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Sample records for waals forces accounts

  1. Evaluation of a density functional with account of van der Waals forces using experimental data of H2 physisorption on Cu(111)

    DEFF Research Database (Denmark)

    Lee, Kyuho; Kelkkanen, Kari André; Berland, Kristian

    2011-01-01

    Detailed experimental data for physisorption potential-energy curves of H2 on low-indexed faces of Cu challenge theory. Recently, density-functional theory has been developed to also account for nonlocal correlation effects, including van der Waals forces. We show that one functional, denoted vd...

  2. Van der Waals-like forces between hadrons induced by color confining potentials

    International Nuclear Information System (INIS)

    Gavela, M.B.; Yaouanc, A. le; Oliver, L.; Pene, O.; Raynal, J.C.; Sood, S.

    1979-01-01

    The London treatment of van der Waals forces is generalized to long-range forces induced by instantaneous confining potentials. Special attention is given to the problem of accounting for the intermediate colour-octet states. The result is in contradiciton with data on nucleon-nucleon phase shifts for any confining potential V(r) = -a(Σsub(A)lambdasup(A)lambda sup(A))rsup(α) for α > 0.1. (Auth.)

  3. Contribution of van der Waals forces to the plasticity of magnesium

    International Nuclear Information System (INIS)

    Ding, Zhigang; Liu, Wei; Li, Shuang; Zhang, Dalong; Zhao, Yonghao; Lavernia, Enrique J.; Zhu, Yuntian

    2016-01-01

    The accurate determination of stacking fault energies (SFE) and associated restoring forces is important for understanding plastic deformation, especially the dislocation emission and motion in metals. In this work, we use density-functional theory (DFT) calculations to, systematically study the all-dimension relaxed atomic models of Mg crystal slip, with a special focus on the “subslip modes” in prismatic and pyramidal slip systems. We find that slip systems with large interplanar distances are readily activated, which agrees well with experimental observations. Inclusion of the ubiquitous van der Waals (vdW) interactions results in lower generalized stacking fault energy curves. Remarkably, the unstable SFE value of pyramidal-II system is strongly reduced by up to 69 mJ/m 2 , and the related restoring stress is lowered by 0.74 GPa after taking into account the vdW energy. Our calculations indicate significant effect of vdW forces on the plasticity of Mg. - Graphical abstract: By using density-functional theory calculations, we systematically study the generalized stacking fault energy for pure Mg, and demonstrated pronounced contributions of van der Waals forces to the plasticity of Mg.

  4. van der Waals forces in density functional theory: Perturbational long-range electron-interaction corrections

    International Nuclear Information System (INIS)

    Angyan, Janos G.; Gerber, Iann C.; Savin, Andreas; Toulouse, Julien

    2005-01-01

    Long-range exchange and correlation effects, responsible for the failure of currently used approximate density functionals in describing van der Waals forces, are taken into account explicitly after a separation of the electron-electron interaction in the Hamiltonian into short- and long-range components. We propose a 'range-separated hybrid' functional based on a local density approximation for the short-range exchange-correlation energy, combined with a long-range exact exchange energy. Long-range correlation effects are added by a second-order perturbational treatment. The resulting scheme is general and is particularly well adapted to describe van der Waals complexes, such as rare gas dimers

  5. Density functional for van der Waals forces accounts for hydrogen bond in benchmark set of water hexamers

    DEFF Research Database (Denmark)

    Kelkkanen, Kari André; Lundqvist, Bengt; Nørskov, Jens Kehlet

    2009-01-01

    A recent extensive study has investigated how various exchange-correlation (XC) functionals treat hydrogen bonds in water hexamers and has shown traditional generalized gradient approximation and hybrid functionals used in density-functional (DF) theory to give the wrong dissociation-energy trend...... of low-lying isomers and van der Waals (vdW) dispersion forces to give key contributions to the dissociation energy. The question raised whether functionals that incorporate vdW forces implicitly into the XC functional predict the correct lowest-energy structure for the water hexamer and yield accurate...

  6. Contribution of the covalent and the Van der Waals force to the nuclear binding

    International Nuclear Information System (INIS)

    Rosina, M.; Povh, B.

    1994-01-01

    The contribution of the covalent and the Van der Waals force to the nuclear binding is estimated in a simplified model for medium distance of about 1 fm. It is shown how colour effects suppress these two forces as compared to the case of the forces between atoms. The covalent and the Van der Waals force represent a minor though noticeable component of the nuclear force. (orig.)

  7. Quark confinement potential and color Van der Waals force

    International Nuclear Information System (INIS)

    Zheng Yuming; Hua Daping; Liu Zuhua

    1985-01-01

    The color-analog Van der Waals force between two hadrons is studied by use of the coupling channel resonating group method in the framework of the Gaussian-type quark confinement potential. The problem of the boundary values for the two channel coupling differential equations is changed to the problem of the initial values. The equations are solved numerically by use of the Gear mehtod. The calculated results show that there is no color Van der Waals force between hadrons in the confinement potential model. This indicates that the confinement potential model not only can describe the internal structure of hadrons but also can be used to calculate the hadron-hadron interactions if the quark confinement potential is chosen properly

  8. 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...

  9. Resonance oscillations of nonreciprocal long-range van der Waals forces between atoms in electromagnetic fields

    Science.gov (United States)

    Sherkunov, Yury

    2018-03-01

    We study theoretically the van der Waals interaction between two atoms out of equilibrium with an isotropic electromagnetic field. We demonstrate that at large interatomic separations, the van der Waals forces are resonant, spatially oscillating, and nonreciprocal due to resonance absorption and emission of virtual photons. We suggest that the van der Waals forces can be controlled and manipulated by tuning the spectrum of artificially created random light.

  10. Accurate van der Waals force field for gas adsorption in porous materials.

    Science.gov (United States)

    Sun, Lei; Yang, Li; Zhang, Ya-Dong; Shi, Qi; Lu, Rui-Feng; Deng, Wei-Qiao

    2017-09-05

    An accurate van der Waals force field (VDW FF) was derived from highly precise quantum mechanical (QM) calculations. Small molecular clusters were used to explore van der Waals interactions between gas molecules and porous materials. The parameters of the accurate van der Waals force field were determined by QM calculations. To validate the force field, the prediction results from the VDW FF were compared with standard FFs, such as UFF, Dreiding, Pcff, and Compass. The results from the VDW FF were in excellent agreement with the experimental measurements. This force field can be applied to the prediction of the gas density (H 2 , CO 2 , C 2 H 4 , CH 4 , N 2 , O 2 ) and adsorption performance inside porous materials, such as covalent organic frameworks (COFs), zeolites and metal organic frameworks (MOFs), consisting of H, B, N, C, O, S, Si, Al, Zn, Mg, Ni, and Co. This work provides a solid basis for studying gas adsorption in porous materials. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  11. Van der Waals Forces and Photon-Less Effective Field Theory

    International Nuclear Information System (INIS)

    Arriola, E.R.

    2011-01-01

    In the ultra-cold regime Van der Waals forces between neutral atoms can be represented by short range effective interactions. We show that universal low energy scaling features of the underlying vdW long range force stemming from two photon exchange impose restrictions on an Effective Field Theory without explicit photons. The role of naively redundant operators, relevant to the definition of three body forces, is also analyzed. (author)

  12. Many body effects in the van der Waals force

    International Nuclear Information System (INIS)

    Perez, P.; Claro, F.

    1985-08-01

    A classical model of fluctuating dipoles is proposed for the evaluation of many-body effects in the van der Waals force between neutral polarizable particles. The method is applied to solid xenon giving the correct low temperature stable structure, unlike the usual two-body potential result. (author)

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

    International Nuclear Information System (INIS)

    Lin, A.Y.M.; Brunner, R.; Chen, P.Y.; Talke, F.E.; Meyers, M.A.

    2009-01-01

    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 (∼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.

  15. 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.

  16. Theoretical investigation of the distance dependence of capillary and van der Waals forces in scanning force microscopy

    International Nuclear Information System (INIS)

    Stifter, Thomas; Marti, Othmar; Bhushan, Bharat

    2000-01-01

    The capillary and van der Waals forces between a tip and a plane in a scanning force microscope (SFM) are calculated. The forces are calculated for a fixed distance of tip and sample, as well as during retracting of the tip from the sample surface. The exact geometric shape of the meniscus is considered, with the boundary condition of fixed liquid volume during retraction. The starting volume is given by the operating and environmental conditions (surface tension, humidity, and tip geometry) at the point of lowest distance between tip and surface. The influence of the different parameters, namely, humidity, tip geometry, tip-sample starting distance, surface tension, and contact angles are studied. For each force curve also the geometric shape of the meniscus is calculated. The capillary forces are compared with van der Waals forces to understand their relative importance in various operating conditions. In addition to application in SFM, this analysis is useful in the design of surface roughness in microdevices for low adhesion in operating environments

  17. 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.

  18. Color van der Waals force acting in heavy-ion scattering at low energies

    International Nuclear Information System (INIS)

    Hussein, M.S.; Lima, C.L.; Pato, M.P.; Bertulani, C.A.

    1990-01-01

    The influence of the color van der Waals force in the elastic scattering of 208 Pb on 208 Pb at sub-barrier energies is studied. The conspicuous changes in the Mott oscillation found here are suggested as a possible experimental test

  19. Closed-form approximation and numerical validation of the influence of van der Waals force on electrostatic cantilevers at nano-scale separations

    Energy Technology Data Exchange (ETDEWEB)

    Ramezani, Asghar [School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Alasty, Aria [Center of Excellence in Design, Robotics, and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of); Akbari, Javad [Center of Excellence in Design, Robotics, and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

    2008-01-09

    In this paper the two-point boundary value problem (BVP) of the cantilever deflection at nano-scale separations subjected to van der Waals and electrostatic forces is investigated using analytical and numerical methods to obtain the instability point of the beam. In the analytical treatment of the BVP, the nonlinear differential equation of the model is transformed into the integral form by using the Green's function of the cantilever beam. Then, closed-form solutions are obtained by assuming an appropriate shape function for the beam deflection to evaluate the integrals. In the numerical method, the BVP is solved with the MATLAB BVP solver, which implements a collocation method for obtaining the solution of the BVP. The large deformation theory is applied in numerical simulations to study the effect of the finite kinematics on the pull-in parameters of cantilevers. The centerline of the beam under the effect of electrostatic and van der Waals forces at small deflections and at the point of instability is obtained numerically. In computing the centerline of the beam, the axial displacement due to the transverse deformation of the beam is taken into account, using the inextensibility condition. The pull-in parameters of the beam are computed analytically and numerically under the effects of electrostatic and/or van der Waals forces. The detachment length and the minimum initial gap of freestanding cantilevers, which are the basic design parameters, are determined. The results of the analytical study are compared with the numerical solutions of the BVP. The proposed methods are validated by the results published in the literature.

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

    KAUST Repository

    Cheng, Yingchun; Zhu, Zhiyong; Schwingenschlö gl, Udo

    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.

  1. Combination Rules for Morse-Based van der Waals Force Fields.

    Science.gov (United States)

    Yang, Li; Sun, Lei; Deng, Wei-Qiao

    2018-02-15

    In traditional force fields (FFs), van der Waals interactions have been usually described by the Lennard-Jones potentials. Conventional combination rules for the parameters of van der Waals (VDW) cross-termed interactions were developed for the Lennard-Jones based FFs. Here, we report that the Morse potentials were a better function to describe VDW interactions calculated by highly precise quantum mechanics methods. A new set of combination rules was developed for Morse-based FFs, in which VDW interactions were described by Morse potentials. The new set of combination rules has been verified by comparing the second virial coefficients of 11 noble gas mixtures. For all of the mixed binaries considered in this work, the combination rules work very well and are superior to all three other existing sets of combination rules reported in the literature. We further used the Morse-based FF by using the combination rules to simulate the adsorption isotherms of CH 4 at 298 K in four covalent-organic frameworks (COFs). The overall agreement is great, which supports the further applications of this new set of combination rules in more realistic simulation systems.

  2. Film Thickness Formation in Nanoscale due to Effects of Elastohydrodynamic, Electrostatic and Surface force of Solvation and Van der Waals

    Directory of Open Access Journals (Sweden)

    M.F. Abd Al-Samieh

    2017-03-01

    Full Text Available The mechanism of oil film with a thickness in the nanoscale is discussed in this paper. A polar lubricant of propylene carbonate is used as the intervening liquid between contiguous bodies in concentrated contacts. A pressure caused by the hydrodynamic viscous action in addition to double layer electrostatic force, Van der Waals inter-molecular forces, and solvation pressure due to inter-surface forces is considered in calculating the ultrathin lubricating films. The numerical solution has been carried out, using the Newton-Raphson iteration technique, applied for the convergence of the hydrodynamic pressure. The results show that, at separations beyond about five molecular diameters of the intervening liquid, the formation of a lubricant film thickness is governed by combined effects of viscous action and surface force of an attractive Van der Waals force and a repulsive double layer force. At smaller separations below about five molecular diameters of the intervening liquid, the effect of solvation force is dominant in determining the oil film thickness

  3. 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.

  4. 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.

  5. 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

  6. Average and extreme multi-atom Van der Waals interactions: Strong coupling of multi-atom Van der Waals interactions with covalent bonding

    Directory of Open Access Journals (Sweden)

    Finkelstein Alexei V

    2007-07-01

    Full Text Available Abstract Background The prediction of ligand binding or protein structure requires very accurate force field potentials – even small errors in force field potentials can make a 'wrong' structure (from the billions possible more stable than the single, 'correct' one. However, despite huge efforts to optimize them, currently-used all-atom force fields are still not able, in a vast majority of cases, even to keep a protein molecule in its native conformation in the course of molecular dynamics simulations or to bring an approximate, homology-based model of protein structure closer to its native conformation. Results A strict analysis shows that a specific coupling of multi-atom Van der Waals interactions with covalent bonding can, in extreme cases, increase (or decrease the interaction energy by about 20–40% at certain angles between the direction of interaction and the covalent bond. It is also shown that on average multi-body effects decrease the total Van der Waals energy in proportion to the square root of the electronic component of dielectric permittivity corresponding to dipole-dipole interactions at small distances, where Van der Waals interactions take place. Conclusion The study shows that currently-ignored multi-atom Van der Waals interactions can, in certain instances, lead to significant energy effects, comparable to those caused by the replacement of atoms (for instance, C by N in conventional pairwise Van der Waals interactions.

  7. 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.

  8. Efimov states near a Feshbach resonance and the limits of van der Waals universality at finite background scattering length

    Science.gov (United States)

    Langmack, Christian; Schmidt, Richard; Zwerger, Wilhelm

    2018-03-01

    We calculate the spectrum of three-body Efimov bound states near a Feshbach resonance within a model which accounts both for the finite range of interactions and the presence of background scattering. The latter may be due to direct interactions in an open channel or a second overlapping Feshbach resonance. It is found that background scattering gives rise to substantial changes in the trimer spectrum as a function of the detuning away from a Feshbach resonance, in particular in the regime where the background channel supports Efimov states on its own. Compared to the situation with negligible background scattering, the regime where van der Waals universality applies is shifted to larger values of the resonance strength if the background scattering length is positive. For negative background scattering lengths, in turn, van der Waals universality extends to even small values of the resonance strength parameter, consistent with experimental results on Efimov states in 39K. Within a simple model, we show that short-range three-body forces do not affect van der Waals universality significantly. Repulsive three-body forces may, however, explain the observed variation between around -8 and -10 of the ratio between the scattering length where the first Efimov trimer appears and the van der Waals length.

  9. The Van der Waals-force-induced phononic band gap and resonant scattering in two-nanosphere aggregate

    International Nuclear Information System (INIS)

    Wu Jiuhui; Zhang Siwen; Zhou Kejiang

    2012-01-01

    A physical mechanism of phononic band gap and resonant nanoacoustic scattering in an aggregate of two elastic nanospheres is presented in this paper. By considering the Van der Waals (VdW) force between two nanospheres illuminated by nanoacoustic wave, phononic band gap and frequency shift at the lower frequency side, and largely enhanced nanoacoustic scattering at the other frequency range have been found through calculating the form function of the acoustic scattering from the nanosystem. This VdW-force-induced band gap is different from the known mechanisms of Bragg scattering and local resonances for periodic media. It is shown that when the separation distance between two nanospheres is decreasing from 20 to 1 nm, due to the increasing VdW force, the nanoacoustic scattering is much heightened by two order of magnitude, and meanwhile the frequency shift and phononic band gap at the low frequencies are both widened. These results could provide potential applications of nanoacoustic devices.

  10. van der Waals interactions in a magnetodielectric medium

    International Nuclear Information System (INIS)

    Spagnolo, S.; Dalvit, D. A. R.; Milonni, P. W.

    2007-01-01

    The van der Waals interaction between two ground-state atoms is calculated for two electrically or magnetically polarizable particles embedded in a dispersive magnetodielectric medium. Unlike previous calculations which infer the atom-atom interaction from the dilute-medium limit of the macroscopic, many-body van der Waals interaction, the interaction is calculated directly for the system of two atoms in a magnetodielectric medium. Two approaches are presented, the first based on the quantized electromagnetic field in a dispersive medium without absorption and the second on Green functions that allow for absorption. We show that the correct van der Waals interactions are obtained regardless of whether absorption in the host medium is explicitly taken into account

  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 interaction between a microparticle and a single-walled carbon nanotube

    International Nuclear Information System (INIS)

    Blagov, E. V.; Mostepanenko, V. M.; Klimchitskaya, G. L.

    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-walled carbon nanotube are obtained. The single-walled 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-walled carbon nanotubes of different radii. Comparison studies of the van der Waals interaction of hydrogen atoms with single-walled and multiwalled 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

  13. van der Waals

    Indian Academy of Sciences (India)

    University education was beyond reach for van der Waals as he had to work for earning his daily bread ... languages, which was a prerequisite for entering a University those days. van der Waals worked as a school ... take academic examinations at the University yet, van der Waals continued studying at Leiden. University ...

  14. Van-der-Waals interaction of atoms in dipolar Rydberg states

    Science.gov (United States)

    Kamenski, Aleksandr A.; Mokhnenko, Sergey N.; Ovsiannikov, Vitaly D.

    2018-02-01

    An asymptotic expression for the van-der-Waals constant C 6( n) ≈ -0.03 n 12 K p ( x) is derived for the long-range interaction between two highly excited hydrogen atoms A and B in their extreme Stark states of equal principal quantum numbers n A = n B = n ≫ 1 and parabolic quantum numbers n 1(2) = n - 1, n 2(1) = m = 0 in the case of collinear orientation of the Stark-state dipolar electric moments and the interatomic axis. The cubic polynomial K 3( x) in powers of reciprocal values of the principal quantum number x = 1/ n and quadratic polynomial K 2( y) in powers of reciprocal values of the principal quantum number squared y = 1/ n 2 were determined on the basis of the standard curve fitting polynomial procedure from the calculated data for C 6( n). The transformation of attractive van-der-Waals force ( C 6 > 0) for low-energy states n < 23 into repulsive force ( C 6 < 0) for all higher-energy states of n ≥ 23, is observed from the results of numerical calculations based on the second-order perturbation theory for the operator of the long-range interaction between neutral atoms. This transformation is taken into account in the asymptotic formulas (in both cases of p = 2, 3) by polynomials K p tending to unity at n → ∞ ( K p (0) = 1). The transformation from low- n attractive van-der-Waals force into high- n repulsive force demonstrates the gradual increase of the negative contribution to C 6( n) from the lower-energy two-atomic states, of the A(B)-atom principal quantum numbers n'A(B) = n-Δ n (where Δ n = 1, 2, … is significantly smaller than n for the terms providing major contribution to the second-order series), which together with the states of n″B(A) = n+Δ n make the joint contribution proportional to n 12. So, the hydrogen-like manifold structure of the energy spectrum is responsible for the transformation of the power-11 asymptotic dependence C 6( n) ∝ n 11of the low-angular-momenta Rydberg states in many-electron atoms into the power

  15. Van der Waals and Molecular Science

    International Nuclear Information System (INIS)

    Kox, A J

    1997-01-01

    For many years it has been a source of amazement to scientists and historians of science that no serious scientific biography of J D van der Waals existed. When, more than ten years ago, I became engaged in a correspondence with the Russian historian of science B E Yavelow on the topic of van der Waals, whose biography he was writing, I was both pleased and a bit puzzled. It was clear that Yavelow had not done any archival research in the Netherlands himself, yet he was intimately familiar with many obscure facts from the life of van der Waals. Naturally, I was very curious to see the end result, which appeared in 1985, but although the Amsterdam University Library obtained a copy, my limited knowledge of Russian kept me from forming a judgement on the book. Finally, after more than ten years, an English edition has appeared. The two original Russian authors have joined forces with the well known scientist J S Rowlinson (who earlier edited an English translation of van der Waals's dissertation) to produce a revised and enlarged English version of the Russian original. Now that I have finally been able to study this work, I must admit to being much impressed. Both the life and the work of van der Waals are dealt with in an exemplary way: the authors' command of primary and secondary sources is impressive, as is their understanding of the Dutch social and educational circumstances in the last century. Teaching and research at the newly-founded University of Amsterdam, as well as activities in the Academy of Sciences, are discussed in great and interesting detail. Van der Waals's education and rise from a simple teacher to one of the foremost theoretical physicists in Europe teaches us much about his personality as well as about the opportunities offered by the Dutch educational system. In their discussion of the development of van der Waals's ideas and their impact (including an interesting chapter on the reception in Russia) the authors are not afraid to go into

  16. van der Waals

    Indian Academy of Sciences (India)

    in the world without learning the 'van der Waals equation'. ... theory”. Those days, however, molecules were assumed to be point masses occupying no .... was 36 to obtain his PhD due to the prevailing social conditions. van der Waals died in ...

  17. van der Waals criticality in AdS black holes: A phenomenological study

    Science.gov (United States)

    Bhattacharya, Krishnakanta; Majhi, Bibhas Ranjan; Samanta, Saurav

    2017-10-01

    Anti-de Sitter black holes exhibit van der Waals-type phase transition. In the extended phase-space formalism, the critical exponents for any spacetime metric are identical to the standard ones. Motivated by this fact, we give a general expression for the Helmholtz free energy near the critical point, which correctly reproduces these exponents. The idea is similar to the Landau model, which gives a phenomenological description of the usual second-order phase transition. Here, two main inputs are taken into account for the analysis: (a) black holes should have van der Waals-like isotherms, and (b) free energy can be expressed solely as a function of thermodynamic volume and horizon temperature. Resulting analysis shows that the form of Helmholtz free energy correctly encapsulates the features of the Landau function. We also discuss the isolated critical point accompanied by nonstandard values of critical exponents. The whole formalism is then extended to two other criticalities, namely, Y -X and T -S (based on the standard; i.e., nonextended phase space), where X and Y are generalized force and displacement, whereas T and S are the horizon temperature and entropy. We observe that in the former case Gibbs free energy plays the role of Landau function, whereas in the later case, that role is played by the internal energy (here, it is the black hole mass). Our analysis shows that, although the existence of a van der Waals phase transition depends on the explicit form of the black hole metric, the values of the critical exponents are universal in nature.

  18. Comparison of frictional forces on graphene and graphite

    International Nuclear Information System (INIS)

    Lee, Hyunsoo; Lee, Naesung; Seo, Yongho; Eom, Jonghwa; Lee, SangWook

    2009-01-01

    We report on the frictional force between an SiN tip and graphene/graphite surfaces using lateral force microscopy. The cantilever we have used was made of an SiN membrane and has a low stiffness of 0.006 N m -1 . We prepared graphene flakes on a Si wafer covered with silicon oxides. The frictional force on graphene was smaller than that on the Si oxide and larger than that on graphite (multilayer of graphene). Force spectroscopy was also employed to study the van der Waals force between the graphene and the tip. Judging that the van der Waals force was also in graphite-graphene-silicon oxide order, the friction is suspected to be related to the van der Waals interactions. As the normal force acting on the surface was much weaker than the attractive force, such as the van der Waals force, the friction was independent of the normal force strength. The velocity dependency of the friction showed a logarithmic behavior which was attributed to the thermally activated stick-slip effect.

  19. The role of van der Waals interactions in chemical reactions

    International Nuclear Information System (INIS)

    Takayanagi, Toshiyuki

    1998-01-01

    We are studying the role of van der Waals interactions in the chemical reactions from the theoretical view point, especially, a case related to the tunnel effect. The fist case that the cumulative reaction probability depends on the tunnel effect was increased by the van der waals force. This case was proved by theoretical calculation of the reaction rate constant of the reaction: Mu + F2 → MuF + F. The second case was that a van der Waals well was so deep that pseudo bound state was observed in the reaction: F + H 2 → HF + H. A van der Waals complex such as AB(v=j=0)...C was excited to the resonance state of AB(vij)...C and A...BC(v,j) by laser, than the resonance state proceeded to AB + C (predissociation) or A + BC(pre-reaction). We succeeded for the first time to calculate theoretically the pre-reaction by the real three dimentional potential curve. The pre-reaction can be observed only the case that the tunnel probability is larger than the non-adiabatic transition probability. The chemical reactions in solid were explained, too. (S.Y.)

  20. Van der Waals potentials between metal clusters and helium atoms obtained with density functional theory and linear response methods

    International Nuclear Information System (INIS)

    Liebrecht, M.

    2014-01-01

    The importance of van der Waals interactions in many diverse research fields such as, e. g., polymer science, nano--materials, structural biology, surface science and condensed matter physics created a high demand for efficient and accurate methods that can describe van der Waals interactions from first principles. These methods should be able to deal with large and complex systems to predict functions and properties of materials that are technologically and biologically relevant. Van der Waals interactions arise due to quantum mechanical correlation effects and finding appropriate models an numerical techniques to describe this type of interaction is still an ongoing challenge in electronic structure and condensed matter theory. This thesis introduces a new variational approach to obtain intermolecular interaction potentials between clusters and helium atoms by means of density functional theory and linear response methods. It scales almost linearly with the number of electrons and can therefore be applied to much larger systems than standard quantum chemistry techniques. The main focus of this work is the development of an ab-initio method to account for London dispersion forces, which are purely attractive and dominate the interaction of non--polar atoms and molecules at large distances. (author) [de

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

    International Nuclear Information System (INIS)

    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 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 accelerated 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

  2. Evaluation of van der Waals density functionals for layered materials

    Science.gov (United States)

    Tawfik, Sherif Abdulkader; Gould, Tim; Stampfl, Catherine; Ford, Michael J.

    2018-03-01

    In 2012, Björkman et al. posed the question "Are we van der Waals ready?" [T. Björkman et al., J. Phys.: Condens. Matter 24, 424218 (2012), 10.1088/0953-8984/24/42/424218] about the ability of ab initio modeling to reproduce van der Waals (vdW) dispersion forces in layered materials. The answer at that time was no, however. Here we report on a new generation of vdW dispersion models and show that one, i.e., the fractionally ionic atom theory with many-body dispersions, offers close to quantitative predictions for layered structures. Furthermore, it does so from a qualitatively correct picture of dispersion forces. Other methods, such as D3 and optB88vdW, also work well, albeit with some exceptions. We thus argue that we are nearly vdW ready and that some modern dispersion methods are accurate enough to be used for nanomaterial prediction, albeit with some caution required.

  3. On van der Waals-like forces in spontaneously broken supersymmetries

    International Nuclear Information System (INIS)

    Radescu, E.E.

    1982-12-01

    In spontaneously broken rigid supersymmetry, Goldstone fermion pair exchange should lead to a universal interaction between massive bodies uniquely fixed by the existing low energy theorem. The resulting van der Waals-like potential is shown to be V(r)=Mmπ -3 F -4 r -7 +O(r -8 ), where M,m are the masses of the interacting bodies while √F is the scale of the breaking. The change in the situation when the supersymmetry is promoted to a local one is briefly discussed. (author)

  4. Dynamical screening of the van der Waals interaction between graphene layers

    International Nuclear Information System (INIS)

    Dappe, Y J; Bolcatto, P G; Ortega, J; Flores, F

    2012-01-01

    The interaction between graphene layers is analyzed combining local orbital DFT and second order perturbation theory. For this purpose we use the linear combination of atomic orbitals-orbital occupancy (LCAO-OO) formalism, that allows us to separate the interaction energy as the sum of a weak chemical interaction between graphene layers plus the van der Waals interaction (Dappe et al 2006 Phys. Rev. B 74 205434). In this work, the weak chemical interaction is calculated by means of corrected-LDA calculations using an atomic-like sp 3 d 5 basis set. The van der Waals interaction is calculated by means of second order perturbation theory using an atom-atom interaction approximation and the atomic-like-orbital occupancies. We also analyze the effect of dynamical screening in the van der Waals interaction using a simple model. We find that this dynamical screening reduces by 40% the van der Waals interaction. Taking this effect into account, we obtain a graphene-graphene interaction energy of 70 ± 5 meV/atom in reasonable agreement with the experimental evidence.

  5. Dynamical screening of the van der Waals interaction between graphene layers.

    Science.gov (United States)

    Dappe, Y J; Bolcatto, P G; Ortega, J; Flores, F

    2012-10-24

    The interaction between graphene layers is analyzed combining local orbital DFT and second order perturbation theory. For this purpose we use the linear combination of atomic orbitals-orbital occupancy (LCAO-OO) formalism, that allows us to separate the interaction energy as the sum of a weak chemical interaction between graphene layers plus the van der Waals interaction (Dappe et al 2006 Phys. Rev. B 74 205434). In this work, the weak chemical interaction is calculated by means of corrected-LDA calculations using an atomic-like sp(3)d(5) basis set. The van der Waals interaction is calculated by means of second order perturbation theory using an atom-atom interaction approximation and the atomic-like-orbital occupancies. We also analyze the effect of dynamical screening in the van der Waals interaction using a simple model. We find that this dynamical screening reduces by 40% the van der Waals interaction. Taking this effect into account, we obtain a graphene-graphene interaction energy of 70 ± 5 meV/atom in reasonable agreement with the experimental evidence.

  6. Evidence for van der Waals adhesion in gecko setae.

    Science.gov (United States)

    Autumn, Kellar; Sitti, Metin; Liang, Yiching A; Peattie, Anne M; Hansen, Wendy R; Sponberg, Simon; Kenny, Thomas W; Fearing, Ronald; Israelachvili, Jacob N; Full, Robert J

    2002-09-17

    Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well to strongly hydrophobic and strongly hydrophilic, polarizable surfaces. Adhesion of a single isolated gecko seta was equally effective on the hydrophobic and hydrophilic surfaces of a microelectro-mechanical systems force sensor. A van der Waals mechanism implies that the remarkable adhesive properties of gecko setae are merely a result of the size and shape of the tips, and are not strongly affected by surface chemistry. Theory predicts greater adhesive forces simply from subdividing setae to increase surface density, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects. Estimates using a standard adhesion model and our measured forces come remarkably close to predicting the tip size of Tokay gecko seta. We verified the dependence on size and not surface type by using physical models of setal tips nanofabricated from two different materials. Both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.

  7. Signatures of van der Waals binding: A coupling-constant scaling analysis

    Science.gov (United States)

    Jiao, Yang; Schröder, Elsebeth; Hyldgaard, Per

    2018-02-01

    The van der Waals (vdW) density functional (vdW-DF) method [Rep. Prog. Phys. 78, 066501 (2015), 10.1088/0034-4885/78/6/066501] describes dispersion or vdW binding by tracking the effects of an electrodynamic coupling among pairs of electrons and their associated exchange-correlation holes. This is done in a nonlocal-correlation energy term Ecnl, which permits density functional theory calculation in the Kohn-Sham scheme. However, to map the nature of vdW forces in a fully interacting materials system, it is necessary to also account for associated kinetic-correlation energy effects. Here, we present a coupling-constant scaling analysis, which permits us to compute the kinetic-correlation energy Tcnl that is specific to the vdW-DF account of nonlocal correlations. We thus provide a more complete spatially resolved analysis of the electrodynamical-coupling nature of nonlocal-correlation binding, including vdW attraction, in both covalently and noncovalently bonded systems. We find that kinetic-correlation energy effects play a significant role in the account of vdW or dispersion interactions among molecules. Furthermore, our mapping shows that the total nonlocal-correlation binding is concentrated to pockets in the sparse electron distribution located between the material fragments.

  8. Defect mediated van der Waals epitaxy of hexagonal boron nitride on graphene

    Science.gov (United States)

    Heilmann, M.; Bashouti, M.; Riechert, H.; Lopes, J. M. J.

    2018-04-01

    Van der Waals heterostructures comprising of hexagonal boron nitride and graphene are promising building blocks for novel two-dimensional devices such as atomically thin transistors or capacitors. However, demonstrators of those devices have been so far mostly fabricated by mechanical assembly, a non-scalable and time-consuming method, where transfer processes can contaminate the surfaces. Here, we investigate a direct growth process for the fabrication of insulating hexagonal boron nitride on high quality epitaxial graphene using plasma assisted molecular beam epitaxy. Samples were grown at varying temperatures and times and studied using atomic force microscopy, revealing a growth process limited by desorption at high temperatures. Nucleation was mostly commencing from morphological defects in epitaxial graphene, such as step edges or wrinkles. Raman spectroscopy combined with x-ray photoelectron measurements confirm the formation of hexagonal boron nitride and prove the resilience of graphene against the nitrogen plasma used during the growth process. The electrical properties and defects in the heterostructures were studied with high lateral resolution by tunneling current and Kelvin probe force measurements. This correlated approach revealed a nucleation apart from morphological defects in epitaxial graphene, which is mediated by point defects. The presented results help understanding the nucleation and growth behavior during van der Waals epitaxy of 2D materials, and point out a route for a scalable production of van der Waals heterostructures.

  9. Interfacial slippage effect on the surface instability of a thin elastic film under van der Waals force

    International Nuclear Information System (INIS)

    Pan Xiahui; Yu Shouwen; Feng Xiqiao; Huang Shiqing

    2009-01-01

    This paper studies the surface instability of an elastic thin solid film lying on a rigid substrate and subjected to van der Waals-like surface interactions. The effect of film-substrate interfacial slippage is accounted for by using a simplified linear cohesive interface model. It is found that the interfacial slippage generally plays a destabilizing role in the surface instability of the thin film. For highly compressible films with Poisson's ratio smaller than 0.25, the surface wrinkling behaviour previously inconceivable in the case of a perfectly bonded interface is now feasible if film-substrate interface slipping is permitted. In addition, our linear perturbation analysis shows that the critical conditions for the onset of surface instability can be modulated by adjusting the slippery stiffness of the interface. The result might be helpful for developing novel techniques to create micro-/nanosized surface patterns.

  10. Nature of bonding forces between two hydrogen-passivated silicon wafers

    DEFF Research Database (Denmark)

    Stokbro, Kurt; Nielsen, E.; Hult, E.

    1998-01-01

    The nature and strength of the bonding forces between two II-passivated Si surfaces are studied with the density-functional theory, using an approach based on recent theoretical advances in understanding of van der Waals forces between two surfaces. Contrary to previous suggestions of van der Waals...

  11. 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.

  12. Strain engineering of van der Waals heterostructures

    NARCIS (Netherlands)

    Vermeulen, Paul A.; Mulder, Jefta; Momand, Jamo; Kooi, Bart J.

    2018-01-01

    Modifying the strain state of solids allows control over a plethora of functional properties. The weak interlayer bonding in van der Waals (vdWaals) materials such as graphene, hBN, MoS2, and Bi2Te3 might seem to exclude strain engineering, since strain would immediately relax at the vdWaals

  13. Virtual Resonance and Frequency Difference Generation by van der Waals Interaction

    Science.gov (United States)

    Tetard, L.; Passian, A.; Eslami, S.; Jalili, N.; Farahi, R. H.; Thundat, T.

    2011-05-01

    The ability to explore the interior of materials for the presence of inhomogeneities was recently demonstrated by mode synthesizing atomic force microscopy [L. Tetard, A. Passian, and T. Thundat, Nature Nanotech. 5, 105 (2009).NNAABX1748-338710.1038/nnano.2009.454]. Proposing a semiempirical nonlinear force, we show that difference frequency ω- generation, regarded as the simplest synthesized mode, occurs optimally when the force is tuned to van der Waals form. From a parametric study of the probe-sample excitation, we show that the predicted ω- oscillation agrees well with experiments. We then introduce the concept of virtual resonance to show that probe oscillations at ω- can efficiently be enhanced.

  14. Theoretical study of noble gases diffraction from Ru(0001) using van der Waals DFT-based potentials

    International Nuclear Information System (INIS)

    Del Cueto, M; Muzas, A S; Martín, F; Díaz, C

    2015-01-01

    This study aims to analyze the role of van der Waals forces in the diffraction process of noble gases from a metal surface. We made use of different vdW implementations to rationalize the effect of dispersion forces on the corrugation of the system, the resulting scattering patterns and on the eventual diffraction results. (paper)

  15. Report of the Material Control and Material Accounting Task Force

    International Nuclear Information System (INIS)

    1978-03-01

    In September 1977 a Task Force was formed to complete a study of the role of material control and material accounting in NRC's safeguards program. The Task Force's assignment was to: define the roles and objectives of material control and material accounting in the NRC safeguards program; recommend goals for the material control and material accounting systems based on their roles and objectives; assess the extent to which the existing safeguards regulatory base meets or provides the capability to meet the recommended goals; and provide direction for material control and material accounting development, including both near-term and long-term upgrades. The study was limited to domestic nuclear facilities possessing significant amounts of plutonium, uranium-233 or highly enriched uranium in unsealed form. The Task Force findings are reported

  16. Long Range Forces between Atomic Impurities in Liquid Helium

    International Nuclear Information System (INIS)

    Dupont-Roc, J.

    2002-01-01

    Van der Waals or Casimir interaction between neutral quantum objects in their ground state is known to be universally attractive. This is not necessarily so when these objects are embedded in a polarizable medium. We show that atomic impurities in liquid helium may indeed realize repulsive forces, and even Van der Waals and Casimir forces with different signs. (author)

  17. Evidence for van der Waals adhesion in gecko setae

    OpenAIRE

    Autumn, Kellar; Sitti, Metin; Liang, Yiching A.; Peattie, Anne M.; Hansen, Wendy R.; Sponberg, Simon; Kenny, Thomas W.; Fearing, Ronald; Israelachvili, Jacob N.; Full, Robert J.

    2002-01-01

    Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well ...

  18. From the Cover: Evidence for van der Waals adhesion in gecko setae

    Science.gov (United States)

    Autumn, Kellar; Sitti, Metin; Liang, Yiching A.; Peattie, Anne M.; Hansen, Wendy R.; Sponberg, Simon; Kenny, Thomas W.; Fearing, Ronald; Israelachvili, Jacob N.; Full, Robert J.

    2002-09-01

    Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for over a century. We provide the first direct experimental evidence for dry adhesion of gecko setae by van der Waals forces, and reject the use of mechanisms relying on high surface polarity, including capillary adhesion. The toes of live Tokay geckos were highly hydrophobic, and adhered equally well to strongly hydrophobic and strongly hydrophilic, polarizable surfaces. Adhesion of a single isolated gecko seta was equally effective on the hydrophobic and hydrophilic surfaces of a microelectro-mechanical systems force sensor. A van der Waals mechanism implies that the remarkable adhesive properties of gecko setae are merely a result of the size and shape of the tips, and are not strongly affected by surface chemistry. Theory predicts greater adhesive forces simply from subdividing setae to increase surface density, and suggests a possible design principle underlying the repeated, convergent evolution of dry adhesive microstructures in gecko, anoles, skinks, and insects. Estimates using a standard adhesion model and our measured forces come remarkably close to predicting the tip size of Tokay gecko seta. We verified the dependence on size and not surface type by using physical models of setal tips nanofabricated from two different materials. Both artificial setal tips stuck as predicted and provide a path to manufacturing the first dry, adhesive microstructures.

  19. Low-energy universality and scaling of van der Waals forces

    International Nuclear Information System (INIS)

    Calle Cordon, A.; Ruiz Arriola, E.

    2010-01-01

    At long distances, interactions between neutral ground-state atoms can be described by the van der Waals potential. In the ultracold regime, atom-atom scattering is dominated by s-waves phase shifts given by an effective range expansion in terms of the scattering length α 0 and the effective range r 0 . We show that while the scattering length cannot be predicted for these potentials, the effective range is given by the universal low-energy theorem r 0 =A+B/α 0 +C/α 0 2 , where A, B, and C depend on the dispersion coefficients C n and the reduced diatom mass. We confront this formula to about 100 determinations of r 0 and α 0 and show why the result is dominated by the leading dispersion coefficient C 6 . Universality and scaling extend much beyond naive dimensional analysis estimates.

  20. 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

    The past decade has seen a dramatic rise in interest in exploring the role that van der Waals (vdW) or dispersion forces play in materials and in material behavior. Part of this stems from the obvious fact that vdW interactions (and other weak forces, such as Casimir) underpin molecular recognition, i.e., nature's approach to search for a match between genes and anti-genes and hence enable biological function. Less obvious is the recognition that vdW interactions affect a multitude of properties of a vast variety of materials in general, some of which also have strong technological applications. While for two atom- or orbital-sized material fragments the dispersive contributions to binding are small compared to those from the better known forms (ionic, covalent, metallic), those between sparse materials (spread over extended areas) can be of paramount importance. For example, an understanding of binding in graphite cannot arise solely from a study of the graphene layers individually, but also requires insight from inter-sheet graphene vdW bonding. It is the extended-area vdW bonding that provides sufficient cohesion to make graphite a robust, naturally occurring material. In fact, it is the vdW-bonded graphite, and not the all-covalently bonded diamond, that is the preferred form of pure carbon under ambient conditions. Also important is the understanding that vdW attraction can attain a dramatic relevance even if the material fragments, the building blocks, are not necessarily parallel from the outset or smooth when viewed in isolation (such as a graphene sheet or a carbon nanotube). This can happen if the building blocks have some softness and flexibility and allow an internal relative alignment to emerge. The vdW forces can then cause increasingly larger parts of the interacting fragments to line up at sub-nanometer separations and thus beget more areas with a sizable vdW bonding contribution. The gecko can scale a wall because it can bring its flexible hairs

  1. 14 CFR 151.51 - Performance of construction work: Sponsor force account.

    Science.gov (United States)

    2010-01-01

    ... 14 Aeronautics and Space 3 2010-01-01 2010-01-01 false Performance of construction work: Sponsor... Development Projects § 151.51 Performance of construction work: Sponsor force account. (a) Before undertaking any force account construction work, the sponsor (or any public agency acting as agent for the sponsor...

  2. Study of the influence of color van der Waals forces and of non-Coulombian effects in 208pb+208pb scattering using a high-precision experiment

    International Nuclear Information System (INIS)

    Casandjian, Jean-Marc

    1996-01-01

    This work deals with the precise measurement of the absolute angular position of the elastic 208 pb+ 208 pb scattering cross section oscillations. The main objective is to verify if all of the elastic scattering ingredients are known even with an angular position precision of a few milli-degrees or if it is necessary to introduce new elements such as the color van der Waals force. This experiment was performed at Ganil. We obtained a precision of 0.004 deg. on the absolute cross section oscillation position and an angular shift of a few hundredths of degrees in relation to the expected position of a pure coulomb scattering. The attainment of this precision required particular precautions in the measurement of the absolute energy target position and scattering angle. First, the angular straggling on a thin target and the production of δ electrons during the scattering is studied. Next the origin of the angular shift is examined by the calculation of all the potentials that act during the scattering. The agreement between experimentation and theory allowed us to set a new limit on the color van der Waals interaction. (author) [fr

  3. Influence of the forces on the adhesion behavior of graphite dust in HTGR

    International Nuclear Information System (INIS)

    Peng Wei; Sun Xiaokai; Zhang Tianqi; Yu Suyuan

    2015-01-01

    The behavior of the graphite dust is important to the safety of High Temperature Gas-cooled Reactors. The present study focuses on the forces which make the graphite dust attach or detach from the surface in HTGR. The effect of graphite dust size, the fluid velocity and the surface energy between the particles and the substrate were investigated. The result showed that van der Waals adhesion force is the main factors affecting the dust attach on the surface, the gravity force and the electrostatic force were much smaller than it. For small particles, both the aerodynamic lift and drag are smaller than van der Waals adhesion force. While for the large particles, the coupled effects of aerodynamic lift and drag can make the dust detach from the substrate easier. Both the aerodynamic lift and drag forces will increase quickly as the fluid velocity increases. The surface energy is an important parameter for van der Waals adhesion force, which will decrease as the surface energy decreases. (author)

  4. Generalized closed form solutions for feasible dimension limit and pull-in characteristics of nanocantilever under the Influences of van der Waals and Casimir forces

    Science.gov (United States)

    Mukherjee, Banibrata; Sen, Siddhartha

    2018-04-01

    This paper presents generalized closed form expressions for determining the dimension limit for the basic design parameters as well as the pull-in characteristics of a nanocantilever beam under the influences of van der Waals and Casimir forces. The coupled nonlinear electromechanical problem of electrostatic nanocantilever is formulated in nondimensional form with Galerkin’s approximation considering the effects of these intermolecular forces and fringe field. The resulting integrals and higher order polynomials are solved numerically to derive the closed form expressions for maximum permissible detachment length, minimum feasible gap spacing and critical pull-in limit. The derived expressions are compared and validated as well with several reported literature showing reasonable agreement. The major advantages of the proposed closed form expressions are that, they do not contain any complex mathematical term or operation unlike in reported literature and thus they will serve as convenient tools for the NEMS community in successful design of various electrostatically actuated nanosystems.

  5. The contribution of the electrostatic proximity force to atomic force microscopy with insulators

    International Nuclear Information System (INIS)

    Stanley Czarnecki, W.; Schein, L.B.

    2005-01-01

    Measurements, using atomic force microscopy, of the force and force derivative on a charged insulating micron sized sphere as a function of gap between the sphere and a conductive plane have revealed attractive forces at finite gaps that are larger than predicted by either van der Waals or conventional electrostatic forces. We suggest that these observations may be due to an electrostatic force that we have identified theoretically and call the proximity force. This proximity force is due to the discrete charges on the surface of the sphere in close proximity to the plane

  6. The contribution of the electrostatic proximity force to atomic force microscopy with insulators

    Energy Technology Data Exchange (ETDEWEB)

    Stanley Czarnecki, W. [Aetas Technology Corporation, P.O. Box 53398, Irvine, CA 92619-3398 (United States); IBM Corporation, 5600 Cottle Rd., Building 13, San Jose, CA 95193 (United States); Schein, L.B. [Aetas Technology Corporation, P.O. Box 53398, Irvine, CA 92619-3398 (United States)]. E-mail: schein@prodigy.net

    2005-05-16

    Measurements, using atomic force microscopy, of the force and force derivative on a charged insulating micron sized sphere as a function of gap between the sphere and a conductive plane have revealed attractive forces at finite gaps that are larger than predicted by either van der Waals or conventional electrostatic forces. We suggest that these observations may be due to an electrostatic force that we have identified theoretically and call the proximity force. This proximity force is due to the discrete charges on the surface of the sphere in close proximity to the plane.

  7. Effect of van der Waals interactions on the structural and binding properties of GaSe

    Energy Technology Data Exchange (ETDEWEB)

    Sarkisov, Sergey Y., E-mail: sarkisov@mail.tsu.ru [Tomsk State University, Lenin Avenue 36, 634050 Tomsk (Russian Federation); Kosobutsky, Alexey V., E-mail: kosobutsky@kemsu.ru [Tomsk State University, Lenin Avenue 36, 634050 Tomsk (Russian Federation); Kemerovo State University, Krasnaya 6, 650043 Kemerovo (Russian Federation); Shandakov, Sergey D. [Kemerovo State University, Krasnaya 6, 650043 Kemerovo (Russian Federation)

    2015-12-15

    The influence of van der Waals interactions on the lattice parameters, band structure, elastic moduli and binding energy of layered GaSe compound has been studied using projector-augmented wave method within density functional theory. We employed the conventional local/semilocal exchange-correlation functionals and recently developed van der Waals functionals which are able to describe dispersion forces. It is found that application of van der Waals density functionals allows to substantially increase the accuracy of calculations of the lattice constants a and c and interlayer distance in GaSe at ambient conditions and under hydrostatic pressure. The pressure dependences of the a-parameter, Ga–Ga, Ga–Se bond lengths and Ga–Ga–Se bond angle are characterized by a relatively low curvature, while c(p) has a distinct downward bowing due to nonlinear shrinking of the interlayer spacing. From the calculated binding energy curves we deduce the interlayer binding energy of GaSe, which is found to be in the range 0.172–0.197 eV/layer (14.2–16.2 meV/Å{sup 2}). - Highlights: • Effects of van der Waals interactions are analyzed using advanced density functionals. • Calculations with vdW-corrected functionals closely agree with experiment. • Interlayer binding energy of GaSe is estimated to be 14.2–16.2 meV/Å{sup 2}.

  8. Modeling noncontact atomic force microscopy resolution on corrugated surfaces

    Directory of Open Access Journals (Sweden)

    Kristen M. Burson

    2012-03-01

    Full Text Available Key developments in NC-AFM have generally involved atomically flat crystalline surfaces. However, many surfaces of technological interest are not atomically flat. We discuss the experimental difficulties in obtaining high-resolution images of rough surfaces, with amorphous SiO2 as a specific case. We develop a quasi-1-D minimal model for noncontact atomic force microscopy, based on van der Waals interactions between a spherical tip and the surface, explicitly accounting for the corrugated substrate (modeled as a sinusoid. The model results show an attenuation of the topographic contours by ~30% for tip distances within 5 Å of the surface. Results also indicate a deviation from the Hamaker force law for a sphere interacting with a flat surface.

  9. Mixed Dimensional Van der Waals Heterostructures for Opto-Electronics.

    Science.gov (United States)

    Jariwala, Deep

    The isolation of a growing number of two-dimensional (2D) materials has inspired worldwide efforts to integrate distinct 2D materials into van der Waals (vdW) heterostructures. While a tremendous amount of research activity has occurred in assembling disparate 2D materials into ``all-2D'' van der Waals heterostructures, this concept is not limited to 2D materials alone. Given that any passivated, dangling bond-free surface will interact with another via vdW forces, the vdW heterostructure concept can be extended to include the integration of 2D materials with non-2D materials that adhere primarily through noncovalent interactions. In the first part of this talk I will present our work on emerging mixed-dimensional (2D + nD, where n is 0, 1 or 3) heterostructure devices performed at Northwestern University. I will present two distinct examples of gate-tunable p-n heterojunctions 1. Single layer n-type MoS2\\ (2D) combined with p-type semiconducting single walled carbon nanotubes (1D) and 2. Single layer MoS2 combined with 0D molecular semiconductor, pentacene. I will present the unique electrical properties, underlying charge transport mechanisms and photocurrent responses in both the above systems using a variety of scanning probe microscopy techniques as well as computational analysis. This work shows that van der Waals interactions are robust across different dimensionalities of materials and can allow fabrication of semiconductor devices with unique geometries and properties unforeseen in bulk semiconductors. Finally, I will briefly discuss our recent work from Caltech on near-unity absorption in atomically-thin photovoltaic devices. This work is supported by the Materials Research Center at Northwestern University, funded by the National Science Foundation (NSF DMR-1121262) and the Resnick Sustainability Institute at Caltech.

  10. Electronic spectral properties of surfaces and adsorbates and atom-adsorbate van der Waals interactions

    International Nuclear Information System (INIS)

    Lovric, D.; Gumhalter, B.

    1988-01-01

    The relevance of van der Waals interactions in the scattering of neutral atoms from adsorbates has been recently confirmed by highly sensitive molecular-beam techniques. The theoretical descriptions of the collision dynamics which followed the experimental studies have necessitated very careful qualitative and quantitative examinations and evaluations of the properties of atom-adsorbate van der Waals interactions for specific systems. In this work we present a microscopic calculation of the strengths and reference-plane positions for van der Waals potentials relevant for scattering of He atoms from CO adsorbed on various metallic substrates. In order to take into account the specificities of the polarization properties of real metals (noble and transition metals) and of chemisorbed CO, we first calculate the spectra of the electronic excitations characteristic of the respective electronic subsystems by using various data sources available and combine them with the existing theoretical models. The reliability of the calculated spectra is then verified in each particular case by universal sum rules which may be established for the electronic excitations of surfaces and adsorbates. The substrate and adsorbate polarization properties which derive from these calculations serve as input data for the evaluation of the strengths and reference-plane positions of van der Waals potentials whose computed values are tabulated for a number of real chemisorption systems. The implications of the obtained results are discussed in regard to the atom-adsorbate scattering cross sections pertinent to molecular-beam scattering experiments

  11. Analyzing the Effect of Capillary Force on Vibrational Performance of the Cantilever of an Atomic Force Microscope in Tapping Mode with Double Piezoelectric Layers in an Air Environment.

    Science.gov (United States)

    Nahavandi, Amir; Korayem, Moharam Habibnejad

    2015-10-01

    The aim of this paper is to determine the effects of forces exerted on the cantilever probe tip of an atomic force microscope (AFM). These forces vary according to the separation distance between the probe tip and the surface of the sample being examined. Hence, at a distance away from the surface (farther than d(on)), these forces have an attractive nature and are of Van der Waals type, and when the probe tip is situated in the range of a₀≤ d(ts) ≤ d(on), the capillary force is added to the Van der Waals force. At a distance of d(ts) ≤ a₀, the Van der Waals and capillary forces remain constant at intermolecular distances, and the contact repulsive force repels the probe tip from the surface of sample. The capillary force emerges due to the contact of thin water films with a thickness of h(c) which have accumulated on the sample and probe. Under environmental conditions a layer of water or hydrocarbon often forms between the probe tip and sample. The capillary meniscus can grow until the rate of evaporation equals the rate of condensation. For each of the above forces, different models are presented. The smoothness or roughness of the surfaces and the geometry of the cantilever tip have a significant effect on the modeling of forces applied on the probe tip. Van der Waals and the repulsive forces are considered to be the same in all the simulations, and only the capillary force is altered in order to evaluate the role of this force in the AFM-based modeling. Therefore, in view of the remarkable advantages of the piezoelectric microcantilever and also the extensive applications of the tapping mode, we investigate vibrational motion of the piezoelectric microcantilever in the tapping mode. The cantilever mentioned is entirely covered by two piezoelectric layers that carry out both the actuation of the probe tip and the measuringof its position.

  12. The scaled-charge additive force field for amino acid based ionic liquids

    DEFF Research Database (Denmark)

    Fileti, E. E.; Chaban, V. V.

    2014-01-01

    Ionic liquids (ILs) constitute an emerging research field. New ILs involve more and more organic and inorganic ions. Amino acid based ILs (AAILs) represent a specific interest due to their evolutional connection to proteins. We report a new non-polarizable force field (FF) for the eight AAILs...... comprising 1-ethyl-3-methylimidazolium cation and amino acid anions. The anions were obtained via deprotonation of carboxyl group. Specific cation-anion non-covalent interactions were taken into account by computing electrostatic potential for ion pairs. The van der Waals interactions were adopted from...

  13. Entry into force and then? The Paris agreement and state accountability

    NARCIS (Netherlands)

    Karlsson-Vinkhuyzen, Sylvia I.; Groff, Maja; Tamás, Peter A.; Dahl, Arthur L.; Harder, Marie K.; Hassall, Graham

    2018-01-01

    The entry into force of the Paris Agreement on climate change brings expectations that states will be held to account for their commitments. The article elaborates on why this is not a realistic assumption unless a broader multilevel perspective is taken on the nature of accountability regimes for

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

    DEFF Research Database (Denmark)

    Kelkkanen, Kari André

    , or even as broken. The hexamer experience of the criteria and effects of vdW forces can be used in interpretation of results of molecular dynamics (MD) simulations of ambient water, where vdW forces qualitatively result in liquid water with fewer, more distorted HBs. This is interesting...... 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...... functionals. DFT calculations are performed for water dimer and hexamer, and for liquid water. Calculations on four low-energetic isomers of the water hexamer show that the vdW-DF accurately determines the energetic trend on these small clusters. How- ever, the dissociation-energy values with the vd...

  15. Characterization of van der Waals type bimodal,- lambda,- meta- and spinodal phase transitions in liquid mixtures, solid suspensions and thin films.

    Science.gov (United States)

    Rosenholm, Jarl B

    2018-03-01

    The perfect gas law is used as a reference when selecting state variables (P, V, T, n) needed to characterize ideal gases (vapors), liquids and solids. Van der Waals equation of state is used as a reference for models characterizing interactions in liquids, solids and their mixtures. Van der Waals loop introduces meta- and unstable states between the observed gas (vapor)-liquid P-V transitions at low T. These intermediate states are shown to appear also between liquid-liquid, liquid-solid and solid-solid phase transitions. First-order phase transitions are characterized by a sharp discontinuity of first-order partial derivatives (P, S, V) of Helmholtz and Gibbs free energies. Second-order partial derivatives (K T , B, C V , C P , E) consist of a static contribution relating to second-order phase transitions and a relaxation contribution representing the degree of first-order phase transitions. Bimodal (first-order) and spinodal (second-order) phase boundaries are used to separate stable phases from metastable and unstable phases. The boundaries are identified and quantified by partial derivatives of molar Gibbs free energy or chemical potentials with respect to P, S, V and composition (mole fractions). Molecules confined to spread Langmuir monolayers or adsorbed Gibbs monolayers are characterized by equation of state and adsorption isotherms relating to a two-dimensional van der Waals equation of state. The basic work of two-dimensional wetting (cohesion, adsorption, spreading, immersion), have to be adjusted by a horizontal surface pressure in the presence of adsorbed vapor layers. If the adsorption is extended to liquid films a vertical surface pressure (Π) may be added to account for the lateral interaction, thus restoring PV = ΠAh dependence of thin films. Van der Waals attraction, Coulomb repulsion and structural hydration forces contribute to the vertical surface pressure. A van der Waals type coexistence of ordered (dispersed) and disordered

  16. 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 (vd...

  17. 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.

  18. Direction-specific van der Waals attraction between rutile TiO 2 nanocrystals

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Xin; He, Yang; Sushko, Maria L.; Liu, Jia; Luo, Langli; De Yoreo, James J.; Mao, Scott X.; Wang, Chongmin; Rosso, Kevin M.

    2017-04-27

    Mutual lattice orientations dictate the types and magnitudes of forces between crystalline particles. When lattice polarizability is anisotropic, the van der Waals dispersion attraction can, in principle, contribute to this direction dependence. Here we report direct measurement of this attraction between rutile nanocrystals, as a function of their mutual orientation and surface hydration extent. At tens of nanometers of separation the attraction is weak and shows no dependence on azimuthal alignment nor surface hydration. At separations of approximately one hydration layer the attraction is strongly dependent on azimuthal alignment, and systematically decreases as intervening water density increases. Measured forces are in close agreement with predictions from Lifshitz theory, and show that dispersion forces are capable of generating a torque between particles interacting in solution and between grains in materials.

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

    International Nuclear Information System (INIS)

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

    2016-01-01

    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

  20. 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

  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. Quantitative analysis of tip-sample interaction in non-contact scanning force spectroscopy

    International Nuclear Information System (INIS)

    Palacios-Lidon, Elisa; Colchero, Jaime

    2006-01-01

    Quantitative characterization of tip-sample interaction in scanning force microscopy is fundamental for optimum image acquisition as well as data interpretation. In this work we discuss how to characterize the electrostatic and van der Waals contribution to tip-sample interaction in non-contact scanning force microscopy precisely. The spectroscopic technique presented is based on the simultaneous measurement of cantilever deflection, oscillation amplitude and frequency shift as a function of tip-sample voltage and tip-sample distance as well as on advanced data processing. Data are acquired at a fixed lateral position as interaction images, with the bias voltage as fast scan, and tip-sample distance as slow scan. Due to the quadratic dependence of the electrostatic interaction with tip-sample voltage the van der Waals force can be separated from the electrostatic force. Using appropriate data processing, the van der Waals interaction, the capacitance and the contact potential can be determined as a function of tip-sample distance. The measurement of resonance frequency shift yields very high signal to noise ratio and the absolute calibration of the measured quantities, while the acquisition of cantilever deflection allows the determination of the tip-sample distance

  3. Instability of nanocantilever arrays in electrostatic and van der Waals interactions

    Energy Technology Data Exchange (ETDEWEB)

    Ramezani, Asghar [Department of Automotive Engineering, Iran University of Science and Technology, Tehran (Iran, Islamic Republic of); Alasty, Aria, E-mail: aramezani@iust.ac.i, E-mail: aalasti@sharif.ed [Center of Excellence in Design, Robotics, and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

    2009-11-21

    The structural instability of an array of cantilevers, each of which interacts with two neighbouring beams through electrostatic and van der Waals forces, is studied. Distributed and lumped parameter modelling of the array result in a set of coupled nonlinear boundary value problems and a set of coupled nonlinear equations, respectively. These coupled nonlinear systems are solved numerically for different numbers of beams in the array to obtain the pull-in parameters. The pull-in parameters converge to constant values with an increase in the number of beams in the array. These constants, which are important in the design of cantilever arrays, are compared for the distributed and lumped parameter models.

  4. 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.

  5. An Analysis of the Cost Accounting System for the Depot Maintenance Service, Air Force Industrial Fund.

    Science.gov (United States)

    1987-09-01

    AN A NALYSIS OF THE COST ACCOUNTING SYSTEM FOR THE DEPOT 1/1 MRINTENANCE SERVI..(U) MIR FORCE INST OF TECH IIGHT-PTTERSON RFB OH SCHOOL OF SYST.. 0 L...I "VV h S~ ~~i FiLE COV, THSI CIO ~OF AN ANALYSIS OF THE COST ACCOUNTING SYSTEM FOR THE DEPOT MAINTENANCE SERVICE, AIR FORCE INDUSTRIAL FUND...Patterson Air Force Base, Ohio ~ p~UOW~~ ’ I ~ 1 12 02 0 AFIT/GLM/LSY/87S-83 AN ANALYSIS OF THE COST ACCOUNTING SYSTEM FOR THE DEPOT MAINTENANCE SERVICE, AIR

  6. On the dynamic London-van der Waals interaction

    International Nuclear Information System (INIS)

    Guzman, A.

    2003-08-01

    We present a theory of atomic reflection by evanescent waves in the quantized electromagnetic field vacuum that yields an analytical expression for the radiation pressure resulting from the combined effect of the evanescent field and spontaneous emission. The dynamic London-van der Waals potential between atoms and a dielectric wall is introduced as the effective interaction between the induced oscillating atomic dipole and its dipole image. Dissipative effects due to the imaginary part of the London-van der Waals potential are predicted. (author)

  7. Multiple critical points and liquid-liquid equilibria from the van der Waals like equations of state

    International Nuclear Information System (INIS)

    Artemenko, Sergey; Lozovsky, Taras; Mazur, Victor

    2008-01-01

    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

  8. Electrostatic forces on grains near asteroids and comets

    Directory of Open Access Journals (Sweden)

    Hartzell Christine

    2017-01-01

    Full Text Available Dust on and near the surface of small planetary bodies (e.g. asteroids, the Moon, Mars’ moons is subject to gravity, cohesion and electrostatic forces. Due to the very low gravity on small bodies, the behavior of small dust grains is driven by non-gravitational forces. Recent work by Scheeres et al. has shown that cohesion, specifically van der Waals force, is significant for grains on asteroids. In addition to van der Waals cohesion, dust grains also experience electrostatic forces, arising from their interaction with each other (through tribocharging and the solar wind plasma (which produces both grain charging and an external electric field. Electrostatic forces influence both the interactions of grains on the surface of small bodies as well as the dynamics of grains in the plasma sheath above the surface. While tribocharging between identical dielectric grains remains poorly understood, we have recently expanded an existing charge transfer model to consider continuous size distributions of grains and are planning an experiment to test the charge predictions produced. Additionally, we will present predictions of the size of dust grains that are capable of detaching from the surface of small bodies.

  9. Exact expressions for colloidal plane-particle interaction forces and energies with applications to atomic force microscopy

    International Nuclear Information System (INIS)

    Zypman, F R

    2006-01-01

    We begin by deriving a general useful theoretical relationship between the plane-particle interaction forces in solution, and the corresponding plane-plane interaction energies. This is the main result of the paper. It provides a simple tool to obtain closed-form particle-plane forces from knowledge of plane-plane interaction energies. To illustrate the simplicity of use of this general formalism, we apply it to find particle-plane interactions within the Derjaguin-Landau-Verwey-Overbeek (DLVO) framework. Specifically, we obtain analytical expressions for forces and interaction energies in the van der Waals and the electrical double layer cases. The van der Waals expression is calculated here for benchmarking purposes and is compared with well-established expressions from Hamaker theory. The interactions for the electric double layer situation are computed in two cases: the linear superposition approximation and the constant surface potential. In both cases, our closed-form expressions were compared with existent numerical results. We also use the main result of this paper to generate an analytical force-separation expression based on atomic force microscope experiments for a tip and surface immersed in an aqueous solution, and compare it with the corresponding numerical results. Finally, based on our main result, we generalize the Derjaguin approximation by calculating the next order of approximation, thus obtaining a formula valuable for colloidal interaction estimations

  10. Macroscopic QED in linearly responding media and a Lorentz-Force approach to dispersion forces

    Energy Technology Data Exchange (ETDEWEB)

    Raabe, Christian

    2008-07-08

    In this thesis, a very general quantization scheme for the macroscopic electromagnetic field in arbitrary linearly responding media is presented. It offers a unified approach to QED in such media. Applying the quantization scheme, a theory of the dispersion forces on the basis of the Lorentz force is developed. By regarding the dispersion force as the (ground-state or thermal-state) expectation value of the Lorentz force that acts on appropriately defined charge and current densities, Casimir, Casimir-Polder, and van der Waals forces are united in a very natural way that makes transparent their common physical basis. Application of the theory to planar structures yields generalizations of well-known Lifschitz and Casimir-type formulas. (orig.)

  11. Macroscopic QED in linearly responding media and a Lorentz-Force approach to dispersion forces

    International Nuclear Information System (INIS)

    Raabe, Christian

    2008-01-01

    In this thesis, a very general quantization scheme for the macroscopic electromagnetic field in arbitrary linearly responding media is presented. It offers a unified approach to QED in such media. Applying the quantization scheme, a theory of the dispersion forces on the basis of the Lorentz force is developed. By regarding the dispersion force as the (ground-state or thermal-state) expectation value of the Lorentz force that acts on appropriately defined charge and current densities, Casimir, Casimir-Polder, and van der Waals forces are united in a very natural way that makes transparent their common physical basis. Application of the theory to planar structures yields generalizations of well-known Lifschitz and Casimir-type formulas. (orig.)

  12. Quantum and classical vacuum forces at zero and finite temperature

    International Nuclear Information System (INIS)

    Niekerken, Ole

    2009-06-01

    In this diploma thesis the Casimir-Polder force at zero temperature and at finite temperatures is calculated by using a well-defined quantum field theory (formulated in position space) and the method of image charges. For the calculations at finite temperature KMS-states are used. The so defined temperature describes the temperature of the electromagnetic background. A one oscillator model for inhomogeneous dispersive absorbing dielectric material is introduced and canonically quantized to calculate the Casimir-Polder force at a dielectric interface at finite temperature. The model fulfils causal commutation relations and the dielectric function of the model fulfils the Kramer-Kronig relations. We then use the same methods to calculate the van der Waals force between two neutral atoms at zero temperature and at finite temperatures. It is shown that the high temperature behaviour of the Casimir-Polder force and the van der Waals force are independent of ℎ. This means that they have to be understood classically, what is then shown in an algebraic statistical theory by using classical KMS states. (orig.)

  13. Origins of the Non-DLVO Force between Glass Surfaces in Aqueous Solution.

    Science.gov (United States)

    Adler, Joshua J.; Rabinovich, Yakov I.; Moudgil, Brij M.

    2001-05-15

    Direct measurement of surface forces has revealed that silica surfaces seem to have a short-range repulsion that is not accounted for in classical DLVO theory. The two leading hypotheses for the origin of the non-DLVO force are (i) structuring of water at the silica interface or (ii) water penetration into the surface resulting in a gel layer. In this article, the interaction of silica surfaces will be reviewed from the perspective of the non-DLVO force origin. In an attempt to more accurately describe the behavior of silica and glass surfaces, alternative models of how surfaces with gel layers should interact are proposed. It is suggested that a lessened van der Waals attraction originating from a thin gel layer may explain both the additional stability and the coagulation behavior of silica. It is important to understand the mechanisms underlying the existence of the non-DLVO force which is likely to have a major influence on the adsorption of polymers and surfactants used to modify the silica surface for practical applications in the ceramic, mineral, and microelectronic industries. Copyright 2001 Academic Press.

  14. Effect of van der Waals interaction on the properties of SnS2 layered semiconductor

    International Nuclear Information System (INIS)

    Seminovski, Y.; Palacios, P.; Wahnón, P.

    2013-01-01

    Nowadays, dispersion correction applied on layered semiconductors is a topic of interest. Among the known layered semiconductors, SnS 2 polytypes are wide gap semiconductors with a van der Waals interaction between their layers, which could form good materials to be used in photovoltaic applications. The present work gives an approach to the SnS 2 geometrical and electronic characterization using an empirical dispersion correction added to the Perdew–Burke–Ernzerhof functional and subsequent actualization of the electronic charge density using the screened hybrid Heyd–Scuseria–Ernzerhof functional using a density functional code. The obtained interlayer distance and band-gap are in good agreement with experimental values when van der Waals dispersion forces are included. - Highlights: ► Tin disulphide (SnS 2 ) has been calculated using density functional theory methods. ► A dispersion correction was also applied for two different SnS 2 polytypes. ► Geometrical parameters and band-gaps were obtained using both approaches. ► Our calculations give a good agreement of the computed band gap with experiment

  15. Capillary force between wetted nanometric contacts and its application to atomic force microscopy.

    Science.gov (United States)

    Crassous, Jérôme; Ciccotti, Matteo; Charlaix, Elisabeth

    2011-04-05

    We extend to the case of perfect wetting the exact calculation of Orr et al. (J. Fluid. Mech. 1975, 67, 723) for a pendular ring connecting two dry surfaces. We derive an approximate analytical expression for the capillary force between two highly curved surfaces covered by a wetting liquid film. The domain of validity of this expression is assessed and extended by a custom-made numerical simulation based on the full exact mathematical description. In the case of attractive liquid-solid van der Waals interactions, the capillary force increases monotonically with decreasing vapor pressure up to several times its saturation value. This accurate description of the capillary force makes it possible to estimate the adhesion force between wet nanoparticles; it can also be used to quantitatively interpret pull-off forces measured by atomic force microscopy.

  16. Classical description of dynamical many-body systems with central forces, spin-orbit forces and spin-spin forces

    International Nuclear Information System (INIS)

    Goepfert, A.

    1994-01-01

    This thesis develops a new model, and related numerical methods, to describe classical time-dependent many-body systems interacting through central forces, spin-orbit forces and spin-spin forces. The model is based on two-particle interactions. The two-body forces consist of attractive and repulsive parts. In this model the investigated multi-particle systems are self-bound. Also the total potential of the whole ensemble is derived from the two-particle potential and is not imposed 'from outside'. Each particle has the three degrees of freedom of its centre-of-mass motion and the spin degree of freedom. The model allows for the particles to be either charged or uncharged. Furthermore, each particle has an angular momentum, an intrinsic spin, and a magnetic dipole moment. Through the electromagnetic forces between these charges and moments there arise dynamical couplings between them. The internal interactions between the charges and moments are well described by electromagnetic coupling mechanisms. In fact, compared to conventional classical molecular dynamics calculations in van der Waals clusters, which have no spin degrees of freedom, or for Heisenberg spin Systems, which have no orbital degrees of freedom, the model presented here contains both types of degrees of freedom with a highly non-trivial coupling. The model allows to study the fundamental effects resulting from the dynamical coupling of the spin and the orbital-motion sub-systems. In particular, the dynamics of the particle mass points show a behaviour basically different from the one of particles in a potential with only central forces. Furthermore, a special type of quenching procedure was invented, which tends to drive the multi-particle Systems into states with highly periodic, non-ergodic behaviour. Application of the model to cluster simulations has provided evidence that the model can also be used to investigate items like solid-to-liquid phase transitions (melting), isomerism and specific heat

  17. Cosmological models constructed by van der Waals fluid approximation and volumetric expansion

    Science.gov (United States)

    Samanta, G. C.; Myrzakulov, R.

    The universe modeled with van der Waals fluid approximation, where the van der Waals fluid equation of state contains a single parameter ωv. Analytical solutions to the Einstein’s field equations are obtained by assuming the mean scale factor of the metric follows volumetric exponential and power-law expansions. The model describes a rapid expansion where the acceleration grows in an exponential way and the van der Waals fluid behaves like an inflation for an initial epoch of the universe. Also, the model describes that when time goes away the acceleration is positive, but it decreases to zero and the van der Waals fluid approximation behaves like a present accelerated phase of the universe. Finally, it is observed that the model contains a type-III future singularity for volumetric power-law expansion.

  18. Molecule Matters van der Waals Molecules

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 14; Issue 12. Molecule Matters van der Waals Molecules - Noble Gas Clusters are London Molecules! E Arunan. Feature Article Volume 14 Issue 12 December 2009 pp 1210-1222 ...

  19. Oscillator representation and generalized van der Waals Hamiltonians

    International Nuclear Information System (INIS)

    Dinejkhan, M.

    1996-01-01

    The method called the oscillator representation is extended to calculate the energy spectrum of bound state described by axially symmetrical potentials in the parabolic system coordinates. In particular, the method is applied to calculate the energy of the ground and excited states of the hydrogen atom in the uniform electric field and van der Waals field. The method gives the perturbation formulas for the analytic spectrum of the hydrogen atom in the generalized van der Waals field and defined oscillator strengths for transitions from the ground state to the perturbed manifold n=10, m=0. 14 refs., 1 fig

  20. Nucleon-nucleon interaction with quark exchange and prediction of the color van der Waals potential

    International Nuclear Information System (INIS)

    Osman, A.

    1988-01-01

    The nucleon-nucleon interaction is considered by including the color nucleon clusters. The nucleon-nucleon system is treated as a six-quark system. The obtained local potentials reduce the short-range repulsion. The resulting nucleon-nucleon potential, using a quark-quark potential, agress well with the central-force potentials. The phase shifts calculated by using these local potentials are in good agreement with those obtained from other methods. Introducing the quark-quark potential in the nucleon-nucleon interaction leads to a color van der Waals potential much stronger than that implied by experiments

  1. Uncertainties in forces extracted from non-contact atomic force microscopy measurements by fitting of long-range background forces

    Directory of Open Access Journals (Sweden)

    Adam Sweetman

    2014-04-01

    Full Text Available In principle, non-contact atomic force microscopy (NC-AFM now readily allows for the measurement of forces with sub-nanonewton precision on the atomic scale. In practice, however, the extraction of the often desired ‘short-range’ force from the experimental observable (frequency shift is often far from trivial. In most cases there is a significant contribution to the total tip–sample force due to non-site-specific van der Waals and electrostatic forces. Typically, the contribution from these forces must be removed before the results of the experiment can be successfully interpreted, often by comparison to density functional theory calculations. In this paper we compare the ‘on-minus-off’ method for extracting site-specific forces to a commonly used extrapolation method modelling the long-range forces using a simple power law. By examining the behaviour of the fitting method in the case of two radically different interaction potentials we show that significant uncertainties in the final extracted forces may result from use of the extrapolation method.

  2. Nucleon-nucleon interaction with quark exchanges and prediction to colour van der Waals potential

    International Nuclear Information System (INIS)

    Osman, A.

    1985-11-01

    The nucleon-nucleon interaction is considered by including the colour nucleon clusters. The nucleon-nucleon system is treated as a six-quark system. The obtained local potentials reduce the short-range repulsion. The resulted nucleon-nucleon potential by using a quark-quark potential well agrees with the central-force potentials. The phase shifts calculated by using these local potentials are in good agreement with those obtained from other methods. Introducing the quark-quark potential in the nucleon-nucleon interaction, leads to a colour van der Waals potential very strong compared with that predicted by experiments. (author)

  3. The van der Waals interaction of microparticles with a substrate characterized by a nonlocal response

    International Nuclear Information System (INIS)

    Dorofeyev, Illarion

    2007-01-01

    The van der Waals energy of the system constituted by a microparticle and a solid surface characterized by a nonlocal response is calculated taking into account an influence of another microparticle. A saturation of the dispersion interaction at short distances from the surface both for the spectral density of energy and for the total energy is shown. The known McLachlan expression for the pair and triple energies in the case of local media directly follows from the obtained general expression

  4. 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.

  5. Effect of van der Waals interaction on the properties of SnS{sub 2} layered semiconductor

    Energy Technology Data Exchange (ETDEWEB)

    Seminovski, Y. [Instituto de Energía Solar, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Dpt. TEAT, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Palacios, P., E-mail: pablo.palacios@upm.es [Instituto de Energía Solar, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Dpt. FyQATA, EIAE, Universidad Politécnica de Madrid, Pz. Cardenal Cisneros, 3, 28040 Madrid (Spain); Wahnón, P. [Instituto de Energía Solar, Universidad Politécnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain); Dpt. TEAT, ETSI Telecomunicacion, Universidad Politecnica de Madrid, Ciudad Universitaria, 28040 Madrid (Spain)

    2013-05-01

    Nowadays, dispersion correction applied on layered semiconductors is a topic of interest. Among the known layered semiconductors, SnS{sub 2} polytypes are wide gap semiconductors with a van der Waals interaction between their layers, which could form good materials to be used in photovoltaic applications. The present work gives an approach to the SnS{sub 2} geometrical and electronic characterization using an empirical dispersion correction added to the Perdew–Burke–Ernzerhof functional and subsequent actualization of the electronic charge density using the screened hybrid Heyd–Scuseria–Ernzerhof functional using a density functional code. The obtained interlayer distance and band-gap are in good agreement with experimental values when van der Waals dispersion forces are included. - Highlights: ► Tin disulphide (SnS{sub 2}) has been calculated using density functional theory methods. ► A dispersion correction was also applied for two different SnS{sub 2} polytypes. ► Geometrical parameters and band-gaps were obtained using both approaches. ► Our calculations give a good agreement of the computed band gap with experiment.

  6. Report of the Material Control and Material Accounting Task Force: summary

    International Nuclear Information System (INIS)

    1978-03-01

    A special review was made of the safeguards maintained by licensees possessing 5 kg or more of strategic special nuclear material (SSNM), i.e., plutonium, uranium-233, or uranium enriched in the uranium-235 isotope to 20 percent or more. A Task Force was formed to define the roles and objectives of material control and material accounting in the NRC safeguards program; recommend goals for material control and material accounting systems based on their roles and objectives; assess the extent to which the existing regulatory base meets or provides the capability to meet the recommended goals; and to provide direction for material control and material accounting development, including both near-term and long-term upgrades. Based on results of Task Force investigations it is recommended that licensee plans for measurement control programs be submitted in response to Section 70.57(c) of Title 10 of the Code of Federal Regulations. Other recommendations include the review and upgrading, as necessary, of measurement error propagation models used by each licensee; revision of Nuclear Materials Management and Safeguards System (NMMSS) reporting entities for SSNM licensees to be consistent with the partitioning of facilities into plants or, if appropriate, accounting units; review of NMMSS reporting entities for SSNM licensees to assure that data for high enriched uranium operations are clearly separated from low enriched uranium operations; upgrading of the editing by NMMSS of reported licensee safeguards data for accuracy and consistency; and the acquisition of (a) a secure interactive computer capability for use in collecting, storing, sorting, and analyzing special nuclear material accounting data, and (b) associated flexible computer software that presents safeguards information in a succinct and comprehensive manner

  7. Effects of nonmagnetic interparticle forces on magnetorheological fluids

    International Nuclear Information System (INIS)

    Klingenberg, D J; Olk, C H; Golden, M A; Ulicny, J C

    2010-01-01

    Effects of nonmagnetic interparticle forces on the on- and off-state behavior of magnetorheological fluids are investigated experimentally and with particle-level simulations. Suspensions of iron particles in an aliphatic oil are modified by surface-active species. The modifications significantly alter the off-state properties, but have little impact on the field-induced stresses. Simulations show similar behavior. Off-state rheological properties are strongly influenced by van der Waals forces and modifications of the short-range repulsive forces. Field-induced stresses are less sensitive to the nonmagnetic forces.

  8. Effects of nonmagnetic interparticle forces on magnetorheological fluids

    International Nuclear Information System (INIS)

    Klingenberg, D J; Olk, C K; Golden, M A; Ulicny, J C

    2009-01-01

    Effects of nonmagnetic interparticle forces on the on- and off-state behavior of MR fluids are investigated experimentally and with particle-level simulations. Suspensions of iron particles in an aliphatic oil are modified by surface-active species. The modifications significantly alter the off-state properties, but have little impact on the field-induced stresses. Simulations show similar behavior. Off-state rheological properties are strongly influenced by van der Waals forces and modifications of the short-range repulsive forces. Field-induced stresses are less sensitive to the nonmagnetic forces.

  9. Local adhesive surface properties studied by force microscopy

    International Nuclear Information System (INIS)

    Lekka, M.; Lekki, J.; Marszalek, M.; Stachura, Z.; Cleff, B.

    1998-01-01

    Scanning force microscopy was used in the contact mode to determine the adhesion force between a mica surface and a silicon nitride tip. The measurements were performed in an aqueous solution of sodium and calcium chlorides. The adhesion force according to the Derjaguin-Landau-Verwey-Overbeek theory depends on the competition between two kinds of forces: van der Waals and electrostatic 'double layer'. Two different curves of adhesion force versus salt concentration were obtained from the experiment with monovalent and divalent ions. The tip-surface adhesion force was determined from a statistical analysis of data obtained from the force vs. distance retracting curves. (author)

  10. Sign change in the net force in sphere-plate and sphere-sphere systems immersed in nonpolar critical fluid due to the interplay between the critical Casimir and dispersion van der Waals forces.

    Science.gov (United States)

    Valchev, Galin; Dantchev, Daniel

    2017-08-01

    We study systems in which both long-ranged van der Waals and critical Casimir interactions are present. The latter arise as an effective force between bodies when immersed in a near-critical medium, say a nonpolar one-component fluid or a binary liquid mixture. They are due to the fact that the presence of the bodies modifies the order parameter profile of the medium between them as well as the spectrum of its allowed fluctuations. We study the interplay between these forces, as well as the total force (TF) between a spherical colloid particle and a thick planar slab and between two spherical colloid particles. We do that using general scaling arguments and mean-field-type calculations utilizing the Derjaguin and the surface integration approaches. They both are based on data of the forces between two parallel slabs separated at a distance L from each other, confining the fluctuating fluid medium characterized by its temperature T and chemical potential μ. The surfaces of the colloid particles and the slab 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. On the other hand, the core region of the slab and the particles influence the fluid by long-ranged competing dispersion potentials. We demonstrate that for a suitable set of colloids-fluid, slab-fluid, and fluid-fluid coupling parameters, the competition between the effects due to the coatings and the core regions of the objects involved result, when one changes T, μ, or L, in sign change of the Casimir force (CF) and the TF acting between the colloid and the slab, as well as between the colloids. This can be used for governing the behavior of objects, say colloidal particles, at small distances, say in colloid suspensions for preventing flocculation. It can also provide a strategy for solving problems with handling, feeding

  11. Sign change in the net force in sphere-plate and sphere-sphere systems immersed in nonpolar critical fluid due to the interplay between the critical Casimir and dispersion van der Waals forces

    Science.gov (United States)

    Valchev, Galin; Dantchev, Daniel

    2017-08-01

    We study systems in which both long-ranged van der Waals and critical Casimir interactions are present. The latter arise as an effective force between bodies when immersed in a near-critical medium, say a nonpolar one-component fluid or a binary liquid mixture. They are due to the fact that the presence of the bodies modifies the order parameter profile of the medium between them as well as the spectrum of its allowed fluctuations. We study the interplay between these forces, as well as the total force (TF) between a spherical colloid particle and a thick planar slab and between two spherical colloid particles. We do that using general scaling arguments and mean-field-type calculations utilizing the Derjaguin and the surface integration approaches. They both are based on data of the forces between two parallel slabs separated at a distance L from each other, confining the fluctuating fluid medium characterized by its temperature T and chemical potential μ . The surfaces of the colloid particles and the slab 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. On the other hand, the core region of the slab and the particles influence the fluid by long-ranged competing dispersion potentials. We demonstrate that for a suitable set of colloids-fluid, slab-fluid, and fluid-fluid coupling parameters, the competition between the effects due to the coatings and the core regions of the objects involved result, when one changes T , μ , or L , in sign change of the Casimir force (CF) and the TF acting between the colloid and the slab, as well as between the colloids. This can be used for governing the behavior of objects, say colloidal particles, at small distances, say in colloid suspensions for preventing flocculation. It can also provide a strategy for solving problems with handling, feeding

  12. Quantum field theory of van der Waals friction

    International Nuclear Information System (INIS)

    Volokitin, A. I.; Persson, B. N. J.

    2006-01-01

    van der Waals friction between two semi-infinite solids, and between a small neutral particle and semi-infinite solid is studied using thermal quantum field theory in the Matsubara formulation. We show that the friction to linear order in the sliding velocity can be obtained from the equilibrium Green functions and that our treatment can be extended for bodies with complex geometry. The calculated friction agrees with the friction obtained using a dynamical modification of the Lifshitz theory, which is based on the fluctuation-dissipation theorem. We show that it should be possible to measure the van der Waals friction in noncontact friction experiment using state-of-the-art equipment

  13. Augmented van der Waals Equations of State: SAFT-VR versus Yukawa Based van der Waals Equation

    Czech Academy of Sciences Publication Activity Database

    Nezbeda, Ivo; Melnyk, R.; Trokhymchuk, A.

    2011-01-01

    Roč. 309, č. 2 (2011), s. 174-178 ISSN 0378-3812 R&D Projects: GA AV ČR IAA400720710 Institutional research plan: CEZ:AV0Z40720504 Keywords : perturbation theory * SAFT-VR * augmented van der Waals Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 2.139, year: 2011

  14. 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...

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

    International Nuclear Information System (INIS)

    Shimamura, Kohei; Misawa, Masaaki; Li, Ying; Kalia, Rajiv K.; Nakano, Aiichiro; Vashishta, Priya; Shimojo, Fuyuki

    2015-01-01

    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 −13 s from the passage of shock front, lateral collision produces NO 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 −12 s, shock normal to multilayers becomes more reactive, producing H 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

  16. 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.

  17. Molecule Matters van der Waals Molecules

    Indian Academy of Sciences (India)

    Home; Journals; Resonance – Journal of Science Education; Volume 15; Issue 7. Molecule Matters van der Waals Molecules - Rg•••HF Complexes are Debye Molecules! E Arunan. Feature Article Volume 15 Issue 7 July 2010 pp 667-674. Fulltext. Click here to view fulltext PDF. Permanent link:

  18. Empathy's purity, sympathy's complexities; De Waal, Darwin and Adam Smith.

    Science.gov (United States)

    van der Weele, Cor

    2011-07-01

    Frans de Waal's view that empathy is at the basis of morality directly seems to build on Darwin, who considered sympathy as the crucial instinct. Yet when we look closer, their understanding of the central social instinct differs considerably. De Waal sees our deeply ingrained tendency to sympathize (or rather: empathize) with others as the good side of our morally dualistic nature. For Darwin, sympathizing was not the whole story of the "workings of sympathy"; the (selfish) need to receive sympathy played just as central a role in the complex roads from sympathy to morality. Darwin's understanding of sympathy stems from Adam Smith, who argued that the presence of morally impure motives should not be a reason for cynicism about morality. I suggest that De Waal's approach could benefit from a more thorough alignment with the analysis of the workings of sympathy in the work of Darwin and Adam Smith.

  19. Combined short scale roughness and surface dielectric function gradient effects on the determination of tip-sample force in atomic force microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Gusso, André, E-mail: gusso@metal.eeimvr.uff.br [Departamento de Ciências Exatas-EEIMVR, Universidade Federal Fluminense, Volta Redonda, RJ 27255-125 (Brazil)

    2013-11-11

    The contribution of tip roughness to the van der Waals force between an atomic force microscopy probe tip and the sample is calculated using the multilayer effective medium model, which allows us to consider the relevant case of roughness characterized by correlation length and amplitude in the nanometer scale. The effect of the surface dielectric function gradient is incorporated in the tip-sample force model. It is concluded that for rms roughness in the few nanometers range the effect of short scale tip roughness is quite significant.

  20. Precise, Self-Limited Epitaxy of Ultrathin Organic Semiconductors and Heterojunctions Tailored by van der Waals Interactions.

    Science.gov (United States)

    Wu, Bing; Zhao, Yinghe; Nan, Haiyan; Yang, Ziyi; Zhang, Yuhan; Zhao, Huijuan; He, Daowei; Jiang, Zonglin; Liu, Xiaolong; Li, Yun; Shi, Yi; Ni, Zhenhua; Wang, Jinlan; Xu, Jian-Bin; Wang, Xinran

    2016-06-08

    Precise assembly of semiconductor heterojunctions is the key to realize many optoelectronic devices. By exploiting the strong and tunable van der Waals (vdW) forces between graphene and organic small molecules, we demonstrate layer-by-layer epitaxy of ultrathin organic semiconductors and heterostructures with unprecedented precision with well-defined number of layers and self-limited characteristics. We further demonstrate organic p-n heterojunctions with molecularly flat interface, which exhibit excellent rectifying behavior and photovoltaic responses. The self-limited organic molecular beam epitaxy (SLOMBE) is generically applicable for many layered small-molecule semiconductors and may lead to advanced organic optoelectronic devices beyond bulk heterojunctions.

  1. 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.

  2. Report of the Material Control and Material Accounting Task Force: the role of material control and material accounting in the safeguards program

    International Nuclear Information System (INIS)

    1978-03-01

    Results are presented of NRC Task Force investigations to identify the functions of a safeguards program in relation to the NRC safeguards objective, define the role and objectives of material control and material accounting systems within that program, develop goals for material control and material accounting based on those roles and objectives, assess current material control and material accounting requirements and performance levels in the light of the goals, and recommend future actions needed to attain the proposed goals. It was found that the major contribution of material accounting to the safeguards program is in support of the assurance function. It also can make secondary contributions to the prevention and response functions. In the important area of loss detection, a response measure, it is felt that limitations inherent in material accounting for some fuel cycle operations limit its ability to operate as a primary detection system to detect a five formula kilogram loss with high assurance (defined by the Task Force as a probability of detection of 90 percent or more) and that, in those cases, material accounting can act only in a backup role. Physical security and material control must make the primary contributions to the prevention and detection of theft, so that safeguards do not rely primarily for detection capabilities on material accounting. There are several areas of accounting that require more emphasis than is offered by the current regulatory base. These areas include: timely shipper-receiver difference analysis and reconciliation; a demand physical inventory capability; improved loss localization;discard measurement verification; timely recovery of scrap; improved measurement and record systems; and limits on cumulative inventory differences and shipper-receiver differences. An increased NRC capability for monitoring and analyzing licensee accounting data and more timely and detailed submittals of data to NRC by licensees are recommended

  3. Closed-form solution for static pull-in voltage of electrostatically actuated clamped-clamped micro/nano beams under the effect of fringing field and van der Waals force

    Science.gov (United States)

    Bhojawala, V. M.; Vakharia, D. P.

    2017-12-01

    This investigation provides an accurate prediction of static pull-in voltage for clamped-clamped micro/nano beams based on distributed model. The Euler-Bernoulli beam theory is used adapting geometric non-linearity of beam, internal (residual) stress, van der Waals force, distributed electrostatic force and fringing field effects for deriving governing differential equation. The Galerkin discretisation method is used to make reduced-order model of the governing differential equation. A regime plot is presented in the current work for determining the number of modes required in reduced-order model to obtain completely converged pull-in voltage for micro/nano beams. A closed-form relation is developed based on the relationship obtained from curve fitting of pull-in instability plots and subsequent non-linear regression for the proposed relation. The output of regression analysis provides Chi-square (χ 2) tolerance value equals to 1  ×  10-9, adjusted R-square value equals to 0.999 29 and P-value equals to zero, these statistical parameters indicate the convergence of non-linear fit, accuracy of fitted data and significance of the proposed model respectively. The closed-form equation is validated using available data of experimental and numerical results. The relative maximum error of 4.08% in comparison to several available experimental and numerical data proves the reliability of the proposed closed-form equation.

  4. 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.

  5. 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...

  6. Anomalous van der Waals-Casimir interactions on graphene: A concerted effect of temperature, retardation, and non-locality

    Science.gov (United States)

    Ambrosetti, Alberto; Silvestrelli, Pier Luigi

    2018-04-01

    Dispersion forces play a major role in graphene, largely influencing adhesion of adsorbate moieties and stabilization of functional multilayered structures. However, the reliable prediction of dispersion interactions on graphene up to the relevant ˜10 nm scale is an extremely challenging task: in fact, electromagnetic retardation effects and the highly non-local character of π electrons can imply sizeable qualitative variations of the interaction with respect to known pairwise approaches. Here we address both issues, determining the finite-temperature van der Waals (vdW)-Casimir interaction for point-like and extended adsorbates on graphene, explicitly accounting for the non-local dielectric permittivity. We find that temperature, retardation, and non-locality play a crucial role in determining the actual vdW scaling laws and the stability of both atomic and larger molecular adsorbates. Our results highlight the importance of these effects for a proper description of systems of current high interest, such as graphene interacting with biomolecules, and self-assembly of complex nanoscale structures. Due to the generality of our approach and the observed non-locality of other 2D materials, our results suggest non-trivial vdW interactions from hexagonal mono-layered materials from group 14 of the periodic table, to transition metal dichalcogenides.

  7. Gravitational potential of perturbed ellipsoidal inhomogeneous configurations with the account of the 'fifth' force

    International Nuclear Information System (INIS)

    Masyukov, V.V.; Tsvetkov, V.P.

    1990-01-01

    The analytical representations of the gravitational potential of perturbed inhomogeneous ellipsoidal configurations with the account of the 'fifth' force are obtained in the form of the series in the parameter of perturbation. 11 refs

  8. DEM modeling of failure mechanisms induced by excavations on the Moon

    Science.gov (United States)

    jiang, mingjing; shen, zhifu; Utili, Stefano

    2013-04-01

    2D Discrete Element Method (DEM) analyses were performed for excavations supported by retaining walls in lunar environment. The lunar terrain is made of a layer of sand (regolith) which differs from terrestrial sands for two main features: the presence of adhesive attractive forces due to van der Waals interactions and grains being very irregular in shape leading to high interlocking. A simplified contact model based on linear elasticity and perfect plasticity was employed. The contact model includes a moment - relative rotation law to account for high interlocking among grains and a normal adhesion law to account for the van der Waals interactions. Analyses of the excavations were run under both lunar and terrestrial environments. Under lunar environment, gravity is approximately one sixth than the value on Earth and adhesion forces between grains of lunar regolith due to van der Waals interactions are not negligible. From the DEM simulations it emerged that van der Waals interactions may significantly increase the bending moment and deflection of the retaining wall, and the ground displacements. Hence this study indicates that an unsafe estimate of the wall response to an excavation on the Moon would be obtained from physical experiments performed in a terrestrial environment, i.e., considering the effect of gravity but neglecting the van der Waals interactions.

  9. Hydration free energies of cyanide and hydroxide ions from molecular dynamics simulations with accurate force fields

    Science.gov (United States)

    Lee, M.W.; Meuwly, M.

    2013-01-01

    The evaluation of hydration free energies is a sensitive test to assess force fields used in atomistic simulations. We showed recently that the vibrational relaxation times, 1D- and 2D-infrared spectroscopies for CN(-) in water can be quantitatively described from molecular dynamics (MD) simulations with multipolar force fields and slightly enlarged van der Waals radii for the C- and N-atoms. To validate such an approach, the present work investigates the solvation free energy of cyanide in water using MD simulations with accurate multipolar electrostatics. It is found that larger van der Waals radii are indeed necessary to obtain results close to the experimental values when a multipolar force field is used. For CN(-), the van der Waals ranges refined in our previous work yield hydration free energy between -72.0 and -77.2 kcal mol(-1), which is in excellent agreement with the experimental data. In addition to the cyanide ion, we also study the hydroxide ion to show that the method used here is readily applicable to similar systems. Hydration free energies are found to sensitively depend on the intermolecular interactions, while bonded interactions are less important, as expected. We also investigate in the present work the possibility of applying the multipolar force field in scoring trajectories generated using computationally inexpensive methods, which should be useful in broader parametrization studies with reduced computational resources, as scoring is much faster than the generation of the trajectories.

  10. Self-Aligned van der Waals Heterojunction Diodes and Transistors.

    Science.gov (United States)

    Sangwan, Vinod K; Beck, Megan E; Henning, Alex; Luo, Jiajia; Bergeron, Hadallia; Kang, Junmo; Balla, Itamar; Inbar, Hadass; Lauhon, Lincoln J; Hersam, Mark C

    2018-02-14

    A general self-aligned fabrication scheme is reported here for a diverse class of electronic devices based on van der Waals materials and heterojunctions. In particular, self-alignment enables the fabrication of source-gated transistors in monolayer MoS 2 with near-ideal current saturation characteristics and channel lengths down to 135 nm. Furthermore, self-alignment of van der Waals p-n heterojunction diodes achieves complete electrostatic control of both the p-type and n-type constituent semiconductors in a dual-gated geometry, resulting in gate-tunable mean and variance of antiambipolar Gaussian characteristics. Through finite-element device simulations, the operating principles of source-gated transistors and dual-gated antiambipolar devices are elucidated, thus providing design rules for additional devices that employ self-aligned geometries. For example, the versatility of this scheme is demonstrated via contact-doped MoS 2 homojunction diodes and mixed-dimensional heterojunctions based on organic semiconductors. The scalability of this approach is also shown by fabricating self-aligned short-channel transistors with subdiffraction channel lengths in the range of 150-800 nm using photolithography on large-area MoS 2 films grown by chemical vapor deposition. Overall, this self-aligned fabrication method represents an important step toward the scalable integration of van der Waals heterojunction devices into more sophisticated circuits and systems.

  11. Stern potential and Debye length measurements in dilute ionic solutions with electrostatic force microscopy.

    Science.gov (United States)

    Kumar, Bharat; Crittenden, Scott R

    2013-11-01

    We demonstrate the ability to measure Stern potential and Debye length in dilute ionic solution with atomic force microscopy. We develop an analytic expression for the second harmonic force component of the capacitive force in an ionic solution from the linearized Poisson-Boltzmann equation. This allows us to calibrate the AFM tip potential and, further, obtain the Stern potential of sample surfaces. In addition, the measured capacitive force is independent of van der Waals and double layer forces, thus providing a more accurate measure of Debye length.

  12. A notable difference between ideal gas and infinite molar volume limit of van der Waals gas

    International Nuclear Information System (INIS)

    Liu, Q H; Shen, Y; Bai, R L; Wang, X

    2010-01-01

    The van der Waals equation of state does not sufficiently represent a gas unless a thermodynamic potential with two proper and independent variables is simultaneously determined. The limiting procedures under which the behaviour of the van der Waals gas approaches that of an ideal gas are letting two van der Waals coefficients be zero rather than letting the molar volume become infinitely large; otherwise, the partial derivative of internal energy with respect to pressure at a fixed temperature does not vanish.

  13. A notable difference between ideal gas and infinite molar volume limit of van der Waals gas

    Science.gov (United States)

    Liu, Q. H.; Shen, Y.; Bai, R. L.; Wang, X.

    2010-05-01

    The van der Waals equation of state does not sufficiently represent a gas unless a thermodynamic potential with two proper and independent variables is simultaneously determined. The limiting procedures under which the behaviour of the van der Waals gas approaches that of an ideal gas are letting two van der Waals coefficients be zero rather than letting the molar volume become infinitely large; otherwise, the partial derivative of internal energy with respect to pressure at a fixed temperature does not vanish.

  14. Dipole-dipole van der Waals interaction in alkali halides

    International Nuclear Information System (INIS)

    Thakur, B.N.; Thakur, K.P.

    1978-01-01

    Values of van der Waals dipole-dipole constants and interaction energetics of alkali halides are reported using the recent data. The values obtained are somewhat larger than those of earlier workers. (orig.) [de

  15. Imaging of Interlayer Coupling in van der Waals Heterostructures Using a Bright-Field Optical Microscope.

    Science.gov (United States)

    Alexeev, Evgeny M; Catanzaro, Alessandro; Skrypka, Oleksandr V; Nayak, Pramoda K; Ahn, Seongjoon; Pak, Sangyeon; Lee, Juwon; Sohn, Jung Inn; Novoselov, Kostya S; Shin, Hyeon Suk; Tartakovskii, Alexander I

    2017-09-13

    Vertically stacked atomic layers from different layered crystals can be held together by van der Waals forces, which can be used for building novel heterostructures, offering a platform for developing a new generation of atomically thin, transparent, and flexible devices. The performance of these devices is critically dependent on the layer thickness and the interlayer electronic coupling, influencing the hybridization of the electronic states as well as charge and energy transfer between the layers. The electronic coupling is affected by the relative orientation of the layers as well as by the cleanliness of their interfaces. Here, we demonstrate an efficient method for monitoring interlayer coupling in heterostructures made from transition metal dichalcogenides using photoluminescence imaging in a bright-field optical microscope. The color and brightness in such images are used here to identify mono- and few-layer crystals and to track changes in the interlayer coupling and the emergence of interlayer excitons after thermal annealing in heterobilayers composed of mechanically exfoliated flakes and as a function of the twist angle in atomic layers grown by chemical vapor deposition. Material and crystal thickness sensitivity of the presented imaging technique makes it a powerful tool for characterization of van der Waals heterostructures assembled by a wide variety of methods, using combinations of materials obtained through mechanical or chemical exfoliation and crystal growth.

  16. Switch on, switch off: stiction in nanoelectromechanical switches

    KAUST Repository

    Wagner, Till J W; Vella, Dominic

    2013-01-01

    . Particular focus is given to the question of whether adhesive van der Waals forces cause the cantilever to remain in the 'ON' state even when the electrostatic forces are removed. In contrast to previous studies, our theory accounts for deflections with large

  17. Isotope engineering of van der Waals interactions in hexagonal boron nitride

    Science.gov (United States)

    Vuong, T. Q. P.; Liu, S.; van der Lee, A.; Cuscó, R.; Artús, L.; Michel, T.; Valvin, P.; Edgar, J. H.; Cassabois, G.; Gil, B.

    2018-02-01

    Hexagonal boron nitride is a model lamellar compound where weak, non-local van der Waals interactions ensure the vertical stacking of two-dimensional honeycomb lattices made of strongly bound boron and nitrogen atoms. We study the isotope engineering of lamellar compounds by synthesizing hexagonal boron nitride crystals with nearly pure boron isotopes (10B and 11B) compared to those with the natural distribution of boron (20 at% 10B and 80 at% 11B). On the one hand, as with standard semiconductors, both the phonon energy and electronic bandgap varied with the boron isotope mass, the latter due to the quantum effect of zero-point renormalization. On the other hand, temperature-dependent experiments focusing on the shear and breathing motions of adjacent layers revealed the specificity of isotope engineering in a layered material, with a modification of the van der Waals interactions upon isotope purification. The electron density distribution is more diffuse between adjacent layers in 10BN than in 11BN crystals. Our results open perspectives in understanding and controlling van der Waals bonding in layered materials.

  18. Van der Waals interactions between planar substrate and tubular lipid membranes undergoing pearling instability

    Science.gov (United States)

    Valchev, G. S.; Djondjorov, P. A.; Vassilev, V. M.; Dantchev, D. M.

    2017-10-01

    In the current article we study the behavior of the van der Waals force between a planar substrate and an axisymmetric bilayer lipid membrane undergoing pearling instability, caused by uniform hydrostatic pressure difference. To do so, the recently suggested "surface integration approach" is used, which can be considered a generalization of the well known and widely used Derjaguin approximation. The static equilibrium shape after the occurrence of the instability is described in the framework of Helfrich's spontaneous curvature model. Some specific classes of exact analytical solutions to the corresponding shape equation are considered, and the components of the respective position vectors given in terms of elliptic integrals and Jacobi elliptic functions. The mutual orientation between the interacting objects is chosen such that the axis of revolution of the distorted cylinder be parallel to the plane bounding the substrate. Based on the discussed models and approaches we made some estimations for the studied force in real experimentally realizable systems, thus showing the possibility of pearling as an useful technique for reduction of the adhesion in variety of industrial processes using lipid membranes as carriers.

  19. Supersonic molecular beam electric resonance spectroscopy and van der Waals molecules

    International Nuclear Information System (INIS)

    Luftman, H.S.

    1982-09-01

    A supersonic molecular beam electric resonance (MBER) spectrometer was built to study the radiofrequency spectra of weakly bound gas phase van der Waals molecules. The instrument and its operating characteristics are described in detail. Sample mass spectra of Ar-ClF gas mixtures are also presented as an illustration of the synthesis of van der Waals molecules. The Stark focusing process for linear polar molecules is discussed and computer-simulated using both second order perturbation and variational methods. Experimental refocusing spectra of OCS and ClF are studied and compared with these trajectory calculations. Though quantitative fitting is poor, there are strong qualitative indicators that the central part of a supersonic beam consists of molecules with a significantly greater population in the lowest energy rotational states than generally assumed. Flop in as opposed to flop out resonance signals for OCS are also numerically predicted and observed. The theoretical properties of the MBER spectrum for linear molecules are elaborated upon with special emphasis on line shape considerations. MBER spectra of OCS and ClF under a variety of conditions are presented and discussed in context to these predictions. There is some uncertainty expressed both in our own modeling and in the manner complex MBER spectra have been analyzed in the past. Finally, an electrostatic potential model is used to quantitatively describe the class of van der Waals molecules Ar-MX, where MX is an alkali halide. Energetics and equilibrium geometries are calculated. The validity of using an electrostatic model to predict van der Waals bond properties is critically discussed

  20. Nucleotide insertion initiated by van der Waals interaction during ...

    Indian Academy of Sciences (India)

    renormalized van der Waals (vdW) interaction of a stronger type, the ..... can be used to determine the electrostatic dipole–dipole, .... water molecule and a surface oxygen atom. ..... understand proteins electronic interaction.54 Here, we.

  1. Effect of adding Te to layered GaSe crystals to increase the van der Waals bonding force

    Science.gov (United States)

    Tanabe, Tadao; Zhao, Shu; Sato, Yohei; Oyama, Yutaka

    2017-10-01

    The interplanar binding strength of layered GaSe1-xTex crystals was directly measured using a tensile testing machine. The GaSe1-xTex crystals were grown by a low temperature liquid phase solution method under a controlled Se vapor pressure. The stoichiometry-controlled GaSe1-xTex crystal has the ɛ-polytype structure of GaSe, where the Te atoms are substituted for some of the Se atoms in the GaSe crystal. The effect of adding Te on the bonding strength between the GaSe layers was determined from direct measurements of the van der Waals bonding energy. The bonding energy was increased from 0.023 × 106 N/m2 for GaSe to 0.16 × 106 N/m2 for GaSe1-xTex (x = 0.106).

  2. On the accuracy of van der Waals inclusive density-functional theory exchange-correlation functionals for ice at ambient and high pressures.

    Science.gov (United States)

    Santra, Biswajit; Klimes, Jirí; Tkatchenko, Alexandre; Alfè, Dario; Slater, Ben; Michaelides, Angelos; Car, Roberto; Scheffler, Matthias

    2013-10-21

    Density-functional theory (DFT) has been widely used to study water and ice for at least 20 years. However, the reliability of different DFT exchange-correlation (xc) functionals for water remains a matter of considerable debate. This is particularly true in light of the recent development of DFT based methods that account for van der Waals (vdW) dispersion forces. Here, we report a detailed study with several xc functionals (semi-local, hybrid, and vdW inclusive approaches) on ice Ih and six proton ordered phases of ice. Consistent with our previous study [B. Santra, J. Klimeš, D. Alfè, A. Tkatchenko, B. Slater, A. Michaelides, R. Car, and M. Scheffler, Phys. Rev. Lett. 107, 185701 (2011)] which showed that vdW forces become increasingly important at high pressures, we find here that all vdW inclusive methods considered improve the relative energies and transition pressures of the high-pressure ice phases compared to those obtained with semi-local or hybrid xc functionals. However, we also find that significant discrepancies between experiment and the vdW inclusive approaches remain in the cohesive properties of the various phases, causing certain phases to be absent from the phase diagram. Therefore, room for improvement in the description of water at ambient and high pressures remains and we suggest that because of the stern test the high pressure ice phases pose they should be used in future benchmark studies of simulation methods for water.

  3. Stern potential and Debye length measurements in dilute ionic solutions with electrostatic force microscopy

    International Nuclear Information System (INIS)

    Kumar, Bharat; Crittenden, Scott R

    2013-01-01

    We demonstrate the ability to measure Stern potential and Debye length in dilute ionic solution with atomic force microscopy. We develop an analytic expression for the second harmonic force component of the capacitive force in an ionic solution from the linearized Poisson–Boltzmann equation. This allows us to calibrate the AFM tip potential and, further, obtain the Stern potential of sample surfaces. In addition, the measured capacitive force is independent of van der Waals and double layer forces, thus providing a more accurate measure of Debye length. (paper)

  4. Interfacial forces in aqueous media

    CERN Document Server

    van Oss, Carel J

    2006-01-01

    Thoroughly revised and reorganized, the second edition of Interfacial Forces in Aqueous Media examines the role of polar interfacial and noncovalent interactions among biological and nonbiological macromolecules as well as biopolymers, particles, surfaces, cells, and both polar and apolar polymers. The book encompasses Lifshitz-van der Waals and electrical double layer interactions, as well as Lewis acid-base interactions between colloidal entities in polar liquids such as water. New in this Edition: Four previously unpublished chapters comprising a new section on interfacial propertie

  5. C6H6/Au(111): Interface dipoles, band alignment, charging energy, and van der Waals interaction

    International Nuclear Information System (INIS)

    Abad, E.; Martinez, J. I.; Flores, F.; Ortega, J.; Dappe, Y. J.

    2011-01-01

    We analyze the benzene/Au(111) interface taking into account charging energy effects to properly describe the electronic structure of the interface and van der Waals interactions to obtain the adsorption energy and geometry. We also analyze the interface dipoles and discuss the barrier formation as a function of the metal work-function. We interpret our DFT calculations within the induced density of interface states (IDIS) model. Our results compare well with experimental and other theoretical results, showing that the dipole formation of these interfaces is due to the charge transfer between the metal and benzene, as described in the IDIS model.

  6. On the validity of Brownian assumptions in the spin van der Waals model

    International Nuclear Information System (INIS)

    Oh, Suhk Kun

    1985-01-01

    A simple Brownian motion theory of the spin van der Waals model, which can be stationary, Markoffian or Gaussian, is studied. By comparing the Brownian motion theory with an exact theory called the generalized Langevin equation theory, the validity of the Brownian assumptions is tested. Thereby, it is shown explicitly how the Markoffian and Gaussian properties are modified in the spin van der Waals model under the influence of quantum fluctuations and long range ordering. (Author)

  7. Combinations of coupled cluster, density functionals, and the random phase approximation for describing static and dynamic correlation, and van der Waals interactions

    Science.gov (United States)

    Garza, Alejandro J.; Bulik, Ireneusz W.; Alencar, Ana G. Sousa; Sun, Jianwei; Perdew, John P.; Scuseria, Gustavo E.

    2016-04-01

    Contrary to standard coupled cluster doubles (CCD) and Brueckner doubles (BD), singlet-paired analogues of CCD and BD (denoted here as CCD0 and BD0) do not break down when static correlation is present, but neglect substantial amounts of dynamic correlation. In fact, CCD0 and BD0 do not account for any contributions from multielectron excitations involving only same-spin electrons at all. We exploit this feature to add - without introducing double counting, self-interaction, or increase in cost - the missing correlation to these methods via meta-GGA (generalised gradient approximation) density functionals (Tao-Perdew-Staroverov-Scuseria and strongly constrained and appropriately normed). Furthermore, we improve upon these CCD0+DFT blends by invoking range separation: the short- and long-range correlations absent in CCD0/BD0 are evaluated with density functional theory and the direct random phase approximation, respectively. This corrects the description of long-range van der Waals forces. Comprehensive benchmarking shows that the combinations presented here are very accurate for weakly correlated systems, while also providing a reasonable description of strongly correlated problems without resorting to symmetry breaking.

  8. Nanostructure van der Waals interaction between a quantum well and a quantum dot atom

    International Nuclear Information System (INIS)

    Horing, Norman J Morgenstern

    2006-01-01

    We examine the van der Waals interaction between mobile plasma electrons in a narrow quantum well nanostructure and a quantum dot atom. This formulation of the van der Waals interaction exhibits it to second order as the correlation energy (self-energy) of the dot-atom electrons mediated by the image potential arising from the dynamic, nonlocal and spatially inhomogeneous polarization of the quantum well plasma electrons. This image potential of the quantum-well plasma is, in turn, determined by the dynamic, nonlocal, inhomogeneous screening function of the quantum well, which involves the space-time matrix inversion of its spatially inhomogeneous, nonlocal and time-dependent dielectric function. The latter matrix inversion is carried out exactly, in closed form, and the van der Waals energy is evaluated in the electrostatic limit to dipole-dipole terms

  9. Measured long-range repulsive Casimir-Lifshitz forces.

    Science.gov (United States)

    Munday, J N; Capasso, Federico; Parsegian, V Adrian

    2009-01-08

    Quantum fluctuations create intermolecular forces that pervade macroscopic bodies. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces. However, as recognized in the theories of Casimir, Polder and Lifshitz, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies. Here we show experimentally that, in accord with theoretical prediction, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir-Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction.

  10. Energy transfer rates in inhomogeneous van der Waals clusters

    International Nuclear Information System (INIS)

    Desfrancois, C.; Schermann, J.P.

    1991-01-01

    The internal energy exchange inside an inhomogeneous van der Waals cluster are investigated by means of molecular dynamic calculations. The very long time scales for relaxation of the high frequency degrees of freedom are examined within the framework of Nekhoroshev's theorem. (orig.)

  11. Assessing photocatalytic power of g-C3N4 for solar fuel production: A first-principles study involving quasi-particle theory and dispersive forces.

    Science.gov (United States)

    Osorio-Guillén, J M; Espinosa-García, W F; Moyses Araujo, C

    2015-09-07

    First-principles quasi-particle theory has been employed to assess catalytic power of graphitic carbon nitride, g-C3N4, for solar fuel production. A comparative study between g-h-triazine and g-h-heptazine has been carried out taking also into account van der Waals dispersive forces. The band edge potentials have been calculated using a recently developed approach where quasi-particle effects are taken into account through the GW approximation. First, it was found that the description of ground state properties such as cohesive and surface formation energies requires the proper treatment of dispersive interaction. Furthermore, through the analysis of calculated band-edge potentials, it is shown that g-h-triazine has high reductive power reaching the potential to reduce CO2 to formic acid, coplanar g-h-heptazine displays the highest thermodynamics force toward H2O/O2 oxidation reaction, and corrugated g-h-heptazine exhibits a good capacity for both reactions. This rigorous theoretical study shows a route to further improve the catalytic performance of g-C3N4.

  12. 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.

  13. Using the van der Waals broadening of spectral atomic lines to measure the gas temperature of an argon-helium microwave plasma at atmospheric pressure

    International Nuclear Information System (INIS)

    Munoz, J.; Dimitrijevic, M.S.; Yubero, C.; Calzada, M.D.

    2009-01-01

    The applications of plasmas generated with gas mixtures have become increasingly common in different scientific and technological fields. In order to understand the advantages of these discharges, for instance in chemical analysis, it is necessary to know the gas temperature (T g , kinetic energy of the heavy particles) since it has a great influence on the atomization reactions of the molecules located in the discharge, along with the dependence of the reaction rate on this parameter. The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure although under some experimental conditions, these are difficult to detect. In such cases, the gas temperature can be determined from the van der Waals broadening of the emitted atomic spectral lines related to this parameter. The method proposed is based on the van der Waals broadening taking into account two perturbers

  14. 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.

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

    Science.gov (United States)

    Govyadinov, Alexander A; Konečná, Andrea; Chuvilin, Andrey; Vélez, Saül; Dolado, Irene; Nikitin, Alexey Y; Lopatin, Sergei; Casanova, Fèlix; Hueso, Luis E; Aizpurua, Javier; Hillenbrand, Rainer

    2017-07-21

    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.

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

    KAUST Repository

    Govyadinov, Alexander A.; Konečná , Andrea; Chuvilin, Andrey; Vé lez, Saü l; Dolado, Irene; Nikitin, Alexey Y.; Lopatin, Sergei; Casanova, Fè lix; Hueso, Luis E.; Aizpurua, Javier; Hillenbrand, Rainer

    2017-01-01

    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.

  17. 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...... 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...

  18. Infrared photodissociation of van der Waals molecules containing ethylene

    International Nuclear Information System (INIS)

    Casassa, M.P.; Bomse, D.S.; Janda, K.C.

    1981-01-01

    Vibrational predissociation line shapes in the n 7 region of the ethylene spectrum are measured for van der Waals molecules of ethylene bound to Ne, Ar, Kr, C 2 H 4 , C 2 F 4 , and larger ethylene clusters. The predissociative rate is very fast for this group of molecules. The vibrationally excited state lifetimes are 0.44, 0.59 and 0.89 x 10 -12 sec for (C 2 H 4 ) 2 , ArxC 2 H 4 , and C 2 H 4 xC 2 F 4 respectively. That the observed line shapes are homogeneous is demonstrated by the fact that a low-power, narrow frequency bandwidth laser can dissociate a large fraction of the initial ensemble of ethylene clusters. The observed transition probability is proportional to the number of ethylene subunits for clusters containing three or fewer ethylene subunits. These observations are interpreted in terms of intramolecular energy flow directly from ethylene n 7 to the weak van der Waals modes of motion

  19. Surface features on Sahara soil dust particles made visible by atomic force microscope (AFM) phase images

    OpenAIRE

    G. Helas; M. O. Andreae

    2008-01-01

    We show that atomic force microscopy (AFM) phase images can reveal surface features of soil dust particles, which are not evident using other microscopic methods. The non-contact AFM method is able to resolve topographical structures in the nanometer range as well as to uncover repulsive atomic forces and attractive van der Waals' forces, and thus gives insight to surface properties. Though the method does not allow quantitative assignment in terms of chemical compound description, it clearly...

  20. Attractive non-DLVO forces induced by adsorption of monovalent organic ions.

    Science.gov (United States)

    Smith, Alexander M; Maroni, Plinio; Borkovec, Michal

    2017-12-20

    Direct force measurements between negatively charged colloidal particles were carried out using an atomic force microscope (AFM) in aqueous solutions containing monovalent organic cations, namely tetraphenylarsonium (Ph 4 As + ), 1-hexyl-3-methylimidazolium (HMIM + ), and 1-octyl-3-methylimidazolium (OMIM + ). These ions adsorb to the particle surface, and induce a charge reversal. The forces become attractive at the charge neutralization point, but they are stronger than van der Waals forces. This additional and unexpected attraction decays exponentially with a decay length of a few nanometers, and is strikingly similar to the one previously observed in the presence of multivalent ions. This attractive force probably originates from coupled spontaneous charge fluctuations on the respective surfaces as initially suggested by Kirkwood and Shumaker.

  1. 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.

  2. Dispersive force between dissimilar materials: Geometrical effects

    International Nuclear Information System (INIS)

    Noguez, Cecilia; Roman-Velazquez, C.E.

    2004-01-01

    We calculate the Casimir force or dispersive van der Waals force between a spherical nanoparticle and a planar substrate, both with arbitrary dielectric properties. We show that the force between the sphere and half-space can be calculated through the interacting surface plasmons of the bodies. Using a Spectral Representation formalism, we show that the force of a sphere made of a material A and a half-space made of a material B differs from the case when the sphere is made of B, and the half-space is made of A. We find that the difference depends on the plasma frequency of the materials, the geometry, and the distance of separation between the sphere and half-space. The differences show the importance of the geometry, and make evident the necessity of realistic descriptions of the system beyond the Derjaguin Approximation or Proximity Theorem Approximation

  3. Quantum and classical vacuum forces at zero and finite temperature; Quantentheoretische und klassische Vakuum-Kraefte bei Temperatur Null und bei endlicher Temperatur

    Energy Technology Data Exchange (ETDEWEB)

    Niekerken, Ole

    2009-06-15

    In this diploma thesis the Casimir-Polder force at zero temperature and at finite temperatures is calculated by using a well-defined quantum field theory (formulated in position space) and the method of image charges. For the calculations at finite temperature KMS-states are used. The so defined temperature describes the temperature of the electromagnetic background. A one oscillator model for inhomogeneous dispersive absorbing dielectric material is introduced and canonically quantized to calculate the Casimir-Polder force at a dielectric interface at finite temperature. The model fulfils causal commutation relations and the dielectric function of the model fulfils the Kramer-Kronig relations. We then use the same methods to calculate the van der Waals force between two neutral atoms at zero temperature and at finite temperatures. It is shown that the high temperature behaviour of the Casimir-Polder force and the van der Waals force are independent of {Dirac_h}. This means that they have to be understood classically, what is then shown in an algebraic statistical theory by using classical KMS states. (orig.)

  4. Interaction forces between nanoparticles in Lennard-Jones (L-J) solvents

    International Nuclear Information System (INIS)

    Sinha, Indrajit; Mukherjee, Ashim K

    2014-01-01

    Molecular simulations, such as Monte Carlo (MC) and molecular dynamics (MD) have been recently used for understanding the forces between colloidal nanoparticles that determine the dispersion and stability of nanoparticle suspensions. Herein we review the current status of research in the area of nanoparticles immersed in L-J solvents. The first study by Shinto et al. used large smooth spheres to depict nanoparticles in L-J and soft sphere solvents. The nanoparticles were held fixed at a particular interparticle distance and only the solvents were allowed to equilibrate. Both Van-der-waals and solvation forces were computed at different but fixed interparticle separation. Later Qin and Fitchthorn improved on this model by considering the nanoparticles as collection of molecules, thus taking into the account the effect of surface roughness of nanoparticles. Although the inter particle distance was fixed, the rotation of such nanoparticles with respect to each other was also investigated. Recently, in keeping with the experimental situation, we modified this model by allowing the nanoparticles to move and rotate freely. Solvophilic, neutral and solvophobic interactions between the solvent atoms and those that make up the nanoparticles were modelled. While neutral and solvophobic nanoparticles coalesce even at intermediate distances, solvophilic nanoparticles are more stable in solution due to the formation of a solvent shield

  5. Vertical electron transport in van der Waals heterostructures with graphene layers

    International Nuclear Information System (INIS)

    Ryzhii, V.; Otsuji, T.; Ryzhii, M.; Aleshkin, V. Ya.; Dubinov, A. A.; Mitin, V.; Shur, M. S.

    2015-01-01

    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. Van der Waals interaction between metal and atom

    International Nuclear Information System (INIS)

    Rao, P.R.; Mukhopadhyay, G.

    1984-07-01

    A dielectric response approach to the Van der Waals interaction between an atom and a planar metal surface is presented. An exact formula in terms of a form factor is derived within the point dipole approximation and non-retarded limit valid for shorter separation. The interaction potential is studied via SCIB model, and a substantial modification over its classical form is found at shorter distances. (author)

  7. Measured long-range repulsive Casimir–Lifshitz forces

    Science.gov (United States)

    Munday, J. N.; Capasso, Federico; Parsegian, V. Adrian

    2014-01-01

    Quantum fluctuations create intermolecular forces that pervade macroscopic bodies1–3. At molecular separations of a few nanometres or less, these interactions are the familiar van der Waals forces4. However, as recognized in the theories of Casimir, Polder and Lifshitz5–7, at larger distances and between macroscopic condensed media they reveal retardation effects associated with the finite speed of light. Although these long-range forces exist within all matter, only attractive interactions have so far been measured between material bodies8–11. Here we show experimentally that, in accord with theoretical prediction12, the sign of the force can be changed from attractive to repulsive by suitable choice of interacting materials immersed in a fluid. The measured repulsive interaction is found to be weaker than the attractive. However, in both cases the magnitude of the force increases with decreasing surface separation. Repulsive Casimir–Lifshitz forces could allow quantum levitation of objects in a fluid and lead to a new class of switchable nanoscale devices with ultra-low static friction13–15. PMID:19129843

  8. Investigating the Role of Ferromagnetic Materials on the Casimir Force & Investigation of the Van Der Waals/Casimir Force with Graphene

    Energy Technology Data Exchange (ETDEWEB)

    Mohideen, Umar [Univ. of California, Riverside, CA (United States)

    2015-04-14

    Duration of award was from 4/15/10-4/14/15. In this grant period our contributions to the field of VdW/Casimir forces are 24 refereed publications in journals such as Physical Review Letters (4) [1-4], Physical Review B (10) [5-14], Physical Review D (2) [15,16], Applied Physics Letters (1) [17], Review of Scientific Instruments (1) [18] and the International Journal of Modern Physics A (5) [19-23] and B(1) (invited review article [24]). We presented 2 plenary conference talks, 3 lectures at the Pan American School on Frontiers in Casimir Physics, 2 conferences, 1 colloquium and 11 APS talks. If publications are restricted to only those with direct connection to the aims proposed in the prior grant period, then it will be a total of 12: Physical Review Letters (3) [2-4], Physical Review B (6) [6-8,12,13,25], Review of Scientific Instruments (1) [18], International Journal of Modern Physics A (1) [19] and B(1) [169]. A brief aggregated description of the directly connected accomplishments is below. The following topics are detailed: dispersion force measurements with graphene, dispersion force from ferromagnetic metals, conclusion on role of electrostatic patches, UV radiation induced modification of the Casimir force, low temperature measurement of the Casimir force, and Casimir force from thin fluctuating membranes.

  9. High quality NMR structures: a new force field with implicit water and membrane solvation for Xplor-NIH

    Energy Technology Data Exchange (ETDEWEB)

    Tian, Ye [Sanford-Burnham-Prebys Medical Discovery Institute (United States); Schwieters, Charles D. [National Institutes of Health, Center for Information Technology (United States); Opella, Stanley J. [University of California San Diego, Department of Chemistry and Biochemistry (United States); Marassi, Francesca M., E-mail: fmarassi@sbmri.org [Sanford-Burnham-Prebys Medical Discovery Institute (United States)

    2017-01-15

    Structure determination of proteins by NMR is unique in its ability to measure restraints, very accurately, in environments and under conditions that closely mimic those encountered in vivo. For example, advances in solid-state NMR methods enable structure determination of membrane proteins in detergent-free lipid bilayers, and of large soluble proteins prepared by sedimentation, while parallel advances in solution NMR methods and optimization of detergent-free lipid nanodiscs are rapidly pushing the envelope of the size limit for both soluble and membrane proteins. These experimental advantages, however, are partially squandered during structure calculation, because the commonly used force fields are purely repulsive and neglect solvation, Van der Waals forces and electrostatic energy. Here we describe a new force field, and updated energy functions, for protein structure calculations with EEFx implicit solvation, electrostatics, and Van der Waals Lennard-Jones forces, in the widely used program Xplor-NIH. The new force field is based primarily on CHARMM22, facilitating calculations with a wider range of biomolecules. The new EEFx energy function has been rewritten to enable OpenMP parallelism, and optimized to enhance computation efficiency. It implements solvation, electrostatics, and Van der Waals energy terms together, thus ensuring more consistent and efficient computation of the complete nonbonded energy lists. Updates in the related python module allow detailed analysis of the interaction energies and associated parameters. The new force field and energy function work with both soluble proteins and membrane proteins, including those with cofactors or engineered tags, and are very effective in situations where there are sparse experimental restraints. Results obtained for NMR-restrained calculations with a set of five soluble proteins and five membrane proteins show that structures calculated with EEFx have significant improvements in accuracy, precision

  10. Dynamic behavior of tuning fork shear-force structures in a SNOM system

    Energy Technology Data Exchange (ETDEWEB)

    Gao, Fengli [Department of Engineering Mechanics, AML, CNMM, Tsinghua University, Beijing 100084 (China); Li, Xide, E-mail: lixide@tsinghua.edu.cn [Department of Engineering Mechanics, AML, CNMM, Tsinghua University, Beijing 100084 (China); Wang, Jia [State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instruments, Tsinghua University, Beijing 100084 (China); Fu, Yu [Temasek Laboratories, Nanyang Technological University, 50 Nanyang Drive, 637553 (Singapore)

    2014-07-01

    Piezoelectric tuning fork shear-force structures are widely used as a distance control unit in a scanning near-field optical microscopy. However, the complex dynamic behavior among the micro-tuning forks (TFs), optical fiber probes, and the probe–surface interactions is still a crucial issue to achieve high-resolution imaging or near-field interaction inspections. Based on nonlinear beam tension-bending vibration theory, vibration equations in both longitudinal and lateral directions have been established when the TF structure and the optical fiber are treated as deformable structures. The relationship of the probe–surface interaction induced by Van der Waals force has been analyzed and the corresponding numerical results used to describe the vibrational behavior of the probe approaching the sample surface are obtained. Meanwhile, the viscous resistance of the liquid film on the sample surface has also been investigated using linear beam-bending vibration theory. Experiments testing the interaction between the probe and the water film on a single crystal silicon wafer have been carried out and the viscous resistance of the water film was estimated using the established equations. Finally, to use the TF-probe structure as a force sensor, the relation between the dynamic response of the TF-probe system and an external force on the probe tip was obtained. - Highlights: • Nonlinear vibration equation is established for a deformable tuning fork probe assembly. • Probe–sample interactions induced by Van der Waals force and viscous resistance are investigated. • The viscous resistance between the probe and the water film is estimated using testing results.

  11. The waaL gene mutation compromised the inhabitation of Enterobacter sp. Ag1 in the mosquito gut environment.

    Science.gov (United States)

    Pei, Dong; Jiang, Jinjin; Yu, Wanqin; Kukutla, Phanidhar; Uentillie, Alejandro; Xu, Jiannong

    2015-08-27

    The mosquito gut harbors a variety of bacteria that are dynamically associated with mosquitoes in various contexts. However, little is known about bacterial factors that affect bacterial inhabitation in the gut microbial community. Enterobacter sp. Ag1 is a predominant Gram negative bacterium in the mosquito midgut. In a mutant library that was generated using transposon Tn5-mediated mutagenesis, a mutant was identified, in which the gene waaL was disrupted by the Tn5 insertion. The waaL encodes O antigen ligase, which is required for the attachment of O antigen to the outer core oligosaccharide of the lipopolysaccharide (LPS). The waaL(-) mutation caused the O antigen repeat missing in the LPS. The normal LPS structure was restored when the mutant was complemented with a plasmid containing waaL gene. The waaL(-) mutation did not affect bacterial proliferation in LB culture, the mutant cells grew at a rate the same as the wildtype (wt) cells. However, when waaL(-) strain were co-cultured with the wt strain or complemented strain, the mutant cells proliferated with a slower rate, indicating that the mutants were less competitive than wt cells in a community setting. Similarly, in a co-feeding assay, when fluorescently tagged wt strain and waaL(-) strain were orally co-introduced into the gut of Anopheles stephensi mosquitoes, the mutant cells were less prevalent in both sugar-fed and blood-fed guts. The data suggest that the mutation compromised the bacterial inhabitation in the gut community. Besides, the mutant was more sensitive to oxidative stress, demonstrated by lower survival rate upon exposure to 20 mM H₂O₂. Lack of the O antigen structure in LPS of Enterobacter compromised the effective growth in co-culture and co-feeding assays. In addition, O-antigen was involved in protection against oxidative stress. The findings suggest that intact LPS is crucial for the bacteria to steadily stay in the gut microbial community.

  12. Holographic Van der Waals phase transition of the higher-dimensional electrically charged hairy black hole

    International Nuclear Information System (INIS)

    Li, Hui-Ling; Feng, Zhong-Wen; Zu, Xiao-Tao

    2018-01-01

    With motivation by holography, employing black hole entropy, two-point connection function and entanglement entropy, we show that, for the higher-dimensional Anti-de Sitter charged hairy black hole in the fixed charged ensemble, a Van der Waals-like phase transition can be observed. Furthermore, based on the Maxwell equal-area construction, we check numerically the equal-area law for a first order phase transition in order to further characterize the Van der Waals-like phase transition. (orig.)

  13. Holographic Van der Waals phase transition of the higher-dimensional electrically charged hairy black hole

    Energy Technology Data Exchange (ETDEWEB)

    Li, Hui-Ling [University of Electronic Science and Technology of China, School of Physical Electronics, Chengdu (China); Shenyang Normal University, College of Physics Science and Technology, Shenyang (China); Feng, Zhong-Wen [China West Normal University, College of Physics and Space Science, Nanchong (China); Zu, Xiao-Tao [University of Electronic Science and Technology of China, School of Physical Electronics, Chengdu (China)

    2018-01-15

    With motivation by holography, employing black hole entropy, two-point connection function and entanglement entropy, we show that, for the higher-dimensional Anti-de Sitter charged hairy black hole in the fixed charged ensemble, a Van der Waals-like phase transition can be observed. Furthermore, based on the Maxwell equal-area construction, we check numerically the equal-area law for a first order phase transition in order to further characterize the Van der Waals-like phase transition. (orig.)

  14. Dynamic forces on agglomerated particles caused by high-intensity ultrasound.

    Science.gov (United States)

    Knoop, Claas; Fritsching, Udo

    2014-03-01

    In this paper the acoustic forces on particles and agglomerates caused by high-intensity ultrasound in gaseous atmosphere are derived by means of computational fluid dynamics (CFD). Sound induced forces cause an oscillating stress scenario where the primary particles of an agglomerate are alternatingly pressed together and torn apart with the frequency of the applied wave. A comparison of the calculated acoustic forces with respect to the inter particle adhesion forces from Van-der-Waals and liquid bridge interactions reveals that the separation forces may reach the same order of magnitude for 80 μm sized SiO2-particles. Hence, with finite probability acoustically agitated gases may de-agglomerate/disperse solid agglomerate structures. This effect is confirmed by dispersion experiments in an acoustic particle levitation setup. Copyright © 2013 Elsevier B.V. All rights reserved.

  15. Legitimatie van de nevengeul voor de Waal langs Varik

    NARCIS (Netherlands)

    During, R.; Pleijte, M.; Vreke, J.

    2016-01-01

    “Wat is de legitimatie van de geprojecteerde nevengeul van de Waal bij Varik en Heesselt?” In het onderzoek dat heeft plaatsgevonden is specifiek gekeken naar de onderbouwing van de maatgevende afvoer van 18.000 m3/s bij Lobith eind 21e eeuw en naar de wijze waarop er in de planvorming met de

  16. Tuning adhesion forces between functionalized gold colloidal nanoparticles and silicon AFM tips: role of ligands and capillary forces.

    Science.gov (United States)

    Oras, Sven; Vlassov, Sergei; Berholts, Marta; Lõhmus, Rünno; Mougin, Karine

    2018-01-01

    Adhesion forces between functionalized gold colloidal nanoparticles (Au NPs) and scanning probe microscope silicon tips were experimentally investigated by atomic force microscopy (AFM) equipped with PeakForce QNM (Quantitative Nanoscale Mechanics) module. Au NPs were synthesized by a seed-mediated process and then functionalized with thiols containing different functional groups: amino, hydroxy, methoxy, carboxy, methyl, and thiol. Adhesion measurements showed strong differences between NPs and silicon tip depending on the nature of the tail functional group. The dependence of the adhesion on ligand density for different thiols with identical functional tail-group was also demonstrated. The calculated contribution of the van der Waals (vdW) forces between particles was in good agreement with experimentally measured adhesive values. In addition, the adhesion forces were evaluated between flat Au films functionalized with the same molecular components and silicon tips to exclude the effect of particle shape on the adhesion values. Although adhesion values on flat substrates were higher than on their nanoparticle counterparts, the dependance on functional groups remained the same.

  17. 77 FR 67285 - Debris Removal: Eligibility of Force Account Labor Straight-Time Costs Under the Public...

    Science.gov (United States)

    2012-11-09

    ... more of its projects. The Appropriations Act did not authorize the participation of private non-profit... accelerate the nation's recovery by maximizing the use of force account labor. A 2011 Department of Homeland... States, Indian Tribal governments, local governments, as well as certain private non-profit organizations...

  18. Selection of option of pregame warm-up in handball taking into account features of force of the nervous system of sportsmen

    Directory of Open Access Journals (Sweden)

    Helen Gant

    2016-06-01

    Full Text Available Purpose: to develop recommendations about the organization of warm-up for handball players of 13–14 years old taking into account force of the nervous system (NS of players. Material & Methods: 28 handball players of 13–14 years old of Kharkov and Ternovka took part in the research; methods were used: analysis of scientific and methodical literature, technique of "Tapping-test". Results: need of the search of new ways of the increase of efficiency of the competitive activity of young handball players is proved theoretically. Psychological characteristics of handball players of 13–14 years old with a different force of the nervous system are provided. Practical recommendations about the organization of pregame warm-up of handball players of 13–14 years old taking into account force of nervous system of sportsmen are developed. Conclusions: handball players of 13–14 years old can be divided into five groups, concerning force of their nervous system by the results of the conducted research: strong NS (28,57%, average (21,43%, weak (17,86% and average and weak (14,29%, average and strong (17,86%. Recommendations about the organization and carrying out pregame warm-up of handball players of 13–14 years old, taking into account force of the nervous system of sportsmen were developed, considering the results of the psychological research of sportsmen.

  19. 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...

  20. Van der Waals Attraction and Coalescence of Aqueous Salt Nanodroplets

    Czech Academy of Sciences Publication Activity Database

    Jungwirth, Pavel; Buch, V.

    2003-01-01

    Roč. 68, č. 12 (2003), s. 2283-2291 ISSN 0010-0765 R&D Projects: GA MŠk LN00A032 Institutional research plan: CEZ:AV0Z4040901 Keywords : van der Waals interactions * aqueous droplets * coalescence Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.041, year: 2003

  1. Interlayer excitons in a bulk van der Waals semiconductor.

    Science.gov (United States)

    Arora, Ashish; Drüppel, Matthias; Schmidt, Robert; Deilmann, Thorsten; Schneider, Robert; Molas, Maciej R; Marauhn, Philipp; Michaelis de Vasconcellos, Steffen; Potemski, Marek; Rohlfing, Michael; Bratschitsch, Rudolf

    2017-09-21

    Bound electron-hole pairs called excitons govern the electronic and optical response of many organic and inorganic semiconductors. Excitons with spatially displaced wave functions of electrons and holes (interlayer excitons) are important for Bose-Einstein condensation, superfluidity, dissipationless current flow, and the light-induced exciton spin Hall effect. Here we report on the discovery of interlayer excitons in a bulk van der Waals semiconductor. They form due to strong localization and spin-valley coupling of charge carriers. By combining high-field magneto-reflectance experiments and ab initio calculations for 2H-MoTe 2 , we explain their salient features: the positive sign of the g-factor and the large diamagnetic shift. Our investigations solve the long-standing puzzle of positive g-factors in transition metal dichalcogenides, and pave the way for studying collective phenomena in these materials at elevated temperatures.Excitons, quasi-particles of bound electron-hole pairs, are at the core of the optoelectronic properties of layered transition metal dichalcogenides. Here, the authors unveil the presence of interlayer excitons in bulk van der Waals semiconductors, arising from strong localization and spin-valley coupling of charge carriers.

  2. 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.

  3. The Role of the Electrostatic Force in Spore Adhesion

    Energy Technology Data Exchange (ETDEWEB)

    Chung, Eunhyea [Georgia Institute of Technology; Yiacoumi, Sotira [Georgia Institute of Technology; Lee, Ida [University of Tennessee, Knoxville (UTK); Tsouris, Costas [ORNL

    2010-01-01

    Electrostatic force is investigated as one of the components of the adhesion force between Bacillus thuringiensis (Bt) spores and planar surfaces. The surface potentials of a Bt spore and a mica surface are experimentally obtained using a combined atomic force microscopy (AFM)-scanning surface potential microscopy technique. On the basis of experimental information, the surface charge density of the spores is estimated at 0.03 {micro}C/cm{sup 2} at 20% relative humidity and decreases with increasing humidity. The Coulombic force is introduced for the spore-mica system (both charged, nonconductive surfaces), and an electrostatic image force is introduced to the spore-gold system because gold is electrically conductive. The Coulombic force for spore-mica is repulsive because the components are similarly charged, while the image force for the spore-gold system is attractive. The magnitude of both forces decreases with increasing humidity. The electrostatic forces are added to other force components, e.g., van der Waals and capillary forces, to obtain the adhesion force for each system. The adhesion forces measured by AFM are compared to the estimated values. It is shown that the electrostatic (Coulombic and image) forces play a significant role in the adhesion force between spores and planar surfaces.

  4. FDTD simulations of forces on particles during holographic assembly.

    Science.gov (United States)

    Benito, David C; Simpson, Stephen H; Hanna, Simon

    2008-03-03

    We present finite-difference time-domain (FDTD) calculations of the forces and torques on dielectric particles of various shapes, held in one or many Gaussian optical traps, as part of a study of the physical limitations involved in the construction of micro- and nanostructures using a dynamic holographic assembler (DHA). We employ a full 3-dimensional FDTD implementation, which includes a complete treatment of optical anisotropy. The Gaussian beams are sourced using a multipole expansion of a fifth order Davis beam. Force and torques are calculated for pairs of silica spheres in adjacent traps, for silica cylinders trapped by multiple beams and for oblate silica spheroids and calcite spheres in both linearly and circularly polarized beams. Comparisons are drawn between the magnitudes of the optical forces and the Van der Waals forces acting on the systems. The paper also considers the limitations of the FDTD approach when applied to optical trapping.

  5. Adhesive force of a single gecko foot-hair

    Science.gov (United States)

    Autumn, Kellar; Liang, Yiching A.; Hsieh, S. Tonia; Zesch, Wolfgang; Chan, Wai Pang; Kenny, Thomas W.; Fearing, Ronald; Full, Robert J.

    2000-06-01

    Geckos are exceptional in their ability to climb rapidly up smooth vertical surfaces. Microscopy has shown that a gecko's foot has nearly five hundred thousand keratinous hairs or setae. Each 30-130µm long seta is only one-tenth the diameter of a human hair and contains hundreds of projections terminating in 0.2-0.5µm spatula-shaped structures. After nearly a century of anatomical description, here we report the first direct measurements of single setal force by using a two-dimensional micro-electro-mechanical systems force sensor and a wire as a force gauge. Measurements revealed that a seta is ten times more effective at adhesion than predicted from maximal estimates on whole animals. Adhesive force values support the hypothesis that individual seta operate by van der Waals forces. The gecko's peculiar behaviour of toe uncurling and peeling led us to discover two aspects of setal function which increase their effectiveness. A unique macroscopic orientation and preloading of the seta increased attachment force 600-fold above that of frictional measurements of the material. Suitably orientated setae reduced the forces necessary to peel the toe by simply detaching above a critical angle with the substratum.

  6. Constraints on Stable Equilibria with Fluctuation-Induced (Casimir) Forces

    International Nuclear Information System (INIS)

    Rahi, Sahand Jamal; Kardar, Mehran; Emig, Thorsten

    2010-01-01

    We examine whether fluctuation-induced forces can lead to stable levitation. First, we analyze a collection of classical objects at finite temperature that contain fixed and mobile charges and show that any arrangement in space is unstable to small perturbations in position. This extends Earnshaw's theorem for electrostatics by including thermal fluctuations of internal charges. Quantum fluctuations of the electromagnetic field are responsible for Casimir or van der Waals interactions. Neglecting permeabilities, we find that any equilibrium position of items subject to such forces is also unstable if the permittivities of all objects are higher or lower than that of the enveloping medium, the former being the generic case for ordinary materials in vacuum.

  7. Constraints on stable equilibria with fluctuation-induced (Casimir) forces.

    Science.gov (United States)

    Rahi, Sahand Jamal; Kardar, Mehran; Emig, Thorsten

    2010-08-13

    We examine whether fluctuation-induced forces can lead to stable levitation. First, we analyze a collection of classical objects at finite temperature that contain fixed and mobile charges and show that any arrangement in space is unstable to small perturbations in position. This extends Earnshaw's theorem for electrostatics by including thermal fluctuations of internal charges. Quantum fluctuations of the electromagnetic field are responsible for Casimir or van der Waals interactions. Neglecting permeabilities, we find that any equilibrium position of items subject to such forces is also unstable if the permittivities of all objects are higher or lower than that of the enveloping medium, the former being the generic case for ordinary materials in vacuum.

  8. 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...

  9. Charge-Induced Fluctuation Forces in Graphitic Nanostructures

    Directory of Open Access Journals (Sweden)

    D. Drosdoff

    2016-01-01

    Full Text Available Charge fluctuations in nanocircuits with capacitor components are shown to give rise to a novel type of long-ranged interaction, which coexist with the regular Casimir–van der Waals force. The developed theory distinguishes between thermal and quantum mechanical effects, and it is applied to capacitors involving graphene nanostructures. The charge fluctuations mechanism is captured via the capacitance of the system with geometrical and quantum mechanical components. The dependence on the distance separation, temperature, size, and response properties of the system shows that this type of force can have a comparable and even dominant effect to the Casimir interaction. Our results strongly indicate that fluctuation-induced interactions due to various thermodynamic quantities can have important thermal and quantum mechanical contributions at the microscale and the nanoscale.

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

    Indian Academy of Sciences (India)

    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, ...

  11. Supramolecular liquid crystalline π-conjugates: the role of aromatic π-stacking and van der Waals forces on the molecular self-assembly of oligophenylenevinylenes.

    Science.gov (United States)

    Goel, Mahima; Jayakannan, M

    2010-10-07

    Here, we report a unique design strategy to trace the role of aromatic π-stacking and van der Waals interactions on the molecular self-organization of π-conjugated building blocks in a single system. A new series of bulky oligophenylenevinylenes (OPVs) bearing a tricyclodecanemethylene (TCD) unit in the aromatic π-core with flexible long methylene chains (n = 0-12 and 16) in the longitudinal position were designed and synthesized. The OPVs were found to be liquid crystalline, and their enthalpies of phase transitions (also entropies) showed odd-even oscillation with respect to the number of carbon atoms in alkyl chains. OPVs with an even number of methylene units in the side chains showed higher enthalpies with respect to their highly packed solid structures compared to odd-numbered ones. Polarized light microscopic analysis confirmed the formation of cholesteric liquid crystalline (LC) phases of fan shaped textures with focal conics in OPVs with 5 ≤ n ≤ 9. OPVs with longer alkyl chains (OPV-10 to OPV-12) produced a birefringence pattern consisting of dark and bright ring-banded suprastructures. The melting temperature followed a sigmoidal trend, indicating the transformation of molecular self-organization in OPVs from solid to ring-banded suprastructures via cholesteric LC intermediates. At longer alkyl chain lengths, the van der Waals interactions among the alkyl chains became predominant and translated the mesogenic effect across the lamellae; as a consequence, the lamellae underwent twisted self-organization along the radial growth direction of the spherulites to produce bright and dark bands. Scanning electron microscope (SEM) analysis of cholesteric LC and ring-banded textures strongly supported the existence of twisted lamellae in the OPVs with ring-banded textures. Variable temperature X-ray diffraction analysis confirmed the reversibility of the molecular self-organization in the solid state and also showed the existence of the higher ordered

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

    KAUST Repository

    Zhu, Jiajie; Schwingenschlö gl, Udo

    2015-01-01

    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

  13. 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

  14. Electric-field switching of two-dimensional van der Waals magnets

    Science.gov (United States)

    Jiang, Shengwei; Shan, Jie; Mak, Kin Fai

    2018-05-01

    Controlling magnetism by purely electrical means is a key challenge to better information technology1. A variety of material systems, including ferromagnetic (FM) metals2-4, FM semiconductors5, multiferroics6-8 and magnetoelectric (ME) materials9,10, have been explored for the electric-field control of magnetism. The recent discovery of two-dimensional (2D) van der Waals magnets11,12 has opened a new door for the electrical control of magnetism at the nanometre scale through a van der Waals heterostructure device platform13. Here we demonstrate the control of magnetism in bilayer CrI3, an antiferromagnetic (AFM) semiconductor in its ground state12, by the application of small gate voltages in field-effect devices and the detection of magnetization using magnetic circular dichroism (MCD) microscopy. The applied electric field creates an interlayer potential difference, which results in a large linear ME effect, whose sign depends on the interlayer AFM order. We also achieve a complete and reversible electrical switching between the interlayer AFM and FM states in the vicinity of the interlayer spin-flip transition. The effect originates from the electric-field dependence of the interlayer exchange bias.

  15. Switch on, switch off: stiction in nanoelectromechanical switches

    KAUST Repository

    Wagner, Till J W

    2013-06-13

    We present a theoretical investigation of stiction in nanoscale electromechanical contact switches. We develop a mathematical model to describe the deflection of a cantilever beam in response to both electrostatic and van der Waals forces. Particular focus is given to the question of whether adhesive van der Waals forces cause the cantilever to remain in the \\'ON\\' state even when the electrostatic forces are removed. In contrast to previous studies, our theory accounts for deflections with large slopes (i.e. geometrically nonlinear). We solve the resulting equations numerically to study how a cantilever beam adheres to a rigid electrode: transitions between \\'free\\', \\'pinned\\' and \\'clamped\\' states are shown to be discontinuous and to exhibit significant hysteresis. Our findings are compared to previous results from linearized models and the implications for nanoelectromechanical cantilever switch design are discussed. © 2013 IOP Publishing Ltd.

  16. Inventarisatie van mogelijke effecten van kribverlaging in de Waal op de beroepsvisserij

    NARCIS (Netherlands)

    Winter, H.V.

    2011-01-01

    Om de hoogwaterveiligheid van het rivierengebied te vergroten is het doel van Rijkswaterstaat om eind 2015 ca. 500 kribben in de Waal verlaagd te hebben en daarnaast langsdammen aangelegd te hebben tussen Wamel en Ophemert. In deze korte deskstudie wordt een inventarisatie gemaakt van mogelijke

  17. Electronic zero-point fluctuation forces inside circuit components

    Science.gov (United States)

    Leonhardt, Ulf

    2018-01-01

    One of the most intriguing manifestations of quantum zero-point fluctuations are the van der Waals and Casimir forces, often associated with vacuum fluctuations of the electromagnetic field. We study generalized fluctuation potentials acting on internal degrees of freedom of components in electrical circuits. These electronic Casimir-like potentials are induced by the zero-point current fluctuations of any general conductive circuit. For realistic examples of an electromechanical capacitor and a superconducting qubit, our results reveal the possibility of tunable forces between the capacitor plates, or the level shifts of the qubit, respectively. Our analysis suggests an alternative route toward the exploration of Casimir-like fluctuation potentials, namely, by characterizing and measuring them as a function of parameters of the environment. These tunable potentials may be useful for future nanoelectromechanical and quantum technologies. PMID:29719863

  18. Electronic zero-point fluctuation forces inside circuit components.

    Science.gov (United States)

    Shahmoon, Ephraim; Leonhardt, Ulf

    2018-04-01

    One of the most intriguing manifestations of quantum zero-point fluctuations are the van der Waals and Casimir forces, often associated with vacuum fluctuations of the electromagnetic field. We study generalized fluctuation potentials acting on internal degrees of freedom of components in electrical circuits. These electronic Casimir-like potentials are induced by the zero-point current fluctuations of any general conductive circuit. For realistic examples of an electromechanical capacitor and a superconducting qubit, our results reveal the possibility of tunable forces between the capacitor plates, or the level shifts of the qubit, respectively. Our analysis suggests an alternative route toward the exploration of Casimir-like fluctuation potentials, namely, by characterizing and measuring them as a function of parameters of the environment. These tunable potentials may be useful for future nanoelectromechanical and quantum technologies.

  19. Reduction of Liquid Bridge Force for 3D Microstructure Measurements

    Directory of Open Access Journals (Sweden)

    Hiroshi Murakami

    2016-05-01

    Full Text Available Recent years have witnessed an increased demand for a method for precise measurement of the microstructures of mechanical microparts, microelectromechanical systems, micromolds, optical devices, microholes, etc. This paper presents a measurement system for three-dimensional (3D microstructures that use an optical fiber probe. This probe consists of a stylus shaft with a diameter of 2.5 µm and a glass ball with a diameter of 5 µm attached to the stylus tip. In this study, the measurement system, placed in a vacuum vessel, is constructed suitably to prevent adhesion of the stylus tip to the measured surface caused by the surface force resulting from the van der Waals force, electrostatic force, and liquid bridge force. First, these surface forces are analyzed with the aim of investigating the causes of adhesion. Subsequently, the effects of pressure inside the vacuum vessel on surface forces are evaluated. As a result, it is found that the surface force is 0.13 µN when the pressure inside the vacuum vessel is 350 Pa. This effect is equivalent to a 60% reduction in the surface force in the atmosphere.

  20. 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.

  1. Probing the probe: AFM tip-profiling via nanotemplates to determine Hamaker constants from phase–distance curves

    International Nuclear Information System (INIS)

    Rodriguez, Raul D.; Lacaze, Emmanuelle; Jupille, Jacques

    2012-01-01

    A method to determine the van der Waals forces from phase–distance curves recorded by atomic force microscopy (AFM) in tapping mode is presented. The relationship between the phase shift and the tip–sample distance is expressed as a function of the product of the Hamaker constant by tip radius. Silica-covered silicon tips are used to probe silica-covered silicon substrate in dry conditions to avoid capillary effects. Tips being assumed spherical, radii are determined in situ by averaging profiles recorded in different directions on hematite nanocrystals acting as nanotemplates, thus accounting for tip anisotropy. Through a series of reproducible measurements performed with tips of various radii (including the in-situ characterization of a damaged tip), a value of (6.3±0.4)×10 −20 J is found for the Hamaker constant of interacting silica surfaces in air, in good agreement with tabulated data. The results demonstrate that the onset of the tip–surface interaction is dominated by the van der Waals forces and that the total force can be modeled in the framework of the harmonic approximation. Based on the tip radius and the Hamaker constant associated to the tip–substrate system, the model is quite flexible. Once the Hamaker constant is known, a direct estimate of the tip size can be achieved whereas when the tip size is known, a quantitative evaluation of the van der Waals force becomes possible on different substrates with a spatial resolution at the nanoscale. -- Highlights: ► Van der Waal forces in tapping mode atomic force microscopy. ► Harmonic approximation model of phase–distance curves probed by simulations. ► Silica tips and surfaces as a model case. ► Tip geometry determined in situ by nanoparticles as nanotemplates. ► Method to derive the Hamaker constant for any tip/surface system.

  2. Pattern-free thermal modulator via thermal radiation between Van der Waals materials

    Science.gov (United States)

    Liu, Xianglei; Shen, Jiadong; Xuan, Yimin

    2017-10-01

    Modulating heat flux provides a platform for a plethora of emerging devices such as thermal diodes, thermal transistors, and thermal memories. Here, a pattern-free noncontact thermal modulator is proposed based on the mechanical rotation between two Van der Waals films with optical axes parallel to the surfaces. A modulation contrast can reach a value higher than 5 for hexagonal Boron Nitride (hBN) films separated by a nanoscale gap distance. The dominant radiative heat exchange comes from the excitation of both Type I and Type II hyperbolic surface phonon polaritons (HSPhPs) at the vacuum-hBN interface for different orientations, while the large modulation contrast is mainly attributed to the mismatching Type I HSPhPs induced by rotation. This work opens the possibility to design cheap thermal modulators without relying on nanofabrication techniques, and paves the way to apply natural Van der Waals materials in manipulating heat currents in an active way.

  3. Van der Waals Attraction of Vortices in Anisotropic and Layered Superconductors

    International Nuclear Information System (INIS)

    Blatter, G.; Geshkenbein, V.

    1996-01-01

    We show that in anisotropic and layered superconductors the fluctuations of vortex lines produce an attractive long-range vortex-vortex interaction of the van der Waals type. This attraction follows from the anisotropic screening properties of the material and has profound consequences for the low-field phase diagram of these materials. copyright 1996 The American Physical Society

  4. Some image artefacts in non-contact mode force microscopy

    International Nuclear Information System (INIS)

    Dinte, B.P.; Watson, G.S.; Dobson, J.F.; Myhra, S.

    1996-01-01

    Full text: Non-contact mode Atomic Force Microscopy (AFM), performed in air, of two-dimensional hexagonal close-packed (2DHCP) layers of 200 nm diameter polystyrene spheres yields images containing artefacts ('ghost spheres') at layer edges and vacancy sites. The origin of these artefacts is clearly not the simple convolution of the tip and sample geometries, but must be the interaction between them. A computer program was written to simulate the experimental contours, assuming that the only force between the tip and the sample is the van der Waals (dispersion) force, and that the contours traced by the AFM tip are those of constant force derivative. The energy was calculated by integrating R -6 over the volumes of the tip and the sample, with a (constant) arbitrary scaling factor. The experimental contours were reproduced by the simulations, except for the 'ghost' artefacts. The assumption that there is only a dispersion force is thus incorrect. The experiments were performed in air, so that all surfaces were coated by a layer of adsorbed moisture. It is proposed that meniscus forces may be the origin of the artefacts

  5. Electronic structure, lattice dynamics, and optical properties of a novel van der Waals semiconductor heterostructure: InGaSe2

    Science.gov (United States)

    Ibarra-Hernández, Wilfredo; Elsayed, Hannan; Romero, Aldo H.; Bautista-Hernández, Alejandro; Olguín, Daniel; Cantarero, Andrés

    2017-07-01

    There is a growing interest in the property dependence of transition metal dichalcogenides as a function of the number of layers and formation of heterostructures. Depending on the stacking, doping, edge effects, and interlayer distance, the properties can be modified, which opens the door to novel applications that require a detailed understanding of the atomic mechanisms responsible for those changes. In this work, we analyze the electronic properties and lattice dynamics of a heterostructure constructed by simultaneously stacking InSe layers and GaSe layers bounded by van der Waals forces. We have assumed the same space group of GaSe, P 6 ¯m 2 as it becomes the lower energy configuration for other considered stackings. The structural, vibrational, and optical properties of this layered compound have been calculated using density functional theory. The structure is shown to be energetically, thermally, and elastically stable, which indicates its possible chemical synthesis. A correlation of the theoretical physical properties with respect to its parent compounds is extensively discussed. One of the most interesting properties is the low thermal conductivity, which indicates its potential use in thermolectric applications. Additionally, we discuss the possibility of using electronic gap engineering methods, which can help us to tune the optical emission in a variable range close to that used in the field of biological systems (NIR). Finally, the importance of considering properly van der Waals dispersion in layered materials has been emphasized as included in the exchange correlation functional. As for the presence of atoms with important spin-orbit coupling, relativistic corrections have been included.

  6. A dynamic force balance model for colloidal expansion and its DLVO-based application.

    Science.gov (United States)

    Liu, Longcheng; Moreno, Luis; Neretnieks, Ivars

    2009-01-20

    A force balance model that describes the dynamic expansion of colloidal bentonite gels/sols is presented. The colloidal particles are assumed to consist of one or several thin sheets with the other dimensions much larger than their thickness. The forces considered include van der Waals force, diffuse double layer force, thermal force giving rise to Brownian motion, gravity, as well as friction force. The model results in an expression resembling the instationary diffusion equation but with an immensely variable diffusivity. This diffusivity is strongly influenced by the concentration of counterions as well as by the particle concentration in the colloid gel/sol. The properties of the model are explored and discussed, exemplified by the upward expansion of an originally highly compacted bentonite tablet in a test tube. Examples are presented for a number of cases with ionic concentrations varying between very dilute waters up to several molar of counterions. The volume fraction of particles ranges from 40% to very dilute sols.

  7. Using the minimum principle for the Helmholtz free energy in the analysis of the equilibria of a van der Waals fluid

    International Nuclear Information System (INIS)

    Ascoli, Sergio; Malvestuto, Vincenzo

    2004-01-01

    For a fluid system, obeying a state equation of the van der Waals type, the gas and the liquid phases can coexist in equilibrium, at a given temperature, only if the volume of the system is kept fixed. Thus, in order to study the two-phase equilibria of a fluid system, it seemed quite natural to choose the molar volume as the independent variable, and, consequently, the Helmholtz free energy as the proper thermodynamic potential for the application of the minimum principle. Specific computations are here carried out for a single van der Waals fluid, namely, pure water at 300 0 C. As a result, the present treatment indicates a simple and effective way to identify the whole range of molar volumes where the equilibrium preferred by the system is a two-phase equilibrium. This range results to be wider than the interval of strict instability of the van der Waals isotherm. Finally, it is pointed out that all the results, obtained here for the van der Waals state equation, can be extended to all the state equations of the same type

  8. Fragmentation of neutral van der Waals clusters with visible laser light: A new variant of the Raman effect?

    International Nuclear Information System (INIS)

    Stamatovic, A.; Howorka, F.; Scheier, P.; Maerk, T.D.

    1989-01-01

    We have observed strong photodissociation (using visible laser light) of neutral van der Waals clusters (Ar, N 2 , O 2 , CO 2 , SO 2 , NH 3 ) produced by supersonic expansion and detected by electron ionization/mass spectrometer. Several tests were performed, all of them supporting this surprising discovery. We suggest that Raman induced photodissociation (RIP) is responsible for this phenomenon. This first observation of Raman induced photodissociation provides a new technique for the study of neutral van der Waals clusters. (orig.)

  9. Dynamic polarizabilities and Van der Waals coefficients for alkali atoms Li, Na and alkali dimer molecules Li2, Na2 and NaLi

    Science.gov (United States)

    Mérawa, M.; Dargelos, A.

    1998-07-01

    The present paper gives an account of investigations of the polarizability of the alkali atoms Li, Na, diatomics homonuclear and heteronuclear Li2, Na2 and NaLi at SCF (Self Consistent Field) level of approximation and at correlated level, using a time Time-Dependent Gauge Invariant method (TDGI). Our static polarizability values agree with the best experimental and theoretical determinations. The Van der Waals C6 coefficients for the atom-atom, atom-dimer and dimer-dimer interactions have been evaluated. Les polarisabilités des atomes alcalins Li, Na, et des molécules diatomiques homonucléaires et hétéronucléaire Li2, Na2 et NaLi, ont été calculées au niveau SCF (Self Consistent Field) et au niveau corrélé à partir d'une méthode invariante de jauge dépendante du temps(TDGI). Nos valeurs des polarisabilités statiques sont en accord avec les meilleurs déterminations expérimentales et théoriques. Les coefficients C6 de Van de Waals pour les interactions atome-atome, atome-dimère et dimère-dimère ont également été évalués.

  10. Van der Waals cohesion and plasmon excitations in C60 fullerite

    International Nuclear Information System (INIS)

    Lambin, P.; Lucas, A.A.

    1993-01-01

    The Van der Waals cohesive energy of C 60 fullerite is evaluated from the zero-point energy of multipole plasmons fluctuating on the highly-polarizable Bucky balls. These hollow molecules are treated as dielectric shells. The shell material is an isotropic continuum with a dielectric function designed to exhibit the plasmon resonances observed in other forms of solid carbon in the ultraviolet. (orig.)

  11. First-principles study of van der Waals interactions in MoS2 and MoO3

    International Nuclear Information System (INIS)

    Peelaers, H; Van de Walle, C G

    2014-01-01

    Van der Waals interactions play an important role in layered materials such as MoS 2 and MoO 3 . Within density functional theory, several methods have been developed to explicitly include van der Waals interactions. We compare the performance of several of these functionals in describing the structural and electronic properties of MoS 2 and MoO 3 . We include functionals based on the local density or generalized gradient approximations, but also based on hybrid functionals. The coupling of the semiempirical Grimme D2 method with the hybrid functional HSE06 is shown to lead to a very good description of both structural and electronic properties. (paper)

  12. Interlayer excitons in a bulk van der Waals semiconductor

    DEFF Research Database (Denmark)

    Arora, Ashish; Drueppel, Matthias; Schmidt, Robert

    2017-01-01

    Bound electron-hole pairs called excitons govern the electronic and optical response of many organic and inorganic semiconductors. Excitons with spatially displaced wave functions of electrons and holes (interlayer excitons) are important for Bose-Einstein condensation, superfluidity......, dissipationless current flow, and the light-induced exciton spin Hall effect. Here we report on the discovery of interlayer excitons in a bulk van der Waals semiconductor. They form due to strong localization and spin-valley coupling of charge carriers. By combining high-field magneto-reflectance experiments...

  13. Nonequilibrium forces between neutral atoms mediated by a quantum field

    International Nuclear Information System (INIS)

    Behunin, Ryan O.; Hu, Bei-Lok

    2010-01-01

    We study forces between two neutral atoms, modeled as three-dimensional harmonic oscillators, arising from mutual influences mediated by an electromagnetic field but not from their direct interactions. We allow as dynamical variables the center-of-mass motion of the atom, its internal degrees of freedom, and the quantum field treated relativistically. We adopt the method of nonequilibrium quantum field theory which can provide a first-principles, systematic, and unified description including the intrinsic and induced dipole fluctuations. The inclusion of self-consistent back-actions makes possible a fully dynamical description of these forces valid for general atom motion. In thermal equilibrium we recover the known forces--London, van der Waals, and Casimir-Polder--between neutral atoms in the long-time limit. We also reproduce a recently reported force between atoms when the system is out of thermal equilibrium at late times. More noteworthy is the discovery of the existence of a type of (or identification of the source of some known) interatomic force which we call the ''entanglement force,'' originating from the quantum correlations of the internal degrees of freedom of entangled atoms.

  14. 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)

  15. Van der Waals dispersion energy between atoms and nanoparticles

    International Nuclear Information System (INIS)

    Boustimi, M; Loulou, M; Natto, S; Belafhal, A; Baudon, J

    2017-01-01

    In this work, we focus on the atom-surface interaction where the geometry of the surface is highly symmetric (i.e. sphere, cylinder and plane) and the atom is in ground state. We first present the main features of our model, based on the susceptibility tensors of the two partners in interaction, to determine a general expression of the dispersive energy of van der Waals interaction. Some results are given as applications of this model which addresses recent nanophysical problems, for example, when atoms are in the vicinity of metallic nanoshells, nanospheres or nanowires. (paper)

  16. Surface features on Sahara soil dust particles made visible by atomic force microscope (AFM phase images

    Directory of Open Access Journals (Sweden)

    M. O. Andreae

    2008-10-01

    Full Text Available We show that atomic force microscopy (AFM phase images can reveal surface features of soil dust particles, which are not evident using other microscopic methods. The non-contact AFM method is able to resolve topographical structures in the nanometer range as well as to uncover repulsive atomic forces and attractive van der Waals' forces, and thus gives insight to surface properties. Though the method does not allow quantitative assignment in terms of chemical compound description, it clearly shows deposits of distinguishable material on the surface. We apply this technique to dust aerosol particles from the Sahara collected over the Atlantic Ocean and describe micro-features on the surfaces of such particles.

  17. Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates

    Science.gov (United States)

    Bonilla, Manuel; Kolekar, Sadhu; Ma, Yujing; Diaz, Horacio Coy; Kalappattil, Vijaysankar; Das, Raja; Eggers, Tatiana; Gutierrez, Humberto R.; Phan, Manh-Huong; Batzill, Matthias

    2018-04-01

    Reduced dimensionality and interlayer coupling in van der Waals materials gives rise to fundamentally different electronic1, optical2 and many-body quantum3-5 properties in monolayers compared with the bulk. This layer-dependence permits the discovery of novel material properties in the monolayer regime. Ferromagnetic order in two-dimensional materials is a coveted property that would allow fundamental studies of spin behaviour in low dimensions and enable new spintronics applications6-8. Recent studies have shown that for the bulk-ferromagnetic layered materials CrI3 (ref. 9) and Cr2Ge2Te6 (ref. 10), ferromagnetic order is maintained down to the ultrathin limit at low temperatures. Contrary to these observations, we report the emergence of strong ferromagnetic ordering for monolayer VSe2, a material that is paramagnetic in the bulk11,12. Importantly, the ferromagnetic ordering with a large magnetic moment persists to above room temperature, making VSe2 an attractive material for van der Waals spintronics applications.

  18. Modeling the effect of intermolecular force on the size-dependent pull-in behavior of beam-type NEMS using modified couple stress theory

    Energy Technology Data Exchange (ETDEWEB)

    Beni, Yaghoub Tadi; Karimipour, Iman [Shahrekord University, Shahrekord (Iran, Islamic Republic of); Abadyan, Mohamadreza [Islamic Azad University, Shahrekord (Iran, Islamic Republic of)

    2014-09-15

    Experimental observations reveal that the physical response of nano structures is size-dependent. Herein, modified couple stress theory has been used to study the effect of intermolecular van der Waals force on the size dependent pull-in of nano bridges and nano cantilevers. Three approaches including using differential transformation method, applying numerical method and developing a simple lumped parameter model have been employed to solve the governing equation of the systems. The pull-in parameters i.e. critical tip deflection and instability voltage of the nano structures have been determined. Effect of the van der Waals attraction and the size dependency and the importance of coupling between them on the pull-in performance have been discussed.

  19. Modeling the effect of intermolecular force on the size-dependent pull-in behavior of beam-type NEMS using modified couple stress theory

    International Nuclear Information System (INIS)

    Beni, Yaghoub Tadi; Karimipour, Iman; Abadyan, Mohamadreza

    2014-01-01

    Experimental observations reveal that the physical response of nano structures is size-dependent. Herein, modified couple stress theory has been used to study the effect of intermolecular van der Waals force on the size dependent pull-in of nano bridges and nano cantilevers. Three approaches including using differential transformation method, applying numerical method and developing a simple lumped parameter model have been employed to solve the governing equation of the systems. The pull-in parameters i.e. critical tip deflection and instability voltage of the nano structures have been determined. Effect of the van der Waals attraction and the size dependency and the importance of coupling between them on the pull-in performance have been discussed.

  20. Phase transitions in the argon, krypton and xenon in generalized Van der Waals theory

    International Nuclear Information System (INIS)

    Cavalcanti, H.M.

    1977-01-01

    Fluid-solid like phase transitions for three monoatomic substances, argon, krypton and xenon are treated, using the extension of the Van der Waals theory to the crystalline state. The method utilized is based on 'Maxwell construction' of identical areas [pt

  1. 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.

  2. Recent progress in predicting structural and electronic properties of organic solids with the van der Waals density functional

    International Nuclear Information System (INIS)

    Yanagisawa, Susumu; Okuma, Koji; Inaoka, Takeshi; Hamada, Ikutaro

    2015-01-01

    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.

  3. van der Waals interaction of excited media

    International Nuclear Information System (INIS)

    Sherkunov, Yury

    2005-01-01

    The Casimir interaction between two media of ground-state atoms is well described with the help of the Lifshitz formula depending upon the permittivity of the media. We will show that this formula is in contradiction with experimental evidence for excited atoms. We calculate the Casimir force between two atoms if one or both of them are excited. We use methods of quantum electrodynamics specially derived for the problem. It enables us to take into account the excited-state radiation widths of atoms. Then we calculate the force between the excited atom and medium of ground-state atoms. The results are in agreement with the ones obtained by other authors who used perturbation theory or linear response theory. Generalization of our results to the case of the interaction between two media of excited atoms results in a formula, which is in not only in quantitative, but in qualitative contradiction with the Lifshitz formula. This contradiction disappears if the media of ground-state atoms are considered. Moreover, our result does not include the permittivity of the media. It includes a quantity which differs from the permittivity only for excited atoms. The main features of our results are as follows. The interaction is resonant, the force may be either attractive or repulsive depending on the resonant frequencies of the atoms of different media, and the value of the Casimir force may be several orders of magnitude lager than that predicted by the Lifshitz formula. The features mentioned here are in agreement with known experimental and theoretical evidence obtained by many authors for the interaction of a single excited atom with dielectric media

  4. Novel operation mode for eliminating influence of inclination angle and friction in atomic force microscopy

    International Nuclear Information System (INIS)

    Wang, Fei; Wang, Yueyu; Zhou, Faquan; Zhao, Xuezeng

    2010-01-01

    The accuracy of topography imaging in contact force mode of atomic force microscopy (AFM) depends on the one-to-one corresponding relationship between the cantilever deflection and the tip-sample distance, whereas such a relationship cannot be always achieved in the presence of friction and incline angle of sample surface. Recently, we have developed a novel operation mode in which we keep the van der Waals force as constant instead of the applied normal force, to eliminate the effect of inclination angle and friction on topography imaging in the contact force mode. We have improved our AFM to enable the new operation mode for validation. Comparative experiments have been performed and the results have shown that the effect of friction and inclination angle on topography imaging in contact mode of AFM can be eliminated or at least decreased effectively by working in the new operation mode we present.

  5. Dependences of the van der Waals atom-wall interaction on atomic and material properties

    International Nuclear Information System (INIS)

    Caride, A.O.; Klimchitskaya, G.L.; Mostepanenko, V.M.; Zanette, S.I.

    2005-01-01

    The 1%-accurate calculations of the van der Waals interaction between an atom and a cavity wall are performed in the separation region from 3 nm to 150 nm. The cases of metastable He * and Na atoms near metal, semiconductor, and dielectric walls are considered. Different approximations to the description of wall material and atomic dynamic polarizability are carefully compared. The smooth transition to the Casimir-Polder interaction is verified. It is shown that to obtain accurate results for the atom-wall van der Waals interaction at short separations with an error less than 1% one should use the complete optical-tabulated data for the complex refractive index of the wall material and the accurate dynamic polarizability of an atom. The obtained results may be useful for the theoretical interpretation of recent experiments on quantum reflection and Bose-Einstein condensation of ultracold atoms on or near surfaces of different kinds

  6. Intermolecular vibronic spectroscopy of small van der Waals clusters: Phenol- and aniline-(argon)2 complexes

    International Nuclear Information System (INIS)

    Schmidt, M.; Mons, M.; Le Calve, J.

    1990-01-01

    We report the clear observation and assignment of the symmetric stretching and bending van der Waals modes in two three-body C 2ν complexes, phenol- and aniline-(Ar) 2 , using resonant two-photon ionization. (orig.)

  7. Improved models for the prediction of activity coefficients in nearly athermal mixtures .2. A theoretically-based G(E)-model based on the van der Waals partition function

    DEFF Research Database (Denmark)

    Kontogeorgis, Georgios; Georgios, Nikolopoulos; Fredenslund, Aage

    1997-01-01

    of the generalized van der Waals partition function and attempts to account for all non-energetic effects of solutions of both short- and long-chain alkanes, including alkane polymers. Both the free-volume effects and the density-dependent rotational degrees of freedom are considered. The resulting G(E)-model which......, despite its derivation from a partition function resembles the Flory-Huggins formula, is suitable for vapor-liquid and solid-liquid equilibrium calculations for nearly athermal polymer solutions as well as for alkane systems. We show that using plausible assumptions for the free-volume and the external...

  8. 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)

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

    Science.gov (United States)

    2018-02-19

    AFRL-AFOSR-JP-TR-2018-0012 Nano Electronics on Atomically Controlled van der Waals Quantum Heterostructures PHILIP Kim HARVARD COLLEGE PRESIDENT...21-02-2018 2.  REPORT TYPE      Final 3.  DATES COVERED (From - To)      15 Aug 2015 to 14 Feb 2017 4.  TITLE AND SUBTITLE Nano Electronics on...NOTES 14.  ABSTRACT We report molecular beam epitaxial growth and electronic transport properties of high quality topological insulator Bi2Se3 thin films

  10. Forced harmonic oscillations of the Euler-Bernoulli beam with resistance forces

    Directory of Open Access Journals (Sweden)

    Yuriy S. Krutiy

    2015-12-01

    Full Text Available The important issue in the oscillation theory is the study of resistance impact on oscillatory processes. Unlike the calculations of free oscillations, that reside in determination of natural frequencies and waveshapes and unlike the calculations of forced oscillations far away from resonance, that are performing without reference to friction, the oscillations researches in vicinity of resonance need accounting of friction forces. Special attention is paid to forced transverse fluctuations in beams as an important technical problem for engineering and building. Aim: The aim of the work is constructing of analytical solution of the problem of forced transverse vibrations of a straight rod with constant cross-section, which is under the influence of the harmonic load taking into account external and internal resistances. Materials and Methods: The internal resistance is taken into account using the corrected hypothesis of Kelvin-Voigt which reflects the empirically proven fact about the frequency-independent internal friction in the material. The external friction is also considered as frequency-independent. Results: An analytical solution is built for the differential equation of forced transverse oscillations of a straight rod with constant cross-section which is under the influence of the harmonic load taking into account external and internal resistances. As a result, analytically derived formulae are presented which describe the forced dynamic oscillations and the dynamic internal forces due to the harmonic load applied to the rod thus reducing the problem with any possible fixed ends to the search of unknown integration constants represented in a form of initial parameters.

  11. Development of a picture of the van der Waals interaction energy between clusters of nanometer-range particles

    International Nuclear Information System (INIS)

    Arunachalam, V.; Marlow, W.H.; Lu, J.X.

    1998-01-01

    The importance of the long-range Lifshitz-van der Waals interaction energy between condensed bodies is well known. However, its implementation for interacting bodies that are highly irregular and separated by distances varying from contact to micrometers has received little attention. As part of a study of collisions of irregular aerosol particles, an approach based on the Lifshitz theory of van der Waals interaction has been developed to compute the interaction energy between a sphere and an aggregate of spheres at all separations. In the first part of this study, the iterated sum-over-dipole interactions between pairs of approximately spherical molecular clusters are compared with the Lifshitz and Lifshitz-Hamaker interaction energies for continuum spheres of radii equal to those of the clusters' circumscribed spheres and of the same masses as the clusters. The Lifshitz energy is shown to converge to the iterated dipolar energy for quasispherical molecular clusters for sufficiently large separations, while the energy calculated by using the Lifshitz-Hamaker approach does not. Next, the interaction energies between a contacting pair of these molecular clusters and a third cluster in different relative positions are calculated first by coupling all molecules in the three-cluster system and second by ignoring the interactions between the molecules of the adhering clusters. The error calculated by this omission is shown to be very small, and is an indication of the error in computing the long-range interaction energy between a pair of interacting spheres and a third sphere as a simple sum over the Lifshitz energies between individual, condensed-matter spheres. This Lifshitz energy calculation is then combined with the short-separation, nonsingular van der Waals energy calculation of Lu, Marlow, and Arunachalam, to provide an integrated picture of the van der Waals energy from large separations to contact. copyright 1998 The American Physical Society

  12. Electrostatically actuated oscillator of bundle and double-walled carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Kang, Jeong Won; Song, Ki Oh; Hwang, Ho Jung [Chung-Ang University, Seoul (Korea, Republic of); Lee, Jun Ha; Lee, Hoong Joo [Sangmyung University, Chonan (Korea, Republic of); Kwon, Oh Keun [Semyung University, Jecheon (Korea, Republic of); Yoon, Young Sik; Song, Young Jin [Konyang University, Nonsan (Korea, Republic of)

    2006-03-15

    Schematics of capacitively driven carbon nanotube (CNT) oscillators were presented and investigated by using classical molecular dynamics simulations. While the capacitive force acting on a CNT oscillator extruded it, the force exerted by the excess van der Waals energy sucked the CNT oscillator into the bundle or outer shell. The CNT oscillator could be oscillated by using both the Coulomb and the van der Waals interactions. The van der Waals force of the bundle-type CNT oscillator was less than the van der Waals force of the double-walled CNT oscillator. Molecular dynamics simulation results showed that double-walled CNT oscillators were better than bundle-type CNT oscillators in the aspects of both energy dissipation and stable operation.

  13. On mobility of ions in thin films in liquid substrates

    International Nuclear Information System (INIS)

    Matveev, Yu.A.

    1984-01-01

    The problem of energy dissipation by emission of ripplons is solved for an ion moving in the media with two interfaces (films on solid and liquid substrates), taking into account the Van der Waals interaction. It is shown that in contrast to the earlier considered case of solid substrate where the action of the Van der Waals forces causes only renormalization of the free fall acceleration, in the vase of liquid substrate the influence of these forces is much more complicated. In addition to renormalization of the amplitude of the emitted surface wave and change of the velocity threshold after which the wave mechanism is effective, in sufficiently thin film, where modes are ''intersected'' the analytical expressions for mobility are also significantly modified. In real experimental environments consideration of all the factors mentioned leads as a rule to higher ion mobility

  14. Random phase approximation applied to solids, molecules, and graphene-metal interfaces

    DEFF Research Database (Denmark)

    Olsen, Thomas; Thygesen, Kristian S.

    2013-01-01

    The random phase approximation (RPA) is attracting renewed interest as a universal and accurate method for first-principles total energy calculations. The RPA naturally accounts for long-range dispersive forces without compromising accuracy for short-range interactions making the RPA superior...... to semilocal and hybrid functionals in systems dominated by weak van der Waals or mixed covalent-dispersive interactions. In this work, we present plane-wave-based RPA calculations for a broad collection of systems with bond types ranging from strong covalent to van der Waals. Our main result is the RPA...... the RPA captures both the weak covalent and dispersive forces, which are equally important for these systems. We benchmark our implementation in the GPAW electronic structure code by calculating cohesive energies of graphite and a range of covalently bonded solids and molecules as well as the dissociation...

  15. Strong interlayer coupling in phosphorene/graphene van der Waals heterostructure: A first-principles investigation

    Science.gov (United States)

    Hu, Xue-Rong; Zheng, Ji-Ming; Ren, Zhao-Yu

    2018-04-01

    Based on first-principles calculations within the framework of density functional theory, we study the electronic properties of phosphorene/graphene heterostructures. Band gaps with different sizes are observed in the heterostructure, and charges transfer from graphene to phosphorene, causing the Fermi level of the heterostructure to shift downward with respect to the Dirac point of graphene. Significantly, strong coupling between two layers is discovered in the band spectrum even though it has a van der Waals heterostructure. A tight-binding Hamiltonian model is used to reveal that the resonance of the Bloch states between the phosphorene and graphene layers in certain K points combines with the symmetry matching between band states, which explains the reason for the strong coupling in such heterostructures. This work may enhance the understanding of interlayer interaction and composition mechanisms in van der Waals heterostructures consisting of two-dimensional layered nanomaterials, and may indicate potential reference information for nanoelectronic and optoelectronic applications.

  16. Observing Imperfection in Atomic Interfaces for van der Waals Heterostructures.

    Science.gov (United States)

    Rooney, Aidan P; Kozikov, Aleksey; Rudenko, Alexander N; Prestat, Eric; Hamer, Matthew J; Withers, Freddie; Cao, Yang; Novoselov, Kostya S; Katsnelson, Mikhail I; Gorbachev, Roman; Haigh, Sarah J

    2017-09-13

    Vertically stacked van der Waals heterostructures are a lucrative platform for exploring the rich electronic and optoelectronic phenomena in two-dimensional materials. Their performance will be strongly affected by impurities and defects at the interfaces. Here we present the first systematic study of interfaces in van der Waals heterostructure using cross-sectional scanning transmission electron microscope (STEM) imaging. By measuring interlayer separations and comparing these to density functional theory (DFT) calculations we find that pristine interfaces exist between hBN and MoS 2 or WS 2 for stacks prepared by mechanical exfoliation in air. However, for two technologically important transition metal dichalcogenide (TMDC) systems, MoSe 2 and WSe 2 , our measurement of interlayer separations provide the first evidence for impurity species being trapped at buried interfaces with hBN interfaces that are flat at the nanometer length scale. While decreasing the thickness of encapsulated WSe 2 from bulk to monolayer we see a systematic increase in the interlayer separation. We attribute these differences to the thinnest TMDC flakes being flexible and hence able to deform mechanically around a sparse population of protruding interfacial impurities. We show that the air sensitive two-dimensional (2D) crystal NbSe 2 can be fabricated into heterostructures with pristine interfaces by processing in an inert-gas environment. Finally we find that adopting glovebox transfer significantly improves the quality of interfaces for WSe 2 compared to processing in air.

  17. Lithium ions in the van der Waals gap of Bi2Se3 single crystals

    Czech Academy of Sciences Publication Activity Database

    Bludská, Jana; Jakubec, Ivo; Karamazov, S.; Horák, Jaromír; Uher, C.

    2010-01-01

    Roč. 183, č. 12 (2010), s. 2813-2817 ISSN 0022-4596 Institutional research plan: CEZ:AV0Z40320502 Keywords : intercalation * van Der Waals gap * Bi2Se3 crystals Subject RIV: CG - Electrochemistry Impact factor: 2.261, year: 2010

  18. Adsorption of Cu, Ag, and Au atoms on graphene including van der Waals interactions

    International Nuclear Information System (INIS)

    Amft, Martin; Eriksson, Olle; Skorodumova, Natalia V; Lebegue, Sebastien

    2011-01-01

    We performed a systematic density functional (DF) study of the adsorption of copper, silver, and gold adatoms on pristine graphene, especially accounting for van der Waals (vdW) interactions by the vdW-DF and PBE + D2 methods. In particular, we analyze the preferred adsorption site (among top, bridge, and hollow positions) together with the corresponding distortion of the graphene sheet and identify diffusion paths. Both vdW schemes show that the coinage metal atoms do bind to the graphene sheet and that in some cases the buckling of the graphene layer can be significant. Only the results for silver are qualitatively at variance with those obtained with the generalized gradient approximation, which gives no binding in this case. However in all three cases, we observe some quantitative differences between the vdW-DF and PBE + D2 methods. For instance the adsorption energies calculated with the PBE + D2 method are systematically higher than the ones obtained with vdW-DF. Moreover, the equilibrium distances computed with PBE + D2 are shorter than those calculated with the vdW-DF method. (paper)

  19. Forces between a rigid probe particle and a liquid interface. II. The general case.

    Science.gov (United States)

    Dagastine, R R; White, L R

    2002-03-15

    The semianalytic theory developed previously (Chan, D. Y. C., Dagastine, R. R., and White, L. R., J. Colloid Interface Sci. 236, 141 (2001)) to predict the force curve of an AFM measurement at a liquid interface using a colloidal probe has been expanded to incorporate a general force law with both attractive and repulsive forces. Expressions for the gradient of the force curve are developed to calculate the point at which the probe particle on the cantilever will spontaneously jump in toward the liquid interface. The calculation of the jump instability is reduced to a straightforward embroidery of the simple algorithms presented in Chan et al. In a variety of sample calculations using force laws including van der Waals, electrostatic, and hydrophobic forces for both oil/water and bubble/water interfaces, we have duplicated the general behaviors observed in several AFM investigations at liquid interfaces. The behavior of the drop as a Hookean spring and the numerical difficulties of a full numerical calculation of F(deltaX) are also discussed.

  20. Present status of controversies regarding the thermal Casimir force

    International Nuclear Information System (INIS)

    Mostepanenko, V M; Bezerra, V B; Decca, R S; Geyer, B; Fischbach, E; Klimchitskaya, G L; Krause, D E; Lopez, D; Romero, C

    2006-01-01

    It is well known that, beginning in 2000, the behaviour of the thermal correction to the Casimir force between real metals has been hotly debated. As was shown by several research groups, the Lifshitz theory, which provides the theoretical foundation for the calculation of both the van der Waals and Casimir forces, leads to different results depending on the model of metal conductivity used. To resolve these controversies, theoretical considerations based on the principles of thermodynamics and new experimental tests were invoked. We analyse the present status of the problem (in particular, the advantages and disadvantages of the approaches based on the surface impedance and on the Drude model dielectric function) using rigorous analytical calculations of the entropy of a fluctuating field. We also discuss the results of a new precise experiment on the determination of the Casimir pressure between two parallel plates by means of a micromechanical torsional oscillator

  1. Accounting for Changes in Labor Force Participation of Married Women: The Case of the U.S. since 1959

    OpenAIRE

    Bar, Michael; Leukhina, Oksana

    2005-01-01

    Using a model of family decision-making with home production and individual heterogeneity, we quantitatively investigate the role of changes in several aspects of the joint earnings distribution of husbands and wives (gender earnings gap, gender-specific inequality and assortativeness of matching) and the decline in prices of home appliances in accounting for the dramatic rise in labor force participation of married women since 1959. The implications of the factors examined are tested agai...

  2. Inter-layer and intra-layer heat transfer in bilayer/monolayer graphene van der Waals heterostructure: Is there a Kapitza resistance analogous?

    Science.gov (United States)

    Rajabpour, Ali; Fan, Zheyong; Vaez Allaei, S. Mehdi

    2018-06-01

    Van der Waals heterostructures have exhibited interesting physical properties. In this paper, heat transfer in hybrid coplanar bilayer/monolayer (BL-ML) graphene, as a model layered van der Waals heterostructure, was studied using non-equilibrium molecular dynamics (MD) simulations. The temperature profile and inter- and intra-layer heat fluxes of the BL-ML graphene indicated that, there is no fully developed thermal equilibrium between layers and the drop in the average temperature profile at the step-like BL-ML interface is not attributable to the effect of Kapitza resistance. By increasing the length of the system up to 1 μm in the studied MD simulations, the thermally non-equilibrium region was reduced to a small area near the step-like interface. All MD results were compared to a continuum model and a good match was observed between the two approaches. Our results provide a useful understanding of heat transfer in nano- and micro-scale layered materials and van der Waals heterostructures.

  3. Analysis of dynamic cantilever behavior in tapping mode atomic force microscopy.

    Science.gov (United States)

    Deng, Wenqi; Zhang, Guang-Ming; Murphy, Mark F; Lilley, Francis; Harvey, David M; Burton, David R

    2015-10-01

    Tapping mode atomic force microscopy (AFM) provides phase images in addition to height and amplitude images. Although the behavior of tapping mode AFM has been investigated using mathematical modeling, comprehensive understanding of the behavior of tapping mode AFM still poses a significant challenge to the AFM community, involving issues such as the correct interpretation of the phase images. In this paper, the cantilever's dynamic behavior in tapping mode AFM is studied through a three dimensional finite element method. The cantilever's dynamic displacement responses are firstly obtained via simulation under different tip-sample separations, and for different tip-sample interaction forces, such as elastic force, adhesion force, viscosity force, and the van der Waals force, which correspond to the cantilever's action upon various different representative computer-generated test samples. Simulated results show that the dynamic cantilever displacement response can be divided into three zones: a free vibration zone, a transition zone, and a contact vibration zone. Phase trajectory, phase shift, transition time, pseudo stable amplitude, and frequency changes are then analyzed from the dynamic displacement responses that are obtained. Finally, experiments are carried out on a real AFM system to support the findings of the simulations. © 2015 Wiley Periodicals, Inc.

  4. Atomic layer MoS2-graphene van der Waals heterostructure nanomechanical resonators.

    Science.gov (United States)

    Ye, Fan; Lee, Jaesung; Feng, Philip X-L

    2017-11-30

    Heterostructures play significant roles in modern semiconductor devices and micro/nanosystems in a plethora of applications in electronics, optoelectronics, and transducers. While state-of-the-art heterostructures often involve stacks of crystalline epi-layers each down to a few nanometers thick, the intriguing limit would be hetero-atomic-layer structures. Here we report the first experimental demonstration of freestanding van der Waals heterostructures and their functional nanomechanical devices. By stacking single-layer (1L) MoS 2 on top of suspended single-, bi-, tri- and four-layer (1L to 4L) graphene sheets, we realize an array of MoS 2 -graphene heterostructures with varying thickness and size. These heterostructures all exhibit robust nanomechanical resonances in the very high frequency (VHF) band (up to ∼100 MHz). We observe that fundamental-mode resonance frequencies of the heterostructure devices fall between the values of graphene and MoS 2 devices. Quality (Q) factors of heterostructure resonators are lower than those of graphene but comparable to those of MoS 2 devices, suggesting interface damping related to interlayer interactions in the van der Waals heterostructures. This study validates suspended atomic layer heterostructures as an effective device platform and provides opportunities for exploiting mechanically coupled effects and interlayer interactions in such devices.

  5. Heterogeneous nucleation of polymorphs on polymer surfaces: polymer-molecule interactions using a Coulomb and van der Waals model.

    Science.gov (United States)

    Wahlberg, Nanna; Madsen, Anders Ø; Mikkelsen, Kurt V

    2018-06-09

    The nucleation processes of acetaminophen on poly(methyl methacrylate) and poly(vinyl acetate) have been investigated and the mechanisms of the processes are studied. This is achieved by a combination of theoretical models and computational investigations within the framework of a modified QM/MM method; a Coulomb-van der Waals model. We have combined quantum mechanical computations and electrostatic models at the atomistic level for investigating the stability of different orientations of acetaminophen on the polymer surfaces. Based on the Coulomb-van der Waals model, we have determined the most stable orientation to be a flat orientation, and the strongest interaction is seen between poly(vinyl acetate) and the molecule in a flat orientation in vacuum.

  6. 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.

  7. 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.

  8. Out-of-plane heat transfer in van der Waals stacks through electron-hyperbolic phonon coupling

    Science.gov (United States)

    Tielrooij, Klaas-Jan; Hesp, Niels C. H.; Principi, Alessandro; Lundeberg, Mark B.; Pogna, Eva A. A.; Banszerus, Luca; Mics, Zoltán; Massicotte, Mathieu; Schmidt, Peter; Davydovskaya, Diana; Purdie, David G.; Goykhman, Ilya; Soavi, Giancarlo; Lombardo, Antonio; Watanabe, Kenji; Taniguchi, Takashi; Bonn, Mischa; Turchinovich, Dmitry; Stampfer, Christoph; Ferrari, Andrea C.; Cerullo, Giulio; Polini, Marco; Koppens, Frank H. L.

    2018-01-01

    Van der Waals heterostructures have emerged as promising building blocks that offer access to new physics, novel device functionalities and superior electrical and optoelectronic properties1-7. Applications such as thermal management, photodetection, light emission, data communication, high-speed electronics and light harvesting8-16 require a thorough understanding of (nanoscale) heat flow. Here, using time-resolved photocurrent measurements, we identify an efficient out-of-plane energy transfer channel, where charge carriers in graphene couple to hyperbolic phonon polaritons17-19 in the encapsulating layered material. This hyperbolic cooling is particularly efficient, giving picosecond cooling times for hexagonal BN, where the high-momentum hyperbolic phonon polaritons enable efficient near-field energy transfer. We study this heat transfer mechanism using distinct control knobs to vary carrier density and lattice temperature, and find excellent agreement with theory without any adjustable parameters. These insights may lead to the ability to control heat flow in van der Waals heterostructures.

  9. Aan der Waals terminated silicon(111) surfaces and interfaces. Preparation, morphology, and electronic properties

    International Nuclear Information System (INIS)

    Fritsche, R.

    2004-01-01

    The aim of this thesis is the implementation of the concept of the quasi-van der Waals epitaxy as a new perspective for the integration of reactive and lattice-defect fitted materials into the silicon technology. The experimental characterization of this approach pursues in two subsequent sections. First the chemical and electronic passivation of a three-dimensional substrate (silicon) is studied by means of an ultrathin buffer layer from the material class of the layered-lattice chalcogenides (GaSe). The substrate surface (Si(111):GaSe) modified in this way possesses an inert van der Waals surface and serves in the following as base for the deposition of the against the non-passivated substrate really reactive and lattice-defect fitted materials (II-VI-compound semiconductors and metals) The characterization of the electronic and chemical properties of the surfaces and interfaces pursues with highly resolved photoelectron spectroscopy (SXPS). The results are supplemented by the characterization of the morphology by the diffraction of low-energy electrons (LEED) and the scanning tunnel microscopy (STM)

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

    International Nuclear Information System (INIS)

    Zeng, Xiao-Xiong; Li, Li-Fang

    2017-01-01

    Phase structure of the quintessence Reissner–Nordström–AdS black hole is probed by 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 Van der Waals-like phase transition. To reinforce this 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.

  11. Van der Waals pressure sensors using reduced graphene oxide composites

    Science.gov (United States)

    Jung, Ju Ra; Ahn, Sung Il

    2018-04-01

    Reduced graphene oxide (RGO) films intercalated with various polymers were fabricated by reaction-based self-assembly, and their characteristics as vacuum pressure sensors based on van der Waals interactions were studied. At low temperature, the electrical resistances of the samples decrease linearly with increasing vacuum pressure, whereas at high temperature the variation of the electrical resistance shows secondary order curves. Among all samples, the poly vinyl alcohol intercalated RGO shows the highest sensitivity, being almost two times more sensitive than reference RGO. All samples show almost the same signal for repetitive sudden pressure changes, indicating reasonable reproducibility and durability.

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

    Energy Technology Data Exchange (ETDEWEB)

    Zeng, Xiao-Xiong, E-mail: xxzeng@itp.ac.cn [State School of Material Science and Engineering, Chongqing Jiaotong University, Chongqing 400074 (China); Institute of Theoretical Physics, Chinese Academy of Sciences, Beijing 100190 (China); Li, Li-Fang, E-mail: lilf@itp.ac.cn [State Key Laboratory of Space Weather, National Space Science Center, Chinese Academy of Sciences, Beijing 100190 (China)

    2017-01-10

    Phase structure of the quintessence Reissner–Nordström–AdS black hole is probed by 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 Van der Waals-like phase transition. To reinforce this 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.

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

    Directory of Open Access Journals (Sweden)

    Xiao-Xiong Zeng

    2017-01-01

    Full Text Available Phase structure of the quintessence Reissner–Nordström–AdS black hole is probed by 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 Van der Waals-like phase transition. To reinforce this 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.

  14. Transport Properties Of Van Der Waals Hybrid Heterostructures.

    Science.gov (United States)

    Pacheco, M.; Orellana, P. A.; Felix, A. B.; Latge, A.

    Here we study transport properties of van der Waals heterostructures composed of carbon nanotubes adsorbed on nanoribbons of distinct 2D materials. Calculations of the electronic density of states and conductance of the hybrid systems are obtained in single band tight-binding approximation in the Green function formalism by adopting real-space renormalization schemes. We show that an analytical approach may be derived when both systems are formed by the same type of atoms. In the coupled structures the different electronic paths along the ribbons and finite nanotubes lead to quantum interference effects which are reflected as Fano antiresonances in the conductance. The electronic and transport properties of these materials are modulated by changing geometrical and structural parameters, such as the nanotube diameter and the widths and edge type of the ribbons. FONDECYT 1151316-1140571.

  15. Probabilistic analysis for identifying the driving force of protein folding

    Science.gov (United States)

    Tokunaga, Yoshihiko; Yamamori, Yu; Matubayasi, Nobuyuki

    2018-03-01

    Toward identifying the driving force of protein folding, energetics was analyzed in water for Trp-cage (20 residues), protein G (56 residues), and ubiquitin (76 residues) at their native (folded) and heat-denatured (unfolded) states. All-atom molecular dynamics simulation was conducted, and the hydration effect was quantified by the solvation free energy. The free-energy calculation was done by employing the solution theory in the energy representation, and it was seen that the sum of the protein intramolecular (structural) energy and the solvation free energy is more favorable for a folded structure than for an unfolded one generated by heat. Probabilistic arguments were then developed to determine which of the electrostatic, van der Waals, and excluded-volume components of the interactions in the protein-water system governs the relative stabilities between the folded and unfolded structures. It was found that the electrostatic interaction does not correspond to the preference order of the two structures. The van der Waals and excluded-volume components were shown, on the other hand, to provide the right order of preference at probabilities of almost unity, and it is argued that a useful modeling of protein folding is possible on the basis of the excluded-volume effect.

  16. Cálculo do Volume Molar de um Gás de van der Waals em SCILAB: o Método Newton-Raphson na Resolução de um Problema Físico-Químico

    Directory of Open Access Journals (Sweden)

    Diogenes Filho

    2014-07-01

    Full Text Available The use of software in chemical calculations is a constant reality in both laboratories as well as in simulation processes of chemical transformations. Around addition, this publication discusses the use of the computer program in Scilab problems of chemical origin, especially in the case of calculating the molar volume of gas van der Waals forces. Discussions on the results of the use of this program with a view to the tools available for the calculation of a polynomial provide satisfactory conclusions on the use of mathematical methods in Physical Chemistry, especially the Newton-Raphson method.

  17. Coulomb replica-exchange method: handling electrostatic attractive and repulsive forces for biomolecules.

    Science.gov (United States)

    Itoh, Satoru G; Okumura, Hisashi

    2013-03-30

    We propose a new type of the Hamiltonian replica-exchange method (REM) for molecular dynamics (MD) and Monte Carlo simulations, which we refer to as the Coulomb REM (CREM). In this method, electrostatic charge parameters in the Coulomb interactions are exchanged among replicas while temperatures are exchanged in the usual REM. By varying the atom charges, the CREM overcomes free-energy barriers and realizes more efficient sampling in the conformational space than the REM. Furthermore, this method requires only a smaller number of replicas because only the atom charges of solute molecules are used as exchanged parameters. We performed Coulomb replica-exchange MD simulations of an alanine dipeptide in explicit water solvent and compared the results with those of the conventional canonical, replica exchange, and van der Waals REMs. Two force fields of AMBER parm99 and AMBER parm99SB were used. As a result, the CREM sampled all local-minimum free-energy states more frequently than the other methods for both force fields. Moreover, the Coulomb, van der Waals, and usual REMs were applied to a fragment of an amyloid-β peptide (Aβ) in explicit water solvent to compare the sampling efficiency of these methods for a larger system. The CREM sampled structures of the Aβ fragment more efficiently than the other methods. We obtained β-helix, α-helix, 3(10)-helix, β-hairpin, and β-sheet structures as stable structures and deduced pathways of conformational transitions among these structures from a free-energy landscape. Copyright © 2012 Wiley Periodicals, Inc.

  18. Fourier Transform Microwave Spectroscopy of Multiconformational Molecules and Van Der Waals Complexes.

    Science.gov (United States)

    Hight Walker, Angela Renee

    1995-01-01

    With the use of a Fourier transform microwave (FTM) spectrometer, structural determinations of two types of species; multiconformational molecules and van der Waals complexes, have been performed. Presented in this thesis are three sections summarizing this research effort. The first section contains a detailed explanation of the FTM instrument. In Section II, the study of three multiconformational molecules is presented as two chapters. Finally, three chapters in Section III outline the work still in progress on many van der Waals complexes. Section I was written to be a "manual" for the FTM spectrometer and to aid new additions to the group in their understanding of the instrument. An instruction guide is necessary for home-built instruments such as this one due to their unique design and application. Vital techniques and theories are discussed and machine operation is outlined. A brief explanation of general microwave spectroscopy as performed on an FTM spectrometer is also given. Section II is composed of two chapters pertaining to multiconformational molecules. In Chapter 2, a complete structural analysis of dipropyl ether is reported. The only conformer assigned had C_{rm s} symmetry. Many transitions are yet unassigned. Chapter 3 summarizes an investigation of two nitrosamines; methyl ethyl and methyl propyl nitrosamine. Only one conformer was observed for methyl ethyl nitrosamine, but two were assigned to methyl propyl nitrosamine. Nuclear hyperfine structure and internal methyl rotation complicated the spectra. The final section, Section III, contains the ongoing progress on weakly bound van der Waals complexes. The analysis of the OCS--HBr complex identified the structure as quasi-linear with large amplitude bending motions. Five separate isotopomers were assigned. Transitions originating from the HBr--DBr complex were measured and presented in Chapter 5. Although early in the analysis, the structure was determined to be bent and deuterium bonded. The

  19. Analysis of dispersive interactions at polymer/TiAlN interfaces by means of dynamic force spectroscopy.

    Science.gov (United States)

    Wiesing, M; de Los Arcos, T; Gebhard, M; Devi, A; Grundmeier, G

    2017-12-20

    The structural and electronic origins of the interactions between polycarbonate and sputter deposited TiAlN were analysed using a combined electron and force spectroscopic approach. Interaction forces were measured by means of dynamic force spectroscopy and the surface polarizability was analysed by X-ray photoelectron valence band spectroscopy. It could be shown that the adhesive interactions between polycarbonate and TiAlN are governed by van der Waals forces. Different surface cleansing and oxidizing treatments were investigated and the effect of the surface chemistry on the force interactions was analysed. Intense surface oxidation resulted in a decreased adhesion force by a factor of two due to the formation of a 2 nm thick Ti 0.21 Al 0.45 O surface oxide layer. The origin of the residual adhesion forces caused by the mixed Ti 0.21 Al 0.45 O surface oxide was clarified by considering the non-retarded Hamaker coefficients as calculated by Lifshitz theory, based on optical data from Reflection Electron Energy Loss Spectroscopy. This disclosed increased dispersion forces of Ti 0.21 Al 0.45 O due to the presence of Ti(iv) ions and related Ti 3d band optical transitions.

  20. Benchmarking Density Functional Theory Based Methods To Model NiOOH Material Properties: Hubbard and van der Waals Corrections vs Hybrid Functionals.

    Science.gov (United States)

    Zaffran, Jeremie; Caspary Toroker, Maytal

    2016-08-09

    NiOOH has recently been used to catalyze water oxidation by way of electrochemical water splitting. Few experimental data are available to rationalize the successful catalytic capability of NiOOH. Thus, theory has a distinctive role for studying its properties. However, the unique layered structure of NiOOH is associated with the presence of essential dispersion forces within the lattice. Hence, the choice of an appropriate exchange-correlation functional within Density Functional Theory (DFT) is not straightforward. In this work, we will show that standard DFT is sufficient to evaluate the geometry, but DFT+U and hybrid functionals are required to calculate the oxidation states. Notably, the benefit of DFT with van der Waals correction is marginal. Furthermore, only hybrid functionals succeed in opening a bandgap, and such methods are necessary to study NiOOH electronic structure. In this work, we expect to give guidelines to theoreticians dealing with this material and to present a rational approach in the choice of the DFT method of calculation.

  1. Layered van der Waals crystals with hyperbolic light dispersion

    DEFF Research Database (Denmark)

    Gjerding, Morten Niklas; Petersen, R.; Pedersen, T.G.

    2017-01-01

    candidates for Purcell factor control of emission from diamond nitrogen-vacancy centers.Natural hyperbolic materials retain the peculiar optical properties of traditional metamaterials whilst not requiring artificial structuring. Here, the authors perform a theoretical screening of a large class of natural......Compared to artificially structured hyperbolic metamaterials, whose performance is limited by the finite size of the metallic components, the sparse number of naturally hyperbolic materials recently discovered are promising candidates for the next generation of hyperbolic materials. Using first......-infrared to the ultraviolet. Combined with the emerging field of van der Waals heterostructuring, we demonstrate how the hyperbolic properties can be further controlled by stacking different two-dimensional crystals opening new perspectives for atomic-scale design of photonic metamaterials. As an application, we identify...

  2. Exfoliation and van der Waals heterostructure assembly of intercalated ferromagnet Cr1/3TaS2

    Science.gov (United States)

    Yamasaki, Yuji; Moriya, Rai; Arai, Miho; Masubuchi, Satoru; Pyon, Sunseng; Tamegai, Tsuyoshi; Ueno, Keiji; Machida, Tomoki

    2017-12-01

    Ferromagnetic van der Waals (vdW) materials are in demand for spintronic devices with all-two-dimensional-materials heterostructures. Here, we demonstrate mechanical exfoliation of magnetic-atom-intercalated transition metal dichalcogenide Cr1/3TaS2 from its bulk crystal; previously such intercalated materials were thought difficult to exfoliate. Magnetotransport in exfoliated tens-of-nanometres-thick flakes revealed ferromagnetic ordering below its Curie temperature T C ~ 110 K as well as strong in-plane magnetic anisotropy; these are identical to its bulk properties. Further, van der Waals heterostructure assembly of Cr1/3TaS2 with another intercalated ferromagnet Fe1/4TaS2 is demonstrated using a dry-transfer method. The fabricated heterojunction composed of Cr1/3TaS2 and Fe1/4TaS2 with a native Ta2O5 oxide tunnel barrier in between exhibits tunnel magnetoresistance (TMR), revealing possible spin injection and detection with these exfoliatable ferromagnetic materials through the vdW junction.

  3. Accurate electrostatic and van der Waals pull-in prediction for fully clamped nano/micro-beams using linear universal graphs of pull-in instability

    Science.gov (United States)

    Tahani, Masoud; Askari, Amir R.

    2014-09-01

    In spite of the fact that pull-in instability of electrically actuated nano/micro-beams has been investigated by many researchers to date, no explicit formula has been presented yet which can predict pull-in voltage based on a geometrically non-linear and distributed parameter model. The objective of present paper is to introduce a simple and accurate formula to predict this value for a fully clamped electrostatically actuated nano/micro-beam. To this end, a non-linear Euler-Bernoulli beam model is employed, which accounts for the axial residual stress, geometric non-linearity of mid-plane stretching, distributed electrostatic force and the van der Waals (vdW) attraction. The non-linear boundary value governing equation of equilibrium is non-dimensionalized and solved iteratively through single-term Galerkin based reduced order model (ROM). The solutions are validated thorough direct comparison with experimental and other existing results reported in previous studies. Pull-in instability under electrical and vdW loads are also investigated using universal graphs. Based on the results of these graphs, non-dimensional pull-in and vdW parameters, which are defined in the text, vary linearly versus the other dimensionless parameters of the problem. Using this fact, some linear equations are presented to predict pull-in voltage, the maximum allowable length, the so-called detachment length, and the minimum allowable gap for a nano/micro-system. These linear equations are also reduced to a couple of universal pull-in formulas for systems with small initial gap. The accuracy of the universal pull-in formulas are also validated by comparing its results with available experimental and some previous geometric linear and closed-form findings published in the literature.

  4. Observation of aggregation triggered by Resonance Energy Transfer (RET) induced intermolecular pairing force.

    Science.gov (United States)

    Pan, Xiaoyong; Wang, Weizhi; Ke, Lin; Zhang, Nan

    2017-07-20

    In this report, we showed the existence of RET induced intermolecular pairing force by comparing their fluorescence behaviors under room illumination vs standing in dark area for either PFluAnt solution or PFluAnt&PFOBT mixture. Their prominent emission attenuation under room illumination brought out the critical role of photo, i.e. RET induced intermolecular pairing force in induction of polymer aggregation. Constant UV-Vis absorption and fluorescence spectra in terms of both peak shapes and maximum wavelengths implied no chemical decomposition was involved. Recoverable fluorescence intensity, fluorescence lifetime as well as NMR spectra further exclude photo induced decomposition. The controllable on/off state of RET induced intermolecular pairing force was verified by the masking effect of outside PFluAnt solution which function as filter to block the excitation of inside PFluAnt and thus off the RET induced intermolecular pairing force. Theoretical calculation suggest that magnitude of RET induced intermolecular pairing force is on the same scale as that of van der Waals interaction. Although the absolute magnitude of RET induced intermolecular pairing force was not tunable, its effect can be magnified by intentionally turn it "on", which was achieved by irradiance with 5 W desk lamp in this report.

  5. Building up a convenient accountability: How the ‘anti-corruption’ law in Brazil was put into force

    Directory of Open Access Journals (Sweden)

    Fernanda Odilla Vasconcellos de Figueiredo

    2016-06-01

    Full Text Available This paper focuses on how Brazil designed and put into force a legal instrument that makes companies strictly liable for domestic and international acts of corruption and highlights the role of external drivers during a 15-year process. It also introduces the concept of ‘convenient accountability’ which suggests that Brazil has adopted the slowest and cheaper methods in order to see to demands of those who want and do not want greater accountability in the case of the new clean company act (Law 12846/2013; also dubbed as ‘anti-corruption law’. Despite the apparent force of the civil society in this case of ‘pressure from below’, until now, no company has been punished under Law 12846/2013. An already over-whelmed anti-corruption agency was chosen to enforce the new legislation in the federal and international spheres against companies, some of them being traditional campaign financers and governmental contractors. Hence, it still remains uncertain whether Brazil will effectively enforce its anti-corruption law that, on paper, even exceeds international requirements.

  6. 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.

  7. Electronic Properties and Device Applications of van-der-Waals Thin Films

    Science.gov (United States)

    Renteria, Jacqueline de Dios

    Successful exfoliation of graphene and discoveries of its unique electrical and thermal properties have motivated searches for other quasi two-dimensional (2D) materials with interesting properties. The layered van der Waals materials can be cleaved mechanically or exfoliated chemically by breaking the relatively weak bonding between the layers. In this dissertation research I addressed a special group of inorganic van der Waals materials -- layered transition metal dichalcogenides (MX2, where M=Mo, W, Nb, Ta or Ti and X=S, Se or Te). The focus of the investigation was electronic properties of thin films of TaSe2 and MoS2 and their device applications. In the first part of the dissertation, I describe the fabrication and performance of all-metallic three-terminal devices with the TaSe2 thin-film conducting channel. The layers of 2H-TaSe2 were exfoliated mechanically from single crystals grown by the chemical vapor transport method. It was established that devices with nanometer-scale thickness channels exhibited strongly non-linear current-voltage characteristics, unusual optical response, and electrical gating at room temperature. It was found that the drain-source current in thin-film 2H-TaSe2--Ti/Au devices reproducibly shows an abrupt transition from a highly resistive to a conductive state, with the threshold tunable via the gate voltage. Such current-voltage characteristics can be used, in principle, for implementing radiation-hard all-metallic logic circuits. In the second part of the dissertation, I describe the fabrication, electrical testing and measurements of the low-frequency 1/f noise in three-terminal devices with the MoS2 thin-film channel (f is the frequency). Analysis of the experimental data allowed us to distinguish channel and contact noise contributions for both as fabricated and aged devices. The noise characteristics of MoS 2--Ti/Au devices are in agreement with the McWhorter model description. The latter is contrary to what is observed in

  8. Characterizing the surface forces between two individual nanowires using optical microscopy based nanomanipulation

    Science.gov (United States)

    Xie, Hongtao; Mead, James L.; Wang, Shiliang; Fatikow, Sergej; Huang, Han

    2018-06-01

    The adhesion and friction between two Al2O3 nanowires (NWs) was characterized by the use of optical microscopy based nanomanipulation, with which peeling, shearing and sliding was performed. The elastically deformed shape of the NWs during peeling and shearing was used to calculate the adhesion and frictional forces; force sensing was not required. The obtained adhesion stress between two Al2O3 NWs varied from 0.14 to 0.25 MPa, lower than that observed for carbon nanotube junctions, and was attributed to van der Waals attraction. Stick-slip was observed during the shearing and sliding of two NWs, and was the consequence of discrete contact between surface asperities. The obtained static and kinetic frictional stresses varied from 0.7 to 1.3 MPa and 0.4 to 0.8 MPa, respectively; significantly greater than the obtained adhesion stress.

  9. Electrostatics of electron-hole interactions in van der Waals heterostructures

    Science.gov (United States)

    Cavalcante, L. S. R.; Chaves, A.; Van Duppen, B.; Peeters, F. M.; Reichman, D. R.

    2018-03-01

    The role of dielectric screening of electron-hole interaction in van der Waals heterostructures is theoretically investigated. A comparison between models available in the literature for describing these interactions is made and the limitations of these approaches are discussed. A simple numerical solution of Poisson's equation for a stack of dielectric slabs based on a transfer matrix method is developed, enabling the calculation of the electron-hole interaction potential at very low computational cost and with reasonable accuracy. Using different potential models, direct and indirect exciton binding energies in these systems are calculated within Wannier-Mott theory, and a comparison of theoretical results with recent experiments on excitons in two-dimensional materials is discussed.

  10. The role of hydrogen bonds in the melting points of sulfonate-based protic organic salts

    DEFF Research Database (Denmark)

    Luo, Jiangshui

    2016-01-01

    There are three main types of interactions inside organic salts - electrostatic interaction, hydrogen bonding and van der Waals force [1-4]. While van der Waals force is relatively weak, it is hydrogen bonding and particularly electrostatic interaction that determine the lattice energies of ionic...

  11. Thoughts on competency integration in accounting education

    NARCIS (Netherlands)

    Lawson, R.A.; Blocher, E.J.; Brewer, P.C.; Morris, J.T.; Stocks, K.D.; Sorensen, J.E.; Stout, D.E.; Wouters, M.J.F.

    2015-01-01

    The paper follows up on Lawson et al. (2014), which reported on the work of a joint task force sponsored by the Management Accounting Section (MAS) of the American Accounting Association (AAA) and the Institute of Management Accountants (IMA) charged with the responsibility of developing curricular

  12. Construction of van der Waals magnetic tunnel junction using ferromagnetic layered dichalcogenide

    Energy Technology Data Exchange (ETDEWEB)

    Arai, Miho; Moriya, Rai, E-mail: moriyar@iis.u-tokyo.ac.jp; Yabuki, Naoto; Masubuchi, Satoru [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan); Ueno, Keiji [Department of Chemistry, Graduate School of Science and Engineering, Saitama University, Saitama 338-8570 (Japan); Machida, Tomoki, E-mail: tmachida@iis.u-tokyo.ac.jp [Institute of Industrial Science, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan); Institute for Nano Quantum Information Electronics, University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan)

    2015-09-07

    We investigate the micromechanical exfoliation and van der Waals (vdW) assembly of ferromagnetic layered dichalcogenide Fe{sub 0.25}TaS{sub 2}. The vdW interlayer coupling at the Fe-intercalated plane of Fe{sub 0.25}TaS{sub 2} allows exfoliation of flakes. A vdW junction between the cleaved crystal surfaces is constructed by dry transfer method. We observe tunnel magnetoresistance in the resulting junction under an external magnetic field applied perpendicular to the plane, demonstrating spin-polarized tunneling between the ferromagnetic layered material and the vdW junction.

  13. Generalized Van der Waals 4-D oscillator. Invariant tori and relative equilibria in Ξ = L = 0 surface

    NARCIS (Netherlands)

    Díaz, G.; Egea, J.; Ferrer, S.; Meer, van der J.C.; Vera, J.A.; Lanchares, V.; Elipe, A.

    2009-01-01

    An uniparametric 4-DOF Hamiltonian family of perturbed oscillators in 1:1:1:1 resonance is studied. The model includes some classical cases, in particular Zeeman and the van der Waals systems. First several invariant manifolds are identified. Normalization by Lie-transforms (only first order is

  14. Is nuclear physics the molecular physics of coloured quarks

    International Nuclear Information System (INIS)

    Freeman, G.; McKellar, H.J.

    1980-01-01

    The possibility that the nucleon-nucleon interaction mimics the molecule-molecule interaction to the extent of having forces of Van de Waals and Axelrod-Teller types was investigated. It was found that low energy p-p scattering rules out Van de Waals forces of the expected strength

  15. Towards unification of the four fundamental forces

    International Nuclear Information System (INIS)

    Sivaram, C.

    1987-01-01

    An account of the principles involved and the progress made in understanding of four fundamental forces of nature, namely, gravitational force, electromagnetic force, electroweak force and electrostrong force is given. The attempts being made to unify these forces are also described. (M.G.B.)

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

    KAUST Repository

    Wang, Zhenwei; He, Xin; Zhang, Xixiang; Alshareef, Husam N.

    2016-01-01

    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

  17. Inelastic transitions of atoms and molecules induced by van der Waals interaction with a surface

    International Nuclear Information System (INIS)

    Baudon, J.; Hamamda, M.; Boustimi, M.; Bocvarski, V.; Taillandier-Loize, T.; Dutier, G.; Perales, F.; Ducloy, M.

    2012-01-01

    Inelastic processes occuring in thermal-velocity metastable atoms and molecules passing at a mean distance (1–100 nm) are investigated. These processes are caused by the quadrupolar part of the van der Waals interaction: fine-structure transitions in atoms (Ar ∗ , Kr ∗ ), rovibrational transitions in N 2 ∗ ( 3 Σ u + ), transitions among magnetic sub-levels in the presence of a magnetic field.

  18. Infrared hyperbolic metasurface based on nanostructured van der Waals materials

    Science.gov (United States)

    Li, Peining; Dolado, Irene; Alfaro-Mozaz, Francisco Javier; Casanova, Fèlix; Hueso, Luis E.; Liu, Song; Edgar, James H.; Nikitin, Alexey Y.; Vélez, Saül; Hillenbrand, Rainer

    2018-02-01

    Metasurfaces with strongly anisotropic optical properties can support deep subwavelength-scale confined electromagnetic waves (polaritons), which promise opportunities for controlling light in photonic and optoelectronic applications. We developed a mid-infrared hyperbolic metasurface by nanostructuring a thin layer of hexagonal boron nitride that supports deep subwavelength-scale phonon polaritons that propagate with in-plane hyperbolic dispersion. By applying an infrared nanoimaging technique, we visualize the concave (anomalous) wavefronts of a diverging polariton beam, which represent a landmark feature of hyperbolic polaritons. The results illustrate how near-field microscopy can be applied to reveal the exotic wavefronts of polaritons in anisotropic materials and demonstrate that nanostructured van der Waals materials can form a highly variable and compact platform for hyperbolic infrared metasurface devices and circuits.

  19. Report of the Material Control and Material Accounting Task Force: appendices

    International Nuclear Information System (INIS)

    1978-03-01

    Five appendixes are presented. The first comprises a chronological development of material control and material accounting requirements. The second gives a description of current NRC control and material accounting requirements, practices, and capabilities. In the third a description is given of NRC's research and technical assistance program concerning the measurement and measurement quality control elements of licensee material control and material accounting systems. The fourth covers some special considerations related to inventory differences and their analysis. In the fifth a detailed description is presented of the evaluation methodologies used in development of improved material control and material accounting systems

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

    KAUST Repository

    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.

    2015-01-01

    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.

  1. 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.

  2. Passivation of Black Phosphorus via Self-Assembled Organic Monolayers by van der Waals Epitaxy.

    Science.gov (United States)

    Zhao, Yinghe; Zhou, Qionghua; Li, Qiang; Yao, Xiaojing; Wang, Jinlan

    2017-02-01

    An effective passivation approach to protect black phosphorus (BP) from degradation based on multi-scale simulations is proposed. The self-assembly of perylene-3,4,9,10-tetracarboxylic dianhydride monolayers via van der Waals epitaxy on BP does not break the original electronic properties of BP. The passivation layer thickness is only 2 nm. This study opens up a new pathway toward fine passivation of BP. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  3. Formation and physical characteristics of van der Waals molecules, cations, and anions: Estimates of complete basis set values

    Czech Academy of Sciences Publication Activity Database

    Zahradník, Rudolf; Šroubková, Libuše

    2005-01-01

    Roč. 104, č. 1 (2005), s. 52-63 ISSN 0020-7608 Institutional research plan: CEZ:AV0Z40400503 Keywords : intermolecular complexes * van der Waals species * ab initio calculations * complete basis set values * estimates Subject RIV: CF - Physical ; Theoretical Chemistry Impact factor: 1.192, year: 2005

  4. Detectability of the impacts of ozone-depleting substances and greenhouse gases upon stratospheric ozone accounting for nonlinearities in historical forcings

    Science.gov (United States)

    Bandoro, Justin; Solomon, Susan; Santer, Benjamin D.; Kinnison, Douglas E.; Mills, Michael J.

    2018-01-01

    We perform a formal attribution study of upper- and lower-stratospheric ozone changes using observations together with simulations from the Whole Atmosphere Community Climate Model. Historical model simulations were used to estimate the zonal-mean response patterns (fingerprints) to combined forcing by ozone-depleting substances (ODSs) and well-mixed greenhouse gases (GHGs), as well as to the individual forcing by each factor. Trends in the similarity between the searched-for fingerprints and homogenized observations of stratospheric ozone were compared to trends in pattern similarity between the fingerprints and the internally and naturally generated variability inferred from long control runs. This yields estimated signal-to-noise (S/N) ratios for each of the three fingerprints (ODS, GHG, and ODS + GHG). In both the upper stratosphere (defined in this paper as 1 to 10 hPa) and lower stratosphere (40 to 100 hPa), the spatial fingerprints of the ODS + GHG and ODS-only patterns were consistently detectable not only during the era of maximum ozone depletion but also throughout the observational record (1984-2016). We also develop a fingerprint attribution method to account for forcings whose time evolutions are markedly nonlinear over the observational record. When the nonlinearity of the time evolution of the ODS and ODS + GHG signals is accounted for, we find that the S/N ratios obtained with the stratospheric ODS and ODS + GHG fingerprints are enhanced relative to standard linear trend analysis. Use of the nonlinear signal detection method also reduces the detection time - the estimate of the date at which ODS and GHG impacts on ozone can be formally identified. Furthermore, by explicitly considering nonlinear signal evolution, the complete observational record can be used in the S/N analysis, without applying piecewise linear regression and introducing arbitrary break points. The GHG-driven fingerprint of ozone changes was not statistically identifiable in either

  5. Scrivere al tornio, modellare il testo: Edmund de Waal tra istallazione e memoir

    Directory of Open Access Journals (Sweden)

    Francesca Cuojati

    2012-11-01

    Full Text Available The Hare with Amber Eyes (2010 by Edmund de Waal is a memoir written by “a very textual potter”. Thanks to the inheritance of a collection of tiny Japanese carvings, de Waal leaves on a journey to Paris, Vienna, Odessa, back to his Jewish roots in nineteenth century aesthtecisism and in the tragedy of the Shoah. Drawing parallels between his writing, collecting and the plastic arts of pottery, the author explores the affinities between artefact and word, installation and proposition, collection and archive. The Hare can be read in the context of what R. Wendorf has defined a “literature of collecting,” including critical theory as well as narratives dealing with its practices. Rich in intertextual excursions, de Waal’s autobiographical writing develops a fruitful conversation with W. Benjamin’s 1931 paradigmatic text “Unpacking my Library”. Also P. Levi’s La chiave a stella riverberates in the writer’s awareness of the importance of precision in practices like creating an installation and writing about the past, involving both aesthetic and moral responsabilities. De Waal’s stance about the transitivity between art and writing finally emerges from the very rhetorics of his work which abounds in circular structures like the red alluminium ring which sustains his installation at the V&A Ceramics Galleries and the figure of the chiasmus which organizes his prose writing, linking him yet again to his Jewish cultural origins.

  6. Nuclear spin-spin coupling in a van der Waals-bonded system: xenon dimer.

    Science.gov (United States)

    Vaara, Juha; Hanni, Matti; Jokisaari, Jukka

    2013-03-14

    Nuclear spin-spin coupling over van der Waals bond has recently been observed via the frequency shift of solute protons in a solution containing optically hyperpolarized (129)Xe nuclei. We carry out a first-principles computational study of the prototypic van der Waals-bonded xenon dimer, where the spin-spin coupling between two magnetically non-equivalent isotopes, J((129)Xe - (131)Xe), is observable. We use relativistic theory at the four-component Dirac-Hartree-Fock and Dirac-density-functional theory levels using novel completeness-optimized Gaussian basis sets and choosing the functional based on a comparison with correlated ab initio methods at the nonrelativistic level. J-coupling curves are provided at different levels of theory as functions of the internuclear distance in the xenon dimer, demonstrating cross-coupling effects between relativity and electron correlation for this property. Calculations on small Xe clusters are used to estimate the importance of many-atom effects on J((129)Xe - (131)Xe). Possibilities of observing J((129)Xe - (131)Xe) in liquid xenon are critically examined, based on molecular dynamics simulation. A simplistic spherical model is set up for the xenon dimer confined in a cavity, such as in microporous materials. It is shown that the on the average shorter internuclear distance enforced by the confinement increases the magnitude of the coupling as compared to the bulk liquid case, rendering J((129)Xe - (131)Xe) in a cavity a feasible target for experimental investigation.

  7. U.S. Air Force Annual Financial Statement 2010

    Science.gov (United States)

    2010-01-01

    agencies must follow generally accepted accounting principles ( GAAP ) promulgated by the Federal Accounting Standards Advisory Board (FASAB). The Air... depreciates all General PP&E, other than land, on a straight-line basis. When it is in the best interest of the government, the Air Force provides...capitalization threshold, Air Force records the applicable asset as though purchased, with an offsetting liability, and depreciates it. The Air Force

  8. Metastable decay and binding energies of van der Waals cluster ions

    International Nuclear Information System (INIS)

    Ernstberger, B.; Krause, H.; Neusser, H.J.

    1991-01-01

    In this work the appearance potentials for the metastable decay channel of a series of van der Waals dimer ions are presented. Ionization and metastable dissociation is achieved by resonance-enhanced two-photon absorption in a linear reflectron time-of-flight mass spectrometer. From the appearance potentials the binding energy of the neutral dimers is obtained and from the additionally measured ionization potentials binding energies of the dimer cations are achieved. The contribution of charge transfer resonance interaction to the binding in cluster ions is evaluated by investigation of several homo- and heterodimers of aromatic components and the heterodimer benzene/cyclohexane as an example for a dimer consisting of an aromatic and a nonaromatic component. (orig.)

  9. 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.

  10. 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

    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...

  11. Using the van der Waals broadening of the spectral atomic lines to measure the gas temperature of an argon microwave plasma at atmospheric pressure

    International Nuclear Information System (INIS)

    Yubero, C.; Dimitrijevic, M.S.; Garcia, M.C.; Calzada, M.D.

    2007-01-01

    The ro-vibrational emission spectra of the molecular species are usually used to measure the gas temperature of a discharge at atmospheric pressure. However, under some experimental conditions, it is difficult to detect them. In order to overcome this difficulty and obtain the temperature, there are methods based on the relation between the gas temperature and the van der Waals broadening of argon atomic spectral lines with a Stark contribution negligible. In this work, we propose a method based on this relation but for lines with a Stark broadening comparable with the van der Waals one

  12. Patient accounting: vital for financial survival.

    Science.gov (United States)

    Puhala, J M; Barrett, M J

    1987-09-01

    The implementation of the prospective payment system has affected the financial stability of hospitals. It has forced them to take a closer look at their patient accounting function as it affects cash flow and patient service revenue. This article addresses several new issues relating to patient accounts processing that have created a need for more emphasis on the patient accounting function. Efficient operations and effective accounts receivable management may be the difference between the success or failure of a hospital in today's competitive environment.

  13. Characterization of rarefaction waves in van der Waals fluids

    Science.gov (United States)

    Yuen, Albert; Barnard, John J.

    2015-12-01

    We calculate the isentropic evolution of an instantaneously heated foil, assuming a van der Waals equation of state with the Maxwell construction. The analysis by Yuen and Barnard [Phys. Rev. E 92, 033019 (2015), 10.1103/PhysRevE.92.033019] is extended for the particular case of three degrees of freedom. We assume heating to temperatures in the vicinity of the critical point. The self-similar profiles of the rarefaction waves describing the evolution of the foil display plateaus in density and temperature due to a phase transition from the single-phase to the two-phase regime. The hydrodynamic equations are expressed in a dimensionless form and the solutions form a set of universal curves, depending on a single parameter: the dimensionless initial entropy. We characterize the rarefaction waves by calculating how the plateau length, density, pressure, temperature, velocity, internal energy, and sound speed vary with dimensionless initial entropy.

  14. Relations between anisotropic defects, structural evolution, and van der Waals bonding in 2H-NbSe2

    International Nuclear Information System (INIS)

    Gavarri, J.R.; Mokrani, R.; Boulesteix, C.; Vacquier, G.

    1988-01-01

    Correlations between anisotropic defects and van der Waals interactions have been established for the layer compound 2H-NbSe 2 which is investigated by low temperature X-ray diffraction techniques. Thermal expansion coefficients and anisotropic Debye temperatures are determined. A diffraction profile analysis reveals the existence of lattice distortions independent of the temperature. They are due to layer defects. To interpret the structural evolution data, the thermal expansion functions, α a (T) and α c (T) are simulated in the low temperature range which yield the elastic constants and the Grueneisen parameters. Using bond energy models, the Van der Waals nature of interlayer Se-Se interactions is confirmed by a model of thermal expansion of bonds and connected with the C 13 component of the elastic tensor. Such interactions can explain the presence of some layer defects that can be 4H-NbSe 2 nuclei in the 2H host lattice. In addition, no strong change in the Grueneisen parameters is clearly shown to occur at the 35 K transition of 2H-NbSe 2 . (author)

  15. Momentum accounting for trends : Relevance, explanatory and predictive power of the framework of triple-entry bookkeeping and momentum accounting of Yuji Ijiri

    NARCIS (Netherlands)

    Melse, E.

    2010-01-01

    The objective of momentum accounting is to improve strategic management accounting practices, enumeration and corporate disclosure for governance purposes. This accounting theory introduces new measurement units: momentum and force. The key development is to see momentum as a rate or the speed of

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

    International Nuclear Information System (INIS)

    Lee, Gwan-Hyoung; Lee, Chul-Ho; Zande, Arend M. van der; Han, Minyong; Cui, Xu; Arefe, Ghidewon; Hone, James; Nuckolls, Colin; Heinz, Tony F.; Kim, Philip

    2014-01-01

    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 MoS 2 heterostructures for memory devices; graphene/MoS 2 /WSe 2 /graphene vertical p-n junctions for photovoltaic devices, and organic crystals on hBN with graphene electrodes for high-performance transistors

  17. Long-range dipolar order and dispersion forces in polar liquids

    Science.gov (United States)

    Besford, Quinn Alexander; Christofferson, Andrew Joseph; Liu, Maoyuan; Yarovsky, Irene

    2017-11-01

    Complex solvation phenomena, such as specific ion effects, occur in polar liquids. Interpretation of these effects in terms of structure and dispersion forces will lead to a greater understanding of solvation. Herein, using molecular dynamics, we probe the structure of polar liquids through specific dipolar pair correlation functions that contribute to the potential of mean force that is "felt" between thermally rotating dipole moments. It is shown that unique dipolar order exists at separations at least up to 20 Å for all liquids studied. When the structural order is compared with a dipolar dispersion force that arises from local co-operative enhancement of dipole moments, a strong agreement is found. Lifshitz theory of dispersion forces was compared with the structural order, where the theory is validated for all liquids that do not have significant local dipole correlations. For liquids that do have significant local dipole correlations, specifically liquid water, Lifshitz theory underestimates the dispersion force by a factor of 5-10, demonstrating that the force that leads to the increased structure in liquid water is missed by Lifshitz theory of van der Waals forces. We apply similar correlation functions to an ionic aqueous system, where long-range order between water's dipole moment and a single chloride ion is found to exist at 20 Å of separation, revealing a long-range perturbation of water's structure by an ion. Furthermore, we found that waters within the 1st, 2nd, and 3rd solvation shells of a chloride ion exhibit significantly enhanced dipolar interactions, particularly with waters at larger distances of separation. Our results provide a link between structures, dispersion forces, and specific ion effects, which may lead to a more robust understanding of solvation.

  18. Effect of three-body forces on the phase behavior of charged colloids

    International Nuclear Information System (INIS)

    Wu, J. Z.; Bratko, D.; Blanch, H. W.; Prausnitz, J. M.

    2000-01-01

    Statistical-thermodynamic theory for predicting the phase behavior of a colloidal solution requires the pair interaction potential between colloidal particles in solution. In practice, it is necessary to assume pairwise additivity for the potential of mean force between colloidal particles, but little is known concerning the validity of this assumption. This paper concerns interaction between small charged colloids, such as surfactant micelles or globular proteins, in electrolyte solutions and the multibody effect on phase behavior. Monte Carlo simulations for isolated colloidal triplets in equilateral configurations show that, while the three-body force is repulsive when the three particles are near contact, it becomes short-ranged attractive at further separations, contrary to a previous study where the triplet force is attractive at all separations. The three-body force arises mainly from hard-sphere collisions between colloids and small ions; it is most significant in solutions of monovalent salt at low concentration where charged colloids experience strong electrostatic interactions. To illustrate the effect of three-body forces on the phase behavior of charged colloids, we calculated the densities of coexisting phases using van der Waals-type theories for colloidal solutions and for crystals. For the conditions investigated in this work, even though the magnitude of the three-body force may be as large as 10% of the total force at small separations, three-body forces do not have a major effect on the densities of binary coexisting phases. However, coexisting densities calculated using Derjaguin-Landau-Verwey-Overbeek theory are much different from those calculated using our simulated potential of mean force. (c) 2000 American Institute of Physics

  19. Accounting for derivative contracts in an energy environment

    International Nuclear Information System (INIS)

    Lewthwaite, T.; Majid, H.; Swingler, N.

    1999-01-01

    This chapter reviews the latest developments in the accounting for derivative contracts in the energy environment, covering the US accounting and disclosure requirements and the Statement of Financial Accounting Standards (SFAS) 133 Accounting for Derivative Instruments and Hedging Activities, and the Emerging Issues Task Force Consensus (EITF) 98-10 accounting for energy trading and risk management activities. UK accounting and disclosure requirements and the international point of view are discussed. Three different types of hedges are described

  20. Accounting for derivative contracts in an energy environment

    Energy Technology Data Exchange (ETDEWEB)

    Lewthwaite, T.; Majid, H.; Swingler, N. [Arthur Andersen (United Kingdom)

    1999-07-01

    This chapter reviews the latest developments in the accounting for derivative contracts in the energy environment, covering the US accounting and disclosure requirements and the Statement of Financial Accounting Standards (SFAS) 133 Accounting for Derivative Instruments and Hedging Activities, and the Emerging Issues Task Force Consensus (EITF) 98-10 accounting for energy trading and risk management activities. UK accounting and disclosure requirements and the international point of view are discussed. Three different types of hedges are described.

  1. Trends in mica–mica adhesion reflect the influence of molecular details on long-range dispersion forces underlying aggregation and coalignment

    Energy Technology Data Exchange (ETDEWEB)

    Li, Dongsheng; Chun, Jaehun; Xiao, Dongdong; Zhou, Weijiang; Cai, Huacheng; Zhang, Lei; Rosso, Kevin M.; Mundy, Christopher J.; Schenter, Gregory K.; De Yoreo, James J.

    2017-07-05

    Oriented attachment of nanocrystalline subunits is recognized as a common crystallization pathway that is closely related to formation of nanoparticle superlattices, mesocrystals, and other kinetically stabilized structures. Approaching particles have been observed to rotate to achieve co-alignment while separated by nanometer-scale solvent layers. Little is known about the forces that drive co-alignment, particularly in this “solvent-separated” regime. To obtain a mechanistic understanding of this process, we used atomic force microscopy-based dynamic force spectroscopy with tips fabricated from oriented mica to measure the adhesion forces between mica (001) surfaces in electrolyte solutions as a function of orientation, temperature, electrolyte type, and electrolyte concentration. The results reveal a ~60° periodicity as well as a complex dependence on electrolyte concentration and temperature. A continuum model that considers the competition between electrostatic repulsion and van der Waals attraction, augmented by microscopic details that include surface separation, water structure, ion hydration, and charge regulation at the interface, qualitatively reproduces the observed trends and implies that dispersion forces are responsible for establishing co-alignment in the solvent-separated state.

  2. A simulation of atomic force microscope microcantilever in the tapping mode utilizing couple stress theory.

    Science.gov (United States)

    Abbasi, Mohammad

    2018-04-01

    The nonlinear vibration behavior of a Tapping mode atomic force microscopy (TM-AFM) microcantilever under acoustic excitation force has been modeled and investigated. In dynamic AFM, the tip-surface interactions are strongly nonlinear, rapidly changing and hysteretic. First, the governing differential equation of motion and boundary conditions for dynamic analysis are obtained using the modified couple stress theory. Afterwards, closed-form expressions for nonlinear frequency and effective nonlinear damping ratio are derived utilizing perturbation method. The effect of tip connection position on the vibration behavior of the microcantilever are also analyzed. The results show that nonlinear frequency is size dependent. According to the results, an increase in the equilibrium separation between the tip and the sample surface reduces the overall effect of van der Waals forces on the nonlinear frequency, but its effect on the effective nonlinear damping ratio is negligible. The results also indicate that both the change in the distance between tip and cantilever free end and the reduction of tip radius have significant effects on the accuracy and sensitivity of the TM-AFM in the measurement of surface forces. The hysteretic behavior has been observed in the near resonance frequency response due to softening and hardening of the forced vibration response. Copyright © 2018 Elsevier Ltd. All rights reserved.

  3. Accounting and Tax Issues Concerning Commercial Discounts

    Directory of Open Access Journals (Sweden)

    Sava Raluca

    2015-12-01

    Full Text Available Commercial discounts accounting presents a particular importance because, on the one hand, of their widely spread on a large scale in the commercial activity and on the second hand, due to the influence of the accounting and reporting method over the value added tax. The paper theoretically addresses commercial reductions and also their reflection in the accounting according with the latest regulations in force.

  4. Color screening effect in the quark potential model

    International Nuclear Information System (INIS)

    Zhang Zongye; Yu Youwen; Shen Pengnian; Shen Xiaoyan; Dong Yubin

    1993-01-01

    By using the color confinement potential which includes the color screening effect, we studied the baryon spectra and the nucleon-nucleon interaction. The results show that the color screening effect not only improves the baryon spectrum calculation, but also can solve the long-tail problem of the color Van der Waals force. A part of the medium attraction of the nuclear force can be obtained from the color Van der Waals force. (orig.)

  5. Reconstructing the early 19th-century Waal River by means of a 2D physics-based numerical model

    NARCIS (Netherlands)

    Montes Arboleda, A.; Crosato, A.; Middelkoop, H.

    2010-01-01

    Suspended-sediment concentration data are a missing link in reconstructions of the River Waal in the early 1800s. These reconstructions serve as a basis for assessing the long-term effects of major interventions carried out between 1850 AD and the early 20th century. We used a 2D physics-based

  6. Scattering theory approach to electrodynamic Casimir forces

    International Nuclear Information System (INIS)

    Rahi, Sahand Jamal; Kardar, Mehran; Emig, Thorsten; Graham, Noah; Jaffe, Robert L.

    2009-01-01

    We give a comprehensive presentation of methods for calculating the Casimir force to arbitrary accuracy, for any number of objects, arbitrary shapes, susceptibility functions, and separations. The technique is applicable to objects immersed in media other than vacuum, nonzero temperatures, and spatial arrangements in which one object is enclosed in another. Our method combines each object's classical electromagnetic scattering amplitude with universal translation matrices, which convert between the bases used to calculate scattering for each object, but are otherwise independent of the details of the individual objects. The method is illustrated by rederiving the Lifshitz formula for infinite half-spaces, by demonstrating the Casimir-Polder to van der Waals crossover, and by computing the Casimir interaction energy of two infinite, parallel, perfect metal cylinders either inside or outside one another. Furthermore, it is used to obtain new results, namely, the Casimir energies of a sphere or a cylinder opposite a plate, all with finite permittivity and permeability, to leading order at large separation.

  7. 2D halide perovskite-based van der Waals heterostructures: contact evaluation and performance modulation

    Science.gov (United States)

    Guo, Yaguang; Saidi, Wissam A.; Wang, Qian

    2017-09-01

    Halide perovskites and van der Waals (vdW) heterostructures are both of current interest owing to their novel properties and potential applications in nano-devices. Here, we show the great potential of 2D halide perovskite sheets (C4H9NH3)2PbX4 (X  =  Cl, Br and I) that were synthesized recently (Dou et al 2015 Science 349 1518-21) as the channel materials contacting with graphene and other 2D metallic sheets to form van der Waals heterostructures for field effect transistor (FET). Based on state-of-the-art theoretical simulations, we show that the intrinsic properties of the 2D halide perovskites are preserved in the heterojunction, which is different from the conventional contact with metal surfaces. The 2D halide perovskites form a p-type Schottky barrier (Φh) contact with graphene, where tunneling barrier exists, and a negative band bending occurs at the lateral interface. We demonstrate that the Schottky barrier can be turned from p-type to n-type by doping graphene with nitrogen atoms, and a low-Φh or an Ohmic contact can be realized by doping graphene with boron atoms or replacing graphene with other high-work-function 2D metallic sheets such as ZT-MoS2, ZT-MoSe2 and H-NbS2. This study not only predicts a 2D halide perovskite-based FETs, but also enhances the understanding of tuning Schottky barrier height in device applications.

  8. 5 CFR 2100.10 - Conditions of disclosure and accounting of certain disclosures.

    Science.gov (United States)

    2010-01-01

    ... 5 Administrative Personnel 3 2010-01-01 2010-01-01 false Conditions of disclosure and accounting of certain disclosures. 2100.10 Section 2100.10 Administrative Personnel ARMED FORCES RETIREMENT HOME ARMED FORCES RETIREMENT HOME PRIVACY ACT PROCEDURES § 2100.10 Conditions of disclosure and accounting of...

  9. Modeling the influence of the Casimir force on the pull-in instability of nanowire-fabricated nanotweezers

    Science.gov (United States)

    Farrokhabadi, Amin; Mokhtari, Javad; Rach, Randolph; Abadyan, Mohamadreza

    2015-09-01

    The Casimir force can strongly interfere with the pull-in performance of ultra-small structures. The strength of the Casimir force is significantly affected by the geometries of interacting bodies. Previous investigators have exclusively studied the effect of the Casimir force on the electromechanical instability of nanostructures with planar geometries. However no work has yet considered this effect on the pull-in instability of systems with cylindrical geometries such as nanotweezers fabricated from nanotube/nanowires. In our present work, the influence of the Casimir attraction on the electrostatic response and pull-in instability of nanotweezers fabricated from cylindrical conductive nanowires/nanotubes is theoretically investigated. An asymptotic solution, based on scattering theory, is applied to consider the effect of vacuum fluctuations in the theoretical model. The Euler-Bernoulli beam model is employed, in conjunction with the size-dependent modified couple stress continuum theory, to derive the governing equation of the nanotweezers. The governing nonlinear equations are solved by two different approaches, i.e., the modified Adomian-Padé method (MAD-Padé) and a numerical solution. Various aspects of the problem, i.e., the variation of pull-in parameters, effect of geometry, coupling between the Casimir force and size dependency effects and comparison with the van der Waals force regime are discussed.

  10. Ab-initio study of structural and electronic properties of WS2/h-BN van der Waals heterostructure

    Science.gov (United States)

    Ghasemi majd, Zahra; Amiri, Peiman; Taghizadeh, Seyed Fardin

    2018-06-01

    First-principle calculations with different exchange-correlation functionals, including LDA, GGA, semi-empirical and ab-initio van der Waals in the forms of vdW-DF2B86R and vdW-DF2 were performed to evaluate the performance of different functionals in describing the bonding mechanism, adsorption energy and interlayer distance of WS2 monolayer on and between h-BN layers. The finding was that the vdW-DF2B86R seems to be the approach best lending itself to this purpose. In order to include the van der Waals (vdW) interactions in our calculations, we used the DFT-D2 and vdW methods, which gave rise to a physical adsorption with no net charge transfer between the WS2 layer and the corresponding substrates. In addition, we investigated the electronic and structural properties of WS2 and h-BN heterolayers, using vdW-DF2B86R functional. Based on density functional theory calculations, WS2 on and between h-BN layers showed a direct band gap at the K-point, which was experimentally observed.

  11. Morse-Morse-Spline-Van der Waals intermolecular potential suitable for hexafluoride gases

    International Nuclear Information System (INIS)

    Coroiu, Ilioara

    2004-01-01

    Several effective isotopic pair potential functions have been proposed to characterize the bulk properties of quasispherical molecules, in particular the hexafluorides, but none got a success. Unfortunately, these potentials have repulsive walls steeper than those which describe the hexafluorides. That these intermolecular potentials are not quite adequate is shown by the lack of complete agreement between theory and experiment even for the rare gases. Not long ago, R. A. Aziz et al. have constructed a Morse-Morse-Spline-Van der Waals (MMSV) potential. The MMSV potential incorporates the determination of C 6 dispersion coefficient and it reasonably correlates second virial coefficients and viscosity data of sulphur hexafluoride at the same time. None of the potential functions previously proposed in literature could predict these properties simultaneously. We calculated the second virial coefficients and a large number of Chapman-Cowling collision integrals for this improved intermolecular potential, the MMSV potential. The results were tabulated for a large reduced temperature range, kT/ε from 0.1 to 100. The treatment was entirely classical and no corrections for quantum effects were made. The higher approximations to the transport coefficients and the isotopic thermal diffusion factor were also calculated and tabulated for the same range. In this paper we present the evaluation of the uranium hexafluoride potential parameters for the MMSV intermolecular potential. To find a single set of potential parameters which could predict all the transport properties (viscosity, thermal conductivity, self diffusion, etc.), as well as the second virial coefficients, simultaneously, the method suggested by Morizot and a large assortment of literature data were used. Our results emphasized that the Morse-Morse-Spline-Van der Waals potential have the best overall predictive ability for gaseous hexafluoride data, certain for uranium hexafluoride. (author)

  12. Bridging C60 by silicon: Towards non-Van der Waals C60-based materials

    International Nuclear Information System (INIS)

    Tournus, F.; Masenelli, B.; Melinon, P.; Blase, X.; Perez, A.; Pellarin, M.; Broyer, M.; Flank, A.M.; Lagarde, P.

    2002-01-01

    We report the three-dimensional packing of C 60 clusters stabilized by the addition of Si. X-ray absorption spectroscopy reveals that Si atoms are in an unusual environment: between two C 60 , with ten or more carbon neighbors. According to ab initio calculations, the cohesive energy is about 2 eV per Si atom, much higher than the Van der Waals binding energy between two C 60 . Experiment and calculations both indicate a charge transfer from Si to C 60 . Eventually, the film may have a local decahedral symmetry

  13. Effect of relative humidity on onset of capillary forces for rough surfaces.

    Science.gov (United States)

    Zarate, Nyah V; Harrison, Aaron J; Litster, James D; Beaudoin, Stephen P

    2013-12-01

    Atomic force microscopy (AFM) was used to investigate the effect of relative humidity (RH) on the adhesion forces between silicon nitride AFM probes, hydrophilic stainless steel, and hydrophobic Perspex® (polymethylmethacrylate, PMMA). In addition, AFM-based phase contrast imaging was used to quantify the amount and location of adsorbed water present on these substrates at RH levels ranging from 15% to 65% at 22°C. Both the adhesion forces and the quantities of adsorbed moisture were seen to vary with RH, and the nature of this variation depended on the hydrophobicity of the substrate. For the Perspex®, both the adhesion force and the amount of adsorbed moisture were essentially independent of RH. For the stainless steel substrate, adsorbed moisture increased continuously with increasing RH, while the adhesion force rose from a minimum at 15% RH to a broad maximum between 25% and 35% RH. From 35% to 55% RH, the adhesion force dropped continuously to an intermediate level before rising again as 65% RH was approached. The changes in adhesion force with increasing relative humidity in the case of the stainless steel substrate were attributed to a balance of effects associated with adsorbed, sub-continuum water on the cantilever and steel. Hydrogen bonding interactions between these adsorbed water molecules were thought to increase the adhesion force. However, when significant quantities of molecular water adsorbed, these molecules were expect to decrease adhesion by screening the van der Waals interactions between the steel and the cantilever tip, and by increasing the separation distance between these solid surfaces when they were 'in contact'. Finally, the slight increase in adhesion between 55% and 65% RH was attributed to true capillary forces exerted by continuum water on the two solid surfaces. Copyright © 2013 Elsevier Inc. All rights reserved.

  14. 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.

  15. Accounting for radiative forcing from albedo change in future global land-use scenarios

    Energy Technology Data Exchange (ETDEWEB)

    Jones, Andrew D. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Calvin, Katherine V. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Collins, William D. [Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); Univ. of California, Berkeley, CA (United States); Edmonds, James A. [Pacific Northwest National Lab. (PNNL), Richland, WA (United States)

    2015-08-01

    We demonstrate the effectiveness of a new method for quantifying radiative forcing from land use and land cover change (LULCC) within an integrated assessment model, the Global Change Assessment Model (GCAM). The method relies on geographically differentiated estimates of radiative forcing from albedo change associated with major land cover transitions derived from the Community Earth System Model. We find that conversion of 1 km² of woody vegetation (forest and shrublands) to non-woody vegetation (crops and grassland) yields between 0 and –0.71 nW/m² of globally averaged radiative forcing determined by the vegetation characteristics, snow dynamics, and atmospheric radiation environment characteristic within each of 151 regions we consider globally. Across a set of scenarios designed to span a range of potential future LULCC, we find LULCC forcing ranging from –0.06 to –0.29 W/m² by 2070 depending on assumptions regarding future crop yield growth and whether climate policy favors afforestation or bioenergy crops. Inclusion of this previously uncounted forcing in the policy targets driving future climate mitigation efforts leads to changes in fossil fuel emissions on the order of 1.5 PgC/yr by 2070 for a climate forcing limit of 4.5 Wm–2, corresponding to a 12–67 % change in fossil fuel emissions depending on the scenario. Scenarios with significant afforestation must compensate for albedo-induced warming through additional emissions reductions, and scenarios with significant deforestation need not mitigate as aggressively due to albedo-induced cooling. In all scenarios considered, inclusion of albedo forcing in policy targets increases forest and shrub cover globally.

  16. INFLUENCING OF FRICTION IN HINGES FORCE SIZE OF BARS

    Directory of Open Access Journals (Sweden)

    BOHOMAZ V. N.

    2016-04-01

    Full Text Available Formulation of the problem. The size of critical force of bar on the traditional method of calculation is determined in supposition of ideal hinge in the place of fixing of bar. There are both a hinge resistance at the turn of bar ends and their moving in the real hinges. Thus, there is the necessity of influencing character determination of these hinge imperfections on the size of critical force. In the existent scientific labours is devoted the alike problems, influencing of friction in the hinges of bar fastening on the size of critical force was not taken into account. At determination of bars stability with no ideality of hinges friction in them it is possible to take into account by the eccentric appendix of loading or appendix of moment. However at such approach it is difficult enough to define the size of attached force or moment. Purpose. To set influencing of friction in the hinge of bar fastening on of his critical force size in sense of Euler, and also build dependences for determination of bar critical force taking into account mechanical descriptions of hinges materials. Conclusion. For the task of determination the size of bar critical force with the joint fastening on ends are got the dependences which take into account mechanical descriptions of material hinge. The received dependences allow to define more exact meaning of critical force for bars. The examples of calculation of whole bar and bar with undercuting in the middle are resulted that values of critical force, certain on a traditional method are overpriced.

  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. Institutions and accounting standard transformation:Observations from Japan

    Institute of Scientific and Technical Information of China (English)

    Naohiro; Urasaki

    2014-01-01

    This paper describes the transformation of Japan’s accounting standards over the past 2 decades and the driving forces behind this transformation. It also analyzes the current state of Japan’s accounting standards, which are characterized by the dichotomy of accounting systems inherited from the country’s political, economic and legal institutions. The discussion in this paper emphasizes that a single set of accounting standards is not always effective for every entity.

  19. Institutions and accounting standard transformation: Observations from Japan

    Directory of Open Access Journals (Sweden)

    Naohiro Urasaki

    2014-03-01

    Full Text Available This paper describes the transformation of Japan’s accounting standards over the past 2 decades and the driving forces behind this transformation. It also analyzes the current state of Japan’s accounting standards, which are characterized by the dichotomy of accounting systems inherited from the country’s political, economic and legal institutions. The discussion in this paper emphasizes that a single set of accounting standards is not always effective for every entity.

  20. Phase diagram of Rydberg atoms with repulsive van der Waals interaction

    International Nuclear Information System (INIS)

    Osychenko, O. N.; Astrakharchik, G. E.; Boronat, J.; Lutsyshyn, Y.; Lozovik, Yu. E.

    2011-01-01

    We report a quantum Monte Carlo calculation of the phase diagram of bosons interacting with a repulsive inverse sixth power pair potential, a model for assemblies of Rydberg atoms in the local van der Waals blockade regime. The model can be parametrized in terms of just two parameters, the reduced density and temperature. Solidification happens to the fcc phase. At zero temperature, the transition density is found with the diffusion Monte Carlo method at density ρ=3.9 ((ℎ/2π) 2 /mC 6 ) 3/4 , where C 6 is the strength of the interaction. The solidification curve at nonzero temperature is studied with the path-integral Monte Carlo approach and is compared with transitions in corresponding harmonic and classical crystals. Relaxation mechanisms are considered in relation to present experiments.

  1. Inelastic neutron scattering, Raman, vibrational analysis with anharmonic corrections, and scaled quantum mechanical force field for polycrystalline L-alanine

    Energy Technology Data Exchange (ETDEWEB)

    Williams, Robert W. [Department of Biomedical Informatics, Uniformed Services University, 4301 Jones Bridge Road, Bethesda, MD 20815 (United States)], E-mail: bob@bob.usuhs.mil; Schluecker, Sebastian [Institute of Physical Chemistry, University of Wuerzburg, Wuerzburg (Germany); Hudson, Bruce S. [Department of Chemistry, Syracuse University, Syracuse, NY (United States)

    2008-01-22

    A scaled quantum mechanical harmonic force field (SQMFF) corrected for anharmonicity is obtained for the 23 K L-alanine crystal structure using van der Waals corrected periodic boundary condition density functional theory (DFT) calculations with the PBE functional. Scale factors are obtained with comparisons to inelastic neutron scattering (INS), Raman, and FT-IR spectra of polycrystalline L-alanine at 15-23 K. Calculated frequencies for all 153 normal modes differ from observed frequencies with a standard deviation of 6 wavenumbers. Non-bonded external k = 0 lattice modes are included, but assignments to these modes are presently ambiguous. The extension of SQMFF methodology to lattice modes is new, as are the procedures used here for providing corrections for anharmonicity and van der Waals interactions in DFT calculations on crystals. First principles Born-Oppenheimer molecular dynamics (BOMD) calculations are performed on the L-alanine crystal structure at a series of classical temperatures ranging from 23 K to 600 K. Corrections for zero-point energy (ZPE) are estimated by finding the classical temperature that reproduces the mean square displacements (MSDs) measured from the diffraction data at 23 K. External k = 0 lattice motions are weakly coupled to bonded internal modes.

  2. Inelastic neutron scattering, Raman, vibrational analysis with anharmonic corrections, and scaled quantum mechanical force field for polycrystalline L-alanine

    International Nuclear Information System (INIS)

    Williams, Robert W.; Schluecker, Sebastian; Hudson, Bruce S.

    2008-01-01

    A scaled quantum mechanical harmonic force field (SQMFF) corrected for anharmonicity is obtained for the 23 K L-alanine crystal structure using van der Waals corrected periodic boundary condition density functional theory (DFT) calculations with the PBE functional. Scale factors are obtained with comparisons to inelastic neutron scattering (INS), Raman, and FT-IR spectra of polycrystalline L-alanine at 15-23 K. Calculated frequencies for all 153 normal modes differ from observed frequencies with a standard deviation of 6 wavenumbers. Non-bonded external k = 0 lattice modes are included, but assignments to these modes are presently ambiguous. The extension of SQMFF methodology to lattice modes is new, as are the procedures used here for providing corrections for anharmonicity and van der Waals interactions in DFT calculations on crystals. First principles Born-Oppenheimer molecular dynamics (BOMD) calculations are performed on the L-alanine crystal structure at a series of classical temperatures ranging from 23 K to 600 K. Corrections for zero-point energy (ZPE) are estimated by finding the classical temperature that reproduces the mean square displacements (MSDs) measured from the diffraction data at 23 K. External k = 0 lattice motions are weakly coupled to bonded internal modes

  3. Numerical simulation of particle settling and cohesion in liquid

    Energy Technology Data Exchange (ETDEWEB)

    Johno, Y; Nakashima, K; Shigematsu, T; Ono, B [SASEBO National College of Technology, 1-1 Okishin, Sasebo, Nagasaki, 857-1193 (Japan); Satomi, M, E-mail: yjohno@post.cc.sasebo.ac.j [Sony Semiconductor Kyushu Corporation, Kikuchigun, Kumamoto (Japan)

    2009-02-01

    In this study, the motions of particles and particle clusters in liquid were numerically simulated. The particles of two sizes (Dp=40mum and 20mum) settle while repeating cohesion and dispersion, and finally the sediment of particles are formed at the bottom of a hexahedron container which is filled up with pure water. The flow field was solved with the Navier-Stokes equations and the particle motions were solved with the Lagrangian-type motion equations, where the interaction between fluid and particles due to drag forces were taken into account. The collision among particles was calculated using Distinct Element Method (DEM), and the effects of cohesive forces by van der Waals force acting on particle contact points were taken into account. Numerical simulations were performed under conditions in still flow and in shear flow. It was found that the simulation results enable us to know the state of the particle settling and the particle condensation.

  4. 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

    2017-06-07

    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 (CrI 3 ) 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 CrI 3 displays suppressed magnetization with a metamagnetic effect, whereas in trilayer CrI 3 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.

  5. 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.

  6. Self-bridging of vertical silicon nanowires and a universal capacitive force model for spontaneous attraction in nanostructures.

    Science.gov (United States)

    Sun, Zhelin; Wang, Deli; Xiang, Jie

    2014-11-25

    Spontaneous attractions between free-standing nanostructures have often caused adhesion or stiction that affects a wide range of nanoscale devices, particularly nano/microelectromechanical systems. Previous understandings of the attraction mechanisms have included capillary force, van der Waals/Casimir forces, and surface polar charges. However, none of these mechanisms universally applies to simple semiconductor structures such as silicon nanowire arrays that often exhibit bunching or adhesions. Here we propose a simple capacitive force model to quantitatively study the universal spontaneous attraction that often causes stiction among semiconductor or metallic nanostructures such as vertical nanowire arrays with inevitably nonuniform size variations due to fabrication. When nanostructures are uniform in size, they share the same substrate potential. The presence of slight size differences will break the symmetry in the capacitive network formed between the nanowires, substrate, and their environment, giving rise to electrostatic attraction forces due to the relative potential difference between neighboring wires. Our model is experimentally verified using arrays of vertical silicon nanowire pairs with varied spacing, diameter, and size differences. Threshold nanowire spacing, diameter, or size difference between the nearest neighbors has been identified beyond which the nanowires start to exhibit spontaneous attraction that leads to bridging when electrostatic forces overcome elastic restoration forces. This work illustrates a universal understanding of spontaneous attraction that will impact the design, fabrication, and reliable operation of nanoscale devices and systems.

  7. FORCE STRUCTURE: Better Management Controls Are Needed to Oversee the Army's Modular Force and Expansion Initiatives and Improve Accountability for Results

    National Research Council Canada - National Science Library

    2007-01-01

    .... For this report, GAO assessed to what extent the Army has accomplished the following: (1) implemented and established management controls for its modular force and force expansion initiatives, and (2...

  8. 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.

  9. Inflationary magnetogenesis, derivative couplings and relativistic Van der Waals interactions

    CERN Document Server

    Giovannini, Massimo

    2015-01-01

    When the gauge fields have derivative couplings to scalars, like in the case of the relativistic theory of Van der Waals (or Casimir-Polder) interactions, conformal invariance is broken but the magnetic and electric susceptibilities are not bound to coincide. We analyze the formation of large-scale magnetic fields in slow-roll inflation and find that they are generated at the level of a few hundredths of a nG and over typical length scales between few Mpc and $100$ Mpc. Using a new time parametrization that reduces to conformal time but only for coincident susceptibilities, the gauge action is quantized while the evolution equations of the corresponding mode functions are more easily solvable. The power spectra depend on the normalized rates of variation of the two susceptibilities (or of the corresponding gauge couplings) and on the absolute value of their ratio at the beginning of inflation. We pin down explicit regions in the parameter space where all the physical requirements (i.e. the backreaction constr...

  10. Standardized accounting ashore for afloat activities

    OpenAIRE

    Burr, Michael J.

    1996-01-01

    With limited resources and reduced funding for Naval forces, there is a need to standardize accounting ashore for all afloat activities. The purpose of this thesis was to review the framework for standardization of inventory reporting afloat under one stores (inventory) accounting system, referred to as the Material Financial Control System-Retail (MFCS-Retail). Additional analysis was conducted on general funds obligational reporting for afloat Operating Targets (OPTARS) and the conversion t...

  11. Explaining the Microtubule Energy Balance: Contributions Due to Dipole Moments, Charges, van der Waals and Solvation Energy

    Directory of Open Access Journals (Sweden)

    Ahmed Taha Ayoub

    2017-09-01

    Full Text Available Microtubules are the main components of mitotic spindles, and are the pillars of the cellular cytoskeleton. They perform most of their cellular functions by virtue of their unique dynamic instability processes which alternate between polymerization and depolymerization phases. This in turn is driven by a precise balance between attraction and repulsion forces between the constituents of microtubules (MTs—tubulin dimers. Therefore, it is critically important to know what contributions result in a balance of the interaction energy among tubulin dimers that make up microtubules and what interactions may tip this balance toward or away from a stable polymerized state of tubulin. In this paper, we calculate the dipole–dipole interaction energy between tubulin dimers in a microtubule as part of the various contributions to the energy balance. We also compare the remaining contributions to the interaction energies between tubulin dimers and establish a balance between stabilizing and destabilizing components, including the van der Waals, electrostatic, and solvent-accessible surface area energies. The energy balance shows that the GTP-capped tip of the seam at the plus end of microtubules is stabilized only by − 9 kcal/mol, which can be completely reversed by the hydrolysis of a single GTP molecule, which releases + 14 kcal/mol and destabilizes the seam by an excess of + 5 kcal/mol. This triggers the breakdown of microtubules and initiates a disassembly phase which is aptly called a catastrophe.

  12. Simulation of imaging in tapping-mode atomic-force microscopy: a comparison amongst a variety of approaches

    Energy Technology Data Exchange (ETDEWEB)

    Pishkenari, H N; Mahboobi, S H; Meghdari, A, E-mail: mahboobi@sharif.edu [Center of Excellence in Design, Robotics and Automation (CEDRA), School of Mechanical Engineering, Sharif University of Technology, Tehran (Iran, Islamic Republic of)

    2011-02-23

    Models capable of accurate simulation of microcantilever dynamics coupled with complex tip-sample interactions are essential for interpretation and prediction of the imaging results in amplitude modulation or tapping-mode atomic-force microscopy (AM-AFM or TM-AFM). In this paper, four approaches based on combinations of lumped and finite element methods for modelling of cantilever dynamics, and van der Waals and molecular dynamics for modelling of tip-sample interactions, are used to simulate the precise imaging by AM-AFM. Based on the simulated imaging and force determination, the efficiency of different modelling schemes is evaluated. This comparison is performed considering their coincidence with the realistic behaviour of AM-AFM in imaging of nanoscale features. In the conducted simulations, a diamond tip is used to scan a C60 molecule absorbed on a graphite substrate. The effects of amplitude set-point, cantilever stiffness and quality factor on the accuracy of different modelling approaches are studied.

  13. Self-Sealed Bionic Long Microchannels with Thin Walls and Designable Nanoholes Prepared by Line-Contact Capillary-Force Assembly.

    Science.gov (United States)

    Lao, Zhao-Xin; Hu, Yan-Lei; Pan, Deng; Wang, Ren-Yan; Zhang, Chen-Chu; Ni, Jin-Cheng; Xu, Bing; Li, Jia-Wen; Wu, Dong; Chu, Jia-Ru

    2017-06-01

    Long microchannels with thin walls, small width, and nanoholes or irregular shaped microgaps, which are similar to capillaries or cancerous vessels, are urgently needed to simulate the physiological activities in human body. However, the fabrication of such channels remains challenging. Here, microchannels with designable holes are manufactured by combining laser printing with line-contact capillary-force assembly. Two microwalls are first printed by femtosecond laser direct-writing, and subsequently driven to collapse into a channel by the capillary force that arises in the evaporation of developer. The channel can remain stable in solvent due to the enhanced Van der Waals' force caused by the line-contact of microwalls. Microchannels with controllable nanoholes and almost arbitrary patterns can be fabricated without any bonding or multistep processes. As-prepared microchannels, with wall thicknesses less than 1 µm, widths less than 3 µm, lengths more than 1 mm, are comparable with human capillaries. In addition, the prepared channels also exhibit the ability to steer the flow of liquid without any external pump. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Dipole polarizabilities and van der Waals coefficients for small molecular systems, from the atomic study to the crystal one

    International Nuclear Information System (INIS)

    Begue, D.

    1999-01-01

    Many criteria have been used to translate correctly the dynamical vectors of the electric properties: taking into account many spectroscopic states, the gauge and the quasi-spectral series to determine the analytical equation of the one order function. This approach is applied to two iso-electronic systems: CO and BF. The TDGI method allows to access the systems properties in their fundamental state and in their excited states. This work is illustrated by the beryllium atom study for the five first spectroscopic states. A theoretical study, based on the perturbations method, is presented for the determination of the interaction energy between two distant atoms. The formalism giving the general expression of the matrix elements of the dispersion energy needed to the Van der Waals, has been developed. Three examples illustrate this work: Be 2 , BeLi and K 2 . For this last one, the correlations between the calculation and the experimental observations are presented. Some theoretical results on the static and dynamic properties of beryllium clusters (Be N with N=2,3 and 4). The developed approach allowed to show the variations laws of polarizability with the cluster size and to show the asymptotical behavior of the property. (A.L.B.)

  15. Comparison of accounting methods for business combinations

    Directory of Open Access Journals (Sweden)

    Jaroslav Sedláček

    2012-01-01

    Full Text Available The revised accounting rules applicable to business combinations in force on July1st 2009, are the result of several years efforts the convergence of U.S. and International Committee of the Financial Accounting Standards. Following the harmonization of global accounting procedures are revised and implemented also Czech accounting regulations. In our research we wanted to see how changes can affect the strategy and timing of business combinations. Comparative analysis is mainly focused on the differences between U.S. and international accounting policies and Czech accounting regulations. Key areas of analysis and synthesis are the identification of business combination, accounting methods for business combinations and goodwill recognition. The result is to assess the impact of the identified differences in the reported financial position and profit or loss of company.

  16. Thz Spectroscopy and DFT Modeling of Intermolecular Vibrations in Hydrophobic Amino Acids

    Science.gov (United States)

    Williams, michael R. C.; Aschaffenburg, Daniel J.; Schmuttenmaer, Charles A.

    2013-06-01

    Vibrations that involve intermolecular displacements occur in molecular crystals at frequencies in the 0.5-5 THz range (˜15-165 cm^{-1}), and these motions are direct indicators of the interaction potential between the molecules. The intermolecular potential energy surface of crystalline hydrophobic amino acids is inherently interesting simply because of the wide variety of forces (electrostatic, dipole-dipole, hydrogen-bonding, van der Waals) that are present. Furthermore, an understanding of these particular interactions is immediately relevant to important topics like protein conformation and pharmaceutical polymorphism. We measured the low-frequency absorption spectra of several polycrystalline hydrophobic amino acids using THz time-domain spectroscopy, and in addition we carried out DFT calculations using periodic boundary conditions and an exchange-correlation functional that accounts for van der Waals dispersion forces. We chose to investigate a series of similar amino acids with closely analogous unit cells (leucine, isoleucine, and allo-isoleucine, in racemic or pseudo-racemic mixtures). This allows us to consider trends in the vibrational spectra as a function of small changes in molecular arrangement and/or crystal geometry. In this way, we gain confidence that peak assignments are not based on serendipitous similarities between calculated and observed features.

  17. Van der Waals epitaxial growth and optoelectronics of large-scale WSe2/SnS2 vertical bilayer p-n junctions.

    Science.gov (United States)

    Yang, Tiefeng; Zheng, Biyuan; Wang, Zhen; Xu, Tao; Pan, Chen; Zou, Juan; Zhang, Xuehong; Qi, Zhaoyang; Liu, Hongjun; Feng, Yexin; Hu, Weida; Miao, Feng; Sun, Litao; Duan, Xiangfeng; Pan, Anlian

    2017-12-04

    High-quality two-dimensional atomic layered p-n heterostructures are essential for high-performance integrated optoelectronics. The studies to date have been largely limited to exfoliated and restacked flakes, and the controlled growth of such heterostructures remains a significant challenge. Here we report the direct van der Waals epitaxial growth of large-scale WSe 2 /SnS 2 vertical bilayer p-n junctions on SiO 2 /Si substrates, with the lateral sizes reaching up to millimeter scale. Multi-electrode field-effect transistors have been integrated on a single heterostructure bilayer. Electrical transport measurements indicate that the field-effect transistors of the junction show an ultra-low off-state leakage current of 10 -14 A and a highest on-off ratio of up to 10 7 . Optoelectronic characterizations show prominent photoresponse, with a fast response time of 500 μs, faster than all the directly grown vertical 2D heterostructures. The direct growth of high-quality van der Waals junctions marks an important step toward high-performance integrated optoelectronic devices and systems.

  18. Many-body study of van der Waals interaction involving lithium and rare-gas atoms and its contribution to hyperfine shifts

    International Nuclear Information System (INIS)

    Rao, B.K.; Das, T.P.

    1982-01-01

    Using linked cluster many-body perturbation theory, the frequency-dependent dipole polarizabilities a(ω) has been calculated for the lithium atom. The value of a(ω) at the static limit (169.04 a 0 3 ) matches well with other available theoretical values and experimental results. These values have been used to calculate the van der Waals constants for interactions of lithium, helium and neon atoms. The values of the van der Waals constants for dipole-dipole interaction in atomic units are -22.9, -44.8, -1465.8, 184950.0, 2011.8, 3896.5, 30.3, 59.0 and 115.1 for Li-He, Li-Ne, Li-Li, Li-Li-Li, Li-Li-He, Li-Li-Ne, Li-He-He, Li-He-Ne and Li-Ne-Ne interactions respectively. Obtaining the suitable response functions for lithium and helium atoms, the long range contribution to Δa(r)/a 0 in the study of fractional frequency shift in hyperfine pressure and temperature shift measurements is obtained as -541 atomic units. (author)

  19. Reactivity of phosphorene with a 3d element trioxide (CrO3) considering van der Waals molecular interactions: a DFT-D2 study.

    Science.gov (United States)

    Rubio-Pereda, Pamela; Cocoletzi, Gregorio H

    2017-02-01

    First-principle calculations are performed to investigate the interaction between clean black phosphorene and the CrO 3 molecule which is known to be a powerful oxidizer and a suspected carcinogen. Van der Waals forces are included in all calculations through empirical corrections. Energetics studies are first done to determine the structural stability. Then charge density, Löwdin population analysis and electronic states are evaluated. Results show that the CrO 3 molecule, with an acceptor electron character, is chemisorbed on the phosphorene surface inducing minimal geometrical distortions, however, after adsorption, a partial charge gradient is produced between the P atoms located at the phosphorene upper and lower planes. Furthermore, variations on the CrO 3 concentration causes different interaction strengths. At high concentrations of adsorbed CrO 3 molecules, the interaction with the surface becomes stronger due to an increased steric effect between neighboring molecules. Nevertheless, this effect along with the geometrical distortions produced on the phosphorene structure, due to the large number of molecules adsorbed, leads to a decrement on the adsorption energy. It is expected that the reported results may render phosphorene as a promising material for application as a gas sensor.

  20. Interview Vincent de Waal over zijn proefschrift: De vooruitgeschoven middenvelder. De innovatiekracht van middenmanagers van welzijnsorganisaties met het oog op actief burgerschap

    NARCIS (Netherlands)

    Vincent de Waal; Eveline Bolt

    2015-01-01

    Vincent de Waal (1951) promoveerde in 2014 aan de Universiteit voor Humanistiek. Hij is werkzaam als docent- onderzoeker bij Hogeschool Utrecht (HU), Instituut Social Work. Sinds 2002 is hij onderzoeker binnen het Kenniscentrum Sociale Innovatie van de HU en vanaf 2012 betrokken bij de

  1. A cutting force model for micromilling applications

    DEFF Research Database (Denmark)

    Bissacco, Giuliano; Hansen, Hans Nørgaard; De Chiffre, Leonardo

    2006-01-01

    In micro milling the maximum uncut chip thickness is often smaller than the cutting edge radius. This paper introduces a new cutting force model for ball nose micro milling that is capable of taking into account the effect of the edge radius.......In micro milling the maximum uncut chip thickness is often smaller than the cutting edge radius. This paper introduces a new cutting force model for ball nose micro milling that is capable of taking into account the effect of the edge radius....

  2. Use of Two-Body Correlated Basis Functions with van der Waals Interaction to Study the Shape-Independent Approximation for a Large Number of Trapped Interacting Bosons

    Science.gov (United States)

    Lekala, M. L.; Chakrabarti, B.; Das, T. K.; Rampho, G. J.; Sofianos, S. A.; Adam, R. M.; Haldar, S. K.

    2017-05-01

    We study the ground-state and the low-lying excitations of a trapped Bose gas in an isotropic harmonic potential for very small (˜ 3) to very large (˜ 10^7) particle numbers. We use the two-body correlated basis functions and the shape-dependent van der Waals interaction in our many-body calculations. We present an exhaustive study of the effect of inter-atomic correlations and the accuracy of the mean-field equations considering a wide range of particle numbers. We calculate the ground-state energy and the one-body density for different values of the van der Waals parameter C6. We compare our results with those of the modified Gross-Pitaevskii results, the correlated Hartree hypernetted-chain equations (which also utilize the two-body correlated basis functions), as well as of the diffusion Monte Carlo for hard sphere interactions. We observe the effect of the attractive tail of the van der Waals potential in the calculations of the one-body density over the truly repulsive zero-range potential as used in the Gross-Pitaevskii equation and discuss the finite-size effects. We also present the low-lying collective excitations which are well described by a hydrodynamic model in the large particle limit.

  3. 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.

  4. Surface force measurements and simulations of mussel-derived peptide adhesives on wet organic surfaces.

    Science.gov (United States)

    Levine, Zachary A; Rapp, Michael V; Wei, Wei; Mullen, Ryan Gotchy; Wu, Chun; Zerze, Gül H; Mittal, Jeetain; Waite, J Herbert; Israelachvili, Jacob N; Shea, Joan-Emma

    2016-04-19

    Translating sticky biological molecules-such as mussel foot proteins (MFPs)-into synthetic, cost-effective underwater adhesives with adjustable nano- and macroscale characteristics requires an intimate understanding of the glue's molecular interactions. To help facilitate the next generation of aqueous adhesives, we performed a combination of surface forces apparatus (SFA) measurements and replica-exchange molecular dynamics (REMD) simulations on a synthetic, easy to prepare, Dopa-containing peptide (MFP-3s peptide), which adheres to organic surfaces just as effectively as its wild-type protein analog. Experiments and simulations both show significant differences in peptide adsorption on CH3-terminated (hydrophobic) and OH-terminated (hydrophilic) self-assembled monolayers (SAMs), where adsorption is strongest on hydrophobic SAMs because of orientationally specific interactions with Dopa. Additional umbrella-sampling simulations yield free-energy profiles that quantitatively agree with SFA measurements and are used to extract the adhesive properties of individual amino acids within the context of MFP-3s peptide adhesion, revealing a delicate balance between van der Waals, hydrophobic, and electrostatic forces.

  5. The mechanisms underlying the enhanced resolution of atomic force microscopy with functionalized tips

    International Nuclear Information System (INIS)

    Moll, Nikolaj; Gross, Leo; Mohn, Fabian; Curioni, Alessandro; Meyer, Gerhard

    2010-01-01

    By functionalizing the tip of an atomic force microscope (AFM) with a molecule or an atom that significantly contributes to the tip-sample interaction, the resolution can be dramatically enhanced. The interaction and therefore the resolution crucially depend on the chemical nature of the tip termination. Employing a tip functionalized with a CO molecule, atomic resolution of a pentacene molecule was recently demonstrated. In this work, the interaction between the CO tip and the pentacene imaged are studied with first principles calculations. The calculated frequency shifts compare very well with the experiment. The different energy contributions are analyzed and the Pauli energy is computed. We demonstrate that the source of the high resolution is Pauli repulsion, whereas van der Waals and electrostatic interactions only add a diffuse attractive background.

  6. Reliable and Accurate Release of Micro-Sized Objects with a Gripper that Uses the Capillary-Force Method

    Directory of Open Access Journals (Sweden)

    Suzana Uran

    2017-06-01

    Full Text Available There have been recent developments in grippers that are based on capillary force and condensed water droplets. These are used for manipulating micro-sized objects. Recently, one-finger grippers have been produced that are able to reliably grip using the capillary force. To release objects, either the van der Waals, gravitational or inertial-forces method is used. This article presents methods for reliably gripping and releasing micro-objects using the capillary force. The moisture from the surrounding air is condensed into a thin layer of water on the contact surfaces of the objects. From the thin layer of water, a water meniscus between the micro-sized object, the gripper and the releasing surface is created. Consequently, the water meniscus between the object and the releasing surface produces a high enough capillary force to release the micro-sized object from the tip of the one-finger gripper. In this case, either polystyrene, glass beads with diameters between 5–60 µm, or irregularly shaped dust particles of similar sizes were used. 3D structures made up of micro-sized objects could be constructed using this method. This method is reliable for releasing during assembly and also for gripping, when the objects are removed from the top of the 3D structure—the so-called “disassembling gripping” process. The accuracy of the release was lower than 0.5 µm.

  7. A van der Waals DFT study of PtH_2 systems absorbed on pristine and defective graphene

    International Nuclear Information System (INIS)

    López-Corral, Ignacio; Piriz, Sebastián; Faccio, Ricardo; Juan, Alfredo; Avena, Marcelo

    2016-01-01

    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_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_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_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.

  8. Consistent force fields for saccharides

    DEFF Research Database (Denmark)

    Rasmussen, Kjeld

    1999-01-01

    Consistent force fields for carbohydrates were hitherto developed by extensive optimization ofpotential energy function parameters on experimental data and on ab initio results. A wide range of experimental data is used: internal structures obtained from gas phase electron diffraction and from x......-anomeric effects are accounted for without addition of specific terms. The work is done in the framework of the Consistent Force Field which originatedin Israel and was further developed in Denmark. The actual methods and strategies employed havebeen described previously. Extensive testing of the force field...

  9. Selfinteraction force in a theory of gravitation with higher derivatives

    International Nuclear Information System (INIS)

    Jankiewicz, C.

    1981-01-01

    Approximate equations of motion are derived from gravitational field equations with higher derivatives. The approximation takes into account the selfinteraction force. The selfinteraction force coincides with the analogous force resulting from the Einstein field equations. (author)

  10. Tip-Enhanced Nano-Spectroscopy, Imaging, and Control: From Single Molecules to van der Waals Materials

    Science.gov (United States)

    Park, Kyoung-Duck

    near-field probe. We reveal nanoscale correlations between surface biomolecules and intracellular organelle structures through near-field imaging of the spatial distribution of EGFRs on the membrane of A431 cancer cells. In addition, to understand modified spontaneous emission properties of single quantum dots coupled strongly with localized plasmon, we perform tip-enhanced photoluminescence (TEPL) spectroscopy of the single CdSe/ZnS quantum dots on gold film. We probe and control nanoscale processes in van der Waals two-dimensional (2D) materials. To understand lattice and electronic structure as well as elastic and phonon scattering properties of grain boundaries (GBs) in large-area graphene, we perform TERS imaging. Through correlated analysis of multispectral TERS images with corresponding topography and near-field scattering image, we reveal bilayer structure of GBs in the form of twisted stacking. In addition, we determine the misorientation angles of the bilayer GBs from a detailed quantitative investigation of the Raman modes. In addition, we present a new hybrid nano-optomechanical tip-enhanced spectroscopy and imaging approach combining TERS, TEPL, and atomic force local strain manipulation to probe the heterogeneous PL responses at nanoscale defects and control the local bandgap in transition metal dichalcogenide (TMD) monolayer. We further extend this approach to probe and control the radiative emission of dark excitons and localized excitons. Based on nano-tip enhanced spectroscopy with 600,000-fold PL enhancement induced by the plasmonic Purcell effect and few-fs radiative dynamics of the optical antenna tip, we can directly probe and actively modulate the dark exciton and localized exciton emissions in time ( ms) and space (<15 nm) at room temperature. Lastly, to extend the range of tip-enhanced microscopy applications to nano-crystallography and nonlinear optics, we present a generalizable approach controlling the excitation polarizability for both in

  11. Electric field modulation of Schottky barrier height in graphene/MoSe2 van der Waals heterointerface

    OpenAIRE

    Sata, Yohta; Moriya, Rai; Morikawa, Sei; Yabuki, Naoto; Masubuchi, Satoru; Machida, Tomoki

    2015-01-01

    We demonstrate a vertical field-effect transistor based on a graphene/MoSe2 van der Waals (vdW) heterostructure. The vdW interface between the graphene and MoSe2 exhibits a Schottky barrier with an ideality factor of around 1.3, suggesting a high-quality interface. Owing to the low density of states in graphene, the position of the Fermi level in the graphene can be strongly modulated by an external electric field. Therefore, the Schottky barrier height at the graphene/MoSe2 vdW interface is ...

  12. Quantum Monte Carlo calculations of van der Waals interactions between aromatic benzene rings

    Science.gov (United States)

    Azadi, Sam; Kühne, T. D.

    2018-05-01

    The magnitude of finite-size effects and Coulomb interactions in quantum Monte Carlo simulations of van der Waals interactions between weakly bonded benzene molecules are investigated. To that extent, two trial wave functions of the Slater-Jastrow and Backflow-Slater-Jastrow types are employed to calculate the energy-volume equation of state. We assess the impact of the backflow coordinate transformation on the nonlocal correlation energy. We found that the effect of finite-size errors in quantum Monte Carlo calculations on energy differences is particularly large and may even be more important than the employed trial wave function. In addition to the cohesive energy, the singlet excitonic energy gap and the energy gap renormalization of crystalline benzene at different densities are computed.

  13. The Effects of Noncellulosic Compounds on the Nanoscale Interaction Forces Measured between Carbohydrate-Binding Module and Lignocellulosic Biomass.

    Science.gov (United States)

    Arslan, Baran; Colpan, Mert; Ju, Xiaohui; Zhang, Xiao; Kostyukova, Alla; Abu-Lail, Nehal I

    2016-05-09

    The lack of fundamental understanding of the types of forces that govern how cellulose-degrading enzymes interact with cellulosic and noncellulosic components of lignocellulosic surfaces limits the design of new strategies for efficient conversion of biomass to bioethanol. In a step to improve our fundamental understanding of such interactions, nanoscale forces acting between a model cellulase-a carbohydrate-binding module (CBM) of cellobiohydrolase I (CBH I)-and a set of lignocellulosic substrates with controlled composition were measured using atomic force microscopy (AFM). The three model substrates investigated were kraft (KP), sulfite (SP), and organosolv (OPP) pulped substrates. These substrates varied in their surface lignin coverage, lignin type, and xylan and acetone extractives' content. Our results indicated that the overall adhesion forces of biomass to CBM increased linearly with surface lignin coverage with kraft lignin showing the highest forces among lignin types investigated. When the overall adhesion forces were decoupled into specific and nonspecific component forces via the Poisson statistical model, hydrophobic and Lifshitz-van der Waals (LW) forces dominated the binding forces of CBM to kraft lignin, whereas permanent dipole-dipole interactions and electrostatic forces facilitated the interactions of lignosulfonates to CBM. Xylan and acetone extractives' content increased the attractive forces between CBM and lignin-free substrates, most likely through hydrogen bonding forces. When the substrates treated differently were compared, it was found that both the differences in specific and nonspecific forces between lignin-containing and lignin-free substrates were the least for OPP. Therefore, cellulase enzymes represented by CBM would weakly bind to organosolv lignin. This will facilitate an easy enzyme recovery compared to other substrates treated with kraft or sulfite pulping. Our results also suggest that altering the surface hydrophobicity

  14. Thermodynamics of hydrogen bonding and van der Waals interactions of organic solutes in solutions of imidazolium based ionic liquids: “Structure-property” relationships

    International Nuclear Information System (INIS)

    Varfolomeev, Mikhail A.; Khachatrian, Artashes A.; Akhmadeev, Bulat S.; Solomonov, Boris N.

    2016-01-01

    Highlights: • Solution enthalpies of organic solutes in imidazolium based ionic liquids were measured. • van der Waals interactions scale of imidazolium based ionic liquids was proposed. • Enthalpies of solvation of organic solutes in ionic liquids were determined. • Hydrogen bond enthalpies of organic solutes with ionic liquids were calculated. • Relationships between structure of ionic liquids and thermochemical data were obtained. - Abstract: In the present work thermochemistry of intermolecular interactions of organic compounds in solutions of imidazolium based ionic liquids (ILs) has been studied using solution calorimetry method. Enthalpies of solution at infinite dilution of non-polar (alkanes, aromatic hydrocarbons) and polar (alcohols, amides, and etc.) organic solutes in two ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium trifluoromethanesulfonate were measured at 298.15 K. The scale of van der Waals interactions of imidazolium based ILs has been proposed on the basis of solution enthalpies of n-alkanes in their media. The effect of the cation and anion structure of ILs on the enthalpies of solvation was analyzed. Enthalpies of hydrogen bonding of organic solutes with imidazolium based ILs were determined. It has been shown that these values are close to zero for proton acceptor solutes. At the same time, enthalpies of hydrogen bonding of proton donor solutes with ionic liquids are increased depending the anion: tetrafluoroborate ≈ bis(trifluoromethylsulfonyl)imide < 2-(2-methoxyethoxy)ethyl sulfate < trifluoromethanesulfonate. Enthalpies of van der Waals interactions and hydrogen bonding in the solutions of imidazolium based ionic liquids were compared with the same data for molecular solvents.

  15. Thermodynamics of hydrogen bonding and van der Waals interactions of organic solutes in solutions of imidazolium based ionic liquids: “Structure-property” relationships

    Energy Technology Data Exchange (ETDEWEB)

    Varfolomeev, Mikhail A., E-mail: vma.ksu@gmail.com; Khachatrian, Artashes A.; Akhmadeev, Bulat S.; Solomonov, Boris N.

    2016-06-10

    Highlights: • Solution enthalpies of organic solutes in imidazolium based ionic liquids were measured. • van der Waals interactions scale of imidazolium based ionic liquids was proposed. • Enthalpies of solvation of organic solutes in ionic liquids were determined. • Hydrogen bond enthalpies of organic solutes with ionic liquids were calculated. • Relationships between structure of ionic liquids and thermochemical data were obtained. - Abstract: In the present work thermochemistry of intermolecular interactions of organic compounds in solutions of imidazolium based ionic liquids (ILs) has been studied using solution calorimetry method. Enthalpies of solution at infinite dilution of non-polar (alkanes, aromatic hydrocarbons) and polar (alcohols, amides, and etc.) organic solutes in two ionic liquids 1-butyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium trifluoromethanesulfonate were measured at 298.15 K. The scale of van der Waals interactions of imidazolium based ILs has been proposed on the basis of solution enthalpies of n-alkanes in their media. The effect of the cation and anion structure of ILs on the enthalpies of solvation was analyzed. Enthalpies of hydrogen bonding of organic solutes with imidazolium based ILs were determined. It has been shown that these values are close to zero for proton acceptor solutes. At the same time, enthalpies of hydrogen bonding of proton donor solutes with ionic liquids are increased depending the anion: tetrafluoroborate ≈ bis(trifluoromethylsulfonyl)imide < 2-(2-methoxyethoxy)ethyl sulfate < trifluoromethanesulfonate. Enthalpies of van der Waals interactions and hydrogen bonding in the solutions of imidazolium based ionic liquids were compared with the same data for molecular solvents.

  16. Vertical dielectric screening of few-layer van der Waals semiconductors.

    Science.gov (United States)

    Koo, Jahyun; Gao, Shiyuan; Lee, Hoonkyung; Yang, Li

    2017-10-05

    Vertical dielectric screening is a fundamental parameter of few-layer van der Waals two-dimensional (2D) semiconductors. However, unlike the widely-accepted wisdom claiming that the vertical dielectric screening is sensitive to the thickness, our first-principles calculation based on the linear response theory (within the weak field limit) reveals that this screening is independent of the thickness and, in fact, it is the same as the corresponding bulk value. This conclusion is verified in a wide range of 2D paraelectric semiconductors, covering narrow-gap ones and wide-gap ones with different crystal symmetries, providing an efficient and reliable way to calculate and predict static dielectric screening of reduced-dimensional materials. Employing this conclusion, we satisfactorily explain the tunable band gap in gated 2D semiconductors. We further propose to engineer the vertical dielectric screening by changing the interlayer distance via vertical pressure or hybrid structures. Our predicted vertical dielectric screening can substantially simplify the understanding of a wide range of measurements and it is crucial for designing 2D functional devices.

  17. Accountability to whom? For what? Teacher identity and the Force ...

    African Journals Online (AJOL)

    These have become increasingly layered into expanding roles and responsibilities being foisted on teachers. The article argues that this could threaten teaching as a career and fewer individuals now willingly choose the teaching profession. If they do, their accountability is seldom to quality teaching and learning as ...

  18. 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

    A refined CCSD(T) intermolecular potential energy surface is developed for the He-C2H2 van der Waals complex. For this, 206 points on the intermolecular potential energy surface, evaluated using the CCSD(T) method and the aug-cc-pVQZ basis set extended with a set of 3s3p2d1f1g midbond functions...

  19. Untitled

    African Journals Online (AJOL)

    corresponds to a physical model for intermole- cular forces involving valence and non-valence binding. ... realistic physical picture of van der Waals electrostatic interaction between the two .... Hydrogen bond energy and equilibrium bond length of some van der Waals systems. (kcal/mol). Multipolar Molecule H.Dipole H..

  20. Production Methods of Van der Waals Heterostructures Based on Transition Metal Dichalcogenides

    Directory of Open Access Journals (Sweden)

    Haimei Qi

    2018-01-01

    Full Text Available Two dimensional (2D materials have gained significant attention since the discovery of graphene in 2004. Layered transition metal dichalcogenides (TMDs have become the focus of 2D materials in recent years due to their wide range of chemical compositions and a variety of properties. These TMDs layers can be artificially integrated with other layered materials into a monolayer (lateral or a multilayer stack (vertical heterostructures. The resulting heterostructures provide new properties and applications beyond their component 2D atomic crystals and many exciting experimental results have been reported during the past few years. In this review, we present the various synthesis methods (mechanical exfoliation, physical vapor transport, chemical vapor deposition, and molecular beam epitaxy method on van der Waals heterostructures based on different TMDs as well as an outlook for future research.

  1. Documentation of Accounting Records in Light of Legislative Innovations

    OpenAIRE

    K. V. BEZVERKHIY

    2017-01-01

    Legislative reforms in accounting aim to simplify accounting records and compilation of financial reports by business entities, thus increasing the position of Ukraine in the global ranking of Doing Business. This simplification is implied in the changes in the Regulation on Documentation of Accounting Records, entered into force to the Resolution of the Ukrainian Ministry of Finance. The objective of the study is to analyze the legislative innovations involved. The review of changes in docum...

  2. A Survey on Forced Oscillations in Power System

    OpenAIRE

    Ghorbaniparvar, Mohammadreza

    2016-01-01

    Oscillations in a power system can be categorized into free oscillations and forced oscillations. Many algorithms have been developed to estimate the modes of free oscillations in a power system. Recently, forced oscillations caught many attentions. Techniques are proposed to detect forced oscillations and locate their sources. In addition, forced oscillations may have negative impact on the estimation of mode and mode-shape if they are not properly accounted for. To improve the power system ...

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

    International Nuclear Information System (INIS)

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

    2015-01-01

    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 Ag 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 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

  4. Adsorption and manipulation of carbon onions on highly oriented pyrolytic graphite studied with atomic force microscopy

    International Nuclear Information System (INIS)

    Zhou Jianfeng; Shen Ziyong; Hou Shimin; Zhao Xingyu; Xue Zengquan; Shi Zujin; Gu Zhennan

    2007-01-01

    Carbon onions produced by DC arc discharge method were deposited on highly oriented pyrolytic graphite (HOPG) surface and their adsorption and manipulation was studied using an atomic force microscopy (AFM). Well-dispersed adsorption of carbon onions on HOPG surface was obtained and aggregations of onions were not observed. The van der Waals interaction between the onion and HOPG surface and that between two onions, were calculated and discussed using Hamaker's theory. The manipulation of adsorbed onions on HOPG surface was realized using the AFM in both the raster mode and the vector mode. The controllability and precision of two manipulation modes were compared and the vector mode manipulation was found superior, and is a useful technique for the construction of nano-scale devices based on carbon onions

  5. A comparison of hydrogen-bonded and van der Waals isomers of phenolṡṡnitrogen and phenolṡṡcarbon monoxide: An ab initio study

    Science.gov (United States)

    Chapman, Darren M.; Müller-Dethlefs, Klaus; Peel, J. Barrie

    1999-08-01

    The hydrogen-bonded and van der Waals isomers of phenolṡṡnitrogen and phenolṡṡcarbon monoxide in their neutral electronic (S0) and cation ground state (D0) were studied using ab initio HF/6-31G*, MP2/6-31G*, and B3LYP/6-31G* methods. The hydrogen-bonded isomers have the ligand bound via the hydroxyl group of the phenol ring, while the van der Waals isomers studied have the ligand located above the aromatic ring. For both complexes, the hydrogen-bonded isomer was found to be the most stable form for both the S0 and the D0 states. For phenolṡṡcarbon monoxide, twice as many isomers as compared to phenolṡṡnitrogen were found. The hydrogen-bonded isomer with the carbon end bonded to the hydroxyl group was the most stable structure for both the S0 and the D0 states.

  6. THE MANAGEMENT ACCOUNTING IN ROMANIA – PAST, PRESENT AND FUTURE

    Directory of Open Access Journals (Sweden)

    Violeta Isai

    2015-05-01

    Full Text Available When managing a company it is important to answer the following question: is it true that the traditional accounting systems are completely inefficient, being just a theoretical chapter in the history of accounting and at the same time, they gave way to the modern accounting systems, the latter being meant to satisfy the present requirements accordingly? All the accounting systems, both traditional and modern have their own roles in accounting. But this fact places the management accounting between the modern and the traditional, entities being forced to choose what is best for them.

  7. Some new exact solitary wave solutions of the van der Waals model arising in nature

    Science.gov (United States)

    Bibi, Sadaf; Ahmed, Naveed; Khan, Umar; Mohyud-Din, Syed Tauseef

    2018-06-01

    This work proposes two well-known methods, namely, Exponential rational function method (ERFM) and Generalized Kudryashov method (GKM) to seek new exact solutions of the van der Waals normal form for the fluidized granular matter, linked with natural phenomena and industrial applications. New soliton solutions such as kink, periodic and solitary wave solutions are established coupled with 2D and 3D graphical patterns for clarity of physical features. Our comparison reveals that the said methods excel several existing methods. The worked-out solutions show that the suggested methods are simple and reliable as compared to many other approaches which tackle nonlinear equations stemming from applied sciences.

  8. Application of the van der Waals equation of state to polymers .4. Correlation and prediction of lower critical solution temperatures for polymer solutions

    DEFF Research Database (Denmark)

    Goncalves, Ana Saraiva; Kontogeorgis, Georgios; Harismiadis, Vassilis I.

    1996-01-01

    The van der Waals equation of state is used for the correlation and the prediction of the lower critical solution behavior or mixtures including a solvent and a polymer. The equation of state parameters for the polymer are estimated from experimental volumetric data at low pressures. The equation...

  9. 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

  10. Stiction in surface micromachining

    NARCIS (Netherlands)

    Tas, Niels Roelof; Sonnenberg, A.H.; Jansen, Henricus V.; Legtenberg, R.; Legtenberg, Rob; Elwenspoek, Michael Curt

    1996-01-01

    Due to the smoothness of the surfaces in surface micromachining, large adhesion forces between fabricated structures and the substrate are encountered. Four major adhesion mechanisms have been analysed: capillary forces, hydrogen bridging, electrostatic forces and van der Waals forces. Once contact

  11. La edad de la empatía. Lecciones de la naturaleza para una sociedad más justa y solidaria, por Fran de Waal

    Directory of Open Access Journals (Sweden)

    Cecilia Milito Barone

    2015-07-01

    Full Text Available Rsseña del libro Fran de Waal, La edad de la empatía. Lecciones de la naturaleza para una sociedad más justa y solidaria (Barcelona: Tusquets Editores, 2011, 258 pp. ISBN: 978-84-8383-350-6

  12. 1-D Van der Waals Foams Heated by Ion Beam Energy Deposition

    International Nuclear Information System (INIS)

    Zylstra, A.B.; Barnard, J.J.; More, R.M.

    2009-01-01

    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.

  13. System analysis of force feedback microscopy

    International Nuclear Information System (INIS)

    Rodrigues, Mario S.; Costa, Luca; Chevrier, Joël; Comin, Fabio

    2014-01-01

    It was shown recently that the Force Feedback Microscope (FFM) can avoid the jump-to-contact in Atomic force Microscopy even when the cantilevers used are very soft, thus increasing force resolution. In this letter, we explore theoretical aspects of the associated real time control of the tip position. We take into account lever parameters such as the lever characteristics in its environment, spring constant, mass, dissipation coefficient, and the operating conditions such as controller gains and interaction force. We show how the controller parameters are determined so that the FFM functions at its best and estimate the bandwidth of the system under these conditions

  14. System analysis of force feedback microscopy

    Energy Technology Data Exchange (ETDEWEB)

    Rodrigues, Mario S. [CFMC/Dep. de Física, Universidade de Lisboa, Campo Grande, 1749-016 Lisboa (Portugal); Costa, Luca [European Synchrotron Radiation Facility, 6 rue Jules Horowitz BP 220, 38043 Grenoble Cedex (France); Université Joseph Fourier BP 53, 38041 Grenoble Cedex 9 (France); Chevrier, Joël [European Synchrotron Radiation Facility, 6 rue Jules Horowitz BP 220, 38043 Grenoble Cedex (France); Université Grenoble Alpes, Inst NEEL, F-38042 Grenoble (France); CNRS, Inst NEEL, F-38042 Grenoble (France); Comin, Fabio [European Synchrotron Radiation Facility, 6 rue Jules Horowitz BP 220, 38043 Grenoble Cedex (France)

    2014-02-07

    It was shown recently that the Force Feedback Microscope (FFM) can avoid the jump-to-contact in Atomic force Microscopy even when the cantilevers used are very soft, thus increasing force resolution. In this letter, we explore theoretical aspects of the associated real time control of the tip position. We take into account lever parameters such as the lever characteristics in its environment, spring constant, mass, dissipation coefficient, and the operating conditions such as controller gains and interaction force. We show how the controller parameters are determined so that the FFM functions at its best and estimate the bandwidth of the system under these conditions.

  15. Projected Costs of U.S. Nuclear Forces, 2017 to 2026

    Science.gov (United States)

    2017-02-01

    amounts at roughly the same rates that costs for similar programs have grown in the past. Nuclear forces account for roughly 6 percent of the total 10...nuclear forces, some published estimates of the total costs of nuclear weapons account for the costs of several related activities. Examples include...based its estimate on historical costs of analogous programs. b. This category includes nuclear-related research and operations support activities by

  16. Van der Waals heterostructure of phosphorene and graphene: tuning the Schottky barrier and doping by electrostatic gating.

    Science.gov (United States)

    Padilha, J E; Fazzio, A; da Silva, Antônio J R

    2015-02-13

    In this Letter, we study the structural and electronic properties of single-layer and bilayer phosphorene with graphene. We show that both the properties of graphene and phosphorene are preserved in the composed heterostructure. We also show that via the application of a perpendicular electric field, it is possible to tune the position of the band structure of phosphorene with respect to that of graphene. This leads to control of the Schottky barrier height and doping of phosphorene, which are important features in the design of new devices based on van der Waals heterostructures.

  17. ENVIRONMENTAL FINANCIAL ACCOUNTING

    Directory of Open Access Journals (Sweden)

    Oana MIHAI

    2006-01-01

    Full Text Available From a company’s perspective, there seem to be two underlying forces driving company interest in various kinds of environmental performance data that might be considered varieties of accounting. The first is a growing demand from company stakeholders, based on an increased interest in environmental issues. Interested stakeholders are not only the consumers, but also industrial customers, financialinstitutions and others. For this reason, more and more companies are producing environmental reports, but these are often low on data content, which adversely affects company credibility on environmental issues.

  18. Manipulating bubbles with secondary Bjerknes forces

    Energy Technology Data Exchange (ETDEWEB)

    Lanoy, Maxime [Institut Langevin, ESPCI ParisTech, CNRS (UMR 7587), PSL Research University, 1 rue Jussieu, 75005 Paris (France); Laboratoire Matière et Systèmes Complexes, Université Paris-Diderot, CNRS (UMR 7057), 10 rue Alice Domon et Léonie Duquet, 75013 Paris (France); Derec, Caroline; Leroy, Valentin [Laboratoire Matière et Systèmes Complexes, Université Paris-Diderot, CNRS (UMR 7057), 10 rue Alice Domon et Léonie Duquet, 75013 Paris (France); Tourin, Arnaud [Institut Langevin, ESPCI ParisTech, CNRS (UMR 7587), PSL Research University, 1 rue Jussieu, 75005 Paris (France)

    2015-11-23

    Gas bubbles in a sound field are submitted to a radiative force, known as the secondary Bjerknes force. We propose an original experimental setup that allows us to investigate in detail this force between two bubbles, as a function of the sonication frequency, as well as the bubbles radii and distance. We report the observation of both attractive and, more interestingly, repulsive Bjerknes force, when the two bubbles are driven in antiphase. Our experiments show the importance of taking multiple scatterings into account, which leads to a strong acoustic coupling of the bubbles when their radii are similar. Our setup demonstrates the accuracy of secondary Bjerknes forces for attracting or repealing a bubble, and could lead to new acoustic tools for noncontact manipulation in microfluidic devices.

  19. Manipulating bubbles with secondary Bjerknes forces

    International Nuclear Information System (INIS)

    Lanoy, Maxime; Derec, Caroline; Leroy, Valentin; Tourin, Arnaud

    2015-01-01

    Gas bubbles in a sound field are submitted to a radiative force, known as the secondary Bjerknes force. We propose an original experimental setup that allows us to investigate in detail this force between two bubbles, as a function of the sonication frequency, as well as the bubbles radii and distance. We report the observation of both attractive and, more interestingly, repulsive Bjerknes force, when the two bubbles are driven in antiphase. Our experiments show the importance of taking multiple scatterings into account, which leads to a strong acoustic coupling of the bubbles when their radii are similar. Our setup demonstrates the accuracy of secondary Bjerknes forces for attracting or repealing a bubble, and could lead to new acoustic tools for noncontact manipulation in microfluidic devices

  20. The self-consistent field model for Fermi systems with account of three-body interactions

    Directory of Open Access Journals (Sweden)

    Yu.M. Poluektov

    2015-12-01

    Full Text Available On the basis of a microscopic model of self-consistent field, the thermodynamics of the many-particle Fermi system at finite temperatures with account of three-body interactions is built and the quasiparticle equations of motion are obtained. It is shown that the delta-like three-body interaction gives no contribution into the self-consistent field, and the description of three-body forces requires their nonlocality to be taken into account. The spatially uniform system is considered in detail, and on the basis of the developed microscopic approach general formulas are derived for the fermion's effective mass and the system's equation of state with account of contribution from three-body forces. The effective mass and pressure are numerically calculated for the potential of "semi-transparent sphere" type at zero temperature. Expansions of the effective mass and pressure in powers of density are obtained. It is shown that, with account of only pair forces, the interaction of repulsive character reduces the quasiparticle effective mass relative to the mass of a free particle, and the attractive interaction raises the effective mass. The question of thermodynamic stability of the Fermi system is considered and the three-body repulsive interaction is shown to extend the region of stability of the system with the interparticle pair attraction. The quasiparticle energy spectrum is calculated with account of three-body forces.

  1. Modeling liquid-vapor equilibria with an equation of state taking into account dipolar interactions and association by hydrogen bonding

    International Nuclear Information System (INIS)

    Perfetti, E.

    2006-11-01

    Modelling fluid-rock interactions as well as mixing and unmixing phenomena in geological processes requires robust equations of state (EOS) which must be applicable to systems containing water, gases over a broad range of temperatures and pressures. Cubic equations of state based on the Van der Waals theory (e. g. Soave-Redlich-Kwong or Peng-Robinson) allow simple modelling from the critical parameters of the studied fluid components. However, the accuracy of such equations becomes poor when water is a major component of the fluid since neither association trough hydrogen bonding nor dipolar interactions are accounted for. The Helmholtz energy of a fluid may be written as the sum of different energetic contributions by factorization of partition function. The model developed in this thesis for the pure H 2 O and H 2 S considers three contributions. The first contribution represents the reference Van der Waals fluid which is modelled by the SRK cubic EOS. The second contribution accounts for association through hydrogen bonding and is modelled by a term derived from Cubic Plus Association (CPA) theory. The third contribution corresponds to the dipolar interactions and is modelled by the Mean Spherical Approximation (MSA) theory. The resulting CPAMSA equation has six adjustable parameters, which three represent physical terms whose values are close to their experimental counterpart. This equation results in a better reproduction of the thermodynamic properties of pure water than obtained using the classical CPA equation along the vapour-liquid equilibrium. In addition, extrapolation to higher temperatures and pressure is satisfactory. Similarly, taking into account dipolar interactions together with the SRK cubic equation of state for calculating molar volume of H 2 S as a function of pressure and temperature results in a significant improvement compared to the SRK equation alone. Simple mixing rules between dipolar molecules are proposed to model the H 2 O-H 2 S

  2. A van der Waals pn heterojunction with organic/inorganic semiconductors

    International Nuclear Information System (INIS)

    He, Daowei; Yang, Ziyi; Wu, Bing; Xu, Bingchen; Zhang, Yuhan; Li, Yun; Shi, Yi; Wang, Xinran; Pan, Yiming; Wang, Baigeng; Nan, Haiyan; Luo, Xiaoguang; Ni, Zhenhua; Gu, Shuai; Zhu, Jia; Chai, Yang

    2015-01-01

    van der Waals (vdW) heterojunctions formed by two-dimensional (2D) materials have attracted tremendous attention due to their excellent electrical/optical properties and device applications. However, current 2D heterojunctions are largely limited to atomic crystals, and hybrid organic/inorganic structures are rarely explored. Here, we fabricate the hybrid 2D heterostructures with p-type dioctylbenzothienobenzothiophene (C 8 -BTBT) and n-type MoS 2 . We find that few-layer C 8 -BTBT molecular crystals can be grown on monolayer MoS 2 by vdW epitaxy, with pristine interface and controllable thickness down to monolayer. The operation of the C 8 -BTBT/MoS 2 vertical heterojunction devices is highly tunable by bias and gate voltages between three different regimes: interfacial recombination, tunneling, and blocking. The pn junction shows diode-like behavior with rectifying ratio up to 10 5 at the room temperature. Our devices also exhibit photovoltaic responses with a power conversion efficiency of 0.31% and a photoresponsivity of 22 mA/W. With wide material combinations, such hybrid 2D structures will offer possibilities for opto-electronic devices that are not possible from individual constituents

  3. A van der Waals pn heterojunction with organic/inorganic semiconductors

    Science.gov (United States)

    He, Daowei; Pan, Yiming; Nan, Haiyan; Gu, Shuai; Yang, Ziyi; Wu, Bing; Luo, Xiaoguang; Xu, Bingchen; Zhang, Yuhan; Li, Yun; Ni, Zhenhua; Wang, Baigeng; Zhu, Jia; Chai, Yang; Shi, Yi; Wang, Xinran

    2015-11-01

    van der Waals (vdW) heterojunctions formed by two-dimensional (2D) materials have attracted tremendous attention due to their excellent electrical/optical properties and device applications. However, current 2D heterojunctions are largely limited to atomic crystals, and hybrid organic/inorganic structures are rarely explored. Here, we fabricate the hybrid 2D heterostructures with p-type dioctylbenzothienobenzothiophene (C8-BTBT) and n-type MoS2. We find that few-layer C8-BTBT molecular crystals can be grown on monolayer MoS2 by vdW epitaxy, with pristine interface and controllable thickness down to monolayer. The operation of the C8-BTBT/MoS2 vertical heterojunction devices is highly tunable by bias and gate voltages between three different regimes: interfacial recombination, tunneling, and blocking. The pn junction shows diode-like behavior with rectifying ratio up to 105 at the room temperature. Our devices also exhibit photovoltaic responses with a power conversion efficiency of 0.31% and a photoresponsivity of 22 mA/W. With wide material combinations, such hybrid 2D structures will offer possibilities for opto-electronic devices that are not possible from individual constituents.

  4. A van der Waals pn heterojunction with organic/inorganic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    He, Daowei; Yang, Ziyi; Wu, Bing; Xu, Bingchen; Zhang, Yuhan; Li, Yun; Shi, Yi, E-mail: yshi@nju.edu.cn, E-mail: xrwang@nju.edu.cn; Wang, Xinran, E-mail: yshi@nju.edu.cn, E-mail: xrwang@nju.edu.cn [National Laboratory of Solid State Microstructures, School of Electronic Science and Engineering, and Collaborative Innovation Center of Advanced Microstructures, Nanjing University, Nanjing 210093 (China); Pan, Yiming; Wang, Baigeng [National Laboratory of Solid State Microstructures, School of Physics, Nanjing University, Nanjing 210093 (China); Nan, Haiyan; Luo, Xiaoguang; Ni, Zhenhua [Department of Physics, Southeast University, Nanjing 211189 (China); Gu, Shuai; Zhu, Jia [College of Engineering and Applied Science, Nanjing University, Nanjing 210093 (China); Chai, Yang [Department of Applied Physics, The Hong Kong Polytechnic University, Hung Hom, Kowloon (Hong Kong)

    2015-11-02

    van der Waals (vdW) heterojunctions formed by two-dimensional (2D) materials have attracted tremendous attention due to their excellent electrical/optical properties and device applications. However, current 2D heterojunctions are largely limited to atomic crystals, and hybrid organic/inorganic structures are rarely explored. Here, we fabricate the hybrid 2D heterostructures with p-type dioctylbenzothienobenzothiophene (C{sub 8}-BTBT) and n-type MoS{sub 2}. We find that few-layer C{sub 8}-BTBT molecular crystals can be grown on monolayer MoS{sub 2} by vdW epitaxy, with pristine interface and controllable thickness down to monolayer. The operation of the C{sub 8}-BTBT/MoS{sub 2} vertical heterojunction devices is highly tunable by bias and gate voltages between three different regimes: interfacial recombination, tunneling, and blocking. The pn junction shows diode-like behavior with rectifying ratio up to 10{sup 5} at the room temperature. Our devices also exhibit photovoltaic responses with a power conversion efficiency of 0.31% and a photoresponsivity of 22 mA/W. With wide material combinations, such hybrid 2D structures will offer possibilities for opto-electronic devices that are not possible from individual constituents.

  5. 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.

  6. The Experimental Role of Accounting in Shaping Project

    DEFF Research Database (Denmark)

    Christensen, Mark; Skærbæk, Peter; Tryggestad, Kjell

    2016-01-01

    , 2009) and the literature on accounting as programs (Miller, 1991, Miller and Power, 2013) by showing how accounting plays an experimental role in shaping the dynamics between a New Public Management programme of outsourcing and its projects. The study illuminates decisionmaking about programs...... and strategic options as a trial of strength involving accounting in an experimental role, in our case, over how to source the facilities management in the Danish Defence Forces. Our contribution is to show how accounting plays an experimental role in generating new and unexpected program options...... of economic experiments with (out-)sourcing options using various accounting data such as; location specific cost data in vivo (real life data like those from the accounting system) for individual barracks, and aggregated cost data and cost projections in vitro ( in a controlled experimental project setting...

  7. Small strain multiphase-field model accounting for configurational forces and mechanical jump conditions

    Science.gov (United States)

    Schneider, Daniel; Schoof, Ephraim; Tschukin, Oleg; Reiter, Andreas; Herrmann, Christoph; Schwab, Felix; Selzer, Michael; Nestler, Britta

    2018-03-01

    Computational models based on the phase-field method have become an essential tool in material science and physics in order to investigate materials with complex microstructures. The models typically operate on a mesoscopic length scale resolving structural changes of the material and provide valuable information about the evolution of microstructures and mechanical property relations. For many interesting and important phenomena, such as martensitic phase transformation, mechanical driving forces play an important role in the evolution of microstructures. In order to investigate such physical processes, an accurate calculation of the stresses and the strain energy in the transition region is indispensable. We recall a multiphase-field elasticity model based on the force balance and the Hadamard jump condition at the interface. We show the quantitative characteristics of the model by comparing the stresses, strains and configurational forces with theoretical predictions in two-phase cases and with results from sharp interface calculations in a multiphase case. As an application, we choose the martensitic phase transformation process in multigrain systems and demonstrate the influence of the local homogenization scheme within the transition regions on the resulting microstructures.

  8. X-ray electron density investigation of chemical bonding in van der Waals materials

    Science.gov (United States)

    Kasai, Hidetaka; Tolborg, Kasper; Sist, Mattia; Zhang, Jiawei; Hathwar, Venkatesha R.; Filsø, Mette Ø.; Cenedese, Simone; Sugimoto, Kunihisa; Overgaard, Jacob; Nishibori, Eiji; Iversen, Bo B.

    2018-03-01

    Van der Waals (vdW) solids have attracted great attention ever since the discovery of graphene, with the essential feature being the weak chemical bonding across the vdW gap. The nature of these weak interactions is decisive for many extraordinary properties, but it is a strong challenge for current theory to accurately model long-range electron correlations. Here we use synchrotron X-ray diffraction data to precisely determine the electron density in the archetypal vdW solid, TiS2, and compare the results with density functional theory calculations. Quantitative agreement is observed for the chemical bonding description in the covalent TiS2 slabs, but significant differences are identified for the interactions across the gap, with experiment revealing more electron deformation than theory. The present data provide an experimental benchmark for testing theoretical models of weak chemical bonding.

  9. Semiempirical calculation of van der Waals coefficients for alkali-metal and alkaline-earth-metal atoms

    International Nuclear Information System (INIS)

    Mitroy, J.; Bromley, M.W.J.

    2003-01-01

    The van der Waals coefficients, C 6 , C 8 , and C 10 for the alkali-metal (Li, Na, K, and Rb) and alkaline-earth-metal (Be, Mg, Ca, and Sr) atoms are estimated by a combination of ab initio and semiempirical methods. Polarizabilities and atom-wall coefficients are given as a diagnostic check, and the lowest order nonadiabatic dispersion coefficient, D 8 and the three-body coefficient, C 9 are also presented. The dispersion coefficients are in agreement with the available relativistic many-body perturbation theory calculations. The contribution from the core was included by using constrained sum rules involving the core polarizability and Hartree-Fock expectation values to estimate the f-value distribution

  10. Ultrafast Exciton Dissociation and Long-Lived Charge Separation in a Photovoltaic Pentacene-MoS2 van der Waals Heterojunction.

    Science.gov (United States)

    Bettis Homan, Stephanie; Sangwan, Vinod K; Balla, Itamar; Bergeron, Hadallia; Weiss, Emily A; Hersam, Mark C

    2017-01-11

    van der Waals heterojunctions between two-dimensional (2D) layered materials and nanomaterials of different dimensions present unique opportunities for gate-tunable optoelectronic devices. Mixed-dimensional p-n heterojunction diodes, such as p-type pentacene (0D) and n-type monolayer MoS 2 (2D), are especially interesting for photovoltaic applications where the absorption cross-section and charge transfer processes can be tailored by rational selection from the vast library of organic molecules and 2D materials. Here, we study the kinetics of excited carriers in pentacene-MoS 2 p-n type-II heterojunctions by transient absorption spectroscopy. These measurements show that the dissociation of MoS 2 excitons occurs by hole transfer to pentacene on the time scale of 6.7 ps. In addition, the charge-separated state lives for 5.1 ns, up to an order of magnitude longer than the recombination lifetimes from previously reported 2D material heterojunctions. By studying the fractional amplitudes of the MoS 2 decay processes, the hole transfer yield from MoS 2 to pentacene is found to be ∼50%, with the remaining holes undergoing trapping due to surface defects. Overall, the ultrafast charge transfer and long-lived charge-separated state in pentacene-MoS 2 p-n heterojunctions suggest significant promise for mixed-dimensional van der Waals heterostructures in photovoltaics, photodetectors, and related optoelectronic technologies.

  11. Effect of the van der Waals interaction on the electron energy-loss near edge structure theoretical calculation

    Energy Technology Data Exchange (ETDEWEB)

    Katsukura, Hirotaka; Miyata, Tomohiro; Tomita, Kota; Mizoguchi, Teruyasu, E-mail: teru@iis.u-tokyo.ac.jp

    2017-07-15

    The effect of the van der Waals (vdW) interaction on the simulation of the electron energy-loss near edge structure (ELNES) by a first-principles band-structure calculation is reported. The effect of the vdW interaction is considered by the Tkatchenko-Scheffler scheme, and the change of the spectrum profile and the energy shift are discussed. We perform calculations on systems in the solid, liquid and gaseous states. The transition energy shifts to lower energy by approximately 0.1 eV in the condensed (solid and liquid) systems by introducing the vdW effect into the calculation, whereas the energy shift in the gaseous models is negligible owing to the long intermolecular distance. We reveal that the vdW interaction exhibits a larger effect on the excited state than the ground state owing to the presence of an excited electron in the unoccupied band. Moreover, the vdW effect is found to depend on the local electron density and the molecular coordination. In addition, this study suggests that the detection of the vdW interactions exhibited within materials is possible by a very stable and high resolution observation. - Highlights: • Effect of van der Waals (vdW) interaction in ELNES calculation is investigated. • The vdW interaction influences more to the excited state owing to the presence of excited electron. • The vdW interaction makes spectral shift to lower energy side by 0.1–0.01 eV. • The vdW interaction is negligible in gaseous materials due to long intermolecular distance.

  12. Classical and quantum ordering of protons in cold solid hydrogen under megabar pressures.

    Science.gov (United States)

    Li, Xin-Zheng; Walker, Brent; Probert, Matthew I J; Pickard, Chris J; Needs, Richard J; Michaelides, Angelos

    2013-02-27

    A combination of state-of-the-art theoretical methods has been used to obtain an atomic-level picture of classical and quantum ordering of protons in cold high-pressure solid hydrogen. We focus mostly on phases II and III of hydrogen, exploring the effects of quantum nuclear motion on certain features of these phases (through a number of ab initio path integral molecular dynamics (PIMD) simulations at particular points on the phase diagram). We also examine the importance of van der Waals forces in this system by performing calculations using the optB88-vdW density functional, which accounts for non-local correlations. Our calculations reveal that the transition between phases I and II is strongly quantum in nature, resulting from a competition between anisotropic inter-molecular interactions that restrict molecular rotation and thermal plus quantum fluctuations of the nuclear positions that facilitate it. The transition from phase II to III is more classical because quantum nuclear motion plays only a secondary role and the transition is determined primarily by the underlying potential energy surface. A structure of P2(1)/c symmetry with 24 atoms in the primitive unit cell is found to be stable when anharmonic quantum nuclear vibrational motion is included at finite temperatures using the PIMD method. This structure gives a good account of the infra-red and Raman vibron frequencies of phase II. We find additional support for a C2/c structure as a strong candidate for phase III, since it remains transparent up to 300 GPa, even when quantum nuclear effects are included. Finally, we find that accounting for van der Waals forces improves the agreement between experiment and theory for the parts of the phase diagram considered, when compared to previous work which employed the widely-used Perdew-Burke-Ernzerhof exchange-correlation functional.

  13. Classical and quantum ordering of protons in cold solid hydrogen under megabar pressures

    International Nuclear Information System (INIS)

    Li Xinzheng; Walker, Brent; Michaelides, Angelos; Probert, Matthew I J; Pickard, Chris J; Needs, Richard J

    2013-01-01

    A combination of state-of-the-art theoretical methods has been used to obtain an atomic-level picture of classical and quantum ordering of protons in cold high-pressure solid hydrogen. We focus mostly on phases II and III of hydrogen, exploring the effects of quantum nuclear motion on certain features of these phases (through a number of ab initio path integral molecular dynamics (PIMD) simulations at particular points on the phase diagram). We also examine the importance of van der Waals forces in this system by performing calculations using the optB88-vdW density functional, which accounts for non-local correlations. Our calculations reveal that the transition between phases I and II is strongly quantum in nature, resulting from a competition between anisotropic inter-molecular interactions that restrict molecular rotation and thermal plus quantum fluctuations of the nuclear positions that facilitate it. The transition from phase II to III is more classical because quantum nuclear motion plays only a secondary role and the transition is determined primarily by the underlying potential energy surface. A structure of P2 1 /c symmetry with 24 atoms in the primitive unit cell is found to be stable when anharmonic quantum nuclear vibrational motion is included at finite temperatures using the PIMD method. This structure gives a good account of the infra-red and Raman vibron frequencies of phase II. We find additional support for a C2/c structure as a strong candidate for phase III, since it remains transparent up to 300 GPa, even when quantum nuclear effects are included. Finally, we find that accounting for van der Waals forces improves the agreement between experiment and theory for the parts of the phase diagram considered, when compared to previous work which employed the widely-used Perdew–Burke–Ernzerhof exchange–correlation functional. (paper)

  14. Application of catastrophe theory to nuclear structure

    International Nuclear Information System (INIS)

    Scharff-Goldhaber, G.; Dresden, M.

    1979-01-01

    Three two-parameter models, one describing an A-body system (the atomic nucleus) and two describing many-body systems (the van der Waals gas and the ferroelectric (perovskite) system) are compared within the framework of catastrophe theory. It is shown that each has a critical point (second-order phase transition) when the two counteracting forces controlling it are in balance; further, each undergoes a first-order phase transition when one of the forces vanishes (the deforming force for the nucleus, the attractive force for the van der Waals gas, and the dielectric constant for the perovskite). Finally, when both parameters are kept constant, a kind of phase transition may occur at a critical angular momentum, critical pressure, and critical electric field. 3 figures, 1 table

  15. Protein Folding: Search for Basic Physical Models

    Directory of Open Access Journals (Sweden)

    Ivan Y. Torshin

    2003-01-01

    Full Text Available How a unique three-dimensional structure is rapidly formed from the linear sequence of a polypeptide is one of the important questions in contemporary science. Apart from biological context of in vivo protein folding (which has been studied only for a few proteins, the roles of the fundamental physical forces in the in vitro folding remain largely unstudied. Despite a degree of success in using descriptions based on statistical and/or thermodynamic approaches, few of the current models explicitly include more basic physical forces (such as electrostatics and Van Der Waals forces. Moreover, the present-day models rarely take into account that the protein folding is, essentially, a rapid process that produces a highly specific architecture. This review considers several physical models that may provide more direct links between sequence and tertiary structure in terms of the physical forces. In particular, elaboration of such simple models is likely to produce extremely effective computational techniques with value for modern genomics.

  16. Making Teachters Accountable for Students'Disruptive Classroom Behaviour

    NARCIS (Netherlands)

    Verkuyten, Maykel

    2002-01-01

    Using a more conversational analytical approach, this paper examines the various situated ways in which secondary school students, in interaction with teachers, describe and explain their disruptive classroom behaviour. The focus is on how students account for their behaviour and force

  17. Accounting Entries Made in Compiling the FY 2000 Air Force General Funds Financial Statements

    National Research Council Canada - National Science Library

    2001-01-01

    ... to the Office of Management and Budget. This audit is one in a series of audits of accounting entries made by the Defense Finance and Accounting Service in preparing the FY 2000 financial statements for DoD...

  18. Quantum levitation of nanoparticles seen with ultracold neutrons

    Energy Technology Data Exchange (ETDEWEB)

    Nesvizhevsky, V. V., E-mail: nesvizhevsky@ill.eu [Institut Laue-Langevin (France); Voronin, A. Yu. [Lebedev Institute (Russian Federation); Lambrecht, A.; Reynaud, S. [Laboratoire Kastler-Brossel, CNRS, ENS, UPMC (France); Lychagin, E. V.; Muzychka, A. Yu.; Strelkov, A. V. [Joint Institute for Nuclear Research (Russian Federation)

    2013-09-15

    Analyzing new experiments with ultracold neutrons (UCNs) we show that physical adsorption of nanoparticles/nanodroplets, levitating in high-excited states in a deep and broad potential well formed by van der Waals/Casimir-Polder (vdW/CP) forces results in new effects on a cross-road of the fields of fundamental interactions, neutron, surface and nanoparticle physics. Accounting for the interaction of UCNs with nanoparticles explains a recently discovered intriguing so-called 'small heating' of UCNs in traps. It might be relevant to the striking conflict of the neutron lifetime experiments with smallest reported uncertainties by adding false effects there.

  19. Quantum levitation of nanoparticles seen with ultracold neutrons

    International Nuclear Information System (INIS)

    Nesvizhevsky, V. V.; Voronin, A. Yu.; Lambrecht, A.; Reynaud, S.; Lychagin, E. V.; Muzychka, A. Yu.; Strelkov, A. V.

    2013-01-01

    Analyzing new experiments with ultracold neutrons (UCNs) we show that physical adsorption of nanoparticles/nanodroplets, levitating in high-excited states in a deep and broad potential well formed by van der Waals/Casimir-Polder (vdW/CP) forces results in new effects on a cross-road of the fields of fundamental interactions, neutron, surface and nanoparticle physics. Accounting for the interaction of UCNs with nanoparticles explains a recently discovered intriguing so-called “small heating” of UCNs in traps. It might be relevant to the striking conflict of the neutron lifetime experiments with smallest reported uncertainties by adding false effects there

  20. Nonlinear Dynamics of Cantilever-Sample Interactions in Atomic Force Microscopy

    Science.gov (United States)

    Cantrell, John H.; Cantrell, Sean A.

    2010-01-01

    The interaction of the cantilever tip of an atomic force microscope (AFM) with the sample surface is obtained by treating the cantilever and sample as independent systems coupled by a nonlinear force acting between the cantilever tip and a volume element of the sample surface. The volume element is subjected to a restoring force from the remainder of the sample that provides dynamical equilibrium for the combined systems. The model accounts for the positions on the cantilever of the cantilever tip, laser probe, and excitation force (if any) via a basis set of set of orthogonal functions that may be generalized to account for arbitrary cantilever shapes. The basis set is extended to include nonlinear cantilever modes. The model leads to a pair of coupled nonlinear differential equations that are solved analytically using a matrix iteration procedure. The effects of oscillatory excitation forces applied either to the cantilever or to the sample surface (or to both) are obtained from the solution set and applied to the to the assessment of phase and amplitude signals generated by various acoustic-atomic force microscope (A-AFM) modalities. The influence of bistable cantilever modes of on AFM signal generation is discussed. The effects on the cantilever-sample surface dynamics of subsurface features embedded in the sample that are perturbed by surface-generated oscillatory excitation forces and carried to the cantilever via wave propagation are accounted by the Bolef-Miller propagating wave model. Expressions pertaining to signal generation and image contrast in A-AFM are obtained and applied to amplitude modulation (intermittent contact) atomic force microscopy and resonant difference-frequency atomic force ultrasonic microscopy (RDF-AFUM). The influence of phase accumulation in A-AFM on image contrast is discussed, as is the effect of hard contact and maximum nonlinearity regimes of A-AFM operation.

  1. Connection between fragility, mean-squared displacement and shear modulus in two van der Waals bonded glass-forming liquids

    DEFF Research Database (Denmark)

    Hansen, Henriette Wase; Frick, Bernhard; Hecksher, Tina

    2017-01-01

    The temperature dependence of the high-frequency shear modulus measured in the kHz range is compared with the mean-squared displacement measured in the nanosecond range for the two van der Waals bonded glass-forming liquids cumene and 5-polyphenyl ether. This provides an experimental test for the...... for the assumption connecting two versions of the shoving model for the non-Arrhenius temperature dependence of the relaxation time in glass formers. The two versions of the model are also tested directly and both are shown to work well for these liquids....

  2. Observation of Atom Wave Phase Shifts Induced by Van Der Waals Atom-Surface Interactions

    International Nuclear Information System (INIS)

    Perreault, John D.; Cronin, Alexander D.

    2005-01-01

    The development of nanotechnology and atom optics relies on understanding how atoms behave and interact with their environment. Isolated atoms can exhibit wavelike (coherent) behavior with a corresponding de Broglie wavelength and phase which can be affected by nearby surfaces. Here an atom interferometer is used to measure the phase shift of Na atom waves induced by the walls of a 50 nm wide cavity. To our knowledge this is the first direct measurement of the de Broglie wave phase shift caused by atom-surface interactions. The magnitude of the phase shift is in agreement with that predicted by Lifshitz theory for a nonretarded van der Waals interaction. This experiment also demonstrates that atom waves can retain their coherence even when atom-surface distances are as small as 10 nm

  3. Revisiting the adsorption of copper-phthalocyanine on Au(111) including van der Waals corrections

    International Nuclear Information System (INIS)

    Lüder, Johann; Eriksson, Olle; Sanyal, Biplab; Brena, Barbara

    2014-01-01

    We have studied the adsorption of copper-phthalocyanine on Au(111) by means of van der Waals corrected density functional theory using the Tkatchenko-Scheffler method. We have compared the element and site resolved adsorption distances to recent experimental normal-incident X-ray standing wave measurements. The measured adsorption distances could be reproduced within a deviation of 1% for the Cu atom, 1% for the C atoms, and 2% for the N atoms. The molecule was found to have a magnetic moment of 1 μ B distributed over the Cu and the N atoms of the pyrrole ring. Simulated scanning tunnel microscopy images based on the total and on the spin-resolved differential charge densities are provided for bias voltages of −1.45 and 1.45 eV

  4. A comprehensive modeling and vibration analysis of AFM microcantilevers subjected to nonlinear tip-sample interaction forces

    International Nuclear Information System (INIS)

    Eslami, Sohrab; Jalili, Nader

    2012-01-01

    Precise and accurate representation of an Atomic Force Microscopy (AFM) system is essential in studying the effects of boundary interaction forces present between the probe's tip and the sample. In this paper, a comprehensive analytical model for the AFM system utilizing a distributed-parameters based approach is proposed. More specifically, we consider two important attributes of these systems; namely the rotary inertia and shear deformation when compared with the Euler–Bernoulli beam theory. Moreover, a comprehensive nonlinear interaction force is assumed between probe's and sample in order to reveal the response of the system more realistically. This nanoscale interaction force is based on a general form consisting of both attractive and repulsive components as well as a function of the tip-sample distance and the microcantilever's base and sample oscillations. Mechanical properties of the sample could interact with the nanomechanical coupling field between the probe' tip and sample and be implemented in studying the composition information of the sample and the ultra-small features inside it. Therefore, by modulating the dynamics of the AFM system such as the driving amplitude of the microcantilever the procedure for the subsurface imaging is described. The presented approach here could be implemented for designing the AFM probes by examining the tip-sample interaction forces dominant by the van der Waals forces. Several numerical case studies are presented and the force–distance diagram reveals that the proposed nonlinear nanomechanical force along with the distributed-parameters model for the microcantilever is able to fulfill the mechanics of the Lennard–Jones potential. -- Highlights: ► We present a comprehensive distributed-parameters model for AFM microcantilever. ► Assuming a nonlinear and implicit interaction force between tip and sample. ► Timoshenko beam is compared with the Euler–Bernoulli having the same force model. ► Frequency

  5. Transport and deposition of cohesive pharmaceutical powders in human airway

    Directory of Open Access Journals (Sweden)

    Wang Yuan

    2017-01-01

    Full Text Available Pharmaceutical powders used in inhalation therapy are in the size range of 1-5 microns and are usually cohesive. Understanding the cohesive behaviour of pharmaceutical powders during their transportation in human airway is significant in optimising aerosol drug delivery and targeting. In this study, the transport and deposition of cohesive pharmaceutical powders in a human airway model is simulated by a well-established numerical model which combines computational fluid dynamics (CFD and discrete element method (DEM. The van der Waals force, as the dominant cohesive force, is simulated and its influence on particle transport and deposition behaviour is discussed. It is observed that even for dilute particle flow, the local particle concentration in the oral to trachea region can be high and particle aggregation happens due to the van der Waals force of attraction. It is concluded that the deposition mechanism for cohesive pharmaceutical powders, on one hand, is dominated by particle inertial impaction, as proven by previous studies; on the other hand, is significantly affected by particle aggregation induced by van der Waals force. To maximum respiratory drug delivery efficiency, efforts should be made to avoid pharmaceutical powder aggregation in human oral-to-trachea airway.

  6. Transport and deposition of cohesive pharmaceutical powders in human airway

    Science.gov (United States)

    Wang, Yuan; Chu, Kaiwei; Yu, Aibing

    2017-06-01

    Pharmaceutical powders used in inhalation therapy are in the size range of 1-5 microns and are usually cohesive. Understanding the cohesive behaviour of pharmaceutical powders during their transportation in human airway is significant in optimising aerosol drug delivery and targeting. In this study, the transport and deposition of cohesive pharmaceutical powders in a human airway model is simulated by a well-established numerical model which combines computational fluid dynamics (CFD) and discrete element method (DEM). The van der Waals force, as the dominant cohesive force, is simulated and its influence on particle transport and deposition behaviour is discussed. It is observed that even for dilute particle flow, the local particle concentration in the oral to trachea region can be high and particle aggregation happens due to the van der Waals force of attraction. It is concluded that the deposition mechanism for cohesive pharmaceutical powders, on one hand, is dominated by particle inertial impaction, as proven by previous studies; on the other hand, is significantly affected by particle aggregation induced by van der Waals force. To maximum respiratory drug delivery efficiency, efforts should be made to avoid pharmaceutical powder aggregation in human oral-to-trachea airway.

  7. THz absorption spectrum of the CO2–H2O complex: Observation and assignment of intermolecular van der Waals vibrations

    DEFF Research Database (Denmark)

    Andersen, Jonas; Heimdal, J.; Wallin Mahler Andersen, Denise

    2014-01-01

    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...

  8. A phenomenological force model of Li-ion battery packs for enhanced performance and health management

    Science.gov (United States)

    Oh, Ki-Yong; Epureanu, Bogdan I.

    2017-10-01

    A 1-D phenomenological force model of a Li-ion battery pack is proposed to enhance the control performance of Li-ion battery cells in pack conditions for efficient performance and health management. The force model accounts for multiple swelling sources under the operational environment of electric vehicles to predict swelling-induced forces in pack conditions, i.e. mechanically constrained. The proposed force model not only incorporates structural nonlinearities due to Li-ion intercalation swelling, but also separates the overall range of states of charge into three ranges to account for phase transitions. Moreover, an approach to study cell-to-cell variations in pack conditions is proposed with serial and parallel combinations of linear and nonlinear stiffness, which account for battery cells and other components in the battery pack. The model is shown not only to accurately estimate the reaction force caused by swelling as a function of the state of charge, battery temperature and environmental temperature, but also to account for cell-to-cell variations due to temperature variations, SOC differences, and local degradation in a wide range of operational conditions of electric vehicles. Considering that the force model of Li-ion battery packs can account for many possible situations in actual operation, the proposed approach and model offer potential utility for the enhancement of current battery management systems and power management strategies.

  9. Nuclear Forces from Effective Field Theory

    International Nuclear Information System (INIS)

    Krebs, H.

    2011-01-01

    Chiral effective field theory allows for a systematic and model-independent derivation of the forces between nucleons in harmony with the symmetries of the quantum chromodynamics. After a brief review on the current status in the development of the chiral nuclear forces I will focus on the role of the Δ-resonance contributions in the nuclear dynamics.We find improvement in the convergence of the chiral expansion of the nuclear forces if we explicitly take into account the Δ-resonance degrees of freedom. The overall results for two-nucleon forces with and without explicit Δ-resonance degrees of freedom are remarkably similar. We discussed the long- and shorter-range N 3 LO contributions to chiral three-nucleon forces. No additional free parameters appear at this order. There are five different topology classes which contribute to the forces. Three of them describe long-range contributions which constitute the first systematic corrections to the leading 2π exchange that appear at N 2 LO. Another two contributions are of a shorter range and include, additionally to an exchange of pions, also one short-range contact interaction and all corresponding 1/m corrections. The requirement of renormalizability leads to unique expressions for N 3 LO contributions to the three-nucleon force (except for 1/m-corrections). We presented the complete N 2 LO analysis of the nuclear forces with explicit Δ-isobar degrees of freedom. Although the overall results in the isospin-conserving case are very similar in the Δ-less and Δ-full theories, we found a much better convergence in all peripheral partial waves once Δ-resonance is explicitly taken into account. The leading CSB contributions to nuclear forces are proportional to nucleon- and Δ-mass splittings. There appear strong cancellations between the two contributions which at leading order yield weaker V III potentials. This effect is, however, entirely compensated at subleading order such that the results in the theories

  10. Climate forcing by anthropogenic aerosols

    Energy Technology Data Exchange (ETDEWEB)

    Charlson, R J; Schwartz, S E; Hales, J M; Cess, R D; Coakley, Jr, J A; Hansen, J E; Hofmann, D J [University of Washington, Seattle, WA (USA). Inst. for Environmental Studies, Dept. of Atmospheric Sciences

    1992-01-24

    Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of short wavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be -1 to -2 watts per square metre, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes. 73 refs., 4 figs., 2 tabs.

  11. Climate forcing by anthropogenic aerosols.

    Science.gov (United States)

    Charlson, R J; Schwartz, S E; Hales, J M; Cess, R D; Coakley, J A; Hansen, J E; Hofmann, D J

    1992-01-24

    Although long considered to be of marginal importance to global climate change, tropospheric aerosol contributes substantially to radiative forcing, and anthropogenic sulfate aerosol in particular has imposed a major perturbation to this forcing. Both the direct scattering of shortwavelength solar radiation and the modification of the shortwave reflective properties of clouds by sulfate aerosol particles increase planetary albedo, thereby exerting a cooling influence on the planet. Current climate forcing due to anthropogenic sulfate is estimated to be -1 to -2 watts per square meter, globally averaged. This perturbation is comparable in magnitude to current anthropogenic greenhouse gas forcing but opposite in sign. Thus, the aerosol forcing has likely offset global greenhouse warming to a substantial degree. However, differences in geographical and seasonal distributions of these forcings preclude any simple compensation. Aerosol effects must be taken into account in evaluating anthropogenic influences on past, current, and projected future climate and in formulating policy regarding controls on emission of greenhouse gases and sulfur dioxide. Resolution of such policy issues requires integrated research on the magnitude and geographical distribution of aerosol climate forcing and on the controlling chemical and physical processes.

  12. The upgrade of nuclear material accounting system at KAERI

    International Nuclear Information System (INIS)

    Kim, Hyun Jo; Kim, Hyun Sook; Park, Ho Jun; Ko, Han Suk; Lee, Byung Doo

    2010-01-01

    The agreement between the government of Republic Of Korea (ROK) and the IAEA for the application of safeguards was signed and entered into force in 1975. The Additional Protocol (AP) to the Safeguards Agreement between the ROK and the IAEA was signed in 1999 and entered into force on 19 February 2004. Also, Implementation of Integrated Safeguards (IS) was started on 1 July, 2008 after a draw of the broader conclusion. The IAEA provides 2 hours notification for Random Interim Inspection (RII) under IS. For RII, the facility has to prepare the inspection documents in a short time. Therefore, KAERI (Korea Atomic Energy Research Institute) developed a new computerized nuclear material accounting system named KASIS (KAERI Safeguards Information treatment System) to treat the data by on-line for RII. For the efficient IS implementation, KAERI has a plan to upgrade the system to reflect the accounting approaches or reporting procedure according to facility characteristic. This paper describes the upgrade of the nuclear material accounting system and the efforts to reduce the burden of the facility operators

  13. 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

    equations of state are sensitive to the mixing and combining rules used. Moreover, it is shown that previously reported deficiencies for size-asymmetric systems are more related to the van der Waals one fluid mixing rules used rather than the functionality of the cubic equation of state itself. Improved...... models for polar systems have been developed using the so-called EoS/GE mixing rules and we illustrate with the same methodology how these mixing rules should best be used for size-asymmetric systems. Despite the significant capabilities of cubic equations of state, their limitations lie especially...... in the description of complex phase behavior, e.g. liquid–liquid equilibria for highly polar and/or hydrogen bonding containing molecules. In these cases, advanced equations of state based on statistical mechanics that incorporate ideas from perturbation (e.g. SAFT and CPA), chemical (e.g. APACT) and lattice (e...

  14. 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.

  15. Material control and accountability alternatives

    International Nuclear Information System (INIS)

    1991-01-01

    Department of Energy and Nuclear Regulatory Commission regulations governing material control and accountability in nuclear facilities have become more restrictive in the past decade, especially in areas that address the insider threat. As the insider threat receives greater credibility, regulations have been strengthened to increase the probability of detecting insider activity and to prevent removal of a significant quantity of Special Nuclear Material (SNM) from areas under control of the protective force

  16. The dynamics of accounting terms in a globalized environment

    DEFF Research Database (Denmark)

    Fuertes-Olivera, Pedro A.; Nielsen, Sandro

    2014-01-01

    European accounting terminology is dynamic as term creation occurs on national, European Union and international levels. English is the lingua franca of accounting, which influences terminologies in other languages, usually through the work of translators, e.g. the translation of existing interna...... into Spanish; and the presence of novel metaphors in Spanish accounting. The data used in the discussion are taken from the accounting dictionaries, a collection of online dictionaries in three languages: Danish, English and Spanish.......European accounting terminology is dynamic as term creation occurs on national, European Union and international levels. English is the lingua franca of accounting, which influences terminologies in other languages, usually through the work of translators, e.g. the translation of existing...... international accounting standards. The combined influence of these forces is discussed in this chapter that explains the existence of a globalized trend towards a kind of cultural uniformity. This manifests itself in many ways, two of which are: the translation of English multiword accounting terms...

  17. Documentation of Accounting Records in Light of Legislative Innovations

    Directory of Open Access Journals (Sweden)

    K. V. BEZVERKHIY

    2017-05-01

    Full Text Available Legislative reforms in accounting aim to simplify accounting records and compilation of financial reports by business entities, thus increasing the position of Ukraine in the global ranking of Doing Business. This simplification is implied in the changes in the Regulation on Documentation of Accounting Records, entered into force to the Resolution of the Ukrainian Ministry of Finance. The objective of the study is to analyze the legislative innovations involved. The review of changes in documentation of accounting records is made. A comparative analysis of changes in the Regulation on Documentation of Accounting Records is made by sections: 1 General; 2 Primary documents; 3 Accounting records; 4 Correction of errors in primary documents and accounting records; 5 Organization of document circulation; 6 Storage of documents. Methods of analysis and synthesis are used for separating the differences in the editions of the Regulation on Documentation of Accounting Records. The result of the study has theoretical and practical value for the domestic business enterprise sector.

  18. New approach to safeguards accounting

    International Nuclear Information System (INIS)

    Pike, D.H.; Morrison, G.W.

    1977-03-01

    In recent years there has been widespread concern over the problem of nuclear safeguards. Due to the proliferation of nuclear reactors throughout the world, the concern about the loss or diversion of nuclear materials at various points in the fuel cycle has greatly increased. To minimize the possibility of material loss, the nuclear industry relies on physical protection systems and materials accountability procedures at licensed facilities. Present techniques of material accountability rely on double-entry accounting systems. For various reasons, only noisy observations of on-hand inventory are available. Hence one is forced to use statistical techniques in an attempt to detect the existence of missing material. Current practice is to use control charts as the basis for detecting significant material losses. Control charts may aid in detecting large material losses but are insensitive to small quantities of material loss, even if these small losses occur repeatedly over a long period of time. The purpose of this research is to show the feasibility of using linear state estimation theory in nuclear material accountability. The Kalman Filter is used as the state estimation technique. The state vector which consists of on-hand inventory and material losses is estimated recursively

  19. Can low energy experiments supply the effective information to determine the inner structure of hadrons

    International Nuclear Information System (INIS)

    Sawada, Tetsuo

    1980-01-01

    It is explained that the low energy experiments with high precision are important sources of information to determine the inner structure of hadrons. For such purpose, the magnetic monopole model of hadron due to Schwinger is reviewed. Appearance of the strong van der Waals force between hadrons is one of the most important consequences of such a model. A technique, which enables us to separate the effect of such a long range force from that of the short range force arising from the exchanges of pions, is introduced. Present status of the related experiments are summarized, and the experiments necessary to confirm the existence of the strong van der Waals force in a clear-cut way are explained. Possible impacts to the hadron physics, when the existence of such a long range force is confirmed, are discussed. (author)

  20. Outline of material accountancy system for Rokkasho reprocessing plant

    International Nuclear Information System (INIS)

    Kitamura, Touko; Yamazaki Yoshihiro; Ai, Hironobu

    2004-01-01

    In January 2004, Facility Attachment (FA) for Rokkasho Reprocessing Plant (RRP) was entered into force and the safeguards has been implemented in accordance with the FA. So operator must carry out the effectual material accountancy on the basis of facility operation. RRP is large and complex facility and operated based on automatic and remote system. For efficient material accounting viewpoint, the system especially automatic data collection is established using RRP computer network. The paper describes the outline of material accountancy system, the structure of RRP computer network including how to collect the source data, to convert the batch data and the reporting. (author)

  1. Lifshitz-type formulas for graphene and single-wall carbon nanotubes: van der Waals and Casimir interactions

    International Nuclear Information System (INIS)

    Bordag, M.; Geyer, B.; Klimchitskaya, G. L.; Mostepanenko, V. M.

    2006-01-01

    Lifshitz-type formulas are obtained for the van der Waals and Casimir interaction between graphene and a material plate, graphene and an atom or a molecule, and between a single-wall carbon nanotube and a plate. The reflection properties of electromagnetic oscillations on graphene are governed by the specific boundary conditions imposed on the infinitely thin positively charged plasma sheet, carrying a continuous fluid with some mass and charge density. The obtained formulas are applied to graphene interacting with Au and Si plates, to hydrogen atoms and molecules interacting with graphene, and to single-wall carbon nanotubes interacting with Au and Si plates. The generalizations to more complicated carbon nanostructures are discussed

  2. Social networks as anti-revolutionary forces: Facebook and political ...

    African Journals Online (AJOL)

    The much celebrated Arab Spring has championed social media as an organizing force. This led to the celebration of a new revolutionary force for people seeking more justice and accountability from their leaders. Maghreb became the example to follow for others across Africa especially given the central role youth played ...

  3. Scattering of thermal He beams by crossed atomic and molecular beams. II. The He--Ar van der Waals potential

    International Nuclear Information System (INIS)

    Keilb, M.; Slankas, J.T.; Kuppermann, A.

    1979-01-01

    Differential cross sections for He--Ar scattering at room temperature have been measured. The experimental consistency of these measurements with others performed in different laboratories is demonstrated. Despite this consistency, the present van der Waals well depth of 1.78 meV, accurate to 10%, is smaller by 20% to 50% than the experimental values obtained previously. These discrepancies are caused by differences between the assumed mathematical forms or between the assumed dispersion coefficients of the potentials used in the present paper and those of previous studies. Independent investigations have shown that the previous assumptions are inappropriate for providing accurate potentials from fits to experimental differential cross section data for He--Ar. We use two forms free of this inadequacy in the present analysis: a modified version of the Simons--Parr--Finlan--Dunham (SPFD) potential, and a double Morse--van der Waals (M 2 SV) type of parameterization. The resulting He--Ar potentials are shown to be equal to with experimental error, throughout the range of interatomic distances to which the scattering data are sensitive. The SPFD or M 2 SV potentials are combined with a repulsive potential previously determined exclusively from fits to gas phase bulk properties. The resulting potentials, valid over the extended range of interatomic distances r> or approx. =2.4 A, are able to reproduce all these bulk properties quite well, without adversely affecting the quality of the fits to the DCS

  4. Redox levels in aqueous solution: Effect of van der Waals interactions and hybrid functionals

    Science.gov (United States)

    Ambrosio, Francesco; Miceli, Giacomo; Pasquarello, Alfredo

    2015-12-01

    We investigate redox levels in aqueous solution using a combination of ab initio molecular dynamics (MD) simulations and thermodynamic integration methods. The molecular dynamics are performed with both the semilocal Perdew-Burke-Ernzerhof functional and a nonlocal functional (rVV10) accounting for van der Waals (vdW) interactions. The band edges are determined through three different schemes, namely, from the energy of the highest occupied and of the lowest unoccupied Kohn-Sham states, from total-energy differences, and from a linear extrapolation of the density of states. It is shown that the latter does not depend on the system size while the former two are subject to significant finite-size effects. For the redox levels, we provide a formulation in analogy to the definition of charge transition levels for defects in crystalline materials. We consider the H+/H2 level defining the standard hydrogen electrode, the OH-/OH∗ level corresponding to the oxidation of the hydroxyl ion, and the H2O/OH∗ level for the dehydrogenation of water. In spite of the large structural modifications induced in liquid water, vdW interactions do not lead to any significant structural effect on the calculated band gap and band edges. The effect on the redox levels is also small since the solvation properties of ionic species are little affected by vdW interactions. Since the electronic properties are not significantly affected by the underlying structural properties, it is justified to perform hybrid functional calculations on the configurations of our MD simulations. The redox levels calculated as a function of the fraction α of Fock exchange are found to remain constant, reproducing a general behavior previously observed for charge transition levels of defects. Comparison with experimental values shows very good agreement. At variance, the band edges and the band gap evolve linearly with α. For α ≃ 0.40, we achieve a band gap, band-edge positions, and redox levels in overall

  5. Redox levels in aqueous solution: Effect of van der Waals interactions and hybrid functionals

    Energy Technology Data Exchange (ETDEWEB)

    Ambrosio, Francesco, E-mail: Francesco.Ambrosio@epfl.ch; Miceli, Giacomo; Pasquarello, Alfredo [Chaire de Simulation à l’Echelle Atomique (CSEA), Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne (Switzerland)

    2015-12-28

    We investigate redox levels in aqueous solution using a combination of ab initio molecular dynamics (MD) simulations and thermodynamic integration methods. The molecular dynamics are performed with both the semilocal Perdew-Burke-Ernzerhof functional and a nonlocal functional (rVV10) accounting for van der Waals (vdW) interactions. The band edges are determined through three different schemes, namely, from the energy of the highest occupied and of the lowest unoccupied Kohn-Sham states, from total-energy differences, and from a linear extrapolation of the density of states. It is shown that the latter does not depend on the system size while the former two are subject to significant finite-size effects. For the redox levels, we provide a formulation in analogy to the definition of charge transition levels for defects in crystalline materials. We consider the H{sup +}/H{sub 2} level defining the standard hydrogen electrode, the OH{sup −}/OH{sup ∗} level corresponding to the oxidation of the hydroxyl ion, and the H{sub 2}O/OH{sup ∗} level for the dehydrogenation of water. In spite of the large structural modifications induced in liquid water, vdW interactions do not lead to any significant structural effect on the calculated band gap and band edges. The effect on the redox levels is also small since the solvation properties of ionic species are little affected by vdW interactions. Since the electronic properties are not significantly affected by the underlying structural properties, it is justified to perform hybrid functional calculations on the configurations of our MD simulations. The redox levels calculated as a function of the fraction α of Fock exchange are found to remain constant, reproducing a general behavior previously observed for charge transition levels of defects. Comparison with experimental values shows very good agreement. At variance, the band edges and the band gap evolve linearly with α. For α ≃ 0.40, we achieve a band gap, band

  6. Printable Transfer-Free and Wafer-Size MoS2/Graphene van der Waals Heterostructures for High-Performance Photodetection.

    Science.gov (United States)

    Liu, Qingfeng; Cook, Brent; Gong, Maogang; Gong, Youpin; Ewing, Dan; Casper, Matthew; Stramel, Alex; Wu, Judy

    2017-04-12

    Two-dimensional (2D) MoS 2 /graphene van der Waals heterostructures integrate the superior light-solid interaction in MoS 2 and charge mobility in graphene for high-performance optoelectronic devices. Key to the device performance lies in a clean MoS 2 /graphene interface to facilitate efficient transfer of photogenerated charges. Here, we report a printable and transfer-free process for fabrication of wafer-size MoS 2 /graphene van der Waals heterostructures obtained using a metal-free-grown graphene, followed by low-temperature growth of MoS 2 from the printed thin film of ammonium thiomolybdate on graphene. The photodetectors based on the transfer-free MoS 2 /graphene heterostructures exhibit extraordinary short photoresponse rise/decay times of 20/30 ms, which are significantly faster than those of the previously reported MoS 2 /transferred-graphene photodetectors (0.28-1.5 s). In addition, a high photoresponsivity of up to 835 mA/W was observed in the visible spectrum on such transfer-free MoS 2 /graphene heterostructures, which is much higher than that of the reported photodetectors based on the exfoliated layered MoS 2 (0.42 mA/W), the graphene (6.1 mA/W), and transfer-free MoS 2 /graphene/SiC heterostructures (∼40 mA/W). The enhanced performance is attributed to the clean interface on the transfer-free MoS 2 /graphene heterostructures. This printable and transfer-free process paves the way for large-scale commercial applications of the emerging 2D heterostructures in optoelectronics and sensors.

  7. Influence of random roughness on the adhesion between metal surfaces due to capillary condensation

    NARCIS (Netherlands)

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

    2007-01-01

    The capillary force was measured by atomic force microscopy between a gold coated sphere mounted on a cantilever and gold surfaces with different roughnesses. For smooth surfaces the capillary adhesive force surpasses in magnitude any dispersion, e.g., van der Waals/Casimir and/or electrostatic

  8. Tunable band gaps in graphene/GaN van der Waals heterostructures

    International Nuclear Information System (INIS)

    Huang, Le; Kang, Jun; Li, Yan; Li, Jingbo; Yue, Qu

    2014-01-01

    Van der Waals (vdW) heterostructures consisting of graphene and other two-dimensional materials provide good opportunities for achieving desired electronic and optoelectronic properties. Here, we focus on vdW heterostructures composed of graphene and gallium nitride (GaN). Using density functional theory, we perform a systematic study on the structural and electronic properties of heterostructures consisting of graphene and GaN. Small band gaps are opened up at or near the Γ point of the Brillouin zone for all of the heterostructures. We also investigate the effect of the stacking sequence and electric fields on their electronic properties. Our results show that the tunability of the band gap is sensitive to the stacking sequence in bilayer-graphene-based heterostructures. In particular, in the case of graphene/graphene/GaN, a band gap of up to 334 meV is obtained under a perpendicular electric field. The band gap of bilayer graphene between GaN sheets (GaN/graphene/graphene/GaN) shows similar tunability, and increases to 217 meV with the perpendicular electric field reaching 0.8 V Å  − 1 . (paper)

  9. The effect of van der Waal's gap expansions on the surface electronic structure of layered topological insulators

    International Nuclear Information System (INIS)

    Eremeev, S V; Vergniory, M G; Chulkov, E V; Menshchikova, T V; Shaposhnikov, A A

    2012-01-01

    On the basis of relativistic ab initio calculations, we show that an expansion of van der Waal's (vdW) spacings in layered topological insulators caused by intercalation of deposited atoms, leads to the simultaneous emergence of parabolic and M-shaped two-dimensional electron gas (2DEG) bands as well as Rashba-splitting of the former states. The expansion of vdW spacings and the emergence of the 2DEG states localized in the (sub)surface region are also accompanied by a relocation of the topological surface state to the lower quintuple layers, that can explain the absence of inter-band scattering found experimentally. (paper)

  10. Temperature dependence of the dielectric permittivity of CaF{sub 2}, BaF{sub 2} and Al{sub 2}O{sub 3}: application to the prediction of a temperature-dependent van der Waals surface interaction exerted onto a neighbouring Cs(8P{sub 3/2}) atom

    Energy Technology Data Exchange (ETDEWEB)

    Passerat de Silans, Thierry; Maurin, Isabelle; Chaves de Souza Segundo, Pedro; Saltiel, Solomon; Gorza, Marie-Pascale; Ducloy, Martial; Bloch, Daniel [Laboratoire de Physique des Lasers, UMR 7538 du CNRS et de l' Universite Paris 13, 99 Avenue JB Clement, Villetaneuse (France); De Sousa Meneses, Domingos; Echegut, Patrick [CNRS, UPR 3079 CEMHTI, 1D Avenue de la Recherche Scientifique, F-45071 Orleans Cedex 2 (France)], E-mail: daniel.bloch@univ-paris13.fr

    2009-06-24

    The temperature behaviour in the range 22-500 deg. C of the dielectric permittivity in the infrared range is investigated for CaF{sub 2}, BaF{sub 2} and Al{sub 2}O{sub 3} through reflectivity measurements. The dielectric permittivity is retrieved by fitting reflectivity spectra with a model taking into account multiphonon contributions. The results extrapolated from the measurements are applied to predict a temperature-dependent atom-surface van der Waals interaction. We specifically consider as the atom of interest Cs(8P{sub 3/2}), the most relevant virtual couplings of which fall in the range of thermal radiation and are located in the vicinity of the reststrahlen band of fluoride materials.

  11. Patterns of Force, Sequences of Resistance

    DEFF Research Database (Denmark)

    Lindegaard, Marie Rosenkrantz; Daniël De Vries, Thomas; Bernasco, Wim

    2018-01-01

    Robberies are improvised encounters involving offender threat, sometimes force, and often victim resistance. While the association between threat, force, and resistance in robberies is well-established, sequential patterns are disputed due to biases of retrospective studies. To overcome these bia...... the likelihood of victim resistance despite having no effect on offender vio- lence. By providing more reliable and detailed accounts of real-life behavior during robberies, our analysis illustrates the potential of a newly emergent field of studies of crimes caught on camera....

  12. [Interaction of mental health and forced married migrants in Germany].

    Science.gov (United States)

    Kizilhan, Jan

    2015-11-01

    The study examines the interaction of the forced married migrants and the frequency of the psychological illness. Forced-married and not forced-married migrants are compared concerning her psychological illness in psychosomatic clinics in Germany. Forced-married women reported significantly more about psychological illness and have undertaken on average at least four times a suicide attempt. Forced-married women suffer lifelong from this event and need, with taking into account cultural migration-specific aspects, special support in the psychosocial consultation and medical-therapeutic treatment. © Georg Thieme Verlag KG Stuttgart · New York.

  13. Role of ligand-ligand vs. core-core interactions in gold nanoclusters.

    Science.gov (United States)

    Milowska, Karolina Z; Stolarczyk, Jacek K

    2016-05-14

    The controlled assembly of ligand-coated gold nanoclusters (NCs) into larger structures paves the way for new applications ranging from electronics to nanomedicine. Here, we demonstrate through rigorous density functional theory (DFT) calculations employing novel functionals accounting for van der Waals forces that the ligand-ligand interactions determine whether stable assemblies can be formed. The study of NCs with different core sizes, symmetry forms, ligand lengths, mutual crystal orientations, and in the presence of a solvent suggests that core-to-core van der Waals interactions play a lesser role in the assembly. The dominant interactions originate from combination of steric effects, augmented by ligand bundling on NC facets, and related to them changes in electronic properties induced by neighbouring NCs. We also show that, in contrast to standard colloidal theory approach, DFT correctly reproduces the surprising experimental trends in the strength of the inter-particle interaction observed when varying the length of the ligands. The results underpin the importance of understanding NC interactions in designing gold NCs for a specific function.

  14. Casimir Force Between Quantum Plasmas

    International Nuclear Information System (INIS)

    Buenzli, P.

    2005-01-01

    Field fluctuations are responsible for an attractive force - the Casimir force - between two parallel (globally neutral) metallic plates separated by a distance d. At high temperature, or equivalently large d, this force is known to exhibit a classical and universal character (independent of the material constitution of the plates). In a recent work, we have displayed the microscopic mechanisms responsible for this universality within a classical model. The plates consist of slabs containing classical charged particles in fluid phase and thermal equilibrium (plasmas). The universality of the force proves to originate from screening sum rules satisfied by the charge correlations. Here we show how this result is altered when the quantum-mechanical nature of the particles is taken into account. It turns out that in addition to the classical result, the asymptotic force for large d comprises a non-universal quantum correction, which is, however, small at high temperature. The method relies on an exact representation of the charge correlations by quantum Mayer graphs, based on the Feynman-Kac path integral formalism. (author)

  15. Task force activity to take the effect of elastic-plastic behaviour into account on the seismic safety evaluation of nuclear piping systems

    International Nuclear Information System (INIS)

    Nakamura, Izumi; Shiratori, Masaki; Morishita, Masaki; Otani, Akihito; Shibutani, Tadahito

    2015-01-01

    According to investigations of several nuclear power plants (NPPs) hit by actual seismic events and a number of experimental researches on the failure behavior of piping systems under seismic loads, it is recognized that piping systems used in NPPs include a large seismic safety margin until boundary failure. Since the stress assessment based on the elastic analysis does not reflect actual seismic capability of piping systems including plastic region, it is necessary to develop a rational procedures to estimate the elastic-plastic behavior of piping systems under a large seismic load. With the aim of establishing a procedure that takes into account the elastic-plastic behavior effect in the seismic safety estimation of nuclear piping systems, a task force activity has been planned. Through the activity, the authors intend to establish guidelines to estimate the elastic-plastic behavior of piping systems rationally and conservatively, and to provide new rational seismic safety criteria taking the effect of elastic-plastic behavior into account. As the first step of making out the analysis guideline, benchmark analyses are conducted for a pipe element test and a piping system test. In this paper, the outline of the research activity and the preliminary results of benchmark analyses are described. (author)

  16. Electronic band structure of Two-Dimensional WS2/Graphene van der Waals Heterostructures

    Science.gov (United States)

    Henck, Hugo; Ben Aziza, Zeineb; Pierucci, Debora; Laourine, Feriel; Reale, Francesco; Palczynski, Pawel; Chaste, Julien; Silly, Mathieu G.; Bertran, François; Le Fèvre, Patrick; Lhuillier, Emmanuel; Wakamura, Taro; Mattevi, Cecilia; Rault, Julien E.; Calandra, Matteo; Ouerghi, Abdelkarim

    2018-04-01

    Combining single-layer two-dimensional semiconducting transition-metal dichalcogenides (TMDs) with a graphene layer in van der Waals heterostructures offers an intriguing means of controlling the electronic properties through these heterostructures. Here, we report the electronic and structural properties of transferred single-layer W S2 on epitaxial graphene using micro-Raman spectroscopy, angle-resolved photoemission spectroscopy measurements, and density functional theory (DFT) calculations. The results show good electronic properties as well as a well-defined band arising from the strong splitting of the single-layer W S2 valence band at the K points, with a maximum splitting of 0.44 eV. By comparing our DFT results with local and hybrid functionals, we find the top valence band of the experimental heterostructure is close to the calculations for suspended single-layer W S2 . Our results provide an important reference for future studies of electronic properties of W S2 and its applications in valleytronic devices.

  17. General theoretical description of angle-resolved photoemission spectroscopy of van der Waals structures

    Science.gov (United States)

    Amorim, B.

    2018-04-01

    We develop a general theory to model the angle-resolved photoemission spectroscopy (ARPES) of commensurate and incommensurate van der Waals (vdW) structures, formed by lattice mismatched and/or misaligned stacked layers of two-dimensional materials. The present theory is based on a tight-binding description of the structure and the concept of generalized umklapp processes, going beyond previous descriptions of ARPES in incommensurate vdW structures, which are based on continuous, low-energy models, being limited to structures with small lattice mismatch/misalignment. As applications of the general formalism, we study the ARPES bands and constant energy maps for two structures: twisted bilayer graphene and twisted bilayer MoS2. The present theory should be useful in correctly interpreting experimental results of ARPES of vdW structures and other systems displaying competition between different periodicities, such as two-dimensional materials weakly coupled to a substrate and materials with density wave phases.

  18. Galileo's kinematical paradox and the role of resistive forces

    International Nuclear Information System (INIS)

    Aguiar, C E; Soares, V; Tort, A C

    2014-01-01

    We discuss Galileo's kinematical ‘paradox’ taking into account the effects of sliding friction and of resistive forces proportional to velocity. We show that sliding friction eliminates the paradox but still allows for very simple synchronous curves. Perhaps surprisingly, Galileo's paradox is preserved when the resistive force is proportional to velocity. (paper)

  19. Understanding and Accounting for National Will in Strategies that Use Military Forces

    Science.gov (United States)

    2015-05-23

    Unified Task Force (UNITAF) in December 1992, ended in disastrous failure for the US at the Battle of Mogadishu in October 1993.17 Additionally, US...is known as the Battle of Mogadishu , resulting in 18 US Soldiers killed, 78 wounded and one captured. The public and political outcry was immediate...Restore Hope, and fell apart following the Battle of Mogadishu and loss of 18 American Soldiers

  20. Accountability: A Watchword for University Administration in Nigeria

    Science.gov (United States)

    Sofoluwe, Abayomi Olumade; Oduwaiye, Rhoda Olape; Ogundele, Michael Olarewaju; Kayode, David Jimoh

    2015-01-01

    The term accountability means different things to different people in different organizations. In the educational setting, the term is seen as liability to one's accomplishment in the educational system. The ever increasing needs of the universities and the dwindling resources available to them have forced university management and other…

  1. TAX AND ACCOUNTING TREATMENT ON THE REVALUATION OF TANGIBLE ASSETS IN ROMANIA

    Directory of Open Access Journals (Sweden)

    NICOLAE ECOBICI

    2017-02-01

    Full Text Available According to the regulations in force, the revaluation is an alternative treatment to the cost method, tangible assets to be presented in accounting to the fair/ reassessed value. In this paper we aim to capture the accounting treatment established under the laws in force in 2017. We will present ways of determining the reassessment differences and their implications on determining the tax on buildings (only tangible assets as buildings. We will also present the way to register the added value (revaluation surplus or minus value (amortization on reassessment and the treatment of the revaluation reserve (surplus from reassessment recorded in account the 105 “Reserve from reassessment” in accounting. Comparing the laws in force and those of IAS 16, we conclude that the accounting treatment related to the revaluation of tangible assets is similar. There remain unusable for the entities that do not apply IFRS in Romania: permanent reassessment of the duration of use and amortization method. Throughout the paper we will present the tax treatment of reassessment through corporate tax implications. Therefore, we will consider that the entities to which we refer are in the category of corporate tax payers and not in that of microenterprises. They no longer feel the influence of corporate tax because are taxed on income and not at the fiscal result (1% for those with at least 1 employee and 3% others. The main findings focus on the issue of identifying the exact moment when the reassessment reserve is taxed and on what are included in items similar to income, corporate tax implications.

  2. Strain-Mediated Interlayer Coupling Effects on the Excitonic Behaviors in an Epitaxially Grown MoS2/WS2 van der Waals Heterobilayer.

    Science.gov (United States)

    Pak, Sangyeon; Lee, Juwon; Lee, Young-Woo; Jang, A-Rang; Ahn, Seongjoon; Ma, Kyung Yeol; Cho, Yuljae; Hong, John; Lee, Sanghyo; Jeong, Hu Young; Im, Hyunsik; Shin, Hyeon Suk; Morris, Stephen M; Cha, SeungNam; Sohn, Jung Inn; Kim, Jong Min

    2017-09-13

    van der Waals heterostructures composed of two different monolayer crystals have recently attracted attention as a powerful and versatile platform for studying fundamental physics, as well as having great potential in future functional devices because of the diversity in the band alignments and the unique interlayer coupling that occurs at the heterojunction interface. However, despite these attractive features, a fundamental understanding of the underlying physics accounting for the effect of interlayer coupling on the interactions between electrons, photons, and phonons in the stacked heterobilayer is still lacking. Here, we demonstrate a detailed analysis of the strain-dependent excitonic behavior of an epitaxially grown MoS 2 /WS 2 vertical heterostructure under uniaxial tensile and compressive strain that enables the interlayer interactions to be modulated along with the electronic band structure. We find that the strain-modulated interlayer coupling directly affects the characteristic combined vibrational and excitonic properties of each monolayer in the heterobilayer. It is further revealed that the relative photoluminescence intensity ratio of WS 2 to MoS 2 in our heterobilayer increases monotonically with tensile strain and decreases with compressive strain. We attribute the strain-dependent emission behavior of the heterobilayer to the modulation of the band structure for each monolayer, which is dictated by the alterations in the band gap transitions. These findings present an important pathway toward designing heterostructures and flexible devices.

  3. Attainment and retention of force moderation following laparoscopic resection training with visual force feedback.

    Science.gov (United States)

    Hernandez, Rafael; Onar-Thomas, Arzu; Travascio, Francesco; Asfour, Shihab

    2017-11-01

    Laparoscopic training with visual force feedback can lead to immediate improvements in force moderation. However, the long-term retention of this kind of learning and its potential decay are yet unclear. A laparoscopic resection task and force sensing apparatus were designed to assess the benefits of visual force feedback training. Twenty-two male university students with no previous experience in laparoscopy underwent relevant FLS proficiency training. Participants were randomly assigned to either a control or treatment group. Both groups trained on the task for 2 weeks as follows: initial baseline, sixteen training trials, and post-test immediately after. The treatment group had visual force feedback during training, whereas the control group did not. Participants then performed four weekly test trials to assess long-term retention of training. Outcomes recorded were maximum pulling and pushing forces, completion time, and rated task difficulty. Extreme maximum pulling force values were tapered throughout both the training and retention periods. Average maximum pushing forces were significantly lowered towards the end of training and during retention period. No significant decay of applied force learning was found during the 4-week retention period. Completion time and rated task difficulty were higher during training, but results indicate that the difference eventually fades during the retention period. Significant differences in aptitude across participants were found. Visual force feedback training improves on certain aspects of force moderation in a laparoscopic resection task. Results suggest that with enough training there is no significant decay of learning within the first month of the retention period. It is essential to account for differences in aptitude between individuals in this type of longitudinal research. This study shows how an inexpensive force measuring system can be used with an FLS Trainer System after some retrofitting. Surgical

  4. OPTIMIZATION OF FINANCIAL PERSONNEL NUMBER IN ARMED FORCES OF THE REPUBLIC OF BELARUS

    Directory of Open Access Journals (Sweden)

    A. V. Bolshakova

    2014-01-01

    Full Text Available The paper considers a problem pertaining to reduction of the Armed Forces of the Republic of Belarus and necessity to carry out economically reasonable reforms optimizing strength of financial personnel with the purpose to decrease its number but without undermining financial and operational activities of the Armed Forces as a whole. It has been proposed to optimize strength of financial personnel in the Armed Forces while executing organizational staff transformations such as introduction of a centralized accounting system for service personnel by an example of the Ministry of Defense of the Russian Federation.Normative for financial personnel strength of the supposed unified financial centre which is involved in accounting recordings on salary and other payments has been calculated on the basis of inter-branch standards. While taking as an example a conventional organization “B” with staff strength which is equal to the strength of the Armed Forces of the Republic of Belarus the possible efficiency in introduction of the centralized accounting system for service personnel has been determined in the paper. According to represented calculations reduction of financial personnel dealing with accounting recordings on salary and other payments in the whole organization “B” can constitute up to 60 persons with more than 200 branches which are carrying out independent payment accounting for personnel concerned.Dependence of strength normative on number of financial bodies, percentage of personnel receiving payments through a unified financial centre and concentration of financial and economic document circulation has been determined in the paper. It has been pointed out that it is not sufficient to determine quantitative indices in order to ensure an objective reflection of the efficiency of possible introduction of the centralized accounting system for service personnel in the Armed Forces. In order to obtain complete information it is

  5. Critical wetting of n-alkanes on water; Mouillage critique des alcanes sur l`eau

    Energy Technology Data Exchange (ETDEWEB)

    Ragil, K

    1996-10-18

    This study concerns the wetting properties of n-alkanes on water under thermodynamic equilibrium conditions, a problem that is interesting for the petroleum industry as well as for the fundamental understanding of wetting phenomena. An experimental study using ellipsometry reveals that pentane on water undergoes a continuous or critical wetting transition at a temperature equal to 53.1 deg. C. This is the first experimental observation of such a transition, confirming theoretical predictions made on this subject over ten years. This transition is characterized by a continuous and reversible evolution of the thickness of the film of pentane with temperature from a thick (but finite film) to a macroscopic film. The critical wetting transition occurs when the Hamaker constant of the system, which gives the net interaction between the two interfaces bounding the wetting layer of pentane in terms of the van der Waals forces, changes sign. A theoretical approach based on the Cahn-Landau theory, which takes into account long range forces (van der Waals forces), enables us to explain the mechanism of the critical wetting transition and to show that a first-order wetting transition should precede it. Because of their similar dispersive properties, linear alkanes could all be able to show such a succession of transitions. An ellipsometry study performed on a brine/hexane/vapor system confirms that a discontinuous transition from a thin microscopic film to a thick but finite adsorbed film takes place. THis study demonstrates that the wetting of alkanes on water is determined by subtle interplay between short range and long range forces, which can lead to an intermediary state between partial and complete wetting. (author)

  6. Properties of Organic Liquids when Simulated with Long-Range Lennard-Jones Interactions.

    Science.gov (United States)

    Fischer, Nina M; van Maaren, Paul J; Ditz, Jonas C; Yildirim, Ahmet; van der Spoel, David

    2015-07-14

    In order to increase the accuracy of classical computer simulations, existing methodologies may need to be adapted. Hitherto, most force fields employ a truncated potential function to model van der Waals interactions, sometimes augmented with an analytical correction. Although such corrections are accurate for homogeneous systems with a long cutoff, they should not be used in inherently inhomogeneous systems such as biomolecular and interface systems. For such cases, a variant of the particle mesh Ewald algorithm (Lennard-Jones PME) was already proposed 20 years ago (Essmann et al. J. Chem. Phys. 1995, 103, 8577-8593), but it was implemented only recently (Wennberg et al. J. Chem. Theory Comput. 2013, 9, 3527-3537) in a major simulation code (GROMACS). The availability of this method allows surface tensions of liquids as well as bulk properties to be established, such as density and enthalpy of vaporization, without approximations due to truncation. Here, we report on simulations of ≈150 liquids (taken from a force field benchmark: Caleman et al. J. Chem. Theory Comput. 2012, 8, 61-74) using three different force fields and compare simulations with and without explicit long-range van der Waals interactions. We find that the density and enthalpy of vaporization increase for most liquids using the generalized Amber force field (GAFF, Wang et al. J. Comput. Chem. 2004, 25, 1157-1174) and the Charmm generalized force field (CGenFF, Vanommeslaeghe et al. J. Comput. Chem. 2010, 31, 671-690) but less so for OPLS/AA (Jorgensen and Tirado-Rives, Proc. Natl. Acad. Sci. U.S.A. 2005, 102, 6665-6670), which was parametrized with an analytical correction to the van der Waals potential. The surface tension increases by ≈10(-2) N/m for all force fields. These results suggest that van der Waals attractions in force fields are too strong, in particular for the GAFF and CGenFF. In addition to the simulation results, we introduce a new version of a web server, http

  7. Modeling and boundary force control of microcantilevers utilized in atomic force microscopy for cellular imaging and characterization

    Science.gov (United States)

    Eslami, Sohrab

    This dissertation undertakes the theoretical and experimental developments microcantilevers utilized in Atomic Force Microscopy (AFM) with applications to cellular imaging and characterization. The capability of revealing the inhomogeneties or interior of ultra-small materials has been of most interest to many researchers. However, the fundamental concept of signal and image formation remains unexplored and not fully understood. For his, a semi-empirical nonlinear force model is proposed to show that virtual frequency generation, regarded as the simplest synthesized subsurface probe, occurs optimally when the force is tuned to the van der Waals form. This is the first-time observation of a novel theoretical dynamic multi-frequency force microscopy that has not been already reported. Owing to the broad applications of microcantilevers in the nanoscale imaging and microscopic techniques, there is an essential feeling to study and propose a comprehensive model of such systems. Therefore, in the theoretical part of this dissertation, a distributed-parameters representation modeling of the microcantilever along with a general interaction force comprising of two attractive and repulsive components with general amplitude and power terms is studied. This model is investigated in a general 2D Cartesian coordinate to consider the motions of the probe with a tip mass. There is an excitation at the microcantilever's base such that the end of the beam is subject to the proposed general force. These forces are very sensitive to the amplitude and power terms of these parts; on the other hand, atomic intermolecular force is a function of the distance such that this distance itself is also a function of the interaction force that will result in a nonlinear implicit equation. From a parametric study in the probe-sample excitation, it is shown that the predicted behavior of the generated difference-frequency oscillation amplitude agrees well with experimental measurements. Following

  8. A model to estimate the size of nanoparticle agglomerates in gas−solid fluidized beds

    Energy Technology Data Exchange (ETDEWEB)

    Martín, Lilian de, E-mail: L.DeMartinMonton@tudelft.nl; Ommen, J. Ruud van [Delft University of Technology, Department of Chemical Engineering (Netherlands)

    2013-11-15

    The estimation of nanoparticle agglomerates’ size in fluidized beds remains an open challenge, mainly due to the difficulty of characterizing the inter-agglomerate van der Waals force. The current approach is to describe micron-sized nanoparticle agglomerates as micron-sized particles with 0.1–0.2-μm asperities. This simplification does not capture the influence of the particle size on the van der Waals attraction between agglomerates. In this paper, we propose a new description where the agglomerates are micron-sized particles with nanoparticles on the surface, acting as asperities. As opposed to previous models, here the van der Waals force between agglomerates decreases with an increase in the particle size. We have also included an additional force due to the hydrogen bond formation between the surfaces of hydrophilic and dry nanoparticles. The average size of the fluidized agglomerates has been estimated equating the attractive force obtained from this method to the weight of the individual agglomerates. The results have been compared to 54 experimental values, most of them collected from the literature. Our model approximates without a systematic error the size of most of the nanopowders, both in conventional and centrifugal fluidized beds, outperforming current models. Although simple, the model is able to capture the influence of the nanoparticle size, particle density, and Hamaker coefficient on the inter-agglomerate forces.

  9. A model to estimate the size of nanoparticle agglomerates in gas−solid fluidized beds

    International Nuclear Information System (INIS)

    Martín, Lilian de; Ommen, J. Ruud van

    2013-01-01

    The estimation of nanoparticle agglomerates’ size in fluidized beds remains an open challenge, mainly due to the difficulty of characterizing the inter-agglomerate van der Waals force. The current approach is to describe micron-sized nanoparticle agglomerates as micron-sized particles with 0.1–0.2-μm asperities. This simplification does not capture the influence of the particle size on the van der Waals attraction between agglomerates. In this paper, we propose a new description where the agglomerates are micron-sized particles with nanoparticles on the surface, acting as asperities. As opposed to previous models, here the van der Waals force between agglomerates decreases with an increase in the particle size. We have also included an additional force due to the hydrogen bond formation between the surfaces of hydrophilic and dry nanoparticles. The average size of the fluidized agglomerates has been estimated equating the attractive force obtained from this method to the weight of the individual agglomerates. The results have been compared to 54 experimental values, most of them collected from the literature. Our model approximates without a systematic error the size of most of the nanopowders, both in conventional and centrifugal fluidized beds, outperforming current models. Although simple, the model is able to capture the influence of the nanoparticle size, particle density, and Hamaker coefficient on the inter-agglomerate forces

  10. Chemical Equilibrium as Balance of the Thermodynamic Forces

    OpenAIRE

    Zilbergleyt, B.

    2004-01-01

    The article sets forth comprehensive basics of thermodynamics of chemical equilibrium as balance of the thermodynamic forces. Based on the linear equations of irreversible thermodynamics, De Donder definition of the thermodynamic force, and Le Chatelier's principle, new thermodynamics of chemical equilibrium offers an explicit account for multiple chemical interactions within the system. Basic relations between energetic characteristics of chemical transformations and reaction extents are bas...

  11. Electric field modulation of Schottky barrier height in graphene/MoSe2 van der Waals heterointerface

    International Nuclear Information System (INIS)

    Sata, Yohta; Moriya, Rai; Morikawa, Sei; Yabuki, Naoto; Masubuchi, Satoru; Machida, Tomoki

    2015-01-01

    We demonstrate a vertical field-effect transistor based on a graphene/MoSe 2 van der Waals (vdW) heterostructure. The vdW interface between the graphene and MoSe 2 exhibits a Schottky barrier with an ideality factor of around 1.3, suggesting a high-quality interface. Owing to the low density of states in graphene, the position of the Fermi level in the graphene can be strongly modulated by an external electric field. Therefore, the Schottky barrier height at the graphene/MoSe 2 vdW interface is also modulated. We demonstrate a large current ON-OFF ratio of 10 5 . These results point to the potential high performance of the graphene/MoSe 2 vdW heterostructure for electronics applications

  12. Rotational study on the van der Waals complex 1-chloro-1,1-difluoroethane-argon

    Science.gov (United States)

    Wang, Juan; Chen, Junhua; Feng, Gang; Xia, Zhining; Gou, Qian

    2018-03-01

    The rotational spectrum of the van der Waals complex formed between 1-chloro-1,1-difluoroethane and argon has been investigated by using a pulsed jet Fourier transform microwave spectrometer. Only one set of rotational transitions belonging to the lowest energy conformer has been observed and assigned, although theoretical calculations suggest six stable conformers that might be observed. The observed conformer, according to the experimental evidence from two isotopologues (35Cl and 37Cl), adopts a configuration in which the argon atom is located, close to the sbnd CF2Cl top, between the CCF and CCCl planes (the dihedral angle ∠ ArCCCl is 65.2°). The distance between argon atom and the center of mass of CH3CF2Cl is 3.949(2) Å. The dissociation energy, with pseudo diatomic approximation, is evaluated to be 2.4 kJ mol- 1.

  13. 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.

  14. Compact two-electron wave function for bond dissociation and Van der Waals interactions: a natural amplitude assessment.

    Science.gov (United States)

    Giesbertz, Klaas J H; van Leeuwen, Robert

    2014-05-14

    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 for a one-dimensional model of a two-electron system 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 (r12) depending on the interelectronic distance r12. 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. Due to this particular form of the wave function, we can prove that none of the amplitudes vanishes and moreover that it displays a distinct sign pattern and a series of avoided crossings as a function of the bond distance in agreement with the exact solution. This shows that the wave function ansatz correctly incorporates the long range Van der Waals interactions. We further show that the approximate wave function gives an excellent binding curve and is able to describe static correlations. We show that in order to do this the correlation function f (r12) needs to diverge for large r12 at large internuclear distances while for shorter bond distances it increases as a function of r12 to a maximum value after which it decays exponentially. We further give a physical interpretation of this behavior.

  15. Robust approach to maximize the range and accuracy of force application in atomic force microscopes with nonlinear position-sensitive detectors

    International Nuclear Information System (INIS)

    Silva, E C C M; Vliet, K J van

    2006-01-01

    The atomic force microscope is used increasingly to investigate the mechanical properties of materials via sample displacement under an applied force. However, both the extent of forces attainable and the accuracy of those forces measurements are significantly limited by the optical lever configuration that is commonly used to infer nanoscale deflection of the cantilever. We present a robust and general approach to characterize and compensate for the nonlinearity of the position-sensitive optical device via data processing, requiring no modification of existing instrumentation. We demonstrate that application of this approach reduced the maximum systematic error on the gradient of a force-displacement response from 50% to 5%, and doubled the calibrated force application range. Finally, we outline an experimental protocol that optimizes the use of the quasi-linear range of the most commonly available optical feedback configurations and also accounts for the residual systematic error, allowing the user to benefit from the full detection range of these indirect force sensors

  16. Effect of temperature and density fluctuations on the spatially heterogeneous dynamics of glass-forming Van der Waals liquids under high pressure.

    Science.gov (United States)

    Koperwas, K; Grzybowski, A; Grzybowska, K; Wojnarowska, Z; Sokolov, A P; Paluch, M

    2013-09-20

    In this Letter, we show how temperature and density fluctuations affect the spatially heterogeneous dynamics at ambient and elevated pressures. By using high-pressure experimental data for van der Waals liquids, we examine contributions of the temperature and density fluctuations to the dynamics heterogeneity. We show that the dynamic heterogeneity decreases significantly with increasing pressure at a constant structural relaxation time (isochronal condition), while the broadening of the relaxation spectrum remains constant. This observation questions the relationship between spectral broadening and dynamic heterogeneity.

  17. Prediction of bubble detachment diameter in flow boiling based on force analysis

    International Nuclear Information System (INIS)

    Chen Deqi; Pan Liangming; Ren Song

    2012-01-01

    Highlights: ► All the forces acting on the growing bubbles are taken into account in the model. ► The bubble contact diameter has significant effect on bubble detachment. ► Bubble growth force and surface tension are more significant in narrow channel. ► A good agreement between the predicted and the measured results is achieved. - Abstract: Bubble detachment diameter is one of the key parameters in the study of bubble dynamics and boiling heat transfer, and it is hard to be measured in a boiling system. In order to predict the bubble detachment diameter, a theoretical model is proposed based on forces analysis in this paper. All the forces acting on a bubble are taken into account to establish a model for different flow boiling configurations, including narrow and conventional channels, upward, downward and horizontal flows. A correlation of bubble contact circle diameter is adopted in this study, and it is found that the bubble contact circle diameter has significant effect on bubble detachment. A new correlation taking the bubble contact circle diameter into account for the evaluation of bubble growth force is proposed in this study, and it is found that the bubble growth force and surface tension force are more significant in narrow channel when comparing with that in conventional channel. A visual experiment was carried out in order to verify present model; and the experimental data from published literature are used also. A good agreement between predicted and measured results is achieved.

  18. Relativistic origin of three-nucleon force

    International Nuclear Information System (INIS)

    Haberzettl, H.; Parke, W.C.

    1995-01-01

    Based on the manifestly covariant cluster-dynamical formalism recently proposed by Haberzettl, the three-body forces entering three-nucleon equations are discussed. It is shown that there exist additional contributions to the (nonrelativistic) three-body force, not taken into account in the usual treatments, arising from the proper nonrelativistic limits of higher-order meson-exchange Feynman diagrams. Using the Paris potential, a five-channel triton bound-state calculation results in additional binding of about 0.6 MeV due to this new mechanism. copyright 1995 American Institute of Physics

  19. Ponderomotive forces in electrodynamics of moving media: The Minkowski and Abraham approaches

    Science.gov (United States)

    Nesterenko, V. V.; Nesterenko, A. V.

    2016-09-01

    In the general setting of the problem, the explicit compact formulae are derived for the ponderomotive forces in the macroscopic electrodynamics of moving media in the Minkowski and Abraham approaches. Taking account of the Minkowski constitutive relations and making use of a special representation for the Abraham energy-momentum tensor enable one to obtain a compact expression for the Abraham force in the case of arbitrary dependence of the medium velocity on spatial coordinates and the time and for nonstationary external electromagnetic field. We term the difference between the ponderomotive forces in the Abraham and Minkowski approaches as the Abraham force not only under consideration of media at rest but also in the case of moving media. The Lorentz force is found which is exerted by external electromagnetic field on the conduction current in a medium, the covariant Ohm law, and the constitutive Minkowski relations being taken into account. The physical argumentation is traced for the definition of the 4-vector of the ponderomotive force as the 4-divergence of the energy-momentum tensor of electromagnetic field in a medium.

  20. Ex-citable Accounting and the Development of Pervasive Innovation

    DEFF Research Database (Denmark)

    Revellino, Silvana; Mouritsen, Jan

    2017-01-01

    Purpose: The purpose of this paper is to explain the role of the performativity theory for understanding how the calculative instruments of accounting provoke innovation and participate in the generation of values by activating processes that pervade everything rather than being limited...... can be imagined ab origine, they may not be contractible to a plan. The calculative instruments of accounting provoke innovation and participate in the generation of value(s) by activating processes that pervade everything rather than being limited to categorical spaces. In the course...... to categorical spaces. Design/methodology/approach: The paper draws on Judith Butler’s work and her notion of excitability to explain how multiple values may arise when accounting interacts with innovation. Through this lens, accounting, as a language based on signs, can be theorised as an ex-citable force...

  1. Resonance April Cover Pg TP

    Indian Academy of Sciences (India)

    Admin

    word possibly having its origin in Sanskrit). W hat is ... History and Some Perspectives on Intermolecular Forces. E Arunan. Keywords van der Waals forces, hydrogen bonding. ... A tom s have rem ained a dom ain of physics, rather than.

  2. Behavior of quasinormal modes and Van der Waals-like phase transition of charged AdS black holes in massive gravity

    Energy Technology Data Exchange (ETDEWEB)

    Zou, De-Cheng; Yue, Ruihong [Yangzhou University, Center for Gravitation and Cosmology, College of Physical Science and Technology, Yangzhou (China); Liu, Yunqi [Huazhong University of Science and Technology, School of Physics, Wuhan (China)

    2017-06-15

    In this work, we utilize the quasinormal modes (QNMs) of a massless scalar perturbation to probe the Van der Waals-like small and large black holes (SBH/LBH) phase transition of charged topological Anti-de Sitter (AdS) black holes in four-dimensional massive gravity. We find that the signature of this SBH/LBH phase transition is detected in the isobaric as well as in the isothermal process. This further supports the idea that the QNMs can be an efficient tool to investigate the thermodynamical phase transition. (orig.)

  3. Financial Accounting for Local and State School Systems: 2014 Edition. NCES 2015-347

    Science.gov (United States)

    Allison, Gregory S.

    2015-01-01

    The 2014 edition of "Financial Accounting for Local and State School Systems" updates the 2009 (see ED505993) and 2003 editions of the handbook. The 2003 edition was the work of the NCES National Forum on Education Statistics, Core Finance Data Task Force. That task force systematically rewrote nearly the entire text, incorporating new…

  4. A note on the history of experimental and theoretical research into molecular attractive forces between solids

    International Nuclear Information System (INIS)

    Danilova, N P

    2015-01-01

    From the Editorial Board. In a brief followup to the talk by E I Kats on 'Van der Waals, Casimir, and Lifshitz forces in soft matter' (see pp. 892 – 896 of this issue) at the E M Lifshitz centennial session of the Physical Sciences Division of the Russian Academy of Sciences, an interesting and instructive story was told by Nina Petrovna Danilova (Department of Low Temperature Physics and Superconductivity, Faculty of Physics, Moscow State University) of how E M Lifshitz was enlisted to explain I I Abrikosova's and B V Derjaguin's experimental results. The Editorial Board of Uspekhi Fizicheskikh Nauk (UFN) [Physics-Uspekhi] journal found the story appropriate to be published in the 'Letters to the Editor' section of UFN in a jubilee selection of works marking the centennial of E M Lifshitz' birth. (letters to the editors)

  5. Integrated reporting – innovation in accounting paradigms

    Directory of Open Access Journals (Sweden)

    Mirosława Kwiecień

    2016-07-01

    Full Text Available The article is an introduction to the issues and results of a new trend in interdisciplinary research, which is integrated reporting. „Violated balance”, characteristic of contemporary global economy, forces us to seek solutions oriented to symbiosis between economic, social and environmental progress, which is the basis for fundamental changes in mental models that determine the way the economic organization oper-ates. On the basis of literature studies, as well as management (of innovation, knowledge, etc. science studies and research on changes in legal regulations of accounting, one can venture to say that the change in accounting paradigms is an innovation which stems from legal requirements. Legislation stimulates conceptuality, including information management, standardization of accounting, etc. Innovation theory refers to technological, organizational and market changes, so a question ariseswhether this theory can be applied to accounting practices as well? In this way an idea emerged for inves-tigating the question if the implementation of legal regulations such as International Financial Reporting Standards (IFRS or the standards of the Global Reporting Initiative (GRI is a manifestation of the inno-vation theory in the development of accounting systems, especially in reporting.

  6. Financial Status of Air Force Expired Year Appropriations

    National Research Council Canada - National Science Library

    1994-01-01

    ... Procurement appropriations. In our report on that audit, we found that the Air Force experienced deficits and accounting problems relating to funding upward cost adjustments to obligations when such costs were charged...

  7. Particle number fluctuations for the van der Waals equation of state

    International Nuclear Information System (INIS)

    Vovchenko, V; Anchishkin, D V; Gorenstein, M I

    2015-01-01

    The van der Waals (VDW) equation of state describes a thermal equilibrium in system of particles, where both repulsive and attractive interactions between them are included. This equation predicts the existence of the first order liquid–gas phase transition and the critical point. The standard form of the VDW equation is given by the pressure function in a canonical ensemble (CE) with a fixed number of particles. In this paper the VDW equation is derived within the grand canonical ensemble (GCE) formulation. We argue that this procedure can be useful for new physical applications, in particular, the fluctuations of the number of particles, which are absent in the CE, can be studied in the GCE. For the VDW equation of state in the GCE the particle number fluctuations are calculated for the whole phase diagram, both outside and inside the liquid–gas mixed phase region. It is shown that the scaled variance of these fluctuations remains finite within the mixed phase and goes to infinity at the critical point. The GCE formulation of the VDW equation of state can also be an important step for its application in the statistical description of hadronic systems, where numbers of different particle species are usually not conserved. (paper)

  8. The formation of quasi-alicyclic rings in alkyl-aromatic compounds

    Science.gov (United States)

    Straka, Pavel; Buryan, Petr; Bičáková, Olga

    2018-02-01

    The alkyl side chains of n-alkyl phenols, n-alkyl benzenes and n-alkyl naphthalenes are cyclised, as demonstrated by GC measurements, FTIR spectroscopy and molecular mechanics calculations. Cyclisation occurs due to the intramolecular interaction between an aromatic ring (-δ) and a hydrogen of the terminal methyl group (+δ) of an alkyl chain. In fact, conventional molecules are not aliphatic-aromatic, but quasi-alicyclic-aromatic. With the aromatic molecules formed with a quasi-alicyclic ring, the effect of van der Waals attractive forces increases not only intramolecularly but also intermolecularly. This effect is strong in molecules with propyl and higher alkyl substituents. The increase of intermolecular van der Waals attractive forces results in bi-linearity in the GC retention time of the compounds in question, observed in the dependence of the logarithm of the relative retention time on the number of carbons in a molecule in both polar and nonpolar stationary phases with both capillary and packed columns. The role of van der Waals forces has been demonstrated using the potential energies of covalent and noncovalent interactions for 2-n-alkyl phenols, n-alkyl benzenes and 1-n-alkyl- and 2-n-alkyl naphthalenes.

  9. The magnetohydrodynamic force experienced by spherical iron particles in liquid metal

    International Nuclear Information System (INIS)

    Ščepanskis, Mihails; Jakovičs, Andris

    2016-01-01

    The paper contains a theoretical investigation of magnetohydrodynamic force experienced by iron particles (well-conducting and ferromagnetic) in well-conducting liquid. The investigation is performed by extending the Leenov and Kolin's theory to take into account the second-order effect. Therefore, the limits of the parent model are taken over to the present results. It is found that the effective conductivity of iron particles in liquid metal, which is important for practical application of the theoretically obtained force, is approximately equal to 1.5·10"6 S/m. The last result is obtained using a quasi-empirical approach – a comparison of experimental results with the results of the numerical simulation that was performed for various conductivities of the iron particles. - Highlights: • We found the expression of an MHD force experienced by a spherical iron particle in a liquid metal taking into account the second order effect additionally to Leenov & Kolin’s theoretical solution. • We found the effective conductivity of an iron particle in a liquid metal in quasi-empirical way equal to 1.5·10"6 S/m. • It is important to use the expression of an MHD force, which takes into account the second-order effect, as well as the correction for effective conductivity of a particle, to describe behaviour of iron particles in liquid metal flows, which are under influence or induced by the Lorentz force.

  10. FDE-vdW: A van der Waals inclusive subsystem density-functional theory

    Energy Technology Data Exchange (ETDEWEB)

    Kevorkyants, Ruslan; Pavanello, Michele, E-mail: m.pavanello@rutgers.edu [Department of Chemistry, Rutgers University, Newark, New Jersey 07102 (United States); Eshuis, Henk [Department of Chemistry and Biochemistry, Montclair State University, Montclair, New Jersey 07043 (United States)

    2014-07-28

    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 subsystem DFT, provided that an appropriate exchange functional is employed. The convergence of FDE-vdW with basis set size is discussed, as well as its dependence on the choice of associated density functional approximant.

  11. Mechanism of electron attachment to van der Waals clusters: Application to carbon dioxide clusters

    International Nuclear Information System (INIS)

    Tsukada, M.; Shima, N.; Tsuneyuki, S.; Kageshima, H.; Kondow, T.

    1987-01-01

    A theory on the attachment of very slow electrons to van der Waals clusters was developed on the basis of the electronic structure theory, and was applied to clarify the mechanism of the collisional electron transfer from a high-Rydberg atom to a CO 2 cluster. The strong coupled electron--phonon model is found to afford a reasonable mechanism of the attachment. The equilibrium geometry of (CO 2 )/sub N/ (2≤N≤13) clusters are determined and their vertical affinity levels are obtained by the DV-X α-transition state method. Using this information, as well as some plausible assumptions on the values of the coupling constants, the attachment cross section σ is evaluated as a function of the energy of the incident electron. The theory predicts the existence of the threshold cluster size for the attachment and a sharp decrease of σ with the energy, which are consistent with the experimental results

  12. Ponderomotive force near cyclotron resonance

    Energy Technology Data Exchange (ETDEWEB)

    Kono, Mitsuo; Sanuki, Heiji

    1987-01-01

    The ponderomotive force, which is involved in the excitation of macroscopic behaviors of plasma caused by wave motion, plays an important role in various non-linear wave motion phenomena. In the present study, equations for the pondermotive force for plasma in a uniform magnetic field is derived using a renormalization theory which is based on the Vlasov equation. It is shown that the pondermotive force, which diverges at the cyclotron resonence point according to adiabatic approximation, can be expressed by a non-divergent equation by taking into account the instability of the cyclotron orbit due to high-order scattering caused by a wave. This is related with chaotic particle behaviors near cyclotron resonance, where the pondermotive force is small and the diffusion process prevails. It is assumed here that the amplitude of the high-frequency electric field is not large and that the broadening of cyclotron levels is smaller than the distance between the levels. A global chaos will be created if the amplitude of the electric field becomes greater to allow the broadening to exceed the distance between the levels. (Nogami, K.).

  13. Tunneling Photocurrent Assisted by Interlayer Excitons in Staggered van der Waals Hetero-Bilayers.

    Science.gov (United States)

    Luong, Dinh Hoa; Lee, Hyun Seok; Neupane, Guru Prakash; Roy, Shrawan; Ghimire, Ganesh; Lee, Jin Hee; Vu, Quoc An; Lee, Young Hee

    2017-09-01

    Vertically stacked van der Waals (vdW) heterostructures have been suggested as a robust platform for studying interfacial phenomena and related electric/optoelectronic devices. While the interlayer Coulomb interaction mediated by the vdW coupling has been extensively studied for carrier recombination processes in a diode transport, its correlation with the interlayer tunneling transport has not been elucidated. Here, a contrast is reported between tunneling and drift photocurrents tailored by the interlayer coupling strength in MoSe 2 /MoS 2 hetero-bilayers (HBs). The interfacial coupling modulated by thermal annealing is identified by the interlayer phonon coupling in Raman spectra and the emerging interlayer exciton peak in photoluminescence spectra. In strongly coupled HBs, positive photocurrents are observed owing to the inelastic band-to-band tunneling assisted by interlayer excitons that prevail over exciton recombinations. By contrast, weakly coupled HBs exhibit a negative photovoltaic diode behavior, manifested as a drift current without interlayer excitonic emissions. This study sheds light on tailoring the tunneling transport for numerous optoelectronic HB devices. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  14. Quantum reflection times and space shifts for Casimir-van der Waals potential tails

    International Nuclear Information System (INIS)

    Jurisch, Alexander; Friedrich, Harald

    2004-01-01

    When cold atoms approach a surface, they can be quantum reflected by quantal regions in the tail of the atom-surface potential. We study the phase of the reflection amplitude for Casimir-van der Waals potential tails, depending on the critical parameter ρ=ρ(C 3 ,C 4 ), which describes the relative importance of the -C 3 /r 3 and -C 4 /r 4 parts of the potential. The phase is related to observable kinematic quantities, the space and time shifts, the reflected atom experiences. We study three different models for the shape of the potential between the asymptotic limits and observe that the phases are more sensitive to the potential shape than the quantum reflection probabilities. At threshold, there are always time delays in comparison to the free movement. This is in contrast to the classical movement, which shows time gains. Further above threshold, the quantum reflected atom experiences a time gain relative to free motion, but this time gain is generally smaller than that of the classical particle

  15. The influence of non-CO2 forcings on cumulative carbon emissions budgets

    Science.gov (United States)

    Tokarska, Katarzyna B.; Gillett, Nathan P.; Arora, Vivek K.; Lee, Warren G.; Zickfeld, Kirsten

    2018-03-01

    Carbon budgets provide a useful tool for policymakers to help meet the global climate targets, as they specify total allowable carbon emissions consistent with limiting warming to a given temperature threshold. Non-CO2 forcings have a net warming effect in the Representative Concentration Pathways (RCP) scenarios, leading to reductions in remaining carbon budgets based on CO2 forcing alone. Carbon budgets consistent with limiting warming to below 2.0 °C, with and without accounting for the effects of non-CO2 forcings, were assessed in inconsistent ways by the Intergovernmental Panel on Climate Change (IPCC), making the effects of non-CO2 forcings hard to identify. Here we use a consistent approach to compare 1.5 °C and 2.0 °C carbon budgets with and without accounting for the effects of non-CO2 forcings, using CO2-only and RCP8.5 simulations. The median allowable carbon budgets for 1.5 °C and 2.0 °C warming are reduced by 257 PgC and 418 PgC, respectively, and the uncertainty ranges on the budgets are reduced by more than a factor of two when accounting for the net warming effects of non-CO2 forcings. While our overall results are consistent with IPCC, we use a more robust methodology, and explain the narrower uncertainty ranges of carbon budgets when non-CO2 forcings are included. We demonstrate that most of the reduction in carbon budgets is a result of the direct warming effect of the non-CO2 forcings, with a secondary contribution from the influence of the non-CO2 forcings on the carbon cycle. Such carbon budgets are expected to play an increasingly important role in climate change mitigation, thus understanding the influence of non-CO2 forcings on these budgets and their uncertainties is critical.

  16. Influence of temperature and salinity on hydrodynamic forces

    Directory of Open Access Journals (Sweden)

    A. Escobar

    2016-12-01

    Full Text Available The purpose of this study is to introduce an innovative approach to offshore engineering so as to take variations in sea temperature and salinity into account in the calculation of hydrodynamic forces. With this in mind, a thorough critical analysis of the influence of sea temperature and salinity on hydrodynamic forces on piles like those used nowadays in offshore wind farms will be carried out. This influence on hydrodynamic forces occurs through a change in water density and viscosity due to temperature and salinity variation. Therefore, the aim here is to observe whether models currently used to estimate wave forces on piles are valid for different ranges of sea temperature and salinity apart from observing the limit when diffraction or nonlinear effects arise combining both effects with the magnitude of the pile diameter. Hence, specific software has been developed to simulate equations in fluid mechanics taking into account nonlinear and diffraction effects. This software enables wave produced forces on a cylinder supported on the sea bed to be calculated. The study includes observations on the calculation model's sensitivity as to a variation in the cylinder's diameter, on the one hand and, on the other, as to temperature and salinity variation. This software will enable an iterative calculation to be made for finding out the shape the pressure wave caused when a wave passes over will have for different pile diameters and water with different temperature and salinity.

  17. Photochemistry of xenon-halogen Van der Waals complexes (X2 = Cl2, Br2, I2): evidence for the intermediate states in the (Xe-X2)*→ XeX* + X reaction

    International Nuclear Information System (INIS)

    Boivineau, Michel

    1987-01-01

    This research thesis addresses the reactivity of excited states of xenon-halogen Van der Waals complexes (Cl 2 , Br 2 , I 2 ) submitted to a multi-photonic excitation. The objective of this study is, by means of a specific experimental approach, to highlight the R*+ X 2 *- to better understand the reaction mechanism, and to study the reactivity of rare gas/halogen systems depending on the halogen nature. After having reported a bibliographical study on each studied system, the author describes the experimental system, reports and discusses experimental results obtained on the different complex systems (chlorine-, bromine- or iodine-based). He finally comments a possible and original application of these works in the development of an excimer laser with a new active medium (the rare gas/halogen Van der Waals complex) which would allow a continuous operation and an easy discharge production [fr

  18. Breaking the Ice: Career Development Activities for Accounting Students

    Science.gov (United States)

    Kilpatrick, Bob G.; Wilburn, Nancy L.

    2010-01-01

    This paper describes two co-curricular career development activities, mock interviews and speed networking that we provide for accounting majors at our university. The driving force behind both activities was to increase comfort levels for students when interacting with professionals and to enhance their job interview and networking skills.…

  19. Features calibration of the dynamic force transducers

    Science.gov (United States)

    Sc., M. Yu Prilepko D.; Lysenko, V. G.

    2018-04-01

    The article discusses calibration methods of dynamic forces measuring instruments. The relevance of work is dictated by need to valid definition of the dynamic forces transducers metrological characteristics taking into account their intended application. The aim of this work is choice justification of calibration method, which provides the definition dynamic forces transducers metrological characteristics under simulation operating conditions for determining suitability for using in accordance with its purpose. The following tasks are solved: the mathematical model and the main measurements equation of calibration dynamic forces transducers by load weight, the main budget uncertainty components of calibration are defined. The new method of dynamic forces transducers calibration with use the reference converter “force-deformation” based on the calibrated elastic element and measurement of his deformation by a laser interferometer is offered. The mathematical model and the main measurements equation of the offered method is constructed. It is shown that use of calibration method based on measurements by the laser interferometer of calibrated elastic element deformations allows to exclude or to considerably reduce the uncertainty budget components inherent to method of load weight.

  20. Exploration of the NH3-H2 van der Waals interaction by high level ab initio calculations

    International Nuclear Information System (INIS)

    Mladenovic, Mirjana; Lewerenz, Marius; Cilpa, Geraldine; Rosmus, Pavel; Chambaud, Gilberte

    2008-01-01

    The intermolecular potential energy for the van der Waals complex between ammonia and the hydrogen molecule has been studied by means of the coupled cluster CCSD(T) method and aug-cc-pVXZ (X = D, T, Q, 5) basis sets and with inclusion of the Boys and Bernardi counterpoise correction. For sufficiently large basis sets the only true electronic minimum energy structure of NH 3 -H 2 is found to possess C 3v point group symmetry. Various minimum energy paths for the relative motion of NH 3 and H 2 are analysed in order to understand the topography of the intermolecular potential. The complete basis set limit for the electronic dissociation energy is estimated to be about 253 cm -1 at the CCSD(T) level

  1. Bandgap engineering in van der Waals heterostructures of blue phosphorene and MoS{sub 2}: A first principles calculation

    Energy Technology Data Exchange (ETDEWEB)

    Zhang, Z.Y. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Si, M.S., E-mail: sims@lzu.edu.cn [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Peng, S.L. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China); Zhang, F. [Key Lab of Photovoltaic Materials of Henan Province, Henan University, Kaifeng 475001 (China); Wang, Y.H.; Xue, D.S. [Key Laboratory for Magnetism and Magnetic Materials of the Ministry of Education, Lanzhou University, Lanzhou 730000 (China)

    2015-11-15

    Blue phosphorene (BP) was theoretically predicted to be thermally stable recently. Considering its similar in-layer hexagonal lattice to MoS{sub 2}, MoS{sub 2} could be an appropriate substrate to grow BP in experiments. In this work, the van der Waals (vdW) heterostructures are constructed by stacking BP on top of MoS{sub 2}. The thermal stability and electronic structures are evaluated based on first principles calculations with vdW-corrected exchange-correlation functional. The formation of the heterostructures is demonstrated to be exothermic and the most stable stacking configuration is confirmed. The heterostructures BP/MoS{sub 2} preserve both the properties of BP and MoS{sub 2} but exhibit relatively narrower bandgaps due to the interlayer coupling effect. The band structures can be further engineered by applying external electric fields. An indirect–direct bandgap transition in bilayer BP/MoS{sub 2} is demonstrated to be controlled by the symmetry property of the built-in electric dipole fields. - Graphical abstract: An indirect-direct band gap transition occurs in van der Waals heterostructure of MoS{sub 2}/BP under external electric fields which is demonstrated to be controlled by the symmetry of the built-in electric dipole fields. - Highlights: • The stacking of heterostructures of BP/MoS{sub 2} is demonstrated to be exothermic. • This suggests that it is possible to grow BP using MoS{sub 2} as the substrate. • The band structures of the heterostructures are exploited. • It realizes an indirect–direct gap transition under external electric fields. • The symmetry of the built-in electric dipole fields controls such gap transition.

  2. Axial and Radial Forces of Cross-Bridges Depend on Lattice Spacing

    Science.gov (United States)

    Williams, C. David; Regnier, Michael; Daniel, Thomas L.

    2010-01-01

    Nearly all mechanochemical models of the cross-bridge treat myosin as a simple linear spring arranged parallel to the contractile filaments. These single-spring models cannot account for the radial force that muscle generates (orthogonal to the long axis of the myofilaments) or the effects of changes in filament lattice spacing. We describe a more complex myosin cross-bridge model that uses multiple springs to replicate myosin's force-generating power stroke and account for the effects of lattice spacing and radial force. The four springs which comprise this model (the 4sXB) correspond to the mechanically relevant portions of myosin's structure. As occurs in vivo, the 4sXB's state-transition kinetics and force-production dynamics vary with lattice spacing. Additionally, we describe a simpler two-spring cross-bridge (2sXB) model which produces results similar to those of the 4sXB model. Unlike the 4sXB model, the 2sXB model requires no iterative techniques, making it more computationally efficient. The rate at which both multi-spring cross-bridges bind and generate force decreases as lattice spacing grows. The axial force generated by each cross-bridge as it undergoes a power stroke increases as lattice spacing grows. The radial force that a cross-bridge produces as it undergoes a power stroke varies from expansive to compressive as lattice spacing increases. Importantly, these results mirror those for intact, contracting muscle force production. PMID:21152002

  3. Gaining insight into the physics of dynamic atomic force microscopy in complex environments using the VEDA simulator

    Science.gov (United States)

    Kiracofe, Daniel; Melcher, John; Raman, Arvind

    2012-01-01

    Dynamic atomic force microscopy (dAFM) continues to grow in popularity among scientists in many different fields, and research on new methods and operating modes continues to expand the resolution, capabilities, and types of samples that can be studied. But many promising increases in capability are accompanied by increases in complexity. Indeed, interpreting modern dAFM data can be challenging, especially on complicated material systems, or in liquid environments where the behavior is often contrary to what is known in air or vacuum environments. Mathematical simulations have proven to be an effective tool in providing physical insight into these non-intuitive systems. In this article we describe recent developments in the VEDA (virtual environment for dynamic AFM) simulator, which is a suite of freely available, open-source simulation tools that are delivered through the cloud computing cyber-infrastructure of nanoHUB (www.nanohub.org). Here we describe three major developments. First, simulations in liquid environments are improved by enhancements in the modeling of cantilever dynamics, excitation methods, and solvation shell forces. Second, VEDA is now able to simulate many new advanced modes of operation (bimodal, phase-modulation, frequency-modulation, etc.). Finally, nineteen different tip-sample models are available to simulate the surface physics of a wide variety different material systems including capillary, specific adhesion, van der Waals, electrostatic, viscoelasticity, and hydration forces. These features are demonstrated through example simulations and validated against experimental data, in order to provide insight into practical problems in dynamic AFM.

  4. Realising traceable electrostatic forces despite non-linear balance motion

    International Nuclear Information System (INIS)

    Stirling, Julian; Shaw, Gordon A

    2017-01-01

    Direct realisation of force, traceable to fundamental constants via electromagnetic balances, is a key goal of the proposed redefinition of the international system of units (SI). This will allow small force metrology to be performed using an electrostatic force balance (EFB) rather than subdivision of larger forces. Such a balance uses the electrostatic force across a capacitor to balance an external force. In this paper we model the capacitance of a concentric cylinder EFB design as a function of the displacement of its free electrode, accounting for the arcuate motion produced by parallelogram linkages commonly used in EFB mechanisms. From this model we suggest new fitting procedures to reduce uncertainties arising from non-linear motion as well as methods to identify misalignment of the mechanism. Experimental studies on both a test capacitor and the NIST EFB validate the model. (paper)

  5. Quantifying electronic band interactions in van der Waals materials using angle-resolved reflected-electron spectroscopy.

    Science.gov (United States)

    Jobst, Johannes; van der Torren, Alexander J H; Krasovskii, Eugene E; Balgley, Jesse; Dean, Cory R; Tromp, Rudolf M; van der Molen, Sense Jan

    2016-11-29

    High electron mobility is one of graphene's key properties, exploited for applications and fundamental research alike. Highest mobility values are found in heterostructures of graphene and hexagonal boron nitride, which consequently are widely used. However, surprisingly little is known about the interaction between the electronic states of these layered systems. Rather pragmatically, it is assumed that these do not couple significantly. Here we study the unoccupied band structure of graphite, boron nitride and their heterostructures using angle-resolved reflected-electron spectroscopy. We demonstrate that graphene and boron nitride bands do not interact over a wide energy range, despite their very similar dispersions. The method we use can be generally applied to study interactions in van der Waals systems, that is, artificial stacks of layered materials. With this we can quantitatively understand the 'chemistry of layers' by which novel materials are created via electronic coupling between the layers they are composed of.

  6. 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.

  7. Chemical free device fabrication of two dimensional van der Waals materials based transistors by using one-off stamping

    International Nuclear Information System (INIS)

    Lee, Young Tack; Choi, Won Kook; Hwang, Do Kyung

    2016-01-01

    We report on a chemical free one-off imprinting method to fabricate two dimensional (2D) van der Waals (vdWs) materials based transistors. Such one-off imprinting technique is the simplest and effective way to prevent unintentional chemical reaction or damage of 2D vdWs active channel during device fabrication process. 2D MoS 2 nanosheets based transistors with a hexagonal-boron-nitride (h-BN) passivation layer, prepared by one-off imprinting, show negligible variations of transfer characteristics after chemical vapor deposition process. In addition, this method enables the fabrication of all 2D MoS 2 transistors consisting of h-BN gate insulator, and graphene source/drain and gate electrodes without any chemical damage.

  8. van der Waals heterostructures of germanene, stanene, and silicene with hexagonal boron nitride and their topological domain walls

    Science.gov (United States)

    Wang, Maoyuan; Liu, Liping; Liu, Cheng-Cheng; Yao, Yugui

    2016-04-01

    We investigate van der Waals (vdW) heterostructures made of germanene, stanene, or silicene with hexagonal boron nitride (h-BN). The intriguing topological properties of these buckled honeycomb materials can be maintained and further engineered in the heterostructures, where the competition between the substrate effect and external electric fields can be used to control the tunable topological phase transitions. Using such heterostructures as building blocks, various vdW topological domain walls (DW) are designed, along which there exist valley polarized quantum spin Hall edge states or valley-contrasting edge states which are protected by valley(spin)- resolved topological charges and can be tailored by the patterning of the heterojunctions and by external fields.

  9. Van der Waals coefficients beyond the classical shell model

    Energy Technology Data Exchange (ETDEWEB)

    Tao, Jianmin, E-mail: jianmint@sas.upenn.edu [Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19104-6323 (United States); Fang, Yuan; Hao, Pan [Department of Physics and Engineering Physics, Tulane University, New Orleans, Louisiana 70118 (United States); Scuseria, G. E. [Department of Chemistry and Department of Physics and Astronomy, Rice University, Houston, Texas 77251-1892, USA and Department of Chemistry, Faculty of Science, King Abdulaziz University, Jeddah 21589 (Saudi Arabia); Ruzsinszky, Adrienn; Perdew, John P. [Department of Physics, Temple University, Philadelphia, Pennsylvania 19122 (United States)

    2015-01-14

    Van der Waals (vdW) coefficients can be accurately generated and understood by modelling the dynamic multipole polarizability of each interacting object. Accurate static polarizabilities are the key to accurate dynamic polarizabilities and vdW coefficients. In this work, we present and study in detail a hollow-sphere model for the dynamic multipole polarizability proposed recently by two of the present authors (JT and JPP) to simulate the vdW coefficients for inhomogeneous systems that allow for a cavity. The inputs to this model are the accurate static multipole polarizabilities and the electron density. A simplification of the full hollow-sphere model, the single-frequency approximation (SFA), circumvents the need for a detailed electron density and for a double numerical integration over space. We find that the hollow-sphere model in SFA is not only accurate for nanoclusters and cage molecules (e.g., fullerenes) but also yields vdW coefficients among atoms, fullerenes, and small clusters in good agreement with expensive time-dependent density functional calculations. However, the classical shell model (CSM), which inputs the static dipole polarizabilities and estimates the static higher-order multipole polarizabilities therefrom, is accurate for the higher-order vdW coefficients only when the interacting objects are large. For the lowest-order vdW coefficient C{sub 6}, SFA and CSM are exactly the same. The higher-order (C{sub 8} and C{sub 10}) terms of the vdW expansion can be almost as important as the C{sub 6} term in molecular crystals. Application to a variety of clusters shows that there is strong non-additivity of the long-range vdW interactions between nanoclusters.

  10. Accounting for Systems Analysts in the 21st Century

    Science.gov (United States)

    Giordano, Thomas; McAleer, Brenda; Szakas, Joseph S.

    2010-01-01

    Computer Information System (CIS) majors are required to successfully complete an introductory accounting course. Given the current forces in the financial world, the appropriateness of this course warrants scrutiny as to whether it properly serves the student, and the degree to which it continues to meet the IS 2002 outcomes. The current business…

  11. Ultrathin Topological Insulator Bi 2 Se 3 Nanoribbons Exfoliated by Atomic Force Microscopy

    KAUST Repository

    Hong, Seung Sae; Kundhikanjana, Worasom; Cha, Judy J.; Lai, Keji; Kong, Desheng; Meister, Stefan; Kelly, Michael A.; Shen, Zhi-Xun; Cui, Yi

    2010-01-01

    Ultrathin topological insulator nanostructures, in which coupling between top and bottom surface states takes place, are of great intellectual and practical importance. Due to the weak van der Waals interaction between adjacent quintuple layers (QLs), the layered bismuth selenide (Bi2Se 3), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi2Se3 nanoribbons (>50 QLs) by an atomic force microscope (AFM) tip down to a single QL. Microwave impedance microscopy is employed to map out the local conductivity of such ultrathin nanoribbons, showing drastic difference in sheet resistance between 1-2 QLs and 4-5 QLs. Transport measurement carried out on an exfoliated (>5 QLs) Bi2Se3 device shows nonmetallic temperature dependence of resistance, in sharp contrast to the metallic behavior seen in thick (>50 QLs) ribbons. These AFM-exfoliated thin nanoribbons afford interesting candidates for studying the transition from quantum spin Hall surface to edge states. © 2010 American Chemical Society.

  12. Ultrathin Topological Insulator Bi 2 Se 3 Nanoribbons Exfoliated by Atomic Force Microscopy

    KAUST Repository

    Hong, Seung Sae

    2010-08-11

    Ultrathin topological insulator nanostructures, in which coupling between top and bottom surface states takes place, are of great intellectual and practical importance. Due to the weak van der Waals interaction between adjacent quintuple layers (QLs), the layered bismuth selenide (Bi2Se 3), a single Dirac-cone topological insulator with a large bulk gap, can be exfoliated down to a few QLs. In this paper, we report the first controlled mechanical exfoliation of Bi2Se3 nanoribbons (>50 QLs) by an atomic force microscope (AFM) tip down to a single QL. Microwave impedance microscopy is employed to map out the local conductivity of such ultrathin nanoribbons, showing drastic difference in sheet resistance between 1-2 QLs and 4-5 QLs. Transport measurement carried out on an exfoliated (>5 QLs) Bi2Se3 device shows nonmetallic temperature dependence of resistance, in sharp contrast to the metallic behavior seen in thick (>50 QLs) ribbons. These AFM-exfoliated thin nanoribbons afford interesting candidates for studying the transition from quantum spin Hall surface to edge states. © 2010 American Chemical Society.

  13. Medicare changes create accounting, reporting, and auditing problems. Task Force on Federal Health Care Legislation, American Institute of Certified Public Accountants.

    Science.gov (United States)

    1984-11-01

    Hospital auditors and financial officers must adjust and react to the changing financial healthcare environment brought about by PPS. A close review of accounting systems, reporting methods, auditing procedures, and internal control systems should be made to determine that assets are safe-guarded and financial information is presented in conformity with GAAP. This article identified new problems and suggested solutions. Old tasks may no longer be necessary. For example, retroactive adjustments are not as important as they used to be. Estimates for capital and outpatient costs may continue to be required, but elaborate cost-finding techniques may no longer be necessary to estimate retroactive adjustments for reimbursable items. We recommend that prior to beginning an audit of a hospital's financial statements, each hospital's financial officers and its auditors discuss the possible accounting, reporting, and auditing implications as a result of PPS.

  14. Adhesion of Spores of Bacillus thuringiensis on a Planar Surface

    Energy Technology Data Exchange (ETDEWEB)

    Chung, Eunhyea [Georgia Institute of Technology; Kweon, Hyojin [Georgia Institute of Technology; Yiacoumi, Sotira [Georgia Institute of Technology; Lee, Ida [University of Tennessee, Knoxville (UTK); Joy, David Charles [ORNL; Palumbo, Anthony Vito [ORNL; Tsouris, Costas [ORNL

    2010-01-01

    Adhesion of spores of Bacillus thuringiensis (Bt) and spherical silica particles on surfaces was experimentally and theoretically investigated in this study. Topography analysis via atomic force microscopy (AFM) and electron microscopy indicates that Bt spores are rod shaped, {approx}1.3 {mu}m in length and {approx}0.8 {mu}m in diameter. The adhesion force of Bt spores and silica particles on gold-coated glass was measured at various relative humidity (RH) levels by AFM. It was expected that the adhesion force would vary with RH because the individual force components contributing to the adhesion force depend on RH. The adhesion force between a particle and a planar surface in atmospheric environments was modeled as the contribution of three major force components: capillary, van der Waals, and electrostatic interaction forces. Adhesion force measurements for Bt spore (silica particle) and the gold surface system were comparable with calculations. Modeling results show that there is a critical RH value, which depends on the hydrophobicity of the materials involved, below which the water meniscus does not form and the contribution of the capillary force is zero. As RH increases, the van der Waals force decreases while the capillary force increases to a maximum value.

  15. An Observational Assessment of Accountability Systems for Our "Handicapped" Students and Their Impact on Educators.

    Science.gov (United States)

    Kunzweiler, Charles

    1981-01-01

    Present systems of accountability, which require excessive paperwork and force teachers into the "Directive Teaching Model," cause special education teachers to be accountable to the system rather than to self-actualization needs of students. Special education teachers must have the freedom and training to create "unique"…

  16. KEY SKILLS REQUIRED TO COLLEGE PUBLIC ACCOUNTANT FOR MICRO AND SMALL ENTERPRISES OF PERU

    OpenAIRE

    Flores Konja, Adrian Alejandro; Hidalgo Tupia, Manuel Alberto

    2014-01-01

    It is proposed to identify the skills required by the Peruvian SMEs to accounting professionals, and other factors related to the professional work force of Chartered Certified Accountants. To do this, based on professional competencies defined in the Educational Project of our School of Accounting at the University Dean of America, contained in Law 28 951 - Professionalization Act of CPA, and the proposal Tuning America as pattern comparison, there have been survey questionnaires applied to ...

  17. Employability profile of the Peruvian public accountant

    OpenAIRE

    Tarazona, Silvia; Maisch, Elena; Arias, Hernán

    2014-01-01

    The traditional perspective on the Public Accountant's professional services is running out of time and, although such services are still valuable for enterprises, the survival of the latter demands a more open and aggressive professional attitude in this field (Lebrija, 1998). Employability profiles respond to this demand by acknowledging the new abilities required of the labor force, which go beyond professional competencies. It is also these profiles which will allow coping with employment...

  18. Three-body ΛNN force due to Λ-Σ coupling

    International Nuclear Information System (INIS)

    Myint, Khin Swe; Akaishi, Yoshinori

    2003-01-01

    The ΛNN three - body force due to coherent Λ - Σ Coupling effect was derived from realistic Nijmegen model D potential. Repulsive and attractive three - body ΛNN forces were reconcilably accounted. For 5 He, within one - channel description, ΛNN force is largely repulsive and its origin comes from Pauli forbidden terms. Within two - channel description, attractive Pauli allowed terms exist and resulting three - body force is always attractive. Large attractive ΛNN force effect due to coherent Λ - Σ coupling effect is predicted in neutron - rich nuclei. The attractive coherent Λ - Σ coupling effect is largely enhanced at high density neutron matter. The attractive three - body ΛNN force effect is essential dynamics of Λ - Σ coupling while the repulsive Nogami three - body effect arises from Pauli forbidden diagrams. (Y. Kazumata)

  19. Manager’s Perception of the Importance of Environmental Accounting and its Effect on the Quality of Corporate Environmental Accounting Disclosures: Case from Indonesia

    Directory of Open Access Journals (Sweden)

    Lindrianasari Lindrianasari

    2010-06-01

    Full Text Available The purpose of this study is to compare perceptions of managers in Indonesia concerning environmental accounting disclosure with actual environmental accounting disclosure. The value of this research is making an original contribution to develop instrument in exploring managerial perception of environmental accounting disclosure. Samples for this study are corporate managerial from listing companies in the Jakarta Stock Exchange and also annual report companies. This research has developed strategies to measure managerial perceptions of environmental accounting disclosure. Mail surveys design used on this study. Analysis used for testing relationship between managerial perception and environmental accounting disclosure is simple regression test. The dependent sample variable data is the latest data published in Jakarta Stock Exchange. This study finds a positive correlation between managerial perception of environmental accounting disclosure and actual environmental accounting disclosure. This result shows that disclosure quality and several legal sanctions in environmental aspects could be empowerment of regulator pasties to force managers to maintain their pollution and reported their activity also in their annual report. In hence, legitimacy theory is used as an explanation for corporate reactions to threats to its legitimacy vis-á-vis the social contract, while legitimacy theory infers motivation to incorporate environmental accounting disclosure.

  20. A Prolegomenon to the Relation Between Accounting, Language and Ethics

    Directory of Open Access Journals (Sweden)

    C. Edward Arrington

    2007-06-01

    Full Text Available This essay outlines the preliminary structure of a moral ontology of accounting understood as discourse. Tospeak of an ontology of accounting is to speak of the most general features of accounting, those features of itsexistence that are present irrespective of variations in observed “accountings,” of ways in which accountingmanifests itself in lived experience. To speak of a moral ontology is to construe those general features asproducts of human choices and actions which follow from axiological (value-based commitments to pursuethe good and just life, however that life might be understood, and indeed understood differently by differentpersons. Thus a moral ontology stands in distinction from, for example, a naturalistic ontology, one “freedfrom the freedom” of axiological horizons. Within its embeddedness in a moral ontology, the enactment ofaccounting takes empirical form as discourse – as an act of someone saying (writing something aboutsomething to someone else (Ricoeur, 1976; Arrington & Francis, 1993. Thus if we seek to understandaccounting’s force in the world, a force that is always valued and evaluated in terms of consequences for thegood and just life, we get our most general understandings from attending to the ethics of language and itsuse. My task in this essay is to introduce the structure of what the elements of accounting’s relation to theethics of language and its use might be. Expanding upon that structure remains a task for future work.