WorldWideScience

Sample records for generation force field

  1. Field measurement of basal forces generated by erosive debris flows

    Science.gov (United States)

    McCoy, S.W.; Tucker, G.E.; Kean, J.W.; Coe, J.A.

    2013-01-01

    It has been proposed that debris flows cut bedrock valleys in steeplands worldwide, but field measurements needed to constrain mechanistic models of this process remain sparse due to the difficulty of instrumenting natural flows. Here we present and analyze measurements made using an automated sensor network, erosion bolts, and a 15.24 cm by 15.24 cm force plate installed in the bedrock channel floor of a steep catchment. These measurements allow us to quantify the distribution of basal forces from natural debris‒flow events that incised bedrock. Over the 4 year monitoring period, 11 debris‒flow events scoured the bedrock channel floor. No clear water flows were observed. Measurements of erosion bolts at the beginning and end of the study indicated that the bedrock channel floor was lowered by 36 to 64 mm. The basal force during these erosive debris‒flow events had a large‒magnitude (up to 21 kN, which was approximately 50 times larger than the concurrent time‒averaged mean force), high‒frequency (greater than 1 Hz) fluctuating component. We interpret these fluctuations as flow particles impacting the bed. The resulting variability in force magnitude increased linearly with the time‒averaged mean basal force. Probability density functions of basal normal forces were consistent with a generalized Pareto distribution, rather than the exponential distribution that is commonly found in experimental and simulated monodispersed granular flows and which has a lower probability of large forces. When the bed sediment thickness covering the force plate was greater than ~ 20 times the median bed sediment grain size, no significant fluctuations about the time‒averaged mean force were measured, indicating that a thin layer of sediment (~ 5 cm in the monitored cases) can effectively shield the subjacent bed from erosive impacts. Coarse‒grained granular surges and water‒rich, intersurge flow had very similar basal force distributions despite

  2. Generation of magnetic fields by the ponderomotive force of electromagnetic waves in dense plasmas

    OpenAIRE

    Shukla, P K; Shukla, Nitin; Stenflo, Lennart

    2010-01-01

    We show that the non-stationary ponderomotive force of a, large-amplitude electromagnetic move in a very dense quantum plasma wall streaming degenerate electrons can spontaneously create d.c. magnetic fields. The present result can account for the seed magnetic fields in compact astrophysical objects and in the next-generation intense laser-solid density, plasma interaction experiments.

  3. CHARMM-GUI ligand reader and modeler for CHARMM force field generation of small molecules.

    Science.gov (United States)

    Kim, Seonghoon; Lee, Jumin; Jo, Sunhwan; Brooks, Charles L; Lee, Hui Sun; Im, Wonpil

    2017-06-05

    Reading ligand structures into any simulation program is often nontrivial and time consuming, especially when the force field parameters and/or structure files of the corresponding molecules are not available. To address this problem, we have developed Ligand Reader & Modeler in CHARMM-GUI. Users can upload ligand structure information in various forms (using PDB ID, ligand ID, SMILES, MOL/MOL2/SDF file, or PDB/mmCIF file), and the uploaded structure is displayed on a sketchpad for verification and further modification. Based on the displayed structure, Ligand Reader & Modeler generates the ligand force field parameters and necessary structure files by searching for the ligand in the CHARMM force field library or using the CHARMM general force field (CGenFF). In addition, users can define chemical substitution sites and draw substituents in each site on the sketchpad to generate a set of combinatorial structure files and corresponding force field parameters for throughput or alchemical free energy simulations. Finally, the output from Ligand Reader & Modeler can be used in other CHARMM-GUI modules to build a protein-ligand simulation system for all supported simulation programs, such as CHARMM, NAMD, GROMACS, AMBER, GENESIS, LAMMPS, Desmond, OpenMM, and CHARMM/OpenMM. Ligand Reader & Modeler is available as a functional module of CHARMM-GUI at http://www.charmm-gui.org/input/ligandrm. © 2017 Wiley Periodicals, Inc. © 2017 Wiley Periodicals, Inc.

  4. An efficient and numerically stable procedure for generating sextic force fields in normal mode coordinates.

    Science.gov (United States)

    Sibaev, M; Crittenden, D L

    2016-06-01

    In this paper, we outline a general, scalable, and black-box approach for calculating high-order strongly coupled force fields in rectilinear normal mode coordinates, based upon constructing low order expansions in curvilinear coordinates with naturally limited mode-mode coupling, and then transforming between coordinate sets analytically. The optimal balance between accuracy and efficiency is achieved by transforming from 3 mode representation quartic force fields in curvilinear normal mode coordinates to 4 mode representation sextic force fields in rectilinear normal modes. Using this reduced mode-representation strategy introduces an error of only 1 cm(-1) in fundamental frequencies, on average, across a sizable test set of molecules. We demonstrate that if it is feasible to generate an initial semi-quartic force field in curvilinear normal mode coordinates from ab initio data, then the subsequent coordinate transformation procedure will be relatively fast with modest memory demands. This procedure facilitates solving the nuclear vibrational problem, as all required integrals can be evaluated analytically. Our coordinate transformation code is implemented within the extensible PyPES library program package, at http://sourceforge.net/projects/pypes-lib-ext/.

  5. Generation of mechanical force by grafted polyelectrolytes in an electric field: application to polyelectrolyte-based nano-devices

    Science.gov (United States)

    Brilliantov, N. V.; Budkov, Yu. A.; Seidel, C.

    2016-11-01

    We analyse theoretically and by means of molecular dynamics (MD) simulations the generation of mechanical force by a polyelectrolyte (PE) chain grafted to a plane. The PE is exposed to an external electric field that favours its adsorption on the plane. The free end of the chain is linked to a deformable target body. By varying the field, one can alter the length of the non-adsorbed part of the chain. This entails variation of the deformation of the target body and hence variation of the force arising in the body. Our theoretical predictions for the generated force are in very good agreement with the MD data. Using the theory developed for the generated force, we study the effectiveness of possible PE-based nano-vices, composed of two clenching planes connected by PEs and exposed to an external electric field. We exploit the Cundall-Strack solid friction model to describe the friction between a particle and the clenching planes. We compute the diffusion coefficient of a clenched particle and show that it drastically decreases even in weak applied fields. This demonstrates the efficacy of the PE-based nano-vices, which may be a possible alternative to the existing nanotube nano-tweezers and optical tweezers. This article is part of the themed issue 'Multiscale modelling at the physics-chemistry-biology interface'.

  6. Many flaked particles generated by electric field stress working as an impulsive force in mass-production plasma etching equipment

    Science.gov (United States)

    Kasashima, Yuji; Uesugi, Fumihiko

    2015-09-01

    Particles generated in plasma etching significantly lower production yield. In plasma etching, etching reaction products adhere to the inner chamber walls, gradually forming films, and particles are generated by flaking of the deposited films due to electric field stress that acts boundary between the inner wall and the film. In this study, we have investigated the mechanism of instantaneous generation of many flaked particles using the mass-production reactive ion etching equipment. Particles, which flake off from the films on the ground electrode, are detected by the in-situ particle monitoring system using a sheet-shaped laser beam. The results indicate that the deposited films are severely damaged and flake off as numerous particles when the floating potential at the inner wall suddenly changes. This is because the rapid change in floating potential, observed when unusual wafer movement and micro-arc discharge occur, causes electric field stress working as an impulsive force. The films are easily detached by the impulsive force and many flaked particles are instantaneously generated. This mechanism can occur on not only a ground electrode but a chamber walls, and cause serious contamination in mass-production line. This work was partially supported by JSPS KAKENHI Grant Number B 26870903.

  7. Electro-hydrodynamic force field and flow patterns generated by a DC corona discharge in the air

    Science.gov (United States)

    Monrolin, Nicolas; Plouraboue, Franck; Praud, Olivier

    2016-11-01

    Ionic wind refers to the electro-convection of ionised air between high voltage electrodes. Microscopic ion-neutral collisions are responsible for momentum transfer from accelerated ions, subjected to the electric field, to the neutral gas molecules resulting in a macroscopic airflow acceleration. In the past decades it has been investigated for various purposes from food drying through aerodynamic flow control and eventually laptop cooling. One consequence of air acceleration between the electrodes is thrust generation, often referred to as the Biefeld-Brown effect or electro-hydrodynamic thrust. In this experimental study, the ionic wind velocity field is measured with the PIV method. From computing the acceleration of the air we work out the electrostatic force field for various electrodes configurations. This enables an original direct evaluation of the force distribution as well as the influence of electrodes shape and position. Thrust computation based on the flow acceleration are compared with digital scale measurements. Complex flow features are highlighted such as vortex shedding, indicating that aerodynamic effects may play a significant role. Furthermore, the aerodynamic drag force exerted on the electrodes is quantified by choosing an appropriate control volume. Authors thank Region Midi-Pyrenee and CNES Launcher Directorate for financial support.

  8. Polarizable force fields.

    Science.gov (United States)

    Antila, Hanne S; Salonen, Emppu

    2013-01-01

    This chapter provides an overview of the most common methods for including an explicit description of electronic polarization in molecular mechanics force fields: the induced point dipole, shell, and fluctuating charge models. The importance of including polarization effects in biomolecular simulations is discussed, and some of the most important achievements in the development of polarizable biomolecular force fields to date are highlighted.

  9. Development of a Polarizable Force Field For Proteins via Ab Initio Quantum Chemistry: First Generation Model and Gas Phase Tests

    Science.gov (United States)

    KAMINSKI, GEORGE A.; STERN, HARRY A.; BERNE, B. J.; FRIESNER, RICHARD A.; CAO, YIXIANG X.; MURPHY, ROBERT B.; ZHOU, RUHONG; HALGREN, THOMAS A.

    2014-01-01

    We present results of developing a methodology suitable for producing molecular mechanics force fields with explicit treatment of electrostatic polarization for proteins and other molecular system of biological interest. The technique allows simulation of realistic-size systems. Employing high-level ab initio data as a target for fitting allows us to avoid the problem of the lack of detailed experimental data. Using the fast and reliable quantum mechanical methods supplies robust fitting data for the resulting parameter sets. As a result, gas-phase many-body effects for dipeptides are captured within the average RMSD of 0.22 kcal/mol from their ab initio values, and conformational energies for the di- and tetrapeptides are reproduced within the average RMSD of 0.43 kcal/mol from their quantum mechanical counterparts. The latter is achieved in part because of application of a novel torsional fitting technique recently developed in our group, which has already been used to greatly improve accuracy of the peptide conformational equilibrium prediction with the OPLS-AA force field.1 Finally, we have employed the newly developed first-generation model in computing gas-phase conformations of real proteins, as well as in molecular dynamics studies of the systems. The results show that, although the overall accuracy is no better than what can be achieved with a fixed-charges model, the methodology produces robust results, permits reasonably low computational cost, and avoids other computational problems typical for polarizable force fields. It can be considered as a solid basis for building a more accurate and complete second-generation model. PMID:12395421

  10. Effect of Magnetic Field on Entropy Generation Due to Laminar Forced Convection Past a Horizontal Flat Plate

    Directory of Open Access Journals (Sweden)

    Moh'd A. Al-Nimr

    2004-06-01

    Full Text Available Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow past a horizontal plate was numerically investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effect of various dimensionless parameters, such as Hartmann number (Ha, Eckert number (Ec, Prandtl number (Pr, Joule heating parameter (R and the free stream temperature parameter (θ∞ on the entropy generation characteristics is analyzed. The dimensionless governing equations in Cartesian coordinate were solved by an implicit finite difference technique. The solutions were carried out for Ha2=0.5-3, Ec=0.01-0.05, Pr=1-5 and θ∞=1.1-2.5. It was found that, the entropy generation increased with increasing Ha, Ec and R. While, increasing the free stream temperature parameter, and Prandtl number tend to decrease the local entropy generation.

  11. A method for mechanical generation of radio frequency fields in nuclear magnetic resonance force microscopy

    CERN Document Server

    Wagenaar, J J T; Donkersloot, R J; Marsman, F; de Wit, M; Bossoni, L; Oosterkamp, T H

    2016-01-01

    We present an innovative method for magnetic resonance force microscopy (MRFM) with ultra-low dissipation, by using the higher modes of the mechanical detector as radio frequency (rf) source. This method allows MRFM on samples without the need to be close to an rf source. Furthermore, since rf sources require currents that give dissipation, our method enables nuclear magnetic resonance experiments at ultra-low temperatures. Removing the need for an on-chip rf source is an important step towards a MRFM which can be widely used in condensed matter physics.

  12. The variational explicit polarization potential and analytical first derivative of energy: Towards a next generation force field

    Science.gov (United States)

    Xie, Wangshen; Song, Lingchun; Truhlar, Donald G.; Gao, Jiali

    2008-01-01

    A previous article proposed an electronic structure-based polarizable potential, called the explicit polarization (X-POL) potential, to treat many-body polarization and charge delocalization effects in polypeptides. Here, we present a variational version of the X-POL potential, in which the wave function of the entire molecular system is variationally optimized to yield the minimum total electronic energy. This allows the calculation of analytic gradients, a necessity for efficient molecular dynamics simulations. In this paper, the detailed derivations of the Fock matrix and analytic force are presented and discussed. The calculations involve a double self-consistent-field procedure in which the wave function of each fragment is self-consistently optimized in the presence of other fragments, and in addition the polarization of the entire system is self-consistently optimized. The variational X-POL potential has been implemented in the Chemistry at Harvard Molecular Mechanics (CHARMM) package and tested successfully for small model compounds. PMID:18570492

  13. Application of Magnetic Force Generator in Cementation

    Institute of Scientific and Technical Information of China (English)

    2000-01-01

    The paper introduces a new behavior of the heat treatment technique that is cementation with magnetic force generator (MFHS). The result shows that due to the strong magnetic field action of MFHS on seep means, the energy and activity of active atom are increased, which accelerates interface activating and atoms diffusing, forms action of speed-up seeping. This technique features are Iow in energy consuming, and high in seeping efficiency.

  14. Computer-Controlled Force Generator Project

    Data.gov (United States)

    National Aeronautics and Space Administration — TDA Research, Inc proposes to develop a compact, low power, high life-cycle computer controlled Programmable Force Generator (PFG) that can generate any force...

  15. Combining configurational energies and forces for molecular force field optimization

    Science.gov (United States)

    Vlcek, Lukas; Sun, Weiwei; Kent, Paul R. C.

    2017-10-01

    While quantum chemical simulations have been increasingly used as an invaluable source of information for atomistic model development, the high computational expenses typically associated with these techniques often limit thorough sampling of the systems of interest. It is therefore of great practical importance to use all available information as efficiently as possible, and in a way that allows for consistent addition of constraints that may be provided by macroscopic experiments. Here we propose a simple approach that combines information from configurational energies and forces generated in a molecular dynamics simulation to increase the effective number of samples. Subsequently, this information is used to optimize a molecular force field by minimizing the statistical distance similarity metric. We illustrate the methodology on an example of a trajectory of configurations generated in equilibrium molecular dynamics simulations of argon and water and compare the results with those based on the force matching method.

  16. Nanometric alternating magnetic field generator.

    Science.gov (United States)

    Espejo, A P; Tejo, F; Vidal-Silva, N; Escrig, J

    2017-07-05

    In this work we introduce an alternating magnetic field generator in a cylindrical nanostructure. This field appears due to the rotation of a magnetic domain wall located at some position, generating a magnetic region that varies its direction of magnetization alternately, thus inducing an alternating magnetic flux in its vicinity. This phenomenon occurs due to the competition between a spin-polarized current and a magnetic field, which allows to control both the angular velocity and the pinning position of the domain wall. As proof of concept, we study the particular case of a diameter-modulated nanowire with a spin-polarized current along its axis and the demagnetizing field produced by its modulation. This inhomogeneous field allows one to control the angular velocity of the domain wall as a function of its position along the nanowire allowing frequencies in the GHz range to be achieved. This generator could be used in telecommunications for devices in the range of radiofrequencies or, following Faraday's induction law, could also induce an electromotive force and be used as a movable alternate voltage source in future nanodevices.

  17. Chiral near fields generated from plasmonic lattices

    CERN Document Server

    Canaguier-Durand, Antoine

    2014-01-01

    Plasmonic fields are usually considered non-chiral because of the transverse magnetic polarization of surface plasmon modes. We however show here that plasmonic lattices built from coherent superpositions of surface plasmons can generate optical chirality in the interfering near field. We reveal in particular the emergence of plasmonic potentials relevant to the generation of near-field chiral forces. This draws promising perspectives for performing enantiomeric separation schemes within the near field.

  18. Computer-Controlled Force Generator Project

    Data.gov (United States)

    National Aeronautics and Space Administration — TDA Research, Inc. is developing a compact, low power, Next-Generation Exercise Device (NGRED) that can generate any force between 5 and 600 lbf. We use a closed...

  19. A polygonal method for haptic force generation

    Energy Technology Data Exchange (ETDEWEB)

    Anderson, T. [Univ. of New Mexico, Albuquerque, NM (United States). Dept. of Electrical and Computer Engineering]|[Sandia National Labs., Albuquerque, NM (United States)

    1996-12-31

    Algorithms for computing forces and associated surface deformations (graphical and physical) are given, which, together with a force feedback device can be used to haptically display virtual objects. The Bendable Polygon algorithm, created at Sandia National Labs and the University of New Mexico, for visual rendering of computer generated surfaces is also presented. An implementation using the EIGEN virtual reality environment, and the PHANToM (Trademark) haptic interface, is reported together with suggestions for future research.

  20. FMNL formins boost lamellipodial force generation

    DEFF Research Database (Denmark)

    Kage, Frieda; Winterhoff, Moritz; Dimchev, Vanessa

    2017-01-01

    Migration frequently involves Rac-mediated protrusion of lamellipodia, formed by Arp2/3 complex-dependent branching thought to be crucial for force generation and stability of these networks. The formins FMNL2 and FMNL3 are Cdc42 effectors targeting to the lamellipodium tip and shown here...... reduces both migration and capability of cells to move against viscous media. Together, we conclude that force generation in lamellipodia strongly depends on FMNL formin activity, operating in addition to Arp2/3 complex-dependent filament branching....

  1. Polarization effects in molecular mechanical force fields

    Science.gov (United States)

    Cieplak, Piotr; Dupradeau, François-Yves; Duan, Yong; Wang, Junmei

    2014-01-01

    The focus here is on incorporating electronic polarization into classical molecular mechanical force fields used for macromolecular simulations. First, we briefly examine currently used molecular mechanical force fields and the current status of intermolecular forces as viewed by quantum mechanical approaches. Next, we demonstrate how some components of quantum mechanical energy are effectively incorporated into classical molecular mechanical force fields. Finally, we assess the modeling methods of one such energy component—polarization energy—and present an overview of polarizable force fields and their current applications. Incorporating polarization effects into current force fields paves the way to developing potentially more accurate, though more complex, parameterizations that can be used for more realistic molecular simulations. PMID:21828594

  2. Polarization effects in molecular mechanical force fields

    Energy Technology Data Exchange (ETDEWEB)

    Cieplak, Piotr [Burnham Institute for Medical Research, 10901 North Torrey Pines Road, La Jolla, CA 92120 (United States); Dupradeau, Francois-Yves [UMR CNRS 6219-Faculte de Pharmacie, Universite de Picardie Jules Verne, 1 rue des Louvels, F-80037 Amiens (France); Duan, Yong [Genome Center and Department of Applied Science, University of California, Davis, One Shields Avenue, Davis, CA 95616 (United States); Wang Junmei, E-mail: pcieplak@burnham.or [Department of Pharmacology, University of Texas Southwestern Medical Center, 6001 Forest Park Boulevard, ND9.136, Dallas, TX 75390-9050 (United States)

    2009-08-19

    The focus here is on incorporating electronic polarization into classical molecular mechanical force fields used for macromolecular simulations. First, we briefly examine currently used molecular mechanical force fields and the current status of intermolecular forces as viewed by quantum mechanical approaches. Next, we demonstrate how some components of quantum mechanical energy are effectively incorporated into classical molecular mechanical force fields. Finally, we assess the modeling methods of one such energy component-polarization energy-and present an overview of polarizable force fields and their current applications. Incorporating polarization effects into current force fields paves the way to developing potentially more accurate, though more complex, parameterizations that can be used for more realistic molecular simulations. (topical review)

  3. Minimizing forced outage risk in generator bidding

    Science.gov (United States)

    Das, Dibyendu

    Competition in power markets has exposed the participating companies to physical and financial uncertainties. Generator companies bid to supply power in a day-ahead market. Once their bids are accepted by the ISO they are bound to supply power. A random outage after acceptance of bids forces a generator to buy power from the expensive real-time hourly spot market and sell to the ISO at the set day-ahead market clearing price, incurring losses. A risk management technique is developed to assess this financial risk associated with forced outages of generators and then minimize it. This work presents a risk assessment module which measures the financial risk of generators bidding in an open market for different bidding scenarios. The day-ahead power market auction is modeled using a Unit Commitment algorithm and a combination of Normal and Cauchy distributions generate the real time hourly spot market. Risk profiles are derived and VaRs are calculated at 98 percent confidence level as a measure of financial risk. Risk Profiles and VaRs help the generators to analyze the forced outage risk and different factors affecting it. The VaRs and the estimated total earning for different bidding scenarios are used to develop a risk minimization module. This module will develop a bidding strategy of the generator company such that its estimated total earning is maximized keeping the VaR below a tolerable limit. This general framework of a risk management technique for the generating companies bidding in competitive day-ahead market can also help them in decisions related to building new generators.

  4. Transition States from Empirical Force Fields

    DEFF Research Database (Denmark)

    Jensen, Frank; Norrby, Per-Ola

    2003-01-01

    This is an overview of the use of empirical force fields in the study of reaction mechanisms. EVB-type methods (including RFF and MCMM) produce full reaction surfaces by mixing, in the simplest case, known force fields describing reactants and products. The SEAM method instead locates approximate...

  5. Deriving force field parameters for coordination complexes

    DEFF Research Database (Denmark)

    Norrby, Per-Ola; Brandt, Peter

    2001-01-01

    The process of deriving molecular mechanics force fields for coordination complexes is outlined. Force field basics are introduced with an emphasis on special requirements for metal complexes. The review is then focused on how to set up the initial model, define the target, refine the parameters,...

  6. Using force fields methods for locating transition structures

    Science.gov (United States)

    Jensen, Frank

    2003-11-01

    A previously proposed strategy of using force field methods for generating approximations to the geometry of transition structures is extended to also estimating an approximate Hessian matrix. These two components allow an automated method for locating first order saddle points, which is an essential requisite for studying chemical reactions of systems with many degrees of freedom. The efficiency of using an approximate force field Hessian matrix for initiating the geometry optimization is compared with the use of an exact Hessian. The force field Hessian in general requires more geometry steps to converge, but the additional computational cost is offset by the savings from not calculating the exact Hessian at the initial geometry.

  7. 10th Generation International Geomagnetic Reference Field

    Science.gov (United States)

    Maus, Stefan; Macmillan, Susan

    2005-04-01

    The International Association of Geomagnetism and Aeronomy (IAGA) released the 10th Generation International Geomagnetic Reference Field (IGRF) on 12 December 2004. This is the latest version of a standard mathematical description of the Earth's main magnetic field, and is used widely in studies of the Earth's deep interior, crust, ionosphere, and magnetosphere. The coefficients were finalized by a task force of IAGA, Division V, Working Group V-MOD: Geomagnetic Field Modeling. The IGRF is the product of a large collaborative effort between magnetic field modelers and the institutes around the world involved in collecting and disseminating magnetic field data from satellites and observatories. The IGRF is a series of mathematical models of the Earth's main field and its annual rate of change (secular variation). The sources of the main magnetic field are electric currents in the Earth and the magnetization of crustal rocks.

  8. Automatic generation of force fields and property surfaces for use in variational vibrational calculations of anharmonic vibrational energies and zero-point vibrational averaged properties.

    Science.gov (United States)

    Kongsted, Jacob; Christiansen, Ove

    2006-09-28

    An automatic and general procedure for the calculation of geometrical derivatives of the energy and general property surfaces for molecular systems is developed and implemented. General expressions for an n-mode representation are derived, where the n-mode representation includes only the couplings between n or less degrees of freedom. The general expressions are specialized to derivative force fields and property surfaces, and a scheme for calculation of the numerical derivatives is implemented. The implementation is interfaced to electronic structure programs and may be used for both ground and excited electronic states. The implementation is done in the context of a vibrational structure program and can be used in combination with vibrational self-consistent field (VSCF), vibrational configuration interaction (VCI), vibrational Moller-Plesset, and vibrational coupled cluster calculations of anharmonic wave functions and calculation of vibrational averaged properties at the VSCF and VCI levels. Sample calculations are presented for fundamental vibrational energies and vibrationally averaged dipole moments and frequency dependent polarizabilities and hyperpolarizabilities of water and formaldehyde.

  9. Solar Force-free Magnetic Fields

    CERN Document Server

    Wiegelmann, Thomas

    2012-01-01

    The structure and dynamics of the solar corona is dominated by the magnetic field. In most areas in the corona magnetic forces are so dominant that all non-magnetic forces like plasma pressure gradient and gravity can be neglected in the lowest order. This model assumption is called the force-free field assumption, as the Lorentz force vanishes. This can be obtained by either vanishing electric currents (leading to potential fields) or the currents are co-aligned with the magnetic field lines. First we discuss a mathematically simpler approach that the magnetic field and currents are proportional with one global constant, the so-called linear force-free field approximation. In the generic case, however, the relation between magnetic fields and electric currents is nonlinear and analytic solutions have been only found for special cases, like 1D or 2D configurations. For constructing realistic nonlinear force-free coronal magnetic field models in 3D, sophisticated numerical computations are required and boundar...

  10. Levitation forces of a bulk YBCO superconductor in gradient varying magnetic fields

    Science.gov (United States)

    Jiang, J.; Gong, Y. M.; Wang, G.; Zhou, D. J.; Zhao, L. F.; Zhang, Y.; Zhao, Y.

    2015-09-01

    The levitation forces of a bulk YBCO superconductor in gradient varying high and low magnetic fields generated from a superconducting magnet were investigated. The magnetic field intensity of the superconducting magnet was measured when the exciting current was 90 A. The magnetic field gradient and magnetic force field were both calculated. The YBCO bulk was cooled by liquid nitrogen in field-cooling (FC) and zero-field-cooling (ZFC) condition. The results showed that the levitation forces increased with increasing the magnetic field intensity. Moreover, the levitation forces were more dependent on magnetic field gradient and magnetic force field than magnetic field intensity.

  11. Control Strategies for Accurate Force Generation and Relaxation.

    Science.gov (United States)

    Ohtaka, Chiaki; Fujiwara, Motoko

    2016-10-01

    Characteristics and motor strategies for force generation and force relaxation were examined using graded tasks during isometric force control. Ten female college students (M age = 20.2 yr., SD = 1.1) were instructed to accurately control the force of isometric elbow flexion using their right arm to match a target force level as quickly as possible. They performed: (1) a generation task, wherein they increased their force from 0% maximum voluntary force to 20% maximum voluntary force (0%-20%), 40% maximum voluntary force (0%-40%), or 60% maximum voluntary force (0%-60%) and (2) and a relaxation task, in which they decreased their force from 60% maximum voluntary force to 40% maximum voluntary force (60%-40%), 20% maximum voluntary force (60%-20%), or to 0% maximum voluntary force (60%-0%). Produced force parameters of point of accuracy (force level, error), quickness (reaction time, adjustment time, rate of force development), and strategy (force wave, rate of force development) were analyzed. Errors of force relaxation were all greater, and reaction times shorter, than those of force generation. Adjustment time depended on the magnitude of force and peak rates of force development and force relaxation differed. Controlled relaxation of force is more difficult with low magnitude of force control.

  12. FMNL formins boost lamellipodial force generation

    Science.gov (United States)

    Kage, Frieda; Winterhoff, Moritz; Dimchev, Vanessa; Mueller, Jan; Thalheim, Tobias; Freise, Anika; Brühmann, Stefan; Kollasser, Jana; Block, Jennifer; Dimchev, Georgi; Geyer, Matthias; Schnittler, Hans-Joachim; Brakebusch, Cord; Stradal, Theresia E. B.; Carlier, Marie-France; Sixt, Michael; Käs, Josef; Faix, Jan; Rottner, Klemens

    2017-01-01

    Migration frequently involves Rac-mediated protrusion of lamellipodia, formed by Arp2/3 complex-dependent branching thought to be crucial for force generation and stability of these networks. The formins FMNL2 and FMNL3 are Cdc42 effectors targeting to the lamellipodium tip and shown here to nucleate and elongate actin filaments with complementary activities in vitro. In migrating B16-F1 melanoma cells, both formins contribute to the velocity of lamellipodium protrusion. Loss of FMNL2/3 function in melanoma cells and fibroblasts reduces lamellipodial width, actin filament density and -bundling, without changing patterns of Arp2/3 complex incorporation. Strikingly, in melanoma cells, FMNL2/3 gene inactivation almost completely abolishes protrusion forces exerted by lamellipodia and modifies their ultrastructural organization. Consistently, CRISPR/Cas-mediated depletion of FMNL2/3 in fibroblasts reduces both migration and capability of cells to move against viscous media. Together, we conclude that force generation in lamellipodia strongly depends on FMNL formin activity, operating in addition to Arp2/3 complex-dependent filament branching. PMID:28327544

  13. Chiral effective field theory and nuclear forces

    CERN Document Server

    Machleidt, R

    2011-01-01

    We review how nuclear forces emerge from low-energy QCD via chiral effective field theory. The presentation is accessible to the non-specialist. At the same time, we also provide considerable detailed information (mostly in appendices) for the benefit of researchers who wish to start working in this field.

  14. Curvature recognition and force generation in phagocytosis

    Directory of Open Access Journals (Sweden)

    Prassler Jana

    2010-12-01

    Full Text Available Abstract Background The uptake of particles by actin-powered invagination of the plasma membrane is common to protozoa and to phagocytes involved in the immune response of higher organisms. The question addressed here is how a phagocyte may use geometric cues to optimize force generation for the uptake of a particle. We survey mechanisms that enable a phagocyte to remodel actin organization in response to particles of complex shape. Results Using particles that consist of two lobes separated by a neck, we found that Dictyostelium cells transmit signals concerning the curvature of a surface to the actin system underlying the plasma membrane. Force applied to a concave region can divide a particle in two, allowing engulfment of the portion first encountered. The phagosome membrane that is bent around the concave region is marked by a protein containing an inverse Bin-Amphiphysin-Rvs (I-BAR domain in combination with an Src homology (SH3 domain, similar to mammalian insulin receptor tyrosine kinase substrate p53. Regulatory proteins enable the phagocyte to switch activities within seconds in response to particle shape. Ras, an inducer of actin polymerization, is activated along the cup surface. Coronin, which limits the lifetime of actin structures, is reversibly recruited to the cup, reflecting a program of actin depolymerization. The various forms of myosin-I are candidate motor proteins for force generation in particle uptake, whereas myosin-II is engaged only in retracting a phagocytic cup after a switch to particle release. Thus, the constriction of a phagocytic cup differs from the contraction of a cleavage furrow in mitosis. Conclusions Phagocytes scan a particle surface for convex and concave regions. By modulating the spatiotemporal pattern of actin organization, they are capable of switching between different modes of interaction with a particle, either arresting at a concave region and applying force in an attempt to sever the particle

  15. MATCH: An Atom- Typing Toolset for Molecular Mechanics Force Fields

    Science.gov (United States)

    Yesselman, Joseph D.; Price, Daniel J.; Knight, Jennifer L.; Brooks, Charles L.

    2011-01-01

    We introduce a toolset of program libraries collectively titled MATCH (Multipurpose Atom-Typer for CHARMM) for the automated assignment of atom types and force field parameters for molecular mechanics simulation of organic molecules. The toolset includes utilities for the conversion from multiple chemical structure file formats into a molecular graph. A general chemical pattern-matching engine using this graph has been implemented whereby assignment of molecular mechanics atom types, charges and force field parameters is achieved by comparison against a customizable list of chemical fragments. While initially designed to complement the CHARMM simulation package and force fields by generating the necessary input topology and atom-type data files, MATCH can be expanded to any force field and program, and has core functionality that makes it extendable to other applications such as fragment-based property prediction. In the present work, we demonstrate the accurate construction of atomic parameters of molecules within each force field included in CHARMM36 through exhaustive cross validation studies illustrating that bond increment rules derived from one force field can be transferred to another. In addition, using leave-one-out substitution it is shown that it is also possible to substitute missing intra and intermolecular parameters with ones included in a force field to complete the parameterization of novel molecules. Finally, to demonstrate the robustness of MATCH and the coverage of chemical space offered by the recent CHARMM CGENFF force field (Vanommeslaeghe, et al., JCC., 2010, 31, 671–690), one million molecules from the PubChem database of small molecules are typed, parameterized and minimized. PMID:22042689

  16. Modeling Enzymatic Transition States by Force Field Methods

    DEFF Research Database (Denmark)

    Hansen, Mikkel Bo; Jensen, Hans Jørgen Aagaard; Jensen, Frank

    2009-01-01

    The SEAM method, which models a transition structure as a minimum on the seam of two diabatic surfaces represented by force field functions, has been used to generate 20 transition structures for the decarboxylation of orotidine by the orotidine-5'-monophosphate decarboxylase enzyme. The dependence...

  17. A deep dynamo generating Mercury's magnetic field.

    Science.gov (United States)

    Christensen, Ulrich R

    2006-12-21

    Mercury has a global magnetic field of internal origin and it is thought that a dynamo operating in the fluid part of Mercury's large iron core is the most probable cause. However, the low intensity of Mercury's magnetic field--about 1% the strength of the Earth's field--cannot be reconciled with an Earth-like dynamo. With the common assumption that Coriolis and Lorentz forces balance in planetary dynamos, a field thirty times stronger is expected. Here I present a numerical model of a dynamo driven by thermo-compositional convection associated with inner core solidification. The thermal gradient at the core-mantle boundary is subadiabatic, and hence the outer region of the liquid core is stably stratified with the dynamo operating only at depth, where a strong field is generated. Because of the planet's slow rotation the resulting magnetic field is dominated by small-scale components that fluctuate rapidly with time. The dynamo field diffuses through the stable conducting region, where rapidly varying parts are strongly attenuated by the skin effect, while the slowly varying dipole and quadrupole components pass to some degree. The model explains the observed structure and strength of Mercury's surface magnetic field and makes predictions that are testable with space missions both presently flying and planned.

  18. Tailor-made force fields for crystal-structure prediction.

    Science.gov (United States)

    Neumann, Marcus A

    2008-08-14

    A general procedure is presented to derive a complete set of force-field parameters for flexible molecules in the crystalline state on a case-by-case basis. The force-field parameters are fitted to the electrostatic potential as well as to accurate energies and forces generated by means of a hybrid method that combines solid-state density functional theory (DFT) calculations with an empirical van der Waals correction. All DFT calculations are carried out with the VASP program. The mathematical structure of the force field, the generation of reference data, the choice of the figure of merit, the optimization algorithm, and the parameter-refinement strategy are discussed in detail. The approach is applied to cyclohexane-1,4-dione, a small flexible ring. The tailor-made force field obtained for cyclohexane-1,4-dione is used to search for low-energy crystal packings in all 230 space groups with one molecule per asymmetric unit, and the most stable crystal structures are reoptimized in a second step with the hybrid method. The experimental crystal structure is found as the most stable predicted crystal structure both with the tailor-made force field and the hybrid method. The same methodology has also been applied successfully to the four compounds of the fourth CCDC blind test on crystal-structure prediction. For the five aforementioned compounds, the root-mean-square deviations between lattice energies calculated with the tailor-made force fields and the hybrid method range from 0.024 to 0.053 kcal/mol per atom around an average value of 0.034 kcal/mol per atom.

  19. Magnetic Field Generation in Stars

    CERN Document Server

    Ferrario, Lilia; Zrake, Jonathan

    2015-01-01

    Enormous progress has been made on observing stellar magnetism in stars from the main sequence through to compact objects. Recent data have thrown into sharper relief the vexed question of the origin of stellar magnetic fields, which remains one of the main unanswered questions in astrophysics. In this chapter we review recent work in this area of research. In particular, we look at the fossil field hypothesis which links magnetism in compact stars to magnetism in main sequence and pre-main sequence stars and we consider why its feasibility has now been questioned particularly in the context of highly magnetic white dwarfs. We also review the fossil versus dynamo debate in the context of neutron stars and the roles played by key physical processes such as buoyancy, helicity, and superfluid turbulence,in the generation and stability of neutron star fields. Independent information on the internal magnetic field of neutron stars will come from future gravitational wave detections. Thus we maybe at the dawn of a ...

  20. Apparatuses and methods for generating electric fields

    Science.gov (United States)

    Scott, Jill R; McJunkin, Timothy R; Tremblay, Paul L

    2013-08-06

    Apparatuses and methods relating to generating an electric field are disclosed. An electric field generator may include a semiconductive material configured in a physical shape substantially different from a shape of an electric field to be generated thereby. The electric field is generated when a voltage drop exists across the semiconductive material. A method for generating an electric field may include applying a voltage to a shaped semiconductive material to generate a complex, substantially nonlinear electric field. The shape of the complex, substantially nonlinear electric field may be configured for directing charged particles to a desired location. Other apparatuses and methods are disclosed.

  1. First Principles Force Field for Metallic Tantalum

    OpenAIRE

    Strachan, Alejandro; Cagin, Tahir; Gulseren, Oguz; Mukherjee, Sonali; Cohen, Ronald E.; Goddard III, William A.

    2002-01-01

    We propose a general strategy to develop accurate Force Fields (FF) for metallic systems derived from ab initio quantum mechanical (QM) calculations; we illustrate this approach for tantalum. As input data to the FF we use the linearized augmented plane wave method (LAPW) with the generalized gradient approximation (GGA) to calculate: (i) the zero temperature equation of state (EOS) of Ta for bcc, fcc, and hcp crystal structures for pressures up to ~500 GPa. (ii) Elastic constants. (iii) We u...

  2. Probing cooperative force generation in collective cancer invasion

    Science.gov (United States)

    Alobaidi, Amani A.; Xu, Yaopengxiao; Chen, Shaohua; Jiao, Yang; Sun, Bo

    2017-08-01

    Collective cellular dynamics in the three-dimensional extracellular matrix (ECM) plays a crucial role in many physiological processes such as cancer invasion. Both chemical and mechanical signaling support cell-cell communications on a variety of length scales, leading to collective migratory behaviors. Here we conduct experiments using 3D in vitro tumor models and develop a phenomenological model in order to probe the cooperativity of force generation in the collective invasion of breast cancer cells. In our model, cell-cell communication is characterized by a single parameter that quantifies the correlation length of cellular migration cycles. We devise a stochastic reconstruction method to generate realizations of cell colonies with specific contraction phase correlation functions and correlation length a. We find that as a increases, the characteristic size of regions containing cells with similar contraction phases grows. For small a values, the large fluctuations in individual cell contraction phases smooth out the temporal fluctuations in the time-dependent deformation field in the ECM. For large a values, the periodicity of an individual cell contraction cycle is clearly manifested in the temporal variation of the overall deformation field in the ECM. Through quantitative comparisons of the simulated and experimentally measured deformation fields, we find that the correlation length for collective force generation in the breast cancer diskoid in geometrically micropatterned ECM (DIGME) system is a≈ 25~μ \\text{m} , which is roughly twice the linear size of a single cell. One possible mechanism for this intermediate cell correlation length is the fiber-mediated stress propagation in the 3D ECM network in the DIGME system.

  3. Management of change through force field analysis.

    Science.gov (United States)

    Baulcomb, Jean Sandra

    2003-07-01

    Today's NHS is rapidly changing, placing more emphasis on the managerial responsibilities of ward managers. Managing change is seen as being skilled at creating, acquiring and transferring knowledge to reflect new knowledge and insights. Defining core concepts is often difficult and requires the drawing on models/theories of change for guidance. Guidance from Lewin's (1951) force field analysis demonstrates the complexities of the change process and how driving and resisting forces were incorporated within the planning and implementation phases. Findings outline the benefits of a small scale change for staff, patients and the organization when successfully used to introduce a change of shift pattern within a progressively busy haematology day unit, in order to meet service demands without additional funding. Conclusions have been drawn in relation to the process and recommendations for practice made to further enhance care delivery within the unit.

  4. Force field dependence of riboswitch dynamics.

    Science.gov (United States)

    Hanke, Christian A; Gohlke, Holger

    2015-01-01

    Riboswitches are noncoding regulatory elements that control gene expression in response to the presence of metabolites, which bind to the aptamer domain. Metabolite binding appears to occur through a combination of conformational selection and induced fit mechanism. This demands to characterize the structural dynamics of the apo state of aptamer domains. In principle, molecular dynamics (MD) simulations can give insights at the atomistic level into the dynamics of the aptamer domain. However, it is unclear to what extent contemporary force fields can bias such insights. Here, we show that the Amber force field ff99 yields the best agreement with detailed experimental observations on differences in the structural dynamics of wild type and mutant aptamer domains of the guanine-sensing riboswitch (Gsw), including a pronounced influence of Mg2+. In contrast, applying ff99 with parmbsc0 and parmχOL modifications (denoted ff10) results in strongly damped motions and overly stable tertiary loop-loop interactions. These results are based on 58 MD simulations with an aggregate simulation time>11 μs, careful modeling of Mg2+ ions, and thorough statistical testing. Our results suggest that the moderate stabilization of the χ-anti region in ff10 can have an unwanted damping effect on functionally relevant structural dynamics of marginally stable RNA systems. This suggestion is supported by crystal structure analyses of Gsw aptamer domains that reveal χ torsions with high-anti values in the most mobile regions. We expect that future RNA force field development will benefit from considering marginally stable RNA systems and optimization toward good representations of dynamics in addition to structural characteristics.

  5. Balancing the Interactions of Ions, Water, and DNA in the Drude Polarizable Force Field

    OpenAIRE

    Savelyev, Alexey; MacKerell, Alexander D.

    2014-01-01

    Recently we presented a first-generation all-atom Drude polarizable force field for DNA based on the classical Drude oscillator model, focusing on optimization of key dihedral angles followed by extensive validation of the force field parameters. Presently, we describe the procedure for balancing the electrostatic interactions between ions, water, and DNA as required for development of the Drude force field for DNA. The proper balance of these interactions is shown to impact DNA stability and...

  6. Strong and superstrong pulsed magnetic fields generation

    CERN Document Server

    Shneerson, German A; Krivosheev, Sergey I

    2014-01-01

    Strong pulsed magnetic fields are important for several fields in physics and engineering, such as power generation and accelerator facilities. Basic aspects of the generation of strong and superstrong pulsed magnetic fields technique are given, including the physics and hydrodynamics of the conductors interacting with the field as well as an account of the significant progress in generation of strong magnetic fields using the magnetic accumulation technique. Results of computer simulations as well as a survey of available field technology are completing the volume.

  7. The interoperability force in the ERP field

    Science.gov (United States)

    Boza, Andrés; Cuenca, Llanos; Poler, Raúl; Michaelides, Zenon

    2015-04-01

    Enterprise resource planning (ERP) systems participate in interoperability projects and this participation sometimes leads to new proposals for the ERP field. The aim of this paper is to identify the role that interoperability plays in the evolution of ERP systems. To go about this, ERP systems have been first identified within interoperability frameworks. Second, the initiatives in the ERP field driven by interoperability requirements have been identified from two perspectives: technological and business. The ERP field is evolving from classical ERP as information system integrators to a new generation of fully interoperable ERP. Interoperability is changing the way of running business, and ERP systems are changing to adapt to the current stream of interoperability.

  8. Particle energization in a chaotic force-free magnetic field

    Science.gov (United States)

    Li, Xiaocan; Li, Gang; Dasgupta, Brahmananda

    2015-04-01

    A force-free field (FFF) is believed to be a reasonable description of the solar corona and in general a good approximation for low-beta plasma. The equations describing the magnetic field of FFF is similar to the ABC fluid equations which has been demonstrated to be chaotic. This implies that charged particles will experience chaotic magnetic field in the corona. Here, we study particle energization in a time-dependent FFF using a test particle approach. An inductive electric field is introduced by turbulent motions of plasma parcels. We find efficient particle acceleration with power-law like particle energy spectra. The power-law indices depend on the amplitude of plasma parcel velocity field and the spatial scales of the magnetic field fluctuation. The spectra are similar for different particle species. This model provide a possible mechanism for seed population generation for particle acceleration by, e.g., CME-driven shocks. Generalization of our results to certain non-force-free-field (NFFF) is straightforward as the sum of two or multiple FFFs naturally yield NFFF.

  9. Modeling Enzymatic Transition States by Force Field Methods

    DEFF Research Database (Denmark)

    Hansen, Mikkel Bo; Jensen, Hans Jørgen Aagaard; Jensen, Frank

    2009-01-01

    The SEAM method, which models a transition structure as a minimum on the seam of two diabatic surfaces represented by force field functions, has been used to generate 20 transition structures for the decarboxylation of orotidine by the orotidine-5'-monophosphate decarboxylase enzyme. The dependence...... by various electronic structure methods, where part of the enzyme is represented by a force field description and the effects of the solvent are represented by a continuum model. The relative energies vary by several hundreds of kJ/mol between the transition structures, and tests showed that a large part...... of this variation is due to changes in the enzyme structure at distances more than 5 Å from the active site. There are significant differences between the results obtained by pure quantum methods and those from mixed quantum and molecular mechanics methods....

  10. Stability of Nonlinear Force-Free Magnetic Fields

    Institute of Scientific and Technical Information of China (English)

    胡友秋

    2001-01-01

    Based on the magnetohydrodynamic energy principle, it is proved that Gold-Hoyle's nonlinear force-free magnetic field is unstable. This disproves the sufficient criterion for stability of nonlinear force-free magnetic fields given by Kriiger that a nonlinear force-free field is stable if the maximum absolute value of the force-free factor is smaller than the lowest eigenvalue associated with the domain of interest.

  11. Force generation by the growth of amyloid aggregates.

    Science.gov (United States)

    Herling, Therese W; Garcia, Gonzalo A; Michaels, Thomas C T; Grentz, Wolfgang; Dean, James; Shimanovich, Ulyana; Gang, Hongze; Müller, Thomas; Kav, Batuhan; Terentjev, Eugene M; Dobson, Christopher M; Knowles, Tuomas P J

    2015-08-01

    The generation of mechanical forces are central to a wide range of vital biological processes, including the function of the cytoskeleton. Although the forces emerging from the polymerization of native proteins have been studied in detail, the potential for force generation by aberrant protein polymerization has not yet been explored. Here, we show that the growth of amyloid fibrils, archetypical aberrant protein polymers, is capable of unleashing mechanical forces on the piconewton scale for individual filaments. We apply microfluidic techniques to measure the forces released by amyloid growth for two systems: insulin and lysozyme. The level of force measured for amyloid growth in both systems is comparable to that observed for actin and tubulin, systems that have evolved to generate force during their native functions and, unlike amyloid growth, rely on the input of external energy in the form of nucleotide hydrolysis for maximum force generation. Furthermore, we find that the power density released from growing amyloid fibrils is comparable to that of high-performance synthetic polymer actuators. These findings highlight the potential of amyloid structures as active materials and shed light on the criteria for regulation and reversibility that guide molecular evolution of functional polymers.

  12. Fibroblasts and myofibroblasts in wound healing: force generation and measurement.

    Science.gov (United States)

    Li, Bin; Wang, James H-C

    2011-11-01

    Fibroblasts are one of the most abundant cell types in connective tissues. These cells are responsible for tissue homeostasis under normal physiological conditions. When tissues are injured, fibroblasts become activated and differentiate into myofibroblasts, which generate large contractions and actively produce extracellular matrix (ECM) proteins to facilitate wound closure. Both fibroblasts and myofibroblasts play a critical role in wound healing by generating traction and contractile forces, respectively, to enhance wound contraction. This review focuses on the mechanisms of force generation in fibroblasts and myofibroblasts and techniques for measuring such cellular forces. Such a topic was chosen specifically because of the dual effects that fibroblasts/myofibroblasts have in wound healing process- a suitable amount of force generation and matrix deposition is beneficial for wound healing; excessive force and matrix production, however, result in tissue scarring and even malfunction of repaired tissues. Therefore, understanding how forces are generated in these cells and knowing exactly how much force they produce may guide the development of optimal protocols for more effective treatment of tissue wounds in clinical settings. Copyright © 2009 Tissue Viability Society. Published by Elsevier Ltd. All rights reserved.

  13. Scaling of motor cortical excitability during unimanual force generation.

    Science.gov (United States)

    Perez, Monica A; Cohen, Leonardo G

    2009-10-01

    During performance of a unimanual force generation task primary motor cortices (M1s) experience clear functional changes. Here, we evaluated the way in which M1s interact during parametric increases in right wrist flexion force in healthy volunteers. We measured the amplitude and the slope of motor evoked potentials (MEP) recruitment curves to transcranial magnetic stimulation (TMS) in the left and right flexor carpi radialis (FCR) muscles at rest and during 10%, 30% and 70% of maximal wrist flexion force. At rest, no differences were observed in the amplitude and slope of MEP recruitment curves in the left and right FCR muscles. With increasing right wrist flexion force, MEP amplitudes increased in both FCR muscles, with larger amplitudes in the right FCR. We found a significant correlation between the left and right MEP amplitudes across conditions. The slope of right and left FCR MEP recruitment curve was significantly steeper at 70% of force compared to rest and 10% of force. A significant correlation between the slope of left and right FCR MEP amplitudes was found at 70% of force only. Our results indicate a differential scaling of excitability in the corticospinal system controlling right and left FCR muscles at increasing levels of unimanual force generation. Specifically, these data highlights that at strong levels of unimanual force the increases in motor cortical excitability with increasing TMS stimulus intensities follow a similar pattern in both M1s, while at low levels of force they do not.

  14. Dynamo generated field emergence through recurrent plasmoid ejections

    CERN Document Server

    Warnecke, Jörn

    2010-01-01

    Magnetic buoyancy is believed to drive the transport of magnetic flux tubes from the convection zone to the surface of the Sun. The magnetic fields form twisted loop-like structures in the solar atmosphere. In this paper we use helical forcing to produce a large-scale dynamo-generated magnetic field, which rises even without magnetic buoyancy. A two layer system is used as computational domain where the upper part represents the solar atmosphere. Here, the evolution of the magnetic field is solved with the stress--and--relax method. Below this region a magnetic field is produced by a helical forcing function in the momentum equation, which leads to dynamo action. We find twisted magnetic fields emerging frequently to the outer layer, forming arch-like structures. In addition, recurrent plasmoid ejections can be found by looking at space--time diagrams of the magnetic field. Recent simulations in spherical coordinates show similar results.

  15. The critical role of force-fields in property prediction

    DEFF Research Database (Denmark)

    Jonsdottir, Svava Osk; Welsh, William J.; Rasmussen, Kjeld

    1999-01-01

    of conformational energydifferences and interaction energies vary significantly from one force-field to another. As a test for the reliability of the non-bonded interactions, vapor-liquid equilibrium (VLE) data have been calculated for a small number of systems using three different force-fields. The force...

  16. Evaluation of carbohydrate molecular mechanical force fields by quantum mechanical calculations

    DEFF Research Database (Denmark)

    Hemmingsen, Lars Bo Stegeager; Madsen, D.E.; Esbensen, A.L.

    2004-01-01

    A quantitative evaluation of 20 second-generation carbohydrate force fields was carried out using ab initio and density functional methods. Geometry-optimized structures (B3LYP/6-31G(d)) and relative energies using augmented correlation consistent basis sets were calculated in gas phase...... for monosaccharide carbohydrate benchmark systems. Selected results are: (i) The interaction energy of the alpha-D-alucopyranose-H2O heterodimer is estimated to be 4.9 kcal/mol, using a composite method including terms at highly correlated (CCSD(T)) level. Most molecular mechanics force fields are in error......-generation carbohydrate force fields. No single force field is consistently better than the others for all the test cases. A statistical assessment of the performance of the force fields indicates that CHEAT(95), CFF, certain versions of Amber and of MM3 have the best overall performance, for these gas phase...

  17. Collective force generated by multiple biofilaments can exceed the sum of forces due to individual ones

    CERN Document Server

    Das, Dipjyoti; Padinhateeri, Ranjith

    2013-01-01

    Collective dynamics and force generation by cytoskeletal filaments are crucial in many cellular processes. Investigating growth dynamics of a bundle of N independent cytoskeletal filaments pushing against a wall, we show that ATP/GTP hydrolysis leads to a collective phenomena that is currently unknown. Obtaining force-velocity relations for different models that capture chemical switching, we show, analytically and numerically, that the collective stall force of N filaments is greater than N times the stall force of a single filament. Simulating growing actin and microtubule bundles, considering both sequential and random hydrolysis, we make quantitative predictions of the excess forces.

  18. Reactive Force Fields via Explicit Valency

    Science.gov (United States)

    Kale, Seyit

    Computational simulations are invaluable in elucidating the dynamics of biological macromolecules. Unfortunately, reactions present a fundamental challenge. Calculations based on quantum mechanics can predict bond formation and rupture; however they suffer from severe length- and time-limitations. At the other extreme, classical approaches provide orders of magnitude faster simulations; however they regard chemical bonds as immutable entities. A few exceptions exist, but these are not always trivial to adopt for routine use. We bridge this gap by providing a novel, pseudo-classical approach, based on explicit valency. We unpack molecules into valence electron pairs and atomic cores. Particles bear ionic charges and interact via pairwise-only potentials. The potentials are informed of quantum effects in the short-range and obey dissociation limits in the long-range. They are trained against a small set of isolated species, including geometries and thermodynamics of small hydrides and of dimers formed by them. The resulting force field captures the essentials of reactivity, polarizability and flexibility in a simple, seamless setting. We call this model LEWIS, after the chemical theory that inspired the use of valence pairs. Following the introduction in Chapter 1, we initially focus on the properties of water. Chapter 2 considers gas phase clusters. To transition to the liquid phase, Chapter 3 describes a novel pairwise long-range compensation that performs comparably to infinite lattice summations. The approach is suited to ionic solutions in general. In Chapters 4 and 5, LEWIS is shown to correctly predict the dipolar and quadrupolar response in bulk liquid, and can accommodate proton transfers in both acid and base. Efficiency permits the study of proton defects at dilutions not accessible to experiment or quantum mechanics. Chapter 6 discusses explicit valency approaches in other hydrides, forming the basis of a reactive organic force field. Examples of simple

  19. Observation of a Turbulence-Generated Large Scale Magnetic Field

    CERN Document Server

    Spence, E J; Kendrick, R D; Nornberg, M D

    2006-01-01

    A uniform magnetic field is applied to a spherical, turbulent flow of liquid sodium. An induced magnetic dipole moment is measured which cannot be generated by the interaction of the axisymmetric mean flow with the applied field, indicating the presence of a turbulent electromotive force. It is shown that the induced dipole moment should vanish for any axisymmetric laminar flow. Also observed is the production of toroidal magnetic field from applied poloidal magnetic field (the omega-effect). Its potential role in the production of the induced dipole is discussed.

  20. The 10th generation international geomagnetic reference field

    Science.gov (United States)

    Maus, S.; Macmillan, S.; Chernova, T.; Choi, S.; Dater, D.; Golovkov, V.; Lesur, V.; Lowes, F.; Lühr, H.; Mai, W.; McLean, S.; Olsen, N.; Rother, M.; Sabaka, T.; Thomson, A.; Zvereva, T.; International Association of Geomagnetism, Aeronomy (IAGA), Division V, Working Group VMOD

    The International Association of Geomagnetism and Aeronomy (IAGA) on 12 December 2004 released the 10th generation International Geomagnetic Reference Field (IGRF)—the latest version of a standard mathematical description of the Earth's main magnetic field and used widely in studies of the Earth's deep interior, its crust, ionosphere and magnetosphere. The coefficients were finalised by a task force of IAGA. The IGRF is the product of a large collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and observatories around the world.

  1. The 10th-Generation International Geomagnetic Reference Field

    Science.gov (United States)

    2005-06-01

    The International Association of Geomagnetism and Aeronomy (IAGA) on 2004 December 12 has released the 10th-Generation International Geomagnetic Reference Field-the latest version of a standard mathematical description of the Earth's main magnetic field used widely in studies of the Earth's deep interior, its crust, ionosphere and magnetosphere. The coefficients were finalized by a task force of IAGA. The IGRF is the product of a large collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and observatories around the world.

  2. Axisymmetric field generation within an ambient axial field

    Science.gov (United States)

    Darah, A. A.; Sarson, G. R.

    2007-01-01

    The generation of magnetic field in a homogeneous, electrically conducting fluid - as required for the dynamo generation of the fields of many astrophysical bodies - is normally a threshold process; the dynamo mechanism, applicable to such bodies in unmagnetised environments, requires motions of sufficient strength to overcome the innate magnetic diffusion. In the presence of an ambient field, however, the critical nature of the field generation process is relaxed. Motions can distort and amplify the ambient field for all amplitudes of flow. For motions with appropriate geometries, an internal `dynamo-like' field of appreciable strength can be generated, even for relatively weak flows. At least a minority of planets, moons and other bodies exist within significant external astrophysical fields. For these bodies, the ambient field problem is more relevant than the classical dynamo problem, yet it remains relatively little studied. In this paper we consider the effect of an axial ambient field on a spherical mean-field α2 ω dynamo model, through nonlinear calculations with α-quenching feedback. Ambient fields of varying strengths, and both stationary and oscillatory in time, are imposed. Particular focus is placed on the effects of these fields on the equatorial symmetry and the time dependence of the preferred solutions.

  3. Precise numerical estimation of the magnetic field generated around recombination

    Science.gov (United States)

    Fidler, Christian; Pettinari, Guido; Pitrou, Cyril

    2016-05-01

    We investigate the generation of magnetic fields from nonlinear effects around recombination. As tight-coupling is gradually lost when approaching z ≃1100 , the velocity difference between photons and baryons starts to increase, leading to an increasing Compton drag of the photons on the electrons. The protons are then forced to follow the electrons due to the electric field created by the charge displacement; the same field, following Maxwell's laws, eventually induces a magnetic field on cosmological scales. Since scalar perturbations do not generate any magnetic field as they are curl-free, one has to resort to second-order perturbation theory to compute the magnetic field generated by this effect. We reinvestigate this problem numerically using the powerful second-order Boltzmann code SONG. We show that: (i) all previous studies do not have a high enough angular resolution to reach a precise and consistent estimation of the magnetic field spectrum; (ii) the magnetic field is generated up to z ≃10 ; (iii) it is in practice impossible to compute the magnetic field with a Boltzmann code for scales smaller than 1 Mpc. Finally we confirm that for scales of a few Mpc, this magnetic field is of order 2 ×10-29 G , many orders of magnitude smaller than what is currently observed on intergalactic scales.

  4. A note on generators of number fields

    CERN Document Server

    Vaaler, Jeffrey D

    2012-01-01

    We establish upper bounds for the smallest height of a generator of a number field $k$ over the rational field $\\Q$. Our first bound applies to all number fields $k$ having at least one real embedding. We also give a second conditional result for all number fields $k$ such that the Dedekind zeta-function associated to the Galois closure of $k/\\Q$ satisfies GRH. This provides a partial answer to a question of W. Ruppert.

  5. Understrength Air Force Officer Career Fields. A Force Management Approach

    Science.gov (United States)

    2005-01-01

    communications, and computers; intelligence, surveillance, and reconnaissance CFM career field manager CGO company-grade officer CMDB Consolidated Manpower...this report were drawn from two data sources. The first is the Consolidated Manpower Data Base ( CMDB ), which is the collection of Unit Manpower

  6. Magnetic Field and Force Calculations for ATLAS Asymmetrical Structure

    CERN Document Server

    Nessi, Marzio

    2001-01-01

    Magnetic field distortion in the assymetrical ATLAS structure are calculated. Magnetic forces in the system are estimated. 3D magnetic field simulation by the Opera3D code for symmetrical and asymmetrical systems is used.

  7. Entanglement Generation by Electric Field Background

    OpenAIRE

    Ebadi, Zahra; Mirza, Behrouz

    2014-01-01

    The quantum vacuum is unstable under the influence of an external electric field and decays into pairs of charged particles, a process which is known as the Schwinger pair production. We propose and demonstrate that this electric field can generate entanglement. Using the Schwinger pair production for constant and pulsed electric fields, we study entanglement for scalar particles with zero spins and Dirac fermions. One can observe the variation of the entanglement produced for bosonic and fer...

  8. Entanglement Generation by Electric Field Background

    CERN Document Server

    Ebadi, Zahra

    2014-01-01

    The quantum vacuum is unstable under the influence of an external electric field and decays into pairs of charged particles, a process which is known as the Schwinger pair production. We propose and demonstrate that this electric field can generate entanglement. Using the Schwinger pair production for constant and pulsed electric fields, we study entanglement for scalar particles with zero spins and Dirac fermions. One can observe the variation of the entanglement produced for bosonic and fermionic modes with respect to different parameters.

  9. Fibroblasts and Myofibroblasts in Wound Healing: Force Generation and Measurement

    OpenAIRE

    Li, Bin; Wang, James H-C

    2009-01-01

    Fibroblasts are one of the most abundant cell types in connective tissues. These cells are responsible for tissue homeostasis under normal physiological conditions. When tissues are injured, fibroblasts become activated and differentiate into myofibroblasts, which generate large contractions and actively produce extracellular matrix (ECM) proteins to facilitate wound closure. Both fibroblasts and myofibroblasts play a critical role in wound healing by generating traction and contractile force...

  10. The harmonic force field and absolute infrared intensities of diacetylene

    NARCIS (Netherlands)

    Koops, Th.; Visser, T.; Smit, W.M.A.

    1984-01-01

    The frequencies, harmonic force field and absolute IR intensities for C4H2 and C4D2 are reported. The experimental harmonized frequencies obey the Teller—Redlich product rule very well. An approximate harmonic force field was obtained from a refinement procedure in which the starting values are adj

  11. Physical Modeling of microtubule force generation and self-organization

    NARCIS (Netherlands)

    Tanase, C.

    2004-01-01

    Biological systems are complex heterogeneous and far from equilibrium systems. The fundamental questions posed by the physics of such systems are what the force generation mechanisms are, and how energy is processed and distributed among the components inside them. In answering these questions we ca

  12. Electric Field Generation in Martian Dust Devils

    Science.gov (United States)

    Barth, Erika L.; Farrell, William M.; Rafkin, Scot C. R.

    2015-01-01

    Terrestrial dust devils are known to generate electric fields from the vertical separation of charged dust particles. The particles present within the dust devils on Mars may also be subject to similar charging processes and so likely contribute to electric field generation there as well. However, to date, no Marsin situ instrumentation has been deployed to measure electric field strength. In order to explore the electric environment of dust devils on Mars, the triboelectric dust charging physics from the MacroscopicTriboelectric Simulation (MTS) code has been coupled to the Mars Regional Atmospheric ModelingSystem (MRAMS). Using this model, we examine how macroscopic electric fields are generated within martian dust disturbances and attempt to quantify the time evolution of the electrodynamical system.Electric fields peak for several minutes within the dust devil simulations. The magnitude of the electric field is a strong function of the size of the particles present, the average charge on the particles and the number of particles lifted. Varying these parameters results in peak electric fields between tens of millivolts per meter and tens of kilovolts per meter.

  13. Quasi-Static Electric Field Generator

    Science.gov (United States)

    Generazio, Edward R. (Inventor)

    2017-01-01

    A generator for producing an electric field for with an inspection technology system is provided. The generator provides the required variable magnitude quasi-static electric fields for the "illumination" of objects, areas and volumes to be inspected by the system, and produces human-safe electric fields that are only visible to the system. The generator includes a casing, a driven, non-conducting and triboelectrically neutral rotation shaft mounted therein, an ungrounded electrostatic dipole element which works in the quasi-static range, and a non-conducting support for mounting the dipole element to the shaft. The dipole element has a wireless motor system and a charging system which are wholly contained within the dipole element and the support that uses an electrostatic approach to charge the dipole element.

  14. An Automated Force Field Topology Builder (ATB) and Repository: Version 1.0.

    Science.gov (United States)

    Malde, Alpeshkumar K; Zuo, Le; Breeze, Matthew; Stroet, Martin; Poger, David; Nair, Pramod C; Oostenbrink, Chris; Mark, Alan E

    2011-12-13

    The Automated force field Topology Builder (ATB, http://compbio.biosci.uq.edu.au/atb ) is a Web-accessible server that can provide topologies and parameters for a wide range of molecules appropriate for use in molecular simulations, computational drug design, and X-ray refinement. The ATB has three primary functions: (1) to act as a repository for molecules that have been parametrized as part of the GROMOS family of force fields, (2) to act as a repository for pre-equilibrated systems for use as starting configurations in molecular dynamics simulations (solvent mixtures, lipid systems pre-equilibrated to adopt a specific phase, etc.), and (3) to generate force field descriptions of novel molecules compatible with the GROMOS family of force fields in a variety of formats (GROMOS, GROMACS, and CNS). Force field descriptions of novel molecules are derived using a multistep process in which results from quantum mechanical (QM) calculations are combined with a knowledge-based approach to ensure compatibility (as far as possible) with a specific parameter set of the GROMOS force field. The ATB has several unique features: (1) It requires that the user stipulate the protonation and tautomeric states of the molecule. (2) The symmetry of the molecule is analyzed to ensure that equivalent atoms are assigned identical parameters. (3) Charge groups are assigned automatically. (4) Where the assignment of a given parameter is ambiguous, a range of possible alternatives is provided. The ATB also provides several validation tools to assist the user to assess the degree to which the topology generated may be appropriate for a given task. In addition to detailing the steps involved in generating a force field topology compatible with a specific GROMOS parameter set (GROMOS 53A6), the challenges involved in the automatic generation of force field parameters for atomic simulations in general are discussed.

  15. Trapped field internal dipole superconducting motor generator

    Energy Technology Data Exchange (ETDEWEB)

    Hull, John R. (Downers Grove, IL)

    2001-01-01

    A motor generator including a high temperature superconductor rotor and an internally disposed coil assembly. The motor generator superconductor rotor is constructed of a plurality of superconductor elements magnetized to produce a dipole field. The coil assembly can be either a conventional conductor or a high temperature superconductor. The superconductor rotor elements include a magnetization direction and c-axis for the crystals of the elements and which is oriented along the magnetization direction.

  16. Modulated Field Synchronous Generator for Wind Turbines

    Directory of Open Access Journals (Sweden)

    Petru Chioncel

    2013-01-01

    Full Text Available This paper presents a modern electromechanical conversion systemsolution as the modulated field synchronous generator, offering on theone hand, an output voltage with constant frequency in terms of speedvariation of the wind turbine and on the other hand an advantagepower / weight ratio due to the high frequency for which the magneticcircuit of the electric machine is sized. The mathematical model of the modulated field synchronous generator is implemented in MatLABmodeling language, highlighting the command structure on thetransistors bases of the inverter transistors, through which thefunctioning of the electric machine can be studied, especially in terms of the frequency of the delivered voltage.

  17. Ponderomotive Force in the Presence of Electric Fields

    Science.gov (United States)

    Khazanov, G. V.; Krivorutsky, E. N.

    2013-01-01

    This paper presents averaged equations of particle motion in an electromagnetic wave of arbitrary frequency with its wave vector directed along the ambient magnetic field. The particle is also subjected to an E cross B drift and a background electric field slowly changing in space and acting along the magnetic field line. The fields, wave amplitude, and the wave vector depend on the coordinate along the magnetic field line. The derivations of the ponderomotive forces are done by assuming that the drift velocity in the ambient magnetic field is comparable to the particle velocity. Such a scenario leads to new ponderomotive forces, dependent on the wave magnetic field intensity, and, as a result, to the additional energy exchange between the wave and the plasma particles. It is found that the parallel electric field can lead to the change of the particle-wave energy exchange rate comparable to that produced by the previously discussed ponderomotive forces.

  18. Field ion source development for neutron generators

    Science.gov (United States)

    Bargsten Johnson, B.; Schwoebel, P. R.; Holland, C. E.; Resnick, P. J.; Hertz, K. L.; Chichester, D. L.

    2012-01-01

    An ion source based on the principles of electrostatic field desorption is being developed to improve the performance of existing compact neutron generators. The ion source is an array of gated metal tips derived from field electron emitter array microfabrication technology. A comprehensive summary of development and experimental activities is presented. Many structural modifications to the arrays have been incorporated to achieve higher tip operating fields, while lowering fields at the gate electrode to prevent gate field electron emission which initiates electrical breakdown in the array. The latest focus of fabrication activities has been on rounding the gate electrode edge and surrounding the gate electrode with dielectric material. Array testing results have indicated a steady progression of increased array tip operating fields with each new design tested. The latest arrays have consistently achieved fields beyond those required for the onset of deuterium desorption (˜20 V/nm), and have demonstrated the desorption of deuterium at fields up to 36 V/nm. The number of ions desorbed from an array has been quantified, and field desorption of metal tip substrate material from array tips has been observed for the first time. Gas-phase field ionization studies with ˜10,000 tip arrays have achieved deuterium ion currents of ˜50 nA. Neutron production by field ionization has yielded ˜10 2 n/s from ˜1 mm 2 of array area using the deuterium-deuterium fusion reaction at 90 kV.

  19. Field ion source development for neutron generators

    Energy Technology Data Exchange (ETDEWEB)

    Bargsten Johnson, B. [University of New Mexico, Albuquerque, NM 87131 (United States); Schwoebel, P.R., E-mail: schwoebel@chtm.unm.edu [University of New Mexico, Albuquerque, NM 87131 (United States); Holland, C.E. [SRI International, Menlo Park, CA 94025 (United States); Resnick, P.J. [Sandia National Laboratories, Albuquerque, NM 87123 (United States); Hertz, K.L. [Sandia National Laboratories, Livermore, CA 94551 (United States); Chichester, D.L. [Idaho National Laboratory, Idaho Falls, ID 83415 (United States)

    2012-01-21

    An ion source based on the principles of electrostatic field desorption is being developed to improve the performance of existing compact neutron generators. The ion source is an array of gated metal tips derived from field electron emitter array microfabrication technology. A comprehensive summary of development and experimental activities is presented. Many structural modifications to the arrays have been incorporated to achieve higher tip operating fields, while lowering fields at the gate electrode to prevent gate field electron emission which initiates electrical breakdown in the array. The latest focus of fabrication activities has been on rounding the gate electrode edge and surrounding the gate electrode with dielectric material. Array testing results have indicated a steady progression of increased array tip operating fields with each new design tested. The latest arrays have consistently achieved fields beyond those required for the onset of deuterium desorption ({approx}20 V/nm), and have demonstrated the desorption of deuterium at fields up to 36 V/nm. The number of ions desorbed from an array has been quantified, and field desorption of metal tip substrate material from array tips has been observed for the first time. Gas-phase field ionization studies with {approx}10,000 tip arrays have achieved deuterium ion currents of {approx}50 nA. Neutron production by field ionization has yielded {approx}10{sup 2} n/s from {approx}1 mm{sup 2} of array area using the deuterium-deuterium fusion reaction at 90 kV.

  20. Field Ion Source Development for Neutron Generators

    Energy Technology Data Exchange (ETDEWEB)

    B. Bargsten Johnson; P. R. Schwoebel; C. E. Holland; P. J. Resnick; K. L. Hertz; D. L. Chichester

    2012-01-01

    An ion source based on the principles of electrostatic field desorption is being developed to improve the performance of existing compact neutron generators. The ion source is an array of gated metal tips derived from field electron emitter array microfabrication technology. A comprehensive summary of development and experimental activities is presented. Many structural modifications to the arrays have been incorporated to achieve higher tip operating fields, while lowering fields at the gate electrode to prevent gate field electron emission which initiates electrical breakdown in the array. The latest focus of fabrication activities has been on rounding the gate electrode edge and surrounding the gate electrode with dielectric material. Array testing results have indicated a steady progression of increased array tip operating fields with each new design tested. The latest arrays have consistently achieved fields beyond those required for the onset of deuterium desorption ({approx}20 V/nm), and have demonstrated the desorption of deuterium at fields up to 36 V/nm. The number of ions desorbed from an array has been quantified, and field desorption of metal tip substrate material from array tips has been observed for the first time. Gas-phase field ionization studies with {approx}10,000 tip arrays have achieved deuterium ion currents of {approx}50 nA. Neutron production by field ionization has yielded {approx}10{sup 2} n/s from {approx}1 mm{sup 2} of array area using the deuterium-deuterium fusion reaction at 90 kV.

  1. Tokamak with in situ magnetohydrodynamic generation of toroidal magnetic field

    Science.gov (United States)

    Schaffer, Michael J.

    1986-01-01

    A tokamak apparatus includes an electrically conductive metal pressure vessel for defining a chamber and confining liquid therein. A liner disposed within said chamber defines a toroidal space within the liner and confines gas therein. The metal vessel provides an electrically conductive path linking the toroidal space. Liquid metal is forced outwardly through the chamber outside of the toroidal space to generate electric current in the conductive path and thereby generate a toroidal magnetic field within the toroidal space. Toroidal plasma is developed within the toroidal space about the major axis thereof.

  2. Idea Generation in Highly Institutionalized Fields

    DEFF Research Database (Denmark)

    Agoguè, Marine; Boxenbaum, Eva

    , bricolage and innovative design reasoning. We identify metaphors and bricolage as central to the subconscious system, which play an important role in maintaining the field frame, whereas conceptual blending and innovative design reasoning can be instrumental in generating ideas in the conscious system...

  3. Approximate photochemical dynamics of azobenzene with reactive force fields

    Science.gov (United States)

    Li, Yan; Hartke, Bernd

    2013-12-01

    We have fitted reactive force fields of the ReaxFF type to the ground and first excited electronic states of azobenzene, using global parameter optimization by genetic algorithms. Upon coupling with a simple energy-gap transition probability model, this setup allows for completely force-field-based simulations of photochemical cis→trans- and trans→cis-isomerizations of azobenzene, with qualitatively acceptable quantum yields. This paves the way towards large-scale dynamics simulations of molecular machines, including bond breaking and formation (via the reactive force field) as well as photochemical engines (presented in this work).

  4. Approximate photochemical dynamics of azobenzene with reactive force fields.

    Science.gov (United States)

    Li, Yan; Hartke, Bernd

    2013-12-14

    We have fitted reactive force fields of the ReaxFF type to the ground and first excited electronic states of azobenzene, using global parameter optimization by genetic algorithms. Upon coupling with a simple energy-gap transition probability model, this setup allows for completely force-field-based simulations of photochemical cis→trans- and trans→cis-isomerizations of azobenzene, with qualitatively acceptable quantum yields. This paves the way towards large-scale dynamics simulations of molecular machines, including bond breaking and formation (via the reactive force field) as well as photochemical engines (presented in this work).

  5. A thermodynamic force generated by chemical gradient and adsorption reaction

    CERN Document Server

    Sugawara, Takeshi

    2009-01-01

    Biological units such as macromolecules, organelles, and cells are directed to a proper location under gradients of relevant chemicals. By considering a macroscopic element that has binding sites for a chemical adsorption reaction to occur on its surface, we show the existence of a thermodynamic force that is generated by the gradient and exerted on the element. By assuming local equilibrium and adopting the grand potential from thermodynamics, we derive a formula for such a thermodynamic force, which depends on the chemical potential gradient and Langmuir isotherm. The conditions under which the formula can be applied are demonstrated to hold in intracellular reactions. The role of the force in the partitioning of bacterial chromosome/plasmid during cell division is discussed.

  6. The interoperability force in the ERP field

    OpenAIRE

    Boza Garcia, Andres; Cuenca, L; Poler Escoto, Raúl; Michaelides, Zenon

    2015-01-01

    Enterprise resource planning (ERP) systems participate in interoperability projects and this participation sometimes leads to new proposals for the ERP field. The aim of this paper is to identify the role that interoperability plays in the evolution of ERP systems. To go about this, ERP systems have been first identified within interoperability frameworks. Second, the initiatives in the ERP field driven by interoperability requirements have been identified from two perspectives: technological...

  7. Optimized molecular force field for sulfur hexafluoride simulations.

    Science.gov (United States)

    Olivet, Aurelio; Vega, Lourdes F

    2007-04-14

    An optimized molecular force field for sulfur hexafluoride (SF6) simulations is presented in this work. The new force field for SF6 contains two parts: a Lennard-Jones potential that deals with F-F intermolecular interactions and the second term dealing with the intramolecular forces. In this second part the flexibility of the molecule is explicitly considered by 6 harmonic stretch terms, modeling the S-F chemical bonds, and 12 harmonic bending terms, modeling the F-S-F angular deformations. The parameters of the new force field have been obtained by a multivariable optimization procedure, whose main feature is the simultaneous fitting of all force field parameters, using as reference data several equilibrium properties (vapor pressure, saturated liquid density, and surface tension) and shear viscosity. The new force field clearly improves the description of the phase envelope and the rest of the properties as compared to previous simulations for a rigid model for the same molecule [A. Olivet et al., J. Chem. Phys. 123, 194508 (2005)]. Results for the optimized force field concerning the vapor-liquid coexistence curve, several thermodynamics states at the homogeneous gas and liquid region, and transport coefficients of SF6 are in good agreement with available experimental data.

  8. Adhesion Force Measurements of Polymer Particles by Detachment Field Method

    Institute of Scientific and Technical Information of China (English)

    Masashi Nagayama; Nobuyasu Sakurai; Tatsuaki Wada; Manabu Takeuchi

    2004-01-01

    The adhesion force distributions of polymer particles to aluminum substrates were measured by the detachment field method. Polymer particles with conducting surface treatment were used for the measurements.Further the conventional detachment field method was modified to be applicable to the adhesion force measurements of a single particle. The adhesion force of the polymer particles increased with an increase in relative humidity. The surface roughness of the substrate influenced the adhesion forces of particles significantly. The influence of the CF4 plasma treatment of the polymer particles and thin layer coating of the substrate surface on the adhesion forces of the polymer particles was also studied, and factors affecting adhesion forces of polymer particles are discussed.

  9. Chiral effective field theory for nuclear forces: Achievements and challenges

    Directory of Open Access Journals (Sweden)

    Machleidt R.

    2014-03-01

    Full Text Available I start with a historical review of the theories of nuclear forces and then shift to the main focus, which is the chiral effective field theory approach to nuclear forces. I summarize the current status of this approach and discuss the most important open issues: the proper renormalization of the chiral two-nucleon potential and sub-leading three-nucleon forces.

  10. Acoustic Force Density Acting on Inhomogeneous Fluids in Acoustic Fields

    DEFF Research Database (Denmark)

    Karlsen, Jonas Tobias; Augustsson, Per; Bruus, Henrik

    2016-01-01

    We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems...

  11. Appearance of gauge fields and forces beyond the adiabatic approximation

    Energy Technology Data Exchange (ETDEWEB)

    Gosselin, Pierre [Institut Fourier, UMR 5582 CNRS-UJF, UFR de Mathematiques, Universite Grenoble I, BP74, 38402 Saint Martin d' Heres, Cedex (France); Mohrbach, Herve, E-mail: mohrbach@univ-metz.f [Laboratoire de Physique Moleculaire et des Collisions, ICPMB-FR CNRS 2843, Universite Paul Verlaine-Metz, 57078 Metz Cedex 3 (France)

    2010-09-03

    We investigate the origin of quantum geometric phases, gauge fields and forces beyond the adiabatic regime. In particular, we extend the notions of geometric magnetic and electric forces discovered in studies of the Born-Oppenheimer approximation to arbitrary quantum systems described by matrix-valued quantum Hamiltonians. The results are illustrated by several physical relevant examples.

  12. DRF90 : a polarizable force field

    NARCIS (Netherlands)

    Swart, M.; van Duijnen, P. Th.

    2006-01-01

    The direct reaction field (DRF) approach has proven to be a useful tool to investigate the influence of solvents on the quantum/classical behaviour of solute molecules. In this paper, we report the latest extension of this DRF approach, which consists of the gradient of the completely classical ener

  13. The electromagnetic force field, fluid flow field and temperature profiles in levitated metal droplets

    Science.gov (United States)

    El-Kaddah, N.; Szekely, J.

    1982-01-01

    A mathematical representation was developed for the electromagnetic force field, the flow field, the temperature field (and for transport controlled kinetics), in a levitation melted metal droplet. The technique of mutual inductances was employed for the calculation of the electromagnetic force field, while the turbulent Navier - Stokes equations and the turbulent convective transport equations were used to represent the fluid flow field, the temperature field and the concentration field. The governing differential equations, written in spherical coordinates, were solved numerically. The computed results were in good agreement with measurements, regarding the lifting force, and the average temperature of the specimen and carburization rates, which were transport controlled.

  14. Force-Free Electromagnetic Fields within Spinor Framework

    Directory of Open Access Journals (Sweden)

    V. N. Trishin

    2016-01-01

    Full Text Available The article deals with spinor representation of the force-free electrodynamics. The equations of the force-free electromagnetic field describe the physics of pulsars and black holes whose magnetospheres are filled with magnetically dominated relativistic plasma.The paper is a brief pedagogical introduction to the mathematics of the subject, based on 2-spinor calculi. The objective is to present the nonlinear theory of force-free fields in a compact and elegant form that the spinor framework provides. First, the algebraic classification of the Maxwell tensor is presented. Then, the reduced system of differential equations is obtained for two types of electromagnetic field and the basic features of the solutions are described.  The null force-free field is connected with the shear-free geodesic null congruence in a space-time and is derived from a linear equation for a complex function. The magnetic force-free field is associated with the time-like 2-surface that represents the world-sheet of magnetic field line. The simplified system includes 4 linear differential equations for a real function. The article is educational in nature and there are no new solutions of force-free equations obtained.

  15. Mapping Nanoscale Electromagnetic Near-Field Distributions Using Optical Forces

    CERN Document Server

    Huang, Fei; Mardy, Zahra; Burdett, Jonathan; Wickramasinghe, H Kumar

    2014-01-01

    We demonstrate the application of Atomic Force Microscopy (AFM) based optical force microscopy to map the optical near-fields with nanometer resolution, limited only by the AFM probe geometry. We map the electric field distributions of tightly focused laser beams with different polarizations and show that the experimentally measured data agrees well with the theoretical predictions from a dipole-dipole interaction model, thereby validating our approach. We further validate the proposed technique by evaluating the optical electric field scattered by a spherical nanoparticle by measuring the optical forces between the nanoparticle and gold coated AFM probe. The technique allows for wavelength independent, background free, thermal noise limited mechanical imaging of optical phenomenon with sensitivity limited by AFM performance. Optical forces due to both electric and magnetic dipole-dipole interactions can be measured using this technique.

  16. Group field theories generating polyhedral complexes

    CERN Document Server

    Thürigen, Johannes

    2015-01-01

    Group field theories are a generalization of matrix models which provide both a second quantized reformulation of loop quantum gravity as well as generating functions for spin foam models. While states in canonical loop quantum gravity, in the traditional continuum setting, are based on graphs with vertices of arbitrary valence, group field theories have been defined so far in a simplicial setting such that states have support only on graphs of fixed valency. This has led to the question whether group field theory can indeed cover the whole state space of loop quantum gravity. In this contribution based on [1] I present two new classes of group field theories which satisfy this objective: i) a straightforward, but rather formal generalization to multiple fields, one for each valency and ii) a simplicial group field theory which effectively covers the larger state space through a dual weighting, a technique common in matrix and tensor models. To this end I will further discuss in some detail the combinatorial ...

  17. Morphological Transformation and Force Generation of Active Cytoskeletal Networks

    Science.gov (United States)

    Maruri, Daniel; Kamm, Roger D.

    2017-01-01

    Cells assemble numerous types of actomyosin bundles that generate contractile forces for biological processes, such as cytokinesis and cell migration. One example of contractile bundles is a transverse arc that forms via actomyosin-driven condensation of actin filaments in the lamellipodia of migrating cells and exerts significant forces on the surrounding environments. Structural reorganization of a network into a bundle facilitated by actomyosin contractility is a physiologically relevant and biophysically interesting process. Nevertheless, it remains elusive how actin filaments are reoriented, buckled, and bundled as well as undergo tension buildup during the structural reorganization. In this study, using an agent-based computational model, we demonstrated how the interplay between the density of myosin motors and cross-linking proteins and the rigidity, initial orientation, and turnover of actin filaments regulates the morphological transformation of a cross-linked actomyosin network into a bundle and the buildup of tension occurring during the transformation. PMID:28114384

  18. Force-field compensation in a manual tracking task.

    Directory of Open Access Journals (Sweden)

    Valentina Squeri

    Full Text Available This study addresses force/movement control in a dynamic "hybrid" task: the master sub-task is continuous manual tracking of a target moving along an eight-shaped Lissajous figure, with the tracking error as the primary performance index; the slave sub-task is compensation of a disturbing curl viscous field, compatibly with the primary performance index. The two sub-tasks are correlated because the lateral force the subject must exert on the eight-shape must be proportional to the longitudinal movement speed in order to perform a good tracking. The results confirm that visuo-manual tracking is characterized by an intermittent control mechanism, in agreement with previous work; the novel finding is that the overall control patterns are not altered by the presence of a large deviating force field, if compared with the undisturbed condition. It is also found that the control of interaction-forces is achieved by a combination of arm stiffness properties and direct force control, as suggested by the systematic lateral deviation of the trajectories from the nominal path and the comparison between perturbed trials and catch trials. The coordination of the two sub-tasks is quickly learnt after the activation of the deviating force field and is achieved by a combination of force and the stiffness components (about 80% vs. 20%, which is a function of the implicit accuracy of the tracking task.

  19. Shape regulation generates elastic interaction between active force dipoles

    CERN Document Server

    Golkov, Roman

    2016-01-01

    The organization of live cells to tissues is associated with the mechanical interaction between cells, which is mediated through their mechanical environment. We model live cells as spherical active force dipoles surrounded by an infinite elastic matrix, and analytically evaluate their elastic interaction energy for different scenarios of their regulatory behavior. For purely dilational eigenstrains the elastic interaction energy between any two bodies vanishes. We identify mechanical interactions between active cells applying non isotropic displacements with a regulation mechanism designed so that they will preserve their spherical shape. We express the resultant non-isotropic deformation field by a multipole expansion in terms of spherical harmonics. Mechanical self-regulation of live cells is not fully understood, and we compare homeostatic (set point) force applied by the cells on their environment versus homeostatic displacements on their surface. By including or excluding the first term of the expansion...

  20. Controlling dispersion forces between small particles with artificially created random light fields

    CERN Document Server

    Bruegger, Georges; Scheffold, Frank; Saenz, Juan Jose

    2015-01-01

    Appropriate combinations of laser beams can be used to trap and manipulate small particles with "optical tweezers" as well as to induce significant "optical binding" forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir-Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light induced interactions open a path towards...

  1. Analysis of flow instabilities in forced-convection steam generator

    Institute of Scientific and Technical Information of China (English)

    2006-01-01

    Because of the practical importance of two-phase instabilities, substantial efforts have been made to date to understand the physical phenomena governing such instabilities and to develop computational tools to model the dynamics. The purpose of this study is to present a numerical model for the analysis of flow-induced instabilities in forced-convection steam generator. The model is based on the assumption of homogeneous two-phase flow and thermodynamic equilibrium of the phases. The thermal capacity of the heater wall has been included in the analysis. The model is used to analyze the flow instabilities in the steam generator and to study the effects of system pressure, mass flux, inlet temperature and inlet/outlet restriction, gap size, the ratio of do /di, and the ratio of qi/qo on the system behavior.

  2. The harmonic force field and vibrational spectra of pyrrole

    Science.gov (United States)

    Xie, Yaoming; Fan, Kangnian; Boggs, James E.

    The complete harmonic vibrational force field of pyrrole has been calculated by the ab initio gradient method at the Hartree-Fock level using the 4-21 basis set. The force field was then scaled with a set of six factors transferred from benzene, and the vibrational spectrum of pyrrole was calculated. This a priori prediction, made with no reference to observations on pyrrole, agreed with the known experimental fundamental frequencies with a mean deviation of 12 cm-1 for in-plane modes and 20 cm-1 for out-of-plane modes except for the NH wagging and NH stretch. A new set of ten scale factors was next obtained by direct fitting of the computed force field to the observed pyrrole spectrum, producing the best force field obtainable by combined use of the theoretical and experimental information. This force field reproduced the entire pyrrole spectrum with mean deviations of 4·2 cm-1 (in-plane) and 5·9 cm-1 (out-of-plane). The spectra of three deuterated forms of pyrrole were also computed. Infrared absorption intensities were calculated and proved very useful in examining assignments of the two ring torsional modes and the CH stretching modes.

  3. Lorentz force electrical impedance tomography using magnetic field measurements.

    Science.gov (United States)

    Zengin, Reyhan; Gençer, Nevzat Güneri

    2016-08-21

    In this study, magnetic field measurement technique is investigated to image the electrical conductivity properties of biological tissues using Lorentz forces. This technique is based on electrical current induction using ultrasound together with an applied static magnetic field. The magnetic field intensity generated due to induced currents is measured using two coil configurations, namely, a rectangular loop coil and a novel xy coil pair. A time-varying voltage is picked-up and recorded while the acoustic wave propagates along its path. The forward problem of this imaging modality is defined as calculation of the pick-up voltages due to a given acoustic excitation and known body properties. Firstly, the feasibility of the proposed technique is investigated analytically. The basic field equations governing the behaviour of time-varying electromagnetic fields are presented. Secondly, the general formulation of the partial differential equations for the scalar and magnetic vector potentials are derived. To investigate the feasibility of this technique, numerical studies are conducted using a finite element method based software. To sense the pick-up voltages a novel coil configuration (xy coil pairs) is proposed. Two-dimensional numerical geometry with a 16-element linear phased array (LPA) ultrasonic transducer (1 MHz) and a conductive body (breast fat) with five tumorous tissues is modeled. The static magnetic field is assumed to be 4 Tesla. To understand the performance of the imaging system, the sensitivity matrix is analyzed. The sensitivity matrix is obtained for two different locations of LPA transducer with eleven steering angles from [Formula: see text] to [Formula: see text] at intervals of [Formula: see text]. The characteristics of the imaging system are shown with the singular value decomposition (SVD) of the sensitivity matrix. The images are reconstructed with the truncated SVD algorithm. The signal-to-noise ratio in measurements is assumed 80 d

  4. Lorentz force electrical impedance tomography using magnetic field measurements

    Science.gov (United States)

    Zengin, Reyhan; Güneri Gençer, Nevzat

    2016-08-01

    In this study, magnetic field measurement technique is investigated to image the electrical conductivity properties of biological tissues using Lorentz forces. This technique is based on electrical current induction using ultrasound together with an applied static magnetic field. The magnetic field intensity generated due to induced currents is measured using two coil configurations, namely, a rectangular loop coil and a novel xy coil pair. A time-varying voltage is picked-up and recorded while the acoustic wave propagates along its path. The forward problem of this imaging modality is defined as calculation of the pick-up voltages due to a given acoustic excitation and known body properties. Firstly, the feasibility of the proposed technique is investigated analytically. The basic field equations governing the behaviour of time-varying electromagnetic fields are presented. Secondly, the general formulation of the partial differential equations for the scalar and magnetic vector potentials are derived. To investigate the feasibility of this technique, numerical studies are conducted using a finite element method based software. To sense the pick-up voltages a novel coil configuration (xy coil pairs) is proposed. Two-dimensional numerical geometry with a 16-element linear phased array (LPA) ultrasonic transducer (1 MHz) and a conductive body (breast fat) with five tumorous tissues is modeled. The static magnetic field is assumed to be 4 Tesla. To understand the performance of the imaging system, the sensitivity matrix is analyzed. The sensitivity matrix is obtained for two different locations of LPA transducer with eleven steering angles from -{{25}\\circ} to {{25}\\circ} at intervals of {{5}\\circ} . The characteristics of the imaging system are shown with the singular value decomposition (SVD) of the sensitivity matrix. The images are reconstructed with the truncated SVD algorithm. The signal-to-noise ratio in measurements is assumed 80 dB. Simulation studies

  5. Strong terahertz field generation, detection, and application

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ki-Yong [Univ. of Maryland, College Park, MD (United States)

    2016-05-22

    This report describes the generation and detection of high-power, broadband terahertz (THz) radiation with using femtosecond terawatt (TW) laser systems. In particular, this focuses on two-color laser mixing in gases as a scalable THz source, addressing both microscopic and macroscopic effects governing its output THz yield and radiation profile. This also includes the characterization of extremely broad THz spectra extending from microwaves to infrared frequencies. Experimentally, my group has generated high-energy (tens of microjoule), intense (>8 MV/cm), and broadband (0.01~60 THz) THz radiation in two-color laser mixing in air. Such an intense THz field can be utilized to study THz-driven extremely nonlinear phenomena in a university laboratory.

  6. Strong terahertz field generation, detection, and application

    Energy Technology Data Exchange (ETDEWEB)

    Kim, Ki-Yong [University of Maryland, College Park

    2016-05-15

    This report describes the generation and detection of high-power, broadband terahertz (THz) radiation with using femtosecond terawatt (TW) laser systems. In particular, this focuses on two-color laser mixing in gases as a scalable THz source, addressing both microscopic and macroscopic effects governing its output THz yield and radiation profile. This also includes the characterization of extremely broad THz spectra extending from microwaves to infrared frequencies. Experimentally, my group has generated high-energy (tens of microjoule), intense (>8 MV/cm), and broadband (0.01~60 THz) THz radiation in two-color laser mixing in air. Such an intense THz field can be utilized to study THz-driven extremely nonlinear phenomena in a university laboratory.

  7. International Geomagnetic Reference Field: the seventh generation.

    Science.gov (United States)

    Barton, C. E.

    A seventh-generation revision of the International Geomagnetic Reference Field (IGRF) was adopted by the International Association of Geomagnetism and Aeronomy (IAGA) at the XXI General Assembly of the International Union of Geodesy and Geophysics in July 1995. The new spherical harmonic models adopted are based on weighted averages of candidate models submitted by NASA's Goddard Space Flight Center, the Russian Institute of Terrestrial Magnetism, Ionospheric, and Radio Wave Propagation - IZMIRAN, and jointly by the US Naval Oceanographic Office and the British Geological Survey. The revised IGRF specifies the Earth's main field from 1900 to 2000 and is declared to be definitive from 1945 to 1990. This paper lists the IGRF coefficients, describes the derivation of the new IGRF models, and examines aspects of the IGRF's accuracy, continuity, and behaviour during the 20th century.

  8. Generation of Cosmic Magnetic Fields at Recombination

    CERN Document Server

    Hogan, C J

    2000-01-01

    It is shown that the standard cosmological model predicts ab initio generation of large-scale cosmic magnetic fields at the epoch of recombination of the primeval plasma. Matter velocities dominated by coherent flows on a scale $L\\approx 50h^{-1}(1+z)^{-1}$ Mpc lead to a dipole of radiation flux in the frame of the moving matter. Thomson scattering of the radiation differentially accelerates the electrons and ions, creating large-scale coherent electric currents and magnetic fields. This process is analyzed using magnetohydrodynamic equations which include a modification of Ohm's law describing the effect of Thomson drag on the electrons. The field strength saturates near equipartition with the baryon kinetic energy density at $B\\simeq 5\\times 10^{-5}$G. Magnetic stresses significantly damp baryonic motions at the epoch of last scattering, reducing the predicted background radiation anisotropy at small angles and changing estimates of fitted cosmological parameters. The field at late times retains its large-s...

  9. MATCH: an atom-typing toolset for molecular mechanics force fields.

    Science.gov (United States)

    Yesselman, Joseph D; Price, Daniel J; Knight, Jennifer L; Brooks, Charles L

    2012-01-15

    We introduce a toolset of program libraries collectively titled multipurpose atom-typer for CHARMM (MATCH) for the automated assignment of atom types and force field parameters for molecular mechanics simulation of organic molecules. The toolset includes utilities for the conversion of multiple chemical structure file formats into a molecular graph. A general chemical pattern-matching engine using this graph has been implemented whereby assignment of molecular mechanics atom types, charges, and force field parameters are achieved by comparison against a customizable list of chemical fragments. While initially designed to complement the CHARMM simulation package and force fields by generating the necessary input topology and atom-type data files, MATCH can be expanded to any force field and program, and has core functionality that makes it extendable to other applications such as fragment-based property prediction. In this work, we demonstrate the accurate construction of atomic parameters of molecules within each force field included in CHARMM36 through exhaustive cross validation studies illustrating that bond charge increment rules derived from one force field can be transferred to another. In addition, using leave-one-out substitution it is shown that it is also possible to substitute missing intra and intermolecular parameters with ones included in a force field to complete the parameterization of novel molecules. Finally, to demonstrate the robustness of MATCH and the coverage of chemical space offered by the recent CHARMM general force field (Vanommeslaeghe, et al., J Comput Chem 2010, 31, 671), one million molecules from the PubChem database of small molecules are typed, parameterized, and minimized.

  10. Dissolution study of active pharmaceutical ingredients using molecular dynamics simulations with classical force fields

    Science.gov (United States)

    Greiner, Maximilian; Elts, Ekaterina; Schneider, Julian; Reuter, Karsten; Briesen, Heiko

    2014-11-01

    The CHARMM, general Amber and OPLS force fields are evaluated for their suitability in simulating the molecular dynamics of the dissolution of the hydrophobic, small-molecule active pharmaceutical ingredients aspirin, ibuprofen, and paracetamol in aqueous media. The force fields are evaluated by comparison with quantum chemical simulations or experimental references on the basis of the following capabilities: accurately representing intra- and intermolecular interactions, appropriately reproducing crystal lattice parameters, adequately describing thermodynamic properties, and the qualitative description of the dissolution behavior. To make this approach easily accessible for evaluating the dissolution properties of novel drug candidates in the early stage of drug development, the force field parameter files are generated using online resources such as the SWISS PARAM servers, and the software packages ACPYPE and Maestro. All force fields are found to reproduce the intermolecular interactions with a reasonable degree of accuracy, with the general Amber and CHARMM force fields showing the best agreement with quantum mechanical calculations. A stable crystal bulk structure is obtained for all model substances, except for ibuprofen, where the reproductions of the lattice parameters and observed crystal stability are considerably poor for all force fields. The heat of solution used to evaluate the solid-to-solution phase transitions is found to be in qualitative agreement with the experimental data for all combinations tested, with the results being quantitatively optimum for the general Amber and CHARMM force fields. For aspirin and paracetamol, stable crystal-water interfaces were obtained. The (100), (110), (011) and (001) interfaces of aspirin or paracetamol and water were simulated for each force field for 30 ns. Although generally expected as a rare event, in some of the simulations, dissolution is observed at 310 K and ambient pressure conditions.

  11. Unsteady hydrodynamic forces acting on a robotic hand and its flow field.

    Science.gov (United States)

    Takagi, Hideki; Nakashima, Motomu; Ozaki, Takashi; Matsuuchi, Kazuo

    2013-07-26

    This study aims to clarify the mechanism of generating unsteady hydrodynamic forces acting on a hand during swimming in order to directly measure the forces, pressure distribution, and flow field around the hand by using a robotic arm and particle image velocimetry (PIV). The robotic arm consisted of the trunk, shoulder, upper arm, forearm, and hand, and it was independently computer controllable in five degrees of freedom. The elbow-joint angle of the robotic arm was fixed at 90°, and the arm was moved in semicircles around the shoulder joint in a plane perpendicular to the water surface. Two-component PIV was used for flow visualization around the hand. The data of the forces and pressure acting on the hand were sampled at 200Hz and stored on a PC. When the maximum resultant force acting on the hand was observed, a pair of counter-rotating vortices appeared on the dorsal surface of the hand. A vortex attached to the hand increased the flow velocity, which led to decreased surface pressure, increasing the hydrodynamic forces. This phenomenon is known as the unsteady mechanism of force generation. We found that the drag force was 72% greater and the lift force was 4.8 times greater than the values estimated under steady flow conditions. Therefore, it is presumable that swimmers receive the benefits of this unsteady hydrodynamic force.

  12. POSSIM: Parameterizing Complete Second-Order Polarizable Force Field for Proteins.

    Science.gov (United States)

    Li, Xinbi; Ponomarev, Sergei Y; Sigalovsky, Daniel L; Cvitkovic, John P; Kaminski, George A

    2014-11-11

    Previously, we reported development of a fast polarizable force field and software named POSSIM (POlarizable Simulations with Second order Interaction Model). The second-order approximation permits the speed up of the polarizable component of the calculations by ca. an order of magnitude. We have now expanded the POSSIM framework to include a complete polarizable force field for proteins. Most of the parameter fitting was done to high-level quantum mechanical data. Conformational geometries and energies for dipeptides have been reproduced within average errors of ca. 0.5 kcal/mol for energies of the conformers (for the electrostatically neutral residues) and 9.7° for key dihedral angles. We have also validated this force field by running Monte Carlo simulations of collagen-like proteins in water. The resulting geometries were within 0.94 Å root-mean-square deviation (RMSD) from the experimental data. We have performed additional validation by studying conformational properties of three oligopeptides relevant in the context of N-glycoprotein secondary structure. These systems have been previously studied with combined experimental and computational methods, and both POSSIM and benchmark OPLS-AA simulations that we carried out produced geometries within ca. 0.9 Å RMSD of the literature structures. Thus, the performance of POSSIM in reproducing the structures is comparable with that of the widely used OPLS-AA force field. Furthermore, our fitting of the force field parameters for peptides and proteins has been streamlined compared with the previous generation of the complete polarizable force field and relied more on transferability of parameters for nonbonded interactions (including the electrostatic component). The resulting deviations from the quantum mechanical data are similar to those achieved with the previous generation; thus, the technique is robust, and the parameters are transferable. At the same time, the number of parameters used in this work was

  13. Spatial Confinement of Ultrasonic Force Fields in Microfluidic Channels

    DEFF Research Database (Denmark)

    Manneberg, O; Hagsäter, Melker; Svennebring, J;

    2009-01-01

    of the microfluidic channel. The channel segments are remotely actuated by the use of frequency-specific external transducers with refracting wedges placed on top of the chips. The force field in each channel segment is characterized by the use of micrometer-resolution particle image velocimetry ( micro......-PIV). The confinement of the ultrasonic fields during single-or dual-segment actuation, as well as the cross-talk between two adjacent. fields, is characterized and quantified. Our results show that the field confinement typically scales with the acoustic wavelength, and that the cross-talk is insignificant between...

  14. Endothermic force generation in skinned cardiac muscle from rat.

    Science.gov (United States)

    Ranatunga, K W

    1999-08-01

    Isometric tension responses to rapid temperature jumps (T-jumps) of 2-6 degrees C were examined in skinned muscle fibre bundles isolated from papillary muscles of the rat heart. T-jumps were induced by an infra-red laser pulse (wave length 1.32 microm, pulse duration 0.2 ms) obtained from a Nd-YAG laser, which heated the fibres and bathing buffer solution in a 50 microl trough; the increased temperature by laser pulse was clamped at the high temperature by a Peltier system (see Ranatunga, 1996). In maximally Ca2+ -activated (pCa ca. 4.5) fibres, the relationship between tension and temperature was non-linear, the increase of active tension with temperature being more pronounced at lower temperatures (below ca. 20 degrees C). A T-jump at any temperature (range 3-35 degrees C) induced an initial step decrease of tension of variable amplitude (Phase 1), probably due to thermal expansion, and it was followed by a tension transient which resulted in a net rise of tension above the pre-T-jump level. The rate of net rise of tension (Phase 2b or endothermic force generation) was 7-10/s at ca. 12 degrees C and its Q10 was 6.3 (below 25 degrees C). In cases where the step decrease of tension in Phase 1 was prominent, an initial quick tension recovery phase (Phase 2a, 70-100/s at 12 degrees C) that did not contribute to a rise of tension above the pre-T-jump level, was also seen. This phase (Phase 2a) appeared to be similar to the quick tension recovery induced by a small length release and its rate increased with temperature with a Q10 of 1.8. In some cases where Phase 2a was present, a slower tension rise (Phase 3) was seen; its rate (ca. 5/s) was temperature-insensitive. The results show that the rate of endothermic force generation in cardiac fibres is clearly different from that of either fast-twitch or slow-twitch mammalian skeletal muscle fibres; implication of such fibre type-specific differences is discussed in relation to the difficulty in identifying the

  15. A New Force-Matched Reactive Force Field for Bulk Water Under Extreme Thermodynamic Conditions

    Science.gov (United States)

    Fried, Laurence; Koziol, Lucas

    2015-06-01

    A many-body classical force field is presented for water under dissociative thermodynamic conditions. The force field is optimized by force-matching to ab initio molecular dynamics (AIMD) simulations calculated with Density Functional Theory (DFT). The force field contains short-ranged central and many-body over-coordination terms, and long-range Ewald electrostatics. It is optimized and tested on water at density 1.5 g/mL and 2000 K, which is approximately 10% dissociated according to DFT. Molecular dynamics simulations closely reproduce DFT radial distribution functions, as well as the distribution of wat and dissociation products. The calculated atomic self-diffusion constants appear about 50% lower than in DFT, although precise comparison is impossible due to the short timescale accessible to AIMD (about 20 ps). The force field is also compared to ReaxFF using the CHO parameter set of Chenowith et al. ReaxFF structural and dynamical properties are in overall fair agreement with DFT, although ReaxFF water is not dissociative at these conditions. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

  16. Mapping the force-field of a hydrogen bonded assembly

    Science.gov (United States)

    Moriarty, Philip

    2014-03-01

    Hydrogen-bonding underpins the structure, properties, and dynamics of a vast array of systems spanning a wide variety of scientific fields. From the striking complexity of the phase diagram of H2O and the elegance of base pair interactions in DNA, to the directionality inherent in supramolecular self-assembly at surfaces, hydrogen bonds play an essential role in directing intermolecular forces. Yet fundamental aspects of the H-bond, including the magnitude of the force and binding energy, force constant, and decay length associated with the interaction, have been vigorously debated for many decades. I will discuss how dynamic force microscopy (DFM) using a qPlus sensor can quantitatively map the tip-sample force-field for naphthalene tetracarboxylic diimide (NTCDI) molecules hydrogen-bonded in 2D assemblies. A comparison of experimental images and force spectra with their simulated counterparts from density functional theory calculations shows that image contrast due to intermolecular hydrogen bonds arises fundamentally from charge density depletion due to strong tip-sample interactions. Interpretation of DFM images of hydrogen bonds therefore necessitates detailed consideration of the coupled tip-molecule system: analyses based on intermolecular charge density in the absence of the tip fail to capture the essential physical chemistry underpinning the imaging mechanism.

  17. Force Structure Matters: The US Field Artillery in Operational Art

    Science.gov (United States)

    2015-05-23

    Force Structure Matters: The US Field Artillery in Operational Art A Monograph by MAJ Alex A. Aquino United States Army...The US Field Artillery in Operational Art 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) MAJ Alex A. Aquino... art . First, the monograph evaluates the fires capability requirements outlined in the US Army capstone concepts and assesses the effectiveness of the

  18. Energy buildup in sheared force-free magnetic fields

    Science.gov (United States)

    Wolfson, Richard; Low, Boon C.

    1992-01-01

    Photospheric displacement of the footpoints of solar magnetic field lines results in shearing and twisting of the field, and consequently in the buildup of electric currents and magnetic free energy in the corona. The sudden release of this free energy may be the origin of eruptive events like coronal mass ejections, prominence eruptions, and flares. An important question is whether such an energy release may be accompanied by the opening of magnetic field lines that were previously closed, for such open field lines can provide a route for matter frozen into the field to escape the sun altogether. This paper presents the results of numerical calculations showing that opening of the magnetic field is permitted energetically, in that it is possible to build up more free energy in a sheared, closed, force-free magnetic field than is in a related magnetic configuration having both closed and open field lines. Whether or not the closed force-free field attains enough energy to become partially open depends on the form of the shear profile; the results presented compare the energy buildup for different shear profiles. Implications for solar activity are discussed briefly.

  19. Regulation of the basement membrane by epithelia generated forces

    Science.gov (United States)

    Tanner, Kandice

    2012-12-01

    Tumor metastasis involves a progressive loss of tissue architecture and dissolution of structural boundaries between the epithelium and connective tissue. The basement membrane (BM), a specialized network of extracellular matrix proteins forms a barrier that physically restricts pre-invasive lesions such that they remain as local insults. The BM is not a static structure, but one that is constantly regenerated and remodeled in the adult organism. Matrix organization also regulates cell function. Thus alterations in the balance of synthesis, remodeling and proteolytic degradation of the extracellular matrix proteins may contribute to a loss of structural integrity. However, the de novo assembly and maintenance of the complex structural properties of in vivo basement membranes remain elusive. Here, this paper highlights the current understanding on the structural properties and the establishment of the BM, and discusses the potential role of self-generated forces in adult tissue remodeling and the maintenance of the BM as a malignancy suppressor.

  20. Machine Learning of Accurate Energy-Conserving Molecular Force Fields

    CERN Document Server

    Chmiela, Stefan; Sauceda, Huziel E; Poltavsky, Igor; Schütt, Kristof; Müller, Klaus-Robert

    2016-01-01

    Using conservation of energy -- a fundamental property of closed classical and quantum mechanical systems -- we develop an efficient gradient-domain machine learning (GDML) approach to construct accurate molecular force fields using a restricted number of samples from ab initio molecular dynamics (AIMD) trajectories. The GDML implementation is able to reproduce global potential-energy surfaces of intermediate-size molecules with an accuracy of 0.3 kcal/mol for energies and 1 kcal/mol/{\\AA} for atomic forces using only 1000 conformational geometries for training. We demonstrate this accuracy for AIMD trajectories of molecules, including benzene, toluene, naphthalene, ethanol, uracil, and aspirin. The challenge of constructing conservative force fields is accomplished in our work by learning in a Hilbert space of vector-valued functions that obey the law of energy conservation. The GDML approach enables quantitative molecular dynamics simulations for molecules at a fraction of cost of explicit AIMD calculations...

  1. Paramfit: automated optimization of force field parameters for molecular dynamics simulations.

    Science.gov (United States)

    Betz, Robin M; Walker, Ross C

    2015-01-15

    The generation of bond, angle, and torsion parameters for classical molecular dynamics force fields typically requires fitting parameters such that classical properties such as energies and gradients match precalculated quantum data for structures that scan the value of interest. We present a program, Paramfit, distributed as part of the AmberTools software package that automates and extends this fitting process, allowing for simplified parameter generation for applications ranging from single molecules to entire force fields. Paramfit implements a novel combination of a genetic and simplex algorithm to find the optimal set of parameters that replicate either quantum energy or force data. The program allows for the derivation of multiple parameters simultaneously using significantly fewer quantum calculations than previous methods, and can also fit parameters across multiple molecules with applications to force field development. Paramfit has been applied successfully to systems with a sparse number of structures, and has already proven crucial in the development of the Assisted Model Building with Energy Refinement Lipid14 force field.

  2. Martini Coarse-Grained Force Field : Extension to DNA

    NARCIS (Netherlands)

    Uusitalo, Jaakko J.; Ingolfsson, Helgi I.; Akhshi, Parisa; Tieleman, D. Peter; Marrink, Siewert J.

    2015-01-01

    We systematically parameterized a coarsegrained (CG) model for DNA that is compatible with the Martini force field. The model maps each nucleotide into six to seven CG beads and is parameterized following the Martini philosophy. The CG nonbonded interactions are based on partitioning of the nudeobas

  3. Martini Coarse-Grained Force Field : Extension to Carbohydrates

    NARCIS (Netherlands)

    Lopez, Cesar A.; Rzepiela, Andrzej J.; de Vries, Alex H.; Dijkhuizen, Lubbert; Huenenberger, Philippe H.; Marrink, Siewert J.

    2009-01-01

    We present an extension of the Martini coarse-grained force field to carbohydrates. The parametrization follows the same philosophy as was used previously for lipids and proteins, focusing on the reproduction of partitioning free energies of small compounds between polar and nonpolar phases. The

  4. Martini Coarse-Grained Force Field : Extension to DNA

    NARCIS (Netherlands)

    Uusitalo, Jaakko J.; Ingolfsson, Helgi I.; Akhshi, Parisa; Tieleman, D. Peter; Marrink, Siewert J.

    2015-01-01

    We systematically parameterized a coarsegrained (CG) model for DNA that is compatible with the Martini force field. The model maps each nucleotide into six to seven CG beads and is parameterized following the Martini philosophy. The CG nonbonded interactions are based on partitioning of the nudeobas

  5. Magnetic field generation by intermittent convection

    CERN Document Server

    Chertovskih, R; Chimanski, E V

    2016-01-01

    Magnetic field generation by convective flows in transition to weak turbulence is studied numerically. By fixing the Prandtl number at P=0.3 and varying the Rayleigh number (Ra) as a control parameter in three-dimensional Rayleigh-Benard convection of an electrically conducting fluid, a recently reported route to hyperchaos involving quasiperiodic regimes, crises and chaotic intermittent attractors is followed, and the critical magnetic Prandtl number ($P_m^c$) for dynamo action is determined as a function of Ra. A mechanism for the onset of on-off intermittency in the magnetic energy is described, the most beneficial convective regimes for dynamo action are identified, and how intermittency affects the dependence of $P_m^c$ on Ra is discussed.

  6. ForceFit: a code to fit classical force fields to quantum mechanical potential energy surfaces.

    Science.gov (United States)

    Waldher, Benjamin; Kuta, Jadwiga; Chen, Samuel; Henson, Neil; Clark, Aurora E

    2010-09-01

    The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under UNIX and is written in C++, is an easy-to-use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field, and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program. Copyright 2010 Wiley Periodicals, Inc.

  7. Sustaining the US Air Force’s Force Support Career Field through Officer Workforce Planning

    Science.gov (United States)

    2012-07-01

    communities upon establishment of the Force Support officer career field. With the 38F career field merger and creation of the FSS, officers previously...section. As the development of a competency model typically entails significant investments of time and money , one should ideally first define the...potential workforce management and assignment shortcomings. Dues (2011) utilized a simulation tool to determine how dynamic endogenous and exogenous

  8. Three-dimensional analysis of optical forces generated by an active tractor beam using radial polarization.

    Science.gov (United States)

    Carretero, Luis; Acebal, Pablo; Blaya, Salvador

    2014-02-10

    We theoretically study the three-dimensional behavior of nanoparticles in an active optical conveyor. To do this, we solved the Langevin equation when the forces are generated by a focusing system at the near field. Analytical expressions for the optical forces generated by the optical conveyor were obtained by solving the Richards and Wolf vectorial diffraction integrals in an approximated form when a mask of two annular pupils is illuminated by a radially polarized Hermite-Gauss beam. Trajectories, in both the transverse plane and the longitudinal direction, are analyzed showing that the behavior of the optical conveyor can be optimized by conveniently choosing the configuration of the mask of the two annular pupils (inner and outer radius of the two rings) in order to trap and transport all particles at the focal plane.

  9. Optimization of force constants with an Urey-Bradley force field avoiding normal mode crossings.

    Science.gov (United States)

    Vivoni, A; Birke, R; Lombardi, J

    2001-03-01

    We present a method that simplifies the refinement of force constants in normal mode calculations and makes the results more reliable. The method avoids normal mode crossings by constraining the force constants during refinement. It was tested with pyrrole, imidazole, benzene, pyridine, pyrimidine, aniline and adenine using a Urey-Bradley force field. The global error of the frequency fit for these molecules was 0.61%. The method reproduced with fewer parameters the accuracy of similar calculations of the single ring aromatic compounds. It improved the accuracy and isotopic shifts of previous empirical calculations of adenine by 40%. The C-C and C-N stretchings differed by less than 7% from the values of force constant-bond length empirical relations.

  10. Magnetic field sensor based on the Ampere's force using dual-polarization DBR fiber laser

    Science.gov (United States)

    Yao, Shuang; Zhang, Yang; Guan, Baiou

    2015-08-01

    A novel magnetic field sensor using distributed Bragg reflector (DBR) fiber laser by Ampere's force effect is proposed and experimentally demonstrated. The key sensing element, that is the dual-polarization DBR fiber laser, is fixed on the middle part of two copper plates which carry the current. Ampere's force is applied onto the coppers due to an external magnetic field generated by a DC solenoid. Thus, the lateral force from the coppers is converted to a corresponding beat frequency signal shift produced by the DBR laser. The electric current sensing is also realized by the same configuration and same principle simultaneously in an intuitive manner. Good agreement between the theory calculation and the experimental results is obtained, which shows a good linearity. This sensor's sensitivity to the magnetic field and to the electric current finally reaches ~258.92 kHz/mT and ~1.08727 MHz/A, respectively.

  11. Materials Bound by Non-Chemical Forces: External Fields and the Quantum Vacuum

    CERN Document Server

    Swain, John; Srivastava, Yogendra

    2014-01-01

    We discuss materials which owe their stability to external fields. These include: 1) external electric or magnetic fields, and 2) quantum vacuum fluctuations in these fields induced by suitable boundary conditions (the Casimir effect). Instances of the first case include the floating water bridge and ferrofluids in magnetic fields. An example of the second case is taken from biology where the Casimir effect provides an explanation of the formation of stacked aggregations or "rouleaux" by negatively charged red blood cells. We show how the interplay between electrical and Casimir forces can be used to drive self-assembly of nano-structured materials, and could be generalized both as a probe of Casimir forces and as a means of manufacturing nanoscale structures. Interestingly, all the cases discussed involve the generation of the somewhat exotic negative pressures. We note that very little is known about the phase diagrams of most materials in the presence of external fields other than those represented by the ...

  12. Machine learning of accurate energy-conserving molecular force fields

    Science.gov (United States)

    Chmiela, Stefan; Tkatchenko, Alexandre; Sauceda, Huziel E.; Poltavsky, Igor; Schütt, Kristof T.; Müller, Klaus-Robert

    2017-01-01

    Using conservation of energy—a fundamental property of closed classical and quantum mechanical systems—we develop an efficient gradient-domain machine learning (GDML) approach to construct accurate molecular force fields using a restricted number of samples from ab initio molecular dynamics (AIMD) trajectories. The GDML implementation is able to reproduce global potential energy surfaces of intermediate-sized molecules with an accuracy of 0.3 kcal mol−1 for energies and 1 kcal mol−1 Å̊−1 for atomic forces using only 1000 conformational geometries for training. We demonstrate this accuracy for AIMD trajectories of molecules, including benzene, toluene, naphthalene, ethanol, uracil, and aspirin. The challenge of constructing conservative force fields is accomplished in our work by learning in a Hilbert space of vector-valued functions that obey the law of energy conservation. The GDML approach enables quantitative molecular dynamics simulations for molecules at a fraction of cost of explicit AIMD calculations, thereby allowing the construction of efficient force fields with the accuracy and transferability of high-level ab initio methods. PMID:28508076

  13. Various aspects of magnetic field influence on forced convection

    Directory of Open Access Journals (Sweden)

    Pleskacz Lukasz

    2016-01-01

    Full Text Available Flows in the channels of various geometry can be found everywhere in industrial or daily life applications. They are used to deliver media to certain locations or they are the place where heat may be exchanged. For Authors both points of view are interesting. The enhancement methods for heat transfer during the forced convection are demanded due to a technological development and tendency to miniaturization. At the same time it is also worth to find mechanisms that would help to avoid negative effects like pressure losses or sedimentation in the channel flows. This paper shows and discuss various aspects of magnetic field influence on forced convection. A mathematical model consisted of the mass, momentum and energy conservation equations. In the momentum conservation equation magnetic force term was included. In order to calculate this magnetic force Biot-Savart’s law was utilized. Numerical analysis was performed with the usage of commonly applied software. However, userdefined functions were implemented. The results revealed that both temperature and velocity fields were influenced by the strong magnetic field.

  14. Atomistic force field for alumina fit to density functional theory.

    Science.gov (United States)

    Sarsam, Joanne; Finnis, Michael W; Tangney, Paul

    2013-11-28

    We present a force field for bulk alumina (Al2O3), which has been parametrized by fitting the energies, forces, and stresses of a large database of reference configurations to those calculated with density functional theory (DFT). We use a functional form that is simpler and computationally more efficient than some existing models of alumina parametrized by a similar technique. Nevertheless, we demonstrate an accuracy of our potential that is comparable to those existing models and to DFT. We present calculations of crystal structures and energies, elastic constants, phonon spectra, thermal expansion, and point defect formation energies.

  15. Dipeptide Aggregation in Aqueous Solution from Fixed Point-Charge Force Fields.

    Science.gov (United States)

    Götz, Andreas W; Bucher, Denis; Lindert, Steffen; McCammon, J Andrew

    2014-04-08

    The description of aggregation processes with molecular dynamics simulations is a playground for testing biomolecular force fields, including a new generation of force fields that explicitly describe electronic polarization. In this work, we study a system consisting of 50 glycyl-l-alanine (Gly-Ala) dipeptides in solution with 1001 water molecules. Neutron diffraction experiments have shown that at this concentration, Gly-Ala aggregates into large clusters. However, general-purpose force fields in combination with established water models can fail to correctly describe this aggregation process, highlighting important deficiencies in how solute-solute and solute-solvent interactions are parametrized in these force fields. We found that even for the fully polarizable AMOEBA force field, the degree of association is considerably underestimated. Instead, a fixed point-charge approach based on the newly developed IPolQ scheme [Cerutti et al. J. Phys. Chem.2013, 117, 2328] allows for the correct modeling of the dipeptide aggregation in aqueous solution. This result should stimulate interest in novel fitting schemes that aim to improve the description of the solvent polarization effect within both explicitly polarizable and fixed point-charge frameworks.

  16. Non-Markovian Brownian motion in a magnetic field and time-dependent force fields

    Science.gov (United States)

    Hidalgo-Gonzalez, J. C.; Jiménez-Aquino, J. I.; Romero-Bastida, M.

    2016-11-01

    This work focuses on the derivation of the velocity and phase-space generalized Fokker-Planck equations for a Brownian charged particle embedded in a memory thermal bath and under the action of force fields: a constant magnetic field and arbitrary time-dependent force fields. To achieve the aforementioned goal we use a Gaussian but non-Markovian generalized Langevin equation with an arbitrary friction memory kernel. In a similar way, the generalized diffusion equation in the zero inertia limit is also derived. Additionally we show, in the absence of the time-dependent external forces, that, if the fluctuation-dissipation relation of the second kind is valid, then the generalized Langevin dynamics associated with the charged particle reaches a stationary state in the large-time limit. The consistency of our theoretical results is also verified when they are compared with those derived in the absence of the force fields and in the Markovian case.

  17. The effect of force feedback delay on stiffness perception and grip force modulation during tool-mediated interaction with elastic force fields.

    Science.gov (United States)

    Leib, Raz; Karniel, Amir; Nisky, Ilana

    2015-05-01

    During interaction with objects, we form an internal representation of their mechanical properties. This representation is used for perception and for guiding actions, such as in precision grip, where grip force is modulated with the predicted load forces. In this study, we explored the relationship between grip force adjustment and perception of stiffness during interaction with linear elastic force fields. In a forced-choice paradigm, participants probed pairs of virtual force fields while grasping a force sensor that was attached to a haptic device. For each pair, they were asked which field had higher level of stiffness. In half of the pairs, the force feedback of one of the fields was delayed. Participants underestimated the stiffness of the delayed field relatively to the nondelayed, but their grip force characteristics were similar in both conditions. We analyzed the magnitude of the grip force and the lag between the grip force and the load force in the exploratory probing movements within each trial. Right before answering which force field had higher level of stiffness, both magnitude and lag were similar between delayed and nondelayed force fields. These results suggest that an accurate internal representation of environment stiffness and time delay was used for adjusting the grip force. However, this representation did not help in eliminating the bias in stiffness perception. We argue that during performance of a perceptual task that is based on proprioceptive feedback, separate neural mechanisms are responsible for perception and action-related computations in the brain.

  18. Evaluation of Sulfide Control by Air-Injection in Sewer Force Mains: Field and Laboratory Study

    Directory of Open Access Journals (Sweden)

    Juan T. García

    2017-03-01

    Full Text Available Chemical and biological processes consume dissolved oxygen (DO in urban wastewater during transportation along sewer systems. Anaerobic conditions (DO < 0.2 mg/L are easily reached, leading to sulfide (S2− generation. Release of free sulfide, hydrogen sulfide gas (H2S, from the liquid to the gaseous phase, causes odor, corrosion of pipes and supposes a risk for health of people working in sewers. These issues get worse in force mains, due to inability to take oxygen from the gaseous phase of pipe. Air injection is a suggested practice to control H2S emission in force mains. That technique aims to keep aerobic conditions in wastewater in order to avoid sulfide generation and favor a decrease of Biochemical Organic Demand (BOD. However, several force mains with air injection are not achieving their goals due to a limited oxygen transfer. Field measurements of dissolved oxygen in urban wastewater are presented in an existing force main with air injection during the summer of 2014 in the southeast of Spain. A laboratory scale model is constructed to quantify two-phase flow conditions in pipe due to air injection for different incoming flows rates of water and air. Particularly, for the case of plug flow, also known as elongated bubble flow. Velocity field measurement of water phase in laboratory allows estimating turbulent diffusivity of oxygen in the water, Em, and inter-phase mass transfer coefficient KL(T. In the laboratory, flow and air depth, bubble length, water velocity field, pressure inside force main and water and airflow rates are determined experimentally. These variables are used to assess DO in water phase of force main by comparison with those obtained from field measurements. This work allows assessing air injection efficiency in wastewater, and, therefore, to predict DO in wastewater in force mains.

  19. Classical 5D fields generated by a uniformly accelerated point source

    CERN Document Server

    Aharonovich, I

    2009-01-01

    Gauge fields associated with the manifestly covariant dynamics of particles in $(3,1)$ spacetime are five-dimensional. In this paper we explore the old problem of fields generated by a source undergoing hyperbolic motion in this framework. The 5D fields are computed numerically using absolute time $\\tau$-retarded Green-functions, and qualitatively compared with Maxwell fields generated by the same motion. We find that although the zero mode of all fields coincides with the corresponding Maxwell problem, the non-zero mode should affect, through the Lorentz force, the observed motion of test particles.

  20. 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.

  1. Mapping the force field of a hydrogen-bonded assembly

    Science.gov (United States)

    Sweetman, A. M.; Jarvis, S. P.; Sang, Hongqian; Lekkas, I.; Rahe, P.; Wang, Yu; Wang, Jianbo; Champness, N. R.; Kantorovich, L.; Moriarty, P.

    2014-05-01

    Hydrogen bonding underpins the properties of a vast array of systems spanning a wide variety of scientific fields. From the elegance of base pair interactions in DNA to the symmetry of extended supramolecular assemblies, hydrogen bonds play an essential role in directing intermolecular forces. Yet fundamental aspects of the hydrogen bond continue to be vigorously debated. Here we use dynamic force microscopy (DFM) to quantitatively map the tip-sample force field for naphthalene tetracarboxylic diimide molecules hydrogen-bonded in two-dimensional assemblies. A comparison of experimental images and force spectra with their simulated counterparts shows that intermolecular contrast arises from repulsive tip-sample interactions whose interpretation can be aided via an examination of charge density depletion across the molecular system. Interpreting DFM images of hydrogen-bonded systems therefore necessitates detailed consideration of the coupled tip-molecule system: analyses based on intermolecular charge density in the absence of the tip fail to capture the essential physical chemistry underpinning the imaging mechanism.

  2. Effect of gust on force generation around a robotic hummingbird wing

    Science.gov (United States)

    Marquez, Eloy; Tian, Ruijun; Shu, Fangjun

    2012-11-01

    Among the computational, theoretical and experimental studies on the high efficiency flapping flight, many are focused on the mystery of hovering. Most of these studies were conducted under steady in flow conditions. However, real-life ornithopters in the field have to routinely tackle gust and directional changes of the wind. These sudden perturbations could produce significant effect on humming bird hovering due to the small Reynolds numbers. Our experimental work was performed in a water channel using a two degree-of-freedom humming bird model. The dynamic response of the hovering motion to gust from different directions was investigated. PIV was used to measure the effect of the gust on the surrounding flow field including vortex evolution. In addition, a six-component force/torque sensor was used to measure the real-time lift and drag forces generated by the wing with and without gust. Results show that gust changes the magnitude of lift force in one stroke. However, the time-averaged lift force keeps approximately constant. Supported by Army High Performance Computing Center.

  3. Tuning the Mass of Chameleon Fields in Casimir Force Experiments

    CERN Document Server

    Brax, Ph; Davis, A C; Shaw, D J; Iannuzzi, D

    2010-01-01

    We have calculated the chameleon pressure between two parallel plates in the presence of an intervening medium that affects the mass of the chameleon field. As intuitively expected, the gas in the gap weakens the chameleon interaction mechanism with a screening effect that increases with the plate separation and with the density of the intervening medium. This phenomenon might open up new directions in the search of chameleon particles with future long range Casimir force experiments.

  4. Systematic Parameterization of Lignin for the CHARMM Force Field

    Energy Technology Data Exchange (ETDEWEB)

    Vermaas, Joshua; Petridis, Loukas; Beckham, Gregg; Crowley, Michael

    2017-07-06

    Plant cell walls have three primary components, cellulose, hemicellulose, and lignin, the latter of which is a recalcitrant, aromatic heteropolymer that provides structure to plants, water and nutrient transport through plant tissues, and a highly effective defense against pathogens. Overcoming the recalcitrance of lignin is key to effective biomass deconstruction, which would in turn enable the use of biomass as a feedstock for industrial processes. Our understanding of lignin structure in the plant cell wall is hampered by the limitations of the available lignin forcefields, which currently only account for a single linkage between lignins and lack explicit parameterization for emerging lignin structures both from natural variants and engineered lignin structures. Since polymerization of lignin occurs via radical intermediates, multiple C-O and C-C linkages have been isolated , and the current force field only represents a small subset of lignin the diverse lignin structures found in plants. In order to take into account the wide range of lignin polymerization chemistries, monomers and dimer combinations of C-, H-, G-, and S-lignins as well as with hydroxycinnamic acid linkages were subjected to extensive quantum mechanical calculations to establish target data from which to build a complete molecular mechanics force field tuned specifically for diverse lignins. This was carried out in a GPU-accelerated global optimization process, whereby all molecules were parameterized simultaneously using the same internal parameter set. By parameterizing lignin specifically, we are able to more accurately represent the interactions and conformations of lignin monomers and dimers relative to a general force field. This new force field will enables computational researchers to study the effects of different linkages on the structure of lignin, as well as construct more accurate plant cell wall models based on observed statistical distributions of lignin that differ between

  5. Generated forces and heat during the critical stages of friction stir welding and processing

    Energy Technology Data Exchange (ETDEWEB)

    Hussein, Sadiq Aziz; Tahir, Abd Salam Md; Izamshah, R. [University Teknikal Malaysia Melaka, Malacca (Malaysia)

    2015-10-15

    The solid-state behavior of friction stir welding process results in violent mechanical forces that should be mitigated, if not eliminated. Plunging and dwell time are the two critical stages of this welding process in terms of the generated forces and the related heat. In this study, several combinations of pre-decided penetration speeds, rotational speeds, tool designs, and dwell time periods were used to investigate these two critical stages. Moreover, a coupled-field thermal-structural finite element model was developed to validate the experimental results and the induced stresses. The experimental results revealed the relatively large changes in force and temperature during the first two stages compared with those during the translational tool movement stage. An important procedure to mitigate the undesired forces was then suggested. The model prediction of temperature values and their distribution were in good agreement with the experimental prediction. Therefore, the thermal history of this non-uniform heat distribution was used to estimate the induced thermal stresses. Despite the 37% increase in these stresses when 40 s dwell time was used instead of 5 s, these stresses showed no effect on the axial force values because of the soft material incidence and stir effects.

  6. Molecular simulations of primary alkanolamines using an extendable force field.

    Science.gov (United States)

    Simond, Mickaël R; Ballerat-Busserolles, Karine; Coxam, Jean-Yves; Pádua, Agílio A H

    2012-12-07

    A classical force field is proposed for the molecular simulation of primary alkanolamines containing a NH(2)-C-C-OH backbone. A method is devised to take into account the polar (H-bonding) environment of the alkanolamines by calculating electrostatic charges in the presence of explicit solvent molecules. The force field does not use a universal set of charges, but is rather constructed by following a general method for obtaining specific charges for the different alkanolamines. The model is parameterized on the two simplest primary alkanolamines and then validated by calculating thermodynamic properties of five other molecules. Experimental liquid densities and enthalpies of vaporization are also reported in order to complete existing literature data. The predicted ability of the force field is evaluated by comparing the simulation results with experimental densities and enthalpies of vaporization. Densities are predicted with an uncertainty of 1.5 % and enthalpies of vaporization with an uncertainty of 1 kJ mol(-1). A decomposition of the interaction energy into electrostatic and repulsive-dispersive interactions and an analysis of hydrogen-bond statistics lead to a complex picture. Some terms of these interactions are related to the molecular structure in a clear way, others are not. The results provide insights into the structure-property relations that contribute to a better description of the thermodynamic properties of alkanolamines.

  7. Accurate Force Field Development for Modeling Conjugated Polymers.

    Science.gov (United States)

    DuBay, Kateri H; Hall, Michelle Lynn; Hughes, Thomas F; Wu, Chuanjie; Reichman, David R; Friesner, Richard A

    2012-11-13

    The modeling of the conformational properties of conjugated polymers entails a unique challenge for classical force fields. Conjugation imposes strong constraints upon bond rotation. Planar configurations are favored, but the concomitantly shortened bond lengths result in moieties being brought into closer proximity than usual. The ensuing steric repulsions are particularly severe in the presence of side chains, straining angles, and stretching bonds to a degree infrequently found in nonconjugated systems. We herein demonstrate the resulting inaccuracies by comparing the LMP2-calculated inter-ring torsion potentials for a series of substituted stilbenes and bithiophenes to those calculated using standard classical force fields. We then implement adjustments to the OPLS-2005 force field in order to improve its ability to model such systems. Finally, we show the impact of these changes on the dihedral angle distributions, persistence lengths, and conjugation length distributions observed during molecular dynamics simulations of poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) and poly 3-hexylthiophene (P3HT), two of the most widely used conjugated polymers.

  8. Secondary Structure of Rat and Human Amylin across Force Fields.

    Directory of Open Access Journals (Sweden)

    Kyle Quynn Hoffmann

    Full Text Available The aggregation of human amylin has been strongly implicated in the progression of Type II diabetes. This 37-residue peptide forms a variety of secondary structures, including random coils, α-helices, and β-hairpins. The balance between these structures depends on the chemical environment, making amylin an ideal candidate to examine inherent biases in force fields. Rat amylin differs from human amylin by only 6 residues; however, it does not form fibrils. Therefore it provides a useful complement to human amylin in studies of the key events along the aggregation pathway. In this work, the free energy of rat and human amylin was determined as a function of α-helix and β-hairpin content for the Gromos96 53a6, OPLS-AA/L, CHARMM22/CMAP, CHARMM22*, Amberff99sb*-ILDN, and Amberff03w force fields using advanced sampling techniques, specifically bias exchange metadynamics. This work represents a first systematic attempt to evaluate the conformations and the corresponding free energy of a large, clinically relevant disordered peptide in solution across force fields. The NMR chemical shifts of rIAPP were calculated for each of the force fields using their respective free energy maps, allowing us to quantitatively assess their predictions. We show that the predicted distribution of secondary structures is sensitive to the choice of force-field: Gromos53a6 is biased towards β-hairpins, while CHARMM22/CMAP predicts structures that are overly α-helical. OPLS-AA/L favors disordered structures. Amberff99sb*-ILDN, AmberFF03w and CHARMM22* provide the balance between secondary structures that is most consistent with available experimental data. In contrast to previous reports, our findings suggest that the equilibrium conformations of human and rat amylin are remarkably similar, but that subtle differences arise in transient alpha-helical and beta-strand containing structures that the human peptide can more readily adopt. We hypothesize that these transient

  9. Resonance in Interacting Induced-Dipole Polarizing Force Fields: Application to Force-Field Derivatives

    Directory of Open Access Journals (Sweden)

    Francisco Torrens

    2009-03-01

    Full Text Available The Silberstein model of the molecular polarizability of diatomic molecules, generalized by Applequist et al. for polyatomic molecules, is analyzed. The atoms are regarded as isotropically polarizable points located at their nuclei, interacting via the fields of their induced dipoles. The use of additive values for atom polarizabilities gives poor results, in some cases leading to artificial predictions of absorption bands. The molecular polarizability of methane and its derivative are computed. The agreement with experimental mean molecular polarizabilities is within 1–5%. A hypothesis is indispensable for a suitable representation of polarizability derivative.

  10. Radiation Fields in the Vicinity of Compact Accelerator Neutron Generators

    Energy Technology Data Exchange (ETDEWEB)

    David L. Chichester; Brandon W. Blackburn; Augustine J. Caffrey

    2006-10-01

    Intense pulsed radiation fields emitted from sealed tube neutron generators provide a challenge for modern health physics survey instrumentation. The spectral sensitivity of these survey instruments requires calibration under realistic field conditions while the pulsed emission characteristics of neutron generators can vary from conditions of steady-state operation. As a general guide for assessing radiological conditions around neutron generators, experiments and modeling simulations have been performed to assess radiation fields near DD and DT neutron generators. The presence of other materials and material configurations can also have important effects on the radiation dose fields around compact accelerator neutron generators.

  11. International Geomagnetic Reference Field: the third generation.

    Science.gov (United States)

    Peddie, N.W.

    1982-01-01

    In August 1981 the International Association of Geomagnetism and Aeronomy revised the International Geomagnetic Reference Field (IGRF). It is the second revision since the inception of the IGRF in 1968. The revision extends the earlier series of IGRF models from 1980 to 1985, introduces a new series of definitive models for 1965-1976, and defines a provisional reference field for 1975- 1980. The revision consists of: 1) a model of the main geomagnetic field at 1980.0, not continuous with the earlier series of IGRF models together with a forecast model of the secular variation of the main field during 1980-1985; 2) definitive models of the main field at 1965.0, 1970.0, and 1975.0, with linear interpolation of the model coefficients specified for intervening dates; and 3) a provisional reference field for 1975-1980, defined as the linear interpolation of the 1975 and 1980 main-field models.-from Author

  12. Accurate Interatomic Force Fields via Machine Learning with Covariant Kernels

    CERN Document Server

    Glielmo, Aldo; De Vita, Alessandro

    2016-01-01

    We present a novel scheme to accurately predict atomic forces as vector quantities, rather than sets of scalar components, by Gaussian Process (GP) Regression. This is based on matrix-valued kernel functions, to which we impose that the predicted force rotates with the target configuration and is independent of any rotations applied to the configuration database entries. We show that such "covariant" GP kernels can be obtained by integration over the elements of the rotation group SO(d) for the relevant dimensionality d. Remarkably, in specific cases the integration can be carried out analytically and yields a conservative force field that can be recast into a pair interaction form. Finally, we show that restricting the integration to a summation over the elements of a finite point group relevant to the target system is sufficient to recover an accurate GP. The accuracy of our kernels in predicting quantum-mechanical forces in real materials is investigated by tests on pure and defective Ni and Fe crystalline...

  13. Accurate interatomic force fields via machine learning with covariant kernels

    Science.gov (United States)

    Glielmo, Aldo; Sollich, Peter; De Vita, Alessandro

    2017-06-01

    We present a novel scheme to accurately predict atomic forces as vector quantities, rather than sets of scalar components, by Gaussian process (GP) regression. This is based on matrix-valued kernel functions, on which we impose the requirements that the predicted force rotates with the target configuration and is independent of any rotations applied to the configuration database entries. We show that such covariant GP kernels can be obtained by integration over the elements of the rotation group SO (d ) for the relevant dimensionality d . Remarkably, in specific cases the integration can be carried out analytically and yields a conservative force field that can be recast into a pair interaction form. Finally, we show that restricting the integration to a summation over the elements of a finite point group relevant to the target system is sufficient to recover an accurate GP. The accuracy of our kernels in predicting quantum-mechanical forces in real materials is investigated by tests on pure and defective Ni, Fe, and Si crystalline systems.

  14. Acoustic manipulation of active spherical carriers: Generation of negative radiation force

    Energy Technology Data Exchange (ETDEWEB)

    Rajabi, Majid, E-mail: majid_rajabi@iust.ac.ir; Mojahed, Alireza

    2016-09-15

    This paper examines theoretically a novel mechanism of generating negative (pulling) radiation force for acoustic manipulation of spherical carriers equipped with piezoelectric actuators in its inner surface. In this mechanism, the spherical particle is handled by common plane progressive monochromatic acoustic waves instead of zero-/higher- order Bessel beams or standing waves field. The handling strategy is based on applying a spatially uniform harmonic electrical voltage at the piezoelectric actuator with the same frequency of handling acoustic waves, in order to change the radiation force effect from repulsive (away from source) to attractive (toward source). This study may be considered as a start point for development of contact-free precise handling and entrapment technology of active carriers which are essential in many engineering and medicine applications.

  15. Acoustic manipulation of active spherical carriers: Generation of negative radiation force

    Science.gov (United States)

    Rajabi, Majid; Mojahed, Alireza

    2016-09-01

    This paper examines theoretically a novel mechanism of generating negative (pulling) radiation force for acoustic manipulation of spherical carriers equipped with piezoelectric actuators in its inner surface. In this mechanism, the spherical particle is handled by common plane progressive monochromatic acoustic waves instead of zero-/higher- order Bessel beams or standing waves field. The handling strategy is based on applying a spatially uniform harmonic electrical voltage at the piezoelectric actuator with the same frequency of handling acoustic waves, in order to change the radiation force effect from repulsive (away from source) to attractive (toward source). This study may be considered as a start point for development of contact-free precise handling and entrapment technology of active carriers which are essential in many engineering and medicine applications.

  16. Active contour model based on force field analysis

    Institute of Scientific and Technical Information of China (English)

    HOU Zhi-qiang; HAN Chong-zhao

    2006-01-01

    The traditional snake initial contour should be close to the true boundary of an object of interest in an image;otherwise,an incorrect result will be obtained.Next,active contours have difficulties progressing into boundary concavities.Moreover,the traditional snake as well as almost all of its improved methods can be easily obtained from the local minimum because snake models are nonconvex.An active contour model based on force field analysis (FFA),namely,FFA snake model,is presented in this paper.Based on analyzing force distribution rules of the distance potential force field,a standard is introduced here to distinguish the false one from contour points.The result is not considered as the final solution when the snake energy is minimal.Furthermore,estimation and calculation should be made according to the established standard;only then can the result be considered final.Thus,the snake is prevented from running into the local minimum.The simulation results show that the FFA snake model has a large capture range and can move a snake into the boundary concavities,and that it is able to obtain the object of interest's contour precisely.Compared with the gradient vector flow snake,this new model has a low computational cost.

  17. Force-field functor theory: classical force-fields which reproduce equilibrium quantum distributions.

    Science.gov (United States)

    Babbush, Ryan; Parkhill, John; Aspuru-Guzik, Alán

    2013-01-01

    Feynman and Hibbs were the first to variationally determine an effective potential whose associated classical canonical ensemble approximates the exact quantum partition function. We examine the existence of a map between the local potential and an effective classical potential which matches the exact quantum equilibrium density and partition function. The usefulness of such a mapping rests in its ability to readily improve Born-Oppenheimer potentials for use with classical sampling. We show that such a map is unique and must exist. To explore the feasibility of using this result to improve classical molecular mechanics, we numerically produce a map from a library of randomly generated one-dimensional potential/effective potential pairs then evaluate its performance on independent test problems. We also apply the map to simulate liquid para-hydrogen, finding that the resulting radial pair distribution functions agree well with path integral Monte Carlo simulations. The surprising accessibility and transferability of the technique suggest a quantitative route to adapting Born-Oppenheimer potentials, with a motivation similar in spirit to the powerful ideas and approximations of density functional theory.

  18. Force-Field Functor Theory: Classical Force-Fields which Reproduce Equilibrium Quantum Distributions

    Directory of Open Access Journals (Sweden)

    Ryan eBabbush

    2013-10-01

    Full Text Available Feynman and Hibbs were the first to variationally determine an effective potential whose associated classical canonical ensemble approximates the exact quantum partition function. We examine the existence of a map between the local potential and an effective classical potential which matches the exact quantum equilibrium density and partition function. The usefulness of such a mapping rests in its ability to readily improve Born-Oppenheimer potentials for use with classical sampling. We show that such a map is unique and must exist. To explore the feasibility of using this result to improve classical molecular mechanics, we numerically produce a map from a library of randomly generated one-dimensional potential/effective potential pairs then evaluate its performance on independent test problems. We also apply the map to simulate liquid para-hydrogen, finding that the resulting radial pair distribution functions agree well with path integral Monte Carlo simulations. The surprising accessibility and transferability of the technique suggest a quantitative route to adapting Born-Oppenheimer potentials, with a motivation similar in spirit to the powerful ideas and approximations of density functional theory.

  19. Fiber optical magnetic field sensor for power generator monitoring

    Science.gov (United States)

    Willsch, Michael; Bosselmann, Thomas; Villnow, Michael

    2014-05-01

    Inside of large electrical engines such as power generators and large drives, extreme electric and magnetic fields can occur which cannot be measured electrically. Novel fiber optical magnetic field sensors are being used to characterize the fields and recognize inner faults of large power generators.

  20. Influence of AC external magnetic field on guidance force relaxation between HTS bulk and NdFeB guideway

    Science.gov (United States)

    Zhang, Longcai; Wang, Suyu; Wang, Jiasu; Zheng, Jun

    2007-12-01

    Superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the HTS bulks are always exposed to time-varying external magnetic field, which is generated by the inhomogeneous surface magnetic field of the NdFeB guideway. So it is required to study whether the guidance force of the bulks is influenced by the inhomogeneity. In this paper, we studied the characteristics of the guidance force relaxation between the HTS bulk and the NdFeB guideway by an experiment in which AC external magnetic field generated by an electromagnet was used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway. From the experiment results, it was found that the guidance force was decreased with the application of the AC external magnetic field, and the decay increased with the amplitude and was almost independent of the frequency.

  1. Acoustics forces on a solid sphere in focused sound fields and their use for acoustical traps

    DEFF Research Database (Denmark)

    Cutanda Henriquez, Vicente; Juhl, Peter Møller; Kristensen, Søren H.

    2009-01-01

    It is known that stationary sound fields can be used to levitate small objects in air; this phenomenon has potential applications in containerless processing of materials. Recently the use of acoustic forces have been considered for the manipulation of small samples, which offers several advantages...... as the medium for the propagation of the acoustic waves. The objective of the work to be presented has been to study the extent to which it is possible to use focused sound fields for the manipulation of a rigid sphere in air. The possibility of developing acoustical tweezers has been the main motivation...... of the work. A theoretical investigation based on the boundary element method (BEM) is first described, where the acoustical forces on a rigid sphere are analyzed. It is assumed that the focused sound field is generated by means of a piezoelectric transducer with a shape of a section of a sphere, which...

  2. Nonlinear gravitational self-force: Field outside a small body

    Science.gov (United States)

    Pound, Adam

    2012-10-01

    A small extended body moving through an external spacetime gαβ creates a metric perturbation hαβ, which forces the body away from geodesic motion in gαβ. The foundations of this effect, called the gravitational self-force, are now well established, but concrete results have mostly been limited to linear order. Accurately modeling the dynamics of compact binaries requires proceeding to nonlinear orders. To that end, I show how to obtain the metric perturbation outside the body at all orders in a class of generalized wave gauges. In a small buffer region surrounding the body, the form of the perturbation can be found analytically as an expansion for small distances r from a representative worldline. Given only a specification of the body’s multipole moments, the field obtained in the buffer region suffices to find the metric everywhere outside the body via a numerical puncture scheme. Following this procedure at first and second order, I calculate the field in the buffer region around an arbitrarily structured compact body at sufficiently high order in r to numerically implement a second-order puncture scheme, including effects of the body’s spin. I also define nth-order (local) generalizations of the Detweiler-Whiting singular and regular fields and show that in a certain sense, the body can be viewed as a skeleton of multipole moments.

  3. Active contour external force using vector field convolution for image segmentation.

    Science.gov (United States)

    Li, Bing; Acton, Scott T

    2007-08-01

    Snakes, or active contours, have been widely used in image processing applications. Typical roadblocks to consistent performance include limited capture range, noise sensitivity, and poor convergence to concavities. This paper proposes a new external force for active contours, called vector field convolution (VFC), to address these problems. VFC is calculated by convolving the edge map generated from the image with the user-defined vector field kernel. We propose two structures for the magnitude function of the vector field kernel, and we provide an analytical method to estimate the parameter of the magnitude function. Mixed VFC is introduced to alleviate the possible leakage problem caused by choosing inappropriate parameters. We also demonstrate that the standard external force and the gradient vector flow (GVF) external force are special cases of VFC in certain scenarios. Examples and comparisons with GVF are presented in this paper to show the advantages of this innovation, including superior noise robustness, reduced computational cost, and the flexibility of tailoring the force field.

  4. Design of the magnetorheological mount with high damping force for medium speed diesel generators

    Science.gov (United States)

    Kang, O.-H.; Kim, W.-H.; Joo, W. H.; Park, J.-H.

    2013-04-01

    This paper investigates the controllable magnetorheological (MR) mount for the marine diesel-generator (D/G) sets. Sometimes, significant vibrations over the allowable limit are observed on the D/G sets due to their huge excitation forces. Because the severe vibration can lead to structural damages to the D/G sets, it should be reduced to below the limit. Although passive mounts with rubber isolators are usually used, the vibration reduction performance is not always sufficient. In addition, expecting that the vibration levels required by customers will get more severe, semi-active vibration isolation system needs to be developed. To the aim, the valve (flow) mode type of MR mount has been designed. Especially, the annular-radial configuration was adopted to enhance the damping force within the restricted space. The geometry of the mount has been optimized to obtain the required damping force and the magnetic field analysis has been carried out using ANSYS APDL. To verify the performance of the developed MR mount, excitation test was conducted and the dynamic characteristics were identified. Since damping property of the MR fluid is changed by the applied magnetic field strength and excitation frequency, responses to changing applied currents and frequencies were obtained. From the results, damping performance of the MR mount was evaluated.

  5. Vibrational Spectra of the Azabenzenes Revisited: Anharmonic Force Fields

    CERN Document Server

    Boese, A D; Martin, Jan M.L.

    2003-01-01

    Anharmonic force fields and vibrational spectra of the azabenzene series (pyridine, pyridazine, pyrimidine, pyrazine, s-triazine, 1,2,3-triazine, 1,2,4-triazine and s-tetrazine) and benzene are obtained using density functional theory (DFT) with the B97-1 exchange-correlation functional and a triple-zeta plus double polarization (TZ2P) basis set. Overall, the fundamental frequencies computed by second-order rovibrational perturbation theory are in excellent agreement with experiment. The resolution of the presently calculated anharmonic spectra is such that they represent an extremely useful tool for the assignment and interpretation of the experimental spectra, especially where resonances are involved.

  6. The role of the cytoskeleton in cellular force generation in 2D and 3D environments

    Science.gov (United States)

    Kraning-Rush, Casey M.; Carey, Shawn P.; Califano, Joseph P.; Smith, Brooke N.; Reinhart-King, Cynthia A.

    2011-02-01

    To adhere and migrate, cells generate forces through the cytoskeleton that are transmitted to the surrounding matrix. While cellular force generation has been studied on 2D substrates, less is known about cytoskeletal-mediated traction forces of cells embedded in more in vivo-like 3D matrices. Recent studies have revealed important differences between the cytoskeletal structure, adhesion, and migration of cells in 2D and 3D. Because the cytoskeleton mediates force, we sought to directly compare the role of the cytoskeleton in modulating cell force in 2D and 3D. MDA-MB-231 cells were treated with agents that perturbed actin, microtubules, or myosin, and analyzed for changes in cytoskeletal organization and force generation in both 2D and 3D. To quantify traction stresses in 2D, traction force microscopy was used; in 3D, force was assessed based on single cell-mediated collagen fibril reorganization imaged using confocal reflectance microscopy. Interestingly, even though previous studies have observed differences in cell behaviors like migration in 2D and 3D, our data indicate that forces generated on 2D substrates correlate with forces within 3D matrices. Disruption of actin, myosin or microtubules in either 2D or 3D microenvironments disrupts cell-generated force. These data suggest that despite differences in cytoskeletal organization in 2D and 3D, actin, microtubules and myosin contribute to contractility and matrix reorganization similarly in both microenvironments.

  7. Crafting a Balanced System of Assessment in Wisconsin. Recommendations of the Next Generation Assessment Task Force

    Science.gov (United States)

    Wisconsin Department of Public Instruction, 2009

    2009-01-01

    The Next Generation Assessment Task Force was convened to formulate Wisconsin's path forward. Task force members listened to leaders from business and technology sectors as well as leaders from PK-12 and higher education. This summary shares the process, definitions, assumptions, and recommendations of the task force. This paper aims to use these…

  8. Generation of Seed Magnetic Field around First Stars: the Biermann Battery Effect

    CERN Document Server

    Doi, Kentaro

    2011-01-01

    We investigate generation processes of magnetic fields around first stars. Since the first stars are expected to form anisotropic ionization fronts in the surrounding clumpy media, magnetic fields are generated by effects of radiation force as well as the Biermann battery effect. We have calculated the amplitude of magnetic field generated by the effects of radiation force around the first stars in the preceding paper, in which the Biermann battery effects are not taken into account.In this paper, we calculate the generation of magnetic fields by the Biermann battery effect as well as the effects of radiation force, utilizing the radiation hydrodynamics simulations. As a result, we find that the generated magnetic field strengths are ~ 10^{-19}G-10^{-17}G at ~ 100pc-1kpc scale mainly by the Biermann battery, which is an order of magnitude larger than the results of our previous study. We also find that this result is insensitive to various physical parameters including the mass of the source star, distance be...

  9. A novel three-filament model of force generation in eccentric contraction of skeletal muscles.

    Directory of Open Access Journals (Sweden)

    Gudrun Schappacher-Tilp

    Full Text Available We propose and examine a three filament model of skeletal muscle force generation, thereby extending classical cross-bridge models by involving titin-actin interaction upon active force production. In regions with optimal actin-myosin overlap, the model does not alter energy and force predictions of cross-bridge models for isometric contractions. However, in contrast to cross-bridge models, the three filament model accurately predicts history-dependent force generation in half sarcomeres for eccentric and concentric contractions, and predicts the activation-dependent forces for stretches beyond actin-myosin filament overlap.

  10. The Quantum Space Phase Transitions for Particles and Force Fields

    Directory of Open Access Journals (Sweden)

    Chung D.-Y.

    2006-07-01

    Full Text Available We introduce a phenomenological formalism in which the space structure is treated in terms of attachment space and detachment space. Attachment space attaches to an object, while detachment space detaches from the object. The combination of these spaces results in three quantum space phases: binary partition space, miscible space and binary lattice space. Binary lattice space consists of repetitive units of alternative attachment space and detachment space. In miscible space, attachment space is miscible to detachment space, and there is no separation between attachment space and detachment spaces. In binary partition space, detachment space and attachment space are in two separat continuous regions. The transition from wavefunction to the collapse of wavefuction under interference becomes the quantum space phase transition from binary lattice space to miscible space. At extremely conditions, the gauge boson force field undergoes a quantum space phase transition to a "hedge boson force field", consisting of a "vacuum" core surrounded by a hedge boson shell, like a bubble with boundary.

  11. Accounting for electronic polarization in nonpolarizable force fields

    CERN Document Server

    Leontyev, Igor

    2015-01-01

    The issues of electronic polarizability in molecular dynamics simulations are discussed. We argue that the charges of ionized groups in proteins, and charges of ions in conventional non-polarizable force fields such as CHARMM, AMBER, GROMOS, etc should be scaled by a factor about 0.7. Our model explains why a neglect of electronic solvation energy, which typically amounts to about a half of total solvation energy, in non-polarizable simulations with un-scaled charges can produce a correct result; however, the correct solvation energy of ions does not guarantee the correctness of ion-ion pair interactions in many non-polarizable simulations. The inclusion of electronic screening for charged moieties is shown to result in significant changes in protein dynamics and can give rise to new qualitative results compared with the traditional non-polarizable force field simulations. The model also explains the striking difference between the value of water dipole $\\mu$~3D reported in recent ab initio and experimental s...

  12. Distortion of magnetic field and magnetic force of a brushless dc motor due to deformed rubber magnet

    Science.gov (United States)

    Lee, C. J.; Jang, G. H.

    2008-04-01

    This paper investigates the distortion of magnetic field of a brushless dc (BLDC) motor due to deformed rubber magnet. Global or local deformation of rubber magnet in the BLDC motor is mathematically modeled by using the Fourier series. Distorted magnetic field is calculated by using the finite element method, and unbalanced magnetic force is calculated by using the Maxwell stress tensor. When the rubber magnet is globally or locally deformed, the unbalanced magnetic force has the frequencies with the first harmonic and the harmonics of slot number ±1. However, the harmonic deformation with multiple of common divisor of pole and slot does not generate unbalanced magnetic force due to the rotational symmetry.

  13. Zinc oxide nanorod field effect transistor for long-time cellular force measurement.

    Science.gov (United States)

    Zong, Xianli; Zhu, Rong

    2017-03-08

    Mechanical forces generated by cells are known to influence a vast range of cellular functions ranging from receptor signaling and transcription to differentiation and proliferation. We report a novel measurement approach using zinc oxide nanorods as a peeping transducer to monitor dynamic mechanical behavior of cellular traction on surrounding substrate. We develop a ZnO nanorod field effect transistor (FET) as an ultrasensitive force sensor to realize long-time, unstained, and in-situ detection of cell cycle phases, including attachment, spread, and mitosis. Excellent biocompatibility and ultra-sensitivity of the biomechanical measurement is ensured by coating a parylene film on the FET sensor as a concealment, which provides complete electronic isolation between the sensor and cell. With unique features of ultra-sensitivity, label-free, easy handling, and good biocompatibility, the force sensor allows feasible for tracking cellular dynamics in physiological contexts and understanding their contribution to biological processes.

  14. Non Linear Force Free Field Modeling for a Pseudostreamer

    Science.gov (United States)

    Karna, Nishu; Savcheva, Antonia; Gibson, Sarah; Tassev, Svetlin V.

    2017-08-01

    In this study we present a magnetic configuration of a pseudostreamer observed on April 18, 2015 on southern west limb embedding a filament cavity. We constructed Non Linear Force Free Field (NLFFF) model using the flux rope insertion method. The NLFFF model produces the three-dimensional coronal magnetic field constrained by observed coronal structures and photospheric magnetogram. SDO/HMI magnetogram was used as an input for the model. The high spatial and temporal resolution of the SDO/AIA allows us to select best-fit models that match the observations. The MLSO/CoMP observations provide full-Sun observations of the magnetic field in the corona. The primary observables of CoMP are the four Stokes parameters (I, Q, U, V). In addition, we perform a topology analysis of the models in order to determine the location of quasi-separatrix layers (QSLs). QSLs are used as a proxy to determine where the strong electric current sheets can develop in the corona and also provide important information about the connectivity in complicated magnetic field configuration. We present the major properties of the 3D QSL and FLEDGE maps and the evolution of 3D coronal structures during the magnetofrictional process. We produce FORWARD-modeled observables from our NLFFF models and compare to a toy MHD FORWARD model and the observations.

  15. Higher Harmonics Generation in Tapping Mode Atomic Force Microscope

    Institute of Scientific and Technical Information of China (English)

    LI Yuan; QIAN Jian-Qiang

    2009-01-01

    The contribution of higher harmonics to the movement of a micro rectangular cantilever in tapping mode AFM is investigated. The dependence between the phase lag of the higher harmonic components and tip-sample separation are found to be an order of magnitude higher than the base one, reflecting an increasing sensitivity to local variations of surface properties compared to the normal phase signal.The strong correlation between the higher harmonic amplitude and average sample deformation implies that the higher harmonic amplitude can be taken to monitor the tapping force or as feedback variable to fulfill a constant repulsive force mode.

  16. Methodology of Parameterization of Molecular Mechanics Force Field From Quantum Chemistry Calculations using Genetic Algorithm: A case study of methanol

    CERN Document Server

    Li, Ying; Chan, Maria K Y; Sankaranarayanan, Subramanian; Rouxb, Benoît

    2016-01-01

    In molecular dynamics (MD) simulation, force field determines the capability of an individual model in capturing physical and chemistry properties. The method for generating proper parameters of the force field form is the key component for computational research in chemistry, biochemistry, and condensed-phase physics. Our study showed that the feasibility to predict experimental condensed phase properties (i.e., density and heat of vaporization) of methanol through problem specific force field from only quantum chemistry information. To acquire the satisfying parameter sets of the force field, the genetic algorithm (GA) is the main optimization method. For electrostatic potential energy, we optimized both the electrostatic parameters of methanol using the GA method, which leads to low deviations of between the quantum mechanics (QM) calculations and the GA optimized parameters. We optimized the van der Waals (vdW) parameters both using GA and guided GA methods by calibrating interaction energy of various met...

  17. A new united atom force field for adsorption of alkenes in zeolites

    NARCIS (Netherlands)

    Liu, B.; Smit, B.; Rey, F.; Valencia, S.; Calero, S.

    2008-01-01

    A new united atom force field was developed that accurately describes the adsorption properties of linear alkenes in zeolites. The force field was specifically designed for use in the inhomogeneous system and therefore a truncated and shifted potential was used. With the determined force field, we p

  18. Validating empirical force fields for molecular-level simulation of cellulose dissolution

    Science.gov (United States)

    The calculations presented here, which include dynamics simulations using analytical force fields and first principles studies, indicate that the COMPASS force field is preferred over the Dreiding and Universal force fields for studying dissolution of large cellulose structures. The validity of thes...

  19. High-order-harmonic generation from field-distorted orbitals

    DEFF Research Database (Denmark)

    Spiewanowski, Maciek; Etches, Adam; Madsen, Lars Bojer

    2013-01-01

    We investigate the effect on high-order-harmonic generation of the distortion of molecular orbitals by the driving laser field. Calculations for high-order-harmonic generation including orbital distortion are performed for N2. Our results allow us to suggest that field distortion is the reason why...

  20. CHARMM-GUI Martini Maker for Coarse-Grained Simulations with the Martini Force Field.

    Science.gov (United States)

    Qi, Yifei; Ingólfsson, Helgi I; Cheng, Xi; Lee, Jumin; Marrink, Siewert J; Im, Wonpil

    2015-09-08

    Coarse-grained simulations are widely used to study large biological systems. Nonetheless, building such simulation systems becomes nontrivial, especially when membranes with various lipid types are involved. Taking advantage of the frameworks in all-atom CHARMM-GUI modules, we have developed CHARMM-GUI Martini Maker for building solution, micelle, bilayer, and vesicle systems as well as systems with randomly distributed lipids using the Martini force field. Martini Maker supports 82 lipid types and different flavors of the Martini force field, including polar and nonpolar Martini, Dry Martini, and ElNeDyn (an elastic network model for proteins). The qualities of the systems generated by Martini Maker are validated by simulations of various examples involving proteins and lipids. We expect Martini Maker to be a useful tool for modeling large, complicated biomolecular systems in a user-friendly way.

  1. OCT-based quantification of flow velocity, shear force, and power generated by a biological ciliated surface (Conference Presentation)

    Science.gov (United States)

    Huang, Brendan K.; Khokha, Mustafa K.; Loewenberg, Michael; Choma, Michael A.

    2016-03-01

    In cilia-driven fluid flow physiology, quantification of flow velocity, shearing force, and power dissipation is important in defining abnormal ciliary function. The capacity to generate flow can be robustly described in terms of shearing force. Dissipated power can be related to net ATP consumption by ciliary molecular motors. To date, however, only flow velocity can be routinely quantified in a non-invasive, non-contact manner. Additionally, traditional power-based metrics rely on metabolic consumption that reflects energy consumption not just from cilia but also from all active cellular processes. Here, we demonstrate the estimation of all three of these quantities (flow velocity, shear force, and power dissipation) using only optical coherence tomography (OCT). Specifically, we develop a framework that can extract force and power information from vectorial flow velocity fields obtained using OCT-based methods. We do so by (a) estimating the viscous stress tensor from flow velocity fields to estimate shearing force and (b) using the viscous stress tensor to estimate the power dissipation function to infer total mechanical power. These estimates have the advantage of (a) requiring only a single modality, (b) being non-invasive in nature, and (c) being reflective of only the net power work generated by a ciliated surface. We demonstrate our all-optical approach to the estimation of these parameters in the Xenopus animal model system under normal and increased viscous loading. Our preliminary data support the hypothesis that the Xenopus ciliated surface can increase force output under loading conditions.

  2. Design of Pulsed Strong Magnetic Fields Generator and Preliminary Application

    Institute of Scientific and Technical Information of China (English)

    WEN Jun; QU Xue-min; WANG Xi-gang; LONG Kai-ping

    2015-01-01

    Objective: This paper aims to designing a pulsed strong magnetic fields generator. Methods: A large value capacitor was used to store electric energy, coil was used for producing magnetic fields, main control, circuit control charge, sampling, discharge, etc. Results: The generator provided a pulsed magnetic field with the ampli-tude of intensity from 0.1-2 T and variable time interval of pulse from 4 s-1 min. It was not only to be operated easily but also performed reliably. Conclusion:The generator will be applied in special clinical diagnosis, therapy and other fields.

  3. Magnetic Energy of Force-Free Fields with Detached Field Lines

    Institute of Scientific and Technical Information of China (English)

    Guo-Qiang Li; You-Qiu Hu

    2003-01-01

    Using an axisymmetrical ideal MHD model in spherical coordinates, we present a numerical study of magnetic configurations characterized by a levitating flux rope embedded in a bipolar background field whose normal field at the solar surface is the same or very close to that of a central dipole. The characteristic plasmaβ (the ratio between gas pressure and magnetic pressure) is taken to be so small (β = 10-4) that the magnetic field is close to being force-free. The system as a whole is then let evolve quasi-statically with a slow increase of either the annular magnetic flux or the axial magnetic flux of the rope, and the total magnetic energy of the system grows accordingly. It is found that there exists an energy threshold: the flux rope sticks to the solar surface in equilibrium if the magnetic energy of the system is below the threshold, whereas it loses equilibrium if the threshold is exceeded. The energy threshold is found to be larger than that of the corresponding fully-open magnetic field by a factor of nearly 1.08 irrespective as to whether the background field is completely closed or partly open, or whether the magnetic energy is enhanced by an increase of annular or axial flux of the rope.This gives an example showing that a force-free magnetic field may have an energylarger than the corresponding open field energy if part of the field lines is allowed to be detached from the solar surface. The implication of such a conclusion in coronal mass ejections is briefly discussed and some comments are made on the maximum energy of force-free magnetic fields.

  4. Electrostatic air filters generated by electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Bergman, W.; Biermann, A.H.; Hebard, H.D.; Lum, B.Y.; Kuhl, W.D.

    1981-01-27

    This paper presents theoretical and experimental findings on fibrous filters converted to electrostatic operation by a nonionizing electric field. Compared to a conventional fibrous filter, the electrostatic filter has a higher efficiency and a longer, useful life. The increased efficiency is attributed to a time independent attraction between polarized fibers and charged, polarized particles and a time dependent attraction between charged fibers and charged, polarized particles. The charge on the fibers results from a dynamic process of charge accumulation due to the particle deposits and a charge dissipation due to the fiber conductivity.

  5. Identification by force modulation microscopy of nanoparticles generated in vacuum arcs Identification by force modulation microscopy of nanoparticles generated in vacuum arcs

    OpenAIRE

    M. Arroyave Franco

    2006-01-01

    An alternative method based on force modulation microscopy (FMM) for identification of nanoparticles produced in the plasma generated by the cathode spots of vacuum arcs is presented. FMM technique is enabled for the detection of variations in the mechanical properties of a surface with high sensitiveness. Titanium nitride (TiN) coatings deposited on oriented silicon by pulsed vacuum arc process have been analyzed. AFM (Atomic Force Microscopy) and FMM images were simultaneously obtained, and...

  6. Can different media generate scattered field with identical spectral coherence?

    Science.gov (United States)

    Wang, Tao; Jiang, Zhenfei; Ji, Xiaoling; Zhao, Daomu

    2016-03-01

    The possibility for different media to generate scattered field with identical spectral coherence is discussed. It is shown that two random media, with different characters of correlation function, may generate scattered field with identical spectral coherence property. An example of light waves on scattering from Gaussian-Schell model media is discussed, and a condition for identical spectral coherence of the far-zone scattered field is obtained.

  7. Transcranial magnetic stimulation during voluntary action: directional facilitation of outputs and relationships to force generation.

    Science.gov (United States)

    Cros, Didier; Soto, Oscar; Chiappa, Keith H

    2007-12-14

    Single-pulse transcranial magnetic stimulation (TMS) of the human motor cortex evokes simple muscle jerks whose physiological significance is unclear. Indeed, in subjects performing a motor task, there is uncertainty as to whether TMS-evoked outputs reflect the ongoing behavior or, alternatively, a disrupted motor plan. Considering force direction and magnitude to reflect qualitative and quantitative features of the motor plan respectively, we studied the relationships between voluntary forces and those evoked by TMS. In five healthy adults, we recorded the isometric forces acting a hand joint and the electromyographic activity in the first dorsal interosseous (FDI) muscle. Responses obtained at rest were highly invariant. Evoked responses obtained while subjects generated static and dynamic contractions were highly codirectional with the voluntary forces. Such directional relationships were independent of stimulation intensity, stimulated cortical volume, or magnitude of voluntary force exerted. Dynamic force generation was associated with a marked increase in the magnitude of the evoked force that was linearly related to the rate of force generation. The timing of central conduction was different depending on functional role of the target muscle, as either agonist or joint fixator. These results indicate that the architecture of motor plans remain grossly undisrupted by cortical stimulation applied during voluntary motor behavior. The significant magnitude modulation of responses during dynamic force generation suggests an essential role of the corticospinal system in the specification of force changes. Finally, the corticospinal activation depends on the functional role assumed by the target muscle, either postural or agonist.

  8. New arrangements in force in the field of transport

    CERN Multimedia

    Tom Wegelius

    2006-01-01

    Please take note of the following information concerning new arrangements in force in the field of transport: China: Regulations applying to wooden packaging materials as of 1st January 2006 As scheduled, China introduced standard ISPM No. 15 on 1st January 2006. This was officially confirmed in a letter from the Federal Minister for Consumer Protection, Food and Agriculture. Henceforth, China will apply the same conditions to the importation of wooden packaging materials as various other countries, including the United States, Mexico and Brazil. This means that items shipped to China in wooden packaging will no longer need to be accompanied by a certificate relating to the protection of plant species or other phytosanitary documents (such as heat treatment certificates). However, a guarantee that the wooden packaging complies with standard ISPM No. 15 will be required. Phase II of US regulations concerning wooden packaging material Phase II of regulations concerning the importation of wooden packaging ma...

  9. A Multiposture Locomotor Training Device with Force-Field Control

    Directory of Open Access Journals (Sweden)

    Jianfeng Sui

    2014-11-01

    Full Text Available This paper introduces a multiposture locomotor training device (MPLTD with a closed-loop control scheme based on joint angle feedback, which is able to overcome various difficulties resulting from mechanical vibration and the weight of trainer to achieve higher accuracy trajectory. By introducing the force-field control scheme used in the closed-loop control, the device can obtain the active-constrained mode including the passive one. The MPLTD is mainly composed of three systems: posture adjusting and weight support system, lower limb exoskeleton system, and control system, of which the lower limb exoskeleton system mainly includes the indifferent equilibrium mechanism with two degrees of freedom (DOF and the driving torque is calculated by the Lagrangian function. In addition, a series of experiments, the weight support and the trajectory accuracy experiment, demonstrate a good performance of mechanical structure and the closed-loop control.

  10. Generation of magnetic field on the accretion disk around a proto-first-star

    Energy Technology Data Exchange (ETDEWEB)

    Shiromoto, Yuki; Susa, Hajime [Department of Physics, Konan University, Kobe 658-8501 (Japan); Hosokawa, Takashi, E-mail: susa@konan-u.ac.jp [Department of Physics and Research Center for the Early Universe, The University of Tokyo, Tokyo 113-0033 (Japan)

    2014-02-20

    The generation process of a magnetic field around a proto-first-star is studied. Utilizing the recent numerical results of proto-first-star formation based on radiation hydrodynamics simulations, we assess the magnetic field strength generated by the radiative force and the Biermann battery effect. We find that a magnetic field of ∼10{sup –9} G is generated on the surface of the accretion disk around the proto-first-star. The field strength on the accretion disk is smaller by two orders of magnitude than the critical value, above which the gravitational fragmentation of the disk is suppressed. Thus, the generated seed magnetic field hardly affect the dynamics of on-site first star formation directly, unless an efficient amplification process is taken into consideration. We also find that the generated magnetic field is continuously blown out from the disk on the outflows to the poles, that are driven by the thermal pressure of photoheated gas. The strength of the diffused magnetic field in low-density regions is ∼10{sup –14}-10{sup –13} G at n {sub H} = 10{sup 3} cm{sup –3}, which could play an important role in the next generation star formation, as well as the seeds of the magnetic field in the present-day universe.

  11. Linear servo-controlled pressure generator for forced oscillation measurements.

    Science.gov (United States)

    de Melo, P L; Werneck, M M; Giannella-Neto, A

    1998-01-01

    In respiratory input impedance measurements, the low-frequency range contains important clinical and physiological information. However, the patient's spontaneous ventilation can contaminate the data in this range, leading to unreliable results. Unbiased estimators are a good alternative to overcome this problem, provided that the generator is considered linear. This condition is not fulfilled by most existing generators as they are based on loudspeakers, which have strong nonlinearities. The present work aims to contribute to the solution of this problem, and describes a pressure generator that minimises the nonlinearities by an optical sensor placed in a position feedback loop. The static evaluation shows a high linearity for the optical system. The well known frequency response of pressure transducers is used in the dynamic evaluation of the instrument. The analysis of the generator shows that the use of position feedback improved the frequency response. The total harmonic distortion (THD) measurement shows that closed loop resulted in an effective decrease in the nonlinearities. The reduction of THD achieved by the servo-controlled generator can contribute to the practical implementation of the unbiased estimators, increasing the reliability of the impedance data, especially in the low-frequency range. This system is compared with conventional generators and with another servo-controlled system.

  12. Accounting for electronic polarization in non-polarizable force fields

    Science.gov (United States)

    Leontyev, Igor; Stuchebrukhov, Alexei

    The issues of electronic polarizability in molecular dynamics simulations are discussed. We argue that the charges of ionized groups in proteins, and charges of ions in conventional non-polarizable force fields such as CHARMM, AMBER, GROMOS, etc should be scaled by a factor about 0.7. Our model explains why a neglect of electronic solvation energy, which typically amounts to about a half of total solvation energy, in non-polarizable simulations with un-scaled charges can produce a correct result; however, the correct solvation energy of ions does not guarantee the correctness of ion-ion pair interactions in many non-polarizable simulations. The inclusion of electronic screening for charged moieties is shown to result in significant changes in protein dynamics and can give rise to new qualitative results compared with the traditional non-polarizable force field simulations. The model also explains the striking difference between the value of water dipole $\\mu$~3D reported in recent ab initio and experimental studies with the value $\\mu_{eff}$~2.3D typically used in the empirical potentials, such as TIP3P or SPC/E. It is shown that the effective dipole of water can be understood as a scaled value $\\mu_{eff}=\\mu/\\sqrt{\\epsilon_{el}}$, where $\\epsilon_{el}$=1.78 is the electronic (high-frequency) dielectric constant of water. This simple theoretical framework provides important insights into the nature of the effective parameters, which is crucial when the computational models of liquid water are used for simulations in different environments, such as proteins, or for interaction with solutes.

  13. Enthalpy of formation and anharmonic force field of diacetylene.

    Science.gov (United States)

    Simmonett, Andrew C; Schaefer, Henry F; Allen, Wesley D

    2009-01-28

    The enthalpy of formation of diacetylene (C4H2) is pinpointed using state-of-the-art theoretical methods, accounting for high-order electron correlation, relativistic effects, non-Born-Oppenheimer corrections, and vibrational anharmonicity. Molecular energies are determined from coupled cluster theory with single and double excitations (CCSD), perturbative triples [CCSD(T)], full triples (CCSDT), and perturbative quadruples [CCSDT(Q)], in concert with correlation-consistent basis sets (cc-pVXZ, X=D, T, Q, 5, 6) that facilitate extrapolations to the complete basis set limit. The first full quartic force field of diacetylene is determined at the highly accurate all-electron CCSD(T) level with a cc-pCVQZ basis, which includes tight functions for core correlation. Application of second-order vibrational perturbation theory to our anharmonic force field yields fundamental frequencies with a mean absolute difference of only 3.9 cm(-1) relative to the experimental band origins, without the use of any empirical scale factors. By a focal point approach, we converge on an enthalpy change for the isogyric reaction 2 H-C[triple bond]C-H-->H-C[triple bond]C-C[triple bond]C-H+H2 of (+0.03, +0.81) kcal mol(-1) at (0, 298.15) K. With the precisely established fHdegrees of acetylene, we thus obtain DeltafHdegrees(C4H2)=(109.4,109.7)+/-0.3 kcal mol(-1) at (0, 298.15) K. Previous estimates of the diacetylene enthalpy of formation range from 102 to 120 kcal mol(-1).

  14. Evolution of Primordial Magnetic Fields: From Generation Till Today

    CERN Document Server

    Kahniashvili, Tina; Tevzadze, Alexander G

    2015-01-01

    In this presentation we summarize our previous results concerning the evolution of primordial magnetic fields with and without helicity during the expansion of the Universe. We address different magnetogenesis scenarios such as inflation, electroweak and QCD phase transitions magnetogenesis. A high Reynolds number in the early Universe ensures strong coupling between magnetic field and fluid motions. After generation the subsequent dynamics of the magnetic field is governed by decaying hydromagnetic turbulence. We claim that primordial magnetic fields can be considered as a seeds for observed magnetic fields in galaxies and clusters. Magnetic field strength bounds obtained in our analysis are consistent with the upper and lower limits of extragalactic magnetic fields.

  15. Generating Functionals for Quantum Field Theories with Random Potentials

    CERN Document Server

    Jain, Mudit

    2015-01-01

    We consider generating functionals for computing correlators in quantum field theories with random potentials. Examples of such theories include condensed matter systems with quenched disorder (e.g. spin glass) or cosmological systems in context of the string theory landscape (e.g. cosmic inflation). We use the so-called replica trick to define two different generating functionals for calculating correlators of the quantum fields averaged over a given distribution of random potentials. The first generating functional is appropriate for calculating averaged (in-out) amplitudes and involves a single replica of fields, but the replica limit is taken to an (unphysical) negative one number of fields outside of the path integral. When the number of replicas is doubled the generating functional can also be used for calculating averaged probabilities (squared amplitudes) using the in-in construction. The second generating functional involves an infinite number of replicas, but can be used for calculating both in-out ...

  16. Direct reaction field force field : A consistent way to connect and combine quantum-chemical and classical descriptions of molecules

    NARCIS (Netherlands)

    VanDuijnen, PT; DeVries, AH

    1996-01-01

    The direct reaction field (DRF) force field gives a classical description of intermolecular interactions based on ab initio quantum-chemical descriptions of matter. The parameters of the DRF force field model molecular electrostatic and response properties, which are represented by distributed charg

  17. Cooperative retraction of bundled type IV pili enables nanonewton force generation.

    Directory of Open Access Journals (Sweden)

    Nicolas Biais

    2008-04-01

    Full Text Available The causative agent of gonorrhea, Neisseria gonorrhoeae, bears retractable filamentous appendages called type IV pili (Tfp. Tfp are used by many pathogenic and nonpathogenic bacteria to carry out a number of vital functions, including DNA uptake, twitching motility (crawling over surfaces, and attachment to host cells. In N. gonorrhoeae, Tfp binding to epithelial cells and the mechanical forces associated with this binding stimulate signaling cascades and gene expression that enhance infection. Retraction of a single Tfp filament generates forces of 50-100 piconewtons, but nothing is known, thus far, on the retraction force ability of multiple Tfp filaments, even though each bacterium expresses multiple Tfp and multiple bacteria interact during infection. We designed a micropillar assay system to measure Tfp retraction forces. This system consists of an array of force sensors made of elastic pillars that allow quantification of retraction forces from adherent N. gonorrhoeae bacteria. Electron microscopy and fluorescence microscopy were used in combination with this novel assay to assess the structures of Tfp. We show that Tfp can form bundles, which contain up to 8-10 Tfp filaments, that act as coordinated retractable units with forces up to 10 times greater than single filament retraction forces. Furthermore, single filament retraction forces are transient, whereas bundled filaments produce retraction forces that can be sustained. Alterations of noncovalent protein-protein interactions between Tfp can inhibit both bundle formation and high-amplitude retraction forces. Retraction forces build over time through the recruitment and bundling of multiple Tfp that pull cooperatively to generate forces in the nanonewton range. We propose that Tfp retraction can be synchronized through bundling, that Tfp bundle retraction can generate forces in the nanonewton range in vivo, and that such high forces could affect infection.

  18. Network representation of electromagnetic fields and forces using generalized bond graphs

    NARCIS (Netherlands)

    Nijen Twilhaar, G.D.

    1985-01-01

    We show that it is possible to describe electromagnetic (E-M) fields with a generalized network representation (generalized bond graphs). E-M fields inmoving matter, forces due to E-M fields (Lorentz force, ets.) and field transformations are included in the network description. The relations of the

  19. Calculating forces on thin flat plates with incomplete vorticity-field data

    Science.gov (United States)

    Limacher, Eric; Morton, Chris; Wood, David

    2016-11-01

    Optical experimental techniques such as particle image velocimetry (PIV) permit detailed quantification of velocities in the wakes of bluff bodies. Patterns in the wake development are significant to force generation, but it is not trivial to quantitatively relate changes in the wake to changes in measured forces. Key difficulties in this regard include: (i) accurate quantification of velocities close to the body, and (ii) the effect of missing velocity or vorticity data in regions where optical access is obscured. In the present work, we consider force formulations based on the vorticity field, wherein mathematical manipulation eliminates the need for accurate near-body velocity information. Attention is restricted to nominally two dimensional problems, namely (i) a linearly accelerating flat plate, investigated using PIV in a water tunnel, and (ii) a pitching plate in a freestream flow, as investigated numerically by Wang & Eldredge (2013). The effect of missing vorticity data on the pressure side of the plate has a significant impact on the calculation of force for the pitching plate test case. Fortunately, if the vorticity on the pressure side remains confined to a thin boundary layer, simple corrections can be applied to recover a force estimate.

  20. Acoustic radiation force in tissue-like solids due to modulated sound field

    Science.gov (United States)

    Dontsov, Egor V.; Guzina, Bojan B.

    2012-10-01

    The focus of this study is the sustained body force (the so-called acoustic radiation force) in homogeneous tissue-like solids generated by an elevated-intensity, focused ultrasound field (Mach number=O(10-3)) in situations when the latter is modulated by a low-frequency signal. This intermediate-asymptotics problem, which bears relevance to a number of emerging biomedical applications, is characterized by a number of small (but non-vanishing) parameters including the Mach number, the ratio between the modulation and ultrasound frequency, the ratio of the shear to bulk modulus, and the dimensionless attenuation coefficient. On approximating the response of soft tissues as that of a nonlinear viscoelastic solid with heat conduction, the featured second-order problem is tackled via a scaling paradigm wherein the transverse coordinates are scaled by the width of the focal region, while the axial and temporal coordinate are each split into a "fast" and "slow" component with the twin aim of: (i) canceling the linear terms from the field equations governing the propagation of elevated-intensity ultrasound, and (ii) accounting for the effect of ultrasound modulation. In the context of the focused ultrasound analyses, the key feature of the proposed study revolves around the dual-time-scale treatment of the temporal variable, which allows one to parse out the contribution of ultrasound and its modulation in the nonlinear solution. In this way the acoustic radiation force (ARF), giving rise to the mean tissue motion, is exacted by computing the "fast" time average of the germane field equations. A comparison with the existing theory reveals a number of key features that are brought to light by the new formulation, including the contributions to the ARF of ultrasound modulation and thermal expansion, as well as the precise role of constitutive nonlinearities in generating the sustained body force in tissue-like solids by a focused ultrasound beam.

  1. ForceFit: a code to fit classical force fields to ab-initio potential energy surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Henson, Neil Jon [Los Alamos National Laboratory; Waldher, Benjamin [WSU; Kuta, Jadwiga [WSU; Clark, Aurora [WSU; Clark, Aurora E [NON LANL

    2009-01-01

    The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under Unix and is written in C++, is an easy to use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program.

  2. ForceFit: a code to fit classical force fields to ab-initio potential energy surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Henson, Neil Jon [Los Alamos National Laboratory; Waldher, Benjamin [WSU; Kuta, Jadwiga [WSU; Clark, Aurora [WSU; Clark, Aurora E [NON LANL

    2009-01-01

    The ForceFit program package has been developed for fitting classical force field parameters based upon a force matching algorithm to quantum mechanical gradients of configurations that span the potential energy surface of the system. The program, which runs under Unix and is written in C++, is an easy to use, nonproprietary platform that enables gradient fitting of a wide variety of functional force field forms to quantum mechanical information obtained from an array of common electronic structure codes. All aspects of the fitting process are run from a graphical user interface, from the parsing of quantum mechanical data, assembling of a potential energy surface database, setting the force field and variables to be optimized, choosing a molecular mechanics code for comparison to the reference data, and finally, the initiation of a least squares minimization algorithm. Furthermore, the code is based on a modular templated code design that enables the facile addition of new functionality to the program.

  3. New Mechanism for Mass Generation of Gauge Field

    Institute of Scientific and Technical Information of China (English)

    WUNing

    2001-01-01

    A new mechanism for mass generation of gauge field is discussed in this paper.By introducing two sets of gauge fields and making the variations of these two sets of gauge fields compensated each other under local gauge transformations,the mass term of gauge fields is introduced into the Lagrangian without violating the local gauge symmetry of the Lagrangian.This model is a renormalizable quantum model.

  4. New Mechanism for Mass Generation of Gauge Field

    Institute of Scientific and Technical Information of China (English)

    WU Ning

    2001-01-01

    A new mechanism for mass generation of gauge field is discussed in this paper. By introducing two sets of gauge fields and making the variations of these two sets of gauge fields compensated each other under local gauge transformations, the mass term of gauge fields is introduced into the Lagrangian without violating the local gauge symmetry of the Lagrangian. This model is a renormalizable quantum model.

  5. Applying the cost of generating force hypothesis to uphill running

    Directory of Open Access Journals (Sweden)

    Wouter Hoogkamer

    2014-07-01

    Full Text Available Historically, several different approaches have been applied to explain the metabolic cost of uphill human running. Most of these approaches result in unrealistically high values for the efficiency of performing vertical work during running uphill, or are only valid for running up steep inclines. The purpose of this study was to reexamine the metabolic cost of uphill running, based upon our understanding of level running energetics and ground reaction forces during uphill running. In contrast to the vertical efficiency approach, we propose that during incline running at a certain velocity, the forces (and hence metabolic energy required for braking and propelling the body mass parallel to the running surface are less than during level running. Based on this idea, we propose that the metabolic rate during uphill running can be predicted by a model, which posits that (1 the metabolic cost of perpendicular bouncing remains the same as during level running, (2 the metabolic cost of running parallel to the running surface decreases with incline, (3 the delta efficiency of producing mechanical power to lift the COM vertically is constant, independent of incline and running velocity, and (4 the costs of leg and arm swing do not change with incline. To test this approach, we collected ground reaction force (GRF data for eight runners who ran thirty 30-second trials (velocity: 2.0–3.0 m/s; incline: 0–9°. We also measured the metabolic rates of eight different runners for 17, 7-minute trials (velocity: 2.0–3.0 m/s; incline: 0–8°. During uphill running, parallel braking GRF approached zero for the 9° incline trials. Thus, we modeled the metabolic cost of parallel running as exponentially decreasing with incline. With that assumption, best-fit parameters for the metabolic rate data indicate that the efficiency of producing mechanical power to lift the center of mass vertically was independent of incline and running velocity, with a value of ∼29

  6. Evaluating Parametrization Protocols for Hydration Free Energy Calculations with the AMOEBA Polarizable Force Field.

    Science.gov (United States)

    Bradshaw, Richard T; Essex, Jonathan W

    2016-08-09

    Hydration free energy (HFE) calculations are often used to assess the performance of biomolecular force fields and the quality of assigned parameters. The AMOEBA polarizable force field moves beyond traditional pairwise additive models of electrostatics and may be expected to improve upon predictions of thermodynamic quantities such as HFEs over and above fixed-point-charge models. The recent SAMPL4 challenge evaluated the AMOEBA polarizable force field in this regard but showed substantially worse results than those using the fixed-point-charge GAFF model. Starting with a set of automatically generated AMOEBA parameters for the SAMPL4 data set, we evaluate the cumulative effects of a series of incremental improvements in parametrization protocol, including both solute and solvent model changes. Ultimately, the optimized AMOEBA parameters give a set of results that are not statistically significantly different from those of GAFF in terms of signed and unsigned error metrics. This allows us to propose a number of guidelines for new molecule parameter derivation with AMOEBA, which we expect to have benefits for a range of biomolecular simulation applications such as protein-ligand binding studies.

  7. Optimized atomistic force fields for aqueous solutions of Magnesium and Calcium Chloride: Analysis, achievements and limitations

    Science.gov (United States)

    Elfgen, Roman; Hülsmann, Marco; Krämer, Andreas; Köddermann, Thorsten; Kirschner, Karl N.; Reith, Dirk

    2016-10-01

    Molecular simulations are an important tool in the study of aqueous salt solutions. To predict the physical properties accurately and reliably, the molecular models must be tailored to reproduce experimental data. In this work, a combination of recent global and local optimization tools is used to derive force fields for MgCl2 (aq) and CaCl2 (aq). The molecular models for the ions are based on a Lennard-Jones (LJ) potential with a superimposed point charge. The LJ parameters are adjusted to reproduce the bulk density and shear viscosity of the different solutions at 1 bar and temperatures of 293.15, 303.15, and 318.15 K. It is shown that the σ-value of chloride consistently has the strongest influence on the system properties. The optimized force field for MgCl2 (aq) provides both properties in good agreement with the experimental data over a wide range of salt concentrations. For CaCl2 (aq), a compromise was made between the bulk density and shear viscosity, since reproducing the two properties requires two different choices of the LJ parameters. This is demonstrated by studying metamodels of the simulated data, which are generated to visualize the correlation between the parameters and observables by using projection plots. Consequently, in order to derive a transferable force field, an error of ˜3% on the bulk density has to be tolerated to yield the shear viscosity in satisfactory agreement with experimental data.

  8. Relativistic Scott correction in self-generated magnetic fields

    DEFF Research Database (Denmark)

    Erdos, Laszlo; Fournais, Søren; Solovej, Jan Philip

    2012-01-01

    /3}$ and it is unchanged by including the self-generated magnetic field. We prove the first correction term to this energy, the so-called Scott correction of the form $S(\\alpha Z) Z^2$. The current paper extends the result of \\cite{SSS} on the Scott correction for relativistic molecules to include a self......-generated magnetic field. Furthermore, we show that the corresponding Scott correction function $S$, first identified in \\cite{SSS}, is unchanged by including a magnetic field. We also prove new Lieb-Thirring inequalities for the relativistic kinetic energy with magnetic fields....

  9. Generation of Electric Field and Net Charge in Hall Reconnection

    Institute of Scientific and Technical Information of China (English)

    MA Zhi-Wei; FENG Shu-Ling

    2008-01-01

    @@ Generation of Hall electric field and net charge associated with magnetic reconnection is studied under different initial conditions of plasma density and magnetic field. With inclusion of the Hall effects, decoupling of the electron and ion motions leads to the formation of a narrow layer with strong electric field and large net charge density along the separatrix. The asymmetry of the plasma density or magnetic field or both across the current sheet will largely increase the magnitude of the electric field and net charge. The results indicate that the asymmetry of the magnetic field is more effective in producing larger electric field and charge density. The electric field and net charge are always much larger in the low density or/and high magnetic field side than those in the high density or/and low magnetic field side. Both the electric field and net charge density are linearly dependent on the ratios of the plasma density or the square of the magnetic field across the current sheet. For the case with both initial asymmetries of the magnetic field and density, rather large Hall electric field and charge density are generated.

  10. ForceGen 3D structure and conformer generation: from small lead-like molecules to macrocyclic drugs

    Science.gov (United States)

    Cleves, Ann E.; Jain, Ajay N.

    2017-03-01

    We introduce the ForceGen method for 3D structure generation and conformer elaboration of drug-like small molecules. ForceGen is novel, avoiding use of distance geometry, molecular templates, or simulation-oriented stochastic sampling. The method is primarily driven by the molecular force field, implemented using an extension of MMFF94s and a partial charge estimator based on electronegativity-equalization. The force field is coupled to algorithms for direct sampling of realistic physical movements made by small molecules. Results are presented on a standard benchmark from the Cambridge Crystallographic Database of 480 drug-like small molecules, including full structure generation from SMILES strings. Reproduction of protein-bound crystallographic ligand poses is demonstrated on four carefully curated data sets: the ConfGen Set (667 ligands), the PINC cross-docking benchmark (1062 ligands), a large set of macrocyclic ligands (182 total with typical ring sizes of 12-23 atoms), and a commonly used benchmark for evaluating macrocycle conformer generation (30 ligands total). Results compare favorably to alternative methods, and performance on macrocyclic compounds approaches that observed on non-macrocycles while yielding a roughly 100-fold speed improvement over alternative MD-based methods with comparable performance.

  11. Lorentz Force on Sodium and Chlorine Ions in a Salt Water Solution Flow under a Transverse Magnetic Field

    Science.gov (United States)

    De Luca, R.

    2009-01-01

    It is shown that, by applying elementary concepts in electromagnetism and electrochemistry to a system consisting of salt water flowing in a thin rectangular pipe at an average velocity v[subscript A] under the influence of a transverse magnetic field B[subscript 0], an electromotive force generator can be conceived. In fact, the Lorentz force…

  12. Polarizable Mean-Field Model of Water for Biological Simulations with Amber and Charmm force fields

    CERN Document Server

    Leontyev, Igor

    2015-01-01

    Although a great number of computational models of water are available today, the majority of current biological simulations are done with simple models, such as TIP3P and SPC, developed almost thirty years ago and only slightly modified since then. The reason is that the non-polarizable force fields that are mostly used to describe proteins and other biological molecules are incompatible with more sophisticated modern polarizable models of water. The issue is electronic polarizability: in liquid state, in protein, and in vacuum the water molecule is polarized differently, and therefore has different properties; thus the only way to describe all these different media with the same model is to use a polarizable water model. However, to be compatible with the force field of the rest of the system, e.g. a protein, the latter should be polarizable as well. Here we describe a novel model of water that is in effect polarizable, and yet compatible with the standard non-polarizable force fields such as AMBER, CHARMM,...

  13. Force field development for actinyl ions via quantum mechanical calculations: an approach to account for many body solvation effects.

    Science.gov (United States)

    Rai, Neeraj; Tiwari, Surya P; Maginn, Edward J

    2012-09-06

    Advances in computational algorithms and methodologies make it possible to use highly accurate quantum mechanical calculations to develop force fields (pair-wise additive intermolecular potentials) for condensed phase simulations. Despite these advances, this approach faces numerous hurdles for the case of actinyl ions, AcO2(n+) (high-oxidation-state actinide dioxo cations), mainly due to the complex electronic structure resulting from an interplay of s, p, d, and f valence orbitals. Traditional methods use a pair of molecules (“dimer”) to generate a potential energy surface (PES) for force field parametrization based on the assumption that many body polarization effects are negligible. We show that this is a poor approximation for aqueous phase uranyl ions and present an alternative approach for the development of actinyl ion force fields that includes important many body solvation effects. Force fields are developed for the UO2(2+) ion with the SPC/Fw, TIP3P, TIP4P, and TIP5P water models and are validated by carrying out detailed molecular simulations on the uranyl aqua ion, one of the most characterized actinide systems. It is shown that the force fields faithfully reproduce available experimental structural data and hydration free energies. Failure to account for solvation effects when generating PES leads to overbinding between UO2(2+) and water, resulting in incorrect hydration free energies and coordination numbers. A detailed analysis of arrangement of water molecules in the first and second solvation shell of UO2(2+) is presented. The use of a simple functional form involving the sum of Lennard-Jones + Coulomb potentials makes the new force field compatible with a large number of available molecular simulation engines and common force fields.

  14. Orbital motion in generalized static fields of FELs accounting for axial magnetic field, beam forces, undulator and external focusing

    Energy Technology Data Exchange (ETDEWEB)

    Papadichev, V.A. [Lebedev Physical Institute, Moscow (Russian Federation)

    1995-12-31

    Various types of undulators with or without axial magnetic field are used in FELs. Supplementary beam focusing can be applied by wedging, inclining or profiling pole faces of plan undulators or superposing external focusing magnetic fields in addition to undulator own focusing. Space-charge forces influence significantly particle motion in high-current, low-energy electron beams. Finally, one can use simultaneously two or more different undulators for some specific purpose: more efficient and selective higher harmonics generation, changing polarization types and direction, gain enhancement in double-period undulator etc. All these cases can be treated by solving the generalized equations of transverse orbital motion in a linear approximation, which is widely used for orbit calculation, gives sufficient accuracy for practical purposes and allows to consider many variants and optimize the chosen one. The undulator field is described as a field of two plane undulators with mutually orthogonal fields and an arbitrary axial (phase) shift between them. Various values of the phase shift correspond to right- or left-handed helical undulators, plane undulator of different polarization etc. The general formulae are reduced to forms that allow easier examination of particular cases: planar or helical undulator combined with axial magnetic field or without it, gyroresonance, limiting beam current, polarization etc.

  15. Symmetron Fields: Screening Long-Range Forces Through Local Symmetry Restoration

    CERN Document Server

    Hinterbichler, Kurt

    2010-01-01

    We present a novel screening mechanism that allows a scalar field to mediate a long range ~Mpc force of gravitational strength in the cosmos while satisfying local tests of gravity. The mechanism hinges on local symmetry restoration in the presence of matter. In regions of sufficiently high matter density, the field is drawn towards \\phi = 0 where its coupling to matter vanishes and the \\phi->-\\phi symmetry is restored. In regions of low density, however, the symmetry is spontaneously broken, and the field couples to matter with gravitational strength. We predict deviations from general relativity in the solar system that are within reach of next-generation experiments, as well as astrophysically observable violations of the equivalence principle. The model can be distinguished experimentally from Brans-Dicke gravity, chameleon theories and brane-world modifications of gravity.

  16. Generating arbitrary ultrasound fields with tailored optoacoustic surface profiles

    Science.gov (United States)

    Brown, M. D.; Nikitichev, D. I.; Treeby, B. E.; Cox, B. T.

    2017-02-01

    Acoustic fields with multiple foci have many applications in physical acoustics ranging from particle manipulation to neural modulation. However, the generation of multiple foci at arbitrary locations in three-dimensional is challenging using conventional transducer technology. In this work, the optical generation of acoustic fields focused at multiple points using a single optical pulse is demonstrated. This is achieved using optically absorbing surface profiles designed to generate specific, user-defined, wavefields. An optimisation approach for the design of these tailored surface profiles is developed. This searches for a smoothly varying surface that will generate a high peak pressure at a set of target focal points. The designed surface profiles are then realised via a combination of additive manufacturing and absorber deposition techniques. Acoustic field measurements from a sample designed to generate the numeral "7" are used to demonstrate the design method.

  17. Changes in muscle activation and force generation patterns during cycling movements because of low-intensity squat training with slow movement and tonic force generation.

    Science.gov (United States)

    Tanimoto, Michiya; Arakawa, Hiroshi; Sanada, Kiyoshi; Miyachi, Motohiko; Ishii, Naokata

    2009-11-01

    Our previous studies showed that relatively low-load (approximately 50-60% 1 repetition maximum [1RM]) resistance training with slow movement and tonic force generation (LST) significantly increased muscle size and strength. However, LST is a very specific movement that differs from natural movements associated with sport activities and activities of daily life, and therefore, it might have some unfavorable effects on dynamic sport movement. We investigated the effects of LST on muscle activity and force generation patterns during cycling movement as a representative dynamic sports movement. Twenty-four healthy young men who were not in the habit of bicycle riding and did not have a history of regular resistance training were randomly assigned to the LST (approximately 60% 1RM load, 3-second lifting, and 3-second lowering movement without a relaxing phase: n = 8), a high-intensity exercise at normal speed (HM) group (85% 1RM load, 1-second lifting, 1-second lowering, and 1-second relaxed movement: n = 8), or sedentary control (CON, n = 8) group. Subjects in the training groups performed vertical squats by the assigned method. Exercise sessions consisted of 3 sets and were performed twice a week for 13 weeks. Pre- and posttraining muscle activation and force generation patterns during the cycling movements were evaluated by the coefficient of variation (CV) of the rectified electromyographic (EMG) wave from the vastus lateralis and CV of pedaling force. Both the CV of the rectified EMG and of pedaling force decreased significantly in the LST group (-21 and -18%, p < 0.05, respectively), whereas there were no significant changes in either the HN or the CON group. This decrease in CV in the LST group could mean that muscle activity and force generation during cycling movement have become more tonic. This result following LST may have an unfavorable effect on cycling movement and other dynamic sports movements.

  18. Shear Forces during Blast, Not Abrupt Changes in Pressure Alone, Generate Calcium Activity in Human Brain Cells

    Science.gov (United States)

    2012-06-29

    Shear Forces during Blast, Not Abrupt Changes in Pressure Alone, Generate Calcium Activity in Human Brain Cells Rea Ravin1, Paul S. Blank1,2, Alex...Brain Cells’’ by Rea Ravin, Paul S. Blank, Alex Steinkamp, Shay Rappaport, Nitay Ravin, Ludmila Bezrukov, Hugo Guerrero-Cazares, Alfredo Quinones...the local strain field. Journal of Neurotrauma 23: 1304–1319. 25. Shin HS, Kim HJ, Sim SJ, Jeon NL (2009) Shear stress effect on transfection of

  19. Giga-Gauss scale quasistatic magnetic field generation with laser

    CERN Document Server

    Korneev, Philipp; Tikhonchuk, Vladimir

    2014-01-01

    A simple setup for the generation of ultra-intense quasistatic magnetic fields is proposed and analysed. Estimations and numerical Particle-In-Cell calculations show that magnetic fields of gigagauss scale may be generated with conventional powerful relativistic lasers interacting with the appropriate targets of a special geometry. The setup may be useful for a wide range of applications, from laboratory astrophysics to magnetized ICF schemes.

  20. Force generation in dividing E. coli cells : A handles-on approach using optical tweezers

    NARCIS (Netherlands)

    Verhoeven, Gertjan Sebastiaan

    2008-01-01

    In bacteria, what ‘drives’ the process of cell division is unknown. Possibly, forces generated by an internal protein ring (termed ‘the Z-ring’) are responsible for the division process, but direct evidence is lacking. Here we describe the development of a method to measure forces in a single dividi

  1. Estimation of aerodynamic noise generated by forced compressible round jets

    Science.gov (United States)

    Maidi, Mohamed

    2006-05-01

    An acoustic numerical code based on Ligthill's analogy is combined with large-eddy simulations techniques in order to evaluate the noise emitted by subsonic (M=0.7) and supersonic (M=1.4) round jets. We show first that, for centerline Mach number M=0.9 and Reynolds number Re=3.6×10, acoustic intensities compare satisfactorily with experimental data of the literature in terms of levels and directivity. Afterwards, high Reynolds number (Re=3.6×10) free and forced jets at Mach 0.7 and 1.4 are studied. Numerical results show that the jet noise intensity depends on the nature of the upstream mixing layer. Indeed, the subsonic jet is 4 dB quieter than the free jet when acting on this shear layer by superposing inlet varicose and flapping perturbations at preferred and first subharmonic frequency, respectively. The maximal acoustic level of the supersonic jet is, on the other hand, 3 dB lower than the free one with a flapping upstream perturbation at the second subharmonic. The results reported in this paper confirm previous works presented in the literature demonstrating that jet noise may be modified according to the inlet conditions. To cite this article: M. Maidi, C. R. Mecanique 334 (2006).

  2. Field-Based Concerns about Fourth-Generation Evaluation Theory.

    Science.gov (United States)

    Lai, Morris K.

    Some aspects of fourth generation evaluation procedures that have been advocated by E. G. Guba and Y. S. Lincoln were examined empirically, with emphasis on areas where there have been discrepancies between theory and field-based experience. In fourth generation evaluation, the product of an evaluation is not a set of conclusions, recommendations,…

  3. Sufficient conditions for the additivity of stall forces generated by multiple filaments or motors

    Science.gov (United States)

    Bameta, Tripti; Das, Dipjyoti; Das, Dibyendu; Padinhateeri, Ranjith; Inamdar, Mandar M.

    2017-02-01

    Molecular motors and cytoskeletal filaments work collectively most of the time under opposing forces. This opposing force may be due to cargo carried by motors or resistance coming from the cell membrane pressing against the cytoskeletal filaments. Some recent studies have shown that the collective maximum force (stall force) generated by multiple cytoskeletal filaments or molecular motors may not always be just a simple sum of the stall forces of the individual filaments or motors. To understand this excess or deficit in the collective force, we study a broad class of models of both cytoskeletal filaments and molecular motors. We argue that the stall force generated by a group of filaments or motors is additive, that is, the stall force of N number of filaments (motors) is N times the stall force of one filament (motor), when the system is reversible at stall. Conversely, we show that this additive property typically does not hold true when the system is irreversible at stall. We thus present a novel and unified understanding of the existing models exhibiting such non-addivity, and generalise our arguments by developing new models that demonstrate this phenomena. We also propose a quantity similar to thermodynamic efficiency to easily predict this deviation from stall-force additivity for filament and motor collectives.

  4. On the generation of magnetic field enhanced microwave plasma line

    Science.gov (United States)

    Chen, Longwei; Zhao, Ying; Wu, Kenan; Wang, Qi; Meng, Yuedong; Ren, Zhaoxing

    2016-12-01

    Microwave linear plasmas sustained by surface waves have attracted much attention due to the potential abilities to generate large-scale and uniform non-equilibrium plasmas. An external magnetic field was generally applied to enhance and stabilize plasma sources because the magnetic field decreased the electron losses on the wall. The effects of magnetic field on the generation and propagation mechanisms of the microwave plasma were tentatively investigated based on a 2-D numerical model combining a coupled system of Maxwell's equations and continuity equations. The mobility of electrons and effective electric conductivity of the plasma were considered as a full tensor in the presence of magnetic field. Numerical results indicate that both cases of magnetic field in the axial-direction and radial-direction benefit the generation of a high-density plasma; the former one allows the microwave to propagate longer in the axis direction compared to the latter one. The time-averaged power flow density and the amplitude of the electric field on the inner rod of coaxial waveguide attenuate with the propagation of the microwave for both cases of with and without external magnetic field. The attenuation becomes smaller in the presence of appropriately higher axial-direction magnetic field, which allows more microwave energies to transmit along the axial direction. Meanwhile, the anisotropic properties of the plasma, like electron mobility, in the presence of the magnetic field confine more charged particles in the direction of the magnetic field line.

  5. Generation of Magnetic Field on the Accretion Disk around a Proto-First-Star

    CERN Document Server

    Shiromoto, Yuki; Hosokawa, Takashi

    2014-01-01

    The generation process of magnetic field around a proto-first-star is studied. Utilizing the recent numerical result of proto-first-star formation based upon the radiation hydrodynamics simulations, we assess the magnetic field strength generated by the radiative force and the Biermann battery effect. We find that magnetic field of \\sim 10^{-9} G is generated on the surface of the accretion disk around the proto-first-star. The field strength on the accretion disk is smaller by two orders of magnitude than the critical value, above which the gravitational fragmentation of the disk is suppressed. Thus, the generated seed magnetic field hardly affect the dynamics of on-site first star formation directly, unless efficient amplification process is taken into consideration. We also find that the generated magnetic field is continuously blown out from the disk on the outflows to the poles, that are driven by the thermal pressure of photoheated gas. The strength of the diffused magnetic field in low density regions ...

  6. International Acquisitons in Multinacionals: Under a Force Field

    Directory of Open Access Journals (Sweden)

    Américo da Costa Ramos Filho

    2010-12-01

    Full Text Available The purpose of this essay is to debate the performance of multinational companies concerning the management alternatives of their foreign unities, especially the ones derived from acquisitions, with consequences on the interaction between the headquarters and its subsidiaries or colligates and the managerial learning and knowledge associated to this process. First the problematic of internationalized companies by foreign direct investments – FDI’s, mainly by acquisitions and strategic alliances, is discussed. The intensity of the assimilation and interchange of values and practices within organizations in interacting process is stressed, including a set of typologies derived from the existing related literature. After this, a more specific approach about intra and interorganization aspects of the multinationals is performed, related to strategies, competences and roles of headquarters and subsidiaries, as well as their impact on the knowledge flux and its derived learning modes, evolving a established typologies set. The next step is to discuss two visions about the opposition between the universal and the particular in international management, with global and contextual aspects: a convergence-divergence opposition, like a force field, impacting on the knowledge transfer. Finally, some concluding comments are made, emphasizing, for the purpose of contribution, another type of multinationals typology relating the convergence-divergence duality to the organizational and national levels, as well the positioning of the companies in the resulted matrix.

  7. Quantum mechanical force fields for condensed phase molecular simulations

    Science.gov (United States)

    Giese, Timothy J.; York, Darrin M.

    2017-09-01

    Molecular simulations are powerful tools for providing atomic-level details into complex chemical and physical processes that occur in the condensed phase. For strongly interacting systems where quantum many-body effects are known to play an important role, density-functional methods are often used to provide the model with the potential energy used to drive dynamics. These methods, however, suffer from two major drawbacks. First, they are often too computationally intensive to practically apply to large systems over long time scales, limiting their scope of application. Second, there remain challenges for these models to obtain the necessary level of accuracy for weak non-bonded interactions to obtain quantitative accuracy for a wide range of condensed phase properties. Quantum mechanical force fields (QMFFs) provide a potential solution to both of these limitations. In this review, we address recent advances in the development of QMFFs for condensed phase simulations. In particular, we examine the development of QMFF models using both approximate and ab initio density-functional models, the treatment of short-ranged non-bonded and long-ranged electrostatic interactions, and stability issues in molecular dynamics calculations. Example calculations are provided for crystalline systems, liquid water, and ionic liquids. We conclude with a perspective for emerging challenges and future research directions.

  8. Generation of primordial magnetic fields on linear overdensity scales.

    Science.gov (United States)

    Naoz, Smadar; Narayan, Ramesh

    2013-08-02

    Magnetic fields appear to be present in all galaxies and galaxy clusters. Recent measurements indicate that a weak magnetic field may be present even in the smooth low density intergalactic medium. One explanation for these observations is that a seed magnetic field was generated by some unknown mechanism early in the life of the Universe, and was later amplified by various dynamos in nonlinear objects like galaxies and clusters. We show that a primordial magnetic field is expected to be generated in the early Universe on purely linear scales through vorticity induced by scale-dependent temperature fluctuations, or equivalently, a spatially varying speed of sound of the gas. Residual free electrons left over after recombination tap into this vorticity to generate magnetic field via the Biermann battery process. Although the battery operates even in the absence of any relative velocity between dark matter and gas at the time of recombination, the presence of such a relative velocity modifies the predicted spatial power spectrum of the magnetic field. At redshifts of order a few tens, we estimate a root mean square field strength of order 10(-25)-10(-24) G on comoving scales ~10 kpc. This field, which is generated purely from linear perturbations, is expected to be amplified significantly after reionization, and to be further boosted by dynamo processes during nonlinear structure formation.

  9. Effective critical electric field for runaway electron generation

    CERN Document Server

    Stahl, Adam; Decker, Joan; Embréus, Ola; Fülöp, Tünde

    2014-01-01

    In this letter we investigate factors that influence the effective critical electric field for runaway electron generation in plasmas. We present numerical solutions of the kinetic equation, and discuss the implications for the threshold electric field. We show that the effective electric field necessary for significant runaway formation often is higher than previously calculated due to both (1) extremely strong dependence of primary generation on temperature, and (2) synchrotron radiation losses. We also address the effective critical field in the context of a transition from runaway growth to decay. We find agreement with recent experiments, but show that the observation of an elevated effective critical field can mainly be attributed to changes in the momentum-space distribution of runaways, and only to a lesser extent to a de facto change in the critical field.

  10. The Properties of Light Pressure Force with High Order in Laser Fields

    Institute of Scientific and Technical Information of China (English)

    陈险峰; 方建兴; 朱士群

    2002-01-01

    In this paper, the light pressure force in low and high intensity laser fields is derived. The exact numerical results of forces Fn∥(n=0,1,2,3,4,5,6…) through the matrix continued fraction method are presented. At low intensity field (G=1), the spatially averaged force F0∥ gives a cooling effect at the negative detuning. At high intensity (G=64), the effects of the forces with higher order (n≥2) appear and the contributes of the forces with odd or even order are opposite. It is great different from no high order force at low intensity.

  11. A precise numerical estimation of the magnetic field generated around recombination

    CERN Document Server

    Fidler, Christian; Pitrou, Cyril

    2015-01-01

    We investigate the generation of magnetic fields from non-linear effects around recombination. As tight-coupling is gradually lost when approaching $z\\simeq 1100$, the velocity difference between photons and baryons starts to increase, leading to an increasing Compton drag of the photons on the electrons. The protons are then forced to follow the electrons due to the electric field created by the charge displacement; the same field, following Maxwell's laws, eventually induces a magnetic field on cosmological scales. Since scalar perturbations do not generate any magnetic field as they are curl-free, one has to resort to second-order perturbation theory to compute the magnetic field generated by this effect. We reinvestigate this problem numerically using the powerful second-order Boltzmann code SONG. We show that: i) all previous studies do not have a high enough angular resolution to reach a precise and consistent estimation of the magnetic field spectrum; ii) the magnetic field is generated up to $z\\simeq ...

  12. Robust Generation of Signed Distance Fields from Triangle Meshes

    DEFF Research Database (Denmark)

    Bærentzen, Jakob Andreas

    2005-01-01

    is then used to convert the binary volume into a distance field. The method is robust and handles holes, spurious triangles and ambiguities. Moreover, the method lends itself to Boolean operations between solids. Since a point cloud as well as a signed distance is generated, it is possible to extract an iso......-surface of the distance field and fit it to the point set. Using this method, one may recover sharp edge information. Examples are given where the method for generating distance fields coupled with mesh fitting is used to perform Boolean and morphological operations on triangle meshes....

  13. International Geomagnetic Reference Field: the 12th generation

    OpenAIRE

    2015-01-01

    International audience; The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, p...

  14. Interstellar Turbulent Magnetic Field Generation by Plasma Instabilities

    CERN Document Server

    Tautz, R C

    2013-01-01

    The maximum magnetic field strength generated by Weibel-type plasma instabilities is estimated for typical conditions in the interstellar medium. The relevant kinetic dispersion relations are evaluated by conducting a parameter study both for Maxwellian and for suprathermal particle distributions showing that micro Gauss magnetic fields can be generated. It is shown that, depending on the streaming velocity and the plasma temperatures, either the longitudinal or a transverse instability will be dominant. In the presence of an ambient magnetic field, the filamentation instability is typically suppressed while the two-stream and the classic Weibel instability are retained.

  15. International Geomagnetic Reference Field: the 12th generation

    DEFF Research Database (Denmark)

    Thébault, Erwan; Finlay, Chris; Beggan, Ciarán D.

    2015-01-01

    The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch...... for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth’s magnetic field....

  16. One dimensional speckle fields generated by three phase level diffusers

    Science.gov (United States)

    Cabezas, L.; Amaya, D.; Bolognini, N.; Lencina, A.

    2015-02-01

    Speckle patterns have usually been obtained by using ground glass as random diffusers. Liquid-crystal spatial light modulators have opened the possibility of engineering tailored speckle fields obtained from designed diffusers. In this work, one-dimensional Gaussian speckle fields with fully controllable features are generated. By employing a low-cost liquid-crystal spatial light modulator, one-dimensional three phase level diffusers are implemented. These diffusers make it possible to control average intensity distribution and statistical independence among the generated patterns. The average speckle size is governed by an external slit pupil. A theoretical model to describe the generated speckle patterns is developed. Experimental and theoretical results confirming the generation of one-dimensional speckle fields are presented. Some possible applications of these speckles, such as atom trapping and super-resolution imaging, are briefly envisaged.

  17. All-Optical Field-Induced Second-Harmonic Generation

    CERN Document Server

    Davidson, Roderick B; Ziegler, Jed I; Avanesyan, Sergey M; Lawrie, Ben J; Haglund, Richard F

    2015-01-01

    Efficient frequency modulation techniques are crucial to the development of plasmonic metasurfaces for information processing and energy conversion. Nanoscale electric-field confinement in optically pumped plasmonic structures enables stronger nonlinear susceptibilities than are attainable in bulk materials. The interaction of three distinct electric fields in (chi)^3 optical processes allows for all-optical modulation of nonlinear signals. Here we demonstrate effcient third-order second harmonic generation (SHG) in a serrated nanogap plasmonic geometry that generates steep electric field gradients within a dielectric material. We utilize an ultrafast optical pump to control the plasmonically induced electric-fields and to generate bandwidth-limited ultrafast second-harmonic pulses driven by the control pulses. The combination of plasmonic metasurfaces with all-optical control and the freedom to choose the dielectric allow multiple generalizations of this concept and geometry to other four-wave mixing process...

  18. Generation of dynamo magnetic fields in the primordial solar nebula

    Science.gov (United States)

    Stepinski, Tomasz F.

    1992-01-01

    The present treatment of dynamo-generated magnetic fields in the primordial solar nebula proceeds in view of the ability of the combined action of Keplerian rotation and helical convention to generate, via alpha-omega dynamo, large-scale magnetic fields in those parts of the nebula with sufficiently high, gas-and magnetic field coupling electrical conductivity. Nebular gas electrical conductivity and the radial distribution of the local dynamo number are calculated for both a viscous-accretion disk model and the quiescent-minimum mass nebula. It is found that magnetic fields can be easily generated and maintained by alpha-omega dynamos occupying the inner and outer parts of the nebula.

  19. The influence of catch trials on the consolidation of motor memory in force field adaptation tasks

    Directory of Open Access Journals (Sweden)

    Anne eFocke

    2013-07-01

    Full Text Available In computational neuroscience it is generally accepted that human motor memory contains neural representations of the physics of the musculoskeletal system and the objects in the environment. These representations are called internal models. Force field studies, in which subjects have to adapt to dynamic perturbations induced by a robotic manipulandum, are an established tool to analyze the characteristics of such internal models. The aim of the current study was to investigate whether catch trials during force field learning could influence the consolidation of motor memory in more complex tasks. Thereby, the force field was more than double the force field of previous studies (35 Ns/m. Moreover, the arm of the subjects was not supported. A total of forty-six subjects participated in this study and performed center-out movements at a robotic manipulandum in two different force fields. Two control groups learned force field A on day 1 and were retested in the same force field on day 3 (AA. Two test groups additionally learned an interfering force field B (=-A on day 2 (ABA. The difference between the two test and control groups, respectively, was the absence (0% or presence (19% of catch trials, in which the force field was turned off suddenly. The results showed consolidation of force field A on day 3 for both control groups. Test groups showed no consolidation of force field A (19% catch trials and even poorer performance on day 3 (0% catch trials. In conclusion, it can be stated that catch trials seem to have a positive effect on the performance on day 3 but do not trigger a consolidation process as shown in previous studies that used a lower force field viscosity with supported arm. These findings indicate that the results of previous studies in which less complex tasks were analyzed, cannot be fully transferred to more complex tasks. Moreover, the effects of catch trials in these situations are insufficiently understood and further research

  20. An improved optical tweezers assay for measuring the force generation of single kinesin molecules.

    Science.gov (United States)

    Nicholas, Matthew P; Rao, Lu; Gennerich, Arne

    2014-01-01

    Numerous microtubule-associated molecular motors, including several kinesins and cytoplasmic dynein, produce opposing forces that regulate spindle and chromosome positioning during mitosis. The motility and force generation of these motors are therefore critical to normal cell division, and dysfunction of these processes may contribute to human disease. Optical tweezers provide a powerful method for studying the nanometer motility and piconewton force generation of single motor proteins in vitro. Using kinesin-1 as a prototype, we present a set of step-by-step, optimized protocols for expressing a kinesin construct (K560-GFP) in Escherichia coli, purifying it, and studying its force generation in an optical tweezers microscope. We also provide detailed instructions on proper alignment and calibration of an optical trapping microscope. These methods provide a foundation for a variety of similar experiments.

  1. Robustness of muscle synergies underlying three-dimensional force generation at the hand in healthy humans

    Science.gov (United States)

    Rymer, William Z.; Beer, Randall F.

    2012-01-01

    Previous studies using advanced matrix factorization techniques have shown that the coordination of human voluntary limb movements may be accomplished using combinations of a small number of intermuscular coordination patterns, or muscle synergies. However, the potential use of muscle synergies for isometric force generation has been evaluated mostly using correlational methods. The results of such studies suggest that fixed relationships between the activations of pairs of muscles are relatively rare. There is also emerging evidence that the nervous system uses independent strategies to control movement and force generation, which suggests that one cannot conclude a priori that isometric force generation is accomplished by combining muscle synergies, as shown in movement control. In this study, we used non-negative matrix factorization to evaluate the ability of a few muscle synergies to reconstruct the activation patterns of human arm muscles underlying the generation of three-dimensional (3-D) isometric forces at the hand. Surface electromyographic (EMG) data were recorded from eight key elbow and shoulder muscles during 3-D force target-matching protocols performed across a range of load levels and hand positions. Four synergies were sufficient to explain, on average, 95% of the variance in EMG datasets. Furthermore, we found that muscle synergy composition was conserved across biomechanical task conditions, experimental protocols, and subjects. Our findings are consistent with the view that the nervous system can generate isometric forces by assembling a combination of a small number of muscle synergies, differentially weighted according to task constraints. PMID:22279190

  2. Using J-coupling constants for force field validation: application to hepta-alanine.

    Science.gov (United States)

    Georgoulia, Panagiota S; Glykos, Nicholas M

    2011-12-29

    A computational solution to the protein folding problem is the holy grail of biomolecular simulation and of the corresponding force fields. The complexity of the systems used for folding simulations precludes a direct feedback between the simulations and the force fields, thus necessitating the study of simpler systems with sufficient experimental data to allow force field optimization and validation. Recent studies on short polyalanine peptides of increasing length (up to penta-alanine) indicated the presence of a systematic deviation between the experimental (NMR-derived) J-couplings and the great majority of biomolecular force fields, with the χ(2) values for even the best-performing force fields being in the 1.4-1.8 range. Here we show that by increasing the number of residues to seven and by achieving convergence through an increase of the simulation time to 2 μs, we can identify one force field (the AMBER99SB force field, out of the three force fields studied) which when compared with the experimental J-coupling data (and for a specific set of Karplus equation parameters and estimated J-coupling errors previously used in the literature) gave a value of χ(2) = 0.99, indicating that full statistical consistency between experiment and simulation is feasible. However, and as a detailed analysis of the effects of estimated errors shows, the χ(2) values may be unsuitable as indicators of the goodness of fit of the various biomolecular force fields. © 2011 American Chemical Society

  3. Distinct haptic cues do not reduce interference when learning to reach in multiple force fields.

    Directory of Open Access Journals (Sweden)

    Nicholas Cothros

    Full Text Available BACKGROUND: Previous studies of learning to adapt reaching movements in the presence of novel forces show that learning multiple force fields is prone to interference. Recently it has been suggested that force field learning may reflect learning to manipulate a novel object. Within this theoretical framework, interference in force field learning may be the result of static tactile or haptic cues associated with grasp, which fail to indicate changing dynamic conditions. The idea that different haptic cues (e.g. those associated with different grasped objects signal motor requirements and promote the learning and retention of multiple motor skills has previously been unexplored in the context of force field learning. METHODOLOGY/PRINCIPLE FINDINGS: The present study tested the possibility that interference can be reduced when two different force fields are associated with differently shaped objects grasped in the hand. Human subjects were instructed to guide a cursor to targets while grasping a robotic manipulandum, which applied two opposing velocity-dependent curl fields to the hand. For one group of subjects the manipulandum was fitted with two different handles, one for each force field. No attenuation in interference was observed in these subjects relative to controls who used the same handle for both force fields. CONCLUSIONS/SIGNIFICANCE: These results suggest that in the context of the present learning paradigm, haptic cues on their own are not sufficient to reduce interference and promote learning multiple force fields.

  4. Power counting for nuclear forces in chiral effective field theory

    CERN Document Server

    Long, Bingwei

    2016-01-01

    The present note summarizes the discourse on power counting issues of chiral nuclear forces, with an emphasis on renormalization-group invariance. Given its introductory nature, I will lean toward narrating a coherent point of view on the concepts, rather than covering comprehensively the development of chiral nuclear forces in different approaches.

  5. Power counting for nuclear forces in chiral effective field theory

    Science.gov (United States)

    Long, Bingwei

    2016-02-01

    The present note summarizes the discourse on power counting issues of chiral nuclear forces, with an emphasis on renormalization-group invariance. Given its introductory nature, I will lean toward narrating a coherent point of view on the concepts, rather than covering comprehensively the development of chiral nuclear forces in different approaches.

  6. The 9th-Generation International Geomagnetic Reference Field

    Science.gov (United States)

    Macmillan, S.; Maus, S.; Bondar, T.; Chambodut, A.; Golovkov, V.; Holme, R.; Langlais, B.; Lesur, V.; Lowes, F.; Lühr, H.; Mai, W.; Mandea, M.; Olsen, N.; Rother, M.; Sabaka, T.; Thomson, A.; Wardinski, I.

    2003-12-01

    The International Association of Geomagnetism and Aeronomy has recently released the 9th-Generation International Geomagnetic Reference Field-the latest version of a standard mathematical description of the Earth's main magnetic field used widely in studies of the Earth's deep interior, its crust and its ionosphere and magnetosphere. The coefficients were recently finalized at the XXIII General Assembly of the International Union of Geophysics and Geodesy, held at Sapporo in Japan in 2003 July. The IGRF is the product of a huge collaborative effort between magnetic field modellers and the institutes involved in collecting and disseminating magnetic field data from satellites and from observatories and surveys around the world.

  7. Real-space phase-field simulation of piezoresponse force microscopy accounting for stray electric fields

    Science.gov (United States)

    Yang, Lun; Dayal, Kaushik

    2012-04-01

    Piezoresponse force microscopy (PFM) is a powerful scanning-probe technique used to characterize important aspects of the microstructure in ferroelectrics. It has been widely applied to understand domain patterns, domain nucleation and the structure of domain walls. In this paper, we apply a real-space phase-field model to consistently simulate various PFM configurations. We model the PFM tip as a charged region that is external to the ferroelectric, and implement a boundary element method to efficiently and accurately account for the external stray fields that mediate the interactions between the tip and the ferroelectric. Our phase-field model and the solution method together are able to account for the electrical fields both within the specimen as well as those outside, and also consistently solve for the resulting electromechanical response with the same phase-field model. We apply this to various problems: first, the effect of crystal lattice orientation on the induced tip displacement and rotation; second, PFM scanning of a 90° domain wall that emerges at a free surface; third, the effect of closure domain microstructure on PFM response; fourth, the effect of surface modulations on PFM response; and fifth, the effect of surface charge compensation on PFM response.

  8. Numerical study of Balearic meteotsunami generation and propagation under synthetic gravity wave forcing

    Science.gov (United States)

    Ličer, Matjaž; Mourre, Baptiste; Troupin, Charles; Krietemeyer, Andreas; Jansá, Agusti; Tintoré, Joaquín

    2017-03-01

    We use a high resolution nested ocean modelling system forced by synthetic atmospheric gravity waves to investigate Balearic meteotsunami generation, amplification and propagation properties. We determine how meteotsunami amplitude outside and inside of the Balearic port of Ciutadella depends on forcing gravity wave direction, speed and trajectory. We quantify the contributions of Mallorca shelves and Menorca Channel for different gravity wave forcing angles and speeds. The Channel is demonstrated to be the key build-up region determining meteotsunami amplitude in Ciutadella while northern and southern Mallorca shelves serve mostly as barotropic wave guides but do not significantly contribute to seiche amplitude in Ciutadella. This fact seriously reduces early-warning alert times in cases of locally generated pressure perturbations. We track meteotsunami propagation paths in the Menorca Channel for several forcing velocities and show that the Channel bathymetry serves as a focusing lens for meteotsunami waves whose paths are constrained by the forcing direction. We show that faster meteotsunamis propagate over deeper ocean regions, as required by Proudman resonance. We estimate meteotsunami speed under sub- and supercritical forcing and derive a first order estimate of its magnitude. We show that meteotsunamis, generated by supercritical gravity waves, propagate with a velocity which is equal to an arithmetic mean of the forcing velocity and local barotropic ocean wave speed.

  9. High harmonic interferometry of the Lorentz force in strong mid-infrared laser fields

    CERN Document Server

    Pisanty, Emilio; Galloway, Benjamin R; Durfee, Charles G; Kapteyn, Henry C; Murnane, Margaret M; Ivanov, Misha

    2016-01-01

    The interaction of intense mid-infrared laser fields with atoms and molecules leads to a range of new opportunities, from the production of bright, coherent radiation in the soft x-ray range to imaging molecular structures and dynamics with attosecond temporal and sub-angstrom spatial resolution. However, all these effects, which rely on laser-driven recollision of an electron removed by the strong laser field and the parent ion, suffer from the rapidly increasing role of the magnetic field component of the driving pulse: the associated Lorentz force pushes the electrons off course in their excursion and suppresses all recollision-based processes, including high harmonic generation, elastic and inelastic scattering. Here we show how the use of two non-collinear beams with opposite circular polarizations produces a forwards ellipticity which can be used to monitor, control, and cancel the effect of the Lorentz force. This arrangement can thus be used to re-enable recollision-based phenomena in regimes beyond t...

  10. QuickFF: A program for a quick and easy derivation of force fields for metal-organic frameworks from ab initio input.

    Science.gov (United States)

    Vanduyfhuys, Louis; Vandenbrande, Steven; Verstraelen, Toon; Schmid, Rochus; Waroquier, Michel; Van Speybroeck, Veronique

    2015-05-15

    QuickFF is a software package to derive accurate force fields for isolated and complex molecular systems in a quick and easy manner. Apart from its general applicability, the program has been designed to generate force fields for metal-organic frameworks in an automated fashion. The force field parameters for the covalent interaction are derived from ab initio data. The mathematical expression of the covalent energy is kept simple to ensure robustness and to avoid fitting deficiencies as much as possible. The user needs to produce an equilibrium structure and a Hessian matrix for one or more building units. Afterward, a force field is generated for the system using a three-step method implemented in QuickFF. The first two steps of the methodology are designed to minimize correlations among the force field parameters. In the last step, the parameters are refined by imposing the force field parameters to reproduce the ab initio Hessian matrix in Cartesian coordinate space as accurate as possible. The method is applied on a set of 1000 organic molecules to show the easiness of the software protocol. To illustrate its application to metal-organic frameworks (MOFs), QuickFF is used to determine force fields for MIL-53(Al) and MOF-5. For both materials, accurate force fields were already generated in literature but they requested a lot of manual interventions. QuickFF is a tool that can easily be used by anyone with a basic knowledge of performing ab initio calculations. As a result, accurate force fields are generated with minimal effort. © 2015 Wiley Periodicals, Inc.

  11. Polarizable Simulations with Second order Interaction Model (POSSIM) force field: Developing parameters for alanine peptides and protein backbone

    Science.gov (United States)

    Ponomarev, Sergei Y.; Kaminski, George A.

    2011-01-01

    A previously introduced POSSIM (POlarizable Simulations with Second order Interaction Model) force field has been extended to include parameters for alanine peptides and protein backbones. New features were introduced into the fitting protocol, as compared to the previous generation of the polarizable force field for proteins. A reduced amount of quantum mechanical data was employed in fitting the electrostatic parameters. Transferability of the electrostatics between our recently developed NMA model and the protein backbone was confirmed. Binding energy and geometry for complexes of alanine dipeptide with a water molecule were estimated and found in a good agreement with high-level quantum mechanical results (for example, the intermolecular distances agreeing within ca. 0.06Å). Following the previously devised procedure, we calculated average errors in alanine di- and tetra-peptide conformational energies and backbone angles and found the agreement to be adequate (for example, the alanine tetrapeptide extended-globular conformational energy gap was calculated to be 3.09 kcal/mol quantim mechanically and 3.14 kcal/mol with the POSSIM force field). However, we have now also included simulation of a simple alpha-helix in both gas-phase and water as the ultimate test of the backbone conformational behavior. The resulting alanine and protein backbone force field is currently being employed in further development of the POSSIM fast polarizable force field for proteins. PMID:21743799

  12. Generation of dynamo magnetic fields in thin Keplerian disks

    Science.gov (United States)

    Stepinski, T. F.; Levy, E. H.

    1990-01-01

    The combined action of nonuniform rotation and helical convection in protoplanetary disks, in the Galaxy, or in accretion disks surrounding black holes and other compact objects, enables an alpha-omega dynamo to generate a large-scale magnetic field. In this paper, the properties of such magnetic fields are investigated using a two-dimensional, partially numerical method. The structures of the lowest-order steady state and oscillatory modes are calculated for two kinds of external boundary conditions. A quadruple, steady state, highly localized mode is the most easily excited for low values of the dynamo number. The results indicate that, except under special conditions, disk dynamo modes tend to consist of relatively localized rings structures. For large values of the dynamo number, the magnetic field consists of a number of quasi-independent, spatially localized modes generated in various concentric rings filling the disk inward of a dynamo generation 'front'.

  13. Generation of dynamo magnetic fields in thin Keplerian disks

    Energy Technology Data Exchange (ETDEWEB)

    Stepinski, T.F.; Levy, E.H. (Arizona Univ., Tucson (USA))

    1990-10-01

    The combined action of nonuniform rotation and helical convection in protoplanetary disks, in the Galaxy, or in accretion disks surrounding black holes and other compact objects, enables an alpha-omega dynamo to generate a large-scale magnetic field. In this paper, the properties of such magnetic fields are investigated using a two-dimensional, partially numerical method. The structures of the lowest-order steady state and oscillatory modes are calculated for two kinds of external boundary conditions. A quadruple, steady state, highly localized mode is the most easily excited for low values of the dynamo number. The results indicate that, except under special conditions, disk dynamo modes tend to consist of relatively localized rings structures. For large values of the dynamo number, the magnetic field consists of a number of quasi-independent, spatially localized modes generated in various concentric rings filling the disk inward of a dynamo generation front. 36 refs.

  14. Analysis of brushless DC generator incorporating an axial field coil

    Energy Technology Data Exchange (ETDEWEB)

    Moradi, Hassan, E-mail: H_moradi@sbu.ac.i [Department of Electrical and Computer Engineering, Shahid Beheshti University, GC, Tehran (Iran, Islamic Republic of); Afjei, E. [Department of Electrical and Computer Engineering, Shahid Beheshti University, GC, Tehran (Iran, Islamic Republic of)

    2011-07-15

    Highlights: {yields} Magnetic analysis and experiment of a three-phase field assisted BLDC generator. {yields} Confirm the accuracy of the predicted flux-linkage by 2-D FE analysis. {yields} Confirm the accuracy of the FE analysis results by coupling the FE and BE method. {yields} Control the output voltage to a desired level by control the amplitude of the I{sub f}. {yields} Compatible with any application that requires variable speed operation. -- Abstract: This paper describes the magnetic analysis and experiment of a three-phase field assisted brushless DC (BLDC) generator. Unlike conventional BLDC generators, the permanent magnet is replaced with an assisted field winding. The stator and rotor are constructed with two dependent magnetically sets, in which each stator set includes nine salient poles with coil windings, and the rotor comprises of six salient poles. Other pole combinations also are possible. This construction is similar to a homopolar inductor alternator. The DC current in the assisted field winding produces axial flux which makes the rotor magnetically polarized at its ends. The magnetic field flows axially through the rotor shaft and closes through the stator teeth and the machine housing. To evaluate the generator performance, two types of analysis, namely the numerical technique and the experimental study have been utilized. In the numerical analysis, 2-D finite element (FE) analysis has been carried out using a MagNet CAD package (Infolytica Corporation Ltd.), to confirm the accuracy of the predicted flux-linkage characteristics, whereas in the experimental study, a prototype BLDC generator was constructed for verifying the actual performance. Furthermore, the evaluation method based on a hybrid numerical method coupling the finite element (FE) analysis and boundary element (BE) method, has been carried out to confirm the accuracy of the 2-D FE analysis simulation results. It provides not only confirmations of the investigation in results

  15. New limits on the generation of magnetic field

    CERN Document Server

    Chuzhoy, L

    2003-01-01

    Magnetic fields are generated in ionized objects rotating with respect to a radiation background. Based on conservation of canonical ion momentum, it has been previously suggested that even if the radiation intensity is unrestricted the maximum field strength generated this way is ~(10^{-4}\\Omega) Gauss, where \\Omega is the initial angular velocity of the object. We show that this limit is valid only for an object made of fully ionized and optically thin plasma. The limit can be relaxed by orders of magnitude in the presence of a high neutral fraction or if the plasma is coupled to other forms of matter such as stars or compact clouds.

  16. Fluorescent lamp unit with magnetic field generating means

    Science.gov (United States)

    Grossman, M.W.; George, W.A.

    1989-08-08

    A fluorescent lamp unit having a magnetic field generating means for improving the performance of the fluorescent lamp is disclosed. In a preferred embodiment the fluorescent lamp comprises four longitudinally extending leg portions disposed in substantially quadrangular columnar array and joined by three generally U-shaped portions disposed in different planes. In another embodiment of the invention the magnetic field generating means comprises a plurality of permanent magnets secured together to form a single columnar structure disposed within a centrally located region defined by the shape of lamp envelope. 4 figs.

  17. Generating nonclassical quantum input field states with modulating filters

    Energy Technology Data Exchange (ETDEWEB)

    Gough, John E. [Aberystwyth University, Department of Physics, Aberystwyth, Wales (United Kingdom); Zhang, Guofeng [The Hong Kong Polytechnic University, Department of Applied Mathematics, Hong Kong (China)

    2015-12-15

    We give explicit constructions of quantum dynamical filters which generate nonclassical states (coherent states, cat states, shaped single and multi-photon states) of quantum optical fields as inputs to general quantum Markov systems. The filters will be quantum harmonic oscillators damped by the input fields, and we exploit the fact that the cascaded filter and system will have a Lindbladian that is naturally Wick-ordered in the filter modes. In particular the initialization of the modulating filter will determine the signal state generated. (orig.)

  18. Modeling HEDLA magnetic field generation experiments on laser facilities

    Science.gov (United States)

    Fatenejad, M.; Bell, A. R.; Benuzzi-Mounaix, A.; Crowston, R.; Drake, R. P.; Flocke, N.; Gregori, G.; Koenig, M.; Krauland, C.; Lamb, D.; Lee, D.; Marques, J. R.; Meinecke, J.; Miniati, F.; Murphy, C. D.; Park, H.-S.; Pelka, A.; Ravasio, A.; Remington, B.; Reville, B.; Scopatz, A.; Tzeferacos, P.; Weide, K.; Woolsey, N.; Young, R.; Yurchak, R.

    2013-03-01

    The Flash Center is engaged in a collaboration to simulate laser driven experiments aimed at understanding the generation and amplification of cosmological magnetic fields using the FLASH code. In these experiments a laser illuminates a solid plastic or graphite target launching an asymmetric blast wave into a chamber which contains either Helium or Argon at millibar pressures. Induction coils placed several centimeters away from the target detect large scale magnetic fields on the order of tens to hundreds of Gauss. The time dependence of the magnetic field is consistent with generation via the Biermann battery mechanism near the blast wave. Attempts to perform simulations of these experiments using the FLASH code have uncovered previously unreported numerical difficulties in modeling the Biermann battery mechanism near shock waves which can lead to the production of large non-physical magnetic fields. We report on these difficulties and offer a potential solution.

  19. International Geomagnetic Reference Field: the 12th generation

    Science.gov (United States)

    Thébault, Erwan; Finlay, Christopher C.; Beggan, Ciarán D.; Alken, Patrick; Aubert, Julien; Barrois, Olivier; Bertrand, Francois; Bondar, Tatiana; Boness, Axel; Brocco, Laura; Canet, Elisabeth; Chambodut, Aude; Chulliat, Arnaud; Coïsson, Pierdavide; Civet, François; Du, Aimin; Fournier, Alexandre; Fratter, Isabelle; Gillet, Nicolas; Hamilton, Brian; Hamoudi, Mohamed; Hulot, Gauthier; Jager, Thomas; Korte, Monika; Kuang, Weijia; Lalanne, Xavier; Langlais, Benoit; Léger, Jean-Michel; Lesur, Vincent; Lowes, Frank J.; Macmillan, Susan; Mandea, Mioara; Manoj, Chandrasekharan; Maus, Stefan; Olsen, Nils; Petrov, Valeriy; Ridley, Victoria; Rother, Martin; Sabaka, Terence J.; Saturnino, Diana; Schachtschneider, Reyko; Sirol, Olivier; Tangborn, Andrew; Thomson, Alan; Tøffner-Clausen, Lars; Vigneron, Pierre; Wardinski, Ingo; Zvereva, Tatiana

    2015-05-01

    The 12th generation of the International Geomagnetic Reference Field (IGRF) was adopted in December 2014 by the Working Group V-MOD appointed by the International Association of Geomagnetism and Aeronomy (IAGA). It updates the previous IGRF generation with a definitive main field model for epoch 2010.0, a main field model for epoch 2015.0, and a linear annual predictive secular variation model for 2015.0-2020.0. Here, we present the equations defining the IGRF model, provide the spherical harmonic coefficients, and provide maps of the magnetic declination, inclination, and total intensity for epoch 2015.0 and their predicted rates of change for 2015.0-2020.0. We also update the magnetic pole positions and discuss briefly the latest changes and possible future trends of the Earth's magnetic field.

  20. Novel system for bite-force sensing and monitoring based on magnetic near field communication.

    Science.gov (United States)

    Lantada, Andres Diaz; Bris, Carlos González; Morgado, Pilar Lafont; Maudes, Jesús Sanz

    2012-01-01

    Intraoral devices for bite-force sensing have several applications in odontology and maxillofacial surgery, as bite-force measurements provide additional information to help understand the characteristics of bruxism disorders and can also be of help for the evaluation of post-surgical evolution and for comparison of alternative treatments. A new system for measuring human bite forces is proposed in this work. This system has future applications for the monitoring of bruxism events and as a complement for its conventional diagnosis. Bruxism is a pathology consisting of grinding or tight clenching of the upper and lower teeth, which leads to several problems such as lesions to the teeth, headaches, orofacial pain and important disorders of the temporomandibular joint. The prototype uses a magnetic field communication scheme similar to low-frequency radio frequency identification (RFID) technology (NFC). The reader generates a low-frequency magnetic field that is used as the information carrier and powers the sensor. The system is notable because it uses an intra-mouth passive sensor and an external interrogator, which remotely records and processes information regarding a patient's dental activity. This permits a quantitative assessment of bite-force, without requiring intra-mouth batteries, and can provide supplementary information to polysomnographic recordings, current most adequate early diagnostic method, so as to initiate corrective actions before irreversible dental wear appears. In addition to describing the system's operational principles and the manufacture of personalized prototypes, this report will also demonstrate the feasibility of the system and results from the first in vitro and in vivo trials.

  1. Novel System for Bite-Force Sensing and Monitoring Based on Magnetic Near Field Communication

    Directory of Open Access Journals (Sweden)

    Jesús Sanz Maudes

    2012-08-01

    Full Text Available Intraoral devices for bite-force sensing have several applications in odontology and maxillofacial surgery, as bite-force measurements provide additional information to help understand the characteristics of bruxism disorders and can also be of help for the evaluation of post-surgical evolution and for comparison of alternative treatments. A new system for measuring human bite forces is proposed in this work. This system has future applications for the monitoring of bruxism events and as a complement for its conventional diagnosis. Bruxism is a pathology consisting of grinding or tight clenching of the upper and lower teeth, which leads to several problems such as lesions to the teeth, headaches, orofacial pain and important disorders of the temporomandibular joint. The prototype uses a magnetic field communication scheme similar to low-frequency radio frequency identification (RFID technology (NFC. The reader generates a low-frequency magnetic field that is used as the information carrier and powers the sensor. The system is notable because it uses an intra-mouth passive sensor and an external interrogator, which remotely records and processes information regarding a patient’s dental activity. This permits a quantitative assessment of bite-force, without requiring intra-mouth batteries, and can provide supplementary information to polysomnographic recordings, current most adequate early diagnostic method, so as to initiate corrective actions before irreversible dental wear appears. In addition to describing the system’s operational principles and the manufacture of personalized prototypes, this report will also demonstrate the feasibility of the system and results from the first in vitro and in vivo trials.

  2. Novel System for Bite-Force Sensing and Monitoring Based on Magnetic Near Field Communication

    Science.gov (United States)

    Lantada, Andres Diaz; Bris, Carlos González; Morgado, Pilar Lafont; Maudes, Jesús Sanz

    2012-01-01

    Intraoral devices for bite-force sensing have several applications in odontology and maxillofacial surgery, as bite-force measurements provide additional information to help understand the characteristics of bruxism disorders and can also be of help for the evaluation of post-surgical evolution and for comparison of alternative treatments. A new system for measuring human bite forces is proposed in this work. This system has future applications for the monitoring of bruxism events and as a complement for its conventional diagnosis. Bruxism is a pathology consisting of grinding or tight clenching of the upper and lower teeth, which leads to several problems such as lesions to the teeth, headaches, orofacial pain and important disorders of the temporomandibular joint. The prototype uses a magnetic field communication scheme similar to low-frequency radio frequency identification (RFID) technology (NFC). The reader generates a low-frequency magnetic field that is used as the information carrier and powers the sensor. The system is notable because it uses an intra-mouth passive sensor and an external interrogator, which remotely records and processes information regarding a patient's dental activity. This permits a quantitative assessment of bite-force, without requiring intra-mouth batteries, and can provide supplementary information to polysomnographic recordings, current most adequate early diagnostic method, so as to initiate corrective actions before irreversible dental wear appears. In addition to describing the system's operational principles and the manufacture of personalized prototypes, this report will also demonstrate the feasibility of the system and results from the first in vitro and in vivo trials. PMID:23112669

  3. Electromagnetic fields and potentials generated by massless charged particles

    CERN Document Server

    Azzurli, Francesco

    2014-01-01

    We provide for the first time the exact solution of Maxwell's equations for a massless charged particle moving on a generic trajectory at the speed of light. In particular we furnish explicit expressions for the vector potential and the electromagnetic field, which were both previously unknown, finding that they entail different physical features for bounded and unbounded trajectories. With respect to the standard Lienard-Wiechert field the electromagnetic field acquires singular delta-like contributions whose support and dimensionality depend crucially on whether the motion is a) linear, b) accelerated unbounded, c) accelerated bounded. In the first two cases the particle generates a planar shock-wave-like electromagnetic field traveling along a straight line. In the second and third cases the field acquires, in addition, a delta-like contribution supported on a physical singularity-string attached to the particle. For generic accelerated motions a genuine radiation field is also present, represented by a re...

  4. Laser-generated magnetic fields in quasi-hohlraum geometries

    Science.gov (United States)

    Pollock, Bradley; Turnbull, David; Ross, Steven; Hazi, Andrew; Ralph, Joseph; Lepape, Sebastian; Froula, Dustin; Haberberger, Dan; Moody, John

    2014-10-01

    Laser-generated magnetic fields of 10--40 T have been produced with 100--4000 J laser drives at Omega EP and Titan. The fields are generated using the technique described by Daido et al. [Phys. Rev. Lett. 56, 846 (1986)], which works by directing a laser through a hole in one plate to strike a second plate. Hot electrons generated in the laser-produced plasma on the second plate collect on the first plate. A strap connects the two plates allowing a current of 10 s of kA to flow and generate a solenoidal magnetic field. The magnetic field is characterized using Faraday rotation, b-dot probes, and proton radiography. Further experiments to study the effect of the magnetic field on hohlraum performance are currently scheduled for Omega. This work was performed under the auspices of the United States Department of Energy by the Lawrence Livermore National Laboratory under Contract No. DE-AC52-07NA-27344.

  5. Fifth generation lithospheric magnetic field model from CHAMP satellite measurements

    OpenAIRE

    Maus, S.; Hermann Lühr; Martin Rother; Hemant, K.; Balasis, G.; Patricia Ritter; Claudia Stolle

    2007-01-01

    Six years of low-orbit CHAMP satellite magnetic measurements have provided an exceptionally high-quality data resource for lithospheric magnetic field modeling and interpretation. Here we describe the fifth-generation satellite-only magnetic field model MF5. The model extends to spherical harmonic degree 100. As a result of careful data selection, extensive corrections, filtering, and line leveling, the model has low noise levels, even if evaluated at the Earth's surface. The model is particu...

  6. Rotordynamic forces generated by discharge-to-suction leakage flows in centrifugal pumps

    Institute of Scientific and Technical Information of China (English)

    LIU Quan-zhong; WANG Hong-jie; LIU Zhan-sheng

    2009-01-01

    In order to investigate the flow-induced vibration in the shroud passage of centrifugal pump and pre-dict rotordynamic forces of centrifugal pump rotor system,an analysis of rotordynamic forces arising from shrou-ded centnlugal pump is presented.CFD techniques were utilized to analyze the full three-dimensional viscous,primary/secondary flow field in a centrifugal pump impeller to determine rotordynamic forces. Multiple quasi-steady solutions of an eccentric three-dimensional model at different whirl frequency ratios yielded the rotordy-namic forces. The skew-symmetric stiffness,damping,and mass matrices were obtained by second-order least-squares analysis.Simulation of the coupled primary/secondary flow field was conducted,and the complex flow characteristcs.in the flow field of a shroud passage were achieved including the mean velocity and pressure,as well as the eddy in a large scale of flow field due to viscosity.The rotordynamic force coefficients were calculat-ed,and the results were in good agreement with those of experiment except for the direct inertial coefficient without the consideration of whirling forces from the impeller primary flow passage.

  7. How sensitive are nanosecond molecular dynamics simulations of proteins to changes in the force field?

    NARCIS (Netherlands)

    Villa, Alessandra; Fan, Hao; Wassenaar, Tsjerk; Mark, Alan E.

    2007-01-01

    The sensitivity of molecular dynamics simulations to variations in the force field has been examined in relation to a set of 36 structures corresponding to 31 proteins simulated by using different versions of the GROMOS force field. The three parameter sets used (43a1, 53a5, and 53a6) differ signifi

  8. Molecular simulation of gas adsorption and diffusion in a breathing MOF using a rigid force field

    NARCIS (Netherlands)

    García-Pérez, E.; Serra-Crespo,P.; Hamad, S.; Kapteijn, F.; Gascon, J.

    2014-01-01

    Simulation of gas adsorption in flexible porous materials is still limited by the slow progress in the development of flexible force fields. Moreover, the high computational cost of such flexible force fields may be a drawback even when they are fully developed. In this work, molecular simulations o

  9. Molecular simulation of gas adsorption and diffusion in a breathing MOF using a rigid force field

    NARCIS (Netherlands)

    García-Pérez, E.; Serra-Crespo,P.; Hamad, S.; Kapteijn, F.; Gascon, J.

    2014-01-01

    Simulation of gas adsorption in flexible porous materials is still limited by the slow progress in the development of flexible force fields. Moreover, the high computational cost of such flexible force fields may be a drawback even when they are fully developed. In this work, molecular simulations

  10. Artificial force fields for multi-agent simulations of maritime traffic and risk estimation

    NARCIS (Netherlands)

    Xiao, F.; Ligteringen, H.; Van Gulijk, C.; Ale, B.J.M.

    2012-01-01

    A probabilistic risk model is designed to estimate probabilities of collisions for shipping accidents in busy waterways. We propose a method based on multi-agent simulation that uses an artificial force field to model ship maneuvers. The artificial force field is calibrated by AIS data (Automatic Id

  11. Pilot Field Demonstration of Alternative Fuels in Force Projection Petroleum and Water Distribution Equipment

    Science.gov (United States)

    2014-09-04

    UNCLASSIFIED UNCLASSIFIED PILOT FIELD DEMONSTRATION OF ALTERNATIVE FUELS IN FORCE PROJECTION PETROLEUM AND WATER DISTRIBUTION EQUIPMENT...Fort Belvoir, Virginia 22060- 6218. Disposition Instructions Destroy this report when no longer needed. Do not return it to the originator ...UNCLASSIFIED UNCLASSIFIED PILOT FIELD DEMONSTRATION OF ALTERNATIVE FUELS IN FORCE PROJECTION PETROLEUM AND WATER DISTRIBUTION EQUIPMENT

  12. Generation of magnetic fields in Einstein-aether gravity

    Science.gov (United States)

    Saga, Shohei; Shiraishi, Maresuke; Ichiki, Kiyotomo; Sugiyama, Naoshi

    2013-05-01

    Recently the lower bounds of the intergalactic magnetic fields 10-16˜10-20G are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector-mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in general relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-aether gravity model, in which the aether field can act as a new source of vector metric perturbations. The vector metric perturbations induce the velocity difference between baryons and photons which then generate magnetic fields. This velocity difference arises from effects at the second order in the tight-coupling approximation. We estimate the angular power spectra of temperature and B-mode polarization of the cosmic microwave background anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the power spectrum of associated magnetic fields around the recombination epoch within this limit. It is found that the spectrum has a characteristic peak at k=0.1hMpc-1, and at that scale the amplitude can be as large as B˜10-22G where the upper bound comes from cosmic microwave background temperature anisotropies. The magnetic fields with this amplitude can be seeds of large scale magnetic fields observed today if the sufficient dynamo mechanism takes place. Analytic interpretation for the power spectra is also given.

  13. Design of a new torque standard machine based on a torque generation method using electromagnetic force

    Science.gov (United States)

    Nishino, Atsuhiro; Ueda, Kazunaga; Fujii, Kenichi

    2017-02-01

    To allow the application of torque standards in various industries, we have been developing torque standard machines based on a lever deadweight system, i.e. a torque generation method using gravity. However, this method is not suitable for expanding the low end of the torque range, because of the limitations to the sizes of the weights and moment arms. In this study, the working principle of the torque generation method using an electromagnetic force was investigated by referring to watt balance experiments used for the redefinition of the kilogram. Applying this principle to a rotating coordinate system, an electromagnetic force type torque standard machine was designed and prototyped. It was experimentally demonstrated that SI-traceable torque could be generated by converting electrical power to mechanical power. Thus, for the first time, SI-traceable torque was successfully realized using a method other than that based on the force of gravity.

  14. Force and torque on an electric dipole by spinning light fields

    CERN Document Server

    Canaguier-Durand, Antoine; Genet, Cyriaque; Ebbesen, Thomas W

    2013-01-01

    We calculate the optical force and torque applied to an electric dipole by a spinning light field. We prove that the dissipative part of the force depends on the orbital energy flow of the field only, while the spin energy flow is involved in the applied torque. The resulting change in the optical force is detailed for different experimentally relevant configurations, and we show in particular how this change is critical when surface plasmon modes are involved.

  15. Effect of oblique force source induced by laser ablation on ultrasonic generation.

    Science.gov (United States)

    Guo, Yuning; Yang, Dexing; Chang, Ying; Gao, Wei

    2014-01-13

    The effect of asymmetry caused by oblique line-shaped laser ablation on the generation of ultrasonic waves in metal, especially the effect of transverse component of the ablation force source on the ultrasonic waves is analyzed. Due to the oblique force source, the displacements of shear wave increase obviously by the enhanced shear force, the energy concentration area of longitudinal wave deflects to the small range centered on the incident direction while that of shear wave is approximately perpendicular to incident direction. In addition, surface wave enhances in the direction of transverse power flow. Furthermore, some ultrasonic characteristics under vortex laser ablation condition are inferred.

  16. Note: 3D printed spheroid for uniform magnetic field generation

    Science.gov (United States)

    Öztürk, Y.; Aktaş, B.

    2016-10-01

    This article is focused on a novel and practical production method for a uniform magnetic field generator. The method involves building of a surface coil template using a desktop 3D printer and winding of a conducting wire onto the structure using surface grooves as a guide. Groove pattern was based on the parametric spheroidal helical coil formula. The coil was driven by a current source and the magnetic field inside was measured using a Hall probe placed into the holes on the printed structure. The measurements are found to be in good agreement with our finite element analysis results and indicate a fairly uniform field inside.

  17. Optical fiber tip for field-enhanced second harmonic generation.

    Science.gov (United States)

    Pal, Sudipta Sarkar; Mondal, Samir K; Bajpai, Phun Phun; Kapur, Pawan

    2012-10-01

    We propose a simple optical fiber tip for field-enhanced second harmonic generation (SHG). The tip shows nonlinear phenomena of SHG over a wide range of sources, at least from 630 to 830 nm. The optical field corresponding to the second harmonic appears as a nondiffracting bottle beam with voids due to the surface curvature of the tip. The field-enhanced second harmonic can also induce surface plasmons, converting the tip to a plasmonic probe with reduced background signal. The tip can be useful in nanophotonics characterization. As an example, we demonstrate the tip's response as a surface-enhanced Raman spectroscopy probe.

  18. Communication: Multiple atomistic force fields in a single enhanced sampling simulation

    Energy Technology Data Exchange (ETDEWEB)

    Hoang Viet, Man [Department of Physics, North Carolina State University, Raleigh, North Carolina 27695-8202 (United States); Derreumaux, Philippe, E-mail: philippe.derreumaux@ibpc.fr [Laboratoire de Biochimie Théorique, UPR 9080, CNRS, Université Denis Diderot, Sorbonne Paris Cité IBPC, 13 rue Pierre et Marie Curie, 75005 Paris (France); Institut Universitaire de France, 103 Bvd Saint-Germain, 75005 Paris (France); Nguyen, Phuong H., E-mail: phuong.nguyen@ibpc.fr [Laboratoire de Biochimie Théorique, UPR 9080, CNRS, Université Denis Diderot, Sorbonne Paris Cité IBPC, 13 rue Pierre et Marie Curie, 75005 Paris (France)

    2015-07-14

    The main concerns of biomolecular dynamics simulations are the convergence of the conformational sampling and the dependence of the results on the force fields. While the first issue can be addressed by employing enhanced sampling techniques such as simulated tempering or replica exchange molecular dynamics, repeating these simulations with different force fields is very time consuming. Here, we propose an automatic method that includes different force fields into a single advanced sampling simulation. Conformational sampling using three all-atom force fields is enhanced by simulated tempering and by formulating the weight parameters of the simulated tempering method in terms of the energy fluctuations, the system is able to perform random walk in both temperature and force field spaces. The method is first demonstrated on a 1D system and then validated by the folding of the 10-residue chignolin peptide in explicit water.

  19. A novel 3D fibril force assay implicates src in tumor cell force generation in collagen networks.

    Directory of Open Access Journals (Sweden)

    Robert J Polackwich

    Full Text Available New insight into the biomechanics of cancer cell motility in 3D extracellular matrix (ECM environments would significantly enhance our understanding of aggressive cancers and help identify new targets for intervention. While several methods for measuring the forces involved in cell-matrix interactions have been developed, previous to this study none have been able to measure forces in a fibrillar environment. We have developed a novel assay for simultaneously measuring cell mechanotransduction and motility in 3D fibrillar environments. The assay consists of a controlled-density fibrillar collagen gel atop a controlled-stiffness polyacrylamide (PAA surface. Forces generated by living cells and their migration in the 3D collagen gel were measured with the 3D motion of tracer beads within the PAA layer. Here, this 3D fibril force assay is used to study the role of the invasion-associated protein kinase Src in mechanotransduction and motility. Src expression and activation are linked with proliferation, invasion, and metastasis, and have been shown to be required in 2D for invadopodia membranes to direct and mediate invasion. Breast cancer cell line MDA-MD-231 was stably transfected with GFP-tagged constitutively active Src or wild-type Src. In 3D fibrillar collagen matrices we found that, relative to wild-type Src, constitutively active Src: 1 increased the strength of cell-induced forces on the ECM, 2 did not significantly change migration speed, and 3 increased both the duration and the length, but not the number, of long membrane protrusions. Taken together, these results support the hypothesis that Src controls invasion by controlling the ability of the cell to form long lasting cellular protrusions to enable penetration through tissue barriers, in addition to its role in promoting invadopodia matrix-degrading activity.

  20. Two-Element Generation of Unitary Groups Over Finite Fields

    Science.gov (United States)

    2013-01-31

    like to praise my Lord and Savior, Jesus Christ , for allowing me this opportunity to work on a Ph.D in mathematics, and for His sustaining grace...Ishibashi’s original result. The paper’s main theorem will show that all unitary groups over finite fields of odd characteristic are generated by only two

  1. Mediation of Supersymmetry Breaking via Anti-Generation Fields

    CERN Document Server

    Ito, M

    2000-01-01

    In the context of the weakly coupled heterotic string, we propose a new model of mediating supersymmetry breaking. The breakdown of supersymmetry in the hidden sector is transmitted to anti-generation fields via gravitational interactions. Subsequent transmission of the breaking to the MSSM sector occurs via gauge interactions. It is shown that the mass spectra of superparticles are phenomenologically viable.

  2. Second order semiclassics with self-generated magnetic fields

    DEFF Research Database (Denmark)

    Erdös, Laszlo; Fournais, Søren; Solovej, Jan Philip

    2012-01-01

    We consider the semiclassical asymptotics of the sum of negative eigenvalues of the three-dimensional Pauli operator with an external potential and a self-generated magnetic field $B$. We also add the field energy $\\beta \\int B^2$ and we minimize over all magnetic fields. The parameter $\\beta......$ effectively determines the strength of the field. We consider the weak field regime with $\\beta h^{2}\\ge {const}>0$, where $h$ is the semiclassical parameter. For smooth potentials we prove that the semiclassical asymptotics of the total energy is given by the non-magnetic Weyl term to leading order...... in the companion paper \\cite{EFS3} to prove the second order Scott correction to the ground state energy of large atoms and molecules....

  3. Relativistic Scott correction in self-generated magnetic fields

    DEFF Research Database (Denmark)

    Erdös, Laszlo; Fournais, Søren; Solovej, Jan Philip

    2012-01-01

    We consider a large neutral molecule with total nuclear charge $Z$ in a model with self-generated classical magnetic field and where the kinetic energy of the electrons is treated relativistically. To ensure stability, we assume that $Z \\alpha .../3}$ and it is unchanged by including the self-generated magnetic field. We prove the first correction term to this energy, the so-called Scott correction of the form $S(\\alpha Z) Z^2$. The current paper extends the result of \\cite{SSS} on the Scott correction for relativistic molecules to include a self-generated...... constant. We are interested in the ground state energy in the simultaneous limit $Z \\rightarrow \\infty$, $\\alpha \\rightarrow 0$ such that $\\kappa=Z \\alpha$ is fixed. The leading term in the energy asymptotics is independent of $\\kappa$, it is given by the Thomas-Fermi energy of order $Z^{7...

  4. A viable non-axisymmetric non-force-free field to represent solar active regions

    CERN Document Server

    Prasad, A

    2016-01-01

    A combination of analytical calculations and vectormagnetogram data are utilized to develop a non-axisymmetric non-force-free magnetic field and asses its viability in describing solar active regions. For the purpose, we construct a local spherical shell where a planar surface, tangential to the inner sphere, represents a Cartesian cutout of an active region. The magnetic field defined on the surface is then correlated with magnetograms. The analysis finds the non-axisymmetric non-force-free magnetic field, obtained by a superposition of two linear-force-free fields, correlates reasonably well with magnetograms.

  5. Reflection type metasurface designed for high efficiency vectorial field generation

    Science.gov (United States)

    Wang, Shiyi; Zhan, Qiwen

    2016-07-01

    We propose a reflection type metal-insulator-metal (MIM) metasurface composed of hybrid nano-antennas for comprehensive spatial engineering of the properties of optical fields. The capability of such structure is illustrated in the design of a device that can be used to produce a radially polarized vectorial beam for optical needle field generation. This device consists of uniformly segmented sectors of high efficiency MIM metasurface. With each of the segment sector functioning as a local quarter-wave-plate (QWP), the device is designed to convert circularly polarized incidence into local linear polarization to create an overall radial polarization with corresponding binary phases and extremely high dynamic range amplitude modulation. The capability of such devices enables the generation of nearly arbitrarily complex optical fields that may find broad applications that transcend disciplinary boundaries.

  6. High-order harmonic generation from inhomogeneous fields

    CERN Document Server

    Ciappina, M F; Quidant, R; Lewenstein, M

    2011-01-01

    We present theoretical studies of high-order harmonic generation (HHG) produced by non-homogeneous fields as resulting from the illumination of plasmonic nanostructures with a short laser pulse. We show that the inhomogeneity of the local fields plays an important role in the HHG process and lead to the generation of even harmonics and a significantly increased cutoff, more pronounced for the longer wavelengths cases studied. In order to understand and characterize the new HHG features we employ two different approaches: the numerical solution of the time dependent Schr\\"odinger equation (TDSE) and the semiclassical approach known as Strong Field Approximation (SFA). Both approaches predict comparable results and show the new features, but using the semiclassical arguments behind the SFA, we are able to fully understand the reasons of the cutoff extension.

  7. Electromagnetic fields and potentials generated by massless charged particles

    Energy Technology Data Exchange (ETDEWEB)

    Azzurli, Francesco, E-mail: francesco.azzurli@gmail.com [Scuola Galileiana di Studi Superiori, Università degli Studi di Padova (Italy); Lechner, Kurt, E-mail: lechner@pd.infn.it [Dipartimento di Fisica e Astronomia, Università degli Studi di Padova (Italy); INFN, Sezione di Padova, Via F. Marzolo, 8, 35131 Padova (Italy)

    2014-10-15

    We provide for the first time the exact solution of Maxwell’s equations for a massless charged particle moving on a generic trajectory at the speed of light. In particular we furnish explicit expressions for the vector potential and the electromagnetic field, which were both previously unknown, finding that they entail different physical features for bounded and unbounded trajectories. With respect to the standard Liénard–Wiechert field the electromagnetic field acquires singular δ-like contributions whose support and dimensionality depend crucially on whether the motion is (a) linear, (b) accelerated unbounded, (c) accelerated bounded. In the first two cases the particle generates a planar shock-wave-like electromagnetic field traveling along a straight line. In the second and third cases the field acquires, in addition, a δ-like contribution supported on a physical singularity-string attached to the particle. For generic accelerated motions a genuine radiation field is also present, represented by a regular principal-part type distribution diverging on the same singularity-string. - Highlights: • First exact solution of Maxwell’s equations for massless charges in arbitrary motion. • Explicit expressions of electromagnetic fields and potentials. • Derivations are rigorous and based on distribution theory. • The form of the field depends heavily on whether the motion is bounded or unbounded. • The electromagnetic field contains unexpected Dirac-delta-function contributions.

  8. Generation of Focused Electric Field Patterns at Dielectric Surfaces

    Science.gov (United States)

    Olofsson, Jessica; Levin, Mikael; Strömberg, Anette; Weber, Stephen G.; Ryttsén, Frida; Orwar, Owe

    2006-01-01

    We here report on a concept for creating well-defined electric field gradients between the boundaries of capillary electrode (a capillary of a nonconducting material equipped with an interior metal electrode) outlets, and dielectric surfaces. By keeping a capillary electrode opening close to a boundary between a conducting solution and a nonconducting medium, a high electric field can be created close to the interface by field focusing effects. By varying the inner and outer diameters of the capillary, the span of electric field strengths and the field gradient obtained can be controlled, and by varying the slit height between the capillary rim and the surface, or the applied current, the average field strength and gradient can be varied. Field focusing effects and generation of electric field patterns were analyzed using finite element method simulations. We experimentally verified the method by electroporation of a fluorescent dye (fluorescein diphosphate) into adherent, monolayered cells (PC-12 and WSS-1) and obtained a pattern of fluorescent cells corresponding to the focused electric field. PMID:16013887

  9. Generation of magnetic fields in Einstein-Aether gravity

    CERN Document Server

    Saga, Shohei; Ichiki, Kiyotomo; Sugiyama, Naoshi

    2013-01-01

    Recently the lower bounds of the intergalactic magnetic fields $10^{-16} \\sim 10^{-20}$ Gauss are set by gamma-ray observations while it is unlikely to generate such large scale magnetic fields through astrophysical processes. It is known that large scale magnetic fields could be generated if there exist cosmological vector mode perturbations in the primordial plasma. The vector mode, however, has only a decaying solution in General Relativity if the plasma consists of perfect fluids. In order to investigate a possible mechanism of magnetogenesis in the primordial plasma, here we consider cosmological perturbations in the Einstein-Aether gravity model, in which the aether field can act as a new source of vector metric perturbations and thus of magnetic fields. We estimate the angular power spectra of temperature and B-mode polarization of the Cosmic Microwave Background (CMB) Anisotropies in this model and put a rough constraint on the aether field parameters from latest observations. We then estimate the pow...

  10. The evolution of primordial magnetic fields since their generation

    Science.gov (United States)

    Kahniashvili, Tina; Brandenburg, Axel; Tevzadze, Alexander G.

    2016-10-01

    We study the evolution of primordial magnetic fields in an expanding cosmic plasma. For this purpose we present a comprehensive theoretical model to consider the evolution of MHD turbulence that can be used over a wide range of physical conditions, including cosmological and astrophysical applications. We model different types of decaying cosmic MHD turbulence in the expanding Universe and characterize the large-scale magnetic fields in such a medium. Direct numerical simulations of freely decaying MHD turbulence are performed for different magnetogenesis scenarios: magnetic fields generated during cosmic inflation as well as electroweak and QCD phase transitions in the early Universe. Magnetic fields and fluid motions are strongly coupled due to the high Reynolds number in the early Universe. Hence, we abandon the simple adiabatic dilution model to estimate magnetic field amplitudes in the expanding Universe and include turbulent mixing effects on the large-scale magnetic field evolution. Numerical simulations have been carried out for non-helical and helical magnetic field configurations. The numerical results show the possibility of inverse transfer of energy in magnetically dominated non-helical MHD turbulence. On the other hand, decay properties of helical turbulence depend on whether the turbulent magnetic field is in a weakly or a fully helical state. Our results show that primordial magnetic fields can be considered as a seed for the observed large-scale magnetic fields in galaxies and clusters. Bounds on the magnetic field strength are obtained and are consistent with the upper and lower limits set by observations of extragalactic magnetic fields.

  11. Active noise control of forced and induced draft fans in power generating plants

    Energy Technology Data Exchange (ETDEWEB)

    Eldada, M.V.

    1985-05-01

    A study was carried out into active noise reduction of forced draft fans in power generation plants. Active noise reduction involves detecting noise, inverting the phase and re-introducing the anti-phase signal into the duct to cancel the noise through destructive interference. Acoustic pressure transfer functions were meaured in-situ along a cross section of a 15 ft diameter fan inlet. A computer modal analysis program was written and used to analyze the field data. It was found that in frequencies between ca 5 Hz and 45 Hz the energy propagates mainly in the plane wave mode, while in higher frequencies the energy was carried mainly by higher order propagation modes. The project objective was to cancel noise up to a frequency of 130 Hz, but current technology restricted active cancellation to plane waves only. Three alternatives were considered: install a feed forward active noise control system to cancel noise at frequencies below 45 Hz; conduct research on active noise control of higher order propagation modes in ducts; or install a feed back active noise control system and a duct splitter in order to cancel noise between 30 and 130 Hz. It was recommended that the third option be selected as the next phase of the research project, which would comprise a 20 ft duct splitter and microphones, filters, amplifiers, loudspekers and cabinets. 6 refs., 12 figs.

  12. Guidelines for random excitation forces due to cross flow in steam generators

    Energy Technology Data Exchange (ETDEWEB)

    Taylor, C.E.; Pettigrew, M.J. [Atomic Energy of Canada Limited, Chalk River, Ontario (Canada)

    1998-07-01

    Random excitation forces can cause low-amplitude tube motion that will result in long-term fretting-wear or fatigue. To prevent these tube failures in steam generators and other heat exchangers, designers and trouble-shooters must have guidelines that incorporate random or turbulent fluid forces. Experiments designed to measure fluid forces have been carried out at Chalk River Laboratories and at other labs around the world. The data from these experiments have been studied and collated to determine suitable guidelines for random excitation forces. In this paper, a guideline for random excitation forces in single-phase cross flow is presented in the form of normalised spectra that are applicable to a wide range of flow conditions and tube frequencies. In particular, the experimental results used in this study were carried out over the full range of flow conditions found in a nuclear steam generator. The proposed guidelines are applicable to steam generators, condensers, reheaters and other shell-and-tube heat exchangers. They may be used for flow-induced vibration analysis of new or existing components, as input to vibration analysis computer codes and as specifications in procurement documents. (author)

  13. Conservative and dissipative force field for simulation of coarse-grained alkane molecules: A bottom-up approach

    Energy Technology Data Exchange (ETDEWEB)

    Trément, Sébastien; Rousseau, Bernard, E-mail: bernard.rousseau@u-psud.fr [Laboratoire de Chimie-Physique, UMR 8000 CNRS, Université Paris-Sud, Orsay (France); Schnell, Benoît; Petitjean, Laurent; Couty, Marc [Manufacture Française des Pneumatiques MICHELIN, Centre de Ladoux, 23 place des Carmes, 63000 Clermont-Ferrand (France)

    2014-04-07

    We apply operational procedures available in the literature to the construction of coarse-grained conservative and friction forces for use in dissipative particle dynamics (DPD) simulations. The full procedure rely on a bottom-up approach: large molecular dynamics trajectories of n-pentane and n-decane modeled with an anisotropic united atom model serve as input for the force field generation. As a consequence, the coarse-grained model is expected to reproduce at least semi-quantitatively structural and dynamical properties of the underlying atomistic model. Two different coarse-graining levels are studied, corresponding to five and ten carbon atoms per DPD bead. The influence of the coarse-graining level on the generated force fields contributions, namely, the conservative and the friction part, is discussed. It is shown that the coarse-grained model of n-pentane correctly reproduces self-diffusion and viscosity coefficients of real n-pentane, while the fully coarse-grained model for n-decane at ambient temperature over-predicts diffusion by a factor of 2. However, when the n-pentane coarse-grained model is used as a building block for larger molecule (e.g., n-decane as a two blobs model), a much better agreement with experimental data is obtained, suggesting that the force field constructed is transferable to large macro-molecular systems.

  14. Microrelief-Controlled Overland Flow Generation: Laboratory and Field Experiments

    Directory of Open Access Journals (Sweden)

    Xuefeng Chu

    2015-01-01

    Full Text Available Surface microrelief affects overland flow generation and the related hydrologic processes. However, such influences vary depending on other factors such as rainfall characteristics, soil properties, and initial soil moisture conditions. Thus, in-depth research is needed to better understand and evaluate the combined effects of these factors on overland flow dynamics. The objective of this experimental study was to examine how surface microrelief, in conjunction with the factors of rainfall, soil, and initial moisture conditions, impacts overland flow generation and runoff processes in both laboratory and field settings. A series of overland flow experiments were conducted for rough and smooth surfaces that represented distinct microtopographic characteristics and the experimental data were analyzed and compared. Across different soil types and initial moisture conditions, both laboratory and field experiments demonstrated that a rough soil surface experienced a delayed initiation of runoff and featured a stepwise threshold flow pattern due to the microrelief-controlled puddle filling-spilling-merging dynamics. It was found from the field experiments that a smooth plot surface was more responsive to rainfall variations especially during an initial rainfall event. However, enhanced capability of overland flow generation and faster puddle connectivity of a rough field plot occurred during the subsequent rain events.

  15. An Analysis of Biomolecular Force Fields for Simulations of Polyglutamine in Solution

    Energy Technology Data Exchange (ETDEWEB)

    Fluitt, Aaron M. [Univ. of Chicago, IL (United States); de Pablo, Juan J. [Argonne National Lab. (ANL), Argonne, IL (United States)

    2015-09-01

    Polyglutamine (polyQ) peptides are a useful model system for biophysical studies of protein folding and aggregation, both for their intriguing aggregation properties and their own relevance to human disease. The genetic expansion of a polyQ tract triggers the formation of amyloid aggregates associated with nine neurodegenerative diseases. Several clearly identifiable and separable factors, notably the length of the polyQ tract, influence the mechanism of aggregation, its associated kinetics, and the ensemble of structures formed. Atomistic simulations are well positioned to answer open questions regarding the thermodynamics and kinetics of polyQ folding and aggregation. The additional, explicit representation of water permits deeper investigation of the role of solvent dynamics, and it permits a direct comparison of simulation results with infrared spectroscopy experiments. The generation of meaningful simulation results hinges on satisfying two essential criteria: achieving sufficient conformational sampling to draw statistically valid conclusions, and accurately reproducing the intermolecular forces that govern system structure and dynamics. In this work, we examine the ability of 12 biomolecular force fields to reproduce the properties of a simple, 30-residue polyQ peptide (Q30) in explicit water. In addition to secondary and tertiary structure, we consider generic structural properties of polymers that provide additional dimensions for analysis of the highly degenerate disordered states of the molecule. We find that the 12 force fields produce a wide range of predictions. We identify AMBER ff99SB, AMBER ff99SB*, and OPLS-AA/L to be most suitable for studies of polyQ folding and aggregation.

  16. Comparison of Forced-Alignment Speech Recognition and Humans for Generating Reference VAD

    DEFF Research Database (Denmark)

    Kraljevski, Ivan; Tan, Zheng-Hua; Paola Bissiri, Maria

    2015-01-01

    This present paper aims to answer the question whether forced-alignment speech recognition can be used as an alternative to humans in generating reference Voice Activity Detection (VAD) transcriptions. An investigation of the level of agreement between automatic/manual VAD transcriptions and the ......This present paper aims to answer the question whether forced-alignment speech recognition can be used as an alternative to humans in generating reference Voice Activity Detection (VAD) transcriptions. An investigation of the level of agreement between automatic/manual VAD transcriptions...... and the reference ones produced by a human expert was carried out. Thereafter, statistical analysis was employed on the automatically produced and the collected manual transcriptions. Experimental results confirmed that forced-alignment speech recognition can provide accurate and consistent VAD labels....

  17. A force-generating machinery maintains the spindle at the cell center during mitosis.

    Science.gov (United States)

    Garzon-Coral, Carlos; Fantana, Horatiu A; Howard, Jonathon

    2016-05-27

    The position and orientation of the mitotic spindle is precisely regulated to ensure the accurate partition of the cytoplasm between daughter cells and the correct localization of the daughters within growing tissue. Using magnetic tweezers to perturb the position of the spindle in intact cells, we discovered a force-generating machinery that maintains the spindle at the cell center during metaphase and anaphase in one- and two-cell Caenorhabditis elegans embryos. The forces increase with the number of microtubules and are larger in smaller cells. The machinery is rigid enough to suppress thermal fluctuations to ensure precise localization of the mitotic spindle, yet compliant enough to allow molecular force generators to fine-tune the position of the mitotic spindle to facilitate asymmetric division.

  18. Comparison of Forced-Alignment Speech Recognition and Humans for Generating Reference VAD

    DEFF Research Database (Denmark)

    Kraljevski, Ivan; Tan, Zheng-Hua; Paola Bissiri, Maria

    2015-01-01

    This present paper aims to answer the question whether forced-alignment speech recognition can be used as an alternative to humans in generating reference Voice Activity Detection (VAD) transcriptions. An investigation of the level of agreement between automatic/manual VAD transcriptions and the ......This present paper aims to answer the question whether forced-alignment speech recognition can be used as an alternative to humans in generating reference Voice Activity Detection (VAD) transcriptions. An investigation of the level of agreement between automatic/manual VAD transcriptions...... and the reference ones produced by a human expert was carried out. Thereafter, statistical analysis was employed on the automatically produced and the collected manual transcriptions. Experimental results confirmed that forced-alignment speech recognition can provide accurate and consistent VAD labels....

  19. The proton motive force generated in Leuconostoc oenos by L-malate fermentation

    NARCIS (Netherlands)

    Salema, Madalena; Lolkema, Juke S.; San Romão, M.V.; Loureiro Dias, Maria C.

    In cells of Leuconostoc oenos, the fermentation of L-malic acid generates both a transmembrane pH gradient, inside alkaline, and an electrical potential gradient, inside negative. In resting cells, the proton motive force ranged from -170 mV to -88 mV between pH 3.1 and 5.6 in the presence of

  20. Forces and overtopping on 2. generation Wave Dragon for Nissum Bredning. Phase 3

    Energy Technology Data Exchange (ETDEWEB)

    Hald, T.; Frigaard, P.

    2001-11-01

    The purpose of this report is to summarize forcing and overtopping on the redesigned Wave Dragon model. The results will establish a basis for the development of the 1:4.5 scale prototype planned for testing in Nissum Bredning, a sea inlet on the Danish West Coast. For comparison also results obtained using the 1. generation are referred in this report. (au)

  1. A test on reactive force fields for the study of silica dimerization reactions

    Energy Technology Data Exchange (ETDEWEB)

    Moqadam, Mahmoud; Riccardi, Enrico; Trinh, Thuat T.; Åstrand, Per-Olof; Erp, Titus S. van, E-mail: titus.van.erp@ntnu.no [Department of Chemistry, Norwegian University of Science and Technology (NTNU), Høgskoleringen 5, Realfagbygget D3-117, 7491 Trondheim (Norway)

    2015-11-14

    We studied silica dimerization reactions in the gas and aqueous phase by density functional theory (DFT) and reactive force fields based on two parameterizations of ReaxFF. For each method (both ReaxFF force fields and DFT), we performed constrained geometry optimizations, which were subsequently evaluated in single point energy calculations using the other two methods. Standard fitting procedures typically compare the force field energies and geometries with those from quantum mechanical data after a geometry optimization. The initial configurations for the force field optimization are usually the minimum energy structures of the ab initio database. Hence, the ab initio method dictates which structures are being examined and force field parameters are being adjusted in order to minimize the differences with the ab initio data. As a result, this approach will not exclude the possibility that the force field predicts stable geometries or low transition states which are realistically very high in energy and, therefore, never considered by the ab initio method. Our analysis reveals the existence of such unphysical geometries even at unreactive conditions where the distance between the reactants is large. To test the effect of these discrepancies, we launched molecular dynamics simulations using DFT and ReaxFF and observed spurious reactions for both ReaxFF force fields. Our results suggest that the standard procedures for parameter fitting need to be improved by a mutual comparative method.

  2. Hierarchical atom type definitions and extensible all-atom force fields.

    Science.gov (United States)

    Jin, Zhao; Yang, Chunwei; Cao, Fenglei; Li, Feng; Jing, Zhifeng; Chen, Long; Shen, Zhe; Xin, Liang; Tong, Sijia; Sun, Huai

    2016-03-15

    The extensibility of force field is a key to solve the missing parameter problem commonly found in force field applications. The extensibility of conventional force fields is traditionally managed in the parameterization procedure, which becomes impractical as the coverage of the force field increases above a threshold. A hierarchical atom-type definition (HAD) scheme is proposed to make extensible atom type definitions, which ensures that the force field developed based on the definitions are extensible. To demonstrate how HAD works and to prepare a foundation for future developments, two general force fields based on AMBER and DFF functional forms are parameterized for common organic molecules. The force field parameters are derived from the same set of quantum mechanical data and experimental liquid data using an automated parameterization tool, and validated by calculating molecular and liquid properties. The hydration free energies are calculated successfully by introducing a polarization scaling factor to the dispersion term between the solvent and solute molecules. © 2015 Wiley Periodicals, Inc.

  3. Analysis of circular wave packets generated by pulsed electric fields

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, S., E-mail: shuhei@concord.itp.tuwien.ac.at [Institute for Theoretical Physics, Vienna University of Technology, Vienna (Austria); Reinhold, C.O. [Physics Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6372 (United States); Department of Physics, University of Tennessee, Knoxville, TN 37996 (United States); Burgdoerfer, J. [Institute for Theoretical Physics, Vienna University of Technology, Vienna (Austria); Department of Physics, University of Tennessee, Knoxville, TN 37996 (United States); Wyker, B.; Ye, S.; Dunning, F.B. [Department of Physics and Astronomy and the Rice Quantum Institute, Rice University, Houston, TX 77005-1892 (United States)

    2012-05-15

    We demonstrate that circular wave packets in high Rydberg states generated by a pulsed electric field applied to extreme Stark states are characterized by a position-dependent energy gradient that leads to a correlation between the principal quantum number n and the spatial coordinate. This correlation is rather insensitive to the initial state and can be seen even in an incoherent mix of states such as is generated experimentally allowing information to be placed into, and extracted from, such wave packets. We show that detailed information on the spatial distribution of a circular wave packet can be extracted by analyzing the complex phase of its expansion coefficients.

  4. Analysis of Circular Wave Packets Generated by Pulsed Electric Fields

    Energy Technology Data Exchange (ETDEWEB)

    Yoshida, S. [Vienna University of Technology, Austria; Reinhold, Carlos O [ORNL; Burgdorfer, J. [Vienna University of Technology, Austria; Wyker, B. [Rice University; Ye, S. [Rice University; Dunning, F. B. [Rice University

    2011-01-01

    We demonstrate that circular wave packets in high Rydberg states generated using a pulsed electric field applied to extreme Stark states are characterized by a position-dependent energy gradient that leads to a correlation between the principal quantum number n and the spatial coordinate. This correlation is rather insensitive to the initial state and can be seen even in an incoherent mix of states such as is generated experimentally allowing information to be placed into, and extracted from, such wavepackets. We show that detailed information on the spatial distribution of a circular wave packet can be extracted by analyzing the complex phase of its expansion coefficient.

  5. Improvement of force factor of magnetostrictive vibration power generator for high efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Kita, Shota, E-mail: happiest3.7@gmail.com; Ueno, Toshiyuki; Yamada, Sotoshi [Kanazawa University, Kakuma-machi, Kanazawa-city, Ishikawa 920-1164 (Japan)

    2015-05-07

    We develop high power magnetostrictive vibration power generator for battery-free wireless electronics. The generator is based on a cantilever of parallel beam structure consisting of coil-wound Galfenol and stainless plates with permanent magnet for bias. Oscillating force exerted on the tip bends the cantilever in vibration yields stress variation of Galfenol plate, which causes flux variation and generates voltage on coil due to the law of induction. This generator has advantages over conventional, such as piezoelectric or moving magnet types, in the point of high efficiency, highly robust, and low electrical impedance. Our concern is the improvement of energy conversion efficiency dependent on the dimension. Especially, force factor, the conversion ratio of the electromotive force (voltage) on the tip velocity in vibration, has an important role in energy conversion process. First, the theoretical value of the force factor is formulated and then the validity was verified by experiments, where we compare four types of prototype with parameters of the dimension using 7.0 × 1.5 × 50 mm beams of Galfenol with 1606-turn wound coil. In addition, the energy conversion efficiency of the prototypes depending on load resistance was measured. The most efficient prototype exhibits the maximum instantaneous power of 0.73 W and energy of 4.7 mJ at a free vibration of frequency of 202 Hz in the case of applied force is 25 N. Further, it was found that energy conversion efficiency depends not only on the force factor but also on the damping (mechanical loss) of the vibration.

  6. Sensing network for electromagnetic fields generated by seismic activities

    Science.gov (United States)

    Gershenzon, Naum I.; Bambakidis, Gust; Ternovskiy, Igor V.

    2014-06-01

    The sensors network is becoming prolific and play now increasingly more important role in acquiring and processing information. Cyber-Physical Systems are focusing on investigation of integrated systems that includes sensing, networking, and computations. The physics of the seismic measurement and electromagnetic field measurement requires special consideration how to design electromagnetic field measurement networks for both research and detection earthquakes and explosions along with the seismic measurement networks. In addition, the electromagnetic sensor network itself could be designed and deployed, as a research tool with great deal of flexibility, the placement of the measuring nodes must be design based on systematic analysis of the seismic-electromagnetic interaction. In this article, we review the observations of the co-seismic electromagnetic field generated by earthquakes and man-made sources such as vibrations and explosions. The theoretical investigation allows the distribution of sensor nodes to be optimized and could be used to support existing geological networks. The placement of sensor nodes have to be determined based on physics of electromagnetic field distribution above the ground level. The results of theoretical investigations of seismo-electromagnetic phenomena are considered in Section I. First, we compare the relative contribution of various types of mechano-electromagnetic mechanisms and then analyze in detail the calculation of electromagnetic fields generated by piezomagnetic and electrokinetic effects.

  7. Computational Models for Creating Homogeneous Magnetic Field Generation Systems

    Directory of Open Access Journals (Sweden)

    Gerlys M. Villalobos-Fontalvo

    2013-11-01

    Full Text Available It is increasingly common to use magnetic fields at the cellular level to assess their interaction with biological tissues. The stimulation is usually done with Helmholtz coils which generate a uniform magnetic field in the center of the system. However, assessing cellular behavior with different magnetic field characteristics can be a long and expensive process. For this, it can be used computational models to previously estimate the cellular behavior due to variety of field characteristics prior to in-vitro stimulation in a laboratory. In this paper, we present a methodology for the development of three computational models of homogeneous magnetic field generation systems for possible application in cell stimulation. The models were developed in the Ansys Workbench environment and it was evaluated the magnetic flux density behavior at different configurations. The results were validated with theoretical calculations from the Biot-Savart law. Validated models will be coupled to Ansys APDL environment in order to assess the harmonic response of the system.

  8. Magnetic Field Generation and Particle Energization in Relativistic Shear Flows

    Science.gov (United States)

    Liang, Edison; Boettcher, Markus; Smith, Ian

    2012-10-01

    We present Particle-in-Cell simulation results of magnetic field generation by relativistic shear flows in collisionless electron-ion (e-ion) and electron-positron (e+e-) plasmas. In the e+e- case, small current filaments are first generated at the shear interface due to streaming instabilities of the interpenetrating particles from boundary perturbations. Such current filaments create transverse magnetic fields which coalesce into larger and larger flux tubes with alternating polarity, eventually forming ordered flux ropes across the entire shear boundary layer. Particles are accelerated across field lines to form power-law tails by semi-coherent electric fields sustained by oblique Langmuir waves. In the e-ion case, a single laminar slab of transverse flux rope is formed at the shear boundary, sustained by thin current sheets on both sides due to different drift velocities of electrons and ions. The magnetic field has a single polarity for the entire boundary layer. Electrons are heated to a fraction of the ion energy, but there is no evidence of power-law tail forming in this case.

  9. The force generated by biological membranes on a polymer rod and its response: Statics and dynamics

    Science.gov (United States)

    Daniels, D. R.; Turner, M. S.

    2004-10-01

    We propose a theory for the force exerted by a fluctuating membrane on a polymer rod tip. Using statistical mechanical methods, the expression for the generated force is written in terms of the distance of the rod tip from the membrane "frame." We apply the theory in calculating the stall force and membrane displacement required to cease the growth of a growing fiber induced by membrane fluctuations, as well as the membrane force and membrane displacement required for rod/fiber buckling. We also consider the dynamics of a growing fiber tip under the influence of a fluctuation-induced membrane force. We discuss the importance of our results in various biological contexts. Finally, we present a method to simultaneously extract both the rigidity of the semiflexible rod and the force applied by, e.g., the membrane from the measurements of the bending fluctuations of the rod. Such a measurement of the force would give information about the thermodynamics of the rod polymerization that involves the usual Brownian ratchet mechanism.

  10. Lightning electromagnetic field generated by grounding electrode considering soil ionization

    Institute of Scientific and Technical Information of China (English)

    ZENG Rong; HE Jinliang; ZHANG Bo; GAO Yanqing

    2006-01-01

    A circuit model with lumped time-variable parameter is proposed to calculate the transient characteristic of grounding electrode under lightning current, which takes into consideration the dynamic and nonlinear effect of soil ionization around the grounding electrode. The ionization phenomena in the soil are simulated by means of time-variable parameters under appropriate conditions. The generated electromagnetic field in the air is analyzed by using electrical dipole theory and image theory when the lightning current flows into the grounding electrode. The influence of soil ionization on the electromagnetic field is investigated.

  11. Hilbert phase dynamometry (HPD) for real-time measurement of cell generated forces (Conference Presentation)

    Science.gov (United States)

    Sridharan, Shamira; Li, Yanfen; Bhaduri, Basanta; Majeed, Hassaan; Dupenloup, Paul; Levine, Alex; Kilian, Kristopher A.; Popescu, Gabriel

    2016-03-01

    Traction force microscopy is the most widely used technique for studying the forces exerted by cells on deformable substrates. However, the method is computationally intense and cells have to be detached from the substrate prior to measuring the displacement map. We have developed a new method, referred to as Hilbert phase dynamometry (HPD), which yields real-time force fields and, simultaneously, cell dry mass and growth information. HPD operates by imaging cells on a deformable substrate that is patterned with a grid of fluorescent proteins. A Hilbert transform is used to extract the phase map associated with the grid deformation, which provides the displacement field. By combining this information with substrate stiffness, an elasticity model was developed to measure forces exerted by cells with high spatial resolution. In our study, we prepared 10kPa gels and them with a 2-D grid of FITC-conjugated fibrinogen/fibronectin mixture, an extracellular matrix protein to which cells adhere. We cultured undifferentiated mesenchymal stem cells (MSC), and MSCs that were in the process of undergoing adipogenesis and osteogenesis. The cells were measured over the course of 24 hours using Spatial Light Interference Microscopy (SLIM) and wide-field epi-fluorescence microscopy allowing us to simultaneously measure cell growth and the forces exerted by the cells on the substrate.

  12. The Krafla Geothermal Field, Iceland: 3. The Generating Capacity of the Field

    Science.gov (United States)

    Bodvarsson, G. S.; Pruess, K.; Stefansson, V.; Eliasson, E. T.

    1984-11-01

    This paper presents analytical and numerical studies of the generating capacity of the Krafla field. A general lumped parameter model is developed which can be used to obtain rough estimates of the generating capacity of a geothermal field based on the size of the wellfield, the average formation porosity, and the amount of recharge to the system. The model is applied to the old wellfield at Krafla. More sophisticated calculations of the generating capacity of the Krafla field are also performed using distributed-parameter models. Two-dimensional areal models of the various reservoir regions at Krafla are developed and their generating capacities (MWe) evaluated. The results obtained indicate that the old wellfield can sustain steam production of 30 MWe for 30 years. The estimated power potential of the new wellfield is 20 MWe for 30 years. To obtain the required steam production several additional wells may be drilled in the old and new wellfields.

  13. Spindle oscillations during asymmetric cell division require a threshold number of active cortical force generators.

    Science.gov (United States)

    Pecreaux, Jacques; Röper, Jens-Christian; Kruse, Karsten; Jülicher, Frank; Hyman, Anthony A; Grill, Stephan W; Howard, Jonathon

    2006-11-07

    Asymmetric division of the C. elegans zygote is due to the posterior-directed movement of the mitotic spindle during metaphase and anaphase. During this movement along the anterior-posterior axis, the spindle oscillates transversely. These motions are thought to be driven by a force-generating complex-possibly containing the motor protein cytoplasmic dynein-that is located at the cell cortex and pulls on microtubules growing out from the spindle poles. A theoretical analysis indicates that the oscillations might arise from mechanical coordination of the force-generating motors, and this coordination is mediated by the load dependence of the motors' detachment from the microtubules. The model predicts that the motor activity must exceed a threshold for oscillations to occur. We have tested the existence of a threshold by using RNA interference to gradually reduce the levels of dynein light intermediate chain as well as GPR-1 and GPR-2 that are involved in the G protein-mediated regulation of the force generators. We found an abrupt cessation of oscillations as expected if the motor activity dropped below a threshold. Furthermore, we can account for the complex choreography of the mitotic spindle-the precise temporal coordination of the buildup and die-down of the transverse oscillations with the posterior displacement-by a gradual increase in the processivity of a single type of motor machinery during metaphase and anaphase. The agreement between our results and modeling suggests that the force generators themselves have the intrinsic capability of generating oscillations when opposing forces exceed a threshold.

  14. Forces exciting generation roll at rotor vibrations when rotor-to-stator rubbing

    Science.gov (United States)

    Shatokhin, V. F.

    2017-07-01

    The consequences of emergencies of turbosets for different application are revealed, the cause of forced shutdown and even catastrophic destructions of which many researchers consider the rotor-to-stator rubbing and development—to a greater or lesser extent—of the phenomena of the rotor generation roll over the stator. The synchronous or asynchronous generation roll is determined by the rotor precession direction, coinciding or not coinciding with the self-rotation direction of the rotor. Asynchronous generation roll is the most dangerous form of the rotor-stator contact interaction with the vibrations with rubbing. The basic equations of rotor vibrations are presented: symmetric rotor fixed on two supports and that fixed on several supports after abrupt imbalance with and without rotor coming in contact with a flexible stator. The vibration process is considered as the rotor motion in a backlash with subsequent contact with the stator, loss of contact, or development of generation roll. The latter essentially depends on the properties of the "rotor-support-stator" dynamic system. The stator stiffness characteristic is specified in "force-deformation" coordinates that make it possible to take into account damping in the supports and power loss in the stator. The diagram of elastic-damping device was presented, which makes it possible to ensure a certain level of power loss at the stator displacements. The exciting forces promoting development of self-exciting vibrations of the rotor in the form of asynchronous generation roll were compared with the exciting forces of oil film of sliding bearings and forces of aerodynamic excitation in the turbine flow path and sealings. For the rotor systems of high and medium pressure of a 300 MW capacity turboset, the simulation results of the process of development of asynchronous generation roll at the vibrations with rubbing were revealed, and the basic characteristics of development of generation roll in a span between

  15. Dark matter and generation of galactic magnetic fields

    CERN Document Server

    Berezhiani, Zurab; Tkachev, I I

    2013-01-01

    A mechanism for creation of galactic and intergalactic magnetic fields at a recent cosmological epoch is proposed. We show that in rotating protogalaxies circular electric currents are generated by the interactions of free electrons with dark matter particles while the impact of such interactions on galactic protons is considerably weaker. Light dark matter particles can be efficient for generation of such currents if these particles have some long range interactions. In particular, millicharged warm dark matter particles or light mirror particles with the photon kinetic mixing to the usual matter are considered. The induced currents may be strong enough to create the observed magnetic fields on the galaxy scales without need for a strong dynamo amplification. On the other hand, the angular momentum transfer from the rotating gas to dark matter component could change the dark matter profile and formation of cusps at galactic centers would be inhibited. We also discuss how the global motion of the ionized gas ...

  16. Experimental demonstration of a fifth force due to chameleon field via cold atoms

    OpenAIRE

    Zhang, Hai-Chao

    2017-01-01

    We tested a fifth force using cold atom experiments. The accelerated expansion of the universe implies the possibility of the presence of a scalar field throughout the universe driving the acceleration. This field would result in a detectable force between normal-matter objects. Theory of the chameleon field states that the force should be strong in a thin shell near the surface of a source object but greatly suppressed inside and outside of the source object. We used two atom clouds: one as ...

  17. Scalar self-force on a static particle in Schwarzschild spacetime using the massive field approach

    Science.gov (United States)

    Rosenthal, Eran

    2004-12-01

    I use the recently developed massive field approach to calculate the scalar self-force on a static particle in a Schwarzschild spacetime. In this approach the scalar self-force is obtained from the difference between the (massless) scalar field, and an auxiliary massive scalar field combined with a certain limiting process. By applying this approach to a static particle in Schwarzschild I show that the scalar self-force vanishes in this case. This result conforms with a previous analysis [A. G. Wiseman, Phys. Rev. D612000084014].

  18. Pull-in control due to Casimir forces using external magnetic fields

    CERN Document Server

    Esquivel-Sirvent, R; Cocoletzi, G H

    2009-01-01

    We present a theoretical calculation of the pull-in control in capacitive micro switches actuated by Casimir forces, using external magnetic fields. The external magnetic fields induces an optical anisotropy due to the excitation of magneto plasmons, that reduces the Casimir force. The calculations are performed in the Voigt configuration, and the results show that as the magnetic field increases the system becomes more stable. The detachment length for a cantilever is also calculated for a cantilever, showing that it increases with increasing magnetic field. At the pull-in separation, the stiffness of the system decreases with increasing magnetic field.

  19. Decay Characteristics of Levitation Force of YBCO Bulk Exposed to AC Magnetic Field above NdFeB Guideway

    Science.gov (United States)

    Liu, Minxian; Lu, Yiyun; Wang, Suyu; Ma, Guangtong

    2011-04-01

    The superconducting maglev vehicle is one of the most promising applications of HTS bulks. In such a system, the nonuniformity of the magnetic field along the movement direction above the NdFeB guideway is inevitable due to the assembly error and inhomogeneity of the material property of the NdFeB magnet. So it is required to study the characteristics of levitation force of the bulks affected by the non-uniform applied magnetic fields along the moving direction. In this paper, we will study the characteristics of the levitation force relaxation between the HTS bulk and the NdFeB guideway by an experiment in which AC external magnetic field generated by an electromagnet is used to simulate the time-varying external magnetic field caused by the inhomogeneity of the guideway. From the experimental results, it has found that the levitation force is decreasing with the application of the AC external magnetic field, and the decay increasing with the amplitude of the applied magnetic field and is almost independent of the frequency.

  20. Generation and near-field imaging of Airy surface plasmons

    CERN Document Server

    Minovich, Alexander; Janunts, Norik; Pertsch, Thomas; Neshev, Dragomir N; Kivshar, Yuri S

    2011-01-01

    We demonstrate experimentally the generation and near-field imaging of nondiffracting surface waves - plasmonic Airy beams, propagating on the surface of a gold metal film. The Airy plasmons are excited by an engineered nanoscale phase grating, and demonstrate significant beam bending over their propagation. We show that the observed Airy plasmons exhibit self-healing properties, suggesting novel applications in plasmonic circuitry and surface optical manipulation.

  1. Dynamical mean field theory of optical third harmonic generation

    OpenAIRE

    Jafari, S. A.; Tohyama, T.; Maekawa, S.

    2006-01-01

    We formulate the third harmonic generation (THG) within the dynamical mean field theory (DMFT) approximation of the Hubbard model. In the limit of large dimensions, where DMFT becomes exact, the vertex corrections to current vertices are identically zero, and hence the calculation of the THG spectrum reduces to a time-ordered convolution, followd by appropriate analytic continuuation. We present the typical THG spectrum of the Hubbard model obtained by this method. Within our DMFT calculation...

  2. The attenuation of the levitation force of HTS bulk exposed to AC magnetic field on the above NdFeB guideway

    Science.gov (United States)

    Liu, Minxian; Wang, Yan

    2012-01-01

    In the present High Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets make the magnetic fields above the NdFeB guideway non-uniform. So it is required to study the characteristics of levitation force of the HTS bulk affected by the non-uniform applied magnetic fields along the moving direction. In this paper, we have studied the characteristics of the levitation force relaxation by an experiment in which AC magnetic field generated by an electromagnet is used to simulate the time-varying magnetic field caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it is found that the levitation force is attenuated with the application of the AC field, and the attenuation is increased with the amplitude of the AC field, but the attenuation is almost independent of the frequency the AC magnetic field.

  3. Real-time Image Generation for Compressive Light Field Displays

    Science.gov (United States)

    Wetzstein, G.; Lanman, D.; Hirsch, M.; Raskar, R.

    2013-02-01

    With the invention of integral imaging and parallax barriers in the beginning of the 20th century, glasses-free 3D displays have become feasible. Only today—more than a century later—glasses-free 3D displays are finally emerging in the consumer market. The technologies being employed in current-generation devices, however, are fundamentally the same as what was invented 100 years ago. With rapid advances in optical fabrication, digital processing power, and computational perception, a new generation of display technology is emerging: compressive displays exploring the co-design of optical elements and computational processing while taking particular characteristics of the human visual system into account. In this paper, we discuss real-time implementation strategies for emerging compressive light field displays. We consider displays composed of multiple stacked layers of light-attenuating or polarization-rotating layers, such as LCDs. The involved image generation requires iterative tomographic image synthesis. We demonstrate that, for the case of light field display, computed tomographic light field synthesis maps well to operations included in the standard graphics pipeline, facilitating efficient GPU-based implementations with real-time framerates.

  4. On parallel electric field generation in transversely inhomogeneous plasmas

    CERN Document Server

    Tsiklauri, David

    2007-01-01

    The generation of parallel electric fields by the propagation of ion cyclotron waves in the plasma with a transverse density inhomogeneity was studied. It was proven that the minimal model required to reproduce the previous kinetic simulation results of E_{||} generation [Tsiklauri et al 2005, Genot et al 2004] is the two-fluid, cold plasma approximation in the linear regime. By considering the numerical solutions it was also shown that the cause of E_{||} generation is the electron and ion flow separation induced by the transverse density inhomogeneity. We also investigate how E_{||} generation is affected by the mass ratio and found that amplitude attained by E_{||} decreases linearly as inverse of the mass ratio m_i/m_e. For realistic mass ratio of m_i/m_e=1836, such empirical scaling law, within a time corresponding to 3 periods of the driving ion cyclotron wave, is producing E_{||}=14 Vm^{-1} for solar coronal parameters. Increase in mass ratio does not have any effect on final parallel (magnetic field a...

  5. Predator Force Structure Changes at Indian Springs Air Force Auxiliary Field, Nevada Environmental Assessment

    Science.gov (United States)

    2003-07-01

    the North Las Vegas Library (Main Branch), the Indian Springs Library, and online at www.cevp.com and www.nellis.af.mil. A Notice of Availability...USGS (U.S. Geological Survey). 2001. Online Table of Seismic Hazards. http://geohazards.cr.usgs.gov/eq/faults/fsrpage11.html Predator Force...Sincerely, __ ~~~-~ Heather K. Elliott Nevada State Clearinghouse/ SPOC NEVADA STATE CLEARINGHOUSE Department of Administration Budget and Planning

  6. Measurements of the force fields within an acoustic standing wave using holographic optical tweezers

    Energy Technology Data Exchange (ETDEWEB)

    Bassindale, P. G.; Drinkwater, B. W. [Faculty of Engineering, Queens building, University of Bristol, Bristol BS8 1TR (United Kingdom); Phillips, D. B. [Department of Physics and Astronomy, University of Glasgow, Glasgow G12 8QQ (United Kingdom); Barnes, A. C. [Department of Physics, H.H.Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL (United Kingdom)

    2014-04-21

    Direct measurement of the forces experienced by micro-spheres in an acoustic standing wave device have been obtained using calibrated optical traps generated with holographic optical tweezers. A micro-sphere, which is optically trapped in three dimensions, can be moved through the acoustic device to measure forces acting upon it. When the micro-sphere is subjected to acoustic forces, it's equilibrium position is displaced to a position where the acoustic forces and optical forces are balanced. Once the optical trapping stiffness has been calibrated, observation of this displacement enables a direct measurement of the forces acting upon the micro-sphere. The measured forces are separated into a spatially oscillating component, attributed to the acoustic radiation force, and a constant force, attributed to fluid streaming. As the drive conditions of the acoustic device were varied, oscillating forces (>2.5 pN{sub pp}) and streaming forces (<0.2 pN) were measured. A 5 μm silica micro-sphere was used to characterise a 6.8 MHz standing wave, λ = 220 μm, to a spatial resolution limited by the uncertainty in the positioning of the micro-sphere (here to within 2 nm) and with a force resolution on the order of 10 fN. The results have application in the design and testing of acoustic manipulation devices.

  7. The generation of forces and moments during visual-evoked steering maneuvers in flying Drosophila.

    Directory of Open Access Journals (Sweden)

    Hiroki Sugiura

    Full Text Available Sideslip force, longitudinal force, rolling moment, and pitching moment generated by tethered fruit flies, Drosophila melanogaster, were measured during optomotor reactions within an electronic flight simulator. Forces and torques were acquired by optically measuring the angular deflections of the beam to which the flies were tethered using a laser and a photodiode. Our results indicate that fruit flies actively generate both sideslip and roll in response to a lateral focus of expansion (FOE. The polarity of this behavior was such that the animal's aerodynamic response would carry it away from the expanding pattern, suggesting that it constitutes an avoidance reflex or centering response. Sideslip forces and rolling moments were sinusoidal functions of FOE position, whereas longitudinal force was proportional to the absolute value of the sine of FOE position. Pitching moments remained nearly constant irrespective of stimulus position or strength, with a direction indicating a tonic nose-down pitch under tethered conditions. These experiments expand our understanding of the degrees of freedom that a fruit fly can actually control in flight.

  8. Dynamics of cross-bridge cycling, ATP hydrolysis, force generation, and deformation in cardiac muscle.

    Science.gov (United States)

    Tewari, Shivendra G; Bugenhagen, Scott M; Palmer, Bradley M; Beard, Daniel A

    2016-07-01

    Despite extensive study over the past six decades the coupling of chemical reaction and mechanical processes in muscle dynamics is not well understood. We lack a theoretical description of how chemical processes (metabolite binding, ATP hydrolysis) influence and are influenced by mechanical processes (deformation and force generation). To address this need, a mathematical model of the muscle cross-bridge (XB) cycle based on Huxley's sliding filament theory is developed that explicitly accounts for the chemical transformation events and the influence of strain on state transitions. The model is identified based on elastic and viscous moduli data from mouse and rat myocardial strips over a range of perturbation frequencies, and MgATP and inorganic phosphate (Pi) concentrations. Simulations of the identified model reproduce the observed effects of MgATP and MgADP on the rate of force development. Furthermore, simulations reveal that the rate of force re-development measured in slack-restretch experiments is not directly proportional to the rate of XB cycling. For these experiments, the model predicts that the observed increase in the rate of force generation with increased Pi concentration is due to inhibition of cycle turnover by Pi. Finally, the model captures the observed phenomena of force yielding suggesting that it is a result of rapid detachment of stretched attached myosin heads.

  9. Cyclic Fatigue Resistance and Force Generated by OneShape Instruments during Curved Canal Preparation

    Science.gov (United States)

    Zhang, Xiaolei

    2016-01-01

    Objectives To evaluate the cyclic fatigue resistance and the force generated by OneShape files during preparation of simulated curved canals. Methods Six OneShape files (the test) and six ProTaper F2 files (the control) were subject to the bending ability test. Another thirty files of each type were used to prepare artificial canals (n = 60), which were divided into 3 groups according to respective curvatures of the canals (30°, 60°, and 90°). The numbers of cycles to fatigue (NCF) as well as the positive and negative forces that were generated by files during canal preparation were recorded. The scanning electron microscopy was applied to detect the fracture surfaces. Results Compared with ProTaper F2 files, the bending loads of OneShape files were significantly lower at deflections of 45°(P ProTaper files in 30° canals. During the preparation of 30° canals by both files, the negative forces were dominant. With the increase of the curvature, more positive forces were observed. When the OneShape Files were compared with the control, significant different forces were found at D3 and D2 (P ProTaper F2 files. PMID:27513666

  10. Nernst advection and the field-generating thermal instability revisited

    Science.gov (United States)

    Bissell, J. J.

    2015-01-01

    It is widely held that the Nernst effect can drive instability in un-magnetised laser-plasmas by laterally compressing seed B-fields arising from the field-generating thermal instability [Tidman & Shanny, Phys. Fluids, 12:1207 (1974)]. Indeed, for wavelike perturbations, differential compression by the Nernst mechanism is thought to be most pronounced in the limit of low wave-number k -> 0, and is considered particularly important given that it can ostensibly lead to instability when the more usual field-generating mechanism is stable. However, as part of a recent article [Bissell et al., New J. Phys., 15:025017 (2013)] we noted some irregularities to the Nernst mechanism which obscure its operation. For example, by taking characteristic density and temperature length-scales ln and lT respectively, we observed that consistent analytical treatment of the instability requires kln,T >> 1, preventing the peak-growth limit k -> 0. Furthermore, the Nernst term-which compresses magnetic field perturbations-does not couple to a corresponding term acting on thermal perturbations, and as such does not describe an unstable feedback mechanism. In this article we probe the origin of such ambiguities more formally, and in so doing argue (contrary to reports existing elsewhere in the literature) that the Nernst effect does not drive instability in un-magnetised conditions, at least not in the fashion typically cited.

  11. Ultrasonographic measurement of tendon displacement caused by active force generation in the psoas major muscle.

    Science.gov (United States)

    Matsubayashi, Takeo; Kubo, Junjiro; Matsuo, Akifumi; Kobayashi, Kando; Ishii, Naokata

    2008-10-01

    The purpose of this study was to examine the validity of using ultrasonography for detecting the force generated by the psoas major muscle, a muscle positioned in the deep trunk. We measured the displacement of central tendon on B-mode ultrasound images of two different longitudinal sections of the muscle during passive hip flexion-extension and isometric hip flexion at varied hip angles. In both tasks, the values of tendon displacement obtained independently from each section coincided well, indicating that tendon displacement took place along a straight trajectory, i.e., close to the nodal line between two scanned planes. It was strongly correlated with both the hip angle (R(2) = 0.98) and the hip-flexion torque (R(2) = 0.83). In the second set of experiment, we measured the tendon displacement during dynamic movements with the combination of ultrasonography and VICON-based motion analysis. From the tendon displacement during dynamic thigh lifting and walking, the force generated by the muscle could be estimated by extracting the force-related component. These results indicate that ultrasonography of the psoas major muscle can measure the displacement of its central tendon accompanied with either length change of the muscle or the elongation of tendon. Although much attention has to be paid to the limitations of this methodology, ultrasonography may be useful for detecting the force generation of the muscle during a variety of dynamic movements.

  12. Near-field second-harmonic generation from gold nanoellipsoids

    Energy Technology Data Exchange (ETDEWEB)

    Celebrano, M.; Zavelani-Rossi, M.; Polli, D.; Cerullo, G. [Istituto di Fotonica e Nanotecnologie, CNR, Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Biagioni, P.; Finazzi, M.; Duo, L. [LNESS - Dipartimento di Fisica, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano (Italy); Labardi, M.; Allegrini, M. [CNR-INFM, polyLab, Dipartimento di Fisica ' Enrico Fermi' , Universita di Pisa, Largo Pontecorvo 3, 56127 Pisa (Italy); Grand, J.; Adam, P.M.; Royer, P. [Laboratoire de Nanotechnologie et d' Instrumentation Optique, Universite de Technologie de Troyes, 12 rue Marie Curie, BP 2060 10010 Troyes cedex (France)

    2008-07-01

    Second-harmonic generation from single gold nanofabricated particles is experimentally investigated by a nonlinear scanning near-field optical microscope (SNOM). High peak power femtosecond polarized light pulses at the output of a hollow pyramid aperture allow for efficient second-harmonic imaging, with sub-100-nm spatial resolution and high contrast. The near-field nonlinear response is found to be directly related to both local surface plasmon resonances and particle morphology. The combined analysis of linear and second-harmonic SNOM images allows one to discriminate among near-field scattering, absorption and re-emission processes, which would not be possible with linear techniques alone. (copyright 2008 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  13. Generation and measurement of pulsed high magnetic field

    CERN Document Server

    Jana, S

    2000-01-01

    Pulsed magnetic field has been generated by discharging a capacitor bank through a 5-layer air-core solenoid. The strength of the magnetic field at its peak has been measured using the voltage induced in various pick-up coils, and also from the Zeeman splitting of an ion having a known g value. Synchronizing a xenon flash at the peak of the magnetic field, this lab-made instrument has been made well suited to study the Zeeman effect, etc. at a temperature of 25 K. As an application of this setup, we have investigated the Zeeman splitting of the sup 4 I sub 9 sub / sub 2-> sup 4 G sub 5 sub / sub 2 transition of the Nd sup 3 sup + -doped CsCdCl sub 3 crystal at 7.8 T, and determined the splitting factors.

  14. Force

    CERN Document Server

    Graybill, George

    2007-01-01

    Forces are at work all around us. Discover what a force is, and different kinds of forces that work on contact and at a distance. We use simple language and vocabulary to make this invisible world easy for students to ""see"" and understand. Examine how forces ""add up"" to create the total force on an object, and reinforce concepts and extend learning with sample problems.

  15. Energy confinement and magnetic field generation in the SSPX spheromak

    Energy Technology Data Exchange (ETDEWEB)

    Hudson, B; McLean, H S; Wood, R D; Hooper, E B; Hill, D N; Jayakumar, J; Moller, J; Romero-Talamas, C; Casper, T A; LoDestro, L L; Pearlstein, L D; Johnson, III, J A; Mezonlin, E

    2008-02-11

    The Sustained Spheromak Physics Experiment (SSPX) [E.B. Hooper, et. al., Nuclear Fusion, Vol. 39, No. 7] explores the physics of efficient magnetic field buildup and energy confinement, both essential parts of advancing the spheromak concept. Extending the spheromak formation phase increases the efficiency of magnetic field generation with the maximum edge magnetic field for a given injector current (B/I) from 0.65 T/MA previously to 0.9 T/MA. We have achieved the highest electron temperatures (T{sub e}) recorded for a spheromak with T{sub e} > 500 eV, toroidal magnetic field {approx}1 T and toroidal current ({approx}1 MA) [R.D. Wood, D.N. Hill, H.S. McLean, E.B. Hooper, B.F. Hudson, J.M. Moller, 'Improved magnetic field generation efficiency and higher temperature spheromak plasmas', submitted to Physical Review Letters]. Extending the sustainment phase to > 8 ms extends the period of low magnetic fluctuations (< 1 %) by 50%. The NIMROD 3-D resistive MHD code [C.R. Sovinec, T.A. Gianakon, E.D. Held, S.E. Kruger and D.D. Schnack, The NIMROD Team, Phys. Plasmas 10, 1727 (2003)] reproduces the observed flux amplification {Psi}{sub pol}/{Psi}{sub gun}. Successive gun pulses are demonstrated to maintain the magnetic field in a quasi-steady state against resistive decay. Initial measurements of neutral particle flux in multi-pulse operation show charge-exchange power loss < 1% of gun input power and dominantly collisional majority ion heating. The evolution of electron temperature shows a distinct and robust feature of spheromak formation: a hollow-to-peaked T{sub e}(r) associated with q {approx} 1/2.

  16. Force-Field Prediction of Materials Properties in Metal-Organic Frameworks

    Science.gov (United States)

    2016-01-01

    In this work, MOF bulk properties are evaluated and compared using several force fields on several well-studied MOFs, including IRMOF-1 (MOF-5), IRMOF-10, HKUST-1, and UiO-66. It is found that, surprisingly, UFF and DREIDING provide good values for the bulk modulus and linear thermal expansion coefficients for these materials, excluding those that they are not parametrized for. Force fields developed specifically for MOFs including UFF4MOF, BTW-FF, and the DWES force field are also found to provide accurate values for these materials’ properties. While we find that each force field offers a moderately good picture of these properties, noticeable deviations can be observed when looking at properties sensitive to framework vibrational modes. This observation is more pronounced upon the introduction of framework charges. PMID:28008758

  17. Global optimization of parameters in the reactive force field ReaxFF for SiOH.

    Science.gov (United States)

    Larsson, Henrik R; van Duin, Adri C T; Hartke, Bernd

    2013-09-30

    We have used unbiased global optimization to fit a reactive force field to a given set of reference data. Specifically, we have employed genetic algorithms (GA) to fit ReaxFF to SiOH data, using an in-house GA code that is parallelized across reference data items via the message-passing interface (MPI). Details of GA tuning turn-ed out to be far less important for global optimization efficiency than using suitable ranges within which the parameters are varied. To establish these ranges, either prior knowledge can be used or successive stages of GA optimizations, each building upon the best parameter vectors and ranges found in the previous stage. We have finally arrive-ed at optimized force fields with smaller error measures than those published previously. Hence, this optimization approach will contribute to converting force-field fitting from a specialist task to an everyday commodity, even for the more difficult case of reactive force fields.

  18. The Rotational Spectrum and Anharmonic Force Field of Chlorine Dioxide, OClO

    Science.gov (United States)

    Muller, Holger S. P.; Sorensen, G.; Birk, Manfred; Friedl, Randy R.

    1997-01-01

    The ground state rotational and quartic centrifugal distortion constants, their vibrational changes, and the sextic centrifugal distortion constants were used in a calculation of the quartic force field together with data from infrared studies.

  19. Unsteady hydrodynamic forces acting on a robotic arm and its flow field: application to the crawl stroke.

    Science.gov (United States)

    Takagi, Hideki; Nakashima, Motomu; Ozaki, Takashi; Matsuuchi, Kazuo

    2014-04-11

    This study aims to clarify the mechanisms by which unsteady hydrodynamic forces act on the hand of a swimmer during a crawl stroke. Measurements were performed for a hand attached to a robotic arm with five degrees of freedom independently controlled by a computer. The computer was programmed so the hand and arm mimicked a human performing the stroke. We directly measured forces on the hand and pressure distributions around it at 200 Hz; flow fields underwater near the hand were obtained via 2D particle image velocimetry (PIV). The data revealed two mechanisms that generate unsteady forces during a crawl stroke. One is the unsteady lift force generated when hand movement changes direction during the stroke, leading to vortex shedding and bound vortex created around it. This bound vortex circulation results in a lift that contributes to the thrust. The other occurs when the hand moves linearly with a large angle of attack, creating a Kármán vortex street. This street alternatively sheds clockwise and counterclockwise vortices, resulting in a quasi-steady drag contributing to the thrust. We presume that professional swimmers benefit from both mechanisms. Further studies are necessary in which 3D flow fields are measured using a 3D PIV system and a human swimmer.

  20. Additional force field in cooling process of cellular Al alloy

    Institute of Scientific and Technical Information of China (English)

    郑明军; 何德坪; 戴戈

    2002-01-01

    The foaming process of Al alloy is similar to that of Al, but there is a solid-liquid state zone in the solidification process of cellular Al alloy which does not exist in the case of Al. In the unidirectional solidification of cellular Al alloy, the proportion of the solid phase gradually reduces from the solid front to the liquid front. This will introduce a force and result in a serious quick shrinkage. By the mathematic and physical mode, the solidification of the cellular Al alloy is studied. The data measured by experiment are close to the result calculated by the mode. This kind of shrinkage can be solved by suitable cooling method in appropriate growth stage. The compressive strength of the cellular Al alloy made by this way is 40% higher than that of cellular Al.

  1. R.E.D. Server: a web service for deriving RESP and ESP charges and building force field libraries for new molecules and molecular fragments

    Science.gov (United States)

    Vanquelef, Enguerran; Simon, Sabrina; Marquant, Gaelle; Garcia, Elodie; Klimerak, Geoffroy; Delepine, Jean Charles; Cieplak, Piotr; Dupradeau, François-Yves

    2011-01-01

    R.E.D. Server is a unique, open web service, designed to derive non-polarizable RESP and ESP charges and to build force field libraries for new molecules/molecular fragments. It provides to computational biologists the means to derive rigorously molecular electrostatic potential-based charges embedded in force field libraries that are ready to be used in force field development, charge validation and molecular dynamics simulations. R.E.D. Server interfaces quantum mechanics programs, the RESP program and the latest version of the R.E.D. tools. A two step approach has been developed. The first one consists of preparing P2N file(s) to rigorously define key elements such as atom names, topology and chemical equivalencing needed when building a force field library. Then, P2N files are used to derive RESP or ESP charges embedded in force field libraries in the Tripos mol2 format. In complex cases an entire set of force field libraries or force field topology database is generated. Other features developed in R.E.D. Server include help services, a demonstration, tutorials, frequently asked questions, Jmol-based tools useful to construct PDB input files and parse R.E.D. Server outputs as well as a graphical queuing system allowing any user to check the status of R.E.D. Server jobs. PMID:21609950

  2. R.E.D. Server: a web service for deriving RESP and ESP charges and building force field libraries for new molecules and molecular fragments.

    Science.gov (United States)

    Vanquelef, Enguerran; Simon, Sabrina; Marquant, Gaelle; Garcia, Elodie; Klimerak, Geoffroy; Delepine, Jean Charles; Cieplak, Piotr; Dupradeau, François-Yves

    2011-07-01

    R.E.D. Server is a unique, open web service, designed to derive non-polarizable RESP and ESP charges and to build force field libraries for new molecules/molecular fragments. It provides to computational biologists the means to derive rigorously molecular electrostatic potential-based charges embedded in force field libraries that are ready to be used in force field development, charge validation and molecular dynamics simulations. R.E.D. Server interfaces quantum mechanics programs, the RESP program and the latest version of the R.E.D. tools. A two step approach has been developed. The first one consists of preparing P2N file(s) to rigorously define key elements such as atom names, topology and chemical equivalencing needed when building a force field library. Then, P2N files are used to derive RESP or ESP charges embedded in force field libraries in the Tripos mol2 format. In complex cases an entire set of force field libraries or force field topology database is generated. Other features developed in R.E.D. Server include help services, a demonstration, tutorials, frequently asked questions, Jmol-based tools useful to construct PDB input files and parse R.E.D. Server outputs as well as a graphical queuing system allowing any user to check the status of R.E.D. Server jobs.

  3. A combined near field optical and force microscope

    NARCIS (Netherlands)

    Moers, M.H.P.; Tack, R.G.; Hulst, van N.F.; Bölger, B.

    1993-01-01

    Scanning near field optical microscopy (SNOM) is the optical alternative of the scanning probe microscopical techniques which enables a lateral resolution down to about 10 nm, unlimited by diffraction. Moreover, the potential of non- destructive imaging of chemical and biological samples with nanome

  4. A Comparison of Classical Force-Fields for Molecular Dynamics Simulations of Lubricants

    Directory of Open Access Journals (Sweden)

    James P. Ewen

    2016-08-01

    Full Text Available For the successful development and application of lubricants, a full understanding of their complex nanoscale behavior under a wide range of external conditions is required, but this is difficult to obtain experimentally. Nonequilibrium molecular dynamics (NEMD simulations can be used to yield unique insights into the atomic-scale structure and friction of lubricants and additives; however, the accuracy of the results depend on the chosen force-field. In this study, we demonstrate that the use of an accurate, all-atom force-field is critical in order to; (i accurately predict important properties of long-chain, linear molecules; and (ii reproduce experimental friction behavior of multi-component tribological systems. In particular, we focus on n-hexadecane, an important model lubricant with a wide range of industrial applications. Moreover, simulating conditions common in tribological systems, i.e., high temperatures and pressures (HTHP, allows the limits of the selected force-fields to be tested. In the first section, a large number of united-atom and all-atom force-fields are benchmarked in terms of their density and viscosity prediction accuracy of n-hexadecane using equilibrium molecular dynamics (EMD simulations at ambient and HTHP conditions. Whilst united-atom force-fields accurately reproduce experimental density, the viscosity is significantly under-predicted compared to all-atom force-fields and experiments. Moreover, some all-tom force-fields yield elevated melting points, leading to significant overestimation of both the density and viscosity. In the second section, the most accurate united-atom and all-atom force-field are compared in confined NEMD simulations which probe the structure and friction of stearic acid adsorbed on iron oxide and separated by a thin layer of n-hexadecane. The united-atom force-field provides an accurate representation of the structure of the confined stearic acid film; however, friction coefficients are

  5. On the Force-Freeness of the Photospheric Sunspot Magnetic Fields as Observed from Hinode (SOT/SP)

    CERN Document Server

    Tiwari, Sanjiv Kumar

    2011-01-01

    A magnetic field is force-free if there is no interaction between the magnetic field and plasma in surrounding atmosphere i.e., electric currents are aligned with the magnetic field, giving rise to zero Lorentz force. Computation of various magnetic parameters such as magnetic energy, gradient of twist of sunspot fields and any kind of extrapolations, heavily hinge on the force-free approximation of the photospheric sunspot magnetic fields. Thus it is important to inspect the force-freeness of sunspot fields. The force-freeness of sunspot magnetic fields has been examined earlier by some researchers ending with incoherent results. Accurate photospheric vector field measurements with high spatial resolution are required to inspect the force-free nature of sunspots. We use several such vector magnetograms obtained from the Solar Optical Telescope/Spectro-Polarimeter aboard the Hinode. Both necessary and sufficient conditions for force-freeness are examined by checking global and local nature of magnetic forces ...

  6. Adaptation of multi-joint balance coordination to whole body force fields

    OpenAIRE

    Engelhart, Denise; Schouten, Alfred; Aarts, Ronald; Pasma, J.; Meskers, Carel; Maier, Andrea; Kooij, van der, Marieke

    2014-01-01

    Background and aim: The ankles and the hips play an important role in standing balance. Multi-joint coordination adapts with task, the magnitude and type of disturbance [1]. Arm studies show that postural responses are highly dependent on externally applied force fields [2]. Our aim is to study how multi-joint postural responses in standing depend on such force fields, using closed loop system identification techniques (CLSIT) where two disturbances are applied [3]. This offers knowledge abou...

  7. Integration of Research for an Exhaust Thermoelectric Generator and the Outer Flow Field of a Car

    Science.gov (United States)

    Jiang, T.; Su, C. Q.; Deng, Y. D.; Wang, Y. P.

    2017-05-01

    The exhaust thermoelectric generator (TEG) can generate electric power from a car engine's waste heat. It is important to maintain a sufficient temperature difference across the thermoelectric modules. The radiator is connected to the cooling units of the thermoelectric modules and used to take away the heat from the TEG system. This paper focuses on the research for the integration of a TEG radiator and the flow field of the car chassis, aiming to cool the radiator by the high speed flow around the chassis. What is more, the TEG radiator is designed as a spoiler to optimize the flow field around the car chassis and even reduce the aerodynamic drag. Concentrating on the flow pressure of the radiator and the aerodynamic drag force, a sedan model with eight different schemes of radiator configurations are studied by computational fluid dynamics simulation. Finally, the simulation results indicate that a reasonable radiator configuration can not only generate high flow pressure to improve the cooling performance, which provides a better support for the TEG system, but also acts as a spoiler to reduce the aerodynamic drag force.

  8. Integration of Research for an Exhaust Thermoelectric Generator and the Outer Flow Field of a Car

    Science.gov (United States)

    Jiang, T.; Su, C. Q.; Deng, Y. D.; Wang, Y. P.

    2016-11-01

    The exhaust thermoelectric generator (TEG) can generate electric power from a car engine's waste heat. It is important to maintain a sufficient temperature difference across the thermoelectric modules. The radiator is connected to the cooling units of the thermoelectric modules and used to take away the heat from the TEG system. This paper focuses on the research for the integration of a TEG radiator and the flow field of the car chassis, aiming to cool the radiator by the high speed flow around the chassis. What is more, the TEG radiator is designed as a spoiler to optimize the flow field around the car chassis and even reduce the aerodynamic drag. Concentrating on the flow pressure of the radiator and the aerodynamic drag force, a sedan model with eight different schemes of radiator configurations are studied by computational fluid dynamics simulation. Finally, the simulation results indicate that a reasonable radiator configuration can not only generate high flow pressure to improve the cooling performance, which provides a better support for the TEG system, but also acts as a spoiler to reduce the aerodynamic drag force.

  9. Ultrafast, green third-harmonic generation and strong-field phenomena in silicon-on-insulator nanoplasmonic waveguides

    CERN Document Server

    Sederberg, Shawn

    2013-01-01

    The emergence of strong-field nanoplasmonics brings extreme laser field-matter interaction into the realm of nanoscale science, unveiling exciting new physics. Highly nonlinear interaction is enabled by tightly confined electric fields in nanoplasmonic structures, permitting use of optical fields from low-power laser oscillators. Here, we report the first demonstration of visible 517nm third harmonic generation in ultracompact nanoplasmonic waveguides on a silicon-on-insulator platform at an unprecedented conversion efficiency of ~10^{-5}. Exponential growth of broadband white light generation confirms a new strong-field phenomenon of ponderomotive force-driven electron avalanche multiplication. Using time-resolved experiments, we show that the strong nanoplasmonic field confinement allows nonlinear interaction to occur on an ultrafast timescale of 1.98 +/- 0.40 ps, despite the long free-carrier lifetime in silicon. These findings uncover a new strong-field interaction that can be used in sensitive nanoplasmo...

  10. Gravitational self-force in nonvacuum spacetimes: An effective field theory derivation

    Science.gov (United States)

    Zimmerman, Peter

    2015-09-01

    In this paper we investigate the motion of small compact objects in nonvacuum spacetimes using methods from effective field theory in curved spacetime. Although a vacuum formulation is sufficient in many astrophysical contexts, there are applications such as the role of the self-force in enforcing cosmic censorship in the context of the overcharging problem, which necessitate an extension into the nonvacuum regime. The defining feature of the self-force problem in nonvacuum spacetimes is the coupling between gravitational and nongravitational field perturbations. The formulation of the self-force problem for nonvacuum spacetimes was recently provided in simultaneous papers by Zimmerman and Poisson [Gravitational self-force in nonvacuum spacetimes, Phys. Rev. D 90, 084030 (2014)] and Linz, Friedmann, and Wiseman [Combined gravitational and electromagnetic self-force on charged particles in electrovac spacetimes, Phys. Rev. D 90, 084031 (2014)]. Here we distinguish ourselves by working with the effective action rather than the field equations. The formalism utilizes the multi-index notation developed by Zimmerman and Poisson [Gravitational self-force in nonvacuum spacetimes, Phys. Rev. D 90, 084030 (2014) to accommodate the coupling between the different fields. Using dimensional regularization, we arrive at a finite expression for the local self-force expressed in terms of multi-index quantities evaluated in the background spacetime. We then apply the formalism to compute the coupled gravitational self-force in two explicit cases. First, we calculate the self-force on a massive particle possessing scalar charge and moving in a scalarvac spacetime. We then derive an expression for the self-force on an electrically charged, massive particle moving in an electrovac spacetime. In both cases, the force is expressed as a sum of local terms involving tensors defined in the background spacetime and evaluated at the current position of the particle, as well as tail integrals

  11. Scalar field self-force effects on a particle orbiting a Reissner-Nordstrom black hole

    CERN Document Server

    Bini, Donato; Geralico, Andrea

    2016-01-01

    Scalar field self-force effects on a scalar charge orbiting a Reissner-Nordstr\\"om black hole are investigated. The scalar wave equation is solved analytically in a post-Newtonian framework, and the solution is used to compute the self-field as well as the components of the self-force at the particle's location up to 7.5 post-Newtonian order. The energy fluxes radiated to infinity and down the hole are also evaluated. Comparison with previous numerical results in the Schwarzschild case shows a good agreement in both strong-field and weak-field regimes.

  12. Second order semiclassics with self-generated magnetic fields

    CERN Document Server

    Erdos, Laszlo; Solovej, Jan Philip

    2011-01-01

    We consider the semiclassical asymptotics of the sum of negative eigenvalues of the three-dimensional Pauli operator with an external potential and a self-generated magnetic field $B$. We also add the field energy $\\beta \\int B^2$ and we minimize over all magnetic fields. The parameter $\\beta$ effectively determines the strength of the field. We consider the weak field regime with $\\beta h^{2}\\ge {const}>0$, where $h$ is the semiclassical parameter. For smooth potentials we prove that the semiclassical asymptotics of the total energy is given by the non-magnetic Weyl term to leading order with an error bound that is smaller by a factor $h^{1+\\e}$, i.e. the subleading term vanishes. However, for potentials with a Coulomb singularity the subleading term does not vanish due to the non-semiclassical effect of the singularity. Combined with a multiscale technique, this refined estimate is used in the companion paper \\cite{EFS3} to prove the second order Scott correction to the ground state energy of large atoms an...

  13. An optimized intermolecular force field for hydrogen-bonded organic molecular crystals using atomic multipole electrostatics

    Science.gov (United States)

    Pyzer-Knapp, Edward O.; Thompson, Hugh P. G.; Day, Graeme M.

    2016-01-01

    We present a re-parameterization of a popular intermolecular force field for describing intermolecular interactions in the organic solid state. Specifically we optimize the performance of the exp-6 force field when used in conjunction with atomic multipole electrostatics. We also parameterize force fields that are optimized for use with multipoles derived from polarized molecular electron densities, to account for induction effects in molecular crystals. Parameterization is performed against a set of 186 experimentally determined, low-temperature crystal structures and 53 measured sublimation enthalpies of hydrogen-bonding organic molecules. The resulting force fields are tested on a validation set of 129 crystal structures and show improved reproduction of the structures and lattice energies of a range of organic molecular crystals compared with the original force field with atomic partial charge electrostatics. Unit-cell dimensions of the validation set are typically reproduced to within 3% with the re-parameterized force fields. Lattice energies, which were all included during parameterization, are systematically underestimated when compared with measured sublimation enthalpies, with mean absolute errors of between 7.4 and 9.0%. PMID:27484370

  14. The Self-Force Problem: Local Behaviour of the Detweiler-Whiting Singular Field

    CERN Document Server

    Heffernan, Anna

    2014-01-01

    The growing reality of gravitational wave astronomy is giving age-old problems a new lease of life; one such problem is that of the self-force. A charged or massive particle moving in a curved background space-time produces a field that affects its motion, pushing it off its expected geodesic. This self-field gives rise to a so-called self-force acting on the particle. In modelling this motion, the self-force approach uses a perturbative expansion in the mass ratio. One of the most interesting sources of gravitational waves are extreme mass ratio inspirals - systems perfectly suited to self-force modelling. One of the key problems within the self-force model is the divergence of the field at the particle. To resolve this, the field is split into a singular component and a smooth regular field. This regular-singular split, introduced by Detweiler and Whiting, is used in most modern self-force calculations. In this thesis, we derive high-order expansions of the Detweiler-Whiting singular field, and use these to...

  15. First principles derived, transferable force fields for CO2 adsorption in Na-exchanged cationic zeolites.

    Science.gov (United States)

    Fang, Hanjun; Kamakoti, Preeti; Ravikovitch, Peter I; Aronson, Matthew; Paur, Charanjit; Sholl, David S

    2013-08-21

    The development of accurate force fields is vital for predicting adsorption in porous materials. Previously, we introduced a first principles-based transferable force field for CO2 adsorption in siliceous zeolites (Fang et al., J. Phys. Chem. C, 2012, 116, 10692). In this study, we extend our approach to CO2 adsorption in cationic zeolites which possess more complex structures. Na-exchanged zeolites are chosen for demonstrating the approach. These methods account for several structural complexities including Al distribution, cation positions and cation mobility, all of which are important for predicting adsorption. The simulation results are validated with high-resolution experimental measurements of isotherms and microcalorimetric heats of adsorption on well-characterized materials. The choice of first-principles method has a significant influence on the ability of force fields to accurately describe CO2-zeolite interactions. The PBE-D2 derived force field, which performed well for CO2 adsorption in siliceous zeolites, does not do so for Na-exchanged zeolites; the PBE-D2 method overestimates CO2 adsorption energies on multi-cation sites that are common in cationic zeolites with low Si/Al ratios. In contrast, a force field derived from the DFT/CC method performed well. Agreement was obtained between simulation and experiment not only for LTA-4A on which the force field fitting is based, but for other two common adsorbents, NaX and NaY.

  16. A transferable force field for CdS-CdSe-PbS-PbSe solid systems.

    Science.gov (United States)

    Fan, Zhaochuan; Koster, Rik S; Wang, Shuaiwei; Fang, Changming; Yalcin, Anil O; Tichelaar, Frans D; Zandbergen, Henny W; van Huis, Marijn A; Vlugt, Thijs J H

    2014-12-28

    A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., "Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth," Nano Lett. 14, 3661-3667 (2014)]. In this work, we extend this force field by including another two important binary semiconductors, PbS and CdS, and provide detailed information on the validation of this force field. The parameterization combines Bader charge analysis, empirical fitting, and ab initio energy surface fitting. When compared with experimental data and density functional theory calculations, it is shown that a wide range of physical properties of bulk PbS, PbSe, CdS, CdSe, and their mixed phases can be accurately reproduced using this force field. The choice of functional forms and parameterization strategy is demonstrated to be rational and effective. This transferable force field can be used in various studies on II-VI and IV-VI semiconductor materials consisting of CdS, CdSe, PbS, and PbSe. Here, we demonstrate the applicability of the force field model by molecular dynamics simulations whereby transformations are initiated by cation exchange.

  17. Analytical solution for the diffusion of a capacitor discharge generated magnetic field pulse in a conductor

    Directory of Open Access Journals (Sweden)

    Ilmārs Grants

    2016-06-01

    Full Text Available Powerful forces arise when a pulse of a magnetic field in the order of a few tesla diffuses into a conductor. Such pulses are used in electromagnetic forming, impact welding of dissimilar materials and grain refinement of solidifying alloys. Strong magnetic field pulses are generated by the discharge current of a capacitor bank. We consider analytically the penetration of such pulse into a conducting half-space. Besides the exact solution we obtain two simple self-similar approximate solutions for two sequential stages of the initial transient. Furthermore, a general solution is provided for the external field given as a power series of time. Each term of this solution represents a self-similar function for which we obtain an explicit expression. The validity range of various approximate analytical solutions is evaluated by comparison to the exact solution.

  18. Analytical solution for the diffusion of a capacitor discharge generated magnetic field pulse in a conductor

    Science.gov (United States)

    Grants, Ilmārs; Bojarevičs, Andris; Gerbeth, Gunter

    2016-06-01

    Powerful forces arise when a pulse of a magnetic field in the order of a few tesla diffuses into a conductor. Such pulses are used in electromagnetic forming, impact welding of dissimilar materials and grain refinement of solidifying alloys. Strong magnetic field pulses are generated by the discharge current of a capacitor bank. We consider analytically the penetration of such pulse into a conducting half-space. Besides the exact solution we obtain two simple self-similar approximate solutions for two sequential stages of the initial transient. Furthermore, a general solution is provided for the external field given as a power series of time. Each term of this solution represents a self-similar function for which we obtain an explicit expression. The validity range of various approximate analytical solutions is evaluated by comparison to the exact solution.

  19. Near-field light detection of a photo induced force by atomic force microscopy with frequency modulation

    Science.gov (United States)

    Satoh, Nobuo; Kobayashi, Kei; Matsushige, Kazumi; Yamada, Hirofumi

    2017-08-01

    We demonstrated near-field light detection using a non contact-mode atomic force microscope (nc-AFM). This system obtains molecular-level resolution by reducing noise in the displacement detection of a Si cantilever. The Si cantilever probe tip was brought close to a glass with a patterned chromium film on a dove prism. The backside of the prism was irradiated by an intensity-modulated laser light to create an evanescent field at the glass surface. We obtained a near-field optical image of the chromium-patterned glass by detecting the amplitude modulation induced by the near-field light while the tip-sample distance was regulated by the frequency modulation method under atmospheric conditions.

  20. Numerical analysis of flow fields generated by accelerating flames

    Energy Technology Data Exchange (ETDEWEB)

    Kurylo, J.

    1977-12-01

    Presented here is a numerical technique for the analysis of non-steady flow fields generated by accelerating flames in gaseous media. Of particular interest in the study is the evaluation of the non-steady effects on the flow field and the possible transition of the combustion process to detonation caused by an abrupt change in the burning speed of an initially steady flame propagating in an unconfined combustible gas mixture. Optically recorded observations of accelerating flames established that the flow field can be considered to consist of non-steady flow fields associated with an assembly of interacting shock waves, contact discontinuities, deflagration and detonation fronts. In the analysis, these flow fields are treated as spatially one-dimensional, the influence of transport phenomena is considered to be negligible, and unburned and burned substances are assumed to behave as perfect gases with constant, but different, specific heats. The basis of the numerical technique is an explicit, two step, second order accurate, finite difference scheme employed to integrate the flow field equations expressed in divergence form. The burning speed, governing the motion of the deflagration, is expressed in the form of a power law dependence on pressure and temperature immediately ahead of its front. The steady wave solution is obtained by the vector polar interaction technique, that is, by determining the point of intersection between the loci of end states in the plane of the two interaction invariants, pressure and particle velocity. The technique is illustrated by a numerical example in which a steady flame experiences an abrupt change in its burning speed. Solutions correspond either to the eventual reestablishment of a steady state flow field commensurate with the burning speed or to the transition to detonation. The results are in satisfactory agreement with experimental observations.

  1. The R.E.D. Tools: Advances in RESP and ESP charge derivation and force field library building

    Science.gov (United States)

    Dupradeau, François-Yves; Pigache, Adrien; Zaffran, Thomas; Savineau, Corentin; Lelong, Rodolphe; Grivel, Nicolas; Lelong, Dimitri; Rosanski, Wilfried; Cieplak, Piotr

    2010-01-01

    Deriving atomic charges and building a force field library for a new molecule are key steps when developing a force field required for conducting structural and energy-based analysis using molecular mechanics. Derivation of popular RESP charges for a set of residues is a complex and error prone procedure, because it depends on numerous input parameters. To overcome these problems, the R.E.D. Tools (RESP and ESP charge Derive, http://q4md-forcefieldtools.org/RED/) have been developed to perform charge derivation in an automatic and straightforward way. The R.E.D. program handles chemical elements up to bromine in the periodic table. It interfaces different quantum mechanical programs employed for geometry optimization and computing molecular electrostatic potential(s), and performs charge fitting using the RESP program. By defining tight optimization criteria and by controlling the molecular orientation of each optimized geometry, charge values are reproduced at any computer platform with an accuracy of 0.0001 e. The charges can be fitted using multiple conformations, making them suitable for molecular dynamics simulations. R.E.D. allows also for defining charge constraints during multiple molecule charge fitting, which are used to derive charges for molecular fragments. Finally, R.E.D. incorporates charges into a force field library, readily usable in molecular dynamics computer packages. For complex cases, such as a set of homologous molecules belonging to a common family, an entire force field topology database is generated. Currently, the atomic charges and force field libraries have been developed for more than fifty model systems and stored in the RESP ESP charge DDataBase. Selected results related to non-polarizable charge models are presented and discussed. PMID:20574571

  2. The R.E.D. tools: advances in RESP and ESP charge derivation and force field library building.

    Science.gov (United States)

    Dupradeau, François-Yves; Pigache, Adrien; Zaffran, Thomas; Savineau, Corentin; Lelong, Rodolphe; Grivel, Nicolas; Lelong, Dimitri; Rosanski, Wilfried; Cieplak, Piotr

    2010-07-28

    Deriving atomic charges and building a force field library for a new molecule are key steps when developing a force field required for conducting structural and energy-based analysis using molecular mechanics. Derivation of popular RESP charges for a set of residues is a complex and error prone procedure because it depends on numerous input parameters. To overcome these problems, the R.E.D. Tools (RESP and ESP charge Derive, ) have been developed to perform charge derivation in an automatic and straightforward way. The R.E.D. program handles chemical elements up to bromine in the periodic table. It interfaces different quantum mechanical programs employed for geometry optimization and computing molecular electrostatic potential(s), and performs charge fitting using the RESP program. By defining tight optimization criteria and by controlling the molecular orientation of each optimized geometry, charge values are reproduced at any computer platform with an accuracy of 0.0001 e. The charges can be fitted using multiple conformations, making them suitable for molecular dynamics simulations. R.E.D. allows also for defining charge constraints during multiple molecule charge fitting, which are used to derive charges for molecular fragments. Finally, R.E.D. incorporates charges into a force field library, readily usable in molecular dynamics computer packages. For complex cases, such as a set of homologous molecules belonging to a common family, an entire force field topology database is generated. Currently, the atomic charges and force field libraries have been developed for more than fifty model systems and stored in the RESP ESP charge DDataBase. Selected results related to non-polarizable charge models are presented and discussed.

  3. Quantum mechanics based force field for carbon (QMFF-Cx) validated to reproduce the mechanical and thermodynamics properties of graphite

    Science.gov (United States)

    Pascal, Tod A.; Karasawa, Naoki; Goddard, William A.

    2010-10-01

    As assemblies of graphene sheets, carbon nanotubes, and fullerenes become components of new nanotechnologies, it is important to be able to predict the structures and properties of these systems. A problem has been that the level of quantum mechanics practical for such systems (density functional theory at the PBE level) cannot describe the London dispersion forces responsible for interaction of the graphene planes (thus graphite falls apart into graphene sheets). To provide a basis for describing these London interactions, we derive the quantum mechanics based force field for carbon (QMFF-Cx) by fitting to results from density functional theory calculations at the M06-2X level, which demonstrates accuracies for a broad class of molecules at short and medium range intermolecular distances. We carried out calculations on the dehydrogenated coronene (C24) dimer, emphasizing two geometries: parallel-displaced X (close to the observed structure in graphite crystal) and PD-Y (the lowest energy transition state for sliding graphene sheets with respect to each other). A third, eclipsed geometry is calculated to be much higher in energy. The QMFF-Cx force field leads to accurate predictions of available experimental mechanical and thermodynamics data of graphite (lattice vibrations, elastic constants, Poisson ratios, lattice modes, phonon dispersion curves, specific heat, and thermal expansion). This validates the use of M06-2X as a practical method for development of new first principles based generations of QMFF force fields.

  4. Quantum force of nanomagnets loosely fastened to the matrix in a magnetic field gradient

    Science.gov (United States)

    Kim, Gwang-Hee

    2016-11-01

    We study nanomagnets that exhibit quantum forces, but are not firmly fixed to the substrate. The Hamiltonian of a rotating spin system is derived in the presence of a microwave field and a transverse field gradient, and analytic expressions for the forces are obtained. We show that the period of the oscillating force depends upon the coupling constant of the system to the matrix and the total angular momentum, and we discuss the conditions under which they can be observed within the framework of experimentally controllable parameters.

  5. Retrofitting Forced Air Combi Systems: A Cold Climate Field Assessment

    Energy Technology Data Exchange (ETDEWEB)

    Schoenbauer, Ben [NorthernSTAR, St. Paul, MN (United States); Bohac, Dave [NorthernSTAR, St. Paul, MN (United States); McAlpine, Jack [NorthernSTAR, St. Paul, MN (United States); Hewett, Martha [NorthernSTAR, St. Paul, MN (United States)

    2017-06-01

    This project analyzed combined condensing water heaters or boilers and hydronic air coils to provide high efficiency domestic hot water (DHW) and forced air space heating. Called "combi" systems, they provided similar space and water heating performance less expensively than installing two condensing appliances. The system's installed costs were cheaper than installing a condensing furnace and either a condensing tankless or condensing storage water heater. However, combi costs must mature and be reduced before they are competitive with a condensing furnace and power vented water heater (energy factor of 0.60). Better insulation and tighter envelopes are reducing space heating loads for new and existing homes. For many homes, decreased space heating loads make it possible for both space and domestic water heating loads to be provided with a single heating plant. These systems can also eliminate safety issues associated with natural draft appliances through the use of one common sealed combustion vent. The combined space and water heating approach was not a new idea. Past systems have used non-condensing heating plants, which limited their usefulness in climates with high heating loads. Previous laboratory work (Schoenbauer et al. 2012a) showed that proper installation was necessary to achieve condensing with high efficiency appliances. Careful consideration was paid to proper system sizing and minimizing the water temperature returning from the air handling unit to facilitate condensing operation.

  6. Retrofitting Forced Air Combi Systems: A Cold Climate Field Assessment

    Energy Technology Data Exchange (ETDEWEB)

    Schoenbauer, Ben [Univ. of Minnesota, St. Paul, MN (United States). NorthernSTAR Building America Partnership; Bohac, Dave [Univ. of Minnesota, St. Paul, MN (United States). NorthernSTAR Building America Partnership; McAlpine, Jake [Univ. of Minnesota, St. Paul, MN (United States). NorthernSTAR Building America Partnership; Hewett, Martha [Univ. of Minnesota, St. Paul, MN (United States). NorthernSTAR Building America Partnership

    2017-06-23

    This project analyzed combined condensing water heaters or boilers and hydronic air coils to provide high efficiency domestic hot water (DHW) and forced air space heating. Called 'combi' systems, they provided similar space and water heating performance less expensively than installing two condensing appliances. The system's installed costs were cheaper than installing a condensing furnace and either a condensing tankless or condensing storage water heater. However, combi costs must mature and be reduced before they are competitive with a condensing furnace and power vented water heater (energy factor of 0.60). Better insulation and tighter envelopes are reducing space heating loads for new and existing homes. For many homes, decreased space heating loads make it possible for both space and domestic water heating loads to be provided with a single heating plant. These systems can also eliminate safety issues associated with natural draft appliances through the use of one common sealed combustion vent. The combined space and water heating approach was not a new idea. Past systems have used non-condensing heating plants, which limited their usefulness in climates with high heating loads. Previous laboratory work (Schoenbauer et al. 2012a) showed that proper installation was necessary to achieve condensing with high efficiency appliances. Careful consideration was paid to proper system sizing and minimizing the water temperature returning from the air handling unit to facilitate condensing operation.

  7. The attenuation of the levitation force of HTS bulk exposed to AC magnetic field on the above NdFeB guideway

    Energy Technology Data Exchange (ETDEWEB)

    Liu Minxian, E-mail: liukey_sjtu@263.net [School of Computer Science and Technology, Southwest University of Science and Technology, Mianyang, Sichuan 621010 (China); Wang Yan [Luoyang Institute of Science and Technology, Luoyang, Henan 471023 (China)

    2012-01-15

    The characteristic of the levitation force relaxation was studied by experiment. The levitation force is attenuated with the application of the AC external magnetic field. The decay increases with the amplitude of the A external magnetic field. The decay is almost independent of the frequency of AC field. In the present High Temperature Superconducting (HTS) maglev vehicle system, the air gaps between the adjacent permanent magnets make the magnetic fields above the NdFeB guideway non-uniform. So it is required to study the characteristics of levitation force of the HTS bulk affected by the non-uniform applied magnetic fields along the moving direction. In this paper, we have studied the characteristics of the levitation force relaxation by an experiment in which AC magnetic field generated by an electromagnet is used to simulate the time-varying magnetic field caused by the inhomogeneity of the NdFeB guideway. From the experiment results, it is found that the levitation force is attenuated with the application of the AC field, and the attenuation is increased with the amplitude of the AC field, but the attenuation is almost independent of the frequency the AC magnetic field.

  8. Vibrational analysis of ferrocyanide complex ion based on density functional force field

    Energy Technology Data Exchange (ETDEWEB)

    Park, Sun Kyung; Lee, Choong Keun; Lee, Nam Soo [Chungbuk National Univ., Cheongju (Korea, Republic of); Lee, Sang Ho [The University of Michigan, Ann Arbor (United States)

    2002-02-01

    Vibrational properties of ferrocyanide complex ion, [Fe(CN){sub 6}]{sup 4-}, have been studied based on the force constants obtained from the density functional calculations at B3LYP/6-31G level by means of the normal mode analysis using new bond angle and linear angle internal coordinates recently developed. Vibrations of ferrocyanide were manipulated by twenty-three symmetry force constants. The angled bending deformations of C-Fe-C, the linear bending deformations of Fe-C{identical_to}N and the stretching vibrations of Fe-C have been quantitatively assigned to the calculated frequencies. The force constants in the internal coordinates employed in the modified Urey-Bradley type potential were evaluated on the density functional force field applied, and better interaction force constants in the internal coordinates have been proposed. The valence force constants in the general quadratic valence force field were also given. The stretch-stretch interaction and stretch-bending interaction constants are not sensitive to the geometrical displacement in the valence force field.

  9. Dependence of levitation force on frequency of an oscillating magnetic levitation field in a bulk YBCO superconductor

    Energy Technology Data Exchange (ETDEWEB)

    Carter, Hamilton, E-mail: hcarter3@nmsu.edu [Department of Physics, New Mexico State University, Las Cruces, NM 88003 (United States); Pate, Stephen, E-mail: pate@nmsu.edu [Department of Physics, New Mexico State University, Las Cruces, NM 88003 (United States); Goedecke, George, E-mail: ggoedeck@nmsu.edu [Department of Physics, New Mexico State University, Las Cruces, NM 88003 (United States)

    2013-02-14

    Highlights: ► AC magnetic field strength required for levitation is independent of frequency. ► RMS magnetic field strength is in good agreement with DC magnetic field strength. ► Dependence of YBCO levitation force on AC magnetic field frequency is investigated. -- Abstract: The dependence of the magnetic field strength required for levitation of a melt textured, single domain YBCO superconductor disk on the frequency of the current generating the levitating magnetic field has been investigated. The magnetic field strength is found to be independent of frequency between 10 and 300 Hz. This required field strength is found to be in good experimental and theoretical agreement with the field strength required to levitate the same superconductor with a non-oscillating magnetic field. Hysteretic losses within the superconductor predicted by Bean’s critical-state model were also calculated. The measured data rules out any significant Bean’s model effects on the required levitation field strength within the measured frequency range.

  10. Change Agent – A Force Generating Resistance To Change Within An Organization?

    Directory of Open Access Journals (Sweden)

    Mariana Prediscan

    2012-12-01

    Full Text Available The purpose of this research is to identify if the change agent represents or not a force generating resistance to change within an organization. The employees affected by a change process are usually the ones who oppose to new implementations. Their opposition is bigger or smaller, depending on the extent that they are affected and also by the direction, either positive or negative. However, employee’s opposition can be potentiated or reduced, depending on the manifestation of the following forces within an organization: communications, the type of organizational structure, management style and organizational culture, forces which refer to the organizational climate. To answer our question, we have researched the current literature and discovered that the change agent can represent a force generating resistance to change within an organization in those situations when he or she identifies with a middle or top manager from the organizational pyramid. This information is valuable to researchers and practitioners, as for a long time, employees were considered the only ones manifesting resistance, the possibility that the change agent can oppose new changes being ignored.

  11. Intermolecular forces between low generation PAMAM dendrimer condensed DNA helices: role of cation architecture.

    Science.gov (United States)

    An, Min; Parkin, Sean R; DeRouchey, Jason E

    2014-01-28

    In recent years, dendriplexes, complexes of cationic dendrimers with DNA, have become attractive DNA delivery vehicles due to their well-defined chemistries. To better understand the nature of the forces condensing dendriplexes, we studied low generation poly(amidoamine) (PAMAM) dendrimer-DNA complexes and compared them to comparably charged linear arginine peptides. Using osmotic stress coupled with X-ray scattering, we have investigated the effect of molecular chain architecture on DNA-DNA intermolecular forces that determine the net attraction and equilibrium interhelical distance within these polycation condensed DNA arrays. In order to compact DNA, linear cations are believed to bind in DNA grooves and to interact with the phosphate backbone of apposing helices. We have previously shown a length dependent attraction resulting in higher packaging densities with increasing charge for linear cations. Hyperbranched polycations, such as polycationic dendrimers, presumably would not be able to bind to DNA and correlate their charges in the same manner as linear cations. We show that attractive and repulsive force amplitudes in PAMAM-DNA assemblies display significantly different trends than comparably charged linear arginines resulting in lower DNA packaging densities with increasing PAMAM generation. The salt and pH dependencies of packaging in PAMAM dendrimer-DNA and linear arginine-DNA complexes were also investigated. Significant differences in the force curve behaviour and salt and pH sensitivities suggest that different binding modes may be present in DNA condensed by dendrimers when compared to linear polycations.

  12. Investigation of Multiscale Non-equilibrium Flow Dynamics Under External Force Field

    CERN Document Server

    Xiao, Tianbai

    2016-01-01

    The multiple scale non-equilibrium gaseous flow behavior under external force field is investigated. Both theoretical analysis based on the kinetic model equation and numerical study are presented to demonstrate the dynamic effect of external force on the flow evolution, especially on the non-equilibrium heat flux. The current numerical experiment is based on the well-balanced unified gas-kinetic scheme (UGKS), which presents accurate solutions in the whole flow regime from the continuum Navier-Stokes solution to the transition and free molecular ones. The heat conduction in the non-equilibrium regime due to the external forcing term is quantitatively investigated. In the lid-driven cavity flow study, due to the external force field the density distribution inside cavity gets stratified and a multiscale non-equilibrium flow transport appears in a single gas dynamic system. With the increment of external forcing term, the flow topological structure changes dramatically, and the temperature gradient, shearing s...

  13. Photonic forces in the near field of statistically homogeneous fluctuating sources

    CERN Document Server

    Aunon, Juan Miguel

    2012-01-01

    Electromagnetic sources, as e.g. lasers, antennas, diffusers or thermal sources, produce a wavefield that interacts with objects to transfer them its momentum. We show that the photonic force exerted on a small particle in the near field of a planar statistically homogeneous fluctuating source uniquely depends and acts along the coordinate perpendicular to its surface. The gradient part of this force is contributed by only the evanescent components of the emitted field, its sign being opposite to that of the real part of the particle polarizability. The non-conservative force part is uniquely due to the propagating components, being repulsive and constant. Also, the source coherence length adds a degree of freedom since it largely affects these forces. The excitation of plasmons in the source surface drastically enhances the gradient force. Hence, partially coherent wavefields from fluctuating sources constitute new concepts for particle manipulation at the subwavelength scale

  14. Orbital angular momentum of scalar field generated by gravitational scatterings

    CERN Document Server

    Nishikawa, Ryusuke; Masuda, Atsuki; Nambu, Yasusada; Ishihara, Hideki

    2016-01-01

    It has been expected that astronomical observations to detect the orbital angular momenta of electromagnetic waves may give us a new insight into astrophysics. Previous works pointed out the possibility that a rotating black hole can produce orbital angular momenta of electromagnetic waves through gravitational scattering, and the spin parameter of the black hole can be measured by observing them. However, the mechanism how the orbital angular momentum of the electromagnetic wave is generated by the gravitational scattering has not been clarified sufficiently. In this paper, in order to understand it from a point of view of gravitational lensing effects, we consider an emitter which radiates a spherical wave of the real massless scalar field and study the deformation of the scalar wave by the gravitational scattering due to a black hole by invoking the geometrical optics approximation. We show that the frame dragging caused by the rotating black hole is not a necessary condition for generating the orbital ang...

  15. First generation leishmaniasis vaccines: a review of field efficacy trials.

    Science.gov (United States)

    Noazin, Sassan; Modabber, Farrokh; Khamesipour, Ali; Smith, Peter G; Moulton, Lawrence H; Nasseri, Kiumarss; Sharifi, Iraj; Khalil, Eltahir A G; Bernal, Ivan Dario Velez; Antunes, Carlos M F; Kieny, Marie Paule; Tanner, Marcel

    2008-12-09

    First generation candidate vaccines against leishmaniasis, prepared using inactivated whole parasites as their main ingredient, were considered as promising because of their relative ease of production and low cost. These vaccines have been the subject of many investigations over several decades and are the only leishmaniasis vaccine candidates which have undergone phase 3 clinical trial evaluation. Although the studies demonstrated the safety of the vaccines and several studies showed reasonable immunogenicity and some indication of protection, an efficacious prophylactic vaccine is yet to be identified. Despite this overall failure, these trials contributed significantly to increasing knowledge on human leishmaniasis immunology. To provide a collective view, this review discusses the methods and findings of field efficacy trials of first generation leishmaniasis vaccine clinical trials conducted in the Old and New Worlds.

  16. Biomolecular adsorption at aqueous silver interfaces: first-principles calculations, polarizable force-field simulations, and comparisons with gold.

    Science.gov (United States)

    Hughes, Zak E; Wright, Louise B; Walsh, Tiffany R

    2013-10-29

    The molecular simulation of biomolecules adsorbed at noble metal interfaces can assist in the development of bionanotechnology applications. In line with advances in polarizable force fields for adsorption at aqueous gold interfaces, there is scope for developing a similar force field for silver. One way to accomplish this is via the generation of in vacuo adsorption energies calculated using first-principles approaches for a wide range of different but biologically relevant small molecules, including water. Here, we present such first-principles data for a comprehensive range of bio-organic molecules obtained from plane-wave density functional theory calculations using the vdW-DF functional. As reported previously for the gold force field, GolP-CHARMM (Wright, L. B.; Rodger, P. M.; Corni, S.; Walsh, T. R. GolP-CHARMM: first-principles based force-fields for the interaction of proteins with Au(111) and Au(100). J. Chem. Theory Comput. 2013, 9, 1616-1630), we have used these data to construct a a new force field, AgP-CHARMM, suitable for the simulation of biomolecules at the aqueous Ag(111) and Ag(100) interfaces. This force field is derived to be consistent with GolP-CHARMM such that adsorption on Ag and Au can be compared on an equal footing. Our force fields are used to evaluate the water overlayer stability on both silver and gold, finding good agreement with known behaviors. We also calculate and compare the structuring (spatial and orientational) of liquid water adsorbed at both silver and gold. Finally, we report the adsorption free energy of a range of amino acids at both the Au(111) and Ag(111) aqueous interfaces, calculated using metadynamics. Stronger adsorption on gold was noted in most cases, with the exception being the carboxylate group present in aspartic acid. Our findings also indicate differences in the binding free energy profile between silver and gold for some amino acids, notably for His and Arg. Our analysis suggests that the relatively

  17. Entropy generation analysis of thermally developing forced convection in fluid-saturated porous medium

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Entropy generation for thermally developing forced convection in a porous medium bounded by two isothermal parallel plates is investigated analytically on the basis of the Darcy flow model where the viscous dissipation effects had also been taken into account.A parametric study showed that decreasing the group parameter and the Péclet number increases the entropy generation while for the Brinkman number the converse is true.Heatline visualization technique is applied with an emphasis on the Br < 0 case where there is somewhere that heat transfer changes direction at some streamwise location to the wall instead of its original direction,i.e.,from the wall.

  18. Nascent Focal Adhesions Are Responsible for the Generation of Strong Propulsive Forces in Migrating Fibroblasts

    OpenAIRE

    2001-01-01

    Fibroblast migration involves complex mechanical interactions with the underlying substrate. Although tight substrate contact at focal adhesions has been studied for decades, the role of focal adhesions in force transduction remains unclear. To address this question, we have mapped traction stress generated by fibroblasts expressing green fluorescent protein (GFP)-zyxin. Surprisingly, the overall distribution of focal adhesions only partially resembles the distribution of traction stress. In ...

  19. The proton motive force generated in Leuconostoc oenos by L-malate fermentation

    NARCIS (Netherlands)

    Salema, Madalena; Lolkema, Juke S.; San Romão, M.V.; Loureiro Dias, Maria C.

    1996-01-01

    In cells of Leuconostoc oenos, the fermentation of L-malic acid generates both a transmembrane pH gradient, inside alkaline, and an electrical potential gradient, inside negative. In resting cells, the proton motive force ranged from -170 mV to -88 mV between pH 3.1 and 5.6 in the presence of L-mala

  20. Defense Science Board Task Force Report on Next-Generation Unmanned Undersea Systems

    Science.gov (United States)

    2016-10-01

    STUDY ON Next-Generation Unmanned Undersea Systems October 2016 Office of the Under Secretary of Defense for Acquisition, Technology, and Logistics ...MEMORANDUM FOR THE UNDER SECRETARY OF DEFENSE FOR ACQUISITION, TECHNOLOGY & LOGISTICS SUBJECT: Final Report of the Defense Science Board (DSB) Task Force on...numbers of low- cost assets. As the report explains, in the undersea domain, quantity has a quality all its own. Furthermore, this report recommends

  1. New wrinkling substrate assay reveals traction force fields of leader and follower cells undergoing collective migration.

    Science.gov (United States)

    Yokoyama, Sho; Matsui, Tsubasa S; Deguchi, Shinji

    2017-01-22

    Physical forces play crucial roles in coordinating collective migration of epithelial cells, but details of such force-related phenomena remain unclear partly due to the lack of robust methodologies to probe the underlying force fields. Here we develop a method for fabricating silicone substrates that detect cellular traction forces with a high sensitivity. Specifically, a silicone elastomer is exposed to oxygen plasma under heating. Removal of the heat shrinks the substrate so as to reduce its critical buckling strain in a spatially uniform manner. Thus, even small cellular traction forces can be visualized as micro-wrinkles that are reversibly emerged on the substrate in a direction orthogonal to the applied forces. Using this technique, we show that so-called leader cells in MDCK-II cell clusters exert significant magnitudes of traction forces distinct from those of follower cells. We reveal that the direction of traction forces is highly correlated with the long axis of the local, individual cells within clusters. These results suggest that the force fields in collective migration of MDCK-II cells are predominantly determined locally at individual cell scale rather than globally at the whole cell cluster scale. Copyright © 2016 Elsevier Inc. All rights reserved.

  2. Spontaneous generation of singularities in paraxial optical fields

    CERN Document Server

    Aiello, Andrea

    2015-01-01

    In nonrelativistic quantum mechanics the spontaneous generation of singularities in continue and finite wave functions, is a well understood phenomenon also occurring for free particles. We use the familiar analogy between the two-dimensional Schroedinger equation and the optical paraxial wave equation to show that even weakly-focused collimated light beams may develop a spatial singularity during free-space propagation. We find that according to the shape of the field, its amplitude may be either finite or infinite at the singular point.

  3. Magnetic field generation during intense laser channelling in underdense plasma

    Science.gov (United States)

    Smyth, A. G.; Sarri, G.; Vranic, M.; Amano, Y.; Doria, D.; Guillaume, E.; Habara, H.; Heathcote, R.; Hicks, G.; Najmudin, Z.; Nakamura, H.; Norreys, P. A.; Kar, S.; Silva, L. O.; Tanaka, K. A.; Vieira, J.; Borghesi, M.

    2016-06-01

    Channel formation during the propagation of a high-energy (120 J) and long duration (30 ps) laser pulse through an underdense deuterium plasma has been spatially and temporally resolved via means of a proton imaging technique, with intrinsic resolutions of a few μm and a few ps, respectively. Conclusive proof is provided that strong azimuthally symmetric magnetic fields with a strength of around 0.5 MG are created inside the channel, consistent with the generation of a collimated beam of relativistic electrons. The inferred electron beam characteristics may have implications for the cone-free fast-ignition scheme of inertial confinement fusion.

  4. Fiber Assignment in Next-generation Wide-field Spectrographs

    OpenAIRE

    Morales, Isaac; Montero-Dorta, Antonio D.; Azzaro, Marco; Prada, Francisco; Sanchez, Justo; Becerril, Santiago

    2011-01-01

    We present an optimized algorithm for assigning fibers to targets in next-generation fiber-fed multi-object spectrographs. The method, that we named draining algorithm, ensures that the maximum number of targets in a given target field is observed in the first few tiles. Using randomly distributed targets and mock galaxy catalogs we have estimated that the gain provided by the draining algorithm as compared to a random assignment can be as much as 2% for the first tiles. This would imply for ...

  5. Proposal for generating Fock states in traveling wave fields

    Energy Technology Data Exchange (ETDEWEB)

    Benmoussa, Adil [Department of Physics and Astronomy, Lehman College, The City University of New York, Bronx, NY 10468-1589 (United States)]. E-mail: adil.benmoussa@lehman.cuny.edu; Gerry, Christopher C. [Department of Physics and Astronomy, Lehman College, The City University of New York, Bronx, NY 10468-1589 (United States)

    2007-05-28

    We describe a proposal for the generation of a single-mode photonic number state, |N>, in a traveling wave optical field. The state is obtained by state reduction from an input coherent state using Kerr media. Our method is based on a previous scheme used for hole burning in the Fock space by minimizing the Mandel Q parameter. The same method was used by Maia et al., but ours is different, it requires only one single photon injected in the entire setup and one photon detection at the end.

  6. Thermodynamic properties for applications in chemical industry via classical force fields.

    Science.gov (United States)

    Guevara-Carrion, Gabriela; Hasse, Hans; Vrabec, Jadran

    2012-01-01

    Thermodynamic properties of fluids are of key importance for the chemical industry. Presently, the fluid property models used in process design and optimization are mostly equations of state or G (E) models, which are parameterized using experimental data. Molecular modeling and simulation based on classical force fields is a promising alternative route, which in many cases reasonably complements the well established methods. This chapter gives an introduction to the state-of-the-art in this field regarding molecular models, simulation methods, and tools. Attention is given to the way modeling and simulation on the scale of molecular force fields interact with other scales, which is mainly by parameter inheritance. Parameters for molecular force fields are determined both bottom-up from quantum chemistry and top-down from experimental data. Commonly used functional forms for describing the intra- and intermolecular interactions are presented. Several approaches for ab initio to empirical force field parameterization are discussed. Some transferable force field families, which are frequently used in chemical engineering applications, are described. Furthermore, some examples of force fields that were parameterized for specific molecules are given. Molecular dynamics and Monte Carlo methods for the calculation of transport properties and vapor-liquid equilibria are introduced. Two case studies are presented. First, using liquid ammonia as an example, the capabilities of semi-empirical force fields, parameterized on the basis of quantum chemical information and experimental data, are discussed with respect to thermodynamic properties that are relevant for the chemical industry. Second, the ability of molecular simulation methods to describe accurately vapor-liquid equilibrium properties of binary mixtures containing CO(2) is shown.

  7. Altered force-generating capacity is well-perceived regardless of the pain presence.

    Science.gov (United States)

    Deschamps, Thibault; Magnard, Justine; Jubeau, Marc; Hug, François; Tucker, Kylie

    2016-09-01

    An inability to perceive changes in action capabilities may result in increased risk of injury and/or reduced performance. We investigated whether the perception of ability to perform a maximal single-leg hop was updated when the actual ability to perform the task was reduced due to experimentally altered force-generating capacity and associated pain. Twenty-five healthy volunteers performed a series of maximal isometric voluntary knee extensions (MVC), performance estimates and actual performances of a maximal single-leg hop. The motor tasks were completed for each leg, before (t), and immediately (t), 48 hr (t) and 1 month (t) after, a neuromuscular electrical stimulation (NMES) protocol was used to decrease the force generating capacity of the quadriceps muscle of 1 leg. MVC torque decreased by ∼30% after the NMES protocol for the stimulated leg at t and t (p estimation of performance and actual performance of the maximal single-leg hop at t and t for the test leg (p estimated their performance capabilities during each testing period. This study provides a critical step toward understanding the potential for decreased force-generating capacity and muscle pain to modify the relationship between motor performance and perceived abilities. (PsycINFO Database Record

  8. Force generation by a dynamic Z-ring in Escherichia coli cell division.

    Science.gov (United States)

    Allard, Jun F; Cytrynbaum, Eric N

    2009-01-06

    FtsZ, a bacterial homologue of tubulin, plays a central role in bacterial cell division. It is the first of many proteins recruited to the division site to form the Z-ring, a dynamic structure that recycles on the time scale of seconds and is required for division to proceed. FtsZ has been recently shown to form rings inside tubular liposomes and to constrict the liposome membrane without the presence of other proteins, particularly molecular motors that appear to be absent from the bacterial proteome. Here, we propose a mathematical model for the dynamic turnover of the Z-ring and for its ability to generate a constriction force. Force generation is assumed to derive from GTP hydrolysis, which is known to induce curvature in FtsZ filaments. We find that this transition to a curved state is capable of generating a sufficient force to drive cell-wall invagination in vivo and can also explain the constriction seen in the in vitro liposome experiments. Our observations resolve the question of how FtsZ might accomplish cell division despite the highly dynamic nature of the Z-ring and the lack of molecular motors.

  9. reaxFF Reactive Force Field for Disulfide Mechanochemistry, Fitted to Multireference ab Initio Data.

    Science.gov (United States)

    Müller, Julian; Hartke, Bernd

    2016-08-09

    Mechanochemistry, in particular in the form of single-molecule atomic force microscopy experiments, is difficult to model theoretically, for two reasons: Covalent bond breaking is not captured accurately by single-determinant, single-reference quantum chemistry methods, and experimental times of milliseconds or longer are hard to simulate with any approach. Reactive force fields have the potential to alleviate both problems, as demonstrated in this work: Using nondeterministic global parameter optimization by evolutionary algorithms, we have fitted a reaxFF force field to high-level multireference ab initio data for disulfides. The resulting force field can be used to reliably model large, multifunctional mechanochemistry units with disulfide bonds as designed breaking points. Explorative calculations show that a significant part of the time scale gap between AFM experiments and dynamical simulations can be bridged with this approach.

  10. Haptic Manipulation of Microspheres Using Optical Tweezers Under the Guidance of Artificial Force Fields

    CERN Document Server

    Bukusoglu, Ibrahim; Kiraz, Alper; Kurt, Adnan

    2007-01-01

    Using optical tweezers and a haptic device, microspheres having diameters ranging from 3 to 4 um (floating in a fluid solution) are manipulated in order to form patterns of coupled optical microresonators by assembling the spheres via chemical binding. For this purpose, biotin-coated microspheres trapped by a laser beam are steered and chemically attached to an immobilized streptavidin-coated sphere (i.e. anchor sphere) one by one using an XYZ piezo scanner controlled by a haptic device. The positions of all spheres in the scene are detected using a CCD camera and a collision-free path for each manipulated sphere is generated using the potential field approach. The forces acting on the manipulated particle due to the viscosity of the fluid and the artificial potential field are scaled and displayed to the user through the haptic device for better guidance and control during steering. In addition, a virtual fixture is implemented such that the desired angle of approach and strength are achieved during the bind...

  11. Generation of the Primordial Magnetic Fields during Cosmological Reionization

    CERN Document Server

    Gnedin, N Yu; Zweibel, E G; Gnedin, Nickolay Y.; Ferrara, Andrea; Zweibel, Ellen G.

    2000-01-01

    We investigate the generation of magnetic field by the Biermann battery in cosmological ionization fronts, using new simulations of the reionization of the universe by stars in protogalaxies. Two mechanisms are primarily responsible for magnetogenesis: i) the breakout of I-fronts from protogalaxies, and ii) the propagation of I-fronts through the high density neutral filaments which are part of the cosmic web. The first mechanism is dominant prior to overlapping of ionized regions (z ~ 7), whereas the second continues to operate even after that epoch. However, after overlap the field strength increase is largely due to the gas compression occurring as cosmic structures form. As a consequence, the magnetic field at z ~ 5 closely traces the gas density, and it is highly ordered on megaparsec scales. The mean mass-weighted field strength is B_0 ~ 10^{-19} G in the simulation box. There is a relatively well-defined, nearly linear correlation between B_0 and the baryonic mass of virialized objects, with B_0 ~ 10^{...

  12. Stochastic Hybrid Systems Modeling and Middleware-enabled DDDAS for Next-generation US Air Force Systems

    Science.gov (United States)

    2017-03-30

    AFRL-AFOSR-VA-TR-2017-0075 Stochastic Hybrid Systems Modeling and Middleware-enabled DDDAS for Next-generation US Air Force Systems Aniruddha...release. Air Force Research Laboratory AF Office Of Scientific Research (AFOSR)/RTA2 4/6/2017https://livelink.ebs.afrl.af.mil/livelink/llisapi.dll a...Sep 2013 to 31 Dec 2016 4. TITLE AND SUBTITLE Stochastic Hybrid Systems Modeling and Middleware-enabled DDDAS for Next- generation US Air Force

  13. Near-Field Second-Harmonic Generation Induced by Local Field Enhancement

    OpenAIRE

    Bouhelier, Alexandre; Beversluis, M.; Hartschuh, Achim; Novotny, Lukas

    2003-01-01

    The field near a sharp metal tip can be strongly enhanced if irradiated with an optical field polarized along the tip axis. We demonstrate that the enhanced field gives rise to local second-harmonic (SH) generation at the tip surface thereby creating a highly confined photon source. A theoretical model for the excitation and emission of SH radiation at the tip is developed and it is found that this source can be represented by a single on-axis oscillating dipole. The model is experimentally v...

  14. How muscle fiber lengths and velocities affect muscle force generation as humans walk and run at different speeds.

    Science.gov (United States)

    Arnold, Edith M; Hamner, Samuel R; Seth, Ajay; Millard, Matthew; Delp, Scott L

    2013-06-01

    The lengths and velocities of muscle fibers have a dramatic effect on muscle force generation. It is unknown, however, whether the lengths and velocities of lower limb muscle fibers substantially affect the ability of muscles to generate force during walking and running. We examined this issue by developing simulations of muscle-tendon dynamics to calculate the lengths and velocities of muscle fibers from electromyographic recordings of 11 lower limb muscles and kinematic measurements of the hip, knee and ankle made as five subjects walked at speeds of 1.0-1.75 m s(-1) and ran at speeds of 2.0-5.0 m s(-1). We analyzed the simulated fiber lengths, fiber velocities and forces to evaluate the influence of force-length and force-velocity properties on force generation at different walking and running speeds. The simulations revealed that force generation ability (i.e. the force generated per unit of activation) of eight of the 11 muscles was significantly affected by walking or running speed. Soleus force generation ability decreased with increasing walking speed, but the transition from walking to running increased the force generation ability by reducing fiber velocities. Our results demonstrate the influence of soleus muscle architecture on the walk-to-run transition and the effects of muscle-tendon compliance on the plantarflexors' ability to generate ankle moment and power. The study presents data that permit lower limb muscles to be studied in unprecedented detail by relating muscle fiber dynamics and force generation to the mechanical demands of walking and running.

  15. Podosome Force Generation Machinery: A Local Balance between Protrusion at the Core and Traction at the Ring.

    Science.gov (United States)

    Bouissou, Anaïs; Proag, Amsha; Bourg, Nicolas; Pingris, Karine; Cabriel, Clément; Balor, Stéphanie; Mangeat, Thomas; Thibault, Christophe; Vieu, Christophe; Dupuis, Guillaume; Fort, Emmanuel; Lévêque-Fort, Sandrine; Maridonneau-Parini, Isabelle; Poincloux, Renaud

    2017-04-25

    Determining how cells generate and transduce mechanical forces at the nanoscale is a major technical challenge for the understanding of numerous physiological and pathological processes. Podosomes are submicrometer cell structures with a columnar F-actin core surrounded by a ring of adhesion proteins, which possess the singular ability to protrude into and probe the extracellular matrix. Using protrusion force microscopy, we have previously shown that single podosomes produce local nanoscale protrusions on the extracellular environment. However, how cellular forces are distributed to allow this protruding mechanism is still unknown. To investigate the molecular machinery of protrusion force generation, we performed mechanical simulations and developed quantitative image analyses of nanoscale architectural and mechanical measurements. First, in silico modeling showed that the deformations of the substrate made by podosomes require protrusion forces to be balanced by local traction forces at the immediate core periphery where the adhesion ring is located. Second, we showed that three-ring proteins are required for actin polymerization and protrusion force generation. Third, using DONALD, a 3D nanoscopy technique that provides 20 nm isotropic localization precision, we related force generation to the molecular extension of talin within the podosome ring, which requires vinculin and paxillin, indicating that the ring sustains mechanical tension. Our work demonstrates that the ring is a site of tension, balancing protrusion at the core. This local coupling of opposing forces forms the basis of protrusion and reveals the podosome as a nanoscale autonomous force generator.

  16. Updated Hungarian Gravity Field Solution Based on Fifth Generation GOCE Gravity Field Models

    Science.gov (United States)

    Toth, Gyula; Foldvary, Lorant

    2015-03-01

    With the completion of the ESA's GOCE satellite's mission fifth generation gravity field models are available from the ESA's GOCE High Processing Facility. Our contribution is an updated gravity field solution for Hungary using the latest DIR R05 GOCE gravity field model. The solution methodology is least squares gravity field parameter estimation using Spherical Radial Base Functions (SRBF). Regional datasets include deflections of the vertical (DOV), gravity anomalies and quasigeoid heights by GPS/levelling. The GOCE DIR R05 model has been combined with the EGM20008 model and has been evaluated in comparison with the EGM2008 and EIGEN-6C3stat models to assess the performance of our regional gravity field solution.

  17. Study of the leakage field of magnetic force microscopy thin-film tips using electron holography

    NARCIS (Netherlands)

    Frost, B.G.; Hulst, van N.F.; Lunedei, E.; Matteucci, G.; Rikkers, E.

    1996-01-01

    Electron holography is applied for the study of the leakage field of thin-film ferromagnetic tips used as probes in magnetic force microscopy. We used commercially available pyramidal tips covered o­n o­ne face with a thin NiCo film, which were then placed in a high external magnetic field directed

  18. VFFDT: A New Software for Preparing AMBER Force Field Parameters for Metal-Containing Molecular Systems.

    Science.gov (United States)

    Zheng, Suqing; Tang, Qing; He, Jian; Du, Shiyu; Xu, Shaofang; Wang, Chaojie; Xu, Yong; Lin, Fu

    2016-04-25

    Force fields are fundamental to molecular dynamics simulations. However, the incompleteness of force field parameters has been a long-standing problem, especially for metal-related systems. In our previous work, we adopted the Seminario method based on the Hessian matrix to systematically derive the zinc-related force field parameters for AMBER. In this work, in order to further simplify the whole protocol, we have implemented a user-friendly Visual Force Field Derivation Toolkit (VFFDT) to derive the force field parameters via simply clicking on the bond or angle in the 3D viewer, and we have further extended our previous program to support the Hessian matrix output from a variety of quantum mechanics (QM) packages, including Gaussian 03/09, ORCA 3.0, QChem, GAMESS-US, and MOPAC 2009/2012. In this toolkit, a universal VFFDT XYZ file format containing the raw Hessian matrix is available for all of the QM packages, and an instant force field parametrization protocol based on a semiempirical quantum mechanics (SQM) method is introduced. The new function that can automatically obtain the relevant parameters for zinc, copper, iron, etc., which can be exported in AMBER Frcmod format, has been added. Furthermore, our VFFDT program can read and write files in AMBER Prepc, AMBER Frcmod, and AMBER Mol2 format and can also be used to customize, view, copy, and paste the force field parameters in the context of the 3D viewer, which provides utilities complementary to ANTECHAMBER, MCPB, and MCPB.py in the AmberTools.

  19. Design principles for high-pressure force fields: Aqueous TMAO solutions from ambient to kilobar pressures

    Science.gov (United States)

    Hölzl, Christoph; Kibies, Patrick; Imoto, Sho; Frach, Roland; Suladze, Saba; Winter, Roland; Marx, Dominik; Horinek, Dominik; Kast, Stefan M.

    2016-04-01

    Accurate force fields are one of the major pillars on which successful molecular dynamics simulations of complex biomolecular processes rest. They have been optimized for ambient conditions, whereas high-pressure simulations become increasingly important in pressure perturbation studies, using pressure as an independent thermodynamic variable. Here, we explore the design of non-polarizable force fields tailored to work well in the realm of kilobar pressures - while avoiding complete reparameterization. Our key is to first compute the pressure-induced electronic and structural response of a solute by combining an integral equation approach to include pressure effects on solvent structure with a quantum-chemical treatment of the solute within the embedded cluster reference interaction site model (EC-RISM) framework. Next, the solute's response to compression is taken into account by introducing pressure-dependence into selected parameters of a well-established force field. In our proof-of-principle study, the full machinery is applied to N,N,N-trimethylamine-N-oxide (TMAO) in water being a potent osmolyte that counteracts pressure denaturation. EC-RISM theory is shown to describe well the charge redistribution upon compression of TMAO(aq) to 10 kbar, which is then embodied in force field molecular dynamics by pressure-dependent partial charges. The performance of the high pressure force field is assessed by comparing to experimental and ab initio molecular dynamics data. Beyond its broad usefulness for designing non-polarizable force fields for extreme thermodynamic conditions, a good description of the pressure-response of solutions is highly recommended when constructing and validating polarizable force fields.

  20. Direct Generation of Intense Compression Waves in Molten Metals by Using a High Static Magnetic Field and Their Application

    Institute of Scientific and Technical Information of China (English)

    2003-01-01

    Compression waves propagating through molten metals are contributed to degassing, accelerating reaction rate,removing exclusions from molten metals and refining solidification structures during metallurgical processing of ma-terials. In the present study, two electromagnetic methods are proposed to generate intense compression wavesdirectly in liquid metals. One is the simultaneous imposition of a high frequency electrical current field and a staticmagnetic field; the other is that of a high frequency magnetic field and a static magnetic field. A mathematical modelbased on compressible fluid dynamics and electromagnetic fields theory has been developed to derive pressure distri-butions of the generated waves in a metal. It shows that the intensity of compression waves is proportional to thatof the high frequency electromagnetic force. And the frequency is the same as that of the imposed electromagneticforce. On the basis of theoretical analyses, pressure change in liquid gallium was examined by a pressure transducerunder various conditions. The observed results approximately agreed with the predictions derived from the theoreticalanalyses and calculations. Moreover, the effect of the generated waves on improvement of solidification structureswas also examined. It shows that the generated compression waves can refine solidification structures when they wereapplied to solidification process of Sn-Pb alloy. This study indicates a new method to generate compression wavesby imposing high frequency electromagnetic force locally on molten metals and this kind of compression waves canprobably overcome the difficulties when waves are excited by mechanical vibration in high temperature environments.

  1. Observation of the Field, Current and Force Distributions in an Optimized Superconducting Levitation with Translational Symmetry

    Science.gov (United States)

    Ye, Chang-Qing; Ma, Guang-Tong; Liu, Kun; Wang, Jia-Su

    2016-08-01

    The superconducting levitation realized by immersing the high-temperature superconductors (HTSs) into nonuniform magnetic field is deemed promising in a wide range of industrial applications such as maglev transportation and kinetic energy storage. Using a well-established electromagnetic model to mathematically describe the HTS, we have developed an efficient scheme that is capable of intelligently and globally optimizing the permanent magnet guideway (PMG) with single or multiple HTSs levitated above for the maglev transportation applications. With maximizing the levitation force as the principal objective, we optimized the dimensions of a Halbach-derived PMG to observe how the field, current and force distribute inside the HTSs when the optimized situation is achieved. Using a pristine PMG as a reference, we have analyzed the critical issues for enhancing the levitation force through comparing the field, current and force distributions between the optimized and pristine PMGs. It was also found that the optimized dimensions of the PMG are highly dependent upon the levitated HTS. Moreover, the guidance force is not always contradictory to the levitation force and may also be enhanced when the levitation force is prescribed to be the principle objective, depending on the configuration of levitation system and lateral displacement.

  2. Observation of the Field, Current and Force Distributions in an Optimized Superconducting Levitation with Translational Symmetry

    Science.gov (United States)

    Ye, Chang-Qing; Ma, Guang-Tong; Liu, Kun; Wang, Jia-Su

    2017-01-01

    The superconducting levitation realized by immersing the high-temperature superconductors (HTSs) into nonuniform magnetic field is deemed promising in a wide range of industrial applications such as maglev transportation and kinetic energy storage. Using a well-established electromagnetic model to mathematically describe the HTS, we have developed an efficient scheme that is capable of intelligently and globally optimizing the permanent magnet guideway (PMG) with single or multiple HTSs levitated above for the maglev transportation applications. With maximizing the levitation force as the principal objective, we optimized the dimensions of a Halbach-derived PMG to observe how the field, current and force distribute inside the HTSs when the optimized situation is achieved. Using a pristine PMG as a reference, we have analyzed the critical issues for enhancing the levitation force through comparing the field, current and force distributions between the optimized and pristine PMGs. It was also found that the optimized dimensions of the PMG are highly dependent upon the levitated HTS. Moreover, the guidance force is not always contradictory to the levitation force and may also be enhanced when the levitation force is prescribed to be the principle objective, depending on the configuration of levitation system and lateral displacement.

  3. Modeling of Centrifugal Force Field and the Effect on Filling and Solidification in Centrifugal Casting

    Science.gov (United States)

    Sheng, Wenbin; Ma, Chunxue; Gu, Wanli

    2011-06-01

    Based on the steady flow in a tube, a mathematical model has been established for the consideration of centrifuging force field by combining the equations of continuity, conservation of momentum and general energy. Effects of centrifugal field on the filling and solidification are modeled by two accessional terms: centrifugal force and Chorios force. In addition, the transfer of heat by convection is considered to achieve a coupling calculation of velocity field and temperature field. The solution of pressure item is avoided by introducing the stream function ψ(x,y) and the eddy function ξ(x,y). Corresponding difference formats for the simultaneous equations of centrifugal filling, the accessional terms and the solidifying latent heat have been established by the finite difference technique. Furthermore, the centrifugal filling and solidification processes in a horizontal tube are summarized to interpret the mechanism by which internal defects are formed in centrifugal castings.

  4. Gravitational self-force in non-vacuum spacetimes: an effective field theory derivation

    CERN Document Server

    Zimmerman, Peter

    2015-01-01

    In this paper we investigate the motion of small compact objects in non-vacuum spacetimes using methods from effective field theory in curved spacetime. Although a vacuum formulation is sufficient in many astrophysical contexts, there are applications such as the role of the self-force in enforcing cosmic-censorship in the context of the overcharging problem, which necessitate an extension into the non-vacuum regime. The defining feature of the self-force problem in non-vacuum spacetimes is the coupling between gravitational and non-gravitational field perturbations. The formulation of the self-force problem for non-vacuum spacetimes was recently provided in simultaneous papers by Zimmerman and Poisson [1] and Linz, Friedmann, Wiseman [2]. Here we distinguish ourselves by working with the effective action rather than the field equations. The formalism utilizes the multi-index notation developed by Zimmerman and Poisson [1] to accommodate the coupling between the different fields. Using dimensional regularizat...

  5. A Synchronous Stream Cipher Generator Based on Quadratic Fields (SSCQF

    Directory of Open Access Journals (Sweden)

    Younes ASIMI

    2015-12-01

    Full Text Available In this paper, we propose a new synchronous stream cipher called SSCQF whose secret-key is Ks=(z1,...zn where zi is a positive integer. Let d1, d2,..., dN be N positive integers in {0,1,...2m -1} such that di=zi mod2m with m and m>=8. Our purpose is to combine a linear feedback shift registers LFSRs, the arithmetic of quadratic fields: more precisely the unit group of quadratic fields, and Boolean functions [14]. Encryption and decryption are done by XRO`ing the output pseudorandom number generator with the plaintext and ciphertext respectively. The basic ingredients of this proposal stream generator SSCQF rely on the three following processes: In process I , we constructed the initial vectors IV={X1,...,Xn} from the secret-key Ks=(z1,...zn by using the fundamental unit of Q( Nvdi if di is a square free integer otherwise by splitting di, and in process II, we regenerate, from the vectors Xi, the vectors Yi having the same length L, that is divisible by 8 (equations (2 and (3 . In process III , for each Yi , we assign L/8 linear feedback shift registers, each of length eight. We then obtain N x L/8 linear feedback shift registers that are initialized by the binary sequence regenerated by process II , filtered by primitive polynomials, and the combine the binary sequence output with L/8 Boolean functions. The keystream generator, denoted K , is a concatenation of the output binary sequences of all Boolean functions.

  6. Field test of thermoelectric generating system at Komatsu plant

    Energy Technology Data Exchange (ETDEWEB)

    Kaibe, Hiromasa T.; Fujimoto, Sinichi; Mizukami, Hiroyuki; Morimoto, Shigeo [Komatsu Ltd., Kanagawa (Japan)

    2011-07-01

    At the end of October 2009, Komatsu Ltd. started a field test of the thermoelectric generation (TEG) system at a carburizing facility of Awazu plant. Residual carburizing gas based on such as CO, N and H{sub 2} is burned resulting that 20-30 kW range of flame constantly heats up the hot side of TEG. 16 of the Bi-Te thermo-modules, which were separated into 4 groups, were employed, each of which has a size of 50 by 50 by 4.2 mm{sup 3} and can generate better than 25 W under the circumstance of 280 C and 30 C of hot side and cold side temperature, respectively. Each module has a single booster-type DC/DC converter controlled by one chip computer and Maximum Power point Tracking (MPPT) was well facilitated to search for the maximum output power depending on the hot and cold side temperature. The electric output power from the four modules is summed up to charge a single lead storage battery (GS Yuasa Corp. 12V-65Ah) and then through a DC/AC inverter electricity goes to fluorescent light tubes inside the factory. Typically from 4 groups 200 W can be generated and 170 W is delivered to the batteries. (orig.)

  7. Generation of scale invariant magnetic fields in bouncing universes

    CERN Document Server

    Sriramkumar, L; Jain, Rajeev Kumar

    2015-01-01

    We consider the generation of primordial magnetic fields in a class of bouncing models when the electromagnetic action is coupled non-minimally to a scalar field that, say, drives the background evolution. For scale factors that have the power law form at very early times and non-minimal couplings which are simple powers of the scale factor, one can easily show that scale invariant spectra for the magnetic fields can arise {\\it before the bounce} for certain values of the indices involved. It will be interesting to examine if these power spectra retain their shape {\\it after the bounce}. However, analytical solutions for the Fourier modes of the electromagnetic vector potential across the bounce are difficult to obtain. In this work, with the help of a new time variable that we introduce, which we refer to as the ${\\rm e}$-${\\cal N}$-fold, we investigate these scenarios numerically. Imposing the initial conditions on the modes in the contracting phase, we numerically evolve the modes across the bounce and eva...

  8. Practical methods for generating alternating magnetic fields for biomedical research

    Science.gov (United States)

    Christiansen, Michael G.; Howe, Christina M.; Bono, David C.; Perreault, David J.; Anikeeva, Polina

    2017-08-01

    Alternating magnetic fields (AMFs) cause magnetic nanoparticles (MNPs) to dissipate heat while leaving surrounding tissue unharmed, a mechanism that serves as the basis for a variety of emerging biomedical technologies. Unfortunately, the challenges and costs of developing experimental setups commonly used to produce AMFs with suitable field amplitudes and frequencies present a barrier to researchers. This paper first presents a simple, cost-effective, and robust alternative for small AMF working volumes that uses soft ferromagnetic cores to focus the flux into a gap. As the experimental length scale increases to accommodate animal models (working volumes of 100s of cm3 or greater), poor thermal conductivity and volumetrically scaled core losses render that strategy ineffective. Comparatively feasible strategies for these larger volumes instead use low loss resonant tank circuits to generate circulating currents of 1 kA or greater in order to produce the comparable field amplitudes. These principles can be extended to the problem of identifying practical routes for scaling AMF setups to humans, an infrequently acknowledged challenge that influences the extent to which many applications of MNPs may ever become clinically relevant.

  9. Identification by force modulation microscopy of nanoparticles generated in vacuum arcs Identification by force modulation microscopy of nanoparticles generated in vacuum arcs

    Directory of Open Access Journals (Sweden)

    M. Arroyave Franco

    2006-06-01

    Full Text Available An alternative method based on force modulation microscopy (FMM for identification of nanoparticles produced in the plasma generated by the cathode spots of vacuum arcs is presented. FMM technique is enabled for the detection of variations in the mechanical properties of a surface with high sensitiveness. Titanium nitride (TiN coatings deposited on oriented silicon by pulsed vacuum arc process have been analyzed. AFM (Atomic Force Microscopy and FMM images were simultaneously obtained, and in all cases it was possible to identify nanoparticle presence. Further X-ray Diffraction spectra of sample coating were taken. Existence of contaminant particles of 47 nanometers in diameter was reported.En este trabajo se presenta un método alternativo basado en microscopia de modulación de fuerza (FMM, para la identificación de nanogotas producidas en el plasma generado por los spots catódicos de los arcos en vacío. La técnica FMM esta habilitada para la detección de variaciones en las propiedades mecánicas de una superficie, con alta sensibilidad. Se han analizado recubrimientos de nitruro de titanio (TiN depositados sobre Silicio orientado por el proceso de arco en vacío pulsado. Se han obtenido simultáneamente imágenes de microscopia de fuerza atómica (AFM y de microscopia FMM mediante las cuales se ha podido identificar la presencia de nanogotas. Adicionalmente se han tomado espectros de difracción de rayos X (XRD de las muestras recubiertas. Se ha reportado la existencia de partículas contaminantes de 47 nanómetros de diámetro sobre los recubrimientos.

  10. Optimizations of force-field parameters for protein systems with the secondary-structure stability and instability

    CERN Document Server

    Sakae, Yoshitake

    2013-01-01

    We propose a novel method for refining force-field parameters of protein systems. In this method, the agreement of the secondary-structure stability and instability between the protein conformations obtained by experiments and those obtained by molecular dynamics simulations is used as a criterion for the optimization of force-field parameters. As an example of the applications of the present method, we refined the force-field parameter set of the AMBER ff99SB force field by searching the torsion-energy parameter spaces of $\\psi$ (N-C$^{\\alpha}$-C-N) and $\\zeta$ (C$^{\\beta}$-C$^{\\alpha}$-C-N) of the backbone dihedral angles. We then performed folding simulations of $\\alpha$-helical and $\\beta$-hairpin peptides, using the optimized force field. The results showed that the new force-field parameters gave structures more consistent with the experimental implications than the original AMBER ff99SB force field.

  11. Physical Limitations of Empirical Field Models: Force Balance and Plasma Pressure

    Energy Technology Data Exchange (ETDEWEB)

    Sorin Zaharia; C.Z. Cheng

    2002-06-18

    In this paper, we study whether the magnetic field of the T96 empirical model can be in force balance with an isotropic plasma pressure distribution. Using the field of T96, we obtain values for the pressure P by solving a Poisson-type equation {del}{sup 2}P = {del} {center_dot} (J x B) in the equatorial plane, and 1-D profiles on the Sun-Earth axis by integrating {del}P = J x B. We work in a flux coordinate system in which the magnetic field is expressed in terms of Euler potentials. Our results lead to the conclusion that the T96 model field cannot be in equilibrium with an isotropic pressure. We also analyze in detail the computation of Birkeland currents using the Vasyliunas relation and the T96 field, which yields unphysical results, again indicating the lack of force balance in the empirical model. The underlying reason for the force imbalance is likely the fact that the derivatives of the least-square fitted model B are not accurate predictions of the actual magnetospheric field derivatives. Finally, we discuss a possible solution to the problem of lack of force balance in empirical field models.

  12. Relationship between the magnetic field distribution and attractive force of single domain YBCO bulk under different field cooling processes

    Institute of Scientific and Technical Information of China (English)

    Yang Wan-Min; Zhou Lian; Feng Yong; Zhang Ping-Xiang; R. Nicolsky

    2004-01-01

    The levitation forces under different field cooling states were measured at 77K by changing the field cooling distance 0Zfc between a YBCO bulk and a permanent magnet. It is found that the relationship between the absolute maximum attractive force (Fmaf) and the corresponding gap distance (Zmaf) to Fmaf can be well described by exponential laws as a function of Zfc, which allow us to predict these values according to Zfc. It is also found that the distance between the Z0fa (gap distance corresponding to the zero force) and Zmaf in the ascending process is a constant value, which is closely related to the constant reduction factor of the axial component of flux density along the axial line of the magnet if Zmaf - Z0fa is a constant value. These results are very interesting for fundamental research and helpful in practical designing and applications.

  13. Generation of antitropic electron beams by self-generated electric field. Kinetic description

    CERN Document Server

    Stepanov, N S

    2016-01-01

    This paper makes use of a one-dimensional kinetic model to investigate the nonlinear longitudinal dynamics of electron beams generated in the plasma under the influence of a self-generated electric field. It is expressed as where is a wave potential, , and charge particle distribution functions satisfy the Vlasov equation. It is proved that its correct solution is characterized by sudden change in the resonant part of the distribution function. Hence, in particular, the incorrectness of the established in the literature point of view follows that the fast, with velocities over V, and slow, with velocities under V, trapped particles are described by the same distribution function. Also for the first time it is shown that the self-generated strong electric field always produces antitropic electron beams with the velocities much larger than the value V, including the cold plasma limit. The possibility of implementing a new class of self-consistent wave structures with a nonzero average potential is shown. Maximu...

  14. Magnetic Helicity of Self-Similar Axisymmetric Force-free Fields

    CERN Document Server

    Zhang, Mei; Low, Boon Chye

    2012-01-01

    In this paper we continue our theoretical studies on addressing what are the possible consequences of magnetic helicity accumulation in the solar corona. Our previous studies suggest that coronal mass ejections (CMEs) are natural products of coronal evolution as a consequence of magnetic helicity accumulation and the triggering of CMEs by surface processes such as flux emergence also have their origin in magnetic helicity accumulation. Here we use the same mathematical approach to study the magnetic helicity of axisymmetric power-law force-free fields, but focus on a family whose surface flux distributions are defined by self-similar force-free fields. The semi-analytical solutions of the axisymmetric self-similar force-free fields enable us to discuss the properties of force-free fields possessing a huge amount of accumulated magnetic helicity. Our study suggests that there may be an absolute upper bound on the total magnetic helicity of all bipolar axisymmetric force-free fields. And with the increase of ac...

  15. Ionic force field optimization based on single-ion and ion-pair solvation properties

    CERN Document Server

    Fyta, Maria; Dzubiella, Joachim; Vrbka, Lubos; Netz, Roland R

    2009-01-01

    Molecular dynamics simulations of ionic solutions depend sensitively on the force fields employed for the ions. To resolve the fine differences between ions of the same valence and roughly similar size and in particular to correctly describe ion-specific effects, it is clear that accurate force fields are necessary. In the past, optimization strategies for ionic force fields either considered single-ion properties (such as the solvation free energy at infinite dilution or the ion-water structure) or ion-pair properties (in the form of ion-ion distribution functions). In this paper we investigate strategies to optimize ionic force fields based on single-ion and ion-pair properties simultaneously. To that end, we simulate five different salt solutions, namely CsCl, KCl, NaI, KF, and CsI, at finite ion concentration. The force fields of these ions are systematically varied under the constraint that the single-ion solvation free energy matches the experimental value, which reduces the two-dimensional $\\{\\sigma,\\e...

  16. Parameterization and optimization of the menthol force field for molecular dynamics simulations.

    Science.gov (United States)

    Jasik, Mateusz; Szefczyk, Borys

    2016-10-01

    Menthol's various biological properties render it a useful component for medical and cosmetological applications, while its three centers of asymmetry mean that it can be used in a range of organic reactions. Menthol-substituted ionic liquids (ILs) have been found to exhibit promising antimicrobial and antielectrostatic properties, as well as being useful in organic catalysis and biochemical studies. However, so far, a force field designed and validated specifically for the menthol molecule has not been constructed. In the present work, the validation and optimization of force field parameters with regard to the ability to reproduce the macroscopic properties of menthol is presented. The set of optimized potentials for liquid simulations all atom (OPLS-AA) compatible parameters was tested and carefully tuned. The refinement of parameters included fitting of partial atomic charges, optimization of Lennard-Jones parameters, and recalculation of the dihedral angle parameters needed to reproduce quantum energy profiles. To validate the force field, a variety of physicochemical properties were calculated for liquid menthol. Both thermodynamic and kinetic properties were taken into account, including density, surface tension, enthalpy of vaporization, and shear viscosity. The obtained force field was proven to accurately reproduce the properties of the investigated compound while being fully compatible with the OPLS-AA force field.

  17. Force-field parameterization of the galactic cosmic ray spectrum: Validation for Forbush decreases

    Science.gov (United States)

    Usoskin, I. G.; Kovaltsov, G. A.; Adriani, O.; Barbarino, G. C.; Bazilevskaya, G. A.; Bellotti, R.; Boezio, M.; Bogomolov, E. A.; Bongi, M.; Bonvicini, V.; Bottai, S.; Bruno, A.; Cafagna, F.; Campana, D.; Carbone, R.; Carlson, P.; Casolino, M.; Castellini, G.; De Donato, C.; De Santis, C.; De Simone, N.; Di Felice, V.; Formato, V.; Galper, A. M.; Karelin, A. V.; Koldashov, S. V.; Koldobskiy, S.; Krutkov, S. Y.; Kvashnin, A. N.; Leonov, A.; Malakhov, V.; Marcelli, L.; Martucci, M.; Mayorov, A. G.; Menn, W.; Mergé, M.; Mikhailov, V. V.; Mocchiutti, E.; Monaco, A.; Mori, N.; Munini, R.; Osteria, G.; Palma, F.; Panico, B.; Papini, P.; Pearce, M.; Picozza, P.; Pizzolotto, C.; Ricci, M.; Ricciarini, S. B.; Rossetto, L.; Sarkar, R.; Scotti, V.; Simon, M.; Sparvoli, R.; Spillantini, P.; Stozhkov, Y. I.; Vacchi, A.; Vannuccini, E.; Vasilyev, G. I.; Voronov, S. A.; Yurkin, Y. T.; Zampa, G.; Zampa, N.; Zverev, V. G.

    2015-06-01

    A useful parametrization of the energy spectrum of galactic cosmic rays (GCR) near Earth is offered by the so-called force-field model which describes the shape of the entire spectrum with a single parameter, the modulation potential. While the usefulness of the force-field approximation has been confirmed for regular periods of solar modulation, it was not tested explicitly for disturbed periods, when GCR are locally modulated by strong interplanetary transients. Here we use direct measurements of protons and α -particles performed by the PAMELA space-borne instrument during December 2006, including a major Forbush decrease, in order to directly test the validity of the force-field parameterization. We conclude that (1) The force-field parametrization works very well in describing the energy spectra of protons and α -particles directly measured by PAMELA outside the Earths atmosphere; (2) The energy spectrum of GCR can be well parameterized by the force-field model also during a strong Forbush decrease; (3) The estimate of the GCR modulation parameter, obtained using data from the world-wide neutron monitor network, is in good agreement with the spectra directly measured by PAMELA during the studied interval. This result is obtained on the basis of a single event analysis, more events need to be analyzed.

  18. First-Principles, Physically Motivated Force Field for the Ionic Liquid [BMIM][BF4].

    Science.gov (United States)

    Choi, Eunsong; McDaniel, Jesse G; Schmidt, J R; Yethiraj, Arun

    2014-08-07

    Molecular simulations play an important role in establishing structure-property relations in complex fluids such as room-temperature ionic liquids. Classical force fields are the starting point when large systems or long times are of interest. These force fields must be not only accurate but also transferable. In this work, we report a physically motivated force field for the ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]) based on symmetry-adapted perturbation theory. The predictions (from molecular dynamics simulations) of the liquid density, enthalpy of vaporization, diffusion coefficients, viscosity, and conductivity are in excellent agreement with experiment, with no adjustable parameters. The explicit energy decomposition inherent in the force field enables a quantitative analysis of the important physical interactions in these systems. We find that polarization is crucial and there is little evidence of charge transfer. We also argue that the often used procedure of scaling down charges in molecular simulations of ionic liquids is unphysical for [BMIM][BF4]. Because all intermolecular interactions in the force field are parametrized from first-principles, we anticipate good transferability to other ionic liquid systems and physical conditions.

  19. The effects of substrate elasticity on endothelial cell network formation and traction force generation.

    Science.gov (United States)

    Califano, Joseph P; Reinhart-King, Cynthia A

    2009-01-01

    While the growth factors and cytokines known to influence angiogenesis and vasculogenesis have garnered widespread attention, less is known about how the mechanical environment affects blood vessel formation and cell assembly. In this study, we investigate the relationship between substrate elasticity, endothelial cell-cell connectivity and traction force generation. We find that on more compliant substrates, endothelial cells self-assemble into network-like structures independently of additional exogenous growth factors or cytokines. These networks form from the assembly of sub-confluent endothelial cells on compliant (E = 200-1000Pa) substrates, and results from both the proliferation and migration of endothelial cells. Interestingly, stabilization of these cell-cell connections and networks requires fibronectin polymerization. Traction Force Microscopy measurements indicate that individual endothelial cells on compliant substrates exert forces which create substrate stains that propagate from the cell edge. We speculate that these strains draw the cells together and initiate self-assembly. Notably, endothelial cell network formation on compliant substrates is dynamic and transient; as cell number and substrate strains increase, the networks fill in through collective cell movements from the network edges. Our results indicate that network formation is mediated in part by substrate mechanics and that cellular traction force may promote cell-cell assembly by directing cell migration.

  20. Optothermally responsive nanocomposite generating mechanical forces for cells enabled by few-walled carbon nanotubes.

    Science.gov (United States)

    Zeng, Yuze; Lu, Jennifer Q

    2014-11-25

    We have designed and fabricated a nanocomposite substrate that can deliver spatially and temporally defined mechanical forces onto cells. This nanocomposite substrate comprises a 1.5-mm-thick near-infrared (NIR) mechanoresponsive bottom layer of few-walled carbon nanotubes (FWCNTs) that are uniformly distributed and covalently connected to thermally responsive poly(N-isopropylacrylamide) and an approximately 0.15-mm-thick cell-seeding top layer of collagen-functionalized poly(acrylic acid)-co-poly(N-isopropylacrylamide) that interpenetrates into the bottom layer. Covalent coupling of all the components and uniform distribution of FWCNTs lead to a large local mechanoresponse. As an example, 50% change in strain at the point of irradiation on the order of 0.05 Hz can be produced reversibly under NIR stimulation with 0.02 wt % FWCNTs. We have further demonstrated that the mechanical strain imposed by NIR stimulation can be transmitted onto cells. Human fetal hepatocytes change shape with no sign of detrimental effect on cell viability. To the best of our knowledge, this is the first demonstration of a nanocomposite platform that can generate fast and controlled mechanical force to actuate cells. Since the amplitude, location, and timing of force can be controlled remotely with NIR, the nanocomposite substrate offers the potential to provide accurately designed force sequences for tissue engineering.

  1. The Sensitivity of Simulated Ocean Biogeochemistry to Forcing Fields Derived from NCEP and MERRA Reanalysis Products

    Science.gov (United States)

    Gregg, Watson; Casey, Nancy

    2010-01-01

    Ocean biogeochemistry models are typically forced by atmospheric and oceanic data derived from reanalysis products. For the NASA Ocean Biogeochemistry Model (NOBM) such reanalysis forcing fields include: surface wind stress, sea surface temperature, ice distributions, shortwave radiation, surface wind speeds and surface atmospheric pressure. Additionally, proper computation of ocean irradiance requires reanalysis products of relative humidity and precipitable water (in addition to aerosol and cloud information which is derived from satellite data). The question posed here is, does the choice of reanalysis products make a difference in the representation of ocean biology and biogeochemistry? NOBM was forced by NCEP and MERRA reanalysis products for the period 2002-2009. We find that in 2009 global distributions and abundances of biological variables (total chlorophyll and nutrients) and carbon (dissolved inorganic and organic carbon and surface pCO2) were similar between the two different forcing fields. Global statistical comparisons with satellite and in situ data also showed negligible differences.

  2. Significance of self magnetic field in long-distance collimation of laser-generated electron beams

    CERN Document Server

    Chen, Shi; Niu, Yifei; Dan, Jiakun; Chen, Ziyu; Li, Jianfeng

    2014-01-01

    Long-distance collimation of fast electron beams generated by laser-metallic-wire targets has been observed in recent experiments, while the mechanism behind this phenomenon remains unclear. In this work, we investigate in detail the laser-wire interaction processes with a simplified model and Classical Trajectory Monte Carlo simulations, and demonstrate the significance of the self magnetic fields of the beams in the long-distance collimation. Good agreements of simulated image plate patterns with various experiments and detailed analysis of electron trajectories show that the self magnetic fields provide restoring force that is critical for the beam collimation. By studying the wire-length dependence of beam divergence in certain experiments, we clarify that the role of the metallic wire is to balance the space-charge effect and thus maintain the collimation.

  3. Quantum Field Theory Tools:. a Mechanism of Mass Generation of Gauge Fields

    Science.gov (United States)

    Flores-Baez, F. V.; Godina-Nava, J. J.; Ordaz-Hernandez, G.

    We present a simple mechanism for mass generation of gauge fields for the Yang-Mills theory, where two gauge SU(N)-connections are introduced to incorporate the mass term. Variations of these two sets of gauge fields compensate each other under local gauge transformations with the local gauge transformations of the matter fields, preserving gauge invariance. In this way the mass term of gauge fields is introduced without violating the local gauge symmetry of the Lagrangian. Because the Lagrangian has strict local gauge symmetry, the model is a renormalizable quantum model. This model, in the appropriate limit, comes from a class of universal Lagrangians which define a new massive Yang-Mills theories without Higgs bosons.

  4. First use of synoptic vector magnetograms for global nonlinear force free coronal magnetic field models

    CERN Document Server

    Tadesse, Tilaye; Gosain, S; MacNeice, P; Pevtsov, Alexei A

    2013-01-01

    The magnetic field permeating the solar atmosphere is generally thought to provide the energy for much of the activity seen in the solar corona, such as flares, coronal mass ejections (CMEs), etc. To overcome the unavailability of coronal magnetic field measurements, photospheric magnetic field vector data can be used to reconstruct the coronal field. Currently there are several modelling techniques being used to calculate three-dimension of the field lines into the solar atmosphere. For the first time, synoptic maps of photospheric vector magnetic field synthesized from Vector Spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) are used to model the coronal magnetic field and estimate free magnetic energy in the global scale. The free energy (i.e., the energy in excess of the potential field energy) is one of the main indicators used in space weather forecasts to predict the eruptivity of active regions. We solve the nonlinear force-free field equations using optimizatio...

  5. Mutability of bifunctional thigh muscle activity in pedaling due to contralateral leg force generation.

    Science.gov (United States)

    Kautz, S A; Brown, D A; Van der Loos, H F M; Zajac, F E

    2002-09-01

    other transition (i.e., flexion-to-extension; predominantly by rectus femoris), hamstrings activity and work output increased in the pedaling leg during its extension-to-flexion transition. Therefore rhythmic isometric force generation in the contralateral leg supported the ongoing bifunctional muscle activity and resulting work output in the pedaling leg. The results suggest that neural interlimb coordinating mechanisms fine-tune bifunctional muscle activity in rhythmic lower-limb tasks to ensure limb flexion/extension transitions are executed successfully.

  6. Hair cell force generation does not amplify or tune vibrations within the chicken basilar papilla.

    Science.gov (United States)

    Xia, Anping; Liu, Xiaofang; Raphael, Patrick D; Applegate, Brian E; Oghalai, John S

    2016-10-31

    Frequency tuning within the auditory papilla of most non-mammalian species is electrical, deriving from ion-channel resonance within their sensory hair cells. In contrast, tuning within the mammalian cochlea is mechanical, stemming from active mechanisms within outer hair cells that amplify the basilar membrane travelling wave. Interestingly, hair cells in the avian basilar papilla demonstrate both electrical resonance and force-generation, making it unclear which mechanism creates sharp frequency tuning. Here, we measured sound-induced vibrations within the apical half of the chicken basilar papilla in vivo and found broadly-tuned travelling waves that were not amplified. However, distortion products were found in live but not dead chickens. These findings support the idea that avian hair cells do produce force, but that their effects on vibration are small and do not sharpen tuning. Therefore, frequency tuning within the apical avian basilar papilla is not mechanical, and likely derives from hair cell electrical resonance.

  7. Diffusion-controlled generation of a proton-motive force across a biomembrane

    CERN Document Server

    Smirnov, Anatoly Yu; Nori, Franco

    2009-01-01

    Respiration in bacteria involves a sequence of energetically-coupled electron and proton transfers creating an electrochemical gradient of protons (a proton-motive force) across the inner bacterial membrane. With a simple kinetic model we analyze a redox loop mechanism of proton-motive force generation mediated by a molecular shuttle diffusing inside the membrane. This model, which includes six electron-binding and two proton-binding sites, reflects the main features of nitrate respiration in E. coli bacteria. We describe the time evolution of the proton translocation process. We find that the electron-proton electrostatic coupling on the shuttle plays a significant role in the process of energy conversion between electron and proton components. We determine the conditions where the redox loop mechanism is able to translocate protons against the transmembrane voltage gradient above 200 mV with a thermodynamic efficiency of about 37%, in the physiologically important range of temperatures from 250 to 350 K.

  8. Free energy simulations with the AMOEBA polarizable force field and metadynamics on GPU platform.

    Science.gov (United States)

    Peng, Xiangda; Zhang, Yuebin; Chu, Huiying; Li, Guohui

    2016-03-05

    The free energy calculation library PLUMED has been incorporated into the OpenMM simulation toolkit, with the purpose to perform enhanced sampling MD simulations using the AMOEBA polarizable force field on GPU platform. Two examples, (I) the free energy profile of water pair separation (II) alanine dipeptide dihedral angle free energy surface in explicit solvent, are provided here to demonstrate the accuracy and efficiency of our implementation. The converged free energy profiles could be obtained within an affordable MD simulation time when the AMOEBA polarizable force field is employed. Moreover, the free energy surfaces estimated using the AMOEBA polarizable force field are in agreement with those calculated from experimental data and ab initio methods. Hence, the implementation in this work is reliable and would be utilized to study more complicated biological phenomena in both an accurate and efficient way. © 2015 Wiley Periodicals, Inc.

  9. Fusing heterogeneous data for the calibration of molecular dynamics force fields using hierarchical Bayesian models.

    Science.gov (United States)

    Wu, Stephen; Angelikopoulos, Panagiotis; Tauriello, Gerardo; Papadimitriou, Costas; Koumoutsakos, Petros

    2016-12-28

    We propose a hierarchical Bayesian framework to systematically integrate heterogeneous data for the calibration of force fields in Molecular Dynamics (MD) simulations. Our approach enables the fusion of diverse experimental data sets of the physico-chemical properties of a system at different thermodynamic conditions. We demonstrate the value of this framework for the robust calibration of MD force-fields for water using experimental data of its diffusivity, radial distribution function, and density. In order to address the high computational cost associated with the hierarchical Bayesian models, we develop a novel surrogate model based on the empirical interpolation method. Further computational savings are achieved by implementing a highly parallel transitional Markov chain Monte Carlo technique. The present method bypasses possible subjective weightings of the experimental data in identifying MD force-field parameters.

  10. Measurement of interaction force between small distances sandwiched with magnetic fluid under magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Miyazaki, T.; Shibayama, A.; Sato, T.; Fujita, T. E-mail: fujita@ipc.akita-u.ac.jp

    2002-11-01

    In this contribution, the interactive force measurement between 10 nm distance under magnetic field is carried out. Previous measurement of the interactive force is reported by Israelachivili et al. However, its measurement under magnetic field has not been performed. The methodology described in this paper is easier as the distance between two surfaces is not measured optically but dynamically. Therefore, it is different from the previous reported studies. Based on the results of the measurement of the interactive force, the diameter of the particle suspended in a solution under magnetic field is also estimated. Moreover, it may be predictable how the clusters have been formed. The method described will be very useful for new productions based on magnetic fluid.

  11. Toward Improved Force-Field Accuracy through Sensitivity Analysis of Host-Guest Binding Thermodynamics.

    Science.gov (United States)

    Yin, Jian; Fenley, Andrew T; Henriksen, Niel M; Gilson, Michael K

    2015-08-13

    Improving the capability of atomistic computer models to predict the thermodynamics of noncovalent binding is critical for successful structure-based drug design, and the accuracy of such calculations remains limited by nonoptimal force field parameters. Ideally, one would incorporate protein-ligand affinity data into force field parametrization, but this would be inefficient and costly. We now demonstrate that sensitivity analysis can be used to efficiently tune Lennard-Jones parameters of aqueous host-guest systems for increasingly accurate calculations of binding enthalpy. These results highlight the promise of a comprehensive use of calorimetric host-guest binding data, along with existing validation data sets, to improve force field parameters for the simulation of noncovalent binding, with the ultimate goal of making protein-ligand modeling more accurate and hence speeding drug discovery.

  12. Determination of Quantum Chemistry Based Force Fields for Molecular Dynamics Simulations of Aromatic Polymers

    Science.gov (United States)

    Jaffe, Richard; Langhoff, Stephen R. (Technical Monitor)

    1995-01-01

    Ab initio quantum chemistry calculations for model molecules can be used to parameterize force fields for molecular dynamics simulations of polymers. Emphasis in our research group is on using quantum chemistry-based force fields for molecular dynamics simulations of organic polymers in the melt and glassy states, but the methodology is applicable to simulations of small molecules, multicomponent systems and solutions. Special attention is paid to deriving reliable descriptions of the non-bonded and electrostatic interactions. Several procedures have been developed for deriving and calibrating these parameters. Our force fields for aromatic polyimide simulations will be described. In this application, the intermolecular interactions are the critical factor in determining many properties of the polymer (including its color).

  13. Modification of 56ACARBO force field for molecular dynamic calculations of chitosan and its derivatives.

    Science.gov (United States)

    Naumov, Vladimir S; Ignatov, Stanislav K

    2017-08-01

    The GROMOS 56ACARBO force field for the description of carbohydrates was modified for calculations of chitosan (poly-1,4-(N-acetyl)-β-D-glucopyranosamine-2) with protonated and non-protonated amino groups and its derivatives. Additional parameterization was developed on the basis of quantum chemical calculations. The modified force field (56ACARBO_CHT) allows performing the molecular dynamic calculations of chitosans with different degrees of protonation corresponding to various acidity of medium. Test calculations of the conformational transitions in the chitosan rings and polymeric chains as well as the chitosan nanocrystal dissolution demonstrate good agreement with experimental data. Graphical abstract The GROMOS 56ACARBO_CHT force field allows performing the molecular dynamic calculations of chitosans with different types of amio-group: free, protonated, substituted.

  14. Magnetic Field, Force, and Inductance Computations for an Axially Symmetric Solenoid

    Science.gov (United States)

    Lane, John E.; Youngquist, Robert C.; Immer, Christopher D.; Simpson, James C.

    2001-01-01

    The pumping of liquid oxygen (LOX) by magnetic fields (B field), using an array of electromagnets, is a current topic of research and development at Kennedy Space Center, FL. Oxygen is paramagnetic so that LOX, like a ferrofluid, can be forced in the direction of a B field gradient. It is well known that liquid oxygen has a sufficient magnetic susceptibility that a strong magnetic gradient can lift it in the earth's gravitational field. It has been proposed that this phenomenon can be utilized in transporting (i.e., pumping) LOX not only on earth, but on Mars and in the weightlessness of space. In order to design and evaluate such a magnetic pumping system, it is essential to compute the magnetic and force fields, as well as inductance, of various types of electromagnets (solenoids). In this application, it is assumed that the solenoids are air wrapped, and that the current is essentially time independent.

  15. Two-Phase Flow Field Simulation of Horizontal Steam Generators

    Directory of Open Access Journals (Sweden)

    Ataollah Rabiee

    2017-02-01

    Full Text Available The analysis of steam generators as an interface between primary and secondary circuits in light water nuclear power plants is crucial in terms of safety and design issues. VVER-1000 nuclear power plants use horizontal steam generators which demand a detailed thermal hydraulics investigation in order to predict their behavior during normal and transient operational conditions. Two phase flow field simulation on adjacent tube bundles is important in obtaining logical numerical results. However, the complexity of the tube bundles, due to geometry and arrangement, makes it complicated. Employment of porous media is suggested to simplify numerical modeling. This study presents the use of porous media to simulate the tube bundles within a general-purpose computational fluid dynamics code. Solved governing equations are generalized phase continuity, momentum, and energy equations. Boundary conditions, as one of the main challenges in this numerical analysis, are optimized. The model has been verified and tuned by simple two-dimensional geometry. It is shown that the obtained vapor volume fraction near the cold and hot collectors predict the experimental results more accurately than in previous studies.

  16. Altered Smooth Muscle Cell Force Generation as a Driver of Thoracic Aortic Aneurysms and Dissections.

    Science.gov (United States)

    Milewicz, Dianna M; Trybus, Kathleen M; Guo, Dong-Chuan; Sweeney, H Lee; Regalado, Ellen; Kamm, Kristine; Stull, James T

    2017-01-01

    The importance of maintaining contractile function in aortic smooth muscle cells (SMCs) is evident by the fact that heterozygous mutations in the major structural proteins or kinases controlling contraction lead to the formation of aneurysms of the ascending thoracic aorta that predispose to life-threatening aortic dissections. Force generation by SMC requires ATP-dependent cyclic interactions between filaments composed of SMC-specific isoforms of α-actin (encoded by ACTA2) and myosin heavy chain (MYH11). ACTA2 and MYH11 mutations are predicted or have been shown to disrupt this cyclic interaction predispose to thoracic aortic disease. Movement of the myosin motor domain is controlled by phosphorylation of the regulatory light chain on the myosin filament, and loss-of-function mutations in the dedicated kinase for this phosphorylation, myosin light chain kinase (MYLK) also predispose to thoracic aortic disease. Finally, a mutation in the cGMP-activated protein kinase (PRKG1) results in constitutive activation of the kinase in the absence of cGMP, thus driving SMC relaxation in part through increased dephosphorylation of the regulatory light chain and predisposes to thoracic aortic disease. Furthermore, SMCs cannot generate force without connections to the extracellular matrix through focal adhesions, and mutations in the major protein in the extracellular matrix, fibrillin-1, linking SMCs to the matrix also cause thoracic aortic disease in individuals with Marfan syndrome. Thus, disruption of the ability of the aortic SMC to generate force through the elastin-contractile units in response to pulsatile blood flow may be a primary driver for thoracic aortic aneurysms and dissections.

  17. IM-UFF: Extending the universal force field for interactive molecular modeling.

    Science.gov (United States)

    Jaillet, Léonard; Artemova, Svetlana; Redon, Stephane

    2017-09-05

    The universal force field (UFF) is a broadly applicable classical force field that contains parameters for almost every atom type of the periodic table. This force field is non-reactive, i.e. the topology of the system under study is considered as fixed and no creation or breaking of covalent bonds is possible. This paper introduces interactive modeling-UFF (IM-UFF), an extension of UFF that combines the possibility to significantly modify molecular structures (as with reactive force fields) with a broad diversity of supported systems thanks to the universality of UFF. Such an extension lets the user easily build and edit molecular systems interactively while being guided by physics based inter-atomic forces. This approach introduces weighted atom types and weighted bonds, used to update topologies and atom parameterizations at every time step of a simulation. IM-UFF has been evaluated on a large set of benchmarks and is proposed as a self-contained implementation integrated in a new module for the SAMSON software platform for computational nanoscience available at http://www.samson-connect.net. Copyright © 2017 Elsevier Inc. All rights reserved.

  18. Automation of the CHARMM General Force Field (CGenFF) I: bond perception and atom typing

    Science.gov (United States)

    Vanommeslaeghe, K.; MacKerell, A. D.

    2012-01-01

    Molecular mechanics force fields are widely used in computer-aided drug design for the study of drug-like molecules alone or interacting with biological systems. In simulations involving biological macromolecules, the biological part is typically represented by a specialized biomolecular force field, while the drug is represented by a matching general (organic) force field. In order to apply these general force fields to an arbitrary drug-like molecule, functionality for assignment of atom types, parameters and charges is required. In the present article, which is part I of a series of two, we present the algorithms for bond perception and atom typing for the CHARMM General Force Field (CGenFF). The CGenFF atom typer first associates attributes to the atoms and bonds in a molecule, such as valence, bond order, and ring membership among others. Of note are a number of features that are specifically required for CGenFF. This information is then used by the atom typing routine to assign CGenFF atom types based on a programmable decision tree. This allows for straightforward implementation of CGenFF’s complicated atom typing rules and for equally straightforward updating of the atom typing scheme as the force field grows. The presented atom typer was validated by assigning correct atom types on 477 model compounds including in the training set as well as 126 test-set molecules that were constructed to specifically verify its different components. The program may be utilized via an online implementation at https://www.paramchem.org/. PMID:23146088

  19. Automation of the CHARMM General Force Field (CGenFF) I: bond perception and atom typing.

    Science.gov (United States)

    Vanommeslaeghe, K; MacKerell, A D

    2012-12-21

    Molecular mechanics force fields are widely used in computer-aided drug design for the study of drug-like molecules alone or interacting with biological systems. In simulations involving biological macromolecules, the biological part is typically represented by a specialized biomolecular force field, while the drug is represented by a matching general (organic) force field. In order to apply these general force fields to an arbitrary drug-like molecule, functionality for assignment of atom types, parameters, and charges is required. In the present article, which is part I of a series of two, we present the algorithms for bond perception and atom typing for the CHARMM General Force Field (CGenFF). The CGenFF atom typer first associates attributes to the atoms and bonds in a molecule, such as valence, bond order, and ring membership among others. Of note are a number of features that are specifically required for CGenFF. This information is then used by the atom typing routine to assign CGenFF atom types based on a programmable decision tree. This allows for straightforward implementation of CGenFF's complicated atom typing rules and for equally straightforward updating of the atom typing scheme as the force field grows. The presented atom typer was validated by assigning correct atom types on 477 model compounds including in the training set as well as 126 test-set molecules that were constructed to specifically verify its different components. The program may be utilized via an online implementation at https://www.paramchem.org/ .

  20. Electromagnetic field generation by ATP-induced reverse electron transfer.

    Science.gov (United States)

    Steele, Richard H

    2003-03-01

    This paper describes a mechanism to explain low-level light emission in biology. A biological analog of the electrical circuitry, modeled on the parallel plate capacitor, traversed by a helical structure, required to generate electromagnetic radiation in the optical spectral range, is described. The charge carrier required for the emissions is determined to be an accelerating electron driven by an ATP-induced reverse electron transfer. The radial velocity component, the emission trajectory, of the moving charges traversing helical protein structures in a cyclotron-type mechanism is proposed to be imposed by the ferromagnetic field components of the iron in the iron-sulfur proteins. The redox systems NADH, riboflavin, and chlorophyll were examined with their long-wavelength absorption maxima determining the energetic parameters for the calculations. Potentials calculated from the axial velocity components for the riboflavin and NADH systems were found to equal the standard redox potentials of these systems as measured electrochemically and enzymatically. The mechanics for the three systems determined the magnetic moments, the angular momenta, and the orbital magnetic fluxes to be adiabatic invariant parameters. The De Broglie dual wave-particle equation, the fundamental equation of wave mechanics, and the key idea of quantum mechanics, establishes the wavelengths for accelerating electrons which, divided into a given radial velocity, gives its respective emission frequency. Electrons propelled through helical structures, traversed by biologically available electric and magnetic fields, make accessible to the internal environment the optical spectral frequency range that the solar spectrum provides to the external environment.

  1. Prediction of adsorption of small molecules in porous materials based on ab initio force field method

    Institute of Scientific and Technical Information of China (English)

    2008-01-01

    Computational prediction of adsorption of small molecules in porous materials has great impact on the basic and applied research in chemical engineering and material sciences. In this work,we report an approach based on grand canonical ensemble Monte Carlo(GCMC) simulations and ab initio force fields. We calculated the adsorption curves of ammonia in ZSM-5 zeolite and hydrogen in MOF-5(a metal-organic-framework material). The predictions agree well with experimental data. Because the predictions are based on the first principle force fields,this approach can be used for the adsorption prediction of new molecules or materials without experimental data as guidance.

  2. The force density and the kinetic energy-momentum tensor of electromagnetic fields in matter

    CERN Document Server

    Medina, Rodrigo

    2014-01-01

    We determine the invariant expression for the force density that the electromagnetic field exerts on dipolar matter. We construct the non-symmetric energy-momentum tensor of the electromagnetic field in matter which is consistent with that force and with Maxwell equations. We recover Minkowski's expression for the momentum density. We use our results to discuss momentum exchange of an electromagnetic wave-packet which falls into a dielectric block. In particular we show that the wave-packet pulls the block when it enters and drags it when it leaves.

  3. Parametrization of a Reactive Force Field (ReaxFF) for Molecular Dynamics Simulations of Si Nanoparticles.

    Science.gov (United States)

    Barcaro, Giovanni; Monti, Susanna; Sementa, Luca; Carravetta, Vincenzo

    2017-08-08

    A novel computational approach, based on classical reactive molecular dynamics simulations (RMD) and quantum chemistry (QC) global energy optimizations, is proposed for modeling large Si nanoparticles. The force field parameters, which can describe bond breaking and formation, are derived by reproducing energetic and structural properties of a set of Si clusters increasing in size. These reference models are obtained through a new protocol based on a joint high temperature RMD/low temperature Basin Hopping QC search. The different procedures of estimating optimal force field parameters and their performance are discussed in detail.

  4. The acoustic force density acting on inhomogeneous fluids in acoustic fields

    CERN Document Server

    Karlsen, Jonas T; Bruus, Henrik

    2016-01-01

    We present a theory for the acoustic force density acting on inhomogeneous fluids in acoustic fields on time scales that are slow compared to the acoustic oscillation period. The acoustic force density depends on gradients in the density and compressibility of the fluid. For microfluidic systems, the theory predicts a relocation of the inhomogeneities into stable field-dependent configurations, which are qualitatively different from the horizontally layered configurations due to gravity. Experimental validation is obtained by confocal imaging of aqueous solutions in a glass-silicon microchip.

  5. A first-principles based force-field for Li+ and OH- in ethanolic solution.

    Science.gov (United States)

    Milek, Theodor; Meyer, Bernd; Zahn, Dirk

    2013-10-14

    We report on the development of force-field parameters for accurately modeling lithium and hydroxide ions in ethanol in solution. Based on quantum calculations of small molecular clusters mimicking the solvent structure of individual ions as well as the solvated LiOH dimer, significant improvements of off-the-shelf force-fields are obtained. The quality of our model is demonstrated by comparison to ab initio molecular dynamics of the bulk solution and to experimental data available for ethanol/water mixtures.

  6. Non-mean-field effects in systems with long-range forces in competition.

    Science.gov (United States)

    Bachelard, R; Staniscia, F

    2012-11-01

    We investigate the canonical equilibrium of systems with long-range forces in competition. These forces create a modulation in the interaction potential and modulated phases appear at the system scale. The structure of these phases differentiate this system from monotonic potentials, where only the mean-field and disordered phases exist. With increasing temperature, the system switches from one ordered phase to another through a first-order phase transition. Both mean-field and modulated phases may be stable, even at zero temperature, and the long-range nature of the interaction will lead to metastability characterized by extremely long time scales.

  7. A transferable force field for CdS-CdSe-PbS-PbSe solid systems

    OpenAIRE

    Fan, Zhaochuan; Koster, Rik S.; Wang, Shuaiwei; Fang, Changming; Anil O. Yalcin; Frans D. Tichelaar; Zandbergen, Henny W.; Van Huis, Marijn A.; Vlugt, Thijs J H

    2014-01-01

    A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., "Atomic resolution monitoring of cation exchange in CdSe-PbSe heteronanocrystals during epitaxial solid-solid-vapor growth," Nano Lett. 14, 3661-3667 (2014)]. In this work, we extend this force field by including another two important binary semiconductors, PbS and C...

  8. Fabrication of nanoparticles for generation of force and torque at nanoscale

    Science.gov (United States)

    Gervinskas, Gediminas; Seniutinas, Gediminas; Rosa, Lorenzo; Brasselet, Etienne; Juodkazis, Saulius

    2013-09-01

    Chiral patterns are created by focused ion-beam milling nano-grooves with sub-15 nm resolution on thin metal films and arrays of nanoparticles, scattering and absorbing light selectively for left and right circularly polarized light, with high fidelity over fields up to 100 x 100 μm2 without positioning errors. This allows to carry out numerical simulations to estimate light enhancement and circular dichroism both on ideal and realistic particles taken from SEM images, showing doubling of scattering cross-section and enhancement changes up to 5 times controlled by dichroism, with localized field enhancements up to 20000. 3D plasmonic structures extending out of a gold film plane are created by dry etching of the film in the openings of a resist mask defined by electron beam lithography. Conical vertical protrusions (nano-wells) are left, and their optical properties are numerically simulated, showing easily reachable out-of-plane trapping of both dielectric and metal plasmonic nano-spheres, with trapping forces up to 20 pN/W/μm2. Wideband refractive index spectra in 3D-FDTD are correctly represented by overcoming the polynomial approximations to give accurate field and force/torque results for generalized artificial materials.

  9. Muscle force generation and force control of finger movements in children with spastic hemiplegia during isometric tasks.

    NARCIS (Netherlands)

    Smits-Engelsman, B.C.M.; Rameckers, E.A.A.; Duysens, J.E.J.

    2005-01-01

    Force control ability was investigated in 10 males and 10 females, between 5 and 15 years old with spastic hemiplegia (mild and moderate hand dysfunction), and an aged-matched control group (eight males, 12 females). An isometric force production task at five different levels of maximum voluntary co

  10. Measurement of the impuslive force generated by colapsing bubble close to a solid boundary

    Directory of Open Access Journals (Sweden)

    Zima Patrik

    2012-04-01

    Full Text Available The article presents experimental results of the acoustical and optical study of cavitation bubble collapse close to a solid boundary in water. The bubble was generated by discharge of low-voltage capacitor into a couple of wires closing a simple circuit. Different distances from the solid wall and different maximum bubble radii were studied. The bubble radius was studied using time-resolved photography and by PVDF film sensor glued on the solid boundary. The illumination was provided by high-power led diode. Synchronization of the system was provided by pulse generator connected to an oscilloscope. The impact power of the bubble to the wall was estimated from the time-resolved photography of the bubble and from the PVDF film sensor signal. The PVDF film sensor calibration was performed by a pendulum test to estimate the impact force.

  11. Field and material stresses predict observable surface forces in optical and electrostatic manipulation

    Science.gov (United States)

    Kemp, Brandon A.; Sheppard, Cheyenne J.

    2016-09-01

    The momentum of light in media has been one of the most debated topics in physics over the past one hundred years. Originally a theoretical debate over the electrodynamics of moving media, practical applications have emerged over the past few decades due to interest in optical manipulation and nanotechnology. Resolution of the debate identifies a kinetic momentum as the momentum of the fields responsible for center of mass translations and a canonical momentum related to the coupled field and material system. The optical momentum resolution has been considered incomplete because it did not uniquely identify the full stress-energy-momentum (SEM) tensor of the field-kinetic subsystem. A consequence of this partial resolution is that the field-kinetic momentum could be described by three of the leading formulations found in the literature. The Abraham, Einstein-Laub, and Chu SEM tensors share the field-kinetic momentum, but their SEM tensors differ resulting in competing force densities. We can show now that the Abraham and Einstein-Laub formulations are invalid since their SEM tensors are not frame invariant, whereas the Chu SEM tensor satisfies relativistic principles as the field-kinetic formulation. However, a number of reports indicate that the force distribution in matter may not accurately represent experimental observations. In this correspondence, we show that the field-kinetic SEM tensor can be used along with the corresponding material subsystem to accurately predict experimental force and stress distributions. We model experimental examples from optical and static manipulation of particles and fluids.

  12. Correlation of embryonic skeletal muscle myotube physical characteristics with contractile force generation on an atomic force microscope-based bio-microelectromechanical systems device

    Science.gov (United States)

    Pirozzi, K. L.; Long, C. J.; McAleer, C. W.; Smith, A. S. T.; Hickman, J. J.

    2013-08-01

    Rigorous analysis of muscle function in in vitro systems is needed for both acute and chronic biomedical applications. Forces generated by skeletal myotubes on bio-microelectromechanical cantilevers were calculated using a modified version of Stoney's thin-film equation and finite element analysis (FEA), then analyzed for regression to physical parameters. The Stoney's equation results closely matched the more intensive FEA and the force correlated to cross-sectional area (CSA). Normalizing force to measured CSA significantly improved the statistical sensitivity and now allows for close comparison of in vitro data to in vivo measurements for applications in exercise physiology, robotics, and modeling neuromuscular diseases.

  13. Influence of an external magnetic field on forced turbulence in a swirling flow of liquid metal

    CERN Document Server

    Gallet, Basile; Mordant, Nicolas

    2009-01-01

    We report an experimental investigation on the influence of an external magnetic field on forced 3D turbulence of liquid gallium in a closed vessel. We observe an exponential damping of the turbulent velocity fluctuations as a function of the interaction parameter N (ratio of Lorentz force over inertial terms of the Navier-Stokes equation). The flow structures develop some anisotropy but do not become bidimensional. From a dynamical viewpoint, the damping first occurs homogeneously over the whole spectrum of frequencies. For larger values of N, a very strong additional damping occurs at the highest frequencies. However, the injected mechanical power remains independent of the applied magnetic field. The simultaneous measurement of induced magnetic field and electrical potential differences shows a very weak correlation between magnetic field and velocity fluctuations. The observed reduction of the fluctuations is in agreement with a previously proposed mechanism for the saturation of turbulent dynamos and wit...

  14. Motion in classical field theories and the foundations of the self-force problem

    CERN Document Server

    Harte, Abraham I

    2014-01-01

    This article serves as a pedagogical introduction to the problem of motion in classical field theories. The primary focus is on self-interaction: How does an object's own field affect its motion? General laws governing the self-force and self-torque are derived using simple, non-perturbative arguments. The relevant concepts are developed gradually by considering motion in a series of increasingly complicated theories. Newtonian gravity is discussed first, then Klein-Gordon theory, electromagnetism, and finally general relativity. Linear and angular momenta as well as centers of mass are defined in each of these cases. Multipole expansions for the force and torque are then derived to all orders for arbitrarily self-interacting extended objects. These expansions are found to be structurally identical to the laws of motion satisfied by extended test bodies, except that all relevant fields are replaced by effective versions which exclude the self-fields in a particular sense. Regularization methods traditionally ...

  15. A Fluid Dynamics Approach for the Computation of Non-linear Force-Free Magnetic Field

    Institute of Scientific and Technical Information of China (English)

    Jing-Qun Li; Jing-Xiu Wang; Feng-Si Wei

    2003-01-01

    Inspired by the analogy between the magnetic field and velocity fieldof incompressible fluid flow, we propose a fluid dynamics approach for comput-ing nonlinear force-free magnetic fields. This method has the advantage that thedivergence-free condition is automatically satisfied, which is a sticky issue for manyother algorithms, and we can take advantage of modern high resolution algorithmsto process the force-free magnetic field. Several tests have been made based on thewell-known analytic solution proposed by Low & Lou. The numerical results arein satisfactory agreement with the analytic ones. It is suggested that the newlyproposed method is promising in extrapolating the active region or the whole sunmagnetic fields in the solar atmosphere based on the observed vector magnetic fieldon the photosphere.

  16. Experimental and theoretical analysis of a hybrid solar thermoelectric generator with forced convection cooling

    Science.gov (United States)

    Sundarraj, Pradeepkumar; Taylor, Robert A.; Banerjee, Debosmita; Maity, Dipak; Sinha Roy, Susanta

    2017-01-01

    Hybrid solar thermoelectric generators (HSTEGs) have garnered significant research attention recently due to their potential ability to cogenerate heat and electricity. In this paper, theoretical and experimental investigations of the electrical and thermal performance of a HSTEG system are reported. In order to validate the theoretical model, a laboratory scale HSTEG system (based on forced convection cooling) is developed. The HSTEG consists of six thermoelectric generator modules, an electrical heater, and a stainless steel cooling block. Our experimental analysis shows that the HSTEG is capable of producing a maximum electrical power output of 4.7 W, an electrical efficiency of 1.2% and thermal efficiency of 61% for an average temperature difference of 92 °C across the TEG modules with a heater power input of 382 W. These experimental results of the HSTEG system are found to be in good agreement with the theoretical prediction. This experimental/theoretical analysis can also serve as a guide for evaluating the performance of the HSTEG system with forced convection cooling.

  17. Simultaneous Knee Extensor Muscle Action Induces an Increase in Voluntary Force Generation of Plantar Flexor Muscles.

    Science.gov (United States)

    Suzuki, Takahito; Shioda, Kohei; Kinugasa, Ryuta; Fukashiro, Senshi

    2017-02-01

    Suzuki, T, Shioda, K, Kinugasa, R, and Fukashiro, S. Simultaneous knee extensor muscle action induces an increase in voluntary force generation of plantar flexor muscles. J Strength Cond Res 31(2): 365-371, 2017-Maximum activation of the plantar flexor muscles is required for various sporting activities that involve simultaneous plantar flexion and knee extension. During a multi-joint movement, activation of the plantar flexor muscles is affected by the activity of the knee extensor muscles. We hypothesized that coactivation of the plantar flexor muscles and knee extensor muscles would result in a higher plantar flexion torque. To test this hypothesis, 8 male volunteers performed maximum voluntary isometric action of the plantar flexor muscles with and without isometric action of the knee extensor muscles. Surface electromyographic data were collected from 8 muscles of the right lower limb. Voluntary activation of the triceps surae muscles, evaluated using the interpolated twitch technique, significantly increased by 6.4 percentage points with intentional knee extensor action (p = 0.0491). This finding is in line with a significant increase in the average rectified value of the electromyographic activity of the vastus lateralis, fibularis longus, and soleus muscles (p = 0.013, 0.010, and 0.045, respectively). The resultant plantar flexion torque also significantly increased by 11.5% of the predetermined maximum (p = 0.031). These results suggest that higher plantar flexor activation coupled with knee extensor activation facilitates force generation during a multi-joint task.

  18. A MODEL OF THE FORCES THAT GENERATE RESISTANCE TO CHANGE WITHIN AN ORGANIZATION

    Directory of Open Access Journals (Sweden)

    Daniela BRADUŢANU

    2015-12-01

    Full Text Available The aim of this article is to present a proposed model of the forces generating resistance to change within an organiza-tion. After analyzing the literature and conducting a survey I concluded that the forces that generate resistance to change have a great impact on employees’ resistance to change and they are both internal, as well as external.UN MODEL AL FORŢELOR GENERATOARE DE REZISTENŢĂ LA SCHIMBARE DIN CADRUL UNEI ORGANIZAŢIIScopul urmărit în acest articol este de a prezenta un model al forţelor generatoare de rezistenţă la schimbare din cadrul unei organizaţii. În urma analizei literaturii de specialitate şi efectuării unui studiu de caz am ajuns la concluzia că forţele care generează rezistenţă la schimbare au un impact semnificativ asupra rezistenţei la schimbare din partea angajaţilor, acestea fiind atât interne, cât şi externe.

  19. Aerodynamic mechanism of forces generated by twisting model-wing in bat flapping flight

    Institute of Scientific and Technical Information of China (English)

    管子武; 余永亮

    2014-01-01

    The aerodynamic mechanism of the bat wing membrane along the lateral border of its body is studied. The twist-morphing that alters the angle of attack (AOA) along the span-wise direction is observed widely during bat flapping flight. An assumption is made that the linearly distributed AOA is along the span-wise direction. The plate with the aspect ratio of 3 is used to model a bat wing. A three-dimensional (3D) unsteady panel method is used to predict the aerodynamic forces generated by the flapping plate with leading edge separation. It is found that, relative to the rigid wing flapping, twisting motion can increase the averaged lift by as much as 25% and produce thrust instead of drag. Furthermore, the aerodynamic forces (lift/drag) generated by a twisting plate-wing are similar to those of a pitching rigid-wing, meaning that the twisting in bat flight has the same function as the supination/pronation motion in insect flight.

  20. Children with developmental coordination disorder are equally able to generate force but show more variability than typically developing children.

    NARCIS (Netherlands)

    Smits-Engelsman, B.C.M.; Westenberg, Y.; Duysens, J.

    2008-01-01

    Several studies have suggested that children with developmental coordination disorder (DCD) have difficulties in the fine-tuning of manual force. However, parameterization of the generated force per se is hard to test under normal circumstances as movement planning and execution are also involved.

  1. The Generation of Coronal Loop Waves below the Photosphere by p-Mode Forcing

    CERN Document Server

    Hindman, Bradley W

    2008-01-01

    Recent observations of coronal-loop waves by TRACE and within the corona as a whole by CoMP clearly indicate that the dominant oscillation period is 5 minutes, thus implicating the solar p modes as a possible source. We investigate the generation of tube waves within the solar convection zone by the buffeting of p modes. The tube waves--in the form of longitudinal sausage waves and transverse kink waves--are generated on the many magnetic fibrils that lace the convection zone and pierce the solar photosphere. Once generated by p-mode forcing, the tube waves freely propagate up and down the tubes, since the tubes act like light fibers and form a waveguide for these magnetosonic waves. Those waves that propagate upward pass through the photosphere and enter the upper atmosphere where they can be measured as loop oscillations and other forms of propagating coronal waves. We treat the magnetic fibrils as vertically aligned, thin flux tubes and compute the energy flux of tube waves that can generated and driven in...

  2. Molecular interactions and residues involved in force generation in the T4 viral DNA packaging motor.

    Science.gov (United States)

    Migliori, Amy D; Smith, Douglas E; Arya, Gaurav

    2014-12-12

    Many viruses utilize molecular motors to package their genomes into preformed capsids. A striking feature of these motors is their ability to generate large forces to drive DNA translocation against entropic, electrostatic, and bending forces resisting DNA confinement. A model based on recently resolved structures of the bacteriophage T4 motor protein gp17 suggests that this motor generates large forces by undergoing a conformational change from an extended to a compact state. This transition is proposed to be driven by electrostatic interactions between complementarily charged residues across the interface between the N- and C-terminal domains of gp17. Here we use atomistic molecular dynamics simulations to investigate in detail the molecular interactions and residues involved in such a compaction transition of gp17. We find that although electrostatic interactions between charged residues contribute significantly to the overall free energy change of compaction, interactions mediated by the uncharged residues are equally if not more important. We identify five charged residues and six uncharged residues at the interface that play a dominant role in the compaction transition and also reveal salt bridging, van der Waals, and solvent hydrogen-bonding interactions mediated by these residues in stabilizing the compact form of gp17. The formation of a salt bridge between Glu309 and Arg494 is found to be particularly crucial, consistent with experiments showing complete abrogation in packaging upon Glu309Lys mutation. The computed contributions of several other residues are also found to correlate well with single-molecule measurements of impairments in DNA translocation activity caused by site-directed mutations.

  3. Three-dimensional cell body shape dictates the onset of traction force generation and growth of focal adhesions.

    Science.gov (United States)

    Fouchard, Jonathan; Bimbard, Célian; Bufi, Nathalie; Durand-Smet, Pauline; Proag, Amsha; Richert, Alain; Cardoso, Olivier; Asnacios, Atef

    2014-09-09

    Cell shape affects proliferation and differentiation, which are processes known to depend on integrin-based focal adhesion (FA) signaling. Because shape results from force balance and FAs are mechanosensitive complexes transmitting tension from the cell structure to its mechanical environment, we investigated the interplay between 3D cell shape, traction forces generated through the cell body, and FA growth during early spreading. Combining measurements of cell-scale normal traction forces with FA monitoring, we show that the cell body contact angle controls the onset of force generation and, subsequently, the initiation of FA growth at the leading edge of the lamella. This suggests that, when the cell body switches from convex to concave, tension in the apical cortex is transmitted to the lamella where force-sensitive FAs start to grow. Along this line, increasing the stiffness resisting cell body contraction led to a decrease of the lag time between force generation and FA growth, indicating mechanical continuity of the cell structure and force transmission from the cell body to the leading edge. Remarkably, the overall normal force per unit area of FA increased with stiffness, and its values were similar to those reported for local tangential forces acting on individual FAs. These results reveal how the 3D cell shape feeds back on its internal organization and how it may control cell fate through FA-based signaling.

  4. 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 com...... the CHARMM36 FF with minor modifications. Compatibility between our parameters and CHARMM36 parameters is preserved. (C) 2014 Elsevier B.V. All rights reserved....

  5. Radiation force on a spherical object in the field of a focused cylindrical transducer.

    Science.gov (United States)

    Chen, X; Apfel, R E

    1997-05-01

    An exact solution of the radiation force on a spherical object, when positioned on the acoustic axis of a cylindrical transducer, is provided. The solution is valid for any type of sphere of any size. The radiation force function allows the calibration of high-frequency focused ultrasound fields from radiation force measurements and expands the utility of the elastic sphere radiometer developed by Dunn et al. [Acustica 38, 58-61 (1977)]. Numeral results reveal an oscillatory behavior of the radiation force function for small spheres near the transducer surface and this behavior may present an opportunity for particle sorting based on the mechanical properties of the particle and other types of manipulation.

  6. Analysis of the magnetic field, force, and torque for two-dimensional Halbach cylinders

    CERN Document Server

    Bjørk, R; Smith, A; Pryds, N

    2014-01-01

    The Halbach cylinder is a construction of permanent magnets used in applications such as nuclear magnetic resonance apparatus, accelerator magnets and magnetic cooling devices. In this paper the analytical expression for the magnetic vector potential, magnetic flux density and magnetic field for a two dimensional Halbach cylinder are derived. The remanent flux density of a Halbach magnet is characterized by the integer $p$. For a number of applications the force and torque between two concentric Halbach cylinders are important. These quantities are calculated and the force is shown to be zero except for the case where $p$ for the inner magnet is one minus $p$ for the outer magnet. Also the force is shown never to be balancing. The torque is shown to be zero unless the inner magnet $p$ is equal to minus the outer magnet $p$. Thus there can never be a force and a torque in the same system.

  7. First Use of Synoptic Vector Magnetograms for Global Nonlinear, Force-Free Coronal Magnetic Field Models

    Science.gov (United States)

    Tadesse, T.; Wiegelmann, T.; Gosain, S.; MacNeice, P.; Pevtsov, A. A.

    2014-01-01

    Context. The magnetic field permeating the solar atmosphere is generally thought to provide the energy for much of the activity seen in the solar corona, such as flares, coronal mass ejections (CMEs), etc. To overcome the unavailability of coronal magnetic field measurements, photospheric magnetic field vector data can be used to reconstruct the coronal field. Currently, there are several modelling techniques being used to calculate three-dimensional field lines into the solar atmosphere. Aims. For the first time, synoptic maps of a photospheric-vector magnetic field synthesized from the vector spectromagnetograph (VSM) on Synoptic Optical Long-term Investigations of the Sun (SOLIS) are used to model the coronal magnetic field and estimate free magnetic energy in the global scale. The free energy (i.e., the energy in excess of the potential field energy) is one of the main indicators used in space weather forecasts to predict the eruptivity of active regions. Methods. We solve the nonlinear force-free field equations using an optimization principle in spherical geometry. The resulting threedimensional magnetic fields are used to estimate the magnetic free energy content E(sub free) = E(sub nlfff) - E(sub pot), which is the difference of the magnetic energies between the nonpotential field and the potential field in the global solar corona. For comparison, we overlay the extrapolated magnetic field lines with the extreme ultraviolet (EUV) observations by the atmospheric imaging assembly (AIA) on board the Solar Dynamics Observatory (SDO). Results. For a single Carrington rotation 2121, we find that the global nonlinear force-free field (NLFFF) magnetic energy density is 10.3% higher than the potential one. Most of this free energy is located in active regions.

  8. A study by computer simulation of the generation and evolution of the Earth`s magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Glatzmaier, G.A.; Hollerbach, R.; Roberts, P.H.

    1995-12-31

    Until recently very little has been known about the maintenance of the Earth`s magnetic field. The general consensus was that some type of convective motion edits in the Earth`s liquid iron alloy core that is affected by rotational forces in a way that continually generates new magnetic field to replace that which diffuses away. Magnetic-field reversals and secular variation have long been measured but no theory existed to explain these phenomena. To gain an understanding of the basic physical mechanisms of the ``geodynamo,`` we produced the first self-consistent computer simulation of convection and magnetic field generation in a rotating three-dimensional spherical fluid shell as an anologue to the Earth`s convective dynamo. This is a final report of a three-year Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL).

  9. A transferable force field to predict phase equilibria and surface tension of ethers and glycol ethers.

    Science.gov (United States)

    Ferrando, Nicolas; Lachet, Véronique; Pérez-Pellitero, Javier; Mackie, Allan D; Malfreyt, Patrice; Boutin, Anne

    2011-09-15

    We propose a new transferable force field to simulate phase equilibrium and interfacial properties of systems involving ethers and glycol ethers. On the basis of the anisotropic united-atom force field, only one new group is introduced: the ether oxygen atom. The optimized Lennard-Jones (LJ) parameters of this atom are identical whatever the molecule simulated (linear ether, branched ether, cyclic ether, aromatic ether, diether, or glycol ether). Accurate predictions are achieved for pure compound saturated properties, critical properties, and surface tensions of the liquid-vapor interface, as well as for pressure-composition binary mixture diagrams. Multifunctional molecules (1,2-dimethoxyethane, 2-methoxyethanol, diethylene glycol) have also been studied using a recently proposed methodology for the calculation of the intramolecular electrostatic energy avoiding the use of additional empirical parameters. This new force field appears transferable for a wide variety of molecules and properties. It is furthermore worth noticing that binary mixtures have been simulated without introducing empirical binary parameters, highlighting also the transferability to mixtures. Hence, this new force field gives future opportunities to simulate complex systems of industrial interest involving molecules with ether functions.

  10. An Energy Conservative Ray-Tracing Method With a Time Interpolation of the Force Field

    Energy Technology Data Exchange (ETDEWEB)

    Yao, Jin [Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

    2015-02-10

    A new algorithm that constructs a continuous force field interpolated in time is proposed for resolving existing difficulties in numerical methods for ray-tracing. This new method has improved accuracy, but with the same degree of algebraic complexity compared to Kaisers method.

  11. Gravitomagnetic Field of the Universe and Coriolis Force on the Rotating Earth

    Science.gov (United States)

    Veto, B.

    2011-01-01

    The Machian effect of distant masses of the universe in the frame of reference of the rotating Earth is demonstrated using the gravitomagnetic approach of general relativity. This effect appears in the form of a gravitomagnetic Lorentz force acting on moving bodies on the Earth. The gravitomagnetic field of the universe--deduced from a simple…

  12. Hybrid simulations : combining atomistic and coarse-grained force fields using virtual sites

    NARCIS (Netherlands)

    Rzepiela, Andrzej J.; Louhivuori, Martti; Peter, Christine; Marrink, Siewert J.

    2011-01-01

    Hybrid simulations, in which part of the system is represented at atomic resolution and the remaining part at a reduced, coarse-grained, level offer a powerful way to combine the accuracy associated with the atomistic force fields to the sampling speed obtained with coarse-grained (CG) potentials. I

  13. OPLS3: A Force Field Providing Broad Coverage of Drug-like Small Molecules and Proteins.

    Science.gov (United States)

    Harder, Edward; Damm, Wolfgang; Maple, Jon; Wu, Chuanjie; Reboul, Mark; Xiang, Jin Yu; Wang, Lingle; Lupyan, Dmitry; Dahlgren, Markus K; Knight, Jennifer L; Kaus, Joseph W; Cerutti, David S; Krilov, Goran; Jorgensen, William L; Abel, Robert; Friesner, Richard A

    2016-01-12

    The parametrization and validation of the OPLS3 force field for small molecules and proteins are reported. Enhancements with respect to the previous version (OPLS2.1) include the addition of off-atom charge sites to represent halogen bonding and aryl nitrogen lone pairs as well as a complete refit of peptide dihedral parameters to better model the native structure of proteins. To adequately cover medicinal chemical space, OPLS3 employs over an order of magnitude more reference data and associated parameter types relative to other commonly used small molecule force fields (e.g., MMFF and OPLS_2005). As a consequence, OPLS3 achieves a high level of accuracy across performance benchmarks that assess small molecule conformational propensities and solvation. The newly fitted peptide dihedrals lead to significant improvements in the representation of secondary structure elements in simulated peptides and native structure stability over a number of proteins. Together, the improvements made to both the small molecule and protein force field lead to a high level of accuracy in predicting protein-ligand binding measured over a wide range of targets and ligands (less than 1 kcal/mol RMS error) representing a 30% improvement over earlier variants of the OPLS force field.

  14. Coarse-graining polymers with the MARTINI force-field: polystyrene as a benchmark case

    DEFF Research Database (Denmark)

    Rossi, G.; Monticelli, L.; Puisto, S. R.

    2011-01-01

    in the parameterization. We refine the MARTINI procedure by including one additional target property related to the structure of the polymer, namely the radius of gyration. The force-field optimization is mainly based on experimental data. We test our procedure on polystyrene, a standard benchmark for coarse-grained (CG...

  15. Transferable force field for carboxylate esters: application to fatty acid methylic ester phase equilibria prediction.

    Science.gov (United States)

    Ferrando, Nicolas; Lachet, Véronique; Boutin, Anne

    2012-03-15

    In this work, a new transferable united-atoms force field for carboxylate esters is proposed. All Lennard-Jones parameters are reused from previous parametrizations of the AUA4 force field, and only a unique set of partial electrostatic charges is introduced for the ester chemical function. Various short alkyl-chain esters (methyl acetate, ethyl acetate, methyl propionate, ethyl propionate) and two fatty acid methylic esters (methyl oleate and methyl palmitate) are studied. Using this new force field in Monte Carlo simulations, we show that various pure compound properties are accurately predicted: saturated liquid densities, vapor pressures, vaporization enthalpies, critical properties, liquid-vapor surface tensions. Furthermore, a good accuracy is also obtained in the prediction of binary mixture pressure-composition diagrams, without introducing empirical binary interaction parameters. This highlights the transferability of the proposed force field and gives the opportunity to simulate mixtures of industrial interest: a demonstration is performed through the simulation of the methyl oleate + methanol mixture involved in the purification sections of biodiesel production processes.

  16. Accelerated Molecular Dynamics Simulations with the AMOEBA Polarizable Force Field on Graphics Processing Units.

    Science.gov (United States)

    Lindert, Steffen; Bucher, Denis; Eastman, Peter; Pande, Vijay; McCammon, J Andrew

    2013-11-12

    The accelerated molecular dynamics (aMD) method has recently been shown to enhance the sampling of biomolecules in molecular dynamics (MD) simulations, often by several orders of magnitude. Here, we describe an implementation of the aMD method for the OpenMM application layer that takes full advantage of graphics processing units (GPUs) computing. The aMD method is shown to work in combination with the AMOEBA polarizable force field (AMOEBA-aMD), allowing the simulation of long time-scale events with a polarizable force field. Benchmarks are provided to show that the AMOEBA-aMD method is efficiently implemented and produces accurate results in its standard parametrization. For the BPTI protein, we demonstrate that the protein structure described with AMOEBA remains stable even on the extended time scales accessed at high levels of accelerations. For the DNA repair metalloenzyme endonuclease IV, we show that the use of the AMOEBA force field is a significant improvement over fixed charged models for describing the enzyme active-site. The new AMOEBA-aMD method is publicly available (http://wiki.simtk.org/openmm/VirtualRepository) and promises to be interesting for studying complex systems that can benefit from both the use of a polarizable force field and enhanced sampling.

  17. Locally varying particle masses due to a scalar fifth-force field

    Energy Technology Data Exchange (ETDEWEB)

    Fujii, Yasunori (Tokyo Univ. (Japan). Inst. of Physics)

    1991-02-14

    If a scalar field mediates a fifth force, masses of elementary particles will be affected locally by massive sources, resulting in a change of size of macroscopic objects. The effect is shown to be testable by using an ultra-sensitive laser interferometric technique when it is fully developed for the use in gravity-wave detectors. (orig.).

  18. Toward a Broadly Applicable Force Field for d(6)-Piano Stool Complexes.

    Science.gov (United States)

    Schmid, Maurus H; Ward, Thomas R; Meuwly, Markus

    2013-05-14

    Three-legged piano stool complexes are prototypical organometallic complexes relevant to a wide range of chemically relevant questions. Force field parametrization of transition-metal complexes is difficult and underdeveloped, and metal-specific force fields and software are required. Here we report our efforts to derive parameters for the conventional CHARMM and the Valbond-CHARMM force fields for d(6)-piano stool complexes. In Valbond-CHARMM, the usual angular term is replaced with hybrid orbital strength functions. These functions describe the energy not only of distorted bond angles around the minimum but also at very large distortions. Structure optimizations led to a good agreement between the calculated force field and the X-ray structures. They were comparable to RMSDs obtained between X-ray and DFT structures. In addition, and contrary to treating the systems with DFT, molecular dynamics simulations on the multiple nanosecond time scale are possible and allow to compute meaningful structural and energetic observables. Explicit solvent simulations of the complexes in methanol and water allow to determine the solvent distribution around the complexes. The parametrization presented here will be a useful starting point for dynamics investigations of catalysts in structurally more demanding environments.

  19. Molecular simulation of gas adsorption and diffusion in a breathing MOF using a rigid force field.

    Science.gov (United States)

    García-Pérez, E; Serra-Crespo, P; Hamad, S; Kapteijn, F; Gascon, J

    2014-08-14

    Simulation of gas adsorption in flexible porous materials is still limited by the slow progress in the development of flexible force fields. Moreover, the high computational cost of such flexible force fields may be a drawback even when they are fully developed. In this work, molecular simulations of gas adsorption and diffusion of carbon dioxide and methane in NH2-MIL-53(Al) are carried out using a linear combination of two crystallographic structures with rigid force fields. Once the interactions of carbon dioxide molecules and the bridging hydroxyls groups of the framework are optimized, an excellent match is found for simulations and experimental data for the adsorption of methane and carbon dioxide, including the stepwise uptake due to the breathing effect. In addition, diffusivities of pure components are calculated. The pore expansion by the breathing effect influences the self-diffusion mechanism and much higher diffusivities are observed at relatively high adsorbate loadings. This work demonstrates that using a rigid force field combined with a minimum number of experiments, reproduces adsorption and simulates diffusion of carbon dioxide and methane in the flexible metal-organic framework NH2-MIL-53(Al).

  20. Gravitomagnetic Field of the Universe and Coriolis Force on the Rotating Earth

    Science.gov (United States)

    Veto, B.

    2011-01-01

    The Machian effect of distant masses of the universe in the frame of reference of the rotating Earth is demonstrated using the gravitomagnetic approach of general relativity. This effect appears in the form of a gravitomagnetic Lorentz force acting on moving bodies on the Earth. The gravitomagnetic field of the universe--deduced from a simple…

  1. Atomic Radii in Molecules for Use in a Polarizable Force Field

    NARCIS (Netherlands)

    Swart, Marcel; Van Duijnen, Piet Th

    2011-01-01

    We report here the results for an ab initio approach to obtain the parameters needed for molecular simulations using a polarizable force field. These parameters consist of the atomic charges, polarizabilities, and radii. The former two are readily obtained using methods reported previously (van Duij

  2. Computer Folding of RNA Tetraloops: Identification of Key Force Field Deficiencies

    CERN Document Server

    Kührová, Petra; Bottaro, Sandro; Bussi, Giovanni; Šponer, Jiří; Otyepka, Michal; Banáš, Pavel

    2016-01-01

    The computer-aided folding of biomolecules, particularly RNAs, is one of the most difficult challenges in computational structural biology. RNA tetraloops are fundamental RNA motifs playing key roles in RNA folding and RNA-RNA and RNA-protein interactions. Although state-of-the-art Molecular Dynamics (MD) force fields correctly describe the native state of these tetraloops as a stable free-energy basin on the microsecond time scale, enhanced sampling techniques reveal that the native state is not the global free energy minimum, suggesting yet unidentified significant imbalances in the force fields. Here, we tested our ability to fold the RNA tetraloops in various force fields and simulation settings. We employed three different enhanced sampling techniques, namely, temperature replica exchange MD (T-REMD), replica exchange with solute tempering (REST2), and well-tempered metadynamics (WT-MetaD). We aimed to separate problems caused by limited sampling from those due to force-field inaccuracies. We found that ...

  3. Supra-Atomic Coarse-Grained GROMOS Force Field for Aliphatic Hydrocarbons in the Liquid Phase.

    Science.gov (United States)

    Eichenberger, Andreas P; Huang, Wei; Riniker, Sereina; van Gunsteren, Wilfred F

    2015-07-14

    A supra-atomic coarse-grained (CG) force field for liquid n-alkanes is presented. The model was calibrated using experimental thermodynamic data and structural as well as energetic properties for 14 n-alkanes as obtained from atomistic fine-grained (FG) simulations of the corresponding hydrocarbons using the GROMOS 45A3 biomolecular force field. A variation of the nonbonded force-field parameters obtained from mapping the FG interactions onto the CG degrees of freedom to fit the density and heat of vaporization to experimental values turned out to be mandatory for a correct reproduction of these data by the CG model, while the bonded force-field parameters for the CG model could be obtained from a Boltzmann-weighted fit with some variations with respect to the corresponding properties from the FG simulations mapped onto the CG degrees of freedom. The model presents 6 different CG bead types, for bead sizes from 2 to 4 distinguishing between terminal and nonterminal beads within an alkane chain (end or middle). It contains different nonbonded Lennard-Jones parameters for the interaction of CG alkanes with CG water. The CG alkane model was further tested by comparing predictions of the excess free energy, the self-diffusion constant, surface tension, isothermal compressibility, heat capacity, thermal expansion coefficient, and shear viscosity for n-alkanes to experimental values. The CG model offers a thermodynamically calibrated basis for the development of CG models of lipids.

  4. Zeolite force fields and experimental siliceous frameworks in a comparative infrared study

    NARCIS (Netherlands)

    Bueno-Perez, R.; Calero, S.; Dubbeldam, D.; Ania, C.O.; Parra, J.B.; Zaderenko, A.P.; Merkling, P.J.

    2012-01-01

    Infrared spectra (IR) of a great variety of zeolite frameworks in the limit of pure silica composition are calculated by molecular dynamics and also recorded experimentally. This enables us to study and assess the effect of three flexible force fields from the literature developed for zeolites in

  5. Adaptation of multi-joint balance coordination to whole body force fields

    NARCIS (Netherlands)

    Engelhart, Denise; Schouten, Alfred; Aarts, Ronald; Pasma, J.; Meskers, Carel; Maier, Andrea; Kooij, van der Herman

    2014-01-01

    Background and aim: The ankles and the hips play an important role in standing balance. Multi-joint coordination adapts with task, the magnitude and type of disturbance [1]. Arm studies show that postural responses are highly dependent on externally applied force fields [2]. Our aim is to study how

  6. A transferable force field for CdS-CdSe-PbS-PbSe solid systems

    NARCIS (Netherlands)

    Fan, Zhaochuan; Koster, Rik S.; Wang, Shuaiwei; Fang, Changming; Yalcin, Anil O.; Tichelaar, Frans D.; Zandbergen, Henny W.; van Huis, Marijn A.; Vlugt, Thijs J. H.

    2014-01-01

    A transferable force field for the PbSe-CdSe solid system using the partially charged rigid ion model has been successfully developed and was used to study the cation exchange in PbSe-CdSe heteronanocrystals [A. O. Yalcin et al., "Atomic resolution monitoring of cation exchange in CdSe-PbSe heterona

  7. Dynamical mass generation in QED with magnetic fields: arbitrary field strength and coupling constant

    CERN Document Server

    Rojas, Eduardo; Bashir, Adnan; Raya, Alfredo

    2008-01-01

    We study the dynamical generation of masses for fundamental fermions in quenched quantum electrodynamics, in the presence of magnetic fields of arbitrary strength, by solving the Schwinger-Dyson equation (SDE) for the fermion self-energy in the rainbow approximation. We employ the Ritus eigenfunction formalism which provides a neat solution to the technical problem of summing over all Landau levels. It is well known that magnetic fields catalyze the generation of fermion mass m for arbitrarily small values of electromagnetic coupling \\alpha. For intense fields it is also well known that m \\propto \\sqrt eB. Our approach allows us to span all regimes of parameters \\alpha and eB. We find that m \\propto \\sqrt eB provided \\alpha is small. However, when \\alpha increases beyond the critical value \\alpha_c which marks the onslaught of dynamical fermion masses in vacuum, we find m \\propto \\Lambda, the cut-off required to regularize the ultraviolet divergences. Our method permits us to verify the results available in l...

  8. Fiber Assignment in Next-generation Wide-field Spectrographs

    CERN Document Server

    Morales, Isaac; Azzaro, Marco; Prada, Francisco; Sanchez, Justo; Becerril, Santiago

    2011-01-01

    We present an optimized algorithm for assigning fibers to targets in next-generation fiber-fed multi-object spectrographs. The method, that we named draining algorithm, ensures that the maximum number of targets in a given target field is observed in the first few tiles. Using randomly distributed targets and mock galaxy catalogs we have estimated that the gain provided by the draining algorithm as compared to a random assignment can be as much as 2% for the first tiles. This would imply for a survey like BigBOSS saving for observation several hundred thousand objects or, alternatively, reducing the covered area in ~350 sq. deg. An important advantage of this method is that the fiber collision problem can be solved easily and in an optimal way. We also discuss additional optimizations of the fiber positioning process. In particular, we show that allowing for rotation of the focal plane can improve the efficiency of the process in ~3.5-4.5% even if only small adjustments are permitted (up to 2 deg). For instru...

  9. Generating the Observed Baryon Asymmetry from the Inflaton Field

    CERN Document Server

    Hertzberg, Mark P

    2013-01-01

    We propose a mechanism by which the inflaton can generate baryogenesis, by taking the inflaton to be a complex scalar field with a weakly broken global symmetry and present a new version of the Affleck-Dine mechanism. The smallness of the breaking is motivated both by technical naturalness and a requirement for inflation. We study inflation driven by a quadratic potential for simplicity and discuss generalizations to other potentials. We compute the inflationary dynamics and find that a conserved particle number is obtained towards the end of inflation. We then explain in detail the later decay to baryons. We present two promising embeddings in particle physics: (i) using high dimension operators for a gauge singlet; we find this leads to the observed asymmetry for decay controlled by the ~GUT scale and this is precisely the regime where the EFT applies. (ii) using a colored inflaton, which requires small couplings. We also point out two observational consequences: a possible large scale dipole in the baryon ...

  10. ON THE FORCE-FREE NATURE OF PHOTOSPHERIC SUNSPOT MAGNETIC FIELDS AS OBSERVED FROM HINODE (SOT/SP)

    Energy Technology Data Exchange (ETDEWEB)

    Tiwari, Sanjiv Kumar, E-mail: tiwari@mps.mpg.de [Udaipur Solar Observatory, Physical Research Laboratory, Dewali, Bari Road, Udaipur 313 001 (India)

    2012-01-01

    A magnetic field is force-free if there is no interaction between it and the plasma in the surrounding atmosphere, i.e., electric currents are aligned with the magnetic field, giving rise to zero Lorentz force. The computation of various magnetic parameters, such as magnetic energy (using the virial theorem), gradient of twist of sunspot magnetic fields (computed from the force-free parameter {alpha}), and any kind of extrapolation, heavily hinges on the force-free approximation of the photospheric sunspot magnetic fields. Thus, it is of vital importance to inspect the force-free behavior of sunspot magnetic fields. The force-free nature of sunspot magnetic fields has been examined earlier by some researchers, ending with incoherent results. Accurate photospheric vector field measurements with high spatial resolution are required to inspect the force-free nature of sunspots. For this purpose, we use several vector magnetograms of high spatial resolution obtained from the Solar Optical Telescope/Spectro-Polarimeter on board Hinode. Both the necessary and sufficient conditions for force-free nature are examined by checking the global and local nature of equilibrium magnetic forces over sunspots. We find that sunspot magnetic fields are not very far from the force-free configuration, although they are not completely force-free on the photosphere. The umbral and inner penumbral fields are more force-free than the middle and outer penumbral fields. During their evolution, sunspot magnetic fields are found to maintain their proximity to force-free field behavior. Although a dependence of net Lorentz force components is seen on the evolutionary stages of the sunspots, we do not find a systematic relationship between the nature of sunspot magnetic fields and the associated flare activity. Further, we examine whether the fields at the photosphere follow linear or nonlinear force-free conditions. After examining this in various complex and simple sunspots, we conclude that

  11. Design of a superconducting insert to obtain a high and quasi-uniform magnetic force field

    Energy Technology Data Exchange (ETDEWEB)

    Leveque, Jean [GREEN, University of Nancy BP 239, 54506 Vandoeuvre (France); Netter, Denis [GREEN, University of Nancy BP 239, 54506 Vandoeuvre (France); Quettier, Lionel [DAPNIA, CEA Saclay (France); Mailfert, Alain [INPL, 2 av de la foret de Haye, 54516 Vandoeuvre (France)

    2005-10-01

    In this paper, we study the magnetic force generated by the combination of a solenoid and a superconducting ring insert. We have focused our study on the uniformity of the magnetic force. We use a genetic algorithm to determine the optimal shape of the superconducting ring. We are able to obtain uniformity of 0.5% variance. We also study the influence of several factors on uniformity, such as the critical current of the coil, the ring, and the size of the working area.

  12. High sensitive space electric field sensing based on micro fiber interferometer with field force driven gold nanofilm

    Science.gov (United States)

    Zhu, Tao; Zhou, Liming; Liu, Min; Zhang, Jingdong; Shi, Leilei

    2015-10-01

    The traditional electrical field sensing can be realized by utilizing electro-optic materials or liquid crystals, and has limitations of easy breakdown, free assembly and difficult measurement of low-frequency. Here, we propose a new method to realize safe measurement of spatial dynamic electric field by using a micro fiber interferometer integrated with gold nanofilm. The energy of the electric charge received through antenna forms the intrinsic electric field with two micro electrodes, one of which is the 120 nm gold film vibration beam micromachined by femtosecond lasers and integrated with the micro fiber. The change of the intrinsic electric field force due to the spatial electric field will cause the vibration of the film beam. By demodulating the output signal of the micro fiber interferometer, the electric field can be measured. We demonstrate the detectable frequency ranges from tens of Hz to tens of KHz, and the minimum electric field intensity is ~200 V/m at 1 KHz. Our electric field measurement technology combining optical fiber interference with gold nanostructures shows the advantages of security, high sensitivity, compact size, and multiplexed multi-point and remote detection.

  13. Convergence of Phase-Field Free Energy and Boundary Force for Molecular Solvation

    Science.gov (United States)

    Dai, Shibin; Li, Bo; Lu, Jianfeng

    2017-08-01

    We study a phase-field variational model for the solvation of charged molecules with an implicit solvent. The solvation free-energy functional of all phase fields consists of the surface energy, solute excluded volume and solute-solvent van der Waals dispersion energy, and electrostatic free energy. The surface energy is defined by the van der Waals-Cahn-Hilliard functional with squared gradient and a double-well potential. The electrostatic part of free energy is defined through the electrostatic potential governed by the Poisson-Boltzmann equation in which the dielectric coefficient is defined through the underlying phase field. We prove the continuity of the electrostatics—its potential, free energy, and dielectric boundary force—with respect to the perturbation of the dielectric boundary. We also prove the {Γ} -convergence of the phase-field free-energy functionals to their sharp-interface limit, and the equivalence of the convergence of total free energies to that of all individual parts of free energy. We finally prove the convergence of phase-field forces to their sharp-interface limit. Such forces are defined as the negative first variations of the free-energy functional; and arise from stress tensors. In particular, we obtain the force convergence for the van der Waals-Cahn-Hilliard functionals with minimal assumptions.

  14. Measurement of hydrodynamic force generation by swimming dolphins using bubble DPIV.

    Science.gov (United States)

    Fish, Frank E; Legac, Paul; Williams, Terrie M; Wei, Timothy

    2014-01-15

    Attempts to measure the propulsive forces produced by swimming dolphins have been limited. Previous uses of computational hydrodynamic models and gliding experiments have provided estimates of thrust production by dolphins, but these were indirect tests that relied on various assumptions. The thrust produced by two actively swimming bottlenose dolphins (Tursiops truncatus) was directly measured using digital particle image velocimetry (DPIV). For dolphins swimming in a large outdoor pool, the DPIV method used illuminated microbubbles that were generated in a narrow sheet from a finely porous hose and a compressed air source. The movement of the bubbles was tracked with a high-speed video camera. Dolphins swam at speeds of 0.7 to 3.4 m s(-1) within the bubble sheet oriented along the midsagittal plane of the animal. The wake of the dolphin was visualized as the microbubbles were displaced because of the action of the propulsive flukes and jet flow. The oscillations of the dolphin flukes were shown to generate strong vortices in the wake. Thrust production was measured from the vortex strength through the Kutta-Joukowski theorem of aerodynamics. The dolphins generated up to 700 N during small amplitude swimming and up to 1468 N during large amplitude starts. The results of this study demonstrated that bubble DPIV can be used effectively to measure the thrust produced by large-bodied dolphins.

  15. Directions in US Air Force space power energy generation and distribution technology

    Science.gov (United States)

    Reinhardt, Kitt; Keener, Dave; Schuller, Mike

    1997-01-01

    Recent trends in the development of high efficiency, light-weight, reliable and cost-effective space power technologies needed to support the development of near-term, next-generation government and commercial satellites will be discussed. Significant advancements in light-weight and reduced volume electrical power system (EPS) components are required to enable the design of future smallsats with power requirements of less than 1000 W to monster-sats having projected power demands ranging from 10-50 kW for civilian and military communications and space based radar needs. For these missions increased emphasis is placed on reducing total satellite mass to enable use of smaller, less costly, and easier to deploy launch vehicles. In support of these requirements a complement of power generation, power management and distribution, and energy storage technologies are under development at the Air Force Phillips Laboratory Space and Missiles Technology Directorate. Specific technologies presented in this paper include high efficiency multijunction solar cells, low-cost thin-film solar cells, ultra light-weight flexible solar arrays, solar electric thermal converters, and high-voltage (70-130 V) and high-efficiency power management and distribution (PMAD) electronics. The projected impact of EPS subsystem performance on existing, near-term, and next-generation 10-50 kW military satellites will be discussed, along with technical issues and status of EPS component development.

  16. Multi-scale analysis of the electromagnetic self-force in a weak gravitational field

    CERN Document Server

    Pound, Adam

    2007-01-01

    We examine the motion of a charged particle in a weak gravitational field. In addition to the Newtonian gravity exerted by a large central body, the particle is subjected to an electromagnetic self-force that contains both a conservative piece and a radiation-reaction piece. This toy problem shares many of the features of the strong-field gravitational self-force problem, and it is sufficiently simple that it can be solved exactly with numerical methods, and approximately with analytical methods. We submit the equations of motion to a multi-scale analysis, and we examine the roles of the conservative and radiation-reaction pieces of the self-force. We show that the radiation-reaction force drives secular changes in the orbit's semilatus rectum and eccentricity, while the conservative force drives a secular regression of the periapsis and affects the orbital time function; neglect of the conservative term can hence give rise to an important phasing error. We next examine what might be required in the formulati...

  17. A reoptimized GROMOS force field for hexopyranose-based carbohydrates accounting for the relative free energies of ring conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic linkage conformers.

    Science.gov (United States)

    Hansen, Halvor S; Hünenberger, Philippe H

    2011-04-30

    This article presents a reoptimization of the GROMOS 53A6 force field for hexopyranose-based carbohydrates (nearly equivalent to 45A4 for pure carbohydrate systems) into a new version 56A(CARBO) (nearly equivalent to 53A6 for non-carbohydrate systems). This reoptimization was found necessary to repair a number of shortcomings of the 53A6 (45A4) parameter set and to extend the scope of the force field to properties that had not been included previously into the parameterization procedure. The new 56A(CARBO) force field is characterized by: (i) the formulation of systematic build-up rules for the automatic generation of force-field topologies over a large class of compounds including (but not restricted to) unfunctionalized polyhexopyranoses with arbritrary connectivities; (ii) the systematic use of enhanced sampling methods for inclusion of experimental thermodynamic data concerning slow or unphysical processes into the parameterization procedure; and (iii) an extensive validation against available experimental data in solution and, to a limited extent, theoretical (quantum-mechanical) data in the gas phase. At present, the 56A(CARBO) force field is restricted to compounds of the elements C, O, and H presenting single bonds only, no oxygen functions other than alcohol, ether, hemiacetal, or acetal, and no cyclic segments other than six-membered rings (separated by at least one intermediate atom). After calibration, this force field is shown to reproduce well the relative free energies of ring conformers, anomers, epimers, hydroxymethyl rotamers, and glycosidic linkage conformers. As a result, the 56A(CARBO) force field should be suitable for: (i) the characterization of the dynamics of pyranose ring conformational transitions (in simulations on the microsecond timescale); (ii) the investigation of systems where alternative ring conformations become significantly populated; (iii) the investigation of anomerization or epimerization in terms of free-energy differences

  18. Nature of the coupling between neural drive and force-generating capacity in the human quadriceps muscle.

    Science.gov (United States)

    Hug, François; Goupille, Clément; Baum, Daniel; Raiteri, Brent J; Hodges, Paul W; Tucker, Kylie

    2015-11-22

    The force produced by a muscle depends on both the neural drive it receives and several biomechanical factors. When multiple muscles act on a single joint, the nature of the relationship between the neural drive and force-generating capacity of the synergistic muscles is largely unknown. This study aimed to determine the relationship between the ratio of neural drive and the ratio of muscle force-generating capacity between two synergist muscles (vastus lateralis (VL) and vastus medialis (VM)) in humans. Twenty-one participants performed isometric knee extensions at 20 and 50% of maximal voluntary contractions (MVC). Myoelectric activity (surface electromyography (EMG)) provided an index of neural drive. Physiological cross-sectional area (PCSA) was estimated from measurements of muscle volume (magnetic resonance imaging) and muscle fascicle length (three-dimensional ultrasound imaging) to represent the muscles' force-generating capacities. Neither PCSA nor neural drive was balanced between VL and VM. There was a large (r = 0.68) and moderate (r = 0.43) correlation between the ratio of VL/VM EMG amplitude and the ratio of VL/VM PCSA at 20 and 50% of MVC, respectively. This study provides evidence that neural drive is biased by muscle force-generating capacity, the greater the force-generating capacity of VL compared with VM, the stronger bias of drive to the VL.

  19. Extension of the GLYCAM06 Biomolecular Force Field to Lipids, Lipid Bilayers and Glycolipids.

    Science.gov (United States)

    Tessier, Matthew B; Demarco, Mari L; Yongye, Austin B; Woods, Robert J

    2008-01-01

    GLYCAM06 is a generalisable biomolecular force field that is extendible to diverse molecular classes in the spirit of a small-molecule force field. Here we report parameters for lipids, lipid bilayers and glycolipids for use with GLYCAM06. Only three lipid-specific atom types have been introduced, in keeping with the general philosophy of transferable parameter development. Bond stretching, angle bending, and torsional force constants were derived by fitting to quantum mechanical data for a collection of minimal molecular fragments and related small molecules. Partial atomic charges were computed by fitting to ensemble-averaged quantum-computed molecular electrostatic potentials.In addition to reproducing quantum mechanical internal rotational energies and experimental valence geometries for an array of small molecules, condensed-phase simulations employing the new parameters are shown to reproduce the bulk physical properties of a DMPC lipid bilayer. The new parameters allow for molecular dynamics simulations of complex systems containing lipids, lipid bilayers, glycolipids, and carbohydrates, using an internally consistent force field. By combining the AMBER parameters for proteins with the GLYCAM06 parameters, it is also possible to simulate protein-lipid complexes and proteins in biologically relevant membrane-like environments.

  20. Force between a magnetic tip and an inhomogeneous superconductor at zero field

    Energy Technology Data Exchange (ETDEWEB)

    Carneiro, Gilson, E-mail: gmc@if.ufrj.b [Instituto de Fisica, Universidade Federal do Rio de Janeiro, C.P. 68528, 21941-972, Rio de Janeiro-RJ (Brazil)

    2010-10-01

    The force exerted by a semi-infinite inhomogeneous superconductor with a planar interface to vacuum on a magnetic tip is studied theoretically in the absence of external magnetic fields. It is shown that the force has a contribution from inhomogeneities due to material defects with unique characteristics. Defects are taken into account in the London limit by allowing the mass parameter to vary spatially. The contribution from defects to the force is calculated analytically to first order in the deviation of the mass parameter from its constant value for the homogeneous superconductor, assuming that the tip is a point dipole perpendicular to the interface, and that it does not spontaneously create vortex matter. Random point defects and linear localized defects are considered phenomenologically. For each defect type the force dependence on the dipole position coordinates is obtained, and the force magnitudes are estimated numerically. The predictions for the dependence of the linear defect force on the dipole lateral position are found to agree qualitatively with experiment.