Effect of nanoholes on the plasmonic properties of star nanostructures

NASA Astrophysics Data System (ADS)

Zhu, Shaoli; Whittaker, Andrew K.; Blakey, Idriss

2011-12-01

The transmission and localized electric field distribution of nanostructures are the most important parameters in the plasmonic field for nano-optics and nanobiosensors. In this paper, we propose a novel nanostructure which may be used for nanobiosensor applications. The effect of nanoholes on the plasmonic properties of star nanostructure was studied via numerical simulation, using the finite-difference time-domain (FDTD) method. In the model, the material type and size of the nanostructures was fixed, but the distance between the monotor and the surface of the nanoholes was varied. For example, nanoholes were located in the center of the nanostructures. The simulation method was as follows. Initially, the wavelength of incident light was varied from 400 to 1200 nm and the transmission spectrum and the electric field distribution were simulated. Then at the resonance wavelength (wavelength where the transmission spectrum has a minimum), the localized electric field distribution was calculated at different distances from the surface of the nanostructures. This study shows that the position of nanoholes has a significant effect on the transmission and localized electric field distribution of star nanostructures. The condition for achieving the maximum localized electric field distribution can be used in nano-optics and nanobiosensors in the future.

Imaging electric field dynamics with graphene optoelectronics

DOE PAGES

Horng, Jason; Balch, Halleh B.; McGuire, Allister F.; ...

2016-12-16

The use of electric fields for signalling and control in liquids is widespread, spanning bioelectric activity in cells to electrical manipulation of microstructures in lab-on-a-chip devices. However, an appropriate tool to resolve the spatio-temporal distribution of electric fields over a large dynamic range has yet to be developed. Here we present a label-free method to image local electric fields in real time and under ambient conditions. Our technique combines the unique gate-variable optical transitions of graphene with a critically coupled planar waveguide platform that enables highly sensitive detection of local electric fields with a voltage sensitivity of a few microvolts,more » a spatial resolution of tens of micrometres and a frequency response over tens of kilohertz. Our imaging platform enables parallel detection of electric fields over a large field of view and can be tailored to broad applications spanning lab-on-a-chip device engineering to analysis of bioelectric phenomena.« less

Imaging electric field dynamics with graphene optoelectronics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horng, Jason; Balch, Halleh B.; McGuire, Allister F.

The use of electric fields for signalling and control in liquids is widespread, spanning bioelectric activity in cells to electrical manipulation of microstructures in lab-on-a-chip devices. However, an appropriate tool to resolve the spatio-temporal distribution of electric fields over a large dynamic range has yet to be developed. Here we present a label-free method to image local electric fields in real time and under ambient conditions. Our technique combines the unique gate-variable optical transitions of graphene with a critically coupled planar waveguide platform that enables highly sensitive detection of local electric fields with a voltage sensitivity of a few microvolts,more » a spatial resolution of tens of micrometres and a frequency response over tens of kilohertz. Our imaging platform enables parallel detection of electric fields over a large field of view and can be tailored to broad applications spanning lab-on-a-chip device engineering to analysis of bioelectric phenomena.« less

Electric Field Encephalography as a tool for functional brain research: a modeling study.

PubMed

Petrov, Yury; Sridhar, Srinivas

2013-01-01

We introduce the notion of Electric Field Encephalography (EFEG) based on measuring electric fields of the brain and demonstrate, using computer modeling, that given the appropriate electric field sensors this technique may have significant advantages over the current EEG technique. Unlike EEG, EFEG can be used to measure brain activity in a contactless and reference-free manner at significant distances from the head surface. Principal component analysis using simulated cortical sources demonstrated that electric field sensors positioned 3 cm away from the scalp and characterized by the same signal-to-noise ratio as EEG sensors provided the same number of uncorrelated signals as scalp EEG. When positioned on the scalp, EFEG sensors provided 2-3 times more uncorrelated signals. This significant increase in the number of uncorrelated signals can be used for more accurate assessment of brain states for non-invasive brain-computer interfaces and neurofeedback applications. It also may lead to major improvements in source localization precision. Source localization simulations for the spherical and Boundary Element Method (BEM) head models demonstrated that the localization errors are reduced two-fold when using electric fields instead of electric potentials. We have identified several techniques that could be adapted for the measurement of the electric field vector required for EFEG and anticipate that this study will stimulate new experimental approaches to utilize this new tool for functional brain research.

Local electric field direct writing – Electron-beam lithography and mechanism

DOE PAGES

Jiang, Nan; Su, Dong; Spence, John C. H.

2017-08-24

Local electric field induced by a focused electron probe in silicate glass thin films is evaluated in this paper by the migration of cations. Extremely strong local electric fields can be obtained by the focused electron probe from a scanning transmission electron microscope. As a result, collective atomic displacements occur. This newly revised mechanism provides an efficient tool to write patterned nanostructures directly, and thus overcome the low efficiency of the conventional electron-beam lithography. Applying this technique to silicate glass thin films, as an example, a grid of rods of nanometer dimension can be efficiently produced by rapidly scanning amore » focused electron probe. This nanopatterning is achieved through swift phase separation in the sample, without any post-development processes. The controlled phase separation is induced by massive displacements of cations (glass modifiers) within the glass-former network, driven by the strong local electric fields. The electric field is induced by accumulated charge within the electron probed region, which is generated by the excitation of atomic electrons by the incident electron. Throughput is much improved compared to other scanning probe techniques. Finally, the half-pitch spatial resolution of nanostructure in this particular specimen is 2.5 nm.« less

Local electric field direct writing – Electron-beam lithography and mechanism

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jiang, Nan; Su, Dong; Spence, John C. H.

Local electric field induced by a focused electron probe in silicate glass thin films is evaluated in this paper by the migration of cations. Extremely strong local electric fields can be obtained by the focused electron probe from a scanning transmission electron microscope. As a result, collective atomic displacements occur. This newly revised mechanism provides an efficient tool to write patterned nanostructures directly, and thus overcome the low efficiency of the conventional electron-beam lithography. Applying this technique to silicate glass thin films, as an example, a grid of rods of nanometer dimension can be efficiently produced by rapidly scanning amore » focused electron probe. This nanopatterning is achieved through swift phase separation in the sample, without any post-development processes. The controlled phase separation is induced by massive displacements of cations (glass modifiers) within the glass-former network, driven by the strong local electric fields. The electric field is induced by accumulated charge within the electron probed region, which is generated by the excitation of atomic electrons by the incident electron. Throughput is much improved compared to other scanning probe techniques. Finally, the half-pitch spatial resolution of nanostructure in this particular specimen is 2.5 nm.« less

Fractional power-law spatial dispersion in electrodynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tarasov, Vasily E., E-mail: tarasov@theory.sinp.msu.ru; Departamento de Análisis Matemático, Universidad de La Laguna, 38271 La Laguna, Tenerife; Trujillo, Juan J., E-mail: jtrujill@ullmat.es

2013-07-15

Electric fields in non-local media with power-law spatial dispersion are discussed. Equations involving a fractional Laplacian in the Riesz form that describe the electric fields in such non-local media are studied. The generalizations of Coulomb’s law and Debye’s screening for power-law non-local media are characterized. We consider simple models with anomalous behavior of plasma-like media with power-law spatial dispersions. The suggested fractional differential models for these plasma-like media are discussed to describe non-local properties of power-law type. -- Highlights: •Plasma-like non-local media with power-law spatial dispersion. •Fractional differential equations for electric fields in the media. •The generalizations of Coulomb’s lawmore » and Debye’s screening for the media.« less

MUSIC for localization of thunderstorm cells

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mosher, J.C.; Lewis, P.S.; Rynne, T.M.

1993-12-31

Lightning represents an event detectable optically, electrically, and acoustically, and several systems are already in place to monitor such activity. Unfortunately, such detection of lightning can occur too late, since operations need to be protected in advance of the first lightning strike. Additionally, the bolt itself can traverse several kilometers before striking the ground, leaving a large region of uncertainty as to the center of the storm and its possible strike regions. NASA Kennedy Space Center has in place an array of electric field mills that monitor the (effectively) DC electric field. Prior to the first lightning strike, the surfacemore » electric fields rise as the storm generator within a thundercloud begins charging. Extending methods we developed for an analogous source localization problem in mangnetoencephalography, we present Cramer-Rao lower bounds and MUSIC scans for fitting a point-charge source model to the electric field mill data. Such techniques can allow for the identification and localization of charge centers in cloud structures.« less

Response of ionospheric electric fields at mid-low latitudes during geomagnetic sudden commencements

NASA Astrophysics Data System (ADS)

Takahashi, N.; Kasaba, Y.; Shinbori, A.; Nishimura, Y.; Kikuchi, T.; Ebihara, Y.; Nagatsuma, T.

2014-12-01

Geomagnetic sudden commencements (SCs) are known as one of the distinct magnetospheric disturbance phenomena triggered by solar wind disturbances. Many previous studies have focused on the generation mechanism of SCs by using in-situ observations and simulations. However, the global evolution of ionospheric electric fields has primarily been estimated from the ionospheric current. Although a few studies utilized electric field data from radar observations, the coverage is limited in time, and limited component of the electric field is obtained. In this study, we investigated the response and local time dependence of the ionospheric electric field at mid-low latitudes associated with 203 SCs occurred from 1999 to 2004 by the in-situ observation of the ROCSAT-1 spacecraft. We found that the ionospheric electric field associated with SCs instantaneously responds to geomagnetic fields regardless of spacecraft local time. Our statistical analysis also showed the instantaneous response of the electric field, which indicates the global instant transmission of the electric field from polar region. In contrast, peak times in the preliminary impulse (PI) and main impulse (MI) phases were different between the ionospheric electric field and equatorial geomagnetic field (20 sec in the PI phase). Based on a comparison to the ground-ionosphere waveguide model by Kikuchi [2014], this time lag is suggested to be due to the latitudinal difference of the ionospheric conductivity. After constructing the local time distribution of the SC amplitude, we found that the dayside feature was seen at 18-22 h even the ionospheric conductivity is lower than that at dayside. We performed a magnetohydrodynamic (MHD) simulation for an ideal SC. The result of the simulation showed that the electric potential distribution is asymmetric with respect to the noon-midnight meridian, which is similar to our observational result. It appears to result from the divergence of the Hall current under the non-uniform ionospheric conductivity near the terminator as well as the auroral region.

Imaging local electric fields produced upon synchrotron X-ray exposure

DOE PAGES

Dettmar, Christopher M.; Newman, Justin A.; Toth, Scott J.; ...

2014-12-31

Electron–hole separation following hard X-ray absorption during diffraction analysis of soft materials under cryogenic conditions produces substantial local electric fields visualizable by second harmonic generation (SHG) microscopy. Monte Carlo simulations of X-ray photoelectron trajectories suggest the formation of substantial local electric fields in the regions adjacent to those exposed to X-rays, indicating a possible electric-field–induced SHG (EFISH) mechanism for generating the observed signal. In studies of amorphous vitreous solvents, analysis of the SHG spatial profiles following X-ray microbeam exposure was consistent with an EFISH mechanism. Within protein crystals, exposure to 12-keV (1.033-Å) X-rays resulted in increased SHG in the regionmore » extending ~3 μm beyond the borders of the X-ray beam. Moderate X-ray exposures typical of those used for crystal centering by raster scanning through an X-ray beam were sufficient to produce static electric fields easily detectable by SHG. The X-ray–induced SHG activity was observed with no measurable loss for longer than 2 wk while maintained under cryogenic conditions, but disappeared if annealed to room temperature for a few seconds. In conclusion, these results provide direct experimental observables capable of validating simulations of X-ray–induced damage within soft materials. Additionally, X-ray–induced local fields may potentially impact diffraction resolution through localized piezoelectric distortions of the lattice.« less

Fano-shaped impurity spectral density, electric-field-induced in-gap state, and local magnetic moment of an adatom on trilayer graphene

NASA Astrophysics Data System (ADS)

Zhang, Zu-Quan; Li, Shuai; Lü, Jing-Tao; Gao, Jin-Hua

2017-08-01

Recently, the existence of local magnetic moment in a hydrogen adatom on graphene was confirmed experimentally [González-Herrero et al., Science 352, 437 (2016), 10.1126/science.aad8038]. Inspired by this breakthrough, we theoretically investigate the top-site adatom on trilayer graphene (TLG) by solving the Anderson impurity model via self-consistent mean field method. The influence of the stacking order, the adsorption site, and external electric field are carefully considered. We find that, due to its unique electronic structure, the situation of TLG is drastically different from that of the monolayer graphene. First, the adatom on rhombohedral stacked TLG (r-TLG) can have a Fano-shaped impurity spectral density, instead of the normal Lorentzian-like one, when the impurity level is around the Fermi level. Second, the impurity level of the adatom on r-TLG can be tuned into an in-gap state by an external electric field, which strongly depends on the direction of the applied electric field and can significantly affect the local magnetic moment formation. Finally, we systematically calculate the impurity magnetic phase diagrams, considering various stacking orders, adsorption sites, doping, and electric field. We show that, because of the in-gap state, the impurity magnetic phase of r-TLG will obviously depend on the direction of the applied electric field as well. All our theoretical results can be readily tested in experiment, and may give a comprehensive understanding about the local magnetic moment of an adatom on TLG.

Relative Localization in Wireless Sensor Networks for Measurement of Electric Fields under HVDC Transmission Lines

PubMed Central

Cui, Yong; Wang, Qiusheng; Yuan, Haiwen; Song, Xiao; Hu, Xuemin; Zhao, Luxing

2015-01-01

In the wireless sensor networks (WSNs) for electric field measurement system under the High-Voltage Direct Current (HVDC) transmission lines, it is necessary to obtain the electric field distribution with multiple sensors. The location information of each sensor is essential to the correct analysis of measurement results. Compared with the existing approach which gathers the location information by manually labelling sensors during deployment, the automatic localization can reduce the workload and improve the measurement efficiency. A novel and practical range-free localization algorithm for the localization of one-dimensional linear topology wireless networks in the electric field measurement system is presented. The algorithm utilizes unknown nodes' neighbor lists based on the Received Signal Strength Indicator (RSSI) values to determine the relative locations of nodes. The algorithm is able to handle the exceptional situation of the output permutation which can effectively improve the accuracy of localization. The performance of this algorithm under real circumstances has been evaluated through several experiments with different numbers of nodes and different node deployments in the China State Grid HVDC test base. Results show that the proposed algorithm achieves an accuracy of over 96% under different conditions. PMID:25658390

Relative localization in wireless sensor networks for measurement of electric fields under HVDC transmission lines.

PubMed

Cui, Yong; Wang, Qiusheng; Yuan, Haiwen; Song, Xiao; Hu, Xuemin; Zhao, Luxing

2015-02-04

In the wireless sensor networks (WSNs) for electric field measurement system under the High-Voltage Direct Current (HVDC) transmission lines, it is necessary to obtain the electric field distribution with multiple sensors. The location information of each sensor is essential to the correct analysis of measurement results. Compared with the existing approach which gathers the location information by manually labelling sensors during deployment, the automatic localization can reduce the workload and improve the measurement efficiency. A novel and practical range-free localization algorithm for the localization of one-dimensional linear topology wireless networks in the electric field measurement system is presented. The algorithm utilizes unknown nodes' neighbor lists based on the Received Signal Strength Indicator (RSSI) values to determine the relative locations of nodes. The algorithm is able to handle the exceptional situation of the output permutation which can effectively improve the accuracy of localization. The performance of this algorithm under real circumstances has been evaluated through several experiments with different numbers of nodes and different node deployments in the China State Grid HVDC test base. Results show that the proposed algorithm achieves an accuracy of over 96% under different conditions.

Passive electrical monitoring and localization of fluid leakages from wells

NASA Astrophysics Data System (ADS)

Revil, A.; Mao, D.; Haas, A. K.; Karaoulis, M.; Frash, L.

2015-02-01

Electrokinetic phenomena are a class of cross-coupling phenomena involving the relative displacement between the pore water (together with the electrical diffuse layer) with respect to the solid phase of a porous material. We demonstrate that electrical fields of electrokinetic nature can be associated with fluid leakages from wells. These leakages can be remotely monitored and the resulting signals used to localize their causative source distribution both in the laboratory and in field conditions. The first laboratory experiment (Experiment #1) shows how these electrical fields can be recorded at the surface of a cement block during the leakage of a brine from a well. The measurements were performed with a research-grade medical electroencephalograph and were inverted using a genetic algorithm to localize the causative source of electrical current and therefore, localize the leak in the block. Two snapshots of electrical signals were used to show how the leak evolved over time. The second experiment (Experiment #2) was performed to see if we could localize a pulse water injection from a shallow well in field conditions in the case of a heterogeneous subsurface. We used the same equipment as in Experiment #1 and processed the data with a trend removal algorithm, picking the amplitude from 24 receiver channels just after the water injection. The amplitude of the electric signals changed from the background level indicating that a volume of water was indeed flowing inside the well into the surrounding soil and then along the well. We used a least-square inversion algorithm to invert a snapshot of the electrical potential data at the injection time to localize the source of the self-potential signals. The inversion results show positive potential anomalies in the vicinity of the well. For both experiments, forward numerical simulations of the problem using a finite element package were performed in order to assess the underlying physics of the causative source of the observed electrical potential anomalies and how they are related to the flow of the water phase.

Effect of the local electric field on the formation of an ordered structure in porous anodic alumina

NASA Astrophysics Data System (ADS)

Lazarouk, S. K.; Katsuba, P. S.; Leshok, A. A.; Vysotskii, V. B.

2015-09-01

Experimental data and a model are presented, and the electric field that appears in porous alumina during electrochemical anodic oxidation of aluminum in electrolytes based on an aqueous solution of oxalic acid at a voltage of 90-250 V is calculated. It is found that the electric field in the layers with a porosity of 1-10% in growing alumina reaches 109-1010 V/m, which exceeds the electric strength of the material and causes microplasma patterns emitting visible light at the pore bottom, the self-organization of the structure of porous alumina, and the anisotropy of local porous anodizing. Moreover, other new effects are to be expected during aluminum anodizing under the conditions that ensure a high electric field inside the barrier layer of porous oxide.

Positron Annihilation Ratio Spectroscopy (PsARS) Applied to Positronium Formation Studies

DTIC Science & Technology

2010-03-01

POSITRON ANNIHILATION RATIO SPECTROSCOPY (PsARS) APPLIED TO POSITRONIUM FORMATION STUDIES THESIS...AFIT/GNE/ENP/10-M07 POSITRON ANNIHILATION RATIO SPECTROSCOPY (PsARS) APPLIED TO POSITRONIUM FORMATION STUDIES ...lifetime studies in local electric field experiments. High local electric fields can polarize a positron -electron pair, which may result in an extended

Specific absorption rate and electric field measurements in the near field of six mobile phone base station antennas.

PubMed

Toivonen, Tommi; Toivo, Tim; Puranen, Lauri; Jokela, Kari

2009-05-01

In this article, the exposure to radio frequency electromagnetic fields was studied in close proximity (distances of 10, 100, 300, and 600 mm) to six base station antennas. The specific absorption rate (SAR) in 800 mm x 500 mm x 200 mm box phantom as well as unperturbed electric field (E) in air was measured. The results were used to determine whether the measurement of local maximum of unperturbed electric field can be used as a compliance check for local exposure. Also, the conservativeness of this assessment method compared to the ICNIRP basic restriction was studied. Moreover, the assessment of whole-body exposure was discussed and the distance ranges presented in which the ICNIRP limit for local exposure could be exceeded before the limit for whole-body SAR. These results show that the electric field measurement alone can be used for easy compliance check for the local exposure at all distances and for all antenna types studied. However, in some cases when the local peak value of E was compared directly to the ICNIRP reference level for unperturbed E, the exposure was overestimated only very slightly (by factor 1.1) compared to the basic restriction for localized SAR in a human, and hence these results can not be generalized to all antenna types. Moreover, it was shown that the limit for localized exposure could be exceeded before the limit for the whole-body average SAR, if the distance to the antenna was less than 240 mm. Copyright 2009 Wiley-Liss, Inc.

Resonance localization and poloidal electric field due to cyclo- tron wave heating in tokamak plasmas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hsu, J.Y.; Chan, V.S.; Harvey, R.W.

1984-08-06

The perpendicular heating in cyclotron waves tends to pile up the resonant particles toward the low magnetic field side with their banana tips localized to the resonant surface. A poloidal electric field with an E x B drift comparable to the ion vertical drift in a toroidal magnetic field may result. With the assumption of anomalous electron and neoclassical ion transport, density variations due to wave heating are discussed.

Sparse Reconstruction of Electric Fields from Radial Magnetic Data

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yeates, Anthony R.

2017-02-10

Accurate estimates of the horizontal electric field on the Sun’s visible surface are important not only for estimating the Poynting flux of magnetic energy into the corona but also for driving time-dependent magnetohydrodynamic models of the corona. In this paper, a method is developed for estimating the horizontal electric field from a sequence of radial-component magnetic field maps. This problem of inverting Faraday’s law has no unique solution. Unfortunately, the simplest solution (a divergence-free electric field) is not realistically localized in regions of nonzero magnetic field, as would be expected from Ohm’s law. Our new method generates instead a localizedmore » solution, using a basis pursuit algorithm to find a sparse solution for the electric field. The method is shown to perform well on test cases where the input magnetic maps are flux balanced in both Cartesian and spherical geometries. However, we show that if the input maps have a significant imbalance of flux—usually arising from data assimilation—then it is not possible to find a localized, realistic, electric field solution. This is the main obstacle to driving coronal models from time sequences of solar surface magnetic maps.« less

Optimization of return electrodes in neurostimulating arrays

NASA Astrophysics Data System (ADS)

Flores, Thomas; Goetz, Georges; Lei, Xin; Palanker, Daniel

2016-06-01

Objective. High resolution visual prostheses require dense stimulating arrays with localized inputs of individual electrodes. We study the electric field produced by multielectrode arrays in electrolyte to determine an optimal configuration of return electrodes and activation sequence. Approach. To determine the boundary conditions for computation of the electric field in electrolyte, we assessed current dynamics using an equivalent circuit of a multielectrode array with interleaved return electrodes. The electric field modeled with two different boundary conditions derived from the equivalent circuit was then compared to measurements of electric potential in electrolyte. To assess the effect of return electrode configuration on retinal stimulation, we transformed the computed electric fields into retinal response using a model of neural network-mediated stimulation. Main results. Electric currents at the capacitive electrode-electrolyte interface redistribute over time, so that boundary conditions transition from equipotential surfaces at the beginning of the pulse to uniform current density in steady state. Experimental measurements confirmed that, in steady state, the boundary condition corresponds to a uniform current density on electrode surfaces. Arrays with local return electrodes exhibit improved field confinement and can elicit stronger network-mediated retinal response compared to those with a common remote return. Connecting local return electrodes enhances the field penetration depth and allows reducing the return electrode area. Sequential activation of the pixels in large monopolar arrays reduces electrical cross-talk and improves the contrast in pattern stimulation. Significance. Accurate modeling of multielectrode arrays helps optimize the electrode configuration to maximize the spatial resolution, contrast and dynamic range of retinal prostheses.

Electric-field control of local ferromagnetism using a magnetoelectric multiferroic.

PubMed

Chu, Ying-Hao; Martin, Lane W; Holcomb, Mikel B; Gajek, Martin; Han, Shu-Jen; He, Qing; Balke, Nina; Yang, Chan-Ho; Lee, Donkoun; Hu, Wei; Zhan, Qian; Yang, Pei-Ling; Fraile-Rodríguez, Arantxa; Scholl, Andreas; Wang, Shan X; Ramesh, R

2008-06-01

Multiferroics are of interest for memory and logic device applications, as the coupling between ferroelectric and magnetic properties enables the dynamic interaction between these order parameters. Here, we report an approach to control and switch local ferromagnetism with an electric field using multiferroics. We use two types of electromagnetic coupling phenomenon that are manifested in heterostructures consisting of a ferromagnet in intimate contact with the multiferroic BiFeO(3). The first is an internal, magnetoelectric coupling between antiferromagnetism and ferroelectricity in the BiFeO(3) film that leads to electric-field control of the antiferromagnetic order. The second is based on exchange interactions at the interface between a ferromagnet (Co(0.9)Fe(0.1)) and the antiferromagnet. We have discovered a one-to-one mapping of the ferroelectric and ferromagnetic domains, mediated by the colinear coupling between the magnetization in the ferromagnet and the projection of the antiferromagnetic order in the multiferroic. Our preliminary experiments reveal the possibility to locally control ferromagnetism with an electric field.

Electric-field control of local ferromagnetism using a magnetoelectric multiferroic

NASA Astrophysics Data System (ADS)

Chu, Ying-Hao; Martin, Lane W.; Holcomb, Mikel B.; Gajek, Martin; Han, Shu-Jen; He, Qing; Balke, Nina; Yang, Chan-Ho; Lee, Donkoun; Hu, Wei; Zhan, Qian; Yang, Pei-Ling; Fraile-Rodríguez, Arantxa; Scholl, Andreas; Wang, Shan X.; Ramesh, R.

2008-06-01

Multiferroics are of interest for memory and logic device applications, as the coupling between ferroelectric and magnetic properties enables the dynamic interaction between these order parameters. Here, we report an approach to control and switch local ferromagnetism with an electric field using multiferroics. We use two types of electromagnetic coupling phenomenon that are manifested in heterostructures consisting of a ferromagnet in intimate contact with the multiferroic BiFeO3. The first is an internal, magnetoelectric coupling between antiferromagnetism and ferroelectricity in the BiFeO3 film that leads to electric-field control of the antiferromagnetic order. The second is based on exchange interactions at the interface between a ferromagnet (Co0.9Fe0.1) and the antiferromagnet. We have discovered a one-to-one mapping of the ferroelectric and ferromagnetic domains, mediated by the colinear coupling between the magnetization in the ferromagnet and the projection of the antiferromagnetic order in the multiferroic. Our preliminary experiments reveal the possibility to locally control ferromagnetism with an electric field.

Complementary structure for designer localized surface plasmons

NASA Astrophysics Data System (ADS)

Gao, Zhen; Gao, Fei; Zhang, Youming; Zhang, Baile

2015-11-01

Magnetic localized surface plasmons (LSPs) supported on metallic structures corrugated by very long and curved grooves have been recently proposed and demonstrated on an extremely thin metallic spiral structure (MSS) in the microwave regime. However, the mode profile for the magnetic LSPs was demonstrated by measuring only the electric field, not the magnetic field. Here, based on Babinet's principle, we propose a Babinet-inverted, or complementary MSS whose electric/magnetic mode profiles match the magnetic/electric mode profiles of MSS. This complementarity of mode profiles allows mapping the magnetic field distribution of magnetic LSP mode profile on MSS by measuring the electric field distribution of the corresponding mode on complementary MSS. Experiment at microwave frequencies also demonstrate the use of complementary MSS in sensing refractive-index change in the environment.

Vibrational spectroscopic determination of local solvent electric field, solute-solvent electrostatic interaction energy, and their fluctuation amplitudes.

PubMed

Lee, Hochan; Lee, Gayeon; Jeon, Jonggu; Cho, Minhaeng

2012-01-12

IR probes have been extensively used to monitor local electrostatic and solvation dynamics. Particularly, their vibrational frequencies are highly sensitive to local solvent electric field around an IR probe. Here, we show that the experimentally measured vibrational frequency shifts can be inversely used to determine local electric potential distribution and solute-solvent electrostatic interaction energy. In addition, the upper limits of their fluctuation amplitudes are estimated by using the vibrational bandwidths. Applying this method to fully deuterated N-methylacetamide (NMA) in D(2)O and examining the solvatochromic effects on the amide I' and II' mode frequencies, we found that the solvent electric potential difference between O(═C) and D(-N) atoms of the peptide bond is about 5.4 V, and thus, the approximate solvent electric field produced by surrounding water molecules on the NMA is 172 MV/cm on average if the molecular geometry is taken into account. The solute-solvent electrostatic interaction energy is estimated to be -137 kJ/mol, by considering electric dipole-electric field interaction. Furthermore, their root-mean-square fluctuation amplitudes are as large as 1.6 V, 52 MV/cm, and 41 kJ/mol, respectively. We found that the water electric potential on a peptide bond is spatially nonhomogeneous and that the fluctuation in the electrostatic peptide-water interaction energy is about 10 times larger than the thermal energy at room temperature. This indicates that the peptide-solvent interactions are indeed important for the activation of chemical reactions in aqueous solution.

Dynamical Generation of Quasi-Stationary Alfvenic Double Layers and Charge Holes and Unified Theory of Quasi-Static and Alfvenic Auroral Arc Formation

NASA Astrophysics Data System (ADS)

Song, Y.; Lysak, R. L.

2015-12-01

Parallel E-fields play a crucial role for the acceleration of charged particles, creating discrete aurorae. However, once the parallel electric fields are produced, they will disappear right away, unless the electric fields can be continuously generated and sustained for a fairly long time. Thus, the crucial question in auroral physics is how to generate such a powerful and self-sustained parallel electric fields which can effectively accelerate charge particles to high energy during a fairly long time. We propose that nonlinear interaction of incident and reflected Alfven wave packets in inhomogeneous auroral acceleration region can produce quasi-stationary non-propagating electromagnetic plasma structures, such as Alfvenic double layers (DLs) and Charge Holes. Such Alfvenic quasi-static structures often constitute powerful high energy particle accelerators. The Alfvenic DL consists of localized self-sustained powerful electrostatic electric fields nested in a low density cavity and surrounded by enhanced magnetic and mechanical stresses. The enhanced magnetic and velocity fields carrying the free energy serve as a local dynamo, which continuously create the electrostatic parallel electric field for a fairly long time. The generated parallel electric fields will deepen the seed low density cavity, which then further quickly boosts the stronger parallel electric fields creating both Alfvenic and quasi-static discrete aurorae. The parallel electrostatic electric field can also cause ion outflow, perpendicular ion acceleration and heating, and may excite Auroral Kilometric Radiation.

The contactless detection of local normal transitions in superconducting coils by using Poynting’s vector method

NASA Astrophysics Data System (ADS)

Habu, K.; Kaminohara, S.; Kimoto, T.; Kawagoe, A.; Sumiyoshi, F.; Okamoto, H.

2010-11-01

We have developed a new monitoring system to detect an unusual event in the superconducting coils without direct contact on the coils, using Poynting's vector method. In this system, the potential leads and pickup coils are set around the superconducting coils to measure local electric and magnetic fields, respectively. By measuring the sets of magnetic and electric fields, the Poynting's vectors around the coil can be obtained. An unusual event in the coil can be detected as the result of the change of the Poynting's vector. This system has no risk of the voltage breakdown which may happen with the balance voltage method, because there is no need of direct contacts on the coil windings. In a previous paper, we have demonstrated that our system can detect the normal transitions in the Bi-2223 coil without direct contact on the coil windings by using a small test system. For our system to be applied to practical devices, it is necessary for the early detection of an unusual event in the coils to be able to detect local normal transitions in the coils. The signal voltages of the small sensors to measure local magnetic and electric fields are small. Although the increase in signals of the pickup coils is attained easily by an increase in the number of turns of the pickup coils, an increase in the signals of the potential lead is not easily attained. In this paper, a new method to amplify the signal of local electric fields around the coil is proposed. The validity of the method has been confirmed by measuring local electric fields around the Bi-2223 coil.

Visualizing Electric Fields at Au(111) Step Edges via Tip-Enhanced Raman Scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

None, None

Tip-enhanced Raman scattering (TERS) can be used to image plasmon-enhanced local electric fields on the nanoscale. This is illustrated through ambient TERS measurements recorded using silver atomic force microscope tips coated with 4-mercaptobenzonitrile molecules and used to image step edges on an Au(111) surface. The observed 2D TERS images uniquely map electric fields localized at Au(111) step edges following 671-nm excitation. We establish that our measurements are not only sensitive to spatial variations in the enhanced electric fields but also to their vector components. We also experimentally demonstrate that (i) few nanometer precision is attainable in TERS nanoscopy using corrugatedmore » tips with nominally radii on the order of 100-200 nm, and (ii) TERS signals do not necessarily exhibit the expected E4 dependence. Overall, we illustrate the concept of electric field imaging via TERS and establish the connections between our observations and conventional TERS chemical imaging measurements.« less

Electrical resistivity of liquid lanthanides using charge hard sphere system

NASA Astrophysics Data System (ADS)

Sonvane, Y. A.; Thakor, P. B.; Jani, A. R.

2013-06-01

In the present paper, we have studied electrical resistivity (ρ) of liquid lanthanides. To describe the structural information, the structure factor S(q) due to the charged hard sphere (CHS) reference systems is used along with our newly constructed model potential. To see the influence of exchange and correlation effect on the electrical resistivity (ρ) have used different local field correction functions like Hartree (H), Sarkar et al (S) and Taylor (T). Lastly we conclude that the proper choice of the model potential along with local field correction function plays a vital role to the study of the electrical resistivity (ρ).

Electric Field Distribution in High Voltage Power Modules Using Finite Element Simulations

NASA Astrophysics Data System (ADS)

Wang, Zhao; Liu, Yaoning

2018-03-01

With the development of the high voltage insulated gate bipolar transistor (IGBT) power module, it leads to serious problems concerning the electric field insulation. The electric field capabilities of the silicone gels used in the power module encapsulation directly affect the module insulation. Some solutions have been developed to optimize the electric field and reliability. In this letter, the finite element simulation was used to analyze and localize the maximum electric field position; solutions were proposed to improve the module insulation. It’s demonstrated that BaTiO3 silicone composite is a promising insulation material for high voltage power device.

[Research advances of anti-tumor immune response induced by pulse electric field ablation].

PubMed

Cui, Guang-ying; Diao, Hong-yan

2015-11-01

As a novel tumor therapy, pulse electric field has shown a clinical perspective. This paper reviews the characteristics of tumor ablation by microsecond pulse and nanosecond pulse electric field, and the research advances of anti-tumor immune response induced by pulse electric field ablation. Recent researches indicate that the pulse electric field not only leads to a complete ablation of local tumor, but also stimulates a protective immune response, thereby inhibiting tumor recurrence and metastasis. These unique advantages will show an extensive clinical application in the future. However, the mechanism of anti-tumor immune response and the development of related tumor vaccine need further studies.

Field emission properties and strong localization effect in conduction mechanism of nanostructured perovskite LaNiO{sub 3}

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kamble, Ramesh B., E-mail: rbk.physics@coep.ac.in; Department of Physics, College of Engineering, Pune 411005, Maharashtra; Tanty, Narendra

2016-08-22

We report the potential field emission of highly conducting metallic perovskite lanthanum nickelate (LaNiO{sub 3}) from the nanostructured pyramidal and whisker shaped tips as electron emitters. Nano particles of lanthanum nickelate (LNO) were prepared by sol-gel route. Structural and morphological studies have been carried out. Field emission of LNO exhibited high emission current density, J = 3.37 mA/cm{sup 2} at a low threshold electric field, E{sub th} = 16.91 V/μm, obeying Fowler–Nordheim tunneling. The DC electrical resistivity exhibited upturn at 11.6 K indicating localization of electron at low temperature. Magnetoresistance measurement at different temperatures confirmed strong localization in nanostructured LNO obeying Anderson localization effect at low temperature.

THREE-DIMENSIONAL NON-VACUUM PULSAR OUTER-GAP MODEL: LOCALIZED ACCELERATION ELECTRIC FIELD IN THE HIGHER ALTITUDES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hirotani, Kouichi

2015-01-10

We investigate the particle accelerator that arises in a rotating neutron-star magnetosphere. Simultaneously solving the Poisson equation for the electro-static potential, the Boltzmann equations for relativistic electrons and positrons, and the radiative transfer equation, we demonstrate that the electric field is substantially screened along the magnetic field lines by pairs that are created and separated within the accelerator. As a result, the magnetic-field-aligned electric field is localized in higher altitudes near the light cylinder and efficiently accelerates the positrons created in the lower altitudes outward but does not accelerate the electrons inward. The resulting photon flux becomes predominantly outward, leadingmore » to typical double-peak light curves, which are commonly observed from many high-energy pulsars.« less

Light localization and SERS in tip-shaped silicon metasurface.

PubMed

Lagarkov, Andrey; Boginskaya, Irina; Bykov, Igor; Budashov, Igor; Ivanov, Andrey; Kurochkin, Ilya; Ryzhikov, Ilya; Rodionov, Ilya; Sedova, Marina; Zverev, Alexander; Sarychev, Andrey K

2017-07-24

Optical properties of two dimensional periodic system of the silicon micro-cones are investigated. The metasurface, composed of the silicon tips, shows enhancement of the local optical field. Finite element computer simulations as well as real experiment reveal anomalous optical response of the dielectric metasurface due to excitation of the dielectric resonances. Various electromagnetic resonances are considered in the dielectric cone. The metal-dielectric resonances, which are excited between metal nanoparticles and dielectric cones, are also considered. The resonance local electric field can be much larger than the field in the usual surface plasmon resonances. To investigate local electric field the signal molecules are deposited on the metal nanoparticles. We demonstrate enhancement of the electromagnetic field and Raman signal from the complex of DTNB acid molecules and gold nanoparticles, which are distributed over the metasurface. The metasurfaces composed from the dielectric resonators can have quasi-continuous spectrum and serve as an efficient SERS substrates.

Local structural behavior of PbZr0.5Ti0.5O3 during electric field application via in situ pair distribution function study

NASA Astrophysics Data System (ADS)

Zhao, Changhao; Hou, Dong; Chung, Ching-Chang; Yu, Yingying; Liu, Wenfeng; Li, Shengtao; Jones, Jacob L.

2017-11-01

The local structural behavior of PbZr0.5Ti0.5O3 (PZT 50/50) ceramics during application of an electric field was investigated using pair distribution function (PDF) analysis. In situ synchrotron total scattering was conducted, and the PDFs were calculated from the Fourier transform of the total scattering data. The PDF refinement of the zero-field data suggests a local-structure model with [001] Ti-displacement and negligible Zr-displacement. The directional PDFs at different field amplitudes indicate the bond-length distribution of the nearest Pb-B (B = Zr/Ti) pair changes significantly with the field. The radial distribution functions (RDFs) of a model for polarization rotation were calculated. The calculated and the experimental RDFs are consistent. This result suggests the changes in Pb-B bond-length distribution could be dominantly caused by polarization rotation. Peak fitting of the experimental RDFs was also conducted. The peak position trends with increasing field are mostly in agreement with the calculation result of the polarization rotation model. The area ratio of the peaks in the experimental RDFs also changed with field amplitude, indicating that Zr atoms have a detectable displacement driven by the electric field. Our study provides an experimental observation of the behaviors of PZT 50/50 under field at a local scale which supports the polarization rotation mechanism.

From Complex B1 Mapping to Local SAR Estimation for Human Brain MR Imaging Using Multi-channel Transceiver Coil at 7T

PubMed Central

Zhang, Xiaotong; Schmitter, Sebastian; Van de Moortel, Pierre-François; Liu, Jiaen

2014-01-01

Elevated Specific Absorption Rate (SAR) associated with increased main magnetic field strength remains as a major safety concern in ultra-high-field (UHF) Magnetic Resonance Imaging (MRI) applications. The calculation of local SAR requires the knowledge of the electric field induced by radiofrequency (RF) excitation, and the local electrical properties of tissues. Since electric field distribution cannot be directly mapped in conventional MR measurements, SAR estimation is usually performed using numerical model-based electromagnetic simulations which, however, are highly time consuming and cannot account for the specific anatomy and tissue properties of the subject undergoing a scan. In the present study, starting from the measurable RF magnetic fields (B1) in MRI, we conducted a series of mathematical deduction to estimate the local, voxel-wise and subject-specific SAR for each single coil element using a multi-channel transceiver array coil. We first evaluated the feasibility of this approach in numerical simulations including two different human head models. We further conducted experimental study in a physical phantom and in two human subjects at 7T using a multi-channel transceiver head coil. Accuracy of the results is discussed in the context of predicting local SAR in the human brain at UHF MRI using multi-channel RF transmission. PMID:23508259

Inner Magnetospheric Electric Fields Derived from IMAGE EUV

NASA Technical Reports Server (NTRS)

Gallagher, D. L.; Adrian, M. L.

2007-01-01

The local and global patterns of plasmaspheric plasma transport reflect the influence of electric fields imposed by all sources in the inner magnetosphere. Image sequences of thermal plasma G:istribution obtained from the IMAGE Mission Extreme Ultraviolet Imager can be used to derive plasma motions and, using a magnetic field model, the corresponding electric fields. These motions and fields directly reflect the dynamic coupling of injected plasmasheet plasma and the ionosphere, in addition to solar wind and atmospheric drivers. What is being learned about the morphology of inner magnetospheric electric fields during storm and quite conditions from this new empirical tool will be presented and discussed.

Tip-Enhanced Raman Nanographs: Mapping Topography and Local Electric Fields

DOE PAGES

El-Khoury, Patrick Z.; Gong, Yu; Abellan, Patricia; ...

2015-03-05

We report tip-enhanced Raman scattering experiments in which topographic and local electric field images are recorded simultaneously. We employ a Raman-active 4,4’-dimercaptostilbene (DMS)-coated gold tip of an atomic force microscope to map the topography and image electric fields localized at nanometric (20 and 5 nm-wide) slits lithographically etched in silver. Bi-modal imaging is feasible by virtue of the recorded scanning probe position-dependent frequency-resolved optical response, which can be sub-divided into two components. The first is a 500-2250 cm-1 Raman-shifted signal, characteristic of DMS. The molecular response reports on topography through intensity contrast in the absence/presence of a plasmonic junction formedmore » between the scanning probe and patterned silver surface. Here, we demonstrate that sub-15 nm spatial resolution is attainable using a 30 nm DMS-coated gold tip. The second response consists of two correlated sub-500 cm-1 signals arising from mirror-like reflections of (i) the incident laser, and (ii) the Raman scattered response of an underlying glass support (at 100-500 cm-1) off the gold tip. We show that both the low-wavenumber signals trace the local electric fields in the vicinity of the nanometric slits.« less

Acceleration of 500 keV Negative Ion Beams By Tuning Vacuum Insulation Distance On JT-60 Negative Ion Source

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kojima, A.; Hanada, M.; Tanaka, Y.

2011-09-26

Acceleration of a 500 keV beam up to 2.8 A has been achieved on a JT-60U negative ion source with a three-stage accelerator by overcoming low voltage holding which is one of the critical issues for realization of the JT-60SA ion source. In order to improve the voltage holding, preliminary voltage holding tests with small-size grids with uniform and locally intense electric fields were carried out, and suggested that the voltage holding was degraded by both the size and local electric field effects. Therefore, the local electric field was reduced by tuning gap lengths between the large size grids andmore » grid support structures of the accelerator. Moreover, a beam radiation shield which limited extension of the minimum gap length was also optimized so as to reduce the local electric field while maintaining the shielding effect. These modifications were based on the experiment results, and significantly increased the voltage holding from <150 kV/stage for the original configuration to 200 kV/stage. These techniques for improvement of voltage holding should also be applicable to other large ion sources accelerators such as those for ITER.« less

Electric field distribution and current emission in a miniaturized geometrical diode

NASA Astrophysics Data System (ADS)

Lin, Jinpu; Wong, Patrick Y.; Yang, Penglu; Lau, Y. Y.; Tang, W.; Zhang, Peng

2017-06-01

We study the electric field distribution and current emission in a miniaturized geometrical diode. Using Schwarz-Christoffel transformation, we calculate exactly the electric field inside a finite vacuum cathode-anode (A-K) gap with a single trapezoid protrusion on one of the electrode surfaces. It is found that there is a strong field enhancement on both electrodes near the protrusion, when the ratio of the A-K gap distance to the protrusion height d /h <2. The calculations are spot checked against COMSOL simulations. We calculate the effective field enhancement factor for the field emission current, by integrating the local Fowler-Nordheim current density along the electrode surfaces. We systematically examine the electric field enhancement and the current rectification of the miniaturized geometrical diode for various geometric dimensions and applied electric fields.

Dynamic Stark spectroscopic measurements of microwave electric fields inside the plasma near a high-power antenna.

PubMed

Klepper, C C; Isler, R C; Hillairet, J; Martin, E H; Colas, L; Ekedahl, A; Goniche, M; Harris, J H; Hillis, D L; Panayotis, S; Pegourié, B; Lotte, Ph; Colledani, G; Martin, V

2013-05-24

Fully dynamic Stark effect visible spectroscopy was used for the first time to directly measure the local rf electric field in the boundary plasma near a high-power antenna in high-performance, magnetically confined, fusion energy experiment. The measurement was performed in the superconducting tokamak Tore Supra, in the near field of a 1–3 MW, lower-hybrid, 3.7 GHz wave-launch antenna, and combined with modeling of neutral atom transport to estimate the local rf electric field amplitude (as low as 1–2 kV/cm) and direction in this region. The measurement was then shown to be consistent with the predicted values from a 2D full-wave propagation model. Notably the measurement confirmed that the electric field direction deviates substantially from the direction in which it is launched by the waveguides as it penetrates only a few cm radially inward into the plasma from the waveguides, consistent with the model.

Large plasmaspheric electric fields at L approximately 2 measured by the S3-3 satellite during strong geomagnetic activity

NASA Technical Reports Server (NTRS)

Gonzalez, W. D.; Pinto, O., Jr.; Mendes, O., Jr.; Mozer, F. S.

1986-01-01

Large plasmaspheric electric fields at L is approximately 2 measured by the S3-3 satellite during strong geomagnetic activity are reported. Since these measurements have amplitudes comparable to those of the local corotation electric field, during such events the plasmasphere is expected to get strongly altered event at such low L-values. Furthermore, those measurements could contribute to the understanding of the physics of the convection/electric field penetration to the low latitude plasmaphere as well as the disturbed dynamo, during strong geomagnetic activity. For this purpose, critical parameters related to geomagnetic activity are also presented for the reported electric field events.

Local time distribution of the SSC-associated HF-Doppler frequency shifts

NASA Technical Reports Server (NTRS)

Kikuchi, T.; Sugiuchi, H.; Ishimine, T.

1985-01-01

The HF-Doppler frequency shift observed at the storm's sudden commencement is composed of a frequency increase (+) and decrease (-), and classified into four types, SCF(+ -), SCF(- +), SCF(+) and SCF(-). Since the latter two types are special cases of the former two types, two different kinds of electrical field exist in the F region and cause the ExB drift motion of plasma. HUANG (1976) interpreted the frequency increase of SCF(+ -) as due to the westward induction electric field proportional to delta H/ delta t and the succeeding frequency decrease due to the eastward conduction electric field which produces ionospheric currents responsible for the magnetic increase on the ground. In spite of his success in interpreting the SCF(+ -), some other interpretations are needed for the explanation of the whole set of SCF's, particularly SCF(- +). Local time distributions of the SCF's are derived from 41 SCF's which are observed on the HF standard signal (JJY) as received in Okinawa (path length =1600 km) and Kokubunji (60 km). It is shown that the SCF(+ -) appears mainly during the day, whereas the SCF(- +) is observed during the night. The results indicate that the preliminary frequency shift (+) of SCF(+ -) and (-) of SCF(- +) is caused by a westward electric field in the dayside hemisphere, while by an eastward electric field in the nightside hemisphere. The main frequency shift (-) of SCF(+ -) and (+) of SCF(- +) is caused by the reversed electric field. Consequently, the preliminary frequency shift is caused by the dusk-to-dawn electric field, while the main frequency shift by the dawn-to-dusk electric field.

Nanomaterial-Enabled Neural Stimulation

PubMed Central

Wang, Yongchen; Guo, Liang

2016-01-01

Neural stimulation is a critical technique in treating neurological diseases and investigating brain functions. Traditional electrical stimulation uses electrodes to directly create intervening electric fields in the immediate vicinity of neural tissues. Second-generation stimulation techniques directly use light, magnetic fields or ultrasound in a non-contact manner. An emerging generation of non- or minimally invasive neural stimulation techniques is enabled by nanotechnology to achieve a high spatial resolution and cell-type specificity. In these techniques, a nanomaterial converts a remotely transmitted primary stimulus such as a light, magnetic or ultrasonic signal to a localized secondary stimulus such as an electric field or heat to stimulate neurons. The ease of surface modification and bio-conjugation of nanomaterials facilitates cell-type-specific targeting, designated placement and highly localized membrane activation. This review focuses on nanomaterial-enabled neural stimulation techniques primarily involving opto-electric, opto-thermal, magneto-electric, magneto-thermal and acousto-electric transduction mechanisms. Stimulation techniques based on other possible transduction schemes and general consideration for these emerging neurotechnologies are also discussed. PMID:27013938

Electric control of emergent magnonic spin current and dynamic multiferroicity in magnetic insulators at finite temperatures

NASA Astrophysics Data System (ADS)

Wang, Xi-guang; Chotorlishvili, L.; Guo, Guang-hua; Berakdar, J.

2018-04-01

Conversion of thermal energy into magnonic spin currents and/or effective electric polarization promises new device functionalities. A versatile approach is presented here for generating and controlling open circuit magnonic spin currents and an effective multiferroicity at a uniform temperature with the aid of spatially inhomogeneous, external, static electric fields. This field applied to a ferromagnetic insulator with a Dzyaloshinskii-Moriya type coupling changes locally the magnon dispersion and modifies the density of thermally excited magnons in a region of the scale of the field inhomogeneity. The resulting gradient in the magnon density can be viewed as a gradient in the effective magnon temperature. This effective thermal gradient together with local magnon dispersion result in an open-circuit, electric field controlled magnonic spin current. In fact, for a moderate variation in the external electric field the predicted magnonic spin current is on the scale of the spin (Seebeck) current generated by a comparable external temperature gradient. Analytical methods supported by full-fledge numerics confirm that both, a finite temperature and an inhomogeneous electric field are necessary for this emergent non-equilibrium phenomena. The proposal can be integrated in magnonic and multiferroic circuits, for instance to convert heat into electrically controlled pure spin current using for example nanopatterning, without the need to generate large thermal gradients on the nanoscale.

Statistical electric field and switching time distributions in PZT 1Nb2Sr ceramics: Crystal- and microstructure effects

NASA Astrophysics Data System (ADS)

Zhukov, Sergey; Kungl, Hans; Genenko, Yuri A.; von Seggern, Heinz

2014-01-01

Dispersive polarization response of ferroelectric PZT ceramics is analyzed assuming the inhomogeneous field mechanism of polarization switching. In terms of this model, the local polarization switching proceeds according to the Kolmogorov-Avrami-Ishibashi scenario with the switching time determined by the local electric field. As a result, the total polarization reversal is dominated by the statistical distribution of the local field magnitudes. Microscopic parameters of this model (the high-field switching time and the activation field) as well as the statistical field and consequent switching time distributions due to disorder at a mesoscopic scale can be directly determined from a set of experiments measuring the time dependence of the total polarization switching, when applying electric fields of different magnitudes. PZT 1Nb2Sr ceramics with Zr/Ti ratios 51.5/48.5, 52.25/47.75, and 60/40 with four different grain sizes each were analyzed following this approach. Pronounced differences of field and switching time distributions were found depending on the Zr/Ti ratios. Varying grain size also affects polarization reversal parameters, but in another way. The field distributions remain almost constant with grain size whereas switching times and activation field tend to decrease with increasing grain size. The quantitative changes of the latter parameters with grain size are very different depending on composition. The origin of the effects on the field and switching time distributions are related to differences in structural and microstructural characteristics of the materials and are discussed with respect to the hysteresis loops observed under bipolar electrical cycling.

Nanomechanical electric and electromagnetic field sensor

DOEpatents

Datskos, Panagiotis George; Lavrik, Nickolay

2015-03-24

The present invention provides a system for detecting and analyzing at least one of an electric field and an electromagnetic field. The system includes a micro/nanomechanical oscillator which oscillates in the presence of at least one of the electric field and the electromagnetic field. The micro/nanomechanical oscillator includes a dense array of cantilevers mounted to a substrate. A charge localized on a tip of each cantilever interacts with and oscillates in the presence of the electric and/or electromagnetic field. The system further includes a subsystem for recording the movement of the cantilever to extract information from the electric and/or electromagnetic field. The system further includes a means of adjusting a stiffness of the cantilever to heterodyne tune an operating frequency of the system over a frequency range.

Electric Field Simulation of Surge Capacitors with Typical Defects

NASA Astrophysics Data System (ADS)

Zhang, Chenmeng; Mao, Yuxiang; Xie, Shijun; Zhang, Yu

2018-03-01

The electric field of power capacitors with different typical defects in DC working condition and impulse oscillation working condition is studied in this paper. According to the type and location of defects and considering the influence of space charge, two-dimensional models of surge capacitors with different typical defects are simulated based on ANSYS. The distribution of the electric field inside the capacitor is analyzed, and the concentration of electric field and its influence on the insulation performance are obtained. The results show that the type of defects, the location of defects and the space charge all affect the electric field distribution inside the capacitor in varying degrees. Especially the electric field distortion in the local area such as sharp corners and burrs is relatively larger, which increases the probability of partial discharge inside the surge capacitor.

Evaluation of the induced electric field and compliance procedure for a wireless power transfer system in an electrical vehicle.

PubMed

Laakso, Ilkka; Hirata, Akimasa

2013-11-07

In this study, an induced electric field in a human body is evaluated for the magnetic field leaked from a wireless power transfer system for charging an electrical vehicle. The magnetic field from the wireless power transfer system is modelled computationally, and its effectiveness is confirmed by comparison with the field measured in a previous study. The induced electric field in a human standing around the vehicle is smaller than the allowable limit prescribed in international guidelines, although the magnetic field strength in the human body is locally higher than the allowable external field strength. Correlation between the external magnetic field and the induced electric field is confirmed to be reasonable at least in the standing posture, which is the case discussed in the international standard. Based on this finding, we discussed and confirmed the applicability of a three-point magnetic field measurement at heights of 0.5, 1.0, and 1.5 m for safety compliance.

Electrostatic ion instabilities in the presence of parallel currents and transverse electric fields

NASA Technical Reports Server (NTRS)

Ganguli, G.; Palmadesso, P. J.

1988-01-01

The electrostatic ion instabilities are studied for oblique propagation in the presence of magnetic field-aligned currents and transverse localized electric fields in a weakly collisional plasma. The presence of transverse electric fields result in mode excitation for magnetic field aligned current values that are otherwise stable. The electron collisions enhance the growth while ion collisions have a damping effect. These results are discussed in the context of observations of low frequency ion modes in the auroral ionosphere by radar and rocket experiments.

Electric-field control of conductance in metal quantum point contacts by electric-double-layer gating

NASA Astrophysics Data System (ADS)

Shibata, K.; Yoshida, K.; Daiguji, K.; Sato, H.; , T., Ii; Hirakawa, K.

2017-10-01

An electric-field control of quantized conductance in metal (gold) quantum point contacts (QPCs) is demonstrated by adopting a liquid-gated electric-double-layer (EDL) transistor geometry. Atomic-scale gold QPCs were fabricated by applying the feedback-controlled electrical break junction method to the gold nanojunction. The electric conductance in gold QPCs shows quantized conductance plateaus and step-wise increase/decrease by the conductance quantum, G0 = 2e2/h, as EDL-gate voltage is swept, demonstrating a modulation of the conductance of gold QPCs by EDL gating. The electric-field control of conductance in metal QPCs may open a way for their application to local charge sensing at room temperature.

Domain switching mechanisms in polycrystalline ferroelectrics with asymmetric hysteretic behavior

NASA Astrophysics Data System (ADS)

Anton, Eva-Maria; García, R. Edwin; Key, Thomas S.; Blendell, John E.; Bowman, Keith J.

2009-01-01

A numerical method is presented to predict the effect of microstructure on the local polarization switching of bulk ferroelectric ceramics. The model shows that a built-in electromechanical field develops in a ferroelectric material as a result of the spatial coupling of the grains and the direct physical coupling between the thermomechanical and electromechanical properties of a bulk ceramic material. The built-in fields that result from the thermomechanically induced grain-grain electromechanical interactions result in the appearance of four microstructural switching mechanisms: (1) simple switching, where the c-axes of ferroelectric domains will align with the direction of the applied macroscopic electric field by starting from the core of each grain; (2) grain boundary induced switching, where the domain's switching response will initiate at grain corners and boundaries as a result of the polarization and stress that is locally generated from the strong anisotropy of the dielectric permittivity and the local piezoelectric contributions to polarization from the surrounding material; (3) negative poling, where abutting ferroelectric domains of opposite polarity actively oppose domain switching by increasing their degree of tetragonality by interacting with the surrounding domains that have already switched to align with the applied electrostatic field. Finally, (4) domain reswitching mechanism is observed at very large applied electric fields, and is characterized by the appearance of polarization domain reversals events in the direction of their originally unswitched state. This mechanism is a consequence of the competition between the macroscopic applied electric field, and the induced electric field that results from the neighboring domains (or grains) interactions. The model shows that these built-in electromechanical fields and mesoscale mechanisms contribute to the asymmetry of the macroscopic hysteretic behavior in poled samples. Furthermore, below a material-dependent operating temperature, the predicted built-in electric fields can potentially drive the aging and electrical fatigue of the system to further skew the shape of the hysteresis loops.

Simulations of electrically induced particle structuring on spherical drop surface

NASA Astrophysics Data System (ADS)

Hu, Yi; Vlahovska, Petia; Miksis, Michael

2016-11-01

Recent experiments (Ouriemi and Vlahovska, 2014) show intriguing surface patterns when a uniform electric field is applied to a droplet covered with colloidal particles. Depending on the particle properties and the electrical field intensity, particles organize into an equatorial belt, pole-to-pole chains, or dynamic vortices. Here we present a model to simulate the collective particle dynamics, which accounts for the electrohydrodynamic flow and particle dielectrophoresis due to the non-uniformity of local electrical field. In stronger electric fields, particles are expected to undergo Quincke rotation, inducing rotating clusters through inter-particle hydrodynamical interaction. We discuss how the field intensity influences the width, orientation and periodicity of the particle clusters. Our results provide insight into the various particle assembles discovered in the experiments.

Electrical coupling of single cardiac rat myocytes to field-effect and bipolar transistors.

PubMed

Kind, Thomas; Issing, Matthias; Arnold, Rüdiger; Müller, Bernt

2002-12-01

A novel bipolar transistor for extracellular recording the electrical activity of biological cells is presented, and the electrical behavior compared with the field-effect transistor (FET). Electrical coupling is examined between single cells separated from the heart of adults rats (cardiac myocytes) and both types of transistors. To initiate a local extracellular voltage, the cells are periodically stimulated by a patch pipette in voltage clamp and current clamp mode. The local extracellular voltage is measured by the planar integrated electronic sensors: the bipolar and the FET. The small signal transistor currents correspond to the local extracellular voltage. The two types of sensor transistors used here were developed and manufactured in the laboratory of our institute. The manufacturing process and the interfaces between myocytes and transistors are described. The recordings are interpreted by way of simulation based on the point-contact model and the single cardiac myocyte model.

Simulation of Space Charge Dynamic in Polyethylene Under DC Continuous Electrical Stress

NASA Astrophysics Data System (ADS)

Boukhari, Hamed; Rogti, Fatiha

2016-10-01

The space charge dynamic plays a very important role in the aging and breakdown of polymeric insulation materials under high voltage. This is due to the intensification of the local electric field and the attendant chemical-mechanical effects in the vicinity around the trapped charge. In this paper, we have investigated the space charge dynamic in low-density polyethylene under high direct-current voltage, which is evaluated by experimental conditions. The evaluation is on the basis of simulation using a bipolar charge transport model consisting of charge injection, transports, trapping, detrapping, and recombination phenomena. The theoretical formulation of the physical problem is based on the Poisson, the continuity, and the transport equations. Numerical results provide temporal and local distributions of the electric field, the space charge density for the different kinds of charges (net charge density, mobile and trapped of electron density, mobile hole density), conduction and displacement current densities, and the external current. The result shows the appearance of the negative packet-like space charge with a large amount of the bulk under the dc electric field of 100 kV/mm, and the induced distortion of the electric field is largely near to the anode, about 39% higher than the initial electric field applied.

Scalable Manufacturing of Plasmonic Nanodisk Dimers and Cusp Nanostructures using Salting-out Quenching Method and Colloidal Lithography

PubMed Central

Juluri, Bala Krishna; Chaturvedi, Neetu; Hao, Qingzhen; Lu, Mengqian; Velegol, Darrell; Jensen, Lasse; Huang, Tony Jun

2014-01-01

Localization of large electric fields in plasmonic nanostructures enables various processes such as single molecule detection, higher harmonic light generation, and control of molecular fluorescence and absorption. High-throughput, simple nanofabrication techniques are essential for implementing plasmonic nanostructures with large electric fields for practical applications. In this article we demonstrate a scalable, rapid, and inexpensive fabrication method based on the salting-out quenching technique and colloidal lithography for the fabrication of two types of nanostructures with large electric field: nanodisk dimers and cusp nanostructures. Our technique relies on fabricating polystyrene doublets from single beads by controlled aggregation and later using them as soft masks to fabricate metal nanodisk dimers and nanocusp structures. Both of these structures have a well-defined geometry for the localization of large electric fields comparable to structures fabricated by conventional nanofabrication techniques. We also show that various parameters in the fabrication process can be adjusted to tune the geometry of the final structures and control their plasmonic properties. With advantages in throughput, cost, and geometric tunability, our fabrication method can be valuable in many applications that require plasmonic nanostructures with large electric fields. PMID:21692473

SAR Reduction in 7T C-Spine Imaging Using a “Dark Modes” Transmit Array Strategy

PubMed Central

Eryaman, Yigitcan; Guerin, Bastien; Keil, Boris; Mareyam, Azma; Herraiz, Joaquin L.; Kosior, Robert K.; Martin, Adrian; Torrado-Carvajal, Angel; Malpica, Norberto; Hernandez-Tamames, Juan A.; Schiavi, Emanuele; Adalsteinsson, Elfar; Wald, Lawrence L.

2016-01-01

Purpose Local specific absorption rate (SAR) limits many applications of parallel transmit (pTx) in ultra high-field imaging. In this Note, we introduce the use of an array element, which is intentionally inefficient at generating spin excitation (a “dark mode”) to attempt a partial cancellation of the electric field from those elements that do generate excitation. We show that adding dipole elements oriented orthogonal to their conventional orientation to a linear array of conventional loop elements can lower the local SAR hotspot in a C-spine array at 7 T. Methods We model electromagnetic fields in a head/torso model to calculate SAR and excitation B1+ patterns generated by conventional loop arrays and loop arrays with added electric dipole elements. We utilize the dark modes that are generated by the intentional and inefficient orientation of dipole elements in order to reduce peak 10g local SAR while maintaining excitation fidelity. Results For B1+ shimming in the spine, the addition of dipole elements did not significantly alter the B1+ spatial pattern but reduced local SAR by 36%. Conclusion The dipole elements provide a sufficiently complimentary B1+ and electric field pattern to the loop array that can be exploited by the radiofrequency shimming algorithm to reduce local SAR. PMID:24753012

The role of Hurst exponent on cold field electron emission from conducting materials: from electric field distribution to Fowler-Nordheim plots

PubMed Central

de Assis, T. A.

2015-01-01

This work considers the effects of the Hurst exponent (H) on the local electric field distribution and the slope of the Fowler-Nordheim (FN) plot when considering the cold field electron emission properties of rough Large-Area Conducting Field Emitter Surfaces (LACFESs). A LACFES is represented by a self-affine Weierstrass-Mandelbrot function in a given spatial direction. For 0.1 ≤ H < 0.5, the local electric field distribution exhibits two clear exponential regimes. Moreover, a scaling between the macroscopic current density () and the characteristic kernel current density (), , with an H-dependent exponent , has been found. This feature, which is less pronounced (but not absent) in the range where more smooth surfaces have been found (), is a consequence of the dependency between the area efficiency of emission of a LACFES and the macroscopic electric field, which is often neglected in the interpretation of cold field electron emission experiments. Considering the recent developments in orthodox field emission theory, we show that the exponent must be considered when calculating the slope characterization parameter (SCP) and thus provides a relevant method of more precisely extracting the characteristic field enhancement factor from the slope of the FN plot. PMID:26035290

Convective Flow Induced by Localized Traveling Magnetic Fields

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Rose, M. Franklin (Technical Monitor)

2001-01-01

An axisymmetric traveling magnetic field induces a meridional base flow in a cylindrical zone of an electrically conducting liquid. This remotely induced flow can be conveniently controlled, in magnitude and direction, and can have benefits for crystal growth applications. In particular, it can be used to offset natural convection. For long vertical cylinders, non-uniform and localized in the propagating direction, magnetic fields are required for this purpose. Here we investigate a particular form of this field, namely that induced by a set of a few electric current coils. An order of magnitude reduction of buoyancy convection is theoretically demonstrated for a vertical Bridgman crystal growth configuration.

Low-intensity electric fields induce two distinct response components in neocortical neuronal populations

PubMed Central

Xu, Weifeng; Wolff, Brian S.

2014-01-01

Low-intensity alternating electric fields applied to the scalp are capable of modulating cortical activity and brain functions, but the underlying mechanisms remain largely unknown. Here, we report two distinct components of voltage-sensitive dye signals induced by low-intensity, alternating electric fields in rodent cortical slices: a “passive component,” which corresponds to membrane potential changes directly induced by the electric field; and an “active component,” which is a widespread depolarization that is dependent on excitatory synaptic transmission. The passive component is stationary, with amplitude and phase accurately reflecting the cortical cytoarchitecture. In contrast, the active component is initiated from a local “hot spot” of activity and spreads to a large population as a propagating wave with rich local dynamics. The propagation of the active component may play a role in modulating large-scale cortical activity by spreading a low level of excitation from a small initiation point to a vast neuronal population. PMID:25122710

Quantitative prediction of radio frequency induced local heating derived from measured magnetic field maps in magnetic resonance imaging: A phantom validation at 7 T

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Xiaotong; Liu, Jiaen; Van de Moortele, Pierre-Francois

2014-12-15

Electrical Properties Tomography (EPT) technique utilizes measurable radio frequency (RF) coil induced magnetic fields (B1 fields) in a Magnetic Resonance Imaging (MRI) system to quantitatively reconstruct the local electrical properties (EP) of biological tissues. Information derived from the same data set, e.g., complex numbers of B1 distribution towards electric field calculation, can be used to estimate, on a subject-specific basis, local Specific Absorption Rate (SAR). SAR plays a significant role in RF pulse design for high-field MRI applications, where maximum local tissue heating remains one of the most constraining limits. The purpose of the present work is to investigate themore » feasibility of such B1-based local SAR estimation, expanding on previously proposed EPT approaches. To this end, B1 calibration was obtained in a gelatin phantom at 7 T with a multi-channel transmit coil, under a particular multi-channel B1-shim setting (B1-shim I). Using this unique set of B1 calibration, local SAR distribution was subsequently predicted for B1-shim I, as well as for another B1-shim setting (B1-shim II), considering a specific set of parameter for a heating MRI protocol consisting of RF pulses plaid at 1% duty cycle. Local SAR results, which could not be directly measured with MRI, were subsequently converted into temperature change which in turn were validated against temperature changes measured by MRI Thermometry based on the proton chemical shift.« less

Heisenberg spin-1/2 XXZ chain in the presence of electric and magnetic fields

NASA Astrophysics Data System (ADS)

Thakur, Pradeep; Durganandini, P.

2018-02-01

We study the interplay of electric and magnetic order in the one-dimensional Heisenberg spin-1/2 XXZ chain with large Ising anisotropy in the presence of the Dzyaloshinskii-Moriya (DM) interaction and with longitudinal and transverse magnetic fields, interpreting the DM interaction as a coupling between the local electric polarization and an external electric field. We obtain the ground state phase diagram using the density matrix renormalization group method and compute various ground state quantities like the magnetization, staggered magnetization, electric polarization and spin correlation functions, etc. In the presence of both longitudinal and transverse magnetic fields, there are three different phases corresponding to a gapped Néel phase with antiferromagnetic (AF) order, gapped saturated phase, and a critical incommensurate gapless phase. The external electric field modifies the phase boundaries but does not lead to any new phases. Both external magnetic fields and electric fields can be used to tune between the phases. We also show that the transverse magnetic field induces a vector chiral order in the Néel phase (even in the absence of an electric field) which can be interpreted as an electric polarization in a direction parallel to the AF order.

The Circle of Apollonius and Its Applications in Introductory Physics

NASA Astrophysics Data System (ADS)

Partensky, Michael B.

2008-02-01

The circle of Apollonius is named after the ancient geometrician Apollonius of Perga. This beautiful geometric construct can be helpful when solving some general problems of geometry and mathematical physics, optics, and electricity. Here we discuss two of its applications: localizing an object in space and calculating electric fields. First, we pose an entertaining localization problem to trigger students' interest in the subject. Analyzing this problem, we introduce the circle of Apollonius and show that this geometric technique helps solve the problem in an elegant and intuitive manner. Then we switch to seemingly unrelated problems of calculating the electric fields. We show that the zero equipotential line for two unlike charges is the Apollonius circle for these two charges and use this discovery to find the electric field of a charge positioned near a grounded conductive sphere. Finally, we pose some questions for further examination.

Regional United States electric field and GIC hazard impacts (Invited)

NASA Astrophysics Data System (ADS)

Gannon, J. L.; Balch, C. C.; Trichtchenko, L.

2013-12-01

Geomagnetically Induced Currents (GICs) are primarily driven by impulsive geomagnetic disturbances created by the interaction between the Earth's magnetosphere and sharp velocity, density, and magnetic field enhancements in the solar wind. However, the magnitude of the induced electric field response at the ground level, and therefore the resulting hazard to the bulk power system, is determined not only by magnetic drivers, but also by the underlying geology. Convolution techniques are used to calculate surface electric fields beginning from the spectral characteristics of magnetic field drivers and the frequency response of the local geology. Using these techniques, we describe historical scenarios for regions across the United States, and the potential impact of large events on electric power infrastructure.

On the generation of double layers from ion- and electron-acoustic instabilities

NASA Astrophysics Data System (ADS)

Fu, Xiangrong; Cowee, Misa M.; Gary, S. Peter; Winske, Dan

2016-03-01

A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric field structures traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs—electron acoustic DLs—generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e., the hypothetical electron acoustic DLs cannot be formed in a way similar to ion acoustic DLs. Linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric field structures that propagate at the electron thermal speed, suggesting another potential explanation for the observations.

In-situ electric field in human body model in different postures for wireless power transfer system in an electrical vehicle.

PubMed

Shimamoto, Takuya; Laakso, Ilkka; Hirata, Akimasa

2015-01-07

The in-situ electric field of an adult male model in different postures is evaluated for exposure to the magnetic field leaked from a wireless power transfer system in an electrical vehicle. The transfer system is located below the centre of the vehicle body and the transferred power and frequency are 7 kW and 85 kHz, respectively. The in-situ electric field is evaluated for a human model (i) crouching near the vehicle, (ii) lying on the ground with or without his arm stretched, (iii) sitting in the driver's seat, and (iv) standing on a transmitting coil without a receiving coil. In each scenario, the maximum in-situ electric fields are lower than the allowable limit prescribed by international guidelines, although the local magnetic field strength in regions of the human body is higher than the allowable external magnetic field strength. The highest in-situ electric field is observed when the human body model is placed on the ground with his arm extended toward the coils, because of a higher magnetic field around the arm.

Theoretical evaluation of maximum electric field approximation of direct band-to-band tunneling Kane model for low bandgap semiconductors

NASA Astrophysics Data System (ADS)

Dang Chien, Nguyen; Shih, Chun-Hsing; Hoa, Phu Chi; Minh, Nguyen Hong; Thi Thanh Hien, Duong; Nhung, Le Hong

2016-06-01

The two-band Kane model has been popularly used to calculate the band-to-band tunneling (BTBT) current in tunnel field-effect transistor (TFET) which is currently considered as a promising candidate for low power applications. This study theoretically clarifies the maximum electric field approximation (MEFA) of direct BTBT Kane model and evaluates its appropriateness for low bandgap semiconductors. By analysing the physical origin of each electric field term in the Kane model, it has been elucidated in the MEFA that the local electric field term must be remained while the nonlocal electric field terms are assigned by the maximum value of electric field at the tunnel junction. Mathematical investigations have showed that the MEFA is more appropriate for low bandgap semiconductors compared to high bandgap materials because of enhanced tunneling probability in low field regions. The appropriateness of the MEFA is very useful for practical uses in quickly estimating the direct BTBT current in low bandgap TFET devices.

Externally-Driven Onset of Localized Magnetic Reconnection in a Magnetotail Configuration

NASA Astrophysics Data System (ADS)

Pritchett, P. L.; Lu, S.

2017-12-01

In observations of the nightside auroral arcs and ionospheric currents, the onset or breakup phase of a substorm is sharply defined in time and is highly localized in space. Attempts to understand this localization in terms of the onset of localized magnetic reconnection have generally been unsuccessful. Thus, a y-localized driving convection electric field Ey applied at the lobe boundaries spreads out before it reaches the equatorial plane and results only in 2-D reconnection. In this work, the response of a magnetotail equilibrium containing a dipole magnetic field and plasma sheet regions to the imposition of a longitudinally-limited, high-latitude driving electric field is investigated using 3-D particle-in-cell simulations. The initial response involves a reduction in the equatorial Bz field that is then followed by the development of a dawn-dusk asymmetric current sheet relative to the meridian plane of the driving field. The key feature is the presence of a dusk-side Hall electric field Ez that drives magnetic flux dawnward and thus further reduces the Bz field on the duskward side. The net result is that Bz is driven through zero in a localized region on the duskward side, leading to the onset of localized reconnection and the emergence of magnetic flux ropes. The cross-tail extent of the reconnection expands but remains limited to ˜30di, where di is the ion inertia length. The dissipation E' \\cdot J is peaked along the finite X line, with a load region (negative E' \\cdot J) forming tailward of this region. The particle energy spectra in the downtail region show shoulders for the ions in the energy range ˜3-8Eth (Eth is the initial thermal energy) and extended tails for the electrons in the range ˜10-20Eth. These results demonstrate the ability of a high-latitude disturbance that may be connected to dayside flow channels [Nishimura et al., 2014] to initiate localized magnetic reconnection in the magnetotail.

Generation of Alfvenic Double Layers, Formation of Auroral Arcs, and Their Impact on Energy and Momentum Transfer in M-I Coupling System

NASA Astrophysics Data System (ADS)

Song, Y.; Lysak, R. L.

2017-12-01

Parallel electrostatic electric fields provide a powerful mechanism to accelerate auroral particles to high energy in the auroral acceleration region (AAR), creating both quasi-static and Alfvenic discrete aurorae. The total field-aligned current can be written as J||total=J||+J||D, where the displacement current is denoted as J||D=(1/4π)(∂E||/∂t), which describes the E||-generation (Song and Lysak, 2006). The generation of the total field-aligned current is related to spatial gradients of the parallel vorticity caused by the axial torque acting on field-aligned flux tubes in M-I coupling system. It should be noticed that parallel electric fields are not produced by the field-aligned current. In fact, the E||-generation is caused by Alfvenic interaction in the M-I coupling system, and is favored by a low plasma density and the enhanced localized azimuthal magnetic flux. We suggest that the nonlinear interaction of incident and reflected Alfven wave packets in the AAR can create reactive stress concentration, and therefore can generate the parallel electrostatic electric fields together with a seed low density cavity. The generated electric fields will quickly deepen the seed low density cavity, which can effectively create even stronger electrostatic electric fields. The electrostatic electric fields nested in a low density cavity and surrounded by enhanced azimuthal magnetic flux constitute Alfvenic electromagnetic plasma structures, such as Alfvenic Double Layers (DLs). The Poynting flux carried by Alfven waves can continuously supply energy from the generator region to the auroral acceleration region, supporting and sustaining Alfvenic DLs with long-lasting electrostatic electric fields which accelerate auroral particles to high energy. The generation of parallel electric fields and the formation of auroral arcs can redistribute perpendicular mechanical and magnetic stresses in auroral flux tubes, decoupling the magnetosphere from ionosphere drag locally. This may enhance the magnetotail earthward shear flows and rapidly buildup stronger parallel electric fields in the auroral acceleration region, leading to a sudden and violent tail energy release, if there is accumulated free magnetic energy in the tail.

Macrocognition in Teams and Analysis of Information Flow During the Haiti Disaster Relief

DTIC Science & Technology

2011-06-01

supplies, clean water and electricity. TIE TIE TIE Local soccer field is now a safe landing ground for helicopters. TIE TIE TIE Five flights have...TIE TIE OR’s adequate medical supplies, clean water and electricity (generator) TIE TIE TIE Local soccer field is landing pad. TIE TIE TIE 5... soccer /helo pad, TIE TIE TIE Have own ambulances for transport. TIE TIE TIE 62 Contact: "NAME" (Ground Coordinator) Haiti cell "PHONE", "E

Communication: Influence of external static and alternating electric fields on water from long-time non-equilibrium ab initio molecular dynamics

NASA Astrophysics Data System (ADS)

Futera, Zdenek; English, Niall J.

2017-07-01

The response of water to externally applied electric fields is of central relevance in the modern world, where many extraneous electric fields are ubiquitous. Historically, the application of external fields in non-equilibrium molecular dynamics has been restricted, by and large, to relatively inexpensive, more or less sophisticated, empirical models. Here, we report long-time non-equilibrium ab initio molecular dynamics in both static and oscillating (time-dependent) external electric fields, therefore opening up a new vista in rigorous studies of electric-field effects on dynamical systems with the full arsenal of electronic-structure methods. In so doing, we apply this to liquid water with state-of-the-art non-local treatment of dispersion, and we compute a range of field effects on structural and dynamical properties, such as diffusivities and hydrogen-bond kinetics.

10 CFR 35.642 - Periodic spot-checks for teletherapy units.

Code of Federal Regulations, 2010 CFR

2010-01-01

... coincidence of the radiation field and the field indicated by the light beam localizing device; (4) The... to assure proper operation of— (1) Electrical interlocks at each teletherapy room entrance; (2) Electrical or mechanical stops installed for the purpose of limiting use of the primary beam of radiation...

Theoretical investigation of discharge parameters in magnetized radio frequency excited CO2 lasers

NASA Astrophysics Data System (ADS)

Tavassoli, H.; Sohbatzadeh, F.; Latifi, H.

2003-06-01

In the present paper the magnetic field effects on discharge parameters in rf excited CO2 lasers are calculated. A rf generated plasma imbedded in an external, constant, and homogeneous magnetic field is considered. The continuity equation is used to derive the electron density. Quasineutrality condition and ambipolar diffusion are used. Electron attachment coefficient is neglected. Local electric field, local electron density, and thickness of charge layers are derived as a function of distance from the electrodes and magnetic field. The thickness of charge layers in the presence of magnetic field is always smaller than one without the magnetic field. When the magnetic field increases, the electron density increases in all regions of discharge, and the electric field reduces in the charge layers but increases in the middle part of discharge.

First and subsequent return stroke properties of cloud-to-ground lightning

NASA Technical Reports Server (NTRS)

Namasivayam, S.; Lundquist, Stig

1991-01-01

Lightning properties obtained by a network of magnetic direction finders and by electric field measurements for distances from 50 to 500 km are compared for three summer thunderstorms in Sweden. The data from direct field recordings indicate 31, 17, and 26 pcts. of negative subsequent return strokes with peak current (as inferred from the peak electric field) higher than the first. Electric fields from first strokes are compared with normalized amplitudes registered by the magnetic direction finding system. The efficiency of detection by the magnetic direction finding system is discussed in terms of the percentage of lightning flashes observed by electric field measurements that are not localized. Statistics of the number of strokes per flash and the interstroke time intervals are presented.

Horizontal electric fields from lightning return strokes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thomson, E.M.; Uman, M.A.; Johnson, J.

1985-01-01

Measurements are presented of simultaneous horizontal and vertical electric fields from both close and distant lightning return strokes. The data were obtained during summer 1984 at the Kennedy Space Center, Florida, using an electrically isolated spherical antenna having a system bandwidth of 3 Hz to 5 MHz. Lightning signals were obtained from flashes at distances from a few to 100 kilometers. Since the horizontal electric field is in part determined by the local ground conductivity, that parameter was measured as a function of depth. The horizontal fields from lightning return strokes had typically 1/50 the peak amplitude of the verticalmore » fields and waveshapes which were consistant with available theory, as expressed by the ''wavetilt'' formula.« less

Electric field measurements in a near atmospheric pressure nanosecond pulse discharge with picosecond electric field induced second harmonic generation

NASA Astrophysics Data System (ADS)

Goldberg, Benjamin M.; Chng, Tat Loon; Dogariu, Arthur; Miles, Richard B.

2018-02-01

We present an optical electric field measurement method for use in high pressure plasma discharges. The method is based upon the field induced second harmonic generation technique and can be used for localized electric field measurements with sub-nanosecond resolution in any gaseous species. When an external electric field is present, a dipole is induced in the typically centrosymmetric medium, allowing for second harmonic generation with signal intensities which scale by the square of the electric field. Calibrations have been carried out in 100 Torr room air, and a minimum sensitivity of 450 V/cm is demonstrated. Measurements were performed with nanosecond or faster temporal resolution in a 100 Torr room air environment both with and without a plasma present. It was shown that with no plasma present, the field follows the applied voltage to gap ratio, as measured using the back current shunt method. When the electric field is strong enough to exceed the breakdown threshold, the measured field was shown to exceed the anticipated voltage to gap ratio which is taken as an indication of the ionization wave front as it sweeps through the plasma volume.

Tissue heterogeneity in structure and conductivity contribute to cell survival during irreversible electroporation ablation by “electric field sinks”

PubMed Central

Golberg, Alexander; Bruinsma, Bote G.; Uygun, Basak E.; Yarmush, Martin L.

2015-01-01

Irreversible electroporation (IRE) is an emerging, minimally invasive technique for solid tumors ablation, under clinical investigation for cancer therapy. IRE affects only the cell membrane, killing cells while preserving the extracellular matrix structure. Current reports indicate tumors recurrence rate after IRE averaging 31% of the cases, of which 10% are local recurrences. The mechanisms for these recurrences are not known and new explanations for incomplete cell death are needed. Using finite elements method for electric field distribution, we show that presence of vascular structures with blood leads to the redistribution of electric fields leading to the areas with more than 60% reduced electric field strength in proximity to large blood vessels and clustered vessel structures. In an in vivo rat model of liver IRE ablation, we show that cells located in the proximity of larger vessel structures and in proximity of clustered vessel structures appear less affected by IRE ablation than cells in the tissue parenchyma or in the proximity of small, more isolated vessels. These findings suggest a role for “electric field sinks” in local tumors recurrences after IRE and emphasize the importance of the precise mapping of the targeted organ structure and conductivity for planning of electroporation procedures. PMID:25684630

Tissue heterogeneity in structure and conductivity contribute to cell survival during irreversible electroporation ablation by "electric field sinks".

PubMed

Golberg, Alexander; Bruinsma, Bote G; Uygun, Basak E; Yarmush, Martin L

2015-02-16

Irreversible electroporation (IRE) is an emerging, minimally invasive technique for solid tumors ablation, under clinical investigation for cancer therapy. IRE affects only the cell membrane, killing cells while preserving the extracellular matrix structure. Current reports indicate tumors recurrence rate after IRE averaging 31% of the cases, of which 10% are local recurrences. The mechanisms for these recurrences are not known and new explanations for incomplete cell death are needed. Using finite elements method for electric field distribution, we show that presence of vascular structures with blood leads to the redistribution of electric fields leading to the areas with more than 60% reduced electric field strength in proximity to large blood vessels and clustered vessel structures. In an in vivo rat model of liver IRE ablation, we show that cells located in the proximity of larger vessel structures and in proximity of clustered vessel structures appear less affected by IRE ablation than cells in the tissue parenchyma or in the proximity of small, more isolated vessels. These findings suggest a role for "electric field sinks" in local tumors recurrences after IRE and emphasize the importance of the precise mapping of the targeted organ structure and conductivity for planning of electroporation procedures.

Physical deposition behavior of stiff amphiphilic polyelectrolytes in an external electric field

NASA Astrophysics Data System (ADS)

Hu, Dongmei; Zuo, Chuncheng; Cao, Qianqian; Chen, Hongli

2017-08-01

Coarse-grained molecular dynamics simulations are conducted to study the physical deposition behavior of stiff amphiphilic polyelectrolytes (APEs) in an external electric field. The effects of chain stiffness, the charge distribution of a hydrophilic block, and electric field strength are investigated. Amphiphilic multilayers, which consist of a monolayer of adsorbed hydrophilic monomers (HLMs), a hydrophobic layer, and another hydrophilic layer, are formed in a selective solvent. All cases exhibit locally ordered hydrophilic monolayers. Two kinds of hydrophobic micelles are distinguished based on local structures. Stripe and network hydrophobic patterns are formed in individual cases. Increasing the chain stiffness decreases the thickness of the deposited layer, the lateral size of the hydrophobic micelles, and the amount of deposition. Increasing the number of positively charged HLMs in a single chain has the same effect as increasing chain stiffness. Moreover, when applied normally to the substrate, the electric field compresses the deposited structures and increases the amount of deposition by pulling more PEs toward the substrate. A stronger electric field also facilitates the formation of a thinner and more ordered hydrophilic adsorption layer. These estimates help us explore how to tailor patterned nano-surfaces, nano-interfaces, or amphiphilic nanostructures by physically depositing semi-flexible APEs which is of crucial importance in physical sciences, life sciences and nanotechnology.

Magnetoelectric effects in the spin-1/2 XXZ model with Dzyaloshinskii-Moriya interaction

DOE Office of Scientific and Technical Information (OSTI.GOV)

Thakur, Pradeep; Durganandini, P., E-mail: pdn@physics.unipune.ac.in

2015-06-24

We study the 1D spin-1/2 XXZ chain in the presence of the Dzyaloshinskii-Moriya (D-M) interaction and with longitudinal and transverse magnetic fields. We assume the spin-current mechanism of Katsura-Nagaosa-Balatsky at play and interpret the D-M interaction as a coupling between the local electric polarization and an external electric field. We study the interplay of electric and magnetic order in the ground state using the numerical density matrix renormalization group(DMRG) method. Specifically, we investigate the dependences of the magnetization and electric polarization on the external electric and magnetic fields. We find that for transverse magnetic fields, there are two different regimesmore » of polarization while for longitudinal magnetic fields, there are three different regimes of polarization. The different regimes can be tuned by the external magnetic fields.« less

Electric-field-driven phase transition in vanadium dioxide

NASA Astrophysics Data System (ADS)

Wu, B.; Zimmers, A.; Aubin, H.; Ghosh, R.; Liu, Y.; Lopez, R.

2011-12-01

We report on local probe measurements of current-voltage and electrostatic force-voltage characteristics of electric-field-induced insulator to metal transition in VO2 thin film. In conducting AFM mode, switching from the insulating to metallic state occurs for electric-field threshold E˜6.5×107Vm-1 at 300K. Upon lifting the tip above the sample surface, we find that the transition can also be observed through a change in electrostatic force and in tunneling current. In this noncontact regime, the transition is characterized by random telegraphic noise. These results show that electric field alone is sufficient to induce the transition; however, the electronic current provides a positive feedback effect that amplifies the phenomena.

The role of the large scale convection electric field in erosion of the plasmasphere during moderate and strong storms

NASA Astrophysics Data System (ADS)

Thaller, S. A.; Wygant, J. R.; Cattell, C. A.; Breneman, A. W.; Bonnell, J. W.; Kletzing, C.; De Pascuale, S.; Kurth, W. S.; Hospodarsky, G. B.; Bounds, S. R.

2015-12-01

The Van Allen Probes offer the first opportunity to investigate the response of the plasmasphere to the enhancement and penetration of the large scale duskward convection electric field in different magnetic local time (MLT) sectors. Using electric field measurements and estimates of the cold plasma density from the Van Allen Probes' Electric Fields and Waves (EFW) instrument, we study erosion of the plasmasphere during moderate and strong geomagnetic storms. We present the electric field and density data both on an orbit by orbit basis and synoptically, showing the behavior of the convection electric field and plasmasphere over a period of months. The data indicate that the large scale duskward electric field penetrates deep (L shell < 3) into the inner magnetosphere on both the dusk and dawn sides, but that the plasmasphere response on the dusk and dawn sides differ. In particular, significant (~2 orders of magnitude) decreases in the cold plasma density occur on the dawn side within hours of the onset of enhanced duskward electric field. In contrast, on the dusk side, the plasmapause is located at higher L shell than it is on the dawn side. In some cases, in the post-noon sector, cold plasma density enhancements accompany duskward electric field enhancements for the first orbit after the electric field enchantment, consistent with a duskside, sunward flowing, drainage plume.

Simulation of electrostatic ion instabilities in the presence of parallel currents and transverse electric fields

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Ganguli, G.; Lee, Y. C.; Palmadesso, P. J.

1989-01-01

A spatially two-dimensional electrostatic PIC simulation code was used to study the stability of a plasma equilibrium characterized by a localized transverse dc electric field and a field-aligned drift for L is much less than Lx, where Lx is the simulation length in the x direction and L is the scale length associated with the dc electric field. It is found that the dc electric field and the field-aligned current can together play a synergistic role to enable the excitation of electrostatic waves even when the threshold values of the field aligned drift and the E x B drift are individually subcritical. The simulation results show that the growing ion waves are associated with small vortices in the linear stage, which evolve to the nonlinear stage dominated by larger vortices with lower frequencies.

Surface electric fields for North America during historical geomagnetic storms

USGS Publications Warehouse

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

2013-01-01

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.

THE ONSET OF ELECTRICAL BREAKDOWN IN DUST LAYERS: II. EFFECTIVE DIELECTRIC CONSTANT AND LOCAL FIELD ENHANCEMENT

EPA Science Inventory

Part 1 of the work has shown that electrical breakdown in dust layers obeys Paschen's Law, but occurs at applied field values which appear too small to initiate the breakdown. In this paper the authors show how an effective dielectric constant characterizing the dust layer can be...

Three-dimensional wave evolution on electrified falling films

NASA Astrophysics Data System (ADS)

Tomlin, Ruben; Papageorgiou, Demetrios; Pavliotis, Greg

2016-11-01

We consider the full three-dimensional model for a thin viscous liquid film completely wetting a flat infinite solid substrate at some non-zero angle to the horizontal, with an electric field normal to the substrate far from the flow. Thin film flows have applications in cooling processes. Many studies have shown that the presence of interfacial waves increases heat transfer by orders of magnitude due to film thinning and convection effects. A long-wave asymptotics procedure yields a Kuramoto-Sivashinsky equation with a non-local term to model the weakly nonlinear evolution of the interface dynamics for overlying film arrangements, with a restriction on the electric field strength. The non-local term is always linearly destabilising and produces growth rates proportional to the cube of the magnitude of the wavenumber vector. A sufficiently strong electric field is able promote non-trivial dynamics for subcritical Reynolds number flows where the flat interface is stable in the absence of an electric field. We present numerical simulations where we observe rich dynamical behavior with competing attractors, including "snaking" travelling waves and other fully three-dimensional wave formations. EPSRC studentship (RJT).

Electric field control in DC cable test termination by nano silicone rubber composite

NASA Astrophysics Data System (ADS)

Song, Shu-Wei; Li, Zhongyuan; Zhao, Hong; Zhang, Peihong; Han, Baozhong; Fu, Mingli; Hou, Shuai

2017-07-01

The electric field distributions in high voltage direct current cable termination are investigated with silicone rubber nanocomposite being the electric stress control insulator. The nanocomposite is composed of silicone rubber, nanoscale carbon black and graphitic carbon. The experimental results show that the physical parameters of the nanocomposite, such as thermal activation energy and nonlinearity-relevant coefficient, can be manipulated by varying the proportion of the nanoscale fillers. The numerical simulation shows that safe electric field distribution calls for certain parametric region of the thermal activation energy and nonlinearity-relevant coefficient. Outside the safe parametric region, local maximum of electric field strength around the stress cone appears in the termination insulator, enhancing the breakdown of the cable termination. In the presence of the temperature gradient, thermal activation energy and nonlinearity-relevant coefficient work as complementary factors to produce a reasonable electric field distribution. The field maximum in the termination insulator show complicate variation in the transient processes. The stationary field distribution favors the increase of the nonlinearity-relevant coefficient; for the transient field distribution in the process of negative lighting impulse, however, an optimized value of the nonlinearity-relevant coefficient is necessary to equalize the electric field in the termination.

Field distribution and DNA transport in solid tumors during electric field-mediated gene delivery.

PubMed

Henshaw, Joshua W; Yuan, Fan

2008-02-01

Gene therapy has a great potential in cancer treatment. However, the efficacy of cancer gene therapy is currently limited by the lack of a safe and efficient means to deliver therapeutic genes into the nucleus of tumor cells. One method under investigation for improving local gene delivery is based on the use of pulsed electric field. Despite repeated demonstration of its effectiveness in vivo, the underlying mechanisms behind electric field-mediated gene delivery remain largely unknown. Without a thorough understanding of these mechanisms, it will be difficult to further advance the gene delivery. In this review, the electric field-mediated gene delivery in solid tumors will be examined by following individual transport processes that must occur in vivo for a successful gene transfer. The topics of examination include: (i) major barriers for gene delivery in the body, (ii) distribution of electric fields at both cell and tissue levels during the application of external fields, and (iii) electric field-induced transport of genes across each of the barriers. Through this approach, the review summarizes what is known about the mechanisms behind electric field-mediated gene delivery and what require further investigations in future studies.

Development and application of measurement techniques for evaluating localised magnetic properties in electrical steel

NASA Astrophysics Data System (ADS)

Lewis, N. J.; Anderson, P. I.; Gao, Y.; Robinson, F.

2018-04-01

This paper reports the development of a measurement probe which couples local flux density measurements obtained using the needle probe method with the local magnetising field attained via a Hall effect sensor. This determines the variation in magnetic properties including power loss and permeability at increasing distances from the punched edge of 2.4% and 3.2% Si non-oriented electrical steel sample. Improvements in the characterisation of the magnetic properties of electrical steels would aid in optimising the efficiency in the design of electric machines.

Electric-field-induced local and mesoscale structural changes in polycrystalline dielectrics and ferroelectrics

DOE PAGES

Usher, Tedi -Marie; Levin, Igor; Daniels, John E.; ...

2015-10-01

In this study, the atomic-scale response of dielectrics/ferroelectrics to electric fields is central to their functionality. Here we introduce an in situ characterization method that reveals changes in the local atomic structure in polycrystalline materials under fields. The method employs atomic pair distribution functions (PDFs), determined from X-ray total scattering that depends on orientation relative to the applied field, to probe structural changes over length scales from sub-Ångstrom to several nanometres. The PDF is sensitive to local ionic displacements and their short-range order, a key uniqueness relative to other techniques. The method is applied to representative ferroelectrics, BaTiO 3 andmore » Na ½Bi ½TiO 3, and dielectric SrTiO 3. For Na ½Bi ½TiO 3, the results reveal an abrupt field-induced monoclinic to rhombohedral phase transition, accompanied by ordering of the local Bi displacements and reorientation of the nanoscale ferroelectric domains. For BaTiO 3 and SrTiO 3, the local/nanoscale structural changes observed in the PDFs are dominated by piezoelectric lattice strain and ionic polarizability, respectively.« less

Rates of Charged Clocks in an Electric Field.

NASA Astrophysics Data System (ADS)

Ozer, Murat

2008-04-01

The gravitational arguments leading to time dilation, redshift, and spacetime curvature are adapted to electric fields. The energy levels of two identical positively charged atoms at different potentials in a static electric field are shown to undergo blueshift. Secondly, the period of a charged simple pendulum (clock) in the electric field of a metallic sphere is shown to vary with the electric potential. The spacetime diagram for the world lines of two photons emitted and absorbed by two pendulums at different potentials at different times and the world lines of the pendulums, as in Schild's argument, is shown to be not a parallelogram in Minkowski spacetime, concluding that spacetime must be curved. A Pound-Rebka-Snider experiment in an electric field is proposed to confirm that photons undergo a frequency shift in an electric field and hence the spacetime manifold is curved. Next, Torretti's gravitational argument that spacetime around a mass distribution concentrated at a point is curved is extended to electric charge distributions to conclude that the nonuniform electric fields of such charge distributions too curve spacetime. Finally, the local equivalence of a uniform electric field times the charge to mass ratio to a uniform acceleration is shown through spacetime transformations and the electrical redshift is obtained in a uniformly accelerated frame by using this principle. These arguments lead to the conclusion that special relativistic electromagnetism is an approximation to a general relativistic multi-metric theory.

On the generation of double layers from ion- and electron-acoustic instabilities

DOE PAGES

Fu, Xiangrong; Cowee, Misa M.; Gary, Stephen Peter; ...

2016-03-17

A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric fields traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs – electron acoustic DLs – generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e.more » the hypothetical electron acoustic DLs cannot be formed in a way similar to ion acoustic DLs. We find that linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric fields that propagate at the electron thermal speed, suggesting another potential explanation for the observations.« less

On the generation of double layers from ion- and electron-acoustic instabilities

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fu, Xiangrong, E-mail: xrfu@lanl.gov; Cowee, Misa M.; Winske, Dan

2016-03-15

A plasma double layer (DL) is a nonlinear electrostatic structure that carries a uni-polar electric field parallel to the background magnetic field due to local charge separation. Past studies showed that DLs observed in space plasmas are mostly associated with the ion acoustic instability. Recent Van Allen Probes observations of parallel electric field structures traveling much faster than the ion acoustic speed have motivated a computational study to test the hypothesis that a new type of DLs—electron acoustic DLs—generated from the electron acoustic instability are responsible for these electric fields. Nonlinear particle-in-cell simulations yield negative results, i.e., the hypothetical electronmore » acoustic DLs cannot be formed in a way similar to ion acoustic DLs. Linear theory analysis and the simulations show that the frequencies of electron acoustic waves are too high for ions to respond and maintain charge separation required by DLs. However, our results do show that local density perturbations in a two-electron-component plasma can result in unipolar-like electric field structures that propagate at the electron thermal speed, suggesting another potential explanation for the observations.« less

Measurement and modeling of electric field and space-charge distributions in obstructed helium discharge

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fendel, Peter; Ganguly, Biswa N.; Bletzinger, Peter

Axial and radial variations of electric field have been measured in dielectric shielded 0.025 m diameter parallel plate electrode with 0.0065 m gap for 1.6 mA, 2260 V helium dc discharge at 1.75 Torr. The axial and radial electric field profiles have been measured from the Stark splitting of 2{sup 1}S→11 {sup 1}P transition through collision induced fluorescence from 4{sup 3}D→2{sup 3}P. The electric field values showed a strong radial variation peaking to 500 kV/m near the cathode radial boundary, and decreasing to about 100 kV/m near the anode edge, suggesting the formation of an obstructed discharge for this low nd condition, where n is the gasmore » density and d is the gap distance. The off-axis Stark spectra showed that the electric field vector deviates from normal to the cathode surface which permits longer path electron trajectories in the inter-electrode gap. Also, the on-axis electric field gradient was very small and off-axis electric field gradient was large indicating a radially non-uniform current density. In order to obtain information about the space charge distribution in this obstructed discharge, it was modeled using the 2-d axisymmetric Poisson solver with the COMSOL finite element modeling program. The best fit to the measured electric field distribution was obtained with a space charge variation of ρ(r) = ρ{sub 0}(r/r{sub 0}){sup 3}, where ρ(r) is the local space charge density, ρ{sub 0} = 6 × 10{sup −3} Coulomb/m{sup 3}, r is the local radial value, and r{sub 0} is the radius of the electrode.« less

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

PubMed

Geng, Yanan; Wu, Weida

2014-05-01

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.

Emission quenching of magnetic dipole transitions near an absorbing nanoparticle (Conference Presentation)

NASA Astrophysics Data System (ADS)

Chigrin, Dmitry N.; Kumar, Deepu; von Plessen, Gero

2016-09-01

Emission quenching is analysed at nanometer distances from the surface of an absorbing nanoparticle. It is demonstrated that emission quenching at small distances to the surface is much weaker for magnetic-dipole (MD) than for electric-dipole (ED) transitions. This difference is explained by the fact that the electric field induced by a magnetic dipole has a weaker distance dependence than the electric field of an electric dipole. It is also demonstrated that in the extreme near-field regime the non-locality of the optical response of the metal results in additional emission quenching for both ED and MD transitions.

Electrodynamic properties and height of atmospheric convective boundary layer

NASA Astrophysics Data System (ADS)

Anisimov, S. V.; Galichenko, S. V.; Mareev, E. A.

2017-09-01

We consider the relations between the mixed layer height and atmospheric electric parameters affected by convective mixing. Vertical turbulent transport of radon, its progeny and electrically charged particles is described under Lagrangian stochastic framework, which is the next step to develop a consistent model for the formation of electrical conditions in the atmospheric boundary layer. Using the data from detailed and complex measurements of vertical profiles of the temperature and turbulence statistics as input, we calculated non-stationary vertical profiles of radon and its daughter products concentrations, atmospheric electric conductivity and intensity of electric field in the convective boundary layer from the morning transition through early afternoon quasi-stationary conditions. These profiles demonstrate substantial variability due to the changing turbulent regime in the evolving boundary layer. We obtained quantitative estimates of the atmospheric electric field variability range essentially related to the sunrise and convection development. It is shown that the local change in the electrical conductivity is the only factor that can change the intensity of electric field at the earth's surface more than twice during the transition from night to day. The established relations between electric and turbulent parameters of the boundary layer indicate that the effect of sunrise is more pronounced in the case when development of convection is accompanied by an increase in aerosol concentration and, hence, a decrease in local conductivity.

Effective electric fields along realistic DTI-based neural trajectories for modelling the stimulation mechanisms of TMS

NASA Astrophysics Data System (ADS)

De Geeter, N.; Crevecoeur, G.; Leemans, A.; Dupré, L.

2015-01-01

In transcranial magnetic stimulation (TMS), an applied alternating magnetic field induces an electric field in the brain that can interact with the neural system. It is generally assumed that this induced electric field is the crucial effect exciting a certain region of the brain. More specifically, it is the component of this field parallel to the neuron’s local orientation, the so-called effective electric field, that can initiate neuronal stimulation. Deeper insights on the stimulation mechanisms can be acquired through extensive TMS modelling. Most models study simple representations of neurons with assumed geometries, whereas we embed realistic neural trajectories computed using tractography based on diffusion tensor images. This way of modelling ensures a more accurate spatial distribution of the effective electric field that is in addition patient and case specific. The case study of this paper focuses on the single pulse stimulation of the left primary motor cortex with a standard figure-of-eight coil. Including realistic neural geometry in the model demonstrates the strong and localized variations of the effective electric field between the tracts themselves and along them due to the interplay of factors such as the tract’s position and orientation in relation to the TMS coil, the neural trajectory and its course along the white and grey matter interface. Furthermore, the influence of changes in the coil orientation is studied. Investigating the impact of tissue anisotropy confirms that its contribution is not negligible. Moreover, assuming isotropic tissues lead to errors of the same size as rotating or tilting the coil with 10 degrees. In contrast, the model proves to be less sensitive towards the not well-known tissue conductivity values.

Intrinsic electric fields and proton diffusion in immobilized protein membranes. Effects of electrolytes and buffers.

PubMed Central

Zabusky, N J; Deem, G S

1979-01-01

We present a theory for proton diffusion through an immobilized protein membrane perfused with an electrolyte and a buffer. Using a Nernst-Planck equation for each species and assuming local charge neutrality, we obtain two coupled nonlinear diffusion equations with new diffusion coefficients dependent on the concentration of all species, the diffusion constants or mobilities of the buffers and salts, the pH-derivative of the titration curves of the mobile buffer and the immobilized protein, and the derivative with respect to ionic strength of the protein titration curve. Transient time scales are locally pH-dependent because of protonation-deprotonation reactions with the fixed protein and are ionic strength-dependent because salts provide charge carriers to shield internal electric fields. Intrinsic electric fields arise proportional to the gradient of an "effective" charge concentration. The field may reverse locally if buffer concentrations are large (greater to or equal to 0.1 M) and if the diffusivity of the electrolyte species is sufficiently small. The "ideal" electrolyte case (where each species has the same diffusivity) reduces to a simple form. We apply these theoretical considerations to membranes composed of papain and bovine serum albumin (BSA) and show that intrinsic electric fields greatly enhance the mobility of protons when the ionic strength of the salts is smaller than 0.1 M. These results are consistent with experiments where pH changes are observed to depend strongly on buffer, salt, and proton concentrations in baths adjacent to the membranes. PMID:233570

Communication: Control of chemical reactions using electric field gradients.

PubMed

Deshmukh, Shivaraj D; Tsori, Yoav

2016-05-21

We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phase or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.

Local time asymmetries and toroidal field line resonances: Global magnetospheric modeling in SWMF

NASA Astrophysics Data System (ADS)

Ellington, S. M.; Moldwin, M. B.; Liemohn, M. W.

2016-03-01

We present evidence of resonant wave-wave coupling via toroidal field line resonance (FLR) signatures in the Space Weather Modeling Framework's (SWMF) global, terrestrial magnetospheric model in one simulation driven by a synthetic upstream solar wind with embedded broadband dynamic pressure fluctuations. Using in situ, stationary point measurements of the radial electric field along the 1500 LT meridian, we show that SWMF reproduces a multiharmonic, continuous distribution of FLRs exemplified by 180° phase reversals and amplitude peaks across the resonant L shells. By linearly increasing the amplitude of the dynamic pressure fluctuations in time, we observe a commensurate increase in the amplitude of the radial electric and azimuthal magnetic field fluctuations, which is consistent with the solar wind driver being the dominant source of the fast mode energy. While we find no discernible local time changes in the FLR frequencies despite large-scale, monotonic variations in the dayside equatorial mass density, in selectively sampling resonant points and examining spectral resonance widths, we observe significant radial, harmonic, and time-dependent local time asymmetries in the radial electric field amplitudes. A weak but persistent local time asymmetry exists in measures of the estimated coupling efficiency between the fast mode and toroidal wave fields, which exhibits a radial dependence consistent with the coupling strength examined by Mann et al. (1999) and Zhu and Kivelson (1988). We discuss internal structural mechanisms and additional external energy sources that may account for these asymmetries as we find that local time variations in the strength of the compressional driver are not the predominant source of the FLR amplitude asymmetries. These include resonant mode coupling of observed Kelvin-Helmholtz surface wave generated Pc5 band ultralow frequency pulsations, local time differences in local ionospheric dampening rates, and variations in azimuthal mode number, which may impact the partitioning of spectral energy between the toroidal and poloidal wave modes.

The effect of substrate on electric field enhancement of Tip-enhanced Raman spectroscopy (TERS)

NASA Astrophysics Data System (ADS)

Bahreini, Maryam

2018-01-01

The characterization of materials down to a few-molecule level is a key challenge in nanotechnology. Raman spectroscopy is a powerful method that provides chemical information via nondestructive vibrational fingerprinting. Unfortunately, this method suffers from signal weakness which prevents the study of small quantities. Tip-enhanced Raman spectroscopy (TERS) which combines the chemical sensitivity of Raman spectroscopy (RS) with high spatial resolution of scanning probe microscopy (SPM), provides chemical images of surfaces at the nanometer scale. In this method, irradiation of an SPM tip by a focused laser beam results in enhancement of local electric field via two reasons of localized surface plasmon resonance and lightning rod effect. This enhancement leads to the enhancement in Raman intensity from the sample surface in the vicinity of tip. In all TERS measurements, samples should be located on a substrate. In this paper, the dependence of the electric field enhancement to the substrate has been investigated. In simulations, three-dimensional finite-difference time-domain (3D-FDTD) method is used for numerical solution of Maxwell's equations. Our results show that the electric field enhancement is weak for the tip alone case. Introducing a substrate provides further electric field enhancement via near field electromagnetic dipole-dipole coupling between the tip and substrate. Since the side-illumination geometry is used for laser irradiation, the vertical component of the incident field plays a dominant role in the electric field enhancement. Therefore, the coupling effect between the tip and the substrate is the key contribution to the enhancement. For the case of silicon tip and the gold substrate, the electric field enhancement is improved considerably. There is an optimal tip size for TERS because of the competing effects of the radiation damping and the surface scattering of the tip. The results show the substrate as an effective tool for the improvement of the TERS detection sensitivity.

Eye/Sensor Protection against Laser Irradiation Organic Nonlinear Optical Materials

DTIC Science & Technology

1989-06-12

the dipole. When the electric field is small compared to the internal fields due to the electron!, the molecular polarizability (p), which is...polarizability tensors, respectively, the linear polarizability and the second and third-order hyperpolarizability. At lower field intensities ( small E’s) only...nonlinear optical effect: the bonding electrons are well localized so only small changes in charge distribution with changes in local field environments

Low reflection and field localization over surface plasmon device with subwavelength patterned aluminum film

NASA Astrophysics Data System (ADS)

Yuan, Ying; Peng, Sha; Long, Huabao; Liu, Runhan; Wei, Dong; Zhang, Xinyu; Wang, Haiwei; Xie, Changsheng

2018-02-01

In this paper, we propose a new device composed of patterned sub-wavelength arrays to investigate surface plasmons (SPs) over sub-wavelength metal nano-structures. The device consists of silicon substrate and sub-wavelength patterns fabricated on a layer of aluminum film with nanometer thickness. Each sub-wavelength pattern formed in aluminum film is composed of a basic nano-square and twelve triangles for shaping single nano-pattern, which are uniformly distributed on the four sides of each square. Reflectance spectra and electric field distribution in infrared region are simulated. Numerical simulation results demonstrate that the device can efficiently lower its reflectance in infrared spectrum, and the response frequency can be controlled by only changing the device parameters such as square side length and then triangle vertex angle. Besides, the simulated electric field distribution of the device shows obviously field localization effect at the edges of aluminum film nano-structure. The electric filed around the tips of aluminum triangles is localized into sub-wavelength scale, so as to be beyond the common diffraction limitation. Our work will help to reveal the interesting properties of SPs device, and also bring new prospect of photonic device.

Uniform and non-uniform modes of nanosecond-pulsed dielectric barrier discharge in atmospheric air: fast imaging and spectroscopic measurements of electric field

PubMed Central

Liu, Chong; Dobrynin, Danil; Fridman, Alexander

2014-01-01

In this study, we report experimental results on fast ICCD imaging of development of nanosecond-pulsed dielectric barrier discharge (DBD) in atmospheric air and spectroscopic measurements of electric field in the discharge. Uniformity of the discharge images obtained with nanosecond exposure times were analyzed using chi-square test. The results indicate that DBD uniformity strongly depends on applied (global) electric field in the discharge gap, and is a threshold phenomenon. We show that in the case of strong overvoltage on the discharge gap (provided by fast rise times), there is transition from filamentary to uniform DBD mode which correlates to the corresponding decrease of maximum local electric field in the discharge. PMID:25071294

Uniform and non-uniform modes of nanosecond-pulsed dielectric barrier discharge in atmospheric air: fast imaging and spectroscopic measurements of electric field.

PubMed

Liu, Chong; Dobrynin, Danil; Fridman, Alexander

2014-06-25

In this study, we report experimental results on fast ICCD imaging of development of nanosecond-pulsed dielectric barrier discharge (DBD) in atmospheric air and spectroscopic measurements of electric field in the discharge. Uniformity of the discharge images obtained with nanosecond exposure times were analyzed using chi-square test. The results indicate that DBD uniformity strongly depends on applied (global) electric field in the discharge gap, and is a threshold phenomenon. We show that in the case of strong overvoltage on the discharge gap (provided by fast rise times), there is transition from filamentary to uniform DBD mode which correlates to the corresponding decrease of maximum local electric field in the discharge.

Analysis of Electrokinetic Mixing Using AC Electric Field and Patchwise Surface Heterogeneities

NASA Astrophysics Data System (ADS)

Luo, Win-Jet; Yarn, Kao-Feng; Hsu, Shou-Ping

2007-04-01

In this paper, the authors investigate the use of an applied AC electric field and microchannel surface heterogeneities to carry out the microfluidic mixing of two-dimensional, time-dependent electroosmotic flows. The time-dependent flow fields within the microchannel are simulated using the backwards-Euler time-stepping numerical method. The mixing efficiencies obtained in microchannels with two different patchwise surface heterogeneity patterns are investigated. In general, the results show that the application of an AC electric field significantly reduces the required mixing length compared with the use of a DC electric field. Furthermore, the presence of oppositely charged surface heterogeneities on the microchannel walls results in the formation of localized flow circulation regions within the bulk flow. These circulation regions grow and decay periodically in accordance with the periodic variation of the AC electric field intensity and provide an effective means of enhancing species mixing in the microchannel. Consequently, the use of an AC electric field together with patchwise surface heterogeneities permits a significant reduction in both the mixing channel length and the retention time required to attain a homogeneous solution.

Assessment of the electrochemical effects of pulsed electric fields in a biological cell suspension.

PubMed

Chafai, Djamel Eddine; Mehle, Andraž; Tilmatine, Amar; Maouche, Bachir; Miklavčič, Damijan

2015-12-01

Electroporation of cells is successfully used in biology, biotechnology and medicine. Practical problems still arise in the electroporation of cells in suspension. For example, the determination of cell electroporation is still a demanding and time-consuming task. Electric pulses also cause contamination of the solution by the metal released from the electrodes and create local enhancements of the electric field, leading to the occurrence of electrochemical reactions at the electrode/electrolyte interface. In our study, we investigated the possibility of assessing modifications to the cell environment caused by pulsed electric fields using electrochemical impedance spectroscopy. We designed an experimental protocol to elucidate the mechanism by which a pulsed electric field affects the electrode state in relation to different electrolyte conductivities at the interface. The results show that a pulsed electric field affects electrodes and its degree depends on the electrolyte conductivity. Evolution of the electrochemical reaction rate depends on the initial free charges and those generated by the pulsed electric field. In the presence of biological cells, the initial free charges in the medium are reduced. The electrical current path at low frequency is longer, i.e., conductivity is decreased, even in the presence of increased permeability of the cell membrane created by the pulsed electric field. Copyright © 2015 Elsevier B.V. All rights reserved.

Methods and apparatus for controlling dispersions of nanoparticles

DOEpatents

Lavrentovich, Oleg D; Golovin, Andrii B

2014-10-21

Electrically reconfigurable metamaterial with spatially varied refractive index is proposed for applications such as optical devices and lenses. The apparatus and method comprises a metamaterial in which the refractive indices are modified in space and time by applying one or more electric fields. The metamaterials are electrically controllable and reconfigurable, and consist of metal (gold, silver, etc.) particles of different shapes, such as rods, with dimension much smaller than the wavelength of light, dispersed in a dielectric medium. The metamaterial is controlled by applying a non-uniform electric field that causes two effects: (1) It aligns the metallic anisometric particles with respect to the direction of the applied electric field and (2) It redistributes particles in space, making their local concentration position dependent.

Surface Plasmon-Mediated Nanoscale Localization of Laser-Driven sub-Terahertz Spin Dynamics in Magnetic Dielectrics.

PubMed

Chekhov, Alexander L; Stognij, Alexander I; Satoh, Takuya; Murzina, Tatiana V; Razdolski, Ilya; Stupakiewicz, Andrzej

2018-05-09

We report spatial localization of the effective magnetic field generated via the inverse Faraday effect employing surface plasmon polaritons (SPPs) at Au/garnet interface. Analyzing both numerically and analytically the electric field of the SPPs at this interface, we corroborate our study with a proof-of-concept experiment showing efficient SPP-driven excitation of coherent spin precession with 0.41 THz frequency. We argue that the subdiffractional confinement of the SPP electric field enables strong spatial localization of the SPP-mediated excitation of spin dynamics. We demonstrate two orders of magnitude enhancement of the excitation efficiency at the surface plasmon resonance within a 100 nm layer of a dielectric garnet. Our findings broaden the horizons of ultrafast spin-plasmonics and open pathways toward nonthermal opto-magnetic recording on the nanoscale.

Phase transition studies of BiMnO3: Mean field theory approximations

NASA Astrophysics Data System (ADS)

Priya K. B, Lakshmi; Natesan, Baskaran

2015-06-01

We studied the phase transition and magneto-electric coupling effect of BiMnO3 by employing mean field theory approximations. To capture the ferromagnetic and ferroelectric transitions of BiMnO3, we construct an extended Ising model in a 2D square lattice, wherein, the magnetic (electric) interactions are described in terms of the direct interactions between the localized magnetic (electric dipole) moments of Mn ions with their nearest neighbors. To evaluate our model, we obtain magnetization, magnetic susceptibility and electric polarization using mean field approximation calculations. Our results reproduce both the ferromagnetic and the ferroelectric transitions, matching very well with the experimental reports. Furthermore, consistent with experimental observations, our mean field results suggest that there is indeed a coupling between the magnetic and electric ordering in BiMnO3.

Anticipating electrical breakdown in dielectric elastomer actuators

NASA Astrophysics Data System (ADS)

Muffoletto, Daniel P.; Burke, Kevin M.; Zirnheld, Jennifer L.

2013-04-01

The output strain of a dielectric elastomer actuator is directly proportional to the square of its applied electric field. However, since the likelihood of electric breakdown is elevated with an increased applied field, the maximum operating electric field of the dielectric elastomer is significantly derated in systems employing these actuators so that failure due to breakdown remains unlikely even as the material ages. In an effort to ascertain the dielectric strength so that stronger electric fields can be applied, partial discharge testing is used to assess the health of the actuator by detecting the charge that is released when localized instances of breakdown partially bridge the insulator. Pre-stretched and unstretched samples of VHB4910 tape were submerged in dielectric oil to remove external sources of partial discharges during testing, and the partial discharge patterns were recorded just before failure of the dielectric sample.

Method for localizing heating in tumor tissue

DOEpatents

Doss, James D.; McCabe, Charles W.

1977-04-12

A method for a localized tissue heating of tumors is disclosed. Localized radio frequency current fields are produced with specific electrode configurations. Several electrode configurations are disclosed, enabling variations in electrical and thermal properties of tissues to be exploited.

Manipulating Traveling Brain Waves with Electric Fields: From Theory to Experiment.

NASA Astrophysics Data System (ADS)

Gluckman, Bruce J.

2004-03-01

Activity waves in disinhibited neocortical slices have been used as a biological model for epileptic seizure propagation [1]. Such waves have been mathematically modeled with integro-differential equations [2] representing non-local reaction diffusion dynamics of an excitable medium with an excitability threshold. Stability and propagation speed of traveling pulse solutions depend strongly on the threshold in the following manner: propagation speed should decrease with increased threshold over a finite range, beyond which the waves become unstable. Because populations of neurons can be polarized with an applied electric field that effectively shifts their threshold for action potential initiation [3], we predicted, and have experimentally verified, that electric fields could be used globally or locally to speed up, slow down and even block wave propagation. [1] Telfeian and Conners, Epilepsia, 40, 1499-1506, 1999. [2] Pinto and Ermentrout, SIAM J. App. Math, 62, 206-225, 2001. [3] Gluckman, et. al. J Neurophysiol. 76, 4202-5, 1996.

A single molecule rectifier with strong push-pull coupling

NASA Astrophysics Data System (ADS)

Saraiva-Souza, Aldilene; Macedo de Souza, Fabricio; Aleixo, Vicente F. P.; Girão, Eduardo Costa; Filho, Josué Mendes; Meunier, Vincent; Sumpter, Bobby G.; Souza Filho, Antônio Gomes; Del Nero, Jordan

2008-11-01

We theoretically investigate the electronic charge transport in a molecular system composed of a donor group (dinitrobenzene) coupled to an acceptor group (dihydrophenazine) via a polyenic chain (unsaturated carbon bridge). Ab initio calculations based on the Hartree-Fock approximations are performed to investigate the distribution of electron states over the molecule in the presence of an external electric field. For small bridge lengths (n =0-3) we find a homogeneous distribution of the frontier molecular orbitals, while for n >3 a strong localization of the lowest unoccupied molecular orbital is found. The localized orbitals in between the donor and acceptor groups act as conduction channels when an external electric field is applied. We also calculate the rectification behavior of this system by evaluating the charge accumulated in the donor and acceptor groups as a function of the external electric field. Finally, we propose a phenomenological model based on nonequilibrium Green's function to rationalize the ab initio findings.

Measurement of Anisotropic Particle Interactions with Nonuniform ac Electric Fields.

PubMed

Rupp, Bradley; Torres-Díaz, Isaac; Hua, Xiaoqing; Bevan, Michael A

2018-02-20

Optical microscopy measurements are reported for single anisotropic polymer particles interacting with nonuniform ac electric fields. The present study is limited to conditions where gravity confines particles with their long axis parallel to the substrate such that particles can be treated using quasi-2D analysis. Field parameters are investigated that result in particles residing at either electric field maxima or minima and with long axes oriented either parallel or perpendicular to the electric field direction. By nonintrusively observing thermally sampled positions and orientations at different field frequencies and amplitudes, a Boltzmann inversion of the time-averaged probability of states yields kT-scale energy landscapes (including dipole-field, particle-substrate, and gravitational potentials). The measured energy landscapes show agreement with theoretical potentials using particle conductivity as the sole adjustable material property. Understanding anisotropic particle-field energy landscapes vs field parameters enables quantitative control of local forces and torques on single anisotropic particles to manipulate their position and orientation within nonuniform fields.

Numerical analysis of multicomponent responses of surface-hole transient electromagnetic method

NASA Astrophysics Data System (ADS)

Meng, Qing-Xin; Hu, Xiang-Yun; Pan, He-Ping; Zhou, Feng

2017-03-01

We calculate the multicomponent responses of surface-hole transient electromagnetic method. The methods and models are unsuitable as geoelectric models of conductive surrounding rocks because they are based on regular local targets. We also propose a calculation and analysis scheme based on numerical simulations of the subsurface transient electromagnetic fields. In the modeling of the electromagnetic fields, the forward modeling simulations are performed by using the finite-difference time-domain method and the discrete image method, which combines the Gaver-Stehfest inverse Laplace transform with the Prony method to solve the initial electromagnetic fields. The precision in the iterative computations is ensured by using the transmission boundary conditions. For the response analysis, we customize geoelectric models consisting of near-borehole targets and conductive wall rocks and implement forward modeling simulations. The observed electric fields are converted into induced electromotive force responses using multicomponent observation devices. By comparing the transient electric fields and multicomponent responses under different conditions, we suggest that the multicomponent-induced electromotive force responses are related to the horizontal and vertical gradient variations of the transient electric field at different times. The characteristics of the response are determined by the varying the subsurface transient electromagnetic fields, i.e., diffusion, attenuation and distortion, under different conditions as well as the electromagnetic fields at the observation positions. The calculation and analysis scheme of the response consider the surrounding rocks and the anomalous field of the local targets. It therefore can account for the geological data better than conventional transient field response analysis of local targets.

Electric field induced sheeting and breakup of dielectric liquid jets

NASA Astrophysics Data System (ADS)

Khoshnevis, Ahmad; Tsai, Scott S. H.; Esmaeilzadeh, Esmaeil

2014-01-01

We report experimental observations of the controlled deformation of a dielectric liquid jet subjected to a local high-voltage electrostatic field in the direction normal to the jet. The jet deforms to the shape of an elliptic cylinder upon application of a normal electrostatic field. As the applied electric field strength is increased, the elliptic cylindrical jet deforms permanently into a flat sheet, and eventually breaks-up into droplets. We interpret this observation—the stretch of the jet is in the normal direction to the applied electric field—qualitatively using the Taylor-Melcher leaky dielectric theory, and develop a simple scaling model that predicts the critical electric field strength for the jet-to-sheet transition. Our model shows a good agreement with experimental results, and has a form that is consistent with the classical drop deformation criterion in the Taylor-Melcher theory. Finally, we statistically analyze the resultant droplets from sheet breakup, and find that increasing the applied electric field strength improves droplet uniformity and reduces droplet size.

New method for solving inductive electric fields in the non-uniformly conducting ionosphere

NASA Astrophysics Data System (ADS)

Vanhamäki, H.; Amm, O.; Viljanen, A.

2006-10-01

We present a new calculation method for solving inductive electric fields in the ionosphere. The time series of the potential part of the ionospheric electric field, together with the Hall and Pedersen conductances serves as the input to this method. The output is the time series of the induced rotational part of the ionospheric electric field. The calculation method works in the time-domain and can be used with non-uniform, time-dependent conductances. In addition, no particular symmetry requirements are imposed on the input potential electric field. The presented method makes use of special non-local vector basis functions called the Cartesian Elementary Current Systems (CECS). This vector basis offers a convenient way of representing curl-free and divergence-free parts of 2-dimensional vector fields and makes it possible to solve the induction problem using simple linear algebra. The new calculation method is validated by comparing it with previously published results for Alfvén wave reflection from a uniformly conducting ionosphere.

Investigation of Influence of Surface Nanoparticle on Emission Properties of Scandia-Doped Dispenser Cathodes

NASA Astrophysics Data System (ADS)

Zhang, Xizhu; Wang, Jinshu; Wang, Yiman; Liu, Wei; Zhou, Meiling; Gao, Zhiyuan

2013-06-01

The microstructure of a fully activated scandia doped dispenser (SDD) cathode has been studied by scanning electron microscope (SEM). The observation results display that nanoparticles appear at the growth steps and the surface of tungsten grains of the fully activated SDD cathode. To study the influence of the nanoparticles on the emission, the local electric field strengths around the nanoparticles have been calculated by Maxwell 2D code and Comsol. The calculation results show that the local electric field strengths are enhanced by 1.1 to 3.8 times to average value based on different model conditions. The highest field strength is about 1.54 × 105 V/cm at an average field strength of 40 KV/cm, which is related to a space-charge limited (SCL) current density of 100 A/cm2 in the experimental configuration. This implies the field strength is not high enough to cause field emission.

Signal Cloaking by Electric Fish

PubMed Central

STODDARD, PHILIP K.; MARKHAM, MICHAEL R.

2010-01-01

Electric fish produce weak electric fields to image their world in darkness and to communicate with potential mates and rivals. Eavesdropping by electroreceptive predators exerts selective pressure on electric fish to shift their signals into less-detectable high-frequency spectral ranges. Hypopomid electric fish evolved a signal-cloaking strategy that reduces their detectability by predators in the lab (and thus presumably their risk of predation in the field). These fish produce broad-frequency electric fields close to the body, but the heterogeneous local fields merge over space to cancel the low-frequency spectrum at a distance. Mature males dynamically regulate this cloaking mechanism to enhance or suppress low-frequency energy. The mechanism underlying electric-field cloaking involves electrogenic cells that produce two independent action potentials. In a unique twist, these cells orient sodium and potassium currents in the same direction, potentially boosting their capabilities for current generation. Exploration of such evolutionary inventions could aid the design of biogenerators to power implantable medical devices, an ambition that would benefit from the complete genome sequence of a gymnotiform fish. PMID:20209064

Remote Sensing of the Reconnection Electric Field From In Situ Multipoint Observations of the Separatrix Boundary

NASA Astrophysics Data System (ADS)

Nakamura, T. K. M.; Nakamura, R.; Varsani, A.; Genestreti, K. J.; Baumjohann, W.; Liu, Y.-H.

2018-05-01

A remote sensing technique to infer the local reconnection electric field based on in situ multipoint spacecraft observation at the reconnection separatrix is proposed. In this technique, the increment of the reconnected magnetic flux is estimated by integrating the in-plane magnetic field during the sequential observation of the separatrix boundary by multipoint measurements. We tested this technique by applying it to virtual observations in a two-dimensional fully kinetic particle-in-cell simulation of magnetic reconnection without a guide field and confirmed that the estimated reconnection electric field indeed agrees well with the exact value computed at the X-line. We then applied this technique to an event observed by the Magnetospheric Multiscale mission when crossing an energetic plasma sheet boundary layer during an intense substorm. The estimated reconnection electric field for this event is nearly 1 order of magnitude higher than a typical value of magnetotail reconnection.

Transport of Energetic Ions in the Ring Current During Geomagnetic Storms

NASA Technical Reports Server (NTRS)

Kistler, Lynn M.; Kaufmann, Richard

2001-01-01

In the final year (plus no-cost extentions) of this grant, we have: Used the particle tracing code to perform a systematic study of the expected energy spectra over the full range of local times in the ring current using a variety of electric and magnetic field models. Shown that the Weimer electric field is superior to the Volland-Stern electric field in reproducing the observed energy spectra on the AMPTE CCE spacecraft. Redone our analysis of the pitch angle spectra of energetic ions during storms in the magnetosphere, using a larger data set, and a more reliable classification technique.

The effect of a radial electric field on ripple-trapped ions observed by neutral particle fluxes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heikkinen, J.A.; Herrmann, W.; Kurki-Suonio, T.

1997-10-01

The effect of a radial electric field on nonthermal ripple-trapped ions is investigated using toroidal Monte Carlo simulations for edge tokamak plasmas. The increase in the neutral particle flux from the ions trapped in local magnetic wells observed by the charge exchange (CX) detector at a low confinement to high confinement transition at ASDEX (Axially Symmetric Divertor Experiment). Upgrade tokamak [{ital Proceedings of the 20th European Conference on Controlled Fusion and Plasma Physics}, Lisbon (European Physical Society, Petit-Lancy, Switzerland, 1993), Vol. 17C, Part I, p. 267] is reproduced in the simulations by turning on a radial electric field near themore » plasma periphery. The poloidal and toroidal angles at which the CX detector signal is most sensitive to the radial electric field are determined. A fast response time of the signal in the range of 50{endash}100 {mu}s to the appearance of the electric field can be found in the simulations with a relatively large half-width of the negative electric field region. {copyright} {ital 1997 American Institute of Physics.}« less

Localized heating of electrons in ionization zones: Going beyond the Penning-Thornton paradigm in magnetron sputtering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Anders, Andre

2014-12-07

The fundamental question of how energy is supplied to a magnetron discharge is commonly answered by the Penning-Thornton paradigm invoking secondary electrons. Huo et al. (Plasma Sources Sci. Technol. 22, 045005, (2013)) used a global discharge model to show that electron heating in the electric field of the magnetic presheath is dominant. In this contribution, this concept is applied locally taking into account the electric potential structure of ionization zones. Images of ionization zones can and should be interpreted as diagrams of the localization of electric potential and related electron energy, where certain collisions promote or dampen their formation.

Characteristics of bowl-shaped coils for transcranial magnetic stimulation

NASA Astrophysics Data System (ADS)

Yamamoto, Keita; Suyama, Momoko; Takiyama, Yoshihiro; Kim, Dongmin; Saitoh, Youichi; Sekino, Masaki

2015-05-01

Transcranial magnetic stimulation (TMS) has recently been used as a method for the treatment of neurological and psychiatric diseases. Daily TMS sessions can provide continuous therapeutic effectiveness, and the installation of TMS systems at patients' homes has been proposed. A figure-eight coil, which is normally used for TMS therapy, induces a highly localized electric field; however, it is challenging to achieve accurate coil positioning above the targeted brain area using this coil. In this paper, a bowl-shaped coil for stimulating a localized but wider area of the brain is proposed. The coil's electromagnetic characteristics were analyzed using finite element methods, and the analysis showed that the bowl-shaped coil induced electric fields in a wider area of the brain model than a figure-eight coil. The expanded distribution of the electric field led to greater robustness of the coil to the coil-positioning error. To improve the efficiency of the coil, the relationship between individual coil design parameters and the resulting coil characteristics was numerically analyzed. It was concluded that lengthening the outer spherical radius and narrowing the width of the coil were effective methods for obtaining a more effective and more uniform distribution of the electric field.

[The Dual Nature of the Electrical Signals of the Brain (Electrical and Electrochemical) Which Were Recorded With the Help Polarizable Electrodes From Inert Metals].

PubMed

Dubinin, A G; Reutov, V P; Svinov, M M; Troshin, G I; Shvets-Teneta-Gurii, T B

2015-01-01

In the modern neurophysiology opinion was confirmed that the electrical signals of the brain in the frequency band from DC to electroencephalogram recorded with metallic conductors of inert metal implanted in the brain are formed solely by changes in the electric field of the brain. This paper presents a review of the literature and our own data, according to which the formation of these signals involves two factors. One factor is a change in the charge of the electric double layer electrode having a capacitor property and change the value of its charge with changes in the electric field volume conductor--the brain. Another factor is an electrochemical signal is defined by local changes in the redox potential (E) neuronal-glial populations surrounding the electrode. The paper provides an overviews the electrical and electrochemical properties of the electrodes of the inert metals used in electrophysiology. It is shown that each of these factors has the characteristic parameters over time and amplitude. The data of own studies of local changes in E cortex accompanying brain's response to the implantation of electrodes in the brain's cortex, the natural behavior of animals in the wake-sleep, integrative brain function and effect of pharmacological agents. These results give evidence of the highly informative study of local changes in brain E in order to study energy metabolism in the brain of waking animals, and lay the foundation for the study of local changes in brain energy metabolism in free animal behavior.

Localized surface plasmon enhanced cellular imaging using random metallic structures

NASA Astrophysics Data System (ADS)

Son, Taehwang; Lee, Wonju; Kim, Donghyun

2017-02-01

We have studied fluorescence cellular imaging with randomly distributed localized near-field induced by silver nano-islands. For the fabrication of nano-islands, a 10-nm silver thin film evaporated on a BK7 glass substrate with an adhesion layer of 2-nm thick chromium. Micrometer sized silver square pattern was defined using e-beam lithography and then the film was annealed at 200°C. Raw images were restored using electric field distribution produced on the surface of random nano-islands. Nano-islands were modeled from SEM images. 488-nm p-polarized light source was set to be incident at 60°. Simulation results show that localized electric fields were created among nano-islands and that their average size was found to be 135 nm. The feasibility was tested using conventional total internal reflection fluorescence microscopy while the angle of incidence was adjusted to maximize field enhancement. Mouse microphage cells were cultured on nano-islands, and actin filaments were selectively stained with FITC-conjugated phalloidin. Acquired images were deconvolved based on linear imaging theory, in which molecular distribution was sampled by randomly distributed localized near-field and blurred by point spread function of far-field optics. The optimum fluorophore distribution was probabilistically estimated by repetitively matching a raw image. The deconvolved images are estimated to have a resolution in the range of 100-150 nm largely determined by the size of localized near-fields. We also discuss and compare the results with images acquired with periodic nano-aperture arrays in various optical configurations to excite localized plasmonic fields and to produce super-resolved molecular images.

Silicon Field Effect Transistors as Dual-Use Sensor-Heater Hybrids

PubMed Central

Reddy, Bobby; Elibol, Oguz H.; Nair, Pradeep R.; Dorvel, Brian R.; Butler, Felice; Ahsan, Zahab; Bergstrom, Donald E.; Alam, Muhammad A.; Bashir, Rashid

2011-01-01

We demonstrate the temperature mediated applications of a previously proposed novel localized dielectric heating method on the surface of dual purpose silicon field effect transistor (FET) sensor-heaters and perform modeling and characterization of the underlying mechanisms. The FETs are first shown to operate as electrical sensors via sensitivity to changes in pH in ionic fluids. The same devices are then demonstrated as highly localized heaters via investigation of experimental heating profiles and comparison to simulation results. These results offer further insight into the heating mechanism and help determine the spatial resolution of the technique. Two important biosensor platform applications spanning different temperature ranges are then demonstrated: a localized heat-mediated DNA exchange reaction and a method for dense selective functionalization of probe molecules via the heat catalyzed complete desorption and reattachment of chemical functionalization to the transistor surfaces. Our results show that the use of silicon transistors can be extended beyond electrical switching and field-effect sensing to performing localized temperature controlled chemical reactions on the transistor itself. PMID:21214189

Ester carbonyl vibration as a sensitive probe of protein local electric field.

PubMed

Pazos, Ileana M; Ghosh, Ayanjeet; Tucker, Matthew J; Gai, Feng

2014-06-10

The ability to quantify the local electrostatic environment of proteins and protein/peptide assemblies is key to gaining a microscopic understanding of many biological interactions and processes. Herein, we show that the ester carbonyl stretching vibration of two non-natural amino acids, L-aspartic acid 4-methyl ester and L-glutamic acid 5-methyl ester, is a convenient and sensitive probe in this regard, since its frequency correlates linearly with the local electrostatic field for both hydrogen-bonding and non-hydrogen-bonding environments. We expect that the resultant frequency-electric-field map will find use in various applications. Furthermore, we show that, when situated in a non-hydrogen-bonding environment, this probe can also be used to measure the local dielectric constant (ε). For example, its application to amyloid fibrils formed by Aβ(16-22) revealed that the interior of such β-sheet assemblies has an ε value of approximately 5.6. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Electric force on plasma ions and the momentum of the ion-neutrals flow

NASA Astrophysics Data System (ADS)

Makrinich, G.; Fruchtman, A.; Zoler, D.; Boxman, R. L.

2018-05-01

The electric force on ions in plasma and the momentum flux carried by the mixed ion-neutral flow were measured and found to be equal. The experiment was performed in a direct-current gas discharge of cylindrical geometry with applied radial electric field and axial magnetic field. The unmagnetized plasma ions, neutralized by magnetized electrons, were accelerated radially outward transferring part of the gained momentum to neutrals. Measurements were taken for various argon gas flow rates between 13 and 100 Standard Cubic Centimeter per Minute, for a discharge current of 1.9 A and a magnetic field intensity of 136 G. The plasma density, electron temperature, and plasma potential were measured at various locations along the flow. These measurements were used to determine the local electric force on the ions. The total electric force on the plasma ions was then determined by integrating radially the local electric force. In parallel, the momentum flux of the mixed ion-neutral flow was determined by measuring the force exerted by the flow on a balance force meter (BFM). The maximal plasma density was between 6 × 1010 cm-3 and 5 × 1011 cm-3, the maximal electron temperature was between 8 eV and 25 eV, and the deduced maximal electric field was between 2200 V/m and 5800 V/m. The force exerted by the mixed ion-neutral flow on the BFM agreed with the total electric force on the plasma ions. This agreement showed that it is the electric force on the plasma ions that is the source of the momentum acquired by the mixed ion-neutral flow.

Surgical wound monitoring by MRI with a metamaterial-based implanted local coil

NASA Astrophysics Data System (ADS)

Kamel, Hanan; Syms, Richard R. A.; Kardoulaki, Evdokia M.; Rea, Marc

2018-03-01

An implantable sensor for monitoring surgical wounds after bowel reconstruction is proposed. The sensor consists of a coupled pair of 8-element magneto-inductive ring resonators, designed for mounting on a biofragmentable anastomosis ring to give a local increase in signal-to-noise ratio near an annular wound during 1H magnetic resonance imaging. Operation on an anti-symmetric spatial mode is used to avoid coupling to the B1 field during excitation, and a single wired connection is used for MRI signal output. The electrical response and field-of-view are estimated theoretically. Prototypes are constructed from flexible elements designed for operation at 1.5 T, electrical responses are characterized and local SNR enhancement is confirmed using agar gel phantoms.

Phase transition studies of BiMnO{sub 3}: Mean field theory approximations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lakshmi Priya, K. B.; Natesan, Baskaran, E-mail: nbaski@nitt.edu

We studied the phase transition and magneto-electric coupling effect of BiMnO{sub 3} by employing mean field theory approximations. To capture the ferromagnetic and ferroelectric transitions of BiMnO{sub 3}, we construct an extended Ising model in a 2D square lattice, wherein, the magnetic (electric) interactions are described in terms of the direct interactions between the localized magnetic (electric dipole) moments of Mn ions with their nearest neighbors. To evaluate our model, we obtain magnetization, magnetic susceptibility and electric polarization using mean field approximation calculations. Our results reproduce both the ferromagnetic and the ferroelectric transitions, matching very well with the experimental reports.more » Furthermore, consistent with experimental observations, our mean field results suggest that there is indeed a coupling between the magnetic and electric ordering in BiMnO{sub 3}.« less

Specific features of electric field in the atmosphere and Radon emanations in Tunkin Basin of Baikal rift zone

NASA Astrophysics Data System (ADS)

Soloviev, S.; Loktev, D.

2013-05-01

Development of methods for diagnosing local crust encourages finding new ways for preventing hazardous geologic phenomena. Using measurements of several geophysical fields in addition to seismic methods enables to improve the existing methods and increase their reliability. In summer of 2009 and 2010, complex geophysical acquisition company was organized in the Tunkin Basin of the Baikal rift zone in South-Eastern Siberia, that runs 200 km to East-West from the southern tip of Baikal. Stationary observations were carried out in the central part of the Tunkin Basin, at the Geophysical observatory "I" of Institute of Solar-Terrestrial Physics of Siberian Branch of RAS and "II" near the Arshan settlement. Along with observations of microseismic noise and electric field variations in soil, there were performed measurements of electric field strength (Ez) in lowest atmosphere and volumetric activity of natural Radon in subsoil. Meteorological parameters were monitored with the use of DavisVantagePro meteorological stations. The analysis of observations showed that characteristic features of electric field in near-surface atmosphere are majorly defined by complex orography of the place and, consequently, by quickly changing meteorological conditions: thunderstorm activity and other mesometeorological events (with characteristic scale of tens of km and few hours long) in nearby rocks. The results of Ez(t) measurements performed under "good" weather conditions showed that the character of field variations depended on the local time with their maximum in daylight hours and minimum in the night. The analysis of Radon volumetric activity evidenced that its variations are influenced by atmospheric pressure and tides, and such influence is different at points "I" and "II". In particular, the tidal and atmospheric influence on Radon variations is more pronounced at "II" if compared to "I", which can be explained by locations of the registration points. Registration Point "II" is located close to tectonic faults, while "I" is in the center of the basin with its quite thick layer of sediments. Axial section observations of spatial inhomogeneities of electric field and Radon emanation were set along and across the Tunkin Basin. Observation points were set 3 to 10 km apart depending on the local relief. Each point was registering for 60 min under the conditions of "good" weather. There were analysed changes in mean strength of electric field and Radon volumetric activity as a function of distance along the axial section. It was found out that volumetric activity and electric field strength change in phase opposition - radon volumetric activity increase results in more intense ionization in near-surface atmosphere and consequently to decrease in the electric field strength. The concentration of Radon in subsoil atmosphere increases, and electric field strength decreases when approaching to rift zones rimming the Tunkin Basin from North and South. The results of axial section observations can be successfully used when mapping geological inhomogeneities in the Earth's crust. The research was done with financial support of RFBR, project# 12-05-00578

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

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gao, Weimin; Niu, Haitao; Lin, Tong

2014-01-28

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

Spectral method for the static electric potential of a charge density in a composite medium

NASA Astrophysics Data System (ADS)

Bergman, David J.; Farhi, Asaf

2018-04-01

A spectral representation for the static electric potential field in a two-constituent composite medium is presented. A theory is developed for calculating the quasistatic eigenstates of Maxwell's equations for such a composite. The local physical potential field produced in the system by a given source charge density is expanded in this set of orthogonal eigenstates for any position r. The source charges can be located anywhere, i.e., inside any of the constituents. This is shown to work even if the eigenfunctions are normalized in an infinite volume. If the microstructure consists of a cluster of separate inclusions in a uniform host medium, then the quasistatic eigenstates of all the separate isolated inclusions can be used to calculate the eigenstates of the total structure as well as the local potential field. Once the eigenstates are known for a given host and a given microstructure, then calculation of the local field only involves calculating three-dimensional integrals of known functions and solving sets of linear algebraic equations.

Magnetic Field Homogenization of the Human Prefrontal Cortex with a Set of Localized Electrical Coils

PubMed Central

Juchem, Christoph; Nixon, Terence W.; McIntyre, Scott; Rothman, Douglas L.; de Graaf, Robin A.

2011-01-01

The prefrontal cortex is a common target brain structure in psychiatry and neuroscience due to its role in working memory and cognitive control. Large differences in magnetic susceptibility between the air-filled sinuses and the tissue/bone in the frontal part of the human head cause a strong and highly localized magnetic field focus in the prefrontal cortex. As a result, image distortion and signal dropout are observed in MR imaging. A set of external, electrical coils is presented that provides localized and high amplitude shim fields in the prefrontal cortex with minimum impact on the rest of the brain when combined with regular zero-to-second order spherical harmonics shimming. The experimental realization of the new shim method strongly minimized or even eliminated signal dropout in gradient-echo images acquired at settings typically used in functional magnetic resonance at 4 Tesla. PMID:19918909

Controlled nanopatterning of a polymerized ionic liquid in a strong electric field

DOE PAGES

Bocharova, Vera; Agapov, Alexander L.; Tselev, Alexander; ...

2014-12-17

Nanolithography has become a driving force in advancements of the modern day's electronics, allowing for miniaturization of devices and a steady increase of the calculation, power, and storage densities. Among various nanofabrication approaches, scanning probe techniques, including atomic force microscopy (AFM), are versatile tools for creating nanoscale patterns utilizing a range of physical stimuli such as force, heat, or electric field confined to the nanoscale. In this study, the potential of using the electric field localized at the apex of an AFM tip to induce and control changes in the mechanical properties of an ion containing polymer—a polymerized ionic liquidmore » (PolyIL)—on a very localized scale is explored. In particular, it is demonstrated that by means of AFM, one can form topographical features on the surface of PolyIL-based thin films with a significantly lower electric potential and power consumption as compared to nonconductive polymer materials. Lastly,, by tuning the applied voltage and ambient air humidity, control over dimensions of the formed structures is reproducibly achieved.« less

Electrical and mechanical characterization of nanoscale-layered cellulose-based electro-active paper.

PubMed

Yun, Gyu-Young; Yun, Ki-Ju; Kim, Joo-Hyung; Kim, Jaehwan

2011-01-01

In order to understand the electro-mechanical behavior of piezoelectric electro active paper (EAPap), the converse and direct piezoelectric characterization of cellulose EAPap was studied and compared. A delay between the electrical field and the induced strain of EAPap was observed due to the inner nano-voids or the localized amorphous regions in layer-by-layered structure to capture or hold the electrical charges and remnant ions. The linear relation between electric field and induced strain is also observed. The electro-mechanical performance of EAPap is discussed in detail in this paper.

Nanoscale electron manipulation in metals with intense THz electric fields

NASA Astrophysics Data System (ADS)

Takeda, Jun; Yoshioka, Katsumasa; Minami, Yasuo; Katayama, Ikufumi

2018-03-01

Improved control over the electromagnetic properties of metals on a nanoscale is crucial for the development of next-generation nanoelectronics and plasmonic devices. Harnessing the terahertz (THz)-electric-field-induced nonlinearity for the motion of electrons is a promising method of manipulating the local electromagnetic properties of metals, while avoiding undesirable thermal effects and electronic transitions. In this review, we demonstrate the manipulation of electron delocalization in ultrathin gold (Au) films with nanostructures, by intense THz electric-field transients. On increasing the electric-field strength of the THz pulses, the transmittance in the THz-frequency region abruptly decreases around the percolation threshold. The observed THz-electric-field-induced nonlinearity is analysed, based on the Drude-Smith model. The results suggest that ultrafast electron delocalization occurs by electron tunnelling across the narrow insulating bridge between the Au nanostructures, without material breakdown. In order to quantitatively discuss the tunnelling process, we perform scanning tunnelling microscopy with carrier-envelope phase (CEP)-controlled single-cycle THz electric fields. By applying CEP-controlled THz electric fields to the 1 nm nanogap between a metal nanotip and graphite sample, many electrons could be coherently driven through the quantum tunnelling process, either from the nanotip to the sample or vice versa. The presented concept, namely, electron tunnelling mediated by CEP-controlled single-cycle THz electric fields, can facilitate the development of nanoscale electron manipulation, applicable to next-generation ultrafast nanoelectronics and plasmonic devices.

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

NASA Technical Reports Server (NTRS)

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

Controlling stray electric fields on an atom chip for experiments on Rydberg atoms

NASA Astrophysics Data System (ADS)

Davtyan, D.; Machluf, S.; Soudijn, M. L.; Naber, J. B.; van Druten, N. J.; van Linden van den Heuvell, H. B.; Spreeuw, R. J. C.

2018-02-01

Experiments handling Rydberg atoms near surfaces must necessarily deal with the high sensitivity of Rydberg atoms to (stray) electric fields that typically emanate from adsorbates on the surface. We demonstrate a method to modify and reduce the stray electric field by changing the adsorbate distribution. We use one of the Rydberg excitation lasers to locally affect the adsorbed dipole distribution. By adjusting the averaged exposure time we change the strength (with the minimal value less than 0.2 V /cm at 78 μ m from the chip) and even the sign of the perpendicular field component. This technique is a useful tool for experiments handling Rydberg atoms near surfaces, including atom chips.

Multiple mobility edges in a 1D Aubry chain with Hubbard interaction in presence of electric field: Controlled electron transport

NASA Astrophysics Data System (ADS)

Saha, Srilekha; Maiti, Santanu K.; Karmakar, S. N.

2016-09-01

Electronic behavior of a 1D Aubry chain with Hubbard interaction is critically analyzed in presence of electric field. Multiple energy bands are generated as a result of Hubbard correlation and Aubry potential, and, within these bands localized states are developed under the application of electric field. Within a tight-binding framework we compute electronic transmission probability and average density of states using Green's function approach where the interaction parameter is treated under Hartree-Fock mean field scheme. From our analysis we find that selective transmission can be obtained by tuning injecting electron energy, and thus, the present model can be utilized as a controlled switching device.

Unmasking local activity within local field potentials (LFPs) by removing distal electrical signals using independent component analysis.

PubMed

Whitmore, Nathan W; Lin, Shih-Chieh

2016-05-15

Local field potentials (LFPs) are commonly thought to reflect the aggregate dynamics in local neural circuits around recording electrodes. However, we show that when LFPs are recorded in awake behaving animals against a distal reference on the skull as commonly practiced, LFPs are significantly contaminated by non-local and non-neural sources arising from the reference electrode and from movement-related noise. In a data set with simultaneously recorded LFPs and electroencephalograms (EEGs) across multiple brain regions while rats perform an auditory oddball task, we used independent component analysis (ICA) to identify signals arising from electrical reference and from volume-conducted noise based on their distributed spatial pattern across multiple electrodes and distinct power spectral features. These sources of distal electrical signals collectively accounted for 23-77% of total variance in unprocessed LFPs, as well as most of the gamma oscillation responses to the target stimulus in EEGs. Gamma oscillation power was concentrated in volume-conducted noise and was tightly coupled with the onset of licking behavior, suggesting a likely origin of muscle activity associated with body movement or orofacial movement. The removal of distal signal contamination also selectively reduced correlations of LFP/EEG signals between distant brain regions but not within the same region. Finally, the removal of contamination from distal electrical signals preserved an event-related potential (ERP) response to auditory stimuli in the frontal cortex and also increased the coupling between the frontal ERP amplitude and neuronal activity in the basal forebrain, supporting the conclusion that removing distal electrical signals unmasked local activity within LFPs. Together, these results highlight the significant contamination of LFPs by distal electrical signals and caution against the straightforward interpretation of unprocessed LFPs. Our results provide a principled approach to identify and remove such contamination to unmask local LFPs. Published by Elsevier Inc.

Unmasking local activity within local field potentials (LFPs) by removing distal electrical signals using independent component analysis

PubMed Central

Whitmore, Nathan W.; Lin, Shih-Chieh

2016-01-01

Local field potentials (LFPs) are commonly thought to reflect the aggregate dynamics in local neural circuits around recording electrodes. However, we show that when LFPs are recorded in awake behaving animals against a distal reference on the skull as commonly practiced, LFPs are significantly contaminated by non-local and non-neural sources arising from the reference electrode and from movement-related noise. In a data set with simultaneously recorded LFPs and electroencephalograms (EEGs) across multiple brain regions while rats perform an auditory oddball task, we used independent component analysis (ICA) to identify signals arising from electrical reference and from volume-conducted noise based on their distributed spatial pattern across multiple electrodes and distinct power spectral features. These sources of distal electrical signals collectively accounted for 23–77% of total variance in unprocessed LFPs, as well as most of the gamma oscillation responses to the target stimulus in EEGs. Gamma oscillation power was concentrated in volume-conducted noise and was tightly coupled with the onset of licking behavior, suggesting a likely origin of muscle activity associated with body movement or orofacial movement. The removal of distal signal contamination also selectively reduced correlations of LFP/EEG signals between distant brain regions but not within the same region. Finally, the removal of contamination from distal electrical signals preserved an event-related potential (ERP) response to auditory stimuli in the frontal cortex and also increased the coupling between the frontal ERP amplitude and neuronal activity in the basal forebrain, supporting the conclusion that removing distal electrical signals unmasked local activity within LFPs. Together, these results highlight the significant contamination of LFPs by distal electrical signals and caution against the straightforward interpretation of unprocessed LFPs. Our results provide a principled approach to identify and remove such contamination to unmask local LFPs. PMID:26899209

Educational application for visualization and analysis of electric field strength in multiple electrode electroporation.

PubMed

Mahnič-Kalamiza, Samo; Kotnik, Tadej; Miklavčič, Damijan

2012-10-30

Electrochemotherapy is a local treatment that utilizes electric pulses in order to achieve local increase in cytotoxicity of some anticancer drugs. The success of this treatment is highly dependent on parameters such as tissue electrical properties, applied voltages and spatial relations in placement of electrodes that are used to establish a cell-permeabilizing electric field in target tissue. Non-thermal irreversible electroporation techniques for ablation of tissue depend similarly on these parameters. In the treatment planning stage, if oversimplified approximations for evaluation of electric field are used, such as U/d (voltage-to-distance ratio), sufficient field strength may not be reached within the entire target (tumor) area, potentially resulting in treatment failure. In order to provide an aid in education of medical personnel performing electrochemotherapy and non-thermal irreversible electroporation for tissue ablation, assist in visualizing the electric field in needle electrode electroporation and the effects of changes in electrode placement, an application has been developed both as a desktop- and a web-based solution. It enables users to position up to twelve electrodes in a plane of adjustable dimensions representing a two-dimensional slice of tissue. By means of manipulation of electrode placement, i.e. repositioning, and the changes in electrical parameters, the users interact with the system and observe the resulting electrical field strength established by the inserted electrodes in real time. The field strength is calculated and visualized online and instantaneously reflects the desired changes, dramatically improving the user friendliness and educational value, especially compared to approaches utilizing general-purpose numerical modeling software, such as finite element modeling packages. In this paper we outline the need and offer a solution in medical education in the field of electroporation-based treatments, e.g. primarily electrochemotherapy and non-thermal irreversible tissue ablation. We present the background, the means of implementation and the fully functional application, which is the first of its kind. While the initial feedback from students that have evaluated this application as part of an e-learning course is positive, a formal study is planned to thoroughly evaluate the current version and identify possible future improvements and modifications.

Magneto-electric Nanoparticles to Enable Field-controlled High-Specificity Drug Delivery to Eradicate Ovarian Cancer Cells

PubMed Central

Guduru, Rakesh; Liang, Ping; Runowicz, Carolyn; Nair, Madhavan; Atluri, Venkata; Khizroev, Sakhrat

2013-01-01

The nanotechnology capable of high-specificity targeted delivery of anti-neoplastic drugs would be a significant breakthrough in Cancer in general and Ovarian Cancer in particular. We addressed this challenge through a new physical concept that exploited (i) the difference in the membrane electric properties between the tumor and healthy cells and (ii) the capability of magneto-electric nanoparticles (MENs) to serve as nanosized converters of remote magnetic field energy into the MENs' intrinsic electric field energy. This capability allows to remotely control the membrane electric fields and consequently trigger high-specificity drug uptake through creation of localized nano-electroporation sites. In in-vitro studies on human ovarian carcinoma cell (SKOV-3) and healthy cell (HOMEC) lines, we applied a 30-Oe d.c. field to trigger high-specificity uptake of paclitaxel loaded on 30-nm CoFe2O4@BaTiO3 MENs. The drug penetrated through the membrane and completely eradicated the tumor within 24 hours without affecting the normal cells. PMID:24129652

Magneto-electric nanoparticles to enable field-controlled high-specificity drug delivery to eradicate ovarian cancer cells.

PubMed

Guduru, Rakesh; Liang, Ping; Runowicz, Carolyn; Nair, Madhavan; Atluri, Venkata; Khizroev, Sakhrat

2013-10-16

The nanotechnology capable of high-specificity targeted delivery of anti-neoplastic drugs would be a significant breakthrough in Cancer in general and Ovarian Cancer in particular. We addressed this challenge through a new physical concept that exploited (i) the difference in the membrane electric properties between the tumor and healthy cells and (ii) the capability of magneto-electric nanoparticles (MENs) to serve as nanosized converters of remote magnetic field energy into the MENs' intrinsic electric field energy. This capability allows to remotely control the membrane electric fields and consequently trigger high-specificity drug uptake through creation of localized nano-electroporation sites. In in-vitro studies on human ovarian carcinoma cell (SKOV-3) and healthy cell (HOMEC) lines, we applied a 30-Oe d.c. field to trigger high-specificity uptake of paclitaxel loaded on 30-nm CoFe₂O₄ @BaTiO₃ MENs. The drug penetrated through the membrane and completely eradicated the tumor within 24 hours without affecting the normal cells.

Optical properties of plasmonic nanostructures: Theory & experiments

NASA Astrophysics Data System (ADS)

Bala Krishna, Juluri

Metal nanoparticles and thin films enable localization of electromagnetic energy in the form of localized surface plasmon resonances (LSPR) and propagating surface plasmons respectively. This research field, also known as plasmonics, involves understanding and fabricating innovative nanostructures designed to manage and utilize localized light in the nanoscale. Advances in plasmonics will facilitate innovation in sensing, biomedical engineering, energy harvesting and nanophotonic devices. In this thesis, three aspects of plasmonics are studied: 1) active plasmonic systems using charge-induced plasmon shifts (CIPS) and plasmon-molecule resonant coupling; 2) scalable solutions to fabricate large electric field plasmonic nanostructures; and 3) controlling the propagation of designer surface plasmons (DSPs) using parabolic graded media. The full potential of plasmonics can be realized with active plasmonic devices which provide tunable plasmon resonances. The work reported here develops both an understanding for and realization of various mechanisms to achieve tunable plasmonic systems. First, we show that certain nanoparticle geometries and material compositions enable large CIPS. Second, we propose and investigate systems which exhibit coupling between molecular and plasmonic resonances where energy splitting is observed due to interactions between plasmons and molecules. Large electric field nanostructures have many promising applications in the areas of surface enhanced Raman spectroscopy, higher harmonic light generation, and enhanced uorescence. High throughput techniques that utilize simple nanofabrication are essential their advancement. We contribute to this effort by using a salting-out quenching technique and colloidal lithography to fabricate nanodisc dimers and cusp nanostructures that allow localization of large electric fields, and are comparable to structures fabricated by conventional lithography/milling techniques. Designer surface plasmons (DSPs) are surface waves that are localized to the interface between a structured perfect electric conductor (PEC) surface and dielectric medium. Terahertz (THz) DSPs excited on microscale structured PEC are localized in the out-of-plane direction, with negligible in-plane localization. We addressed this problem by subjecting DSPs to a parabolic graded-index structure. Lateral confinement such as focusing, collimation, and waveguiding of DSPs is demonstrated. Such control will pave the way towards THz energy concentration, diffusion, guiding, and beam aperture modifcation.

Micro-Hall devices for magnetic, electric and photo-detection

NASA Astrophysics Data System (ADS)

Gilbertson, A.; Sadeghi, H.; Panchal, V.; Kazakova, O.; Lambert, C. J.; Solin, S. A.; Cohen, L. F.

Multifunctional mesoscopic sensors capable of detecting local magnetic (B) , electric (E) , and optical fields can greatly facilitate image capture in nano-arrays that address a multitude of disciplines. The use of micro-Hall devices as B-field sensors and, more recently as E-field sensors is well established. Here we report the real-space voltage response of InSb/AlInSb micro-Hall devices to not only local E-, and B-fields but also to photo-excitation using scanning probe microscopy. We show that the ultrafast generation of localised photocarriers results in conductance perturbations analogous to those produced by local E-fields. Our experimental results are in good agreement with tight-binding transport calculations in the diffusive regime. At room temperature, samples exhibit a magnetic sensitivity of >500 nT/ √Hz, an optical noise equivalent power of >20 pW/ √Hz (λ = 635 nm) comparable to commercial photoconductive detectors, and charge sensitivity of >0.04 e/ √Hz comparable to that of single electron transistors. Work done while on sabbatical from Washington University. Co-founder of PixelEXX, a start-up whose focus is imaging nano-arrays.

Skin Rejuvenation with Non-Invasive Pulsed Electric Fields

NASA Astrophysics Data System (ADS)

Golberg, Alexander; Khan, Saiqa; Belov, Vasily; Quinn, Kyle P.; Albadawi, Hassan; Felix Broelsch, G.; Watkins, Michael T.; Georgakoudi, Irene; Papisov, Mikhail; Mihm, Martin C., Jr.; Austen, William G., Jr.; Yarmush, Martin L.

2015-05-01

Degenerative skin diseases affect one third of individuals over the age of sixty. Current therapies use various physical and chemical methods to rejuvenate skin; but since the therapies affect many tissue components including cells and extracellular matrix, they may also induce significant side effects, such as scarring. Here we report on a new, non-invasive, non-thermal technique to rejuvenate skin with pulsed electric fields. The fields destroy cells while simultaneously completely preserving the extracellular matrix architecture and releasing multiple growth factors locally that induce new cells and tissue growth. We have identified the specific pulsed electric field parameters in rats that lead to prominent proliferation of the epidermis, formation of microvasculature, and secretion of new collagen at treated areas without scarring. Our results suggest that pulsed electric fields can improve skin function and thus can potentially serve as a novel non-invasive skin therapy for multiple degenerative skin diseases.

Theory of charge density wave depinning by electromechanical effect

NASA Astrophysics Data System (ADS)

Quémerais, P.

2017-03-01

We discuss the first theory for the depinning of low-dimensional, incommensurate, charge density waves (CDWs) in the strong electron-phonon (e-p) regime. Arguing that most real CDWs systems invariably develop a gigantic dielectric constant (GDC) at very low frequencies, we propose an electromechanical mechanism which is based on a local field effect. At zero electric field and large enough e-p coupling the structures are naturally pinned by the lattice due to its discreteness, and develop modulation functions which are characterized by discontinuities. When the electric field is turned on, we show that it exists a finite threshold value for the electric field above which the discontinuities of the modulation functions vanish due to CDW deformation. The CDW is then free to move. The signature of this pinning/depinning transition as a function of the increasing electric field can be directly observed in the phonon spectrum by using inelastic neutrons or X-rays experiments.

Cosmic rays and the electric field of thunderclouds: Evidence for acceleration of particles (runaway electrons)

NASA Astrophysics Data System (ADS)

Khaerdinov, N. S.; Lidvansky, A. S.; Petkov, V. B.

2005-07-01

We present the data on correlations of the intensity of the soft component of cosmic rays with the local electric field of the near-earth atmosphere during thunderstorm periods at the Baksan Valley (North Caucasus, 1700 m a.s.l.). The large-area array for studying the extensive air showers of cosmic rays is used as a particle detector. An electric field meter of the 'electric mill' type (rain-protected) is mounted on the roof of the building in the center of this array. The data were obtained in the summer seasons of 2000-2002. We observe strong enhancements of the soft component intensity before some lightning strokes. At the same time, the analysis of the regression curve 'intensity versus field' discovers a bump at the field sign that is opposite to the field sign corresponding to acceleration of electrons. It is interpreted as a signature of runaway electrons from the region of the strong field (with opposite sign) overhead.

Hydrogel Actuation by Electric Field Driven Effects

NASA Astrophysics Data System (ADS)

Morales, Daniel Humphrey

Hydrogels are networks of crosslinked, hydrophilic polymers capable of absorbing and releasing large amounts of water while maintaining their structural integrity. Polyelectrolyte hydrogels are a subset of hydrogels that contain ionizable moieties, which render the network sensitive to the pH and the ionic strength of the media and provide mobile counterions, which impart conductivity. These networks are part of a class of "smart" material systems that can sense and adjust their shape in response to the external environment. Hence, the ability to program and modulate hydrogel shape change has great potential for novel biomaterial and soft robotics applications. We utilized electric field driven effects to manipulate the interaction of ions within polyelectrolyte hydrogels in order to induce controlled deformation and patterning. Additionally, electric fields can be used to promote the interactions of separate gel networks, as modular components, and particle assemblies within gel networks to develop new types of soft composite systems. First, we present and analyze a walking gel actuator comprised of cationic and anionic gel legs attached by electric field-promoted polyion complexation. We characterize the electro-osmotic response of the hydrogels as a function of charge density and external salt concentration. The gel walkers achieve unidirectional motion on flat elastomer substrates and exemplify a simple way to move and manipulate soft matter devices in aqueous solutions. An 'ionoprinting' technique is presented with the capability to topographically structure and actuate hydrated gels in two and three dimensions by locally patterning ions induced by electric fields. The bound charges change the local mechanical properties of the gel to induce relief patterns and evoke localized stress, causing rapid folding in air. The ionically patterned hydrogels exhibit programmable temporal and spatial shape transitions which can be tuned by the duration and/or strength of the applied electric field. We extend the use of ionoprinting to develop multi-responsive bilayer gel systems capable of more complex shape transformation. The localized crosslinked regions determine the bending axis as the gel responds to the external environment. The bending can be tuned to reverse direction isothermally by changing the solvent quality or by changing the temperature at a fixed concentration. The multi-responsive behavior is caused by the volume transitions of a non-ionic, thermos-sensitive hydrogel coupled with a superabsorbent ionic hydrogel. Lastly, electric field driven microparticle assembly, using dielectrophoretic (DEP) forces, organized colloidal microparticles within a hydrogel matrix. The use of DEP forces enables rapid, efficient and precise control over the colloidal distribution. The resulting supracolloidal endoskeleton structures impart directional bending as the hydrogel shrinks. We compare the ordered particles structures to random particle distributions in affecting the hydrogel sheet bending response. This study demonstrates a universal technique for imparting directional properties in hydrogels towards new generations of hybrid soft materials.

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

NASA Astrophysics Data System (ADS)

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

2014-03-01

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.

Progress Towards a New Technique for Measuring Local Electric and Magnetic Field Fluctuations in High Temperature Plasmas

NASA Astrophysics Data System (ADS)

Burke, M. G.; Fonck, R. J.; McKee, G. R.; Winz, G. R.

2017-10-01

Local measurements of electrostatic and magnetic turbulence in fusion grade plasmas is a critical missing component in advancing our understanding of current experiments and validating nonlinear turbulence simulations. A novel diagnostic for measuring local electric and magnetic field fluctuations (Ẽ and B ) is being developed to address this need. It employs high-speed measurements of the spectral linewidth and/or line intensities of the Motional Stark Effect split neutral beam emission. This emission is split into several spectral components, with the amount of splitting being proportional to local magnetic and electric fields at the emission site. High spectral resolution ( 0.025 nm), high throughput ( 0.01 cm2str), and high speed (f 250 kHz) are required for the measurement of fast changes in the MSE spectrum. Spatial heterodyne spectroscopy (SHS) techniques coupled to a CMOS detector can meet these demands. A prototype SHS has been deployed to DIII-D for initial testing in the tokamak environment, SNR evaluation, and neutral beam efficacy. In addition, design studies of the SHS interferogram are ongoing to further optimize the measurement technique. One major contributor to loss of fringe contrast is line broadening arising from employing a large collection lens. This broadening can be mitigated by making the lens at the tokamak wall optically conjugate with the interference fringes image field. Work supported by US DOE Grant DE-FG02-89ER53296.

Calculating the electric field in real human head by transcranial magnetic stimulation with shield plate

NASA Astrophysics Data System (ADS)

Lu, Mai; Ueno, Shoogo

2009-04-01

In this paper, we present a transcranial magnetic stimulation (TMS) system by incorporating a conductive shield plate. The magnetic field, induced current density, and electric field in a real human head were calculated by impedance method and the results were compared with TMS without shielding. Our results show that the field localization can be improved by introducing a conductive shield plate; the stimulation magnitude (depth) in the brain is reduced comparing with the TMS without shielding. The strong magnetic field near the TMS coil is difficult to be efficiently shielded by a thinner conductive shield plate.

Long term electromagnetic monitoring at Parkfield, CA

NASA Astrophysics Data System (ADS)

Kappler, Karl Neil

Electric and magnetic fields in the (10-4-1.0) Hz band were monitored at two sites adjacent to the San Andreas Fault near Parkfield and Hollister, California. Observed fields typically comprise natural magnetotelluric fields, with cultural and instrument noise. A data window [2002-2005], enclosing the September 28, 2004 M6 Parkfield earthquake, was analyzed to determine if anomalous electric or magnetic fields, or changes in ground conductivity, occurred before the earthquake. The data were edited, removing intervals of instrument malfunction, leaving 875 days left in the four-year period. Frequent, local spike-like disturbances were removed. The distribution of these spikes was not biased around the time of the earthquake. Signal to noise ratios, estimated via magnetotelluric processing techniques, provided an index of data quality. Plots of signal and noise amplitude spectra, showed the behavior of the ULF fields to be remarkably constant over the period of analysis. From these first-order plots, it is clear that most of the recorded energy is coherent over the spatial extent of the array. Three main statistical techniques were employed to separate local anomalous electrical or magnetic fields from the dominant coherent natural fields: transfer function estimates between components at each site were employed to subtract the dominant field, and look deeper at the 'residual' fields; the data were decomposed into principal components to identify linear combinations of array channels, which are maximally uncorrelated; the technique of canonical coherences was employed to distinguish anomalous fields which are spatially broad from anomalies which occur at a single site only, and furthermore to distinguish anomalies which are present in both the electric and magnetic fields form those which are present in only one field type. Standard remote reference apparent resistivity estimates were generated daily at Parkfield. Most of the variation was observed to be seasonal, and frequency independent, suggesting a local seasonal distortion effect. Once corrected for distortion, nearly all of the variability in the apparent resistivity was removed. In all cases, high levels of sensitivity to subtle electromagnetic effects were demonstrated, but no effects which can be described as precursors to the Parkfield earthquake were found.

Directed motion of vortices and annihilation of vortex-antivortex pairs in finite-gap superconductors via hot-lattice routes

NASA Astrophysics Data System (ADS)

Gulian, Ellen D.; Melkonyan, Gurgen G.; Gulian, Armen M.

2017-07-01

Using finite gap, time-dependent Ginzburg-Landau equations, generalized to include non-thermal phonons, we report numerical simulations of vortex nucleation, propagation, and annihilation in thin, finite strips of magnetic-impurity free, perfectly homogeneous superconductors. When a steady electric current passes through the strip with either surface defects or nonequilibrium phonon sources (e.g., local ;hotspots;), periodic vortex generation and annihilation is observed even in the absence of external magnetic fields. Local pulses of electric field are produced upon annihilation. The injected phonon lines steer the vortices during their motion within the strip, potentially allowing control of the annihilation site.

High-frequency, transient magnetic susceptibility of ferroelectrics

NASA Astrophysics Data System (ADS)

Grimes, Craig A.

1996-10-01

A significant high-frequency magnetic susceptibility was measured both in weakly polarized and nonpolarized samples of barium titanate, lead zirconate titanate, and carnauba wax. Magnetic susceptibility measurements were made from 10 to 500 MHz using a thin film permeameter at room temperature; initial susceptibilities ranged from 0.1 to 2.5. These values are larger than expected for paramagnets and smaller than expected for ferromagnets. It was found that the magnetic susceptibility decreases rapidly with exposure to the exciting field. The origin of the magnetic susceptibility is thought to originate with the applied time varying electric field associated with the susceptibility measurements. An electric field acts to rotate an electric dipole, creating a magnetic quadrupole if the two moments are balanced, and a net magnetic dipole moment if imbalanced. It is thought that local electrostatic fields created at ferroelectric domain discontinuities associated with grain boundaries create an imbalance in the anion rotation that results in a net, measurable, magnetic moment. The origin of the magnetic aftereffect may be due to the local heating of the material through the moving charges associated with the magnetic moment.

A current disruption mechanism in the neutral sheet - A possible trigger for substorm expansions

NASA Technical Reports Server (NTRS)

Lui, A. T. Y.; Mankofsky, A.; Chang, C.-L.; Papadopoulos, K.; Wu, C. S.

1990-01-01

A linear analysis is performed to investigate the kinetic cross-field streaming instability in the earth's magnetotail neutral sheet region. Numerical solution of the dispersion equation shows that the instability can occur under conditions expected for the neutral sheet just prior to the onset of substorm expansion. The excited waves are obliquely propagating whistlers with a mixed polarization in the lower hybrid frequency range. The ensuing turbulence of this instability can lead to a local reduction of the cross-tail current causing it to continue through the ionosphere to form a substorm current wedge. A substorm expansion onset scenario is proposed based on this instability in which the relative drift between ions and electrons is primarily due to unmagnetized ions undergoing current sheet acceleration in the presence of a cross-tail electric field. The required electric field strength is within the range of electric field values detected in the neutral sheet region during substorm intervals. The skew in local time of substorm onset location and the three conditions under which substorm onset is observed can be understood on the basis of the proposed scenario.

Local ion direction of motion and electron flow in a magnetically insulated diode

DOE Office of Scientific and Technical Information (OSTI.GOV)

Maron, Y.; Litwin, C.

Ion motion in the acceleration region of a magnetically insulated ion diode and electron flux to the anode are studied locally. Two classes of slowly growing ion deflections are observed, indicating the presence of transverse electric fields in the diode gap. A simple model, which treates the diode as an emitting surface perturbed away from planarity, is offered to infer profiles of the electric field. These profiles are consistent with the observation that one of the ion-deflection classes is associated with a significant fraction of the increases of the electron flux to the anode. The inferred growth rates of themore » perturbations suggest that the observed ion deflections are caused by a nonuniform expansion of the anode plasma. The transverse electric fields associated with the perturbations constitute a significant (as much as 20%) fraction of the diode accelerating field. Short duration ion deflections accompanied by intense electron bursts to the anode are also observed. The data suggest that these deflections and the electron bursts originate at processes in the cathode plasma.« less

Calibrating MMS Electron Drift Instrument (EDI) Ambient Electron Flux Measurements and Characterizing 3D Electric Field Signatures of Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Shuster, J. R.; Torbert, R. B.; Vaith, H.; Argall, M. R.; Li, G.; Chen, L. J.; Ergun, R. E.; Lindqvist, P. A.; Marklund, G. T.; Khotyaintsev, Y. V.; Russell, C. T.; Magnes, W.; Le Contel, O.; Pollock, C. J.; Giles, B. L.

2015-12-01

The electron drift instruments (EDIs) onboard each MMS spacecraft are designed with large geometric factors (~0.01cm2 str) to facilitate detection of weak (~100 nA) electron beams fired and received by the two gun-detector units (GDUs) when EDI is in its "electric field mode" to determine the local electric and magnetic fields. A consequence of the large geometric factor is that "ambient mode" electron flux measurements (500 eV electrons having 0°, 90°, or 180° pitch angle) can vary depending on the orientation of the EDI instrument with respect to the magnetic field, a nonphysical effect that requires a correction. Here, we present determinations of the θ- and ø-dependent correction factors for the eight EDI GDUs, where θ (ø) is the polar (azimuthal) angle between the GDU symmetry axis and the local magnetic field direction, and compare the corrected fluxes with those measured by the fast plasma instrument (FPI). Using these corrected, high time resolution (~1,000 samples per second) ambient electron fluxes, combined with the unprecedentedly high resolution 3D electric field measurements taken by the spin-plane and axial double probes (SDP and ADP), we are equipped to accurately detect electron-scale current layers and electric field waves associated with the non-Maxwellian (anisotropic and agyrotropic) particle distribution functions predicted to exist in the reconnection diffusion region. We compare initial observations of the diffusion region with distributions and wave analysis from PIC simulations of asymmetric reconnection applicable for modeling reconnection at the Earth's magnetopause, where MMS will begin Science Phase 1 as of September 1, 2015.

Transient electroosmotic flow induced by AC electric field in micro-channel with patchwise surface heterogeneities.

PubMed

Luo, Win-Jet

2006-03-15

This paper investigates two-dimensional, time-dependent electroosmotic flow driven by an AC electric field via patchwise surface heterogeneities distributed along the micro-channel walls. The time-dependent flow fields through the micro-channel are simulated for various patchwise heterogeneous surface patterns using the backwards-Euler time stepping numerical method. Different heterogeneous surface patterns are found to create significantly different electrokinetic transport phenomena. The transient behavior characteristics of the generated electroosmotic flow are then discussed in terms of the influence of the patchwise surface heterogeneities, the direction of the applied AC electric field, and the velocity of the bulk flow. It is shown that the presence of oppositely charged surface heterogeneities on the micro-channel walls results in the formation of localized flow circulations within the bulk flow. These circulation regions grow and decay periodically in phase with the applied periodic AC electric field intensity. The location and rotational direction of the induced circulations are determined by the directions of the bulk flow velocity and the applied electric field.

Controlled modulation of hard and soft X-ray induced tunneling currents utilizing coaxial metal-insulator-metal probe tips

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cummings, Marvin; Shirato, Nozomi; Kersell, Heath

Here, the effect of a local external electric field on the barrier potential of a tunneling gap is studied utilizing an emerging technique, synchrotron x-ray scanning tunneling microscopy. Here, we demonstrate that the shape of the potential barrier in the tunneling gap can be altered by a localized external electric field, generated by voltages placed on the metallic outer shield of a nanofabricated coaxial metal-insulator-metal tip, resulting in a controlled linear modulation of the tunneling current. Experiments at hard and soft x-ray synchrotron beamlines reveal that both the chemical contrast and magnetic contrast signals measured by the tip can bemore » drastically enhanced, resulting in improved local detection of chemistry and magnetization at the surface.« less

Controlled modulation of hard and soft X-ray induced tunneling currents utilizing coaxial metal-insulator-metal probe tips

DOE PAGES

Cummings, Marvin; Shirato, Nozomi; Kersell, Heath; ...

2017-01-05

Here, the effect of a local external electric field on the barrier potential of a tunneling gap is studied utilizing an emerging technique, synchrotron x-ray scanning tunneling microscopy. Here, we demonstrate that the shape of the potential barrier in the tunneling gap can be altered by a localized external electric field, generated by voltages placed on the metallic outer shield of a nanofabricated coaxial metal-insulator-metal tip, resulting in a controlled linear modulation of the tunneling current. Experiments at hard and soft x-ray synchrotron beamlines reveal that both the chemical contrast and magnetic contrast signals measured by the tip can bemore » drastically enhanced, resulting in improved local detection of chemistry and magnetization at the surface.« less

Motions of charged particles in the magnetosphere under the influence of a time-varying large scale convection electric field

NASA Technical Reports Server (NTRS)

Smith, P. H.; Hoffman, R. A.; Bewtra, N. K.

1979-01-01

The motions of charged particles under the influence of the geomagnetic and electric fields are quite complex in the region of the inner magnetosphere. The Volland-Stern type large-scale convection electric field with gamma = 2 has been used successfully to predict both the plasmapause location and particle enhancements determined from Explorer 45 (S3-A) measurements. Recently introduced into the trajectory calculations of Ejiri et al. (1978) is a time dependence in this electric field based on the variation in Kp for actual magnetic storm conditions. The particle trajectories are computed as they change in this time-varying electric field. Several storm fronts of particles of different magnetic moments are allowed to be injected into the inner magnetosphere from L = 10 in the equatorial plane. The motions of these fronts are presented in a movie format. The local time of injection, the particle magnetic moments and the subsequent temporal history of the magnetospheric electric field play important roles in determining whether the injected particles are trapped within the ring current region or whether they are convected to regions outside the inner magnetosphere.

Electronic functions of solid-to-liquid interfaces of organic semiconductor crystals and ionic liquid

NASA Astrophysics Data System (ADS)

Takeya, J.

2008-10-01

The environment of surface electrons at 'solid-to-liquid' interfaces is somewhat extreme, subjected to intense local electric fields or harsh chemical pressures that high-density ionic charge or polarization of mobile molecules create. In this proceedings, we argue functions of electronic carriers generated at the surface of organic semiconductor crystals in response to the local electric fields in the very vicinity of the interface to ionic liquid. The ionic liquids (ILs), or room temperature molten salts, are gaining considerable interest in the recent decade at the prospect of nonvolatile 'green solvents', with the development of chemically stable and nontoxic compounds. Moreover, such materials are also applied to electrolytes for lithium ion batteries and electric double-layer (EDL) capacitors. Our present solid-to-liquid interfaces of rubrene single crystals and ionic liquids work as fast-switching organic field-effect transistors (OFETs) with the highest transconductance, i.e. the most efficient response of the output current to the input voltage, among the OFETs ever built.

Spatial averaging of fields from half-wave dipole antennas and corresponding SAR calculations in the NORMAN human voxel model between 65 MHz and 2 GHz.

PubMed

Findlay, R P; Dimbylow, P J

2009-04-21

If an antenna is located close to a person, the electric and magnetic fields produced by the antenna will vary in the region occupied by the human body. To obtain a mean value of the field for comparison with reference levels, the Institute of Electrical and Electronic Engineers (IEEE) and International Commission on Non-Ionizing Radiation Protection (ICNIRP) recommend spatially averaging the squares of the field strength over the height the body. This study attempts to assess the validity and accuracy of spatial averaging when used for half-wave dipoles at frequencies between 65 MHz and 2 GHz and distances of lambda/2, lambda/4 and lambda/8 from the body. The differences between mean electric field values calculated using ten field measurements and that of the true averaged value were approximately 15% in the 600 MHz to 2 GHz range. The results presented suggest that the use of modern survey equipment, which takes hundreds rather than tens of measurements, is advisable to arrive at a sufficiently accurate mean field value. Whole-body averaged and peak localized SAR values, normalized to calculated spatially averaged fields, were calculated for the NORMAN voxel phantom. It was found that the reference levels were conservative for all whole-body SAR values, but not for localized SAR, particularly in the 1-2 GHz region when the dipole was positioned very close to the body. However, if the maximum field is used for normalization of calculated SAR as opposed to the lower spatially averaged value, the reference levels provide a conservative estimate of the localized SAR basic restriction for all frequencies studied.

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

NASA Technical Reports Server (NTRS)

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

Effects of microstructural defects on the performance of base-metal multilayer ceramic capacitors

NASA Astrophysics Data System (ADS)

Samantaray, Malay M.

Multilayer ceramic capacitors (MLCCs), owing to their processing conditions, can exhibit microstructure defects such as electrode porosity and roughness. The effect of such extrinsic defects on the electrical performance of these devices needs to be understood in order to achieve successful miniaturization into the submicron dielectric layer thickness regime. Specifically, the presence of non-planar and discontinuous electrodes can lead to local field enhancements while the relative morphologies of two adjacent electrodes determine variations in the local dielectric thickness. To study the effects of electrode morphologies, an analytical approach is taken to calculate the electric field enhancement and leakage current with respect to an ideal parallel-plate capacitor. Idealized electrode defects are used to simulate the electric field distribution. It is shown that the electrode roughness causes both the electric field and the leakage current to increase with respect to that of the ideal flat parallel-plate capacitor. Moreover, finite element methods are used to predict electric field enhancements by as high as 100% within capacitor structures containing rough interfaces and porosity. To understand the influence of microstructural defects on field distributions and leakage current, the real three-dimensional microstructure of local regions in MLCCs are reconstructed using a serial-sectioning technique in the focused ion beam. These microstructures are then converted into a finite element model in order to simulate the perturbations in electric field due to the presence of electrode defects. The electric field is three times the average value, and this leads to increase in current density of these devices. It is also shown that increasing sintering rates of MLCCs leads to improved electrode morphology with smoother more continuous electrodes, which in turn leads to a decrease in electric field enhancement and calculated leakage current density. To simulate scaling effects, the dielectric layer thickness is reduced from 2.0mum to 0.5mum in the three-dimensional microstructure keeping the same electrode morphology. It is seen that the effect of microstructure defects is more pronounced as one approaches thinner layers, leading to higher local electric field concentrations and a concomitant drop in insulation resistance. It is also seen that the electric field values are as high as 3.8 times the average field in termination regions due the disintegrated structure of the electrodes. In order to assess the effect of microstructure on MLCC performance, two sets of multilayer capacitors subjected to two vastly different sintering rates of 150ºC/hr and 3000ºC/hr are compared for their electrical properties. Capacitors with higher electrode continuity exhibit proportionally higher capacitance, provided the grain size distributions are similar. From the leakage current measurements, it is found that the Schottky barrier at the electrode-dielectric interface controls the conduction mechanism. This barrier height is calculated to be 1.06 eV for slow-fired MLCCs and was 1.15 for fast-fired MLCCs. This shows that high concentration of electrode defects cause field perturbations and subsequent drop in the net Schottky barrier height. These results are further supported by frequency-dependent impedance measurements. With temperature dependence behavior of current-voltage trends we note that below temperatures of 135°C, the conduction is controlled by interfacial effects, whereas at higher temperatures it is consistent with bulk-controlled space charge limited current for the samples that are highly reoxidized. The final part of this work studies the various aspects of the initial stages of degradation of MLCCs. MLCCs subjected to unipolar and bipolar degradation are studied for changes in microstructure and electrical properties. With bipolar degradation studies new insights into degradation are gained. First, the ionic accumulation with oxygen vacancies at cathodes is only partially reversible. This has implications on the controlling interface with electronic conduction. Also, it is shown that oxygen vacancy accumulation near the cathodes leads to a drop in insulation resistance. The capacitance also increases with progressive steps of degradation due to the effective thinning of dielectric layer. The reduction in interfacial resistance is also confirmed by impedance analysis. Finally, it is observed that on degradation, the dominant leakage current mechanism changes from being controlled by cathodic injection of electrons to being controlled by their anodic extraction. (Abstract shortened by UMI.)

Geomagnetic responses to the solar wind and the solar activity

NASA Technical Reports Server (NTRS)

Svalgaard, L.

1975-01-01

Following some historical notes, the formation of the magnetosphere and the magnetospheric tail is discussed. The importance of electric fields is stressed and the magnetospheric convection of plasma and magnetic field lines under the influence of large-scale magnetospheric electric fields is outlined. Ionospheric electric fields and currents are intimately related to electric fields and currents in the magnetosphere and the strong coupling between the two regions is discussed. The energy input of the solar wind to the magnetosphere and upper atmosphere is discussed in terms of the reconnection model where interplanetary magnetic field lines merge or connect with the terrestrial field on the sunward side of the magnetosphere. The merged field lines are then stretched behind earth to form the magnetotail so that kinetic energy from the solar wind is converted into magnetic energy in the field lines in the tail. Localized collapses of the crosstail current, which is driven by the large-scale dawn/dusk electric field in the magnetosphere, divert part of this current along geomagnetic field lines to the ionosphere, causing substorms with auroral activity and magnetic disturbances. The collapses also inject plasma into the radiation belts and build up a ring current. Frequent collapses in rapid succession constitute the geomagnetic storm.

Theoretical Investigations of Dielectric Breakdown in CO2: Implications for Atmospheric Discharges on Mars (and Venus)

NASA Astrophysics Data System (ADS)

Riousset, J. A.

2017-12-01

The detection of an atmospheric discharge in the Martian atmosphere by Ruf et al. [GRL, 36, L13202, 2009] supports the idea of a Martian atmospheric electric circuit [Farrell and Desch, JGR, 106, E4, 2001]. However, the lack of subsequent detection of similar events raises the question of the conditions of their initiation, and the existence of Martian lightning remains a controversial question. On Earth, atmospheric electricity manifests itself in the form of glow, corona, streamer, and leader discharges observed as Saint Elmo's fire, sprites, lightning and jets discharges, and other Transient Luminous Events (TLEs). All of these are dielectric breakdown governed by different physics. Their initiation is associated with the crossing of specific electric field thresholds: relativistic runaway, streamer propagation, conventional breakdown, or thermal runaway thresholds, some better understood than others. For example, the initiation of a lightning discharge is known to occur when the local electric field exceeds a value similar to relativistic runaway field, but the exact threshold, as well as the physical mechanisms at work, remain unclear to date. Scaling laws for electric fields (and other quantities) have been established by Pasko et al. [GRL, 25(12), 2123-2126, 1998] and Pasko [NATO Sci. Series, Springer, 253-311, 2006]. In this work, we develop profiles for initiation criteria in air and in other atmospheric environments. We further calculate their associated scaling laws to determine the ability to trigger lightning flashes and TLEs on Mars. This lets us predict the likelihood of electrical discharges and calculate the expected electric field conditions, under which discharges could be observed. We develop the analogy between Earth sand storm [Nicoll et al., Env. Res. Lett., 6, 014001, 2001] and Martian dust storms [Melnik and Parrot, JGR, 103(A12), 1998] to investigate the charge structure and resulting electric fields necessary to initiate dielectric breakdown in the Martian atmosphere. Initiation of electric discharges will be susceptible to local pressure, density, atmospheric composition, and charge structure, and will impact charge moment variations detectable by remote sensing.

A scanning probe mounted on a field-effect transistor: Characterization of ion damage in Si.

PubMed

Shin, Kumjae; Lee, Hoontaek; Sung, Min; Lee, Sang Hoon; Shin, Hyunjung; Moon, Wonkyu

2017-10-01

We have examined the capabilities of a Tip-On-Gate of Field-Effect Transistor (ToGoFET) probe for characterization of FIB-induced damage in Si surface. A ToGoFET probe is the SPM probe which the Field Effect Transistor(FET) is embedded at the end of a cantilever and a Pt tip was mounted at the gate of FET. The ToGoFET probe can detect the surface electrical properties by measuring source-drain current directly modulated by the charge on the tip. In this study, a Si specimen whose surface was processed with Ga+ ion beam was prepared. Irradiation and implantation with Ga+ ions induce highly localized modifications to the contact potential. The FET embedded on ToGoFET probe detected the surface electric field profile generated by schottky contact between the Pt tip and the sample surface. Experimentally, it was shown that significant differences of electric field due to the contact potential barrier in differently processed specimens were observed using ToGOFET probe. This result shows the potential that the local contact potential difference can be measured by simple working principle with high sensitivity. Copyright © 2017 Elsevier Ltd. All rights reserved.

Electrochemically induced maskless metal deposition on micropore wall.

PubMed

Liu, Jie; Hébert, Clément; Pham, Pascale; Sauter-Starace, Fabien; Haguet, Vincent; Livache, Thierry; Mailley, Pascal

2012-05-07

By applying an external electric field across a micropore via an electrolyte, metal ions in the electrolyte can be reduced locally onto the inner wall of the micropore, which was fabricated in a silica-covered silicon membrane. This maskless metal deposition on the silica surface is a result of the pore membrane polarization in the electric field. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Band-Like Behavior of Localized States of Metal Silicide Precipitate in Silicon

NASA Astrophysics Data System (ADS)

Bondarenko, Anton; Vyvenko, Oleg

2018-03-01

Deep-level transient spectroscopy (DLTS) investigations of energy levels of charge-carrier traps associated with precipitates of metal silicide often show that they behave not like localized monoenergetic traps but as a continuous density of allowed states in the bandgap with fast carrier exchange between these states, so-called band-like behavior. This kind of behavior was ascribed to the dislocation loop bounding the platelet, which in addition exhibits an attractive potential caused by long-range elastic strain. In previous works, the presence of the dislocation-related deformation potential in combination with the external electric field of the Schottky diode was included to obtain a reasonable fit of the proposed model to experimental data. Another well-known particular property of extended defects—the presence of their own strong electric field in their vicinity that is manifested in the logarithmic kinetics of electron capture—was not taken into account. We derive herein a theoretical model that takes into account both the external electric field and the intrinsic electric field of dislocation self-charge as well as its deformation potential, which leads to strong temporal variation of the activation energy during charge-carrier emission. We performed numerical simulations of the DLTS spectra based on such a model for a monoenergetic trap, finding excellent agreement with available experimental data.

Effect of bipolar electric fatigue on polarization switching in lead-zirconate-titanate ceramics

NASA Astrophysics Data System (ADS)

Zhukov, Sergey; Fedosov, Sergey; Glaum, Julia; Granzow, Torsten; Genenko, Yuri A.; von Seggern, Heinz

2010-07-01

From comparison of experimental results on polarization switching in fresh and electrically fatigued lead-zirconate-titanate (PZT) over a wide range of applied fields and switching times it is concluded that fatigue alters the local field distribution inside the sample due to the generation of discrete defects, such as voids and cracks. Such defects have a strong influence on the overall electric field distribution by their shape and dielectric permittivity. On this hypothesis, a new phenomenological model of polarization switching in fatigued PZT is proposed. The model assumes that the fatigued sample can be composed of different local regions which exhibit different field strengths but otherwise can be considered as unfatigued. Consequently the temporal response of a fatigued sample is assumed to be the superposition of the field-dependent temporal responses of unfatigued samples weighted by their respective volume fraction. A certain part of the volume is excluded from the overall switching process due to the domain pinning even at earlier stages of fatigue, which can be recovered by annealing. Suitability of the proposed model is demonstrated by a good correlation between experimental and calculated data for differently fatigued samples. Plausible cause of the formation of such regions is the generation of defects such as microcracks and the change in electrical properties at imperfections such as pores or voids.

On Electron-Positron Pair Production by a Spatially Inhomogeneous Electric Field

NASA Astrophysics Data System (ADS)

Chervyakov, A.; Kleinert, H.

2018-05-01

A detailed analysis of electron-positron pair creation induced by a spatially non-uniform and static electric field from vacuum is presented. A typical example is provided by the Sauter potential. For this potential, we derive the analytic expressions for vacuum decay and pair production rate accounted for the entire range of spatial variations. In the limit of a sharp step, we recover the divergent result due to the singular electric field at the origin. The limit of a constant field reproduces the classical result of Euler, Heisenberg and Schwinger, if the latter is properly averaged over the width of a spatial variation. The pair production by the Sauter potential is described for different regimes from weak to strong fields. For all these regimes, the locally constant-field rate is shown to be the upper limit.

Electrical transport properties of CuXSn1-X metallic glasses

NASA Astrophysics Data System (ADS)

Vora, A. M.; Gajjar, P. N.

2018-05-01

In the present paper, we report the electrical resistivity (ρ), the thermoelectric power (TEP) and thermal conductivity (σ) of CuXSn1-X metallic glasses computed from Faber-Ziman formulation with Percus-Yevic (PY) hard sphere structure factors of Ashcroft and Langreth. Our well-recognized model potential is used to represent ionic interaction for the first time with seven local field correction functions due to Hartree (H), Hubbard-Sham (HS), Vashishta-Singwi (VS), Taylor (T), Ichimaru-Utsumi (IU), Farid et al. (F) and Sarkar et al. (S) in the present computation and found suitable for such study. The percentile influence of various local field corrections with respect to Hartree (H) is found in the range of 17.35%-71.55%. It is concluded that, the comparison of present and experimental findings of electrical resistivity (ρ) is highly promising.

Local Magnetic Measurements of Trapped Flux Through a Permanent Current Path in Graphite

NASA Astrophysics Data System (ADS)

Stiller, Markus; Esquinazi, Pablo D.; Quiquia, José Barzola; Precker, Christian E.

2018-04-01

Temperature- and field-dependent measurements of the electrical resistance of different natural graphite samples suggest the existence of superconductivity at room temperature in some regions of the samples. To verify whether dissipationless electrical currents are responsible for the trapped magnetic flux inferred from electrical resistance measurements, we localized them using magnetic force microscopy on a natural graphite sample in remanent state after applying a magnetic field. The obtained evidence indicates that at room temperature a permanent current flows at the border of the trapped flux region. The current path vanishes at the same transition temperature T_c≈ 370 K as the one obtained from electrical resistance measurements on the same sample. This sudden decrease in the phase is different from what is expected for a ferromagnetic material. Time-dependent measurements of the signal show the typical behavior of flux creep of a permanent current flowing in a superconductor. The overall results support the existence of room-temperature superconductivity at certain regions in the graphite structure and indicate that magnetic force microscopy is suitable to localize them. Magnetic coupling is excluded as origin of the observed phase signal.

Remote sensing of mesospheric electric fields using MF radars

NASA Astrophysics Data System (ADS)

Meek, C. E.; Manson, A. H.; Martynenko, S. I.; Rozumenko, V. T.; Tyrnov, O. F.

2004-07-01

Large mesospheric electric fields can play an essential role in middle atmospheric electrodynamics (see, e.g., Goldberg, R. A., Middle Atmospheric Electrodynamics during MAP, Adv. Space Res. 10 (10) (1990) 209). The V/m electric fields of atmospheric origin can be the possible cause of large variations in the electron collision frequency at mesospheric altitudes, and this provides a unique opportunity to take measurements of electric fields in the lower ionosphere by using remote sensing instruments employing radiowave techniques. A technique has been proposed for making estimates of large mesospheric electric field intensities on the lower edge of the ionosphere by using MF radar data and the inherent effective electron collision frequency. To do this, data collected in Canada and Ukraine were utilized. The developed technique permits the changes in mesospheric electric field intensities to be derived from MF radar data in real time. The statistical analysis of data consistent with large mesospheric electric field intensities in the 60-67km region resulted in the following inferences. There are at least two mechanisms for the generation of large mesospheric electric fields in the mesosphere. The most likely mechanism, with a probability of 60-70%, is the summation of random fields from a large number of elementary small-scale mesospheric generators, which results in a one-parameter Rayleigh distribution of the total large mesospheric electric field intensity E with a mean value of approximately 0.7-0.9V/m in the 60-67km altitude region, or in the corresponding one-parameter exponential distribution of the intensity squared E2 of large mesospheric electric fields. The second mechanism of unknown nature, with 5-15% probability, gives rise to the sporadic appearance of large mesospheric electric field intensities E>2.5V/m with a mean of 4V/m. Statistically significant seasonal differences in the averaged large mesospheric electric field parameters have not been revealed. The probability of the absence of local large mesospheric electric fields amounts to approximately 25% for Ukraine and approximately 30% for Canada. A comparison of the Ukrainian and Canadian data indicates the possible existence of a latitudinal dependence in mean large mesospheric electric field features. Hence, the large electric fields are an additional source of electron heating that must be taken into account in studying a disturbed lower ionosphere and radio wave propagation within it.

Geometrical Effects on Nonlinear Electrodiffusion in Cell Physiology

NASA Astrophysics Data System (ADS)

Cartailler, J.; Schuss, Z.; Holcman, D.

2017-12-01

We report here new electrical laws, derived from nonlinear electrodiffusion theory, about the effect of the local geometrical structure, such as curvature, on the electrical properties of a cell. We adopt the Poisson-Nernst-Planck equations for charge concentration and electric potential as a model of electrodiffusion. In the case at hand, the entire boundary is impermeable to ions and the electric field satisfies the compatibility condition of Poisson's equation. We construct an asymptotic approximation for certain singular limits to the steady-state solution in a ball with an attached cusp-shaped funnel on its surface. As the number of charge increases, they concentrate at the end of cusp-shaped funnel. These results can be used in the design of nanopipettes and help to understand the local voltage changes inside dendrites and axons with heterogeneous local geometry.

Modeling of electric field distribution in tissues during electroporation

PubMed Central

2013-01-01

Background Electroporation based therapies and treatments (e.g. electrochemotherapy, gene electrotransfer for gene therapy and DNA vaccination, tissue ablation with irreversible electroporation and transdermal drug delivery) require a precise prediction of the therapy or treatment outcome by a personalized treatment planning procedure. Numerical modeling of local electric field distribution within electroporated tissues has become an important tool in treatment planning procedure in both clinical and experimental settings. Recent studies have reported that the uncertainties in electrical properties (i.e. electric conductivity of the treated tissues and the rate of increase in electric conductivity due to electroporation) predefined in numerical models have large effect on electroporation based therapy and treatment effectiveness. The aim of our study was to investigate whether the increase in electric conductivity of tissues needs to be taken into account when modeling tissue response to the electroporation pulses and how it affects the local electric distribution within electroporated tissues. Methods We built 3D numerical models for single tissue (one type of tissue, e.g. liver) and composite tissue (several types of tissues, e.g. subcutaneous tumor). Our computer simulations were performed by using three different modeling approaches that are based on finite element method: inverse analysis, nonlinear parametric and sequential analysis. We compared linear (i.e. tissue conductivity is constant) model and non-linear (i.e. tissue conductivity is electric field dependent) model. By calculating goodness of fit measure we compared the results of our numerical simulations to the results of in vivo measurements. Results The results of our study show that the nonlinear models (i.e. tissue conductivity is electric field dependent: σ(E)) fit experimental data better than linear models (i.e. tissue conductivity is constant). This was found for both single tissue and composite tissue. Our results of electric field distribution modeling in linear model of composite tissue (i.e. in the subcutaneous tumor model that do not take into account the relationship σ(E)) showed that a very high electric field (above irreversible threshold value) was concentrated only in the stratum corneum while the target tumor tissue was not successfully treated. Furthermore, the calculated volume of the target tumor tissue exposed to the electric field above reversible threshold in the subcutaneous model was zero assuming constant conductivities of each tissue. Our results also show that the inverse analysis allows for identification of both baseline tissue conductivity (i.e. conductivity of non-electroporated tissue) and tissue conductivity vs. electric field (σ(E)) of electroporated tissue. Conclusion Our results of modeling of electric field distribution in tissues during electroporation show that the changes in electrical conductivity due to electroporation need to be taken into account when an electroporation based treatment is planned or investigated. We concluded that the model of electric field distribution that takes into account the increase in electric conductivity due to electroporation yields more precise prediction of successfully electroporated target tissue volume. The findings of our study can significantly contribute to the current development of individualized patient-specific electroporation based treatment planning. PMID:23433433

Local nematic susceptibility in stressed BaFe2As2 from NMR electric field gradient measurements

NASA Astrophysics Data System (ADS)

Kissikov, T.; Sarkar, R.; Lawson, M.; Bush, B. T.; Timmons, E. I.; Tanatar, M. A.; Prozorov, R.; Bud'ko, S. L.; Canfield, P. C.; Fernandes, R. M.; Goh, W. F.; Pickett, W. E.; Curro, N. J.

2017-12-01

The electric field gradient (EFG) tensor at the 75As site couples to the orbital occupations of the As p orbitals and is a sensitive probe of local nematicity in BaFe2As2 . We use nuclear magnetic resonance to measure the nuclear quadrupolar splittings and find that the EFG asymmetry responds linearly to the presence of a strain field in the paramagnetic phase. We extract the nematic susceptibility from the slope of this linear response as a function of temperature and find that it diverges near the structural transition, in agreement with other measures of the bulk nematic susceptibility. Our work establishes an alternative method to extract the nematic susceptibility which, in contrast to transport methods, can be extended inside the superconducting state.

Core-protective half-metallicity in trilayer graphene nanoribbons

NASA Astrophysics Data System (ADS)

Jeon, Gi Wan; Lee, Kyu Won; Lee, Cheol Eui

2017-07-01

Half-metals, playing an important role in spintronics, can be described as materials that enable fully spin-polarized electrical current. Taking place in graphene-based materials, half-metallicity has been shown in zigzag-edged graphene nanoribbons (ZGNRs) under an electric field. Localized electron states on the edge carbons are a key to enabling half-metallicity in ZGNRs. Thus, modification of the localized electron states is instrumental to the carbon-based spintronics. Our simple model shows that in a trilayer ZGNRs (triZGNRs) only the middle layer may become half-metallic leaving the outer layers insulating in an electric field, as confirmed by our density functional theory (DFT) calculations. Due to the different circumstances of the edge carbons, the electron energies at the edge carbons are different near the Fermi level, leading to a layer-selective half-metallicity. We believe that triZGNRs can be the tiniest electric cable (nanocable) form and can open a route to graphene-based spintronics applications.

Effect of cholesterol on electrostatics in lipid-protein films of a pulmonary surfactant.

PubMed

Finot, Eric; Leonenko, Yuri; Moores, Brad; Eng, Lukas; Amrein, Matthias; Leonenko, Zoya

2010-02-02

We report the changes in the electrical properties of the lipid-protein film of pulmonary surfactant produced by excess cholesterol. Pulmonary surfactant (PS) is a complex lipid-protein mixture that forms a molecular film at the interface of the lung's epithelia. The defined molecular arrangement of the lipids and proteins of the surfactant film gives rise to the locally highly variable electrical surface potential of the interface, which becomes considerably altered in the presence of cholesterol. With frequency modulation Kelvin probe force microscopy (FM-KPFM) and force measurements, complemented by theoretical analysis, we showed that excess cholesterol significantly changes the electric field around a PS film because of the presence of nanometer-sized electrostatic domains and affects the electrostatic interaction of an AFM probe with a PS film. These changes in the local electrical field would greatly alter the interaction of the surfactant film with charged species and would immediately impact the manner in which inhaled (often charged) airborne nanoparticles and fibers might interact with the lung interface.

Controlling successive ionic layer absorption and reaction cycles to optimize silver nanoparticle-induced localized surface plasmon resonance effects on the paper strip

NASA Astrophysics Data System (ADS)

Lee, Jae-Chul; Kim, Wansun; Park, Hun-Kuk; Choi, Samjin

2017-03-01

This study investigates why a silver nanoparticle (SNP)-induced surface-enhanced Raman scattering (SERS) paper chip fabricated at low successive ionic layer absorption and reaction (SILAR) cycles leads to a high SERS enhancement factor (7 × 108) with an inferior nanostructure and without generating a hot spot effect. The multi-layered structure of SNPs on cellulose fibers, verified by magnified scanning electron microscopy (SEM) and analyzed by a computational simulation method, was hypothesized as the reason. The pattern of simulated local electric field distribution with respect to the number of SILAR cycles showed good agreement with the experimental Raman intensity, regardless of the wavelength of the excitation laser sources. The simulated enhancement factor at the 785-nm excitation laser source (2.8 × 109) was 2.5 times greater than the experimental enhancement factor (1.1 × 109). A 532-nm excitation laser source exhibited the highest maximum local electric field intensity (1.9 × 1011), particularly at the interparticle gap called a hot spot. The short wavelength led to a strong electric field intensity caused by strong electromagnetic coupling arising from the SNP-induced local surface plasmon resonance (LSPR) effects through high excitation energy. These findings suggest that our paper-based SILAR-fabricated SNP-induced LSPR model is valid for understanding SNP-induced LSPR effects.

3D modeling of electric fields in the LUX detector

DOE Office of Scientific and Technical Information (OSTI.GOV)

Akerib, D. S.; Alsum, S.; Araújo, H. M.

This work details the development of a three-dimensional (3D) electric field model for the LUX detector. The detector took data to search for weakly interacting massive particles (WIMPs) during two periods. After the first period completed, a time-varying non-uniform negative charge developed in the polytetrafluoroethylene (PTFE) panels that define the radial boundary of the detector's active volume. This caused electric field variations in the detector in time, depth and azimuth, generating an electrostatic radially-inward force on electrons on their way upward to the liquid surface. To map this behavior, 3D electric field maps of the detector's active volume were generatedmore » on a monthly basis. This was done by fitting a model built in COMSOL Multiphysics to the uniformly distributed calibration data that were collected on a regular basis. The modeled average PTFE charge density increased over the course of the exposure from -3.6 to -5.5 μC/m 2. Here, from our studies, we deduce that the electric field magnitude varied locally while the mean value of the field of ~200 V/cm remained constant throughout the exposure. As a result of this work the varying electric fields and their impact on event reconstruction and discrimination were successfully modeled.« less

3D modeling of electric fields in the LUX detector

DOE PAGES

Akerib, D. S.; Alsum, S.; Araújo, H. M.; ...

2017-11-24

This work details the development of a three-dimensional (3D) electric field model for the LUX detector. The detector took data to search for weakly interacting massive particles (WIMPs) during two periods. After the first period completed, a time-varying non-uniform negative charge developed in the polytetrafluoroethylene (PTFE) panels that define the radial boundary of the detector's active volume. This caused electric field variations in the detector in time, depth and azimuth, generating an electrostatic radially-inward force on electrons on their way upward to the liquid surface. To map this behavior, 3D electric field maps of the detector's active volume were generatedmore » on a monthly basis. This was done by fitting a model built in COMSOL Multiphysics to the uniformly distributed calibration data that were collected on a regular basis. The modeled average PTFE charge density increased over the course of the exposure from -3.6 to -5.5 μC/m 2. Here, from our studies, we deduce that the electric field magnitude varied locally while the mean value of the field of ~200 V/cm remained constant throughout the exposure. As a result of this work the varying electric fields and their impact on event reconstruction and discrimination were successfully modeled.« less

3D modeling of electric fields in the LUX detector

NASA Astrophysics Data System (ADS)

Akerib, D. S.; Alsum, S.; Araújo, H. M.; Bai, X.; Bailey, A. J.; Balajthy, J.; Beltrame, P.; Bernard, E. P.; Bernstein, A.; Biesiadzinski, T. P.; Boulton, E. M.; Brás, P.; Byram, D.; Cahn, S. B.; Carmona-Benitez, M. C.; Chan, C.; Currie, A.; Cutter, J. E.; Davison, T. J. R.; Dobi, A.; Druszkiewicz, E.; Edwards, B. N.; Fallon, S. R.; Fan, A.; Fiorucci, S.; Gaitskell, R. J.; Genovesi, J.; Ghag, C.; Gilchriese, M. G. D.; Hall, C. R.; Hanhardt, M.; Haselschwardt, S. J.; Hertel, S. A.; Hogan, D. P.; Horn, M.; Huang, D. Q.; Ignarra, C. M.; Jacobsen, R. G.; Ji, W.; Kamdin, K.; Kazkaz, K.; Khaitan, D.; Knoche, R.; Larsen, N. A.; Lenardo, B. G.; Lesko, K. T.; Lindote, A.; Lopes, M. I.; Manalaysay, A.; Mannino, R. L.; Marzioni, M. F.; McKinsey, D. N.; Mei, D.-M.; Mock, J.; Moongweluwan, M.; Morad, J. A.; Murphy, A. St. J.; Nehrkorn, C.; Nelson, H. N.; Neves, F.; O'Sullivan, K.; Oliver-Mallory, K. C.; Palladino, K. J.; Pease, E. K.; Rhyne, C.; Shaw, S.; Shutt, T. A.; Silva, C.; Solmaz, M.; Solovov, V. N.; Sorensen, P.; Sumner, T. J.; Szydagis, M.; Taylor, D. J.; Taylor, W. C.; Tennyson, B. P.; Terman, P. A.; Tiedt, D. R.; To, W. H.; Tripathi, M.; Tvrznikova, L.; Uvarov, S.; Velan, V.; Verbus, J. R.; Webb, R. C.; White, J. T.; Whitis, T. J.; Witherell, M. S.; Wolfs, F. L. H.; Xu, J.; Yazdani, K.; Young, S. K.; Zhang, C.

2017-11-01

This work details the development of a three-dimensional (3D) electric field model for the LUX detector. The detector took data to search for weakly interacting massive particles (WIMPs) during two periods. After the first period completed, a time-varying non-uniform negative charge developed in the polytetrafluoroethylene (PTFE) panels that define the radial boundary of the detector's active volume. This caused electric field variations in the detector in time, depth and azimuth, generating an electrostatic radially-inward force on electrons on their way upward to the liquid surface. To map this behavior, 3D electric field maps of the detector's active volume were generated on a monthly basis. This was done by fitting a model built in COMSOL Multiphysics to the uniformly distributed calibration data that were collected on a regular basis. The modeled average PTFE charge density increased over the course of the exposure from -3.6 to -5.5 μC/m2. From our studies, we deduce that the electric field magnitude varied locally while the mean value of the field of ~200 V/cm remained constant throughout the exposure. As a result of this work the varying electric fields and their impact on event reconstruction and discrimination were successfully modeled.

Local and Average Structures in Ferroelectrics under Perturbing Fields

NASA Astrophysics Data System (ADS)

Usher, Tedi-Marie

Ferroelectric and dielectric ceramics are used in a multitude of applications including sonar, micro-positioning, actuators, transducers, and capacitors. The most widely used compositions are lead (Pb)-based, however there is an ongoing effort to reduce lead-based materials in consumer applications. Many lead-free compositions are under investigation; some are already in production and others have been identified as suitable for certain applications. For any such material system, there is a need to thoroughly characterize the structure in order to develop robust structure-property relationships, particularly during in situ application of different stimuli (e.g. electric field and mechanical stress). This work investigates two lead-free material systems of interest, (1-x)Na1/2Bi1/2TiO3 - (x)BaTiO3 (NBT-xBT) and (1-x)BaTiO3 - (x)Bi(Zn1/2Ti1/2)O3 (BT-xBZT), as well as the constituent compounds Na1/2Bi1/2TiO3 and BaTiO3. Both systems exhibit compositional boundaries between unique phases exhibiting different functional properties. Advanced scattering techniques are used to characterize the atomic structures and how they change during in situ application of different stimuli. The long-range, average structures are probed using high-resolution X-ray diffraction (HRXRD) and neutron diffraction (ND) and local scale structures are probed using X-ray or neutron total scattering, which are converted to pair distribution functions (PDFs). First, two in situ ND experiments which investigate structural changes to NBT-xBT in response to uniaxial stresses and electric fields are presented. In response to stresses, different crystallographic directions strain differently. The elastic anisotropy, (i.e., the orientation-dependence of elastic stiffness) for the studied compositions is characterized. A general inverse relationship between elastic anisotropy and piezoelectric anisotropy is demonstrated for three common ferroelectric point groups. In response to electric fields, different crystallographic directions respond by either domain reorientation or lattice strain, as governed by the material's symmetry. The composition at the phase boundary responds at a lower field and undergoes a phase transition. Next, the PDF method is described and then applied to a structural study of BT-xBZT in combination with HRXRD and ND studies. For BZT >9%, the structure is pseudocubic at the long-range with short-range tetragonal distortions. This structural length-scale dependence is characterized with a box-car fitting method and suggests that with sufficient BZT content, local tetragonal distortions are disrupted at length scales > 40 A. By combining long- and short-range studies, structural variations from the sub-nm to long-range are characterized and enhance the understanding of this and similar material systems. In the final chapters, the local-scale responses of ferroelectric and dielectric materials to electric fields are investigated by PDFs. The novel methodology of measuring X-ray total scattering during in situ application of electric fields is presented and results are shown for piezoelectric (BT), relaxor-ferroelectric (NBT), and dielectric materials (SrTiO3 and HfO2), as well as for NBT-xBT. Local-scale cation reorientation in NBT is evidenced and corresponds to an electric-field-induced phase transition. The ability to quantify local-scale atomic rearrangements during field application is unique to in situ PDF studies; it is not possible through in situ diffraction methods like those presented earlier. This method is extended to neutron-PDFs and ex situ results for NBT are shown. In order to interpret the local scale-changes observed in the in situ PDF studies, the local structures of a series of models with different real, physical effects (strains, polarization, changes in thermal motion, etc) are analyzed and characterized. Finally, the samples used are characterized in terms of grain size/appearance and piezoelectric and ferroelectric properties. In summary, this research demonstrates the use of detailed and in situ structural studies that contribute new knowledge to structure-property relationships for several ferroelectric and dielectric material systems. Additionally, the novel technique of in situ PDFs with electric fields is evidenced to provide unique information on atomic rearrangements caused by in situ stimuli.

A key discovery at the TiO2/dye/electrolyte interface: slow local charge compensation and a reversible electric field.

PubMed

Yang, Wenxing; Pazoki, Meysam; Eriksson, Anna I K; Hao, Yan; Boschloo, Gerrit

2015-07-14

Dye-sensitized mesoporous TiO2 films have been widely applied in energy and environmental science related research fields. The interaction between accumulated electrons inside TiO2 and cations in the surrounding electrolyte at the TiO2/dye/electrolyte interface is, however, still poorly understood. This interaction is undoubtedly important for both device performance and fundamental understanding. In the present study, Stark effects of an organic dye, LEG4, adsorbed on TiO2 were well characterized and used as a probe to monitor the local electric field at the TiO2/dye/electrolyte interface. By using time-resolved photo- and potential-induced absorption techniques, we found evidence for a slow (t > 0.1 s) local charge compensation mechanism, which follows electron accumulation inside the mesoporous TiO2. This slow local compensation was attributed to the penetration of cations from the electrolyte into the adsorbed dye layer, leading to a more localized charge compensation of the electrons inside TiO2. Importantly, when the electrons inside TiO2 were extracted, a remarkable reversal of the surface electric field was observed for the first time, which is attributed to the penetrated and/or adsorbed cations now being charge compensated by anions in the bulk electrolyte. A cation electrosorption model is developed to account for the overall process. These findings give new insights into the mesoporous TiO2/dye/electrolyte interface and the electron-cation interaction mechanism. Electrosorbed cations are proposed to act as electrostatic trap states for electrons in the mesoporous TiO2 electrode.

Nanoscale Control over the Mixing Behavior of Surface-Confined Bicomponent Supramolecular Networks Using an Oriented External Electric Field

PubMed Central

2017-01-01

Strong electric fields are known to influence the properties of molecules as well as materials. Here we show that by changing the orientation of an externally applied electric field, one can locally control the mixing behavior of two molecules physisorbed on a solid surface. Whether the starting two-component network evolves into an ordered two-dimensional (2D) cocrystal, yields an amorphous network where the two components phase separate, or shows preferential adsorption of only one component depends on the solution stoichiometry. The experiments are carried out by changing the orientation of the strong electric field that exists between the tip of a scanning tunneling microscope and a solid substrate. The structure of the two-component network typically changes from open porous at negative substrate bias to relatively compact when the polarity of the applied bias is reversed. The electric-field-induced mixing behavior is reversible, and the supramolecular system exhibits excellent stability and good response efficiency. When molecular guests are adsorbed in the porous networks, the field-induced switching behavior was found to be completely different. Plausible reasons behind the field-induced mixing behavior are discussed. PMID:29112378

Electric-field-stimulated protein mechanics

PubMed Central

Hekstra, Doeke R.; White, K. Ian; Socolich, Michael A.; Henning, Robert W.; Šrajer, Vukica; Ranganathan, Rama

2017-01-01

The internal mechanics of proteins—the coordinated motions of amino acids and the pattern of forces constraining these motions—connects protein structure to function. Here we describe a new method combining the application of strong electric field pulses to protein crystals with time-resolved X-ray crystallography to observe conformational changes in spatial and temporal detail. Using a human PDZ domain (LNX2PDZ2) as a model system, we show that protein crystals tolerate electric field pulses strong enough to drive concerted motions on the sub-microsecond timescale. The induced motions are subtle, involve diverse physical mechanisms, and occur throughout the protein structure. The global pattern of electric-field-induced motions is consistent with both local and allosteric conformational changes naturally induced by ligand binding, including at conserved functional sites in the PDZ domain family. This work lays the foundation for comprehensive experimental study of the mechanical basis of protein function. PMID:27926732

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deshmukh, Shivaraj D.; Tsori, Yoav, E-mail: tsori@bgu.ac.il

We examine theoretically a new idea for spatial and temporal control of chemical reactions. When chemical reactions take place in a mixture of solvents, an external electric field can alter the local mixture composition, thereby accelerating or decelerating the rate of reaction. The spatial distribution of electric field strength can be non-trivial and depends on the arrangement of the electrodes producing it. In the absence of electric field, the mixture is homogeneous and the reaction takes place uniformly in the reactor volume. When an electric field is applied, the solvents separate and the reactants are concentrated in the same phasemore » or separate to different phases, depending on their relative miscibility in the solvents, and this can have a large effect on the kinetics of the reaction. This method could provide an alternative way to control runaway reactions and to increase the reaction rate without using catalysts.« less

Numerical dosimetry of transcranial magnetic stimulation coils

NASA Astrophysics Data System (ADS)

Crowther, Lawrence; Hadimani, Ravi; Jiles, David

2014-03-01

Transcranial magnetic stimulation (TMS) is a non-invasive neuromodulation technique capable of stimulating neurons by means of electromagnetic induction. TMS can be used to map brain function and shows promise for the diagnosis and treatment of neurological and psychiatric disorders. Calculation of fields induced in the brain are necessary to accurately identify stimulated neural tissue during TMS. This allows the development of novel TMS coil designs capable of stimulating deeper brain regions and increasing the localization of stimulation that can be achieved. We have performed numerical calculations of magnetic and electric field with high-resolution anatomically realistic human head models to find these stimulated brain regions for a variety of proposed TMS coil designs. The realistic head models contain heterogeneous tissue structures and electrical conductivities, yielding superior results to those obtained from the simplified homogeneous head models that are commonly employed. The attenuation of electric field as a function of depth in the brain and the localization of stimulating field have been methodically investigated. In addition to providing a quantitative comparison of different TMS coil designs the variation of induced field between subjects has been investigated. We also show the differences in induced fields between adult, adolescent and child head models to preemptively identify potential safety issues in the application of pediatric TMS.

Structure-dependent localized surface plasmon resonance characteristics and surface enhanced Raman scattering performances of quasi-periodic nanoarrays: Measurements and analysis

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Dong; Zhou, Jun, E-mail: zhoujun@nbu.edu.cn; Rippa, Massimo

A set of periodic and quasi-periodic Au nanoarrays with different morphologies have been fabricated by using electron beam lithography technique, and their optical properties have been examined experimentally and analyzed theoretically by scanning near-field optical microscope and finite element method, respectively. Results present that the localized surface plasmon resonance of the as-prepared Au nanoarrays exhibit the structure-depended characteristics. Comparing with the periodic nanoarrays, the quasi-periodic ones demonstrate stronger electric field enhancement, especially for Thue-Morse nanoarray. Meanwhile, the surface enhanced Raman scattering (SERS) spectra of 4-mercaptobenzoic acid molecular labeled nanoarrays show that the quasi-periodic nanoarrays exhibit distinct SERS enhancement, for example,more » a higher enhancement factor of ∼10{sup 7} is obtained for the Thue-Morse nanoarray consisted of square pillars of 100 nm size. Therefore, it is significant to optimally design and fabricate the chip-scale quasi-periodic nanoarrays with high localized electric field enhancement for SERS applications in biosensing field.« less

Electrical manipulation of oligonucleotides grafted to charged surfaces.

PubMed

Rant, Ulrich; Arinaga, Kenji; Fujita, Shozo; Yokoyama, Naoki; Abstreiter, Gerhard; Tornow, Marc

2006-09-21

The electrical manipulation of short DNA molecules on surfaces offers novel functionalities with fascinating possibilities in the field of bio-interfaces. Here we present systematic investigations of the electrical interactions which govern the structure of oligonucleotides on charged gold surfaces. Successively, we address influences of the applied field strength, the role of DC electrode potentials, in particular for polycrystalline surfaces, as well as screening effects of the surrounding electrolyte solution. Data obtained for single and double stranded DNA exhibit differences which can be attributed to the dissimilar flexibility of the different molecular conformations. A comparison of the experimental results with a basic model shows how the alignment of the molecules adjusts according to a balance between electrically induced ordering and stochastic thermal motions. The presented conclusions are expected to be of general relevance for the behaviour of polyelectrolytes exposed to localized electric fields at interfaces.

Effects of radial electric fields on linear ITG instabilities in W7-X and LHD

NASA Astrophysics Data System (ADS)

Riemann, J.; Kleiber, R.; Borchardt, M.

2016-07-01

The impact of radial electric fields on the properties of linear ion-temperature-gradient (ITG) modes in stellarators is studied. Numerical simulations have been carried out with the global particle-in-cell (PIC) code EUTERPE, modelling the behaviour of ITG modes in Wendelstein 7-X and an LHD-like configuration. In general, radial electric fields seem to lead to a reduction of ITG instability growth, which can be related to the action of an induced E× B -drift. Focus is set on the modification of mode properties (frequencies, power spectrum, spatial structure and localization) to understand the observed growth rates as the result of competing stabilizing mechanisms.

Magnetic Activity Dependence of the Electric Drift Below L = 3

NASA Astrophysics Data System (ADS)

Lejosne, Solène; Mozer, F. S.

2018-05-01

More than 2 years of magnetic and electric field measurements by the Van Allen Probes are analyzed with the objective of determining the average effects of magnetic activity on the electric drift below L = 3. The study finds that an increase in magnetospheric convection leads to a decrease in the magnitude of the azimuthal component of the electric drift, especially in the nightside. The amplitude of the slowdown is a function of L, magnetic local time, and Kp, in a pattern consistent with the storm time dynamics of the ionosphere and thermosphere. To a lesser extent, magnetic activity also alters the average radial component of the electric drift below L = 3. A global picture for the average variations of the electric drift with Kp is provided as a function of L and magnetic local time. It is the first time that the signature of the ionospheric disturbance dynamo is observed in near-equatorial electric drift measurements.

Influence of tissue resistivities on neuromagnetic fields and electric potentials studied with a finite element model of the head.

PubMed

Haueisen, J; Ramon, C; Eiselt, M; Brauer, H; Nowak, H

1997-08-01

Modeling in magnetoencephalography (MEG) and electroencephalography (EEG) requires knowledge of the in vivo tissue resistivities of the head. The aim of this paper is to examine the influence of tissue resistivity changes on the neuromagnetic field and the electric scalp potential. A high-resolution finite element method (FEM) model (452,162 elements, 2-mm resolution) of the human head with 13 different tissue types is employed for this purpose. Our main finding was that the magnetic fields are sensitive to changes in the tissue resistivity in the vicinity of the source. In comparison, the electric surface potentials are sensitive to changes in the tissue resistivity in the vicinity of the source and in the vicinity of the position of the electrodes. The magnitude (strength) of magnetic fields and electric surface potentials is strongly influenced by tissue resistivity changes, while the topography is not as strongly influenced. Therefore, an accurate modeling of magnetic field and electric potential strength requires accurate knowledge of tissue resistivities, while for source localization procedures this knowledge might not be a necessity.

Generation of dynamo magnetic fields in the primordial solar nebula

NASA Technical Reports Server (NTRS)

Stepinski, Tomasz F.

1992-01-01

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

Evaluation of local electric fields generated by transcranial direct current stimulation with an extracephalic reference electrode based on realistic 3D body modeling

NASA Astrophysics Data System (ADS)

Im, Chang-Hwan; Park, Ji-Hye; Shim, Miseon; Chang, Won Hyuk; Kim, Yun-Hee

2012-04-01

In this study, local electric field distributions generated by transcranial direct current stimulation (tDCS) with an extracephalic reference electrode were evaluated to address extracephalic tDCS safety issues. To this aim, we generated a numerical model of an adult male human upper body and applied the 3D finite element method to electric current conduction analysis. In our simulations, the active electrode was placed over the left primary motor cortex (M1) and the reference electrode was placed at six different locations: over the right temporal lobe, on the right supraorbital region, on the right deltoid, on the left deltoid, under the chin, and on the right buccinator muscle. The maximum current density and electric field intensity values in the brainstem generated by the extracephalic reference electrodes were comparable to, or even less than, those generated by the cephalic reference electrodes. These results suggest that extracephalic reference electrodes do not lead to unwanted modulation of the brainstem cardio-respiratory and autonomic centers, as indicated by recent experimental studies. The volume energy density was concentrated at the neck area by the use of deltoid reference electrodes, but was still smaller than that around the active electrode locations. In addition, the distributions of elicited cortical electric fields demonstrated that the use of extracephalic reference electrodes might allow for the robust prediction of cortical modulations with little dependence on the reference electrode locations.

The Electric Field of a Weakly Electric Fish

NASA Astrophysics Data System (ADS)

Rasnow, Brian K.

Freshwater fish of the genus Apteronotus (family Gymnotidae) generate a weak, high frequency electric field (<100 mV/cm, 0.5-10 kHz) which permeates their local environment. These nocturnal fish are acutely sensitive to perturbations in their electric field caused by other electric fish, and nearby objects whose impedance is different from the surrounding water. This thesis presents high temporal and spatial resolution maps of the electric potential and field on and near Apteronotus. The fish's electric field is a complicated and highly stable function of space and time. Its characteristics, such as spectral composition, timing, and rate of attenuation, are examined in terms of physical constraints, and their possible functional roles in electroreception. Temporal jitter of the periodic field is less than 1 musec. However, electrocyte activity is not globally synchronous along the fish's electric organ. The propagation of electrocyte activation down the fish's body produces a rotation of the electric field vector in the caudal part of the fish. This may assist the fish in identifying nonsymmetrical objects, and could also confuse electrosensory predators that try to locate Apteronotus by following its fieldlines. The propagation also results in a complex spatiotemporal pattern of the EOD potential near the fish. Visualizing the potential on the same and different fish over timescales of several months suggests that it is stable and could serve as a unique signature for individual fish. Measurements of the electric field were used to calculate the effects of simple objects on the fish's electric field. The shape of the perturbation or "electric image" on the fish's skin is relatively independent of a simple object's size, conductivity, and rostrocaudal location, and therefore could unambiguously determine object distance. The range of electrolocation may depend on both the size of objects and their rostrocaudal location. Only objects with very large dielectric constants cause appreciable phase shifts, and these are strongly dependent on the water conductivity.

Computer simulation of the linear and nonlinear optical susceptibilities of p-nitroaniline in cyclohexane, 1,4-dioxane, and tetrahydrofuran in quadrupolar approximation. II. Local field effects and optical susceptibilitities.

PubMed

Reis, H; Papadopoulos, M G; Grzybowski, A

2006-09-21

This is the second part of a study to elucidate the local field effects on the nonlinear optical properties of p-nitroaniline (pNA) in three solvents of different multipolar character, that is, cyclohexane (CH), 1,4-dioxane (DI), and tetrahydrofuran (THF), employing a discrete description of the solutions. By the use of liquid structure information from molecular dynamics simulations and molecular properties computed by high-level ab initio methods, the local field and local field gradients on p-nitroaniline and the solvent molecules are computed in quadrupolar approximation. To validate the simulations and the induction model, static and dynamic (non)linear properties of the pure solvents are also computed. With the exception of the static dielectric constant of pure THF, a good agreement between computed and experimental refractive indices, dielectric constants, and third harmonic generation signals is obtained for the solvents. For the solutions, it is found that multipole moments up to two orders higher than quadrupole have a negligible influence on the local fields on pNA, if a simple distribution model is employed for the electric properties of pNA. Quadrupole effects are found to be nonnegligible in all three solvents but are especially pronounced in the 1,4-dioxane solvent, in which the local fields are similar to those in THF, although the dielectric constant of DI is 2.2 and that of the simulated THF is 5.4. The electric-field-induced second harmonic generation (EFISH) signal and the hyper-Rayleigh scattering signal of pNA in the solutions computed with the local field are in good to fair agreement with available experimental results. This confirms the effect of the "dioxane anomaly" also on nonlinear optical properties. Predictions based on an ellipsoidal Onsager model as applied by experimentalists are in very good agreement with the discrete model predictions. This is in contrast to a recent discrete reaction field calculation of pNA in 1,4-dioxane, which found that the predicted first hyperpolarizability of pNA deviated strongly from the predictions obtained using Onsager-Lorentz local field factors.

Prediction of the Seizure Suppression Effect by Electrical Stimulation via a Computational Modeling Approach.

PubMed

Ahn, Sora; Jo, Sumin; Jun, Sang Beom; Lee, Hyang Woon; Lee, Seungjun

2017-01-01

In this paper, we identified factors that can affect seizure suppression via electrical stimulation by an integrative study based on experimental and computational approach. Preferentially, we analyzed the characteristics of seizure-like events (SLEs) using our previous in vitro experimental data. The results were analyzed in two groups classified according to the size of the effective region, in which the SLE was able to be completely suppressed by local stimulation. However, no significant differences were found between these two groups in terms of signal features or propagation characteristics (i.e., propagation delays, frequency spectrum, and phase synchrony). Thus, we further investigated important factors using a computational model that was capable of evaluating specific influences on effective region size. In the proposed model, signal transmission between neurons was based on two different mechanisms: synaptic transmission and the electrical field effect. We were able to induce SLEs having similar characteristics with differentially weighted adjustments for the two transmission methods in various noise environments. Although the SLEs had similar characteristics, their suppression effects differed. First of all, the suppression effect occurred only locally where directly received the stimulation effect in the high noise environment, but it occurred in the entire network in the low noise environment. Interestingly, in the same noise environment, the suppression effect was different depending on SLE propagation mechanism; only a local suppression effect was observed when the influence of the electrical field transmission was very weak, whereas a global effect was observed with a stronger electrical field effect. These results indicate that neuronal activities synchronized by a strong electrical field effect respond more sensitively to partial changes in the entire network. In addition, the proposed model was able to predict that stimulation of a seizure focus region is more effective for suppression. In conclusion, we confirmed the possibility of a computational model as a simulation tool to analyze the efficacy of deep brain stimulation (DBS) and investigated the key factors that determine the size of an effective region in seizure suppression via electrical stimulation.

Tailored Fano resonance and localized electromagnetic field enhancement in Ag gratings

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Zhaozhu; Klopf, J. Michael; Wang, Lei

Metallic gratings can support Fano resonances when illuminated with EM radiation, and their characteristic reflectivity versus incident angle lineshape can be greatly affected by the surrounding dielectric environment and the grating geometry. By using conformal oblique incidence thin film deposition onto an optical grating substrate, it is possible to increase the grating amplitude due to shadowing effects, thereby enabling tailoring of the damping processes and electromagnetic field couplings of the Fano resonances, hence optimizing the associated localized electric field intensity. To investigate these effects we compare the optical reflectivity under resonance excitation in samples prepared by oblique angle deposition (OAD)more » and under normal deposition (ND) onto the same patterned surfaces. We observe that by applying OAD method, the sample exhibits a deeper and narrower reflectivity dip at resonance than that obtained under ND. This can be explained in terms of a lower damping of Fano resonance on obliquely deposited sample and leads to a stronger localized electric field. This approach opens a fabrication path for applications where tailoring the electromagnetic field induced by Fano resonance can improve the figure of merit of specific device characteristics, e.g. quantum efficiency (QE) in grating-based metallic photocathodes.« less

Tailored Fano resonance and localized electromagnetic field enhancement in Ag gratings

DOE PAGES

Li, Zhaozhu; Klopf, J. Michael; Wang, Lei; ...

2017-03-14

Metallic gratings can support Fano resonances when illuminated with EM radiation, and their characteristic reflectivity versus incident angle lineshape can be greatly affected by the surrounding dielectric environment and the grating geometry. By using conformal oblique incidence thin film deposition onto an optical grating substrate, it is possible to increase the grating amplitude due to shadowing effects, thereby enabling tailoring of the damping processes and electromagnetic field couplings of the Fano resonances, hence optimizing the associated localized electric field intensity. To investigate these effects we compare the optical reflectivity under resonance excitation in samples prepared by oblique angle deposition (OAD)more » and under normal deposition (ND) onto the same patterned surfaces. We observe that by applying OAD method, the sample exhibits a deeper and narrower reflectivity dip at resonance than that obtained under ND. This can be explained in terms of a lower damping of Fano resonance on obliquely deposited sample and leads to a stronger localized electric field. This approach opens a fabrication path for applications where tailoring the electromagnetic field induced by Fano resonance can improve the figure of merit of specific device characteristics, e.g. quantum efficiency (QE) in grating-based metallic photocathodes.« less

A new theoretical formulation of coupling thermo-electric breakdown in LDPE film under dc high applied fields

NASA Astrophysics Data System (ADS)

Boughariou, F.; Chouikhi, S.; Kallel, A.; Belgaroui, E.

2015-12-01

In this paper, we present a new theoretical and numerical formulation for the electrical and thermal breakdown phenomena, induced by charge packet dynamics, in low-density polyethylene (LDPE) insulating film under dc high applied field. The theoretical physical formulation is composed by the equations of bipolar charge transport as well as by the thermo-electric coupled equation associated for the first time in modeling to the bipolar transport problem. This coupled equation is resolved by the finite-element numerical model. For the first time, all bipolar transport results are obtained under non-uniform temperature distributions in the sample bulk. The principal original results show the occurring of very sudden abrupt increase in local temperature associated to a very sharp increase in external and conduction current densities appearing during the steady state. The coupling between these electrical and thermal instabilities reflects physically the local coupling between electrical conduction and thermal joule effect. The results of non-uniform temperature distributions induced by non-uniform electrical conduction current are also presented for several times. According to our formulation, the strong injection current is the principal factor of the electrical and thermal breakdown of polymer insulating material. This result is shown in this work. Our formulation is also validated experimentally.

Methods and devices for high-throughput dielectrophoretic concentration

DOEpatents

Simmons, Blake A.; Cummings, Eric B.; Fiechtner, Gregory J.; Fintschenko, Yolanda; McGraw, Gregory J.; Salmi, Allen

2010-02-23

Disclosed herein are methods and devices for assaying and concentrating analytes in a fluid sample using dielectrophoresis. As disclosed, the methods and devices utilize substrates having a plurality of pores through which analytes can be selectively prevented from passing, or inhibited, on application of an appropriate electric field waveform. The pores of the substrate produce nonuniform electric field having local extrema located near the pores. These nonuniform fields drive dielectrophoresis, which produces the inhibition. Arrangements of electrodes and porous substrates support continuous, bulk, multi-dimensional, and staged selective concentration.

Correlating Nitrile IR Frequencies to Local Electrostatics Quantifies Noncovalent Interactions of Peptides and Proteins.

PubMed

Deb, Pranab; Haldar, Tapas; Kashid, Somnath M; Banerjee, Subhrashis; Chakrabarty, Suman; Bagchi, Sayan

2016-05-05

Noncovalent interactions, in particular the hydrogen bonds and nonspecific long-range electrostatic interactions are fundamental to biomolecular functions. A molecular understanding of the local electrostatic environment, consistently for both specific (hydrogen-bonding) and nonspecific electrostatic (local polarity) interactions, is essential for a detailed understanding of these processes. Vibrational Stark Effect (VSE) has proven to be an extremely useful method to measure the local electric field using infrared spectroscopy of carbonyl and nitrile based probes. The nitrile chemical group would be an ideal choice because of its absorption in an infrared spectral window transparent to biomolecules, ease of site-specific incorporation into proteins, and common occurrence as a substituent in various drug molecules. However, the inability of VSE to describe the dependence of IR frequency on electric field for hydrogen-bonded nitriles to date has severely limited nitrile's utility to probe the noncovalent interactions. In this work, using infrared spectroscopy and atomistic molecular dynamics simulations, we have reported for the first time a linear correlation between nitrile frequencies and electric fields in a wide range of hydrogen-bonding environments that may bridge the existing gap between VSE and H-bonding interactions. We have demonstrated the robustness of this field-frequency correlation for both aromatic nitriles and sulfur-based nitriles in a wide range of molecules of varying size and compactness, including small molecules in complex solvation environments, an amino acid, disordered peptides, and structured proteins. This correlation, when coupled to VSE, can be used to quantify noncovalent interactions, specific or nonspecific, in a consistent manner.

Chronic exposure to ELF fields may induce depression

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wilson, B.W.

Exposure to extremely-low-frequency (ELF) electric or magnetic fields has been postulated as a potentially contributing factor in depression. Epidemiologic studies have yielded positive correlations between magnetic- and/or electric-field strengths in local environments and the incidence of depression-related suicide. Chronic exposure to ELF electric or magnetic fields can disrupt normal circadian rhythms in rat pineal serotonin-N-acetyltransferase activity as well as in serotonin and melatonin concentrations. Such disruptions in the circadian rhythmicity of pineal melatonin secretion have been associated with certain depressive disorders in human beings. In the rat, ELF fields may interfere with tonic aspects of neuronal input to the pinealmore » gland, giving rise to what may be termed functional pinealectomy. If long-term exposure to ELF fields causes pineal dysfunction in human beings as it does in the rat, such dysfunction may contribute to the onset of depression or may exacerbate existing depressive disorders. 85 references.« less

Hydrogen atom in a quantum plasma environment under the influence of Aharonov-Bohm flux and electric and magnetic fields.

PubMed

Falaye, Babatunde James; Sun, Guo-Hua; Silva-Ortigoza, Ramón; Dong, Shi-Hai

2016-05-01

This study presents the confinement influences of Aharonov-Bohm (AB) flux and electric and magnetic fields directed along the z axis and encircled by quantum plasmas on the hydrogen atom. The all-inclusive effects result in a strongly attractive system while the localizations of quantum levels change and the eigenvalues decrease. We find that the combined effect of the fields is stronger than a solitary effect and consequently there is a substantial shift in the bound state energy of the system. We also find that to perpetuate a low-energy medium for the hydrogen atom in quantum plasmas, a strong electric field and weak magnetic field are required, whereas the AB flux field can be used as a regulator. The application of the perturbation technique utilized in this paper is not restricted to plasma physics; it can also be applied in molecular physics.

Magnetic-field enhancement beyond the skin-depth limit

NASA Astrophysics Data System (ADS)

Shin, Jonghwa; Park, Namkyoo; Fan, Shanhui; Lee, Yong-Hee

2010-02-01

Electric field enhancement has been actively studied recently and many metallic structures that are capable of locally enhancing electric field have been reported. The Babinet's principle can be utilized, especially in the form of Booker's extension, to transform the known electric field enhancing structures into magnetic field enhancing structures. The authors explain this transformation process and discuss the regime in which this principle breaks down. Unless the metals used can be well approximated with a PEC model, the principle's predictions fails to hold true. Authors confirm this aspect using numerical simulations based on realistic material parameters for actual metals. There is large discrepancy especially when the structural dimensions are comparable or less than the skin-depth at the wavelength of interest. An alternative way to achieve magnetic field enhancement is presented and the design of a connected bow-tie structure is proposed as an example. FDTD simulation results confirm the operation of the proposed structure.

New Method for Solving Inductive Electric Fields in the Ionosphere

NASA Astrophysics Data System (ADS)

Vanhamäki, H.

2005-12-01

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

Predicting the Electric Field Distribution in the Brain for the Treatment of Glioblastoma

PubMed Central

Miranda, Pedro C.; Mekonnen, Abeye; Salvador, Ricardo; Basser, Peter J.

2014-01-01

The use of alternating electric fields has been recently proposed for the treatment of recurrent glioblastoma. In order to predict the electric field distribution in the brain during the application of such tumor treating fields (TTF), we constructed a realistic head model from MRI data and placed transducer arrays on the scalp to mimic an FDA-approved medical device. Values for the tissue dielectric properties were taken from the literature; values for the device parameters were obtained from the manufacturer. The finite element method was used to calculate the electric field distribution in the brain. We also included a “virtual lesion” in the model to simulate the presence of an idealized tumor. The calculated electric field in the brain varied mostly between 0.5 and 2.0 V/cm and exceeded 1.0 V/cm in 60% of the total brain volume. Regions of local field enhancement occurred near interfaces between tissues with different conductivities wherever the electric field was perpendicular to those interfaces. These increases were strongest near the ventricles but were also present outside the tumor’s necrotic core and in some parts of the gray matter-white matter interface. The electric field values predicted in this model brain are in reasonably good agreement with those that have been shown to reduce cancer cell proliferation in vitro. The electric field distribution is highly non-uniform and depends on tissue geometry and dielectric properties. This could explain some of the variability in treatment outcomes. The proposed modeling framework could be used to better understand the physical basis of TTF efficacy through retrospective analysis and to improve TTF treatment planning. PMID:25003941

Predicting the electric field distribution in the brain for the treatment of glioblastoma

NASA Astrophysics Data System (ADS)

Miranda, Pedro C.; Mekonnen, Abeye; Salvador, Ricardo; Basser, Peter J.

2014-08-01

The use of alternating electric fields has been recently proposed for the treatment of recurrent glioblastoma. In order to predict the electric field distribution in the brain during the application of such tumor treating fields (TTF), we constructed a realistic head model from MRI data and placed transducer arrays on the scalp to mimic an FDA-approved medical device. Values for the tissue dielectric properties were taken from the literature; values for the device parameters were obtained from the manufacturer. The finite element method was used to calculate the electric field distribution in the brain. We also included a ‘virtual lesion’ in the model to simulate the presence of an idealized tumor. The calculated electric field in the brain varied mostly between 0.5 and 2.0 V cm - 1 and exceeded 1.0 V cm - 1 in 60% of the total brain volume. Regions of local field enhancement occurred near interfaces between tissues with different conductivities wherever the electric field was perpendicular to those interfaces. These increases were strongest near the ventricles but were also present outside the tumor’s necrotic core and in some parts of the gray matter-white matter interface. The electric field values predicted in this model brain are in reasonably good agreement with those that have been shown to reduce cancer cell proliferation in vitro. The electric field distribution is highly non-uniform and depends on tissue geometry and dielectric properties. This could explain some of the variability in treatment outcomes. The proposed modeling framework could be used to better understand the physical basis of TTF efficacy through retrospective analysis and to improve TTF treatment planning.

Predicting the electric field distribution in the brain for the treatment of glioblastoma.

PubMed

Miranda, Pedro C; Mekonnen, Abeye; Salvador, Ricardo; Basser, Peter J

2014-08-07

The use of alternating electric fields has been recently proposed for the treatment of recurrent glioblastoma. In order to predict the electric field distribution in the brain during the application of such tumor treating fields (TTF), we constructed a realistic head model from MRI data and placed transducer arrays on the scalp to mimic an FDA-approved medical device. Values for the tissue dielectric properties were taken from the literature; values for the device parameters were obtained from the manufacturer. The finite element method was used to calculate the electric field distribution in the brain. We also included a 'virtual lesion' in the model to simulate the presence of an idealized tumor. The calculated electric field in the brain varied mostly between 0.5 and 2.0 V cm( - 1) and exceeded 1.0 V cm( - 1) in 60% of the total brain volume. Regions of local field enhancement occurred near interfaces between tissues with different conductivities wherever the electric field was perpendicular to those interfaces. These increases were strongest near the ventricles but were also present outside the tumor's necrotic core and in some parts of the gray matter-white matter interface. The electric field values predicted in this model brain are in reasonably good agreement with those that have been shown to reduce cancer cell proliferation in vitro. The electric field distribution is highly non-uniform and depends on tissue geometry and dielectric properties. This could explain some of the variability in treatment outcomes. The proposed modeling framework could be used to better understand the physical basis of TTF efficacy through retrospective analysis and to improve TTF treatment planning.

Two-path plasmonic interferometer with integrated detector

DOEpatents

Dyer, Gregory Conrad; Shaner, Eric A.; Aizin, Gregory

2016-03-29

An electrically tunable terahertz two-path plasmonic interferometer with an integrated detection element can down convert a terahertz field to a rectified DC signal. The integrated detector utilizes a resonant plasmonic homodyne mixing mechanism that measures the component of the plasma waves in-phase with an excitation field that functions as the local oscillator in the mixer. The plasmonic interferometer comprises two independently tuned electrical paths. The plasmonic interferometer enables a spectrometer-on-a-chip where the tuning of electrical path length plays an analogous role to that of physical path length in macroscopic Fourier transform interferometers.

Transient electroosmotic flow induced by DC or AC electric fields in a curved microtube.

PubMed

Luo, W-J

2004-10-15

This study investigates transient electroosmotic flow in a rectangular curved microtube in which the fluid is driven by the application of an external DC or AC electric field. The resultant flow-field evolutions within the microtube are simulated using the backwards-Euler time-stepping numerical method to clarify the relationship between the changes in the axial-flow velocity and the intensity of the applied electric field. When the electric field is initially applied or varies, the fluid within the double layer responds virtually immediately, and the axial velocity within the double layer tends to follow the varying intensity of the applied electric field. The greatest net charge density exists at the corners of the microtube as a result of the overlapping electrical double layers of the two walls. It results in local maximum or minimum axial velocities in the corners during increasing or decreasing applied electric field intensity in either the positive or negative direction. As the fluid within the double layer starts to move, the bulk fluid is gradually dragged into motion through the diffusion of momentum from the double layer. A finite time is required for the full momentum of the double layer to diffuse to the bulk fluid; hence, a certain phase shift between the applied electric field and the flow response is inevitable. The patterns of the axial velocity contours during the transient evolution are investigated in this study. It is found that these patterns are determined by the efficiency of momentum diffusion from the double layer to the central region of the microtube.

Analysis of multifunctional piezoelectric metastructures for low-frequency bandgap formation and energy harvesting

NASA Astrophysics Data System (ADS)

Sugino, C.; Erturk, A.

2018-05-01

Vibration-based energy harvesting is a growing field for generating low-power electricity to use in wireless electronic devices, such as the sensor networks used in structural health monitoring applications. Locally resonant metastructures, which are structures that comprise locally resonant metamaterial components, enable bandgap formation at wavelengths much longer than the lattice size, for critical applications such as low-frequency vibration attenuation in flexible structures. This work aims to bridge the domains of energy harvesting and locally resonant metamaterials to form multifunctional structures that exhibit both low-power electricity generation and vibration attenuation capabilities. A fully coupled electromechanical modeling framework is developed for two characteristic systems and their modal analysis is presented. Simulations are performed to explore the vibration and electrical power frequency response maps for varying electrical load resistance, and optimal loading conditions are presented. Case studies are presented to understand the interaction of bandgap formation and energy harvesting capabilities of this new class of multifunctional energy-harvesting locally resonant metastructures. It is shown that useful energy can be harvested from locally resonant metastructures without significantly diminishing their dramatic vibration attenuation in the locally resonant bandgap. Thus, integrating energy harvesters into a locally resonant metastructure enables a new potential for multifunctional locally resonant metastructures that can host self-powered sensors.

Control of the Intrinsic Sensor Response to Volatile Organic Compounds with Fringing Electric Fields.

PubMed

Henning, Alex; Swaminathan, Nandhini; Vaknin, Yonathan; Jurca, Titel; Shimanovich, Klimentiy; Shalev, Gil; Rosenwaks, Yossi

2018-01-26

The ability to control surface-analyte interaction allows tailoring chemical sensor sensitivity to specific target molecules. By adjusting the bias of the shallow p-n junctions in the electrostatically formed nanowire (EFN) chemical sensor, a multiple gate transistor with an exposed top dielectric layer allows tuning of the fringing electric field strength (from 0.5 × 10 7 to 2.5 × 10 7 V/m) above the EFN surface. Herein, we report that the magnitude and distribution of this fringing electric field correlate with the intrinsic sensor response to volatile organic compounds. The local variations of the surface electric field influence the analyte-surface interaction affecting the work function of the sensor surface, assessed by Kelvin probe force microscopy on the nanometer scale. We show that the sensitivity to fixed vapor analyte concentrations can be nullified and even reversed by varying the fringing field strength, and demonstrate selectivity between ethanol and n-butylamine at room temperature using a single transistor without any extrinsic chemical modification of the exposed SiO 2 surface. The results imply an electric-field-controlled analyte reaction with a dielectric surface extremely compelling for sensitivity and selectivity enhancement in chemical sensors.

Ion confinement and transport in a toroidal plasma with externally imposed radial electric fields

NASA Technical Reports Server (NTRS)

Roth, J. R.; Krawczonek, W. M.; Powers, E. J.; Kim, Y. C.; Hong, H. Y.

1979-01-01

Strong electric fields were imposed along the minor radius of the toroidal plasma by biasing it with electrodes maintained at kilovolt potentials. Coherent, low-frequency disturbances characteristic of various magnetohydrodynamic instabilities were absent in the high-density, well-confined regime. High, direct-current radial electric fields with magnitudes up to 135 volts per centimeter penetrated inward to at least one-half the plasma radius. When the electric field pointed radially toward, the ion transport was inward against a strong local density gradient; and the plasma density and confinement time were significantly enhanced. The radial transport along the electric field appeared to be consistent with fluctuation-induced transport. With negative electrode polarity the particle confinement was consistent with a balance of two processes: a radial infusion of ions, in those sectors of the plasma not containing electrodes, that resulted from the radially inward fields; and ion losses to the electrodes, each of the which acted as a sink and drew ions out of the plasma. A simple model of particle confinement was proposed in which the particle confinement time is proportional to the plasma volume. The scaling predicted by this model was consistent with experimental measurements.

Ground-based measurements of the vertical E-field in mountainous regions and the "Austausch" effect

NASA Astrophysics Data System (ADS)

Yaniv, Roy; Yair, Yoav; Price, Colin; Mkrtchyan, Hripsime; Lynn, Barry; Reymers, Artur

2017-06-01

Past measurements of the atmospheric vertical electric field (Ez or potential gradient) at numerous land stations showed a strong response of the daily electric field to a morning local effect known as ;Austausch; - the transport of electrical charges due to increased turbulence. In mountainous regions, nocturnal charge accumulation, followed by an attachment process to aerosols near the surface in valleys, known as the electrode effect, is lifted as a charged aerosol layer by anabatic (upslope) winds during the morning hours due to solar heating. Ground-based measurements during fair weather days were conducted at three mountain stations in Israel and Armenia. We present results of the mean diurnal variation of Ez and make comparisons with the well-known Carnegie curve and with past measurements of Ez on mountains. We report a good agreement between the mean diurnal curves of Ez at various mountain stations and the time of local sunrise when the Ez is found to increase. We attribute this morning maximum to the Austausch (or exchange) layer effect. We support our findings with conduction and turbulent current measurements showing high values of ions and charged aerosols being transported by winds from morning to noon local time, and by model simulations showing the convergence of winds in the early morning hours toward the mountain peak.

Local nematic susceptibility in stressed BaFe 2 As 2 from NMR electric field gradient measurements

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kissikov, T.; Sarkar, R.; Lawson, M.

The electric field gradient (EFG) tensor at the 75As site couples to the orbital occupations of the As p orbitals and is a sensitive probe of local nematicity in BaFe 2As 2. We use nuclear magnetic resonance to measure the nuclear quadrupolar splittings and find that the EFG asymmetry responds linearly to the presence of a strain field in the paramagnetic phase. We extract the nematic susceptibility from the slope of this linear response as a function of temperature and find that it diverges near the structural transition, in agreement with other measures of the bulk nematic susceptibility. In conclusion,more » our work establishes an alternative method to extract the nematic susceptibility which, in contrast to transport methods, can be extended inside the superconducting state.« less

Local nematic susceptibility in stressed BaFe 2 As 2 from NMR electric field gradient measurements

DOE PAGES

Kissikov, T.; Sarkar, R.; Lawson, M.; ...

2017-12-15

The electric field gradient (EFG) tensor at the 75As site couples to the orbital occupations of the As p orbitals and is a sensitive probe of local nematicity in BaFe 2As 2. We use nuclear magnetic resonance to measure the nuclear quadrupolar splittings and find that the EFG asymmetry responds linearly to the presence of a strain field in the paramagnetic phase. We extract the nematic susceptibility from the slope of this linear response as a function of temperature and find that it diverges near the structural transition, in agreement with other measures of the bulk nematic susceptibility. In conclusion,more » our work establishes an alternative method to extract the nematic susceptibility which, in contrast to transport methods, can be extended inside the superconducting state.« less

Measurement System of Surface Electrostatic Potential on Insulation Board in Vacuum and its Application

NASA Astrophysics Data System (ADS)

Morita, Hiroshi; Hatanaka, Ayumu; Yokosuka, Toshiyuki; Seki, Yoshitaka; Tsumuraya, Yoshiaki; Doi, Motomichi

The measurement system of the surface electrostatic potential on a solid insulation board in vacuum has been developed. We used this system to measure the electrostatic potential distribution of the surface of a borosilicate glass plate applied a high voltage. A local increase in the electric field was observed. It is considered that this phenomenon is caused by a positive electrostatic charge generated by a secondary emission of field emission electrons from an electrode. On the other hand, a local increase in the electric field was not observed on a glass plate coated with silica particles and a glass plate roughened by sandblast. We reasoned that this could be because the electrons were trapped by the roughness of the surface. It is considered that these phenomena make many types of equipment using the vacuum insulation more reliable.

Kinetic Electric Field Signatures Associated with Magnetic Turbulence and Their Impact on Space Plasma Environments

NASA Astrophysics Data System (ADS)

Goodrich, K. A.

Magnetic turbulence is a universal phenomenon that occurs in space plasma physics, the small-scale processes of which is not well understood. This thesis presents on observational analysis of kinetic electric field signatures associated with magnetic turbulence, in an attempt to examine its underlying microphysics. Such kinetic signatures include small-scale magnetic holes, double layers, and phase-space holes. The first and second parts of this thesis presents observations of small-scale magnetic holes, observed depressions in total magnetic field strength with spatial widths on the order of or less than the ion Larmor radius, in the near-Earth plasmasheet. Here I demonstrate electric field signatures associated small-scale magnetic holes are consistent with the presence of electron Hall currents, currents oriented perpendicularly to the magnetic field. Further investigation of these fields indicates that the Hall electron current is primarily responsible for the depletion of | B| associated with small-scale magnetic holes. I then present evidence that suggests these currents can descend to smaller spatial scales, indicating they participate in a turbulent cascade to smaller scales, a link that has not been observable suggested until now. The last part of this thesis investigates the presence of double layers and phase-space holes in a magnetically turbulent region of the terrestrial bow shock. In this part, I present evidence that these same signatures can be generated via field-aligned currents generated by strong magnetic fluctuations. I also show that double layers and phase-space holes, embedded within localized nonlinear ion acoustic waves, correlate with localized electron heating and possible ion deceleration, indicating they play a role in turbulent dissipation of kinetic to thermal energy. This thesis clearly demonstrates that energy dissipation in turbulent plasma is closely linked to the small-scale electric field environment.

Polar Spacecraft Based Comparisons of Intense Electric Fields and Poynting Flux Near and Within the Plasma Sheet-Tail Lobe Boundary to UVI Images: An Energy Source for the Aurora

NASA Technical Reports Server (NTRS)

Wygant, J. R.; Keiling, A.; Cattell, C. A.; Johnson, M.; Lysak, R. L.; Temerin, M.; Mozer, F. S.; Kletzing, C. A.; Scudder, J. D.; Peterson, W.;

Polar spacecraft based comparisons of intense electric fields and Poynting flux near and within the plasma sheet-tail lobe boundary to UVI images: An energy source for the aurora

NASA Astrophysics Data System (ADS)

Wygant, J. R.; Keiling, A.; Cattell, C. A.; Johnson, M.; Lysak, R. L.; Temerin, M.; Mozer, F. S.; Kletzing, C. A.; Scudder, J. D.; Peterson, W.; Russell, C. T.; Parks, G.; Brittnacher, M.; Germany, G.; Spann, J.

2000-08-01

In this paper, we present measurements from two passes of the Polar spacecraft of intense electric and magnetic field structures associated with Alfven waves at and within the outer boundary of the plasma sheet at geocentric distances of 4-6 RE near local midnight. The electric field variations have maximum values exceeding 100 mV/m and are typically polarized approximately normal to the plasma sheet boundary. The electric field structures investigated vary over timescales (in the spacecraft frame) ranging from 1 to 30 s. They are associated with strong magnetic field fluctuations with amplitudes of 10-40 nT which lie predominantly in the plane of the plasma sheet and are perpendicular to the local magnetic field. The Poynting flux associated with the perturbation fields measured at these altitudes is about 1-2 ergs cm-2 s-1 and is directed along the average magnetic field direction toward the ionosphere. If the measured Poynting flux is mapped to ionospheric altitudes along converging magnetic field lines, the resulting energy flux ranges up to 100 ergs cm-2s-1. These strongly enhanced Poynting fluxes appear to occur in layers which are observed when the spacecraft is magnetically conjugate (to within a 1° mapping accuracy) to intense auroral structures as detected by the Polar UV Imager (UVI). The electron energy flux (averaged over a spatial resolution of 0.5° ) deposited in the ionosphere due to auroral electron beams as estimated from the intensity in the UVI Lyman-Birge-Hopfield-long filters is 15-30 ergs cm-2s-1. Thus there is evidence that these electric field structures provide sufficient Poynting flux to power the acceleration of auroral electrons (as well as the energization of upflowing ions and Joule heating of the ionosphere). During some events the phasing and ratio of the transverse electric and magnetic field variations are consistent with earthward propagation of Alfven surface waves with phase velocities of 4000-10000 km/s. During other events the phase shifts between electric and magnetic fields suggest interference between upward and downward propagating Alfven waves. The E/B ratios are about an order of magnitude larger than typical values of c/Σp, where Σp is the height integrated Pedersen conductivity. The contribution to the total energy flux at these altitudes from Poynting flux associated with Alfven waves is comparable to or larger than the contribution from the particle energy flux and 1-2 orders of magnitude larger than that estimated from the large-scale steady state convection electric field and field-aligned current system.

Towards more Global Coordination of Atmospheric Electricity Measurements (GloCAEM)

NASA Astrophysics Data System (ADS)

Nicoll, Keri; Harrison, Giles

2017-04-01

Earth's atmospheric electrical environment has been studied since the 1750s but its more recent applications to science questions around clouds and climate highlight the incompleteness of our understanding, in part due to lack of suitable global measurements. The Global Electric Circuit (GEC) sustains the near-surface fair weather (FW) electric field, which is present globally in regions which are not strongly electrically disturbed by weather or pollution. It can be measured routinely at the surface using well established instrumentation such as electric field mills. Despite the central role of lightning as a weather hazard and the potentially widespread importance of charge for atmospheric processes, research is hampered by the fragmented nature of surface atmospheric electricity measurements. This makes anything other than local studies in fortuitous fair weather conditions difficult. In contrast to detection of global lightning using satellite measurements and ground-based radio networks, the FW electric field and GEC cannot be measured by remote sensing and no similar measurement networks exist for its study. This presents an opportunity as many researchers worldwide now make high temporal resolution measurements of the FW electric field routinely, which is neither coordinated nor exploited. The GLOCAEM (Global Coordination of Atmospheric Electricity Measurements) project is currently bringing some of these experts together to make the first steps towards an effective global network for FW atmospheric electricity monitoring. A specific objective of the project is to establish the first modern archive of international FW atmospheric electric field data in close to real time to allow global studies of atmospheric electricity to be straightforwardly and robustly performed. Data will be archived through the UK Centre for Environmental Data Analysis (CEDA) and will be available for download by users from early 2018. Both 1 second and 1 minute electric field data will be archived, along with meteorological measurements (if available) for ease of interpretation of electrical measurements. Although the primary aim of the project is to provide a close to real time electric field database, archiving of existing historical electric field datasets is also planned to extend the range of studies possible. This presentation will provide a summary of progress with the GLOCAEM project.

Strategies for discovery and optimization of thermoelectric materials: Role of real objects and local fields

NASA Astrophysics Data System (ADS)

Zhu, Hao; Xiao, Chong

2018-06-01

Thermoelectric materials provide a renewable and eco-friendly solution to mitigate energy shortages and to reduce environmental pollution via direct heat-to-electricity conversion. Discovery of the novel thermoelectric materials and optimization of the state-of-the-art material systems lie at the core of the thermoelectric society, the basic concept behind these being comprehension and manipulation of the physical principles and transport properties regarding thermoelectric materials. In this mini-review, certain examples for designing high-performance bulk thermoelectric materials are presented from the perspectives of both real objects and local fields. The highlights of this topic involve the Rashba effect, Peierls distortion, local magnetic field, and local stress field, which cover several aspects in the field of thermoelectric research. We conclude with an overview of future developments in thermoelectricity.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levin, I.; Krayzman, V.; Woicik, J. C.

Local structures in cubic perovskite-type (Ba 0.6Bi 0.4)(Ti 0.6Sc 0.4)O 3 solid solutions that exhibit reentrant dipole glass behavior have been studied with variable-temperature x-ray/neutron total scattering, extended x-ray absorption fine structure, and electron diffraction methods. Simultaneous fitting of these data using a reverse Monte Carlo algorithm provided instantaneous atomic configurations, which have been used to extract local displacements of the constituent species. The smaller Bi and Ti atoms exhibit probability density distributions that consist of 14 and 8 split sites, respectively. In contrast, Ba and Sc feature single-site distributions. The multisite distributions arise from large and strongly anisotropic off-centermore » displacements of Bi and Ti. The cation displacements are correlated over a short range, with a correlation length limited by chemical disorder. The magnitudes of these displacements and their anisotropy, which are largely determined by local chemistry, change relatively insignificantly on cooling from room temperature. The structure features a nonrandom distribution of local polarization with low-dimensional polar clusters that are several unit cells in size. In situ measurements of atomic pair-distribution function under applied electric field were used to study field-induced changes in the local structure; however, no significant effects besides lattice expansion in the direction of the field could be observed up to electric-field values of 4 kVmm -1.« less

Corrected body surface potential mapping.

PubMed

Krenzke, Gerhard; Kindt, Carsten; Hetzer, Roland

2007-02-01

In the method for body surface potential mapping described here, the influence of thorax shape on measured ECG values is corrected. The distances of the ECG electrodes from the electrical heart midpoint are determined using a special device for ECG recording. These distances are used to correct the ECG values as if they had been measured on the surface of a sphere with a radius of 10 cm with its midpoint localized at the electrical heart midpoint. The equipotential lines of the electrical heart field are represented on the virtual surface of such a sphere. It is demonstrated that the character of a dipole field is better represented if the influence of the thorax shape is reduced. The site of the virtual reference electrode is also important for the dipole character of the representation of the electrical heart field.

Turbulent Flame Stabilization Methods Using Confinement, Diluents, and High-Potential Electric Fields

DTIC Science & Technology

2014-08-03

the corona discharge was optimal for flame stabilization when it was located where fuel/air mixtures were within flammability limits locally...field [56]. This ionic wind is also known as the “ corona wind” [57] due to the corona discharge that develops at the sharp edge of the charged... Corona Discharge ,” Transactions of the American Institute of Electrical Engineers, Part I: Communication and Electronics, vol. 80, no. 2, pp. 143-150

Electric wind in a Differential Mobility Analyzer

DOE PAGES

Palo, Marus; Meelis Eller; Uin, Janek; ...

2015-10-25

Electric wind -- the movement of gas, induced by ions moving in an electric field -- can be a distorting factor in size distribution measurements using Differential Mobility Analyzers (DMAs). The aim of this study was to determine the conditions under which electric wind occurs in the locally-built VLDMA (Very Long Differential Mobility Analyzer) and TSI Long-DMA (3081) and to describe the associated distortion of the measured spectra. Electric wind proved to be promoted by the increase of electric field strength, aerosol layer thickness, particle number concentration and particle size. The measured size spectra revealed three types of distortion: wideningmore » of the size distribution, shift of the mode of the distribution to smaller diameters and smoothing out the peaks of the multiply charged particles. Electric wind may therefore be a source of severe distortion of the spectrum when measuring large particles at high concentrations.« less

The influence of local electric fields on photoinduced absorption in dye-sensitized solar cells.

PubMed

Cappel, Ute B; Feldt, Sandra M; Schöneboom, Jan; Hagfeldt, Anders; Boschloo, Gerrit

2010-07-07

The dye-sensitized solar cell (DSC) challenges conventional photovoltaics with its potential for low-cost production and its flexibility in terms of color and design. Transient absorption spectroscopy is widely used to unravel the working mechanism of DSCs. A surprising, unexplained feature observed in these studies is an apparent bleach of the ground-state absorption of the dye, under conditions where the dye is in the ground state. Here, we demonstrate that this feature can be attributed to a change of the local electric field affecting the absorption spectrum of the dye, an effect related to the Stark effect first reported in 1913. We present a method for measuring the effect of an externally applied electric field on the absorption of dye monolayers adsorbed on flat TiO(2) substrates. The measured signal has the shape of the first derivative of the absorption spectra of the dyes and reverses sign along with the reversion of the direction of the change in dipole moment upon excitation relative to the TiO(2) surface. A very similar signal is observed in photoinduced absorption spectra of dye-sensitized TiO(2) electrodes under solar cell conditions, demonstrating that the electric field across the dye molecules changes upon illumination. This result has important implications for the analysis of transient absorption spectra of DSCs and other molecular optoelectronic devices and challenges the interpretation of many previously published results.

Local structure in BaTi O 3 - BiSc O 3 dipole glasses

DOE PAGES

Levin, I.; Krayzman, V.; Woicik, J. C.; ...

2016-03-14

Local structures in cubic perovskite-type (Ba 0.6Bi 0.4)(Ti 0.6Sc 0.4)O 3 solid solutions that exhibit reentrant dipole glass behavior have been studied with variable-temperature x-ray/neutron total scattering, extended x-ray absorption fine structure, and electron diffraction methods. Simultaneous fitting of these data using a reverse Monte Carlo algorithm provided instantaneous atomic configurations, which have been used to extract local displacements of the constituent species. The smaller Bi and Ti atoms exhibit probability density distributions that consist of 14 and 8 split sites, respectively. In contrast, Ba and Sc feature single-site distributions. The multisite distributions arise from large and strongly anisotropic off-centermore » displacements of Bi and Ti. The cation displacements are correlated over a short range, with a correlation length limited by chemical disorder. The magnitudes of these displacements and their anisotropy, which are largely determined by local chemistry, change relatively insignificantly on cooling from room temperature. The structure features a nonrandom distribution of local polarization with low-dimensional polar clusters that are several unit cells in size. In situ measurements of atomic pair-distribution function under applied electric field were used to study field-induced changes in the local structure; however, no significant effects besides lattice expansion in the direction of the field could be observed up to electric-field values of 4 kVmm -1.« less

Long-range Coulomb forces and localized bonds.

PubMed

Preiser; Lösel; Brown; Kunz; Skowron

1999-10-01

The ionic model is shown to be applicable to all compounds in which the atoms carry a net charge and their electron density is spherically symmetric regardless of the covalent character of the bonding. By examining the electric field generated by an array of point charges placed at the positions of the ions in over 40 inorganic compounds, we show that the Coulomb field naturally partitions itself into localized regions (bonds) which are characterized by the electric flux that links neighbouring ions of opposite charge. This flux is identified with the bond valence, and Gauss' law with the valence-sum rule, providing a secure theoretical foundation for the bond-valence model. The localization of the Coulomb field provides an unambiguous definition of coordination number and our calculations show that, in addition to the expected primary coordination sphere, there are a number of weak bonds between cations and the anions in the second coordination sphere. Long-range Coulomb interactions are transmitted through the crystal by the application of Gauss' law at each of the intermediate atoms. Bond fluxes have also been calculated for compounds containing ions with non-spherical electron densities (e.g. cations with stereoactive lone electron pairs). In these cases the point-charge model continues to describe the distant field, but multipoles must be added to the point charges to give the correct local field.

Microscopic studies of the fate of charges in organic semiconductors: Scanning Kelvin probe measurements of charge trapping, transport, and electric fields in p- and n-type devices

NASA Astrophysics Data System (ADS)

Smieska, Louisa Marion

Organic semiconductors could have wide-ranging applications in lightweight, efficient electronic circuits. However, several fundamental questions regarding organic electronic device behavior have not yet been fully addressed, including the nature of chemical charge traps, and robust models for injection and transport. Many studies focus on engineering devices through bulk transport measurements, but it is not always possible to infer the microscopic behavior leading to the observed measurements. In this thesis, we present scanning-probe microscope studies of organic semiconductor devices in an effort to connect local properties with local device behavior. First, we study the chemistry of charge trapping in pentacene transistors. Working devices are doped with known pentacene impurities and the extent of charge trap formation is mapped across the transistor channel. Trap-clearing spectroscopy is employed to measure an excitation of the pentacene charge trap species, enabling identification of the degradationrelated chemical trap in pentacene. Second, we examine transport and trapping in peryelene diimide (PDI) transistors. Local mobilities are extracted from surface potential profiles across a transistor channel, and charge injection kinetics are found to be highly sensitive to electrode cleanliness. Trap-clearing spectra generally resemble PDI absorption spectra, but one derivative yields evidence indicating variation in trap-clearing mechanisms for different surface chemistries. Trap formation rates are measured and found to be independent of surface chemistry, contradicting a proposed silanol trapping mechanism. Finally, we develop a variation of scanning Kelvin probe microscopy that enables measurement of electric fields through a position modulation. This method avoids taking a numeric derivative of potential, which can introduce high-frequency noise into the electric field signal. Preliminary data is presented, and the theoretical basis for electric field noise in both methods is examined.

Electric field measurements across the harang discontinuity. [of the auroral zone

NASA Technical Reports Server (NTRS)

Maynard, N. C.

1974-01-01

The Harang discontinuity, the area separating the positive and negative bay regions in the midnight sector of the auroral zone, is a focal point for changes in behavior of many phenomena. Through this region the electric field rotates through the west from a basically northward field in the positive bay region to a basically southward field in the negative bay region, appearing as a reversal in a single axis measurement; 32 of these reversals have been identified in the OGO-6 data from November and December, 1969. The discontinuity is dynamic in nature, moving southward and steepening its latitudinal profile as magnetic activity is increased. As activity decreases it relaxes poleward and spreads out in latitudinal width. It occurs over several hours of magnetic local time. The boundary in the electric field data is consistent with the reversal of ground magnetic disturbances from a positive to negative bay condition. The discontinuity is present in the electric field data both during substorms and during quiet times and appears to define a pattern on which other effects can occur.

Optogenetic versus electrical stimulation of dopamine terminals in the nucleus accumbens reveals local modulation of presynaptic release

PubMed Central

Melchior, James R.; Ferris, Mark J.; Stuber, Garret D.; Riddle, David R.; Jones, Sara R.

2015-01-01

The nucleus accumbens is highly heterogeneous, integrating regionally distinct afferent projections and accumbal interneurons, resulting in diverse local microenvironments. Dopamine (DA) neuron terminals similarly express a heterogeneous collection of terminal receptors that modulate DA signaling. Cyclic voltammetry is often used to probe DA terminal dynamics in brain slice preparations; however, this method traditionally requires electrical stimulation to induce DA release. Electrical stimulation excites all of the neuronal processes in the stimulation field, potentially introducing simultaneous, multi-synaptic modulation of DA terminal release. We used optogenetics to selectively stimulate DA terminals and used voltammetry to compare DA responses from electrical and optical stimulation of the same area of tissue around a recording electrode. We found that with multiple pulse stimulation trains, optically stimulated DA release increasingly exceeded that of electrical stimulation. Furthermore, electrical stimulation produced inhibition of DA release across longer duration stimulations. The GABAB antagonist, CGP 55845, increased electrically stimulated DA release significantly more than light stimulated release. The nicotinic acetylcholine receptor antagonist, dihydro-β-erythroidine hydrobromide, inhibited single pulse electrically stimulated DA release while having no effect on optically stimulated DA release. Our results demonstrate that electrical stimulation introduces local multi-synaptic modulation of DA release that is absent with optogenetically targeted stimulation. PMID:26011081

Influence of Direct Current Electric Field on Corrosion Behavior of Tin Under a Thin Electrolyte Layer

NASA Astrophysics Data System (ADS)

Huang, H. L.; Bu, F. R.; Tian, J.; Liu, D.

2017-12-01

The influence of a direct current electric field (DCEF) on corrosion behavior of tin under a thin electrolyte layer was investigated based on an array electrode technology by polarization, electrochemical impedance spectroscopy and surface analysis. The experimental results indicate that the corrosion rate of tin near the positive plate of DCEF increases with increased electric field intensity, which could be attributed to the acceleration of the migration of ions, the removal of corrosion products under DCEF and the damage of tin surface oxide film. Furthermore, tin at different positions in a DCEF exhibits different corrosion behavior, which could be ascribed to the difference of the local corrosion environment caused by the DCEF.

Micromachined electrical cauterizer

DOEpatents

Lee, Abraham P.; Krulevitch, Peter A.; Northrup, M. Allen

1999-01-01

A micromachined electrical cauterizer. Microstructures are combined with microelectrodes for highly localized electro cauterization. Using boron etch stops and surface micromachining, microneedles with very smooth surfaces are made. Micromachining also allows for precision placement of electrodes by photolithography with micron sized gaps to allow for concentrated electric fields. A microcauterizer is fabricated by bulk etching silicon to form knife edges, then parallelly placed microelectrodes with gaps as small as 5 .mu.m are patterned and aligned adjacent the knife edges to provide homeostasis while cutting tissue. While most of the microelectrode lines are electrically insulated from the atmosphere by depositing and patterning silicon dioxide on the electric feedthrough portions, a window is opened in the silicon dioxide to expose the parallel microelectrode portion. This helps reduce power loss and assist in focusing the power locally for more efficient and safer procedures.

Micromachined electrical cauterizer

DOEpatents

Lee, A.P.; Krulevitch, P.A.; Northrup, M.A.

1999-08-31

A micromachined electrical cauterizer is disclosed. Microstructures are combined with microelectrodes for highly localized electro cauterization. Using boron etch stops and surface micromachining, microneedles with very smooth surfaces are made. Micromachining also allows for precision placement of electrodes by photolithography with micron sized gaps to allow for concentrated electric fields. A microcauterizer is fabricated by bulk etching silicon to form knife edges, then parallelly placed microelectrodes with gaps as small as 5 {mu}m are patterned and aligned adjacent the knife edges to provide homeostasis while cutting tissue. While most of the microelectrode lines are electrically insulated from the atmosphere by depositing and patterning silicon dioxide on the electric feedthrough portions, a window is opened in the silicon dioxide to expose the parallel microelectrode portion. This helps reduce power loss and assist in focusing the power locally for more efficient and safer procedures. 7 figs.

Comparison of Nightside Midlatitude Ionospheric Flows from DMSP and SuperDARN During Stormtime Penetration Events

NASA Astrophysics Data System (ADS)

Hairston, M. R.; Coley, W. R.; Ruohoniemi, J. M.

2016-12-01

July through September 2015 was a relatively quiet period punctuated by nine small to moderate geomagnetic storms (Dst minima ranging from -25 to -98 nT). We are conducting a study of the subauroral midlatitude ionospheric zonal flows in the predawn morning sector (magnetic local times ranging from 2.2 to 5.6 hours) using satellite data from DMSP F15 and F16 along with the midlatitude SuperDARN radars. We will present an empirical model of the background quiettime flows based on these data and then compare those flows to the observed stormtimes flows. The stormtime data will be used to explore the extent of the penetration electric field in this predawn region. Additional satellite flow data from other local times (evening and dayside) will also be presented to check for any local time variation in the extent of the penetration electric field.

Modifying the electronic and optical properties of carbon nanotubes

NASA Astrophysics Data System (ADS)

Kinder, Jesse M.

The intrinsic electronic and optical properties of carbon nanotubes make them promising candidates for circuit elements and LEDs in nanoscale devices. However, applied fields and interactions with the environment can modify these intrinsic properties. This dissertation is a theoretical study of perturbations to an ideal carbon nanotube. It illustrates how transport and optical properties of carbon nanotubes can be adversely affected or intentionally modified by the local environment. The dissertation is divided into three parts. Part I analyzes the effect of a transverse electric field on the single-electron energy spectrum of semiconducting carbon nanotubes. Part II analyzes the effect of the local environment on selection rules and decay pathways relevant to dark excitons. Part III is a series of 26 appendices. Two different models for a transverse electric field are introduced in Part I. The first is a uniform field perpendicular to the nanotube axis. This model suggests the field has little effect on the band gap until it exceeds a critical value that can be tuned with strain or a magnetic field. The second model is a transverse field localized to a small region along the nanotube axis. The field creates a pair of exponentially localized bound states but has no effect on the band gap for particle transport. Part II explores the physics of dark excitons in carbon nanotubes. Two model calculations illustrate the effect of the local environment on allowed optical transitions and nonradiative recombination pathways. The first model illustrates the role of inversion symmetry in the optical spectrum. Broken inversion symmetry may explain low-lying peaks in the exciton spectrum of boron nitride nanotubes and localized photoemission around impurities and interfaces in carbon nanotubes. The second model in Part II suggests that free charge carriers can mediate an efficient nonradiative decay process for dark excitons in carbon nanotubes. The appendices in Part III provide background material and details of calculations relevant to the main text. These appendices may be useful to researchers new to the study of carbon nanotubes.

Comparative In Situ Measurements of Plasma Instabilities in the Equatorial and Auroral Electrojets

NASA Technical Reports Server (NTRS)

Pfaff, Robert F.

2008-01-01

This presentation provides a comparison of in situ measurements of plasma instabilities gathered by rocket-borne probes in the equatorial and auroral electrojets. Specifically, using detailed measurements of the DC electric fields, current density, and plasma number density within the unstable daytime equatorial electrojet from Brazil (Guara Campaign) and in the auroral electrojet from Sweden (ERRIS Campaign), we present comparative observations and general conclusions regarding the observed physical properties of Farley-Buneman two-stream waves and large scale, gradient drift waves. The two stream observations reveal coherent-like waves propagating near the E x B direction but at reduced speeds (nearer to the presumed acoustic velocity) with wavelengths of approximately 5-10m in both the equatorial and auroral electrojet, as measured using the spaced-receiver technique. The auroral electrojet data generally shows extensions to shorter wavelengths, in concert with the fact that these waves are driven harder. With respect to gradient-drift driven waves, observations of this instability are much more pronounced in the equatorial electrojet, given the more favorable geometry for growth provided by the vertical gradient and horizontal magnetic field lines. We present new analysis of Guara rocket observations of electric field and plasma density data that reveal considerable structuring in the middle and lower portion of the electrojet (90-105 km) where the ambient plasma density gradient is unstable. Although the electric field amplitudes are largest (approximately 10-15 mV/m) in the zonal direction, considerable structure (approximately 5-10 mV/m) is also observed in the vertical electric field component as well, implying that the dominant large scale waves involve significant vertical interaction and coupling within the narrow altitude range where they are observed. Furthermore, a detailed examination of the phase of the waveforms show that on some, but not all occasions, locally enhanced eastward fields are associated with locally enhanced upwards (polarization) electric fields. The measurements are discussed in terms of theories involving the non-linear evolution and structuring of plasma waves.

Chiral Plasmonic Nanostructures Fabricated by Circularly Polarized Light.

PubMed

Saito, Koichiro; Tatsuma, Tetsu

2018-05-09

The chirality of materials results in a wide variety of advanced technologies including image display, data storage, light management including negative refraction, and enantioselective catalysis and sensing. Here, we introduce chirality to plasmonic nanostructures by using circularly polarized light as the sole chiral source for the first time. Gold nanocuboids as precursors on a semiconductor were irradiated with circularly polarized light to localize electric fields at specific corners of the cuboids depending on the handedness of light and deposited dielectric moieties as electron oscillation boosters by the localized electric field. Thus, plasmonic nanostructures with high chirality were developed. The present bottom-up method would allow the large-scale and cost-effective fabrication of chiral materials and further applications to functional materials and devices.

Solid-state nanopore localization by controlled breakdown of selectively thinned membranes

NASA Astrophysics Data System (ADS)

Carlsen, Autumn T.; Briggs, Kyle; Hall, Adam R.; Tabard-Cossa, Vincent

2017-02-01

We demonstrate precise positioning of nanopores fabricated by controlled breakdown (CBD) on solid-state membranes by spatially varying the electric field strength with localized membrane thinning. We show 100 × 100 nm2 precision in standard SiN x membranes (30-100 nm thick) after selective thinning by as little as 25% with a helium ion beam. Control over nanopore position is achieved through the strong dependence of the electric field-driven CBD mechanism on membrane thickness. Confinement of pore formation to the thinned region of the membrane is confirmed by TEM imaging and by analysis of DNA translocations. These results enhance the functionality of CBD as a fabrication approach and enable the production of advanced nanopore devices for single-molecule sensing applications.

Long-term monitoring of ULF electromagnetic fields at Parkfield, CA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kappler, K.N.; Morrison, H.F.; Egbert, G.D.

2009-08-01

Electric and magnetic fields in the (10{sup -4}-1.0) Hz band were monitored at two sites adjacent to the San Andreas Fault near Parkfield and Hollister, California from 1995 to present. A data window [2002-2005], enclosing the September 28, 2004 M6 Parkfield earthquake, was analyzed to determine if anomalous electric or magnetic fields, or changes in ground conductivity, occurred before the earthquake. The data were edited, removing intervals of instrument malfunction leaving 875 days in the four-year period. Frequent, spike-like disturbances were common, but were not more frequent around the time of the earthquake; these were removed before subsequent processing. Signalmore » to noise amplitude spectra, estimated via magnetotelluric processing showed the behavior of the ULF fields to be remarkably constant over the period of analysis. These first-order plots make clear that most of the recorded energy is coherent over the spatial extent of the array. Three main statistical techniques were employed to separate local anomalous electrical or magnetic fields from the dominant coherent natural fields: transfer function estimates between components at each site were employed to subtract the dominant field, and look deeper at the 'residual' fields; the data were decomposed into principal components to identify the dominant coherent array modes; and the technique of canonical coherences was employed to distinguish anomalous fields which are spatially broad from anomalies which occur at a single site only, and furthermore to distinguish anomalies which are present in both the electric and magnetic fields from those which are present in only one field type. Standard remote reference apparent resistivity estimates were generated daily at Parkfield. A significant seasonal component of variability was observed suggesting local distortion due to variations in near surface resistance. In all cases, high levels of sensitivity to subtle electromagnetic effects were demonstrated, but no effects which can be reasonably characterized as precursors to the Parkfield earthquake were found.« less

The Circle of Apollonius and Its Applications in Introductory Physics

ERIC Educational Resources Information Center

Partensky, Michael B.

2008-01-01

The circle of Apollonius is named after the ancient geometrician Apollonius of Perga. This beautiful geometric construct can be helpful when solving some general problems of geometry and mathematical physics, optics, and electricity. Here we discuss two of its applications: localizing an object in space and calculating electric fields. First, we…

Numerical Simulation of Non-Thermal Food Preservation

NASA Astrophysics Data System (ADS)

Rauh, C.; Krauss, J.; Ertunc, Ö.; Delgado, a.

2010-09-01

Food preservation is an important process step in food technology regarding product safety and product quality. Novel preservation techniques are currently developed, that aim at improved sensory and nutritional value but comparable safety than in conventional thermal preservation techniques. These novel non-thermal food preservation techniques are based for example on high pressures up to one GPa or pulsed electric fields. in literature studies the high potential of high pressures (HP) and of pulsed electric fields (PEF) is shown due to their high retention of valuable food components as vitamins and flavour and selective inactivation of spoiling enzymes and microorganisms. for the design of preservation processes based on the non-thermal techniques it is crucial to predict the effect of high pressure and pulsed electric fields on the food components and on the spoiling enzymes and microorganisms locally and time-dependent in the treated product. Homogenous process conditions (especially of temperature fields in HP and PEF processing and of electric fields in PEF) are aimed at to avoid the need of over-processing and the connected quality loss and to minimize safety risks due to under-processing. the present contribution presents numerical simulations of thermofluiddynamical phenomena inside of high pressure autoclaves and pulsed electric field treatment chambers. in PEF processing additionally the electric fields are considered. Implementing kinetics of occurring (bio-) chemical reactions in the numerical simulations of the temperature, flow and electric fields enables the evaluation of the process homogeneity and efficiency connected to different process parameters of the preservation techniques. Suggestions to achieve safe and high quality products are concluded out of the numerical results.

Driving spin transition at interface: Role of adsorption configurations

NASA Astrophysics Data System (ADS)

Zhang, Yachao

2018-01-01

A clear insight into the electrical manipulation of molecular spins at interface is crucial to the design of molecule-based spintronic devices. Here we report on the electrically driven spin transition in manganocene physisorbed on a metallic surface in two different adsorption configurations predicted by ab initio techniques, including a Hubbard-U correction at the manganese site and accounting for the long-range van der Waals interactions. We show that the application of an electric field at the interface induces a high-spin to low-spin transition in the flat-lying manganocene, while it could hardly alter the high-spin ground state of the standing-up molecule. This phenomenon cannot be explained by either the molecule-metal charge transfer or the local electron correlation effects. We demonstrate a linear dependence of the intra-molecular spin-state splitting on the energy difference between crystal-field splitting and on-site Coulomb repulsion. After considering the molecule-surface binding energy shifts upon spin transition, we reproduce the obtained spin-state energetics. We find that the configuration-dependent responses of the spin-transition originate from the binding energy shifts instead of the variation of the local ligand field. Through these analyses, we obtain an intuitive understanding of the effects of molecule-surface contact on spin-crossover under electrical bias.

Electric-field-enhanced nutrient consumption in dielectric biomaterials that contain anchorage-dependent cells.

PubMed

Belfiore, Laurence A; Floren, Michael L; Belfiore, Carol J

2012-02-01

This research contribution addresses electric-field stimulation of intra-tissue mass transfer and cell proliferation in viscoelastic biomaterials. The unsteady state reaction-diffusion equation is solved according to the von Kármán-Pohlhausen integral method of boundary layer analysis when nutrient consumption and tissue regeneration occur in response to harmonic electric potential differences across a parallel-plate capacitor in a dielectric-sandwich configuration. The partial differential mass balance with diffusion and electro-kinetic consumption contains the Damköhler (Λ(2)) and Deborah (De) numbers. Zero-field and electric-field-sensitive Damköhler numbers affect nutrient boundary layer growth. Diagonal elements of the 2nd-rank diffusion tensor are enhanced in the presence of weak electric fields, in agreement with the formalism of equilibrium and nonequilibrium thermodynamics. Induced dipole polarization density within viscoelastic biomaterials is calculated via the real and imaginary components of the complex dielectric constant, according to the Debye equation, to quantify electro-kinetic stimulation. Rates of nutrient consumption under zero-field conditions are described by third-order kinetics that include local mass densities of nutrients, oxygen, and attached cells. Thinner nutrient boundary layers are stabilized at shorter dimensionless diffusion times when the zero-field intra-tissue Damköhler number increases above its initial-condition-sensitive critical value [i.e., {Λ(2)(zero-field)}(critical)≥53, see Eq. (23)], such that the biomaterial core is starved of essential ingredients required for successful proliferation. When tissue regeneration occurs above the critical electric-field-sensitive intra-tissue Damköhler number, the electro-kinetic contribution to nutrient consumption cannot be neglected. The critical electric-field-sensitive intra-tissue Damköhler number is proportional to the Deborah number. Copyright © 2011 Elsevier B.V. All rights reserved.

The Effect of Precipitating Electrons and Ions on Ionospheric Conductance and Inner Magnetospheric Electric Fields 142106

NASA Astrophysics Data System (ADS)

Chen, M.; Lemon, C.; Hecht, J. H.; Evans, J. S.; Boyd, A. J.

2016-12-01

We investigate how scattering of electrons by waves and of ions by field-line curvature in the inner magnetosphere affect precipitating energy flux distributions and how the precipitating particles modify the ionospheric conductivity and electric potentials during magnetic storms. We examine how particle precipitation in the evening sector affects the development of the Sub-Auroral Polarization Stream (SAPS) electric field that is observed at sub-auroral latitudes in that sector as well as the electric field in the morning sector. Our approach is to use the magnetically and electrically self-consistent Rice Convection Model - Equilibrium (RCM-E) of the inner magnetosphere to simulate the stormtime precipitating particle distributions and the electric field. We use parameterized rates of whistler-generated electron pitch-angle scattering from Orlova and Shprits [JGR, 2014] that depend on equatorial radial distance, magnetic activity (Kp), and magnetic local time (MLT) outside the simulated plasmasphere. Inside the plasmasphere, parameterized scattering rates due to hiss [Orlova et al., GRL, 2014] are employed. Our description for the rate of ion scattering is more simplistic. We assume that the ions are scattered at a fraction of strong pitch-angle scattering where the fraction is scaled by epsilon, the ratio of the gyroradius to the field-line radius of curvature, when epsilon is greater than 0.1. We compare simulated trapped and precipitating electron/ion flux distributions with measurements from Van Allen Probes/MagEIS, POES and DMSP, respectively, to validate the particle loss models. DMSP observations of electric fields are compared with the simulation results. We discuss the effect of precipitating electrons and ions on the SAPS and the inner magnetospheric electric field through the data-model comparisons.

Giant electrocaloric effect in a cracked ferroelectrics

NASA Astrophysics Data System (ADS)

Huang, Cheng; Yang, Hai-Bing; Gao, Cun-Fa

2018-04-01

The electrocaloric effect (ECE) is the temperature change in a material induced by electrical field variation under adiabatic condition. Considering an external electric load applied on a cracked ferroelectric solid, a non-uniform electric field would be induced at the crack tip, and thus, incompatible strain field and local stress concentration would be generated around it. Furthermore, the enormous strain energy and the electrostatic energy would affect the polarization switching of the ferroelectric solid, important for the electrocaloric response. In this paper, the large negative and positive ECEs in a ferroelectric sheet with a conducting crack are investigated by the phase field method with the consideration of time-dependent Ginzburg-Landau equation. The numerical calculations indicated that the polarization field generates a sharp rise during the domain transition from polydomain to monodomain under a certain electric load. Large negative ECEs, about -10.21 K and -7.55 K, are obtained at 135 °C and 85 °C, respectively. The domain transition temperature is much lower than the Curie temperature, which enlarges the existence scope of the large ECE in ferroelectrics. The results also imply that the domain transition from a multi-domain state to a single domain takes place with the minimization of total free energy, which involves the courses of the electric field, stress field, temperature, and polarization interaction. Therefore, the non-uniform distributions of the stress-electric fields induced by the crack play an important role in ECE.

A generalized electro-elastic theory of polymer networks

NASA Astrophysics Data System (ADS)

Cohen, Noy

2018-01-01

A rigorous multi-scale analysis of the electromechanical coupling in dielectric polymers is conducted. The body couples stemming from a misalignment between the electric field and the electric-dipole density vector are studied and the conservation laws for polymer networks are derived. Using variational principles, expressions for the polarization and the stress are determined. Interestingly, it is found that the stress tensor resulting from coupled loadings in which the electric field is misaligned with the principal stretch directions is not symmetric and the asymmetry arises from the body couples. Next, the electro-mechanical response of a chain is analyzed. The deformations of the individual polymer chains are related to the macroscopic deformation via two highly non-linear constraints - the first pertaining to the compatibility of the local deformations with the imposed macroscopic one and the second stems from the symmetric part of the stress at equilibrium. In accord with the proposed framework, an amended three-chains model is introduced. The predictions of this model are found to be in excellent agreement with experimental findings. Lastly, the behavior of a polymer subjected to a simple shear and an electric field is studied. The offset between the electric field and the principal directions gives rise to body couples, a polarization that is not aligned with the electric field, and an asymmetric stress tensor.

Modeling of asymmetric degradation based on a non-uniform electric field and temperature in amorphous In-Ga-Zn-O thin film transistors

NASA Astrophysics Data System (ADS)

In Kim, Jong; Jeong, Chan-Yong; Kwon, Hyuck-In; Jung, Keum Dong; Park, Mun Soo; Kim, Ki Hwan; Seo, Mi Seon; Lee, Jong-Ho

2017-03-01

We propose a new local degradation model based on a non-uniform increase in donor-like traps (DLTs) determined by distributions of an electric field and measured device temperature in amorphous In-Ga-Zn-O (a-IGZO) thin film transistors (TFTs). A systematic investigation of the degradation model reveals that vertical field-dependent DLTs are essential for modeling of measured asymmetric electrical characteristics between the source and drain after positive gate and drain bias stressing. An increased temperature due to self-heating is found to play a role in intensifying the asymmetric degradation. From the individual simulation of measured transfer curves at different stress times, the model parameters and an asymmetry index as a function of stress time are extracted. It is expected that this novel methodology will provide new insight into asymmetric degradation and be utilized to predict the influence of electric field and heat on degradation under various bias-stress conditions in a-IGZO TFTs.

Design and fabrication of a 3D-structured gold film with nanopores for local electric field enhancement in the pore

NASA Astrophysics Data System (ADS)

Grant-Jacob, James A.; Zin Oo, Swe; Carpignano, Francesca; Boden, Stuart A.; Brocklesby, William S.; Charlton, Martin D. B.; Melvin, Tracy

2016-02-01

Three-dimensionally structured gold membrane films with nanopores of defined, periodic geometries are designed and fabricated to provide the spatially localised enhancement of electric fields by manipulation of the plasmons inside nanopores. Square nanopores of different size and orientation relative to the pyramid are considered for films in aqueous and air environments, which allow for control of the position of electric fields within the structure. Designs suitable for use with 780 nm light were created. Here, periodic pyramidal cavities produced by potassium hydroxide etching to the {111} planes of (100) silicon substrates are used as templates for creating a periodic, pyramidal structured, free-standing thin gold film. Consistent with the findings from the theoretical studies, a nano-sized hole of 50 nm square was milled through the gold film at a specific location in the cavity to provide electric field control which can subsequently used for enhancement of fluorescence or Raman scattering of molecules in the nanopore.

Design and fabrication of a 3D-structured gold film with nanopores for local electric field enhancement in the pore.

PubMed

Grant-Jacob, James A; Oo, Swe Zin; Carpignano, Francesca; Boden, Stuart A; Brocklesby, William S; Charlton, Martin D B; Melvin, Tracy

2016-02-12

Three-dimensionally structured gold membrane films with nanopores of defined, periodic geometries are designed and fabricated to provide the spatially localised enhancement of electric fields by manipulation of the plasmons inside nanopores. Square nanopores of different size and orientation relative to the pyramid are considered for films in aqueous and air environments, which allow for control of the position of electric fields within the structure. Designs suitable for use with 780 nm light were created. Here, periodic pyramidal cavities produced by potassium hydroxide etching to the {111} planes of (100) silicon substrates are used as templates for creating a periodic, pyramidal structured, free-standing thin gold film. Consistent with the findings from the theoretical studies, a nano-sized hole of 50 nm square was milled through the gold film at a specific location in the cavity to provide electric field control which can subsequently used for enhancement of fluorescence or Raman scattering of molecules in the nanopore.

Reversible control of magnetic interactions by electric field in a single-phase material.

PubMed

Ryan, P J; Kim, J-W; Birol, T; Thompson, P; Lee, J-H; Ke, X; Normile, P S; Karapetrova, E; Schiffer, P; Brown, S D; Fennie, C J; Schlom, D G

2013-01-01

Intrinsic magnetoelectric coupling describes the interaction between magnetic and electric polarization through an inherent microscopic mechanism in a single-phase material. This phenomenon has the potential to control the magnetic state of a material with an electric field, an enticing prospect for device engineering. Here, we demonstrate 'giant' magnetoelectric cross-field control in a tetravalent titanate film. In bulk form, EuTiO(3), is antiferromagnetic. However, both anti and ferromagnetic interactions coexist between different nearest europium neighbours. In thin epitaxial films, strain was used to alter the relative strength of the magnetic exchange constants. We not only show that moderate biaxial compression precipitates local magnetic competition, but also demonstrate that the application of an electric field at this strain condition switches the magnetic ground state. Using first-principles density functional theory, we resolve the underlying microscopic mechanism resulting in G-type magnetic order and illustrate how it is responsible for the 'giant' magnetoelectric effect.

Non-localized trapping effects in AlGaN/GaN heterojunction field-effect transistors subjected to on-state bias stress

NASA Astrophysics Data System (ADS)

Hu, Cheng-Yu; Hashizume, Tamotsu

2012-04-01

For AlGaN/GaN heterojunction field-effect transistors, on-state-bias-stress (on-stress)-induced trapping effects were observed across the entire drain access region, not only at the gate edge. However, during the application of on-stress, the highest electric field was only localized at the drain side of the gate edge. Using the location of the highest electric field as a reference, the trapping effects at the gate edge and at the more distant access region were referred to as localized and non-localized trapping effect, respectively. Using two-dimensional-electron-gas sensing-bar (2DEG-sensing-bar) and dual-gate structures, the non-localized trapping effects were investigated and the trap density was measured to be ˜1.3 × 1012 cm-2. The effect of passivation was also discussed. It was found that both surface leakage currents and hot electrons are responsible for the non-localized trapping effects with hot electrons having the dominant effect. Since hot electrons are generated from the 2DEG channel, it is highly likely that the involved traps are mainly in the GaN buffer layer. Using monochromatic irradiation (1.24-2.81 eV), the trap levels responsible for the non-localized trapping effects were found to be located at 0.6-1.6 eV from the valence band of GaN. Both trap-assisted impact ionization and direct channel electron injection are proposed as the possible mechanisms of the hot-electron-related non-localized trapping effect. Finally, using the 2DEG-sensing-bar structure, we directly confirmed that blocking gate injected electrons is an important mechanism of Al2O3 passivation.

Gate-defined quantum confinement in suspended bilayer graphene

NASA Astrophysics Data System (ADS)

Allen, M. T.; Martin, J.; Yacoby, A.

2012-07-01

Quantum-confined devices that manipulate single electrons in graphene are emerging as attractive candidates for nanoelectronics applications. Previous experiments have employed etched graphene nanostructures, but edge and substrate disorder severely limit device functionality. Here we present a technique that builds quantum-confined structures in suspended bilayer graphene with tunnel barriers defined by external electric fields that open a bandgap, thereby eliminating both edge and substrate disorder. We report clean quantum dot formation in two regimes: at zero magnetic field B using the energy gap induced by a perpendicular electric field and at B>0 using the quantum Hall ν=0 gap for confinement. Coulomb blockade oscillations exhibit periodicity consistent with electrostatic simulations based on local top-gate geometry, a direct demonstration of local control over the band structure of graphene. This technology integrates single electron transport with high device quality and access to vibrational modes, enabling broad applications from electromechanical sensors to quantum bits.

Large magnetic to electric field contrast in azimuthally polarized vortex beams generated by a metasurface (Presentation Recording)

NASA Astrophysics Data System (ADS)

Veysi, Mehdi; Guclu, Caner; Capolino, Filippo

2015-09-01

We investigate azimuthally E-polarized vortex beams with enhanced longitudinal magnetic field. Ideally, such beams possess strong longitudinal magnetic field on the beam axis where there is no electric field. First we formulate the electric field vector and the longitudinal magnetic field of an azimuthally E-polarized beam as an interference of right- and left-hand circularly polarized Laguerre Gaussian (LG) beams carrying the orbital angular momentum (OAM) states of -1 and +1, respectively. Then we propose a metasurface design that is capable of converting a linearly polarized Gaussian beam into an azimuthally E-polarized vortex beam with longitudinal magnetic field. The metasurface is composed of a rectangular array of double-layer double split-ring slot elements, though other geometries could be adopted as well. The element is specifically designed to have nearly a 180° transmission phase difference between the two polarization components along two orthogonal axes, similar to the optical axes of a half-wave plate. By locally rotating the optical axes of each metasurface element, the transmission phase profile of the circularly polarized waves over the metasurface can be tailored. Upon focusing of the generated vortex beam through a lens with a numerical aperture of 0.7, a 41-fold enhancement of the magnetic to electric field ratio is achieved on the beam axis with respect to that of a plane wave. Generation of beams with large magnetic field to electric field contrast can find applications in future spectroscopy systems based on magnetic dipole transitions, which are usually much weaker than electric dipole transitions.

Quasi-elastic light scattering of carnauba wax in the liquid phase: dynamics 2.

PubMed

de Almeida, F J; Barbosa, G A

1983-12-01

Quasi-elastic light scattering of carnauba wax in the liquid phase is obtained in a heterodyne setup, and dynamic processes are analyzed through electrophoresis. Nonspherical polar clusters are found, containing a net electrical charge. An applied square-wave electric field induces drift and rotation of these clusters.These effects are dependent on strength and frequency of the applied electric field. At 373 K and in the low frequency limit the local electric field strength is approximately 70 times the strength of the applied one. This enhancement is believed to be caused by collective orientation of the clusters. The electrophoretic mobility is 1.1 X 10(-12) m2/V sec in the high frequency limit and 7.4 X 10(-11) m2/V sec in the low frequency limit. The electric dipole moment is 6.3 X 10(-16) N(-1/2) m(-1/2) where N is the cluster density/cubic meter and the net charge is about one or two elementary charges.

Complementary bowtie aperture for localizing and enhancing optical magnetic field

NASA Astrophysics Data System (ADS)

Zhou, Nan; Kinzel, Edward C.; Xu, Xianfan

2011-08-01

Nanoscale bowtie antenna and bowtie aperture antenna have been shown to generate strongly enhanced and localized electric fields below the diffraction limit in the optical frequency range. According to Babinet's principle, their complements will be efficient for concentrating and enhancing magnetic fields. In this Letter, we discuss the enhancement of magnetic field intensity of nanoscale complementary bowtie aperture as well as complementary bowtie aperture antenna, or diabolo nanoantenna. We show that the complementary bowtie antenna resonates at a smaller wavelength and thus is more suitable for applications near visible wavelengths. The near-field magnetic intensity can be further enhanced by the addition of groove structures that scatter surface plasmon.

Effect of Precipitating Electrons on Stormtime Inner Magnetospheric Electric Fields during the 17 March 2013 Storm

NASA Astrophysics Data System (ADS)

Chen, M.; Lemon, C. L.; Sazykin, S. Y.; Wolf, R.; Hecht, J. H.; Walterscheid, R. L.; Boyd, A. J.; Turner, D. L.

2015-12-01

We investigate how scattering of electrons by waves in the plasma sheet and plasmasphere affects precipitating energy flux distributions and how the precipitating electrons modify the ionospheric conductivity and electric potentials during the large 17 March 2013 magnetic storm. Of particular interest is how electron precipitation in the evening sector affects the development of the Sub-auroral Polarization Stream (SAPS) electric field that is observed at sub-auroral latitudes in that sector. Our approach is to use the magnetically and electrically self-consistent Rice Convection Model - Equilibrium (RCM-E) of the inner magnetosphere to simulate the stormtime precipitating electron distributions and the electric field. We use parameterized rates of whistler-generated electron pitch-angle scattering from Orlova and Shprits [JGR, 2014] that depend on equatorial radial distance, magnetic activity (Kp), and magnetic local time (MLT) outside the simulated plasmasphere. Inside the plasmasphere, parameterized scattering rates due to hiss [Orlova et al., GRL, 2014] are used. We compare simulated trapped and precipitating electron flux distributions with measurements from Van Allen Probes/MagEIS, POES/TED and MEPED, respectively, to validate the electron loss model. Ground-based (SuperDARN) and in-situ (Van Allen Probes/EFW) observations of electric fields are compared with the simulation results. We discuss the effect of precipitating electrons on the SAPS and inner magnetospheric electric field through the data-model comparisons.

First Results on the Variability of Mid- and High-Latitude Ionospheric Electric Fields at 1- Second Time Scales

NASA Astrophysics Data System (ADS)

Ruohoniemi, J. M.; Greenwald, R. A.; Oksavik, K.; Baker, J. B.

2007-12-01

The electric fields at high latitudes are often modeled as a static pattern in the absence of variation in solar wind parameters or geomagnetic disturbance. However, temporal variability in the local electric fields on time scales of minutes for stable conditions has been reported and characterized statistically as an intrinsic property amounting to turbulence. We describe the results of applying a new technique to SuperDARN HF radar observations of ionospheric plasma convection at middle and high latitudes that gives views of the variability of the electric fields at sub-second time scales. We address the question of whether there is a limit to the temporal scale of the electric field variability and consider whether the turbulence on minute time scales is due to organized but unresolved behavior. The basis of the measurements is the ability to record raw samples from the individual multipulse sequences that are transmitted during the standard 3 or 6-second SuperDARN integration period; a backscattering volume is then effectively sampled at a cadence of 200 ms. The returns from the individual sequences are often sufficiently well-ordered to permit a sequence-by-sequence characterization of the electric field and backscattered power. We attempt a statistical characterization of the variability at these heretofore inaccessible time scales and consider how variability is influenced by solar wind and magentospheric factors.

The FIELDS Instrument Suite on MMS: Scientific Objectives, Measurements, and Data Products

NASA Astrophysics Data System (ADS)

Torbert, R. B.; Russell, C. T.; Magnes, W.; Ergun, R. E.; Lindqvist, P.-A.; Le Contel, O.; Vaith, H.; Macri, J.; Myers, S.; Rau, D.; Needell, J.; King, B.; Granoff, M.; Chutter, M.; Dors, I.; Olsson, G.; Khotyaintsev, Y. V.; Eriksson, A.; Kletzing, C. A.; Bounds, S.; Anderson, B.; Baumjohann, W.; Steller, M.; Bromund, K.; Le, Guan; Nakamura, R.; Strangeway, R. J.; Leinweber, H. K.; Tucker, S.; Westfall, J.; Fischer, D.; Plaschke, F.; Porter, J.; Lappalainen, K.

2016-03-01

The FIELDS instrumentation suite on the Magnetospheric Multiscale (MMS) mission provides comprehensive measurements of the full vector magnetic and electric fields in the reconnection regions investigated by MMS, including the dayside magnetopause and the night-side magnetotail acceleration regions out to 25 Re. Six sensors on each of the four MMS spacecraft provide overlapping measurements of these fields with sensitive cross-calibrations both before and after launch. The FIELDS magnetic sensors consist of redundant flux-gate magnetometers (AFG and DFG) over the frequency range from DC to 64 Hz, a search coil magnetometer (SCM) providing AC measurements over the full whistler mode spectrum expected to be seen on MMS, and an Electron Drift Instrument (EDI) that calibrates offsets for the magnetometers. The FIELDS three-axis electric field measurements are provided by two sets of biased double-probe sensors (SDP and ADP) operating in a highly symmetric spacecraft environment to reduce significantly electrostatic errors. These sensors are complemented with the EDI electric measurements that are free from all local spacecraft perturbations. Cross-calibrated vector electric field measurements are thus produced from DC to 100 kHz, well beyond the upper hybrid resonance whose frequency provides an accurate determination of the local electron density. Due to its very large geometric factor, EDI also provides very high time resolution (˜1 ms) ambient electron flux measurements at a few selected energies near 1 keV. This paper provides an overview of the FIELDS suite, its science objectives and measurement requirements, and its performance as verified in calibration and cross-calibration procedures that result in anticipated errors less than 0.1 nT in B and 0.5 mV/m in E. Summaries of data products that result from FIELDS are also described, as well as algorithms for cross-calibration. Details of the design and performance characteristics of AFG/DFG, SCM, ADP, SDP, and EDI are provided in five companion papers.

Non-linear non-local molecular electrodynamics with nano-optical fields.

PubMed

Chernyak, Vladimir Y; Saurabh, Prasoon; Mukamel, Shaul

2015-10-28

The interaction of optical fields sculpted on the nano-scale with matter may not be described by the dipole approximation since the fields may vary appreciably across the molecular length scale. Rather than incrementally adding higher multipoles, it is advantageous and more physically transparent to describe the optical process using non-local response functions that intrinsically include all multipoles. We present a semi-classical approach for calculating non-local response functions based on the minimal coupling Hamiltonian. The first, second, and third order response functions are expressed in terms of correlation functions of the charge and the current densities. This approach is based on the gauge invariant current rather than the polarization, and on the vector potential rather than the electric and magnetic fields.

First electric field measurements from the plasma environment of comet 67P/Churyumov-Gerasimenko

NASA Astrophysics Data System (ADS)

Karlsson, Tomas; Eriksson, Anders; Odelstad, Elias; André, Mats; Dickeli, Guillaume; Kullen, Anita; Lindqvist, Per-Arne

2017-04-01

We present the first electric field measurements from the plasma environment of comet 67P/Churyumov-Gerasimenko, performed by the Rosetta dual Langmuir probe instrument LAP. For two time intervals, measurements of the electric field from cometocentric distances of 149 and 348 km are presented together with estimates of the spacecraft potential, which can be used as an indicator of plasma density changes. Persistent wave activity around the local water ion lower hybrid frequency (determined from the magnetic field measurements from the fluxgate magnetometer MAG) is observed. The largest amplitudes are observed at sharp plasma gradients. We discuss the probability that these waves are excited by the lower hybrid drift instability (LHDI), and conclude that the necessary requirements for the LHDI to be operating are fulfilled. We also present first statistical results of the electric field measurements, showing that the wave activity is concentrated to certain regions of the comet, and varies with heliocentric distance. We also discuss the possible effects the waves have on the ambient plasma, and suggest that they may explain hot plasma populations.

Response to 'Comment on 'Three-dimensional numerical investigation of electron transport with rotating spoke in a cylindrical anode layer Hall plasma accelerator''[Phys. Plasmas 20, 014701 (2013)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tang, D. L.; Qiu, X. M.; Geng, S. F.

The numerical simulation described in our paper [D. L. Tang et al., Phys. Plasmas 19, 073519 (2012)] shows a rotating dense plasma structure, which is the critical characteristic of the rotating spoke. The simulated rotating spoke has a frequency of 12.5 MHz with a rotational speed of {approx}1.0 Multiplication-Sign 10{sup 6} m/s on the surface of the anode. Accompanied by the almost uniform azimuthal ion distribution, the non-axisymmetric electron distribution introduces two azimuthal electric fields with opposite directions. The azimuthal electric fields have the same rotational frequency and speed together with the rotating spoke. The azimuthal electric fields excite themore » axial electron drift upstream and downstream due to the additional E{sub {theta}} x B field and then the axial shear flow is generated. The axial local charge separation induced by the axial shear electron flow may be compensated by the azimuthal electron transport, finally resulting in the azimuthal electric field rotation and electron transport with the rotating spoke.« less

Two Step Acceleration Process of Electrons in the Outer Van Allen Radiation Belt by Time Domain Electric Field Bursts and Large Amplitude Chorus Waves

NASA Astrophysics Data System (ADS)

Agapitov, O. V.; Mozer, F.; Artemyev, A.; Krasnoselskikh, V.; Lejosne, S.

2014-12-01

A huge number of different non-linear structures (double layers, electron holes, non-linear whistlers, etc) have been observed by the electric field experiment on the Van Allen Probes in conjunction with relativistic electron acceleration in the Earth's outer radiation belt. These structures, found as short duration (~0.1 msec) quasi-periodic bursts of electric field in the high time resolution electric field waveform, have been called Time Domain Structures (TDS). They can quite effectively interact with radiation belt electrons. Due to the trapping of electrons into these non-linear structures, they are accelerated up to ~10 keV and their pitch angles are changed, especially for low energies (˜1 keV). Large amplitude electric field perturbations cause non-linear resonant trapping of electrons into the effective potential of the TDS and these electrons are then accelerated in the non-homogeneous magnetic field. These locally accelerated electrons create the "seed population" of several keV electrons that can be accelerated by coherent, large amplitude, upper band whistler waves to MeV energies in this two step acceleration process. All the elements of this chain acceleration mechanism have been observed by the Van Allen Probes.

MMS Multipoint Electric Field Observations of Small-Scale Magnetic Holes

NASA Technical Reports Server (NTRS)

Goodrich, Katherine A.; Ergun, Robert E.; Wilder, Frederick; Burch, James; Torbert, Roy; Khotyaintsev, Yuri; Lindqvist, Per-Arne; Russell, Christopher; Strangeway, Robert; Magnus, Werner

2016-01-01

Small-scale magnetic holes (MHs), local depletions in magnetic field strength, have been observed multiple times in the Earths magnetosphere in the bursty bulk flow (BBF) braking region. This particular subset of MHs has observed scale sizes perpendicular to the background magnetic field (B) less than the ambient ion Larmor radius (p(sib i)). Previous observations by Time History of Events and Macroscale Interactions during Substorms (THEMIS) indicate that this subset of MHs can be supported by a current driven by the E x B drift of electrons. Ions do not participate in the E x B drift due to the small-scale size of the electric field. While in the BBF braking region, during its commissioning phase, the Magnetospheric Multiscale (MMS) spacecraft observed a small-scale MH. The electric field observations taken during this event suggest the presence of electron currents perpendicular to the magnetic field. These observations also suggest that these currents can evolve to smaller spatial scales.

Typical values of the electric drift E × B/B2 in the inner radiation belt and slot region as determined from Van Allen Probe measurements

NASA Astrophysics Data System (ADS)

Lejosne, Solène; Mozer, F. S.

2016-12-01

The electric drift E × B/B2 plays a fundamental role for the description of plasma flow and particle acceleration. Yet it is not well-known in the inner belt and slot region because of a lack of reliable in situ measurements. In this article, we present an analysis of the electric drifts measured below L 3 by both Van Allen Probes A and B from September 2012 to December 2014. The objective is to determine the typical components of the equatorial electric drift in both radial and azimuthal directions. The dependences of the components on radial distance, magnetic local time, and geographic longitude are examined. The results from Van Allen Probe A agree with Van Allen Probe B. They show, among other things, a typical corotation lag of the order of 5 to 10% below L 2.6, as well as a slight radial transport of the order of 20 m s-1. The magnetic local time dependence of the electric drift is consistent with that of the ionosphere wind dynamo below L 2 and with that of a solar wind-driven convection electric field above L 2. A secondary longitudinal dependence of the electric field is also found. Therefore, this work also demonstrates that the instruments on board Van Allen Probes are able to perform accurate measurements of the electric drift below L 3.

Influence of quantum well inhomogeneities on absorption, spontaneous emission, photoluminescence decay time, and lasing in polar InGaN quantum wells emitting in the blue-green spectral region

NASA Astrophysics Data System (ADS)

Gladysiewicz, M.; Kudrawiec, R.; Syperek, M.; Misiewicz, J.; Siekacz, M.; Cywinski, G.; Khachapuridze, A.; Suski, T.; Skierbiszewski, C.

2014-06-01

It is shown that in polar InGaN QWs emitting in the blue-green spectral region a Stokes shift between spontaneous emission (SE) and optical transition observed in contactless electroreflectance (CER) spectrum (absorption-like technique) can be observed even at room temperature, despite the fact that the SE is not associated with localized states. Time resolved photoluminescence measurements clearly confirm that the SE is strongly localized at low temperatures whereas at room temperature the carrier localization disappears and the SE can be attributed to the fundamental transition in this QW. The Stokes shift is observed in this QW system because of the large built-in electric field, i.e., the CER transition is a superposition of all optical transitions with non-zero electron-hole overlap integrals and, therefore, the energy of this transition does not correspond to the fundamental transition of InGaN QW. Lasing from this QW has been observed at the wavelength of 475 nm, whereas the SE was observed at 500 nm. The 25 nm shift between the lasing and SE is observed because of a screening of the built-in electric field by photogenerated carriers. However, our analysis shows that the built-in electric field inside the InGaN QW region is not fully screened under the lasing conditions.

Electrokinetic mixing vortices due to electrolyte depletion at microchannel junctions.

PubMed

Takhistov, Paul; Duginova, Ksenia; Chang, Hsueh-Chia

2003-07-01

Due to electric field leakage across sharp corners, the irrotational character of Ohmic electroosmotic flow is violated. Instead, we demonstrate experimentally and theoretically evidence of electrolyte depletion and vortex separation in electroosmotic flow around a junction between wide and narrow channels. When the penetration length of the electric field exceeds the width of the narrow channel and if the electric field is directed from the narrow to the wide channel, the electromigration of ions diminishes significantly at the junction end of the narrow channel due to this leakage. Concentration depletion then develops at that location to maintain current balance but it also increases the corner zeta potential and the local electroosmotic slip velocity. A back pressure gradient hence appears to maintain flow balance and, at a sufficient magnitude, generates a pair of vortices.

The trapping and distribution of charge in polarized polymethylmethacrylate under electron-beam irradiation

NASA Astrophysics Data System (ADS)

Song, Z. G.; Gong, H.; Ong, C. K.

1997-06-01

A scanning electron microscope (SEM) mirror-image method (MIM) is employed to investigate the charging behaviour of polarized polymethylmethacrylate (PMMA) under electron-beam irradiation. An ellipsoid is used to model the trapped charge distribution and a fitting method is employed to calculate the total amount of the trapped charge and its distribution parameters. The experimental results reveal that the charging ability decreases with increasing applied electric field, which polarizes the PMMA sample, whereas the trapped charge distribution is elongated along the direction of the applied electric field and increases with increasing applied electric field. The charges are believed to be trapped in some localization states, of activation energy and radius estimated to be about 19.6 meV and 0022-3727/30/11/004/img6, respectively.

DC Stark addressing for quantum memory in Tm:YAG

NASA Astrophysics Data System (ADS)

Gerasimov, Konstantin; Minnegaliev, Mansur; Urmancheev, Ravil; Moiseev, Sergey

2017-10-01

We observed a linear DC Stark effect for 3H6 - 3H4 optical transition of Tm3+ ions in Y3Al5O12. We observed that application of electric field pulse suppresses the two-pulse photon echo signal. If we then apply a second electric pulse of opposite polarity the echo signal is restored again, which indicates the linear nature of the observed effect. The effect is present despite the D2 symmetry of the Tm3+ sites that prohibits a linear Stark effect. Experimental data analysis shows that the observed electric field influence can be attributed to defects that break the local crystal field symmetry near Tm3+ ions. Using this effect we demonstrate selective retrieval of light pulses in two-pulse photon echo.

Field-aligned currents, convection electric fields, and ULF-ELF waves in the cusp

NASA Technical Reports Server (NTRS)

Saflekos, N. A.; Potemra, T. A.; Kintner, P. M., Jr.; Green, J. L.

1979-01-01

Nearly simultaneous observations from the Triad and Hawkeye satellites over the Southern Hemisphere, at low altitudes near the noon meridian and close to the usual polar cusp latitudes, show that in and near the polar cusp there exist several relationships between field-aligned currents (FACs), convection electric fields, ULF-ELF magnetic noise, broadband electrostatic noise and interplanetary magnetic fields. The most important findings are (1) the FACs directed into the ionosphere in the noon-to-dusk local time sector and directed away from the ionosphere in the noon-to-dawn local time sector and identified as region-1 permanent FACs (Iijima and Potemra, 1976a) and are located equatorward of the regions of antisunward (westward) convection; (2) the observations are consistent with a two-cell convection pattern symmetric in one case (throat positioned at noon) and asymmetric in another (throat located in a sector on the forenoon side in juxtaposition to the region of strong convection on the afternoon side); and (3) fine-structure FACs are responsible for the generation of ULF-ELF noise in the polar cusp.

Ultra-Sensitive Magnetoresistive Displacement Sensing Device

NASA Technical Reports Server (NTRS)

Olivas, John D. (Inventor); Lairson, Bruce M. (Inventor); Ramesham, Rajeshuni (Inventor)

2003-01-01

An ultrasensitive displacement sensing device for use in accelerometers, pressure gauges, temperature transducers, and the like, comprises a sputter deposited, multilayer, magnetoresistive field sensor with a variable electrical resistance based on an imposed magnetic field. The device detects displacement by sensing changes in the local magnetic field about the magnetoresistive field sensor caused by the displacement of a hard magnetic film on a movable microstructure. The microstructure, which may be a cantilever, membrane, bridge, or other microelement, moves under the influence of an acceleration a known displacement predicted by the configuration and materials selected, and the resulting change in the electrical resistance of the MR sensor can be used to calculate the displacement. Using a micromachining approach, very thin silicon and silicon nitride membranes are fabricated in one preferred embodiment by means of anisotropic etching of silicon wafers. Other approaches include reactive ion etching of silicon on insulator (SOI), or Low Pressure Chemical Vapor Deposition of silicon nitride films over silicon substrates. The device is found to be improved with the use of giant magnetoresistive elements to detect changes in the local magnetic field.

Signatures of moderate (M-class) and low (C and B class) intensity solar flares on the equatorial electrojet current: Case studies

NASA Astrophysics Data System (ADS)

Chakrabarty, D.; Bagiya, Mala S.; Thampi, Smitha V.; Pathan, B. M.; Sekar, R.

2013-12-01

The present investigation brings out, in contrast to the earlier works, the changes in the equatorial electrojet (EEJ) current in response to a few moderate (M-class) and low (C and B class) intensity solar flares during 2005-2010. Special care is taken to pick these flare events in the absence of prompt electric field perturbations associated with geomagnetic storms and substorms that also affect the electrojet current. Interestingly, only the normalized (with respect to the pre-flare level) deviations of daytime EEJ (and not the deviations alone) change linearly with the increases in the EUV and X-ray fluxes. These linear relationships break down during local morning hours when the E-region electric field approaches zero before reversal of polarity. This elicits that the response of EEJ strength corresponding to less-intense flares can be appropriately gauged only when the local time variation of the quiet time E-region zonal electric field is taken into account. The flare events enhanced the EEJ strength irrespective of normal or counter electrojet (CEJ) conditions that shows that solar flares change the E-region ionization density and not the electric field. In addition, the enhancements in the X-ray and EUV fluxes, for these flares occurring during this solar minimum period, are found to be significantly correlated as opposed to the solar maximum period, indicating the differences in the solar processes in different solar epochs.

Local conductance: A means to extract polarization and depolarizing fields near domain walls in ferroelectrics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Douglas, A. M.; Kumar, A.; Gregg, J. M.

Conducting atomic force microscopy images of bulk semiconducting BaTiO{sub 3} surfaces show clear stripe domain contrast. High local conductance correlates with strong out-of-plane polarization (mapped independently using piezoresponse force microscopy), and current-voltage characteristics are consistent with dipole-induced alterations in Schottky barriers at the metallic tip-ferroelectric interface. Indeed, analyzing current-voltage data in terms of established Schottky barrier models allows relative variations in the surface polarization, and hence the local domain structure, to be determined. Fitting also reveals the signature of surface-related depolarizing fields concentrated near domain walls. Domain information obtained from mapping local conductance appears to be more surface-sensitive than thatmore » from piezoresponse force microscopy. In the right materials systems, local current mapping could therefore represent a useful complementary technique for evaluating polarization and local electric fields with nanoscale resolution.« less

Utilizing Four Dimensional Lightning and Dual-Polarization Radar to Develop Lightning Initiation Forecast Guidance

DTIC Science & Technology

2015-03-26

Electrification . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 2.3 Lightning Discharge ...charge is caused by falling graupel that is positively charged (Wallace and Hobbs 2006). 2.3 Lightning Discharge Lightning occurs when the electric...emission of positive corona from the surface of precipitation particles, causing the electric field to become locally enhanced and supporting the

Localized heating on silicon field effect transistors: device fabrication and temperature measurements in fluid.

PubMed

Elibol, Oguz H; Reddy, Bobby; Nair, Pradeep R; Dorvel, Brian; Butler, Felice; Ahsan, Zahab S; Bergstrom, Donald E; Alam, Muhammad A; Bashir, Rashid

2009-10-07

We demonstrate electrically addressable localized heating in fluid at the dielectric surface of silicon-on-insulator field-effect transistors via radio-frequency Joule heating of mobile ions in the Debye layer. Measurement of fluid temperatures in close vicinity to surfaces poses a challenge due to the localized nature of the temperature profile. To address this, we developed a localized thermometry technique based on the fluorescence decay rate of covalently attached fluorophores to extract the temperature within 2 nm of any oxide surface. We demonstrate precise spatial control of voltage dependent temperature profiles on the transistor surfaces. Our results introduce a new dimension to present sensing systems by enabling dual purpose silicon transistor-heaters that serve both as field effect sensors as well as temperature controllers that could perform localized bio-chemical reactions in Lab on Chip applications.

Pulse shape optimization for electron-positron production in rotating fields

NASA Astrophysics Data System (ADS)

Fillion-Gourdeau, François; Hebenstreit, Florian; Gagnon, Denis; MacLean, Steve

2017-07-01

We optimize the pulse shape and polarization of time-dependent electric fields to maximize the production of electron-positron pairs via strong field quantum electrodynamics processes. The pulse is parametrized in Fourier space by a B -spline polynomial basis, which results in a relatively low-dimensional parameter space while still allowing for a large number of electric field modes. The optimization is performed by using a parallel implementation of the differential evolution, one of the most efficient metaheuristic algorithms. The computational performance of the numerical method and the results on pair production are compared with a local multistart optimization algorithm. These techniques allow us to determine the pulse shape and field polarization that maximize the number of produced pairs in computationally accessible regimes.

Generation and detection of pure valley current by electrically induced Berry curvature in bilayer graphene

NASA Astrophysics Data System (ADS)

Shimazaki, Y.; Yamamoto, M.; Borzenets, I. V.; Watanabe, K.; Taniguchi, T.; Tarucha, S.

2015-12-01

The field of `Valleytronics’ has recently been attracting growing interest as a promising concept for the next generation electronics, because non-dissipative pure valley currents with no accompanying net charge flow can be manipulated for computational use, akin to pure spin currents. Valley is a quantum number defined in an electronic system whose energy bands contain energetically degenerate but non-equivalent local minima (conduction band) or maxima (valence band) due to a certain crystal structure. Specifically, spatial inversion symmetry broken two-dimensional honeycomb lattice systems exhibiting Berry curvature is a subset of possible systems that enable optical, magnetic and electrical control of the valley degree of freedom. Here we use dual-gated bilayer graphene to electrically induce and control broken inversion symmetry (or Berry curvature) as well as the carrier density for generating and detecting the pure valley current. In the insulating regime, at zero-magnetic field, we observe a large nonlocal resistance that scales cubically with the local resistivity, which is evidence of pure valley current.

Electric-field induced surface instabilities of soft dielectrics and their effects on optical transmittance and scattering

NASA Astrophysics Data System (ADS)

Shian, Samuel; Kjeer, Peter; Clarke, David R.

2018-03-01

When a voltage is applied to a percolative, mechanically compliant mat of carbon nanotubes (CNTs) on a smooth elastomer bilayer attached to an ITO coated glass substrate, the in-line optical transmittance decreases with increasing voltage. Two regimes of behavior have been identified based on optical scattering, bright field optical microscopy, and confocal optical microscopy. In the low field regime, the electric field produces a spatially inhomogeneous surface deformation of the elastomer that causes local variations in optical refraction and modulates the light transmittance. The spatial variation is associated with the distribution of the CNTs over the surface. At higher fields, above a threshold voltage, an array of pits in the surface form by a nucleation and growth mechanism and these also scatter light. The formation of pits, and creases, in the thickness of the elastomer, is due to a previously identified electro-mechanical surface instability. When the applied voltage is decreased from its maximum, the transmittance returns to its original value although there is a transmittance hysteresis and a complicated time response. When the applied voltage exceeds the threshold voltage, there can be remnant optical contrast associated with creasing of the elastomer and the recovery time appears to be dependent on local jamming of CNTs in areas where the pits formed. A potential application of this work as an electrically tunable privacy window or camouflaging devices is demonstrated.

Circularly polarized few-cycle optical rogue waves: rotating reduced Maxwell-Bloch equations.

PubMed

Xu, Shuwei; Porsezian, K; He, Jingsong; Cheng, Yi

2013-12-01

The rotating reduced Maxwell-Bloch (RMB) equations, which describe the propagation of few-cycle optical pulses in a transparent media with two isotropic polarized electronic field components, are derived from a system of complete Maxwell-Bloch equations without using the slowly varying envelope approximations. Two hierarchies of the obtained rational solutions, including rogue waves, which are also called few-cycle optical rogue waves, of the rotating RMB equations are constructed explicitly through degenerate Darboux transformation. In addition to the above, the dynamical evolution of the first-, second-, and third-order few-cycle optical rogue waves are constructed with different patterns. For an electric field E in the three lower-order rogue waves, we find that rogue waves correspond to localized large amplitude oscillations of the polarized electric fields. Further a complementary relationship of two electric field components of rogue waves is discussed in terms of analytical formulas as well as numerical figures.

Electrokinetically driven microfluidic mixing with patchwise surface heterogeneity and AC applied electric field

NASA Astrophysics Data System (ADS)

Luo, Win-Jet; Yue, Cheng-Feng

2004-12-01

This paper investigates two-dimensional, time-dependent electroosmotic flows driven by an AC electric field via patchwise surface heterogeneities distributed along the microchannel walls. The time-dependent flow fields through the microchannel are simulated for various patchwise heterogeneous surface patterns using the backwards-Euler time stepping numerical method. Different heterogeneous surface patterns are found to create significantly different electrokinetic transport phenomena. It is shown that the presence of oppositely charged surface heterogeneities on the microchannel walls results in the formation of localized flow circulations within the bulk flow. These circulation regions grow and decay periodically in accordance with the applied periodic AC electric field intensity. The circulations provide an effective means of enhancing species mixing in the microchannel. A suitable design of the patchwise heterogeneous surface pattern permits the mixing channel length and the retention time required to attain a homogeneous solution to be reduced significantly.

Accurate Computation of Electric Field Enhancement Factors for Metallic Nanoparticles Using the Discrete Dipole Approximation

PubMed Central

2010-01-01

We model the response of nanoscale Ag prolate spheroids to an external uniform static electric field using simulations based on the discrete dipole approximation, in which the spheroid is represented as a collection of polarizable subunits. We compare the results of simulations that employ subunit polarizabilities derived from the Clausius–Mossotti relation with those of simulations that employ polarizabilities that include a local environmental correction for subunits near the spheroid’s surface [Rahmani et al. Opt Lett 27: 2118 (2002)]. The simulations that employ corrected polarizabilities give predictions in very good agreement with exact results obtained by solving Laplace’s equation. In contrast, simulations that employ uncorrected Clausius–Mossotti polarizabilities substantially underestimate the extent of the electric field “hot spot” near the spheroid’s sharp tip, and give predictions for the field enhancement factor near the tip that are 30 to 50% too small. PMID:20672062

Initial Results from the Vector Electric Field Investigation on the C/NOFS Satellite

NASA Technical Reports Server (NTRS)

Pfaff, R.; Rowland, D.; Acuna, M.; Le, G.; Farrell, W.; Holzworth, R.; Wilson, G.; Burke, W.; Freudenreich, H.; Bromund, K.;

Geomagnetic storm effects on the occurrences of ionospheric irregularities over the African equatorial/low-latitude region

NASA Astrophysics Data System (ADS)

Amaechi, P. O.; Oyeyemi, E. O.; Akala, A. O.

2018-04-01

The study investigated the effects of intense geomagnetic storms of 2015 on the occurrences of large scale ionospheric irregularities over the African equatorial/low-latitude region. Four major/intense geomagnetic storms of 2015 were analyzed for this study. These storms occurred on 17th March 2015 (-229 nT), 22nd June 2015 (-204 nT), 7th October 2015 (-124 nT), and 20th December 2015 (-170 nT). Total Electron Content (TEC) data obtained from five African Global Navigation Satellite Systems (GNSS) stations, grouped into eastern and western sectors were used to derive the ionospheric irregularities proxy indices, e.g., rate of change of TEC (ROT), ROT index (ROTI) and ROTI daily average (ROTIAVE). These indices were characterized alongside with the disturbance storm time (Dst), the Y component of the Interplanetary Electric Field (IEFy), polar cap (PC) index and the H component of the Earth's magnetic field from ground-based magnetometers. Irregularities manifested in the form of fluctuations in TEC. Prompt penetration of electric field (PPEF) and disturbance dynamo electric field (DDEF) modulated the behaviour of irregularities during the main and recovery phases of the geomagnetic storms. The effect of electric field over both sectors depends on the local time of southward turning of IMF Bz. Consequently, westward electric field inhibited irregularities during the main phase of March and October 2015 geomagnetic storms, while for the June 2015 storm, eastward electric field triggered weak irregularities over the eastern sector. The effect of electric field on irregularities during December 2015 storm was insignificant. During the recovery phase of the storms, westward DDEF suppressed irregularities.

Enhanced electrocatalytic CO2 reduction via field-induced reagent concentration

NASA Astrophysics Data System (ADS)

Liu, Min; Pang, Yuanjie; Zhang, Bo; de Luna, Phil; Voznyy, Oleksandr; Xu, Jixian; Zheng, Xueli; Dinh, Cao Thang; Fan, Fengjia; Cao, Changhong; de Arquer, F. Pelayo García; Safaei, Tina Saberi; Mepham, Adam; Klinkova, Anna; Kumacheva, Eugenia; Filleter, Tobin; Sinton, David; Kelley, Shana O.; Sargent, Edward H.

2016-09-01

Electrochemical reduction of carbon dioxide (CO2) to carbon monoxide (CO) is the first step in the synthesis of more complex carbon-based fuels and feedstocks using renewable electricity. Unfortunately, the reaction suffers from slow kinetics owing to the low local concentration of CO2 surrounding typical CO2 reduction reaction catalysts. Alkali metal cations are known to overcome this limitation through non-covalent interactions with adsorbed reagent species, but the effect is restricted by the solubility of relevant salts. Large applied electrode potentials can also enhance CO2 adsorption, but this comes at the cost of increased hydrogen (H2) evolution. Here we report that nanostructured electrodes produce, at low applied overpotentials, local high electric fields that concentrate electrolyte cations, which in turn leads to a high local concentration of CO2 close to the active CO2 reduction reaction surface. Simulations reveal tenfold higher electric fields associated with metallic nanometre-sized tips compared to quasi-planar electrode regions, and measurements using gold nanoneedles confirm a field-induced reagent concentration that enables the CO2 reduction reaction to proceed with a geometric current density for CO of 22 milliamperes per square centimetre at -0.35 volts (overpotential of 0.24 volts). This performance surpasses by an order of magnitude the performance of the best gold nanorods, nanoparticles and oxide-derived noble metal catalysts. Similarly designed palladium nanoneedle electrocatalysts produce formate with a Faradaic efficiency of more than 90 per cent and an unprecedented geometric current density for formate of 10 milliamperes per square centimetre at -0.2 volts, demonstrating the wider applicability of the field-induced reagent concentration concept.

Localized Electron Heating by Strong Guide-Field Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Guo, Xuehan; Sugawara, Takumichi; Inomoto, Michiaki; Yamasaki, Kotaro; Ono, Yasushi; UTST Team

2015-11-01

Localized electron heating of magnetic reconnection was studied under strong guide-field (typically Bt 15Bp) using two merging spherical tokamak plasmas in Univ. Tokyo Spherical Tokamak (UTST) experiment. Our new slide-type two-dimensional Thomson scattering system documented for the first time the electron heating localized around the X-point. The region of high electron temperature, which is perpendicular to the magnetic field, was found to have a round shape with radius of 2 [cm]. Also, it was localized around the X-point and does not agree with that of energy dissipation term Et .jt . When we include a guide-field effect term Bt / (Bp + αBt) for Et .jt where α =√{ (vin2 +vout2) /v∥2 } , the energy dissipation area becomes localized around the X-point, suggesting that the electrons are accelerated by the reconnection electric field parallel to the magnetic field and thermalized around the X-point. This work was supported by JSPS A3 Foresight Program ``Innovative Tokamak Plasma Startup and Current Drive in Spherical Torus,'' a Grant-in-Aid from the Japan Society for the Promotion of Science (JSPS) Fellows 15J03758.

The Storm Time Evolution of the Ionospheric Disturbance Plasma Drifts

NASA Astrophysics Data System (ADS)

Zhang, Ruilong; Liu, Libo; Le, Huijun; Chen, Yiding; Kuai, Jiawei

2017-11-01

In this paper, we use the C/NOFS and ROCSAT-1 satellites observations to analyze the storm time evolution of the disturbance plasma drifts in a 24 h local time scale during three magnetic storms driven by long-lasting southward IMF Bz. The disturbance plasma drifts during the three storms present some common features in the periods dominated by the disturbance dynamo. The newly formed disturbance plasma drifts are upward and westward at night, and downward and eastward during daytime. Further, the disturbance plasma drifts are gradually evolved to present significant local time shifts. The westward disturbance plasma drifts gradually migrate from nightside to dayside. Meanwhile, the dayside downward disturbance plasma drifts become enhanced and shift to later local time. The local time shifts in disturbance plasma drifts are suggested to be mainly attributed to the evolution of the disturbance winds. The strong disturbance winds arisen around midnight can constantly corotate to later local time. At dayside the westward and equatorward disturbance winds can drive the F region dynamo to produce the poleward and westward polarization electric fields (or the westward and downward disturbance drifts). The present results indicate that the disturbance winds corotated to later local time can affect the local time features of the disturbance dynamo electric field.

Evolution of Some Particle Detectors Based On the Discharge in Gases

DOE R&D Accomplishments Database

Charpak, G.

1969-11-19

Summary of the properties of some of the detectors that are commonly used in counter experiments to localize charged particles, and which are based on discharge in gases under the influence of electric fields and some basic facts of gaseous amplification in homogeneous and inhomogeneous fields.

Electron Demagnetization and Collisionless Magnetic Reconnection in βe ≪ 1 Plasmas: Theory and Observations

NASA Astrophysics Data System (ADS)

Scudder, J. D.; Mozer, F. S.

2005-05-01

Abrupt, intense bipolar and unipolar electric spikes with E > 100mV/m surveyed over 3 years of Polar data (Mozer et al 2005) have been organized to answer the limited question: can they be involved in the local demagnetization of thermal electrons? We determine a lower bound on the electric strength sufficient to cause non-gyrotropic effects on the electron pressure tensor of the form E>E*=B{we}/{8c Im}, where B is the ambient magnetic field strength, we=√2kTe/me, c is the speed of light, and Im is an electron velocity space weighted average displacement along the electric field while transiting the layer (assumed localized with a scale Δ x=a ρe, where ρe is the electron thermal gyroradius). The variation of Im as a function of a for equal mean energy Maxwellian and more typical κ distributions seen in the Earth's magnetosphere provides strong evidence that the surveyed electric field spikes are generally smaller than E* (assuming ≍ 1), although 23% (n=57) exceed E* . Only 11% (n=6) of the bipolar class exceed E* ; the frequency of occurrence distribution for the bipolar class of spikes is peaked at 0.1E*. The unipolar occurrence is flat below E*, but has a significant 26% subgroup (n=51) that exceed E* . While E* does not depend on the ambient density, the occurrence distribution of all demagnetizing events is well organized by the ratio ℜ=λDe/ρe=&Omegace/ωpe, residing almost exclusively in the regime ℜ <1. Spikes with E < E* generally occur with ℜ >1 . All the electrostatic spike events surveyed occur in the regime 10-8≤βe≤3×10-2. The demagnetizing events of either class occupy the more restricted low beta regime 10-3≤βe≤3×10-2. Because these demagnetizing events occur in βe ≪ 1 they would not, however, be considered unmagnetized at current channels as thin as the electron skin depth, de, since for such current channels ρe ≡ βe-1/2de ≪ de. As a group the subset of unipolar events with E > E* are consistently understood as sites where the electron pressure tensor could become deformed from cylindrical symmetry by electric field enhancement in layers with scale sizes up to the local thermal electron's gyroradius. Such a deformation is critical for a viable mechanism that supports collisionless reconnection. After selecting events as demagnetizing based on the size of the relevant forces and work done, the geophysical locale of their detection has been investigated. Previously, all E spikes in this survey were found near the invariant latitudes Λ of the earth's magnetic cusps but at all magnetic local times. The demagnetizing events identified here via E* are strongly organized at magnetic local noon (with a secondary, much shallower maximum at local magnetic midnight), occur preferentially at orbit apogee, and without significant preference for the magnetic latitude of the spacecraft. These geophysical organizations are consistent with the demagnetizing E spikes as indices of ongoing, collisionless reconnection in low βe regimes at the earth's subsolar magnetopause. The identification of this sub-class of electric spikes at low βe with E>E* widens the observed venues in the E and B fields where topology changing departures from ideal MHD should be anticipated in collisionless astrophysical plasmas.

Estimating the stability of electrical conductivity of filled polymers under the influence of negative temperatures

NASA Astrophysics Data System (ADS)

Minakova, N. N.; Ushakov, V. Ya.

2017-12-01

One of the key problems in modern materials technology is synthesis of materials for electrotechnical devices capable of operating under severe conditions. Electrical and power engineering, in particular, demands for electrically conductive composite materials operating at high and low temperatures, various mechanical loads, electric fields, etc. Chaotic arrangement of electrically conductive component in the matrix and its structural and geometrical inhomogeneity can increase the local electric and thermal energy flux densities up to critical values even when their average values remain moderate. Elastomers filled with technical carbon being a promising component for electrotechnical devices was chosen as an object of study.

Missile launch detection electric field perturbation experiment. Final report

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kane, R.J.; Rynne, T.M.

1993-04-28

The Lawrence Livermore National Laboratory and SARA Inc. participated in the ATMD missile launch activities that occurred at WSMR during January 1993. LLNL and SARA deployed sensors for monitoring of basic phenomena. An attempt was made to measure perturbations of the earth geo-potential during the launch of a Lance missile. The occurrence of the perturbation is expected from the conducting body of the missile and the exhaust plume. A set of voltage-probe antennas were used to monitor the local electric field perturbation from the launch at ranges of approximately 1 km. Examination of the data acquired during the launch periodmore » failed to show identifiable correlation of the field variations with the launch event. Three reasons are ascribed to this lack of event data: (1) The electric field potential variations have a limited spatial correlation length - the fields measured in one region have little correlation to measurements made at distances of a kilometer away. The potential variations are related to localized atmospheric disturbances and are generally unpredictable. A value for the spatial correlation length is also not known. (2) The conductivity of the plume and missile body are not adequate to produce a field perturbation of adequate magnitude. Phenomena related to the exhaust plume and missile may exist and be outside of the collection range of the equipment employed for these measurements. (3) The presence of 60 Hz power line noise was of sufficient magnitude to irreversibly contaminate measurements.« less

The Locations of Ring Current Pressure Peaks: Comparison of TWINS Measurements and CIMI Simulations for the 7-10 September 2015 CIR Storm

NASA Astrophysics Data System (ADS)

Hill, S. C.; Edmond, J. A.; Xu, H.; Perez, J. D.; Fok, M. C. H.; Goldstein, J.; McComas, D. J.; Valek, P. W.

2017-12-01

The characteristics of a four day 7-10 September 2015 co-rotating interaction region (CIR) storm (min. SYM/H ≤ -110 nT) are categorized by storm phase. Ion distributions of trapped particles in the ring current as measured by the Two Wide-Angle Imaging Neutral Atom Spectrometers (TWINS) are compared with the simulated ion distributions of the Comprehensive Inner Magnetosphere-Ionosphere Model (CIMI). The energetic neutral atom (ENA) images obtained by TWINS are deconvolved to extract equatorial pitch angle, energy spectra, ion pressure intensity, and ion pressure anisotropy distributions in the inner magnetosphere. CIMI, using either a self-consistent electric field or a semi-empirical electric field, simulates comparable distributions. There is good agreement between the data measured by TWINS and the different distributions produced by the self-consistent electric field and the semi-empirical electric field of CIMI. Throughout the storm the pitch angle distribution (PAD) is mostly perpendicular in both CIMI and TWINS and there is agreement between the anisotropy distributions. The locations of the ion pressure peaks seen by TWINS and by the self-consistent and semi empirical electric field parameters in CIMI are usually between dusk and midnight. On average, the self-consistent electric field in CIMI reveals ion pressure peaks closer to Earth than its semi empirical counterpart, while TWINS reports somewhat larger radial values for the ion pressure peak locations. There are also notable events throughout the storm during which the simulated observations show some characteristics that differ from those measured by TWINS. At times, there are ion pressure peaks with magnetic local time on the dayside and in the midnight to dawn region. We discuss these events in light of substorm injections indicated by fluctuating peaks in the AE index and a positive By component in the solar wind. There are also times in which there are multiple ion pressure peaks. This may imply that there are time dependent and spatially dependent injection events that are influenced by local reconnection regions in the tail of the magnetosphere. Using CIMI simulations, we present paths of particles with various energies to assist in interpreting these notable events.

Electrokinetic framework of dielectrophoretic deposition devices

NASA Astrophysics Data System (ADS)

Burg, Brian R.; Bianco, Vincenzo; Schneider, Julian; Poulikakos, Dimos

2010-06-01

Numerical modeling and experiments are performed investigating the properties of a dielectrophoresis-based deposition device, in order to establish the electrokinetic framework required to understand the effects of applied inhomogeneous electric fields while moving particles to desired locations. By capacitively coupling electrodes to a conductive substrate, the controlled large-scale parallel dielectrophoretic assembly of nanostructures in individually accessible devices at a high integration density is accomplished. Thermal gradients in the solution, which give rise to local permittivity and conductivity changes, and velocity fields are solved by coupling electric, thermal, and fluid-mechanical equations. The induced electrothermal flow (ETF) causes vortices above the electrode gap, attracting particles, such as single-walled carbon nanotubes (SWNTs), before they are trapped by the dielectrophoretic force and deposit across the electrodes. Long-range carbon nanotube transport is governed by hydrodynamic effects, while local trapping is dominated by dielectrophoretic forces in low concentration SWNT dispersions. Results show that by decreasing the ac frequency ac electroosmosis on the metallic electrodes occurs due to the emergence of an electric double layer, disturbing the initial flow pattern of the system. By superimposing a dc potential offset, a generated tangential electroosmotic fluid flow in the dielectric electrode gap also disrupts the ETF. Capacitive coupling is most efficient in the high frequency regime where it is the dominating impedance contribution. Understanding the occurrence and interaction of these different effects, including a self-limiting integration mechanism for individual nanostructures, allows an increased deposition yield at overall lower electric field strengths through a prudent choice of electric field parameters. The findings provide important avenues toward gentler particle handling, without direct current throughput, a relevant aspect for limiting process effects during device fabrication, all while increasing dielectrophoretic deposition efficiency in nanostructured networks.

Spontaneous and electrically modulated spatiotemporal dynamics of the neocortical slow oscillation and associated local fast activity.

PubMed

Greenberg, Anastasia; Dickson, Clayton T

2013-12-01

The neocortical slow oscillation (SO; ~1Hz) of non-REM sleep and anesthesia reflects synchronized network activity composed of alternating active and silent (ON/OFF) phases at the local network and cellular level. The SO itself shows self-organized spatiotemporal dynamics as it appears to originate at unique foci on each cycle and then propagates across the cortical surface. During sleep, this rhythm is relevant for neuroplastic processes mediating memory consolidation especially since its enhancement by slow, rhythmic electrical fields improves subsequent recall. However, the neurobiological mechanism by which spontaneous or enhanced SO activity might operate on memory traces is unknown. Here we show a series of original results, using cycle to cycle tracking across multiple neocortical sites in urethane anesthetized rats: The spontaneous spatiotemporal dynamics of the SO are complex, showing interfering propagation patterns in the anterior-to-posterior plane. These patterns compete for expression and tend to alternate following phase resets that take place during the silent OFF phase of the SO. Applying sinusoidal electrical field stimulation to the anterior pole of the cerebral cortex progressively entrained local field, gamma, and multi-unit activity at all sites, while disrupting the coordination of endogenous SO activity. Field stimulation also biased propagation in the anterior-to-posterior direction and more notably, enhanced the long-range gamma synchrony between cortical regions. These results are the first to show that changes to slow wave dynamics cause enhancements in high frequency cortico-cortical communication and provide mechanistic clues into how the SO is relevant for sleep-dependent memory consolidation. © 2013.

Electric field-mediated transport of plasmid DNA in tumor interstitium in vivo.

PubMed

Henshaw, Joshua W; Zaharoff, David A; Mossop, Brian J; Yuan, Fan

2007-11-01

Local pulsed electric field application is a method for improving non-viral gene delivery. Mechanisms of the improvement include electroporation and electrophoresis. To understand how electrophoresis affects pDNA delivery in vivo, we quantified the magnitude of electric field-induced interstitial transport of pDNA in 4T1 and B16.F10 tumors implanted in mouse dorsal skin-fold chambers. Four different electric pulse sequences were used in this study, each consisted of 10 identical pulses that were 100 or 400 V/cm in strength and 20 or 50 ms in duration. The interval between consecutive pulses was 1 s. The largest distance of transport was obtained with the 400 V/cm and 50 ms pulse, and was 0.23 and 0.22 microm/pulse in 4T1 and B16.F10 tumors, respectively. There were no significant differences in transport distances between 4T1 and B16.F10 tumors. Results from in vivo mapping and numerical simulations revealed an approximately uniform intratumoral electric field that was predominantly in the direction of the applied field. The data in the study suggested that interstitial transport of pDNA induced by a sequence of ten electric pulses was ineffective for macroscopic delivery of genes in tumors. However, the induced transport was more efficient than passive diffusion.

Nanoscale thermal imaging of VO2 via Poole-Frenkel conduction

NASA Astrophysics Data System (ADS)

Spitzig, Alyson; Hoffman, Jason D.; Pivonka, Adam E.; Mickalide, Harry; Frenzel, Alex; Kim, Jeehoon; Ko, Changhyun; Zhou, You; O'Connor, Kevin; Hudson, Eric W.; Ramanathan, Shriram; Hoffman, Jennifer E.

We present a novel method for nanoscale thermal imaging of insulating thin films. We demonstrate this method on VO2, which undergoes a sharp insulator-to-metal transition at 340 K. We sweep the voltage applied to a conducting atomic force microscope tip in contact mode at room temperature and measure the resultant current through a VO2 film. The Poole-Frenkel (PF) conduction mechanism, which dominates in the insulating state of VO2, is fit to extract the local temperature of the film using fundamental constants and known film properties. We measure the local electric field and temperature immediately preceding the insulator-to-metal transition in VO2 to determine whether the transition can be triggered by an applied electric field alone. We calculate an average temperature of 334 +/- 5 K, implying that Joule heating has locally warmed the sample very close to the transition temperature. Our thermometry technique opens up the possibility to measure the local temperature of any film dominated by the PF conduction mechanism, and presents the opportunity to extend our technique to other conduction mechanisms. Canada Excellence Research Chair program and NSERC - CGSM.

Electric Dipole Moment Results from lattice QCD

NASA Astrophysics Data System (ADS)

Dragos, Jack; Luu, Thomas; Shindler, Andrea; de Vries, Jordy

2018-03-01

We utilize the gradient flow to define and calculate electric dipole moments induced by the strong QCD θ-term and the dimension-6 Weinberg operator. The gradient flow is a promising tool to simplify the renormalization pattern of local operators. The results of the nucleon electric dipole moments are calculated on PACS-CS gauge fields (available from the ILDG) using Nf = 2+1, of discrete size 323×64 and spacing a ≃ 0.09 fm. These gauge fields use a renormalization-group improved gauge action and a nonperturbatively O(a) improved clover quark action at β = 1.90, with cSW = 1.715. The calculation is performed at pion masses of mπ ≃ 411, 701 MeV.

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

PubMed Central

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

2014-01-01

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

Synthesis of Natural Electric and Magnetic Time Series Using Impulse Responses of Inter-station Transfer Functions and a Reference

NASA Astrophysics Data System (ADS)

Wang, H.; Cheng, J.

2017-12-01

A method to Synthesis natural electric and magnetic Time series is proposed whereby the time series of local site are derived using an Impulse Response and a reference (STIR). The method is based on the assumption that the external source of magnetic fields are uniform, and the electric and magnetic fields acquired at the surface satisfy a time-independent linear relation in frequency domain.According to the convolution theorem, we can synthesize natural electric and magnetic time series using the impulse responses of inter-station transfer functions with a reference. Applying this method, two impulse responses need to be estimated: the quasi-MT impulse response tensor and the horizontal magnetic impulse response tensor. These impulse response tensors relate the local horizontal electric and magnetic components with the horizontal magnetic components at a reference site, respectively. Some clean segments of times series are selected to estimate impulse responses by using least-square (LS) method. STIR is similar with STIN (Wang, 2017), but STIR does not need to estimate the inter-station transfer functions, and the synthesized data are more accurate in high frequency, where STIN fails when the inter-station transfer functions are contaminated severely. A test with good quality of MT data shows that synthetic time-series are similar to natural electric and magnetic time series. For contaminated AMT example, when this method is used to remove noise present at the local site, the scatter of MT sounding curves are clear reduced, and the data quality are improved. *This work is funded by National Key R&D Program of China(2017YFC0804105),National Natural Science Foundation of China (41604064, 51574250), State Key Laboratory of Coal Resources and Safe Mining ,China University of Mining & Technology,(SKLCRSM16DC09)

Local probing of thermal energy transfer and conversion processes in VO2 nanostructures

NASA Astrophysics Data System (ADS)

Menges, Fabian

Nanostructures of strongly correlated materials, such as metal-insulator transition (MIT) oxides, enable unusual coupling of charge and heat transport. Hence, they provide an interesting pathway to the development of non-linear thermal devices for active heat flux control. Here, we will report the characterization of local thermal non-equilibrium processes in vanadium dioxide (VO2) thin films and single-crystalline nanobeams. Using a scanning thermal microscope and calorimetric MEMS platforms, we studied the MIT triggered by electrical currents, electrical fields, near-field thermal radiation and thermal conduction. Based on out recently introduced scanning probe thermometry method, which enables direct imaging of local Joule and Peltier effects, we quantified self-heating processes in VO2 memristors using the tip of a resistively heated scanning probe both as local sensor and nanoscopic heat source. Finally, we will report on recent approaches to build radiative thermal switches and oscillators using VO2 nanostructures. We quantified variations of near-field radiative thermal transport between silicon dioxide and VO2 down to nanoscopic gap sizes, and will discuss its implications for the development of phonon polariton based radiative thermal devices. Funding of the Swiss Federal Office of Energy under Grant Agreement No. SI/501093-01 is gratefully acknowledged.

Dipolarizing flux bundles in the cis-geosynchronous magnetosphere: relationship between electric fields and energetic particle injections

NASA Astrophysics Data System (ADS)

Liu, J.; Angelopoulos, V.; Zhang, X. J.; Turner, D. L.; Gabrielse, C.; Runov, A.; Funsten, H. O.; Spence, H. E.

2015-12-01

Dipolarizing flux bundles (DFBs) are small flux tubes (typically < 3 RE in XGSM and YGSM) in the nightside magnetosphere that have magnetic field more dipolar than the background field. Although DFBs are known to accelerate particles to create energetic particle injections, their acceleration mechanism and importance in generating injections inside geosynchronous orbit remain open questions. To answer these questions, we investigate DFBs in the inner magnetosphere by conducting a statistical study with data from the Van Allen Probes. The results show that just like DFBs outside geosynchronous orbit, those inside that orbit occur most often in the pre-midnight sector. Half the DFBs are accompanied by energetic particle injection. Statistically, DFBs with injection have an electric field three times that of those without. All the injections accompanying DFBs appear dispersionless within the temporal and energy resolution considered. These findings suggest that the injections are ushered or locally produced by the DFB, and the DFB's strong electric field is an important aspect of the injection generation mechanism.

Dependence of electrical and time stress in organic field effect transistor with low temperature forming gas treated Al2O3 gate dielectrics.

PubMed

Lee, Sunwoo; Chung, Keum Jee; Park, In-Sung; Ahn, Jinho

2009-12-01

We report the characteristics of the organic field effect transistor (OFET) after electrical and time stress. Aluminum oxide (Al2O3) was used as a gate dielectric layer. The surface of the gate oxide layer was treated with hydrogen (H2) and nitrogen (N2) mixed gas to minimize the dangling bond at the interface layer of gate oxide. According to the two stress parameters of electrical and time stress, threshold voltage shift was observed. In particular, the mobility and subthreshold swing of OFET were significantly decreased due to hole carrier localization and degradation of the channel layer between gate oxide and pentacene by electrical stress. Electrical stress is a more critical factor in the degradation of mobility than time stress caused by H2O and O2 in the air.

Unavoidable electric current caused by inhomogeneities and its influence on measured material parameters of thermoelectric materials

NASA Astrophysics Data System (ADS)

Song, K.; Song, H. P.; Gao, C. F.

2018-03-01

It is well known that the key factor determining the performance of thermoelectric materials is the figure of merit, which depends on the thermal conductivity (TC), electrical conductivity, and Seebeck coefficient (SC). The electric current must be zero when measuring the TC and SC to avoid the occurrence of measurement errors. In this study, the complex-variable method is used to analyze the thermoelectric field near an elliptic inhomogeneity in an open circuit, and the field distributions are obtained in closed form. Our analysis shows that an electric current inevitably exists in both the matrix and the inhomogeneity even though the circuit is open. This unexpected electric current seriously affects the accuracy with which the TC and SC are measured. These measurement errors, both overall and local, are analyzed in detail. In addition, an error correction method is proposed based on the analytical results.

Study on temperature distribution effect on internal charging by computer simulation

NASA Astrophysics Data System (ADS)

Yi, Zhong

2016-07-01

Internal charging (or deep dielectric charging) is a great threaten to spacecraft. Dielectric conductivity is an important parameter for internal charging and it is sensitive to temperature. Considering the exposed dielectric outside a spacecraft may experience a relatively large temperature range, temperature effect can't be ignored in internal charging assessment. We can see some reporters on techniques of computer simulation of internal charging, but the temperature effect has not been taken into accounts. In this paper, we realize the internal charging simulation with consideration of temperature distribution inside the dielectric. Geant4 is used for charge transportation, and a numerical method is proposed for solving the current reservation equation. The conductivity dependences on temperature, radiation dose rate and intense electric field are considered. Compared to the case of uniform temperature, the internal charging with temperature distribution is more complicated. Results show that temperature distribution can cause electric field distortion within the dielectric. This distortion refers to locally considerable enlargement of electric field. It usually corresponds to the peak electric field which is critical for dielectric breakdown judgment. The peak electric field can emerge inside the dielectric, or appear on the boundary. This improvement of internal charging simulation is beneficial for the assessment of internal charging under multiple factors.

Novel circuit design for high-impedance and non-local electrical measurements of two-dimensional materials

NASA Astrophysics Data System (ADS)

De Sanctis, Adolfo; Mehew, Jake D.; Alkhalifa, Saad; Tate, Callum P.; White, Ashley; Woodgate, Adam R.; Craciun, Monica F.; Russo, Saverio

2018-02-01

Two-dimensional materials offer a novel platform for the development of future quantum technologies. However, the electrical characterisation of topological insulating states, non-local resistance, and bandgap tuning in atomically thin materials can be strongly affected by spurious signals arising from the measuring electronics. Common-mode voltages, dielectric leakage in the coaxial cables, and the limited input impedance of alternate-current amplifiers can mask the true nature of such high-impedance states. Here, we present an optical isolator circuit which grants access to such states by electrically decoupling the current-injection from the voltage-sensing circuitry. We benchmark our apparatus against two state-of-the-art measurements: the non-local resistance of a graphene Hall bar and the transfer characteristic of a WS2 field-effect transistor. Our system allows the quick characterisation of novel insulating states in two-dimensional materials with potential applications in future quantum technologies.

Instrumentation for measurement of aircraft noise and sonic boom

NASA Technical Reports Server (NTRS)

Zuckerwar, A. J. (Inventor)

1975-01-01

A jet aircraft noise and sonic boom measuring device which converts sound pressure into electric current is described. An electric current proportional to the sound pressure level at a condenser microphone is produced and transmitted over a cable, amplified by a zero drive amplifier and recorded on magnetic tape. The converter is comprised of a local oscillator, a dual-gate field-effect transistor (FET) mixer and a voltage regulator/impedance translator. A carrier voltage that is applied to one of the gates of the FET mixer is generated by the local oscillator. The microphone signal is mixed with the carrier to produce an electrical current at the frequency of vibration of the microphone diaphragm by the FET mixer. The voltage of the local oscillator and mixer stages is regulated, the carrier at the output is eliminated, and a low output impedance at the cable terminals is provided by the voltage regulator/impedance translator.

Localized basis sets for unbound electrons in nanoelectronics.

PubMed

Soriano, D; Jacob, D; Palacios, J J

2008-02-21

It is shown how unbound electron wave functions can be expanded in a suitably chosen localized basis sets for any desired range of energies. In particular, we focus on the use of Gaussian basis sets, commonly used in first-principles codes. The possible usefulness of these basis sets in a first-principles description of field emission or scanning tunneling microscopy at large bias is illustrated by studying a simpler related phenomenon: The lifetime of an electron in a H atom subjected to a strong electric field.

Modeling the electrostatic field localization in nanostructures based on DLC films using the tunneling microscopy methods

NASA Astrophysics Data System (ADS)

Yakunin, Alexander N.; Aban'shin, Nikolay P.; Avetisyan, Yuri A.; Akchurin, Georgy G.; Akchurin, Garif G.

2018-04-01

A model for calculating the electrostatic field in the system "probe of a tunnel microscope - a nanostructure based on a DLC film" was developed. A finite-element modeling of the localization of the field was carried out, taking into account the morphological and topological features of the nanostructure. The obtained results and their interpretation contribute to the development of the concepts to the model of tunnel electric transport processes. The possibility for effective usage of the tunneling microscopy methods in the development of new nanophotonic devices is shown.

Gate-defined Quantum Confinement in Suspended Bilayer Graphene

NASA Astrophysics Data System (ADS)

Allen, Monica

2013-03-01

Quantum confined devices in carbon-based materials offer unique possibilities for applications ranging from quantum computation to sensing. In particular, nanostructured carbon is a promising candidate for spin-based quantum computation due to the ability to suppress hyperfine coupling to nuclear spins, a dominant source of spin decoherence. Yet graphene lacks an intrinsic bandgap, which poses a serious challenge for the creation of such devices. We present a novel approach to quantum confinement utilizing tunnel barriers defined by local electric fields that break sublattice symmetry in suspended bilayer graphene. This technique electrostatically confines charges via band structure control, thereby eliminating the edge and substrate disorder that hinders on-chip etched nanostructures to date. We report clean single electron tunneling through gate-defined quantum dots in two regimes: at zero magnetic field using the energy gap induced by a perpendicular electric field and at finite magnetic fields using Landau level confinement. The observed Coulomb blockade periodicity agrees with electrostatic simulations based on local top-gate geometry, a direct demonstration of local control over the band structure of graphene. This technology integrates quantum confinement with pristine device quality and access to vibrational modes, enabling wide applications from electromechanical sensors to quantum bits. More broadly, the ability to externally tailor the graphene bandgap over nanometer scales opens a new unexplored avenue for creating quantum devices.

SL(2,R) duality-symmetric action for electromagnetic theory with electric and magnetic sources

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Choonkyu, E-mail: cklee@phya.snu.ac.kr; School of Physics, Korea Institute for Advanced Study, Seoul 130-722; Min, Hyunsoo, E-mail: hsmin@dirac.uos.ac.kr

2013-12-15

For the SL(2,R) duality-invariant generalization of Maxwell electrodynamics in the presence of both electric and magnetic sources, we formulate a local, manifestly duality-symmetric, Zwanziger-type action by introducing a pair of four-potentials A{sup μ} and B{sup μ} in a judicious way. On the two potentials A{sup μ} and B{sup μ} the SL(2,R) duality transformation acts in a simple linear manner. In quantum theory including charged source fields, this action can be recast as a SL(2,Z)-invariant action. Also given is a Zwanziger-type action for SL(2,R) duality-invariant Born–Infeld electrodynamics which can be important for D-brane dynamics in string theory. -- Highlights: •We formulatemore » a local, manifestly duality-symmetric, Zwanziger-type action. •Maxwell electrodynamics is generalized to include dilaton and axion fields. •SL(2,R) symmetry is manifest. •We formulate a local, manifestly duality-symmetric, nonlinear Born–Infeld action with SL(2,R) symmetry.« less

A high-resolution computational localization method for transcranial magnetic stimulation mapping.

PubMed

Aonuma, Shinta; Gomez-Tames, Jose; Laakso, Ilkka; Hirata, Akimasa; Takakura, Tomokazu; Tamura, Manabu; Muragaki, Yoshihiro

2018-05-15

Transcranial magnetic stimulation (TMS) is used for the mapping of brain motor functions. The complexity of the brain deters determining the exact localization of the stimulation site using simplified methods (e.g., the region below the center of the TMS coil) or conventional computational approaches. This study aimed to present a high-precision localization method for a specific motor area by synthesizing computed non-uniform current distributions in the brain for multiple sessions of TMS. Peritumoral mapping by TMS was conducted on patients who had intra-axial brain neoplasms located within or close to the motor speech area. The electric field induced by TMS was computed using realistic head models constructed from magnetic resonance images of patients. A post-processing method was implemented to determine a TMS hotspot by combining the computed electric fields for the coil orientations and positions that delivered high motor-evoked potentials during peritumoral mapping. The method was compared to the stimulation site localized via intraoperative direct brain stimulation and navigated TMS. Four main results were obtained: 1) the dependence of the computed hotspot area on the number of peritumoral measurements was evaluated; 2) the estimated localization of the hand motor area in eight non-affected hemispheres was in good agreement with the position of a so-called "hand-knob"; 3) the estimated hotspot areas were not sensitive to variations in tissue conductivity; and 4) the hand motor areas estimated by this proposal and direct electric stimulation (DES) were in good agreement in the ipsilateral hemisphere of four glioma patients. The TMS localization method was validated by well-known positions of the "hand-knob" in brains for the non-affected hemisphere, and by a hotspot localized via DES during awake craniotomy for the tumor-containing hemisphere. Copyright © 2018 Elsevier Inc. All rights reserved.

Localized Heating on Silicon Field Effect Transistors: Device Fabrication and Temperature Measurements in Fluid

PubMed Central

Elibol, Oguz H.; Reddy, Bobby; Nair, Pradeep R.; Dorvel, Brian; Butler, Felice; Ahsan, Zahab; Bergstrom, Donald E.; Alam, Muhammad A.; Bashir, Rashid

2010-01-01

We demonstrate electrically addressable localized heating in fluid at the dielectric surface of silicon-on-insulator field-effect transistors via radio-frequency Joule heating of mobile ions in the Debye layer. Measurement of fluid temperatures in close vicinity to surfaces poses a challenge due to the localized nature of the temperature profile. To address this, we developed a localized thermometry technique based on the fluorescence decay rate of covalently attached fluorophores to extract the temperature within 2 nm of any oxide surface. We demonstrate precise spatial control of voltage dependent temperature profiles on the transistor surfaces. Our results introduce a new dimension to present sensing systems by enabling dual purpose silicon transistor-heaters that serve both as field effect sensors as well as temperature controllers that could perform localized bio-chemical reactions in Lab on Chip applications. PMID:19967115

Using EarthScope magnetotelluric data to improve the resilience of the US power grid: rapid predictions of geomagnetically induced currents

NASA Astrophysics Data System (ADS)

Schultz, A.; Bonner, L. R., IV

2016-12-01

Existing methods to predict Geomagnetically Induced Currents (GICs) in power grids, such as the North American Electric Reliability Corporation standard adopted by the power industry, require explicit knowledge of the electrical resistivity structure of the crust and mantle to solve for ground level electric fields along transmission lines. The current standard is to apply regional 1-D resistivity models to this problem, which facilitates rapid solution of the governing equations. The systematic mapping of continental resistivity structure from projects such as EarthScope reveals several orders of magnitude of lateral variations in resistivity on local, regional and continental scales, resulting in electric field intensifications relative to existing 1-D solutions that can impact GICs to first order. The computational burden on the ground resistivity/GIC problem of coupled 3-D solutions inhibits the prediction of GICs in a timeframe useful to protecting power grids. In this work we reduce the problem to applying a set of filters, recognizing that the magnetotelluric impedance tensors implicitly contain all known information about the resistivity structure beneath a given site, and thus provides the required relationship between electric and magnetic fields at each site. We project real-time magnetic field data from distant magnetic observatories through a robustly calculated multivariate transfer function to locations where magnetotelluric impedance tensors had previously been obtained. This provides a real-time prediction of the magnetic field at each of those points. We then project the predicted magnetic fields through the impedance tensors to obtain predictions of electric fields induced at ground level. Thus, electric field predictions can be generated in real-time for an entire array from real-time observatory data, then interpolated onto points representing a power transmission line contained within the array to produce a combined electric field prediction necessary for GIC prediction along that line. This method produces more accurate predictions of ground electric fields in conductively heterogeneous areas that are not limited by distance from the nearest observatory, while still retaining comparable computational speeds as existing methods.

Transient electrophoretic motion of a charged particle through a converging-diverging microchannel: effect of direct current-dielectrophoretic force.

PubMed

Ai, Ye; Joo, Sang W; Jiang, Yingtao; Xuan, Xiangchun; Qian, Shizhi

2009-07-01

Transient electrophoretic motion of a charged particle through a converging-diverging microchannel is studied by solving the coupled system of the Navier-Stokes equations for fluid flow and the Laplace equation for electrical field with an arbitrary Lagrangian-Eulerian finite-element method. A spatially non-uniform electric field is induced in the converging-diverging section, which gives rise to a direct current dielectrophoretic (DEP) force in addition to the electrostatic force acting on the charged particle. As a sequence, the symmetry of the particle velocity and trajectory with respect to the throat is broken. We demonstrate that the predicted particle trajectory shifts due to DEP show quantitative agreements with the existing experimental data. Although converging-diverging microchannels can be used for super fast electrophoresis due to the enhancement of the local electric field, it is shown that large particles may be blocked due to the induced DEP force, which thus must be taken into account in the study of electrophoresis in microfluidic devices where non-uniform electric fields are present.

Ba doped Fe3O4 nanocrystals: Magnetic field and temperature tuning dielectric and electrical transport

NASA Astrophysics Data System (ADS)

Dutta, Papia; Mandal, S. K.; Nath, A.

2018-05-01

Nanocrystalline BaFe2O4 has been prepared through low temperature pyrophoric reaction method. The structural, dielectric and electrical transport properties of BaFe2O4 are investigated in detail. AC electrical properties have been studied over the wide range of frequencies with applied dc magnetic fields and temperatures. The value of impedance is found to increase with increase in magnetic field attributing the magnetostriction property of the sample. The observed value of magneto-impedance and magnetodielectric is found to ∼32% and ∼33% at room temperature. Nyquist plots have been fitted using resistance-capacitor circuits at different magnetic fields and temperatures showing the dominant role of grain and grain boundaries of the sample. Metal-semiconductor transition ∼403 K has been discussed in terms of delocalized and localized charge carrier.We have estimated activation energy using Arrhenius relation indicating temperature dependent electrical relaxation process in the system. Ac conductivity follow a Jonscher’s single power law indicating the large and small polaronic hopping conduction mechanism in the system.

Statistical Properties of Ribbon Evolution and Reconnection Electric Fields in Eruptive and Confined Flares

NASA Astrophysics Data System (ADS)

Hinterreiter, J.; Veronig, A. M.; Thalmann, J. K.; Tschernitz, J.; Pötzi, W.

2018-03-01

A statistical study of the chromospheric ribbon evolution in Hα two-ribbon flares was performed. The data set consists of 50 confined (62%) and eruptive (38%) flares that occurred from June 2000 to June 2015. The flares were selected homogeneously over the Hα and Geostationary Operational Environmental Satellite (GOES) classes, with an emphasis on including powerful confined flares and weak eruptive flares. Hα filtergrams from the Kanzelhöhe Observatory in combination with Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) magnetograms were used to derive the ribbon separation, the ribbon-separation velocity, the magnetic-field strength, and the reconnection electric field. We find that eruptive flares reveal statistically larger ribbon separation and higher ribbon-separation velocities than confined flares. In addition, the ribbon separation of eruptive flares correlates with the GOES SXR flux, whereas no clear dependence was found for confined flares. The maximum ribbon-separation velocity is not correlated with the GOES flux, but eruptive flares reveal on average a higher ribbon-separation velocity (by ≈ 10 km s-1). The local reconnection electric field of confined (cc=0.50 ±0.02) and eruptive (cc=0.77 ±0.03) flares correlates with the GOES flux, indicating that more powerful flares involve stronger reconnection electric fields. In addition, eruptive flares with higher electric-field strengths tend to be accompanied by faster coronal mass ejections.

METHOD OF PRODUCING NEUTRONS

DOEpatents

Imhoff, D.H.; Harker, W.H.

1964-02-01

A method for producing neutrons is described in which there is employed a confinement zone defined between longitudinally spaced localized gradient regions of an elongated magnetic field. Changed particles and neutralizing electrons, more specifically deuterons and tritons and neutralizng electrons, are injected into the confinement field from ion sources located outside the field. The rotational energy of the parrticles is increased at the gradients by imposing an oscillating transverse electrical field thereacross. The imposition of such oscillating transverse electrical fields improves the reflection capability of such gradient fielda so that the reactive particles are retained more effectively within the zone. With the attainment of appropriate densities of plasma particles and provided that such particles are at a sufficiently high temperature, neutron-producing reactions ensue and large quantities of neutrons emerge from the containment zone. (AEC)

Magnetic field and electric current structure in the chromosphere

NASA Technical Reports Server (NTRS)

Dravins, D.

1974-01-01

The three-dimensional vector magnetic field structure in the chromosphere above an active region is deduced by using high-resolution H-alpha filtergrams together with a simultaneous digital magnetogram. An analog model of the field is made with 400 metal wires representing field lines that outline the H-alpha structure. The height extent of the field is determined from vertical field-gradient observations around sunspots, from observed fibril heights, and from an assumption that the sources of the field are largely local. The computed electric currents (typically 10 mA/sq m) are found to flow in patterns not similar to observed features and not parallel to magnetic fields. Force structures correspond to observed solar features; the dynamics to be expected include: downward motion in bipolar areas in the lower chromosphere, an outflow of the outer chromosphere into the corona with radially outward flow above bipolar plage regions, and motion of arch filament systems.

Investigation of the linear and second-order nonlinear optical properties of molecular crystals within the local field theory.

PubMed

Seidler, Tomasz; Stadnicka, Katarzyna; Champagne, Benoît

2013-09-21

In this paper it is shown that modest calculations combining first principles evaluations of the molecular properties with electrostatic interaction schemes to account for the crystal environment effects are reliable for predicting and interpreting the experimentally measured electric linear and second-order nonlinear optical susceptibilities of molecular crystals within the experimental error bars. This is illustrated by considering two molecular crystals, namely: 2-methyl-4-nitroaniline and 4-(N,N-dimethylamino)-3-acetamidonitrobenzene. Three types of surrounding effects should be accounted for (i) the polarization due to the surrounding molecules, described here by static electric fields originating from their electric dipoles or charge distributions, (ii) the intermolecular interactions, which affect the geometry and particularly the molecular conformation, and (iii) the screening of the external electric field by the constitutive molecules. This study further highlights the role of electron correlation on the linear and nonlinear responses of molecular crystals and the challenge of describing frequency dispersion.

Evolution of space open electric arc burning in the external axial magnetic field

NASA Astrophysics Data System (ADS)

Urusova, I. R.; Urusova, T. E.

2018-06-01

The calculation was made for open DC electric arc burning in an external uniform axial magnetic field. It was performed within the framework of a nonstationary three-dimensional mathematical model in approximation of partial local thermodynamic equilibrium of plasma. A "schematic" analog of electron temperature fluctuations was proposed for numerical realization of the open electric arc column of a helical shape. According to calculations, it was established that the column of the open electric arc takes a helical space shape. Plasma rotates around a longitudinal axis of the arc, at that the directions of plasma rotation near the cathode and the anode are opposite. In the arc cross-sections, the velocity of plasma rotation is unequal and the deviation value of the same part of the arc from the central axis varies in time. A helical shape of the open arc is not stable and varies in time. Apparently, the open arc cannot remain stable and invariable in the time helical shape in the external axial magnetic field.

Transcranial Magnetic Stimulation-coil design with improved focality

NASA Astrophysics Data System (ADS)

Rastogi, P.; Lee, E. G.; Hadimani, R. L.; Jiles, D. C.

2017-05-01

Transcranial Magnetic Stimulation (TMS) is a technique for neuromodulation that can be used as a non-invasive therapy for various neurological disorders. In TMS, a time varying magnetic field generated from an electromagnetic coil placed on the scalp is used to induce an electric field inside the brain. TMS coil geometry plays an important role in determining the focality and depth of penetration of the induced electric field responsible for stimulation. Clinicians and basic scientists are interested in stimulating a localized area of the brain, while minimizing the stimulation of surrounding neural networks. In this paper, a novel coil has been proposed, namely Quadruple Butterfly Coil (QBC) with an improved focality over the commercial Figure-8 coil. Finite element simulations were conducted with both the QBC and the conventional Figure-8 coil. The two coil's stimulation profiles were assessed with 50 anatomically realistic MRI derived head models. The coils were positioned on the vertex and the scalp over the dorsolateral prefrontal cortex to stimulate the brain. Computer modeling of the coils has been done to determine the parameters of interest-volume of stimulation, maximum electric field, location of maximum electric field and area of stimulation across all 50 head models for both coils.

Electric-field induced spin accumulation in the Landau level states of topological insulator thin films

NASA Astrophysics Data System (ADS)

Siu, Zhuo Bin; Chowdhury, Debashree; Basu, Banasri; Jalil, Mansoor B. A.

2017-08-01

A topological insulator (TI) thin film differs from the more typically studied thick TI system in that the former has both a top and a bottom surface where the states localized at both surfaces can couple to one other across the finite thickness. An out-of-plane magnetic field leads to the formation of discrete Landau level states in the system, whereas an in-plane magnetization breaks the angular momentum symmetry of the system. In this work, we study the spin accumulation induced by the application of an in-plane electric field to the TI thin film system where the Landau level states and inter-surface coupling are simultaneously present. We show, via Kubo formula calculations, that the in-plane spin accumulation perpendicular to the magnetization due to the electric field vanishes for a TI thin film with symmetric top and bottom surfaces. A finite in-plane spin accumulation perpendicular to both the electric field and magnetization emerges upon applying either a differential magnetization coupling or a potential difference between the two film surfaces. This spin accumulation results from the breaking of the antisymmetry of the spin accumulation around the k-space equal-energy contours.

Drift of charge carriers in crystalline organic semiconductors

NASA Astrophysics Data System (ADS)

Dong, Jingjuan; Si, Wei; Wu, Chang-Qin

2016-04-01

We investigate the direct-current response of crystalline organic semiconductors in the presence of finite external electric fields by the quantum-classical Ehrenfest dynamics complemented with instantaneous decoherence corrections (IDC). The IDC is carried out in the real-space representation with the energy-dependent reweighing factors to account for both intermolecular decoherence and energy relaxation by which conduction occurs. In this way, both the diffusion and drift motion of charge carriers are described in a unified framework. Based on an off-diagonal electron-phonon coupling model for pentacene, we find that the drift velocity initially increases with the electric field and then decreases at higher fields due to the Wannier-Stark localization, and a negative electric-field dependence of mobility is observed. The Einstein relation, which is a manifestation of the fluctuation-dissipation theorem, is found to be restored in electric fields up to ˜105 V/cm for a wide temperature region studied. Furthermore, we show that the incorporated decoherence and energy relaxation could explain the large discrepancy between the mobilities calculated by the Ehrenfest dynamics and the full quantum methods, which proves the effectiveness of our approach to take back these missing processes.

Drift of charge carriers in crystalline organic semiconductors.

PubMed

Dong, Jingjuan; Si, Wei; Wu, Chang-Qin

2016-04-14

We investigate the direct-current response of crystalline organic semiconductors in the presence of finite external electric fields by the quantum-classical Ehrenfest dynamics complemented with instantaneous decoherence corrections (IDC). The IDC is carried out in the real-space representation with the energy-dependent reweighing factors to account for both intermolecular decoherence and energy relaxation by which conduction occurs. In this way, both the diffusion and drift motion of charge carriers are described in a unified framework. Based on an off-diagonal electron-phonon coupling model for pentacene, we find that the drift velocity initially increases with the electric field and then decreases at higher fields due to the Wannier-Stark localization, and a negative electric-field dependence of mobility is observed. The Einstein relation, which is a manifestation of the fluctuation-dissipation theorem, is found to be restored in electric fields up to ∼10(5) V/cm for a wide temperature region studied. Furthermore, we show that the incorporated decoherence and energy relaxation could explain the large discrepancy between the mobilities calculated by the Ehrenfest dynamics and the full quantum methods, which proves the effectiveness of our approach to take back these missing processes.

Investigation of Parallel Radiofrequency Transmission for the Reduction of Heating in Long Conductive Leads in 3 Tesla Magnetic Resonance Imaging

PubMed Central

McElcheran, Clare E.; Yang, Benson; Anderson, Kevan J. T.; Golenstani-Rad, Laleh; Graham, Simon J.

2015-01-01

Deep Brain Stimulation (DBS) is increasingly used to treat a variety of brain diseases by sending electrical impulses to deep brain nuclei through long, electrically conductive leads. Magnetic resonance imaging (MRI) of patients pre- and post-implantation is desirable to target and position the implant, to evaluate possible side-effects and to examine DBS patients who have other health conditions. Although MRI is the preferred modality for pre-operative planning, MRI post-implantation is limited due to the risk of high local power deposition, and therefore tissue heating, at the tip of the lead. The localized power deposition arises from currents induced in the leads caused by coupling with the radiofrequency (RF) transmission field during imaging. In the present work, parallel RF transmission (pTx) is used to tailor the RF electric field to suppress coupling effects. Electromagnetic simulations were performed for three pTx coil configurations with 2, 4, and 8-elements, respectively. Optimal input voltages to minimize coupling, while maintaining RF magnetic field homogeneity, were determined for all configurations using a Nelder-Mead optimization algorithm. Resulting electric and magnetic fields were compared to that of a 16-rung birdcage coil. Experimental validation was performed with a custom-built 4-element pTx coil. In simulation, 95-99% reduction of the electric field at the tip of the lead was observed between the various pTx coil configurations and the birdcage coil. Maximal reduction in E-field was obtained with the 8-element pTx coil. Magnetic field homogeneity was comparable to the birdcage coil for the 4- and 8-element pTx configurations. In experiment, a temperature increase of 2±0.15°C was observed at the tip of the wire using the birdcage coil, whereas negligible increase (0.2±0.15°C) was observed with the optimized pTx system. Although further research is required, these initial results suggest that the concept of optimizing pTx to reduce DBS heating effects holds considerable promise. PMID:26237218

Investigation of Parallel Radiofrequency Transmission for the Reduction of Heating in Long Conductive Leads in 3 Tesla Magnetic Resonance Imaging.

PubMed

McElcheran, Clare E; Yang, Benson; Anderson, Kevan J T; Golenstani-Rad, Laleh; Graham, Simon J

2015-01-01

Deep Brain Stimulation (DBS) is increasingly used to treat a variety of brain diseases by sending electrical impulses to deep brain nuclei through long, electrically conductive leads. Magnetic resonance imaging (MRI) of patients pre- and post-implantation is desirable to target and position the implant, to evaluate possible side-effects and to examine DBS patients who have other health conditions. Although MRI is the preferred modality for pre-operative planning, MRI post-implantation is limited due to the risk of high local power deposition, and therefore tissue heating, at the tip of the lead. The localized power deposition arises from currents induced in the leads caused by coupling with the radiofrequency (RF) transmission field during imaging. In the present work, parallel RF transmission (pTx) is used to tailor the RF electric field to suppress coupling effects. Electromagnetic simulations were performed for three pTx coil configurations with 2, 4, and 8-elements, respectively. Optimal input voltages to minimize coupling, while maintaining RF magnetic field homogeneity, were determined for all configurations using a Nelder-Mead optimization algorithm. Resulting electric and magnetic fields were compared to that of a 16-rung birdcage coil. Experimental validation was performed with a custom-built 4-element pTx coil. In simulation, 95-99% reduction of the electric field at the tip of the lead was observed between the various pTx coil configurations and the birdcage coil. Maximal reduction in E-field was obtained with the 8-element pTx coil. Magnetic field homogeneity was comparable to the birdcage coil for the 4- and 8-element pTx configurations. In experiment, a temperature increase of 2±0.15°C was observed at the tip of the wire using the birdcage coil, whereas negligible increase (0.2±0.15°C) was observed with the optimized pTx system. Although further research is required, these initial results suggest that the concept of optimizing pTx to reduce DBS heating effects holds considerable promise.

Onset of 2D magnetic reconnection in the solar photosphere, chromosphere, and corona

NASA Astrophysics Data System (ADS)

Snow, B.; Botha, G. J. J.; McLaughlin, J. A.; Hillier, A.

2018-01-01

Aims: We aim to investigate the onset of 2D time-dependent magnetic reconnection that is triggered using an external (non-local) velocity driver located away from, and perpendicular to, an equilibrium Harris current sheet. Previous studies have typically utilised an internal trigger to initiate reconnection, for example initial conditions centred on the current sheet. Here, an external driver allows for a more naturalistic trigger as well as the study of the earlier stages of the reconnection start-up process. Methods: Numerical simulations solving the compressible, resistive magnetohydrodynamic (MHD) equations were performed to investigate the reconnection onset within different atmospheric layers of the Sun, namely the corona, chromosphere and photosphere. Results: A reconnecting state is reached for all atmospheric heights considered, with the dominant physics being highly dependent on atmospheric conditions. The coronal case achieves a sharp rise in electric field (indicative of reconnection) for a range of velocity drivers. For the chromosphere, we find a larger velocity amplitude is required to trigger reconnection (compared to the corona). For the photospheric environment, the electric field is highly dependent on the inflow speed; a sharp increase in electric field is obtained only as the velocity entering the reconnection region approaches the Alfvén speed. Additionally, the role of ambipolar diffusion is investigated for the chromospheric case and we find that the ambipolar diffusion alters the structure of the current density in the inflow region. Conclusions: The rate at which flux enters the reconnection region is controlled by the inflow velocity. This determines all aspects of the reconnection start-up process, that is, the early onset of reconnection is dominated by the advection term in Ohm's law in all atmospheric layers. A lower plasma-β enhances reconnection and creates a large change in the electric field. A high plasma-β hinders the reconnection, yielding a sharp rise in the electric field only when the velocity flowing into the reconnection region approaches the local Alfvén speed.

Standard Practices for Usage of Inductive Magnetic Field Probes with Application to Electric Propulsion Testing

NASA Technical Reports Server (NTRS)

Polzin, Kurt A.; Hill, Carrie S.; Turchi, Peter J.; Burton, Rodney L.; Messer, Sarah; Lovberg, Ralph H.; Hallock, Ashley K.

2013-01-01

Inductive magnetic field probes (also known as B-dot probes and sometimes as B-probes or magnetic probes) are often employed to perform field measurements in electric propulsion applications where there are time-varying fields. Magnetic field probes provide the means to measure these magnetic fields and can even be used to measure the plasma current density indirectly through the application of Ampere's law. Measurements of this type can yield either global information related to a thruster and its performance or detailed, local data related to the specific physical processes occurring in the plasma. Results of the development of a standard for B-dot probe measurements are presented, condensing the available literature on the subject into an accessible set of rules, guidelines, and techniques to standardize the performance and presentation of future measurements.

Magnetospheric disturbance effects on the Equatorial Ionization Anomaly (EIA) : an overview

NASA Astrophysics Data System (ADS)

Abdu, M. A.; Sobral, J. H. A.; de Paula, E. R.; Batista, I. S.

1992-12-01

The Equatorial lonization Anomaly (EIA) development can undergo drastic modification in the form of an anomalous occurrence at local times outside that of its quiet time development and/or inhibition/enhancement at local times of its normal occurrences. This happens for disturbed electrodynamic conditions of the global ionosphere-thermosphere-magnetosphere system, consequent upon the triggering of a magnetospheric storm event. Direct penetration to equatorial latitudes of the magnetospheric electric fields and the thermospheric disturbances involving winds, electric fields and composition changes produce significant alteration in the EIA morphology and dynamics. Results on statistical behaviour based on accumulated ground-based data sets, and those from recent theoretical modelling efforts and from satellite and ground-based observations, are reviewed. Some outstanding problems of the EIA response to magnetospheric disturbances that deserve attention in the coming years are pointed out.

Micropulsations in the electric field near the plasmapause, observed by Isee 1

NASA Technical Reports Server (NTRS)

Moe, T. E.; Maynard, N. C.; Heppner, J. P.

1980-01-01

The results of a survey of occurrence of micropulsations near and inside the plasmapause, made on the basis of 1 year of data from the double probe electric field instrument on Isee 1, are presented. It is reported that the observed pulsations are classified as Pc 3 and P 2, and that one single Pc 1 event is observed. It is found that Pc 3 events are common during the local day, with a maximum percentage of occurrence as high as 72 in the morning hours. Attention is given to Pi 2 events showing that they are concentrated on the local nightside. Finally, it is noted that pulsations in the Pc 1 range appear on only one inbound pass, which makes the Pc 1 a rare phenomenon at low and moderate latitudes in the plasmasphere.

Dephasing effects on ac-driven triple quantum dot systems

NASA Astrophysics Data System (ADS)

Maldonado, I.; Villavicencio, J.; Contreras-Pulido, L. D.; Cota, E.; Maytorena, J. A.

2018-05-01

We analyze the effect of environmental dephasing on the electrical current in an ac-driven triple quantum dot system in a symmetric Λ configuration. The current is explored by solving the time evolution equation of the density matrix as a function of the frequency and amplitude of the driving field. Two characteristic spectra are observed depending on the field amplitude. At the resonance condition, when the frequency matches the interdot energy difference, one spectrum shows a distinctive Fano-type peak, while the other, occurring at larger values of the field amplitude, exhibits a strong current suppression due to dynamic localization. In the former case we observe that the current maximum is reduced due to dephasing, while in the latter it is shown that dephasing partially alleviates the localization. In both cases, away from resonance, we observe current oscillations which are dephasing-enhanced for a wide range of frequencies. These effects are also discussed using Floquet theory, and analytical expressions for the electrical current are obtained within the rotating wave approximation.

An analytical expression for ion velocities at the wall including the sheath electric field and surface biasing for erosion modeling at JET ILW

DOE PAGES

Borodkina, I.; Borodin, D.; Brezinsek, S.; ...

2017-04-12

For simulation of plasma-facing component erosion in fusion experiments, an analytical expression for the ion velocity just before the surface impact including the local electric field and an optional surface biasing effect is suggested. Energy and angular impact distributions and the resulting effective sputtering yields were produced for several experimental scenarios at JET ILW mostly involving PFCs exposed to an oblique magnetic field. The analytic solution has been applied as an improvement to earlier ERO modelling of localized, Be outer limiter, RF-enhanced erosion, modulated by toggling of a remote, however magnetically connected ICRH antenna. The effective W sputtering yields duemore » to D and Be ion impact in Type-I and Type-III ELMs and inter-ELM conditions were also estimated using the analytical approach and benchmarked by spectroscopy. The intra-ELM W sputtering flux increases almost 10 times in comparison to the inter-ELM flux.« less

Jumping-droplet electronics hot-spot cooling

NASA Astrophysics Data System (ADS)

Oh, Junho; Birbarah, Patrick; Foulkes, Thomas; Yin, Sabrina L.; Rentauskas, Michelle; Neely, Jason; Pilawa-Podgurski, Robert C. N.; Miljkovic, Nenad

2017-03-01

Demand for enhanced cooling technologies within various commercial and consumer applications has increased in recent decades due to electronic devices becoming more energy dense. This study demonstrates jumping-droplet based electric-field-enhanced (EFE) condensation as a potential method to achieve active hot spot cooling in electronic devices. To test the viability of EFE condensation, we developed an experimental setup to remove heat via droplet evaporation from single and multiple high power gallium nitride (GaN) transistors acting as local hot spots (4.6 mm × 2.6 mm). An externally powered circuit was developed to direct jumping droplets from a copper oxide (CuO) nanostructured superhydrophobic surface to the transistor hot spots by applying electric fields between the condensing surface and the transistor. Heat transfer measurements were performed in ambient air (22-25 °C air temperature, 20%-45% relative humidity) to determine the effect of gap spacing (2-4 mm), electric field (50-250 V/cm) and applied heat flux (demonstrated to 13 W/cm2). EFE condensation was shown to enhance the heat transfer from the local hot spot by ≈200% compared to cooling without jumping and by 20% compared to non-EFE jumping. Dynamic switching of the electric field for a two-GaN system reveals the potential for active cooling of mobile hot spots. The opportunity for further cooling enhancement by the removal of non-condensable gases promises hot spot heat dissipation rates approaching 120 W/cm2. This work provides a framework for the development of active jumping droplet based vapor chambers and heat pipes capable of spatial and temporal thermal dissipation control.

Improved field localization in transcranial magnetic stimulation of the brain with the utilization of a conductive shield plate in the stimulator.

PubMed

Kim, Dong-Hun; Georghiou, George E; Won, Chulho

2006-04-01

In this paper, a carefully designed conductive shield plate is presented, which helps to improve localization of the electric field distribution induced by transcranial magnetic stimulation for neuron stimulation. The shield plate is introduced between a figure-of-eight coil and the head. In order to accurately predict the field distribution inside the brain and to examine the effects of the shield plate, a realistic head model is constructed from magnetic resonance image data with the help of image processing tools and the finite-element method in three dimensions is employed. Finally, to show the improvements obtained, the results are compared with two conventional coil designs. It is found that an incorporation of the shield plate into the coil, effectively improves the induced field localization by more than 50%, and prevents other parts of the brain from exposure to high pulsed magnetic fields.

Vapor-liquid coexistence of the Stockmayer fluid in nonuniform external fields.

PubMed

Samin, Sela; Tsori, Yoav; Holm, Christian

2013-05-01

We investigate the structure and phase behavior of the Stockmayer fluid in the presence of nonuniform electric fields using molecular simulation. We find that an initially homogeneous vapor phase undergoes a local phase separation in a nonuniform field due to the combined effect of the field gradient and the fluid vapor-liquid equilibrium. This results in a high-density fluid condensing in the strong field region. The system polarization exhibits a strong field dependence due to the fluid condensation.

The separated electric and magnetic field responses of luminescent bacteria exposed to pulsed microwave irradiation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Williams, Catrin F., E-mail: williamscf@cardiff.ac.uk; School of Biosciences, Cardiff University, Main Building, Cathays Park, Cardiff, CF10 3AT Wales; Geroni, Gilles M.

Electromagnetic fields (EMFs) are ubiquitous in the digital world we inhabit, with microwave and millimetre wave sources of non-ionizing radiation employed extensively in electronics and communications, e.g., in mobile phones and Wi-Fi. Indeed, the advent of 5G systems and the “internet of things” is likely to lead to massive densification of wireless networks. Whilst the thermal effects of EMFs on biological systems are well characterised, their putative non-thermal effects remain a controversial subject. Here, we use the bioluminescent marine bacterium, Vibrio fischeri, to monitor the effects of pulsed microwave electromagnetic fields, of nominal frequency 2.5 GHz, on light emission. Separatedmore » electric and magnetic field effects were investigated using a resonant microwave cavity, within which the maxima of each field are separated. For pulsed electric field exposure, the bacteria gave reproducible responses and recovery in light emission. At the lowest pulsed duty cycle (1.25%) and after short durations (100 ms) of exposure to the electric field at power levels of 4.5 W rms, we observed an initial stimulation of bioluminescence, whereas successive microwave pulses became inhibitory. Much of this behaviour is due to thermal effects, as the bacterial light output is very sensitive to the local temperature. Conversely, magnetic field exposure gave no measurable short-term responses even at the highest power levels of 32 W rms. Thus, we were able to detect, de-convolute, and evaluate independently the effects of separated electric and magnetic fields on exposure of a luminescent biological system to microwave irradiation.« less

The separated electric and magnetic field responses of luminescent bacteria exposed to pulsed microwave irradiation

NASA Astrophysics Data System (ADS)

Williams, Catrin F.; Geroni, Gilles M.; Pirog, Antoine; Lloyd, David; Lees, Jonathan; Porch, Adrian

2016-08-01

Electromagnetic fields (EMFs) are ubiquitous in the digital world we inhabit, with microwave and millimetre wave sources of non-ionizing radiation employed extensively in electronics and communications, e.g., in mobile phones and Wi-Fi. Indeed, the advent of 5G systems and the "internet of things" is likely to lead to massive densification of wireless networks. Whilst the thermal effects of EMFs on biological systems are well characterised, their putative non-thermal effects remain a controversial subject. Here, we use the bioluminescent marine bacterium, Vibrio fischeri, to monitor the effects of pulsed microwave electromagnetic fields, of nominal frequency 2.5 GHz, on light emission. Separated electric and magnetic field effects were investigated using a resonant microwave cavity, within which the maxima of each field are separated. For pulsed electric field exposure, the bacteria gave reproducible responses and recovery in light emission. At the lowest pulsed duty cycle (1.25%) and after short durations (100 ms) of exposure to the electric field at power levels of 4.5 W rms, we observed an initial stimulation of bioluminescence, whereas successive microwave pulses became inhibitory. Much of this behaviour is due to thermal effects, as the bacterial light output is very sensitive to the local temperature. Conversely, magnetic field exposure gave no measurable short-term responses even at the highest power levels of 32 W rms. Thus, we were able to detect, de-convolute, and evaluate independently the effects of separated electric and magnetic fields on exposure of a luminescent biological system to microwave irradiation.

Determination of the Influence of Electric Fields upon the Densification of Ionic Ceramics

DTIC Science & Technology

2017-07-21

and assisting the development of new techniques to expose nanoparticles to non -contacting electrostatic fields at temperatures as high as 900...through TEM imaging, and assisting the development of new techniques to expose nanoparticles to non -contacting electrostatic fields at temperatures as...during flash sintering lead to non -homogeneous microstructures. We expect that therefore physical properties may be inhomogeneous depending local

Mapping and quantifying electric and magnetic dipole luminescence at the nanoscale.

PubMed

Aigouy, L; Cazé, A; Gredin, P; Mortier, M; Carminati, R

2014-08-15

We report on an experimental technique to quantify the relative importance of electric and magnetic dipole luminescence from a single nanosource in structured environments. By attaching a Eu^{3+}-doped nanocrystal to a near-field scanning optical microscope tip, we map the branching ratios associated with two electric dipole and one magnetic dipole transitions in three dimensions on a gold stripe. The relative weights of the electric and magnetic radiative local density of states can be recovered quantitatively, based on a multilevel model. This paves the way towards the full electric and magnetic characterization of nanostructures for the control of single emitter luminescence.

A pilot study with very low-intensity, intermediate-frequency electric fields in patients with locally advanced and/or metastatic solid tumors.

PubMed

Salzberg, Marc; Kirson, Eilon; Palti, Yoram; Rochlitz, Christoph

2008-07-01

The transmission of electric fields using insulated electrodes has demonstrated that very low-intensity, properly tuned, intermediate-frequency electric fields, termed tumor-treating fields (TTFields), selectively stunts tumor cell growth and is accompanied by a decrease in tumor angiogenesis. This open, prospective pilot study was designed to evaluate the safety, tolerability, and efficacy profile of TTFields treatment in patients with locally advanced and/or metastatic solid tumors using the NovoTTF100A(TM) device. All 6 patients were heavily pre-treated with several lines of therapy; no additional standard treatment option was available to them. TTFields treatment using continuous NovoTTF-100A lasted a minimum of 14 days and was very well tolerated. No related serious adverse events occurred. Outcomes showed 1 partial response of a treated skin metastasis from a primary breast cancer, 3 cases where tumor growth was arrested during treatment, and 1 case of disease progression. One mesothelioma patient experienced lesion regression near TTFields with simultaneous tumor stability or progression in distal areas. Although the number of patients in this study is small, the lack of therapy toxicity and the efficacy observed in data gathered to date indicate the potential of TTFields as a new treatment modality for solid tumors, definitely warranting further investigation. (c) 2008 S. Karger AG, Basel

Observations of subauroral ion drift (SAID) occurrence statistics and associated ionospheric conditions measured by the Defense Meteorological Satellite Program (DMSP) and Dynamics Explorer 2 (DE-2).

NASA Astrophysics Data System (ADS)

Landry, R. G.; Anderson, P. C.

2017-12-01

Subauroral ion drifts (SAID) are a phenomenon sometimes observed in the subauroral ionosphere in dusk to post-midnight magnetic local time sectors during magnetically active periods characterized by strong poleward electric fields that drive westward ion drifts greater than 1 km/s. SAIDs typically will span 1-2 degrees magnetic latitude and several hours in magnetic local time. SAIDs are often observed colocated with the midlatitude trough. The strong electric field can act to reduce the ionospheric conductivity further through enhanced recombination and vertical transport. The theory that SAIDs are generated by ionospheric Pedersen currents fed by ring current driven field-aligned currents (FAC) requires the decreased conductance associated with the midlatitude trough to produce the latitudinally narrow, large amplitude SAID electric field. Using Dynamics Explorer 2 (DE 2) plasma measurements of SAIDs from altitudes of 200 to 1000 km, we investigate the statistical variation of the ionospheric composition, temperature, and vertical ion drifts as a function of altitude. Using Defense Meteorological Satellite Program (DMSP) measurements from 1987-2012, we extend the empirical study at the DMSP altitude of 830 km to investigate how season, longitude, and any ionospheric preconditioning before SAID formation affect the likelihood of SAID occurrence and coincidence with FACs and ion density troughs.

A New Kinetic Simulation Model with Self-Consistent Calculation of Regolith Layer Charging for Moon-Plasma Interactions

NASA Astrophysics Data System (ADS)

Han, D.; Wang, J.

2015-12-01

The moon-plasma interactions and the resulting surface charging have been subjects of extensive recent investigations. While many particle-in-cell (PIC) based simulation models have been developed, all existing PIC simulation models treat the surface of the Moon as a boundary condition to the plasma flow. In such models, the surface of the Moon is typically limited to simple geometry configurations, the surface floating potential is calculated from a simplified current balance condition, and the electric field inside the regolith layer cannot be resolved. This paper presents a new full particle PIC model to simulate local scale plasma flow and surface charging. A major feature of this new model is that the surface is treated as an "interface" between two mediums rather than a boundary, and the simulation domain includes not only the plasma but also the regolith layer and the bedrock underneath it. There are no limitations on the surface shape. An immersed-finite-element field solver is applied which calculates the regolith surface floating potential and the electric field inside the regolith layer directly from local charge deposition. The material property of the regolith layer is also explicitly included in simulation. This new model is capable of providing a self-consistent solution to the plasma flow field, lunar surface charging, the electric field inside the regolith layer and the bedrock for realistic surface terrain. This new model is applied to simulate lunar surface-plasma interactions and surface charging under various ambient plasma conditions. The focus is on the lunar terminator region, where the combined effects from the low sun elevation angle and the localized plasma wake generated by plasma flow over a rugged terrain can generate strongly differentially charged surfaces and complex dust dynamics. We discuss the effects of the regolith properties and regolith layer charging on the plasma flow field, dust levitation, and dust transport.

Computational modeling of chemo-electro-mechanical coupling: A novel implicit monolithic finite element approach

PubMed Central

Wong, J.; Göktepe, S.; Kuhl, E.

2014-01-01

Summary Computational modeling of the human heart allows us to predict how chemical, electrical, and mechanical fields interact throughout a cardiac cycle. Pharmacological treatment of cardiac disease has advanced significantly over the past decades, yet it remains unclear how the local biochemistry of an individual heart cell translates into global cardiac function. Here we propose a novel, unified strategy to simulate excitable biological systems across three biological scales. To discretize the governing chemical, electrical, and mechanical equations in space, we propose a monolithic finite element scheme. We apply a highly efficient and inherently modular global-local split, in which the deformation and the transmembrane potential are introduced globally as nodal degrees of freedom, while the chemical state variables are treated locally as internal variables. To ensure unconditional algorithmic stability, we apply an implicit backward Euler finite difference scheme to discretize the resulting system in time. To increase algorithmic robustness and guarantee optimal quadratic convergence, we suggest an incremental iterative Newton-Raphson scheme. The proposed algorithm allows us to simulate the interaction of chemical, electrical, and mechanical fields during a representative cardiac cycle on a patient-specific geometry, robust and stable, with calculation times on the order of four days on a standard desktop computer. PMID:23798328

Weak interactions in Graphane/BN systems under static electric fields—A periodic ab-initio study.

PubMed

Steinkasserer, Lukas Eugen Marsoner; Gaston, Nicola; Paulus, Beate

2015-04-21

Ab-initio calculations via periodic Hartree-Fock (HF) and local second-order Møller-Plesset perturbation theory (LMP2) are used to investigate the adsorption properties of combined Graphane/boron nitride systems and their response to static electric fields. It is shown how the latter can be used to alter both structural as well as electronic properties of these systems.

Aircraft electric field measurements: Calibration and ambient field retrieval

NASA Technical Reports Server (NTRS)

Koshak, William J.; Bailey, Jeff; Christian, Hugh J.; Mach, Douglas M.

1994-01-01

An aircraft locally distorts the ambient thundercloud electric field. In order to determine the field in the absence of the aircraft, an aircraft calibration is required. In this work a matrix inversion method is introduced for calibrating an aircraft equipped with four or more electric field sensors and a high-voltage corona point that is capable of charging the aircraft. An analytic, closed form solution for the estimate of a (3 x 3) aircraft calibration matrix is derived, and an absolute calibration experiment is used to improve the relative magnitudes of the elements of this matrix. To demonstrate the calibration procedure, we analyze actual calibration date derived from a Lear jet 28/29 that was equipped with five shutter-type field mill sensors (each with sensitivities of better than 1 V/m) located on the top, bottom, port, starboard, and aft positions. As a test of the calibration method, we analyze computer-simulated calibration data (derived from known aircraft and ambient fields) and explicitly determine the errors involved in deriving the variety of calibration matrices. We extend our formalism to arrive at an analytic solution for the ambient field, and again carry all errors explicitly.

Effect of Electromechanical Properties in Mn-doped BaTiO3

NASA Astrophysics Data System (ADS)

Takenaka, Hiroyuki; Cohen, R. E.

Experimental studies reported that Mn doping in BaTiO3 could improve their electromechanical properties. In addition, ageing process gives rise to a significant reversible strain effect. Performing density functional theory (DFT) calculations, we find that Mn dopant with oxygen vacancy induces local electric field of 20 MV/m in 2x2x2 (39 atom) supercell. In order to understand effects of the electromechanical properties from phenomenological point of view, we optimize electric enthalpies in Landau-Devonshire model, parametrized from DFT results, under applying electric fields. We show dielectric constant and piezoelectric coefficients from the optimized polarization paths. supported by ONR, the ERC Advanced Grant ToMCaT, and the Carnegie Institution for Science.

Lunar magnetic permeability, magnetic fields, and electrical conductivity temperature

NASA Technical Reports Server (NTRS)

Parkin, C. W.

1978-01-01

In the time period 1969-1972 a total of five magnetometers were deployed on the lunar surface during four Apollo missions. Data from these instruments, along with simultaneous measurements from other experiments on the moon and in lunar orbit, were used to study properties of the lunar interior and the lunar environment. The principal scientific results from analyses of the magnetic field data are discussed. The results are presented in the following main categories: (1) lunar electrical conductivity, temperature, and structure; (2) lunar magnetic permeability, iron abundance, and core size limits; (3) the local remnant magnetic fields, their interaction with the solar wind, and a thermoelectric generator model for their origin. Relevant publications and presented papers are listed.

Analysis of Laser Injection Condition and Electrical Properties in Local BSF for Laser Fired Contact c-Si Solar Cell Applications.

PubMed

Park, Cheolmin; Choi, Gyuho; Balaji, Nagarajan; Ju, Minkyu; Lee, Youn-Jung; Lee, Haeseok; Yi, Junsin

2018-07-01

A crystalline silicon (c-Si) local-back-contact (LBC) solar cell for which a laser-condition-optimized surface-recombination velocity (SRV), a contact resistance (Rc), and local back surface fields (LBSFs) were utilized is reported. The effect of the laser condition on the rear-side electrical properties of the laser-fired LBC solar cell was studied. The Nd:YAG-laser (1064-nm wavelength) power and frequency were varied to obtain LBSF values with a lower contact resistance. A 10-kHz laser power of 44 mW resulted in an Rc of 0.125 ohms with an LBSF thickness of 2.09 μm and a higher open-circuit voltage (VOC) of 642 mV.

Effects of electric field methods on modeling the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics

DOE PAGES

Yu, Yiqun; Jordanova, Vania Koleva; Ridley, Aaron J.; ...

2017-05-10

Here, we report a self-consistent electric field coupling between the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics represented in a kinetic ring current model. This implementation in the model features another self-consistency in addition to its already existing self-consistent magnetic field coupling with plasma. The model is therefore named as Ring current-Atmosphere interaction Model with Self-Consistent magnetic (B) and electric (E) fields, or RAM-SCB-E. With this new model, we explore, by comparing with previously employed empirical Weimer potential, the impact of using self-consistent electric fields on the modeling of storm time global electric potential distribution, plasma sheet particle injection, andmore » the subauroral polarization streams (SAPS) which heavily rely on the coupled interplay between the inner magnetosphere and midlatitude ionosphere. We find the following phenomena in the self-consistent model: (1) The spatially localized enhancement of electric field is produced within 2.5 < L < 4 during geomagnetic active time in the dusk-premidnight sector, with a similar dynamic penetration as found in statistical observations. (2) The electric potential contours show more substantial skewing toward the postmidnight than the Weimer potential, suggesting the resistance on the particles from directly injecting toward the low-L region. (3) The proton flux indeed indicates that the plasma sheet inner boundary at the dusk-premidnight sector is located further away from the Earth than in the Weimer potential, and a “tongue” of low-energy protons extends eastward toward the dawn, leading to the Harang reversal. (4) SAPS are reproduced in the subauroral region, and their magnitude and latitudinal width are in reasonable agreement with data.« less

Effects of electric field methods on modeling the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Yiqun; Jordanova, Vania Koleva; Ridley, Aaron J.

Here, we report a self-consistent electric field coupling between the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics represented in a kinetic ring current model. This implementation in the model features another self-consistency in addition to its already existing self-consistent magnetic field coupling with plasma. The model is therefore named as Ring current-Atmosphere interaction Model with Self-Consistent magnetic (B) and electric (E) fields, or RAM-SCB-E. With this new model, we explore, by comparing with previously employed empirical Weimer potential, the impact of using self-consistent electric fields on the modeling of storm time global electric potential distribution, plasma sheet particle injection, andmore » the subauroral polarization streams (SAPS) which heavily rely on the coupled interplay between the inner magnetosphere and midlatitude ionosphere. We find the following phenomena in the self-consistent model: (1) The spatially localized enhancement of electric field is produced within 2.5 < L < 4 during geomagnetic active time in the dusk-premidnight sector, with a similar dynamic penetration as found in statistical observations. (2) The electric potential contours show more substantial skewing toward the postmidnight than the Weimer potential, suggesting the resistance on the particles from directly injecting toward the low-L region. (3) The proton flux indeed indicates that the plasma sheet inner boundary at the dusk-premidnight sector is located further away from the Earth than in the Weimer potential, and a “tongue” of low-energy protons extends eastward toward the dawn, leading to the Harang reversal. (4) SAPS are reproduced in the subauroral region, and their magnitude and latitudinal width are in reasonable agreement with data.« less

Effects of electric field methods on modeling the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics

NASA Astrophysics Data System (ADS)

Yu, Yiqun; Jordanova, Vania K.; Ridley, Aaron J.; Toth, Gabor; Heelis, Roderick

2017-05-01

We report a self-consistent electric field coupling between the midlatitude ionospheric electrodynamics and inner magnetosphere dynamics represented in a kinetic ring current model. This implementation in the model features another self-consistency in addition to its already existing self-consistent magnetic field coupling with plasma. The model is therefore named as Ring current-Atmosphere interaction Model with Self-Consistent magnetic (B) and electric (E) fields, or RAM-SCB-E. With this new model, we explore, by comparing with previously employed empirical Weimer potential, the impact of using self-consistent electric fields on the modeling of storm time global electric potential distribution, plasma sheet particle injection, and the subauroral polarization streams (SAPS) which heavily rely on the coupled interplay between the inner magnetosphere and midlatitude ionosphere. We find the following phenomena in the self-consistent model: (1) The spatially localized enhancement of electric field is produced within 2.5 < L < 4 during geomagnetic active time in the dusk-premidnight sector, with a similar dynamic penetration as found in statistical observations. (2) The electric potential contours show more substantial skewing toward the postmidnight than the Weimer potential, suggesting the resistance on the particles from directly injecting toward the low-L region. (3) The proton flux indeed indicates that the plasma sheet inner boundary at the dusk-premidnight sector is located further away from the Earth than in the Weimer potential, and a "tongue" of low-energy protons extends eastward toward the dawn, leading to the Harang reversal. (4) SAPS are reproduced in the subauroral region, and their magnitude and latitudinal width are in reasonable agreement with data.

Dynamic behaviour of the silica-water-bio electrical double layer in the presence of a divalent electrolyte.

PubMed

Lowe, B M; Maekawa, Y; Shibuta, Y; Sakata, T; Skylaris, C-K; Green, N G

2017-01-25

Electronic devices are becoming increasingly used in chemical- and bio-sensing applications and therefore understanding the silica-electrolyte interface at the atomic scale is becoming increasingly important. For example, field-effect biosensors (BioFETs) operate by measuring perturbations in the electric field produced by the electrical double layer due to biomolecules binding on the surface. In this paper, explicit-solvent atomistic calculations of this electric field are presented and the structure and dynamics of the interface are investigated in different ionic strengths using molecular dynamics simulations. Novel results from simulation of the addition of DNA molecules and divalent ions are also presented, the latter of particular importance in both physiological solutions and biosensing experiments. The simulations demonstrated evidence of charge inversion, which is known to occur experimentally for divalent electrolyte systems. A strong interaction between ions and DNA phosphate groups was demonstrated in mixed electrolyte solutions, which are relevant to experimental observations of device sensitivity in the literature. The bound DNA resulted in local changes to the electric field at the surface; however, the spatial- and temporal-mean electric field showed no significant change. This result is explained by strong screening resulting from a combination of strongly polarised water and a compact layer of counterions around the DNA and silica surface. This work suggests that the saturation of the Stern layer is an important factor in determining BioFET response to increased salt concentration and provides novel insight into the interplay between ions and the EDL.

Multifunctional semiconductor micro-Hall devices for magnetic, electric, and photo-detection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gilbertson, A. M.; Cohen, L. F.; Sadeghi, Hatef

2015-12-07

We report the real-space voltage response of InSb/AlInSb micro-Hall devices to local photo-excitation, electric, and magnetic fields at room temperature using scanning probe microscopy. We show that the ultrafast generation of localised photocarriers results in conductance perturbations analogous to those produced by local electric fields. Experimental results are in good agreement with tight-binding transport calculations in the diffusive regime. The magnetic, photo, and charge sensitivity of a 2 μm wide probe are evaluated at a 10 μA bias current in the Johnson noise limit (valid at measurement frequencies > 10 kHz) to be, respectively, 500 nT/√Hz; 20 pW/√Hz (λ = 635 nm) comparable to commercial photoconductive detectors;more » and 0.05 e/√Hz comparable to that of single electron transistors. These results demonstrate the remarkably versatile sensing attributes of simple semiconductor micro-Hall devices that can be applied to a host of imaging and sensing applications.« less

Aircraft measurements of the atmospheric electrical global circuit during the period 1971-1984

NASA Technical Reports Server (NTRS)

Markson, R.

1985-01-01

This report will update an investigation of the global circuit conducted over the last 14 years through aircraft measurements of the variation of ionospheric potential and associated parameters. The data base included electric field, conductivity, and air-earth current density profiles from the tropics (25 deg N) to the Arctic (79 deg N). Almost all of the data have been obtained over the ocean to reduce noise associated with local generators, aerosols, and convection. Recently, two aircraft have been utilized to obtain, for the first time, quasi-periodic sets of simultaneous ionospheric potential (VI) soundings at remote locations and extending over time spans sufficiently long so that the universal time diurnal variation (Carnegie curve) could be observed. In additon, these measurements provided the first detection of the modulation of electric fields in the troposphere caused by the double vortex ionospheric convection pattern. Besides summarizing these measurements and comparing them to similar data obtained by other groups, this report discusses meteorological sources of error and criteria for determining if the global circuit is being measured rather than variations caused by local meteorological processes.

Electron-ion hybrid instability experiment upgrades to the Auburn Linear Experiment for Instability Studies.

PubMed

DuBois, A M; Arnold, I; Thomas, E; Tejero, E; Amatucci, W E

2013-04-01

The Auburn Linear EXperiment for Instability Studies (ALEXIS) is a laboratory plasma physics experiment used to study spatially inhomogeneous flows in a magnetized cylindrical plasma column that are driven by crossed electric (E) and magnetic (B) fields. ALEXIS was recently upgraded to include a small, secondary plasma source for a new dual source, interpenetrating plasma experiment. Using two plasma sources allows for highly localized electric fields to be made at the boundary of the two plasmas, inducing strong E × B velocity shear in the plasma, which can give rise to a regime of instabilities that have not previously been studied in ALEXIS. The dual plasma configuration makes it possible to have independent control over the velocity shear and the density gradient. This paper discusses the recent addition of the secondary plasma source to ALEXIS, as well as the plasma diagnostics used to measure electric fields and electron densities.

Jet formation at the interaction of localized waves on the free surface of dielectric liquid in a tangential electric field

NASA Astrophysics Data System (ADS)

Kochurin, E. A.; Zubarev, N. M.

2018-01-01

Nonlinear dynamics of the free surface of finite depth non-conducting fluid with high dielectric constant subjected to a strong horizontal electric field is considered. Using the conformal transformation of the region occupied by the fluid into a strip, the process of interaction of counter-propagating waves is numerically simulated. The nonlinear solitary waves on the surface can separately propagate along or against the direction of electric field without distortion. At the same time, the shape of the oppositely traveling waves can be distorted as the result of their interaction. In the problem under study, the nonlinearity leads to increasing the wave amplitudes and the duration of their interaction. This effect is inversely proportional to the fluid depth. In the shallow water limit, the tendency to the formation of a vertical liquid jet is observed.

Determinants of the electric field during transcranial direct current stimulation.

PubMed

Opitz, Alexander; Paulus, Walter; Will, Susanne; Antunes, Andre; Thielscher, Axel

2015-04-01

Transcranial direct current stimulation (tDCS) causes a complex spatial distribution of the electric current flow in the head which hampers the accurate localization of the stimulated brain areas. In this study we show how various anatomical features systematically shape the electric field distribution in the brain during tDCS. We constructed anatomically realistic finite element (FEM) models of two individual heads including conductivity anisotropy and different skull layers. We simulated a widely employed electrode montage to induce motor cortex plasticity and moved the stimulating electrode over the motor cortex in small steps to examine the resulting changes of the electric field distribution in the underlying cortex. We examined the effect of skull thickness and composition on the passing currents showing that thinner skull regions lead to higher electric field strengths. This effect is counteracted by a larger proportion of higher conducting spongy bone in thicker regions leading to a more homogenous current over the skull. Using a multiple regression model we could identify key factors that determine the field distribution to a significant extent, namely the thicknesses of the cerebrospinal fluid and the skull, the gyral depth and the distance to the anode and cathode. These factors account for up to 50% of the spatial variation of the electric field strength. Further, we demonstrate that individual anatomical factors can lead to stimulation "hotspots" which are partly resistant to electrode positioning. Our results give valuable novel insights in the biophysical foundation of tDCS and highlight the importance to account for individual anatomical factors when choosing an electrode montage. Copyright © 2015 Elsevier Inc. All rights reserved.

Particle Simulations of the Guard Electrode Effects on the Photoelectron Distribution Around an Electric Field Sensor

NASA Astrophysics Data System (ADS)

Miyake, Y.; Usui, H.; Kojima, H.

2010-12-01

In tenuous space plasma environment, photoelectrons emitted due to solar illumination produce a high-density photoelectron cloud localized in the vicinity of a spacecraft body and an electric field sensor. The photoelectron current emitted from the sensor has also received considerable attention because it becomes a primary factor in determining floating potentials of the sunlit spacecraft and sensor bodies. Considering the fact that asymmetric photoelectron distribution between sunlit and sunless sides of the spacecraft occasionally causes a spurious sunward electric field, we require quantitative evaluation of the photoelectron distribution around the spacecraft and its influence on electric field measurements by means of a numerical approach. In the current study, we applied the Particle-in-Cell plasma simulation to the analysis of the photoelectron environment around spacecraft. By using the PIC modeling, we can self-consistently consider the plasma kinetics. This enables us to simulate the formation of the photoelectron cloud as well as the spacecraft and sensor charging in a self-consistent manner. We report the progress of an analysis on photoelectron environment around MEFISTO, which is an electric field instrument for the BepiColombo/MMO spacecraft to Mercury’s magnetosphere. The photoelectron guard electrode is a key technology for ensuring an optimum photoelectron environment. We show some simulation results on the guard electrode effects on surrounding photoelectrons and discuss a guard operation condition for producing the optimum photoelectron environment. We also deal with another important issue, that is, how the guard electrode can mitigate an undesirable influence of an asymmetric photoelectron distribution on electric field measurements.

Interhemispheric Poynting Flux Associated with Postsunset Equatorial Plasma Depletions as Observed by Swarm

NASA Astrophysics Data System (ADS)

Rodriguez-Zuluaga, J.; Stolle, C.; Park, J.

2017-12-01

By using simultaneous measurements of electric and magnetic fields gathered by the Swarm constellation, the direction of both Poynting flux and field-aligned currents (FACs) associated with topside equatorial plasma depletions (EPDs) is derived. Contrary to expectations, FACs are found to flow at the walls of EPDs from one magnetic hemisphere to the other rather than flowing away from and towards the dip equator, as has been suggested so far. In turn, an interhemispheric Poynting flux is observed to flow into the E region of the hemisphere with larger ionospheric conductivity when eastward polarisation electric field is present across the depletion. However, also westward electric field is often observed but without a change in the FACs orientation, that would preserve the direction of the Poynting flux. The interhemispheric flows show seasonal, longitudinal and local time dependence. Empirical models are used to substantiate the conclusions of this study. After these new findings, the question about the location of a generator and load in terms of electromagnetic energy flow remains open.

Probing the radio emission from air showers with polarization measurements

NASA Astrophysics Data System (ADS)

Aab, A.; Abreu, P.; Aglietta, M.; Ahlers, M.; Ahn, E. J.; Albuquerque, I. F. M.; Allekotte, I.; Allen, J.; Allison, P.; Almela, A.; Alvarez Castillo, J.; Alvarez-Muñiz, J.; Alves Batista, R.; Ambrosio, M.; Aminaei, A.; Anchordoqui, L.; Andringa, S.; Antičić, T.; Aramo, C.; Arqueros, F.; Asorey, H.; Assis, P.; Aublin, J.; Ave, M.; Avenier, M.; Avila, G.; Badescu, A. M.; Barber, K. B.; Bardenet, R.; Bäuml, J.; Baus, C.; Beatty, J. J.; Becker, K. H.; Bellido, J. A.; BenZvi, S.; Berat, C.; Bertou, X.; Biermann, P. L.; Billoir, P.; Blanco, F.; Blanco, M.; Bleve, C.; Blümer, H.; Boháčová, M.; Boncioli, D.; Bonifazi, C.; Bonino, R.; Borodai, N.; Brack, J.; Brancus, I.; Brogueira, P.; Brown, W. C.; Buchholz, P.; Bueno, A.; Buscemi, M.; Caballero-Mora, K. S.; Caccianiga, B.; Caccianiga, L.; Candusso, M.; Caramete, L.; Caruso, R.; Castellina, A.; Cataldi, G.; Cazon, L.; Cester, R.; Cheng, S. H.; Chiavassa, A.; Chinellato, J. A.; Chudoba, J.; Cilmo, M.; Clay, R. W.; Cocciolo, G.; Colalillo, R.; Collica, L.; Coluccia, M. R.; Conceição, R.; Contreras, F.; Cooper, M. J.; Coutu, S.; Covault, C. E.; Criss, A.; Cronin, J.; Curutiu, A.; Dallier, R.; Daniel, B.; Dasso, S.; Daumiller, K.; Dawson, B. R.; de Almeida, R. M.; De Domenico, M.; de Jong, S. J.; De La Vega, G.; de Mello Junior, W. J. M.; de Mello Neto, J. R. T.; De Mitri, I.; de Souza, V.; de Vries, K. D.; del Peral, L.; Deligny, O.; Dembinski, H.; Dhital, N.; Di Giulio, C.; Di Matteo, A.; Diaz, J. C.; Díaz Castro, M. L.; Diep, P. N.; Diogo, F.; Dobrigkeit, C.; Docters, W.; D'Olivo, J. C.; Dong, P. N.; Dorofeev, A.; dos Anjos, J. C.; Dova, M. T.; Ebr, J.; Engel, R.; Erdmann, M.; Escobar, C. O.; Espadanal, J.; Etchegoyen, A.; Facal San Luis, P.; Falcke, H.; Fang, K.; Farrar, G.; Fauth, A. C.; Fazzini, N.; Ferguson, A. P.; Fick, B.; Figueira, J. M.; Filevich, A.; Filipčič, A.; Foerster, N.; Fox, B. D.; Fracchiolla, C. E.; Fraenkel, E. D.; Fratu, O.; Fröhlich, U.; Fuchs, B.; Gaior, R.; Gamarra, R. F.; Gambetta, S.; García, B.; Garcia Roca, S. T.; Garcia-Gamez, D.; Garcia-Pinto, D.; Garilli, G.; Gascon Bravo, A.; Gemmeke, H.; Ghia, P. L.; Giammarchi, M.; Giller, M.; Gitto, J.; Glaser, C.; Glass, H.; Gomez Albarracin, F.; Gómez Berisso, M.; Gómez Vitale, P. F.; Gonçalves, P.; Gonzalez, J. G.; Gookin, B.; Gorgi, A.; Gorham, P.; Gouffon, P.; Grebe, S.; Griffith, N.; Grillo, A. F.; Grubb, T. D.; Guardincerri, Y.; Guarino, F.; Guedes, G. P.; Hansen, P.; Harari, D.; Harrison, T. A.; Harton, J. L.; Haungs, A.; Hebbeker, T.; Heck, D.; Herve, A. E.; Hill, G. C.; Hojvat, C.; Hollon, N.; Holt, E.; Homola, P.; Hörandel, J. R.; Horvath, P.; Hrabovský, M.; Huber, D.; Huege, T.; Insolia, A.; Isar, P. G.; Jansen, S.; Jarne, C.; Josebachuili, M.; Kadija, K.; Kambeitz, O.; Kampert, K. H.; Karhan, P.; Kasper, P.; Katkov, I.; Kégl, B.; Keilhauer, B.; Keivani, A.; Kemp, E.; Kieckhafer, R. M.; Klages, H. O.; Kleifges, M.; Kleinfeller, J.; Knapp, J.; Krause, R.; Krohm, N.; Krömer, O.; Kruppke-Hansen, D.; Kuempel, D.; Kunka, N.; La Rosa, G.; LaHurd, D.; Latronico, L.; Lauer, R.; Lauscher, M.; Lautridou, P.; Le Coz, S.; Leão, M. S. A. B.; Lebrun, D.; Lebrun, P.; Leigui de Oliveira, M. A.; Letessier-Selvon, A.; Lhenry-Yvon, I.; Link, K.; López, R.; Lopez Agüera, A.; Louedec, K.; Lozano Bahilo, J.; Lu, L.; Lucero, A.; Ludwig, M.; Lyberis, H.; Maccarone, M. C.; Malacari, M.; Maldera, S.; Maller, J.; Mandat, D.; Mantsch, P.; Mariazzi, A. G.; Marin, V.; Mariş, I. C.; Marquez Falcon, H. R.; Marsella, G.; Martello, D.; Martin, L.; Martinez, H.; Martínez Bravo, O.; Martraire, D.; Masías Meza, J. J.; Mathes, H. J.; Matthews, J.; Matthews, J. A. J.; Matthiae, G.; Maurel, D.; Maurizio, D.; Mayotte, E.; Mazur, P. O.; Medina, C.; Medina-Tanco, G.; Melissas, M.; Melo, D.; Menichetti, E.; Menshikov, A.; Messina, S.; Meyhandan, R.; Mićanović, S.; Micheletti, M. I.; Middendorf, L.; Minaya, I. A.; Miramonti, L.; Mitrica, B.; Molina-Bueno, L.; Mollerach, S.; Monasor, M.; Monnier Ragaigne, D.; Montanet, F.; Morales, B.; Morello, C.; Moreno, J. C.; Mostafá, M.; Moura, C. A.; Muller, M. A.; Müller, G.; Münchmeyer, M.; Mussa, R.; Navarra, G.; Navarro, J. L.; Navas, S.; Necesal, P.; Nellen, L.; Nelles, A.; Neuser, J.; Nhung, P. T.; Niechciol, M.; Niemietz, L.; Niggemann, T.; Nitz, D.; Nosek, D.; Nožka, L.; Oehlschläger, J.; Olinto, A.; Oliveira, M.; Ortiz, M.; Pacheco, N.; Pakk Selmi-Dei, D.; Palatka, M.; Pallotta, J.; Palmieri, N.; Parente, G.; Parra, A.; Pastor, S.; Paul, T.; Pech, M.; PeÂķala, J.; Pelayo, R.; Pepe, I. M.; Perrone, L.; Pesce, R.; Petermann, E.; Petrera, S.; Petrolini, A.; Petrov, Y.; Piegaia, R.; Pierog, T.; Pieroni, P.; Pimenta, M.; Pirronello, V.; Platino, M.; Plum, M.; Pontz, M.; Porcelli, A.; Preda, T.; Privitera, P.; Prouza, M.; Quel, E. J.; Querchfeld, S.; Quinn, S.; Rautenberg, J.; Ravel, O.; Ravignani, D.; Revenu, B.; Ridky, J.; Riggi, S.; Risse, M.; Ristori, P.; Rivera, H.; Rizi, V.; Roberts, J.; Rodrigues de Carvalho, W.; Rodriguez Cabo, I.; Rodriguez Fernandez, G.; Rodriguez Martino, J.; Rodriguez Rojo, J.; Rodríguez-Frías, M. D.; Ros, G.; Rosado, J.; Rossler, T.; Roth, M.; Rouillé-d'Orfeuil, B.; Roulet, E.; Rovero, A. C.; Rühle, C.; Saffi, S. J.; Saftoiu, A.; Salamida, F.; Salazar, H.; Salesa Greus, F.; Salina, G.; Sánchez, F.; Sanchez-Lucas, P.; Santo, C. E.; Santos, E.; Santos, E. M.; Sarazin, F.; Sarkar, B.; Sarmento, R.; Sato, R.; Scharf, N.; Scherini, V.; Schieler, H.; Schiffer, P.; Schmidt, A.; Scholten, O.; Schoorlemmer, H.; Schovánek, P.; Schröder, F. G.; Schulz, A.; Schulz, J.; Sciutto, S. J.; Scuderi, M.; Segreto, A.; Settimo, M.; Shadkam, A.; Shellard, R. C.; Sidelnik, I.; Sigl, G.; Sima, O.; Śmiałkowski, A.; Šmída, R.; Snow, G. R.; Sommers, P.; Sorokin, J.; Spinka, H.; Squartini, R.; Srivastava, Y. N.; Stanič, S.; Stapleton, J.; Stasielak, J.; Stephan, M.; Straub, M.; Stutz, A.; Suarez, F.; Suomijärvi, T.; Supanitsky, A. D.; Šuša, T.; Sutherland, M. S.; Swain, J.; Szadkowski, Z.; Szuba, M.; Tapia, A.; Tartare, M.; Taşcǎu, O.; Thao, N. T.; Tiffenberg, J.; Timmermans, C.; Tkaczyk, W.; Todero Peixoto, C. J.; Toma, G.; Tomankova, L.; Tomé, B.; Tonachini, A.; Torralba Elipe, G.; Torres Machado, D.; Travnicek, P.; Tridapalli, D. B.; Trovato, E.; Tueros, M.; Ulrich, R.; Unger, M.; Valdés Galicia, J. F.; Valiño, I.; Valore, L.; van Aar, G.; van den Berg, A. M.; van Velzen, S.; van Vliet, A.; Varela, E.; Vargas Cárdenas, B.; Varner, G.; Vázquez, J. R.; Vázquez, R. A.; Veberič, D.; Verzi, V.; Vicha, J.; Videla, M.; Villaseñor, L.; Wahlberg, H.; Wahrlich, P.; Wainberg, O.; Walz, D.; Watson, A. A.; Weber, M.; Weidenhaupt, K.; Weindl, A.; Werner, F.; Westerhoff, S.; Whelan, B. J.; Widom, A.; Wieczorek, G.; Wiencke, L.; Wilczyńska, B.; Wilczyński, H.; Will, M.; Williams, C.; Winchen, T.; Wundheiler, B.; Wykes, S.; Yamamoto, T.; Yapici, T.; Younk, P.; Yuan, G.; Yushkov, A.; Zamorano, B.; Zas, E.; Zavrtanik, D.; Zavrtanik, M.; Zaw, I.; Zepeda, A.; Zhou, J.; Zhu, Y.; Zimbres Silva, M.; Ziolkowski, M.; Pierre Auger Collaboration

2014-03-01

The emission of radio waves from air showers has been attributed to the so-called geomagnetic emission process. At frequencies around 50 MHz this process leads to coherent radiation which can be observed with rather simple setups. The direction of the electric field induced by this emission process depends only on the local magnetic field vector and on the incoming direction of the air shower. We report on measurements of the electric field vector where, in addition to this geomagnetic component, another component has been observed that cannot be described by the geomagnetic emission process. The data provide strong evidence that the other electric field component is polarized radially with respect to the shower axis, in agreement with predictions made by Askaryan who described radio emission from particle showers due to a negative charge excess in the front of the shower. Our results are compared to calculations which include the radiation mechanism induced by this charge-excess process.

Electron avalanche structure determined by random walk theory

NASA Technical Reports Server (NTRS)

Englert, G. W.

1973-01-01

A self-consistent avalanche solution which accounts for collective long range Coulomb interactions as well as short range elastic and inelastic collisions between electrons and background atoms is made possible by a random walk technique. Results show that the electric field patterns in the early formation stages of avalanches in helium are close to those obtained from theory based on constant transport coefficients. Regions of maximum and minimum induced electrostatic potential phi are located on the axis of symmetry and within the volume covered by the electron swarm. As formation time continues, however, the region of minimum phi moves to slightly higher radii and the electric field between the extrema becomes somewhat erratic. In the intermediate formation periods the avalanche growth is slightly retarded by the high concentration of ions in the tail which oppose the external electric field. Eventually the formation of ions and electrons in the localized regions of high field strength more than offset this effect causing a very abrupt increase in avalanche growth.

Parameters of a collisional radio-frequency sheath and dust characteristics resulting from the microparticle levitation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yaroshenko, V. V.; Antonova, T.; Thomas, H. M.

2009-10-15

The screening length, the time-average electric field, and the particle charge as well as the local vertical gradients of these quantities are determined experimentally within a sheath of a capacitively coupled rf, 13.56 MHz, discharge at enhanced argon gas pressures of 30, 55, and 100 Pa. The parameters are derived directly from comparative measurements of levitation positions of the particles of different sizes and variations in the levitation heights caused by formation of new dust layers. The electrostatic effect of the horizontally extended dust layers on the sheath electric field is investigated.

Individual analysis of inter and intragrain defects in electrically characterized polycrystalline silicon nanowire TFTs by multicomponent dark-field imaging based on nanobeam electron diffraction two-dimensional mapping

NASA Astrophysics Data System (ADS)

Asano, Takanori; Takaishi, Riichiro; Oda, Minoru; Sakuma, Kiwamu; Saitoh, Masumi; Tanaka, Hiroki

2018-04-01

We visualize the grain structures for individual nanosized thin film transistors (TFTs), which are electrically characterized, with an improved data processing technique for the dark-field image reconstruction of nanobeam electron diffraction maps. Our individual crystal analysis gives the one-to-one correspondence of TFTs with different grain boundary structures, such as random and coherent boundaries, to the characteristic degradations of ON-current and threshold voltage. Furthermore, the local crystalline uniformity inside a single grain is detected as the difference in diffraction intensity distribution.

Formation of Singularities at the Interface of Liquid Dielectrics in a Horizontal Electric Field in the Presence of Tangential Velocity Discontinuity

NASA Astrophysics Data System (ADS)

Zubarev, N. M.; Kochurin, E. A.

2018-03-01

Nonlinear dynamics of the interface of dielectric liquids under the conditions of suppression of the Kelvin-Helmholz instability by a tangential electric field has been investigated. Two broad classes of exact analytical solutions to the equations of motion describing the evolution of spatially localized and periodic interface perturbations have been found. Both classes of solutions tend to the formation of strong singularities: interface discontinuities with formally infinite amplitudes. The discontinuity sign is determined by the sign of liquid velocity jump at the interface.

Avoiding the side effects of electric current pulse application to electroporated cells in disposable small volume cuvettes assures good cell survival.

PubMed

Grys, Maciej; Madeja, Zbigniew; Korohoda, Włodzimierz

2017-01-01

The harmful side effects of electroporation to cells due to local changes in pH, the appearance of toxic electrode products, temperature increase, and the heterogeneity of the electric field acting on cells in the cuvettes used for electroporation were observed and discussed in several laboratories. If cells are subjected to weak electric fields for prolonged periods, for example in experiments on cell electrophoresis or galvanotaxis the same effects are seen. In these experiments investigators managed to reduce or eliminate the harmful side effects of electric current application. For the experiments, disposable 20 μl cuvettes with two walls made of dialysis membranes were constructed and placed in a locally focused electric field at a considerable distance from the electrodes. Cuvettes were mounted into an apparatus for horizontal electrophoresis and the cells were subjected to direct current electric field (dcEF) pulses from a commercial pulse generator of exponentially declining pulses and from a custom-made generator of double and single rectangular pulses. More than 80% of the electroporated cells survived the dcEF pulses in both systems. Side effects related to electrodes were eliminated in both the flow through the dcEF and in the disposable cuvettes placed in the focused dcEFs. With a disposable cuvette system, we also confirmed the sensitization of cells to a dcEF using procaine by observing the loading of AT2 cells with calceine and using a square pulse generator, applying 50 ms single rectangular pulses. We suggest that the same methods of avoiding the side effects of electric current pulse application as in cell electrophoresis and galvanotaxis should also be used for electroporation. This conclusion was confirmed in our electroporation experiments performed in conditions assuring survival of over 80% of the electroporated cells. If the amplitude, duration, and shape of the dcEF pulse are known, then electroporation does not depend on the type of pulse generator. This knowledge of the characteristics of the pulse assures reproducibility of electroporation experiments using different equipment.

3D PIC-MCC simulations of positive streamers in air gaps

NASA Astrophysics Data System (ADS)

Jiang, M.; Li, Y.; Wang, H.; Liu, C.

2017-10-01

Simulation of positive streamer evolution is important for understanding the microscopic physical process in discharges. Simulations described in this paper are done using a 3D Particle-In-Cell, Monte-Carlo-Collision code with photoionization. Three phases of a positive streamer evolution, identified as initiation, propagation, and branching are studied during simulations. A homogeneous electric field is applied between parallel-flat electrodes forming a millimeter air gap to make simulations and analysis more simple and general. Free electrons created by the photoionization process determine initiation, propagation, and branching of the streamers. Electron avalanches form a positive streamer tip, when the space charge of ions at the positive tip dominates the local electric field. The propagation of the positive tip toward a cathode is the result of combinations of the positive tip and secondary avalanches ahead of it. A curved feather-like channel is formed without obvious branches when the electric field between electrodes is 50 kV/cm. However, a channel is formed with obvious branches when the electric field increases up to 60 kV/cm. In contrast to the branches around a sharp needle electrode, branches near the flat anode are formed at a certain distance away from it. Simulated parameters of the streamer such as diameter, maximum electric field, propagation velocity, and electron density at the streamer tip are in a good agreement with those published earlier.

Equatorial Plasma Bubble Development and Dynamics, and Sporadic E Layer Structuring, under Storm Time Electric Fields.

NASA Astrophysics Data System (ADS)

Abdu, M. A.; Batista, I. S.; Sobral, J. H. A.; Souza, J.; Santos, A.

2016-12-01

Equatorial and low - midlatitude ionospheric plasma dynamics and related phenomenology can be severely affected by disturbance electric fields associated with magnetic storms. Penetration electric fields, of under-shielding or over-shielding types, can cause anomalous development of plasma bubbles even during their non-occurrence season, or can lead to suppression of their normal development. Depending upon the longitude sector and local time, large relative changes in the Hall and Pedersen conductivities can occur due to storm induced extra E layer ionization or modifications in F layer plasma density, as a result of which the penetration electric fields may produce, among other effects, (1) plasma bubble zonal drift velocity reversal to westward, (2) large/abnormal F layer plasma uplift, (3) sporadic E layer disruption or its formation with instabilities. Beside these effects, the equatorial ionization anomaly is known to suffer latitudinal expansion and retraction. In this paper we will discuss some outstanding response features of the low altitude ionosphere under disturbance electric field as diagnosed by Digisondes, radars and optical imagers in the South American longitude sector, a region that is strongly influenced by the South Atlantic Magnetic anomaly (SAMA). The results will be discussed in the context of satellite observations (from C/NOFS) and modeling results based on SUPIM simulation of a realistic low latitude ionosphere.

Conditions for Destabilizing Pickering emulsions using external electric fields

NASA Astrophysics Data System (ADS)

Hwang, Kyuho; Singh, Pushpendra; Aubry, Nadine

2009-11-01

Fine particles are readily adsorbed at fluid-fluid interfaces, and can be used as stabilizers in emulsion technology by preventing adjacent drops from coalescing with each other. We investigate a new technique to destabilize such emulsions, or Pickering emulsions, by applying an external electric field. Experiments show that the latter has two effects: (i) the drops elongate in the direction of the electric field, (ii) the local particle density varies on the drop surface due to the dielectrophoretic (DEP) force acting on the particles. It is shown that the latter is the dominant factor in the destabilization process. Particularly, the success of the method depends on the values of certain dimensionless parameters; specifically, the ratio of the work done by the dielectrophoretic force must be larger than the work done by the buoyant force. Moreover, drops do not coalesce through the regions where the particles locally cluster, whether those are gathered at the poles or at the equator of the drops. As particles move, particle-free openings form on the drop's surface, which allow for adjacent drops to merge. This process takes place even if the particles are fully packed on the drops' surfaces as particles get ejected from the clustering areas due to a buckling phenomenon.

Imaging ac losses in superconducting films via scanning Hall probe microscopy

NASA Astrophysics Data System (ADS)

Dinner, Rafael B.; Moler, Kathryn A.; Feldmann, D. Matthew; Beasley, M. R.

2007-04-01

Various local probes have been applied to understanding current flow through superconducting films, which are often surprisingly inhomogeneous. Here, we show that magnetic imaging allows quantitative reconstruction of both current density J and electric field E resolved in time and space in a film carrying subcritical ac current. Current reconstruction entails inversion of the Biot-Savart law, while electric fields are reconstructed using Faraday’s law. We describe the corresponding numerical procedures, largely adapting existing work to the case of a strip carrying ac current, but including other methods of obtaining the complete electric field from the inductive portion determined by Faraday’s law. We also delineate the physical requirements behind the mathematical transformations. We then apply the procedures to images of a strip of YBa2Cu3O7-δ carrying an ac current at 400Hz . Our scanning Hall probe microscope produces a time series of magnetic images of the strip with 1μm spatial resolution and 25μs time resolution. Combining the reconstructed J and E , we obtain a complete characterization including local critical current density, E-J curves, and power losses. This analysis has a range of applications from fundamental studies of vortex dynamics to practical coated conductor development.

Van Allen Probes Measurements of Energetic Particle Deep Penetration Into the Low L Region (L < 4) During the Storm on 8 April 2016

NASA Astrophysics Data System (ADS)

Zhao, H.; Baker, D. N.; Califf, S.; Li, X.; Jaynes, A. N.; Leonard, T.; Kanekal, S. G.; Blake, J. B.; Fennell, J. F.; Claudepierre, S. G.; Turner, D. L.; Reeves, G. D.; Spence, H. E.

2017-12-01

Using measurements from the Van Allen Probes, a penetration event of tens to hundreds of keV electrons and tens of keV protons into the low L shells (L < 4) is studied. Timing and magnetic local time (MLT) differences of energetic particle deep penetration are unveiled and underlying physical processes are examined. During this event, both proton and electron penetrations are MLT asymmetric. The observed MLT difference of proton penetration is consistent with convection of plasma sheet protons, suggesting enhanced convection during geomagnetic active times to be the cause of energetic proton deep penetration during this event. The observed MLT difference of tens to hundreds of keV electron penetration is completely different from tens of keV protons and cannot be well explained by inward radial diffusion, convection of plasma sheet electrons, or transport of trapped electrons by enhanced convection electric field represented by the Volland-Stern model or a uniform dawn-dusk electric field model based on the electric field measurements. It suggests that the underlying physical mechanism responsible for energetic electron deep penetration, which is very important for fully understanding energetic electron dynamics in the low L shells, should be MLT localized.

Neutron spectroscopic study of crystalline electric field excitations in stoichiometric and lightly stuffed Yb 2 Ti 2 O 7

DOE PAGES

Gaudet, J.; Maharaj, D. D.; Sala, G.; ...

2015-10-27

Time-of-flight neutron spectroscopy has been used to determine the crystalline electric field Hamiltonian, eigenvalues and eigenvectors appropriate to the J=7/2 Yb 3+ ion in the candidate quantum spin ice pyrochlore magnet Yb 2Ti 2O 7. The precise ground state of this exotic, geometrically frustrated magnet is known to be sensitive to weak disorder associated with the growth of single crystals from the melt. Such materials display weak “stuffing,” wherein a small proportion, approximately 2%, of the nonmagnetic Ti 4+ sites are occupied by excess Yb 3+. We have carried out neutron spectroscopic measurements on a stoichiometric powder sample of Ybmore » 2Ti 2O 7, as well as a crushed single crystal with weak stuffing and an approximate composition of Yb 2+xTi 2–xO 7+y with x = 0.046. All samples display three crystalline electric field transitions out of the ground state, and the ground state doublet itself is identified as primarily composed of m J = ±1/2, as expected. However, stuffing at low temperatures in Yb 2+xTi 2–xO 7+y induces a similar finite crystalline electric field lifetime as is induced in stoichiometric Yb 2Ti 2O 7 by elevated temperature. In conclusion, an extended strain field exists about each local “stuffed” site, which produces a distribution of random crystalline electric field environments in the lightly stuffed Yb 2+xTi 2–xO 7+y, in addition to producing a small fraction of Yb ions in defective environments with grossly different crystalline electric field eigenvalues and eigenvectors.« less

Computational dosimetry for grounded and ungrounded human models due to contact current

NASA Astrophysics Data System (ADS)

Chan, Kwok Hung; Hattori, Junya; Laakso, Ilkka; Hirata, Akimasa; Taki, Masao

2013-08-01

This study presents the computational dosimetry of contact currents for grounded and ungrounded human models. The uncertainty of the quasi-static (QS) approximation of the in situ electric field induced in a grounded/ungrounded human body due to the contact current is first estimated. Different scenarios of cylindrical and anatomical human body models are considered, and the results are compared with the full-wave analysis. In the QS analysis, the induced field in the grounded cylindrical model is calculated by the QS finite-difference time-domain (QS-FDTD) method, and compared with the analytical solution. Because no analytical solution is available for the grounded/ungrounded anatomical human body model, the results of the QS-FDTD method are then compared with those of the conventional FDTD method. The upper frequency limit for the QS approximation in the contact current dosimetry is found to be 3 MHz, with a relative local error of less than 10%. The error increases above this frequency, which can be attributed to the neglect of the displacement current. The QS or conventional FDTD method is used for the dosimetry of induced electric field and/or specific absorption rate (SAR) for a contact current injected into the index finger of a human body model in the frequency range from 10 Hz to 100 MHz. The in situ electric fields or SAR are compared with the basic restrictions in the international guidelines/standards. The maximum electric field or the 99th percentile value of the electric fields appear not only in the fat and muscle tissues of the finger, but also around the wrist, forearm, and the upper arm. Some discrepancies are observed between the basic restrictions for the electric field and SAR and the reference levels for the contact current, especially in the extremities. These discrepancies are shown by an equation that relates the current density, tissue conductivity, and induced electric field in the finger with a cross-sectional area of 1 cm2.

Double layer-like structures in the core of an argon helicon plasma source with uniform magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Umair Siddiqui, M., E-mail: musiddiqui@wisc.edu; Hershkowitz, Noah

2014-02-15

A hot (T{sub e} ≈ 10 eV) electron population is observed in the core of a 3 mTorr argon helicon plasma source at 500 W RF power and 900 G uniform axial magnetic field strength, 12 cm from the edge of the helicon antenna. A double layer-like structure consisting of a localized axial electric field of approximately 8 V/cm over 1–2 cm is observed adjacent to the hot electron population. The potential step generated by the electric field is shown to be large enough to trap the hot electrons. To our knowledge this is the first observation of these structures in the core of amore » helicon discharge.« less

Pulsed hybrid field emitter

DOEpatents

Sampayan, Stephen E.

1998-01-01

A hybrid emitter exploits the electric field created by a rapidly depoled ferroelectric material. Combining the emission properties of a planar thin film diamond emitter with a ferroelectric alleviates the present technological problems associated with both types of emitters and provides a robust, extremely long life, high current density cathode of the type required by emerging microwave power generation, accelerator technology and display applications. This new hybrid emitter is easy to fabricate and not susceptible to the same failures which plague microstructure field emitter technology. Local electrode geometries and electric field are determined independently from those for optimum transport and brightness preservation. Due to the large amount of surface charge created on the ferroelectric, the emitted electrons have significant energy, thus eliminating the requirement for specialized phosphors in emissive flat-panel displays.

Pulsed hybrid field emitter

DOEpatents

Sampayan, S.E.

1998-03-03

A hybrid emitter exploits the electric field created by a rapidly depoled ferroelectric material. Combining the emission properties of a planar thin film diamond emitter with a ferroelectric alleviates the present technological problems associated with both types of emitters and provides a robust, extremely long life, high current density cathode of the type required by emerging microwave power generation, accelerator technology and display applications. This new hybrid emitter is easy to fabricate and not susceptible to the same failures which plague microstructure field emitter technology. Local electrode geometries and electric field are determined independently from those for optimum transport and brightness preservation. Due to the large amount of surface charge created on the ferroelectric, the emitted electrons have significant energy, thus eliminating the requirement for specialized phosphors in emissive flat-panel displays. 11 figs.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shao, Jiahang; Antipov, Sergey P.; Baryshev, Sergey V.

Field emission from a solid metal surface has been continuously studied for a century over macroscopic to atomic scales. It is general knowledge that, other than the surface properties, the emitted current is governed solely by the applied electric field. A pin cathode has been used to study the dependence of field emission on stored energy in an L-band rf gun. The stored energy was changed by adjusting the axial position (distance between the cathode base and the gun back surface) of the cathode while the applied electric field on the cathode tip is kept constant. Avery strong correlation ofmore » the field-emission current with the stored energy has been observed. While eliminating all possible interfering sources, an enhancement of the current by a factor of 5 was obtained as the stored energy was increased by a factor of 3. It implies that under certain circumstances a localized field emission may be significantly altered by the global parameters in a system.« less

Investigation of Electric and Self-Generated Magnetic Fields in Implosion Experiments on OMEGA

NASA Astrophysics Data System (ADS)

Igumenshchev, I. V.; Nilson, P. M.; Goncharov, V. N.; Li, C. K.; Zylstra, A. B.; Petrasso, R. D.

2013-10-01

Electric and self-generated magnetic fields in direct-drive implosion experiments on the OMEGA laser were investigated using proton radiography. The experiments use plastic-shell targets with various surface defects (glue spot, wire, and stalk mount) to seed perturbations and generate localized electromagnetic fields at the ablation surface and in the plasma corona surrounding the targets. Proton radiographs show features from these perturbations and quasi-spherical multiple shell structures around the capsules at earlier times of implosions (up to ~700 ps for a 1-ns laser pulse) indicating the development of the fields. Two-dimensional magnetohydrodynamic simulations of these experiments predict the growth of magnetic fields up to several MG. The simulated distributions of electromagnetic fields were used to produce proton images, which show good agreement with experimental radiographs. This material is based upon work supported by the Department of Energy National Nuclear Security Administration under Award Number DE-NA0001944.

Dielectrophoresis of Cells

PubMed Central

Pohl, Herbert A.; Crane, Joe S.

1971-01-01

Dielectrophoresis, the motion produced by the action of nonuniform electric field upon a neutral object, is shown to be a simple and useful technique for the study of cellular organisms. In the present study of yeast (Saccharomyces cerevisiae) using a simple pin-pin electrode system of platinum and high-frequency alternating fields, one observes that the collectability of cells at the electrode tip, i.e. at the region of highest field strength, depends upon physical parameters such as field strength, field uniformity, frequency, cell concentration, suspension conductivity, and time of collection. The yield of cells collected is also observed to depend upon biological factors such as colony age, thermal treatment of the cells, and chemical poisons, but not upon irradiation with ultraviolet light. Several interesting side effect phenomena coincident with nonuniform electric field conditions were observed, including stirring (related to “jet” effects at localized electrode sites), discontinuous repulsions, and cellular rotation which was found to be frequency dependent. ImagesFIGURE 2 PMID:5132497

Sondrestrom radar measurements of the reconnection electric field

NASA Technical Reports Server (NTRS)

De La Beaujardiere, O.; Lyons, L. R.; Friis-Christensen, E.

1991-01-01

The possibility of using Sondrestrom incoherent radar scatter to estimate the rate of solar-wind energy transfer is examined by using plasma-velocity measurements in the separatrix reference frame. The separatrix is the boundary between open and closed field lines, and its orientation is deduced from all-sky images. The radar observations are used to determine the separatrix location and the ionospheric plasma drift. Measurements of the reconnection electric field in the midnight sector for one night are taken, revealing that the field is less than 15 mV/m during the time of local polar-cap extension. During polar-cap contraction the field range is 30-40 mV/m, and these periods correspond to substorm expansive phases. The limitations associated with measuring ionospheric plasma drift, the boundary orientation, and boundary location are enumerated. The measurements in the experimental case demonstrate the possibility of plasma transfer from closed to open field lines.

Interface Magnetoelectric Coupling in Co/Pb(Zr,Ti)O3.

PubMed

Vlašín, Ondřej; Jarrier, Romain; Arras, Rémi; Calmels, Lionel; Warot-Fonrose, Bénédicte; Marcelot, Cécile; Jamet, Matthieu; Ohresser, Philippe; Scheurer, Fabrice; Hertel, Riccardo; Herranz, Gervasi; Cherifi-Hertel, Salia

2016-03-23

Magnetoelectric coupling at multiferroic interfaces is a promising route toward the nonvolatile electric-field control of magnetization. Here, we use optical measurements to study the static and dynamic variations of the interface magnetization induced by an electric field in Co/PbZr0.2Ti0.8O3 (Co/PZT) bilayers at room temperature. The measurements allow us to identify different coupling mechanisms. We further investigate the local electronic and magnetic structure of the interface by means of transmission electron microscopy, soft X-ray magnetic circular dichroism, and density functional theory to corroborate the coupling mechanism. The measurements demonstrate a mixed linear and quadratic optical response to the electric field, which results from a magneto-electro-optical effect. We propose a decomposition method of the optical signal to discriminate between different components involved in the electric field-induced polarization rotation of the reflected light. This allows us to extract a signal that we can ascribe to interface magnetoelectric coupling. The associated surface magnetization exhibits a clear hysteretic variation of odd symmetry with respect to the electric field and nonzero remanence. The interface coupling is remarkably stable over a wide frequency range (1-50 kHz), and the application of a bias magnetic field is not necessary for the coupling to occur. These results show the potential of exploiting interface coupling with the prospect of optimizing the performance of magnetoelectric memory devices in terms of stability, as well as fast and dissipationless operation.

Enhanced cell trapping throughput using DC-biased AC electric field in a dielectrophoresis-based fluidic device with densely packed silica beads.

PubMed

Lewpiriyawong, Nuttawut; Xu, Guolin; Yang, Chun

2018-03-01

This paper presents the use of DC-biased AC electric field for enhancing cell trapping throughput in an insulator-based dielectrophoretic (iDEP) fluidic device with densely packed silica beads. Cell suspension is carried through the iDEP device by a pressure-driven flow. Under an applied DC-biased AC electric field, DEP trapping force is produced as a result of non-uniform electric field induced by the gap of electrically insulating silica beads packed between two mesh electrodes that allow both fluid and cells to pass through. While the AC component is mainly to control the magnitude of DEP trapping force, the DC component generates local electroosmotic (EO) flow in the cavity between the beads and the EO flow can be set to move along or against the main pressure-driven flow. Our experimental and simulation results show that desirable trapping is achieved when the EO flow direction is along (not against) the main flow direction. Using our proposed DC-biased AC field, the device can enhance the trapping throughput (in terms of the flowrate of cell suspension) up to five times while yielding almost the same cell capture rates as compared to the pure AC field case. Additionally, the device was demonstrated to selectively trap dead yeast cells from a mixture of flowing live and dead yeast cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Dependence of field-aligned electron precipitation on season, altitude and pitch angle

NASA Technical Reports Server (NTRS)

Berko, F. W.; Hoffman, R. A.

1973-01-01

The occurrence of field-aligned 2.3 keV electron precipitation was examined by using data from more than 7500 orbits of the polar-orbiting satellite, OGO-4. The frequency of occurrence of field aligned precipitation was highest at actual pitch angles between 7 and 10 deg, being highest in the winter months, at highest satellite altitudes. Acceleration by a localized parallel electric field established by electrostatic charge layers is proposed to explain particle observations.

Surface enhanced Raman scattering of amino acids assisted by gold nanoparticles and Gd(3+) ions.

PubMed

López-Neira, Juan Pablo; Galicia-Hernández, José Mario; Reyes-Coronado, Alejandro; Pérez, Elías; Castillo-Rivera, Francisco

2015-05-07

The surface enhanced raman scattering (SERS) signal from the l-tyrosine (tyr) molecule adsorbed on gold nanoparticles (Au-tyr) is compared with the SERS signal assisted by the presence of gadolinium ions (Gd(3+)) coordinated with the Au-tyr system. An enhancement factor of the SERS signal in the presence of Gd(3+) ions was ∼5 times higher than that produced by l-tyrosine adsorbed on gold nanoparticles. The enhancement of the SERS signal can be attributed to a corresponding increase in the local electric field due to the presence of Gd(3+) ions in the vicinity of a gold dimer configuration. This scenario was confirmed by solving numerically Maxwell equations, showing an increase of 1 order of magnitude in the local electric scattered field when the Gd(3+) ion is located in between a gold dimer compared with naked gold nanoparticles.

On error sources during airborne measurements of the ambient electric field

NASA Technical Reports Server (NTRS)

Evteev, B. F.

1991-01-01

The principal sources of errors during airborne measurements of the ambient electric field and charge are addressed. Results of their analysis are presented for critical survey. It is demonstrated that the volume electric charge has to be accounted for during such measurements, that charge being generated at the airframe and wing surface by droplets of clouds and precipitation colliding with the aircraft. The local effect of that space charge depends on the flight regime (air speed, altitude, particle size, and cloud elevation). Such a dependence is displayed in the relation between the collector conductivity of the aircraft discharging circuit - on one hand, and the sum of all the residual conductivities contributing to aircraft discharge - on the other. Arguments are given in favor of variability in the aircraft electric capacitance. Techniques are suggested for measuring from factors to describe the aircraft charge.

The effects of interfacial recombination and injection barrier on the electrical characteristics of perovskite solar cells

NASA Astrophysics Data System (ADS)

Shi, Lin Xing; Wang, Zi Shuai; Huang, Zengguang; Sha, Wei E. I.; Wang, Haoran; Zhou, Zhen

2018-02-01

Charge carrier recombination in the perovskite solar cells (PSCs) has a deep influence on the electrical performance, such as open circuit voltage, short circuit current, fill factor and ultimately power conversion efficiency. The impacts of injection barrier, recombination channels, doping properties of carrier transport layers and light intensity on the performance of PSCs are theoretically investigated by drift-diffusion model in this work. The results indicate that due to the injection barrier at the interfaces of perovskite and carrier transport layer, the accumulated carriers modify the electric field distribution throughout the PSCs. Thus, a zero electric field is generated at a specific applied voltage, with greatly increases the interfacial recombination, resulting in a local kink of current density-voltage (J-V) curve. This work provides an effective strategy to improve the efficiency of PSCs by pertinently reducing both the injection barrier and interfacial recombination.

Electronic spin transport in gate-tunable black phosphorus spin valves

NASA Astrophysics Data System (ADS)

Liu, Jiawei; Avsar, Ahmet; Tan, Jun You; Oezyilmaz, Barbaros

High charge mobility, the electric field effect and small spin-orbit coupling make semiconducting black phosphorus (BP) a promising material for spintronics device applications requiring long spin distance spin communication with all rectification and amplification actions. Towards this, we study the all electrical spin injection, transport and detection under non-local spin valve geometry in fully encapsulated ultra-thin BP devices. We observe spin relaxation times as high as 4 ns, with spin relaxation lengths exceeding 6 μm. These values are an order of magnitude higher than what have been measured in typical graphene spin valve devices. Moreover, the spin transport depends strongly on charge carrier concentration and can be manipulated in a spin transistor-like manner by controlling electric field. This behaviour persists even at room temperature. Finally, we will show that similar to its electrical and optical properties, spin transport property is also strongly anisotropic.

Near-microsecond human aquaporin 4 gating dynamics in static and alternating external electric fields: Non-equilibrium molecular dynamics

NASA Astrophysics Data System (ADS)

English, Niall J.; Garate, José-A.

2016-08-01

An extensive suite of non-equilibrium molecular-dynamics simulation has been performed for ˜0.85-0.9 μs of human aquaporin 4 in the absence and presence of externally applied static and alternating electric fields applied along the channels (in both axial directions in the static case, taken as the laboratory z-axis). These external fields were of 0.0065 V/Å (r.m.s.) intensity (of the same order as physiological electrical potentials); alternating fields ranged in frequency from 2.45 to 500 GHz. In-pore gating dynamics was studied, particularly of the relative propensities for "open" and "closed" states of the conserved arginines in the arginine/aromatic area (itself governed in no small part by external-field response of the dipolar alignment of the histidine-201 residue in the selectivity filter). In such a manner, the intimate connection of field-response governing "two-state" histidine states was established statistically and mechanistically. Given the appreciable size of the energy barriers for histidine-201 alignment, we have also performed non-equilibrium metadynamics/local-elevation of static fields applied along both directions to construct the free-energy landscape thereof in terms of external-field direction, elucidating the importance of field direction on energetics. We conclude from direct measurement of deterministic molecular dynamics in conjunction with applied-field metadynamics that the intrinsic electric field within the channel points along the +z-axis, such that externally applied static fields in this direction serve to "open" the channel in the selectivity-filter and the asparagine-proline-alanine region.

Near-microsecond human aquaporin 4 gating dynamics in static and alternating external electric fields: Non-equilibrium molecular dynamics.

PubMed

English, Niall J; Garate, José-A

2016-08-28

An extensive suite of non-equilibrium molecular-dynamics simulation has been performed for ∼0.85-0.9 μs of human aquaporin 4 in the absence and presence of externally applied static and alternating electric fields applied along the channels (in both axial directions in the static case, taken as the laboratory z-axis). These external fields were of 0.0065 V/Å (r.m.s.) intensity (of the same order as physiological electrical potentials); alternating fields ranged in frequency from 2.45 to 500 GHz. In-pore gating dynamics was studied, particularly of the relative propensities for "open" and "closed" states of the conserved arginines in the arginine/aromatic area (itself governed in no small part by external-field response of the dipolar alignment of the histidine-201 residue in the selectivity filter). In such a manner, the intimate connection of field-response governing "two-state" histidine states was established statistically and mechanistically. Given the appreciable size of the energy barriers for histidine-201 alignment, we have also performed non-equilibrium metadynamics/local-elevation of static fields applied along both directions to construct the free-energy landscape thereof in terms of external-field direction, elucidating the importance of field direction on energetics. We conclude from direct measurement of deterministic molecular dynamics in conjunction with applied-field metadynamics that the intrinsic electric field within the channel points along the +z-axis, such that externally applied static fields in this direction serve to "open" the channel in the selectivity-filter and the asparagine-proline-alanine region.

Correlation between electric field pulse induced long-lived permeabilization and fusogenicity in cell membranes.

PubMed Central

Teissié, J; Ramos, C

1998-01-01

Electric field pulses have been reported to induce long-lived permeabilization and fusogenicity on cell membranes. The two membrane property alterations are under the control of the field strength, the pulse duration, and the number of pulses. Experiments on mammalian cells pulsed by square wave form pulses and then brought into contact randomly through centrifugation revealed an even stronger analogy between the two processes. Permeabilization was known to affect well-defined regions of the cell surface. Fusion can be obtained only when permeabilized surfaces on the two partners were brought into contact. Permeabilization was under the control of the pulse duration and of the number of pulses. A similar relationship was observed as far as fusion is concerned. But a critical level of local permeabilization must be present for fusion to take place when contacts are created. The same conclusions are obtained from previous experiments on ghosts subjected to exponentially decaying field pulses and then brought into contact by dielectrophoresis. These observations are in agreement with a model of membrane fusion in which the merging of local random defects occurs when the two membranes are brought into contact. The local defects are considered part of the structural membrane reorganization induced by the external field. Their density is dependent on the pulse duration and number of pulses. They support the long-lived permeabilization. Their number must be very large to support the occurrence of membrane fusion. PMID:9545050

Correlation between electric field pulse induced long-lived permeabilization and fusogenicity in cell membranes.

PubMed

Teissié, J; Ramos, C

1998-04-01

Electric field pulses have been reported to induce long-lived permeabilization and fusogenicity on cell membranes. The two membrane property alterations are under the control of the field strength, the pulse duration, and the number of pulses. Experiments on mammalian cells pulsed by square wave form pulses and then brought into contact randomly through centrifugation revealed an even stronger analogy between the two processes. Permeabilization was known to affect well-defined regions of the cell surface. Fusion can be obtained only when permeabilized surfaces on the two partners were brought into contact. Permeabilization was under the control of the pulse duration and of the number of pulses. A similar relationship was observed as far as fusion is concerned. But a critical level of local permeabilization must be present for fusion to take place when contacts are created. The same conclusions are obtained from previous experiments on ghosts subjected to exponentially decaying field pulses and then brought into contact by dielectrophoresis. These observations are in agreement with a model of membrane fusion in which the merging of local random defects occurs when the two membranes are brought into contact. The local defects are considered part of the structural membrane reorganization induced by the external field. Their density is dependent on the pulse duration and number of pulses. They support the long-lived permeabilization. Their number must be very large to support the occurrence of membrane fusion.

Performance Improvement of Diagonal Type MHD Generator by Modification of PTO Electrode Configuration

NASA Astrophysics Data System (ADS)

Takahashi, Toru; Fujino, Takayasu; Ishikawa, Motoo

Time dependent three-dimensional numerical analysis is carried out in order to clarify causes of voltage loss occurring near power takeoff regions and to suggest how to reduce the voltage loss for the scramjet engine driven MHD generator which was developed under the hypersonic vehicle electric power system program in USA. The numerical results under the experimental condition show that the local positive electric field is induced near the power takeoff electrodes. The phenomenon is due to the electric field loss by the high electric current through the weakly ionized plasma with low temperature and also by the low electromotive force near the power takeoff electrodes. When the configuration of power takeoff electrodes is modified, the current density near the power takeoff electrodes becomes small and the electromotive force becomes strong. The electric power output under the optimum electrode configuration of power takeoff is improved by 22 percent, compared with the value under the experimental condition.

Study of diffusion of wave packets in a square lattice under external fields along the discrete nonlinear Schrödinger equation

NASA Astrophysics Data System (ADS)

de Brito, P. E.; Nazareno, H. N.

2012-09-01

The object of the present work is to analyze the effect of nonlinearity on wave packet propagation in a square lattice subject to a magnetic and an electric field in the Hall configuration, by using the Discrete Nonlinear Schrödinger Equation (DNLSE). In previous works we have shown that without the nonlinear term, the presence of the magnetic field induces the formation of vortices that remain stationary, while a wave packet is introduced in the system. As for the effect of an applied electric field, it was shown that the vortices propagate in a direction perpendicular to the electric field, similar behavior as presented in the classical treatment, we provide a quantum mechanics explanation for that. We have performed the calculations considering first the action of the magnetic field as well as the nonlinearity. The results indicate that for low values of the nonlinear parameter U the vortices remain stationary while preserving the form. For greater values of the parameter the picture gets distorted, the more so, the greater the nonlinearity. As for the inclusion of the electric field, we note that for small U, the wave packet propagates perpendicular to the applied field, until for greater values of U the wave gets partially localized in a definite region of the lattice. That is, for strong nonlinearity the wave packet gets partially trapped, while the tail of it can propagate through the lattice. Note that this tail propagation is responsible for the over-diffusion for long times of the wave packet under the action of an electric field. We have produced short films that show clearly the time evolution of the wave packet, which can add to the understanding of the dynamics.

Near Earth Current Meander (Necm) Model of Substorms

NASA Astrophysics Data System (ADS)

Heikkila, W. J.; Chen, T.; Liu, Z. X.; Pu, Z. Y.; Pellinen, R. J.; Pulkkinen, T. I.

2001-01-01

We propose that the appropriate instability to trigger a substorm is a tailward meander (in the equatorial plane) of the strong current filament that develops during the growth phase. From this single assumption follows the entire sequence of events for a substorm. The main particle acceleration mechanism in the plasma sheet is curvature drift with a dawn-dusk electric field, leading to the production of auroral arcs. Eventually the curvature becomes so high that the ions cannot negotiate the sharp turn at the field-reversal region, locally, at a certain time. The particle motion becomes chaotic, causing a local outward meander of the cross-tail current. An induction electric field is produced by Lenz's law, E^ind=-∂A/∂t. An outward meander with B_z>0 will cause E×B flow everywhere out from the disturbance; this reaction is a macroscopic instability which we designate the electromotive instability. The response of the plasma is through charge separation and a scalar potential, E^es=-∇φ. Both types of electric fields have components parallel to B in a realistic magnetic field. For MHD theory to hold the net E_∥ must be small; this usually seems to happen (because MHD often does hold), but not always. Part of the response is the formation of field-aligned currents producing the well-known substorm current diversion. This is a direct result of a strong E_∥^ind (the cause) needed to overcome the mirror force of the current carriers; this enables charge separation to produce an opposing electrostatic field E_∥^es (the effect). Satellite data confirm the reality of a strong E_∥ in the plasma sheet by counter-streaming of electrons and ions, and by the inverse ion time dispersion, up to several 100 keV. The electron precipitation is associated with the westward traveling surge (WTS) and the ion with omega (Ω) bands, respectively. However, with zero curl, E^es cannot modify the emf ɛ=∮E.dl=-dΦ^M/dt of the inductive electric field E^ind (a property of vector fields); the charge separation that produces a reduction of E_∥ must enhance the transverse component E_⊥. The new plasma flow becomes a switch for access to the free energy of the stressed magnetotail. On the tailward side the dusk-dawn electric field with E.J<0 will cause tailward motion of the plasma and a plasmoid may be created; it will move in the direction of least magnetic pressure, tailward. On the earthward side the enhanced dawn-dusk induction electric field with E.J>0 will cause injection into the inner plasma sheet, repeatedly observed at moderate energies of 1-50 keV. This same electric field near the emerging X-line will accelerate particles non-adiabatically to moderate energies. With high magnetic moments in a weak magnetic field, electrons (ions) can benefit from gradient and curvature drift to attain high energies (by the ratio of the magnetic field magnitude) in seconds (minutes).

Novel Parallelized Electroporation by Electrostatic Manipulation of a Water-in-Oil Droplet as a Microreactor

PubMed Central

Takahashi, Shota; Asada, Atsushi; Matsuo, Minako; Kishikawa, Kenta; Mizuno, Akira

2015-01-01

Electroporation is the most widely used transfection method for delivery of cell-impermeable molecules into cells. We developed a novel gene transfection method, water-in-oil (W/O) droplet electroporation, using dielectric oil and an aqueous droplet containing mammalian cells and transgene DNA. When a liquid droplet suspended between a pair of electrodes in dielectric oil is exposed to a DC electric field, the droplet moves between the pair of electrodes periodically and droplet deformation occurs under the intense DC electric field. During electrostatic manipulation of the droplet, the local intense electric field and instantaneous short circuit via the droplet due to droplet deformation facilitate gene transfection. This method has several advantages over conventional transfection techniques, including co-transfection of multiple transgene DNAs into even as few as 103 cells, transfection into differentiated neural cells, and the capable establishment of stable cell lines. In addition, there have been improvements in W/O droplet electroporation electrodes for disposable 96-well plates making them suitable for concurrent performance without thermal loading by a DC electric field. This technique will lead to the development of cell transfection methods for novel regenerative medicine and gene therapy. PMID:26649904

Electric field effect on the electronic structure of 2D Y2C electride

NASA Astrophysics Data System (ADS)

Oh, Youngtek; Lee, Junsu; Park, Jongho; Kwon, Hyeokshin; Jeon, Insu; Wng Kim, Sung; Kim, Gunn; Park, Seongjun; Hwang, Sung Woo

2018-07-01

Electrides are ionic compounds in which electrons confined in the interstitial spaces serve as anions and are attractive owing to their exotic physical and chemical properties in terms of their low work function and efficient charge-transfer characteristics. Depending on the topology of the anionic electrons, the surface electronic structures of electrides can be significantly altered. In particular, the electronic structures of two-dimensional (2D) electride surfaces are of interest because the localized anionic electrons at the interlayer space can be naturally exposed to cleaved surfaces. In this paper, we report the electronic structure of 2D Y2C electride surface using scanning tunneling microscopy (STM) and first-principles calculations, which reveals that anionic electrons at a cleaved surface are absorbed by the surface and subsequently resurged onto the surface due to an applied electric field. We highlight that the estranged anionic electrons caused by the electric field occupy the slightly shifted crystallographic site compared with a bulk Y2C electride. We also measure the work function of the Y2C single crystal, and it shows a slightly lower value than the calculated one, which appears to be due to the electric field from the STM junction.

Spin-orbit torque in a thin film of the topological insulator Bi2Se3: Crossover from the ballistic to diffusive regime

NASA Astrophysics Data System (ADS)

Ren, Y. J.; Deng, W. Y.; Geng, H.; Shen, R.; Shao, L. B.; Sheng, L.; Xing, D. Y.

2017-12-01

The spin-orbit torque provides an efficient method for switching the direction of a magnetization by using an electric field. Owing to the spin-orbit coupling, when an electric field is applied, a nonequilibrium spin density is generated, which exerts a torque on the local magnetization. Here, we investigate the spin-orbit torque in a thin film of topological insulator \\text{Bi}2\\text{Se}3 based upon a Boltzmann equation, with proper boundary conditions, which is applicable from the ballistic regime to the diffusive regime. It is shown that due to the spin-momentum interlocking of the electron surface states, the magnitude of the field-like torque is simply in linear proportion to the longitudinal electrical current. For a fixed electric field, the spin-orbit torque is proportional to the sample length in the ballistic limit, and saturates to a constant in the diffusive limit. The dependence of the torque on the magnetization direction and exchange coupling strength is also studied. Our theory may offer useful guidance for experimental investigations of the spin-orbit torque in finite-size systems.

The electro-mechanical effect from charge dynamics on polymeric insulation lifetime

DOE Office of Scientific and Technical Information (OSTI.GOV)

Alghamdi, H., E-mail: haalghamdi@nu.edu.sa; Faculty of Engineering, Najran University, Najran, P.O.Box 1988; Chen, G.

For polymeric material used as electrical insulation, the presence of space charges could be the consequence of material degradations that are thermally activated but increased by the application of an electric field. The dynamics of space charge, therefore, can be potentially used to characterize the material. In this direction, a new aging model in which parameters have clear physical meanings has been developed and applied to the material to extrapolate the lifetime. The kinetic equation has been established based on charge trapping and detrapping of the injected charge from the electrodes. The local electromechanical energy stored in the region surroundingmore » the trap is able to reduce the trap-depth with a value related to the electric field. At a level where the internal electric field exceeds the detrapping field in the material, an electron can be efficiently detrapped and the released energy from detrapping process can cause a weak bond or chain scission i.e. material degradation. The model has been applied to the electro-thermally aged low density polyethylene film samples, showing well fitted result, as well as interesting relationships between parameter estimates and insulation morphology.« less

Frequency and Voltage Dependence of the Dielectrophoretic Trapping of Short Lengths of DNA and dCTP in a Nanopipette

PubMed Central

Ying, Liming; White, Samuel S.; Bruckbauer, Andreas; Meadows, Lisa; Korchev, Yuri E.; Klenerman, David

2004-01-01

The study of the properties of DNA under high electric fields is of both fundamental and practical interest. We have exploited the high electric fields produced locally in the tip of a nanopipette to probe the motion of double- and single-stranded 40-mer DNA, a 1-kb single-stranded DNA, and a single-nucleotide triphosphate (dCTP) just inside and outside the pipette tip at different frequencies and amplitudes of applied voltages. We used dual laser excitation and dual color detection to simultaneously follow two fluorophore-labeled DNA sequences with millisecond time resolution, significantly faster than studies to date. A strong trapping effect was observed during the negative half cycle for all DNA samples and also the dCTP. This effect was maximum below 1 Hz and decreased with higher frequency. We assign this trapping to strong dielectrophoresis due to the high electric field and electric field gradient in the pipette tip. Dielectrophoresis in electrodeless tapered nanostructures has potential applications for controlled mixing and manipulation of short lengths of DNA and other biomolecules, opening new possibilities in miniaturized biological analysis. PMID:14747337

Investigations of CuFeS{sub 2} semiconductor mineral from ocean rift hydrothermal vent fields by Cu NMR in a local field

DOE Office of Scientific and Technical Information (OSTI.GOV)

Matukhin, V. L.; Pogoreltsev, A. I.; Gavrilenko, A. N., E-mail: ang-2000@mail.ru

The results of investigating natural samples of chalcopyrite mineral CuFeS{sub 2} from massive oceanic sulfide ores of the Mid-Atlantic ridge by the {sup 63}Cu nuclear magnetic resonance (NMR {sup 63}Cu) in a local field at room temperature are presented. The significant width of the resonance lines found in the {sup 63}Cu NMR spectrum directly testifies to a wide distribution of local magnetic and electric fields in the investigated chalcopyrite samples. This distribution can be the consequence of an appreciable deviation of the structure of the investigated chalcopyrite samples from the stoichiometric one. The obtained results show that the pulsed {supmore » 63}Cu NMR can be an efficient method for studying the physical properties of deep-water polymetallic sulfides of the World Ocean.« less

Electrical control of optical orientation of neutral and negatively charged excitons in an n -type semiconductor quantum well

NASA Astrophysics Data System (ADS)

Dzhioev, R. I.; Korenev, V. L.; Lazarev, M. V.; Sapega, V. F.; Gammon, D.; Bracker, A. S.

2007-01-01

We report electric field induced increase of spin orientation of negatively charged excitons (trions) localized in n -type GaAs/AlGaAs quantum well. Under resonant excitation of free neutral heavy-hole excitons, the polarization of trions increases dramatically with electrical injection of electrons. The polarization enhancement correlates strongly with trion/exciton luminescence intensity ratio. This effect results from a very efficient trapping of free neutral excitons by the quantum well interfacial fluctuations (“natural” quantum dots) containing resident electrons.

Response of energetic particles to local magnetic dipolarization inside geosynchronous orbit

NASA Astrophysics Data System (ADS)

Motoba, T.; Ohtani, S.; Gkioulidou, M.; Takahashi, K.

2017-12-01

Magnetic field dipolarization and energetic particle injections are the most distinct phenomena observed in the inner magnetosphere during the substorm expansion phase. Compared to a wealth of knowledge about the phenomenology of magnetic dipolarizations and particle injections at/outside geosynchronous orbit (GEO), our understanding of them inside GEO remains incomplete because of a very limited number of previous studies. In the present study, we statistically examine the response of 1-1000 keV energetic particles to local magnetic dipolarization by performing a superposed epoch analysis of energetic particle fluxes with the zero epoch defined as the dipolarization onset times. Based on data from the Van Allen Probes tail seasons in 2012-2016, we identified a total of 97 magnetic dipolarization events which occurred closer to the magnetic equator (i.e., BH, which is antiparallel to the Earth's dipole axis, is the dominant component of the local magnetic field at least for 5 min before the onset). For major ion species (hydrogen, helium, and oxygen ions), the relative flux intensity to the pre-onset level increases at > 50 keV and decreases at < 30 keV. The hydrogen and helium ion fluxes in the hundreds of keV range sharply increase within a minute after the onset and then decay. Compared to the short-lived nature of hydrogen and helium ion flux enhancements, oxygen ion fluxes are enhanced more gradually (on the order of several minutes). The relative ion flux intensity and peak energy generally tend to increase for stronger dipolarization-related impulsive westward electric field. This suggests that the impulsive electric field is responsible for the energization and/or transport of energetic ions inside GEO. On the other hand, the electron flux enhancement first appears from several tens of keV to a few hundreds of keV, and then exhibits an inverse energy dispersion. For dipolarizations with strong impulsive westward electric fields, the relative electron flux intensity increases up to 5-10 times, in particular most significant at several tens of keV. This result suggests that the impulsive electric field acts as an efficient factor in the rapid energization of the tens-of-keV electrons. We also discuss how the response of energetic particles to dipolarization depends on MLT, radial distance, and pitch angle.

Charged hadrons in local finite-volume QED+QCD with C⋆ boundary conditions

NASA Astrophysics Data System (ADS)

Lucini, B.; Patella, A.; Ramos, A.; Tantalo, N.

2016-02-01

In order to calculate QED corrections to hadronic physical quantities by means of lattice simulations, a coherent description of electrically-charged states in finite volume is needed. In the usual periodic setup, Gauss's law and large gauge transformations forbid the propagation of electrically-charged states. A possible solution to this problem, which does not violate the axioms of local quantum field theory, has been proposed by Wiese and Polley, and is based on the use of C⋆ boundary conditions. We present a thorough analysis of the properties and symmetries of QED in isolation and QED coupled to QCD, with C⋆ boundary conditions. In particular we learn that a certain class of electrically-charged states can be constructed in a fully consistent fashion without relying on gauge fixing and without peculiar complications. This class includes single particle states of most stable hadrons. We also calculate finite-volume corrections to the mass of stable charged particles and show that these are much smaller than in non-local formulations of QED.

Method, system and computer program product for monitoring and optimizing fluid extraction from geologic strata

DOEpatents

Medizade, Masoud [San Luis Obispo, CA; Ridgely, John Robert [Los Osos, CA

2009-12-15

An arrangement which utilizes an inexpensive flap valve/flow transducer combination and a simple local supervisory control system to monitor and/or control the operation of a positive displacement pump used to extract petroleum from geologic strata. The local supervisory control system controls the operation of an electric motor which drives a reciprocating positive displacement pump so as to maximize the volume of petroleum extracted from the well per pump stroke while minimizing electricity usage and pump-off situations. By reducing the electrical demand and pump-off (i.e., "pounding" or "fluid pound") occurrences, operating and maintenance costs should be reduced sufficiently to allow petroleum recovery from marginally productive petroleum fields. The local supervisory control system includes one or more applications to at least collect flow signal data generated during operation of the positive displacement pump. No flow, low flow and flow duration are easily evaluated using the flap valve/flow transducer arrangement.

Measurement of the magnetotail reconnection rate

NASA Astrophysics Data System (ADS)

Blanchard, G. T.; Lyons, L. R.; de la Beaujardière, O.; Doe, R. A.; Mendillo, M.

1996-07-01

A technique to measure the magnetotail reconnection rate from the ground is described and applied to 71 hours of measurements from 20 nights. The reconnection rate is obtained from the ionospheric flow across the polar cap boundary in the frame of reference of the boundary, measured by the Sondrestrom incoherent scatter radar. For our measurements, the polar cap boundary is located using 6300 Å auroral emissions and E region electron density. The average experimental uncertainty of the reconnection rate measurement is 11.6 mVm-1 in the ionospheric electric field. By using a large data set, we obtain the dependence of the reconnection rate on magnetic local time, the interplanetary magnetic field, and substorm activity, with much higher accuracy. We find that two thirds of the average polar cap potential drop occurs over the 4-hour segment of the separatrix centered on 2330 MLT, that the linear correlation between the reconnection electric field and the half-wave rectified dawn-dusk solar wind electric field VBs peaks between 1.0 and 1.5 hours, with a maximum linear correlation coefficient of 0.46 at 70 min; and that following substorm expansion phase onset, the reconnection electric field becomes larger than the experimental uncertainty, with an average delay of 23 min. The 70-min delay of the reconnection rate with respect to VBs is a typical convection time for a flux tube across the polar cap. This result indicates that reconnection in the magnetotail is influenced by the solar wind electric field VBs on the field line being reconnected.

Jumping-droplet electronics hot-spot cooling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Oh, Junho; Birbarah, Patrick; Foulkes, Thomas

Demand for enhanced cooling technologies within various commercial and consumer applications has increased in recent decades due to electronic devices becoming more energy dense. This study demonstrates jumping-droplet based electric-field-enhanced (EFE) condensation as a potential method to achieve active hot spot cooling in electronic devices. To test the viability of EFE condensation, we developed an experimental setup to remove heat via droplet evaporation from single and multiple high power gallium nitride (GaN) transistors acting as local hot spots (4.6 mm x 2.6 mm). An externally powered circuit was developed to direct jumping droplets from a copper oxide (CuO) nanostructured superhydrophobicmore » surface to the transistor hot spots by applying electric fields between the condensing surface and the transistor. Heat transfer measurements were performed in ambient air (22-25°C air temperature, 20-45% relative humidity) to determine the effect of gap spacing (2-4 mm), electric field (50-250 V/cm), and heat flux (demonstrated to 13 W/cm 2). EFE condensation was shown to enhance the heat transfer from the local hot spot by ≈ 200% compared to cooling without jumping and by 20% compared to non-EFE jumping. Dynamic switching of the electric field for a two-GaN system reveals the potential for active cooling of mobile hot spots. The opportunity for further cooling enhancement by the removal of non-condensable gases promises hot spot heat dissipation rates approaching 120 W/cm 2. Finally, this work provides a framework for the development of active jumping droplet based vapor chambers and heat pipes capable of spatial and temporal thermal dissipation control.« less

Jumping-droplet electronics hot-spot cooling

DOE PAGES

Oh, Junho; Birbarah, Patrick; Foulkes, Thomas; ...

2017-03-20

Demand for enhanced cooling technologies within various commercial and consumer applications has increased in recent decades due to electronic devices becoming more energy dense. This study demonstrates jumping-droplet based electric-field-enhanced (EFE) condensation as a potential method to achieve active hot spot cooling in electronic devices. To test the viability of EFE condensation, we developed an experimental setup to remove heat via droplet evaporation from single and multiple high power gallium nitride (GaN) transistors acting as local hot spots (4.6 mm x 2.6 mm). An externally powered circuit was developed to direct jumping droplets from a copper oxide (CuO) nanostructured superhydrophobicmore » surface to the transistor hot spots by applying electric fields between the condensing surface and the transistor. Heat transfer measurements were performed in ambient air (22-25°C air temperature, 20-45% relative humidity) to determine the effect of gap spacing (2-4 mm), electric field (50-250 V/cm), and heat flux (demonstrated to 13 W/cm 2). EFE condensation was shown to enhance the heat transfer from the local hot spot by ≈ 200% compared to cooling without jumping and by 20% compared to non-EFE jumping. Dynamic switching of the electric field for a two-GaN system reveals the potential for active cooling of mobile hot spots. The opportunity for further cooling enhancement by the removal of non-condensable gases promises hot spot heat dissipation rates approaching 120 W/cm 2. Finally, this work provides a framework for the development of active jumping droplet based vapor chambers and heat pipes capable of spatial and temporal thermal dissipation control.« less

Long-term stability of Cu surface nanotips

NASA Astrophysics Data System (ADS)

Jansson, V.; Baibuz, E.; Djurabekova, F.

2016-07-01

Sharp nanoscale tips on the metal surfaces of electrodes enhance locally applied electric fields. Strongly enhanced electric fields trigger electron field emission and atom evaporation from the apexes of nanotips. Together, these processes may explain electric discharges in the form of small local arcs observed near metal surfaces in the presence of electric fields, even in ultra-high vacuum conditions. In the present work, we investigate the stability of nanoscale tips by means of computer simulations of surface diffusion processes on copper, the main material used in high-voltage electronics. We study the stability and lifetime of thin copper (Cu) surface nanotips at different temperatures in terms of diffusion processes. For this purpose we have developed a surface kinetic Monte Carlo (KMC) model where the jump processes are described by tabulated precalculated energy barriers. We show that tall surface features with high aspect ratios can be fairly stable at room temperature. However, the stability was found to depend strongly on the temperature: 13 nm nanotips with the major axes in the < 110> crystallographic directions were found to flatten down to half of the original height in less than 100 ns at temperatures close to the melting point, whereas no significant change in the height of these nanotips was observed after 10 {{μ }}{{s}} at room temperature. Moreover, the nanotips built up along the < 110> crystallographic directions were found to be significantly more stable than those oriented in the < 100> or < 111> crystallographic directions. The proposed KMC model has been found to be well-suited for simulating atomic surface processes and was validated against molecular dynamics simulation results via the comparison of the flattening times obtained by both methods. We also note that the KMC simulations were two orders of magnitude computationally faster than the corresponding molecular dynamics calculations.

Tutorial: Physics and modeling of Hall thrusters

NASA Astrophysics Data System (ADS)

Boeuf, Jean-Pierre

2017-01-01

Hall thrusters are very efficient and competitive electric propulsion devices for satellites and are currently in use in a number of telecommunications and government spacecraft. Their power spans from 100 W to 20 kW, with thrust between a few mN and 1 N and specific impulse values between 1000 and 3000 s. The basic idea of Hall thrusters consists in generating a large local electric field in a plasma by using a transverse magnetic field to reduce the electron conductivity. This electric field can extract positive ions from the plasma and accelerate them to high velocity without extracting grids, providing the thrust. These principles are simple in appearance but the physics of Hall thrusters is very intricate and non-linear because of the complex electron transport across the magnetic field and its coupling with the electric field and the neutral atom density. This paper describes the basic physics of Hall thrusters and gives a (non-exhaustive) summary of the research efforts that have been devoted to the modelling and understanding of these devices in the last 20 years. Although the predictive capabilities of the models are still not sufficient for a full computer aided design of Hall thrusters, significant progress has been made in the qualitative and quantitative understanding of these devices.

Numerical evaluation of lactoperoxidase inactivation during continuous pulsed electric field processing.

PubMed

Buckow, Roman; Semrau, Julius; Sui, Qian; Wan, Jason; Knoerzer, Kai

2012-01-01

A computational fluid dynamics (CFD) model describing the flow, electric field and temperature distribution of a laboratory-scale pulsed electric field (PEF) treatment chamber with co-field electrode configuration was developed. The predicted temperature increase was validated by means of integral temperature studies using thermocouples at the outlet of each flow cell for grape juice and salt solutions. Simulations of PEF treatments revealed intensity peaks of the electric field and laminar flow conditions in the treatment chamber causing local temperature hot spots near the chamber walls. Furthermore, thermal inactivation kinetics of lactoperoxidase (LPO) dissolved in simulated milk ultrafiltrate were determined with a glass capillary method at temperatures ranging from 65 to 80 °C. Temperature dependence of first order inactivation rate constants was accurately described by the Arrhenius equation yielding an activation energy of 597.1 kJ mol(-1). The thermal impact of different PEF processes on LPO activity was estimated by coupling the derived Arrhenius model with the CFD model and the predicted enzyme inactivation was compared to experimental measurements. Results indicated that LPO inactivation during combined PEF/thermal treatments was largely due to thermal effects, but 5-12% enzyme inactivation may be related to other electro-chemical effects occurring during PEF treatments. Copyright © 2012 American Institute of Chemical Engineers (AIChE).

Negative index of refraction in a four-level system with magnetoelectric cross coupling and local field corrections

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bello, F.

2011-07-15

This research focuses on a coherently driven four-level atomic medium with the aim of inducing a negative index of refraction while taking into consideration local field corrections as well as magnetoelectric cross coupling (i.e.,chirality) within the material's response functions. Two control fields are used to render the medium transparent for a probe field which simultaneously couples to an electric and a magnetic dipole transition, thus allowing one to test the permittivity and permeability of the material at the same time. Numerical simulations show that a negative index of refraction with low absorption can be obtained for a range of probemore » detunings while depending on number density and the ratio between the intensities of the control fields.« less

Methodology for time-domain estimation of storm time geoelectric fields using the 3-D magnetotelluric response tensors

USGS Publications Warehouse

Kelbert, Anna; Balch, Christopher; Pulkkinen, Antti; Egbert, Gary D; Love, Jeffrey J.; Rigler, E. Joshua; Fujii, Ikuko

2017-01-01

Geoelectric fields at the Earth's surface caused by magnetic storms constitute a hazard to the operation of electric power grids and related infrastructure. The ability to estimate these geoelectric fields in close to real time and provide local predictions would better equip the industry to mitigate negative impacts on their operations. Here we report progress toward this goal: development of robust algorithms that convolve a magnetic storm time series with a frequency domain impedance for a realistic three-dimensional (3-D) Earth, to estimate the local, storm time geoelectric field. Both frequency domain and time domain approaches are presented and validated against storm time geoelectric field data measured in Japan. The methods are then compared in the context of a real-time application.

Methodology for time-domain estimation of storm time geoelectric fields using the 3-D magnetotelluric response tensors

NASA Astrophysics Data System (ADS)

Kelbert, Anna; Balch, Christopher C.; Pulkkinen, Antti; Egbert, Gary D.; Love, Jeffrey J.; Rigler, E. Joshua; Fujii, Ikuko

2017-07-01

Geoelectric fields at the Earth's surface caused by magnetic storms constitute a hazard to the operation of electric power grids and related infrastructure. The ability to estimate these geoelectric fields in close to real time and provide local predictions would better equip the industry to mitigate negative impacts on their operations. Here we report progress toward this goal: development of robust algorithms that convolve a magnetic storm time series with a frequency domain impedance for a realistic three-dimensional (3-D) Earth, to estimate the local, storm time geoelectric field. Both frequency domain and time domain approaches are presented and validated against storm time geoelectric field data measured in Japan. The methods are then compared in the context of a real-time application.

Label-free electrical detection of pyrophosphate generated from DNA polymerase reactions on field-effect devices.

PubMed

Credo, Grace M; Su, Xing; Wu, Kai; Elibol, Oguz H; Liu, David J; Reddy, Bobby; Tsai, Ta-Wei; Dorvel, Brian R; Daniels, Jonathan S; Bashir, Rashid; Varma, Madoo

2012-03-21

We introduce a label-free approach for sensing polymerase reactions on deoxyribonucleic acid (DNA) using a chelator-modified silicon-on-insulator field-effect transistor (SOI-FET) that exhibits selective and reversible electrical response to pyrophosphate anions. The chemical modification of the sensor surface was designed to include rolling-circle amplification (RCA) DNA colonies for locally enhanced pyrophosphate (PPi) signal generation and sensors with immobilized chelators for capture and surface-sensitive detection of diffusible reaction by-products. While detecting arrays of enzymatic base incorporation reactions is typically accomplished using optical fluorescence or chemiluminescence techniques, our results suggest that it is possible to develop scalable and portable PPi-specific sensors and platforms for broad biomedical applications such as DNA sequencing and microbe detection using surface-sensitive electrical readout techniques.

Cosmic-ray streaming and anisotropies

NASA Technical Reports Server (NTRS)

Forman, M. A.; Gleeson, L. J.

1975-01-01

The paper is concerned with the differential current densities and anisotropies that exist in the interplanetary cosmic-ray gas, and in particular with a correct formulation and simple interpretation of the momentum equation that describes these on a local basis. Two examples of the use of this equation in the interpretation of previous data are given. It is demonstrated that in interplanetary space, the electric-field drifts and convective flow parallel to the magnetic field of cosmic-ray particles combine as a simple convective flow with the solar wind, and that there exist diffusive currents and transverse gradient drift currents. Thus direct reference to the interplanetary electric-field drifts is eliminated, and the study of steady-state and transient cosmic-ray anisotropies is both more systematic and simpler.

HIGH VOLTAGE ELECTRODES

DOEpatents

Murray, J.J.

1963-04-23

S>This patent relates to electrode structure for creating an intense direct current electric field which may have a field strength of the order of two to three times that heretofore obtained, with automatic suppression of arcing. The positive electrode is a conventional conductive material such as copper while the negative electrode is made from a special material having a resistivity greater than that of good conductors and less than that of good insulators. When an incipient arc occurs, the moderate resistivity of the negative electrode causes a momentary, localized decrease in the electric field intensity, thus suppressing the flow of electrons and avoiding arcing. Heated glass may be utilized for the negative electrode, since it provides the desired combination of resistivity, capacity, dielectric strength, mechani-cal strength, and thermal stability. (AEC)

Fluctuations of local electric field and dipole moments in water between metal walls.

PubMed

Takae, Kyohei; Onuki, Akira

2015-10-21

We examine the thermal fluctuations of the local electric field Ek (loc) and the dipole moment μk in liquid water at T = 298 K between metal walls in electric field applied in the perpendicular direction. We use analytic theory and molecular dynamics simulation. In this situation, there is a global electrostatic coupling between the surface charges on the walls and the polarization in the bulk. Then, the correlation function of the polarization density pz(r) along the applied field contains a homogeneous part inversely proportional to the cell volume V. Accounting for the long-range dipolar interaction, we derive the Kirkwood-Fröhlich formula for the polarization fluctuations when the specimen volume v is much smaller than V. However, for not small v/V, the homogeneous part comes into play in dielectric relations. We also calculate the distribution of Ek (loc) in applied field. As a unique feature of water, its magnitude |Ek (loc)| obeys a Gaussian distribution with a large mean value E0 ≅ 17 V/nm, which arises mainly from the surrounding hydrogen-bonded molecules. Since |μk|E0 ∼ 30kBT, μk becomes mostly parallel to Ek (loc). As a result, the orientation distributions of these two vectors nearly coincide, assuming the classical exponential form. In dynamics, the component of μk(t) parallel to Ek (loc)(t) changes on the time scale of the hydrogen bonds ∼5 ps, while its smaller perpendicular component undergoes librational motions on time scales of 0.01 ps.

Impact of local electrostatic field rearrangement on field ionization

NASA Astrophysics Data System (ADS)

Katnagallu, Shyam; Dagan, Michal; Parviainen, Stefan; Nematollahi, Ali; Grabowski, Blazej; Bagot, Paul A. J.; Rolland, Nicolas; Neugebauer, Jörg; Raabe, Dierk; Vurpillot, François; Moody, Michael P.; Gault, Baptiste

2018-03-01

Field ion microscopy allows for direct imaging of surfaces with true atomic resolution. The high charge density distribution on the surface generates an intense electric field that can induce ionization of gas atoms. We investigate the dynamic nature of the charge and the consequent electrostatic field redistribution following the departure of atoms initially constituting the surface in the form of an ion, a process known as field evaporation. We report on a new algorithm for image processing and tracking of individual atoms on the specimen surface enabling quantitative assessment of shifts in the imaged atomic positions. By combining experimental investigations with molecular dynamics simulations, which include the full electric charge, we confirm that change is directly associated with the rearrangement of the electrostatic field that modifies the imaging gas ionization zone. We derive important considerations for future developments of data reconstruction in 3D field ion microscopy, in particular for precise quantification of lattice strains and characterization of crystalline defects at the atomic scale.

Manifestations of geometric phases in a proton electric-dipole-moment experiment in an all-electric storage ring

NASA Astrophysics Data System (ADS)

Silenko, Alexander J.

2017-12-01

We consider a proton electric-dipole-moment experiment in an all-electric storage ring when the spin is frozen and local longitudinal and vertical electric fields alternate. In this experiment, the geometric (Berry) phases are very important. Due to the these phases, the spin rotates about the radial axis. The corresponding systematic error is rather important while it can be canceled with clockwise and counterclockwise beams. The geometric phases also lead to the spin rotation about the radial axis. This effect can be canceled with clockwise and counterclockwise beams as well. The sign of the azimuthal component of the angular velocity of the spin precession depends on the starting point where the spin orientation is perfect. The radial component of this quantity keeps its value and sign for each starting point. When the longitudinal and vertical electric fields are joined in the same sections without any alternation, the systematic error due to the geometric phases does not appear but another systematic effect of the spin rotation about the azimuthal axis takes place. It has opposite signs for clockwise and counterclockwise beams.

Laboratory-Scale Evidence for Lightning-Mediated Gene Transfer in Soil

PubMed Central

Demanèche, Sandrine; Bertolla, Franck; Buret, François; Nalin, Renaud; Sailland, Alain; Auriol, Philippe; Vogel, Timothy M.; Simonet, Pascal

2001-01-01

Electrical fields and current can permeabilize bacterial membranes, allowing for the penetration of naked DNA. Given that the environment is subjected to regular thunderstorms and lightning discharges that induce enormous electrical perturbations, the possibility of natural electrotransformation of bacteria was investigated. We demonstrated with soil microcosm experiments that the transformation of added bacteria could be increased locally via lightning-mediated current injection. The incorporation of three genes coding for antibiotic resistance (plasmid pBR328) into the Escherichia coli strain DH10B recipient previously added to soil was observed only after the soil had been subjected to laboratory-scale lightning. Laboratory-scale lightning had an electrical field gradient (700 versus 600 kV m−1) and current density (2.5 versus 12.6 kA m−2) similar to those of full-scale lightning. Controls handled identically except for not being subjected to lightning produced no detectable antibiotic-resistant clones. In addition, simulated storm cloud electrical fields (in the absence of current) did not produce detectable clones (transformation detection limit, 10−9). Natural electrotransformation might be a mechanism involved in bacterial evolution. PMID:11472916

Local-Field Distribution of Two Dielectric Inclusions at Small Separation

NASA Astrophysics Data System (ADS)

Siu, Yuet-Lun; Yu, Kin-Wah

2001-03-01

When two dielectric inclusions approach to each other in a composite medium, significant mutual polarization effects must occur. These effects are multipolar in nature and are difficult to treat from first principles(J. D. Jackson, Classical Electrodynamics), 2nd edition, (Wiley, New York, 1975).. In this work, we employ the discrete-dipole theory(B. T. Draine and P. J. Flatau, J. Opt. Soc. Am. A 11) 1491 (1994). to account for the mutual polarization effects by dividing the inclusions into many small subparts. We begin the calculation at small inclusion sizes and large separation, where the point-dipole limit being valid, and proceed to larger inclusion sizes and small separation, for which the mutual polarization effect becomes important. Then, we apply the theory to determine the dipole moment of each subpart self-consistently. In this way, each dipole moment yields the local electric field, which in turn polarizes the neighboring dipoles. We also begin the calculation at small inclusion sizes and large separation, where the point-dipole limit being valid, and proceed to larger inclusion sizes and small separation. Our resluts indicate that convergence is achieved with moderate computational effects. The results produce valuable information about the local electric field distribution, which is relevant to optical absorption due to surface phonon-polaritons of ionic microcrystals.

The local density of optical states of a metasurface

NASA Astrophysics Data System (ADS)

Lunnemann, Per; Koenderink, A. Femius

2016-02-01

While metamaterials are often desirable for near-field functions, such as perfect lensing, or cloaking, they are often quantified by their response to plane waves from the far field. Here, we present a theoretical analysis of the local density of states near lattices of discrete magnetic scatterers, i.e., the response to near field excitation by a point source. Based on a pointdipole theory using Ewald summation and an array scanning method, we can swiftly and semi-analytically evaluate the local density of states (LDOS) for magnetoelectric point sources in front of an infinite two-dimensional (2D) lattice composed of arbitrary magnetoelectric dipole scatterers. The method takes into account radiation damping as well as all retarded electrodynamic interactions in a self-consistent manner. We show that a lattice of magnetic scatterers evidences characteristic Drexhage oscillations. However, the oscillations are phase shifted relative to the electrically scattering lattice consistent with the difference expected for reflection off homogeneous magnetic respectively electric mirrors. Furthermore, we identify in which source-surface separation regimes the metasurface may be treated as a homogeneous interface, and in which homogenization fails. A strong frequency and in-plane position dependence of the LDOS close to the lattice reveals coupling to guided modes supported by the lattice.

Band-like temperature dependence of mobility in a solution-processed organic semiconductor

NASA Astrophysics Data System (ADS)

Sakanoue, Tomo; Sirringhaus, Henning

2010-09-01

The mobility μ of solution-processed organic semiconductorshas improved markedly to room-temperature values of 1-5cm2V-1s-1. In spite of their growing technological importance, the fundamental open question remains whether charges are localized onto individual molecules or exhibit extended-state band conduction like those in inorganic semiconductors. The high bulk mobility of 100cm2V-1s-1 at 10K of some molecular single crystals provides clear evidence that extended-state conduction is possible in van-der-Waals-bonded solids at low temperatures. However, the nature of conduction at room temperature with mobilities close to the Ioffe-Regel limit remains controversial. Here we investigate the origin of an apparent `band-like', negative temperature coefficient of the mobility (dμ/dT<0) in spin-coated films of 6,13-bis(triisopropylsilylethynyl)-pentacene. We use optical spectroscopy of gate-induced charge carriers to show that, at low temperature and small lateral electric field, charges become localized onto individual molecules in shallow trap states, but that a moderate lateral electric field is able to detrap them resulting in highly nonlinear, low-temperature transport. The negative temperature coefficient of the mobility at high fields is not due to extended-state conduction but to localized transport limited by thermal lattice fluctuations.

Band-like temperature dependence of mobility in a solution-processed organic semiconductor.

PubMed

Sakanoue, Tomo; Sirringhaus, Henning

2010-09-01

The mobility mu of solution-processed organic semiconductors has improved markedly to room-temperature values of 1-5 cm(2) V(-1) s(-1). In spite of their growing technological importance, the fundamental open question remains whether charges are localized onto individual molecules or exhibit extended-state band conduction like those in inorganic semiconductors. The high bulk mobility of 100 cm(2) V(-1) s(-1) at 10 K of some molecular single crystals provides clear evidence that extended-state conduction is possible in van-der-Waals-bonded solids at low temperatures. However, the nature of conduction at room temperature with mobilities close to the Ioffe-Regel limit remains controversial. Here we investigate the origin of an apparent 'band-like', negative temperature coefficient of the mobility (dmu/dT<0) in spin-coated films of 6,13-bis(triisopropylsilylethynyl)-pentacene. We use optical spectroscopy of gate-induced charge carriers to show that, at low temperature and small lateral electric field, charges become localized onto individual molecules in shallow trap states, but that a moderate lateral electric field is able to detrap them resulting in highly nonlinear, low-temperature transport. The negative temperature coefficient of the mobility at high fields is not due to extended-state conduction but to localized transport limited by thermal lattice fluctuations.

Vector-beam solutions of Maxwell's wave equation.

PubMed

Hall, D G

1996-01-01

The Hermite-Gauss and Laguerre-Gauss modes are well-known beam solutions of the scalar Helmholtz equation in the paraxial limit. As such, they describe linearly polarized fields or single Cartesian components of vector fields. The vector wave equation admits, in the paraxial limit, of a family of localized Bessel-Gauss beam solutions that can describe the entire transverse electric field. Two recently reported solutions are members of this family of vector Bessel-Gauss beam modes.

Solution pH change in non-uniform alternating current electric fields at frequencies above the electrode charging frequency

PubMed Central

An, Ran; Massa, Katherine

2014-01-01

AC Faradaic reactions have been reported as a mechanism inducing non-ideal phenomena such as flow reversal and cell deformation in electrokinetic microfluidic systems. Prior published work described experiments in parallel electrode arrays below the electrode charging frequency (fc), the frequency for electrical double layer charging at the electrode. However, 2D spatially non-uniform AC electric fields are required for applications such as in plane AC electroosmosis, AC electrothermal pumps, and dielectrophoresis. Many microscale experimental applications utilize AC frequencies around or above fc. In this work, a pH sensitive fluorescein sodium salt dye was used to detect [H+] as an indicator of Faradaic reactions in aqueous solutions within non-uniform AC electric fields. Comparison experiments with (a) parallel (2D uniform fields) electrodes and (b) organic media were employed to deduce the electrode charging mechanism at 5 kHz (1.5fc). Time dependency analysis illustrated that Faradaic reactions exist above the theoretically predicted electrode charging frequency. Spatial analysis showed [H+] varied spatially due to electric field non-uniformities and local pH changed at length scales greater than 50 μm away from the electrode surface. Thus, non-uniform AC fields yielded spatially varied pH gradients as a direct consequence of ion path length differences while uniform fields did not yield pH gradients; the latter is consistent with prior published data. Frequency dependence was examined from 5 kHz to 12 kHz at 5.5 Vpp potential, and voltage dependency was explored from 3.5 to 7.5 Vpp at 5 kHz. Results suggest that Faradaic reactions can still proceed within electrochemical systems in the absence of well-established electrical double layers. This work also illustrates that in microfluidic systems, spatial medium variations must be considered as a function of experiment time, initial medium conditions, electric signal potential, frequency, and spatial position. PMID:25553200

Measurement of Ohms Law and Transport with Two Interacting Flux Ropes

NASA Astrophysics Data System (ADS)

Gekelman, Walter; Dehaas, Tim; Vincena, Steve; Daughton, Bill

2016-10-01

Two flux ropes, which are kink unstable, and repeatedly collide, were generated in a laboratory magnetoplasma. All the electric field terms in Ohms law: - ∇ ϕ -∂/A-> ∂ t ,1/ne , J-> × B-> , -1/ne ∇ P , u-> × B-> were measured at 48,000 spatial locations and thousands of time steps. All quantities oscillate at the flux rope collision frequency. The resistivity was derived from these quantities and could locally be 30 times the classical value. The resistivity, which was evaluated by integrating the electric field and current along 3D magnetic field is not largest at the quasi-seperatrix layer (QSL) where reconnection occurs. The relative size and spatial distribution of the Ohms law terms will be presented. The reconnection rate, Ξ = ∫ E-> . dl-> was largest near the QSL and could be positive or negative. Regions of negative resistivity exists (the volume integrated resistivity is positive) indicating dynamo action or the possibility of a non-local Ohms law. Volumetric temperature and density measurements are used to estimate electron heat transport and particle diffusion across the magnetic field. Work supported by UC office of the President (LANL-UCLA Grant) and done at the BAPSF which is supported by NSF-DOE.

Probing quantum Hall states with single-electron transistors at high magnetic fields

NASA Astrophysics Data System (ADS)

Gustafsson, Martin; Yankowitz, Matthew; Forsythe, Carlos; Zhu, Xiaoyang; Dean, Cory

The sequence of fractional quantum Hall states in graphene is not yet fully understood, largely due to disorder-induced limitations of conventional transport studies. Measurements of magnetotransport in other 2D crystals are further complicated by the difficulties in making ohmic contact to the materials. On the other hand, bulk electronic compressibility can provide clear signatures of the integer and fractional quantum Hall effects, does not require ohmic contact, and can be localized to regions of low disorder. The single-electron transistor (SET) is a suitable tool for such experiments due to its small size and high charge sensitivity, which allow electric fields penetrating the 2D electron system to be detected locally and with high fidelity. Here we report studies of exfoliated 2D van der Waals materials fully encapsulated in flakes of hexagonal boron nitride. SETs are fabricated lithographically on top of the encapsulation, yielding a structure which lends itself to experiments at high electric and magnetic fields. We demonstrate the method on monolayer graphene, where we observe fractional quantum Hall states at all filling factors ν = n / 3 up to n = 17 and extract their associated energy gaps for magnetic fields up to 31 tesla.

Electrical properties of double layer dielectric structures for space technology

NASA Astrophysics Data System (ADS)

Lian, Anqing

1993-04-01

Polymeric films such as polyimide (PI) and polyethylene terephthalate (PET) are used in space technology as thermal blankets. Thin SiO2 and SiN coatings plasma deposited onto PI and PET surfaces were proposed to protect the blanket materials against the space environment. The electrical properties of this kind of dual layer dielectric structure were investigated to understand the mechanisms for suppressing charge accumulation and flashover. Bulk and surface electrical conductivities of thin single-layer PI and PET samples and of the dual layer SiO2 and SiN combinations with PI and PET were measured in a range of applied electrical fields. The capacitance voltage (CV) technique was used for analyzing charge transport and distribution in the structures. The electric current in the bulk of the SiO2/PI and SiN/PI samples was found to depend on the polarity of the electric field. Other samples did not exhibit any such polarity effect. The polarity dependence is attributed to charge trapping at the PI/plasma deposit interface. The CV characteristics of the Al-PI-SiO2-Si structure confirm that charges which can modify the local electric field can be trapped near the interface. A model is proposed to interpret the properties of the currents in dual layer structures. This model can semi-quantitatively explain all the observed results.

Penetration of Large Scale Electric Field to Inner Magnetosphere

NASA Astrophysics Data System (ADS)

Chen, S. H.; Fok, M. C. H.; Sibeck, D. G.; Wygant, J. R.; Spence, H. E.; Larsen, B.; Reeves, G. D.; Funsten, H. O.

2015-12-01

The direct penetration of large scale global electric field to the inner magnetosphere is a critical element in controlling how the background thermal plasma populates within the radiation belts. These plasma populations provide the source of particles and free energy needed for the generation and growth of various plasma waves that, at critical points of resonances in time and phase space, can scatter or energize radiation belt particles to regulate the flux level of the relativistic electrons in the system. At high geomagnetic activity levels, the distribution of large scale electric fields serves as an important indicator of how prevalence of strong wave-particle interactions extend over local times and radial distances. To understand the complex relationship between the global electric fields and thermal plasmas, particularly due to the ionospheric dynamo and the magnetospheric convection effects, and their relations to the geomagnetic activities, we analyze the electric field and cold plasma measurements from Van Allen Probes over more than two years period and simulate a geomagnetic storm event using Coupled Inner Magnetosphere-Ionosphere Model (CIMI). Our statistical analysis of the measurements from Van Allan Probes and CIMI simulations of the March 17, 2013 storm event indicate that: (1) Global dawn-dusk electric field can penetrate the inner magnetosphere inside the inner belt below L~2. (2) Stronger convections occurred in the dusk and midnight sectors than those in the noon and dawn sectors. (3) Strong convections at multiple locations exist at all activity levels but more complex at higher activity levels. (4) At the high activity levels, strongest convections occur in the midnight sectors at larger distances from the Earth and in the dusk sector at closer distances. (5) Two plasma populations of distinct ion temperature isotropies divided at L-Shell ~2, indicating distinct heating mechanisms between inner and outer radiation belts. (6) CIMI simulations reveal alternating penetration and shielding electric fields during the main phase of the geomagnetic storm, indicating an impulsive nature of the large scale penetrating electric field in regulating the gain and loss of radiation belt particles. We will present the statistical analysis and simulations results.

Propulsion of Active Colloids by Self-Induced Field Gradients.

PubMed

Boymelgreen, Alicia; Yossifon, Gilad; Miloh, Touvia

2016-09-20

Previously, metallodielectric Janus particles have been shown to travel with their dielectric hemisphere forward under low frequency applied electric fields as a result of asymmetric induced-charge electroosmotic flow. Here, it is demonstrated that at high frequencies, well beyond the charge relaxation time of the electric double layer induced around the particle, rather than the velocity decaying to zero, the Janus particles reverse direction, traveling with their metallic hemisphere forward. It is proposed that such motion is the result of a surface force, arising from localized nonuniform electric field gradients, induced by the dual symmetry-breaking of an asymmetric particle adjacent to a wall, which act on the induced dipole of the particle to drive net motion even in a uniform AC field. Although the field is external, since the driving gradient is induced on the particle level, it may be considered an active colloid. We have thus termed this propulsion mechanism "self-dielectrophoresis", to distinguish from traditional dielectrophoresis where the driving nonuniform field is externally fixed and the particle direction is restricted. It is demonstrated theoretically and experimentally that the critical frequency at which the particle reverses direction can be characterized by a nondimensional parameter which is a function of electrolyte concentration and particle size.

Modulating the Electron-Hole Interaction in a Hybrid Lead Halide Perovskite with an Electric Field.

PubMed

Leijtens, Tomas; Srimath Kandada, Ajay Ram; Eperon, Giles E; Grancini, Giulia; D'Innocenzo, Valerio; Ball, James M; Stranks, Samuel D; Snaith, Henry J; Petrozza, Annamaria

2015-12-16

Despite rapid developments in both photovoltaic and light-emitting device performance, the understanding of the optoelectronic properties of hybrid lead halide perovskites is still incomplete. In particular, the polarizability of the material, the presence of molecular dipoles, and their influence on the dynamics of the photoexcitations remain an open issue to be clarified. Here, we investigate the effect of an applied external electric field on the photoexcited species of CH3NH3PbI3 thin films, both at room temperature and at low temperature, by monitoring the photoluminescence (PL) yield and PL decays. At room temperature we find evidence for electric-field-induced reduction of radiative bimolecular carrier recombination together with motion of charged defects that affects the nonradiative decay rate of the photoexcited species. At low temperature (190 K), we observe a field-induced enhancement of radiative free carrier recombination rates that lasts even after the removal of the field. We assign this to field-induced alignment of the molecular dipoles, which reduces the vibrational freedom of the lattice and the associated local screening and hence results in a stronger electron-hole interaction.

On the electrophonic generation of audio frequency sound by meteors

NASA Astrophysics Data System (ADS)

Kelley, Michael C.; Price, Colin

2017-04-01

Recorded for centuries, people can hear and see meteors nearly concurrently. Electromagnetic energy clearly propagates at the speed of light and converts to sound (called electrophonics) when coupled to metals. An explanation for the electromagnetic energy source is suggested. Coma ions around the meteor head can easily travel across magnetic field lines up to 120 km. The electrons, however, are tied to magnetic field lines, since they must gyrate around the field above 75 km. A large ambipolar electric field must be generated to conserve charge neutrality. This localized electric field maps to the E region then drives a large Hall current that launches the electromagnetic wave. Using antenna theory and following, a power flux of over 10-8 W/m2 at the ground is found. Electrophonic conversion to sound efficiency then needs to be only 0.1% to explain why humans can hear and see meteors nearly concurrently.

Mechanical Modulation of Phonon-Assisted Field Emission in a Silicon Nanomembrane Detector for Time-of-Flight Mass Spectrometry

PubMed Central

Park, Jonghoo; Blick, Robert H.

2016-01-01

We demonstrate mechanical modulation of phonon-assisted field emission in a free-standing silicon nanomembrane detector for time-of-flight mass spectrometry of proteins. The impacts of ion bombardment on the silicon nanomembrane have been explored in both mechanical and electrical points of view. Locally elevated lattice temperature in the silicon nanomembrane, resulting from the transduction of ion kinetic energy into thermal energy through the ion bombardment, induces not only phonon-assisted field emission but also a mechanical vibration in the silicon nanomembrane. The coupling of these mechanical and electrical phenomenon leads to mechanical modulation of phonon-assisted field emission. The thermal energy relaxation through mechanical vibration in addition to the lateral heat conduction and field emission in the silicon nanomembrane offers effective cooling of the nanomembrane, thereby allowing high resolution mass analysis. PMID:26861329

A dawn to dusk electric field in the Jovian magnetosphere

NASA Technical Reports Server (NTRS)

Goertz, C. K.; Ip, W. I.

1983-01-01

It is shown that if Io-injected plasma is lost via a planetary wind-fixed Birkeland current system may result. This is due to the fact that the azimuthal centrifugal current flows across a density gradient produced by the loss of plasma through the planetary wind in the tail. The divergent centrifugal current is connected to field-aligned Birkeland currents which flow into the ionosphere at dawn and out of it at dusk. The closure currents in the ionosphere require a dawn to dusk electric field which at the orbit of Io is estimated to have a strength of 0.2 mV/m. However, the values of crucial parameters are not well known and the field at Io's orbit may well be significantly larger. Independent estimates derived from the local time asymmetry of the torus UV emission indicate a field of 1.5 mV/m.

Macroscopic Models of Local Field Potentials and the Apparent 1/f Noise in Brain Activity

PubMed Central

Bédard, Claude; Destexhe, Alain

2009-01-01

The power spectrum of local field potentials (LFPs) has been reported to scale as the inverse of the frequency, but the origin of this 1/f noise is at present unclear. Macroscopic measurements in cortical tissue demonstrated that electric conductivity (as well as permittivity) is frequency-dependent, while other measurements failed to evidence any dependence on frequency. In this article, we propose a model of the genesis of LFPs that accounts for the above data and contradictions. Starting from first principles (Maxwell equations), we introduce a macroscopic formalism in which macroscopic measurements are naturally incorporated, and also examine different physical causes for the frequency dependence. We suggest that ionic diffusion primes over electric field effects, and is responsible for the frequency dependence. This explains the contradictory observations, and also reproduces the 1/f power spectral structure of LFPs, as well as more complex frequency scaling. Finally, we suggest a measurement method to reveal the frequency dependence of current propagation in biological tissue, and which could be used to directly test the predictions of this formalism. PMID:19348744

Optical Vector Near-Field Imaging for the Design of Impedance Matched Optical Antennas and Devices

NASA Astrophysics Data System (ADS)

Olmon, Robert L.

Antennas control and confine electromagnetic energy, transforming free-space propagating modes to localized regions. This is not only true for the traditional classical radio antenna, but also for structures that interact resonantly at frequencies throughout the visible regime, that are on the micro- and nanometer size scales. The investigation of these optical antennas has increased dramatically in recent years. They promise to bring the transformative capabilities of radio antennas to the nanoscale in fields such as plasmonics, photonics, spectroscopy, and microscopy. However, designing optical antennas with desired properties is not straightforward due to different material properties and geometric considerations in the optical regime compared to the RF. New antenna characterization tools and techniques must be developed for the optical frequency range. Here, the optical analogue of the vector network analyzer, based on a scattering-type scanning near-field optical microscope, is described and demonstrated for the investigation of the electric and magnetic properties of optical antennas through their electromagnetic vector near-field. Specifically, bringing this microwave frequency tool to the optical regime enables the study of antenna resonant length scaling, optical frequency electromagnetic parameters including current density and impedance, optical antenna coupling to waveguides and nanoloads, local electric field enhancement, and electromagnetic duality of complementary optical antenna geometries.

C/NOFS Measurements of Stormtime Magnetic Perturbations in the Low-latitude Ionosphere

NASA Technical Reports Server (NTRS)

Le, Guan; Burke, William J.; Pfaff, Robert F.; Freudenreich, Henry; Maus, Stefan; Luehr, Hermann

2012-01-01

The Vector Electric Field Investigation suite on the C/NOFS satellite includes a fluxgate magnetometer to monitor the Earth's magnetic fields in the low-latitude ionosphere. Measurements yield full magnetic vectors every second over the range of +/- 45,000 nT with a one-bit resolution of 1.37 nT (16 bit AID) in each component. The sensor's primary responsibility is to support calculations of both VxB and ExB with greater accuracy than can be obtained using standard magnetic field models. The data also contain information about large-scale current systems, that, when analyzed in conjunction with electric field measurements, promise to significantly expand understanding of equatorial electrodynamics. We first compare in situ measurements with the POMME (POtsdam Magnetic Model of the Earth) model to establish in-flight sensor "calibrations" and to compute magnetic residuals. At low latitudes the residuals are predominately products of the stormtime ring current. Since C/NOFS provides a complete coverage of all local times every 97 minutes, magnetic field data allow studies of the temporal evolution and local-time variations of stormtime ring current. The analysis demonstrates the feasibility of using instrumented spacecraft in low-inclination orbits to extract a timely proxy for the provisional Dst index and to specify the ring current's evolution.

Photocurrent mapping of near-field optical antenna resonances

NASA Astrophysics Data System (ADS)

Barnard, Edward S.; Pala, Ragip A.; Brongersma, Mark L.

2011-09-01

An increasing number of photonics applications make use of nanoscale optical antennas that exhibit a strong, resonant interaction with photons of a specific frequency. The resonant properties of such antennas are conventionally characterized by far-field light-scattering techniques. However, many applications require quantitative knowledge of the near-field behaviour, and existing local field measurement techniques provide only relative, rather than absolute, data. Here, we demonstrate a photodetector platform that uses a silicon-on-insulator substrate to spectrally and spatially map the absolute values of enhanced fields near any type of optical antenna by transducing local electric fields into photocurrent. We are able to quantify the resonant optical and materials properties of nanoscale (~50 nm) and wavelength-scale (~1 µm) metallic antennas as well as high-refractive-index semiconductor antennas. The data agree well with light-scattering measurements, full-field simulations and intuitive resonator models.

Controlling molecular condensation/diffusion of copper phthalocyanine by local electric field induced with scanning tunneling microscope tip

NASA Astrophysics Data System (ADS)

Nagaoka, Katsumi; Yaginuma, Shin; Nakayama, Tomonobu

2018-02-01

We have discovered the condensation/diffusion phenomena of copper phthalocyanine (CuPc) molecules controlled with a pulsed electric field induced by the scanning tunneling microscope tip. This behavior is not explained by the conventional induced dipole model. In order to understand the mechanism, we have measured the electronic structure of the molecule by tunneling spectroscopy and also performed theoretical calculations on molecular orbitals. These data clearly indicate that the molecule is positively charged owing to charge transfer to the substrate, and that hydrogen bonding exists between CuPc molecules, which makes the molecular island stable.

System and Method of Locating Lightning Strikes

NASA Technical Reports Server (NTRS)

Medelius, Pedro J. (Inventor); Starr, Stanley O. (Inventor)

2002-01-01

A system and method of determining locations of lightning strikes has been described. The system includes multiple receivers located around an area of interest, such as a space center or airport. Each receiver monitors both sound and electric fields. The detection of an electric field pulse and a sound wave are used to calculate an area around each receiver in which the lighting is detected. A processor is coupled to the receivers to accurately determine the location of the lighting strike. The processor can manipulate the receiver data to compensate for environmental variables such as wind, temperature, and humidity. Further, each receiver processor can discriminate between distant and local lightning strikes.

On-demand trajectory control of continuously generated airborne microdroplets

NASA Astrophysics Data System (ADS)

Ishiwata, Tomoki; Sakai, Keiji

2011-05-01

A technique to control the trajectory of in-flight microdroplets is described. The localized electric field generated by a needle electrode applies the dielectrophoretic force to the droplet to deflect its trajectory. Deflection by as much as 0.2 rad can be achieved, sufficient for industrial use. Moreover, highly selective control among droplets in a stream was demonstrated with the electric field modulations of 10 μs, which corresponds to the sorting speed of 105 s-1. In contrast to the conventional electrostatic control, the proposed technique is effective also for insulating liquids, allowing it to be applied to a wider range of materials.

Toward microscale flow control using non-uniform electro-osmotic flow

NASA Astrophysics Data System (ADS)

Paratore, Federico; Boyko, Evgeniy; Gat, Amir D.; Kaigala, Govind V.; Bercovici, Moran

2018-02-01

We present a novel method that allows establishing desired flow patterns in a Hele-Shaw cell, solely by controlling the surface chemistry, without the use of physical walls. Using weak electrolytes, we locally pattern the chamber's ceiling and/or floor, thus defining a spatial distribution of surface charge. This translates to a non-uniform electric double layer which when subjected to an external electric field applied along the chamber, gives rise to non-uniform electroosmotic flow (EOF). We present the theory that allows prediction and design of such flows fields, as well as experimental demonstrations opening the door to configurable microfluidic devices.

From static electric images to electric flow: towards dynamic perceptual cues in active electroreception.

PubMed

Hofmann, Volker; Sanguinetti-Scheck, Juan I; Gómez-Sena, Leonel; Engelmann, Jacob

2013-01-01

Active electroreception is an ancestral trait found in many aquatic vertebrates and has evolved independently in two teleost lineages, the Gymnotiformes and the Mormyriformes. Unique to these so-called weakly electric fish is their ability to actively generate electrical currents in the water and sense the electrical properties of the environment. How natural behavior contributes to this sensory system has been of interest to neuroethologists since the pioneering works of Lissmann. Here we report on a mutual modeling and experimental study of the stimuli available during active electrolocation of Gnathonemus petersii (Mormyridae). We show the validity of the model (I) by demonstrating that localized spatial patterns of object induced modulations in the electric field (electric images) are comparable to experimentally mapped 2-dimensional electric images and (II) by replicating earlier key findings showing that a normalized metric of electric image width provides an unambiguous cue for distance estimation. We then show that electric images and the distance metric vary systematically when an object is moved along the trunk. These potential ambiguities with regard to localization lead us to a spatiotemporal analysis of electric images. We introduce a new temporal metric for distance estimation that is based on the normalized spatial properties of electrical images. Finally, based on a survey of exploratory behavior, we show how objects situated at the tail, a region previously neglected, cast global electric images that extend over the whole sensory epithelium of the animals. Copyright © 2012 Elsevier Ltd. All rights reserved.

Quantum dot-based local field imaging reveals plasmon-based interferometric logic in silver nanowire networks.

PubMed

Wei, Hong; Li, Zhipeng; Tian, Xiaorui; Wang, Zhuoxian; Cong, Fengzi; Liu, Ning; Zhang, Shunping; Nordlander, Peter; Halas, Naomi J; Xu, Hongxing

2011-02-09

We show that the local electric field distribution of propagating plasmons along silver nanowires can be imaged by coating the nanowires with a layer of quantum dots, held off the surface of the nanowire by a nanoscale dielectric spacer layer. In simple networks of silver nanowires with two optical inputs, control of the optical polarization and phase of the input fields directs the guided waves to a specific nanowire output. The QD-luminescent images of these structures reveal that a complete family of phase-dependent, interferometric logic functions can be performed on these simple networks. These results show the potential for plasmonic waveguides to support compact interferometric logic operations.

Tortuosity of lightning return stroke channels

NASA Technical Reports Server (NTRS)

Levine, D. M.; Gilson, B.

1984-01-01

Data obtained from photographs of lightning are presented on the tortuosity of return stroke channels. The data were obtained by making piecewise linear fits to the channels, and recording the cartesian coordinates of the ends of each linear segment. The mean change between ends of the segments was nearly zero in the horizontal direction and was about eight meters in the vertical direction. Histograms of these changes are presented. These data were used to create model lightning channels and to predict the electric fields radiated during return strokes. This was done using a computer generated random walk in which linear segments were placed end-to-end to form a piecewise linear representation of the channel. The computer selected random numbers for the ends of the segments assuming a normal distribution with the measured statistics. Once the channels were simulated, the electric fields radiated during a return stroke were predicted using a transmission line model on each segment. It was found that realistic channels are obtained with this procedure, but only if the model includes two scales of tortuosity: fine scale irregularities corresponding to the local channel tortuosity which are superimposed on large scale horizontal drifts. The two scales of tortuosity are also necessary to obtain agreement between the electric fields computed mathematically from the simulated channels and the electric fields radiated from real return strokes. Without large scale drifts, the computed electric fields do not have the undulations characteristics of the data.

Correlation Of Terrestrial gamma flashes, Electric fields, and Lightning strikes (COTEL) in thunderstorms using networked balloon payloads developed by university and community college students

NASA Astrophysics Data System (ADS)

Landry, B. J.; Blair, D.; Causey, J.; Collins, J.; Davis, A.; Fernandez-Kim, V.; Kennedy, J.; Pate, N.; Kearney, C.; Schayer, C.; Turk, E.; Cherry, M. L.; Fava, C.; Granger, D.; Stewart, M.; Guzik, T. G.

2017-12-01

High energy gamma ray flashes from terrestrial sources have been observed by satellites for decades, but the actual mechanism, assumed to be thunderstorm lightning, has yet to be fully characterized. The goal of COTEL, funded by NASA through the University Student Instrument Project (USIP) program, is to correlate in time TGF events, lightning strikes, and electric fields inside of thunderstorms. This will be accomplished using a small network of balloon-borne payloads suspended in and around thunderstorm environments. The payloads will detect and timestamp gamma radiation bursts, lightning strikes, and the intensity of localized electric fields. While in flight, data collected by the payloads will be transmitted to a ground station in real-time and will be analyzed post-flight to investigate potential correlations between lightning, TGFs, and electric fields. The COTEL student team is in its second year of effort having spent the first year developing the basic balloon payloads and ground tracking system. Currently the team is focusing on prototype electric field and gamma radiation detectors. Testing and development of these systems will continue into 2018, and flight operations will take place during the spring 2018 Louisiana thunderstorm season. The presentation, led by undergraduate Physics student Brad Landry, will cover the student team effort in developing the COTEL system, an overview of the system architecture, balloon flight tests conducted to date, preliminary results from prototype detectors, lessons learned for student-led science projects, and future plans.

Local bias-induced phase transitions

DOE PAGES

Seal, Katyayani; Baddorf, Arthur P.; Jesse, Stephen; ...

2008-11-27

Electrical bias-induced phase transitions underpin a wide range of applications from data storage to energy generation and conversion. The mechanisms behind these transitions are often quite complex and in many cases are extremely sensitive to local defects that act as centers for local transformations or pinning. Furthermore, using ferroelectrics as an example, we review methods for probing bias-induced phase transitions and discuss the current limitations and challenges for extending the methods to field-induced phase transitions and electrochemical reactions in energy storage, biological and molecular systems.

Applying electric field to charged and polar particles between metallic plates: extension of the Ewald method.

PubMed

Takae, Kyohei; Onuki, Akira

2013-09-28

We develop an efficient Ewald method of molecular dynamics simulation for calculating the electrostatic interactions among charged and polar particles between parallel metallic plates, where we may apply an electric field with an arbitrary size. We use the fact that the potential from the surface charges is equivalent to the sum of those from image charges and dipoles located outside the cell. We present simulation results on boundary effects of charged and polar fluids, formation of ionic crystals, and formation of dipole chains, where the applied field and the image interaction are crucial. For polar fluids, we find a large deviation of the classical Lorentz-field relation between the local field and the applied field due to pair correlations along the applied field. As general aspects, we clarify the difference between the potential-fixed and the charge-fixed boundary conditions and examine the relationship between the discrete particle description and the continuum electrostatics.

Investigating large-scale brain dynamics using field potential recordings: analysis and interpretation.

PubMed

Pesaran, Bijan; Vinck, Martin; Einevoll, Gaute T; Sirota, Anton; Fries, Pascal; Siegel, Markus; Truccolo, Wilson; Schroeder, Charles E; Srinivasan, Ramesh

2018-06-25

New technologies to record electrical activity from the brain on a massive scale offer tremendous opportunities for discovery. Electrical measurements of large-scale brain dynamics, termed field potentials, are especially important to understanding and treating the human brain. Here, our goal is to provide best practices on how field potential recordings (electroencephalograms, magnetoencephalograms, electrocorticograms and local field potentials) can be analyzed to identify large-scale brain dynamics, and to highlight critical issues and limitations of interpretation in current work. We focus our discussion of analyses around the broad themes of activation, correlation, communication and coding. We provide recommendations for interpreting the data using forward and inverse models. The forward model describes how field potentials are generated by the activity of populations of neurons. The inverse model describes how to infer the activity of populations of neurons from field potential recordings. A recurring theme is the challenge of understanding how field potentials reflect neuronal population activity given the complexity of the underlying brain systems.

Creating Rydberg electron wave packets using terahertz pulses

NASA Astrophysics Data System (ADS)

Bromage, Jake

1999-10-01

In this thesis I present experiments in which we excited classical-limit states of an atom using terahertz pulses. In a classical-limit state, an atom's outer electron is confined to a wave packet that orbits the core along a classical trajectory. Researchers have excited states with classical traits, but wave packets localized in all three dimensions have proved elusive. Theoretical studies have shown such states can be created using terahertz pulses. Using these techniques, we created a linear-orbit wave packet (LOWP), that is three-dimensionally localized and orbits along a line on one side of the atom's core. Terahertz pulses are sub-picosecond bursts of far- infrared radiation. Unlike ultrashort optical pulses, the electric field of terahertz pulses barely completes a single cycle. Our simulations of the atom-pulse interaction show that this electric field profile is critical in determining the quality of the wave packet. To characterize our terahertz pulses, we invented dithered-edge sampling which time- resolves the electric field using a photoconductive receiver and a triggered attenuator. We also studied how pulses are distorted after propagating through metallic structures, and used our findings to design our atomic experiments. We excited wave packets in atomic sodium using a two-step process. First, we used tunable, nanosecond dye lasers to excite an extreme Stark state. Next, we used a terahertz pump pulse to coherently redistribute population among extreme Stark states in neighboring manifolds. Interference between the final states produces a localized, dynamic LOWP. To analyze the LOWP, we ionized it with a stronger terahertz probe pulse, varying the pump-probe delay to map out its motion. We observed two strong LOWP signatures. Changing the static electric field produced small changes (2%) in the orbital period that agreed with our theoretical predictions. Secondly, because the LOWP scatters off the core, the pump-probe signal depended on the direction of the kick the LOWP received from the robe pulse. These observations, combined with our detailed simulations that used sodium parameters and the actual shape of the terahertz pulse, lead us to conclude that we excited a LOWP.

Impact of local environmental conditions on atmospheric electrical potential gradient measurements

NASA Astrophysics Data System (ADS)

Buzás, Attila; Barta, Veronika; Steinbach, Péter; Bór, József

2017-04-01

The atmospheric electrical potential gradient (PG) is a fundamental parameter of the global electric circuit (GEC) which comprises all large scale quasi-static electrical processes occurring in between the surface of the Earth and the lower ionosphere. The observation of PG near the Earth's surface plays a pivotal role in surveying our atmospheric electrical environment. The PG shows high variability in different temporal and spatial scales and it is especially sensitive to local effects. Therefore, obtaining a PG value which represents the general state of the GEC over a larger area rather than various effects due to measuring site-specific local factors is a challenging task. PG measurements are going on in the Széchenyi István Geophysical Observatory (NCK, 47°38' N, 16°43' E) of the Research Centre for Astronomy and Earth Sciences, Hungarian Academy of Sciences near Nagycenk, Hungary since 1961. PG sensors are set up in NCK in an open area surrounded by buildings and trees within 20 m distance. The effect of the changing vegetation on the long-term trend observed in the PG variation at NCK has been subject of debates [1,2,3]. In order to examine the possible bias in the measured PG values due to the relatively close buildings and trees at NCK, two sets of simultaneous PG measurements from two EFM-100 field mills were compared. One field mill was kept at a fixed location while the other was moved to grid points covering the open area around the fixed field mill. The measurement was done in fair weather conditions in summer and was repeated during the winter. The poster demonstrates the performance of this method in surveying the effect of various objects and the state of vegetation on the measured PG values by comparing the measured PG differences to those obtained from electrostatic models calculated by the finite element method using the FEMM 4.2 software package. [1] F. Märcz and R. G. Harrison, 2003, Annales Gephysicae, 21: 2193-2200 [2] F. Märcz and R. G. Harrison, 2005, Annales Gephysicae, 23: 1987-1995 [3] E. Williams, R. Markson and S. Heckman, 2005, Geophysical Research Letters, vol. 32

Saccade Modulation by Optical and Electrical Stimulation in the Macaque Frontal Eye Field

PubMed Central

Grimaldi, Piercesare; Schweers, Nicole

2013-01-01

Recent studies have demonstrated that strong neural modulations can be evoked with optogenetic stimulation in macaque motor cortex without observing any evoked movements (Han et al., 2009, 2011; Diester et al., 2011). It remains unclear why such perturbations do not generate movements and if conditions exist under which they may evoke movements. In this study, we examine the effects of five optogenetic constructs in the macaque frontal eye field and use electrical microstimulation to assess whether optical perturbation of the local network leads to observable motor changes during optical, electrical, and combined stimulation. We report a significant increase in the probability of evoking saccadic eye movements when low current electrical stimulation is coupled to optical stimulation compared with when electrical stimulation is used alone. Experiments combining channelrhodopsin 2 (ChR2) and electrical stimulation with simultaneous fMRI revealed no discernible fMRI activity at the electrode tip with optical stimulation but strong activity with electrical stimulation. Our findings suggest that stimulation with current ChR2 optogenetic constructs generates subthreshold activity that contributes to the initiation of movements but, in most cases, is not sufficient to evoke a motor response. PMID:24133271

Modelling of streamer ignition and propagation in the system of two approaching hydrometeors

NASA Astrophysics Data System (ADS)

Jansky, J.; Pasko, V. P.

2017-12-01

The lightning initiation in low thundercloud fields represents an unsolved problem in lightning discharge physics. One of the initial conditions required for formation of a hot leader channel is initiation of non-thermal streamer discharges. Streamers can be initiated from electron avalanches, however, the problem of existence of an electric field strong enough for streamer initiation in thunderclouds is still open. The maximum electric field in thunderstorms measured by balloons is typically 3-4 kV cm-1 atm-1, that is significantly smaller than the breakdown electric field needed for avalanche multiplication of electrons Ek≃28.7 kV cm-1 atm-1. One of the possible explanations for the streamer corona initiation is that hydrometeors greatly intensify the local electric field by at least an order of magnitude to initiate an electron avalanche. It was suggested that a particle pair or chain create more favorable conditions for initiation of lightning discharge than a single precipitation particle in low electric fields. Recently Cai et al. [GRL, 44, 5758-5765, 2017] analyzed the ignition conditions for two hydrometeors of same radii. In the present work we use streamer fluid model to study streamer initiation scenarios in a system of two hydrometeors with different radii. When the hydrometeors are approaching the Townsend discharge may develop first between them. Then the Townsend discharge transforms to streamer and two hydrometeors connect electrically, which leads to increase of the electric field on the outside hemispheres of hydrometeors. This increase of field for two particles of same radii was analyzed by Cooray et al. [Proceedings of 24th International Conference on Lightning Protection, Birmingham, United Kingdom, 1998]. The combination of small and large hydrometeors leads to higher enhancement on the outside of small hydrometeor. Simulation results show that streamer ignites there and propagates away from two hydrometeors. The streamer ignites at fields below Meek criterion due to the effects of photoionization feedback [Naidis, JPD, 38, 2211-2214, 2005; Liu et al., JASTP, 80, 179-186, 2012].

Statistical Properties of Ribbon Evolution and Reconnection Electric Fields in Eruptive and Confined Flares.

PubMed

Hinterreiter, J; Veronig, A M; Thalmann, J K; Tschernitz, J; Pötzi, W

2018-01-01

A statistical study of the chromospheric ribbon evolution in H[Formula: see text] two-ribbon flares was performed. The data set consists of 50 confined (62%) and eruptive (38%) flares that occurred from June 2000 to June 2015. The flares were selected homogeneously over the H[Formula: see text] and Geostationary Operational Environmental Satellite (GOES) classes, with an emphasis on including powerful confined flares and weak eruptive flares. H[Formula: see text] filtergrams from the Kanzelhöhe Observatory in combination with Michelson Doppler Imager (MDI) and Helioseismic and Magnetic Imager (HMI) magnetograms were used to derive the ribbon separation, the ribbon-separation velocity, the magnetic-field strength, and the reconnection electric field. We find that eruptive flares reveal statistically larger ribbon separation and higher ribbon-separation velocities than confined flares. In addition, the ribbon separation of eruptive flares correlates with the GOES SXR flux, whereas no clear dependence was found for confined flares. The maximum ribbon-separation velocity is not correlated with the GOES flux, but eruptive flares reveal on average a higher ribbon-separation velocity (by ≈ 10 km s -1 ). The local reconnection electric field of confined ([Formula: see text]) and eruptive ([Formula: see text]) flares correlates with the GOES flux, indicating that more powerful flares involve stronger reconnection electric fields. In addition, eruptive flares with higher electric-field strengths tend to be accompanied by faster coronal mass ejections. The online version of this article (10.1007/s11207-018-1253-1) contains supplementary material, which is available to authorized users.

Streamer properties and associated x-rays in perturbed air

NASA Astrophysics Data System (ADS)

Köhn, C.; Chanrion, O.; Babich, L. P.; Neubert, T.

2018-01-01

Streamers are ionization waves in electric discharges. One of the key ingredients of streamer propagation is an ambient gas that serves as a source of free electrons. Here, we explore the dependence of streamer dynamics on different spatial distributions of ambient air molecules. We vary the spatial profile of air parallel and perpendicular to the ambient electric field. We consider local sinusoidal perturbations of 5%-100%, as induced from discharge shock waves. We use a cylindrically symmetric particle-in-cell code to simulate the evolution of bidirectional streamers and compare the electron density, electric field, streamer velocity and electron energy of streamers in uniform air and in perturbed air. In all considered cases, the motion is driven along in decreasing air density and damped along increasing air density. Perturbations of at most 5%-10% change the velocity differences by up to approximately 40%. Perturbations perpendicular to the electric field additionally squeeze or branch streamers. Air variations can thus partly explain the difference of velocities and morphologies of streamer discharges. In cases with large perturbations, electrons gain energies of up to 30 keV compared to 100 eV in uniformly distributed air. For such perturbations parallel to the ambient electric field, we see the spontaneous initiation of a negative streamer; for perpendicular perturbations, x-rays with energies of up to 20 keV are emitted within 0.17 ns.

Effect of conductor geometry on source localization: Implications for epilepsy studies

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schlitt, H.; Heller, L.; Best, E.

1994-07-01

We shall discuss the effects of conductor geometry on source localization for applications in epilepsy studies. The most popular conductor model for clinical MEG studies is a homogeneous sphere. However, several studies have indicated that a sphere is a poor model for the head when the sources are deep, as is the case for epileptic foci in the mesial temporal lobe. We believe that replacing the spherical model with a more realistic one in the inverse fitting procedure will improve the accuracy of localizing epileptic sources. In order to include a realistic head model in the inverse problem, we mustmore » first solve the forward problem for the realistic conductor geometry. We create a conductor geometry model from MR images, and then solve the forward problem via a boundary integral equation for the electric potential due to a specified primary source. One the electric potential is known, the magnetic field can be calculated directly. The most time-intensive part of the problem is generating the conductor model; fortunately, this needs to be done only once for each patient. It takes little time to change the primary current and calculate a new magnetic field for use in the inverse fitting procedure. We present the results of a series of computer simulations in which we investigate the localization accuracy due to replacing the spherical model with the realistic head model in the inverse fitting procedure. The data to be fit consist of a computer generated magnetic field due to a known current dipole in a realistic head model, with added noise. We compare the localization errors when this field is fit using a spherical model to the fit using a realistic head model. Using a spherical model is comparable to what is usually done when localizing epileptic sources in humans, where the conductor model used in the inverse fitting procedure does not correspond to the actual head.« less

Extensive electron transport and energization via multiple, localized dipolarizing flux bundles

NASA Astrophysics Data System (ADS)

Gabrielse, Christine; Angelopoulos, Vassilis; Harris, Camilla; Artemyev, Anton; Kepko, Larry; Runov, Andrei

2017-05-01

Using an analytical model of multiple dipolarizing flux bundles (DFBs) embedded in earthward traveling bursty bulk flows, we demonstrate how equatorially mirroring electrons can travel long distances and gain hundreds of keV from betatron acceleration. The model parameters are constrained by four Time History of Events and Macroscale Interactions during Substorms satellite observations, putting limits on the DFBs' speed, location, and magnetic and electric field magnitudes. We find that the sharp, localized peaks in magnetic field have such strong spatial gradients that energetic electrons ∇B drift in closed paths around the peaks as those peaks travel earthward. This is understood in terms of the third adiabatic invariant, which remains constant when the field changes on timescales longer than the electron's drift timescale: An energetic electron encircles a sharp peak in magnetic field in a closed path subtending an area of approximately constant flux. As the flux bundle magnetic field increases the electron's drift path area shrinks and the electron is prevented from escaping to the ambient plasma sheet, while it continues to gain energy via betatron acceleration. When the flux bundles arrive at and merge with the inner magnetosphere, where the background field is strong, the electrons suddenly gain access to previously closed drift paths around the Earth. DFBs are therefore instrumental in transporting and energizing energetic electrons over long distances along the magnetotail, bringing them to the inner magnetosphere and energizing them by hundreds of keV.