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1

Contrasting studentsâ understanding of electric field and electric force  

NSDL National Science Digital Library

Students may have greater difficulties in understanding electric interactions because they have less day to day experience with them than with mechanics. There may also be differences in understanding of different electric concepts like electric force and field. This study presents the results of studentsâ responses to two sequences of superposition principle isomorphic questions in which the only difference was that in one of the sequences, the electric force was used and in the other, the electric field. We administered one of the sequences to 249 students at a large private Mexican university after covering electrostatics in an Electricity and Magnetism class. The studentsâ answers, reasoning and drawings were analyzed. We found that students who took the force sequence were better able to correctly answer the questions using the superposition principle than those students with the field sequence. The analysis of the studentsâ reasoning and drawings helped us to examine their understanding of electric field and the use of electric field lines.

Garza, Alejandro; Zavala, Genaro

2014-04-11

2

Contrasting students' understanding of electric field and electric force  

NASA Astrophysics Data System (ADS)

Students may have greater difficulties in understanding electric interactions because they have less day to day experience with them than with mechanics. There may also be differences in understanding of different electric concepts like electric force and field. This study presents the results of students' responses to two sequences of superposition principle isomorphic questions in which the only difference was that in one of the sequences, the electric force was used and in the other, the electric field. We administered one of the sequences to 249 students at a large private Mexican university after covering electrostatics in an Electricity and Magnetism class. The students' answers, reasoning and drawings were analyzed. We found that students who took the force sequence were better able to correctly answer the questions using the superposition principle than those students with the field sequence. The analysis of the students' reasoning and drawings helped us to examine their understanding of electric field and the use of electric field lines.

Garza, Alejandro; Zavala, Genaro

2013-01-01

3

Context Rich Problems Online Archives: Electric Field and Electric Force  

NSDL National Science Digital Library

This page provides a set of context-rich physics problems relating to electric forces and fields. Each context-rich problem is based on a real-world situation, and includes both information that is relevant to solving the problem and extraneous information. Strategies for problem solving are not explicitly provided. Each problem is formulated so it is too difficult for one student to solve alone, yet not too difficult for a group to master. This resource is based on the research results of the Minnesota Physics Education Research group. See Related items on this page for a link to the full collection.

Group, University O.; Heller, Kenneth; Heller, Patricia

2008-09-29

4

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

NASA Astrophysics Data System (ADS)

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.

Geng, Yanan; Wu, Weida

2014-05-01

5

Characteristics of convection of an electrically conducting liquid in an additional external force field  

SciTech Connect

The authors analyze, theoretically and experimentally, the combined effects of gravitational and electric fields along with inertial forces on convective heat and mass transfer in liquid metals undergoing vortex flow in the presence of constant magnetic fields. The experimental data are derived for a eutectic indium-gallium-tin alloy. The flow model incorporates electrical conductivity and Hartmann number as well as other properties.

Mikel'son, A.E.; Karklin, Ya.Kh.

1987-07-01

6

Electrostatic Force Microscopy Study of the Electric Field Distribution in Semiconductor Laser Diodes Under Applied Biases.  

National Technical Information Service (NTIS)

In conclusion we present a new and direct electrostatic force microscopy method to resolve the electric field and capacitance distributions in laser diodes. Using this method we have investigated the fine structure of the electric field in AlGaAs/GaAs and...

A. Ankudinov A. Titkov D. Livshiz E. Kotelnikov V. Evtikhiev

2001-01-01

7

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

8

Forces and torque on a pair of uncharged conducting spheres in an external electric field  

NASA Astrophysics Data System (ADS)

Exact results are given for the forces acting on two conducting spheres in an applied electric field E. The torque acting on the two-sphere system is proportional to the difference between the longitudinal and transverse polarizabilities: ? =(??-?t)E sin? cos? (? is the angle between the applied field and the line-of-centers of the spheres). The forces acting on the two spheres are equal and opposite, and given by the derivatives of ?? and ?t with respect to the sphere separation. Simple analytic forms for the torque and forces are found at small and at large separations. At all separations, the torque always acts to align the line of centers of the spheres with the external field. Possible applications are to colloidal suspensions of spherical conducting particles.

Lekner, John

2013-12-01

9

DOE Task Force meeting on Electrical Breakdown of Insulating Ceramics in a High Radiation Field  

SciTech Connect

This volume contains the abstracts and presentation material from the Research Assistance Task Force Meeting Electrical Breakdown of Insulating Ceramics in a High-Radiation Field.'' The meeting was jointly sponsored by the Office of Basic Energy Sciences and the Office of Fusion Energy of the US Department of Energy in Vail, Colorado, May 28--June 1, 1991. The 26 participants represented expertise in fusion, radiation damage, electrical breakdown, ceramics, and semiconductor and electronic structures. These participants came from universities, industries, national laboratories, and government. The attendees represented eight nations. The Task Force meeting was organized in response to the recent discovery that a combination of temperature, electric field, and radiation for an extended period of time has an unexplained adverse effect in ceramics, termed radiation-enhanced electrical degradation (REED). REED occurs after an incubation period and continues to accelerate with irradiation until the ceramics can no longer be regarded as insulators. It appears that REED is irreversible and the ceramic insulators cannot be readily annealed or otherwise repaired for future services. This effect poses a serious threat for fusion reactors, which require electrical insulators in diagnostic devices, in radio frequency and neutral beam systems, and in magnetic assemblies. The problem of selecting suitable electrical insulating materials in thus far more serious than previously anticipated.

Green, P.H. (comp.) [comp.

1991-08-01

10

Direct actuation of cantilever in aqueous solutions by electrostatic force using high-frequency electric fields  

NASA Astrophysics Data System (ADS)

We recently developed a method to directly actuate a cantilever in aqueous solutions by electrostatic force [K.-I. Umeda et al., Appl. Phys. Express 3, 065205 (2010)]. However, the cantilever was actuated by surface stress in a low frequency regime. We solved this problem by applying amplitude-modulated high-frequency electric fields, which actuates the cantilever solely by electrostatic force. The time variations of the self-oscillation frequency of a cantilever and the Au(111) surface images by frequency-modulation atomic force microscopy using acoustic, photothermal, and the improved electrostatic actuation methods were compared, which demonstrates the advantages of the last method such as stability and simplicity in instrumentation.

Umeda, Ken-ichi; Kobayashi, Kei; Matsushige, Kazumi; Yamada, Hirofumi

2012-09-01

11

Forces at the nuclei of a molecule in the presence of non-uniform electric field  

Microsoft Academic Search

The interaction Hamiltonian within the Bloch gauge for the potentials of the electric field has been used to define electric multipole moment operators. Perturbation theory has been applied to evaluate the induced electronic moments and electric field at the nuclei in the presence of spatially non-uniform electric fields of high intensity. Multipole nuclear electric shielding tensors have been defined to

P. Lazzeretti; A. Courtot; M. Defranceschi; G. Berthier

1997-01-01

12

Molecular Tweezers: Using the Electric Field in a Synthetic Nanopore to Disrupt Biomolecular Binding Forces  

NASA Astrophysics Data System (ADS)

The forces binding proteins to DNA in an aqueous solution are vital to biology, but inadequately understood. In particular, restriction enzymes like EcoRI are extraordinarily sequence-specific and yet the complex with DNA is very stable. To stringently test these forces, we use the electric field inside a synthetic nanometer-diameter pore in a thin membrane to pull on double-stranded DNA bound to EcoRI and BamHI, introducing a shear between the enzyme and their respective cognate sites in DNA. We observe a sharp threshold near 1nN in the force required to disrupt the binding in the complex, which is in stark contrast with previous measurements of the force (10pN) accomplished by unzipping the DNA molecule at a constant loading rates (1nN/sec). This force, acting over a distance corresponding to the separation between bases, coincidentally corresponds to the free energy of formation for the EcoRI-DNA complex. Using molecular dynamics, we interpret the measurements and elucidate the binding with atomic precision.

Timp, Gregory

2007-03-01

13

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

14

Analytical solutions of ac electrokinetics in interdigitated electrode arrays: Electric field, dielectrophoretic and traveling-wave dielectrophoretic forces  

NASA Astrophysics Data System (ADS)

Analysis of the movement of particles in a nonuniform field requires accurate knowledge of the electric field distribution in the system. This paper describes a method for analytically solving the electric field distribution above interdigitated electrode arrays used for dielectrophoresis (DEP) and traveling wave dielectrophoresis (twDEP), using the Schwarz-Christoffel mapping method. The electric field solutions are used to calculate the dielectrophoretic force in both cases, and the traveling wave dielectrophoretic force and the electrorotational torque for the twDEP case. This method requires no approximations and can take into account the Neumann boundary condition used to represent an insulating lid and lower substrate. The analytical results of the electric field distributions are validated for different geometries by comparison with numerical simulations using the finite element method.

Sun, Tao; Morgan, Hywel; Green, Nicolas G.

2007-10-01

15

Analytical formulation of electric field and dielectrophoretic force for moving dielectrophoresis using Fourier series  

Microsoft Academic Search

Electrokinetics manipulation and separation of living cells employing microfluidic devices require good knowledge of the strength\\u000a and distribution of electric field in such devices. AC dielectrophoresis is performed by generating non-uniform electric field\\u000a using microsize electrodes. Among the several applications of dielectrophoretic phenomenon, this present study considers the\\u000a recently introduced phenomenon of moving dielectrophoresis. An analytical solution using Fourier series

Anas AlazzamDacian; Dacian Roman; Vahé Nerguizian; Ion Stiharu; Rama Bhat

2010-01-01

16

Electric-field-induced forces between two surfaces filled with an insulating liquid: the role of adsorbed water  

NASA Astrophysics Data System (ADS)

A systematic study of the electric-field-induced forces between a solid glass sphere and a flat gold-plated substrate filled with an insulating liquid has been carried out. Using atomic force microscopy, we measure the electrostatic force f(s, V) between the sphere and substrate as a function of the surface separation s and applied voltage V. The measured f(s, V) is found to be well described by an equation for a conducting sphere. Further force measurements for the "wet" porous glass spheres filled with an aqueous solution of urea and the dried porous glass spheres filled with (dry) air suggest that there is a water layer of a few nanometers in thickness adsorbed on the hydrophilic glass surface under ambient conditions. This adsorbed water layer is more conductive than the dielectric core of the glass sphere, making the sphere surface to be at a potential close to that of the cantilever electrode. As a result, the electric field is strongly concentrated in the gap region between the glass sphere and gold-plate substrate and thus their electrostatic attraction is enhanced. This surface conductivity effect is further supported by the thermal gravimetric analysis (TGA) and force response measurements to a time-dependent electric field. The experiment clearly demonstrates that the adsorption of a conductive water layer on a hydrophilic surface plays a dominant role in determining the electrostatic interaction between the dielectric sphere and substrate.

Wang, Yong Jian; Xu, Zuli; Sheng, Ping; Tong, Penger

2014-06-01

17

Deflection and the Dielectrophoresis Force of Multi-Wall Carbon Nanotube/Gelatin Hydrogel Composites under Electric Field  

NASA Astrophysics Data System (ADS)

The Multi-wall carbon nanotubes (MWNT) /gelatin hydrogel composites are prepared by the dispersion of MWNT into the gelatin aqueous solution with sodium dodecyl sulfate (SDS) and by the solvent casting. The effect of electric field strength on the deflection distance and the dielectrophoresis force of the MWNT/gelatin hydrogel composites are investigated. The dielectrophoresis force, using a vertical cantilever fixture, is determined by measuring the deflection of the specimen under applied electric field strengths between 0 and 600 V/mm. The dielectrophoresis force of the MWNT/gelatin hydrogel composites and pure gelatin hydrogel increase monotonically with electric field strength. The deflection suggests the attractive interaction between the anode and the polarlized caboxyl group, in which the gelatin structure possesses negative charges. Surprisingly, the 1vol%MWNT/gelatin hydrogel composite has a smaller deflection and response under the applied electric field than those of the 0.1vol%MWNT/gelatin hydrogel composite and the pure gelatin hydrogel, due to the diminishing particle polarization by agglomeration.

Tungkavet, Thawatchai; Sirivat, Anuvat

2013-03-01

18

Effects of electrostatic force on piezoelectric materials under high electric field: Impact on GaN-based nanoscale structures  

NASA Astrophysics Data System (ADS)

The determination of the electromechanical properties of materials for a parallel-plate capacitor structure is affected by the electrostatic force between their electrodes. The corrections resulting from this electric-field-induced stress are usually assumed to be linked to the quadratic dependence of the strain on the electric field (electrostriction). Here we show by calculations based on thermodynamic grounds for this simple structure that the effect of the electrostatic force on piezoelectric materials can lead to both quadratic and linear corrections through the combination of the piezoelectric coupling and spontaneous polarization. The case of GaN-based capacitor nanoscale structures is presented taking into account the boundary conditions imposed as well as the effect of geometry. The results in this example point to corrections in the piezoelectric and electrostrictive coefficients higher than 0.3 pm V-1 and 2.6×10-22 m2 V-2, respectively.

Rivera, Carlos

2011-01-01

19

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

20

The action of a non-uniform electric field upon lossy dielectric systems-ponderomotive force on a dielectric sphere in the field of a point charge  

Microsoft Academic Search

The use of the Maxwell stress tensor method is shown to calculate forces and torques acting in non-homogeneous dielectric systems under the influence of non-uniform electric fields in the case of lossy dielectrics without confining the treatment to the dipole approximation, as usually made. The method is applied to the particular case of a lossy dielectric sphere subject to the

E. R. Mognaschi; A. Savini

1983-01-01

21

Tuning the instability in static mode atomic force spectroscopy as obtained in an AFM by applying an electric field between the tip and the substrate.  

PubMed

We have investigated experimentally the role of cantilever instabilities in determination of the static mode force-distance curves in presence of a dc electric field. The electric field has been applied between the tip and the sample in an atomic force microscope working in ultra-high vacuum. We have shown how an electric field modifies the observed force (or cantilever deflection)-vs-distance curves, commonly referred to as the static mode force spectroscopy curves, taken using an atomic force microscope. The electric field induced instabilities shift the jump-into-contact and jump-off-contact points and also the deflection at these instability points. We explained the experimental results using a model of the tip-sample interaction and quantitatively established a relation between the observed static mode force spectroscopy curves and the applied electric field which modifies the effective tip-sample interaction in a controlled manner. The investigation establishes a way to quantitatively evaluate the electrostatic force in an atomic force microscope using the static mode force spectroscopy curves. PMID:22960002

Biswas, Soma; Raychaudhuri, A K; Sreeram, P A; Dietzel, Dirk

2012-11-01

22

Hyperphysics-Electric Field  

NSDL National Science Digital Library

In this free resource, topics pertaining to electric field are connected in a well-organized concept map. One click takes the user to related topics such as Gauss' Law, capacitance, and calculations related to force and field potential. This item is part of a larger collection under continuing development.

Nave, Carl R.

2006-10-31

23

Analytical solutions of ac electrokinetics in interdigitated electrode arrays: Electric field, dielectrophoretic and traveling-wave dielectrophoretic forces  

Microsoft Academic Search

Analysis of the movement of particles in a nonuniform field requires accurate knowledge of the electric field distribution in the system. This paper describes a method for analytically solving the electric field distribution above interdigitated electrode arrays used for dielectrophoresis (DEP) and traveling wave dielectrophoresis (twDEP), using the Schwarz-Christoffel mapping method. The electric field solutions are used to calculate the

Tao Sun; Hywel Morgan; Nicolas G. Green

2007-01-01

24

Alternating electric force microscopy: Static electric field gradient imaging in an air atmosphere for Ba0.7Sr0.3TiO3 ferroelectric thin film  

NASA Astrophysics Data System (ADS)

An alternating electric force microscopy (A-EFM) technique, which is effective for the imaging of static electric field gradient in an air atmosphere, is proposed by using our developed alternating force microscopy. A-EFM uses a frequency modulation of a mechanically oscillating conductive tip, which is induced by applying off-resonant AC voltage to the tip. The AC voltage generates off-resonant alternating electric force at the tip. A-EFM detects static electric field gradient with the field polarity from a sample without involving surface forces by using a lock-in detection technique. For a Ba0.7Sr0.3TiO3 ferroelectric thin film, A-EFM clearly imaged the static electric field gradient with field polarity and the boundary of electric domain in an air atmosphere.

Lu, Jia; Kinoshita, Yukinori; Egawa, Genta; Yoshimura, Satoru; Asano, Hidefumi; Saito, Hitoshi

2012-12-01

25

Forces acting on dielectric colloidal spheres at a water/nonpolar-fluid interface in an external electric field. 1. Uncharged particles.  

PubMed

Here, we calculate the electric forces acting on uncharged dielectric colloidal particles, which are attached to the interface between a nonpolar fluid (air, oil) and water, in the presence of an applied uniform external electric field directed normal to the interface. The uncharged particle becomes a source of dipolar electric field because it is polarized by the external field. Our goal is to calculate the normal (electrodipping) force acting on each separate particle, and the force of interaction between two identical particles. An exact analytical solution is obtained by solving the Laplace equation in toroidal coordinates and by separating the variables using the Mehler-Fock integral transform. The results show that the dependence of the normal force on particle contact angle is non-monotonic, with a maximum and a minimum. This force can be directed upward or downward depending on the particle contact angle and dielectric constant. An analytical asymptotic expression is derived for the force of interaction between two floating particles in external field. The magnitude of the latter force depends strongly on the particle contact angle ?. At a certain value of ?, the leading dipolar term becomes zero, and the interaction force is determined by the short-range octupolar term. Then, the attractive lateral capillary forces and van der Waals forces can overcome the electrostatic repulsion and can induce two-dimensional coagulation of the particles at the interface. The effects of the external electric field could find applications for control of the distances between particles in non-densely packed interfacial colloid crystals used in lithographic masks for the production of antireflective coatings, microlens arrays, etc. The case of charged particles in external field is considered in the second part of this study. PMID:23768629

Danov, Krassimir D; Kralchevsky, Peter A

2013-09-01

26

Three-dimensional observation of nanoscale ferroelectric domains using scanning nonlinear dielectric microscopy with electric field correction by Kelvin probe force microscopy.  

PubMed

An advanced technique for the measurement of three-dimensional ferroelectric domain structure is described. Scanning nonlinear dielectric microscopy is used to measure the polarization components both perpendicular and parallel to the specimen surface. A nanoscale electric field correction is devised and performed using Kelvin probe force microscopy to allow more precise measurement of the nanoscale polarization component parallel to the specimen surface. Using this electric field correction, three-dimensional imaging of the ferroelectric polarization orientation is demonstrated. PMID:21727408

Sugihara, Tomoyuki; Cho, Yasuo

2006-04-14

27

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

28

Electric and Magnetic Forces: Electric Charges  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach.This Science Object is the first of three Science Objects in the Electric and Magnetic Forces SciPack.

National Science Teachers Association (NSTA)

2008-10-30

29

Electric and Magnetic Forces: Electromagnetism  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach.This Science Object is the last of three Science Objects in the Electric and Magnetic Forces SciPack.

National Science Teachers Association (NSTA)

2008-10-30

30

Forces acting on dielectric colloidal spheres at a water/nonpolar fluid interface in an external electric field. 2. Charged particles.  

PubMed

Here, we calculate the electric forces acting on charged dielectric colloidal particles, which are attached to the interface between a nonpolar fluid (air and oil) and water in the presence of applied uniform external electric field, E0, directed normal to the interface. Electric charges are present on the particle-nonpolar fluid interface. The solution to the problem represents a superposition of the solutions of two simpler problems: (i) charged particle in the absence of external field and (ii) uncharged particle in the presence of external field. Because the external field can be directed upward or downward, it enhances or opposes the effect of the particle surface charges. As a result, the vertical (electrodipping) force vs. E0 may have a maximum or minimum and can be positive or negative depending on the particle contact angle and dielectric constant. In contrast, the lateral electric force between two identical charged floating particles is always positive (repulsive), but it can vary by many orders of magnitude with E0. This is because at a certain value of E0, the net dipolar moment of the particle becomes zero. Then, the interparticle force is governed by the octupolar moment, which leads to a much weaker and short-range repulsion. In the vicinity of this special value of E0, the interparticle repulsion is very sensitive to the variations in the external field. These effects can be used for a fine control of the lattice spacing in non-densely packed interfacial colloidal crystals of regular hexagonal packing for producing lithographic masks with various applications in nanotechnology. PMID:23759324

Danov, Krassimir D; Kralchevsky, Peter A

2013-09-01

31

In-situ quantitative measurement of electric fields in zinc oxide thin films using electrostatic force microscopy  

Microsoft Academic Search

Zinc oxide (ZnO) is the most important material for the fabrication of modern varistors (variable resistors). It is known that the highly nonlinear current-voltage relationship of ZnO varistors is due to effects taking place at the grain boundaries. For an accurate investigation of the mechanism of this process, techniques are required that allow a direct observation of local electric fields

Jan Harloff

2010-01-01

32

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

33

Electric field imaging  

Microsoft Academic Search

The physical user interface is an increasingly significant factor limiting the effectiveness of our interactions with and through technology. This thesis introduces Electric Field Imaging, a new physical channel and inference framework for machine perception of human action. Though electric field sensing is an important sensory modality for several species of fish, it has not been seriously explored as a

Joshua Reynolds Smith

1999-01-01

34

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

35

Electric Field and Potential Model  

NSDL National Science Digital Library

The EJS Electric Field and Potential Model shows the electric field and potential for cylindrical and spherical symmetry. In both symmetries, there are co-centric charged surfaces where the outer surface is grounded. The model reports the force on a test charge (yellow) between the co-centric surfaces as well as the voltage. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Electric Field and Potential model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_ElectricFieldPotential.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Cox, Anne

2009-11-06

36

Turbulence generation by electric body forces  

Microsoft Academic Search

The effect of an electric body force on vorticity production and turbulence generation in a gas is investigated by examination of the governing electrohydrodynamic equations. The theoretical concepts are illustrated by hot-film anemometer measurements of the electrically induced turbulence in a large scale electrostatic precipitator. The results indicate dramatic increases in turbulence and diffusivity due to the corona discharge and

J. H. Davidson; E. J. Shaughnessy

1986-01-01

37

Electric Multipole Field Model  

NSDL National Science Digital Library

The EJS Electric Multipole Model of a point charge (monopole), a dipole, or a quadrupole can show either field vectors or the scalar potential (voltage). A slider changes the charge and a movable detector shows the electric field direction and magnitude or measures the potential. Detector values can be recorded into a data table and analyzed using a built-in data analysis tool. Users can modify this simulation by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Electric Multipole Field model was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_ElectricMultipoleField.jar file will run the program if Java is installed. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Cox, Anne; Christian, Wolfgang; Franciscouembre

2010-01-31

38

Equatorial electric field observations  

NASA Technical Reports Server (NTRS)

The paper reports both dc and ac measurements of equatorial electric fields from the San Marco D satellite. These measurements were performed with double floating probe sensors and have yielded a surprising number of new phenomena and effects in regions of equatorial spread-F. Among the phenomena observed are unexpected large-amplitude Rayleigh-Taylor updrafting velocities in equatorial bubbles.

Aggson, T. L.; Hanson, W. B.; Herrero, F. A.; Maynard, N. C.; Pfaff, R. F.; Saba, J. L.; Tsunoda, R. T.

1993-01-01

39

Electric and magnetic fields  

NASA Technical Reports Server (NTRS)

A number of energy momentum anomalies are described that result from the use of Abraham-Lorentz electromagnetic theory. These anomalies have in common the motion of charged bodies or current carrying conductors relative to the observer. The anomalies can be avoided by using the nonflow approach, based on internal energy of the electromagnetic field. The anomalies can also be avoided by using the flow approach, if all contributions to flow work are included. The general objective of this research is a fundamental physical understanding of electric and magnetic fields which, in turn, might promote the development of new concepts in electric space propulsion. The approach taken is to investigate quantum representations of these fields.

Kaufman, H. R.; Robinson, R. S.; Etters, R. D.

1982-01-01

40

Electric field imaging  

NASA Astrophysics Data System (ADS)

The physical user interface is an increasingly significant factor limiting the effectiveness of our interactions with and through technology. This thesis introduces Electric Field Imaging, a new physical channel and inference framework for machine perception of human action. Though electric field sensing is an important sensory modality for several species of fish, it has not been seriously explored as a channel for machine perception. Technological applications of field sensing, from the Theremin to the capacitive elevator button, have been limited to simple proximity detection tasks. This thesis presents a solution to the inverse problem of inferring geometrical information about the configuration and motion of the human body from electric field measurements. It also presents simple, inexpensive hardware and signal processing techniques for makin the field measurements, and several new applications of electric field sensing. The signal processing contribution includes synchronous undersampling, a narrowband, phase sensitive detection technique that is well matched to the capabilities of contemporary microcontrollers. In hardware, the primary contributions are the School of Fish, a scalable network of microcontroller-based transceive electrodes, and the LazyFish, a small footprint integrated sensing board. Connecting n School of Fish electrodes results in an array capable of making heterodyne measurements of any or all n(n - 1) off-diagonal entries in the capacitance matrix. The LazyFish uses synchronous undersampling to provide up to 8 high signal- to-noise homodyne measurements in a very small package. The inverse electrostatics portion of the thesis presents a fast, general method for extracting geometrical information about the configuration and motion of the human body from field measurements. The method is based on the Sphere Expansion, a novel fast method for generating approximate solutions to the Laplace equation. Finally, the thesis describes a variety of applications of electric field sensing, many enabled by the small footprint of the LazyFish. To demonstrate the School of Fish hardware and the Sphere Expansion inversion method, the thesis presents 3 dimensional position and orientation tracking of two hands. 1 (Copies available exclusively from MIT Libraries, Rm. 14- 0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.) 1Please see the URL http://www.media.mit.edu/people/jrs/thesis.html for video clips, code, and other information related to this thesis.

Smith, Joshua Reynolds

41

Geometrical structures, vibrational frequencies, force constants and dissociation energies of isotopic water molecules (H2O, HDO, D2O, HTO, DTO, and T2O) under dipole electric field  

NASA Astrophysics Data System (ADS)

The dissociation limits of isotopic water molecules are derived for the ground state. The equilibrium geometries, the vibrational frequencies, the force constants and the dissociation energies for the ground states of all isotopic water molecules under the dipole electric fields from -0.05 a.u. to 0.05 a.u. are calculated using B3P86/6-311++G(3df,3pf). The results show that when the dipole electric fields change from -0.05 a.u. to 0.05 a.u., the bond length of H—O increases whereas the bond angle of H—O—H decreases because of the charge transfer induced by the applied dipole electric field. The vibrational frequencies and the force constants of isotopic water molecules change under the influence of the strong external torque. The dissociation energies increase when the dipole electric fields change from -0.05 a.u. to 0.05 a.u. and the increased dissociation energies are in the order of H2O, HDO, HTO, D2O, DTO, and T2O under the same external electric fields.

Shi, Shun-Ping; Zhang, Quan; Zhang, Li; Wang, Rong; Zhu, Zheng-He; Jiang, Gang; Fu, Yi-Bei

2011-06-01

42

Formation mechanism of electrical damage on sliding lubricated contacts for steel pair under DC electric field  

Microsoft Academic Search

A dynamic electrical pitting tester has been developed to investigate the effects of supply voltage, supply current, and oil film thickness on the electrical behavior, the normal and frictional forces, and the formation mechanism of electric damage for the sliding lubricated contacts of steel pair under DC electric field. Based on the experimental results for the normal and frictional forces,

Yuang-Cherng Chiou; Rong-Tsong Lee; Sing-Ming Lin

2009-01-01

43

Electrical characterization of zinc oxide/aluminum nitride thin film precursor field effect transistor structures: A conducting atomic force microscopy and density functional theoretical study  

NASA Astrophysics Data System (ADS)

Electrical transport across pulsed laser deposited zinc oxide (ZnO)/aluminum nitride (AlN)/Si(100) thin film structures has been studied using conducting atomic force microscopy. Current versus voltage spectroscopy performed on the samples with varying AlN layer thickness (t), revealed asymmetric nonlinear behavior with a finite zero current region. The effective barrier height of the system is found to be (~0.2 eV). The width of the zero current region was found to decrease exponentially with respect to t finally attaining the bulk band gap value. Density functional theory based calculations were carried out on the AlN and AlN-ZnO composite surface to investigate the band gap variation and ZnO adsorption on AlN. Results obtained by these calculations are in harmony with the experimental findings. Calculated values of the bulk cohesive energy explain the growth of the ZnO in an axis perpendicular to the surface supporting the experimentally observed results. Constant voltage current scans studies on the same sample showed the existence of current leakage spots. Current scans performed with varying bias voltages described an unambiguous growth profile of current leakage spots. These leakage spots were observed to evolve in a self similar pattern with the bias, which implied a possible existence of fractal dimension in the pattern of their growth. Mass fractal analysis is therefore carried out to model the growth pattern. Evolution of the mass-fractal with respect to the applied bias is found to be a case of Rayleigh distribution on a two-dimensional Poisson field, in the limiting case.

Dey, Shirshendu; Jejurikar, Suhas; Bhattacharya, Somesh Kumar; Banerji, Anirban; Adhi, K. P.; Dharmadhikari, C. V.

2010-11-01

44

Fundamentals of Ion Motion in Electric Radiofrequency Multipole Fields.  

National Technical Information Service (NTIS)

The fundamentals of ion motion in electromagnetic fields are reviewed in detail with a special emphasis on electric radiofrequency (RF) fields which are used frequently in dynamic mass spectrometry. Forces and effects on ions in electromagnetic fields whi...

M. H. Friedman A. L. Yergey J. E. Campana L. Kelner

1981-01-01

45

Near-field photonic forces  

Microsoft Academic Search

A review of recent advancements in photonic forces is presented. We discuss in detail the interaction of light and sub-wavelength particles on a substrate illuminated by total internal reflection, and we study the optical forces experienced by the particles. The effects of plasmon-mode excitations on the resulting photonic forces on metallic particles are also addressed. Moreover, we explore the possibility

P. C. C haumet

2004-01-01

46

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

47

Electric and Magnetic Forces: Electrostatics and Current Electricity  

NSDL National Science Digital Library

Science Objects are two hour on-line interactive inquiry-based content modules that help teachers better understand the science content they teach.This Science Object is the second of three Science Objects in the Electric and Magnetic Forces SciPack.

National Science Teachers Association (NSTA)

1900-01-01

48

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.

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

2014-01-01

49

Particle patterning using fluidics and electric fields  

Microsoft Academic Search

Electric-field manipulation of micro-particles in suspension can create patterns via a number of particle forces and fluid flows. These effects are assessed for their suitability for down-scaling to form nano-patterns such as may be incorporated into structured nano-composites. Consideration is given not only to the assembly of field-aligned chains or wires, but also to methods that can give cross-field assembly

W. Michael Arnold

2008-01-01

50

Electrical fields and soil properties  

Microsoft Academic Search

The electrical fields in the surface of soils appear as many different kinds. Methods of self- potential (SP), electrical profiling (EP), vertical electrical sounding (VES), and non-contact electromagnetic profiling (NEP) was used to measure the electrical properties of basic soil types, such as Spodosols, Alfisols, Histosols, Mollisols, and Aridisols (USA Soil Classification) of Russia in situ. The density of mobile

POZDNYAKOV Anatoly; POZDNYAKOVA Larisa

51

Dielectrophoresis of bubbles in isomotive electric fields  

Microsoft Academic Search

The behaviour of bubbles rising in AC isomotive electric fields of 50 Hertz frequency was investigated in several dielectric liquids. Isomotive electrodes were immersed in the sample liquids and aligned so that the motion of single bubbles of nitrogen rising in the interelectrode space was opposed by the dielectrophoretic force. The transit time of each bubble was timed over two

C. M. Feeley; F. McGovern

1988-01-01

52

Force Field for SiF4.  

National Technical Information Service (NTIS)

The force field of SiF4 has been determined using both Coriolis coupling constants obtained from an investigation of the band contour of v3 at 195 K and isotopic shifts. The force fields are equally well determined using both methods and are in agreement....

I. W. Levin S. Abramowitz

1968-01-01

53

Force field feature extraction for ear biometrics  

Microsoft Academic Search

The overall objective in defining feature space is to reduce the dimensionality of the original pattern space, whilst maintaining discriminatory power for classification. To meet this objec- tive in the context of ear biometrics a new force field transformation treats the image as an array of mutually attracting particles that act as the source of a Gaussian force field. Under-

David J. Hurley; Mark S. Nixon; John N. Carter

2005-01-01

54

Electric Field Induced Interfacial Instabilities  

NASA Technical Reports Server (NTRS)

The study of the interface in a charge-free, nonpolar, critical and near-critical binary fluid in the presence of an externally applied electric field is presented. At sufficiently large fields, the interface between the two phases of the binary fluid should become unstable and exhibit an undulation with a predefined wavelength on the order of the capillary length. As the critical point is approached, this wavelength is reduced, potentially approaching length-scales such as the correlation length or critical nucleation radius. At this point the critical properties of the system may be affected. In zero gravity, the interface is unstable at all long wavelengths in the presence of a field applied across it. It is conjectured that this will cause the binary fluid to break up into domains small enough to be outside the instability condition. The resulting pattern formation, and the effects on the critical properties as the domains approach the correlation length are of acute interest. With direct observation, laser light scattering, and interferometry, the phenomena can be probed to gain further understanding of interfacial instabilities and the pattern formation which results, and dimensional crossover in critical systems as the critical fluctuations in a particular direction are suppressed by external forces.

Kusner, Robert E.; Min, Kyung Yang; Wu, Xiao-Lun; Onuki, Akira

1996-01-01

55

Electric field induced changes in protein conformation.  

PubMed

The effect of a low strength oscillating electric field on the conformation of Bovine Serum Albumin (BSA) and Lysozyme in solution has been measured. A purpose built cell has been used to measure the real time autofluorescence and Circular Dichroism of the protein solutions exposed to electric fields of differing strength and frequency. Exposure to the electric fields results in protein unfolding for both Lysozyme and BSA. The applied field strengths are extremely small compared to the protein inter-chain intra-molecular forces. We propose a model whereby the electrophoretic motion of the proteins leads to a frictional force that results in protein unfolding. For BSA and Lysozyme in the electric fields used in this study, the shear rates at the protein surface under electrophoretic motion are of order 10(3) and 10(4) s(-1) respectively. Prolonged electric field exposure results in significant frictional energy dissipation in the proteins. The energy dissipated in the proteins results in protein unfolding, which is a critical initial step for protein aggregation and potentially amyloid fibril formation. PMID:24652412

Bekard, Innocent; Dunstan, Dave E

2014-01-21

56

Timing of pair production in time-dependent force fields  

NASA Astrophysics Data System (ADS)

We examine the creation and annihilation dynamics for electron-positron pairs in a time-dependent but subcritical electric force using a simplified model system. Numerical and semianalytical solutions to computational quantum field theory show that despite the continuity of the quantum field operator in time, the actual number of created particles can change in a discontinuous way if the field changes abruptly. The number of permanently created particles after the pulse, however, increases continuously with the duration of the electric field pulse, suggesting a transition from an exclusive annihilation to a creation regime.

Gerry, Christopher C.; Su, Q.; Grobe, R.

2006-10-01

57

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.

Daniels, Charlotte S.; Rubinsky, Boris

2011-01-01

58

Cryosurgery with pulsed electric fields.  

PubMed

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

59

Vorticity Field Evolution in a Forced Wake.  

National Technical Information Service (NTIS)

The purpose of this work is to quantify the vorticity evolution in the flow field of the forced wake of a splitter plate inside a confining geometry. The interest in this flow stems from the fact that forcing a low Reynolds number 2-D wake can lead to a h...

R. Cohn, M. Koochesfahani

1999-01-01

60

Electric Field and Wind Motion at the Magnetic Equator  

Microsoft Academic Search

The vertical electric field due to charge separation is calculated for a horizontal wind motion periodic with height, latitude, and longitude under magnetical equatorial conditions. It is found that the electric field is less than (W x B0) in magnitude at the magnetic equator in the presence of the curved lines of force of geomagnetic field B0, where W is

Susumu Kato

1973-01-01

61

A Simple Demonstration of Lorentz Force in Electrically-Conductive Fluid  

NASA Astrophysics Data System (ADS)

Flows driven by electromagnetic Lorentz forces are ubiquitous in the universe. Lorentz forces are essential, for example, in the dynamics of planetary cores and astrophysical plasmas. In an electrically-conducting fluid, this force is defined as the vector cross product of the magnetic field with the electric current density. We have built an easily-replicated desktop device to demonstrate the effects of Lorentz forces in a copper sulfate solution. The electric current is controlled by a DC power supply, and the magnetic field is imposed using neodymium magnets. By varying the electric current, it is possible to tune the Lorentz forces and, thus, the resulting drive motions in the copper sulfate solution. Experiments will be carried out onsite, along with real time measurements of electric potential, magnetic field strength and local flow velocities.

Ribeiro, A.; Aurnou, J.

2013-12-01

62

Electric field control of the cell orientation  

NASA Astrophysics Data System (ADS)

Many physiological processes depend on the response of biological cells to external forces. The natural electric field at a wound controls the orientation of the cell and its division.[1] We model the cell as an elongated elliptical particle with given Young's modulus with surface charge distribution in the external electric field. Using this simple theoretical model that includes the forces due to electrostatics and the elasticity of cells, we calculated analytically the response of the cell orientation and its dynamics in the presence of time varying electric field. The calculations reflect many experimentally observed features. Our model predicts the response of the cellular orientation to a sinusoidally varying applied electric field as a function of frequency similar to recent stress-induced effects.[2] *Bing Song, Min Zhao, John V. Forrester, and Colin D. McCaig, ``Electrical cues regulate the orientation and frequency of cell division and the rate of wound healing in vivo'', PNAS 2002, vol. 99 , 13577-13582. *R. De, A. Zemel, and S.A. Safran, ``Dynamics of cell orientation'', Nature Physics 2007, vol.3, 655.

Westman, Christopher; Sabirianov, Renat

2008-03-01

63

Assembly of LIGA using Electric Fields  

SciTech Connect

The goal of this project was to develop a device that uses electric fields to grasp and possibly levitate LIGA parts. This non-contact form of grasping would solve many of the problems associated with grasping parts that are only a few microns in dimensions. Scaling laws show that for parts this size, electrostatic and electromagnetic forces are dominant over gravitational forces. This is why micro-parts often stick to mechanical tweezers. If these forces can be controlled under feedback control, the parts could be levitated, possibly even rotated in air. In this project, we designed, fabricated, and tested several grippers that use electrostatic and electromagnetic fields to grasp and release metal LIGA parts. The eventual use of this tool will be to assemble metal and non-metal LIGA parts into small electromechanical systems.

FEDDEMA, JOHN T.; WARNE, LARRY K.; JOHNSON, WILLIAM A.; OGDEN, ALLISON J.; ARMOUR, DAVID L.

2002-04-01

64

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

65

MAGNETIC BRAIDING AND PARALLEL ELECTRIC FIELDS  

SciTech Connect

The braiding of the solar coronal magnetic field via photospheric motions-with subsequent relaxation and magnetic reconnection-is one of the most widely debated ideas of solar physics. We readdress the theory in light of developments in three-dimensional magnetic reconnection theory. It is known that the integrated parallel electric field along field lines is the key quantity determining the rate of reconnection, in contrast with the two-dimensional case where the electric field itself is the important quantity. We demonstrate that this difference becomes crucial for sufficiently complex magnetic field structures. A numerical method is used to relax a braided magnetic field toward an ideal force-free equilibrium; the field is found to remain smooth throughout the relaxation, with only large-scale current structures. However, a highly filamentary integrated parallel current structure with extremely short length-scales is found in the field, with the associated gradients intensifying during the relaxation process. An analytical model is developed to show that, in a coronal situation, the length scales associated with the integrated parallel current structures will rapidly decrease with increasing complexity, or degree of braiding, of the magnetic field. Analysis shows the decrease in these length scales will, for any finite resistivity, eventually become inconsistent with the stability of the coronal field. Thus the inevitable consequence of the magnetic braiding process is a loss of equilibrium of the magnetic field, probably via magnetic reconnection events.

Wilmot-Smith, A. L.; Hornig, G.; Pontin, D. I. [Division of Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom)], E-mail: antonia@maths.dundee.ac.uk

2009-05-10

66

Coulomb's Law and Electric Field Package  

NSDL National Science Digital Library

The EJS Coulomb's Law and Electric Field Package is a collection of models for electrostatics. Users can move charges around and see the force, observe the electric field generated by charge configurations, and observe the motion of test particles in electric fields. Also included are student worksheets in pdf format to supplement each simulation. Users can inspect and modify any simulation in the package by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The Coulomb's Law and Electric Field Package was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_electric_sampler.jar file will launch the package if Java is installed. Navigate within the package and click on a green triangle to run a particular simulation. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available. They can be found by searching ComPADRE for Open Source Physics, OSP, or Ejs.

Cox, Anne; Christian, Wolfgang; Franciscouembre

2009-12-07

67

Electric Field: What is Wrong? Package  

NSDL National Science Digital Library

The EJS Electric Field: What is Wrong? Package is a collection of models for electrostatics with errors intentionally built into each model. Users can move charges around and see the force, observe the electric field generated by charge configurations, and observe the motion of test particles in electric fields to try to identify the errors in the simulation. Users can inspect, modify and correct any simulation in the package by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item. The package also includes a brief overview of programming basics needed to correct the models. The Electric Field: What is Wrong? Package was created using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. Double clicking the ejs_em_electric_wiw.jar file will launch the package if Java is installed. Navigate within the package and click on a green triangle to run a particular simulation. Ejs is a part of the Open Source Physics Project and is designed to make it easier to access, modify, and generate computer models. Additional Ejs models are available on ComPADRE.

Cox, Anne; Christian, Wolfgang; Franciscouembre

2010-04-16

68

Fiber Optic Electric Field Micro Sensor  

NASA Astrophysics Data System (ADS)

A novel method and apparatus for sensing AC and DC electric fields incorporating a fiber-optic transducer mounted directly on the tip of an optical fiber waveguide has been demonstrated. The transducer employs a conductive Fabry-Perot microcavity bounded by a conductive, thin and corrugated silicon diaphragm. When the conductive microcavity is placed into an electric field, the electric field is excluded from within the equipotential cavity, which acts as a Faraday cage, and a net electrostatic force exerted on the surface of the diaphragm. The diaphragm deflects linearly and uniformly under the influence of the extremely low electrostatic pressures which are induced. The diaphragm deflection modulates the reflectance within the optical fiber by varying the gap of the cavity. The change in reflected light is measured and correlated to the field strength using and improved dual-wavelength referencing technique which compensates for bending and transmission losses in the optical fiber. Electric fields in the range of 0 to 300KV/m were successfully measured. The minimum intensity detected was of the order of 40KV/m. This relatively low intensity is due to the high boron-diffusion of the fabricated silicon diaphragms. However, higher sensitivities are possible by thinning the diaphragm, increasing its radius, reducing the boss ratio or decreasing the corrugation depth. No corona or discharge effects were noticed and a good repeatability was observed in the measurements.

Mendez Chamorro, Alexis

69

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.

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

2010-01-01

70

Multi robot mapping using force field simulation  

Microsoft Academic Search

This paper describes a novel approach, called Force Field Simulation, to multi robot map- ping that works under the constraints given in autonomous search and rescue robotics. Extremely poor prealignment, lack of landmarks, and minimal overlap between scans are the main challenges. The presented algorithm solves the alignment problem of such laser scans utilizing a gradient descent approach motivated by

Rolf Lakaemper; Nagesh Adluru; Longin Jan Latecki; Raj Madhavan

2007-01-01

71

Investigation on charge deterioration of electrically charged filter media using electric force microscopy  

NASA Astrophysics Data System (ADS)

Electret filter media is widely used in filtration application as the presence of embedded electrostatic charges allows for better particle capture efficiency with lower pressure drop. The effect of exposure to organic solvents on filtration performance of electret filter media was investigated using several different organic solvents and electret filter media. The exposure of electret filter media to liquid organic solvents caused a decrease in filtration performance without significant changes in resistance. It is hypothesized that the lowered performance of the electret filter media is due to the changes in electric field caused by the liquid organic solvents or to morphological changes. Scanning Electron Microscopy (SEM) was used to examine any observable morphological changes in the fibers after exposure to liquid organic solvents. There were no observable changes in morphology of fibers, suggesting the performance deterioration by chemical exposure was not caused by morphological changes in fibers. Electric Force Microscopy (EFM) was used to analyze the electric field of electret filter media prior to and after exposure to organic liquid solvents. Changes in the electric field were detected and quantified. Electric field gradient imaging (EFGI) by phase and frequency detection was shown to be a feasible method for the analysis of charge deterioration in electret filtration media. Two mathematical models based on electrostatics fundamentals were used to explain the behavior of EFM experimental data. Model I accounted for both a coulombic force and induced polarization phenomena. Model II incorporates a capacitance term. Both models exhibited good quantitative agreement with the experimental data hence the performance deterioration of the electret filter media after chemical immersion was proven to be directly related to changes in the electric field of the sample.

Kim, Jooyoun

72

Interactive calculations of electric fields  

SciTech Connect

In many experimental design situations it is valuable to know what the time-dependent electric and magnetic fields are likely to be so that such things as electric breakdown and ohmic heating as a result of magnetic field penetration canb e estimated. Because of the advent of extensions in the speed and memory of large electronic computers it has become easier to extend the scope of these calculations. Even so, it is necessary to use advanced sparse matrix techniques and to take as much advantage as possible of vectorization of code loops. In developing these codes extensive use has been made of the 2-D counterparts to test various aspects of the algorithms and of the code architecture. In addition, attempts have been made to make the user interface to these codes as simple and easy as possible. This paper addresses the problem of implementing this system for the 2-D calculation of electric fields. 3 refs., 4 figs.

Weiss, D.L.; Oliphant, T.A.

1986-07-01

73

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

74

Optical Near-field Interactions and Forces for Optoelectronic Devices  

NASA Astrophysics Data System (ADS)

Throughout history, as a particle view of the universe began to take shape, scientists began to realize that these particles were attracted to each other and hence came up with theories, both analytical and empirical in nature, to explain their interaction. The interaction pair potential (empirical) and electromagnetics (analytical) theories, both help to explain not only the interaction between the basic constituents of matter, such as atoms and molecules, but also between macroscopic objects, such as two surfaces in close proximity. The electrostatic force, optical force, and Casimir force can be categorized as such forces. A surface plasmon (SP) is a collective motion of electrons generated by light at the interface between two mediums of opposite signs of dielectric susceptibility (e.g. metal and dielectric). Recently, surface plasmon resonance (SPR) has been exploited in many areas through the use of tiny antennas that work on similar principles as radio frequency (RF) antennas in optoelectronic devices. These antennas can produce a very high gradient in the electric field thereby leading to an optical force, similar in concept to the surface forces discussed above. The Atomic Force Microscope (AFM) was introduced in the 1980s at IBM. Here we report on its uses in measuring these aforementioned forces and fields, as well as actively modulating and manipulating multiple optoelectronic devices. We have shown that it is possible to change the far field radiation pattern of an optical antenna-integrated device through modification of the near-field of the device. This modification is possible through change of the local refractive index or reflectivity of the "hot spot" of the device, either mechanically or optically. Finally, we have shown how a mechanically active device can be used to detect light with high gain and low noise at room temperature. It is the aim of several of these integrated and future devices to be used for applications in molecular sensing, and we believe that these methods show their potential for a chip-scale sensing device.

Kohoutek, John Michael

75

Electric fields yield chaos in microflows  

PubMed Central

We present an investigation of chaotic dynamics of a low Reynolds number electrokinetic flow. Electrokinetic flows arise due to couplings of electric fields and electric double layers. In these flows, applied (steady) electric fields can couple with ionic conductivity gradients outside electric double layers to produce flow instabilities. The threshold of these instabilities is controlled by an electric Rayleigh number, Rae. As Rae increases monotonically, we show here flow dynamics can transition from steady state to a time-dependent periodic state and then to an aperiodic, chaotic state. Interestingly, further monotonic increase of Rae shows a transition back to a well-ordered state, followed by a second transition to a chaotic state. Temporal power spectra and time-delay phase maps of low dimensional attractors graphically depict the sequence between periodic and chaotic states. To our knowledge, this is a unique report of a low Reynolds number flow with such a sequence of periodic-to-aperiodic transitions. Also unique is a report of strange attractors triggered and sustained through electric fluid body forces.

Posner, Jonathan D.; Perez, Carlos L.; Santiago, Juan G.

2012-01-01

76

Harmonic force field for nitro compounds.  

PubMed

Molecular simulations leading to sensors for the detection of explosive compounds require force field parameters that can reproduce the mechanical and vibrational properties of energetic materials. We developed precise harmonic force fields for alanine polypeptides and glycine oligopeptides using the FUERZA procedure that uses the Hessian tensor (obtained from ab initio calculations) to calculate precise parameters. In this work, we used the same procedure to calculate generalized force field parameters of several nitro compounds. We found a linear relationship between force constant and bond distance. The average angle in the nitro compounds was 116°, excluding the 90° angle of the carbon atoms in the octanitrocubane. The calculated parameters permitted the accurate molecular modeling of nitro compounds containing many functional groups. Results were acceptable when compared with others obtained using methods that are specific for one type of molecule, and much better than others obtained using methods that are too general (these ignore the chemical effects of surrounding atoms on the bonding and therefore the bond strength, which affects the mechanical and vibrational properties of the whole molecule). PMID:22119786

Bellido, Edson P; Seminario, Jorge M

2012-06-01

77

Field study on moving force identification  

NASA Astrophysics Data System (ADS)

A field measurement to validate a moving force identification method was carried out on an existing prestressed concrete highway bridge with a span length of 28 m. The test bridge is located at Ma Tau Wai, Kowloon, Hong Kong. A heavy 2-axle truck with known axle loads was used as a control vehicle. Besides the control vehicle, axle load data of in-service vehicles were also collected. The bridge responses acquired for the identification were indirectly measured using strain gauges. Results show that dynamic axle loads induced from both control and in-service vehicles can be identified indicating the method is valid for identification of moving forces.

Chan, Hung-tin Tommy; Yung, Tak H.; Law, S. S.

2001-08-01

78

Electric field effects in bacteriorhodopsin.  

PubMed Central

Exposure of aqueous suspensions of fragments of the purple membrane of Halobacterium halobium to electric field pulses leads to transient linear dichroism phenomena. The effects are interpreted in terms of field-induced alignments of the bacteriorhodopsin chromophore. Two observed relaxation times (tau) are attributed to rotation of the whole membrane fragments (tau s approximately 100 ms), and to a much faster reorientation of the chromophore within membrane (tau f approximately 260 microns).

Shinar, R; Druckmann, S; Ottolenghi, M; Korenstein, R

1977-01-01

79

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

80

Electrically driven vortices in multipolar magnetic fields  

NASA Astrophysics Data System (ADS)

The flow generated in a thin layer of an electrically conducting fluid by the interaction of a steady, uniform electric current with a superposition of dipolar permanent magnets, is studied experimentally and theoretically. The experiment is carried out in a rectangular plexiglass cell with a shallow layer of an electrolytic solution. Small permanent magnets are placed externally in the central part of the cell bottom in an array that may include one, two or four dipole magnets. The direct electric current which is injected thorugh two opposite walls (copper electrodes) interacts with the magnetic field distribution generating a Lorentz force that drives different vortex patterns depending on the number of dipoles, their location and the orientation of their magnetic dipole moment. The theoretical two-dimensional model that describes the flow produced by a single dipole magnet, providing non-linear convective effects are neglected, is extended to consider the influence of additional magnets.

Cuevas, Sergio

2002-11-01

81

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

82

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

83

Linear electric field mass spectrometry  

DOEpatents

A mass spectrometer and methods for mass spectrometry. 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.

McComas, David J. (Los Alamos, NM); Nordholt, Jane E. (Los Alamos, NM)

1992-01-01

84

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

85

Apparatuses and methods for generating electric fields  

DOEpatents

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

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

2013-08-06

86

Vibrational spectra and force field of dimethylphosphines  

NASA Astrophysics Data System (ADS)

Vibrational spectra in the range 200-3000 cm -1 are reported and assigned for the species (CH 3) 2PH, (CH 3) 2PD, (CD 3) 2PH, (CD 3) 2PD, CH 3CD 3PH and CH 3CD 3PD. The spectra in the range 1020-500 cm -1 are complicated due to the coupling between ?PH, ?Me and the skeletal modes of the molecule. Interpretation is only possible through a force field which is markedly different from an earlier one of dimethyl sulphide. This force field predicts uncoupled ?PH frequencies of 835 ( a) and 909 cm -1 ( a), couples PH bending largely to out-of-skeletal plane methyl rocking (? i) and includes a low p¦¦( a) bending constant, a high skeletal bending constant and unusual signs for two interaction constants. In the crystalline phase at 78 K, the two methyl groups are non-equivalent.

McKean, D. C.; McQuillan, G. P.

1980-04-01

87

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

88

Oscillatory Squeeze Flow of Electrorheological Fluid with Transitional Electric Field  

NASA Astrophysics Data System (ADS)

The oscillatory squeeze flow of electrorheological (ER) fluid between two parallel discal electrode with transitional electric field is studied numerically in this paper. The ER fluid is modeled as Bingham-like fluid with the continuous modification model proposed by Papanastasiou. The numerical solutions based on the Navier-Stokes equations are presented by using the finite volume methods on the deforming grid. The force transmitted across the fluid under dc and ac electric fields are calculated. The effects of the electric field frequency and the phase difference between the ac electric field and mechanical oscillation are studied. The magnitude and the shape of the transmitted forces is shown to be not only a function of the applied voltage and the mechanical frequency but also the phase difference.

Peng, Jie; Zhu, Ke-Qin

89

A Mechanism for Action of Oscillating Electric Fields on Cells  

Microsoft Academic Search

The biological effects of electromagnetic fields have seriously concerned the scientific community and the public as well in the past decades as more and more evidence has accumulated about the hazardous consequences of so-called “electromagnetic pollution.” This theoretical model is based on the simple hypothesis that an oscillating external electric field will exert an oscillating force to each of the

Dimitris J. Panagopoulos; Niki Messini; Andreas Karabarbounis; Alexandros L. Philippetis; Lukas H. Margaritis

2000-01-01

90

A supervised fitting approach to force field parametrization with application to the SIBFA polarizable force field.  

PubMed

A supervised, semiautomated approach to force field parameter fitting is described and applied to the SIBFA polarizable force field. The I-NoLLS interactive, nonlinear least squares fitting program is used as an engine for parameter refinement while keeping parameter values within a physical range. Interactive fitting is shown to avoid many of the stability problems that frequently afflict highly correlated, nonlinear fitting problems occurring in force field parametrizations. The method is used to obtain parameters for the H2 O, formamide, and imidazole molecular fragments and their complexes with the Mg(2+) cation. Reference data obtained from ab initio calculations using an auc-cc-pVTZ basis set exploit advances in modern computer hardware to provide a more accurate parametrization of SIBFA than has previously been available. © 2014 Wiley Periodicals, Inc. PMID:24965869

Devereux, Mike; Gresh, Nohad; Piquemal, Jean-Philip; Meuwly, Markus

2014-08-01

91

Downward Mapping of Equatorial Ionospheric Electric Fields.  

National Technical Information Service (NTIS)

The problem of downward mapping of equatorial ionospheric electric fields is studied in two dimensions. Numerical solutions are shown and are compared with the corresponding ones for high latitudes. It is found that ionospheric electric fields can map dow...

W. D. Gonzalez S. L. G. Dutra A. L. C. Gonzalez A. E. C. Pereira

1985-01-01

92

Electric-field ion cyclotron resonance.  

PubMed

We consider the possibility that DC magnetic fields can interact in a resonant manner with endogenous AC electric fields in biological systems. Intrinsic electric-field ion cyclotron resonance (ICR) interactions would be more physically credible than models based on external AC magnetic fields and might be expected as an evolutionary response to the long-term constancy of the geomagnetic field. PMID:9125238

Liboff, A R

1997-01-01

93

Electric-field ion cyclotron resonance  

Microsoft Academic Search

The authors consider the possibility that DC magnetic fields can interact in a resonant manner with endogenous AC electric fields in biological systems. Intrinsic electric-field ion cyclotron resonance (ICR) interactions would be more physically credible than models based on external AC magnetic fields and might be expected as an evolutionary response to the long-term constancy of the geomagnetic field.

Liboff

1997-01-01

94

Electrical Current in Sinai Billiards Under General Small Forces  

NASA Astrophysics Data System (ADS)

The Lorentz gas of -periodic scatterers (or the so called Sinai billiards) can be used to model motion of electrons on a metal. We investigate the linear response for the system under various external forces (during both the flight and the collision). We give some characterizations under which the forced system is time-reversible, and derive an estimate of the electrical current generated by the forced system. Moreover, applying Pesin entropy formula and Young dimension formula, we get several characterizations of the non-equilibrium steady state of the forced system.

Chernov, Nikolai; Zhang, Hong-Kun; Zhang, Pengfei

2013-12-01

95

Electrical Field Modelling at the Cable Joints  

Microsoft Academic Search

There is a large number of parameters that influence to the way of the producing cable joints, and therefore the greatest attenti on is paid on the electrical field density shaping. This is done in order to efficiently red uce electrical field den- sity, especially the tangential electrical field component at the insulator surface. The described problem solving presents very

Nebojsa B. Rai

2007-01-01

96

Electric Field Induced Interfacial Instabilities  

NASA Technical Reports Server (NTRS)

The study of the interface in a charge-free, critical and near-critical binary fluid in the presence of an externally applied electric field is presented. At sufficiently large fields, the interface between the two phases of the binary fluid should become unstable and exhibit an undulation with a predefined wavelength on the order of the capillary length. As the critical point is approached, this wavelength is reduced, potentially approaching length-scales such as the correlation length or critical nucleation radius. At this point the critical properties of the system may be affected. In this paper, the flat interface of a marginally polar binary fluid mixture is stressed by a perpendicular alternating electric field and the resulting instability is characterized by the critical electric field E(sub c) and the pattern observed. The character of the surface dynamics at the onset of instability is found to be strongly dependent on the frequency f of the field applied. The plot of E(sub c) vs. f for a fixed temperature shows a sigmoidal shape, whose low and high frequency limits are well described by a power-law relationship, E(sub c) = epsilon(exp zeta) with zeta = 0.35 and zeta = 0.08, respectively. The low-limit exponent compares well with the value zeta = 4 for a system of conducting and non-conducting fluids. On the other hand, the high-limit exponent coincides with what was first predicted by Onuki. The instability manifests itself as the conducting phase penetrates the non-conducting phase. As the frequency increases, the shape of the pattern changes from an array of bifurcating strings to an array of column-like (or rod-like) protrusions, each of which spans the space between the plane interface and one of the electrodes. For an extremely high frequency, the disturbance quickly grows into a parabolic cone pointing toward the upper plate. As a result, the interface itself changes its shape from that of a plane to that of a high sloping pyramid.

Kusner, Robert E.; Min, Kyung Yang; Wu, Xiao-lun; Onuki, Akira

1999-01-01

97

ELECTRIC ADHESION FORCE OF A SINGLE PARTICLE AND OF A POWDER AT ROOM TEMPERATURE AND ABOVE AMBIENT TEMPERATURE AND ITS APPLICATION TO A FLUIDIZED BED  

Microsoft Academic Search

Adhesion forces of a single particle and of a powder in the presence of d.c. electric field were analysed both at and above room temperature. At room temperature the adhesion force was measured and found to increase almost linearly with the increase of applied electric field strength and decrease with the decrease of air humidity. Calculated forces showed good agreement

FUMIKAZU IKAZAKI; MITSUTAKA KAMAMURA

1984-01-01

98

A Gravitational Experiment Involving Inhomogeneous Electric Fields  

SciTech Connect

Unification of gravitation with other forms of interactions, particularly with electromagnetism, will have tremendous impacts on technology and our understanding of nature. The economic impact of such an achievement will also be unprecedented and far more extensive than the impact experienced in the past century due to the unification of electricity with magnetism and optics. Theoretical unification of gravitation with electromagnetism using classical differential geometry has been pursued since the late nineteen twenties, when Einstein and Cartan used teleparallelism for the task. Recently, Vargas and Torr have followed the same line of research with more powerful mathematics in a more general geometric framework, which allows for the presence of other interactions. Their approach also uses Kaehler generalization of Cartan's exterior calculus, which constitutes a language appropriate for both classical and quantum physics. Given the compelling nature of teleparallelism (path-independent equality of vectors at a distance) and the problems still existing with energy-momentum in general relativity, it is important to seek experimental evidence for such expectations. Such experimental programs are likely to provide quantitative guidance to the further development of current and future theories. We too, have undertaken an experimental search for potential electrically induced gravitational (EIG) effects. This presentation describes some of the practical concerns that relates to our investigation of electrical influences on laboratory size test masses. Preliminary results, appear to indicate a correlation between the application of a spatially inhomogeneous electric field and the appearance of an additional force on the test mass. If confirmed, the presence of such a force will be consistent with the predictions of Vargas-Torr. More importantly, proven results will shed new light and clearer understanding of the interactions between gravitational and electromagnetic effects.

Datta, T. [University of South Carolina, Columbia, SC 29208 (United States); Yin Ming [Benedict College, Columbia, SC 29204 (United States); Vargas, Jose [PST Associates, 600 Westover Rd. Columbia, SC 29210 (United States)

2004-02-04

99

Cell separation using electric fields  

NASA Technical Reports Server (NTRS)

The present invention involves methods and devices which enable discrete objects having a conducting inner core, surrounded by a dielectric membrane to be selectively inactivated by electric fields via irreversible breakdown of their dielectric membrane. One important application of the invention is in the selection, purification, and/or purging of desired or undesired biological cells from cell suspensions. According to the invention, electric fields can be utilized to selectively inactivate and render non-viable particular subpopulations of cells in a suspension, while not adversely affecting other desired subpopulations. According to the inventive methods, the cells can be selected on the basis of intrinsic or induced differences in a characteristic electroporation threshold, which can depend, for example, on a difference in cell size and/or critical dielectric membrane breakdown voltage. The invention enables effective cell separation without the need to employ undesirable exogenous agents, such as toxins or antibodies. The inventive method also enables relatively rapid cell separation involving a relatively low degree of trauma or modification to the selected, desired cells. The inventive method has a variety of potential applications in clinical medicine, research, etc., with two of the more important foreseeable applications being stem cell enrichment/isolation, and cancer cell purging.

Mangano, Joseph A. (Inventor); Eppich, Henry M. (Inventor)

2003-01-01

100

Cell separation using electric fields  

NASA Technical Reports Server (NTRS)

The present invention involves methods and devices which enable discrete objects having a conducting inner core, surrounded by a dielectric membrane to be selectively inactivated by electric fields via irreversible breakdown of their dielectric membrane. One important application of the invention is in the selection, purification, and/or purging of desired or undesired biological cells from cell suspensions. According to the invention, electric fields can be utilized to selectively inactivate and render non-viable particular subpopulations of cells in a suspension, while not adversely affecting other desired subpopulations. According to the inventive methods, the cells can be selected on the basis of intrinsic or induced differences in a characteristic electroporation threshold, which can depend, for example, on a difference in cell size and/or critical dielectric membrane breakdown voltage. The invention enables effective cell separation without the need to employ undesirable exogenous agents, such as toxins or antibodies. The inventive method also enables relatively rapid cell separation involving a relatively low degree of trauma or modification to the selected, desired cells. The inventive method has a variety of potential applications in clinical medicine, research, etc., with two of the more important foreseeable applications being stem cell enrichment/isolation, and cancer cell purging.

Mangano, Joseph (Inventor); Eppich, Henry (Inventor)

2009-01-01

101

ELECTRIC-FIELD-ENHANCED FABRIC FILTRATION OF ELECTRICALLY CHARGED FLYASH  

EPA Science Inventory

The paper summarizes measurements in which both external electric field (applied by electrodes at the fabric surface) and flyash electrical charge (controlled by an upstream corona precharger) are independent variables in a factorial performance experiment carried out in a labora...

102

Carbynes phonons: A tight binding force field  

NASA Astrophysics Data System (ADS)

Modeling the vibrational structure of linear carbon chains has proved to be a difficult task with present first-principles calculations. This limits their applicability for the interpretation of experimental data, such as Raman scattering experiments on linear carbon chains within nanotubes. These limitations can be overcome by means of a simple tight binding scheme for ?-electrons. In this work a force field for the calculation of longitudinal phonon dispersion branches is built on the basis of bond-bond polarizabilities and just three parameters. The so obtained phonon dispersion branches are in very good agreement with the experimental data on carbynes in different environments and polyynes of any length. The model is discussed in relation to the importance of long range vibrational interactions in carbynes. The physical phenomena affecting their vibrational properties (i.e., Kohn anomaly, electron-phonon coupling) can be accurately and analytically described by the present approach.

Milani, Alberto; Tommasini, Matteo; Zerbi, Giuseppe

2008-02-01

103

Terrestrial and microgravity boiling heat transfer in a dielectrophoretic force field  

Microsoft Academic Search

In order to maintain steady nucleate boiling in microgravity another force must be imposed on the boiling process to replace the buoyancy force. The objective of this study is to investigate the effectiveness of a static electric field for maintaining nucleate boiling in microgravity. Semi-transparent gold-film heaters are used to measure the instantaneous average heater surface temperature and to provide

T. J. Snyder; J. N. Chung

2000-01-01

104

Electric field probes for cellular phone dosimetry  

Microsoft Academic Search

Miniature implantable electric field probes (E-field Probes) enable the measurements of microwave electric fields induced in biological subjects by relatively low level exposures. Using these instruments, the rate of energy deposition (Specific Absorption Rate or SAR) can be determined throughout models or actual bodies of laboratory animals and humans exposed to emissions from cellular phones and other radiators. E-field probes

Howard I. Bassen

1997-01-01

105

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

106

Force-Field Analysis: Incorporating Critical Thinking in Goal Setting.  

ERIC Educational Resources Information Center

Force field analysis encourages members to examine the probability of reaching agreed-upon goals. It can help groups avoid working toward goals that are unlikely to be reached. In every situation are three forces: forces that encourage maintenance of the status quo or change; driving or helping forces that push toward change; and restraining…

Hustedde, Ron; Score, Michael

1995-01-01

107

Electric Field Controlled Self-Assembly of Hierarchically Ordered Membranes  

PubMed Central

Self-assembly in the presence of external forces is an adaptive, directed organization of molecular components under nonequilibrium conditions. While forces may be generated as a result of spontaneous interactions among components of a system, intervention with external forces can significantly alter the final outcome of self-assembly. Superimposing these intrinsic and extrinsic forces provides greater degrees of freedom to control the structure and function of self-assembling materials. In this work we investigate the role of electric fields during the dynamic self-assembly of a negatively charged polyelectrolyte and a positively charged peptide amphiphile in water leading to the formation of an ordered membrane. In the absence of electric fields, contact between the two solutions of oppositely charged molecules triggers the growth of closed membranes with vertically oriented fibrils that encapsulate the polyelectrolyte solution. This process of self-assembly is intrinsically driven by excess osmotic pressure of counterions, and the electric field is found to modify the kinetics of membrane formation, and also its morphology and properties. Depending on the strength and orientation of the field we observe a significant increase or decrease of up to nearly 100% in membrane thickness, as well as the controlled rotation of nanofiber growth direction by 90 degrees, resulting in a significant increase in mechanical stiffness. These results suggest the possibility of using electric fields to control structure in self-assembly processes involving diffusion of oppositely charged molecules.

Velichko, Yuri S.; Mantei, Jason R.; Bitton, Ronit; Carvajal, Daniel; Shull, Kenneth R.; Stupp, Samuel I.

2012-01-01

108

Manipulation of red blood cells with electric field  

NASA Astrophysics Data System (ADS)

Manipulation of bioparticles and macromolecules is the central task in many biological and biotechnological processes. The current methods for physical manipulation takes advantage of different forces such as acoustic, centrifugal, magnetic, electromagnetic, and electric forces, as well as using optical tweezers or filtration. Among all these methods, however, the electrical forces are particularly attractive because of their favorable scale up with the system size which makes them well-suited for miniaturization. Currently the electric field is used for transportation, poration, fusion, rotation, and separation of biological cells. The aim of the current research is to gain fundamental understanding of the effect of electric field on the human red blood cells (RBCs) using direct numerical simulation. A front tracking/finite difference technique is used to solve the fluid flow and electric field equations, where the fluid in the cell and the blood (plasma) is modeled as Newtonian and incompressible, and the interface separating the two is treated as an elastic membrane. The behavior of RBCs is investigated as a function of the controlling parameters of the problem such as the strength of the electric field.

Saboonchi, Hossain; Esmaeeli, Asghar

2009-11-01

109

Hydrodynamic Mapping of Two-Dimensional Electric Fields in Monolayers  

NASA Astrophysics Data System (ADS)

We have measured the 2D dipolar electric fields generated by surface density fluctuations in Langmuir monolayers using optical microscopy to monitor the motion of micron-size, electrically charged, particles trapped at the air-water interface. The particle velocity is directly proportional to the local electric field gradient. Quantitative agreement with the theory is demonstrated for charged polystyrene latex particles interacting with liquid condensed domains of pentadecanoic acid. Typical velocities are of order 0.1--10 ?m/s, corresponding to forces in the 10-15--10-12 N range.

Nassoy, Pierre; Birch, William R.; Andelman, David; Rondelez, Francis

1996-01-01

110

Work against an Electric Force: The Van De Graaff generator  

NSDL National Science Digital Library

This page illustrates the concept of work against an electric force using the examples of the Van de Graaff generator and lightening. There are also shorter examples of the Xerox machine and electric charge on transparency sheets as well as links to sites relating to the Van de Graaff machine or lightening. This is an optional section of "From Stargazers to Starships". French and Italian translations are available.

Stern, David

2005-01-04

111

The Introduction of Fields in Relation to Force  

ERIC Educational Resources Information Center

The introduction of force at age 14-16 years is considered, starting with elementary student experiments using magnetic force fields. The meaningless use of terms such as "action" and "reaction", or "agent" and "receiver" is discussed. (Contains 6 figures.)

Brunt, Marjorie; Brunt, Geoff

2012-01-01

112

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

2014-07-10

113

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

114

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

115

On the electric and magnetic field generation in expanding plasmas  

Microsoft Academic Search

A general method that decomposes each of the forces terms in Ohm's law in a component that induces a charge separation in the plasma and a component that can drive current is given. This decomposition is unambiguous and depends on the boundary conditions for the electric potential. It is shown that in calculating the electromagnetic field quantities in a plasma

Herman Johannes Gertrudis Gielen

1989-01-01

116

Charged Hadron Properties in Background Electric Fields  

SciTech Connect

We report on a lattice calculation demonstrating a novel new method to extract the electric polarizability of charged pseudo-scalar mesons by analyzing two point correlation functions computed in classical background electric fields.

William Detmold, Brian C. Tiburzi, Andre Walker-Loud

2010-02-01

117

The effect of electromagnetic forces on the penetrator formation during high-frequency electric resistance welding  

Microsoft Academic Search

During high-frequency electric resistance welding (HF-ERW), the electromagnetic force induced by the high-frequency electric current was studied to improve the understanding of penetrator formation mechanism. ERW melting zone behavior is investigated by the cinematography and the three-dimensional numerical analysis of electromagnetic field around molten metal bridge. Based on the results, the penetrator formation is mainly influenced by the narrow gap

Choong-Myeong Kim; Jung-Kyu Kim

2009-01-01

118

Lightning Location Using Electric Field Change Meters  

Microsoft Academic Search

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

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

2010-01-01

119

Compact Electric- And Magnetic-Field Sensor  

NASA Technical Reports Server (NTRS)

Compact sensor measures both electric and magnetic fields. Includes both short electric-field dipole and search-coil magnetometer. Three mounted orthogonally providing triaxial measurements of electromagnetic field at frequencies ranging from near 0 to about 10 kHz.

Winterhalter, Daniel; Smith, Edward

1994-01-01

120

Electric Field in Materials, Containing Conductive Nanofibers  

Microsoft Academic Search

Concentrated electric field and its energy in materials, containing nanofibers, are discussed. It is shown that the electric field in the vicinity of the end of a fiber is proportional to the external applied field and to the fiber length, whilst it is inversely proportional to the fiber diameter. Specific electrostatic energy of a fiber in a sample under the

Yuri Kornyushin

2010-01-01

121

Trapping of DNA in nonuniform oscillating electric fields.  

PubMed Central

DNA molecules can be manipulated in aqueous solution in a manner analogous to optical trapping. Due to the induction of an electric dipole, DNA molecules are pulled by a gradient force to regions of high electric field strength. Molecules can be locally trapped in an oscillating field using strips of very thin gold film to generate strong electric fields with steep gradients. Spatial control over the trapped molecules is achieved because they are confined to a width of approximately 5 microm along the edges of the gold-film strips. By mixing static and oscillating electric fields, trapped molecules can be moved from one edge to another or made to follow precise trajectories along the edges. This phenomenon should be useful in microdevices for manipulation of small quantities or single molecules of DNA.

Asbury, C L; van den Engh, G

1998-01-01

122

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

123

Superconducting granular balls in ac electric field with low frequency  

NASA Astrophysics Data System (ADS)

An AC electric field with low frequency is applied to a suspension of high Tc superconducting (HTSC) granular particles in liquid nitrogen. The particles are in ? m size. There are two critical electric fields E_c1electric field is below E_c1, the HTSC particles form chains along the field direction. As the applied field exceeds E_c1, round macroscopic balls are formed. Each ball holds over 10^6 particles and is very stable. As the field further increases, the balls get smaller. The fact that the balls are bouncing between the two electrodes indicates some net charges on the balls when the frequency is low. If the applied electric field exceeds E_c2, the balls suddenly break into small pieces, which all fly to the electrodes and cling there. This phenomenon can be explained by a new positive surface energy of superconductors induced by a strong electric field. The surface energy is associated with the induced surface charge density. When the HTSC particles aggregate together to form balls, the surface charges are redistributed to the outer surface. Thus the positive surface energy is greatly reduced. However, if the applied the applied electric field is too high, the Coulomb interaction is too strong and forces the balls to break into small pieces.

Tao, R.; Xu, Xiaojun; Amr, Eyas

2003-03-01

124

49 CFR 236.10 - Electric locks, force drop type; where required.  

Code of Federal Regulations, 2013 CFR

...2013-10-01 2013-10-01 false Electric locks, force drop type; where required...Rules and Instructions: All Systems General § 236.10 Electric locks, force drop type; where required. Electric locks on new installations and...

2013-10-01

125

Force-Freeness of Solar Magnetic Fields in the Photosphere  

Microsoft Academic Search

It is widely believed that solar magnetic fields are force-free in the solar corona but not in the solar photosphere at all. In order to examine the force-freeness of active region magnetic fields at the photospheric level, we have calculated the integrated magnetic forces for 12 vector magnetograms of three flare-productive active regions. The magnetic field vectors are derived from

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

2002-01-01

126

Force-Freeness of Solar Magnetic Fields in the Photosphere  

Microsoft Academic Search

It is widely believed that solar magnetic fields are force-free in the solar corona, but not in the solar photosphere. In order to examine the force-freeness of active region magnetic fields at the photospheric level, we have calculated the integrated magnetic forces for 33 vector magnetograms of four flare-productive active regions. The magnetic field vectors are derived from simultaneous Stokes

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

2001-01-01

127

Force?Freeness of Solar Magnetic Fields in the Photosphere  

Microsoft Academic Search

Q2 It is widely believed that solar magnetic fields are force-free in the solar corona but not in the solar photo- sphere at all. In order to examine the force-freeness of active region magnetic fields at the photospheric level, we have calculated the integrated magnetic forces for 12 vector magnetograms of three flare-productive active regions. The magnetic field vectors are

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

2002-01-01

128

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

129

Plasma heating by electric field compression.  

PubMed

Plasma heating by compression of electric fields is proposed. It is shown that periodic cycles of external compression followed by the free expansion of electric fields in the plasma cause irreversible, collisionless plasma heating and corresponding entropy generation. As a demonstration of general ideas and scalings, the heating is shown in the case of a dusty plasma, where electric fields are created due to the presence of charged dust. The method is expected to work in the cases of compression of low frequency or dc electric fields created by other methods. Applications to high power laser heating of plasmas using this scheme are discussed. PMID:24856702

Avinash, K; Kaw, P K

2014-05-01

130

Plasma Heating by Electric Field Compression  

NASA Astrophysics Data System (ADS)

Plasma heating by compression of electric fields is proposed. It is shown that periodic cycles of external compression followed by the free expansion of electric fields in the plasma cause irreversible, collisionless plasma heating and corresponding entropy generation. As a demonstration of general ideas and scalings, the heating is shown in the case of a dusty plasma, where electric fields are created due to the presence of charged dust. The method is expected to work in the cases of compression of low frequency or dc electric fields created by other methods. Applications to high power laser heating of plasmas using this scheme are discussed.

Avinash, K.; Kaw, P. K.

2014-05-01

131

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.

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

2013-01-01

132

Electric-field-induced crack patterns: Experiments and simulation  

NASA Astrophysics Data System (ADS)

We report a study of crack patterns formed in laponite gel drying in an electric field. The sample dries in a circular petri dish and the field is radial, acting inward or outward. A system of radial cracks forms in the setup with the center terminal positive, while predominantly cross-radial cracks form when the center is at a negative potential. The laponite accumulates near the negative terminal making the layer thicker at this end. A spring model on a square lattice is used to simulate the desiccation crack formation, with an additional radial force acting due to the electric field. With the radial force acting outward, radial cracks form and for the reversed field cross-radial cracks form. This conforms to the observation that laponite platelets become effectively positive due to overcharging and are attracted towards the negative terminal.

Khatun, Tajkera; Choudhury, Moutushi Dutta; Dutta, Tapati; Tarafdar, Sujata

2012-07-01

133

Brief: Field measurements of casing tension forces  

SciTech Connect

Tension forces acting on individual casing joints were accurately measured during installation of 10,158 ft of 9 5/8-in. {times} 47-lbm/ft casing and 11,960 ft of 11 7/8-in. {times} 71.8-lbm/ft casing. A unique casing load table (CLT) weighed the casing string after the addition of each casing joint. Strain gauges attached inside the pin ends of instrumented casing joints (ICJ`s) directly measured tension force on those joints. A high-speed computer data-acquisition system (DAS) automatically recorded data from all the sensors. Several casing joints were intentionally subjected to extreme deceleration to determine upper limits for dynamic tension forces. Data from these tests clearly show effects of wellbore friction and casing handling conditions. In every case, tension forces in the casing during maximum deceleration were considerably less than expected. In some cases, the highest tension forces occurred when the casing lifted out of the slips. Peak tension forces caused by setting the casing slips were typically no more than 5% greater than tension forces in the casing at rest. This dynamic amplification was far less than the 60% value used in the previous casing design method. Reducing the safety factor for installation loads has permitted use of lighter, less-expensive casing than dictated by older design criteria.

Quigley, M.S.; Lewis, D.B. [Mobil E and P Technical Center, Dallas, TX (United States); Boswell, R.S. [Stress Engineering Services, Houston, TX (United States)

1995-02-01

134

Localized induced electric field within the magnetotail  

NASA Technical Reports Server (NTRS)

The conversion of magnetic energy, stored within the magnetotail during the growth phase, into particle kinetic energy is studied by taking induced electric fields, due to explicit time dependence of magnetic fields, into consideration. The polarization of a plasma in the presence of such a field is discussed, and the topological difference between a polarized and an induced electric field, namely that one is irrotational and the other is not, is pointed out. A localized perturbation in neutral sheet current is also discussed.

Heikkila, W. J.; Pellinen, R. J.

1977-01-01

135

Electric-field sensing using single diamond spins  

NASA Astrophysics Data System (ADS)

The ability to sensitively detect individual charges under ambient conditions would benefit a wide range of applications across disciplines. However, most current techniques are limited to low-temperature methods such as single-electron transistors, single-electron electrostatic force microscopy and scanning tunnelling microscopy. Here we introduce a quantum-metrology technique demonstrating precision three-dimensional electric-field measurement using a single nitrogen-vacancy defect centre spin in diamond. An a.c. electric-field sensitivity reaching 202+/-6Vcm-1Hz-1/2 has been achieved. This corresponds to the electric field produced by a single elementary charge located at a distance of ~150nm from our spin sensor with averaging for one second. The analysis of the electronic structure of the defect centre reveals how an applied magnetic field influences the electric-field-sensing properties. We also demonstrate that diamond-defect-centre spins can be switched between electric- and magnetic-field sensing modes and identify suitable parameter ranges for both detector schemes. By combining magnetic- and electric-field sensitivity, nanoscale detection and ambient operation, our study should open up new frontiers in imaging and sensing applications ranging from materials science to bioimaging.

Dolde, F.; Fedder, H.; Doherty, M. W.; Nöbauer, T.; Rempp, F.; Balasubramanian, G.; Wolf, T.; Reinhard, F.; Hollenberg, L. C. L.; Jelezko, F.; Wrachtrup, J.

2011-06-01

136

Engineering aspects of pulsed electric field pasteurization  

Microsoft Academic Search

Pulsed electric fields (PEF) is a promising technology for the non-thermal pasteurization of foods and a sound complement or replacement to traditional thermal pasteurization, which inactivates bacteria and other microorganisms harmful to humans, but also degrades color, flavor, texture and nutrients. Foods can be pasteurized with pulsed electric fields at ambient or refrigerated temperatures for a short treatment time of

Qinghua Zhang; Gustavo V. Barbosa-Cánovas; Barry G. Swanson

1995-01-01

137

Modeling the electric field of weakly electric fish.  

PubMed

Weakly electric fish characterize the environment in which they live by sensing distortions in their self-generated electric field. These distortions result in electric images forming across their skin. In order to better understand electric field generation and image formation in one particular species of electric fish, Apteronotus leptorhynchus, we have developed three different numerical models of a two-dimensional cross-section of the fish's body and its surroundings. One of these models mimics the real contour of the fish; two other geometrically simple models allow for an independent study of the effects of the fish's body geometry and conductivity on electric field and image formation. Using these models, we show that the fish's tapered body shape is mainly responsible for the smooth, uniform field in the rostral region, where most electroreceptors are located. The fish's narrowing body geometry is also responsible for the relatively large electric potential in the caudal region. Numerical tests also confirm the previous hypothesis that the electric fish body acts approximately like an ideal voltage divider; this is true especially for the tail region. Next, we calculate electric images produced by simple objects and find they vary according to the current density profile assigned to the fish's electric organ. This explains some of the qualitative differences previously reported for different modeling approaches. The variation of the electric image's shape as a function of different object locations is explained in terms of the fish's geometrical and electrical parameters. Lastly, we discuss novel cues for determining an object's rostro-caudal location and lateral distance using these electric images. PMID:16943504

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

2006-09-01

138

Forces on Dust Grains Exposed to Anisotropic Interstellar Radiation Fields  

Microsoft Academic Search

Grains exposed to anisotropic radiation fields are subjected to forces due to\\u000athe asymmetric photon-stimulated ejection of particles. These forces act in\\u000aaddition to the ``radiation pressure'' due to absorption and scattering. Here\\u000awe model the forces due to photoelectron emission and the photodesorption of\\u000aadatoms. The ``photoelectric'' force depends on the ambient conditions relevant\\u000ato grain charging. We find

Joseph C. Weingartner; B. T. Draine

2000-01-01

139

Lorentz Body Force Induced by Traveling Magnetic Fields  

NASA Technical Reports Server (NTRS)

The Lorentz force induced by a traveling magnetic field (TMF) in a cylindrical container has been calculated. The force can be used to control flow in dectrically conducting melts and the direction of the magnetic field and resulting flow can be reversed. A TMF can be used to partially cancel flow driven by buoyancy. The penetration of the field into the cylinder decreases as the frequency increases, and there exists an optimal value of frequency for which the resulting force is a maximum. Expressions for the Lorentz force in the limiting cases of low frequency and infinite cylinder are also given and compared to the numerical calculations.

Volz, M. P.; Mazuruk, K.

2003-01-01

140

Large electric fields in the magnetosphere  

NASA Technical Reports Server (NTRS)

The Langmuir solitonlike structures which contain plasma frequency oscillations of 500 mV/m and parallel electric fields of about 100 mV/m, observed in the auroral zone below 1000 km, are studied. The characteristics of electrostatic shocks that contain perpendicular fields of 1000 mV/m and parallel fields of 100 mV/m, and of double layers that have parallel fields of 10 mV/m are described. Observations of the geomagnetic tail reveal the presence of 100 mV/m turbulent electric fields and 5-10 mV/m quasi-static fields in the high latitude boundary of the plasma sheet, and inside the plasma sheet fields of 5-10 mV/m are detected. The large amplitude quasi-static electric field fluctuations of 100 mV/m and the dc fields of approximately 5 mV/m observed in the bow shock are examined.

Mozer, F. S.; Boehm, M. H.; Cattell, C. A.; Temerin, M.; Wygant, J. R.

1985-01-01

141

Atoms in crossed electric and magnetic fields  

SciTech Connect

Extensive experimental and theoretical work pertaining to three interesting aspects of the interaction of atoms with crossed electric and magnetic fields is presented. The first experiment discussed deals with the effects of weak crossed fields on sodium atoms. A fluorescence spectrum of laser-excited sodium n = 11 states in an electric field of 2560 V/cm perpendicular to a magnetic field of 4.4 kG is presented, along with a comparison to theory. The data show the important effects of m-mixing and residual degeneracies that remain in the crossed fields. The next topic presented is the theoretical prediction of novel resonances, termed quasi-Penning resonances, corresponding to electron states localized away from the nucleus at the Stark saddlepoint in strong crossed electric and magnetic fields. The stability and possibility for observation of these resonances is explored. Finally, extensive experimental maps of data are presented that compare laser-induced ionization spectra of sodium atoms in crossed electric and magnetic fields to spectra in an electric field atone. The experiment explores the energy region of the electric-field saddlepoint, where quasi-Penning resonances are predicted to occur. The magnetic field is too weak for the observation of these resonances, but the experiment provides important groundwork for the understanding of future experiments in strong crossed fields.

Korevaar, E.J.

1987-01-01

142

Measurement of the body force field of plasma actuators  

Microsoft Academic Search

A novel technique is proposed and investigated for the estimation of the body force field resulting from the operation of a dielectric barrier discharge plasma actuator. The technique relies on the measurement of the spatio-temporal evolution of the induced velocity field using high-speed particle image velocimetry (PIV). The technique has the advantage of providing spatial distribution of the body force

M. Kotsonis; S. Ghaemi; L. Veldhuis; F. Scarano

2011-01-01

143

Tailored Force Fields for Space-Based Construction  

Microsoft Academic Search

In Space, minor forces exerted over long periods can produce major results. Force fields of various kinds can be used to build large structures, superseding the human-intensive construction techniques of today. In this paper we consider how several techniques now used in other fields can be generalized and applied to Space-based construction. Radiation pressure exerted by coherent beams on scattering

Narayanan M. Komerath; Sameh S. Wanis; Joseph Czechowski

2003-01-01

144

Electrohydrodynamics of a drop under nonaxisymmetric electric fields.  

PubMed

We consider the electrohydrodynamics of a spherical drop in a nonaxisymmetric electric field, which can be approximated by the sum of a uniform field and a linear straining field. We obtain the analytic solution of the three-dimensional flow fields inside and outside a drop for the Stokes flow regime by using Lamb's general solution and the leaky dielectric model. With the analytic solution, the dielectrophoretic migration velocity of a drop is obtained as a function of the type and the frequency of the imposed electric field. The direction of drop motion is found to be parallel to the dielectrophoretic force. The analytic solution is also used to investigate the characteristics of the interfacial flow under various nonaxisymmetric electric fields. While investigating the interfacial flow, we find a surface vortex structure under certain nonaxisymmetric electric fields, which is found to be related to the chaotic mixing inside the drop. Finally, we consider the chaotic features of three-dimensional flows inside the drop under static nonaxisymmetric electric fields. PMID:12957591

Im, Do Jin; Kang, In Seok

2003-10-01

145

Potential distribution for a spheroidal cell having a conductive membrane in an electric field  

Microsoft Academic Search

When a cell is situated in a uniform electric field, the field is modified due to the relatively low conductance of the cell membrane compared to that of the surrounding fluids. In certain cases, such as in the estimation of internal and external electrokinetic forces, one requires a means of estimating the magnitude of the electric field inside and outside

Rocco A. Jerry; Aleksander S. Popel; William E. Brownell

1996-01-01

146

Dynamic electrostatic force microscopy technique for the study of electrical properties with improved spatial resolution  

NASA Astrophysics Data System (ADS)

The need to resolve the electrical properties of confined structures (CNTs, quantum dots, nanorods, etc) is becoming increasingly important in the field of electronic and optoelectronic devices. Here we propose an approach based on amplitude modulated electrostatic force microscopy to obtain measurements at small tip-sample distances, where highly nonlinear forces are present. We discuss how this improves the lateral resolution of the technique and allows probing of the electrical and surface properties. The complete force field at different tip biases is employed to derive the local work function difference. Then, by appropriately biasing the tip-sample system, short-range forces are reconstructed. The short-range component is then separated from the generic tip-sample force in order to recover the pure electrostatic contribution. This data can be employed to derive the tip-sample capacitance curve and the sample dielectric constant. After presenting a theoretical model that justifies the need for probing the electrical properties of the sample in the vicinity of the surface, the methodology is presented in detail and verified experimentally.

Maragliano, C.; Heskes, D.; Stefancich, M.; Chiesa, M.; Souier, T.

2013-06-01

147

Dynamic electrostatic force microscopy technique for the study of electrical properties with improved spatial resolution.  

PubMed

The need to resolve the electrical properties of confined structures (CNTs, quantum dots, nanorods, etc) is becoming increasingly important in the field of electronic and optoelectronic devices. Here we propose an approach based on amplitude modulated electrostatic force microscopy to obtain measurements at small tip-sample distances, where highly nonlinear forces are present. We discuss how this improves the lateral resolution of the technique and allows probing of the electrical and surface properties. The complete force field at different tip biases is employed to derive the local work function difference. Then, by appropriately biasing the tip-sample system, short-range forces are reconstructed. The short-range component is then separated from the generic tip-sample force in order to recover the pure electrostatic contribution. This data can be employed to derive the tip-sample capacitance curve and the sample dielectric constant. After presenting a theoretical model that justifies the need for probing the electrical properties of the sample in the vicinity of the surface, the methodology is presented in detail and verified experimentally. PMID:23635384

Maragliano, C; Heskes, D; Stefancich, M; Chiesa, M; Souier, T

2013-06-01

148

Ionization induced by strong electromagnetic field in low dimensional systems bound by short range forces  

NASA Astrophysics Data System (ADS)

Ionization processes for a two dimensional quantum dot subjected to combined electrostatic and alternating electric fields of the same direction are studied using quantum mechanical methods. We derive analytical equations for the ionization probability in dependence on characteristic parameters of the system for both extreme cases of a constant electric field and of a linearly polarized electromagnetic wave. The ionization probabilities for a superposition of dc and low frequency ac electric fields of the same direction are calculated. The impulse distribution of ionization probability for a system bound by short range forces is found for a superposition of constant and alternating fields. The total probability for this process per unit of time is derived within exponential accuracy. For the first time the influence of alternating electric field on electron tunneling probability induced by an electrostatic field is studied taking into account the pre-exponential term.

Eminov, P. A.

2013-10-01

149

Polarizable and nonpolarizable force fields for alkyl nitrates.  

PubMed

Quantum-chemistry-based many-body polarizable and two-body nonpolarizable atomic force fields were developed for alkyl nitrate liquids and pentaerythritol tetranitrate (PETN) crystal. Bonding, bending, and torsional parameters, partial charges, and atomic polarizabilities for the polarizable force field were determined from gas-phase quantum chemistry calculations for alkyl nitrate oligomers and PETN performed at the MP2/aug-cc-pvDz level of theory. Partial charges for the nonpolarizable force field were determined by fitting the dipole moments and electrostatic potential to values for PETN molecules in the crystal phase obtained from molecular dynamics simulations using the polarizable force field. Molecular dynamics simulations of alkyl nitrate liquids and two polymorphs of PETN crystal demonstrate the ability of the quantum-chemistry-based force fields to accurately predict thermophysical and mechanical properties of these materials. PMID:18085767

Borodin, Oleg; Smith, Grant D; Sewell, Thomas D; Bedrov, Dmitry

2008-01-24

150

Fiber-Optic Electric-Field Meter  

NASA Technical Reports Server (NTRS)

Sensor for measuring electric-field strength does not greatly alter field in which placed. Sensor used to map fields in electric power substation or under high-voltage transmission line. Also used for laboratory measurements. Fused-silica fibers guide light from source to photometer. Light emerges from tip of source fiber, passes through curved coupler, and enters tip of photometer fiber. Attenuation of coupler changes with distance between fiber tips.

Johnston, A. R.

1986-01-01

151

Induced electric fields in anisotropic thermoelectric materials  

Microsoft Academic Search

Transport in an anisotropic material can create potentially large induced transverse fields which reduce the measured electric and thermal conductivities relative to those computed without the induced fields. These affect the thermoelectric figure of merit ZT modestly. The induced electric field in n-type Bi2Te3 is predicted to be as much as 76% of the external one and can lower the

W. E. Bies; R. J. Radtke; H. Ehrenreich

1999-01-01

152

Note: Electrical resolution during conductive atomic force microscopy measurements under different environmental conditions and contact forces  

SciTech Connect

Conductive atomic force microscopy experiments on gate dielectrics in air, nitrogen, and UHV have been compared to evaluate the impact of the environment on topography and electrical measurements. In current images, an increase of the lateral resolution and a reduction of the conductivity were observed in N{sub 2} and, especially, in UHV (where current depends also on the contact force). Both effects were related to the reduction/elimination of the water layer between the tip and the sample in N{sub 2}/UHV. Therefore, since current measurements are very sensitive to environmental conditions, these factors must be taken into consideration when comparisons between several experiments are performed.

Lanza, M.; Porti, M.; Nafria, M.; Aymerich, X. [Dept. Enginyeria Electronica, Universitat Autonoma de Barcelona, Edifici Q, 08193 Bellaterra (Spain); Whittaker, E.; Hamilton, B. [University of Manchester, Sackville Street, Manchester M60 JQD (United Kingdom)

2010-10-15

153

Concentrating colloids with electric field gradients. I. Particle transport and growth mechanism of hard-sphere-like crystals in an electric bottle  

Microsoft Academic Search

This work concerns the use of electric field gradients to manipulate the local particle concentration in a hard-sphere-like suspension. Inside a specially designed ``electric bottle,'' we observed our colloids to collect in the regions of lowest field strength (``negative dielectrophoresis''). This allows for the use of larger field gradients and stronger dielectrophoretic forces than in the original electric bottle design,

Mirjam E. Leunissen; Matthew T. Sullivan; Paul M. Chaikin; Alfons van Blaaderen

2008-01-01

154

Concentrating colloids with electric field gradients. I. Particle transport and growth mechanism of hard-sphere-like crystals in an electric bottle  

Microsoft Academic Search

This work concerns the use of electric field gradients to manipulate the local particle concentration in a hard-sphere-like suspension. Inside a specially designed “electric bottle,” we observed our colloids to collect in the regions of lowest field strength (“negative dielectrophoresis”). This allows for the use of larger field gradients and stronger dielectrophoretic forces than in the original electric bottle design,

Mirjam E. Leunissen; Matthew T. Sullivan; Paul M. Chaikin; Alfons van Blaaderen

2008-01-01

155

Thin film transistors fabricated by evaporating pentacene under electric field  

NASA Astrophysics Data System (ADS)

Organizing the pentacene molecules with respect to the substrate is an essential prerequisite for achieving high field effect mobility in organic thin film transistors. Here, we report electrical characteristics of bottom gate, top contact Sin++/SiO2/pentacene/gold thin film transistors using electric field assisted thermal evaporation of pentacene. We find that the field assisted devices exhibit a five-fold enhancement in the field effect mobility, along with improvement in the saturation current as compared with a standard device. Simulation of electric field distribution in the substrate-electrode arrangement due to the application of external voltage during pentacene deposition shows an existence of a non-uniform electric field in the bottom gate top contact configuration and hence another configuration that avoids metal before pentacene deposition is proposed. The observed improvement in the transistor characteristics of field assisted device is explained by ab-initio calculation of anisotropy in the polarizability of isolated pentacene molecule, followed by an estimate of molecules that would align due to the field. Furthermore, the preferential molecular alignment in field deposited pentacene films is confirmed using X-ray diffraction and atomic force microscopy.

Mandal, Tapendu; Garg, Ashish; Deepak

2013-10-01

156

Heat Transfer Control in Quiescent Air with Thermal Gradient by Magnetizing Force Under both Gravitational and Nongravitational Fields  

Microsoft Academic Search

Two-dimensional numerical computations were carried out to clarify the influence of magnetizing force on quiescent air with thermal gradient in a vertical cylindrical container under both gravitational and nongravitational fields. Several sizes and axial positions of a circular electric coil were tested so that the magnetizing force depended on the magnetic gradient. Under both gravitational and nongravitational fields, the convection

Masato Akamatsu; Mitsuo Higano; Yoshio Takahashi; Hiroyuki Ozoe

2005-01-01

157

Parallel Microassembly with Electrostatic Force Fields  

Microsoft Academic Search

Assembly is a fundamental issue in the volume productionof products that include microscopic (submillimeter)parts. These parts are often fabricated in parallelat high density but must then be assembled intopatterns with lower spatial density. In this paper wepropose a new approach to microassembly using 1) ultrasonicvibration to eliminate friction and adhesion,and 2) electrostatic forces to position and align partsin parallel. We

Karl-friedrich Böhringer; Kenneth Y. Goldberg; Michael Cohn; Roger Howe; Al Pisano

1998-01-01

158

Magnetotail electric fields observed from lunar orbit  

NASA Technical Reports Server (NTRS)

Direct observations of convection electric fields in the earth's magnetotail are reported. The electric fields have been measured from lunar orbit by detection of the E x B/B-squared drift displacement of low-energy electrons at the limb of the moon. It is found that electric fields range in magnitude from a value less than or equal to 0.02 mV/m, the limit of sensitivity of the method, to 2 mV/M. The typical value is 0.15 mV/M, and the corresponding convection velocity is 15 km/s. The sense of the electric field is almost always dawn to dusk. The electric field is often variable on a time scale of hours and sometimes minutes. The observations indicate that the electric field is not uniform across the magnetotail. If it is assumed that the typical measured electric-field value represents an average over the inhomogeneities, the potential drop across the entire tail is of the order of 40 kV.

Mccoy, J. E.; Lin, R. P.; Mcguire, R. E.; Chase, L. M.; Anderson, K. A.

1975-01-01

159

Atoms in Crossed Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

In this dissertation, extensive experimental and theoretical work pertaining to three interesting aspects of the interaction of atoms with crossed electric and magnetic fields is presented. The first experiment discussed deals with the effects of weak crossed fields on sodium atoms. A fluorescence spectrum of laser excited sodium n = 11 states in an electric field of 2560 V/cm perpendicular to a magnetic field of 4.4 kG is presented, along with a comparison to theory. The data show the important effects of m-mixing and residual degeneracies which remain in the crossed fields. The next topic presented is the theoretical prediction of novel resonances, termed "quasi-Penning resonances," corresponding to electron states localized away from the nucleus at the Stark saddlepoint in strong crossed electric and magnetic fields. The stability and possibility for observation of these resonances is explored. Finally, extensive experimental maps of data are presented which compare laser induced ionization spectra of sodium atoms in crossed electric and magnetic fields to spectra in an electric field atone. The experiment explores the energy region of the electric field saddlepoint, where quasi-Penning resonances are predicted to occur. The magnetic field is too weak for the observation of these resonances, but the experiment provides important groundwork for the understanding of future experiments in strong crossed fields. The magnetic field is seen to cause splitting of some transitions due to the interaction of the electron spin with the magnetic field. Also, magnetic field induced state mixing causes a redistribution of oscillator strengths leading to changes in peak heights and auto-ionizing line widths. On the whole, however, the effect of the weak crossed magnetic field on the sodium Stark spectra remains small.

Korevaar, Eric John

1987-09-01

160

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.

161

Numerical simulation of Brownian particles in optical force fields  

NASA Astrophysics Data System (ADS)

Optical forces can affect the motion of a Brownian particle. For example, optical tweezers use optical forces to trap a particle at a desirable position. Using more complex force fields it is possible to generate more complex configurations. For example, by using two optical traps placed next to each other, it is possible to obtain a bistable potential where a particle can jump between the two potentials with a characteristic time scale. In this proceeding, we discuss a simple finite difference algorithm that can be used to simulate the motion of a Brownian particle in a one-dimensional field of optical forces.

Volpe, Giorgio; Volpe, Giovanni

2013-09-01

162

ESTIMATING ELECTRIC FIELDS FROM VECTOR MAGNETOGRAM SEQUENCES  

SciTech Connect

Determining the electric field distribution on the Sun's photosphere is essential for quantitative studies of how energy flows from the Sun's photosphere, through the corona, and into the heliosphere. This electric field also provides valuable input for data-driven models of the solar atmosphere and the Sun-Earth system. We show how observed vector magnetogram time series can be used to estimate the photospheric electric field. Our method uses a 'poloidal-toroidal decomposition' (PTD) of the time derivative of the vector magnetic field. These solutions provide an electric field whose curl obeys all three components of Faraday's Law. The PTD solutions are not unique; the gradient of a scalar potential can be added to the PTD electric field without affecting consistency with Faraday's Law. We then present an iterative technique to determine a potential function consistent with ideal MHD evolution; but this field is also not a unique solution to Faraday's Law. Finally, we explore a variational approach that minimizes an energy functional to determine a unique electric field, a generalization of Longcope's 'Minimum Energy Fit'. The PTD technique, the iterative technique, and the variational technique are used to estimate electric fields from a pair of synthetic vector magnetograms taken from an MHD simulation; and these fields are compared with the simulation's known electric fields. The PTD and iteration techniques compare favorably to results from existing velocity inversion techniques. These three techniques are then applied to a pair of vector magnetograms of solar active region NOAA AR8210, to demonstrate the methods with real data. Careful examination of the results from all three methods indicates that evolution of the magnetic vector by itself does not provide enough information to determine the true electric field in the photosphere. Either more information from other measurements, or physical constraints other than those considered here are necessary to find the true electric field. However, we show it is possible to construct physically reasonable electric field distributions whose curl matches the evolution of all three components of B. We also show that the horizontal and vertical Poynting flux patterns derived from the three techniques are similar to one another for the cases investigated.

Fisher, G. H.; Welsch, B. T.; Abbett, W. P.; Bercik, D. J. [Space Sciences Laboratory, University of California, Berkeley, CA 94720-7450 (United States)

2010-05-20

163

Electric/Magnetic Field Sensor.  

National Technical Information Service (NTIS)

A UNLV novel electric/magnetic dot sensor comprises: a loop of conductor having two ends to the loop, a first end and a second end; the first end of the conductor seamlessly secured to a first conductor within a first sheath; the second end of the conduct...

M. Popek R. A. Schill

2005-01-01

164

Are Current Molecular Dynamics Force Fields too Helical?  

PubMed Central

Accurate force fields are essential for the success of molecular dynamics simulations. In apparent contrast to the conformational preferences of most force fields, recent NMR experiments suggest that short polyalanine peptides in water populate the polyproline II structure almost exclusively. To investigate this apparent contradiction, with its ramifications for the assessment of molecular force fields and the structure of unfolded proteins, we performed extensive simulations of Ala5 in water (?5 ?s total time), using twelve different force fields and three different peptide terminal groups. Using either empirical or density-functional-based Karplus relations for the J-couplings, we find that most current force fields do overpopulate the ?-region, with quantitative results depending on the choice of Karplus relation and on the peptide termini. Even after reweighting to match experiment, we find that Ala5 retains significant ?- and ?-populations. In fact, several force fields match the experimental data well before reweighting and have a significant helical population. We conclude that radical changes to the best current force fields are not necessary, based on the NMR data. Nevertheless, experiments on short peptides open the way toward the systematic improvement of current simulation models.

Best, Robert B.; Buchete, Nicolae-Viorel; Hummer, Gerhard

2008-01-01

165

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

166

Electric and magnetic field exposure associated with electric blankets  

SciTech Connect

electric blankets may be important contributors to the public's overall exposure to 60 Hz electric and magnetic fields (EMFs) since they are common appliances that are used close to the body for long periods of time. This report describes a series of experimental and computer analyses characterizing various aspects of EMF exposure from electric blankets in use prior to Fall 1990. Almost of electric blankets were found to use on/off controllers with cycle periods of minutes. Calculations of magnetic fields within the body show that, when blankets are heating, flux densities averaged over the whole body range from 15--33 mG during the on'' cycle with typical values of 22 mG. Duty cycles are predicted to vary widely from user-to-user, with typical values of perhaps 40%. Given typical blanket usage patterns, the long-term body-averaged magnetic field exposure from blankets is expected to be comparable to that form other EMF sources for a significant fraction of the blanket-using population. No significant differences were found between time-averaged magnetic field exposures from blankets with metal alloy and plastic polymer heating elements. Blankets with alloy and polymer heating elements did differ significantly in electric field exposure. Calculations show that the unperturbed field 5 cm above flat blankets range from 60--150 V/m for alloy heating cables and unperturbed field 5 cm above flat blankets range from 60--150 V/m for alloy heating cables and 10--40 V/m polymer cables. Starting in Fall 1990, electric blanket manufactures introduced new designs that produce much smaller magnetic fields. These are expected to replace the current in-use stock at a rate of 10--15% per year.

Florig, H.K.; Hoburg, J.F. (Carnegie-Mellon Univ., Pittsburgh, PA (United States). Dept. of Engineering and Public Policy)

1991-12-01

167

Electric field-induced magnetization switching in epitaxial columnar nanostructures.  

PubMed

We present direct evidence for room-temperature magnetization reversal induced by an electric field in epitaxial ferroelectric BiFeO3-ferrimagnetic CoFe2O4 columnar nanostructures. Piezoelectric force microscopy and magnetic force microscopy were used to locally image the coupled piezoelectric-magnetic switching. Quantitative analyses give a perpendicular magnetoelectric susceptibility of approximately 1.0 x 10(-2) G cm/V. The observed effect is due to the strong elastic coupling between the two ferric constituents as the result of the three-dimensional heteroepitaxy. PMID:16159226

Zavaliche, F; Zheng, H; Mohaddes-Ardabili, L; Yang, S Y; Zhan, Q; Shafer, P; Reilly, E; Chopdekar, R; Jia, Y; Wright, P; Schlom, D G; Suzuki, Y; Ramesh, R

2005-09-01

168

Prediction of Mechanical Properties of Polymers With Various Force Fields  

NASA Technical Reports Server (NTRS)

The effect of force field type on the predicted elastic properties of a polyimide is examined using a multiscale modeling technique. Molecular Dynamics simulations are used to predict the atomic structure and elastic properties of the polymer by subjecting a representative volume element of the material to bulk and shear finite deformations. The elastic properties of the polyimide are determined using three force fields: AMBER, OPLS-AA, and MM3. The predicted values of Young s modulus and shear modulus of the polyimide are compared with experimental values. The results indicate that the mechanical properties of the polyimide predicted with the OPLS-AA force field most closely matched those from experiment. The results also indicate that while the complexity of the force field does not have a significant effect on the accuracy of predicted properties, small differences in the force constants and the functional form of individual terms in the force fields determine the accuracy of the force field in predicting the elastic properties of the polyimide.

Odegard, Gregory M.; Clancy, Thomas C.; Gates, Thomas S.

2005-01-01

169

Interaction Between Flames and Electric Fields Studied.  

National Technical Information Service (NTIS)

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 io...

Z. G. Yuan U. Hegde

2003-01-01

170

Azimuthal Electric Fields and Tandem Ambipolarity.  

National Technical Information Service (NTIS)

The importance of retaining the azimuthal variation of the electrostatic potential in transport and ambipolarity studies is demonstrated. Because the azimuthal electric field must satisfy quasi-neutrality, equilibrium ambipolar operation permitting differ...

P. J. Catto J. R. Myra X. S. Lee G. L. Francis

1984-01-01

171

Metrology system for pulsed electric fields processing  

Microsoft Academic Search

Efficient process monitoring and accurate measurement of the electrical parameters defining pulsed electric fields (PEF) treatment and lethality are key factors in the implementation of PEF. A metrology system that can accurately evaluate and record treatment delivery was developed. To achieve this end one current sensor and two high voltage sensors were placed in a food PEF coaxial treatment chamber,

M. M Góngora-Nieto; F Younce; G. M Hyde; P. D Pedrow; B. G Swanson; G. V Barbosa-Cánovas

2002-01-01

172

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

173

Pair production in rotating electric fields  

NASA Astrophysics Data System (ADS)

We explore Schwinger pair production in rotating time-dependent electric fields using the real-time Dirac-Heisenberg-Wigner formalism. We determine the time evolution of the Wigner function as well as asymptotic particle distributions neglecting backreactions on the electric field. Whereas qualitative features can be understood in terms of effective Keldysh parameters, the field rotation leaves characteristic imprints in the momentum distribution that can be interpreted in terms of interference and multiphoton effects. These phenomena may seed characteristic features of QED cascades created in the antinodes of a high-intensity standing wave laser field.

Blinne, Alexander; Gies, Holger

2014-04-01

174

An investigation of behaviours of a single bubble in a uniform electric field  

Microsoft Academic Search

The effects of a d.c. electric field on bubble behaviours such as bubble growth, deformation and detachment are investigated. The bubble behaviours are simulated experimentally and the electric force acting on bubble is calculated numerically. The results indicate that bubbles are compressed intensely by the horizontal component of the electric stress and elongated by the vertical component, thus prolate spherical

W. Dong; R. Y. Li; H. L. Yu; Y. Y. Yan

2006-01-01

175

Flow Field and Wall Forces of Yawed and Curved Cylinders  

Microsoft Academic Search

Measurements have been performed in an acoustic wind tunnel and tow tank to quantify the mean and fluctuating wall forces and flow fields on yawed and curved sections of cylinders. Of particular interest is the influence of inflow boundary layer thickness on the separation and shedding characteristics and the dynamic wall forces as a function of local yaw angle and

Stephen R. Snarski; William L. Keith

2003-01-01

176

Acculturation in Acquired Organizations: A Force-Field Perspective  

Microsoft Academic Search

The acculturation process involved when one organization is acquired by another, and the two organizational cultures merge, has not been adequately conceptualized in the strategic management literature. It is argued here that the acculturation process can be more fully understood by utilizing Lewin's (1951) force-field approach. In addition, major forces of cultural differentiation and organizational integration are identified. It is

Priscilla M. Elsass; John F. Veiga

1994-01-01

177

Optical fiber sensor for electric field and electric charge using low-coherence, Fabry-Perot interferometry.  

PubMed

An optical fiber sensor for electric field and electric charge, based on the deflection of a small cantilever, has been developed. When the sensor head is placed in an electric field, induced charging produces deflection of the cantilever, which is measured using low-coherence, Fabry-Perot interferometry. The sensor has been used to measure the electric field in the vicinity of a Van de Graaff generator, in the range 135-650 V/cm. The measured deflections are in good agreement with the predictions of a simple model equating the electrostatic and mechanical forces acting on the cantilever. PMID:18259242

Priest, T S; Scelsi, G B; Woolsey, G A

1997-07-01

178

Electric/magnetic field sensor  

DOEpatents

A UNLV novel electric/magnetic dot sensor includes a loop of conductor having two ends to the loop, a first end and a second end; the first end of the conductor seamlessly secured to a first conductor within a first sheath; the second end of the conductor seamlessly secured to a second conductor within a second sheath; and the first sheath and the second sheath positioned adjacent each other. The UNLV novel sensor can be made by removing outer layers in a segment of coaxial cable, leaving a continuous link of essentially uncovered conductor between two coaxial cable legs.

Schill, Jr., Robert A. (Henderson, NV); Popek, Marc [Las Vegas, NV

2009-01-27

179

Electric field gradient focusing in microchannels with embedded bipolar electrode.  

PubMed

The complex interplay of electrophoretic, electroosmotic, bulk convective, and diffusive mass/charge transport in a hybrid poly(dimethylsiloxane) (PDMS)/glass microchannel with embedded floating electrode is analyzed. The thin floating electrode attached locally to the wall of the straight microchannel results in a redistribution of local field strength after the application of an external electric field. Together with bulk convection based on cathodic electroosmotic flow, an extended field gradient is formed in the anodic microchannel segment. It imparts a spatially dependent electrophoretic force on charged analytes and, in combination with the bulk convection, results in an electric field gradient focusing at analyte-specific positions. Analyte concentration in the enriched zone approaches a maximum value which is independent of its concentration in the supplying reservoirs. A simple approach is shown to unify the temporal behavior of the concentration factors under general conditions. PMID:19532966

Hlushkou, Dzmitry; Perdue, Robbyn K; Dhopeshwarkar, Rahul; Crooks, Richard M; Tallarek, Ulrich

2009-07-01

180

Liquid crystal fiber optic electric field probe  

NASA Astrophysics Data System (ADS)

Polymer dispersed liquid crystal inserted between two multimode optical fiber end faces forms the basis of an electric field probe. This probe has an active volume of about 0.001 mm3 and approximates a point measurement. The linear relation between detector output and electric field in the 600-800 V/cm range is adequate for most electric power distribution systems. As the contrast ratio of this transducer is large, it can be used as an on-off detector for high voltage equipment.

Lacquet, Beatrys M.; Swart, Pieter L.; Spammer, Stephanus J.

1995-09-01

181

Electric field measurements with stratospheric balloons  

NASA Technical Reports Server (NTRS)

Electric fields and currents in the middle atmosphere are important elements of the modern picture of this region. Balloon instruments, reaching the level of the stratosphere, were used extensively for the experimental work. The research has shown good progress, both in the MAP period and in the years before and after. The knowledge was increased about, e.g., the upper atmosphere potential, the electric properties of the medium itself and about the coupling with magnetospheric (ionospheric) fields and currents. Also various measurements have brought about a discussion of the possible existence of hitherto unknown sources. Throughout the MAP period the work on a possible definition of an electric index has continued.

Iversen, I. B.

1989-01-01

182

Research of optical electric field probe  

NASA Astrophysics Data System (ADS)

As an important modern measurement equipment of the electromagnetic field, electric field probe can measure the industrial, scientific and medical aspects of the leakage field. In the Electro Magnetic Compatibility (EMC) experiment, it can also check the high-frequency-sensitive parts of the devices and the parasitic radiations due to the mechanical movement. Especially in the field of Electromagnetic Compatibility, electric field probe is one of the most important test equipment. This paper introduces a type of optical electric field probe. In the system, a kind of antenna, which could provide a response nearly isotropic for all polarizations of the incident field, is used for receiving the signal of the electric field. The high-frequency signal received by the antenna then is detected by Schottky barrier diode detector. This low-frequency or Direct Current (DC) signal can be modulated to the band of light by the Electro-Absorption-Distributed Feed Back (EA-DFB) modulator, thus the probe can provide a wild band responds. Through the optical fiber, the optical signal is sent to the photoelectric detector. Based on the optical power value, the field intensity can be calculated. In this system, compared with traditional transmission line, optical fiber can minimize the electromagnetic interference and transmission-line attenuation. In addition to this, the system also has high test sensitivity and wide measurement bandwidth. Furthermore, the whole system has a simple structure and low manufacturing cost.

Zhang, Wan; Li, Bin; Chen, Jingyao; Wang, Jifeng; Lu, Guizhen

2012-10-01

183

Fluid flow induced by nonuniform ac electric fields in electrolytes on microelectrodes. I. Experimental measurements  

Microsoft Academic Search

Under the influence of an ac electric field, electrolytes on planar microelectrodes exhibit fluid flow. The nonuniform electric field generated by the electrodes interacts with the suspending fluid through a number of mechanisms, giving rise to body forces and fluid flow. This paper presents the detailed experimental measurements of the velocity of fluid flow on microelectrodes at frequencies below the

N. G. Green; A. Ramos; A. González; H. Morgan; A. Castellanos

2000-01-01

184

Stability of Spherical Vesicles in Electric Fields  

PubMed Central

The stability of spherical vesicles in alternating (ac) electric fields is studied theoretically for asymmetric conductivity conditions across their membranes. The vesicle deformation is obtained from a balance between the curvature elastic energies and the work done by the Maxwell stresses. The present theory describes and clarifies the mechanisms for the four types of morphological transitions observed experimentally on vesicles exposed to ac fields in the frequency range from 500 to 2 × 107 Hz. The displacement currents across the membranes redirect the electric fields toward the membrane normal to accumulate electric charges by the Maxwell?Wagner mechanism. These accumulated electric charges provide the underlying molecular mechanism for the morphological transitions of vesicles as observed on the micrometer scale.

2010-01-01

185

Rotationally Vibrating Electric-Field Mill  

NASA Technical Reports Server (NTRS)

A proposed instrument for measuring a static electric field would be based partly on a conventional rotating-split-cylinder or rotating-split-sphere electric-field mill. However, the design of the proposed instrument would overcome the difficulty, encountered in conventional rotational field mills, of transferring measurement signals and power via either electrical or fiber-optic rotary couplings that must be aligned and installed in conjunction with rotary bearings. Instead of being made to rotate in one direction at a steady speed as in a conventional rotational field mill, a split-cylinder or split-sphere electrode assembly in the proposed instrument would be set into rotational vibration like that of a metronome. The rotational vibration, synchronized with appropriate rapid electronic switching of electrical connections between electric-current-measuring circuitry and the split-cylinder or split-sphere electrodes, would result in an electrical measurement effect equivalent to that of a conventional rotational field mill. A version of the proposed instrument is described.

Kirkham, Harold

2008-01-01

186

D-branes in overcritical electric fields  

SciTech Connect

We collect some arguments for treating a D-brane with overcritical electric field as a well-posed initial condition for a D-brane decay. Within the field theoretical toy model of Minahan and Zwiebach we give an estimate for the condensates of the related infinite tower of tachyonic excitations.

Dorn, Harald; Salizzoni, Mario; Torrielli, Alessandro [Humboldt-Universitaet zu Berlin, Institut fuer Physik, Newtonstrasse 15, D-12489 Berlin (Germany)

2006-01-15

187

Induced electric fields in anisotropic thermoelectric materials  

NASA Astrophysics Data System (ADS)

Transport in an anisotropic material can create potentially large induced transverse fields which reduce the measured electric and thermal conductivities relative to those computed without the induced fields. These affect the thermoelectric figure of merit ZT modestly. The induced electric field in n-type Bi2Te3 is predicted to be as much as 76% of the external one and can lower the measured electrical conductivity by up to 60%. In Hg1-xCdxTe superlattices, the anisotropy may be increased by varying the composition and width of the barrier and well to give induced fields much larger than the applied one. These effects should be easily observable. The present work utilizes general results applied to a microscopic model relevant for multivalleyed materials within the effective-mass and relaxation-time approximations.

Bies, W. E.; Radtke, R. J.; Ehrenreich, H.

1999-11-01

188

Apparatus having reduced mechanical forces for supporting high magnetic fields  

DOEpatents

The present invention identifies several configurations of conducting elements capable of supporting extremely high magnetic fields suitable for plasma confinement, wherein forces experienced by the conducting elements are significantly reduced over those which are present as a result of the generation of such high fields by conventional techniques. It is anticipated that the use of superconducting materials will both permit the attainment of such high fields and further permit such fields to be generated with vastly improved efficiency.

Prueitt, Melvin L. (Los Alamos, NM); Mueller, Fred M. (Los Alamos, NM); Smith, James L. (Los Alamos, NM)

1991-01-01

189

Force Field Parameter Estimation of Functional Perfluoropolyether Lubricants  

SciTech Connect

The head disk interface in a hard disk drive can be considered to be one of the hierarchical multiscale systems, which require the hybridization of multiscale modeling methods with coarse-graining procedure. However, the fundamental force field parameters are required to enable the coarse-graining procedure from atomistic/molecular scale to mesoscale models. In this paper, we investigate beyond molecular level and perform ab initio calculations to obtain the force field parameters. Intramolecular force field parameters for Zdol and Ztetraol were evaluated with truncated PFPE molecules to allow for feasible quantum calculations while still maintaining the characteristic chemical structure of the end groups. Using the harmonic approximation to the bond and angle potentials, the parameters were derived from the Hessian matrix, and the dihedral force constants are fit to the torsional energy profiles generated by a series of constrained molecular geometry optimization.

Smith, R.; Chung, P.S.; Steckel, J; Jhon, M.S.; Biegler, L.T.

2011-01-01

190

Force field parameter estimation of functional perfluoropolyether lubricants  

NASA Astrophysics Data System (ADS)

The head disk interface in a hard disk drive can be considered to be one of the hierarchical multiscale systems, which require the hybridization of multiscale modeling methods with coarse-graining procedure. However, the fundamental force field parameters are required to enable the coarse-graining procedure from atomistic/molecular scale to mesoscale models. In this paper, we investigate beyond molecular level and perform ab initio calculations to obtain the force field parameters. Intramolecular force field parameters for Zdol and Ztetraol were evaluated with truncated PFPE molecules to allow for feasible quantum calculations while still maintaining the characteristic chemical structure of the end groups. Using the harmonic approximation to the bond and angle potentials, the parameters were derived from the Hessian matrix, and the dihedral force constants are fit to the torsional energy profiles generated by a series of constrained molecular geometry optimization.

Smith, Robert; Seung Chung, Pil; Steckel, Janice A.; Jhon, Myung S.; Biegler, Lorenz T.

2011-04-01

191

Alternating magnetic field forces for satellite formation flying  

NASA Astrophysics Data System (ADS)

Selected future space missions, such as large aperture telescopes and multi-component interferometers, will require the precise positioning of a number of isolated satellites, yet many of the suggested approaches for providing satellite positioning forces have serious limitations. In this paper we propose a new approach, capable of providing both position and orientation forces, that resolves or alleviates many of these problems. We show that by using alternating fields and currents that finely-controlled forces can be induced on the satellites, which can be individually selected through frequency allocation. We also show, through analysis and experiment, that near field operation is feasible and can provide sufficient force and the necessary degrees of freedom to accurately position and orient small satellites relative to one another. In particular, the case of a telescope with a large number of free mirrors is developed to provide an example of the concept. We also discuss the far field extension of this concept.

Youngquist, Robert C.; Nurge, Mark A.; Starr, Stanley O.

2013-03-01

192

Alternating Magnetic Field Forces for Satellite Formation Flying  

NASA Technical Reports Server (NTRS)

Selected future space missions, such as large aperture telescopes and multi-component interferometers, will require the precise positioning of a number of isolated satellites, yet many of the suggested approaches for providing satellites positioning forces have serious limitations. In this paper we propose a new approach, capable of providing both position and orientation forces, that resolves or alleviates many of these problems. We show that by using alternating fields and currents that finely-controlled forces can be induced on the satellites, which can be individually selected through frequency allocation. We also show, through analysis and experiment, that near field operation is feasible and can provide sufficient force and the necessary degrees of freedom to accurately position and orient small satellites relative to one another. In particular, the case of a telescope with a large number of free mirrors is developed to provide an example of the concept. We. also discuss the far field extension of this concept.

Youngquist, Robert C.; Nurge, Mark A.; Starr, Stnaley O.

2012-01-01

193

Control of the Electric Field Profile in the Hall Thruster  

SciTech Connect

Control of the electric field profile in the Hall Thruster through the positioning of an additional electrode along the channel is shown theoretically to enhance the efficiency. The reduction of the potential drop near the anode by use of the additional electrode increases the plasma density there, through the increase of the electron and ion transit times, causing the ionization in the vicinity of the anode to increase. The resulting separation of the ionization and acceleration regions increases the propellant and energy utilizations. An abrupt sonic transition is forced to occur at the axial location of the additional electrode, accompanied by the generation of a large (theoretically infinite) electric field. This ability to generate a large electric field at a specific location along the channel, in addition to the ability to specify the electric potential there, allows one further control of the electric field profile in the thruster. In particular, when the electron temperature is high, a large abrupt voltage drop is induced at the vicinity of the additional electrode, a voltage drop that can comprise a significant part of the applied voltage.

A. Fruchtman; N. J. Fisch; Y. Raitses

2000-10-05

194

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

195

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

196

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

197

Optical trapping with photorefractive electric fields  

NASA Astrophysics Data System (ADS)

Trapping with evanescent fields has become an important tool in many research fields. Evanescent fields allow trapping of particles in close proximity to a surface. However, excitation of these waves may be cumbersome. Recently, trapping with photorefractive electric fields has been demonstrated using dielectric and metallic nano and microparticles. Excitation of these fields is straight forward and, in principle, can be excited with microwatt power level. In this work, we give a comparison of photorefractive and plasmonic trapping emphasizing its advantages and disadvantages. We show that single beam and holographic photorefractive photovoltaic trapping in LiNbO3 of microparticle in water is possible.

Torres-Hurtado, S. A.; Villegas-Vargas, B. M.; Korneev, N.; Ramirez-San-Juan, J. C.; Ramos-Garcia, R.

2012-10-01

198

Simulation of electrical discharges in gases. Uniform electric fields  

Microsoft Academic Search

This paper reviews various methods used to simulate avalanche growth due to electron multiplication in gases in uniform electric fields. The Monte Carlo simulation method and the Boltzmann equation methods are considered and data in sulfur hexafluoride are summarized in view of its use in engineering applications

G. R. Govinda Raju; Jianfen Liu

1995-01-01

199

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.

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

2010-01-01

200

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

201

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

202

Modeling of Nanoparticle-Mediated Electric Field Enhancement Inside Biological Cells Exposed to AC Electric Fields  

Microsoft Academic Search

We present in this article the effect of alternating electric field at kilohertz (kHz) and megahertz (MHz) frequencies on the biological cells in presence and absence of nanoparticles. The induced electric field strength distribution in the region around cell membrane and nucleus envelope display different behavior at kHz and MHz frequencies. The attachment of gold nanoparticles (GNPs), especially gold nanowires

Pawan K. Tiwari; Sung Kil Kang; Gon Jun Kim; Jun Choi; A.-A. H. Mohamed; Jae Koo Lee

2009-01-01

203

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

Microsoft Academic Search

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

Fred J

1992-01-01

204

Manipulation of red blood cells with electric field  

Microsoft Academic Search

Manipulation of bioparticles and macromolecules is the central task in many biological and biotechnological processes. The current methods for physical manipulation takes advantage of different forces such as acoustic, centrifugal, magnetic, electromagnetic, and electric forces, as well as using optical tweezers or filtration. Among all these methods, however, the electrical forces are particularly attractive because of their favorable scale up

Hossain Saboonchi; Asghar Esmaeeli

2009-01-01

205

Lipid nanotube formation using space-regulated electric field above interdigitated electrodes.  

PubMed

Lipid nanotubes have great potential in biology and nanotechnology. Here we demonstrate a method to form lipid nanotubes using space-regulated AC electric fields above coplanar interdigitated electrodes. The AC electric field distribution can be regulated by solution height above the electrodes. The ratio of field component in x axis (Ex) to field component in z axis (Ez) increases dramatically at solution height below 50 ?m; therefore, at lower solution height, the force from Ex predominantly drives lipids to form lipid nanotubes along with the electric field direction. The forces exerted on the lipid nanotube during its formation were analyzed in detail, and an equation was obtained to describe the relationship among nanotube length and field frequency, amplitude, and time. We believe that the presented approach opens a way to design and prepare nanoscale materials with unique structural and functional properties using space-regulated electric fields. PMID:24669822

Bi, Hongmei; Fu, Dingguo; Wang, Lei; Han, Xiaojun

2014-04-22

206

Tracing optical force fields within graded-index media  

NASA Astrophysics Data System (ADS)

The mechanical interaction between light and graded index media (both isotropic and anisotropic) is presented from the geometrical optics (GO) perspective. Utilizing Hamiltonian equations to determine ray trajectories combined with a description of the Lorentz force exerted on bound currents and charges, we provide a general method that we denote ‘force tracing’ for determining the direction and magnitude of the bulk and surface force density in arbitrarily anisotropic and inhomogeneous media. This technique provides the optical community with machinery which can give a good estimation of the force field distribution in different complex media, and with significantly faster computation speeds than full-wave methods allow. Comparison of force tracing against analytical solutions shows some unusual limitations of GO, which we also illustrate.

Akbarzadeh, Alireza; Danesh, Mohammad; Qiu, Cheng-Wei; Danner, Aaron J.

2014-05-01

207

Liquid crystalline corannulene responsive to electric field.  

PubMed

An amide-appended corannulene derivative (3) with tribranched paraffinic side chains self-assembles into a hexagonal columnar liquid crystalline (LC) mesophase over a wide temperature range from 154 to -10 degrees C. In contrast with columnar LC assemblies of planar polycyclic aromatic hydrocarbons, the LC assembly of nonplanar 3 responds to an applied electric field and can align homeotropically to the electrode surface. Even after the electric field is switched off, this alignment is memorized for a long period of time unless the material is heated above the clearing temperature. PMID:19128171

Miyajima, Daigo; Tashiro, Kentaro; Araoka, Fumito; Takezoe, Hideo; Kim, Jungeun; Kato, Kenichi; Takata, Masaki; Aida, Takuzo

2009-01-14

208

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

209

Empirical high-latitude electric field models  

NASA Technical Reports Server (NTRS)

The present analysis of electric field measurements from the Dynamics Explorer 2 satellite, which extends previous empirical models, emcompasses much data from polar crossings entering and exiting the high latitudes in all magnetic local time zones. The goal is to represent the typical distributions of convective electric fields with a minimum number of characteristic patterns. Significant large-scale revisions of the OGO 6 dawn-dusk measurement models are made. The deformations of the two-cell patterns lead to sunward convection in dayside polar regions, while maintaining the integrity of the nightside convection pattern.

Heppner, J. P.; Maynard, N. C.

1987-01-01

210

Three-dimensional electric field traps for manipulation of cells--calculation and experimental verification.  

PubMed

The forces acting on dielectric particles and living cells exposed to alternating and rotating fields generated by three-dimensional multi-electrode arrangements are investigated. Numerical procedures are described for the calculation of the electric field distribution and forces. The physical treatment considers electrodes of any shape and dielectric particles of complex structure. Particle and cell trapping are based on negative dielectrophoretic forces produced by high-frequency a.c. or rotating electric fields up to 400 MHz. Various multi-electrode systems were realised in commercially fabricated microelectrode systems, and tested for their ability to move and assemble microparticles or living cells without contact with the electrodes. The field distribution and accuracy of phase-controlled power application was tested using individual artificial particles trapped in the electric field cage. Position and trajectories of particle motion were measured. The paper gives an overview of electrode and field cage design in the microscale range. PMID:8507649

Schnelle, T; Hagedorn, R; Fuhr, G; Fiedler, S; Müller, T

1993-06-11

211

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; Tencate, James A [Los Alamos National Laboratory; Allured, Bradley [UNIV NEVADA, RENO; Carpenter, Michael A [CAMBRIDGE UNIV. UK

2009-01-01

212

Proton Deflectometry of Electric and Magnetic Fields  

NASA Astrophysics Data System (ADS)

Highly penetrating proton beams, generated by irradiating a thin foil target with picosecond laser pulses at intensities up to 10^20 Wcm-2 have been used to detect electric and magnetic fields in laser-produced plasmas [1]. More recently experiments to characterize the transient electric and magnetic fields using mono-energetic protons from imploding D^3He-filled capsules have been performed [2]. In the deflectometry technique a beam of protons is passed through a mesh to generate a grid of proton beamlets. This proton beam is passed through the laser-generated plasma and the grid deflection can be measured. We report on LASNEX calculations of such laser-produced plasmas, which predict electric fields of the order of 10^9V/m and 1MG magnetic fields. We will show Lsp calculations of proton transport through such electric and magnetic fields and compare them to the experimental data. [1] A. J. Mackinnon, et al., Rev. Sci. Instrum. 75, 3531 (2004). [2] C. K. Li, et al., Bull. Am. Phys. Soc 50, 266 (2005). This work was performed under the auspices of the U.S. Department of Energy by the University of California, Lawrence Livermore National Laboratory under contract No. W-7405-Eng-48. The experimental work was performed at the LLE National User's Facility under grant number DE-SC52-04NA25436.

Town, R. P. J.; Edwards, M. J.; Landen, O. L.; MacKinnon, A. J.; Patel, P. K.; Tabak, M.; Li, C. K.; Petrasso, R. D.; Seguin, F. H.

2006-10-01

213

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

214

Electric Fields within Martian Dust Storms  

NASA Astrophysics Data System (ADS)

Mars analog and laboratory studies and field campaigns on Earth provide strong evidence for the existence of active electrodynamic processes on Mars. Dust charging studies using Mars soil simulant suggest that the triboelectric charging of dust observed within terrestrial dust disturbances is very possible on Mars. Recent microwave detection of a lightning signature correlated with a Martian dust storm suggests large electric fields do exist. We have developed a physically consistent model of triboelectric dust charging and atmospheric dynamics by coupling the Microscopic Triboelectric Simulator (MTS) with the Mars Regional Atmospheric Modeling System (MRAMS). We have used the combined model to simulate the dynamics of charged particles in Martian dust devils and examine the resulting electric field environment. We have shown that the mixing of negatively charged (metallic) and positively charged (basaltic) particles within a dust devil typically results in electric fields of order a few kV/m. In some cases, brief periods (few minutes) of much higher electric fields, 10s - 100s kV/m, are seen.

Barth, E. L.; Rafkin, S. C.; Farrell, W. M.

2010-12-01

215

Force-free magnetic fields - The magneto-frictional method  

NASA Technical Reports Server (NTRS)

The problem under discussion is that of calculating magnetic field configurations in which the Lorentz force j x B is everywhere zero, subject to specified boundary conditions. We choose to represent the magnetic field in terms of Clebsch variables in the form B = grad alpha x grad beta. These variables are constant on any field line so that each field line is labeled by the corresponding values of alpha and beta. When the field is described in this way, the most appropriate choice of boundary conditions is to specify the values of alpha and beta on the bounding surface. We show that such field configurations may be calculated by a magneto-frictional method. We imagine that the field lines move through a stationary medium, and that each element of magnetic field is subject to a frictional force parallel to and opposing the velocity of the field line. This concept leads to an iteration procedure for modifying the variables alpha and beta, that tends asymptotically towards the force-free state. We apply the method first to a simple problem in two rectangular dimensions, and then to a problem of cylindrical symmetry that was previously discussed by Barnes and Sturrock (1972). In one important respect, our new results differ from the earlier results of Barnes and Sturrock, and we conclude that the earlier article was in error.

Yang, W. H.; Sturrock, P. A.; Antiochos, S. K.

1986-01-01

216

Evolving force-free magnetic fields. III - States of nonequilibrium and the preflare stage. [in solar atmosphere  

NASA Technical Reports Server (NTRS)

The paper considers whether a neighboring magnetostatic equilibrium exists to allow a magnetic field initially in a force-free configuration to accommodate any imposed weak pressure. The following problem is treated. The foot points of the field are fixed and the plasma is frozen into the field lines under the approximation of infinite electrical conductivity. A weak pressure is introduced. It is determined infinitesimal plasma displacements exist to adjust the field lines to a new equilibrium without changing the field line connectivity. The analysis is carried out for the bipolar force-free fields forming one of two evolutionary sequences modeling the development of the preflare stage. It was found that for the force-free field corresponding to the quasi-static stage of evolution, the neighboring magnetostatic equilibrium always exists and the imposed gas pressure can be accommodated with a slight departure of the field from being exactly force free.

Low, B. C.

1980-01-01

217

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

218

General Analytical Relationship for Electric Field of Gated Field Emitters  

NASA Astrophysics Data System (ADS)

Current-voltage I(V) measurements are used for the characterization of metallic Spindt-type and Si gated emitters, in conjunction with the Fowler-Nordheim (FN) current density-electric field J(E) relationship describing the local tunneling process. For proper device modeling, the electric field on the emitter should be linked to the applied voltage. A general analytical relationship for computing the electric field on the emitter apex for planar and volcano-shaped gated emitters has been derived. The relationship is valid for a wide range of the parameters, taking into account the emitter radius and cone angle as well as the gate aperture radius. An example of device modeling concerning HfC-coated poly-Si gated emitters is presented.

Nicolaescu, Dan; Nagao, Masayoshi; Filip, Valeriu; Kanemaru, Seigo; Itoh, Junji

2005-06-01

219

Magnetic Explosions: Role of the Inductive Electric Field  

NASA Astrophysics Data System (ADS)

Inclusion of the inductive electric field, E ind, due to the temporally changing B, in magnetic explosions is discussed, with emphasis on solar flares. Several roles played by E ind are identified: on a global scale, E ind produces the electromotive force that drives the explosion; the associated E ind × B drift is identified with the inflow of magnetic field lines into a reconnection region; the polarization current, associated with ?E ind/?t, implies a J × B force that accelerates this inflow; and the component of E ind parallel to B accelerates the energetic electrons that cause hard X-ray emission and type III radio bursts. Some simple models that describe these effects are presented. A resolution of the long-standing "number problem" in solar flares is suggested.

Melrose, D. B.

2012-04-01

220

Trajectories in Electric and Magnetic Fields Model  

NSDL National Science Digital Library

The Trajectories in Electric and Magnetic Fields model computes a family of trajectories of charges emitted from a point source isotropically and with the same energy. These trajectories create focal points and caustic surfaces meeting the symmetry line in conical cusps. The simulation enables users to study these trajectories in both crossed and parallel magnetic fields. The user can vary the initial particle velocity and the field strengths. The Trajectories in Electric and Magnetic Fields model was developed using the Easy Java Simulations (Ejs) modeling tool. It is distributed as a ready-to-run (compiled) Java archive. You can modify this simulation if you have Ejs installed by right-clicking within the plot and selecting âOpen Ejs Modelâ from the pop-up menu item.

Christian, Wolfgang

2012-10-25

221

Electric field mediated colloidal assembly and control  

NASA Astrophysics Data System (ADS)

This dissertation presents video microscopy measurements and computer simulations of colloidal particle interactions in inhomogeneous, high-frequency AC electric fields. The interactions of particles with each other and inhomogeneous electric fields are quantified as a function of concentration, field amplitude, and frequency. Visual state diagrams show that these interactions in concentrated systems produce quasi-two dimensional microstructures including confined hard disk fluids, oriented dipolar chains, and oriented hexagonal close packed crystals. The interaction of a particle interacting with an electric field is directly measured with analyses of a single diffusing colloid within electric fields in the absence of many body effects. Concentrated systems are characterized in terms of density profiles across the electrode gap and angular pair distribution functions. An inverse Monte Carlo analysis extracted the induced dipole-induced dipole interaction from concentrated measurements. A single adjustable parameter consistently modified the induced dipole-field potential and the induced dipole-induced dipole potential to account for modification of the local electric field as the result of the local particle concentration, frequency and configuration. Confocal laser scanning microscopy (CLSM) perform sensitive measurements of internal three dimensional structure of crystals assembled in an interfacial quadrupole electrode device. Radial distributions as functions of elevation are used to characterize the equilibrium structure. A single adjustable parameter modified known potentials to match Monte Carlo simulations with experiment. The local density from experiment and simulation matched the expected density calculated from a balance of osmotic pressure and dielectrophoretic compression. Simulations qualitatively matched experimental observations of microstructure as a function of field amplitude. Programmable assembly for colloidal crystals is implemented in the quadrupole electrode device by guiding the dynamic evolution of a colloidal ensemble. A feedback method is used to control electric field mediated assembly based on real-time sensing and actuation single and multiple electrokinetic mechanisms. Sensing is achieved using particle tracking and order parameter computation to quantify the degree of order during the assembly process. A geometrical parameter for hexagonal close packing and radius of gyration are investigated as order parameters for quantifying condensation and crystallization. Colloidal crystal assembly and disassembly is actuated using electroosmosis and negative and positive dielectrophoresis (i.e. dipole-field interactions).

Juarez, Jaime Javier

222

Molecular Dynamics Simulation of Tri-n-Butyl-Phophate Liquid: A Force Field Comparative Study  

SciTech Connect

Molecular dynamics (MD) simulations were conducted to compare the performance of four force fields in predicting thermophysical properties of tri-n-butyl-phosphate (TBP) in the liquid phase. The intramolecular force parameters used were from the Assisted Model Building with Energy Refinement (AMBER) force field model. The van der Waals parameters were based on either the AMBER or the Optimized Potential for Liquid Simulation (OPLS) force fields. The atomic partial charges were either assigned by performing quantum chemistry calculations or utilized previously published data, and were scaled to approximate the average experimental value of the electric dipole moment. Canonical ensemble computations based on the aforementioned parameters were performed near the atmospheric pressure and temperature to obtain the electric dipole moment, mass density, and self-diffusion coefficient. In addition, the microscopic structure of the liquid was characterized via pair correlation functions between selected atoms. It has been demonstrated that the electric dipole moment can be approximated within 1% of the average experimental value by virtue of scaled atomic partial charges. The liquid mass density can be predicted within 0.5-1% of its experimentally determined value when using the corresponding charge scaling. However, in all cases the predicted self- diffusion coefficient is significantly smaller than a commonly quoted experimental measurement; this result is qualified by the fact that the uncertainty of the experimental value was not available.

Cui, Shengting [ORNL; de Almeida, Valmor F [ORNL; Hay, Benjamin [ORNL; Ye, Xianggui [ORNL; Khomami, Bamin [ORNL

2012-01-01

223

Molecular dynamics simulation of tri-n-butyl-phosphate liquid: a force field comparative study.  

PubMed

Molecular dynamics (MD) simulations were conducted to compare the performance of four force fields in predicting thermophysical properties of tri-n-butyl-phosphate (TBP) in the liquid phase. The intramolecular force parameters used were from the Assisted Model Building with Energy Refinement (AMBER) force field model. The van der Waals parameters were based on either the AMBER or the Optimized Potential for Liquid Simulation (OPLS) force fields. The atomic partial charges were either assigned by performing quantum chemistry calculations or utilized previously published data, and were scaled to approximate the average experimental value of the electric dipole moment. Canonical ensemble computations based on the aforementioned parameters were performed near atmospheric pressure and temperature to obtain the electric dipole moment, mass density, and self-diffusion coefficient. In addition, the microscopic structure of the liquid was characterized via pair correlation functions between selected atoms. It has been demonstrated that the electric dipole moment can be approximated within 1% of the average experimental value by virtue of scaled atomic partial charges. The liquid mass density can be predicted within 0.5-1% of its experimentally determined value when using the corresponding charge scaling. However, in all cases, the predicted self-diffusion coefficient is significantly smaller than a commonly quoted experimental measurement; this result is qualified by the fact that the uncertainty of the experimental value was not available. PMID:22126596

Cui, Shengting; de Almeida, Valmor F; Hay, Benjamin P; Ye, Xianggui; Khomami, Bamin

2012-01-12

224

Force-free field model of ball lightning  

NASA Astrophysics Data System (ADS)

Due to the nature that the force-free magnetic field, whose current carried by the conducting plasma is everywhere parallel to the magnetic field it generates, is the minimum energy configuration under the constraint of magnetic helicity conservation, ball lightning is considered as a self-organized phenomenon with a plasma fireball immersed in a spherical force-free magnetic field. Since this field does not exert force on the plasma, the plasma pressure, by itself, is in equilibrium with the surrounding environment, and the force-free magnetic field can take on any value without affecting the plasma. Due to this second feature, singular solutions of the magnetic field that are otherwise excluded are allowed, which enable a large amount of energy to be stored to sustain the ball lightning. The singularity is truncated only by the physical limit of current density that a plasma can carry. Scaling the customary soccer-size fireball to larger dimensions could account for day and night sightings of luminous objects in the sky.

Tsui, K. H.

2001-03-01

225

Electrical circuit modeling of reversed field pinches  

NASA Astrophysics Data System (ADS)

Equations are proposed to describe the radial variation of the magnetic field and current density in a circular, cylindrical RFP. These equations are used to derive the electrical circuit parameters (inductance, resistance, and coupling coefficient) for an RFP discharge. The circuit parameters are used to evaluate the flux and energy consumption for various startup modes and for steady-state operation using oscillating field current drive. The results are applied to the MST device.

Sprott, J. C.

1988-02-01

226

Difficulties in learning the concept of electric field  

NSDL National Science Digital Library

Analyzes students' main difficulties in learning the concept of electric field. Briefly describes the main conceptual profiles within which electric interactions can be interpreted and concludes that most students have difficulty using the idea of electric field. (Contains 28 references.)

Furiã³, C.; Guisasola, Jenaro

2005-10-21

227

Magnetospheric electric fields and currents and their influence on large scale thermospheric circulation and composition  

Microsoft Academic Search

The magnetospheric electric convection field is a major momentum and heat source which drives atmospheric wind fields. In the present paper, simplified models of momentum force and Joule heating, caused by the convection field, are developed in terms of series of lowest-order spherical harmonics. These source terms drive global wind systems which depend on the latitude, longitude, local time, and

H. Volland

1979-01-01

228

OBSERVED RELATIONSHIPS BETWEEN ELECTRIC FIELDS AND AURORAL PARTICLE PRECIPITATION  

Microsoft Academic Search

Simultaneous electric field and plasma observations with the low-altitude polar-orbiting satellite Injun 5 have provided a comprehensive survey of convection electric fields and their association with magnetospheric plasma phenomena. The most prominent features of the convection electric fields are reversals located at high magnetic latitudes, with generally antisunward convection poleward and sunward convection equatorward of the electric field reversal location.

D. A. Gurnett; L. A. Frank

1973-01-01

229

On the motion of a charged particle in a uniform electric field with radiation reaction  

Microsoft Academic Search

It is shown that the motion of a charged particle in a uniform electric field, obeying Dirac-Lorentz relativistic equation of motion with radiation reaction, is confined in a plane. Further, the component of velocity normal to the lines of force continuously decreases to zero. Thus, the motion asymptotically tends to a rectilinear motion along the line of force. The motion

N. D. Sen Gupta

1971-01-01

230

Formation of cell protrusions by an electric field: a thermodynamic analysis  

Microsoft Academic Search

This work gives a thermodynamic analysis of outgrowth extraction from the cell body by a pulling force. The results are applied for a case when the pulling force is generated by an external high-frequency electric field. Two equilibrium conditions are analyzed: internal equilibrium of an outgrowth and equilibrium between the outgrowth and the cell body. In both cases the stability

Michael M. Kozlov; Peter I. Kuzmin; Sergey V. Popov

1992-01-01

231

Understanding dielectrophoretic trapping of neuronal cells: modelling electric field, electrode-liquid interface and fluid flow  

Microsoft Academic Search

By application of dielectrophoresis neuronal cells can be trapped successfully. Several trapping experiments have been performed using a quadrupole electrode structure at different amplitudes (1, 3, and 5 Vpp) and frequencies (10-50 MHz). Due to the high conductivity of the suspending medium negative dielectrophoretic forces are created. The dielectrophoretic force is determined by the gradient of the electric field. However,

T. Heida; W. L. C. Rutten; E. Marani

2002-01-01

232

Longitudinal ultrasonic waves in DC electric field  

NASA Astrophysics Data System (ADS)

The results of experimental studies of the propagation of longitudinal waves in saturated rock samples in which there is a flow of electric charges are presented. It is shown that the electric field affects elastic parameters in heterophase media by changing their dynamic characteristics. The aim of the study of the effect of electric field on the propagation of elastic waves in saturated porous media was to determine the optimum conditions for this effect, and to construct a set of effective parameters which could be used to increase the effectiveness of seismoacoustic prospecting methods, particularly acoustic logging, and be helpful for developing new methods of increasing the effectiveness of oil extraction from productive wells.

Sobotka, Jerzy

2009-06-01

233

Bloch electron in a uniform electric field  

Microsoft Academic Search

A formula for calculating the interband matrix elements of X for a Bloch electron in a uniform electric field is derived, from which it is found that the interband matrix elements of X are only determined by the interband matrix elements of the derivative of the periodic potential. Using this formula with a Kronig-Penney potential leads to nonvanishing interband matrix

Xian-Geng Zhao

1992-01-01

234

Non-intrusive electric field sensing  

NASA Astrophysics Data System (ADS)

This paper presents an overview of non-intrusive electric field sensing. The non-intrusive nature is attained by creating a sensor that is entirely dielectric, has a small cross-sectional area, and has the interrogation electronics a long distance away from the system under test. One non-intrusive electric field sensing technology is the slab coupled optical fiber sensor (SCOS). The SCOS consists of an electro-optic crystal attached to the surface of a D-shaped optical fiber. It is entirely dielectric and has a cross-sectional area down to 0.3mm by 0.3mm. The SCOS device functions as an electric field sensor through use of resonant mode coupling between the crystal waveguide and the core of a D-shaped optical fiber. The resonant mode coupling of a SCOS device occurs at specific wavelengths whose spectral locations are determined in part by the effective refractive index of the modes in the slab. An electric field changes the refractive index of the slab causing a shift in the spectral position of the resonant modes. This paper describes an overview of the SCOS technology including the theory, fabrication, and operation. The effect of crystal orientation and crystal type are explained with respect to directional sensitivity and frequency response.

Schultz, S. M.; Selfridge, R.; Chadderdon, S.; Perry, D.; Stan, N.

2014-04-01

235

Spherical Probe Electric Field and Wave Experiment.  

National Technical Information Service (NTIS)

The experiment is designed to measure the electric field and density fluctuations with sampling rates up to 40,000 samples/sec. The description includes Langmuir sweeps that can be made to determine the electron density and temperature, the study of nonli...

G. Gustafsson T. Aggson R. Bostrom L. P. Block C. Cattell

1988-01-01

236

Guiding Electric Fields for Electroporation Applications  

Microsoft Academic Search

Electroporation is the critical step in an electric field mediated drug or gene delivery protocol. Electroporation based protocols have been successfully demonstrated in cancer clinical trials, however, its impact in other applications is still under investigation. A significant roadblock to long term functioning of implantable biosensors in vivo is the tissue reaction in the form of fibrous encapsulation that results

Jose Rey

2011-01-01

237

Field Testing of Electrical Grounding Rods.  

National Technical Information Service (NTIS)

A 7-year program of field testing metal rods for electrical grounding was conducted. Single rods of galvanized steel, copper-clad steel, Ni-Resist cast iron, type 302 stainless steel, type 304 stainless-clad steel, zinc, magnesium, and aluminum were teste...

R. W. Drisko A. E. Hanna

1970-01-01

238

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

239

Electrostatic filters generated by electric fields  

Microsoft Academic Search

The theoretical and experimental findings on fibrous filters converted to electrostatic operation by a nonionizing electric field are presented. Compared to a conventional fibrous filter, the electrostatic filter has a much higher efficiency and significantly lower pressure drop at the same level of particle loading. Two theoretical models of filter clogging are presented. The dendrite model simulates filter clogging of

W. Bergman; H. Hebard; R. Taylor; B. Lum

1979-01-01

240

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

241

Role of inductive electric fields in substorm development  

NASA Technical Reports Server (NTRS)

A study discussing and investigating the role of inductive electric fields in substorm development is presented. It is common to use the scalar potential phi to calculate the electrostatic field E(sup ES)-(inverted Delta)(phi). However, vector potential A has not been extensively used to analyze results by the relation for the inductive electric field E(sup IND)-delta A/delta t. Because of the weak dependence in distance (1/r) these potentials show the effect of distant sources, unlike MHD (Magnetohydrodynamic) theory which is strictly local. The two can be separated by the choice of the Coulomb (transverse) gauge. It is proper to consider that the plasma polarizes to counteract the activation of the inductive electric field; this is a matter of cause and effect. However, such polarization produces a curl free electrostatic field and thus cannot alter the electromotive force due to induction. This idea has some interesting consequences for plasma physics, including violations of MHD theory, creation of the substorm current diversion, and a fresh look at dayside merging via plasma transfer events.

Heikkila, Walter J.

1992-01-01

242

Field-aligned currents and ionospheric electric fields  

NASA Technical Reports Server (NTRS)

It is shown that the observed distribution of the ionospheric electric field can be deduced from an equation combining Ohm's law with the current continuity equation by using the 'observed' distribution of field-aligned currents as the boundary condition for two models of the ionosphere. The first model has one conductive annular ring representing the quiet-time auroral precipitation belt; the second has two conductive annular rings that simulate the discrete and diffuse auroral regions. An analysis is performed to determine how well the electric-field distribution can be reproduced. The results indicate that the first model reproduces the Sq(p)-type distribution, the second model reproduces reasonably well a substorm-type potential and ionospheric current patterns together with the Harang discontinuity, and that the distribution of field-aligned currents is the same for both models.

Yasuhara, F.; Akasofu, S.-I.

1977-01-01

243

A Laboratory Investigation of the Effect of Particle Collisions on the Generation of Electric Fields in Thunderstorms  

Microsoft Academic Search

A laboratory experiment has been performed to study the relative effect of aerodynamic and electrical forces an small electrically conducting particles of radii 100-200 colliding with a particle of 2 mm radius suspended in an upward moving vertical air stream of a wind tunnel and placed in a vertical polarizing electric field. It has been observed, in a low electric

A. K. Kamra; B. Vonnegut

1971-01-01

244

Swarm SCARF equatorial electric field inversion chain  

NASA Astrophysics Data System (ADS)

The day-time eastward equatorial electric field (EEF) in the ionospheric E-region plays a crucial role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring and modeling the EEF for both climatological and near real-time studies. The Swarm satellite mission offers a unique opportunity to estimate the equatorial electric field from measurements of the geomagnetic field. Due to the near-polar orbits of each satellite, the on-board magnetometers record a full profile in latitude of the ionospheric current signatures at satellite altitude. These latitudinal magnetic profiles are then modeled using a first principles approach with empirical climatological inputs specifying the state of the ionosphere. Since the EEF is the primary driver of the low-latitude ionospheric current system, the observed magnetic measurements can then be inverted for the EEF. This paper details the algorithm for recovering the EEF from Swarm geomagnetic field measurements. The equatorial electric field estimates are an official Swarm level-2 product developed within the Swarm SCARF (Satellite Constellation Application Research Facility). They will be made freely available by ESA after the commissioning phase.

Alken, P.; Maus, S.; Vigneron, P.; Sirol, O.; Hulot, G.

2013-11-01

245

Swarm Equatorial Electric Field Inversion Chain  

NASA Astrophysics Data System (ADS)

The day-time eastward equatorial electric field (EEF) in the ionospheric E-region plays a crucial role in equatorial ionospheric dynamics. It is responsible for driving the equatorial electrojet (EEJ) current system, equatorial vertical ion drifts, and the equatorial ionization anomaly (EIA). Due to its importance, there is much interest in accurately measuring and modeling the EEF for both climatological and near real-time studies. The Swarm satellite mission offers a unique opportunity to estimate the equatorial electric field from measurements of the geomagnetic field. Due to the near-polar orbits of each satellite, the on-board magnetometers record a full profile in latitude of the ionospheric current signatures at satellite altitude. These latitudinal magnetic profiles are then modeled using a first principles approach with empirical climatological inputs specifying the state of the ionosphere, in order to recover the EEF. We will present preliminary estimates of the EEF using the first Swarm geomagnetic field measurements, and compare them with independently measured electric fields from the JULIA ground-based radar in Peru.

Alken, Patrick; Maus, Stefan; Vigneron, Pierre; Sirol, Olivier; Hulot, Gauthier

2014-05-01

246

Numerical simulation of bubble dynamics in a micro-channel under a nonuniform electric field.  

PubMed

A numerical method is used to simulate the motion and coalescence of air bubbles in a micro-channel under a nonuniform electric field. The channel is equipped with arrays of electrodes embedded in its wall and voltages are applied on the electrodes to generate a specified electric field gradient in the longitudinal direction. In the study, the Navier-Stokes equations are solved by using the level set method handling the deformable/moving interfaces between the bubbles and the ambient liquid. Both the polarization Coulomb force and the dielectrophoresis force are considered as the force source of the Navier-Stokes equations by solving the Maxwell's equations. The flow field equations and the electric field equations are coupled and solved by using the finite element method. The electric field characteristics and the dynamic behavior of a bubble are analyzed by studying the distributions of the electric field and the force, the deformation and the moving velocity of the air bubble. The result suggests that the model of dispersed drops suspended in the immiscible dielectric liquid and driven by a nonuniform electric field is an effective method for the transportation and coalescence of micro-drops. PMID:21259283

Jing, Luo; Dan, Guo; Jianbin, Luo; Guoxin, Xie

2011-02-01

247

Observations of large transient magnetospheric electric fields  

NASA Technical Reports Server (NTRS)

Transient electric field events were observed with the long, double probe instrumentation carried by the IMP-6 satellite. Nine, clearly defined, exceptionally large amplitude events are presented here. The events are observed in the midnight sector at geocentric distances 3.5 to .5.5 R sub e at middle latitudes within a magnetic L-shell range of 4.8 to 7.5. They usually have a total duration of one to several minutes, with peak power spectra amplitudes occurring at a frequency of about 0.3 Hz. The events occur under magnetically disturbed conditions, and in most cases they can be associated with negative dH/dt excursions at magnetic observatories located near the foot of the magnetic field line intersecting IMP-6. The magnetospheric motions calculated for these electric fields indicated a quasi-stochastical diffusive process rather than the general inward magnetospheric collapsing motion expected during the expansive phases of auroral substorm activity.

Aggson, T. L.; Heppner, J. P.

1977-01-01

248

Excitonic Effects on Dielectric Properties of Solids in a Uniform Electric Field  

Microsoft Academic Search

The imaginary part of the dielectric function for excitonic transitions and different types of critical points of a solid in a uniform electric field are presented in a closed form. The time-dependent Schrödinger equation, with a time-dependent gauge for the applied electric field which includes the electron-hole interaction forces is treated within the effective-mass approximation. In the weak fields and

E. Yang

1971-01-01

249

The Vector Electric Field Investigation on the C\\/NOFS Satellite  

Microsoft Academic Search

We provide an overview of the Vector Electric Field Investigation (VEFI) on the Air Force Communication\\/Navigation Outage Forecasting System (C\\/NOFS) satellite, a mission designed to understand, model, and forecast the presence of equatorial ionospheric irregularities. VEFI is a NASA\\/GSFC instrument funded by the Air Force Research Laboratory whose main objectives are to: 1) investigate the role of the ambient electric

R. Pfaff; M. Acuna; J. Kujawski; R. Fourre; P. Uribe; K. Bromund; F. Hunsaker; D. Rowland; W. Farrell; N. Maynard; R. Holzworth; G. Wilson; J. Berthelier; C. Steigies; G. Le; H. Freudenreich; M. McCarthy; S. Martin; C. Liebrecht

2008-01-01

250

Electric-field-mediated fabrication of nano/microstructures  

NASA Astrophysics Data System (ADS)

Notable recent developments toward the realization of electronic nanocomputers have assembled logic circuits from semiconductor nanowires and individual carbon nanotube molecules. In spite of the broadly based and encouraging recent progress, a set of technical challenges still must be overcome to make a robust, commercially viable computer integrated on the molecular scale. The assembly of colloidal particles under an electric field offers many opportunities for the fabrication of ordered arrays, nanostructured films and microwires. We describe a method for the fabrication of gold nano/microstructures such as wires and dendrites on a lithographically patterned aluminium electrode with electric-field-induced assembly. The simple fabrication process will make these structures suitable for the miniaturisation of electronic circuits that can find application in sensors, actuators, and lab-on-a-chip devices. Our approach to electric-field-mediated fabrication exposes colloidal gold particles to the high electric field that can be generated between electrodes only 200 mm apart. We introduce an electric field of 100 Hz to 10 MHz by application of an alternating voltage of 5 to 10 V to the lithographically patterned microelectrodes. A suspension of gold nanoparticles of diameter 2.5 nm is added. We observe three types of fabrication, represented by three zones due to the different dielectophoretic force and convection effects. Some fibres grow through the liquid from one electrode toward the other, as could be seen in-situ by inverse optical microscopy. Dielectrophoretic-force-mediated fabrication, which is very flexible depending on the magnitudes of electric-field strength and frequency applied, has produced a notable advance in making mechanically flexible nano/microelectronic devices and led to a new understanding of the factors controlling the growth of nano/microstructures. When drops of suspension are patterned on the faces of components, three-dimensional structures can be generated. This type of system indicates how functional, self-assembling nano/microelectronic systems may be made. It provides a faster way of making devices, and the process can be very economical.

Yuan, Yong J.; Andrews, Mike K.; Arnold, W. M.; Marlow, Barry K.

2003-04-01

251

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

252

A polarizable ellipsoidal force field for halogen bonds.  

PubMed

The anisotropic effects and short-range quantum effects are essential characters in the formation of halogen bonds. Since there are an array of applications of halogen bonds and much difficulty in modeling them in classical force fields, the current research reports solely the polarizable ellipsoidal force field (PEff) for halogen bonds. The anisotropic charge distribution was represented with the combination of a negative charged sphere and a positively charged ellipsoid. The polarization energy was incorporated by the induced dipole model. The resulting force field is "physically motivated," which includes separate, explicit terms to account for the electrostatic, repulsion/dispersion, and polarization interaction. Furthermore, it is largely compatible with existing, standard simulation packages. The fitted parameters are transferable and compatible with the general AMBER force field. This PEff model could correctly reproduces the potential energy surface of halogen bonds at MP2 level. Finally, the prediction of the halogen bond properties of human Cathepsin L (hcatL) has been found to be in excellent qualitative agreement with the cocrystal structures. PMID:23804187

Du, Likai; Gao, Jun; Bi, Fuzhen; Wang, Lili; Liu, Chengbu

2013-09-01

253

Operational Art in I Field Force, 1965 to 1967.  

National Technical Information Service (NTIS)

I Field Force effectively conducted operational art from 1965 through 1967 under the leadership of LTG Stanley Larsen in the II Corps Tactical Zone (II CORPS). This accomplishment is all the more noteworthy considering LTG Larsen and his staff built I Fie...

J. E. Turner

2012-01-01

254

Spatial confinement of ultrasonic force fields in microfluidic channels  

Microsoft Academic Search

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

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

2009-01-01

255

Evaluation of TiO2 Force Fields.  

National Technical Information Service (NTIS)

A total of nine force fields for TiO2 have been compared and evaluated using bulk lattice and surface energy minimization procedures. Calculated crystal properties of four polymorphs of TiO2 (rutile, anatase, brookite and a high pressure phase TiO2(ii)) a...

D. R. Collins W. Smith

1996-01-01

256

Extending the AMBER Force Field to Describe Fluorescent Probes  

Microsoft Academic Search

We are developing a method for studying the structural dynamics of biomolecules, which couples fluorescence spectroscopy and computational modeling, providing a more complete understanding than is possible with either technique alone. The computational modeling will be based primarily on molecular dynamics (MD) simulation. Before running MD, dye parameters were determined that are consistent with the Cornell et al. force field

Andrew Cook; Arcelia Ortega; Alyssa Stevenson; Derek Summers; Alyssa Cassabaum; Christine Gobrogge; Bryan Leland; David Paul; Amy Speelman

2012-01-01

257

The effect of gravitational tidal forces on renormalized quantum fields  

NASA Astrophysics Data System (ADS)

The effect of gravitational tidal forces on renormalized quantum fields propagating in curved spacetime is investigated and a generalisation of the optical theorem to curved spacetime is proved. In the case of QED, the interaction of tidal forces with the vacuum polarization cloud of virtual e + e - pairs dressing the renormalized photon has been shown to produce several novel phenomena. In particular, the photon field amplitude can locally increase as well as decrease, corresponding to a negative imaginary part of the refractive index, in apparent violation of unitarity and the optical theorem. Below threshold decays into e + e - pairs may also occur. In this paper, these issues are studied from the point of view of a non-equilibrium initial-value problem, with the field evolution from an initial null surface being calculated for physically distinct initial conditions and for both scalar field theories and QED. It is shown how a generalised version of the optical theorem, valid in curved spacetime, allows a local increase in amplitude while maintaining consistency with unitarity. The picture emerges of the field being dressed and undressed as it propagates through curved spacetime, with the local gravitational tidal forces determining the degree of dressing and hence the amplitude of the renormalized quantum field. These effects are illustrated with many examples, including a description of the undressing of a photon in the vicinity of a black hole singularity.

Hollowood, Timothy J.; Shore, Graham M.

2012-02-01

258

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

259

Dielectrophoretic manipulation of macromolecules: The electric field  

SciTech Connect

The use of dielectrophoresis is fast becoming a proven technique for manipulating particles and macromolecules in microfluidic systems. Here an analytic solution for the gradient in the electric field strength, {nable}{center_dot}(E{center_dot}E), produced by a two-dimensional array of parallel electodes is derived using the method of Green's functions. The boundary condition for the potential between electrodes is estimated by using a linear approximation. While the Green's function used here is somewhat different from Wang , J. Phys. D 29, 1649 (1996), the resulting analytic expression for the potential field is in exact agreement with their result. Selected results for equispaced electrodes with equal widths are compared with Wang , J. Phys. D 29, 1649 (1996). The analytic solution is employed to study the effects of electrode spacing and electrode width on the gradient in electric field intensity. Results show that the magnitude in the gradient in the electric field intensity exhibited the expected dependence on the applied voltage; however, the dependence on electrode width was found to be on the order of the electrode width squared. Results to explore the effects of electrode spacing show that as the spacing is reduced below two electrode widths the magnitude of the gradient increases exponentially.

Clague, D. S.; Wheeler, E. K.

2001-08-01

260

On the Force-free Nature of Photospheric Sunspot Magnetic Fields as Observed from Hinode (SOT/SP)  

NASA Astrophysics Data System (ADS)

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 ?), 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

2012-01-01

261

On the influence of an external electric field on magnetotail reconnection  

NASA Technical Reports Server (NTRS)

Magnetotail reconnection is studied under the influence of a dawn to dusk electric field applied at the high-latitude tail boundary using a two-dimensional resistive MHD code. It is found that the basic unstable sequence of tearing and plasmoid formation and ejection was not changed if the external electric field was fairly uniform. The externally forced compression, however, could shorten the onset time and the growth time of the evolution. The faster growth can be understood by the fact that the forced compression gradually alters the lobe field strength and the plasma sheet width and reduces thereby the relevant Alfven time. In fact, if the evolution of the cases with imposed electric field is rescaled on the basis of these characteristic parameters, a good quantitative agreement with the case without external electric field is found.

Birn, J.; Schindler, K.

1986-01-01

262

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

263

DNA fragmentation induced by Intense Burst Sinusoidal Electric Fields  

Microsoft Academic Search

It is a well known fact that intense electric fields with frequencies exceeding MHz ranges cause intracellular effect to mammalian cells. We have used the Intense Burst Sinusoidal Electric Field (IBSEF) which is narrow band spectra, to put the electrical energy into biological cells efficiently. We have experimentally demonstrated here the presence of intense electric fields inside the cell membrane,

N. Nomura; Y. Yamamoto; R. Hayashi; K. Uto; S. Katsuki; H. Akiyama; I. Uchida; S. I. Abe; H. Takano

2007-01-01

264

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

265

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) [Naperville, IL

1992-01-01

266

Fiber optic electric field sensor technology  

NASA Technical Reports Server (NTRS)

The properties of piezoactive plastics are reviewed as well as the fiber-optic electric field sensors studied so far. A particular configuration consisting of a concentric piezoactive jacket on the glass fiber is discussed in detail and the frequency response of this sensor is projected over a wide range of frequencies. The present design has the practical advantages of leading to a compact lightweight sensor; longer fiber lengths may be used to increase sensitivity. It is predicted that, at low frequencies, a fiber-optic antenna using a 1-km length of fiber would be capable of detecting a minimum electric field of 43 microV/m assuming a minimum phase sensitivity of 10 to the -6th radians for the optical Mach-Zehnder interferometer.

Jarzynski, J.; De Paula, R. P.

1987-01-01

267

Spin effects in coupled quantum dots under ac electric fields  

NASA Astrophysics Data System (ADS)

Spin control has recently attracted attention for applications in spin-based devices. Different effects and applied fields have been suggested to accomplish the goal. We explore the time evolution of electronic spin in coupled quantum dots under harmonic electric fields. Using the Floquet formalism, we obtain the time dependent wave function in terms of the Floquet states and the quasi-energy spectrum for a single electron in double InSb dots. The spatial part of the wave function includes the SIA and BIA spin-orbit effects. The spectral force is analyzed at anti-crossings of the quasi-energy bands as a function of the field strength. The resulting dynamical symmetries and the way they reflect in the time evolution of the spin clouds will be discussed.

Meza-Montes, Lilia; Hernandez, Arezky H.; Ulloa, Sergio E.

2007-03-01

268

Atomistic force field for alumina fit to density functional theory.  

PubMed

We present a force field for bulk alumina (Al2O3), which has been parametrized by fitting the energies, forces, and stresses of a large database of reference configurations to those calculated with density functional theory (DFT). We use a functional form that is simpler and computationally more efficient than some existing models of alumina parametrized by a similar technique. Nevertheless, we demonstrate an accuracy of our potential that is comparable to those existing models and to DFT. We present calculations of crystal structures and energies, elastic constants, phonon spectra, thermal expansion, and point defect formation energies. PMID:24289366

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

2013-11-28

269

Experimental demonstration of electric field tomography.  

PubMed

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 have been demonstrated and discussed. PMID:20647616

Korjenevsky, A V; Tuykin, T S

2010-08-01

270

Phase measurement for electric field tomography.  

PubMed

The basic principles of electric field tomography (EFT) are briefly explained. EFT system numerical simulation results are given. The comparison of images reconstructed by systems with planar and round electrode arrays is presented. Some aspects of transmitting and measuring stages are discussed. The accuracy of the phase-sensitive demodulator, which is the key element of an EFT measuring system, is evaluated experimentally. PMID:18544795

Korjenevsky, A V; Tuykin, T S

2008-06-01

271

Killing of microorganisms by pulsed electric fields  

Microsoft Academic Search

Lethal effects of pulsed electric fields (PEF) on suspensions of various bacteria, yeast, and spores in buffer solutions and\\u000a liquid foodstuffs were examined. Living-cell counts of vegetative cell types were reduced by PEF treatment by up to more than\\u000a four orders of magnitude (> 99.99%). On the other hand, endoand ascospores were not inactivated or killed to any great extent.

T. Grahl; H. Märkl

1996-01-01

272

Asymmetric electric field enhancement in nanocrystal memories  

Microsoft Academic Search

The electrostatic model for nanocrystal memories is used to illustrate the fundamental difference of the metal nanocrystal memory in low-voltage program\\/erase (P\\/E) operations in comparison with semiconductor nanocrystal and trap-based memories. Due to repulsion of potential contours inside conductors, the metal nanocrystals will significantly enhance the electric field between the nanocrystal and the sensing channel set up by the control

Chungho Lee; Udayan Ganguly; Venkat Narayanan; Tuo-Hung Hou; Jinsook Kim; Edwin C. Kan

2005-01-01

273

Electric Field Generation in Martian Dust Devils  

NASA Astrophysics Data System (ADS)

Triboelectric dust charging physics via the Macroscopic Triboelectric Simulation (MTS) code has been added to the Mars Regional Atmospheric Modeling System (MRAMS) in order to simulate the electrodynamics of dust devils and dust disturbances on Mars. Using the model, we explore how macroscopic electric fields are generated within storms and attempt to quantify the time evolution of the electrodynamical system. This research was supported by the Mars Fundamental Research Program, NASA Grant NX07AR69G.

Barth, E. L.; Farrell, W. M.; Rafkin, S. C. R.

2011-10-01

274

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

275

Application of the drag force method to evaluate magnetic property degradation near the cut edges of electrical steels  

NASA Astrophysics Data System (ADS)

The increase in hysteresis loss associated with the altered microstructure and residual stress fields in regions near the cut edges of electrical steels is investigated by means of drag force measurements. Measurements are made using relatively narrow magnets on samples of two grades of nonoriented steels cut by laser or mechanical processes. Largest drag forces, hence losses, are consistently found in slow laser cut samples, smallest drag forces with fast laser cut samples, and moderately higher losses in mechanically cut samples. These results are consistent with other measurement methods.

Garshelis, Ivan J.; Crevecoeur, Guillaume; Tollens, Stijn P. L.; Dupre, Luc

2011-04-01

276

Manipulation of nano-entities in suspension by electric fields  

NASA Astrophysics Data System (ADS)

Nanoscale entities, including nanospheres, nanodisks, nanorings, nanowires and nanotubes are potential building blocks for nanoscale devices. Among them, nanowires is an important type of nanoparticles, due to the potential application in microelectronics and bio-diagnosis. Manipulation of nanowires in suspension has been a formidable problem. As described in this thesis, using AC electric fields applied to strategically designed microelectrodes, nanowires in suspension can be driven to align, to chain, to accelerate in directions parallel and perpendicular to its orientation, to concentrate onto designated places, and to disperse in a controlled manner with high efficiency despite an extremely low Reynolds number at the level of 10-5. Randomly oriented nanowires in suspension can be rapidly assembled into extended nonlinear structures within seconds. We show that both the electric field and its gradient play the essential roles of aligning and transporting the nanowires into scaffolds according to the electric field distributions inherent to the geometry of the microelectrodes. The assembling efficiency depends strongly on the frequency of the applied AC voltages and varies as square of the voltage. Furthermore, nanowires have been rotated by AC electric fields applied to strategically designed electrodes. The rotation of the nanowires can be instantly switched on or off with precisely controlled rotation speed (to at least 25000 rpm), definite chirality, and total angle of rotation. This new method has been used to controllably rotate magnetic and non-magnetic nanowires as well as multi-wall carbon nanotubes. We have also produced a micromotor using a rotating nanowire that can drive particles into circular motion. This has application to microfluidic devices, micro-stirrers, and micro electromechanical systems (MEMS). To move and place nanowires onto designated locations with high precision, electrophoretic force has been combined with dielectrophoretic force to transport charged Au nanowires with length longer than 4 mum. The surface of Au nanowires has been chemical functionalized by either positive or negative charges. High frequency AC electric field has been applied to align and fix the orientation of the charged nanowires, though not to induce any motions, whereas a small DC voltage causes linear motion. The velocity of nanowires increases linearly with the DC electric field. The moving direction can be either parallel or perpendicular to the orientation of nanowires. Nanowires modified with different charges behave differently due to the electroosmosis flow induced by the DC electric field on the negatively charged quartz substrate. The zeta potential of quartz surface and the ratio of Stokes coefficients for longitudinal nano-entities suspended in a low Reynolds number regime (< 10-5) has been determined. Due to the small size of the nanowires, the nanowires suspended in liquids such as DI water are in extremely low Reynolds number regime (< 10-5). Manipulation due to DEP and EP forces are versatile and precise. Nanowires have been set into motion with prescribed tracks, such as squares and zigzags. The manipulation is also so precise that oppositely charged nanowires with radius of 150 nm have been moved to contact and connected end to end. A nanowire clipper have been assembled by this technique and set into oscillation. This method is not only applicable to nanowires, it has been successfully applied to multiwall carbon nanotubes as well. To demonstrate the complete control and flexibility of manipulating nanoparticles by E field, we have programmed nanowires to dance with music by Mozart with regard to clearly demonstrating the versatility of manipulating small entities of metallic, semiconductor, and biological materials. This work has been conducted under the guidance of the author's thesis advisors, Prof. Robert C. Cammarata, chair of the Department of Materials Science and Engineering of the Johns Hopkins University, and Prof. Chia-Ling Chien in the Department of Physics and Astronomy, and the

Fan, Donglei

277

Control of the interface between (He-3)-rich and (He-4)-rich phases using electric fields  

NASA Technical Reports Server (NTRS)

A microgravity dilution refrigerator is considered, and it is shown that electric-field generated forces can be used to control the interface line between (He-3)-rich and (He-3)-poor phases. Fields as high as 13 MV/m are obtained in the present v-shaped geometry which correspond to positioning forces comparable to gravity. Good agreement is found between experimental results on the movements of the interface line and calculations obtained with a two-fluid model.

Israelsson, Ulf E.; Jackson, H. W.; Petrac, D.

1988-01-01

278

Biological effects of narrow band pulsed electric fields  

Microsoft Academic Search

This paper describes the process of narrow band pulsed electric fields (NPEFs) and its effect on mammalian cells. The NPEF consists of a pulse modulated sinusoidal wave (PMSW), which allows delivery of well-defined electric fields in terms of frequency, field strength and deposition energy to the biological systems. 100 mus long sinusoidal electric fields with a frequency of 0.02, 2

Sunao Katsuki; Naoyuki Nomura; Hideto Koga; Hidenori Akiyama; Ichiro Uchida; Shin-ichi Abe

2007-01-01

279

Optimal bounds on electric-field fluctuations for random composites  

Microsoft Academic Search

It is important to understand the behavior of the local electric field in composite materials as regions containing high fields are most often the first to suffer damage during service. The higher moments of the electric field provide information on the variation of the local electric field that is not revealed by the effective properties of the composite. Unfortunately, higher

Robert Liptona

280

Surface electric fields and impedance matrix elements of stratified media  

Microsoft Academic Search

For the various geometrical configurations of waves in stratified media, we consider the important case when both source and field points are located on the same interface separating two different dielectric media. We denote this configuration as surface electric field case. In this paper, the electric fields are calculated numerically without using potentials. For the surface electric field case the

Leung Tsang; Chuag-Chi Huang; Chi Hou Chan

2000-01-01

281

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

282

Extremely low frequency electric fields and cancer: assessing the evidence.  

PubMed

Much of the research and reviews on extremely low frequency (ELF) electric and magnetic fields (EMFs) have focused on magnetic rather than electric fields. Some have considered such focus to be inappropriate and have argued that electric fields should be part of both epidemiologic and laboratory work. This paper fills the gap by systematically and critically reviewing electric-fields literature and by comparing overall strength of evidence for electric versus magnetic fields. The review of possible mechanisms does not provide any specific basis for focusing on electric fields. While laboratory studies of electric fields are few, they do not indicate that electric fields should be the exposure of interest. The existing epidemiology on residential electric-field exposures and appliance use does not support the conclusion of adverse health effects from electric-field exposure. Workers in close proximity to high-voltage transmission lines or substation equipment can be exposed to high electric fields. While there are sporadic reports of increase in cancer in some occupational studies, these are inconsistent and fraught with methodologic problems. Overall, there seems little basis to suppose there might be a risk for electric fields, and, in contrast to magnetic fields, and with a possible exception of occupational epidemiology, there seems little basis for continued research into electric fields. PMID:19650076

Kheifets, Leeka; Renew, David; Sias, Glenn; Swanson, John

2010-02-01

283

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

284

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

285

Measuring SWNT depth in electroactive polymer nanocomposite films using electric force microscopy  

NASA Astrophysics Data System (ADS)

Although a number of hypotheses have been presented to explain the enhanced electromechanical performance observed in electroactive polymer nanocomposite materials, many of the underlying mechanisms responsible for this behavior remain unclear. In this report, electric force microscopy (EFM) is used to investigate the near surface morphology of an electroactive polyimide-based nanocomposite film containing SWNTs in an effort to gain insight into the electrical interactions occurring at the polymer-electrode interface. As a means of measuring the proximity of SWNTs to this interface, the depths of SWNTs buried beneath a processing-induced polymer skin layer are determined using EFM measurements derived from a sample standard. In this way, evaluation of the ability for embedded SWNT structures to behave as extensions of surface electrodes is possible, a scenario that could potentially reduce the applied field required to elicit electromechanical actuation.

Sellinger, Aaron T.; Deshmukh, Sujay; Ounaies, Zoubeida; Kim, Sang Nyon; Vaia, Richard A.

2010-03-01

286

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

287

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

288

Mapping the force field of a hydrogen-bonded assembly.  

PubMed

Hydrogen bonding underpins the properties of a vast array of systems spanning a wide variety of scientific fields. From the elegance of base pair interactions in DNA to the symmetry of extended supramolecular assemblies, hydrogen bonds play an essential role in directing intermolecular forces. Yet fundamental aspects of the hydrogen bond continue to be vigorously debated. Here we use dynamic force microscopy (DFM) to quantitatively map the tip-sample force field for naphthalene tetracarboxylic diimide molecules hydrogen-bonded in two-dimensional assemblies. A comparison of experimental images and force spectra with their simulated counterparts shows that intermolecular contrast arises from repulsive tip-sample interactions whose interpretation can be aided via an examination of charge density depletion across the molecular system. Interpreting DFM images of hydrogen-bonded systems therefore necessitates detailed consideration of the coupled tip-molecule system: analyses based on intermolecular charge density in the absence of the tip fail to capture the essential physical chemistry underpinning the imaging mechanism. PMID:24875276

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

2014-01-01

289

Mapping the force field of a hydrogen-bonded assembly  

PubMed Central

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

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

2014-01-01

290

Stochastic dynamics of electric dipole in external electric fields: A perturbed nonlinear pendulum approach  

NASA Astrophysics Data System (ADS)

The motion of a dipole in external electric fields is considered in the framework of nonlinear pendulum dynamics. A stochastic layer is formed near the separatrix of the dipole pendulum in a restoring static electric field under the periodic perturbation by plane-polarized electric fields. The width of the stochastic layer depends on the direction of the forcing field variation, and this width can be evaluated as a function of perturbation frequency, amplitude, and duration. A numerical simulation of the approximate stochastic layer width of a perturbed pendulum yields a multi-peak frequency spectrum. It is described well enough at high perturbation amplitudes by an analytical estimation based on the separatrix map with an introduced expression of the most effective perturbation phase. The difference in the fractal dimensions of the phase spaces calculated geometrically and using the time-delay reconstruction is attributed to the predominant development of periodic and chaotic orbits, respectively. The correlation of the stochastic layer width with the phase space fractal dimensions is discussed.

Kapranov, Sergey V.; Kouzaev, Guennadi A.

2013-06-01

291

Normal force reduction: a variable activation energy process? [electrical contact springs  

Microsoft Academic Search

An experimental and theoretical analysis has been carried out into normal force reduction in electrical contact springs. This is a phenomenon whereby the force produced by the contact spring reduces with time. A series of ten elevated temperature heat age tests were carried out for time periods of up to three months. Over 6500 normal force reduction measurements have been

N. A. Stennett; D. S. Campbell

1994-01-01

292

Folding of Gas-Phase Polyalanines in a Static Electric Field: Alignment, Deformations, and Polarization Effects  

PubMed Central

Monte Carlo simulations of the temperature-induced unfolding of small gas-phase polyalanines in a static, homogeneous electric field are reported, based on the AMBER ff96 force field. The peptides exhibit a structural transition from the native ?-helix state to entropically favored ?-sheet conformations, before eventually turning to extended coil at higher temperatures. Upon switching the electric field, the molecules undergo preferential alignment of their dipole moment vector toward the field axis and a shift of the ?-? transition to higher temperatures. At higher field strengths (>108 V/m) the molecules stretch and the ?-? and ?-coil transitions merge. A simple three-state model is shown to account for the observed behavior. Under even higher fields, density functional theory calculations and a polarizable force field both show that electronic rearrangements tend to further increase the dipole moment, polarization effects being approximately half in magnitude with respect to stretching effect. Finally a tentative (temperature, field-strength) phase diagram is sketched.

Calvo, F.; Dugourd, P.

2008-01-01

293

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

294

Low frequency electric and magnetic fields  

NASA Technical Reports Server (NTRS)

Following preliminary investigations of the low frequency electric and magnetic fields that may exists in the Earth-ionospheric cavity, measurements were taken with state-of-the art spectrum analyzers. As a follow up to this activity, an investigation was initiated to determine sources and values for possible low frequency signal that would appear in the cavity. The lowest cavity resonance is estimated at about 8 Hz, but lower frequencies may be an important component of our electromagnetic environment. The potential field frequencies produced by the electron were investigated by a classical model that included possible cross coupling of the electric and gravitation fields. During this work, an interesting relationship was found that related the high frequency charge field with the extremely low frequency of the gravitation field. The results of numerical calculations were surprisingly accurate and this area of investigation is continuing. The work toward continued development of a standardized monitoring facility is continuing with the potential of installing the prototype at West Virginia State College early in 1990. This installation would be capable of real time monitoring of ELF signals in the Earth-ionoshpere cavity and would provide some directional information. A high gain, low noise, 1/f frequency corrected preamplifier was designed and tested for the ferrite core magnetic sensor. The potential application of a super conducting sensor for the ELF magnetic field detection is under investigation. It is hoped that a fully operational monitoring network could pinpoint the location of ELF signal sources and provide new information on where these signals originate and what causes them, assuming that they are natural in origin.

Spaniol, Craig

1989-01-01

295

Electric Fields in Tumors Exposed to External Voltage Sources: Implication for Electric Field-Mediated Drug and Gene Delivery  

Microsoft Academic Search

The intratumoral field, which determines the efficiency of electric field-mediated drug and gene delivery, can differ significantly from the applied field. Therefore, we investigated the distribution of the electric field in mouse tumors and tissue phantoms exposed to a large range of electric stimuli, and quantified the resistances of tumor, skin, and electrode-tissue interface. The samples used in the study

Brian J. Mossop; Roger C. Barr; Joshua W. Henshaw; David A. Zaharoff; Fan Yuan

2006-01-01

296

Coupled electrical-fluid model of pulsed electric field treatment in a model food system  

Microsoft Academic Search

A coupled electrical-fluid model of a pulsed electric field (PEF) treatment is presented. The modeling of PEF food treatment to date has been limited to a separate study of the electric field distribution and the product flow. A model was developed that couples the electric field and fluid dynamics analysis. The main feature of the model is that parameters vital

Ales Fiala; Patrick C Wouters; Erik van den Bosch; Yves L. M Creyghton

2001-01-01

297

A quantum mechanical scaled force field for tetranitromethane  

NASA Astrophysics Data System (ADS)

Infrared and Raman spectra of tetranitromethane have been recorded in the liquid and vapour phases as well as in solutions of several solvents. On the basis of theoretical predictions, the general assignment of the vibrational spectrum has been modified with respect to previous studies. The computed force field has been scaled to reproduce the experimental frequencies and the prediction capabilities of the method are discussed.

Arenas, J. F.; Otero, J. C.; Soto, J.

1993-10-01

298

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

299

Tuning the mass of chameleon fields in Casimir force experiments.  

PubMed

We have calculated the chameleon pressure between two parallel plates in the presence of an intervening medium that affects the mass of the chameleon field. As intuitively expected, the gas in the gap weakens the chameleon interaction mechanism with a screening effect that increases with the plate separation and with the density of the intervening medium. This phenomenon might open up new directions in the search of chameleon particles with future long-range Casimir force experiments. PMID:20867290

Brax, Ph; van de Bruck, C; Davis, A C; Shaw, D J; Iannuzzi, D

2010-06-18

300

Quantum mechanical force field for water with explicit electronic polarization.  

PubMed

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(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. PMID:23927266

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

2013-08-01

301

Molecular force field parametrization using multi-objective evolutionary algorithms  

Microsoft Academic Search

We suggest a novel tool for the parametrization of molecular force fields by using multi-objective optimization algorithms with a new set of physically motivated objective functions. The new approach is validated in the parametrization of the bonded terms for the homologous series of primary alcohols. Multi-objective evolutionary algorithms (MOEAs) and particularly multi-objective particle swarm optimization (MOPSO) are applied. The results

S. Mostaghim; M. Hoffmann; P. H. Konig; T. Frauenheim; J. Teich

2004-01-01

302

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

303

Nucleation rate enhancement of porcine insulin by application of an external AC electric field  

NASA Astrophysics Data System (ADS)

The nucleation rate of porcine insulin increased under application of an external AC electric field at 3 MHz. This is attributed to the electrostatic energy added to the chemical potentials of both the liquid and solid phases; the chemical potential of the solid was significantly changed compared with that of the liquid, which lead to an increase in the driving force for nucleation. Therefore, application of an external AC electric field can be a useful technique for protein crystallization.

Koizumi, H.; Tomita, Y.; Uda, S.; Fujiwara, K.; Nozawa, J.

2012-08-01

304

From force fields to dynamics: Classical and quantal paths  

SciTech Connect

Reaction path provides a powerful tool for bridging the gap between electronic structure and chemical dynamics. Classical mechanical reaction paths may usually be understood in terms of the force field in the vicinity of a minimum energy path (MEP). When there is a significant component of hydrogenic motion along the MEP and a barrier much higher than the average energy of reactants, quantal tunneling paths must be considered, and these tend to be located on the corner-cutting side of the MEP. As the curvature of the MEP in mass-scaled coordinates is increased, the quantal reaction paths may deviate considerably from the classical ones, and the force field must be mapped out over a wider region, called the reaction swath. The required force fields may be presented by global or semiglobal analytic functions, or the dynamics may be computed directly from the electronic structure results without the intermediacy of potential energy functions. Applications to atom and diatom reactions in the gas phase and at gas-solid interfaces and to reactions of polyatomic molecules in the gas phase, in clusters, and in aqueous solution are discussed as examples. 106 refs., 2 figs.

Truhlar, D.G. (Univ. of Minnesota, Minneapolis (USA)); Gordon, M.S. (North Dakota State Univ., Fargo (USA))

1990-08-03

305

Molecular simulations of primary alkanolamines using an extendable force field.  

PubMed

A classical force field is proposed for the molecular simulation of primary alkanolamines containing a NH(2)-C-C-OH backbone. A method is devised to take into account the polar (H-bonding) environment of the alkanolamines by calculating electrostatic charges in the presence of explicit solvent molecules. The force field does not use a universal set of charges, but is rather constructed by following a general method for obtaining specific charges for the different alkanolamines. The model is parameterized on the two simplest primary alkanolamines and then validated by calculating thermodynamic properties of five other molecules. Experimental liquid densities and enthalpies of vaporization are also reported in order to complete existing literature data. The predicted ability of the force field is evaluated by comparing the simulation results with experimental densities and enthalpies of vaporization. Densities are predicted with an uncertainty of 1.5 % and enthalpies of vaporization with an uncertainty of 1 kJ mol(-1). A decomposition of the interaction energy into electrostatic and repulsive-dispersive interactions and an analysis of hydrogen-bond statistics lead to a complex picture. Some terms of these interactions are related to the molecular structure in a clear way, others are not. The results provide insights into the structure-property relations that contribute to a better description of the thermodynamic properties of alkanolamines. PMID:23047473

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

2012-12-01

306

Design and optimization of force-reduced high field magnets  

NASA Astrophysics Data System (ADS)

High field magnets have many important applications in different areas of research, in the power industry and also for military purposes. For example, high field magnets are particularly useful in: material sciences, high energy physics, plasma physics (as fusion magnets), high power applications (as energy storage devices), and space applications (in propulsion systems). One of the main issues with high-field magnets is the presence of very large electromagnetic stresses that must be counteracted and therefore require heavy support structures. In superconducting magnets, the problems caused by Lorentz forces are further complicated by the fact that superconductors for high field applications are pressure sensitive. The current carrying capacity is greatly reduced under stress and strain (especially in the case of Nb 3Sn and the new high temperature superconductors) so the reduction of the acting forces is of even greater importance. Different force-reduced magnet concepts have been studied in the past, both numerical and analytical methods have been used to solve this problem. The developed concepts are based on such complex winding geometries that the realization and manufacturing of such coils is extremely difficult and these concepts are mainly of theoretical interest. In the presented research, a novel concept for force-reduced magnets has been developed and analyzed which is easy to realize and therefore is of practical interest. The analysis has been performed with a new methodology, which does not require the time consuming finite element calculations. The developed computer models describe the 3-dimensional winding configuration by sets of filaments (filamentary approximation). This approach is much faster than finite element analysis and therefore allows rapid optimization of concepts. The method has been extensively tested on geometries of force-reduced solenoids where even analytical solutions exist. As a further cross check, the developed computer codes have been tested against qualified finite element codes and found to be in excellent agreement. The developed concept of force-reduced coils is directly applicable to pulsed magnets and a conceptual design of a 25 Tesla magnet has been developed. Although no experimental proof was possible within the scope of this research, there is strong evidence to believe that the developed concept is also applicable to superconducting magnets operating in a constant current mode.

Rembeczki, Szabolcs

307

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

308

Convection electric fields and polar thermospheric winds.  

NASA Technical Reports Server (NTRS)

Use of the qualitative ideas of convection electric fields over the earth's polar regions to demonstrate the importance of ion drag in establishing a thermospheric wind system. Recent measurements indicate that uniform electric fields of 10 to 40 mV/m are a regular feature of the polar-cap ionosphere. Calculations of the neutral thermospheric wind, using these measured fields in a simple ionospheric model, have been made. The time scale for motion of the neutral gas ranges from less than 1 hour at F-region heights to about 2 hours in the dynamo region of the ionosphere. It has been found that the viscosity of the atmosphere is important in determining the winds in the dynamo region. Results are given that show ion-temperature enhancements of hundreds of degrees that are due to ion-neutral frictional effects. In addition, the total deposition rate of convection energy in the polar thermosphere is shown to be of the same order of magnitude as that due to absorption of solar EUV radiation. The implications of these results for the dynamics and energetics of the thermosphere are discussed.

Fedder, J. A.; Banks, P. M.

1972-01-01

309

Motional sideband excitation using rotating electric fields  

NASA Astrophysics Data System (ADS)

A form of motional sideband excitation is described in which a rotating dipole electric field is applied asymmetrically onto a Penning-type trap in the presence of a mechanism for cooling the axial motion of the trapped particles. In contrast to the traditional motional sideband excitation, which uses an oscillating electric field, the rotating field results in only one active sideband in each sense of rotation and so avoids accidental excitation of the other sideband making it applicable to Penning-type traps with a large degree of anharmonicity. Expressions are derived for the magnetron radius expansion and compression rates attainable, and approximations are made for the case of strong and weak drives. A comparison is made with data, taken using a two-stage positron accumulator presented by Isaac [C. A. Isaac, C. J. Baker, T. Mortensen, D. P. van der Werf, and M. Charlton, Phys. Rev. Lett.PRLTAO0031-900710.1103/PhysRevLett.107.033201 107, 033201 (2011)], showing good agreement between the model and experiment.

Isaac, C. A.

2013-04-01

310

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

NASA Astrophysics Data System (ADS)

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 work by Chuang and Beard (1990) in which this problem is approached by adjusting an empirical pressure distribution for the distortion, our model considers simple local pressure balance to determine the drop shape. This computation aims at characterizing drop distortion, falling speed modification, and disruption. The overall present results are similar to those of Chuang and Beard's more sophisticated model, and the predicted critical fields are even closer to wind tunnel measurements by Richards and Dawson (1971). The disruption of positively charged drops requires lower ambient fields than that of the negatively charged drops, and for highly charged and large drops they are of the order of those commonly measured within thunderclouds. At last, the terminal velocity is highly affected by net charge and ambient field. These processes are probably important in lightning initiation during drop disruption.

Coquillat, Sylvain; Chauzy, Serge

1993-06-01

311

Vectorial electric field measurement using isotropic electro-optic crystals  

SciTech Connect

The authors present a two-component electric field measurement using a single electro-optic crystal and a single laser probe beam. This vectorial electric field measurement based on polarization state modulation is possible using isotropic electro-optic crystals for which directions of the eigendielectric axes are directly linked to the direction of the applied electric field. The proposed method can be used either for continuous wave or single shot measurements as the two electric field components are measured simultaneously.

Gaborit, G.; Coutaz, J.-L.; Duvillaret, L. [LAHC, Universite de Savoie, 73376 Le Bourget du Lac cedex (France); IMEP, Minatec-INPG, 3 parvis Louis Neel, 38016 Grenoble cedex 1 (France)

2007-06-11

312

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

313

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

314

An oppositely charged insect exclusion screen with gap-free multiple electric fields  

NASA Astrophysics Data System (ADS)

An electric field screen was constructed to examine insect attraction mechanisms in multiple electric fields generated inside the screen. The screen consisted of two parallel insulated conductor wires (ICWs) charged with equal but opposite voltages and two separate grounded nets connected to each other and placed on each side of the ICW layer. Insects released inside the fields were charged either positively or negatively as a result of electricity flow from or to the insect, respectively. The force generated between the charged insects and opposite ICW charges was sufficient to capture all insects.

Matsuda, Yoshinori; Kakutani, Koji; Nonomura, Teruo; Kimbara, Junji; Kusakari, Shin-ichi; Osamura, Kazumi; Toyoda, Hideyoshi

2012-12-01

315

The Effect of a Radial Electric Field in The Structure of a Polytropic Star  

NASA Astrophysics Data System (ADS)

In this work we show how a radial electric field can affect the structure of a relativistic star. For this, we assumed that the star is spherically symmetric. We see that this kind of electric field introduces a change in the gravitational force generated by the star, and consequently in the structure of the star. We also assume that the pressure caused by the electric field obeys a polytropic equation of state, and then we derive an equation analogous to the Lane - Emden equation for a charged polytropic star.

Picanço, Rodrigo; Malheiro, Manuel; Ray, Subharthi

2004-12-01

316

Destabilization of Turing Structures by Electric Fields  

NASA Astrophysics Data System (ADS)

The dynamic behavior of hexagonal Turing patterns in the chlorine dioxide-iodine-malonic acid reaction was studied in a newly developed open reactor under the influence of externally applied weak directed current up to 17.5mA. A transition from stationary hexagonal patterns to spots moving parallel to the direction of the applied electric field could be observed. The velocity of the drift increases monotonously with the applied current. Experimental results could be qualitatively reproduced in numerical simulations with a reaction-diffusion-advection model, based on a realistic kinetic mechanism.

Schmidt, B.; de Kepper, P.; Müller, S. C.

2003-03-01

317

Spatial aspects of the electric fields generated by weakly electric fish  

Microsoft Academic Search

1.The electric fields of four species of wave type, gymnotid fishes were measured and mapped using a technique that allowed accurate assessment of small electric fields, free of unknown field compression and distortion artifacts.2.Dipole moment values were calculated for each fish's electric field from measurements made at a sufficient distance (Table 1). A dipole moment is an absolute evaluation of

Eric I. Knudsen

1975-01-01

318

Structural Relaxation of Water-in-Oil Emulsion under Direct Current Electric Field  

NASA Astrophysics Data System (ADS)

In this study, electrorheology of water-in-oil emulsion is explored in the presence of direct current (DC) electric fields. DC electrorheological (ER) experiments in dynamic mode are performed to study the structural evolution of emulsions from a random configuration to organized microstructures. Critical electric field (CEF), i.e. value of field at which the emulsion structure breakdown occurs, is measured. In this work, all the ER experiments are completed at electric field strength below CEF. Since ER emulsion behavior is controlled by electrical and hydrodynamic forces, structural relaxation of emulsions as a function of electric field strength, dynamic frequency and continuous phase viscosity is investigated. Time evolution of viscosity and electrical current are measured to reflect characteristics of the system microstructure. Also, hysteresis is measured at low electric fields to study the rheological properties restoration after the field has been turned off. The results on the relaxation process show that the electric field induces increase in viscosity as well as electrical current.

Moradi, Mehrnoosh; Alvarado, Vladimir

2010-11-01

319

Electric field measurements during the Condor critical velocity experiment  

Microsoft Academic Search

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

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

1986-01-01

320

Interactions between Biological Cells and Intense Pulsed Electrical Fields  

Microsoft Academic Search

Biological cell behaviors under electrical fields have been researched for several decades. At early time, biological cells are researched as special dielectric under pulsed electrical fields. Some models are prompted to explain these biological cell behaviors. With the developments of modern microscopy technology and compact pulsed power technology, researches on the interactions between biological cells and intense pulsed electrical fields

Xupeng Chen; Yuanfang Wen; Weixin Liu

2007-01-01

321

Vibrational spectra and harmonic force fields of pyrrolidine derivatives: comparison between HF, MP2 and DFT force fields  

Microsoft Academic Search

Infrared and Raman spectra are reported for the isotopic species of pyrrolidine-d0 (PY) and -d1 and for N-methylpyrrolidine-d0 (NMP), -d2, -d3 and -d8. A complete assignment of the experimentally observed bands to normal modes is presented and discussed in particular in the CH\\/CD stretching region. The molecular structures and harmonic force fields were calculated ab initio at the Hartree–Fock (HF),

Ferenc Billes; Ekkehard Geidel

1997-01-01

322

Ab initio valence force field calculations for quartz  

NASA Astrophysics Data System (ADS)

We have derived valence force constants for the tetrahedral SiO4 unit and the inter-tetrahedral SiOSi linkage from previous ab initio molecular orbital calculations on H4SiO4 and H6Si2O7 using a split-valence polarized Gaussian basis set (6-31G*), and used these to calculate the infrared and Raman active vibrational modes of ?-quartz. The calculation gives frequencies approximately 15% greater than experiment, as expected from harmonic force constants obtained at this level of Hartree-Fock theory, but the calculation gives the correct distribution of modes within each frequency range. Calculated 28 30 Si and 16 18 O isotope shifts and pressure shifts to 6 GPa are also in reasonable agreement with experiment. We have also used our ab initio force field to calculate the vibrational spectrum for ?-quartz. The results suggest either that inclusion of a torsional force constant is important for determining the stability of this high temperature polymorph, or that the ?-quartz has a disordered structure with lower symmetry (P62) domains, as suggested by earlier diffraction studies.

McMillan, Paul F.; Hess, Anthony C.

1990-03-01

323

Exposure assessment for electric and magnetic fields  

SciTech Connect

Exposure assessment for extremely low frequency (ELF) electric and magnetic fields (EMF) is discussed. It is suggested that such assessments can be designed by attempting to mimic the receptor's experience of interest. Present efforts are, however, hampered by the lack of clearly defined human health effects, or even important interaction mechanisms, which might be used to define the appropriate exposure measure, the experience of interest. The state of the art of ELF EMF exposure assessment is described, including the use of surrogates, models, and available instrumentation. Data indicate that magnetic field levels in the home are of the order of 0.1 microT and that nonoccupational total exposures may best be predicted by levels in the bedroom. Occupational exposures may be orders of magnitude higher where high currents are present.51 references.

Patterson, R.M. (College of Engineering, Temple University, Philadelphia, PA (United States))

1992-04-01

324

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.

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

2014-01-01

325

Large electric field-enhanced-hardness effect in a SiO2 film.  

PubMed

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

326

Coarse-grained force field; general folding theory  

PubMed Central

We review the coarse-grained UNited RESidue (UNRES) force field for the simulations of protein structure and dynamics, which is being developed in our laboratory over the last several years. UNRES is a physics-based force field, the prototype of which is defined as a potential of mean force of polypeptide chains in water, where all the degrees of freedom except the coordinates of ?-carbon atoms and side-chain centers have been integrated out. We describe the initial implementation of UNRES to protein-structure prediction formulated as a search for the global minimum of the potential-energy function and its subsequent molecular dynamics and extensions of molecular-dynamics implementation, which enabled us to study protein-folding pathways and thermodynamics, as well as to reformulate the protein-structure prediction problem as a search for the conformational ensemble with the lowest free energy at temperatures below the folding-transition temperature. Applications of UNRES to study biological problems are also described.

Liwo, Adam; He, Yi; Scheraga, Harold A.

2012-01-01

327

Evaluation of Electromagnetic Force and Magnetic Laval Nozzle Acceleration in an Applied-Field MPD Thruster  

NASA Astrophysics Data System (ADS)

A magneto-plasma-dynamic thruster (MPDT) is expected as one of the promising electric propulsion systems owing to features of a relatively large thrust, high specific impulse that is unattainable by conventional chemical or nuclear propulsion required for space missions such as a manned Mars mission. To clarify the electromagnetic acceleration mechanism of a plasma flow in an applied-field MPDT, detailed flow field and electromagnetic force field are evaluated experimentally with spectroscopic technique and magnetic probe array. It is found that an axial drag force generated by an interaction between azimuthal plasma current and radial magnetic field cancels an acceleration force in a uniform magnetic field. A thermal energy component is much larger than a flow energy component in Bernoulli's equation and ion acoustic Mach number is limited less than unity in the muzzle region of MPD arcjet. In order to convert the thermal energy to the flow energy, magnetic Laval nozzle acceleration with a local magnetic coil is attempted. The ion Mach number after passing through the nozzle throat exceeds unity and a production of supersonic plasma flow is achieved. An optimum magnetic nozzle configuration is discussed with the experimental results.

Tobari, Hiroyuki; Sato, Ryuichi; Harata, Kenji; Hattori, Kunihiko; Ando, Akira; Inutake, Masaaki

2003-10-01

328

Field ion microscopy characterized tips in noncontact atomic force microscopy: Quantification of long-range force interactions  

NASA Astrophysics Data System (ADS)

Direct comparison of tip-sample forces obtained by dynamic force spectroscopy experiments with theoretical simulations is extremely difficult, since the precise tip shape and chemical identity of the apex atoms of the force sensing tip remain unknown in most experiments. Here, we present force curves measured with a tungsten tip on a Ag(111) surface obtained in a low-temperature atomic force microscope using tips that were analyzed by field ion microscopy down to atomic levels. The resulting van der Waals and electrostatic forces were found to be in quantitative agreement with analytical models, if the tip shape parameters from the field ion microscopy analysis were used. Furthermore, our analysis shows an additional long-range force interaction at tip-sample distances above 1.3 nm. We suggest that this unexpected force is related to patch charges arising from the inhomogeneous work function distribution on the surface of highly faceted sharp tips.

Falter, J.; Langewisch, G.; Hölscher, H.; Fuchs, H.; Schirmeisen, A.

2013-03-01

329

Manipulating colloids with charges and electric fields  

NASA Astrophysics Data System (ADS)

This thesis presents the results of experimental investigations on a variety of colloidal suspensions. Colloidal particles are at least a hundred times larger than atoms or molecules, but suspended in a liquid they display the same phase behavior, including fluid and crystalline phases. Due to their relatively large size, colloids are much easier to investigate and manipulate, though. This makes them excellent condensed matter model systems. With this in mind, we studied micrometer-sized perspex (‘PMMA’) spheres, labeled with a fluorescent dye for high-resolution confocal microscopy imaging, and suspended in a low-polar mixture of the organic solvents cyclohexyl bromide and cis-decalin. This system offered us the flexibility to change the interactions between the particles from ‘hard-sphere-like’ to long-ranged repulsive (between like-charged particles), long-ranged attractive (between oppositely charged particles) and dipolar (in an electric field). We investigated the phase behavior of our suspensions as a function of the particle concentration, the ionic strength of the solvent and the particles’ charges. In this way, we obtained new insight in the freezing and melting behavior of like-charged and oppositely charged colloids. Interestingly, we found that the latter can readily form large crystals, thus defying the common belief that plus-minus interactions inevitably lead to aggregation. Moreover, we demonstrated that these systems can serve as a reliable model system for classical ionic matter (‘salts’), and that opposite-charge interactions can greatly facilitate the self-assembly of new structures with special properties for applications. On a slightly different note, we also studied electrostatic effects in mixtures of the cyclohexyl bromide solvent and water, both with and without colloidal particles present. This provided new insight in the stabilization mechanisms of oil-water emulsions and gave us control over the self-assembly of various useful colloidal structures. Besides modifying the particle charge, we employed the sensitivity of colloids to ‘external fields’ to manipulate the structure and dynamics of our suspensions. In particular, we used an electric field, in which the particles acquired a dipole moment. The induced dipole-dipole interactions gave rise to uniquely different crystalline and non-crystalline structures, due to their anisotropic nature. We explored the phase behavior as a function of the particle concentration, the electric field strength and the field geometry, and showed how one can rapidly switch from one structure to another. The latter is particularly interesting for applications. Finally, we also studied much weaker, inhomogeneous electric fields. In this case, the dipole moment of the particles was too small to change the phase behavior, but large enough to induce dielectrophoretic motion, driving the particles to the areas with the lowest field strength. We demonstrated how this can be used to manipulate the local particle concentration inside a sealed sample, on a time scale of minutes-weeks. The combination with real-time confocal microscopy allowed us to follow all particle rearrangements during the densification. Such controlled compression is of interest to colloidal model studies and the fabrication of high-quality crystals for applications. After all, for all suspensions the particle concentration is one of the most important factors determining the behavior.

Leunissen, M. E.

2007-02-01

330

Kelvin probe force microscope with near-field photoexcitation  

NASA Astrophysics Data System (ADS)

We developed a combined probe microscope-a scanning probe near-field optical microscope (SNOM) combined with Kelvin probe force microscope (KFM) that uses a slim and bent optical fiber probe (S/B fiber probe). The developed SNOM-KFM system enables near-field photoexcitation through an apex of the S/B fiber probe during KFM measurement, so that the photoexcitation effects on surface potential (SP) can be measured with submicron spatial resolution. By measuring the SP of tris(8-hydroxyquinolinato) aluminum(III) (Alq3) thin films, we found that the S/B fiber probes have large negative values in the KFM transfer function. Near-field photoexcitation was performed on Alq3 thin films through the S/B fiber probes, and the spatial pattern of photoinduced reduction in SP was visualized by KFM measurement with the same probe.

Ozasa, Kazunari; Nemoto, Shigeyuki; Maeda, Mizuo; Hara, Masahiko

2010-05-01

331

Deformation field of the soft substrate induced by capillary force  

NASA Astrophysics Data System (ADS)

Prediction on the deformation of a soft substrate induced by capillary force has been widely paid attention in the broad range of applications, such as metallurgy, material science, astronavigation, micro/nano-technology, etc., which is also a supplementary result to the classical Young's equation. We quantitatively analyzed the deformation of an elastic substrate under capillary force by means of the energy principle and the continuum mechanics method. The actual drop's morphology was investigated and was compared with that calculated based on the classical spherical shape assumption of the droplet. The displacement field of the substrate was obtained, especially, its singularity at the droplet edge was also discussed. The results are beneficial to engineering application and micro/nano-measurement.

Liu, J. L.; Nie, Z. X.; Jiang, W. G.

2009-05-01

332

Voltage response and field reconstruction for a miniature field probe in a spatially nonuniform electric field  

Microsoft Academic Search

A miniature E-field probe employing a 0.6-mm linear dipole antenna has been developed. The authors describe an analytical study of the probe's response to a spatially varying electric field. On the basis of the Nyquist sampling theorem, the spatial sampling frequency at which an electric field should be measured for good reconstruction is established. Using antenna theory, the voltage response

STEVEN D. HARRAH; K. T. Ng; T. E. Batchman

1990-01-01

333

Force-free coronal magnetic field modeling using vector fields from Hinode and SDO  

NASA Astrophysics Data System (ADS)

Given the lack of routine direct measurements of the magnetic field in the solar corona, force-free reconstruction methods are a promising tool for the diagnostics of the magnetic structure there. Routine photospheric magnetic field measurements which monitor the temporal evolution of an active region and contain information on the non-potentiality of the field above are used as an input. Based on the assumption that magnetic forces dominate the solar atmosphere, these models allow estimates of the total and free magnetic energy content and the structure of the magnetic field above active regions. The outcome of force-free field modeling strongly depends on the vector magnetic field data used as boundary condition. We compare the model results based on simultaneously observed vector maps from the Helioseismic and Magnetic Imager (HMI) on board Solar Dynamics Observatory and from the Solar Optical Telescope Spectropolarimeter (SP) on board Hinode. We find substantial differences in the absolute estimates of the magnetic field energy but very similar relative estimates, e.g., the fraction of energy to be set free during an eruption or the fraction of flux linking distinct areas within an active region. Our study reveals that only relative estimates of coronal physical quantities from force-free models might be save and conclusions about the magnetic field topology might be drawn with caution.

Thalmann, Julia K.; Tiwari, Sanjiv K.; Wiegelmann, Thomas

2013-04-01

334

A phenomenological model that predicts forces generated when electrical stimulation is superimposed on submaximal volitional contractions  

PubMed Central

Superimposition of electrical stimulation during voluntary contractions is used to produce functional movements in individuals with central nervous system impairment, to evaluate the ability to activate a muscle, to characterize the nature of fatigue, and to improve muscle strength during postsurgical rehabilitation. Currently, the manner in which voluntary contractions and electrically elicited forces summate is not well understood. The objective of the present study is to develop a model that predicts the forces obtained when electrical stimulation is superimposed on a volitional contraction. Quadriceps femoris muscles of 12 able-bodied subjects were tested. Our results showed that the total force produced when electrical stimulation was superimposed during a volitional contraction could be modeled by the equation T = V + S[(MaxForce ? V)/MaxForce]N, where T is the total force produced, V is the force in response to volitional contraction alone, S is the force response to the electrical stimulation alone, MaxForce is the maximum force-generating ability of the muscle, and N is a parameter that we posit depends on the differences in the motor unit recruitment order and firing rates between volitional and electrically elicited contractions. In addition, our results showed that the model predicted accurately (intraclass correlation coefficient ?0.97) the total force in response to a wide range of stimulation intensities and frequencies superimposed on a wide range of volitional contraction levels. Thus the model will be helpful to clinicians and scientists to predict the amount of stimulation needed to produce the targeted force levels in individuals with partial paralysis.

Perumal, Ramu; Wexler, Anthony S.; Kesar, Trisha M.; Jancosko, Angela; Laufer, Yocheved

2010-01-01

335

The electrically detected magnetic resonance microscope: Combining conductive atomic force microscopy with electrically detected magnetic resonance  

NASA Astrophysics Data System (ADS)

We present the design and implementation of a scanning probe microscope, which combines electrically detected magnetic resonance (EDMR) and (photo-)conductive atomic force microscopy ((p)cAFM). The integration of a 3-loop 2-gap X-band microwave resonator into an AFM allows the use of conductive AFM tips as a movable contact for EDMR experiments. The optical readout of the AFM cantilever is based on an infrared laser to avoid disturbances of current measurements by absorption of straylight of the detection laser. Using amorphous silicon thin film samples with varying defect densities, the capability to detect a spatial EDMR contrast is demonstrated. Resonant current changes as low as 20 fA can be detected, allowing the method to realize a spin sensitivity of 8 × 10^6spins/?Hz at room temperature.

Klein, Konrad; Hauer, Benedikt; Stoib, Benedikt; Trautwein, Markus; Matich, Sonja; Huebl, Hans; Astakhov, Oleksandr; Finger, Friedhelm; Bittl, Robert; Stutzmann, Martin; Brandt, Martin S.

2013-10-01

336

Magnetic resonance electrical impedance tomography for determining electric field distribution during electroporation  

NASA Astrophysics Data System (ADS)

Electroporation is a phenomenon caused by externally applied electric field to cells that results in an increase of cell membrane permeability to various molecules. Accurate coverage of the tissue with a sufficiently large electric field presents one of the most important conditions for successful membrane permeabilization. Applications based on electroporation would greatly benefit with a method for monitoring the electric field, especially if it could be done in situ. As the membrane electroporation is a consequence of an induced transmembrane potential, which is directly proportional to the local electric field, we have been investigating current density imaging and magnetic resonance electrical impedance tomography techniques to determine the electric field distribution during electroporation. In this paper, we present comparison of current density and electric field distribution in an agar phantom and in a liver tissue exposed to electroporation pulses. As expected, a region of increased electrical conductivity was observed in the liver tissue exposed to sufficiently high electric field but not in agar phantom.

Kranjc, Matej; Bajd, Franci; Serša, Igor; Miklav?i?, Damijan

2013-04-01

337

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

338

Emitting waves from heterogeneity by a rotating electric field.  

PubMed

In a generic model of excitable media, we simulate wave emission from a heterogeneity (WEH) induced by an electric field. Based on the WEH effect, a rotating electric field is proposed to terminate existed spatiotemporal turbulence. Compared with the effects resulted by a periodic pulsed electric field, the rotating electric field displays several improvements, such as lower required intensity, emitting waves on smaller obstacles, and shorter suppression time. Furthermore, due to rotation of the electric field, it can automatically source waves from the boundary of an obstacle with small curvature. PMID:24089977

Zhao, Ye-Hua; Lou, Qin; Chen, Jiang-Xing; Sun, Wei-Gang; Ma, Jun; Ying, He-Ping

2013-09-01

339

Saturation of the Electric Field Transmitted to the Magnetosphere  

NASA Technical Reports Server (NTRS)

We reexamined the processes leading to saturation of the electric field, transmitted into the Earth's ionosphere from the solar wind, incorporating features of the coupled system previously ignored. We took into account that the electric field is transmitted into the ionosphere through a region of open field lines, and that the ionospheric conductivity in the polar cap and auroral zone may be different. Penetration of the electric field into the magnetosphere is linked with the generation of the Alfven wave, going out from the ionosphere into the solar wind and being coupled with the field-aligned currents at the boundary of the open field limes. The electric field of the outgoing Alfven wave reduces the original electric field and provides the saturation effect in the electric field and currents during strong geomagnetic disturbances, associated with increasing ionospheric conductivity. The electric field and field-aligned currents of this Alfven wave are dependent on the ionospheric and solar wind parameters and may significantly affect the electric field and field-aligned currents, generated in the polar ionosphere. Estimating the magnitude of the saturation effect in the electric field and field-aligned currents allows us to improve the correlation between solar wind parameters and resulting disturbances in the Earth's magnetosphere.

Lyatsky, Wladislaw; Khazanov, George V.; Slavin, James A.

2010-01-01

340

Nonlinear response of electric fields at a neutral point  

NASA Astrophysics Data System (ADS)

The complex dynamics of electric fields at a neutral point in a plasma is studied via a model of noninteracting ``quasiparticles.'' The simplicity of the model allows the reduction of the many-body problem to an effective single-particle analysis-all properties of interest can be reduced to quadratures. Still, the final calculations to extract a quantitative or even qualitative understanding of the field dynamics can be difficult. Attention here is focused on the dynamics of the conditional electric field: the field value at time t for a given initial value of the field. In addition to the relevant linear response function (electric field time correlation function), this property provides the complete nonlinear response of the electric field to arbitrary initial field perturbations. The static properties (distribution of electric fields and field time derivatives) and the electric field time correlation function have been known for some time for this model. We compare these results and the present result for the conditional electric field with molecular dynamics simulations including interactions. The comparisons suggest that the model provides a quantitative representation of electric field dynamics in real plasmas, except at strong coupling. The exact theoretical results are compared also with those obtained by modeling the electric field as a stochastic variable obeying a kangaroo process. The latter can be constructed to yield both the exact stationary distribution and the exact electric field time correlation function. However, we find that the conditional field is never well approximated by this process. An alternative representation of the joint distribution for electric fields, consistent with the exact stationary distribution, field correlation function, and conditional electric field, is suggested.

Berkovsky, Mikhail; Dufty, James W.; Calisti, Annette; Stamm, Roland; Talin, Bernard

1995-05-01

341

AFMM: A molecular mechanics force field vibrational parametrization program  

NASA Astrophysics Data System (ADS)

AFMM (Automated Frequency Matching Method) is a program package for molecular mechanics force field parametrization. The method used fits the molecular mechanics potential function to both vibrational frequencies and eigenvector projections derived from quantum chemical calculations. The program optimizes an initial parameter set (either pre-existing or using chemically-reasonable estimation) by iteratively changing them until the optimal fit with the reference set is obtained. By implementing a Monte Carlo-like algorithm to vary the parameters, the tedious task of manual parametrization is replaced by an efficient automated procedure. The program is best suited for optimization of small rigid molecules in a well-defined energy minimum, for which the harmonic approximation to the energy surface is appropriate for describing the intra-molecular degrees of freedom. Program summaryTitle of program: AFMM Catalogue identifier: ADUZ Program summary URL:http://cpc.cs.qub.ac.uk/summaries/ADUZ Program obtainable from: CPC Program Library, Queen's University of Belfast, N. Ireland Computer: x86 PC, SGI, Sun Microsystems Operating system: GNU/Linux, BSD, IRIX, Solaris Programming language used: Python Memory required: 10 Mbytes No. of bits in a word: 32 or 64 No. of processors used: 1 Parallelized?: No No. of lines in distributed program, including test data, etc.:13 127 No. of bytes in distributed program, including test data, etc.: 182 550 Distribution format: tar.gz Typical running time: 24 h Nature of the physical problem: Molecular mechanics force field parametrization. Method of solution:Fitting of the molecular mechanics potential to normal modes derived from quantum chemical calculations. The missing force field parameters are optimized via a merit function to obtain the optimal fit with the reference quantum mechanical set.

Vaiana, A. C.; Cournia, Z.; Costescu, I. B.; Smith, J. C.

2005-04-01

342

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

343

Predicting mutation-induced Stark shifts in the active site of a protein with a polarized force field.  

PubMed

The electric field inside a protein has a significant effect on the protein structure, function, and dynamics. Recent experimental developments have offered a direct approach to measure the electric field by utilizing a nitrile-containing inhibitor as a probe that can deliver a unique vibration to the specific site of interest in the protein. The observed frequency shift of the nitrile stretching vibration exhibits a linear dependence on the electric field at the nitrile site, thus providing a direct measurement of the relative electric field. In the present work, molecular dynamics simulations were carried out to compute the electric field shift in human aldose reductase (hALR2) using a polarized protein-specific charge (PPC) model derived from fragment-based quantum-chemistry calculations in implicit solvent. Calculated changes of electric field in the active site of hALR2 between the wild type and mutants were directly compared with measured vibrational frequency shifts (Stark shifts). Our study demonstrates that the Stark shifts calculated using the PPC model are in much better agreement with the experimental data than widely used nonpolarizable force fields, indicating that the electronic polarization effect is important for the accurate prediction of changes in the electric field inside proteins. PMID:23517423

Wang, Xianwei; He, Xiao; Zhang, John Z H

2013-07-25

344

Micro-gravity: current distributions creating a uniform force field  

NASA Astrophysics Data System (ADS)

This paper presents two structures of superconducting coils able to give satisfactory solutions to the problem of generation of uniform field of high magnetic forces. The first structure is modeled by the use of purely surface current densities, whereas the second one can be described with volume current densities. Both of these structures proceed from the study of a particular expression of the complex magnetic potential introduced for structures with two-dimensional geometry. This work is carried out in a research collaboration between the GREEN and the DSM-DAPNIA department of the CEA Saclay.

Vincent-Viry, O.; Mailfert, A.; Colteu, A.; Dael, A.; Gourdin, C.; Quettier, L.

2001-02-01

345

Development of accurate force fields for the simulation of biomineralization.  

PubMed

The existence of an accurate force field (FF) model that reproduces the free-energy landscape is a key prerequisite for the simulation of biomineralization. Here, the stages in the development of such a model are discussed including the quality of the water model, the thermodynamics of polymorphism, and the free energies of solvation for the relevant species. The reliability of FFs can then be benchmarked against quantities such as the free energy of ion pairing in solution, the solubility product, and the structure of the mineral-water interface. PMID:24188760

Raiteri, Paolo; Demichelis, Raffaella; Gale, Julian D

2013-01-01

346

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

347

Manipulation of molecules with electric fields  

NASA Astrophysics Data System (ADS)

During the last few years we have been experimentally exploring the possibilities of manipulating neutral polar molecules with electric fields [1]. Arrays of time-varying, inhomogeneous electric fields have been used to reduce in a stepwise fashion the forward velocity of molecules in a beam. With this so-called 'Stark-decelerator', the equivalent of a LINear ACcelerator (LINAC) for charged particles, one can transfer the high phase-space density that is present in the moving frame of a pulsed molecular beam to a reference frame at any desired velocity; molecular beams with a computer-controlled (calibrated) velocity and with a narrow velocity distribution, corresponding to sub-mK longitudinal temperatures, can be produced. These decelerated beams offer new possibilities for collision studies, for instance, and enable spectroscopic studies with an improved spectral resolution; first proof-of-principle high-resolution spectroscopic studies have been performed. These decelerated beams have also been used to load neutral ammonia molecules in an electrostatic trap at a density of (better than) 10^7 mol/cm^3 and at temperatures of around 25 mK. In another experiment, a decelerated beam of ammonia molecules is injected in an electrostatic storage ring. The package of molecules in the ring can be observed for more than 50 distinct round trips, corresponding to 40 meter in circular orbit and almost 0.5 sec. storage time, sufficiently long for a first investigation of its transversal motion in the ring. A scaled up version of the Stark-decelerator and molecular beam machine has just become operational, and has been used to produce decelerated beams of ground-state OH and electronically excited (metastable) NH radicals. The NH radical is particularly interesting, as an optical pumping scheme enables the accumulation of decelerated bunches of slow NH molecules, either in a magnetic or in an optical trap. By miniaturizing the electrode geometries, high electric fields can be produced using only modest voltages. A micro-structured mirror for neutral molecules that can rapidly be switched on and off has been constructed and used to retro-reflect a beam of ammonia molecules with a forward velocity of about 30 m/s. This holds great promise for miniaturizing the whole decelerator, trap and storage ring for future applications. [1] H.L. Bethlem and G. Meijer, Int. Rev. Phys. Chem. 22, 73 (2003)

Meijer, Gerard

2004-05-01

348

Electric and magnetic field exposure, chemical exposure, and leukemia risk in electrical'' occupations  

SciTech Connect

This project was conducted to address what are the extremely low frequency (ELF) magnetic and electric field exposures of workers in electrical'' occupations and do they exceed exposures encountered in non-electrical'' occupations and what are the chemical and physical exposures in the electrical'' occupations and do they exceed exposures encountered in non-electrical'' occupations Two subsidiary issues were does characterization and quantification of ELF magnetic field exposure in the electrical'' occupations provide data to support a dose response relationship between leukemia risk and electric or magnetic field exposure and do dffferences in chemical exposure between the occupations help explain the previously observed leukemia risk associated with these electrical'' occupations Data were collected in 3 regions in which electrical workers had been reported to have an excess of leukemia - New Zealand, Los Angeles and Seattle Measurements of magnetic fields were made on 493 electrical workers and 163 non-electrical workers.

Bowman, J.D.; Sobel, E.; London, S.J.; Thomas, D.C.; Garabrant, D.H.; Pearce, N.; Peters, J.M. (University of Southern California, Los Angeles, CA (United States). Dept. of Preventive Medicine)

1992-12-01

349

Dynamics of an electric dipole moment in a stochastic electric field.  

PubMed

The mean-field dynamics of an electric dipole moment in a deterministic and a fluctuating electric field is solved to obtain the average over fluctuations of the dipole moment and the angular momentum as a function of time for a Gaussian white-noise stochastic electric field. The components of the average electric dipole moment and the average angular momentum along the deterministic electric-field direction do not decay to zero, despite fluctuations in all three components of the electric field. This is in contrast to the decay of the average over fluctuations of a magnetic moment in a stochastic magnetic field with Gaussian white noise in all three components. The components of the average electric dipole moment and the average angular momentum perpendicular to the deterministic electric-field direction oscillate with time but decay to zero, and their variance grows with time. PMID:24032795

Band, Y B

2013-08-01

350

Electric field observations of equatorial bubbles  

NASA Technical Reports Server (NTRS)

Results from the double floating probe experiment performed on the San Marco D satellite are presented, with emphasis on the observation of large incremental changes in the convective electric field vector at the boundary of equatorial plasma bubbles. Attention is given to isolated bubble structures in the upper ionospheric F regions; these observed bubble encounters are divided into two types - type I (live bubbles) and type II (dead bubbles). Type I bubbles show varying degrees of plasma depletion and large upward velocities range up to 1000 km/s. The geometry of these bubbles is such that the spacecraft orbit may cut them where they are tilting either eastward or (more often) westward. Type II bubbles exhibit plasma density depletion but no appreciable upward convection. Both types of events are usually surrounded by a halo of plasma turbulence, which can extend considerably beyond the region of plasma depletion.

Aggson, T. L.; Maynard, N. C.; Hanson, W. B.; Saba, Jack L.

1992-01-01

351

Electric field representation of pulsar intensity spectra  

NASA Astrophysics Data System (ADS)

Pulsar dynamic spectra exhibit high-visibility fringes arising from interference between scattered radiowaves. These fringes may be random or of 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 a very high angular resolution and mitigating pulse arrival time fluctuations due to interstellar scattering.

Walker, M. A.; Stinebring, D. R.

2005-10-01

352

Molecular dynamics simulation of nanosized water droplet spreading in an electric field.  

PubMed

Molecular dynamics (MD) simulations are performed for the spreading of a nanosized water droplet on a solid substrate subject to a parallel electric field. A combined electrostatic and Lennard-Jones potential is employed to represent the intermolecular interactions. Results show that in response to the applied field, polar water molecules realign themselves and this microscopic reorientation of molecular dipoles combines with the intermolecular forces to produce a macroscopic deformation of a free spherical water droplet into an ellipsoid. The applied field has a strong effect on the spreading of the water droplet on a solid substrate. For a weaker parallel field, the droplet spreading is asymmetric with the leading contact angle being greater than the trailing contact angle. With an increase in field strength, this asymmetry continues to increase, culminates, and then decreases until it disappears. The symmetric spreading remains with a further increase in the field strength until the saturation point is reached. This transition from the asymmetric to symmetric spreading is a manifestation of the interaction of the electric field with polar water molecules and the intermolecular forces within the droplet and between the water and solid; the interaction also leads to a change in hydrogen bonds along the droplet surface. The dynamics of the droplet spreading is entailed by the electrically induced motion of molecules along the liquid surface toward the solid substrate and is controlled by a competing mechanism among the electric, water-water, and water-solid intermolecular forces. PMID:23488748

Song, F H; Li, B Q; Liu, C

2013-04-01

353

Electropumping of water with rotating electric fields  

NASA Astrophysics Data System (ADS)

Pumping of fluids confined to nanometer dimension spaces is a technically challenging yet vitally important technological application with far reaching consequences for lab-on-a-chip devices, biomimetic nanoscale reactors, nanoscale filtration devices and the like. All current pumping mechanisms require some sort of direct intrusion into the nanofluidic system, and involve mechanical or electronic components. In this paper, we present the first nonequilibrium molecular dynamics results to demonstrate that non-intrusive electropumping of liquid water on the nanoscale can be performed by subtly exploiting the coupling of spin angular momentum to linear streaming momentum. A spatially uniform rotating electric field is applied to water molecules, which couples to their permanent electric dipole moments. The resulting molecular rotational momentum is converted into linear streaming momentum of the fluid. By selectively tuning the degree of hydrophobicity of the solid walls one can generate a net unidirectional flow. Our results for the linear streaming and angular velocities of the confined water are in general agreement with the extended hydrodynamical theory for this process, though also suggest refinements to the theory are required. These numerical experiments confirm that this new concept for pumping of polar nanofluids can be employed under laboratory conditions, opening up significant new technological possibilities.

De Luca, Sergio; Todd, B. D.; Hansen, J. S.; Daivis, Peter J.

2013-04-01

354

Electropumping of water with rotating electric fields.  

PubMed

Pumping of fluids confined to nanometer dimension spaces is a technically challenging yet vitally important technological application with far reaching consequences for lab-on-a-chip devices, biomimetic nanoscale reactors, nanoscale filtration devices and the like. All current pumping mechanisms require some sort of direct intrusion into the nanofluidic system, and involve mechanical or electronic components. In this paper, we present the first nonequilibrium molecular dynamics results to demonstrate that non-intrusive electropumping of liquid water on the nanoscale can be performed by subtly exploiting the coupling of spin angular momentum to linear streaming momentum. A spatially uniform rotating electric field is applied to water molecules, which couples to their permanent electric dipole moments. The resulting molecular rotational momentum is converted into linear streaming momentum of the fluid. By selectively tuning the degree of hydrophobicity of the solid walls one can generate a net unidirectional flow. Our results for the linear streaming and angular velocities of the confined water are in general agreement with the extended hydrodynamical theory for this process, though also suggest refinements to the theory are required. These numerical experiments confirm that this new concept for pumping of polar nanofluids can be employed under laboratory conditions, opening up significant new technological possibilities. PMID:23614441

De Luca, Sergio; Todd, B D; Hansen, J S; Daivis, Peter J

2013-04-21

355

Quantifying electrostatic force contributions in electrically biased nanoscale interactions  

NASA Astrophysics Data System (ADS)

A study of the validity of analytical methods for calculating the electrostatic force interaction in alternating current electrostatic force microscopy is presented. Using a simple harmonic oscillator model, two analytical frameworks aimed at relating the electrostatic force between the cantilever tip and the sample with measurable parameters (amplitude and phase of the cantilever) are derived. The validity of the frameworks is examined based on two parameters that define the oscillation amplitude of the cantilever (tip voltage and tip-sample distance). Results are compared with an analytical model of the electrostatic interaction between tip and sample (tip-sample capacitance) and the range of validity of these two frameworks is provided. Our analysis confirms that the commonly used interpretation of the amplitude and the phase as a measure for the electrostatic force and for the derivative of the electrostatic force is only valid for very small oscillation amplitudes and depends on the tip geometry. Furthermore, this study demonstrates that these two techniques suffer from sensitivity limitations at large tip-sample distances. Finally, we compare the two frameworks with an alternative technique for the quantification of the tip-sample electrostatic interaction we have recently proposed and we discuss and experimentally demonstrate its advantages in terms of reliability and sensitivity, providing an example of dielectric constant measurement of a thin insulating film.

Maragliano, C.; Glia, A.; Stefancich, M.; Chiesa, M.

2014-03-01

356

Beaming Electricity via Relay Satellites in Support of Deployed Combat Forces.  

National Technical Information Service (NTIS)

The logistics required to supply military forces based in remote hostile territory can be onerous. A major component of those supplies is the fuel required to operate generators that provide electrical power. This research sought to determine the feasibil...

T. R. Essenpreis

2012-01-01

357

Plasma Expansion in Presence of Electric and Magnetic Fields  

SciTech Connect

The presence of electric and magnetic fields in high enthalpy nozzle flows can produce strong effects. In particular, non equilibrium conditions can be observed when this field are present. In this work we have investigated two different field configurations in supersonic nozzle: first of all we have studied the cooperative effect of electric and magnetic field applied inside the nozzle and secondly we have investigated the role of non equilibrium distribution produced in the reservoir by electric discharge (plasma jet)

Colonna, Gianpiero; Capitelli, Mario [Dipartimento di Chimica, Universita di Bari (Italy); CNR-IMIP, Bari Section (Italy)

2005-05-16

358

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

359

Core/mantle-like interactions in an electric field  

NASA Astrophysics Data System (ADS)

Reactions between metal and silicate phases, such as those that may occur at the core/mantle boundary, are charge transfer reactions—involving oxidation and reduction of chemical species. Therefore, the chemical potential driving force can be recast as an electric potential difference. Conversely, the application of an electric field across a metal/silicate interface is capable of driving chemical reactions. To explore the electrochemical behavior of a core/mantle-like boundary, the behavior of a liquid sulfide/silicate boundary in the presence of an externally applied electric potential difference was examined experimentally. The physical and chemical responses of this electrified interface include: (1) reaction zones containing new oxide phases at the ˜1 V level, (2) unusual partitioning of highly siderophile elements at ˜100 mV, (3) electrowetting at 10-100 mV, and (4) valence changes, indicating oxygen fugacity perturbations, at a level of ˜1-10 ?V. An equivalent circuit diagram representing the experimental results is introduced, and extended to processes at the Earth's core/mantle boundary.

Kavner, A.; Walker, D.

2006-08-01

360

Milk processing by high intensity pulsed electric fields  

Microsoft Academic Search

Pulsed electric field (PEF) processing of food consists of treatment with very short electric pulses (?s) at high electric field intensities at moderate temperatures. This treatment could be an alternative to traditional thermal processes since it is capable of destroying micro-organisms and some enzymes while maintaining the freshness of food products. A product most commonly used to study the effects

S??lvia Bendicho; Gustavo V. Barbosa-Cánovas; Olga Mart??n

2002-01-01

361

Electric fields in fluidic channels and sensor applications with capacitance  

Microsoft Academic Search

The application of common printed circuit board (PCB) technology to fluidic microsystems allows the generation of an electric field around two opposite copper walls of a fluidic channel. The shape of the electric field depends on the geometry of the channel construction and the fluid inside the channel. When passing a fluid between the tracks, the electrical capacitance changes as

Tobias Merkel; Lienhard Pagel; Hans-Walter Glock

2000-01-01

362

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

363

Automated conformational energy fitting for force-field development  

PubMed Central

We present a general conformational-energy fitting procedure based on Monte Carlo simulated annealing (MCSA) for application in the development of molecular mechanics force fields. Starting with a target potential energy surface and an unparameterized molecular mechanics potential energy surface, an optimized set of either dihedral or grid-based correction map (CMAP) parameters is produced that minimizes the root mean squared error (RMSE) between the parameterized and targeted energies. The fitting is done using an MCSA search in parameter space and consistently converges to the same RMSE irrespective of the randomized parameters used to seed the search. Any number of dihedral parameters can be simultaneously parameterized, allowing for fitting to multi-dimensional potential energy scans. Fitting options for dihedral parameters include non-uniform weighting of the target data, constraining multiple optimized parameters to the same value, constraining parameters to be no greater than a user-specified maximum value, including all or only a subset of multiplicities defining the dihedral Fourier series, and optimization of phase angles in addition to force constants. The dihedral parameter fitting algorithm’s performance is characterized through multi-dimensional fitting of cyclohexane, tetrahydropyran, and hexopyranose monosaccharide energetics, with the latter case having a 30-dimensional parameter space. The CMAP fitting is applied in the context of polypeptides, and is used to develop a parameterization that simultaneously captures the ?, ? energetics of the alanine dipeptide and the alanine tetrapeptide. Because the dihedral energy term is common to many force fields, we have implemented the dihedral-fitting algorithm in the portable Python scripting language and have made it freely available as Supplementary Material.

Guvench, Olgun; MacKerell, Alexander D.

2010-01-01

364

Improved force field for molecular modeling of poly(3-hexylthiophene).  

PubMed

An ab initio-based improved force field is reported for poly(3-hexylthiophene) (P3HT) in the solid state, deriving torsional parameters and partial atomic charges from ab initio molecular structure calculations with explicit treatment of the hexyl side chains. The force field is validated by molecular dynamics (MD) simulations of solid P3HT with different molecular weights including calculation of structural parameters, mass density, melting temperature, glass transition temperature, and surface tension. At 300 K, the P3HT crystalline structure features planar backbones with non-interdigitated all-trans hexyl side chains twisted ~90° from the plane of the backbone. For crystalline P3HT with infinitely long chains, the calculated 300 K mass density (1.05 g cm(-3)), the melting temperature (490 K), and the 300 K surface tension (32 mN/m) are all in agreement with reported experimental values, as is the glass transition temperature (300 K) for amorphous 20-mers. PMID:23899343

Bhatta, Ram S; Yimer, Yeneneh Y; Perry, David S; Tsige, Mesfin

2013-08-29

365

Development of force field parameters for molecular simulation of polylactide  

PubMed Central

Polylactide is a biodegradable polymer that is widely used for biomedical applications, and it is a replacement for some petroleum based polymers in applications that range from packaging to carpeting. Efforts to characterize and further enhance polylactide based systems using molecular simulations have to this point been hindered by the lack of accurate atomistic models for the polymer. Thus, we present force field parameters specifically suited for molecular modeling of PLA. The model, which we refer to as PLAFF3, is based on a combination of the OPLS and CHARMM force fields, with modifications to bonded and nonbonded parameters. Dihedral angle parameters were adjusted to reproduce DFT data using newly developed CMAP dihedral cross terms, and the model was further adjusted to reproduce experimentally resolved crystal structure conformations, melt density, volume expansivity, and the glass transition temperature of PLA. We recommend the use of PLAFF3 in modeling PLA in its crystalline or amorphous states and have provided the necessary input files required for the publicly available molecular dynamics code GROMACS.

McAliley, James H.; Bruce, David A.

2011-01-01

366

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

367

Thermomechanical properties of graphene: valence force field model approach.  

PubMed

Using the valence force field model of Perebeinos and Tersoff (2009 Phys. Rev. B 79 241409(R)), different energy modes of suspended graphene subjected to tensile or compressive strain are studied. By carrying out Monte Carlo simulations it is found that: (i) only for small strains (|?| force field model results in a temperature independent bending modulus for graphene, and (viii) the Grüneisen parameter is estimated to be 0.64. PMID:22475745

Lajevardipour, A; Neek-Amal, M; Peeters, F M

2012-05-01

368

Developing Force Fields from the Microscopic Structure of Solutions  

PubMed Central

We have been developing force fields designed for the eventual simulation of peptides and proteins using the Kirkwood-Buff (KB) theory of solutions as a guide. KB theory provides exact information on the relative distributions for each species present in solution. This information can also be obtained from computer simulations. Hence, one can use KB theory to help test and modify the parameters commonly used in biomolecular studies. A series of small molecule force fields representative of the fragments found in peptides and proteins have been developed. Since this approach is guided by the KB theory, our results provide a reasonable balance in the interactions between self-association of solutes and solute solvation. Here, we present our progress to date. In addition, our investigations have provided a wealth of data concerning the properties of solution mixtures, which is also summarized. Specific examples of the properties of aromatic (benzene, phenol, p-cresol) and sulfur compounds (methanethiol, dimethylsulfide, dimethyldisulfide) and their mixtures with methanol or toluene are provided as an illustration of this kind of approach.

Ploetz, Elizabeth A.; Bentenitis, Nikolaos; Smith, Paul E.

2009-01-01

369

A bidirectional brain-machine interface algorithm that approximates arbitrary force-fields.  

PubMed

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

Vato, Alessandro; Szymanski, Francois D; Semprini, Marianna; Mussa-Ivaldi, Ferdinando A; Panzeri, Stefano

2014-01-01

370

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.

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

2014-01-01

371

A quadruple-scanning-probe force microscope for electrical property measurements of microscopic materials  

Microsoft Academic Search

Four-terminal electrical measurement is realized on a microscopic structure in air, without a lithographic process, using a home-built quadruple-scanning-probe force microscope (QSPFM). The QSPFM has four probes whose positions are individually controlled by obtaining images of a sample in the manner of atomic force microscopy (AFM), and uses the probes as contacting electrodes for electrical measurements. A specially arranged tuning

Seiji Higuchi; Osamu Kubo; Hiromi Kuramochi; Masakazu Aono; Tomonobu Nakayama

2011-01-01

372

Bubble Detachment in Variable Gravity Under the Influence of a Non-Uniform Electric Field  

NASA Technical Reports Server (NTRS)

The objective of the study reported in this paper is to investigate the effects of variable, reduced gravity on the formation and detachment behavior of individual air bubbles under the influence of a non-uniform electric field. For this purpose, variable gravity experiments were carried out in parabolic nights. The non-uniform electric field was generated by a spherical electrode and a plate electrode. The effect of the magnitude of the non-uniform electric field and gravity level on bubble formation, development and detachment at an orifice was investigated. An image processing code was developed that allows the measurement of bubble volume, dimensions and contact angle at detachment. The results of this research can be used to explore the possibility of enhancing boiling heat transfer in the variable and low gravity environments by substituting the buoyancy force with a force induced by the electric field. The results of experiments and measurements indicate that the level of gravity significantly affects bubble shape, size and frequency. The electric field magnitude also influences bubble detachment, however, its impact is not as profound as that of variable gravity for the range of electric field magnitudes investigated in the present study.

Chang, Shinan; Herman, Cila; Iacona, Estelle

2002-01-01

373

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

374

Time variation of forces in a synchronous machine using electric coupled network model  

Microsoft Academic Search

Radial forces between the stator teeth and rotor claw inside a claw-pole alternator are investigated. Typically three dimensional, the complete machine has been modelled as a coupled electric and magnetic circuit, with the aim of saving simulation time. Radial forces are obtained for several rotation speeds and stator currents. These results are compared with those of a 3D finite element

M. Hecquet; P. Brochet

1998-01-01

375

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

376

Deviation from Ohm's law in electric field assisted capillary liquid chromatography.  

PubMed

Earlier studies of electric field assisted LC (EF-LC) have shown that the effect on charged analytes of the application of an electric field over a capillary LC column is relatively small. Charged analytes can only be affected by the electric field while present in the mobile phase, which makes the effective time for influence of the electric field t(0) independent of retention time. Because the charged analytes only can be affected for a short time the electric field strength ought to be high in order to increase the impact of the electric field on the separation. We have, however, found that only a relatively low electric field strength can be used in EF-LC when pressure is used as main driving force. The useful field strength was limited by a dramatic increase in the current. This increase in current was found to origin from an increased concentration of buffer ions that have an electrophoretic mobility towards the pumped flow. PMID:14503812

Eriksson, Björn O; Andersson, Magnus B O; Blomberg, Lars G

2003-08-22

377

Electromagnetic self-forces and generalized Killing fields  

NASA Astrophysics Data System (ADS)

Building upon previous results in scalar field theory, a formalism is developed that uses generalized Killing fields to understand the behavior of extended charges interacting with their own electromagnetic fields. New notions of effective linear and angular momenta are identified, and their evolution equations are derived exactly in arbitrary (but fixed) curved spacetimes. A slightly modified form of the Detweiler-Whiting axiom that a charge's motion should only be influenced by the so-called regular component of its self-field is shown to follow very easily. It is exact in some interesting cases and approximate in most others. Explicit equations describing the center-of-mass motion, spin angular momentum and changes in mass of a small charge are also derived in a particular limit. The chosen approximations—although standard—incorporate dipole and spin forces that do not appear in the traditional Abraham-Lorentz-Dirac or Dewitt-Brehme equations. They have, however, been previously identified in the test body limit.

Harte, Abraham I.

2009-08-01

378

FEM analysis of carbon nanotube induced cell poration under electric field  

Microsoft Academic Search

Carbon nanotubes (CNTs) are promising nanomaterials for biomedical applications in view of their excellent mechanical, chemical and electrical properties. Recently, CNTs have been used as electroporation agents because they are able to reduce significantly the required electroporation field. However, mechanism of CNT mediated electroporation enhancement is not fully understood. In this finite element method (FEM) modeling study, an electrokinetic-induced force

Dun Liu; Zhigang Wang; Lijun Wang; Alfred Cuschieri

2010-01-01

379

Combined treatment of apples by pulsed electric fields and by heating at moderate temperature  

Microsoft Academic Search

In this work, the specific influence of combined pulsed electric fields (PEF) and thermal treatment on the textural properties of apple tissue and apple juice expression are discussed. Force relaxation curves were analysed for different regimes of PEF and thermal pretreatment of apple tissue. The concept of the effective relaxation time t? was used to characterise the different modes of

Nikolai I. Lebovka; Iurie Praporscic; Eugene Vorobiev

2004-01-01

380

Influence of grain boundary on electrical properties of organic crystalline grains investigated by dual-probe atomic force microscopy  

NASA Astrophysics Data System (ADS)

We performed electrical transport measurements on ?-sexithiophene crystalline grains using a dual-probe atomic force microscopy system having two independently controlled cantilever probes. The field-effect transistor characteristics were measured by varying the distances between the two probes brought in contact with the surface of the grains. It was clearly shown by the transfer line method that the grain boundary is the dominant factor limiting the electrical properties of organic thin films. Moreover, the hole transport across the grain boundary was found to be more affected by the oxygen hole doping than that within the crystalline grain.

Hirose, Masaharu; Tsunemi, Eika; Kobayashi, Kei; Yamada, Hirofumi

2013-10-01

381

Field electron emission from carbon nanotubes in the presence of a weak high-frequency electric field  

NASA Astrophysics Data System (ADS)

Series of narrow peaks in the frequency range of f ? 50-1200 MHz have been revealed in the frequency responses of the emission current from carbon nanotubes in the presence of a weak high-frequency electric field. The analysis makes it possible to attribute these peaks to resonance of the first and second harmonics of forced mechanical vibrations of carbon nanotubes in a high-frequency electric field. The determined Q factor of nanotubes is in the range of 100-300.

Musatov, A. L.; Izrael'yants, K. R.; Blagov, E. V.

2014-04-01

382

Simulation and experimental demonstration of the electric field assisted electroporation microchip for in vitro gene delivery enhancement.  

PubMed

Simulation and experimental demonstration of the in vitro gene delivery enhancement using electrostatic forces and electroporation (EP) microchips were conducted. Electroporation is a technique with which DNA molecules can be delivered into cells using electric field pulses. This study demonstrates that plasmid DNA can be attracted to the cell surfaces at the specific regions using an electrostatic force. Therefore, the DNA concentration on the cell surface is dramatically increased, which highly enhances the gene transfection efficiency compared to that without an attracting-electric field. The electrostatic force can be designed into specific regions, where the DNA plasmids are attracted to, to provide the region-targeting function. In this micro-device, the top electrode and the interdigitated electrodes provided the DNA attracting-electric field, and the interdigitated electrodes provided adequate electric fields for the electroporation process on the chip surface. Using the EP microchip, cells could be manipulated in situ without detachment if adherent cells were used for electroporation. Five different cells of two different types, primary cell and cell line, were successfully transfected under multi-pulse or single pulse electric field stimulation without applying an attracting-electric field. This study simulated and analyzed the electric field distributions at the DNA attracting and electroporation processes, and successfully demonstrated that the electrostatic force attracted DNA plasmids to specific regions and highly enhanced the gene delivery. In summary, this EP microchip should provide many potential applications for gene therapy. PMID:15052348

Lin, Yu-Cheng; Li, Min; Wu, Chao-Chin

2004-04-01

383

A new probe for measuring small electric fields in plasmas  

NASA Technical Reports Server (NTRS)

A dipolar double probe has been developed for in situ measurements of small electric fields in laboratory plasmas. The probe measures dc to ac electric fields (f values between 0 and 20 MHz) with high sensitivity (Emin about 10 microV/cm) and responds to both space charge electric fields and inductive electric fields. Using voltage-to-frequency conversion, the probe signal is obtained free of errors and loading effects by a transmission line. Various examples of useful applications for the new probe are presented, such as measurements of dc ambipolar fields, ac space-charge fields of ion acoustic waves, ac inductive fields of whistler waves, and mixed inductive and space-charge electric fields in current-carrying magnetoplasmas.

Stenzel, R. L.

1991-01-01

384

Thermodynamics of water octamer in a uniform electric field  

Microsoft Academic Search

We study the water octamer in a uniform electric field using the all-exchanges parallel tempering Monte Carlo method in the canonical ensemble. The heat capacity, quenched energy configurations, and the order parameter Q4 are employed to understand the phase changes observed as a function of temperature and the strength of the applied electric field. At a low field strength of

Javier Hernández-Rojas; Briesta S. González; Tim James; David J. Wales

2006-01-01

385

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

386

Measured distribution of electric field in GTEM-cell  

Microsoft Academic Search

The electric field inside the GTEM-cell was measured with the field probe. The variation of the electric field was within 3 dB. The measured results were compared with the numerical model performed with finite element method (FEM). There is a very good agreement between measured results and the computer model. Both results prove that almost 80% of the area below

Kresimir Malaric; Antonio Sarolic; Vesna Roje; J. Bartolic; B. Modlic

2001-01-01

387

Search for the Effects of Inhomogenous Electric Fields on Gravitation  

Microsoft Academic Search

The effect of inhomogenous electric fields on the weight of test masses is being investigated. Inhomogenous field is produced by applying dc bias between a horizontal flat electrode and the tip of a conical bottom electrode of an electrostatic capacitor. The equipotentials and the electric field distribution has been numerically calculated using ``MATLAB'' software. The test masses are gold-coated metal

Ming Yin; Michael Bleiweiss; Ruslan Prozorov; Timir Datta

2002-01-01

388

Electric field measurements around a metal oxide surge arrester  

Microsoft Academic Search

Aim of the current work is the experimental study of the electric field distribution around a medium voltage metal oxide gapless polymeric housing surge arrester, since the study and the knowledge of the electric field around an arrester can be useful for diagnostic tests and design procedures. The measurements were carried out, using two appropriate calibrated field meters. The results

C. A. Spanias; C. A. Christodoulou; I. F. Gonos; I. A. Stathopulos

2010-01-01

389

The Electric Field, Atmosphere and Effective Temperature of the Sun  

Microsoft Academic Search

The study of important electromagnetic effects in the solar atmosphere undertaken in previous papers is continued. It is shown that the large observed spread of effective temperatures of the sun's radiation can be accounted for by the presence of electric and magnetic fields in the solar atmosphere. The magnitude of the electric field at a level where the magnetic field

Ross Gunn

1931-01-01

390

Electric fields in nonhomogeneously doped silicon. Summary of simulations  

Microsoft Academic Search

Variations of the doping concentration inside a silicon device result in electric field distortions. These distortions, “parasitic” fields, have been observed in Silicon Drift Detectors [D. Nouais, et al., Nucl. Instr. and Meth. A 501 (2003) 119; E. Crescio, et al., Nucl. Instr. and Meth. A 539 (2005) 250]. Electric fields inside a silicon device can be calculated for a

I. V. Kotov; T. J. Humanic; D. Nouais; J. Randel; A. Rashevsky

2006-01-01

391

Electric field generated by longitudinal axial microtubule vibration modes with high spatial resolution microtubule model  

NASA Astrophysics Data System (ADS)

Microtubules are electrically polar structures fulfilling prerequisites for generation of oscillatory electric field in the kHz to GHz region. Energy supply for excitation of elasto-electrical vibrations in microtubules may be provided from GTP-hydrolysis; motor protein-microtubule interactions; and energy efflux from mitochondria. It recently was determined from anisotropic elastic network modeling of entire microtubules that the frequencies of microtubule longitudinal axial eigenmodes lie in the region of tens of GHz for the physiologically common microtubule lengths. We calculated electric field generated by axial longitudinal vibration modes of microtubule, which model is based on subnanometer precision of charge distribution. Due to elastoelectric nature of the vibrations, the vibration wavelength is million-fold shorter than that of the electromagnetic field in free space and the electric field around the microtubule manifests rich spatial structure with multiple minima. The dielectrophoretic force exerted by electric field on the surrounding molecules will influence the kinetics of reactions via change in the probability of the transport of charge and mass particles. The electric field generated by vibrations of electrically polar cellular structures is expected to play a role in biological self-organization.

Cifra, M.; Havelka, D.; Deriu, M. A.

2011-12-01

392

Neutral winds and electric fields in the dusk auroral oval. I - Measurements  

NASA Technical Reports Server (NTRS)

Two rockets carrying an upleg and downleg trimethyl aluminum chemical trail release and three barium cannisters were launched from Poker Flat, Alaska on Feb. 28, 1978 and Mar. 2, 1978 in order to study neutral winds and electric fields in the dusk auroral oval. Electric field measurements were also made with a radar system to supplement the barium cloud data. The barium cloud drifts on both days showed intense poleward electric fields in the subauroral region. The drifts were nearly latitude-independent and were equivalent to electric fields of 60 mV/m of February 2 and 40 mV/m on March 2. The data indicate that the Lorentz force and Joule heating had a strong influence on the observed neutral winds.

Mikkelsen, I. S.; Jorgensen, T. S.; Kelley, M. C.; Larsen, M. F.; Pereira, E.; Vickrey, J.

1981-01-01

393

Electrostatics of conductive particles in contact with a plate electrode affected by a non-uniform electric field  

Microsoft Academic Search

Analytical formulae are available for the estimation of the electric forces on conductive bodies of regular shape (spherical, hemi-spherical, hemi-ellipsoidal, cylindrical) in contact with a plate electrode affected by a uniform electric field. The electrode arrangements employed in some electrostatic processes generate non-uniform electric fields for which no such formulae can be derived. The aim of this paper is to

Lucian Dascalescu; Simona Vlad; Alexandru Iuga; Peter L. Levin

2001-01-01

394

Centrifugal Force Based Magnetic Micro-Pump Driven by Rotating Magnetic Fields  

NASA Astrophysics Data System (ADS)

This paper presents a centrifugal force based magnetic micro-pump for the pumping of blood. Most blood pumps are driven by an electrical motor with wired control. To develop a wireless and battery-free blood pump, the proposed pump is controlled by external rotating magnetic fields with a synchronized impeller. Synchronization occurs because the rotor is divided into multi-stage impeller parts and NdFeB permanent magnet. Finally, liquid is discharged by the centrifugal force of multi-stage impeller. The proposed pump length is 30 mm long and19 mm in diameter which much smaller than currently pumps; however, its pumping ability satisfies the requirement for a blood pump. The maximum pressure is 120 mmHg and the maximum flow rate is 5000ml/min at 100 Hz. The advantage of the proposed pump is that the general mechanical problems of a normal blood pump are eliminated by the proposed driving mechanism.

Kim, S. H.; Hashi, S.; Ishiyama, K.

2011-01-01

395

Electric field and plasma observations in the magnetosphere  

NASA Technical Reports Server (NTRS)

Satellite-borne electric field measurements using the double probe technique have now provided a comprehensive survey of convection electric fields at low altitudes in the magnetosphere. The most prominent features of the convection electric fields are reversals located at high magnetic latitudes, with generally anti-sunward convection poleward and sunward convection equatorward of the electric field reversal location. On the day side of the magnetosphere the electric field reversal is observed to coincide with the equatorward boundary of the polar cusp. In the local afternoon and evening regions inverted V electron precipitation bands occur at or near the electric field reversal and in regions usually characterized by large fluctuations in the electric field. In the local midnight region strong convection electric fields have also been observed deep within the magnetosphere, near the equatorward boundary of the plasma sheet. Recent measurements of electric fields near the inverted V electron precipitation bands suggests that these events are associated with large electrostatic potential gradients along the geomagnetic field.

Gurnett, D. A.

1972-01-01

396

Introduction to extremely-low-frequency electric and magnetic fields  

SciTech Connect

The interaction with living systems of electromagnetic fields in the extremely-low-frequency (ELF) range below 300 Hz will be summarized briefly in this paper. In materials with the electrical and magnetic properties of living tissues, these fields have a long wavelength (5000 m) and skin depth (150 m). As a consequence, in their interactions with humans and other living organisms ELF fields behave as though they are composed of independent electric and magnetic components of an ELF field is commonly referred to as the quasi-static approximation,'' which permits the radiating properties of the field to be neglected in describing its interaction with living organisms. The electric and magnetic components of an ELF field have several distinctly different features in their interactions with humans and other living organisms. First, the electrical conductivity of tissue is approximately 14 to 15 orders of magnitude greater than that of air at ELF electric fields. Consequently, the body behaves like a good electrical conductor in ELF electric fields. As a result, an electrical charge is developed on the surface of a living object in an external ELF field, but the electric field penetrates into the body only to a very limited extent.

Tenforde, T.S.

1989-07-01

397

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 active regions that locally have a potential bipolar-type magnetic field with a thin force-free flux rope embedded inside it. The flux rope has a circular-arc axis and circular cross-section in which the interior magnetic field is predominantly toroidal (axial). Its magnetic pressure is balanced outside by that of the poloidal (azimuthal) field created at the boundary by the electric current sheathing the flux rope. To facilitate the implementation of the method in our numerical magnetohydrodynamic (MHD) code, the entire solution is described in terms of the vector potential of the magnetic field. The parameters of the flux rope can be chosen so that a subsequent MHD relaxation of the constructed configuration under line-tied conditions at the boundary provides a numerically exact equilibrium. Such equilibria are an approximation for the magnetic configuration preceding solar eruptions, which can be triggered in our model by imposing suitable photospheric flows beneath the flux rope. The proposed method is a useful tool for constructing pre-eruption magnetic fields in data-driven simulations of solar active events. Research supported by NASA's Heliophysics Theory and LWS Programs, and NSF/SHINE and NSF/FESD.

Titov, V. S.; Torok, T.; Mikic, Z.; Linker, J.

2013-12-01

398

Spiking patterns of a hippocampus model in electric fields  

NASA Astrophysics Data System (ADS)

We develop a model of CA3 neurons embedded in a resistive array to mimic the effects of electric fields from a new perspective. Effects of DC and sinusoidal electric fields on firing patterns in CA3 neurons are investigated in this study. The firing patterns can be switched from no firing pattern to burst or from burst to fast periodic firing pattern with the increase of DC electric field intensity. It is also found that the firing activities are sensitive to the frequency and amplitude of the sinusoidal electric field. Different phase-locking states and chaotic firing regions are observed in the parameter space of frequency and amplitude. These findings are qualitatively in accordance with the results of relevant experimental and numerical studies. It is implied that the external or endogenous electric field can modulate the neural code in the brain. Furthermore, it is helpful to develop control strategies based on electric fields to control neural diseases such as epilepsy.

Men, Cong; Wang, Jiang; Qin, Ying-Mei; Wei, Xi-Le; Che, Yan-Qiu; Deng, Bin

2011-12-01

399

Computation of induced electric field for the sacral nerve activation.  

PubMed

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. PMID:24140875

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

2013-11-01

400

Electric field-controlled rippling of graphene  

NASA Astrophysics Data System (ADS)

Metal-graphene interfaces generated by electrode deposition induce barriers or potential modulations influencing the electronic transport properties of graphene based devices. However, their impact on the local mechanical properties of graphene is much less studied. Here we show that graphene near a metallic interface can exhibit a set of ripples self-organized into domains whose topographic roughness is controlled by the tip bias of a scanning tunneling microscope. The reconstruction from topographic images of graphene bending energy maps sheds light on the local electro-mechanical response of graphene under STM imaging and unveils the role of the stress induced by the vicinity of the graphene-metal interface in the formation and the manipulation of these ripples. Since microscopic rippling is one of the important factors that limit charge carrier mobility in graphene, the control of rippling with a gate voltage may have important consequences in the conductance of graphene devices where transverse electric fields are created by contactless suspended gate electrodes. This opens up also the possibility to dynamically control the local morphology of graphene nanomembranes.Metal-graphene interfaces generated by electrode deposition induce barriers or potential modulations influencing the electronic transport properties of graphene based devices. However, their impact on the local mechanical properties of graphene is much less studied. Here we show that graphene near a metallic interface can exhibit a set of ripples self-organized into domains whose topographic roughness is controlled by the tip bias of a scanning tunneling microscope. The reconstruction from topographic images of graphene bending energy maps sheds light on the local electro-mechanical response of graphene under STM imaging and unveils the role of the stress induced by the vicinity of the graphene-metal interface in the formation and the manipulation of these ripples. Since microscopic rippling is one of the important factors that limit charge carrier mobility in graphene, the control of rippling with a gate voltage may have important consequences in the conductance of graphene devices where transverse electric fields are created by contactless suspended gate electrodes. This opens up also the possibility to dynamically control the local morphology of graphene nanomembranes. Electronic supplementary information (ESI) available: STM image of the metal-graphene boundary, as well as Fourier-filtered STM images of graphene to separate the large wavelength roughness from the contribution from rippling. See DOI: 10.1039/c3nr02934d

Osváth, Zoltán; Lefloch, François; Bouchiat, Vincent; Chapelier, Claude

2013-10-01

401

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...

402

Atmospheric Electric Fields: A Numerical Approach.  

National Technical Information Service (NTIS)

In this work some numerical methods for the resolution of the atmospheric electric potential equation are presented and discussed. Some applications related to different sources of the atmospheric electric potential for equatorial latitudes are also given...

S. L. G. Dutra A. E. C. Pereira A. L. C. Gonzalez W. D. Gonzalez

1985-01-01

403

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

404

A comparison of sublimation enthalpies with lattice energies calculated using force fields  

NASA Astrophysics Data System (ADS)

Experimental sublimation enthalpies in a range of molecular crystals were compared with their lattice energies as calculated by molecular mechanics, using several force fields. This enables an evaluation of the capability of these force fields to determine intermolecular interaction energies. The best agreement between calculated energies and sublimation enthalpies is found in the case of Gavezzotti's force field, while significant discrepancies are found with the DREIDING force field and CVFF. With all force fields, the level of accuracy obtained in energy calculation is insufficient for confident use in determining the enthalpy difference between two polymorphs of a given compound.

Osborn, J. C.; York, P.

1999-01-01

405

A fast path integral method for polarizable force fields.  

PubMed

A quantum simulation of an imaginary time path integral typically requires around n times more computational effort than the corresponding classical simulation, where n is the number of ring polymer beads (or imaginary time slices) used in the calculation. It is however possible to improve on this estimate by decomposing the potential into a sum of slowly and rapidly varying contributions. If the slowly varying contribution changes only slightly over the length scale of the ring polymer, it can be evaluated on a contracted ring polymer with fewer than the full n beads (or equivalently on a lower order Fourier decomposition of the imaginary time path). Here we develop and test this idea for systems with polarizable force fields. The development consists of iterating the induction on the contracted ring polymer and applying an appropriate transformation to obtain the forces on the original n beads. In combination with a splitting of the Coulomb potential into its short- and long-range parts, this results in a method with little more than classical computational effort in the limit of large system size. The method is illustrated with simulations of liquid water at 300 K and hexagonal ice at 100 K using a recently developed flexible and polarizable Thole-type potential energy model. PMID:19739844

Fanourgakis, George S; Markland, Thomas E; Manolopoulos, David E

2009-09-01

406

Efficient parameterization of torsional terms for force fields.  

PubMed

A novel method is presented for fitting force-field dihedral angles using an ensemble of structures generated from an ab initio Monte Carlo simulation. Importance sampling is used to achieve an efficient algorithm using a low level of theory to minimize the system at each step with the dihedral angles constrained, followed by dihedral fitting using the single point energies at a higher level of theory. The resulting method is an order of magnitude more efficient than the traditional method of doing a constrained scan over each dihedral independently. Also as the sampling is more uniformly distributed, the full surface is approximated to a greater accuracy. The dihedral fitting is done with a nonlinear optimization method to vary the phase as well as the force constant. The utility of the method is demonstrated by fitting dihedrals of methyl L-lactate, diisopropyl fluorophosphate, isopentenyl phosphate, a leucine dipeptide, and two inhibitors of Signal Transducer and Activator of Transcription 5. The results show that the Monte Carlo scheme is more efficient than constrained scans and is particularly effective at approximating the underlying potential energy surface when the dihedral degrees are coupled. © 2014 Wiley Periodicals, Inc. PMID:24831846

Burger, Steven K; Ayers, Paul W; Schofield, Jeremy

2014-07-15

407

Electric and magnetic fields in the high-latitude magnetosphere  

NASA Technical Reports Server (NTRS)

The configuration of high-latitude electric and magnetic fields is reviewed. Various results suggest that high-latitude magnetic field lines from the outermost regions of the dayside magnetosphere converge toward a point near the noon meridian. Plasma flows, the midday cusp, and a dawn-dusk electric field across the polar cap are characterized. The electric fields associated with plasma flows produce Hall currents on the polar cap which vary with sector structure. Some evidence indicates that polar cap convection may reverse during intervals of strong northward interplanetary field. It is concluded that most observations are consistent with an open field magnetosphere model.

Fairfield, D. H.

1977-01-01

408

The effect of spatially inhomogeneous extracellular electric fields on neurons.  

PubMed

The cooperative action of neurons and glia generates electrical fields, but their effect on individual neurons via ephaptic interactions is mostly unknown. Here, we analyze the impact of spatially inhomogeneous electric fields on the membrane potential, the induced membrane field, and the induced current source density of one-dimensional cables as well as morphologically realistic neurons and discuss how the features of the extracellular field affect these quantities. We show through simulations that endogenous fields, associated with hippocampal theta and sharp waves, can greatly affect spike timing. These findings imply that local electric fields, generated by the cooperative action of brain cells, can influence the timing of neural activity. PMID:20130201

Anastassiou, Costas A; Montgomery, Sean M; Barahona, Mauricio; Buzsáki, György; Koch, Christof

2010-02-01

409

Thermophysical responses of polymeric composites tailored by electric field  

Microsoft Academic Search

Applying an electric field to a liquid suspension redistributes the inclusions, arranges them in chain-like structures and\\/or orients fibrous inclusions or chain-like structures parallel to electric field. The present paper shows micro-tailored polymer composites including orthotropic structures and describes physical mechanisms influencing the microstructure in an electric field. Mechanical and thermal properties of orthotropic and random composites containing glass-fiber or

GeunHyung Kim

2005-01-01

410

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

411

A quantum mechanical polarizable force field for biomolecular interactions  

PubMed Central

We introduce a quantum mechanical polarizable force field (QMPFF) fitted solely to QM data at the MP2/aTZ(-hp) level. Atomic charge density is modeled by point-charge nuclei and floating exponentially shaped electron clouds. The functional form of interaction energy parallels quantum mechanics by including electrostatic, exchange, induction, and dispersion terms. Separate fitting of each term to the counterpart calculated from high-quality QM data ensures high transferability of QMPFF parameters to different molecular environments, as well as accurate fit to a broad range of experimental data in both gas and liquid phases. QMPFF, which is much more efficient than ab initio QM, is optimized for the accurate simulation of biomolecular systems and the design of drugs.

Donchev, A. G.; Ozrin, V. D.; Subbotin, M. V.; Tarasov, O. V.; Tarasov, V. I.

2005-01-01

412

A quantum mechanical polarizable force field for biomolecular interactions.  

PubMed

We introduce a quantum mechanical polarizable force field (QMPFF) fitted solely to QM data at the MP2/aTZ(-hp) level. Atomic charge density is modeled by point-charge nuclei and floating exponentially shaped electron clouds. The functional form of interaction energy parallels quantum mechanics by including electrostatic, exchange, induction, and dispersion terms. Separate fitting of each term to the counterpart calculated from high-quality QM data ensures high transferability of QMPFF parameters to different molecular environments, as well as accurate fit to a broad range of experimental data in both gas and liquid phases. QMPFF, which is much more efficient than ab initio QM, is optimized for the accurate simulation of biomolecular systems and the design of drugs. PMID:15911753

Donchev, A G; Ozrin, V D; Subbotin, M V; Tarasov, O V; Tarasov, V I

2005-05-31

413

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

414

The Bonding Forces In Liquid Metals And Ultrasonic Field Action  

NASA Astrophysics Data System (ADS)

The understanding of the liquid metals properties is still imperfect. Assuming that the liquids are isotropic and show some elasticity properties, there are no physical reasons for rejecting the applicability of the fundamental ideas of the Debye theory to the description of the properties of liquid state. The approach is intended to relate the temperature Debye to the intensity of bonding forces between neighboring atoms and, in turn, to correlate this with the high power ultrasonic field action. In order to highlight the effect of the ultrasonic wave on the Debye temperature values, the experiments were carried out under similar conditions both with and without sonication. The relationship between the Debye temperature for both liquid and solid state is ?Dsolid / ?Dliquid = 0.85.

Moraru, Luminita; Murariu, Gabriel

2007-04-01

415

Investigation of crossed SAW fields by scanning acoustic force microscopy.  

PubMed

We used multimode scanning acoustic force microscopy (SAFM) for studying noncollinearly propagating Rayleigh and Love wave fields. By analyzing torsion and bending movement of SAFM cantilever, normal and in-plane wave oscillation components are accessible. The SAFM principle is the down-conversion of surface oscillations into cantilever vibrations caused by the nonlinearity of the tip-sample interaction. Through mixing of complementary oscillation components, phase velocities of crossed Rayleigh waves on GaAs and crossed Rayleigh and Love waves on the layered system SiO2/ST-cut quartz were obtained simultaneously. Now, it is possible to investigate elastic properties of submicron areas through multimode SAFM measurements. Finally, we present mixing experiments of four SAWs on GaAs and discuss the various influences on the measured SAFM amplitude and phase contrast. PMID:11477772

Behme, G; Hesjedal, T

2001-07-01

416

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

417

The eccentric frame decomposition of central force fields  

NASA Astrophysics Data System (ADS)

The rosette-shaped motion of a particle in a central force field is known to be classically solvable by quadratures. We present a new approach of describing and characterizing such motion based on the eccentricity vector of the two body problem. In general, this vector is not an integral of motion. However, the orbital motion, when viewed from the nonuniformly rotating frame defined by the orientation of the eccentricity vector, can be solved analytically and will either be a closed periodic circulation or libration. The motion with respect to inertial space is then given by integrating the argument of periapsis with respect to time. Finally we will apply the decomposition to a modern central potential, the spherical Hernquist Newton potential, which models dark matter halos of galaxies with central black holes.

Maruskin, Jared M.; Scheeres, Daniel J.; Adams, Fred C.; Bloch, Anthony M.

2008-01-01

418

Measurements of the vertical atmospheric electric field and of the electrical conductivity with stratospheric balloons  

NASA Technical Reports Server (NTRS)

Measurements of the atmospheric (vertical) electric field with balloons in the stratosphere are reported. The atmospheric electrical conductivity is also measured and the current density inferred. The average vertical current shows the expected variation with universal time and is also seen to be influenced by external (magnetospheric) electric fields.

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

1985-01-01

419

Balloon observations of stratospheric electricity above the South Pole - Vertical electric field, conductivity, and conduction current  

Microsoft Academic Search

Results are summarized of measurements of the electrical conductivity and vertical component of the vector electric field acquired from eight stratospheric balloon flights launched from the South Pole in the austral summer of 1985-1986. The data are a contribution to the set of global atmospheric electricity measurements and extend the work of Cobb (1977) to determine the electrical environment of

G. J. Byrne; J. R. Benbrook; E. A. Bering

1991-01-01

420

Substorm electric fields in the earth's magnetotail  

NASA Technical Reports Server (NTRS)

A survey has been made of all the electric field data from the University of California, Berkeley, double probe experiment on ISEE-1 (apogee approximately 22 earth radii) during 1980 when the satellite was in the magnetotail. This study was restricted to the 74 events where E cross B flows could be calculated and were equal to or greater than 100 km/s. Substorm times were determined by examining the Ae index for peaks equal to or greater than 250 gamma. In association with substorms, approximately 70 percent of the flows were earthward, and approximately 20 percent had a signature called 'near satellite reconnection' (first described by Nishida et al. (1983) of tailward flow followed by earthward flow which can be interpreted in terms of a model where the x-line forms earthward of the satellite and subsequently propagates tailward of X(GSM) = -21 earth radii and within the absolute value of Y(GSM) equal to or less than 4.5 earth radii. These data suggest that the near earth x-line usually forms tailward of X(GSM) approximately -20 earth radii.

Cattell, C. A.; Mozer, F. S.

1984-01-01

421

Pulsed electric field assisted assembly of polyaniline.  

PubMed

Assembling conducting polyaniline (PANi) on pre-patterned nano-structures by a high rate, commercially viable route offers an opportunity for manufacturing devices with nanoscale features. In this work we report for the first time the use of pulsed electric field to assist electrophoresis for the assembly of conducting polyaniline on gold nanowire interdigitated templates. This technique offers dynamic control over heat build-up, which has been a main drawback in the DC electrophoresis and AC dielectrophoresis as well as the main cause of nanowire template damage. The use of this technique allowed higher voltages to be applied, resulting in shorter assembly times (e.g., 17.4 s, assembly resolution of 100 nm). Moreover, the area coverage increases with the increase in number of pulses. A similar trend was observed with the deposition height and the increase in deposition height followed a linear trend with a correlation coefficient of 0.95. When the experimental mass deposited was compared with Hamaker's theoretical model, the two were found to be very close. The pre-patterned templates with PANi deposition were subsequently used to transfer the nanoscale assembled PANi from the rigid templates to thermoplastic polyurethane using the thermoforming process. PMID:22863729

Kumar, Arun; Kazmer, David O; Barry, Carol M F; Mead, Joey L

2012-08-24

422

Formation of a local atmospheric electric field  

NASA Astrophysics Data System (ADS)

We have estimated the variations in the atmospheric electrostatic field (AEF, E Z(0)) strength in the surface layer caused by variations in conductivity due to radon influences, cosmic ray intensity, changes in the balance of light and heavy ions during sunset and sunrise, and under the effect of the ionospheric electric current potential on the AEF potential. It is shown that the air conductivity varies due to ionization under the effect of radon emanations and is determined by the radon exhalation and turbulent diffusion of the surface air layer, while the cosmic ray intensity affects the surface air conductivity through changes in the ion recombination conditions. A decrease in the air conductivity due to a decrease in the cosmic ray intensity (Forbush decrease) also decreases E Z(0), while a decrease in radon fluxes results in an increase in E Z(0). We have estimated the effect of illumination conditions on the AEF due to variations in the relative concentration of heavy and light ions under the influence of photodetachment and photoattachment processes. The work has been done on the basis of data received from the Paratunka observatory (Kamchatka).

Ponomarev, E. A.; Cherneva, N. V.; Firstov, P. P.

2011-06-01

423

The theory research and electric field simulation of the AHPC  

NASA Astrophysics Data System (ADS)

Diameter of different corona electrode, distance of lines and distribution of the electric field of the porous dust collection plate of the AHPC electrostatic fabric filter were studied and analyzed on the basis of MATLAB PDE Toolbox. The simulation results of the AHPC electric-bag composite dust collector electrical fields show that when the corona polar diameter was 4 mm and distance between neighboring electrodes was 196 mm, the performance of the electric field was better. And the larger the aperture was, the higher the electric potential of the porous plate would be. Compared with the experimental research, it is simpler, visual and economical to use the MATLAB PDE to find the electric-field distribution of the electric-bag composite dust collector, it can provide theoretical basis for design and modification of corona wire diameter, line-spaces and precipitating plate aperture.

Tang, Minkang; Ma, Yanling; Yang, Ping

2013-03-01

424

Surface electric fields for North America during historical geomagnetic storms  

NASA Astrophysics Data System (ADS)

To better understand the impact of geomagnetic disturbances on the electric grid, we recreate surface electric fields from two historical geomagnetic storms—the 1989 "Quebec" storm and the 2003 "Halloween" storms. Using the Spherical Elementary Current Systems method, we interpolate sparsely distributed magnetometer data across North America. We find good agreement between the measured and interpolated data, with larger RMS deviations at higher latitudes corresponding to larger magnetic field variations. The interpolated magnetic field data are combined with surface impedances for 25 unique physiographic regions from the United States Geological Survey and literature to estimate the horizontal, orthogonal surface electric fields in 1 min time steps. The induced horizontal electric field strongly depends on the local surface impedance, resulting in surprisingly strong electric field amplitudes along the Atlantic and Gulf Coast. The relative peak electric field amplitude of each physiographic region, normalized to the value in the Interior Plains region, varies by a factor of 2 for different input magnetic field time series. The order of peak electric field amplitudes (largest to smallest), however, does not depend much on the input. These results suggest that regions at lower magnetic latitudes with high ground resistivities are also at risk from the effect of geomagnetically induced currents. The historical electric field time series are useful for estimating the flow of the induced currents through long transmission lines to study power flow and grid stability during geomagnetic disturbances.

Wei, Lisa H.; Homeier, Nicole; Gannon, Jennifer L.

2013-08-01

425

Electric Field and Density Measurements with STEREO-SWaves.  

NASA Astrophysics Data System (ADS)

The STEREO experiment SWaves has a low frequency part which is designed to make measurements of low frequency electric fields and rapid measurements of density fluctuations, using the three 6 meter stacer monopole antennas. The short antennas of STEREO respond both to density fluctuations and to electric fields. Therefore, it is desired to obtain four quantities, density and 3 components of electric field, from three measurements, the potentials on the three orthogonal antennas relative to the spacecraft, which requires some additional information. One possibility is to add a fourth equation implied by the large plasma conductivity, so large that electric field parallel to the magnetic field is zero, a condition which has often been used in electric field measurements. Under selected conditions, this seems to work. There are also conditions, for example ion acoustic waves, where the responses to density fluctuations and to electric fields are available from dispersion relations, and this provides another possible solution. A situation where it is not likely that the parallel electric field is zero is the case of solitary, intense bursts of Langmuir waves. For this case, it is expected that there is an electron density depression due to the ponderomotive pressure, and a resulting low frequency electric field from the non-neutrality which would be expected to have components parallel to the magnetic field. Examples will be discussed.

Kellogg, P. J.; Goetz, K.; Monson, S. J.; Bale, S. D.; Maksimovic, M.

2007-12-01

426

A Wearable Force Plate Designed Using Pressure Sensitive Electric Conductive Rubber  

NASA Astrophysics Data System (ADS)

To perform 3D ground reaction force (GRF) and moments measurement with a comfortable interface for the foot, this paper presents a new 3D force sensor cell designed using pressure sensitive electric conductive rubber (PSECR). A wearable force plate with a four-support mechanism was proposed for measuring triaxial forces and moments. A compact electrical hardware system including amplifier modules, conditioning circuits, and then a micro-computer controller was developed and integrated into the sensor system. A shoes-based sensor system composed of two developed force plates was constructed for GRF and moment measurement. Calibration experiments were conducted, and a stationary force plate was used as a reference device to verify the measures of GRF and moment using the sensor system in trials by a normal walking speed. The results show a good correspondence between the developed sensor system and the reference system, which was examined by a root mean square (RMS) difference of 7.2N for x-axial force, 11.1N for y-axial force, and 9.5N for z-axial force. The RMS difference of the measured x-, y-, and z- directional moments was 6.4Nm, 1.9Nm, and 1.4Nm, respectively.

Liu, Tao; Inoue, Yoshio; Shibata, Kyoko

427

Simultaneous electric-field measurements on nearby balloons.  

NASA Technical Reports Server (NTRS)

Electric-field payloads were flown simultaneously on two balloons from Great Whale River, Canada, on September 21, 1971, to provide data at two points in the upper atmosphere that differed in altitude by more than one atmospheric density scale height and in horizontal position by 30-140 km. The altitude dependences in the two sets of data prove conclusively that the vertical electric field at balloon altitudes stems from fair-weather atmospheric electricity sources and that the horizontal fields are mapped down ionospheric fields, since the weather-associ