01

    Electrical conductivity, optical transmittance and microstructure of multiwalled carbon nanotubes (MWCNTs) dispersed in nematic liquid crystal 4-ethoxybenzylidene-4'-n-butylaniline (EBBA) were studied in the temperature range between 287 and 363 K. The concentration C of MWCNTs was varied within 0.01-1% wt. The percolation threshold with a noticeable increase in electrical conductivity (by many orders of magnitude) was observed in the vicinity of C ≈ 0.1% wt. The heating-cooling hysteretic behaviour of electrical conductivity and optical transmittance thermal pre-history effects were studied. These effects reflected strong agglomeration and rearrangement of nanotubes during the thermal incubation. The estimates show that transient behaviour during the thermal incubation can be caused by Brownian motion of MWCNTs. The solidification of MWCNT + EBBA composite in the nematic range extended by conditions of supercooling was also studied as a function of temperature using electrical conductivity measurements. The solidification lag-time dependence on supercooling temperature followed the classical heterogeneous nucleation law, with MWCNTs serving as centres of EBBA solidification.

  17. Aggregation, percolation and phase transitions in nematic liquid crystal EBBA doped with carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Goncharuk, A I; Lebovka, N I [F Ovcharenko Institute of Biocolloidal Chemistry, NAS of Ukraine, 42 Vernadskii Prosp., Kyiv 03142 (Ukraine); Lisetski, L N; Minenko, S S, E-mail: lebovka@gmail.co [Institute for Scintillation Materials of STC ' Institute for Single Crystals' , NAS of Ukraine, 60 Lenin Ave., Kharkov 61001 (Ukraine)

    2009-08-21

    Electrical conductivity, optical transmittance and microstructure of multiwalled carbon nanotubes (MWCNTs) dispersed in nematic liquid crystal 4-ethoxybenzylidene-4'-n-butylaniline (EBBA) were studied in the temperature range between 287 and 363 K. The concentration C of MWCNTs was varied within 0.01-1% wt. The percolation threshold with a noticeable increase in electrical conductivity (by many orders of magnitude) was observed in the vicinity of C {approx} 0.1% wt. The heating-cooling hysteretic behaviour of electrical conductivity and optical transmittance thermal pre-history effects were studied. These effects reflected strong agglomeration and rearrangement of nanotubes during the thermal incubation. The estimates show that transient behaviour during the thermal incubation can be caused by Brownian motion of MWCNTs. The solidification of MWCNT + EBBA composite in the nematic range extended by conditions of supercooling was also studied as a function of temperature using electrical conductivity measurements. The solidification lag-time dependence on supercooling temperature followed the classical heterogeneous nucleation law, with MWCNTs serving as centres of EBBA solidification.

  18. Numerical investigation of influence of ionic space charge and flexoelectric polarization on measurements of elastic constants in nematic liquid crystals

    Science.gov (United States)

    Buczkowska, M.; Derfel, G.; Konowalski, M.

    2009-06-01

    Deformations of nematic layers caused by magnetic field allow determination of the elastic constants of liquid crystal. In this paper, we simulated numerically the deformations of planar and homeotropic nematic layers. The flexoelectric properties of the nematic and presence of ions were taken into account. Our aim was to show the influence of flexoelectricity on the results of the real measurement of the elastic constants k33 and k11. In these simulations, we calculated the optical phase difference ΔΦ between the ordinary and extraordinary rays of light passing through the layer placed between crossed polarizers as a function of the magnetic field induction B. One of the elastic constants can be calculated from the magnetic field threshold for deformation. The ratio k33/k11 can be found by means of fitting theoretical ΔΦ(B) dependence to the experimental results. The calculations reveal that the flexoelectric properties influence the deformations induced by the external magnetic field. In the case of highly pure samples, this may lead to false results of measurement of the elastic constants ratio k33/k11. This influence can be reduced if the nematic material contains ions of sufficiently high concentration. These results show that the flexoelectric properties may play an important role, especially in well purified samples.

  19. Saturation and stability of nonlinear photonic crystals

    International Nuclear Information System (INIS)

    Franco-Ortiz, M; Corella-Madueño, A; Rosas-Burgos, R A; Adrian Reyes, J; Avendaño, Carlos G

    2017-01-01

    We consider a one-dimensional photonic crystal made by an infinite set of nonlinear nematic films immersed in a linear dielectric medium. The thickness of each equidistant film is negligible and its refraction index depends continuously on the electric field intensity, giving rise to all the involved nonlinear terms, which joints from a starting linear index for negligible amplitudes to a final saturation index for extremely large field intensities. We show that the nonlinear exact solutions of this system form an intensity-dependent band structure which we calculate and analyze. Next, we ponder a finite version of this system; that is, we take a finite array of linear dielectric stacks of the same size separated by the same nonlinear extremely thin nematic slabs and find the reflection coefficients for this arrangement and obtain the dependence on the wave number and intensity of the incident wave. As a final step we analyze the stability of the analytical solutions of the nonlinear crystal by following the evolution of an additive amplitude to the analytical nonlinear solution we have found here. We discuss our results and state our conclusions. (paper)

  20. Effect of Molecular Flexibility on the Nematic-to-Isotropic Phase Transition for Highly Biaxial Molecular Non-Symmetric Liquid Crystal Dimers

    Science.gov (United States)

    Sebastián, Nerea; López, David Orencio; Diez-Berart, Sergio; de la Fuente, María Rosario; Salud, Josep; Pérez-Jubindo, Miguel Angel; Ros, María Blanca

    2011-01-01

    In this work, a study of the nematic (N)–isotropic (I) phase transition has been made in a series of odd non-symmetric liquid crystal dimers, the α-(4-cyanobiphenyl-4’-yloxy)-ω-(1-pyrenimine-benzylidene-4’-oxy) alkanes, by means of accurate calorimetric and dielectric measurements. These materials are potential candidates to present the elusive biaxial nematic (NB) phase, as they exhibit both molecular biaxiality and flexibility. According to the theory, the uniaxial nematic (NU)–isotropic (I) phase transition is first-order in nature, whereas the NB–I phase transition is second-order. Thus, a fine analysis of the critical behavior of the N–I phase transition would allow us to determine the presence or not of the biaxial nematic phase and understand how the molecular biaxiality and flexibility of these compounds influences the critical behavior of the N–I phase transition. PMID:28824100

  1. Suscetibilidade de fungos nematófagos a fármacos antiparasitários

    OpenAIRE

    VIEIRA, Juliana Nunes

    2012-01-01

    O rápido desenvolvimento de resistência de parasitos do trato gastrintestinal a antihelmínticos tem demonstrado limitada eficiência desse método para o controle de determinadas endoparasitoses em ruminantes, incentivado assim, pesquisas com métodos alternativos de controle parasitário. A utilização de compostos químicos no tratamento anti-helmíntico de animais, em associação com fungos nematófagos usados no controle biológico, é uma estratégia que vem se mostrando eficaz para a redução da den...

  2. Alignment characteristic of nematic liquid crystals on orientational patterns realized by interfering laser light

    International Nuclear Information System (INIS)

    Lee, Eun-Kyu; Kim, Jong-Hyun

    2008-01-01

    We have observed the alignment property and switching behaviour of nematic liquid crystals (NLCs) on orientation patterns that were realized on a photo-active alignment layer by using interferring beams of two coherent laser lights. Linearly polarized light orients the liquid crystals in a direction perpendicular to the polarization and the interferring laser light induced a one-dimensional periodic texture following the interference pattern. Using double irradiation, in which the direction of the second irradiation was rotated by 90 0 to the first irradiation, we constructed a quasi-four-fold symmetric orientation pattern. The NLCs exhibited bistability in two average directions of polarization of the laser light, and they stably switched between the two directions by the in-plane electric field. Furthermore, the NLCs indicated the capability of continuous and memorized switching with a changing electric field on the orientation pattern

  3. Microscopic observation of zenithal bistable switching in nematic devices with different surface relief structures

    International Nuclear Information System (INIS)

    Uche, C; Elston, S J; Parry-Jones, L A

    2005-01-01

    Nematic liquid crystals have been shown to exhibit zenithal electro-optic bistability in devices containing sinusoidal and deformed sinusoidal gratings. Recently it has been shown that zenithal bistable states can also be supported at isolated edges of square gratings. In this paper, we present microscopic observations of bistability in cells containing sinusoidal gratings and long-pitch square gratings. We have also investigated a novel display based on square wells. High frame-rate video microscopy was used to obtain time-sequenced images when the devices were switched with monopolar pulses. These show that zenithal bistable switching can occur by two different processes: (i) domain growth (observed in cells containing sinusoidal gratings) and (ii) homogenous switching (observed in cells containing isolated edges

  4. Symmetry of Uniaxial Global Landau--de Gennes Minimizers in the Theory of Nematic Liquid Crystals

    KAUST Repository

    Henao, Duvan

    2012-01-01

    We extend the recent radial symmetry results by Pisante [J. Funct. Anal., 260 (2011), pp. 892-905] and Millot and Pisante [J. Eur. Math. Soc. (JEMS), 12 (2010), pp. 1069- 1096] (who show that the equivariant solutions are the only entire solutions of the three-dimensional Ginzburg-Landau equations in superconductivity theory) to the Landau-de Gennes framework in the theory of nematic liquid crystals. In the low temperature limit, we obtain a characterization of global Landau-de Gennes minimizers, in the restricted class of uniaxial tensors, in terms of the well-known radial-hedgehog solution. We use this characterization to prove that global Landau-de Gennes minimizers cannot be purely uniaxial for sufficiently low temperatures. Copyright © by SIAM.

  5. The Landau-de Gennes theory of nematic liquid crystals: Uniaxiality versus Biaxiality

    KAUST Repository

    Majumdar, Apala

    2011-12-01

    We study small energy solutions within the Landau-de Gennes theory for nematic liquid crystals, subject to Dirichlet boundary conditions. We consider two-dimensional and three-dimensional domains separately. In the two-dimensional case, we establish the equivalence of the Landau-de Gennes and Ginzburg-Landau theory. In the three-dimensional case, we give a new definition of the defect set based on the normalized energy. In the threedimensional uniaxial case, we demonstrate the equivalence between the defect set and the isotropic set and prove the C 1,α-convergence of uniaxial small energy solutions to a limiting harmonic map, away from the defect set, for some 0 < a < 1, in the vanishing core limit. Generalizations for biaxial small energy solutions are also discussed, which include physically relevant estimates for the solution and its scalar order parameters. This work is motivated by the study of defects in liquid crystalline systems and their applications.

  6. Voltage-controlled optical switch in planar nematic liquid crystal film

    Science.gov (United States)

    Shih, Chia-Chi; Chen, Yu-Jen; Wu, Sean; Tsai, Cheng-Che; Jiang, I.-Min

    2009-10-01

    This study presents an integrated device that consists of a directional coupler and an electro-optic switch. The device is designed to include a nematic liquid crystal cell, comprising a grating-like electrode. Applying the appropriate voltage to the cell yields a periodically distributed refractive index. An incident polarized beam will couple to an adjacent channel if it is parallel to the channel. The coupling efficiency is controlled by applied voltage. An obliquely injected polarized beam will be reflected and refracted in the channel, and propagated along a curved path. The route of the beam can be controlled by applying the voltage. A multiport routing was achieved for voltage modulation. In addition, the distribution of refractive index is also investigated by employing conoscopic technique experimentally and numerically.

  7. Angular structure of light polarization and singularities in transmittance of nematic liquid crystal cells

    Science.gov (United States)

    Kiselev, Alexei D.; Vovk, Roman G.; Buinyi, Igor O.; Soskin, Marat S.

    2007-06-01

    We study the angular structure of polarization of light transmitted through a nematic liquid crystal (NLC) cell by analyzing the polarization state as a function of the incidence angles. Our theoretical results are obtained by evaluating the Stokes parameters that characterize the polarization state of plane waves propagating through the NLC layer at varying direction of incidence. Using the Stokes polarimetry technique we carried out the measurements of the polarization resolved conoscopic patterns emerging after the homeotropically aligned NLC cell illuminated by the convergent light beam. The resulting polarization resolved angular patterns are described both theoretically and experimentally in terms of the polarization singularities such as C-points (points of circular polarization) and L-lines (lines of linear polarization). When the ellipticity of the incident light varies, the angular patterns are found to undergo transformations involving the processes of creation and annihilation of the C-points.

  8. Topological structure in polarization resolved conoscopic patterns for nematic liquid crystal cells

    Science.gov (United States)

    Buinyi, Igor O.; Denisenko, Vladimir G.; Soskin, Marat S.

    2009-01-01

    We investigate the polarization structure of coherent light, produced by a convergent light beam transmitted through nematic liquid crystal (NLC) cells with different director configurations. Employing solutions to the transmission problem for the case when plane wave propagates through an anisotropic layer, we analyze the arrangement of the topological elements, such as polarization singularities (C points with circular polarization and L lines with linear polarization), saddle points and extrema of polarization azimuth. We observe transformations of the topological structure under the variation of the incident light ellipticity and represent it by corresponding trajectories of topological elements in three-dimensional space. For the cells with uniform and non-uniform director configuration we describe the processes of creation/annihilation of C point pairs, which can be controlled precisely in the case of the cell with non-uniform director. Our experimental measurements for the homeotropically oriented NLC cells are in good agreement with the theoretical predictions.

  9. Extensional flow of nematic liquid crystal with an applied electric field

    KAUST Repository

    CUMMINGS, L. J.

    2013-10-17

    Systematic asymptotic methods are used to formulate a model for the extensional flow of a thin sheet of nematic liquid crystal. With no external body forces applied, the model is found to be equivalent to the so-called Trouton model for Newtonian sheets (and fibres), albeit with a modified \\'Trouton ratio\\'. However, with a symmetry-breaking electric field gradient applied, behaviour deviates from the Newtonian case, and the sheet can undergo finite-time breakup if a suitable destabilizing field is applied. Some simple exact solutions are presented to illustrate the results in certain idealized limits, as well as sample numerical results to the full model equations. Copyright © Cambridge University Press 2013.

  10. Symmetry breaking and structure of a mixture of nematic liquid crystals and anisotropic nanoparticles

    Directory of Open Access Journals (Sweden)

    Marjan Krasna

    2010-07-01

    Full Text Available Orientational ordering of a homogeneous mixture of uniaxial liquid crystalline (LC molecules and magnetic nanoparticles (NPs is studied using the Lebwohl–Lasher lattice model. We consider cases where NPs tend to be oriented perpendicularly to LC molecules due to elastic forces. We study domain-type configurations of ensembles, which are quenched from the isotropic phase. We show that for large enough concentrations of NPs the long range uniaxial nematic ordering is replaced by short range order exhibiting strong biaxiality. This suggests that the impact of NPs on orientational ordering of LCs for appropriate concentrations of NPs is reminiscent to the influence of quenched random fields which locally enforce a biaxial ordering.

  11. All-optical modulation in dye-doped nematic liquid crystal photonic bandgap fibers

    DEFF Research Database (Denmark)

    Alkeskjold, Thomas Tanggaard; Lægsgaard, Jesper; Bjarklev, Anders Overgaard

    2004-01-01

    Photonic crystal fibers (PCFs) have attracted significant attention during the last years and much research has been devoted to develop fiber designs for various applications, hereunder tunable fiber devices. Recently, thermally and electrically tunable PCF devices based on liquid crystals (LCs......) have been demonstrated. However, optical tuning of the LC PCF has until now not been demonstrated. Here we demonstrate an all-optical modulator, which utilizes a pulsed 532nm laser to modulate the spectral position of the bandgaps in a photonic crystal fiber infiltrated with a dye-doped nematic liquid...... crystal. We demonstrate a modulation frequency of 2kHz for a moderate pump power of 2-3mW and describe two pump pulse regimes in which there is an order of magnitude difference between the decay times....

  12. Time-resolved sign-dependent switching in a hybrid aligned nematic liquid crystal cell

    International Nuclear Information System (INIS)

    Taphouse, T S; Cornford, S L; Birkett, J E; Sambles, J R

    2008-01-01

    An optical waveguide technique is used to determine the director tilt profile across a hybrid aligned nematic (HAN) liquid crystal cell, in which the optical response is dependent on the sign of the applied voltage. Two physical models are shown that fit the equilibrium experimental data, but with alternative explanations for this sign dependence. Models with either a flexoelectric coefficient of 2.25x10 -11 C m -1 or a bound surface charge of 12.2 μC m -2 are shown that fit this equilibrium data. In an attempt to resolve this degeneracy sign-dependent switching data are analysed. However, neither model can explain these switching data, which are affected by slow transients of ∼100 ms which are believed to be due to the motion of free ions in the liquid crystal. From the form of these slow transients, it is suggested that the equilibrium position of the ions is next to a cell substrate

  13. Photosensitive soft matter: mixtures of nematic liquid crystal with azo molecules

    International Nuclear Information System (INIS)

    Petrov, A.G.; Marinov, I.G.; Hadjichristov, G.B.; Sridevi, S.; Hiremath, U.S.; Yelamaggad, C.V.; Prasad, S.K.

    2013-01-01

    Photosensitive soft matter based upon guest-host liquid crystal systems was prepared by mixing azobenzene-containing mesogens with the nematic liquid crystal 4-butyl-cyclohexane carboxylic acid 4-pentyloxy-phenyl ester (CM80). Binary mixtures of the host CM80 with three azo-bonded compounds as UV-active dopants (guests) at a relatively small concentration of 1~wt.% were characterized by thermo-optical, dielectric, spectral and flexoelectric measurements. The study aimed to determine the mechanisms that result in variations of material parameters caused by light-driven molecular conformation change of the azo-dye guest molecules (the transition from rod-shaped trans isomers to bent-shaped cis isomers)

  14. Ion adsorption and its influence on direct current electric field induced deformations of flexoelectric nematic layers.

    Science.gov (United States)

    Derfel, Grzegorz; Buczkowska, Mariola

    2011-07-07

    The influence of ion adsorption on the behavior of the nematic liquid crystal layers is studied numerically. The homeotropic flexoelectric layer subjected to the dc electric field is considered. Selective adsorption of positive ions is assumed. The analysis is based on the free energy formalism for ion adsorption. The distributions of director orientation angle, electric potential, and ion concentrations are calculated by numerical resolving of suitable torques equations and Poisson equation. The threshold voltages for the deformations are also determined. It was shown that adsorption affects the distributions of both cations and anions. Sufficiently large number of adsorbed ions leads to spontaneous deformation arising without any threshold if the total number of ions creates sufficiently strong electric field with significant field gradients in the neighborhood of electrodes. The spontaneous deformations are favored by strong flexoelectricity, large thickness, large ion concentrations, weak anchoring, and large adsorption energy.

  15. Analysis of the sign-dependent switching observed in a hybrid aligned nematic cell

    International Nuclear Information System (INIS)

    Cornford, S L; Taphouse, T S; Sambles, J R

    2009-01-01

    An optical waveguide experiment was used to study the influence of dc electric fields on a hybrid aligned nematic liquid crystal cell. This dc switching differed from ac switching in two ways: first, the equilibrium states depended on the sign of the applied voltage, and second, there was transient activity over long (∼100 ms) timescales. To understand both of these, a numerical model of the cell's dynamics, which included both the Ericksen-Leslie theory and a drift-diffusion model of mobile ions, has been developed. Comparing modelling with observations, we find that the transients are caused by the motion of tiny concentrations of ionic impurities, and that the sign dependence is caused by an asymmetric distribution of surface charge, rather than the flexoelectric effect.

  16. Optical transitions driven by self-induced walk-off in nematic liquid crystals

    International Nuclear Information System (INIS)

    Brasselet, E.

    2004-01-01

    Optical field induced reorientation of a nematic liquid crystals film is investigated for finite cross-section of the excitation beam. An approach based on self-induced walk-off between extraordinary and ordinary waves is proposed, including the geometrical aspect ratio between the beam diameter and the cell thickness in a perturbative fashion. The bifurcation scenario when the intensity is taken as the control parameter is calculated in the case of a circularly polarized excitation beam at normal incidence. The sudden appearance of a new saddle-node bifurcation is predicted for a walk-off corresponding to realistic experimental conditions. Changes of the light angular momentum transfer induced by walk-off are singled out as a valid candidate to explain observed nonlinear dynamics whose origin is not yet well understood

  17. Director gliding in a nematic liquid crystal layer: Quantitative comparison with experiments

    Science.gov (United States)

    Mema, E.; Kondic, L.; Cummings, L. J.

    2018-03-01

    The interaction between nematic liquid crystals and polymer-coated substrates may lead to slow reorientation of the easy axis (so-called "director gliding") when a prolonged external field is applied. We consider the experimental evidence of zenithal gliding observed by Joly et al. [Phys. Rev. E 70, 050701 (2004), 10.1103/PhysRevE.70.050701] and Buluy et al. [J. Soc. Inf. Disp. 14, 603 (2006), 10.1889/1.2235686] as well as azimuthal gliding observed by S. Faetti and P. Marianelli [Liq. Cryst. 33, 327 (2006), 10.1080/02678290500512227], and we present a simple, physically motivated model that captures the slow dynamics of gliding, both in the presence of an electric field and after the electric field is turned off. We make a quantitative comparison of our model results and the experimental data and conclude that our model explains the gliding evolution very well.

  18. Thermal optical nonlinearity in photonic crystal fibers filled with nematic liquid crystals doped with gold nanoparticles

    Science.gov (United States)

    Lesiak, Piotr; Budaszewski, Daniel; Bednarska, Karolina; Wójcik, Michał; Sobotka, Piotr; Chychłowski, Miłosz; Woliński, Tomasz R.

    2017-05-01

    In this work we studied a newly reported class of nonlinear effects observed in 5CB liquid crystals doped with gold nanoparticles (GNPs). The size of the GNP was determined by direct TEM imaging and by X-ray scattering of the diluted NP solution. GNPs was coated by thiols with the ratio of mesogenic to n-alkyl thiols varying from 1:2 to 1:1. The research involved comparing properties of both undoped and doped 5CB (nematic LC) by infiltrating LC cell and microholes of the photonic crystal fiber (PCF) separately. In our experiment the PCF fiber type LMA-10 made by NKT Photonics as host material has been used.

  19. Influence of modified detonation nanodiamonds on electrooptical properties of nematic liquid crystals

    International Nuclear Information System (INIS)

    Vashkevich, Vera; Minko, Anatoly; Lapanik, Valeri

    2016-01-01

    To modify the structure of detonation nanodiamonds (DNDs) several carboxylate groups were added to DNDs. Activation of COOH-surface functionalized groups allowed attaching of various organic tails to molecules. It was investigated that dielectric and electrooptical properties of nematic liquid crystalline mixtures (LCMs) doped with modified DNDs (MDNDs). It is established that the effect of DNDs on mesomorphic, dielectric and electrooptical properties depends on the size of nanoparticles (NPs) and the type of tail-like organic molecules grafted to DNDs. It is found that NPs of a small size (5-6 nm) do not significantly affect on the parameters of LCMs. At the same time conglomerates of a larger size (50 and 100 nm) depending on the tails polarity can increase or decrease the dielectric anisotropy and response time of LCMs in about 1.2-1.4 times. (paper)

  20. Pair creation, motion, and annihilation of topological defects in two-dimensional nematic liquid crystals

    Science.gov (United States)

    Cortese, Dario; Eggers, Jens; Liverpool, Tanniemola B.

    2018-02-01

    We present a framework for the study of disclinations in two-dimensional active nematic liquid crystals and topological defects in general. The order tensor formalism is used to calculate exact multiparticle solutions of the linearized static equations inside a planar uniformly aligned state so that the total charge has to vanish. Topological charge conservation then requires that there is always an equal number of q =1 /2 and q =-1 /2 charges. Starting from a set of hydrodynamic equations, we derive a low-dimensional dynamical system for the parameters of the static solutions, which describes the motion of a half-disclination pair or of several pairs. Within this formalism, we model defect production and annihilation, as observed in experiments. Our dynamics also provide an estimate for the critical density at which production and annihilation rates are balanced.

  1. Temperature Driven Topological Switch in 1T'-MoTe2 and Strain Induced Nematicity in NaFeAs

    Science.gov (United States)

    Berger, Ayelet Denise Notis

    Quasiparticle interference (QPI) is a powerful technique within Scanning Tunneling Microscopy (STM) that is used to probe the electronic bandstructure of materials. This thesis presents two examples using QPI to measure the bandstructure in materials with exotic electronic states that can be tuned via outside parameters (temperature and strain). In Part I of the thesis, we discuss the temperature dependence of Fermi Arcs in 1T'-MoTe 2, and then in Part II, the strain dependent nematic state in NaFeAs. The recent discovery of Weyl semimetals has introduced a new family of materials with topologically protected electronic properties and potential applications due to their anomalous transport effects. Even more useful is a Weyl semimetal that can be turned "on" and "off," switching between a topological and trivial state. One possible material is MoTe2, which undergoes a phase transition at 240K. This thesis consists of experiments using Scanning Tunneling Microscopy (STM) and Spectroscopy (STS) at different temperatures to visualize changes in the electronic bandstructure of MoTe2 across the topological phase transition. We show that a signature of topologically protected Fermi Arcs is present at low temperatures but disappears at room temperature, in the trivial phase. We include an in-depth discussion of how to account for thermal effects when comparing these two types of measurements. In Part II, we discuss strain induced nematicity in NaFeAs, an iron pnictide. Nematic fluctuations and spin correlations play an important role in the phase diagram of the iron pnictides, a family of unconventional superconductors. Illuminating the mechanism behind this symmetry breaking is key to understanding the superconducting state. Previous work has shown that nematicity in the iron pnictides responds strongly to applied strain [1, 2]. In this thesis, I present results from a new experimental technique, elasto-scanning tunneling microscopy (E-STM), which combines in situ strain

  2. Creation of tunable absolute bandgaps in a two-dimensional anisotropic photonic crystal modulated by a nematic liquid crystal

    International Nuclear Information System (INIS)

    Liu Chenyang

    2008-01-01

    Photonic crystals (PCs) have many potential applications because of their ability to control light-wave propagation. We have investigated the tunable absolute bandgap in a two-dimensional anisotropic photonic crystal structures modulated by a nematic liquid crystal. The PC structure composed of an anisotropic-dielectric cylinder in the liquid crystal medium is studied by solving Maxwell's equations using the plane wave expansion method. The photonic band structures are found to exhibit absolute bandgaps for the square and triangular lattices. Numerical simulations show that the absolute bandgaps can be continuously tuned in the square and triangular lattices consisting of anisotropic-dielectric cylinders by infiltrating nematic liquid crystals. Such a mechanism of bandgap adjustment should open up a new application for designing components in photonic integrated circuits

  3. Tunable Channel Drop Filter in a Two-Dimensional Photonic Crystal Modulated by a Nematic Liquid Crystal

    Directory of Open Access Journals (Sweden)

    2006-01-01

    Full Text Available Photonic crystals (PCs have many potential applications because of their ability to control light-wave propagation and because PC-based waveguides may be integrated into optical circuits. We propose a novel tunable PC channel drop filter based on nematic liquid crystals and investigate its properties numerically by using the finite-difference time-domain (FDTD method. The refractive indices of liquid crystals can be actively modulated after infiltrating nematic liquid crystals into the microcavity in PC waveguides with square lattices. Then we can control light propagation in a PC waveguide. We analyze the Q -factors and resonance frequencies of a tunable PC channel drop filter by considering various indices modulation of liquid crystals. The novel component can be used as wavelength division multiplexing in photonic integrated circuits.

  4. Light- and electric-field-induced first-order orientation transitions in a dendrimer-doped nematic liquid crystal.

    Science.gov (United States)

    Babayan, E A; Budagovsky, I A; Shvetsov, S A; Smayev, M P; Zolot'ko, A S; Boiko, N I; Barnik, M I

    2010-12-01

    Interaction of light and ac electric fields with a nematic liquid crystal (NLC) doped with nanosized second-generation carbosilane codendrimers containing terminal azobenzene fragments has been studied. A first-order Freedericksz transition in the linearly polarized light, accompanied by an intrinsic bistability in a wide region, was observed. An additional ac electric field decreases the light-induced Freedericksz transition threshold and narrows the bistability region. Light illumination transforms the second-order electric-field-induced Freedericksz transition to a first-order one. The width of the bistability region increases with the light wave intensity. The theory of the interaction of light and ac electric fields with the dendrimer-doped NLCs is developed taking into account an additional (with respect to the undoped nematic host) dependence of the optical torque on the angle between the director and the light field.

  5. Non-linear optical measurement of the twist elastic constant in thermotropic and DNA lyotropic chiral nematics

    OpenAIRE

    Lucchetti, Liana; Fraccia, Tommaso P.; Ciciulla, Fabrizio; Bellini, Tommaso

    2017-01-01

    Throughout the whole history of liquid crystals science, the balancing of intrinsic elasticity with coupling to external forces has been the key strategy for most application and investigation. While the coupling of the optical field to the nematic director is at the base of a wealth of thoroughly described optical effects, a significant variety of geometries and materials have not been considered yet. Here we show that by adopting a simple cell geometry and measuring the optically induced bi...

  6. Topological events in polarization resolved angular patterns of nematic liquid crystal cells at varying ellipticity of incident wave

    OpenAIRE

    Kiselev, Alexei D.; Vovk, Roman G.

    2008-01-01

    We study the angular structure of polarization of light transmitted through a nematic liquid crystal (NLC) cell by analyzing the polarization state as a function of the incidence angles and the polarization of the incident wave. The polarization resolved angular patterns emerging after the NLC cell illuminated by the convergent light beam are described in terms of the polarization singularities such as C-points (points of circular polarization) and L-lines (lines of linear polarization). For ...

  7. Effects of size and ligand density on the chirality transfer from chiral-ligand-capped nanoparticles to nematic liquid crystals

    Science.gov (United States)

    Mori, Taizo; Sharma, Anshul; Nemati, Ahlam; Bergquist, Leah; Hegmann, Torsten

    2017-08-01

    Studies of chiroptical effects of chiral ligand-capped gold nanoparticles (Au NPs) are a fascinating and rapidly evolving field in nanomaterial research with promising applications of such chiral metal NPs in catalysis and metamaterials as well as chiral sensing and separation. The aim of our studies was to seek out a system that not only allows the detection and understanding of Au NP chirality but also permits visualization and ranking — considering size, shape and nature as well as density of the ligand shell — of the extent of chirality transfer to a surrounding medium. Nematic liquid crystal (N-LC) phases are an ideal platform to examine these effects, exhibiting characteristic defect textures upon doping with a chiral additive. To test this, we synthesized series of Au NPs capped with two structurally different chiral ligands and studied well-dispersed mixtures in two nematic liquid crystal hosts. Induced circular dichroism (ICD) spectropolarimetry and polarized light optical microscopy (POM) confirmed that all Au NPs induce chiral nematic (N*-LC) phases, and measurements of the helical pitch as well as calculation of the helical twisting power (HTP) in various cell geometries allowed for an insightful ranking of the efficiency of chirality transfer of all Au NPs as well as their free ligands.

  8. Anomalous behavior in the crossover between the negative and positive biaxial nematic mesophases in a lyotropic liquid crystal.

    Science.gov (United States)

    Akpinar, Erol; Reis, Dennys; Figueiredo Neto, Antonio M

    2014-05-19

    A novel quaternary lyotropic liquid-crystalline mixture of dodecyltrimethylammonium bromide (DDTMABr)/sodium bromide/1-dodecanol/water, presenting the biaxial nematic phase (NB ) in addition to two uniaxial discotic (ND) and calamitic (NC) nematic ones, was synthesized. The partial phase diagram of this new mixture was constructed as a function of the DDTMABr molar-fraction concentration. The phase transitions from uniaxial to biaxial nematic phases were studied by means of the temperature dependence of the optical birefringence. In a particular region of the phase diagram, anomalous behavior was observed in the crossover from N-B to N+b: the contrast of the conoscopic fringes, which allows the birefringence measurements, almost vanishes, and the sample loses its alignment. This behavior, which was not observed before in lyotropics, was interpreted as a decrease in the mean diamagnetic susceptibility anisotropy (Δχ) of the sample, which was related to the shape anisotropy of the micelles. Small-angle X-ray scattering measurements were performed to evaluate the micellar shape anisotropy; these revealed that this mixture presented a smaller shape anisotropy than those of other lyotropic micellar systems presenting the NB phase. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  9. Flexoelectric instability and a spontaneous chiral-symmetry breaking in a nematic liquid crystal cell with asymmetric boundary conditions.

    Science.gov (United States)

    Palto, S P; Mottram, N J; Osipov, M A

    2007-06-01

    Using both numerical simulations and an approximate analytical theory we describe a flexoelectric-induced instability in a thin nematic liquid crystal layer with asymmetric boundary conditions subjected to an applied electric field. The dependence of the threshold value of the electric field on principal material parameters of the nematic liquid crystal and the director distribution in different regions of the cell have been studied in detail numerically. The results have been compared with a simple analytical theory that enables us to obtain explicit expressions for the threshold electric field and the period of modulation above the threshold. It has been found that in the hybrid aligned nematic cell with homeotropic anchoring on one surface and planar homogeneous anchoring on the other surface, a periodic flexoelectric-induced domain structure appears, above a critical threshold, with a chiral director distribution. The director rotates about the alignment axis when moving along a perpendicular direction in the plane of the cell. The absolute value of the threshold field has been found to depend on the direction of the field due to the initial symmetry of the hybrid aligned cell and the presence of flexoelectricity.

  10. A small-angle X-ray scattering study of the lyotropic nematic phase of vanadium pentoxide gels

    Energy Technology Data Exchange (ETDEWEB)

    Davidson, P. [Universite de Paris-Sud, Orsay (France). Lab. de Phys. des Solides; Bourgaux, C.; Sergot, P.; Livage, J.

    1997-10-01

    Aqueous suspensions of vanadium pentoxide (V{sub 2}O{sub 5}) ribbons, also called Zocher phases, are known to display a lyotropic nematic phase. In this paper, it is shown how the small-angle X-ray scattering (SAXS) technique can provide useful information on the building blocks and their organization in this phase. SAXS experiments were performed either on unoriented samples or on samples aligned by a magnetic field or by shear flow. The scattering is comparable to that of the other classic lyotropic nematic phases displayed by stiff organic rod-like particles such as the tobacco mosaic virus. Scattering studies show that the building blocks have a ribbon shape, that their thickness is 9(1) A and indirectly that their width is several 100 A. Their length is known to be around a few thousand A and therefore could not be measured by SAXS. By following the average distance between the ribbons as a function of concentration, it is shown that the swelling of the phase is one-dimensional at large concentrations and two-dimensional at low concentrations. Finally, estimates of the nematic order parameter of a single domain sample and of samples sheared in a Couette cell have been obtained. (orig.). 24 refs.

  11. Flexible and Responsive Chiral Nematic Cellulose Nanocrystal/Poly(ethylene glycol) Composite Films with Uniform and Tunable Structural Color.

    Science.gov (United States)

    Yao, Kun; Meng, Qijun; Bulone, Vincent; Zhou, Qi

    2017-07-01

    The fabrication of responsive photonic structures from cellulose nanocrystals (CNCs) that can operate in the entire visible spectrum is challenging due to the requirements of precise periodic modulation of the pitch size of the self-assembled multilayer structures at the length scale within the wavelength of the visible light. The surface charge density of CNCs is an important factor in controlling the pitch size of the chiral nematic structure of the dried solid CNC films. The assembly of poly(ethylene glycol) (PEG) together with CNCs into smaller chiral nematic domains results in solid films with uniform helical structure upon slow drying. Large, flexible, and flat photonic composite films with uniform structure colors from blue to red are prepared by changing the composition of CNCs and PEG. The CNC/PEG(80/20) composite film demonstrates a reversible and smooth structural color change between green and transparent in response to an increase and decrease of relative humidity between 50% and 100% owing to the reversible swelling and dehydration of the chiral nematic structure. The composite also shows excellent mechanical and thermal properties, complementing the multifunctional property profile. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. On the Landau-de Gennes Elastic Energy of a Q-Tensor Model for Soft Biaxial Nematics

    Science.gov (United States)

    Mucci, Domenico; Nicolodi, Lorenzo

    2017-12-01

    In the Landau-de Gennes theory of liquid crystals, the propensities for alignments of molecules are represented at each point of the fluid by an element Q of the vector space S_0 of 3× 3 real symmetric traceless matrices, or Q-tensors. According to Longa and Trebin (1989), a biaxial nematic system is called soft biaxial if the tensor order parameter Q satisfies the constraint tr(Q^2) = {const}. After the introduction of a Q-tensor model for soft biaxial nematic systems and the description of its geometric structure, we address the question of coercivity for the most common four-elastic-constant form of the Landau-de Gennes elastic free-energy (Iyer et al. 2015) in this model. For a soft biaxial nematic system, the tensor field Q takes values in a four-dimensional sphere S^4_ρ of radius ρ ≤ √{2/3} in the five-dimensional space S_0 with inner product = tr(QP). The rotation group it{SO}(3) acts orthogonally on S_0 by conjugation and hence induces an action on S^4_ρ \\subset {S}_0. This action has generic orbits of codimension one that are diffeomorphic to an eightfold quotient S^3/H of the unit three-sphere S^3, where H={± 1, ± i, ± j, ± k} is the quaternion group, and has two degenerate orbits of codimension two that are diffeomorphic to the projective plane RP^2. Each generic orbit can be interpreted as the order parameter space of a constrained biaxial nematic system and each singular orbit as the order parameter space of a constrained uniaxial nematic system. It turns out that S^4_ρ is a cohomogeneity one manifold, i.e., a manifold with a group action whose orbit space is one-dimensional. Another important geometric feature of the model is that the set Σ _ρ of diagonal Q-tensors of fixed norm ρ is a (geodesic) great circle in S^4_ρ which meets every orbit of S^4_ρ orthogonally and is then a section for S^4_ρ in the sense of the general theory of canonical forms. We compute necessary and sufficient coercivity conditions for the elastic energy by

  13. Controlling defects in nematic and smectic liquid crystals through boundary geometry

    Science.gov (United States)

    Beller, Daniel A.

    Liquid crystals (LCs), presently the basis of the dominant electronics display technology, also hold immense potential for the design of new self-assembling, self-healing, and "smart" responsive materials. Essential to many of these novel materials are liquid crystalline defects, places where the liquid crystalline order is forced to break down, replacing the LC locally with a higher-symmetry phase. Despite the energetic cost of this local melting, defects are often present at equilibrium when boundary conditions frustrate the material order. These defects provide micron-scale tools for organizing colloids, focusing light, and generating micropatterned materials. Manipulating the shapes of the boundaries thus offers a route to obtaining new and desirable self-assembly outcomes in LCs, but each added degree of complexity in the boundary geometry increases the complexity of the liquid crystal's response. Therefore, conceptually minimal changes to boundary geometry are investigated for their effects on the self-assembled defect arrangements that result in nematic and smectic-A LCs in three dimensions as well as two-dimensional smectic LCs on curved substrates. In nematic LCs, disclination loops are studied in micropost confining environments and in the presence of sharp-edged colloidal inclusions, using both numerical modeling and topological reasoning. In both scenarios, sharp edges add new possibilities for the shape or placement of disclinations, permitting new types of colloidal self-assembly beyond simple chains and hexagonal lattices. Two-dimensional smectic LCs on curved substrates are examined in the special cases where the substrate curvature is confined to points or curves, providing an analytically tractable route to demonstrate how Gaussian curvature is associated with disclinations and grain boundaries, as well as these defects' likely experimental manifestations. In three-dimensional smectic-A LCs, novel self-assembled arrangements of focal conic domains

  14. Optical monitoring of surface anchoring changes for nematic liquid crystal based chemical and biological sensors

    Science.gov (United States)

    Zou, Yang

    In this dissertation, optically monitoring the surface anchoring changes of liquid crystal (LC) due to the chemical or biological bindings is presented. The deformation of LC director with different anchoring energies is simulated using Finite Element Method and continuum theory of nematic LC. The optical properties of the LC film are simulated using the Finite Difference Time Domain method. First, the interference color method was used to monitor the anchoring change. The calculated and experimental interference colors of liquid crystal films due to the optical retardation of two orthogonal electromagnetic components at different surface anchoring conditions and applied voltages are studied. The calculated colors were converted into sRGB parameters so that the corresponding colors can be displayed on a color computer monitor and printed out on a color printer. A gold micro-structure was fabricated and used to control the optical retardation. Polarizing micrographs were collected and compared with the calculated colors. Second, the influence of a bias voltage on the surface-driven orientational transition of liquid crystals resulted from the weakening anchoring and anchoring transition is analyzed theoretically and experimentally. The same interdigitated Au micro-structure was used in the nematic LC based chemical and biological sensors. With a suitable bias electric field, the process of the weakening anchoring energy and the uniform surface-driven orientational transition due to targeted molecules binding to a functionalized surface were observed optically. Finally, measurement of optical transmission was used to monitor the anchoring change. Polarizing micrographs were collected and compared with simulated textures. Experimental and simulation results both demonstrate the optical method can effectively monitor the surface anchoring change due to the presence of targeted analytes. These results show that these optical techniques are suitable for LC based sensing

  15. Geometric approach to the Miesowicz coefficients at the region of the crystalline-nematic transition and a universal relation for their ratio

    Science.gov (United States)

    Simões, M.; Domiciano, S. M.

    2002-12-01

    In this work the ratios between the Miesowicz coefficients of rigid calamitic nematic liquid crystals will be studied. It will be shown that the microscopic theory that describes these coefficients, the kinetic theory [M. Doi and S. F. Edwards, The Theory of Polymer Dynamics (Oxford Press, New York, 1986)], suggests that some ratios between the Miesowicz coefficients would have a universal character, that does not depend on the nematic material being examined. A set of experimental data has been collected from the liquid crystal literature and, once these data are rescaled in a common temperature scale, they point to the existence of such a universality. Nevertheless, only in the neighborhoods of the nematic-isotropic transition, do the theoretical calculations of the kinetic theory and the experimental data predict the same profile for this universality; when the region of the crystalline-nematic transition is approached theory and experiment present severe discrepancies. The reason for this disagreement is studied and it is proposed that it results from the fact that the kinetic theory does not take into account the packing properties of the nematic medium. A different approach to the calculation of these ratios is proposed and it is shown that it describes the experimental data for all temperatures.

  16. Note on the hydrodynamic description of thin nematic films: Strong anchoring model

    KAUST Repository

    Lin, Te-Sheng

    2013-01-01

    We discuss the long-wave hydrodynamic model for a thin film of nematic liquid crystal in the limit of strong anchoring at the free surface and at the substrate. We rigorously clarify how the elastic energy enters the evolution equation for the film thickness in order to provide a solid basis for further investigation: several conflicting models exist in the literature that predict qualitatively different behaviour. We consolidate the various approaches and show that the long-wave model derived through an asymptotic expansion of the full nemato-hydrodynamic equations with consistent boundary conditions agrees with the model one obtains by employing a thermodynamically motivated gradient dynamics formulation based on an underlying free energy functional. As a result, we find that in the case of strong anchoring the elastic distortion energy is always stabilising. To support the discussion in the main part of the paper, an appendix gives the full derivation of the evolution equation for the film thickness via asymptotic expansion. © 2013 AIP Publishing LLC.

  17. Order reconstruction in inverse twisted nematic cell with an applied electric field

    Science.gov (United States)

    Sun, Yang; Ye, Wenjiang; Zhang, Zhidong

    2016-05-01

    Order reconstruction in an inverse twisted nematic (ITN) liquid crystal cell with an applied electric field is investigated based on Landau-de Gennes theory and the two-dimensional finite-difference iterative method. Twice eigenvalue exchange in three-axis layer configuration, thrice eigenvalue exchange in four-axis layer configuration, and negative order parameter uniaxial twisted state exist in this cell, which can be described by the order parameter tensor Q in equilibrium state. The twice eigenvalue exchange also has two degenerate configurations with reduced electric field E from 0.8 to 2.8 in 10ξ cell (ξ is the biaxial correlation length). Moreover, two critical cell gaps dc* * = 7 ξ and dc* = 12 ξ are included in the study of the ITN cell. When d ≤ dc* * , only the eigenvalue change state exists. When d ≥ dc*, only a positive order parameter uniaxial twisted state exists near the threshold electric field. When dc* * concept of eigenvalue exchange.

  18. Numerical analysis of nematic liquid crystals as applied to tunable antennas

    Science.gov (United States)

    Papanicolaou, N. C.; Christou, M. A.; Polycarpou, A. C.

    2014-11-01

    In the current work we examine the application of Nematic Liquid Crystals (N-LCs) to frequency-agile antennas. A patch antenna design with a liquid crystal base is proposed. N-LCs are anisotropic and their electrical properties are determined by the macroscopic orientation of their molecules (director tilt-angle). However, these depend on the applied electric field, which means that the electric properties of the N-LC base can be effectively controlled. The above described problem is governed by a coupled system of PDEs. It is solved iteratively using a finite-difference scheme with relaxation. Once the director field is obtained, the dielectric properties of the material are determined for each value of the bias voltage. The proposed antenna is then simulated using HFSS. The return loss and resonant frequency are computed for each of value of the applied voltage. It is shown that the antennas under consideration can be tuned using relatively low applied voltages. This demonstrates the potential of liquid crystal based antennas in frequency-agile antenna design.

  19. Competing Spin Liquids and Hidden Spin-Nematic Order in Spin Ice with Frustrated Transverse Exchange

    Directory of Open Access Journals (Sweden)

    Mathieu Taillefumier

    2017-12-01

    Full Text Available Frustration in magnetic interactions can give rise to disordered ground states with subtle and beautiful properties. The spin ices Ho_{2}Ti_{2}O_{7} and Dy_{2}Ti_{2}O_{7} exemplify this phenomenon, displaying a classical spin-liquid state, with fractionalized magnetic-monopole excitations. Recently, there has been great interest in closely related “quantum spin-ice” materials, following the realization that anisotropic exchange interactions could convert spin ice into a massively entangled, quantum spin liquid, where magnetic monopoles become the charges of an emergent quantum electrodynamics. Here we show that even the simplest model of a quantum spin ice, the XXZ model on the pyrochlore lattice, can realize a still-richer scenario. Using a combination of classical Monte Carlo simulation, semiclassical molecular-dynamics simulation, and analytic field theory, we explore the properties of this model for frustrated transverse exchange. We find not one, but three competing forms of spin liquid, as well as a phase with hidden, spin-nematic order. We explore the experimental signatures of each of these different states, making explicit predictions for inelastic neutron scattering. These results show an intriguing similarity to experiments on a range of pyrochlore oxides.

  20. Nematic Liquid Crystals: From Maier-Saupe to a Continuum Theory

    KAUST Repository

    Ball, John M.

    2010-07-20

    We define a continuum energy functional that effectively interpolates between the mean-field Maier-Saupe energy and the continuum Landau-de Gennes energy functional and can describe both spatially homogeneous and inhomogeneous systems. In the mean-field approach the main macroscopic variable, the Q-tensor order parameter, is defined in terms of the second moment of a probability distribution function. This definition imposes certain constraints on the eigenvalues of the Q-tensor order parameter, which may be interpreted as physical constraints. We define a thermotropic bulk potential which blows up whenever the eigenvalues of the Q-tensor order parameter approach physically unrealistic values. As a consequence, the minimizers of this continuum energy functional have physically realistic order parameters in all temperature regimes. We study the asymptotics of this bulk potential and show that this model also predicts a first-order nematic-isotropic phase transition, whilst respecting the physical constraints. In contrast, in the Landau-de Gennes framework the Q-tensor order parameter is often defined independently of the probability distribution function, and the theory makes physically unrealistic predictions about the equilibrium order parameters in the low-temperature regime. Copyright © Taylor & Francis Group, LLC.

  1. Kibble-Zurek Scaling during Defect Formation in a Nematic Liquid Crystal.

    Science.gov (United States)

    Fowler, Nicholas; Dierking, Dr Ingo

    2017-04-05

    Symmetry-breaking phase transitions are often accompanied by the formation of topological defects, as in cosmological theories of the early universe, superfluids, liquid crystals or solid-state systems. This scenario is described by the Kibble-Zurek mechanism, which predicts corresponding scaling laws for the defect density ρ. One such scaling law suggests a relation ρ≈τ Q -1/2 with τ Q the change of rate of a control parameter. In contrast to the scaling of the defect density during annihilation with ρ≈t -1 , which is governed by the attraction of defects of the same strength but opposite sign, the defect formation process, which depends on the rate of change of a physical quantity initiating the transition, has only rarely been investigated. Herein, we use nematic liquid crystals as a different system to demonstrate the validity of the predicted scaling relation for defect formation. It is found that the scaling exponent is independent of temperature and material employed, thus universal, as predicted. © 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Poincaré-sphere representation of phase-mostly twisted nematic liquid crystal spatial light modulators

    Science.gov (United States)

    Durán, V.; Clemente, P.; Martínez-León, Ll; Climent, V.; Lancis, J.

    2009-08-01

    We establish necessary conditions in order to build a phase-only wavefront modulation system from a liquid crystal display. These conditions determine the dependence of the polarization state of the light emerging from the display on the addressing gray level. The analysis, which is carried out by means of the coherence-matrix formalism, includes the depolarization properties of the device. Two different types of polarization distributions at the output of the liquid crystal cells are found. This approach is applied to a twisted nematic liquid crystal display. In this case, an optimization algorithm must be designed in order to select the input polarization state that leads to the required distributions. We show that the Poincaré-sphere representation provides a convenient framework to design the optimization algorithm as it allows for a reduced number of degrees of freedom. This feature significantly decreases the computation time. Laboratory results are presented for a liquid crystal on silicon display showing a phase modulation depth greater than 2π rad with an intensity variation lower than 6%. In addition, a hybrid ternary modulation (HTM), an operation regime employed in holographic data storage, is achieved.

  3. De Gennes model of the nematic to smectic-A transition: dislocations and gauge properties

    International Nuclear Information System (INIS)

    Day, A.R.

    1984-01-01

    The de Gennes model is used to study the nematic to smectic-A (N-A) transition of liquid crystals. The analogy between the Ginzburg-Landau model for the normal metal to superconducting transition and the role of the splay elastic constant K 1 is stressed. It is found that, in contrast to what was previously thought, the de Gennes model is gauge invariant, irrespective of the value of k 1 . The model is studied in an arbitrary gauge, and it is shown that the renormalization group recursion relations in the epsilon expansion are independent of gauge. The critical exponent eta, with governs the power law decay of the smectic correlations at the critical point, is found to depend on the gauge, and, in the physical gauge, to diverge at the accessible fixed point, K 1 /sup XX.XX/ = 0. This is indicative of the nonpower law decay of the correlation function at the critical point. The author introduces an extension of the de Gennes model that describes a liquid crystal, with negative dielectric anisotropy, in an applied electric field. It is shown that there are at least two possible extensions to 4-epsilon dimensions and that they predict different critical behavior

  4. Competing Spin Liquids and Hidden Spin-Nematic Order in Spin Ice with Frustrated Transverse Exchange

    Science.gov (United States)

    Taillefumier, Mathieu; Benton, Owen; Yan, Han; Jaubert, L. D. C.; Shannon, Nic

    2017-10-01

    Frustration in magnetic interactions can give rise to disordered ground states with subtle and beautiful properties. The spin ices Ho2 Ti2 O7 and Dy2 Ti2 O7 exemplify this phenomenon, displaying a classical spin-liquid state, with fractionalized magnetic-monopole excitations. Recently, there has been great interest in closely related "quantum spin-ice" materials, following the realization that anisotropic exchange interactions could convert spin ice into a massively entangled, quantum spin liquid, where magnetic monopoles become the charges of an emergent quantum electrodynamics. Here we show that even the simplest model of a quantum spin ice, the XXZ model on the pyrochlore lattice, can realize a still-richer scenario. Using a combination of classical Monte Carlo simulation, semiclassical molecular-dynamics simulation, and analytic field theory, we explore the properties of this model for frustrated transverse exchange. We find not one, but three competing forms of spin liquid, as well as a phase with hidden, spin-nematic order. We explore the experimental signatures of each of these different states, making explicit predictions for inelastic neutron scattering. These results show an intriguing similarity to experiments on a range of pyrochlore oxides.

  5. Defects in Nematic Shells: A Γ-Convergence Discrete-to-Continuum Approach

    Science.gov (United States)

    Canevari, Giacomo; Segatti, Antonio

    2018-01-01

    In this paper we rigorously investigate the emergence of defects on Nematic Shells with a genus different from one. This phenomenon is related to a non-trivial interplay between the topology of the shell and the alignment of the director field. To this end, we consider a discrete XY system on the shell M, described by a tangent vector field with unit norm sitting at the vertices of a triangulation of the shell. Defects emerge when we let the mesh size of the triangulation go to zero, namely in the discrete-to-continuum limit. In this paper we investigate the discrete-to-continuum limit in terms of Γ-convergence in two different asymptotic regimes. The first scaling promotes the appearance of a finite number of defects whose charges are in accordance with the topology of shell M, via the Poincaré-Hopf Theorem. The second scaling produces the so called Renormalized Energy that governs the equilibrium of the configurations with defects.

  6. Highly sensitive and selective glucose sensor based on ultraviolet-treated nematic liquid crystals.

    Science.gov (United States)

    Zhong, Shenghong; Jang, Chang-Hyun

    2014-09-15

    Glucose is an extremely important biomolecule, and the ability to sense it has played a significant role in facilitating the understanding of many biological processes. Here, we report a novel glucose sensor based on ultraviolet (UV)-treated nematic liquid crystals. Submerging UV-treated 4-cyano-4'-pentylbiphenyl (5CB) in a glucose solution (while carefully adjusting its pH to 7.5 with NaOH and HCl) triggered an optical response, from dark to bright, observed with a polarized microscope. Notably, 5CB was located inside a glucose oxidase (GOx)-modified gold grid. We exploited this pH-driven phenomenon to design a new glucose sensor. This device could detect as little as 1 pM analyte, which is 3 orders of magnitude lower than the detection limit of the most sensitive glucose sensor currently available. It also exhibits high selectivity due to GOx modification. Thus, this is a promising technique for glucose detection, not only for clinical diagnostics, but also for sensing low levels of glucose in a biological environment (e.g., single cells and bacterial cultures). Copyright © 2014 Elsevier B.V. All rights reserved.

  7. Electrically Tunable Open-Stub Bandpass Filters Based on Nematic Liquid Crystals

    Science.gov (United States)

    Economou, E. C.; Lovejoy, J.; Harward, I.; Nobles, J. E.; Kula, P.; Herman, J.; Glushchenko, A.; Celinski, Z.

    2017-12-01

    Electrically tunable bandpass filters based on liquid crystals are designed, built, and characterized using a vector network analyzer. The filters are composed of half-wavelength open stubs and quarter-wavelength connecting lines in an inverted microstrip geometry. The filters are modeled using computational electromagnetics software utilizing the finite integration technique. Photolithography and thin-film deposition processes are employed, and standard liquid-crystal cell-assembly techniques are used to make the final filter structures. The three-stub filters with passband central frequencies of 30, 50, and 85 GHz are filled with the nematic liquid crystal, LC1917, and tested. 10% tuning of the central frequency is achieved with a 14-volt peak-to-peak ac bias across the 38 -μ m liquid-crystal layer (electric field of 0.19 V / μ m ). At 50 GHz, the insertion loss is -3.76 dB , while the return loss ranges from -9 to -25 dB , indicating a good impedance match for a proof-of-concept device. The passband widths of the 30-, 50-, and 85-GHz filters are 5, 9, and 14 GHz, respectively, resulting in a Q factor of 6. The filter devices presented in this study, although intended for microwave signal-processing applications, furnish an effective methodology for characterizing the dielectric properties of liquid-crystal materials (and fluids or solids in general) up to the terahertz frequency range.

  8. Low-frequency electrohydrodynamic convection patterns in nematic liquid crystal aligned using parallel-oriented nanofiber

    Science.gov (United States)

    Mahendra, Bhisma; Nugroho, Fahrudin; Yusuf, Yusril

    2018-02-01

    Parallel-aligned poly(vinyl alcohol) (PVA) nanofiber with a diameter of 240 ± 60 nm and an alignment parameter (S) of 0.95 ± 0.16 was obtained by a gap collector electrospinning that used copper (Cu) as a collector. The sandwiched cells (the horizontal-view and longitudinal-view) nematic liquid crystal was prepared by treating glass surfaces with the aligned PVA nanofiber to provide uniform anchoring of the director. When an electric field was applied to these samples, the electrohydrodynamic convection (EHC) pattern was observed. In the longitudinal-view cells, above a threshold voltage at low frequency, a typically low-frequency EHC rolls i.e., a Williams domain (WD) pattern was observed. By increasing the voltage, a fluctuating Williams domain (FWD) and grid patterns (GPs) could also be observed. In the transverse-view cells, at low-frequency regimes, WD, sawtooth patterned (STP), and dynamic scattering mode (DSM) patterns were observed. By replacing the conventional rubbing method with the use of parallel-aligned nanofibers, the well-known EHC phenomenon also could be observed.

  9. 3D Printing of Liquid Crystal Elastomeric Actuators with Spatially Programed Nematic Order.

    Science.gov (United States)

    Kotikian, Arda; Truby, Ryan L; Boley, John William; White, Timothy J; Lewis, Jennifer A

    2018-03-01

    Liquid crystal elastomers (LCEs) are soft materials capable of large, reversible shape changes, which may find potential application as artificial muscles, soft robots, and dynamic functional architectures. Here, the design and additive manufacturing of LCE actuators (LCEAs) with spatially programed nematic order that exhibit large, reversible, and repeatable contraction with high specific work capacity are reported. First, a photopolymerizable, solvent-free, main-chain LCE ink is created via aza-Michael addition with the appropriate viscoelastic properties for 3D printing. Next, high operating temperature direct ink writing of LCE inks is used to align their mesogen domains along the direction of the print path. To demonstrate the power of this additive manufacturing approach, shape-morphing LCEA architectures are fabricated, which undergo reversible planar-to-3D and 3D-to-3D' transformations on demand, that can lift significantly more weight than other LCEAs reported to date. © 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  10. AC electric field assisted orientational photorefractive effect in C60-doped nematic liquid crystal

    International Nuclear Information System (INIS)

    Sun Xiudong; Pei Yanbo; Yao Fengfeng; Zhang Jianlong; Hou Chunfeng

    2007-01-01

    Photorefractive gratings were produced in a C 60 -doped nematic liquid crystal cell under the application of two coherent beams and a nonbiased sinusoidal ac electric field. The beam coupling and diffraction of the ac electric field assisted gratings were studied systematically. A stable asymmetric energy transference was obtained. Diffraction was observed when the angle (between the normal of the cell and the bisector of the writing beams) was 0 0 , and the dependence of diffraction efficiency on the peak-to-peak value of the ac voltage was similar to that at an incidence angle of 45 0 , suggesting that the role of the ac field was to facilitate the charge separation, and the space-charge field (SCF) originated predominantly from the diffusion of the ac electric field assisted photo-induced carriers under the application of nonuniform illumination and an applied ac field. The grating was produced by director reorientation induced by the cooperation of the SCF and the applied ac electric field. A self-erasing phenomenon was observed in this cell. An explanation in terms of the movement of two kinds of carriers with opposite signs was proposed

  11. Converse flexoelectric effect in a bent-core nematic liquid crystal.

    Science.gov (United States)

    Harden, J; Teeling, R; Gleeson, J T; Sprunt, S; Jákli, A

    2008-09-01

    Flexoelectricity is a unique property of liquid crystals; it is a linear coupling between electric polarizations and bend and/or splay distortions of the direction of average molecular orientation. Recently it was shown [J. Harden, Phys. Rev. Lett. 97, 157802 (2006)] that the bend flexoelectric coefficient in bent-core nematic liquid crystals can be three orders of magnitude higher than the effect with calamitic (rod-shaped) molecular shape. Here we report the converse of the flexoelectric effect: An electric field applied across a bent-core liquid crystal sandwiched between thin flexible substrates produces a director distortion which is manifested as a polarity-dependent flexing of the substrates. The flex magnitude is shown to be consistent with predictions based upon both the measured value of the bend flexoelectric constant and the elastic properties of the substrates. Converse flexoelectricity makes possible a new class of microactuators with no internal moving parts, which offers applications as diverse as optical beam steering to artificial muscles.

  12. Extraordinary properties of nematic phases of bent-core liquid crystals

    Science.gov (United States)

    Jákli, A.; Chambers, M.; Harden, J.; Madhabi, M.; Teeling, R.; Kim, J.; Li, Q.; Nair, G. G.; Éber, N.; Fodor-Csorba, K.; Gleeson, J. T.; Sprunt, S.

    2008-02-01

    We briefly review systematic and comprehensive studies on several chlorine-substituted bent-core liquid crystal materials in their nematic phases. The results, in comparison to rod-shaped molecules, are both extraordinary and technologically significant. Specifically: a) Electrohydrodynamic instabilities provide unique patterns including well defined, periodic stripes and optically isotropic structures. b) Rheological measurements using different probe techniques (dynamic light scattering, pulsed magnetic field, electrorotation) reveal that the ratio of the flow and rotational viscosities are over two orders of magnitudes larger in bentcore than in calamitic materials which proves that the molecule shape and not its size is responsible for this behaviour. c) Giant flexoelectric response, as measured by dynamic light scattering and by directly probing the induced current when the material is subject to oscillatory bend deformation, turns out to be more than three orders of magnitude larger than in calamitics and 50 times larger than molecular shape considerations alone would predict. The magnitude of this effect renders these materials as promising candidates for efficient conversion between mechanical and electrical energy. d) The converse of this effect when the bent-core material sandwiched between plastic substrates 4 times thicker than the liquid crystal material provided displacements in the range of 100nm that is sensitive to the polarity of the applied field thus suggesting applications as beam steering and precision motion controls.

  13. Ultraweak azimuthal anchoring of a nematic liquid crystal on a planar orienting photopolymer

    International Nuclear Information System (INIS)

    Nespoulous, Mathieu; Blanc, Christophe; Nobili, Maurizio

    2007-01-01

    The search of weak anchoring is an important issue for a whole class of liquid crystal displays. In this paper we present an orienting layer showing unreached weak planar azimuthal anchoring for 4-n-pentyl-4 ' -cyanobiphenyl nematic liquid crystal (5CB). Azimuthal extrapolation lengths as large as 80 μm are easily obtained. Our layers are made with the commercial photocurable polymer Norland optical adhesive 60. The anisotropy of the film is induced by the adsorption of oriented liquid crystal molecules under a 2 T magnetic field applied parallel to the surfaces. We use the width of surface π-walls and a high-field electro-optical method to measure, respectively, the azimuthal and the zenithal anchorings. The azimuthal anchoring is extremely sensitive to the ultraviolet (UV) dose and it also depends on the magnetic field application duration. On the opposite, the zenithal anchoring is only slightly sensitive to the preparation parameters. All these results are discussed in terms of the adsorption/desorption mechanisms of the liquid crystal molecules on the polymer layer and of the flexibility of the polymer network

  14. Nematic long-range ordering of topological defects in active liquid crystals

    Science.gov (United States)

    Dunkel, Jorn; Oza, Anand

    2015-11-01

    Identifying the ordering principles of intracellular matter is key to understanding the physics of microbiological systems. Recent experiments demonstrated that ATP-driven microtubule-kinesin bundles can self-assemble into two-dimensional active liquid crystals that exhibit a rich creation and annihilation dynamics of topological defects, reminiscent of particle-pair production processes in quantum systems. This remarkable discovery has sparked considerable theoretical and experimental interest, yet a satisfactory mathematical description remains elusive. Here, we present and validate a continuum theory for this new class of active matter systems by merging universality ideas with the classical Landau-de Gennes theory. The resulting model agrees quantitatively with recently published data and, in particular, predicts correctly a previously unexplained regime of long-range nematic ordering of defects observed in experiments. Our analysis implies that active liquid crystals are governed by the same generic ordering principles that determine the non-equilibrium dynamics of dense bacterial suspensions and elastic bilayer materials. Moreover, the theory suggests an energetic analogy with strongly interacting quantum gases.

  15. Lasing in a nematic liquid crystal cell with an interdigitated electrode system

    Energy Technology Data Exchange (ETDEWEB)

    Shtykov, N M; Palto, S P; Umanskii, B A; Geivandov, A R [Shubnikov Institute of Crystallography, Russian Academy of Sciences, Moscow (Russian Federation)

    2015-04-30

    Waveguide lasing in a layer of a dye-doped nematic liquid crystal has been observed. The liquid-crystal layer was sandwiched between a quartz substrate and a glass cover plate on whose surface was deposited an interdigitated electrode system. This system had a period of 3.75 μm and played a dual role, namely, it created a spatial periodicity of the waveguide medium refractive index (thus creating distributed feedback) and served as a diffraction grating coupling out a part of waveguide radiation into the glass cover plate. The distributed feedback ensured lasing in the 18th diffraction order for the TE modes and in the 19th order for the TM modes of the waveguide. The generated radiation was observed at the exit from the glass plate end face at the angles to the waveguide plane of 33.1 ± 1.5° for TM modes and 21.8 ± 1.8° for TE modes. The intensity and position of the TE emission line showed no regular dependence on the voltage on the electrodes. In the case of TM radiation, an increase in the voltage led to a short-wavelength shift of the laser line and to a decrease in its intensity. (lasers)

  16. Controle biológico de nematóides gastrintestinais de ovinos, ovos de Trichuris trichiura, Trichuris vulpis e de Anoplocephala perfoliata por fungos nematófagos

    OpenAIRE

    Silva, André Ricardo e

    2011-01-01

    As helmintoses gastrointestinais provocam danos e podem matar ruminantes e outros animais, incluindo o homem. O uso indiscriminado de anti-helmínticos provocou a seleção de populações de helmintos resistentes aos diferentes grupos químicos utilizados. Fungos nematófagos, como Duddingtonia flagrans, Monacrosporium thaumasium e Pochonia chlamydosporia são utilizados no controle biológico das helmintoses gastrintestinais. No primeiro experimento, ovelhas foram tratadas com péletes contendo D. fl...

  17. Cable Stability

    CERN Document Server

    Bottura, L

    2014-01-01

    Superconductor stability is at the core of the design of any successful cable and magnet application. This chapter reviews the initial understanding of the stability mechanism, and reviews matters of importance for stability such as the nature and magnitude of the perturbation spectrum and the cooling mechanisms. Various stability strategies are studied, providing criteria that depend on the desired design and operating conditions.

  18. Conoscopic evidence of the UV light-induced flexoelectric effect in homeotropic layers of nematic liquid crystal doped with azobenzene derivatives

    Science.gov (United States)

    Marinov, Y. G.; Hadjichristov, G. B.; Petrov, A. G.; Sridevi, S.; Hiremath, U. S.; Yelamaggad, C. V.; Prasad, S. K.

    2010-11-01

    A digitalized version of the standard method of conoscopy was employed to register the bend deformation of molecular orientation in homeotropic nematic layers caused by an in-plane applied DC electric field, and influenced by UV light illumination. Two guest-host systems prepared by mixing of a nematic liquid crystal and an azobenzene-containing photochromic liquid crystalline material featuring a longitudinal molecular asymmetry, were studied. Upon continuous UV irradiation, a photo-isomerization of the photochromic molecules occurs resulting in an enhanced flexoelectric response of the guest-host mixtures. The dependence of the photoflexoeffect on the field strength and UV light intensity was also examined.

  19. Conoscopic evidence of the UV light-induced flexoelectric effect in homeotropic layers of nematic liquid crystal doped with azobenzene derivatives

    International Nuclear Information System (INIS)

    Marinov, Y G; Hadjichristov, G B; Petrov, A G; Sridevi, S; Hiremath, U S; Yelamaggad, C V; Prasad, S K

    2010-01-01

    A digitalized version of the standard method of conoscopy was employed to register the bend deformation of molecular orientation in homeotropic nematic layers caused by an in-plane applied DC electric field, and influenced by UV light illumination. Two guest-host systems prepared by mixing of a nematic liquid crystal and an azobenzene-containing photochromic liquid crystalline material featuring a longitudinal molecular asymmetry, were studied. Upon continuous UV irradiation, a photo-isomerization of the photochromic molecules occurs resulting in an enhanced flexoelectric response of the guest-host mixtures. The dependence of the photoflexoeffect on the field strength and UV light intensity was also examined.

  20. Eficácia da doramectina no tratamento de caes com sarna sarcóptica e nematódeos gastrintestinais

    OpenAIRE

    Franco, Michelle Baranski

    2012-01-01

    A escabiose e os parasitas intestinais são afecções bastante comuns em cães, especialmente em canis ou locais com superpopulação de animais. Algumas espécies de nematódeos caninos e o ácaro Sarcoptes scabiei podem ocasionar zoonoses, apresentando maior relevância clínica. O objetivo principal do presente estudo consistiu na avaliação da eficácia da doramectina, em dose única, contra o ácaro Sarcoptes scabiei e nematódeos gastrintestinais caninos. O experimento foi realizado com 26 cães, natur...

  1. Maier-Saupe model of polymer nematics: Comparing free energies calculated with Self Consistent Field theory and Monte Carlo simulations.

    Science.gov (United States)

    Greco, Cristina; Jiang, Ying; Chen, Jeff Z Y; Kremer, Kurt; Daoulas, Kostas Ch

    2016-11-14

    Self Consistent Field (SCF) theory serves as an efficient tool for studying mesoscale structure and thermodynamics of polymeric liquid crystals (LC). We investigate how some of the intrinsic approximations of SCF affect the description of the thermodynamics of polymeric LC, using a coarse-grained model. Polymer nematics are represented as discrete worm-like chains (WLC) where non-bonded interactions are defined combining an isotropic repulsive and an anisotropic attractive Maier-Saupe (MS) potential. The range of the potentials, σ, controls the strength of correlations due to non-bonded interactions. Increasing σ (which can be seen as an increase of coarse-graining) while preserving the integrated strength of the potentials reduces correlations. The model is studied with particle-based Monte Carlo (MC) simulations and SCF theory which uses partial enumeration to describe discrete WLC. In MC simulations the Helmholtz free energy is calculated as a function of strength of MS interactions to obtain reference thermodynamic data. To calculate the free energy of the nematic branch with respect to the disordered melt, we employ a special thermodynamic integration (TI) scheme invoking an external field to bypass the first-order isotropic-nematic transition. Methodological aspects which have not been discussed in earlier implementations of the TI to LC are considered. Special attention is given to the rotational Goldstone mode. The free-energy landscape in MC and SCF is directly compared. For moderate σ the differences highlight the importance of local non-bonded orientation correlations between segments, which SCF neglects. Simple renormalization of parameters in SCF cannot compensate the missing correlations. Increasing σ reduces correlations and SCF reproduces well the free energy in MC simulations.

  2. Reverse-mode thermoresponsive light attenuators produced by optical anisotropic composites of nematic liquid crystals and reactive mesogens

    Science.gov (United States)

    Kakiuchida, Hiroshi; Ogiwara, Akifumi

    2018-04-01

    Polymer network liquid crystals (PNLCs) whose optical transmittance state switches between transparence at low temperatures and haze at high temperatures were fabricated from mixtures of nematic liquid crystals (LCs) and reactive mesogens (RMs). This PNLC structure is simple but effective, namely, consists of micro-scale domains of orientation-ordered LCs and anisotropically polymerized RMs. The domains form through photopolymerization induced phase separation with inhomogeneous irradiation projected by laser speckling techniques. This irradiation method enables you to control the size and shape of phase-separation domains, and these PNLCs can be applied to novel thermoresponsive optical devices; optical isolators, thermometric sheets, and smart windows.

  3. Numerical simulation of generation of optical vortices at light beam propagation through a layer of a nematic liquid crystal

    Science.gov (United States)

    Galev, Roman; Kudryavtsev, Alexey; Trashkeev, Sergey

    2017-10-01

    Light beam propagation through an anisotropic liquid crystal medium is numerically simulated. The Maxwell equations are solved by the FDTD method on computational grids with up to 6 . 108 nodes. Propagation of the fundamental mode HE11 of the fiber-optical light guide through a layer of a nematic liquid crystal filling a transverse gap in the optical fiber and containing a disclination. The behavior of the angular moment as a function of the layer thickness and disclination power is studied. System parameters that ensure the most effective generation of twisted light beams are found.

  4. Lie point symmetries and reductions of one-dimensional equations describing perfect Korteweg-type nematic fluids

    Science.gov (United States)

    De Matteis, Giovanni; Martina, Luigi

    2012-03-01

    A system of partial differential equations, describing one-dimensional nematic liquid crystals is studied by Lie group analysis. These equations are the Euler-Lagrange equations associated with a free energy functional that depends on the mass density and the gradient of the mass density. The group analysis is an algorithmic approach that allows us to show all the point symmetries of the system, to determine all possible symmetry reductions and, finally, to obtain invariant solutions in the form of travelling waves. The Hamiltonian formulation of the dynamical equations is also considered and the conservation laws found by exploiting the local symmetries.

  5. A new family of four-ring bent-core nematic liquid crystals with highly polar transverse and end groups

    Directory of Open Access Journals (Sweden)

    Kalpana Upadhyaya

    2013-01-01

    Full Text Available Non-symmetrically substituted four-ring achiral bent-core compounds with polar substituents, i.e.., chloro in the bent or transverse direction in the central core and cyano in the lateral direction at one terminal end of the molecule, are designed and synthesized. These molecules possess an alkoxy chain attached at only one end of the bent-core molecule. The molecular structure characterization is consistent with data from elemental and spectroscopic analysis. The materials thermal behaviour and phase characterization have been investigated by differential scanning calorimetry and polarizing microscopy. All the compounds exhibit a wide-ranging monotropic nematic phase.

  6. Electronic structure and pair potential energy analysis of 4-n-methoxy-4′-cyanobiphenyl: A nematic liquid crystal

    Energy Technology Data Exchange (ETDEWEB)

    Sharma, Dipendra, E-mail: d-11sharma@rediffmail.com; Tiwari, S. N., E-mail: sntiwari123@rediffmail.com [Department of Physics, DDU Gorakhpur University, Gorakhpur (India); Dwivedi, M. K., E-mail: dwivedi-ji@gmail.com [Department of Physics, Banaras Hindu University, Varanasi (India)

    2016-05-06

    Electronic structure properties of 4-n-methoxy-4′-cyanobiphenyl, a pure nematic liquid crystal have been examined using an ab‒initio, HF/6‒31G(d,p) technique with GAMESS program. Conformational and charge distribution analysis have been carried out. MEP, HOMO and LUMO surfaces have been scanned. Ionization potential, electron affinity, electronegativity, global hardness and softness of the liquid crystal molecule have been calculated. Further, stacking, side by side and end to end interactions between a molecular pair have been evaluated. Results have been used to elucidate the physico-chemical and liquid crystalline properties of the system.

  7. Effect of gold nano-particles on switch-on voltage and relaxation frequency of nematic liquid crystal cell

    Directory of Open Access Journals (Sweden)

    M. Inam

    2011-12-01

    Full Text Available We report the observation of large changes in the electro-optical properties of nematic liquid crystal (NLC due to inclusion of small concentration of 10 nm diameter gold nanoparticles (GNPs. It is observed that GNPs lower switch-on voltage and also lower the relaxation frequency with applied voltage (AC field to NLC cell. These studies of GNP doped NLC cell have been done using optical interferometry and capacity measurement by impedance analyzer. The change in threshold voltage and relaxation frequency by doping GNPs in NLC is explained theoretically.

  8. Coupled effects of director orientations and boundary conditions on light induced bending of monodomain nematic liquid crystalline polymer plates

    International Nuclear Information System (INIS)

    You, Yue; Ding, Shurong; Huo, Yongzhong; Xu, Changwei

    2012-01-01

    A photo-chromic liquid crystal polymers (LCPs) is a smart material for large light-activated variation or bending to transfer luminous energy into mechanical energy. We study the light induced behavior by modeling planar and homeotropic nematic network polymer plates. We effectively illustrate some reported experimental outcomes and theoretically predict some possible bending patterns. This paper constructs an understanding between the bending behaviors and interactions among the alignments, aspect ratios and boundary conditions, etc. Our work provides information on optimizing light induced bending in the process of micro-opto-mechanical system (MOMS) design. (paper)

  9. Dynamic Response of Graphitic Flakes in Nematic Liquid Crystals: Confinement and Host Effect

    Directory of Open Access Journals (Sweden)

    Weiwei Tie

    2017-09-01

    Full Text Available Electric field-induced reorientation of suspended graphitic (GP flakes and its relaxation back to the original state in a nematic liquid crystal (NLC host are of interest not only in academia, but also in industrial applications, such as polarizer-free and optical film-free displays, and electro-optic light modulators. As the phenomenon has been demonstrated by thorough observation, the detailed study of the physical properties of the host NLC (the magnitude of dielectric anisotropy, elastic constants, and rotational viscosity, the size of the GP flakes, and cell thickness, are urgently required to be explored and investigated. Here, we demonstrate that the response time of GP flakes reorientation associated with an NLC host can be effectively enhanced by controlling the physical properties. In a vertical field-on state, higher dielectric anisotropy and higher elasticity of NLC give rise to quicker reorientation of the GP flakes (switching from planar to vertical alignment due to the field-induced coupling effect of interfacial Maxwell-Wagner polarization and NLC reorientation. In a field off-state, lower rotational viscosity of NLC and lower cell thickness can help to reduce the decay time of GP flakes reoriented from vertical to planar alignment. This is mainly attributed to strong coupling between GP flakes and NLC originating from the strong π-π interaction between benzene rings in the honeycomb-like graphene structure and in NLC molecules. The high-uniformity of reoriented GP flakes exhibits a possibility of new light modulation with a relatively faster response time in the switching process and, thus, it can show potential application in field-induced memory and modulation devices.

  10. Aplicação de formulação do fungo predador de nematóides Monacrosporium thaumasium (Drechsler, 1937 no controle de nematóides de bovinos

    Directory of Open Access Journals (Sweden)

    Alves P.H.

    2003-01-01

    Full Text Available A viabilidade de uma formulação do fungo Monacrosporium thaumasium (Drechsler, 1937 foi avaliada no controle biológico de nematóides parasitos gastrintestinais de bovinos. Dois grupos de sete bezerras cada, mestiças Holandês ´ Zebu, de quatro a seis meses de idade, foram colocados em pastagens de Cynodon dactilon. No grupo A, cada animal recebeu 20g de pellets (formulação granulada de M. thaumasium via oral, duas vezes por semana, durante quatro meses, com início na estação chuvosa (outubro, 2001. No grupo B (controle, as bezerras não receberam nenhum tratamento. As contagens de ovos por grama de fezes (OPG e das larvas infectantes encontradas na pastagem do grupo B foram significativamente maiores (P<0,05 do que as do grupo A e a diferença entre o OPG dos animais dos grupos A e B, no final do experimento, foi de 88,8%. O gênero Cooperia foi o mais prevalente em ambas as pastagens. Conclui-se que a aplicação de pellets de M. thaumasium na dosagem e periodicidade de aplicação usadas foi eficiente no controle de nematóides parasitos gastrintestinais de bovinos.

  11. Spin Triplet Nematic Pairing Symmetry and Superconducting Double Transition in U1-xThxBe13

    Science.gov (United States)

    Machida, Kazushige

    2018-03-01

    Motivated by a recent experiment on U1-xThxBe13 with x = 3%, we develop a theory to narrow down the possible pair symmetry to consistently describe the double transition utilizing various theoretical tools, including group theory and Ginzburg-Landau theory. It is explained in terms of the two-dimensional representation Eu with spin triplet. Symmetry breaking causes the degenerate Tc to split into two. The low-temperature phase is identified as the cyclic p wave: d(k) = \\hat{x}kx + ɛ \\hat{y}ky + ɛ 2\\hat{z}kz with ɛ3 = 1, whereas the biaxial nematic phase: d(k) = √{3} (\\hat{x}kx - \\hat{y}ky) is the high-temperature one. This allows us to simultaneously identify the uniaxial nematic phase: d(k) = 2\\hat{z}kz - \\hat{x}kx - \\hat{y}ky for UBe13, which spontaneously breaks the cubic symmetry of the system. Those pair functions are fully consistent with this description and existing data. We comment on the accidental scenario in addition to this degeneracy scenario and the intriguing topological nature hidden in this long-known material.

  12. Signatures of electronic nematicity in (111) LaAlO3/SrTiO3 interfaces

    Science.gov (United States)

    Davis, S.; Huang, Z.; Han, K.; Ariando, Venkatesan, T.; Chandrasekhar, V.

    2018-01-01

    The two-dimensional conducting gas (2DCG) that forms at the interface between LaAlO3 (LAO) and SrTiO3 (STO) has been widely studied due to the multitude of in situ tunable phenomena that exist at the interface. Recently it has been shown that nearly every property of the 2DEG that forms at the interface of (111) oriented LAO/STO is strongly anisotropic with respect to the in-plane crystal direction. This in-plane rotational symmetry breaking points to the existence of an electronic nematic phase at the interface that can be modified by an in situ electrostatic back-gate potential. Here we show that the onset temperature of the anisotropy in the longitudinal resistance is T ≈22 K , which does not match up with any known structural transition, and coincides with the onset of anisotropy in the Hall response of the system. Furthermore, below 22 K, charge transport is activated in nature with different activation energies along the two in-plane crystal directions. Such a response implies that the band edges along the two directions are different and provides further evidence of an electronic nematic state at the interface.

  13. Non-linear optical measurement of the twist elastic constant in thermotropic and DNA lyotropic chiral nematics.

    Science.gov (United States)

    Lucchetti, Liana; Fraccia, Tommaso P; Ciciulla, Fabrizio; Bellini, Tommaso

    2017-07-10

    Throughout the whole history of liquid crystals science, the balancing of intrinsic elasticity with coupling to external forces has been the key strategy for most application and investigation. While the coupling of the optical field to the nematic director is at the base of a wealth of thoroughly described optical effects, a significant variety of geometries and materials have not been considered yet. Here we show that by adopting a simple cell geometry and measuring the optically induced birefringence, we can readily extract the twist elastic coefficient K 22 of thermotropic and lyotropic chiral nematics (N*). The value of K 22 we obtain for chiral doped 5CB thermotropic N* well matches those reported in the literature. With this same strategy, we could determine for the first time K 22 of the N* phase of concentrated aqueous solutions of DNA oligomers, bypassing the limitations that so far prevented measuring the elastic constants of this class of liquid crystalline materials. The present study also enlightens the significant nonlinear optical response of DNA liquid crystals.

  14. Correlation length and chirality of the fluctuations in the isotropic phase of nematic and cholesteric liquid crystals.

    Science.gov (United States)

    Krich, Jacob J; Romanowsky, Mark B; Collings, Peter J

    2005-05-01

    Light-scattering measurements of the correlation length in the isotropic phase of a nematic liquid crystal reveal a temperature dependence following Landau-de Gennes theory for the isotropic phase with a bare correlation length smaller than has been measured in other liquid crystals. Similar measurements in a cholesteric liquid crystal demonstrate that the correlation length in the isotropic phase is larger than typically found in nematics and that the chirality of the fluctuations in the isotropic phase is slightly higher than the chirality of the cholesteric phase. Landau-de Gennes theory of the cholesteric phase describes the chirality in the cholesteric phase well but predicts that the chirality in the isotropic phase is temperature independent, which is not consistent with the data. There is a discontinuity in the chirality at the cholesteric-isotropic transition of about 15%, which is less than the predictions of Landau-de Gennes theory but more than the typical specific volume discontinuity at transitions to the isotropic phase. Except for a mismatch in the discontinuities at the transition, the chirality data resemble the temperature behavior of variables just below a critical point, in spite of the fact that this system is far from a critical point.

  15. The effects of lateral halogen substituents on the low-temperature cybotactic nematic phase in oxadiazole based bent-core liquid crystals

    NARCIS (Netherlands)

    Jason Nguyen, [Unknown; Wonderly, William; Tauscher, Tatum; Harkins, Robin; Vita, Francesco; Portale, Giuseppe; Francescangeli, Oriano; Samulski, Edward T.; Scharrer, Eric

    2015-01-01

    We have previously demonstrated that the incorporation of lateral methyl groups on oxadiazole-based liquid crystals leads to relatively low-temperature cybotactic nematic phases which, in some cases, supercool to room temperature. We report here the synthesis and phase behaviour of related compounds

  16. Significant Enhancement of the Chiral Correlation Length in Nematic Liquid Crystals by Gold Nanoparticle Surfaces Featuring Axially Chiral Binaphthyl Ligands.

    Science.gov (United States)

    Mori, Taizo; Sharma, Anshul; Hegmann, Torsten

    2016-01-26

    Chirality is a fundamental scientific concept best described by the absence of mirror symmetry and the inability to superimpose an object onto its mirror image by translation and rotation. Chirality is expressed at almost all molecular levels, from single molecules to supramolecular systems, and present virtually everywhere in nature. Here, to explore how chirality propagates from a chiral nanoscale surface, we study gold nanoparticles functionalized with axially chiral binaphthyl molecules. In particular, we synthesized three enantiomeric pairs of chiral ligand-capped gold nanoparticles differing in size, curvature, and ligand density to tune the chirality transfer from nanoscale solid surfaces to a bulk anisotropic liquid crystal medium. Ultimately, we are examining how far the chirality from a nanoparticle surface reaches into a bulk material. Circular dichroism spectra of the gold nanoparticles decorated with binaphthyl thiols confirmed that the binaphthyl moieties form a cisoid conformation in isotropic organic solvents. In the chiral nematic liquid crystal phase, induced by dispersing the gold nanoparticles into an achiral anisotropic nematic liquid crystal solvent, the binaphthyl moieties on the nanoparticle surface form a transoid conformation as determined by imaging the helical twist direction of the induced cholesteric phase. This suggests that the ligand density on the nanoscale metal surfaces provides a dynamic space to alter and adjust the helicity of binaphthyl derivatives in response to the ordering of the surrounding medium. The helical pitch values of the induced chiral nematic phase were determined, and the helical twisting power (HTP) of the chiral gold nanoparticles calculated to elucidate the chirality transfer efficiency of the binaphthyl ligand capped gold nanoparticles. Remarkably, the HTP increases with increasing diameter of the particles, that is, the efficiency of the chirality transfer of the binaphthyl units bound to the nanoparticle

  17. Nano to Meso-scale Structure in Liquid Crystals: the Cybotactic Nematic Phase of Bent-core Mesogens

    Science.gov (United States)

    Francescangeli, Oriano

    2012-02-01

    The extent of molecular order and the resulting broken symmetry determine the properties and mesophase type of liquid crystals (LCs). Thermotropic bent-core mesogens (BCMs) represent a new class of LCs exhibiting substantially different physical properties than traditional linear (calamitic) materials. In recent years BCMs have become the focus of intense experimental and theoretical investigation, with several exciting new developments. These include chiral mesophases composed of achiral BCMs, giant flexoelectricity, biaxial nematic (N) order, a ferroelectric response in the N phase, and a large flow birefringence. A key issue that is currently widely debated concerns the actual nature of the N phase of BCMs which gives rise to some of the above mentioned effects and is unambiguously identified by a peculiar low-angle X-ray diffraction pattern (the ``four-spot pattern''). The consensus emerging is that this N phase of BCMs constitutes a new type of mesophase, namely, a cybotactic nematic (Ncyb) phase unrelated to pretransition cybotaxis, in agreement with experimental [1-3] and theoretical findings [4]. This Ncyb phase is composed of nanometer-size clusters of BCMs exhibiting a relatively high degree of internal order---orientational as well as translational order (strata) imposed by close packing the BCM nonlinear shape. This peculiar supramolecular structure of the Ncyb mesophase of BCMs---evanescent, biaxial clusters of tilted and stratified nonlinear mesogens percolating the nematic fluid---accounts for their unusual properties, e.g., biaxial order [4], ferroelectric response [1], and extraordinary field-induced effects [5]. In this talk I will give an overview of the most recent developments and the current state of research on this subject. [4pt] [1] O. Francescangeli et al., Adv. Funct. Mater. 19,2592 (2009). [0pt] [2] O. Francescangeli and E.T. Samulski, Soft Matter 6, 2413 (2010) [0pt] [3] O. Francescangeli et al., Soft Matter 7, 895 (2011). [0pt] [4] A

  18. Temperature dependences of the electrooptical properties of rodlike nematic liquid crystals doped with hockey-stick-shaped liquid crystals

    Science.gov (United States)

    Yeo, Sunggu; Srivastava, Anoop Kumar; Lee, Hyojin; Lee, Ji-Hoon; Choi, E.-Joon

    2016-01-01

    We investigated the temperature dependences of the dielectric anisotropy, birefringence, order parameter, splay elastic constant, and rotational viscosity of rodlike nematic liquid crystals (RLCs) doped with hockey-stick-shaped liquid crystals (HLCs). Although the order parameter of the HLC-RLC mixtures was similar to that of the pure RLC, the dielectric anisotropy and the birefringence of the mixtures were decreased or increased depending on the structure of the HLC molecule. In addition, the activation energies of the mixtures were different, which implies that the intramolecular structure of the HLC molecule had more influence on the electrooptical properties of the HLC-RLC binary mixtures than the inter-molecular interaction between the HLC and the RLC molecules.

  19. Optimal Boundary Control of a Simplified Ericksen-Leslie System for Nematic Liquid Crystal Flows in 2 D

    Science.gov (United States)

    Cavaterra, Cecilia; Rocca, Elisabetta; Wu, Hao

    2017-06-01

    In this paper, we investigate an optimal boundary control problem for a two dimensional simplified Ericksen-Leslie system modelling the incompressible nematic liquid crystal flows. The hydrodynamic system consists of the Navier-Stokes equations for the fluid velocity coupled with a convective Ginzburg-Landau type equation for the averaged molecular orientation. The fluid velocity is assumed to satisfy a no-slip boundary condition, while the molecular orientation is subject to a time-dependent Dirichlet boundary condition that corresponds to the strong anchoring condition for liquid crystals. We first establish the existence of optimal boundary controls. Then we show that the control-to-state operator is Fréchet differentiable between appropriate Banach spaces and derive first-order necessary optimality conditions in terms of a variational inequality involving the adjoint state variables.

  20. Evidence for a Nematic Phase in La1.75Sr0.25NiO4

    Science.gov (United States)

    Zhong, Ruidan; Winn, Barry L.; Gu, Genda; Reznik, Dmitry; Tranquada, J. M.

    2017-04-01

    Determining the nature of electronic states in doped Mott insulators remains a challenging task. In the case of tetragonal La2 -xSrxNiO4, the occurrence of diagonal charge and spin stripe order in the ground state is now well established. In contrast, the nature of the high-temperature "disordered" state from which the stripe order develops has long been a subject of controversy, with considerable speculation regarding a polaronic liquid. Following the recent detection of dynamic charge stripes, we use neutron scattering measurements on an x =0.25 crystal to demonstrate that the dispersion of the charge-stripe excitations is anisotropic. This observation provides compelling evidence for the presence of electronic nematic order.

  1. Electrically tunable whispering gallery mode microresonator based on a grapefruit-microstructured optical fiber infiltrated with nematic liquid crystals.

    Science.gov (United States)

    Yang, Chengkun; Zhang, Hao; Liu, Bo; Lin, Shiwei; Li, Yuetao; Liu, Haifeng

    2017-08-01

    An electrically tunable whispering gallery mode (WGM) microresonator based on an HF-etched microstructured optical fiber (MOF) infiltrated with nematic liquid crystals (NLCs) is proposed and experimentally demonstrated. Experimental results indicate that as the peak-to-peak voltage of the applied AC electric field increases from 160 to 220 V, WGM resonance peaks gradually move toward a shorter wavelength region by 0.527 nm with a wavelength sensitivity up to 0.01  nm/V for a TM1691 mode, and the Q-factor for each WGM resonance peak rapidly decreases with the increment of applied electric voltage. The proposed electrically controlled WGM tuning scheme shows a linear resonance wavelength shift with good spectral reversibility, which makes it a promising candidate to serve as an integrated functional photonic device in practical use and in related fundamental scientific studies.

  2. Critical linear thermal expansion in the smectic-A phase near the nematic-smectic phase transition.

    Science.gov (United States)

    Anesta, E; Iannacchione, G S; Garland, C W

    2004-10-01

    Recent high-resolution x-ray investigations of the smectic- A (SmA) phase near the nematic-to-SmA transition provide information about the critical behavior of the linear thermal expansion coefficient alpha// parallel to the director. Combining such data with available volume thermal expansion alpha(V) data yields the in-plane linear expansion coefficient alpha(perpendicular) . The critical behaviors of alpha// and alpha(perpendicular) are the same as those for alpha(V) and the heat capacity Cp. However, for any given liquid crystal, alpha//(crit) and alpha(perpendicular)(crit) differ in sign. Furthermore, the quantity alpha// (crit) is positive for SmAd partial bilayer smectics, while it is negative for nonpolar SmAm monomeric smectics. This feature is discussed in terms of the molecular structural aspects of these smectic phases.

  3. Large-area graphene-based nanofiltration membranes by shear alignment of discotic nematic liquid crystals of graphene oxide

    Science.gov (United States)

    Akbari, Abozar; Sheath, Phillip; Martin, Samuel T.; Shinde, Dhanraj B.; Shaibani, Mahdokht; Banerjee, Parama Chakraborty; Tkacz, Rachel; Bhattacharyya, Dibakar; Majumder, Mainak

    2016-03-01

    Graphene-based membranes demonstrating ultrafast water transport, precise molecular sieving of gas and solvated molecules shows great promise as novel separation platforms; however, scale-up of these membranes to large-areas remains an unresolved problem. Here we demonstrate that the discotic nematic phase of graphene oxide (GO) can be shear aligned to form highly ordered, continuous, thin films of multi-layered GO on a support membrane by an industrially adaptable method to produce large-area membranes (13 × 14 cm2) in 90%) for charged and uncharged organic probe molecules with a hydrated radius above 5 Å as well as modest (30-40%) retention of monovalent and divalent salts. The highly ordered graphene sheets in the plane of the membrane make organized channels and enhance the permeability (71+/-5 l m-2 hr-1 bar-1 for 150+/-15 nm thick membranes).

  4. Spherical microparticles with Saturn ring defects and their self-assembly across the nematic to smectic-A phase transition.

    Science.gov (United States)

    Zuhail, K P; Čopar, S; Muševič, I; Dhara, Surajit

    2015-11-01

    We report experimental studies on the Saturn ring defect associated with a spherical microparticle across the nematic (N) to smectic-A (SmA) phase transition. We observe that the director distortion around the microparticle changes rapidly with temperature. The equilibrium interparticle separation and the angle between two quadrupolar particles in the N phase are larger than those of the SmA phase. They are almost independent of the temperature in both phases, except for a discontinuous jump at the transition. We assembled a few particles using a laser tweezer to form a two-dimensional colloidal crystal in the N phase. The lattice structure of the crystal dissolves irreversibly across the N-SmA phase transition. The results on the pretransitional behavior of the defect are supported by the Landau-de Gennes Q-tensor modeling.

  5. Possible quadrupolar nematic phase in the frustrated spin chain LiCuSbO4: An NMR investigation

    Science.gov (United States)

    Bosiočić, M.; Bert, F.; Dutton, S. E.; Cava, R. J.; Baker, P. J.; Požek, M.; Mendels, P.

    2017-12-01

    The frustrated one-dimensional quantum magnet LiCuSbO4 is a rare realization of the J1-J2 spin chain model with an easily accessible saturation field, formerly estimated at 12 T. Exotic multipolar nematic phases were theoretically predicted in such compounds just below the saturation field, but without unambiguous experimental observation so far. In this paper we present extensive experimental research on the compound in a wide temperature (30 mK to 300 K) and field (0-13.3 T) range by muon spin rotation (μ SR ), 7Li nuclear magnetic resonance (NMR), and magnetic susceptibility (SQUID). μ SR experiments in zero magnetic field demonstrate the absence of long-range 3D ordering down to 30 mK. Together with former heat capacity data [Dutton et al., Phys. Rev. Lett. 108, 187206 (2012), 10.1103/PhysRevLett.108.187206], magnetic susceptibility measurements suggest a short-range-correlated vector chiral phase in the field range 0-4 T. At the intermediate-field values (5-12 T), the system enters a 3D-ordered spin density wave phase with 0.75 μB per copper site at lowest temperatures (125 mK), estimated by NMR. At still higher field, the magnetization is found to be saturated above 13 T where the spin lattice T1-1 relaxation reveals a spin gap estimated at 3.2(2) K. We narrow down the possibility of observing a multipolar nematic phase to the range 12.5-13 T.

  6. Nutrição e crescimento do fungo nematófago Arthrobotrys oligospora

    Directory of Open Access Journals (Sweden)

    Eliane R. Cardoso

    2009-12-01

    Full Text Available As condições de crescimento e os requerimentos nutricionais de Arthrobotrys oligospora, um fungo nematófago, foram investigados em meio líquido. O organismo foi incubado em meio sintético, a 30º C e em cultura estacionária. O perfil da curva de crescimento do fungo ajustou-se a uma equação de 3º grau, mesmo após 15 dias de incubação. A temperatura e o pH ótimos para produção de micélio foram observados a 25º C e pH 5,0, respectivamente. Contudo, não foram observadas diferenças significativas entre a produção de biomassa nas temperaturas de 25º C e 30º C ou pH 5.0 e 6.0. Várias fontes de carbono foram utilizadas pelo fungo, porém a maior produção de biomassa foi verificada com maltose e sacarose. Das fontes de nitrogênio testadas, várias proteínas (triptona, extrato de levedura, caseína, peptona e casaminoácidos e fontes inorgânicas (nitrato de sódio e cloreto de amônio estimularam a maior produção de biomassa. Das várias vitaminas experimentadas, o crescimento do fungo aumentou 2,2 vezes com riboflavina e 2,3 vezes com a mistura biotina e tiamina em relação ao controle, sem vitamina. De modo geral, constatou-se, após o período de incubação, que o pH inicial do meio de cultura pode aumentar até 8,4. Estes resultados sugerem que as variáveis estudadas podem ter papel importante no crescimento do organismo no solo.The growth conditions and the nutritional requirements of Arthrobotrys oligospora, a nematophagous fungus, were investigated in liquid culture. The organism was incubated in a synthetic medium, at 30º C in a static culture. Time course of growth was adjusted to a 3º degree equation, even after 15 days of incubation. Optimal temperature and pH for mycelium production were observed at 25º C and pH 5.0, respectively. However, significant differences were not found among the biomass production at temperatures 25º C and 30º C or pH 5.0 and 6.0. Several carbon sources were used by the fungus

  7. Non-Fermi liquid transport phenomena in SrIrO3 thin films: Role of disorder in a nematic phase

    Science.gov (United States)

    Kim, Kyoung-Min; Kim, Ki-Seok

    Recently, non-Fermi liquid transport phenomena have been found in SrIrO3 thin films on various substrates: Increasing the lattice mismatch between SrIrO3 thin films and substrates, the exponent α of electrical resistivity Δρ Tα shows the variation from α = 4/5, α = 1, to α = 3/2. Such experiments confirmed that these thin films lie away from a magnetic quantum critical point. On the other hand, we suggest that the presence of strong spin orbit coupling may give rise to an electron nematic phase. As a result of combined effects between quantum criticality of electron nematicity and nonmagnetic quenched disorders, we suspect that the continuous evolution of the power-law exponent may be involved with quantum Griffiths effects. Performing the renormalization group analysis, we discuss a possible origin of this non-Fermi liquid physics.

  8. Optical trapping of colloidal particles and measurement of the defect line tension and colloidal forces in a thermotropic nematic liquid crystal

    International Nuclear Information System (INIS)

    Smalyukh, I.I.; Kuzmin, A.N.; Kachynski, A.V.; Prasad, P.N.; Lavrentovich, O.D.

    2005-01-01

    We demonstrate optical trapping and manipulation of transparent microparticles suspended in a thermotropic nematic liquid crystal with low birefringence. We employ the particle manipulation to measure line tension of a topologically stable disclination line and to determine colloidal interaction of particles with perpendicular surface anchoring of the director. The three-dimensional director fields and positions of the particles manipulated by laser tweezers are visualized by fluorescence confocal polarizing microscopy

  9. Molecular orientational re-ordering and the transformation of a Landau second order phase transition to first order in a nematic liquid crystal

    International Nuclear Information System (INIS)

    Ponce, T.C.

    1988-08-01

    We consider the nature of the nematic to isotropic phase transition in terms of the molecular orientational re-ordering, expressed by the variation of the order parameter, s, in the light of Landau's theory of second order phase transition. Then, we show how the de Gennes modification to the Landau thermodynamic potential converts the transition to first order which is in better agreement with the experimental observations. (author). 9 refs, 2 figs, 1 tab

  10. A parity-breaking electronic nematic phase transition in the spin-orbit coupled correlated metal Cd2Re2O7

    Science.gov (United States)

    Harter, J. W.; Zhao, Z. Y.; Yan, J.-Q.; Mandrus, D. G.; Hsieh, D.

    Strong interactions between electrons are known to drive metallic systems toward a variety of well-known symmetry-broken phases, including superconducting, electronic liquid crystalline, and charge- and spin-density wave ordered states. In contrast, the electronic instabilities of correlated metals with strong spin-orbit coupling have only recently begun to be explored. We uncover a novel multipolar nematic phase of matter in the metallic pyrochlore Cd2Re2O7 using spatially-resolved second-harmonic optical anisotropy measurements. Like previously discovered electronic liquid crystalline phases, this multipolar nematic phase spontaneously breaks rotational symmetry while preserving translational invariance. However, it has the distinguishing property of being odd under spatial inversion, which is allowed only in the presence of spin-orbit coupling. By examining the critical behavior of the multipolar nematic order parameter, we show that it drives the thermal phase transition near 200 K in Cd2Re2O7 and induces a parity-breaking lattice distortion as a secondary order parameter.

  11. Direct observation of electronic nematicity in charge and orbital ordered La0.33Ca0.67MnO3

    Science.gov (United States)

    Tao, J.; Sun, K.; Zuo, J. M.; Zhu, Y.

    2013-03-01

    Nematic and smectic states have been demonstrated to be very important in understanding high-Tc superconductivity. Here we report similar observations of electronic nematicity in doped manganites. Both the electron diffraction results and HRTEM images obtained from single crystal domain of La0.33Ca0.67MnO3 clearly show a C4 to C2 symmetry broken in charge ordered (CO) and orbital ordered superstructures at intermediate temperature range. The electronic nematicity persists in the crystal until long-range CO forms as a stripe phase at lower temperatures upon cooling. During warming process, we observed topological defects in the charge ordering superstructures, indicating that the melting of the CO superstructure is defect mediated. Theoretical simulations will also be provided for better interpretation of the phenomenon. Research at Brookhaven National Laboratory was sponsored by the US Department of Energy (DOE)/Basic Energy Sciences, Materials Sciences and Engineering Division under Contract DE-AC02-98CH10886.

  12. Synergistic effect of non-covalent interaction in colloidal nematic liquid crystal doped with magnetic functionalized single-walled carbon nanotubes

    Science.gov (United States)

    Dalir, Nima; Javadian, Soheila

    2018-03-01

    Single-walled carbon nanotubes (SWCNTs), CNT@Fe3O4, and Fe3O4 nanocomposites were doped to eutectic uniaxial nematic liquid crystal (NLC's) (E5CN7) to improve physiochemical properties such as phase transition temperature, activation energy (Ea), dielectric anisotropy, and electro-optical properties. The thermal study of nematic phase shows a decrease in the nematic to isotropic phase transition temperature as CNT is doped. However, higher doping concentration of CNTs leads to the further increase in transition temperature. The anchoring effect or π-π interaction plays a key role in N-I phase transition. The functionalization of SWCNTs with Fe3O4 diminishes the CNT aggregation while the magnetic susceptibility is increased. The functionalized CNT doping to NLC's decrease significantly the phase transition temperature compared to doping of non-functionalized CNTs. Attractive interaction between guest and host molecules by magnetic and geometry effect increased the enthalpy and entropy of phase transition in the SWCNT@Fe3O4 sample compared to non-functionalized CNT doped system. Also, the Ea values are decreased as SWCNT@Fe3O4 is doped to pure E5CN7. The difference of N-I phase transition temperature was observed in Fe3O4 and CNT@Fe3O4 compared to SWCNT doped systems. Finally, dielectric anisotropy was increased in the doped system compared to pure NLC.

  13. Control of infective larvae of gastrointestinal nematodes in heifers using different isolates of nematophagous fungi Controle de larvas infectantes de nematóides gastrintestinais de novilhas por diferentes isolados dos fungos nematófagos

    Directory of Open Access Journals (Sweden)

    Manoel Eduardo da Silva

    Full Text Available The effect of different nematophagous fungi [Duddingtonia flagrans (AC001 and CG722 and Monacrosporium thaumasium (NF34] with regard to controlling infective larvae (L3 of nematodes after gastrointestinal transit in female cattle (3/4 Holstein × Zebu was evaluated. A total of 24 pubescent female cattle were used, weighing approximately 320 kg each one. There were three treatment groups, each contained six animals that received 150 g of pellets (0.2 g of mycelium, orally in a single dose, in a sodium alginate matrix containing mycelial mass of the fungus D. flagrans (AC001 or CG722 or M. thaumasium (NF34; and one control group (without fungi. Fecal samples were collected from the animals at intervals of 12, 15, 18, 21, 24, 48, and 72 hours. At the end of 17 days, the L3 not subjected to predation were recovered by means of the Baermann method. The fungal isolates tested were capable of destroying the L3 after gastrointestinal transit. It was observed that within 72 hours, the isolates AC001, CG722, and NF34 showed a higher predatory activity (81.2%, 97.3%, and 98.3%, respectively. The results justify the need for studies in the field, and over longer intervals, in order to observe the efficiency of the fungus D. flagrans, or even M. thaumasium, for environmental control over nematodes in naturally infected cattle.No presente estudo, foi avaliado o efeito de diferentes fungos nematófagos [Duddingtonia flagrans (AC001 e CG722 e Monacrosporium thaumasium (NF34] no controle de larvas infectantes (L3 de nematóides após o trânsito gastrointestinal em fêmeas bovinas (3/4 Holandês x Zebu. Um total de 24 fêmeas bovinas pubescentes foram utilizadas, pesando aproximadamente 320 kg cada. Foram utilizados três grupos de tratamento; cada um contendo seis animais que receberam por via oral de 150 g de péletes (0,2 g de micélio, em dose única, em uma matriz de alginato de sódio contendo massa micelial dos fungos D. flagrans (AC001 ou

  14. Macroeconomic stability

    DEFF Research Database (Denmark)

    Jespersen, Jesper

    2004-01-01

    It is demonstrated that full employment and sustainable development not necessarily are conflicting goals. On the other hand macroeconomic stability cannot be obtained without a deliberate labour sharing policy and a shift in the composition of private consumption away from traditional material...

  15. A model-free temperature-dependent conformational study of n-pentane in nematic liquid crystals

    International Nuclear Information System (INIS)

    Burnell, E. Elliott; Weber, Adrian C. J.; Dong, Ronald Y.; Meerts, W. Leo; Lange, Cornelis A. de

    2015-01-01

    The proton NMR spectra of n-pentane orientationally ordered in two nematic liquid-crystal solvents are studied over a wide temperature range and analysed using covariance matrix adaptation evolutionary strategy. Since alkanes possess small electrostatic moments, their anisotropic intermolecular interactions are dominated by short-range size-and-shape effects. As we assumed for n-butane, the anisotropic energy parameters of each n-pentane conformer are taken to be proportional to those of ethane and propane, independent of temperature. The observed temperature dependence of the n-pentane dipolar couplings allows a model-free separation between conformer degrees of order and conformer probabilities, which cannot be achieved at a single temperature. In this way for n-pentane 13 anisotropic energy parameters (two for trans trans, tt, five for trans gauche, tg, and three for each of gauche + gauche + , pp, and gauche + gauche − , pm), the isotropic trans-gauche energy difference E tg and its temperature coefficient E tg ′ are obtained. The value obtained for the extra energy associated with the proximity of the two methyl groups in the gauche + gauche − conformers (the pentane effect) is sensitive to minute details of other assumptions and is thus fixed in the calculations. Conformer populations are affected by the environment. In particular, anisotropic interactions increase the trans probability in the ordered phase

  16. Tunable, multiwavelength-swept fiber laser based on nematic liquid crystal device for fiber-optic electric-field sensor

    Science.gov (United States)

    Lee, Hyun Ji; Kim, Sung-Jo; Ko, Myeong Ock; Kim, Jong-Hyun; Jeon, Min Yong

    2018-03-01

    We propose a tunable multiwavelength-swept laser based on a nematic liquid crystal (NLC) Fabry-Perot (FP) etalon, which is embedded in the resonator of a wavelength-swept laser. We achieve the continuous wavelength tuning of the multiwavelength-swept laser by applying the electric field to the NLC FP etalon. The free spectral range of the fabricated NLC FP etalon is approximately 7.9 nm. When the electric field applied to the NLC FP etalon exceeds the threshold value (Fréedericksz threshold voltage), the output of the multiwavelength-swept laser can be tuned continuously. The tuning range of the multiwavelength-swept laser can be achieved at a value greater than 75 nm, which has a considerably wider tunable range than a conventional multiwavelength laser based on an NLC FP etalon. The slope efficiencies in the spectral and temporal domains for the tunable multiwavelength-swept laser are 22.2 nm/(mVrms / μm) and 0.17 ms/(mVrms / μm), respectively in the linear region. Therefore, the developed multiwavelength-swept laser based on the NLC FP etalon can be applied to an electric-field sensor. Because the wavelength measurement and time measurement have a linear relationship, the electric-field sensor can detect a rapid change in the electric-field intensity by measuring the peak change of the pulse in the temporal domain using the NLC FP etalon-based multiwavelength-swept laser.

  17. Polarization-resolved angular patterns of nematic liquid crystal cells: Topological events driven by incident light polarization

    Science.gov (United States)

    Kiselev, Alexei D.; Vovk, Roman G.; Egorov, Roman I.; Chigrinov, Vladimir G.

    2008-09-01

    We study the angular structure of polarization of light transmitted through a nematic liquid crystal (NLC) cell by analyzing the polarization state as a function of the incidence angles and the polarization of the incident wave. The polarization-resolved angular (conoscopic) patterns emerging after the NLC cell illuminated by the convergent light beam are described in terms of the polarization singularities such as C points (points of circular polarization) and L lines (lines of linear polarization). For the homeotropically aligned cell, the Stokes polarimetry technique is used to measure the polarization resolved conoscopic patterns at different values of the ellipticity of the incident light, γell(inc) , impinging onto the cell. Using the exact analytical expressions for the transfer matrix we show that variations of the ellipticity, γell(inc) , induce transformations of the angular pattern exhibiting the effect of avoided L -line crossings and characterized by topological events such as creation and annihilation of the C points. The predictions of the theory are found to be in good agreement with the experimental results.

  18. Experimental study of coarsening dynamics of the zigzag wall in a nematic liquid crystal with negative dielectric anisotropy.

    Science.gov (United States)

    Nagaya, Tomoyuki; Gilli, Jean-Marc

    2002-05-01

    When a homeotropically aligned nematic liquid crystal cell is placed above two permanent magnets forming a magnetic quadrupole, a straight splay-bend wall, or a so-called Ising wall, is formed. With a material of positive dielectric anisotropy, it has been shown that the application of an electric field perpendicular to the plates leads to a zigzag instability of the wall, exclusively related to the elastic anisotropy of the liquid crystal. In this case, the coarsening process of the zigzag is very slow, which in turn leads to experimental difficulties concerning its quantitative investigation. If a material of negative dielectric anisotropy is used under an electric field with low voltage and low frequency, two convective rolls appear along the Ising wall due to the charge focusing effect, which is also responsible, at a higher voltage in the homogenous tilted regions, for the appearance of Williams domains electrohydrodynamic instability. If the voltage is higher than a threshold value, the straight Ising wall spontaneously breaks into a zigzag shape and a fast coarsening of the zigzag proceeds, associated with the annihilation of two neighboring vertices. In the present paper, the coarsening dynamics of this system, which can be considered as a one-dimensional Ising situation, are investigated experimentally. At late times, the average width of the zigzag increases logarithmically with time. This finding is consistent with the theory and also with the numerical simulation of a one-dimensional Cahn-Hilliard situation having a conserved order parameter. The scaling analysis of size distribution of the Ising domain, the shape of the power spectrum, and of the correlation function of the Ising order parameter, as well as the number density correlation functions of kinks also confirms that the dynamical scaling law predicted for one-dimensional conservative systems holds for the coarsening process. As supposed from symmetry arguments, it is confirmed that this

  19. Stereochemical control of nonamphiphilic lyotropic liquid crystals: chiral nematic phase of assemblies separated by six nanometers of aqueous solvents.

    Science.gov (United States)

    Yang, Sijie; Wang, Bing; Cui, Dawei; Kerwood, Deborah; Wilkens, Stephan; Han, Junjie; Luk, Yan-Yeung

    2013-06-13

    Unlike conventional thermotropic and lyotropic liquid crystals, nonamphiphilic lyotropic liquid crystals consist of hydrated assemblies of nonamphiphilic molecules that are aligned with a separation of about 6 nm between assemblies in an aqueous environment. This separation raises the question of how chirality, either from chiral mesogens or chiral dopants, would impact the phase as the assemblies that need to interact with each other are about 6 nm apart. Here, we report the synthesis of three stereoisomers of disodium chromonyl carboxylate, 5'DSCG-diviol, and the correlation between the molecular structure, bulk assembly, and liquid crystal formation. We observed that the chiral isomers (enantiomers 5'DSCG-(R,R)-diviol and 5'DSCG-(S,S)-diviol) formed liquid crystals while the achiral isomer 5'DSCG-meso-diviol did not. Circular dichroism indicated a chiral conformation with bisignate cotton effect. The nuclear Overhauser effect in proton NMR spectroscopy revealed conformations that are responsible for liquid crystal formation. Cryogenic transmission electron microscopy showed that chiral 5'DSCG-diviols form assemblies with crossings. Interestingly, only planar alignment of the chiral nematic phase was observed in liquid crystal cells with thin spacers. The homeotropic alignment that permitted a fingerprint texture was obtained only when the thickness of the liquid crystal cell was increase to above ~500 μm. These studies suggest that hydrated assemblies of chiral 5'DSCG-diviol can interact with each other across a 6 nm separation in an aqueous environment by having a twist angle of about 0.22° throughout the sample between the neighboring assemblies.

  20. Nematic liquid crystals confined in microcapillaries for imaging phenomena at liquid-liquid interfaces.

    Science.gov (United States)

    Zhong, Shenghong; Jang, Chang-Hyun

    2015-09-21

    Here, we report the development of an experimental system based on liquid crystals (LCs) confined in microcapillaries for imaging interfacial phenomena. The inner surfaces of the microcapillaries were modified with octadecyltrichlorosilane to promote an escaped-radial configuration of LCs. We checked the optical appearance of the capillary-confined LCs under a crossed polarizing microscope and determined their arrangement based on side and top views. We then placed the capillary-confined LCs in contact with non-surfactant and surfactant solutions, producing characteristic textures of two bright lines and a four-petal shape, respectively. We also evaluated the sensitivity, stability, and reusability of the system. Our imaging system was more sensitive than previously reported LC thin film systems. The textures formed in microcapillaries were stable for more than 120 h and the capillaries could be reused at least 10 times. Finally, we successfully applied our system to image the interactions of phospholipids and bivalent metal ions. In summary, we developed a simple, small, portable, sensitive, stable, and reusable experimental system that can be broadly applied to monitor liquid-liquid interfacial phenomena. These results provide valuable information for designs using confined LCs as chemoresponsive materials in optical sensors.

  1. Surface Anchoring of Nematic Phase on Carbon Nanotubes: Nanostructure of Ultra-High Temperature Materials

    Energy Technology Data Exchange (ETDEWEB)

    Ogale, Amod A

    2012-04-27

    consisting of strong carbon fibers embedded in a carbon matrix are needed. Such carbon/carbon (C/C) composites have been used in aerospace industry to produce missile nose cones, space shuttle leading edge, and aircraft brake-pads. However, radiation-tolerance of such materials is not adequately known because only limited radiation studies have been performed on C/C composites, which suggest that pitch-based carbon fibers have better dimensional stability than that of polyacrylonitrile (PAN) based fibers [4]. The thermodynamically-stable state of graphitic crystalline packing of carbon atoms derived from mesophase pitch leads to a greater stability during neutron irradiation [5]. The specific objectives of this project were: (i) to generating novel carbonaceous nanostructures, (ii) measure extent of graphitic crystallinity and the extent of anisotropy, and (iii) collaborate with the Carbon Materials group at Oak Ridge National Lab to have neutron irradiation studies and post-irradiation examinations conducted on the carbon fibers produced in this research project.

  2. Dynamic states of swimming bacteria in a nematic liquid crystal cell with homeotropic alignment

    Science.gov (United States)

    Zhou, Shuang; Tovkach, Oleh; Golovaty, Dmitry; Sokolov, Andrey; Aranson, Igor S.; Lavrentovich, Oleg D.

    2017-05-01

    Flagellated bacteria such as Escherichia coli and Bacillus subtilis exhibit effective mechanisms for swimming in fluids and exploring the surrounding environment. In isotropic fluids such as water, the bacteria change swimming direction through the run-and-tumble process. Lyotropic chromonic liquid crystals (LCLCs) have been introduced recently as an anisotropic environment in which the direction of preferred orientation, the director, guides the bacterial trajectories. In this work, we describe the behavior of bacteria B. subtilis in a homeotropic LCLC geometry, in which the director is perpendicular to the bounding plates of a shallow cell. We demonstrate that the bacteria are capable of overcoming the stabilizing elastic forces of the LCLC and swim perpendicularly to the imposed director (and parallel to the bounding plates). The effect is explained by a finite surface anchoring of the director at the bacterial body; the role of surface anchoring is analyzed by numerical simulations of a rod realigning in an otherwise uniform director field. Shear flows produced by a swimming bacterium cause director distortions around its body, as evidenced both by experiments and numerical simulations. These distortions contribute to a repulsive force that keeps the swimming bacterium at a distance of a few micrometers away from the bounding plates. The homeotropic alignment of the director imposes two different scenarios of bacterial tumbling: one with an 180° reversal of the horizontal velocity and the other with the realignment of the bacterium by two consecutive 90° turns. In the second case, the angle between the bacterial body and the imposed director changes from 90° to 0° and then back to 90° the new direction of swimming does not correlate with the previous swimming direction.

  3. Simultaneous determination of ordinary and extraordinary refractive index dispersions of nematic liquid crystals in the visible and near-infrared regions from an interference spectrum

    Science.gov (United States)

    Ozaki, Ryotaro; Nishi, Koji; Kan, Takayuki; Kadowaki, Kazunori

    2016-10-01

    An improved interference method is proposed to determine ordinary and extraordinary refractive index dispersions of nematic liquid crystals (LCs). In this method, an LC cell coated with a thin metal layer is used as a Fabry-Perot interferometer, which shows us a sharp transmission fringe. To ensure high reliability, the wavelength dispersion of the refractive index of the metal is taken into account in fitting calculation. In spite of measuring ordinary and extraordinary components, the LC cell, polarizers, and other equipment are not rotated during the experiment. The index evaluation from a single spectrum avoids errors depending on the measurement position owing to non-uniformities of molecular orientation and cell thickness because we can obtain the two indices at exactly the same position. This system can adapt to a wide frequency range and does not require any specific wavelength light source or laser. We demonstrate the determination of ordinary and extraordinary refractive index dispersions of a nematic liquid crystal in the visible and near-infrared regions. Furthermore, we quantitatively reproduce the measured spectrum by calculation using the measured refractive indices.

  4. Optical sensor platform based on cellulose nanocrystals (CNC) - 4'-(hexyloxy)-4-biphenylcarbonitrile (HOBC) bi-phase nematic liquid crystal composite films.

    Science.gov (United States)

    Santos, Moliria V; Tercjak, Agnieszka; Gutierrez, Junkal; Barud, Hernane S; Napoli, Mariana; Nalin, Marcelo; Ribeiro, Sidney J L

    2017-07-15

    The preparation of composite materials has gained tremendous attention due to the potential synergy of the combined materials. Here we fabricate novel thermal/electrical responsive photonic composite films combining cellulose nanocrystals (CNC) with a low molecular weight nematic liquid crystal (NLC), 4'-(hexyloxy)-4-biphenylcarbonitrile (HOBC). The obtained composite material combines both intense structural coloration of photonic cellulose and thermal and conductive properties of NLC. Scanning electron microscopy (SEM) results confirmed that liquid crystals coated CNC films maintain chiral nematic structure characteristic of CNC film and simultaneously, transversal cross-section scanning electron microscopy images indicated penetration of liquid crystals through the CNC layers. Investigated composite film maintain NLC optical properties being switchable as a function of temperature during heating/cooling cycles. The relationship between the morphology and thermoresponsive in the micro/nanostructured materials was investigated by using transmission optical microscopy (TOM). Conductive response of the composite films was proved by Electrostatic force microscopy (EFM) measurement. Designed thermo- and electro-responsive materials open novel simple pathway of fabrication of CNC-based materials with tunable properties. Copyright © 2017. Published by Elsevier Ltd.

  5. Efeitos do suco de alho (Allium sativum Linn. sobre nematódeos gastrintestinais de caprinos Effects of garlic juice (Allium sativum Linn. on gastrintestinal nematodes of goats

    Directory of Open Access Journals (Sweden)

    Maria José Moreira Batatinha

    2004-08-01

    Full Text Available O objetivo deste trabalho foi avaliar os efeitos do suco de alho sobre nematódeos gastrintestinais de caprinos. Foram utilizados 20 animais, distribuídos em dois grupos tratados com o suco de alho, um grupo tratado com ivermectina e um grupo controle sem tratamento. Os percentuais de redução do número de ovos e larvas de Strongyloidea foram inferiores a 95% para todos os grupos. O tratamento de caprinos com o suco de alho não foi eficiente no controle de nematódeos gastrintestinais.The objective of this work was to evaluate the effects of the garlic juice on goat gastrointestinal nematodes. Twenty animals were alocated into two groups and treated with garlic juice. One group was treated with ivermectin and one control group was not treated. The percentage reductions in egg and larvae counts of the Strongyloidea were under 95% for all groups. The treatment of goats with garlic juice was not an effective control of gastrointestinal nematodes.

  6. Nematic electronic structure in the "parent" state of the iron-based superconductor Ca(Fe(1-x)Co(x))2As2.

    Science.gov (United States)

    Chuang, T-M; Allan, M P; Lee, Jinho; Xie, Yang; Ni, Ni; Bud'ko, S L; Boebinger, G S; Canfield, P C; Davis, J C

    2010-01-08

    The mechanism of high-temperature superconductivity in the newly discovered iron-based superconductors is unresolved. We use spectroscopic imaging-scanning tunneling microscopy to study the electronic structure of a representative compound CaFe1.94Co0.06As2 in the "parent" state from which this superconductivity emerges. Static, unidirectional electronic nanostructures of dimension eight times the inter-iron-atom distance a(Fe-Fe) and aligned along the crystal a axis are observed. In contrast, the delocalized electronic states detectable by quasiparticle interference imaging are dispersive along the b axis only and are consistent with a nematic alpha2 band with an apparent band folding having wave vector q vector congruent with +/-2pi/8a(Fe-Fe) along the a axis. All these effects rotate through 90 degrees at orthorhombic twin boundaries, indicating that they are bulk properties. As none of these phenomena are expected merely due to crystal symmetry, underdoped ferropnictides may exhibit a more complex electronic nematic state than originally expected.

  7. Effect of Pyridine on the Mesophase of Teraryl Liquid Crystals: A New Series of Nematic Liquid Crystals Named 2-(4-Alkoxybiphen-4'-yl)-5-methylpyridines.

    Science.gov (United States)

    Chia, Win-Long; Huang, Yu-Sin

    2016-03-07

    A new series of teraryl 2-(4-alkoxybiphen-4'-yl)-5-methylpyridines (nO-PPPyMe, n = 3-8) nematic liquid crystal compounds, bearing a biphenylene core and a picoline terminus, were synthesized using a short two-step reaction, and overall yields between 34% and 38% were obtained. Spectral analysis results were in accordance with the expected structures. The thermotropic behavior of the teraryl liquid crystal compounds was investigated through polarized optical microscopy and differential scanning calorimetry. All compounds exhibited a solely enantiotropic nematic phase at the medium-high temperature range of 162.4-234.2 °C. Furthermore, the results for the nO-PPPyMe series were analyzed relative to three other compound series, mO-PPPyCN (m = 2-8), iO-PPQMe (i = 3-8) and xO-PPyPMe (x = 1-10). Consequently, the effect of pyridine on the mesophase of teraryl liquid crystals was demonstrated.

  8. Control of bovine gastrointestinal nematode parasites using pellets of the nematode-trapping fungus Monacrosporium thaumasium Controle de nematóides parasitos gastrintestinais de bovinos com pellets do fungo predador de nematóides Monacrosporium thaumasium

    Directory of Open Access Journals (Sweden)

    Jackson Victor de Araújo

    2004-04-01

    Full Text Available The viability of a formulation of the fungus Monacrosporium thaumasium associated with ivermectin was evaluated for the biological control of bovine gastrointestinal nematode parasites. Four groups of five calves each were placed in pastures with a stocking rate of 1.6 animal/hectare. In group 1 (control, the calves did not receive any treatment. In group 2, each animal received 20g of pellets of M. thaumasium orally twice a week during a six-month period that began with the onset of the rainy season (October 23, 2000. In group 3, each animal received 20g of pellets of M. thaumasium orally twice a week during the same period as 2, as well as two strategic treatments with ivermectin (200 mcg/kg on May 10, 2001 and July 5, 2001. In group 4, the animals were treated with ivermectin alone as described for group 3. EPG counts for group 1 were significantly greater (PA viabilidade de uma formulação do fungo Monacrosporium thaumasium associada com ivermectina foi avaliada no controle biológico de nematóides parasitos gastrintestinais de bovinos. Quatro grupos de cinco bezerros foram colocados em pastagens com uma taxa de lotação de 1,6 animal/hectare. No grupo 1 (controle, os bezerros não receberam nenhum tratamento. No grupo 2, cada animal recebeu 20 g de pellets de M. thaumasium, via oral, duas vezes por semana e durante um período de seis meses que começou na estação chuvosa (23 de outubro, 2000. No grupo 3, cada animal recebeu 20g de pellets de M. thaumasium, via oral, duas vezes por semana e durante o mesmo período do grupo 2, assim como dois tratamentos estratégicos com ivermectina (200 mcg/kg em 10 de maio de 2001 e em 5 de julho de 2001. No grupo 4, os animais foram tratados somente com ivermectina como descrito no grupo 3. As contagens de OPG dos animais do grupo 1 foram significativamente maiores (P< 0,01 do que os animais dos grupos 2 e 3 e a diferença no final do experimento foi próxima de 100%. Os OPGs dos animais do grupo 4

  9. Photo-alignment of low-molecular mass nematic liquid crystals on photochemically bifunctional chalcone-epoxy film by irradiation of a linearly polarized UV light

    Energy Technology Data Exchange (ETDEWEB)

    Choi, Dong Hoon; Cha, Young Kwan [Kyunghee Univ., Yongin (Korea, Republic of)

    2002-04-01

    Photocrosslinkable chalcone-epoxy compound comprising 1,3-bis-(4-hydroxy-phenyl)-propenone was synthesized for fabricating the photo-alignment layer of liquid crystals. Chalcone group was introduced into the main chain unit of the epoxy oligomer. We observed a photodimerization behavior and an optical anisotropy of this material by irradiation of a linearly polarized UV(LP-UV) light. With a trace amount of cationic photo initiator (TRS-HFA), polymerization of epoxy groups was also conducted at the similar wavelength range used for photodimerization . Linearly polarized UV irradiation on the chalcone-epoxy films with cationic photoinitiator induced optical anisotropy of the film and the resultant film can be used for alignment layers for low molecular weight nematic liquid crystals.

  10. Two Glass Transitions Associated to Different Dynamic Disorders in the Nematic Glassy State of a Non-Symmetric Liquid Crystal Dimer Dopped with γ-Alumina Nanoparticles

    Science.gov (United States)

    Diez-Berart, Sergio; López, David O.; Salud, Josep; Diego, José Antonio; Sellarès, Jordi; Robles-Hernández, Beatriz; de la Fuente, María Rosario; Ros, María Blanca

    2015-01-01

    In the present work, the nematic glassy state of the non-symmetric LC dimer α-(4-cyanobiphenyl-4′-yloxy)-ω-(1-pyrenimine-benzylidene-4′-oxy) undecane is studied by means of calorimetric and dielectric measurements. The most striking result of the work is the presence of two different glass transition temperatures: one due to the freezing of the flip-flop motions of the bulkier unit of the dimer and the other, at a lower temperature, related to the freezing of the flip-flop and precessional motions of the cyanobiphenyl unit. This result shows the fact that glass transition is the consequence of the freezing of one or more coupled dynamic disorders and not of the disordered phase itself. In order to avoid crystallization when the bulk sample is cooled down, the LC dimer has been confined via the dispersion of γ-alumina nanoparticles, in several concentrations.

  11. Parallel and cross-like domains due to d.c. and low frequency (< 2 Hz) electric fields in nematic liquid crystal layers with negative dielectric anisotropy

    International Nuclear Information System (INIS)

    Hinov, H.P.; Vistin, L.K.

    1979-01-01

    Parallel and cross-like domains due to d.c. and low frequency (< 2 Hz) electric fields, in nematic liquid crystal layers with negative dielectric anisotropy - MBBA and 440 are obtained experimentally and investigated. The basic experimental results are: the easy reproducibility of the parallel domains particularly in tilted LC layers 5-90μm with weak anchoring, synthesized on Schiff bases and when the cover glasses are treated with a surfactant - common soap; the creation of cross-like domains in thin homeotropic layers; the demonstration that these domains arise in the cathode region due to the strong inhomogeneous electric field which brings about a periodic bend-splay usually divided by disclinations. Out of the known electroslatic and electrohydrodynamic mechanisms only the flexoelectric effect, due to the gradient electric field, can explain the initial formation of these domains

  12. Photo-alignment of low-molecular mass nematic liquid crystals on photochemically bifunctional chalcone-epoxy film by irradiation of a linearly polarized UV light

    CERN Document Server

    Choi, D H

    2002-01-01

    Photocrosslinkable chalcone-epoxy compound comprising 1,3-bis-(4-hydroxy-phenyl)-propenone was synthesized for fabricating the photo-alignment layer of liquid crystals. Chalcone group was introduced into the main chain unit of the epoxy oligomer. We observed a photodimerization behavior and an optical anisotropy of this material by irradiation of a linearly polarized UV(LP-UV) light. With a trace amount of cationic photo initiator (TRS-HFA), polymerization of epoxy groups was also conducted at the similar wavelength range used for photodimerization . Linearly polarized UV irradiation on the chalcone-epoxy films with cationic photoinitiator induced optical anisotropy of the film and the resultant film can be used for alignment layers for low molecular weight nematic liquid crystals.

  13. New theories for smectic and nematic liquid-crystal polymers: Backbone LCPs [liquid crystalline polymers] and their mixtures and side-chain LCPs

    International Nuclear Information System (INIS)

    Dowell, F.

    1987-01-01

    A summary of predictions and explanations from statistical-physics theories for both backbone and side-chain liquid crystalline polymers (LCPs) and for mixtures with backbone LCPs are presented. Trends in the thermodynamic and molecular ordering properties have been calculated as a function of pressure, density, temperature, and molecule chemical structures (including degree of polymerization and the following properties of the chemical structures of the repeat units: lengths and shapes, intra-chain rotation energies, dipole moments, site-site polarizabilities and Lennard-Jones potentials, etc.) in nematic and multiple smectic-A LC phases and in the isotropic liquid phase. The theoretical results are found to be in good agreement with existing experimental data. These theories can also be applied to combined LCPs. Since these theories have no ad hoc or arbitrarily adjustable parameters, these theories can be used to design new LCPs and new solvents as well as to predict and explain properties. 27 refs., 4 tabs

  14. InP/ZnS quantum-dot-dispersed nematic liquid crystal illustrating characteristic birefringence and enhanced electro-optical parameters

    Science.gov (United States)

    Roy, Aradhana; Pathak, Govind; Herman, Jakub; Inamdar, Sanjeev R.; Srivastava, Atul; Manohar, Rajiv

    2018-03-01

    The present study investigates the influence of InP/ZnS core/shell QDs on various parameters of Nematic LC sample 1832A, based on 4-(4-alkyl-cyclohexyl)benzene isothiocyanates and 4-(4-alkyl-cyclohexyl)biphenyl isothiocyanates. Observations recorded consist of distinguished functioning of birefringence phenomenon along with characteristic response time measurement. Further study of rotational viscosity and splay elastic constant portrays stupendous behavior strengthening the appositeness of the composites for low-charge consumable devices. The addition of 0.2 ml of core/shell QDs producing more than two times faster response and enhanced birefringence at low-temperature range can be employed in development of thermostable photonic devices. In addition, dielectric properties comprising of relative permittivity and conductivity have been reported supporting the outcome of the investigation in applicative LC-based technologies.

  15. Two Glass Transitions Associated to Different Dynamic Disorders in the Nematic Glassy State of a Non-Symmetric Liquid Crystal Dimer Dopped with g-Alumina Nanoparticles

    Directory of Open Access Journals (Sweden)

    Sergio Diez-Berart

    2015-06-01

    Full Text Available In the present work, the nematic glassy state of the non-symmetric LC dimer α-(4-cyanobiphenyl-4′-yloxy-ω-(1-pyrenimine-benzylidene-4′-oxy undecane is studied by means of calorimetric and dielectric measurements. The most striking result of the work is the presence of two different glass transition temperatures: one due to the freezing of the flip-flop motions of the bulkier unit of the dimer and the other, at a lower temperature, related to the freezing of the flip-flop and precessional motions of the cyanobiphenyl unit. This result shows the fact that glass transition is the consequence of the freezing of one or more coupled dynamic disorders and not of the disordered phase itself. In order to avoid crystallization when the bulk sample is cooled down, the LC dimer has been confined via the dispersion of γ-alumina nanoparticles, in several concentrations.

  16. Right-handed double-helix ultrashort DNA yields chiral nematic phases with both right- and left-handed director twist.

    Science.gov (United States)

    Zanchetta, Giuliano; Giavazzi, Fabio; Nakata, Michi; Buscaglia, Marco; Cerbino, Roberto; Clark, Noel A; Bellini, Tommaso

    2010-10-12

    Concentrated solutions of duplex-forming DNA oligomers organize into various mesophases among which is the nematic (N(∗)), which exhibits a macroscopic chiral helical precession of molecular orientation because of the chirality of the DNA molecule. Using a quantitative analysis of the transmission spectra in polarized optical microscopy, we have determined the handedness and pitch of this chiral nematic helix for a large number of sequences ranging from 8 to 20 bases. The B-DNA molecule exhibits a right-handed molecular double-helix structure that, for long molecules, always yields N(∗) phases with left-handed pitch in the μm range. We report here that ultrashort oligomeric duplexes show an extremely diverse behavior, with both left- and right-handed N(∗) helices and pitches ranging from macroscopic down to 0.3 μm. The behavior depends on the length and the sequence of the oligomers, and on the nature of the end-to-end interactions between helices. In particular, the N(∗) handedness strongly correlates with the oligomer length and concentration. Right-handed phases are found only for oligomers shorter than 14 base pairs, and for the sequences having the transition to the N(∗) phase at concentration larger than 620 mg/mL. Our findings indicate that in short DNA, the intermolecular double-helical interactions switch the preferred liquid crystal handedness when the columns of stacked duplexes are forced at high concentrations to separations comparable to the DNA double-helix pitch, a regime still to be theoretically described.

  17. Nematódeos resistentes a anti-helmíntico em rebanhos de ovinos e caprinos do estado do Ceará, Brasil

    Directory of Open Access Journals (Sweden)

    Melo Ana Carolina Fonseca Lindoso

    2003-01-01

    Full Text Available O controle do parasitismo por nematódeos gastrintestinais é feito basicamente com a utilização de anti-helmínticos. Falhas no controle são o primeiro sinal do aparecimento de resistência anti-helmíntica. A real situação da prevalência da resistência anti-helmíntica, em fazendas comerciais de criação de ovinos e caprinos no Brasil, é desconhecida. Esse experimento teve como objetivo, estimar a ocorrência de resistência ao oxfendazol, levamisol e ivermectina em propriedades comerciais de criação de ovinos e caprinos, na região do médio e baixo Jaguaribe, através do teste de redução na contagem de ovos nas fezes acompanhados de coproculturas. O trabalho foi realizado em 25 criações, sendo 16 de ovinos, 7 de caprinos e uma de ovinos e caprinos. Os dados obtidos foram analisados pelo programa estatístico RESO (1989. A prevalência de nematódeos resistentes ao oxfendazol, levamisol e ivermectina em ovinos foi de 88%, 41% e 59%, e em caprinos de 87,5%, 75% e 37,5%, respectivamente. Observou-se que o gênero Haemonchus foi o mais prevalente na população resistente a todos os anti-helmínticos, tanto em ovinos quanto em caprinos, seguido de Trichostrongylus e Oesophagostomum.

  18. Relato de nematóides da família Anisakidae em bacalhau comercializado em Ribeirão Preto, SP Report of nematodes of the Anisakidae family in codfish commercialized in Ribeirão Preto, SP

    Directory of Open Access Journals (Sweden)

    Sonia de Paula Toledo Prado

    2006-12-01

    Full Text Available A anisaquíase é uma parasitose gastrointestinal dos seres humanos, resultante da ingestão acidental de larvas infectantes de nematóides da família Anisakidae. Foram analisadas 11 amostras de bacalhau sendo que 64% estavam em desacordo com a legislação em vigor por conter nematóides da família Anisakidae e, portanto, impróprias para o consumo.Anisakiasis is a human gastrointestinal parasitosis that results from accidental ingestion of infective larvae belonging to the Anisakidae family. Eleven codfish samples were analyzed and 64% did not conform to the present legislation, because they contained nematode larvae from the Anisakidae family and were therefore unfit for consumption.

  19. Nematóide de galha em rabanete: suscetibilidade de cultivares e patogenicidade Root-knot nematode: cultivars reaction and damage to radish

    Directory of Open Access Journals (Sweden)

    Carlos Eduardo Rossi

    2004-03-01

    Full Text Available Pesquisaram-se as reações de 11 cultivares de rabanete a Meloidogyne javanica e sua patogenicidade a uma dessas cultivares. No estudo de reações, os tratamentos/cultivares foram 'Comprido Branco', 'Crimson Gigante', 'Ponta Branca', 'Comprido Vermelho', 'Serrano', 'Gigante Wurzburgo', 'Saxa', 'Redondo Vermelho', 'Redondo Gigante', 'Cometo' e 'Akamaru Hatsuka'. Determinaram-se os índices de galhas (IG e de massas de ovos (IMO, o número de nematóides no sistema radicular (NSR e por grama de raiz (NGR e o fator de reprodução (FR 53 dias após a inoculação artificial com 2.000 ovos do parasito. Em outro experimento, avaliaram-se os efeitos de três densidades populacionais do nematóide [0, 500 (nível populacional baixo e 10.000 (nível populacional alto ovos/planta] sobre as massas frescas e secas de túberas e de parte aérea da cultivar 'Redondo Gigante', 39 dias após a inoculação. Os resultados mostraram que todas as cultivares permitiram a reprodução de M. javanica, sendo portanto consideradas suscetíveis. Valores de IG e IMO foram maiores ou iguais a 2,5 e os de FR, maiores do que 8,0 para todas as cultivares estudadas. O parasito causou diminuição significativa nas massas frescas e secas de túberas e de partes aéreas nos dois níveis populacionais estudados comparados com o controle não inoculado. As médias dos tratamentos contendo níveis populacionais baixo e alto do nematóide também diferiram estatisticamente entre si, comprovando-se, assim, a sua ação patogênica sobre a cultivar avaliada.Experiments were conducted under greenhouse conditions to determine the reaction of eleven radish (Raphanus sativus cultivars to Meloidogyne javanica and the pathogenicity of this nematode to a previously selected cultivar. The cultivars tested were 'Comprido Branco', 'Crimson Gigante', 'Ponta Branca', 'Comprido Vermelho', 'Serrano', 'Gigante Wurzburgo', 'Saxa', 'Redondo Vermelho', 'Redondo Gigante', 'Cometo' and 'Akamaru

  20. Stability of parallel flows

    CERN Document Server

    Betchov, R

    2012-01-01

    Stability of Parallel Flows provides information pertinent to hydrodynamical stability. This book explores the stability problems that occur in various fields, including electronics, mechanics, oceanography, administration, economics, as well as naval and aeronautical engineering. Organized into two parts encompassing 10 chapters, this book starts with an overview of the general equations of a two-dimensional incompressible flow. This text then explores the stability of a laminar boundary layer and presents the equation of the inviscid approximation. Other chapters present the general equation

  1. Feedback stabilization initiative

    International Nuclear Information System (INIS)

    1997-06-01

    Much progress has been made in attaining high confinement regimes in magnetic confinement devices. These operating modes tend to be transient, however, due to the onset of MHD instabilities, and their stabilization is critical for improved performance at steady state. This report describes the Feedback Stabilization Initiative (FSI), a broad-based, multi-institutional effort to develop and implement methods for raising the achievable plasma betas through active MHD feedback stabilization. A key element in this proposed effort is the Feedback Stabilization Experiment (FSX), a medium-sized, national facility that would be specifically dedicated to demonstrating beta improvement in reactor relevant plasmas by using a variety of MHD feedback stabilization schemes

  2. Feedback stabilization initiative

    Energy Technology Data Exchange (ETDEWEB)

    NONE

    1997-06-01

    Much progress has been made in attaining high confinement regimes in magnetic confinement devices. These operating modes tend to be transient, however, due to the onset of MHD instabilities, and their stabilization is critical for improved performance at steady state. This report describes the Feedback Stabilization Initiative (FSI), a broad-based, multi-institutional effort to develop and implement methods for raising the achievable plasma betas through active MHD feedback stabilization. A key element in this proposed effort is the Feedback Stabilization Experiment (FSX), a medium-sized, national facility that would be specifically dedicated to demonstrating beta improvement in reactor relevant plasmas by using a variety of MHD feedback stabilization schemes.

  3. Polymer-Stabilized Micropixelated Liquid Crystals with Tunable Optical Properties Fabricated by Double Templating.

    Science.gov (United States)

    Sasaki, Yuji; Ueda, Motoshi; Le, Khoa V; Amano, Reo; Sakane, Shin; Fujii, Shuji; Araoka, Fumito; Orihara, Hiroshi

    2017-10-01

    Self-organized nano- and microstructures of soft materials are attracting considerable attention because most of them are stimuli-responsive due to their soft nature. In this regard, topological defects in liquid crystals (LCs) are promising not only for self-assembling colloids and molecules but also for electro-optical applications such as optical vortex generation. However, there are currently few bottom-up methods for patterning a large number of defects periodically over a large area. It would be highly desirable to develop more effective techniques for high-throughput and low-cost fabrication. Here, a micropixelated LC structure consisting of a square array of topological defects is stabilized by photopolymerization. A polymer network is formed on the structure of a self-organized template of a nematic liquid crystal (NLC), and this in turn imprints other nonpolymerizable NLC molecules, which maintains their responses to electric field and temperature. Photocuring of specific local regions is used to create a designable template for the reproducible self-organization of defects. Moreover, a highly diluted polymer network (≈0.1 wt% monomer) exhibits instant on-off switching of the patterns. Beyond the mere stabilization of patterns, these results demonstrate that the incorporation of self-organized NLC patterns offers some unique and unconventional applications for anisotropic polymer networks. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  4. Study of variation in thermal width of nematic and induced smectic ordering phase of citric acid (CA) and 4-heptyloxybenzoic acid (7OBA) hydrogen bonded liquid crystal complexes

    Science.gov (United States)

    Sundaram, S.; Jayaprakasam, R.; Praveena, R.; Rajasekaran, T. R.; Senthil, T. S.; Vijayakumar, V. N.

    2018-01-01

    Hydrogen-bonded liquid crystals (HBLCs) have been derived from nonmesogenic citric acid (CA) and mesogenic 4-heptyloxybenzoic acid (7OBA) yielding a highly ordered smectic C (Sm C) phase along with the new smectic X (Sm X) phase which has been identified as fingerprint-type texture. Optical (polarizing optical microscopy), thermal (differential scanning calorimetry) and structural (Fourier transform infrared spectroscopy and nuclear magnetic resonance spectroscopy) properties are studied. A noteworthy observation is that the intermolecular H-bond (between CA and 7OBA) influences on its melting point and clearing temperature of the HBLCs which exhibits lower value than those of the individual compounds. A typical extended mesophase region has been observed in the present complex while varying the mixture ratio (1:1 to 1:3) than those of individual compounds. The change in the ratio of the mesogenic compound in the mixture alters thermal properties such as enthalpy value and thermal span width in nematic (N) region of HBLC complex. Optical tilt angle measurement of CA+7OBA in Sm C phase has been discussed to identify the molecular position in the mesophase.

  5. Soluções de alho (Allium sativum L. no controle de nematódeos gastrintestinais em bovinos jovens da raça Holandesa

    Directory of Open Access Journals (Sweden)

    C.L.C. Parra

    2014-09-01

    Full Text Available Para avaliar o efeito da atividade anti-helmíntica do alho suplementado, foram utilizadas 24 bezerras e novilhas da raça Holandesa, naturalmente infectadas. As soluções foram preparadas triturando-se o alho, (50%, mais água ou álcool 92º, (50%, administrando-se oralmente aos animais. Os tratamentos (T foram constituídos pelo grupo controle negativo (T1; extrato alcoólico de alho a 60g e 120g/100Kg de peso vivo (T2 e (T3; extrato aquoso de alho a 60 e 120g/100kg de peso vivo (T4 e (T5; e o grupo controle positivo com albendazol a 10% (T6. Os tratamentos fitoterápicos foram repetidos a cada 14 dias, caso a infecção fosse superior a 400 ovos por grama de fezes (OPG. A técnica de coprocultura quantitativa e qualitativa foi empregada para avaliar a eficácia anti-helmíntica dos tratamentos. Foram observadas diferenças entre os grupos controle e tratados para OPG e na porcentagem relativa de larvas infectantes e desenvolvimento larval. O uso das soluções de alho demonstrou controle parcial de nematódeos gastrintestinais.

  6. [Human thrombin: drug stability and stabilization].

    Science.gov (United States)

    Kolodzeĭskaia, M V; Sokolovskiĭ, V A; Volkov, G L

    2006-01-01

    Stabilization of enzymes is a key factor when using biocatalysis in practice. Each enzyme stability depends both on the structure of its molecule and on the effect of various environmental factors, thus, one of the methods of the enzyme stability preservation is the formation of optimal macromedium. Thus, water structure and enzyme hydration change in the presence of solvable additives that affects its stability and catalytic properties. The paper deals with a new method of stabilization of human thrombin developed by the authors. It is proposed to use some known organic-ligands which have ion group and different nonpolar hydrophobic groups instead of traditional additives (salts, aminoacids, polyols, polyethylene glycols etc.). Thrombin stabilization proceeds in the conditions something changed compared with traditional ones. Processes of thrombin stabilization by the above compound have been investigated, enzyme stability at different temperatures and long-term storage of diluted solutions of the preparation in different conditions have been studied. It has been established that rosselin and orange II are the most efficient ligands. Optimal finite concentrations of stabilizing agents make approximately 0.0012-0.0014 M which are rather low in the system thrombin-ligand. It has been found that diluted solutions of thrombin are more stable, than concentrated ones. In the latter case the process of autolysis is included that affects negatively the catalytic effect of the enzyme, as far as there occurs the change of thrombin molecule structure, especially of thrombin beta-chain sections, evoking conformational changes of some sites of its active centre. The experiments directed to increasing thrombin intensity in the presence of organic ligands rosselin and orange II are discussed in details. Special attention is given to autolytic method of thrombin inactivation. It is admitted on the basis of already obtained data that thrombin binding with organic ligands proceeds

  7. Internet Addiction: Stability and Change

    Science.gov (United States)

    Huang, Chiungjung

    2010-01-01

    This longitudinal study examined five indices of stability and change in Internet addiction: structural stability, mean-level stability, differential stability, individual-level stability, and ipsative stability. The study sample was 351 undergraduate students from end of freshman year to end of junior year. Convergent findings revealed stability…

  8. Structural Stability and Vibration

    DEFF Research Database (Denmark)

    Wiggers, Sine Leergaard; Pedersen, Pauli

    This book offers an integrated introduction to the topic of stability and vibration. Strikingly, it describes stability as a function of boundary conditions and eigenfrequency as a function of both boundary conditions and column force. Based on a post graduate course held by the author at the Uni......This book offers an integrated introduction to the topic of stability and vibration. Strikingly, it describes stability as a function of boundary conditions and eigenfrequency as a function of both boundary conditions and column force. Based on a post graduate course held by the author...... and their derivation, thus stimulating them to write interactive and dynamic programs to analyze instability and vibrational modes....

  9. Stability of Hyperthermophilic Proteins

    DEFF Research Database (Denmark)

    Stiefler-Jensen, Daniel

    to life at high temperatures so are their enzymes, as a result the high stability is accompanied by low activity at moderate temperatures. Thus, much effort had been put into decoding the mechanisms behind the high stability of the thermophilic enzymes. The hope is to enable scientist to design enzymes...... in the high stability of hyperthermophilic enzymes. The thesis starts with an introduction to the field of protein and enzyme stability with special focus on the thermophilic and hyperthermophilic enzymes and proteins. After the introduction three original research manuscripts present the experimental data...

  10. Atividade predatória, crescimento radial e esporulação de fungos predadores de nematóides Monacrosporium spp, submetidos à criopreservação

    OpenAIRE

    Campos, Artur Kanadani; Mota, Marcelo de Andrade; Araújo, Jackson Victor de; Cecon, Paulo Roberto

    2004-01-01

    Testes in vitro foram realizados para avaliar o efeito da criopreservação em nitrogênio líquido com e sem adição de crioprotetores (DMSO ou glicerol), na atividade predatória sobre larvas infectantes de Cooperia sp e Haemonchus sp, crescimento radial e produção de conídios de dois isolados de fungos predadores de nematóides (Monacrosporium sinense e Monacrosporium appendiculatum). A capacidade predatória dos fungos sobre larvas infectantes de Cooperia sp e Haemonchus sp dos fungos previamente...

  11. Infecções naturais em cervídeos (Mammalia: Cervidae procedentes dos Estados do Mato Grosso do Sul e São Paulo, por nematódeos Trichostrongyloidea Cram, 1927

    Directory of Open Access Journals (Sweden)

    Adjair Antonio do Nascimento

    2000-01-01

    Full Text Available No período compreendido entre 1985 e 1996 foram necropsiados, para pesquisa de helmintos, 42 cervídeos, sendo sete Mazama americana, 16 M. gouazoubira, 13 Ozotoceros bezoarticus e seis Blastocerus dichotomus. Desses animais, foram colhidos 14.426 nematódeos Trichostrongyloidea, sendo 13.281 (92,06% parasitos de abomaso e 1.145 (7,94%, de intestino delgado. Nesses órgãos, foram identificadas seis espécies de nematódeos: Haemonchus contortus, H. similis, Trichostrongylus axei, T. colubriformis, Cooperia punctata e C. pectinata. Todos os animais apresentaram infecções helmínticas por uma ou mais espécies, ocorrendo grande variação na intensidade de infecção (1 a 4.345 nematódeos. Ainda com relação à intensidade de infecção, os dados expressavam valores menores que 100 parasitos em 25 (59,52% animais. Os valores mais altos de intensidade média das infecções foram observados em M. gouazoubira (596,37 helmintos e em O. bezoarticus (331, e os menores, em M. americana (17,57 e B. dichotomus (75,5. Os dados mais expressivos de intensidade de infecção, abundância e prevalência foram observados para Haemonchus (larvas de 4º estágio, H. contortus, H. similis e T. axei. O gênero Haemonchus foi constatado em 35 animais, com prevalência de 83,33%; apresentou carga parasitária de 11.616 exemplares, representando 80,52% dos nematódeos verificados, sendo a maioria (8.903 constituída por formas imaturas. Por outro lado, H. similis foi a espécie predominante nas infecções e, portanto, a que apresentou maiores valores de abundância. Verificou-se o gênero Trichostrongylus em 24 (57,14% animais, com carga parasitária de 2.444 exemplares, sendo 1.665 espécimes de T. axei, que representou 11,54% da carga parasitária obtida. As seis espécies de vermes identificadas nos cervídeos são comuns aos ruminantes domésticos nos Estados de São Paulo e Mato Grosso do Sul e dessa maneira não se observou nenhuma espécie de

  12. Conformational stability of calreticulin

    DEFF Research Database (Denmark)

    Jørgensen, C.S.; Trandum, C.; Larsen, N.

    2005-01-01

    The conformational stability of calreticulin was investigated. Apparent unfolding temperatures (T-m) increased from 31 degrees C at pH 5 to 51 degrees C at pH 9, but electrophoretic analysis revealed that calreticulin oligomerized instead of unfolding. Structural analyses showed that the single C......-terminal a-helix was of major importance to the conformational stability of calreticulin....

  13. Structural Stability and Vibration

    DEFF Research Database (Denmark)

    Wiggers, Sine Leergaard; Pedersen, Pauli

    This book offers an integrated introduction to the topic of stability and vibration. Strikingly, it describes stability as a function of boundary conditions and eigenfrequency as a function of both boundary conditions and column force. Based on a post graduate course held by the author...

  14. Microwave stability at transition

    International Nuclear Information System (INIS)

    Holt, J.A.; Colestock, P.L.

    1995-05-01

    The question of microwave stability at transition is revisited using a Vlasov approach retaining higher order terms in the particle dynamics near the transition energy. A dispersion relation is derived which can be solved numerically for the complex frequency in terms of the longitudinal impedance and other beam parameters. Stability near transition is examined and compared with simulation results

  15. Visual attention and stability

    NARCIS (Netherlands)

    Mathot, Sebastiaan; Theeuwes, Jan

    2011-01-01

    In the present review, we address the relationship between attention and visual stability. Even though with each eye, head and body movement the retinal image changes dramatically, we perceive the world as stable and are able to perform visually guided actions. However, visual stability is not as

  16. Conformational stability of calreticulin

    DEFF Research Database (Denmark)

    Jørgensen, Charlotte S; Trandum, Christa; Larsen, Nanna Brink

    2005-01-01

    The conformational stability of calreticulin was investigated. Apparent unfolding temperatures (Tm) increased from 31 degrees C at pH 5 to 51 degrees C at pH 9, but electrophoretic analysis revealed that calreticulin oligomerized instead of unfolding. Structural analyses showed that the single C......-terminal alpha-helix was of major importance to the conformational stability of calreticulin....

  17. The statistical stability phenomenon

    CERN Document Server

    Gorban, Igor I

    2017-01-01

    This monograph investigates violations of statistical stability of physical events, variables, and processes and develops a new physical-mathematical theory taking into consideration such violations – the theory of hyper-random phenomena. There are five parts. The first describes the phenomenon of statistical stability and its features, and develops methods for detecting violations of statistical stability, in particular when data is limited. The second part presents several examples of real processes of different physical nature and demonstrates the violation of statistical stability over broad observation intervals. The third part outlines the mathematical foundations of the theory of hyper-random phenomena, while the fourth develops the foundations of the mathematical analysis of divergent and many-valued functions. The fifth part contains theoretical and experimental studies of statistical laws where there is violation of statistical stability. The monograph should be of particular interest to engineers...

  18. Substrates for storing entomopathogenic nematodes (Rhabditida: Steinernematidae, Heterorhabditidae Substratos para armazenar nematóides entomopatogênicos (Rhabditida: Steinernematidae, Heterorhabditidae

    Directory of Open Access Journals (Sweden)

    Vanessa Andaló

    2010-01-01

    Full Text Available The survival of entomopathogenic nematodes under laboratory conditions is low. With the aim of evaluating substrates to extend the survival of entomopathogenic nematodes, suspensions of Heterorhabditis sp. JPM4 and Steinernema carpocapsae All (3,000 IJ mL-1 were added to dirt, fine sand, coarse sand, foam, expanded clay, phenolic foam, agar, corn starch, Plantmax®, and water. The substrates were placed on Petri dishes (5 cm and kept at 16 ± 1°C. Survival evaluations were made after 30, 60, 90, 120, 150, and 180 days, with three replicates. After 180 d, a greater percentage of S. carpocapsae infective juveniles (IJs were still alive in the foam treatment (57.5% as compared to other treatments, while expanded clay (28.4%, Plantmax® (9.3% and phenolic foam (11% were not effective in maintaining the survival rate. Foam (55.6%, coarse sand (53.1%, and fine sand (50.6% provided greater Heterorhabditis sp. JPM4 IJ survival at 180 days. Agar (19.3%, phenolic foam (11.6%, and Plantmax® (10.7% had lower survival indices than the control (29.7%. The use of an appropriate substrate can provide greater IJ survival.Os nematóides entomopatogênicos apresentam baixa viabilidade em condições de laboratório. Com o objetivo de avaliar substratos para prolongar a sobrevivência dos nematóides entomopatogênicos, suspensões de Heterorhabditis sp. JPM4 e Steinernema carpocapsae All (3.000 JI mL-1 foram adicionadas aos substratos solo, areia fina, areia grossa, espuma, argila expandida, esponja fenólica, ágar, amido de milho, Plantmax® e água. Estes foram colocados em placas de Petri (5 cm e mantidos a 16 ± 1°C. As avaliações foram feitas após 30, 60, 90, 120, 150 e 180 dias, com três repetições para cada dia. Após 180 dias, para S. carpocapsae All o substrato espuma (57,5% manteve maior porcentagem de juvenis infectantes (JI vivos; argila expandida (28,4%, Plantmax® (9,3% e esponja fenólica (11% não foram eficientes para manutenção da

  19. Quantum irreversible decoherence behaviour in open quantum systems with few degrees of freedom: application to 1H NMR reversion experiments in nematic liquid crystals.

    Science.gov (United States)

    Segnorile, H H; Zamar, R C

    2013-10-21

    An experimental study of NMR spin decoherence in nematic liquid crystals is presented. Decoherence dynamics can be put in evidence by means of refocusing experiments of the dipolar interactions. The experimental technique used in this work is based on the MREV8 pulse sequence. The aim of the work is to detect the main features of the irreversible quantum decoherence in liquid crystals, on the basis of the theory presented by the authors recently. The focus is laid on experimentally probing the eigen-selection process in the intermediate time scale, between quantum interference of a closed system and thermalization, as a signature of the quantum spin decoherence of the open quantum system, as well as on quantifying the effects of non-idealities as possible sources of signal decays which could mask the intrinsic decoherence. In order to contrast experiment and theory, the theory was adapted to obtain the decoherence function corresponding to the MREV8 reversion experiments. Non-idealities of the experimental setting, like external field inhomogeneity, pulse misadjustments, and the presence of non-reverted spin interaction terms are analysed in detail within this framework, and their effects on the observed signal decay are numerically estimated. It is found that though all these non-idealities could in principle affect the evolution of the spin dynamics, their influence can be mitigated and they do not present the characteristic behaviour of the irreversible spin decoherence. As unique characteristic of decoherence, the experimental results clearly show the occurrence of eigen-selectivity in the intermediate timescale, in complete agreement with the theoretical predictions. We conclude that the eigen-selection effect is the fingerprint of decoherence associated with a quantum open spin system in liquid crystals. Besides, these features of the results account for the quasi-equilibrium states of the spin system, which were observed previously in these mesophases, and

  20. Evaluación in vitro de hongos nematófagos en zonas arroceras de Costa Rica contra el nematodo agallador Meloidogyne javanica

    Directory of Open Access Journals (Sweden)

    Walter Peraza Padilla

    2014-12-01

    Full Text Available Se evaluó el parasitismo in vitro de 14 aislamientos de hongos nematófagos (6 Trichoderma sp., 4 Paecilomyces sp., 2 Fusarium oxysporum, y 2 Monacrosporium sp. contra juveniles y huevos del nematodo agallador Meloidogyne javanica. Los hongos, de 3 regiones productoras de arroz en Costa Rica, (Pacífico Central, Huetar Atlántica y Chorotega, se aislaron mediante el método de espolvoreado en placas, durante abril del 2008 a agosto de 2009. Se utilizó un diseño completamente al azar con 10 repeticiones por hongo, en agar-agua (AA. Se inoculó una suspensión de 1 a 1,5x10 6 conidios (ufc.ml -1 por plato Petri, y al cuarto día se depositó en 0,5 ml una suspensión de 150 juveniles y 100 huevos de M. javanica previamente desinfectados, a temperatura ambiente (23-26°C y con luz natural. Transcurridas 96 h se contó en cada plato el número de nematodos vivos, muertos ó parasi- tados y de huevos parasitados o no parasitados. Se realizó un análisis de regresión logística (RL para las variables evaluadas, el cual mostró diferencias significativas (p<0,0001 en el desempeño de los hongos evaluados, presentando rangos de entre 10% a 56% en nematodos muertos, de 13% a 79% en nematodos parasitados y de 1% a 96% en huevos parasitados. En general, los hongos del género Trichoderma (Tri1, Tri2, Tri3 y Tri4 fueron los más eficientes en el parasitismo sobre juveniles y huevos de M. javanica.

  1. Dispersal and metapopulation stability

    Directory of Open Access Journals (Sweden)

    Shaopeng Wang

    2015-10-01

    Full Text Available Metapopulation dynamics are jointly regulated by local and spatial factors. These factors may affect the dynamics of local populations and of the entire metapopulation differently. Previous studies have shown that dispersal can stabilize local populations; however, as dispersal also tends to increase spatial synchrony, its net effect on metapopulation stability has been controversial. Here we present a simple metapopulation model to study how dispersal, in interaction with other spatial and local processes, affects the temporal variability of metapopulations in a stochastic environment. Our results show that in homogeneous metapopulations, the local stabilizing and spatial synchronizing effects of dispersal cancel each other out, such that dispersal has no effect on metapopulation variability. This result is robust to moderate heterogeneities in local and spatial parameters. When local and spatial dynamics exhibit high heterogeneities, however, dispersal can either stabilize or destabilize metapopulation dynamics through various mechanisms. Our findings have important theoretical and practical implications. We show that dispersal functions as a form of spatial intraspecific mutualism in metapopulation dynamics and that its effect on metapopulation stability is opposite to that of interspecific competition on local community stability. Our results also suggest that conservation corridors should be designed with appreciation of spatial heterogeneities in population dynamics in order to maximize metapopulation stability.

  2. Gravity stabilizes itself

    Energy Technology Data Exchange (ETDEWEB)

    Chakraborty, Sumanta; SenGupta, Soumitra [Indian Association for the Cultivation of Science, Department of Theoretical Physics, Kolkata (India)

    2017-08-15

    We show that a possible resolution to the stabilization of an extra spatial dimension (radion) can be obtained solely in the context of gravitational dynamics itself without the necessity of introducing any external stabilizing field. In this scenario the stabilized value of the radion field gets determined in terms of the parameters appearing in the higher curvature gravitational action. Furthermore, the mass of the radion field and its coupling to the standard model fields are found to be in the weak scale implying possible signatures in the TeV scale colliders. Some resulting implications are also discussed. (orig.)

  3. Atividade ovicida de dois fármacos em caprinos naturalmente parasitados por nematódeos gastrintestinais, RS, Brasil Ovicidal activity of two medicaments against goat gastrointestinal nematode in RS, Brazil

    Directory of Open Access Journals (Sweden)

    Mary Jane Tweedie de Mattos

    2000-10-01

    Full Text Available A eficácia comparativa entre levamisole em duas doses diferentes e closantel foi avaliada sobre ovos de nematódeos gastrintestinais de caprinos naturalmente parasitados. Observou-se que a redução de ovos de nematódeos gastrintestinais foi de 93,23%, 91,25% e 70,42% nos grupos medicados com levamisole 8mg/kg, levamisole 11mg/kg e closantel 10mg/kg, respectivamente. O teste de desenvolvimento embrionário revelou que levamisole, nas duas doses, foi eficaz sobre Haemonchus spp., Ostertagia spp., Cooperia spp. e Oesophagostomum spp. O closantel não foi eficaz para Cooperia spp e Oesophagostomum spp.The efficacy of the anthelmintics levamisole in two different doses (8mg/kg and 11mg/kg and closantel (10mg/kg were compared against gastrointestinal nematodes in naturally infected goats. The reduction on the faecal egg count was 93.23% in the group treated with levamisole at the dose of 8mg/kg, 91.25% in the group treated with the dose of 11mg/kg and 70.42% in the group treated with closantel. The anthelmintic levamisole was effective against Haemonchus spp., Ostertagia spp., Cooperia spp and Oesophagostomum spp. However, closantel wasn't effective against Cooperia spp and Oesophagostomum spp.

  4. Core stability exercise principles.

    Science.gov (United States)

    Akuthota, Venu; Ferreiro, Andrea; Moore, Tamara; Fredericson, Michael

    2008-02-01

    Core stability is essential for proper load balance within the spine, pelvis, and kinetic chain. The so-called core is the group of trunk muscles that surround the spine and abdominal viscera. Abdominal, gluteal, hip girdle, paraspinal, and other muscles work in concert to provide spinal stability. Core stability and its motor control have been shown to be imperative for initiation of functional limb movements, as needed in athletics. Sports medicine practitioners use core strengthening techniques to improve performance and prevent injury. Core strengthening, often called lumbar stabilization, also has been used as a therapeutic exercise treatment regimen for low back pain conditions. This article summarizes the anatomy of the core, the progression of core strengthening, the available evidence for its theoretical construct, and its efficacy in musculoskeletal conditions.

  5. Gyroscopic Control and Stabilization

    National Research Council Canada - National Science Library

    Wang, Li-Sheng; Krishnaprasad, P. S

    1991-01-01

    .... To assess the stability of relative equilibria in the resultant feedback systems, they extend the energy-momentum block-diagonalization theorem of Simo, Lewis, Posbergh, and Marsden to gyroscopic systems with symmetry...

  6. Thermal Stabilization Blend Plan

    Energy Technology Data Exchange (ETDEWEB)

    RISENMAY, H.R.

    2000-05-02

    This Blend Plan documents the feed material items that are stored in 2736-2 vaults, the 2736-ZB 638 cage, the 192C vault, and the 225 vault that will be processed through the thermal stabilization furnaces. The purpose of thermal stabilization is to heat the material to 1000 degrees Celsius to drive off all water and leave the plutonium and/or uranium as oxides. The stabilized material will be sampled to determine the Loss On Ignition (LOI) or percent water. The stabilized material must meet water content or LOI of less than 0.5% to be acceptable for storage under DOE-STD-3013-99 specifications. Out of specification material will be recycled through the furnaces until the water or LOI limits are met.

  7. Intelligent passively stabilized quadrotor

    Science.gov (United States)

    Sayfeddine, D.; Bulgakov, A. G.; Kruglova, T. N.

    2017-10-01

    Quadrotor stability is one of the most topical researches worldwide. It is due to the simplicity, availability and cost of such platform. This miniature aerial vehicle is highly manoeuvrable, straight forward to use and to maintain. It can be deployed to perform wide variety of tasks. On the other hand, the quadrotor suffers from non-stability, which makes it unreliable, especially when flying on low speed, high altitude and in windy circumstances. This paper discusses the improvement of the quadrotor by adding a stabilizing mechanism working as a passive breaking system in sharp and spontaneous turns. The mechanism is described and simulated as a standalone module. The end result represents the determination of the stiffness coefficient of the stabilizing actuator using fuzzy logic controller.

  8. Contagion and Stability

    National Research Council Canada - National Science Library

    Reynolds, Jeffrey

    2001-01-01

    The Contagion and Stability Game provided a forum% for discussing the military, economic, informational, political, and medical aspects of contagion in an environmentally stressed region of the less-developed world-South Asia...

  9. Automatic Fiscal Stabilizers

    Directory of Open Access Journals (Sweden)

    Narcis Eduard Mitu

    2013-11-01

    Full Text Available Policies or institutions (built into an economic system that automatically tend to dampen economic cycle fluctuations in income, employment, etc., without direct government intervention. For example, in boom times, progressive income tax automatically reduces money supply as incomes and spendings rise. Similarly, in recessionary times, payment of unemployment benefits injects more money in the system and stimulates demand. Also called automatic stabilizers or built-in stabilizers.

  10. METHOD FOR STABILIZING KLYSTRONS

    Science.gov (United States)

    Magnuson, D.W.; Smith, D.F.

    1959-04-14

    High-frequency oscillators for the generation of microwaves, particularly a system for stabilizing frequency-modulated klystron oscillators of the reflex type, are described. The system takos advantage of the fact that a change in oscillator frequency will alter the normal phase displacement between the cavity and its modulator, creating an error voltage which is utilized to regulate the frequency of the oscillator and stabilize it.

  11. PFP solution stabilization

    Energy Technology Data Exchange (ETDEWEB)

    Aftanas, B.L.

    1996-04-30

    This Functional Design Criteria (FDC) addresses remediation of the plutonium-bearing solutions currently in inventory at the Plutonium Finishing Plant (PFP). The recommendation from the Environmental Impact Statement (EIS) is that the solutions be treated thermally and stabilized as a solid for long term storage. For solutions which are not discardable, the baseline plan is to utilize a denitration process to stabilize the solutions prior to packaging for storage.

  12. Financial System Stability

    OpenAIRE

    Freund, Christian

    2017-01-01

    Three essays on financial system stability. The first paper explores the stability of core-periphery interbank networks in a static simulation framework. The results are then compared to a meanfield approximation. While this proves accurate in early rounds of default, precision of this approximation suffers as the simulation evolves. The second essay contributes to the empirical literature on real-world economic and financial networks. We explore the topology of the Spanish bank-firm credi...

  13. Cyber Deterrence and Stability

    Energy Technology Data Exchange (ETDEWEB)

    Goychayev, Rustam [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Carr, Geoffrey A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Weise, Rachel A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Donnelly, David A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Clements, Samuel L. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Benz, Jacob M. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Rodda, Kabrena E. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Bartholomew, Rachel A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); McKinnon, Archibald D. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Andres, Richard B. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2017-09-30

    Throughout the 20th and early 21st centuries, deterrence and arms control have been cornerstones of strategic stability between the superpowers. However, the weaponization of the cyber realm by State actors and the multipolar nature of cyber conflict now undermines that stability. Strategic stability is the state in which nations believe that if they act aggressively to undermine U.S. national interests and the post-World War II liberal democratic order, the consequences will outweigh the benefits. The sense of lawlessness and lack of consequences in the cyber realm embolden States to be more aggressive in taking actions that undermine stability. Accordingly, this paper examines 1) the role of deterrence and arms control in securing cyber stability, and 2) the limitations and challenges associated with these traditional national security paradigms as applied to this emerging threat domain. This paper demonstrates that many 20th-century deterrence and arms control concepts are not particularly applicable in the cyber realm. However, they are not entirely irrelevant. The United States can distill lessons learned from this rich deterrence and arms control experience to develop and deploy a strategy to advance cyber stability.

  14. Hydrodynamic and hydromagnetic stability

    CERN Document Server

    Chandrasekhar, S

    1981-01-01

    Dr. Chandrasekhar's book received high praise when it first appeared in 1961 as part of Oxford University Press' International Series of Monographs on Physics. Since then it has been reprinted numerous times in its expensive hardcover format. This first lower-priced, sturdy paperback edition will be welcomed by graduate physics students and scientists familiar with Dr. Chandrasekhar's work, particularly in light of the resurgence of interest in the Rayleigh-Bénard problem. This book presents a most lucid introduction to the Rayleigh-Bénard problem: it has also been applauded for its thorough, clear coverage of the theory of instabilities causing convection. Dr. Chandrasekhar considers most of the typical problems in hydromagnetic stability, with the exception of viscous shear flow; a specialized domain deserving a book unto itself. Contents include: Rotation; Stability of More General Flows; Bénard Problem; Gravitational Equilibrium and Instability; Stability of a Magnetic Field; Thermal Instability of a L...

  15. Magnetohydrodynamic stability of tokamaks

    CERN Document Server

    Zohm, Hartmut

    2014-01-01

    This book bridges the gap between general plasma physics lectures and the real world problems in MHD stability. In order to support the understanding of concepts and their implication, it refers to real world problems such as toroidal mode coupling or nonlinear evolution in a conceptual and phenomenological approach. Detailed mathematical treatment will involve classical linear stability analysis and an outline of more recent concepts such as the ballooning formalism. The book is based on lectures that the author has given to Master and PhD students in Fusion Plasma Physics. Due its strong lin

  16. Accelerator terminal voltage stability

    Science.gov (United States)

    Ferry, J. A.; Kolonko, J. J.; Phillips, S. H.; Lunstrum, S. J.

    1992-02-01

    Measurements reported at the 11th International Conference on Applications of Accelerators in Research and Industry [Schroeder et al., Nucl. Instr. and Meth. B56/B57 (1991) 1033] for a 1 MV single-ended Pelletron accelerator equipped with corona probe and tank liner voltage stabilizers have been extended by measuring the resonant yield of γ-rays from the 27Al(p, γ) 28Si reaction at 992 keV. Results show that terminal voltage stability is consistent with the earlier measurement of 31 V FWHM for ripple at 1 MV for periods of about one-half ( {1}/{2}) hour.

  17. Accelerator terminal voltage stability

    International Nuclear Information System (INIS)

    Ferry, J.A.; Kolonko, J.J.; Phillips, S.H.; Lunstrum, S.J.

    1992-01-01

    Measurements reported at the 11th International Conference on Applications of Accelerators in Research and Industry for a 1 MV single-ended Pelletron accelerator equipped with corona probe and tank liner voltage stabilizers have been extended by measuring the resonant yield of γ-rays from the 27 Al(p,γ) 28 Si reaction at 992 keV. Results show that terminal voltage stability is consistent with the earlier measurement of 31 V FWHM for ripple at 1 MV for periods of about one-half (1/2) hour. (orig.)

  18. Premixed conical flame stabilization

    Science.gov (United States)

    Krikunova, A. I.; Son, E. E.; Saveliev, A. S.

    2016-11-01

    In the current work, stabilization of premixed laminar and lean turbulent flames for wide range of flow rates and equivalence ratios was performed. Methane-air mixture was ignited after passing through premixed chamber with beads and grids, and conical nozzle (Bunsen-type burner). On the edge of the nozzle a stabilized body-ring was mounted. Ring geometry was varied to get the widest stable flame parameters. This work was performed as part of the project on experimental investigation of premixed flames under microgravity conditions.

  19. Stability of dynamical systems

    CERN Document Server

    Liao, Xiaoxin; Yu, P 0

    2007-01-01

    The main purpose of developing stability theory is to examine dynamic responses of a system to disturbances as the time approaches infinity. It has been and still is the object of intense investigations due to its intrinsic interest and its relevance to all practical systems in engineering, finance, natural science and social science. This monograph provides some state-of-the-art expositions of major advances in fundamental stability theories and methods for dynamic systems of ODE and DDE types and in limit cycle, normal form and Hopf bifurcation control of nonlinear dynamic systems.ʺ Presents

  20. Efeito anti-helmíntico do hidrolato de Mentha villosa Huds. (Lamiaceae em nematóides gastrintestinais de bovinos Anthelmintic effect of hidrolact of Mentha villosa Huds. (Lamiaceae in gastrointestinal nematodes of cattle

    Directory of Open Access Journals (Sweden)

    Érica Maria Nascimento

    2009-06-01

    Full Text Available Atualmente, o estudo da atividade anti-helmíntica de plantas medicinais em ruminantes tem atraído bastante interesse. Mentha villosa Huds. (Lamiaceae é uma das espécies de hortelã que tem sido utilizada popularmente devido às diversas propriedades medicinais, inclusive para o controle de verminoses. O presente estudo teve como objetivo testar a atividade anti-helmíntica do hidrolato dessa planta em bezerras infectadas por nematóides gastrintestinais, tanto in vitro, pelo método de coprocultura quantitativa, quanto in vivo, por meio do teste de redução no número de ovos de nematóides nas fezes dos hospedeiros. No teste in vitro, o hidrolato nas concentrações de 40%, 60% e 80% e 100% apresentou porcentagem de eficácia de 91,88%, 94,15%, 98,40% e 100%, respectivamente, mostrando atividade ovicida significativa sobre nematóides gastrintestinais em bezerras. Entretanto, os resultados do teste in vivo mostraram ausência de atividade anti-helmíntica do hidrolato de M. villosa na dose de 0,1ml kg dia-1, nos animais tratados.Currently, it has been of great interest to study the anthelmintic activity of medicinal plants in ruminants. Mentha villosa Huds. (Lamiaceae is one of the mint species that has been popularly used based on various medicinal properties, even for the control of nematode infections. This study aimed to test the anthelmintic activity of hidrolact of this plant, both in vitro, by the quantitative coproculture method, and in vivo, in calves infected with gastrointestinal nematodes, through the egg count reduction test in feces of the hosts. In in vitro tests, the hidrolact at the concentrations 40%, 60% and 80% and 100% obtained percentage of effectiveness of 91.88%, 94.15%, 98.40% and 100% respectively, showing significant ovicidal activity against gastrointestinal nematodes in calves. However, the hidrolact of M. villosa showed no in vivo anthelmintic activity at 0.1ml kg-1 day-1 on the treated animals.

  1. Marital stability and repartnering

    DEFF Research Database (Denmark)

    Martins, Mariana V; Costa, Patrício; Peterson, Brennan D

    2014-01-01

    a second union have higher initial levels of stress in their original relationship and higher changes in stress levels over the course of treatments. These findings suggest that high infertility-related stress levels before entering fertility treatment can negatively affect the stability of marital...

  2. Ractor stability monitor

    International Nuclear Information System (INIS)

    Takeuchi, Yutaka.

    1991-01-01

    A stability monitor for a BWR type reactor determines the index of stability by statistic processing of signals from an average power region monitor or the like, but it takes much time and the reliability thereof is not always high. Then, parameters such as reactor core power are measured on every sampling periods as observation data and pretreatments such as normalization are applied successively, to obtain monitored amount and store them successively. Differentiation coefficient relative to time are calculated by using the observed amount at present and that one sample period before, to evaluate on a phasal plane using the amount of observation and the differentiation coefficient with time on the axes of coordinate. As a result, information relative to the stability can be represented accurately, thereby enabling to monitor the stability at a high accuracy. Further, judgement for the condition considering the amplitude is conducted upon oscillation, thereby enabling to conduct control operation certainly. The operation in a region where it has been limited under great caution can be conducted appropriately and safely, enabling to conduct controlled operation of excellent economical property. (N.H.)

  3. Stability of mixing layers

    Science.gov (United States)

    Tam, Christopher; Krothapalli, A

    1993-01-01

    The research program for the first year of this project (see the original research proposal) consists of developing an explicit marching scheme for solving the parabolized stability equations (PSE). Performing mathematical analysis of the computational algorithm including numerical stability analysis and the determination of the proper boundary conditions needed at the boundary of the computation domain are implicit in the task. Before one can solve the parabolized stability equations for high-speed mixing layers, the mean flow must first be found. In the past, instability analysis of high-speed mixing layer has mostly been performed on mean flow profiles calculated by the boundary layer equations. In carrying out this project, it is believed that the boundary layer equations might not give an accurate enough nonparallel, nonlinear mean flow needed for parabolized stability analysis. A more accurate mean flow can, however, be found by solving the parabolized Navier-Stokes equations. The advantage of the parabolized Navier-Stokes equations is that its accuracy is consistent with the PSE method. Furthermore, the method of solution is similar. Hence, the major part of the effort of the work of this year has been devoted to the development of an explicit numerical marching scheme for the solution of the Parabolized Navier-Stokes equation as applied to the high-seed mixing layer problem.

  4. Stability in straight stellarators

    International Nuclear Information System (INIS)

    Kulsrud, R.M.; Yoshikawa, S.

    1981-07-01

    The stability of the straight stellarator against localized interchange modes is investigated employing the Mercier-Greene-Johnson criterion. Critical values of β are obtained both numerically and analytically. The conclusion is that for classical helical stellarators the average limiting β's are quite low of order three to four percent

  5. Ventil – ochrana stability

    Czech Academy of Sciences Publication Activity Database

    Řípa, Milan

    Červenec (2017) ISSN 2464-7888 Institutional support: RVO:61389021 Keywords : fusion * ITER * tokamak * valve * VAT * gyrotron Subject RIV: BL - Plasma and Gas Discharge Physics OBOR OECD: Fluids and plasma physics (including surface physics) http://www.3pol.cz/cz/rubriky/jaderna-fyzika-a-energetika/2035-ventil-ochrana-stability

  6. Surface-stabilized gold nanocatalysts

    Science.gov (United States)

    Dai, Sheng [Knoxville, TN; Yan, Wenfu [Oak Ridge, TN

    2009-12-08

    A surface-stabilized gold nanocatalyst includes a solid support having stabilizing surfaces for supporting gold nanoparticles, and a plurality of gold nanoparticles having an average particle size of less than 8 nm disposed on the stabilizing surfaces. The surface-stabilized gold nanocatalyst provides enhanced stability, such as at high temperature under oxygen containing environments. In one embodiment, the solid support is a multi-layer support comprising at least a first layer having a second layer providing the stabilizing surfaces disposed thereon, the first and second layer being chemically distinct.

  7. Diet and genomic stability.

    Science.gov (United States)

    Young, Graeme P

    2007-01-01

    Cancer results from a disordered and unstable genome - the degree of abnormality progresses as the process of oncogenesis proceeds. Such genomic instability appears to be subject to control by environmental factors as evidenced by the number of cancers that are either caused by specific environmental agents (lung, skin, cervix) or else regulated by a broader range of agents such as effect of diet on gastric and colorectal cancers. Dietary factors might interact in several ways with the genome to protect against cancer. An agent might interact directly with the genome and regulate expression (as a genetic or epigenetic regulator) or indirectly by influencing DNA 'repair' responses and so improve genomic stability. Research now shows that diet-genomic interactions in cancer go beyond interactions with the normal genome and involve enhancement of normal cellular responses to DNA damage such that genome stability is more effectively maintained. Activation of apoptosis may be a key to protection.

  8. Hillslope hydrology and stability

    Science.gov (United States)

    Lu, Ning; Godt, Jonathan

    2012-01-01

    Landslides are caused by a failure of the mechanical balance within hillslopes. This balance is governed by two coupled physical processes: hydrological or subsurface flow and stress. The stabilizing strength of hillslope materials depends on effective stress, which is diminished by rainfall. This book presents a cutting-edge quantitative approach to understanding hydro-mechanical processes across variably saturated hillslope environments and to the study and prediction of rainfall-induced landslides. Topics covered include historic synthesis of hillslope geomorphology and hydrology, total and effective stress distributions, critical reviews of shear strength of hillslope materials and different bases for stability analysis. Exercises and homework problems are provided for students to engage with the theory in practice. This is an invaluable resource for graduate students and researchers in hydrology, geomorphology, engineering geology, geotechnical engineering and geomechanics and for professionals in the fields of civil and environmental engineering and natural hazard analysis.

  9. Glycosylation and thermodynamic versus kinetic stability of horseradish peroxidase

    DEFF Research Database (Denmark)

    Tams, J.W.; Welinder, Karen G.

    1998-01-01

    Glycoprotein stability, glycoprotein unfolding, horseradish peroxidase, thermodynamic stability, kinetik stability......Glycoprotein stability, glycoprotein unfolding, horseradish peroxidase, thermodynamic stability, kinetik stability...

  10. Phase Stabilization of Zirconia.

    Science.gov (United States)

    1997-01-30

    Case No. 77,410 nickel or iron. The bond coat protects and is disposed over a superalloy substrate, such as nickel or a cobalt superalloy . The...conductivity, and a relatively high thermal coefficient of expansion to match expansion of the underlying superalloy 20 substrate, if one is present...multilayer construction, with an MCrAlY (M=Ni, Co, or Fe) inner coating, known as the bond coat, on a superalloy substrate and yttria-stabilized

  11. TOOMPEA HILL STABILITY ANALYSIS

    OpenAIRE

    Pastarus, Jüri-Rivaldo

    1997-01-01

    On Toompea Hill situated in the center of Tallinn there are several natural, ancient architectural and historical monuments. It has become apparent that the processes in the rock mass caused an unfavorable environmental side effect accompanied by significant subsidence of the Toompea Hill. Identification of the reasons of the Toompea Hill's subsidence and opening the physical substance of these processes is the main aim of the present work. For the feasibility study stability problems were in...

  12. Determining postural stability

    Science.gov (United States)

    Lieberman, Erez (Inventor); Forth, Katharine E. (Inventor); Paloski, William H. (Inventor)

    2011-01-01

    A method for determining postural stability of a person can include acquiring a plurality of pressure data points over a period of time from at least one pressure sensor. The method can also include the step of identifying a postural state for each pressure data point to generate a plurality of postural states. The method can include the step of determining a postural state of the person at a point in time based on at least the plurality of postural states.

  13. Rotations in Stability Operations

    Science.gov (United States)

    2012-04-25

    forces to the protected population .” An “ overwhelming presence” was essential to the initial success in Haiti and an “inadequate” number of troops was...stability operations until they achieve the endstate rather than rotating them allows the military to use overwhelming presence, successfully handle...must deploy a force that provides an overwhelming presence in the area of operations with the mission to achieve the endstate. 14. SUBJECT

  14. Limits of Nuclear Stability

    CERN Document Server

    Nerlo-Pomorska, B; Kleban, M

    2003-01-01

    The modern version of the liquid-drop model (LSD) is compared with the macroscopic part of the binding energy evaluated within the Hartree-Fock- Bogoliubov procedure with the Gogny force and the relativistic mean field theory. The parameters of a liquid-drop like mass formula which approximate on the average the self-consistent results are compared with other models. The limits of nuclear stability predicted by these models are discussed.

  15. Oxidative stability of polyaniline

    Czech Academy of Sciences Publication Activity Database

    Stejskal, Jaroslav; Exnerová, Milena; Morávková, Zuzana; Trchová, Miroslava; Hromádková, Jiřina; Prokeš, J.

    2012-01-01

    Roč. 97, č. 6 (2012), s. 1026-1033 ISSN 0141-3910 R&D Projects: GA ČR GA202/09/1626; GA ČR GAP205/12/0911 Institutional research plan: CEZ:AV0Z40500505 Institutional support: RVO:61389013 Keywords : polyaniline * nanotubes * oxidation stability Subject RIV: BK - Fluid Dynamics Impact factor: 2.770, year: 2012

  16. Improved roof stabilization technologies

    International Nuclear Information System (INIS)

    Ebadian, M.A.

    1998-01-01

    Decontamination and decommissioning (D and D) activities require that personnel have access to all areas of structures, some of which are more than 40 years old. In many cases, these structures have remained in a standby condition for up to 10 years; few preventative maintenance activities have been performed on them because of lack of funding or a defined future plan of action. This situation has led to deteriorated building conditions, resulting in potential personnel safety hazards. In addition, leaky roofs allow water to enter the buildings, which can cause the spread of contamination and increase building deterioration, worsening the already unsafe working conditions. To ensure worker safety and facilitate building dismantlement, the assessment of roof stabilization techniques applicable to US Department of Energy (DOE) structures has become an important issue. During Fiscal year 1997 (FY97), a comprehensive reliability-based model for the structural stabilization analysis of roof system in complex structures was developed. The model consists of three major components: a material testing method, a deterministic structural computer model, and a reliability-based optimization, and probabilistic analyses of roof structures can be implemented. Given site-specific needs, this model recommends the most appropriate roof stabilization system. This model will give not only an accurate evaluation of the existing roof system in complex structures, but it will also be a reliable method to aid the decision-making process. This final report includes in its appendix a Users' Manual for the Program of Deterministic and Reliability Analysis of Roof Structures

  17. Heterotic moduli stabilization

    Energy Technology Data Exchange (ETDEWEB)

    Cicoli, M. [Bologna Univ. (Italy). Dipt. Fisica ed Astronomia; INFN, Bologna (Italy); Adbus Salam ICTP, Trieste (Italy); De Alwis, S. [Adbus Salam ICTP, Trieste (Italy); Colorado Univ., Boulder, CO (United States). UCB 390 Physics Dept.; Westphal, A. [DESY Hamburg (Germany). Theory Group

    2013-04-15

    We perform a systematic analysis of moduli stabilization for weakly coupled heterotic string theory compactified on smooth Calabi-Yau three-folds. We focus on both supersymmetric and supersymmetry breaking vacua of generic (0,2) compactifications obtained by minimising the total (F+D)-term scalar potential. After reviewing how to stabilise all the geometric moduli in a supersymmetric way by including fractional fluxes, non-perturbative and threshold effects, we show that the inclusion of {alpha}' corrections leads to new de Sitter or nearly Minkowski vacua which break supersymmetry spontaneously. The minimum lies at moderately large volumes of all the geometric moduli, at perturbative values of the string coupling and at the right phenomenological value of the GUT gauge coupling. However the structure of the heterotic 3-form flux used for complex structure moduli stabilization does not contain enough freedom to tune the superpotential. This results in the generic prediction of high-scale supersymmetry breaking around the GUT scale. We finally provide a dynamical derivation of anisotropic compactifications with stabilized moduli which allow for perturbative gauge coupling unification around 10{sup 16} GeV.

  18. Improved roof stabilization technologies

    Energy Technology Data Exchange (ETDEWEB)

    Ebadian, M.A.

    1998-01-01

    Decontamination and decommissioning (D and D) activities require that personnel have access to all areas of structures, some of which are more than 40 years old. In many cases, these structures have remained in a standby condition for up to 10 years; few preventative maintenance activities have been performed on them because of lack of funding or a defined future plan of action. This situation has led to deteriorated building conditions, resulting in potential personnel safety hazards. In addition, leaky roofs allow water to enter the buildings, which can cause the spread of contamination and increase building deterioration, worsening the already unsafe working conditions. To ensure worker safety and facilitate building dismantlement, the assessment of roof stabilization techniques applicable to US Department of Energy (DOE) structures has become an important issue. During Fiscal year 1997 (FY97), a comprehensive reliability-based model for the structural stabilization analysis of roof system in complex structures was developed. The model consists of three major components: a material testing method, a deterministic structural computer model, and a reliability-based optimization, and probabilistic analyses of roof structures can be implemented. Given site-specific needs, this model recommends the most appropriate roof stabilization system. This model will give not only an accurate evaluation of the existing roof system in complex structures, but it will also be a reliable method to aid the decision-making process. This final report includes in its appendix a Users` Manual for the Program of Deterministic and Reliability Analysis of Roof Structures.

  19. Vibrational stability of graphene

    Directory of Open Access Journals (Sweden)

    Yangfan Hu

    2013-05-01

    Full Text Available The mechanical stability of graphene as temperature rises is analyzed based on three different self-consistent phonon (SCP models. Compared with three-dimensional (3-D materials, the critical temperature Ti at which instability occurs for graphene is much closer to its melting temperature Tm obtained from Monte Carlo simulation (Ti ≃ 2Tm, K. V. Zakharchenko, A. Fasolino, J. H. Los, and M. I. Katsnelson, J. Phys. Condens. Matter 23, 202202. This suggests that thermal vibration plays a significant role in melting of graphene while melting for 3-D materials is often dominated by topologic defects. This peculiar property of graphene derives from its high structural anisotropy, which is characterized by the vibrational anisotropic coefficient (VAC, defined upon its Lindermann ratios in different directions. For any carbon based material with a graphene-like structure, the VAC value must be smaller than 5.4 to maintain its stability. It is also found that the high VAC value of graphene is responsible for its negative thermal expansion coefficient at low temperature range. We believe that the VAC can be regarded as a new criterion concerning the vibrational stability of any low-dimensional (low-D materials.

  20. Stability of surface nanobubbles

    Science.gov (United States)

    Maheshwari, Shantanu; van der Hoef, Martin; Zhang, Xuehua; Lohse, Detlef

    2015-11-01

    We have studied the stability and dissolution of surface nanobubbles on the chemical heterogenous surface by performing Molecular Dynamics (MD) simulations of binary mixture consists of Lennard-Jones (LJ) particles. Recently our group has derived the exact expression for equilibrium contact angle of surface nanobubbles as a function of oversaturation of the gas concentration in bulk liquid and the lateral length of bubble. It has been showed that the contact line pinning and the oversaturation of gas concentration in bulk liquid is crucial in the stability of surface nanobubbles. Our simulations showed that how pinning of the three-phase contact line on the chemical heterogenous surface lead to the stability of the nanobubble. We have calculated the equilibrium contact angle by varying the gas concentration in bulk liquid and the lateral length of the bubble. Our results showed that the equilibrium contact angle follows the expression derived analytically by our group. We have also studied the bubble dissolution dynamics and showed the ''stick-jump'' mechanism which was also observed experimentally in case of dissolution of nanodrops.

  1. Uranium mill tailings stabilization

    International Nuclear Information System (INIS)

    Hartley, J.N.; Koehmstedt, P.L.; Esterl, D.J.; Freeman, H.D.

    1980-02-01

    Uranium mill tailings pose a potential radiation health hazard to the public. Therefore, stabilization or disposal of these tailings in a safe and environmentally sound way is needed to minimize radon exhalation and other environmental hazards. One of the most promising concepts for stabilizing U tailings is the use of asphalt emulsion to contain radon and other hazardous materials within uranium tailings. This approach is being investigated at the Pacific Northwest Laboratory. Results of these studies indicate that a radon flux reduction of greater than 99% can be obtained using either a poured-on/sprayed-on seal (3.0 to 7.0 mm thick) or an admixture seal (2.5 to 12.7 cm thick) containing about 18 wt % residual asphalt. A field test was carried out in June 1979 at the Grand Junction tailings pile in order to demonstrate the sealing process. A reduction in radon flux ranging from 4.5 to greater than 99% (76% average) was achieved using a 15.2-cm (6-in.) admix seal with a sprayed-on top coat. A hydrostatic stabilizer was used to apply the admix. Following compaction, a spray coat seal was applied over the admix as the final step in construction of a radon seal. Overburden was applied to provide a protective soil layer over the seal. Included in part of the overburden was a herbicide to prevent root penetration

  2. Modulational instability of nematic phase

    Indian Academy of Sciences (India)

    2014-02-08

    Feb 8, 2014 ... all phases show MI, but at the same time it has also been found that for antiferro- magnetic phase, MI depends on the relative .... with wave functions, time and spatial coordinates are measured in the units of. (¯h/2mωz)−3/2, ω−1 ... The manipulation of the resulting matrix gives eigenvalues. From the form of ...

  3. Modulational instability of nematic phase

    Indian Academy of Sciences (India)

    2014-02-08

    Feb 8, 2014 ... T Mithun K Porsezian. Contributed Papers Volume 82 Issue 2 February 2014 pp 307-312 ... Abstract. We numerically observe the effect of homogeneous magnetic field on the modulationally stable case of polar phase in = 2 spinor Bose–Einstein condensates (BECs). Also we investigate the modulational ...

  4. Active turbulence in active nematics

    Science.gov (United States)

    Thampi, S. P.; Yeomans, J. M.

    2016-07-01

    Dense, active systems show active turbulence, a state characterised by flow fields that are chaotic, with continually changing velocity jets and swirls. Here we review our current understanding of active turbulence. The development is primarily based on the theory and simulations of active liquid crystals, but with accompanying summaries of related literature.

  5. Elements of magnetohydrodynamic stability theory

    International Nuclear Information System (INIS)

    Spies, G.O.

    1976-11-01

    The nonlinear equations of ideal magnetohydrodynamics are discussed along with the following topics: (1) static equilibrium, (2) strict linear theory, (3) stability of a system with one degree of freedom, (4) spectrum and variational principles in magnetohydrodynamics, (5) elementary proof of the modified energy principle, (6) sufficient stability criteria, (7) local stability, and (8) normal modes

  6. Hyperparasitism by helminths: new records of cestodes and nematodes in proteocephalid cestodes from South American siluriform fishes Hiperparasitismo por helmintos: novas ocorrências de cestóides e nematóides em cestóides proteocefalídeos de peixes siluriformes da América do Sul

    Directory of Open Access Journals (Sweden)

    Amilcar Arandas Rego

    1989-09-01

    Full Text Available Proteocephalid cestode hyperparasite are reported from numerous proteocephalids occurring in pimelodid fishes in different regions of Brazil. In addition, three specimens of a nematode hyperparasite are reported from the proteocephalid cestode Choanoscolex abscissus from the pimelodid fish Pseudoplatystoma corruscans in Brazil. Previous records of cestode and nematode hyperparasite of cestode are listed, and the possible identities of the Brazilian records are discussed.Cestóides hiperparasitos são descritos de espécies de proteocefalídeos, que ocorrem em peixes pimelodídeos de diferentes regiões do Brasil. Referimos ainda, a ocorrência de nematóide hiperparasito em espécimes de Choanoscolex abscissus, do peixe pimelodídeo, Pseudoplatystoma carruscans. São citadas as referências anteriores de cestóides e nematóides hiperparasitos, e discutida a possível identificação dos mesmos.

  7. Moral Hazard and Stability

    DEFF Research Database (Denmark)

    Tumennasan, Norovsambuu

    2014-01-01

    Economists perceive moral hazard as an undesirable problem because it undermines efficiency. Carefully designed contracts can mitigate the moral hazard problem, but this assumes that a team is already formed. This paper demonstrates that these contracts are sometimes the reason why teams do...... not form. Formally, we study the team formation problem in which the agents’ efforts are not verifiable and the size of teams does not exceed quota r . We show that if the team members cannot make transfers, then moral hazard affects stability positively in a large class of games. For example, a stable...

  8. Core stability and bicycling.

    Science.gov (United States)

    Asplund, Chad; Ross, Michael

    2010-01-01

    Bicycling is a popular fitness activity in the United States and around the world. Because of the nature of the bicycling position, the neck and back are at risk for injury. One method to prevent these injuries is to ensure that the body's "core" is strong and stable. A strong and stable core also provides a platform to maximize power transfer, improving performance. Core exercises also may enhance recovery from intense bicycling efforts. Simple stability exercises can improve performance and may prevent injuries in bicyclists.

  9. Regional Stability & Peacebuilding

    DEFF Research Database (Denmark)

    . With contributions from leading international scholars within the field of security studies this book sets out to explain the main security knots preventing stability to emerge and on that basis to test whether a different approach in addressing these knots. By pursuing an innovative and different approach...... to the process of peacebuilding, this could prove as a useful tool, and for this reason politicians, officials, and persons in general with an interest in this region will benefit from the perspectives presented here....

  10. Stability of Streamer Chamber

    Science.gov (United States)

    Wada, Toshiaki; Ogawa, Masato; Takahashi, Kaoru; Sugiyama, Tsunetoshi; Kobayashi, Shigeharu; Kohno, Hirobumi

    1982-08-01

    The quality of tracks obtained from a streamer chamber is studied through the measurement of the streamer brightness. The stability of streamer tracks depends on the value of the high voltage applied and its shape. By using a single conical-type spark gap as the pulse shaper, stable brightness of the streamer tracks is attained. The data on the streamer brightness are compared with the result by Bulos et al. and it is found that the brightness is more strongly affected by field parameters than in their result.

  11. Stability of streamer chamber

    International Nuclear Information System (INIS)

    Wada, Toshiaki; Ogawa, Masato; Takahashi, Kaoru; Sugiyama, Tsunetoshi; Kobayashi, Shigeharu; Kohno, Hirobumi.

    1982-01-01

    The quality of tracks obtained from a streamer chamber is studied through the measurement of the streamer brightness. The stability of streamer tracks depends on the value of the high voltage applied and its shape. By using a single conical-type spark gap as the pulse shaper, stable brightness of the streamer tracks is attained. The data on the streamer brightness are compared with the result by Bulos et al. and it is found that the brightness is more strongly affected by field parameters than in their result. (author)

  12. Measuring autocratic regime stability

    Directory of Open Access Journals (Sweden)

    Joseph Wright

    2016-01-01

    Full Text Available Researchers measure regime stability in autocratic contexts using a variety of data sources that capture distinct concepts. Often this research uses concepts developed for the study of democratic politics, such as leadership change or institutionalized authority, to construct measures of regime breakdown in non-democratic contexts. This article assesses whether the measure a researcher chooses influences the results they obtain by examining data on executive leadership, political authority, and autocratic regimes. We illustrate the conceptual differences between these variables by extending recent studies in the literature on the political consequences of non-tax revenue and unearned foreign income.

  13. Stability Landscape of Shell Buckling

    Science.gov (United States)

    Virot, Emmanuel; Kreilos, Tobias; Schneider, Tobias M.; Rubinstein, Shmuel M.

    2017-12-01

    We measure the response of cylindrical shells to poking and identify a stability landscape, which fully characterizes the stability of perfect shells and imperfect ones in the case where a single defect dominates. We show that the landscape of stability is independent of the loading protocol and the poker geometry. Our results suggest that the complex stability of shells reduces to a low dimensional description. Tracking ridges and valleys of this landscape defines a natural phase-space coordinates for describing the stability of shells.

  14. Viabilidade de formulação peletizada do fungo nematófago Monacrosporium sinense, no controle biológico de nematóides parasitos gastrintestinais de bezerros Viability of pellet formulation of Monacrosporium sinense as biological control of gastrointestinal nematodes of calves

    Directory of Open Access Journals (Sweden)

    A.K. Campos

    2007-02-01

    Full Text Available A viabilidade de uma formulação do fungo Monacrosporium sinense foi avaliada no controle de nematóides parasitos gastrintestinais de bovinos. Dois grupos de 10 bezerros cada um, mestiços Holandês x Zebu, de seis a nove meses de idade, foram colocados em pastagem de Brachiaria brizantha. Em um dos grupos, cada animal recebeu 20g de péletes em matriz de alginato de sódio, contendo massa miceliana do fungo M. sinense via oral, duas vezes por semana, durante seis meses, com início no mês de outubro; no outro grupo, controle, os bezerros não receberam esse tratamento. As contagens de ovos por grama de fezes (OPG e de larvas infectantes por kg de matéria seca foram maiores (PThe viability of a formulation of the fungus Monacrosporium sinense was evaluated as control of bovine gastrointestinal nematodes parasites. Two groups were used and they were made up of 10 Holstein X Zebu crossbred, six to eight-month-old. They were grazing on Brachiaria brizantha pasture. In the treated group, each animal received orally, twice a week 20g of pellets of sodium alginate containing mycelial of the fungus M. sinense, during six months, with the onset in October. In the control group, the calves did not receive that treatment. The counting of eggs per gram of faeces (EPG and the counting of infective larvae per kg of dry matter were higher (P<0.05 in the control group than in the treated group. The difference of the EPG between the groups at the end of the experimental period was 79%. The viability of the pellets germination and the predatory activity of the fungus after the encapsulation were evaluated in vitro. The percentage of pellets with positive culture for fungus varied between 90-100% and the percentage of reduction of infective larvae varied between 90.6-100%. The use of that dose and the periodic application of M. sinense pellets were efficient as control of bovine gastrointestinal nematode parasites.

  15. Plasma stabilization experiment

    Science.gov (United States)

    Sziklas, E. A.; Fader, W. J.; Jong, R. A.; Stufflebeam, J. H.

    1980-07-01

    The plasma stabilization experiment is an effort to enhance stability in a mirror-confined plasma by trapping cold ions with rf fields applied near the mirror throats. Nagoya Type 3 antennas, coupled to a 60 kW rf power supply are mounted in the throats of the UTRC baseball magnet. An external washer gun provides a source of plasma for both streaming and confined plasma tests. Results show a strong stoppering effect on streaming plasmas and a marginal effect on confined plasmas. Theoretical calculations provide an explanation for the experimental observations. The field generates a ponderomotive force acting on the electrons. The resultant improvement in electron confinement changes the ambipolar potential and inhibits the flow of ions through the mirror throat. Criteria are derived for the validity of this trapping concept. The requisite field strengths are significantly lower than those required to trap ions directly. Scaling laws are developed for application of cold ion trapping to large mirror devices containing dense plasmas. The use of slow-wave antenna structures operated at frequencies above the lower hybrid frequency is recommended for these applications.

  16. Containment vessel stability analysis

    International Nuclear Information System (INIS)

    Harstead, G.A.; Morris, N.F.; Unsal, A.I.

    1983-01-01

    The stability analysis for a steel containment shell is presented herein. The containment is a freestanding shell consisting of a vertical cylinder with a hemispherical dome. It is stiffened by large ring stiffeners and relatively small longitudinal stiffeners. The containment vessel is subjected to both static and dynamic loads which can cause buckling. These loads must be combined prior to their use in a stability analysis. The buckling loads were computed with the aid of the ASME Code case N-284 used in conjunction with general purpose computer codes and in-house programs. The equations contained in the Code case were used to compute the knockdown factors due to shell imperfections. After these knockdown factors were applied to the critical stress states determined by freezing the maximum dynamic stresses and combining them with other static stresses, a linear bifurcation analysis was carried out with the aid of the BOSOR4 program. Since the containment shell contained large penetrations, the Code case had to be supplemented by a local buckling analysis of the shell area surrounding the largest penetration. This analysis was carried out with the aid of the NASTRAN program. Although the factor of safety against buckling obtained in this analysis was satisfactory, it is claimed that the use of the Code case knockdown factors are unduly conservative when applied to the analysis of buckling around penetrations. (orig.)

  17. Gender and family stability

    Directory of Open Access Journals (Sweden)

    2001-02-01

    Full Text Available The increasing trend of partnership disruption among families with children in recent decades has been accompanied by substantial changes in traditional gender roles in industrialized countries. Yet, relatively little is known about the effects of changing gender relations on family stability in the European context. In this paper, we study such gender influences at the familial and societal level in Sweden and Hungary between the mid-1960s and the early 1990s. We focus on the disruption of the first parental union (i.e. the union in which a couple's first child was born. Our analysis is based on data extracted from the Swedish and Hungarian Fertility and Family Surveys of 1992/93. We use the method of hazard regression. The results suggest (i that the establishment of the dual-earner family model influences family stability only if it is accompanied by some changes in traditional gender relations within the family, and (ii that women's and men's labor-market behavior have different effects in spite of the relatively long history of women's (also mothers' labor-force participation in both Sweden and Hungary.

  18. Food Fortification Stability Study

    Science.gov (United States)

    Abdulmalik, T. O.; Cooper, M. R.; Douglas, G. L.

    2015-01-01

    NASA has established the goal of traveling beyond low-Earth orbit and extending manned exploration to Mars. The extended length of a Mars mission, along with the lack of resupply missions increases the importance of nutritional content in the food system. The purpose of this research is to assess the stability of vitamin supplementation in traditionally processed spaceflight foods. It is expected that commercially available fortificants will remain stable through long-duration missions if proper formulation, processing, and storage temperatures are all achieved. Five vitamins (vitamin E, vitamin K, pantothenic acid, folic acid, and thiamin) were blended into a vitamin premix (DSM, Freeport, TX); premixes were formulated to be compatible with current processing techniques (retort or freeze-dried), varied water activities (high or low), and packaging material. The overall goal of this process is to provide 25% of the recommended daily intake of each vitamin (per serving), following processing and two years of ambient storage. Four freeze-dried foods (Scrambled Eggs, Italian Vegetables, Potatoes Au Gratin, Noodles and Chicken) and four thermostabilized foods (Curry Sauce with Vegetables, Chicken Noodle Soup, Grilled Pork Chop, Rice with Butter) were produced (with and without the vitamin premix), to assess the impact of the added fortificant on color and taste, and to determine the stability of supplemental vitamins in spaceflight foods. The use of fortification in spaceflight foods appears to be a plausible mitigation step to inadequate nutrition. This is due to the ease of vitamin addition as well as the sustainability of the premixes through initial processing steps. Postprocessing analysis indicated that vitamin fortification with this premix did not immediately impact organoleptic properties of the food. At this stage, the largest hurdle to fortification is the preciseness to which vitamins can be added; the total amount of vitamins required for production is 10

  19. Food Fortification Stability Study

    Science.gov (United States)

    Sirmons, T.; Cooper, M.; Douglas, G.

    2017-01-01

    NASA has established the goal of traveling beyond low-Earth orbit and extending manned exploration to Mars. The length of proposed Mars missions and the lack of resupply missions increases the importance of nutritional content in the food system, which will need a five-year shelf life. The purpose of this research is to assess the stability of vitamin supplementation in traditionally processed spaceflight foods. It is expected that commercially available fortification nutrients will remain stable through a long duration exploration mission at sufficient levels if compatible formulation, processing, and storage temperatures are achieved. Five vitamins (vitamin E, vitamin K, pantothenic acid, folic acid, and thiamin) were blended into a vitamin premix (DSM, Freeport, TX) such that the vitamin concentration per serving equaled 25% of the recommended daily intake after two years of ambient storage. Four freeze-dried foods (Scrambled Eggs, Italian Vegetables, Potatoes Au Gratin, Noodles and Chicken) and four thermo-stabilized foods (Curry Sauce with Vegetables, Chicken Noodle Soup, Grilled Pork Chop, Rice with Butter) were produced, with and without the vitamin premix, to assess the impact of the added fortification on color and taste and to determine the stability of supplemental vitamins in spaceflight foods. The addition of fortification to spaceflight foods did not greatly alter the organoleptic properties of most products. In most cases, overall acceptability scores remained above 6.0 (minimum acceptable score) following six months and one year of low-temperature storage. Likewise, the color of fortified products appears to be preserved over one year of storage. The only exceptions were Grilled pork Chop and Chicken Noodle Soup whose individual components appeareddegrade rapidly over one year of storage. Finally, most vitamins appeared to be stable during long-term storage. The only exception was thiamin, which degraded rapidly during the first year of storage at

  20. Exploiting sequence and stability information for directing nanobody stability engineering.

    Science.gov (United States)

    Kunz, Patrick; Flock, Tilman; Soler, Nicolas; Zaiss, Moritz; Vincke, Cécile; Sterckx, Yann; Kastelic, Damjana; Muyldermans, Serge; Hoheisel, Jörg D

    2017-09-01

    Variable domains of camelid heavy-chain antibodies, commonly named nanobodies, have high biotechnological potential. In view of their broad range of applications in research, diagnostics and therapy, engineering their stability is of particular interest. One important aspect is the improvement of thermostability, because it can have immediate effects on conformational stability, protease resistance and aggregation propensity of the protein. We analyzed the sequences and thermostabilities of 78 purified nanobody binders. From this data, potentially stabilizing amino acid variations were identified and studied experimentally. Some mutations improved the stability of nanobodies by up to 6.1°C, with an average of 2.3°C across eight modified nanobodies. The stabilizing mechanism involves an improvement of both conformational stability and aggregation behavior, explaining the variable degree of stabilization in individual molecules. In some instances, variations predicted to be stabilizing actually led to thermal destabilization of the proteins. The reasons for this contradiction between prediction and experiment were investigated. The results reveal a mutational strategy to improve the biophysical behavior of nanobody binders and indicate a species-specificity of nanobody architecture. This study illustrates the potential and limitations of engineering nanobody thermostability by merging sequence information with stability data, an aspect that is becoming increasingly important with the recent development of high-throughput biophysical methods. Copyright © 2017 The Authors. Published by Elsevier B.V. All rights reserved.

  1. Nematóides que parasitam a soja na região de Bauru Nematode parasites of soybean in the Bauru region

    Directory of Open Access Journals (Sweden)

    Luiz Gonzaga E. Lordello

    1956-01-01

    Full Text Available Entre os sérios fatôres que atuam contra a expansão da cultura da soja no Estado de São Paulo, acha-se o representado por nematóides parasitos. Dêstes, os que mais têm atraído a atenção dos cultivadores e fitopatologistas são as espécies formadoras de galhas no sistema radicular (Meloidogyne spp.. O estudo do material atacado coligido em Bauru revelou que, naquela região, três formas se acham envolvidas, a saber : Pratylenchus sp., Meloidogyne incognita (Kofoid & White, 1919 Chitwood, 1949 e M. javanica bauruensis n. subsp. Neste trabalho é estudada a nova subespécie, sendo também apresentadas algumas observações sobre a população de M. incognita.One of the serious detriments to soybean (Glycine max (L. Merr. cultivation in the State of S. Paulo, Brazil, are root-parasitic nematodes. A study of infected material collected at Bauru, where at least two distinct soybean varieties were cultivated, disclosed that three forms were involved: a meadow nematode (Pralylenchus sp. and two root-knot nematodes (Meloidogyne incognita (Kofoid & White, 1919 Chitwood, 1949, and M. javanica bauruensis n. subsp.. Silva, Lordello & Miyasaka (3 published some observations about the resistance of several soybean varieties to the attacks by root-knot nematodes in Campinas. A detailed study of the nematodes involved in those experiments, which were considered as related do M. incognita, has not yet been made. One of the varieties tested, La 41-1219, proved to be resistant, thereby providing promising material for further studies and breeding. Unfortunately, such a variety when planted in Bauru, was severely attacked by a root-knot species, which is identified as M. incognita. Attacks by M. javanica bauruensis was not noted in that variety but was noted in another variety (Abura growing adjacent in the same field. The host preference of those two nematodes was specific and very marked. M. incognita attacked only var. La 41-1219 and M. javanica

  2. Vibrations and Stability

    DEFF Research Database (Denmark)

    Thomsen, Jon Juel

    About this textbook An ideal text for students that ties together classical and modern topics of advanced vibration analysis in an interesting and lucid manner. It provides students with a background in elementary vibrations with the tools necessary for understanding and analyzing more complex...... dynamical phenomena that can be encountered in engineering and scientific practice. It progresses steadily from linear vibration theory over various levels of nonlinearity to bifurcation analysis, global dynamics and chaotic vibrations. It trains the student to analyze simple models, recognize nonlinear...... and physics. This edition includes a new chapter on the useful effects of fast vibrations and many new exercise problems. Written for: Students in mechanical or structural engineering. Keywords: Nonlinear Vibrations, Bifurcations, Chaotic Vibrations, Vibrations and Stability....

  3. HMD symbol stabilization concepts

    Science.gov (United States)

    Newman, Richard L.; Greeley, Kevin W.

    1995-05-01

    Helmet-mounted displays (HMDs) present flight, navigation, and weapon information in the pilot's line of sight. The HMD was developed to allow the pilot to retain aircraft and weapon information while looking off boresight. Symbol stabilization is a key issue for HMDs. In current equipment, the lack of compensation for pilot head motion creates excessive workload during hovering and nap-of-the-earth flight. This high workload translates into excessive training requirements. At the same time, misleading symbology makes interpretation of the height of obstructions impossible. A set of standardized coordinate transformations are necessary for the development of HMD symbology and the control laws. Part of the problem is there is no agreed upon set of definitions or descriptions for how HMD symbols are driven to compensate for pilot head motion. A candidate set of coordinate definitions is proposed to address this issue.

  4. Entrepreneurship and Employment Stability

    DEFF Research Database (Denmark)

    Failla, Virgilio; Melillo, Francesca; Reichstein, Toke

    2017-01-01

    are identified and empirically explored: (i) job matching, (ii) labour market value, and (iii) personal commitment. Entrepreneurs appear to be more productive and thus better matched compared to wageworkers. However, they also appear to be locked in entrepreneurship because of their anticipated lower value......This paper challenges the conventional belief that entrepreneurship is an unstable career path. Using longitudinal matched employer–employee data from Denmark, the analysis reveals that a transition to entrepreneurship decreases individual's employment turnover tendency. Three explanations...... in the labour market and because of their personal attachment to the venture. The counter-intuitive finding – entrepreneurship yields greater employment stability – only holds with respect to subsequent transitions to wagework and not for new venture founding. The results have implications for our understanding...

  5. IMPROVED ROOF STABILIZATION TECHNOLOGIES

    Energy Technology Data Exchange (ETDEWEB)

    M.A. Ebadian, Ph.D.

    1999-01-01

    Many U.S. Department of Energy (DOE) remediation sites have performed roof repair and roof replacement to stabilize facilities prior to performing deactivation and decommissioning (D&D) activities. This project will review the decision criteria used by these DOE sites, along with the type of repair system used for each different roof type. Based on this information, along with that compiled from roofing experts, a decision-making tool will be generated to aid in selecting the proper roof repair systems. Where appropriate, innovative technologies will be reviewed and applied to the decision-making tool to determine their applicability. Based on the results, applied research and development will be conducted to develop a method to repair these existing roofing systems, while providing protection for the D and D worker in a cost-efficient manner.

  6. IMPROVED ROOF STABILIZATION TECHNOLOGIES

    International Nuclear Information System (INIS)

    Ebadian, M.A.

    1999-01-01

    Many U.S. Department of Energy (DOE) remediation sites have performed roof repair and roof replacement to stabilize facilities prior to performing deactivation and decommissioning (D and D) activities. This project will review the decision criteria used by these DOE sites, along with the type of repair system used for each different roof type. Based on this information, along with that compiled from roofing experts, a decision-making tool will be generated to aid in selecting the proper roof repair systems. Where appropriate, innovative technologies will be reviewed and applied to the decision-making tool to determine their applicability. Based on the results, applied research and development will be conducted to develop a method to repair these existing roofing systems, while providing protection for the D and D worker in a cost-efficient manner

  7. From Crisis to Stability

    DEFF Research Database (Denmark)

    Ban, Cornel; Seabrooke, Leonard

    The European Stability Mechanism (ESM) was created to save the euro from collapse. But the Eurozone’s bailout fund is not actually an EU institution. This has a series of knock-on effects, making it difficult to hold the ESM to EU standards as regards transparency, legal review by the CJEU......, but also access to documents regulation and accountability vis-à-vis the European Parliament, the Court of Auditors and Anti-Fraud Office. Transparency International EU’s in-depth study of the governance and accountability of the ESM provides the first comprehensive analysis of the newest European economic...... governance institution, and makes a number of concrete recommendations. To make the ESM accountable, more transparency is in order, about where decisions are taken and who calls the shots. Is it the ESM, the Eurogroup, the Commission, or a coalition of Member States? Our report launch attempts to answer...

  8. Vibrations and Stability

    DEFF Research Database (Denmark)

    Thomsen, Jon Juel

    dynamical phenomena that can be encountered in engineering and scientific practice. It progresses steadily from linear vibration theory over various levels of nonlinearity to bifurcation analysis, global dynamics and chaotic vibrations. It trains the student to analyze simple models, recognize nonlinear...... and physics. This edition includes a new chapter on the useful effects of fast vibrations and many new exercise problems. Written for: Students in mechanical or structural engineering. Keywords: Nonlinear Vibrations, Bifurcations, Chaotic Vibrations, Vibrations and Stability.......About this textbook An ideal text for students that ties together classical and modern topics of advanced vibration analysis in an interesting and lucid manner. It provides students with a background in elementary vibrations with the tools necessary for understanding and analyzing more complex...

  9. Complementarity and stability conditions

    Directory of Open Access Journals (Sweden)

    Howard Georgi

    2017-08-01

    Full Text Available We discuss the issue of complementarity between the confining phase and the Higgs phase for gauge theories in which there are no light particles below the scale of confinement or spontaneous symmetry breaking. We show with a number of examples that even though the low energy effective theories are the same (and trivial, discontinuous changes in the structure of heavy stable particles can signal a phase transition and thus we can sometimes argue that two phases which have different structures of heavy particles that cannot be continuously connected and thus the phases cannot be complementary. We discuss what this means and suggest that such “stability conditions” can be a useful physical check for complementarity.

  10. Parabolized stability equations

    Science.gov (United States)

    Herbert, Thorwald

    1994-01-01

    The parabolized stability equations (PSE) are a new approach to analyze the streamwise evolution of single or interacting Fourier modes in weakly nonparallel flows such as boundary layers. The concept rests on the decomposition of every mode into a slowly varying amplitude function and a wave function with slowly varying wave number. The neglect of the small second derivatives of the slowly varying functions with respect to the streamwise variable leads to an initial boundary-value problem that can be solved by numerical marching procedures. The PSE approach is valid in convectively unstable flows. The equations for a single mode are closely related to those of the traditional eigenvalue problems for linear stability analysis. However, the PSE approach does not exploit the homogeneity of the problem and, therefore, can be utilized to analyze forced modes and the nonlinear growth and interaction of an initial disturbance field. In contrast to the traditional patching of local solutions, the PSE provide the spatial evolution of modes with proper account for their history. The PSE approach allows studies of secondary instabilities without the constraints of the Floquet analysis and reproduces the established experimental, theoretical, and computational benchmark results on transition up to the breakdown stage. The method matches or exceeds the demonstrated capabilities of current spatial Navier-Stokes solvers at a small fraction of their computational cost. Recent applications include studies on localized or distributed receptivity and prediction of transition in model environments for realistic engineering problems. This report describes the basis, intricacies, and some applications of the PSE methodology.

  11. Nematodes in Hoplerytrinus unitaeniatus, Hoplias malabaricus and Pygocentrus nattereri (pisces characiformes in Marajó Island, Brazil Nematóides em Hoplerytrinus unitaeniatus, Hoplias malabaricus e Pygocentrus nattereri (pisces characiformes na Ilha de Marajó, Brasil

    Directory of Open Access Journals (Sweden)

    Raimundo Nonato Moraes Benigno

    2012-06-01

    Full Text Available The aim of this study was to evaluate the tegument, musculature and mesentery of 102 specimens of Hoplerytrinus unitaeniatus, 104 of Hoplias malabaricus and 101 of Pygocentrus nattereri, from Arari Lake, Marajó Island, State of Pará, Brazil. Were identified the nematodes Contracaecum sp., Eustrongylides sp. and Procamallanus sp. Contracaecum sp. was the most prevalent, with rates of 84.31% (H. unitaeniatus, 95.19% (H. malabaricus, and 89.11% (P. nattereri. The highest prevalences of Eustrongylides sp. occurred in H. unitaeniatus (56.86% and H. malabaricus (53.84%. Procamallanus sp. was only collected in the mesentery. Specimens of Eustrongylides sp. collected from the musculature were 91.9% of its population. Among the nematodes found in the mesentery, 98.34% were Contracaecum sp. with a mean intensity (MI of 7.92 ± 8.11 (H. unitaeniatus, 8.49 ± 8.34 (H. malabaricus and 7 ± 6.40 (P. nattereri. Contracaecum sp. presented the highest MI (8.49 ± 8.34 and mean abundance (8.09 ± 8.34. The highest MI values were observed in the mesentery. Eustrongylides sp. presented MI of 2.65 ± 3.21 (H. unitaeniatus, 3.41 ± 3.27 (H. malabaricus and 2.17 ± 1.18 (P. nattereri. Nematodes with zoonotic potential that were found with high prevalence, shows the importance of actions by the health authorities.Examinou-se o tegumento, mesentério e musculatura de 102 espécimes de Hoplerytrinus unitaeniatus, 104 de Hoplias malabaricus e 101 de Pygocentrus nattereri, do Lago Arari, Ilha do Marajó, Estado do Pará, Brasil. Foram identificados os nematóides Contracaecum sp., Eustrongylides sp. e Procamallanus sp. nas três espécies de peixes. Contracaecum sp. foi o mais prevalente, com índices de 84,31% (H. unitaeniatus, 95,19% (H. malabaricus e 89,11% (P. nattereri. As maiores prevalências de Eustrongylides sp. foram observadas em H. unitaeniatus (56,86% e H. malabaricus (53,84%. Procamallanus sp. só foi coletado no mesentério, sendo o sítio de infec

  12. Emulsion stability: determination from turbidity

    Energy Technology Data Exchange (ETDEWEB)

    Reddy, S.R.; Fogler, H.S.

    1981-01-01

    The relationship between particle size and concentration and turbidity has been developed for a polydispersed system. The stability of acoustically prepared emulsions of C36H74 in water were determined from turbidimetry and found to be in agreement with the stability determined by the freezing method. The turbidimetry method can be used for determining the stability of various emulsions easily and inexpensively. 11 references.

  13. Radiohumeral stability to forced translation

    DEFF Research Database (Denmark)

    Jensen, Steen Lund; Olsen, Bo Sanderhoff; Seki, Atsuhito

    2002-01-01

    Radiohumeral stability to forced translation was experimentally analyzed in 8 osteocartilaginous joint preparations. The joints were dislocated in 8 centrifugal directions at 12 different combinations of joint flexion and rotation while a constant joint compression force of 23 N was applied....... Stability was measured as the maximum resistance to translation. On average, the specimens could resist a transverse force of 16.4 N (range, 13.0-19.1 N). Stability was greater in some directions than in others. Rotating the joint changed the direction at which stability was greatest, whereas joint flexion...

  14. Control of Strongyloides westeri by nematophagous fungi after passage through the gastrointestinal tract of donkeys Controle de Strongyloides westeri por fungos nematófagos após trânsito gastrintestinal em jumentas

    Directory of Open Access Journals (Sweden)

    Juliana Milani Araujo

    2012-06-01

    Full Text Available Strongyloides westeri is the most prevalent nematode among equines aged up to four months and causes gastrointestinal disorders. The objective of this study was to observe the control of infective S. westeri larvae (L3 by the nematophagous fungi Duddingtonia flagrans (AC001 and Monacrosporium thaumasium (NF34 after passage through the gastrointestinal tract of female donkeys. Twelve dewormed female donkeys that were kept in stables were used. Two treatment groups each comprising four animals received orally 100 g of pellets made of sodium alginate matrix containing a mycelial mass of either D. flagrans (AC001 or M. thaumasium (NF34. The control group consisted of four animals that received pellets without fungus. Feces samples were then collected from the animal groups at different times (after 12, 24, 48 and 72 hours. These feces were placed in Petri dishes containing 2% water-agar medium and 1000 L3 of S. westeri. AC001 and NF34 isolates showed the ability to destroy the L3, after gastrointestinal transit, thus demonstrating their viability and predatory activity.O Strongyloides westeri é o nematóide de maior prevalência entre equídeos com idade até quatro meses, causando distúrbios gastrintestinais. O objetivo do presente trabalho foi observar o controle de larvas infectantes (L3 de Strongyloides westeri pelos fungos nematófagos Duddingtonia flagrans (AC001 e Monacrosporium thaumasium (NF34 após trânsito gastrintestinal em jumentas. Foram utilizadas 12 jumentas, estabuladas e previamente vermifugadas. A seguir, dois grupos tratados, contendo cada um 4 animais receberam por via oral 100 g de péletes em matriz de alginato de sódio, contendo massa miceliana dos fungos D. flagrans (AC001 ou M. thaumasium (NF34. O grupo controle foi constituído de 4 animais que receberam péletes sem fungo. A seguir, amostras de fezes dos grupos de animais foram coletadas em distintos intervalos de horas (12, 24, 48 e 72. Essas fezes foram vertidas em

  15. An Adaptive Deadbeat Stabilizer for Power System Dynamic Stability

    OpenAIRE

    Rajkumar, V

    1989-01-01

    This paper discusses an adaptive deadbeat stabilizer to improve power system damping. The method involves normalized recursive least squares estimation to yield a reduced order state space model of the power system. This reduced order model is used to design the required deadbeat stabilizer recursively, along with an adaptive observer to estimate the unknown states.

  16. Optimal allosteric stabilization sites using contact stabilization analysis.

    Science.gov (United States)

    Dickson, Alex; Bailey, Christopher T; Karanicolas, John

    2017-06-05

    Proteins can be destabilized by a number of environmental factors such as temperature, pH, and mutation. The ability to subsequently restore function under these conditions by adding small molecule stabilizers, or by introducing disulfide bonds, would be a very powerful tool, but the physical principles that drive this stabilization are not well understood. The first problem lies is in choosing an appropriate binding site or disulfide bond location to best confer stability to the active site and restore function. Here, we present a general framework for predicting which allosteric binding sites correlate with stability in the active site. Using the Karanicolas-Brooks Gō-like model, we examine the dynamics of the enzyme β-glucuronidase using an Umbrella Sampling method to thoroughly sample the conformational landscape. Each intramolecular contact is assigned a score termed a "stabilization factor" that measures its correlation with structural changes in the active site. We have carried out this analysis for three different scaling strengths for the intramolecular contacts, and we examine how the calculated stabilization factors depend on the ensemble of destabilized conformations. We further examine a locally destabilized mutant of β-glucuronidase that has been characterized experimentally, and show that this brings about local changes in the stabilization factors. We find that the proximity to the active site is not sufficient to determine which contacts can confer active site stability. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

  17. Stabilized thermally compensated mirror

    International Nuclear Information System (INIS)

    Dunn, C. III; Tobin, R.D.; Bergstreser, N.E.; Heinz, T.A.

    1975-01-01

    A thermally compensated mirror is described that is formed by a laminated structure. The structure is comprised of a front plate having a reflective front surface and having a plurality of grooves formed in the rear surface for conducting coolant fluid in heat exchanging relation with said reflective surface, a rear plate having coolant inlet and coolant outlet openings extending therethrough, a minimum temperature plate interposed between said front and rear plates and formed with a plurality of coolant distribution passageways coupled to receive coolant fluid from said coolant inlet and oriented to distribute said coolant fluid in a manner to establish a minimum temperature plane parallel to said reflective surface, a temperature stabilization plate interposed between said front plate and said minimum temperature plate and formed with a plurality of coolant distribution channels coupled to receive said coolant fluid after said coolant fluid has passed in heat exchanging relation with said reflective surface and oriented to distribute said coolant fluid in a manner to establish a uniform temperature plane parallel to said reflective surface, and means for circulating said coolant fluid through said structure in a predetermined path. (U.S.)

  18. Ferrocyanide tank waste stability

    International Nuclear Information System (INIS)

    Fowler, K.D.

    1993-01-01

    Ferrocyanide wastes were generated at the Hanford Site during the mid to late 1950s as a result of efforts to create more tank space for the storage of high-level nuclear waste. The ferrocyanide process was developed to remove 137 CS from existing waste and newly generated waste that resulted from the recovery of valuable uranium in Hanford Site waste tanks. During the course of research associated with the ferrocyanide process, it was recognized that ferrocyanide materials, when mixed with sodium nitrate and/or sodium nitrite, were capable of violent exothermic reaction. This chemical reactivity became an issue in the 1980s, when safety issues associated with the storage of ferrocyanide wastes in Hanford Site tanks became prominent. These safety issues heightened in the late 1980s and led to the current scrutiny of the safety issues associated with these wastes, as well as current research and waste management programs. Testing to provide information on the nature of possible tank reactions is ongoing. This document supplements the information presented in Summary of Single-Shell Tank Waste Stability, WHC-EP-0347, March 1991 (Borsheim and Kirch 1991), which evaluated several issues. This supplement only considers information particular to ferrocyanide wastes

  19. Stabilizing Waste Materials for Landfills

    Science.gov (United States)

    Environmental Science and Technology, 1977

    1977-01-01

    The test procedures used to evaluate the suitability of landfilled materials of varying stability and to determine the leachate from such materials are reviewed. A process for stabilizing a mixture of sulfur dioxide sludge, fly ash, and bottom ash with lime and other additives for deposition in landfills is detailed. (BT)

  20. BWR Stability Issues in Japan

    Directory of Open Access Journals (Sweden)

    Hideaki Ikeda

    2008-01-01

    Full Text Available The present paper reviews activates relevant to the boiling water reactor (BWR stability phenomenon, which has a coupled neutronic and thermal-hydraulic nature, from the viewpoint of model and code developments and their applications to the BWR stability solution methodology in Japan.

  1. Exponential Stabilization of Underactuated Vehicles

    Energy Technology Data Exchange (ETDEWEB)

    Pettersen, K.Y.

    1996-12-31

    Underactuated vehicles are vehicles with fewer independent control actuators than degrees of freedom to be controlled. Such vehicles may be used in inspection of sub-sea cables, inspection and maintenance of offshore oil drilling platforms, and similar. This doctoral thesis discusses feedback stabilization of underactuated vehicles. The main objective has been to further develop methods from stabilization of nonholonomic systems to arrive at methods that are applicable to underactuated vehicles. A nonlinear model including both dynamics and kinematics is used to describe the vehicles, which may be surface vessels, spacecraft or autonomous underwater vehicles (AUVs). It is shown that for a certain class of underactuated vehicles the stabilization problem is not solvable by linear control theory. A new stability result for a class of homogeneous time-varying systems is derived and shown to be an important tool for developing continuous periodic time-varying feedback laws that stabilize underactuated vehicles without involving cancellation of dynamics. For position and orientation control of a surface vessel without side thruster a new continuous periodic feedback law is proposed that does not cancel any dynamics, and that exponentially stabilizes the origin of the underactuated surface vessel. A further issue considered is the stabilization of the attitude of an AUV. Finally, the thesis discusses stabilization of both position and attitude of an underactuated AUV. 55 refs., 28 figs.

  2. Stability of Polymer Solar Cells

    DEFF Research Database (Denmark)

    Jørgensen, Mikkel; Norrman, Kion; Gevorgyan, Suren

    2012-01-01

    Organic photovoltaics (OPVs) evolve in an exponential manner in the two key areas of efficiency and stability. The power conversion efficiency (PCE) has in the last decade been increased by almost a factor of ten approaching 10%. A main concern has been the stability that was previously measured ...

  3. Project Management Plan Solution Stabilization

    Energy Technology Data Exchange (ETDEWEB)

    SATO, P.K.

    1999-08-31

    This plan presents the overall objectives, description, justification and planning for the Plutonium Finishing Plant (PFP) Solutions Stabilization subproject. The intent of this plan is to describe how this project will be managed and integrated with other facility stabilization and deactivation activities. This plan supplements the overall integrated plan presented in the Integrated Project Management Plan (IPMP) for the Plutonium Finishing Plant Stabilization and Deactivation Project, HNF-3617. This project plan is the top-level definitive project management document for the PFP Solution Stabilization subproject. It specifies the technical, schedule, requirements and the cost baselines to manage the execution of the Solution Stabilization subproject. Any deviations to the document must be authorized through the appropriate change control process.

  4. Project Management Plan Solution Stabilization

    International Nuclear Information System (INIS)

    SATO, P.K.

    1999-01-01

    This plan presents the overall objectives, description, justification and planning for the Plutonium Finishing Plant (PFP) Solutions Stabilization subproject. The intent of this plan is to describe how this project will be managed and integrated with other facility stabilization and deactivation activities. This plan supplements the overall integrated plan presented in the Integrated Project Management Plan (IPMP) for the Plutonium Finishing Plant Stabilization and Deactivation Project, HNF-3617. This project plan is the top-level definitive project management document for the PFP Solution Stabilization subproject. It specifies the technical, schedule, requirements and the cost baselines to manage the execution of the Solution Stabilization subproject. Any deviations to the document must be authorized through the appropriate change control process

  5. Stochastic stabilization of cosmological photons

    International Nuclear Information System (INIS)

    Dettmann, C P; Keating, J P; Prado, S D

    2004-01-01

    The stability of photon trajectories in models of the universe that have constant spatial curvature is determined by the sign of the curvature: they are exponentially unstable if the curvature is negative and stable if it is positive or zero. We demonstrate that random fluctuations in the curvature provide an additional stabilizing mechanism. This mechanism is analogous to the one responsible for stabilizing the stochastic Kapitsa pendulum. When the mean curvature is negative it is capable of stabilizing the photon trajectories; when the mean curvature is zero or positive it determines the characteristic frequency with which neighbouring trajectories oscillate about each other. In constant negative curvature models of the universe that have compact topology, exponential instability implies chaos (e.g. mixing) in the photon dynamics. We discuss some consequences of stochastic stabilization in this context. (letter to the editor)

  6. Dispersion stability of thermal nanofluids

    Directory of Open Access Journals (Sweden)

    Fan Yu

    2017-10-01

    Full Text Available Thermal nanofluids, the engineered fluids with dispersed functional nanoparticles, have exhibited extraordinary thermophysical properties and added functionalities, and thus have enabled a broad range of important applications. The poor dispersion stability of thermal nanofluids, however, has been considered as a long-existing issue that limits their further development and practical application. This review overviews the recent efforts and progresses in improving the dispersion stability of thermal nanofluids such as mechanistic understanding of dispersion behavior of nanofluids, examples of both water-based and oil-based nanofluids, strategies to stabilize nanofluids, and characterization techniques for dispersion behavior of nanofluids. Finally, on-going research needs, and possible solutions to research challenges and future research directions in exploring stably dispersed thermal nanofluids are discussed. Keywords: Thermal nanofluids, Dispersion, Aggregation, Electrostatic stabilization, Steric stabilization

  7. Magnetohydodynamics stability of compact stellarators

    International Nuclear Information System (INIS)

    Fu, G.Y.; Ku, L.P.; Cooper, W.A.; Hirshman, S.H.

    2000-01-01

    Recent stability results of external kink modes and vertical modes in compact stellarators are presented. The vertical mode is found to be stabilized by externally generated poloidal flux. A simple stability criterion is derived in the limit of large aspect ratio and constant current density. For a wall at infinite distance from the plasma, the amount of external flux needed for stabilization is given by Fi = (k2 minus k)=(k2 + 1), where k is the axisymmetric elongation and Fi is the fraction of the external rotational transform. A systematic parameter study shows that the external kink mode in QAS can be stabilized at high beta (approximately 5%) without a conducting wall by magnetic shear via 3D shaping. It is found that external kinks are driven by both parallel current and pressure gradient. The pressure contributes significantly to the overall drive through the curvature term and the Pfirsch-Schluter current

  8. Protein stability, flexibility and function

    DEFF Research Database (Denmark)

    Teilum, Kaare; Olsen, Johan G; Kragelund, Birthe B

    2011-01-01

    Proteins rely on flexibility to respond to environmental changes, ligand binding and chemical modifications. Potentially, a perturbation that changes the flexibility of a protein may interfere with its function. Millions of mutations have been performed on thousands of proteins in quests...... for a delineation of the molecular details of their function. Several of these mutations interfered with the binding of a specific ligand with a concomitant effect on the stability of the protein scaffold. It has been ambiguous and not straightforward to recognize if any relationships exist between the stability...... of a protein and the affinity for its ligand. In this review, we present examples of proteins where changes in stability results in changes in affinity and of proteins where stability and affinity are uncorrelated. We discuss the possibility for a relationship between stability and binding. From the data...

  9. Montmorillonite stability - experimental results

    International Nuclear Information System (INIS)

    Karnland, Ola; Birgersson, Martin; Olsson, Siv

    2012-01-01

    Document available in extended abstract form only. Several repository concepts for spent nuclear fuel comprise a bentonite buffer which encloses the fuel containers. The function of this bentonite buffer is critically dependent on the properties of the swelling mineral in the bentonite, which typically is montmorillonite in commercial high quality bentonites. The physical and chemical properties of the montmorillonite in bentonites have consequently been studied in various types of analyses in several countries, and the results have been the basis for the design of the bentonite buffer with respect to size, degree of compaction etc (SKB TR-10-47). Significant changes in the montmorillonite structure with time may change the properties of the bentonite buffer and jeopardize the isolating function. In nature, illite is the most common alteration product from montmorillonite, and a 50% alteration reduces, for instance, the swelling pressure by one order of magnitude. Fortunately, the process is very slow at typical repository temperatures, and also in the perspective of repository life-time no significant alteration is expected according to the available kinetic models. The models are, however, based on laboratory batch experiments performed at temperatures, which by necessity are much higher than what is planned for in a repository. Alternatively, the models are based on natural montmorillonite-to-illite alteration in e.g. deep sediments. In both cases there are divergences from repository conditions which limit the arguments for the bentonite buffer stability. The mechanism by which the montmorillonite-to-illite reaction takes place is not fully understood, but the overall process may be represented by the following schematic reaction: Na + montmorillonite + K + + Al 3+ → illite + SiO 2 + Na + . Aluminum may be supplied from the bentonite itself, but potassium has to be transported to the buffer from an external source in order to give a significant alteration in

  10. New stability and stabilization for switched neutral control systems

    International Nuclear Information System (INIS)

    Xiong Lianglin; Zhong Shouming; Ye Mao; Wu Shiliang

    2009-01-01

    This paper concerns stability and stabilization issues for switched neutral systems and presents new classes of piecewise Lyapunov functionals and multiple Lyapunov functionals, based on which, two new switching rules are introduced to stabilize the neutral systems. One switching rule is designed from the solution of the so-called Lyapunov-Metzler linear matrix inequalities. The other is based on the determination of average dwell time computed from a new class of linear matrix inequalities (LMIs). And then, state-feedback control is derived for the switched neutral control system mainly based on the state switching rules. Finally, three examples are given to demonstrate the effectiveness of the proposed method.

  11. Quantifying Stability in Complex Networks: From Linear to Basin Stability

    Science.gov (United States)

    Kurths, Jürgen

    The human brain, power grids, arrays of coupled lasers and the Amazon rainforest are all characterized by multistability. The likelihood that these systems will remain in the most desirable of their many stable states depends on their stability against significant perturbations, particularly in a state space populated by undesirable states. Here we claim that the traditional linearization-based approach to stability is in several cases too local to adequately assess how stable a state is. Instead, we quantify it in terms of basin stability, a new measure related to the volume of the basin of attraction. Basin stability is non-local, nonlinear and easily applicable, even to high-dimensional systems. It provides a long-sought-after explanation for the surprisingly regular topologies of neural networks and power grids, which have eluded theoretical description based solely on linear stability. Specifically, we employ a component-wise version of basin stability, a nonlinear inspection scheme, to investigate how a grid's degree of stability is influenced by certain patterns in the wiring topology. Various statistics from our ensemble simulations all support one main finding: The widespread and cheapest of all connection schemes, namely dead ends and dead trees, strongly diminish stability. For the Northern European power system we demonstrate that the inverse is also true: `Healing' dead ends by addition of transmission lines substantially enhances stability. This indicates a crucial smart-design principle for tomorrow's sustainable power grids: add just a few more lines to avoid dead ends. Further, we analyse the particular function of certain network motifs to promote the stability of the system. Here we uncover the impact of so-called detour motifs on the appearance of nodes with a poor stability score and discuss the implications for power grid design. Moreover, it will be shown that basin stability enables uncovering the mechanism for explosive synchronization and

  12. Stability of dispersions in polar organic media. I. Electrostatic stabilization

    NARCIS (Netherlands)

    Rooy, N. de; Bruyn, P.L. de; Overbeek, J.Th.G.

    Electrostatically stabilized sols of silver, silver iodide, α-goethite, and copper phthalocyanine in methanol, ethanol, isopropanol, and acetone have been prepared and characterized. Coagulation concentrations with electrolytes of various charge numbers have been determined in water, in organic

  13. Stability indicators in network reconstruction.

    Directory of Open Access Journals (Sweden)

    Michele Filosi

    Full Text Available The number of available algorithms to infer a biological network from a dataset of high-throughput measurements is overwhelming and keeps growing. However, evaluating their performance is unfeasible unless a 'gold standard' is available to measure how close the reconstructed network is to the ground truth. One measure of this is the stability of these predictions to data resampling approaches. We introduce NetSI, a family of Network Stability Indicators, to assess quantitatively the stability of a reconstructed network in terms of inference variability due to data subsampling. In order to evaluate network stability, the main NetSI methods use a global/local network metric in combination with a resampling (bootstrap or cross-validation procedure. In addition, we provide two normalized variability scores over data resampling to measure edge weight stability and node degree stability, and then introduce a stability ranking for edges and nodes. A complete implementation of the NetSI indicators, including the Hamming-Ipsen-Mikhailov (HIM network distance adopted in this paper is available with the R package nettools. We demonstrate the use of the NetSI family by measuring network stability on four datasets against alternative network reconstruction methods. First, the effect of sample size on stability of inferred networks is studied in a gold standard framework on yeast-like data from the Gene Net Weaver simulator. We also consider the impact of varying modularity on a set of structurally different networks (50 nodes, from 2 to 10 modules, and then of complex feature covariance structure, showing the different behaviours of standard reconstruction methods based on Pearson correlation, Maximum Information Coefficient (MIC and False Discovery Rate (FDR strategy. Finally, we demonstrate a strong combined effect of different reconstruction methods and phenotype subgroups on a hepatocellular carcinoma miRNA microarray dataset (240 subjects, and we

  14. Radiochemical stability of radiopharmaceutical preparations

    International Nuclear Information System (INIS)

    Martins, Patricia de A.; Silva, Jose L. da; Ramos, Marcelo P.S.; Oliveira, Ideli M. de; Felgueiras, Carlos F.; Herrerias, Rosana; Zapparoli Junior, Carlos L.; Mengatti, Jair; Fukumori, Neuza T.O.; Matsuda, Margareth M.N.

    2011-01-01

    The 'in vitro' stability studies of the radiopharmaceutical preparations are an essential requirement for routine practice in nuclear medicine and are an important parameter for evaluating the quality, safety and efficacy required for the sanitary registration of pharmaceutical products. Several countries have published guidelines for the evaluation of pharmaceutical stability. In Brazil, the stability studies should be conducted according to the Guide for Conducting Stability Studies published in the Resolution-RE n. 1, of 29th July 2005. There are also for radiopharmaceutical products, two specific resolutions: RDC-63 regulates the Good Manufacturing Practices for Radiopharmaceuticals and RDC-64 provides the Registration of Radiopharmaceuticals, both published on the 18th December 2009. The radiopharmaceutical stability is defined as the time during which the radioisotope can be safely used for the intended purpose. The radiochemical stability can be affected by a variety of factors, including storage temperature, amount of radioactivity, radioactive concentration, presence or absence of antioxidants or other stabilizing agents. The radiochemical stability studies must be established under controlled conditions determined by the effective use of the product. The aim of this work was to evaluate the radiochemical stability of labeled molecules with 131 I, 123 I, 153 Sm, 18 F, 51 Cr, 177 Lu and 111 In as well as 67 Ga and 201 Tl radiopharmaceuticals. Radiochemical purity was evaluated after production and in the validity period, with the maximum activity and in the recommended storage conditions. The analyses were carried out by thin-layer silica gel plate, paper chromatography and gel chromatography. The experimental results showed to be in accordance with the specified limits for all the analysed products. (author)

  15. MATLAB Stability and Control Toolbox Trim and Static Stability Module

    Science.gov (United States)

    Kenny, Sean P.; Crespo, Luis

    2012-01-01

    MATLAB Stability and Control Toolbox (MASCOT) utilizes geometric, aerodynamic, and inertial inputs to calculate air vehicle stability in a variety of critical flight conditions. The code is based on fundamental, non-linear equations of motion and is able to translate results into a qualitative, graphical scale useful to the non-expert. MASCOT was created to provide the conceptual aircraft designer accurate predictions of air vehicle stability and control characteristics. The code takes as input mass property data in the form of an inertia tensor, aerodynamic loading data, and propulsion (i.e. thrust) loading data. Using fundamental nonlinear equations of motion, MASCOT then calculates vehicle trim and static stability data for the desired flight condition(s). Available flight conditions include six horizontal and six landing rotation conditions with varying options for engine out, crosswind, and sideslip, plus three take-off rotation conditions. Results are displayed through a unique graphical interface developed to provide the non-stability and control expert conceptual design engineer a qualitative scale indicating whether the vehicle has acceptable, marginal, or unacceptable static stability characteristics. If desired, the user can also examine the detailed, quantitative results.

  16. Stability of holonomic quantum computations

    International Nuclear Information System (INIS)

    Kuvshinov, V.I.; Kuzmin, A.V.

    2003-01-01

    We study the stability of holonomic quantum computations with respect to errors in assignment of control parameters. The general expression for fidelity is obtained. In the small errors limit the simple formulae for the fidelity decrease rate is derived

  17. Linear stability of tearing modes

    International Nuclear Information System (INIS)

    Cowley, S.C.; Kulsrud, R.M.; Hahm, T.S.

    1986-05-01

    This paper examines the stability of tearing modes in a sheared slab when the width of the tearing layer is much smaller than the ion Larmor radius. The ion response is nonlocal, and the quasineutrality retains its full integal form. An expansion procedure is introduced to solve the quasineutrality equation in powers of the width of the tearing layer over the ion Larmor radius. The expansion procedure is applied to the collisionless and semi-collisional tearing modes. The first order terms in the expansion we find to be strongly stabilizing. The physics of the mode and of the stabilization is discussed. Tearing modes are observed in experiments even though the slab theory predicts stability. It is proposed that these modes grow from an equilibrium with islands at the rational surfaces. If the equilibrium islands are wider than the ion Larmor radius, the mode is unstable when Δ' is positive

  18. Reliability criteria for voltage stability

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, Carson W.; Silverstein, Brian L. [Bonneville Power Administration, Portland, OR (United States)

    1994-12-31

    In face of costs pressures, there is need to allocate scare resources more effectively in order to achieve voltage stability. This naturally leads to development of probabilistic criteria and notions of rick management. In this paper it is presented a discussion about criteria for long term voltage stability limited to the case in which the time frames are topically several minutes. (author) 14 refs., 1 fig.

  19. Financial Stability and Financial Inclusion

    OpenAIRE

    Peter J. Morgan; Victor Pontines

    2014-01-01

    Developing economies are seeking to promote financial inclusion, i.e., greater access to financial services for low-income households and firms, as part of their overall strategies for economic and financial development. This raises the question of whether financial stability and financial inclusion are, broadly speaking, substitutes or complements. In other words, does the move toward greater financial inclusion tend to increase or decrease financial stability? A number of studies have sugge...

  20. Market liquidity and financial stability.

    OpenAIRE

    Crockett, A.

    2008-01-01

    Stability in financial institutions and in financial markets are closely intertwined. Banks and other financial institutions need liquid markets through which to conduct risk management. And markets need the back-up liquidity lines provided by financial institutions. Market liquidity depends not only on objective, exogenous factors, but also on endogenous market dynamics. Central banks responsible for systemic stability need to consider how far their traditional responsibility for the health ...