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Sample records for surface van der

  1. Poisson-Boltzmann Calculations: van der Waals or Molecular Surface?

    Science.gov (United States)

    Pang, Xiaodong; Zhou, Huan-Xiang

    2013-01-01

    The Poisson-Boltzmann equation is widely used for modeling the electrostatics of biomolecules, but the calculation results are sensitive to the choice of the boundary between the low solute dielectric and the high solvent dielectric. The default choice for the dielectric boundary has been the molecular surface, but the use of the van der Waals surface has also been advocated. Here we review recent studies in which the two choices are tested against experimental results and explicit-solvent calculations. The assignment of the solvent high dielectric constant to interstitial voids in the solute is often used as a criticism against the van der Waals surface. However, this assignment may not be as unrealistic as previously thought, since hydrogen exchange and other NMR experiments have firmly established that all interior parts of proteins are transiently accessible to the solvent.

  2. Density-functional calculation of van der Waals forces for free-electron-like surfaces

    DEFF Research Database (Denmark)

    Hult, E.; Hyldgaard, P.; Rossmeisl, Jan;

    2001-01-01

    A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well as for the in......A recently proposed general density functional for asymptotic van der Waals forces is used to calculate van der Waals coefficients and reference-plane positions for realistic low-indexed Al surfaces. Results are given for a number of atoms and molecules outside the surfaces, as well...... as for the interaction between the surfaces themselves. The densities and static image-plane positions that are needed as input in the van der Waals functional are calculated self-consistently within density-functional theory using the generalized-gradient approximation, pseudopotentials, and plane waves. This study...... shows that the van der Waals density functional is applicable to realistic surfaces. The need for physically correct surface models, especially for open surfaces, is also illustrated. Finally the parameters for the anisotropic interaction of O-2 with Al are calculated....

  3. Influence of ultrathin water layer on the van der Waals/Casimir force between gold surfaces

    NARCIS (Netherlands)

    Palasantzas, G.; Svetovoy, V. B.; van Zwol, P. J.

    In this paper we investigate the influence of ultrathin water layer (similar to 1-1.5 nm) on the van der Waals/Casimir force between gold surfaces. Adsorbed water is inevitably present on gold surfaces at ambient conditions as jump-up-to contact during adhesion experiments demonstrate. Calculations

  4. Competition of van der Waals and chemical forces on gold–sulfur surfaces and nanoparticles

    DEFF Research Database (Denmark)

    Reimers, Jeffrey R.; Ford, Michael J.; Marcuccio, Sebastian M.

    2017-01-01

    Chemists generally believe that covalent and ionic bonds form much stronger links between atoms than the van der Waals force does. However, this is not always so. We present cases in which van der Waals dispersive forces introduce new competitive bonding possibilities rather than just modulating...... traditional bonding scenarios. Although the new possibilities could arise from any soft–soft chemical interaction, we focus on bonding between gold atoms and alkyl or arylsulfur ligands, RS. Consideration of all the interactions at play in sulfur-protected gold surfaces and gold nanoparticles is necessary...

  5. Theoretical investigation of van der Waals forces between solid surfaces at nanoscales

    NARCIS (Netherlands)

    Kudryavtsev, Y.V.; Gelinck, E.R.M.; Fischer, H.R.

    2009-01-01

    A theoretical investigation of van der Waals forces acting between two solid silicon surfaces at separations from zero to approximately 20 nm is presented. We focused our efforts on the analysis of different factors that can cause deviations from the classical pressure-distance dependence p ∼ 1/D3.

  6. Theoretical investigation of van der Waals forces between solid surfaces at nanoscales

    NARCIS (Netherlands)

    Kudryavtsev, Y.V.; Gelinck, E.R.M.; Fischer, H.R.

    2009-01-01

    A theoretical investigation of van der Waals forces acting between two solid silicon surfaces at separations from zero to approximately 20 nm is presented. We focused our efforts on the analysis of different factors that can cause deviations from the classical pressure-distance dependence p ∼ 1/D3.

  7. van der Waals torque

    Science.gov (United States)

    Esquivel-Sirvent, Raul; Schatz, George

    2014-03-01

    The theory of generalized van der Waals forces by Lifshtz when applied to optically anisotropic media predicts the existence of a torque. In this work we present a theoretical calculation of the van der Waals torque for two systems. First we consider two isotropic parallel plates where the anisotropy is induced using an external magnetic field. The anisotropy will in turn induce a torque. As a case study we consider III-IV semiconductors such as InSb that can support magneto plasmons. The calculations of the torque are done in the Voigt configuration, that occurs when the magnetic field is parallel to the surface of the slabs. The change in the dielectric function as the magnetic field increases has the effect of decreasing the van der Waals force and increasing the torque. Thus, the external magnetic field is used to tune both the force and torque. The second example we present is the use of the torque in the non retarded regime to align arrays of nano particle slabs. The torque is calculated within Barash and Ginzburg formalism in the nonretarded limit, and is quantified by the introduction of a Hamaker torque constant. Calculations are conducted between anisotropic slabs of materials including BaTiO3 and arrays of Ag nano particles. Depending on the shape and arrangement of the Ag nano particles the effective dielectric function of the array can be tuned as to make it more or less anisotropic. We show how this torque can be used in self assembly of arrays of nano particles. ref. R. Esquivel-Sirvent, G. C. Schatz, Phys. Chem C, 117, 5492 (2013). partial support from DGAPA-UNAM.

  8. Finite-size nanowire at a surface: Unconventional power laws of the van der Waals interaction

    Science.gov (United States)

    Makhnovets, K. A.; Kolezhuk, A. K.

    2017-09-01

    We study the van der Waals interaction of a metallic or narrow-gap semiconducting nanowire with a surface, in the regime of intermediate wire-surface distances (vF/c )L ≪d ≪L or L ≪d ≪(c /vF)L , where L is the nanowire length, d is the distance to the surface, and vF is the characteristic velocity of nanowire electrons (for a metallic wire, it is the Fermi velocity). Our approach, based on the Luttinger liquid framework, allows one to analyze the dependence of the interaction on the interplay between the nanowire length, wire-surface distance, and characteristic length scales related to the spectral gap and temperature. We show that this interplay leads to nontrivial modifications of the power law that governs van der Waals forces, in particular to a nonmonotonic dependence of the power-law exponent on the wire-surface separation.

  9. van der Waals interaction of a neutral atom with the surface of a metal or dielectric nanosphere

    Energy Technology Data Exchange (ETDEWEB)

    Schmidt, Regine; Chormaic, Sile Nic [Photonics Centre, Tyndall National Institute, Prospect Row, Cork (Ireland); Minogin, Vladimir G, E-mail: s.nicchormaic@ucc.ie [Institute of Spectroscopy Russ. Ac. of Sciences, 142190 Troitsk, Moscow region (Russian Federation)

    2011-01-14

    We analyse the van der Waals interaction of a neutral atom with the internal and external surfaces of either a metal or dielectric nanosphere. We derive closed analytical equations for the van der Waals interaction energy using an electrostatic approximation and show that the energy increases or decreases as a function of the atom's distance from the surface, depending on the surface curvature. For concave spherical surfaces, the van der Waals energy can increase by up to a factor of 6, while for convex surfaces it decreases by as much as a factor of 2, when compared to that obtained for a flat surface. The derived analytical equations are very simple and can be used for a comparison between theory and experimental measurements of the van der Waals constant, C{sub 3}.

  10. Surface Roughness and Material Optical Properties Influence on Casimir/van der Waals and Capillary Surface Forces

    NARCIS (Netherlands)

    Zwol, P.J. van; Palasantzas, G.

    2010-01-01

    Theory calculations using the Lifshitz theory and atomic force microscopy force measurements show that Casimir/van der Weals dispersive forces have a strong dependence on material optical properties and surface roughness. At separations below 100 nm the roughness effect is manifested through a

  11. Van der Waals-Casimir-Polder interaction of an atom with a composite surface

    CERN Document Server

    Eizner, Elad; Henkel, Carsten

    2012-01-01

    We study the dispersion interaction of the van der Waals and Casimir-Polder (vdW-CP) type between a neutral atom and the surface of a metal by allowing for nonlocal electrodynamics, i.e. electron diffusion. We consider two models: (i) bulk diffusion, and (ii) diffusion in a surface charge layer. In both cases the transition to a semiconductor is continuous as a function of the conductivity, unlike the case of a local model. The relevant parameter is the electric screening length and depends on the carrier diffusion constant. We find that for distances comparable to the screening length, vdW-CP data can distinguish between bulk and surface diffusion, hence it can be a sensitive probe for surface states.

  12. Exploring the van der Waals Atom-Surface attraction in the nanometric range

    CERN Document Server

    Fichet, M; Yarovitski, A; Todorov, P; Hamdi, I; Maurin, I; Saltiel, S; Sarkisyan, D; Gorza, M P; Bloch, D; Ducloy, M; Fichet, Mich\\`{e}le; Dutier, Gabriel; Yarovitski, Alexander; Todorov, Petko; Hamdi, Ismah\\`{e}ne; Maurin, Isabelle; Saltiel, Solomon; Sarkisyan, David; Gorza, Marie-Pascale; Bloch, Daniel; Ducloy, Martial

    2006-01-01

    The van der Waals atom-surface attraction, scaling as C3 z-3 for z the atom-surface distance, is expected to be valid for ~ 1-1000 nm, covering 8-10 orders of magnitudes in the interaction energy. Thanks to a Cs vapor nanocell, we analyze the spectroscopic modifications induced by the atom-surface attraction on the 6P3/2->6D5/2 transition. The C3 value, extracted independently for various thicknesses ranging from 40 nm to 130 nm, is found to be independent of the thickness. It agrees, but only within a factor of 2, with an elementary theoretical prediction, whose validity is discussed.

  13. Image method in the calculation of the van der Waals force between an atom and a conducting surface

    CERN Document Server

    Souza, Reinaldo de Melo e; Sigaud, C; Farina, C

    2012-01-01

    Initially, we make a detailed historical survey of van der Waals forces, collecting the main references on the subject. Then, we review a method recently proposed by Eberlein and Zietal to compute the dispersion van der Waals interaction between a neutral but polarizable atom and a perfectly conducting surface of arbitrary shape. This method has the advantage of relating the quantum problem to a corresponding classical one in electrostatics so that all one needs is to compute an appropriate Green function. We show how the image method of electrostatics can be conveniently used together with the Eberlein and Zietal mehtod (when the problem admits an image solution). We then illustrate this method in a couple of simple but important cases, including the atom-sphere system. Particularly, in our last example, we present an original result, namely, the van der Waals force between an atom and a boss hat made of a grounded conducting material.

  14. Image method in the calculation of the van der Waals force between an atom and a conducting surface

    Science.gov (United States)

    de Melo e Souza, Reinaldo; Kort-Kamp, W. J. M.; Sigaud, C.; Farina, C.

    2013-05-01

    After a brief survey of van der Waals forces, we review a method recently proposed by Eberlein and Zietal to compute the dispersion van der Waals interaction between a neutral but polarizable atom and a perfectly conducting surface of arbitrary shape. This method has the advantage of relating the quantum problem to a corresponding classical one in electrostatics in an enlightening way so that all one needs is to compute an appropriate Green function. We show how the image method of electrostatics can be conveniently used together with the Eberlein and Zietal method (when the image solution is known). We then illustrate this method in some simple but important cases, including the atom-sphere system. Finally, we present an original result for the van der Waals force between an atom and a boss hat made of a grounded conducting material.

  15. Effect of surface roughness on van der Waals and Casimir-Polder/Casimir attraction energies

    Science.gov (United States)

    Makeev, Maxim A.

    2017-09-01

    A theoretical model is devised to assess effects of surface roughness on dispersion interactions between macroscopic bodies, bounded by self-affine fractal surfaces and separated by a vacuum gap. The rough-surface profiles are described statistically by the saturation values of surface width and the correlation lengths; i.e., in terms of experimentally measurable quantities. The model devised takes into account the separation distance-dependent nature of dispersive interactions. The case of non-retarded van der Waals interactions, known to operate at smaller separation distances between the bodies, and that of retarded attractions, operative at larger separation length-scales, are treated separately in this work. Analytical formulae for the roughness corrections are deduced for the two aforementioned types of attractions. The model is employed to compute roughness corrections to interactions between an extended body, bounded by a self-affine surface, and: a) a point-like adherent; and b) a planar half-space. Furthermore, the roughness-induced corrections to dispersive interaction energies between half-spaces, both bounded by self-affine surfaces, are obtained under assumption that the corresponding surface profiles are not correlated. The predictions of the model are compared with some previously reported theoretical studies and available experimental data on the theme of dispersive adhesion between macroscopic bodies.

  16. Non-additivity of molecule-surface van der Waals potentials from force measurements.

    Science.gov (United States)

    Wagner, Christian; Fournier, Norman; Ruiz, Victor G; Li, Chen; Müllen, Klaus; Rohlfing, Michael; Tkatchenko, Alexandre; Temirov, Ruslan; Tautz, F Stefan

    2014-11-26

    Van der Waals (vdW) forces act ubiquitously in condensed matter. Despite being weak on an atomic level, they substantially influence molecular and biological systems due to their long range and system-size scaling. The difficulty to isolate and measure vdW forces on a single-molecule level causes our present understanding to be strongly theory based. Here we show measurements of the attractive potential between differently sized organic molecules and a metal surface using an atomic force microscope. Our choice of molecules and the large molecule-surface separation cause this attraction to be purely of vdW type. The experiment allows testing the asymptotic vdW force law and its validity range. We find a superlinear growth of the vdW attraction with molecular size, originating from the increased deconfinement of electrons in the molecules. Because such non-additive vdW contributions are not accounted for in most first-principles or empirical calculations, we suggest further development in that direction.

  17. Electronic Properties of Surfaces and Interfaces with Self-Consistent van der Waals Density Functional

    Science.gov (United States)

    Ferri, Nicola; Distasio, Robert A., Jr.; Car, Roberto; Tkatchenko, Alexandre; Scheffler, Matthias

    2014-03-01

    The long-range van der Waals (vdW) energy is only a small part of the total energy, hence it is typically assumed to have a minor influence on the electronic properties. Here, we address this question through a fully self-consistent (SC) implementation of the Tkatchenko-Scheffler (TS) density functional. The analysis of TS-vdWSC effects on electron density differences for atomic and molecular dimers reveals quantitative agreement with correlated densities obtained from ``gold standard'' coupled-cluster quantum-chemical calculations. In agreement with previous work, we find a very small overall contribution from self-consistency in the structure and stability of vdW-bound molecular complexes. However, TS-vdWSC (coupled with PBE functional) significantly affects electronic properties of coinage metal (111) surfaces, leading to an increase of up to 0.3 eV in the workfunction in agreement with experiments. Furthermore, vdW interactions visibly influence workfunctions in hybrid organic/metal interfaces, changing Pauli push-back and charge transfer contributions.

  18. Combined Effect of Surface Tension, Gravity and van der Waals Force Induced by a Non-Contact Probe Tip on the Shape of Liquid Surface

    Institute of Scientific and Technical Information of China (English)

    LIU Nan; BAI Yi-Long; XIA Meng-Fen; KE Fu-Jiu

    2005-01-01

    @@ Aiming at understanding how a liquid film on a substrate affects the atomic force microscopic image in experiments, we present an analytical representation of the shape of liquid surface under van der Waals interaction induced by a non-contact probe tip. The analytical expression shows good consistence with the corresponding numerical results. According to the expression, we find that the vertical scale of the liquid dome is mainly gov erned by a combination of van der Waals force, surface tension and probe tip radius, and is weekly related to gravity. However, its horizontal extension is determined by the capillary length.

  19. Five-body van der Waals interactions

    Science.gov (United States)

    Han, Jianing

    2017-06-01

    We report on the five-body repulsive and attractive van der Waals interactions between the strongly dipole-dipole coupled Rydberg states. Compared to four-body van der Waals interactions, five-body van der Waals interactions show more energy levels and more potential wells caused by avoided crossings. This research bridges the few-body physics and many-body physics. Other disciplines, such as chemistry, biology, and medical fields, will also benefit from better understanding van der Waals interactions.

  20. Fabrication and characterization of PbSe nanostructures on van der Waals surfaces of GaSe layered semiconductor crystals

    Science.gov (United States)

    Kudrynskyi, Z. R.; Bakhtinov, A. P.; Vodopyanov, V. N.; Kovalyuk, Z. D.; Tovarnitskii, M. V.; Lytvyn, O. S.

    2015-11-01

    The growth morphology, composition and structure of PbSe nanostructures grown on the atomically smooth, clean, nanoporous and oxidized van der Waals (0001) surfaces of GaSe layered crystals were studied by means of atomic force microscopy, x-ray diffractometry, photoelectron spectroscopy and Raman spectroscopy. Semiconductor heterostructures were grown by the hot-wall technique in vacuum. Nanoporous GaSe substrates were fabricated by the thermal annealing of layered crystals in a molecular hydrogen atmosphere. The irradiation of the GaSe(0001) surface by UV radiation was used to fabricate thin Ga2O3 layers with thickness clusters with a square or rectangular symmetry on the clean low-energy (0001) GaSe surface, and (001)-oriented growth of PbSe thin films takes place on this surface. Using this growth technique it is possible to grow PbSe nanostructures with different morphologies: continuous epitaxial layers with thickness quantum dots with a high lateral density (more than 1011 cm-2) on the oxidized van der Waals (0001) surfaces and faceted square pillar-like nanostructures with a low lateral density (˜108 cm-2) on the nanoporous GaSe substrates. We exploit the ‘vapor-liquid-solid’ growth with low-melting metal (Ga) catalyst of PbSe crystalline branched nanostructures via a surface-defect-assisted mechanism.

  1. Van der Waals black hole

    Directory of Open Access Journals (Sweden)

    Aruna Rajagopal

    2014-10-01

    Full Text Available In the context of extended phase space, where the negative cosmological constant is treated as a thermodynamic pressure in the first law of black hole thermodynamics, we find an asymptotically AdS metric whose thermodynamics matches exactly that of the Van der Waals fluid. We show that as a solution of Einstein's equations, the corresponding stress energy tensor obeys (at least for certain range of metric parameters all three weak, strong, and dominant energy conditions.

  2. Surface and interface of epitaxial CdTe film on CdS buffered van der Waals mica substrate

    Science.gov (United States)

    Yang, Y.-B.; Seewald, L.; Mohanty, Dibyajyoti; Wang, Y.; Zhang, L. H.; Kisslinger, K.; Xie, Weiyu; Shi, J.; Bhat, I.; Zhang, Shengbai; Lu, T.-M.; Wang, G.-C.

    2017-08-01

    Single crystal CdTe films are desirable for optoelectronic device applications. An important strategy of creating films with high crystallinity is through epitaxial growth on a proper single crystal substrate. We report the metalorganic chemical vapor deposition of epitaxial CdTe films on the CdS/mica substrate. The epitaxial CdS film was grown on a mica surface by thermal evaporation. Due to the weak van der Waals forces, epitaxy is achieved despite the very large interface lattice mismatch between CdS and mica (∼21-55%). The surface morphology of mica, CdS and CdTe were quantified by atomic force microscopy. The near surface structures, orientations and texture of CdTe and CdS films were characterized by the unique reflection high-energy electron diffraction surface pole figure technique. The interfaces of CdTe and CdS films and mica were characterized by X-ray pole figure technique and transmission electron microscopy. The out-of-plane and in-plane epitaxy of the heteroepitaxial films stack are determined to be CdTe(111)//CdS(0001)//mica(001) and [ 1 bar2 1 bar]CdTe//[1 bar100]CdS//[010]mica, respectively. The measured photoluminescence (PL), time resolved PL, photoresponse, and Hall mobility of the CdTe/CdS/mica indicate quality films. The use of van der Waals surface to grow epitaxial CdTe/CdS films offers an alternative strategy towards infrared imaging and solar cell applications.

  3. Effect of van der Waals interactions on the chemisorption and physisorption of phenol and phenoxy on metal surfaces

    Science.gov (United States)

    Peköz, Rengin; Donadio, Davide

    2016-09-01

    The adsorption of phenol and phenoxy on the (111) surface of Au and Pt has been investigated by density functional theory calculations with the conventional PBE functional and three different non-local van der Waals (vdW) exchange and correlation functionals. It is found that both phenol and phenoxy on Au(111) are physisorbed. In contrast, phenol on Pt(111) presents an adsorption energy profile with a stable chemisorption state and a weakly metastable physisorbed precursor. While the use of vdW functionals is essential to determine the correct binding energy of both chemisorption and physisorption states, the relative stability and existence of an energy barrier between them depend on the semi-local approximations in the functionals. The first dissociation mechanism of phenol, yielding phenoxy and atomic hydrogen, has been also investigated, and the reaction and activation energies of the resulting phenoxy on the flat surfaces of Au and Pt were discussed.

  4. Electronic Properties of Molecules and Surfaces with a Self-Consistent Interatomic van der Waals Density Functional

    Science.gov (United States)

    Ferri, Nicola; DiStasio, Robert A.; Ambrosetti, Alberto; Car, Roberto; Tkatchenko, Alexandre

    2015-05-01

    How strong is the effect of van der Waals (vdW) interactions on the electronic properties of molecules and extended systems? To answer this question, we derived a fully self-consistent implementation of the density-dependent interatomic vdW functional of Tkatchenko and Scheffler [Phys. Rev. Lett. 102, 073005 (2009)]. Not surprisingly, vdW self-consistency leads to tiny modifications of the structure, stability, and electronic properties of molecular dimers and crystals. However, unexpectedly large effects were found in the binding energies, distances, and electrostatic moments of highly polarizable alkali-metal dimers. Most importantly, vdW interactions induced complex and sizable electronic charge redistribution in the vicinity of metallic surfaces and at organic-metal interfaces. As a result, a substantial influence on the computed work functions was found, revealing a nontrivial connection between electrostatics and long-range electron correlation effects.

  5. Rememorant a Mies van der Rohe

    OpenAIRE

    Gómez Montenegro, Carlos

    1999-01-01

    Imatges del primer gratacels de Mies Van Der Rohe a través dels mitjans tècnics actuals. Imágenes del primer rascacielos de Mies Van Der Rohe através de los medios técnicos actuales. Peer Reviewed

  6. Dynamical and non-additive atomic van der Waals phases

    CERN Document Server

    Impens, François; Neto, Paulo A Maia

    2013-01-01

    We investigate dynamical corrections to the van der Waals phase induced by the non-unitary evolution of atomic waves propagating near a perfectly conducting surface. These corrections reflect the interplay between field retardation effects and the dynamics of the external atomic degrees of freedom. The dynamical atom-surface interaction phase shift contains both local and non-local contributions. We derive the local contributions and show that they are equivalent to coarse-graining the instantaneous van der Waals potential over the time scale corresponding to the round-trip travel time of light between atom and surface. We show that the non-local phase contributions are non-additive, and propose to use this property in a multiple-path van der Waals interferometer in order to isolate them from the standard (and much larger) quasi-static van der Waals phase.

  7. Quantitative relationships for the prediction of the vapor pressure of some hydrocarbons from the van der Waals molecular surface

    Directory of Open Access Journals (Sweden)

    Olariu Tudor

    2015-01-01

    Full Text Available A quantitative structure - property relationship (QSPR modeling of vapor pressure at 298.15 K, expressed as log (VP / Pa was performed for a series of 84 hydrocarbons (63 alkanes and 21 cycloalkanes using the van der Waals (vdW surface area, SW/Å2, calculated by the Monte Carlo method, as the molecular descriptor. The QSPR model developed from the subset of 63 alkanes (C1-C16, deemed as the training set, was successfully used for the prediction of the log (VP / Pa values of the 21 cycloalkanes, which was the external prediction (test subset. A QSPR model was also developed for a series composed of all 84 hydrocarbons. Both QSPR models were statistically tested for their ability to fit the data and for prediction. The results showed that the vdW molecular surface used as molecular descriptor (MD explains the variance of the majority of the log (VP / Pa values in this series of 84 hydrocarbons. This MD describes very well the intermolecular forces that hold neutral molecules together. The clear physical meaning of the molecular surface values, SW/Å2, could explain the success of the QSPR models obtained with a single structural molecular descriptor.

  8. Testing the distance-dependence of the van der Waals interaction between an atom and a surface through spectroscopy in a vapor nanocell

    CERN Document Server

    Laliotis, A; Todorov, P; Hamdi, I; Dutier, G; Yarovitski, A; Saltiel, S; Gorza, M P; Fichet, M; Ducloy, M; Bloch, D; Laliotis, Athanasdios; Maurin, Isabelle; Todorov, Petko; Hamdi, Ismah\\`{e}ne; Dutier, Gabriel; Yarovitski, Alexander; Saltiel, Solomon; Gorza, Marie-Pascale; Fichet, Mich\\`{e}le; Ducloy, Martial; Bloch, Daniel

    2007-01-01

    This paper presents our current measurements in a vapor nanocell aiming at a test of the distance-dependence of the atom-surface interaction, when simple asymptotic descriptions may turn to be not valid. A state-of-the-art of atom-surface interaction measurements is provided as an introduction, along with the comparison with the theory of the van der Waals (or Casimir-Polder) interaction; it is followed by a presentation of the most salient features of nanocell spectroscopy

  9. Professor Willem van der Angeliaan / Aive Sarjas

    Index Scriptorium Estoniae

    Sarjas, Aive

    2010-01-01

    Läänemaal Koluvere hooldekodus kord nädalas tegevusteraapia teenust osutavast väikesest šetlandi tõugu ruunast Willem van der Angeliaanist ning tegevusterapeudi Moonika Salumaa tegevusteraapias kasutatavatest teooriatest ja meetoditest

  10. Professor Willem van der Angeliaan / Aive Sarjas

    Index Scriptorium Estoniae

    Sarjas, Aive

    2010-01-01

    Läänemaal Koluvere hooldekodus kord nädalas tegevusteraapia teenust osutavast väikesest šetlandi tõugu ruunast Willem van der Angeliaanist ning tegevusterapeudi Moonika Salumaa tegevusteraapias kasutatavatest teooriatest ja meetoditest

  11. Effects of van der Waals Interactions in the Adsorption of Isooctane and Ethanol on Fe(100) Surfaces.

    Science.gov (United States)

    Bedolla, Pedro O; Feldbauer, Gregor; Wolloch, Michael; Eder, Stefan J; Dörr, Nicole; Mohn, Peter; Redinger, Josef; Vernes, András

    2014-08-07

    van der Waals (vdW) forces play a fundamental role in the structure and behavior of diverse systems. Because of development of functionals that include nonlocal correlation, it is possible to study the effects of vdW interactions in systems of industrial and tribological interest. Here we simulated within the framework of density functional theory (DFT) the adsorption of isooctane (2,2,4-trimethylpentane) and ethanol on an Fe(100) surface, employing various exchange-correlation functionals to take vdW forces into account. In particular, this paper discusses the effect of vdW forces on the magnitude of adsorption energies, equilibrium geometries, and their role in the binding mechanism. According to our calculations, vdW interactions increase the adsorption energies and reduce the equilibrium distances. Nevertheless, they do not influence the spatial configuration of the adsorbed molecules. Their effect on the electronic density is a nonisotropic, delocalized accumulation of charge between the molecule and the slab. In conclusion, vdW forces are essential for the adsorption of isooctane and ethanol on a bcc Fe(100) surface.

  12. Van der Waals Interactions and Exciton Condensation

    Science.gov (United States)

    Handel, P. H.; Kittel, C.

    1971-01-01

    It is shown that the van der Waals interaction can lead at low temperatures to a condensed state of excitons with properties in qualitative agreement with the observations of exciton droplets. Our calculation gives a binding energy of the correct sign and magnitude for the exciton condensate. In a diclectric medium, the strong enhancement of the exciton polarizability leads to a giant van der Waals interaction, and this interaction appears to make possible a condensed exciton phase. PMID:16591958

  13. van der Waals Heterostructures Grown by MBE

    Science.gov (United States)

    Hinkle, Christopher

    In this work, we demonstrate the high-quality MBE heterostructure growth of various layered 2D materials by van der Waals epitaxy (VDWE). The coupling of different types of van der Waals materials including transition metal dichalcogenide thin films (e.g., WSe2, WTe2, HfSe2) , insulating hexagonal boron nitride (h-BN), and topological insulators (e.g., Bi2Se3) allows for the fabrication of novel electronic devices that take advantage of unique quantum confinement and spin-based characteristics. The relaxed lattice-matching criteria of van der Waals epitaxy has allowed for high-quality heterostructure growth with atomically abrupt interfaces, allowing us to couple these materials based primarily on their band alignment and electronic properties. We will discuss the impact of sample preparation, surface reactivity, and lattice mismatch of various substrates (sapphire, graphene, TMDs, Bi2Se3) on the growth mode and quality of the films and will discuss our studies of substrate temperature and flux rates on the resultant growth and grain size. Structural and chemical characterization was conducted via reflection high energy electron diffraction (RHEED, X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning tunneling microscopy/spectroscopy (STM/S), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. Experimentally determined band alignments have been determined and compared with first-principles calculations allowing the design of novel low-power logic and magnetic memory devices. Initial results from the electrical characterization of these grown thin films and some simple devices will also be presented. These VDWE grown layered 2D materials show significant potential for fabricating novel heterostructures with tunable band alignments and magnetic properties for a variety of nanoelectronic and optoelectronic applications.

  14. Rotational superstructure in van der Waals heterostructure of self-assembled C60 monolayer on the WSe2 surface

    Energy Technology Data Exchange (ETDEWEB)

    Santos, Elton J.G.; Sullion, Declan; Chu, Ximo S.; Li, Duo O.; Guisinger, Nathan P.; Wang, Qing Hua

    2017-09-21

    Hybrid van der Waals (vdW) heterostructures composed of two-dimensional (2D) layered materials and self-assembled organic molecules are promising systems for electronic and optoelectronic applications with enhanced properties and performance. Control of molecular assembly is therefore paramount to fundamentally understand the nucleation, ordering, alignment, and electronic interaction of organic molecules with 2D materials. Here, we report the formation and detailed study of highly ordered, crystalline monolayers of C60 molecules self-assembled on the surface of WSe2 in well-ordered arrays with large grain sizes (∼5 μm). Using high-resolution scanning tunneling microscopy (STM), we observe a periodic 2 × 2 superstructure in the C60 monolayer and identify four distinct molecular appearances. Using vdW-corrected ab initio density functional theory (DFT) simulations, we determine that the interplay between vdW and Coulomb interactions as well as adsorbate–adsorbate and adsorbate–substrate interactions results in specific rotational arrangements of the molecules forming the superstructure. The orbital ordering through the relative positions of bonds in adjacent molecules creates a charge redistribution that links the molecule units in a long-range network. This rotational superstructure extends throughout the self-assembled monolayer and opens a pathway towards engineering aligned hybrid organic/inorganic vdW heterostructures with 2D layered materials in a precise and controlled way.

  15. The role of the van der Waals interactions in the adsorption of anthracene and pentacene on the Ag(111) surface

    Science.gov (United States)

    Morbec, Juliana M.; Kratzer, Peter

    2017-01-01

    Using first-principles calculations based on density-functional theory (DFT), we investigated the effects of the van der Waals (vdW) interactions on the structural and electronic properties of anthracene and pentacene adsorbed on the Ag(111) surface. We found that the inclusion of vdW corrections strongly affects the binding of both anthracene/Ag(111) and pentacene/Ag(111), yielding adsorption heights and energies more consistent with the experimental results than standard DFT calculations with generalized gradient approximation (GGA). For anthracene/Ag(111) the effect of the vdW interactions is even more dramatic: we found that "pure" DFT-GGA calculations (without including vdW corrections) result in preference for a tilted configuration, in contrast to the experimental observations of flat-lying adsorption; including vdW corrections, on the other hand, alters the binding geometry of anthracene/Ag(111), favoring the flat configuration. The electronic structure obtained using a self-consistent vdW scheme was found to be nearly indistinguishable from the conventional DFT electronic structure once the correct vdW geometry is employed for these physisorbed systems. Moreover, we show that a vdW correction scheme based on a hybrid functional DFT calculation (HSE) results in an improved description of the highest occupied molecular level of the adsorbed molecules.

  16. Potential energy surface of the CO{sub 2}–N{sub 2} van der Waals complex

    Energy Technology Data Exchange (ETDEWEB)

    Nasri, Sameh; Ajili, Yosra [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA, Université de Tunis El Manar, Tunis (Tunisia); Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France); Jaidane, Nejm-Eddine [Laboratoire de Spectroscopie Atomique, Moléculaire et Applications-LSAMA, Université de Tunis El Manar, Tunis (Tunisia); Kalugina, Yulia N. [Department of Optics and Spectroscopy, Tomsk State University, 36 Lenin Ave., Tomsk 634050 (Russian Federation); Halvick, Philippe; Stoecklin, Thierry [Institut des Sciences Moléculaires, Université de Bordeaux, CNRS UMR 5255, 33405 Talence Cedex (France); Hochlaf, Majdi, E-mail: hochlaf@univ-mlv.fr [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France)

    2015-05-07

    Four-dimensional potential energy surface (4D-PES) of the atmospherically relevant CO{sub 2}–N{sub 2} van der Waals complex is generated using the explicitly correlated coupled cluster with single, double, and perturbative triple excitation (CCSD(T)-F12) method in conjunction with the augmented correlation consistent triple zeta (aug-cc-pVTZ) basis set. This 4D-PES is mapped along the intermonomer coordinates. An analytic fit of this 4D-PES is performed. Our extensive computations confirm that the most stable form corresponds to a T-shape structure where the nitrogen molecule points towards the carbon atom of CO{sub 2}. In addition, we located a second isomer and two transition states in the ground state PES of CO{sub 2}–N{sub 2}. All of them lay below the CO{sub 2} + N{sub 2} dissociation limit. This 4D-PES is flat and strongly anisotropic along the intermonomer coordinates. This results in the possibility of the occurrence of large amplitude motions within the complex, such as the inversion of N{sub 2}, as suggested in the recent spectroscopic experiments. Finally, we show that the experimentally established deviations from the C{sub 2v} structure at equilibrium for the most stable isomer are due to the zero-point out-of-plane vibration correction.

  17. Integrable extended van der Waals model

    Science.gov (United States)

    Giglio, Francesco; Landolfi, Giulio; Moro, Antonio

    2016-10-01

    Inspired by the recent developments in the study of the thermodynamics of van der Waals fluids via the theory of nonlinear conservation laws and the description of phase transitions in terms of classical (dissipative) shock waves, we propose a novel approach to the construction of multi-parameter generalisations of the van der Waals model. The theory of integrable nonlinear conservation laws still represents the inspiring framework. Starting from a macroscopic approach, a four parameter family of integrable extended van der Waals models is indeed constructed in such a way that the equation of state is a solution to an integrable nonlinear conservation law linearisable by a Cole-Hopf transformation. This family is further specified by the request that, in regime of high temperature, far from the critical region, the extended model reproduces asymptotically the standard van der Waals equation of state. We provide a detailed comparison of our extended model with two notable empirical models such as Peng-Robinson and Soave's modification of the Redlich-Kwong equations of state. We show that our extended van der Waals equation of state is compatible with both empirical models for a suitable choice of the free parameters and can be viewed as a master interpolating equation. The present approach also suggests that further generalisations can be obtained by including the class of dispersive and viscous-dispersive nonlinear conservation laws and could lead to a new type of thermodynamic phase transitions associated to nonclassical and dispersive shock waves.

  18. Opening van vier nieuwe laboratoria van de Afdeling der Werktuigbouwkunde van de Technische Hogeschool Delft

    NARCIS (Netherlands)

    Boon, E.F.; Boot, J.; Vahl, L.; Van Eldik Thieme, H.C.A.; Blok, H.

    1959-01-01

    Samenvatting van de toespraak door Prof.ir, R. van Hasselt bij de officiele opening van vier nieuwe laboratoriavan de Afdeling der Werktuigbouwkunde Boon, E.F. en Boot, J.: het Laboratorium voor Chemische Werktuigen Vahl, L.: het Laboratorium voor Koudetechniek Van Eldik Thieme, H.C.A.: het

  19. Andreev reflection without Fermi surface alignment in high-T c van der Waals heterostructures

    Science.gov (United States)

    Zareapour, Parisa; Hayat, Alex; Zhao, Shu Yang F.; Kreshchuk, Michael; Xu, Zhijun; Liu, T. S.; Gu, G. D.; Jia, Shuang; Cava, Robert J.; Yang, H.-Y.; Ran, Ying; Burch, Kenneth S.

    2017-04-01

    We address the controversy over the proximity effect between topological materials and high-T c superconductors. Junctions are produced between Bi2Sr2CaCu2O{}8+δ and materials with different Fermi surfaces (Bi2Te3 and graphite). Both cases reveal tunneling spectra that are consistent with Andreev reflection. This is confirmed by a magnetic field that shifts features via the Doppler effect. This is modeled with a single parameter that accounts for tunneling into a screening supercurrent. Thus the tunneling involves Cooper pairs crossing the heterostructure, showing that the Fermi surface mismatch does not hinder the ability to form transparent interfaces, which is accounted for by the extended Brillouin zone and different lattice symmetries.

  20. Ab initio intermolecular potential energy surfaces for the Ar-NCCN van der Waals complexes

    Science.gov (United States)

    Solimannejad, Mohammad; Jouypazadeh, Hamidreza; Farrokhpour, Hossein

    2014-11-01

    The intermolecular potential energy surface of complex pairing argon with cyanogen molecule (NCCN) was calculated using the coupled cluster with single and double and perturbative triple excitations (CCSD(T)) with aug-cc-pvdz basis set extended with a set of mid-bond (3s3p2d1f1g) functions. The interaction energies were calculated by the supermolecular approach with the full counterpoise correction for the basis set superposition error. The calculated potential energies were fitted to an analytical expression. The calculated Ar-NCCN potential energy surface shows a global minimum at 3.35 Å, the distance between argon and centre of mass of cyanogen, for the T-shaped geometry and two local minimum at distance of 5.54 Å for the linear geometry on one side of cyanogen. Finally, the interaction second virial coefficients were calculated using the fitted potential energy surface and were compared with those obtained by the parameters of the Beattie-Bridgeman equation of states of pure argon and cyanogens fluids, approximately.

  1. Mass Transport in Surface Diffusion of van der Waals Bonded Systems: Boosted by Rotations?

    Science.gov (United States)

    Hedgeland, Holly; Sacchi, Marco; Singh, Pratap; McIntosh, Andrew J; Jardine, Andrew P; Alexandrowicz, Gil; Ward, David J; Jenkins, Stephen J; Allison, William; Ellis, John

    2016-12-01

    Mass transport at a surface is a key factor in heterogeneous catalysis. The rate is determined by excitation across a translational barrier and depends on the energy landscape and the coupling to the thermal bath of the surface. Here we use helium spin-echo spectroscopy to track the microscopic motion of benzene adsorbed on Cu(001) at low coverage (θ ∼ 0.07 ML). Specifically, our combined experimental and computational data determine both the absolute rate and mechanism of the molecular motion. The observed rate is significantly higher by a factor of 3.0 ± 0.1 than is possible in a conventional, point-particle model and can be understood only by including additional molecular (rotational) coordinates. We argue that the effect can be described as an entropic contribution that enhances the population of molecules in the transition state. The process is generally relevant to molecular systems and illustrates the importance of the pre-exponential factor alongside the activation barrier in studies of surface kinetics.

  2. Potential energy surface and rovibrational energy levels of the H2-CS van der Waals complex.

    Science.gov (United States)

    Denis-Alpizar, Otoniel; Stoecklin, Thierry; Halvick, Philippe; Dubernet, Marie-Lise; Marinakis, Sarantos

    2012-12-21

    Owing to its large dipole, astrophysicists use carbon monosulfide (CS) as a tracer of molecular gas in the interstellar medium, often in regions where H(2) is the most abundant collider. Predictions of the rovibrational energy levels of the weakly bound complex CS-H(2) (not yet observed) and also of rate coefficients for rotational transitions of CS in collision with H(2) should help to interpret the observed spectra. This paper deals with the first goal, i.e., the calculation of the rovibrational energy levels. A new four-dimensional intermolecular potential energy surface for the H(2)-CS complex is presented. Ab initio potential energy calculations were carried out at the coupled-cluster level with single and double excitations and a perturbative treatment of triple excitations, using a quadruple-zeta basis set and midbond functions. The potential energy surface was obtained by an analytic fit of the ab initio data. The equilibrium structure of the H(2)-CS complex is found to be linear with the carbon pointing toward H(2) at the intermolecular separation of 8.6 a(o). The corresponding well depth is -173 cm(-1). The potential was used to calculate the rovibrational energy levels of the para-H(2)-CS and ortho-H(2)-CS complexes. The present work provides the first theoretical predictions of these levels. The calculated dissociation energies are found to be 35.9 cm(-1) and 49.9 cm(-1), respectively, for the para and ortho complexes. The second virial coefficient for the H(2)-CS pair has also been calculated for a large range of temperature. These results could be used to assign future experimental spectra and to check the accuracy of the potential energy surface.

  3. Van der Waals Layered Materials: Surface Morphology, Interlayer Interaction, and Electronic Structure

    Science.gov (United States)

    Yeh, Po-Chun

    The search for new ultrathin materials as the "new silicon" has begun. In this dissertation, I examine (1) the surface structure, including the growth, the crystal quality, and thin film surface corrugation of a monolayer sample and a few layers of MoS2 and WSe2, and (2) their electronic structure. The characteristics of these electronic systems depend intimately on the morphology of the surfaces they inhabit, and their interactions with the substrate or within layers. These physical properties will be addressed in each chapter. This thesis has dedicated to the characterization of mono- and a few layers of MoS2 and WSe2 that uses surface-sensitive probes such as low-energy electron microscopy and diffraction (LEEM and LEED). Prior to our studies, the characterization of monolayer MoS2 and WSe2 has been generally limited to optical and transport probes. Furthermore, the heavy use of thick silicon oxide layer as the supporting substrate has been important in order to allow optical microscopic characterization of the 2D material. Hence, to the best of our knowledge, this has prohibited studies of this material on other surfaces, and it has precluded the discovery of potentially rich interface interactions that may exist between MoS 2 and its supporting substrate. Thus, in our study, we use a so-called SPELEEM system (Spectroscopic Photo-Emission and Low Energy Electron Microscopy) to address these imaging modalities: (1) real-space microscopy, which would allow locating of monolayer MoS2 samples, (2) spatially-resolved low-energy diffraction which would allow confirmation of the crystalline quality and domain orientation of MoS2 samples, and, (3) spatially-resolved spectroscopy, which would allow electronic structure mapping of MoS2 samples. Moreover, we have developed a preparation procedure for samples that yield, a surface-probe ready, ultra-clean, and can be transferred on an arbitrary substrate. To fully understand the physics in MoS2 such as direct

  4. a Code for Automated Construction of Potential Energy Surfaces for Van Der Waals Systems

    Science.gov (United States)

    Quintas Sánchez, Ernesto; Dawes, Richard

    2017-06-01

    The potential energy surface (PES) constitutes a cornerstone for theoretical studies of spectroscopy and dynamics. We fit PESs using a local interpolating moving least squares (L-IMLS) approach. The L-IMLS method is interpolative and has the flexibility to fit energies or energies and gradients, where inclusion of gradient information significantly reduces the number of points required for an accurate fit. The method permits fully automated PES generation: beginning with an initial set of seed points, an automatic point selection scheme determines where new data are required and, in a series of iterations, computes new ab initio data and updates the fit until a specified accuracy is reached. We have interfaced this fitting approach to popular electronic structure codes such as Molpro and CFOUR to automatically generate ab initio 4D PESs for vdWs systems composed of two (rigid) linear fragments. We present here our freely distributed code designed to run in parallel on a computing cluster, allowing the user to specify the system (masses, interatomic equilibrium distances, symmetry, energy range of interest, etc.) through an input file. For a selection of benchmark systems, we show that PESs with fitting errors below 1 \\wn can be constructed using only a few hundred ab initio points. M. Majumder, S. Ndengue and R. Dawes, Molecular Physics 114, 1 (2016).

  5. Graphene on metals: A van der Waals density functional study

    DEFF Research Database (Denmark)

    Vanin, Marco; Mortensen, Jens Jørgen; Kelkkanen, Kari André;

    2010-01-01

    We use density functional theory (DFT) with a recently developed van der Waals density functional (vdW-DF) to study the adsorption of graphene on Co, Ni, Pd, Ag, Au, Cu, Pt, and Al(111) surfaces. In contrast to the local-density approximation (LDA) which predicts relatively strong binding for Ni...

  6. Walter van der Cruijsen / Walter van der Cruijsen ; interv. Tilman Baumgärtel

    Index Scriptorium Estoniae

    Cruijsen, Walter van der

    2006-01-01

    1997. a. Berliinis tehtud intervjuu hollandi maali, võrgu- ja installatsioonikunstniku Walter van der Cruijseniga (sünd. 1958), kes kuulub Euroopa ühe edukama 1990-ndatel loodud võrguprojekti De Digitale Stad Amsterdam loojate hulka

  7. Walter van der Cruijsen / Walter van der Cruijsen ; interv. Tilman Baumgärtel

    Index Scriptorium Estoniae

    Cruijsen, Walter van der

    2006-01-01

    1997. a. Berliinis tehtud intervjuu hollandi maali, võrgu- ja installatsioonikunstniku Walter van der Cruijseniga (sünd. 1958), kes kuulub Euroopa ühe edukama 1990-ndatel loodud võrguprojekti De Digitale Stad Amsterdam loojate hulka

  8. Van der Waals forces and spatial dispersion

    OpenAIRE

    2009-01-01

    A version of the Green's functions theory of the Van der Waals forces which can be conveniently used in the presence of spatial dispersion is presented. The theory is based on the fluctuation-dissipation theorem and is valid for interacting bodies, separated by vacuum. Objections against theories acounting for the spatial dispersion are discussed.

  9. Women Screenwriters : Paula van der Oest

    NARCIS (Netherlands)

    Willemsen, Steven; Nelmes, Jill; Selbo, Jule

    2015-01-01

    Contribution discussing the work of screenwriter and director Paula van der Oest (Laag-Soeren, 1965), who has been prolific in Dutch film and television from the 1990s up to the present, and whose screenplays are characterized by an empathetic take on societal and interpersonal themes.

  10. Cluster ions and van der Waals molecules

    CERN Document Server

    Smirnov, Boris M

    1992-01-01

    This review discusses current ideas in the physics and chemistry of cluster ions and Van der Waals molecules as well as presenting numerical data on their parameters and the processes involving them. It is also a detailed reference on basic data relating to many species.

  11. The Economics of van der Waals Force Engineering

    Science.gov (United States)

    Pinto, Fabrizio

    2008-01-01

    As micro-electro-mechanical system (MEMS) fabrication continues on an ever-decreasing scale, new technological challenges must be successfully negotiated if Moore's Law is to be an even approximately valid model of the future of device miniaturization. Among the most significant obstacles is the existence of strong surface forces related to quantum mechanical van der Waals interatomic interactions, which rapidly diverge as the distance between any two neutral boundaries decreases. The van der Waals force is a contributing factor in several device failures and limitations, including, for instance, stiction and oscillator non-linearities. In the last decade, however, it has been conclusively shown that van der Waals forces are not just a MEMS limitation but can be engineered in both magnitude and sign so as to enable classes of proprietary inventions which either deliver novel capabilities or improve upon existing ones. The evolution of van der Waals force research from an almost exclusively theoretical field in quantum-electro-dynamics to an enabling nanotechnology discipline represents a useful example of the ongoing paradigm shift from government-centered to private-capital funded R&D in cutting-edge physics leading to potentially profitable products. In this paper, we discuss the reasons van der Waals force engineering may lead to the creation of thriving markets both in the short and medium terms by highlighting technical challenges that can be competitively addressed by this novel approach. We also discuss some notable obstacles to the cultural transformation of the academic research community required for the emergence of a functional van der Waals force engineering industry worldwide.

  12. Thermodynamics of Van der Waals Fluids with quantum statistics

    CERN Document Server

    Redlich, Krzysztof

    2016-01-01

    We consider thermodynamics of the van der Waals fluid of quantum systems. We derive general relations of thermodynamic functions and parameters of any ideal gas and the corresponding van der Waals fluid. This provides unambiguous generalization of the classical van der Waals theory to quantum statistical systems. As an example, we apply the van der Waals fluid with fermi statistics to characterize the liquid-gas critical point in nuclear matter. We also introduce the Bose-Einstein condensation in the relativistic van der Waals boson gas, and argue, that it exhibits two-phase structure separated in space.

  13. Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag2/graphene

    Science.gov (United States)

    de Lara-Castells, María Pilar; Mitrushchenkov, Alexander O.; Stoll, Hermann

    2015-09-01

    A combined density functional (DFT) and incremental post-Hartree-Fock (post-HF) approach, proven earlier to calculate He-surface potential energy surfaces [de Lara-Castells et al., J. Chem. Phys. 141, 151102 (2014)], is applied to describe the van der Waals dominated Ag2/graphene interaction. It extends the dispersionless density functional theory developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] by including periodic boundary conditions while the dispersion is parametrized via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. Starting with the elementary cluster unit of the target surface (benzene), continuing through the realistic cluster model (coronene), and ending with the periodic model of the extended system, modern ab initio methodologies for intermolecular interactions as well as state-of-the-art van der Waals-corrected density functional-based approaches are put together both to assess the accuracy of the composite scheme and to better characterize the Ag2/graphene interaction. The present work illustrates how the combination of DFT and post-HF perspectives may be efficient to design simple and reliable ab initio-based schemes in extended systems for surface science applications.

  14. Combining density functional and incremental post-Hartree-Fock approaches for van der Waals dominated adsorbate-surface interactions: Ag{sub 2}/graphene

    Energy Technology Data Exchange (ETDEWEB)

    Lara-Castells, María Pilar de, E-mail: Pilar.deLara.Castells@csic.es [Instituto de Física Fundamental (C.S.I.C.), Serrano 123, E-28006 Madrid (Spain); Mitrushchenkov, Alexander O. [Université Paris-Est, Laboratoire Modélisation et Simulation Multi Echelle, MSME UMR 8208 CNRS, 5 bd Descartes, 77454 Marne-la-Vallée (France); Stoll, Hermann [Institut für Theoretische Chemie, Universität Stuttgart, D-70550 Stuttgart (Germany)

    2015-09-14

    A combined density functional (DFT) and incremental post-Hartree-Fock (post-HF) approach, proven earlier to calculate He-surface potential energy surfaces [de Lara-Castells et al., J. Chem. Phys. 141, 151102 (2014)], is applied to describe the van der Waals dominated Ag{sub 2}/graphene interaction. It extends the dispersionless density functional theory developed by Pernal et al. [Phys. Rev. Lett. 103, 263201 (2009)] by including periodic boundary conditions while the dispersion is parametrized via the method of increments [H. Stoll, J. Chem. Phys. 97, 8449 (1992)]. Starting with the elementary cluster unit of the target surface (benzene), continuing through the realistic cluster model (coronene), and ending with the periodic model of the extended system, modern ab initio methodologies for intermolecular interactions as well as state-of-the-art van der Waals-corrected density functional-based approaches are put together both to assess the accuracy of the composite scheme and to better characterize the Ag{sub 2}/graphene interaction. The present work illustrates how the combination of DFT and post-HF perspectives may be efficient to design simple and reliable ab initio-based schemes in extended systems for surface science applications.

  15. van der Waals-corrected Density Functional Theory simulation of adsorption processes on noble-metal surfaces: Xe on Ag(111), Au(111), and Cu(111)

    CERN Document Server

    Silvestrelli, Pier Luigi

    2016-01-01

    The DFT/vdW-WF2s1 method based on the generation of localized Wannier functions, recently developed to include the van der Waals interactions in the Density Functional Theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe with noble-metal surfaces, namely Ag(111), Au(111), and Cu(111). The study is also repeated by adopting the DFT/vdW-QHO-WF variant relying on the Quantum Harmonic Oscillator model which describes well many-body effects. Comparison of the computed equilibrium binding energies and distances, and the $C_3$ coefficients characterizing the adatom-surface van der Waals interactions, with available experimental and theoretical reference data shows that the methods perform well and elucidate the importance of properly including screening effects. The results are also compared with those obtained by other vdW-corrected DFT schemes, including PBE-D, vdW-DF, vdW-DF2, rVV10, and by the simpler Local Dens...

  16. Van Der Waals-Corrected Density Functional Theory Simulation of Adsorption Processes on Noble-Metal Surfaces: Xe on Ag(111), Au(111), and Cu(111)

    Science.gov (United States)

    Silvestrelli, Pier Luigi; Ambrosetti, Alberto

    2016-10-01

    The DFT/vdW-WF2s1 method based on the generation of localized Wannier functions, recently developed to include the van der Waals interactions in the density functional theory and describe adsorption processes on metal surfaces by taking metal-screening effects into account, is applied to the case of the interaction of Xe with noble-metal surfaces, namely Ag(111), Au(111), and Cu(111). The study is also repeated by adopting the DFT/vdW-QHO-WF variant relying on the quantum harmonic oscillator model which describes well many body effects. Comparison of the computed equilibrium binding energies and distances, and the C_3 coefficients characterizing the adatom-surface van der Waals interactions, with available experimental and theoretical reference data shows that the methods perform well and elucidates the importance of properly including screening effects. The results are also compared with those obtained by other vdW-corrected DFT schemes, including PBE-D, vdW-DF, vdW-DF2, rVV10, and by the simpler local density approximation and semi-local (PBE) generalized gradient approximation approaches.

  17. TiO2 anatase's bulk and (001) surface, structural and electronic properties: A DFT study on the importance of Hubbard and van der Waals contributions

    Science.gov (United States)

    Araujo-Lopez, Eduard; Varilla, Luis Alcala; Seriani, Nicola; Montoya, Javier A.

    2016-11-01

    Theoretical ab initio studies done so far on the structural properties of the titanium dioxide anatase (001) surface, have not reported simultaneously the complete set of cell and interatomic parameters for this system or its bulk. Here we present a complete report of these quantities within a spin polarized Density Functional Theory calculation, including also the Hubbard term and the van der Waals dispersion contribution. We show that within this approach it is possible to find a description of TiO2 anatase using DFT, that correlates better with experimental results than most theoretical studies reported previously. This good level of agreement has an advantage with respect to other very accurate studies which have performed computationally expensive calculations involving hybrid functionals, in that our method tends to be faster while also including the van der Waals dispersion contributions in addition to the treatment of correlations. The observed high-quality description of a system like TiO2 within this approach is important and encouraging; specially because it treats properly a d-shell element that is possibly going to have, for many applications of interest, long-range interaction with molecules, e.g. in studies of photocatalysis, where one needs all the relevant physics of the system to be included. We support this claim with an example of the effects that long-range interactions have on a CO2 molecule at the (001) surface.

  18. Thermal response in van der Waals heterostructures

    Science.gov (United States)

    Naidu Gandi, Appala; Alshareef, Husam N.; Schwingenschlögl, Udo

    2017-01-01

    We solve numerically the Boltzmann transport equations of the phonons and electrons to understand the thermoelectric response in heterostructures of M2CO2 (M: Ti, Zr, Hf) MXenes with transition metal dichalcogenide monolayers. Low frequency optical phonons are found to occur as a consequence of the van der Waals bonding, contribute significantly to the thermal transport, and compensate for the reduced contributions of the acoustic phonons (increased scattering cross-sections in heterostructures), such that the thermal conductivities turn out to be similar to those of the bare MXenes. Our results indicate that the important superlattice design approach of thermoelectrics (to reduce the thermal conductivity) may be effective for two-dimensional van der Waals materials when used in conjunction with intercalation.

  19. Thermal response in van der Waals heterostructures

    KAUST Repository

    Gandi, Appala

    2016-11-21

    We solve numerically the Boltzmann transport equations of the phonons and electrons to understand the thermoelectric response in heterostructures of M2CO2 (M: Ti, Zr, Hf) MXenes with transition metal dichalcogenide monolayers. Low frequency optical phonons are found to occur as a consequence of the van der Waals bonding, contribute significantly to the thermal transport, and compensate for the reduced contributions of the acoustic phonons (increased scattering cross-sections in heterostructures), such that the thermal conductivities turn out to be similar to those of the bare MXenes. Our results indicate that the important superlattice design approach of thermoelectrics (to reduce the thermal conductivity) may be effective for two-dimensional van der Waals materials when used in conjunction with intercalation. © 2016 IOP Publishing Ltd.

  20. Structure and dynamics of small van der Waals complexes

    Energy Technology Data Exchange (ETDEWEB)

    Loreau, J. [Service de Chimie Quantique et Photophysique, Université Libre de Bruxelles (ULB) CP 160/09, 1050 Brussels (Belgium)

    2014-10-06

    We illustrate computational aspects of the calculation of the potential energy surfaces of small (up to five atoms) van der Waals complexes with high-level quantum chemistry techniques such as the CCSD(T) method with extended basis sets. We discuss the compromise between the required accuracy and the computational time. Further, we show how these potential energy surfaces can be fitted and used in dynamical calculations such as non-reactive inelastic scattering.

  1. {InSe}/{GaSe} heterointerfaces prepared by Van der Waals epitaxy

    Science.gov (United States)

    Lang, O.; Klein, A.; Schlaf, R.; Löher, T.; Pettenkofer, C.; Jaegermann, W.; Chevy, A.

    1995-01-01

    Epitaxial films of layered substrates can be prepared onto layered substrates even for large lattice mismatch, when the growth is attempted with the Van der Waals surfaces opposing each other (Van der Waals epitaxy). Thin epitaxial InSe(GaSe) films are prepared onto ultrahigh vacuum (UHV) cleaved GaSe(InSe) Van der Waals (0001) surfaces. The films and the heterointerface are characterized by photoelectron spectroscopy, electron diffraction and scanning tunneling microscopy (STM). High quality and stoichiometric films are obtained by direct InSe(GaSe) evaporation from a Knudsen cell at sample temperatures between 520 and 620 K. Despite a 6% lattice mismatch the deposited films are oriented with their c- and α-axis to the hexagonal substrate. The growth mostly follows the Frank-Van der Merwe mode. This rather ideal growth behaviour is related to the specific properties of the Van der Waals plane which contains no dangling bonds.

  2. Effects of van der Waals density functional corrections on trends in furfural adsorption and hydrogenation on close-packed transition metal surfaces

    Science.gov (United States)

    Liu, Bin; Cheng, Lei; Curtiss, Larry; Greeley, Jeffrey

    2014-04-01

    The hydrogenation of furfural to furfuryl alcohol on Pd(111), Cu(111) and Pt(111) is studied with both standard Density Functional Theory (DFT)-GGA functionals and with van der Waals-corrected density functionals. VdW-DF functionals, including optPBE, optB88, optB86b, and Grimme's method, are used to optimize the adsorption configurations of furfural, furfuryl alcohol, and related intermediates resulting from hydrogenation of furfural, and the results are compared to corresponding values determined with GGA functionals, including PW91 and PBE. On Pd(111) and Pt(111), the adsorption geometries of the intermediates are not noticeably different between the two classes of functionals, while on Cu(111), modest changes are seen in both the perpendicular distance and the orientation of the aromatic ring with respect to the planar surface. In general, the binding energies increase substantially in magnitude as a result of van der Waals contributions on all metals. In contrast, however, dispersion effects on the kinetics of hydrogenation are relatively small. It is found that activation barriers are not significantly affected by the inclusion of dispersion effects, and a Brønsted-Evans-Polanyi relationship developed solely from PW91 calculations on Pd(111) is capable of describing corresponding results on Cu(111) and Pt(111), even when the dispersion effects are included. Finally, the reaction energies and barriers derived from the dispersion-corrected and pure GGA calculations are used to plot simple potential energy profiles for furfural hydrogenation to furfuryl alcohol on the three considered metals, and an approximately constant downshift of the energetics due to the dispersion corrections is observed.

  3. Effects of van der Waals Density Functional Corrections on Trends in Furfural Adsorption and Hydrogenation on Close-Packed Transition Metal Surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Bin; Cheng, Lei; Curtiss, Larry A.; Greeley, Jeffrey P.

    2014-04-01

    The hydrogenation of furfural to furfuryl alcohol on Pd(111), Cu(111) and Pt(111) is studied with both standard Density Functional Theory (DFT)-GGA functionals and with van der Waals-corrected density functionals. VdWDF functionals, including optPBE, optB88, optB86b, and Grimme's method, are used to optimize the adsorption configurations of furfural, furfuryl alcohol, and related intermediates resulting from hydrogenation of furfural, and the results are compared to corresponding values determined with GGA functionals, including PW91 and PBE. On Pd(111) and Pt(111), the adsorption geometries of the intermediates are not noticeably different between the two classes of functionals, while on Cu(111), modest changes are seen in both the erpendicular distance and the orientation of the aromatic ringwith respect to the planar surface. In general, the binding energies increase substantially in magnitude as a result of van derWaals contributions on all metals. In contrast, however, dispersion effects on the kinetics of hydrogenation are relatively small. It is found that activation barriers are not significantly affected by the inclusion of dispersion effects, and a Brønsted–Evans–Polanyi relationship developed solely fromPW91 calculations on Pd(111) is capable of describing corresponding results on Cu(111) and Pt(111), even when the dispersion effects are included. Finally, the reaction energies and barriers derived from the dispersion-corrected and pure GGA calculations are used to plot simple potential energy profiles for furfural hydrogenation to furfuryl alcohol on the three considered metals, and an approximately constant downshift of the energetics due to the dispersion corrections is observed.

  4. Dr Jacob van der Land, marine biologist extraordinary

    NARCIS (Netherlands)

    Bruggen, van A.C.

    2001-01-01

    This contribution is an attempt to sketch the life and works of Dr Jacob van der Land, curator of worms and chief marine biologist of the National Museum of Natural History, on the occasion of his official retirement. Born in 1935, Jacob van der Land read biology at Leiden University (1958-1964), wh

  5. Dr Jacob van der Land, marine biologist extraordinary

    NARCIS (Netherlands)

    Bruggen, van A.C.

    2001-01-01

    This contribution is an attempt to sketch the life and works of Dr Jacob van der Land, curator of worms and chief marine biologist of the National Museum of Natural History, on the occasion of his official retirement. Born in 1935, Jacob van der Land read biology at Leiden University (1958-1964),

  6. Hollandse zee- en scheepstermen in het Russisch: Anna Croiset van der Kop versus Reinder van der Meulen

    Directory of Open Access Journals (Sweden)

    Nadja Louwerse

    2010-03-01

    Full Text Available Dutch nautical terms in Russian. Anna Croiset van der Kop versus Reinder van der Meulen This article explores the controversy in the beginning of the 20th century between de Dutch slavists Anna Croiset van der Kop and Reindert van der Meulen, author of the book De Hollandsche Zee- en Scheepstermen in het Russisch (Dutch Nautical Terms in Russian. After publication, she reacted with an undeniably negative and unusually elaborate review (72 pages!, written not in Dutch, but in Russian and published in one of the most leading, scientific series in Russia. Van der Meulen has never directly reacted to this review: in 1959 he published a supplement to his earlier work from 1909: Nederlandse woorden in het Russisch (Dutch words in Russian, not mentioning Croiset van der Kops name, nor her review. Obviously he felt hurt by her merciless criticism. The article focuses on the motives underlying her strong reaction. It will be argued that her severe criticism was not really inspired by Van der Meulen’s subject, but by his failing research methods. Furthermore, it will be pointed out that this review seemed to offer her an opportunity to measure up to her Dutch colleagues and to present herself internationally as a slavist. On the basis of the now available data it is hard to say, which motives really brought Croiset van der Kop to write her review. Investigation of her archives, preserved in St- Petersburg, and until now hardly studied, may perhaps reveal her real motives.

  7. Spherical and hyperspherical harmonics representation of van der Waals aggregates

    Science.gov (United States)

    Lombardi, Andrea; Palazzetti, Federico; Aquilanti, Vincenzo; Grossi, Gaia; Albernaz, Alessandra F.; Barreto, Patricia R. P.; Cruz, Ana Claudia P. S.

    2016-12-01

    The representation of the potential energy surfaces of atom-molecule or molecular dimers interactions should account faithfully for the symmetry properties of the systems, preserving at the same time a compact analytical form. To this aim, the choice of a proper set of coordinates is a necessary precondition. Here we illustrate a description in terms of hyperspherical coordinates and the expansion of the intermolecular interaction energy in terms of hypersherical harmonics, as a general method for building potential energy surfaces suitable for molecular dynamics simulations of van der Waals aggregates. Examples for the prototypical case diatomic-molecule-diatomic-molecule interactions are shown.

  8. van der Waals energy under strong atom-field coupling in doped carbon nanotubes

    OpenAIRE

    Bondarev, Igor; Lambin, Philippe

    2004-01-01

    Using a unified macroscopic QED formalism, we derive an integral equation for the van der Waals energy of a two-level atomic system near a carbon nanotube. The equation is valid for both strong and weak atom-vacuum-field coupling. By solving it numerically, we demonstrate the inapplicability of weak-coupling-based van der Waals interaction models in a close vicinity of the nanotube surface.

  9. van der Waals energy under strong atom field coupling in doped carbon nanotubes

    Science.gov (United States)

    Bondarev, I. V.; Lambin, Ph.

    2004-10-01

    Using a unified macroscopic QED formalism, we derive an integral equation for the van der Waals energy of a two-level atomic system near a carbon nanotube. The equation is valid for both strong and weak atom-vacuum-field coupling. By solving it numerically, we demonstrate the inapplicability of weak-coupling-based van der Waals interaction models in a close vicinity of the nanotube surface.

  10. Interpretation of van der Waal density functionals

    CERN Document Server

    Hyldgaard, Per; Schröder, Elsebeth

    2014-01-01

    The nonlocal correlation energy in the van der Waals density functional (vdW-DF) method [Phys. Rev. Lett. 92, 246401 (2004); Phys. Rev. B 76, 125112 (2007); Phys. Rev. B 89, 035412 (2014)] can be interpreted in terms of a coupling of zero-point energies of characteristic modes of semilocal exchange-correlation (xc) holes. These xc holes reflect the internal functional in the framework of the vdW-DF method [Phys. Rev. B 82, 081101(2010)]. We explore the internal xc hole components, showing that they share properties with those of the generalized-gradient approximation. We use these results to illustrate the nonlocality in the vdW-DF description and analyze the vdW-DF formulation of nonlocal correlation.

  11. Theoretical studies for the N{sub 2}–N{sub 2}O van der Waals complex: The potential energy surface, intermolecular vibrations, and rotational transition frequencies

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Rui [Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); School of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou 450011 (China); Zheng, Limin; Yang, Minghui, E-mail: yplu@ntu.edu.sg, E-mail: yangmh@wipm.ac.cn [Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan 430071 (China); Lu, Yunpeng, E-mail: yplu@ntu.edu.sg, E-mail: yangmh@wipm.ac.cn [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, 21 Nanyang Link, Singapore 637371 (Singapore)

    2015-10-21

    Theoretical studies of the potential energy surface (PES) and bound states are performed for the N{sub 2}–N{sub 2}O van der Waals (vdW) complex. A four-dimensional intermolecular PES is constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. Two equivalent T-shaped global minima are located, in which the O atom of N{sub 2}O monomer is near the N{sub 2} monomer. The intermolecular fundamental vibrational states are assigned by inspecting the orientation of the nodal surface of the wavefunctions. The calculated frequency for intermolecular disrotation mode is 23.086 cm{sup −1}, which is in good agreement with the available experimental data of 22.334 cm{sup −1}. A negligible tunneling splitting with the value of 4.2 MHz is determined for the ground vibrational state and the tunneling splitting increases as the increment of the vibrational frequencies. Rotational levels and transition frequencies are calculated for both isotopomers {sup 14}N{sub 2}–N{sub 2}O and {sup 15}N{sub 2}–N{sub 2}O. The accuracy of the PES is validated by the good agreement between theoretical and experimental results for the transition frequencies and spectroscopic parameters.

  12. Synchronization law for a van der Pol array.

    Science.gov (United States)

    Peles, Slaven; Wiesenfeld, Kurt

    2003-08-01

    We explore the transition to in-phase synchronization in globally coupled oscillator arrays, and compare results for van der Pol arrays with Josephson junction arrays. Our approach yields in each case an analytically tractable iterative map; the resulting stability formulas are simple because the expansion procedure identifies natural parameter groups. A third example, an array of Duffing-van der Pol oscillators, is found to be of the same fundamental type as the van der Pol arrays, but the Josephson arrays are fundamentally different owing to the absence of self-resonant interactions.

  13. The van der Waals fluid and its role in cosmology

    Science.gov (United States)

    Jantsch, Rudinei C. S.; Christmann, Marcus H. B.; Kremer, Gilberto M.

    2016-01-01

    We analyze the properties of a generic cosmological fluid described by the van der Waals equation-of-state. Exact solutions for the energy-density evolution are found as implicit functions of the scale factor for a flat Friedmann-Robertson-Walker (FRW) spacetime. The possible values of the free parameter in the van der Waals equation are selected a posteriori, in accordance with asymptotic behaviors that are physically relevant. The stability of the model against small perturbations is studied through the hydrodynamic perturbations of the fluid for the relevant cases. It is found that a van der Waals fluid seems appropriate to describe noneternal inflationary scenarios.

  14. The van der Waals fluid and its role in cosmology

    CERN Document Server

    Jantsch, Rudinei C S; Kremer, Gilberto M

    2016-01-01

    We analyze the properties of a generic cosmological fluid described by the van der Waals equation of state. Exact solutions for the energy density evolution are found as implicit functions of the scale factor for a flat Friedmann-Robertson-Walker space-time. The possible values of the free parameter in the van der Waals equation are selected \\emph{a posteriori}, in accordance with asymptotic behaviors that are physically relevant. The stability of the model against small perturbations is studied through the hydrodynamic perturbations of the fluid for the relevant cases. It is found that a van der Waals fluid seems appropriate to describe non-eternal inflationary scenarios.

  15. The van der Waals force and gravitational force in matter

    CERN Document Server

    Zhang, Lei

    2013-01-01

    It was thought that the van der Waals force and gravitational force were distinct. Now a model is used to describe the attraction between macroscopic objects according to van der Waals interaction. The force between two objects with thermal equilibrium deviates from the law of universal gravitation slightly, and the gravity on the earth is explained approximately. We argue that the gravitational force is the van der Waals force actually. In other words, the gravitational force and mass are related to the quantum fluctuations of electron clouds in atoms, and these parameters are dictated by dielectric susceptibility.

  16. Investigation of the range of validity of the pairwise summation method applied to the calculation of the surface roughness correction to the van der Waals force

    Science.gov (United States)

    Gusso, André; Burnham, Nancy A.

    2016-09-01

    It has long been recognized that stochastic surface roughness can considerably change the van der Waals (vdW) force between interacting surfaces and particles. However, few analytical expressions for the vdW force between rough surfaces have been presented in the literature. Because they have been derived using perturbative methods or the proximity force approximation the expressions are valid when the roughness correction is small and for a limited range of roughness parameters and surface separation. In this work, a nonperturbative approach, the effective density method (EDM) is proposed to circumvent some of these limitations. The method simplifies the calculations of the roughness correction based on pairwise summation (PWS), and allows us to derive simple expressions for the vdW force and energy between two semispaces covered with stochastic rough surfaces. Because the range of applicability of PWS and, therefore, of our results, are not known a priori, we compare the predictions based on the EDM with those based on the multilayer effective medium model, whose range of validity can be defined more properly and which is valid when the roughness correction is comparatively large. We conclude that the PWS can be used for roughness characterized by a correlation length of the order of its rms amplitude, when this amplitude is of the order of or smaller than a few nanometers, and only for typically insulating materials such as silicon dioxide, silicon nitride, diamond, and certain glasses, polymers and ceramics. The results are relevant for the correct modeling of systems where the vdW force can play a significant role such as micro and nanodevices, for the calculation of the tip-sample force in atomic force microscopy, and in problems involving adhesion.

  17. Strong Van der Waals force in the hadron physics

    CERN Document Server

    Sawada, T

    2000-01-01

    Possible strong Van der Waals interaction between hadrons is searched in the P-wave amplitude of the pi-pi scattering by removing the cut of the two-pion exchange spectrum as well as the unitarity cut.

  18. (AJST) ANALYSIS OF VAN DER WAAL EQUATION NEAR THE ...

    African Journals Online (AJOL)

    Department of Physics, University of Nairobi, P.O. Box 30197, 00100 Nairobi ... some additional critical parameters and presents the ideal gas temperature as a lower limit to the van der ... sufficiently low pressures, the relations among these.

  19. Lifshitz theory of van der Waals pressure in dissipative media

    CERN Document Server

    Zheng, Yi

    2010-01-01

    We derive a first--principles method of determining the van der Waals or Casimir pressure in a dissipative and dispersive planar multilayered system by calculating the Maxwell stress tensor in a fictitious layer of vacuum, that is eventually made to vanish, introduced in the structure. This is illustrated by calculating the van der Waals pressure in a thin film with dissipative properties embedded between two semi--infinite media.

  20. Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures

    Science.gov (United States)

    2015-03-30

    Final 3. DATES COVERED (From - To) 14 Aug 13 to 13 Feb 15 4. TITLE AND SUBTITLE Nano Electronics on Atomically Controlled van der Waals...OMB control number. 1. REPORT DATE 14 MAY 2015 2. REPORT TYPE Final 3. DATES COVERED 14-08-2013 to 13-02-2015 4. TITLE AND SUBTITLE Nano ...AOARD Grant 134122 “ Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures” 3/30/2015 Name of Principal

  1. Modified Van der Waals equation and law of corresponding states

    Science.gov (United States)

    Zhong, Wei; Xiao, Changming; Zhu, Yongkai

    2017-04-01

    It is well known that the Van der Waals equation is a modification of the ideal gas law, yet it can be used to describe both gas and liquid, and some important messages can be obtained from this state equation. However, the Van der Waals equation is not a precise state equation, and it does not give a good description of the law of corresponding states. In this paper, we expand the Van der Waals equation into its Taylor's series form, and then modify the fourth order expansion by changing the constant Virial coefficients into their analogous ones. Via this way, a more precise result about the law of corresponding states has been obtained, and the law of corresponding states can then be expressed as: in terms of the reduced variables, all fluids should obey the same equation with the analogous Virial coefficients. In addition, the system of 3 He with quantum effects has also been taken into consideration with our modified Van der Waals equation, and it is found that, for a normal system without quantum effect, the modification on ideal gas law from the Van der Waals equation is more significant than the real case, however, for a system with quantum effect, this modification is less significant than the real case, thus a factor is introduced in this paper to weaken or strengthen the modification of the Van der Waals equation, respectively.

  2. Van der Waals Force Assisted Heat Transfer

    Science.gov (United States)

    Sasihithlu, K.; Pendry, J. B.; Craster, R. V.

    2017-02-01

    Phonons (collective atomic vibrations in solids) are more effective in transporting heat than photons. This is the reason why the conduction mode of heat transport in nonmetals (mediated by phonons) is dominant compared to the radiation mode of heat transport (mediated by photons). However, since phonons are unable to traverse a vacuum gap (unlike photons), it is commonly believed that two bodies separated by a gap cannot exchange heat via phonons. Recently, a mechanism was proposed [J. B. Pendry, K. Sasihithlu, and R. V. Craster, Phys. Rev. B 94, 075414 (2016)] by which phonons can transport heat across a vacuum gap - through the Van der Waals interaction between two bodies with gap less than the wavelength of light. Such heat transfer mechanisms are highly relevant for heating (and cooling) of nanostructures; the heating of the flying heads in magnetic storage disks is a case in point. Here, the theoretical derivation for modelling phonon transmission is revisited and extended to the case of two bodies made of different materials separated by a vacuum gap. Magnitudes of phonon transmission, and hence the heat transfer, for commonly used materials in the micro- and nano-electromechanical industry are calculated and compared with the calculation of conduction heat transfer through air for small gaps as well as the heat transfer calculation due to photon exchange.

  3. Simon van der Meer (1925-2011)

    CERN Multimedia

    2011-01-01

    Simon van der Meer was a true giant of modern particle physics, though a gentle one. His contributions to accelerator science remain vital for the operation of accelerators such as the LHC today. Simon was an electrical engineer who grew up in The Hague, moving on to Delft University to study electrical engineering. After a short stint with Philips, he came to CERN in 1956, just two years after the lab opened, and remained with us until his retirement in 1990.   Simon was an incredibly inventive man. When confronted with a problem, he would sink into deep reflection, rarely emerging until he had a solution. One of us, Steve Myers, remembers him as a man who did not suffer fools gladly, and who was extremely taciturn. Simon would never use two words where one would suffice. But that one word would invariably be the right one. Simon is best known for his contribution to the SPS collider project, for which he was awarded the Nobel Prize, jointly with Carlo Rubbia, in 1984. Stochastic cooling, the in...

  4. Van der Waals Interactions in Aspirin

    Science.gov (United States)

    Reilly, Anthony; Tkatchenko, Alexandre

    2015-03-01

    The ability of molecules to yield multiple solid forms, or polymorphs, has significance for diverse applications ranging from drug design and food chemistry to nonlinear optics and hydrogen storage. In particular, aspirin has been used and studied for over a century, but has only recently been shown to have an additional polymorphic form, known as form II. Since the two observed solid forms of aspirin are degenerate in terms of lattice energy, kinetic effects have been suggested to determine the metastability of the less abundant form II. Here, first-principles calculations provide an alternative explanation based on free-energy differences at room temperature. The explicit consideration of many-body van der Waals interactions in the free energy demonstrates that the stability of the most abundant form of aspirin is due to a subtle coupling between collective electronic fluctuations and quantized lattice vibrations. In addition, a systematic analysis of the elastic properties of the two forms of aspirin rules out mechanical instability of form II as making it metastable.

  5. THE PORTRAITS OF SIMON VAN DER STEL, FIRST GOVERNOR ...

    African Journals Online (AJOL)

    van Riebeeck, and the other that of his first wife, Maria. Quevellerius (Fig ... Jan Weenix (attributed), Portrait of Simon van der Stel and his son Willem Adriaan. Canvas, 112 x ... In the distance we see five natives of a dark skin colour, dressed in ...

  6. Beschrijving der ontwikkelingsstadia van Thosea asigna V.E.

    NARCIS (Netherlands)

    Eecke, van R.

    1930-01-01

    Namens den Directeur van het Deli-Proefstation te Medan, Sumatra, werd mij de hieronder volgende beschrijving der ontwikkelingsstadia van Thosea asigna v. E., eene Limacodide, beschreven in de Zool. Meded. Mus. Leiden XII, p. 113, pl. XII, f. 10, 1929, toegezonden. Ei: de eieren worden afgezet tegen

  7. Calculation of the structure, potential energy surface, vibrational dynamics, and electric dipole properties for the Xe:HI van der Waals complex.

    Science.gov (United States)

    Preller, M; Grunenberg, J; Bulychev, V P; Bulanin, M O

    2011-05-07

    We report the structure and spectroscopic characteristics for the Xe:HI van der Waals binary isomers determined from variational solutions of two-dimensional and three-dimensional (3D) vibrational Schrödinger equations. The solutions are based on a potential energy surface computed at the coupled-cluster level of theory including single and double excitations and a non-iterative perturbation treatment of triple excitations [CCSD(T)]. The dipole moment surface was calculated using quadratic configuration interaction (QCISD). The global potential minimum is shown to be located at the anti-hydrogen-bonded Xe-IH isomer, 21 cm(-1) below the secondary local minimum associated with the hydrogen-bonded Xe-HI isomeric form. The dissociation energy from the global minimum is 245.9 cm(-1). 3D Schrödinger equations are solved for the rotational quantum numbers J = k = 0, 1, and 2, without invoking an adiabatic separation of high- and low-frequency degrees of freedom. The vibrational ground state resides in the Xe-HI potential well, while the first excited state, 8.59 cm(-1) above the ground, occupies the Xe-IH well. We find that intra-complex dynamics exhibits a sudden transformation upon increase of the r(HI) bond length, accompanied by abrupt changes in the geometric and dipole parameters. A similar chaotic behavior is predicted to occur for Xe:DI at a shorter r(DI) bond length, which implies stronger coupling between low- and high-frequency motions in the heavier complex. Our calculations confirm a strong enhancement for the r(HI) stretch fundamental and a significant weakening for the first overtone vibrational transitions in Xe:HI, as compared to those in the free HI molecule. A qualitative explanation of this, earlier experimentally detected effect is suggested.

  8. Thermohydrodynamics of boiling in a van der Waals fluid.

    Science.gov (United States)

    Laurila, T; Carlson, A; Do-Quang, M; Ala-Nissila, T; Amberg, G

    2012-02-01

    We present a modeling approach that enables numerical simulations of a boiling Van der Waals fluid based on the diffuse interface description. A boundary condition is implemented that allows in and out flux of mass at constant external pressure. In addition, a boundary condition for controlled wetting properties of the boiling surface is also proposed. We present isothermal verification cases for each element of our modeling approach. By using these two boundary conditions we are able to numerically access a system that contains the essential physics of the boiling process at microscopic scales. Evolution of bubbles under film boiling and nucleate boiling conditions are observed by varying boiling surface wettability. We observe flow patters around the three-phase contact line where the phase change is greatest. For a hydrophilic boiling surface, a complex flow pattern consistent with vapor recoil theory is observed.

  9. Materials perspective on Casimir and van der Waals interactions

    Science.gov (United States)

    Woods, L. M.; Dalvit, D. A. R.; Tkatchenko, A.; Rodriguez-Lopez, P.; Rodriguez, A. W.; Podgornik, R.

    2016-10-01

    Interactions induced by electromagnetic fluctuations, such as van der Waals and Casimir forces, are of universal nature present at any length scale between any types of systems. Such interactions are important not only for the fundamental science of materials behavior, but also for the design and improvement of micro- and nanostructured devices. In the past decade, many new materials have become available, which has stimulated the need for understanding their dispersive interactions. The field of van der Waals and Casimir forces has experienced an impetus in terms of developing novel theoretical and computational methods to provide new insights into related phenomena. The understanding of such forces has far reaching consequences as it bridges concepts in materials, atomic and molecular physics, condensed-matter physics, high-energy physics, chemistry, and biology. This review summarizes major breakthroughs and emphasizes the common origin of van der Waals and Casimir interactions. Progress related to novel ab initio modeling approaches and their application in various systems, interactions in materials with Dirac-like spectra, force manipulations through nontrivial boundary conditions, and applications of van der Waals forces in organic and biological matter are examined. The outlook of the review is to give the scientific community a materials perspective of van der Waals and Casimir phenomena and stimulate the development of experimental techniques and applications.

  10. Evolutionary design of interfacial phase change van der Waals heterostructures.

    Science.gov (United States)

    Kalikka, Janne; Zhou, Xilin; Behera, Jitendra; Nannicini, Giacomo; Simpson, Robert E

    2016-10-27

    We use an evolutionary algorithm to explore the design space of hexagonal Ge2Sb2Te5; a van der Waals layered two dimensional crystal heterostructure. The Ge2Sb2Te5 structure is more complicated than previously thought. Predominant features include layers of Ge3Sb2Te6 and Ge1Sb2Te4 two dimensional crystals that interact through Te-Te van der Waals bonds. Interestingly, (Ge/Sb)-Te-(Ge/Sb)-Te alternation is a common feature for the most stable structures of each generation's evolution. This emergent rule provides an important structural motif that must be included in the design of high performance Sb2Te3-GeTe van der Waals heterostructure superlattices with interfacial atomic switching capability. The structures predicted by the algorithm agree well with experimental measurements on highly oriented, and single crystal Ge2Sb2Te5 samples. By analysing the evolutionary algorithm optimised structures, we show that diffusive atomic switching is probable by Ge atoms undergoing a transition at the van der Waals interface from layers of Ge3Sb2Te6 to Ge1Sb2Te4 thus producing two blocks of Ge2Sb2Te5. Evolutionary methods present an efficient approach to explore the enormous multi-dimensional design parameter space of van der Waals bonded heterostructure superlattices.

  11. CoPt alloy grown on the WSe 2(0 0 0 1) van der Waals surface

    Science.gov (United States)

    Makarov, D.; Liscio, F.; Brombacher, C.; Simon, J. P.; Schatz, G.; Maret, M.; Albrecht, M.

    The structural and magnetic properties of 3-nm-thick CoPt alloys grown on WSe 2(0 0 0 1) at various temperature are investigated. Deposition at room temperature leads to the formation of a chemically disordered fcc CoPt alloy with [1 1 1] orientation. Growth at elevated temperatures induces L1 0 chemical order starting at 470 K accompanied with an increase in grain size and a change in grain morphology. As a consequence of the [1 1 1] growth direction, the CoPt grains can adopt one of the three possible variants of the L1 0 phase with tetragonal c-axis tilted from the normal to the film plane direction at 54°. The average long-range order parameter is found to be 0.35(±0.05) and does not change with the increase in the deposition temperature from 570 to 730 K. This behavior might be related to Se segregation towards the growing facets and surface disorder effects promoted by a high surface-to-volume ratio. Magnetic studies reveal a superparamagnetic behavior for the films grown at 570 and 730 K in agreement with the film morphology and degree of chemical order. The measurements at 10 K reveal the orientation of the easy axis of the magnetization lying basically in the film plane.

  12. CoPt alloy grown on the WSe{sub 2}(0 0 0 1) van der Waals surface

    Energy Technology Data Exchange (ETDEWEB)

    Makarov, D. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany)], E-mail: denys.makarov@uni-konstanz.de; Liscio, F. [SIMAP, INP Grenoble-CNRS-UJF, 1130 rue de la Piscine, BP 75, 38402 Saint Martin d' Heres (France); Brombacher, C. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany); Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz (Germany); Simon, J.P. [SIMAP, INP Grenoble-CNRS-UJF, 1130 rue de la Piscine, BP 75, 38402 Saint Martin d' Heres (France); Schatz, G. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany); Maret, M. [SIMAP, INP Grenoble-CNRS-UJF, 1130 rue de la Piscine, BP 75, 38402 Saint Martin d' Heres (France); Albrecht, M. [Department of Physics, University of Konstanz, D-78457 Konstanz (Germany); Institute of Physics, Chemnitz University of Technology, D-09107 Chemnitz (Germany)

    2008-06-15

    The structural and magnetic properties of 3-nm-thick CoPt alloys grown on WSe{sub 2}(0 0 0 1) at various temperature are investigated. Deposition at room temperature leads to the formation of a chemically disordered fcc CoPt alloy with [1 1 1] orientation. Growth at elevated temperatures induces L1{sub 0} chemical order starting at 470 K accompanied with an increase in grain size and a change in grain morphology. As a consequence of the [1 1 1] growth direction, the CoPt grains can adopt one of the three possible variants of the L1{sub 0} phase with tetragonal c-axis tilted from the normal to the film plane direction at 54 deg. The average long-range order parameter is found to be 0.35({+-}0.05) and does not change with the increase in the deposition temperature from 570 to 730 K. This behavior might be related to Se segregation towards the growing facets and surface disorder effects promoted by a high surface-to-volume ratio. Magnetic studies reveal a superparamagnetic behavior for the films grown at 570 and 730 K in agreement with the film morphology and degree of chemical order. The measurements at 10 K reveal the orientation of the easy axis of the magnetization lying basically in the film plane.

  13. Theoretical investigation of potential energy surface and bound states for the van der Waals complex Ar–BrCl dimer

    Energy Technology Data Exchange (ETDEWEB)

    Zheng, Rui [School of Mathematics and Information Science, North China University of Water Resources and Electric Power, Zhengzhou (China); Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan (China); Li, Song, E-mail: lsong@yangtzeu.edu.cn [School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou (China); Chen, Shan-Jun; Chen, Yan [School of Physics and Optoelectronic Engineering, Yangtze University, Jingzhou (China); Zheng, Li-Min [Key Laboratory of Magnetic Resonance in Biological Systems, State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics, Wuhan Centre for Magnetic Resonance, Wuhan Institute of Physics and Mathematics, Chinese Academy of Sciences, Wuhan (China)

    2015-09-08

    Highlights: • A two-dimensional potential for Ar–BrCl is constructed at the CCSD(T) level. • The PES is characterized by three minima and two saddle points between them. • Bound state calculations were carried out for the complex. - Abstract: The intermolecular potential energy surface (PES) of the ground electronic state for the Ar–BrCl dimer is constructed at the CCSD(T) level with the aug-cc-pVQZ basis set and mid-bond functions. The PES is characterized by three minima and two saddle points. The global minimum corresponding to a collinear Ar–BrCl configuration, which has been observed experimentally, is located at R = 4.10 Å and θ = 2.5° with a well depth of −285.207 cm{sup −1}. A nearly T-shaped structure and an anti-linear Ar–ClBr geometry is also predicted. The bound state calculations are preformed to study intermolecular vibrational modes, rotational levels and average structures for the complex. Our transition frequencies, spectroscopic constants and average structures for all isotopomers of the collinear isomer agree well with experimental data. We have also provided pure rotational transitional frequencies for both nearly T-shaped and anti-linear isomers. These results are significant for further experimental investigations of the Ar–BrCl dimer.

  14. Benzene on Cu(111): II. Molecular assembly due to Lateral van der Waals and Surface-State-Mediated Indirect Interactions

    Science.gov (United States)

    Hyldgaard, Per; Berland, Kristian; Einstein, T. L.

    2010-03-01

    Experiments show that benzene condenses into two different structural phases: a compact and a sparse phase, both of approximately hexagonal symmetry. The vdW-DF calculations demonstrate that the denser benzene-overlayer phase, with lattice constant 6.74 ,s due to direct benzene-benzene vdW attraction. The structure of the second, sparser phase, with lattice spacing 10.24 ,s attributed to the indirect electronic interactions mediated by the well-known metallic surface state on Cu(111). To support this claim, we use a formal Harris-functional approach to evaluate nonperturbatively the asymptotic form of this indirect interaction. Our extended vdW-DF scheme---which combines calculations of molecular physisorption, of direct intermolecular vdW coupling, and of indirect electronic interactions between the molecular adsorbates---accounts well for the structural phases of benzene on Cu(111). Our preliminary vdW-DF study of acene and quinone interactions provides building blocks for modeling of anthraquinone assembly on Cu(111).footnotetextG. Pawin, , L. Bartels, Science 313 (2006) 961

  15. Brane cosmology with a van der Waals equation of state

    CERN Document Server

    Kremer, G M

    2004-01-01

    The evolution of a Universe confined onto a 3-brane embedded in a five-dimensional space-time is investigated where the cosmological fluid on the brane is modeled by the van der Waals equation of state. It is shown that the Universe on the brane evolves in such a manner that three distinct periods concerning its acceleration field are attained: (a) an initial accelerated epoch where the van der Waals fluid behaves like a scalar field with a negative pressure; (b) a past decelerated period which has two contributions, one of them is related to the van der Waals fluid which behaves like a matter field with a positive pressure, whereas the other contribution comes from a term of the Friedmann equation on the brane which is inversely proportional to the scale factor to the fourth power and can be interpreted as a radiation field, and (c) a present accelerated phase due to a cosmological constant on the brane.

  16. A cartography of the van der Waals territories.

    Science.gov (United States)

    Alvarez, Santiago

    2013-06-28

    The distribution of distances from atoms of a particular element E to a probe atom X (oxygen in most cases), both bonded and intermolecular non-bonded contacts, has been analyzed. In general, the distribution is characterized by a maximum at short E···X distances corresponding to chemical bonds, followed by a range of unpopulated distances--the van der Waals gap--and a second maximum at longer distances--the van der Waals peak--superimposed on a random distribution function that roughly follows a d(3) dependence. The analysis of more than five million interatomic "non-bonded" distances has led to the proposal of a consistent set of van der Waals radii for most naturally occurring elements, and its applicability to other element pairs has been tested for a set of more than three million data, all of them compared to over one million bond distances.

  17. Dr Jacob van der Land, marine biologist extraordinary

    OpenAIRE

    Bruggen, van, A.

    2001-01-01

    This contribution is an attempt to sketch the life and works of Dr Jacob van der Land, curator of worms and chief marine biologist of the National Museum of Natural History, on the occasion of his official retirement. Born in 1935, Jacob van der Land read biology at Leiden University (1958-1964), where he obtained his Ph.D. in 1970 on a treatise on the Priapulida under the supervision of Prof. Dr L.D. Brongersma. In 1964 he was appointed curator of worms in the museum. Later on he took over l...

  18. Van der Waals interactions and the limits of isolated atom models at interfaces.

    Science.gov (United States)

    Kawai, Shigeki; Foster, Adam S; Björkman, Torbjörn; Nowakowska, Sylwia; Björk, Jonas; Canova, Filippo Federici; Gade, Lutz H; Jung, Thomas A; Meyer, Ernst

    2016-05-13

    Van der Waals forces are among the weakest, yet most decisive interactions governing condensation and aggregation processes and the phase behaviour of atomic and molecular matter. Understanding the resulting structural motifs and patterns has become increasingly important in studies of the nanoscale regime. Here we measure the paradigmatic van der Waals interactions represented by the noble gas atom pairs Ar-Xe, Kr-Xe and Xe-Xe with a Xe-functionalized tip of an atomic force microscope at low temperature. Individual rare gas atoms were fixed at node sites of a surface-confined two-dimensional metal-organic framework. We found that the magnitude of the measured force increased with the atomic radius, yet detailed simulation by density functional theory revealed that the adsorption induced charge redistribution strengthened the van der Waals forces by a factor of up to two, thus demonstrating the limits of a purely atomic description of the interaction in these representative systems.

  19. Eglon Hendrik van der Neer (1635/36 - 1703) : Zijn leven en werk

    NARCIS (Netherlands)

    Schavemaker, E.

    2009-01-01

    Eglon van der Neer. His Life and His Work In his own time Eglon van der Neer was highly successful. His acclaim endured throughout the eighteenth century. Nowadays he is rated as a second-rate master. Van der Neer was born in Amsterdam in 1635 or 1636 as the son of the now more famous landscape pain

  20. Dynamics of Gold Nanoparticles on Carbon Nanostructures Driven by van der Waals and Electrostatic Interactions.

    Science.gov (United States)

    La Torre, Alessandro; Gimenez-Lopez, Maria del Carmen; Fay, Michael W; Lucas, Carlos Herreros; Brown, Paul D; Khlobystov, Andrei N

    2015-06-01

    Transmission electron microscopy studies on the assembly and growth of gold nanoparticles on carbon nanotubes supported on few-layer graphene and amorphous carbon reveal a competition between van der Waals forces and electrostatic interactions, enabling controlled positioning and sizing of adsorbed nanoparticles at the nanochannels formed between the carbon nanotube and the few-layer graph-ene surface.

  1. Kinetic Roughening and Material Optical Properties Influence on Van der Waals/Casimir Forces

    NARCIS (Netherlands)

    van Zwol, P. J.; Palasantzas, G.

    Atomic force microscopy measurements and force theory calculations using the Lifshitz theory show that van der Waals/Casimir dispersive forces have a strong dependence on surface roughness and material optical properties. It is found that at separations below 100 nm the roughness effect is

  2. Van der Waals forces in pNRQED

    Energy Technology Data Exchange (ETDEWEB)

    Shtabovenko, Vladyslav [Physik-Department, Technische Universität München, James-Franck-Str. 1, 85748 Garching (Germany)

    2016-01-22

    We report on the calculation of electromagnetic van der Waals forces [1] between two hydrogen atoms using non-relativistic effective field theories (EFTs) of QED for large and small momentum transfers with respect to the intrinsic energy scale of the hydrogen atom. Our results reproduce the well known London and Casimir-Polder forces.

  3. Šveitsi hommage Mies van der Rohele / Kai Lobjakas

    Index Scriptorium Estoniae

    Lobjakas, Kai, 1975-

    1999-01-01

    Šveitsi väikelinna Buschi ehitatud voolava ruumilahendusega maja meenutab Mies van der Rohe kujundatud saksa paviljoni maailmanäitusel Barcelonas. Materjalideks betoon, puit, klaas. Loodud on palju erineva kõrgusega pindu maja ja seda ümbritseva müüri vahel. Interjööris punakas tammepuit. Arhitekt: Peter+Christian Frei, Architekten.

  4. Higher-accuracy van der Waals density functional

    DEFF Research Database (Denmark)

    Lee, Kyuho; Murray, Éamonn D.; Kong, Lingzhu

    2010-01-01

    We propose a second version of the van der Waals density functional of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)], employing a more accurate semilocal exchange functional and the use of a large-N asymptote gradient correction in determining the vdW kernel. The predicted binding energy...

  5. Comment on the Paper by van der Smagt

    OpenAIRE

    Schwaninger, Markus

    2006-01-01

    The article comments on a paper by van der Smagt on the social construction of shared realities and models. According to the theory of social constructivism, collective cognition is perceived as a social process by which such creation and representation often take place. The research focuses on the difference between causation and constitution.

  6. Šveitsi hommage Mies van der Rohele / Kai Lobjakas

    Index Scriptorium Estoniae

    Lobjakas, Kai, 1975-

    1999-01-01

    Šveitsi väikelinna Buschi ehitatud voolava ruumilahendusega maja meenutab Mies van der Rohe kujundatud saksa paviljoni maailmanäitusel Barcelonas. Materjalideks betoon, puit, klaas. Loodud on palju erineva kõrgusega pindu maja ja seda ümbritseva müüri vahel. Interjööris punakas tammepuit. Arhitekt: Peter+Christian Frei, Architekten.

  7. The Lyapunov exponents of the Van der Pol oscillator

    NARCIS (Netherlands)

    Grasman, J.; Verhulst, F.; Shih, S.D.

    2005-01-01

    Lyapunov exponents characterize the dynamics of a system near its attractor. For the Van der Pol oscillator these are quantities for which an approximation should be at hand. Similar to the asymptotic approximation of amplitude and period, expressions are derived for the non-zero Lyapunov exponent

  8. Een concentratieprobleem bij B.J. van der Walt

    Directory of Open Access Journals (Sweden)

    S. Griffioen

    2010-07-01

    Full Text Available B.J. van der Walt’s concentration problem This contribution probes the concept of secularism, a key notion of B.J. van der Walt’s “Transforming power” (2007. It is found that Van der Walt’s interpretation of secularism rests on a double assumption. The first assumption is that human nature is intrinsically religious. Humans cannot live without putting their trust in something. The second is that this religious nature manifests itself in “concentrated” ways, rather than dispersing itself over a plurality of objects. These assumptions in tandem explain why Van der Walt holds the view that atheism, agnosticism and even overt indifference in matters of faith are at heart propelled by convictions that share the main features of positive religions. It also explains why he assumes that all these convictions tend towards one and the same goal: to gain dominance in the public realm. This article is sympathetic towards the first assumption, and skeptical towards the second. It is argued that the “concentration- thesis” fails to do justice to world and life-views that obviously do not claim total allegiance. To illustrate this point it turns to the phenomenon of “multiple religious participation”, as well as to different strands within contemporary humanism. It concludes that the main problem may well be that secular culture has little to offer to satisfy the innate religious drive in humankind.

  9. Mies van der Rohe preemia 2011 / Karen Jagodin

    Index Scriptorium Estoniae

    Jagodin, Karen, 1982-

    2011-01-01

    20. juunil antakse Barcelonas inglise arhitektile Sir David Chipperfieldile Berliini Neues Museumi restaureerimise eest üle 2011. aasta Mies van der Rohe arhitektuuripreemia. Nimetatud võidutöö viis suuremat konkurenti, varem preemia pälvinud hooneid ja nende autoreid. Sir David Chipperfieldist, Berliini Neues Muuseumi restaureerimisest. Loetletud preemia nominendid Eestist

  10. Mies van der Rohe preemia 2011 / Karen Jagodin

    Index Scriptorium Estoniae

    Jagodin, Karen, 1982-

    2011-01-01

    20. juunil antakse Barcelonas inglise arhitektile Sir David Chipperfieldile Berliini Neues Museumi restaureerimise eest üle 2011. aasta Mies van der Rohe arhitektuuripreemia. Nimetatud võidutöö viis suuremat konkurenti, varem preemia pälvinud hooneid ja nende autoreid. Sir David Chipperfieldist, Berliini Neues Muuseumi restaureerimisest. Loetletud preemia nominendid Eestist

  11. The role of van der waals interaction on quantum-mechanical tunneling

    Energy Technology Data Exchange (ETDEWEB)

    Takayanagi, Toshiyuki; Kurosaki, Yuzuru [Japan Atomic Energy Research Inst., Tokai, Ibaraki (Japan). Tokai Research Establishment

    1998-10-01

    We present three-dimensional quantum cumulative reaction probabilities for the F + H{sub 2}, D{sub 2}, and HD reactions with a special emphasis on resonances associated with quasi-bound states localized in the reactant van der Waals region of the potential energy surface. The accurate ab initio potential surface of Stark and Werner and the less accurate 5SEC-W surface developed by Truhlar and co-workers have been employed. (author)

  12. Electromagnetically induced transparency with controlled van der Waals interaction

    CERN Document Server

    Wu, Huaizhi; Shen, Li-Tuo; Chen, Rong-Xin; Yang, Zhen-Biao; Zheng, Shi-Biao

    2014-01-01

    The transmission of light through cold Rydberg atoms controlled by a second laser beam under the condition of the electromagnetically induced transparency (EIT) has been shown to exhibit highly optical nonlinearity. Here we study this effect with two individually addressed Rydberg atoms under the influence of the interatomic van der Waals interaction. We derive an effectively atomic Raman transition model that can potentially overcome the limits of applications for EIT with atoms of the ladder-type level configuration. By probing one of the atoms, we observe four doublets of absorption induced by the Autler-Townes (AT) splitting and van der Waals interaction. In particular, we find that the EIT center keeps unshifted compared with the case of interatomic interaction free, which demonstrated that the interference among the multiple transition channels is basically destructive. The EIT with controlled Rydberg-Rydberg interaction among few atoms provides a versatile tool for engineering the propagation dynamics ...

  13. Persistent hysteresis in graphene-mica van der Waals heterostructures.

    Science.gov (United States)

    Mohrmann, Jens; Watanabe, Kenji; Taniguchi, Takashi; Danneau, Romain

    2015-01-09

    We report the study of electronic transport in graphene-mica van der Waals heterostructures. We have designed various graphene field-effect devices in which mica is utilized as a substrate and/or gate dielectric. When mica is used as a gate dielectric we observe a very strong positive gate voltage hysteresis of the resistance, which persists in samples that were prepared in a controlled atmosphere down to even millikelvin temperatures. In a double-gated mica-graphene-hBN van der Waals heterostructure, we found that while a strong hysteresis occurred when mica was used as a substrate/gate dielectric, the same graphene sheet on mica substrate no longer showed hysteresis when the charge carrier density was tuned through a second gate with the hBN dielectric. While this hysteretic behavior could be useful for memory devices, our findings confirm that the environment during sample preparation has to be controlled strictly.

  14. Van der Waals explosion of cold Rydberg clusters

    CERN Document Server

    Faoro, R; Archimi, M; Masella, G; Valado, M M; Arimondo, E; Mannella, R; Ciampini, D; Morsch, O

    2015-01-01

    We report on the direct measurement in real space of the effect of the van der Waals forces between individual Rydberg atoms on their external degrees of freedom. Clusters of Rydberg atoms with inter-particle distances of around 5 {\\mu}m are created by first generating a small number of seed excitations in a magneto-optical trap, followed by off-resonant excitation that leads to a chain of facilitated excitation events. After a variable expansion time the Rydberg atoms are field ionized, and from the arrival time distributions the size of the Rydberg cluster after expansion is calculated. Our experimental results agree well with a numerical simulation of the van der Waals explosion.

  15. Goden en mensen. De godsdienstwetenschap van Gerardus van der Leeuw 1890-1950

    NARCIS (Netherlands)

    Hofstee, Willem

    1997-01-01

    This study examines Van der Leeuw's science of religion as it developed in the years between the two world wars. In the first chapter I give a theoretical justification for the questions I raise and provide a short historical introduction to the development of the history of religion in the Netherla

  16. Van der Waals interaction between two crossed carbon nanotubes

    OpenAIRE

    Zhbanov, Alexander I.; Pogorelov, Evgeny G.; Chang, Yia-Chung

    2008-01-01

    The analytical expressions for the van der Waals potential energy and force between two crossed carbon nanotubes are presented. The Lennard-Jones potential for two carbon atoms and the method of the smeared out approximation suggested by L.A. Girifalco were used. The exact formula is expressed in terms of rational and elliptical functions. The potential and force for carbon nanotubes were calculated. The uniform potential curves for single- and multi- wall nanotubes were plotted. The equilibr...

  17. Van der Waals interactions of parallel and concentric nanotubes

    OpenAIRE

    Schroder, Elsebeth; Hyldgaard, Per

    2003-01-01

    For sparse materials like graphitic systems and carbon nanotubes the standard density functional theory (DFT) faces significant problems because it cannot accurately describe the van der Waals interactions that are essential to the carbon-nanostructure materials behavior. While standard implementations of DFT can describe the strong chemical binding within an isolated, single-walled carbon nanotube, a new and extended DFT implementation is needed to describe the binding between nanotubes. We ...

  18. Dynamic changes of phase in a van der Waals fluid

    Science.gov (United States)

    Hagan, R.; Serrin, J.

    1984-03-01

    This paper gives sufficient conditions to guarantee the existence of a shock layer solution connecting two different equilibrium states in a van der Waals fluid. In particular, the equilibrium states can belong to two different phases of the fluid. The constitutive laws come from a modified Korteweg theory which is compatible with the Clausius Duhem inequality. The Clausius Duhem inequality in turn gives rise to a Liapunov function. The main mathematical tool is the LaSalle invariance principle.

  19. Impulsive Homoclinic Chaos in Van der Pol Jerk System

    Institute of Scientific and Technical Information of China (English)

    丁玉梅; 张琪昌

    2010-01-01

    A 3D continuous autonomous chaotic system is reported, which contains a cubic term and six system parameters. Basic dynamic properties of the new Van der Pol Jerk system are studied by means of theoretical analysis and numerical simulation. Based on the Silnikov theorem, the chaotic characterisitics of the dynamic system are discussed. Using Cardano formula and series solution of differential equation, eigenvalue problem and the existence of homoclinic orbit are studied. Furthermore, a rigorous proof for th...

  20. Van der Waals and Casimir-Polder interactions between neutrons

    Directory of Open Access Journals (Sweden)

    Babb James F.

    2016-01-01

    Full Text Available We investigate the van der Waals interaction between neutrons using the theory of Casimir and Polder, wherein the potential for asymptotically large separations falls off as the inverse seventh power, and compare it to the similar interaction between a neutron and a proton, for which the asymptotic interaction falls off as the inverse fourth power. Modifications of the formalism to extend the validity to smaller separations using dynamic electric and magnetic dipole polarizability data are discussed.

  1. Approximate transformations for van der Pol-type equations

    Directory of Open Access Journals (Sweden)

    R. K. Gazizov

    2006-01-01

    Full Text Available Classification of van der Pol-type equations with respect to admitted approximate transformation groups transforming a small parameter is given. It is shown that approximate symmetries transforming the small parameter as well as the usual approximate symmetries can be used for approximate integration (e.g., by method of successive reduction of order of ordinary differential equations with a small parameter.

  2. Scaling Laws for van der Waals Interactions in Nanostructured Materials

    Science.gov (United States)

    Gobre, Vivekanand; Tkatchenko, Alexandre

    2014-03-01

    Van der Waals (vdW) forces originate from interactions between fluctuating multipoles in matter and play a significant role in the structure and stability of nanostructured materials. Many models used to describe vdW interactions in nanomaterials are based on a simple pairwise-additive approximation, neglecting the strong electrodynamic response effects caused by long-range fluctuations in matter. We develop and utilize an efficient microscopic method to demonstrate that vdW interactions in nanomaterials act at distances greater than typically assumed, and can be characterized by different scaling laws depending on the dimensionality and size of the system. Specifically, we study the behaviour of vdW interactions in single-layer and multilayer graphene, fullerenes of varying size, single-wall carbon nanotubes and graphene nanoribbons. As a function of nanostructure size, the van der Waals coefficients follow unusual trends for all of the considered systems, and deviate significantly from the conventionally employed pairwise-additive picture. We propose that the peculiar van der Waals interactions in nanostructured materials could be exploited to control their self-assembly.

  3. Van der Waals torque induced by external magnetic fields

    CERN Document Server

    Esquivel-Sirvent, R; Palomono-Ovando, M

    2010-01-01

    We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III-IV semiconductors such as $InSb$, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of $InSb$. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of $InSb$ increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropic materials when the magnetic fields is close to 1 T.

  4. Van der Waals torque induced by external magnetic fields

    Energy Technology Data Exchange (ETDEWEB)

    Esquivel-Sirvent, R.; Cocoletzi, G. H.; Palomino-Ovando, M.

    2010-01-01

    We present a method for inducing and controlling van der Waals torques between two parallel slabs using a constant magnetic field. The torque is calculated using the Barash theory of dispersive torques. In III–IV semiconductors such as InSb, the effect of an external magnetic field is to induce an optical anisotropy, in an otherwise isotropic material, that will in turn induce a torque. The calculations of the torque are done in the Voigt configuration, with the magnetic field parallel to the surface of the slabs. As a case study we consider a slab made of calcite and a second slab made of InSb. In the absence of magnetic field there is no torque. As the magnetic field increases, the optical anisotropy of InSb increases and the torque becomes different from zero, increasing with the magnetic field. The resulting torque is of the same order of magnitude as that calculated using permanent anisotropicmaterials when the magnetic fields is close to 1 T.

  5. Spatially Correlated Disorder in Epitaxial van der Waals Heterostructures

    Science.gov (United States)

    Laanait, Nouamane; Zhang, Zhan; Schleputz, Christian; Liu, Ying; Wojcik, Michael; Myers-Ward, Rachael; Gaskill, D. Kurt; Fenter, Paul; Li, Lian

    The structural cohesion of van der Waals (vdW) heterostructures relies upon a cooperative balance between strong intra-layer bonded interactions and weak inter-layer coupling. The confinement of extended defects to within a single vdW layer and competing interactions introduced by epitaxial constraints could generate fundamentally new structural disorders. Here we report on the presence of spatially correlated and localized disorder states that coexist with the near perfect crystallographic order along the growth direction of epitaxial vdW heterostructure of Bi2Se3/graphene/SiC grown by molecular beam epitaxy. With the depth penetration of hard X-ray diffraction microscopy and high-resolution surface scattering, we imaged local structural configurations from the atomic to mesoscopic length scales, and found that these disorder states result as a confluence of atomic scale modulations in the strength of vdW layer-layer interactions and nanoscale boundary conditions imposed by the substrate. These findings reveal a vast landscape of novel disorder states that can be manifested in epitaxial vdW heterostructures. Supported by the Wigner Fellowship program at Oak Ridge Nat'l Lab.

  6. Measuring the thermal boundary resistance of van der Waals contacts using an individual carbon nanotube.

    Science.gov (United States)

    Hirotani, Jun; Ikuta, Tatsuya; Nishiyama, Takashi; Takahashi, Koji

    2013-01-16

    Interfacial thermal transport via van der Waals interaction is quantitatively evaluated using an individual multi-walled carbon nanotube bonded on a platinum hot-film sensor. The thermal boundary resistance per unit contact area was obtained at the interface between the closed end or sidewall of the nanotube and platinum, gold, or a silicon dioxide surface. When taking into consideration the surface roughness, the thermal boundary resistance at the sidewall is found to coincide with that at the closed end. A new finding is that the thermal boundary resistance between a carbon nanotube and a solid surface is independent of the materials within the experimental errors, which is inconsistent with a traditional phonon mismatch model, which shows a clear material dependence of the thermal boundary resistance. Our data indicate the inapplicability of existing phonon models when weak van der Waals forces are dominant at the interfaces.

  7. Cl-intercalated graphene on SiC: Influence of van der Waals forces

    KAUST Repository

    Cheng, Yingchun

    2013-01-01

    The atomic and electronic structures of Cl-intercalated epitaxial graphene on SiC are studied by first-principles calculations. By increasing the Cl concentration, doping levels from n-type to slightly p-type are achieved on the SiC(0001) surface, while a wider range of doping levels is possible on the SiC(0001̄) surface. We find that the Cl atoms prefer bonding to the substrate rather than to the graphene. By varying the Cl concentration the doping level can be tailored. Consideration of van der Waals forces improves the distance between the graphene and the substrate as well as the binding energy, but it is not essential for the formation energy. For understanding the doping mechanism the introduction of non-local van der Waals contributions to the exchange correlation functional is shown to be essential. Copyright © EPLA, 2013.

  8. Disaini ja rahvaste saatusest / Daniel Van der Velden ; interv. Kristjan Mändmaa

    Index Scriptorium Estoniae

    Van der Velden, Daniel

    2008-01-01

    17.-27. X 2008 oli Eesti Kunstiakadeemias näitus "Marsilt. Omaalgatuslikud projektid graafilises disainis". Kuraatorid: tšehhi disainerid Adam Machacek ja Radim Peshko. 17. X esinesid EKA saalis loengutega James Goggin Londoni firmast Practice ja Daniel van der Velden Hollandi disainikollektiivist Metahaven. 16. V osales D. van der Velden Eesti Disainiinstituudi korraldatud kohabrändingu-teemalises ümarlauas. D. van der Velden disaini, poliitika ja kohabrändingu tulevikust, Metahaveni disainitöödest

  9. Disaini ja rahvaste saatusest / Daniel Van der Velden ; intervjueerinud Kristjan Mändmaa

    Index Scriptorium Estoniae

    Van der Velden, Daniel

    2011-01-01

    17.-27. X 2008 oli Eesti Kunstiakadeemias näitus "Marsilt. Omaalgatuslikud projektid graafilises disainis". Kuraatorid: tšehhi disainerid Adam Machacek ja Radim Peshko. 17. X esinesid EKA saalis loengutega James Goggin Londoni firmast Practice ja Daniel van der Velden Hollandi disainikollektiivist Metahaven. 16. V osales D. van der Velden Eesti Disainiinstituudi korraldatud kohabrändingu-teemalises ümarlauas. D. van der Velden disaini, poliitika ja kohabrändingu tulevikust, Metahaveni disainitöödest

  10. Disaini ja rahvaste saatusest / Daniel Van der Velden ; intervjueerinud Kristjan Mändmaa

    Index Scriptorium Estoniae

    Van der Velden, Daniel

    2011-01-01

    17.-27. X 2008 oli Eesti Kunstiakadeemias näitus "Marsilt. Omaalgatuslikud projektid graafilises disainis". Kuraatorid: tšehhi disainerid Adam Machacek ja Radim Peshko. 17. X esinesid EKA saalis loengutega James Goggin Londoni firmast Practice ja Daniel van der Velden Hollandi disainikollektiivist Metahaven. 16. V osales D. van der Velden Eesti Disainiinstituudi korraldatud kohabrändingu-teemalises ümarlauas. D. van der Velden disaini, poliitika ja kohabrändingu tulevikust, Metahaveni disainitöödest

  11. Disaini ja rahvaste saatusest / Daniel Van der Velden ; interv. Kristjan Mändmaa

    Index Scriptorium Estoniae

    Van der Velden, Daniel

    2008-01-01

    17.-27. X 2008 oli Eesti Kunstiakadeemias näitus "Marsilt. Omaalgatuslikud projektid graafilises disainis". Kuraatorid: tšehhi disainerid Adam Machacek ja Radim Peshko. 17. X esinesid EKA saalis loengutega James Goggin Londoni firmast Practice ja Daniel van der Velden Hollandi disainikollektiivist Metahaven. 16. V osales D. van der Velden Eesti Disainiinstituudi korraldatud kohabrändingu-teemalises ümarlauas. D. van der Velden disaini, poliitika ja kohabrändingu tulevikust, Metahaveni disainitöödest

  12. k Sequences of Generalized Van der Laan and Generalized Perrin Polynomials

    CERN Document Server

    Kaygisiz, Kenan

    2011-01-01

    In this paper, we present k sequences of Generalized Van der Laan Polynomials and Generalized Perrin Polynomials using Genaralized Fibonacci and Lucas Polynomials. We give some properties of these polynomials. We also obtain generalized order-k Van der Laan Numbers, k sequences of generalized order-k Van der Laan Numbers, generalized order-k Perrin Numbers and k sequences of generalized order-k Perrin Numbers. In addition, we examine the relationship between them.

  13. Theoretical Study of the Pyridine-Helium van der Waals Complexes

    DEFF Research Database (Denmark)

    v, Hubert; Henriksen, Christian; Fernandez, Berta

    2015-01-01

    In this study we evaluate a high-level ab initio ground-state intermolecular potential-energy surface for the pyridine–He van der Waals complex, using the CCSD(T) method and Dunning’s augmented correlation consistent polarized valence double-ζ basis set extended with a set of 3s3p2d1f1g midbond f...

  14. Van der Waals density functional study of water binding in metal-organic frameworks

    Science.gov (United States)

    Lee, Kyuho; Smit, Berend; Neaton, Jeffrey B.

    2013-03-01

    Metal-organic frameworks (MOFs) are promising candidate materials for gas storage, gas separation and catalysis. However, MOFs are vulnerable to humid air and effective surface area drops dramatically on an exposure to water. In this theoretical study, we investigate the interaction of single water molecule with MOF-74 on different binding sites by using van der Waals density functionals. We also explore how different type of metal cations affect the interaction.

  15. Carvacrolreiches Oregano-Öl als Futterzusatz: Interview met Hans van der Mheen

    NARCIS (Netherlands)

    Grohs, Birgit; Mheen, van der H.J.C.J.

    2011-01-01

    In dit interview met Hans van der Mheen van het PPO-agv te Lelystad worden de mogelijkheden van het gebruik van etherische olie gewonnen uit oregano; origanum vulgare en origanum heracleoticum, geteeld in Nederland besproken. De olie kan gebruikt worden in voer voor pluimvee en varkens. Gezocht word

  16. van der Waals Equation of State and Solution Theories%van der Waals状态方程与溶液理论

    Institute of Scientific and Technical Information of China (English)

    刘国杰; 黑恩成

    2007-01-01

    阐明了van der Waals状态方程与溶液理论间的密切关系.由van der Waals状态方程中的内压力和自由体积简捷地导得Scatchard-Hildebrand正规溶液理论、无热溶液理论和Flory-Huggins聚合物溶液理论.表明这些理论都是建立在van der Waals流体的基础上,为进一步改进这些理论提供了一条切实可行的思路.

  17. Universal curves for the van der Waals interaction between single-walled carbon nanotubes.

    Science.gov (United States)

    Pogorelov, Evgeny G; Zhbanov, Alexander I; Chang, Yia-Chung; Yang, Sung

    2012-01-17

    We report very simple and accurate algebraic expressions for the van der Waals (VDW) potentials and the forces between two parallel and crossed carbon nanotubes. The Lennard-Jones potential for two carbon atoms and the method of the smeared-out approximation suggested by Girifalco were used. It is found that the interaction between parallel and crossed tubes is described by two universal curves for parallel and crossed configurations that do not depend on the van der Waals constants, the angle between tubes, and the surface density of atoms and their nature but only on the dimensionless distance. The explicit functions for equilibrium VDW distances, well depths, and maximal attractive forces have been given. These results may be used as a guide for the analysis of experimental data to investigate the interaction between nanotubes of various natures.

  18. van der Waals binding and band structure effects in graphene overlayers and graphane multilayers

    Science.gov (United States)

    Hyldgaard, Per; Rohrer, Jochen

    2011-03-01

    We study graphene formation (by selective Si evaporation) and adhesion on SiC surfaces as well as stacking and binding of graphane multilayers using a number of versions of the van der Waals Density Functional (vdW-DF) method and plane-wave density functional theory calculations. For the graphene/SiC systems and for the graphane multilayers we document that the bonding is entirely dominated by van der Waals (vdW) forces. At the same time we find that dispersive forces acting on the layers produce significant modifications in the graphene and graphane band structure. We interpret the changes and discuss a competition between wave function hybridization and interaction with the charge enhancement (between the layers) that results from density overlap. Supported by Svenska Vetenskapsrådet VR #621-2008-4346.

  19. Van der Waals interaction between two crossed carbon nanotubes.

    Science.gov (United States)

    Zhbanov, Alexander I; Pogorelov, Evgeny G; Chang, Yia-Chung

    2010-10-26

    The analytical expressions for the van der Waals potential energy and force between two crossed carbon nanotubes are presented. The Lennard-Jones potential between pairs of carbon atoms and the smeared-out approximation suggested by L. A. Girifalco (J. Phys. Chem. 1992, 96, 858) were used. The exact formula is expressed in terms of rational and elliptical functions. The potential and force for carbon nanotubes were calculated. The uniform potential curves for single- and multiwall nanotubes were plotted. The equilibrium distance, maximal attractive force, and potential energy have been evaluated.

  20. Analytical solution for Van der Pol-Duffing oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Kimiaeifar, A. [Department of Mechanical Engineering, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of); Saidi, A.R. [Department of Mechanical Engineering, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of)], E-mail: saidi@mail.uk.ac.ir; Bagheri, G.H.; Rahimpour, M. [Department of Mechanical Engineering, Shahid Bahonar University of Kerman, Kerman (Iran, Islamic Republic of); Domairry, D.G. [Department of Mechanical Engineering, Noshirvani Institute of Technology, Babol (Iran, Islamic Republic of)

    2009-12-15

    In this paper, the problem of single-well, double-well and double-hump Van der Pol-Duffing oscillator is studied. Governing equation is solved analytically using a new kind of analytic technique for nonlinear problems namely the 'Homotopy Analysis Method' (HAM), for the first time. Present solution gives an expression which can be used in wide range of time for all domain of response. Comparisons of the obtained solutions with numerical results show that this method is effective and convenient for solving this problem. This method is a capable tool for solving this kind of nonlinear problems.

  1. Simon van der Meer in the AA Control Room

    CERN Multimedia

    CERN PhotoLab

    1984-01-01

    Simon van der Meer, spiritus rector of the Antiproton Accumulator, in the AA Control Room. Inventor of stochastic cooling, on which the AA was based, and of the magnetic horn, with which the antiprotons were focused, he also wrote most of the software with which the AA was controlled, and spent uncountable numbers of hours in this chair to tickle the AA to top performance. 8 months after this picture was taken, he received, in October 1984, the Nobel prize, together with Carlo Rubbia, the moving force behind the whole Proton-Antiproton Collider project that led to the discovery, in 1983, of the W and Z intermediate bosons.

  2. Van der Woude syndrome with unusual developmental disorders

    Directory of Open Access Journals (Sweden)

    Vijay Kumar Ambaldhage

    2014-01-01

    Full Text Available Van der Woude syndrome is a rare developmental disorder characterized by a combination of congenital lower lip pits, cleft palate alone or with cleft lip in some cases, and hypodontia. It occurs in approximately 2% of the population with facial clefts. Its prevalence varies from one in 100,000 to 200,000 births. This case report details a unique case of Vander Woude syndrome in a seven-year-old girl and her mother, with median lip pits, cleft lip and cleft palate, missing lateral incisors, and retained deciduous teeth, along with transposition of teeth.

  3. Casa 50' x 50': Ludwig Mies van der Rohe

    OpenAIRE

    Mantovani Genari, Eduardo

    2007-01-01

    El trabajo se enfoca hacia el análisis arquitectónico del material producido por el arquitecto [Mies van der Rohe] y sus colaboradores. Este análisis, realizado a partir de la información recopilada, tiene por objeto aclarar el orden interno del proyecto de la Casa 50' x 50', comprender la jerarquía de las decisiones y determinar los elementos básicos y sus criterios de relación. Se propone un acercamiento sensible y directo a la obra de arquitectura, a su realidad física y constructiva, basa...

  4. Field Effect in Graphene-Based van der Waals Heterostructures

    DEFF Research Database (Denmark)

    Stradi, Daniele; Papior, Nick Rübner; Hansen, Ole

    2017-01-01

    Stacked van der Waals (vdW) heterostructures where semiconducting two-dimensional (2D) materials are contacted by overlaid graphene electrodes enable atomically thin, flexible electronics. We use first-principles quantum transport simulations of graphene-contacted MoS2 devices to show how...... the transistor effect critically depends on the stacking configuration relative to the gate electrode. We can trace this behavior to the stacking-dependent response of the contact region to the capacitive electric field induced by the gate. The contact resistance is a central parameter and our observation...

  5. Van der Woude syndrome: Management in the mixed dentition

    Directory of Open Access Journals (Sweden)

    Sonahita Agarwal

    2013-01-01

    Full Text Available This article presents the case of a patient with Van der Woude syndrome treated with orthodontic and orthopedic intervention in the mixed dentition stage. The patient had a bilateral cleft of the lip and alveolus accompanied by lip pits on the lower lip. Intra-orally, there was bilateral anterior and posterior cross-bite with a collapsed maxilla. The maxillary transverse deficiency was managed with orthopedic expansion and the second phase of treatment involved secondary alveolar bone grafting followed by retention with functional regulator-3. The mild maxillary retrognathia and deficient lip support was managed with dental compensation.

  6. Van der Waals phase transition in the framework of holography

    CERN Document Server

    Zeng, Xiao-Xiong

    2015-01-01

    Phase structure of the quintessence Reissner-Nordstr\\"{o}m-AdS black hole is probed with the nonlocal observables such as holographic entanglement entropy and two point correlation function. Our result shows that, as the case of the thermal entropy, both the observables exhibit the similar Van der Waals-like phase transition. To reinforce the conclusion, we further check the equal area law for the first order phase transition and critical exponent of the heat capacity for the second order phase transition. We also discuss the effect of the state parameter on the phase structure of the nonlocal observables.

  7. Skynbaar ‘onmoontlike’ kunsvorme: Strijdom van der Merwe se aardkuns in die konteks van die Suid-Afrikaanse kunsmark

    Directory of Open Access Journals (Sweden)

    Jean le Clus-Theron

    2012-11-01

    Full Text Available Hierdie artikel bied ’n ondersoek na die werk van Strijdom van der Merwe, die gedagte van aardkuns en die kunstenaarsboek in die konteks van die historiese en eietydse kunsmark. Die stelling dat ‘indien iets kuns genoem kan word, kan dit ook verkoop word’ word gebruik as vertrekpunt – ook in die geval van kunsvorme wat skynbaar ‘onmoontlik’ is om te verkoop, soos aardkuns. Hierdie artikel besin oor die werk van Strijdom van der Merwe, die bekendste Suid Afrikaanse aardkunstenaar, binne die ietwat ongewone konteks (vir aardkuns van die Suid-Afrikaanse kunsmark. Hy is ’n suksesvolle voltydse aardkunstenaar; nogal ’n uitsonderlike verskynsel binne die Suid-Afrikaanse kunsomgewing. Aardkuns is allerweë in die 1960s beskou as ’n ‘onmoontlike’ kunsvorm om te verkoop, en hierdie artikel ondersoek die geldigheid van hierdie stelling vir vandag. Die navorsingsmetode van die artikel is semi-gestruktureerde onderhoude en ’n literatuurstudie. My argument is, met verwysing na Van der Merwe se werk, dat die stelling ‘indien iets kuns genoem kan word, dit verkoopbaar is’ waar mag wees, maar met die moontlike voorbehoud van ‘verkoopbaar – op die een of ander manier’.

  8. Franckeite as a naturally occurring van der Waals heterostructure

    Science.gov (United States)

    Molina-Mendoza, Aday J.; Giovanelli, Emerson; Paz, Wendel S.; Niño, Miguel Angel; Island, Joshua O.; Evangeli, Charalambos; Aballe, Lucía; Foerster, Michael; van der Zant, Herre S. J.; Rubio-Bollinger, Gabino; Agraït, Nicolás; Palacios, J. J.; Pérez, Emilio M.; Castellanos-Gomez, Andres

    2017-01-01

    The fabrication of van der Waals heterostructures, artificial materials assembled by individual stacking of 2D layers, is among the most promising directions in 2D materials research. Until now, the most widespread approach to stack 2D layers relies on deterministic placement methods, which are cumbersome and tend to suffer from poor control over the lattice orientations and the presence of unwanted interlayer adsorbates. Here, we present a different approach to fabricate ultrathin heterostructures by exfoliation of bulk franckeite which is a naturally occurring and air stable van der Waals heterostructure (composed of alternating SnS2-like and PbS-like layers stacked on top of each other). Presenting both an attractive narrow bandgap (<0.7 eV) and p-type doping, we find that the material can be exfoliated both mechanically and chemically down to few-layer thicknesses. We present extensive theoretical and experimental characterizations of the material's electronic properties and crystal structure, and explore applications for near-infrared photodetectors. PMID:28194037

  9. Equations of State: From the Ideas of van der Waals to Association Theories

    DEFF Research Database (Denmark)

    Kontogeorgis, Georgios; Economou, Ioannis G.

    2010-01-01

    The ideas of van der Waals have resulted to cubic equations of state like Soave–Redlich–Kwong (SRK) and Peng–Robinson (PR) which are widely used in the petroleum and chemical industries. It is often thought that the range of applicability of van der Waals-type models is limited to mixtures...

  10. Mihkelson paljastas van der Lindeni ärihuvid Venemaal / Helga Koger

    Index Scriptorium Estoniae

    Koger, Helga, 1945-

    2007-01-01

    Riigikogu EL asjade komisjoni esimees Marko Mihkelson tutvustas materjale, mis viitavad hiljuti Eestit kritiseerinud Euroopa Nõukogu Parlamentaarse Assamblee presidendi Rene van der Linderi ärihuvile Venemaal. Mihkelsoni sõnade järgi võivad van der Lindenil olla majandushuvid seoses Vladimiri oblasti Sobinski rajooni rajatava tööstuspargiga

  11. Mihkelson paljastas van der Lindeni ärihuvid Venemaal / Helga Koger

    Index Scriptorium Estoniae

    Koger, Helga, 1945-

    2007-01-01

    Riigikogu EL asjade komisjoni esimees Marko Mihkelson tutvustas materjale, mis viitavad hiljuti Eestit kritiseerinud Euroopa Nõukogu Parlamentaarse Assamblee presidendi Rene van der Linderi ärihuvile Venemaal. Mihkelsoni sõnade järgi võivad van der Lindenil olla majandushuvid seoses Vladimiri oblasti Sobinski rajooni rajatava tööstuspargiga

  12. Bartholomeus van der Helst (1613-1670): een studie naar zijn leven en zijn werk

    NARCIS (Netherlands)

    van Gent, J.F.J.M.

    2011-01-01

    Bartholomeus van der Helst was a leading portrait painter in the Northern Netherlands in the 17th century. This monograph reconstructs his career and his circle of patrons based on the surviving works and documents. Van der Helst was born in Haarlem around 1613. In the early 1630s he moved to

  13. Underwater adhesion of abalone: The role of van der Waals and capillary forces

    Energy Technology Data Exchange (ETDEWEB)

    Lin, A.Y.M., E-mail: albertlin22@yahoo.com [Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093 (United States); Brunner, R. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States)] [Department of Nanoengineering, University of California, San Diego, La Jolla, CA 92093 (United States); Chen, P.Y. [Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093 (United States); Talke, F.E. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States)] [Center for Magnetic Recording Research, University of California, San Diego, La Jolla, CA 92093 (United States); Meyers, M.A. [Department of Mechanical and Aerospace Engineering, University of California, San Diego, La Jolla, CA 92093 (United States)] [Department of Nanoengineering, University of California, San Diego, La Jolla, CA 92093 (United States)] [Materials Science and Engineering Program, University of California, San Diego, La Jolla, CA 92093 (United States)

    2009-08-15

    The observation of the pedal foot of the red abalone Haliotis rufescens reveals the presence of micrometer-scaled setae terminating in nanometer-sized cylindrical fibrils, with some resemblance to those found on the gecko foot. Atomic force microscopy (AFM) pull-off force measurements on a single seta are compared with theoretical estimates for van der Waals attraction obtained through the Johnson-Kendall-Roberts (JKR) equation, approximately 600 nN, and show agreement. The use of the JKR equation is justified through an analysis of the shape of the fibril extremities (parabolic) as well as their diameter ({approx}200 nm). Measurements under varying humidity conditions indicate that additional capillary interactions play a role, since the pull-off force increases with humidity. It is proposed that both van der Waals and capillary forces play a role in the attachment mechanism of H. rufescens, effectively enabling suction to reach its theoretical limit. Bulk pull-off force measurements on entire live animals yield an average detachment stress of 115 kPa, consistent with theoretical estimates. The setae and nanoscale fibril terminations enable compliance to surfaces with a variety of roughnesses, effectively sealing the interface, in addition to providing capillary and van der Waals forces.

  14. Van der Waals interaction between microparticle and uniaxial crystal with application to hydrogen atoms and multiwall carbon nanotubes

    CERN Document Server

    Blagov, E V; Mostepanenko, V M

    2005-01-01

    The Lifshitz theory of the van der Waals force is extended for the case of an atom (molecule) interacting with a plane surface of an uniaxial crystal or with a long solid cylinder or cylindrical shell made of isotropic material or uniaxial crystal. For a microparticle near a semispace or flat plate made of an uniaxial crystal the exact expressions for the free energy of the van der Waals and Casimir-Polder interaction are presented. An approximate expression for the free energy of microparticle- cylinder interaction is obtained which becomes precise for microparticle-cylinder separations much smaller than cylinder radius. The obtained expressions are used to investigate the van der Waals interaction between hydrogen atoms (molecules) and graphite plates or multiwall carbon nanotubes. To accomplish this the behavior of graphite dielectric permittivities along the imaginary frequency axis is found using the optical data for the complex refractive index of graphite for the ordinary and extraordinary rays. It is ...

  15. Ds Dirk van der Hoff se bydrae tot die ontwikkeling van die Christelik-nasionale onderwysstelsel in die ZAR

    Directory of Open Access Journals (Sweden)

    E. Oliver

    1992-01-01

    Full Text Available Reverend Dirk van der Hoff's contribution to the development of Christian National Education in the Zuid-Afrikaansche Republiek Today, Afrikaners are closely associated with the Christian National system of education. This system has a long and interesting history and many people have been involved in its development. This article shows the vital and essential role that Reverend Dirk van der Hoff, the first resident minister of religion in the ZAR, played in the structuring of CNE.

  16. Implication of Two-Coupled Differential Van der Pol Duffing Oscillator in Weak Signal Detection

    Science.gov (United States)

    Peng, Hang-hang; Xu, Xue-mei; Yang, Bing-chu; Yin, Lin-zi

    2016-04-01

    The principle of the Van der Pol Duffing oscillator for state transition and for determining critical value is described, which has been studied to indicate that the application of the Van der Pol Duffing oscillator in weak signal detection is feasible. On the basis of this principle, an improved two-coupled differential Van der Pol Duffing oscillator is proposed which can identify signals under any frequency and ameliorate signal-to-noise ratio (SNR). The analytical methods of the proposed model and the construction of the proposed oscillator are introduced in detail. Numerical experiments on the properties of the proposed oscillator compared with those of the Van der Pol Duffing oscillator are carried out. Our numerical simulations have confirmed the analytical treatment. The results demonstrate that this novel oscillator has better detection performance than the Van der Pol Duffing oscillator.

  17. Cosmological models described by a mixture of van der Waals fluid and dark energy

    CERN Document Server

    Kremer, G M

    2003-01-01

    The Universe is modeled as a binary mixture whose constituents are described by a van der Waals fluid and by a dark energy density. The dark energy density is considered either as the quintessence or as the Chaplygin gas. The irreversible processes concerning the energy transfer between the van der Waals fluid and the gravitational field are taken into account. This model can simulate: (a) an inflationary period where the acceleration grows exponentially and the van der Waals fluid behaves like an inflaton; (b) an inflationary period where the acceleration is positive but it decreases and tends to zero whereas the energy density of the van der Waals fluid decays; (c) a decelerated period which corresponds to a matter dominated period with a non-negative pressure; and (d) a present accelerated period where the dark energy density outweighs the energy density of the van der Waals fluid.

  18. Influence of van der Waals forces on the adsorption structure of benzene on silicon studied using density functional theory

    DEFF Research Database (Denmark)

    Johnston, Karen; Kleis, Jesper; Lundqvist, Bengt

    2008-01-01

    Two different adsorption configurations of benzene on the Si(001)-(2×1) surface, the tight-bridge and butterfly structures, were studied using density functional theory. Several exchange and correlation functionals were used, including the recently developed van der Waals density functional (vdW-...

  19. Flexible ferroelectric element based on van der Waals heteroepitaxy.

    Science.gov (United States)

    Jiang, Jie; Bitla, Yugandhar; Huang, Chun-Wei; Do, Thi Hien; Liu, Heng-Jui; Hsieh, Ying-Hui; Ma, Chun-Hao; Jang, Chi-Yuan; Lai, Yu-Hong; Chiu, Po-Wen; Wu, Wen-Wei; Chen, Yi-Chun; Zhou, Yi-Chun; Chu, Ying-Hao

    2017-06-01

    We present a promising technology for nonvolatile flexible electronic devices: A direct fabrication of epitaxial lead zirconium titanate (PZT) on flexible mica substrate via van der Waals epitaxy. These single-crystalline flexible ferroelectric PZT films not only retain their performance, reliability, and thermal stability comparable to those on rigid counterparts in tests of nonvolatile memory elements but also exhibit remarkable mechanical properties with robust operation in bent states (bending radii down to 2.5 mm) and cycling tests (1000 times). This study marks the technological advancement toward realizing much-awaited flexible yet single-crystalline nonvolatile electronic devices for the design and development of flexible, lightweight, and next-generation smart devices with potential applications in electronics, robotics, automotive, health care, industrial, and military systems.

  20. Engineering Low Dimensional Materials with van der Waals Interaction

    Science.gov (United States)

    Jin, Chenhao

    Two-dimensional van der Waals materials grow into a hot and big field in condensed matter physics in the past decade. One particularly intriguing thing is the possibility to stack different layers together as one wish, like playing a Lego game, which can create artificial structures that do not exist in nature. These new structures can enable rich new physics from interlayer interaction: The interaction is strong, because in low-dimension materials electrons are exposed to the interface and are susceptible to other layers; and the screening of interaction is less prominent. The consequence is rich, not only from the extensive list of two-dimensional materials available nowadays, but also from the freedom of interlayer configuration, such as displacement and twist angle, which creates a gigantic parameter space to play with. On the other hand, however, the huge parameter space sometimes can make it challenging to describe consistently with a single picture. For example, the large periodicity or even incommensurability in van der Waals systems creates difficulty in using periodic boundary condition. Worse still, the huge superlattice unit cell and overwhelming computational efforts involved to some extent prevent the establishment of a simple physical picture to understand the evolution of system properties in the parameter space of interlayer configuration. In the first part of the dissertation, I will focus on classification of the huge parameter space into subspaces, and introduce suitable theoretical approaches for each subspace. For each approach, I will discuss its validity, limitation, general solution, as well as a specific example of application demonstrating how one can obtain the most important effects of interlayer interaction with little computation efforts. Combining all the approaches introduced will provide an analytic solution to cover majority of the parameter space, which will be very helpful in understanding the intuitive physical picture behind

  1. Chaos of the Relativistic Forced van der Pol Oscillator

    CERN Document Server

    Ashkenazy, Yu; Horwitz, L P

    1997-01-01

    A manifestly relativistically covariant form of the van der Pol oscillator in 1+1 dimensions is studied. We show that the driven relativistic equations, for which x and t are coupled, relax very quickly to a pair ofidenticaldecoupled equations, due to a rapid vanishing of the ``angular momentum'' (the boost in 1+1 dimensions). A similar effect occurs in the damped driven covariant Duffing oscillator previously treated. This effect is an example of entrainment, or synchronization (phase locking), of coupled chaotic systems. The Lyapunov exponents are calculated using the very efficient method of Habib and Ryne. We show a Poincare map that demonstrates this effect and maintains remarkable stability in spite of the inevitable accumulation of computer error in the chaotic region. For our choice of parameters, the positive Lyapunov exponent is about 0.242 almost independently of the integration method.

  2. Critical fluctuations in models with van der Waals interactions

    CERN Document Server

    Vovchenko, V; Gorenstein, M I; Poberezhnyuk, R V; Stoecker, H

    2016-01-01

    Particle number fluctuations are considered within the van der Waals (VDW) equation, which contains both attractive (mean-field) and repulsive (eigenvolume) interactions. The VDW equation is used to calculate the scaled variance of particle number fluctuations in generic Boltzmann VDW system and in nuclear matter. The strongly intensive measures $\\Delta[E^*,N]$ and $\\Sigma[E^*,N]$ of the particle number and excitation energy fluctuations are also considered, and, similarly, show singular behavior near the critical point. The $\\Delta[E^*,N]$ measure is shown to attain both positive and negative values in the vicinity of critical point. Based on universality argument, similar behavior is expected to occur in the vicinity of the QCD critical point.

  3. Heterostructures based on inorganic and organic van der Waals systems

    Directory of Open Access Journals (Sweden)

    Gwan-Hyoung Lee

    2014-09-01

    Full Text Available The two-dimensional limit of layered materials has recently been realized through the use of van der Waals (vdW heterostructures composed of weakly interacting layers. In this paper, we describe two different classes of vdW heterostructures: inorganic vdW heterostructures prepared by co-lamination and restacking; and organic-inorganic hetero-epitaxy created by physical vapor deposition of organic molecule crystals on an inorganic vdW substrate. Both types of heterostructures exhibit atomically clean vdW interfaces. Employing such vdW heterostructures, we have demonstrated various novel devices, including graphene/hexagonal boron nitride (hBN and MoS2 heterostructures for memory devices; graphene/MoS2/WSe2/graphene vertical p-n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high-performance transistors.

  4. A crossover in anisotropic nanomechanochemistry of van der Waals crystals

    Energy Technology Data Exchange (ETDEWEB)

    Shimamura, Kohei [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan); Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Graduate School of System Informatics, Kobe University, Kobe 657-8501 (Japan); Misawa, Masaaki [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan); Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Li, Ying [Argonne Leadership Computing Facility, Argonne National Laboratory, Argonne, Illinois 60439 (United States); Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya [Collaboratory for Advanced Computing and Simulations, Department of Physics and Astronomy, Department of Computer Science, Department of Chemical Engineering and Materials Science, University of Southern California, Los Angeles, California 90089-0242 (United States); Shimojo, Fuyuki [Department of Physics, Kumamoto University, Kumamoto 860-8555 (Japan)

    2015-12-07

    In nanoscale mechanochemistry, mechanical forces selectively break covalent bonds to essentially control chemical reactions. An archetype is anisotropic detonation of layered energetic molecular crystals bonded by van der Waals (vdW) interactions. Here, quantum molecular dynamics simulations reveal a crossover of anisotropic nanomechanochemistry of vdW crystal. Within 10{sup −13} s from the passage of shock front, lateral collision produces NO{sub 2} via twisting and bending of nitro-groups and the resulting inverse Jahn-Teller effect, which is mediated by strong intra-layer hydrogen bonds. Subsequently, as we transition from heterogeneous to homogeneous mechanochemical regimes around 10{sup −12} s, shock normal to multilayers becomes more reactive, producing H{sub 2}O assisted by inter-layer N-N bond formation. These time-resolved results provide much needed atomistic understanding of nanomechanochemistry that underlies a wider range of technologies.

  5. Jet-Cooled Infrared Laser Spectroscopy in the Umbrella νb{2} Vibration Region of NH_3: Improving the Potential Energy Surface Model of the NH_3-Ar Van Der Waals Complex

    Science.gov (United States)

    Asselin, Pierre; Jabri, Atef; Potapov, Alexey; Loreau, Jérome; van der Avoird, Ad

    2017-06-01

    Taking advantage of our sensitive laser spectrometer coupled to a pulsed slit jet, we recorded near the νb{2} vibration a series of rovibrational transitions of the NH_3-Ar van der Waals (vdW) complex. These transitions involve in the ground vibrational state several internal rotor states corresponding to the ortho{NH_3} and para{NH_3} spin modifications of the complex. They are labeled by Σ_{a}(j,k), Σ_{s}(j,k), Π_{a}(j,k) and Π_{s}(j,k) where Σ(K=0) and Π(K=1) indicate the projection K of the total rotational angular momentum J on the vdW axis, the superscripts s and a designate a symmetric or antisymmetric NH_3 inversion wave function, and j, k quantum numbers indicate the correlation between the internal-rotor state of the complex and the j, k rotational state of the free NH_3 monomer. Five bands have been identified, only one of which was partly observed before. They include transitions starting from the Σ_{a}(j=0 or j=1) state without any internal angular momentum, consequently they can be assigned from the band contour of a linear-molecule-like K=0, ΔJ=1 transition. The energies and splittings of the rovibrational levels of the νb{2}=1←0 spectrum derived from the analysis of the Π_{s}, Σ_{s}(j=1)← Σ_{a}(j=0), k=0 bands and mostly of the Σ_{s}, Π_{s} and Σ_{a}(j=1)←Σ_{a}(j=1), k=1 bands bring relevant information about the νb{2} dependence of the NH_3-Ar interaction, the rovibrational dynamics of the NH_3-Ar complex and provide a sensitive test of a recently developed 4D potential energy surface that includes explicitly its dependence on the umbrella motion. P. Asselin, Y. Berger, T. R. Huet, R. Motiyenko, L. Margulès, R. J. Hendricks, M. R. Tarbutt, S. Tokunaga, B. Darquié, PCCP 19, 4576 (2017), G. T. Fraser, A.S. Pine and W. A. Kreiner, J. Chem. Phys. 94, 7061 (1991). J. Loreau, J. Liévin, Y. Scribano and A. van der Avoird, J. Chem. Phys. 141, 224303 (2014).

  6. Ontogenic Caste Differences in the Van der Vecht Organ of Primitively Eusocial Neotropical Paper Wasps

    Science.gov (United States)

    de Souza, André Rodrigues; Petrocelli, Iacopo; Lino-Neto, José; Santos, Eduardo Fernando; Noll, Fernando Barbosa; Turillazzi, Stefano

    2016-01-01

    Recent studies have reported incipient morphological caste dimorphism in the Van der Vecht organ size of some temperate Polistes paper wasps. Whether species other than the temperate ones show a similar pattern remains elusive. Here, we have studied some Neotropical Polistes species. By comparing females collected through the year, we showed caste related differences in the size of the Van der Vecht organ in P. ferreri (body size corrected Van der Vech organ size of queens = 0.45 ± 0.06, workers = 0.38 ± 0.07 mm2, p = 0.0021), P. versicolor (body size corrected Van der Vech organ size of queens = 0.54 ± 0.11, workers = 0.46 ± 0.09 mm2, p = 0.010), but not P. simillimus (body size corrected Van der Vech organ size of queens = 0.52 ± 0.05, workers = 0.49 ± 0.06 mm2, p = 0.238). Therefore, it seems that queens and workers of some Neotropical Polistes have diverged in their ontogenic trajectory of the Van der Vecht organ size, providing clear evidence for incipient morphological caste dimorphism. As Polistes are distributed mostly in the tropics, we propose that physical caste differences may be widespread in the genus. Also, we highlight that morphological divergence in the queen–worker phenotypes may have started through differential selection of body structures, like the Van der Vecht organ. PMID:27167514

  7. Investigations of the Rg-BrCl (Rg = He, Ne, Ar, Kr, Xe) binary van der Waals complexes: ab initio intermolecular potential energy surfaces, vibrational states and predicted pure rotational transition frequencies

    Science.gov (United States)

    Li, Song; Zheng, Rui; Chen, Shan-Jun; Chen, Yan; Chen, Peng

    2017-03-01

    The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg = He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species.

  8. Investigations of the Rg-BrCl (Rg=He, Ne, Ar, Kr, Xe) binary van der Waals complexes: ab initio intermolecular potential energy surfaces, vibrational states and predicted pure rotational transition frequencies.

    Science.gov (United States)

    Li, Song; Zheng, Rui; Chen, Shan-Jun; Chen, Yan; Chen, Peng

    2017-03-05

    The intermolecular potential energy surfaces (PESs) of the ground electronic state for the Rg-BrCl (Rg=He, Ne, Ar, Kr, Xe) van der Waals complexes have been constructed by using the coupled-cluster method in combination with the augmented quadruple-zeta correlation-consistent basis sets supplemented with an additional set of bond functions. The features of the anisotropic PESs for these complexes are remarkably similar, which are characterized by three minima and two saddle points between them. The global minimum corresponds to a collinear Rg-Br-Cl configuration. Two local minima, correlate with an anti-linear Rg-Cl-Br geometry and a nearly T-shaped structure, can also be located on each PES. The quantum bound state calculations enable us to investigate intermolecular vibrational states and rotational energy levels of the complexes. The transition frequencies are predicted and are fitted to obtain their corresponding spectroscopic constants. In general, the periodic trends are observed for this complex family. Comparisons with available experimental data for the collinear isomer of Ar-BrCl demonstrate reliability of our theoretical predictions, and our results for the other two isomers of Ar-BrCl as well as for other members of the complex family are also anticipated to be trustable. Except for the collinear isomer of Ar-BrCl, the data presented in this paper would be beneficial to improve our knowledge for these experimentally unknown species.

  9. Concurrent Van der Woude syndrome and Turner syndrome: A case report

    OpenAIRE

    Los, Evan; Baines, Hayley; Guttmann-Bauman, Ines

    2017-01-01

    Most cases of Van der Woude syndrome are caused by a mutation to interferon regulatory factor 6 on chromosome 1. Turner syndrome is caused by complete or partial absence of the second sex chromosome in girls. We describe a unique case of the two syndromes occurring concurrently though apparently independently in a girl with Van der Woude syndrome diagnosed at birth and Turner syndrome at 14 years 9 months. Short stature was initially misattributed to Van der Woude syndrome and pituitary insuf...

  10. Influence of van der Waals forces on the adsorption structure of benzene on silicon

    CERN Document Server

    Johnston, Karen; Lundqvist, Bengt I; Nieminen, Risto M

    2008-01-01

    Two different adsorption configurations of benzene on the Si(001)-(2x1) surface, the tight-bridge and butterfly structures, were studied using density functional theory. Several exchange and correlation functionals were used, including the recently developed vdW-DF functional, which accounts for the effect of van der Waals forces. In contrast to the PBE, revPBE and other GGA functionals, the vdW-DF functional finds that, for most coverages, the adsorption energy of the butterfly structure is greater than that of the tight-bridge structure.

  11. van der Waals interactions between nanotubes and nanoparticles for controlled assembly of composite nanostructures.

    Science.gov (United States)

    Rance, Graham A; Marsh, Dan H; Bourne, Stephen J; Reade, Thomas J; Khlobystov, Andrei N

    2010-08-24

    We have demonstrated that ubiquitous van der Waals forces are significant in controlling the interactions between nanoparticles and nanotubes. The adsorption of gold nanoparticles (AuNPs) on nanotubes (MWNTs) obeys a simple quadratic dependence on the nanotube surface area, regardless of the source of AuNPs and MWNTs. Changes in the geometric parameters of the components have pronounced effects on the affinity of nanoparticles for nanotubes, with larger, more polarizable nanostructures exhibiting stronger attractive interactions, the impact of which changes in the following order MWNT diameter > AuNP diameter > MWNT length.

  12. Interfactant-mediated quasi-Frank-van der Merwe growth of Pb on Si(111)

    Science.gov (United States)

    Schmidt, Th.; Bauer, E.

    2000-12-01

    The influence of interfactants (Au, Ag) on the growth of Pb on Si(111) is studied by low-energy electron microscopy in the temperature range from 260 K to 460 K. On the Si(111)-(7×7) surface Pb grows in the Stranski-Krastanov mode, on the Si(111)-(3×3)R30°-Au and on the Si(111)-(6×6)-Au surface in the quasi-Frank-van der Merwe (layer-by-layer) mode. On the Si(111)-(3×3)R30°-Ag surface the growth mode changes from layer-by-layer below 300 K to the Stranski-Krastanov mode above 300 K. The temperature dependence of the growth cannot be explained by thermodynamics but is governed by kinetics. The analysis of the maximum island density in terms of the atomistic nucleation theory gives acceptable values for nucleus size and energies only in the layer-by-layer growth regime. In the Stranski-Krastanov growth regime abnormal values are obtained that are attributed to high cluster mobility on the initial two-dimensional layer. The conditions leading to quasi-Frank-van der Merwe growth are discussed.

  13. NATO Advanced Research Workshop on Dynamics of Polyatomic Van der Waals Complexes

    CERN Document Server

    Janda, Kenneth

    1991-01-01

    This publication is the Proceedings of the NATO Advanced Research Workshop (ARW) on the Dynamics of Polyatomic Van der Waals Molecules held at the Chateau de Bonas, Castera-Verduzan, France, from August 21 through August 26, 1989. Van der Waals complexes provide important model problems for understanding energy transfer and dissipation. These processes can be described in great detail for Van der Waals complexes, and the insight gained from such studies can be applied to more complicated chemical problems that are not amenable to detailed study. The workshop concentrated on the current questions and future prospects for extend­ ing our highly detailed knowledge of triatomic Van der Waals molecule dynamics to polyatomic molecules and clusters (one molecule surrounded by several, or up to sev­ eral tens of, atoms). Both experimental and theoretical studies were discussed, with particular emphasis on the dynamical behavior of dissociation as observed in the dis­ tributions of quantum states of the dissociatio...

  14. Jazõk do demokrati ne dovedjot / Max van der Stoel

    Index Scriptorium Estoniae

    Stoel, Max van der, 1924-2011

    1999-01-01

    OSCE vähemusrahvuste ülemkomissari Max van der Stoeli pöördumine Lennart Meri poole seoses riigikeele oskuse nõude sisseviimisega Riigikogu valimise ja kohaliku omavalitsuse volikogu valimise seadusesse

  15. ENPA juht usub Vene arengusse / Rene van der Linden ; interv. Erkki Bahovski

    Index Scriptorium Estoniae

    Linden, Rene van der

    2006-01-01

    Vt. ka Postimees : na russkom jazõke 2. juuni lk. 7. Euroopa Nõukogu Parlamentaarse Assamblee president Rene van der Linden Euroopa Nõukogu (EN) rollist, Venemaa ja Eesti arengutest EN-i liikmena. Lisa: Euroopa parlamentide kogu

  16. Jazõk do demokrati ne dovedjot / Max van der Stoel

    Index Scriptorium Estoniae

    Stoel, Max van der, 1924-2011

    1999-01-01

    OSCE vähemusrahvuste ülemkomissari Max van der Stoeli pöördumine Lennart Meri poole seoses riigikeele oskuse nõude sisseviimisega Riigikogu valimise ja kohaliku omavalitsuse volikogu valimise seadusesse

  17. ENPA juht usub Vene arengusse / Rene van der Linden ; interv. Erkki Bahovski

    Index Scriptorium Estoniae

    Linden, Rene van der

    2006-01-01

    Vt. ka Postimees : na russkom jazõke 2. juuni lk. 7. Euroopa Nõukogu Parlamentaarse Assamblee president Rene van der Linden Euroopa Nõukogu (EN) rollist, Venemaa ja Eesti arengutest EN-i liikmena. Lisa: Euroopa parlamentide kogu

  18. The scholar and the state in search of van der Waerden

    CERN Document Server

    Soifer, Alexander

    2015-01-01

    Bartel Leendert van der Waerden made major contributions to algebraic geometry, abstract algebra, quantum mechanics, and other fields. He liberally published on the history of mathematics. His 2-volume work Modern Algebra is one of the most influential and popular mathematical books ever written. It is therefore surprising that no monograph has been dedicated to his life and work. Van der Waerden’s record is complex. In attempting to understand his life, the author assembled thousands of documents from numerous archives in Germany, the Netherlands, Switzerland and the United States which revealed fascinating and often surprising new information about van der Waerden. Soifer traces Van der Waerden’s early years in a family of great Dutch public servants, his life as professor in Leipzig during the entire Nazi period, and his personal and professional friendship with one of the great physicists Werner Heisenberg. We encounter heroes and villains and a much more numerous group in between these two extremes. ...

  19. De mens in zijn totaliteit. De antropologische benadering in het werk van Lammert van der Horst (1893-1978

    Directory of Open Access Journals (Sweden)

    Bart Karstens

    2010-09-01

    Full Text Available The totality of man. The anthropological approach to psychiatry in the work of Lammert van der Horst (1893-1978 The anthropological approach was one of the new approaches to psychiatry that emerged in the interbellum. In the Netherlands professor Van der Horst (VU-university Amsterdam and the municipal University of Amsterdam was its most prominent proponent. The general idea of the anthropological approach was to integrate the various ways of knowing then available. A psychiatric disease was seen as the result of a failure in the self-realisation of the individual person. This required to consider all relevant aspects relating to the patient’s existence. How to tailor these ideas to concrete forms of diagnosis and methods of treatment was no easy matter and Van der Horst devoted himself all his life to this task. He first sought to classify man in three or four types of character inspired by the works of Heymans and Kretschmer. Then he tried to give the specific human aspect its place in psychiatry by introducing a ‘pneumatic’ dimension in his analysis of persons. He also connected this dimension to Calvinism, the church he belonged to. In the 1940’s he made a turn towards existentialism and tried to connect this philosophy to anthropological psychiatry. In spite of its fragmentary appearance I believe it is possible to discern a degree of continuity in the work of Van der Horst. The concern with the specifically human was always central to him. Moreover Van der Horst saw no strict divide between addressing questions in psychiatry and thinking about the greater questions of life which provides an explanation for his meandering thoughts. The dissertation of J.H. van den Berg which appeared in 1946 offers an interesting contrast to Van der Horst. To Van den Berg the anthropological approach was no more than a method best developed by Binswanger. Van den Berg tested this method and concluded that the approach could offer hermeneutic

  20. Van der Waals interactions and Photoelectric Effect in Noncommutative Quantum Mechanics

    Institute of Scientific and Technical Information of China (English)

    LI Kang; CHAMOUN Nidal

    2007-01-01

    We calculate the long-range Van der Waals force and the photoelectric cross section in a noncommutative setup. It is argued that non-commutativity effects could not be discerned for the Van der Waals interactions. The result for the photoelectric effect shows deviation from the usual commutative one, which in principle can be used to put bounds on the space-space non-commutativity parameter.

  1. Modified van der Pauw method based on formulas solvable by the Banach fixed point method

    OpenAIRE

    2012-01-01

    We propose a modification of the standard van der Pauw method for determining the resistivity and Hall coefficient of flat thin samples of arbitrary shape. Considering a different choice of resistance measurements we derive a new formula which can be numerically solved (with respect to sheet resistance) by the Banach fixed point method for any values of experimental data. The convergence is especially fast in the case of almost symmetric van der Pauw configurations (e.g., clover shaped samples).

  2. to different joint combinations and the Sharp/van der Heijde radiographic score

    DEFF Research Database (Denmark)

    Ejbjerg, Bo Jannik; Vestergaard, Aage; Jacobsen, Søren;

    2005-01-01

    To compare 2 magnetic resonance imaging (MRI) approaches and radiographic evaluation according to the Sharp/van der Heijde method with respect to sensitivity to change in joint destruction in patients with rheumatoid arthritis (RA).......To compare 2 magnetic resonance imaging (MRI) approaches and radiographic evaluation according to the Sharp/van der Heijde method with respect to sensitivity to change in joint destruction in patients with rheumatoid arthritis (RA)....

  3. El Legado de Johannes Diderik van der Waals y su Conferencia Nobel The Legacy of Johannes Diderik van der Waals and his Nobel Lecture

    Directory of Open Access Journals (Sweden)

    José O Valderrama

    2010-01-01

    Full Text Available El autor presenta la conferencia que dictó Johannes Diderik van der Waals cuando recibió el premio Nobel de física el año 1910. Este trabajo es una contribución a las celebraciones que se realizan alrededor del mundo para conmemorar los cien años desde que van der Waals recibiera el máximo galardón. La conferencia resume en forma simple pero detallada algunos de sus principales logros; en particular la ecuación de estado, el principio de estados correspondientes y la teoría de mezclas. Estas pioneras ideas de van der Waals han influenciado efectivamente varias áreas de la ciencia, pero en particular estos tres conceptos, y que fueron los que motivaron su merecido premio Nobel. Este artículo concluye que aún después de 100 años del Nobel y más de 125 de la Tesis doctoral, y a pesar de muchos otros extraordinarios logros en la física y en la termodinámica, los conceptos de van der Waals siguen más vigentes que nunca.The author presents the conference that van der Waals delivered when he received the Nobel Prize for Physics in 1910. This work is a contribution to the several commemorating activities that are be-ing organized around the world to celébrate the 100 years since van der Waals was awarded the máximum prize. The conference summarizes some of the main achievements and in particular the equation of state, the principie of corresponding states and the theory of mixtures. These pioneering ideas of van der Waals have influenced several áreas of physics and thermodynamics but in particular these three concepts, which motivated his merited Nobel Prize. The paper concludes that even after a hundred years since the Nobel and more than 125 years since the doctoral thesis, and despite of many other extraordinary advances in physics and thermodynamics, the concepts of van der Waals continué more valid than ever.

  4. Curious and Interesting——Products from Van Eijk & Van der Lubbe%奇趣设计

    Institute of Scientific and Technical Information of China (English)

    夏天

    2009-01-01

    @@ 来自荷兰的Van Eijk & Van der Lubbe是近些年来业界最受瞩目的设计组合之一.用设计师自己的话说,他们的设计总是趋向于提出问题,将人们生活中熟知的事物,例如生活用品或是陈设等,重新设计改良.

  5. Molecular interactions in particular Van der Waals nanoclusters

    Energy Technology Data Exchange (ETDEWEB)

    Jungclas, Hartmut; Schmidt, Lothar [Marburg Univ. (Germany). Chemistry Dept.; Komarov, Viacheslav V.; Popova, Anna M. [Marburg Univ. (Germany). Chemistry Dept.; Lomonosov Moscow State Univ. (Russian Federation). Skobeltzin Inst. of Nuclear Physics

    2017-04-01

    A method is presented to analyse the interaction energies in a nanocluster, which is consisting of three neutral molecules bound by non-covalent long range Van der Waals forces. One of the molecules (M{sub 0}) in the nanocluster has a permanent dipole moment, whereas the two other molecules (M{sub 1} and M{sub 2}) are non-polar. Analytical expressions are obtained for the numerical calculation of the dispersion and induction energies of the molecules in the considered nanocluster. The repulsive forces at short intermolecular distances are taken into account by introduction of damping functions. Dispersion and induction energies are calculated for a nanocluster with a definite geometry, in which the polar molecule M{sub 0} is a linear hydrocarbon molecule C{sub 5}H{sub 10} and M{sub 1} and M{sub 2} are pyrene molecules. The calculations are done for fixed distances between the two pyrene molecules. The results show that the induction energies in the considered three-molecular nanocluster are comparable with the dispersion energies. Furthermore, the sum of induction energies in the substructure (M{sub 0}, M{sub 1}) of the considered nanocluster is much higher than the sum of induction energies in a two-molecular nanocluster with similar molecules (M{sub 0}, M{sub 1}) because of the absence of an electrostatic field in the latter case. This effect can be explained by the essential intermolecular induction in the three-molecular nanocluster.

  6. Thermionic Energy Conversion Based on Graphene van der Waals Heterostructures

    Science.gov (United States)

    Liang, Shi-Jun; Liu, Bo; Hu, Wei; Zhou, Kun; Ang, L. K.

    2017-01-01

    Seeking for thermoelectric (TE) materials with high figure of merit (or ZT), which can directly converts low-grade wasted heat (400 to 500 K) into electricity, has been a big challenge. Inspired by the concept of multilayer thermionic devices, we propose and design a solid-state thermionic devices (as a power generator or a refrigerator) in using van der Waals (vdW) heterostructure sandwiched between two graphene electrodes, to achieve high energy conversion efficiency in the temperature range of 400 to 500 K. The vdW heterostructure is composed of suitable multiple layers of transition metal dichalcogenides (TMDs), such as MoS2, MoSe2, WS2 and WSe2. From our calculations, WSe2 and MoSe2 are identified as two ideal TMDs (using the reported experimental material’s properties), which can harvest waste heat at 400 K with efficiencies about 7% to 8%. To our best knowledge, this design is the first in combining the advantages of graphene electrodes and TMDs to function as a thermionic-based device. PMID:28387363

  7. Consistent van der Waals radii for the whole main group.

    Science.gov (United States)

    Mantina, Manjeera; Chamberlin, Adam C; Valero, Rosendo; Cramer, Christopher J; Truhlar, Donald G

    2009-05-14

    Atomic radii are not precisely defined but are nevertheless widely used parameters in modeling and understanding molecular structure and interactions. The van der Waals radii determined by Bondi from molecular crystals and data for gases are the most widely used values, but Bondi recommended radius values for only 28 of the 44 main-group elements in the periodic table. In the present Article, we present atomic radii for the other 16; these new radii were determined in a way designed to be compatible with Bondi's scale. The method chosen is a set of two-parameter correlations of Bondi's radii with repulsive-wall distances calculated by relativistic coupled-cluster electronic structure calculations. The newly determined radii (in A) are Be, 1.53; B, 1.92; Al, 1.84; Ca, 2.31; Ge, 2.11; Rb, 3.03; Sr, 2.49; Sb, 2.06; Cs, 3.43; Ba, 2.68; Bi, 2.07; Po, 1.97; At, 2.02; Rn, 2.20; Fr, 3.48; and Ra, 2.83.

  8. LA CASA CON PATIO EN MIES VAN DER ROHE / House with patio from Mies van der Rohe

    Directory of Open Access Journals (Sweden)

    José Altés Bustelo

    2013-05-01

    Full Text Available RESUMEN Una revisión del tema Casa con Patio, con especial atención a los planteamientos desarrollados por Mies van der Rohe durante sus últimos años en Berlín, a propósito del conocido dibujo denominado “Casa con tres patios”. Se explora su pensamiento arquitectónico a partir de los datos historiográficos de su trayectoria, más los que se pueden deducir del análisis de los dibujos y croquis previos del arquitecto. El conjunto de proyectos en que aparece el tema es muy amplio durante ese tiempo y los dibujos conservados ofrecen múltiples reflexiones. Sobre ese soporte se examinan conceptos relativos a la definición espacial y formal, donde aparecen cuestiones que ligan esa definición con los sistemas y materiales constructivos. Malla estructural, muro, pared de vidrio y patio vividero, vinculados necesariamente a sus respectivas cualidades tectónicas, adquieren el sentido de materiales de proyecto utilizados para definir un particular modo de entender la arquitectura en el que el usuario está presente siempre como destinatario de la misma. Finalmente, se plantea la utilidad didáctica del análisis de esos dibujos para el progreso del conocimiento en el proyecto arquitectónico.SUMMARY A review of the theme, House with Patio, with special reference to the plans developed by Mies van der Rohe during his last years in Berlin, in relation to the well–known drawing called: “House with three patios”. His architectural thoughts are explored through the historiographic data of his career, plus those that can be deduced from the analysis of the architect’s previous drawings and sketches. The group of projects, in which the theme appears is prolific from that time, and the preserved drawings offer multiple opportunities for reflection. Concepts on that medium are examined, relative to spatial and formal definition, where questions appear that link that definition with the constructive systems and materials. Structural mesh

  9. EDITORIAL: Van der Waals interactions in advanced materials, in memory of David C Langreth Van der Waals interactions in advanced materials, in memory of David C Langreth

    Science.gov (United States)

    Hyldgaard, Per; Rahman, Talat S.

    2012-10-01

    rationale for considering a more general switch to nonlocal functionals. Graziano et al note that the accuracy in the description of some soft layered systems like graphene and boron-nitride can be increased by changing the exchange description away from what was suggested in the original vdW-DF method. Hanke et al focused on the weak chemisorption of ethene on the various Cu facets that have an increasing degree of openness and provide a method for benchmarking through comparison with experimental observations. Finally, Björkman et al raise the question 'Are we van der Waals ready?' and proceed to test our readiness by benchmarking the performance of a range of vdW-aware methods for the group of 96 known layered structures. We have also included in this special issue one study of nonequilibrium transport which is linked to David's work in formal scattering theory [1, 2] and which observes that vdW forces (and possible generalizations to nonequilibrium transport conditions) will be of central importance in a richer computational characterization of molecular electronics under operational conditions. David was always keen to spearhead the development of tools that improved descriptions of nature and addressed actual experiments. We know that he was happy that DMP started the focused session on vdW and materials in 2011. We know that he would have thoroughly appreciated the articles in this special issue. He would have hoped, as we do, that materials theory may continue to learn how to tackle even more exciting experimental problems and that we may continue to deepen our understanding of materials and their functionality. Bibliography [1]Langreth D C 1976 1975 Nato Advanced Study Institute on Linear and Nonlinear Transport in Solids, Antwerben vol B17 (New York: Plenum) pp 3-32 [2]Langreth D C 1966 Friedel sum rule for Anderson's model of localized impurity states Phys. Rev. 150 516 [3]Langreth D C and Perdew J P 1975 The exchange-correlation energy of a metallic surface

  10. Refined ab initio intermolecular ground-state potential energy surface for the He-C2H2 van der Waals complex

    DEFF Research Database (Denmark)

    Fernández, Berta; Henriksen, Christian; Farrelly, David

    2013-01-01

    , are fitted to a 15-parameter analytic function. The potential is characterised by minima of-24.21 cm-1 at distances between the rare gas atom and the C2H2 centre of mass of 4.3453 Å, and with the complex in a linear configuration. At intermediate distances the surface is rather similar to that developed...

  11. Critical and near-critical phase behavior and interplay between the thermodynamic Casimir and van der Waals forces in a confined nonpolar fluid medium with competing surface and substrate potentials

    Science.gov (United States)

    Valchev, Galin; Dantchev, Daniel

    2015-07-01

    We study, using general scaling arguments and mean-field type calculations, the behavior of the critical Casimir force and its interplay with the van der Waals force acting between two parallel slabs separated at a distance L from each other, confining some fluctuating fluid medium, say a nonpolar one-component fluid or a binary liquid mixture. The surfaces of the slabs are coated by thin layers exerting strong preference to the liquid phase of the fluid, or one of the components of the mixture, modeled by strong adsorbing local surface potentials ensuring the so-called (+,+) boundary conditions. The slabs, on the other hand, influence the fluid by long-range competing dispersion potentials, which represent irrelevant interactions in renormalization-group sense. Under such conditions, one usually expects attractive Casimir force governed by universal scaling function, pertinent to the extraordinary surface universality class of Ising type systems, to which the dispersion potentials provide only corrections to scaling. We demonstrate, however, that below a given threshold thickness of the system Lcrit for a suitable set of slabs-fluid and fluid-fluid coupling parameters the competition between the effects due to the coatings and the slabs can result in sign change of the Casimir force acting between the surfaces confining the fluid when one changes the temperature T , the chemical potential of the fluid μ , or L . The last implies that by choosing specific materials for the slabs, coatings, and the fluid for L ≲Lcrit one can realize repulsive Casimir force with nonuniversal behavior which, upon increasing L , gradually turns into an attractive one described by a universal scaling function, depending only on the relevant scaling fields related to the temperature and the excess chemical potential, for L ≫Lcrit . We present arguments and relevant data for specific substances in support of the experimental feasibility of the predicted behavior of the force. It can

  12. Understanding corrosion inhibition with van der Waals DFT methods: the case of benzotriazole.

    Science.gov (United States)

    Gattinoni, Chiara; Michaelides, Angelos

    2015-01-01

    The corrosion of materials is an undesirable and costly process affecting many areas of technology and everyday life. As such, considerable effort has gone into understanding and preventing it. Organic molecule based coatings can in certain circumstances act as effective corrosion inhibitors. Although they have been used to great effect for more than sixty years, how they function at the atomic-level is still a matter of debate. In this work, computer simulation approaches based on density functional theory are used to investigate benzotriazole (BTAH), one of the most widely used and studied corrosion inhibitors for copper. In particular, the structures formed by protonated and deprotonated BTAH molecules on Cu(111) have been determined and linked to their inhibiting properties. It is found that hydrogen bonding, van der Waals interactions and steric repulsions all contribute in shaping how BTAH molecules adsorb, with flat-lying structures preferred at low coverage and upright configurations preferred at high coverage. The interaction of the dehydrogenated benzotriazole molecule (BTA) with the copper surface is instead dominated by strong chemisorption via the azole moiety with the aid of copper adatoms. Structures of dimers or chains are found to be the most stable structures at all coverages, in good agreement with scanning tunnelling microscopy results. Benzotriazole thus shows a complex phase behaviour in which van der Waals forces play an important role and which depends on coverage and on its protonation state and all of these factors feasibly contribute to its effectiveness as a corrosion inhibitor.

  13. Chemical sensing by band modulation of a black phosphorus/molybdenum diselenide van der Waals hetero-structure

    Science.gov (United States)

    Feng, Zhihong; Chen, Buyun; Qian, Shuangbei; Xu, Linyan; Feng, Liefeng; Yu, Yuanyuan; Zhang, Rui; Chen, Jiancui; Li, Qianqian; Li, Quanning; Sun, Chongling; Zhang, Hao; Liu, Jing; Pang, Wei; Zhang, Daihua

    2016-09-01

    We report on a new chemical sensor based on black phosphorus/molybdenum diselenide van der Waals hetero-junctions. Due to the atomically thin nature of two-dimensional (2D) materials, surface adsorption of gas molecules can effectively modulate the band alignment at the junction interface, making the device a highly sensitive detector for chemical adsorptions. Compared to sensors made of homogeneous nanomaterials, the hetero-junction demonstrates considerably lower detection limit and higher sensitivity toward nitrogen dioxide. Kelvin probe force microscopy and finite element simulations have provided experimental and theoretical explanations for the enhanced performance, proving that chemical adsorption can induce significant changes in band alignment and carrier transport behaviors. The study demonstrates the potential of van der Waals hetero-junction as a new platform for sensing applications, and provides more insights into the interaction between gaseous molecules and 2D hetero-structures.

  14. CoPt and FePt magnetic alloys grown on van der Waals WSe{sub 2}(0001) surfaces and on arrays of SiO{sub 2} spherical particles

    Energy Technology Data Exchange (ETDEWEB)

    Makarov, Denys

    2008-06-06

    Modern magnetic recording is based on usage of hard magnetic alloys as a recording media. In order to increase the areal storage density (number of stored bits per square inch), materials with a high value of magnetic anisotropy are required to stabilize the direction of the magnetization and thus satisfy the criteria of thermal stability. The magnetic alloy currently used for hard disk drive production is a granular CoCrPt:SiO2 alloy with a grain size of approximately 7 nm and an anisotropy constant of about 0.4 MJ/m{sup 3}. However, the predicted limit of the highest achievable areal density of this type of granular media is 500-600 Gbit/in{sup 2}. To satisfy the demand of higher densities, new magnetic alloys have to be introduced. The most promising candidates for future ultra-high density magnetic recording applications are chemically L10 ordered FePt and CoPt alloys with anisotropy constants of about 10 MJ/m{sup 3} and 3 MJ/m{sup 3}, respectively. In order to obtain a high value of uniaxial magnetic anisotropy, the substrate temperature during molecular beam epitaxy or sputtering deposition has to be higher than 500 C. For practical use in industrial applications the ordering temperature of the FePt and CoPt alloys has to be reduced. One of the promising approaches to reduce the ordering temperature is related to the enhancement of the adatom mobility by growing the alloy on the chemically saturated surface. In this regard an attempt to reduce the ordering temperature of the CoPt alloy with equiatomic composition was performed in the scope of present work by growing the CoPt alloy on van der Waals WSe{sub 2}(0001) substrates. Moreover, an increase in data density can be gained using the concept of patterned media, where an information unit (bit) is stored in a single nanostructure. The most attractive way to produce patterned magnetic media for ultra-high density magnetic recording applications is based on self-assembly of the magnetic nanostructures. In this

  15. Maria van der Hoeven, the Netherlands minister for education, culture and science, visited CERN

    CERN Multimedia

    maximilien Brice

    2005-01-01

    On 21 April, the Netherlands Minister for Education, Culture and Science, Mrs Maria van der Hoeven, was welcomed to CERN by the Director-General, Robert Aymar, and the Chief Scientific Officer, Jos Engelen. Minister van der Hoeven visited the ATLAS installations, the LHC tunnel and the magnet assembly and test hall before meeting a group of young scientists from the Netherlands. Picture 05 : from left to right, Frank Linde, Director of the Netherlands National Institute for Nuclear Physics and High Energy Physics (NIKHEF), Jos Engelen, CERN's Chief Scientific Officer, Maria van der Hoeven, Netherlands Minister for Education, Culture and Science, and Herman Ten Kate, Head of the ATLAS magnet project, visiting the ATLAS assembly hall.Picture 09 ; Here she talks with, from left to right, Jos Engelen, CERN's chief scientific officer, Peter Jenni, the ATLAS spokesman, Herman Ten Kate, head of the ATLAS magnet project, and Frank Linde, director of the Netherlands National Institute for Nuclear Physics and High Ener...

  16. Van der Waals interaction torque and force between dielectrically anisotropic layered media

    CERN Document Server

    Lu, Bing-Sui

    2016-01-01

    We analyse the van der Waals interaction for a pair of dielectrically anisotropic plane-layered media interacting across a dielectrically isotropic medium. We investigate the van der Waals torque and force for the following cases: (i) a pair of single anisotropic layers, (ii) a single anisotropic layer interacting with a multilayered slab consisting of alternating anisotropic and isotropic layers, and (iii) a pair of multilayered slabs each consisting of alternating anisotropic and isotropic layers, looking at the cases where the optical axes lie parallel and/or perpendicular to the plane of the layers. For the first case, the optical axes of the oppositely facing anisotropic layers of the two interacting slabs generally have an angular mismatch, and within each multilayered slab the optical axes may either be the same, or undergo constant angular increments across the anisotropic layers. In particular, we examine how the behaviors of the van der Waals torque and force can be "tuned" by adjusting the layer th...

  17. Van der Waals interaction between a microparticle and a single-wall carbon nanotube

    CERN Document Server

    Blagov, E V; Mostepanenko, V M

    2007-01-01

    The Lifshitz-type formulas describing the free energy and the force of the van der Waals interaction between an atom (molecule) and a single-wall carbon nanotube are obtained. The single-wall nanotube is considered as a cylindrical sheet carrying a two-dimensional free electron gas with appropriate boundary conditions on the electromagnetic field. The obtained formulas are used to calculate the van der Waals free energy and force between a hydrogen atom (molecule) and single-wall carbon nanotubes of different radia. Comparison studies of the van der Waals interaction of hydrogen atoms with single- and multi-wall carbon nanotubes show that depending on atom-nanotube separation distance the idealization of graphite dielectric permittivity is already applicable to nanotubes with only two or three walls.

  18. Concurrent Van der Woude syndrome and Turner syndrome: A case report

    Science.gov (United States)

    Los, Evan; Baines, Hayley; Guttmann-Bauman, Ines

    2017-01-01

    Most cases of Van der Woude syndrome are caused by a mutation to interferon regulatory factor 6 on chromosome 1. Turner syndrome is caused by complete or partial absence of the second sex chromosome in girls. We describe a unique case of the two syndromes occurring concurrently though apparently independently in a girl with Van der Woude syndrome diagnosed at birth and Turner syndrome at 14 years 9 months. Short stature was initially misattributed to Van der Woude syndrome and pituitary insufficiency associated with clefts before correctly diagnosing Turner syndrome. We discuss the prevalence of delayed diagnosis of Turner syndrome, the rarity of reports of concurrent autosomal chromosome mutation and sex chromosome deletion, as well as the need to consider the diagnosis of Turner syndrome in all girls with short stature regardless of prior medical history. PMID:28228961

  19. Simon van der Meer (1925-2011): A modest genius of accelerator science

    CERN Document Server

    Chohan, Vinod C

    2011-01-01

    Simon van der Meer was a brilliant scientist and a true giant of accelerator science. His seminal contributions to accelerator science have been essential to this day in our quest for satisfying the demands of modern particle physics. Whether we talk of long base-line neutrino physics or antiproton-proton physics at Fermilab or proton-proton physics at LHC, his techniques and inventions have been a vital part of the modern day successes. Simon van der Meer and Carlo Rubbia were the first CERN scientists to become Nobel laureates in Physics, in 1984. Van der Meer's lesser-known contributions spanned a whole range of subjects in accelerator science, from magnet design to power supply design, beam measurements, slow beam extraction, sophisticated programs and controls.

  20. Professor Bennie van der Walt: a bridge between white Afrikaners and black Africans

    Directory of Open Access Journals (Sweden)

    Y. Turaki

    2010-07-01

    Full Text Available This article honours Professor Bennie van der Walt as a bridge builder between white Afrikaners and black Africans as well as a renowned Christian scholar. Historical Western colonialism in South Africa divided its citizens against each other by means of white racism and apartheid. The whites in general were pitched against the blacks on the basis of white racism and its doctrine of apartheid. This doctrine of separation of races kept the white Afrikaners from the Bantu Africans. However, apartheid as a form of political, social, cultural and religious racism is now history in South Africa. The role which Professor Van der Walt played in bridging the gap between this racial divide is highly commendable and needs to be acknowledged and appreciated, hence the primary objective of this article in honour of his 71st birthday. Furthermore, the article discusses the immense contributions of Professor Bennie van der Walt to Christian scholarship in Africa.

  1. Bell's palsy before Bell: Cornelis Stalpart van der Wiel's observation of Bell's palsy in 1683.

    Science.gov (United States)

    van de Graaf, Robert C; Nicolai, Jean-Philippe A

    2005-11-01

    Bell's palsy is named after Sir Charles Bell (1774-1842), who has long been considered to be the first to describe idiopathic facial paralysis in the early 19th century. However, it was discovered that Nicolaus Anton Friedreich (1761-1836) and James Douglas (1675-1742) preceded him in the 18th century. Recently, an even earlier account of Bell's palsy was found, as observed by Cornelis Stalpart van der Wiel (1620-1702) from The Hague, The Netherlands in 1683. Because our current knowledge of the history of Bell's palsy before Bell is limited to a few documents, it is interesting to discuss Stalpart van der Wiel's description and determine its additional value for the history of Bell's palsy. It is concluded that Cornelis Stalpart van der Wiel was the first to record Bell's palsy in 1683. His manuscript provides clues for future historical research.

  2. Observation of scalar nuclear spin-spin coupling in van der Waals molecules

    CERN Document Server

    Ledbetter, Micah; Bagno, Alessandro; Tran, Nhan; Romalis, Michael

    2011-01-01

    Scalar couplings between covalently bound nuclear spins are a ubiquitous feature in nuclear magnetic resonance (NMR) experiments, imparting valuable information to NMR spectra regarding molecular structure and conformation. Such couplings arise due to a second-order hyperfine interaction, and, in principle, the same mechanism should lead to scalar couplings between nuclear spins in unbound van der Waals complexes. Here, we report the first observation of scalar couplings between nuclei in van der Waals molecules. Our measurements are performed in a solution of hyperpolarized ${\\rm ^{129}Xe}$ and pentane, using superconducting quantum interference devices to detect NMR in 10 mG fields, and are in good agreement with calculations based on density functional theory. van der Waals forces play an important role in many physical phenomena, and hence the techniques presented here may provide a new method for probing such interactions.

  3. Cohesive properties of noble metals by van der Waals-corrected Density Functional Theory

    CERN Document Server

    Ambrosetti, Alberto

    2016-01-01

    The cohesive energy, equilibrium lattice constant, and bulk modulus of noble metals are computed by different van der Waals-corrected Density Functional Theory methods, including vdW-DF, vdW-DF2, vdW-DF-cx, rVV10 and PBE-D. Two specifically-designed methods are also developed in order to effectively include dynamical screening effects: the DFT/vdW-WF2p method, based on the generation of Maximally Localized Wannier Functions, and the RPAp scheme (in two variants), based on a single-oscillator model of the localized electron response. Comparison with results obtained without explicit inclusion of van der Waals effects, such as with the LDA, PBE, PBEsol, or the hybrid PBE0 functional, elucidates the importance of a suitable description of screened van der Waals interactions even in the case of strong metal bonding. Many-body effects are also quantitatively evaluated within the RPAp approach.

  4. Many-body effects in the van der Waals-Casimir interaction between graphene layers

    Science.gov (United States)

    Sarabadani, Jalal; Naji, Ali; Asgari, Reza; Podgornik, Rudolf

    2011-10-01

    Van der Waals-Casimir dispersion interactions between two apposed graphene layers, a graphene layer and a substrate, and in a multilamellar graphene system are analyzed within the framework of the Lifshitz theory. This formulation hinges on a known form of the dielectric response function of an undoped or doped graphene sheet, assumed to be of a random-phase-approximation form. In the geometry of two apposed layers, the separation dependence of the van der Waals-Casimir interaction for both types of graphene sheets is determined and critically compared with some well-known limiting cases. In a multilamellar array, the many-body effects are quantified and shown to increase the magnitude of the van der Waals-Casimir interactions.

  5. Molecular recognition by van der Waals interaction between polymers with sequence-specific polarizabilities

    CERN Document Server

    Lu, Bing-Sui; Podgornik, Rudolf

    2016-01-01

    We analyze van der Waals interactions between two rigid polymers with sequence-specific, anisotropic polarizabilities along the polymer backbones, so that the dipole moments fluctuate parallel to the polymer backbones. Assuming that each polymer has a quenched-in polarizability sequence which reflects, for example, the polynucleotide sequence of a double-stranded DNA molecule, we study the van der Waals interaction energy between a pair of such polymers with rod-like structure for the cases where their respective polarizability sequences are (i) distinct and (ii) identical, with both zero and non-zero correlation length of the polarizability correlator along the polymer backbones in the latter case. For identical polymers, we find a novel $r^{-5}$ scaling behavior of the van der Waals interaction energy for small inter-polymer separation $r$, in contradistinction to the $r^{-4}$ scaling behavior of distinct polymers, with furthermore a pronounced angular dependence favoring attraction between sufficiently ali...

  6. Concurrent Van der Woude syndrome and Turner syndrome: A case report

    Directory of Open Access Journals (Sweden)

    Evan Los

    2017-01-01

    Full Text Available Most cases of Van der Woude syndrome are caused by a mutation to interferon regulatory factor 6 on chromosome 1. Turner syndrome is caused by complete or partial absence of the second sex chromosome in girls. We describe a unique case of the two syndromes occurring concurrently though apparently independently in a girl with Van der Woude syndrome diagnosed at birth and Turner syndrome at 14 years 9 months. Short stature was initially misattributed to Van der Woude syndrome and pituitary insufficiency associated with clefts before correctly diagnosing Turner syndrome. We discuss the prevalence of delayed diagnosis of Turner syndrome, the rarity of reports of concurrent autosomal chromosome mutation and sex chromosome deletion, as well as the need to consider the diagnosis of Turner syndrome in all girls with short stature regardless of prior medical history.

  7. Concurrent Van der Woude syndrome and Turner syndrome: A case report.

    Science.gov (United States)

    Los, Evan; Baines, Hayley; Guttmann-Bauman, Ines

    2017-01-01

    Most cases of Van der Woude syndrome are caused by a mutation to interferon regulatory factor 6 on chromosome 1. Turner syndrome is caused by complete or partial absence of the second sex chromosome in girls. We describe a unique case of the two syndromes occurring concurrently though apparently independently in a girl with Van der Woude syndrome diagnosed at birth and Turner syndrome at 14 years 9 months. Short stature was initially misattributed to Van der Woude syndrome and pituitary insufficiency associated with clefts before correctly diagnosing Turner syndrome. We discuss the prevalence of delayed diagnosis of Turner syndrome, the rarity of reports of concurrent autosomal chromosome mutation and sex chromosome deletion, as well as the need to consider the diagnosis of Turner syndrome in all girls with short stature regardless of prior medical history.

  8. Van der Waals universality in homonuclear atom-dimer elastic collisions

    CERN Document Server

    Giannakeas, P

    2016-01-01

    The universal aspects of atom-dimer elastic collisions are investigated within the framework of Faddeev equations. The two-body interactions between the neutral atoms are approximated by the separable potential approach. Our analysis considers a pure van der Waals potential tail as well as soft-core van der Waals interactions permitting us in this manner to address the universally general features of atom-dimer resonant spectra. In particular, we show that the atom-dimer resonances are solely associated with the {\\it excited} Efimov states. Furthermore, the positions of the corresponding resonances for a soft-core potentials with more than 5 bound states are in good agreement with the corresponding results from an infinitely deep pure van der Waals tail potential.

  9. Measurement of van-der-Waals interaction by atom trajectory imaging

    CERN Document Server

    Thaicharoen, N; Raithel, G

    2015-01-01

    We study the repulsive van der Waals interaction of cold rubidium $70S_{1/2}$ Rydberg atoms by analysis of time-delayed pair correlation functions. After excitation, Rydberg atoms are allowed to accelerate under the influence of the van der Waals force. Their positions are then measured using a single-atom imaging technique. From the average pair correlation function of the atom positions we obtain the initial atom-pair separation and the terminal velocity, which yield the van der Waals interaction coefficient $C_{6}$. The measured $C_{6}$ value agrees well with calculations. The experimental method has been validated by simulations. The data hint at anisotropy in the overall expansion, caused by the shape of the excitation volume. Our measurement implies that the interacting entities are individual Rydberg atoms, not groups of atoms that coherently share a Rydberg excitation.

  10. Van der Waals Interactions among Alkali Rydberg Atoms with Excitonic States

    CERN Document Server

    Zoubi, Hashem

    2015-01-01

    We investigate the influence of the appearance of excitonic states on van der Waals interactions among two Rydberg atoms. The atoms are assumed to be in different Rydberg states, e.g., in the $|ns\\rangle$ and $|np\\rangle$ states. The resonant dipole-dipole interactions yield symmetric and antisymmetric excitons, with energy splitting that give rise to new resonances as the atoms approach each other. Only far from these resonances the van der Waals coefficients, $C_6^{sp}$, can be defined. We calculate the $C_6$ coefficients for alkali atoms and present the results for lithium by applying perturbation theory. At short interatomic distances of several $\\mu m$, we show that the widely used simple model of two-level systems for excitons in Rydberg atoms breaks down, and the correct representation implies multi-level atoms. Even though, at larger distances one can keep the two-level systems but in including van der Waals interactions among the atoms.

  11. Accurate treatment of nanoelectronics through improved description of van der Waals Interactions

    DEFF Research Database (Denmark)

    Kelkkanen, Kari André

    W-DF functional are too small, as the exchange approximation used is too repulsive. With the vdW-DF and other functionals that account for vdW forces, the total isomer energies are minimized in molecular configurations, which are compact, and in which many hydrogen bonds (HBs) can be described as distorted......This thesis emerges from a patented idea to utilize intentionally structured sur- faces and differences in adsorption strengths to self-assemble some source mate- rial into nanoelectronic components, and ends up in the heated debate regarding structure of ambient water . It investigates the role...... and relevance of van der Waals (vdW) forces in molecular surface adsorption and water through density- functional theory (DFT), using the exchange-correlation functional vdW-DF [Dion et al., Phys. Rev. Lett. 92, 246401 (2004)] and developments based on it. Results are first computed for adsorption with vd...

  12. Coulomb expansion of a van der Waals C60 solid film

    Institute of Scientific and Technical Information of China (English)

    薛其坤; 厉建龙; 孙牧; 陆华; T.Hashizume; Y.Hasegawa; K.Ohno; Y.Kawazoe; T.Sakurai; H.Kamiyama; H.Shinohara

    2000-01-01

    Scanning tunneling microscopy study revealed a van der Waals C60, solid film with 13% room-temperature lattice expansion on the GaAs(001) 2×4 surface. The mechanism involves fundamental Coulomb interaction due to charge transfer from the GaAs substrate. Theoretical calculation determines the charge transfer to be 1.76 electrons per C60 molecule. Oriented at its (110) crystallo-graphic axis this film also distinguishes itself from those formed on all other semiconductor and metal substrates where only the low-energy (111) hexagonal packing of C60 molecules was developed. It is shown that this is due to the one-dimensional confinement effect of the anisotropic substrate, which may have the prospect of controlling crystal growth.

  13. Experiment and computation: a combined approach to study the van der Waals complexes

    Directory of Open Access Journals (Sweden)

    Surin L.A.

    2017-01-01

    Full Text Available A review of recent results on the millimetre-wave spectroscopy of weakly bound van der Waals complexes, mostly those which contain H2 and He, is presented. In our work, we compared the experimental spectra to the theoretical bound state results, thus providing a critical test of the quality of the M–H2 and M–He potential energy surfaces (PESs which are a key issue for reliable computations of the collisional excitation and de-excitation of molecules (M = CO, NH3, H2O in the dense interstellar medium. The intermolecular interactions with He and H2 play also an important role for high resolution spectroscopy of helium or para-hydrogen clusters doped by a probe molecule (CO, HCN. Such experiments are directed on the detection of superfluid response of molecular rotation in the He and p-H2 clusters.

  14. Enhanced van der Waals epitaxy via electron transfer-enabled interfacial dative bond formation

    CERN Document Server

    Xie, Weiyu; Wang, Gwo-Ching; Bhat, Ishwara; Zhang, Shengbai

    2016-01-01

    Enhanced van der Waals (vdW) epitaxy of semiconductors on layered vdW substrate is identified as the formation of dative bonds. For example, despite that NbSe2 is a vdW layered material, first-principles calculations reveal that the bond strength at CdTe-NbSe2 interface is five times as large as that of vdW interaction at CdTe-graphene interface. The unconventional chemistry here is enabled by an effective net electron transfer from Cd dangling-bond states at CdTe surface to metallic non-bonding NbSe2 states, which is a necessary condition to activate the Cd for enhanced binding with Se.

  15. Understanding the nanoscale local buckling behavior of vertically aligned MWCNT arrays with van der Waals interactions

    Science.gov (United States)

    Li, Yupeng; Kim, Hyung-Ick; Wei, Bingqing; Kang, Junmo; Choi, Jae-Boong; Nam, Jae-Do; Suhr, Jonghwan

    2015-08-01

    The local buckling behavior of vertically aligned carbon nanotubes (VACNTs) has been investigated and interpreted in the view of a collective nanotube response by taking van der Waals interactions into account. To the best of our knowledge, this is the first report on the case of collective VACNT behavior regarding van der Waals force among nanotubes as a lateral support effect during the buckling process. The local buckling propagation and development of VACNTs were experimentally observed and theoretically analyzed by employing finite element modeling with lateral support from van der Waals interactions among nanotubes. Both experimental and theoretical analyses show that VACNTs buckled in the bottom region with many short waves and almost identical wavelengths, indicating a high mode buckling. Furthermore, the propagation and development mechanism of buckling waves follow the wave damping effect.The local buckling behavior of vertically aligned carbon nanotubes (VACNTs) has been investigated and interpreted in the view of a collective nanotube response by taking van der Waals interactions into account. To the best of our knowledge, this is the first report on the case of collective VACNT behavior regarding van der Waals force among nanotubes as a lateral support effect during the buckling process. The local buckling propagation and development of VACNTs were experimentally observed and theoretically analyzed by employing finite element modeling with lateral support from van der Waals interactions among nanotubes. Both experimental and theoretical analyses show that VACNTs buckled in the bottom region with many short waves and almost identical wavelengths, indicating a high mode buckling. Furthermore, the propagation and development mechanism of buckling waves follow the wave damping effect. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr03581c

  16. Versatile van der Waals Density Functional Based on a Meta-Generalized Gradient Approximation

    Directory of Open Access Journals (Sweden)

    Haowei Peng

    2016-10-01

    Full Text Available A “best-of-both-worlds” van der Waals (vdW density functional is constructed, seamlessly supplementing the strongly constrained and appropriately normed (SCAN meta-generalized gradient approximation for short- and intermediate-range interactions with the long-range vdW interaction from rVV10, the revised Vydrov–van Voorhis nonlocal correlation functional. The resultant SCAN+rVV10 is the only vdW density functional to date that yields excellent interlayer binding energies and spacings, as well as intralayer lattice constants in 28 layered materials. Its versatility for various kinds of bonding is further demonstrated by its good performance for 22 interactions between molecules; the cohesive energies and lattice constants of 50 solids; the adsorption energy and distance of a benzene molecule on coinage-metal surfaces; the binding energy curves for graphene on Cu(111, Ni(111, and Co(0001 surfaces; and the rare-gas solids. We argue that a good semilocal approximation should (as SCAN does capture the intermediate-range vdW through its exchange term. We have found an effective range of the vdW interaction between 8 and 16 Å for systems considered here, suggesting that this interaction is negligibly small at the larger distances where it reaches its asymptotic power-law decay.

  17. Versatile van der Waals Density Functional Based on a Meta-Generalized Gradient Approximation

    Science.gov (United States)

    Peng, Haowei; Yang, Zeng-Hui; Perdew, John P.; Sun, Jianwei

    2016-10-01

    A "best-of-both-worlds" van der Waals (vdW) density functional is constructed, seamlessly supplementing the strongly constrained and appropriately normed (SCAN) meta-generalized gradient approximation for short- and intermediate-range interactions with the long-range vdW interaction from r VV 10 , the revised Vydrov-van Voorhis nonlocal correlation functional. The resultant SCAN +r VV 10 is the only vdW density functional to date that yields excellent interlayer binding energies and spacings, as well as intralayer lattice constants in 28 layered materials. Its versatility for various kinds of bonding is further demonstrated by its good performance for 22 interactions between molecules; the cohesive energies and lattice constants of 50 solids; the adsorption energy and distance of a benzene molecule on coinage-metal surfaces; the binding energy curves for graphene on Cu(111), Ni(111), and Co(0001) surfaces; and the rare-gas solids. We argue that a good semilocal approximation should (as SCAN does) capture the intermediate-range vdW through its exchange term. We have found an effective range of the vdW interaction between 8 and 16 Å for systems considered here, suggesting that this interaction is negligibly small at the larger distances where it reaches its asymptotic power-law decay.

  18. High broad-band photoresponsivity of mechanically formed InSe-graphene van der Waals heterostructures.

    Science.gov (United States)

    Mudd, Garry W; Svatek, Simon A; Hague, Lee; Makarovsky, Oleg; Kudrynskyi, Zakhar R; Mellor, Christopher J; Beton, Peter H; Eaves, Laurence; Novoselov, Kostya S; Kovalyuk, Zakhar D; Vdovin, Evgeny E; Marsden, Alex J; Wilson, Neil R; Patanè, Amalia

    2015-07-01

    High broad-band photoresponsivity of mechanically formed InSe-graphene van der Waals heterostructures is achieved by exploiting the broad-band transparency of graphene, the direct bandgap of InSe, and the favorable band line up of InSe with graphene. The photoresponsivity exceeds that for other van der Waals heterostructures and the spectral response extends from the near-infrared to the visible spectrum. © 2015 The Authors. Published by WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  19. A high-pressure van der Waals compound in solid nitrogen-helium mixtures

    Science.gov (United States)

    Vos, W. L.; Finger, L. W.; Hemley, R. J.; Hu, J. Z.; Mao, H. K.; Schouten, J. A.

    1992-01-01

    A detailed diamond anvil-cell study using synchrotron X-ray diffraction, Raman scattering, and optical microscopy has been conducted for the He-N system, with a view to the weakly-bound van der Waals molecule interactions that can be formed in the gas phase. High pressure is found to stabilize the formation of a stoichiometric, solid van der Waals compound of He(N2)11 composition which may exemplify a novel class of compounds found at high pressures in the interiors of the outer planets and their satellites.

  20. Solution of the Duffing-van der Pol oscillator equation by a differential transform method

    Energy Technology Data Exchange (ETDEWEB)

    Mukherjee, Supriya [Department of Mathematics, Swami Vivekananda Institute for Science and Technology, South Gobindapur, P S - Sonarpur, Kolkata 700145, West Bengal (India); Roy, Banamali [Department of Mathematics, Bangabasi Evening College, 19 Rajkumar Chakraborty Sarani, Kolkata 700009, West Bengal (India); Dutta, Sourav, E-mail: supriya_ju@yahoo.com, E-mail: banamaliroy@yahoo.co.in [Department of Electrical Engineering, Jadavpur University, Kolkata 700032, West Bengal (India)

    2011-01-15

    In this paper, we have tried to implement a relatively new exact series method of solution, known as the differential transform method, for solving one of the widely studied and challenging equations in nonlinear dynamics, the Duffing-van der Pol oscillator equation. Chandrasekar et al (2004 J. Phys. A 37 4527) showed that the force-free Duffing-van der Pol oscillator is completely integrable for a specific parametric choice, and they derived a general solution for this parametric choice. The results of this paper are in sufficient agreement with those of Chandrasekar et al.

  1. Anisotropic spheres with Van derWaals-type equation of state

    Indian Academy of Sciences (India)

    S Thirukkanesh; F C Ragel

    2014-07-01

    We study static spherically symmetric space-time to describe relativistic compact objects with anisotropic matter distribution and derive two classes of exact models to the Einstein–Maxwell system with a modified Van derWaals equation of state. We motivate a Van derWaals-type equation of state to physically signify a high-density domain of quark matter, and the generated exact solutions are shown to contain several classes of exact models reported previously that correspond to various physical scenarios. Geometrical analysis shows that the physical quantities are well behaved so that these models may be used to describe anisotropic charged compact spheres.

  2. A modified van der Pol equation with delay in a description of the heart action

    Directory of Open Access Journals (Sweden)

    Zduniak Beata

    2014-12-01

    Full Text Available In this paper, a modified van der Pol equation is considered as a description of the heart action. This model has a number of interesting properties allowing reconstruction of phenomena observed in physiological experiments as well as in Holter electrocardiographic recordings. Our aim is to study periodic solutions of the modified van der Pol equation and take into consideration the influence of feedback and delay which occur in the normal heart action mode as well as in pathological modes. Usage of certain values for feedback and delay parameters allows simulating the heart action when an accessory conducting pathway is present (Wolff-Parkinson-White syndrome.

  3. Near-Unity Absorption in van der Waals Semiconductors for Ultrathin Optoelectronics.

    Science.gov (United States)

    Jariwala, Deep; Davoyan, Artur R; Tagliabue, Giulia; Sherrott, Michelle C; Wong, Joeson; Atwater, Harry A

    2016-09-14

    We demonstrate near-unity, broadband absorbing optoelectronic devices using sub-15 nm thick transition metal dichalcogenides (TMDCs) of molybdenum and tungsten as van der Waals semiconductor active layers. Specifically, we report that near-unity light absorption is possible in extremely thin (<15 nm) van der Waals semiconductor structures by coupling to strongly damped optical modes of semiconductor/metal heterostructures. We further fabricate Schottky junction devices using these highly absorbing heterostructures and characterize their optoelectronic performance. Our work addresses one of the key criteria to enable TMDCs as potential candidates to achieve high optoelectronic efficiency.

  4. Nanoscale Tail Aggregation in Ionic Liquids: Roles of Electrostatic and van der Waals Interactions

    Institute of Scientific and Technical Information of China (English)

    赵海清; 石锐; 王延颋

    2011-01-01

    Nanoscale spatial heterogeneity in ionic liquids is formed by the aggregation of cationic tail groups. The electrostatic interactions between polar groups and the collective van der Waals interactions between nonpolar tail groups both contribute to the formation of tail domains, but the degrees of their contributions were unknown. In this work, by applying a strong external electric field to effectively overpower the electrostatic interactions between polar groups, we have determined that the tail aggregation is majorly attributed to the electrostatic interactions and the van der Waals interactions only have minor influence on the spatial heterogeneity phenomenon of ionic liquids.

  5. Using computation to teach the properties of the van der Waals fluid

    Science.gov (United States)

    Swendsen, Robert H.

    2013-10-01

    The calculation of the thermodynamic properties of the van der Waals fluid is not trivial and most of its properties are rarely discussed because of mathematical difficulties. I describe a numerical approach that produces the full thermodynamic behavior of the van der Waals fluid with little effort. The numerical approach is particularly useful for showing the behavior of the specific heat, the isothermal compressibility, and the coefficient of thermal expansion at and near the critical point. The results of these computations show some surprising properties and give new insights into the mean-field description of the liquid-gas transition.

  6. Oscillation death in a coupled van der Pol–Mathieu system

    Indian Academy of Sciences (India)

    Madhurjya P Bora; Dipak Sarmah

    2013-10-01

    We report an investigation of the oscillation death (OD) of a parametrically excited coupled van der Pol–Mathieu (vdPM) system. The system can be considered as a pair of harmonically forced van der Pol oscillators under a double-well potential. The two oscillators are coupled with a cubic nonlinearity. We have shown that the system arrives at an OD regime when coupling strength crosses a threshold value at which the system undergoes saddle-node bifurcation and two limit cycles coalesce onto a fixed point of the system. We have further shown that this nonautonomous system possesses a centre manifold corresponding to the OD regime.

  7. Ab initio studies of coherent spin transport in Fe-hBN/graphene van der Waals multilayers

    Science.gov (United States)

    Magnus Ukpong, Aniekan

    2017-07-01

    This paper presents the results of ab initio studies of the electronic spin inversion and filtering in a ferromagnetic multilayer heterostructure. Spin-polarized electronic structure calculations are performed based on van der Waals density functional theory to give unique insights in to the generation, manipulation and transport of coherent spin conductance. By using an exact theory of the self-consistent ground state of the Fe-hBN/graphene multilayer as a model of the magnetic tunnel junction, hidden asymmetries are unraveled in the spin-resolved charge densities. It is shown that the injection of spin into the graphene/boron nitride tunnel layer from a ferromagnetic contact gives rise to coherent spin current. The projected Fermi surfaces of the up and down spin channels are analyzed to reveal Fermi arc topologies and spin anisotropies. It is also demonstrated that the coherent transport of pure spin-down current in the topological Weyl semimetal phase is robust. The implications of the results on out-of-plane transport of spin polarized conductance in van der Waals multilayer spintronic devices is discussed. The insights derived from this study are expected to open up prospects for further exploration of van der Waals magnetic multilayer heterostructures as a versatile platform for developing materials for Weyltronic applications.

  8. The hot pick-up technique for batch assembly of van der Waals heterostructures

    DEFF Research Database (Denmark)

    Pizzocchero, Filippo; Gammelgaard, Lene; Jessen, Bjarke Sørensen

    2016-01-01

    The assembly of individual two-dimensional materials into van der Waals heterostructures enables the construction of layered three-dimensional materials with desirable electronic and optical properties. A core problem in the fabrication of these structures is the formation of clean interfaces bet...

  9. Probing low-energy hyperbolic polaritons in van der Waals crystals with an electron microscope

    KAUST Repository

    Govyadinov, Alexander A.

    2017-07-14

    Van der Waals materials exhibit intriguing structural, electronic, and photonic properties. Electron energy loss spectroscopy within scanning transmission electron microscopy allows for nanoscale mapping of such properties. However, its detection is typically limited to energy losses in the eV range-too large for probing low-energy excitations such as phonons or mid-infrared plasmons. Here, we adapt a conventional instrument to probe energy loss down to 100 meV, and map phononic states in hexagonal boron nitride, a representative van der Waals material. The boron nitride spectra depend on the flake thickness and on the distance of the electron beam to the flake edges. To explain these observations, we developed a classical response theory that describes the interaction of fast electrons with (anisotropic) van der Waals slabs, revealing that the electron energy loss is dominated by excitation of hyperbolic phonon polaritons, and not of bulk phonons as often reported. Thus, our work is of fundamental importance for interpreting future low-energy loss spectra of van der Waals materials.Here the authors adapt a STEM-EELS system to probe energy loss down to 100 meV, and apply it to map phononic states in hexagonal boron nitride, revealing that the electron loss is dominated by hyperbolic phonon polaritons.

  10. Control of excitons in multi-layer van der Waals heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Calman, E. V., E-mail: ecalman@gmail.com; Dorow, C. J.; Fogler, M. M.; Butov, L. V. [Department of Physics, University of California at San Diego, La Jolla, California 92093-0319 (United States); Hu, S.; Mishchenko, A.; Geim, A. K. [School of Physics and Astronomy, University of Manchester, Manchester M13 9PL (United Kingdom)

    2016-03-07

    We report an experimental study of excitons in a double quantum well van der Waals heterostructure made of atomically thin layers of MoS{sub 2} and hexagonal boron nitride. The emission of neutral and charged excitons is controlled by gate voltage, temperature, and both the helicity and the power of optical excitation.

  11. Molecular interpretation of nonclassical gas dynamics of dense vapors under the van der Waals model

    NARCIS (Netherlands)

    Colonna, P.; Guardone, A.

    2006-01-01

    The van der Waals polytropic gas model is used to investigate the role of attractive and repulsive intermolecular forces and the influence of molecular complexity on the possible nonclassical gas dynamic behavior of vapors near the liquid-vapor saturation curve. The decrease of the sound speed upon

  12. Molecular van der Waals Space and Topological Indices from the Distance Matrix

    Directory of Open Access Journals (Sweden)

    Seiman Corina

    2004-12-01

    Full Text Available A comparative study of 36 molecular descriptors derived from the topologicaldistance matrix and van der Waals space is carried out within this paper. They arepartitioned into 16 generalized topological distance matrix indices, 11 topologicaldistance indices known in the literature (seven obtained from eigenvalues/eigenvectors ofdistance matrix, and 9 van der Waals molecular descriptors. The generalized topologicaldistance indices, kδλ (λ = 1 – 3, k = 1 – 4, are introduced in this work on the basis ofreciprocical distance matrix. Intercorrelation analysis reveals that topological distanceindices mostly contain the same type of information, while van der Waals indices can bebound to the shape or the size of molecules. Furthermore, we found that topologicaldistance indices are good for describing molecular size, and they may be viewed as bulkparameters. The most accurate QSPR models for predicting boiling point of alkanes arebased on some of the generalized, eigenvalues/eigenvectors topological distance indicesand the van der Waals descriptors of molecular size.

  13. Influence of dielectric properties on van der Waals/Casimir forces in solid-liquid systems

    NARCIS (Netherlands)

    van Zwol, P. J.; Palasantzas, G.; De Hosson, J. Th. M.

    In this paper, we present calculations of van der Waals/Casimir forces, described by Lifshitz theory, for the solid-liquid-solid system using measured dielectric functions of all involved materials for the wavelength range from millimeters down to subnanometers. It is shown that even if the

  14. Molecular interpretation of nonclassical gas dynamics of dense vapors under the van der Waals model

    NARCIS (Netherlands)

    Colonna, P.; Guardone, A.

    2006-01-01

    The van der Waals polytropic gas model is used to investigate the role of attractive and repulsive intermolecular forces and the influence of molecular complexity on the possible nonclassical gas dynamic behavior of vapors near the liquid-vapor saturation curve. The decrease of the sound speed upon

  15. A van der Waals Equation of State for a Dilute Boson Gas

    Science.gov (United States)

    Deeney, F. A.; O'Leary, J. P.

    2012-01-01

    An equation of state of a system is a relationship that connects the thermodynamic variables of the system such as pressure and temperature. Such equations are well known for classical gases but less so for quantum systems. In this paper we develop a van der Waals equation of state for a dilute boson gas that may be used to explain the occurrence…

  16. Beam-Beam effects at the CMS BRIL van-der-Meer scans

    CERN Document Server

    CMS Collaboration

    2017-01-01

    The CMS Beam Radiation Instrumentation and Luminosity Project (BRIL) is devoted to the simulation and measurement of luminosity, beam conditions and radiation fields in the CMS Experiment at CERN. The project is engaged in operating and developing new detectors, compatible with the high luminosity experimental environments at the LHC. BRIL operates several detectors based on different physical principles and technologies. The detectors are calibrated using van-der-Meer scans to measure the luminosity that is a fundamental quantity of the LHC beam. In van-der-Meer scans the count rate in a detector is measured as a function of the distance between beams in the plane perpendicular to beam direction, to extract the underlying beam overlap area. The goal of the van-der-Meer scans is to obtain the calibration constant for each luminometer to be used at calibration then in physics data taking runs. The note presents the overview of beam-beam effects at the van-der-Meer scan and the corresponding corrections that sh...

  17. The Hopf-van der Pol system: Failure of a homotopy method

    NARCIS (Netherlands)

    Meijer, H.G.E.; Kalmár-Nagy, T.

    2012-01-01

    The purpose of this article to provide an explicit example where continuation based on the homotopy method fails. The example is a one-parameter homotopy for periodic orbits between two well-known nonlinear systems, the normal form of the Hopf bifurcation and the van der Pol system. Our analysis sho

  18. On the history of van der Waerden's theorem on arithmetic progressions

    Directory of Open Access Journals (Sweden)

    Tom C. Brown

    2001-12-01

    Full Text Available In this expository note, we discuss the celebrated theorem known as ``van der Waerden's theorem on arithmetic progressions", the history of work on upper and lower bounds for the function associated with this theorem, a number of generalizations, and some open problems.

  19. Van der Waals Type Model for Neutron-Proton Elastic Scattering at High Energies

    Science.gov (United States)

    Aleem, F.

    1980-12-01

    The most recent measurements of the angular distribution and total cross-section for neutron-proton elastic scattering between 70< pL <400 GeV/c with squared four momentum transfer -t ≤ 3.6 (GeV/c)2 have been explained using Van der Waals type model.

  20. van der Waals Density Functional Theory vdW-DFq for Semihard Materials

    Science.gov (United States)

    Peng, Qing; de, Suvranu

    There are a large number of materials with mild stiffness, which are not as soft as tissues and not as strong as metals. These semihard materials includes energetic materials, molecular crystals, layered materials, and van der Waals crystals. The integrity and mechanical stability are mainly determined by the interactions between instantaneously induced dipoles, the so called London dispersion force or van der Waals force. It is challenging to accurately model the structural and mechanical properties of these semihard materials in the frame of density functional theory where the non-local correlation functionals are not well known. Here we propose a van der Waals density functional named vdW-DFq to accurately model the density and geometry of semihard materials. Using β-cyclotetramethylene tetranitramine as a prototype, we adjust the enhancement factor of the exchange energy functional with generalized gradient approximations. We find this method to be simple and robust over a wide tuning range when calibrating the functional on-demand with experimental data. With a calibrated value q = 1 . 05 , the proposed vdW-DFq method shows good performance in predicting the geometries of 11 common energetic material molecular crystals and 3 typical layered van der Waals crystals. The authors would like to acknowledge the generous financial support from the Defense Threat Reduction Agency (DTRA) Grant # HDTRA1-13-1-0025.

  1. Cort van der Linden (1846-1935) : Minister-president in oorlogstijd : een politieke biografie

    NARCIS (Netherlands)

    Hertog, Johannes Paul den

    2007-01-01

    This political biography analyzes the political influence of, and methods used by, P.W.A. Cort van der Linden (1846-1935), Dutch Prime-Minister from 1913 to 1918. While he was a Professor of Economics he developed a view of liberalism based on German idealism which also included a progressive use o

  2. Bonded Paths and van der Waals Interactions in Orpiment, As2S3

    Energy Technology Data Exchange (ETDEWEB)

    Gibbs, Gerald V.; Wallace, Adam F.; Zallen, Richard; Downs, R. T.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.

    2010-06-17

    Bond critical properties and bond paths have been calculated for the thioarsenide molecular crystal orpiment, As2S3. In addition to the intramolecular As-S bond paths and van der Waals As-S and S-S bond paths within the layers, intermolecular S-S, As-S and As-As van der Waals paths exist between the layers. The S-S bond paths between the layers are identified with the main interlayer restoring forces responsible for the vibrational internal-mode splitting and the low frequency rigid layer modes previously documented in infrared and Raman studies of orpiment. These S-S bond paths are comparable with those calculated for orthorhombic native sulfur and the As4Sn (n = 3,4,5) molecules for several arsenide molecular crystals. The As-S bond paths show that the two nonequivalent arsenic atoms are each coordinated by a highly distorted octahedral array of sulfur atoms. The octahedra consist of three As-S intramolecular bonded interactions and three longer van der Waals interactions (two intramolecular and one intermolecular). One of the arsenic atoms is also coordinated by an arsenic atom in an interlayer As-As bonded interaction. Laplacian isosurface envelopes calculated for the arsenic and sulfur atoms are comparable with those calculated for native arsenic and orthorhombic sulfur. The intermolecular As-S bond paths connect Lewis acid domains on arsenic and an Lewis base domains on sulfur. Van der Waals interactions are traditionally defined as attractive interactions other than those ascribed to bond formation. However, theoretical evidence and arguments, as well as the connection between the bond paths and the vibrational spectra, indicate that the van der Waals interactions in orpiment are directed bonded interactions in the Slater sense. The experimental bond lengths for the As-S and S-S bonded interactions decrease nonlinearly with the increasing value of the electron density at the bond critical point, concomitant with a decrease in the bonded radii of arsenic and

  3. Between Looking and Making: Unravelling Dom Hans van der Laan’s Plastic Number

    Directory of Open Access Journals (Sweden)

    Caroline Voet

    2016-01-01

    Full Text Available Between 1920 and 1991, the Dutch Benedictine monk and architect Dom Hans van der Laan (1904–91 developed his own proportional system based on the ratio 3:4, or the irrational number 1.3247. . ., which he called the plastic number. According to him, this ratio directly grew from discernment, the human ability to differentiate sizes, and as such would be an improvement over the golden ratio. To put his theories to the test, he developed an architectural language, which can best be described as elementary architecture. His oeuvre — four convents and a house — is published on an international scale. His buildings have become pilgrimage sites for practicing architects and institutions that want to study and experience his spaces. His 1977 book 'Architectonic Space: Fifteen Lessons on the Disposition of the Human Habitat', translated into English, French, German and Italian, still inspires architects today, as does his biography, 'Modern Primitive', written by the architect Richard Padovan in 1994. But beyond the inspiration of his writings and realisations, the actual application of the plastic number in Van der Laan’s designs is unclear. Moreover, Van der Laan’s theories seem to be directed towards one goal only: to present the plastic number as the only possible means by which eminent architecture can be achieved, making them a target for suspicion and critique. To understand and evaluate Van der Laan’s application of the plastic number, this paper approaches it as a practical design tool. It analyses its genealogy and defines its key concepts. From that framework, Van der Laan’s architectonic space is interpreted as a design methodology that combines antique tectonic theories reminiscent of writers from Plato to Vitruvius with more recent atectonic approaches towards space through experience and movement.

  4. "Neue Liebe, neues Leben" - Ein Goethe-Gedicht in der Vertonung durch Ludwig van Beethoven

    Directory of Open Access Journals (Sweden)

    Körndle, Franz

    2001-12-01

    Full Text Available Ludwig van Beethoven composed two versions of Goethe's poem „Neue Liebe, neues Leben" in 1798/99 and 1810 respectively. A comparison of both versions reveals a change in the composer's intention. At first in several passages he followed the more traditional technique of transferring single words of the text directly into musical figures. Later on he seemed more intent on expressing the general mood and eliminated some of the rather simplistic details in favour of a more subjective rendering of the poems content.

    [de] Ludwig van Beethoven vertonte das Goethe-Gedicht „Neue Liebe, neues Leben" in zwei Fassungen 1798/99 und 1810. Der Vergleich der beiden Fassungen ergibt, daß sich in der Zeit zwischen diesen beiden Fassungen die Vorstellungen des Komponisten von der musikalischen Umsetzung teilweise gewandelt haben müssen. Zunächst scheint Beethoven eher nach der traditionellen Méthode einer direkten Übertragung von Begriffen aus dem Text komponiert zu haben. Später war er dann aber eher an einer subjektiven Darstellung des Inhalts interessiert und drângte drängte zu einfach gerate Einzelheiten zugunsten der - nunmehr freilich recht differenziert gestalteten - Gesamtstimmung zurück.

  5. Imidacloprid of niet? (interview met Sjef van der Steen)

    NARCIS (Netherlands)

    Kleis, R.; Steen, van der J.J.M.

    2014-01-01

    Is bijensterfte het werk van neonicotinoïden? Ja, zeggen en denken velen. Volgens hen zijn de neo’s rechtstreeks verantwoordelijk voor de hoge sterfte onder bijen. Nee, toont Wagenings onderzoek aan. Intussen lijkt het met de sterfte voorzichtig de goede kant op te gaan.

  6. Imidacloprid of niet? (interview met Sjef van der Steen)

    NARCIS (Netherlands)

    Kleis, R.; Steen, van der J.J.M.

    2014-01-01

    Is bijensterfte het werk van neonicotinoïden? Ja, zeggen en denken velen. Volgens hen zijn de neo’s rechtstreeks verantwoordelijk voor de hoge sterfte onder bijen. Nee, toont Wagenings onderzoek aan. Intussen lijkt het met de sterfte voorzichtig de goede kant op te gaan.

  7. In-situ epitaxial growth of graphene/h-BN van der Waals heterostructures by molecular beam epitaxy.

    Science.gov (United States)

    Zuo, Zheng; Xu, Zhongguang; Zheng, Renjing; Khanaki, Alireza; Zheng, Jian-Guo; Liu, Jianlin

    2015-10-07

    Van der Waals materials have received a great deal of attention for their exceptional layered structures and exotic properties, which can open up various device applications in nanoelectronics. However, in situ epitaxial growth of dissimilar van der Waals materials remains challenging. Here we demonstrate a solution for fabricating van der Waals heterostructures. Graphene/hexagonal boron nitride (h-BN) heterostructures were synthesized on cobalt substrates by using molecular beam epitaxy. Various characterizations were carried out to evaluate the heterostructures. Wafer-scale heterostructures consisting of single-layer/bilayer graphene and multilayer h-BN were achieved. The mismatch angle between graphene and h-BN is below 1°.

  8. Interaction of boron with graphite: A van der Waals density functional study

    Energy Technology Data Exchange (ETDEWEB)

    Liu, Juan; Wang, Chen [Beijing Key Lab of Fine Ceramics, Institute of Nuclear and New Energy Technology, Tsinghua University, Beijing 100084 (China); Liang, Tongxiang, E-mail: txliang@tsinghua.edu.cn [State Key Lab of New Ceramic and Fine Processing, Tsinghua University, Beijing 100084 (China); Lai, Wensheng [Advanced Material Laboratory, School of Materials Science & Engineering, Tsinghua University, Beijing, 100084 (China)

    2016-08-30

    Highlights: • A van der Waals density-functional approach is applied to study the interaction of boron with graphite. • VdW-DF functionals give fair agreement of crystal parameters with experiments. • The π electron approaches boron while adsorbing on graphite surface. • The hole introduced by boron mainly concentrates on boron and the nearest three carbon atoms. • PBE cannot describe the interstitial boron in graphite because of the ignoring binding of graphite sheets. - Abstract: Boron doping has been widely investigated to improve oxidation resistance of graphite. In this work the interaction of boron with graphite is investigated by a van der Waals density-functional approach (vdW-DF). The traditional density-functional theory (DFT) is well accounted for the binding in boron-substituted graphite. However, to investigate the boron atom on graphite surface and the interstitial impurities require use of a description of graphite interlayer binding. Traditional DFT cannot describe the vdW physics, for instance, GGA calculations show no relevant binding between graphite sheets. LDA shows some binding, but they fail to provide an accurate account of vdW forces. In this paper, we compare the calculation results of graphite lattice constant and cohesive energy by several functionals, it shows that vdW-DF such as two optimized functionals optB88-vdW and optB86b-vdW give much improved results than traditional DFT. The vdW-DF approach is then applied to study the interaction of boron with graphite. Boron adsorption, substitution, and intercalation are discussed in terms of structural parameters and electronic structures. When adsorbing on graphite surface, boron behaves as π electron acceptor. The π electron approaches boron atom because of more electropositive of boron than carbon. For substitution situation, the hole introduced by boron mainly concentrates on boron and the nearest three carbon atoms. The B-doped graphite system with the hole has less

  9. Hybrid van der Waals p-n Heterojunctions based on SnO and 2D MoS2

    KAUST Repository

    Wang, Zhenwei

    2016-08-30

    A p-type oxide/2D hybrid van der Waals p-n heterojunction is demonstrated for the first time between SnO (tin monoxide) (the p-type oxide) and 2D MoS2 (molybdenum disulfide), showing an ideality factor of 2 and rectification ratio up to 10(4) . The reported heterojunction is gate-tunable with typical anti-ambipolar transfer characteristics. Surface potential mapping is performed and a current model for such a heterojunction is proposed.

  10. Are non-linear C-H⋯O contacts hydrogen bonds or Van der Waals interactions?. Establishing the limits between hydrogen bonds and Van der Waals interactions

    Science.gov (United States)

    Novoa, Juan J.; Lafuente, Pilar; Mota, Fernando

    1998-07-01

    The hydrogen bond nature of angular C-H⋯O contacts is examined to determine when these contacts are better classified as hydrogen bonds or as Van der Waals bonds. To classify the bond we propose to look at the nature of the intermolecular bond critical point present in the electron density of the complex containing the bond. The physics behind this approach is explained using a qualitative orbital overlap model aimed at describing the main changes in the electronic density of the complex produced by the C-H⋯O bending.

  11. Electronic Properties of Polarizable Systems with Self-Consistent Interatomic van der Waals Density Functional

    Science.gov (United States)

    Ferri, Nicola; Distasio, Robert A., Jr.; Ambrosetti, Alberto; Car, Roberto; Scheffler, Matthias; Tkatchenko, Alexandre

    2015-03-01

    Ubiquitous long-range van der Waals (vdW) interactions play a fundamental role in the structure and stability of a wide range of systems. Within the DFT framework, the vdW energy represents a crucial, but tiny part of the total energy, hence its influence on the electronic density, n (r) , and electronic properties is typically assumed to be rather small. Here, we address this question via a fully self-consistent (SC) implementation of the interatomic Tkatchenko-Scheffler vdW functional and its extension to surfaces. Self-consistency leads to large changes in the binding energies and electrostatic moments of highly polarizable alkali metal dimers. For some metal surfaces, vdW interactions increase dipole moments and induce non-trivial charge rearrangements, leading to visible changes in the metal workfunctions. Similar behavior is observed for molecules adsorbed on metals. Our study reveals a non-trivial connection between electrostatics and long-range electron correlation effects.

  12. Effects of the van der Waals Force on the Dynamics Performance for a Micro Resonant Pressure Sensor

    Directory of Open Access Journals (Sweden)

    Lizhong Xu

    2016-01-01

    Full Text Available The micro resonant pressure sensor outputs the frequency signals where the distortion does not take place in a long distance transmission. As the dimensions of the sensor decrease, the effects of the van der Waals forces should be considered. Here, a coupled dynamic model of the micro resonant pressure sensor is proposed and its coupled dynamic equation is given in which the van der Waals force is considered. By the equation, the effects of the van der Waals force on the natural frequencies and vibration amplitudes of the micro resonant pressure sensor are investigated. Results show that the natural frequency and the vibrating amplitudes of the micro resonant pressure sensor are affected significantly by van der Waals force for a small clearance between the film and the base plate, a small initial tension stress of the film, and some other conditions.

  13. Spectroscopic measurement of the titanium-helium van der Waals molecule: TiHe

    Science.gov (United States)

    Quiros, Nancy; Tariq, Naima; Weinstein, Jonathan

    2016-05-01

    Atoms that are weakly bound by the van der Waals (vdW) interaction are known as van der Waals molecules. The existence and formation of vdW molecules is favorable at low temperatures due to their weak binding energy. We have used laser ablation and helium buffer gas cooling to create the exotic vdW diatomic molecule made of titanium (Ti) and helium (He). TiHe molecules were detected through laser-induced-fluorescence spectroscopy closely blue-detuned from the a3F2 --> y3F3 atomic Ti transition at 25227 cm-1. Measurements of the binding energy of TiHe were obtained by studying its equilibrium thermodynamic properties. It is believed the molecules are formed from the constituent cold atoms through three-body recombination. Progress towards measuring the three-body recombination rate coefficient will be discussed. This material is based upon work supported by National Science Foundation under Grant No. PHY 1265905.

  14. A simplified implementation of van der Waals density functionals for first-principles molecular dynamics applications

    Science.gov (United States)

    Wu, Jun; Gygi, François

    2012-06-01

    We present a simplified implementation of the non-local van der Waals correlation functional introduced by Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)] and reformulated by Román-Pérez et al. [Phys. Rev. Lett. 103, 096102 (2009)]. The proposed numerical approach removes the logarithmic singularity of the kernel function. Complete expressions of the self-consistent correlation potential and of the stress tensor are given. Combined with various choices of exchange functionals, five versions of van der Waals density functionals are implemented. Applications to the computation of the interaction energy of the benzene-water complex and to the computation of the equilibrium cell parameters of the benzene crystal are presented. As an example of crystal structure calculation involving a mixture of hydrogen bonding and dispersion interactions, we compute the equilibrium structure of two polymorphs of aspirin (2-acetoxybenzoic acid, C9H8O4) in the P21/c monoclinic structure.

  15. Simon van der Meer and his legacy to CERN and particle accelerators

    CERN Document Server

    Chohan, Vinod

    2012-01-01

    Simon van der Meer was a brilliant scientist and a true giant in the field of accelerators. His seminal contributions to accelerator science are essential to this day in our quest to satisfy the demands of modern particle physics. Whether we are talking of long-baseline neutrino physics or antiproton-proton physics at CERN and Fermilab, or proton-proton physics at the LHC, his techniques and inventions have been a vital and necessary part of modern-day successes. Simon van der Meer and Carlo Rubbia were the first CERN scientists to become Nobel laureates in Physics in 1984. His less well-known contributions spanned a whole range of subjects in accelerator science from magnet design to power supply design, beam measurements, slow beam extraction, sophisticated programs, and controls.

  16. First principles calculations of solid-state thermionic transport in layered van der Waals heterostructures

    Science.gov (United States)

    Wang, Xiaoming; Zebarjadi, Mona; Esfarjani, Keivan

    2016-08-01

    This work aims at understanding solid-state energy conversion and transport in layered (van der Waals) heterostructures in contact with metallic electrodes via a first-principles approach. As an illustration, a graphene/phosphorene/graphene heterostructure in contact with gold electrodes is studied by using density functional theory (DFT)-based first principles calculations combined with real space Green's function (GF) formalism. We show that for a monolayer phosphorene, quantum tunneling dominates the transport. By adding more phosphorene layers, one can switch from tunneling-dominated transport to thermionic-dominated transport, resulting in transporting more heat per charge carrier, thus, enhancing the cooling coefficient of performance. The use of layered van der Waals heterostructures has two advantages: (a) thermionic transport barriers can be tuned by changing the number of layers, and (b) thermal conductance across these non-covalent structures is very weak. The phonon thermal conductance of the present van der Waals heterostructure is found to be 4.1 MW m-2 K-1 which is one order of magnitude lower than the lowest value for that of covalently-bonded interfaces. The thermionic coefficient of performance for the proposed device is 18.5 at 600 K corresponding to an equivalent ZT of 0.13, which is significant for nanoscale devices. This study shows that layered van der Waals structures have great potential to be used as solid-state energy-conversion devices.This work aims at understanding solid-state energy conversion and transport in layered (van der Waals) heterostructures in contact with metallic electrodes via a first-principles approach. As an illustration, a graphene/phosphorene/graphene heterostructure in contact with gold electrodes is studied by using density functional theory (DFT)-based first principles calculations combined with real space Green's function (GF) formalism. We show that for a monolayer phosphorene, quantum tunneling dominates the

  17. Two dimensional graphene nanogenerator by coulomb dragging: Moving van der Waals heterostructure

    Energy Technology Data Exchange (ETDEWEB)

    Zhong, Huikai; Li, Xiaoqiang; Wu, Zhiqian; Zhang, Shengjiao; Xu, Zhijuan [Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027 (China); Chen, Hongsheng; Lin, Shisheng, E-mail: shishenglin@zju.edu.cn [Department of Information Science and Electronic Engineering, Zhejiang University, Hangzhou 310027 (China); State Key Laboratory of Modern Optical Instrumentation, Zhejiang University, Hangzhou 310027 (China)

    2015-06-15

    Harvesting energy from environment is the current focus of scientific community. Here, we demonstrate a graphene nanogenerator, which is based on moving van der Waals heterostructure formed between graphene and two dimensional (2D) graphene oxide (GO). This nanogenerator can convert mechanical energy into electricity with a voltage output of around 10 mV. Systematic experiments reveal the generated electricity originates from the coulomb interaction induced momentum transfer between 2D GO and holes in graphene. 2D boron nitride was also demonstrated to be effective in the framework of moving van der Waals heterostructure nanogenerator. This investigation of nanogenerator based on the interaction between 2D macromolecule materials will be important to understand the origin of the flow-induced potential in nanomaterials and may have great potential in practical applications.

  18. Two dimensional graphene nanogenerator by coulomb dragging: Moving van der Waals heterostructure

    Science.gov (United States)

    Zhong, Huikai; Li, Xiaoqiang; Wu, Zhiqian; Zhang, Shengjiao; Xu, Zhijuan; Chen, Hongsheng; Lin, Shisheng

    2015-06-01

    Harvesting energy from environment is the current focus of scientific community. Here, we demonstrate a graphene nanogenerator, which is based on moving van der Waals heterostructure formed between graphene and two dimensional (2D) graphene oxide (GO). This nanogenerator can convert mechanical energy into electricity with a voltage output of around 10 mV. Systematic experiments reveal the generated electricity originates from the coulomb interaction induced momentum transfer between 2D GO and holes in graphene. 2D boron nitride was also demonstrated to be effective in the framework of moving van der Waals heterostructure nanogenerator. This investigation of nanogenerator based on the interaction between 2D macromolecule materials will be important to understand the origin of the flow-induced potential in nanomaterials and may have great potential in practical applications.

  19. Formation and dynamics of van der Waals molecules in buffer-gas traps

    CERN Document Server

    Brahms, Nathan; Zhang, Peng; Kłos, Jacek; Forrey, Robert C; Au, Yat Shan; Sadeghpour, H R; Dalgarno, A; Doyle, John M; Walker, Thad G

    2011-01-01

    We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxations are too slow to affect trap lifetimes. However, helium-3-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag3He molecules, using ab initio calc...

  20. Exfoliation of natural van der Waals heterostructures to a single unit cell thickness

    Science.gov (United States)

    Velický, Matěj; Toth, Peter S.; Rakowski, Alexander M.; Rooney, Aidan P.; Kozikov, Aleksey; Woods, Colin R.; Mishchenko, Artem; Fumagalli, Laura; Yin, Jun; Zólyomi, Viktor; Georgiou, Thanasis; Haigh, Sarah J.; Novoselov, Kostya S.; Dryfe, Robert A. W.

    2017-02-01

    Weak interlayer interactions in van der Waals crystals facilitate their mechanical exfoliation to monolayer and few-layer two-dimensional materials, which often exhibit striking physical phenomena absent in their bulk form. Here we utilize mechanical exfoliation to produce a two-dimensional form of a mineral franckeite and show that the phase segregation of chemical species into discrete layers at the sub-nanometre scale facilitates franckeite's layered structure and basal cleavage down to a single unit cell thickness. This behaviour is likely to be common in a wider family of complex minerals and could be exploited for a single-step synthesis of van der Waals heterostructures, as an alternative to artificial stacking of individual two-dimensional crystals. We demonstrate p-type electrical conductivity and remarkable electrochemical properties of the exfoliated crystals, showing promise for a range of applications, and use the density functional theory calculations of franckeite's electronic band structure to rationalize the experimental results.

  1. Van der Waals interactions in rare-gas dimers: The role of interparticle interactions

    CERN Document Server

    Chen, Yu-Ting; Chai, Jeng-Da

    2015-01-01

    We investigate the potential energy curves of rare-gas dimers with various ranges and strengths of interparticle interactions (nuclear-electron, electron-electron, and nuclear-nuclear interactions). Our investigation is based on the highly accurate coupled-cluster theory associated with those interparticle interactions. For comparison, the performance of the corresponding Hartree-Fock theory, second-order Moller-Plesset perturbation theory, and density functional theory is also investigated. Our results reveal that when the interparticle interactions retain the long-range Coulomb tails, the nature of van der Waals interactions in the rare-gas dimers remains similar. By contrast, when the interparticle interactions are sufficiently short-range, the conventional van der Waals interactions in the rare-gas dimers completely disappear, yielding purely repulsive potential energy curves.

  2. Effects of a periodic drive and correlated noise on birhythmic van der Pol systems

    Science.gov (United States)

    Yonkeu, R. Mbakob; Yamapi, R.; Filatrella, G.; Tchawoua, C.

    2017-01-01

    This paper considers the dynamics of a van der Pol birhythmic oscillator submitted both to colored noise and harmonic excitation. Applying the quasi-harmonic assumption to the corresponding Langevin equation we derive an approximated Fokker-Planck equation, that is compared with the results of computer simulations. We thus derive both the effects of the correlation time and the harmonic excitation on the parameter space where birhythmicity appears. In this region, we find that the multi-limit-cycle van der Pol oscillator reduces to an asymmetric bistable system where the sinusoidal drive intensity plays the role of asymmetric parameter, and noise can lead to stochastic bifurcations, consisting in a qualitative change of the stationary amplitude distribution. Under both influence of noise and harmonic excitation, the dynamics can be well characterized through the concepts of pseudo-potential, that regulates the low noise Arrhenius-like behavior.

  3. Stochastic Bifurcations induced by correlated Noise in a Birhythmic van der Pol System

    CERN Document Server

    Yonkeu, R Mbakob; Filatrella, G; Tchawoua, C

    2015-01-01

    We investigate the effects of exponentially correlated noise on birhythmic van der Pol type oscillators. The analytical results are obtained applying the quasi-harmonic assumption to the Langevin equation to derive an approximated Fokker-Planck equation. This approach allows to analytically derive the probability distributions as well as the activation energies associated to switching between coexisting attractors. The stationary probability density function of the van der Pol oscillator reveals the influence of the correlation time on the dynamics. Stochastic bifurcations are discussed through a qualitative change of the stationary probability distribution, which indicates that noise intensity and correlation time can be treated as bifurcation parameters. Comparing the analytical and numerical results, we find good agreement both when the frequencies of the attractors are about equal or when they are markedly different.

  4. Stochastic bifurcations in a bistable Duffing-Van der Pol oscillator with colored noise.

    Science.gov (United States)

    Xu, Yong; Gu, Rencai; Zhang, Huiqing; Xu, Wei; Duan, Jinqiao

    2011-05-01

    This paper aims to investigate Gaussian colored-noise-induced stochastic bifurcations and the dynamical influence of correlation time and noise intensity in a bistable Duffing-Van der Pol oscillator. By using the stochastic averaging method, theoretically, one can obtain the stationary probability density function of amplitude for the Duffing-Van der Pol oscillator and can reveal interesting dynamics under the influence of Gaussian colored noise. Stochastic bifurcations are discussed through a qualitative change of the stationary probability distribution, which indicates that system parameters, noise intensity, and noise correlation time, respectively, can be treated as bifurcation parameters. They also imply that the effects of multiplicative noise are rather different from that of additive noise. The results of direct numerical simulation verify the effectiveness of the theoretical analysis. Moreover, the largest Lyapunov exponent calculations indicate that P and D bifurcations have no direct connection.

  5. Electrical and optical properties of SnS2/WSe2 van der Waals Heterojunction FETs

    Science.gov (United States)

    Zubair, Ahmad; Nourbakhsh, Amirhasan; Dresselhaus, Mildred; Palacios, Tomas

    Two dimensional crystals based on atomically thin films of transition metal dichalcogenides offer an exciting platform for various optoelectronic applications. Their unique crystal properties make them particularly attractive for van der Waals heterostructures which open up an additional degree of freedom to tailor the material properties into new physics and device applications. In this work, we explore, for the first time, the optoelectronic properties of van der Waals SnS2/WSe2 heterojunction. WSe2 is an ambipolar semiconductor while SnS2 is an n-type wide bandgap semiconductor. We use the pickup and dry transfer methods to fabricate SnS2/WSe2 heterojunction transistors (hetero-FETs). We observe negative differential transconductance in the SnS2/WSe2 hetero-FET. Also, the heterostructure couples strongly to incident light and shows high photovoltaic responsivity which can find applications in nano-devices such as photo-detectors and solar cells.

  6. Steady dynamics of exothermic chemical wave fronts in van der Waals fluids

    Science.gov (United States)

    Dumazer, G.; Antoine, C.; Lemarchand, A.; Nowakowski, B.

    2009-12-01

    We study the steady dynamics of an exothermic Fisher-Kolmogorov-Petrovsky-Piskunov chemical wave front traveling in a one-dimensional van der Waals fluid. The propagating wave is initiated by a nonuniformity in reactant concentration contrary to usual combustion ignition processes. The heat release and activation energy of the reaction play the role of control parameters. We recently proved that the propagation of an exothermic chemical wave front in a perfect gas displays a forbidden interval of stationary wave front speeds [G. Dumazer, M. Leda, B. Nowakowski, and A. Lemarchand, Phys. Rev. E 78, 016309 (2008)]. We examine how this result is modified for nonideal fluids and determine the effect of the van der Waals parameters and fluid density on the bifurcation between diffusion flames and Chapman-Jouguet detonation waves as heat release increases. Analytical predictions are confirmed by the numerical solution of the hydrodynamic equations including reaction kinetics.

  7. Bonding in Mercury-Alkali Molecules: Orbital-driven van der Waals Complexes

    Directory of Open Access Journals (Sweden)

    Dieter Cremer

    2008-06-01

    Full Text Available The bonding situation in mercury-alkali diatomics HgA (2Σ+ (A = Li, Na, K, Rb has been investigated employing the relativistic all-electron method Normalized Elimination of the Small Component (NESC, CCSD(T, and augmented VTZ basis sets. Although Hg,A interactions are typical of van der Waals complexes, trends in calculated De values can be explained on the basis of a 3-electron 2-orbital model utilizing calculated ionization potentials and the De values of HgA+(1Σ+ diatomics. HgA molecules are identified as orbital-driven van der Waals complexes. The relevance of results for the understanding of the properties of liquid alkali metal amalgams is discussed.

  8. Holographic Van der Waals-like phase transition in the Gauss–Bonnet gravity

    Energy Technology Data Exchange (ETDEWEB)

    He, Song, E-mail: hesong17@gmail.com [Max Planck Institute for Gravitational Physics (Albert Einstein Institute), Am Mühlenberg 1, 14476 Golm (Germany); State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Li-Fang, E-mail: lilf@itp.ac.cn [Center for Space Science and Applied Research, Chinese Academy of Sciences, Beijing 100190 (China); Zeng, Xiao-Xiong, E-mail: xxzeng@itp.ac.cn [State Key Laboratory of Theoretical Physics, Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); School of Material Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China)

    2017-02-15

    The Van der Waals-like phase transition is observed in temperature–thermal entropy plane in spherically symmetric charged Gauss–Bonnet–AdS black hole background. In terms of AdS/CFT, the non-local observables such as holographic entanglement entropy, Wilson loop, and two point correlation function of very heavy operators in the field theory dual to spherically symmetric charged Gauss–Bonnet–AdS black hole have been investigated. All of them exhibit the Van der Waals-like phase transition for a fixed charge parameter or Gauss–Bonnet parameter in such gravity background. Further, with choosing various values of charge or Gauss–Bonnet parameter, the equal area law and the critical exponent of the heat capacity are found to be consistent with phase structures in temperature–thermal entropy plane.

  9. Response to Sijtsma and van der Ark (2015): "Conceptions of reliability revisited and practical recommendations".

    Science.gov (United States)

    Gajewski, Byron; Price, Larry R; Bott, Marjorie

    2015-01-01

    Sijtsma and van der Ark present a broad set of models and methods for reliability estimation, and their discussion of similarities and differences provides clear information for nurse researchers to move forward in their instrument development projects. In particular, we applaud the authors' clear exposition of the factor analytic model and its utility for providing a framework for unifying reliability and validity. However, we do not want to be constrained only to the point estimates. We also need to ascertain the uncertainty in the point estimate-usually in the form of a 95% confidence interval-or, as the Bayesians refer to, a credible interval. Another issue not discussed by Sijtsma and van der Ark is conditional standard errors of measurement along the score scale measuring latent traits or true scores. In our response, practical tools for estimating intervals and a brief discussion of conditional standard errors of measurement are presented.

  10. Van der Waals force: a dominant factor for reactivity of graphene.

    Science.gov (United States)

    Lee, Jong Hak; Avsar, Ahmet; Jung, Jeil; Tan, Jun You; Watanabe, K; Taniguchi, T; Natarajan, Srinivasan; Eda, Goki; Adam, Shaffique; Castro Neto, Antonio H; Özyilmaz, Barbaros

    2015-01-14

    Reactivity control of graphene is an important issue because chemical functionalization can modulate graphene's unique mechanical, optical, and electronic properties. Using systematic optical studies, we demonstrate that van der Waals interaction is the dominant factor for the chemical reactivity of graphene on two-dimensional (2D) heterostructures. A significant enhancement in the chemical stability of graphene is achieved by replacing the common SiO2 substrate with 2D crystals such as an additional graphene layer, WS2, MoS2, or h-BN. Our theoretical and experimental results show that its origin is a strong van der Waals interaction between the graphene layer and the 2D substrate. This results in a high resistive force on graphene toward geometric lattice deformation. We also demonstrate that the chemical reactivity of graphene can be controlled by the relative lattice orientation with respect to the substrates and thus can be used for a wide range of applications including hydrogen storage.

  11. Holographic Van der Waals-like phase transition in the Gauss-Bonnet gravity

    Science.gov (United States)

    He, Song; Li, Li-Fang; Zeng, Xiao-Xiong

    2017-02-01

    The Van der Waals-like phase transition is observed in temperature-thermal entropy plane in spherically symmetric charged Gauss-Bonnet-AdS black hole background. In terms of AdS/CFT, the non-local observables such as holographic entanglement entropy, Wilson loop, and two point correlation function of very heavy operators in the field theory dual to spherically symmetric charged Gauss-Bonnet-AdS black hole have been investigated. All of them exhibit the Van der Waals-like phase transition for a fixed charge parameter or Gauss-Bonnet parameter in such gravity background. Further, with choosing various values of charge or Gauss-Bonnet parameter, the equal area law and the critical exponent of the heat capacity are found to be consistent with phase structures in temperature-thermal entropy plane.

  12. Van der Waals and Casimir interactions between atoms and carbon nanotubes

    OpenAIRE

    Klimchitskaya, G. L.(Central Astronomical Observatory at Pulkovo of the Russian Academy of Sciences, 196140, St. Petersburg, Russia); Blagov, E. V.; Mostepanenko, V. M.

    2008-01-01

    The van der Waals and Casimir interactions of a hydrogen atom (molecule) with a single-walled and a multiwalled carbon nanotubes are compared. It is shown that the macroscopic concept of graphite dielectric permittivity is already applicable for nanotubes with only two or three walls. The absorption of hydrogen atoms by a nanotube at separations below one nanometer is considered. The lateral force due to exchange repulsion moves the atom to a position above the cell center, where it is absorb...

  13. Collective behaviour in a square lattice of driven Duffing resonators coupled to van der Pol oscillators

    OpenAIRE

    Randrianandrasana, Michel; Wei, Xueyong; Lowe, David

    2010-01-01

    The global and local synchronisation of a square lattice composed of alternating Duffing resonators and van der Pol oscillators coupled through displacement is studied. The lattice acts as a sensing device in which the input signal is characterised by an external driving force that is injected into the system through a subset of the Duffing resonators. The parameters of the system are taken from MEMS devices. The effects of the system parameters, the lattice architecture and size are discussed.

  14. PRINCIPAL RESPONSE OF VAN DER POL-DUFFING OSCILLATOR UNDER COMBINED DETERMINISTIC AND RANDOM PARAMETRIC EXCITATION

    Institute of Scientific and Technical Information of China (English)

    戎海武; 徐伟; 王向东; 孟光; 方同

    2002-01-01

    The principal resonance of Van der Pol-Duffing oscillator to combined determin istic and random parametric excitations is investigated. The method of multiple scales was used to determine the equations of modulation of amplitude and phase. The behavior, stability and bifurcation of steady state response were studied. Jumps were shown to occur under some conditions. The effects of damping, detuning , bandwidth, and magnitudes of deterministic and random excitations are analyzed. The theoretical analysis were verified by numerical results.

  15. Adaptive backstepping control and synchronization of a modified and chaotic Van der Pol-Duffing oscillator

    Institute of Scientific and Technical Information of China (English)

    2011-01-01

    In this paper,we propose a backstepping approach for the synchronization and control of modified Van-der Pol Duffing oscillator circuits.The method is such that one controller function that depends essentially on available circuit parameters that is sufficient to drive the two coupled circuits to a synchronized state as well achieve the global stabilization of the system to its regular dynamics.Numerical simulations are given to demonstrate the effectiveness of the technique.

  16. Stability analysis for periodic solutions of the Van der Pol-Duffing forced oscillator

    Science.gov (United States)

    Cui, Jifeng; Liang, Jiaming; Lin, Zhiliang

    2016-01-01

    Based on the homotopy analysis method (HAM), the high accuracy frequency response curve and the stable/unstable periodic solutions of the Van der Pol-Duffing forced oscillator with the variation of the forced frequency are obtained and studied. The stability of the periodic solutions obtained is analyzed by use of Floquet theory. Furthermore, the results are validated in the light of spectral analysis and bifurcation theory.

  17. Period-Doubling Cascades and Strange Attractors in Extended Duffing-Van der Pol Oscillator

    Institute of Scientific and Technical Information of China (English)

    YU Jun; PAN Wei-Zhen; ZHANG Rong-Bo

    2009-01-01

    The dynamical behavior of the extended Dulling-Van der Pol oscillator is investigated numerically in detail. With the aid of some numerical simulation tools such as bifurcation diagrams and Poincaré maps, the different routes to chaos and various shapes of strange attractors are observed. To characterize chaotic behavior of this oscillator system, the spectrum of Lyapunov exponent and Lyapunov dimension are also employed.

  18. Chaos synchronization between single and double wells Duffing-Van der Pol oscillators using active control

    Energy Technology Data Exchange (ETDEWEB)

    Njah, A.N. [Department of Physics, University of Agriculture, P.M.B 2240, Abeokuta (Nigeria)], E-mail: njahabdul@yahoo.com; Vincent, U.E. [Department of Physics, Olabisi Onabanjo University, P.M.B 2002, Ago-Iwoye (Nigeria)], E-mail: ue_vincent@yahoo.com

    2008-09-15

    This paper presents chaos synchronization between single and double wells Duffing-Van der Pol (DVP) oscillators with {phi}{sup 4} potential based on the active control technique. The technique is applied to achieve global synchronization between identical double-well DVP oscillators, identical single-well DVP oscillators and non-identical DVP oscillators, consisting of the double-well and the single-well DVP oscillators, respectively. Numerical simulations are also presented to verify the analytical results.

  19. Quasi-1D van der Waals materials as high current-density local interconnects (Conference Presentation)

    Science.gov (United States)

    Stolyarov, Maxim; Aytan, Ece; Bloodgood, Matthew; Salguero, Tina T.; Balandin, Alexander A.

    2016-09-01

    The continuous downscaling of interconnect dimensions in combination with the introduction of low-k dielectrics has increased the number of heat dissipation, integration and reliability challenges in modern electronics. As a result, there is a strong need for new materials that have high current-carrying capacity for applications as nanoscale interconnects. In this presentation, we show that quasi-one-dimensional (1D) van der Waals metals such as TaSe3 have excellent breakdown current density exceeding that of 5 MA/cm2. This value is above that currently achievable in conventional copper or aluminum wires. The quasi-1D van der Waals materials are characterized by strong bonds along one dimension and weak van der Waals bonds along two other dimensions. The material for this study was grown by the chemical vapor transport (CVT) method. Both mechanical and chemical exfoliation methods were used to fabricate nanowires with lateral dimensions below 100 nm. The dimensions of the quasi-1D nanowires were verified with scanning electron microscopy (SEM) and atomic force microscopy (AFM). The metal (Ti/Au) contacts for the electrical characterization were deposited using electron beam evaporation (EBE). The measurements were conducted on a number of prototype interconnects with multiple electric contacts to ensure reproducibility. The obtained results suggest that quasi-1D van der Waals metals present a feasible alternative to conventional copper interconnects in terms of the current-carrying capacity and the breakdown current-density. This work was supported, in part, by the SRC and DARPA through STARnet Center for Function Accelerated nanoMaterial Engineering (FAME).

  20. Van der Waals equation of state revisited: importance of the dispersion correction.

    Science.gov (United States)

    de Visser, Sam P

    2011-04-28

    One of the most basic equations of state describing nonideal gases and liquids is the van der Waals equation of state, and as a consequence, it is generally taught in most first year undergraduate chemistry courses. In this work, we show that the constants a and b in the van der Waals equation of state are linearly proportional to the polarizability volume of the molecules in a gas or liquid. Using this information, a new thermodynamic one-parameter equation of state is derived that contains experimentally measurable variables and physics constants only. This is the first equation of state apart from the Ideal Gas Law that contains experimentally measurable variables and physics constants only, and as such, it may be a very useful and practical equation for the description of dilute gases and liquids. The modified van der Waals equation of state describes pV as the sum of repulsive and attractive intermolecular interaction energies that are represented by an exponential repulsion function between the electron clouds of the molecules and a London dispersion component, respectively. The newly derived equation of state is tested against experimental data for several gas and liquid examples, and the agreement is satisfactory. The description of the equation of state as a one-parameter function also has implications on other thermodynamic functions, such as critical parameters, virial coefficients, and isothermal compressibilities. Using our modified van der Waals equation of state, we show that all of these properties are a function of the molecular polarizability volume. Correlations of experimental data confirm the derived proportionalities.

  1. Measuring anisotropic resistivity of single crystals using the van der Pauw technique

    OpenAIRE

    2015-01-01

    Anisotropy in properties of materials is important in materials science and solid-state physics. Measurement of the full resistivity tensor of crystals using the standard four-point method with bar shaped samples requires many measurements and may be inaccurate due to misalignment of the bars along crystallographic directions. Here an approach to extracting the resistivity tensor using van der Pauw measurements is presented. This reduces the number of required measurements. The theory of the ...

  2. van der Waals epitaxy and photoresponse of two-dimensional CdSe plates

    Science.gov (United States)

    Zhu, Dan-Dan; Xia, Jing; Wang, Lei; Li, Xuan-Ze; Tian, Li-Feng; Meng, Xiang-Min

    2016-06-01

    Here we demonstrate the first growth of two-dimensional (2D) single-crystalline CdSe plates on mica substrates via van der Waals epitaxy. The as-synthesized 2D plates exhibit hexagonal, truncated triangular and triangular shapes with the lateral size around several microns. Photodetectors based on 2D CdSe plates present a fast response time of 24 ms, revealing that 2D CdSe is a promising building block for ultrathin optoelectronic devices.

  3. Moire superlattice effects in graphene/boron-nitride van der Waals heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Wallbank, John R.; Chen, Xi; Fal' ko, Vladimir I. [Department of Physics, Lancaster University, Lancaster (United Kingdom); Mucha-Kruczynski, Marcin [Department of Physics, University of Bath (United Kingdom)

    2015-06-15

    Van der Waals heterostructures of graphene and hexagonal boron nitride feature a moire superlattice for graphene's Dirac electrons. Here, we review the effects generated by this superlattice, including a specific miniband structure featuring gaps and secondary Dirac points, and a fractal spectrum of magnetic minibands known as Hofstadter's butterfly. (copyright 2015 by WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  4. Van der Waals epitaxial double heterostructure: InAs/single-layer graphene/InAs.

    Science.gov (United States)

    Hong, Young Joon; Yang, Jae Won; Lee, Wi Hyoung; Ruoff, Rodney S; Kim, Kwang S; Fukui, Takashi

    2013-12-17

    Van der Waals (vdW) epitaxial double heterostructures have been fabricated by vdW epitaxy of InAs nanostructures on both sides of graphene. InAs nanostructures diametrically form on/underneath graphene exclusively along As-polar direction, indicating polarity inversion of the double heterostructures. First-principles and density functional calculations demonstrate how and why InAs easily form to be double heterostructures with polarity inversion.

  5. First-principles study of two-dimensional van der Waals heterojunctions

    OpenAIRE

    Hu, Wei; Yang, Jinlong

    2015-01-01

    Research on graphene and other two-dimensional (2D) materials, such as silicene, germanene, phosphorene, hexagonal boron nitride (h-BN), graphitic carbon nitride (g-C3N4), graphitic zinc oxide (g-ZnO) and molybdenum disulphide (MoS2), has recently received considerable interest owing to their outstanding properties and wide applications. Looking beyond this field, combining the electronic structures of 2D materials in ultrathin van der Waals heterojunctions has also emerged to widely study th...

  6. Van der Waals Type Model and Structure in π-p Elastic Scattering at High Energies

    Science.gov (United States)

    Aleem, F.

    1982-10-01

    The most recent measurement of the angular distribution for π-p elastic scattering at pL =50 and 200 GeV/c which show a structure near -t ≈ 4(GeV/c)2, with squared four momentum transfer -t extended to 10(GeV/c)2, and the total cross section data for 50 ≤ pL ≤ 370 GeV/c have been simultaneously explained by using Van der Waal's type model.

  7. Effect of van der Waals interactions on the structural and elastic properties of black phosphorus

    DEFF Research Database (Denmark)

    Appalakondaiah, S.; Vaitheeswaran, G.; Lebègue, S.;

    2012-01-01

    The structural and elastic properties of orthorhombic black phosphorus have been investigated using first-principles calculations based on density functional theory. The structural parameters have been calculated using the local density approximation (LDA), the generalized gradient approximation...... (GGA), and with several dispersion corrections to include van der Waals interactions. It is found that the dispersion corrections improve the lattice parameters over LDA and GGA in comparison with experimental results. The calculations reproduce well the experimental trends under pressure and show...

  8. Large area molybdenum disulphide- epitaxial graphene vertical Van der Waals heterostructures

    Science.gov (United States)

    Pierucci, Debora; Henck, Hugo; Naylor, Carl H.; Sediri, Haikel; Lhuillier, Emmanuel; Balan, Adrian; Rault, Julien E.; Dappe, Yannick J.; Bertran, François; Fèvre, Patrick Le; Johnson, A. T. Charlie; Ouerghi, Abdelkarim

    2016-06-01

    Two-dimensional layered transition metal dichalcogenides (TMDCs) show great potential for optoelectronic devices due to their electronic and optical properties. A metal-semiconductor interface, as epitaxial graphene - molybdenum disulfide (MoS2), is of great interest from the standpoint of fundamental science, as it constitutes an outstanding platform to investigate the interlayer interaction in van der Waals heterostructures. Here, we study large area MoS2-graphene-heterostructures formed by direct transfer of chemical-vapor deposited MoS2 layer onto epitaxial graphene/SiC. We show that via a direct transfer, which minimizes interface contamination, we can obtain high quality and homogeneous van der Waals heterostructures. Angle-resolved photoemission spectroscopy (ARPES) measurements combined with Density Functional Theory (DFT) calculations show that the transition from indirect to direct bandgap in monolayer MoS2 is maintained in these heterostructures due to the weak van der Waals interaction with epitaxial graphene. A downshift of the Raman 2D band of the graphene, an up shift of the A1g peak of MoS2 and a significant photoluminescence quenching are observed for both monolayer and bilayer MoS2 as a result of charge transfer from MoS2 to epitaxial graphene under illumination. Our work provides a possible route to modify the thin film TDMCs photoluminescence properties via substrate engineering for future device design.

  9. Application of the van der Pauw method for samples with holes

    Science.gov (United States)

    Oh, Donggeon; Ahn, Cheongeung; Kim, Minchul; Park, Eung-Kyu; Kim, Yong-Sang

    2016-12-01

    Modifications of the original van der Pauw relation were suggested recently. The methods are applicable to samples with a hole, unlike the original van der Pauw relation, but it takes too much time and effort to apply the methods to samples with high randomness. So in this paper we suggest two generalizations of the van der Pauw method which are applicable for two-dimensional homogeneous systems with a finite number of holes. Both methods rely on obtaining a crucial constant of the system, ν. The first method involves setting the probes far from each other while conducting the experiment using a sample with a small hole, approximating a relation that gives ν as a linear function of the area ratio of the hole only. The second method produces an identical sample of known resistivity and thickness to obtain ν, which is believed to be dependent on the geometrical properties only. Unlike the earlier methods, which entailed complex procedures, little in the way of measurements and computation is needed for the new methods. The methods will be very useful in electric experiments or industries which need to measure the resistivity of samples.

  10. Spooky correlations and unusual van der Waals forces between gapless and near-gapless molecules

    CERN Document Server

    Dobson, John F; Angyan, Janos G; Liu, Ru-Fen

    2016-01-01

    We consider the zero-temperature van der Waals interaction between two molecules, each of which has a zero or near-zero electronic gap between a groundstate and the first excited state, using a toy model molecule ( equilateral H3) as an example. We show that the van der Waals energy between two groundstate molecules falls off as D^(-3) instead of the usual D^(-6) dependence, when the molecules are separated by distance D: We show that this is caused by perfect "spooky" correlation between the two fluctuating electric dipoles. The phenomenon is related to, but not the same as, the "resonant" interaction between an electronically excited and a groundstate molecule introduced by Eisenschitz and London in 1930. It is also an example of "type C van der Waals non- additivity" recently introduced by one of us ( Int. J. Quantum Chem. 114, 1157 (2014)). Our toy molecule H3 is not stable, but symmetry considerations suggest that a similar vdW phenomenon may be observable, despite Jahn-Teller effects, in molecules with ...

  11. Molecular recognition by van der Waals interaction between polymers with sequence-specific polarizabilities

    Science.gov (United States)

    Lu, Bing-Sui; Naji, Ali; Podgornik, Rudolf

    2015-06-01

    We analyze van der Waals interactions between two rigid polymers with sequence-specific, anisotropic polarizabilities along the polymer backbones, so that the dipole moments fluctuate parallel to the polymer backbones. Assuming that each polymer has a quenched-in polarizability sequence which reflects, for example, the polynucleotide sequence of a double-stranded DNA molecule, we study the van der Waals interaction energy between a pair of such polymers with rod-like structure for the cases where their respective polarizability sequences are (i) distinct and (ii) identical, with both zero and non-zero correlation length of the polarizability correlator along the polymer backbones in the latter case. For identical polymers, we find a novel r-5 scaling behavior of the van der Waals interaction energy for small inter-polymer separation r, in contradistinction to the r-4 scaling behavior of distinct polymers, with furthermore a pronounced angular dependence favoring attraction between sufficiently aligned identical polymers. Such behavior can assist the molecular recognition between polymers.

  12. Van der Pol and the history of relaxation oscillations: toward the emergence of a concept.

    Science.gov (United States)

    Ginoux, Jean-Marc; Letellier, Christophe

    2012-06-01

    Relaxation oscillations are commonly associated with the name of Balthazar van der Pol via his paper (Philosophical Magazine, 1926) in which he apparently introduced this terminology to describe the nonlinear oscillations produced by self-sustained oscillating systems such as a triode circuit. Our aim is to investigate how relaxation oscillations were actually discovered. Browsing the literature from the late 19th century, we identified four self-oscillating systems in which relaxation oscillations have been observed: (i) the series dynamo machine conducted by Gérard-Lescuyer (1880), (ii) the musical arc discovered by Duddell (1901) and investigated by Blondel (1905), (iii) the triode invented by de Forest (1907), and (iv) the multivibrator elaborated by Abraham and Bloch (1917). The differential equation describing such a self-oscillating system was proposed by Poincaré for the musical arc (1908), by Janet for the series dynamo machine (1919), and by Blondel for the triode (1919). Once Janet (1919) established that these three self-oscillating systems can be described by the same equation, van der Pol proposed (1926) a generic dimensionless equation which captures the relevant dynamical properties shared by these systems. Van der Pol's contributions during the period of 1926-1930 were investigated to show how, with Le Corbeiller's help, he popularized the "relaxation oscillations" using the previous experiments as examples and, turned them into a concept.

  13. Study of van der Waals bonding and interactions in metal organic framework materials.

    Science.gov (United States)

    Zuluaga, Sebastian; Canepa, Pieremanuele; Tan, Kui; Chabal, Yves J; Thonhauser, Timo

    2014-04-02

    Metal organic framework (MOF) materials have attracted a lot of attention due to their numerous applications in fields such as hydrogen storage, carbon capture and gas sequestration. In all these applications, van der Waals forces dominate the interaction between the small guest molecules and the walls of the MOFs. In this review article, we describe how a combined theoretical and experimental approach can successfully be used to study those weak interactions and elucidate the adsorption mechanisms important for various applications. On the theory side, we show that, while standard density functional theory is not capable of correctly describing van der Waals interactions, functionals especially designed to include van der Waals forces exist, yielding results in remarkable agreement with experiment. From the experimental point of view, we show examples in which IR adsorption and Raman spectroscopy are essential to study molecule/MOF interactions. Importantly, we emphasize throughout this review that a combination of theory and experiment is crucial to effectively gain further understanding. In particular, we review such combined studies for the adsorption mechanism of small molecules in MOFs, the chemical stability of MOFs under humid conditions, water cluster formation inside MOFs, and the diffusion of small molecules into MOFs. The understanding of these phenomena is critical for the rational design of new MOFs with desired properties.

  14. Li intercalation in graphite: A van der Waals density-functional study

    Science.gov (United States)

    Hazrati, E.; de Wijs, G. A.; Brocks, G.

    2014-10-01

    Modeling layered intercalation compounds from first principles poses a problem, as many of their properties are determined by a subtle balance between van der Waals interactions and chemical or Madelung terms, and a good description of van der Waals interactions is often lacking. Using van der Waals density functionals we study the structures, phonons and energetics of the archetype layered intercalation compound Li-graphite. Intercalation of Li in graphite leads to stable systems with calculated intercalation energies of -0.2 to -0.3 eV/Li atom, (referred to bulk graphite and Li metal). The fully loaded stage 1 and stage 2 compounds LiC6 and Li1 /2C6 are stable, corresponding to two-dimensional √{3 }×√{3 } lattices of Li atoms intercalated between two graphene planes. Stage N >2 structures are unstable compared to dilute stage 2 compounds with the same concentration. At elevated temperatures dilute stage 2 compounds easily become disordered, but the structure of Li3 /16C6 is relatively stable, corresponding to a √{7 }×√{7 } in-plane packing of Li atoms. First-principles calculations, along with a Bethe-Peierls model of finite temperature effects, allow for a microscopic description of the observed voltage profiles.

  15. The hot pick-up technique for batch assembly of van der Waals heterostructures.

    Science.gov (United States)

    Pizzocchero, Filippo; Gammelgaard, Lene; Jessen, Bjarke S; Caridad, José M; Wang, Lei; Hone, James; Bøggild, Peter; Booth, Timothy J

    2016-06-16

    The assembly of individual two-dimensional materials into van der Waals heterostructures enables the construction of layered three-dimensional materials with desirable electronic and optical properties. A core problem in the fabrication of these structures is the formation of clean interfaces between the individual two-dimensional materials which would affect device performance. We present here a technique for the rapid batch fabrication of van der Waals heterostructures, demonstrated by the controlled production of 22 mono-, bi- and trilayer graphene stacks encapsulated in hexagonal boron nitride with close to 100% yield. For the monolayer devices, we found semiclassical mean-free paths up to 0.9 μm, with the narrowest samples showing clear indications of the transport being affected by boundary scattering. The presented method readily lends itself to fabrication of van der Waals heterostructures in both ambient and controlled atmospheres, while the ability to assemble pre-patterned layers paves the way for complex three-dimensional architectures.

  16. Spooky correlations and unusual van der Waals forces between gapless and near-gapless molecules

    Science.gov (United States)

    Dobson, John F.; Savin, Andreas; Ángyán, János G.; Liu, Ru-Fen

    2016-11-01

    We consider the zero-temperature van der Waals (vdW) interaction between two molecules, each of which has a zero or near-zero electronic gap between a ground state and the first excited state, using a toy model molecule (equilateral H3) as an example. We show that the van der Waals energy between two ground state molecules falls off as D-3 instead of the usual D-6 dependence, when the molecules are separated by distance D. We show that this is caused by a perfect "spooky" correlation between the two fluctuating electric dipoles. The phenomenon is related to, but not the same as, the "resonant" interaction between an electronically excited and a ground state molecule introduced by Eisenschitz and London in 1930. It is also an example of "type C van der Waals non-additivity" recently introduced by one of us [J. F. Dobson, Int. J. Quantum Chem. 114, 1157 (2014)]. Our toy molecule H3 is not stable, but symmetry considerations suggest that a similar vdW phenomenon may be observable, despite Jahn-Teller effects, in molecules with a discrete rotational symmetry and broken inversion symmetry, such as certain metal atom clusters. The motion of the nuclei will need to be included for a definitive analysis of such cases, however.

  17. Adsorption of small aromatic molecules on gold: a DFT localized basis set study including van der Waals effects

    CERN Document Server

    Buimaga-Iarinca, Luiza

    2014-01-01

    We compare the density functional theory (DFT) results on the adsorption of small aromatic molecules (benzene, pyridine and thiophene) on gold surfaces obtained by using three types of van der Waals exchange-correlation functionals and localized basis set calculations. We show that the value of the molecule surface binding energy depends on the interplay between the BSSE effect and the tendency of the exchange-correlation functionals to overestimate both the molecule-surface as well as the gold-gold distances within the relaxed systems. Consequently, we find that by using different types of LCAO basis sets or geometric models for the adsorption of the molecules on the surface, the binding energy can vary up to 100 %. A critical analysis of the physical parameters resulting from the calculations is presented for each exchange-correlation functional.

  18. On van der Waals friction between half-spaces at low temperature.

    Science.gov (United States)

    Barton, Gabriel

    2011-09-07

    We determine, in the van der Waals regime (neglecting retardation and relativistic effects), the frictional power loss P and the drag force F = P/u per unit area between two Drude-modelled half-spaces, with surface plasmon frequency ω(S) and realistically weak dissipation, separated by a gap of width ζ, and constrained to uniform parallel motion with relative speed u. The calculation uses only textbook-level adiabatic and perturbative methods of nonrelativistic quantum mechanics. The initial temperature is taken to be low, with τ ≡ k(B)T/ħω(S) 1. But at fixed nonzero τ, as v rises from zero, P is at first dominated by a temperature-dependent component proportional to u(2)T(2)/ζ(4). The assumptions of the model as regards the half-spaces are satisfied by most quantum-electrodynamics-based approaches, whose results in the nonretarded limit should therefore be the same as ours. We also find that the frequency distribution of the friction-induced energy increments is not thermal, suggesting that in this respect the Huttner-Barnett theory (which we use to describe dissipative materials) needs further refinement.

  19. Evolution of Moiré Profiles from van der Waals Superstructures of Boron Nitride Nanosheets

    Science.gov (United States)

    Liao, Yunlong; Cao, Wei; Connell, John W.; Chen, Zhongfang; Lin, Yi

    2016-05-01

    Two-dimensional (2D) van der Waals (vdW) superstructures, or vdW solids, are formed by the precise restacking of 2D nanosheet lattices, which can lead to unique physical and electronic properties that are not available in the parent nanosheets. Moiré patterns formed by the crystalline mismatch between adjacent nanosheets are the most direct features for vdW superstructures under microscopic imaging. In this article, transmission electron microscopy (TEM) observation of hexagonal Moiré patterns with unusually large micrometer-sized lateral areas (up to ~1 μm2) and periodicities (up to ~50 nm) from restacking of liquid exfoliated hexagonal boron nitride nanosheets (BNNSs) is reported. This observation was attributed to the long range crystallinity and the contaminant-free surfaces of these chemically inert nanosheets. Parallel-line-like Moiré fringes with similarly large periodicities were also observed. The simulations and experiments unambiguously revealed that the hexagonal patterns and the parallel fringes originated from the same rotationally mismatched vdW stacking of BNNSs and can be inter-converted by simply tilting the TEM specimen following designated directions. This finding may pave the way for further structural decoding of other 2D vdW superstructure systems with more complex Moiré images.

  20. Evaluating dispersion forces for optimization of van der Waals complexes using a non-empirical functional.

    Science.gov (United States)

    Arabi, Alya A

    2016-11-13

    Modelling dispersion interactions with traditional density functional theory (DFT) is a challenge that has been extensively addressed in the past decade. The exchange-dipole moment (XDM), among others, is a non-empirical add-on dispersion correction model in DFT. The functional PW86+PBE+XDM for exchange, correlation and dispersion, respectively, compromises an accurate functional for thermochemistry and for van der Waals (vdW) complexes at equilibrium and non-equilibrium geometries. To use this functional in optimizing vdW complexes, rather than computing single point energies, it is necessary to evaluate accurate forces. The purpose of this paper is to validate that, along the potential energy surface, the distance at which the energy is minimum is commensurate with the distance at which the forces vanish to zero. This test was validated for 10 rare gas diatomic molecules using various integration grids and different convergence criteria. It was found that the use of either convergence criterion, 10(-6) or 10(-8), in Gaussian09, does not affect the accuracy of computed optimal distances and binding energies. An ultra-fine grid needs to be used when computing accurate energies using generalized gradient approximation functionals.This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'. © 2016 The Author(s).

  1. Evaluating dispersion forces for optimization of van der Waals complexes using a non-empirical functional

    Science.gov (United States)

    Arabi, Alya A.

    2016-11-01

    Modelling dispersion interactions with traditional density functional theory (DFT) is a challenge that has been extensively addressed in the past decade. The exchange-dipole moment (XDM), among others, is a non-empirical add-on dispersion correction model in DFT. The functional PW86+PBE+XDM for exchange, correlation and dispersion, respectively, compromises an accurate functional for thermochemistry and for van der Waals (vdW) complexes at equilibrium and non-equilibrium geometries. To use this functional in optimizing vdW complexes, rather than computing single point energies, it is necessary to evaluate accurate forces. The purpose of this paper is to validate that, along the potential energy surface, the distance at which the energy is minimum is commensurate with the distance at which the forces vanish to zero. This test was validated for 10 rare gas diatomic molecules using various integration grids and different convergence criteria. It was found that the use of either convergence criterion, 10-6 or 10-8, in Gaussian09, does not affect the accuracy of computed optimal distances and binding energies. An ultra-fine grid needs to be used when computing accurate energies using generalized gradient approximation functionals. This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'.

  2. Thin film solar cells based on layered chalcogenides: Fundamentals and perspectives of van der Waals epitaxy

    Energy Technology Data Exchange (ETDEWEB)

    Jaegermann, W.; Pettenkofer, C.; Lang, O.; Schlaf, R.; Tiefenbacher, S.; Tomm, Y. [Hahn-Meitner-Inst., Berlin (Germany)

    1994-12-31

    The preparation of thin films of layered chalcogenide semiconductors as MX and MX{sub 2} (X = S, Se) based on the concept of van der Waals epitaxy (VDWE) is presented for different substrate/overlayer combinations as GaSe, InSe, SnSe{sub 2}, WS{sub 2} on WSe{sub 2}, GaSe, MoTe{sub 2}, graphite and mica. In all cases stoichiometric films are formed either as epitaxial layers or strongly textured films with the c-axis aligned in spite of strong lattice mismatch. The interfaces are non-reactive and atomically abrupt. The electronic properties of the interfaces are mostly ideal showing band offsets according to the electron affinity rule and no operative interface states. However, doping of the films is still a problem which limits the band bending and the attainable surface photovoltage. The perspectives and preconditions for the further development of layered semiconductor VDWE films for solar cells will be critically discussed.

  3. Self-Consistent Density Functional Including Long-Range van der Waals Interactions

    Science.gov (United States)

    Ferri, Nicola; Distasio, Robert A., Jr.; Car, Roberto; Scheffler, Matthias; Tkatchenko, Alexandre

    2013-03-01

    Van der Waals (vdW) interactions are significant for a wide variety of systems, from noble-gas dimers to organic/inorganic interfaces. The long-range vdW energy is a tiny fraction (0.001%) of the total energy, hence it is typically assumed not to change electronic properties. Although the vdW-DF functional includes the effect of vdW energy on electronic structure, the influence of ``true'' long-range vdW interactions is difficult to assess since a significant part of vdW-DF energy arises from short distances. Here, we present a self-consistent (SC) implementation of the long-range Tkatchenko-Scheffler (TS) functional, including its extension to surfaces. The analysis of self-consistency for rare-gas dimers allows us to reconcile two different views on vdW interactions: (i) Feynman's view that claims changes in the electron density and (ii) atoms separated by infinite barrier. In agreement with previous work, we find negligible contribution from self-consistency in the structure and stability of vdW-bound complexes. However, a closer look at organic/inorganic interfaces reveals notable modification of energy levels when using the SC-TS vdW density functional.

  4. Het werk van een klerk: een stylometrische verkenning van het auteurschap achter 'Der ystorien bloeme'

    NARCIS (Netherlands)

    Hogenbirk, M.; Kestemont, M.

    2013-01-01

    Der ystorien bloeme is a rhymed Middle Dutch adaptation (ca. 1300?) of the Legenda aurea by Jacobus de Voragine. The anonymous author identifies himself as a ‘clerk’. The ystorien only survive in a single - possible incomplete - early fourteenth-century copy in the convoluted manuscript Leiden, Univ

  5. A van der Waals DFT study of PtH{sub 2} systems absorbed on pristine and defective graphene

    Energy Technology Data Exchange (ETDEWEB)

    López-Corral, Ignacio [Instituto de Química del Sur (INQUISUR), UNS-CONICET, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Departamento de Química, Universidad Nacional del Sur, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Piriz, Sebastián; Faccio, Ricardo [Centro NanoMat/DETEMA, Facultad de Química, Universidad de la República, Montevideo (Uruguay); Centro Interdisciplinario de Nanotecnología, Química y Física de Materiales (CINQUIFIMA), Facultad de Química, Universidad de la República, Montevideo (Uruguay); Juan, Alfredo, E-mail: cajuan@uns.edu.ar [Instituto de Física del Sur (IFISUR), UNS-CONICET, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Departamento de Física, Universidad Nacional del Sur, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Avena, Marcelo [Instituto de Química del Sur (INQUISUR), UNS-CONICET, Av. Alem 1253, B8000 Bahía Blanca (Argentina); Departamento de Química, Universidad Nacional del Sur, Av. Alem 1253, B8000 Bahía Blanca (Argentina)

    2016-09-30

    Highlights: • We performed DFT calculations including van der Waals interactions. • Kubas-type Pt-H2 complex is stable on defective graphene. • Carbon vacancy decreases the reactivity of the metal decoration. • The interaction between σ-H and π-C states favors the Kubas-type complex. - Abstract: We used a density functional that incorporates van der Waals interactions to study hydrogen adsorption onto Pt atoms attached to carbon-vacancies on graphene layers, considering molecular and dissociated hydrogen-platinum coordination structures. PtH{sub 2} complexes adsorbed on several sites of pristine graphene were also studied for comparison. Our results indicate that both a Kubas-type dihydrogen complex and a classic hydride without H−H bond are the preferential PtH{sub 2} systems on the vacancy site of graphene. In contrast, the Kubas complex is unstable onto pristine graphene and the hydride is obtained at all adsorption sites. Our simulations suggest that the C-vacancy decreases the reactivity of the metal decoration, allowing a non-dissociative hydrogen adsorption. The H{sub 2} molecule is oriented almost perpendicular to the outermost C−Pt bond, interacting also with the graphene surface through σ-H and π-C states. This stabilization of the Kubas-type complex could play a very important role for hydrogen storage in Pt-decorated carbon adsorbents with vacancies.

  6. Density functional results for isotropic and anisotropic multipole polarizabilities and C6, C7, and C8 Van der Waals dispersion coefficients for molecules

    Science.gov (United States)

    Osinga, V. P.; van Gisbergen, S. J. A.; Snijders, J. G.; Baerends, E. J.

    1997-03-01

    The generalized gradient-approximated (GGA) energy functionals used in density functional theory (DFT) provide accurate results for many different properties. However, one of their weaknesses lies in the fact that Van der Waals forces are not described. In spite of this, it is possible to obtain reliable long-range potential energy surfaces within DFT. In this paper, we use time-dependent density functional response theory to obtain the Van der Waals dispersion coefficients C6, C7, and C8 (both isotropic and anisotropic). They are calculated from the multipole polarizabilities at imaginary frequencies of the two interacting molecules. Alternatively, one might use one of the recently-proposed Van der Waals energy functionals for well-separated systems, which provide fairly good approximations to our isotropic results. Results with the local density approximation (LDA), Becke-Perdew (BP) GGA and the Van Leeuwen-Baerends (LB94) exchange-correlation potentials are presented for the multipole polarizabilities and the dispersion coefficients of several rare gases, diatomics and the water molecule. The LB94 potential clearly performs best, due to its correct Coulombic asymptotic behavior, yielding results which are close to those obtained with many-body perturbation theory (MBPT). The LDA and BP results are systematically too high for the isotropic properties. This becomes progressively worse for the higher dispersion coefficients. The results for the relative anisotropies are quite satisfactory for all three potentials, however.

  7. Interaction of boron with graphite: A van der Waals density functional study

    Science.gov (United States)

    Liu, Juan; Wang, Chen; Liang, Tongxiang; Lai, Wensheng

    2016-08-01

    Boron doping has been widely investigated to improve oxidation resistance of graphite. In this work the interaction of boron with graphite is investigated by a van der Waals density-functional approach (vdW-DF). The traditional density-functional theory (DFT) is well accounted for the binding in boron-substituted graphite. However, to investigate the boron atom on graphite surface and the interstitial impurities require use of a description of graphite interlayer binding. Traditional DFT cannot describe the vdW physics, for instance, GGA calculations show no relevant binding between graphite sheets. LDA shows some binding, but they fail to provide an accurate account of vdW forces. In this paper, we compare the calculation results of graphite lattice constant and cohesive energy by several functionals, it shows that vdW-DF such as two optimized functionals optB88-vdW and optB86b-vdW give much improved results than traditional DFT. The vdW-DF approach is then applied to study the interaction of boron with graphite. Boron adsorption, substitution, and intercalation are discussed in terms of structural parameters and electronic structures. When adsorbing on graphite surface, boron behaves as π electron acceptor. The π electron approaches boron atom because of more electropositive of boron than carbon. For substitution situation, the hole introduced by boron mainly concentrates on boron and the nearest three carbon atoms. The B-doped graphite system with the hole has less ability to offer electrons to oxygen, ultimately resulted in the inhibition of carbon oxidation. For interstitial doping, vdW-DFs show more accurate formation energy than LDA. PBE functional cannot describe the interstitial boron in graphite reasonably because of the ignoring binding of graphite sheets. The investigation of electron structures of boron doped graphite will play an important role in understanding the oxidation mechanism in further study.

  8. van't Hoff-van der Waals osmotic pressure and energy transformers

    OpenAIRE

    Zener, Clarence; Levenson, William

    1983-01-01

    We find the van't Hoff relations between osmotic pressure, freezing point depression, and boiling point elevation provide a clue on how, by using salt solutions, one may lower the cost of extracting power from low-grade heat sources. In particular, the ratio of 7 between the heat of evaporation and the heat of freezing of pure water suggests a chemical system that raises 7-fold the temperature difference between heat source and heat sink, while decreasing by the same factor the heat flux. Hea...

  9. Spontaneous doping on high quality talc-graphene-hBN van der Waals heterostructures

    Science.gov (United States)

    Mania, E.; Alencar, A. B.; Cadore, A. R.; Carvalho, B. R.; Watanabe, K.; Taniguchi, T.; Neves, B. R. A.; Chacham, H.; Campos, L. C.

    2017-09-01

    Steady doping, added to its remarkable electronic properties, would make graphene a valuable commodity in the solar cell market, as energy power conversion could be substantially increased. Here we report a graphene van der Waals heterostructure which is able to spontaneously dope graphene (p-type) up to n ~ 2.2  ×  1013 cm-2 while providing excellent charge mobility (μ ~ 25 000 cm2 V-1 s-1). Such properties are achieved via deposition of graphene on atomically flat layered talc, a natural and abundant dielectric crystal. Raman investigation shows a preferential charge accumulation on graphene-talc van der Waals heterostructures, which are investigated through the electronic properties of talc/graphene/hBN heterostructure devices. These heterostructures preserve graphene’s good electronic quality, verified by the observation of quantum Hall effect at low magnetic fields (B  =  0.4 T) at T  =  4.2 K. In order to investigate the physical mechanisms behind graphene-on-talc p-type doping, we performed first-principles calculations of their interface structural and electronic properties. In addition to potentially improving solar cell efficiency, graphene doping via van der Waals stacking is also a promising route towards controlling the band gap opening in bilayer graphene, promoting a steady n or p type doping in graphene and, eventually, providing a new path to access superconducting states in graphene, predicted to exist only at very high doping.

  10. Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals

    Science.gov (United States)

    Gong, Cheng; Li, Lin; Li, Zhenglu; Ji, Huiwen; Stern, Alex; Xia, Yang; Cao, Ting; Bao, Wei; Wang, Chenzhe; Wang, Yuan; Qiu, Z. Q.; Cava, R. J.; Louie, Steven G.; Xia, Jing; Zhang, Xiang

    2017-06-01

    The realization of long-range ferromagnetic order in two-dimensional van der Waals crystals, combined with their rich electronic and optical properties, could lead to new magnetic, magnetoelectric and magneto-optic applications. In two-dimensional systems, the long-range magnetic order is strongly suppressed by thermal fluctuations, according to the Mermin-Wagner theorem; however, these thermal fluctuations can be counteracted by magnetic anisotropy. Previous efforts, based on defect and composition engineering, or the proximity effect, introduced magnetic responses only locally or extrinsically. Here we report intrinsic long-range ferromagnetic order in pristine Cr2Ge2Te6 atomic layers, as revealed by scanning magneto-optic Kerr microscopy. In this magnetically soft, two-dimensional van der Waals ferromagnet, we achieve unprecedented control of the transition temperature (between ferromagnetic and paramagnetic states) using very small fields (smaller than 0.3 tesla). This result is in contrast to the insensitivity of the transition temperature to magnetic fields in the three-dimensional regime. We found that the small applied field leads to an effective anisotropy that is much greater than the near-zero magnetocrystalline anisotropy, opening up a large spin-wave excitation gap. We explain the observed phenomenon using renormalized spin-wave theory and conclude that the unusual field dependence of the transition temperature is a hallmark of soft, two-dimensional ferromagnetic van der Waals crystals. Cr2Ge2Te6 is a nearly ideal two-dimensional Heisenberg ferromagnet and so will be useful for studying fundamental spin behaviours, opening the door to exploring new applications such as ultra-compact spintronics.

  11. Local Probe Spectroscopy of Two-Dimensional van der Waals Heterostructures

    Science.gov (United States)

    Yankowitz, Matthew Abraham

    A large family of materials, collectively known as "van der Waals materials", have attracted enormous research attention over the past decade following the realization that they could be isolated into individual crystalline monolayers, with charge carriers behaving effectively two-dimensionally. More recently, an even larger class of composite materials has been realized, made possible by combining the isolated atomic layers of different materials into "van der Waals heterostructures", which can exhibit electronic and optical behaviors not observed in the parent materials alone. This thesis describes efforts to characterize the atomic-scale structural and electronic properties of these van der Waals materials and heterostructures through scanning tunneling microscopy measurements. The majority of this work addresses the properties of monolayer and few-layer graphene, whose charge carriers are described by massless and massive chiral Dirac Hamiltonians, respectively. In heterostructures with hexagonal boron nitride, an insulating isomorph of graphene, we observe electronic interference patterns between the two materials which depend on their relative rotation. As a result, replica Dirac cones are formed in the valence and conduction bands of graphene, with their energy tuned by the rotation. Further, we are able to dynamically drag the graphene lattice in these heterostructures, owing to an interaction between the scanning probe tip and the domain walls formed by the electronic interference pattern. Similar dragging is observed in domain walls of trilayer graphene, whose electronic properties are found to depend on the stacking configuration of the three layers. Scanning tunneling spectroscopy provides a direct method for visualizing the scattering pathways of electrons in these materials. By analyzing the scattering, we can directly infer properties of the band structures and local environments of these heterostructures. In bilayer graphene, we map the electrically

  12. Henry constants in polymer solutions with the van der Waals equation of state

    DEFF Research Database (Denmark)

    Bithas, Sotiris; Kalospiros, Nikolaos; Kontogeorgis, Georgios

    1996-01-01

    The simple der Waals equation of state, as extended to polymer systems, is applied to the correlation and prediction of Henry constants in polymer solutions comprising five polymers and many nonpolar and polar solvents, including supercritical gases. The correlation achieved with one adjustable...... parameter is satisfactory, with typical errors within the experimental uncertainty and comparable to those with the more complex Perturbed Hard Chain Theory-based equations of state with the same number of adjustable parameters. A predictive scheme for calculating Henry constants is also presented, which...... is a corresponding-states correlation for a dimensionless Henry constant defined based on the van der Waals equation of state. Satisfactory results-often close to the ones from the one-parameter correlation-are obtained for all systems investigated in this work. Compared with literature models that have been applied...

  13. Dynamical screening of van der Waals interactions in nanostructured solids: Sublimation of fullerenes

    Energy Technology Data Exchange (ETDEWEB)

    Tao, Jianmin; Yang, Jing; Rappe, Andrew M. [Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323 (United States)

    2015-04-28

    Sublimation energy is one of the most important properties of molecular crystals, but it is difficult to study, because the attractive long-range van der Waals (vdW) interaction plays an important role. Here, we apply efficient semilocal density functional theory (DFT), corrected with the dynamically screened vdW interaction (DFT + vdW), the Rutgers-Chalmers nonlocal vdW-DF, and the pairwise-based dispersion-corrected DFT-D2 developed by Grimme and co-workers, to study the sublimation of fullerenes. We find that the short-range part, which accounts for the interaction due to the orbital overlap between fullerenes, is negligibly small. Our calculation shows that there exists a strong screening effect on the vdW interaction arising from the valence electrons of fullerenes. On the other hand, higher-order contributions can be as important as the leading-order term. The reasons are that (i) the surface of fullerene molecules is metallic and thus highly polarizable, (ii) the band gap of fullerene solids is small (less than 2 eV), and (iii) fullerene molecules in the solid phase are so densely packed, yielding the high valence electron density and small equilibrium intermolecular distances (the first nearest neighbor distance is only about 10 Å for C{sub 60}). However, these two effects make opposite contributions, leading to significant error cancellation between these two contributions. We demonstrate that, by considering higher-order contributions and the dynamical screening, the DFT + vdW method can yield sublimation energies of fullerenes in good agreement with reference values, followed by vdW-DF and DFT-D2. The insights from this study are important for a better understanding of the long-range nature of vdW interactions in nanostructured solids.

  14. Dynamical screening of van der Waals interactions in nanostructured solids: Sublimation of fullerenes.

    Science.gov (United States)

    Tao, Jianmin; Yang, Jing; Rappe, Andrew M

    2015-04-28

    Sublimation energy is one of the most important properties of molecular crystals, but it is difficult to study, because the attractive long-range van der Waals (vdW) interaction plays an important role. Here, we apply efficient semilocal density functional theory (DFT), corrected with the dynamically screened vdW interaction (DFT + vdW), the Rutgers-Chalmers nonlocal vdW-DF, and the pairwise-based dispersion-corrected DFT-D2 developed by Grimme and co-workers, to study the sublimation of fullerenes. We find that the short-range part, which accounts for the interaction due to the orbital overlap between fullerenes, is negligibly small. Our calculation shows that there exists a strong screening effect on the vdW interaction arising from the valence electrons of fullerenes. On the other hand, higher-order contributions can be as important as the leading-order term. The reasons are that (i) the surface of fullerene molecules is metallic and thus highly polarizable, (ii) the band gap of fullerene solids is small (less than 2 eV), and (iii) fullerene molecules in the solid phase are so densely packed, yielding the high valence electron density and small equilibrium intermolecular distances (the first nearest neighbor distance is only about 10 Å for C60). However, these two effects make opposite contributions, leading to significant error cancellation between these two contributions. We demonstrate that, by considering higher-order contributions and the dynamical screening, the DFT + vdW method can yield sublimation energies of fullerenes in good agreement with reference values, followed by vdW-DF and DFT-D2. The insights from this study are important for a better understanding of the long-range nature of vdW interactions in nanostructured solids.

  15. Communication: THz absorption spectrum of the CO2-H2O complex: Observation and assignment of intermolecular van der Waals vibrations

    Science.gov (United States)

    Andersen, J.; Heimdal, J.; Mahler, D. W.; Nelander, B.; Larsen, R. Wugt

    2014-03-01

    Terahertz absorption spectra have been recorded for the weakly bound CO2-H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems' flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point energy of 273 ± 15 cm-1 from the class of intermolecular van der Waals vibrations is proposed and the combination with high-level quantum chemical calculations provides a value of 726 ± 15 cm-1 for the dissociation energy D0.

  16. Communication: THz absorption spectrum of the CO{sub 2}–H{sub 2}O complex: Observation and assignment of intermolecular van der Waals vibrations

    Energy Technology Data Exchange (ETDEWEB)

    Andersen, J.; Mahler, D. W.; Larsen, R. Wugt, E-mail: rewl@kemi.dtu.dk [Department of Chemistry, Technical University of Denmark, Kemitorvet 206, 2800 Kgs. Lyngby (Denmark); Heimdal, J.; Nelander, B. [MAX-IV Laboratory, Lund University, P. O. Box 118, 22100 Lund (Sweden)

    2014-03-07

    Terahertz absorption spectra have been recorded for the weakly bound CO{sub 2}–H{sub 2}O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H{sub 2}O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems’ flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point energy of 273 ± 15 cm{sup −1} from the class of intermolecular van der Waals vibrations is proposed and the combination with high-level quantum chemical calculations provides a value of 726 ± 15 cm{sup −1} for the dissociation energy D{sub 0}.

  17. Van der Waals-coupled electronic states in incommensurate double-walled carbon nanotubes

    Science.gov (United States)

    Liu, Kaihui; Jin, Chenhao; Hong, Xiaoping; Kim, Jihoon; Zettl, Alex; Wang, Enge; Wang, Feng

    2014-10-01

    Non-commensurate two-dimensional materials such as a twisted graphene bilayer or graphene on boron nitride, consisting of components that have no finite common unit cell, exhibit emerging moiré physics such as novel Van Hove singularities, Fermi velocity renormalization, mini Dirac points and Hofstadter butterflies. Here we use double-walled carbon nanotubes as a model system for probing moiré physics in incommensurate one-dimensional systems, by combining structural and optical characterizations. We show that electron wavefunctions between incommensurate inner- and outer-wall nanotubes can hybridize strongly, contrary to the conventional wisdom of negligible electron hybridization due to destructive interference. The chirality-dependent inter-tube electronic coupling is described by one-dimensional zone folding of the electronic structure of twisted-and-stretched graphene bilayers. Our results demonstrate that incommensurate van der Waals interactions can be important for engineering the electronic structure and optical properties of one-dimensional materials.

  18. Atomically thin resonant tunnel diodes built from synthetic van der Waals heterostructures

    Science.gov (United States)

    Lin, Yu-Chuan; Ghosh, Ram Krishna; Addou, Rafik; Lu, Ning; Eichfeld, Sarah M.; Zhu, Hui; Li, Ming-Yang; Peng, Xin; Kim, Moon J.; Li, Lain-Jong; Wallace, Robert M.; Datta, Suman; Robinson, Joshua A.

    2015-06-01

    Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalcogenides: molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). The realization of MoS2-WSe2-graphene and WSe2-MoS2-graphene heterostructures leads to resonant tunnelling in an atomically thin stack with spectrally narrow, room temperature negative differential resistance characteristics.

  19. Bond paths and van der Waals interactions in orpiment, As2S3.

    Science.gov (United States)

    Gibbs, G V; Wallace, A F; Zallen, R; Downs, R T; Ross, N L; Cox, D F; Rosso, K M

    2010-06-17

    The calculated electron density distribution for orpiment, As(2)S(3), reveals that As-S, S-S, and As-As bond paths are associated with the experimental interlayer directed bonded interactions detected in a combined infrared and Raman study. The successful modeling of the infrared- and Raman-determined interlayer bonded interactions together with bond paths and the structuralization of a variety of inorganic molecules in terms of "key-lock" bond path mainstays support the argument that van der Waals forces in inorganic molecular crystals are directional.

  20. Lag Synchronization in Coupled Multistable van der Pol-Duffing Oscillators

    Directory of Open Access Journals (Sweden)

    Dawid Dudkowski

    2014-01-01

    Full Text Available We consider the system of externally excited identical van der Pol-Duffing oscillators unidirectionally coupled in a ring. When the coupling is introduced, each of the oscillator’s trajectories is on different attractor. We study the changes in the dynamics due to the increase in the coupling coefficient. Studying the phase of the oscillators, we calculate the parameter value for which we obtain the antiphase lag synchronization of the system and also the bifurcation values for which we observe qualitative changes in the dynamics of already synchronized system. We give evidence that lag synchronization is typical for coupled multistable systems.

  1. Period-doubling cascades of canards from the extended Bonhoeffer-van der Pol oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Sekikawa, Munehisa, E-mail: sekikawa@dove.kuee.kyoto-u.ac.j [Department of Electrical Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto, 615-8510 (Japan); Inaba, Naohiko [Department of Electronics and Bioinformatics, Meiji University, 1-1-1 Higashi-Mita, Tama-ku, Kawasaki, 214-8571 (Japan); Yoshinaga, Tetsuya [Institute of Health Biosciences, The University of Tokushima, 3-18-15 Kuramoto-cho, Tokushima, 770-8509 (Japan); Hikihara, Takashi [Department of Electrical Engineering, Graduate School of Engineering, Kyoto University, Katsura, Nishikyo, Kyoto, 615-8510 (Japan)

    2010-08-09

    This Letter investigates the period-doubling cascades of canards, generated in the extended Bonhoeffer-van der Pol oscillator. Canards appear by Andronov-Hopf bifurcations (AHBs) and it is confirmed that these AHBs are always supercritical in our system. The cascades of period-doubling bifurcation are followed by mixed-mode oscillations. The detailed two-parameter bifurcation diagrams are derived, and it is clarified that the period-doubling bifurcations arise from a narrow parameter value range at which the original canard in the non-extended equation is observed.

  2. Electro-photo modulation of the fermi level in WSe2/graphene van der Waals heterojunction

    Science.gov (United States)

    Sun, Honghui; Yang, Hang; Fang, Liang; Zhang, Jiangwei; Wang, Zhiyuan; Jiang, Tian

    2017-04-01

    We report an electro-photo double modulation of the fermi level in a WSe2/graphene heterojunction. The heterojunction exhibits high ION/IOFF ratio ( 103) in transfer characteristic in dark and distinct rectification behavior in output characteristic under light illumination, respectively. Time-dependent photoresponse reveals that the heterojunction has a considerable potential in the application of photodetection. Interestingly, an exotic current peak is observed in transfer characteristic under light illumination. This novel behavior is attributed to the tunable fermi level at the WSe2/graphene heterojunction by electro-photo double modulation. The results may be helpful to develop tunable photovoltaic optoelectronics based on van der Waals heterojunctions.

  3. From Canards of Folded Singularities to Torus Canards in a Forced van der Pol Equation

    DEFF Research Database (Denmark)

    Burke, John; Desroches, Mathieu; Granados, Albert;

    2016-01-01

    to the intermediate- and high-frequency forcing regimes and show that the forced van der Pol possesses torus canards instead. These torus canards consist of long segments near families of attracting and repelling limit cycles of the fast system, in alternation. We also derive explicit formulas for the parameter......-frequency periodically driven slow/fast systems with two fast variables and one slow variable which possess a non-degenerate fold of limit cycles. The analytic techniques used herein rely on geometric desingularisation, invariant manifold theory, Melnikov theory, and normal form methods. The numerical methods used...

  4. Protein Adsorption into Mesopores: A Combination of Electrostatic Interaction, Counterion Release and van der Waals Forces

    CERN Document Server

    Moerz, Sebastian T

    2015-01-01

    Bovine heart cytochrome c has been immobilized into the mesoporous silica host material SBA-15 in both its native folded and urea-unfolded state. The comparison of the two folding states' behavior casts doubt on the commonly used explanation of cytochrome c adsorption, i.e. the electrostatic interaction model. A detailed investigation of the protein binding as a function of pH and ionic strength of the buffer solution reveals the complex nature of the protein-silica interaction. Electrostatic interaction, van der Waals forces and entropic contributions by counterion release each contribute to adsorption on the silica pore walls.

  5. Droplet evaporation in one-component fluids: Dynamic van der Waals theory

    OpenAIRE

    Teshigawara, Ryohei; Onuki, Akira

    2008-01-01

    In a one-component fluid, we investigate evaporation of a small axysymmetric liquid droplet in the partial wetting condition on a heated wall at $T\\sim 0.9 T_c$. In the dynamic van der Waals theory (Phys. Rev. E {\\bf 75}, 036304 (2007)), we take into account the latent heat transport from liquid to gas upon evaporation. Along the gas-liquid interface, the temperature is nearly equal to the equilibrium coexisting temperature away from the substrate, but it rises sharply to the wall temperature...

  6. Field effect in graphene-based van der Waals heterostructures: Stacking sequence matters.

    Science.gov (United States)

    Stradi, Daniele; Papior, Nick; Hansen, Ole; Brandbyge, Mads

    2017-03-06

    Stacked van der Waals (vdW) heterostructures where semi-conducting two-dimensional (2D) materials are contacted by overlayed graphene electrodes enable atomically-thin, flexible electronics. We use first-principles quantum transport simulations of graphene- contacted MoS2 devices to show how the transistor effect critically depends on the stacking configuration relative to the gate electrode. We can trace this behavior to the stacking-dependent response of the contact region to the capacitive electric field induced by the gate. The contact resistance is a central parameter and our observation establishes an important design rule for ultra-thin devices based on 2D atomic crystals.

  7. Van der Waals coefficients for alkali metal clusters and their size dependence

    Indian Academy of Sciences (India)

    Arup Banerjee; Manoj K Harbola

    2006-02-01

    In this paper we employ the hydrodynamic formulation of time-dependent density functional theory to obtain the van der Waals coefficients 6 and 8 of alkali metal clusters of various sizes including very large clusters. Such calculations become computationally very demanding in the orbital-based Kohn-Sham formalism, but are quite simple in the hydrodynamic approach. We show that for interactions between the clusters of the same sizes, 6 and 8 scale as the sixth and the eighth power of the cluster radius, respectively, and approach their classically predicted values for the large size clusters.

  8. Variations of the Lifshitz-van der Waals force between metals immersed in liquids

    CERN Document Server

    Esquivel-Sirvent, R

    2010-01-01

    We present a theoretical calculation of the Lifshitz-van der Waals force between two metallic slabs embedded in a fluid, taking into account the change of the Drude parameters of the metals when in contact with liquids of different index of refraction. For the three liquids considered in this work, water, $CCl_3F$ and $ CBr_3F$ the change in the Drude parameters of the metal imply a difference of up to 15% in the determination of the force at short separations. These variations in the force is bigger for liquids with a higher index of refraction.

  9. Stability of Multidimensional Phase Transitions in a Steady van der Waals Flow

    Institute of Scientific and Technical Information of China (English)

    Shuyi ZHANG

    2008-01-01

    In this paper,the author studies the multidimensional stability of subsonic phase transitions in a steady supersonic flow of van der Waals type.The viscosity capillarity criterion (in "Arch.Rat.Mech.Anal.,81(4),1983,301-315") is used to seek physical admissible planar waves.By showing the Lopatinski determinant being non-zero,it is proved that subsonic phase transitions are uniformly stable in the sense of Majda (in "Mem.Amer.Math.Soc.,41(275),1983,1-95") under both one dimensional and multidimensional perturbations.

  10. Hopf Bifurcations of a Stochastic Fractional-Order Van der Pol System

    Directory of Open Access Journals (Sweden)

    Xiaojun Liu

    2014-01-01

    Full Text Available The Hopf bifurcation of a fractional-order Van der Pol (VDP for short system with a random parameter is investigated. Firstly, the Chebyshev polynomial approximation is applied to study the stochastic fractional-order system. Based on the method, the stochastic system is reduced to the equivalent deterministic one, and then the responses of the stochastic system can be obtained by numerical methods. Then, according to the existence conditions of Hopf bifurcation, the critical parameter value of the bifurcation is obtained by theoretical analysis. Then, numerical simulations are carried out to verify the theoretical results.

  11. Controlled Synthesis of Organic/Inorganic van der Waals Solid for Tunable Light-Matter Interactions.

    Science.gov (United States)

    Niu, Lin; Liu, Xinfeng; Cong, Chunxiao; Wu, Chunyang; Wu, Di; Chang, Tay Rong; Wang, Hong; Zeng, Qingsheng; Zhou, Jiadong; Wang, Xingli; Fu, Wei; Yu, Peng; Fu, Qundong; Najmaei, Sina; Zhang, Zhuhua; Yakobson, Boris I; Tay, Beng Kang; Zhou, Wu; Jeng, Horng Tay; Lin, Hsin; Sum, Tze Chien; Jin, Chuanhong; He, Haiyong; Yu, Ting; Liu, Zheng

    2015-12-16

    High-quality organic and inorganic van der Waals (vdW) solids are realized using methylammonium lead halide (CH3 NH3 PbI3 ) as the organic part (organic perovskite) and 2D inorganic monolayers as counterparts. By stacking on various 2D monolayers, the vdW solids exhibit dramatically different light emissions. Futhermore, organic/h-BN vdW solid arrays are patterned for red-light emission. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  12. Atomically thin resonant tunnel diodes built from synthetic van der Waals heterostructures

    KAUST Repository

    Lin, Yu-Chuan

    2015-06-19

    Vertical integration of two-dimensional van der Waals materials is predicted to lead to novel electronic and optical properties not found in the constituent layers. Here, we present the direct synthesis of two unique, atomically thin, multi-junction heterostructures by combining graphene with the monolayer transition-metal dichalcogenides: molybdenum disulfide (MoS2), molybdenum diselenide (MoSe2) and tungsten diselenide (WSe2). The realization of MoS2–WSe2–graphene and WSe2–MoS2–graphene heterostructures leads to resonant tunnelling in an atomically thin stack with spectrally narrow, room temperature negative differential resistance characteristics.

  13. Room temperature electroluminescence from mechanically formed van der Waals III–VI homojunctions and heterojunctions

    OpenAIRE

    Balakrishnan, Nilanthy; Kudrynskyi, Zakhar R.; Fay, Mike W.; Mudd, Garry W.; Svatek, Simon A; Makarovsky, Oleg; Kovalyuk, Zakhar D.; Eaves, Laurence; Peter H. Beton; Patanè, Amalia

    2014-01-01

    Room temperature electroluminescence from semiconductor junctions is demonstrated. The junctions are fabricated by the exfoliation and direct mechanical adhesion of InSe and GaSe van der Waals layered crystals. Homojunction diodes formed from layers of p- and n-type InSe exhibit electroluminescence at energies close to the bandgap energy of InSe (Eg= 1.26 eV). In contrast, heterojunction diodes formed by combining layers of p-type GaSe and n-type InSe emit photons at lower energies, which is ...

  14. Interlayer coupling effects on Schottky barrier in the arsenene-graphene van der Waals heterostructures

    Energy Technology Data Exchange (ETDEWEB)

    Xia, Congxin, E-mail: xiacongxin@htu.edu.cn; Xue, Bin; Wang, Tianxing; Peng, Yuting [Department of Physic, Henan Normal University, Xinxiang 453007 (China); Jia, Yu [School of Physics and Engineering, Zhengzhou University, Zhengzhou 450052 (China)

    2015-11-09

    The electronic characteristics of arsenene-graphene van der Waals (vdW) heterostructures are studied by using first-principles methods. The results show that a linear Dirac-like dispersion relation around the Fermi level can be quite well preserved in the vdW heterostructures. Moreover, the p-type Schottky barrier (0.18 eV) to n-type Schottky barrier (0.31 eV) transition occurs when the interlayer distance increases from 2.8 to 4.5 Å, which indicates that the Schottky barrier can be tuned effectively by the interlayer distance in the vdW heterostructures.

  15. Microwave probes Dipole Blockade and van der Waals Forces in a Cold Rydberg Gas

    CERN Document Server

    Teixeira, R Celistrino; Nguyen, Thanh Long; Cantat-Moltrecht, T; Raimond, Jean-Michel; Haroche, S; Gleyzes, S; Brune, M

    2015-01-01

    We show that microwave spectroscopy of a dense Rydberg gas trapped on a superconducting atom chip in the dipole blockade regime reveals directly the dipole-dipole many-body interaction energy spectrum. We use this method to investigate the expansion of the Rydberg cloud under the effect of repulsive van der Waals forces and the breakdown of the frozen gas approximation. This study opens a promising route for quantum simulation of many-body systems and quantum information transport in chains of strongly interacting Rydberg atoms.

  16. Silicene on MoS2: role of the van der Waals interaction

    KAUST Repository

    Jiajie Zhu,

    2015-10-13

    We demonstrate for silicene on MoS2 substrate the limitations of the predictive power of first principles calculations based on van der Waals density functional theory. Only the optB86b-vdW functional is found to give reasonable agreement with experimental results on structural properties, while for all other investigated functionals the interlayer interaction is underestimated or the charge redistribution at the interface is not described correctly so that the predicted electronic structure is qualitatively wrong. © 2015 IOP Publishing Ltd.

  17. Feedback control and adaptive synchronization of chaotic forced Bonhoeffer-van der Pol oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Kontchou, E W Chimi; Fotsin, H B [Laboratoire d' Electronique, Departement de Physique, Faculte des Sciences, Universite de Dschang, B P 67 Dschang (Cameroon); Woafo, P [Laboratory of Modelling and Simulation in Engineering and Biological Physics, Faculty of Science, University of Yaounde I, Box 812, Yaounde (Cameroon)], E-mail: hbfotsin@yahoo.fr

    2008-04-15

    This paper deals with chaos control and synchronization in forced Bonhoeffer-van der Pol (FBVP) oscillators. The state equations of the model are first established and the stability is analysed. A feedback control strategy for stabilizing the chaotic dynamics on a periodic orbit of the phase space is investigated. Adaptive synchronization of two FBVP oscillators, based on parameter estimation and a nonlinear observer approach, is also investigated. It appears that a particular unknown parameter of the model can be estimated, which gives the possibility of recovering information through chaotic masking. An application in secure communications is presented.

  18. Sindrome de Van der Knaap megalencefalia com leucodistrofia: a respeito de dois casos na mesma família Van Der Knaap syndrome (megalencephaly with leukodystrophy: report of two cases in the same family

    Directory of Open Access Journals (Sweden)

    CARLOS EDUARDO CAVALCANTI

    2000-03-01

    Full Text Available Relatamos os casos de dois irmãos, com quatro e seis anos de idade, com achados característicos da síndrome de Van Der Knaap. Discutimos os seus aspectos clínicos e radiológicos, assim como suas peculiaridades. Comparamos aos dados da literatura e analisamos os possíveis mecanismos etiopatogênicos envolvidos.We report on two brothers, aged four and six years-old, evidencing the Van Der Knaap syndrome. Clinical and radiological aspects are discussed as well their peculiarities. Data are compared with related literature, as etiopathogenic mechanisms possibly involved.

  19. Simple model for analyzing Efimov energy and three-body recombination of three identical bosons with van der Waals interactions

    Science.gov (United States)

    Li, Jing-Lun; Hu, Xue-Jin; Han, Yong-Chang; Cong, Shu-Lin

    2016-09-01

    We construct a simple model to calculate the trimer bound state energy ET(n ) and three-body recombination rate K30 of three identical bosons with van der Waals interaction without using any two- or three-body fitting parameter. Using this simple model, we investigate the influence of the van der Waals finite-range effect on ET(n ) and K30. Our calculation shows that the finite-range effect leads to the ground trimer state energy ET(0 ) not crossing the atom-dimer threshold, and the scaled three-body recombination rate K30/a4 deviating from the universal three-body theory. The results of our simple model agree within a few percent with other theoretical works with van der Waals interaction and also the experimental data.

  20. Hyperchaos control and adaptive synchronization with uncertain parameter for fractional-order Mathieu–van der Pol systems

    Indian Academy of Sciences (India)

    Kumar Vishal; Saurabh K Agrawal; Subir Das

    2016-01-01

    In this paper, we have discussed the local stability of the Mathieu–van der Pol hyperchaotic system with the fractional-order derivative. The fractional Routh–Hurwitz stability conditions were provided and were used to discuss the stability. Feedback control method was used to control chaos in the Mathieu–van der Pol system with fractional-order derivative and after controlling the chaotic behaviour of the system the synchronization between the fractional-order hyperchaotic Mathieu–van der Pol system and controlled system was introduced. In this study, modified adaptive control methods with uncertain parameters at various equilibrium points were used. Also the analysis of control time with respect to different fractional-order derivatives is the key feature of this paper. Numerical simulation results achieved using Adams–Boshforth–Moulton method show that the method is effective and reliable.

  1. Self-Assembly of Nanoclusters into Mono-, Few-, and Multilayered Sheets via Dipole-Induced Asymmetric van der Waals Attraction.

    Science.gov (United States)

    Wu, Zhennan; Liu, Jiale; Li, Yanchun; Cheng, Ziyi; Li, Tingting; Zhang, Hao; Lu, Zhongyuan; Yang, Bai

    2015-06-23

    Two-dimensional (2D) nanomaterials possessing regular layered structures and versatile chemical composition are highly expected in many applications. Despite the importance of van der Waals (vdW) attraction in constructing and maintaining layered structures, the origin of 2D anisotropy is not fully understood, yet. Here, we report the 2D self-assembly of ligand-capped Au15 nanoclusters into mono-, few-, and multilayered sheets in colloidal solution. Both the experimental results and computer simulation reveal that the 2D self-assembly is initiated by 1D dipolar attraction common in nanometer-sized objects. The dense 1D attachment of Au15 leads to a redistribution of the surface ligands, thus generating asymmetric vdW attraction. The deliberate control of the coordination of dipolar and vdW attraction further allows to manipulate the thickness and morphologies of 2D self-assembly architectures.

  2. Novel Approach for a van der Pol Oscillator in the Continuous Time Domain

    Institute of Scientific and Technical Information of China (English)

    Junaid Ali Khan; Muhammad Asif Zahoor Raja; IJaz MansoorQureshi

    2011-01-01

    We investigate the continuous time domain numerical treatment of a van der Pol oscillator, applying the trial solution as an artiScial feed-forward neural network model containing unknown adjustable parameters. The optimization of the network is performed by simulated annealing in an unsupervised method. The proposed scheme is tested successfully by its application in both non-stiff and stiff conditions. Its reliability and effectiveness is validated through comprehensive statistical analyses. The obtained results are in good agreement with the classical RK45 method.%We investigate the continuous time domain numerical treatment of a van der Pol oscillator,applying the trial solution as an artificial feed-forward neural network model containing unknown adjustable parameters.The optimization of the network is performed by simulated annealing in an unsupervised method.The proposed scheme is tested successfully by its application in both non-stiff and stiff conditions.Its reliability and effectiveness is validated through comprehensive statistical analyses.The obtained results are in good agreement with the classical RK45 method.

  3. An equal area law for the van der Waals transition of holographic entanglement entropy

    CERN Document Server

    Nguyen, Phuc H

    2015-01-01

    The Anti-de Sitter-Reissner-Nordstrom (AdS-RN) black hole in the canonical ensemble undergoes a phase transition similar to the liquid-gas phase transition. i.e. the isocharges on the entropy-temperature plane develop an unstable branch when the charge is smaller than a critical value. It was later discovered that the isocharges on the entanglement entropy-temperature plane also exhibit the same van der Waals-like structure. In this paper, we present numerical results which sharpen this similarity between entanglement entropy and black hole entropy, by showing that both of these entropies obey Maxwell's equal area law. Moreover, we checked this for two disk-shaped entangling regions of different sizes, and the conclusion seems to be valid regardless of the region's size. We checked the equal area law for AdS-RN in 4 and 5 dimensions, so that the conclusion seems to hold for any dimension. Finally, we also checked that the equal area law holds for a similar, van der Waals-like transition of the dyonic black ho...

  4. Droplet spreading driven by van der Waals force: a molecular dynamics study

    Energy Technology Data Exchange (ETDEWEB)

    Wu Congmin [Department of Mathematics, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong); Qian Tiezheng [Department of Mathematics and Joint KAUST-HKUST Micro/Nanofluidics Laboratory, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong); Sheng Ping, E-mail: maqian@ust.h [Department of Physics and William Mong Institute of Nano Science and Technology, Hong Kong University of Science and Technology, Clear Water Bay, Kowloon (Hong Kong)

    2010-08-18

    The dynamics of droplet spreading is investigated by molecular dynamics simulations for two immiscible fluids of equal density and viscosity. All the molecular interactions are modeled by truncated Lennard-Jones potentials and a long-range van der Waals force is introduced to act on the wetting fluid. By gradually increasing the coupling constant in the attractive van der Waals interaction between the wetting fluid and the substrate, we observe a transition in the initial stage of spreading. There exists a critical value of the coupling constant, above which the spreading is pioneered by a precursor film. In particular, the dynamically determined critical value quantitatively agrees with that determined by the energy criterion that the spreading coefficient equals zero. The latter separates partial wetting from complete wetting. In the regime of complete wetting, the radius of the spreading droplet varies with time as R(t){approx}{radical}t, a behavior also found in molecular dynamics simulations where the wetting dynamics is driven by the short-range Lennard-Jones interaction between liquid and solid.

  5. Formation and dynamics of van der Waals molecules in buffer-gas traps.

    Science.gov (United States)

    Brahms, Nathan; Tscherbul, Timur V; Zhang, Peng; Kłos, Jacek; Forrey, Robert C; Au, Yat Shan; Sadeghpour, H R; Dalgarno, A; Doyle, John M; Walker, Thad G

    2011-11-14

    We show that weakly bound He-containing van der Waals molecules can be produced and magnetically trapped in buffer-gas cooling experiments, and provide a general model for the formation and dynamics of these molecules. Our analysis shows that, at typical experimental parameters, thermodynamics favors the formation of van der Waals complexes composed of a helium atom bound to most open-shell atoms and molecules, and that complex formation occurs quickly enough to ensure chemical equilibrium. For molecular pairs composed of a He atom and an S-state atom, the molecular spin is stable during formation, dissociation, and collisions, and thus these molecules can be magnetically trapped. Collisional spin relaxation is too slow to affect trap lifetimes. However, (3)He-containing complexes can change spin due to adiabatic crossings between trapped and untrapped Zeeman states, mediated by the anisotropic hyperfine interaction, causing trap loss. We provide a detailed model for Ag(3)He molecules, using ab initio calculation of Ag-He interaction potentials and spin interactions, quantum scattering theory, and direct Monte Carlo simulations to describe formation and spin relaxation in this system. The calculated rate of spin-change agrees quantitatively with experimental observations, providing indirect evidence for molecular formation in buffer-gas-cooled magnetic traps. Finally, we discuss the possibilities for spectroscopic detection of these complexes, including a calculation of expected spectra for Ag(3)He, and report on our spectroscopic search for Ag(3)He, which produced a null result.

  6. Van der Waals and resonance interactions between accelerated atoms in vacuum and the Unruh effect

    Science.gov (United States)

    Lattuca, M.; Marino, J.; Noto, A.; Passante, R.; Rizzuto, L.; Spagnolo, S.; Zhou, W.

    2017-08-01

    We discuss different physical effects related to the uniform acceleration of atoms in vacuum, in the framework of quantum electrodynamics. We first investigate the van der Waals/Casimir-Polder dispersion and resonance interactions between two uniformly accelerated atoms in vacuum. We show that the atomic acceleration significantly affects the van der Waals force, yielding a different scaling of the interaction with the interatomic distance and an explicit time dependence of the interaction energy. We argue how these results could allow for an indirect detection of the Unruh effect through dispersion interactions between atoms. We then consider the resonance interaction between two accelerated atoms, prepared in a correlated Bell-type state, and interacting with the electromagnetic field in the vacuum state, separating vacuum fluctuations and radiation reaction contributions, both in the free-space and in the presence of a perfectly reflecting plate. We show that nonthermal effects of acceleration manifest in the resonance interaction, yielding a change of the distance dependence of the resonance interaction energy. This suggests that the equivalence between temperature and acceleration does not apply to all radiative properties of accelerated atoms. To further explore this aspect, we evaluate the resonance interaction between two atoms in non inertial motion in the coaccelerated (Rindler) frame and show that in this case the assumption of an Unruh temperature for the field is not required for a complete equivalence of locally inertial and coaccelerated points of views.

  7. Structural and quantum properties of van der Waals cluster near the unitary regime

    Science.gov (United States)

    Lekala, M. L.; Chakrabarti, B.; Haldar, S. K.; Roy, R.; Rampho, G. J.

    2017-07-01

    We study the structural and several quantum properties of three-dimensional bosonic cluster interacting through van der Waals potential at large scattering length. We use Faddeev-type decomposition of the many-body wave function which includes all possible two-body correlations. At large scattering length, we observe spatially extended states which exhibit the exponential dependence on the state number. The cluster ground state energy shows universal nature at large negative scattering length. We also find the existence of generalized Tjon lines for N-body clusters. Signature of universal behaviour of weakly bound clusters can be observed in experiments of ultracold Bose gases. We also study the spectral statistics of the system. We calculate both the short-range fluctuation and long-range correlation and observe semi-Poisson distribution which interpolates the Gaussian Orthogonal Ensemble (GOE) and Poisson statistics of random matrix theory. It indicates that the van der Waal cluster near the unitary becomes highly complex and correlated. However additional study of P (r) distribution (without unfolding of energy spectrum) reveals the possibility of chaos for larger cluster.

  8. Thermal transport in van der Waals solids from first-principles calculations

    Science.gov (United States)

    Lindroth, Daniel O.; Erhart, Paul

    2016-09-01

    The lattice thermal expansion and conductivity in bulk Mo and W-based transition metal dichalcogenides are investigated by means of density functional and Boltzmann transport theory calculations. To this end, a recent van der Waals density functional (vdW-DF-CX) is employed, which is shown to yield excellent agreement with reference data for the structural parameters. The calculated in-plane thermal conductivity compares well with experimental room-temperature values, when phonon-phonon and isotopic scattering are included. To explain the behavior over the entire available temperature range one must, however, include additional (temperature independent) scattering mechanisms that limit the mean free path. Generally, the primary heat carrying modes have mean free paths of 1 μ m or more, which makes these materials very susceptible to structural defects. The conductivity of Mo- and W-based transition metal dichalcogenides is primarily determined by the chalcogenide species and increases in the order Te-Se-S. While for the tellurides and selenides the transition metal element has a negligible effect, the conductivity of WS2 is notably higher than for MoS2, which may be traced to the much larger phonon band gap of the former. Overall, the present study provides a consistent set of thermal conductivities that reveal chemical trends and constitute the basis for future investigations of van der Waals solids.

  9. Droplet spreading driven by van der Waals force: a molecular dynamics study

    KAUST Repository

    Wu, Congmin

    2010-07-07

    The dynamics of droplet spreading is investigated by molecular dynamics simulations for two immiscible fluids of equal density and viscosity. All the molecular interactions are modeled by truncated Lennard-Jones potentials and a long-range van der Waals force is introduced to act on the wetting fluid. By gradually increasing the coupling constant in the attractive van der Waals interaction between the wetting fluid and the substrate, we observe a transition in the initial stage of spreading. There exists a critical value of the coupling constant, above which the spreading is pioneered by a precursor film. In particular, the dynamically determined critical value quantitatively agrees with that determined by the energy criterion that the spreading coefficient equals zero. The latter separates partial wetting from complete wetting. In the regime of complete wetting, the radius of the spreading droplet varies with time as R(t) ∼ √t, a behavior also found in molecular dynamics simulations where the wetting dynamics is driven by the short-range Lennard-Jones interaction between liquid and solid. © 2010 IOP Publishing Ltd.

  10. An introduction to the Dieterici Equation and the van der Waal Equation

    Science.gov (United States)

    Sheldon, John

    2003-11-01

    The derivation of the ideal gas law by using the kinetic theory of gases is usually presented in an undergraduate physics thermodynamics texts and physical chemistry texts. Following these derivations is the introduction of nonideal effects and the empirical equations of state: the van der Waals equation and the Dieterici equation. These are sometimes are simply given without comment as to the origin of the terms in them. An introduction to a "derivation" of these equations, appropriate for the undergraduate thermodynamics course, is given herein. Empirical equations are not rigorously derived, but rather they are invented, the so-called derivation simply serves to make the empirical terms appear reasonable.The barometric equation is exploited to get an expression for the effective attractive molecular forces. The differential form of the barometric is derived using kinetic theory, then from the barometric equation we get the Dieterici Equation an expansion of the Dieterici Equation, yields the van der Waals Equation of state. The relationship between the empirical constants is also discussed

  11. van der Waals interaction energy and disjoining pressure at small separation.

    Science.gov (United States)

    White, Lee R

    2010-03-01

    The divergence of the van der Waals interaction energy E(132)(L) between plane half-spaces 1 and 2 separated by medium 3 as the separation distance L tends to zero is naively thought of as due to the overlap of the atomic polarization centers. It follows that it may therefore be prevented by properly allowing for the finite size of the atomic species which would prevent the overlap. The distance cutoff model is a simple example of such a modification. The present paper demonstrates that this is not ultimately the origin of the divergence and, that although finite atomic dimensions would alleviate the embarrassment, non-overlap does not properly address the thermodynamic restriction that pertains to the interaction energy. By allowing in an albeit approximate way for the wavelength dependence of the material dielectric response functions epsilon(i xi, k) which arise naturally in the modern Lifshitz theory for this interaction, a form for the van der Waals energy and the corresponding disjoining pressure may be derived which obey the thermodynamic constraint and remove the divergence as L-->0. The energy and disjoining pressure in this new model are compared with the classic non-retarded results and the length cutoff model.

  12. Band Alignment and Minigaps in Monolayer MoS2-Graphene van der Waals Heterostructures.

    Science.gov (United States)

    Pierucci, Debora; Henck, Hugo; Avila, Jose; Balan, Adrian; Naylor, Carl H; Patriarche, Gilles; Dappe, Yannick J; Silly, Mathieu G; Sirotti, Fausto; Johnson, A T Charlie; Asensio, Maria C; Ouerghi, Abdelkarim

    2016-07-13

    Two-dimensional layered MoS2 shows great potential for nanoelectronic and optoelectronic devices due to its high photosensitivity, which is the result of its indirect to direct band gap transition when the bulk dimension is reduced to a single monolayer. Here, we present an exhaustive study of the band alignment and relativistic properties of a van der Waals heterostructure formed between single layers of MoS2 and graphene. A sharp, high-quality MoS2-graphene interface was obtained and characterized by micro-Raman spectroscopy, high-resolution X-ray photoemission spectroscopy (HRXPS), and scanning high-resolution transmission electron microscopy (STEM/HRTEM). Moreover, direct band structure determination of the MoS2/graphene van der Waals heterostructure monolayer was carried out using angle-resolved photoemission spectroscopy (ARPES), shedding light on essential features such as doping, Fermi velocity, hybridization, and band-offset of the low energy electronic dynamics found at the interface. We show that, close to the Fermi level, graphene exhibits a robust, almost perfect, gapless, and n-doped Dirac cone and no significant charge transfer doping is detected from MoS2 to graphene. However, modification of the graphene band structure occurs at rather larger binding energies, as the opening of several miniband-gaps is observed. These miniband-gaps resulting from the overlay of MoS2 and the graphene layer lattice impose a superperiodic potential.

  13. Exciton–polaritons in van der Waals heterostructures embedded in tunable microcavities

    Science.gov (United States)

    Dufferwiel, S.; Schwarz, S.; Withers, F.; Trichet, A. A. P.; Li, F.; Sich, M.; Del Pozo-Zamudio, O.; Clark, C.; Nalitov, A.; Solnyshkov, D. D.; Malpuech, G.; Novoselov, K. S.; Smith, J. M.; Skolnick, M. S.; Krizhanovskii, D. N.; Tartakovskii, A. I.

    2015-01-01

    Layered materials can be assembled vertically to fabricate a new class of van der Waals heterostructures a few atomic layers thick, compatible with a wide range of substrates and optoelectronic device geometries, enabling new strategies for control of light–matter coupling. Here, we incorporate molybdenum diselenide/hexagonal boron nitride (MoSe2/hBN) quantum wells in a tunable optical microcavity. Part-light–part-matter polariton eigenstates are observed as a result of the strong coupling between MoSe2 excitons and cavity photons, evidenced from a clear anticrossing between the neutral exciton and the cavity modes with a splitting of 20 meV for a single MoSe2 monolayer, enhanced to 29 meV in MoSe2/hBN/MoSe2 double-quantum wells. The splitting at resonance provides an estimate of the exciton radiative lifetime of 0.4 ps. Our results pave the way for room-temperature polaritonic devices based on multiple-quantum-well van der Waals heterostructures, where polariton condensation and electrical polariton injection through the incorporation of graphene contacts may be realized. PMID:26446783

  14. Direct measurement of the van der Waals interaction between two single atoms

    CERN Document Server

    Béguin, Lucas; Chicireanu, Radu; Lahaye, Thierry; Browaeys, Antoine

    2013-01-01

    We report on the direct measurement of the van der Waals interaction between two isolated, single Rydberg atoms separated by a controlled distance of a few micrometers. By working in a regime where the single-atom Rabi frequency of the laser used for excitation to the Rydberg state is comparable to the interaction energy, we observe a \\emph{partial} Rydberg blockade, whereby the time-dependent populations of the various two-atom states exhibit coherent oscillations with several frequencies. A quantitative comparison of the data with a simple model based on the optical Bloch equations allows us to extract the van der Waals energy, and to observe its characteristic $C_6/R^6$ dependence. The magnitude of the measured $C_6$ coefficient agrees well with an \\emph{ab-initio} theoretical calculation, and we observe its dramatic increase with the principal quantum number $n$ of the Rydberg state. Our results not only allow to test an important physical law, but also demonstrate a degree of experimental control which o...

  15. Van der Waals effect in weak adsorption affecting trends in adsorption, reactivity, and the view of substrate nobility

    DEFF Research Database (Denmark)

    Kelkkanen, Kari André; Lundqvist, Bengt; Nørskov, Jens Kehlet

    2011-01-01

    The ubiquitous van der Waals (vdW) force, particularly discernible in weak adsorption, is studied on noble and transition metals. In calculations with the vdW density functional (DF) [ M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)], the atomic structure near the adsorption site is systematic......The ubiquitous van der Waals (vdW) force, particularly discernible in weak adsorption, is studied on noble and transition metals. In calculations with the vdW density functional (DF) [ M. Dion et al., Phys. Rev. Lett. 92, 246401 (2004)], the atomic structure near the adsorption site...

  16. van der Waals-Tonks-type equations of state for hard-hypersphere fluids in four and five dimensions.

    Science.gov (United States)

    Wang, Xian-Zhi

    2004-04-15

    Recently, we developed accurate van der Waals-Tonks-type equations of state for hard-disk and hard-sphere fluids by using the known virial coefficients. In this paper, we derive the van der Waals-Tonks-type equations of state. We further apply these equations of state to hard-hypersphere fluids in four and five dimensions. In the low-density fluid regime, these equations of state are in good agreement with the simulation results and existing equations of state.

  17. Simon van der Meer and Carlo Rubbia celebrate their awarding of the Nobel Prize in 1984 with a toast at CERN.

    CERN Multimedia

    CERN PhotoLab

    1984-01-01

    CERN's 1984 Nobel prizewinners Carlo Rubbia (left) and Simon van der Meer, who were awarded the prize for their roles in discovering the W+, W- and Z0 particles, the carriers of Nature's weak force. Carlo Rubbia's work allowed CERN's Super Proton Synchrotron (SPS) to collide protons and antiprotons, while Simon van der Meer's technical virtuosity made the project possible.

  18. Application of Solution-blown 20-50 nm Nanofibers in Filtration of Nanoparticles: The Efficient van der Waals Collectors

    Science.gov (United States)

    Sinha-Ray, Sumit; Sinha-Ray, Suman; Yarin, Alexander; Pourdeyhimi, Behnam

    2015-11-01

    Filtration efficiency of commercially available filter media with fiber/pore sizes on the scale of 10 μm can be dramatically increased by adding a layer of ultrafine supersonically-blown 20-50 nm nanofibers. Different commercial filters were modified with (i) electrospun nanofibers alone, (ii) solution-blown 20-50 nm alone, and (iii) the dual coating with electrospun nanofibers deposited first and the solution-blown 20-50 nm nanofibers deposited on top of them. Detailed observations of nanoparticle removal revealed that the above-mentioned modified filters, especially those with the dual nanofiber coating with the 20-50 nm nanofibers deposited on top, are the most effective in removing the below-200 nm Cu nanoparticles/clusters from aqueous suspensions, in particular at the lowest concentrations of 0.2-0.5 ppm. The theory developed in the present work dealing with convective transport of nanoparticles in the fluid flow along with diffusion of nanoparticles and the van der Waals attraction explains and describes how the smallest solution-blown nanofibers introduce a novel physical mechanism of nanoparticle interception (the attractive van der Waals forces) and become significantly more efficient collectors compared to the larger electrospun nanofibers. The theory also elucidates the morphology of the nanoparticle clusters being accumulated at the smallest nanofiber surfaces, including the clusters growing at the windward side, or in some cases also on the leeward side of a nanofiber. This work is supported by the Nonwovens Cooperative Research Center (NCRC), grant No. 12-144SB.

  19. 一类时变分岔问题与Duffing-Van der Pol振子%CLASS OF TIME-DEPENDENT BIFURCATION PROBLEMAND THE DUFFING-VAN DER POL OSCILLATOR

    Institute of Scientific and Technical Information of China (English)

    化存才; 陆启韶

    2001-01-01

    用量级平衡方法分析一类时变分岔问题,得出正反两个方向的分岔转迁滞后且具有对称性. 将Duffing-Van der Pol 振动方程转化为对该时变分岔的反馈控制问题,得出在适当的条件下,Duffing-Van der Pol 振子的相图是一动态滞后环.%A class of time-dependent bifurcation problem has been analyzed by using the methodof scaling balance. It is concluded that the bifurcation transitions in positive and negative directionsare both delayed and have symmetry. The Duffing-Van der Pol oscillation equation has beenchanged into a feedback control problem of the time-dependent bifurcation. Under certainconditions, the phase diagram of the Duffing-Van der Pol oscillator is a dynamical hysteresiscycle.

  20. From Canards of Folded Singularities to Torus Canards in a Forced van der Pol Equation

    Science.gov (United States)

    Burke, John; Desroches, Mathieu; Granados, Albert; Kaper, Tasso J.; Krupa, Martin; Vo, Theodore

    2016-04-01

    In this article, we study canard solutions of the forced van der Pol equation in the relaxation limit for low-, intermediate-, and high-frequency periodic forcing. A central numerical observation made herein is that there are two branches of canards in parameter space which extend across all positive forcing frequencies. In the low-frequency forcing regime, we demonstrate the existence of primary maximal canards induced by folded saddle nodes of type I and establish explicit formulas for the parameter values at which the primary maximal canards and their folds exist. Then, we turn to the intermediate- and high-frequency forcing regimes and show that the forced van der Pol possesses torus canards instead. These torus canards consist of long segments near families of attracting and repelling limit cycles of the fast system, in alternation. We also derive explicit formulas for the parameter values at which the maximal torus canards and their folds exist. Primary maximal canards and maximal torus canards correspond geometrically to the situation in which the persistent manifolds near the family of attracting limit cycles coincide to all orders with the persistent manifolds that lie near the family of repelling limit cycles. The formulas derived for the folds of maximal canards in all three frequency regimes turn out to be representations of a single formula in the appropriate parameter regimes, and this unification confirms the central numerical observation that the folds of the maximal canards created in the low-frequency regime continue directly into the folds of the maximal torus canards that exist in the intermediate- and high-frequency regimes. In addition, we study the secondary canards induced by the folded singularities in the low-frequency regime and find that the fold curves of the secondary canards turn around in the intermediate-frequency regime, instead of continuing into the high-frequency regime. Also, we identify the mechanism responsible for this

  1. Role of Lewis basicity and van der Waals forces in adhesion of silica MFI zeolites (010) with polyimides.

    Science.gov (United States)

    Lee, Jung-Hyun; Thio, Beng Joo Reginald; Bae, Tae-Hyun; Meredith, J Carson

    2009-08-18

    Adhesion between zeolites and polymers is a central factor in achieving defect-free mixed-matrix membranes for energy-efficient gas separations. In this work, atomic force microscopy (AFM) was used to measure adhesion forces between a pure silica MFI (ZSM-5: Zeolite Socony Mobil-Five) (010) zeolite probe and a series of polyimide (Matrimid 5218, 6FDA-DAM, 6FDA-6FpDA, and 6FDA-DAM:DABA (3:2)) and polyetherimide (Ultem 1000) polymers in air. Combined with measurements of surface energy of the polymer surfaces, the dependence of adhesion on polymer structure was determined. Adhesion force was strongly dependent on the Lewis basicity component of polymer surface energy and was less dependent on van der Waals (VDW) components, by a factor of about 6. Hydrogen bonding likely occurs between the acidic (electron acceptor) component of the zeolite surface (silanols or adsorbed water) and the basic (electron donor) component of the polymer surface. Adhesion force was strongly correlated with the mole fraction of carbonyls per monomer. We conclude that differences in adhesion as a function of polymer structure were primarily controlled by the polymer's Lewis basicity, contributed primarily by carbonyl groups.

  2. Sacred History And Sacred Texts In Early Judaism : A Symposium In Honour Of A.s. Van Der Woude

    NARCIS (Netherlands)

    Bremmer, J.N.; García Martínez, F.

    1992-01-01

    After a long and distinguished career Adam S. van der Woude will retire on Reformation Day (October 31) from the Chair of Old Testament Studies and Intertestamental Literature of the Faculty of Theology of the Rijksuniversiteit Groningen. In order not to let this occasion go unnoticed, the Center of

  3. Adaptive synchronization of a modified and uncertain chaotic Van der Pol-Duffing oscillator based on parameter identification

    Energy Technology Data Exchange (ETDEWEB)

    Fotsin, H.B. [Faculte des Sciences, Universite de Dschang, B.P. 067 Dschang (Cameroon)]. E-mail: hbfotsin@yahoo.fr; Woafo, P. [Faculte des Sciences, Universite de Yaounde I, B.P. 812 Yaounde (Cameroon)

    2005-06-01

    This paper considers the problem of adaptive synchronization and parameter identification of an uncertain chaotic oscillator. Using recent results on adaptive control, we design a controller which enables both the synchronization of two unidirectionally coupled modified Van der Pol-Duffing oscillators and the estimation of unknown parameters of the drive oscillator.

  4. J.A. van der Kloes (1845-1935): A professional biography of the first Dutch professor in building materials

    NARCIS (Netherlands)

    Quist, W.J.

    2015-01-01

    Prof. Jacobus Alida van der Kloes (1845-1935) was appointed teacher in building materials at the “Polytechnische school” of Delft in 1882. From 1905 until his retirement in 1915 he was promoted to full professor on the subject of knowledge and research of building materials at the “Technische

  5. Wolff algorithm and anisotropic continuous-spin models: An application to the spin-van der Waals model

    Science.gov (United States)

    D'onorio de Meo, Marco; Oh, Suhk Kun

    1992-07-01

    The problem of applying Wolff's cluster algorithm to anisotropic classical spin models is resolved by modifying a part of the Wolff algorithm. To test the effectiveness of our modified algorithm, the spin-van der Waals model is investigated in detail. Our estimate of the dynamical exponent of the model is z=0.19+/-0.04.

  6. Bundle and chirality influences on properties of carbon nanotubes studied with van der Waals density functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Dumlich, Heiko; Gegg, Michael; Reich, Stephanie [Fachbereich Physik, Freie Universitaet Berlin, Arnimallee 14, 14195 Berlin (Germany); Hennrich, Frank [Institut fuer Nanotechnologie, Karlsruhe Institute of Technology, 76021 Karlsruhe (Germany)

    2011-11-15

    We study the binding strength and intertube distance of carbon nanotube bundles in dependence of their structure (chirality) with van der Waals density functional theory. We try to understand the bundling and debundling process of nanotube bundles and test whether an influence of chirality exists. The distance between the nanotubes in the bundles vary only in a small range within 3.3 and 3.4A, without any chiral angle and diameter dependence. We find an increase of van der Waals energy per length with increasing diameter of the nanotubes (E{sub vdW}{sup length}{proportional_to} d or{radical}(d)) for tubes with diameters between 5.6 and 27.3A, but no obvious correlation between the chirality of the tubes and the van der Waals energy per length. The van der Waals energy per atom is decreasing with increasing tube diameter (E{sub vdW}{sup atom}{proportional_to} 1/d or1/{radical}(d)). (Copyright copyright 2011 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  7. J.A. van der Kloes (1845-1935): A professional biography of the first Dutch professor in building materials

    NARCIS (Netherlands)

    Quist, W.J.

    2015-01-01

    Prof. Jacobus Alida van der Kloes (1845-1935) was appointed teacher in building materials at the “Polytechnische school” of Delft in 1882. From 1905 until his retirement in 1915 he was promoted to full professor on the subject of knowledge and research of building materials at the “Technische Hooges

  8. High Energy Proton-Proton Elastic Scattering for Large Momentum Transfers and Van der Waals Type Model

    Science.gov (United States)

    Aleem, F.

    1980-03-01

    The most recent measurements of the angular distribution in proton-proton elastic scattering at sqrt{s}=27.4, 45 and 62GeV with squared four momentum transfer, -t, extending up to 14(GeV/c)2, have been explained using Van der Waals type model.

  9. Nonlocal van der Waals functionals: The case of rare-gas dimers and solids

    CERN Document Server

    Tran, Fabien

    2013-01-01

    Recently, the nonlocal van der Waals (vdW) density functionals [M. Dion, H. Rydberg, E. Schroeder, D. C. Langreth, and B. I. Lundqvist, Phys. Rev. Lett. 92, 246401 (2004)] have attracted considerable attention due to their good performance for systems where weak interactions are important. Since the physics of dispersion is included in these functionals, they are usually more accurate and show less erratic behavior than the semilocal and hybrid methods. In this work, several variants of the vdW functionals have been tested on rare-gas dimers (from He2 to Kr2) and solids (Ne, Ar, and Kr) and their accuracy compared to standard semilocal approximations supplemented or not by an atom-pairwise dispersion correction [S. Grimme, J. Antony, S. Ehrlich, and H. Krieg, J. Chem. Phys. 132, 154104 (2010)]. An analysis of the results in terms of energy decomposition is also provided.

  10. Encapsulation of organic molecules in carbon nanotubes: role of the van der Waals interactions

    Science.gov (United States)

    Dappe, Y. J.

    2014-02-01

    Carbon nanotubes are fascinating nano-objects not only from a fundamental point of view but also with respect to their remarkable properties, holding great potential in new materials design. When combined with organic molecules, these properties can be enhanced or modulated in order to fulfil the demand in domains as diverse as molecular electronics, biomaterials or even construction engineering, to name a few. To adequately conceive these hybrid materials it is essential to fully appreciate the nature of molecule-carbon nanotube interactions. In this review, we will discuss some relevant fundamental and applied research done on encapsulated molecules in carbon nanotubes. We will particularly focus on the weak and van der Waals interactions which rule the molecule-tube coupling. Therefore a small state of the art on the theoretical methods used to describe these interactions is presented here. Then, we will discuss various applications of molecular encapsulation, where we will consider structural, magnetic, charge transfer and transport, and optical properties.

  11. Efficient implementation of a van der Waals density functional: application to double-wall carbon nanotubes.

    Science.gov (United States)

    Román-Pérez, Guillermo; Soler, José M

    2009-08-28

    We present an efficient implementation of the van der Waals density functional of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)], which expresses the nonlocal correlation energy as a double spatial integral. We factorize the integration kernel and use fast Fourier transforms to evaluate the self-consistent potential, total energy, and atomic forces, in O(NlogN) operations. The resulting overhead, for medium and large systems, is a small fraction of the total computational cost, representing a dramatic speedup over the O(N(2)) evaluation of the double integral. This opens the realm of first-principles simulations to the large systems of interest in soft matter and biomolecular problems. We apply the method to calculate the binding energies and the barriers for relative translation and rotation in double-wall carbon nanotubes.

  12. Graphene/h-BN/ZnO van der Waals tunneling heterostructure based ultraviolet photodetector.

    Science.gov (United States)

    Wu, Zhiqian; Li, Xiaoqiang; Zhong, Huikai; Zhang, Shengjiao; Wang, Peng; Kim, Tae-ho; Kwak, Sung Soo; Liu, Cheng; Chen, Hongsheng; Kim, Sang-Woo; Lin, Shisheng

    2015-07-27

    We report a novel ultraviolet photodetector based on graphene/h-BN/ZnO van der Waals heterostructure. Graphene/ZnO heterostructure shows poor rectification behavior and almost no photoresponse. In comparison, graphene/h-BN/ZnO structure shows improved electrical rectified behavior and surprising high UV photoresponse (1350AW(-1)), which is two or three orders magnitude larger than reported GaN UV photodetector (0.2~20AW(-1)). Such high photoresponse mainly originates from the introduction of ultrathin two-dimensional (2D) insulating h-BN layer, which behaves as the tunneling layer for holes produced in ZnO and the blocking layer for holes in graphene. The graphene/h-BN/ZnO heterostructure should be a novel and representative 2D heterostructure for improving the performance of 2D materials/Semiconductor heterostructure based optoelectronic devices.

  13. Strain induced piezoelectric effect in black phosphorus and MoS2 van der Waals heterostructure.

    Science.gov (United States)

    Huang, Le; Li, Yan; Wei, Zhongming; Li, Jingbo

    2015-11-10

    The structural, electronic, transport and optical properties of black phosphorus/MoS2 (BP/MoS2) van der Waals (vdw) heterostructure are investigated by using first principles calculations. The band gap of BP/MoS2 bilayer decreases with the applied normal compressive strain and a semiconductor-to-metal transition is observed when the applied strain is more than 0.85 Å. BP/MoS2 bilayer also exhibits modulation of its carrier effective mass and carrier concentration by the applied compressive strain, suggesting that mobility engineering and good piezoelectric effect can be realized in BP/MoS2 heterostructure. Because the type-II band alignment can facilitate the separation of photo-excited electrons and holes, and it can benefit from the great absorption coefficient in ultra-violet region, the BP/MoS2 shows great potential to be a very efficient ultra-violet photodetector.

  14. Thermal electron attachment to oxygen and van der Waals molecules containing oxygen

    Science.gov (United States)

    Shimamori, Hiroshi; Fessenden, Richard W.

    1981-01-01

    Thermal electron attachment to O2 has been studied for pure O2 (16O2 and 18O2), O2-N2, O2-CO, and O2-n-C4H10 (16O2 and 18O2) systems at temperatures from ˜330 down to 78° K using pulse radiolysis and microwave conductivity. For pure O2, O2-N2, and O2-CO mixtures, the electron attachment rates showed three-body pressure dependences at all temperatures over the pressure range studied (PO2<10Torr, PN2<60 Torr, PCO<40 Torr). The three-body rate constant of 16O2 decreases from ˜2.4×10-30 cm6 molecule-2 sec-1 at 330 °K to about 0.9×10-30 cm6 molecule-2 sec-1 at ˜ 140 °K but unexpectedly increases again to about 1.7×10-30 cm6 molecule-2 sec-1 at 79 °K. Similarly, the three-body rate constant of 18O2 decreases from 5.1×10-30 cm6 molecule-2 sec-1 at 300 °K to 1.8×10-30 cm6 molecule-2 sec-1 at ˜110 °K but increases to 2.3×10-30 cm6 molecule-2 sec-1 at 80 °K. The three-body rate constant of N2 shows a more dramatic monotonic increase from 0.9×10-31 cm6 molecule-2 sec-1 at 300 °K to 9.4×10-31 cm6 molecule-2 sec-1 at 78 °K. In the case of CO, the three-body rate constant appears to have a very shallow minimum around 170 °K and again increases with further decrease of temperature. Since theory predicts a simple decrease in rate constant with reduced temperature, an extra contribution to the rate constant which increases with lowered temperature is evident. Electron attachment to the van der Waals molecules (O2)2, (O2ṡN2), and (O2ṡCO) is proposed to account for this behavior. It has been found that the dependence of the excess rate on temperature follows rather closely the predicted concentration of van der Waals molecules. Qualitatively, this observation suggests that the rate constant for electron attachment to the van der Waals molecules is only weakly dependent on temperature. The estimated rate constants for this attachment are nearly two orders of magnitude larger than for O2 itself. A discussion of possible reasons for this large increase is given

  15. Van der Waals potential and vibrational energy levels of the ground state radon dimer

    Science.gov (United States)

    Sheng, Xiaowei; Qian, Shifeng; Hu, Fengfei

    2017-08-01

    In the present paper, the ground state van der Waals potential of the Radon dimer is described by the Tang-Toennies potential model, which requires five essential parameters. Among them, the two dispersion coefficients C6 and C8 are estimated from the well determined dispersion coefficients C6 and C8 of Xe2. C10 is estimated by using the approximation equation that C6C10 / C82 has an average value of 1.221 for all the rare gas dimers. With these estimated dispersion coefficients and the well determined well depth De and Re the Born-Mayer parameters A and b are derived. Then the vibrational energy levels of the ground state radon dimer are calculated. 40 vibrational energy levels are observed in the ground state of Rn2 dimer. The last vibrational energy level is bound by only 0.0012 cm-1.

  16. Communication: evidence of stable van der Waals CO2 clusters relevant to Venus atmosphere conditions.

    Science.gov (United States)

    Asfin, Ruslan E; Buldyreva, Jeanna V; Sinyakova, Tatyana N; Oparin, Daniil V; Filippov, Nikolai N

    2015-02-07

    Non-intrusive spectroscopic probing of weakly bound van der Waals complexes forming in gaseous carbon dioxide is generally performed at low pressures, for instance in supersonic jets, where the low temperature favors dimers, or in few-atmosphere samples, where the signature of dimers varying as the squared gas density is entangled with the dominating collision-induced absorption. We report experimental and theoretical results on CO2 dimers at very high pressures approaching the liquid phase. We observe that the shape of the CO2-dimer bands undergoes a distinctive line-mixing transformation, which reveals an unexpected stability of the dimers despite the collisions with the surrounding particles and negates the common belief that CO2 dimers are short-lived complexes. Our results furnish a deeper insight allowing a better modeling of CO2-rich atmospheres and provide also a new spectroscopic tool for studying the robustness of molecular clusters.

  17. Van Der Waals Heterostructures between Small Organic Molecules and Layered Substrates

    Directory of Open Access Journals (Sweden)

    Han Huang

    2016-09-01

    Full Text Available Two dimensional atomic crystals, like grapheme (G and molybdenum disulfide (MoS2, exhibit great interest in electronic and optoelectronic applications. The excellent physical properties, such as transparency, semiconductivity, and flexibility, make them compatible with current organic electronics. Here, we review recent progress in the understanding of the interfaces of van der Waals (vdW heterostructures between small organic molecules (pentacene, copper phthalocyanine (CuPc, perylene-3,4,9,10-tetracarboxylic dianhydride (PTCDA, and dioctylbenzothienobenzothiophene (C8-BTBT and layered substrates (G, MoS2 and hexagonal boron nitride (h-BN. The influences of the underlying layered substrates on the molecular arrangement, electronic and vibrational properties will be addressed.

  18. Stability and dynamics of a controlled van der Pol-Duffing oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Ji, J.C. [School of Mechanical Engineering, University of Adelaide, SA 5005 (Australia)] e-mail: jcji@mecheng.adelaide.edu.au; Hansen, C.H. [School of Mechanical Engineering, University of Adelaide, SA 5005 (Australia)] e-mail: chansen@mecheng.adelaide.edu.au

    2006-04-01

    The trivial equilibrium of a van der Pol-Duffing oscillator under a linear-plus-nonlinear feedback control may change its stability either via a single or via a double Hopf bifurcation if the time delay involved in the feedback reaches certain values. It is found that the trivial equilibrium may lose its stability via a subcritical or supercritical Hopf bifurcation and regain its stability via a reverse subcritical or supercritical Hopf bifurcation as the time delay increases. A stable limit cycle appears after a supercritical Hopf bifurcation occurs and disappears through a reverse supercritical Hopf bifurcation. The interaction of the weakly periodic excitation and the stable bifurcating solution is investigated for the forced system under primary resonance conditions. It is shown that the forced periodic response may lose its stability via a Neimark-Sacker bifurcation. Analytical results are validated by a comparison with those of direct numerical integration.

  19. Nonlinear dynamics of plasma oscillations modeled by a forced modified Van der Pol-Duffing oscillator

    CERN Document Server

    Miwadinou, C H; Monwanou, A V; Orou, J B Chabi

    2013-01-01

    This paper considers nonlinear dynamics of plasma oscillations modeled by a forced modified Van der Pol-Duffing oscillator. These plasma oscillations are described by a nonlinear differential equation of the form $ \\ddot{x}+ \\epsilon (1 +{x}^{2}){\\dot{x}} + x+ \\alpha \\epsilon{x}{\\dot{x}} + {\\beta}x^{2}+\\gamma x^{3}= F\\cos{\\Omega t}.$ The amplitudes of the forced harmonic, superharmonic and subharmonic oscillatory states are obtained using the harmonic balance technique and the multiple time scales methods. Bifurcation sequences displayed by the model for each type of oscillatory states are performed numerically through the fourth order Runge- Kutta scheme. The influences of the differents parameters and of amplitude of external forced have been found.

  20. Difference resonances in a controlled van der Pol-Duffing oscillator involving time delay

    Energy Technology Data Exchange (ETDEWEB)

    Ji, J.C. [Faculty of Engineering, University of Technology, Sydney, Level 20, Building 1, PO Box 123, Broadway, NSW 2007 (Australia)], E-mail: jin.ji@uts.edu.au; Zhang, N.; Gao Wei [Faculty of Engineering, University of Technology, Sydney, Level 20, Building 1, PO Box 123, Broadway, NSW 2007 (Australia)

    2009-10-30

    A non-resonant interaction of two Hopf bifurcations may appear after the trivial solution of a controlled van der Pol-Duffing oscillator without external excitation loses its stability, when two critical time delays corresponding to two Hopf bifurcations have the same value. In the vicinity of the non-resonant Hopf bifurcations, the presence of a periodic excitation in the controlled oscillator can induce difference resonances in the forced response, when the forcing frequency and the frequencies of the two Hopf bifurcations satisfy certain relationships. It is found that the frequency response curves of the controlled system under difference resonances are an isolated closed curve. The difference resonance response may admit two stable motions on a three-dimensional torus consisting of three frequencies. Illustrative examples are given to show the quasi-periodic motions.

  1. Cavitation inception of a van der Waals fluid at a sack-wall obstacle

    CERN Document Server

    Kaehler, G; Gonnella, G; Lamura, A

    2016-01-01

    Cavitation in a liquid moving past a constraint is numerically investigated by means of a free-energy lattice Boltzmann simulation based on the van der Waals equation of state. The fluid is streamed past an obstacle and, depending on the pressure drop between inlet and outlet, vapor formation underneath the corner of the sack-wall is observed. The circumstances of cavitation formation are investigated and it is found that the local bulk pressure and mean stress are insufficient to explain the phenomenon. Results obtained in this study strongly suggest that the viscous stress, interfacial contributions to the local pressure, and the Laplace pressure are relevant to the opening of a vapor cavity. This can be described by a generalization of Joseph's criterion that includes these contributions. A macroscopic investigation measuring mass flow rate behavior and discharge coefficient was also performed. As theoretically predicted, mass flow rate increases linearly with the square root of the pressure drop. However,...

  2. Scanning tunneling spectroscopy of van der Waals graphene/semiconductor interfaces: absence of Fermi level pinning

    Science.gov (United States)

    Le Quang, T.; Cherkez, V.; Nogajewski, K.; Potemski, M.; Dau, M. T.; Jamet, M.; Mallet, P.; Veuillen, J.-Y.

    2017-09-01

    We have investigated the electronic properties of two-dimensional (2D) transition metal dichalcogenides (TMDs), namely trilayer WSe2 and monolayer MoSe2, deposited on epitaxial graphene on silicon carbide, by using scanning tunneling microscopy and spectroscopy (STM/STS) in ultra-high vacuum. Depending on the number of graphene layers below the TMD flakes, we identified variations in the electronic dI/dV(V) spectra measured by the STM tip: the most salient feature is a rigid shift of the TMD spectra (i.e. of the different band onset positions) towards occupied states by about 120 mV when passing from bilayer to monolayer underlying graphene. Since both graphene phases are metallic and present a work function difference in the same energy range, our measurements point towards the absence of Fermi-level pinning for such van der Waals 2D TMD/Metal heterojunctions, following the prediction of the Schottky-Mott model.

  3. Bounds of Falk and Bruch in the low temperature Van der Waals model

    Energy Technology Data Exchange (ETDEWEB)

    Lee, M.H.; Kim, I.M. (Georgia Univ., Athens (USA). Dept. of Physics)

    For many-body systems, the susceptibility and the fluctuation in the long-range order can be different. There are bounds on the ratio of the susceptibility to the fluctuation due to Falk and Bruch, according to which the two correlation functions cannot be entirely independent. For the spin van der Waals model, we obtain exact expressions for the susceptibility and fluctuation in the low temperature region. We find that the susceptibilty are the same in the XY-like regime of the model but they are different in the Ising-like regime. In both cases the bounds do not merge. Thus, the bounds alone are not sufficient to explain the relative behavior of the susceptibility and fluctuation.

  4. Band structure engineering in van der Waals heterostructures via dielectric screening: the GΔW method

    DEFF Research Database (Denmark)

    Winther, Kirsten Trøstrup; Thygesen, Kristian Sommer

    2017-01-01

    precise magnitude is non-trivial to predict because of the non-local nature of the screening in quasi-2D crystals. Moreover, the effect is not captured by effective single-particle methods such as density functional theory. Here we present an efficient and general method for calculating the band gap......The idea of combining different two-dimensional (2D) crystals in van der Waals heterostructures (vdWHs) has led to a new paradigm for band structure engineering with atomic precision. Due to the weak interlayer couplings, the band structures of the individual 2D crystals are largely preserved upon...... formation of the heterostructure. However, regardless of the details of the interlayer hybridisation, the size of the 2D crystal band gaps are always reduced due to the enhanced dielectric screening provided by the surrounding layers. The effect can be significant (on the order of electron volts) but its...

  5. Solutions of the Force-Free Duffing-van der Pol Oscillator Equation

    Directory of Open Access Journals (Sweden)

    Najeeb Alam Khan

    2011-01-01

    Full Text Available A new approximate method for solving the nonlinear Duffing-van der pol oscillator equation is proposed. The proposed scheme depends only on the two components of homotopy series, the Laplace transformation and, the Padé approximants. The proposed method introduces an alternative framework designed to overcome the difficulty of capturing the behavior of the solution and give a good approximation to the solution for a large time. The Runge-Kutta algorithm was used to solve the governing equation via numerical solution. Finally, to demonstrate the validity of the proposed method, the response of the oscillator, which was obtained from approximate solution, has been shown graphically and compared with that of numerical solution.

  6. Formation of van der Waals molecules in buffer-gas-cooled magnetic traps [corrected].

    Science.gov (United States)

    Brahms, N; Tscherbul, T V; Zhang, P; Kłos, J; Sadeghpour, H R; Dalgarno, A; Doyle, J M; Walker, T G

    2010-07-16

    We predict that a large class of helium-containing cold polar molecules form readily in a cryogenic buffer gas, achieving densities as high as 10(12)  cm(-3). We explore the spin relaxation of these molecules in buffer-gas-loaded magnetic traps and identify a loss mechanism based on Landau-Zener transitions arising from the anisotropic hyperfine interaction. Our results show that the recently observed strong T(-6) thermal dependence of the spin-change rate of silver (Ag) trapped in dense (3)He is accounted for by the formation and spin change of Ag(3)He van der Waals molecules, thus providing indirect evidence for molecular formation in a buffer-gas trap.

  7. On the van der Pauw's method applied to the measurement of low thermal conductivity materials.

    Science.gov (United States)

    Morales, C; Flores, E; Bodega, J; Leardini, F; Ferrer, I J; Ares, J R; Sánchez, C

    2016-08-01

    The electrical van der Pauw's method has recently been extended to measure the thermal conductivity of different elements and compounds. This technique provides an easy way to determine the sample in-plane thermal conductivity by avoiding the influence of the thermal contact resistances. However, the reported calculated error values appear to be underestimated when dealing with the materials with low thermal conductivity (conduction heat losses through the thermo-resistance wires as well as the resulting modification of the sample temperature map. Both phenomena lead to experimental values of the sample thermal conductivity, which are systematically higher than the tabulated ones. The magnitude of this systematic error is ∼100% dealing with the samples of macroscopic dimensions, and low thermal conductivity indicated that the obtained accurate measurements can be quite challenging.

  8. Tuning the Schottky barrier in the arsenene/graphene van der Waals heterostructures by electric field

    Science.gov (United States)

    Li, Wei; Wang, Tian-Xing; Dai, Xian-Qi; Wang, Xiao-Long; Ma, Ya-Qiang; Chang, Shan-Shan; Tang, Ya-Nan

    2017-04-01

    Using density functional theory calculations, we investigate the electronic properties of arsenene/graphene van der Waals (vdW) heterostructures by applying external electric field perpendicular to the layers. It is demonstrated that weak vdW interactions dominate between arsenene and graphene with their intrinsic electronic properties preserved. We find that an n-type Schottky contact is formed at the arsenene/graphene interface with a Schottky barrier of 0.54 eV. Moreover, the vertical electric field can not only control the Schottky barrier height but also the Schottky contacts (n-type and p-type) and Ohmic contacts (n-type) at the interface. Tunable p-type doping in graphene is achieved under the negative electric field because electrons can transfer from the Dirac point of graphene to the conduction band of arsenene. The present study would open a new avenue for application of ultrathin arsenene/graphene heterostructures in future nano- and optoelectronics.

  9. Free-Standing GaMnAs Nanomachined Sheets for van der Pauw Magnetotransport Measurements

    Directory of Open Access Journals (Sweden)

    Jae-Hyun Lee

    2016-12-01

    Full Text Available We report on the realization of free-standing GaMnAs epilayer sheets using nanomachining techniques. By optimizing the growth conditions of the sacrificial Al0.75Ga0.25As layer, free-standing metallic GaMnAs (with ~6% Mn microsheets (with TC ~85 K with integrated electrical probes are realized for magnetotransport measurements in the van der Pauw geometry. GaMnAs epilayer needs to be physically isolated to avoid buckling effects stemming from the release of lattice mismatch strain during the removal of the AlGaAs sacrificial layer. From finite element analysis, symmetrically placed and serpentine-shaped electrical leads induce minimal thermal stress at low temperatures. From magnetotransport measurements, changes in magnetic anisotropy are readily observed.

  10. The Van der Waals interaction of the hydrogen molecule an exact local energy density functional

    CERN Document Server

    Choy, T C

    1999-01-01

    We verify that the van der Waals interaction and hence all dispersion interactions for the hydrogen molecule given by: W''= -{A/R^6}-{B/R^8}-{C/R^10}- ..., in which R is the internuclear separation, are exactly soluble. The constants A=6.4990267..., B=124.3990835 ... and C=1135.2140398... (in Hartree units) first obtained approximately by Pauling and Beach (PB) [1] using a linear variational method, can be shown to be obtainable to any desired accuracy via our exact solution. In addition we shall show that a local energy density functional can be obtained, whose variational solution rederives the exact solution for this problem. This demonstrates explicitly that a static local density functional theory exists for this system. We conclude with remarks about generalising the method to other hydrogenic systems and also to helium.

  11. On the van der Pauw's method applied to the measurement of low thermal conductivity materials

    Science.gov (United States)

    Morales, C.; Flores, E.; Bodega, J.; Leardini, F.; Ferrer, I. J.; Ares, J. R.; Sánchez, C.

    2016-08-01

    The electrical van der Pauw's method has recently been extended to measure the thermal conductivity of different elements and compounds. This technique provides an easy way to determine the sample in-plane thermal conductivity by avoiding the influence of the thermal contact resistances. However, the reported calculated error values appear to be underestimated when dealing with the materials with low thermal conductivity (temperature. The causes of this underestimation are investigated in this communication and it has been found that they are due to the drastic influence of conduction heat losses through the thermo-resistance wires as well as the resulting modification of the sample temperature map. Both phenomena lead to experimental values of the sample thermal conductivity, which are systematically higher than the tabulated ones. The magnitude of this systematic error is ˜100% dealing with the samples of macroscopic dimensions, and low thermal conductivity indicated that the obtained accurate measurements can be quite challenging.

  12. Van der Waals interactions between polymers with sequence-specific polarizabilities: Stiff polymers and Gaussian coils

    Science.gov (United States)

    Lu, Bing-Sui; Naji, Ali; Podgornik, Rudolf

    2016-01-01

    We consider the van der Waals interaction between a pair of polymers with quenched heterogeneous sequences of local polarizabilities along their backbones, and study the effective pairwise interaction energy for both stiff polymers and flexible Gaussian coils. In particular, we focus on the cases where the pair of polarizability sequences are (i) distinct and (ii) identical. We find that the pairwise interaction energies of distinct and identical Gaussian coils are both isotropic and exhibit the same decay behavior for separations larger than their gyration radius, in contradistinction to the orientationally anisotropic interaction energies of distinct and identical stiff polymers. For both Gaussian coils and stiff polymers, the attractive interaction between identical polymers is enhanced if the polarizability sequence is more heterogeneous.

  13. Continuatio naturae. La arquitectura monástica de Dom Hans van der Laan

    OpenAIRE

    Sainz Gutiérrez, Victoriano

    2009-01-01

    En un texto de carácter autobiográfico redactado hacia el final de su vida, Hans van der Laan señalaba, al recordar sus años de infancia y adolescencia, que el principal objetivo en esos años cruciales para su formación había sido el conocimiento de la naturaleza: «Lento pero seguro escribe, me adentraba en la vida de la naturaleza, siendo consciente de que había sido creada por Dios. Mi hermana mayor, la que murió durante la guerra, tuvo como profesora, tanto en la enseñanza primaria como en...

  14. Isobaric first-principles molecular dynamics of liquid water with nonlocal van der Waals interactions

    CERN Document Server

    Miceli, Giacomo; Pasquarello, Alfredo

    2016-01-01

    We investigate the structural properties of liquid water at near ambient conditions using first-principles molecular dynamics simulations based on a semilocal density functional augmented with nonlocal van der Waals interactions. The adopted scheme offers the advantage of simulating liquid water at essentially the same computational cost of standard semilocal functionals. Applied to the water dimer and to ice Ih, we find that the hydrogen-bond energy is only slightly enhanced compared to a standard semilocal functional. We simulate liquid water through molecular dynamics in the NpH statistical ensemble allowing for fluctuations of the system density. The structure of the liquid departs from that found with a semilocal functional leading to more compact structural arrangements. This indicates that the directionality of the hydrogen-bond interaction has a diminished role as compared to the overall attractions, as expected when dispersion interactions are accounted for. This is substantiated through a detailed a...

  15. Van der Pol and the history of relaxation oscillations: toward the emergence of a concept

    CERN Document Server

    Ginoux, Jean-Marc

    2014-01-01

    Relaxation oscillations are commonly associated with the name of Balthazar van der Pol via his eponymous paper (Philosophical Magazine, 1926) in which he apparently introduced this terminology to describe the nonlinear oscillations produced by self-sustained oscillating systems such as a triode circuit. Our aim is to investigate how relaxation oscillations were actually discovered. Browsing the literature from the late 19th century, we identified four self-oscillating systems in which relaxation oscillations have been observed: i) the series dynamo machine conducted by G\\'erard-Lescuyer (1880), ii) the musical arc discovered by Duddell (1901) and investigated by Blondel (1905), iii) the triode invented by de Forest (1907) and, iv) the multivibrator elaborated by Abraham and Bloch (1917). The differential equation describing such a self-oscillating system was proposed by Poincar\\'e for the musical arc (1908), by Janet for the series dynamo machine (1919), and by Blondel for the triode (1919). Once Janet (1919)...

  16. The T-shaped KrI2(ion-pair states) van der Waals complexes

    Science.gov (United States)

    Baturo, V. V.; Kevorkyants, R.; Lukashov, S. S.; Poretsky, S. A.; Pravilov, A. M.; Zhironkin, A. I.

    2017-09-01

    The T-shaped KrI2(E0g+) van der Waals complexes have been observed and studied for the first time. Analysis of the luminescence excitation spectra as well as luminescence spectra themselves in the spectral ranges, where the I2(E0g+ → B0u+, D0u+ → X0g+, β1g → A1u and D‧2g → A‧2u) transitions can occur, has been carried out. Branching ratios of the iodine molecule state formation and vibronic level population, as well as the potential parameters of the KrI2(E,vE = 0-8, nE) complexes have been determined. Binding energies of the KrI2(X0g+,vX = 0, nX = 0 and B0u+, vB = 19, nB = 0) complexes have been also estimated.

  17. Thermodynamic properties of van der Waals fluids from Monte Carlo simulations and perturbative Monte Carlo theory.

    Science.gov (United States)

    Díez, A; Largo, J; Solana, J R

    2006-08-21

    Computer simulations have been performed for fluids with van der Waals potential, that is, hard spheres with attractive inverse power tails, to determine the equation of state and the excess energy. On the other hand, the first- and second-order perturbative contributions to the energy and the zero- and first-order perturbative contributions to the compressibility factor have been determined too from Monte Carlo simulations performed on the reference hard-sphere system. The aim was to test the reliability of this "exact" perturbation theory. It has been found that the results obtained from the Monte Carlo perturbation theory for these two thermodynamic properties agree well with the direct Monte Carlo simulations. Moreover, it has been found that results from the Barker-Henderson [J. Chem. Phys. 47, 2856 (1967)] perturbation theory are in good agreement with those from the exact perturbation theory.

  18. Improving the accuracy of the nonlocal van der Waals density functional with minimal empiricism.

    Science.gov (United States)

    Vydrov, Oleg A; Van Voorhis, Troy

    2009-03-14

    The nonlocal van der Waals density functional (vdW-DF) captures the essential physics of the dispersion interaction not only in the asymptotic regime but also for a general case of overlapping fragment densities. A balanced treatment of other energetic contributions, such as exchange, is crucial if we aim for accurate description of various properties of weakly bound systems. In this paper, the vdW-DF correlation functional is modified to make it better compatible with accurate exchange functionals. We suggest a slightly simplified construction of the nonlocal correlation, yielding more accurate asymptotic C(6) coefficients. We also derive a gradient correction, containing a parameter that can be adjusted to suit an exchange functional of choice. We devise a particularly apt combination of exchange and correlation terms, which satisfies many important constraints and performs well for our benchmark tests.

  19. Quantum transport across van der Waals domain walls in bilayer graphene

    Science.gov (United States)

    Abdullah, H. M.; Van Duppen, B.; Zarenia, M.; Bahlouli, H.; Peeters, F. M.

    2017-10-01

    Bilayer graphene can exhibit deformations such that the two graphene sheets are locally detached from each other resulting in a structure consisting of domains with different van der Waals inter-layer coupling. Here we investigate how the presence of these domains affects the transport properties of bilayer graphene. We derive analytical expressions for the transmission probability, and the corresponding conductance, across walls separating different inter-layer coupling domains. We find that the transmission can exhibit a valley-dependent layer asymmetry and that the domain walls have a considerable effect on the chiral tunnelling properties of the charge carriers. We show that transport measurements allow one to obtain the strength with which the two layers are coupled. We perform numerical calculations for systems with two domain walls and find that the availability of multiple transport channels in bilayer graphene significantly modifies the conductance dependence on inter-layer potential asymmetry.

  20. Van der Hoeve综合征合并太田痣一例

    Institute of Scientific and Technical Information of China (English)

    韦萍

    2007-01-01

    Van der Hoeve综合征即蓝色巩膜一脆骨(耳聋)综合征。太田痣(nevus of ota)即先天性眼皮肤黑色素细胞增多痣,又称Ota综合征,是围绕眼眶、眼睑及眉部皮肤的一种蓝痣,伴同侧结膜、巩膜及葡萄膜弥散性痣。遗传方式多为常染色体显性遗传,但也有隐性者。笔者于2006年8月诊治了1例该病患者。

  1. Bifurcation threshold of the delayed van der Pol oscillator under stochastic modulation.

    Science.gov (United States)

    Gaudreault, Mathieu; Drolet, François; Viñals, Jorge

    2012-05-01

    We obtain the location of the Hopf bifurcation threshold for a modified van der Pol oscillator, parametrically driven by a stochastic source and including delayed feedback in both position and velocity. We introduce a multiple scale expansion near threshold, and we solve the resulting Fokker-Planck equation associated with the evolution at the slowest time scale. The analytical results are compared with a direct numerical integration of the model equation. Delay modifies the Hopf frequency at threshold and leads to a stochastic bifurcation that is shifted relative to the deterministic limit by an amount that depends on the delay time, the amplitude of the feedback terms, and the intensity of the noise. Interestingly, stochasticity generally increases the region of stability of the limit cycle.

  2. 1-D Van der Waals Foams Heated by Ion Beam Energy Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Zylstra, A; Barnard, J J; More, R M

    2010-03-19

    One dimensional simulations of various initial average density aluminum foams (modeled as slabs of solid metal separated by low density regions) heated by volumetric energy deposition are conducted with a Lagrangian hydrodynamics code using a van der Waals equation of state (EOS). The resulting behavior is studied to facilitate the design of future warm dense matter (WDM) experiments at LBNL. In the simulations the energy deposition ranges from 10 to 30 kJ/g and from 0.075 to 4.0 ns total pulse length, resulting in temperatures from approximately 1 to 4 eV. We study peak pressures and temperatures in the foams, expansion velocity, and the phase evolution. Five relevant time scales in the problem are identified. Additionally, we present a method for characterizing the level of inhomogeneity in a foam target as it is heated and the time it takes for a foam to homogenize.

  3. 1-D Van der Waals Foams Heated by Ion Beam Energy Deposition

    Energy Technology Data Exchange (ETDEWEB)

    Zylstra, A. B.; Barnard, J. J.; More, R. M.

    2009-12-23

    One dimensional simulations of various initial average density aluminum foams (modeled as slabs of solid metal separated by low density regions) heated by volumetric energy deposition are conducted with a Lagrangian hydrodynamics code using a van der Waals equation of tate (EOS). The resulting behavior is studied to facilitate the design of future warm dense matter (WDM) experiments at LBNL. In the simulations the energy deposition ranges from 10 to 30 kJ/g and from 0.075 to 4.0 ns total pulse length, resulting in temperatures from approximately 1 o 4 eV. We study peak pressures and temperatures in the foams, expansion velocity, and the phase evolution. Five relevant time scales in the problem are identified. Additionally, we present a method for characterizing the level of inhomogeneity in a foam target as it is heated and the time it takes for a foam to homogenize.

  4. Nonclassical Riemann solvers and kinetic relations III: A nonconvex hyperbolic model for Van der Waals fluids

    Directory of Open Access Journals (Sweden)

    Philippe G. LeFloch

    2000-12-01

    Full Text Available This paper deals with the so-called p-system describing the dynamics of isothermal and compressible fluids. The constitutive equation is assumed to have the typical convexity/concavity properties of the van der Waals equation. We search for discontinuous solutions constrained by the associated mathematical entropy inequality. First, following a strategy proposed by Abeyaratne and Knowles and by Hayes and LeFloch, we describe here the whole family of nonclassical Riemann solutions for this model. Second, we supplement the set of equations with a kinetic relation for the propagation of nonclassical undercompressive shocks, and we arrive at a uniquely defined solution of the Riemann problem. We also prove that the solutions depend $L^1$-continuously upon their data. The main novelty of the present paper is the presence of two inflection points in the constitutive equation. The Riemann solver constructed here is relevant for fluids in which viscosity and capillarity effects are kept in balance.

  5. Turbulent mixing of a slightly supercritical Van der Waals fluid at Low-Mach number

    CERN Document Server

    Battista, Francesco; Casciola, Carlo Massimo

    2014-01-01

    Supercritical fluids near the critical point are characterized by liquid-like densities and gas-like transport properties. These features are purposely exploited in different contexts ranging from natural products extraction/fractionation to aerospace propulsion. Large part of studies concerns this last context, focusing on the dynamics of supercritical fluids at high Mach number where compressibility and thermodynamics strictly interact. Despite the widespread use also at low Mach number, the turbulent mixing properties of slightly supercritical fluids have still not investigated in detail in this regime. This topic is addressed here by dealing with Direct Numerical Simulations (DNS) of a coaxial jet of a slightly supercritical Van der Waals fluid. Since acoustic effects are irrelevant in the Low Mach number conditions found in many industrial applications, the numerical model is based on a suitable low-Mach number expansion of the governing equation. According to experimental observations, the weakly superc...

  6. Nucleotide insertion initiated by van derWaals interaction during polymerase beta DNA replication

    Indian Academy of Sciences (India)

    Andrew Das Arulsamy

    2013-09-01

    We present here an unambiguous theoretical analyses and to show that the exclusive biochemical reaction involved in a single nucleotide insertion into the DNA primer can be efficiently tracked using the renormalized van derWaals (vdW) interaction of a stronger type, the Hermansson blue-shifting hydrogen bond effect, and the Arunan composite hydrogen-vdW bond. We find that there are two biochemical steps involved to complete the insertion of a single base (cytosine) into the 3' end of a DNA primer. First, the O3' (from a DNA primer) initiates the nucleophilic attack on P (from an incoming dCTP), in response, O3 (bonded to P) interacts with H' (bonded to O3'). These interactions are shown to be strongly interdependent and require the forming and breaking of P—O and H—O covalent bonds, which in turn imply that we do not need any external energy supply.

  7. A self-consistent GW approach to the van der Waals potential for a helium dimer.

    Science.gov (United States)

    Shoji, Toru; Kuwahara, Riichi; Ono, Shota; Ohno, Kaoru

    2016-09-21

    van der Waals interaction between two helium (He) atoms is studied by calculating the total energy as a function of the He-He distance within the self-consistent GW approximation, which is expected to behave correctly in the long wavelength limit. In the Born-Oppenheimer (BO) approximation, the pair potential curve has its minimum value at 2.87 Å, which is somewhat larger than the local density approximation result, 2.40 Å, and is closer to previous quantum chemistry results. The expectation value for the interatomic distance, calculated by solving the Schrödinger equation for the two nuclei problem using the BO potential energy curve, is 30 Å, which is smaller but of the same order as previous experimental and theoretical results.

  8. Van der Woude syndrome: Report of two cases with supplementary findings

    Directory of Open Access Journals (Sweden)

    Chandramani B More

    2013-01-01

    Full Text Available Van der Woude syndrome (VWS is a rare developmental disorder with an autosomal dominant inheritance and variable expressivity, occurring in about 1 of every 1,00,000-2,00,000 people. This syndrome is remarkably variable. It is characterized by orofacial manifestations like lower lip pits, cleft lip and/or cleft palate, hypodontia, cleft or bifid uvula, syngnathia, narrow high arched palate, ankyloglossia and hyper nasal voice. We report two interesting cases of VWS with characteristic orofacial features and an unusual additional finding of bilateral commissural pits. The purpose of this article is to facilitate understanding of etio-pathogenesis, clinical manifestations, role of genetic counseling and with special emphasis on commissural pits as an additional feature in VWS.

  9. Thioarsenides: A case for long-range Lewis acid-base-directed van der Waals interactions

    Energy Technology Data Exchange (ETDEWEB)

    Gibbs, Gerald V.; Wallace, Adam F.; Downs, R. T.; Ross, Nancy L.; Cox, David F.; Rosso, Kevin M.

    2011-04-01

    Electron density distributions, bond paths, Laplacian and local energy density properties have been calculated for a number of As4Sn (n = 3,4,5) thioarsenide molecular crystals. On the basis of the distributions, the intramolecular As-S and As-As interactions classify as shared bonded interactions and the intermolecular As-S, As-As and S-S interactions classify as closed-shell van der Waals bonded interactions. The bulk of the intermolecular As-S bond paths link regions of locally concentrated electron density (Lewis base regions) with aligned regions of locally depleted electron density (Lewis acid regions) on adjacent molecules. The paths are comparable with intermolecular paths reported for several other molecular crystals that link aligned Lewis base and acid regions in a key-lock fashion, interactions that classified as long range Lewis acid-base directed van der Waals interactions. As the bulk of the intermolecular As-S bond paths (~70%) link Lewis acid-base regions on adjacent molecules, it appears that molecules adopt an arrangement that maximizes the number of As-S Lewis acid-base intermolecular bonded interactions. The maximization of the number of Lewis acid-base interactions appears to be connected with the close-packed array adopted by molecules: distorted cubic close-packed arrays are adopted for alacránite, pararealgar, uzonite, realgar and β-AsS and the distorted hexagonal close-packed arrays adopted by α- and β-dimorphite. A growth mechanism is proposed for thioarsenide molecular crystals from aqueous species that maximizes the number of long range Lewis acid-base vdW As-S bonded interactions with the resulting directed bond paths structuralizing the molecules as a molecular crystal.

  10. Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit

    Science.gov (United States)

    Huang, Bevin; Clark, Genevieve; Navarro-Moratalla, Efrén; Klein, Dahlia R.; Cheng, Ran; Seyler, Kyle L.; Zhong, Ding; Schmidgall, Emma; McGuire, Michael A.; Cobden, David H.; Yao, Wang; Xiao, Di; Jarillo-Herrero, Pablo; Xu, Xiaodong

    2017-06-01

    Since the discovery of graphene, the family of two-dimensional materials has grown, displaying a broad range of electronic properties. Recent additions include semiconductors with spin-valley coupling, Ising superconductors that can be tuned into a quantum metal, possible Mott insulators with tunable charge-density waves, and topological semimetals with edge transport. However, no two-dimensional crystal with intrinsic magnetism has yet been discovered; such a crystal would be useful in many technologies from sensing to data storage. Theoretically, magnetic order is prohibited in the two-dimensional isotropic Heisenberg model at finite temperatures by the Mermin-Wagner theorem. Magnetic anisotropy removes this restriction, however, and enables, for instance, the occurrence of two-dimensional Ising ferromagnetism. Here we use magneto-optical Kerr effect microscopy to demonstrate that monolayer chromium triiodide (CrI3) is an Ising ferromagnet with out-of-plane spin orientation. Its Curie temperature of 45 kelvin is only slightly lower than that of the bulk crystal, 61 kelvin, which is consistent with a weak interlayer coupling. Moreover, our studies suggest a layer-dependent magnetic phase, highlighting thickness-dependent physical properties typical of van der Waals crystals. Remarkably, bilayer CrI3 displays suppressed magnetization with a metamagnetic effect, whereas in trilayer CrI3 the interlayer ferromagnetism observed in the bulk crystal is restored. This work creates opportunities for studying magnetism by harnessing the unusual features of atomically thin materials, such as electrical control for realizing magnetoelectronics, and van der Waals engineering to produce interface phenomena.

  11. An oscillation free shock-capturing method for compressible van der Waals supercritical fluid flows

    Science.gov (United States)

    Pantano, C.; Saurel, R.; Schmitt, T.

    2017-04-01

    Numerical solutions of the Euler equations using real gas equations of state (EOS) often exhibit serious inaccuracies. The focus here is the van der Waals EOS and its variants (often used in supercritical fluid computations). The problems are not related to a lack of convexity of the EOS since the EOS are considered in their domain of convexity at any mesh point and at any time. The difficulties appear as soon as a density discontinuity is present with the rest of the fluid in mechanical equilibrium and typically result in spurious pressure and velocity oscillations. This is reminiscent of well-known pressure oscillations occurring with ideal gas mixtures when a mass fraction discontinuity is present, which can be interpreted as a discontinuity in the EOS parameters. We are concerned with pressure oscillations that appear just for a single fluid each time a density discontinuity is present. The combination of density in a nonlinear fashion in the EOS with diffusion by the numerical method results in violation of mechanical equilibrium conditions which are not easy to eliminate, even under grid refinement. A cure to this problem is developed in the present paper for the van der Waals EOS based on previous ideas. A special extra field and its corresponding evolution equation is added to the flow model. This new field separates the evolution of the nonlinear part of the density in the EOS and produce oscillation free solutions. The extra equation being nonconservative the behavior of two established numerical schemes on shocks computation is studied and compared to exact reference solutions that are available in the present context. The analysis shows that shock conditions of the nonconservative equation have important consequence on the results. Last, multidimensional computations of a supercritical gas jet is performed to illustrate the benefits of the present method, compared to conventional flow solvers.

  12. Density, structure, and dynamics of water: the effect of van der Waals interactions.

    Science.gov (United States)

    Wang, Jue; Román-Pérez, G; Soler, Jose M; Artacho, Emilio; Fernández-Serra, M-V

    2011-01-14

    It is known that ab initio molecular dynamics (AIMD) simulations of liquid water at ambient conditions, based on the generalized gradient approximation (GGA) to density functional theory (DFT), with commonly used functionals fail to produce structural and diffusive properties in reasonable agreement with experiment. This is true for canonical, constant temperature simulations where the density of the liquid is fixed to the experimental density. The equilibrium density, at ambient conditions, of DFT water has recently been shown by Schmidt et al. [J. Phys. Chem. B, 113, 11959 (2009)] to be underestimated by different GGA functionals for exchange and correlation, and corrected by the addition of interatomic pair potentials to describe van der Waals (vdW) interactions. In this contribution we present a DFT-AIMD study of liquid water using several GGA functionals as well as the van der Waals density functional (vdW-DF) of Dion et al. [Phys. Rev. Lett. 92, 246401 (2004)]. As expected, we find that the density of water is grossly underestimated by GGA functionals. When a vdW-DF is used, the density improves drastically and the experimental diffusivity is reproduced without the need of thermal corrections. We analyze the origin of the density differences between all the functionals. We show that the vdW-DF increases the population of non-H-bonded interstitial sites, at distances between the first and second coordination shells. However, it excessively weakens the H-bond network, collapsing the second coordination shell. This structural problem is partially associated to the choice of GGA exchange in the vdW-DF. We show that a different choice for the exchange functional is enough to achieve an overall improvement both in structure and diffusivity.

  13. Band structure engineering in van der Waals heterostructures via dielectric screening: the GΔW method

    Science.gov (United States)

    Winther, Kirsten T.; Thygesen, Kristian S.

    2017-06-01

    The idea of combining different two-dimensional (2D) crystals in van der Waals heterostructures (vdWHs) has led to a new paradigm for band structure engineering with atomic precision. Due to the weak interlayer couplings, the band structures of the individual 2D crystals are largely preserved upon formation of the heterostructure. However, regardless of the details of the interlayer hybridisation, the size of the 2D crystal band gaps are always reduced due to the enhanced dielectric screening provided by the surrounding layers. The effect can be significant (on the order of electron volts) but its precise magnitude is non-trivial to predict because of the non-local nature of the screening in quasi-2D crystals. Moreover, the effect is not captured by effective single-particle methods such as density functional theory. Here we present an efficient and general method for calculating the band gap renormalization of a 2D material embedded in an arbitrary vdWH. The method evaluates the change in the GW self-energy of the 2D material from the change in the screened Coulomb interaction. The latter is obtained using the quantum-electrostatic heterostructure (QEH) model. We benchmark the GΔW method against full first-principles GW calculations and use it to unravel the importance of screening-induced band structure renormalisation in various vdWHs. A main result is the observation that the size of the band gap reduction of a given 2D material when inserted into a heterostructure scales inversely with the polarisability of the 2D material. Our work demonstrates that dielectric engineering via van der Waals heterostructuring represents a promising strategy for tailoring the band structure of 2D materials.

  14. Electrical Transport and Thermal Expansion in van der Waals Materials: Graphene and Topological Insulator

    Science.gov (United States)

    Jing, Lei

    Novel two-dimensional materials with weak interlayer Van der Waals interaction are fantastic platforms to study novel physical phenomena. This thesis describes our investigation on two different Van der Waals materials: graphene and bismuth selenide with calcium doping (CaxBi 2-xSe3, x as the doping level) in the topological insulator family. Firstly, we characterize the electrical transport behaviors of high-quality substrate-supported bilayer graphene devices with suspended metal gates. The device exhibits a transport gap induced by external electric field with an on/off ratio of 20,000, which could be explained by variable range hoping between localized states or disordered charge puddles. At large magnetic field, the device presents quantum Hall plateau at fractional values of conductance quantum, which arises from the equilibration of edge states between differentially doped regions. Secondly, we present our study on the electronic transport of CaxBi 2-xSe3 thin films, which are three-dimensional topological insulators and coupled with superconducting leads. In these novel Josephson transistors, we observe different characteristic features by energy dispersion spectrum (EDS) and Raman spectroscopy, and the weak suppression in the critical current Ic. Thirdly, we explore the thermal expansion of suspended graphene. By in-situ scanning electron microscope (SEM), we measure the thickness-dependence of graphene's negative thermal expansion coefficient (TEC). We propose that there is a competitive relation between the intrinsic TEC and the friction from the substrate and the graphene. Lastly, in collaboration with Dr. Nikolai Kalugin from New Mexico Tech., we explore the graphene's application as a quantum Hall effect infrared photodetector. This graphene-based detector can be operated at higher temperature (liquid nitrogen) and wider frequency than the previous implementations of quantum Hall detector.

  15. Jet-Cooled High Resolution Infrared Spectroscopy of Small Van Der Waals SF_6 Clusters

    Science.gov (United States)

    Asselin, Pierre; Boudon, Vincent; Potapov, Alexey; Bruel, Laurent; Gaveau, Marc-André; Mons, Michel

    2016-06-01

    Using a pulsed slit nozzle multipass absorption spectrometer with a tunable quantum cascade laser we investigated van der Waals clusters involving sulfur hexafluoride in the spectral range near the νb{3} stretching vibration. Different sized homo-complexes were generated in a planar supersonic expansion with typically 0,5 % SF_6 diluted in 6 bar He. Firstly, several rotationally resolved parallel and perpendicular bands of (SF_6)_2, at 934,0 and 956,1 wn (#1 structure) in agreement with Takami et al. but also one band at 933,6 wn (#2 structure) never observed previously, were analyzed in light of a recent theoretical study predicting three nearly isoenergetic isomers of D2d, C2h and C_2 symmetry for the dimer. Furthermore, some broader bands were detected around 938 and 964 wn and assigned to (SF_6)_3 and (SF_6)_4 clusters on the grounds of concentration effects and/or ab initio calculations. Lastly, with 0,5 % rare gas Rg (Rg = Ne, Ar, Kr and Xe) added to the SF_6:He gas mixture, a series of van der Waals (SF_6)_2-Rg hetero-trimers were observed, which display a remarkable linear dependence of the vibrational shift with the polarizability of the rare gas atom provided that the initial SF_6 dimer structure is #2 . In the same time no transitions belonging to the binary complexes SF_6-Rg were found near the νb{3} monomer band. This result suggests a complex thermodynamics within the pulsed supersonic expansion leading to the preponderance of (SF_6)_2-Rg clusters over SF_6-Rg binary systems. R. D. Urban and M. Takami, J. Chem. Phys. 103, 9132 (1995). T. Vazhappily, A. Marjolin and K. D. Jordan, J. Phys. Chem. B, DOI: 10.1021/acs.jpcb.5b09419 (2015).

  16. El todo en el fragmento. Arquitectura y Bankunst en Mies Van der Rohe = The whole in the fragment. Mies van der Rohe´s Architecture and Bankunst

    Directory of Open Access Journals (Sweden)

    Antonio Juárez Chicote

    2013-10-01

    Full Text Available ResumenEl texto pretende asomarse a la mirada interior de Ludwig Mies van der Rohe y tomar conciencia del ejercicio visual y mental que la noción de ‘construcción’ tiene para el arquitecto. A partir de los ejercicios de adiestramiento visual (visual training propuestos en el IIT de Chicago a partir de 1938 propuestos por Mies van der Rohe y desarrollados por Walter Perterhans, y de los collage realizados por Mies para ilustrar su obra de arquitectura, como los realizados para el edificio de oficinas Bacardí en Santiago de Cuba el texto disecciona el universo mental de Mies.El adiestramiento del ojo propuesto por Mies en el IIT supone un adiestramiento en el orden de lo visual de enorme complejidad, pues el orden de la percepción no coincide con el orden de la construcción.Este desfase entre ambos universos plantea problemas casi irresolubles entre los que se debate el arquitecto y que el artículo, tras las lecturas que William Jordy, Robin Evans y Colin Rowe han realizado de la obra miesiana, pretende sintetizar y clarificar.El texto pretende asomarse a la tensión interna que, en la propia mente del arquitecto, alcanzan algunas de sus piezas, en un equilibrio altamente inestable, en el que la estructura superpuesta de la piel del edificio –la ‘representación de la estructura’– no puede sino anunciar con nostalgia el esplendor perdido del primer orden jerárquico estructural, que es de acero recubierto de hormigón, quedando, de esta manera a la vista, su condición inestable que se debate entre ser muro y ser esqueleto.Se proponen algunos conceptos clave extraídos de los cursos de Adiestramiento Visual y de algunos aspectos de la obra europea y americana de Mies a la luz de los cuales se puede hacer una relectura global de su obra: horizonte / obstáculo, textura / estructura, paisaje / material, percepción / construcción, totalidad / fragmento.Palabras claveforma, estructura, textura, percepción, construcci

  17. Tjaart van der Walt: slaaf van Christus – δοῦλος Χριστοῦ

    Directory of Open Access Journals (Sweden)

    E.J. Smit

    2011-06-01

    Full Text Available Tjaart van der Walt: slave of Christ – δοῦλος Χριστοῦ Tjaart van der Walt has carried an array of titles: from Boy, to Young Man, to Mister, to Reverend, to Doctorandus, to Doctor,to Professor, to Rector, to Vice-Chancellor, to CEO, to Ambassador! But the one title he gladly accepts, is “slave of Christ” – or in the Greek he loves so much: δοῦλος Χριστοῦ (doulos Christou! This has become typical of him and his life: a slave taking his instructions from Jesus Christ as his Owner, his Κύριος (Kurios, being willing to – in each situation and in relationship with any person or organisation – put on his slave clothing, roll up his sleeves, and serve! In this narrative of the life of Tjaart van der Walt we do not want to share lists of successes and failures, but rather we survey the serving life of this “slave of Christ”, as if from an Archimedes vantage point. The present, November 2011, is this Archimedes vantage point.

  18. De petten van de agent : Opkomst en ontwikkeling van de nieuwsagent in de Republiek der Nederlanden, 1600–1795

    NARCIS (Netherlands)

    Feringa, J

    2015-01-01

    Dit artikel beschrijft de opkomst van de ‘agent’ in de zeventiende eeuw. Meer specifiek komen de agenten aan bod die vanuit de Republiek hun opdrachtgevers bedienden, die zich voornamelijk buiten de Republiek bevonden. Aan de hand van de agency theory betoogt Feringa dat het ontstaan van het fenomee

  19. THz absorption spectrum of the CO2–H2O complex: Observation and assignment of intermolecular van der Waals vibrations

    OpenAIRE

    Andersen, Jonas; Heimdal, J.; Wallin Mahler Andersen, Denise; Nelander, B.; Larsen, René Wugt

    2014-01-01

    Terahertz absorption spectra have been recorded for the weakly bound CO2–H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems’ flat intermolecular potential energy surface. A (semi)-empirical value for the zero-point e...

  20. Communication: THz absorption spectrum of the CO2-H2O complex: Observation and assignment of intermolecular van der Waals vibrations.

    OpenAIRE

    Andersen, J.; Heimdal, Jimmy; Mahler, D W; Nelander, Bengt; Wugt Larsen, R

    2014-01-01

    Terahertz absorption spectra have been recorded for the weakly bound CO2-H2O complex embedded in cryogenic neon matrices at 2.8 K. The three high-frequency van der Waals vibrational transitions associated with out-of-plane wagging, in-plane rocking, and torsional motion of the isotopic H2O subunit have been assigned and provide crucial observables for benchmark theoretical descriptions of this systems' flat intermolecular potential energy surface. A (semi)-empirical value for the zero-poi...

  1. Mr. Jan van der Boon, Leader personnel division (PE) from 01.04.99 to 31.03.02. CERN Council 2000, new position, Mr. Jan van der Boon was nominated Director of Admnistration from 01.01.01 to 31.12.03.

    CERN Multimedia

    Paulo Pascoal

    1999-01-01

    Mr. Jan van der Boon, Leader personnel division (PE) from 01.04.99 to 31.03.02. CERN Council 2000, new position, Mr. Jan van der Boon was nominated Director of Admnistration from 01.01.01 to 31.12.03.

  2. Augmented van der Waals Compressibility Factor and its Application to Supercritical Fluids%推广的van der Waals 压缩因子及其对超临界流体的应用

    Institute of Scientific and Technical Information of China (English)

    窦晓冬; 刘国杰

    2001-01-01

    利用实验测得的液体的热压力系数,修正原始van der Waals模型中的排斥体积,得到了一个适用于高密度流体的推广的van der Waals压缩因子。将它与Redlich和Kwong提出的吸引项相结合,建立了一个流体状态方程。用某些有代表性的超临界流体的pVT数据检验,结果表明,其对体积、压力和逸度系数的计算准确度可与CS-RK方程相媲美。

  3. Photoionisation study of Xe.CF4 and Kr.CF4 van-der-Waals molecules.

    Science.gov (United States)

    Alekseev, V A; Garcia, G A; Kevorkyants, R; Nahon, L

    2016-05-14

    We report on photoionization studies of Xe.CF4 and Kr.CF4 van-der-Waals complexes produced in a supersonic expansion and detected using synchrotron radiation and photoelectron-photoion coincidence techniques. The ionization potential of CF4 is larger than those of the Xe and Kr atoms and the ground state of the Rg.CF4 (+) ion correlates with Rg(+) ((2)P3/2) + CF4. The onset of the Rg.CF4 (+) signals was found to be only ∼0.2 eV below the Rg ionization potential. In agreement with experiment, complementary ab initio calculations show that vertical transitions originating from the potential minimum of the ground state of Rg.CF4 terminate at a part of the potential energy surfaces of Rg.CF4 (+), which are approximately 0.05 eV below the Rg(+) ((2)P3/2) + CF4 dissociation limit. In contrast to the neutral complexes, which are most stable in the face geometry, for the Rg.CF4 (+) ions, the calculations show that the minimum of the potential energy surface is in the vertex geometry. Experiments which have been performed only with Xe.CF4 revealed no Xe.CF4 (+) signal above the first ionization threshold of Xe, suggesting that the Rg.CF4 (+) ions are not stable above the first dissociation limit.

  4. Review of “The kitchen as laboratory” edited by César Vega, Job Ubbink, and Erik van der Linden

    Directory of Open Access Journals (Sweden)

    Mouritsen Ole G

    2012-08-01

    Full Text Available Book details Vega C, Ubbink J, van der Linden E The Kitchen as Laboratory. Reflections on the Science of Food and Cooking. New York: Columbia University Press; 2012 312 pages, ISBN 978-0-231-15344-7

  5. Tuning electronic transport in epitaxial graphene-based van der Waals heterostructures

    Science.gov (United States)

    Lin, Yu-Chuan; Li, Jun; de La Barrera, Sergio C.; Eichfeld, Sarah M.; Nie, Yifan; Addou, Rafik; Mende, Patrick C.; Wallace, Robert M.; Cho, Kyeongjae; Feenstra, Randall M.; Robinson, Joshua A.

    2016-04-01

    Two-dimensional tungsten diselenide (WSe2) has been used as a component in atomically thin photovoltaic devices, field effect transistors, and tunneling diodes in tandem with graphene. In some applications it is necessary to achieve efficient charge transport across the interface of layered WSe2-graphene, a semiconductor to semimetal junction with a van der Waals (vdW) gap. In such cases, band alignment engineering is required to ensure a low-resistance, ohmic contact. In this work, we investigate the impact of graphene electronic properties on the transport at the WSe2-graphene interface. Electrical transport measurements reveal a lower resistance between WSe2 and fully hydrogenated epitaxial graphene (EGFH) compared to WSe2 grown on partially hydrogenated epitaxial graphene (EGPH). Using low-energy electron microscopy and reflectivity on these samples, we extract the work function difference between the WSe2 and graphene and employ a charge transfer model to determine the WSe2 carrier density in both cases. The results indicate that WSe2-EGFH displays ohmic behavior at small biases due to a large hole density in the WSe2, whereas WSe2-EGPH forms a Schottky barrier junction.Two-dimensional tungsten diselenide (WSe2) has been used as a component in atomically thin photovoltaic devices, field effect transistors, and tunneling diodes in tandem with graphene. In some applications it is necessary to achieve efficient charge transport across the interface of layered WSe2-graphene, a semiconductor to semimetal junction with a van der Waals (vdW) gap. In such cases, band alignment engineering is required to ensure a low-resistance, ohmic contact. In this work, we investigate the impact of graphene electronic properties on the transport at the WSe2-graphene interface. Electrical transport measurements reveal a lower resistance between WSe2 and fully hydrogenated epitaxial graphene (EGFH) compared to WSe2 grown on partially hydrogenated epitaxial graphene (EGPH). Using low

  6. Systematic study of electronic structure and band alignment of monolayer transition metal dichalcogenides in Van der Waals heterostructures

    Science.gov (United States)

    Zhang, Chenxi; Gong, Cheng; Nie, Yifan; Min, Kyung-Ah; Liang, Chaoping; Oh, Young Jun; Zhang, Hengji; Wang, Weihua; Hong, Suklyun; Colombo, Luigi; Wallace, Robert M.; Cho, Kyeongjae

    2017-03-01

    Two-dimensional transition metal dichalcogenides (TMDs) are promising low-dimensional materials which can produce diverse electronic properties and band alignment in van der Waals heterostructures. Systematic density functional theory (DFT) calculations are performed for 24 different TMD monolayers and their bilayer heterostacks. DFT calculations show that monolayer TMDs can behave as semiconducting, metallic or semimetallic depending on their structures; we also calculated the band alignment of the TMDs to predict their alignment in van der Waals heterostacks. We have applied the charge equilibration model (CEM) to obtain a quantitative formula predicting the highest occupied state of any type of bilayer TMD heterostacks (552 pairs for 24 TMDs). The CEM predicted values agree quite well with the selected DFT simulation results. The quantitative prediction of the band alignment in the TMD heterostructures can provide an insightful guidance to the development of TMD-based devices.

  7. Adaptive synchronization of two chaotic systems consisting of modified Van der Pol-Duffing and Chua oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Fotsin, Hilaire [Laboratoire d' electronique, Departement de Physique, Faculte des Sciences, Universite de Dschang, BP 067 Dschang (Cameroon); Laboratoire de Mathematiques Appliquees, Departement de Mathematiques et d' lnformatique, Faculte des sciences, Universite de Douala, BP 24157 Douala (Cameroon); E-mail: hbfotsin@yahoo.fr; Bowong, Samuel [CRAN-INPL-ENSEM-2, Avenue de la Foret de Haye-54516, Vandoeuvre-les-Nancy Cedex (France); E-mail: sbowong@uycdc.uninet.cm; Daafouz, Jamal [Laboratoire de Mathematiques Appliquees, Departement de Mathematiques et d' lnformatique, Faculte des sciences, Universite de Douala, BP 24157 Douala (Cameroon)

    2005-10-01

    In this paper, chaos synchronization between two chaotic systems consisting of modified Van der Pol-Duffing (MVDPD) and Chua oscillators is studied. Such a problem is related to chaos synchronization of different systems. An adaptive feedback synchronization with two controllers is proposed to ensure global chaos synchronization of the modified Van der Pol-Duffing and Chua circuit oscillators. Numerical simulations show the effectiveness of the proposed control method. Moreover, as an application, the proposed scheme is then applied to secure communication whose process consists of a robust filter that recovers the information signal from the scalar transmitted signal. Also, simulation results verify the proposed scheme's success in the communication application.

  8. Thermodynamics of lithium intercalation into graphite studied using density functional theory calculations incorporating van der Waals correlation and uncertainty estimation

    CERN Document Server

    Pande, Vikram

    2016-01-01

    Graphite is the most widely used and among the most widely-studied anode materials for lithium-ion batteries. Lithium intercalation into graphite has been extensively studied theoretically using density functional theory (DFT) calculations, complemented by experimental studies through X-ray diffraction, spectroscopy, optical imaging and other techniques. However, previous theoretical studies have not directly included van der Waals (vdW) interactions in their density functional theory calculations and vdW interactions play a crucial role in determining the stable phases. In this work, we present a first principles based model using DFT calculations, employing Bayesian Error Estimation Functional with van der Waals (BEEF-vdW) as the exchange correlation functional, and statistical thermodynamics to determine the phase transformations and subsequently, the thermodynamic intercalation potential diagram. We explore the entire configurational phase space by determining the important interactions and applying clust...

  9. The physics behind Van der Burgh's empirical equation, providing a new predictive equation for salinity intrusion in estuaries

    Science.gov (United States)

    Zhang, Zhilin; Savenije, Hubert H. G.

    2017-07-01

    The practical value of the surprisingly simple Van der Burgh equation in predicting saline water intrusion in alluvial estuaries is well documented, but the physical foundation of the equation is still weak. In this paper we provide a connection between the empirical equation and the theoretical literature, leading to a theoretical range of Van der Burgh's coefficient of 1/2 residual circulation. This type of mixing is relevant in the wider part of alluvial estuaries where preferential ebb and flood channels appear. Subsequently, this dispersion equation is combined with the salt balance equation to obtain a new predictive analytical equation for the longitudinal salinity distribution. Finally, the new equation was tested and applied to a large database of observations in alluvial estuaries, whereby the calibrated K values appeared to correspond well to the theoretical range.

  10. Quantum Transport Detected by Strong Proximity Interaction at a Graphene-WS2 van der Waals Interface.

    Science.gov (United States)

    O'Farrell, E C T; Avsar, A; Tan, J Y; Eda, G; Özyilmaz, B

    2015-09-09

    Magnetotransport measurements demonstrate that graphene in a van der Waals heterostructure is a sensitive probe of quantum transport in an adjacent WS2 layer via strong Coulomb interactions. We observe a large low-field magnetoresistance (≫ e(2)/h) and a -ln T temperature dependence of the resistance. In-plane magnetic field resistance indicates the origin is orbital and nonclassical. We demonstrate a strong electron-hole asymmetry in the mobility and coherence length of graphene demonstrating the presence of localized Coulomb interactions with ionized donors in the WS2 substrate, which ultimately leads to screening as the Fermi level of graphene is tuned toward the conduction band of WS2. This leads us to conclude that graphene couples to quantum localization processes in WS2 via the Coulomb interaction and results in the observed signatures of quantum transport. Our results show that theoretical descriptions of the van der Waals interface should not ignore localized strong correlations.

  11. Analysis of stochastic bifurcation and chaos in stochastic Duffing-van der Pol system via Chebyshev polynomial approximation

    Institute of Scientific and Technical Information of China (English)

    Ma Shao-Juan; Xu Wei; Li Wei; Fang Tong

    2006-01-01

    The Chebyshev polynomial approximation is applied to investigate the stochastic period-doubling bifurcation and chaos problems of a stochastic Duffing-van der Pol system with bounded random parameter of exponential probability density function subjected to a harmonic excitation. Firstly the stochastic system is reduced into its equivalent deterministic one, and then the responses of stochastic system can be obtained by numerical methods. Nonlinear dynamical behaviour related to stochastic period-doubling bifurcation and chaos in the stochastic system is explored. Numerical simulations show that similar to its counterpart in deterministic nonlinear system of stochastic period-doubling bifurcation and chaos may occur in the stochastic Duffing-van der Pol system even for weak intensity of random parameter.Simply increasing the intensity of the random parameter may result in the period-doubling bifurcation which is absent from the deterministic system.

  12. van der Waals forces in density functional theory: a review of the vdW-DF method.

    Science.gov (United States)

    Berland, Kristian; Cooper, Valentino R; Lee, Kyuho; Schröder, Elsebeth; Thonhauser, T; Hyldgaard, Per; Lundqvist, Bengt I

    2015-06-01

    A density functional theory (DFT) that accounts for van der Waals (vdW) interactions in condensed matter, materials physics, chemistry, and biology is reviewed. The insights that led to the construction of the Rutgers-Chalmers van der Waals density functional (vdW-DF) are presented with the aim of giving a historical perspective, while also emphasizing more recent efforts which have sought to improve its accuracy. In addition to technical details, we discuss a range of recent applications that illustrate the necessity of including dispersion interactions in DFT. This review highlights the value of the vdW-DF method as a general-purpose method, not only for dispersion bound systems, but also in densely packed systems where these types of interactions are traditionally thought to be negligible.

  13. Period-doubling cascades and strange attractors in the triple-well {phi}{sup 6}-Van der Pol oscillator

    Energy Technology Data Exchange (ETDEWEB)

    Yu Jun; Zhang Rongbo; Pan Weizhen [Department of Physics, Shaoxing University, Shaoxing 312000 (China); Schimansky-Geier, L [Institute of Physics, Humboldt-University at Berlin, Newton strasse 15, 12489 Berlin (Germany)

    2008-08-15

    Duffing-Van der Pol equation with the fifth nonlinear-restoring force is investigated. The bifurcation structure and chaotic motion under the periodic perturbation are obtained by numerical simulations. Numerical simulations, including bifurcation diagrams, Lyapunov exponents, phase portraits and Poincare maps, exhibit some new complex dynamical behaviors of the system. Different routes to chaos, such as period doubling and quasi-periodic routes, and various kinds of strange attractors are also demonstrated.

  14. Quasi-periodic bifurcations and “amplitude death” in low-dimensional ensemble of van der Pol oscillators

    Energy Technology Data Exchange (ETDEWEB)

    Emelianova, Yu.P., E-mail: yuliaem@gmail.com [Department of Electronics and Instrumentation, Saratov State Technical University, Polytechnicheskaya 77, Saratov 410054 (Russian Federation); Kuznetsov, A.P., E-mail: apkuz@rambler.ru [Kotel' nikov' s Institute of Radio-Engineering and Electronics of RAS, Saratov Branch, Zelyenaya 38, Saratov 410019 (Russian Federation); Turukina, L.V., E-mail: lvtur@rambler.ru [Kotel' nikov' s Institute of Radio-Engineering and Electronics of RAS, Saratov Branch, Zelyenaya 38, Saratov 410019 (Russian Federation); Institute for Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Str. 24-25, 14476 Potsdam (Germany)

    2014-01-10

    The dynamics of the four dissipatively coupled van der Pol oscillators is considered. Lyapunov chart is presented in the parameter plane. Its arrangement is discussed. We discuss the bifurcations of tori in the system at large frequency detuning of the oscillators. Here are quasi-periodic saddle-node, Hopf and Neimark–Sacker bifurcations. The effect of increase of the threshold for the “amplitude death” regime and the possibilities of complete and partial broadband synchronization are revealed.

  15. Chaotic vibration of the one-dimensional linear wave equation with a van der Pol nonlinear boundary condition

    Institute of Scientific and Technical Information of China (English)

    Guogang LIU; Yi ZHAO

    2004-01-01

    The one-dimensional linear wave equation with a van der Pol nonlinear boundary condition is one of the simplest models that may cause isotropic or nonisotropic chaotic vibrations.It characterizes the nonisotropic chaotic vibration by means of the total variation theory.Some results are derived on the exponential growth of total variation of the snapshots on the spatial interval in the long-time horizon when the map and the initial condition satisfy some conditions.

  16. A Componentwise Convex Splitting Scheme for Diffuse Interface Models with Van der Waals and Peng--Robinson Equations of State

    KAUST Repository

    Fan, Xiaolin

    2017-01-19

    This paper presents a componentwise convex splitting scheme for numerical simulation of multicomponent two-phase fluid mixtures in a closed system at constant temperature, which is modeled by a diffuse interface model equipped with the Van der Waals and the Peng-Robinson equations of state (EoS). The Van der Waals EoS has a rigorous foundation in physics, while the Peng-Robinson EoS is more accurate for hydrocarbon mixtures. First, the phase field theory of thermodynamics and variational calculus are applied to a functional minimization problem of the total Helmholtz free energy. Mass conservation constraints are enforced through Lagrange multipliers. A system of chemical equilibrium equations is obtained which is a set of second-order elliptic equations with extremely strong nonlinear source terms. The steady state equations are transformed into a transient system as a numerical strategy on which the scheme is based. The proposed numerical algorithm avoids the indefiniteness of the Hessian matrix arising from the second-order derivative of homogeneous contribution of total Helmholtz free energy; it is also very efficient. This scheme is unconditionally componentwise energy stable and naturally results in unconditional stability for the Van der Waals model. For the Peng-Robinson EoS, it is unconditionally stable through introducing a physics-preserving correction term, which is analogous to the attractive term in the Van der Waals EoS. An efficient numerical algorithm is provided to compute the coefficient in the correction term. Finally, some numerical examples are illustrated to verify the theoretical results and efficiency of the established algorithms. The numerical results match well with laboratory data.

  17. Van der Waals Type Model and Structure in bar{p}p Elastic Scattering at High Energies

    Science.gov (United States)

    Aleem, F.

    1983-10-01

    The most recent measurements of the angular distribution for bar{p}p elastic scattering at pL=50, 100 and 200 GeV/ c which show a structure near -t=1.4 (GeV/ c)2, with squared four momentum transter -t extended to 5(GeV/ c)2, and the total cross section data for 50 <= pL <= 280GeV/ c have been simultaneously fitted by using the Van der Waals type model.

  18. Recent progress in predicting structural and electronic properties of organic solids with the van der Waals density functional

    Energy Technology Data Exchange (ETDEWEB)

    Yanagisawa, Susumu, E-mail: shou@sci.u-ryukyu.ac.jp [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan); Okuma, Koji; Inaoka, Takeshi [Department of Physics and Earth Sciences, Faculty of Science, University of the Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213 (Japan); Hamada, Ikutaro, E-mail: Hamada.Ikutaro@nims.go.jp [International Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), Tsukuba 305-0044 (Japan)

    2015-10-01

    Highlights: • Review of theoretical studies on organic solids with the density-functional methods. • van der Waals (vdW)-inclusive methods to predict cohesive properties of oligoacenes. • A variant of the vdW density functional describes the structures accurately. • The molecular configuration and conformation crucially affects the band dispersion. - Abstract: We review recent studies on electronic properties of the organic solids with the first-principles electronic structure methods, with the emphasis on the roles of the intermolecular van der Waals (vdW) interaction in electronic properties of the organic semiconductors. After a brief summary of the recent vdW inclusive first-principle theoretical methods, we discuss their performance in predicting cohesive properties of oligoacene crystals as examples of organic crystals. We show that a variant of the van der Waals density functional describes structure and energetics of organic crystals accurately. In addition, we review our recent study on the zinc phthalocyanine crystal and discuss the importance of the intermolecular distance and orientational angle in the band dispersion. Finally, we draw some general conclusions and the future perspectives.

  19. Counterpoise correction is not useful for short and Van der Waals distances but may be useful at long range.

    Science.gov (United States)

    Sheng, Xiao Wei; Mentel, Lukasz; Gritsenko, Oleg V; Baerends, Evert Jan

    2011-10-01

    This article investigates the errors in supermolecule calculations for the helium dimer. In a full CI calculation, there are two errors. One is the basis set superposition error (BSSE), the other is the basis set convergence error (BSCE). Both of the errors arise from the incompleteness of the basis set. These two errors make opposite contributions to the interaction energies. The BSCE is by far the largest error in the short range and larger than (but much closer to) BSSE around the Van der Waals minimum. Only at the long range, the BSSE becomes the larger error. The BSCE and BSSE largely cancel each other over the Van der Waals well. Accordingly, it may be recommended to not include the BSSE for the calculation of the potential energy curve from short distance till well beyond the Van der Waals minimum, but it may be recommended to include the BSSE correction if an accurate tail behavior is required. Only if the calculation has used a very large basis set, one can refrain from including the counterpoise correction in the full potential range. These results are based on full CI calculations with the aug-cc-pVXZ (X = D, T, Q, 5) basis sets.

  20. Multiple critical points and liquid-liquid equilibria from the van der Waals like equations of state

    Energy Technology Data Exchange (ETDEWEB)

    Artemenko, Sergey; Lozovsky, Taras; Mazur, Victor [Thermodynamics Department, Academy of Refrigeration, 65082 Odessa (Ukraine)

    2008-06-18

    The principal aim of this work is a comprehensive analysis of the phase diagram of water via the van der Waals like equations of state (EoSs) which are considered as superpositions of repulsive and attractive forces. We test more extensively the modified van der Waals EoS (MVDW) proposed by Skibinski et al (2004 Phys. Rev. E 69 061206) and refine this model by introducing instead of the classical van der Waals repulsive term a very accurate hard sphere EoS over the entire stable and metastable regions (Liu 2006 Preprint cond-mat/0605392). It was detected that the simplest form of MVDW EoS displays a complex phase behavior, including three critical points, and identifies four fluid phases (gas, low density liquid (LDL), high density liquid (HDL), and very high density liquid (VHDL)). Moreover the experimentally observed (Mallamace et al 2007 Proc. Natl Acad. Sci. USA 104 18387) anomalous behavior of the density of water in the deeply supercooled region (a density minimum) is reproduced by the MWDW EoS. An improvement of the repulsive part does not change the topological picture of the phase behavior of water in the wide range of thermodynamic variables. The new parameters set for second and third critical points are recognized by thorough analysis of experimental data for the loci of thermodynamic response function extrema.

  1. Assessing the influence of van der Waals corrected exchange-correlation functionals on the anisotropic mechanical properties of coinage metals

    Science.gov (United States)

    Lee, Ji-Hwan; Park, Jong-Hun; Soon, Aloysius

    2016-07-01

    Current materials-related calculations employ density-functional theory (DFT), commonly using the (semi-)local-density approximations for the exchange-correlation (xc) functional. The difficulties in arriving at a reasonable description of van der Waals (vdW) interactions by DFT-based models is to date a big challenge. In this work, we use various flavors of vdW-corrected DFT xc functionals—ranging from the quasiempirical force-field add-on vdW corrections to self-consistent nonlocal correlation functionals—to study the bulk lattice and mechanical properties (including the elastic constants and anisotropic indices) of the coinage metals (copper, silver, and gold). We critically assess the reliability of the different vdW-corrected DFT methods in describing their anisotropic mechanical properties which have been less reported in the literature. In the context of this work, we regard that our results reiterate the fact that advocating a so-called perfect vdW-inclusive xc functional for describing the general physics and chemistry of these coinage metals could be a little premature. These challenges to modern-day functionals for anisotropically strained coinage metals (e.g., at the faceted surfaces of nanostructures) may well be relevant to other strained material systems.

  2. Binding mechanisms of DNA/RNA nucleobases adsorbed on graphene under charging: first-principles van der Waals study

    Science.gov (United States)

    Gürel, Hikmet Hakan; Salmankurt, Bahadır

    2017-06-01

    Graphene is a 2D material that has attracted much attention due to its outstanding properties. Because of its high surface area and unique chemical and physical properties, graphene is a good candidate for biological applications. For this reason, a deep understanding of the mechanism of interaction of graphene with biomolecules is required. In this study, theoretical investigation of van der Waals effects has been conducted using density functional theory. Here we show that the order of the binding energies of five nucleobases with graphene is G  >  A  >  T  >  C  >   U. This trend is in good agreement with most of the theoretical and experimental data. Also, the effects of charging on the electronic and structural properties of the graphene-nucleubase systems are studied for the first time. We show that the binding energy can be changed by adding or removing an electron from the system. The results presented in this work provide fundamental insights into the quantum interactions of DNA with carbon-based nanostructures and will be useful for developments in biotechnology and nanotechnology.

  3. Modulation of interfacial electronic properties in PbI2 and BN van der Waals heterobilayer via external electric field

    Science.gov (United States)

    Ma, Yaqiang; Zhao, Xu; Niu, Mengmeng; Dai, Xianqi; Li, Wei; Wang, Xiaolong; Zhao, Mingyu; Wang, Tianxing; Tang, Yanan

    2017-07-01

    The interfacial electronic properties of PbI2 and BN van der Waals (vdW) heterobilayer are explored by using density functional theory (DFT) method. An intrinsic type-II heterostructure with a wide bandgap is demonstrated. The spatial separation of the lowest energy electron-hole pairs can be actualised and make PbI2/BN heterostructure as a good candidate for applications in optoelectronics and solar cell. A simulation of Efield is actualized to modify its electronic properties. Band alignment converts from type-II to type-I heterostructure separated by a forward voltage with the value of about 0.07 V/Å. Three regions implying different Efield-sensitive properties are obtained from the variations of bandgap with Efield. The charge redistribution with an Efield is mainly on the surface of PbI2 and BN layers as well as the amount of electrons depends on the strength of Efield. In addition, the PbI2/BN heterobilayer exhibits more outstanding optical conductivity capability. Our results could bring forward a new perspective on sensor and shed light on the design of novel nano- and optoelectronics based on the PbI2/BN vdW heterostructure.

  4. A van der Waals DFT study of PtH2 systems absorbed on pristine and defective graphene

    Science.gov (United States)

    López-Corral, Ignacio; Piriz, Sebastián; Faccio, Ricardo; Juan, Alfredo; Avena, Marcelo

    2016-09-01

    We used a density functional that incorporates van der Waals interactions to study hydrogen adsorption onto Pt atoms attached to carbon-vacancies on graphene layers, considering molecular and dissociated hydrogen-platinum coordination structures. PtH2 complexes adsorbed on several sites of pristine graphene were also studied for comparison. Our results indicate that both a Kubas-type dihydrogen complex and a classic hydride without Hsbnd H bond are the preferential PtH2 systems on the vacancy site of graphene. In contrast, the Kubas complex is unstable onto pristine graphene and the hydride is obtained at all adsorption sites. Our simulations suggest that the C-vacancy decreases the reactivity of the metal decoration, allowing a non-dissociative hydrogen adsorption. The H2 molecule is oriented almost perpendicular to the outermost Csbnd Pt bond, interacting also with the graphene surface through σ-H and π-C states. This stabilization of the Kubas-type complex could play a very important role for hydrogen storage in Pt-decorated carbon adsorbents with vacancies.

  5. Vertical electron transport in van der Waals heterostructures with graphene layers

    Energy Technology Data Exchange (ETDEWEB)

    Ryzhii, V., E-mail: v-ryzhii@riec.tohoku.ac.jp [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Center for Photonics and Infrared Engineering, Bauman Moscow State Technical University and Institute of Ultra High Frequency Semiconductor Electronics of RAS, Moscow 111005 (Russian Federation); Otsuji, T. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Ryzhii, M. [Department of Computer Science and Engineering, University of Aizu, Aizu-Wakamatsu 965-8580 (Japan); Aleshkin, V. Ya.; Dubinov, A. A. [Institute for Physics of Microstructures of RAS and Lobachevsky State University of Nizhny Novgorod, Nizhny Novgorod 603950 (Russian Federation); Mitin, V. [Research Institute for Electrical Communication, Tohoku University, Sendai 980-8577 (Japan); Department of Electrical Engineering, University at Buffalo, Buffalo, New York 1460-1920 (United States); Shur, M. S. [Department of Electrical, Electronics, and Systems Engineering and Department of Physics, Applied Physics, and Astronomy, Rensselaer Polytechnic Institute, Troy, New York 12180 (United States)

    2015-04-21

    We propose and analyze an analytical model for the self-consistent description of the vertical electron transport in van der Waals graphene-layer (GL) heterostructures with the GLs separated by the barriers layers. The top and bottom GLs serve as the structure emitter and collector. The vertical electron transport in such structures is associated with the propagation of the electrons thermionically emitted from GLs above the inter-GL barriers. The model under consideration describes the processes of the electron thermionic emission from and the electron capture to GLs. It accounts for the nonuniformity of the self-consistent electric field governed by the Poisson equation which accounts for the variation of the electron population in GLs. The model takes also under consideration the cooling of electrons in the emitter layer due to the Peltier effect. We find the spatial distributions of the electric field and potential with the high-electric-field domain near the emitter GL in the GL heterostructures with different numbers of GLs. Using the obtained spatial distributions of the electric field, we calculate the current-voltage characteristics. We demonstrate that the Peltier cooling of the two-dimensional electron gas in the emitter GL can strongly affect the current-voltage characteristics resulting in their saturation. The obtained results can be important for the optimization of the hot-electron bolometric terahertz detectors and different devices based on GL heterostructures.

  6. Non-technical approach to the challenges of ecological architecture: Learning from Van der Laan

    Directory of Open Access Journals (Sweden)

    María-Jesús González-Díaz

    2016-06-01

    Full Text Available Up to now, ecology has a strong influence on the development of technical and instrumental aspects of architecture, such as renewable and efficient of resources and energy, CO2 emissions, air quality, water reuse, some social and economical aspects. These concepts define the physical keys and codes of the current ׳sustainable׳ architecture, normally instrumental but rarely and insufficiently theorised. But is not there another way of bringing us to nature? We need a theoretical referent. This is where we place the Van der Laan׳s thoughts: he considers that art completes nature and he builds his theoretical discourse on it, trying to better understand many aspects of architecture. From a conceptual point of view, we find in his works sense of timelessness, universality, special attention on the ׳locus׳ and a strict sense of proportions and use of materials according to nature. Could these concepts complement our current sustainable architecture? How did Laan apply the current codes of ecology in his architecture? His work may help us to get a theoretical interpretation of nature and not only physical. This paper develops this idea through the comparison of thoughts and works of Laan with the current technical approach to ׳sustainable׳ architecture.

  7. Nucleotide insertion initiated by van der Waals interaction during polymerase beta DNA replication

    CERN Document Server

    Arulsamy, Andrew Das

    2011-01-01

    Immortality will remain a fantasy for as long as aging is determined by the erroneous biochemical reactions during a particular DNA replication. The replication and base excision repair mechanism, associated to eukaryotic DNA polymerase-beta enzyme are central to maintaining a healthy cell. Here, we give a series of unambiguous theoretical analyses and prove that the exclusive biochemical reaction involved in a single nucleotide insertion into the DNA primer can be efficiently tracked using the renormalized van der Waals interaction of the stronger type, and the Hermansson blue-shifting hydrogen bond effect. We found that there are two biochemical steps involved to complete the insertion of a single dCTP into the 3' end of a DNA primer. First, the O3' (from a DNA primer) initiates the nucleophilic attack on P_alpha?(from an incoming dCTP), in response, O3_alpha (bonded to P_alpha) retaliates by interacting with H' (bonded to O3'). These interactions are shown to be strongly interdependent and require the form...

  8. Enthalpy, geometric volume and logarithmic correction to entropy for van der Waals black hole

    Science.gov (United States)

    Pradhan, Parthapratim

    2016-10-01

    If the negative cosmological constant is treated as a dynamical pressure and if the volume is its thermodynamically conjugate variable then the gravitational mass can be expressed as the total gravitational enthalpy rather than the energy. Under these circumtances, a new phenomenon emerges in the context of extended phase space thermodynamics. We examine here these features for the recently discovered van der Waals (VDW) black hole (BH) (Rajagopal A. et al., Phys. Lett. B, 737 (2014) 277) which is analogous to the VDW fluid. We show that the thermodynamic volume is greater than the naive geometric volume. We also show that the Smarr-Gibbs-Duhem relation is satisfied for this BH. Furthermore, by computing the thermal specific heat we find the local thermodynamic stability criterion for this BH. It has been observed that the BH does not possess any kind of second-order phase transition. This is an interesting feature of VDW BH by its own right. Moreover, we also derive the Cosmic-Censorship-Inequality for this class of BH. In addition finally, we compute the logarithmic correction to the entropy of this BH due to the quantum fluctuations around the thermal equilibrium.

  9. Enthalpy, Geometric Volume and Logarithmic correction to Entropy for Van-der-Waals Black Hole

    CERN Document Server

    Pradhan, Parthapratim

    2016-01-01

    If the negative cosmological constant is treated as a dynamical pressure and if the volume be its thermodynamically conjugate variable then the gravitational mass can be expressed as the total gravitational enthalpy rather than the energy. Under these circumstances, a new phenomena emerges in the context of extended phase space thermodynamics. We \\emph{examine} here these features for recently discovered Van-der-Waal (VDW) black hole (BH) \\cite{mann15} which is analogous to the VDW fluid. We show that the thermodynamic volume is \\emph{greater} than the naive geometric volume. We also show that the \\emph{Smarr-Gibbs-Duhem} relation is satisfied for this BH. Furthermore, by computing the thermal specific heat we find the local thermodynamic stability criterion for this BH. It has been observed that the BH does \\emph{not} possess any kind of second order phase transition. This is an interesting feature of VDW BH by its own right. Moreover, we also derive \\emph{Cosmic-Censorship-Inequality} for this class of BH. ...

  10. RESPONSE OF PARAMETRICALLY EXCITED DUFFING-VAN DER POL OSCILLATOR WITH DELAYED FEEDBACK

    Institute of Scientific and Technical Information of China (English)

    LI Xin-ye; CHEN Yu-shu; WU Zhi-qiang; SONG Tao

    2006-01-01

    The dynamical behaviour of a parametrically excited Duffing-van der Pol oscillator under linear-plus-nonlinear state feedback control with a time delay is concerned.By means of the method of averaging together with truncation of Taylor expansions, two slow-flow equations on the amplitude and phase of response were derived for the case of principal parametric resonance. It is shown that the stability condition for the trivial solution is only associated with the linear terms in the original systems besides the amplitude and frequency of parametric excitation. And the trivial solution can be stabilized by appreciate choice of gains and time delay in feedback control. Different from the case of the trivial solution, the stability condition for nontrivial solutions is also associated with nonlinear terms besides linear terms in the original system. It is demonstrated that nontrivial steady state responses may lose their stability by saddle-node (SN) or Hopf bifurcation (HB) as parameters vary. The simulations, obtained by numerically integrating the original system, are in good agreement with the analytical results.

  11. Stabilization of thin liquid films by repulsive van der waals force

    KAUST Repository

    Li, Erqiang

    2014-05-13

    Using high-speed video recording of bubble rise experiments, we study the stability of thin liquid films trapped between a rising bubble and a surfactant-free liquid-liquid meniscus interface. Using different combinations of nonpolar oils and water that are all immiscible, we investigate the extent to which film stability can be predicted by attractive and repulsive van der Waals (vdW) interactions that are indicated by the relative magnitude of the refractive indices of the liquid combinations, for example, water (refractive index, n = 1.33), perfluorohexane (n = 1.23), and tetradecane (n = 1.43). We show that, when the film-forming phase was oil (perfluorohexane or tetradecane), the stability of the film could always be predicted from the sign of the vdW interaction, with a repulsive vdW force resulting in a stable film and an attractive vdW force resulting in film rupture. However, if aqueous electrolyte is the film-forming bulk phase between the rising air bubble and the upper oil phase, the film always ruptured, even when a repulsive vdW interaction was predicted. We interpret these results as supporting the hypothesis that a short-ranged hydrophobic attraction determines the stability of the thin water film formed between an air phase and a nonpolar oil phase. © 2014 American Chemical Society.

  12. van der Waals Interactions in Hadron Resonance Gas: From Nuclear Matter to Lattice QCD.

    Science.gov (United States)

    Vovchenko, Volodymyr; Gorenstein, Mark I; Stoecker, Horst

    2017-05-05

    An extension of the ideal hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters a and b are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within the VDW-HRG model. Compared to the ideal HRG model, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of second and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region T∼140-190  MeV. For many observables this behavior resembles closely the results obtained from lattice QCD simulations. This hadronic model also predicts nontrivial behavior of net-baryon fluctuations in the region of phase diagram probed by heavy-ion collision experiments. These results imply that VDW interactions play a crucial role in the thermodynamics of hadron gas. Thus, the commonly performed comparisons of the ideal HRG model with the lattice and heavy-ion data may lead to misconceptions and misleading conclusions.

  13. Van der Waals-like behaviour of charged black holes and hysteresis in the dual QFTs

    Directory of Open Access Journals (Sweden)

    Mariano Cadoni

    2017-05-01

    Full Text Available Using the rules of the AdS/CFT correspondence, we compute the spherical analogue of the shear viscosity, defined in terms of the retarded Green function for the stress-energy tensor for QFTs dual to five-dimensional charged black holes of general relativity with a negative cosmological constant. We show that the ratio between this quantity and the entropy density, η˜/s, exhibits a temperature-dependent hysteresis. We argue that this hysteretic behaviour can be explained by the Van der Waals-like character of charged black holes, considered as thermodynamical systems. Under the critical charge, hysteresis emerges owing to the presence of two stable states (small and large black holes connected by a meta-stable region (intermediate black holes. A potential barrier prevents the equilibrium path between the two stable states; the system evolution must occur through the meta-stable region, and a path-dependence of η˜/s is generated.

  14. Esaki Diodes in van der Waals Heterojunctions with Broken-Gap Energy Band Alignment.

    Science.gov (United States)

    Yan, Rusen; Fathipour, Sara; Han, Yimo; Song, Bo; Xiao, Shudong; Li, Mingda; Ma, Nan; Protasenko, Vladimir; Muller, David A; Jena, Debdeep; Xing, Huili Grace

    2015-09-09

    van der Waals (vdW) heterojunctions composed of two-dimensional (2D) layered materials are emerging as a solid-state materials family that exhibits novel physics phenomena that can power a range of electronic and photonic applications. Here, we present the first demonstration of an important building block in vdW solids: room temperature Esaki tunnel diodes. The Esaki diodes were realized in vdW heterostructures made of black phosphorus (BP) and tin diselenide (SnSe2), two layered semiconductors that possess a broken-gap energy band offset. The presence of a thin insulating barrier between BP and SnSe2 enabled the observation of a prominent negative differential resistance (NDR) region in the forward-bias current-voltage characteristics, with a peak to valley ratio of 1.8 at 300 K and 2.8 at 80 K. A weak temperature dependence of the NDR indicates electron tunneling being the dominant transport mechanism, and a theoretical model shows excellent agreement with the experimental results. Furthermore, the broken-gap band alignment is confirmed by the junction photoresponse, and the phosphorus double planes in a single layer of BP are resolved in transmission electron microscopy (TEM) for the first time. Our results represent a significant advance in the fundamental understanding of vdW heterojunctions and broaden the potential applications of 2D layered materials.

  15. Global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback

    Institute of Scientific and Technical Information of China (English)

    2010-01-01

    This paper presents both analytical and numerical studies on the global view of Hopf bifurcations of a van der Pol oscillator with delayed state feedback.Based on a detailed analysis of the stability switches of the trivial equilibrium of the system,the stability charts are given in a parameter space consisting of the time delay and the feedback gains.The center manifold reduc-tion and the normal form method are used to study Hopf bifurcations with respect to the time delay.To gain an insight into the persistence of a Hopf bifurcation as the time delay varies farther away from its critical value,the method of multiple scales is used to obtain the global view of Hopf bifurcations with respect to the time delay.Both the analytical results of Hopf bifurca-tions and global view of those bifurcations are validated via a collocation scheme implemented on DDE-Biftool.The most important discovery in this paper is the well-structured global view of Hopf bifurcations for the system of concern,showing the generality of the persistence of Hopf bifurcations.

  16. Flexible Multiferroic Bulk Heterojunction with Giant Magnetoelectric Coupling via van der Waals Epitaxy.

    Science.gov (United States)

    Amrillah, Tahta; Bitla, Yugandhar; Shin, Kwangwoo; Yang, Tiannan; Hsieh, Ying-Hui; Chiou, Yu-You; Liu, Heng-Jui; Do, Thi Hien; Su, Dong; Chen, Yi-Chun; Jen, Shien-Uang; Chen, Long-Qing; Kim, Kee Hoon; Juang, Jenh-Yih; Chu, Ying-Hao

    2017-06-27

    Magnetoelectric nanocomposites have been a topic of intense research due to their profound potential in the applications of electronic devices based on spintronic technology. Nevertheless, in spite of significant progress made in the growth of high-quality nanocomposite thin films, the substrate clamping effect still remains a major hurdle in realizing the ultimate magnetoelectric coupling. To overcome this obstacle, an alternative strategy of fabricating a self-assembled ferroelectric-ferrimagnetic bulk heterojunction on a flexible muscovite via van der Waals epitaxy is adopted. In this study, we investigated the magnetoelectric coupling in a self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) bulk heterojunction epitaxially grown on a flexible muscovite substrate. The obtained heterojunction is composed of vertically aligned multiferroic BFO nanopillars embedded in a ferrimagnetic CFO matrix. Moreover, due to the weak interaction between the flexible substrate and bulk heterojunction, the interface is incoherent and, hence, the substrate clamping effect is greatly reduced. The phase-field simulation model also complements our results. The magnetic and electrical characterizations highlight the improvement in magnetoelectric coupling of the BFO-CFO bulk heterojunction. A magnetoelectric coupling coefficient of 74 mV/cm·Oe of this bulk heterojunction is larger than the magnetoelectric coefficient reported earlier on flexible substrates. Therefore, this study delivers a viable route of fabricating a remarkable magnetoelectric heterojunction and yet flexible electronic devices that are robust against extreme conditions with optimized performance.

  17. Optoelectronic Properties of Van Der Waals Hybrid Structures: Fullerenes on Graphene Nanoribbons

    Science.gov (United States)

    Correa, Julián David; Orellana, Pedro Alejandro; Pacheco, Mónica

    2017-01-01

    The search for new optical materials capable of absorbing light in the frequency range from visible to near infrared is of great importance for applications in optoelectronic devices. In this paper, we report a theoretical study of the electronic and optical properties of hybrid structures composed of fullerenes adsorbed on graphene and on graphene nanoribbons. The calculations are performed in the framework of the density functional theory including the van der Waals dispersive interactions. We found that the adsorption of the C60 fullerenes on a graphene layer does not modify its low energy states, but it has strong consequences for its optical spectrum, introducing new absorption peaks in the visible energy region. The optical absorption of fullerenes and graphene nanoribbon composites shows a strong dependence on photon polarization and geometrical characteristics of the hybrid systems, covering a broad range of energies. We show that an external electric field across the nanoribbon edges can be used to tune different optical transitions coming from nanoribbon–fullerene hybridized states, which yields a very rich electro-absorption spectrum for longitudinally polarized photons. We have carried out a qualitative analysis on the potential of these hybrids as possible donor-acceptor systems in photovoltaic cells. PMID:28336904

  18. Van der Waals forces and electron-electron interactions in two strained graphene layers

    Science.gov (United States)

    Sharma, Anand; Harnish, Peter; Sylvester, Alexander; Kotov, Valeri N.

    2014-03-01

    We evaluate the van der Waals (vdW) interaction energy at T=0 between two undoped graphene layers which are separated by a finite distance. Our study is carried out within the Random Phase Approximation and the interaction energy is obtained for variation in the strength of effective Coulomb interaction and anisotropy due to applied uniaxial strain. We consider the following three models for the anisotropic case: a) where one of the two layers is uniaxially strained, b) the two layers are strained in the same direction, and c) one of the layers is strained in the perpendicular direction. We find that for all the three models and any given value of the coupling, the vdW interaction energy increases with increasing anisotropy. The effect is most striking for the case when both the layers are strained in the parallel direction where we observe up to an order of magnitude increase in the strained graphene relative to the unstrained case. We also investigate the effect of intra-layer electron-electron interactions in the region of large separation between the strained graphene layers. We conclude that the many-body contributions to the correlation energy are non-negligible and the vdW interaction energy decreases as a function of increasing distance between the layers. Alexander Sylvester acknowledges financial assistance from the Research Experiences for Undergraduates (REU) Program of the National Science Foundation (NSF) focussing on complex materials.

  19. Stabilization of thin liquid films by repulsive van der Waals force.

    Science.gov (United States)

    Li, Er Qiang; Vakarelski, Ivan U; Chan, Derek Y C; Thoroddsen, Sigurdur T

    2014-05-13

    Using high-speed video recording of bubble rise experiments, we study the stability of thin liquid films trapped between a rising bubble and a surfactant-free liquid-liquid meniscus interface. Using different combinations of nonpolar oils and water that are all immiscible, we investigate the extent to which film stability can be predicted by attractive and repulsive van der Waals (vdW) interactions that are indicated by the relative magnitude of the refractive indices of the liquid combinations, for example, water (refractive index, n = 1.33), perfluorohexane (n = 1.23), and tetradecane (n = 1.43). We show that, when the film-forming phase was oil (perfluorohexane or tetradecane), the stability of the film could always be predicted from the sign of the vdW interaction, with a repulsive vdW force resulting in a stable film and an attractive vdW force resulting in film rupture. However, if aqueous electrolyte is the film-forming bulk phase between the rising air bubble and the upper oil phase, the film always ruptured, even when a repulsive vdW interaction was predicted. We interpret these results as supporting the hypothesis that a short-ranged hydrophobic attraction determines the stability of the thin water film formed between an air phase and a nonpolar oil phase.

  20. How van der Waals interactions determine the unique properties of water

    CERN Document Server

    Morawietz, Tobias; Dellago, Christoph; Behler, Jörg

    2016-01-01

    While the interactions between water molecules are dominated by strongly directional hydrogen bonds (HBs), it was recently proposed that relatively weak, isotropic van der Waals (vdW) forces are essential for understanding the properties of liquid water and ice. This insight was derived from ab initio computer simulations, which provide an unbiased description of water at the atomic level and yield information on the underlying molecular forces. However, the high computational cost of such simulations prevents the systematic investigation of the influence of vdW forces on the thermodynamic anomalies of water. Here we develop efficient ab initio-quality neural network potentials and use them to demonstrate that vdW interactions are crucial for the formation of water's density maximum and its negative volume of melting. Both phenomena can be explained by the flexibility of the HB network, which is the result of a delicate balance of weak vdW forces, causing e.g. a pronounced contraction of the second solvation ...

  1. Novel bursting patterns in a Van der pol-Duffing oscillator with slow varying external force

    Science.gov (United States)

    Yu, Yue; Zhao, Min; Zhang, Zhengdi

    2017-09-01

    In this paper, we investigate the emergence of bursting dynamics with complex waveforms and their relation to periodic behavior in typical Van der pol-Duffing equation with fifth order polynomial stiffness nonlinearity, when the external force changes slowly with the variation of time. We exploit bifurcation characteristics of the fast subsystem using the slowly changing periodic excitation as a bifurcation parameter to show how the bursting oscillations are created in this model. We also identify that some regimes of bursting patterns are related to codimension two bifurcation type over a wide range of parameters. A subsequent two-parameter continuation reveals a transition in the bursting behavior from fold/fold hysteresis cycle to sup-Hopf/sup-Hopf or limit point cycle/sub-Hopf bursting type. Furthermore, the effects of external forcing item on bursting oscillations are investigated. For instance, the time interval between two adjacent spikes of bursting oscillations is dependent on the forcing frequency. Some numerical simulations are included to illustrate the validity of our study.

  2. The influence of van der Waals interactions on a bubble moving in a tube

    CERN Document Server

    Hammoud, Naima; Howell, Peter D; Stone, Howard A

    2016-01-01

    We consider the unsteady thin-film dynamics of a long bubble of negligible viscosity that advances at a uniform speed in a cylindrical capillary tube. The bubble displaces a viscous non-wetting fluid, creating a thin film between its interface and the tube walls. The film is considered thin enough that intermolecular forces in the form of van der Waals attractions are significant and thin-film rupture is possible. In the absence of intermolecular forces, the bubble has a steady-state where a film of uniform thickness is deposited in the annular region between the bubble interface and the tube walls. However, once intermolecular forces are present, the bubble interface is perturbed out of its steady-state and either (i) the perturbation grows sufficiently before reaching the rear meniscus of the bubble such that rupture occurs; or (ii) the perturbation remains small due to weak intermolecular forces until it leaves the bubble interface through the rear meniscus. We obtain, both numerically and asymptotically, ...

  3. Neutron Reflectivity Study of Interdiffusion of Ionomers into Van der Waals Polymer Thin Films

    Science.gov (United States)

    Etampawala, Thusitha; Ratnaweera, Dilru; Wijesinghe, Sidath; Perahia, Dvora; Majewski, Jaroslaw

    2012-02-01

    The slow dynamic processes in amorphous ionic polymers are affected by physical cross-links resulting from clustering of the ionic groups. Therefore in addition to entanglement barriers, the motion of the polymers is coupled to the dynamics of the ionic clusters where the resulting dynamics is an interplay between the effects of the two types of barriers. Using neutron reflectometry we have probed a model system where interfacial diffusion of a Van der Waals polymer, polystyrene, into its sulfonated analogs. Results controlling the molecular weights that determine the overall number of entanglements as well as the degree of sulfonation which affects the strength and number of the ionic clusters will be presented. Comparison to the diffusion of polystyrene into polystyrene will resolve the effects of the ionic clusters from those of entanglements. The presence of the physical cross-links slows down the dynamics significantly with respect to that of polystyrene and an asymmetric process where the non-ionic blocks migrate into the ionic one is observed. Further rearrangements take place at a later stage.

  4. Resistive sensitivity functions for van der Pauw astroid and rounded crosses and cloverleafs

    Science.gov (United States)

    Koon, Daniel; Hansen, Ole

    2014-03-01

    We have calculated the sensitivity of van der Pauw resistances to local resistive variations for circular, square and astroid discs of infinitesimal thickness, as well as for the families of rounded crosses and cloverleafs, as a function of specimen parameters, using the direct formulas of our recent paper (Koon et al. 2013 J. Appl. Phys.114 163710) applied to ``reciprocally dual geometries'' (swapped Dirichlet and Neumann boundary conditions) described by Mareš et al.(2012 Meas. Sci. Technol. 23 045004). These results show that (a) the product of any such sensitivity function times differential area, and thus (b) the ratio of any two sensitivities, is invariant under conformal mapping, allowing for the pointwise determination of the conformal mapping function. The family of rounded crosses, which is bounded in parameter space by the square, the astroid and an ``infinitesimally thin'' cross, seems to represent the best geometry for focusing transport measurements on the center of the specimen while minimizing errors due to edge- or contact-effects. Made possible by an SLU Faculty research grant.

  5. FDE-vdW: A van der Waals Inclusive Subsystem Density-Functional Theory

    CERN Document Server

    Kevorkyants, Ruslan; Pavanello, Michele

    2014-01-01

    We present a formally exact van der Waals inclusive electronic structure theory, called FDE-vdW, based on the Frozen Density Embedding formulation of subsystem Density-Functional Theory. In subsystem DFT, the energy functional is composed of subsystem additive and non-additive terms. We show that an appropriate definition of the long-range correlation energy is given by the value of the non-additive correlation functional. This functional is evaluated using the Fluctuation-Dissipation Theorem aided by a formally exact decomposition of the response functions into subsystem contributions. FDE-vdW is derived in detail and several approximate schemes are proposed, which lead to practical implementations of the method. We show that FDE-vdW is Casimir-Polder consistent, i.e. it reduces to the generalized Casimir-Polder formula for asymptotic inter-subsystems separations. Pilot calculations of binding energies of 13 weakly bound complexes singled out from the S22 set show a dramatic improvement upon semilocal subsys...

  6. Role of van der Waals interactions for the intrinsic stability of polyalanine helices

    Science.gov (United States)

    Tkatchenko, Alexandre; Blum, Volker; Ireta, Joel; Scheffler, Matthias

    2009-03-01

    The helical motif is an ubiquitous conformation adopted by aminoacid residues in a protein structure and helix formation is the simplest example of the protein folding process. How stable is the folded peptide helix in comparison to a random coil structure? What are the interactions responsible for stabilizing the helical conformation? Answering these questions has thus a direct implication for understanding protein folding. In this work we use density functional theory (DFT) augmented with a non-empirical correction for van der Waals (vdW) forces to study the stability of alanine polypeptide helices in vacuo. We find a large stabilization of the native helical forms when vdW correction is used. It amounts to 121%, 157% and 83% on top of the Perdew-Burke-Ernzerhof (PBE) functional in the case of infinite α, π and 310 helices, respectively. Thus, the experimentally observed α helix is significantly stabilized by vdW forces both over the fully extended and the 310 conformations. Our findings also suggest an explanation to the remarkable stability of gas-phase alanine helices up to high temperatures [M. Kohtani et al. JACS 126, 7420 (2004)].

  7. Van der Waals interactions in hadron resonance gas: From nuclear matter to lattice QCD

    CERN Document Server

    Vovchenko, Volodymyr; Stoecker, Horst

    2016-01-01

    An extension of the ideal non-interacting hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters $a$ and $b$ are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within VDW-HRG model. Compared to the ideal non-interacting HRG, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of 2nd and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region $T \\sim 140 \\div 190$ MeV. For many observables this behavior resembles closely the results obtained from lattice QCD simulations. These results imply that VDW interactions play a crucial role in thermodynamics of hadron gas. Thus, the commonly performed compar...

  8. Density functional approximation for van der Waals fluids: based on hard sphere density functional approximation

    Institute of Scientific and Technical Information of China (English)

    Zhou Shi-Qi

    2007-01-01

    A universal theoretical approach is proposed which enables all hard sphere density functional approximations(DFAs) applicable to van der Waals fluids. The resultant DFA obtained by combining the universal theoretical approach with any hard sphere DFAs only needs as input a second-order direct correlation function (DCF) of a coexistence bulk fluid, and is applicable in both supercritical and subcritical temperature regions. The associated effective hard sphere density can be specified by a hard wall sum rule. It is indicated that the value of the effective hard sphere density so determined can be universal, i.e. can be applied to any external potentials different from the single hard wall. As an illustrating example, the universal theoretical approach is combined with a hard sphere bridge DFA to predict the density profile of a hard core attractive Yukawa model fluid influenced by diverse external fields; agreement between the present formalism's predictions and the corresponding simulation data is good or at least comparable to several previous DFT approaches. The primary advantage of the present theoretical approach combined with other hard sphere DFAs is discussed.

  9. Enhanced Li capacity in functionalized graphene: A first principle study with van der Waals correction

    Science.gov (United States)

    Chouhan, Rajiv K.; Raghani, Pushpa

    2015-09-01

    We have investigated the adsorption of Li on graphene oxide using density functional theory. We show a novel and simple approach to achieve a positive lithiation potential on epoxy and hydroxyl functionalized graphene, compared to the negative lithiation potential that has been found on prestine graphene. We included the van der Waals correction into the calculation so as to get a better picture of weak interactions. A positive lithiation potential suggests a favorable adsorption of Li on graphene oxide sheets that can lead to an increase in the specific capacity, which in turn can be used as an anode material in Li-batteries. We find a high specific capacity of ˜860 mAhg-1 by functionalizing the graphene sheet. This capacity is higher than the previously reported capacities that were achieved on graphene with high concentration of Stone-Wales (75%) and divacancy (16%) defects. Creating such high density of defects can make the entire system energetically unstable, whereas graphene oxide is a naturally occurring substance.

  10. Unusually efficient photocurrent extraction in monolayer van der Waals heterostructure by tunnelling through discretized barriers

    Science.gov (United States)

    Yu, Woo Jong; Vu, Quoc An; Oh, Hyemin; Nam, Hong Gi; Zhou, Hailong; Cha, Soonyoung; Kim, Joo-Youn; Carvalho, Alexandra; Jeong, Munseok; Choi, Hyunyong; Castro Neto, A. H.; Lee, Young Hee; Duan, Xiangfeng

    2016-11-01

    Two-dimensional layered transition-metal dichalcogenides have attracted considerable interest for their unique layer-number-dependent properties. In particular, vertical integration of these two-dimensional crystals to form van der Waals heterostructures can open up a new dimension for the design of functional electronic and optoelectronic devices. Here we report the layer-number-dependent photocurrent generation in graphene/MoS2/graphene heterostructures by creating a device with two distinct regions containing one-layer and seven-layer MoS2 to exclude other extrinsic factors. Photoresponse studies reveal that photoresponsivity in one-layer MoS2 is surprisingly higher than that in seven-layer MoS2 by seven times. Spectral-dependent studies further show that the internal quantum efficiency in one-layer MoS2 can reach a maximum of 65%, far higher than the 7% in seven-layer MoS2. Our theoretical modelling shows that asymmetric potential barriers in the top and bottom interfaces of the graphene/one-layer MoS2/graphene heterojunction enable asymmetric carrier tunnelling, to generate usually high photoresponsivity in one-layer MoS2 device.

  11. Free-standing electronic character of monolayer MoS2 in van der Waals epitaxy

    Science.gov (United States)

    Kim, HoKwon; Dumcenco, Dumitru; Frégnaux, Mathieu; Benayad, Anass; Chen, Ming-Wei; Kung, Yen-Cheng; Kis, Andras; Renault, Olivier

    2016-08-01

    We have evaluated as-grown Mo S2 crystals, epitaxially grown on a monocrystalline sapphire by chemical vapor deposition (CVD), with direct electronic band-structure measurements by energy-filtered k -space photoelectron emission microscopy performed with a conventional laboratory vacuum ultraviolet He I light source under off-normal illumination. The valence states of the epitaxial Mo S2 were mapped in momentum space down to 7 eV below the Fermi level. Despite the high nucleation density within the imaged area, the CVD Mo S2 possesses an electronic structure similar to the free-standing monolayer Mo S2 single crystal, and it exhibits hole effective masses of 2.41 ±0.05 m0 , and 0.81 ±0.05 m0 , respectively, at Γ and K high-symmetry points that are consistent with the van der Waals epitaxial growth mechanism. This demonstrates the excellent ability of the Mo S2 CVD on sapphire to yield a highly aligned growth of well-stitched grains through epitaxial registry with a strongly preferred crystallographic orientation.

  12. Rydberg blockade with multivalent atoms: effect of Rydberg series perturbation on van der Waals interactions

    CERN Document Server

    Topcu, Turker

    2015-01-01

    We investigate the effect of series perturbation on the second order dipole-dipole interactions between strontium atoms in $5sns({^1}S_0)$ and $5snp({^1}P_1)$ Rydberg states as a means of engineering long-range interactions between atoms in a way that gives an exceptional level of control over the strength and the sign of the interaction by changing $n$. We utilize experimentally available data to estimate the importance of perturber states at low $n$, and find that van der Waals interaction between two strontium atoms in the $5snp({^1}P_1)$ states shows strong peaks outside the usual hydrogenic $n^{11}$ scaling. We identify this to be the result of the perturbation of $5snd({^1}D_2)$ intermediate states by the $4d^2({^1}D_2)$ and $4dn's({^1}D_2)$ states in the $n<20$ range. This demonstrates that divalent atoms in general present a unique advantage for creating substantially stronger or weaker interaction strengths than those can be achieved using alkali metal atoms due to their highly perturbed spectra t...

  13. van der Waals Interactions in Hadron Resonance Gas: From Nuclear Matter to Lattice QCD

    Science.gov (United States)

    Vovchenko, Volodymyr; Gorenstein, Mark I.; Stoecker, Horst

    2017-05-01

    An extension of the ideal hadron resonance gas (HRG) model is constructed which includes the attractive and repulsive van der Waals (VDW) interactions between baryons. This VDW-HRG model yields the nuclear liquid-gas transition at low temperatures and high baryon densities. The VDW parameters a and b are fixed by the ground state properties of nuclear matter, and the temperature dependence of various thermodynamic observables at zero chemical potential are calculated within the VDW-HRG model. Compared to the ideal HRG model, the inclusion of VDW interactions between baryons leads to a qualitatively different behavior of second and higher moments of fluctuations of conserved charges, in particular in the so-called crossover region T ˜140 - 190 MeV . For many observables this behavior resembles closely the results obtained from lattice QCD simulations. This hadronic model also predicts nontrivial behavior of net-baryon fluctuations in the region of phase diagram probed by heavy-ion collision experiments. These results imply that VDW interactions play a crucial role in the thermodynamics of hadron gas. Thus, the commonly performed comparisons of the ideal HRG model with the lattice and heavy-ion data may lead to misconceptions and misleading conclusions.

  14. Van der Waals Interactions and Dipole Blockade in a Cold Rydberg Gas Probed by Microwave Spectroscopy

    Science.gov (United States)

    Nguyen, Thanh Long; Celistrino Teixeira, Raul; Hermann Avigliano, Carla; Cantat Moltrecht, Tigrane; Raimond, Jean Michel; Haroche, Serge; Gleyzes, Sebastiens; Brune, Michel

    2016-05-01

    Dipole-dipole interactions between Rydberg atoms are a flourishing tool for quantum information processing and for quantum simulation of complex many-body problems. Microwave spectroscopy of a dense Rydberg gas trapped close to a superconducting atom chip in the strong dipole blockade regime reveals directly the many-body atomic interaction spectrum. We present here a direct measurement of the interaction energy distribution in the strong dipole blockade regime, based on microwave spectroscopy. We first apply this method to the observation of the excitation dynamics of the Rydberg gas, conditioned by dipole-dipole interactions, in either the strong blockade regime or the so-called facilitation regime. We also observe with this method the atomic cloud expansion driven by the repulsive Van der Waals interaction after excitation. This measurement, in good agreement with Monte Carlo simulations of the excitation process and of the cloud dynamics, reveals the limits of the frozen gas approximation. This method can help investigate self-organization and dynamical phase transitions in Rydberg-atom based quantum simulators. This study thus opens a promising route for quantum simulation of many-body systems and quantum information transport in chains of strongly interacting Rydberg atom.

  15. Analytical modeling of static behavior of electrostatically actuated nano/micromirrors considering van der Waals forces

    Institute of Scientific and Technical Information of China (English)

    Hamid Moeenfard; Mohammad Taghi Ahmadian

    2012-01-01

    In this paper,the effect of van der Waals (vdW)force on the pull-in behavior of electrostatically actuated nano/micromirrors is investigated.First,the minimum potential energy principle is utilized to find the equation governing the static behavior of nano/microminror under electrostatic and vdW forces.Then,the stability of static equilibrium points is analyzed using the energy method.It is found that when there exist two equilibrium points,the smaller one is stable and the larger one is unstable.The effects of different design parameters on the mirror's pull-in angle and pull-in voltage are studied and it is found that vdW force can considerably reduce the stability limit of the mirror.At the end,the nonlinear equilibrium equation is solved numerically and analytically using homotopy perturbation method (HPM).It is observed that a sixth order perturbation approximation can precisely model the mirror's behavior.The resuits of this paper can be used for stable operation design and safe fabrication of torsional nano/micro actuators.

  16. Stochastic period-doubling bifurcation analysis of stochastic Bonhoeffer-van der Pol system

    Institute of Scientific and Technical Information of China (English)

    Zhang Ying; Xu Wei; Fang Tong; Xu Xu-Lin

    2007-01-01

    In this paper, the Chebyshev polynomial approximation is applied to the problem of stochastic period-doubling bifurcation of a stochastic Bonhoeffer-van der Pol (BVP for short) system with a bounded random parameter. In the analysis, the stochastic BVP system is transformed by the Chebyshev polynomial approximation into an equivalent deterministic system, whose response can be readily obtained by conventional numerical methods. In this way we have explored plenty of stochastic period-doubling bifurcation phenomena of the stochastic BVP system. The numerical simulations show that the behaviour of the stochastic period-doubling bifurcation in the stochastic BVP system is by and large similar to that in the deterministic mean-parameter BVP system, but there are still some featured differences between them. For example, in the stochastic dynamic system the period-doubling bifurcation point diffuses into a critical interval and the location of the critical interval shifts with the variation of intensity of the random parameter.The obtained results show that Chebyshev polynomial approximation is an effective approach to dynamical problems in some typical nonlinear systems with a bounded random parameter of an arch-like probability density function.

  17. Interface thermal conductance of van der Waals monolayers on amorphous substrates

    Science.gov (United States)

    Correa, Gabriela C.; Foss, Cameron J.; Aksamija, Zlatan

    2017-03-01

    Heterostructures based on atomic monolayers are emerging as leading materials for future energy efficient and multifunctional electronics. Due to the single atom thickness of monolayers, their properties are strongly affected by interactions with the external environment. We develop a model for interface thermal conductance (ITC) in an atomic monolayer van der Waals bonded to a disordered substrate. Graphene on SiO2 is initially used in our model and contrasted against available experimental data; the model is then applied to monolayer molybdenum disulfide (MoS2) on SiO2 substrate. Our findings show the dominant carrier of heat in both graphene and MoS2 in the cross-plane direction is the flexural (ZA) phonon mode, owing to the large overlap between graphene ZA and substrate vibrational density of states. The rate of phonon transfer across the interface depends quadratically on the substrate coupling constant K a , but this interaction also causes a lifting of the lowest flexural phonon modes. As a result, ITC depends roughly linearly on the strength of the coupling between a monolayer and its substrate. We conclude that, in both graphene and MoS2 on SiO2, substrate adhesion plays a strong role in determining ITC, requiring further study of substrate coupling in TMDCs.

  18. Compact wave function for bond dissociation and Van der Waals interactions: A natural amplitude assessment

    CERN Document Server

    Giesbertz, K J H

    2014-01-01

    Electron correlations in molecules can be divided in short range dynamical correlations, long range Van der Waals type interactions and near degeneracy static correlations. In this work we analyze how these three types of correlations can be incorporated in a simple wave function of restricted functional form consisting of an orbital product multiplied by a single correlation function $f(r_{12})$ depending on the interelectronic distance $r_{12}$. Since the three types of correlations mentioned lead to different signatures in terms of the natural orbital (NO) amplitudes in two-electron systems we make an analysis of the wave function in terms of the NO amplitudes for a model system of a diatomic molecule. In our numerical implementation we fully optimize the orbitals and the correlation function on a spatial grid without restrictions on their functional form. For the model system we can prove that none of the amplitudes vanishes and moreover that it displays a distinct sign pattern and a series of avoided cro...

  19. Subharmonic Resonance of Van Der Pol Oscillator with Fractional-Order Derivative

    Directory of Open Access Journals (Sweden)

    Yongjun Shen

    2014-01-01

    Full Text Available The subharmonic resonance of van der Pol (VDP oscillator with fractional-order derivative is studied by the averaging method. At first, the first-order approximate solutions are obtained by the averaging method. Then the definitions of equivalent linear damping coefficient (ELDC and equivalent linear stiffness coefficient (ELSC for subharmonic resonance are established, and the effects of the fractional-order parameters on the ELDC, the ELSC, and the dynamical characteristics of system are also analysed. Moreover, the amplitude-frequency equation and phase-frequency equation of steady-state solution for subharmonic resonance are established. The corresponding stability condition is presented based on Lyapunov theory, and the existence condition for subharmonic resonance (ECSR is also obtained. At last, the comparisons of the fractional-order and the traditional integer-order VDP oscillator are fulfilled by the numerical simulation. The effects of the parameters in fractional-order derivative on the steady-state amplitude, the amplitude-frequency curves, and the system stability are also studied.

  20. Infrared Spectroscopy of the H2/HD/D2-O2 Van Der Waals Complexes

    Science.gov (United States)

    Raston, Paul; Bunn, Hayley

    2016-06-01

    Hydrogen is the most abundant element in the universe and oxygen is the third, so understanding the interaction between the two in their different forms is important to understanding astrochemical processes. The interaction between H2 and O2 has been explored in low energy scattering experiments and by far infrared synchrotron spectroscopy of the van der Waals complex. The far infrared spectra suggest a parallel stacked average structure with seven bound rotationally excited states. Here, we present the far infrared spectrum of HD/D2-O2 and the mid infrared spectrum of H2-O2 at 80 K, recorded at the infrared beamline facility of the Australian Synchrotron. We observed 'sharp' peaks in the mid infrared region, corresponding to the end over end rotation of H2-O2, that are comparatively noisier than analogous peaks in the far infrared where the synchrotron light is brightest. The larger reduced mass of HD and D2 compared to H2 is expected to result in more rotational bound states and narrower bands. The latest results in our ongoing efforts to explore this system will be presented. Y. Kalugina, et al., Phys. Chem. Chem. Phys. 14, 16458 (2012) S. Chefdeville et al. Science 341, 1094 (2013) H. Bunn et al. ApJ 799, 65 (2015)

  1. Classical photodissociation dynamics with Bohr quantization: Application to the fragmentation of a van der Waals cluster

    Energy Technology Data Exchange (ETDEWEB)

    Arbelo-Gonzalez, W., E-mail: wilmer@instec.cu [Institut des Sciences Moleculaires, Universite Bordeaux 1, 351 Cours de la Liberation, 33405 Talence Cedex (France); Departamento de Fisica General, Instituto Superior de Tecnologias y Ciencias Aplicadas, Habana 10600 (Cuba); Bonnet, L., E-mail: l.bonnet@ism.u-bordeaux1.fr [Institut des Sciences Moleculaires, Universite Bordeaux 1, 351 Cours de la Liberation, 33405 Talence Cedex (France); Larregaray, P.; Rayez, J.-C. [Institut des Sciences Moleculaires, Universite Bordeaux 1, 351 Cours de la Liberation, 33405 Talence Cedex (France); Rubayo-Soneira, J. [Departamento de Fisica General, Instituto Superior de Tecnologias y Ciencias Aplicadas, Habana 10600 (Cuba)

    2012-05-03

    Graphical abstract: A recent classical description of photodissociation dynamics in a quantum spirit is applied for the first time to a realistic process, the fragmentation of NeBr{sub 2}. Highlights: Black-Right-Pointing-Pointer The photo-dissociation of NeBr{sub 2} is studied by means of two approaches. Black-Right-Pointing-Pointer The first is the standard classical one with Gaussian binning. Black-Right-Pointing-Pointer The second is a new method applied for the first time to a realistic system. Black-Right-Pointing-Pointer The new method leads to exactly the same results as the standard one. Black-Right-Pointing-Pointer However, it requires about 10 times less trajectories in the present case. - Abstract: The recent classical dynamical approach of photodissociations with Bohr quantization [L. Bonnet, J. Chem. Phys. 133 (2010) 174108] is applied for the first time to a realistic process, the photofragmentation of the van der Waals cluster NeBr{sub 2}. We illustrate the fact that this approach, formally equivalent to the standard one, may be numerically much more efficient.

  2. Efficient Oscillator-Based Approach for Polarizability and van der Waals Interactions

    Science.gov (United States)

    Gobre, Vivekanand; Distasio, Robert A., Jr.; Car, Roberto; Scheffler, Matthias; Tkatchenko, Alexandre

    2013-03-01

    The dynamic polarizability measures the response to an applied time-dependent electric field, and its accurate determination is crucial for van der Waals (vdW) interactions and other response properties. First-principles calculations of polarizabilities in principle require a computationally expensive explicit treatment of many-electron excitations, and are only applicable in practice to systems with less than about 100 atoms. In this work, we present an efficient parameter-free approach for calculating accurate frequency dependent polarizabilities for molecules with thousands of atoms, as well as periodic materials. This is achieved by the synergistic coupling of the Tkatchenko-Scheffler method, which accurately treats short-range hybridization effects, with the self-consistent screening equation from classical electrodynamics. Using only the electron density and free atom reference, we obtain an accuracy of 7% for both static polarizabilities and vdW coefficients for an extensive database of gas-phase molecules and crystals. We analyze the interplay of hybridization and long-range electrostatic screening effects on the polarizability.

  3. Comparing van der Waals DFT methods for water on NaCl(001) and MgO(001).

    Science.gov (United States)

    Kebede, Getachew G; Spångberg, Daniel; Mitev, Pavlin D; Broqvist, Peter; Hermansson, Kersti

    2017-02-14

    In this work, a range of van der Waals type density functionals are applied to the H2O/NaCl(001) and H2O/MgO(001) interface systems to explore the effect of an explicit dispersion treatment. The functionals we use are the self-consistent vdW functionals vdW-DF, vdW-DF2, optPBE-vdW, optB88-vdW, optB86b-vdW, and vdW-DF-cx, as well as the dispersion-corrected PBE-TS and PBE-D2 methods; they are all compared with the standard PBE functional. For both NaCl(001) and MgO(001), we find that the dispersion-flavoured functionals stabilize the water-surface interface by approximately 20%-40% compared to the PBE results. For NaCl(001), where the water molecules remain intact for all overlayers, the dominant contribution to the adsorption energy from "density functional theory dispersion" stems from the water-surface interactions rather than the water-water interactions. The optPBE-vdW and vdW-DF-cx functionals yield adsorption energies in good agreement with available experimental values for both NaCl and MgO. To probe the strengths of the perturbations of the adsorbed water molecules, we also calculated water dipole moments and found an increase up to 85% for water at the MgO(001) surface and 70% at the NaCl(001) surface, compared to the gas-phase dipole moment.

  4. Thermal electron attachment to oxygen and van der Waals molecules containing oxygen

    Energy Technology Data Exchange (ETDEWEB)

    Shimamori, H.; Fessenden, R.W.

    1981-01-01

    Thermal electron attachment to O/sub 2/ has been studied for pure O/sub 2/ (/sup 16/O/sub 2/ and /sup 18/O/sub 2/), O/sub 2/--N/sub 2/, O/sub 2/--CO, and O/sub 2/--n-C/sub 4/H/sub 10/ (/sup 16/O/sub 2/ and /sup 18/O/sub 2/) systems at temperatures from approx.330 down to 78/sup 0/ K using pulse radiolysis and microwave conductivity. For pure O/sub 2/, O/sub 2/--N/sub 2/, and O/sub 2/--CO mixtures, the electron attachment rates showed three-body pressure dependences at all temperatures over the pressure range studied (P/sub O2/<10Torr, P/sub N2/<60 Torr, P/sub CO/<40 Torr). The three-body rate constant of /sup 16/O/sub 2/ decreases from approx.2.4 x 10/sup -30/ cm/sup 6/ molecule/sup -2/ sec/sup -1/ at 330 /sup 0/K to about 0.9 x 10/sup -30/ cm/sup 6/ molecule/sup -2/ sec/sup -1/ at approx. 140 /sup 0/K but unexpectedly increases again to about 1.7 x 10/sup -30/ cm/sup 6/ molecule/sup -2/ sec/sup -1/ at 79 /sup 0/K. Similarly, the three-body rate constant of /sup 18/O/sub 2/ decreases from 5.1 x 10/sup -30/ cm/sup 6/ molecule/sup -2/ sec/sup -1/ at 300 /sup 0/K to 1.8 x 10/sup -30/ cm/sup 6/ molecule/sup -2/ sec/sup -1/ at approx.110 /sup 0/K but increases to 2.3 x 10/sup -30/ cm/sup 6/ molecule/sup -2/ sec/sup -1/ at 80 /sup 0/K. The three-body rate constant of N/sub 2/ shows a more dramatic monotonic increase from 0.9 x 10/sup -31/ cm/sup 6/ molecule/sup -2/ sec/sup -1/ at 300 /sup 0/K to 9.4 x 10/sup -31/ cm/sup 6/ molecule/sup -2/ sec/sup -1/ at 78 /sup 0/K. In the case of CO, the three-body rate constant appears to have a very shallow minimum around 170 /sup 0/K and again increases with further decrease of temperature. Since theory predicts a simple decrease in rate constant with reduced temperature, an extra contribution to the rate constant which increases with lowered temperature is evident. Electron attachment to the van der Waals molecules (O/sub 2/)/sub 2/, (O/sub 2/xN/sub 2/), and (O/sub 2/xCO) is proposed to account for this behavior. It has been found

  5. Macht, machinaties en musea. Jan van der Hoeven, Hermann Schlegel en hun strijd om het Rijksmuseum van natuurlijke historie te Leiden

    Directory of Open Access Journals (Sweden)

    H.L. de Jonge

    2005-01-01

    Full Text Available Might, machinations and museums. Jan van der Hoeven, Hermann Schlegel and their battle over the National Museum for Natural History in LeidenMuseums had a central place in nineteenth-century natural history. Aside from being important places for carrying out research into nature, they were also powerful vehicles for transmitting and communicating scientific knowledge. That is why, in the nineteenth century, natural history museums were frequently battlegrounds for rival scientists. Often, clashes over scientific matters were at the same time conflicts about power and space. After all, the naturalist who could get control over a museum’s collection and decide how the specimens should be classified and exhibited ultimately had the power to dictate which scientific knowledge was communicated; which story was told by a collection of specimens. This article is about the power struggle over the directorate of the National Museum of Natural History in Leiden that broke out between Jan van der Hoeven, Professor of Natural History and Comparative Anatomy at Leiden and Herman Schlegel, the museum’s chief curator. Both were rooted in very different natural historical traditions and had completely different views on the role of the museum and how the collection should be arranged and exhibited. In this article, we follow the two scientists in their attempts to gain support for their nominations. In this way, we also get a picture of nineteenth century Dutch political culture and the role scientists could play in it.

  6. Vibrations of double-nanotube systems with mislocation via a newly developed van der Waals model

    Science.gov (United States)

    Kiani, Keivan

    2015-06-01

    This study deals with transverse vibrations of two adjacent-parallel-mislocated single-walled carbon nanotubes (SWCNTs) under various end conditions. These tubes interact with each other and their surrounding medium through the intertube van der Waals (vdW) forces, and existing bonds between their atoms and those of the elastic medium. The elastic energy of such forces due to the deflections of nanotubes is appropriately modeled by defining a vdW force density function. In the previous works, vdW forces between two identical tubes were idealized by a uniform form of this function. The newly introduced function enables us to investigate the influences of both intertube free distance and longitudinal mislocation on the natural transverse frequencies of the nanosystem which consists of two dissimilar tubes. Such crucial issues have not been addressed yet, even for simply supported tubes. Using nonlocal Timoshenko and higher-order beam theories as well as Hamilton's principle, the strong form of the equations of motion is established. Seeking for an explicit solution to these integro-partial differential equations is a very problematic task. Thereby, an energy-based method in conjunction with an efficient meshfree method is proposed and the nonlocal frequencies of the elastically embedded nanosystem are determined. For simply supported nanosystems, the predicted first five frequencies of the proposed model are checked with those of assumed mode method, and a reasonably good agreement is achieved. Through various studies, the roles of the tube's length ratio, intertube free space, mislocation, small-scale effect, slenderness ratio, radius of SWCNTs, and elastic constants of the elastic matrix on the natural frequencies of the nanosystem with various end conditions are explained. The limitations of the nonlocal Timoshenko beam theory are also addressed. This work can be considered as a vital step towards better realizing of a more complex system that consists of

  7. Spectral mixing formulations for van der Waals-London dispersion interactions between multicomponent carbon nanotubes.

    Science.gov (United States)

    Rajter, Rick; French, Roger H; Podgornik, Rudi; Ching, W Y; Parsegian, V Adrian

    2008-09-01

    Recognition of spatially varying optical properties is a necessity when studying the van der Waals-London dispersion (vdW-Ld) interactions of carbon nanotubes (CNTs) that have surfactant coatings, tubes within tubes, andor substantial core sizes. The ideal way to address these radially dependent optical properties would be to have an analytical add-a-layer solution in cylindrical coordinates similar to the one readily available for the plane-plane geometry. However, such a formulation does not exist nor does it appear trivial to be obtained exactly. The best and most pragmatic alternative for end-users is to take the optical spectra of the many components and to use a spectral mixing formulation so as to create effective solid-cylinder spectra for use in the far-limit regime. The near-limit regime at "contact" is dominated by the optical properties of the outermost layer, and thus no spectral mixing is required. Specifically we use a combination of a parallel capacitor in the axial direction and the Bruggeman effective medium in the radial direction. We then analyze the impact of using this mixing formulation upon the effective vdW-Ld spectra and the resulting Hamaker coefficients for small and large diameter single walled CNTs (SWCNTs) in both the near- and far-limit regions. We also test the spectra of a [16,0,s+7,0,s] multiwalled CNT (MWCNT) with an effective MWCNT spectrum created by mixing its [16,0,s] and [7,0,s] SWCNT components to demonstrate nonlinear coupling effects that exist between neighboring layers. Although this paper is primarily on nanotubes, the strategies, implementation, and analysis presented are applicable and likely necessary to any system where one needs to resolve spatially varying optical properties in a particular Lifshitz formulation.

  8. Thermal transport across carbon nanotube-graphene covalent and van der Waals junctions

    Science.gov (United States)

    Shi, Jingjing; Dong, Yalin; Fisher, Timothy; Ruan, Xiulin

    2015-07-01

    Carbon nanotubes and graphene are promising materials for thermal management applications due to their high thermal conductivities. However, their thermal properties are anisotropic, and the radial or cross-plane direction thermal conductivity is low. A 3D Carbon nanotube (CNT)-graphene structure has previously been proposed to address this limitation, and direct molecular dynamics simulations have been used to predict the associated thermal conductivity. In this work, by recognizing that thermal resistance primarily comes from CNT-graphene junctions, a simple network model of thermal transport in pillared graphene structure is developed. Using non-equilibrium molecular dynamics, the resistance across an individual CNT-graphene junction with sp2 covalent bonds is found to be around 6 ×10-11 m2K/W, which is significantly lower than typical values reported for planar interfaces between dissimilar materials. In contrast, the resistance across a van der Waals junction is about 4 ×10-8 m2K/W. Interestingly, when the CNT pillar length is small, the interfacial resistance of the sp2 covalent junction is found to decrease as the CNT pillar length decreases, suggesting the presence of coherence effects. To explain this intriguing trend, the junction thermal resistance is decomposed into interfacial region and boundary components, and it is found that while the boundary resistance has little dependence on the pillar length, the interfacial region resistance decreases as the pillar length decreases. This is explained by calculating the local phonon density of states (LDOS) of different regions near the boundary. The LDOS overlap between the interfacial region and the center region of CNT increases as the pillar length decreases, leading to the decrease of interfacial region resistance. The junction resistance Rj is eventually used in the network model to estimate the effective thermal conductivity, and the results agree well with direct MD simulation data, demonstrating the

  9. van der Waals epitaxy of CdTe thin film on graphene

    Science.gov (United States)

    Mohanty, Dibyajyoti; Xie, Weiyu; Wang, Yiping; Lu, Zonghuan; Shi, Jian; Zhang, Shengbai; Wang, Gwo-Ching; Lu, Toh-Ming; Bhat, Ishwara B.

    2016-10-01

    van der Waals epitaxy (vdWE) facilitates the epitaxial growth of materials having a large lattice mismatch with the substrate. Although vdWE of two-dimensional (2D) materials on 2D materials have been extensively studied, the vdWE for three-dimensional (3D) materials on 2D substrates remains a challenge. It is perceived that a 2D substrate passes little information to dictate the 3D growth. In this article, we demonstrated the vdWE growth of the CdTe(111) thin film on a graphene buffered SiO2/Si substrate using metalorganic chemical vapor deposition technique, despite a 46% large lattice mismatch between CdTe and graphene and a symmetry change from cubic to hexagonal. Our CdTe films produce a very narrow X-ray rocking curve, and the X-ray pole figure analysis showed 12 CdTe (111) peaks at a chi angle of 70°. This was attributed to two sets of parallel epitaxy of CdTe on graphene with a 30° relative orientation giving rise to a 12-fold symmetry in the pole figure. First-principles calculations reveal that, despite the relatively small energy differences, the graphene buffer layer does pass epitaxial information to CdTe as the parallel epitaxy, obtained in the experiment, is energetically favored. The work paves a way for the growth of high quality CdTe film on a large area as well as on the amorphous substrates.

  10. Controlling Electronic Transitions in Fullerene van der Waals Aggregates via Supramolecular Assembly.

    Science.gov (United States)

    Das, Saunak; Herrmann-Westendorf, Felix; Schacher, Felix H; Täuscher, Eric; Ritter, Uwe; Dietzek, Benjamin; Presselt, Martin

    2016-08-24

    Morphologies crucially determine the optoelectronic properties of organic semiconductors. Therefore, hierarchical and supramolecular approaches have been developed for targeted design of supramolecular ensembles of organic semiconducting molecules and performance improvement of, e.g., organic solar cells (OSCs), organic light emitting diodes (OLEDs), and organic field-effect transistors (OFETs). We demonstrate how the photonic properties of fullerenes change with the formation of van der Waals aggregates. We identified supramolecular structures with broadly tunable absorption in the visible spectral range and demonstrated how to form aggregates with targeted visible (vis) absorption. To control supramolecular structure formation, we functionalized the C60-backbone with polar (bis-polyethylene glycol malonate-MPEG) tails, thus yielding an amphiphilic fullerene derivative that self-assembles at interfaces. Aggregates of systematically tuned size were obtained from concentrating MPEGC60 in stearic acid matrices, while different supramolecular geometries were provoked via different thin film preparation methods, namely spin-casting and Langmuir-Blodgett (LB) deposition from an air-water interface. We demonstrated that differences in molecular orientation in LB films (C2v type point group aggregates) and spin-casting (stochastic aggregates) lead to huge changes in electronic absorption spectra due to symmetry and orientation reasons. These differences in the supramolecular structures, causing the different photonic properties of spin-cast and LB films, could be identified by means of quantum chemical calculations. Employing supramolecular assembly, we propounded that molecular symmetry in fullerene aggregates is extremely important in controlling vis absorption to harvest photons efficiently, when mixed with a donor molecule, thus improving active layer design and performance of OSCs.

  11. Comparative study of van der Waals corrections to the bulk properties of graphite.

    Science.gov (United States)

    Rêgo, Celso R C; Oliveira, Luiz N; Tereshchuk, Polina; Da Silva, Juarez L F

    2015-10-21

    Graphite is a stack of honeycomb (graphene) layers bound together by nonlocal, long-range van der Waals (vdW) forces, which are poorly described by density functional theory (DFT) within local or semilocal exchange-correlation functionals. Several approximations have been proposed to add a vdW correction to the DFT total energies (Stefan Grimme (D2 and D3) with different damping functions (D3-BJ), Tkatchenko-Scheffler (TS) without and with self-consistent screening (TS  +  SCS) effects). Those corrections have remarkly improved the agreement between our results and experiment for the interlayer distance (from 3.9 to 0.6%) [corrected] and high-level random-phase approximation (RPA) calculations for interlayer binding energy (from 69.5 to 1.5%). [corrected]. We report a systematic investigation of various structural, energetic and electron properties with the aforementioned vdW corrections followed by comparison with experimental and theoretical RPA data. Comparison between the resulting relative errors shows that the TS  +  SCS correction provides the best results; the other corrections yield significantly larger errors for at least one of the studied properties. If considerations of computational costs or convergence problems rule out the TS  +  SCS approach, we recommend the D3-BJ correction. Comparison between the computed π(z)Γ-splitting and experimental results shows disagreements of 10% or more with all vdW corrections. Even the computationally more expensive hybrid PBE0 has proved unable to improve the agreement with the measured splitting. Our results indicate that improvements of the exchange-correlation functionals beyond the vdW corrections are necessary to accurately describe the band structure of graphite.

  12. PENELITIAN SPESIES SIBLING NYAMUK ANOPHELES BARBIROSTRIS VAN DER WULP DI INDONESIA

    Directory of Open Access Journals (Sweden)

    S. Sukowati

    2012-11-01

    Full Text Available Malaria continues to be a public health problem of high priority in the majority of malaria endemic countries of the South East Asia region, such as Indonesia. Vector control remain the most effective measure to prevent malaria transmission. The study of mosquito species complexes and the understanding of the biology, evolution as well as epidemiology of malaria transmission and the possibly of development of efficient control measures against malaria have been subjects of greatly increased interest in recent years. Natural populations of Anopheles barbirostris Van der Wulp were sampled from 5 geographically isolated populations in Indonesia: (1 Ambarawa, Central Java. (2 Tara-Tara, North Sulawesi, (3 Boru-Boru, (4 Konga and (5 Tanjung Bunga, the last three in Flores, East Nusa Tenggara. Analysis of larval mitotic chromosomes had been made from F I progeny of isofemale lines derived from these 5 populations. Specimens from these populations appear to share a similar mitotic karyotype (2n=6 consisting of two pairs of autosomes and one pair of sex chromosomes. The Giemsa staining of mitotic chromosomes of the An. barbirostris complex showed considerable variation in the amount and distribution of constitutive heterochromatin in sex chromosomes. These cytological differences have led to the recognation of 4 distinct cytological forms within the taxon An. barbirostris, viz., form A (X1,X2,X3,Y1, form B (X1,X2,X3,Y2 form C (X2,X3,Y3 and form D (X2,X3,Y4. Form A is widely distributed in Indonesia, while, form Band D have been found in sympatric association with form A in Tara-tara 2, North Sulawesi; Konga, Flores and Tanjung Bunga, Form C, however, has been found only in Boru-Boru, and sympatric with forms A and B. Keywords: Anopheles barbirostris, malaria, mitotic chromosome, sibling species

  13. Aggregation of BiTe monolayer on Bi2Te3 (111) induced by diffusion of intercalated atoms in the van der Waals gap

    Science.gov (United States)

    Wang, Zhi-Wen; Huang, Wen-Kai; Zhang, Kai-Wen; Shu, Da-Jun; Wang, Mu; Li, Shao-Chun

    2017-03-01

    We report a postgrowth aging mechanism of Bi2Te3 (111) films with scanning tunneling microscopy in combination with density functional theory calculation. It is found that a monolayered structure with a squared lattice symmetry gradually aggregates from the surface steps. Theoretical calculations indicate that the van der Waals (vdW) gap not only acts as a natural reservoir for self-intercalated Bi and Te atoms, but also provides them easy diffusion pathways. Once hopping out of the gap, these defective atoms prefer to develop into a two-dimensional BiTe superstructure on the Bi2Te3 (111) surface driven by positive energy gain. Considering the common nature of weak bonding between vdW layers, we expect such unusual diffusion and aggregation of the intercalated atoms may be of general importance for most kinds of vdW layered materials.

  14. Growth and characterization of van der Waals heterostuctures formed by the topological insulator Bi2Se3 and the trivial insulator SnSe2

    Science.gov (United States)

    Matetskiy, A. V.; Kibirev, I. A.; Zotov, A. V.; Saranin, A. A.

    2016-07-01

    The formation, structure and electronic properties of SnSe2-Bi2Se3 van der Waals heterostructures were studied. Both heterostructures, SnSe2 on Bi2Se3 and Bi2Se3 on SnSe2, were grown epitaxially with high crystallinity and sharp interfaces. Their electron band structures are of trivial and topological insulators, respectively. The Dirac surface states of Bi2Se3 survive under the SnSe2 overlayer. One triple layer of SnSe2 was found to be an efficient spacer for separating a Bi2Se3 topological-insulator slab into two and creating the corresponding topological surface states.

  15. Concordancia radiológica intra e interobservador del método de Sharp-Van der Heijde / Radiological agreement intra and interobserver of Sharp–Van der Heijde method

    OpenAIRE

    Luna Hernández, David Ricardo

    2010-01-01

    El método de Sharp–Van der Heijde es utilizado para evaluar y medir la progresión del daño articular y establecer los efectos del tratamiento en radiografías de manos y pies de pacientes con artritis reumatoidea. El objetivo de este estudio fue evaluar la confiabilidad de la escala de SVdH determinando la concordancia intra e interobservador entre radiólogos utilizando radiografías de pacientes colombianos con artritis reumatoidea. Se incluyeron 102 radiografías digitalizadas (51 de manos (en...

  16. Determination of silicon and chromium content in gray cast iron by the Van der Pauw method; Determinacion del contenido de silicio y cromo en fundiciones grises mediante el metodo de Van der Pauw

    Energy Technology Data Exchange (ETDEWEB)

    Tremps, E.; Enrique, J. L.; Moron, C.; Garcia, A.; Gomez, A.

    2013-07-01

    In this paper we show a system based on the resistivity measurement of samples of gray cast iron by the Van der Pauw method to calculate the silicon content in the samples. Twenty five trials have been carried out, studying resistive and metallographic characteristics of the samples. This has demonstrated that it is possible to obtain, by this method, the silicon content in molten flat with low content of alloying elements, also the content of chromium in series smelters where the rate of silicon remains constant. (Author)

  17. Cálculo do volume na equação de van der Waals pelo método de cardano Volume calculation in van der Waals equation by the cardano method

    Directory of Open Access Journals (Sweden)

    Nelson H. T. Lemes

    2010-01-01

    Full Text Available Analytical solutions of a cubic equation with real coefficients are established using the Cardano method. The method is first applied to simple third order equation. Calculation of volume in the van der Waals equation of state is afterwards established. These results are exemplified to calculate the volumes below and above critical temperatures. Analytical and numerical values for the compressibility factor are presented as a function of the pressure. As a final example, coexistence volumes in the liquid-vapor equilibrium are calculated. The Cardano approach is very simple to apply, requiring only elementary operations, indicating an attractive method to be used in teaching elementary thermodynamics.

  18. Comments on "Changing attitudes towards the care of children in hospital: a new assessment of the influence of the work of Bowlby and Robertson in the UK, 1940-1970" by Frank C.P. van der Horst and Rene van der Veer (Attachment & Human Development Vol 11, No 2, March 2009, 119-142).

    Science.gov (United States)

    Robertson, Joyce; McGilly, Katherine

    2009-11-01

    The importance of James Robertson's work in changing the hospital conditions for young children is widely acknowledged but disputed by van der Horst and van der Veer (2009), although they presented evidence supporting his influence, they also presented considerable evidence showing that others were ignored, including writers in The Lancet and the British Medical Journal. van der Horst and van der Veer presented a muddled picture by failing to understand how the work of James Robertson influenced a wide range of people, opened up the debate and, through the Platt Report, gave parents the authority and confidence to challenge hospitals and stay with their young children. James Robertson's 1952 film "a Two-year-old Goes to Hospital" provided the 'visual communication to pierce defences as the spoken word cannot do'. This film continues to be widely used today in teaching about young children.

  19. Effect of van der Waals forces on thermal conductance at the interface of a single-wall carbon nanotube array and silicon

    Science.gov (United States)

    Feng, Ya; Zhu, Jie; Tang, Dawei

    2014-12-01

    Molecular dynamics simulations are performed to evaluate the effect of van der Waals forces among single-wall carbon nanotubes (SWNTs) on the interfacial thermal conductance between a SWNT array and silicon substrate. First, samples of SWNTs vertically aligned on silicon substrate are simulated, where both the number and arrangement of SWNTs are varied. Results reveal that the interfacial thermal conductance of a SWNT array/Si with van der Waals forces present is higher than when they are absent. To better understand how van der Waals forces affect heat transfer through the interface between SWNTs and silicon, further constructs of one SWNT surrounded by different numbers of other ones are studied, and the results show that the interfacial thermal conductance of the central SWNT increases with increasing van der Waals forces. Through analysis of the covalent bonds and vibrational density of states at the interface, we find that heat transfer across the interface is enhanced with a greater number of chemical bonds and that improved vibrational coupling of the two sides of the interface results in higher interfacial thermal conductance. Van der Waals forces stimulate heat transfer at the interface.

  20. Effect of van der Waals forces on thermal conductance at the interface of a single-wall carbon nanotube array and silicon

    Directory of Open Access Journals (Sweden)

    Ya Feng

    2014-12-01

    Full Text Available Molecular dynamics simulations are performed to evaluate the effect of van der Waals forces among single-wall carbon nanotubes (SWNTs on the interfacial thermal conductance between a SWNT array and silicon substrate. First, samples of SWNTs vertically aligned on silicon substrate are simulated, where both the number and arrangement of SWNTs are varied. Results reveal that the interfacial thermal conductance of a SWNT array/Si with van der Waals forces present is higher than when they are absent. To better understand how van der Waals forces affect heat transfer through the interface between SWNTs and silicon, further constructs of one SWNT surrounded by different numbers of other ones are studied, and the results show that the interfacial thermal conductance of the central SWNT increases with increasing van der Waals forces. Through analysis of the covalent bonds and vibrational density of states at the interface, we find that heat transfer across the interface is enhanced with a greater number of chemical bonds and that improved vibrational coupling of the two sides of the interface results in higher interfacial thermal conductance. Van der Waals forces stimulate heat transfer at the interface.