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1

Magnetoelectric force microscopy based on magnetic force microscopy with modulated electric field.  

PubMed

We present the realization of a mesoscopic imaging technique, namely, the Magnetoelectric Force Microscopy (MeFM), for visualization of local magnetoelectric effect. The basic principle of MeFM is the lock-in detection of local magnetoelectric response, i.e., the electric field-induced magnetization, using magnetic force microscopy. We demonstrate MeFM capability by visualizing magnetoelectric domains on single crystals of multiferroic hexagonal manganites. Results of several control experiments exclude artifacts or extrinsic origins of the MeFM signal. The parameters are tuned to optimize the signal to noise ratio. PMID:24880381

Geng, Yanan; Wu, Weida

2014-05-01

2

Electricity: The Mysterious Force  

NSDL National Science Digital Library

This document examines the mysterious force of electricity. The reading will focus on the physical properties of electricity and discuss topics such as (1) The Atom of Carbon, (2) Static electricity, (3) Magnets are special, (4) Magnetic fields can produce electricity, (5) Batteries produce electricity, (6) Electricity travels in circuits, (7) Secondary energy source, (8) Making electricity, (9) Moving electricity from power plants to homes, (10) Fuels that make electricity, (11) Fossil fuel power plants, (12) Nuclear power plants, (13) Hydropower plants, (14) What's a Watt, and (15) Cost of electricity. The document also depicts illustrations of a bar magnet, turbine generator, transporting electricity, U.S. electricity production, peak demand, and energy efficiency. This resource is structured as an informational booklet to supplement your energy activities or to generate discussion questions.

2008-01-01

3

Forces acting on a particle in a concentration gradient under an externally applied oscillating electric field  

NASA Astrophysics Data System (ADS)

We report a force field on a particle in a concentration (conductivity) gradient under an externally applied oscillating electric field. The conductivity gradient was established through integrated microcapillaries bridging high- and low-conductivity streams in dedicated microchannels. Particles in low-conductivity electrolyte were observed to experience a strong force with the application of an oscillating field and pulled to the microcapillary openings where they were held against the flow. Particle trapping was accompanied by a concurrent electrolyte injection from high- to low-conductivity channel, triggered with the externally applied field and further contributed to the conductivity gradient near the trapping sites. We experimentally evaluated the force dependence on the magnitude and frequency of the excitation field for 10 ?m polystyrene particles immersed at various conductivity levels. The experiments suggest that the observed force cannot be simply explained by dielectrophoresis or diffusiophoresis alone and further requires the consideration of a so-called concentration polarization force. This force has been rather recently postulated based on a theoretical treatment and yet to be experimentally validated. Using the theoretical treatment of this force, together with fluidic drag and diffusiophoresis, we correctly predicted trapping trajectories of particles based on a simultaneous solution of Poisson-Nernst-Planck and Stokes equations. The predicted and measured trapping velocities were found in reasonable agreement (within a factor of <1.6), suggesting that the consideration of the concentration polarization force is necessary for describing the observed particle behavior.

Luo, Yuan; Yobas, Levent

2014-09-01

4

Analytical solutions and validation of electric field and dielectrophoretic force in a bio-microfluidic channel.  

PubMed

In a microbiological device, cell or particle manipulation and characterization require the use of electric field on different electrodes in several configurations and shapes. To efficiently design microelectrodes within a microfluidic channel for dielectrophoresis focusing, manipulation and characterization of cells, the designer will seek the exact distribution of the electric potential, electric field and hence dielectrophoresis force exerted on the cell within the microdevice. In this paper we describe the approach attaining the analytical solution of the dielectrophoretic force expression within a microchannel with parallel facing same size electrodes present on the two faces of channel substrates, with opposite voltages on the pair electrodes. Simple Fourier series mathematical expressions are derived for electric potential, electric field and dielectric force between two distant finite-size electrodes. Excellent agreement is found by comparing the analytical results calculated using MATLAB™ with numerical ones obtained by Comsol. This analytical result can help the designer to perform simple design parametric analysis. Bio-microdevices are also designed and fabricated to illustrate the theoretical solution results with the experimental data. Experiments with red blood cells show the dielectrophoretic force contour plots of the analytical data matched to the experimental results. PMID:22287173

Nerguizian, Vahé; Alazzam, Anas; Roman, Dacian; Stiharu, Ion; Burnier, Miguel

2012-02-01

5

The Effect of Electric Fields In A Classic Introductory Physics Treatment of Eddy Current Forces  

E-print Network

A simple model of eddy currents in which current is computed solely from magnetic forces acting on electrons proves accessible to introductory students and gives a good qualitative account of eddy current forces. However, this model cannot be complete; it ignores the electric fields that drive current outside regions of significant magnetic field. In this paper we show how to extend the model to obtain a boundary value problem for current density. Solution of this problem in polar coordinates shows that the electric field significantly affects the quantitative results and presents an exercise suitable for upper division students. We apply elliptic cylindrical coordinates to generalize the result and offer an exercise useful for teaching graduate students how to use non-standard coordinate systems.

P. J. Salzman; John Robert Burke; Susan M. Lea

2006-07-23

6

Investigation of domain structure of TGS single crystal after a transverse electric field by piezoresponse force microscopy  

Microsoft Academic Search

An investigation of the influence of electric field transverse to the ferroelectric axis bHOP and parallel to cHOP axis of triglycine sulfate (TGS) single crystal on ferroelectric domain structure was performed by piezoresponse force microscopy. To check if the applied electric field changed the dielectric properties and ferroelectric domain structure the hysteresis loop measurements were carried out as well as

K. ?wikiel; D. Kajewski

2010-01-01

7

Effects of AC Electrical Field on the Dielectrophoresis Force of Dielectric Elastomers and Blends  

NASA Astrophysics Data System (ADS)

The effects of frequency and amplitude of AC electric field on the deflection and the dielectrophoresis force of an acrylic elastomer (AR71), styrene copolymers (SAR and SBR), and the blends of doped PPP and AR71 are investigated. The dielectrophoresis forces of the dielectric elastomers and blends were measured by using a vertical cantilever fixture at various frequencies (0.3 to 60 Hz) and at AC electric field strengths of 200-800 Vpp/mm. The effects of the thicknesses of the specimens and the particle concentration are studied. The doped PPP particles are embedded in the AR71 with concentrations of 1, 10, and 20 %vol. The dielectrophoresis forces and deflection distance of the dielectric elastomers and blends generally increase with increasing amplitude but slightly decrease with increasing frequency; and they dramatically drop at the cut-off frequency. The cut-off frequencies are 7.84, 1.45, and 0.74 Hz for AR71, SAR, and SBR, respectively, at E of 800 Vpp/mm and a thickness of 0.7 to 0.8 mm. After blending the AR71 with doped PPP, the cut-off frequencies of the 1 %vol, 10 %vol and 20 %vol of doped PPP are 18.51, 15.28, and 10.67 Hz, respectively, at an E of 800 Vpp/mm and a thickness of 0.2 to 0.3 mm. The conductive polymer particles are shown here to improve the electromechanical responses at high frequency.

Sirivat, Anuvat; Kunanuruksapong, Ruksapong

2011-03-01

8

Molecular dynamics study of response of liquid N,N-dimethylformamide to externally applied electric field using a polarizable force field  

SciTech Connect

The behavior of Liquid N,N-dimethylformamide subjected to a wide range of externally applied electric fields (from 0.001 V/nm to 1 V/nm) has been investigated through molecular dynamics simulation. To approach the objective the AMOEBA polarizable force field was extended to include the interaction of the external electric field with atomic partial charges and the contribution to the atomic polarization. The simulation results were evaluated with quantum mechanical calculations. The results from the present force field for the liquid at normal conditions were compared with the experimental and molecular dynamics results with non-polarizable and other polarizable force fields. The uniform external electric fields of higher than 0.01 V/nm have a significant effect on the structure of the liquid, which exhibits a variation in numerous properties, including molecular polarization, local cluster structure, rotation, alignment, energetics, and bulk thermodynamic and structural properties.

Gao, Weimin; Niu, Haitao; Lin, Tong; Wang, Xungai; Kong, Lingxue [Institute for Frontier Materials, Deakin University, Waurn Ponds VIC 3216 (Australia)] [Institute for Frontier Materials, Deakin University, Waurn Ponds VIC 3216 (Australia)

2014-01-28

9

Molecular dynamics study of response of liquid N,N-dimethylformamide to externally applied electric field using a polarizable force field  

NASA Astrophysics Data System (ADS)

The behavior of Liquid N,N-dimethylformamide subjected to a wide range of externally applied electric fields (from 0.001 V/nm to 1 V/nm) has been investigated through molecular dynamics simulation. To approach the objective the AMOEBA polarizable force field was extended to include the interaction of the external electric field with atomic partial charges and the contribution to the atomic polarization. The simulation results were evaluated with quantum mechanical calculations. The results from the present force field for the liquid at normal conditions were compared with the experimental and molecular dynamics results with non-polarizable and other polarizable force fields. The uniform external electric fields of higher than 0.01 V/nm have a significant effect on the structure of the liquid, which exhibits a variation in numerous properties, including molecular polarization, local cluster structure, rotation, alignment, energetics, and bulk thermodynamic and structural properties.

Gao, Weimin; Niu, Haitao; Lin, Tong; Wang, Xungai; Kong, Lingxue

2014-01-01

10

Field Measurements of Heating Efficiency of Electric Forced-Air Furnaces in Six Manufactured Homes.  

SciTech Connect

This report presents the results of field measurements of heating efficiency for six manufactured homes in the Pacific Northwest heated with electric forced-air systems. This is the first in a series of regional and national efforts to measure in detail the heating efficiency of manufactured homes. Only six homes were included in this study because of budgetary constraints; therefore this is not a representative sample. These investigations do provide some useful information on the heating efficiency of these homes. Useful comparisons can be drawn between these study homes and site-built heating efficiencies measured with a similar protocol. The protocol used to test these homes is very similar to another Ecotope protocol used in the study conducted in 1992 and 1993 for the Bonneville Power Administration to test the heating efficiency of 24 homes. This protocol combined real-time power measurements of furnace energy usage with energy usage during co-heat periods. Accessory data such as house and duct tightness measurements and tracer gas measurements were used to describe these homes and their heating system efficiency. Ensuring that manufactured housing is constructed in an energy and resource efficient manner is of increasing concern to manufactured home builders and consumers. No comparable work has been done to measure the heating system efficiency of MCS manufactured homes, although some co-heat tests have been performed on manufactured homes heated with natural gas to validate HUD thermal standards. It is expected that later in 1994 more research of this kind will be conducted, and perhaps a less costly and less time-consuming method for testing efficiencies will be develops.

Davis, Bob; Palmiter, Larry S.; Siegel, Jeff

1994-07-26

11

Exploring Forces: Static Electricity  

NSDL National Science Digital Library

In this activity, learners investigate what happens when you build up static electricity on plastic balls. Learners discover that electrostatic forces cause smaller balls to suspend in a tube, while larger balls fall to the bottom. This activity shows learners that size can affect the way a material behaves. This activity is a great way to talk about how different things behave at the nanoscale.

Network, Nanoscale I.; Sciencenter

2010-01-01

12

Study of electric field distribution in AlGalnP light-emitting diode by Kelvin probe force microscopy  

NASA Astrophysics Data System (ADS)

This work presents results of study of different AlGaInP light-emitting diodes by using Kelvin force probe microscopy. Study of current-voltage characteristics and electric field distribution had shown that for all type of experimental samples containing multiple quantum wells the most significant series resistance of heterostructures is determined by p-isotype heterojunction and confinement p-layer.

Oleynik, V. L.; Prudaev, I. A.; Novikov, Vad A.; Ryaboshtan, Yu L.; Gorlachuk, P. V.

2014-10-01

13

Specific features of the thermal electromotive force in Bi quantum wires in transverse magnetic and electric fields  

NASA Astrophysics Data System (ADS)

The thermal electromotive force (emf) in Bi quantum wires has been calculated in the model of potential in the form of a paraboloid of revolution in a uniform magnetic field H, which is normal to the axis of the studied nanostructure, and in a direct-current (dc) electric field E ? H. It has been shown that, with an increase in E, the thermal emf ?xx is described by a nonmonotonic function at different values of H. A physical interpretation of this behavior of ?xx as a function of E is proposed with account for the interaction between carriers and the rough surface of the nanowire.

Sinyavskii, E. P.; Solovenko, V. G.

2014-11-01

14

Influence of electric and gravitational force fields on nucleate boiling of FC72 on a wire: Results of a sounding rocket campaign  

NASA Astrophysics Data System (ADS)

The paper reports the main results obtained during a sounding rocket experiment about the effect of gravity and electric field on nucleate pool boiling of saturated FC72 on a wire. The effect of gravitational and electric forces on the nucleate pool boiling regime have been experimentally studied. The nucleate boiling region has been found to narrow at low gravity (corresponding to a decreasing critical heat flux, CHF) and to widen thanks to the action of an imposed electric field, that increases the CHF value. Both nucleate boiling heat transfer and CHF becomes insensitive to gravity beyond a certain threshold of the applied electric field. .

di Marco, P.; Grassi, W.

2002-01-01

15

Electric and Magnetic Forces  

NSDL National Science Digital Library

SciGuides are a collection of thematically aligned lesson plans, simulations, and web-based resources for teachers to use with their students centered on standards-aligned science concepts. People have known about and experienced electricity an

2010-02-10

16

Physics 2000: The Electric Force  

NSDL National Science Digital Library

This webpage demonstrates electric force exerted by positive and negative charges through a simulation of the behaviour of an electron in the presence of a proton. The concept is explained in the form of a conversation between two people to make learning more interesting. This webpage is a part of an extensive collection of physics tutorials.

Physics 2000

2006-07-06

17

Lattice QCD with strong external electric fields.  

PubMed

We study particle generation by a strong electric field in lattice QCD. To avoid the sign problem of the Minkowskian electric field, we adopt the "isospin" electric charge. When a strong electric field is applied, the insulating vacuum is broken down and pairs of charged particles are produced by the Schwinger mechanism. The competition against the color confining force is also discussed. PMID:25166523

Yamamoto, Arata

2013-03-15

18

Fluid Mechanical and Electrical Fluctuation Forces in Colloids  

E-print Network

Fluctuations in fluid velocity and fluctuations in electric fields may both give rise to forces acting on small particles in colloidal suspensions. Such forces in part determine the thermodynamic stability of the colloid. At the classical statistical thermodynamic level, the fluid velocity and electric field contributions to the forces are comparable in magnitude. When quantum fluctuation effects are taken into account, the electric fluctuation induced van der Waals forces dominate those induced by purely fluid mechanical motions. The physical principles are applied in detail for the case of colloidal particle attraction to the walls of the suspension container and more briefly for the case of forces between colloidal particles.

D. Drosdoff; A. Widom

2004-10-06

19

Forces Between Electrical Current Elements  

NASA Astrophysics Data System (ADS)

The momentum of a charged particle is p*=mv*-qA*, where m, v*, q and A* are respectively mass, velocity, charge and vector potential, and * denotes vector. Hence current element I'ds'* exerts a force on Ids*: ddF*=b(II'/r3)(r*.ds*)ds'*=ddF*(magnetic)+b(II'/r3)(ds*.ds'*)r*(nonmagnetic), where b=10-7 Newton/Ampere2. From ds'* to ds* is r*. This causes a nonuniform charge distribution along the circuit(s) containing Ids* and I'ds'* whose field transfers ddF* from conduction electrons to ions. The line integral of ddF* is tensile between points of a rectilinear portion of a circuit. The Lorentz force and Ampere's third law of magnetostatic force are invalid if ddF* is confirmed by a nonzero torque of a Marinov motor. If Ids* has velocity w* relative to I'ds'*: ddF* acts on conduction electrons of ds* as when w=0 and also acts on electrons and nuclei of ions of ds* as current elements w*dq=Dw*ds; D is linear charge density of ions. Resulting polarization by equal but opposite forces on electrons and nuclei of ions transfers ddF* from conduction electrons to ions. J. P. Wesley's intuitive assumption is justified.

Driscoll, Robert B.

2003-04-01

20

Field-regulated force by grafted polyelectrolytes  

E-print Network

Generation of mechanical force regulated by external electric field is studied both theoretically and by molecular dynamics (MD) simulations. The force arises in deformable bodies linked to the free end of a grafted polyelectrolyte chain which is exposed to electric field that favours its adsorption. We consider a few target bodies with different force-deformation relations including (i) linear and (ii) cubic dependences as well as (iii) Hertzian-like force. Such force-deformation relations mimic the behaviour of (i) coiled and (ii) stretched polymer chains, respectively, or (iii) that of a squeezed colloidal particle. The magnitude of the arising force varies over a wide interval although the electric field alters within a relatively narrow range only. The predictions of our theory agree quantitatively well with the results of numerical simulations. Both cases of zero and finite electrical current are investigated and we do not obtain substantial differences in the force generated. The phenomenon studied could possibly be utilised to design, e.g., vice-like devices to fix nano-sized objects.

Christian Seidel; Yury A. Budkov; Nikolay V. Brilliantov

2014-11-08

21

Interpreting Kelvin probe force microscopy under an applied electric field: local electronic behavior of vapor-liquid-solid Si nanowires.  

PubMed

Kelvin probe force microscopy (KPFM) is used to characterize the electrical characteristics of vapor-liquid-solid (VLS) Si nanowires (NWs) that are grown in-place between two predefined electrodes. KPFM measurements are performed under an applied bias. Besides contact potential differences due to differing materials, the two other primary contributions to measured variations on Si NWs between electrodes are: trapped charges at interfaces, and the parallel and serial capacitance, which are accounted for with voltage normalization and oxide normalization. These two normalization processes alongside finite-element-method simulations are necessary to characterize the bias-dependent response of Si NWs. After applying both normalization methods on open-circuit NWs, which results in a baseline of zero, we conclude that we have accounted for all the major contributions to CPDs and we can isolate effects due to applied bias such as impurity states and charged carrier flow, as well as find open connections when NWs are connected in parallel. These characterization and normalization methods can also be used to determine that the specific contact resistance of electrodes to the NWs is on the order of ?? cm². Thus, the VLS growth method between predefined electrodes overcomes the challenge of making low-resistance contacts to nanoscale systems. Thereby, the experiments and analysis presented outline a systematic method for characterizing nanowires in parallel arrays under device operation conditions. PMID:23609527

Quitoriano, Nathaniel J; Sanderson, Robert N; Bae, Sung-Soo; Ragan, Regina

2013-05-24

22

Interpreting Kelvin probe force microscopy under an applied electric field: local electronic behavior of vapor-liquid-solid Si nanowires  

NASA Astrophysics Data System (ADS)

Kelvin probe force microscopy (KPFM) is used to characterize the electrical characteristics of vapor-liquid-solid (VLS) Si nanowires (NWs) that are grown in-place between two predefined electrodes. KPFM measurements are performed under an applied bias. Besides contact potential differences due to differing materials, the two other primary contributions to measured variations on Si NWs between electrodes are: trapped charges at interfaces, and the parallel and serial capacitance, which are accounted for with voltage normalization and oxide normalization. These two normalization processes alongside finite-element-method simulations are necessary to characterize the bias-dependent response of Si NWs. After applying both normalization methods on open-circuit NWs, which results in a baseline of zero, we conclude that we have accounted for all the major contributions to CPDs and we can isolate effects due to applied bias such as impurity states and charged carrier flow, as well as find open connections when NWs are connected in parallel. These characterization and normalization methods can also be used to determine that the specific contact resistance of electrodes to the NWs is on the order of ?? cm2. Thus, the VLS growth method between predefined electrodes overcomes the challenge of making low-resistance contacts to nanoscale systems. Thereby, the experiments and analysis presented outline a systematic method for characterizing nanowires in parallel arrays under device operation conditions.

Quitoriano, Nathaniel J.; Sanderson, Robert N.; Bae, Sung-Soo; Ragan, Regina

2013-05-01

23

Electric Field Example 10  

NSDL National Science Digital Library

The square represents a cross section of a cube. Use the test charge to explore the direction of the electric field inside the cube. Click the cursor anywhere inside the cube to measure the magnitude of the electric field. Use it also to determine the dimensions of the cube. Find the flux through each side of the cube.

Christian, Wolfgang; Belloni, Mario

2008-02-19

24

Force field parameters for aminoorganosilanes  

NASA Astrophysics Data System (ADS)

Force field parameters for new compound classes are an important prerequisite for the fast and reliable modeling of these compounds with commercial available modeling software. The development of MMX force field parameters for aminoorganosilanes is described in this work. Combined efforts have been undertaken including synthesis, structural characterization of suitable compounds, and quantum chemical calculation with a systematic set of model compounds. 1,2-Dibenzylamino-1,2-dichloro-dimethyldisilane has been synthesized and characterized by X-ray structure analysis. It is possible to calculate bond lengths and angles of this and other aminosilanes with the new force field parameters.

Meinel, Birgit; Günther, Betty; Böhme, Uwe

2015-01-01

25

Formation, characterization and dynamics of onion like carbon structures from nanodiamonds using reactive force-fields for electrical energy storage  

SciTech Connect

We simulate the experimentally observed graphitization of nanodiamonds into multi-shell onion-like carbon nanostructures, also called carbon onions, at different temperatures, using reactive force fields. The simulations include long-range Coulomb and van der Waals interactions. Our results suggest that long-range interactions play a crucial role in the phase-stability and the graphitization process. Graphitization is both enthalpically and entropically driven and can hence be controlled with temperature. The outer layers of the nanodiamond have a lower kinetic barrier toward graphitization irrespective of the size of the nanodiamond and graphitize within a few-hundred picoseconds, with a large volume increase. The inner core of the nanodiamonds displays a large size-dependent kinetic barrier, and graphitizes much more slowly with abrupt jumps in the internal energy. It eventually graphitizes by releasing pressure and expands once the outer shells have graphitized. The degree of transformation at a particular temperature is thereby determined by a delicate balance between the thermal energy, long-range interactions, and the entropic/enthalpic free energy gained by graphitization. Upon full graphitization, a multi-shell carbon nanostructure appears, with a shell-shell spacing of about {approx}3.4 {angstrom} for all sizes. The shells are highly defective with predominantly five- and seven-membered rings to curve space. Larger nanodiamonds with a diameter of 4 nm can graphitize into spiral structures with a large ({approx}29-atom carbon ring) pore opening on the outermost shell. Such a large one-way channel is most attractive for a controlled insertion of molecules/ions such as Li ions, water, or ionic liquids, for increased electrochemical capacitor or battery electrode applications.

Ganesh, Panchapakesan [ORNL; Kent, Paul R [ORNL; Mochalin, Vadym N [ORNL

2011-01-01

26

Nonconservative electric and magnetic optical forces on submicron dielectric particles  

SciTech Connect

We present a study of the total force on a small lossless dielectric particle, which presents both an electric and magnetic response, in a optical vortex wave field. We show that the force is a simple combination of conservative and nonconservative steady forces that can rectify the flow of magnetodielectric particles. In a vortex lattice the electric-magnetic dipolar interaction can spin the particles either in or out of the whirl sites leading to trapping or diffusion. Specifically, we analyze force effects on submicron silicon spheres in the near infrared, proving that the results previously discussed for hypothetical magnetodielectric particles can be observed for these Si particles.

Gomez-Medina, Raquel; Nieto-Vesperinas, Manuel [Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientificas, Campus de Cantoblanco, Madrid E-28049 (Spain); Saenz, Juan Jose [Departamento de Fisica de la Materia Condensada, Universidad Autonoma de Madrid, E-28049 Madrid (Spain); Donostia International Physics Center (DIPC), Paseo Manuel Lardizabal 4, 20018 Donostia-San Sebastian (Spain)

2011-03-15

27

Drawing Electric Field Lines  

NSDL National Science Digital Library

The panel on the left displays an equipotential plot. The contours represent points at the exact same potential. Draw the electric field lines for this potential by dragging the pencil (at its tip) after clicking the "draw on" button.

Wolfgang Christian

28

Electric Field Example 8  

NSDL National Science Digital Library

One or more objects with uniform charge on them are located just off the screen on the left-hand side. Use the test charge to measure the electric field, and from that determine what type of object they are.

Christian, Wolfgang; Belloni, Mario

2008-02-19

29

Applications of Lorentz force in medical acoustics: Lorentz force hydrophone, Lorentz Force Electrical Impedance Tomography, Imaging of shear waves induced by Lorentz force  

E-print Network

The ability of the Lorentz force to link a mechanical displacement to an electrical current presents a strong interest for medical acoustics, and three applications were studied in this thesis. In the first part of this work, a hydrophone was developed for mapping the particle velocity of an acoustic field. This hydrophone was constructed using a thin copper wire and an external magnetic field. A model was elaborated to determine the relationship between the acoustic pressure and the measured electrical current, which is induced by Lorentz force when the wire vibrates in the acoustic field of an ultrasound transducer. The built prototype was characterized and its spatial resolution, frequency response, sensitivity, robustness and directivity response were investigated. An imaging method called Lorentz Force Electrical Impedance Tomography was also studied. In this method, a biological tissue is vibrated by ultrasound in a magnetic field, which induces an electrical current by Lorentz force. The electrical imp...

Grasland-Mongrain, Pol

2014-01-01

30

Ch 16 Electric Charge &Ch 16. Electric Charge & Electric Field  

E-print Network

Ch 16 Electric Charge &Ch 16. Electric Charge & Electric Field Liu UCD Phy1B 2012 #12;I Basic ConceptsI. Basic Concepts Static electricity: charges at rest Electric charge Like charges repel Unlike charges attract Liu UCD Phy1B 2012 #12;Electric ChargeElectric Charge Electron charge: -eElectron charge

Yoo, S. J. Ben

31

Electrically silent magnetic fields.  

PubMed Central

There has been a significant controversy over the past decade regarding the relative information content of bioelectric and biomagnetic signals. In this paper we present a new, theoretical example of an electrically-silent magnetic field, based on a bidomain model of a cylindrical strand of tissue generalized to include off-diagonal components in the conductivity tensors. The physical interpretation of the off-diagonal components is explained, and analytic expressions for the electrical potential and the magnetic field are found. These expressions show that information not obtainable from electrical potential measurements can be obtained from measurements of the magnetic field in systems with conductivity tensors more complicated than those previously examined. PMID:3779008

Roth, B J; Wikswo, J P

1986-01-01

32

Electricity and Magnetic Fields  

NSDL National Science Digital Library

The grand challenge for this legacy cycle unit is for students to design a way to help a recycler separate aluminum from steel scrap metal. In previous lessons, they have looked at how magnetism might be utilized. In this lesson, students think about how they might use magnets and how they might confront the problem of turning the magnetic field off. Through the accompanying activity students explore the nature of an electrically induced magnetic field and its applicability to the needed magnet.

VU Bioengineering RET Program,

33

Interaction Between Flames and Electric Fields Studied  

NASA Technical Reports Server (NTRS)

The interaction between flames and electric fields has long been an interesting research subject that has theoretical importance as well as practical significance. Many of the reactions in a flame follow an ionic pathway: that is, positive and negative ions are formed during the intermediate steps of the reaction. When an external electric field is applied, the ions move according to the electric force (the Coulomb force) exerted on them. The motion of the ions modifies the chemistry because the reacting species are altered, it changes the velocity field of the flame, and it alters the electric field distribution. As a result, the flame will change its shape and location to meet all thermal, chemical, and electrical constraints. In normal gravity, the strong buoyant effect often makes the flame multidimensional and, thus, hinders the detailed study of the problem.

Yuan, Zeng-Guang; Hegde, Uday

2003-01-01

34

Electric Potential Problem: Drawing Electric Fields  

NSDL National Science Digital Library

Draw the electric field lines for this potential by dragging the pencil (at its tip) after clicking the "draw on" button. After you have drawn your lines, determine which field best corresponds to your potential plot.

Wolfgang Christian

35

Force modulation for enhanced nanoscale electrical sensing.  

PubMed

Scanning probe microscopy employing conductive probes is a powerful tool for the investigation and modification of electrical properties at the nanoscale. Application areas include semiconductor metrology, probe-based data storage and materials research. Conductive probes can also be used to emulate nanoscale electrical contacts. However, unreliable electrical contact and tip wear have severely hampered the widespread usage of conductive probes for these applications. In this paper we introduce a force modulation technique for enhanced nanoscale electrical sensing using conductive probes. This technique results in lower friction, reduced tip wear and enhanced electrical contact quality. Experimental results using phase-change material stacks and platinum silicide conductive probes clearly demonstrate the efficacy of the proposed technique. Furthermore, conductive-mode imaging experiments on specially prepared platinum/carbon samples are presented to demonstrate the widespread applicability of this technique. PMID:21821873

Koelmans, W W; Sebastian, A; Abelmann, L; Despont, M; Pozidis, H

2011-09-01

36

Lorentz Force Electrical Impedance Tomography Pol Grasland-Mongrain1  

E-print Network

Lorentz Force Electrical Impedance Tomography Pol Grasland-Mongrain1 , Jean-Martial Mari1 , Jean-Cl´es Medical Imaging, Electrical Conductivity Ima- ging, Magneto-Acousto-Electrical Tomography, Ultrasonically-Induced Lorentz Force, Lorentz Force Electrical Impedance Tomography, Hall Effect Imaging I. INTRODUCTION

Paris-Sud XI, Université de

37

Electric field replaces gravity in laboratory  

NASA Astrophysics Data System (ADS)

For several years experiments in physical laboratories and in the fitotron have shown that one can replace gravitational field with electrical fields for plants. First obvious experiments in strong electrical fields in the MV/m regi on show that any materials and living plants respond immediately to Coulomb forces. Such fields are found in nature during thunderstorms. One has to be very careful in handling such strong fields for safety reasons. The fair weather global electrical field is about 20,000 times weaker. The coulomb forces are proportional to the square of the field strength and are thus 400 milion times weaker for a field of the order of 100 V/m.Yet it was found that some plants respond to such "weak" fields. We must remember that the electrical field is a factor of 10 38 times stronger than gravitational interaction. In plants we have dissociated in water mineral salts and the ions are subject to such ernormous forces. It was shown and published that the positive charges in the air in fields of the order of 3kV/m enhance lettuce growth by a factor of four relative to fields about 30 times weaker (100V/m). Reversal of the field polarity reverses the direction of plant growth and retards the plant's growth. Such fields overpower the gravitropism in the laboratory. More so horizontal electrical field is othogonal to gravity, now the fields do not see each other. Lettuce now growth horizontally ignoring the gravitational field. We can thus select the plants whose electrotropism even in the laboratory overwhelms gravity. This is important for the long space flights that we must grow vegetarian food for the crew. The successful harvesting of wheat in orbit does not contradict our experimental findings because wheat is not electrotropic like all plants from the grass family. The results of fitotron experiments with kV/m electrical fields are richly illustrated with colour digital photographs. We also subjected the candle flame to very strong horizontal electrical fields. The flame splits into two horizontal flames, ignoring the gravitational field in the laboratory. This result is similar to the behaviour of ions in plants which are responsible for the transport of nutrients from the roots to leaves and opposite ions to roots from the leaves. It shows that we can control the transport phenomena in the process of growth in plants as well as of combustion in space with proper electrical fields.

Gorgolewski, S.

38

Overview - Electric fields. [in magnetosphere  

NASA Technical Reports Server (NTRS)

The electric fields session is designed to review progress in observation, theory, and modeling of magnetospheric electric fields, and to expose important new results. The present report comments on the state and prospects of electric field research, with particular emphasis on relevance to quantitative modeling of the magnetospheric processes. Attention is given to underlying theories and models. Modeling philosophy is discussed relative to explanatory models and representative models. Modeling of magnetospheric electric fields, while in its infancy, is developing rapidly on many fronts employing a variety of approaches. The general topic of magnetospheric electric fields is becoming of prime importance in understanding space plasmas.

Cauffman, D. P.

1979-01-01

39

Magnetospheric electric fields and currents  

NASA Technical Reports Server (NTRS)

The progress made in the years 1983-1986 in understanding the character and operation of magnetospheric electric fields and electric currents is discussed, with emphasis placed on the connection with the interior regions. Special attention is given to determinations of global electric-field configurations, measurements of the response of magnetospheric particle populations to the electric-field configurations, and observations of the magnetospheric currents at high altitude and during northward IMF. Global simulations of current distributions are discussed, and the sources of global electric fields and currents are examined. The topics discussed in the area of impulsive and small-scale phenomena include substorm current systems, impulsive electric fields and associated currents, and field-aligned electrodynamics. A key finding of these studies is that the electric fields and currents are interrelated and cannot be viewed as separate entities.

Mauk, B. H.; Zanetti, L. J.

1987-01-01

40

Point Charge Electric Field in 1D Model  

NSDL National Science Digital Library

The Point Charge Electric Field in 1D model investigates the electric field at various positions along a line, when there are either one or two charged particles on that line. The electric field is represented in two ways. First, there is a movable positive test charge that you can move along the line to sample the field at various locations - the direction of the force on that test charge is the same as the direction of the electric force on the test charge. The second way to represent the electric field is to plot a graph of the electric field as a function of position. For the graph, we define positive field as a field pointing to the right, and negative field as a field pointing to the left.

Duffy, Andrew

2009-10-21

41

Cryosurgery with Pulsed Electric Fields  

PubMed Central

This study explores the hypothesis that combining the minimally invasive surgical techniques of cryosurgery and pulsed electric fields will eliminate some of the major disadvantages of these techniques while retaining their advantages. Cryosurgery, tissue ablation by freezing, is a well-established minimally invasive surgical technique. One disadvantage of cryosurgery concerns the mechanism of cell death; cells at high subzero temperature on the outer rim of the frozen lesion can survive. Pulsed electric fields (PEF) are another minimally invasive surgical technique in which high strength and very rapid electric pulses are delivered across cells to permeabilize the cell membrane for applications such as gene delivery, electrochemotherapy and irreversible electroporation. The very short time scale of the electric pulses is disadvantageous because it does not facilitate real time control over the procedure. We hypothesize that applying the electric pulses during the cryosurgical procedure in such a way that the electric field vector is parallel to the heat flux vector will have the effect of confining the electric fields to the frozen/cold region of tissue, thereby ablating the cells that survive freezing while facilitating controlled use of the PEF in the cold confined region. A finite element analysis of the electric field and heat conduction equations during simultaneous tissue treatment with cryosurgery and PEF (cryosurgery/PEF) was used to study the effect of tissue freezing on electric fields. The study yielded motivating results. Because of decreased electrical conductivity in the frozen/cooled tissue, it experienced temperature induced magnified electric fields in comparison to PEF delivered to the unfrozen tissue control. This suggests that freezing/cooling confines and magnifies the electric fields to those regions; a targeting capability unattainable in traditional PEF. This analysis shows how temperature induced magnified and focused PEFs could be used to ablate cells in the high subzero freezing region of a cryosurgical lesion. PMID:22087224

Daniels, Charlotte S.; Rubinsky, Boris

2011-01-01

42

Polarization effects in molecular mechanical force fields  

PubMed Central

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

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

2014-01-01

43

Lipid14: The Amber Lipid Force Field  

PubMed Central

The AMBER lipid force field has been updated to create Lipid14, allowing tensionless simulation of a number of lipid types with the AMBER MD package. The modular nature of this force field allows numerous combinations of head and tail groups to create different lipid types, enabling the easy insertion of new lipid species. The Lennard-Jones and torsion parameters of both the head and tail groups have been revised and updated partial charges calculated. The force field has been validated by simulating bilayers of six different lipid types for a total of 0.5 ?s each without applying a surface tension; with favorable comparison to experiment for properties such as area per lipid, volume per lipid, bilayer thickness, NMR order parameters, scattering data, and lipid lateral diffusion. As the derivation of this force field is consistent with the AMBER development philosophy, Lipid14 is compatible with the AMBER protein, nucleic acid, carbohydrate, and small molecule force fields. PMID:24803855

2015-01-01

44

Electric and Magnetic Forces between Parallel-Wire Conductors.  

ERIC Educational Resources Information Center

Discusses electric and magnetic forces between parallel-wire conductors and derives, in a simple fashion, order of magnitude estimates of the ratio of the likely electrostatic and electromagnetic forces for a simple parallel-wire balance. (Author/HM)

Morton, N.

1979-01-01

45

Modeling solar force-free magnetic fields  

Microsoft Academic Search

A class of nonlinear force-free magnetic fields is presented, described in terms of the solutions to a second-order, nonlinear ordinary differential equation. These magnetic fields are three-dimensional, filling the infinite half-space above a plane where the lines of force are anchored. They model the magnetic fields of the sun over active regions with a striking geometric realism. The total energy

B. C. Low; Y. Q. Lou

1990-01-01

46

Introduction to power-frequency electric and magnetic fields.  

PubMed Central

This paper introduces the reader to electric and magnetic fields, particularly those fields produced by electric power systems and other sources using frequencies in the power-frequency range. Electric fields are produced by electric charges; a magnetic field also is produced if these charges are in motion. Electric fields exert forces on other charges; if in motion, these charges will experience magnetic forces. Power-frequency electric and magnetic fields induce electric currents in conducting bodies such as living organisms. The current density vector is used to describe the distribution of current within a body. The surface of the human body is an excellent shield for power-frequency electric fields, but power-frequency magnetic fields penetrate without significant attenuation; the electric fields induced inside the body by either exposure are comparable in magnitude. Electric fields induced inside a human by most environmental electric and magnetic fields appear to be small in magnitude compared to levels naturally occurring in living tissues. Detection of such fields thus would seem to require the existence of unknown biological mechanisms. Complete characterization of a power-frequency field requires measurement of the magnitudes and electrical phases of the fundamental and harmonic amplitudes of its three vector components. Most available instrumentation measures only a small subset, or some weighted average, of these quantities. Hand-held survey meters have been used widely to measure power-frequency electric and magnetic fields. Automated data-acquisition systems have come into use more recently to make electric- and magnetic-field recordings, covering periods of hours to days, in residences and other environments.(ABSTRACT TRUNCATED AT 250 WORDS) PMID:8206045

Kaune, W T

1993-01-01

47

Photocatalysts with internal electric fields.  

PubMed

The photocatalytic activity of materials for water splitting is limited by the recombination of photogenerated electron-hole pairs as well as the back-reaction of intermediate species. This review concentrates on the use of electric fields within catalyst particles to mitigate the effects of recombination and back-reaction and to increase photochemical reactivity. Internal electric fields in photocatalysts can arise from ferroelectric phenomena, p-n junctions, polar surface terminations, and polymorph junctions. The manipulation of internal fields through the creation of charged interfaces in hierarchically structured materials is a promising strategy for the design of improved photocatalysts. PMID:24084897

Li, Li; Salvador, Paul A; Rohrer, Gregory S

2014-01-01

48

Molecular simulations: Force fields for carbon capture  

NASA Astrophysics Data System (ADS)

Force fields have been generated that enable accurate simulations of interactions occurring between CO2 molecules and metal-organic frameworks featuring 'open' metal sites, which are promising for carbon capture applications.

Getman, Rachel B.

2012-10-01

49

Cell Membrane Tethers Generate Mechanical Force in Response to Electrical Stimulation  

PubMed Central

Living cells maintain a huge transmembrane electric field across their membranes. This electric field exerts a force on the membrane because the membrane surfaces are highly charged. We have measured electromechanical force generation by cell membranes using optically trapped beads to detach the plasma membrane from the cytoskeleton and form long thin cylinders (tethers). Hyperpolarizing potentials increased and depolarizing potentials decreased the force required to pull a tether. The membrane tether force in response to sinusoidal voltage signals was a function of holding potential, tether diameter, and tether length. Membrane electromechanical force production can occur at speeds exceeding those of ATP-based protein motors. By harnessing the energy in the transmembrane electric field, cell membranes may contribute to processes as diverse as outer hair cell electromotility, ion channel gating, and transport. PMID:20682262

Brownell, William E.; Qian, Feng; Anvari, Bahman

2010-01-01

50

Common Force Field Thermodynamics of Cholesterol  

PubMed Central

Four different force fields are examined for dynamic characteristics using cholesterol as a case study. The extent to which various types of internal degrees of freedom become thermodynamically relevant is evaluated by means of principal component analysis. More complex degrees of freedom (angle bending, dihedral rotations) show a trend towards force field independence. Moreover, charge assignments for membrane-embedded compounds are revealed to be critical with significant impact on biological reasoning. PMID:24302856

Giangreco, Francesco; Yamamoto, Eiji; Hirano, Yoshinori; di Giosia, Matteo; Zerbetto, Francesco; Yasuoka, Kenji; Narumi, Tetsu; Yasui, Masato; Höfinger, Siegfried

2013-01-01

51

General Multiobjective Force Field Optimization Framework, with Application to Reactive Force Fields for Silicon Carbide  

E-print Network

Fields for Silicon Carbide Andres Jaramillo-Botero,* Saber Naserifar, and William A. Goddard, III: (1) the ReaxFF reactive force field for modeling the adiabatic reactive dynamics of silicon carbide, and atom coordinations; and used it to optimize a silicon-silicon force field. Handley and Deeth9 describe

Goddard III, William A.

52

Force modulation for enhanced nanoscale electrical sensing  

Microsoft Academic Search

Scanning probe microscopy employing conductive probes is a powerful tool for the investigation and modification of electrical properties at the nanoscale. Application areas include semiconductor metrology, probe-based data storage and materials research. Conductive probes can also be used to emulate nanoscale electrical contacts. However, unreliable electrical contact and tip wear have severely hampered the widespread usage of conductive probes for

W. W. Koelmans; A. Sebastian; L. Abelmann; M. Despont; H. Pozidis

2011-01-01

53

Speed, Acceleration, and Velocity: Level II, Unit 9, Lesson 1; Force, Mass, and Distance: Lesson 2; Types of Motion and Rest: Lesson 3; Electricity and Magnetism: Lesson 4; Electrical, Magnetic, and Gravitational Fields: Lesson 5; The Conservation and Conversion of Matter and Energy: Lesson 6; Simple Machines and Work: Lesson 7; Gas Laws: Lesson 8; Principles of Heat Engines: Lesson 9; Sound and Sound Waves: Lesson 10; Light Waves and Particles: Lesson 11; Program. A High.....  

ERIC Educational Resources Information Center

This self-study program for high-school level contains lessons on: Speed, Acceleration, and Velocity; Force, Mass, and Distance; Types of Motion and Rest; Electricity and Magnetism; Electrical, Magnetic, and Gravitational Fields; The Conservation and Conversion of Matter and Energy; Simple Machines and Work; Gas Laws; Principles of Heat Engines;…

Manpower Administration (DOL), Washington, DC. Job Corps.

54

Current status of protein force fields for molecular dynamics simulations.  

PubMed

The current status of classical force fields for proteins is reviewed. These include additive force fields as well as the latest developments in the Drude and AMOEBA polarizable force fields. Parametrization strategies developed specifically for the Drude force field are described and compared with the additive CHARMM36 force field. Results from molecular simulations of proteins and small peptides are summarized to illustrate the performance of the Drude and AMOEBA force fields. PMID:25330958

Lopes, Pedro E M; Guvench, Olgun; MacKerell, Alexander D

2015-01-01

55

Electrical body forces and electrical tractions in the nonlinear response of ferroelectric actuators  

Microsoft Academic Search

The influence of the electrical body forces and electrical tractions on the nonlinear response of ferroelectric stack actuators is analytically investigated. While the role of the electrical body forces and tractions in the response of piezoelectric actuators is well documented (and in many cases is not significant), the questions of their effect on ferroelectric active materials is still of interest.

Uri Kushnir; Oded Rabinovitch

2011-01-01

56

Electrophoresis in strong electric fields.  

PubMed

Two kinds of non-linear electrophoresis (ef) that can be detected in strong electric fields (several hundred V/cm) are considered. The first ("classical" non-linear ef) is due to the interaction of the outer field with field-induced ionic charges in the electric double layer (EDL) under conditions, when field-induced variations of electrolyte concentration remain to be small comparatively to its equilibrium value. According to the Shilov theory, the non-linear component of the electrophoretic velocity for dielectric particles is proportional to the cubic power of the applied field strength (cubic electrophoresis) and to the second power of the particles radius; it is independent of the zeta-potential but is determined by the surface conductivity of particles. The second one, the so-called "superfast electrophoresis" is connected with the interaction of a strong outer field with a secondary diffuse layer of counterions (space charge) that is induced outside the primary (classical) diffuse EDL by the external field itself because of concentration polarization. The Dukhin-Mishchuk theory of "superfast electrophoresis" predicts quadratic dependence of the electrophoretic velocity of unipolar (ionically or electronically) conducting particles on the external field gradient and linear dependence on the particle's size in strong electric fields. These are in sharp contrast to the laws of classical electrophoresis (no dependence of V(ef) on the particle's size and linear dependence on the electric field gradient). A new method to measure the ef velocity of particles in strong electric fields is developed that is based on separation of the effects of sedimentation and electrophoresis using videoimaging and a new flowcell and use of short electric pulses. To test the "classical" non-linear electrophoresis, we have measured the ef velocity of non-conducting polystyrene, aluminium-oxide and (semiconductor) graphite particles as well as Saccharomice cerevisiae yeast cells as a function of the electric field strength, particle size, electrolyte concentration and the adsorbed polymer amount. It has been shown that the electrophoretic velocity of the particles/cells increases with field strength linearly up to about 100 and 200 V/cm (for cells) without and with adsorbed polymers both in pure water and in electrolyte solutions. In line with the theoretical predictions, in stronger fields substantial non-linear effects were recorded (V(ef)~E(3)). The ef velocity of unipolar ion-type conducting (ion-exchanger particles and fibres), electron-type conducting (magnesium and Mg/Al alloy) and semiconductor particles (graphite, activated carbon, pyrite, molybdenite) increases significantly with the electric field (V(ef)~E(2)) and the particle's size but is almost independent of the ionic strength. These trends are inconsistent with Smoluchowski's equation for dielectric particles, but are consistent with the Dukhin-Mishchuk theory of superfast electrophoresis. PMID:19041962

Barany, Sandor

2009-01-01

57

Additive empirical force field for hexopyranose monosaccharides  

PubMed Central

We present an all-atom additive empirical force field for the hexopyranose monosaccharide form of glucose and its diastereomers allose, altrose, galactose, gulose, idose, mannose, and talose. The model is developed to be consistent with the CHARMM all-atom biomolecular force fields, and the same parameters are used for all diastereomers, including both the ?- and ?-anomers of each monosaccharide. The force field is developed in a hierarchical manner and reproduces the gas-phase and condensed-phase properties of small-molecule model compounds corresponding to fragments of pyranose monosaccharides. The resultant parameters are transferred to the full pyranose monosaccharides and additional parameter development is done to achieve a complete hexopyranose monosaccharide force field. Parametrization target data include vibrational frequencies, crystal geometries, solute – water interaction energies, molecular volumes, heats of vaporization, and conformational energies, including those for over 1800 monosaccharide conformations at the MP2/cc-pVTZ//MP2/6-31G(d) level of theory. Though not targeted during parametrization, free energies of aqueous solvation for the model compounds compare favorably with experimental values. Also well-reproduced are monosaccharide crystal unit cell dimensions and ring pucker, densities of concentrated aqueous glucose systems, and the thermodynamic and dynamic properties of the exocyclic torsion in dilute aqueous systems. The new parameter set expands the CHARMM additive force field to allow for simulation of heterogeneous systems that include hexopyranose monosaccharides in addition to proteins, nucleic acids, and lipids. PMID:18470966

Guvench, Olgun; Greene, Shannon N.; Kamath, Ganesh; Brady, John W.; Venable, Richard M.; Pastor, Richard W.; MacKerell, Alexander D.

2010-01-01

58

Linear electric field mass spectrometry  

DOEpatents

A mass spectrometer and methods for mass spectrometry are described. The apparatus is compact and of low weight and has a low power requirement, making it suitable for use on a space satellite and as a portable detector for the presence of substances. High mass resolution measurements are made by timing ions moving through a gridless cylindrically symmetric linear electric field. 8 figs.

McComas, D.J.; Nordholt, J.E.

1992-12-01

59

Electric field divertor plasma pump  

DOEpatents

An electric field plasma pump includes a toroidal ring bias electrode positioned near the divertor strike point of a poloidal divertor of a tokamak, or similar plasma-confining apparatus. For optimum plasma pumping, the separatrix of the poloidal divertor contacts the ring electrode, which then also acts as a divertor plate. A plenum or other duct near the electrode includes an entrance aperture open to receive electrically-driven plasma. The electrode is insulated laterally with insulators, one of which is positioned opposite the electrode at the entrance aperture. An electric field E is established between the ring electrode and a vacuum vessel wall, with the polarity of the bias applied to the electrode being relative to the vessel wall selected such that the resultant electric field E interacts with the magnetic field B already existing in the tokamak to create an E [times] B/B[sup 2] drift velocity that drives plasma into the entrance aperture. The pumped plasma flow into the entrance aperture is insensitive to variations, intentional or otherwise, of the pump and divertor geometry. Pressure buildups in the plenum or duct connected to the entrance aperture in excess of 10 mtorr are achievable. 11 figs.

Schaffer, M.J.

1994-10-04

60

Electric fields in irradiated dielectrics  

NASA Technical Reports Server (NTRS)

An existing model for quantitatively predicting electric field build-up in dielectrics is used to demonstrate the importance of material parameters. Results indicate that electron irradiation will produce 10 to the 6th power V/cm in important materials. Parameters which can alter this build-up are discussed. Comparison to known irradiation induced dielectric charging experiments is discussed.

Frederickson, A. R.

1979-01-01

61

Electric field divertor plasma pump  

DOEpatents

An electric field plasma pump includes a toroidal ring bias electrode (56) positioned near the divertor strike point of a poloidal divertor of a tokamak (20), or similar plasma-confining apparatus. For optimum plasma pumping, the separatrix (40) of the poloidal divertor contacts the ring electrode (56), which then also acts as a divertor plate. A plenum (54) or other duct near the electrode (56) includes an entrance aperture open to receive electrically-driven plasma. The electrode (56) is insulated laterally with insulators (63,64), one of which (64) is positioned opposite the electrode at the entrance aperture. An electric field E is established between the ring electrode (56) and a vacuum vessel wall (22), with the polarity of the bias applied to the electrode being relative to the vessel wall selected such that the resultant electric field E interacts with the magnetic field B already existing in the tokamak to create an E.times.B/B.sup.2 drift velocity that drives plasma into the entrance aperture. The pumped plasma flow into the entrance aperture is insensitive to variations, intentional or otherwise, of the pump and divertor geometry. Pressure buildups in the plenum or duct connected to the entrance aperture in excess of 10 mtorr are achievable.

Schaffer, Michael J. (San Diego, CA)

1994-01-01

62

Behavior of precipitating water drops under the influence of electrical and aerodynamical forces  

Microsoft Academic Search

The present work performs a realistic modeling of precipitating charged water drops under the influence of electrical and dynamical forces in the vertical and downward electric field of a thundercloud. The following factors which control the shape of an individual raindrop are taken into account: surface tension, internal hydrostatic pressure, aerodynamic pressure, and electrostatic pressure. Unlike a recent and notable

Sylvain Coquillat; Serge Chauzy

1993-01-01

63

Measuring electric fields from surface contaminants with neutral atoms  

SciTech Connect

In this paper we demonstrate a technique of utilizing magnetically trapped neutral {sup 87}Rb atoms to measure the magnitude and direction of stray electric fields emanating from surface contaminants. We apply an alternating external electric field that adds to (or subtracts from) the stray field in such a way as to resonantly drive the trapped atoms into a mechanical dipole oscillation. The growth rate of the oscillation's amplitude provides information about the magnitude and sign of the stray field gradient. Using this measurement technique, we are able to reconstruct the vector electric field produced by surface contaminants. In addition, we can accurately measure the electric fields generated from adsorbed atoms purposely placed onto the surface and account for their systematic effects, which can plague a precision surface-force measurement. We show that baking the substrate can reduce the electric fields emanating from adsorbate and that the mechanism for reduction is likely surface diffusion, not desorption.

Obrecht, J. M.; Wild, R. J.; Cornell, E. A. [JILA, National Institute of Standards and Technology and University of Colorado, Boulder, Colorado 80309-0440 (United States) and Department of Physics, University of Colorado, Boulder, Colorado 80309-0390 (United States)

2007-06-15

64

Longitudinal forces in pinched electric currents  

E-print Network

It is shown that the theory of Mbelek and Lachi\\`eze-Rey predicts longitudinal forces of gravitational origin in pinched current distributions, with magnitudes large enough to have noticeable effects.

F. O. Minotti

2014-02-13

65

Minds on Physics: Fundamental Forces and Fields, Activities and Reader  

NSDL National Science Digital Library

This is the fourth in a series of six books which involves activities designed for students. This volume deals with the basics of gravitational, electric, and magnetic forces and fields. The activities part contains guidelines with which teachers can base activities and many questions which can be raised in class. The reader part creates opportunity for discussion and summarizes content covered after the activities have been performed.

Leonard, William J.; Dufresne, Robert J.; Gerace, William J.; Mestre, Jose P.

2006-07-22

66

Reactive Force Field & Molecular Dynamics Simulations  

E-print Network

: Parallel reactive molecular dynamics (MD) RMD ReaxFF · Applications: 1. Combustion of aluminum · Large scale (multimillion atoms) · Long time (nanosecond) #12;Reactive force field (RMD & ReaxFF (ReaxFF) #12;Classification of ReaxFF Potential Bonded Non-bonded E = Elp + Eover + Eunder + Ebond

Southern California, University of

67

GROUNDWATER AND SOIL REMEDIATION USING ELECTRICAL FIELD  

EPA Science Inventory

Enhancements of contaminants removal and degradation in low permeability soils by electrical fields are achieved by the processes of electrical heating, electrokinetics, and electrochemical reactions. Electrical heating increases soil temperature resulting in the increase of cont...

68

Energy buildup in sheared force-free magnetic fields  

NASA Technical Reports Server (NTRS)

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.

Wolfson, Richard; Low, Boon C.

1992-01-01

69

Perfluoroalkane force field for lipid membrane environments.  

PubMed

In this work, we present atomic parameters of perfluoroalkanes for use within the CHARMM force field. Perfluorinated alkanes represent a special class of molecules. On the one hand, they are considerably more hydrophobic than lipids, but on the other hand, they are not lipophilic either. Instead, they represent an independent class of philicity, enabling a whole portfolio of applications within both materials science and biochemistry. We performed a thorough parametrization of all bonded and nonbonded parameters with a particular focus on van der Waals parameters. Here, the general framework of the CHARMM and CGenFF force fields has been followed. The van der Waals parameters have been fitted to experimental densities over a wide range of temperatures and pressures. This newly parametrized class of molecules will open the gate for a variety of simulations of biologically relevant systems within the CHARMM force field. A particular perspective for the present work is the influence of polyphilic transmembrane molecules on membrane properties, aggregation phenomena, and transmembrane channels. PMID:25275859

von Rudorff, Guido Falk; Watermann, Tobias; Sebastiani, Daniel

2014-10-30

70

SOLAR WIND ELECTRIC FIELDS IN THE ION CYCLOTRON FREQUENCY RANGE P. J. Kellogg,1  

E-print Network

SOLAR WIND ELECTRIC FIELDS IN THE ION CYCLOTRON FREQUENCY RANGE P. J. Kellogg,1 S. D. Bale,2 F. S in the plasma frame. The electric fields are large enough to provide the dominant force on the ions of the solar of the conservation of magnetic mo- ment in the solar wind, it was pointed out that electric fields in the range

California at Berkeley, University of

71

A compact high field magnetic force microscope.  

PubMed

We present the design and performance of a simple and compact magnetic force microscope (MFM), whose tip-sample coarse approach is implemented by the piezoelectric tube scanner (PTS) itself. In brief, a square rod shaft is axially spring-clamped on the inner wall of a metal tube which is glued inside the free end of the PTS. The shaft can thus be driven by the PTS to realize image scan and inertial stepping coarse approach. To enhance the inertial force, each of the four outer electrodes of the PTS is driven by an independent port of the controller. The MFM scan head is so compact that it can easily fit into the 52mm low temperature bore of a 20T superconducting magnet. The performance of the MFM is demonstrated by imaging a manganite thin film at low temperature and in magnetic fields up to 15T. PMID:25189114

Zhou, Haibiao; Wang, Ze; Hou, Yubin; Lu, Qingyou

2014-12-01

72

A conducting ball in an axial electric field  

E-print Network

We describe the distribution of a charge, the electric moments of arbitrary order and the force acting on a conducting ball on the axis of the axial electric field. We determine the full charge and the dipole moments of the first order for a conducting ball in an arbitrary inhomogeneous harmonic electric field. All statements are formulated in the form of theorems with proofs basing on properties of the matrix of moments of the Legendre polynomials. The analysis and proof of these properties are presented in Appendix.

Alexander Savchenko

2012-12-26

73

ECE 390 Electric & Magnetic Fields Catalog Description: Static and quasi-static electric and magnetic fields.  

E-print Network

electric fields in presence of material medium: conductors, dielectrics, polarization, electric fluxECE 390 ­ Electric & Magnetic Fields Catalog Description: Static and quasi-static electric), A. Jander (secondary) Course Content: · Introduction, review of vector analysis · Static electric

74

Point Charge Electric Field Demo Model  

NSDL National Science Digital Library

The Point Charge Electric Field Demo model shows the electric field with multiple point charge configurations and vector field visualizations. Users can select these configurations from a drop down menu or can create their own configurations. The Point Charge Electric Field Demo model was created using the Easy Java Simulations (EJS) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double click the ejs_em_PointChargeElectricFieldDemo.jar file to run the program if Java is installed.

Christian, Wolfgang

2010-08-11

75

Transient Charge Accumulation Applied Electric Field  

E-print Network

Transient Charge Accumulation Applied Electric Field Charge Buildup in Sandstorms Zack Lasner1 Park Introduction Electrical insulators of identical material become statically charged upon contact in a poorly understood but broadly occurring process known as triboelectric charging. This phenomenon

Anlage, Steven

76

Efficient forced vibration reanalysis method for rotating electric machines  

NASA Astrophysics Data System (ADS)

Rotating electric machines are subject to forced vibration by magnetic force excitation with wide-band frequency spectrum that are dependent on the operating conditions. Therefore, when designing the electric machines, it is inevitable to compute the vibration response of the machines at various operating conditions efficiently and accurately. This paper presents an efficient frequency-domain vibration analysis method for the electric machines. The method enables the efficient re-analysis of the vibration response of electric machines at various operating conditions without the necessity to re-compute the harmonic response by finite element analyses. Theoretical background of the proposed method is provided, which is based on the modal reduction of the magnetic force excitation by a set of amplitude-modulated standing-waves. The method is applied to the forced response vibration of the interior permanent magnet motor at a fixed operating condition. The results computed by the proposed method agree very well with those computed by the conventional harmonic response analysis by the FEA. The proposed method is then applied to the spin-up test condition to demonstrate its applicability to various operating conditions. It is observed that the proposed method can successfully be applied to the spin-up test conditions, and the measured dominant frequency peaks in the frequency response can be well captured by the proposed approach.

Saito, Akira; Suzuki, Hiromitsu; Kuroishi, Masakatsu; Nakai, Hideo

2015-01-01

77

An electric force facilitator in descending vortex tornadogenesis  

Microsoft Academic Search

We present a novel explanation of the physical processes behind one type of cloud and ground-level tornadogenesis within a supercell. We point out that the charge separation naturally found in these large thunderstorms can potentially serve to contract the preexisting angular momentum through the additional process of the electric force. On the basis of this, we present a plausible geometry

Forest S. Patton; Gregory D. Bothun; Sharon L. Sessions

2008-01-01

78

Enhanced Fair-Weather Electric Fields Soon After Sunrise  

NASA Technical Reports Server (NTRS)

The typical fair weather electric field at the ground is between -100 and -300 V/m. At the NASA Kennedy Space Center and US Air Force Cape Canaveral Air Station (KSC) the electric field at the ground sometimes reaches -400 to -1200 V/m within an hour or two after sunrise on days that otherwise seem to be fair weather. We refer to the enhanced negative electric fields as the "sunrise enhancement." To investigate the sunrise enhancement at KSC we measured the electric field (E) in the first few hundred meters above the ground before and during several sunrise enhancements. From these E soundings we can infer the presence of charge layers and determine their thickness and charge density.

Marshall, T. C.; Rust, W. D.; Stolzenburg, M.; Roeder, W.; Krehbiel, P. R.

1999-01-01

79

Point Charge Electric Field and Potential Model  

NSDL National Science Digital Library

This is an Easy Java Simulation based model where students can explore the concepts of the electric field and the electric potential, in a two-dimensional situation. The model can include between 1 to 5 charged particles, and a test charge can be moved around the plane near these charged particles to sample both the electric field and the electric potential, produced by the charged particles. The simulation also can display a grid of field vectors, which show the direction and, qualitatively, the magnitude of the field.

Duffy, Andrew

2009-10-20

80

Electric Field Driven Torque in ATP Synthase  

PubMed Central

FO-ATP synthase (FO) is a rotary motor that converts potential energy from ions, usually protons, moving from high- to low-potential sides of a membrane into torque and rotary motion. Here we propose a mechanism whereby electric fields emanating from the proton entry and exit channels act on asymmetric charge distributions in the c-ring, due to protonated and deprotonated sites, and drive it to rotate. The model predicts a scaling between time-averaged torque and proton motive force, which can be hindered by mutations that adversely affect the channels. The torque created by the c-ring of FO drives the ?-subunit to rotate within the ATP-producing complex (F1) overcoming, with the aid of thermal fluctuations, an opposing torque that rises and falls with angular position. Using the analogy with thermal Brownian motion of a particle in a tilted washboard potential, we compute ATP production rates vs. proton motive force. The latter shows a minimum, needed to drive ATP production, which scales inversely with the number of proton binding sites on the c-ring. PMID:24040370

Miller, John H.; Rajapakshe, Kimal I.; Infante, Hans L.; Claycomb, James R.

2013-01-01

81

Recent Developments and Applications of the CHARMM force fields  

PubMed Central

Empirical force fields commonly used to describe the condensed phase properties of complex systems such as biological macromolecules are continuously being updated. Improvements in quantum mechanical (QM) methods used to generate target data, availability of new experimental target data, incorporation of new classes of compounds and new theoretical developments (eg. polarizable methods) make force-field development a dynamic domain of research. Accordingly, a number of improvements and extensions of the CHARMM force fields have occurred over the years. The objective of the present review is to provide an up-to-date overview of the CHARMM force fields. A limited presentation on the historical aspects of force fields will be given, including underlying methodologies and principles, along with a brief description of the strategies used for parameter development. This is followed by information on the CHARMM additive and polarizable force fields, including examples of recent applications of those force fields. PMID:23066428

Zhu, Xiao; Lopes, Pedro E.M.; MacKerell, Alexander D.

2011-01-01

82

The Energetics of Motivated Cognition: A Force-Field Analysis  

ERIC Educational Resources Information Center

A force-field theory of motivated cognition is presented and applied to a broad variety of phenomena in social judgment and self-regulation. Purposeful cognitive activity is assumed to be propelled by a "driving force" and opposed by a "restraining force". "Potential" driving force represents the maximal amount of energy an individual is prepared…

Kruglanski, Arie W.; Belanger, Jocelyn J.; Chen, Xiaoyan; Kopetz, Catalina; Pierro, Antonio; Mannetti, Lucia

2012-01-01

83

Magnetic-field-induced ferroelectric polarization reversal in magnetoelectric composites revealed by piezoresponse force microscopy.  

PubMed

Controlling electric polarization (or magnetization) in multiferroic materials with external magnetic fields (or electric fields) is very important for fundamental physics and spintronic devices. Although there has been some progress on magnetic-field-induced polarization reversal in single-phase multiferroics, such behavior has so far never been realized in composites. Here we show that it is possible to reverse ferroelectric polarization using magnetic fields in a bilayer Terfenol-D/PMN-33%PT composite. We realized this by ferroelectric domain imaging using piezoresponse force microscopy (PFM) under applied magnetic field loading. The internal electric field caused by the magnetoelectric (ME) effect in the PMN-PT crystal is considered as the driving force for the 180° polarization switching, and its existence is verified by switching spectroscopy PFM testing under a series of external magnetic fields. A quantitative method is further suggested to estimate the local ME coefficient based on the switching spectroscopy PFM testing results. PMID:24953042

Miao, Hongchen; Zhou, Xilong; Dong, Shuxiang; Luo, Haosu; Li, Faxin

2014-08-01

84

An ab initio parametrized interatomic force field for silica  

NASA Astrophysics Data System (ADS)

We present a classical interatomic force field for liquid SiO2 which has been parametrized using the forces, stresses and energies extracted from ab initio calculations. We show how inclusion of more electronic effects in a phenomenological way and parametrization at the relevant conditions of pressure and temperature allow the creation of more accurate force fields. We compare the results of simulations with this force field both to experiment and to the results of ab initio molecular dynamics simulations and show how our procedure leads to comparisons which are greatly improved with respect to the most widely used force fields for silica.

Tangney, P.; Scandolo, S.

2002-11-01

85

Field-induced forces at dielectric interfaces as a possible mechanism of RF hearing effects  

Microsoft Academic Search

A possible mechanism for effects of microwave radiation on the auditory system is the generation of field-induced forces at\\u000a interfaces that divide materials of dissimilar electrical properties. A general expression for these “Maxwell stresses” is\\u000a derived and then used to calculate the approximate magnitude of field-induced force within the organ of Corti during microwave\\u000a exposure. Comparison of the results with

William T. Joines; Blake S. Wilson

1981-01-01

86

Horizontal electric fields from lightning return strokes  

NASA Technical Reports Server (NTRS)

An experiment to measure simultaneously the wideband horizontal and vertical electric fields from lightning return strokes is described. Typical wave shapes of the measured horizontal and vertical fields are presented, and the horizontal fields are characterized. The measured horizontal fields are compared with calculated horizontal fields obtained by applying the wavetilt formula to the vertical fields. The limitations and sources of error in the measurement technique are discussed.

Thomson, E. M.; Medelius, P. J.; Rubinstein, M.; Uman, M. A.; Johnson, J.

1988-01-01

87

Theory and numerical calculation of the acoustic field exerted by eddy-current forces  

Microsoft Academic Search

The equations for calculating the acoustic field produced within a nonmagnetic metal by interaction of eddy currents with a static magnetic field were obtained on the assumptions that: (1) an ultrasonic wave is generated by the electromagnetic force through classical and macroscopic phenomena; (2) the electric, magnetic, and elastic properties of the metal are linear, isotropic, and homogeneous throughout the

K. Kawashima

1976-01-01

88

Electric field generation in the plasma sheet  

NASA Astrophysics Data System (ADS)

The plasma sheet is considered as a thin electrically conducting layer with a prescribe flow across the magnetic field lines at the equatorial plane of the magnetotail. Electric field resulting from the geomagnetic field diffusion into the solar wind is also added to the model. This gives a defined electric potential distribution at the flanks of the plasma sheet. The calculated electric potential from the plasma sheet and from the diffusive magnetopause is projected to the ionosphere along the magnetic field lines. At the ionospheric level they map to an oval strip at the polar cap boundary. Electric potential in the regions of the ionosphere both poleward and equatorward of this region is obtained by numerical solving of the problem of electric conductivity in the ionosphere. The patterns of electric potential contours in the ionosphere are similar to that known from observations. The positive and negative peaks of electric potential located at dawn and dusk sides of the polar oval correspond to the same peaks in the far plasma sheet at distance of about 150 RE. The influence of the flow in the plasma sheet and other parameters of the model on the electric potential distribution in the ionosphere is discussed. The total potential drop across the polar cap is equal to 100 kV that exceed observed value. A conclusion is made that resistance to the field-aligned currents in the tail lobes should be taken into account.

Denissenko, Valery V.; Kitaev, Anatoly V.

2002-02-01

89

Reactive Force Fields via Explicit Valency  

NASA Astrophysics Data System (ADS)

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 proton transfer and more complex reactions are discussed. Chapter 7 provides a framework for variable electron spread. This addition resolves some of the inherent limitations of the former model which implicitly assumed that electron spread was not affected by the environment. A brief summary is provided in Chapter 8.

Kale, Seyit

90

Axial Current Generation from Electric Field: Chiral Electric Separation Effect  

E-print Network

We study a relativistic plasma containing charged chiral fermions in an external electric field. We show that with the presence of both vector and axial charge densities, the electric field can induce an axial current along its direction and thus cause chirality separation. We call it the Chiral Electric Separation Effect (CESE). On very general basis, we argue that the strength of CESE is proportional to $\\mu_V\\mu_A$ with $\\mu_V$ and $\\mu_A$ the chemical potentials for vector charge and axial charge. We then explicitly calculate this CESE conductivity coefficient in thermal QED at leading-log order. The CESE can manifest a new gapless wave mode propagating along the electric field. Potential observable of CESE in heavy-ion collisions is also discussed.

Xu-Guang Huang; Jinfeng Liao

2013-03-28

91

Electric fields in the middle atmosphere  

NASA Technical Reports Server (NTRS)

Middle atmospheric electrodynamics is characterized by discussing the present understanding of the background electrical conductivity and the sources for electric fields and currents within the medium. Results of recent research that contradicts the historical view of the region are presented. Of principal interest to the present direction of the field is the attempt to quantize the low and high altitude electric generators such as thunderstorms or ionospheric convection. It is noted that the many-fold increase in available electric parameter data from within the middle atmosphere has been a great stimulus to recent research; however, these measurements have tended to raise more questions than they give answers.

Holzworth, Robert H.

1987-01-01

92

DNA Polymorphism: A Comparison of Force Fields for Nucleic Acids  

Microsoft Academic Search

The improvements of the force fields and the more accurate treatment of long-range interactions are providing more reliable molecular dynamics simulations of nucleic acids. The abilities of certain nucleic acid force fields to represent the structural and conformational properties of nucleic acids in solution are compared. The force fields are AMBER 4.1, BMS, CHARMM22, and CHARMM27; the comparison of the

Swarnalatha Y. Reddy; Fabrice Leclerc; Martin Karplus

2003-01-01

93

General Physics II Exam 1 -Chs. 16,17,18 -Electric Fields, Potential, Current Feb. 11, 2013 Name Rec. Instr. Rec. Time  

E-print Network

General Physics II Exam 1 - Chs. 16,17,18 - Electric Fields, Potential, Current Feb. 11, 2013 Name charge can experience an electric force. 4. (2) T F The smallest magnitude (non-zero) net charge of the electric force on Q1 due to Q2. b) (3) The direction of the electric force acting on Q1 is a. pushing Q1

Wysin, Gary

94

Dipole relaxation in an electric field  

NASA Astrophysics Data System (ADS)

From Boltzmann's equation, S=k ln?, an expression for the orientational entropy, S of a rigid rod (electric dipole) is derived. The free energy of the dipole in an electric field is then calculated as a function of both the dipole's average orientation and the field strength. Application of the equilibrium criterion to the free energy yields the field dependence of the entropy of the dipole. Irreversible thermodynamics is used to derive the general form of the equation of motion of the dipole's average orientation. Subsequent application of Newton's second law of motion produces Debye's classical expression for the relaxation of an electric dipole in a viscous medium.

Neumann, Richard M.

1980-07-01

95

Evolution of tachyon kink with electric field  

Microsoft Academic Search

We investigate the decay of an inhomogeneous D1-brane wrapped on a S1 with an electric field. The model that we consider consists of an array of tachyon kink and anti-kink with a constant electric flux. Beginning with an initially static configuration, we numerically evolve the tachyon field with some perturbations under a fixed boundary condition at diametrically opposite points on

Inyong Cho; O.-Kab Kwon; Chong Oh Lee

2007-01-01

96

Longitudinal plasma oscillations in an electric field  

Microsoft Academic Search

The properties of longitudinal plasma oscillations in an external electric field are investigated. In a completely linear approximation, it is found that the direct-current electric field introduces essentially no new effects. A quasi-linear approximation is also considered, in which couplings between different plasma modes are neglected while the space-averaged distribution functions are assumed to be approximately independent of time. In

B. D. Fried; M. Gell-mann; J. D. Jackson; H. W. Wyld

1960-01-01

97

Electric field control of the magnetocaloric effect.  

PubMed

Through strain-mediated magnetoelectric coupling, it is demonstrated that the magnetocaloric effect of a ferromagnetic shape-memory alloy can be controlled by an electric field. Large hysteresis and the limited operating temperature region are effectively overcome by applying an electric field on a laminate comprising a piezoelectric and the alloy. Accordingly, a model for an active magnetic refrigerator with high efficiency is proposed in principle. PMID:25522356

Gong, Yuan-Yuan; Wang, Dun-Hui; Cao, Qing-Qi; Liu, En-Ke; Liu, Jian; Du, You-Wei

2015-02-01

98

The Electric Force - Concepts and Principles (Calculus-based)  

NSDL National Science Digital Library

An activity based chapter discussing the concept of Electrical Force. It is part of Spiral Physics, a research based introductory physics curriculum developed at Monroe Community College with partial funding from the National Science Foundation. The workbook is designed for use in an active learning environment. Topics are arranged such that students receive repeated exposure to concepts over an extended time interval, each time with an incremental increase in complexity. The workbook emphasize multiple representations in problem solving, and goal-less problem statements.

D'Alessandris, Paul

2011-01-23

99

Enhanced momentum delivery by electric force to ions due to collisions of ions with neutrals  

SciTech Connect

Ions in partially ionized argon, nitrogen, and helium gas discharges are accelerated across a magnetic field by an applied electric field, colliding with neutrals during the acceleration. The momentum delivered by the electric force to the ions, which is equal to the momentum carried by the mixed ion-neutral flow, is found by measuring the force exerted on a balance force meter by that flow exiting the discharge. The power deposited in the ions is calculated by measuring the ion flux and the accelerating voltage. The ratio of force over power is found for the three gases, while the gas flow rates and magnetic field intensities are varied over a wide range of values, resulting in a wide range of gas pressures and applied voltages. The measurements for the three different gases confirm our previous suggestion [G. Makrinich and A. Fruchtman, Appl. Phys. Lett. 95, 181504 (2009)] that the momentum delivered to the ions for a given power is enhanced by ion-neutral collisions during the acceleration and that this enhancement is proportional to the square root of the number of ion-neutral collisions.

Makrinich, G.; Fruchtman, A. [H.I.T.-Holon Institute of Technology, Holon 5810201 (Israel)

2013-04-15

100

Enhanced momentum delivery by electric force to ions due to collisions of ions with neutrals  

NASA Astrophysics Data System (ADS)

Ions in partially ionized argon, nitrogen, and helium gas discharges are accelerated across a magnetic field by an applied electric field, colliding with neutrals during the acceleration. The momentum delivered by the electric force to the ions, which is equal to the momentum carried by the mixed ion-neutral flow, is found by measuring the force exerted on a balance force meter by that flow exiting the discharge. The power deposited in the ions is calculated by measuring the ion flux and the accelerating voltage. The ratio of force over power is found for the three gases, while the gas flow rates and magnetic field intensities are varied over a wide range of values, resulting in a wide range of gas pressures and applied voltages. The measurements for the three different gases confirm our previous suggestion [G. Makrinich and A. Fruchtman, Appl. Phys. Lett. 95, 181504 (2009)] that the momentum delivered to the ions for a given power is enhanced by ion-neutral collisions during the acceleration and that this enhancement is proportional to the square root of the number of ion-neutral collisions.

Makrinich, G.; Fruchtman, A.

2013-04-01

101

Calculations of the Electric Fields in Liquid Solutions  

PubMed Central

The electric field created by a condensed phase environment is a powerful and convenient descriptor for intermolecular interactions. Not only does it provide a unifying language to compare many different types of interactions, but it also possesses clear connections to experimental observables, such as vibrational Stark effects. We calculate here the electric fields experienced by a vibrational chromophore (the carbonyl group of acetophenone) in an array of solvents of diverse polarities using molecular dynamics simulations with the AMOEBA polarizable force field. The mean and variance of the calculated electric fields correlate well with solvent-induced frequency shifts and band broadening, suggesting Stark effects as the underlying mechanism of these key solution phase spectral effects. Compared to fixed-charge and continuum models, AMOEBA was the only model examined that could describe non-polar, polar, and hydrogen bonding environments in a consistent fashion. Nevertheless, we found that fixed-charge force fields and continuum models were able to replicate some results of the polarizable simulations accurately, allowing us to clearly identify which properties and situations require explicit polarization and/or atomistic representations to be modeled properly, and for which properties and situations simpler models are sufficient. We also discuss the ramifications of these results for modeling electrostatics in complex environments, such as proteins. PMID:24304155

Fried, Stephen D.; Wang, Lee-Ping; Boxer, Steven G.; Ren, Pengyu; Pande, Vijay S.

2014-01-01

102

Spinmotive force due to motion of magnetic bubble arrays driven by magnetic field gradient.  

PubMed

Interaction between local magnetization and conduction electrons is responsible for a variety of phenomena in magnetic materials. It has been recently shown that spin current and associated electric voltage can be induced by magnetization that depends on both time and space. This effect, called spinmotive force, provides for a powerful tool for exploring the dynamics and the nature of magnetic textures, as well as a new source for electromotive force. Here we theoretically demonstrate the generation of electric voltages in magnetic bubble array systems subjected to a magnetic field gradient. It is shown by deriving expressions for the electric voltages that the present system offers a direct measure of phenomenological parameter ? that describes non-adiabaticity in the current induced magnetization dynamics. This spinmotive force opens a door for new types of spintronic devices that exploit the field-gradient. PMID:25365971

Yamane, Yuta; Hemmatiyan, Shayan; Ieda, Jun'ichi; Maekawa, Sadamichi; Sinova, Jairo

2014-01-01

103

Spinmotive force due to motion of magnetic bubble arrays driven by magnetic field gradient  

PubMed Central

Interaction between local magnetization and conduction electrons is responsible for a variety of phenomena in magnetic materials. It has been recently shown that spin current and associated electric voltage can be induced by magnetization that depends on both time and space. This effect, called spinmotive force, provides for a powerful tool for exploring the dynamics and the nature of magnetic textures, as well as a new source for electromotive force. Here we theoretically demonstrate the generation of electric voltages in magnetic bubble array systems subjected to a magnetic field gradient. It is shown by deriving expressions for the electric voltages that the present system offers a direct measure of phenomenological parameter ? that describes non-adiabaticity in the current induced magnetization dynamics. This spinmotive force opens a door for new types of spintronic devices that exploit the field-gradient. PMID:25365971

Yamane, Yuta; Hemmatiyan, Shayan; Ieda, Jun'ichi; Maekawa, Sadamichi; Sinova, Jairo

2014-01-01

104

Full 180° magnetization reversal with electric fields.  

PubMed

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Wang, J J; Hu, J M; Ma, J; Zhang, J X; Chen, L Q; Nan, C W

2014-01-01

105

Full 180° Magnetization Reversal with Electric Fields  

NASA Astrophysics Data System (ADS)

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals.

Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

2014-12-01

106

Full 180° Magnetization Reversal with Electric Fields  

PubMed Central

Achieving 180° magnetization reversal with an electric field rather than a current or magnetic field is a fundamental challenge and represents a technological breakthrough towards new memory cell designs. Here we propose a mesoscale morphological engineering approach to accomplishing full 180° magnetization reversals with electric fields by utilizing both the in-plane piezostrains and magnetic shape anisotropy of a multiferroic heterostructure. Using phase-field simulations, we examined a patterned single-domain nanomagnet with four-fold magnetic axis on a ferroelectric layer with electric-field-induced uniaxial strains. We demonstrated that the uniaxial piezostrains, if non-collinear to the magnetic easy axis of the nanomagnet at certain angles, induce two successive, deterministic 90° magnetization rotations, thereby leading to full 180° magnetization reversals. PMID:25512070

Wang, J. J.; Hu, J. M.; Ma, J.; Zhang, J. X.; Chen, L. Q.; Nan, C. W.

2014-01-01

107

Comparison of Cellulose Ib Simulations with Three Carbohydrate Force Fields  

Microsoft Academic Search

Molecular dynamics simulations of cellulose have recently become more prevalent due to increased interest in renewable energy applications, and many atomistic and coarse-grained force fields exist that can be applied to cellulose. However, to date no systematic comparison between carbohydrate force fields has been conducted for this important system. To that end, we present a molecular dynamics simulation study of

J. F. Matthews; G. T. Beckham; M. Bergenstrahle; J. W. Brady; M. E. Himmel; M. F. Crowley

2012-01-01

108

Biological effects of electric fields: EPRI's role  

SciTech Connect

Since 1973 the Electric Power Research Institute (EPRI) has supported research to evaluate the biological effects which may result from exposure to electric fields produced by AC overhead transmission lines; more recently, EPRI has also begun DC research. Through 1981 EPRI will have expended $8.7M on these efforts. Ongoing AC projects are studying a variety of lifeforms exposed to electric fields; these include humans, miniature swine, rats, honeybees, chick embryos, and crops. The status of these projects is discussed. The DC program has not as yet produced data. These studies will add to the current data base so as to enable a more complete assessment of health risks which may be associated with exposure to electric fields at power frequencies.

Kavet, R.

1982-07-01

109

Evolution of Tachyon Kink with Electric Field  

E-print Network

We investigate the decay of an inhomogeneous D1-brane wrapped on a $S^1$ with an electric field. The model that we consider consists of an array of tachyon kink and anti-kink with a constant electric flux. Beginning with an initially static configuration, we numerically evolve the tachyon field with some perturbations under a fixed boundary condition at diametrically opposite points on the circle $S^1$. When the electric flux is smaller than the critical value, the tachyon kink becomes unstable; the tachyon field rolls down the potential, and the lower dimensional D0- and $\\bar {\\rm D}0$-brane become thin, which resembles the caustic formation known for this type of the system in the literature. For the supercritical values of the electric flux, the tachyon kink remains stable.

Inyong Cho; O-Kab Kwon; Chong Oh Lee

2006-11-05

110

Evolution of tachyon kink with electric field  

NASA Astrophysics Data System (ADS)

We investigate the decay of an inhomogeneous D1-brane wrapped on a S1 with an electric field. The model that we consider consists of an array of tachyon kink and anti-kink with a constant electric flux. Beginning with an initially static configuration, we numerically evolve the tachyon field with some perturbations under a fixed boundary condition at diametrically opposite points on the circle S1. When the electric flux is smaller than the critical value, the tachyon kink becomes unstable; the tachyon field rolls down the potential, and the lower dimensional D0- and bar D0-brane become thin, which resembles the caustic formation known for this type of the system in the literature. For the supercritical values of the electric flux, the tachyon kink remains stable.

Cho, Inyong; Kwon, O.-Kab; Lee, Chong Oh

2007-04-01

111

Evolution of Tachyon Kink with Electric Field  

E-print Network

We investigate the decay of an inhomogeneous D1-brane wrapped on an $S^1/Z_2$ orbifold with an electric field. The model that we consider consists of an array of tachyon kink and anti-kink with a constant electric flux. Beginning with an initially static configuration, we numerically evolve the tachyon field with some perturbations. When the electric flux is smaller than the critical value, the tachyon kink becomes unstable; the tachyon field rolls down the potential, and the lower dimensional D0- and $\\bar {\\rm D}0$-brane become thin, which resembles the caustic formation known for this type of the system in the literature. For the supercritical values of the electric flux, the tachyon kink remains stable.

Cho, I; Lee, C O; Cho, Inyong; Lee, Chong Oh

2007-01-01

112

Solidification processing superalloys in an electric field  

NASA Technical Reports Server (NTRS)

The phase morphology of a given superalloy's microstructure is established during solidification. Solidification-processing in an applied electric field is a technique currently undergoing experimental characterization at NASA-Marshall. The method is predicated on the simplest model of a metallic solid, in which ions are arranged in basic space lattices that are permeated by an 'electron gas' whose valence electrons are free to move in the solid. When in a superheated liquid state, the metal is seen as a dense 'cold plasma' of electrons and ions. The application of an electric field during solidification establishes a steady, continuous current flow; the direction of propagation of the plasma waves coincides with the direction of the electric field. Such an alignment introduces an ordered arrangement of the electric vectors and introduces an additional degree of order in an already highly ordered alloy.

Ahmed, Shaffiq; Bond, Robert; Mckannan, Eugene C.

1991-01-01

113

Electric force microscopy of semiconductors: Theory of cantilever frequency fluctuations and noncontact friction  

SciTech Connect

An electric force microscope employs a charged atomic force microscope probe in vacuum to measure fluctuating electric forces above the sample surface generated by dynamics of molecules and charge carriers. We present a theoretical description of two observables in electric force microscopy of a semiconductor: the spectral density of cantilever frequency fluctuations (jitter), which are associated with low-frequency dynamics in the sample, and the coefficient of noncontact friction, induced by higher-frequency motions. The treatment is classical-mechanical, based on linear response theory and classical electrodynamics of diffusing charges in a dielectric continuum. Calculations of frequency jitter explain the absence of contributions from carrier dynamics to previous measurements of an organic field effect transistor. Calculations of noncontact friction predict decreasing friction with increasing carrier density through the suppression of carrier density fluctuations by intercarrier Coulomb interactions. The predicted carrier density dependence of the friction coefficient is consistent with measurements of the dopant density dependence of noncontact friction over Si. Our calculations predict that in contrast to the measurement of cantilever frequency jitter, a noncontact friction measurement over an organic semiconductor could show appreciable contributions from charge carriers.

Lekkala, Swapna; Marohn, John A.; Loring, Roger F., E-mail: roger.loring@cornell.edu [Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853 (United States)

2013-11-14

114

Electric field induced cracking in PLZT ceramics  

Microsoft Academic Search

The growth of cracks under the influence of high voltage cyclic electric field in 8\\/65\\/35 lanthanum lead zirconate titanate samples was studied. The remanent polarization, coercive field and complex dielectric constant were measured as a function of the number of switching cycles. During the measurement the salt water solution was penetrating through the sample.

A. Levstik; C. Filipi?; V. Bobnar; M. Kosec

1997-01-01

115

Locating source regions of precursory seismo-electric fields and the mechanism generating electric field variations  

NASA Astrophysics Data System (ADS)

Electrodes consisting of a steel pipe in a deep borehole and a grounded wire surrounding the borehole were constructed to measure vertical electric fields, whereas conventional electrodes measure horizontal fields. Three years of monitoring showed that the anomalous variations in vertical underground electric fields preceding earthquakes and volcanic eruptions are much clearer than the variations in horizontal fields. The data also showed that there is much less man-made noise in the vertical fields. To determine whether these observed anomalies are forerunners of seismic disturbance, a system developed to locate precisely the source regions of underground vertical electric fields or volcanic tremors has been continuously operated. The system uses three or more time lags calculated by cross-correlating the electric fields or volcanic tremors recorded at four, or more, monitoring stations. If this system reveals the intensity distributions of the sources, prediction of imminent earthquakes and volcanic eruptions will become possible. To explain the mechanisms by which precursory electric field variations are generated, a model is proposed in which the electric field variations are generated by Earth current variations caused by increased electric conductivity in source regions before an earthquake. The conductivity is increased by free electrons and positive holes created on the fresh fracture surfaces caused by microcracks that occur before rock failure in the Earth's crust. The model can explain precursory electrical phenomena which are observed not only in the field before an earthquake but also in the laboratory before rock failure.

Takahashi, Kozo; Fujinawa, Yukio

1993-04-01

116

Drag forces on inclusions in classical fields with dissipative dynamics  

E-print Network

We study the drag force on uniformly moving inclusions which interact linearly with dynamical free field theories commonly used to study soft condensed matter systems. Drag forces are shown to be nonlinear functions of the inclusion velocity and depend strongly on the field dynamics. The general results obtained can be used to explain drag forces in Ising systems and also predict the existence of drag forces on proteins in membranes due to couplings to various physical parameters of the membrane such as composition, phase and height fluctuations.

Vincent Demery; D. S. Dean

2010-04-01

117

Electric Fields Produced by Florida Thunderstorms  

Microsoft Academic Search

Electric fields produced by air mass thunderstorms have been recorded at 25 field mill sites at the NASA Kennedy Space Center (KSC) during the summers of 1975 and 1976. Time- and area-averaged fields produced by individual storms are typically -0.8 to -2.1 kV m - during periods of intense lightning activity and usually 2-4 times larger (-2.3 to -4.3 kV

John M. Livingston; E. Philip Krider

1978-01-01

118

Computational Investigation of Helical Traveling Wave Tube Transverse RF Field Forces  

NASA Technical Reports Server (NTRS)

In a previous study using a fully three-dimensional (3D) helical slow-wave circuit cold- test model it was found, contrary to classical helical circuit analyses, that transverse FF electric fields have significant amplitudes compared with the longitudinal component. The RF fields obtained using this helical cold-test model have been scaled to correspond to those of an actual TWT. At the output of the tube, RF field forces reach 61%, 26% and 132% for radial, azimuthal and longitudinal components, respectively, compared to radial space charge forces indicating the importance of considering them in the design of electron beam focusing.

Kory, Carol L.; Dayton, James A.

1998-01-01

119

Fort Future: Virtual Installation supports rapidly changing needs of armed forces in the field  

E-print Network

and electric utility modeling and planning tools for the Virtual Instal- lation. For water utilities, ArgonneFort Future: Virtual Installation supports rapidly changing needs of armed forces in the field FORT- ports the Fort Future Program by developing modeling and simulation tools for the Virtual Installation

Kemner, Ken

120

Magnetic Forces and Field Line Density  

NSDL National Science Digital Library

This is an activity about depicting the relative strength of magnetic fields using field line density. Learners will use the magnetic field line drawing of six magnetic poles created in a previous activity and identify the areas of strong, weak, and medium magnetic intensity using the density of magnetic field lines. This is the fifth activity in the Magnetic Math booklet; this booklet can be found on the Space Math@NASA website. How to Draw Magnetic Fields - II in the Magnetic Math booklet must be completed prior to this activity.

121

Comparison of Cellulose Ib Simulations with Three Carbohydrate Force Fields  

SciTech Connect

Molecular dynamics simulations of cellulose have recently become more prevalent due to increased interest in renewable energy applications, and many atomistic and coarse-grained force fields exist that can be applied to cellulose. However, to date no systematic comparison between carbohydrate force fields has been conducted for this important system. To that end, we present a molecular dynamics simulation study of hydrated, 36-chain cellulose I{beta} microfibrils at room temperature with three carbohydrate force fields (CHARMM35, GLYCAM06, and Gromos 45a4) up to the near-microsecond time scale. Our results indicate that each of these simulated microfibrils diverge from the cellulose I{beta} crystal structure to varying degrees under the conditions tested. The CHARMM35 and GLYCAM06 force fields eventually result in structures similar to those observed at 500 K with the same force fields, which are consistent with the experimentally observed high-temperature behavior of cellulose I. The third force field, Gromos 45a4, produces behavior significantly different from experiment, from the other two force fields, and from previously reported simulations with this force field using shorter simulation times and constrained periodic boundary conditions. For the GLYCAM06 force field, initial hydrogen-bond conformations and choice of electrostatic scaling factors significantly affect the rate of structural divergence. Our results suggest dramatically different time scales for convergence of properties of interest, which is important in the design of computational studies and comparisons to experimental data. This study highlights that further experimental and theoretical work is required to understand the structure of small diameter cellulose microfibrils typical of plant cellulose.

Matthews, J. F.; Beckham, G. T.; Bergenstrahle, M.; Brady, J. W.; Himmel, M. E.; Crowley, M. F.

2012-02-14

122

Electric field controlled emulsion phase contactor  

DOEpatents

A system is described for contacting liquid phases comprising a column for transporting a liquid phase contacting system, the column having upper and lower regions. The upper region has a nozzle for introducing a dispersed phase and means for applying thereto a vertically oriented high intensity pulsed electric field. This electric field allows improved flow rates while shattering the dispersed phase into many micro-droplets upon exiting the nozzle to form a dispersion within a continuous phase. The lower region employs means for applying to the dispersed phase a horizontally oriented high intensity pulsed electric field so that the dispersed phase undergoes continuous coalescence and redispersion while being urged from side to side as it progresses through the system, increasing greatly the mass transfer opportunity. 5 figs.

Scott, T.C.

1995-01-31

123

Approximate photochemical dynamics of azobenzene with reactive force fields  

SciTech Connect

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)

Li, Yan; Hartke, Bernd [Institute for Physical Chemistry, Christian-Albrechts-University, Olshausenstr. 40, 24098 Kiel (Germany)] [Institute for Physical Chemistry, Christian-Albrechts-University, Olshausenstr. 40, 24098 Kiel (Germany)

2013-12-14

124

Approximate photochemical dynamics of azobenzene with reactive force fields.  

PubMed

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). PMID:24329064

Li, Yan; Hartke, Bernd

2013-12-14

125

Approximate photochemical dynamics of azobenzene with reactive force fields  

NASA Astrophysics Data System (ADS)

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).

Li, Yan; Hartke, Bernd

2013-12-01

126

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

PubMed

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. PMID:20340109

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

2010-09-01

127

An Electric Force Facilitator in Descending TVS Tornadogenesis  

E-print Network

We present a novel explanation of the physical processes behind tornadogenesis. We suggest that charge separation found in supercell thunderstorms serves to condense the existing angular momentum through the additional process of the electric force. Based on this, we present a plausible geometry that explains why many tornadoes begin at storm mid-levels and build downward. We show that this geometry can explain the observations that ground level tornadoes thrive in regions with high shear and large convective available potential energy (CAPE). A simple model based on this geometry leads to rational time scales spanning from the birth of a supercell to the touchdown of a tornado. We make some predictions of specific measurable quantities.

Patton, F S; Bothun, Gregory D.; Patton, Forest S.

2006-01-01

128

Picosecond Electrical Sampling with a Scanning Force Microscope.  

NASA Astrophysics Data System (ADS)

The miniaturization of electronic devices and circuits has been progressing at an astounding pace. Advance research devices are using linewidths in the tens of nanometers, with frequency cutoffs beyond 100 GHz. Conventional measurement techniques lack the ability to probe signals on specific lines with both fine lateral resolution and high bandwidth. Recently, electrical sampling with an atomic force microscope (AFM) has been demonstrated at Stanford. This technique makes use of an AFM to sample voltage waveforms with nanometer scale lateral resolution and temporal resolution limited only by the bandwidth of the sampling signal source. This thesis describes advances in this technique which bring the measurement bandwidth into the GHz range, with measured frequencies as high as 333 GHz and measured signal transients as fast as 1 ps. This technique involves the use of a specially designed AFM cantilever with a conductive tip floating over a sample under test. The electrical force on the tip is proportional to the square of the voltage between the tip and the sample. This square law dependence is then used to perform equivalent-time sampling, so that the measured deflection of the cantilever is proportional to a time-expanded version of the signal under test. The measurement bandwidth of this technique is limited to that of the sampling voltage source. Therefore, in order to obtain the highest measurement frequencies, nonlinear transmission line (NLTL) technology (which can generate voltage transients as fast as 480 fs) has been used. The fastest results have been obtained with devices which monolithically integrate the NLTL circuits with specially designed AFM cantilevers and tips.

Nechay, Bettina Anne

129

Drug Release from Electric Field Responsive Nanoparticles  

PubMed Central

We describe a new temperature and electric field dual-stimulus responsive nanoparticle system for programmed drug delivery. Nanoparticles of a conducting polymer (polypyrrole) are loaded with therapeutic pharmaceuticals and are subcutaneously localized in vivo with the assistance of a temperature-sensitive hydrogel (PLGA-PEG-PLGA). We have shown that drug release from the conductive nanoparticles is controlled by the application of a weak, external DC electric field. This approach represents a novel interactive drug delivery system that can show an externally tailored release profile with an excellent spatial, temporal, and dosage control. PMID:22111891

Ge, Jun; Neofytou, Evgenios; Cahill, Thomas J.; Beygui, Ramin E.; Zare, Richard N.

2012-01-01

130

Students' understanding of superposition of electric fields  

NSDL National Science Digital Library

In this article an analysis of the difficulties experienced by students when applying the principle of superposition to electric fields is presented. A study of university level students in France and Sweden revealed the existence of difficulties arising out of two issues: (1) a causal interpretation of some relationships, (2) the student's need for an effect, motion of some kind, to accept the existence of a field. The links between these obstacles and a lack of a unified view on electric phenomena are discussed from a pedagogical point of view.

Rainson, Sylvie; Transtrã¶mer, G.; Viennot, Laurence

2005-10-24

131

Dynamics of the structure of electric currents and electrodynamic forces in current sheets  

SciTech Connect

Specific features of the spatial distributions of the electric current and electrodynamic forces in current sheets are examined by studying the magnetic fields in them. It is shown that the j Multiplication-Sign B forces should lead to a gradual increase in the kinetic energy of the plasma accelerated along the current sheet surface. Excitation of currents directed oppositely to the main current in the central part of the sheet is observed for the first time, and the time evolution of the forward and reverse currents is investigated. Generation of reversed currents is a manifestation of the dynamic effects caused by the motion of plasma flows in the magnetic field and leading to a change in the magnetic structure of the current sheet.

Frank, A. G.; Satunin, S. N. [Russian Academy of Sciences, Prokhorov General Physics Institute (Russian Federation)

2011-10-15

132

Electric Field Effects in RUS Measurements  

SciTech Connect

Much of the power of the Resonant Ultrasound Spectroscopy (RUS) technique is the ability to make mechanical resonance measurements while the environment of the sample is changed. Temperature and magnetic field are important examples. Due to the common use of piezoelectric transducers near the sample, applied electric fields introduce complications, but many materials have technologically interesting responses to applied static and RF electric fields. Non-contact optical, buffered, or shielded transducers permit the application of charge and externally applied electric fields while making RUS measurements. For conducting samples, in vacuum, charging produces a small negative pressure in the volume of the material - a state rarely explored. At very high charges we influence the electron density near the surface so the propagation of surface waves and their resonances may give us a handle on the relationship of electron density to bond strength and elasticity. Our preliminary results indicate a charge sign dependent effect, but we are studying a number of possible other effects induced by charging. In dielectric materials, external electric fields influence the strain response, particularly in ferroelectrics. Experiments to study this connection at phase transformations are planned. The fact that many geological samples contain single crystal quartz suggests a possible use of the piezoelectric response to drive vibrations using applied RF fields. In polycrystals, averaging of strains in randomly oriented crystals implies using the 'statistical residual' strain as the drive. The ability to excite vibrations in quartzite polycrystals and arenites is explored. We present results of experimental and theoretical approaches to electric field effects using RUS methods.

Darling, Timothy W [Los Alamos National Laboratory; Ten Cate, James A [Los Alamos National Laboratory; Allured, Bradley [UNIV NEVADA, RENO; Carpenter, Michael A [CAMBRIDGE UNIV. UK

2009-09-21

133

Electric fields and double layers in plasmas  

NASA Technical Reports Server (NTRS)

Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamical features of the double layers are discussed. These features, as seen in simulations, laboratory experiments, and theory, indicate that double layers and the currents through them undergo slow oscillations which are determined by the ion transit time across an effective length of the system in which double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations were considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields and double layers in an expanding plasma is discussed.

Singh, Nagendra; Thiemann, H.; Schunk, R. W.

1987-01-01

134

Field-aligned currents and large scale magnetospheric electric fields  

NASA Technical Reports Server (NTRS)

D'Angelo's model of polar cap electric fields (1977) was used to visualize how high-latitude field-aligned currents are driven by the solar wind generator. The region 1 and region 2 currents of Iijima and Potemra (1976) and the cusp field-aligned currents of Wilhjelm et al. (1978) and McDiarmid et al. (1978) are apparently driven by different generators, although in both cases the solar wind is their ultimate source.

Dangelo, N.

1980-01-01

135

Harnessing Electric Fields for Microfluidics - From Lightni ng Sparks to Tiny Tornadoes  

Microsoft Academic Search

The dominance of surface tension and viscous effects over body forces such as inertia, gravity or centrifugal force makes fl uid actuation and particle manipulation at microscale dimensions extremely difficult. We demonstrate the possibility of expl oiting electric fields to drive unstable turbulent-like flows for mi cro- mixing and complex flows for efficient particle separation an d concentration. In particular,

Leslie Y. Yeo; James R. Friend

136

Dielectric Character Modified by Perpendicular Electric Field in Triglycine Sulfate  

Microsoft Academic Search

The dielectric dispersion of a triglycine sulfate single crystal has been measured after a prolonged application of the electric field perpendicular to the ferroelectric b axis. As the perpendicular electric field dwarfs the dielectric dispersion, the influence on the dielectric permittivity by the perpendicular electric field looks like the influence by the DC bias electric field parallel to the ferroelectric

T. Kikuta; T. Yamazaki; N. Nakatani

2008-01-01

137

Generative morphologies of architectural organization in matter force field  

E-print Network

This thesis investigates generative methods of architectural form finding in matter force fields that produce spatial subdivision and organizational variation. Unlike the style driven contemporary free-form architecture ...

Mutlu, Murat

2010-01-01

138

Molecular dynamics simulations of methane hydrate using polarizable force fields  

SciTech Connect

Molecular dynamics simulations of methane hydrate have been carried out using the polarizable AMOEBA and COS/G2 force fields. Properties calculated include the temperature dependence of the lattice constant, the OC and OO radial distribution functions, and the vibrational spectra. Both the AMOEBA and COS/G2 force fields are found to successfully account for the available experimental data, with overall somewhat better agreement with experiment being found for the AMOEBA model. Comparison is made with previous results obtained using TIP4P and SPC/E effective two-body force fields and the polarizable TIP4P-FQ force field, which allows for in-plane polarization only. Significant differences are found between the properties calculated using the TIP4P-FQ model and those obtained using the other models, indicating an inadequacy of restricting explicit polarization to in-plane onl

Jiang, H.N.; Jordan, K.D.; Taylor, C.E.

2007-06-14

139

A reactive force field (ReaxFF) for zinc oxide  

Microsoft Academic Search

We have developed a reactive force field (FF) within the ReaxFF framework, for use in molecular dynamics (MD) simulations to investigate structures and reaction dynamics for ZnO catalysts. The force field parameters were fitted to a training set of data points (energies, geometries, charges) derived from quantum-mechanical (QM) calculations. The data points were chosen to give adequate descriptions of (the

David Raymand; Adri C. T. van Duin; Micael Baudin; Kersti Hermansson

2008-01-01

140

Electric field-enhanced coalescence of liquid drops  

SciTech Connect

A fundamental understanding of drop coalescence and growth is of importance to separations and materials processing. Under external driving forces, drops dispersed in an immiscible fluid collide and coalesce with each other due to their relative motion. As a result of drop coalescence, the average drop size in the dispersion increases over time, improving the separation process. Collision and coalescence of spherical, conducting drops bearing no net charge in dilute, homogeneous dispersions are considered theoretically under conditions where drop motion results from gravity settling and electric field-induced attraction. A trajectory analysis is used to follow the relative motion of two drops and predict pairwise collision rates. A population dynamics equation is then solved to predict the time evolution of the size distribution and the average size of drops. The results show that the rate of drop collision and growth can be increased significantly by applying an electric field, in accord with fundamental experiments and patents on electrocoalescence.

Zhang, Xiaoguang [Univ. of Tennessee, Knoxville, TN (United States); Basaran, O.A. [Oak Ridge National Laboratory, TN (United States)

1995-04-01

141

Square water in an electric field  

NASA Astrophysics Data System (ADS)

The physical properties of the square water model, which is a generalization of the square ice to nonzero temperatures, is studied as a function of temperature and electric field. We determined the fraction of hydrogen bonds (HBs), the electric susceptibility, and the entropy of the model. We found that the usual independent-bond approximation gives poor predictions for the HB number when a polarization field is present. We compare the independent-bond results with Monte Carlo simulations, and with more accurate mean-field approximations obtained by the study of clusters of water molecules. At zero temperature, this model presents a first-order phase transition driven by the external electric field. The discontinuity in the HB number gives support to this behavior. We also obtained the exact partition function of the square water model in one dimension employing the transfer matrix technique. The zero field free energy in one dimension displays the same functional form on temperature as the one obtained in the two-dimensional version of the model via mean field approach.

Girardi, M.; Figueiredo, W.

2002-11-01

142

Experimental demonstration of electric field tomography  

Microsoft Academic Search

Electric field tomography (EFT) has recently been introduced in theory. It is a new kind of quasistatic tomography suitable for contactless imaging of biological tissues. Single-channel measurements have already proven the theory. Herein the first multi-channel measuring system for EFT is presented. Experiments on imaging of a test object with different geometries are described. The first EFT images obtained experimentally

A. V. Korjenevsky; T. S. Tuykin

2010-01-01

143

PHASE EQUILIBRIA MODIFICATION BY ELECTRIC FIELDS  

EPA Science Inventory

The primary focus of this program is to obtain a fundamental understanding of the effects of electric fields on polar and nonpolar mixtures in gas and liquid phases, with the ultimate goal of using this understanding in devising novel means to dramatically improve existing enviro...

144

Empirical high-latitude electric field models  

Microsoft Academic Search

Electric field measurements from the Dynamics Explorer 2 satellite have been analyzed to extend the empirical models previously developed from dawn-dusk OGO 6 measurements (J.P. Heppner, 1977). The analysis embraces large quantities of data from polar crossings entering and exiting the high latitudes in all magnetic local time zones. Paralleling the previous analysis, the modeling is based on the distinctly

J. P. Heppner; N. C. Maynard

1987-01-01

145

Brownian motion in a non-homogeneous force field and photonic force microscope  

E-print Network

The Photonic Force Microscope (PFM) is an opto-mechanical technique based on an optical trap that can be assumed to probe forces in microscopic systems. This technique has been used to measure forces in the range of pico- and femto-Newton, assessing the mechanical properties of biomolecules as well as of other microscopic systems. For a correct use of the PFM, the force field to measure has to be invariable (homogeneous) on the scale of the Brownian motion of the trapped probe. This condition implicates that the force field must be conservative, excluding the possibility of a rotational component. However, there are cases where these assumptions are not fulfilled Here, we show how to improve the PFM technique in order to be able to deal with these cases. We introduce the theory of this enhanced PFM and we propose a concrete analysis workflow to reconstruct the force field from the experimental time-series of the probe position. Furthermore, we experimentally verify some particularly important cases, namely the case of a conservative or rotational force-field.

Giorgio Volpe; Giovanni Volpe; Dmitri Petrov

2007-08-03

146

Electrodynamics as a particular case of the most general relativistic force field  

E-print Network

A new approach to classical electrodynamics is presented, showing that it can be regarded as a particular case of the most general relativistic force field. In particular, at first it is shown that the structure of the Lorentz force comes directly from the structure of the three-force transformation law, and that E and B fields can be defined, which in general will depend not only on the space-time coordinate, but also on the velocity of the body acted upon. Then it is proved that these fields become independent from the body velocity if the force field propagates throughout space at the relativistic speed limit c. Finally, field sources are introduced by defining them as perturbations of the field itself, obtaining a generalization of Maxwell equations which allow to express the field in terms sources, if these last are known a priori. Electrodynamics follows simply assuming, in addition to the postulate of field propagation at the speed c, that scalar sources of the B field are missing and that electric charge is an invariant characteristic of matter, acting both as source of the field and sensing property. The presented approach may have valuable didactic effectiveness in showing that space-time structure, as defined by Special Relativity postulates, is the ultimate responsible of the structure of electrodynamics laws.

Stefano Re Fiorentin

2009-05-21

147

Analysis Of Shifts In Students' Reasoning Regarding Electric Field And Potential Concepts  

NSDL National Science Digital Library

Students' reasoning regarding the relationships among electric fields, forces, and equipotential line patterns was explored using pre- and post-test responses to selected multiple-choice questions on the Conceptual Survey of Electricity and Magnetism. Students' written explanations of their reasoning, provided both pre- and post-instruction, allowed additional assessment of the changes in their thinking. In particular, the data indicate that although students largely abandon an initial tendency to associate stronger fields with wider equipotential line spacing, many of them persist in incorrectly associating electric field magnitude at a point with the electric potential at that point.

Meltzer, David E.

2007-11-25

148

Acceleration of particles in an isotropic random force field  

E-print Network

If we have a particle immersed in a field of random forces, each interaction of the particle with the field can enlarge or diminish its kinetic energy. In this work is shown that in general, for any field of random force with uniform distribution of directions, the probability to gain kinetic energy is larger that the probability to lose it. Therefore, if the particle is submitted to a great number of interactions with the force stochastic field, the final result will be that the particle will gain energy. The probability to gain energy in each interaction is Pg=1/2 (1+T/(2Po)), where T is the impulse given by the field and Po is the momentum of the particle before the interaction. The probability to lose energy in each interaction is Pl=1/2 (1-T/(2Po)).

Hector Javier Durand-Manterola

2012-04-18

149

Electric field distribution on knife-edge field emitters  

NASA Astrophysics Data System (ADS)

Of critical importance to advanced High Power Microwave (HPM) generators is the development and understanding of robust cold cathodes with low turn-on electric fields. Recent interesting candidates include ridged metallic cathodes fabricated by either laser ablation or other microfabrication methods [1]. We use conformal mapping to calculate the electric field on a knife-edge cathode. We find that the field enhancement factor scales approximately as the square root of the height-width ratio of the knife-edge [2]. An analytic approximation for the divergent electric field in the immediate vicinity of the sharp edge is derived. A smaller knife-edge placed on top of a larger one demonstrates that the composite field enhancement factor is approximately equal to the product of the field enhancement factor of the individual knife-edges. This proves the conjecture [3] on multiplication of field enhancement factors for one special case. This work was supported by AFOSR/MURI and by AFRL. [1] M.C. Jones, et al, Rev .Sci.Instrum.,75, 2976 (2004) [2] R. Miller, Y. Y. Lau, J. H. Booske, Appl. Phys. Lett., (to be published) [3] W. Schottky, Z. Physik, 14, 63 (1923).

Miller, Ryan; Lau, Yue Ying; Booske, John

2007-11-01

150

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

NASA Technical Reports Server (NTRS)

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.

El-Kaddah, N.; Szekely, J.

1982-01-01

151

Electric field distribution characteristics of photoconductive antennas  

NASA Astrophysics Data System (ADS)

Photoexcitation of biased semiconductor photoconductive antennas by femtosecond pulses is the most common and convenient technique for generating strong terahertz (THz) pulses. In this paper, we use the three-dimensional (3D) finite-difference-time-domain (FDTD) to analyze electric field distribution of THz pulses in the near-field from a photoconductive antenna. The simulation is based on solving Maxwell's equations and the carrier rate equations simultaneously on realistic dipole antenna structures. The 3D FDTD simulation gives detailed features of THz electric field distribution in and out of the antenna. It is found that the difference of near-field distribution between the substrate and free space is considerably large. The fields of the alternating-current dipole exhibit an unsymmetrical distribution and a large deviation from those calculated using the simple Hertzian dipole theory. The magnitude of THz field in and out of the substrate attenuates rapidly while it holds the line in the gap center. The high-frequency components of THz radiation emission come only from the dipole antenna, while the low-frequency components are from both the center electrodes and coplanar stripline waveguide. This work can be used to optimize the design of antenna geometry and raise the radiation field power.

Zou, Sheng-Wu; Zhang, Tong-Yi

2012-10-01

152

Reversible shear thickening at low shear rates of electrorheological fluids under electric fields  

E-print Network

Shear thickening is a phenomenon of significant viscosity increase of colloidal suspensions. While electrorheological (ER) fluids can be turned into a solid-like material by applying an electric field, their shear strength is widely represented by the attractive electrostatic interaction between ER particles. By shearing ER fluids between two concentric cylinders, we show a reversible shear thickening of ER fluids above a low critical shear rate (100 V/mm), which could be characterized by a modified Mason number. Shear thickening and electrostatic particle interaction-induced inter-particle friction forces is considered to be the real origin of the high shear strength of ER fluids, while the applied electric field controls the extent of shear thickening. The electric field-controlled reversible shear thickening has implications for high-performance ER/magnetorheological (MR) fluid design, clutch fluids with high friction forces triggered by applying local electric field, other field-responsive materials and intelligent systems.

Yu Tian; Minliang Zhang; Jile Jiang; Noshir Pesika; Hongbo Zeng; Jacob Israelachvili; Yonggang Meng; Shizhu Wen

2010-08-24

153

Reversible shear thickening at low shear rates of electrorheological fluids under electric fields.  

PubMed

By shearing electrorheological (ER) fluids between two concentric cylinders, we show a reversible shear thickening of ER fluids above a low critical shear rate (<1?s(-1)) and a high critical electric field strength (>100 V/mm), which can be characterized by a critical apparent viscosity. Shear thickening and electrostatic particle interaction-induced interparticle friction forces are considered to play an important role in the origin of lateral shear resistance of ER fluids, while the applied electric field controls the extent of shear thickening. The electric-field-controlled reversible shear thickening has implications for high-performance electrorheological-magnetorheological fluid design, clutch fluids with high friction forces triggered by applying a local electric field, other field-responsive materials, and intelligent systems. PMID:21405692

Tian, Yu; Zhang, Minliang; Jiang, Jile; Pesika, Noshir; Zeng, Hongbo; Israelachvili, Jacob; Meng, Yonggang; Wen, Shizhu

2011-01-01

154

Three-dimensional electric field visualization utilizing electric-field-induced second-harmonic generation in nematic liquid crystals  

Microsoft Academic Search

An electric-field-induced second-harmonic-generation signal in a nematic liquid crystal is used to map the electric field in an integrated-circuit-like sample. Since the electric-field-induced second-harmonic-generation signal intensity exhibits a strong dependence on the polarization of the incident laser beam, both the amplitude and the orientation of the electric field vectors can be measured. Combined with scanning second-harmonic-generation microscopy, three-dimensional electric field

I.-Hsiu Chen; Shi-Wei Chu; Francois Bresson; Ming-Chun Tien; Jin-Wei Shi; Chi-Kuang Sun

2003-01-01

155

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS B. Fornberg,2  

E-print Network

MAGNETIC FIELD CONFINEMENT IN THE SOLAR CORONA. I. FORCE-FREE MAGNETIC FIELDS N. Flyer,1 B Axisymmetric force-free magnetic fields external to a unit sphere are studied as solutions to boundary value against expansion into the unbounded space. This property as a basic mechanism for solar coronal mass

Fornberg, Bengt

156

Dynamics of Drop Formation in an Electric Field.  

PubMed

The effect of an electric field on the formation of a drop of an inviscid, perfectly conducting liquid from a capillary which protrudes from the top plate of a parallel-plate capacitor into a surrounding dynamically inactive, insulating gas is studied computationally. This free boundary problem which is comprised of the surface Bernoulli equation for the transient drop shape and the Laplace equation for the velocity potential inside the drop and the electrostatic potential outside the drop is solved by a method of lines incorporating the finite element method for spatial discretization. The finite element algorithm employed relies on judicious use of remeshing and element addition to a two-region adaptive mesh to accommodate large domain deformations, and allows the computations to proceed until the thickness of the neck connecting an about to form drop to the rest of the liquid in the capillary is less than 0.1% of the capillary radius. The accuracy of the computations is demonstrated by showing that in the absence of an electric field predictions made with the new algorithm are in excellent agreement with boundary integral calculations (Schulkes, R. M. S. M. J. Fluid Mech. 278, 83 (1994)) and experimental measurements on water drops (Zhang, X., and Basaran, O. A. Phys. Fluids 7(6), 1184 (1995)). In the presence of an electric field, the algorithm predicts that as the strength of the applied field increases, the mode of drop formation changes from simple dripping to jetting to so-called microdripping, in accordance with experimental observations (Cloupeau, M., and Prunet-Foch, B. J. Aerosol Sci. 25(6), 1021 (1994); Zhang, X., and Basaran, O. A. J. Fluid Mech. 326, 239 (1996)). Computational predictions of the primary drop volume and drop length at breakup are reported over a wide range of values of the ratios of electrical, gravitational, and inertial forces to surface tension force. In contrast to previously mentioned cases where both the flow rate in the tube and the electric field strength are nonzero, situations are also considered in which the flow rate is zero and the dynamics are initiated by impulsively changing the field strength from a certain value to a larger value. When the magnitude of the step change in field strength is small, the results of the new transient calculations accord well with those of an earlier stability analysis (Basaran, O. A., and Scriven, L. E. J. Colloid Interface Sci. 140(1), 10 (1990)) and thereby provide yet another testament to the accuracy of the new algorithm. Copyright 1999 Academic Press. PMID:10191025

Notz; Basaran

1999-05-01

157

Tunable control of antibody immobilization using electric field.  

PubMed

The controlled immobilization of proteins on solid-state surfaces can play an important role in enhancing the sensitivity of both affinity-based biosensors and probe-free sensing platforms. Typical methods of controlling the orientation of probe proteins on a sensor surface involve surface chemistry-based techniques. Here, we present a method of tunably controlling the immobilization of proteins on a solid-state surface using electric field. We study the ability to orient molecules by immobilizing IgG molecules in microchannels while applying lateral fields. We use atomic force microscopy to both qualitatively and quantitatively study the orientation of antibodies on glass surfaces. We apply this ability for controlled orientation to enhance the performance of affinity-based assays. As a proof of concept, we use fluorescence detection to indirectly verify the modulation of the orientation of proteins bound to the surface. We studied the interaction of fluorescently tagged anti-IgG with surface immobilized IgG controlled by electric field. Our study demonstrates that the use of electric field can result in more than 100% enhancement in signal-to-noise ratio compared with normal physical adsorption. PMID:25650429

Emaminejad, Sam; Javanmard, Mehdi; Gupta, Chaitanya; Chang, Shuai; Davis, Ronald W; Howe, Roger T

2015-02-17

158

Force-Field Compensation in a Manual Tracking Task  

PubMed Central

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. PMID:20567516

Squeri, Valentina; Masia, Lorenzo; Casadio, Maura; Morasso, Pietro; Vergaro, Elena

2010-01-01

159

Particle acceleration by fluctuating electric fields  

NASA Astrophysics Data System (ADS)

Release of stored magnetic energy via particle acceleration is a characteristic feature of astrophysical plasmas. Magnetic reconnection is one of the primary candidate mechanisms for releasing non-potential energy from magnetized plasmas. A collisionless magnetic reconnection scenario could provide both the energy release mechanism and the particle accelerator in flares. We studied particle acceleration consequences from fluctuating (in-time) electric fields superposed on an X-type magnetic field in collisionless hot solar plasma. This system is chosen to mimic generic features of dynamic reconnection, or the reconnective dissipation of a linear disturbance. Time evolution of thermal particle distributions are obtained by numerically integrating particle orbits. A range of frequencies of the electric field is used, representing a turbulent range of waves. Depending on the frequency and amplitude of the electric field, electrons and ions are accelerated to different degrees and often have energy distributions of bimodal form. Protons are accelerated to gamma-ray producing energies and electrons to and above hard X-ray producing energies in timescales of less than 1 second. The acceleration mechanism could be applicable to all collisionless plasmas.

Petkaki, P.; MacKinnon, A. L.

2008-12-01

160

Lightning Location Using Electric Field Change Meters  

NASA Astrophysics Data System (ADS)

Briefly introduced last year, the Huntsville Alabama Field Change Array (HAFCA) is a collection of electric field change meters deployed in and around Huntsville. Armed with accurate GPS timing, the array is able to sample electric field changes due to lightning strokes simultaneously at several locations. For the first time, different components of the lightning flash can be located in three dimensions using only electric field change records. In particular, this research will show spacetime locations throughout entire lightning strokes, from preliminary breakdown pulses to the return stroke and later processes that may be related to charge neutralization. To find the spacetime locations, standard time of arrival methods will be used: finding the parameters that best fit the model using the Marquardt method. However, we will also discuss using Markov Chain Monte Carlo methods which yield a better estimation of errors. With this information, we will discuss selected cases from the array to date. In particular, we will discuss the inter-comparison of HAFCA with two other well known lightning location arrays, NLDN and NALMA. Specifically, we will explore the relationship between the first LMA pulse in a lightning stroke and the locations of preliminary breakdown pulses and the implications on lightning initiation. Further, the return stroke locations will be shown to agree reasonably well with NLDN locations. We will also locate compact intracloud discharges (CIDs) and compare with NLDN locations.

Bitzer, P. M.; Christian, H.; Burchfield, J.

2010-12-01

161

Pulsed Direct Current Electric Fields Enhance Osteogenesis in Adipose-Derived Stromal Cells  

PubMed Central

Adipose-derived stromal cells (ASCs) constitute a promising source of cells for regenerative medicine applications. Previous studies of osteogenic potential in ASCs have focused on chemicals, growth factors, and mechanical stimuli. Citing the demonstrated role electric fields play in enhancing healing in bone fractures and defects, we investigated the ability of pulsed direct current electric fields to drive osteogenic differentiation in mouse ASCs. Employing 50?Hz direct current electric fields in concert with and without osteogenic factors, we demonstrated increased early osteoblast-specific markers. We were also able to establish that commonly reported artifacts of electric field stimulation are not the primary mediators of the observed effects. The electric fields caused marked changes in the cytoskeleton. We used atomic force microscopy–based force spectroscopy to record an increase in the cytoskeletal tension after treatment with electric fields. We abolished the increased cytoskeletal stresses with the rho-associated protein kinase inhibitor, Y27632, and did not see any decrease in osteogenic gene expression, suggesting that the pro-osteogenic effects of the electric fields are not transduced via cytoskeletal tension. Electric fields may show promise as candidate enhancers of osteogenesis of ASCs and may be incorporated into cell-based strategies for skeletal regeneration. PMID:19824802

Hammerick, Kyle E.; James, Aaron W.; Huang, Zubin; Prinz, Fritz B.

2010-01-01

162

niversal Force Field Can Uniquely Orient Non-Symmetric Parts  

Microsoft Academic Search

Recent work in parts handling advocates the investigation of a new generation of devices for parts feeding, sorting, positioning, and assembly. Unlike robot grippers, conveyor belts, or vibratory bowl feeders, these devices generate fo rce fields in which the parts move until they may reach a stable equilibrium pose. The development of the theory of programmable force fields has yielded

B. R. Donald; L. E. Kavraki; F. Lamiraux

163

FIELD manual: Calculation of electric fields in conducting media  

NASA Astrophysics Data System (ADS)

A computer program (FIELD) written in BASIC that may be used to calculate electric potential, gradient, and power density distribution in conducting media is discussed. Either cylindrical or rectangular coordinate systems may be used. Information is supplied to assist users in providing necessary data for the program and in interpreting output. A program listing is appended.

Doss, J. D.

1981-10-01

164

Visualization of Force Fields in Protein StructurePrediction  

SciTech Connect

The force fields used in molecular computational biology are not mathematically defined in such a way that their mathematical representation would facilitate the straightforward application of volume visualization techniques. To visualize energy, it is necessary to define a spatial mapping for these fields. Equipped with such a mapping, we can generate volume renderings of the internal energy states in a molecule. We describe our force field, the spatial mapping that we used for energy, and the visualizations that we produced from this mapping. We provide images and animations that offer insight into the computational behavior of the energy optimization algorithms that we employ.

Crawford, Clark; Kreylos, Oliver; Hamann, Bernd; Crivelli, Silvia

2005-04-26

165

Calculation of electric fields in conductive media  

SciTech Connect

A method is presented, based upon finite-difference forms of Laplace's equation, for the iterative calculation of three-dimensional electric field distributions in electrically conductive media. The method, while generally applicable to any conductive media, will be presented with emphasis on its use for the prediction of power density in tissue when radio-frequency hyperthermia is utilized in the treatment of cancer. A computer code which performs these calculations has been written in BASIC so that it may be adapted to relatively inexpensive desktop computers for use in treatment planning. Example calculations of the distribution of electric potential, gradient, and power density with specific electrode configurations are presented. Applications and limitations of the technique are discussed.

Doss, J.D.

1982-07-01

166

Analysis of electrical tomography sensitive field based on multi-terminal network and electric field  

Microsoft Academic Search

Electrical tomography (ET) aims at the study of the conductivity\\/permittivity distribution of the interested field non-intrusively via the boundary voltage\\/current. The sensor is usually regarded as an electric field, and finite element method (FEM) is commonly used to calculate the sensitivity matrix and to optimize the sensor architecture. However, only the lumped circuit parameters can be measured by the data

Yongbo He; Xingguo Su; Meng Xu; Huaxiang Wang

2010-01-01

167

Method of electric field flow fractionation wherein the polarity of the electric field is periodically reversed  

DOEpatents

A novel method of electric field flow fractionation for separating solute molecules from a carrier solution is disclosed. The method of the invention utilizes an electric field that is periodically reversed in polarity, in a time-dependent, wave-like manner. The parameters of the waveform, including amplitude, frequency and wave shape may be varied to optimize separation of solute species. The waveform may further include discontinuities to enhance separation.

Stevens, Fred J. (Naperville, IL)

1992-01-01

168

Tailor-made force fields for crystal-structure prediction.  

PubMed

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. PMID:18642947

Neumann, Marcus A

2008-08-14

169

Electric Field and Humidity Trigger Contact Electrification  

NASA Astrophysics Data System (ADS)

Here, we study the old problem of why identical insulators can charge one another on contact. We perform several experiments showing that, if driven by a preexisting electric field, charge is transferred between contacting insulators. This transfer happens because the insulator surfaces adsorb small amounts of water from a humid atmosphere. We believe the electric field then separates positively from negatively charged ions prevailing within the water, which we believe to be hydronium and hydroxide ions, such that at the point of contact, positive ions of one insulator neutralize negative ions of the other one, charging both of them. This mechanism can explain for the first time the observation made four decades ago that wind-blown sand discharges in sparks if and only if a thunderstorm is nearby.

Zhang, Yanzhen; Pähtz, Thomas; Liu, Yonghong; Wang, Xiaolong; Zhang, Rui; Shen, Yang; Ji, Renjie; Cai, Baoping

2015-01-01

170

Electric Field and Humidity Trigger Contact Electrification  

E-print Network

Here, we study the old problem of why identical insulators can charge one another on contact. We perform several experiments showing that, if driven by a preexisting electric field, charge is transferred between contacting insulators. This happens because the insulator surfaces adsorb small amounts of water from a humid atmosphere. We believe the electric field then separates positively from negatively charged ions prevailing within the water, which we believe to be hydronium and hydroxide ions, such that at the point of contact, positive ions of one insulator neutralize negative ions of the other one, charging both of them. This mechanism can explain for the first time the observation made four decades ago that wind-blown sand discharges in sparks if and only if a thunderstorm is nearby.

Zhang, Yanzhen; Liu, Yonghong; Wang, Xiaolong; Zhang, Rui; Shen, Yang; Ji, Renjie; Cai, Baoping

2015-01-01

171

DNA Polymorphism: A Comparison of Force Fields for Nucleic Acids  

PubMed Central

The improvements of the force fields and the more accurate treatment of long-range interactions are providing more reliable molecular dynamics simulations of nucleic acids. The abilities of certain nucleic acid force fields to represent the structural and conformational properties of nucleic acids in solution are compared. The force fields are AMBER 4.1, BMS, CHARMM22, and CHARMM27; the comparison of the latter two is the primary focus of this paper. The performance of each force field is evaluated first on its ability to reproduce the B-DNA decamer d(CGATTAATCG)2 in solution with simulations in which the long-range electrostatics were treated by the particle mesh Ewald method; the crystal structure determined by Quintana et al. (1992) is used as the starting point for all simulations. A detailed analysis of the structural and solvation properties shows how well the different force fields can reproduce sequence-specific features. The results are compared with data from experimental and previous theoretical studies. PMID:12609851

Reddy, Swarnalatha Y.; Leclerc, Fabrice; Karplus, Martin

2003-01-01

172

Electric-field induced magnetization reversal using multiferroics  

NASA Astrophysics Data System (ADS)

Controlling magnetism using solely electric fields is interesting not only from a fundamental standpoint, but presents great potential for ultimately low energy consumption logic and memory. The evidence of the electrically controllable antiferromagnetic ordering in the multiferroic magnetoelectric bismuth ferrite (BiFeO3) drew an increasing interest in the pursuit for new emerging devices. To use such functionality for device applications, deterministic control not only of antiferromagnetism, but also ferromagnetism is essential. To achieve this goal, a ferromagnet/multiferroic heterostructure has been proposed based on the combination of magnetoelectric coupling in BiFeO3 and exchange coupling between magnetic materials and offers a new pathway for the electrical control of magnetism. By combination of a piezoresponse force microscopy, photoemission electron microscopy and anisotropic magnetoresistance measurements, we demonstrated the non-volatile reversal of a CoFe layer magnetization induced solely by the application of an electric field at room temperature. This 180 degree rotation of the magnetization of the ferromagnetic layer is mediated by a strong interfacial coupling. The correlation between the ferroelectric state in the multiferroic layer and the CoFe ferromagnetic domain architecture is evidenced. The projection of this strong magnetoelectric coupling in an out-of-plane configuration, allowing the reduction by an order of magnitude of voltage required, will be discussed. Our results show the high potential of magnetoelectric-based heterostructures for future low energy consumption data storage devices.

Trassin, Morgan

2012-02-01

173

Electric Field and Microphysics of Hurricanes  

NASA Astrophysics Data System (ADS)

The Tropical Cloud Systems and Processes (TCSP) project was a campaign to primarily study tropical storm and hurricane genesis, based in San José, Costa Rica, during July 2005. The main research platform was a NASA ER-2, high altitude (~21 km) aircraft, which carried a number of instruments, including the Lightning Instrument Package consisting of electric field mills and an air conductivity probe, two Doppler radar systems, and the Advanced Microwave Precipitation Radiometer (AMPR). The field mills allow us to determine the vector electric field along the aircraft path. The AMPR allows us to determine ice particle concentration from passive microwave ice scattering signatures. TCSP was the third program in which we have measured electrification above hurricanes. In the previous programs, we have found oceanic hurricanes to be at most only weakly electrified with little or no lightning in the central part of the storm. During the flight over Hurricane Emily (17 July 2005) we found strong electrification and significant lightning flash rates (over 9 flashes/min) in the eye wall. The ER-2 made several passes over and around the eyewall of Hurricane Emily during the flight. During the overpasses, the hurricane was almost constantly producing lightning. Vaisala's long range lightning detection system indicated that this remarkable lightning activity in the storm core persisted for several hours. We present the vector electric field, lightning rates, passive microwave microphysics, and Doppler radar data from Hurricane Emily and compare these observations with data from other hurricanes we have studied. We will address the question as to why Hurricane Emily was electrically so different from the other tropical storms.

Bateman, M. G.; Blakeslee, R. J.; Mach, D. M.; Bailey, J. C.

2005-12-01

174

Investigation of electric fields of EHV substations  

Microsoft Academic Search

60-Hz and 24-kHz capacitive and monopole probes and testing techniques were developed for full-scale and model ground level electric field strength measurements for EHV substations. A model of an existing 345-kV substation was designed and built. The model was energized using a three phase 24-kHz regulated source. Comparison of corresponding test points shows that the agreement between substation and model

S. A. Sebo; R. Caldecott

1977-01-01

175

Apricot Nectar Processing by Pulsed Electric Fields  

Microsoft Academic Search

Application of Pulsed Electric Fields (PEF's) to process apricot nectar by determining the pH, °Brix, total acidity, conductivity, color, non-enzymatic browning index, concentration of mineral ions and retention of ascorbic acid and beta carotene as well as inactivation of Escherichia coli O157:H7, Listeria monocytogenes, Staphylococcus aureus, Pseudomonas syringae subs. syringae, Erwinia carotowora, Penicillum expansum and Botrytis cinerea was explored in

Gulsun Akdemir Evrendilek; Julide Altuntas; Mustafa Kemal Sangun; Howard Q. Zhang

2011-01-01

176

HIGH ELECTRIC FIELD DRYING OF JAPANESE RADISH  

Microsoft Academic Search

Japanese radish (Raphanus sativus L.) slices were dried under an alternating current (AC) high electric field (HEF) of 430 kV\\/m using a multiple point electrode and a grounded copper mesh. HEF with multipoint to a mesh electrode system could evaporate 87.5% of the total moisture from fresh radish slices on 7 h exposure. Oven-drying at 60°C and ambient air at

T. R. Bajgai; F. Hashinaga

2001-01-01

177

Electric field shielding in dielectric nanosolutions  

E-print Network

To gain some insight into electrochemical activity of dielectric colloids of technical and biomedical interest we investigate a model of dielectric nanosolution whose micro-constitution is dominated by dipolarions -- positively and negatively charged spherically symmetric nano-structures composed of ionic charge surrounded by cloud of radially polarized dipoles of electrically neutral molecules of solvent. Combing the standard constitutive equations of an isotropic dielectric liquid with Maxwell equation of electrostatics and presuming the Boltzmann shape of the particle density of bound-charge we derive equation for the in-medium electrostatic field. Particular attention is given to numerical analysis of obtained analytic solutions of this equation describing the exterior fields of dipolarions with dipolar atmospheres of solvent molecules endowed with either permanent or field-induced dipole moments radially polarized by central symmetric field of counterions. The presented computations show that the electric field shielding of dipolarions in dielectric nanosolutions is quite different from that of counterionic nano-complexes of Debye-H\\"uckel theory of electrolytes.

Sergey Bastrukov; Pik-Yin Lai; Irina Molodtsova

2014-03-26

178

Electrical discharge in a nanometer-sized air/water gap observed by atomic force microscopy.  

PubMed

We report a method to initiate and investigate electrical discharges of ambient air/water molecules in a nanometer-sized gap. Our methodology is based on a typical atomic force microscopy (AFM) setup, in which a cylinder discharge gap of < or =5 nm could be configured between the AFM probe and substrate. We observed highly localized stochastic nanoexplosions in which the discharge probability is dominated by the electric field, material-specific surface reactions, and humidity. AFM results, coupled with the boundary element method (BEM), finite element method (FEM), and method of characteristics (MOC) simulations, further revealed the generation of transient shock waves in the nanoscale discharge. The propagation of shock fronts significantly facilitates the radial expansion of the ionized particles, leading to the formation of microscale patterns on selected substrates. Our findings provide an initial understanding of nanoscale discharge and could be relevant to a few applications including nano/microstructuring, microelectronics, and plasma-assisted depositions. PMID:16262421

Xie, Xian Ning; Chung, Hong Jing; Sow, Chorng Haur; Adamiak, Kazimierz; Wee, Andrew Thye Shen

2005-11-01

179

The effect of electromotive-force generation on electrical properties of thin samarium sulfide films  

SciTech Connect

Electrical properties of thin SmS polycrystalline films with various values of the lattice constant at T = 300-580 K are studied. Specific features of the temperature dependences of electrical conductivity at T > 450 K are revealed. The effect of generation of the electromotive force with magnitude as large as 1.3 V at T = 440-470 K is observed when the films were subjected to the pressure of a spherical indenter. It is shown that it is possible to transform SmS films into a high-resistivity state (with the difference in the resistivity by three orders of magnitude) by applying an electric field with the strength higher than 100 V/cm. All the results obtained are accounted for using a model of the phenomenon of the electromotive-force generation in SmS under uniform heating of the sample and can also be attributed to the variable valence of samarium ions with respect to the lattice defects.

Kaminskii, V. V., E-mail: Vladimir.Kaminski@mail.ioffe.ru; Kazanin, M. M.; Solov'ev, S. M.; Sharenkova, N. V.; Volodin, N. M. [Russian Academy of Sciences, Ioffe Physicotechnical Institute (Russian Federation)

2006-06-15

180

What Are Electric and Magnetic Fields? (EMF)  

MedlinePLUS

... 60 hertz (Hz). If something uses batteries, the electric current flows in one direction only, and it is ... practical situations, DC electric power does not induce electric currents in humans. AC electric power produces electric and ...

181

Force-field calculation and geometry of the HOOO radical.  

PubMed

High-level ab initio calculations using the Davidson-corrected multireference configuration interaction (MRCI) level of theory with Dunning's correlation consistent basis sets and force-field calculations were performed for the HOOO radical. The harmonic vibrational frequencies and their anharmonic constants obtained by the force-field calculations reproduce the IR-UV experimental vibrational frequencies with errors less than 19 cm(-1). The rotational constants for the ground vibrational state obtained using the vibration-rotation interaction constants of the force-field calculations also reproduce the experimentally determined rotational constants with errors less than 0.9%, indicating that the present quantum chemical calculations and the derived spectroscopic constants have high accuracy. The equilibrium structure was determined from the experimentally determined rotational constants combined with the theoretically derived vibration-rotation interaction constants. The determined geometrical parameters agree well with the results of the present MRCI calculation. PMID:24028111

Suma, Kohsuke; Sumiyoshi, Yoshihiro; Endo, Yasuki

2013-09-01

182

Water-Silica Force Field for Simulating Nanodevices  

PubMed Central

Amorphous silica is an inorganic material that is central for many nanotechnology appplications, such as nanoelectronics, microfluidics, and nanopore technology. In order to use molecular dynamics (MD) simulations to study the behavior of biomolecules with silica, we developed a force field for amorphous silica surfaces based on their macroscopic wetting properties that is compatible with the CHARMM force field and TIP3P water model. The contact angle of a water droplet with silica served as a criterion to tune the intermolecular interactions. The resulting force field was used to study the permeation of water through silica nanopores, illustrating the influence of the surface topography and the intermolecular parameters on permeation kinetics. We find that minute modeling of the amorphous surface is critical for MD studies, since the particular arrangement of surface atoms controls sensitively electrostatic interactions between silica and water. PMID:17064100

Cruz-Chu, Eduardo R.; Aksimentiev, Aleksei; Schulten, Klaus

2008-01-01

183

Interaction Forces Between Multiple Bodies in a Magnetic Field  

NASA Technical Reports Server (NTRS)

Some of the results from experiments to determine the interaction forces between multiple bodies in a magnetic field are presented in this paper. It is shown how the force values and the force directions depend on the configuration of the bodies, their relative positions to each other, and the vector of the primary magnetic field. A number of efficient new automatic loading and assembly machines, as well as manipulators and robots, have been created based on the relationship between bodies and magnetic fields. A few of these patented magnetic devices are presented. The concepts involved open a new way to design universal grippers for robot and other kinds of mechanisms for the manipulation of objects. Some of these concepts can be used for space applications.

Joffe, Benjamin

1996-01-01

184

Force-field calculation and geometry of the HOOO radical  

NASA Astrophysics Data System (ADS)

High-level ab initio calculations using the Davidson-corrected multireference configuration interaction (MRCI) level of theory with Dunning's correlation consistent basis sets and force-field calculations were performed for the HOOO radical. The harmonic vibrational frequencies and their anharmonic constants obtained by the force-field calculations reproduce the IR-UV experimental vibrational frequencies with errors less than 19 cm-1. The rotational constants for the ground vibrational state obtained using the vibration-rotation interaction constants of the force-field calculations also reproduce the experimentally determined rotational constants with errors less than 0.9%, indicating that the present quantum chemical calculations and the derived spectroscopic constants have high accuracy. The equilibrium structure was determined from the experimentally determined rotational constants combined with the theoretically derived vibration-rotation interaction constants. The determined geometrical parameters agree well with the results of the present MRCI calculation.

Suma, Kohsuke; Sumiyoshi, Yoshihiro; Endo, Yasuki

2013-09-01

185

Comparison of Nonlinear Force-Free Field and Potential Field in the Quiet Sun  

Microsoft Academic Search

In this paper, a potential field extrapolation and three nonlinear force-free (NLFF) field extrapolations (optimization, direct boundary integral (DBIE), and approximate vertical integration (AVI) methods) are used to study the spatial configuration of magnetic field in the quiet Sun. It is found that differences in the computed field strengths among the three NLFF and potential fields exist in the low

S. Liu; H. Q. Zhang; J. T. Su

2011-01-01

186

PRIMO: A Transferable Coarse-grained Force Field for Proteins  

PubMed Central

We describe here the PRIMO (PRotein Intermediate Model) force field, a physics-based fully transferable additive coarse-grained potential energy function that is compatible with an all-atom force field for multi-scale simulations. The energy function consists of standard molecular dynamics energy terms plus a hydrogen-bonding potential term and is mainly parameterized based on the CHARMM22/CMAP force field in a bottom-up fashion. The solvent is treated implicitly via the generalized Born model. The bonded interactions are either harmonic or distance-based spline interpolated potentials. These potentials are defined on the basis of all-atom molecular dynamics (MD) simulations of dipeptides with the CHARMM22/CMAP force field. The non-bonded parameters are tuned by matching conformational free energies of diverse set of conformations with that of CHARMM all-atom results. PRIMO is designed to provide a correct description of conformational distribution of the backbone (?/?) and side chains (?1) for all amino acids with a CMAP correction term. The CMAP potential in PRIMO is optimized based on the new CHARMM C36 CMAP. The resulting optimized force field has been applied in MD simulations of several proteins of 36–155 amino acids and shown that the root-mean-squared-deviation of the average structure from the corresponding crystallographic structure varies between 1.80 and 4.03 Å. PRIMO is shown to fold several small peptides to their native-like structures from extended conformations. These results suggest the applicability of the PRIMO force field in the study of protein structures in aqueous solution, structure predictions as well as ab initio folding of small peptides. PMID:23997693

Kar, Parimal; Gopal, Srinivasa Murthy; Cheng, Yi-Ming; Predeus, Alexander; Feig, Michael

2013-01-01

187

PRIMO: A Transferable Coarse-grained Force Field for Proteins.  

PubMed

We describe here the PRIMO (PRotein Intermediate Model) force field, a physics-based fully transferable additive coarse-grained potential energy function that is compatible with an all-atom force field for multi-scale simulations. The energy function consists of standard molecular dynamics energy terms plus a hydrogen-bonding potential term and is mainly parameterized based on the CHARMM22/CMAP force field in a bottom-up fashion. The solvent is treated implicitly via the generalized Born model. The bonded interactions are either harmonic or distance-based spline interpolated potentials. These potentials are defined on the basis of all-atom molecular dynamics (MD) simulations of dipeptides with the CHARMM22/CMAP force field. The non-bonded parameters are tuned by matching conformational free energies of diverse set of conformations with that of CHARMM all-atom results. PRIMO is designed to provide a correct description of conformational distribution of the backbone (?/?) and side chains (?1) for all amino acids with a CMAP correction term. The CMAP potential in PRIMO is optimized based on the new CHARMM C36 CMAP. The resulting optimized force field has been applied in MD simulations of several proteins of 36-155 amino acids and shown that the root-mean-squared-deviation of the average structure from the corresponding crystallographic structure varies between 1.80 and 4.03 Å. PRIMO is shown to fold several small peptides to their native-like structures from extended conformations. These results suggest the applicability of the PRIMO force field in the study of protein structures in aqueous solution, structure predictions as well as ab initio folding of small peptides. PMID:23997693

Kar, Parimal; Gopal, Srinivasa Murthy; Cheng, Yi-Ming; Predeus, Alexander; Feig, Michael

2013-08-13

188

PhET Simulation: Electric Field Hockey  

NSDL National Science Digital Library

This webpage contains an activity that allows users to guide a charged object, or "puck", through a maze using the electric field created by point charges placed by the user. Options exist to control the mass and sign of the charge of the puck. There are four levels of difficulty that change the barrier placement. Barriers do not affect the fields, only define the path of the puck. The user can view a vector representation of the electric field, as well as trace the path of the puck. After each attempt the user may move the existing charge or place more charges and try again. This activity gives users an immediate experience with the interaction between fields and charges. The page also contains samples of learning goals as well as user-submitted ideas and activities for use with the simulation. This simulation is part of a large and growing collection. It has been designed using principles from physics education research and refined based on student interviews.

Project, Physics E.

2006-10-31

189

Electrical Grounding - a Field for Geophysicists and Electrical Engineers Partnership  

NASA Astrophysics Data System (ADS)

Technology for designing ground electrodes for high-voltage direct current transmission systems (HVDC) has being using in the last years, deep soil models based on a wide range of geophysical methods. These models shall include detailed representation of shallow soil, down to 100 meters, in order to allow the evaluation of the soil conditions where the ground electrodes will be buried. Also deep soil models are needed, to be used for the interference studies, which shall represent a soil volume of about 15 km deep and a surface area of about 15 to 30 km radius. Large facilities for power plants (hydroelectric and wind farms, for example) and industrial complexes (such as petrochemical plants) has become usual at the current stage of Brazil industrialization. Grounding mats for these facilities are made of a buried cooper mesh, interconnected to a wide variety of metallic masses, such as steel reinforced concrete foundations, ducts in general etc. These grounding systems may present dimensions with the order of hundreds of meters, and, at least in Brazil, are usually calculated by using electrical resistivity soil models, based on short spacing Wenner measurements (with maximum spacing of about 64 m.). The soil model shall be the best possible representation of the environment in which the grounding electrodes are immersed, for the purpose of calculation of resistance or for digital simulation. The model to be obtained is limited by the amount and quality of soil resistivity measurements are available, and the resources to be used in the calculations and simulations. Geophysics uses a wide range of technologies for exploring subsoil, ranging from surface measurements to wells logging - seismic, gravimetric, magnetic, electrical, electromagnetic and radiometric. The electrical and electromagnetic methods includes various measurement techniques (Wenner, Schlumberger, TDEM, Magneto-telluric etc.), which together allow the development of complex resistivity soil models, layered stratified or showing lateral variations, ranging down to several tens of kilometers deep, reaching the crust-mantle interface (typically with the order of 30-40 km). This work aims to analyze the constraints of the current soil models being used for grounding electrodes design, and suggests the need of a soil modeling methodology compatible with large grounding systems. Concerning the aspects related to soil modeling, electrical engineers need to get aware of geophysics resources, such as: - geophysical techniques for soil electrical resistivity prospection (down to about 15 kilometers deep); and - techniques for converting field measured data, from many different geophysical techniques, into adequate soil models for grounding grid simulation. It is also important to equalize the basic knowledge for the professionals that are working together for the specific purpose of soil modeling for electrical grounding studies. The authors have experienced the situation of electrical engineers working with geophysicists, but it was not clear for the latter the effective need of the electrical engineers, and for the engineers it was unknown the available geophysical resources, and also, what to do convert the large amount of soil resistivity data into a reliable soil model.

Freire, P. F.; Pane, E.; Guaraldo, N.

2012-12-01

190

Force field inside the void in complex plasmas under microgravity conditions  

SciTech Connect

Observations of complex plasmas under microgravity conditions onboard the International Space Station performed with the Plasma-Kristall experiment-Nefedov facility are reported. A weak instability of the boundary between the central void (region free of microparticles) and the microparticle cloud is observed at low gas pressures. The instability leads to periodic injections of a relatively small number of particles into the void region (by analogy this effect is called the 'trampoline effect'). The trajectories of injected particles are analyzed providing information on the force field inside the void. The experimental results are compared with theory which assumes that the most important forces inside the void are the electric and the ion drag forces. Good agreement is found clearly indicating that under conditions investigated the void formation is caused by the ion drag force.

Kretschmer, M.; Khrapak, S.A.; Zhdanov, S.K.; Thomas, H.M.; Morfill, G.E.; Fortov, V.E.; Lipaev, A.M.; Molotkov, V.I.; Ivanov, A.I.; Turin, M.V. [Centre for Interdisciplinary Plasma Science, Max-Planck-Institut fuer extraterrestrische Physik, D-85741 Garching (Germany); Institute for High Energy Densities, Russian Academy of Sciences, Izhorskaya 13/19, 125412 Moscow (Russian Federation); RSC 'Energia' Korolev, 141070 Moscow Region (Russian Federation)

2005-05-01

191

Dynamics of drop formation in an electric field  

SciTech Connect

The effect of an electric field on the formation of a drop of an inviscid, perfectly conducting liquid from a capillary which protrudes from the top plate of a parallel-plate capacitor into a surrounding dynamically inactive, insulating gas is studied computationally. This free boundary problem which is comprised of the surface Bernoulli equation for the transient drop shape and the Laplace equation for the velocity potential inside the drop and the electrostatic potential outside the drop is solved by a method of lines incorporating the finite element method for spatial discretization. The finite element algorithm employed relies on judicious use of remeshing and element addition to a two-region adaptive mesh to accommodate large domain deformations, and allows the computations to proceed until the thickness of the neck connecting an about to form drop to the rest of the liquid in the capillary is less than 0.1% of the capillary radius. The accuracy of the computations is demonstrated by showing that in the absence of an electric field predictions made with the new algorithm are in excellent agreement with boundary integral calculations and experimental measurements on water drops. Computational predictions of the primary drop volume and drop length at breakup are reported over a wide range of values of the ratios of electrical gravitational, and inertial forces to surface tension force. When the magnitude of the step change in field strength is small, the results of the new transient calculations accord well with those of an earlier stability analysis and thereby provide yet another testament to the accuracy of the new algorithm.

Notz, P.K.; Basaran, O.A. [Purdue Univ., West Lafayette, IN (United States). School of Chemical Engineering] [Purdue Univ., West Lafayette, IN (United States). School of Chemical Engineering

1999-05-01

192

Electron distribution functions in electric field environments  

NASA Technical Reports Server (NTRS)

The amount of current carried by an electric discharge in its early stages of growth is strongly dependent on its geometrical shape. Discharges with a large number of branches, each funnelling current to a common stem, tend to carry more current than those with fewer branches. The fractal character of typical discharges was simulated using stochastic models based on solutions of the Laplace equation. Extension of these models requires the use of electron distribution functions to describe the behavior of electrons in the undisturbed medium ahead of the discharge. These electrons, interacting with the electric field, determine the propagation of branches in the discharge and the way in which further branching occurs. The first phase in the extension of the referenced models , the calculation of simple electron distribution functions in an air/electric field medium, is discussed. Two techniques are investigated: (1) the solution of the Boltzmann equation in homogeneous, steady state environments, and (2) the use of Monte Carlo simulations. Distribution functions calculated from both techniques are illustrated. Advantages and disadvantages of each technique are discussed.

Rudolph, Terence H.

1991-01-01

193

ON THE FORCE-FREE NATURE OF PHOTOSPHERIC SUNSPOT MAGNETIC FIELDS AS OBSERVED FROM HINODE (SOT/SP)  

SciTech Connect

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, in either case, photospheric sunspot magnetic fields are closer to satisfying the nonlinear force-free field approximation.

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

194

Kelvin Probe Force Microscopy for in situ Electrical Characterization of Organic Solar Cells  

E-print Network

Kelvin Probe Force Microscopy for in situ Electrical Characterization of Organic Solar Cells solar cell performance. Guangyong Li is currently an Assistant Professor in the Department of Electrical Wednesday October 19, 2011, Babbio 122, 11am Professor Guangyong Li Dep. of Electrical and Computer Eng

Fisher, Frank

195

Experimental Investigation of Pool Boiling Heat Transfer Enhancement in Microgravity in the Presence of Electric Fields  

NASA Technical Reports Server (NTRS)

The research carried out in the Heat Transfer Laboratory of the Johns Hopkins University was motivated by previous studies indicating that in terrestrial applications nucleate boiling heat transfer can be increased by a factor of 50 when compared to values obtained for the same system without electric fields. Imposing an external electric field holds the promise to improve pool boiling heat transfer in low gravity, since a phase separation force other than gravity is introduced. The influence of electric fields on bubble formation has been investigated both experimentally and theoretically.

Herman, C.

2000-01-01

196

Phosphate vibrations probe local electric fields and hydration in biomolecules  

PubMed Central

The role of electric fields in important biological processes like binding and catalysis has been studied almost exclusively by computational methods. Experimental measurements of the local electric field in macromolecules are possible using suitably calibrated vibrational probes. Here we demonstrate that the vibrational transitions of phosphate groups are highly sensitive to an electric field and quantify that sensitivity, allowing local electric field measurements to be made in phosphate-containing biological systems without chemical modification. PMID:21809829

Levinson, Nicholas M.; Bolte, Erin E.; Miller, Carrie S.

2011-01-01

197

Spiral Wave Generation in a Vortex Electric Field  

NASA Astrophysics Data System (ADS)

The effect of a vortical electric field on nonlinear patterns in excitable media is studied. When an appropriate vortex electric field is applied, the system exhibits pattern transition from chemical turbulence to spiral waves, which possess the same chirality as the vortex electric field. The underlying mechanism of this is discussed. We also show the meandering behavior of a spiral under the taming of a vortex electric field. The results obtained here may contribute to control strategies of patterns on surface reaction.

Yuan, Xiao-Ping; Chen, Jiang-Xing; Zhao, Ye-Hua; Lou, Qin; Wang, Lu-Lu; Shen, Qian

2011-10-01

198

Mitigated-force carriage for high magnetic field environments  

DOEpatents

A carriage for high magnetic field environments includes a first work-piece holding means for holding a first work-piece, the first work-piece holding means being disposed in an operable relationship with a work-piece processing magnet having a magnetic field strength of at least 1 Tesla. The first work-piece holding means is further disposed in operable connection with a second work-piece holding means for holding a second work-piece so that, as the first work-piece is inserted into the magnetic field, the second work-piece is simultaneously withdrawn from the magnetic field, so that an attractive magnetic force imparted on the first work-piece offsets a resistive magnetic force imparted on the second work-piece.

Ludtka, Gerard M; Ludtka, Gail M; Wilgen, John B; Murphy, Bart L

2014-05-20

199

Einstein's osmotic equilibrium of colloidal suspensions in conservative force fields  

NASA Astrophysics Data System (ADS)

Predicted by Einstein in his 1905 paper on Brownian motion, colloidal particles in suspension reach osmotic equilibrium under gravity. The idea was demonstrated by J.B. Perrin to win Nobel Prize in Physics in 1926. We show Einstein's equation for osmotic equilibrium can be applied to colloids in a conservative force field generated by optical gradient forces. We measure the osmotic equation of state of 100nm Polystyrene latex particles in the presence of KCl salt and PEG polymer. We also obtain the osmotic compressibility, which is important for determining colloidal stability and the internal chemical potential, which is useful for predicting the phase transition of colloidal systems. This generalization allows for the use of any conservative force fields for systems ranging from colloidal systems to macromolecular solutions.

Fu, Jinxin; Ou-Yang, H. Daniel

2014-09-01

200

Applying Electric Field Sensing to Human-Computer Interfaces  

E-print Network

.mit.edu ABSTRACT A non-contact sensor based on the interaction of a person with electric fields for human. KEYWORDS: user interface, input device, gesture interface, non-contact sensing, electric field. TO BE PUBLISHED IN (IEEE SIG) CHI MAY 1995 Since electric fields pass through non-conductors, passive materials

Herr, Hugh

201

Radial-Electric-Field Piezoelectric Diaphragm Pumps  

NASA Technical Reports Server (NTRS)

In a recently invented class of piezoelectric diaphragm pumps, the electrode patterns on the piezoelectric diaphragms are configured so that the electric fields in the diaphragms have symmetrical radial (along-the-surface) components in addition to through-the-thickness components. Previously, it was accepted in the piezoelectric-transducer art that in order to produce the out-of-plane bending displacement of a diaphragm needed for pumping, one must make the electric field asymmetrical through the thickness, typically by means of electrodes placed on only one side of the piezoelectric material. In the present invention, electrodes are placed on both sides and patterned so as to produce substantial radial as well as through-the-thickness components. Moreover, unlike in the prior art, the electric field can be symmetrical through the thickness. Tests have shown in a given diaphragm that an electrode configuration according to this invention produces more displacement than does a conventional one-sided electrode pattern. The invention admits of numerous variations characterized by various degrees of complexity. Figure 1 is a simplified depiction of a basic version. As in other piezoelectric diaphragm pumps of similar basic design, the prime mover is a piezoelectric diaphragm. Application of a suitable voltage to the electrodes on the diaphragm causes it to undergo out-of-plane bending. The bending displacement pushes a fluid out of, or pulls the fluid into, a chamber bounded partly by the diaphragm. Also as in other diaphragm pumps in general, check valves ensure that the fluid flows only in through one port and only out through another port.

Bryant, Robert G.; Working, Dennis C.; Mossi, Karla; Castro, Nicholas D.; Mane, Pooma

2009-01-01

202

Large Electric Field–Enhanced–Hardness Effect in a SiO2 Film  

PubMed Central

Silicon dioxide films are extensively used in nano and micro–electromechanical systems. Here we studied the influence of an external electric field on the mechanical properties of a SiO2 film by using nanoindentation technique of atomic force microscopy (AFM) and friction force microscopy (FFM). A giant augmentation of the relative elastic modulus was observed by increasing the localized electric field. A slight decrease in friction coefficients was also clearly observed by using FFM with the increase of applied tip voltage. The reduction of the friction coefficients is consistent with the great enhancement of sample hardness by considering the indentation–induced deformation during the friction measurements. PMID:24681517

Revilla, Reynier I.; Li, Xiao-Jun; Yang, Yan-Lian; Wang, Chen

2014-01-01

203

Electric current generation in photorefractive bismuth silicon oxide without application of external electric field  

NASA Astrophysics Data System (ADS)

A holographic radial diffraction grating (HRDG) is an efficient optical element for splitting single laser beam on three 0, -1st, and +1st- diffraction order beams. The rotation of the grating at certain velocity allows a window for quality control over the frequency detuning between -1st, and +1st diffracted beams. The running interference fringes produced by the beams and projected on photorefractive crystal induce running holographic gratings in the crystal. This simple configuration is an effective tool for the study of such phenomena as space charge waves [1], domains motion [2], and electric current generation [3]. Specifics of photorefractive mechanism in cubic photorefractive crystals (BSO, BTO) normally require a use of external electric field to produce reasonable degree of refractive index modulation to observe associated with it phenomena. In this work we provide a direct experimental observation of the electric current generated in photorefractive BSO using running grating technique without an applied electric field. Moving interference fringes modulate a photoconductivity and an electric field in photorefractive crystal thus creating the photo electro-motive force (emf) and the current. The magnitude of the current varies between 1 and 10 nA depending on the rotation speed of HRDG. The peculiarities of the current behavior include a backward current flow, and current oscillations. The holographic current generated through this technique can find applications in non-destructive testing for ultra-sensitive vibrometry, materials characterization, and for motion sensors. References [1] S.F. Lyuksyutov, P. Buchhave, and M.V. Vasnetsov, Physical Review Letters, 79, No.1, 67-70 (1997) [2] P. Buchhave, S. Lyuksyutov, M. Vasnetsov, and C. Heyde, Journal Optical Society of America B, 13, No.11 2595-2602 (1996) [3] M. Vasnetsov, P. Buchhave, and S. Lyuksyutov Optics Communications, 137, 181-191 (1997)

Buchhave, Preben; Kukhtarev, Nickolai; Kukhtareva, Tatiana; Edwards, Matthew E.; Reagan, Michael A.; Lyuksyutov, Sergei F.

2003-10-01

204

Amino acid similarity matrices based on force fields  

Microsoft Academic Search

Motivation: We propose a general method for deriving amino acid substitution matrices from low resolution force fields. Unlike current popular methods, the approach does not rely on evolutionary arguments or alignment of sequences or structures. Instead, residues are com- putationally mutated and their contribution to the total energy\\/score is collected. The average of these values over each position within a

Zsuzsanna Dosztányi; Andrew E. Torda

2001-01-01

205

Comparison of different force fields for the study of disaccharides  

Technology Transfer Automated Retrieval System (TEKTRAN)

Eighteen empirical force fields and the semi-empirical quantum method PM3CARB-1 were compared for studying ß-cellobiose, a-maltose, and a-galabiose [a-D-Galp-(1'4)-a-D-Galp]. For each disaccharide, the energies of 54 conformers with differing hydroxymethyl, hydroxyl and glycosidic linkage orientatio...

206

Force, current and field effects in single atom manipulation  

E-print Network

Force, current and field effects in single atom manipulation K.-F. Braun , S.-W. Hla , N. Pertaya present a detailed investigation of the manipulation of Ag and Au atoms with a STM tip on the Ag(111 of the atom during manipulation. The threshold tunnelling resistance and tip-height to move a Au/Ag atom have

Hla, Saw-Wai

207

Impact of electric fields on honey bees  

SciTech Connect

Biological effects in honey bee colonies under a 765-kV, 60-Hz transmission line (electric (E) field = 7 kV/m) were confirmed using controlled dosimetry and treatment reversal to replicate findings within the same season. Hives in the same environment but shielded from E field are normal, suggesting effects are caused by interaction of E field with the hive. Bees flying through the ambient E field are not demonstrably affected. Different thresholds and severity of effects were found in colonies exposed to 7, 5.5, 4.1, 1.8, and 0.65 to 0.85 kV/m at incremental distances from the line. Most colonies exposed at 7 kV/m failed in 8 weeks and failed to overwinter at greater than or equal to4.1 kV/m. Data suggest the limit of a biological effects corridor lies between 15 and 27 m (4.1 and 1.8 kV/m) beyond the outer phase of the transmission line. Mechanisms to explain colony disturbance fall into two categories, direct perception of enhanced in-hive E fields, and perception of shock from induced currents. The same effects induced in colonies with total-hive E-field exposure can be reproduced with shock or E-field exposure of worker bees in extended hive entranceways (= porches). Full-scale experiments demonstrate bee exposure to E fields including 100 kV/m under moisture-free conditions within a non-conductive porch causes no detectable effect on colony behavior. Exposure of bees on a conductive (e.g. wet) substrate produces been disturbance, increased mortality, abnormal propolization, and possible impairment of colony growth. Thresholds for effects caused by step-potential-induced currents are: 275-350 nA - disturbance of single bees; 600 nA - onset of abnormal propolization; and 900 nA - sting.

Bindokas, V.P.

1985-01-01

208

The Induced Electric Field Distribution in Solar Atmosphere  

E-print Network

A method of calculating induced electric field is presented in this paper. Induced electric field in solar atmosphere is derived by the time variation of magnetic field when the charged particle accumulation is neglected. In order to get the spatial distribution of magnetic field, several extrapolation methods are introduced. With observational data from Helioseismic and Magnetic Imager (HMI) aboard the NASA's Solar Dynamics Observatory (SDO) on May 20th, 2010, we extrapolate the magnetic field to the upper atmosphere from the photosphere. By calculating the time variation of magnetic field, we can get the induced electric field. The derived induced electric field can reach a value of 100 V/cm and the average electric field has a maximum point at the layer of 360 km above the photosphere. The Monte Carlo statistics method is used to compute the triple integration of induced electric field.

Chen, Rong; Deng, Yuanyong

2013-01-01

209

Electric contributions to magnetic force microscopy response from graphene and MoS2 nanosheets  

NASA Astrophysics Data System (ADS)

Magnetic force microscopy (MFM) signals have recently been detected from whole pieces of mechanically exfoliated graphene and molybdenum disulfide (MoS2) nanosheets, and magnetism of the two nanomaterials was claimed based on these observations. However, non-magnetic interactions or artefacts are commonly associated with MFM signals, which make the interpretation of MFM signals not straightforward. A systematic investigation has been done to examine possible sources of the MFM signals from graphene and MoS2 nanosheets and whether the MFM signals can be correlated with magnetism. It is found that the MFM signals have significant non-magnetic contributions due to capacitive and electrostatic interactions between the nanosheets and conductive cantilever tip, as demonstrated by electric force microscopy and scanning Kevin probe microscopy analyses. In addition, the MFM signals of graphene and MoS2 nanosheets are not responsive to reversed magnetic field of the magnetic cantilever tip. Therefore, the observed MFM response is mainly from electric artefacts and not compelling enough to correlate with magnetism of graphene and MoS2 nanosheets.

Li, Lu Hua; Chen, Ying

2014-12-01

210

Point Charge Electric Field and Potential 2D Model  

NSDL National Science Digital Library

The Point Charge Electric Field and Potential model explores the concepts of the electric field and the electric potential, in a two-dimensional situation. You can turn on 1 to 5 charged particles, and move a test charge around the plane near these charged particles to sample both the electric field and the electric potential, produced by the charged particles, at various points. You can also turn on a grid of field vectors, which show the direction and, qualitatively, the magnitude of the field at a grid of equally spaced points in the plane in which the charged particles are located.

Duffy, Andrew

2009-10-20

211

Convolutional virtual electric field for image segmentation using active contours.  

PubMed

Gradient vector flow (GVF) is an effective external force for active contours; however, it suffers from heavy computation load. The virtual electric field (VEF) model, which can be implemented in real time using fast Fourier transform (FFT), has been proposed later as a remedy for the GVF model. In this work, we present an extension of the VEF model, which is referred to as CONvolutional Virtual Electric Field, CONVEF for short. This proposed CONVEF model takes the VEF model as a convolution operation and employs a modified distance in the convolution kernel. The CONVEF model is also closely related to the vector field convolution (VFC) model. Compared with the GVF, VEF and VFC models, the CONVEF model possesses not only some desirable properties of these models, such as enlarged capture range, u-shape concavity convergence, subject contour convergence and initialization insensitivity, but also some other interesting properties such as G-shape concavity convergence, neighboring objects separation, and noise suppression and simultaneously weak edge preserving. Meanwhile, the CONVEF model can also be implemented in real-time by using FFT. Experimental results illustrate these advantages of the CONVEF model on both synthetic and natural images. PMID:25360586

Wang, Yuanquan; Zhu, Ce; Zhang, Jiawan; Jian, Yuden

2014-01-01

212

Convolutional Virtual Electric Field for Image Segmentation Using Active Contours  

PubMed Central

Gradient vector flow (GVF) is an effective external force for active contours; however, it suffers from heavy computation load. The virtual electric field (VEF) model, which can be implemented in real time using fast Fourier transform (FFT), has been proposed later as a remedy for the GVF model. In this work, we present an extension of the VEF model, which is referred to as CONvolutional Virtual Electric Field, CONVEF for short. This proposed CONVEF model takes the VEF model as a convolution operation and employs a modified distance in the convolution kernel. The CONVEF model is also closely related to the vector field convolution (VFC) model. Compared with the GVF, VEF and VFC models, the CONVEF model possesses not only some desirable properties of these models, such as enlarged capture range, u-shape concavity convergence, subject contour convergence and initialization insensitivity, but also some other interesting properties such as G-shape concavity convergence, neighboring objects separation, and noise suppression and simultaneously weak edge preserving. Meanwhile, the CONVEF model can also be implemented in real-time by using FFT. Experimental results illustrate these advantages of the CONVEF model on both synthetic and natural images. PMID:25360586

Wang, Yuanquan; Zhu, Ce; Zhang, Jiawan; Jian, Yuden

2014-01-01

213

Perturbative treatment of lattice dynamics in finite electric fields  

NASA Astrophysics Data System (ADS)

The methods of density-functional perturbation theory have been shown to be very powerful for realistic calculations of lattice-vibrational, dielectric, elastic, and other response properties of crystals.(S. Baroni et al.), Rev. Mod. Phys. 73, 515 (2001). Recently, a total-energy method for insulators in nonzero electric fields has been proposed.(I. Souza, J. Íñiguez, and D. Vanderbilt, Phys. Rev. Lett. 89), 117602 (2002). However, the perturbative computation of response properties under a dc bias field has not previously been addressed. Here, perturbation theory is applied to a variational total-energy functional in the presence of a static, homogeneous electric field. An analytic expression is derived for the second derivative with respect to the phonon perturbation using the 2n+1 theorem. The expression is variational with respect to the first-order Bloch-like states, and can be minimized using standard conjugate-gradients methods. We implement the method in the ABINIT code and perform illustrative calculations of the interatomic force constant matrix of III-V semiconductors.

Wang, Xinjie; Souza, Ivo; Vanderbilt, David

2004-03-01

214

Atomistic force field for alumina fit to density functional theory  

SciTech Connect

We present a force field for bulk alumina (Al{sub 2}O{sub 3}), 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.

Sarsam, Joanne [Department of Materials, Imperial College London, London SW7 2AZ (United Kingdom) [Department of Materials, Imperial College London, London SW7 2AZ (United Kingdom); Thomas Young Centre, Imperial College London, London SW7 2AZ (United Kingdom); Finnis, Michael W.; Tangney, Paul, E-mail: p.tangney@imperial.ac.uk [Department of Materials, Imperial College London, London SW7 2AZ (United Kingdom) [Department of Materials, Imperial College London, London SW7 2AZ (United Kingdom); Thomas Young Centre, Imperial College London, London SW7 2AZ (United Kingdom); Department of Physics, Imperial College London, London SW7 2AZ (United Kingdom)

2013-11-28

215

The Physics Classroom: Electric Force - Inverse Square Law  

NSDL National Science Digital Library

This tutorial for introductory physics explores the inverse square relationship between electrostatic force and separation distance, with descriptions, definitions and explanations of how electrostatic forces obey the inverse square law. An interactive question-and-answer set allows students to self-test their understanding. This page is part of The Physics Classroom tutorials for students of introductory physics. SEE RELATED ITEMS on this page for a link to a closely related tutorial on Coulomb's Law by the same author.

Henderson, Tom; Foundation, National S.

2006-11-18

216

Aircraft measurement of electric field - Self-calibration  

NASA Technical Reports Server (NTRS)

Aircraft measurement of electric fields is difficult as the electrically conducting surface of the aircraft distorts the electric field. Calibration requires determining the relations between the undistorted electric field in the absence of the vehicle and the signals from electric field meters that sense the local distorted fields in their immediate vicinity. This paper describes a generalization of a calibration method which uses pitch and roll maneuvers. The technique determines both the calibration coefficients and the direction of the electric vector. The calibration of individual electric field meters and the elimination of the aircraft's self-charge are described. Linear combinations of field mill signals are examined and absolute calibration and error analysis are discussed. The calibration method was applied to data obtained during a flight near thunderstorms.

Winn, W. P.

1993-01-01

217

Electric field effect in ultrathin black phosphorus  

SciTech Connect

Black phosphorus exhibits a layered structure similar to graphene, allowing mechanical exfoliation of ultrathin single crystals. Here, we demonstrate few-layer black phosphorus field effect devices on Si/SiO{sub 2} and measure charge carrier mobility in a four-probe configuration as well as drain current modulation in a two-point configuration. We find room-temperature mobilities of up to 300 cm{sup 2}/Vs and drain current modulation of over 10{sup 3}. At low temperatures, the on-off ratio exceeds 10{sup 5}, and the device exhibits both electron and hole conduction. Using atomic force microscopy, we observe significant surface roughening of thin black phosphorus crystals over the course of 1 h after exfoliation.

Koenig, Steven P.; Schmidt, Hennrik [Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546 (Singapore); Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Doganov, Rostislav A.; Castro Neto, A. H.; Özyilmaz, Barbaros [Graphene Research Centre, National University of Singapore, 6 Science Drive 2, Singapore 117546 (Singapore); Department of Physics, National University of Singapore, 2 Science Drive 3, Singapore 117542 (Singapore); Graduate School for Integrative Sciences and Engineering (NGS), National University of Singapore, 28 Medical Drive, Singapore 117456 (Singapore)

2014-03-10

218

Optical forces in coupled plasmonic nanosystems: Near field and far field interaction regimes.  

PubMed

We study the forces generated by an electromagnetic field on two coupled gold nanowires at the vicinity of the plasmon resonance wavelength. Two different regimes are observed, depending on the separation distance between the wires. In the near field coupling regime, both attractive and repulsive forces can be generated, depending on and the illumination wavelength. Furthermore, at the plasmon resonance, it is possible to create forces 100 times larger than the radiation pressure. In the far field coupling regime, both particles are pushed by the incident field. However, the force amplitude applied on each wire is modulated as a function of , even for large separations. This indicates that the system behaves like a cavity and pseudo Fabry-Perot modes can be excited between the particles. The interaction of these modes with the plasmon resonances of the nanowires, determines the forces on the particles. Around the plasmon resonance wavelength, when the cavity is tuned to the incident light, forces are close to the average value corresponding to the radiation pressure of the incident field. On the other hand, when the cavity is detuned, the particles are retained or pushed anti-symmetrically. We finally study the forces applied on these nanowires in the centre of mass reference frame (CMRF) for the far field coupling regime. For any separation distance we observe equilibrium positions in the CMRF for at least one illumination wavelength. The stability of these equilibrium positions is discussed in detail. PMID:19547312

Lamothe, Elodie; Lévêque, Gaëtan; Martin, Olivier J F

2007-07-23

219

Electric field studies: TLE-induced waveforms and ground conductivity impact on electric field propagation  

Microsoft Academic Search

We review in this paper main results obtained from electric field (from VLF to HF) measurement campaigns realized by CEA in the framework of the Eurosprite program [Neubert et al., 2005, 2008] from 2003 to 2009 in France in different configurations. Two main topics have been studied: sprite or elve induced phenomena (radiation or perturbation) and wave propagation. Using a

Thomas Farges; Geraldine Garcia; Elisabeth Blanc

2010-01-01

220

An attempt in assessing contact forces from a kinematic field  

NASA Astrophysics Data System (ADS)

In granular materials, it is not so simple to assess experimentally the contact forces. Photoelasticity is generally used for this purpose but this technique involves some constraints that may limit its use. We propose a different solution, which implements both the digital image correlation (DIC) technique and the non-smooth contact dynamics (NSCD) formalism. In a nutshell, the technique aims to find a set of contact forces mechanically admissible given a set of measured contact velocities. We used photographs of a simple shear test of a two-dimensional analogue granular material (about 1000 aluminum rods) to apply the solution, and we showed that valuable information about the contact forces can be extracted from the kinematic field provided that no major rearrangement occurs for at least five image shots.

Richefeu, Vincent; Combe, Gaël; Maurin, Raphaël

2013-06-01

221

Field forced antiferroelectric-to-ferroelectric switching in modified lead zirconate titanate stannate ceramics  

SciTech Connect

Electric-field-forced antiferroelectric- to-ferroelectric phase transitions in several compositions of modified lead zirconate titanate stannate antiferroelectric ceramics are studied for ultra-high-field-induced strain actuator applications. Two types of fatigue effects are observed in these ceramic compositions. In one, the fatigue effects only proceed to a limited extent and the properties may be restored by annealing above the Curie temperature, while in the other, the fatigue effects proceed to a large extent and the properties cannot be restored completely by heat treatment.

Pan, W.; Zhang, Q.; Bhalla, A.; Cross, L.E. (Materials Research Lab., Pennsylvania State Univ., University Park, PA (US))

1989-04-01

222

Multi-parameter Hopf-bifurcation in HHM Model Exposed to ELF Electric Field.  

PubMed

The variation of cell trans-membrane voltage exposed to extremely low frequency (ELF) electric field is analyzed; a modified Hodgkin-Huxley model of muscle (HHM) is established by introducing a new parameter denoting the effect of external electric field, and the bifurcation caused by the new parameter as well as leakage conductance and sodium ions anti-electromotive force is studied. The algebra criterion in high dimension equations is employed to perform the analysis of multi-parameter dynamical bifurcation. The results are of biological significance and suggest that the aberration of dynamics in bio-systems may be accounted for diseases caused by electric exposure. PMID:17281276

Jiang, Wang; Yanqiu, Che; Xiangyang, Fei; Feng, Dong

2005-01-01

223

Comparison of Nonlinear Force-Free Field and Potential Field in the Quiet Sun  

Microsoft Academic Search

In this paper, a potential field extrapolation and three nonlinear force-free (NLFF) field extrapolations (optimization, direct\\u000a boundary integral (DBIE), and approximate vertical integration (AVI) methods) are used to study the spatial configuration\\u000a of magnetic field in the quiet Sun. It is found that differences in the computed field strengths among the three NLFF and\\u000a potential fields exist in the low

S. Liu; H. Q. Zhang; J. T. Su

2011-01-01

224

Liquid methanol under a static electric field.  

PubMed

We report on an ab initio molecular dynamics study of liquid methanol under the effect of a static electric field. We found that the hydrogen-bond structure of methanol is more robust and persistent for field intensities below the molecular dissociation threshold whose value (?0.31 V/Å) turns out to be moderately larger than the corresponding estimate obtained for liquid water. A sustained ionic current, with ohmic current-voltage behavior, flows in this material for field intensities above 0.36 V/Å, as is also the case of water, but the resulting ionic conductivity (?0.40 S cm(-1)) is at least one order of magnitude lower than that of water, a circumstance that evidences a lower efficiency of proton transfer processes. We surmise that this study may be relevant for the understanding of the properties and functioning of technological materials which exploit ionic conduction, such as direct-methanol fuel cells and Nafion membranes. PMID:25662649

Cassone, Giuseppe; Giaquinta, Paolo V; Saija, Franz; Saitta, A Marco

2015-02-01

225

Advancement of polarizable force field and its use for molecular modeling and design.  

PubMed

The most important requirement of biomolecular modeling is to deal with electrostatic energies. The electrostatic polarizability is an important part of electrostatic interaction for simulation systems. However, AMBER, CHARMM, OPLS, GROMOS, MMFF force fields etc. used in the past mostly apply fixed atomic center point charge to describe electrostatic energies, and are not sufficient for considering the influence of the electrostatic polarization. The emergence of polarizable force fields has solved this problem. In recent years, quickly developed polarizable force fields have involved a lot of fields. The chapter relating to polarizable force fields spread over several aspects. Firstly, we reviewed the history of the classical force fields and compared with polarizable force fields to elucidate the advancements of polarizable force fields. Secondly, it is introduced that the application of polarizable force fields to small molecules and biological macromolecules simulation, including molecular design. Finally, a brief development trend and perspective is given on rapidly growing polarizable force fields. PMID:25387957

Xu, Peijun; Wang, Jinguang; Xu, Yong; Chu, Huiying; Liu, Jiahui; Zhao, Meixia; Zhang, Depeng; Mao, Yingchen; Li, Beibei; Ding, Yang; Li, Guohui

2015-01-01

226

Spatial confinement of ultrasonic force fields in microfluidic channels.  

PubMed

We demonstrate and investigate multiple localized ultrasonic manipulation functions in series in microfluidic chips. The manipulation functions are based on spatially separated and confined ultrasonic primary radiation force fields, obtained by local matching of the resonance condition 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 adjacent fields. The goal is to define design strategies for implementing several spatially separated ultrasonic manipulation functions in series for use in advanced particle or cell handling and processing applications. One such proof-of-concept application is demonstrated, where flow-through-mode operation of a chip with flow splitting elements is used for two-dimensional pre-alignment and addressable merging of particle tracks. PMID:18701122

Manneberg, Otto; Melker Hagsäter, S; Svennebring, Jessica; Hertz, Hans M; Kutter, Jörg P; Bruus, Henrik; Wiklund, Martin

2009-01-01

227

DIVERSION OF ADULT SALMON BY AN ELECTRICAL FIELD  

E-print Network

DIVERSION OF ADULT SALMON BY AN ELECTRICAL FIELD Marine Biological Laboratory : -1958 WOODS HOLE OF ADULT SALMON BY AN ELECTRICAL FIELD By Roger E. Burrows Fishery Research Biologist Entiat, Wash. Bureau 1957 #12;ABSTRACT An electrical weir consisting of a line of hanging electrodes and a submerged ground

228

Relationship between the ion drag and electric forces in dense dust clouds  

SciTech Connect

It is shown that the relation between the ion drag and electric forces is strongly dependent on the dust number density in complex plasmas. The effect of the particle size and discharge parameters on the force balance is investigated. Examples are given for realistic complex plasma parameters and comparison with microgravity experiments is presented.

Yaroshenko, V. V.; Khrapak, S. A.; Morfill, G. E. [Max-Planck-Institut fuer extraterrestrische Physik, D-85748 Garching (Germany)

2013-04-15

229

Review Of Fiber-Optic Electric-Field Sensors  

NASA Technical Reports Server (NTRS)

Tutorial paper reviews state of art in fiber-optic sensors of alternating electric fields. Because such sensors are made entirely of dielectric materials, they are relatively transparent to incident electric fields; they do not distort fields significantly. Paper presents equations that express relationships among stress, strain, and electric field in piezoactive plastic and equations for phase shift in terms of photoelastic coefficients and strains in optical fiber.

De Paula, Ramon P.; Jarzynski, Jacek

1989-01-01

230

Direct computation of parameters for accurate polarizable force fields  

NASA Astrophysics Data System (ADS)

We present an improved electronic linear response model to incorporate polarization and charge-transfer effects in polarizable force fields. This model is a generalization of the Atom-Condensed Kohn-Sham Density Functional Theory (DFT), approximated to second order (ACKS2): it can now be defined with any underlying variational theory (next to KS-DFT) and it can include atomic multipoles and off-center basis functions. Parameters in this model are computed efficiently as expectation values of an electronic wavefunction, obviating the need for their calibration, regularization, and manual tuning. In the limit of a complete density and potential basis set in the ACKS2 model, the linear response properties of the underlying theory for a given molecular geometry are reproduced exactly. A numerical validation with a test set of 110 molecules shows that very accurate models can already be obtained with fluctuating charges and dipoles. These features greatly facilitate the development of polarizable force fields.

Verstraelen, Toon; Vandenbrande, Steven; Ayers, Paul W.

2014-11-01

231

In-plane force fields and elastic properties of graphene  

NASA Astrophysics Data System (ADS)

Bond stretching and angle bending force fields, appropriate to describe in-plane properties of graphene sheets, are derived using first principles' methods. The obtained force fields are fitted by analytical anharmonic potential energy functions, providing efficient means of calculations in molecular mechanics simulations. Using both molecular dynamics simulations and first principles' methods, numerical results regarding the mechanical behavior of graphene monolayers under various loads, like uniaxial tension in different directions or hydrostatic tension, are presented and compared. Graphene's response in shear stress is also investigated using molecular dynamics, where a noticeable asymmetric mechanical behavior is found. Stress-strain curves and elastic constants, such as, Young modulus, Poisson's ratio, bulk modulus, and shear modulus, are calculated. Our results are compared with available experimental estimates, as well as, with corresponding theoretical calculations. Finally, the effects of the anharmonicity of the extracted bond stretching and angle bending potentials on the mechanical properties of graphene are discussed.

Kalosakas, G.; Lathiotakis, N. N.; Galiotis, C.; Papagelis, K.

2013-04-01

232

Dust particles under the influence of crossed electric and magnetic fields in the sheath of an rf discharge  

NASA Astrophysics Data System (ADS)

Experimental studies on the interaction of micron-sized dust particles in plasmas with external magnetic fields are presented. The particles are levitated in the sheath region of an rf discharge by gravity and electric field force under the presence of a horizontal magnetic field of up to 50 mT. It is observed that the dust particles are pushed either in the E ? × B ? - or in the opposite direction depending on magnetic field strength, particle properties, and discharge conditions. This transport behavior is described by a competition between horizontal ambipolar electric field force and ion and neutral drag.

Puttscher, M.; Melzer, A.

2014-12-01

233

Electric field representation of pulsar intensity spectra  

E-print Network

Pulsar dynamic spectra exhibit high visibility fringes arising from interference between scattered radio waves. These fringes may be random or highly ordered patterns, depending on the nature of the scattering or refraction. Here we consider the possibility of decomposing pulsar dynamic spectra -- which are intensity measurements -- into their constituent scattered waves, i.e. electric field components. We describe an iterative method of achieving this decomposition and show how the algorithm performs on data from the pulsar B0834+06. The match between model and observations is good, although not formally acceptable as a representation of the data. Scattered wave components derived in this way are immediately useful for qualitative insights into the scattering geometry. With some further development this approach can be put to a variety of uses, including: imaging the scattering and refracting structures in the interstellar medium; interstellar interferometric imaging of pulsars at very high angular resolution; and mitigating pulse arrival time fluctuations due to interstellar scattering.

Mark Walker; Dan Stinebring

2005-08-08

234

Quantum mechanical force field for water with explicit electronic polarization  

SciTech Connect

A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensed-phase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen- and hydrogen-containing compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a three-point charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with three-point-charge potential) model, is suitable for modeling both gas-phase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 10{sup 6} self-consistent-field calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across biological ion channels through membranes.

Han, Jaebeom; Mazack, Michael J. M.; Zhang, Peng; Truhlar, Donald G.; Gao, Jiali [Department of Chemistry and Supercomputing Institute, University of Minnesota, 207 Pleasant Street, SE, Minneapolis, Minnesota 55455-0431 (United States)] [Department of Chemistry and Supercomputing Institute, University of Minnesota, 207 Pleasant Street, SE, Minneapolis, Minnesota 55455-0431 (United States)

2013-08-07

235

Quantum mechanical force field for water with explicit electronic polarization  

PubMed Central

A quantum mechanical force field (QMFF) for water is described. Unlike traditional approaches that use quantum mechanical results and experimental data to parameterize empirical potential energy functions, the present QMFF uses a quantum mechanical framework to represent intramolecular and intermolecular interactions in an entire condensed-phase system. In particular, the internal energy terms used in molecular mechanics are replaced by a quantum mechanical formalism that naturally includes electronic polarization due to intermolecular interactions and its effects on the force constants of the intramolecular force field. As a quantum mechanical force field, both intermolecular interactions and the Hamiltonian describing the individual molecular fragments can be parameterized to strive for accuracy and computational efficiency. In this work, we introduce a polarizable molecular orbital model Hamiltonian for water and for oxygen- and hydrogen-containing compounds, whereas the electrostatic potential responsible for intermolecular interactions in the liquid and in solution is modeled by a three-point charge representation that realistically reproduces the total molecular dipole moment and the local hybridization contributions. The present QMFF for water, which is called the XP3P (explicit polarization with three-point-charge potential) model, is suitable for modeling both gas-phase clusters and liquid water. The paper demonstrates the performance of the XP3P model for water and proton clusters and the properties of the pure liquid from about 900 × 106 self-consistent-field calculations on a periodic system consisting of 267 water molecules. The unusual dipole derivative behavior of water, which is incorrectly modeled in molecular mechanics, is naturally reproduced as a result of an electronic structural treatment of chemical bonding by XP3P. We anticipate that the XP3P model will be useful for studying proton transport in solution and solid phases as well as across biological ion channels through membranes. PMID:23927266

Han, Jaebeom; Mazack, Michael J. M.; Zhang, Peng; Truhlar, Donald G.; Gao, Jiali

2013-01-01

236

Four-nucleon force in chiral effective field theory  

SciTech Connect

We derive the leading contribution to the four--nucleon force within the framework of chiral effective field theory. It is governed by the exchange of pions and the lowest--order nucleon--nucleon contact interaction and includes effects due to the nonlinear pion--nucleon couplings and the pion self interactions constrained by the chiral symmetry of QCD. The resulting 4NF does not contain any unknown parameters and can be tested in future few--and many--nucleon studies.

Evgeny Epelbaum

2005-10-25

237

Current Status of the AMOEBA Polarizable Force Field  

PubMed Central

Molecular force fields have been approaching a generational transition over the past several years, moving away from well-established and well-tuned, but intrinsically limited, fixed point charge models towards more intricate and expensive polarizable models that should allow more accurate description of molecular properties. The recently introduced AMOEBA force field is a leading publicly available example of this next generation of theoretical model, but to date has only received relatively limited validation, which we address here. We show that the AMOEBA force field is in fact a significant improvement over fixed charge models for small molecule structural and thermodynamic observables in particular, although further fine-tuning is necessary to describe solvation free energies of drug-like small molecules, dynamical properties away from ambient conditions, and possible improvements in aromatic interactions. State of the art electronic structure calculations reveal generally very good agreement with AMOEBA for demanding problems such as relative conformational energies of the alanine tetrapeptide and isomers of water sulfate complexes. AMOEBA is shown to be especially successful on protein-ligand binding and computational X-ray crystallography where polarization and accurate electrostatics are critical. PMID:20136072

Ponder, Jay W.; Wu, Chuanjie; Ren, Pengyu; Pande, Vijay S.; Chodera, John D.; Schnieders, Michael J.; Haque, Imran; Mobley, David L.; Lambrecht, Daniel S.; DiStasio, Robert A.; Head-Gordon, Martin; Clark, Gary N. I.; Johnson, Margaret E.

2010-01-01

238

XVI. On the distribution of electric force and rise of temperature in the glow discharge  

Microsoft Academic Search

1. 1. It is suggested that the results of Messrs. Finch and Cowen's experiments upon gaseous combustion and ignition in electric discharges might be explained equally well upon the thermal theory.2. 2. Experiments made to test the accuracy of the two-probe method of' determining the electric force in glow discharges are described. These lead to the conclusion that above a

John M. Holm

1931-01-01

239

Structure of Electrorheological Fluids under an Electric Field and a Shear Flow: Experiment and Computer Simulation  

E-print Network

results will also hold for other suspensions such as magnetorheological suspensions,9 ferro- fluids,10Structure of Electrorheological Fluids under an Electric Field and a Shear Flow: Experiment, Brownian, and hydrodynamic (if any) forces. We take electrorheological (ER) fluids as an example. By using

Huang, Ji-Ping

240

Theoretical prediction of electric field-enhanced coalescence of spherical drops  

Microsoft Academic Search

A fundamental study of drop collision, coalescence and growth induced by combined effects of gravitational and electrostatic forces is presented. The focus is on the enhancement of rates of collision and growth of spherical, conducting drops bearing zero net charge in dilute, homogeneous dispersions by an external electric field. By completely accounting for hydrodynamic and electrostatic interactions, a trajectory analysis

Xiaoguang Zhang; Osman A. Basaran; Robart M. Wham

1995-01-01

241

Temperature gradient and electric field driven electrostatic instabilities  

NASA Technical Reports Server (NTRS)

The stability of electrostatic waves to thermodynamic and electric potential gradients was investigated. It is shown that thermodynamic gradients drive instabilities even when the internal electric field vanishes. Skewing of the distribution function is not included in the dielectric.

Morrison, P. J.; Ionson, J. A.

1982-01-01

242

Observations of field-aligned currents, waves, and electric fields at substorm onset  

NASA Technical Reports Server (NTRS)

Substorm onsets, identified Pi 2 pulsations observed on the Air Force Geophysics Laboratory Magnetometer Network, are studied using magnetometer and electric field data from ISEE 1 as well as magnetometer data from the geosynchronous satellites GOES 2 and 3. The mid-latitude magnetometer data provides the means of both timing and locating the substorm onset so that the spacecraft locations with respect to the substorm current systems are known. During two intervals, each containing several onsets or intensifications, ISEE 1 observed field-aligned current signatures beginning simultaneously with the mid-latitude Pi 2 pulsation. Close to the earth broadband bursts of wave noise were observed in the electric field data whenever field-aligned currents were detected. One onset occurred when ISEE 1 and GOES 2 were on the same field line but in opposite hemispheres. During this onset ISEE 1 and GOES 2 saw magnetic signatures which appear to be due to conjugate field-aligned currents flowing out of the western end of the westward auroral electrojets. The ISEE 1 signature is of a line current moving westward past the spacecraft. During the other interval, ISEE 1 was in the near-tail region near the midnight meridian. Plasma data confirms that the plasma sheet thinned and subsequently expanded at onset. Electric field data shows that the plasma moved in the opposite direction to the plasma sheet boundary as the boundary expanded which implies that there must have been an abundant source of hot plasma present. The plasma motion was towards the center of the plasma sheet and earthwards and consisted of a series of pulses rather than a steady flow.

Smits, D. P.; Hughes, W. J.; Cattell, C. A.; Russell, C. T.

1986-01-01

243

A fluorometric approach to local electric field measurements in a voltage-gated ion channel.  

PubMed

Site-specific electrostatic measurements have been limited to soluble proteins purified for in vitro spectroscopic characterization or proteins of known structure; however, comparable measurements have not been made for functional membrane bound proteins. Here, using an electrochromic fluorophore, we describe a method to monitor localized electric field changes in a voltage-gated potassium channel. By coupling the novel probe Di-1-ANEPIA to cysteines in Shaker and tracking field-induced optical changes, in vivo electrostatic measurements were recorded with submillisecond resolution. This technique reports dynamic changes in the electric field during the gating process and elucidates the electric field profile within Shaker. The extension of this method to other membrane bound proteins, including transporters, will yield insight into the role of electrical forces on protein function. PMID:12526775

Asamoah, Osei Kwame; Wuskell, Joseph P; Loew, Leslie M; Bezanilla, Francisco

2003-01-01

244

Biological effects of electric fields: an overview  

SciTech Connect

An overview of the literature suggests tha electric-field exposure is an environmental agent/influence of relatively low potential toxicity to biological systems. Generally, many of the biological effects which have been reported are quite subtle and differences between exposed and unexposed subjects may be masked by normal biological variations. However, several recent reports indicate possibly more serious consequences from chronic exposure, emphasizing the need for more research in epidemiology and laboratory experiments. This paper presents a cursory overview of investigations on the biological consequences of exposure to ELF electromagnetic fields. Three important topics are discussed, including: 1) the general methodology of exposure experiments, including those elements which are critical for definitive studies in biological systems; 2) a brief discussion of epidemiological and clinical studies conducted to date; and 3) a somewhat more extensive examination of animal experiments representing major areas of investigation (behavior, biological rhythms, nervous and endocrine systems, bone growth and repair, cardiovascular system and blood chemistry, immunology, reproduction, growth and development mortality and pathology, cellular and membrane studies, and mutagenesis). A discussion of current concepts, possible mechanisms and future directions of research is presented. 110 references.

Anderson, L.E.; Phillips, R.D.

1983-11-01

245

EFFECT OF ELECTRIC FIELD INDUCED PERTURBATION OF THE DISTRIBUTION OF IONS NEAR THE CELL SURFACE ON MIGRATION OF CHARGED MEMBRANE COMPONENTS  

EPA Science Inventory

It has demonstrated that an externally applied electric field perturbs the distribution of some of the macromolecules in biological membranes. Various electrostatic, hydrodynamic and structural forces resulting from the external field influence the movement of intramembraneous pa...

246

The effect of electric field polarization on indoor propagation  

Microsoft Academic Search

We have carried out a study on the effects of electric field polarization on the received power in indoor locations predicted using a 3-D ray tracing tool. We assess the importance of including depolarization losses when considering propagation between vertically polarized antennas. These losses are incurred as the vertically polarized electric field is coupled into the horizontally polarized field as

Dmitry Chizhik; Jonathan Ling; Reinaldo A. Valenzuela

1998-01-01

247

The electric field gradient in heavy rare earth metals  

Microsoft Academic Search

Estimates of the electric field gradient in heavy rare earth metals have been evaluated from experimental hyperfine interaction data. In addition, the magnetic hyperfine fields are analyzed. In the metals the effective radial integrals r-3>4f of the magnetic and quadrupole hyperfine interaction are reduced at most by 10% compared with the free ion values. The electric field gradients due to

J. Pelzl; Fachbereich Physik

1972-01-01

248

Thermodynamically consistent force fields for the assembly of inorganic, organic, and biological nanostructures: the INTERFACE force field.  

PubMed

The complexity of the molecular recognition and assembly of biotic-abiotic interfaces on a scale of 1 to 1000 nm can be understood more effectively using simulation tools along with laboratory instrumentation. We discuss the current capabilities and limitations of atomistic force fields and explain a strategy to obtain dependable parameters for inorganic compounds that has been developed and tested over the past decade. Parameter developments include several silicates, aluminates, metals, oxides, sulfates, and apatites that are summarized in what we call the INTERFACE force field. The INTERFACE force field operates as an extension of common harmonic force fields (PCFF, COMPASS, CHARMM, AMBER, GROMACS, and OPLS-AA) by employing the same functional form and combination rules to enable simulations of inorganic-organic and inorganic-biomolecular interfaces. The parametrization builds on an in-depth understanding of physical-chemical properties on the atomic scale to assign each parameter, especially atomic charges and van der Waals constants, as well as on the validation of macroscale physical-chemical properties for each compound in comparison to measurements. The approach eliminates large discrepancies between computed and measured bulk and surface properties of up to 2 orders of magnitude using other parametrization protocols and increases the transferability of the parameters by introducing thermodynamic consistency. As a result, a wide range of properties can be computed in quantitative agreement with experiment, including densities, surface energies, solid-water interface tensions, anisotropies of interfacial energies of different crystal facets, adsorption energies of biomolecules, and thermal and mechanical properties. Applications include insight into the assembly of inorganic-organic multiphase materials, the recognition of inorganic facets by biomolecules, growth and shape preferences of nanocrystals and nanoparticles, as well as thermal transitions and nanomechanics. Limitations and opportunities for further development are also described. PMID:23276161

Heinz, Hendrik; Lin, Tzu-Jen; Mishra, Ratan Kishore; Emami, Fateme S

2013-02-12

249

Computation of induced electric field for the sacral nerve activation  

NASA Astrophysics Data System (ADS)

The induced electric field/current in the sacral nerve by stimulation devices for the treatment of bladder overactivity is investigated. Implanted and transcutaneous electrode configurations are considered. The electric field induced in the sacral nerve by the implanted electrode is largely affected by its surrounding tissues, which is attributable to the variation in the input impedance of the electrode. In contrast, the electric field induced by the transcutaneous electrode is affected by the tissue conductivity and anatomical composition of the body. In addition, the electric field induced in the subcutaneous fat in close proximity of the electrode is comparable with the estimated threshold electric field for pain. These computational findings explain the clinically observed weakness and side effect of each configuration. For the transcutaneous stimulator, we suggest that the electrode contact area be increased to reduce the induced electric field in the subcutaneous fat.

Hirata, Akimasa; Hattori, Junya; Laakso, Ilkka; Takagi, Airi; Shimada, Takuo

2013-11-01

250

Reorganization of microfilament structure induced by ac electric fields.  

PubMed

AC electric fields induce redistribution of integral membrane proteins. Cell-surface receptor redistribution does not consistently follow electric field lines and depends critically on the frequency of the applied ac electric fields, suggesting that mechanisms other than electroosmosis are involved. We hypothesized that cytoskeletal reorganization is responsible for electric field-induced cell-surface receptor redistribution, and used fluorescence video microscopy to study the reorganization of microfilaments in human hepatoma (Hep3B) cells exposed to low-frequency electric fields ranging in strength from 25 mV/cm to 20 V/cm (peak to peak). The frequency of the applied electric field was varied from 1 to 120 Hz and the field exposure duration from 1 to 60 min. In control cells, cytoplasmic microfilaments were aligned in the form of continuous parallel cables along the longitudinal axis of the cell. Exposure of cells to ac electric fields induced alterations in microfilament structure in a manner that depended on the frequency of the applied field. A 1 or 10 Hz ac field caused microfilament reorganization from continuous, aligned cable structures to discontinuous globular patches. In contrast, the structure of microfilaments in cells exposed to 20-120 Hz electric fields did not differ from that in control cells. The extent of microfilament reorganization increased nonlinearly with the electric field strength. The characteristic time for microfilament reorganization in cells exposed to a 1 Hz, 20 V/cm electric field was approximately 5 min. Applied ac electric fields could initiate signal transduction cascades, which in turn cause reorganization of cytoskeletal structures. PMID:8940302

Cho, M R; Thatte, H S; Lee, R C; Golan, D E

1996-11-01

251

Electric field induced bacterial flocculation of enteroaggregative Escherichia coli 042  

NASA Astrophysics Data System (ADS)

A response of the aggregation dynamics of enteroaggregative Escherichia coli under low magnitude steady and oscillating electric fields is presented. The presence of uniform electric fields hampered microbial adhesion and biofilm formation on a transverse glass surface, but instead promoted the formation of flocs. Extremely heterogenous distribution of live and dead cells was observed among the flocs. Moreover, floc formation was largely observed to be independent of the frequency of alternating electric fields.

Kumar, Aloke; Mortensen, Ninell P.; Mukherjee, Partha P.; Retterer, Scott T.; Doktycz, Mitchel J.

2011-06-01

252

Dynamical effects in ab initio NMR calculations: Classical force fields fitted to quantum forces  

NASA Astrophysics Data System (ADS)

NMR chemical shifts for an L-alanine molecular crystal are calculated using ab initio plane wave density functional theory. Dynamical effects including anharmonicity may be included by averaging chemical shifts over an ensemble of structural configurations generated using molecular dynamics (MD). The time scales required mean that ab initio MD is prohibitively expensive. Yet the sensitivity of chemical shifts to structural details requires that the methodologies for performing MD and calculating NMR shifts be consistent. This work resolves these previously competing requirements by fitting classical force fields to reproduce ab initio forces. This methodology is first validated by reproducing the averaged chemical shifts found using ab initio molecular dynamics. Study of a supercell of L-alanine demonstrates that finite size effects can be significant when accounting for dynamics.

Robinson, Mark; Haynes, Peter D.

2010-08-01

253

Linear electric field time-of-flight ion mass spectrometer  

DOEpatents

A linear electric field ion mass spectrometer having an evacuated enclosure with means for generating a linear electric field located in the evacuated enclosure and means for injecting a sample material into the linear electric field. A source of pulsed ionizing radiation injects ionizing radiation into the linear electric field to ionize atoms or molecules of the sample material, and timing means determine the time elapsed between ionization of atoms or molecules and arrival of an ion out of the ionized atoms or molecules at a predetermined position.

Funsten, Herbert O. (Los Alamos, NM); Feldman, William C. (Los Alamos, NM)

2008-06-10

254

Interfacial Force Field Characterization in a Constrained Vapor Bubble Thermosyphon  

NASA Technical Reports Server (NTRS)

Isothermal profiles of the extended meniscus in a quartz cuvette were measured in the earth's gravitational field using an image-analyzing interferometer that is based on computer-enhanced video microscopy of the naturally occurring interference fringes. These profiles are a function of the stress field. Experimentally, the augmented Young-Laplace equation is an excellent model for the force field at the solid-liquid-vapor interfaces for heptane and pentane menisci on quartz and tetradecane on SFL6. The effects of refractive indices of the solid and liquid on the measurement techniques were demonstrated. Experimentally obtained values of the disjoining pressure and dispersion constants were compared to those predicted from the Dzyaloshinskii - Lifshitz - Pilaevskii theory for an ideal surface and reasonable agreements were obtained. A parameter introduced gives a quantitative measurement of the closeness of the system to equilibrium. The nonequilibrium behavior of this parameter is also presented

DasGupta, Sunando; Plawsky, Joel L.; Wayner, Peter C., Jr.

1995-01-01

255

Electric field enhanced spreading of partially wetting thin liquid films.  

PubMed

Equilibrium and dynamic electrowetting behavior of ultrathin liquid films of surfactant (SDS) laden water over silicon substrate (with native oxide) is investigated. A nonobtrusive optical method, namely, image analyzing interferometry, is used to measure the meniscus profile, adsorbed film thickness, and the curvature of the capillary meniscus. Significant advancement of the contact line of the liquid meniscus, as a result of the application of electric field, is observed even at relatively lower values of applied voltages. The results clearly demonstrate the balance of intermolecular and surface forces with additional contribution from Maxwell stress at the interline. The singular nature of Maxwell stress is exploited in this analysis to model the equilibrium meniscus profile using the augmented Young-Laplace equation, leading to the in situ evaluation of the dispersion constant. The electrowetting dynamics has been explored by measuring the velocity of the advancing interline. The interplay of different forces at the interface is modeled using a control volume approach, leading to an expression for the interline velocity. The model-predicted interline velocities are successfully compared with the experimentally measured velocities. Beyond a critical voltage, contact line instability resulting in emission of droplets from the curved meniscus has been observed. PMID:21910451

Bhaumik, Soubhik Kumar; Chakraborty, Monojit; Ghosh, Somnath; Chakraborty, Suman; DasGupta, Sunando

2011-11-01

256

Comparison of Nonlinear Force-free Field and Potential Field in the Quiet Sun  

E-print Network

In this paper, a potential field extrapolation and three nonlinear force-free (NLFF) field extrapolations (optimization, direct boundary integral (DBIE) and approximate vertical integration (AVI) methods) are used to study the spatial configuration of magnetic field in the quiet Sun. It is found that the strength differences between the three NLFF and potential fields exist in the low layers. However, they tend to disappear as the height increases, which are of the order of 0.1 G when the height exceeds $\\sim$ 2000 km above the photosphere. The absolute azimuth difference between one NLFF field and the potential field is as follows: for the optimization field, it decreases evidently as the height increases; for the DBIE field, it almost keeps constant and shows no significant change as the height increases; for the AVI field, it increases slowly as the height increases. The analysis shows that the reconstructed NLFF fields deviate significantly from the potential field in the quiet Sun.

S., Liu; T, Su J

2014-01-01

257

Self-force on an electric dipole in the spacetime of a cosmic string  

SciTech Connect

We calculate the electrostatic self-force on an electric dipole in the spacetime generated by a static, thin, infinite and straight cosmic string. The electric dipole is held fixed in different configurations, namely, parallel, perpendicular to the cosmic string and oriented along the azimuthal direction around this topological defect, which is stretched along the z axis. We show that the self-force is equivalent to an interaction of the electric dipole with an effective dipole moment which depends on the linear mass density of the cosmic string and on the configuration. The plots of the self-forces as functions of the parameter which determines the angular deficit of the cosmic string are shown for those different configurations. -- Highlights: •Review of regularized Green’s function applied to the problem. •Self-force on an electric dipole in the string spacetime for some orientations. •Representation via graphs of the self-forces versus angular parameter of the cosmic string. •Self-force induced by the string seen as an interaction between two dipoles. •Discussion about the superposition principle in this non-trivial background.

Muniz, C.R., E-mail: celiomuniz@yahoo.com [Grupo de Física Teórica (GFT), Universidade Estadual do Ceará, UECE-FECLI, Iguatu, Ceará (Brazil); Bezerra, V.B., E-mail: valdir@ufpb.br [Departamento de Física, Universidade Federal da Paraíba, Caixa Postal 5008, CEP 58051-970, João Pessoa, PB (Brazil)

2014-01-15

258

Acanthamoeba Migration in an Electric Field  

PubMed Central

Purpose. We investigated the in vitro response of Acanthamoeba trophozoites to electric fields (EFs). Methods. Acanthamoeba castellanii were exposed to varying strengths of an EF. During EF exposure, cell migration was monitored using an inverted microscope equipped with a CCD camera and the SimplePCI 5.3 imaging system to capture time-lapse images. The migration of A. castellanii trophozoites was analyzed and quantified with ImageJ software. For analysis of cell migration in a three-dimensional culture system, Acanthamoeba trophozoites were cultured in agar, exposed to an EF, digitally video recorded, and analyzed at various Z focal planes. Results. Acanthamoeba trophozoites move at random in the absence of an EF, but move directionally in response to an EF. Directedness in the absence of an EF is 0.08 ± 0.01, while in 1200 mV/mm EF, directedness is significantly higher at ?0.65 ± 0.01 (P < 0.001). We find that the trophozoite migration response is voltage-dependent, with higher directionality with higher voltage application. Acanthamoeba move directionally in a three-dimensional (3D) agar system as well when exposed to an EF. Conclusions. Acanthamoeba trophozoites move directionally in response to an EF in a two-dimensional and 3D culture system. Acanthamoeba trophozoite migration is also voltage-dependent, with increased directionality with increasing voltage. This may provide new treatment modalities for Acanthamoeba keratitis. PMID:23716626

Rudell, Jolene Chang; Gao, Jing; Sun, Yuxin; Sun, Yaohui; Chodosh, James; Schwab, Ivan; Zhao, Min

2013-01-01

259

Rapid parameterization of small molecules using the Force Field Toolkit  

PubMed Central

The inability to rapidly generate accurate and robust parameters for novel chemical matter continues to severely limit the application of molecular dynamics (MD) simulations to many biological systems of interest, especially in fields such as drug discovery. Although the release of generalized versions of common classical force fields, e.g., GAFF and CGenFF, have posited guidelines for parameterization of small molecules, many technical challenges remain that have hampered their wide-scale extension. The Force Field Toolkit (ffTK), described herein, minimizes common barriers to ligand parameterization through algorithm and method development, automation of tedious and error-prone tasks, and graphical user interface design. Distributed as a VMD plugin, ffTK facilitates the traversal of a clear and organized workflow resulting in a complete set of CHARMM-compatible parameters. A variety of tools are provided to generate quantum mechanical target data, set up multidimensional optimization routines, and analyze parameter performance. Parameters developed for a small test set of molecules using ffTK were comparable to existing CGenFF parameters in their ability to reproduce experimentally measured values for pure-solvent properties (<15% error from experiment) and free energy of solvation (±0.5 kcal/mol from experiment). PMID:24000174

Mayne, Christopher G.; Saam, Jan; Schulten, Klaus; Tajkhorshid, Emad; Gumbart, James C.

2013-01-01

260

A Bidirectional Brain-Machine Interface Algorithm That Approximates Arbitrary Force-Fields  

PubMed Central

We examine bidirectional brain-machine interfaces that control external devices in a closed loop by decoding motor cortical activity to command the device and by encoding the state of the device by delivering electrical stimuli to sensory areas. Although it is possible to design this artificial sensory-motor interaction while maintaining two independent channels of communication, here we propose a rule that closes the loop between flows of sensory and motor information in a way that approximates a desired dynamical policy expressed as a field of forces acting upon the controlled external device. We previously developed a first implementation of this approach based on linear decoding of neural activity recorded from the motor cortex into a set of forces (a force field) applied to a point mass, and on encoding of position of the point mass into patterns of electrical stimuli delivered to somatosensory areas. However, this previous algorithm had the limitation that it only worked in situations when the position-to-force map to be implemented is invertible. Here we overcome this limitation by developing a new non-linear form of the bidirectional interface that can approximate a virtually unlimited family of continuous fields. The new algorithm bases both the encoding of position information and the decoding of motor cortical activity on an explicit map between spike trains and the state space of the device computed with Multi-Dimensional-Scaling. We present a detailed computational analysis of the performance of the interface and a validation of its robustness by using synthetic neural responses in a simulated sensory-motor loop. PMID:24626393

Semprini, Marianna; Mussa-Ivaldi, Ferdinando A.; Panzeri, Stefano

2014-01-01

261

Continuum Polarizable Force Field within the Poisson-Boltzmann Framework  

PubMed Central

We have developed and tested a complete set of nonbonded parameters for a continuum polarizable force field. Our analysis shows that the new continuum polarizable model is consistent with B3LYP/cc-pVTZ in modeling electronic response upon variation of dielectric environment. Comparison with experiment also shows that the new continuum polarizable model is reasonable, with similar accuracy as B3LYP/cc-pVTZ in reproduction of dipole moments of selected organic molecules in the gas phase. We have further tested the validity to interchange the Amber van der Waals parameters between the explicit and continuum polarizable force fields with a series of dimers. It can be found that the continuum polarizable model agrees well with MP2/cc-pVTZ, with deviations in dimer binding energies less than 0.9 kcal/mol in the aqueous dielectric environment. Finally we have optimized atomic cavity radii with respect to experimental solvation free energies of 177 training molecules. To validate the optimized cavity radii, we have tested these parameters against 176 test molecules. It is found that the optimized PB atomic cavity radii transfer well from the training set to the test set, with an overall root-mean-squared deviation of 1.30 kcal/mol, unsigned average error of 1.07 kacl/mol, and correlation coefficient of 92% for all 353 molecules in both the training and test sets. Given the development documented here, the next natural step is the construction of a full protein/nucleic acid force field within the new continuum polarization framework. PMID:18507452

Tan, Yu-Hong; Tan, Chunhu; Wang, Junmei; Luo, Ray

2008-01-01

262

Influence of polyelectrolyte shape on its sedimentation behavior: effect of relaxation electric field.  

PubMed

The sedimentation of an isolated, charged polyelectrolyte (PE) subjected to an applied field is modeled theoretically, taking into account the variation of its shape. In particular, the effects of double-layer relaxation, effective charge density, and strength of the induced relaxation electric field are examined. We show that the interaction of these effects yields complex and interesting sedimentation behaviors. For example, the behavior of the electric force acting on a loosely structured PE can be different from that on a compactly structured one; the former is dominated mainly by the convective fluid flow. For thick double layers, electric force has a local maximum as the Reynolds number varies, but tends to increase monotonically with increasing Reynolds number if the layer is thin. The drag factor is found to behave differently from literature results. The shape of a PE significantly influences its sedimentation behavior by affecting the amount of counterions attracted to its interior and the associated local electric field. Interestingly, a more stretched PE has a higher effective charge density but experiences a weaker electric force. PMID:25283952

Yeh, Pin-Hua; Hsu, Jyh-Ping; Tseng, Shiojenn

2014-11-28

263

Dielectrophoresis Force and Deflection of Dielectric Elastomers and Blends under AC field  

NASA Astrophysics Data System (ADS)

The effects of frequency and amplitude of AC electric field on the deflection distance and the dielectrophoresis force of the of acrylic elastomers (AR71), styrene copolymers (SAR and SBR), and blends with poly(p-phenylene) (AR71:PPP and SAR:PPP) were investigated. The dielectrophoresis forces of the dielectric elastomers and blends were measured by a vertical cantilever under various frequencies (0.3-60 Hz) and at the amplitudes of 200, 300, 500, 600 and 800 Vpp/mm. In addition, the effect of thickness of specimens and the particle concentration on the dielectrophoresis force were studied. Poly(p-phenylene) particles were added into AR71 and SAR with particle concentrations of 5, 10, 15 and 20 vol%. The forces were calculated from the non-linear deflection theory of the cantilever. The dielectrophoresis forces and deflection distances of the dielectric elastomers and blends generally increase with increasing amplitude but slightly decrease with increasing frequency, and they dramatically drop at the cut-off frequency. The cutoff frequencies are 12.0, 1.5 and 1.5 Hz for AR71, SAR, and SBR, at E = 800 Vpp/mm, respectively.

Kunanuraksapong, Ruksapong; Sirivat, Anuvat

2010-03-01

264

The Anharmonic Force Field of BeH2 Revisited  

NASA Technical Reports Server (NTRS)

The anharmonic force field of BeH2 has been calculated near the basis set and n-particle space limits. The computed antisymmetric stretch frequencies of BeH2 and BeD2 are in excellent agreement with recent high-resolution gas-phase measurements. The agreement between theory and experiment for the other spectroscopic constants is also excellent, except for omega(sub 3) and X(sub 33) for BeH2 and G(sub 22) for BeD2. It is concluded that further experimental work is needed in order to resolve these discrepancies.

Martin, Jan M. L.; Lee, Timothy J.

2003-01-01

265

Nature of electric and magnetic dipoles gleaned from the Poynting theorem and the Lorentz force law of classical electrodynamics  

NASA Astrophysics Data System (ADS)

Starting with the most general form of Maxwell's macroscopic equations in which the free charge and free current densities, ?free and Jfree, as well as the densities of polarization and magnetization, P and M, are arbitrary functions of space and time, we compare and contrast two versions of the Poynting vector, namely, S = ?o- 1 E × B and S = E × H. Here E is the electric field, H is the magnetic field, B is the magnetic induction, and ?o is the permeability of free space. We argue that the identification of one or the other of these Poynting vectors with the rate of flow of electromagnetic energy is intimately tied to the nature of magnetic dipoles and the way in which these dipoles exchange energy with the electromagnetic field. In addition, the manifest nature of both electric and magnetic dipoles in their interactions with the electromagnetic field has consequences for the Lorentz law of force. If the conventional identification of magnetic dipoles with Amperian current loops is extended beyond Maxwell's macroscopic equations to the domain where energy, force, torque, momentum, and angular momentum are active participants, it will be shown that "hidden energy" and "hidden momentum" become inescapable consequences of such identification with Amperian current loops. Hidden energy and hidden momentum can be avoided, however, if we adopt S = E × H as the true Poynting vector, and also accept a generalized version of the Lorentz force law. We conclude that the identification of magnetic dipoles with Amperian current loops, while certainly acceptable within the confines of Maxwell's macroscopic equations, is inadequate and leads to complications when considering energy, force, torque, momentum, and angular momentum in electromagnetic systems that involve the interaction of fields and matter.

Mansuripur, Masud

2011-01-01

266

Vector field statistical analysis of kinematic and force trajectories.  

PubMed

When investigating the dynamics of three-dimensional multi-body biomechanical systems it is often difficult to derive spatiotemporally directed predictions regarding experimentally induced effects. A paradigm of 'non-directed' hypothesis testing has emerged in the literature as a result. Non-directed analyses typically consist of ad hoc scalar extraction, an approach which substantially simplifies the original, highly multivariate datasets (many time points, many vector components). This paper describes a commensurately multivariate method as an alternative to scalar extraction. The method, called 'statistical parametric mapping' (SPM), uses random field theory to objectively identify field regions which co-vary significantly with the experimental design. We compared SPM to scalar extraction by re-analyzing three publicly available datasets: 3D knee kinematics, a ten-muscle force system, and 3D ground reaction forces. Scalar extraction was found to bias the analyses of all three datasets by failing to consider sufficient portions of the dataset, and/or by failing to consider covariance amongst vector components. SPM overcame both problems by conducting hypothesis testing at the (massively multivariate) vector trajectory level, with random field corrections simultaneously accounting for temporal correlation and vector covariance. While SPM has been widely demonstrated to be effective for analyzing 3D scalar fields, the current results are the first to demonstrate its effectiveness for 1D vector field analysis. It was concluded that SPM offers a generalized, statistically comprehensive solution to scalar extraction's over-simplification of vector trajectories, thereby making it useful for objectively guiding analyses of complex biomechanical systems. PMID:23948374

Pataky, Todd C; Robinson, Mark A; Vanrenterghem, Jos

2013-09-27

267

Lightning strikes to aircraft radome: Electric field shielding simulation  

Microsoft Academic Search

Electric field calculations to determine the field distributions at the nose of the aircraft and inside the dielectric radome, and experimental tests of segmented diverter strips on a real aircraft radome are reported.

N. I. Petrov; A. Haddad; H. Griffiths; R. T. Waters

2008-01-01

268

Biological Effects of Electrical and Magnetic Fields: Is It Real?  

E-print Network

The hazardous effect of electric and magnetic fields on biological systems is the subject of considerable debate. Traditional methods have failed to provide a correlation between the fields and biological effects. A model is presented that solves...

Durham, M. O.

269

Electric Fields Caused by Blood Flow Modulate Vascular Endothelial Electrophysiology and Nitric Oxide Production  

PubMed Central

Endothelial cells are exposed to a ubiquitous, yet unexamined electrical force caused by blood flow: the electrokinetic vascular streaming potential (EVSP). In this study, the hypothesis that extremely low frequency (ELF) electric fields parameterized by the EVSP have significant biological effects on endothelial cell properties was studied by measuring membrane potential and nitric oxide production under ELF stimulation between 0–2 Hz and 0–6.67 volts per meter. Using membrane potential and nitric oxide sensitive fluorescent dyes, bovine aortic endothelial cells (BAECs) in culture were studied in the presence and absence of EVSP-modeled electric fields. The transmembrane potential of BAECs was shown to depolarize between 1–7 mV with a strong dependency on both the magnitude and frequency of the isolated ELF field. The findings also support a field interaction with a frequency-dependent tuning curve. The ELF field complexly modulates the nitric oxide response to adenosine triphosphate stimulation with potentiation seen with up to a seven-fold increase. This potentiation was also frequency and magnitude dependent. An early logarithmic phase of NO production is enhanced in a field strength- dependent manner, but the ELF field does not modify a later exponential phase. This study shows that using electric fields on the order of those generated by blood flow influences the essential biology of endothelial cells. The inclusion of ELF electric fields in the paradigm of vascular biology may create novel opportunities for advancing both the understanding and therapies for treatment of vascular diseases. PMID:22674251

Trivedi, Darshan P.; Hallock, Kevin J.; Bergethon, Peter R.

2012-01-01

270

High-frequency electric field measurement using a toroidal antenna  

DOEpatents

A simple and compact method and apparatus for detecting high frequency electric fields, particularly in the frequency range of 1 MHz to 100 MHz, uses a compact toroidal antenna. For typical geophysical applications the sensor will be used to detect electric fields for a wide range of spectrum starting from about 1 MHz, in particular in the frequency range between 1 to 100 MHz, to detect small objects in the upper few meters of the ground. Time-varying magnetic fields associated with time-varying electric fields induce an emf (voltage) in a toroidal coil. The electric field at the center of (and perpendicular to the plane of) the toroid is shown to be linearly related to this induced voltage. By measuring the voltage across a toroidal coil one can easily and accurately determine the electric field.

Lee, Ki Ha (Lafayette, CA)

2002-01-01

271

Electric fields in unsteady wind-blown sand.  

PubMed

The electrification of wind-blown sand has been widely confirmed by field and wind-tunnel measurements. It plays an important role in the lifting and transport of sand particles. In this study we investigated the behavior of electric fields in unsteady saltation by adopting periodic variation wind sequences. The influence of electric fields on sand transport rate was also discussed. The results show that both horizontal and vertical electric fields exist in unsteady saltation, and the transport rate in unsteady saltation is less than that in steady saltation. An interesting result is that the directions of vertical electric field fluctuate upward and downward-pointing with time in the unsteady saltation. This provides a possible explanation for the bipolar pattern of the vertical electric field in wind-blown sand. PMID:24574056

Zhang, Huan; Zheng, Xiao-Jing; Bo, Tian-Li

2014-02-01

272

Multiple superimposed probability tomography on a second electrical field  

NASA Astrophysics Data System (ADS)

Based on the requirement of probability tomography, we developed two-directional pole-pole measurement on a 2D electrical imaging survey which is able to extract all second electrical field profiles to participate in probability tomography. The concept of charge occurrence probability (COP) is defined as the average of cross-correlation of the space domain scanning (SDS) function with the second electrical field being generated by a whole set of point current sources. To quantitatively analyse the results of the tomography, the COP values are normalized. Finally, in order to test the effectiveness of the tomography, we use a finite element algorithm to synthesize the potential data for 2D models, and the profiles of the second electrical field are extracted by eliminating the primary field from the total field. Using the second electrical field of all profiles, the geometric patterns of normalized COP (NCOP) values are reconstructed by means of multiple superimposed probability tomography. The results are quite satisfactory.

Yan, Yongli; Chen, Benchi; Chen, Yun; Ma, Xiaobing

2009-03-01

273

Probing university students' understanding of electromotive force in electricity  

NASA Astrophysics Data System (ADS)

The goal of this study is to identify students' difficulties with learning the concepts of electromotive force (emf) and potential difference in the context of transitory currents and resistive direct-current circuits. To investigate these difficulties, we developed a questionnaire based on an analysis of the theoretical and epistemological framework of physics, which was then administered to first-year engineering and physics students at universities in Spain, Colombia, and Belgium. The results of the study show that student difficulties seem to be strongly linked to the absence of an analysis of the energy balance within the circuit and that most university students do not clearly understand the usefulness of and the difference between the concepts of potential difference and emf.

Garzón, Isabel; De Cock, Mieke; Zuza, Kristina; van Kampen, Paul; Guisasola, Jenaro

2014-01-01

274

Relative importance of electric fields and neutral winds in polar-cap Es formation  

NASA Astrophysics Data System (ADS)

Previous statistical studies of sporadic E layers have shown that Es formation within the polar cap is, generally, controlled by the electric field. However, case studies show that the effect of neutral wind, which obviously has its own effect on ion motion, cannot be ruled out. Four Es layers, observed by the EISCAT Svalbard Radar (ESR), were chosen for investigating the role played by electric field and neutral wind in their formation and evolution. Estimates of the ionospheric electric field were obtained from the statistical APL model, which uses observations of F region plasma drift and interplanetary magnetic field as inputs. The neutral wind was obtained from the NRLMSISE-00 model. A flat height profile of metal ions was assumed in the beginning, and the time development of layers was constructed by integrating the continuity equation under the action of driving forces due to neutral wind and electric field. The results indicate that electric field and neutral wind, both separately and together, could create a layer at the times of radar observations. However, the agreement between the observed and calculated layer altitudes was poor. A better agreement was obtained, if the electric field was assumed to be stronger than the statistical value given by the APL model. In one case, when the observed layer lied below 100 km in altitude, it also seemed that neutral winds at these heights were weaker than given by the model.

Voiculescu, Mirela; Nygren, Tuomo; Aikio, Anita

275

Massive-Field Approach to the Scalar Self Force in Curved Spacetime  

E-print Network

We derive a new regularization method for the calculation of the (massless) scalar self force in curved spacetime. In this method, the scalar self force is expressed in terms of the difference between two retarded scalar fields: the massless scalar field, and an auxiliary massive scalar field. This field difference combined with a certain limiting process gives the expression for the scalar self-force. This expression provides a new self force calculation method.

Eran Rosenthal

2004-10-05

276

Reception and learning of electric fields in bees  

PubMed Central

Honeybees, like other insects, accumulate electric charge in flight, and when their body parts are moved or rubbed together. We report that bees emit constant and modulated electric fields when flying, landing, walking and during the waggle dance. The electric fields emitted by dancing bees consist of low- and high-frequency components. Both components induce passive antennal movements in stationary bees according to Coulomb's law. Bees learn both the constant and the modulated electric field components in the context of appetitive proboscis extension response conditioning. Using this paradigm, we identify mechanoreceptors in both joints of the antennae as sensors. Other mechanoreceptors on the bee body are potentially involved but are less sensitive. Using laser vibrometry, we show that the electrically charged flagellum is moved by constant and modulated electric fields and more strongly so if sound and electric fields interact. Recordings from axons of the Johnston organ document its sensitivity to electric field stimuli. Our analyses identify electric fields emanating from the surface charge of bees as stimuli for mechanoreceptors, and as biologically relevant stimuli, which may play a role in social communication. PMID:23536603

Greggers, Uwe; Koch, Gesche; Schmidt, Viola; Dürr, Aron; Floriou-Servou, Amalia; Piepenbrock, David; Göpfert, Martin C.; Menzel, Randolf

2013-01-01

277

Electric Fields, Cloud Microphysics, and Reflectivity in Anvils of Florida Thunderstorms  

NASA Technical Reports Server (NTRS)

A coordinated aircraft - radar project that investigated the electric fields, cloud microphysics and radar reflectivity of thunderstorm anvils near Kennedy Space Center is described. Measurements from two cases illustrate the extensive nature of the microphysics and electric field observations. As the aircraft flew from the edges of anvils into the interior, electric fields very frequently increased abruptly from approx.1 to >10 kV/m even though the particle concentrations and radar reflectivity increased smoothly. The abrupt increase in field usually occurred when the aircraft entered regions with a reflectivity of 10 to 15 dBZ. It is suggested that the abrupt increase in electric field may be because the charge advection from the storm core did not occur across the entire breadth of the anvil and was not constant in time. Screening layers were not detected near the edges of the anvils. Some long-lived anvils showed subsequent enhancement of electric field and reflectivity and growth of particles, which if localized, might be a factor in explaining the abrupt change of field in some cases. Comparisons of electric field magnitude with particle concentration or reflectivity for a combined data set that included all anvil measurements showed a threshold behavior. When the average reflectivity, such as in a 3-km cube, was less than approximately 5 dBZ, the electric field magnitude was <3 kV/m. Based on these findings, the Volume Averaged Height Integrated Radar Reflectivity (VAHIRR) is now being used by NASA, the Air Force and Federal Aviation Administration in new Lightning Launch Commit Criteria as a diagnostic for high electric fields in anvils.

Dye, J. E.; Bateman, M. G.; Christian, H. J.; Grainger, C. A.; Hall, W. D.; Krider, E. P.; Lewis, S. A.; Mach, D. M.; Merceret, F. J.; Willett, J. C.; Willis, P. T.

2006-01-01

278

Rocket borne instrument to measure electric fields inside electrified clouds  

NASA Technical Reports Server (NTRS)

An apparatus for measuring the electric field in the atmosphere which includes a pair of sensors carried on a rocket for sensing the voltages in the atmosphere being measured is described. One of the sensors is an elongated probe with a fine point which causes a corona current to be produced as it passes through the electric field. An electric circuit is coupled between the probe and the other sensor and includes a high ohm resistor which linearizes the relationship between the corona current and the electric field being measured. A relaxation oscillator and transmitter are provided for generating and transmitting an electric signal having a frequency corresponding to the magnitude of the electric field.

Ruhnke, L. H. (inventor)

1973-01-01

279

A Second Generation Force Field for the Simulation of Proteins, Nucleic Acids, and Organic Molecules  

Microsoft Academic Search

We present the derivation of a new molecular mechanical force field for simulating the structures, conformational energies, and interaction energies of proteins, nucleic acids, and many related organic molecules in condensed phases. This effective two-body force field is the successor to the Weiner et al. force field and was developed with some of the same philosophies, such as the use

Wendy D. Cornell; Piotr Cieplak; Christopher I. Bayly; Ian R. Gould; Kenneth M. Merz; David M. Ferguson; David C. Spellmeyer; Thomas Fox; James W. Caldwell

1995-01-01

280

PULSED ELECTRIC FIELD PROCESSING FACT SHEET FOR FOOD PROCESSORS  

Technology Transfer Automated Retrieval System (TEKTRAN)

Pulsed Electric Fields (PEF) apply intensive, high voltage electric field pulses to biological materials and cause cell membrane, primarily lipid bi-layers, to breakdown. PEF may be used to pasteurize fluid and pumpable foods. The benefit of PEF is the retention of product quality and freshness. A p...

281

Electric Field Intensity of the Lightning Return Stroke  

Microsoft Academic Search

From an examination of about 1000 electric field wave forms produced by lightning return strokes in 16 storms at distances between 20 and 100 km from an observation site at the Kennedy Space Center, Florida, a typical return stroke current wave form is derived. For this current wave form, the electric field intensity at distances between 0.5 and 100 km

Martin A. Uman; D. Kenneth McLain; Richard J. Fisher; E. Philip Krider

1973-01-01

282

Penetration electric fields: Efficiency and characteristic time scale  

Microsoft Academic Search

Penetration of the interplanetary electric field (IEF) to the middle- and low-latitude ionosphere has been investigated for nearly four decades. Most previous studies focused on the correlation between the interplanetary and ionospheric electric field perturbations. Very little attention has been paid to a quantitative relationship except for a recent case analysis by Kelley et al. [2003. Penetration of the solar

Chao-Song Huang; Stanislav Sazykin; Jorge L. Chau; Naomi Maruyama; Michael C. Kelley

2007-01-01

283

Effects of Radial Electric Fields on ICRF Waves  

SciTech Connect

Equilibrium considerations infer that large localized radial electric fields are associated with internal transport barrier structures in tokamaks and other toroidal magnetic confinement configurations. In this paper, the effects of an equilibrium electric field on fast magnetosonic wave propagation are considered in the context of a cold plasma model.

C.K. Phillips; J.C. Hosea; M. Ono; J.R. Wilson

2001-06-18

284

DESIGN WEB GIS APPLICATION FOR ENVIRONMENTAL ELECTRIC FIELD RECORD  

Microsoft Academic Search

The GIS Web technology provides new mechanics to develop tools by engineering application, is a system for capturing, storing, analyzing and managing data and associated attributes which are spatially referenced to the earth. This paper develops a design GIS Web application to environmental electric field record in Bogotá D.C., Colombia, was based on the existing network of Electric Field Machine

J. C. Aponte; D. Aranguren; E. E. Olarte; I. Santoyo; J. Amortegui

285

Electric Field Modulation of Galvanomagnetic Properties of Mesoscopic Graphite  

Microsoft Academic Search

We use a unique micromechanical method to extract extremely thin graphite crystallites from bulk highly oriented pyrolitic graphite samples. Electric field effect devices are subsequently fabricated for galvanomagnetic measurements. Strong modulation of magneto- resistance and Hall resistance as a function of gate voltage is observed as the sample thickness approaches the screening length of graphite. Electric field dependent Landau level

Yuanbo Zhang; Joshua P. Small; Philip Kim

2005-01-01

286

Evolution of Magnetic Field in AR 5747 and Its Approximation as a Linear Force Free Field  

E-print Network

The evolution of nonpotential characteristics of magnetic fields in AR 5747 is presented using Mees Solar Observatory magnetograms taken on Oct. 20, 1989 to Oct. 22, 1989. The active region showed such violent flaring activities during the observational span that strong X-ray flares took place including a 2B/X3 flare. The magnetogram data were obtained by the Haleakala Stokes Polarimeter which provides simultaneous Stokes profiles of the Fe I doublet 6301.5 and 6302.5. A nonlinear least square method was adopted to derive the magnetic field vectors from the observed Stokes profiles and a multi-step ambiguity solution method was employed to resolve the 180 degree ambiguity. From the ambiguity-resolved vector magnetograms, we have derived a set of physical quantities characterizing the field configuration, which are magnetic flux, vertical current density, magnetic shear angle, angular shear, magnetic free energy density and a measure of magnetic field discontinuity MAD (Maximum Angular Difference between two adjacent field vectors). In our results, all the physical parameters decreased with time, which implies that the active region was in a relaxation stage of its evolution. To examine the force-free characteristics of the field, we calculated the integrated Lorentz force and and also compared the longitudinal field component with the corresponding vertical current density. In this investigation, we found that the magnetic field in this active region was approximately linearly force-free throughout the observing period. The time variation of the linear force-free coefficient is consistent with the evolutionary trend of other nonpotentiality parameters. This suggests that the linear force-free coefficient could be a good indicator of the evolutionary status of active regions.

Y. -J. Moon; H. S. Yun; G. S. Choe; Y. D. Park; D. L. Mickey

1999-10-05

287

Middle atmospheric electric fields over thunderstorms  

NASA Technical Reports Server (NTRS)

This grant has supported a variety of investigations all having to do with the external electrodynamics of thunderstorms. The grant was a continuation of work begun while the PI was at the Aerospace Corporation (under NASA Grant NAS6-3109) and the general line of investigation continues today under NASA Grants NAG5-685 and NAG6-111. This report will briefly identify the subject areas of the research and associated results. The period actually covered by the grant NAG5-604 included the following analysis and flights: (1) analysis of five successful balloon flights in 1980 and 1981 (under the predecessor NASA grant) in the stratosphere over thunderstorms; (2) development and flight of the Hy-wire tethered balloon system for direct measurement of the atmospheric potential to 250 kV (this involved multiple tethered balloon flight periods from 1981 through 1986 from several locations including Wallops Island, VA, Poker Flat and Ft. Greely, AK and Holloman AFB, NM.); (3) balloon flights in the stratosphere over thunderstorms to measure vector electric fields and associated parameters in 1986 (2 flights), 1987 (4 flights), and 1988 (2 flights); and (4) rocket-borne optical lightning flash detectors on two rocket flights (1987 and 1988) (the same detector design that was used for the balloon flights listed under #3). In summary this grant supported 8 stratospheric zero-pressure balloon flights, tethered aerostat flights every year between 1982-1985, instruments on 2 rockets, and analysis of data from 6 stratospheric flights in 1980/81.

Holzworth, Robert H.

1992-01-01

288

A new spectroscopic molecular mechanics force field. Parameters for proteins  

NASA Astrophysics Data System (ADS)

We present the development of a new spectroscopic molecular mechanics potential for proteins. SPASIBA merges the torsional, van der Waals, electrostatic, and hydrogen bond potentials of AMBER with the Urey-Bradley-Shimanouchi terms for bond lengths and bond angles. To begin, SPASIBA was consistently parametrized to structural, energies, and vibrational frequency data of model compounds representative of the 16 nonaromatic acids: n-alkanes, alcohols, acids, ethyl methyl sulfide, methyl sulfide in water, ethanethiol, dimethyl disulfide, guanidium ion, propionamide, N-methylacetamide, N-methylisobutyramide, and N-isopropylacetamide. The parameters were then transferred to N-acetyl-X methylamides (where X=Gly, L-Ala, L-Pro), the L-Leu, L-Cys, and L-Thr amino acids blocked by the carboxylate and ammonium ions, and the right-handed deca-alanine and Gly-L-Pro-Gly-Gly peptides. Results show that SPASIBA reproduces vibrational frequencies (with much higher accuracy than present molecular mechanics potentials), as well as potential energy distributions of normal modes. For the 532 fundamental frequencies considered for refining the force field, the mean frequency error is 13 cm-1. This force field, which can be incorporated in molecular dynamics simulations, is also found to provide useful insights into the conformation/vibrational spectrum relationships. This ability is illustrated on the Gly and L-Ala dipeptides, as well as the polypeptides.

Derreumaux, Philippe; Vergoten, Gérard

1995-06-01

289

Reactive force field potential for carbon deposition on silicon surfaces  

NASA Astrophysics Data System (ADS)

In this paper a new interatomic potential based on the Kieffer force field and designed to perform molecular dynamics (MD) simulations of carbon deposition on silicon surfaces is implemented. This potential is a third-order reactive force field that includes a dynamic charge transfer and allows for the formation and breaking of bonds. The parameters for Si-C and C-C interactions are optimized using a genetic algorithm. The quality of the potential is tested on its ability to model silicon carbide and diamond physical properties as well as the formation energies of point defects. Furthermore, MD simulations of carbon deposition on reconstructed (100) silicon surfaces are carried out and compared to similar simulations using a Tersoff-like bond order potential. Simulations with both potentials produce similar results showing the ability to extend the use of the Kieffer potential to deposition studies. The investigation reveals the presence of a channelling effect when depositing the carbon at 45° incidence angle. This effect is due to channels running in directions symmetrically equivalent to the (110) direction. The channelling is observed to a lesser extent for carbon atoms with 30° and 60° incidence angles relative to the surface normal. On a pristine silicon surface, sticking coefficients were found to vary between 100 and 73%, depending on deposition conditions.

Briquet, Ludovic G. V.; Jana, Arindam; Mether, Lotta; Nordlund, Kai; Henrion, Gérard; Philipp, Patrick; Wirtz, Tom

2012-10-01

290

Electric and Magnetic Field Detection in Elasmobranch Fishes  

NASA Astrophysics Data System (ADS)

Sharks, skates, and rays receive electrical information about the positions of their prey, the drift of ocean currents, and their magnetic compass headings. At sea, dogfish and blue sharks were observed to execute apparent feeding responses to dipole electric fields designed to mimic prey. In training experiments, stingrays showed the ability to orient relative to uniform electric fields similar to those produced by ocean currents. Voltage gradients of only 5 nanovolts per centimeter would elicit either behavior.

Kalmijn, Ad. J.

1982-11-01

291

Electric and magnetic field detection in elasmobranch fishes.  

PubMed

Sharks, skates, and rays receive electrical information about the positions of their prey, the drift of ocean currents, and their magnetic compass headings. At sea, dogfish and blue sharks were observed to execute apparent feeding responses to dipole electric fields designed to mimic prey. In training experiments, stingrays showed the ability to orient relative to uniform electric fields similar to those produced by ocean currents. Voltage gradients of only 5 nanovolts per centimeter would elicit either behavior. PMID:7134985

Kalmijn, A J

1982-11-26

292

The Effect of Electric Field Magnitude and Frequency on Caenorhabditis Elegans  

NASA Astrophysics Data System (ADS)

Low magnitude, DC electric fields have been used to guide the motion of the wild-type nematode (worm) Caenorhabditis elegans. Low intensity AC fields (<100 Hz) can even be utilized to localize the worm. However, the worm appears oblivious to the electric field as the frequency is higher than several hundreds of Hz. In contrast, in the presence of nonuniform, moderate AC fields (˜15--50 kV/m) at higher frequencies (>10 kHz), the worm is restrained by the field's maximum. This is the first demonstration of dielectrophoretic trapping of an animal. With certain electrode arrangements, only the worm's tail is immobilized, and the worm's swimming motion does not appear to be affected by the trapping force. Similar trapping conditions with transitional frequencies (˜10--100 kHz) can cause paralysis. The worm is (irreversibly) paralyzed with lower frequencies (e.g. 45 kV/m, 2 kHz) or electrified with higher electric field intensities (e.g. 10 Hz, 70 kV/m). We report on the results of a parametric study that delineates the effect of the electric field on the worm as a function of the worm's stage and the electric field intensity and frequency. Worm-dielectrophoresis can be used, among other things, to sort worms by size, to temporarily immobilize worms to enable their characterization and study, and to use worms to induce fluid motion and mixing.

Chuang, Han-Sheng; Raizen, David; Dabbish, Nooreen; Lamb, Annesai; Bau, Haim

2010-11-01

293

A new model for electric force microscopy and its application for electrostatically generated phase difference in tapping mode AFM  

E-print Network

The harmonic force balance method was used to model and simulate electric force microscopy (EFM) and electrostatically generated phase difference in tapping mode AFM (EPTA) measurements. Simulations show that the harmonic ...

Stone, Peter (Peter Robert)

2005-01-01

294

Electric Field Distribution of Cadmium Zinc Telluride (CZT)  

SciTech Connect

Cadmium Zinc Telluride (CZT) is attracting increasing interest with its promise as a room-temperature nuclear-radiation-detector material. The distribution of the electric field in CZT detectors substantially affects their detection performance. At Brookhaven National Laboratory (BNL), we employed a synchrotron X-Ray mapping technique and a Pockels-effect measurement system to investigate this distribution in different detectors. Here, we report our latest experimental results with three detectors of different width/height ratios. A decrease in this ratio aggravates the non-uniform distribution of electric field, and focuses it on the central volume. Raising the bias voltage effectively can minimize such non-uniformity of the electric field distribution. The position of the maximum electric field is independent of the bias voltage; the difference between its maximum- and minimum-intensity of electric field increases with the applied bias voltage.

Yang,G.; Bolotnikov, A.; Camarda, G.S.; Cui, Y.; Hossain, A.; Kim, K.; James, R.B.

2009-08-02

295

Electric field quench in AdS/CFT  

NASA Astrophysics Data System (ADS)

An electric field quench, a suddenly applied electric field, can induce nontrivial dynamics in confining systems which may lead to thermalization as well as a deconfinement transition. In order to analyze this nonequilibrium transitions, we use the AdS/CFT correspondence for supersymmetric QCD that has a confining meson sector. We find that the electric field quench causes the deconfinement transition even when the magnitude of the applied electric field is smaller than the critical value for the static case (which is the QCD Schwinger limit for quark-antiquark pair creation). The time dependence is crucial for this phenomenon, and the gravity dual explains it as an oscillation of a D-brane in the bulk AdS spacetime. Interestingly, the deconfinement time takes only discrete values as a function of the magnitude of the electric field. We advocate that the new deconfinement phenomenon is analogous to the exciton Mott transition.

Hashimoto, Koji; Kinoshita, Shunichiro; Murata, Keiju; Oka, Takashi

2014-09-01

296

Semiconductor crystal growth in crossed electric and magnetic fields: Center Director's Discretionary Fund  

NASA Technical Reports Server (NTRS)

A unique growth cell was designed in which crossed electric and magnetic fields could be separately or simultaneously applied during semiconductor crystal growth. A thermocouple was inserted into an InSb melt inside the growth cell to examine the temperature response of the fluid to applied electromagnetic fields. A static magnetic field suppressed time-dependent convection when a destabilizing thermal field was applied. The simultaneous application of electric and magnetic fields resulted in forced convection in the melt. The InSb ingots grown in the cell were polycrystalline. An InGaSb crystal, 0.5 cm in diameter and 23-cm long, was grown without electromagnetic fields applied. The axial composition results indicated that complete mixing in the melt occurred for this large aspect ratio.

Mazuruk, K.; Volz, M. P.

1996-01-01

297

Electric field-mediated processing of polymer blend solutions  

NASA Technical Reports Server (NTRS)

Multiphase polymer blends in which the minor phases are oriented in a desired direction may demonstrate unique optical, electrical, and mechanical properties. While morphology development in shear fields was studied extensively, little work has focused on effects of electric fields on phase structure. The use of electric fields for blend morphology modulation with particular attention given to solvent casting of blends in d.c. fields was explored. Both homopolymer blends (average phase sizes of several microns) and diblock copolymer/homopolymer blends (average phase sizes of hundreds of Angstroms) were investigated. Summarized are important observations and conclusions.

Wnek, G. E.; Krause, S.

1993-01-01

298

Superconductors in strong static or quasi-static electric fields  

NASA Astrophysics Data System (ADS)

The electric field induced superconducting ball formation has been found to be general for all powdered superconductors, including low temperature superconductors (LTSC), both type I and type II, and high temperature superconductors (HTSC), in either a static or a quasi-static electric field. Both LTSC and HTSC in either static or low frequency ac fields form balls consisting of up to million particles but only for fields E between two critical fields Ec1, and Ec2. The balls formed from LTSC powders are generally weaker than the HTSC balls and easy to break. In contrast to the behavior in a static electric field. Both the LTSC and the HTSC particles first form chains along the field direction in a low frequency ac field if the electric field is below the critical value Ec1. As soon as the electric field exceeds Ec1, the chains are broken and the particles form balls. For both static and low frequency cases the ball size decreases with further increase of the electric field. Ec1 as a function of frequency, first drops from the value for the static field and reaches a minimum at a very low frequency and then increases monotonically with the frequency. The ball formation has also been observed in a strong static or quasi-static electric field with MgB2 powder, which has Tc around 39K. The effect of temperature and magnetic field on the ball formation shows surprising features. The ball size of MgB2 is proportional to 1-TTc from 39 K down to about 20 K. Below 20 K the ball size becomes almost constant. If MgB2 particles are in a strong electric field and a moderate magnetic field, the electric field induced balls align in the magnetic field direction to form ball chains. This phenomenon comes from the interaction between Cooper pairs and the applied electric field. A positive surface energy associated with the induced surface charge distribution on superconductors provides an explanation of the phenomenon. The critical fields and ball size derived from theoretical calculations seem to agree with the experimental results reasonably well.

Amr, Eyas

299

Plasma rotation by electric and magnetic fields in a discharge cylinder  

NASA Technical Reports Server (NTRS)

A theoretical model for an electric discharge consisting of a spatially diverging plasma sustained electrically between a small ring cathode and a larger ring anode in a cylindrical chamber with an axial magnetic field is developed to study the rotation of the discharge plasma in the crossed electric and magnetic fields. The associated boundary-value problem for the coupled partial differential equations which describe the electric potential and the plasma velocity fields is solved in closed form. The electric field, current density, and velocity distributions are discussed in terms of the Hartmann number and the Hall coefficient. As a result of Lorentz forces, the plasma rotates with speeds as high as 1 million cm/sec around its axis of symmetry at typical conditions. As an application, it is noted that rotating discharges of this type could be used to develop a high-density plasma-ultracentrifuge driven by j x B forces, in which the lighter (heavier) ion and atom components would be enriched in (off) the center of the discharge cylinder.

Wilhelm, H. E.; Hong, S. H.

1977-01-01

300

Electric field measurements during the MAC/EPSILON campaign  

NASA Technical Reports Server (NTRS)

The MAC/EPSILON observational campaign in northern Norway involved the taking of three-axis electric field measurements of the middle atmosphere by means of five rocketborne payloads during October and November, 1987. Simultaneous horizontal electric field measurements made by two of the rocket flights were in general agreement in their limited overlap region. The more extensive horizontal E-field measurements exhibited a decreasing mapping function with decreasing altitude, thereby indicating the presence of fields from a local auroral patch. Small-scale variations in the horizontal fields of the lights were similar to observed wavelike variations in the neutral wind field.

Croskey, C. L.; Hale, L. C.; Mitchell, J. D.; Schmidlin, F. J.; Hoppe, U.-P.

1990-01-01

301

Aircraft measurement of electric field: Self-Calibration  

NASA Astrophysics Data System (ADS)

The electric field of a thunderstorm is distorted by the metallic surfaces of airplanes and rockets. The amplitude of the local, distorted electric field can be measured at selected locations on the surface of the vehicle with electric field meters. Measuring the thunderstorm field entails finding the relations between the local fields at the meters and the ambient, undistorted electric field that would exist in the absence of the vehicle. Calibration can be performed in the following steps: (1)Find linear combinations F0, F1, …, of local field amplitudes that are independent of the charge on the vehicle. (2) While the ambient electric field is constant in the Earth coordinate system, rotate the vehicle (roll and turn or roll and pitch) and record the local field amplitudes and the roll, pitch, and heading angles. Find the direction of the electric vector and the ratios between all of the calibration coefficients that best fit the linear combinations of local field amplitudes. (3) Find the magnitude of one of the coefficients by comparison with a calibrated instrument; from this magnitude and all of the ratios, find all of the magnitudes. With this method of calibration, finding out how the linear combinations F0, F1, … depend on the ambient electric field does not require a symmetric placement of the electric field meters, nor does it require any knowledge of the locations of the field meters. However, inverting the expressions to find the ambient field components as functions of the F�� does place constraints on the locations of the field meters. The results of the above calibration can be used only when the signal at each field meter is a linear function of four parameters: the charge on the airplane and the three components of a uniform electric field from distant charge. When there are five or more electric field meters, the presence of nearby charge can be detected because it is possible to find linear combinations of the signals from five field meters whose value is not zero only when there is nearby charge. This paper presents one method of finding the linear combinations.

Winn, W. P.

1993-04-01

302

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

SciTech Connect

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.

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

2009-01-01

303

Coherent control of a single electron spin with electric fields.  

PubMed

Manipulation of single spins is essential for spin-based quantum information processing. Electrical control instead of magnetic control is particularly appealing for this purpose, because electric fields are easy to generate locally on-chip. We experimentally realized coherent control of a single-electron spin in a quantum dot using an oscillating electric field generated by a local gate. The electric field induced coherent transitions (Rabi oscillations) between spin-up and spin-down with 90 degrees rotations as fast as approximately 55 nanoseconds. Our analysis indicated that the electrically induced spin transitions were mediated by the spin-orbit interaction. Taken together with the recently demonstrated coherent exchange of two neighboring spins, our results establish the feasibility of fully electrical manipulation of spin qubits. PMID:17975030

Nowack, K C; Koppens, F H L; Nazarov, Yu V; Vandersypen, L M K

2007-11-30

304

Collapse of Gels in an Electric Field  

Microsoft Academic Search

An infinitesimal change in electric potential across a polyelectrolyte gel produces a discrete, reversible volume change. The volume of the collapsed gel can be several hundred times smaller than that of the swollen gel.

Toyoichi Tanaka; Izumi Nishio; Shao-Tang Sun; Shizue Ueno-Nishio

1982-01-01

305

The Effects of an Induced Electric Dipole Moment due to Earth's Electric Field on the Artificial Satellites Orbit  

NASA Astrophysics Data System (ADS)

The orbits of artificial satellites are very sensitive to a large number of disturbances, whose effects add to the main force exerted by Earth's gravitational field. The most important perturbations, caused by solar radiation pressure, the Moon and the Sun gravitational fields, have been extensively discussed in the literature, and must be taken into account in order to correct the orbital motion, to prevent collisions between satellites in close orbits. In this paper we consider an additional source of acceleration arising from an electric dipole moment induced by the high altitude Earth electric field in a metallic satellite of spherical shape. The order of magnitude of such effect is estimated to be in the range of 10 - 23m/s2. It is emphasized that the electric dipole moment effect(EDME) is dependent on the satellite shape and geometry and proportional to E_0 v/r^4. The Earth electric field E 0 is largely influenced by atmospheric electromagnetic phenomena, such as whistler waves and thunderstorms.

Heilmann, Armando; Ferreira, Luiz Danilo Damasceno; Dartora, Cesar Augusto

2012-04-01

306

Electrically Switchable Magnetic Molecules: Inducing a Magnetic Coupling by Means of an External Electric Field in a Mixed-Valence Polyoxovanadate Cluster.  

PubMed

Herein we evaluate the influence of an electric field on the coupling of two delocalized electrons in the mixed-valence polyoxometalate (POM) [GeV14 O40 ](8-) (in short V14 ) by using both a t-J model Hamiltonian and DFT calculations. In absence of an electric field the compound is paramagnetic, because the two electrons are localized on different parts of the POM. When an electric field is applied, an abrupt change of the magnetic coupling between the two delocalized electrons can be induced. Indeed, the field forces the two electrons to localize on nearest-neighbors metal centers, leading to a very strong antiferromagnetic coupling. Both theoretical approaches have led to similar results, emphasizing that the sharp spin transition induced by the electric field in the V14 system is a robust phenomenon, intramolecular in nature, and barely influenced by small changes on the external structure. PMID:25430555

Cardona-Serra, Salvador; Clemente-Juan, Juan M; Coronado, Eugenio; Gaita-Ariño, Alejandro; Suaud, Nicolas; Svoboda, Ondrej; Bastardis, Roland; Guihéry, Nathalie; Palacios, Juan J

2014-11-27

307

Analysis of electrical tomography sensitive field based on multi-terminal network and electric field  

NASA Astrophysics Data System (ADS)

Electrical tomography (ET) aims at the study of the conductivity/permittivity distribution of the interested field non-intrusively via the boundary voltage/current. The sensor is usually regarded as an electric field, and finite element method (FEM) is commonly used to calculate the sensitivity matrix and to optimize the sensor architecture. However, only the lumped circuit parameters can be measured by the data acquisition electronics, it's very meaningful to treat the sensor as a multi terminal network. Two types of multi terminal network with common node and common loop topologies are introduced. Getting more independent measurements and making more uniform current distribution are the two main ways to minimize the inherent ill-posed effect. By exploring the relationships of network matrixes, a general formula is proposed for the first time to calculate the number of the independent measurements. Additionally, the sensitivity distribution is analyzed with FEM. As a result, quasi opposite mode, an optimal single source excitation mode, that has the advantages of more uniform sensitivity distribution and more independent measurements, is proposed.

He, Yongbo; Su, Xingguo; Xu, Meng; Wang, Huaxiang

2010-08-01

308

IMF changes and polar-cap electric fields and currents  

NASA Technical Reports Server (NTRS)

The polar cap, defined as the region of the auroral oval, is magnetically connected to the solar wind; currents may flow easily between the two regions, and polar cap electric fields and currents respond sensitively to variations in the interplanetary magnetic field (IMF). In the present paper, the response of polar cap electric field and currents to variations in IMF x, y, and z components is discussed.

Burch, J. L.; Heelis, R. A.

1980-01-01

309

On intense diverging electric fields associated with black aurora  

Microsoft Academic Search

Results are presented from the double-probe electric field instrument on the Freja satellite with particular focus on the fine-structured and dynamic plasma of the upper auroral ionosphere. The high-resolution measurements show frequently occurring intense and irregular fine-scale electric fields similar to those observed at higher altitudes by, for example, the S3-3 and Viking satellites. Whereas the high-altitude fields tend to

Göran Marklund; Lars Blomberg; Carl-Gunne Fälthammar; Per-Arne Lindqvist

1994-01-01

310

Maximum electric charge of a hydrometeor in the electric field of a thundercloud  

Microsoft Academic Search

Computations have been made for the maximum electric charge that a hydrometeor can retain in the ambient field of a thundrcloud. Two processes contribute to this limitation: water drop instability and corona discharge initiation. Solid hydrometeors are only affected by corona emission. Therefore, the numerical method presented here consists of computing the local electric field everywhere at the surface of

Christine Bourdeau; Serge Chauzy

1989-01-01

311

Variation of The Magnetotail Electric Fields During Magnetospheric Substorms  

NASA Astrophysics Data System (ADS)

The behaviour of the midtail electric fields during two magnetospheric substorms on November, 22, 1995, is investigated. The magnetospheric electric field is supposed to consist of two components: a potential electric field penetrating into the magneto- sphere from the solar wind, and an inductive electric field associated with variation of the geomagnetic field. The first component is supposed to be proportional (with some time delay) to the Y -component of the solar wind electric field, and the second one is estimated from the time derivative of the tail lobe magnetic flux. The latter is obtained by converting total pressure to lobe magnetic field by assuming pressure balance be- tween lobe and plasma sheet (Nakamura et al., 1999). The Y -component of the total electric field is calculated from GEOTAIL spacecraft data as Ey = -[v × B]y. Analysis of experimental data shows that the inductive electric field (Ec) is "switched on" in the magnetotail practically simultaneously with the intensification of the IMF southern component. At the preliminary phase of the substorm, the Ec field within the plasmasheet is directed from dusk to dawn compensating the potential field Ep, so that the total field Ey is rather small there (Semenov and Sergeev, 1981). With the beginning of the active phase, the Ec changes its sign, and adding to the Ep, provides a rapid increase of the dawn­dusk Ey field. As the intensity of Ep during the active phase of the substorm is less than the intensity of the induced field, Ey is determined during this period by the latter mainly and does not correlate with the Esw field. However, the intensity of the potential electric field at this time may be obtained from the data on the velocity of the auroral arc motion (Pudovkin et al., 1992). So, judging by the dynamics of aurorae at the Poker Flat (Alaska) station, Ep field in the inner magnetosphere (X -10 RE) amounts the value of 0.7 mV/m, and it varies in proportion to Esw with the time delay of about 20 minutes. Intensity of the inductive electric field Ec during the active phase of the substorm depends on the amount of the magnetic field energy accumulated in the magnetotail lobes, and is determined by the rate of the reconnection of the magnetotail magnetic fields.

Pudovkin, M.; Zaitseva, S.; Nakamura, R.

312

Reactive force fields for surface chemical reactions: A case study with hydrogen dissociation on Pd surfaces.  

PubMed

An approach based on reactive force fields is applied to the parametrization of potential energy surface (PES) for chemical reactions on surfaces with a benchmark system, H(2)/Pd(111). We show that a simple reactive force field based on the second moment approximation does not allow for obtaining reliable results of reaction dynamics for the considered system. With a more elaborate reactive force field, i.e., reactive bond order (REBO) force field, we succeeded in obtaining a reliable PES for H(2)/Pd(111). The accuracy of the constructed REBO force field is carefully checked through various tests including the comparison not only between energies calculated with density functional theory and those with REBO force field but also between the available results of ab initio molecular dynamics simulations and those with our force field. Moreover, our REBO force field is endowed with some transferability since the force field constructed with a database containing only information on H(2)/Pd(111) allows for obtaining also accurate results for H(2)/Pd(100) and qualitatively correct results for H(2)/Pd(110) without any refitting. With the help of our reactive force field, the molecular dynamics simulation for the dissociation of H(2) on the considered Pd surfaces is speeded up by five orders of magnitude compared to ab initio molecular dynamics method. The demonstrated reliability and the very high computational efficiency of reactive force fields open extremely attractive perspectives for studying large-scale complex reacting systems. PMID:20078177

Xiao, Y; Dong, W; Busnengo, H F

2010-01-01

313

Enhancing field emission from a carbon nanotube array by lateral control of electrodynamic force field  

Microsoft Academic Search

Fluctuation of field emission current from carbon nanotubes (CNTs) poses certain difficulties for their use in nano-biomedical X-ray devices and imaging probes. This problem arises due to deformation of the CNTs due to electrodynamic force field and electron–phonon interaction. It is of great importance to have precise control of emitted electron beams very near the CNT tips. In this paper,

D. Roy Mahapatra; S. V. Anand; N. Sinha; R. V. N. Melnik

2009-01-01

314

Local field loop measurements by magnetic force microscopy  

NASA Astrophysics Data System (ADS)

Magnetic force microscopy (MFM) is a valuable technique to investigate the reversal mechanisms of the magnetization in micrometric and sub-micrometric-patterned thin films that cannot be studied by means of magneto-optical methods because of their limited resolution. However, acquiring tens or hundreds of images consecutively at different applied magnetic fields is often impossible or impractical. Therefore, a field-dependent MFM-derived technique is discussed and applied on square and circular dots of different materials (Ni80Fe20, Co67Fe4Si14.5B14.5, Fe78Si9B13) having sizes ranging from 800 nm to 20 µm. Experimental local hysteresis loops are obtained by properly analysing the phase signal of the MFM along a selected profile of the studied patterned structure, as a function of the applied magnetic field. Characteristic features of the magnetization process, such as vortex nucleation and expulsion, transition from C-state to saturated state or domain wall motion in Landau-like domain configuration are identified, and their evolution with the applied field is followed. The necessity to combine experimental and theoretical analyses is addressed by micromagnetic simulations on a model system (a Ni80Fe20 square dot with a lateral size of 800 nm), comparable to one of the studied samples. The agreement between experimental and simulated MFM maps, at different applied fields, and hysteresis loops provides the necessary validation for the technique. Additionally, the simulations have been proven to be necessary to understand the magnetization reversal processes occurring in the studied sub-micrometric structures and to associate them with characteristic features of the hysteresis loops measured with the proposed technique.

Coïsson, Marco; Barrera, Gabriele; Celegato, Federica; Enrico, Emanuele; Manzin, Alessandra; Olivetti, Elena S.; Tiberto, Paola; Vinai, Franco

2014-08-01

315

Experimental studies on affinity chromatography in an electric field.  

PubMed

A multicompartment electrolyzer, which has been used for preparative electrophoresis [Z. Liu, Z. Huang, J.-Y. Cong, et al., Sep. Sci. Technol. 31 (1996) 427], is applied for carrying out affinity chromatography in an alternating electric field. The effect of electric field strength on the adsorption and desorption characteristics is experimentally examined with human serum albumin and Blue Sepharose Fast Flow as a model system. It is shown that the existence of an electric field leads to a significant change in the adsorption capacity of the blue dye, which may be used for establishing a preferential adsorption to achieve a high resolution. The adsorption speed increases slightly with respect to the increase of electric field strength, while adsorption capacity in the presence of an electric field is independent of the electric field strength. Different elution behavior is observed as function of adsorption condition and a high recovery of the adsorbed protein is obtained when the adsorption is carried out in the presence of an electric field. PMID:10480257

Liu, Z; Feng, S; Yin, J; Ding, F; Yuan, N

1999-08-01

316

The hydrogen atom in plasmas with an external electric field  

SciTech Connect

We numerically solve the Schrödinger equation, using a more general exponential cosine screened Coulomb (MGECSC) potential with an electric field, in order to investigate the screening and weak external electric field effects on the hydrogen atom in plasmas. The MGECSC potential is examined for four different cases, corresponding to different screening parameters of the potential and the external electric field. The influences of the different screening parameters and the weak external electric field on the energy eigenvalues are determined by solving the corresponding equations using the asymptotic iteration method (AIM). It is found that the corresponding energy values shift when a weak external electric field is applied to the hydrogen atom in a plasma. This study shows that a more general exponential cosine screened Coulomb potential allows the influence of an applied, weak, external electric field on the hydrogen atom to be investigated in detail, for both Debye and quantum plasmas simultaneously. This suggests that such a potential would be useful in modeling similar effects in other applications of plasma physics, and that AIM is an appropriate method for solving the Schrödinger equation, the solution of which becomes more complex due to the use of the MGECSC potential with an applied external electric field.

Bahar, M. K. [Department of Physics, Karamano?lu Mehmetbey University, 70100 Karaman (Turkey); Soylu, A. [Department of Physics, Ni?de University, 51240 Ni?de (Turkey)

2014-09-15

317

The hydrogen atom in plasmas with an external electric field  

NASA Astrophysics Data System (ADS)

We numerically solve the Schrödinger equation, using a more general exponential cosine screened Coulomb (MGECSC) potential with an electric field, in order to investigate the screening and weak external electric field effects on the hydrogen atom in plasmas. The MGECSC potential is examined for four different cases, corresponding to different screening parameters of the potential and the external electric field. The influences of the different screening parameters and the weak external electric field on the energy eigenvalues are determined by solving the corresponding equations using the asymptotic iteration method (AIM). It is found that the corresponding energy values shift when a weak external electric field is applied to the hydrogen atom in a plasma. This study shows that a more general exponential cosine screened Coulomb potential allows the influence of an applied, weak, external electric field on the hydrogen atom to be investigated in detail, for both Debye and quantum plasmas simultaneously. This suggests that such a potential would be useful in modeling similar effects in other applications of plasma physics, and that AIM is an appropriate method for solving the Schrödinger equation, the solution of which becomes more complex due to the use of the MGECSC potential with an applied external electric field.

Bahar, M. K.; Soylu, A.

2014-09-01

318

On the Use of Quartic Force Fields in Variational Calculations  

NASA Technical Reports Server (NTRS)

The use of quartic force fields (QFFs) has been shown to be one of the most effective ways to efficiently compute vibrational frequencies for small molecules. In this paper we outline and discuss how the simple-internal or bond-length bond-angle (BLBA) coordinates can be transformed into Morse-cosine(-sine) coordinates which produce potential energy surfaces from QFFs that possess proper limiting behavior and can effectively describe the vibrational (or rovibrational) energy levels of an arbitrary molecular system. We investigate parameter scaling in the Morse coordinate, symmetry considerations, and examples of transformed QFFs making use of the MULTIMODE, TROVE, and VTET variational vibrational methods. Cases are referenced where variational computations coupled with transformed QFFs produce accuracies compared to experiment for fundamental frequencies on the order of 5 cm(exp -1) and often as good as 1 cm(exp -1).

Fortenberry, Ryan C.; Huang, Xinchuan; Yachmenev, Andrey; Thiel, Walter; Lee, Timothy J.

2013-01-01

319

Parametrization of a reactive force field for aluminum hydride  

SciTech Connect

A reactive force field, REAXFF, for aluminum hydride has been developed based on density functional theory (DFT) derived data. REAXFF{sub AlH{sub 3}} is used to study the dynamics governing hydrogen desorption in AlH{sub 3}. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by REAXFF{sub AlH{sub 3}}. Results on heat of desorption versus cluster size show that there is a strong dependence of the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. In the gas phase, it was observed that small alane clusters agglomerated into a bigger cluster. After agglomeration molecular hydrogen was desorbed from the structure. This thermodynamically driven spontaneous agglomeration followed by desorption of molecular hydrogen provides a mechanism on how mobile alane clusters can facilitate the mass transport of aluminum atoms during the thermal decomposition of NaAlH{sub 4}.

Ojwang, J. G. O. [Schuit Institute of Catalysis, Eindhoven University of Technology, Postbus 513, Den Dolech 2, Eindhoven 5600 MB (Netherlands); Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington D.C. 20012 (United States); Santen, Rutger A. van; Kramer, Gert Jan [Schuit Institute of Catalysis, Eindhoven University of Technology, Postbus 513, Den Dolech 2, Eindhoven 5600 MB (Netherlands); Duin, Adri C. T. van [Department of Mechanical and Nuclear Engineering, Pennsylvania State University, University Park, Pennsylvania 16802 (United States); Goddard, William A. III [Materials and Process Simulation Center (MSC), California Institute of Technology, 1200 East California Boulevard, Pasadena, California 91125 (United States)

2009-07-28

320

Parametrization of a reactive force field for aluminum hydride  

NASA Astrophysics Data System (ADS)

A reactive force field, REAXFF, for aluminum hydride has been developed based on density functional theory (DFT) derived data. REAXFFAlH3 is used to study the dynamics governing hydrogen desorption in AlH3. During the abstraction process of surface molecular hydrogen charge transfer is found to be well described by REAXFFAlH3. Results on heat of desorption versus cluster size show that there is a strong dependence of the heat of desorption on the particle size, which implies that nanostructuring enhances desorption process. In the gas phase, it was observed that small alane clusters agglomerated into a bigger cluster. After agglomeration molecular hydrogen was desorbed from the structure. This thermodynamically driven spontaneous agglomeration followed by desorption of molecular hydrogen provides a mechanism on how mobile alane clusters can facilitate the mass transport of aluminum atoms during the thermal decomposition of NaAlH4.

Ojwang, J. G. O.; van Santen, Rutger A.; Kramer, Gert Jan; van Duin, Adri C. T.; Goddard, William A.

2009-07-01

321

An accurate ab initio quartic force field for ammonia  

NASA Technical Reports Server (NTRS)

The quartic force field of ammonia is computed using basis sets of spdf/spd and spdfg/spdf quality and an augmented coupled cluster method. After correcting for Fermi resonance, the computed fundamentals and nu 4 overtones agree on average to better than 3/cm with the experimental ones except for nu 2. The discrepancy for nu 2 is principally due to higher-order anharmonicity effects. The computed omega 1, omega 3, and omega 4 confirm the recent experimental determination by Lehmann and Coy (1988) but are associated with smaller error bars. The discrepancy between the computed and experimental omega 2 is far outside the expected error range, which is also attributed to higher-order anharmonicity effects not accounted for in the experimental determination. Spectroscopic constants are predicted for a number of symmetric and asymmetric top isotopomers of NH3.

Martin, J. M. L.; Lee, Timothy J.; Taylor, Peter R.

1992-01-01

322

Derivation of a Molecular Mechanics Force Field for Cholesterol  

SciTech Connect

As a necessary step toward realistic cholesterol:biomembrane simulations, we have derived CHARMM molecular mechanics force-field parameters for cholesterol. For the parametrization we use an automated method that involves fitting the molecular mechanics potential to both vibrational frequencies and eigenvector projections derived from quantum chemical calculations. Results for another polycyclic molecule, rhodamine 6G, are also given. The usefulness of the method is thus demonstrated by the use of reference data from two molecules at different levels of theory. The frequency-matching plots for both cholesterol and rhodamine 6G show overall agreement between the CHARMM and quantum chemical normal modes, with frequency matching for both molecules within the error range found in previous benchmark studies.

Cournia, Zoe; Vaiana, Andrea C.; Smith, Jeremy C.; Ullmann, G. Matthias M.

2004-01-01

323

Molecular dynamics simulations of methane hydrate using polarizable force fields  

SciTech Connect

Molecular dynamics simulations of methane hydrate have been carried out using the AMOEBA and COS/G2 polarizable force fields. Properties examined include the temperature dependence of the lattice constant, the OC and OO radial distribution functions and the vibrational spectra. Both the AMOEBA and COS/G2 models are found to successfully account for the available experimental data, with overall slightly better agreement with experiment being found for the AMOEBA model. Several properties calculated using the AMOEBA and COS/G2 models differ appreciable from the corresponding results obtained previously using the polarizable TIP4P-FQ model. This appears to be due to the inadequacy of the treatment of polarization, especially, the restriction of polarization to in-plane only, in the TIP4P-FQ model.

Jiang, H.N.; Jordan, K.D.; Taylor, C.E.

2007-03-01

324

Video: Animals; Electric Current; Force; Science Activities. Learning in Science Project. Working Papers 51-54.  

ERIC Educational Resources Information Center

Four papers to be used in conjunction with video-tapes developed by the Learning in Science Project are presented. Topic areas of the papers focus on: (1) animals; (2) electric current; (3) force; and (4) science activities. The first paper presents transcripts of class discussions focusing on the scientific meaning of the word animal. The second…

Bell, Beverley; And Others

325

FEASIBILITY OF PRODUCING COMMODITIES AND ELECTRICITY FOR SPACE SHUTTLE OPERATIONS AT VANDENBERG AIR FORCE BASE  

EPA Science Inventory

The report gives results of a preliminary screening study of the technical and economic feasibility of the on-site production of commodities (liquid propellant and gases) and electricity to support space shuttle launch activities at Vandenberg Air Force Base (VAFB). Both commerci...

326

Effect of induced electric field on migration of a charged porous particle.  

PubMed

The effect of ambient fluid flow on a charged porous spherical particle suspended in an aqueous medium is analyzed. The porous particle is ion permeable and fluid penetrable. The induced electric field due to the polarization of the particle's electric double layer and counterion condensation leads to a hindrance effect on particle migration by producing an electric force. The influence of this retardation force on the hydrodynamics of the particle is studied through the Nernst-Planck equations, which are coupled with the Stokes-Brinkman equation. The interactions of the double-layer polarization, shielding effect, electroosmosis of unbalanced ions and fluid convection are analyzed. The settling velocity and fluid collection efficiency of the charged aggregate is determined. We have studied the electrokinetics for a wide range of fixed charge density and permeability of the particle with no assumption made on the thickness of the double layer relative to the dimension of the particle. PMID:25374308

Gopmandal, Partha P; Bhattacharyya, S; Barman, Bhanuman

2014-11-01

327

Nanoscale Lubrication of Ionic Surfaces Controlled via a Strong Electric Field  

PubMed Central

Frictional forces arise whenever objects around us are set in motion. Controlling them in a rational manner means gaining leverage over mechanical energy losses and wear. This paper presents a way of manipulating nanoscale friction by means of in situ lubrication and interfacial electrochemistry. Water lubricant is directionally condensed from the vapor phase at a moving metal-ionic crystal interface by a strong confined electric field, thereby allowing friction to be tuned up or down via an applied bias. The electric potential polarity and ionic solid solubility are shown to strongly influence friction between the atomic force microscope (AFM) tip and salt surface. An increase in friction is associated with the AFM tip digging into the surface, whereas reducing friction does not influence its topography. No current flows during friction variation, which excludes Joule heating and associated electrical energy losses. The demonstrated novel effect can be of significant technological importance for controlling friction in nano- and micro-electromechanical systems. PMID:25623295

Strelcov, Evgheni; Kumar, Rajeev; Bocharova, Vera; Sumpter, Bobby G.; Tselev, Alexander; Kalinin, Sergei V.

2015-01-01

328

Nanoscale Lubrication of Ionic Surfaces Controlled via a Strong Electric Field.  

PubMed

Frictional forces arise whenever objects around us are set in motion. Controlling them in a rational manner means gaining leverage over mechanical energy losses and wear. This paper presents a way of manipulating nanoscale friction by means of in situ lubrication and interfacial electrochemistry. Water lubricant is directionally condensed from the vapor phase at a moving metal-ionic crystal interface by a strong confined electric field, thereby allowing friction to be tuned up or down via an applied bias. The electric potential polarity and ionic solid solubility are shown to strongly influence friction between the atomic force microscope (AFM) tip and salt surface. An increase in friction is associated with the AFM tip digging into the surface, whereas reducing friction does not influence its topography. No current flows during friction variation, which excludes Joule heating and associated electrical energy losses. The demonstrated novel effect can be of significant technological importance for controlling friction in nano- and micro-electromechanical systems. PMID:25623295

Strelcov, Evgheni; Kumar, Rajeev; Bocharova, Vera; Sumpter, Bobby G; Tselev, Alexander; Kalinin, Sergei V

2015-01-01

329

Galvanotactic behavior of Tetrahymena pyriformis under electric fields  

NASA Astrophysics Data System (ADS)

Tetrahymena pyriformis, a eukaryotic ciliate, swims toward a cathode in straight or cross-shaped microchannels under an applied electric field, a behavioral response called cathodal galvanotaxis. In straight channel experiments, a one-dimensional electric field was applied, and the galvanotactic swimming behavior of Tetrahymena pyriformis was observed and described in detail while the polarity of this field is switched. In most individual cases, the cell would immediately switch its direction toward the cathode; however, exceptional cases have been observed where cells exhibit a turning delay or do not turn after a polarity switch. In cross-channel experiments, feedback control using vision-based tracking was used to steer a cell in the microchannel intersection using a two-dimensional electric field generated by four electrodes placed at four ends of the cross channel. The motivation for this work is to study the swimming behavior of Tetrahymena pyriformis as a microrobot under the control of electric fields.

Kim, Dal Hyung; Kim, Paul Seung Soo; Lee, Kyoungwoo; Kim, JinSeok; Kim, Min Jun

2013-12-01

330

Molecular-scale measurements of electric fields at electrochemical interfaces.  

SciTech Connect

Spatially resolved measurements of electric fields at electrochemical interfaces would be a critical step toward further understanding and modeling the detailed structure of electric double layers. The goal of this project was to perform proof-of-principle experiments to demonstrate the use of field-sensitive dyes for optical measurements of fields in electrochemical systems. A confocal microscope was developed that provides sensitive detection of the lifetime and high resolution spectra of excited fluorescence for dyes tethered to electrically conductive surfaces. Excited state lifetimes for the dyes were measured and found to be relatively unquenched when linked to indium tin oxide, but strongly quenched on gold surfaces. However, our fluorescence detection is sufficiently sensitive to measure spectra of submonolayer dye coatings even when the fluorescence was strongly quenched. Further work to create dye labeled interfaces on flat, uniform and durable substrates is necessary to make electric field measurements at interfaces using field sensitive dyes.

Hayden, Carl C.; Farrow, Roger L.

2011-01-01

331

Simulating a charged spherical pendulum in time-varying electric and magnetic fields  

NASA Astrophysics Data System (ADS)

We simulate and analyze the dynamics of a charged spherical pendulum in time-varying electric and magnetic fields. The time-varying electric field is directed perpendicular to the gravitational field and serves as a driving force for the pendulum. The time-varying magnetic field is directed parallel to the gravitational field and serves to deflect the motion of the pendulum. We analyze the dynamics of the system to determine the conditions for which chaotic behavior is observed. We also include viscosity to look for strange attractors. The equations of motion are integrated using Objective C and the graphical user interface, including the three dimensional graphical representation of the system, is developed using Cocoa.

Wellons, Mark; King, Frank; McAlpine, Todd

2008-03-01

332

Electric-field-induced structure and optical properties of electrorheological fluids with attapulgite nanorods  

NASA Astrophysics Data System (ADS)

Attapulgite (ATP) is a type of crystalloid hydrous magnesium-aluminum silicate mineral with natural one-dimensional (1D) fibrous morphology. In this study, the authors investigated the optical and mechanical performances of ATP nanorods in silicone oil under an electric field. It was observed that the optical transmittance of ATP suspensions decreased rapidly under the low electric field, using ultraviolet-visible (UV-Vis) spectroscopy. The results of optical microscopy and scanning electron microscopy (SEM) indicated that the electromigration of ATP nanorods was the major cause of such an aberrant optical phenomenon. Further, the electrorheological (ER) response of the samples was measured by the height-controlled method. The change trend of the normal force was illustrated by the dynamic assembly behavior of ATP in the applied electric field. This work provided intuitive evidence for an in-depth understanding of the mechanism of ER fluids containing 1D dielectric materials.

Jin, Ting; Cheng, Yuchuan; He, Ru; Luo, Yuxia; Jiang, Meng; Chen, Chao; Xu, Gaojie

2014-07-01

333

Theoretical prediction of electric field-enhanced coalescence of spherical drops  

SciTech Connect

A fundamental study of drop collision, coalescence and growth induced by combined effects of gravitational and electrostatic forces is presented. The focus is on the enhancement of rates of collision and growth of spherical, conducting drops bearing zero net charge in dilute, homogeneous dispersions by an external electric field. By completely accounting for hydrodynamic and electrostatic interactions, a trajectory analysis is used to follow the relative motion of two drops and predict pairwise collision and coalescence rates. A population dynamics equation is then solved to predict the evolution in time of the size distribution and the average size of drops. The results show that the rates of drop collision and growth can be increased significantly by applying an electric field, in accord with fundamental experiments and patents on electrocoalescence. The enhancement of drop collision and coalescence is especially pronounced when the imposed electric field acts horizontally, that is, in a direction perpendicular to gravity.

Zhang, X. [Oak Ridge National Lab., TN (United States). Chemical Technology Div.] [Oak Ridge National Lab., TN (United States). Chemical Technology Div.; [Univ. of Tennessee, Knoxville, TN (United States). Dept. of Chemical Engineering; Basaran, O.A.; Wham, R.M. [Oak Ridge National Lab., TN (United States). Chemical Technology Div.] [Oak Ridge National Lab., TN (United States). Chemical Technology Div.

1995-07-01

334

Defect control of local electric fields in inhomogeneous media  

SciTech Connect

The interaction of surface and bulk defects in dielectric media can lead to marked variations in the local electric field from the macroscopic value. Inherent to fabrication processes, these defects impose complex boundary conditions which prevent analytical solutions for the electric fields. To approach this problem, a self-consistent, numerical method to determine the local electric field in inhomogeneous media has been developed. Previous work has shown that microstructural defects tend to focus and enhance the local field vectors, which serve to effectively map the microstructure of dielectric media. In this paper, the authors report on field enhancement factors resulting from the orientation of these defects with respect to an applied field, and the effect of inclusions characterized by low dielectric constants. Results will contrast the direct determination of the local field with EMA and random resistor models to demonstrate their characteristic differences.

Ferris, K.F.; Exarhos, G.J. [Pacific Northwest Lab., Richland, WA (United States); Risser, S.M. [East Texas State Univ., Commerce, TX (United States)

1995-12-01

335

Streamer discharges can move perpendicularly to the electric field  

NASA Astrophysics Data System (ADS)

Streamer discharges are a primary mode of electric breakdown in thunderstorms and high voltage technology; they are generally believed to grow along electric field lines. However, we here give experimental and numerical evidence that streamers can propagate nearly perpendicularly to the background electric field. These streamers are guided by pre-ionization that is orders of magnitude lower than the ionization density in a streamer channel, hardly affecting the background field. Positive streamers could be guided in nitrogen with 0.5% of oxygen or less, but not in air. This observation also tests the role of photo-ionization in gas mixtures with varying nitrogen–oxygen ratio.

Nijdam, S.; Takahashi, E.; Teunissen, J.; Ebert, U.

2014-10-01

336

Giant and tunable electric field enhancement in the terahertz regime.  

PubMed

A novel array of slits design combining the nano-slit grating and dielectric-metal is proposed to obtain giant and tunable electric field enhancement in the terahertz regime. The maximum amplitude of electric field is more than 6000 times larger than that of the incident electric field. It is found that the enhancement depends primarily on the stripe and nano-slits width of grating, as well as the thickness of spacer layer. This property is particularly beneficial for the realization of ultra-sensitive nanoparticles detection and nonlinear optics in the terahertz range, such as the second harmonic generation (SHG). PMID:25401850

Lu, Xiaoyuan; Wan, Rengang; Wang, Guoxi; Zhang, Tongyi; Zhang, Wenfu

2014-11-01

337

The source of the electric field in the nightside magnetosphere  

NASA Technical Reports Server (NTRS)

In the open magnetosphere model magnetic field lines from the polar caps connect to the interplanetary magnetic field and conduct an electric field from interplanetary space to the polar ionosphere. By examining the magnetic flux involved it is concluded that only slightly more than half of the magnetic flux in the polar caps belongs to open field lines and that such field lines enter or leave the magnetosphere through narrow elongated windows stretching the tail. These window regions are identified with the tail's boundary region and shift their position with changes in the interplanetary magnetic field, in particular when a change of interplanetary magnetic sector occurs. The circuit providing electric current in the magnetopause and the plasma sheet is extended across those windows; thus energy is drained from the interplanetary electric field and an electric potential drop is produced across the plasma sheet. The polar cap receives its electric field from interplanetary space on the day side from open magnetic field lines and on the night side from closed field lines leading to the plasma sheet. The theory described provides improved understanding of magnetic flux bookkeeping, of the origin of Birkeland currents, and of the boundary layer of the geomagnetic tail.

Stern, D. P.

1975-01-01

338

Formation of magnetic discontinuities through superposition of force-free magnetic fields: Periodic boundaries  

NASA Astrophysics Data System (ADS)

In ideal magnetohydrodynamics characterized by an infinite electrical conductivity, the magnetic flux across an arbitrary fluid surface is conserved in time. The magnetofluid then can be partitioned into contiguous subvolumes of fluid, each of which entraps its own subsystem of magnetic flux. During dynamical evolution of the magnetofluid, these subvolumes press into each other; and in the process, two such subvolumes may come into direct contact while ejecting a third interstitial subvolume. Depending on the orientations of magnetic fields of the two interacting subvolumes, the magnetic field at the common surface of interaction may become discontinuous and a current sheet is formed there. This process of current sheet formation and their subsequent decay is believed to be a plausible mechanism for coronal heating and may also be responsible for various eruptive phenomena at the solar corona. In this work, we explore this theoretical concept through numerical simulations of a viscous, incompressible magnetofluid characterized by infinite electrical conductivity. In particular, we show that if the initial magnetic field is prescribed by superposition of two linear force-free fields with different torsion coefficients, then formation of current sheets are numerically realizable in the neighborhood of magnetic nulls.

Kumar, Dinesh; Bhattacharyya, R.; Smolarkiewicz, P. K.

2013-11-01

339

Feather release force in minimally scalded broilers stunned with carbon dioxide or electricity.  

PubMed

Broilers were stunned with carbon dioxide or electricity prior to slaughter to evaluate feather release force (FRF) following scalding with conventional or abbreviated scald methods. Broilers (n = 72) were stunned using an electrical saline stunner (35 mA, 60 Hz AC, 7 s) or shackle-line CO2 gas stunning tunnel (15 to 40% CO2 gradient for 90 s). After bleeding for 90 s, the broilers were then scalded with a soft scald (53 C for 120 s) or a softer scald (53 C for 90 s). Within 2 min after scalding, feathers from the right femoral feather tract were removed perpendicularly using a force gauge to evaluate FRF. The FRF for the soft scald was higher than that for the softer scald. The FRF results indicated that there were no significant differences between the two stunning treatments (CO2 and electrical) for either scalding treatment. PMID:10947196

Krupala, J K; Sams, A R

2000-08-01

340

Calculation of atmospheric electric fields penetrating from the ionosphere  

NASA Astrophysics Data System (ADS)

The spatial distributions of electric fields and currents in the Earth’s atmosphere are calculated. Electric potential distributions typical of substorms and quiet geomagnetic conditions are specified in the ionosphere. The Earth is treated as a perfect conductor. The atmosphere is considered as a spherical layer with a given height dependence of electrical conductivity. With the chosen conductivity model and an ionospheric potential of 300 kV with respect to the Earth, the electric field near the ground is vertical and reaches 110 Vm-1. With the 60-kV potential difference in the polar cap of the ionosphere, the electric field disturbances with a vertical component of up to 13 V m-1 can occur in the atmosphere. These disturbances are maximal near the ground. If the horizontal scales of field nonuniformity are over 100 km, the vertical component of the electric field near the ground can be calculated with the one-dimensional model. The field and current distributions in the upper atmosphere can be obtained only from the three-dimensional model. The numerical method for solving electrical conductivity problems makes it possible to take into account conductivity inhomogeneities and the ground relief.

Denisenko, V. V.; Bychkov, V. V.; Pomozov, E. V.

2009-12-01

341

Time-resolved electric-field-induced second harmonic  

Microsoft Academic Search

One limitation of using electric field induced second harmonic (EFISH) to determine the molecular first hyperpolarizability (beta) of nonlinear optical molecules lies in the fact that part of the second harmonic signal comes from the second hyperpolarizability (gamma) produced by mixing two optical fields with the DC field. In analyzing EFISH results, the second hyperpolarizability contribution of the studied molecules

Guilia Meshulam; Garry Berkovic; Zvi Kotler

2001-01-01

342

The responses of cells to electrical fields: a review  

Microsoft Academic Search

The application of DC electric fields to cells has a long and contentious history. The interpretation of the response of cells to such fields was hampered by lack of adequate recording technique, contamination of cultures by electrode products, uncertainty about the magnitude of fields, and sometimes by the complexity of the biological system under study. Never- theless, when Jaffe and

KENNETH R. ROBINSON

1985-01-01

343

A latent force model for describing electric propagation in deep brain stimulation: A simulation study.  

PubMed

Deep brain stimulation (DBS) is a neurosurgical method used to treat symptoms of movement disorders by implanting electrodes in deep brain areas. Often, the DBS modeling approaches found in the literature assume a quasi-static approximation, and discard any dynamic behavior. Nevertheless, in a real DBS system the stimulus corresponds to a wave that changes as a function of time. It is clear that DBS demands an approach that takes into account the time-varying behavior of the input stimulus. In this work, we present a novel latent force model for describing the dynamic electric propagation occurred during DBS. The performance of the proposed model was studied by simulations under different conditions. The results show that our approach is able to take into account the time variations of the source and the produced field. Moreover, by restricting our model it is possible to obtain solutions for electrostatic formulations, here experimental results were compared with the finite element method. Additionally, our approach allows a solution to the inverse problem, which is a valuable clinical application allowing the appropriate tuning of the DBS device by the expert physician. PMID:25570527

Alvarado, Pablo A; Alvarez, Mauricio A; Daza-Santacoloma, Genaro; Orozco, Alvaro; Castellanos-Dominguez, German

2014-08-01

344

Evaluating shock absorption behavior of small-sized systems under programmable electric field  

NASA Astrophysics Data System (ADS)

A simple ball-drop impact tester is developed for studying the dynamic response of hierarchical, complex, small-sized systems and materials. The developed algorithm and set-up have provisions for applying programmable potential difference along the height of a test specimen during an impact loading; this enables us to conduct experiments on various materials and smart structures whose mechanical behavior is sensitive to electric field. The software-hardware system allows not only acquisition of dynamic force-time data at very fast sampling rate (up to 2 × 106 samples/s), but also application of a pre-set potential difference (up to ±10 V) across a test specimen for a duration determined by feedback from the force-time data. We illustrate the functioning of the set-up by studying the effect of electric field on the energy absorption capability of carbon nanotube foams of 5 × 5 × 1.2 mm3 size under impact conditions.

Jagtap, Piyush; Kumar, Praveen

2014-11-01

345

Electric field studies: TLE-induced waveforms and ground conductivity impact on electric field propagation  

NASA Astrophysics Data System (ADS)

We review in this paper main results obtained from electric field (from VLF to HF) measurement campaigns realized by CEA in the framework of the Eurosprite program [Neubert et al., 2005, 2008] from 2003 to 2009 in France in different configurations. Two main topics have been studied: sprite or elve induced phenomena (radiation or perturbation) and wave propagation. Using a network of 4 stations, VLF radiations from sprite have been successfully located at 10 km from the sprite parent lightning, in agreement with possible sprite location, generally displaced from the parent lightning. The MF (300 kHz - 3 MHz) source bursts were identified simultaneously with the occurrence of sprites observed with cameras [Farges et al., 2004; Neubert et al., 2008]. These observations are compared to recent broadband measurements, assumed to be due to relativistic electron beam radiation related to sprites [Fullekrug et al., 2009]. Recently, in 2009, with a new instrumentation, an ELF tail has been clearly measured after the lightning waveform, while sprites were observed at about 500 km from our station. This ELF tail is usually observed at distances higher than thousand km and is associated to sprite generation. This opens the capacity to measure the charge moment of the parent-lightning, using such measurement close to the source. Farges et al. [2007] showed that just after a lightning return stroke, a strong transient attenuation is very frequently observed in the MF waves of radio transmissions. They showed that this perturbation is due to heating of the lower ionosphere by the lightning-induced EMP during few milliseconds. These perturbations are then the MF radio signature of the lightning EMP effects on the lower ionosphere, in the same way as elves correspond to their optical signature. The experiment also provided the electric field waveforms directly associated to elves, while lightning were not detected by Météorage. Many of them present a double peak feature. The propagation of the electromagnetic waves generated by lightning has also been studied in the frequency range 1 kHz-1MHz at distances lower than 1000 km from the lightning source. A propagation model has been developed to determine the ground waves which propagate in a homogenous medium using the analytical expression given by Maclean and Wu [1993]. This approach takes into account the electric finite conductivity and the fact that the Earth is spherical, which allow us to deal with over-the-horizon propagation. We installed in 2008 four stations which were more or less aligned - the maximum distance between two stations was about 870 km. Two stations were located close to the Mediterranean Sea and the two others inside the continent, at the centre of France. This station distribution and the observation period (from August to December) allowed statistical and physical studies, such as the influence of the electric conductivity on wave propagation. Comparison of electric field spectra, measured after propagation only over sea and only over ground, showed clearly the effects of ground conductivity on propagation. Comparison between observations and modelling has been used to evaluate the ground conductivity. In the future we will implement the sky-wave inside our model and validate it with the database.

Farges, Thomas; Garcia, Geraldine; Blanc, Elisabeth

2010-05-01

346

Electric-field-driven Phenomena for Manipulating Particles in Micro-Devices  

NASA Technical Reports Server (NTRS)

Compared to other available methods, ac dielectrophoresis is particularly well-suited for the manipulation of minute particles in micro- and nano-fluidics. The essential advantage of this technique is that an ac field at a sufficiently high frequency suppresses unwanted electric effects in a liquid. To date very little has been achieved towards understanding the micro-scale field-and shear driven behavior of a suspension in that, the concepts currently favored for the design and operation of dielectrophoretic micro-devices adopt the approach used for macro-scale electric filters. This strategy considers the trend of the field-induced particle motions by computing the spatial distribution of the field strength over a channel as if it were filled only with a liquid and then evaluating the direction of the dielectrophoretic force, exerted on a single particle placed in the liquid. However, the exposure of suspended particles to a field generates not only the dielectrophoretic force acting on each of these particles, but also the dipolar interactions of the particles due to their polarization. Furthermore, the field-driven motion of the particles is accompanied by their hydrodynamic interactions. We present the results of our experimental and theoretical studies which indicate that, under certain conditions, these long-range electrical and hydrodynamic interparticle interactions drastically affect the suspension behavior in a micro-channel due to its small dimensions.

Khusid, Boris; Acrivos, Andreas

2004-01-01

347

Magnetic resonance electrical impedance tomography for monitoring electric field distribution during tissue electroporation.  

PubMed

Electroporation is a phenomenon caused by externally applied electric field of an adequate strength and duration to cells that results in the increase of cell membrane permeability to various molecules, which otherwise are deprived of transport mechanism. As accurate coverage of the tissue with a sufficiently large electric field presents one of the most important conditions for successful electroporation, applications based on electroporation would greatly benefit with a method of monitoring the electric field, especially if it could be done during the treatment. As the membrane electroporation is a consequence of an induced transmembrane potential which is directly proportional to the local electric field, we propose current density imaging (CDI) and magnetic resonance electrical impedance tomography (MREIT) techniques to measure the electric field distribution during electroporation. The experimental part of the study employs CDI with short high-voltage pulses, while the theoretical part of the study is based on numerical simulations of MREIT. A good agreement between experimental and numerical results was obtained, suggesting that CDI and MREIT can be used to determine the electric field during electric pulse delivery and that both of the methods can be of significant help in planning and monitoring of future electroporation based clinical applications. PMID:21521664

Kranjc, M; Bajd, F; Serša, I; Miklav?i?, D

2011-10-01

348

Comparison of Nonlinear Force-Free Field and Potential Field in the Quiet Sun  

NASA Astrophysics Data System (ADS)

In this paper, a potential field extrapolation and three nonlinear force-free (NLFF) field extrapolations (optimization, direct boundary integral (DBIE), and approximate vertical integration (AVI) methods) are used to study the spatial configuration of magnetic field in the quiet Sun. It is found that differences in the computed field strengths among the three NLFF and potential fields exist in the low layers. However, they tend to disappear as the height increases, and the differences are of the order of 0.1 gauss when the height exceeds ? 2000 km above the photosphere. The difference in azimuth angles between each NLFF field model and the potential field is as follows: for the optimization field, it decreases evidently as the height increases; for the DBIE field, it almost stays constant and shows no significant change as the height increases; for the AVI field, it increases slowly as the height increases. Our analysis shows that the reconstructed NLFF fields deviate significantly from the potential field in the quiet Sun.

Liu, S.; Zhang, H. Q.; Su, J. T.

2011-05-01

349

Atomistic simulations of electric field effects on the Young?s modulus of metal nanowires  

NASA Astrophysics Data System (ADS)

We present a computational, atomistic study of electric field effects on the Young?s modulus of metal nanowires. The simulations are electromechanically coupled, where the mechanical forces on the atoms are obtained from realistic embedded atom method potentials, and where the electrostatic forces on the atoms are obtained using a point dipole electrostatic model that is modified to account for the different polarizability and bonding environment of surface atoms. By considering three different nanowire axial orientations (< 100> , < 110> and < 111> ) of varying cross sectional sizes and aspect ratios, we find that the Young?s modulus of the nanowires differs from that predicted for the purely mechanical case due to the elimination of nonlinear elastic stiffening or softening effects due to the electric field-induced positive relaxation strain relative to the relaxed mechanical configuration. We further find that < 100> nanowires are most sensitive to the applied electric field, with Young?s moduli that can be increased more than 20% with increasing aspect ratio. Finally, while the orientation of the transverse surfaces does impact the Young?s modulus of the nanowires under applied electric field, the key factor controlling the magnitude of the stiffness change of the nanowires is the distance between atomic planes along the axial direction of the nanowire bulk.

Ben, Xue; Park, Harold S.

2014-11-01

350

Ion trap electric field measurements using slab coupled optical sensors  

NASA Astrophysics Data System (ADS)

Ion traps are widely used in the field of mass spectrometry. These devices use high electric fields to mass-selectively trap, eject, and count the particles of a material, producing a mass spectrum of the given material. Because of their usefulness, technology pushes for smaller, more portable ion traps for field use. Making internal ion trap field measurements not yet feasible because current electric field sensors are often too bulky or their metallic composition perturbs field measurements. Using slab coupled optical sensor (SCOS) technology, we are able to build sensors that are compatible with the spacing constraints of the ion trap. These sensors are created by attaching a nonlinear crystal slab waveguide to an optical fiber. When a laser propagates through the fiber, certain wavelengths of light couple out of the fiber via the crystal and create "resonances" in the output light spectrum. These resonances shift in proportion to a given applied electric field, and by measuring that shift, we can approximate the electric field. Developing a sensor that can effectively characterize the electric fields within an ion trap will greatly assist in ion trap design, fabrication, and troubleshooting techniques.

Shumway, L.; Chadderdon, S.; Powell, A.; Li, A.; Austin, D.; Hawkins, A.; Selfridge, R.; Schultz, S.

2014-03-01

351

Variations in Gravitational Field, Tidal Force, Electromagnetic Waves and Earthquakes  

NASA Astrophysics Data System (ADS)

This paper is the report on an experiment carried out between the month of December 2009 and the month of April 2010 between the Venetian Lagoon and the Northern Apennines in Italy, to check on a potential relationship between earthquakes and variations in the local gravitational field, the effect on the tide exercised by the interaction between the moon and the Sun, the appearance of anomalous light effects in the atmosphere ("Earth lights"), and the emission of radio waves caused by stresses in the Earth's crust. The cases studied show that there is indeed some concomitance between the periodic rising and falling of the sea level and the terrestrial tide effect, due to the gravitational attraction of the moon and sun on the Earth. In fact, changes in the local force of gravity coincided with the cycle of high and low tides and, in certain cases, with a variation in the electromagnetic field that preceded the occurrence of a seismic event by just a few hours. The o! bservations in the article are limited to the magnitude range discussed in the paper.

Strasser, Valentino

2010-12-01

352

Ordered behaviour in force-free magnetic fields  

NASA Astrophysics Data System (ADS)

Conditions in order that the trajectories of a force-free vectorfield lie on the level sets of a given function are studied. Force-free vectorfields symmetric under translations, rotations and roto-translations are also considered.

Gonzalez-Gascon, F.; Peralta-Salas, D.

2001-12-01

353

Study of pulsed electric field treated citrus juices  

Microsoft Academic Search

The effect of pulsed electric field (PEF) treatment, applied in a continuous system, on physical and chemical properties of freshly squeezed citrus juices (grapefruit, lemon, orange, tangerine) was studied. The aim of the present work was to investigate the effect of PEF technology on pH, Brix°, electric conductivity, viscosity, nonenzymatic browning index (NEBI), hydroxymethylfurfurol (HMF), color, organic acid content, and

Zs. Cserhalmi; Á. Sass-Kiss; M. Tóth-Markus; N. Lechner

2006-01-01

354

SIMULATION OF THE ELECTRIC FIELD IN A SUBMERGED ARC FURNACE  

Microsoft Academic Search

This paper presents computations of the electric field inside a furnace. We first look at the effect of contact between two coke particles from an electrical point of view. We give values for the amount of contact resistance in the total resistance of the system formed by the two coke particles. We show that the effect of contact resistance decreases

M. Dhainaut

355

DC link stabilized field oriented control of electric propulsion systems  

Microsoft Academic Search

Induction motor based electric propulsion systems can be used in a wide variety of applications including locomotives, hybrid electric vehicles, and ships. Field oriented control of these drives is attractive since it allows the torque to be tightly and nearly instantaneously controlled. However, such systems can be prone to negative impedance instability of the DC link. This paper examines this

S. D. Sudhoff; K. A. Corzine; S. F. Glover; H. J. Hegner

1998-01-01

356

Calculating Electric Field Using Flux Detector and Gauss's Law  

NSDL National Science Digital Library

The learner is asked to calculate the electric field due to a charge filament as shown in the animation. Given are three different detectors and three different viewpoints: intermediate distance, very close, and very far from the filament.

Christian, Wolfgang; Belloni, Mario

2006-01-14

357

Probing surface electric field noise with a single ion  

E-print Network

We report room-temperature electric field noise measurements combined with in-situ surface characterization and cleaning of a microfabricated ion trap. We used a single-ion electric field noise sensor in combination with surface cleaning and analysis tools, to investigate the relationship between electric field noise from metal surfaces in vacuum and the composition of the surface. These experiments were performed in a novel setup that integrates ion trapping capabilities with surface analysis tools. We find that surface cleaning of an aluminum-copper surface significantly reduces the level of electric field noise, but the surface does not need to be atomically clean to show noise levels comparable to those of the best cryogenic traps. The post-cleaning noise levels are low enough to allow fault-tolerant trapped-ion quantum information processing on a microfabricated surface trap.

Daniilidis, N; Bolloten, G; Ramm, M; Ransford, A; Ulin-Avila, E; Talukdar, I; Häffner, H

2013-01-01

358

Electric field effects on alanine tripeptide in sodium halide solutions.  

PubMed

Abstract The electric field effects on conformational properties of trialanine in different halide solutions were explored with long-scale molecular dynamics simulations. NaF, NaCl, NaBr and NaI solutions of low (0.2?M) and high (2?M) concentrations were exposed to a constant electric field of 1000?V/m. Generally, the electric field does not disturb trialanine's structure. Large structural changes appear only in the case of the supersaturated 2.0?M NaF solution containing NaF crystals. Although the electric field affects in a complex way, all the ions-water-peptide interactions, it predominantly affects the electroselectivity effect, which describes specific interactions such as the ion-pair formation. PMID:25006865

Astrakas, Loukas G; Gousias, Christos; Tzaphlidou, Margaret

2014-07-01

359

Electric field measurements during the Condor critical velocity experiment  

NASA Technical Reports Server (NTRS)

The instrumentation of the Condor critical velocity Ba experiment (Wescott et al., 1986) for the measurements of the energetic particles and the electric field associated with a Ba explosion is described. The Ba explosion created a complex electric field pulse detected in situ by a single-axis double electric-field probe on a separate spacecraft. The measurements provide evidence of several important links in the critical-velocity chain, and are consistent with two hypotheses. The first hypothesis involves the creation of large polarization electric field due to charge separation; the second hypothesis implies a polarization of the beam by currents flowing across it. The chain of physical processes inferred from the observations is in agreement with most theories for the Alfven process.

Kelley, M. C.; Pfaff, R. F.; Haerendel, G.

1986-01-01

360

PARALLEL ELECTRIC FIELD SPECTRUM OF SOLAR WIND TURBULENCE  

SciTech Connect

By searching through more than 10 satellite years of THEMIS and Cluster data, 3 reliable examples of parallel electric field turbulence in the undisturbed solar wind have been found. The perpendicular and parallel electric field spectra in these examples have similar shapes and amplitudes, even at large scales (frequencies below the ion gyroscale), where Alfvenic turbulence with no parallel electric field component is thought to dominate. The spectra of the parallel electric field fluctuations are power laws with exponents near -5/3 below the ion scales ({approx}0.1 Hz), and with a flattening of the spectrum in the vicinity of this frequency. At small scales (above a few Hz), the spectra are steeper than -5/3 with values in the range of -2.1 to -2.8. These steeper slopes are consistent with expectations for kinetic Alfven turbulence, although their amplitude relative to the perpendicular fluctuations is larger than expected.

Mozer, F. S.; Chen, C. H. K., E-mail: fmozer@ssl.berkeley.edu [Space Sciences Laboratory, University of California, Berkeley, CA 94720 (United States)

2013-05-01

361

Droplet charging regimes for ultrasonic atomization of a liquid electrolyte in an external electric field  

PubMed Central

Distinct regimes of droplet charging, determined by the dominant charge transport process, are identified for an ultrasonic droplet ejector using electrohydrodynamic computational simulations, a fundamental scale analysis, and experimental measurements. The regimes of droplet charging are determined by the relative magnitudes of the dimensionless Strouhal and electric Reynolds numbers, which are a function of the process (pressure forcing), advection, and charge relaxation time scales for charge transport. Optimal (net maximum) droplet charging has been identified to exist for conditions in which the electric Reynolds number is of the order of the inverse Strouhal number, i.e., the charge relaxation time is on the order of the pressure forcing (droplet formation) time scale. The conditions necessary for optimal droplet charging have been identified as a function of the dimensionless Debye number (i.e., liquid conductivity), external electric field (magnitude and duration), and atomization drive signal (frequency and amplitude). The specific regime of droplet charging also determines the functional relationship between droplet charge and charging electric field strength. The commonly expected linear relationship between droplet charge and external electric field strength is only found when either the inverse of the Strouhal number is less than the electric Reynolds number, i.e., the charge relaxation is slower than both the advection and external pressure forcing, or in the electrostatic limit, i.e., when charge relaxation is much faster than all other processes. The analysis provides a basic understanding of the dominant physics of droplet charging with implications to many important applications, such as electrospray mass spectrometry, ink jet printing, and drop-on-demand manufacturing. PMID:21301636

Forbes, Thomas P.; Degertekin, F. Levent; Fedorov, Andrei G.

2011-01-01

362

A Method for Embedding Circular Force-Free Flux Ropes in Potential Magnetic Fields  

NASA Astrophysics Data System (ADS)

We propose a method for constructing approximate force-free equilibria in pre-eruptive configurations that locally are a bipolar-type potential magnetic field with a thin force-free flux rope embedded inside it. The flux rope is assumed to have a circular-arc axis, circular cross-section, and electric current that is either concentrated in a thin layer at the boundary of the rope or smoothly distributed across it with a maximum of the current density at the center.The entire solution is described in terms of the magnetic vector potential in order to facilitate the implementation of the method in numerical magnetohydrodynamic (MHD) codes that evolve the vector potential rather than the magnetic field itself. The parameters of the flux rope can be chosen so that its subsequent MHD relaxation under photospheric line-tied boundary conditions leads to nearly exact numerical equilibria. To show the capabilities of our method, we apply it to several cases with different ambient magnetic fields and internal flux-rope structures. These examples demonstrate that the proposed method is a useful tool for initializing data-driven simulations of solar eruptions.

Titov, Viacheslav; Torok, Tibor; Mikic, Zoran; Linker, Jon A.

2014-06-01

363

Finite Element Studies of Colloidal Mixtures Influenced by Electric Fields  

E-print Network

FINITE ELEMENT STUDIES OF COLLOIDAL MIXTURES INFLUENCED BY ELECTRIC FIELDS A Thesis by FRANKLIN JERREL DRUMMOND Submitted to the Office of Graduate Studies of Texas A&M University in partial fulfillment of the requirements... for the degree of MASTER OF SCIENCE August 2011 Major Subject: Aerospace Engineering FINITE ELEMENT STUDIES OF COLLOIDAL MIXTURES INFLUENCED BY ELECTRIC FIELDS A Thesis by FRANKLIN JERREL DRUMMOND Submitted to the Office of Graduate...

Drummond, Franklin Jerrel

2011-10-21

364

Electric-field distribution near current contacts of anisotropic materials  

NASA Astrophysics Data System (ADS)

We have measured the nonuniformity of the electric field near lateral current contacts of the charge-density-wave materials NbSe3 and o-TaS3. In this contact geometry, the electric field increases considerably near a current contact. Fitting our data to an existing model yields values for the conduction anisotropy and a characteristic longitudinal length scale. This length scale is on the same order as the mesoscopic phenomena in charge-density-wave devices.

Slot, E.; van der Zant, H. S.; Thorne, R. E.

2002-01-01

365

Ionizing gas breakdown waves in strong electric fields.  

NASA Technical Reports Server (NTRS)

A previous analysis by Albright and Tidman (1972) of the structure of an ionizing potential wave driven through a dense gas by a strong electric field is extended to include atomic structure details of the background atoms and radiative effects, especially, photoionization. It is found that photoionization plays an important role in avalanche propagation. Velocities, electron densities, and temperatures are presented as a function of electric field for both negative and positive breakdown waves in nitrogen.

Klingbeil, R.; Tidman, D. A.; Fernsler, R. F.

1972-01-01

366

A New Electric Field in Asymmetric Magnetic Reconnection  

NASA Astrophysics Data System (ADS)

Magnetic reconnection is an important plasma process that drives the dynamics of the plasma in the magnetosphere and plays a crucial role in the interaction between magnetospheric and magnetosheath plasma. It has been shown that when a reconnection occurs in a collisionless plasma, it exhibits the Hall electric field, an in-plane electric field structure pointing toward the X-line. In this work, we show that when the reconnection has asymmetric inflow conditions such as the reconnection at the day-side magnetopause, a new in-plane electric field structure can exist. This electric field points away from the X-line and is distinct from the known Hall electric field. We argue that the origin of the electric field is associated with the physics of finite Larmor radius. A theory and predictions of the electric field properties are presented and backed up by results from fully kinetic particle-in-cell simulations of asymmetric reconnection with various inflow conditions. Under normal day-side reconnection inflow conditions, the electric field is expected to occur on the magnetospheric side of the X-line pointing Earthward. Hence, it has a potential to be used as a signature for satellites, such as the upcoming Magnetospheric Multi-Scale (MMS) mission, to locate the reconnection sites at the day-side magnetopause. This research was supported by the postdoctoral research sponsorship of Mahidol University (KM), NSF grants ATM-0645271 - Career Award (MAS) and AGS-0953463 (PAC), NASA grants NNX08A083G - MMS IDS, NNX11AD69G, and NNX13AD72G (MAS) and NNX10AN08A (PAC), and the Thailand Research Fund (DR).

Malakit, K.; Shay, M. A.; Cassak, P.; Ruffolo, D. J.

2013-12-01

367

Orientation of native cellulose in an electric field.  

PubMed

Native cellulose has been oriented in an ac electric field at both the macroscopic and colloidal level. Ramie fiber fragments suspended in chloroform have been shown to point along the field. Cellulose microcrystal suspensions in cyclohexane have also been allowed to evaporate in an electric field and have exhibited a high degree of orientation when further examined by TEM and electron diffraction. Similarly, cellulose whisker suspensions showed increasing birefringence with increasing field strength and displayed interference Newton colors that saturated at around 2000 V cm(-)(1). A high degree of order of this suspension was also obtained by evaluating the induced birefringence with color charts. PMID:16700569

Bordel, Damien; Putaux, Jean-Luc; Heux, Laurent

2006-05-23

368

Control of magnetic and electric responses with electric and magnetic fields in magnetoelectric heterostructures  

NASA Astrophysics Data System (ADS)

This paper reports on the tuning of both magnetic and electric responses with electric and magnetic fields for metglas-Pb (Zr,Ti)O3 based magnetoelectric (ME) heterostructures that can be promising for communication and sensor applications. The hysteresis loop results indicate a change in the in-plane magnetization due to application of voltages that leads to a tuning of the ferromagnetic resonance frequency by up to about 210 MHz with electric field. Furthermore, these structures show a high ME voltage coefficient that results in the detection of a 2 nT ac magnetic field and a low noise floor.

Das, J.; Li, M.; Kalarickal, S. S.; Altmannshofer, S.; Buchanan, K. S.; Li, J. F.; Viehland, D.

2010-05-01

369

Electroplastic effect under the simultaneous superposition of electric and magnetic fields  

NASA Astrophysics Data System (ADS)

In recent years a number of models were proposed in which the electroplastic effect in the process of thermal fluctuation motion and generation of dislocations was considered to be a result of lowering potential barriers by the electromagnetic field. The experiments carried out so far reveal the surface character of the electroplastic deformation. To test the effect, the free surface has been perturbed by an electromagnetic field. The deformation of a bismuth crystal in response to application of mechanical stress and concurrent constant magnetic field and an impulse electric current has been studied. To illustrate the deformation process in single crystals of bismuth under the simultaneous effect of the electric and magnetic fields, a special device was designed as a supplement to the standard microhardness measuring equipment. There are two factors that increase plasticity in the case of the concurrent application of magnetic and electric fields. The first one is the damped elastic sonic vibrations caused by the Ampere force. In the case of deformation by twinning, these vibrations result in an increase of wedge-shaped twin around the imprint of the diamond indentor. The second factor is the electric charge on the free surface. The electric charge on the cleavage face increases the run of the twinning dislocations.

Pinchook, A. I.; Savenko, V. S.

1999-09-01

370

Effective force field for liquid hydrogen fluoride from ab initio molecular dynamics simulation using the force-matching method.  

PubMed

A recently developed force-matching method for obtaining effective force fields for condensed matter systems from ab initio molecular dynamics (MD) simulations has been applied to fit a simple nonpolarizable two-site pairwise force field for liquid hydrogen fluoride. The ab initio MD in this case was a Car-Parrinello (CP) MD simulation of 64 HF molecules at nearly ambient conditions within the Becke-Lee-Yang-Parr approximation to the electronic density functional theory. The force-matching procedure included a fit of short-ranged nonbonded forces, bonded forces, and atomic partial charges. The performance of the force-match potential was examined for the gas-phase dimer and for the liquid phase at various temperatures. The model was able to reproduce correctly the bent structure and energetics of the gas-phase dimer, while the results for the structural properties, self-diffusion, vibrational spectra, density, and thermodynamic properties of liquid HF were compared to both experiment and the CP MD simulation. The force-matching model performs well in reproducing nearly all of the liquid properties as well as the aggregation behavior at different temperatures. The model is computationally cheap and compares favorably to many more computationally expensive potential energy functions for liquid HF. PMID:16851738

Izvekov, Sergei; Voth, Gregory A

2005-04-14

371

The Dynamics of Ultrasonically Levitated Drops in an Electric Field  

NASA Technical Reports Server (NTRS)

Ultrasonic and electrostatic levitation techniques have allowed the experimental investigation of the nonlinear oscillatory dynamics of free droplets with diameter between 0.1 and 0.4 cm. The measurement of the resonance frequencies of the first three normal modes of large amplitude shape oscillations in an electric field of varying magnitude has been carried out with and without surface charges for weakly conducting liquids in air. These oscillations of nonspherical levitated drops have been driven by either modulating the ultrasonic field or by using a time-varying electric field, and the free decay from the oscillatory state has been recorded. A decrease in the resonance frequency of the driven fundamental quadrupole mode has been measured for increasing oblate deformation in the absence of an electric field. Similarly, a decrease in this frequency has also been found for increasing DC electric field magnitude. A soft nonlinearity exists in the amplitude dependence of the resonant mode frequencies for freely decaying as well as ultrasonically and electrically driven uncharged drops. This decrease in resonance frequency is accentuated by the presence of free surface charge on the drop. Subharmonic resonance excitation has been observed for drops in a time-varying electric field, and hysteresis exists for resonant modes driven to large amplitude. Mode coupling from lower-order resonances to higher-order modes has been found to be very weak, even for fairly large amplitude shape oscillations. Most of these results are in general agreement with predictions from recent analytical and numerical investigations.

Trinh, E. H.; Holt, R. G.; Thiessen, D. B.

1996-01-01

372

PhET Simulation: Electric Field of Dreams  

NSDL National Science Digital Library

This page contains an interactive simulation of charges in an electric field. Users add or delete charges to see how they react to the field. The user can also activate an external field and control its magnitude and direction. For more advanced learners, the field can be set to varying levels of discreteness. This item is part of a larger collection of materials developed and maintained by the Physics Education Technology project (PhET) based on principles of physics education research.

2008-11-19

373

Numerical calculation and simulation analysis of electrical field characteristics for the electrical resistance tomography system  

Microsoft Academic Search

Sensitivity field in electrical resistance tomography system is affected by the distribution of multiphase medium, and the data of sensitivity distribution which are obtained by theoretical calculation can be used as prior experimental knowledge for image reconstruction, so it is necessary to analyze the distribution of the sensitivity field to decrease error of soft field and improve the quality of

Yanjun Zhang; Deyun Chen; Lili Wang

2009-01-01

374

Report on Non-Contact DC Electric Field Sensors  

SciTech Connect

This document reports on methods used to measure DC electrostatic fields in the range of 100 to 4000 V/m using a non-contact method. The project for which this report is written requires this capability. Non-contact measurements of DC fields is complicated by the effect of the accumulation of random space-charges near the sensors which interfere with the measurement of the field-of-interest and consequently, many forms of field measurements are either limited to AC measurements or use oscillating devices to create pseudo-AC fields. The intent of this document is to report on methods discussed in the literature for non-contact measurement of DC fields. Electric field meters report either the electric field expressed in volts per distance or the voltage measured with respect to a ground reference. Common commercial applications for measuring static (DC) electric fields include measurement of surface charge on materials near electronic equipment to prevent arcing which can destroy sensitive electronic components, measurement of the potential for lightning to strike buildings or other exposed assets, measurement of the electric fields under power lines to investigate potential health risks from exposure to EM fields and measurement of fields emanating from the brain for brain diagnostic purposes. Companies that make electric field sensors include Trek (Medina, NY), MKS Instruments, Boltek, Campbell Systems, Mission Instruments, Monroe Electronics, AlphaLab, Inc. and others. In addition to commercial vendors, there are research activities continuing in the MEMS and optical arenas to make compact devices using the principles applied to the larger commercial sensors.

Miles, R; Bond, T; Meyer, G

2009-06-16

375

Unusual structures of high-latitude stratospheric electric fields  

NASA Technical Reports Server (NTRS)

A possible explanation is given for three unusual stratospheric electric field structures reported by Madsen et al. (1983). It is suggested that stratospheric vertical electric-current structures may arise as extensions into the stratosphere of tropospheric currents generated by convective charge transport. A convective tropospheric current generator is presented which is capable of producing, at altitudes of about 30 km, the vertical electric field intensities of several volts per meter that are sometimes (although very rarely) observed by balloon-borne sensors (Madsen et al., 1983).

Dangelo, N.; Iversen, I. B.; Madsen, M. M.

1984-01-01

376

Reversible electric-field control of magnetization at oxide interfaces  

NASA Astrophysics Data System (ADS)

Electric-field control of magnetism has remained a major challenge which would greatly impact data storage technology. Although progress in this direction has been recently achieved, reversible magnetization switching by an electric field requires the assistance of a bias magnetic field. Here we take advantage of the novel electronic phenomena emerging at interfaces between correlated oxides and demonstrate reversible, voltage-driven magnetization switching without magnetic field. Sandwiching a non-superconducting cuprate between two manganese oxide layers, we find a novel form of magnetoelectric coupling arising from the orbital reconstruction at the interface between interfacial Mn spins and localized states in the CuO2 planes. This results in a ferromagnetic coupling between the manganite layers that can be controlled by a voltage. Consequently, magnetic tunnel junctions can be electrically toggled between two magnetization states, and the corresponding spin-dependent resistance states, in the absence of a magnetic field.

Cuellar, F. A.; Liu, Y. H.; Salafranca, J.; Nemes, N.; Iborra, E.; Sanchez-Santolino, G.; Varela, M.; Hernandez, M. Garcia; Freeland, J. W.; Zhernenkov, M.; Fitzsimmons, M. R.; Okamoto, S.; Pennycook, S. J.; Bibes, M.; Barthélémy, A.; Te Velthuis, S. G. E.; Sefrioui, Z.; Leon, C.; Santamaria, J.

2014-06-01

377

Helical multiferroics for electric field controlled quantum information processing  

NASA Astrophysics Data System (ADS)

Magnetoelectric coupling in helical multiferroics allows us to steer spin order with electric fields. Here we show theoretically that in a helical multiferroic chain quantum information processing as well as quantum phases are highly sensitive to electric (E) field. Applying E field, the quantum state transfer fidelity can be increased and made directionally dependent. We also show that E field transforms the spin-density-wave/nematic or multipolar phases of a frustrated ferromagnetic spin-1/2 chain in chiral phase with a strong magnetoelectric coupling. We find sharp reorganization of the entanglement spectrum as well as a large enhancement of fidelity susceptibility at Ising quantum phase transition from nematic to chiral states driven by electric field. These findings point to a tool for quantum information with low power consumption.

Azimi, M.; Chotorlishvili, L.; Mishra, S. K.; Greschner, S.; Vekua, T.; Berakdar, J.

2014-01-01

378

Reversible electric-field control of magnetization at oxide interfaces.  

PubMed

Electric-field control of magnetism has remained a major challenge which would greatly impact data storage technology. Although progress in this direction has been recently achieved, reversible magnetization switching by an electric field requires the assistance of a bias magnetic field. Here we take advantage of the novel electronic phenomena emerging at interfaces between correlated oxides and demonstrate reversible, voltage-driven magnetization switching without magnetic field. Sandwiching a non-superconducting cuprate between two manganese oxide layers, we find a novel form of magnetoelectric coupling arising from the orbital reconstruction at the interface between interfacial Mn spins and localized states in the CuO2 planes. This results in a ferromagnetic coupling between the manganite layers that can be controlled by a voltage. Consequently, magnetic tunnel junctions can be electrically toggled between two magnetization states, and the corresponding spin-dependent resistance states, in the absence of a magnetic field. PMID:24953219

Cuellar, F A; Liu, Y H; Salafranca, J; Nemes, N; Iborra, E; Sanchez-Santolino, G; Varela, M; Garcia Hernandez, M; Freeland, J W; Zhernenkov, M; Fitzsimmons, M R; Okamoto, S; Pennycook, S J; Bibes, M; Barthélémy, A; te Velthuis, S G E; Sefrioui, Z; Leon, C; Santamaria, J

2014-01-01

379

New Method for Solving Inductive Electric Fields in the Ionosphere  

NASA Astrophysics Data System (ADS)

We present a new method for calculating inductive electric fields in the ionosphere. It is well established that on large scales the ionospheric electric field is a potential field. This is understandable, since the temporal variations of large scale current systems are generally quite slow, in the timescales of several minutes, so inductive effects should be small. However, studies of Alfven wave reflection have indicated that in some situations inductive phenomena could well play a significant role in the reflection process, and thus modify the nature of ionosphere-magnetosphere coupling. The input to our calculation method are the time series of the potential part of the ionospheric electric field together with the Hall and Pedersen conductances. The output is the time series of the induced rotational part of the ionospheric electric field. The calculation method works in the time-domain and can be used with non-uniform, time-dependent conductances. In addition no particular symmetry requirements are imposed on the input potential electric field. The presented method makes use of special non-local vector basis functions called Cartesian Elementary Current Systems (CECS). This vector basis offers a convenient way of representing curl-free and divergence-free parts of 2-dimensional vector fields and makes it possible to solve the induction problem using simple linear algebra. The new calculation method is validated by comparing it with previously published results for Alfven wave reflection from uniformly conducting ionosphere.

Vanhamäki, H.

2005-12-01

380

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

PubMed Central

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, GROMOS, OPLS, etc. Thus the model resolves the outstanding problem of incompatibility.

Leontyev, Igor V.

2014-01-01

381

Limiting electric fields of HVDC overhead power lines.  

PubMed

As a consequence of the increased use of renewable energy and the now long distances between energy generation and consumption, in Europe, electric power transfer by high-voltage (HV) direct current (DC) overhead power lines gains increasing importance. Thousands of kilometers of them are going to be built within the next years. However, existing guidelines and regulations do not yet contain recommendations to limit static electric fields, which are one of the most important criteria for HVDC overhead power lines in terms of tower design, span width and ground clearance. Based on theoretical and experimental data, in this article, static electric fields associated with adverse health effects are analysed and various criteria are derived for limiting static electric field strengths. PMID:24573710

Leitgeb, N

2014-05-01

382

Electric field interactions in pairs of electric fish: modeling and mimicking naturalistic inputs.  

PubMed

Weakly electric fish acquire information about their surroundings by detecting and interpreting the spatial and temporal patterns of electric potential across their skin, caused by perturbations in a self-generated, oscillating electric field. Computational and experimental studies have focused on understanding the electric images due to simple, passive objects. The present study considers electric images of a conspecific fish. It is known that the electric fields of two fish interact to produce beats with spatially varying profiles of amplitude and phase. Such patterns have been shown to be critical for electrosensory-mediated behaviours, such as the jamming avoidance response, but they have yet to be well described. We have created a biophysically realistic model of a wave-type weakly electric fish by using a genetic algorithm to calibrate the parameters to the electric field of a real fish. We use the model to study a pair of fish and compute the electric images of one fish onto the other at three representative phases within a beat cycle. Analysis of the images reveals rostral/caudal and ipsilateral/contralateral patterns of amplitude and phase that have implications for localization of conspecifics (both position and orientation) and communication between conspecifics. We then show how the common stimulation paradigm used to mimic a conspecific during in vivo electrophysiological experiments, based on a transverse arrangement of two electrodes, can be improved in order to more accurately reflect the important qualitative features of naturalistic inputs, as revealed by our model. PMID:18491161

Kelly, Marc; Babineau, David; Longtin, André; Lewis, John E

2008-06-01

383

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

PubMed Central

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 N·s/m). Moreover, the arm of the subjects was not supported. A total of 46 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 is needed. PMID:23898319

Focke, Anne; Stockinger, Christian; Diepold, Christina; Taubert, Marco; Stein, Thorsten

2013-01-01

384

A reactive force field for aqueous-calcium carbonate systems.  

PubMed

A new reactive force field has been derived that allows the modelling of speciation in the aqueous-calcium carbonate system. Using the ReaxFF methodology, which has now been implemented in the program GULP, calcium has been simulated as a fixed charge di-cation species in both crystalline phases, such as calcite and aragonite, as well as in the solution phase. Excluding calcium from the charge equilibration process appears to have no adverse effects for the simulation of species relevant to the aqueous environment. Based on this model, the speciation of carbonic acid, bicarbonate and carbonate have been examined in microsolvated conditions, as well as bulk water. When immersed in a droplet of 98 water molecules and two hydronium ions, the carbonate ion is rapidly converted to bicarbonate, and ultimately carbonic acid, which is formed as the metastable cis-trans isomer under kinetic control. Both first principles and ReaxFF calculations exhibit the same behaviour, but the longer timescale accessible to the latter allows the diffusion of the carbonic acid to the surface of the water to be observed, where it is more stable at the interface. Calcium carbonate is also examined as ion pairs in solution for both CaCO(3)(0)((aq)) and CaHCO(3)(+)((aq)), in addition to the (1014) surface in contact with water. PMID:21850319

Gale, Julian D; Raiteri, Paolo; van Duin, Adri C T

2011-10-01

385

Coarse-grained force fields for molecular simulations.  

PubMed

Molecular dynamics (MD) simulations at the atomic scale are a powerful tool to study the structure and dynamics of model biological systems. However, because of their high computational cost, the time and length scales of atomistic simulations are limited. Biologically important processes, such as protein folding, ion channel gating, signal transduction, and membrane remodeling, are difficult to investigate using atomistic simulations. Coarse-graining reduces the computational cost of calculations by reducing the number of degrees of freedom in the model, allowing simulations of larger systems for longer times. In the first part of this chapter we review briefly some of the coarse-grained models available for proteins, focusing on the specific scope of each model. Then we describe in more detail the MARTINI coarse-grained force field, and we illustrate how to set up and run a simulation of a membrane protein using the Gromacs software package. We explain step-by-step the preparation of the protein and the membrane, the insertion of the protein in the membrane, the equilibration of the system, the simulation itself, and the analysis of the trajectory. PMID:25330962

Barnoud, Jonathan; Monticelli, Luca

2015-01-01

386

Force Field Independent Metal Parameters Using a Nonbonded Dummy Model  

PubMed Central

The cationic dummy atom approach provides a powerful nonbonded description for a range of alkaline-earth and transition-metal centers, capturing both structural and electrostatic effects. In this work we refine existing literature parameters for octahedrally coordinated Mn2+, Zn2+, Mg2+, and Ca2+, as well as providing new parameters for Ni2+, Co2+, and Fe2+. In all the cases, we are able to reproduce both M2+–O distances and experimental solvation free energies, which has not been achieved to date for transition metals using any other model. The parameters have also been tested using two different water models and show consistent performance. Therefore, our parameters are easily transferable to any force field that describes nonbonded interactions using Coulomb and Lennard-Jones potentials. Finally, we demonstrate the stability of our parameters in both the human and Escherichia coli variants of the enzyme glyoxalase I as showcase systems, as both enzymes are active with a range of transition metals. The parameters presented in this work provide a valuable resource for the molecular simulation community, as they extend the range of metal ions that can be studied using classical approaches, while also providing a starting point for subsequent parametrization of new metal centers. PMID:24670003

2014-01-01

387

Induced water condensation and bridge formation by electric fieldsin Atomic Force Microscopy  

SciTech Connect

We present an analytical model that explains how in humidenvironments the electric field near a sharp tip enhances the formationof water meniscii and bridges between tip and sample. The predictions ofthe model are compared with experimental measurements of the criticaldistance where the field strength causes bridge formation.

Sacha, G.M.; Verdaguer, A.; Salmeron, M.

2006-02-22

388

Experimental Investigation of Pool Boiling Heat Transfer Enhancement in Microgravity in the Presence of Electric Fields  

NASA Technical Reports Server (NTRS)

Boiling is an effective mode of heat transfer since high heat flux levels are possible driven by relatively small temperature differences. The high heat transfer coefficients associated with boiling have made the use of these processes increasingly attractive to aerospace engineering. Applications of this type include compact evaporators in the thermal control of aircraft avionics and spacecraft environments, heat pipes, and use of boiling to cool electronic equipment. In spite of its efficiency, cooling based on liquid-vapor phase change processes has not yet found wide application in aerospace engineering due to specific problems associated with the low gravity environment. After a heated surface has reached the superheat required for the initiation of nucleate boiling, bubbles will start forming at nucleation sites along the solid interface by evaporation of the liquid. Bubbles in contact with the wall will continue growing by this mechanism until they detach. In terrestrial conditions, bubble detachment is determined by the competition between body forces (e.g. buoyancy) and surface tension forces that act to anchor the bubble along the three phase contact line. For a given body force potential and a balance of tensions along the three phase contact line, bubbles must reach a critical size before the body force can cause them to detach from the wall. In a low gravity environment the critical bubble size for detachment is much larger than under terrestrial conditions, since buoyancy is a less effective means of bubble removal. Active techniques of heat transfer enhancement in single phase and phase change processes by utilizing electric fields have been the subject of intensive research during recent years. The field of electrohydrodynamics (EHD) deals with the interactions between electric fields, flow fields and temperature fields. Previous studies indicate that in terrestrial applications nucleate boiling heat transfer can be increased by a factor of 50 as compared to values obtained for the same system without electric fields. Imposing an external electric field holds the promise to improve pool boiling heat transfer in low gravity, since a phase separation force other than gravity is introduced. The goal of our research is to experimentally investigate the potential of EHD and the mechanisms responsible for EHD heat transfer enhancement in boiling in low gravity conditions.

Herman, Cila

1996-01-01

389

The stability properties of cylindrical force-free fields - Effect of an external potential field  

NASA Technical Reports Server (NTRS)

A large-scale potential field with an embedded smaller-scale force-free structure gradient x B equals alpha B is studied in cylindrical geometry. Cases in which alpha goes continuously from a constant value alpha 0 on the axis to zero at large r are considered. Such a choice of alpha (r) produces fields which are realistic (few field reversals) but not completely stable. The MHD-unstable wavenumber regime is found. Since the considered equilibrium field exhibits a certain amount of magnetic shear, resistive instabilities can arise. The growth rates of the tearing mode in the limited MHD-stable region of k space are calculated, showing time-scales much shorter than the resistive decay time.

Chiuderi, C.; Einaudi, G.; Ma, S. S.; Van Hoven, G.

1980-01-01

390

Critical Points of the Electric Field from a Collection of Point Charges  

SciTech Connect

The electric field around a molecule is generated by the charge distribution of its constituents: positively charged atomic nuclei, which are well approximated by point charges, and negatively charged electrons, whose probability density distribution can be computed from quantum mechanics. For the purposes of molecular mechanics or dynamics, the charge distribution is often approximated by a collection of point charges, with either a single partial charge at each atomic nucleus position, representing both the nucleus and the electrons near it, or as several different point charges per atom. The critical points in the electric field are useful in visualizing its geometrical and topological structure, and can help in understanding the forces and motion it induces on a charged ion or neutral dipole. Most visualization tools for vector fields use only samples of the field on the vertices of a regular grid, and some sort of interpolation, for example, trilinear, on the grid cells. There is less risk of missing or misinterpreting topological features if they can be derived directly from the analytic formula for the field, rather than from its samples. This work presents a method which is guaranteed to find all the critical points of the electric field from a finite set of point charges. To visualize the field topology, we have modified the saddle connector method to use the analytic formula for the field.

Max, N; Weinkauf, T

2007-02-16

391

Accurate Quartic Force Fields and Vibrational Frequencies for HCN and HNC  

NASA Technical Reports Server (NTRS)

The quartic force fields of HCN and HNC are determined using atomic natural orbital one-particle basis sets of spdf/spd and spdfg/spdf quality in conjunction with the CCSD(T) electron correlation method (singles and doubles coupled-cluster theory plus a perturbational estimate of the effects of connected triple excitations). The HCN force field is in good agreement with a recent experimentally derived force field and also with the force field recently computed by Wong and Bacskay. On the basis of the good agreement obtained for HCN, it is argued that the ab initio quartic force field for HNC is superior to a prior force field derived from experiment. The harmonic frequencies of HNC are predicted to be 3822 +/- 10,472 +/- 5, and 2051 +/-10/cm for omega1, omega2, and omega3, respectively; the experimentally derived values are above these values and fall outside the estimated uncertainties. Using the quartic force field, spectroscopic constants are predicted for HNC based on a vibrational second-order perturbation theory analysis. It is also asserted that the gas-phase fundamental v(sub 3) for HNC is slightly lower than the matrix isolation value. The range of validity of the quartic force fields is investigated by comparison of variational vibrational energies computed with the quartic force fields to those obtained from our recently reported global HCN/HNC potential energy surface and also to experimental data.

Lee, Timothy J.; Dateo, Christopher E.; Gazdy, Bela; Bowman, Joel M.

1993-01-01

392

Accurate Quartic Force Fields and Vibrational Frequencies for HCN and HNC  

NASA Technical Reports Server (NTRS)

The quartic force fields of HCN and HNC are determined using atomic natural orbital one-particle basis sets of spdf/spd and spdfg/spdf quality in conjunction with the CCSD(T) electron correlation method (singles and doubles coupled-cluster theory plus a perturbation estimate of the effects of connected triple excitations). The HCN force field is in good agreement with a recent experimentally derived force field and also with the force field recently computed by Wong and Bacskay. On the basis of the good agreement obtained for HCN, it is argued that the ab initio quartic force field for HNC is superior to a prior force field derived from experiment. The harmonic frequencies of HNC are predicted to be 3822 +/- 10, 472 +/- 5, and 2051 +/- 10 cm(exp -1) for omega(sub 1), omega(sub 2), and omega(sub 3), respectively; the experimentally derived values are above these values and fall outside the estimated uncertainties. Using the quartic force field, spectroscopic constants are predicted for HNC based on a vibrational second-order perturbation theory analysis. It is also asserted that the gas-phase fundamental nu(sub 3) for HNC is slightly lower than the matrix isolation value. The range of validity of the quartic force fields is investigated by comparison of variational vibrational energies computed with the quartic force fields to those obtained from our recently reported global HCN/HNC potential energy surface and also to experimental data.

Lee, Timothy J.; Dateo, Christopher E.; Gazdy, Bela; Bowman, Joel M.

1993-01-01

393

Using Gravitational Analogies to Introduce Elementary Electrical Field Theory Concepts  

ERIC Educational Resources Information Center

Since electrical field concepts are usually unfamiliar, abstract, and difficult to visualize, conceptual analogies from familiar gravitational phenomena are valuable for teaching. Such analogies emphasize the underlying continuity of field concepts in physics and support the spiral development of student understanding. We find the following four…

Saeli, Susan; MacIsaac, Dan

2007-01-01

394

How single conjugated polymer molecules respond to electric fields  

Microsoft Academic Search

Conjugated polymers find applications in a range of devices such as light-emitting diodes, field-effect transistors and solar cells. The elementary electronic response of these semiconductors to electric fields is understood in terms of nanoscale perturbations of charge density. We demonstrate a general breaking of spatial charge symmetry by considering the linear Stark effect in the emission of single chromophores on

Florian Schindler; John M. Lupton; Josef Müller; Jochen Feldmann; Ullrich Scherf

2006-01-01

395

Electric Field in a Double Layer and the Imparted Momentum  

Microsoft Academic Search

It is shown that the net momentum delivered by the large electric field inside a one-dimensional double layer is zero. This is demonstrated through an analysis of the momentum balance in the double layer at the boundary between the ionosphere and the aurora cavity. For the recently observed double layer in a current-free plasma expanding along a divergent magnetic field,

A. Fruchtman

2006-01-01

396

The behaviour of low conducting liquid in modulated electric field  

Microsoft Academic Search

The electrothermoconvective instability of a low conducting liquid in modulated electric field of a plane horizontal capacitor is investigated in the electrohydrodynamic (EHD) approximation for arbitrary field modulation frequencies and various shapes (harmonic and triangular). The charge formation is produced either due to dielectrophoresis or due to the nonhomogeneous conductivity. The Floquet theory is used to find the convection thresholds.

B. L. Smorodin

2002-01-01

397

Excitation by Local Electric Fields in the Aurora and Airglow  

Microsoft Academic Search

We have developed a method for accurate calculation of the distribution of electron energies in the ionosphere under the influence of an electric field. From this calculation we can predict rates of excitation of radiating states of N., O., and O as a function of the strength of a hypothetical applied field. We find that it is unreasonable to expect

L. R. Megill; N. P. Carleton

1964-01-01

398

Electric field effect on low temperature nanoscale oxidation  

NASA Astrophysics Data System (ADS)

The influence of electric fields on the low temperature oxidation of individual nanoscale tungsten wires was investigated. In the experiments at room temperature, the nanowires were biased as anode opposite to a macroscopic cathode and H 2O-vapor with a pressure of 10 -7-10 1 mbar was provided as oxygen source. Under the influence of an electric field, a dramatic change of the oxidation behavior is observed with the formation of several 10 nm thick oxide layers for electric fields exceeding a threshold. The chemical composition of the layers formed is determined with laser-assisted atom probe tomography to be slightly understoichiometric WO 3. After an initial period of fast growth, the oxidation rate later rapidly decreases to immeasurable low values. Evaluation of the electric field distribution in the vicinity of the sample by the finite element method reveals that oxide formation only proceeds if a critical field in the range of 0.7-5.0 V/nm, depending on the H 2O-pressure, is present. This critical field is attributed to a field-activated reaction of H 2O at the oxide-vapor interface. Besides for tungsten, field-induced oxidation is also observed for aluminum and p-doped silicon and thus apparently is a widely material independent phenomenon.

Nowak, Carsten; Schmitz, Guido; Kirchheim, Reiner

2010-04-01

399

Electric Field Control of Ferromagnetism and Magnetic Devices Using Multiferroics  

NASA Astrophysics Data System (ADS)

This dissertation presents a study of a heterostructure composed of room temperature magnetoelectric multiferroic BiFeO3 and ferromagnetic Co.90Fe.10, with specific interest in understanding the interfacial coupling mechanisms in this system and establishing the electric field control of a magnetization and spintronic devices. The field of spintronics has been plagued with the problem of a large energy dissipation as a consequence of the resistive losses that come during the writing of the magnetic state (i.e. reversing the magnetization direction). The primary aim of the work presented here is to investigate and understand a novel heterostructure and materials interface that can be demonstrated as a pathway to low energy spintronics. In this dissertation, I will address the specific aspects of multiferroicity, magnetoelectricity, and interface coupling that must be addressed in order to reverse a magnetization with an electric field. Furthermore, I will demonstrate the reversal of a magnetization with an electric field in single and multilayer magnetic devices. The primary advances made as a result of the work described herein are the use of epitaxial constraints to control the nanoscale domain structure of a multiferroic which is then correlated to the domain structure of the exchange coupled ferromagnet. Additionally, the magnetization direction of the ferromagnetic layer is controlled with only an applied electric field at both macroscopic and microscopic scales. Lastly, using this electric field control of ferromagnetism, the first demonstration of a magnetoelectric memory bit is presented.

Heron, John Thomas

400

The Effects of Altitude and Electrical Force on the Terminal Velocity of Hydrometeors  

Microsoft Academic Search

A formula has been developed for computing the terminal velocity V from a reference velocity V0 by use of an adjustment factor f=V\\/V0 for a change in altitude or electric force. The drag coefficients for bodies of regular geometry were analyzed, and found to be sufficiently similar that a single adjustment formula could be used for all hydrometeor shapes. Comparisons

K. V. Beard

1980-01-01

401

Electric field alignment of nanofibrillated cellulose (NFC) in silicone oil: impact on electrical properties.  

PubMed

This work aims to study how the magnitude, frequency, and duration of an AC electric field affect the orientation of two kinds of nanofibrillated cellulose (NFC) dispersed in silicone oil that differ by their surface charge density and aspect ratio. In both cases, the electric field alignment occurs in two steps: first, the NFC makes a gyratory motion oriented by the electric field; second, NFC interacts with itself to form chains parallel to the electric field lines. It was also observed that NFC chains become thicker and longer when the duration of application of the electric field is increased. In-situ dielectric properties have shown that the dielectric constant of the medium increases in comparison to the randomly dispersed NFC (when no electric field is applied). The optimal parameters of alignment were found to be 5000 Vpp/mm and 10 kHz for a duration of 20 min for both kinds of NFC. The highest increase in dielectric constant was achieved with NFC oxidized for 5 min (NFC-O-5 min) at the optimum conditions mentioned above. PMID:24848447

Kadimi, Amal; Benhamou, Karima; Ounaies, Zoubeida; Magnin, Albert; Dufresne, Alain; Kaddami, Hamid; Raihane, Mustapha

2014-06-25

402

Electroacoustic interaction in ferroelectric ceramics in a rotating electric field  

SciTech Connect

A boundary-value problem was solved for transverse acoustic waves by using conductive ferroelectric ceramic with nonstationary anisotropy induced by a rotating electric field. The wave numbers, ellipticities, and amplitudes of the acoustic field eigenwaves were calculated with allowance for the interaction between the ultrasound and the conduction electrons. The reflected and transmitted wave intensities were studied as a function of the specimen thickness in the case of resonance interaction, where the ultrasound frequency was equal to the frequency of the rotating electric field. The conditions of specimen thicknesses providing the minimal and maximal values of the wave intensities were established. 8 refs., 2 figs.

Semchenko, I.V.; Sevruk, B.B.; Khakhomov, S.A. [Frantsiask Skorina State Univ., Gomel (Belarus)

1994-12-31

403

Relativistic Bosons in Time-Harmonic Electric Fields  

NASA Astrophysics Data System (ADS)

In the present paper, we consider a bi-dimensional thin sample, placed in a strong harmonically oscillating electric field and a static magnetic induction, both directed along the normal to the sample's plane. The Klein-Gordon equation describing the relativistic bosons leads to a Mathieu's type equation for the temporal part of the wave functions. It follows that, for the electric field pulsation inside a computable range, depending on the external fields intensities, the amplitude functions are turning from oscillatory to exponentially growing modes. For ultra-relativistic particles, one can recover the periodic stationary amplitude behavior.

Buhucianu, Ovidiu; Dariescu, Marina-Aura; Dariescu, Ciprian

2012-02-01

404

Decay of H atoms excited in small electric fields  

NASA Astrophysics Data System (ADS)

The way that various H-emission intensities observed during proton auroras are influenced by the motion of fast-emitting H atoms across the earth's magnetic field is investigated. Branching-ratio data calculated by Rouze et al. (1986) for the decay of the 3l excited states of H are extended to higher principal quantum numbers, with particular emphasis on electric fields in the range of 1 or 2 V/cm. The results show that branching ratios depend quite strongly on electric-field magnitude, pointing to the need to exercise caution in measurements of H emissions and in application of the available data to other problems.

van Zyl, B.; van Zyl, B. K.; Westerveld, W. B.

1988-06-01

405

Pattern formation of charged particles in an electric field.  

PubMed

The application of an electric field to a suspension of charged particles can lead to the formation of patterns due to electrohydrodynamic instabilities which remain poorly understood. We elucidate this behavior by visualizing the dynamics of charged carbon black particles suspended in a nonpolar solvent in response to an electric field. As the particles are transported across a microfluidic channel, an instability occurs in which the initially uniform, rapidly advancing particle front develops fingers. Furthermore, when the direction of the applied field is repeatedly switched, the particles localize into a remarkably well-defined periodic pattern which reflects an interplay between the fingering instability and particle diffusion. PMID:25227689

Lin, Tina; Rubinstein, Shmuel M; Korchev, Andriy; Weitz, David A

2014-10-21

406

60-Hertz electric-field exposures in transmission line towers.  

PubMed

This article reports on an investigation of 60-Hz electric-field exposures of line workers in 230- to 765-kV transmission line towers. The exposures were based on computations of the unperturbed electric field along climbing routes and at work positions on the towers and on insulated ladders suspended in towers. Computed exposures were expressed in terms of the unperturbed electric field averaged over the body as stipulated by guidelines. For the realistic on-tower positions, the worker's posture, the uniformity of the field, and the field orientation differed from the guideline exposure scenario of standing erect in a vertical uniform field. These differences suggest the need for care in comparing electric-field exposures in towers with guideline limits. The unperturbed nonuniform fields at discrete points near steel and aluminum lattice structures were computed using Monte Carlo methods that model surface and spatial electric fields on and near standard geometrical elements. To estimate a whole-body average, fields were computed at 10 discrete points positioned on segments of an articulated stick-figure model of the human body. The whole-body average field was computed from fields at all the points weighted by the fraction of body volume that the corresponding segment represented. We estimated the average unperturbed electric field, the space potential at the torso, and the induced short-circuit current for 19 climbing and work positions in six towers. The maximum average electric-field exposure during climbing ranged from 10 kV/m for a 230-kV tower to 31 kV/m for a 765-kV tower. Exposures at on-tower work positions were lower than the estimated maximum exposures during climbing. For 500- and 765-kV towers, computed exposures while climbing and at some on-tower positions exceeded the limit of 20 kV/m given in the recently adopted IEEE Standard C95.6 2002. For lower voltage towers, exposures did not exceed 20 kV/m. PMID:16048846

Bracken, T; Senior, Russell; Dudman, Joseph

2005-09-01

407

Magnetic response of zigzag nanoribbons under electric fields.  

PubMed

Spin excitations in zigzag graphene nanoribbons are studied when the system is subjected to an electric field in the transversal direction. The magnetic properties and the lifetime of the spin excitations are systematically investigated and compared using a tight-binding electron-electron model treated by a mean-field Hubbard model. The effects of electron-hole asymmetry introduced by next-nearest neighbor hopping are also investigated. We show that by increasing the electric field, the antiferromagnetic correlations between the edges of the nanoribbons are decreased due to a reduction of the magnetic moments. The results show that the spin wave lifetime may be controlled by the intensity of the transversal electric field, indicating that zigzag nanoribbons may be considered great candidates for future spintronic applications. PMID:24806106

Culchac, F J; Capaz, Rodrigo B; Costa, A T; Latgé, A

2014-05-28

408

Understanding Rocket-Borne Electric Field Measurements in the Mesosphere  

NASA Astrophysics Data System (ADS)

Accurate in-situ vector electric field measurements are important for studying the dynamics of mesospheric phenomenon. Previous rocket-borne electric field experiments have reported large vertical electric fields (>400 V/m) in Polar Mesosphere Summer Echo (PMSE) and noctilucent cloud (NCL) layers. DROPPS 1 was launched into one of the strongest PMSE events of the 1999 season and Holzworth et al (GRL, 28, 1435, 2001) report large potential perturbations resulted from the rocket wake, while the environmental fields were small (<30 V/m). Here we present a detailed look at the DROPPS 1 rocket environment in the PMSE. Using measurements from the twelve independent high impedance Langmuir probes, we reconstruct the potential structure of the rocket wake. The electromagnetic wake was asymmetric, but similar to the expected aerodynamic wake, and potentials as high as 10 volts were seen on probes within one meter of the vehicle while it was in the PMSE region.

Marcoline, F. V.; Holzworth, R. H.

2001-12-01

409

Intense ionospheric electric and magnetic field pulses generated by lightning  

NASA Technical Reports Server (NTRS)

Electric and magnetic field measurements have been made in the ionosphere over an active thunderstorm and an optical detector onboard the same rocket yielded an excellent time base for the study of waves radiated into space from the discharge. In addition to detection of intense, but generally well understood whistler mode waves, very unusual electric and magnetic field pulses preceded the 1-10 kHz component of the radiated signal. These pulses lasted several ms and had a significant electric field component parallel to the magnetic field. No known propagating wave mode has this polarization nor a signal propagation velocity as high as those measured here. This study investigated and rejected an explanation based on an anomalous skin depth effect. Although only a hypothesis at this time, a more promising explanation involving the generation of the pulse via a nonlinear decay of whistler mode waves in the frequency range 10-80 kHz is being investigated.

Kelley, M. C.; Ding, J. G.; Holzworth, R. H.

1990-01-01

410

Ionization of N2 in radio-frequent electric field  

NASA Astrophysics Data System (ADS)

Rate coefficients for the electron impact ionization of the N2 molecule are calculated in non-equilibrium conditions in the presence of time-dependent electric field. A Monte Carlo simulation has been developed in order to determine non-equilibrium electron energy distribution functions within one period of the radio-frequent (RF) electric field. By using these distribution functions, rate coefficients for ionization of the N2 molecule have been obtained time resolved within one period in the frequency range from 13.56 up to 500 MHz, at effective reduced electric field values up to 700 Td. This work presents an insight into the temporal characteristics of ionizing process and provides the ionization rate coefficients that can be of great use for correct implementation in modeling RF plasma discharges. A behavior of rate coefficients under the influence of magnitude and frequency of the fields was studied separately revealing some interesting features in time dependence.

Popovi?, M. P.; Vojnovi?, M. M.; Aoneas, M. M.; Risti?, M. M.; Vi?i?, M. D.; Popari?, G. B.

2014-06-01

411

Experimental evidence that a high electric field acts as an efficient external parameter during crystalline growth of bulk oxide  

NASA Astrophysics Data System (ADS)

A new crystal growth device, in which a high static external electric voltage (up to 14 kV) is added to a floating zone method, is described. Our first experiments show that the application of such an electric field acts like an external force, introducing a pressure effect which is in direct competition with temperature in the solid/liquid thermodynamic equilibrium. High electric fields could therefore be an additional parameter in crystal growth, opening original routes to the synthesis of new materials.

Hicher, P.; Haumont, R.; Saint-Martin, R.; Mininger, X.; Berthet, P.; Revcolevschi, A.

2015-01-01

412

Current Status of the AMOEBA Polarizable Force Field Jay W. Ponder and Chuanjie Wu  

E-print Network

#12;Current Status of the AMOEBA Polarizable Force Field Jay W. Ponder and Chuanjie Wu Department that should allow more accurate description of molecular properties. The recently introduced AMOEBA force, it has only received relatively limited validation, which we address here. We show that the AMOEBA force

Ponder, Jay

413

ELF electric and magnetic fields: Pacific Northwest Laboratory studies  

SciTech Connect

Studies have been conducted at Battelle, Pacific Northwest Laboratory, to examine extremely-low-frequency (ELF) electromagnetic fields for possible biological effects in animals. Three areas of investigation are reported here: (1) studies on the nervous system, including behavior and neuroendocrine function, (2) experiments on cancer development in animals, and (3) measurements of currents and electric fields induced in animal models by exposure to external magnetic fields. In behavioral experiments, rats have been shown to be responsive to ELF electric field exposure. Furthermore, experimental data indicate that short-term memory may be affected in albino rats exposed to combined ELF and static magnetic fields. Neuroendocrine studies have been conducted to demonstrate an apparent stress-related response in rats exposed to 60-Hz electric fields. Nighttime pineal melatonin levels have been shown to be significantly depressed in animals exposed to either electric or magnetic fields. A number of animal tumor models are currently under investigation to examine possible relationships between ELF exposure and carcinogenesis. Finally, theoretical and experimental measurements have been performed which form the basis for animals and human exposure comparisons.

Anderson, L.E.

1992-06-01

414

III. Electric Field By a single point charge  

E-print Network

III. Electric Field By a single point charge: Extends from the charge and permeates all of space q Not a kind of matter Test Charge: q q very little charge, almost zero E=F/q, vector F EF=qE E =[kQq/r2]/q =k independent of test charge everywhere Liu UCD Phy1B 2012 #12;Visualization: Field LinesVisualization: Field

Yoo, S. J. Ben

415

Pigtailed electro-optic probes for vectorial electric field mapping  

Microsoft Academic Search

Electro-optic measurement (EO) constitutes an efficient technique to characterize electrical (E) fields : indeed, the Pockel's effect properties (linear modification of refractive indices of some non-centrosymetric crystals induced by the E-field)1 leads to a vectorial measurement. Thus, it allows to map the E-field vector and its transient evolution, either in free space or inside guiding structures. Pigtailed EO sensors are

Adriana Warzecha; Gwenaël Gaborit; Mickael Ruaro; Lionel Duvillaret; Jean-Louis Lassere

2010-01-01

416

Cavitation nanopore in the dielectric fluid in the inhomogeneous, pulsed electric fields  

E-print Network

This paper discusses the nanopores emerging and developing in a liquid dielectric under the action of the ponderomotive electrostrictive forces in a nonuniform electric field. It is shown that the gradient of the electric field in the vicinity of the rupture (cavitation nanopore) substantially increases and determines whether the rupture grows or collapses. The cavitation rupture in the liquid (nanopore) tends to stretch along the lines of the original field. The mechanism of the breakdown associated with the generation of secondary ruptures in the vicinity of the poles of the nanopore is proposed. The estimations of the extension time for nanopore in water and oil (polar and nonpolar liquids, respectively) are presented. A new mechanism of nano- and subnanosecond breakdown in the insulating (transformer) oil that can be realized in the vicinity of water microdroplets in modern nanosecond high-voltage devices is considered

M. Pekker; M. N. Shneider

2014-12-19

417

Cavitation nanopore in the dielectric fluid in the inhomogeneous, pulsed electric fields  

E-print Network

This paper discusses the nanopores emerging and developing in a liquid dielectric under the action of the ponderomotive electrostrictive forces in a nonuniform electric field. It is shown that the gradient of the electric field in the vicinity of the rupture (cavitation nanopore) substantially increases and determines whether the rupture grows or collapses. The cavitation rupture in the liquid (nanopore) tends to stretch along the lines of the original field. The mechanism of the breakdown associated with the generation of secondary ruptures in the vicinity of the poles of the nanopore is proposed. The estimations of the extension time for nanopore in water and oil (polar and nonpolar liquids, respectively) are presented. A new mechanism of nano- and subnanosecond breakdown in the insulating (transformer) oil that can be realized in the vicinity of water microdroplets in modern nanosecond high-voltage devices is considered

Pekker, M

2014-01-01

418

Electric Field Detection in Sawfish and Shovelnose Rays  

PubMed Central

In the aquatic environment, living organisms emit weak dipole electric fields, which spread in the surrounding water. Elasmobranchs detect these dipole electric fields with their highly sensitive electroreceptors, the ampullae of Lorenzini. Freshwater sawfish, Pristis microdon, and two species of shovelnose rays, Glaucostegus typus and Aptychotrema rostrata were tested for their reactions towards weak artificial electric dipole fields. The comparison of sawfishes and shovelnose rays sheds light on the evolution and function of the elongated rostrum (‘saw’) of sawfish, as both groups evolved from a shovelnose ray-like ancestor. Electric stimuli were presented both on the substrate (to mimic benthic prey) and suspended in the water column (to mimic free-swimming prey). Analysis of around 480 behavioural sequences shows that all three species are highly sensitive towards weak electric dipole fields, and initiate behavioural responses at median field strengths between 5.15 and 79.6 nVcm?1. The response behaviours used by sawfish and shovelnose rays depended on the location of the dipoles. The elongation of the sawfish’s rostrum clearly expanded their electroreceptive search area into the water column and enables them to target free-swimming prey. PMID:22848543

Wueringer, Barbara E.; Jnr, Lyle Squire; Kajiura, Stephen M.; Tibbetts, Ian R.; Hart, Nathan S.; Collin, Shaun P.

2012-01-01

419

Probing electric field control of magnetism using ferromagnetic resonance.  

PubMed

Exchange coupled CoFe/BiFeO3 thin-film heterostructures show great promise for power-efficient electric field-induced 180° magnetization switching. However, the coupling mechanism and precise qualification of the exchange coupling in CoFe/BiFeO3 heterostructures have been elusive. Here we show direct evidence for electric field control of the magnetic state in exchange coupled CoFe/BiFeO3 through electric field-dependent ferromagnetic resonance spectroscopy and nanoscale spatially resolved magnetic imaging. Scanning electron microscopy with polarization analysis images reveal the coupling of the magnetization in the CoFe layer to the canted moment in the BiFeO3 layer. Electric field-dependent ferromagnetic resonance measurements quantify the exchange coupling strength and reveal that the CoFe magnetization is directly and reversibly modulated by the applied electric field through a ~180° switching of the canted moment in BiFeO3. This constitutes an important step towards robust repeatable and non-volatile voltage-induced 180° magnetization switching in thin-film multiferroic heterostructures and tunable RF/microwave devices. PMID:25631924

Zhou, Ziyao; Trassin, Morgan; Gao, Ya; Gao, Yuan; Qiu, Diana; Ashraf, Khalid; Nan, Tianxiang; Yang, Xi; Bowden, S R; Pierce, D T; Stiles, M D; Unguris, J; Liu, Ming; Howe, Brandon M; Brown, Gail J; Salahuddin, S; Ramesh, R; Sun, Nian X

2015-01-01

420

Modeling electron transport in the presence of electric and magnetic fields.  

SciTech Connect

This report describes the theoretical background on modeling electron transport in the presence of electric and magnetic fields by incorporating the effects of the Lorentz force on electron motion into the Boltzmann transport equation. Electromagnetic fields alter the electron energy and trajectory continuously, and these effects can be characterized mathematically by differential operators in terms of electron energy and direction. Numerical solution techniques, based on the discrete-ordinates and finite-element methods, are developed and implemented in an existing radiation transport code, SCEPTRE.

Fan, Wesley C.; Drumm, Clifton Russell; Pautz, Shawn D.; Turner, C. David

2013-09-01

421

Numerical calculation and simulation analysis of electrical field characteristics for the electrical resistance tomography system  

NASA Astrophysics Data System (ADS)

Sensitivity field in electrical resistance tomography system is affected by the distribution of multiphase medium, and the data of sensitivity distribution which are obtained by theoretical calculation can be used as prior experimental knowledge for image reconstruction, so it is necessary to analyze the distribution of the sensitivity field to decrease error of soft field and improve the quality of the image reconstruction. In this paper at the basis of analyzing the principle of electrical resistance tomography system, the mathematical model of sensitivity field is built by utilizing finite element method. Through study field with disperse phase, the factors affecting the distribution of the sensitivity field and rules are analyzed, the calculation of sensitivity distribution and visualized simulation are achieved The experiments show that the finite element model is right, the sensitivity field proposed is in accordance with the practice and the computation velocity is about 10seconds, which provides the basis for related image reconstruction algorithms.

Zhang, Yanjun; Chen, Deyun; Wang, Lili

2009-07-01

422

Intraoral conversion of occlusal force to electricity and magnetism by biting of piezoelectric elements.  

PubMed

Very weak electrical, magnetic and ultrasound signal stimulations are known to promote the formation, metabolism, restoration and stability of bone and surrounding tissues after treatment and operations. We have therefore investigated the possibility of intraoral generation of electricity and magnetism by occlusal force in an in vitro study. Biting bimorph piezoelectric elements with lead zirconate titanate (PZT) using dental models generated appropriate magnetism for bone formation, i. e. 0.5-0.6 gauss, and lower electric currents and higher voltages, i. e. 2.0-6.0 ?A at 10-22 V (appropriate levels are 30 ?A and 1.25 V), as observed by a universal testing machine. The electric currents and voltages could be changed using amplifier circuits. These results show that intraoral generation of electricity and magnetism is possible and could provide post-operative stabilization and activation of treated areas of bone and the surrounding tissues directly and/or indirectly by electrical, magnetic and ultrasound stimulation, which could accelerate healing. PMID:23207207

Kameda, Takashi; Ohkuma, Kazuo; Sano, Natsuki; Ogura, Hideo; Terada, Kazuto

2012-01-01

423

Electric field enhanced hydrogen storage on polarizable materials substrates  

PubMed Central

Using density functional theory, we show that an applied electric field can substantially improve the hydrogen storage properties of polarizable substrates. This new concept is demonstrated by adsorbing a layer of hydrogen molecules on a number of nanomaterials. When one layer of H2 molecules is adsorbed on a BN sheet, the binding energy per H2 molecule increases from 0.03 eV/H2 in the field-free case to 0.14 eV/H2 in the presence of an electric field of 0.045 a.u. The corresponding gravimetric density of 7.5 wt% is consistent with the 6 wt% system target set by Department of Energy for 2010. The strength of the electric field can be reduced if the substrate is more polarizable. For example, a hydrogen adsorption energy of 0.14 eV/H2 can be achieved by applying an electric field of 0.03 a.u. on an AlN substrate, 0.006 a.u. on a silsesquioxane molecule, and 0.007 a.u. on a silsesquioxane sheet. Thus, application of an electric field to a polarizable substrate provides a novel way to store hydrogen; once the applied electric field is removed, the stored H2 molecules can be easily released, thus making storage reversible with fast kinetics. In addition, we show that materials with rich low-coordinated nonmetal anions are highly polarizable and can serve as a guide in the design of new hydrogen storage materials. PMID:20133647

Zhou, J.; Wang, Q.; Sun, Q.; Jena, P.; Chen, X. S.

2010-01-01

424

Electric Field Effects on the Thermodynamics of Multiferroic Chains  

Microsoft Academic Search

The thermodynamic properties of the helical spins with a magnetoelectric coupling are studied theoretically using Monte Carlo\\u000a simulations. It is shown that the spin–spin correlations are affected by thermal fluctuations and by an electric field. Results\\u000a for the temperature-dependence of the ferroelectric polarization and for the electric susceptibility are presented and analyzed\\u000a with a focus on the multiferroic phase transition.

Chenglong Jia; Jamal Berakdar

425

A bacterial spore model of pulsed electric fields on spore morphology change revealed by simulation and SEM.  

PubMed

A two-layered spore model was proposed to analyze morphological change of bacterial spores subjected under pulsed electric fields. The outer layer, i.e. spore coat, was defined by Mooney-Rivlin hyper-elastic material model. The inner layer, i.e. peptidoglycan and spore core, was modeled by applying additional adhesion forces. The effect of pulsed electric fields on surface displacement was simulated in COMSOL Multiphysics and verified by SEM. The electro-mechanical theory, considering spore coat as a capacitor, was used to explain concavity; and the thin viscoelastic film theory, considering membrane bilayer as fluctuating surfaces, was used to explain leakage forming. Mutual interaction of external electric fields, charged spores, adhesion forces and ions movement were all predicted to contribute to concavity and leakage. PMID:25571563

Xing Qiu; Yin Tung Lee; Pun To Yung

2014-08-01

426

Lateral Reorganization of Fluid Lipid Membranes in Response to the Electric Field Produced by a Buried Charge  

E-print Network

Lateral Reorganization of Fluid Lipid Membranes in Response to the Electric Field Produced A thermodynamic model describing multicomponent fluid membranes under the influence of lateral forces due dielectric environment of a membrane, for example, during electron transfer. The model includes molecular

Boxer, Steven G.

427

The lift forces acting on a submarine composite pipeline in a wave-current coexisting field  

SciTech Connect

The composite pipeline is defined as a main big pipe composed with one or several small pipes. The flow behavior around a submarine composite pipeline is more complicated than that around a single submarine pipeline. A series model test of composite pipelines in a wave-current coexisting field was conducted by the authors. Both in-line and lift forces were measured, and the resultant forces are also analyzed. The results of lift forces and resultant forces are reported in this paper. It is found that the lift force coefficients for composite pipelines are well related to the KC number. The lift force coefficients in an irregular wave-current coexisting field are smaller than those in regular wave-current coexisting field. The frequency of lift force is usually the twice or higher than the wave frequency. It is indicated by the authors` test that the resultant forces are larger than in-line forces (horizontal forces) about 10 to 20 percent. The effect of water depth was analyzed. Finally, the relationship between lift force coefficient C{sub l} and KC number, the statistical characteristics of lift and resultant forces, are given in this paper, which may be useful for practical engineering application.

Li, Y.C.; Zhang, N.C. [Dalian Univ. of Technology (China). Dept. of Civil Engineering

1994-12-31

428

Electric currents and voltage drops along auroral field lines  

NASA Technical Reports Server (NTRS)

An assessment is presented of the current state of knowledge concerning Birkeland currents and the parallel electric field, with discussions focusing on the Birkeland primary region 1 sheets, the region 2 sheets which parallel them and appear to close in the partial ring current, the cusp currents (which may be correlated with the interplanetary B(y) component), and the Harang filament. The energy required by the parallel electric field and the associated particle acceleration processes appears to be derived from the Birkeland currents, for which evidence is adduced from particles, inverted V spectra, rising ion beams and expanded loss cones. Conics may on the other hand signify acceleration by electrostatic ion cyclotron waves associated with beams accelerated by the parallel electric field.

Stern, D. P.

1983-01-01

429

Electric currents and voltage drops along auroral field lines  

NASA Astrophysics Data System (ADS)

An assessment is presented of the current state of knowledge concerning Birkeland currents and the parallel electric field, with discussions focusing on the Birkeland primary region 1 sheets, the region 2 sheets which parallel them and appear to close in the partial ring current, the cusp currents (which may be correlated with the interplanetary B(y) component), and the Harang filament. The energy required by the parallel electric field and the associated particle acceleration processes appears to be derived from the Birkeland currents, for which evidence is adduced from particles, inverted V spectra, rising ion beams and expanded loss cones. Conics may on the other hand signify acceleration by electrostatic ion cyclotron waves associated with beams accelerated by the parallel electric field.

Stern, D. P.

1983-03-01

430

Calculation and measurement of electric field under HVDC transmission lines  

NASA Astrophysics Data System (ADS)

A stable corona discharge in a two conductors-to-plane configuration is analysed in this paper. A linear biased probe, without end-effect, has been adapted to a linear geometry and is used for the first time to measure the ground-plane current density and electric field during the bipolar corona. The values of the electric field and the current density are maximum under the two coronating conductors and decrease when moving away from them. Furthermore, a hybrid technique is developed to obtain a general solution of the governing equations of the coupled space-charge and electric field problem. The technique is to use the finite-element method (FEM) to solve Poisson's equation, and the method of characteristic (MOC) to find the charge density from a current-continuity relation. The model avoids resorting to the Deutsch assumption. The computed values are in good agreement with experimental data.

Kasdi, A.; Zebboudj, Y.; Yala, H.

2007-03-01

431

Exactly calculable field components of electric dipoles in planar boundary  

NASA Astrophysics Data System (ADS)

The Sommerfeld integrals for the electromagnetic fields in the planar boundary between air and a homogeneous, isotropic medium, due to a horizontal and a vertical electric dipole each lying along the interface, are examined in detail. In the case of the horizontal dipole, the tangential electric field is given in terms of series that involve confluent hypergeometric functions, namely, the Fresnel and exponential integrals. A similar exposition is presented for the magnetic and vertical electric fields of the vertical dipole. When the index of refraction of the adjacent space is of a sufficiently large magnitude, the derived series converge rapidly and uniformly with the distance from the source. Specifically, their rates of convergence are shown to be independent of distance. It is pointed out that the corresponding formulas of King et al. are valid down to any distance close to the source, where they smoothly connect to known "quasi-static" approximations.

Margetis, Dionisios; Wu, Tai Tsun

2001-02-01

432

Method of using an electric field controlled emulsion phase contactor  

DOEpatents

A system is described for contacting liquid phases comprising a column for transporting a liquid phase contacting system, the column having upper and lower regions. The upper region has a nozzle for introducing a dispersed phase and means for applying thereto a vertically oriented high intensity pulsed electric field. This electric field allows improved flow rates while shattering the dispersed phase into many micro-droplets upon exiting the nozzle to form a dispersion within a continuous phase. The lower region employs means for applying to the dispersed phase a horizontally oriented high intensity pulsed electric field so that the dispersed phase undergoes continuous coalescence and redispersion while being urged from side to side as it progresses through the system, increasing greatly the mass transfer opportunity. 5 figures.

Scott, T.C.

1993-11-16

433

Dielectronic recombination as a function of electric field strength  

NASA Technical Reports Server (NTRS)

Dielectronic recombination (DR) is the dominant recombination mechanism at coronal temperatures and densities. We present a procedure for calculating DR rate coefficients as a function of electric field strength and apply this method to carbon ions. We focus on the competing effects of enhancement by plasma microfields and rate decrease through collisional excitation and ionization. We find that, in the case of C(3+), a significant rate enhancement results, leading to a reinterpretation of C IV emission-line in