Scaling of Dielectric Breakdown Thresholds in Earth's and CO2-rich atmospheres: Impact for Predictions of Extraterrestrial Transient Luminous Events and Lightning Discharges

NASA Astrophysics Data System (ADS)

Riousset, J. A.

2016-12-01

Earth's 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 types of dielectric breakdown, but are governed by different physics. In particular, 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 rather 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 in our solar system. This lets us predict the likelihood of electrical discharges on, e.g., Mars, Venus and Titan, and calculate the expected electric field conditions, under which discharges have been observed on Jupiter, Saturn, Uranus, and Neptune [Leblanc et al., ISSI Spa. Sci. Series, Springer, 2008, Yair, Adv. Space Res., 50(3), 293-310, 2012]. Our results anticipate the arrival of ExoMars 2016's Schiaparelli module, which will provide the first records of electric field at the surface of the planet [Déprez et al., EGU GA, 16, 16613, 2014]. This research is also motived by the increasing probability of manned missions to Mars and the potential electrostatic hazards it may face [Yair, 2012], and by the role of electrical discharges in the creation of active radicals, some of which may be of biological importance [Miller, Science, 117, 528-529, 1953; Biochem. Biophys. Acta, 23, 480-489, 1957].

Electrically controllable liquid crystal random lasers below the Fréedericksz transition threshold.

PubMed

Lee, Chia-Rong; Lin, Jia-De; Huang, Bo-Yuang; Lin, Shih-Hung; Mo, Ting-Shan; Huang, Shuan-Yu; Kuo, Chie-Tong; Yeh, Hui-Chen

2011-01-31

This investigation elucidates for the first time electrically controllable random lasers below the threshold voltage in dye-doped liquid crystal (DDLC) cells with and without adding an azo-dye. Experimental results show that the lasing intensities and the energy thresholds of the random lasers can be decreased and increased, respectively, by increasing the applied voltage below the Fréedericksz transition threshold. The below-threshold-electric-controllability of the random lasers is attributable to the effective decrease of the spatial fluctuation of the orientational order and thus of the dielectric tensor of LCs by increasing the electric-field-aligned order of LCs below the threshold, thereby increasing the diffusion constant and decreasing the scattering strength of the fluorescence photons in their recurrent multiple scattering. This can result in the decrease in the lasing intensity of the random lasers and the increase in their energy thresholds. Furthermore, the addition of an azo-dye in DDLC cell can induce the range of the working voltage below the threshold for the control of the random laser to reduce.

Improved outcomes in auditory brainstem implantation with the use of near-field electrical compound action potentials.

PubMed

Mandalà, Marco; Colletti, Liliana; Colletti, Giacomo; Colletti, Vittorio

2014-12-01

To compare the outcomes (auditory threshold and open-set speech perception at 48-month follow-up) of a new near-field monitoring procedure, electrical compound action potential, on positioning the auditory brainstem implant electrode array on the surface of the cochlear nuclei versus the traditional far-field electrical auditory brainstem response. Retrospective study. Tertiary referral center. Among the 202 patients with auditory brainstem implants fitted and monitored with electrical auditory brainstem response during implant fitting, 9 also underwent electrical compound action potential recording. These subjects were matched retrospectively with a control group of 9 patients in whom only the electrical auditory brainstem response was recorded. Electrical compound action potentials were obtained using a cotton-wick recording electrode located near the surface of the cochlear nuclei and on several cranial nerves. Significantly lower potential thresholds were observed with the recording electrode located on the cochlear nuclei surface compared with the electrical auditory brainstem response (104.4 ± 32.5 vs 158.9 ± 24.2, P = .0030). Electrical brainstem response and compound action potentials identified effects on the neighboring cranial nerves on 3.2 ± 2.4 and 7.8 ± 3.2 electrodes, respectively (P = .0034). Open-set speech perception outcomes at 48-month follow-up had improved significantly in the near- versus far-field recording groups (78.9% versus 56.7%; P = .0051). Electrical compound action potentials during auditory brainstem implantation significantly improved the definition of the potential threshold and the number of auditory and extra-auditory waves generated. It led to the best coupling between the electrode array and cochlear nuclei, significantly improving the overall open-set speech perception. © American Academy of Otolaryngology—Head and Neck Surgery Foundation 2014.

Biological and Agricultural Studies on Application of Discharge Plasma and Electromagnetic Fields 5. Effects of High Electric Fields on Animals

NASA Astrophysics Data System (ADS)

Isaka, Katsuo

The biological effects of extremely low frequency electric fields on animals are reviewed with emphasis on studies of the nervous system, behavior, endocrinology, and blood chemistry. First, this paper provides a histrical overview of studies on the electric field effects initiated in Russia and the United States mainly regarding electric utility workers in high voltage substations and transmission lines. Then, the possible mechanisms of electric field effects are explained using the functions of surface electric fields and induced currents in biological objects. The real mechanisms have not yet been identified. The thresholds of electric field perception levels for rats, baboons, and humans are introduced and compared. The experimental results concerning the depression of melatonin secretion in rats exposed to electric fields are described.

Transport of ions through a (6,6) carbon nanotube under electric fields

NASA Astrophysics Data System (ADS)

Shen, Li; Xu, Zhen; Zhou, Zhe-Wei; Hu, Guo-Hui

2014-11-01

The transport of water and ions through carbon nanotubes (CNTs) is crucial in nanotechnology and biotechnology. Previous investigation indicated that the ions can hardly pass through (6,6) CNTs due to their hydrated shells. In the present study, utilizing molecular dynamics simulation, it is shown that the energy barrier mainly originating from the hydrated water molecules could be overcome by applying an electric field large enough in the CNT axis direction. Potential of mean force is calculated to show the reduction of energy barrier when the electric field is present for (Na+, K+, Cl-) ions. Consequently, ionic flux through (6,6) CNTs can be found once the electric field becomes larger than a threshold value. The variation of the coordination numbers of ions at different locations from the bulk to the center of the CNT is also explored to elaborate this dynamic process. The thresholds of the electric field are different for Na+, K+, and Cl- due to their characteristics. This consequence might be potentially applied in ion selectivity in the future.

Electrokinetic instability in microchannel ferrofluid/water co-flows

PubMed Central

Song, Le; Yu, Liandong; Zhou, Yilong; Antao, Asher Reginald; Prabhakaran, Rama Aravind; Xuan, Xiangchun

2017-01-01

Electrokinetic instability refers to unstable electric field-driven disturbance to fluid flows, which can be harnessed to promote mixing for various electrokinetic microfluidic applications. This work presents a combined numerical and experimental study of electrokinetic ferrofluid/water co-flows in microchannels of various depths. Instability waves are observed at the ferrofluid and water interface when the applied DC electric field is beyond a threshold value. They are generated by the electric body force that acts on the free charge induced by the mismatch of ferrofluid and water electric conductivities. A nonlinear depth-averaged numerical model is developed to understand and simulate the interfacial electrokinetic behaviors. It considers the top and bottom channel walls’ stabilizing effects on electrokinetic flow through the depth averaging of three-dimensional transport equations in a second-order asymptotic analysis. This model is found accurate to predict both the observed electrokinetic instability patterns and the measured threshold electric fields for ferrofluids of different concentrations in shallow microchannels. PMID:28406228

Multipactor susceptibility on a dielectric with a bias dc electric field and a background gas

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

Zhang Peng; Lau, Y. Y.; Franzi, Matthew

2011-05-15

We use Monte Carlo simulations and analytical calculations to derive the condition for the onset of multipactor discharge on a dielectric surface at various combinations of the bias dc electric field, rf electric field, and background pressures of noble gases, such as Argon. It is found that the presence of a tangential bias dc electric field on the dielectric surface lowers the magnitude of rf electric field threshold to initiate multipactor, therefore plausibly offering robust protection against high power microwaves. The presence of low pressure gases may lead to a lower multipactor saturation level, however. The combined effects of tangentialmore » dc electric field and external gases on multipactor susceptibility are presented.« less

Colloidal particle electrorotation in a nonuniform electric field

NASA Astrophysics Data System (ADS)

Hu, Yi; Vlahovska, Petia M.; Miksis, Michael J.

2018-01-01

A model to study the dynamics of colloidal particles in nonuniform electric fields is proposed. For an isolated sphere, the conditions and threshold for sustained (Quincke) rotation in a linear direct current (dc) field are determined. Particle dynamics becomes more complex with increasing electric field strength, changing from steady spinning around the particle center to time-dependent orbiting motion around the minimum field location. Pairs of particles exhibit intricate trajectories, which are a combination of translation, due to dielectrophoresis, and rotation, due to the Quincke effect. Our model provides a basis to study the collective dynamics of many particles in a general electric field.

Colloidal particle electrorotation in a nonuniform electric field.

PubMed

Hu, Yi; Vlahovska, Petia M; Miksis, Michael J

2018-01-01

A model to study the dynamics of colloidal particles in nonuniform electric fields is proposed. For an isolated sphere, the conditions and threshold for sustained (Quincke) rotation in a linear direct current (dc) field are determined. Particle dynamics becomes more complex with increasing electric field strength, changing from steady spinning around the particle center to time-dependent orbiting motion around the minimum field location. Pairs of particles exhibit intricate trajectories, which are a combination of translation, due to dielectrophoresis, and rotation, due to the Quincke effect. Our model provides a basis to study the collective dynamics of many particles in a general electric field.

Effects of uniform extracellular DC electric fields on excitability in rat hippocampal slices in vitro.

PubMed

Bikson, Marom; Inoue, Masashi; Akiyama, Hiroki; Deans, Jackie K; Fox, John E; Miyakawa, Hiroyoshi; Jefferys, John G R

2004-05-15

The effects of uniform steady state (DC) extracellular electric fields on neuronal excitability were characterized in rat hippocampal slices using field, intracellular and voltage-sensitive dye recordings. Small electric fields (1 s) changes in neuronal excitability. Electric fields perpendicular to the apical-dendritic axis did not induce somatic polarization, but did modulate orthodromic responses, indicating an effect on afferents. These results demonstrate that DC fields can modulate neuronal excitability in a time-dependent manner, with no clear threshold, as a result of interactions between neuronal compartments, the non-linear properties of the cell membrane, and effects on afferents.

Multipactor susceptibility on a dielectric with two carrier frequencies

NASA Astrophysics Data System (ADS)

Iqbal, Asif; Verboncoeur, John; Zhang, Peng

2018-04-01

This work investigates multipactor discharge on a single dielectric surface with two carrier frequencies of an rf electric field. We use Monte Carlo simulations and analytical calculations to obtain susceptibility diagrams in terms of the rf electric field and normal electric field due to the residual charge on the dielectric. It is found that in contrast to the single frequency case, in general, the presence of a second carrier frequency of the rf electric field increases the threshold of the magnitude of the rf electric field to initiate multipactor. The effects of the relative strength and phase, and the frequency separation of the two carrier frequencies are examined. The conditions to minimize mulitpactor are derived.

Electrical switching in cadmium boracite single crystals

NASA Technical Reports Server (NTRS)

Takahashi, T.; Yamada, O.

1981-01-01

Cadmium boracite single crystals at high temperatures ( 300 C) were found to exhibit a reversible electric field-induced transition between a highly insulative and a conductive state. The switching threshold is smaller than a few volts for an electrode spacing of a few tenth of a millimeter corresponding to an electric field of 100 to 1000 V/cm. This is much smaller than the dielectric break-down field for an insulator such as boracite. The insulative state reappears after voltage removal. A pulse technique revealed two different types of switching. Unstable switching occurs when the pulse voltage slightly exceeds the switching threshold and is characterized by a pre-switching delay and also a residual current after voltage pulse removal. A stable type of switching occurs when the voltage becomes sufficiently high. Possible device applications of this switching phenomenon are discussed.

Roll-to-Roll Continuous Manufacturing Multifunctional Nanocomposites by Electric-Field-Assisted "Z" Direction Alignment of Graphite Flakes in Poly(dimethylsiloxane).

PubMed

Guo, Yuanhao; Chen, Yuwei; Wang, Enmin; Cakmak, Miko

2017-01-11

A roll-to-roll continuous process was developed to manufacture large-scale multifunctional poly(dimethylsiloxane) (PDMS) films embedded with thickness direction ("Z" direction) aligned graphite nanoparticles by application of electric field. The kinetics of particle "Z" alignment and chain formation was studied by tracking the real-time change of optical light transmission through film thickness direction. Benefiting from the anisotropic structure of aligned particle chains, the electrical and thermal properties of the nanocomposites were dramatically enhanced through the thickness direction as compared to those of the nanocomposites containing the same particle loading without electrical field alignment. With 5 vol % graphite loading, 250 times higher electrical conductivity, 43 times higher dielectric permittivity, and 1.5 times higher thermal conductivity was achieved in the film thickness direction after the particles were aligned under electrical field. Moreover, the aligned nanocomposites with merely 2 vol % graphite particles exhibit even higher electric conductivity and dielectric permittivity than those of the nonaligned nanocomposites at random percolation threshold (10 vol % particles), as the "electric-field-directed" percolation threshold concentration is substantially decreased using this process. As the graphite loading increases to 20 vol %, the aligned nanocomposites exhibit thermal conductivity as high as 6.05 W/m·K, which is 35 times the thermal conductivity of pure matrix. This roll-to-roll electric field continuous process provides a simple, low-cost, and commercially viable method to manufacture multifunctional nanocomposites for applications as embedded capacitor, electromagnetic (EM) shielding, and thermal interface materials.

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.

The temporal evolution of 3-m striations in the modified ionosphere

NASA Technical Reports Server (NTRS)

Coster, A. J.; Djuth, F. T.; Jost, R. J.; Gordon, W. E.

1985-01-01

Experiments were performed at Arecibo, Puerto Rico, to investigate the evolution times of 3-m field-aligned striations produced in the ionosphere by powerful high-frequency (HF) radio waves. The results of this investigation are now summarized. First, the striations' rise times are dependent on the HF electric field. The E region data suggest that this dependence is nonlinear. Second, the threshold value of the HF electric field required to produce detectable striations was experimentally determined. At threshold the component of the HF electric field perpendicular to the geomagnetic field is calculated to be 0.09 V/m in the F region and 0.37 V/m in the E region. Third, both the E and the F region data verify theoretical predictions that the striations' decay times are directly proportional to the electron diffusion across B. Finally, a one-to-one correspondence between the growth of the 3-m striations and the decline of the HF-enhanced plasma line during overshoot is sometimes observed.

Step-wise potential development across the lipid bilayer under external electric fields

NASA Astrophysics Data System (ADS)

Majhi, Amit Kumar

2018-04-01

Pore formation across the bilayers under external electric field is an important phenomenon, which has numerous applications in biology and bio-engineering fields. However, it is not a ubiquitous event under all field applications. To initiate a pore in the bilayer a particular threshold electric field is required. The electric field alters the intrinsic potential distribution across the bilayer as we as it enhances total potential drop across the bilayer, which causes the pore formation. The intrinsic potential profile has a maximum peak value, which is 0.8 V and it gets enhanced under application of external field, 0.43 V/nm. The peak value becomes 1.4 V when a pore appears in the bilayer and it continues to evolve as along as the external electric field remains switched on.

Linking the micro and macro: L-H transition dynamics and threshold physics

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

Malkov, M. A., E-mail: mmalkov@ucsd.edu; Diamond, P. H.; Miki, K.

2015-03-15

The links between the microscopic dynamics and macroscopic threshold physics of the L → H transition are elucidated. Emphasis is placed on understanding the physics of power threshold scalings, and especially on understanding the minimum in the power threshold as a function of density P{sub thr} (n). By extending a numerical 1D model to evolve both electron and ion temperatures, including collisional coupling, we find that the decrease in P{sub thr} (n) along the low-density branch is due to the combination of an increase in collisional electron-to-ion energy transfer and an increase in the heating fraction coupled to the ions.more » Both processes strengthen the edge diamagnetic electric field needed to lock in the mean electric field shear for the L→H transition. The increase in P{sub thr} (n) along the high-density branch is due to the increase with ion collisionality of damping of turbulence-driven shear flows. Turbulence driven shear flows are needed to trigger the transition by extracting energy from the turbulence. Thus, we identify the critical transition physics components of the separatrix ion heat flux and the zonal flow excitation. The model reveals a power threshold minimum in density scans as a crossover between the threshold decrease supported by an increase in heat fraction received by ions (directly or indirectly, from electrons) and a threshold increase, supported by the rise in shear flow damping. The electron/ion heating mix emerges as important to the transition, in that it, together with electron-ion coupling, regulates the edge diamagnetic electric field shear. The importance of possible collisionless electron-ion heat transfer processes is explained.« less

Electrical characteristics of silicon percolating nanonet-based field effect transistors in the presence of dispersion

NASA Astrophysics Data System (ADS)

Cazimajou, T.; Legallais, M.; Mouis, M.; Ternon, C.; Salem, B.; Ghibaudo, G.

2018-05-01

We studied the current-voltage characteristics of percolating networks of silicon nanowires (nanonets), operated in back-gated transistor mode, for future use as gas or biosensors. These devices featured P-type field-effect characteristics. It was found that a Lambert W function-based compact model could be used for parameter extraction of electrical parameters such as apparent low field mobility, threshold voltage and subthreshold slope ideality factor. Their variation with channel length and nanowire density was related to the change of conduction regime from direct source/drain connection by parallel nanowires to percolating channels. Experimental results could be related in part to an influence of the threshold voltage dispersion of individual nanowires.

Optimization design and laser damage threshold analysis of pulse compression multilayer dielectric gratings

NASA Astrophysics Data System (ADS)

Fan, Shuwei; Bai, Liang; Chen, Nana

2016-08-01

As one of the key elements of high-power laser systems, the pulse compression multilayer dielectric grating is required for broader band, higher diffraction efficiency and higher damage threshold. In this paper, the multilayer dielectric film and the multilayer dielectric gratings(MDG) were designed by eigen matrix and optimized with the help of generic algorithm and rigorous coupled wave method. The reflectivity was close to 100% and the bandwith were over 250nm, twice compared to the unoptimized film structure. The simulation software of standing wave field distribution within MDG was developed and the electric field of the MDG was calculated. And the key parameters which affected the electric field distribution were also studied.

Diamond-Coated Carbon Nanotubes for Efficient Field Emission

NASA Technical Reports Server (NTRS)

Dimitrijevic, Stevan; Withers, James C.

2005-01-01

Field-emission cathodes containing arrays of carbon nanotubes coated with diamond or diamondlike carbon (DLC) are undergoing development. Multiwalled carbon nanotubes have been shown to perform well as electron field emitters. The idea underlying the present development is that by coating carbon nanotubes with wideband- gap materials like diamond or DLC, one could reduce effective work functions, thereby reducing threshold electric-field levels for field emission of electrons and, hence, improving cathode performance. To demonstrate feasibility, experimental cathodes were fabricated by (1) covering metal bases with carbon nanotubes bound to the bases by an electrically conductive binder and (2) coating the nanotubes, variously, with diamond or DLC by plasma-assisted chemical vapor deposition. In tests, the threshold electric-field levels for emission of electrons were reduced by as much as 40 percent, relative to those of uncoated- nanotube cathodes. Coating with diamond or DLC could also make field emission-cathodes operate more stably by helping to prevent evaporation of carbon from nanotubes in the event of overheating of the cathodes. Cathodes of this type are expected to be useful principally as electron sources for cathode-ray tubes and flat-panel displays.

Quantitative Observation of Threshold Defect Behavior in Memristive Devices with Operando X-ray Microscopy.

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

Liu, Huajun; Dong, Yongqi; Cherukara, Matthew J.

Memristive devices are an emerging technology that enables both rich interdisciplinary science and novel device functionalities, such as nonvolatile memories and nanoionics-based synaptic electronics. Recent work has shown that the reproducibility and variability of the devices depend sensitively on the defect structures created during electroforming as well as their continued evolution under dynamic electric fields. However, a fundamental principle guiding the material design of defect structures is still lacking due to the difficulty in understanding dynamic defect behavior under different resistance states. Here, we unravel the existence of threshold behavior by studying model, single-crystal devices: resistive switching requires that themore » pristine oxygen vacancy concentration reside near a critical value. Theoretical calculations show that the threshold oxygen vacancy concentration lies at the boundary for both electronic and atomic phase transitions. Through operando, multimodal X-ray imaging, we show that field tuning of the local oxygen vacancy concentration below or above the threshold value is responsible for switching between different electrical states. These results provide a general strategy for designing functional defect structures around threshold concentrations to create dynamic, field-controlled phases for memristive devices.« less

Direct observation of λ-DNA molecule reversal movement within microfluidic channels under electric field with single molecule imaging technique

NASA Astrophysics Data System (ADS)

Fengyun, Yang; Kaige, Wang; Dan, Sun; Wei, Zhao; Hai-qing, Wang; Xin, He; Gui-ren, Wang; Jin-tao, Bai

2016-07-01

The electrodynamic characteristics of single DNA molecules moving within micro-/nano-fluidic channels are important in the design of biomedical chips and bimolecular sensors. In this study, the dynamic properties of λ-DNA molecules transferring along the microchannels driven by the external electrickinetic force were systemically investigated with the single molecule fluorescence imaging technique. The experimental results indicated that the velocity of DNA molecules was strictly dependent on the value of the applied electric field and the diameter of the channel. The larger the external electric field, the larger the velocity, and the more significant deformation of DNA molecules. More meaningfully, it was found that the moving directions of DNA molecules had two completely different directions: (i) along the direction of the external electric field, when the electric field intensity was smaller than a certain threshold value; (ii) opposite to the direction of the external electric field, when the electric field intensity was greater than the threshold electric field intensity. The reversal movement of DNA molecules was mainly determined by the competition between the electrophoresis force and the influence of electro-osmosis flow. These new findings will theoretically guide the practical application of fluidic channel sensors and lab-on-chips for precisely manipulating single DNA molecules. Project supported by the National Natural Science Foundation of China (Grant No. 61378083), the International Cooperation Foundation of the National Science and Technology Major Project of the Ministry of Science and Technology of China (Grant No. 2011DFA12220), the Major Research Plan of National Natural Science Foundation of China (Grant No. 91123030), and the Natural Science Foundation of Shaanxi Province of China (Grant Nos. 2010JS110 and 2013SZS03-Z01).

A weak electric field-assisted ultrafast electrical switching dynamics in In3SbTe2 phase-change memory devices

NASA Astrophysics Data System (ADS)

Pandey, Shivendra Kumar; Manivannan, Anbarasu

2017-07-01

Prefixing a weak electric field (incubation) might enhance the crystallization speed via pre-structural ordering and thereby achieving faster programming of phase change memory (PCM) devices. We employed a weak electric field, equivalent to a constant small voltage (that is incubation voltage, Vi of 0.3 V) to the applied voltage pulse, VA (main pulse) for a systematic understanding of voltage-dependent rapid threshold switching characteristics and crystallization (set) process of In3SbTe2 (IST) PCM devices. Our experimental results on incubation-assisted switching elucidate strikingly one order faster threshold switching, with an extremely small delay time, td of 300 ps, as compared with no incubation voltage (Vi = 0 V) for the same VA. Also, the voltage dependent characteristics of incubation-assisted switching dynamics confirm that the initiation of threshold switching occurs at a lower voltage of 0.82 times of VA. Furthermore, we demonstrate an incubation assisted ultrafast set process of IST device for a low VA of 1.7 V (˜18 % lesser compared to without incubation) within a short pulse-width of 1.5 ns (full width half maximum, FWHM). These findings of ultrafast switching, yet low power set process would immensely be helpful towards designing high speed PCM devices with low power operation.

Development of a statistical model for cervical cancer cell death with irreversible electroporation in vitro.

PubMed

Yang, Yongji; Moser, Michael A J; Zhang, Edwin; Zhang, Wenjun; Zhang, Bing

2018-01-01

The aim of this study was to develop a statistical model for cell death by irreversible electroporation (IRE) and to show that the statistic model is more accurate than the electric field threshold model in the literature using cervical cancer cells in vitro. HeLa cell line was cultured and treated with different IRE protocols in order to obtain data for modeling the statistical relationship between the cell death and pulse-setting parameters. In total, 340 in vitro experiments were performed with a commercial IRE pulse system, including a pulse generator and an electric cuvette. Trypan blue staining technique was used to evaluate cell death after 4 hours of incubation following IRE treatment. Peleg-Fermi model was used in the study to build the statistical relationship using the cell viability data obtained from the in vitro experiments. A finite element model of IRE for the electric field distribution was also built. Comparison of ablation zones between the statistical model and electric threshold model (drawn from the finite element model) was used to show the accuracy of the proposed statistical model in the description of the ablation zone and its applicability in different pulse-setting parameters. The statistical models describing the relationships between HeLa cell death and pulse length and the number of pulses, respectively, were built. The values of the curve fitting parameters were obtained using the Peleg-Fermi model for the treatment of cervical cancer with IRE. The difference in the ablation zone between the statistical model and the electric threshold model was also illustrated to show the accuracy of the proposed statistical model in the representation of ablation zone in IRE. This study concluded that: (1) the proposed statistical model accurately described the ablation zone of IRE with cervical cancer cells, and was more accurate compared with the electric field model; (2) the proposed statistical model was able to estimate the value of electric field threshold for the computer simulation of IRE in the treatment of cervical cancer; and (3) the proposed statistical model was able to express the change in ablation zone with the change in pulse-setting parameters.

Maximum Langmuir Fields in Planetary Foreshocks Determined from the Electrostatic Decay Threshold

NASA Technical Reports Server (NTRS)

Robinson, P. A.; Cairns, Iver H.

1995-01-01

Maximum electric fields of Langmuir waves at planetary foreshocks are estimated from the threshold for electrostatic decay, assuming it saturates beam driven growth, and incorporating heliospheric variation of plasma density and temperature. Comparisons with spacecraft observations yields good quantitative agreement. Observations in type 3 radio sources are also in accord with this interpretation. A single mechanism can thus account for the highest fields of beam driven waves in both contexts.

An electric field induced in the retina and brain at threshold magnetic flux density causing magnetophosphenes.

PubMed

Hirata, Akimasa; Takano, Yukinori; Fujiwara, Osamu; Dovan, Thanh; Kavet, Robert

2011-07-07

For magnetic field exposures at extremely low frequencies, the electrostimulatory response with the lowest threshold is the magnetophosphene, a response that corresponds to an adult exposed to a 20 Hz magnetic field of nominally 8.14 mT. In the IEEE standard C95.6 (2002), the corresponding in situ field in the retinal locus of an adult-sized ellipsoidal was calculated to be 53 mV m(-1). However, the associated dose in the retina and brain at a high level of resolution in anatomically correct human models is incompletely characterized. Furthermore, the dose maxima in tissue computed with voxel human models are prone to staircasing errors, particularly for the low-frequency dosimetry. In the analyses presented in this paper, analytical and quasi-static finite-difference time-domain (FDTD) solutions were first compared for a three-layer sphere exposed to a uniform 50 Hz magnetic field. Staircasing errors in the FDTD results were observed at the tissue interface, and were greatest at the skin-air boundary. The 99th percentile value was within 3% of the analytic maximum, depending on model resolution, and thus may be considered a close approximation of the analytic maximum. For the adult anatomical model, TARO, exposed to a uniform magnetic field, the differences in the 99th percentile value of in situ electric fields for 2 mm and 1 mm voxel models were at most several per cent. For various human models exposed at the magnetophosphene threshold at three orthogonal field orientations, the in situ electric field in the brain was between 10% and 70% greater than the analytical IEEE threshold of 53 mV m(-1), and in the retina was lower by roughly 50% for two horizontal orientations (anterior-posterior and lateral), and greater by about 15% for a vertically oriented field. Considering a reduction factor or safety factors of several folds applied to electrostimulatory thresholds, the 99th percentile dose to a tissue calculated with voxel human models may be used as an estimate of the tissue's maximum dose.

Effects of surface anchoring on the electric Frederiks transition in ferronematic systems

NASA Astrophysics Data System (ADS)

Farrokhbin, Mojtaba; Kadivar, Erfan

2016-11-01

The effects of anchoring phenomenon on the electric Frederiks transition threshold field in a nematic liquid crystal doped with ferroelectric nanoparticles are discussed. The polarizability of these nanoparticles in combination with confinement effects cause the drastic effects on the ferronematic systems. This study is based on Frank free energy and Rapini-Papoular surface energy for ferronematic liquid crystal having finite anchoring condition. In the case of different anchoring boundary conditions, the Euler-Lagrange equation of the total free energy is numerically solved by using the finite difference method together with the relaxation method and Maxwell construction to select the physical solutions and therefore investigate the effects of different anchoring strengths on the Frederiks transition threshold field. Maxwell construction method is employed to select three periodic solutions for nematic liquid crystal director at the interfaces of a slab. In the interval from zero to half- π, there is only one solution for the director orientation. In this way, NLC director rotates toward the normal to the surface as the applied electric field increases at the walls. Our numerical results illustrate that above Frederiks transition and in the intermediate anchoring strength, nematic molecules illustrate the different orientation at slab boundaries. We also study the effects of different anchoring strengths, nanoparticle volume fractions and polarizations on the Frederiks transition threshold field. We report that decreasing in the nanoparticle polarization results in the saturation Frederiks threshold. However, this situation does not happen for the nanoparticles volume fraction.

Electrically controllable photonic molecule laser.

PubMed

Fasching, G; Deutsch, Ch; Benz, A; Andrews, A M; Klang, P; Zobl, R; Schrenk, W; Strasser, G; Ragulis, P; Tamosiūnas, V; Unterrainer, K

2009-10-26

We have studied the coherent intercavity coupling of the evanescent fields of two microdisk terahertz quantum-cascade lasers. The electrically controllable optical coupling of the single-mode operating lasers has been observed for cavity spacings up to 30 mum. The strongest coupled photonic molecule with 2 mum intercavity spacing allows to conditionally switch the optical emission by the electrical modulation of only one microdisk. The lasing threshold characteristics demonstrate the linear dependence of the gain of a quantum-cascade laser on the applied electric field.

Effect of an electric field on the orientation of a liquid crystal in a cell with a nonuniform director distribution

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

Aksenova, E. V., E-mail: e.aksenova@spbu.ru; Karetnikov, A. A.; Karetnikov, N. A.

2016-05-15

The electric field-induced reorientation of a nematic liquid crystal in cells with a planar helicoidal or a homeoplanar structure of a director field is studied theoretically and experimentally. The dependences of the capacitances of these systems on the voltage in an applied electric field below and above the Fréedericksz threshold are experimentally obtained and numerically calculated. The calculations use the director distribution in volume that is obtained by direct minimization of free energy at various voltages. The inhomogeneity of the electric field inside a cell is taken into account. The calculation results are shown to agree with the experimental data.

Runaway electron behavior in the Frascati Tokamak Upgrade (FTU)

NASA Astrophysics Data System (ADS)

Popovic, Zana; Martin-Solis, Jose Ramon; Esposito, Basilio; Marocco, Daniele; Causa, Federica; Buratti, Paolo; Boncagni, Luca; Carnevale, Daniele; Gospodarczyk, Mateusz

2016-10-01

Several recent experiments in the FTU tokamak are dedicated to the study of runaway electrons (RE), both in the flattop and disruption phases of the discharge. Experiments have been carried out to evaluate the threshold electric field for RE generation during the flattop of ohmic discharges. The measured threshold electric field during RE electron generation and suppression experiments for a wide range of plasma parameters is found to be 2-5 times larger than predicted by the relativistic collisional theory, ER = nee3ln Λ/4 πɛ02 mec2, and is consistent with an increase of the critical field due to the RE synchrotron radiation. Runaway evolution has been numerically simulated using a test particle model including toroidal electric field acceleration, collisions and synchrotron radiation losses. Estimates of RE energy distribution are consistent with the measurements of two recently installed RE diagnostics: HXR-camera and RE Imaging and Spectroscopy (REIS) system. Supported by MINECO (Spain), Projects ENE2012-31753.

Particle-in-Cell Simulations of the Twisted Magnetospheres of Magnetars. I.

NASA Astrophysics Data System (ADS)

Chen, Alexander Y.; Beloborodov, Andrei M.

2017-08-01

The magnetospheres of magnetars are believed to be filled with electron-positron plasma generated by electric discharge. We present a first numerical experiment demonstrating this process in an axisymmetric magnetosphere with a simple threshold prescription for pair creation, which is applicable to the inner magnetosphere with an ultrastrong field. The {e}+/- discharge occurs in response to the twisting of the closed magnetic field lines by a shear deformation of the magnetar surface, which launches electric currents into the magnetosphere. The simulation shows the formation of an electric “gap” with an unscreened electric field ({\\boldsymbol{E}}\\cdot {\\boldsymbol{B}}\

Tunable, multiwavelength-swept fiber laser based on nematic liquid crystal device for fiber-optic electric-field sensor

NASA Astrophysics Data System (ADS)

Lee, Hyun Ji; Kim, Sung-Jo; Ko, Myeong Ock; Kim, Jong-Hyun; Jeon, Min Yong

2018-03-01

We propose a tunable multiwavelength-swept laser based on a nematic liquid crystal (NLC) Fabry-Perot (FP) etalon, which is embedded in the resonator of a wavelength-swept laser. We achieve the continuous wavelength tuning of the multiwavelength-swept laser by applying the electric field to the NLC FP etalon. The free spectral range of the fabricated NLC FP etalon is approximately 7.9 nm. When the electric field applied to the NLC FP etalon exceeds the threshold value (Fréedericksz threshold voltage), the output of the multiwavelength-swept laser can be tuned continuously. The tuning range of the multiwavelength-swept laser can be achieved at a value greater than 75 nm, which has a considerably wider tunable range than a conventional multiwavelength laser based on an NLC FP etalon. The slope efficiencies in the spectral and temporal domains for the tunable multiwavelength-swept laser are 22.2 nm/(mVrms / μm) and 0.17 ms/(mVrms / μm), respectively in the linear region. Therefore, the developed multiwavelength-swept laser based on the NLC FP etalon can be applied to an electric-field sensor. Because the wavelength measurement and time measurement have a linear relationship, the electric-field sensor can detect a rapid change in the electric-field intensity by measuring the peak change of the pulse in the temporal domain using the NLC FP etalon-based multiwavelength-swept laser.

Narrowband noise study of sliding charge density waves in NbSe3 nanoribbons

NASA Astrophysics Data System (ADS)

Onishi, Seita; Jamei, Mehdi; Zettl, Alex

2017-02-01

Transport properties (dc electrical resistivity, threshold electric field, and narrow-band noise) are reported for nanoribbon specimens of NbSe3 with thicknesses as low as 18 nm. As the sample thickness decreases, the resistive anomalies characteristic of the charge density wave (CDW) state are suppressed and the threshold fields for nonlinear CDW conduction apparently diverge. Narrow-band noise measurements allow determination of the concentration of carriers condensed in the CDW state n c , reflective of the CDW order parameter Δ. Although the CDW transition temperatures are relatively independent of sample thickness, in the lower CDW state Δ decreases dramatically with decreasing sample thickness.

Plasma Membrane Permeabilization by Trains of Ultrashort Electric Pulses

PubMed Central

Ibey, Bennett L.; Mixon, Dustin G.; Payne, Jason A.; Bowman, Angela; Sickendick, Karl; Wilmink, Gerald J.; Roach, W. Patrick; Pakhomov, Andrei G.

2010-01-01

Ultrashort electric pulses (USEP) cause long-lasting increase of cell membrane electrical conductance, and that a single USEP increased cell membrane electrical conductance proportionally to the absorbed dose (AD) with a threshold of about 10 mJ/g. The present study extends quantification of the membrane permeabilization effect to multiple USEP and employed a more accurate protocol that identified USEP effect as the difference between post- and pre-exposure conductance values (Δg) in individual cells. We showed that Δg can be increased by either increasing the number of pulses at a constant E-field, or by increasing the E-field at a constant number of pulses. For 60-ns pulses, an E-field threshold of 6 kV/cm for a single pulse was lowered to less than 1.7 kV/cm by applying 100-pulse or longer trains. However, the reduction of the E-field threshold was only achieved at the expense of a higher AD compared to a single pulse exposure. Furthermore, the effect of multiple pulses was not fully determined by AD, suggesting that cells permeabilized by the first pulse(s) in the train become less vulnerable to subsequent pulses. This explanation was corroborated by a model that treated multiple-pulse exposures as a series of single-pulse exposures and assumed an exponential decline of cell susceptibility to USEP as Δg increased after each pulse during the course of the train. PMID:20171148

Back-and-forth micromotion of aqueous droplets in a dc electric field.

PubMed

Kurimura, Tomo; Ichikawa, Masatoshi; Takinoue, Masahiro; Yoshikawa, Kenichi

2013-10-01

Recently, it was reported that an aqueous droplet in an oil phase exhibited rhythmic back-and-forth motion under stationary dc voltage on the order of 100 V. Here, we demonstrate that the threshold voltage for inducing such oscillation is successfully decreased to the order of 10 V through downsizing of the experimental system. Notably, the threshold electric field tends to decrease with a nonlinear scaling relationship accompanied by the downsizing. We derive a simple theoretical model to interpret the system size dependence of the threshold voltage. This model equation suggests the unique effect of additional noise, which is qualitatively characterized as a coherent resonance by an actual experiment as a kind of coherent resonance. Our result would provide insight into the construction of micrometer-sized self-commutating motors and actuators in microfluidic and micromechanical devices.

A percolation approach to study the high electric field effect on electrical conductivity of insulating polymer

NASA Astrophysics Data System (ADS)

Benallou, Amina; Hadri, Baghdad; Martinez-Vega, Juan; El Islam Boukortt, Nour

2018-04-01

The effect of percolation threshold on the behaviour of electrical conductivity at high electric field of insulating polymers has been briefly investigated in literature. Sometimes the dead ends links are not taken into account in the study of the electric field effect on the electrical properties. In this work, we present a theoretical framework and Monte Carlo simulation of the behaviour of the electric conductivity at high electric field based on the percolation theory using the traps energies levels which are distributed according to distribution law (uniform, Gaussian, and power-law). When a solid insulating material is subjected to a high electric field, and during trapping mechanism the dead ends of traps affect with decreasing the electric conductivity according to the traps energies levels, the correlation length of the clusters, the length of the dead ends, and the concentration of the accessible positions for the electrons. A reasonably good agreement is obtained between simulation results and the theoretical framework.

Theoretical temperature-dependent branching ratios and laser thresholds of the 3F4 to 3H6 levels of Tm(3+) in ten garnets

NASA Technical Reports Server (NTRS)

Filer, Elizabeth D.; Barnes, Norman P.; Morrison, Clyde A.

1991-01-01

The calculated energy levels, the branching ratios, and the estimated thresholds for thulium operating on the 3F4 to 3H6 transitions are reported. Garnet materials with the general formula A3B2C3O12 are evaluated. Calculations are performed for the A side under the assumption of D2 symmetry. X-ray data available in the literature are used to evaluate the crystal-field components, A sub nm. Even-n components are employed to calculate the crystal-field splittings within the manifold. Thermal occupation factors are determined in a straightforward manner using a Boltzmann distribution for the respective manifolds. Odd-n components are applied to calculate the transition probabilities for electric field transitions. It is determined that the magnetic dipole contributions to the transition probability are comparable to the electric dipole contributions in some cases. Thresholds as a function of the density of thulium atoms are calculated.

Robust optimization of the laser induced damage threshold of dielectric mirrors for high power lasers.

PubMed

Chorel, Marine; Lanternier, Thomas; Lavastre, Éric; Bonod, Nicolas; Bousquet, Bruno; Néauport, Jérôme

2018-04-30

We report on a numerical optimization of the laser induced damage threshold of multi-dielectric high reflection mirrors in the sub-picosecond regime. We highlight the interplay between the electric field distribution, refractive index and intrinsic laser induced damage threshold of the materials on the overall laser induced damage threshold (LIDT) of the multilayer. We describe an optimization method of the multilayer that minimizes the field enhancement in high refractive index materials while preserving a near perfect reflectivity. This method yields a significant improvement of the damage resistance since a maximum increase of 40% can be achieved on the overall LIDT of the multilayer.

Electric field strength and focality in electroconvulsive therapy and magnetic seizure therapy: a finite element simulation study

NASA Astrophysics Data System (ADS)

Deng, Zhi-De; Lisanby, Sarah H.; Peterchev, Angel V.

2011-02-01

We present the first computational study comparing the electric field induced by various electroconvulsive therapy (ECT) and magnetic seizure therapy (MST) paradigms. Four ECT electrode configurations (bilateral, bifrontal, right unilateral, and focal electrically administered seizure therapy) and three MST coil configurations (circular, cap, and double cone) were modeled. The model incorporated a modality-specific neural activation threshold. ECT (0.3 ms pulse width) and MST induced the maximum electric field of 2.1-2.5 V cm-1 and 1.1-2.2 V cm-1 in the brain, corresponding to 6.2-7.2 times and 1.2-2.3 times the neural activation threshold, respectively. The MST electric field is more confined to the superficial cortex compared to ECT. The brain volume stimulated was much larger with ECT (up to 100%) than with MST (up to 8.2%). MST with the double-cone coil was the most focal, and bilateral ECT was the least focal. Our results suggest a possible biophysical explanation of the reduced side effects of MST compared to ECT. Our results also indicate that the conventional ECT pulse amplitude (800-900 mA) is much higher than necessary for seizure induction. Reducing the ECT pulse amplitude should be explored as a potential means of diminishing side effects.

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.

Human perception of electric fields and ion currents associated with high-voltage DC transmission lines.

PubMed

Blondin, J P; Nguyen, D H; Sbeghen, J; Goulet, D; Cardinal, C; Maruvada, P S; Plante, M; Bailey, W H

1996-01-01

The objective of this study was to assess the ability of humans to detect the presence of DC electric field and ion currents. An exposure chamber simulating conditions present in the vicinity of high-voltage DC (HVDC) lines was designed and built for this purpose. In these experiments, the facility was used to expose observers to DC electric fields up to 50 kV/m and ion current densities up to 120 nA/m2. Forty-eight volunteers (25 women and 23 men) between the ages of 18 and 57 years served as observers. Perception of DC fields was examined by using two psychophysical methods: an adaptive staircase procedure and a rating method derived from signal-detection theory. Subjects completed three different series of observations by using each of these methods; one was conducted without ion currents, and the other two involved various combinations of electric fields and ion currents. Overall, subjects were significantly more likely to detect DC fields as the intensity increased. Observers were able to detect the presence of DC fields alone, but only at high intensities; the average threshold was 45 kV/m. Except in the most sensitive individuals, ion current densities up to 60 nA/m2 did not significantly facilitate the detection of DC fields. However, higher ion current densities were associated with a substantial lowering of sensory thresholds in a large majority of observers. Data analysis also revealed large variations in perceptual thresholds among observers. Normative data indicating DC field and ion current intensities that can be detected by 50% of all observers are provided. In addition, for the most sensitive observers, several other detection proportions were derived from the distribution of individual detection capabilities. These data can form the basis for environmental guidelines relating to the design of HVDC lines.

Field-effect transistors as electrically controllable nonlinear rectifiers for the characterization of terahertz pulses

NASA Astrophysics Data System (ADS)

Lisauskas, Alvydas; Ikamas, Kestutis; Massabeau, Sylvain; Bauer, Maris; ČibiraitÄ--, DovilÄ--; Matukas, Jonas; Mangeney, Juliette; Mittendorff, Martin; Winnerl, Stephan; Krozer, Viktor; Roskos, Hartmut G.

2018-05-01

We propose to exploit rectification in field-effect transistors as an electrically controllable higher-order nonlinear phenomenon for the convenient monitoring of the temporal characteristics of THz pulses, for example, by autocorrelation measurements. This option arises because of the existence of a gate-bias-controlled super-linear response at sub-threshold operation conditions when the devices are subjected to THz radiation. We present measurements for different antenna-coupled transistor-based THz detectors (TeraFETs) employing (i) AlGaN/GaN high-electron-mobility and (ii) silicon CMOS field-effect transistors and show that the super-linear behavior in the sub-threshold bias regime is a universal phenomenon to be expected if the amplitude of the high-frequency voltage oscillations exceeds the thermal voltage. The effect is also employed as a tool for the direct determination of the speed of the intrinsic TeraFET response which allows us to avoid limitations set by the read-out circuitry. In particular, we show that the build-up time of the intrinsic rectification signal of a patch-antenna-coupled CMOS detector changes from 20 ps in the deep sub-threshold voltage regime to below 12 ps in the vicinity of the threshold voltage.

Field-induced strain degradation of AlGaN/GaN high electron mobility transistors on a nanometer scale

NASA Astrophysics Data System (ADS)

Lin, Chung-Han; Doutt, D. R.; Mishra, U. K.; Merz, T. A.; Brillson, L. J.

2010-11-01

Nanoscale Kelvin probe force microscopy and depth-resolved cathodoluminescence spectroscopy reveal an electronic defect evolution inside operating AlGaN/GaN high electron mobility transistors with degradation under electric-field-induced stress. Off-state electrical stress results in micron-scale areas within the extrinsic drain expanding and decreasing in electric potential, midgap defects increasing by orders-of-magnitude at the AlGaN layer, and local Fermi levels lowering as gate-drain voltages increase above a characteristic stress threshold. The pronounced onset of defect formation, Fermi level movement, and transistor degradation at the threshold gate-drain voltage of J. A. del Alamo and J. Joh [Microelectron. Reliab. 49, 1200 (2009)] is consistent with crystal deformation and supports the inverse piezoelectric model of high electron mobility transistor degradation.

Field emission from isolated individual vertically aligned carbon nanocones

NASA Astrophysics Data System (ADS)

Baylor, L. R.; Merkulov, V. I.; Ellis, E. D.; Guillorn, M. A.; Lowndes, D. H.; Melechko, A. V.; Simpson, M. L.; Whealton, J. H.

2002-04-01

Field emission from isolated individual vertically aligned carbon nanocones (VACNCs) has been measured using a small-diameter moveable probe. The probe was scanned parallel to the sample plane to locate the VACNCs, and perpendicular to the sample plane to measure the emission turn-on electric field of each VACNC. Individual VACNCs can be good field emitters. The emission threshold field depends on the geometric aspect ratio (height/tip radius) of the VACNC and is lowest when a sharp tip is present. VACNCs exposed to a reactive ion etch process demonstrate a lowered emission threshold field while maintaining a similar aspect ratio. Individual VACNCs can have low emission thresholds, carry high current densities, and have long emission lifetime. This makes them very promising for various field emission applications for which deterministic placement of the emitter with submicron accuracy is needed.

Narrowband noise study of sliding charge density waves in NbSe 3 nanoribbons

DOE PAGES

Onishi, Seita; Jamei, Mehdi; Zettl, Alex

2017-01-12

Transport properties (dc electrical resistivity, threshold electric field, and narrow-band noise) are reported for nanoribbon specimens of NbSe 3 with thicknesses as low as 18 nm. As the sample thickness decreases, the resistive anomalies characteristic of the charge density wave (CDW) state are suppressed and the threshold fields for nonlinear CDW conduction apparently diverge. Narrow-band noise measurements allow determination of the concentration of carriers condensed in the CDW state n c , reflective of the CDW order parameter Δ. Although the CDW transition temperatures are relatively independent of sample thickness, in the lower CDW state Δ decreases dramatically with decreasingmore » sample thickness.« less

Comparison of electric field strength and spatial distribution of electroconvulsive therapy and magnetic seizure therapy in a realistic human head model

PubMed Central

Lee, Won Hee; Lisanby, Sarah H.; Laine, Andrew F.; Peterchev, Angel V.

2017-01-01

Background This study examines the strength and spatial distribution of the electric field induced in the brain by electroconvulsive therapy (ECT) and magnetic seizure therapy (MST). Methods The electric field induced by standard (bilateral, right unilateral, and bifrontal) and experimental (focal electrically administered seizure therapy and frontomedial) ECT electrode configurations as well as a circular MST coil configuration was simulated in an anatomically realistic finite element model of the human head. Maps of the electric field strength relative to an estimated neural activation threshold were used to evaluate the stimulation strength and focality in specific brain regions of interest for these ECT and MST paradigms and various stimulus current amplitudes. Results The standard ECT configurations and current amplitude of 800–900 mA produced the strongest overall stimulation with median of 1.8–2.9 times neural activation threshold and more than 94% of the brain volume stimulated at suprathreshold level. All standard ECT electrode placements exposed the hippocampi to suprathreshold electric field, although there were differences across modalities with bilateral and right unilateral producing respectively the strongest and weakest hippocampal stimulation. MST stimulation is up to 9 times weaker compared to conventional ECT, resulting in direct activation of only 21% of the brain. Reducing the stimulus current amplitude can make ECT as focal as MST. Conclusions The relative differences in electric field strength may be a contributing factor for the cognitive sparing observed with right unilateral compared to bilateral ECT, and MST compared to right unilateral ECT. These simulations could help understand the mechanisms of seizure therapies and develop interventions with superior risk/benefit ratio. PMID:27318858

Understanding the Percolation Characteristics of Nonlinear Composite Dielectrics

PubMed Central

Yang, Xiao; Hu, Jun; Chen, Shuiming; He, Jinliang

2016-01-01

Nonlinear composite dielectrics can function as smart materials for stress control and field grading in all fields of electrical insulations. The percolation process is a significant issue of composite dielectrics. However, the classic percolation theory mainly deals with traditional composites in which the electrical parameters of both insulation matrix and conducting fillers are independent of the applied electric field. This paper measured the nonlinear V-I characteristics of ZnO microvaristors/silicone rubber composites with several filler concentrations around an estimated percolation threshold. For the comparison with the experiment, a new microstructural model is proposed to simulate the nonlinear conducting behavior of the composite dielectrics modified by metal oxide fillers, which is based on the Voronoi network and considers the breakdown feature of the insulation matrix for near percolated composites. Through both experiment and simulation, the interior conducting mechanism and percolation process of the nonlinear composites were presented and a specific percolation threshold was determined as 33%. This work has provided a solution to better understand the characteristics of nonlinear composite dielectrics. PMID:27476998

Electric Organ Discharges of Mormyrid Fish as a Possible Cue for Predatory Catfish

NASA Astrophysics Data System (ADS)

Hanika, S.; Kramer, B.

During reproductive migration the electroreceptive African sharptooth catfish, Clarias gariepinus (Siluriformes), preys mainly on a weakly electric fish, the bulldog Marcusenius macrolepidotus (Mormyridae; Merron 1993). This is puzzling because the electric organ discharges of known Marcusenius species are pulses of a duration (<1ms) too short for being detected by the catfishes' low-frequency electroreceptive system (optimum sensitivity, 10-30Hz Peters and Bretschneider 1981). On the recent discovery that M. macrolepidotus males emit discharges lasting approximately ten times longer than those of females (Kramer 1997a) we determined behavioral thresholds for discharges of both sexes, using synthetic playbacks of field-recorded discharges. C. gariepinus detected M. macrolepidotus male discharges down to a field gradient of 103μVpeak-peak/cm and up to a distance of 1.5m at natural field conditions. In contrast, thresholds for female discharges were not reached with our setup, and we presume the bulldogs eaten by catfish are predominantly male.

Understanding the Percolation Characteristics of Nonlinear Composite Dielectrics

NASA Astrophysics Data System (ADS)

Yang, Xiao; Hu, Jun; Chen, Shuiming; He, Jinliang

2016-08-01

Nonlinear composite dielectrics can function as smart materials for stress control and field grading in all fields of electrical insulations. The percolation process is a significant issue of composite dielectrics. However, the classic percolation theory mainly deals with traditional composites in which the electrical parameters of both insulation matrix and conducting fillers are independent of the applied electric field. This paper measured the nonlinear V-I characteristics of ZnO microvaristors/silicone rubber composites with several filler concentrations around an estimated percolation threshold. For the comparison with the experiment, a new microstructural model is proposed to simulate the nonlinear conducting behavior of the composite dielectrics modified by metal oxide fillers, which is based on the Voronoi network and considers the breakdown feature of the insulation matrix for near percolated composites. Through both experiment and simulation, the interior conducting mechanism and percolation process of the nonlinear composites were presented and a specific percolation threshold was determined as 33%. This work has provided a solution to better understand the characteristics of nonlinear composite dielectrics.

First-principles simulation for strong and ultra-short laser pulse propagation in dielectrics

NASA Astrophysics Data System (ADS)

Yabana, K.

2016-05-01

We develop a computational approach for interaction between strong laser pulse and dielectrics based on time-dependent density functional theory (TDDFT). In this approach, a key ingredient is a solver to simulate electron dynamics in a unit cell of solids under a time-varying electric field that is a time-dependent extension of the static band calculation. This calculation can be regarded as a constitutive relation, providing macroscopic electric current for a given electric field applied to the medium. Combining the solver with Maxwell equations for electromagnetic fields of the laser pulse, we describe propagation of laser pulses in dielectrics without any empirical parameters. An important output from the coupled Maxwell+TDDFT simulation is the energy transfer from the laser pulse to electrons in the medium. We have found an abrupt increase of the energy transfer at certain laser intensity close to damage threshold. We also estimate damage threshold by comparing the transferred energy with melting and cohesive energies. It shows reasonable agreement with measurements.

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.

Comparison between field mill and corona point instrumentation at Kennedy Space Center - Use of these data with a model to determine cloudbase electric fields

NASA Technical Reports Server (NTRS)

Markson, R.; Anderson, B.; Govaert, J.; Fairall, C. W.

1989-01-01

A novel coronal current-determining instrument is being used at NASA-KSC which overcomes previous difficulties with wind sensitivity and a voltage-threshold 'deadband'. The mounting of the corona needle at an elevated location reduces coronal and electrode layer space-charge influences on electric fields, rendering the measurement of space charge density possible. In conjunction with a space-charge compensation model, these features allow a more realistic estimation of cloud base electric fields and the potential for lightning strike than has previously been possible with ground-based sensors.

Fermionic Schwinger effect and induced current in de Sitter space

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

Hayashinaka, Takahiro; Department of Physics, Graduate School of Science, The University of Tokyo,Bunkyo-ku, Tokyo, 113-0033; Fujita, Tomohiro

We explore Schwinger effect of spin 1/2 charged particles with static electric field in 1+3 dimensional de Sitter spacetime. We analytically calculate the vacuum expectation value of the spinor current which is induced by the produced particles in the electric field. The renormalization is performed with the adiabatic subtraction scheme. We find that the current becomes negative, namely it flows in the direction opposite to the electric field, if the electric field is weaker than a certain threshold value depending on the fermion mass, which is also known to happen in the case of scalar charged particles in 1+3 demore » Sitter spacetime. Contrary to the scalar case, however, the IR hyperconductivity is absent in the spinor case.« less

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.

Atomic physics effects on tokamak edge drift-tearing modes

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

Hahm, T.S.

1993-03-01

The effects of ionization and charge exchange on the linear stability of drift-tearing modes are analytically investigated. In particular, the linear instability threshold {Delta}{sup Th}, produced by ion sound wave coupling is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semi-collisional regime, both ionization and charge exchange act as drag on the ion parallel velocity, and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

Atomic physics effects on tokamak edge drift-tearing modes

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

Hahm, T.S.

1993-03-01

The effects of ionization and charge exchange on the linear stability of drift-tearing modes are analytically investigated. In particular, the linear instability threshold [Delta][sup Th], produced by ion sound wave coupling is modified. In the strongly collisional regime, the ionization breaks up the near cancellation of the perturbed electric field and the pressure gradient along the magnetic field, and increases the threshold. In the semi-collisional regime, both ionization and charge exchange act as drag on the ion parallel velocity, and consequently decrease the threshold by reducing the effectiveness of ion sound wave propagation.

Controllable chaos in hybrid electro-optomechanical systems

PubMed Central

Wang, Mei; Lü, Xin-You; Ma, Jin-Yong; Xiong, Hao; Si, Liu-Gang; Wu, Ying

2016-01-01

We investigate the nonlinear dynamics of a hybrid electro-optomechanical system (EOMS) that allows us to realize the controllable opto-mechanical nonlinearity by driving the microwave LC resonator with a tunable electric field. A controllable optical chaos is realized even without changing the optical pumping. The threshold and lifetime of the chaos could be optimized by adjusting the strength, frequency, or phase of the electric field. This study provides a method of manipulating optical chaos with an electric field. It may offer the prospect of exploring the controllable chaos in on-chip optoelectronic devices and its applications in secret communication. PMID:26948505

Controllable chaos in hybrid electro-optomechanical systems.

PubMed

Wang, Mei; Lü, Xin-You; Ma, Jin-Yong; Xiong, Hao; Si, Liu-Gang; Wu, Ying

2016-03-07

We investigate the nonlinear dynamics of a hybrid electro-optomechanical system (EOMS) that allows us to realize the controllable opto-mechanical nonlinearity by driving the microwave LC resonator with a tunable electric field. A controllable optical chaos is realized even without changing the optical pumping. The threshold and lifetime of the chaos could be optimized by adjusting the strength, frequency, or phase of the electric field. This study provides a method of manipulating optical chaos with an electric field. It may offer the prospect of exploring the controllable chaos in on-chip optoelectronic devices and its applications in secret communication.

The relativistic feedback discharge model of terrestrial gamma ray flashes

NASA Astrophysics Data System (ADS)

Dwyer, Joseph R.

2012-02-01

As thunderclouds charge, the large-scale fields may approach the relativistic feedback threshold, above which the production of relativistic runaway electron avalanches becomes self-sustaining through the generation of backward propagating runaway positrons and backscattered X-rays. Positive intracloud (IC) lightning may force the large-scale electric fields inside thunderclouds above the relativistic feedback threshold, causing the number of runaway electrons, and the resulting X-ray and gamma ray emission, to grow exponentially, producing very large fluxes of energetic radiation. As the flux of runaway electrons increases, ionization eventually causes the electric field to discharge, bringing the field below the relativistic feedback threshold again and reducing the flux of runaway electrons. These processes are investigated with a new model that includes the production, propagation, diffusion, and avalanche multiplication of runaway electrons; the production and propagation of X-rays and gamma rays; and the production, propagation, and annihilation of runaway positrons. In this model, referred to as the relativistic feedback discharge model, the large-scale electric fields are calculated self-consistently from the charge motion of the drifting low-energy electrons and ions, produced from the ionization of air by the runaway electrons, including two- and three-body attachment and recombination. Simulation results show that when relativistic feedback is considered, bright gamma ray flashes are a natural consequence of upward +IC lightning propagating in large-scale thundercloud fields. Furthermore, these flashes have the same time structures, including both single and multiple pulses, intensities, angular distributions, current moments, and energy spectra as terrestrial gamma ray flashes, and produce large current moments that should be observable in radio waves.

Communication: Polarizable polymer chain under external electric field in a dilute polymer solution.

PubMed

Budkov, Yu A; Kolesnikov, A L; Kiselev, M G

2015-11-28

We study the conformational behavior of polarizable polymer chain under an external homogeneous electric field within the Flory type self-consistent field theory. We consider the influence of electric field on the polymer coil as well as on the polymer globule. We show that when the polymer chain conformation is a coil, application of external electric field leads to its additional swelling. However, when the polymer conformation is a globule, a sufficiently strong field can induce a globule-coil transition. We show that such "field-induced" globule-coil transition at the sufficiently small monomer polarizabilities goes quite smoothly. On the contrary, when the monomer polarizability exceeds a certain threshold value, the globule-coil transition occurs as a dramatic expansion in the regime of first-order phase transition. The developed theoretical model can be applied to predicting polymer globule density change under external electric field in order to provide more efficient processes of polymer functionalization, such as sorption, dyeing, and chemical modification.

Electric field strength and focality in electroconvulsive therapy and magnetic seizure therapy: A finite element simulation study

PubMed Central

Deng, Zhi-De; Lisanby, Sarah H.; Peterchev, Angel V.

2014-01-01

We present the first computational study comparing the electric field induced by various electroconvulsive therapy (ECT) and magnetic seizure therapy (MST) paradigms. Four ECT electrode configurations (bilateral, bifrontal, right unilateral, and focal electrically administered seizure therapy) and three MST coil configurations (circular, cap, and double cone) were modeled. The model incorporated a modality-specific neural activation threshold. ECT (0.3 ms pulse width) and MST induced maximum electric field in the brain of 2.1–2.5 V/cm and 1.1–2.2 V/cm, corresponding to 6.2–7.2 times and 1.2–2.3 times the neural activation threshold, respectively. The MST electric field is more confined to the superficial cortex compared to ECT. The brain volume stimulated was much higher with ECT (up to 100%) than MST (up to 8.2%). MST with the double cone coil was the most focal and bilateral ECT was the least focal. Our results suggest a possible biophysical explanation of the reduced side effects of MST compared to ECT. Our results also indicate that the conventional ECT pulse amplitude (800–900 mA) is much higher than necessary for seizure induction. Reducing the ECT pulse amplitude should be explored as a potential means of diminishing side effects. PMID:21248385

Initiation of Positive Streamers near Uncharged Ice Hydrometeors in the Thundercloud Field

NASA Astrophysics Data System (ADS)

Babich, L. P.; Bochkov, E. I.

2018-05-01

Since the threshold electric field required for breakdown of air is much higher than the maximum field strength measured in thunderstorm clouds, the problem of lightning initiation still remains unsolved. According to the popular hypothesis, lightning can be initiated by a streamer discharge in the field enhanced near a hydrometeor. To verify the adequacy of this hypothesis, the development of a positive streamer propagating along the thunderstorm electric field in the vicinity of an ice needle at an air pressure corresponding to an altitude of 5 km (which is typical of the lightning initiation conditions) was simulated numerically. The hydrometeor dimensions are determined at which streamers can be initiated at different strengths of the thunderstorm electric field.

Analyzing the tradeoff between electrical complexity and accuracy in patient-specific computational models of deep brain stimulation.

PubMed

Howell, Bryan; McIntyre, Cameron C

2016-06-01

Deep brain stimulation (DBS) is an adjunctive therapy that is effective in treating movement disorders and shows promise for treating psychiatric disorders. Computational models of DBS have begun to be utilized as tools to optimize the therapy. Despite advancements in the anatomical accuracy of these models, there is still uncertainty as to what level of electrical complexity is adequate for modeling the electric field in the brain and the subsequent neural response to the stimulation. We used magnetic resonance images to create an image-based computational model of subthalamic DBS. The complexity of the volume conductor model was increased by incrementally including heterogeneity, anisotropy, and dielectric dispersion in the electrical properties of the brain. We quantified changes in the load of the electrode, the electric potential distribution, and stimulation thresholds of descending corticofugal (DCF) axon models. Incorporation of heterogeneity altered the electric potentials and subsequent stimulation thresholds, but to a lesser degree than incorporation of anisotropy. Additionally, the results were sensitive to the choice of method for defining anisotropy, with stimulation thresholds of DCF axons changing by as much as 190%. Typical approaches for defining anisotropy underestimate the expected load of the stimulation electrode, which led to underestimation of the extent of stimulation. More accurate predictions of the electrode load were achieved with alternative approaches for defining anisotropy. The effects of dielectric dispersion were small compared to the effects of heterogeneity and anisotropy. The results of this study help delineate the level of detail that is required to accurately model electric fields generated by DBS electrodes.

Analyzing the tradeoff between electrical complexity and accuracy in patient-specific computational models of deep brain stimulation

NASA Astrophysics Data System (ADS)

Howell, Bryan; McIntyre, Cameron C.

2016-06-01

Objective. Deep brain stimulation (DBS) is an adjunctive therapy that is effective in treating movement disorders and shows promise for treating psychiatric disorders. Computational models of DBS have begun to be utilized as tools to optimize the therapy. Despite advancements in the anatomical accuracy of these models, there is still uncertainty as to what level of electrical complexity is adequate for modeling the electric field in the brain and the subsequent neural response to the stimulation. Approach. We used magnetic resonance images to create an image-based computational model of subthalamic DBS. The complexity of the volume conductor model was increased by incrementally including heterogeneity, anisotropy, and dielectric dispersion in the electrical properties of the brain. We quantified changes in the load of the electrode, the electric potential distribution, and stimulation thresholds of descending corticofugal (DCF) axon models. Main results. Incorporation of heterogeneity altered the electric potentials and subsequent stimulation thresholds, but to a lesser degree than incorporation of anisotropy. Additionally, the results were sensitive to the choice of method for defining anisotropy, with stimulation thresholds of DCF axons changing by as much as 190%. Typical approaches for defining anisotropy underestimate the expected load of the stimulation electrode, which led to underestimation of the extent of stimulation. More accurate predictions of the electrode load were achieved with alternative approaches for defining anisotropy. The effects of dielectric dispersion were small compared to the effects of heterogeneity and anisotropy. Significance. The results of this study help delineate the level of detail that is required to accurately model electric fields generated by DBS electrodes.

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.

Comparisons between detection threshold and loudness perception for individual cochlear implant channels

PubMed Central

Bierer, Julie Arenberg; Nye, Amberly D

2014-01-01

Objective The objective of the present study, performed in cochlear implant listeners, was to examine how the level of current required to detect single-channel electrical pulse trains relates to loudness perception on the same channel. The working hypothesis was that channels with relatively high thresholds, when measured with a focused current pattern, interface poorly to the auditory nerve. For such channels a smaller dynamic range between perceptual threshold and the most comfortable loudness would result, in part, from a greater sensitivity to changes in electrical field spread compared to low-threshold channels. The narrower range of comfortable listening levels may have important implications for speech perception. Design Data were collected from eight, adult cochlear implant listeners implanted with the HiRes90k cochlear implant (Advanced Bionics Corp.). The partial tripolar (pTP) electrode configuration, consisting of one intracochlear active electrode, two flanking electrodes carrying a fraction (σ) of the return current, and an extracochlear ground, was used for stimulation. Single-channel detection thresholds and most comfortable listening levels were acquired using the most focused pTP configuration possible (σ ≥ 0.8) to identify three channels for further testing – those with the highest, median, and lowest thresholds – for each subject. Threshold, equal-loudness contours (at 50% of the monopolar dynamic range), and loudness growth functions were measured for each of these three test channels using various partial tripolar fractions. Results For all test channels, thresholds increased as the electrode configuration became more focused. The rate of increase with the focusing parameter σ was greatest for the high-threshold channel compared to the median- and low-threshold channels. The 50% equal-loudness contours exhibited similar rates of increase in level across test channels and subjects. Additionally, test channels with the highest thresholds had the narrowest dynamic ranges (for σ ≥ 0.5) and steepest growth of loudness functions for all electrode configurations. Conclusions Together with previous studies using focused stimulation, the results suggest that auditory responses to electrical stimuli at both threshold and suprathreshold current levels are not uniform across the electrode array of individual cochlear implant listeners. Specifically, the steeper growth of loudness and thus smaller dynamic ranges observed for high-threshold channels are consistent with a degraded electrode-neuron interface, which could stem from lower numbers of functioning auditory neurons or a relatively large distance between the neurons and electrodes. These findings may have potential implications for how stimulation levels are set during the clinical mapping procedure, particularly for speech-processing strategies that use focused electrical fields. PMID:25036146

Self-consistent theory of nanodomain formation on non-polar surfaces of ferroelectrics

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

Morozovska, Anna N.; Obukhovskii, Vyacheslav; Fomichov, Evhen

2016-04-28

We propose a self-consistent theoretical approach capable of describing the features of the anisotropic nanodomain formation induced by a strongly inhomogeneous electric field of a charged scanning probe microscopy tip on nonpolar cuts of ferroelectrics. We obtained that a threshold field, previously regarded as an isotropic parameter, is an anisotropic function that is specified from the polar properties and lattice pinning anisotropy of a given ferroelectric in a self-consistent way. The proposed method for the calculation of the anisotropic threshold field is not material specific, thus the field should be anisotropic in all ferroelectrics with the spontaneous polarization anisotropy alongmore » the main crystallographic directions. The most evident examples are uniaxial ferroelectrics, layered ferroelectric perovskites, and low-symmetry incommensurate ferroelectrics. Obtained results quantitatively describe the differences at several times in the nanodomain length experimentally observed on X and Y cuts of LiNbO3 and can give insight into the anisotropic dynamics of nanoscale polarization reversal in strongly inhomogeneous electric fields.« less

Role of near-field enhancement in plasmonic laser nanoablation using gold nanorods on a silicon substrate.

PubMed

Harrison, R K; Ben-Yakar, Adela

2010-10-11

We present experimental results for the plasmonic laser ablation of silicon with nanoscale features as small as 22 x 66 nm using single near-infrared, femtosecond laser pulses incident on gold nanorods. Near the ablation threshold, these features are photo-imprints of gold nanorod particles positioned on the surface of the silicon and have feature sizes similar to the nanorods. The single rod-shaped ablation pattern matches the enhancement patterns of the Poynting vector magnitude on the surface of silicon, implying that the ablation is a result of the plasmonic enhancement of the incident electromagnetic waves in the near-field of the particles. Interestingly, the ablation pattern is different from the two separated holes at the ends of the nanorod, as would be expected from the electric field--|E|(2) enhancement pattern. We measured the plasmonic ablation threshold fluence to be almost two orders of magnitude less than the femtosecond laser ablation threshold of silica, present in the thin native oxide layer on the surface of silicon. This value also agrees with the enhancement of the Poynting vector of a nanorod on silicon as calculated with electromagnetic simulations. We thus conclude that plasmonic ablation with plasmonic nanoparticles depends directly on the polarization and the value of the near-field enhancement of the Poynting vector and not the square of the electric field as previously suggested.

Analysis of induced electrical currents from magnetic field coupling inside implantable neurostimulator leads.

PubMed

Pantchenko, Oxana S; Seidman, Seth J; Guag, Joshua W

2011-10-21

Over the last decade, the number of neurostimulator systems implanted in patients has been rapidly growing. Nearly 50, 000 neurostimulators are implanted worldwide annually. The most common type of implantable neurostimulators is indicated for pain relief. At the same time, commercial use of other electromagnetic technologies is expanding, making electromagnetic interference (EMI) of neurostimulator function an issue of concern. Typically reported sources of neurostimulator EMI include security systems, metal detectors and wireless equipment. When near such sources, patients with implanted neurostimulators have reported adverse events such as shock, pain, and increased stimulation. In recent in vitro studies, radio frequency identification (RFID) technology has been shown to inhibit the stimulation pulse of an implantable neurostimulator system during low frequency exposure at close distances. This could potentially be due to induced electrical currents inside the implantable neurostimulator leads that are caused by magnetic field coupling from the low frequency identification system. To systematically address the concerns posed by EMI, we developed a test platform to assess the interference from coupled magnetic fields on implantable neurostimulator systems. To measure interference, we recorded the output of one implantable neurostimulator, programmed for best therapy threshold settings, when in close proximity to an operating low frequency RFID emitter. The output contained electrical potentials from the neurostimulator system and those induced by EMI from the RFID emitter. We also recorded the output of the same neurostimulator system programmed for best therapy threshold settings without RFID interference. Using the Spatially Extended Nonlinear Node (SENN) model, we compared threshold factors of spinal cord fiber excitation for both recorded outputs. The electric current induced by low frequency RFID emitter was not significant to have a noticeable effect on electrical stimulation. We demonstrated a method for analyzing effects of coupled magnetic field interference on implantable neurostimulator system and its electrodes which could be used by device manufacturers during the design and testing phases of the development process.

Analysis of induced electrical currents from magnetic field coupling inside implantable neurostimulator leads

PubMed Central

2011-01-01

Background Over the last decade, the number of neurostimulator systems implanted in patients has been rapidly growing. Nearly 50, 000 neurostimulators are implanted worldwide annually. The most common type of implantable neurostimulators is indicated for pain relief. At the same time, commercial use of other electromagnetic technologies is expanding, making electromagnetic interference (EMI) of neurostimulator function an issue of concern. Typically reported sources of neurostimulator EMI include security systems, metal detectors and wireless equipment. When near such sources, patients with implanted neurostimulators have reported adverse events such as shock, pain, and increased stimulation. In recent in vitro studies, radio frequency identification (RFID) technology has been shown to inhibit the stimulation pulse of an implantable neurostimulator system during low frequency exposure at close distances. This could potentially be due to induced electrical currents inside the implantable neurostimulator leads that are caused by magnetic field coupling from the low frequency identification system. Methods To systematically address the concerns posed by EMI, we developed a test platform to assess the interference from coupled magnetic fields on implantable neurostimulator systems. To measure interference, we recorded the output of one implantable neurostimulator, programmed for best therapy threshold settings, when in close proximity to an operating low frequency RFID emitter. The output contained electrical potentials from the neurostimulator system and those induced by EMI from the RFID emitter. We also recorded the output of the same neurostimulator system programmed for best therapy threshold settings without RFID interference. Using the Spatially Extended Nonlinear Node (SENN) model, we compared threshold factors of spinal cord fiber excitation for both recorded outputs. Results The electric current induced by low frequency RFID emitter was not significant to have a noticeable effect on electrical stimulation. Conclusions We demonstrated a method for analyzing effects of coupled magnetic field interference on implantable neurostimulator system and its electrodes which could be used by device manufacturers during the design and testing phases of the development process. PMID:22014169

Electric field strength determination in filamentary DBDs by CARS-based four-wave mixing

NASA Astrophysics Data System (ADS)

Boehm, Patrick; Kettlitz, Manfred; Brandenburg, Ronny; Hoeft, Hans; Czarnetzki, Uwe

2016-09-01

The electric field strength is a basic parameter of non-thermal plasmas. Therefore, a profound knowledge of the electric field distribution is crucial. In this contribution a four wave mixing technique based on Coherent Anti-Stokes Raman spectroscopy (CARS) is used to measure electric field strengths in filamentary dielectric barrier discharges (DBDs). The discharges are operated with a pulsed voltage in nitrogen at atmospheric pressure. Small amounts hydrogen (10 vol%) are admixed as tracer gas to evaluate the electric field strength in the 1 mm discharge gap. Absolute values of the electric field strength are determined by calibration of the CARS setup with high voltage amplitudes below the ignition threshold of the arrangement. Alteration of the electric field strength has been observed during the internal polarity reversal and the breakdown process. In this case the major advantage over emission based methods is that this technique can be used independently from emission, e.g. in the pre-phase and in between two consecutive, opposite discharge pulses where no emission occurs at all. This work was supported by the Deutsche Forschungsgemeinschaft, Forschergruppe FOR 1123 and Sonderforschungsbereich TRR 24 ``Fundamentals of complex plasmas''.

Spontaneous reorientations of meta-atoms and electromagnetic spatial solitons in a liquid metacrystal.

PubMed

Zharov, Alexander A; Zharov, Alexander A; Zharova, Nina A

2014-08-01

We show that transverse electromagnetic waves propagating along an external static electric field in liquid metacrystal (LMC) can provoke spontaneous rearrangement of elongated meta-atoms that changes the direction of the anisotropy axis of the LMC. This kind of instability may reorient the meta-atoms from the equilibrium state parallel to a static field to the state along a high-frequency field and back at the different threshold intensities of electromagnetic waves in such a way that bistability in the system takes place. Reorientation of meta-atoms causes a change in the effective refraction index of LMC that creates, in turn, the conditions for the formation of bright spatial solitons. Such spatial solitons are the self-consistent domains of redirected meta-atoms with trapped photons. We find that the instability thresholds as well as energy flux captured by the spatial soliton can be easily managed by variation of the static electric field applied to the LMC. We study the effects of soliton excitation and collisions via numerical simulations.

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.

Creating and optimizing interfaces for electric-field and photon-induced charge transfer.

PubMed

Park, Byoungnam; Whitham, Kevin; Cho, Jiung; Reichmanis, Elsa

2012-11-27

We create and optimize a structurally well-defined electron donor-acceptor planar heterojunction interface in which electric-field and/or photon-induced charge transfer occurs. Electric-field-induced charge transfer in the dark and exciton dissociation at a pentacene/PCBM interface were probed by in situ thickness-dependent threshold voltage shift measurements in field-effect transistor devices during the formation of the interface. Electric-field-induced charge transfer at the interface in the dark is correlated with development of the pentacene accumulation layer close to PCBM, that is, including interface area, and dielectric relaxation time in PCBM. Further, we demonstrate an in situ test structure that allows probing of both exciton diffusion length and charge transport properties, crucial for optimizing optoelectronic devices. Competition between the optical absorption length and the exciton diffusion length in pentacene governs exciton dissociation at the interface. Charge transfer mechanisms in the dark and under illumination are detailed.

On conductivity changes in shocked potassium chloride

NASA Astrophysics Data System (ADS)

Bourne, N. K.; Townsend, D.; Braithwaite, M.

2005-06-01

A previous work has reported that shock loading of ionic crystals produces an induced polarization and changes in electrical conductivity. However, previous measurements recorded an integrated electrical signal comprising the induced electrical field and that due to current flow. For this reason a differential system was designed to separate these effects that was adapted from that used in the investigation of the conductivity of hydrogen under shock. The measurement removes voltages produced in the shock-induced electrical field, allowing determination of those resulting from resistance changes. Although the mechanical response of potassium chloride to shock has been studied extensively, the electrical response is less studied. Here, experiments are reported in which it is shocked to various stresses in order to observe conductivity changes. The range of stresses induced includes several mechanical thresholds, including the elastic-plastic transition, the B1:B2 phase transformation, and the overdriving of the shock faster than the elastic wave. The behavior observed when single crystal and targets pressed from granular material (to close to full density) are shocked around each of these thresholds is presented. The effects of loading to a particular stress in a single step or in multiple steps are discussed.

Evidence for thermally assisted threshold switching behavior in nanoscale phase-change memory cells

NASA Astrophysics Data System (ADS)

Le Gallo, Manuel; Athmanathan, Aravinthan; Krebs, Daniel; Sebastian, Abu

2016-01-01

In spite of decades of research, the details of electrical transport in phase-change materials are still debated. In particular, the so-called threshold switching phenomenon that allows the current density to increase steeply when a sufficiently high voltage is applied is still not well understood, even though there is wide consensus that threshold switching is solely of electronic origin. However, the high thermal efficiency and fast thermal dynamics associated with nanoscale phase-change memory (PCM) devices motivate us to reassess a thermally assisted threshold switching mechanism, at least in these devices. The time/temperature dependence of the threshold switching voltage and current in doped Ge2Sb2Te5 nanoscale PCM cells was measured over 6 decades in time at temperatures ranging from 40 °C to 160 °C. We observe a nearly constant threshold switching power across this wide range of operating conditions. We also measured the transient dynamics associated with threshold switching as a function of the applied voltage. By using a field- and temperature-dependent description of the electrical transport combined with a thermal feedback, quantitative agreement with experimental data of the threshold switching dynamics was obtained using realistic physical parameters.

Giant Permittivity in Epitaxial Ferroelectric Heterostructures

NASA Astrophysics Data System (ADS)

Erbil, A.; Kim, Y.; Gerhardt, R. A.

1996-08-01

A giant permittivity associated with the motion of domain walls is reported in epitaxial hetero- structures having alternating layers of ferroelectric and nonferroelectric oxides. At low frequencies, permittivities as high as 420 000 are found. Real and imaginary parts of the dielectric constant show large dispersion at high frequencies. In dc measurements, a nonlinear resistance is observed with a well-defined threshold field correlated with the dc bias-field dependence of ac permittivities. We interpret the observations as a result of the motion of a pinned domain wall lattice at low electric fields and sliding-mode motion at high electric fields.

Born in weak fields: below-threshold photoelectron dynamics

NASA Astrophysics Data System (ADS)

Williams, J. B.; Saalmann, U.; Trinter, F.; Schöffler, M. S.; Weller, M.; Burzynski, P.; Goihl, C.; Henrichs, K.; Janke, C.; Griffin, B.; Kastirke, G.; Neff, J.; Pitzer, M.; Waitz, M.; Yang, Y.; Schiwietz, G.; Zeller, S.; Jahnke, T.; Dörner, R.

2017-02-01

We investigate the dynamics of ultra-low kinetic energy photoelectrons. Many experimental techniques employed for the detection of photoelectrons require the presence of (more or less) weak electric extraction fields in order to perform the measurement. Our studies show that ultra-low energy photoelectrons exhibit a characteristic shift in their apparent measured momentum when the target system is exposed to such static electric fields. Already fields as weak as 1 V cm-1 have an observable influence on the detected electron momentum. This apparent shift is demonstrated by an experiment on zero energy photoelectrons emitted from He and explained through theoretical model calculations.

Quantum control via a genetic algorithm of the field ionization pathway of a Rydberg electron

NASA Astrophysics Data System (ADS)

Gregoric, Vincent C.; Kang, Xinyue; Liu, Zhimin Cheryl; Rowley, Zoe A.; Carroll, Thomas J.; Noel, Michael W.

2017-08-01

Quantum control of the pathway along which a Rydberg electron field ionizes is experimentally and computationally demonstrated. Selective field ionization is typically done with a slowly rising electric field pulse. The (1/n*)4 scaling of the classical ionization threshold leads to a rough mapping between arrival time of the electron signal and principal quantum number of the Rydberg electron. This is complicated by the many avoided level crossings that the electron must traverse on the way to ionization, which in general leads to broadening of the time-resolved field ionization signal. In order to control the ionization pathway, thus directing the signal to the desired arrival time, a perturbing electric field produced by an arbitrary wave-form generator is added to a slowly rising electric field. A genetic algorithm evolves the perturbing field in an effort to achieve the target time-resolved field ionization signal.

Quasi-electrostatic twisted waves in Lorentzian dusty plasmas

NASA Astrophysics Data System (ADS)

Arshad, Kashif; Lazar, M.; Poedts, S.

2018-07-01

The quasi electrostatic modes are investigated in non thermal dusty plasma using non-gyrotropic Kappa distribution in the presence of helical electric field. The Laguerre Gaussian (LG) mode function is employed to decompose the perturbed distribution function and helical electric field. The modified dielectric function is obtained for the dust ion acoustic (DIA) and dust acoustic (DA) twisted modes from the solution of Vlasov-Poisson equation. The threshold conditions for the growing modes is also illustrated.

Alignment of carbon iron into polydimethylsiloxane to create conductive composite with low percolation threshold and high piezoresistivity: experiment and simulation

NASA Astrophysics Data System (ADS)

Dong, Shuai; Wang, Xiaojie

2017-04-01

In this study, various amounts of carbonyl iron particles (CIPs) were cured into polydimethylsiloxane (PDMS) matrix under a magnetic field up to 1.0 T to create anisotropy of conductive composite materials. The electrical resistivity for the longitudinal direction was measured as a function of filler volume fraction to understand the electrical percolation behavior. The electrical percolation threshold (EPT) of CIPs-PDMS composite cured under a magnetic field can be as low as 0.1 vol%, which is much less than most of those studies in particulate composites. Meanwhile, the effects of compressive strain on the electrical properties of CIPs-PDMS composites were also investigated. The strain sensitivity depends on filler volume fraction and decreases with the increasing of compressive strain. It has been found that the composites containing a small amount of CI particles curing under a magnetic field exhibit a high strain sensitivity of over 150. Based on the morphological observation of the composite structures, a two-dimensional stick percolation model for the CIPs-PDMS composites has been established. The Monte Carlo simulation is performed to obtain the percolation probability. The simulation results in prediction of the values of EPTs are close to that of experimental measurements. It demonstrates that the low percolation behavior of CIPs-PDMS composites is due to the average length of particle chains forming by external magnetic field.

Electric-field-induced motion of colloid particles in smectic liquid crystals

NASA Astrophysics Data System (ADS)

Jakli, Antal

2005-03-01

We present the first observations of DC electric-field-induced rotational and translational motion of finite particles in liquid crystals. The electro-rotation is basically identical to the well known Quincke rotation, which triggers the translational motion at higher fields. From the electric field dependence of the angular velocity of the rotation we obtain the viscosity of the liquid crystals. The analysis of the translational motion in smectic liquid crystals indicates elastic responses near the threshold for translation. At increasing fields the speed of the particles is increasing and at sufficiently high speeds the flow of the smectic A and smectic C liquid crystal around the beads become purely viscous. Colloid particles in smectic materials maybe considered as model systems for understanding motion of proteins in cell membranes.

Softened Mechanical Properties of Graphene Induced by Electric Field.

PubMed

Huang, Peng; Guo, Dan; Xie, Guoxin; Li, Jian

2017-10-11

The understanding on the mechanical properties of graphene under the applications of physical fields is highly relevant to the reliability and lifetime of graphene-based nanodevices. In this work, we demonstrate that the application of electric field could soften the mechanical properties of graphene dramatically on the basis of the conductive AFM nanoindentation method. It has been found that the Young's modulus and fracture strength of graphene nanosheets suspended on the holes almost stay the same initially and then exhibit a sharp drop when the normalized electric field strength increases to be 0.18 ± 0.03 V/nm. The threshold voltage of graphene nanosheets before the onset of fracture under the fixed applied load increases with the thickness. Supported graphene nanosheets can sustain larger electric field under the same applied load than the suspended ones. The excessively regional Joule heating caused by the high electric current under the applied load is responsible for the electromechanical failure of graphene. These findings can provide a beneficial guideline for the electromechanical applications of graphene-based nanodevices.

Minimum Electric Field Exposure for Seizure Induction with Electroconvulsive Therapy and Magnetic Seizure Therapy.

PubMed

Lee, Won H; Lisanby, Sarah H; Laine, Andrew F; Peterchev, Angel V

2017-05-01

Lowering and individualizing the current amplitude in electroconvulsive therapy (ECT) has been proposed as a means to produce stimulation closer to the neural activation threshold and more focal seizure induction, which could potentially reduce cognitive side effects. However, the effect of current amplitude on the electric field (E-field) in the brain has not been previously linked to the current amplitude threshold for seizure induction. We coupled MRI-based E-field models with amplitude titrations of motor threshold (MT) and seizure threshold (ST) in four nonhuman primates (NHPs) to determine the strength, distribution, and focality of stimulation in the brain for four ECT electrode configurations (bilateral, bifrontal, right-unilateral, and frontomedial) and magnetic seizure therapy (MST) with cap coil on vertex. At the amplitude-titrated ST, the stimulated brain subvolume (23-63%) was significantly less than for conventional ECT with high, fixed current (94-99%). The focality of amplitude-titrated right-unilateral ECT (25%) was comparable to cap coil MST (23%), demonstrating that ECT with a low current amplitude and focal electrode placement can induce seizures with E-field as focal as MST, although these electrode and coil configurations affect differently specific brain regions. Individualizing the current amplitude reduced interindividual variation in the stimulation focality by 40-53% for ECT and 26% for MST, supporting amplitude individualization as a means of dosing especially for ECT. There was an overall significant correlation between the measured amplitude-titrated ST and the prediction of the E-field models, supporting a potential role of these models in dosing of ECT and MST. These findings may guide the development of seizure therapy dosing paradigms with improved risk/benefit ratio.

Dipole interaction of the Quincke rotating particles.

PubMed

Dolinsky, Yu; Elperin, T

2012-02-01

We study the behavior of particles having a finite electric permittivity and conductivity in a weakly conducting fluid under the action of the external electric field. We consider the case when the strength of the external electric field is above the threshold, and particles rotate due to the Quincke effect. We determine the magnitude of the dipole interaction of the Quincke rotating particles and the shift of frequency of the Quincke rotation caused by the dipole interaction between the particles. It is demonstrated that depending on the mutual orientation of the vectors of angular velocities of particles, vector-directed along the straight line between the centers of the particles and the external electric field strength vector, particles can attract or repel each other. In contrast to the case of nonrotating particles when the magnitude of the dipole interaction increases with the increase of the strength of the external electric field, the magnitude of the dipole interaction of the Quincke rotating particles either does not change or decreases with the increase of the strength of the external electric field depending on the strength of the external electric field and electrodynamic parameters of the particles.

Dipole interaction of the Quincke rotating particles

NASA Astrophysics Data System (ADS)

Dolinsky, Yu.; Elperin, T.

2012-02-01

We study the behavior of particles having a finite electric permittivity and conductivity in a weakly conducting fluid under the action of the external electric field. We consider the case when the strength of the external electric field is above the threshold, and particles rotate due to the Quincke effect. We determine the magnitude of the dipole interaction of the Quincke rotating particles and the shift of frequency of the Quincke rotation caused by the dipole interaction between the particles. It is demonstrated that depending on the mutual orientation of the vectors of angular velocities of particles, vector-directed along the straight line between the centers of the particles and the external electric field strength vector, particles can attract or repel each other. In contrast to the case of nonrotating particles when the magnitude of the dipole interaction increases with the increase of the strength of the external electric field, the magnitude of the dipole interaction of the Quincke rotating particles either does not change or decreases with the increase of the strength of the external electric field depending on the strength of the external electric field and electrodynamic parameters of the particles.

Electrical field imaging as a means to predict the loudness of monopolar and tripolar stimuli in cochlear implant patients.

PubMed

Berenstein, Carlo K; Vanpoucke, Filiep J; Mulder, Jef J S; Mens, Lucas H M

2010-12-01

Tripolar and other electrode configurations that use simultaneous stimulation inside the cochlea have been tested to reduce channel interactions compared to the monopolar stimulation conventionally used in cochlear implant systems. However, these "focused" configurations require increased current levels to achieve sufficient loudness. In this study, we investigate whether highly accurate recordings of the intracochlear electrical field set up by monopolar and tripolar configurations correlate to their effect on loudness. We related the intra-scalar potential distribution to behavioral loudness, by introducing a free parameter (α) which parameterizes the degree to which the potential field peak set up inside the scala tympani is still present at the location of the targeted neural tissue. Loudness balancing was performed on four levels between behavioral threshold and the most comfortable loudness level in a group of 10 experienced Advanced Bionics cochlear implant users. The effect of the amount of focusing on loudness was well explained by α per subject location along the basilar membrane. We found that α was unaffected by presentation level. Moreover, the ratios between the monopolar and tripolar currents, balanced for equal loudness, were approximately the same for all presentation levels. This suggests a linear loudness growth with increasing current level and that the equal peak hypothesis may predict the loudness of threshold as well as at supra-threshold levels. These results suggest that advanced electrical field imaging, complemented with limited psychophysical testing, more specifically at only one presentation level, enables estimation of the loudness growth of complex electrode configurations. Copyright © 2010 Elsevier B.V. All rights reserved.

Electric-acoustic interactions in the hearing cochlea: single fiber recordings.

PubMed

Tillein, J; Hartmann, R; Kral, A

2015-04-01

The present study investigates interactions of simultaneous electric and acoustic stimulation in single auditory nerve fibers in normal hearing cats. First, the auditory nerve was accessed with a microelectrode and response areas of single nerve fibers were determined for acoustic stimulation. Second, response thresholds to extracochlear sinusoidal electric stimulation using ball electrodes positioned at the round window were measured. Third, interactions that occurred with combined electric-acoustic stimulation were investigated in two areas: (1) the spectral domain (frequency response areas) and (2) the temporal domain (phase-locking to each stimulus) at moderate stimulus intensities (electric: 6 dB re threshold, acoustic: 20-40 dB re threshold at the characteristic frequency, CF). For fibers responding to both modalities responses to both electric and acoustic stimulation could be clearly identified. CFs, thresholds, and bandwidth (Q10dB) of acoustic responses were not significantly affected by simultaneous electric stimulation. Phase-locking of electric responses decreased in the presence of acoustic stimulation. Indication for electric stimulation of inner hair cells with 125 and 250 Hz were observed. However, these did not disturb the acoustic receptive fields of auditory nerve fibers. There was a trade-off between these responses when the intensities of the stimulation were varied: Relatively more intense stimulation dominated less intense stimulation. The scarcity of interaction between the different stimulus modalities demonstrates the ability of electric-acoustic stimulation to transfer useful information through both stimulation channels at the same time despite cochlear electrophonic effects. Application of 30 Hz electric stimulation resulted in a strong suppression of acoustic activity in the anodic phase of the stimulus. An electric stimulation like this might thus be used to control acoustic responses. This article is part of a Special Issue entitled . Copyright © 2014 Elsevier B.V. All rights reserved.

Terahertz radiation-induced sub-cycle field electron emission across a split-gap dipole antenna

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

Zhang, Jingdi; Averitt, Richard D., E-mail: xinz@bu.edu, E-mail: raveritt@ucsd.edu; Department of Physics, Boston University, Boston, Massachusetts 02215

We use intense terahertz pulses to excite the resonant mode (0.6 THz) of a micro-fabricated dipole antenna with a vacuum gap. The dipole antenna structure enhances the peak amplitude of the in-gap THz electric field by a factor of ∼170. Above an in-gap E-field threshold amplitude of ∼10 MV/cm{sup −1}, THz-induced field electron emission is observed as indicated by the field-induced electric current across the dipole antenna gap. Field emission occurs within a fraction of the driving THz period. Our analysis of the current (I) and incident electric field (E) is in agreement with a Millikan-Lauritsen analysis where log (I) exhibits amore » linear dependence on 1/E. Numerical estimates indicate that the electrons are accelerated to a value of approximately one tenth of the speed of light.« less

Strong anisotropy of electric field effects on uniaxial relaxor ferroelectric Sr0.75Ba0.25Nb2O6 crystals proved by acoustic emission

NASA Astrophysics Data System (ADS)

Dul'kin, E.; Kojima, S.; Roth, M.

2018-01-01

[001] oriented Sr0.75Ba0.25Nb2O6 uniaxial relaxor ferroelectric crystals have been studied by acoustic emission in the temperature range of 20÷200 °C and under an external electric field up to 1 kV/cm. Under the application of an electric field the temperature of a dielectric maximum exhibits a nontrivial behavior: it remains constant at first, secondly steep decreases down to some threshold field, and thirdly starts to increase as a field enhances, whereas the same temperature of a dielectric maximum under a bias electric field to [100] oriented Sr0.75Ba0.25Nb2O6 crystals exhibits a smoothed minimum before the start to increase as a field enhances (E. Dul'kin et al., J. Appl. Phys. 110, 044106 (2011)). Such a difference of electric field effects in c- and a-cut crystals is discussed from the viewpoint of random-bond-random-field model of relaxor ferroelectrics. By the comparison between experimental and theoretical data, a dipole moment of the PNR was estimated to be 0.1 (C cm).

Electric fields yield chaos in microflows

PubMed Central

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

2012-01-01

We present an investigation of chaotic dynamics of a low Reynolds number electrokinetic flow. Electrokinetic flows arise due to couplings of electric fields and electric double layers. In these flows, applied (steady) electric fields can couple with ionic conductivity gradients outside electric double layers to produce flow instabilities. The threshold of these instabilities is controlled by an electric Rayleigh number, Rae. As Rae increases monotonically, we show here flow dynamics can transition from steady state to a time-dependent periodic state and then to an aperiodic, chaotic state. Interestingly, further monotonic increase of Rae shows a transition back to a well-ordered state, followed by a second transition to a chaotic state. Temporal power spectra and time-delay phase maps of low dimensional attractors graphically depict the sequence between periodic and chaotic states. To our knowledge, this is a unique report of a low Reynolds number flow with such a sequence of periodic-to-aperiodic transitions. Also unique is a report of strange attractors triggered and sustained through electric fluid body forces. PMID:22908251

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.

Giant lipid vesicles under electric field pulses assessed by non invasive imaging.

PubMed

Mauroy, Chloé; Portet, Thomas; Winterhalder, Martin; Bellard, Elisabeth; Blache, Marie-Claire; Teissié, Justin; Zumbusch, Andreas; Rols, Marie-Pierre

2012-10-01

We present experimental results regarding the effects of electric pulses on giant unilamellar vesicles (GUVs). We have used phase contrast and coherent anti-Stokes Raman scattering (CARS) microscopy as relevant optical approaches to gain insight into membrane changes under electropermeabilization. No addition of exogenous molecules (lipid analogue, fluorescent dye) was needed. Therefore, experiments were performed on pure lipid systems avoiding possible artefacts linked to their use. Structural membrane changes were assessed by loss of contrast inside the GUVs due to sucrose and glucose mixing. Our observations, performed at the single vesicle level, indicate these changes are under the control of the number of pulses and field intensity. Larger number of pulses enhances membrane alterations. A threshold value of the field intensity must be applied to allow exchange of molecules between GUVs and the external medium. This threshold depends on the size of the vesicles, the larger GUVs being affected at lower electric field strengths than the smaller ones. Our experimental data are well described by a simple model in which molecule entry is driven by direct exchange. The CARS microscopic study of the effect of pulse duration confirms that pulses, in the ms time range, induce loss of lipids and membrane deformations facing the electrodes. Copyright © 2012 Elsevier B.V. All rights reserved.

Chaotic behavior in electro-rotation

NASA Astrophysics Data System (ADS)

Lemaire, E.; Lobry, L.

2002-11-01

We study the dynamics of an insulating cylinder in a weakly conducting liquid when submitted to a DC electric field. The cylinder is free to rotate along its long axis which is perpendicular to the applied field. Above a threshold value of the electric field, the cylinder rotates in either direction with constant angular velocity. This instability is known as Quincke rotation and can be easily understood by considering the polarization induced by the free charges accumulation on the cylinder surface. Here we present preliminary experimental results which exhibit a chaotic dynamics of the cylinder for higher electric fields: the velocity is no longer constant and the rotation direction changes randomly. By taking into account the finite Maxwell-Wagner polarization relaxation time, we show that this chaotic behavior can be described by the Lorenz equations.

Antinociception induced by epidural motor cortex stimulation in naive conscious rats is mediated by the opioid system.

PubMed

Fonoff, Erich Talamoni; Dale, Camila Squarzoni; Pagano, Rosana Lima; Paccola, Carina Cicconi; Ballester, Gerson; Teixeira, Manoel Jacobsen; Giorgi, Renata

2009-01-03

Epidural motor cortex stimulation (MCS) has been used for treating patients with neuropathic pain resistant to other therapeutic approaches. Experimental evidence suggests that the motor cortex is also involved in the modulation of normal nociceptive response, but the underlying mechanisms of pain control have not been clarified yet. The aim of this study was to investigate the effects of epidural electrical MCS on the nociceptive threshold of naive rats. Electrodes were placed on epidural motor cortex, over the hind paw area, according to the functional mapping accomplished in this study. Nociceptive threshold and general activity were evaluated under 15-min electrical stimulating sessions. When rats were evaluated by the paw pressure test, MCS induced selective antinociception in the paw contralateral to the stimulated cortex, but no changes were noticed in the ipsilateral paw. When the nociceptive test was repeated 15 min after cessation of electrical stimulation, the nociceptive threshold returned to basal levels. On the other hand, no changes in the nociceptive threshold were observed in rats evaluated by the tail-flick test. Additionally, no behavioral or motor impairment were noticed in the course of stimulation session at the open-field test. Stimulation of posterior parietal or somatosensory cortices did not elicit any changes in the general activity or nociceptive response. Opioid receptors blockade by naloxone abolished the increase in nociceptive threshold induced by MCS. Data shown herein demonstrate that epidural electrical MCS elicits a substantial and selective antinociceptive effect, which is mediated by opioids.

Why intra-epidermal electrical stimulation achieves stimulation of small fibres selectively: a simulation study

NASA Astrophysics Data System (ADS)

Motogi, Jun; Sugiyama, Yukiya; Laakso, Ilkka; Hirata, Akimasa; Inui, Koji; Tamura, Manabu; Muragaki, Yoshihiro

2016-06-01

The in situ electric field in the peripheral nerve of the skin is investigated to discuss the selective stimulation of nerve fibres. Coaxial planar electrodes with and without intra-epidermal needle tip were considered as electrodes of a stimulator. From electromagnetic analysis, the tip depth of the intra-epidermal electrode should be larger than the thickness of the stratum corneum, the electrical conductivity of which is much lower than the remaining tissue. The effect of different radii of the outer ring electrode on the in situ electric field is marginal. The minimum threshold in situ electric field (rheobase) for free nerve endings is estimated to be 6.3 kV m-1. The possible volume for electrostimulation, which can be obtained from the in situ electric field distribution, becomes deeper and narrower with increasing needle depth, suggesting that possible stimulation sites may be controlled by changing the needle depth. The injection current amplitude should be adjusted when changing the needle depth because the peak field strength also changes. This study shows that intra-epidermal electrical stimulation can achieve stimulation of small fibres selectively, because Aβ-, Aδ-, and C-fibre terminals are located at different depths in the skin.

Increasing the switching speed of liquid crystal devices with magnetic nanorods

NASA Astrophysics Data System (ADS)

Garbovskiy, Yu.; Baptist, J. R.; Thompson, J.; Hunter, T.; Lim, J. H.; Gi Min, Seong; Wiley, J. B.; Malkinski, L. M.; Glushchenko, A.; Celinski, Z.

2012-10-01

Liquid crystal (LC)/magnetic nanorods colloids were fabricated and tested using a magneto-optical setup. These thermotropic ferronematics do not show any signs of macroscopic aggregation, exhibit enhanced magnetic sensitivity, and faster time response in the simultaneous presence of crossed electric and magnetic fields. Magnetic nanorods increase an effective magnetic anisotropy of the colloid and decrease magnetic Freedericksz threshold. Applying a magnetic field along the direction perpendicular to the applied electric field leads to a decrease of the time OFF by a factor of 6 for pure liquid crystals, and by a factor of 9—for ferronematics.

Evidence for thermally assisted threshold switching behavior in nanoscale phase-change memory cells

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

Le Gallo, Manuel; Athmanathan, Aravinthan; Krebs, Daniel

2016-01-14

In spite of decades of research, the details of electrical transport in phase-change materials are still debated. In particular, the so-called threshold switching phenomenon that allows the current density to increase steeply when a sufficiently high voltage is applied is still not well understood, even though there is wide consensus that threshold switching is solely of electronic origin. However, the high thermal efficiency and fast thermal dynamics associated with nanoscale phase-change memory (PCM) devices motivate us to reassess a thermally assisted threshold switching mechanism, at least in these devices. The time/temperature dependence of the threshold switching voltage and current inmore » doped Ge{sub 2}Sb{sub 2}Te{sub 5} nanoscale PCM cells was measured over 6 decades in time at temperatures ranging from 40 °C to 160 °C. We observe a nearly constant threshold switching power across this wide range of operating conditions. We also measured the transient dynamics associated with threshold switching as a function of the applied voltage. By using a field- and temperature-dependent description of the electrical transport combined with a thermal feedback, quantitative agreement with experimental data of the threshold switching dynamics was obtained using realistic physical parameters.« less

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.

A theoretical investigation on the parametric instability excited by X-mode polarized electromagnetic wave at Tromsø

NASA Astrophysics Data System (ADS)

Wang, Xiang; Cannon, Patrick; Zhou, Chen; Honary, Farideh; Ni, Binbin; Zhao, Zhengyu

2016-04-01

Recent ionospheric modification experiments performed at Tromsø, Norway, have indicated that X-mode pump wave is capable of stimulating high-frequency enhanced plasma lines, which manifests the excitation of parametric instability. This paper investigates theoretically how the observation can be explained by the excitation of parametric instability driven by X-mode pump wave. The threshold of the parametric instability has been calculated for several recent experimental observations at Tromsø, illustrating that our derived equations for the excitation of parametric instability for X-mode heating can explain the experimental observations. According to our theoretical calculation, a minimum fraction of pump wave electric field needs to be directed along the geomagnetic field direction in order for the parametric instability threshold to be met. A full-wave finite difference time domain simulation has been performed to demonstrate that a small parallel component of pump wave electric field can be achieved during X-mode heating in the presence of inhomogeneous plasma.

Computational estimation of magnetically induced electric fields in a rotating head

NASA Astrophysics Data System (ADS)

Ilvonen, Sami; Laakso, Ilkka

2009-01-01

Change in a magnetic field, or similarly, movement in a strong static magnetic field induces electric fields in human tissues, which could potentially cause harmful effects. In this paper, the fields induced by different rotational movements of a head in a strong homogeneous magnetic field are computed numerically. Average field magnitudes near the retinas and inner ears are studied in order to gain insight into the causes of phosphenes and vertigo-like effects, which are associated with extremely low-frequency (ELF) magnetic fields. The induced electric fields are calculated in four different anatomically realistic head models using an efficient finite-element method (FEM) solver. The results are compared with basic restriction limits by IEEE and ICNIRP. Under rotational movement of the head, with a magnetic flux rate of change of 1 T s-1, the maximum IEEE-averaged electric field and maximum ICNIRP-averaged current density were 337 mV m-1 and 8.84 mA m-2, respectively. The limits by IEEE seem significantly stricter than those by ICNIRP. The results show that a magnetic flux rate of change of 1 T s-1 may induce electric field in the range of 50 mV m-1 near retinas, and possibly even larger values near the inner ears. These results provide information for approximating the threshold electric field values of phosphenes and vertigo-like effects.

Study on statistical breakdown delay time in argon gas using a W-band millimeter-wave gyrotron

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

Kim, Dongsung; Yu, Dongho; Choe, MunSeok

2016-04-15

In this study, we investigated plasma initiation delay times for argon volume breakdown at the W-band frequency regime. The threshold electric field is defined as the minimum electric field amplitude needed for plasma breakdown at various pressures. The measured statistical delay time showed an excellent agreement with the theoretical Gaussian distribution and the theoretically estimated formative delay time. Also, we demonstrated that the normalized effective electric field as a function of the product of pressure and formative time shows an outstanding agreement to that of 1D particle-in-cell simulation coupled with a Monte Carlo collision model [H. C. Kim and J.more » P. Verboncoeur, Phys. Plasmas 13, 123506 (2006)].« less

Easily installable behavioral monitoring system with electric field sensor.

PubMed

Tsukamoto, Sosuke; Machida, Yuichiro; Kameda, Noriyuki; Hoshino, Hiroshi; Tamura, Toshiyo

2007-01-01

This paper describes a wireless behavioral monitoring system equipped with an electric field sensor. The sensor unit was designed to obtain information regarding the usage of home electric appliances such as the television, microwave oven, coffee maker, etc. by measuring the electric field surrounding them. It is assumed that these usage statistics could provide information regarding the indoor behavior of a subject. Since the sensor can be used by simply attaching it to an appliance and does not require any wiring for its installation, this system can be temporarily installed in any ordinary house. A simple interface for selecting the threshold value of appliances' power on/off states was introduced. The experimental results reveal that the proposed system can be installed by individuals in their residences in a short time and the usage statistics of home appliances can be gathered.

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.;

Effects of stimulation parameters and electrode location on thresholds for epidural stimulation of cat motor cortex

NASA Astrophysics Data System (ADS)

Wongsarnpigoon, Amorn; Grill, Warren M.

2011-12-01

Epidural electrical stimulation (ECS) of the motor cortex is a developing therapy for neurological disorders. Both placement and programming of ECS systems may affect the therapeutic outcome, but the treatment parameters that will maximize therapeutic outcomes and minimize side effects are not known. We delivered ECS to the motor cortex of anesthetized cats and investigated the effects of electrode placement and stimulation parameters on thresholds for evoking motor responses in the contralateral forelimb. Thresholds were inversely related to stimulation frequency and the number of pulses per stimulus train. Thresholds were lower over the forelimb representation in motor cortex (primary site) than surrounding sites (secondary sites), and thresholds at sites <4 mm away from the primary site were significantly lower than at sites >4 mm away. Electrode location and montage influenced the effects of polarity on thresholds: monopolar anodic and cathodic thresholds were not significantly different over the primary site, cathodic thresholds were significantly lower than anodic thresholds over secondary sites and bipolar thresholds were significantly lower with the anode over the primary site than with the cathode over the primary site. A majority of bipolar thresholds were either between or equal to the respective monopolar thresholds, but several bipolar thresholds were greater than or less than the monopolar thresholds of both the anode and cathode. During bipolar stimulation, thresholds were influenced by both electric field superposition and indirect, synaptically mediated interactions. These results demonstrate the influence of stimulation parameters and electrode location during cortical stimulation, and these effects should be considered during the programming of systems for therapeutic cortical stimulation.

Effects of coil orientation and magnetic field shield on transcranial magnetic stimulation in cats.

PubMed

Nakatoh, S; Kitagawa, H; Kawaguchi, Y; Nakamura, H; Takano, H; Tsuji, H

1998-09-01

To obtain suitable stimulus conditions for transcranial magnetic stimulation, the evoked compound muscle action potential (ECMAP), evoked spinal cord potential (ESCP), and magnetic and electric fields were analyzed in cats with and without the use of a magnetic field shield. Cats were stimulated using a figure 8 magnetic coil placed on the cranium above the motor cortex. The maximum ECMAP amplitude was recorded when the electric current in the coil was in the mediolateral direction, regardless of whether a magnetic shield with a 5 x 5 cm window was used. ECMAP and ESCP thresholds were reduced when magnetic shielding was in place. Due to the edge effect, the strengths of the magnetic and electric fields were highest in the brainstem area, which is an inhomogeneous volume conductor of the cat's cranium. A large induced electric field directed caudally elicited ECMAP and ESCP responses effectively when a magnetic shield with a 5 x 5 cm window was in place.

Adrenal Chromaffin Cells Exposed to 5-ns Pulses Require Higher Electric Fields to Porate Intracellular Membranes than the Plasma Membrane: An Experimental and Modeling Study.

PubMed

Zaklit, Josette; Craviso, Gale L; Leblanc, Normand; Yang, Lisha; Vernier, P Thomas; Chatterjee, Indira

2017-10-01

Nanosecond-duration electric pulses (NEPs) can permeabilize the endoplasmic reticulum (ER), causing release of Ca 2+ into the cytoplasm. This study used experimentation coupled with numerical modeling to understand the lack of Ca 2+ mobilization from Ca 2+ -storing organelles in catecholamine-secreting adrenal chromaffin cells exposed to 5-ns pulses. Fluorescence imaging determined a threshold electric (E) field of 8 MV/m for mobilizing intracellular Ca 2+ whereas whole-cell recordings of membrane conductance determined a threshold E-field of 3 MV/m for causing plasma membrane permeabilization. In contrast, a 2D numerical model of a chromaffin cell, which was constructed with internal structures representing a nucleus, mitochondrion, ER, and secretory granule, predicted that exposing the cell to the same 5-ns pulse electroporated the plasma and ER membranes at the same E-field amplitude, 3-4 MV/m. Agreement of the numerical simulations with the experimental results was obtained only when the ER interior conductivity was 30-fold lower than that of the cytoplasm and the ER membrane permittivity was twice that of the plasma membrane. A more realistic intracellular geometry for chromaffin cells in which structures representing multiple secretory granules and an ER showed slight differences in the thresholds necessary to porate the membranes of the secretory granules. We conclude that more sophisticated cell models together with knowledge of accurate dielectric properties are needed to understand the effects of NEPs on intracellular membranes in chromaffin cells, information that will be important for elucidating how NEPs porate organelle membranes in other cell types having a similarly complex cytoplasmic ultrastructure.

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

Nonlinear electromagnetic responses of active membrane protein complexes in live cells and organelles

NASA Astrophysics Data System (ADS)

Nawarathna, Dharmakirthi

The response of biological cells to an applied oscillating electric field contains both linear and nonlinear components (eg. induced harmonics). Such noninvasive measurements can be used to study active processes taking place inside the cells. The measurement of induced harmonics is the tool used for the study described here. A highly sensitive superconducting quantum interference device (SQUID) is used to detect the response at low frequencies, which greatly reduces electrode polarization effects. At high frequencies, a four- probe method is used. At low frequencies, harmonic generation by budding yeast cells in response to a sinusoidal electric field is reported, which is seen to be minimal when the field amplitude is less than a threshold value. Surprisingly, sodium metavanadate, an inhibitor of P-type ATPases and glucose, a substrate of P-type ATPase responsible for nonlinear response in yeast, reduces the threshold field amplitude, increasing harmonic generation at low amplitudes while reducing it at large amplitudes. We have thus proposed a model that explicitly introduces a threshold field, similar to those observed in density waves, where fields above threshold drive charge transport through an energy landscape with multiple wells, and in Coulomb blockade tunnel junctions, recently exploited to define the current standard. At high frequencies, the induced harmonics exhibit pronounced features that depend on the specific organism. Budding yeast (S. cerevisiae ) cells produce numerous harmonics. When the second or third harmonic amplitude is plotted vs. applied frequency, we observe two peaks, around 3 kHz and 12 kHz, which are suppressed by the respiratory inhibitor potassium cyanide. We then measured the response to oscillatory electric fields of intact bovine heart mitochondria, a reproducible second harmonic (at ˜3-4 kHz applied frequency) was detected. Further, with coupled mouse mitochondria, an ADP sensitive peak (˜ 12-15 kHz applied frequency) was observed, possibly due to the F0 domain of ATP synthase. Finally, harmonics generated by chloroplasts, the plant organelles responsible for photosynthesis, were measured, which are similar in structure and function to mitochondria, depend dramatically on incident light, and vanish in the absence of light. Using spinach chloroplasts, light sensitive peaks were detected in the range of 0--12 kHz, again suggesting that these harmonics are indicative of electron processes in the light harvesting complexes, reaction center, and/or photosynthetic electron transport chain.

Energy spectrum and thermal properties of a terahertz quantum-cascade laser based on the resonant-phonon depopulation scheme

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

Khabibullin, R. A., E-mail: khabibullin@isvch.ru; Shchavruk, N. V.; Klochkov, A. N.

The dependences of the electronic-level positions and transition oscillator strengths on an applied electric field are studied for a terahertz quantum-cascade laser (THz QCL) with the resonant-phonon depopulation scheme, based on a cascade consisting of three quantum wells. The electric-field strengths for two characteristic states of the THz QCL under study are calculated: (i) “parasitic” current flow in the structure when the lasing threshold has not yet been reached; (ii) the lasing threshold is reached. Heat-transfer processes in the THz QCL under study are simulated to determine the optimum supply and cooling conditions. The conditions of thermocompression bonding of themore » laser ridge stripe with an n{sup +}-GaAs conductive substrate based on Au–Au are selected to produce a mechanically stronger contact with a higher thermal conductivity.« less

Measurements of electron avalanche formation time in W-band microwave air breakdown

NASA Astrophysics Data System (ADS)

Cook, Alan M.; Hummelt, Jason S.; Shapiro, Michael A.; Temkin, Richard J.

2011-08-01

We present measurements of formation times of electron avalanche ionization discharges induced by a focused 110 GHz millimeter-wave beam in atmospheric air. Discharges take place in a free volume of gas, with no nearby surfaces or objects. When the incident field amplitude is near the breakdown threshold for pulsed conditions, measured formation times are ˜0.1-2 μs over the pressure range 5-700 Torr. Combined with electric field breakdown threshold measurements, the formation time data shows the agreement of 110 GHz air breakdown with the similarity laws of gas discharges.

Interaction of Low Frequency External Electric Fields and Pancreatic β-Cell: A Mathematical Modeling Approach to Identify the Influence of Excitation Parameters.

PubMed

Farashi, Sajjad; Sasanpour, Pezhman; Rafii-Tabar, Hashem

2018-05-24

Purpose-Although the effect of electromagnetic fields on biological systems has attracted attraction in recent years, there has not been any conclusive result concerning the effects of interaction and the underlying mechanisms involved. Besides the complexity of biological systems, the parameters of the applied electromagnetic field have not been estimated in most of the experiments. Material and Method-In this study, we have used computational approach in order to find the excitation parameters of an external electric field which produces sensible effects in the function of insulin secretory machinery, whose failure triggers the diabetes disease. A mathematical model of the human β-cell has been used and the effects of external electric fields with different amplitudes, frequencies and wave shapes have been studied. Results-The results from our simulations show that the external electric field can influence the membrane electrical activity and perhaps the insulin secretion when its amplitude exceeds a threshold value. Furthermore, our simulations reveal that different waveforms have distinct effects on the β-cell membrane electrical activity and the characteristic features of the excitation like frequency would change the interaction mechanism. Conclusion-The results could help the researchers to investigate the possible role of the environmental electromagnetic fields on the promotion of diabetes disease.

DC conductivity of a suspension of insulating particles with internal rotation

NASA Astrophysics Data System (ADS)

Pannacci, N.; Lemaire, E.; Lobry, L.

2009-04-01

We analyse the consequences of Quincke rotation on the conductivity of a suspension. Quincke rotation refers to the spontaneous rotation of insulating particles dispersed in a slightly conducting liquid and subject to a high DC electric field: above a critical field, each particle rotates continuously around itself with an axis pointing in any direction perpendicular to the DC field. When the suspension is subject to an electric field lower than the threshold one, the presence of insulating particles in the host liquid decreases the bulk conductivity since the particles form obstacles to ion migration. But for electric fields higher than the critical one, the particles rotate and facilitate ion migration: the effective conductivity of the suspension is increased. We provide a theoretical analysis of the impact of Quincke rotation on the apparent conductivity of a suspension and we present experimental results obtained with a suspension of PMMA particles dispersed in weakly conducting liquids.

Methanol clusters (CH3OH)n, n = 3-6 in external electric fields: density functional theory approach.

PubMed

Rai, Dhurba; Kulkarni, Anant D; Gejji, Shridhar P; Pathak, Rajeev K

2011-07-14

Structural evolution of cyclic and branched-cyclic methanol clusters containing three to six molecules, under the influence of externally applied uniform static electric field is studied within the density functional theory. Akin to the situation for water clusters, the electric field is seen to stretch the intermolecular hydrogen bonds, and eventually break the H-bonded network at certain characteristic threshold field values of field strength in the range 0.009-0.016 a.u., yielding linear or branched structures with a lower energy. These structural transitions are characterized by an abrupt increase in the electric dipole moment riding over its otherwise steady nonlinear increase with the applied field. The field tends to rupture the H-bonded structure; consequently, the number of hydrogen bonds decreases with increasing field strength. Vibrational spectra analyzed for fields applied perpendicular to the cyclic ring structures bring out the shifts in the OH ring vibrations (blueshift) and the CO stretch vibrations (redshift). For a given field strength, the blueshifts increase with the number of molecules in the ring and are found to be generally larger than those in the corresponding water cluster counterparts.

Differences in two-point discrimination and sensory threshold in the blind between braille and text reading: a pilot study.

PubMed

Noh, Ji-Woong; Park, Byoung-Sun; Kim, Mee-Young; Lee, Lim-Kyu; Yang, Seung-Min; Lee, Won-Deok; Shin, Yong-Sub; Kang, Ji-Hye; Kim, Ju-Hyun; Lee, Jeong-Uk; Kwak, Taek-Yong; Lee, Tae-Hyun; Kim, Ju-Young; Kim, Junghwan

2015-06-01

[Purpose] This study investigated two-point discrimination (TPD) and the electrical sensory threshold of the blind to define the effect of using Braille on the tactile and electrical senses. [Subjects and Methods] Twenty-eight blind participants were divided equally into a text-reading and a Braille-reading group. We measured tactile sensory and electrical thresholds using the TPD method and a transcutaneous electrical nerve stimulator. [Results] The left palm TPD values were significantly different between the groups. The values of the electrical sensory threshold in the left hand, the electrical pain threshold in the left hand, and the electrical pain threshold in the right hand were significantly lower in the Braille group than in the text group. [Conclusion] These findings make it difficult to explain the difference in tactility between groups, excluding both palms. However, our data show that using Braille can enhance development of the sensory median nerve in the blind, particularly in terms of the electrical sensory and pain thresholds.

Differences in two-point discrimination and sensory threshold in the blind between braille and text reading: a pilot study

PubMed Central

Noh, Ji-Woong; Park, Byoung-Sun; Kim, Mee-Young; Lee, Lim-Kyu; Yang, Seung-Min; Lee, Won-Deok; Shin, Yong-Sub; Kang, Ji-Hye; Kim, Ju-Hyun; Lee, Jeong-Uk; Kwak, Taek-Yong; Lee, Tae-Hyun; Kim, Ju-Young; Kim, Junghwan

2015-01-01

[Purpose] This study investigated two-point discrimination (TPD) and the electrical sensory threshold of the blind to define the effect of using Braille on the tactile and electrical senses. [Subjects and Methods] Twenty-eight blind participants were divided equally into a text-reading and a Braille-reading group. We measured tactile sensory and electrical thresholds using the TPD method and a transcutaneous electrical nerve stimulator. [Results] The left palm TPD values were significantly different between the groups. The values of the electrical sensory threshold in the left hand, the electrical pain threshold in the left hand, and the electrical pain threshold in the right hand were significantly lower in the Braille group than in the text group. [Conclusion] These findings make it difficult to explain the difference in tactility between groups, excluding both palms. However, our data show that using Braille can enhance development of the sensory median nerve in the blind, particularly in terms of the electrical sensory and pain thresholds. PMID:26180348

Solitons induced by alternating electric fields in surface-stabilized ferroelectric liquid crystals

NASA Astrophysics Data System (ADS)

Jeżewski, W.; Kuczyński, W.; Hoffmann, J.

2011-04-01

Propagation of solitary waves activated in thin ferroelectric liquid crystal cells under external, sinusoidally alternating electric fields is investigated using the electro-optic technique. It is shown that solitons give contributions only to the loss component of the response spectrum, within rather narrow ranges of frequencies and in sufficiently strong fields. The limit frequency, at which the amplitude of the velocity of the solitary waves is greatest, is found to be related to material constants of liquid crystals. Measuring this threshold frequency provides the capability to determine the elastic constant of surface stabilized liquid crystalline materials in the bookshelf or chevron layer geometries.

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.;

Ionic liquid versus SiO 2 gated a-IGZO thin film transistors: A direct comparison

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

Pudasaini, Pushpa Raj; Noh, Joo Hyon; Wong, Anthony T.

Here, ionic liquid gated field effect transistors have been extensively studied due to their low operation voltage, ease of processing and the realization of high electric fields at low bias voltages. Here, we report ionic liquid (IL) gated thin film transistors (TFTs) based on amorphous Indium Gallium Zinc Oxide (a-IGZO) active layers and directly compare the characteristics with a standard SiO 2 gated device. The transport measurements of the top IL gated device revealed the n-channel property of the IGZO thin film with a current ON/OFF ratio ~10 5, a promising field effect mobility of 14.20 cm 2V –1s –1,more » and a threshold voltage of 0.5 V. Comparable measurements on the bottom SiO2 gate insulator revealed a current ON/OFF ratio >108, a field effect mobility of 13.89 cm 2V –1s –1 and a threshold voltage of 2.5 V. Furthermore, temperature-dependent measurements revealed that the ionic liquid electric double layer can be “frozen-in” by cooling below the glass transition temperature with an applied electrical bias. Positive and negative freezing bias locks-in the IGZO TFT “ON” and “OFF” state, respectively, which could lead to new switching and possibly non-volatile memory applications.« less

Morphological Influence of Solution-Processed Zinc Oxide Films on Electrical Characteristics of Thin-Film Transistors.

PubMed

Lee, Hyeonju; Zhang, Xue; Hwang, Jaeeun; Park, Jaehoon

2016-10-19

We report on the morphological influence of solution-processed zinc oxide (ZnO) semiconductor films on the electrical characteristics of ZnO thin-film transistors (TFTs). Different film morphologies were produced by controlling the spin-coating condition of a precursor solution, and the ZnO films were analyzed using atomic force microscopy, X-ray diffraction, X-ray photoemission spectroscopy, and Hall measurement. It is shown that ZnO TFTs have a superior performance in terms of the threshold voltage and field-effect mobility, when ZnO crystallites are more densely packed in the film. This is attributed to lower electrical resistivity and higher Hall mobility in a densely packed ZnO film. In the results of consecutive TFT operations, a positive shift in the threshold voltage occurred irrespective of the film morphology, but the morphological influence on the variation in the field-effect mobility was evident. The field-effect mobility in TFTs having a densely packed ZnO film increased continuously during consecutive TFT operations, which is in contrast to the mobility decrease observed in the less packed case. An analysis of the field-effect conductivities ascribes these results to the difference in energetic traps, which originate from structural defects in the ZnO films. Consequently, the morphological influence of solution-processed ZnO films on the TFT performance can be understood through the packing property of ZnO crystallites.

Morphological Influence of Solution-Processed Zinc Oxide Films on Electrical Characteristics of Thin-Film Transistors

PubMed Central

Lee, Hyeonju; Zhang, Xue; Hwang, Jaeeun; Park, Jaehoon

2016-01-01

We report on the morphological influence of solution-processed zinc oxide (ZnO) semiconductor films on the electrical characteristics of ZnO thin-film transistors (TFTs). Different film morphologies were produced by controlling the spin-coating condition of a precursor solution, and the ZnO films were analyzed using atomic force microscopy, X-ray diffraction, X-ray photoemission spectroscopy, and Hall measurement. It is shown that ZnO TFTs have a superior performance in terms of the threshold voltage and field-effect mobility, when ZnO crystallites are more densely packed in the film. This is attributed to lower electrical resistivity and higher Hall mobility in a densely packed ZnO film. In the results of consecutive TFT operations, a positive shift in the threshold voltage occurred irrespective of the film morphology, but the morphological influence on the variation in the field-effect mobility was evident. The field-effect mobility in TFTs having a densely packed ZnO film increased continuously during consecutive TFT operations, which is in contrast to the mobility decrease observed in the less packed case. An analysis of the field-effect conductivities ascribes these results to the difference in energetic traps, which originate from structural defects in the ZnO films. Consequently, the morphological influence of solution-processed ZnO films on the TFT performance can be understood through the packing property of ZnO crystallites. PMID:28773973

Ionic liquid versus SiO 2 gated a-IGZO thin film transistors: A direct comparison

DOE PAGES

Pudasaini, Pushpa Raj; Noh, Joo Hyon; Wong, Anthony T.; ...

2015-08-12

Here, ionic liquid gated field effect transistors have been extensively studied due to their low operation voltage, ease of processing and the realization of high electric fields at low bias voltages. Here, we report ionic liquid (IL) gated thin film transistors (TFTs) based on amorphous Indium Gallium Zinc Oxide (a-IGZO) active layers and directly compare the characteristics with a standard SiO 2 gated device. The transport measurements of the top IL gated device revealed the n-channel property of the IGZO thin film with a current ON/OFF ratio ~10 5, a promising field effect mobility of 14.20 cm 2V –1s –1,more » and a threshold voltage of 0.5 V. Comparable measurements on the bottom SiO2 gate insulator revealed a current ON/OFF ratio >108, a field effect mobility of 13.89 cm 2V –1s –1 and a threshold voltage of 2.5 V. Furthermore, temperature-dependent measurements revealed that the ionic liquid electric double layer can be “frozen-in” by cooling below the glass transition temperature with an applied electrical bias. Positive and negative freezing bias locks-in the IGZO TFT “ON” and “OFF” state, respectively, which could lead to new switching and possibly non-volatile memory applications.« less

An apoptosis targeted stimulus with nanosecond pulsed electric fields (nsPEFs) in E4 squamous cell carcinoma.

PubMed

Ren, Wei; Beebe, Stephen J

2011-04-01

Stimuli directed towards activation of apoptosis mechanisms are an attractive approach to eliminate evasion of apoptosis, a ubiquitous cancer hallmark. In these in vitro studies, kinetics and electric field thresholds for several apoptosis characteristics are defined in E4 squamous carcinoma cells (SCC) exposed to ten 300 ns pulses with increasing electric fields. Cell death was >95% at the highest electric field and coincident with phosphatidylserine externalization, caspase and calpain activation in the presence and absence of cytochrome c release, decreases in Bid and mitochondria membrane potential (Δψm) without apparent changes reactive oxygen species levels or in Bcl2 and Bclxl levels. Bid cleavage was caspase-dependent (55-60%) and calcium-dependent (40-45%). Intracellular calcium as an intrinsic mechanism and extracellular calcium as an extrinsic mechanism were responsible for about 30 and 70% of calcium dependence for Bid cleavage, respectively. The results reveal electric field-mediated cell death induction and progression, activating pro-apoptotic-like mechanisms and affecting plasma membrane and intracellular functions, primarily through extrinsic-like pathways with smaller contributions from intrinsic-like pathways. Nanosecond second pulsed electric fields trigger heterogeneous cell death mechanisms in E4 SCC populations to delete them, with caspase-associated cell death as a predominant, but not an unaccompanied event.

Calculation of femtosecond pulse laser induced damage threshold for broadband antireflective microstructure arrays.

PubMed

Jing, Xufeng; Shao, Jianda; Zhang, Junchao; Jin, Yunxia; He, Hongbo; Fan, Zhengxiu

2009-12-21

In order to more exactly predict femtosecond pulse laser induced damage threshold, an accurate theoretical model taking into account photoionization, avalanche ionization and decay of electrons is proposed by comparing respectively several combined ionization models with the published experimental measurements. In addition, the transmittance property and the near-field distribution of the 'moth eye' broadband antireflective microstructure directly patterned into the substrate material as a function of the surface structure period and groove depth are performed by a rigorous Fourier model method. It is found that the near-field distribution is strongly dependent on the periodicity of surface structure for TE polarization, but for TM wave it is insensitive to the period. What's more, the femtosecond pulse laser damage threshold of the surface microstructure on the pulse duration taking into account the local maximum electric field enhancement was calculated using the proposed relatively accurate theoretical ionization model. For the longer incident wavelength of 1064 nm, the weak linear damage threshold on the pulse duration is shown, but there is a surprising oscillation peak of breakdown threshold as a function of the pulse duration for the shorter incident wavelength of 532 nm.

Ionomycin-Induced Changes in Membrane Potential Alter Electroporation Outcomes in HL-60 Cells.

PubMed

Aiken, Erik J; Kilberg, Brian G; Yu, Siyuan; Hagness, Susan C; Booske, John H

2018-06-19

Previous studies have shown greater fluorophore uptake during electroporation on the anode-facing side of the cell than on the cathode-facing side. Based on these observations, we hypothesized that hyperpolarizing a cell before electroporation would decrease the requisite pulsed electric field intensity for electroporation outcomes, thereby yielding a higher probability of reversible electroporation at lower electric field strengths and a higher probability of irreversible electroporation (IRE) at higher electric field strengths. In this study, we tested this hypothesis by hyperpolarizing HL-60 cells using ionomycin before electroporation. These cells were then electroporated in a solution containing propidium iodide, a membrane integrity indicator. After 20 min, we added trypan blue to identify IRE cells. Our results showed that hyperpolarizing cells before electroporation alters the pulsed electric field intensity thresholds for reversible electroporation and IRE, allowing for greater control and selectivity of electroporation outcomes. Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.

The interference of electronic implants in low frequency electromagnetic fields.

PubMed

Silny, J

2003-04-01

Electronic implants such as cardiac pacemakers or nerve stimulators can be impaired in different ways by amplitude-modulated and even continuous electric or magnetic fields of strong field intensities. For the implant bearer, possible consequences of a temporary electromagnetic interference may range from a harmless impairment of his well-being to a perilous predicament. Electromagnetic interferences in all types of implants cannot be covered here due to their various locations in the body and their different sensing systems. Therefore, this presentation focuses exemplarily on the most frequently used implant, the cardiac pacemaker. In case of an electromagnetic interference the cardiac pacemaker reacts by switching to inhibition mode or to fast asynchronous pacing. At a higher disturbance voltage on the input of the pacemaker, a regular asynchronous pacing is likely to arise. In particular, the first-named interference could be highly dangerous for the pacemaker patient. The interference threshold of cardiac pacemakers depends in a complex way on a number of different factors such as: electromagnetic immunity and adjustment of the pacemaker, the composition of the applied low-frequency fields (only electric or magnetic fields or combinations of both), their frequencies and modulations, the type of pacemaker system (bipolar, unipolar) and its location in the body, as well as the body size and orientation in the field, and last but not least, certain physiological conditions of the patient (e.g. inhalation, exhalation). In extensive laboratory studies we have investigated the interference mechanisms in more than 100 cardiac pacemakers (older types as well as current models) and the resulting worst-case conditions for pacemaker patients in low-frequency electric and magnetic fields. The verification of these results in different practical everyday-life situations, e.g. in the fields of high-voltage overhead lines or those of electronic article surveillance systems is currently in progress. In case of the vertically-oriented electric 50 Hz fields preliminary results show that per 1 kV/m unimpaired electrical field strength (rms) an interference voltage of about 400 microVpp as worst-case could occur at the input of a unipolar ventricularly controlled, left-pectorally implanted cardiac pacemaker. Thus, already a field strength above ca. 5 kV/m could cause an interference with an implanted pacemaker. The magnetic fields induces an electric disturbance voltage at the input of the pacemaker. The body and the pacemaker system compose several induction loops, whose induced voltages rates add or subtract. The effective area of one representing inductive loop ranges from 100 to 221 cm2. For the unfavourable left-pectorally implantated and atrially-controlled pacemaker with a low interference threshold, the interference threshold ranges between 552 and 16 microT (rms) for magnetic fields at frequencies between 10 and 250 Hz. On this basis the occurrence of interferences with implanted pacemakers is possible in everyday-life situations. But experiments demonstrate a low probability of interference of cardiac pacemakers in practical situations. This apparent contradiction can be explained by a very small band of inhibition in most pacemakers and, in comparison with the worst-case, deviating conditions.

Middle Electrode in a Vertical Transistor Structure Using an Sn Layer by Thermal Evaporation

NASA Astrophysics Data System (ADS)

Nogueira, Gabriel Leonardo; da Silva Ozório, Maiza; da Silva, Marcelo Marques; Morais, Rogério Miranda; Alves, Neri

2018-05-01

We report a process for performing the middle electrode for a vertical field effect transistor (VOFET) by the evaporation of a tin (Sn) layer. Bare aluminum oxide (Al2O3), obtained by anodization, and Al2O3 covered with a polymethylmethacrylate (PMMA) layer were used as the gate dielectric. We measured the electrical resistance of Sn while the evaporation was carried out to find the best condition to prepare the middle electrode, that is, good lateral conduction associated with openings that give permeability to the electric field in a vertical direction. This process showed that 55 nm Sn thick is suitable for use in a VOFET, being easier to achieve optimal thickness when the Sn is evaporated onto PMMA than onto bare Al2O3. The addition of a PMMA layer on the Al2O3 surface modifies the morphology of the Sn layer, resulting in a lowering of the threshold voltage. The values of threshold voltage and electric field, VTH = - 8 V and ETH = 354.5 MV/m respectively, were calculated using an Al2O3 film 20 nm thick covered with a 14 nm PMMA layer as gate dielectric, while for bare Al2O3 these values were VTH = - 10 V and ETH = 500 MV/m.

Modification of turbulence and turbulent transport associated with a confinement transition in LAPD

NASA Astrophysics Data System (ADS)

Carter, Troy

2009-11-01

Azimuthal flow is driven in the edge of the Large Plasma Device (LAPD) through biasing a section of the vacuum vessel relative to the plasma source cathode. As the applied bias exceeds a threshold, a transition in radial particle confinement is observed, evidenced by a dramatic steepening in the density profile, similar to the L- to H-mode transition in toroidal confinement devices. The threshold behavior and dynamic behavior of radial transport is related to flow penetration and the degree of spatial overlap between the flow shear and density gradient profiles. An investigation of the changes in turbulence and turbulent particle transport associated with the confinement transition is presented. Two-dimensional cross-correlation measurements show that the spatial coherence of edge turbulence in LAPD changes significantly with biasing. The azimuthal correlation in the turbulence increases dramatically, while the radial correlation length is little altered. Turbulent amplitude is reduced at the transition, particularly in electric field fluctuations, but the dominant change observed is in the cross-phase between density and electric field fluctuations. The changes in cross-phase lead to a suppression and then apparent reversal of turbulent particle flux as the threshold is exceeded.

The inception of pulsed discharges in air: simulations in background fields above and below breakdown

NASA Astrophysics Data System (ADS)

Sun, Anbang; Teunissen, Jannis; Ebert, Ute

2014-11-01

We investigate discharge inception in air, in uniform background electric fields above and below the breakdown threshold. We perform 3D particle simulations that include a natural level of background ionization in the form of positive and \\text{O}2- ions. In background fields below breakdown, we use a strongly ionized seed of electrons and positive ions to enhance the field locally. In the region of enhanced field, we observe the growth of positive streamers, as in previous simulations with 2D plasma fluid models. The inclusion of background ionization has little effect in this case. When the background field is above the breakdown threshold, the situation is very different. Electrons can then detach from \\text{O}2- and start ionization avalanches in the whole volume. These avalanches together create one extended discharge, in contrast to the ‘double-headed’ streamers found in many fluid simulations.

Electrohydrodynamics of a particle-covered drop

NASA Astrophysics Data System (ADS)

Ouriemi, Malika; Vlahovska, Petia

2014-11-01

We study the dynamics of a drop nearly-completely covered with a particle monolayer in a uniform DC electric field. The weakly conducting fluid system consists of a silicon oil drop suspended in castor oil. A broad range of particle sizes, conductivities, and shapes is explored. In weak electric fields, the presence of particles increases drop deformation compared to a particle-free drop and suppresses the electrohydrodynamic flow. Very good agreement is observed between the measured drop deformation and the small deformation theory derived for surfactant-laden drops (Nganguia et al., 2013). In stronger electric fields, where drops are expected to undergo Quincke rotation (Salipante and Vlahovska, 2010), the presence of the particles greatly decreases the threshold for rotation and the stationary tilted drop configuration observed for clean drop is replaced by a spinning drop with either a wobbling inclination or a very low inclination. These behaviors resemble the predicted response of rigid ellipsoids in uniform electric fields. At even stronger electric fields, the particles can form dynamic wings or the drop implodes. The similar behavior of particle-covered and surfactant-laden drops provides new insights into understanding stability of Pickering emulsions. Supported by NSF-CBET 1437545.

Deformation and Rotation of a Drop in a Uniform Electric Field

NASA Astrophysics Data System (ADS)

Salipante, Paul; Hanna, James; Vlahovska, Petia

2009-11-01

Drop deformation in uniform electric fields is a classic problem. The pioneering work of G.I.Taylor demonstrated that for weakly conducting media, the drop fluid undergoes a toroidal flow and the drop adopts a prolate or oblate spheroidal shape, the flow and shape being axisymmetrically aligned with the applied field. However, recent studies have revealed a nonaxisymmetric rotational mode for drops of lower conductivity than the surrounding medium, similar to the rotation of solid dielectric particles observed by Quincke in the 19th century. We will present an experimental and theoretical study of this phenomenon in DC fields. The critical electric field, drop inclination angle, and rate of rotation are measured. For small, high viscosity drops, the threshold field strength is well approximated by the Quincke rotation criterion. Reducing the viscosity ratio shifts the onset for rotation to stronger fields. The drop inclination angle increases with field strength. The rotation rate is approximately given by the inverse Maxwell-Wagner polarization time. We also observe a hysteresis in the tilt angle for low-viscosity drops. The effects of AC fields and surfactants are also explored.

Comparative simulation analysis on the ignition threshold of atmospheric He and Ar dielectric barrier discharge

NASA Astrophysics Data System (ADS)

Yao, Congwei; Chang, Zhengshi; Chen, Sile; Ma, Hengchi; Mu, Haibao; Zhang, Guan-Jun

2017-09-01

Dielectric barrier discharge (DBD) is widely applied in many fields, and the discharge characteristics of insert gas have been the research focus for years. In this paper, fluid models of atmospheric Ar and He DBDs driven by 22 kHz sinusoidal voltage are built to analyze their ignition processes. The contributions of different electron sources in ignition process are analyzed, including the direct ionization of ground state atom, stepwise ionization of metastable particles, and secondary electron emission from dielectric wall, and they play different roles in different discharge stages. The Townsend direct ionization coefficient of He is higher than Ar with the same electrical field intensity, which is the direct reason for the different ignition thresholds between He and Ar. Further, the electron energy loss per free electron produced in Ar and He DBDs is discussed. It is found that the total electron energy loss rate of Ar is higher than He when the same electrical field is applied. The excitation reaction of Ar consumes the major electron energy but cannot produce free electrons effectively, which is the essential reason for the higher ignition threshold of Ar. The computation results of He and Ar extinction voltages can be explained in the view of electron energy loss, as well as the experimental results of different extinction voltages between Ar/NH3 and He DBDs.

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.

On the Modeling of Electrical Effects Experienced by Space Explorers During Extra Vehicular Activities: Intracorporal Currents, Resistances, and Electric Fields

NASA Technical Reports Server (NTRS)

Cela, Carlos J.; Loizos, Kyle; Lazzi, Gianluca; Hamilton, Douglas; Lee, Raphael C.

2011-01-01

Recent research has shown that space explorers engaged in Extra Vehicular Activities (EVAs) may be exposed, under certain conditions, to undesired electrical currents. This work focuses on determining whether these undesired induced electrical currents could be responsible for involuntary neuromuscular activity in the subjects, possibly caused by either large diameter peripheral nerve activation or reflex activity from cutaneous afferent stimulation. An efficient multiresolution variant of the admittance method along with a millimeter-resolution model of a male human body were used to calculate induced electric fields, resistance between contact electrodes used to simulate the potential exposure condition, and currents induced in the human body model. Results show that, under realistic exposure conditions using a 15V source, current density magnitudes and total current injected are well above previously reported startle reaction thresholds. This indicates that, under the considered conditions, the subjects could experience involuntary motor response.

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.

Modeling Proton Irradiation in AlGaN/GaN HEMTs: Understanding the Increase of Critical Voltage

NASA Astrophysics Data System (ADS)

Patrick, Erin; Law, Mark E.; Liu, Lu; Cuervo, Camilo Velez; Xi, Yuyin; Ren, Fan; Pearton, Stephen J.

2013-12-01

A combination of TRIM and FLOODS models the effect of radiation damage on AlGaN/GaN HEMTs. While excellent fits are obtained for threshold voltage shift, the models do not fully explain the increased reliability observed experimentally. In short, the addition of negatively-charged traps in the GaN buffer layer does not significantly change the electric field at the gate edges at radiation fluence levels seen in this study. We propose that negative trapped charge at the nitride/AlGaN interface actually produces the virtual-gate effect that results in decreasing the magnitude of the electric field at the gate edges and thus the increase in critical voltage. Simulation results including nitride interface charge show significant changes in electric field profiles while the I-V device characteristics do not change.

Input-output relationship in galvanotactic response of Dictyostelium cells.

PubMed

Sato, Masayuki J; Ueda, Michihito; Takagi, Hiroaki; Watanabe, Tomonobu M; Yanagida, Toshio; Ueda, Masahiro

2007-04-01

Under a direct current electric field, Dictyostelium cells exhibit migration towards the cathode. To determine the input-output relationship of the cell's galvanotactic response, we developed an experimental instrument in which electric signals applied to the cells are highly reproducible and the motile response are analyzed quantitatively. With no electric field, the cells moved randomly in all directions. Upon applying an electric field, cell migration speeds became about 1.3 times faster than those in the absence of an electric field. Such kinetic effects of electric fields on the migration were observed for cells stimulated between 0.25 and 10 V/cm of the field strength. The directions of cell migrations were biased toward the cathode in a positive manner with field strength, showing galvanotactic response in a dose-dependent manner. Quantitative analysis of the relationship between field strengths and directional movements revealed that the biased movements of the cells depend on the square of electric field strength, which can be described by one simple phenomenological equation. The threshold strength for the galvanotaxis was between 0.25 and 1 V/cm. Galvanotactic efficiency reached to half-maximum at 2.6 V/cm, which corresponds to an approximate 8 mV voltage difference between the cathode and anode direction of 10 microm wide, round cells. Based on these results, possible mechanisms of galvanotaxis in Dictyostelium cells were discussed. This development of experimental system, together with its good microscopic accessibility for intracellular signaling molecules, makes Dictyostelium cells attractive as a model organism for elucidating stochastic processes in the signaling systems responsible for cell motility and its regulations.

Electrohydrodynamics of drops in strong uniform dc electric fields

NASA Astrophysics Data System (ADS)

Salipante, Paul F.; Vlahovska, Petia M.

2010-11-01

Drop deformation in an uniform dc electric field is a classic problem. The pioneering work of Taylor demonstrated that for weakly conducting media, the drop fluid undergoes a toroidal flow and the drop adopts a prolate or oblate spheroidal shape, the flow and shape being axisymmetrically aligned with the applied field. However, recent studies have revealed a nonaxisymmetric rotational flow in strong fields, similar to the rotation of solid dielectric particles observed by Quincke in the 19th century. We present a systematic experimental study of this phenomenon, which highlights the importance of charge convection along the drop surface. The critical electric field, drop inclination angle, and rate of rotation are measured. We find that for small, high viscosity drops, the threshold field strength is well approximated by the Quincke rotation criterion. Reducing the viscosity ratio shifts the onset for rotation to stronger fields. The drop inclination angle increases with field strength. The rotation rate is approximately given by the inverse Maxwell-Wagner polarization time. Novel features are also observed such as a hysteresis in the tilt angle for large low-viscosity drops.

Dynamic characteristics of electric discharge in liquid under ultrasonic cavitation

NASA Astrophysics Data System (ADS)

Bulychev, N. A.; Kazaryan, M. A.; Averyushkin, A. S.; Kirichenko, M. N.; Zakharyan, Robert; Chernov, A. A.

2018-04-01

The characteristics of electrical discharges in liquid media under the influence of intense ultrasonic vibrations are investigated and the difference in dynamic characteristics of discharges before cavitation and after cavitation begins. The experiments carried out during this work made it possible to establish that in a liquid in an intense ultrasonic field above the cavitation threshold there exists a special form of an electric discharge characterized by volumetric luminescence in the entire space between the electrodes and the current-voltage characteristic inherent in an anomalous glow discharge in a gas.

Optimal delineation of single C-tactile and C-nociceptive afferents in humans by latency slowing.

PubMed

Watkins, Roger H; Wessberg, Johan; Backlund Wasling, Helena; Dunham, James P; Olausson, Håkan; Johnson, Richard D; Ackerley, Rochelle

2017-04-01

C-mechanoreceptors in humans comprise a population of unmyelinated afferents exhibiting a wide range of mechanical sensitivities. C-mechanoreceptors are putatively divided into those signaling gentle touch (C-tactile afferents, CTs) and nociception (C-mechanosensitive nociceptors, CMs), giving rise to positive and negative affect, respectively. We sought to distinguish, compare, and contrast the properties of a population of human C-mechanoreceptors to see how fundamental the divisions between these putative subpopulations are. We used microneurography to record from individual afferents in humans and applied electrical and mechanical stimulation to their receptive fields. We show that C-mechanoreceptors can be distinguished unequivocally into two putative populations, comprising CTs and CMs, by electrically evoked spike latency changes (slowing). After both natural mechanical stimulation and repetitive electrical stimulation there was markedly less latency slowing in CTs compared with CMs. Electrical receptive field stimulation, which bypasses the receptor end organ, was most effective in classifying C-mechanoreceptors, as responses to mechanical receptive field stimulation overlapped somewhat, which may lead to misclassification. Furthermore, we report a subclass of low-threshold CM responding to gentle mechanical stimulation and a potential subclass of CT afferent displaying burst firing. We show that substantial differences exist in the mechanisms governing axonal conduction between CTs and CMs. We provide clear electrophysiological "signatures" (extent of latency slowing) that can be used in unequivocally identifying populations of C-mechanoreceptors in single-unit and multiunit microneurography studies and in translational animal research into affective touch. Additionally, these differential mechanisms may be pharmacologically targetable for separate modulation of positive and negative affective touch information. NEW & NOTEWORTHY Human skin encodes a plethora of touch interactions, and affective tactile information is primarily signaled by slowly conducting C-mechanoreceptive afferents. We show that electrical stimulation of low-threshold C-tactile afferents produces markedly different patterns of activity compared with high-threshold C-mechanoreceptive nociceptors, although the populations overlap in their responses to mechanical stimulation. This fundamental distinction demonstrates a divergence in affective touch signaling from the first stage of sensory processing, having implications for the processing of interpersonal touch. Copyright © 2017 the American Physiological Society.

Effects of 60-Heartz electric and magnetic fields on implanted cardiac pacemakers. Final report. [Hazards of power transmission line frequencies

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

Bridges, J.E.; Frazier, M.J.

1979-09-01

The effects of 60-Hz electric and magnetic fields of exta-high voltage (EHV) transmission lines on the performance of implanted cardiac pacemakers were studied by: (1) in vitro bench tests of a total of thirteen cardiac pacemakers; (2) in vivo tests of six implanted cardiac pacemakers in baboons; and (3) non-hazardous skin measurement tests on four humans. Analytical methods were developed to predict the thresholds of body current and electric fields capable of affecting normal pacemaker operation in humans. The field strengths calculated to alter implanted pacemaker performance were compared with the range of maximum electric and magnetic field strengths amore » human would normally encounter under transmission lines of various voltages. Results indicate that the electric field or body current necessary to alter the normal operation of pacemakers is highly dependent on the type of pacemaker and the location of the implanted electrodes. However, cardiologists have not so far detected harmful effects of pacemaker reversion to the asynchronous mode in current types of pacemakers and with present methods of implantation. Such interferences can be eliminated by using advanced pacemakers less sensitive to 60-Hz voltages or by using implantation lead arrangements less sensitive to body current.« less

Assembling Ordered Nanorod Superstructures and Their Application as Microcavity Lasers

NASA Astrophysics Data System (ADS)

Liu, Pai; Singh, Shalini; Guo, Yina; Wang, Jian-Jun; Xu, Hongxing; Silien, Christophe; Liu, Ning; Ryan, Kevin M.

2017-03-01

Herein we report the formation of multi-layered arrays of vertically aligned and close packed semiconductor nanorods in perfect registry at a substrate using electric field assisted assembly. The collective properties of these CdSexS1-x nanorod emitters are harnessed by demonstrating a relatively low amplified spontaneous emission (ASE) threshold and a high net optical gain at medium pump intensity. The importance of order in the system is highlighted where a lower ASE threshold is observed compared to disordered samples.

A physical mechanism for the onset of radial electric fields in magnetically confined plasmas

NASA Astrophysics Data System (ADS)

Moleti, A.

1996-04-01

A simple physical mechanism is described, which could trigger the Low-mode to High-mode (L-H) transition. The instantaneous ion density profile is significantly modified by a sudden temperature increase, because Larmor radii and banana orbit widths are proportional to thermal velocity. The electric fields that are observed in H-mode plasmas could be produced in the radial region where a large second derivative of the density profile exists, either by strong additional heating or by the heat pulse associated to a sawtooth crash. The L-H transition threshold for the time derivative of the ion temperature is of the order of magnitude of the values that are measured in the outer part of the plasma by electron temperature fast diagnostics at sawtooth crashes. This model agrees with the experimental evidence that L-H transitions are often triggered by a sawtooth crash, and the predicted dependence of the threshold on plasma parameters is fairly consistent with available data.

The effects of electric field and gate bias pulse on the migration and stability of ionized oxygen vacancies in amorphous In–Ga–Zn–O thin film transistors

PubMed Central

Oh, Young Jun; Noh, Hyeon-Kyun; Chang, Kee Joo

2015-01-01

Oxygen vacancies have been considered as the origin of threshold voltage instability under negative bias illumination stress in amorphous oxide thin film transistors. Here we report the results of first-principles molecular dynamics simulations for the drift motion of oxygen vacancies. We show that oxygen vacancies, which are initially ionized by trapping photoexcited hole carriers, can easily migrate under an external electric field. Thus, accumulated hole traps near the channel/dielectric interface cause negative shift of the threshold voltage, supporting the oxygen vacancy model. In addition, we find that ionized oxygen vacancies easily recover their neutral defect configurations by capturing electrons when the Fermi level increases. Our results are in good agreement with the experimental observation that applying a positive gate bias pulse of short duration eliminates hole traps and thus leads to the recovery of device stability from persistent photoconductivity. PMID:27877799

Observation of the thunderstorm-related ground cosmic ray flux variations by ARGO-YBJ

NASA Astrophysics Data System (ADS)

Bartoli, B.; Bernardini, P.; Bi, X. J.; Cao, Z.; Catalanotti, S.; Chen, S. Z.; Chen, T. L.; Cui, S. W.; Dai, B. Z.; D'Amone, A.; Danzengluobu; De Mitri, I.; D'Ettorre Piazzoli, B.; Di Girolamo, T.; Di Sciascio, G.; Feng, C. F.; Feng, Zhaoyang; Feng, Zhenyong; Gao, W.; Gou, Q. B.; Guo, Y. Q.; He, H. H.; Hu, Haibing; Hu, Hongbo; Iacovacci, M.; Iuppa, R.; Jia, H. Y.; Labaciren; Li, H. J.; Liu, C.; Liu, J.; Liu, M. Y.; Lu, H.; Ma, L. L.; Ma, X. H.; Mancarella, G.; Mari, S. M.; Marsella, G.; Mastroianni, S.; Montini, P.; Ning, C. C.; Perrone, L.; Pistilli, P.; Salvini, P.; Santonico, R.; Shen, P. R.; Sheng, X. D.; Shi, F.; Surdo, A.; Tan, Y. H.; Vallania, P.; Vernetto, S.; Vigorito, C.; Wang, H.; Wu, C. Y.; Wu, H. R.; Xue, L.; Yang, Q. Y.; Yang, X. C.; Yao, Z. G.; Yuan, A. F.; Zha, M.; Zhang, H. M.; Zhang, L.; Zhang, X. Y.; Zhang, Y.; Zhao, J.; Zhaxiciren; Zhaxisangzhu; Zhou, X. X.; Zhu, F. R.; Zhu, Q. Q.; D'Alessandro, F.; ARGO-YBJ Collaboration

2018-02-01

A correlation between the secondary cosmic ray flux and the near-earth electric field intensity, measured during thunderstorms, has been found by analyzing the data of the ARGO-YBJ experiment, a full coverage air shower array located at the Yangbajing Cosmic Ray Laboratory (4300 m a. s. l., Tibet, China). The counting rates of showers with different particle multiplicities (m =1 , 2, 3, and ≥4 ) have been found to be strongly dependent upon the intensity and polarity of the electric field measured during the course of 15 thunderstorms. In negative electric fields (i.e., accelerating negative charges downwards), the counting rates increase with increasing electric field strength. In positive fields, the rates decrease with field intensity until a certain value of the field EFmin (whose value depends on the event multiplicity), above which the rates begin increasing. By using Monte Carlo simulations, we found that this peculiar behavior can be well described by the presence of an electric field in a layer of thickness of a few hundred meters in the atmosphere above the detector, which accelerates/decelerates the secondary shower particles of opposite charge, modifying the number of particles with energy exceeding the detector threshold. These results, for the first time to our knowledge, give a consistent explanation for the origin of the variation of the electron/positron flux observed for decades by high altitude cosmic ray detectors during thunderstorms.

L to H mode transition: Parametric dependencies of the temperature threshold

DOE PAGES

Bourdelle, C.; Chone, L.; Fedorczak, N.; ...

2015-06-15

The L to H mode transition occurs at a critical power which depends on various parameters, such as the magnetic field, the density, etc. Experimental evidence on various tokamaks (JET, ASDEX-Upgrade, DIII-D, Alcator C-Mod) points towards the existence of a critical temperature characterizing the transition. This criterion for the L-H transition is local and is therefore easier to be compared to theoretical approaches. In order to shed light on the mechanisms of the transition, simple theoretical ideas are used to derive a temperature threshold (T th). They are based on the stabilization of the underlying turbulence by a mean radialmore » electric field shear. The nature of the turbulence varies as the collisionality decreases, from resistive ballooning modes to ion temperature gradient and trapped electron modes. The obtained parametric dependencies of the derived T th are tested versus magnetic field, density, effective charge. Furthermore, various robust experimental observations are reproduced, in particular T th increases with magnetic field B and increases with density below the density roll-over observed on the power threshold.« less

Pulsating Magnetic Reconnection Driven by Three-Dimensional Flux-Rope Interactions.

PubMed

Gekelman, W; De Haas, T; Daughton, W; Van Compernolle, B; Intrator, T; Vincena, S

2016-06-10

The dynamics of magnetic reconnection is investigated in a laboratory experiment consisting of two magnetic flux ropes, with currents slightly above the threshold for the kink instability. The evolution features periodic bursts of magnetic reconnection. To diagnose this complex evolution, volumetric three-dimensional data were acquired for both the magnetic and electric fields, allowing key field-line mapping quantities to be directly evaluated for the first time with experimental data. The ropes interact by rotating about each other and periodically bouncing at the kink frequency. During each reconnection event, the formation of a quasiseparatrix layer (QSL) is observed in the magnetic field between the flux ropes. Furthermore, a clear correlation is demonstrated between the quasiseparatrix layer and enhanced values of the quasipotential computed by integrating the parallel electric field along magnetic field lines. These results provide clear evidence that field lines passing through the quasiseparatrix layer are undergoing reconnection and give a direct measure of the nonlinear reconnection rate. The measurements suggest that the parallel electric field within the QSL is supported predominantly by electron pressure; however, resistivity may play a role.

Continuum percolation of polydisperse rods in quadrupole fields: Theory and simulations.

PubMed

Finner, Shari P; Kotsev, Mihail I; Miller, Mark A; van der Schoot, Paul

2018-01-21

We investigate percolation in mixtures of nanorods in the presence of external fields that align or disalign the particles with the field axis. Such conditions are found in the formulation and processing of nanocomposites, where the field may be electric, magnetic, or due to elongational flow. Our focus is on the effect of length polydispersity, which-in the absence of a field-is known to produce a percolation threshold that scales with the inverse weight average of the particle length. Using a model of non-interacting spherocylinders in conjunction with connectedness percolation theory, we show that a quadrupolar field always increases the percolation threshold and that the universal scaling with the inverse weight average no longer holds if the field couples to the particle length. Instead, the percolation threshold becomes a function of higher moments of the length distribution, where the order of the relevant moments crucially depends on the strength and type of field applied. The theoretical predictions compare well with the results of our Monte Carlo simulations, which eliminate finite size effects by exploiting the fact that the universal scaling of the wrapping probability function holds even in anisotropic systems. Theory and simulation demonstrate that the percolation threshold of a polydisperse mixture can be lower than that of the individual components, confirming recent work based on a mapping onto a Bethe lattice as well as earlier computer simulations involving dipole fields. Our work shows how the formulation of nanocomposites may be used to compensate for the adverse effects of aligning fields that are inevitable under practical manufacturing conditions.

Determination of the electric field strength of filamentary DBDs by CARS-based four-wave mixing

NASA Astrophysics Data System (ADS)

Böhm, P.; Kettlitz, M.; Brandenburg, R.; Höft, H.; Czarnetzki, U.

2016-10-01

It is demonstrated that a four-wave mixing technique based on coherent anti-Stokes Raman spectroscopy (CARS) can determine the electric field strength of a pulsed-driven filamentary dielectric barrier discharge (DBD) of 1 mm gap, using hydrogen as a tracer medium in nitrogen at atmospheric pressure. The measurements are presented for a hydrogen admixture of 10%, but even 5% H2 admixture delivers sufficient infrared signals. The lasers do not affect the discharge by photoionization or by other radiation-induced processes. The absolute values of the electric field strength can be determined by the calibration of the CARS setup with high voltage amplitudes below the ignition threshold of the arrangement. This procedure also enables the determination of the applied breakdown voltage. The alteration of the electric field is observed during the internal polarity reversal and the breakdown process. One advantage of the CARS technique over emission-based methods is that it can be used independently of emission, e.g. in the pre-phase and in between two consecutive discharges, where no emission occurs at all.

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.

Model predictions for atmospheric air breakdown by radio-frequency excitation in large gaps

NASA Astrophysics Data System (ADS)

Nguyen, H. K.; Mankowski, J.; Dickens, J. C.; Neuber, A. A.; Joshi, R. P.

2017-07-01

The behavior of the breakdown electric field versus frequency (DC to 100 MHz) for different gap lengths has been studied numerically at atmospheric pressure. Unlike previous reports, the focus here is on much larger gap lengths in the 1-5 cm range. A numerical analysis, with transport coefficients obtained from Monte Carlo calculations, is used to ascertain the electric field thresholds at which the growth and extinction of the electron population over time are balanced. Our analysis is indicative of a U-shaped frequency dependence, lower breakdown fields with increasing gap lengths, and trends qualitatively similar to the frequency-dependent field behavior for microgaps. The low frequency value of ˜34 kV/cm for a 1 cm gap approaches the reported DC Paschen limit.

Effect of A-site La and Ba doping on threshold field and characteristic temperatures of PbSc0.5Ta0.5O3 relaxor studied by acoustic emission

NASA Astrophysics Data System (ADS)

Dul'kin, E.; Mihailova, B.; Gospodinov, M.; Roth, M.

2012-09-01

The structural transitions in Pb1-xLaxSc(1+x)/2Ta(1-x)/2O3, x = 0.08 (PLST) relaxor crystals were studied by means of acoustic emission (AE) under an external electric field (E) and compared with those observed in pure PbSc0.5Ta0.5O3 (PST) and Pb0.78Ba0.22Sc0.5Ta0.5O3 (PBST) [E. Dul'kin et al., EPL 94, 57002 (2011)]. Similar to both the PST and PBST compounds, in zero field PLST exhibits AE corresponding to a para-to-antiferroelectric incommensurate phase transition at Tn = 276 K, lying in the vicinity of dielectric temperature maximum (Tm). This AE signal exhibits a nontrivial behavior when applying E resembling the electric-field-dependence of Tn previously observed for both the PST and PBST, namely, Tn initially decreases with the increase of E, attains a minimum at a threshold field Eth = 0.5 kV/cm, accompanied by a pronounced maximum of the AE count rate Ṅ = 12 s-1, and then starts increasing as E enhances. The similarities and difference between PST, PLST, and PBST with respect to Tn, Eth, and Ṅ are discussed from the viewpoint of three mechanisms: (i) chemically induced random local electric field due to the extra charge on the A-site ion, (ii) disturbance of the system of stereochemically active lone-pair electrons of Pb2+ by the isotropic outermost electron shell of substituting ion, and (iii) change in the tolerance factor and elastic field to the larger ionic radius of the substituting A-site ion due to the different radius of the substituting ion. The first two mechanisms influence the actual values of Tn and Eth, whereas the latter is shown to affect the normalized Ṅ, indicating the fractions undergoing a field-induced crossover from a modulated antiferroelectric to a ferroelectric state. Creation of secondary random electric field, caused by doping-induced A-site-O ionic chemical bonding, is discussed.

Continuum percolation of polydisperse rods in quadrupole fields: Theory and simulations

NASA Astrophysics Data System (ADS)

Finner, Shari P.; Kotsev, Mihail I.; Miller, Mark A.; van der Schoot, Paul

2018-01-01

We investigate percolation in mixtures of nanorods in the presence of external fields that align or disalign the particles with the field axis. Such conditions are found in the formulation and processing of nanocomposites, where the field may be electric, magnetic, or due to elongational flow. Our focus is on the effect of length polydispersity, which—in the absence of a field—is known to produce a percolation threshold that scales with the inverse weight average of the particle length. Using a model of non-interacting spherocylinders in conjunction with connectedness percolation theory, we show that a quadrupolar field always increases the percolation threshold and that the universal scaling with the inverse weight average no longer holds if the field couples to the particle length. Instead, the percolation threshold becomes a function of higher moments of the length distribution, where the order of the relevant moments crucially depends on the strength and type of field applied. The theoretical predictions compare well with the results of our Monte Carlo simulations, which eliminate finite size effects by exploiting the fact that the universal scaling of the wrapping probability function holds even in anisotropic systems. Theory and simulation demonstrate that the percolation threshold of a polydisperse mixture can be lower than that of the individual components, confirming recent work based on a mapping onto a Bethe lattice as well as earlier computer simulations involving dipole fields. Our work shows how the formulation of nanocomposites may be used to compensate for the adverse effects of aligning fields that are inevitable under practical manufacturing conditions.

Microplasma illumination enhancement of vertically aligned conducting ultrananocrystalline diamond nanorods

PubMed Central

2012-01-01

Vertically aligned conducting ultrananocrystalline diamond (UNCD) nanorods are fabricated using the reactive ion etching method incorporated with nanodiamond particles as mask. High electrical conductivity of 275 Ω·cm−1 is obtained for UNCD nanorods. The microplasma cavities using UNCD nanorods as cathode show enhanced plasma illumination characteristics of low threshold field of 0.21 V/μm with plasma current density of 7.06 mA/cm2 at an applied field of 0.35 V/μm. Such superior electrical properties of UNCD nanorods with high aspect ratio potentially make a significant impact on the diamond-based microplasma display technology. PMID:23009733

Microfluidic Screening of Electric Fields for Electroporation

PubMed Central

Garcia, Paulo A.; Ge, Zhifei; Moran, Jeffrey L.; Buie, Cullen R.

2016-01-01

Electroporation is commonly used to deliver molecules such as drugs, proteins, and/or DNA into cells, but the mechanism remains poorly understood. In this work a rapid microfluidic assay was developed to determine the critical electric field threshold required for inducing bacterial electroporation. The microfluidic device was designed to have a bilaterally converging channel to amplify the electric field to magnitudes sufficient to induce electroporation. The bacterial cells are introduced into the channel in the presence of SYTOX®, which fluorescently labels cells with compromised membranes. Upon delivery of an electric pulse, the cells fluoresce due to transmembrane influx of SYTOX® after disruption of the cell membranes. We calculate the critical electric field by capturing the location within the channel of the increase in fluorescence intensity after electroporation. Bacterial strains with industrial and therapeutic relevance such as Escherichia coli BL21 (3.65 ± 0.09 kV/cm), Corynebacterium glutamicum (5.20 ± 0.20 kV/cm), and Mycobacterium smegmatis (5.56 ± 0.08 kV/cm) have been successfully characterized. Determining the critical electric field for electroporation facilitates the development of electroporation protocols that minimize Joule heating and maximize cell viability. This assay will ultimately enable the genetic transformation of bacteria and archaea considered intractable and difficult-to-transfect, while facilitating fundamental genetic studies on numerous diverse microbes. PMID:26893024

Design and simulation of a novel E-mode GaN MIS-HEMT based on a cascode connection for suppression of electric field under gate and improvement of reliability

NASA Astrophysics Data System (ADS)

Li, Weiyi; Zhang, Zhili; Fu, Kai; Yu, Guohao; Zhang, Xiaodong; Sun, Shichuang; Song, Liang; Hao, Ronghui; Fan, Yaming; Cai, Yong; Zhang, Baoshun

2017-07-01

We proposed a novel AlGaN/GaN enhancement-mode (E-mode) high electron mobility transistor (HEMT) with a dual-gate structure and carried out the detailed numerical simulation of device operation using Silvaco Atlas. The dual-gate device is based on a cascode connection of an E-mode and a D-mode gate. The simulation results show that electric field under the gate is decreased by more than 70% compared to that of the conventional E-mode MIS-HEMTs (from 2.83 MV/cm decreased to 0.83 MV/cm). Thus, with the discussion of ionized trap density, the proposed dual-gate structure can highly improve electric field-related reliability, such as, threshold voltage stability. In addition, compared with HEMT with field plate structure, the proposed structure exhibits a simplified fabrication process and a more effective suppression of high electric field. Project supported by the Key Technologies Support Program of Jiangsu Province (No. BE2013002-2) and the National Key Scientific Instrument and Equipment Development Projects of China (No. 2013YQ470767).

Spatiotemporal Evolution of Runaway Electron Momentum Distributions in Tokamaks

DOE PAGES

Paz-Soldan, Carlos; Cooper, Christopher M.; Aleynikov, Pavel; ...

2017-06-22

Novel spatial, temporal, and energetically resolved measurements of bremsstrahlung hard-x-ray (HXR) emission from runaway electron (RE) populations in tokamaks reveal nonmonotonic RE distribution functions whose properties depend on the interplay of electric field acceleration with collisional and synchrotron damping. Measurements are consistent with theoretical predictions of momentum-space attractors that accumulate runaway electrons. RE distribution functions are measured to shift to a higher energy when the synchrotron force is reduced by decreasing the toroidal magnetic field strength. Increasing the collisional damping by increasing the electron density (at a fixed magnetic and electric field) reduces the energy of the nonmonotonic feature andmore » reduces the HXR growth rate at all energies. Higher-energy HXR growth rates extrapolate to zero at the expected threshold electric field for RE sustainment, while low-energy REs are anomalously lost. The compilation ofHXR emission from different sight lines into the plasma yields energy and pitch-angle-resolved RE distributions and demonstrates increasing pitch-angle and radial gradients with energy.« less

Effects of Various Passivation Layers on Electrical Properties of Multilayer MoS₂ Transistors.

PubMed

Ma, Jiyeon; Yoo, Geonwook

2018-09-01

So far many of research on transition metal dichalcogenides (TMDCs) are based on a bottomgate device structure due to difficulty with depositing a dielectric film on top of TMDs channel layer. In this work, we study different effects of various passivation layers on electrical properties of multilayer MoS2 transistors: spin-coated CYTOP, SU-8, and thermal evaporated MoOX. The SU-8 passivation layer alters device performance least significantly, and MoOX induces positive threshold voltage shift of ~8.0 V due to charge depletion at the interface, and the device with CYTOP layer exhibits decreased field-effect mobility by ~50% due to electric dipole field effect of C-F bonds in the end groups. Our results imply that electrical properties of the multilayer MoS2 transistors can be modulated using a passivation layer, and therefore a proper passivation layer should be considered for MoS2 device structures.

Effects of Small Electrostatic Fields on the Ionospheric Density Profile

NASA Astrophysics Data System (ADS)

Salem, M. A.; Liu, N.; Rassoul, H.

2014-12-01

It is well known that short-lived strong electric fields produced by natural lightning activities in tropospheric altitudes can significantly affect the upper atmosphere. This effect is directly evidenced by the production of transient luminous events (TLEs), such as sprites, jets, and elves. It has also been demonstrated that thunderstorms can modify ionospheric densities on a longer time scale, during which TLEs may or may not occur [e.g., Cheng and Cummer, GRL, 32, L08804, 2005; Han and Cummer, JGR, 115, A09323, 2010; Shao et al., Nat. Geosci., doi: 10.1038/NGEO1668, 2012]. In particular, according to Shao et al. [2012], the electron density at 75-80 km altitudes may be reduced by about 2-3 orders of magnitude. In this talk, we study the modification of the ionospheric density profile by small electrostatic fields that may exist in the upper atmosphere during a thunderstorm. A simplified ion chemistry model described by Liu [JGR, 117, A03308, 2012] has been used to conduct this study. The model is based on the one developed by Lehtinen and Inan [GRL, 34, L08804, 2007], which is in turn an improved version of the GPI model discussed in Glukhov et al. [JGR, 97, 16971, 1992]. According to this model, the charged particles can be grouped into five species: electrons, light negative ions, cluster negative ions, light positive ions, and cluster positive ions. In this chemistry model, the three-body electron attachment is the only process whose rate constant depends on the electric field, when it is below about one third of the conventional breakdown threshold field. We have compared various sources of the three-body attachment rate constant. The result shows that the rate constant increases linearly with the reduced electric field in the range of 0 to 0.1 Td, while decreases exponentially from 0.1 Td to about one third of the conventional breakdown threshold field. With this dependence, our modeling results indicate that under the steady-state condition, the nighttime electron density profile can be reduced by about 40% or enhanced by a factor of about 6 when the electric field varies in the aforementioned range.

Electric field mediated breakdown of thin liquid films separating microscopic emulsion droplets

NASA Astrophysics Data System (ADS)

Mostowfi, Farshid; Khristov, Khristo; Czarnecki, Jan; Masliyah, Jacob; Bhattacharjee, Subir

2007-04-01

The authors present a microfluidic technique for electrically induced breakup of thin films formed between microscopic emulsion droplets. The method involves creating a stationary film at the intersection of two microchannels etched onto a glass substrate. After stabilizing the film, a ramped potential is applied across it. The electrical stresses developed at the film interfaces lead to its rupture above a threshold potential. The potential difference at which the film ruptures assesses the film stability. This approach is employed to demonstrate how surfactant (lecithin) adsorption imparts stability to an ultrathin oil film formed between two water droplets.

Electrically Guided Assembly of Colloidal Particles

NASA Astrophysics Data System (ADS)

Ristenpart, W. D.; Aksay, I. A.; Saville, D. A.

2002-11-01

In earlier work it was shown that the strength and frequency of an applied electric field alters the dynamic arrangement of particles on an electrode. Two-dimensional 'gas,' 'liquid' and 'solid' arrangements were formed, depending on the field strength and frequency. Since the particles are similarly charged, yet migrate over large distances under the influence of steady or oscillatory fields, it is clear that both hydrodynamic and electrical processes are involved. Here we report on an extensive study of electrically induced ordering in a parallel electrode cell. First, we discuss the kinetics of aggregation in a DC field as measured using video microscopy and digital image analysis. Rate constants were determined as a function of applied electric field strength and particle zeta potential. The kinetic parameters are compared to models based on electrohydrodynamic and electroosmotic fluid flow mechanisms Second, using monodisperse micron-sized particles, we examined the average interparticle spacing over a wide range of applied frequencies and field strengths. Variation of these parameters allows formation of closely-spaced arrangements and ordered arrays of widely separated particles. We find that there is a strong dependence on frequency, but there is surprisingly little influence of the electric field strength past a small threshold. Last, we present experiments with binary suspensions of similarly sized particles with negative but unequal surface potentials. A long-range lateral attraction is observed in an AC field. Depending on the frequency, this attractive interaction results in a diverse set of aggregate morphologies, including superstructured hexagonal lattices. These results are discussed in terms of induced dipole-dipole interactions and electrohydrodynamic flow. Finally, we explore the implications for practical applications.

Electrostatic Levitation of Lunar Dust: Preliminary Experimental Observations

NASA Astrophysics Data System (ADS)

Marshall, J.; Davis, S.; Laub, J.

2007-12-01

A lunar dust laboratory has been established in the Space Science Division at NASA Ames to evaluate fundamental electrostatic processes at the Moon's surface. Photoelectric charging, triboelectric charging, and interactions of these processes are investigated for dust-size materials. An electric field simulating the solar- plasma induced E-field of the lunar surface has been created with parallel charged capacitance plates. The field is linear, but field-shaping to create lunar-like exponentially decaying E-fields will be conducted in the near future. Preliminary tests of dust tribocharging have been conducted using a vibrating base plate within the electric field and have produced electrostatic levitation of 1.6 micron diameter silicate particles. We were able to achieve levitation in a modest vacuum environment (1.7 Torr) with the particles charged to approximately 15 percent of the Gaussian limit (defined as 2.64 E-5 C/m-2 for atmospheric air) at a threshold field strength of 2250 V/m. This charging corresponds to only a few hundred (negative) charges per particle; the field strength drops to 375 V/m when gravitationally scaled for the Moon, while dust tribocharging to greater than 100 percent of the Gaussian limit would be possible in the ultra high vacuum environment on the Moon and result in even lower threshold field strengths. We conclude therefore, that anthropogenic disturbance of lunar dust (as a result of NASA's proposed base construction, mining, vehicle motion, etc) could potentially pollute the lunar environment with levitated dust and severely impair scientific experiments requiring a pristine lunar exosphere.

Dynamical properties of epitaxial ferroelectric superlattices

NASA Astrophysics Data System (ADS)

Kim, Y.; Gerhardt, R. A.; Erbil, A.

1997-04-01

The dynamical properties of epitaxial ferroelectric heterostructures have been investigated by studying the dielectric behavior under external electric field. A phenomenon with a giant permittivity was observed. At low frequencies, real permittivities as high as 420 000 have been measured. Real and imaginary parts of the dielectric constant show large dispersion at high frequencies. In dc measurements, a nonlinear resistance is observed with a well-defined threshold field, correlating with the dc bias-field dependence of ac permittivities. We model these observations as a result of the motion of pinned domain-wall lattices, having sliding-mode motion at high electric fields. The good agreement between the experimental and theoretical results suggests that the deposited interdigitated electrode pattern plays a crucial role in controlling domain-wall dynamics. The pinning of the domain wall comes from a nucleation barrier to the creation of new domain walls.

Electromagnetic Field Modeling of Transcranial Electric and Magnetic Stimulation: Targeting, Individualization, and Safety of Convulsive and Subconvulsive Applications

NASA Astrophysics Data System (ADS)

Deng, Zhi-De

The proliferation of noninvasive transcranial electric and magnetic brain stimulation techniques and applications in recent years has led to important insights into brain function and pathophysiology of brain-based disorders. Transcranial electric and magnetic stimulation encompasses a wide spectrum of methods that have developed into therapeutic interventions for a variety of neurological and psychiatric disorders. Although these methods are at different stages of development, the physical principle underlying these techniques is the similar. Namely, an electromagnetic field is induced in the brain either via current injection through scalp electrodes or via electromagnetic induction. The induced electric field modulates the neuronal transmembrane potentials and, thereby, neuronal excitability or activity. Therefore, knowledge of the induced electric field distribution is key in the design and interpretation of basic research and clinical studies. This work aims to delineate the fundamental physical limitations, tradeoffs, and technological feasibility constraints associated with transcranial electric and magnetic stimulation, in order to inform the development of technologies that deliver safer, and more spatially, temporally, and patient specific stimulation. Part I of this dissertation expounds on the issue of spatial targeting of the electric field. Contrasting electroconvulsive therapy (ECT) and magnetic seizure therapy (MST) configurations that differ markedly in efficacy, side effects, and seizure induction efficiency could advance our understanding of the principles linking treatment parameters and therapeutic outcome and could provide a means of testing hypotheses of the mechanisms of therapeutic action. Using the finite element method, we systematically compare the electric field characteristics of existing forms of ECT and MST. We introduce a method of incorporating a modality-specific neural activation threshold in the electric field models that can inform dosage requirements in convulsive therapies. Our results indicate that the MST electric field is more focal and more confined to the superficial cortex compared to ECT. Further, the conventional ECT current amplitude is much higher than necessary for seizure induction. One of the factors important to clinical outcome is seizure expression. However, it is unknown how the induced electric field is related to seizure onset and propagation. In this work, we explore the effect of the electric field distribution on the quantitative ictal electroencephalography and current source density in ECT and MST. We further demonstrate how the ECT electrode shape, size, spacing, and current can be manipulated to yield more precise control of the induced electric field. If desirable, ECT can be made as focal as MST while using simpler stimulation equipment. Next, we demonstrate how the electric field induced by transcranial magnetic stimulation (TMS) can be controlled. We present the most comprehensive comparison of TMS coil electric field penetration and focality to date. The electric field distributions of more than 50 TMS coils were simulated. We show that TMS coils differ markedly in their electric field characteristics, but they all are subject to a consistent depth-focality tradeoff. Specifically, the ability to directly stimulate deeper brain structures is obtained at the expense of inducing wider electric field spread. Figure-8 type coils are fundamentally more focal compared to circular type coils. Understanding the depth-focality tradeoff can help researchers and clinicians to appropriately select coils and interpret TMS studies. This work also enables the development of novel TMS coils with electronically switchable active and sham modes as well as for deep TMS. Design considerations of these coils are extensively discussed. Part II of the dissertation aims to quantify the effect of individual, sex, and age differences in head geometry and conductivity on the induced neural stimulation strength and focality of ECT and MST. Across and within ECT studies, there is marked unexplained variability in seizure threshold and clinical outcomes. It is not known to what extent the age and sex effects on seizure threshold are mediated by interindividual variation in neural excitability and/or anatomy of the head. Addressing this question, we examine the effect on ECT and MST induced field characteristics of the variability in head diameter, scalp and skull thicknesses and conductivities, as well as brain volume, in a range of values that are representative of the patient population. Variations in the local tissue properties such as scalp and skull thickness and conductivity affect the existing ECT configurations more than MST. On the other hand, the existing MST coil configurations show greater sensitivity to head diameter variation compared to ECT. Due to the high focality of MST compared to ECT, the stimulated brain volume in MST is more sensitive to variation in tissue layer thicknesses. We further demonstrate how individualization of the stimulus pulse current amplitude, which is not presently done in ECT or MST, can be used as a means of compensating for interindividual anatomical variability, which could lead to better and more consistent clinical outcomes. Part III of the dissertation aims to systemically investigate, both computationally and experimentally, the safety of TMS and ECT in patients with a deep-brain stimulation system, and propose safety guidelines for the dual-device therapy. We showed that the induction of significant voltages in the subcutaneous leads in the scalp during TMS could result in unintended and potentially dangerous levels of electrical currents in the DBS electrode contacts. When applying ECT in patients with intracranial implants, we showed that there is an increase in the electric field strength in the brain due to conduction through the burr holes, especially when the burr holes are not fitted with nonconductive caps. Safety concerns presently limit the access of patients with intracranial electronic devices to therapies involving transcranial stimulation technology, which may preclude them from obtaining appropriate medical treatments. Gaining better understanding of the interactions between transcranial and implanted stimulation devices will demarcate significant safety risks from benign interactions, and will provide recommendations for reducing risk, thus enhancing the patient's therapeutic options.

Water-processed carbon nanotube/graphene hybrids with enhanced field emission properties

NASA Astrophysics Data System (ADS)

Song, Meng; Xu, Peng; Song, Yenan; Wang, Xu; Li, Zhenhua; Shang, Xuefu; Wu, Huizhen; Zhao, Pei; Wang, Miao

2015-09-01

Integrating carbon nanotubes (CNTs) and graphene into hybrid structures provides a novel approach to three dimensional (3D) materials with advantageous properties. Here we present a water-processing method to create integrated CNT/graphene hybrids and test their field emission properties. With an optimized mass ratio of CNTs to graphene, the hybrid shows a significantly enhanced field emission performance, such as turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum current density of 0.1 mA/cm2, and field enhancement factor of ˜1.3 × 104. The optimized mass ratio for field emission emphasizes the importance of both CNTs and graphene in the hybrid. We also hypothesize a possible mechanism for this enhanced field emission performance from the CNT/graphene hybrid. During the solution treatment, graphene oxide behaves as surfactant sheets for CNTs to form a well dispersed solution, which leads to a better organized 3D structure with more conducting channels for electron transport.

Identifying cochlear implant channels with poor electrode-neuron interface: partial tripolar, single-channel thresholds and psychophysical tuning curves.

PubMed

Bierer, Julie Arenberg; Faulkner, Kathleen F

2010-04-01

The goal of this study was to evaluate the ability of a threshold measure, made with a restricted electrode configuration, to identify channels exhibiting relatively poor spatial selectivity. With a restricted electrode configuration, channel-to-channel variability in threshold may reflect variations in the interface between the electrodes and auditory neurons (i.e., nerve survival, electrode placement, and tissue impedance). These variations in the electrode-neuron interface should also be reflected in psychophysical tuning curve (PTC) measurements. Specifically, it is hypothesized that high single-channel thresholds obtained with the spatially focused partial tripolar (pTP) electrode configuration are predictive of wide or tip-shifted PTCs. Data were collected from five cochlear implant listeners implanted with the HiRes90k cochlear implant (Advanced Bionics Corp., Sylmar, CA). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the pTP configuration for which a fraction of current (sigma) from a center-active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. Forward-masked PTCs were obtained for channels with the highest, lowest, and median tripolar (sigma = 1 or 0.9) thresholds. The probe channel and level were fixed and presented with either the monopolar (sigma = 0) or a more focused pTP (sigma > or = 0.55) configuration. The masker channel and level were varied, whereas the configuration was fixed to sigma = 0.5. A standard, three-interval, two-alternative forced choice procedure was used for thresholds and masked levels. Single-channel threshold and variability in threshold across channels systematically increased as the compensating current, sigma, increased and the presumed electrical field became more focused. Across subjects, channels with the highest single-channel thresholds, when measured with a narrow, pTP stimulus, had significantly broader PTCs than the lowest threshold channels. In two subjects, the tips of the tuning curves were shifted away from the probe channel. Tuning curves were also wider for the monopolar probes than with pTP probes for both the highest and lowest threshold channels. These results suggest that single-channel thresholds measured with a restricted stimulus can be used to identify cochlear implant channels with poor spatial selectivity. Channels having wide or tip-shifted tuning characteristics would likely not deliver the appropriate spectral information to the intended auditory neurons, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception.

Transition from order to chaos, and density limit, in magnetized plasmas.

PubMed

Carati, A; Zuin, M; Maiocchi, A; Marino, M; Martines, E; Galgani, L

2012-09-01

It is known that a plasma in a magnetic field, conceived microscopically as a system of point charges, can exist in a magnetized state, and thus remain confined, inasmuch as it is in an ordered state of motion, with the charged particles performing gyrational motions transverse to the field. Here, we give an estimate of a threshold, beyond which transverse motions become chaotic, the electrons being unable to perform even one gyration, so that a breakdown should occur, with complete loss of confinement. The estimate is obtained by the methods of perturbation theory, taking as perturbing force acting on each electron that due to the so-called microfield, i.e., the electric field produced by all the other charges. We first obtain a general relation for the threshold, which involves the fluctuations of the microfield. Then, taking for such fluctuations, the formula given by Iglesias, Lebowitz, and MacGowan for the model of a one component plasma with neutralizing background, we obtain a definite formula for the threshold, which corresponds to a density limit increasing as the square of the imposed magnetic field. Such a theoretical density limit is found to fit pretty well the empirical data for collapses of fusion machines.

Evaluation of patient suitability for a retinal prosthesis using structural and functional tests of inner retinal integrity

NASA Astrophysics Data System (ADS)

Huang, Qiuhen; Chowdhury, Vivek; Coroneo, Minas Theodore

2009-06-01

The purpose of this study was to assess inner retinal structure and function in patients with retinitis pigmentosa (RP) using optical coherence tomography (OCT) imaging of the retina, and electrical stimulation of the retina with a contact lens electrode. OCT images of 17 RP patients were acquired at the macula and at four quadrants of the peripheral retina in both eyes. Analysis was made of the residual inner retinal thickness and nerve fibre layer thickness in RP patients, and this was compared to normal controls. Eight of these patients further underwent contact lens electrical stimulation of one eye and thresholds for phosphene perception were obtained. OCT imaging showed a significant amount of inner retinal preservation in the peripheral retina and the macula of RP patients despite severe visual acuity and visual field loss. Phosphene thresholds were obtained across the range of pulse durations tested but were much higher than those obtained in normal controls. Phosphene thresholds in RP patients moderately correlated with inner retinal thicknesses as measured by OCT. Preservation of inner retinal structure in patients with RP and the responsiveness of these eyes to electrical stimulation suggest adequate inner retinal preservation for a retinal prosthesis to be successful.

Mechanism of biological effects observed in honey bees (Apis mellifera, L. ) hived under extra-high-voltage transmission lines: implications derived from bee exposure to simulated intense electric fields and shocks

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

Bindokas, V.P.; Gauger, J.R.; Greenberg, B.

This work explores mechanisms for disturbance of honey bee colonies under a 765 kV, 60-Hz transmission line (electric (E) field = 7 kV/m) observed in previous studies. Proposed mechanisms fell into two categories: direct bee perception of enhanced in-hive E fields and perception of shock from induced currents. The adverse biological effects could be reproduced in simulations where only the worker bees were exposed to shock or to E field in elongated hive entranceways (= tunnels). We now report the results of full-scale experiments using the tunnel exposure scheme, which assesses the contribution of shock and intense E field tomore » colony disturbance. Exposure of worker bees (1400 h) to 60-Hz E fields including 100 kV/m under moisture-free conditions within a nonconductive tunnel causes no deleterious affect on colony behavior. Exposure of bees in conductive (e.g., wet) tunnels produces bee disturbance, increased mortality, abnormal propolization, and possible impairment of colony growth. We propose that this substrate dependence of bee disturbance is the result of perception of shock from coupled body currents and enhanced current densities postulated to exist in the legs and thorax of bees on conductors. Similarly, disturbance occurs when bees are exposed to step-potential-induced currents. At 275-350 nA single bees are disturbed; at 600 nA bees begin abnormal propolization behavior; and stinging occurs at 900 nA. We conclude that biological effects seen in bee colonies under a transmission line are primarily the result of electric shock from induced hive currents. This evaluation is based on the limited effects of E-field exposure in tunnels, the observed disturbance thresholds caused by shocks in tunnels, and the ability of hives exposed under a transmission line to source currents 100-1,000 times the shock thresholds.« less

Feasibility of producing a short, high energy s-band linear accelerator using a klystron power source.

PubMed

Baillie, Devin; St Aubin, J; Fallone, B G; Steciw, S

2013-04-01

To use a finite-element method (FEM) model to study the feasibility of producing a short s-band (2.9985 GHz) waveguide capable of producing x-rays energies up to 10 MV, for applications in a linac-MR, as well as conventional radiotherapy. An existing waveguide FEM model developed by the authors' group is used to simulate replacing the magnetron power source with a klystron. Peak fields within the waveguide are compared with a published experimental threshold for electric breakdown. The RF fields in the first accelerating cavity are scaled, approximating the effect of modifications to the first coupling cavity. Electron trajectories are calculated within the RF fields, and the energy spectrum, beam current, and focal spot of the electron beam are analyzed. One electron spectrum is selected for Monte Carlo simulations and the resulting PDD compared to measurement. When the first cavity fields are scaled by a factor of 0.475, the peak magnitude of the electric fields within the waveguide are calculated to be 223.1 MV∕m, 29% lower than the published threshold for breakdown at this operating frequency. Maximum electron energy increased from 6.2 to 10.4 MeV, and beam current increased from 134 to 170 mA. The focal spot FWHM is decreased slightly from 0.07 to 0.05 mm, and the width of the energy spectrum increased slightly from 0.44 to 0.70 MeV. Monte Carlo results show dmax is at 2.15 cm for a 10 × 10 cm(2) field, compared with 2.3 cm for a Varian 10 MV linac, while the penumbral widths are 4.8 and 5.6 mm, respectively. The authors' simulation results show that a short, high-energy, s-band accelerator is feasible and electric breakdown is not expected to interfere with operation at these field strengths. With minor modifications to the first coupling cavity, all electron beam parameters are improved.

Lethal effect of electric fields on isolated ventricular myocytes.

PubMed

de Oliveira, Pedro Xavier; Bassani, Rosana Almada; Bassani, José Wilson Magalhães

2008-11-01

Defibrillator-type shocks may cause electric and contractile dysfunction. In this study, we determined the relationship between probability of lethal injury and electric field intensity (E in isolated rat ventricular myocytes, with emphasis on field orientation and stimulus waveform. This relationship was sigmoidal with irreversible injury for E > 50 V/cm . During both threshold and lethal stimulation, cells were twofold more sensitive to the field when it was applied longitudinally (versus transversally) to the cell major axis. For a given E, the estimated maximum variation of transmembrane potential (Delta V(max)) was greater for longitudinal stimuli, which might account for the greater sensitivity to the field. Cell death, however, occurred at lower maximum Delta V(max) values for transversal shocks. This might be explained by a less steep spatial decay of transmembrane potential predicted for transversal stimulation, which would possibly result in occurrence of electroporation in a larger membrane area. For the same stimulus duration, cells were less sensitive to field-induced injury when shocks were biphasic (versus monophasic). Ours results indicate that, although significant myocyte death may occur in the E range expected during clinical defibrillation, biphasic shocks are less likely to produce irreversible cell injury.

Effect of ferroelectric BaTiO3 particles on the threshold voltage of a smectic A liquid crystal.

PubMed

Imamaliyev, Abbas Rahim; Ramazanov, Mahammadali Ahmad; Humbatov, Shirkhan Arastun

2018-01-01

The influence of small ferroelectric BaTiO 3 particles on the planar-homeotropic transition threshold voltage in smectic A liquid crystals consisting of p -nitrophenyl p -decyloxybenzoate and 4-cyano-4'-pentylbiphenyl were studied by using capacitance-voltage ( C - V ) measurements. It was shown that the BaTiO 3 particles significantly reduce the threshold voltage. The obtained result is explained by two factors: an increase of dielectric anisotropy of the liquid crystals and the formation of a strong electric field near polarized particles of BaTiO 3 . It was shown that the role of the second factor is dominant. The explanations of some features observed in the C - V characteristics are given.

A case study of the Thunderstorm Research International Project storm of July 11, 1978. I - Analysis of the data base

NASA Technical Reports Server (NTRS)

Nisbet, John S.; Barnard, Theresa A.; Forbes, Gregory S.; Krider, E. Philip; Lhermitte, Roger

1990-01-01

The data obtained at the time of the Thunderstorm Research International Project storm at the Kennedy Space Center on July 11, 1978 are analyzed in a model-independent manner. The data base included data from three Doppler radars, a lightning detection and ranging system and a network of 25 electric field mills, and rain gages. Electric field measurements were used to analyze the charge moments transferred by lightning flashes, and the data were fitted to Weibull distributions; these were used to estimate statistical parameters of the lightning for both intracloud and cloud-to-ground flashes and to estimate the fraction of the flashes which were below the observation threshold. The displacement and the conduction current densities were calculated from electric field measurements between flashes. These values were used to derive the magnitudes and the locations of dipole and monopole generators by least squares fitting the measured Maxwell current densities to the displacement-dominated equations.

Analytical theory for extracellular electrical stimulation of nerve with focal electrodes. I. Passive unmyelinated axon.

PubMed Central

Rubinstein, J T; Spelman, F A

1988-01-01

The cable model of a passive, unmyelinated fiber in an applied extracellular field is derived. The solution is valid for an arbitrary, time-varying, applied field, which may be determined analytically or numerically. Simple analytical computations are presented. They explain a variety of known phenomena and predict some previously undescribed properties of extracellular electrical stimulation. The polarization of a fiber in an applied field behaves like the output of a spatial high-pass and temporal low-pass filter of the stimulus. High-frequency stimulation results in a more spatially restricted region of fiber excitation, effectively reducing current spread relative to that produced by low-frequency stimulation. Chronaxie measured extracellularly is a function of electrode position relative to the stimulated fiber, and its value may differ substantially from that obtained intracellularly. Frequency dependence of psychophysical threshold obtained by electrical stimulation of the macaque cochlea closely follows the frequency dependence of single-fiber passive response. PMID:3233274

Acute microwave irradiation and cataract formation in rabbits and monkeys.

PubMed

Kramar, P; Harris, C; Emery, A F; Guy, A W

1978-09-01

Rabbits and monkeys were irradiated in the near field of a cavity-backed 2450 MHz resonant slot radiator, to determine the cataractogenic threshold. Rabbits developed cataracts at incident "apparent" power densities of 180 mW/cm2 (E2/120 pi, where E=rms/electric field strength). Monkeys sustained facial burns, but no lens damage, even at incident "apparent" power densities of 500 mW/cm2. These results were substantiated by computer thermal models.

Liquid methanol under a static electric field

NASA Astrophysics Data System (ADS)

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

2015-02-01

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

Anomalous Rashba spin-orbit interaction in electrically controlled topological insulator based on InN/GaN quantum wells

NASA Astrophysics Data System (ADS)

Łepkowski, Sławomir P.; Bardyszewski, Witold

2017-05-01

We study theoretically the topological phase transition and the Rashba spin-orbit interaction in electrically biased InN/GaN quantum wells. We show that that for properly chosen widths of quantum wells and barriers, one can effectively tune the system through the topological phase transition applying an external electric field perpendicular to the QW plane. We find that in InN/GaN quantum wells with the inverted band structure, when the conduction band s-type level is below the heavy hole and light hole p-type levels, the spin splitting of the subbands decreases with increasing the amplitude of the electric field in the quantum wells, which reveals the anomalous Rashba effect. Derived effective Rashba Hamiltonians can describe the subband spin splitting only for very small wave vectors due to strong coupling between the subbands. Furthermore, we demonstrate that for InN/GaN quantum wells in a Hall bar geometry, the critical voltage for the topological phase transition depends distinctly on the width of the structure and a significant spin splitting of the edge states lying in the 2D band gap can be almost switched off by increasing the electric field in quantum wells only by a few percent. We show that the dependence of the spin splitting of the upper branch of the edge state dispersion curve on the wave vector has a threshold-like behavior with the on/off spin splitting ratio reaching two orders of magnitude for narrow Hall bars. The threshold wave vector depends weakly on the Hall bar width, whereas it increases significantly with the bias voltage due to an increase of the energetic distance between the s-type and p-type quantum well energy levels and a reduction of the coupling between the subbands.

Anomalous Rashba spin-orbit interaction in electrically controlled topological insulator based on InN/GaN quantum wells.

PubMed

Łepkowski, Sławomir P; Bardyszewski, Witold

2017-05-17

We study theoretically the topological phase transition and the Rashba spin-orbit interaction in electrically biased InN/GaN quantum wells. We show that that for properly chosen widths of quantum wells and barriers, one can effectively tune the system through the topological phase transition applying an external electric field perpendicular to the QW plane. We find that in InN/GaN quantum wells with the inverted band structure, when the conduction band s-type level is below the heavy hole and light hole p-type levels, the spin splitting of the subbands decreases with increasing the amplitude of the electric field in the quantum wells, which reveals the anomalous Rashba effect. Derived effective Rashba Hamiltonians can describe the subband spin splitting only for very small wave vectors due to strong coupling between the subbands. Furthermore, we demonstrate that for InN/GaN quantum wells in a Hall bar geometry, the critical voltage for the topological phase transition depends distinctly on the width of the structure and a significant spin splitting of the edge states lying in the 2D band gap can be almost switched off by increasing the electric field in quantum wells only by a few percent. We show that the dependence of the spin splitting of the upper branch of the edge state dispersion curve on the wave vector has a threshold-like behavior with the on/off spin splitting ratio reaching two orders of magnitude for narrow Hall bars. The threshold wave vector depends weakly on the Hall bar width, whereas it increases significantly with the bias voltage due to an increase of the energetic distance between the s-type and p-type quantum well energy levels and a reduction of the coupling between the subbands.

Internal Electrostatic Discharge Monitor - IESDM

NASA Technical Reports Server (NTRS)

Kim, Wousik; Goebel, Dan M.; Jun, Insoo; Garrett, Henry B.

2011-01-01

A document discusses an innovation designed to effectively monitor dielectric charging in spacecraft components to measure the potential for discharge in order to prevent damage from internal electrostatic discharge (IESD). High-energy electrons penetrate the structural materials and shielding of a spacecraft and then stop inside dielectrics and keep accumulating. Those deposited charges generate an electric field. If the electric field becomes higher than the breakdown threshold (approx. =2 x 10(exp 5) V/cm), discharge occurs. This monitor measures potentials as a function of dielectric depth. Differentiation of potential with respect to the depth yields electric field. Direct measurement of the depth profile of the potential in a dielectric makes real-time electronic field evaluation possible without simulations. The IESDM has been designed to emulate a multi-layer circuit board, to insert very thin metallic layers between the dielectric layers. The conductors serve as diagnostic monitoring locations to measure the deposited electron-charge and the charge dynamics. Measurement of the time-dependent potential of the metal layers provides information on the amount of charge deposited in the dielectrics and the movement of that charge with time (dynamics).

Negative permittivity and permeability spectra of Cu/yttrium iron garnet hybrid granular composite materials in the microwave frequency range

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

Tsutaoka, Takanori, E-mail: tsutaok@hiroshima-u.ac.jp; Fukuyama, Koki; Kinoshita, Hideaki

2013-12-23

The relative complex permittivity and permeability spectra of the coagulated copper and yttrium iron garnet (Cu/YIG) hybrid granular composite materials have been studied in the microwave range. The insulator to metal transition was observed at the percolation threshold of Cu particle content (φ{sub Cu} = 16.0 vol. %) in the electrical conductivity. In the percolation threshold, the low frequency plasmonic state caused by the metallic Cu particle networks was observed. The percolated Cu/YIG granular composites show simultaneous negative permittivity and permeability spectra under external magnetic fields.

Secondary electron emission from a dielectric film subjected to an electric field. M.S. Thesis

NASA Technical Reports Server (NTRS)

Quoc-Nguyen, N.

1977-01-01

An electric field in the range of 0.3,3.3 kV/mm is created normal to a thin film FEP teflon sample which accumulates potential of up to 8.8, 13.7 or 18.3 kV when exposed to an electron beam having energy of 10.0, 15.0 or 20.0 kV, respectively. It is found that the secondary electron emission from the charged sample varies with field. The threshold voltage, at which the secondary electron emission coefficient sigma is unity, drops down from a low field value of 13.73 kV to a high field value of 13.11 kV for a 15.0 kV beam. A computational technique was developed that generates equipotential lines or contours and field vectors above a plane where potential is known. The utilization of conformal transformations allows the extension of the technique to configurations which map into a plane.

Chronic intravitreous infusion of ciliary neurotrophic factor modulates electrical retinal stimulation thresholds in the RCS rat.

PubMed

Kent, Tiffany L; Glybina, Inna V; Abrams, Gary W; Iezzi, Raymond

2008-01-01

To determine whether the sustained intravitreous delivery of CNTF modulates cortical response thresholds to electrical retinal stimulation in the RCS rat model of retinal degeneration. Animals were assigned to four groups: untreated, nonsurgical control and infusion groups of 10 ng/d CNTF, 1 ng/d CNTF, and PBS vehicle control. Thresholds for electrically evoked cortical potentials (EECPs) were recorded in response to transcorneal electrical stimulation of the retina at p30 and again at p60, after a three-week infusion. As the retina degenerated over time, EECP thresholds in response to electrical retinal stimulation increased. Eyes treated with 10 ng/d CNTF demonstrated significantly greater retinal sensitivity to electrical stimulation when compared with all other groups. In addition, eyes treated with 1 ng/d CNTF demonstrated significantly greater retinal sensitivity than both PBS-treated and untreated control groups. Retinal sensitivity to electrical stimulation was preserved in animals treated with chronic intravitreous infusion of CNTF. These data suggest that CNTF-mediated retinal neuroprotection may be a novel therapy that can lower stimulus thresholds in patients about to undergo retinal prosthesis implantation. Furthermore, it may maintain the long-term efficacy of these devices in patients.

Electric field measurements in nanosecond pulse discharges in air over liquid water surface

NASA Astrophysics Data System (ADS)

Simeni Simeni, Marien; Baratte, Edmond; Zhang, Cheng; Frederickson, Kraig; Adamovich, Igor V.

2018-01-01

Electric field in nanosecond pulse discharges in ambient air is measured by picosecond four-wave mixing, with absolute calibration by a known electrostatic field. The measurements are done in two geometries, (a) the discharge between two parallel cylinder electrodes placed inside quartz tubes, and (b) the discharge between a razor edge electrode and distilled water surface. In the first case, breakdown field exceeds DC breakdown threshold by approximately a factor of four, 140 ± 10 kV cm-1. In the second case, electric field is measured for both positive and negative pulse polarities, with pulse durations of ˜10 ns and ˜100 ns, respectively. In the short duration, positive polarity pulse, breakdown occurs at 85 kV cm-1, after which the electric field decreases over several ns due to charge separation in the plasma, with no field reversal detected when the applied voltage is reduced. In a long duration, negative polarity pulse, breakdown occurs at a lower electric field, 30 kV cm-1, after which the field decays over several tens of ns and reverses direction when the applied voltage is reduced at the end of the pulse. For both pulse polarities, electric field after the pulse decays on a microsecond time scale, due to residual surface charge neutralization by transport of opposite polarity charges from the plasma. Measurements 1 mm away from the discharge center plane, ˜100 μm from the water surface, show that during the voltage rise, horizontal field component (Ex ) lags in time behind the vertical component (Ey ). After breakdown, Ey is reduced to near zero and reverses direction. Further away from the water surface (≈0.9 mm), Ex is much higher compared to Ey during the entire voltage pulse. The results provide insight into air plasma kinetics and charge transport processes near plasma-liquid interface, over a wide range of time scales.

A low threshold nanocavity in a two-dimensional 12-fold photonic quasicrystal

NASA Astrophysics Data System (ADS)

Ren, Jie; Sun, XiaoHong; Wang, Shuai

2018-05-01

In this article, a low threshold nanocavity is built and investigated in a two-dimensional 12-fold holographic photonic quasicrystal (PQC). The cavity is formed by using the method of multi-beam common-path interference. By finely adjusting the structure parameters of the cavity, the Q factor and the mode volume are optimized, which are two keys to low-threshold on the basis of Purcell effect. Finally, an optimal cavity is obtained with Q value of 6023 and mode volume of 1.24 ×10-12cm3 . On the other hand, by Fourier Transformation of the electric field components in the cavity, the in-plane wave vectors are calculated and fitted to evaluate the cavity performance. The performance analysis of the cavity further proves the effectiveness of the optimization process. This has a guiding significance for the research of low threshold nano-laser.

Effects of Electron Beam Irradiation and Thiol Molecule Treatment on the Properties of MoS2 Field Effect Transistors

NASA Astrophysics Data System (ADS)

Choi, Barbara Yuri; Cho, Kyungjune; Pak, Jinsu; Kim, Tae-Young; Kim, Jae-Keun; Shin, Jiwon; Seo, Junseok; Chung, Seungjun; Lee, Takhee

2018-05-01

We investigated the effects of the structural defects intentionally created by electron-beam irradiation with an energy of 30 keV on the electrical properties of monolayer MoS2 field effect transistors (FETs). We observed that the created defects by electron beam irradiation on the MoS2 surface working as trap sites deteriorated the carrier mobility and carrier concentration with increasing the subthreshold swing value and shifting the threshold voltage in MoS2 FETs. The electrical properties of electron-beam irradiated MoS2 FETs were slightly improved by treating the devices with thiol-terminated molecules which presumably passivated the structural defects of MoS2. The results of this study may enhance the understanding of the electrical properties of MoS2 FETs in terms of creating and passivating defect sites.

Investigation of Characteristics of Large dB/dt for Geomagnetically Induced Currents

NASA Astrophysics Data System (ADS)

Munoz, D.; Ngwira, C.; Damas, M. C.

2016-12-01

When geomagnetically induced currents (GICs) flow through electrical networks, they become a potential threat for electrical power systems. Changes in the geomagnetic field (dB/dt) during severe geomagnetic disturbances are the main sources of GICs. These dB/dt phenomena were studied by selecting 24 strong geomagnetic storms with Dst ≤ - 150 nT. ACE spacecraft solar wind data: flow speed, proton density, By and Bz IMF components of the solar wind were correlated with measurements of the magnetic field detected on ground stations at different latitudes. This article reports characteristics of the solar wind during time intervals of large changes in the horizontal geomagnetic field with a threshold of dB/dt ≥ ± 20 nT/min for the 24 geomagnetic storms. The results of this investigation can help scientists to understand the mechanisms responsible for causing large magnetic field variations in order to predict and mitigate possible large events in the future, which is critical for our society that relies constantly on electricity for livelihood and security. In addition, this ongoing project will continue to investigate electron flux response before, during, and after large changes in geomagnetic field.

Electric field induced metal-insulator transition in VO2 thin film based on FTO/VO2/FTO structure

NASA Astrophysics Data System (ADS)

Hao, Rulong; Li, Yi; Liu, Fei; Sun, Yao; Tang, Jiayin; Chen, Peizu; Jiang, Wei; Wu, Zhengyi; Xu, Tingting; Fang, Baoying

2016-03-01

A VO2 thin film has been prepared using a DC magnetron sputtering method and annealing on an F-doped SnO2 (FTO) conductive glass substrate. The FTO/VO2/FTO structure was fabricated using photolithography and a chemical etching process. The temperature dependence of the I-V hysteresis loop for the FTO/VO2/FTO structure has been analyzed. The threshold voltage decreases with increasing temperature, with a value of 9.2 V at 20 °C. The maximum transmission modulation value of the FTO/VO2/FTO structure is 31.4% under various temperatures and voltages. Optical modulation can be realized in the structure by applying an electric field.

Electric-field-driven phase transition in vanadium dioxide

NASA Astrophysics Data System (ADS)

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

2011-03-01

In recent years, various strongly correlated materials have shown sharp switching from insulator to metallic state in their I(V) transport curves. Determining if this is purely an out of equilibrium phenomena (due to the strong electric field applied throughout the sample) or simply a Joule heating issue is still an open question. To address this issue, we have first measured local I(V) curves in vanadium dioxide (VO2) Mott insulator at various temperatures using a conducting AFM setup and determined the voltage threshold of the insulator to metal switching. By lifting the tip above the surface (> 35 nm) , wehavethenmeasuredthepurelyelectrostaticforcebetweenthetipandsamplesurfaceasthevoltagebetweenthesetwowasincreased . Inaverynarrowtemperaturerange (below 360 K) , atipheightrange (below 60 nm) andavoltageappliedrange (above 8 V) , weobservedswitchingintheelectrostaticforce (telegraphicnoisevs . timeandvs . voltage) . ThispurelyelectricfieldeffectshowsthattheswitchingphenomenonisstillpresentevenwithoutJouleheatinginVO 2 .

Investigation of electrophysical properties of allotropic modifications of carbon in the range of temperatures 140-400 K

NASA Astrophysics Data System (ADS)

Goshev, A. A.; Eseev, M. K.; Volkov, A. S.; Lyah, N. L.

2017-09-01

The paper presents the results of the investigation of allotropic modifications of carbon (coal, graphite, fullerenes, CNTs. Dependences of conductivity on the field frequency in the temperature range 140-400 K are presented. The characteristic features associated with the structure and types of hybridization are revealed. Calculation of the activation energy of carriers was performed. As well article presents experimental study of electrical properties of polymeric composites, reinforced different types of allotropic modifications of carbon (CNTs, graphite, fullerenes, coal) in alternating electrical field in frequency band from 0.01 Hz to 10 MHz. The threshold of percolation of polymer composites with various types of additives and their influence for conduction properties was estimated.

Electrical characteristic fluctuation of 16-nm-gate high-κ/metal gate bulk FinFET devices in the presence of random interface traps

NASA Astrophysics Data System (ADS)

Hsu, Sheng-Chia; Li, Yiming

2014-11-01

In this work, we study the impact of random interface traps (RITs) at the interface of SiO x /Si on the electrical characteristic of 16-nm-gate high-κ/metal gate (HKMG) bulk fin-type field effect transistor (FinFET) devices. Under the same threshold voltage, the effects of RIT position and number on the degradation of electrical characteristics are clarified with respect to different levels of RIT density of state ( D it). The variability of the off-state current ( I off) and drain-induced barrier lowering (DIBL) will be severely affected by RITs with high D it varying from 5 × 1012 to 5 × 1013 eV-1 cm-2 owing to significant threshold voltage ( V th) fluctuation. The results of this study indicate that if the level of D it is lower than 1 × 1012 eV-1 cm-2, the normalized variability of the on-state current, I off, V th, DIBL, and subthreshold swing is within 5%.

GIANT DIELECTRIC TUNABLE BEHAVIOR OF Pr-DOPED SrTiO3 AT LOW TEMPERATURE

NASA Astrophysics Data System (ADS)

Wei, T.; Song, Q. G.; Zhou, Q. J.; Li, Z. P.; Chen, Y. F.; Qi, X. L.; Guo, S. Q.; Liu, J.-M.

2012-03-01

Contrast with conventional dielectric tunable materials such as barium strontium titanate (BST), here, we report one new dielectric tunable behavior for Sr1-xPrxTiO3 system at low temperature. Giant dielectric tunability is confirmed in this system. More importantly, the efficient dielectric tunability can be realized just using small bias field. In addition, critical threshold electric field is also confirmed. This phenomenon may be related with the competition interaction of polar state with quantum fluctuations.

Individualized Low-Amplitude Seizure Therapy: Minimizing Current for Electroconvulsive Therapy and Magnetic Seizure Therapy.

PubMed

Peterchev, Angel V; Krystal, Andrew D; Rosa, Moacyr A; Lisanby, Sarah H

2015-08-01

Electroconvulsive therapy (ECT) at conventional current amplitudes (800-900 mA) is highly effective but carries the risk of cognitive side effects. Lowering and individualizing the current amplitude may reduce side effects by virtue of a less intense and more focal electric field exposure in the brain, but this aspect of ECT dosing is largely unexplored. Magnetic seizure therapy (MST) induces a weaker and more focal electric field than ECT; however, the pulse amplitude is not individualized and the minimum amplitude required to induce a seizure is unknown. We titrated the amplitude of long stimulus trains (500 pulses) as a means of determining the minimum current amplitude required to induce a seizure with ECT (bilateral, right unilateral, bifrontal, and frontomedial electrode placements) and MST (round coil on vertex) in nonhuman primates. Furthermore, we investigated a novel method of predicting this amplitude-titrated seizure threshold (ST) by a non-convulsive measurement of motor threshold (MT) using single pulses delivered through the ECT electrodes or MST coil. Average STs were substantially lower than conventional pulse amplitudes (112-174 mA for ECT and 37.4% of maximum device amplitude for MST). ST was more variable in ECT than in MST. MT explained 63% of the ST variance and is hence the strongest known predictor of ST. These results indicate that seizures can be induced with less intense electric fields than conventional ECT that may be safer; efficacy and side effects should be evaluated in clinical studies. MT measurement could be a faster and safer alternative to empirical ST titration for ECT and MST.

Identifying cochlear implant channels with poor electrode-neuron interface: partial tripolar, single-channel thresholds and psychophysical tuning curves

PubMed Central

Bierer, Julie Arenberg; Faulkner, Kathleen F.

2010-01-01

Objectives The goal of this study was to evaluate the ability of a threshold measure, made with a restricted electrode configuration, to identify channels exhibiting relatively poor spatial selectivity. With a restricted electrode configuration, channel-to-channel variability in threshold may reflect variations in the interface between the electrodes and auditory neurons (i.e., nerve survival, electrode placement, tissue impedance). These variations in the electrode-neuron interface should also be reflected in psychophysical tuning curve measurements. Specifically, it is hypothesized that high single-channel thresholds obtained with the spatially focused partial tripolar electrode configuration are predictive of wide or tip-shifted psychophysical tuning curves. Design Data were collected from five cochlear implant listeners implanted with the HiRes 90k cochlear implant (Advanced Bionics). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the partial tripolar configuration, for which a fraction of current (σ) from a center active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. Forward-masked psychophysical tuning curves were obtained for channels with the highest, lowest, and median tripolar (σ=1 or 0.9) thresholds. The probe channel and level were fixed and presented with either the monopolar (σ=0) or a more focused partial tripolar (σ ≥ 0.55) configuration. The masker channel and level were varied while the configuration was fixed to σ = 0.5. A standard, three-interval, two-alternative forced choice procedure was used for thresholds and masked levels. Results Single-channel threshold and variability in threshold across channels systematically increased as the compensating current, σ, increased and the presumed electrical field became more focused. Across subjects, channels with the highest single-channel thresholds, when measured with a narrow, partial tripolar stimulus, had significantly broader psychophysical tuning curves than the lowest threshold channels. In two subjects, the tips of the tuning curves were shifted away from the probe channel. Tuning curves were also wider for the monopolar probes than with partial tripolar probes, for both the highest and lowest threshold channels. Conclusions These results suggest that single-channel thresholds measured with a restricted stimulus can be used to identify cochlear implant channels with poor spatial selectivity. Channels having wide or tip-shifted tuning characteristics would likely not deliver the appropriate spectral information to the intended auditory neurons, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception. PMID:20090533

Determining which mechanisms lead to activation in the motor cortex: a modeling study of transcranial magnetic stimulation using realistic stimulus waveforms and sulcal geometry1

PubMed Central

Salvador, R.; Silva, S.; Basser, P. J.; Miranda, P. C.

2010-01-01

Objective To determine which mechanisms lead to activation of neurons in the motor cortex during transcranial magnetic stimulation (TMS) with different current directions and pulse waveforms. Methods The total electric field induced in a simplified model of a cortical sulcus by a figure-eight coil was calculated using the finite element method (FEM). This electric field was then used as the input to determine the response of compartmental models of several types of neurons. Results The modeled neurons were stimulated at different sites: fiber bends for pyramidal tract neurons, axonal terminations for cortical interneurons and axon collaterals, and a combination of both for pyramidal association fibers. All neurons were more easily stimulated by a PA directed electric field, except association fibers. Additionally, the second phase of a biphasic pulse was found to be more efficient than the first phase of either monophasic or biphasic pulses. Conclusion The stimulation threshold for different types of neurons depends on the pulse waveform and current direction. The reported results might account for the range of responses obtained in TMS of the motor cortex when using different stimulation parameters. Significance Modeling studies combining electric field calculations and neuronal models may lead to a deeper understanding of the effect of the TMS-induced electric field on cortical tissue, and may be used to evaluate improvements in TMS coil and waveform design. PMID:21035390

3D finite element modeling of epiretinal stimulation: Impact of prosthetic electrode size and distance from the retina.

PubMed

Sui, Xiaohong; Huang, Yu; Feng, Fuchen; Huang, Chenhui; Chan, Leanne Lai Hang; Wang, Guoxing

2015-05-01

A novel 3-dimensional (3D) finite element model was established to systematically investigate the impact of the diameter (Φ) of disc electrodes and the electrode-to-retina distance on the effectiveness of stimulation. The 3D finite element model was established based on a disc platinum stimulating electrode and a 6-layered retinal structure. The ground electrode was placed in the extraocular space in direct attachment with sclera and treated as a distant return electrode. An established criterion of electric-field strength of 1000 Vm-1 was adopted as the activation threshold for RGCs. The threshold current (TC) increased linearly with increasing Φ and electrode-to-retina distance and remained almost unchanged with further increases in diameter. However, the threshold charge density (TCD) increased dramatically with decreasing electrode diameter. TCD exceeded the electrode safety limit for an electrode diameter of 50 µm at an electrode-to-retina distance of 50 to 200 μm. The electric field distributions illustrated that smaller electrode diameters and shorter electrode-to-retina distances were preferred due to more localized excitation of RGC area under stimulation of different threshold currents in terms of varied electrode size and electrode-to-retina distances. Under the condition of same-amplitude current stimulation, a large electrode exhibited an improved potential spatial selectivity at large electrode-to-retina distances. Modeling results were consistent with those reported in animal electrophysiological experiments and clinical trials, validating the 3D finite element model of epiretinal stimulation. The computational model proved to be useful in optimizing the design of an epiretinal stimulating electrode for prosthesis.

Analysis of retinal function using chromatic pupillography in retinitis pigmentosa and the relationship to electrically evoked phosphene thresholds.

PubMed

Kelbsch, Carina; Maeda, Fumiatsu; Lisowska, Jolanta; Lisowski, Lukasz; Strasser, Torsten; Stingl, Krunoslav; Wilhelm, Barbara; Wilhelm, Helmut; Peters, Tobias

2017-06-01

To analyse pupil responses to specific chromatic stimuli in patients with advanced retinitis pigmentosa (RP) to ascertain whether chromatic pupillography can be used as an objective marker for residual retinal function. To examine correlations between parameters of the pupil response and the perception threshold of electrically evoked phosphenes. Chromatic pupillography was performed in 40 patients with advanced RP (visual acuity < 0.02 or visual field ≤5°, non-recordable ERGs) and 40 age-matched healthy subjects. Pupil responses to full-field red (605 nm) and blue (420 nm) stimuli of 28 lx corneal illumination were recorded and analysed for two stimulus durations (1 and 4 seconds). The perception threshold of phosphenes to transcorneal electrostimulation was ascertained and correlated to the pupil responses and visual acuity. Patients with RP showed significantly reduced pupil responses to red and blue stimuli compared with the controls. With red stimuli, pupillary escape could be observed; blue stimuli resulted in a well-preserved postillumination pupil response. Phosphene thresholds were significantly increased in patients with RP and correlated with the parameters of the pupil response if all subjects were considered. Within the RP group alone, this relationship was less pronounced and statistically not significant. Chromatic pupillography demonstrated a significant decrease in outer retinal photoreceptor responses but a persisting and disinhibited intrinsic photosensitive retinal ganglion cell function in advanced RP. These phenomena may be useful as an objective marker for the efficacy of any interventional treatment for hereditary retinal diseases as well as for the selection of suitable patients for an electronic retinal implant. © 2016 Acta Ophthalmologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

Identifying cochlear implant channels with poor electrode-neuron interfaces: electrically evoked auditory brain stem responses measured with the partial tripolar configuration.

PubMed

Bierer, Julie Arenberg; Faulkner, Kathleen F; Tremblay, Kelly L

2011-01-01

The goal of this study was to compare cochlear implant behavioral measures and electrically evoked auditory brain stem responses (EABRs) obtained with a spatially focused electrode configuration. It has been shown previously that channels with high thresholds, when measured with the tripolar configuration, exhibit relatively broad psychophysical tuning curves. The elevated threshold and degraded spatial/spectral selectivity of such channels are consistent with a poor electrode-neuron interface, defined as suboptimal electrode placement or reduced nerve survival. However, the psychophysical methods required to obtain these data are time intensive and may not be practical during a clinical mapping session, especially for young children. Here, we have extended the previous investigation to determine whether a physiological approach could provide a similar assessment of channel functionality. We hypothesized that, in accordance with the perceptual measures, higher EABR thresholds would correlate with steeper EABR amplitude growth functions, reflecting a degraded electrode-neuron interface. Data were collected from six cochlear implant listeners implanted with the HiRes 90k cochlear implant (Advanced Bionics). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the partial tripolar configuration, for which a fraction of current (σ) from a center active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. EABRs were obtained in each subject for the two channels having the highest and lowest tripolar (σ = 1 or 0.9) behavioral threshold. Evoked potentials were measured with both the monopolar (σ = 0) and a more focused partial tripolar (σ ≥ 0.50) configuration. Consistent with previous studies, EABR thresholds were highly and positively correlated with behavioral thresholds obtained with both the monopolar and partial tripolar configurations. The Wave V amplitude growth functions with increasing stimulus level showed the predicted effect of shallower growth for the partial tripolar than for the monopolar configuration, but this was observed only for the low-threshold channels. In contrast, high-threshold channels showed the opposite effect; steeper growth functions were seen for the partial tripolar configuration. These results suggest that behavioral thresholds or EABRs measured with a restricted stimulus can be used to identify potentially impaired cochlear implant channels. Channels having high thresholds and steep growth functions would likely not activate the appropriate spatially restricted region of the cochlea, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception.

Effect of ferroelectric BaTiO3 particles on the threshold voltage of a smectic A liquid crystal

PubMed Central

Imamaliyev, Abbas Rahim; Ramazanov, Mahammadali Ahmad

2018-01-01

The influence of small ferroelectric BaTiO3 particles on the planar–homeotropic transition threshold voltage in smectic A liquid crystals consisting of p-nitrophenyl p-decyloxybenzoate and 4-cyano-4′-pentylbiphenyl were studied by using capacitance–voltage (C–V) measurements. It was shown that the BaTiO3 particles significantly reduce the threshold voltage. The obtained result is explained by two factors: an increase of dielectric anisotropy of the liquid crystals and the formation of a strong electric field near polarized particles of BaTiO3. It was shown that the role of the second factor is dominant. The explanations of some features observed in the C–V characteristics are given. PMID:29600143

Heat transport in electrically aligned multiwalled carbon nanotubes dispersed in water

NASA Astrophysics Data System (ADS)

Cervantes-Alvarez, F.; Macias, J. D.; Alvarado-Gil, J. J.

2018-02-01

A modified Ångström method was used to determine the thermal diffusivity and thermal conductivity of aqueous dispersions of multiwalled carbon nanotubes as a function of their weight fraction concentration and in the presence of an externally applied electric field. Measurements were performed in planar samples, with a fixed thickness of 3.18 mm applying an AC voltage in the range from 0 to 70~V_RMS and for concentrations of carbon nanotubes from 0 to 2 wf%. It is shown that this field induces the formation of clusters followed by their alignment along the electric field, which can favor heat transfer in that direction. Heat transfer measurements show two regimes, in the first one under 0.5 wf%, voltages lower than 30~V_RMS are not strong enough to induce the adequate order of the carbon nanostructures, and as a consequence, thermal diffusivity of the dispersion remains close to the thermal diffusivity of water. In contrast for higher concentrations (above 1.5 wf%), 10~V_RMS are enough to get a good alignment. Above such thresholds of concentrations and voltages, thermal diffusivity and conductivity increase, when the electric field is increased, in such a way that for an applied voltage of 20~V_RMS and for a concentration of 1.5 wf%, an increase of 49% of the thermal conductivity was obtained. It is also shown that this approach exhibits limits, due to the fact that the electric-field induced structure, can act as a heating element at high electric field intensities and carbon nanotubes concentrations, which can induce convection and evaporation of the liquid matrix.

Experimental characterization of intrapulse tissue conductivity changes for electroporation.

PubMed

Neal, Robert E; Garcia, Paulo A; Robertson, John L; Davalos, Rafael V

2011-01-01

Cells exposed to short electric pulses experience a change in their transmembrane potential, which can lead to increased membrane permeability of the cell. When the energy of the pulses surpasses a threshold, the cell dies in a non-thermal manner known as irreversible electroporation (IRE). IRE has shown promise in the focal ablation of pathologic tissues. Its non-thermal mechanism spares sensitive structures and facilitates rapid lesion resolution. IRE effects depend on the electric field distribution, which can be predicted with numerical modeling. When the cells become permeabilized, the bulk tissue properties change, affecting this distribution. For IRE to become a reliable and successful treatment of diseased tissues, robust predictive treatment planning methods must be developed. It is vital to understand the changes in tissue properties undergoing the electric pulses to improve numerical models and predict treatment volumes. We report on the experimental characterization of these changes for kidney tissue. Tissue samples were pulsed between plate electrodes while intrapulse voltage and current data were measured to determine the conductivity of the tissue during the pulse. Conductivity was then established as a function of the electric field to which the tissue is exposed. This conductivity curve was used in a numerical model to demonstrate the impact of accounting for these changes when modeling electric field distributions to develop treatment plans.

High duty cycle far-infrared germanium lasers

NASA Astrophysics Data System (ADS)

Chamberlin, Danielle Russell

The effects of crystal geometry, heat transport, and optics on high duty cycle germanium hole population inversion lasers are investigated. Currently the laser's low duty cycle limits its utility for many applications. This low duty cycle is a result of the combination of the large electrical input power necessary and insufficient heat extraction. In order to achieve a continuous-wave device, the input power must be decreased and the cooling power increased. In order to improve laser efficiency and lower the input power, the effect of laser crystal geometry on the electric field uniformity is considered. Geometries with d/L>>1 or <<1 are shown to have improved electric field uniformity, where d is the distance between electrical contacts and L is the length in the direction of the Hall electric field. A geometry with d/L>>1 is shown to decrease the threshold voltage for lasing. Laser crystals with the traditional contact geometry have been compared to a new, planar contact design with both electrical contacts on the same side of the laser crystal. This new geometry provides a large d/L ratio while also allowing effective heat sinking. A pure, single-crystal silicon heat sink is developed for planar contact design lasers, which improves the duty cycle tenfold. For the traditional contact design, copper heat sinks are developed that demonstrate cooling powers up to 10 Watts. The effects of thermal conductivity, surface area, and interfacial thermal resistance on the heat transport are compared. To improve the cavity quality, thereby allowing for smaller crystal volumes, new optical designs are investigated. A vertical cavity structure is demonstrated for the planar contact structure using strontium titanate single crystals as mirrors. A mode-selecting cavity is implemented for the traditional contact design. The spectra of small-volume, near-threshold lasers are measured. In contrast to the emission of larger lasers, these lasers emit within narrow frequency peaks that do not shift smoothly with magnetic field. The details of the emission are shown to strongly depend on the optical cavity. A record duty cycle of 5% is achieved using a laser of dimensions 0.80 x 3 x 11 mm3 with the traditional contact geometry, improved copper heat sinks, and carefully etched crystal surfaces.

Convective Electrokinetic Instability With Conductivity Gradients

NASA Astrophysics Data System (ADS)

Chen, Chuan-Hua; Lin, Hao; Lele, Sanjiva; Santiago, Juan

2003-11-01

Electrokinetic flow instability has been experimentally identified and quantified in a glass T-junction microchannel system with a cross section of 11 um x 155 um. In this system, buffers of different conductivities were electrokinetically driven into a common mixing channel by a DC electric field. A convective instability was observed with a threshold electric field of 0.45 kV/cm for a 10:1 conductivity ratio. A physical model has been developed which consists of a modified Ohmic model formulation for electrolyte solutions and the Navier-Stokes equations with an electric body force term. The model and experiments show that bulk charge accumulation in regions of conductivity gradients is the key mechanism of such instabilities. A linear stability analysis was performed in a convective framework, and Briggs-Bers criteria were applied to determine the nature of instability. The analysis shows the instability is governed by two key parameters: the ratio of molecular diffusion to electroviscous time scale which governs the onset of instability, and the ratio of electroviscous to electroosmotic velocity which governs whether the instability is convective or absolute. The model predicted critical electric field, growth rate, wavelength, and phase speed which were comparable to experimental data.

Permeabilization of the nuclear envelope following nanosecond pulsed electric field exposure.

PubMed

Thompson, Gary L; Roth, Caleb C; Kuipers, Marjorie A; Tolstykh, Gleb P; Beier, Hope T; Ibey, Bennett L

2016-01-29

Permeabilization of cell membranes occurs upon exposure to a threshold absorbed dose (AD) of nanosecond pulsed electric fields (nsPEF). The ultimate, physiological bioeffect of this exposure depends on the type of cultured cell and environment, indicating that cell-specific pathways and structures are stimulated. Here we investigate 10 and 600 ns duration PEF effects on Chinese hamster ovary (CHO) cell nuclei, where our hypothesis is that pulse disruption of the nuclear envelope membrane leads to observed cell death and decreased viability 24 h post-exposure. To observe short-term responses to nsPEF exposure, CHO cells have been stably transfected with two fluorescently-labeled proteins known to be sequestered for cellular chromosomal function within the nucleus - histone-2b (H2B) and proliferating cell nuclear antigen (PCNA). H2B remains associated with chromatin after nsPEF exposure, whereas PCNA leaks out of nuclei permeabilized by a threshold AD of 10 and 600 ns PEF. A downturn in 24 h viability, measured by MTT assay, is observed at the number of pulses required to induce permeabilization of the nucleus. Copyright © 2015 Elsevier Inc. All rights reserved.

Electrical and optical co-stimulation in the deaf white cat

NASA Astrophysics Data System (ADS)

Cao, Zhiping; Xu, Yingyue; Tan, Xiaodong; Suematsu, Naofumi; Robinson, Alan; Richter, Claus-Peter

2018-02-01

Spatial selectivity of neural stimulation with photons, such as infrared neural stimulation (INS) is higher than the selectivity obtained with electrical stimulation. To obtain more independent channels for stimulation in neural prostheses, INS may be implemented to better restore the fidelity of the damaged neural system. However, irradiation with infrared light also bares the risk of heat accumulation in the target tissue with subsequent neural damage. Lowering the threshold for stimulation could reduce the amount of heat delivered to the tissue and the risk for subsequent tissue damage. It has been shown in the rat sciatic nerve that simultaneous irradiation with infrared light and the delivery of biphasic sub-threshold electrical pulses can reduce the threshold for INS [1]. In this study, deaf white cats have been used to test whether opto-electrical co-stimulation can reduce the stimulation threshold for INS in the auditory system too. The cochleae of the deaf white cats have largely reduced spiral ganglion neuron counts and significant degeneration of the organ of Corti and do not respond to acoustic stimuli. Combined electrical and optical stimulation was used to demonstrate that simultaneous stimulation with infrared light and biphasic electrical pulses can reduce the threshold for stimulation.

Novel Aspects of Evolution of the Stokes Parameters for an Electromagnetic Wave in Anisotropic Media

NASA Astrophysics Data System (ADS)

Botet, R.; Kuratsuji, H.; Seto, R.

2006-08-01

Polarization of a plane electromagnetic wave travelling through a medium is studied in the slowly-varying field envelope approximation. It is shown that the problem is identical to the 4-momentum evolution of a negatively-charged massless relativistic particle in an electromagnetic field. The approach is exemplified by the resonant oscillations of circular polarization in a medium embedded in a static magnetic field and a modulated electric field. The effect of dissipation in the medium is discussed. It is shown that the Rabi oscillations are stable below a threshold depending on the absorption coefficient. Above it, oscillations disappear.

Non-Equilibrium Effects on the Hidden Order of Microstructured URu2Si2

NASA Astrophysics Data System (ADS)

Winter, Laurel E.; Moll, Philip J. W.; Ramshaw, B. J.; Shekhter, Arkady; Harrison, N.; Bauer, Eric D.; McDonald, Ross D.

Despite extensive studies on the heavy-fermion URu2Si2, the order parameter associated with the hidden order state has yet to be established. It is known, however that the hidden order can be suppressed with pressure and high magnetic fields, which results in the development of antiferromagnetism, and the realization of a polarized state respectively. Focused Ion Beam lithography (FIB) of URu2Si2 has enabled high magnetic field observation of quantum oscillations in the resistance, indicating the preservation of sample quality to micron scale structures. These recent advances in FIB lithography have enabled the application of unprecedented electric fields while minimizing the effects of Joule heating in highly conductive metals at cryogenic temperatures. To this end, we have been able to create the necessary sample geometry to study the effect of an electric field upon hidden order in magnetic fields up to 15 T. Preliminary results suggest that above a characteristic threshold electric field, hidden order is suppressed revealing a state with similar magnetoresistive properties to the Kondo lattice in the absence of hidden order. Work supported by US Dept. of Energy through LANL/LDRD Program and G.T. Seaborg Institute, as well as NSF DMR-1157490 and the State of Florida.

Anomalous threshold voltage change by 2 MeV electron irradiation at 100 °C in deep submicron metal-oxide-semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Hayama, K.; Ohyama, H.; Simoen, E.; Rafí, J. M.; Mercha, A.; Claeys, C.

2004-04-01

The degradation of the electrical properties of deep submicron metal-oxide-semiconductor field-effect transistors (MOSFETs) by 2 MeV electron irradiation at high temperatures was studied. The irradiation temperatures were 30, 100, 150 and 200 °C, and the fluence was fixed at 1015e/cm2. For most experimental conditions, the threshold voltage (VT) is observed to reduce in absolute value both for n- and p-MOSFETs. This reduction is most pronounced at 100 °C, as at this irradiation temperature, the radiation-induced density of interface traps is highest. It is proposed that hydrogen neutralization of the dopants in the substrate plays a key role, whereby the hydrogen is released from the gate by the 2 MeV electrons.

Electrical power distribution control methods, electrical energy demand monitoring methods, and power management devices

DOEpatents

Chassin, David P [Pasco, WA; Donnelly, Matthew K [Kennewick, WA; Dagle, Jeffery E [Richland, WA

2011-12-06

Electrical power distribution control methods, electrical energy demand monitoring methods, and power management devices are described. In one aspect, an electrical power distribution control method includes providing electrical energy from an electrical power distribution system, applying the electrical energy to a load, providing a plurality of different values for a threshold at a plurality of moments in time and corresponding to an electrical characteristic of the electrical energy, and adjusting an amount of the electrical energy applied to the load responsive to an electrical characteristic of the electrical energy triggering one of the values of the threshold at the respective moment in time.

Electrical power distribution control methods, electrical energy demand monitoring methods, and power management devices

DOEpatents

Chassin, David P.; Donnelly, Matthew K.; Dagle, Jeffery E.

2006-12-12

Electrical power distribution control methods, electrical energy demand monitoring methods, and power management devices are described. In one aspect, an electrical power distribution control method includes providing electrical energy from an electrical power distribution system, applying the electrical energy to a load, providing a plurality of different values for a threshold at a plurality of moments in time and corresponding to an electrical characteristic of the electrical energy, and adjusting an amount of the electrical energy applied to the load responsive to an electrical characteristic of the electrical energy triggering one of the values of the threshold at the respective moment in time.

Ab Initio Calculation of Photoionization and Inelastic Photon Scattering Spectra of He below the N=2 Threshold in a dc Electric Field

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

Mihelic, Andrej; Zitnik, Matjaz

2007-06-15

We study the Stark effect on doubly excited states of the helium atom below N=2. We present the ab initio photoionization and total inelastic photon scattering cross sections calculated with the method of complex scaling for field strengths F{<=}100 kV/cm. The calculations are compared to the measurements of the ion [Phys. Rev. Lett. 90, 133002 (2003)] and vacuum ultraviolet fluorescence yields [Phys. Rev. Lett. 96, 093001 (2006)]. For the case of photoionization and for incident photons with polarization vector P parallel to the electric field F, we confirm the propensity rule proposed by Tong and Lin [Phys. Rev. Lett. 92,more » 223003 (2004)]. Furthermore, the rule is also shown to apply for F perpendicular P and for the case of the inelastic scattering in both experimental geometries.« less

Optical and electrical properties of indium tin oxide films near their laser damage threshold [Electrical and optical properties of indium tin oxide films under multi-pulse laser irradiation at 1064 nm

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

Yoo, Jae -Hyuck; Lange, Andrew; Bude, Jeff

In this paper, we investigated whether the optical and electrical properties of indium tin oxide (ITO) films are degraded under laser irradiation below their laser ablation threshold. While performing multi-pulse laser damage experiments on a single ITO film (4.7 ns, 1064 nm, 10 Hz), we examined the optical and electrical properties in situ. A decrease in reflectance was observed prior to laser damage initiation. However, under sub-damage threshold irradiation, conductivity and reflectance of the film were maintained without measurable degradation. This indicates that ITO films in optoelectronic devices may be operated below their lifetime laser damage threshold without noticeable performancemore » degradation.« less

Optical and electrical properties of indium tin oxide films near their laser damage threshold [Electrical and optical properties of indium tin oxide films under multi-pulse laser irradiation at 1064 nm

DOE PAGES

Yoo, Jae -Hyuck; Lange, Andrew; Bude, Jeff; ...

2017-02-10

In this paper, we investigated whether the optical and electrical properties of indium tin oxide (ITO) films are degraded under laser irradiation below their laser ablation threshold. While performing multi-pulse laser damage experiments on a single ITO film (4.7 ns, 1064 nm, 10 Hz), we examined the optical and electrical properties in situ. A decrease in reflectance was observed prior to laser damage initiation. However, under sub-damage threshold irradiation, conductivity and reflectance of the film were maintained without measurable degradation. This indicates that ITO films in optoelectronic devices may be operated below their lifetime laser damage threshold without noticeable performancemore » degradation.« less

Constellation of CubeSats for Realtime Ionospheric E-field Measurements for Global Space Weather

NASA Astrophysics Data System (ADS)

Crowley, G.; Swenson, C.; Pilinski, M.; Fish, C. S.; Neilsen, T. L.; Stromberg, E. M.; Azeem, I.; Barjatya, A.

2014-12-01

Inexpensive and robust space-weather monitoring instruments are needed to fill upcoming gaps in the Nation's ability to meet requirements for space weather specification and forecasting. Foremost among the needed data are electric fields, since they drive global ionospheric and thermospheric behavior, and because there are relatively few ground-based measurements. We envisage a constellation of CubeSats to provide global coverage of the electric field and its variability. The DICE (Dynamic Ionosphere CubeSat Experiment) mission was a step towards this goal, with two identical 1.5U CubeSats, each carrying three space weather instruments: (1) double probe instruments to measure AC and DC electric fields; (2) Langmuir probes to measure ionospheric electron density, and; (3) a magnetometer to measure field-aligned currents. DICE launched in October 2011. DICE was the first CubeSat mission to observe a Storm Enhanced Density event, fulfilling a major goal of the mission. Due to attitude control anomalies encountered in orbit, the DICE electric field booms have not yet been deployed. Important lessons have been learned for the implementation of a spin-stabilized CubeSat, and the design and performance of the Attitude Determination & Control System (ADCS). These lessons are now being applied to the DIME SensorSat, a risk-reduction mission that is capable of deploying flexible electric field booms up to a distance of 10-m tip-to-tip from a 1.5U CubeSat. DIME will measure AC and DC electric fields, and will exceed several IORD-2 threshold requirements. Ion densities, and magnetic fields will also be measured to characterize the performance of the sensor in different plasma environments. We show the utility of a constellation of electric field measurements, describe the DIME SensorSat, and demonstrate how the measurement will meet or exceed IORD requirements. The reduced cost of these sensors will enable constellations that can, for the first time, adequately resolve the spatial and temporal variability in ionospheric electrodynamics. DICE and DIME are collaborations between ASTRA and Space Dynamics Lab/Utah State University.

Efficient pre-ionization by direct X-B mode conversion in VEST

NASA Astrophysics Data System (ADS)

Jo, JongGab; Lee, H. Y.; Kim, S. C.; Kim, S. H.; An, Y. H.; Hwang, Y. S.

2017-01-01

Pre-ionization experiments with pure toroidal field have been carried out in VEST (Versatile Experiment Spherical Torus) to investigate the feasibility of direct XB mode conversion from perpendicular LFS (Low Field Side) injection for efficient pre-ionization. Pre-ionization plasmas are studied by measuring the electron density and temperature profiles with respect to microwave power and toroidal field strength, and 2D full wave cold plasma simulation using the COMSOL Multiphysics is performed for the comparison. It is experimentally figured out that exceeding the threshold microwave power (>3 kW), the parametric decay and localized collisional heating is observed near the UHR (Upper Hybrid Resonance), and the efficient XB mode conversion can be achieved in both short density scale length (Ln) and magnetic scale length (LB) region positioned at outboard and inboard sides, respectively. From the 2D full wave simulations, the reflection and tunneling of X-wave near the R-cutoff layer according to the measured electron density profiles are analyzed with electric field polarization and power flow. Threshold electric field and wave power density for parametric decay are evaluated at least more than 4.8 × 104 V/m and 100 W/cm2, respectively. This study shows that efficient pre-ionization schemes using direct XB mode conversion can be realized by considering the key factors such as Ln, LB, and transmitted wave power at the UHR. Application to Ohmic start-up experiment is carried out to confirm the effect of the pre-ionization schemes on tokamak plasma start-up in VEST.

Mirror symmetry of ions and electron temperature variations within the dusty dynamo layer of the auroral ionosphere

NASA Astrophysics Data System (ADS)

Timofeev, Evgeny; Kangas, Jorma; Vallinkoski, Matti

Quasi-periodic (consisting of a dozen electro-thermal structures, ETS) variations of ionospheric parameters during April, 10 and March, 23 1988 substorms were investigated using the data of EISCAT radars in Tromso. These variations were measured at the lower edge of dynamo-layer 106 km and include the ion and electron temperature, electron density and ionospheric electric field; all data were smoothed out using moving average with optimal lag window. It was shown that: 1) ETS clusters are observed when value of the electric field is < 10 mV/m and average electron density is about (5-10)*10 (4) /sm (3) , 2) For each ETS the envelop demonstrate the so called mirror symmetry, that is antiphased variations of the ion and electron temperature (when Ti increases and Te decreases), 3) The symmetry breaks when the electric field is larger than FB instability threshold (15-20 mVm), 4) The periods of these variations is in the range of 3-10 min, 5) The self-similarity of the scales is observed: smaller scales are included into the larger scales, 6) Temperature variations were accompanied by the electric field variations with amplitude of 4-7 mV/m, 7) Large scale structures (and sometimes dyads formed by two subsequent structures) were accompanied by the electric field rotation up to the whole circle. Specific ETS and plasma parameters variations can be interpreted as a result of Ekman-type instability in the dusty plasma of the dynamo layer. The mirror symmetry of plasma temperature variations is an evidence of a partial blocking of energy transfer between the ions and electrons at low values of the external electric field (below FB instability threshold) because the main energy in such a kind of plasma is attributed to dusty macro-particles (Fortov et al., 2010). Under these conditions the time scale of the dust particle energy variations are considerably larger than the corresponding scales of the temperature variations. According to our previous results (Timofeev et al, 2009-2013) the coherent increase of correlation coefficient (CC) of plasma temperature time variations and smoothed value of the electric field means that the CC can be used as an indicator of the ETS "rigidity" (hence the energy and charge of macro-particles). We used this coherence to estimate the time scale of the macro-particles energy growth (during preliminary phase of March 23, 1988 substorm) and get values of 12-19 min. In the present study we used the same event to estimate the time scale of the plasma temperatures mirror variations and obtained that they are at least 2-3 times shorter. Such a difference in the time scale determines the ETS formation. Finally, after FB instability excitation the electrons can quickly exchange their energy with plasmons, so that the mirror symmetry in temperature variations breaks down.

Anhydrous octyl-glucoside phase transition from lamellar to isotropic induced by electric and magnetic fields.

PubMed

Hashim, Rauzah; Sugimura, Akihiko; Nguan, Hock-Seng; Rahman, Matiur; Zimmermann, Herbert

2017-02-28

A static deuterium nuclear magnetic resonance ( 2 HNMR) technique (magnetic field, B = 7.05 T) was employed to monitor the thermotropic lamellar phase of the anhydrous 1:1 mixture sample of octyl-b-D-glucoside (βOG) and that of partially deuterium labelled at the alpha position on the chain, i.e.,βOG-d 2 In the absence of an electric field, the 2 H NMR spectrum of the mixture gives a typical quadrupolar doublet representing the aligned lamellar phase. Upon heating to beyond the clearing temperature at 112 °C, this splitting converts to a single line expected for an isotropic phase. Simultaneous application of magnetic and electric fields (E = 0.4 MV/m) at 85 °C in the lamellar phase, whose direction was set to be parallel or perpendicular to the magnetic field, resulted in the change of the doublet into a single line and this recovers to the initial doublet with time for both experimental geometries. This implies E- and B-field-induced phase transitions from the lamellar to an isotropic phase and a recovery to the lamellar phase again with time. Moreover, these phase transformations are accompanied by a transient current. A similar observation was made in a computational study when an electric field was applied to a water cluster system. Increasing the field strength distorts the water cluster and weakens its hydrogen bonds leading to a structural breakdown beyond a threshold field-strength. Therefore, we suggest the observed field-induced transition is likely due to a structure change of the βOG lamellar assembly caused by the field effect and not due to Joule heating.

Negative bias-and-temperature stress-assisted activation of oxygen-vacancy hole traps in 4H-silicon carbide metal-oxide-semiconductor field-effect transistors

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

Ettisserry, D. P., E-mail: deva@umd.edu, E-mail: neil@umd.edu; Goldsman, N., E-mail: deva@umd.edu, E-mail: neil@umd.edu; Akturk, A.

We use hybrid-functional density functional theory-based Charge Transition Levels (CTLs) to study the electrical activity of near-interfacial oxygen vacancies located in the oxide side of 4H-Silicon Carbide (4H-SiC) power Metal-Oxide-Semiconductor Field-Effect Transistors (MOSFETs). Based on the “amorphousness” of their local atomic environment, oxygen vacancies are shown to introduce their CTLs either within (permanently electrically active) or outside of (electrically inactive) the 4H-SiC bandgap. The “permanently electrically active” centers are likely to cause threshold voltage (V{sub th}) instability at room temperature. On the other hand, we show that the “electrically inactive” defects could be transformed into various “electrically active” configurations undermore » simultaneous application of negative bias and high temperature stresses. Based on this observation, we present a model for plausible oxygen vacancy defects that could be responsible for the recently observed excessive worsening of V{sub th} instability in 4H-SiC power MOSFETs under high temperature-and-gate bias stress. This model could also explain the recent electrically detected magnetic resonance observations in 4H-SiC MOSFETs.« less

40 CFR 98.41 - Reporting threshold.

Code of Federal Regulations, 2011 CFR

2011-07-01

...) MANDATORY GREENHOUSE GAS REPORTING Electricity Generation § 98.41 Reporting threshold. You must report GHG emissions under this subpart if your facility contains one or more electricity generating units and the...

40 CFR 98.41 - Reporting threshold.

Code of Federal Regulations, 2010 CFR

2010-07-01

...) MANDATORY GREENHOUSE GAS REPORTING Electricity Generation § 98.41 Reporting threshold. You must report GHG emissions under this subpart if your facility contains one or more electricity generating units and the...

40 CFR 98.41 - Reporting threshold.

Code of Federal Regulations, 2014 CFR

2014-07-01

...) MANDATORY GREENHOUSE GAS REPORTING Electricity Generation § 98.41 Reporting threshold. You must report GHG emissions under this subpart if your facility contains one or more electricity generating units and the...

40 CFR 98.41 - Reporting threshold.

Code of Federal Regulations, 2013 CFR

2013-07-01

...) MANDATORY GREENHOUSE GAS REPORTING Electricity Generation § 98.41 Reporting threshold. You must report GHG emissions under this subpart if your facility contains one or more electricity generating units and the...

40 CFR 98.41 - Reporting threshold.

Code of Federal Regulations, 2012 CFR

2012-07-01

...) MANDATORY GREENHOUSE GAS REPORTING Electricity Generation § 98.41 Reporting threshold. You must report GHG emissions under this subpart if your facility contains one or more electricity generating units and the...

Observations of the initial stages of colloidal band formation

NASA Astrophysics Data System (ADS)

Li, Yanrong; Tagawa, Yoshiyuki; Yee, Andrew; Yoda, Minami

2017-11-01

A number of studies have shown that particles suspended in a conducting fluid near a wall are subject to wall-normal repulsive ``lift'' forces, even in the absence of interparticle interactions, in a flowing suspension. Evanescent-wave visualizations have shown that colloidal particles in a dilute (volume fractions <0.4%) suspension are instead attracted to the wall when the suspension is driven through 30 μm deep channels by a pressure gradient and an electric field when the resulting combined Poiseuille and electroosmotic (EO) flow are in opposite direction, i.e., ``counterflow,'' although the particles and channel walls both have negative zeta-potentials. Above a minimum ``threshold'' electric field magnitude |Emin | , the particles assemble into dense ``bands'' with cross-sectional dimensions of a few μm and length comparable to that of the channel (i.e., a few cm). The results suggest that the threshold field |Emin | is large enough so that there is a region of ``reverse'' flow, along the direction of the EO flow, near the wall. Visualization of a large segment of the channel (>300 hydraulic diameters) at frame rates as great as 1 kHz is used to determine banding maps for a variety of dilute colloidal suspensions and to investigate the initial stages of band formation over a wide range of flow conditions. Supported by US Army Research Office.

Electrical characteristics of tunneling field-effect transistors with asymmetric channel thickness

NASA Astrophysics Data System (ADS)

Kim, Jungsik; Oh, Hyeongwan; Kim, Jiwon; Meyyappan, M.; Lee, Jeong-Soo

2017-02-01

Effects of using asymmetric channel thickness in tunneling field-effect transistors (TFET) are investigated in sub-50 nm channel regime using two-dimensional (2D) simulations. As the thickness of the source side becomes narrower in narrow-source wide-drain (NSWD) TFETs, the threshold voltage (V th) and the subthreshold swing (SS) decrease due to enhanced gate controllability of the source side. The narrow source thickness can make the band-to-band tunneling (BTBT) distance shorter and induce much higher electric field near the source junction at the on-state condition. In contrast, in a TFET with wide-source narrow-drain (WSND), the SS shows almost constant values and the V th slightly increases with narrowing thickness of the drain side. In addition, the ambipolar current can rapidly become larger with smaller thickness on the drain side because of the shorter BTBT distance and the higher electric-field at the drain junction. The on-current of the asymmetric channel TFET is lower than that of conventional TFETs due to the volume limitation of the NSWD TFET and high series resistance of the WSND TFET. The on-current is almost determined by the channel thickness of the source side.

Multi-threshold de-noising of electrical imaging logging data based on the wavelet packet transform

NASA Astrophysics Data System (ADS)

Xie, Fang; Xiao, Chengwen; Liu, Ruilin; Zhang, Lili

2017-08-01

A key problem of effectiveness evaluation for fractured-vuggy carbonatite reservoir is how to accurately extract fracture and vug information from electrical imaging logging data. Drill bits quaked during drilling and resulted in rugged surfaces of borehole walls and thus conductivity fluctuations in electrical imaging logging data. The occurrence of the conductivity fluctuations (formation background noise) directly affects the fracture/vug information extraction and reservoir effectiveness evaluation. We present a multi-threshold de-noising method based on wavelet packet transform to eliminate the influence of rugged borehole walls. The noise is present as fluctuations in button-electrode conductivity curves and as pockmarked responses in electrical imaging logging static images. The noise has responses in various scales and frequency ranges and has low conductivity compared with fractures or vugs. Our de-noising method is to decompose the data into coefficients with wavelet packet transform on a quadratic spline basis, then shrink high-frequency wavelet packet coefficients in different resolutions with minimax threshold and hard-threshold function, and finally reconstruct the thresholded coefficients. We use electrical imaging logging data collected from fractured-vuggy Ordovician carbonatite reservoir in Tarim Basin to verify the validity of the multi-threshold de-noising method. Segmentation results and extracted parameters are shown as well to prove the effectiveness of the de-noising procedure.

Study of electrical conductivity and memory switching in the zinc-vanadium-phosphate glasses

NASA Astrophysics Data System (ADS)

Mirzayi, M.; Hekmatshoar, M. H.

2013-07-01

Vanadium zinc phosphate glasses were prepared by the conventional melt quenching technique and effect of V2O5 concentration on d.c. conductivity of prepared samples were investigated. X-ray diffraction patterns confirmed the glassy character of the samples. The d.c. conductivity increased with increase in V2O5 content. Results showed that activation energy has a single value in the investigated range of temperature, which can be explained in accordance with Mott small pollaron hopping model. I-V characteristics at high electric field showed that switching in these glasses was memory type. The threshold field of switching was found to decrease with increase in V2O5 content. Non-linear behavior and switching phenomenon was explained by Pool-Frenkel effect and thermal model.

High-order above-threshold ionization beyond the electric dipole approximation

NASA Astrophysics Data System (ADS)

Brennecke, Simon; Lein, Manfred

2018-05-01

Photoelectron momentum distributions from strong-field ionization are calculated by numerical solution of the one-electron time-dependent Schrödinger equation for a model atom including effects beyond the electric dipole approximation. We focus on the high-energy electrons from rescattering and analyze their momentum component along the field propagation direction. We show that the boundary of the calculated momentum distribution is deformed in accordance with the classical three-step model including the beyond-dipole Lorentz force. In addition, the momentum distribution exhibits an asymmetry in the signal strengths of electrons emitted in the forward/backward directions. Taken together, the two non-dipole effects give rise to a considerable average forward momentum component of the order of 0.1 a.u. for realistic laser parameters.

Electronic and magneto-transport in chirality sorted carbon nanotube films

NASA Astrophysics Data System (ADS)

Janas, Dawid; Czechowski, Nikodem; Adamus, Zbigniew; GiŻewski, Tomasz

2018-01-01

This research details electronic and magneto-transport in unsorted and chirality-enriched carbon nanotube (CNT) films. By measuring the electrical conductivity from 4 K to 297 K, we were able to assign the governing mechanism of electronic transport. Fluctuation-induced tunnelling was in accordance with the obtained data and very well matched the underlying physics. We demonstrated how a change in the type of CNT to make the film affects its electrical performance. As the temperature was decreased down to cryogenic conditions, up to a 56-fold increase in resistance was noted. Moreover, the measurement of magnetoresistance (MR) revealed a non-monotonic dependence on the applied magnetic field. The initial negative component of MR was eventually overpowered by the positive MR component as the field strength was increased beyond a certain threshold.

Generation Process of Large-Amplitude Upper-Band Chorus Emissions Observed by Van Allen Probes

DOE PAGES

Kubota, Yuko; Omura, Yoshiharu; Kletzing, Craig; ...

2018-04-19

In this paper, we analyze large-amplitude upper-band chorus emissions measured near the magnetic equator by the Electric and Magnetic Field Instrument Suite and Integrated Science instrument package on board the Van Allen Probes. In setting up the parameters of source electrons exciting the emissions based on theoretical analyses and observational results measured by the Helium Oxygen Proton Electron instrument, we calculate threshold and optimum amplitudes with the nonlinear wave growth theory. We find that the optimum amplitude is larger than the threshold amplitude obtained in the frequency range of the chorus emissions and that the wave amplitudes grow between themore » threshold and optimum amplitudes. Finally, in the frame of the wave growth process, the nonlinear growth rates are much greater than the linear growth rates.« less

Generation Process of Large-Amplitude Upper-Band Chorus Emissions Observed by Van Allen Probes

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

Kubota, Yuko; Omura, Yoshiharu; Kletzing, Craig

In this paper, we analyze large-amplitude upper-band chorus emissions measured near the magnetic equator by the Electric and Magnetic Field Instrument Suite and Integrated Science instrument package on board the Van Allen Probes. In setting up the parameters of source electrons exciting the emissions based on theoretical analyses and observational results measured by the Helium Oxygen Proton Electron instrument, we calculate threshold and optimum amplitudes with the nonlinear wave growth theory. We find that the optimum amplitude is larger than the threshold amplitude obtained in the frequency range of the chorus emissions and that the wave amplitudes grow between themore » threshold and optimum amplitudes. Finally, in the frame of the wave growth process, the nonlinear growth rates are much greater than the linear growth rates.« less

Modeling Plasma Formation in a Micro-gap at Microwave Frequency

NASA Astrophysics Data System (ADS)

Bowman, Arthur; Remillard, Stephen

2013-03-01

In the presence of a strong electric field, gas molecules become ionized, forming a plasma. The study of this dielectric breakdown at microwave frequency has important applications in improving the operation of radio frequency (RF) devices, where the high electric fields present in small gaps can easily ionize gases like air. A cone and tuner resonant structure was used to induce breakdown of diatomic Nitrogen in adjustable micro-gaps ranging from 13 to 1,156 μm. The electric field for plasma formation exhibited strong pressure dependence in the larger gap sizes, as predicted by previous theoretical and experimental work. Pressure is proportional to the frequency of collision between electrons and molecules, which increases with pressure when the gap is large, but levels off in the micro-gap region. A separate model of the breakdown electric field based on the characteristic diffusion length of the plasma also fit the data poorly for these smaller gap sizes. This may be explained by a hypothesis that dielectric breakdown at and below the 100 μm gap size occurs outside the gap, an argument that is supported by the observation of very high breakdown threshold electric fields in this region. Optical emissions revealed that vibrational and rotational molecular transitions of the first positive electronic system are suppressed in micro-gaps, indicating that transitions into the molecular ground state do not occur in micro-gap plasmas. Acknowledgements: National Science Foundation under NSF-REU Grant No. PHY/DMR-1004811, the Provost's Office of Hope College, and the Hope College Division of Natural and Applied Sciences.

Individualized Low-Amplitude Seizure Therapy: Minimizing Current for Electroconvulsive Therapy and Magnetic Seizure Therapy

PubMed Central

Peterchev, Angel V; Krystal, Andrew D; Rosa, Moacyr A; Lisanby, Sarah H

2015-01-01

Electroconvulsive therapy (ECT) at conventional current amplitudes (800–900 mA) is highly effective but carries the risk of cognitive side effects. Lowering and individualizing the current amplitude may reduce side effects by virtue of a less intense and more focal electric field exposure in the brain, but this aspect of ECT dosing is largely unexplored. Magnetic seizure therapy (MST) induces a weaker and more focal electric field than ECT; however, the pulse amplitude is not individualized and the minimum amplitude required to induce a seizure is unknown. We titrated the amplitude of long stimulus trains (500 pulses) as a means of determining the minimum current amplitude required to induce a seizure with ECT (bilateral, right unilateral, bifrontal, and frontomedial electrode placements) and MST (round coil on vertex) in nonhuman primates. Furthermore, we investigated a novel method of predicting this amplitude-titrated seizure threshold (ST) by a non-convulsive measurement of motor threshold (MT) using single pulses delivered through the ECT electrodes or MST coil. Average STs were substantially lower than conventional pulse amplitudes (112–174 mA for ECT and 37.4% of maximum device amplitude for MST). ST was more variable in ECT than in MST. MT explained 63% of the ST variance and is hence the strongest known predictor of ST. These results indicate that seizures can be induced with less intense electric fields than conventional ECT that may be safer; efficacy and side effects should be evaluated in clinical studies. MT measurement could be a faster and safer alternative to empirical ST titration for ECT and MST. PMID:25920013

Topology optimization for three-dimensional electromagnetic waves using an edge element-based finite-element method.

PubMed

Deng, Yongbo; Korvink, Jan G

2016-05-01

This paper develops a topology optimization procedure for three-dimensional electromagnetic waves with an edge element-based finite-element method. In contrast to the two-dimensional case, three-dimensional electromagnetic waves must include an additional divergence-free condition for the field variables. The edge element-based finite-element method is used to both discretize the wave equations and enforce the divergence-free condition. For wave propagation described in terms of the magnetic field in the widely used class of non-magnetic materials, the divergence-free condition is imposed on the magnetic field. This naturally leads to a nodal topology optimization method. When wave propagation is described using the electric field, the divergence-free condition must be imposed on the electric displacement. In this case, the material in the design domain is assumed to be piecewise homogeneous to impose the divergence-free condition on the electric field. This results in an element-wise topology optimization algorithm. The topology optimization problems are regularized using a Helmholtz filter and a threshold projection method and are analysed using a continuous adjoint method. In order to ensure the applicability of the filter in the element-wise topology optimization version, a regularization method is presented to project the nodal into an element-wise physical density variable.

Topology optimization for three-dimensional electromagnetic waves using an edge element-based finite-element method

PubMed Central

Korvink, Jan G.

2016-01-01

This paper develops a topology optimization procedure for three-dimensional electromagnetic waves with an edge element-based finite-element method. In contrast to the two-dimensional case, three-dimensional electromagnetic waves must include an additional divergence-free condition for the field variables. The edge element-based finite-element method is used to both discretize the wave equations and enforce the divergence-free condition. For wave propagation described in terms of the magnetic field in the widely used class of non-magnetic materials, the divergence-free condition is imposed on the magnetic field. This naturally leads to a nodal topology optimization method. When wave propagation is described using the electric field, the divergence-free condition must be imposed on the electric displacement. In this case, the material in the design domain is assumed to be piecewise homogeneous to impose the divergence-free condition on the electric field. This results in an element-wise topology optimization algorithm. The topology optimization problems are regularized using a Helmholtz filter and a threshold projection method and are analysed using a continuous adjoint method. In order to ensure the applicability of the filter in the element-wise topology optimization version, a regularization method is presented to project the nodal into an element-wise physical density variable. PMID:27279766

Suppressing the memory state of floating gate transistors with repeated femtosecond laser backside irradiations

NASA Astrophysics Data System (ADS)

Chambonneau, Maxime; Souiki-Figuigui, Sarra; Chiquet, Philippe; Della Marca, Vincenzo; Postel-Pellerin, Jérémy; Canet, Pierre; Portal, Jean-Michel; Grojo, David

2017-04-01

We demonstrate that infrared femtosecond laser pulses with intensity above the two-photon ionization threshold of crystalline silicon induce charge transport through the tunnel oxide in floating gate Metal-Oxide-Semiconductor transistor devices. With repeated irradiations of Flash memory cells, we show how the laser-produced free-electrons naturally redistribute on both sides of the tunnel oxide until the electric field of the transistor is suppressed. This ability enables us to determine in a nondestructive, rapid and contactless way the flat band and the neutral threshold voltages of the tested device. The physical mechanisms including nonlinear ionization, quantum tunneling of free-carriers, and flattening of the band diagram are discussed for interpreting the experiments. The possibility to control the carriers in memory transistors with ultrashort pulses holds promises for fast and remote device analyses (reliability, security, and defectivity) and for considerable developments in the growing field of ultrafast microelectronics.

Pseudo-diode based on protonic/electronic hybrid oxide transistor

NASA Astrophysics Data System (ADS)

Fu, Yang Ming; Liu, Yang Hui; Zhu, Li Qiang; Xiao, Hui; Song, An Ran

2018-01-01

Current rectification behavior has been proved to be essential in modern electronics. Here, a pseudo-diode is proposed based on protonic/electronic hybrid indium-gallium-zinc oxide electric-double-layer (EDL) transistor. The oxide EDL transistors are fabricated by using phosphorous silicate glass (PSG) based proton conducting electrolyte as gate dielectric. A diode operation mode is established on the transistor, originating from field configurable proton fluxes within the PSG electrolyte. Current rectification ratios have been modulated to values ranged between ˜4 and ˜50 000 with gate electrode biased at voltages ranged between -0.7 V and 0.1 V. Interestingly, the proposed pseudo-diode also exhibits field reconfigurable threshold voltages. When the gate is biased at -0.5 V and 0.3 V, threshold voltages are set to ˜-1.3 V and -0.55 V, respectively. The proposed pseudo-diode may find potential applications in brain-inspired platforms and low-power portable systems.

Hillslope run-off thresholds with shrink–swell clay soils

USGS Publications Warehouse

Stewart, Ryan D.; Abou Najm, Majdi R.; Rupp, David E.; Lane, John W.; Uribe, Hamil C.; Arumí, José Luis; Selker, John S.

2015-01-01

Irrigation experiments on 12 instrumented field plots were used to assess the impact of dynamic soil crack networks on infiltration and run-off. During applications of intensity similar to a heavy rainstorm, water was seen being preferentially delivered within the soil profile. However, run-off was not observed until soil water content of the profile reached field capacity, and the apertures of surface-connected cracks had closed >60%. Electrical resistivity measurements suggested that subsurface cracks persisted and enhanced lateral transport, even in wet conditions. Likewise, single-ring infiltration measurements taken before and after irrigation indicated that infiltration remained an important component of the water budget at high soil water content values, despite apparent surface sealing. Overall, although the wetting and sealing of the soil profile showed considerable complexity, an emergent property at the hillslope scale was observed: all of the plots demonstrated a strikingly similar threshold run-off response to the cumulative precipitation amount. 

Effects of various gate materials on electrical degradation of a-Si:H TFT in industrial display application

NASA Astrophysics Data System (ADS)

Ho, Ching-Yuan; Chang, Yaw-Jen

2016-02-01

Both aluminum (Al) and copper (Cu), acting as transmission lines in the hydrogenated amorphous silicon of a thin film transistor (a-Si:H TFT), were studied to investigate electrical degradation including electron-migration (EM) and threshold voltage (Vt) stability and recovery performance. Under long-term current stress, the Cu material exhibited excellent resistance to EM properties, but a passivated SiNx crack was observed due to fast heat conductivity. By applying electrical stress on the gate and drain for 5 × 104 s, the power-law time dependency of the threshold voltage shift (ΔVt) indicated that the defective state creation dominated the TFT device's instability. The presence of drain stress increased the overall ΔVt because the high longitudinal field induced impact ionization and then, enhanced hot-carrier-induced electron trapping within the gate SiNx dielectric. An annealing effect prompted a stressed a-Si:H TFT back to virgin status. This study proposes better ΔVt stability and excellent resistance against electron-migration in a Cu gate device which can be considered as a candidate for a transmission line on prolonged TFT applications.

Design of a tunable graphene plasmonic-on-white graphene switch at infrared range

NASA Astrophysics Data System (ADS)

Farmani, Ali; Zarifkar, Abbas; Sheikhi, Mohammad H.; Miri, Mehdi

2017-12-01

A tunable Y-branch graphene plasmonic switch operating at the wavelength of 1.55 μm is proposed in which graphene is placed on white graphene. The switch structure is investigated analytically and numerically by the finite difference time domain method. The graphene plasmonic switch considered here supports both transverse magnetic and transverse electric graphene plasmons whose propagation characteristics can be controlled by modulating the external electric field and the temperature of graphene. Our calculations show that by strong coupling between the incident waves and the graphene plasmons of the structure, a high polarization extinction ratio of 45 dB and relatively large bandwidth of 150 nm around the central wavelength of 1.55 μm are achievable. Furthermore, the application of white graphene as the substrate of graphene decreases the propagation loss of the graphene plasmons and the required applied electric field. It is also shown that the propagation mode of the graphene plasmons can be tuned by changing the temperature and the calculated threshold temperature is 650 K.

Identifying cochlear implant channels with poor electrode-neuron interface: electrically-evoked auditory brainstem responses measured with the partial tripolar configuration

PubMed Central

Bierer, Julie Arenberg; Faulkner, Kathleen F.; Tremblay, Kelly L.

2011-01-01

Objectives The goal of this study was to compare cochlear implant behavioral measures and electrically-evoked auditory brainstem responses (EABRs) obtained with a spatially focused electrode configuration. It has been shown previously that channels with high thresholds, when measured with the tripolar configuration, exhibit relatively broad psychophysical tuning curves (Bierer and Faulkner, 2010). The elevated threshold and degraded spatial/spectral selectivity of such channels are consistent with a poor electrode-neuron interface, such as suboptimal electrode placement or reduced nerve survival. However, the psychophysical methods required to obtain these data are time intensive and may not be practical during a clinical mapping procedure, especially for young children. Here we have extended the previous investigation to determine if a physiological approach could provide a similar assessment of channel functionality. We hypothesized that, in accordance with the perceptual measures, higher EABR thresholds would correlate with steeper EABR amplitude growth functions, reflecting a degraded electrode-neuron interface. Design Data were collected from six cochlear implant listeners implanted with the HiRes 90k cochlear implant (Advanced Bionics). Single-channel thresholds and most comfortable listening levels were obtained for stimuli that varied in presumed electrical field size by using the partial tripolar configuration, for which a fraction of current (σ) from a center active electrode returns through two neighboring electrodes and the remainder through a distant indifferent electrode. EABRs were obtained in each subject for the two channels having the highest and lowest tripolar (σ=1 or 0.9) behavioral threshold. Evoked potentials were measured with both the monopolar (σ=0) and a more focused partial tripolar (σ ≥ 0.50) configuration. Results Consistent with previous studies, EABR thresholds were highly and positively correlated with behavioral thresholds obtained with both the monopolar and partial tripolar configurations. The Wave V amplitude growth functions with increasing stimulus level showed the predicted effect of shallower growth for the partial tripolar than for the monopolar configuration, but this was observed only for the low threshold channel. In contrast, high-threshold channels showed the opposite effect; steeper growth functions were seen for the partial tripolar configuration. Conclusions These results suggest that behavioral thresholds or EABRs measured with a restricted stimulus can be used to identify potentially impaired cochlear implant channels. Channels having high thresholds and steep growth functions would likely not activate the appropriate spatially restricted region of the cochlea, leading to suboptimal perception. As a clinical tool, quick identification of impaired channels could lead to patient-specific mapping strategies and result in improved speech and music perception. PMID:21178633

Phase-resolved analysis of the susceptibility of pinned spiral waves to far-field pacing in a two-dimensional model of excitable media

PubMed Central

Bittihn, Philip; Squires, Amgad; Luther, Gisa; Bodenschatz, Eberhard; Krinsky, Valentin; Parlitz, Ulrich; Luther, Stefan

2010-01-01

Life-threatening cardiac arrhythmias are associated with the existence of stable and unstable spiral waves. Termination of such complex spatio-temporal patterns by local control is substantially limited by anchoring of spiral waves at natural heterogeneities. Far-field pacing (FFP) is a new local control strategy that has been shown to be capable of unpinning waves from obstacles. In this article, we investigate in detail the FFP unpinning mechanism for a single rotating wave pinned to a heterogeneity. We identify qualitatively different phase regimes of the rotating wave showing that the concept of vulnerability is important but not sufficient to explain the failure of unpinning in all cases. Specifically, we find that a reduced excitation threshold can lead to the failure of unpinning, even inside the vulnerable window. The critical value of the excitation threshold (below which no unpinning is possible) decreases for higher electric field strengths and larger obstacles. In contrast, for a high excitation threshold, the success of unpinning is determined solely by vulnerability, allowing for a convenient estimation of the unpinning success rate. In some cases, we also observe phase resetting in discontinuous phase intervals of the spiral wave. This effect is important for the application of multiple stimuli in experiments. PMID:20368243

Unraveling the mechanism of ultraviolet-induced optical gating in Zn1-x Mg x O nanocrystal solid solution field effect transistors

NASA Astrophysics Data System (ADS)

Kim, Youngjun; Cho, Seongeun; Park, Byoungnam

2018-03-01

We report ultraviolet (UV)-induced optical gating in a Zn1-x Mg x O nanocrystal solid solution (NCSS) field effect transistor (FET) through a systematic study in which UV-induced charge transport properties are probed as a function of Mg composition. Change in the electrical properties of Zn1-x Mg x O NCSS associated with electronic traps is investigated by field effect-modulated current-voltage characteristic curves in the dark and under illumination. Under UV illumination, significant threshold voltage shift to a more negative value in an n-channel Zn1-x Mg x O NCSS FET is observed. Importantly, as the Mg composition increases, the effect of UV illumination on the threshold voltage shift is alleviated. We found that threshold voltage shift as a function of Mg composition in the dark and under illumination is due to difference in the deep trap density in the Zn1-x Mg x O NCSS. This is supported by Mg composition dependent photoluminescence intensity in the visible range and reduced FET mobility with Mg addition. The presence of the deep traps and the corresponding trap energy levels in the Zn1-x Mg x O NCSS are ensured by photoelectron spectroscopy in air.

Charge transport model in solid-state avalanche amorphous selenium and defect suppression design

NASA Astrophysics Data System (ADS)

Scheuermann, James R.; Miranda, Yesenia; Liu, Hongyu; Zhao, Wei

2016-01-01

Avalanche amorphous selenium (a-Se) in a layer of High Gain Avalanche Rushing Photoconductor (HARP) is being investigated for its use in large area medical imagers. Avalanche multiplication of photogenerated charge requires electric fields greater than 70 V μm-1. For a-Se to withstand this high electric field, blocking layers are used to prevent the injection of charge carriers from the electrodes. Blocking layers must have a high injection barrier and deep trapping states to reduce the electric field at the interface. In the presence of a defect in the blocking layer, a distributed resistive layer (DRL) must be included into the structure to build up space charge and reduce the electric field in a-Se and the defect. A numerical charge transport model has been developed to optimize the properties of blocking layers used in various HARP structures. The model shows the incorporation of a DRL functionality into the p-layer can reduce dark current at a point defect by two orders of magnitude by reducing the field in a-Se to the avalanche threshold. Hole mobility in a DRL of ˜10-8 cm2 V-1 s-1 at 100 V μm-1 as demonstrated by the model can be achieved experimentally by varying the hole mobility of p-type organic or inorganic semiconductors through doping, e.g., using Poly(9-vinylcarbozole) doped with 1%-3% (by weight) of poly(3-hexylthiopene).

Impact of electric fields on honey bees

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

Bindokas, V.P.

1985-01-01

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

Models of second-order effects in metal-oxide-semiconductor field-effect transistors for computer applications

NASA Technical Reports Server (NTRS)

Benumof, Reuben; Zoutendyk, John; Coss, James

1988-01-01

Second-order effects in metal-oxide-semiconductor field-effect transistors (MOSFETs) are important for devices with dimensions of 2 microns or less. The short and narrow channel effects and drain-induced barrier lowering primarily affect threshold voltage, but formulas for drain current must also take these effects into account. In addition, the drain current is sensitive to channel length modulation due to pinch-off or velocity saturation and is diminished by electron mobility degradation due to normal and lateral electric fields in the channel. A model of a MOSFET including these considerations and emphasizing charge conservation is discussed.

New Hypotesis of Combined Magnetic Field Action on Gravitropic Reaction

NASA Astrophysics Data System (ADS)

Bogatina, Nina; Sheykina, Nadezhda

2012-07-01

It is shown in the work that all biological effects of combined magnetic field (CMF) may be explained if we take into account the electrical field of cell membrane. We noticed before, that the pressure of starch gain and of calcium ion on membrane were of the one and the same order ~ 10-5 N/ m2. Such a small pressure was supposed not enough to lead to any biological effects. But if we take into account the pressure of calcium ion in electric field of membrane, that is more by many orders, we can see that even very small pressure adding may change the picture. New channels for Ca2+ ions may be opened and the size of channels may be increased. It is shown in the work that such a hypothesis may explain all biological effects of CMF on gravitropic reaction of roots obtained by us before. That were negative gravitropism of roots in CMF tuned on cyclotron resonance of Ca2+ ions, starch gains distribution in cell, noise effects, the threshold effect of static magnetic field and so on.

Redox processes at a nanostructured interface under strong electric fields.

PubMed

Steurer, Wolfram; Surnev, Svetlozar; Netzer, Falko P; Sementa, Luca; Negreiros, Fabio R; Barcaro, Giovanni; Durante, Nicola; Fortunelli, Alessandro

2014-09-21

Manipulation of chemistry and film growth via external electric fields is a longstanding goal in surface science. Numerous systems have been predicted to show such effects but experimental evidence is sparse. Here we demonstrate in a custom-designed UHV apparatus that the application of spatially extended, homogeneous, very high (>1 V nm(-1)) DC-fields not only changes the system energetics but triggers dynamic processes which become important much before static contributions appreciably modify the potential energy landscape. We take a well characterized ultrathin NiO film on a Ag(100) support as a proof-of-principle test case, and show how it gets reduced to supported Ni clusters under fields exceeding the threshold of +0.9 V nm(-1). Using an effective model, we trace the observed interfacial redox process down to a dissociative electron attachment resonant mechanism. The proposed approach can be easily implemented and generally applied to a wide range of interfacial systems, thus opening new opportunities for the manipulation of film growth and reaction processes at solid surfaces under strong external fields.

FIBER AND INTEGRATED OPTICS. OTHER TOPICS IN QUANTUM ELECTRONICS: Monokinetization of atomic beams by the method of laser photodetachment of electrons

NASA Astrophysics Data System (ADS)

Rivlin, Lev A.

1990-05-01

A method is suggested for the generation of atomic beams with a high degree of monokinetization from beams of negative ions accelerated in an electric field up to a threshold moment at which, subject to the Doppler effect, the longitudinal component of the ion velocity becomes sufficient for the photodetachment of an electron from an ion by photons in a laser beam collinear with the ion beam. The resultant neutral atoms continue to move without acceleration and at the same longitudinal velocities equal to the threshold value. An analysis of a number of factors limiting this effect is given below.

Response of Cultured Neuronal Network Activity After High-Intensity Power Frequency Magnetic Field Exposure

PubMed Central

Saito, Atsushi; Takahashi, Masayuki; Makino, Kei; Suzuki, Yukihisa; Jimbo, Yasuhiko; Nakasono, Satoshi

2018-01-01

High-intensity and low frequency (1–100 kHz) time-varying electromagnetic fields stimulate the human body through excitation of the nervous system. In power frequency range (50/60 Hz), a frequency-dependent threshold of the external electric field-induced neuronal modulation in cultured neuronal networks was used as one of the biological indicator in international guidelines; however, the threshold of the magnetic field-induced neuronal modulation has not been elucidated. In this study, we exposed rat brain-derived neuronal networks to a high-intensity power frequency magnetic field (hPF-MF), and evaluated the modulation of synchronized bursting activity using a multi-electrode array (MEA)-based extracellular recording technique. As a result of short-term hPF-MF exposure (50–400 mT root-mean-square (rms), 50 Hz, sinusoidal wave, 6 s), the synchronized bursting activity was increased in the 400 mT-exposed group. On the other hand, no change was observed in the 50–200 mT-exposed groups. In order to clarify the mechanisms of the 400 mT hPF-MF exposure-induced neuronal response, we evaluated it after blocking inhibitory synapses using bicuculline methiodide (BMI); subsequently, increase in bursting activity was observed with BMI application, and the response of 400 mT hPF-MF exposure disappeared. Therefore, it was suggested that the response of hPF-MF exposure was involved in the inhibitory input. Next, we screened the inhibitory pacemaker-like neuronal activity which showed autonomous 4–10 Hz firing with CNQX and D-AP5 application, and it was confirmed that the activity was reduced after 400 mT hPF-MF exposure. Comparison of these experimental results with estimated values of the induced electric field (E-field) in the culture medium revealed that the change in synchronized bursting activity occurred over 0.3 V/m, which was equivalent to the findings of a previous study that used the external electric fields. In addition, the results suggested that the potentiation of neuronal activity after 400 mT hPF-MF exposure was related to the depression of autonomous activity of pacemaker-like neurons. Our results indicated that the synchronized bursting activity was increased by hPF-MF exposure (E-field: >0.3 V/m), and the response was due to reduced inhibitory pacemaker-like neuronal activity. PMID:29662453

Electric and magnetic field exposures for people living near a 735-kilovolt power line.

PubMed Central

Levallois, P; Gauvin, D; St-Laurent, J; Gingras, S; Deadman, J E

1995-01-01

The purpose of this study was to assess the effect of a 735-kV transmission line on the electric and magnetic field exposures of people living at the edge of the line's right of way. Exposure of 18 adults, mostly white-collar workers, living in different bungalows located 190-240 feet from the line (exposed subjects) was compared to that of 17 adults living in similar residences far away from any transmission line. Each subject carried a Positron meter for 24 hr during 1 workday, which measured 60-Hz electric and magnetic fields every minute. All measurements were carried out in parallel for exposed and unexposed subjects during the same weeks between September and December. During measurements the average loading on the line varied between 600 and 1100 A. The average magnetic field intensity while at home was 4.4 times higher among exposed subjects than unexposed (7.1 versus 1.6 mG, p = 0.0001) and 6.2 times higher when considering only the sleeping period (6.8 versus 1.1 mG, p = 0.0001). Based on the 24-hr measurement, average magnetic field exposure was three times higher among the exposed. Electric field intensity was also higher among the exposed while at home (26.3 versus 14.0 V/m, p = 0.03). Magnetic field intensity among the exposed was positively correlated with the loading on the line (r = 0.8, p = 0.001). Percentage of time above a magnetic field threshold (2 mG or 7.8 mG) was a good indicator to distinguish the two types of exposure.(ABSTRACT TRUNCATED AT 250 WORDS) Images Figure 1. PMID:7498095

Hybrid Lead Halide Perovskites for Ultrasensitive Photoactive Switching in Terahertz Metamaterial Devices.

PubMed

Manjappa, Manukumara; Srivastava, Yogesh Kumar; Solanki, Ankur; Kumar, Abhishek; Sum, Tze Chien; Singh, Ranjan

2017-08-01

The recent meteoric rise in the field of photovoltaics with the discovery of highly efficient solar-cell devices is inspired by solution-processed organic-inorganic lead halide perovskites that exhibit unprecedented light-to-electricity conversion efficiencies. The stunning performance of perovskites is attributed to their strong photoresponsive properties that are thoroughly utilized in designing excellent perovskite solar cells, light-emitting diodes, infrared lasers, and ultrafast photodetectors. However, optoelectronic application of halide perovskites in realizing highly efficient subwavelength photonic devices has remained a challenge. Here, the remarkable photoconductivity of organic-inorganic lead halide perovskites is exploited to demonstrate a hybrid perovskite-metamaterial device that shows extremely low power photoswitching of the metamaterial resonances in the terahertz part of the electromagnetic spectrum. Furthermore, a signature of a coupled phonon-metamaterial resonance is observed at higher pump powers, where the Fano resonance amplitude is extremely weak. In addition, a low threshold, dynamic control of the highly confined electric field intensity is also observed in the system, which could tremendously benefit the new generation of subwavelength photonic devices as active sensors, low threshold optically controlled lasers, and active nonlinear devices with enhanced functionalities in the infrared, optical, and the terahertz parts of the electromagnetic spectrum. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Cortical activation following chronic passive implantation of a wide-field suprachoroidal retinal prosthesis

NASA Astrophysics Data System (ADS)

Villalobos, Joel; Fallon, James B.; Nayagam, David A. X.; Shivdasani, Mohit N.; Luu, Chi D.; Allen, Penelope J.; Shepherd, Robert K.; Williams, Chris E.

2014-08-01

Objective. The research goal is to develop a wide-field retinal stimulating array for prosthetic vision. This study aimed at evaluating the efficacy of a suprachoroidal electrode array in evoking visual cortex activity after long term implantation. Approach. A planar silicone based electrode array (8 mm × 19 mm) was implanted into the suprachoroidal space in cats (ntotal = 10). It consisted of 20 platinum stimulating electrodes (600 μm diameter) and a trans-scleral cable terminated in a subcutaneous connector. Three months after implantation (nchronic = 6), or immediately after implantation (nacute = 4), an electrophysiological study was performed. Electrode total impedance was measured from voltage transients using 500 μs, 1 mA pulses. Electrically evoked potentials (EEPs) and multi-unit activity were recorded from the visual cortex in response to monopolar retinal stimulation. Dynamic range and cortical activation spread were calculated from the multi-unit recordings. Main results. The mean electrode total impedance in vivo following 3 months was 12.5 ± 0.3 kΩ. EEPs were recorded for 98% of the electrodes. The median evoked potential threshold was 150 nC (charge density 53 μC cm-2). The lowest stimulation thresholds were found proximal to the area centralis. Mean thresholds from multiunit activity were lower for chronic (181 ± 14 nC) compared to acute (322 ± 20 nC) electrodes (P < 0.001), but there was no difference in dynamic range or cortical activation spread. Significance. Suprachoroidal stimulation threshold was lower in chronic than acute implantation and was within safe charge limits for platinum. Electrode-tissue impedance following chronic implantation was higher, indicating the need for sufficient compliance voltage (e.g. 12.8 V for mean impedance, threshold and dynamic range). The wide-field suprachoroidal array reliably activated the retina after chronic implantation.

A novel thin-film transistor with step gate-overlapped lightly doped drain and raised source/drain design

NASA Astrophysics Data System (ADS)

Chien, Feng-Tso; Chen, Jian-Liang; Chen, Chien-Ming; Chen, Chii-Wen; Cheng, Ching-Hwa; Chiu, Hsien-Chin

2017-11-01

In this paper, a novel step gate-overlapped lightly doped drain (GOLDD) with raised source/drain (RSD) structure (SGORSD) is proposed for TFT electronic device application. The new SGORSD structure could obtain a low electric field at channel near the drain side owing to a step GOLDD design. Compared to the conventional device, the SGORSD TFT exhibits a better kink effect and higher breakdown performance due to the reduced drain electric field (D-EF). In addition, the leakage current also can be suppressed. Moreover, the device stability, such as the threshold voltage shift and drain current degradation under a high gate bias, is improved by the design of SGORSD structure. Therefore, this novel step GOLDD structure can be a promising design to be used in active-matrix flat panel electronics.

Electrical injection Ga(AsBi)/(AlGa)As single quantum well laser

NASA Astrophysics Data System (ADS)

Ludewig, P.; Knaub, N.; Hossain, N.; Reinhard, S.; Nattermann, L.; Marko, I. P.; Jin, S. R.; Hild, K.; Chatterjee, S.; Stolz, W.; Sweeney, S. J.; Volz, K.

2013-06-01

The Ga(AsBi) material system opens opportunities in the field of high efficiency infrared laser diodes. We report on the growth, structural investigations, and lasing properties of dilute bismide Ga(AsBi)/(AlGa)As single quantum well lasers with 2.2% Bi grown by metal organic vapor phase epitaxy on GaAs (001) substrates. Electrically injected laser operation at room temperature is achieved with a threshold current density of 1.56 kA/cm2 at an emission wavelength of ˜947 nm. These results from broad area devices show great promise for developing efficient IR laser diodes based on this emerging materials system.

Asymmetrical electrically induced injury of rabbit ventricular myocytes.

PubMed

Knisley, S B; Grant, A O

1995-05-01

Strong defibrillation-type electric field stimulation may injure myocytes when transmembrane potentials during the pulse exceed the threshold for membrane permeabilization. The location of injury may depend on intrinsic transmembrane potential or influx of calcium by "electro-osmosis" during the stimulation pulse in addition to the transmembrane potential changes induced by the pulse. We have studied injury by examining contracture and changes in transmembrane potential-sensitive dye fluorescence induced by electric field stimulation (St) with a duration of 20 ms and strength of 16-400 V/cm in isolated rabbit ventricular myocytes. St of 100-150 V/cm produced injury in myocytes oriented parallel to the St field frequently without injuring myocytes oriented perpendicular to the field. Injury required calcium in the solution and was asymmetric, occurring first at the myocyte and facing the St anode in 100% of injured myocytes in normal Tyrode's solution. Injury depended significantly on whether the product of the electric field strength and myocyte length exceeded a threshold of 1.1 V (P < 0.05). Asymmetric injury at the end facing the anode was still present in 96% of injured myocytes for stimulation after depolarization by an action potential or 20 mM or 125 mM potassium, suggesting that intrinsic transmembrane potential is not responsible for asymmetry. In 125 mM potassium, eliminating calcium from the bathing solution during the St pulse and introducing calcium after the pulse decreased the fraction of injured myocytes in which injury occurred at the end facing the anode to 62%, suggesting that calcium influx by "electro-osmosis" at the myocyte end facing the anode contributes to asymmetry. Asymmetric injury at the end facing the anode was still present in 100% of injured myocytes after adding 1 mM tetraethylammonium chloride, indicating that asymmetry is not sensitive to the potassium channel blockade. For stimulation pulses stronger than 50 V/cm given after depolarization by an action potential, transmembrane potentials at both myocyte ends decayed after the initial deflection indicating that permeabilization occurred at both ends. In conclusion, injury depends on myocyte orientation and is asymmetric occurring first at the myocyte end facing the anode. Asymmetric injury is not explained by asymmetric permeabilization, is independent of the intrinsic transmembrane potential and may result from "electro-osmosis" during the stimulation pulse.

Facial arthralgia and myalgia: can they be differentiated by trigeminal sensory assessment?

PubMed

Eliav, Eli; Teich, Sorin; Nitzan, Dorit; El Raziq, Daood Abid; Nahlieli, Oded; Tal, Michael; Gracely, Richard H; Benoliel, Rafael

2003-08-01

Heat and electrical detection thresholds were assessed in 72 patients suffering from painful temporomandibular disorder. Employing widely accepted criteria, 44 patients were classified as suffering from temporomandibular joint (TMJ) arthralgia (i.e. pain originating from the TMJ) and 28 from myalgia (i.e. pain originating from the muscles of mastication). Electrical stimulation was employed to assess thresholds in large myelinated nerve fibers (Abeta) and heat application to assess thresholds in unmyelinated nerve fibers (C). The sensory tests were performed bilaterally in three trigeminal nerve sites: the auriculotemporal nerve territory (AUT), buccal nerve territory (BUC) and the mental nerve territory (MNT). In addition, 22 healthy asymptomatic controls were examined. A subset of ten arthralgia patients underwent arthrocentesis and electrical detection thresholds were additionally assessed following the procedure. Electrical detection threshold ratios were calculated by dividing the affected side by the control side, thus reduced ratios indicate hypersensitivity of the affected side. In control patients, ratios obtained at all sites did not vary significantly from the expected value of 'one' (mean with 95% confidence intervals; AUT, 1:0.95-1.06; BUC, 1.01:0.93-1.11; MNT, 0.97:0.88-1.05, all areas one sample analysis P>0.05). In arthralgia patients mean ratios (+/-SEM) obtained for the AUT territory (0.63+/-0.03) were significantly lower compared to ratios for the MNT (1.02+/-0.03) and BUC (0.96+/-0.04) territories (repeated measures analysis of variance (RANOVA), P<0.0001) and compared to the AUT ratios in myalgia (1.27+/-0.09) and control subjects (1+/-0.06, ANOVA, P<0.0001). In the myalgia group the electrical detection threshold ratios in the AUT territory were significantly elevated compared to the AUT ratios in control subjects (Dunnett test, P<0.05), but only approached statistical significance compared to the MNT (1.07+/-0.04) and BUC (1.11+/-0.06) territories (RANOVA, F(2,27)=3.12, P=0.052). There were no significant differences between and within the groups for electrical detection threshold ratios in the BUC and MNT nerve territories, and for the heat detection thresholds in all tested sites. Following arthrocentesis, mean electrical detection threshold ratios in the AUT territory were significantly elevated from 0.64+/-0.06 to 0.99+/-0.04 indicating resolution of the hypersensitivity (paired t-test, P=0.001). In conclusion, large myelinated fiber hypersensitivity is found in the skin overlying TMJs with clinical pain and pathology but is not found in controls. In patients with muscle-related facial pain there was significant elevation of the electrical detection threshold in the AUT region.

AC electrified jets in a flow-focusing device: Jet length scaling

PubMed Central

García-Sánchez, Pablo; Alzaga-Gimeno, Javier; Baret, Jean-Christophe

2016-01-01

We use a microfluidic flow-focusing device with integrated electrodes for controlling the production of water-in-oil drops. In a previous work, we reported that very long jets can be formed upon application of AC fields. We now study in detail the appearance of the long jets as a function of the electrical parameters, i.e., water conductivity, signal frequency, and voltage amplitude. For intermediate frequencies, we find a threshold voltage above which the jet length rapidly increases. Interestingly, this abrupt transition vanishes for high frequencies of the signal and the jet length grows smoothly with voltage. For frequencies below a threshold value, we previously reported a transition from a well-behaved uniform jet to highly unstable liquid structures in which axisymmetry is lost rather abruptly. These liquid filaments eventually break into droplets of different sizes. In this work, we characterize this transition with a diagram as a function of voltage and liquid conductivity. The electrical response of the long jets was studied via a distributed element circuit model. The model allows us to estimate the electric potential at the tip of the jet revealing that, for any combination of the electrical parameters, the breakup of the jet occurs at a critical value of this potential. We show that this voltage is around 550 V for our device geometry and choice of flow rates. PMID:27375826

AC electrified jets in a flow-focusing device: Jet length scaling.

PubMed

Castro-Hernández, Elena; García-Sánchez, Pablo; Alzaga-Gimeno, Javier; Tan, Say Hwa; Baret, Jean-Christophe; Ramos, Antonio

2016-07-01

We use a microfluidic flow-focusing device with integrated electrodes for controlling the production of water-in-oil drops. In a previous work, we reported that very long jets can be formed upon application of AC fields. We now study in detail the appearance of the long jets as a function of the electrical parameters, i.e., water conductivity, signal frequency, and voltage amplitude. For intermediate frequencies, we find a threshold voltage above which the jet length rapidly increases. Interestingly, this abrupt transition vanishes for high frequencies of the signal and the jet length grows smoothly with voltage. For frequencies below a threshold value, we previously reported a transition from a well-behaved uniform jet to highly unstable liquid structures in which axisymmetry is lost rather abruptly. These liquid filaments eventually break into droplets of different sizes. In this work, we characterize this transition with a diagram as a function of voltage and liquid conductivity. The electrical response of the long jets was studied via a distributed element circuit model. The model allows us to estimate the electric potential at the tip of the jet revealing that, for any combination of the electrical parameters, the breakup of the jet occurs at a critical value of this potential. We show that this voltage is around 550 V for our device geometry and choice of flow rates.

Void structure of O+ ions in the inner magnetosphere observed by the Van Allen Probes

NASA Astrophysics Data System (ADS)

Nakayama, Y.; Ebihara, Y.; Ohtani, S.; Gkioulidou, M.; Takahashi, K.; Kistler, L. M.; Tanaka, T.

2016-12-01

The Van Allen Probes Helium Oxygen Proton Electron instrument observed a new type of enhancement of O+ ions in the inner magnetosphere during substorms. As the satellite moved outward in the premidnight sector, the flux of the O+ ions with energy 10 keV appeared first in the energy-time spectrograms. Then, the enhancement of the flux spread toward high and low energies. The enhanced flux of the O+ ions with the highest energy remained, whereas the flux of the ions with lower energy vanished near apogee, forming what we call the void structure. The structure cannot be found in the H+ spectrogram. We studied the generation mechanism of this structure by using numerical simulation. We traced the trajectories of O+ ions in the electric and magnetic fields from the global magnetohydrodynamics simulation and calculated the flux of O+ ions in the inner magnetosphere in accordance with the Liouville theorem. The simulated spectrograms are well consistent with the ones observed by Van Allen Probes. We suggest the following processes. (1) When magnetic reconnection starts, an intensive equatorward and tailward plasma flow appears in the plasma lobe. (2) The flow transports plasma from the lobe to the plasma sheet where the radius of curvature of the magnetic field line is small. (3) The intensive dawn-dusk electric field transports the O+ ions earthward and accelerates them nonadiabatically to an energy threshold; (4) the void structure appears at energies below the threshold.

Influence of different frequencies of transcutaneous electrical nerve stimulation on the threshold and pain intensity in young subjects

PubMed Central

Gomes, Adriana de Oliveira; Silvestre, Ana Caroline; da Silva, Cristina Ferreira; Gomes, Mariany Ribeiro; Bonfleur, Maria Lúcia; Bertolini, Gladson Ricardo Flor

2014-01-01

Objective To investigate the effects of different transcutaneous electrical nerve stimulation frequencies in nociception front of a pressure pain threshold and cold in healthy individuals. Methods Twenty healthy subjects were divided into four groups, all of which have gone through all forms of electrical stimulation at different weeks. Assessments were pre and post-therapy, 20 and 60 minutes after stimulation. To evaluate the pressure pain threshold, an algometer was used with one tapered tip, pressing the hypothenar region until voluntary report the word “pain”. Cold pain intensity was assessed by immersion in water at 5°C for 30 seconds; at the end, the subject was asked to quantify the pain intensity on a Visual Analog Scale for Pain. For electrical stimulation, two electrodes were used near the elbow, for 20 minutes, with an intensity strong, but not painful. The frequency was in accordance with the group: 0Hz (placebo); 7Hz; 100Hz; and 255Hz. Results Both for the assessment of pressure pain threshold as the cold pain intensity, there was no significant difference (p>0.05). Conclusion We conclude that the use of transcutaneous electrical nerve stimulation on dermatomes C6 to C8 produced no significant change in pressure pain threshold or cold discomfort. PMID:25295453

Thresholds of arsenic toxicity to Eisenia fetida in field-collected agricultural soils exposed to copper mining activities in Chile.

PubMed

Bustos, Víctor; Mondaca, Pedro; Verdejo, José; Sauvé, Sébastien; Gaete, Hernán; Celis-Diez, Juan L; Neaman, Alexander

2015-12-01

Several previous studies highlighted the importance of using field-collected soils-and not artificially-contaminated soils-for ecotoxicity tests. However, the use of field-collected soils presents several difficulties for interpretation of results, due to the presence of various contaminants and unavoidable differences in the physicochemical properties of the tested soils. The objective of this study was to estimate thresholds of metal toxicity in topsoils of 24 agricultural areas historically contaminated by mining activities in Chile. We performed standardized earthworm reproduction tests (OECD 222 and ISO 11268-2) with Eisenia fetida. Total soil concentrations of Cu, As, Zn, and Pb were in the ranges of 82-1295 mg kg(-1), 7-41 mg kg(-1), 86-345 mg kg(-1), and 25-97 mg kg(-1), respectively. In order to differentiate between the effects of different metals, we used regression analysis between soil metal concentrations and earthworm responses, as well as between metal concentrations in earthworm tissues and earthworm responses. Based on regression analysis, we concluded that As was a metal of prime concern for Eisenia fetida in soils affected by Cu mining activities, while Cu exhibited a secondary effect. In contrast, the effects of Zn and Pb were not significant. Soil electrical conductivity was another significant contributor to reproduction toxicity in the studied soils, forcing its integration in the interpretation of the results. By using soils with electrical conductivity ≤ 0.29 dS m(-1) (which corresponds to EC50 of salt toxicity to Eisenia fetida), it was possible to isolate the effect of soil salinity on earthworm reproduction. Despite the confounding effects of Cu, it was possible to determine EC10, EC25 and EC50 values for total soil As at 8 mg kg(-1), 14 mg kg(-1) and 22 mg kg(-1), respectively, for the response of the cocoon production. However, it was not possible to determine these threshold values for juvenile production. Likewise, we were able to determine EC10, EC25 and EC50 of earthworm tissue As of 38 mg kg(-1), 47 mg kg(-1), and 57 mg kg(-1), respectively, for the response of the cocoon production. Finally, we determined the no-observed effect concentration of tissue As in E. fetida of 24 mg kg(-1). Thus, earthworm reproduction test is applicable for assessment of metal toxicity in field-collected soils with low electrical conductivity, while it might have a limited applicability in soils with high electrical conductivity because the salinity-induced toxicity will hinder the interpretation of the results. Copyright © 2015 Elsevier Inc. All rights reserved.

Electric Current Activated Combustion Synthesis and Chemical Ovens Under Terrestrial and Reduced Gravity Conditions

NASA Technical Reports Server (NTRS)

Unuvar, C.; Fredrick, D.; Anselmi-Tamburini, U.; Manerbino, A.; Guigne, J. Y.; Munir, Z. A.; Shaw, B. D.

2004-01-01

Combustion synthesis (CS) generally involves mixing reactants together (e.g., metal powders) and igniting the mixture. Typically, a reaction wave will pass through the sample. In field activated combustion synthesis (FACS), the addition of an electric field has a marked effect on the dynamics of wave propagation and on the nature, composition, and homogeneity of the product as well as capillary flow, mass-transport in porous media, and Marangoni flows, which are influenced by gravity. The objective is to understand the role of an electric field in CS reactions under conditions where gravity-related effects are suppressed or altered. The systems being studied are Ti+Al and Ti+3Al. Two different ignition orientations have been used to observe effects of gravity when one of the reactants becomes molten. This consequentially influences the position and concentration of the electric current, which in turn influences the entire process. Experiments have also been performed in microgravity conditions. This process has been named Microgravity Field Activated Combustion Synthesis (MFACS). Effects of gravity have been demonstrated, where the reaction wave temperature and velocity demonstrate considerable differences besides the changes of combustion mechanisms with the different high currents applied. Also the threshold for the formation of a stable reaction wave is increased under zero gravity conditions. Electric current was also utilized with a chemical oven technique, where inserts of aluminum with minute amounts of tungsten and tantalum were used to allow observation of effects of settling of the higher density solid particles in liquid aluminum at the present temperature profile and wave velocity of the reaction.

Ion transport and softening in a polymerized ionic liquid

DOE PAGES

Kumar, Rajeev; Bocharova, Vera; Strelcov, Evgheni; ...

2014-11-13

Polymerized ionic liquids (PolyILs) are promising materials for various solid state electronic applications such as dye-sensitized solar cells, lithium batteries, actuators, field-effect transistors, light emitting electrochemical cells, and electrochromic devices. However, fundamental understanding of interconnection between ionic transport and mechanical properties in PolyILs is far from complete. In this paper, local charge transport and structural changes in films of a PolyIL are studied using an integrated experiment-theory based approach. Experimental data for the kinetics of charging and steady state current–voltage relations can be explained by taking into account the dissociation of ions under an applied electric field (known as themore » Wien effect). Onsager's theory of the Wien effect coupled with the Poisson–Nernst–Planck formalism for the charge transport is found to be in excellent agreement with the experimental results. The agreement between the theory and experiments allows us to predict structural properties of the PolyIL films. We have observed significant softening of the PolyIL films beyond certain threshold voltages and formation of holes under a scanning probe microscopy (SPM) tip, through which an electric field was applied. Finally, the observed softening is explained by the theory of depression in glass transition temperature resulting from enhanced dissociation of ions with an increase in applied electric field.« less

CRF-PEPICO: Double velocity map imaging photoelectron photoion coincidence spectroscopy for reaction kinetics studies

NASA Astrophysics Data System (ADS)

Sztáray, Bálint; Voronova, Krisztina; Torma, Krisztián G.; Covert, Kyle J.; Bodi, Andras; Hemberger, Patrick; Gerber, Thomas; Osborn, David L.

2017-07-01

Photoelectron photoion coincidence (PEPICO) spectroscopy could become a powerful tool for the time-resolved study of multi-channel gas phase chemical reactions. Toward this goal, we have designed and tested electron and ion optics that form the core of a new PEPICO spectrometer, utilizing simultaneous velocity map imaging for both cations and electrons, while also achieving good cation mass resolution through space focusing. These optics are combined with a side-sampled, slow-flow chemical reactor for photolytic initiation of gas-phase chemical reactions. Together with a recent advance that dramatically increases the dynamic range in PEPICO spectroscopy [D. L. Osborn et al., J. Chem. Phys. 145, 164202 (2016)], the design described here demonstrates a complete prototype spectrometer and reactor interface to carry out time-resolved experiments. Combining dual velocity map imaging with cation space focusing yields tightly focused photoion images for translationally cold neutrals, while offering good mass resolution for thermal samples as well. The flexible optics design incorporates linear electric fields in the ionization region, surrounded by dual curved electric fields for velocity map imaging of ions and electrons. Furthermore, the design allows for a long extraction stage, which makes this the first PEPICO experiment to combine ion imaging with the unimolecular dissociation rate constant measurements of cations to detect and account for kinetic shifts. Four examples are shown to illustrate some capabilities of this new design. We recorded the threshold photoelectron spectrum of the propargyl and the iodomethyl radicals. While the former agrees well with a literature threshold photoelectron spectrum, we have succeeded in resolving the previously unobserved vibrational structure in the latter. We have also measured the bimolecular rate constant of the CH2I + O2 reaction and observed its product, the smallest Criegee intermediate, CH2OO. Finally, the second dissociative photoionization step of iodocyclohexane ions, the loss of ethylene from the cyclohexyl cation, is slow at threshold, as illustrated by the asymmetric threshold photoionization time-of-flight distributions.

Cell separation using electric fields

NASA Technical Reports Server (NTRS)

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

2003-01-01

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

A novel electrostatic precipitator

NASA Astrophysics Data System (ADS)

Tang, Minkang; Wang, Liqian; Lin, Zhigui

2013-03-01

ESP (Electrostatic Precipitation) has been widely used in the mining, building materials, metallurgy and power industries. Dust particles or other harmful particles from the airstream can be precipitated by ESP with great collecting efficiency. Because of its' large size, high cost and energy consumption, the scope of application of ESP has been limited to a certain extent. By means of the theory of electrostatics and fluid dynamics, a corona assembly with a self-cleaning function and a threshold voltage automatic tracking technology has been developed and used in ESP. It is indicated that compared with conventional ESP, the electric field length has been reduced to 1/10 of the original, the current density on the collecting electrode increased 3-5 times at the maximum, the approach speed of dust particles in the electric field towards the collecting electrode is 4 times that in conventional ESP and the electric field wind speed may be enhanced by 2-3 times the original. Under the premise of ESP having a high efficiency of dust removal, equipment volume may be actually reduced to 1/5 to 1/10 of the original volume and energy consumption may be reduced by more than 50%.

Cell separation using electric fields

NASA Technical Reports Server (NTRS)

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

2009-01-01

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

Resistive switching phenomena: A review of statistical physics approaches

DOE PAGES

Lee, Jae Sung; Lee, Shinbuhm; Noh, Tae Won

2015-08-31

Here we report that resistive switching (RS) phenomena are reversible changes in the metastable resistance state induced by external electric fields. After discovery ~50 years ago, RS phenomena have attracted great attention due to their potential application in next-generation electrical devices. Considerable research has been performed to understand the physical mechanisms of RS and explore the feasibility and limits of such devices. There have also been several reviews on RS that attempt to explain the microscopic origins of how regions that were originally insulators can change into conductors. However, little attention has been paid to the most important factor inmore » determining resistance: how conducting local regions are interconnected. Here, we provide an overview of the underlying physics behind connectivity changes in highly conductive regions under an electric field. We first classify RS phenomena according to their characteristic current–voltage curves: unipolar, bipolar, and threshold switchings. Second, we outline the microscopic origins of RS in oxides, focusing on the roles of oxygen vacancies: the effect of concentration, the mechanisms of channel formation and rupture, and the driving forces of oxygen vacancies. Third, we review RS studies from the perspective of statistical physics to understand connectivity change in RS phenomena. We discuss percolation model approaches and the theory for the scaling behaviors of numerous transport properties observed in RS. Fourth, we review various switching-type conversion phenomena in RS: bipolar-unipolar, memory-threshold, figure-of-eight, and counter-figure-of-eight conversions. Finally, we review several related technological issues, such as improvement in high resistance fluctuations, sneak-path problems, and multilevel switching problems.« less

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

Lee, Jae Sung; Lee, Shinbuhm; Noh, Tae Won

Here we report that resistive switching (RS) phenomena are reversible changes in the metastable resistance state induced by external electric fields. After discovery ~50 years ago, RS phenomena have attracted great attention due to their potential application in next-generation electrical devices. Considerable research has been performed to understand the physical mechanisms of RS and explore the feasibility and limits of such devices. There have also been several reviews on RS that attempt to explain the microscopic origins of how regions that were originally insulators can change into conductors. However, little attention has been paid to the most important factor inmore » determining resistance: how conducting local regions are interconnected. Here, we provide an overview of the underlying physics behind connectivity changes in highly conductive regions under an electric field. We first classify RS phenomena according to their characteristic current–voltage curves: unipolar, bipolar, and threshold switchings. Second, we outline the microscopic origins of RS in oxides, focusing on the roles of oxygen vacancies: the effect of concentration, the mechanisms of channel formation and rupture, and the driving forces of oxygen vacancies. Third, we review RS studies from the perspective of statistical physics to understand connectivity change in RS phenomena. We discuss percolation model approaches and the theory for the scaling behaviors of numerous transport properties observed in RS. Fourth, we review various switching-type conversion phenomena in RS: bipolar-unipolar, memory-threshold, figure-of-eight, and counter-figure-of-eight conversions. Finally, we review several related technological issues, such as improvement in high resistance fluctuations, sneak-path problems, and multilevel switching problems.« less

Determination of silica deposition rates and thresholds applied towards protection of injection reservoirs

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

Geothermal Development Associates; Don Michels Associates

1999-07-01

This program was instituted to quantify certain aspects of silica scaling deposition processes at the Miravalles Geothermal Field, Costa Rica. The program objective was to identify the highest temperature at which silica scale will develop from partially evaporated and significantly cooled geothermal liquid under operating conditions. Integral to the study objective was the quantification of certain aspects of silica deposition processes at the Miravalles Geothermal Field, Costa Rica. There, the objective was to reduce the scaling risk associated with adding a bottoming-cycle to generate more electricity from the liquids already being produced.

Significance of the gate voltage-dependent mobility in the electrical characterization of organic field effect transistors

NASA Astrophysics Data System (ADS)

Kim, Jong Beom; Lee, Dong Ryeol

2018-04-01

We studied the effect of the addition of free hole- and electron-rich organic molecules to organic semiconductors (OSCs) in organic field effect transistors (OFETs) on the gate voltage-dependent mobility. The drain current versus gate voltage characteristics were quantitatively analyzed using an OFET mobility model of power law behavior based on hopping transport in an OSC. This analysis distinguished the threshold voltage shifts, depending on the materials and structures of the OFET device, and properly estimated the hopping transport of the charge carriers induced by the gate bias within the OSC from the power law exponent parameter. The addition of pentacene or C60 molecules to a one-monolayer pentacene-based OFET shifted the threshold voltages negatively or positively, respectively, due to the structural changes that occurred in the OFET device. On the other hand, the power law parameters revealed that the addition of charge carriers of the same or opposite polarity enhanced or hindered hopping transport, respectively. This study revealed the need for a quantitative analysis of the gate voltage-dependent mobility while distinguishing this effect from the threshold voltage effect in order to understand OSC hopping transport in OFETs.

Polymer composites with graphene nanofillers: electrical properties and applications.

PubMed

Tjong, Sie Chin

2014-02-01

Graphene with extraordinary high elastic modulus and excellent electrical conductivity has good prospects for use as the filler material for fabricating novel polymer composites designed for electrostatic discharge and EMI shielding protection, field emission, gas sensor, and fuel cell applications. Large amounts of graphene oxide (GO) can be obtained by wet chemical oxidation of graphite into a mixture of concentrated sulfuric acid, sodium nitrate and potassium permanganate. Accordingly, carbon atoms in the basal plane and edges of GO are decorated with oxygenated functional groups, forming an electrical insulator. To restore electrical conductivity, chemical reduction or thermal annealing is needed to eliminate oxygenated groups of GO. However, such treatments induce internal defects and remove oxygenated atoms of GO partially. The remnant-oxygenated groups affect electrical conductivity of graphene greatly. Nevertheless, reduced graphene oxide and thermally reduced graphene oxide are sufficiently conductive to form polymer nanocomposites at very low percolation threshold. This review provides the fundamentals and state-of-the-art developments in the fabrication methods and electrical property characterizations as well as the applications of novel graphene/polymer nanocomposites. Particular attention is paid to their processing-structural-electrical property relationships.

Electroporation of DC-3F cells is a dual process.

PubMed

Wegner, Lars H; Frey, Wolfgang; Silve, Aude

2015-04-07

Treatment of biological material by pulsed electric fields is a versatile technique in biotechnology and biomedicine used, for example, in delivering DNA into cells (transfection), ablation of tumors, and food processing. Field exposure is associated with a membrane permeability increase usually ascribed to electroporation, i.e., formation of aqueous membrane pores. Knowledge of the underlying processes at the membrane level is predominantly built on theoretical considerations and molecular dynamics (MD) simulations. However, experimental data needed to monitor these processes with sufficient temporal resolution are scarce. The whole-cell patch-clamp technique was employed to investigate the effect of millisecond pulsed electric fields on DC-3F cells. Cellular membrane permeabilization was monitored by a conductance increase. For the first time, to our knowledge, it could be established experimentally that electroporation consists of two clearly separate processes: a rapid membrane poration (transient electroporation) that occurs while the membrane is depolarized or hyperpolarized to voltages beyond so-called threshold potentials (here, +201 mV and -231 mV, respectively) and is reversible within ∼100 ms after the pulse, and a long-term, or persistent, permeabilization covering the whole voltage range. The latter prevailed after the pulse for at least 40 min, the postpulse time span tested experimentally. With mildly depolarizing or hyperpolarizing pulses just above threshold potentials, the two processes could be separated, since persistent (but not transient) permeabilization required repetitive pulse exposure. Conductance increased stepwise and gradually with depolarizing and hyperpolarizing pulses, respectively. Persistent permeabilization could also be elicited by single depolarizing/hyperpolarizing pulses of very high field strength. Experimental measurements of propidium iodide uptake provided evidence of a real membrane phenomenon, rather than a mere patch-clamp artifact. In short, the response of DC-3F cells to strong pulsed electric fields was separated into a transient electroporation and a persistent permeabilization. The latter dominates postpulse membrane properties but to date has not been addressed by electroporation theory or MD simulations. Copyright © 2015 Biophysical Society. Published by Elsevier Inc. All rights reserved.

Electrical guidance efficiency of downstream-migrating juvenile Sea Lamprey decreases with increasing water velocity

USGS Publications Warehouse

Miehls, Scott M.; Johnson, Nicholas; Haro, Alexander

2017-01-01

We tested the efficacy of a vertically oriented field of pulsed direct current (VEPDC) created by an array of vertical electrodes for guiding downstream-moving juvenile Sea Lampreys Petromyzon marinus to a bypass channel in an artificial flume at water velocities of 10–50 cm/s. Sea Lampreys were more likely to be captured in the bypass channel than in other sections of the flume regardless of electric field status (on or off) or water velocity. Additionally, Sea Lampreys were more likely to be captured in the bypass channel when the VEPDC was active; however, an interaction between the effects of VEPDC and water velocity was observed, as the likelihood of capture decreased with increases in water velocity. The distribution of Sea Lampreys shifted from right to left across the width of the flume toward the bypass channel when the VEPDC was active at water velocities less than 25 cm/s. The VEPDC appeared to have no effect on Sea Lamprey distribution in the flume at water velocities greater than 25 cm/s. We also conducted separate tests to determine the threshold at which Sea Lampreys would become paralyzed. Individuals were paralyzed at a mean power density of 37.0 µW/cm3. Future research should investigate the ability of juvenile Sea Lampreys to detect electric fields and their specific behavioral responses to electric field characteristics so as to optimize the use of this technology as a nonphysical guidance tool across variable water velocities.

Engineering of oriented myocardium on three-dimensional micropatterned collagen-chitosan hydrogel.

PubMed

Chiu, Loraine L Y; Janic, Katarina; Radisic, Milica

2012-04-30

Surface topography and electrical field stimulation are important guidance cues that aid the organization and contractility of cardiomyocytes in vivo. We report here on the use of these biomimetic cues in vitro to engineer an implantable contractile cardiac tissue. Photocrosslinkable collagen-chitosan hydrogels with microgrooves of 10 µm, 20 µm and 100 µm in width were fabricated using polydimethylsiloxane (PDMS) molds. The hydrogels were seeded with cardiomyocytes, placed into a bioreactor array with the microgrooves aligned with the electrical field lines, and stimulated with biphasic square pulses at 1 Hz and 2.5 V/cm. At Day 6, cardiomyocytes were aligned in the direction of the microgrooves. When cultivated without electrical stimulation, the excitation threshold of engineered cardiac tissues using micropatterned hydrogels was significantly lower than using smooth hydrogels, thus showing the importance of cell alignment to cardiac function. The success rate of achieving beating constructs was higher with the application of electrical stimulation. In addition, formation of dense contractile cardiac organoids was observed in groups with both biomimetic cues. The cultivation of cardiomyocytes on hydrogels with 10 µm grooves yielded 100% beating tissues with or without electrical stimulation, thus suggesting a smaller groove width is necessary for cells to communicate and form proper gap junctions. However, electrical field stimulation further increased cell density and enhanced tissue morphology which may be essential for the integration of the tissue construct to the native heart tissue upon implantation. The biodegradability of the hydrogel substrate allows for the rapid translation of the engineered, oriented cardiac tissue to clinical applications.

Changes in ganglion cell physiology during retinal degeneration influence excitability by prosthetic electrodes

NASA Astrophysics Data System (ADS)

Cho, Alice; Ratliff, Charles; Sampath, Alapakkam; Weiland, James

2016-04-01

Objective. Here we investigate ganglion cell physiology in healthy and degenerating retina to test its influence on threshold to electrical stimulation. Approach. Age-related Macular Degeneration and Retinitis Pigmentosa cause blindness via outer retinal degeneration. Inner retinal pathways that transmit visual information to the central brain remain intact, so direct electrical stimulation from prosthetic devices offers the possibility for visual restoration. Since inner retinal physiology changes during degeneration, we characterize physiological properties and responses to electrical stimulation in retinal ganglion cells (RGCs) of both wild type mice and the rd10 mouse model of retinal degeneration. Main results. Our aggregate results support previous observations that elevated thresholds characterize diseased retinas. However, a physiology-driven classification scheme reveals distinct sub-populations of ganglion cells with thresholds either normal or strongly elevated compared to wild-type. When these populations are combined, only a weakly elevated threshold with large variance is observed. The cells with normal threshold are more depolarized at rest and exhibit periodic oscillations. Significance. During degeneration, physiological changes in RGCs affect the threshold stimulation currents required to evoke action potentials.

The Fano-type transmission and field enhancement in heterostructures composed of epsilon-near-zero materials and truncated photonic crystals

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

Zhang, Zhi-fang; Jiang, Hai-tao, E-mail: davies2000@163.com, E-mail: jiang-haitao@tongji.edu.cn; Li, Yun-hui

2013-11-11

The Fano-type interference effect is studied in the heterostructure composed of an epsilon-near-zero (ENZ) material and a truncated photonic crystal for transverse magnetic polarized light. In the Fano-type interference effect, the ENZ material provides narrow reflection pathway and the photonic crystal provides broadband reflection pathway. The boundary condition across the ENZ interface and the confinement effect provided by the photonic crystal can enhance the electric fields in the ENZ material greatly. The field enhancements, together with the asymmetric property of Fano-type spectrum, possess potential applications for significantly lowering the threshold of nonlinear processes such as optical switching and bistability.

Magnetic Field Control of Cycloidal Domains and Electric Polarization in Multiferroic BiFeO3

NASA Astrophysics Data System (ADS)

Bordács, S.; Farkas, D. G.; White, J. S.; Cubitt, R.; DeBeer-Schmitt, L.; Ito, T.; Kézsmárki, I.

2018-04-01

The magnetic field induced rearrangement of the cycloidal spin structure in ferroelectric monodomain single crystals of the room-temperature multiferroic BiFeO3 is studied using small-angle neutron scattering. The cycloid propagation vectors are observed to rotate when magnetic fields applied perpendicular to the rhombohedral (polar) axis exceed a pinning threshold value of ˜5 T . In light of these experimental results, a phenomenological model is proposed that captures the rearrangement of the cycloidal domains, and we revisit the microscopic origin of the magnetoelectric effect. A new coupling between the magnetic anisotropy and the polarization is proposed that explains the recently discovered magnetoelectric polarization perpendicular to the rhombohedral axis.

Method and system for managing an electrical output of a turbogenerator

DOEpatents

Stahlhut, Ronnie Dean; Vuk, Carl Thomas

2009-06-02

The system and method manages an electrical output of a turbogenerator in accordance with multiple modes. In a first mode, a direct current (DC) bus receives power from a turbogenerator output via a rectifier where turbogenerator revolutions per unit time (e.g., revolutions per minute (RPM)) or an electrical output level of a turbogenerator output meet or exceed a minimum threshold. In a second mode, if the turbogenerator revolutions per unit time or electrical output level of a turbogenerator output are less than the minimum threshold, the electric drive motor or a generator mechanically powered by the engine provides electrical energy to the direct current bus.

Method and system for managing an electrical output of a turbogenerator

DOEpatents

Stahlhut, Ronnie Dean; Vuk, Carl Thomas

2010-08-24

The system and method manages an electrical output of a turbogenerator in accordance with multiple modes. In a first mode, a direct current (DC) bus receives power from a turbogenerator output via a rectifier where turbogenerator revolutions per unit time (e.g., revolutions per minute (RPM)) or an electrical output level of a turbogenerator output meet or exceed a minimum threshold. In a second mode, if the turbogenerator revolutions per unit time or electrical output level of a turbogenerator output are less than the minimum threshold, the electric drive motor or a generator mechanically powered by the engine provides electrical energy to the direct current bus.

Dynamic of microwave breakdown in the localized places of transmitting line driving by Cherenkov-type oscillator

NASA Astrophysics Data System (ADS)

Xie, Jialing; Chen, Changhua; Chang, Chao; Wu, Cheng; Shi, Yanchao; Cao, Yibing; Song, Zhimin; Zhang, Yuchuan

2018-02-01

A breakdown cavity is designed to study the breakdown phenomena of high-power microwaves in transmission waveguides. The maximum electric field within the cavity varies in amplitude from 400 kV/cm to 1.8 MV/cm and may surpass breakdown thresholds. The breakdown cavities were studied in particle-in-cell simulations and experiments, the results of which yielded waveforms that were consistent. The experimental results indicate that the microwave pulse does not shorten, and the amplitude of the electric field does not fall below 800 kV/cm. Moreover, large numbers of electrons are not emitted in microwaves below 670 kV/cm at 9.75 GHz frequency and 25-ns pulse width transmitted in stainless steel waveguides. The radiation waveforms of breakdown cavity with different materials are compared in experiments, with titanium material performing better.

The influence of an external electric field on the propagation of light waves in cholesteric liquid crystal cells

NASA Astrophysics Data System (ADS)

Aksenova, E. V.; Karetnikov, A. A.; Kovshik, A. P.; Krainyukov, E. S.; Svanidze, A. V.

2017-05-01

The specific features of light transmission in a cholesteric liquid crystal (LC) cell with a director rotated by 90° have been investigated. In this structure, where a light wave is incident at a large angle with respect to the LC surface, the light is reflected (refracted) in the LC layer near the opposite boundary. It is shown that the application of an electric field changes the character of extraordinary wave refraction, as a result of which light starts passing through a cell. The transmission threshold voltage is determined, and its dependence on the angle of incidence of light is obtained. The dependence of the transmitted-light intensity on the voltage across the cell is obtained as well. The same dependences are also derived by numerical calculations with allowance for the turning points and extinction.

Plasma Membrane Permeabilization by 60- and 600-ns Electric Pulses Is Determined by the Absorbed Dose

PubMed Central

Ibey, Bennett L.; Xiao, Shu; Schoenbach, Karl H.; Murphy, Michael R.; Pakhomov, Andrei G.

2008-01-01

We explored how the effect of plasma membrane permeabilization by nanosecond-duration electric pulses (nsEP) depends on the physical characteristics of exposure. The resting membrane resistance (Rm) and membrane potential (MP) were measured in cultured GH3 and CHO cells by conventional whole-cell patch-clamp technique. Intact cells were exposed to a single nsEP (60 or 600 ns duration, 0-22 kV/cm), followed by patch-clamp measurements after a 2-3 min delay. Consistent with earlier findings, nsEP caused long-lasting Rm decrease, accompanied by the loss of MP. The threshold for these effects was about 6 kV/cm for 60 ns pulses, and about 1 kV/cm for 600 ns pulses. Further analysis established that it was neither pulse duration nor the E-field amplitude per se, but the absorbed dose that determined the magnitude of the biological effect. In other words, exposure to nsEP at either pulse duration caused equal effects if the absorbed doses were equal. The threshold absorbed dose to produce plasma membrane effects in either GH3 or CHO cells at either pulse duration was found to be at or below 10 mJ/g. Despite being determined by the dose, the nsEP effect clearly is not thermal, as the maximum heating at the threshold dose is less than 0.01 °C. The use of the absorbed dose as a universal exposure metric may help to compare and quantify nsEP sensitivity of different cell types and of cells in different physiological conditions. The absorbed dose may also prove to be a more useful metric than the incident E-field in determining safety limits for high peak, lowaverage power EMF emissions. PMID:18839412

Optimization of pillar electrodes in subretinal prosthesis for enhanced proximity to target neurons

NASA Astrophysics Data System (ADS)

Flores, Thomas; Lei, Xin; Huang, Tiffany; Lorach, Henri; Dalal, Roopa; Galambos, Ludwig; Kamins, Theodore; Mathieson, Keith; Palanker, Daniel

2018-06-01

Objective. High-resolution prosthetic vision requires dense stimulating arrays with small electrodes. However, such miniaturization reduces electrode capacitance and penetration of electric field into tissue. We evaluate potential solutions to these problems with subretinal implants based on utilization of pillar electrodes. Approach. To study integration of three-dimensional (3D) implants with retinal tissue, we fabricated arrays with varying pillar diameter, pitch, and height, and implanted beneath the degenerate retina in rats (Royal College of Surgeons, RCS). Tissue integration was evaluated six weeks post-op using histology and whole-mount confocal fluorescence imaging. The electric field generated by various electrode configurations was calculated in COMSOL, and stimulation thresholds assessed using a model of network-mediated retinal response. Main results. Retinal tissue migrated into the space between pillars with no visible gliosis in 90% of implanted arrays. Pillars with 10 μm height reached the middle of the inner nuclear layer (INL), while 22 μm pillars reached the upper portion of the INL. Electroplated pillars with dome-shaped caps increase the active electrode surface area. Selective deposition of sputtered iridium oxide onto the cap ensures localization of the current injection to the pillar top, obviating the need to insulate the pillar sidewall. According to computational model, pillars having a cathodic return electrode above the INL and active anodic ring electrode at the surface of the implant would enable six times lower stimulation threshold, compared to planar arrays with circumferential return, but suffer from greater cross-talk between the neighboring pixels. Significance. 3D electrodes in subretinal prostheses help reduce electrode-tissue separation and decrease stimulation thresholds to enable smaller pixels, and thereby improve visual acuity of prosthetic vision.

Thermoplastic-based conductive composites containing multi-wall carbon nanotubes aligned under the application of external electric fields

NASA Astrophysics Data System (ADS)

Osazuwa, Osayuki

The objective of this thesis is to prepare thermoplastic/multi-wall carbon nanotubes (MWCNTs) and to apply external alternating current (AC) electric fields to achieve enhanced conductivity and dielectric properties. The first part of the thesis focuses on preparing polyolefin-based composites containing welldispersed MWCNTs. MWCNTs are functionalized with a hyperbranched polyethylene (HBPE) using a non-covalent, non-specific functionalization approach and melt compounded with an ethylene-octene copolymer (EOC) matrix. The improved filler dispersion in the functionalized EOC/MWCNT composite results in higher elongation at break compared to the non-functionalized composite. However, the electrical percolation threshold and the ultimate conductivity of the composites are not affected considerably, suggesting that this functionalization approach leaves the inherent properties of the nanotubes intact. EOC/HBPE-functionalized MWCNT composites are further subjected to external AC electric fields (35 -- 212 kV/m), which induce the formation of aligned columnar structures, as evidenced by Scanning Electron Microscopy. Experimentally acquired resistivity data are used to derive correlations between the characteristic insulator-to-conductor transition times of the composites and the electric field strength (E), polymer viscosity (eta) and MWCNT volume fraction (φ). A criterion for the selection of (eta, E, φ) conditions that enable MWCNT assembly under an electric field controlled regime (minimal Brownian motion-driven aggregation effects) is developed. The dielectric properties of the solidified aligned EOC/MWCNT composites are further studied using dielectric spectroscopy. Annealing of the composites at 160 °C results in the formation of interconnected structures, whereas electrification, using AC field of 71 and 212 kV/m induces the formation of aligned columnar structures. The electrified and annealed composites have increased real and imaginary permittivity compared to the as-compounded composite, resulting in improved conductivity and storage capacity. An equivalent circuit model is fitted to the experimentally obtained impedance data in order to correlate the effects of electric field and processing time to the dielectric characteristics of the treated composites. Finally poly(ethylene succinate) (PESu) composites containing well-dispersed MWCNT were prepared by an in-situ polymerization method. Composite electrification results in improvements in the electrical conductivity by up to 12 orders of magnitude, and a retention of high conductivity in the solidified state.

Oesophageal sensation assessed by electrical stimuli and brain evoked potentials--a new model for visceral nociception.

PubMed Central

Frøbert, O; Arendt-Nielsen, L; Bak, P; Funch-Jensen, P; Bagger, J P

1995-01-01

Sensory thresholds and brain evoked potentials were determined in 12 healthy volunteers using electrical stimulation of the oesophagus 28 and 38 cm from the nares. The peaks of the evoked potentials were designated N for negative deflections and P for positive. Continuous electrical stimulation (40 Hz) at the 38 cm position resembled heartburn (five of 12 subjects) while non-specific ('electrical') sensations were provoked at 28 cm (10 of 12). Thresholds of sensation and of pain were lower at the initial than the second determination, but did not differ with respect to stimulation site. The pain summation threshold to repeated stimuli (2 Hz, 5 stimuli) was determined for the first time in a viscus. This threshold was lower than the pain threshold to single stimuli at 38 cm (p < 0.02). Evoked potential latencies did not change significantly over a six month period while the N1/P2 amplitude was higher at the first measurement (p < 0.05). P1 and N1 latencies were significantly shorter 38 cm (medians 100 and 141 ms) than 28 cm from the nares (102 and 148 ms) (p = 0.04 and p = 0.008). Electrical stimulation of the oesophagus may serve as a human experimental model for visceral pain. Longer evoked potential latencies from the proximal compared with distal stimulations provide new information about the sensory pathways of the oesophagus. PMID:8549932

High-order-harmonic generation from Rydberg atoms driven by plasmon-enhanced laser fields

NASA Astrophysics Data System (ADS)

Tikman, Y.; Yavuz, I.; Ciappina, M. F.; Chacón, A.; Altun, Z.; Lewenstein, M.

2016-02-01

We theoretically investigate high-order-harmonic generation (HHG) in Rydberg atoms driven by spatially inhomogeneous laser fields, induced, for instance, by plasmonic enhancement. It is well known that the laser intensity should exceed a certain threshold in order to stimulate HHG when noble gas atoms in their ground state are used as an active medium. One way to enhance the coherent light coming from a conventional laser oscillator is to take advantage of the amplification obtained by the so-called surface plasmon polaritons, created when a low-intensity laser field is focused onto a metallic nanostructure. The main limitation of this scheme is the low damage threshold of the materials employed in the nanostructure engineering. In this work we propose the use of Rydberg atoms, driven by spatially inhomogeneous, plasmon-enhanced laser fields, for HHG. We exhaustively discuss the behavior and efficiency of these systems in the generation of coherent harmonic emission. Toward this aim we numerically solve the time-dependent Schrödinger equation for an atom, with an electron initially in a highly excited n th Rydberg state, located in the vicinity of a metallic nanostructure. In this zone the electric field changes spatially on scales relevant for the dynamics of the laser-ionized electron. We first use a one-dimensional model to investigate systematically the phenomena. We then employ a more realistic situation, in which the interaction of a plasmon-enhanced laser field with a three-dimensional hydrogen atom is modeled. We discuss the scaling of the relevant input parameters with the principal quantum number n of the Rydberg state in question and demonstrate that harmonic emission can be achieved from Rydberg atoms well below the damage threshold, thus without deterioration of the geometry and properties of the metallic nanostructure.

Experimental and theoretical study on field emission properties of zinc oxide nanoparticles decorated carbon nanotubes

NASA Astrophysics Data System (ADS)

Li, Xin; Zhou, Wei-Man; Liu, Wei-Hua; Wang, Xiao-Li

2015-05-01

Field emission properties of zinc oxide (ZnO) nanoparticles (NPs) decorated carbon nanotubes (CNTs) are investigated experimentally and theoretically. CNTs are in situ decorated with ZnO NPs during the growth process by chemical vapor deposition using a carbon source from the iron phthalocyanine pyrolysis. The experimental field emission test shows that the ZnO NP decoration significantly improves the emission current from 50 μA to 275 μA at 550 V and the reduced threshold voltage from 450 V to 350 V. The field emission mechanism of ZnO NPs on CNTs is theoretically studied by the density functional theory (DFT) combined with the Penn-Plummer method. The ZnO NPs reconstruct the ZnO-CNT structure and pull down the surface barrier of the entire emitter system to 0.49 eV so as to reduce the threshold electric field. The simulation results suggest that the presence of ZnO NPs would increase the LDOS near the Fermi level and increase the emission current. The calculation results are consistent with the experiment results. Project supported by the National Natural Science Foundation of China (Grant Nos. 91123018, 61172040, and 61172041) and the Natural Science Foundation of Shaanxi Province, China (Grant No. 2014JM7277).

Effect of thermal insulation on the electrical characteristics of NbOx threshold switches

NASA Astrophysics Data System (ADS)

Wang, Ziwen; Kumar, Suhas; Wong, H.-S. Philip; Nishi, Yoshio

2018-02-01

Threshold switches based on niobium oxide (NbOx) are promising candidates as bidirectional selector devices in crossbar memory arrays and building blocks for neuromorphic computing. Here, it is experimentally demonstrated that the electrical characteristics of NbOx threshold switches can be tuned by engineering the thermal insulation. Increasing the thermal insulation by ˜10× is shown to produce ˜7× reduction in threshold current and ˜45% reduction in threshold voltage. The reduced threshold voltage leads to ˜5× reduction in half-selection leakage, which highlights the effectiveness of reducing half-selection leakage of NbOx selectors by engineering the thermal insulation. A thermal feedback model based on Poole-Frenkel conduction in NbOx can explain the experimental results very well, which also serves as a piece of strong evidence supporting the validity of the Poole-Frenkel based mechanism in NbOx threshold switches.

Synergistic effect of electrical and chemical factors on endocytosis in micro-discharge plasma gene transfection

NASA Astrophysics Data System (ADS)

Jinno, M.; Ikeda, Y.; Motomura, H.; Isozaki, Y.; Kido, Y.; Satoh, S.

2017-06-01

We have developed a new micro-discharge plasma (MDP)-based gene transfection method, which transfers genes into cells with high efficiency and low cytotoxicity; however, the mechanism underlying the method is still unknown. Studies revealed that the N-acetylcysteine-mediated inhibition of reactive oxygen species (ROS) activity completely abolished gene transfer. In this study, we used laser-produced plasma to demonstrate that gene transfer does not occur in the absence of electrical factors. Our results show that both electrical and chemical factors are necessary for gene transfer inside cells by microplasma irradiation. This indicates that plasma-mediated gene transfection utilizes the synergy between electrical and chemical factors. The electric field threshold required for transfection was approximately 1 kV m-1 in our MDP system. This indicates that MDP irradiation supplies sufficient concentrations of ROS, and the stimulation intensity of the electric field determines the transfection efficiency in our system. Gene transfer by plasma irradiation depends mainly on endocytosis, which accounts for at least 80% of the transfer, and clathrin-mediated endocytosis is a dominant endocytosis. In plasma-mediated gene transfection, alterations in electrical and chemical factors can independently regulate plasmid DNA adhesion and triggering of endocytosis, respectively. This implies that plasma characteristics can be adjusted according to target cell requirements, and the transfection process can be optimized with minimum damage to cells and maximum efficiency. This may explain how MDP simultaneously achieves high transfection efficiency with minimal cell damage.

Bulk heterojunction polymer memory devices with reduced graphene oxide as electrodes.

PubMed

Liu, Juqing; Yin, Zongyou; Cao, Xiehong; Zhao, Fei; Lin, Anping; Xie, Linghai; Fan, Quli; Boey, Freddy; Zhang, Hua; Huang, Wei

2010-07-27

A unique device structure with a configuration of reduced graphene oxide (rGO) /P3HT:PCBM/Al has been designed for the polymer nonvolatile memory device. The current-voltage (I-V) characteristics of the fabricated device showed the electrical bistability with a write-once-read-many-times (WORM) memory effect. The memory device exhibits a high ON/OFF ratio (10(4)-10(5)) and low switching threshold voltage (0.5-1.2 V), which are dependent on the sheet resistance of rGO electrode. Our experimental results confirm that the carrier transport mechanisms in the OFF and ON states are dominated by the thermionic emission current and ohmic current, respectively. The polarization of PCBM domains and the localized internal electrical field formed among the adjacent domains are proposed to explain the electrical transition of the memory device.

Interaction Of CO2 Laser Nanosecond Pulse Train With The Metallic Targets In Optical Breakdown Regime

NASA Astrophysics Data System (ADS)

Apollonov, V. V.; Firsov, K. N.; Konov, V. I.; Nikitin, P. I.; Prokhorov, A. M.; Silenok, A. S.; Sorochenko, V. R.

1986-11-01

In the present paper the electric field and currents in the air-breakdown plasma, produced by the train of nanosecond pulses of TEA-002 - regenerative amplifier near the un-charged targets are studied. The breakdown thresholds and the efficiency of plasma-target heat transmission are also measured. The results of numerical calculations made for increasing of the pulse train contrast with respect to the background in a regenerative amplifier are advanced.

Facilitation of Ferroelectric Switching via Mechanical Manipulation of Hierarchical Nanoscale Domain Structures.

PubMed

Chen, Zibin; Hong, Liang; Wang, Feifei; Ringer, Simon P; Chen, Long-Qing; Luo, Haosu; Liao, Xiaozhou

2017-01-06

Heterogeneous ferroelastic transition that produces hierarchical 90° tetragonal nanodomains via mechanical loading and its effect on facilitating ferroelectric domain switching in relaxor-based ferroelectrics were explored. Combining in situ electron microscopy characterization and phase-field modeling, we reveal the nature of the transition process and discover that the transition lowers by 40% the electrical loading threshold needed for ferroelectric domain switching. Our results advance the fundamental understanding of ferroelectric domain switching behavior.

Dual-mode E region plasma wave observations from Millstone Hill

NASA Astrophysics Data System (ADS)

del Pozo, C. F.; Foster, J. C.; St.-Maurice, J.-P.

1993-04-01

Observations and analysis of the unstable auroral E region during local afternoon to early morning hours, and modified two-stream waves as well as two kinds of waves associated with the turbulence created by such waves are identified. One of these types exhibits properties similar to those of type II waves reported in the literature, whereas the second type has a broader spectrum, is detected in all directions, and appears to be new. The onset of turbulence corresponds to an electric field threshold of the order of 20 m/Vm. The presence of an azimuthal asymmetry in both the threshold field and the observed phase velocities with systematically greater values is detected; they are attributed to the presence of a 50-m/s E-W neutral wind at E region heights. The maximum observed volume reflectivity for type I wave ranges exceeded 10 exp -11, and that of the secondaries was of the order of 20 dB smaller.

2D modeling based comprehensive analysis of short channel effects in DMG strained VSTB FET

NASA Astrophysics Data System (ADS)

Saha, Priyanka; Banerjee, Pritha; Sarkar, Subir Kumar

2018-06-01

The paper aims to develop two dimensional analytical model of the proposed dual material (DM) Vertical Super Thin Body (VSTB) strained Field Effect Transistor (FET) with focus on its short channel behaviour in nanometer regime. Electrostatic potential across gate/channel and dielectric wall/channel interface is derived by solving 2D Poisson's equation with parabolic approximation method by applying appropriate boundary conditions. Threshold voltage is then calculated by using the criteria of minimum surface potential considering both gate and dielectric wall side potential. Performance analysis of the present structure is demonstrated in terms of potential, electric field, threshold voltage characteristics and subthreshold behaviour by varying various device parameters and applied biases. Effect of application of strain in channel is further explored to establish the superiority of the proposed device in comparison to conventional VSTB FET counterpart. All analytical results are compared with Silvaco ATLAS device simulated data to substantiate the accuracy of our derived model.

Nanosecond pulsed electric field thresholds for nanopore formation in neural cells

NASA Astrophysics Data System (ADS)

Roth, Caleb C.; Tolstykh, Gleb P.; Payne, Jason A.; Kuipers, Marjorie A.; Thompson, Gary L.; DeSilva, Mauris N.; Ibey, Bennett L.

2013-03-01

The persistent influx of ions through nanopores created upon cellular exposure to nanosecond pulse electric fields (nsPEF) could be used to modulate neuronal function. One ion, calcium (Ca), is important to action potential firing and regulates many ion channels. However, uncontrolled hyper-excitability of neurons leads to Ca overload and neurodegeneration. Thus, to prevent unintended consequences of nsPEF-induced neural stimulation, knowledge of optimum exposure parameters is required. We determined the relationship between nsPEF exposure parameters (pulse width and amplitude) and nanopore formation in two cell types: rodent neuroblastoma (NG108) and mouse primary hippocampal neurons (PHN). We identified thresholds for nanoporation using Annexin V and FM1-43, to detect changes in membrane asymmetry, and through Ca influx using Calcium Green. The ED50 for a single 600 ns pulse, necessary to cause uptake of extracellular Ca, was 1.76 kV/cm for NG108 and 0.84 kV/cm for PHN. At 16.2 kV/cm, the ED50 for pulse width was 95 ns for both cell lines. Cadmium, a nonspecific Ca channel blocker, failed to prevent Ca uptake suggesting that observed influx is likely due to nanoporation. These data demonstrate that moderate amplitude single nsPEF exposures result in rapid Ca influx that may be capable of controllably modulating neurological function.

Sub-threshold depolarizing pre-pulses can enhance the efficiency of biphasic stimuli in transcutaneous neuromuscular electrical stimulation.

PubMed

Vargas Luna, Jose Luis; Mayr, Winfried; Cortés-Ramirez, Jorge-Armando

2018-06-09

There is multiple evidence in the literature that a sub-threshold pre-pulse, delivered immediately prior to an electrical stimulation pulse, can alter the activation threshold of nerve fibers and motor unit recruitment characteristics. So far, previously published works combined monophasic stimuli with sub-threshold depolarizing pre-pulses (DPPs) with inconsistent findings-in some studies, the DPPs decreased the activation threshold, while in others it was increased. This work aimed to evaluate the effect of DPPs during biphasic transcutaneous electrical stimulation and to study the possible mechanism underlying those differences. Sub-threshold DPPs between 0.5 and 15 ms immediately followed by biphasic or monophasic pulses were administered to the tibial nerve; the electrophysiological muscular responses (motor-wave, M-wave) were monitored via electromyogram (EMG) recording from the soleus muscle. The data show that, under the specific studied conditions, DPPs tend to lower the threshold for nerve fiber activation rather than elevating it. DPPs with the same polarity as the leading phase of biphasic stimuli are more effective to increase the sensitivity. This work assesses for the first time the effect of DPPs on biphasic pulses, which are required to achieve charge-balanced stimulation, and it provides guidance on the effect of polarity and intensity to take full advantage of this feature. Graphical abstract In this work, the effect of sub-threshold depolarizing pre-pulses (DPP) is investigated in a setup with transcutaneous electrical stimulation. We found that, within the tested 0-15 ms DPP duration range, the DPPs administered immediately before biphasic pulses proportionally increase the nerve excitability as visible in the M-waves recorded from the soleus muscle. Interestingly, these findings oppose published results, where DPPs, administered immediately before monophasic stimuli via implanted electrodes, led to decrease of nerve excitability.

Gas Composition Sensing Using Carbon Nanotube Arrays

NASA Technical Reports Server (NTRS)

Li, Jing; Meyyappan, Meyya

2012-01-01

This innovation is a lightweight, small sensor for inert gases that consumes a relatively small amount of power and provides measurements that are as accurate as conventional approaches. The sensing approach is based on generating an electrical discharge and measuring the specific gas breakdown voltage associated with each gas present in a sample. An array of carbon nanotubes (CNTs) in a substrate is connected to a variable-pulse voltage source. The CNT tips are spaced appropriately from the second electrode maintained at a constant voltage. A sequence of voltage pulses is applied and a pulse discharge breakdown threshold voltage is estimated for one or more gas components, from an analysis of the current-voltage characteristics. Each estimated pulse discharge breakdown threshold voltage is compared with known threshold voltages for candidate gas components to estimate whether at least one candidate gas component is present in the gas. The procedure can be repeated at higher pulse voltages to estimate a pulse discharge breakdown threshold voltage for a second component present in the gas. The CNTs in the gas sensor have a sharp (low radius of curvature) tip; they are preferably multi-wall carbon nanotubes (MWCNTs) or carbon nanofibers (CNFs), to generate high-strength electrical fields adjacent to the tips for breakdown of the gas components with lower voltage application and generation of high current. The sensor system can provide a high-sensitivity, low-power-consumption tool that is very specific for identification of one or more gas components. The sensor can be multiplexed to measure current from multiple CNT arrays for simultaneous detection of several gas components.

Properties of excited states in organic light emitting diodes and lasers

NASA Astrophysics Data System (ADS)

Giebink, Noel C.

The field of organic semiconductors has grown rapidly over the past decade with the development of light emitting diodes, solar cells, and lasers that promise a new generation of low-cost, flexible optoelectronic devices. In each case, the behavior of molecular excited states, or excitons, is of fundamental importance. The present study explores the nature and interactions of such excited states in the attempt to develop an electrically pumped organic semiconductor laser, and to improve the performance and operational stability of organic light emitting diodes. We begin by investigating intrinsic loss processes in optically pumped organic semiconductor lasers and demonstrate that exciton annihilation implies a fundamental limit that will prevent lasing by electrical injection in currently known materials. Searching for an alternative approach to reach threshold leads us to study metastable geminate charge pairs, where we find that optically generated excitons can be accumulated over time in an external electric field via these intermediate states. Upon field turn-off, the excitons are immediately restored, leading to a sudden burst of excitation density over 30 times higher than that generated by the pump alone. Unfortunately, we identify limitations that have thus far prevented reaching laser threshold with this technique. In a parallel push toward high power density, we investigate the origins of quantum efficiency roll-off in organic light emitting diodes (OLEDs) and find that it is dominated by loss of charge balance in the majority of fluorescent and phosphorescent devices. The second major theme of this work involves understanding the intrinsic modes of OLED operational degradation. Based on extensive modeling and supported directly by experimental evidence, we identify exciton-charge carrier annihilation reactions as a principle degradation pathway. Exploiting the diffusion of triplet excitons, we show that fluorescence and phosphorescence can be combined to increase the operational lifetime of white OLEDs and still retain the potential for unity internal quantum efficiency.

Effect of Se substitution on the phase change properties of Ge2Sb2Te5

NASA Astrophysics Data System (ADS)

Shekhawat, Roopali; Rangappa, Ramanna; Gopal, E. S. R.; Ramesh, K.

2018-05-01

Ge2Sb2Te5 popularly known as GST is being explored for non-volatile phase change random access memory(PCRAM) applications. Under high electric field, thin films of amorphous GST undergo a phase change from amorphous to crystalline with a high contrast in electrical resistivity (about 103). The phase change is between amorphous and metastable NaCl structure occurs at about 150°C and not to the stable hexagonal phase which occurs at a high temperature (> 250 °C). In GST, about 50 % of Te substituted by Se (Ge2Sb2Te2.5Se2.5) is found to increase the contrast in electrical resistivity by 7 orders of magnitude (about 4 orders of magnitude higher than GST). The phase transition in Se added GST also found to be between amorphous and the stable hexagonal structure. The threshold voltage at which the Ge2Sb2Te2.5Se2.5 switches to the high conducting state increases to 9V as compared to 2V in GST. Interestingly, the threshold current decrease to 1mA as compared to 1.8mA in GST indicating the Se substitution reduces the power needed for switching between the low and high conducting states. The reduction in power needed for phase change, high contrast in electrical resistivity with high thermal stability makes Ge2Sb2Te2.5Se2.5 as a better candidate for PCRAM.

Dependence of positive and negative sprite morphology on lightning characteristics and upper atmospheric ambient conditions

NASA Astrophysics Data System (ADS)

Qin, Jianqi; Celestin, Sebastien; Pasko, Victor P.

2013-05-01

Carrot sprites, exhibiting both upward and downward propagating streamers, and columniform sprites, characterized by predominantly vertical downward streamers, represent two distinct morphological classes of lightning-driven transient luminous events in the upper atmosphere. It is found that positive cloud-to-ground lightning discharges (+CGs) associated with large charge moment changes (QhQ) tend to produce carrot sprites with the presence of a mesospheric region where the electric field exceeds the value 0.8Ek and persists for >˜2 ms, whereas those associated with small QhQ are only able to produce columniform sprites. Columniform sprites may also appear in the periphery of a sprite halo produced by +CGs associated with large QhQ. For a sufficiently large QhQ, the time dynamics of the QhQ determines the specific shape of the carrot sprites. In the case when the sufficiently large QhQ is produced mainly by an impulsive return stroke, strong electric field is produced at high altitudes and manifests as a bright halo, and the corresponding conductivity enhancement lowers/enhances the probability of streamer initiation inside/below the sprite halo. A more impulsive return stroke leads to a more significant conductivity enhancement (i.e., a brighter halo). This conductivity enhancement also leads to fast decay and termination of the upper diffuse region of carrot sprites because it effectively screens out the electric field at high altitudes. On the contrary, if the sufficiently large QhQ is produced by a weak return stroke (i.e., a dim halo) accompanied by intense continuing current, the lightning-induced electric field at high altitudes persists at a level that is comparable to Ek, and therefore an extensive upper diffuse region can develop. Furthermore, we demonstrate that `negative sprites' (produced by -CGs) should be necessarily carrot sprites and most likely accompanied by a detectable halo, since the initiation of upward positive streamers is always easier than that of downward negative streamers, and -CGs are usually associated with impulsive return stroke with no continuing current. We also conjecture that in some cases, fast decaying single-headed upward positive streamers produced by -CGs may appear as bright spots/patches. We show that the threshold charge moment changes of positive and negative sprites are, respectively, ~320 and ~500 C km under typical nighttime conditions assumed in this study. These different initiation thresholds, along with the different applied electric field required for stable propagation of positive and negative streamers and the fact that +CGs much more frequently produce large charge moment changes, represent three major factors in the polarity asymmetry of +CGs and -CGs in producing sprite streamers. We further demonstrate that lower mesospheric ambient conductivity leads to smaller threshold charge moment change required for the production of carrot sprites. We suggest that geographical and temporal conductivity variations in the lower ionosphere documented in earlier studies, along with the seasonal and inter-annual variations of thunderstorm activity that lead to different lightning characteristics in the troposphere, account for the different morphological features of sprites observed in different observation campaigns.

An inappropriate pacing threshold increase after repeated electrical storm in a patient with implantable cardioverter defibrillator.

PubMed

Zhu, Ye; Gu, Xiang; Xu, Chao

2017-10-16

Implantable cardioverter defibrillators (ICD) are capable of effectively terminating malignant ventricular arrhythmia and are the most effective way to prevent sudden cardiac death. However, some evidences demonstrated that both anti-tachycardia pacing (ATP) and ICD shock can also bring adverse prognosis. A 66-year-old Han Chinese man with prior ICD implantation was admitted to our hospital because of frequent ICD shocks. Although intravenous amiodarone and esmolol succinate were administered daily, the patient suffered 155 episodes of VT/VF during 8 weeks after implantation. After repeated discharge of the device, the pacing threshold of the patient increased gradually. Considering the inappropriate increase of the pacing threshold, we decided to reposition the right ventricular (RV) lead with good sensing and threshold parameters confirmed. Subsequent 22 months interrogation follow-up revealed a stable lead position and electrical specifications. Furthermore, antiarrhythmic drugs were maximally increased, while ATP burst was remarkably decreased and the inappropriate ICD shock never occurred until now. An inappropriate pacing threshold was increased secondary to repeated ICD electrical storm. A timely active lead position adjustment reduced the pacing threshold and eliminated the risk of premature battery depletion.

Comparison of Pain Thresholds and Analgesic Effects of Parecoxib Sodium in Surgical Patients of Different Racial and Religious Backgrounds.

PubMed

Li, Li-Biao; Hu, Yu; Liu, Chao; Gu, Miao-Ning

2015-06-01

To explore the differences of the thresholds of pain and analgesic effects of parecoxib sodium among patients with different racial and religious backgrounds. A total of 48 male patients aged 18 to 38 years who had undergone elective laparoscopic appendectomy under general anesthesia in our centers were enrolled in our study and then divided into 6 groups(n=8 in each group)based on their racial backgrounds(three levels:Mongoloid,Negroid,and Europoid)and religious backgrounds(two levels:without religion background,with religion background).All subjects received the same anesthesia,surgical procedure,and postoperative analgesia with parecoxib sodium. The temperature pain threshold and electrical pain threshold were detected 1h before and after analgesia. The threshold of pain was higher in Europoids than in Negroids and Mongoloids before and after treatment. The temperature pain threshold and electrical pain threshold were not significantly different between subjects with or without religious background(before analgesic therapy:F=251.119,P=0.130,F=275.861,P=0.059;after analgesic therapy:F=308.531,P=0.086,F=180.062,P=0.078). Also,there was no interaction between the racial and religious backgrous in terms of temperature pain threshold and electrical pain threshold(F=13.553,P=0.091,F=22.001,P= 0.089;after analgesic therapy:F=4.624,P=0.089,F=15.935,P=0.094). The threshold of pain differs among individuals with different racial background:it is highest in Europoids,followed by Negroids and Mongoloids. It shows no obvious difference in people with different religious backgrounds.

Electric breakdowns of the "plasma capacitors" occurs on insulation coating of the ISS surface

NASA Astrophysics Data System (ADS)

Homin, Taras; Korsun, Anatolii

High electric fields and currents are occurred in the spacecrafts plasma environment by onboard electric generators. Thus the high voltage solar array (SA) of the American segment of International Space Station (ISS) generates potential 160 V. Its negative pole is shorted to the frames of all the ISS segments. There is electric current between the SA and the frame through the plasma environment, i.e. electric discharge occurs. As a result a potential drop exists between the frames of all the ISS segments and the environmental plasma [1], which is cathode drop potential varphi _{c} defined. When ISS orbiting, the φc varies greatly in the range 0-100 V. A large area of the ISS frames and SA surface is coated with a thin dielectric film. Because of cathode drop potential the frame surfaces accumulate ion charges and the SA surfaces accumulate electron charges. These surfaces become plasma capacitors, which accumulate much charge and energy. Micrometeorite impacts or buildup of potential drop in excess of breakdown threshold varphi_{b} (varphi _{c} > varphi _{b} = 60 V) may cause breakdowns of these capacitors. Following a breakdown, the charge collected at the surfaces disperses and transforms into a layer of dense plasma [2]. This plasma environment of the spacecraft produces great pulsed electric fields E at the frame surfaces as well as heavy currents between construction elements which in turn induce great magnetic fields H. Therefore the conductive frame and the environmental plasma is plasma inductors. We have calculated that the densities of these pulsing and high-frequency fields E and H generated in the plasma environment of the spacecraft may exceed values hazardous to human. Besides, these fields must induce large electromagnetic impulses in the space-suit and in the power supply and control circuits of onboard systems. During astronaut’s space-suit activity, these fields will penetrate the space-suit and the human body with possible hazardous effects. These effects need to be studied, and appropriate remedies are to be developed. References 1. Mikatarian, R., et al., «Electrical Charging of the International Space Station», AIAA Paper No. 2003-1079, 41th. Aerospace Sciences Meeting and Exhibit, January 2003. 2. A.G. Korsun, «Electric discharge processes intensification mechanisms on International Space Station surface». Astronautics and rocket production, 1, 2011 (in Russian).

Electrodynamic smooth muscle sphincter: development and biomechanical evaluation of a novel porcine artificial smooth muscle sphincter in a new in vitro stoma simulator.

PubMed

Schrag, H J; Karwath, D; Grub, C; Fragoza Padilla, F; Noack, T; Hopt, U T

2005-07-01

Many authors have suggested that the activity of the enteric inhibitory nerves is important in regulating normal gastrointestinal motility and inducing smooth muscle relaxation. Hitherto, no experimental or clinical models exist that transfer these physiological aspects to creating an autologous artificial sphincter for the treatment of major incontinence. Therefore, this study was performed to determine the contractile and relaxant capacity of gastrointestinal muscle types and to investigate the efficiency of a novel smooth muscle sphincter, based on the non-adrenergic, non-cholinergic (NANC) receptive relaxation under electrical field stimulation (EFS). For the first step, the isometric tension from isolated circular porcine fundus and colon muscle strips was recorded during pharmacological stimulation (TTX, L-NNA and atropine) and EFS. As a result, a continent electrodynamic smooth muscle sphincter (ESMS) was created by wrapping a fundus muscle flap around an isolated segment of porcine distal colon. The EFS of the free nerve fibers of the flap was realized using a circular platinum wire electrode. Parameters such as threshold of continence, intra/preluminal pressure and fluid passage were analyzed in a newly designed in vitro stoma simulator. Electrical field stimulation produced a maximal and voltage-dependent fundus relaxation to --12.4 mN/mm(2) (frequency of 40 Hz, pulse duration, train duration and voltage of 5 ms, 1 s and 60 mA respectively), which were abolished by N-nitro-L -arginine (L-NNA; 10(-4) M) in a dose-dependent manner, confirming that relaxant responses were mediated by NANC nerves. The results of eight ESMS showed that circular electrical stimulation of the muscle flap caused muscle relaxation with a concomitant and effective reduction in the occlusion pressure. The NANC-induced relaxation mechanism of porcine fundus preparations could be transferred to an efficient smooth muscle sphincter with a high threshold of continence and electrically controlled defecation.

Laser-driven interactions and resultant instabilities in materials with high dielectric constant

NASA Astrophysics Data System (ADS)

Rajpoot, Moolchandra; Dixit, Sanjay

2015-07-01

An analytical investigation of nonlinear interactions resulting in parametric amplification of acoustic wave is made by obtaining the dispersion relation using hydrodynamic model of inhomogeneous plasma by applying large static field at an arbitrary angle with the pump wave. The investigation shows that many early studies have neglected dependence of dielectric constant on deformation of materials but deformation of materials does infect depends on the dielectric constant of medium. Thus we have assumed to high dielectric material like BaTiO3 which resulted in substantially high growth rate of threshold electric field which opens a new dimension to study nonlinear interactions and instabilities.

Hall-effect arc protector

DOEpatents

Rankin, R.A.; Kotter, D.K.

1997-05-13

The Hall-Effect Arc Protector is used to protect sensitive electronics from high energy arcs. The apparatus detects arcs by monitoring an electrical conductor, of the instrument, for changes in the electromagnetic field surrounding the conductor which would be indicative of a possible arcing condition. When the magnitude of the monitored electromagnetic field exceeds a predetermined threshold, the potential for an instrument damaging are exists and the control system logic activates a high speed circuit breaker. The activation of the breaker shunts the energy imparted to the input signal through a dummy load to the ground. After the arc condition is terminated, the normal signal path is restored. 2 figs.

Hall-effect arc protector

DOEpatents

Rankin, Richard A.; Kotter, Dale K.

1997-01-01

The Hall-Effect Arc Protector is used to protect sensitive electronics from high energy arcs. The apparatus detects arcs by monitoring an electrical conductor, of the instrument, for changes in the electromagnetic field surrounding the conductor which would be indicative of a possible arcing condition. When the magnitude of the monitored electromagnetic field exceeds a predetermined threshold, the potential for an instrument damaging are exists and the control system logic activates a high speed circuit breaker. The activation of the breaker shunts the energy imparted to the input signal through a dummy load to the ground. After the arc condition is terminated, the normal signal path is restored.

Simultaneous masking between electric and acoustic stimulation in cochlear implant users with residual low-frequency hearing.

PubMed

Krüger, Benjamin; Büchner, Andreas; Nogueira, Waldo

2017-09-01

Ipsilateral electric-acoustic stimulation (EAS) is becoming increasingly important in cochlear implant (CI) treatment. Improvements in electrode designs and surgical techniques have contributed to improved hearing preservation during implantation. Consequently, CI implantation criteria have been expanded toward people with significant residual low-frequency hearing, who may benefit from the combined use of both the electric and acoustic stimulation in the same ear. However, only few studies have investigated the mutual interaction between electric and acoustic stimulation modalities. This work characterizes the interaction between both stimulation modalities using psychophysical masking experiments and cone beam computer tomography (CBCT). Two psychophysical experiments for electric and acoustic masking were performed to measure the hearing threshold elevation of a probe stimulus in the presence of a masker stimulus. For electric masking, the probe stimulus was an acoustic tone while the masker stimulus was an electric pulse train. For acoustic masking, the probe stimulus was an electric pulse train and the masker stimulus was an acoustic tone. Five EAS users, implanted with a CI and ipsilateral residual low-frequency hearing, participated in the study. Masking was determined at different electrodes and different acoustic frequencies. CBCT scans were used to determine the individual place-pitch frequencies of the intracochlear electrode contacts by using the Stakhovskaya place-to-frequency transformation. This allows the characterization of masking as a function of the difference between electric and acoustic stimulation sites, which we term the electric-acoustic frequency difference (EAFD). The results demonstrate a significant elevation of detection thresholds for both experiments. In electric masking, acoustic-tone thresholds increased exponentially with decreasing EAFD. In contrast, for the acoustic masking experiment, threshold elevations were present regardless of the tested EAFDs. Based on the present findings, we conclude that there is an asymmetry between the electric and the acoustic masker modalities. These observations have implications for the design and fitting of EAS sound-coding strategies. Copyright © 2017 Elsevier B.V. All rights reserved.

Neurosensory findings among electricians with self-reported remaining symptoms after an electrical injury: A case series.

PubMed

Rådman, Lisa; Gunnarsson, Lars-Gunnar; Nilsagård, Ylva; Nilsson, Tohr

2016-12-01

Symptoms described in previous studies indicate that electrical injury can cause longstanding injuries to the neurosensory nerves. The aim of the present case series was to objectively assess the profile of neurosensory dysfunction in electricians in relation to high voltage or low voltage electrical injury and the "no-let-go phenomenon". Twenty-three Swedish male electricians exposed to electrical injury were studied by using a battery of clinical instruments, including quantitative sensory testing (QST). The clinical test followed a predetermined order of assessments: thermal perceptions thresholds, vibration perception thresholds, tactile gnosis (the Shape and Texture Identification test), manual dexterity (Purdue Pegboard Test), and grip strength. In addition, pain was studied by means of a questionnaire, and a colour chart was used for estimation of white fingers. The main findings in the present case series were reduced thermal perceptions thresholds, where half of the group showed abnormal values for warm thermal perception and/or cold thermal perception. Also, the tactile gnosis and manual dexterity were reduced. High voltage injury was associated with more reduced sensibility compared to those with low voltage. Neurosensory injury can be objectively assessed after an electrical injury by using QST with thermal perception thresholds. The findings are consistent with injuries to small nerve fibres. In the clinical setting thermal perception threshold is therefore recommended, in addition to tests of tactile gnosis and manual dexterity (Purdue Pegboard). Copyright © 2016 Elsevier Ltd and ISBI. All rights reserved.

Characterization of emitted light from travelling Gunn domains in Al0.08Ga0.92As alloy based Gunn devices

NASA Astrophysics Data System (ADS)

Cetinkaya, Caglar; Mutlu, Selman; Donmez, Omer; Erol, Ayse

2017-11-01

We report room temperature operation of light emitters based on Al0.08Ga0.92As Gunn devices fabricated in a simple bar geometry with wedged-shaped electrodes. High-speed I-V measurements reveal that, at the threshold of negative differential resistance region at around 3.8 kV/cm, current instabilities, i.e., Gunn oscillations, are created with a 3.8 ns period. Both edge and surface light emission are observed when the device is biased at an electric field of onset of the negative differential resistance (NDR) region at around 3.8 kV/cm and the intensity of the light exponentially increases at applied fields just above NDR threshold likewise in a conventional laser. The origin of the light emission, which has peak wavelength is around 816 nm corresponds to the band-gap energy of Al0.08Ga0.92As, is recombination of electrons and holes generated by impact ionisation process in travelling space charge domains, i.e., Gunn domains. We demonstrate that, with increasing applied field, the amplitude of Gunn domains increases which is a result of the enhanced generation of electrons and holes via impact ionisation. The intensity of the emitted light is observed to be dependent on applied electric field. At low electric fields, light intensity increases linearly then, when applied electric field reaches the onset of NDR region, increases exponentially. Besides, as applied field is increased, full width at half maximum (FWHM) of emitted light decreases to 56.5 nm from 62 nm, evolving into higher selective emission line in wavelength. The light emission from the device is determined to be independent of the polarity of the applied voltage. A comparison of surface emission and edge emission characteristics of the waveguided device are different from each other. Edge emission has higher electroluminescence intensity and better spectral purity than surface emission with well-defined longitudinal modes of Fabry-Pérot cavity, which indicates that, in such a device, lasing action arises from the recombination of excess carriers generated via impact ionisation in travelling Gunn domains. Besides, the edge emission peak of waveguided Al0.08Ga0.92As Gunn device at 4.1 kV/cm is split into two peaks with FWHM of 8 and 6 nm as well as neighbouring sharper minor peaks due to stimulated emission dominates by building-up photons in the cavity. Our results reveal that the proposed Gunn device can be a promising alternative to conventional diode lasers with its simpler design, only one type doped active region and voltage polarity-independent operation, but the duty cycle has to be chosen small enough to make the device operate at room temperature.

Band-to-band tunneling field effect transistor for low power logic and memory applications: Design, fabrication and characterization

NASA Astrophysics Data System (ADS)

Mookerjea, Saurabh A.

Over the past decade the microprocessor clock frequency has hit a plateau. The main reason for this has been the inability to follow constant electric field scaling, which requires the transistor supply voltage to be scaled down as the transistor dimensions are reduced. Scaling the supply voltage down reduces the dynamic power quadratically but increases the static leakage power exponentially due to non-scalability of threshold voltage of the transistor, which is required to maintain the same ON state performance. This limitation in supply voltage scaling is directly related to MOSFET's (Metal Oxide Semiconductor Field Effect Transistor) sub-threshold slope (SS) limitation of 60 mV/dec at room temperature. Thus novel device design/materials are required that would allow the transistor to switch with sub-threshold slopes steeper than 60 mV/dec at room temperature, thus facilitating supply voltage scaling. Recently, a new class of devices known as super-steep slope (SS<60 mV/dec) transistors are under intense research for its potential to replace the ubiquitous MOSFET. The focus of this dissertation is on the design, fabrication and characterization of band-to-band tunneling field effect transistor (TFET) which belongs to the family of steep slope transistors. TFET with a gate modulated zener tunnel junction at the source allows sub-kT/q (sub-60 mV/dec at room temperature) sub-threshold slope (SS) device operation over a certain gate bias range near the off-state. This allows TFET to achieve much higher I ON-IOFF ratio over a specified gate voltage swing compared to MOSFETs, thus enabling aggressive supply voltage scaling for low power logic operation without impacting its ON-OFF current ratio. This dissertation presents the operating principle of TFET, the material selection strategy and device design for TFET fabrication. This is followed by a novel 6T SRAM design which circumvents the issue of unidirectional conduction in TFET. The switching behavior of TFET is studied through mixed-mode numerical simulations. The significance of correct benchmarking methodology to estimate the effective drive current and capacitance in TFET is highlighted and compared with MOSFET. This is followed by the fabrication details of homo-junction TFET. Analysis of the electrical characteristics of homo-junction TFET gives key insight into its device operation and identifies the critical factors that impact its performance. In order to boost the ON current, the design and fabrication of hetero-junction TFET is also presented.

Quantifying colloidal particle bands and their formation in combined electroosmotic and Poiseuille flow

NASA Astrophysics Data System (ADS)

Yee, Andrew; Cevheri, Necmettin; Yoda, Minami

2015-11-01

Recently, we have shown that suspended radii a = 245 nm particles flowing through a microchannel driven by the combination of a dc electric field and pressure gradient (where the resulting electroosmotic and shear flows are in opposite directions) are attracted to the wall at low electric field magnitude | E | , then assemble into concentrated bands that only exist within a few μm of the wall above a threshold value of | E | , | Ecr | . The ~ 6 μ m wide bands are aligned with the flow direction and are roughly periodic along the cross-stream direction. This talk focuses on quantitative characterization of these bands, for example how | Ecr | , the time required for bands to form after applying the electric field To, and the number of bands depend upon parameters such as particle volume fraction φ, shear rate γ˙ , | E | , and a. The dynamics of the particles within the bands are visualized by imaging a mixture of particles with different fluorescent labels. The visualizations show that the particles are in a liquid state within these bands, and suggest that the particles nearest the wall move in the direction of the electroosmotic flow, while those farther from the wall move in the direction of the shear flow. Supported by NSF.

Influence of quasi-particle density over polaron mobility in armchair graphene nanoribbons.

PubMed

Silva, Gesiel Gomes; da Cunha, Wiliam Ferreira; de Sousa Junior, Rafael Timóteo; Almeida Fonseca, Antonio Luciano; Ribeiro Júnior, Luiz Antônio; E Silva, Geraldo Magela

2018-06-20

An important aspect concerning the performance of armchair graphene nanoribbons (AGNRs) as materials for conceiving electronic devices is related to the mobility of charge carriers in these systems. When several polarons are considered in the system, a quasi-particle wave function can be affected by that of its neighbor provided the two are close enough. As the overlap may affect the transport of the carrier, the question concerning how the density of polarons affect its mobility arises. In this work, we investigate such dependence for semiconducting AGNRs in the scope of nonadiabatic molecular dynamics. Our results unambiguously show an impact of the density on both the stability and average velocity of the quasi-particles. We have found a phase transition between regimes where increasing density stops inhibiting and starts promoting mobility; densities higher than 7 polarons per 45 Å present increasing mean velocity with increasing density. We have also established three different regions relating electric field and average velocity. For the lowest electric field regime, surpassing the aforementioned threshold results in overcoming the 0.3 Å fs-1 limit, thus representing a transition between subsonic and supersonic regimes. For the highest of the electric fields, density effects alone are responsible for a stunning difference of 1.5 Å fs-1 in the mean carrier velocity.

Non-trivial behavior of the low temperature maximum of dielectric constant and location of the end critical point in Na0.5Bi0.5TiO3-0.06BaTiO3 lead free relaxor ferroelectrics crystals detected by acoustic emission

NASA Astrophysics Data System (ADS)

Dul'kin, Evgeniy; Tiagunova, Jenia; Mojaev, Evgeny; Roth, Michael

2018-01-01

[001] lead free relaxor ferroelectrics crystals of Na0.5Bi0.5TiO3-0.06BaTiO3 were studied by means of dielectric and acoustic emission methods in the temperature range of 25-240 °C and under a dc bias electric field up to 0.4 kV/cm. A temperature maximum of the dielectric constant was found near 170 °C, as well as the acoustic emission bursts pointed out to both the depolarization temperature near 120 °C and the temperature, corresponding to the maximum of dielectric constant, near 170 °C. While the depolarization temperature increased linearly, the temperature of the dielectric constant maximum was shown to exhibit a V-shape behavior under an electric field: it initially decreases, reaches a sharp minimum at some small threshold electric field of 0.15 kV/cm, and then starts to increase similar to the Curie temperature of the normal ferroelectrics, as the field enhances. Acoustic emission bursts, accompanying the depolarization temperature, weakened with the enhancing field, whereas the ones accompanying the temperature of the dielectric constant maximum exhibited two maxima: near 0.1 kV/cm and near 0.3 kV/cm. The meaning of these two acoustic emission maxima is discussed.

Spike-Interval Triggered Averaging Reveals a Quasi-Periodic Spiking Alternative for Stochastic Resonance in Catfish Electroreceptors

PubMed Central

Lankheet, Martin J. M.; Klink, P. Christiaan; Borghuis, Bart G.; Noest, André J.

2012-01-01

Catfish detect and identify invisible prey by sensing their ultra-weak electric fields with electroreceptors. Any neuron that deals with small-amplitude input has to overcome sensitivity limitations arising from inherent threshold non-linearities in spike-generation mechanisms. Many sensory cells solve this issue with stochastic resonance, in which a moderate amount of intrinsic noise causes irregular spontaneous spiking activity with a probability that is modulated by the input signal. Here we show that catfish electroreceptors have adopted a fundamentally different strategy. Using a reverse correlation technique in which we take spike interval durations into account, we show that the electroreceptors generate a supra-threshold bias current that results in quasi-periodically produced spikes. In this regime stimuli modulate the interval between successive spikes rather than the instantaneous probability for a spike. This alternative for stochastic resonance combines threshold-free sensitivity for weak stimuli with similar sensitivity for excitations and inhibitions based on single interspike intervals. PMID:22403709

Investigation of ionospheric stimulated Brillouin scatter generated at pump frequencies near electron gyroharmonics

NASA Astrophysics Data System (ADS)

Mahmoudian, A.; Scales, W. A.; Bernhardt, P. A.; Fu, H.; Briczinski, S. J.; McCarrick, M. J.

2013-11-01

Stimulated Electromagnetic Emissions (SEEs), secondary electromagnetic waves excited by high power electromagnetic waves transmitted into the ionosphere, produced by the Magnetized Stimulated Brillouin Scatter (MSBS) process are investigated. Data from four recent research campaigns at the High Frequency Active Auroral Research Program (HAARP) facility is presented in this work. These experiments have provided additional quantitative interpretation of the SEE spectrum produced by MSBS to yield diagnostic measurements of the electron temperature and ion composition in the heated ionosphere. SEE spectral emission lines corresponding to ion acoustic (IA) and electrostatic ion cyclotron (EIC) mode excitation were observed with a shift in frequency up to a few tens of Hz from the pump frequency for heating near the third harmonic of the electron gyrofrequency 3fce. The threshold of each emission line has been measured by changing the pump wave power. The excitation threshold of IA and EIC emission lines originating at the reflection and upper hybrid altitudes is measured for various beam angles relative to the magnetic field. Variation of strength of MSBS emission lines with pump frequency relative to 3fce and 4fce is also studied. A full wave solution has been used to estimate the amplitude of the electric field at the interaction altitude. The estimated instability threshold using the theoretical model is compared with the threshold of MSBS lines in the experiment and possible diagnostic information for the background ionospheric plasma is discussed. Simultaneous formation of artificial field-aligned irregularities (FAIs) and suppression of the MSBS process is investigated. This technique can be used to estimate the growth time of artificial FAIs which may result in determination of plasma waves and physical process involved in the formation of FAIs.

Transformation of nonlinear behaviors: from bright- to dark-gap soliton in a one-dimensional photonic crystal containing a nonlinear indefinite metamaterial defect.

PubMed

Zhang, Wei; Chen, Yuanyuan; Hou, Peng; Shi, Jielong; Wang, Qi

2010-12-01

Nonlinear propagation characteristics are investigated theoretically in a one-dimensional photonic band-gap structure doped with a nonlinear indefinite metamaterial defect for five distinct frequency intervals. It is found from the electric field distribution that there exists the bright gap solitonlike when the nonlinear indefinite metamaterial defect is a cut-off medium, while the dark gap solitonlike can appear in the nonlinear never cut-off defect layer. It is also found that there exists corresponding bistable lateral shift the properties of which are strongly dependent on the permittivity and permeability of nonlinear indefinite metamaterials. Moreover, in contrast to the switch-down threshold value, the switch-up threshold value is more sensitive to the incident frequency.

Eradication of multidrug-resistant pseudomonas biofilm with pulsed electric fields.

PubMed

Khan, Saiqa I; Blumrosen, Gaddi; Vecchio, Daniela; Golberg, Alexander; McCormack, Michael C; Yarmush, Martin L; Hamblin, Michael R; Austen, William G

2016-03-01

Biofilm formation is a significant problem, accounting for over eighty percent of microbial infections in the body. Biofilm eradication is problematic due to increased resistance to antibiotics and antimicrobials as compared to planktonic cells. The purpose of this study was to investigate the effect of Pulsed Electric Fields (PEF) on biofilm-infected mesh. Prolene mesh was infected with bioluminescent Pseudomonas aeruginosa and treated with PEF using a concentric electrode system to derive, in a single experiment, the critical electric field strength needed to kill bacteria. The effect of the electric field strength and the number of pulses (with a fixed pulse length duration and frequency) on bacterial eradication was investigated. For all experiments, biofilm formation and disruption were confirmed with bioluminescent imaging and Scanning Electron Microscopy (SEM). Computation and statistical methods were used to analyze treatment efficiency and to compare it to existing theoretical models. In all experiments 1500 V are applied through a central electrode, with pulse duration of 50 μs, and pulse delivery frequency of 2 Hz. We found that the critical electric field strength (Ecr) needed to eradicate 100-80% of bacteria in the treated area was 121 ± 14 V/mm when 300 pulses were applied, and 235 ± 6.1 V/mm when 150 pulses were applied. The area at which 100-80% of bacteria were eradicated was 50.5 ± 9.9 mm(2) for 300 pulses, and 13.4 ± 0.65 mm(2) for 150 pulses. 80% threshold eradication was not achieved with 100 pulses. The results indicate that increased efficacy of treatment is due to increased number of pulses delivered. In addition, we that showed the bacterial death rate as a function of the electrical field follows the statistical Weibull model for 150 and 300 pulses. We hypothesize that in the clinical setting, combining systemic antibacterial therapy with PEF will yield a synergistic effect leading to improved eradication of mesh infections. © 2015 Wiley Periodicals, Inc.

Macroscopic response in active nonlinear photonic crystals.

PubMed

Alagappan, Gandhi; John, Sajeev; Li, Er Ping

2013-09-15

We derive macroscopic equations of motion for the slowly varying electric field amplitude in three-dimensional active nonlinear optical nanostructures. We show that the microscopic Maxwell equations and polarization dynamics can be simplified to a macroscopic one-dimensional problem in the direction of group velocity. For a three-level active material, we derive the steady-state equations for normal mode frequency, threshold pumping, nonlinear Bloch mode amplitude, and lasing in photonic crystals. Our analytical results accurately recapture the results of exact numerical methods.

Ponderomotive effects in multiphoton pair production

NASA Astrophysics Data System (ADS)

Kohlfürst, Christian; Alkofer, Reinhard

2018-02-01

The Dirac-Heisenberg-Wigner formalism is employed to investigate electron-positron pair production in cylindrically symmetric but otherwise spatially inhomogeneous, oscillating electric fields. The oscillation frequencies are hereby tuned to obtain multiphoton pair production in the nonperturbative threshold regime. An effective mass, as well as a trajectory-based semiclassical analysis, is introduced in order to interpret the numerical results for the distribution functions as well as for the particle yields and spectra. The results, including the asymptotic particle spectra, display clear signatures of ponderomotive forces.

The Role of Nuclei Size in Transient Cavitation Threshold Measurements

DTIC Science & Technology

1984-09-01

resonance frequency of about 50 kHz. Also epoxied to the cell are a minature PZT-5 pill transducer (to monitor the sound field) and an omega Engineering model...44018 linear thermistor. The glass inlet and- outlet tubes have an o.d. of roughly 3.5mm and are held in place by a - 25 - 26 * two hole rubber...wrapped in black electrical tape, provide a tortuous path for outside light which helps to preserve the integrity of the light tight enclosure. The

Robot gripper

NASA Technical Reports Server (NTRS)

Webb, Winston S. (Inventor)

1987-01-01

An electronic force-detecting robot gripper for gripping objects and attaching to an external robot arm is disclosed. The gripper comprises motor apparatus, gripper jaws, and electrical circuits for driving the gripper motor and sensing the amount of force applied by the jaws. The force applied by the jaws is proportional to a threshold value of the motor current. When the motor current exceeds the threshold value, the electrical circuits supply a feedback signal to the electrical control circuit which, in turn, stops the gripper motor.

Data-fusion receiver

DOEpatents

Gabelmann, Jeffrey M.; Kattner, J. Stephen; Houston, Robert A.

2006-12-19

This invention is an ultra-low frequency electromagnetic telemetry receiver which fuses multiple input receive sources to synthesize a decodable message packet from a noise corrupted telemetry message string. Each block of telemetry data to be sent to the surface receiver from a borehole tool is digitally encoded into a data packet prior to transmission. The data packet is modulated onto the ULF EM carrier wave and transmitted from the borehole to the surface and then are simultaneously detected by multiple receive sensors disbursed within the rig environment. The receive sensors include, but are not limited to, electric field and magnetic field sensors. The spacing of the surface receive elements is such that noise generators are unequally coupled to each receive element due to proximity and/or noise generator type (i.e. electric or magnetic field generators). The receiver utilizes a suite of decision metrics to reconstruct the original, non noise-corrupted data packet from the observation matrix via the estimation of individual data frames. The receiver will continue this estimation process until: 1) the message validates, or 2) a preset "confidence threshold" is reached whereby frames within the observation matrix are no longer "trusted".

Estimating neuromuscular stimulation within the human torso with Taser stimulus.

PubMed

Sun, Hongyu; Webster, John G

2007-11-07

Designers of electromuscular incapacitation devices need to know efficacy. Which areas of nerve and muscle are stimulated and are these areas adequate to cause incapacitation? This paper focuses on efficacy, which used a torso-sized finite element model with a mesh of about 5 mm. To estimate the neuromuscular regions stimulated by the Taser X26, calculations of electric current density and field strength values with 1 A inserted into the torso using the Utah 3D mesh were made. Field-times-duration values for given Taser stimulation were calculated. Then the region where the motor nerve was stimulated by the Taser was estimated by using a field-times-duration threshold from Reilly (1998 'Applied Bioelectricity: From Electrical Stimulation to Electropathology ' (New York: Springer)). Neuromuscular stimulation occurred up to about 19 cm away from the darts and included the spinal cord. The current density at the heart for dart separation less than 10 cm was smaller than for larger dart separation. Users of finite element computer models will find information for torso models and their creation, meshing and operation.

Estimating neuromuscular stimulation within the human torso with Taser® stimulus

NASA Astrophysics Data System (ADS)

Sun, Hongyu; Webster, John G.

2007-11-01

Designers of electromuscular incapacitation devices need to know efficacy. Which areas of nerve and muscle are stimulated and are these areas adequate to cause incapacitation? This paper focuses on efficacy, which used a torso-sized finite element model with a mesh of about 5 mm. To estimate the neuromuscular regions stimulated by the Taser® X26, calculations of electric current density and field strength values with 1 A inserted into the torso using the Utah 3D mesh were made. Field-times-duration values for given Taser stimulation were calculated. Then the region where the motor nerve was stimulated by the Taser was estimated by using a field-times-duration threshold from Reilly (1998 Applied Bioelectricity: From Electrical Stimulation to Electropathology (New York: Springer)). Neuromuscular stimulation occurred up to about 19 cm away from the darts and included the spinal cord. The current density at the heart for dart separation less than 10 cm was smaller than for larger dart separation. Users of finite element computer models will find information for torso models and their creation, meshing and operation.

Improving Tumor Treating Fields Treatment Efficacy in Patients With Glioblastoma Using Personalized Array Layouts

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

Wenger, Cornelia, E-mail: cwenger@fc.ul.pt; Salvador, Ricardo; Basser, Peter J.

Purpose: To investigate tumors of different size, shape, and location and the effect of varying transducer layouts on Tumor Treating Fields (TTFields) distribution in an anisotropic model. Methods and Materials: A realistic human head model was generated from MR images of 1 healthy subject. Four different virtual tumors were placed at separate locations. The transducer arrays were modeled to mimic the TTFields-delivering commercial device. For each tumor location, varying array layouts were tested. The finite element method was used to calculate the electric field distribution, taking into account tissue heterogeneity and anisotropy. Results: In all tumors, the average electric field inducedmore » by either of the 2 perpendicular array layouts exceeded the 1-V/cm therapeutic threshold value for TTFields effectiveness. Field strength within a tumor did not correlate with its size and shape but was higher in more superficial tumors. Additionally, it always increased when the array was adapted to the tumor's location. Compared with a default layout, the largest increase in field strength was 184%, and the highest average field strength induced in a tumor was 2.21 V/cm. Conclusions: These results suggest that adapting array layouts to specific tumor locations can significantly increase field strength within the tumor. Our findings support the idea of personalized treatment planning to increase TTFields efficacy for patients with GBM.« less

Nitrogen anion doping as a strategy to suppress negative gate-bias illumination instability of ZnSnO thin film transistor

NASA Astrophysics Data System (ADS)

Li, Jun; Fu, Yi-Zhou; Huang, Chuan-Xin; Zhang, Jian-Hua; Jiang, Xue-Yin; Zhang, Zhi-Lin

2016-04-01

This work presents a strategy of nitrogen anion doping to suppress negative gate-bias illumination instability. The electrical performance and negative gate-bias illumination stability of the ZnSnON thin film transistors (TFTs) are investigated. Compared with ZnSnO-TFT, ZnSnON-TFT has a 53% decrease in the threshold voltage shift under negative bias illumination stress and electrical performance also progresses obviously. The stability improvement of ZnSnON-TFT is attributed to the reduction in ionized oxygen vacancy defects and the photodesorption of oxygen-related molecules. It suggests that anion doping can provide an effective solution to the adverse tradeoff between field effect mobility and negative bias illumination stability.

Estimated intensity of the EMP from lightning discharges necessary for elves initiation based on balloon experiment

NASA Astrophysics Data System (ADS)

Kondo, S.; Yoshida, A.; Takahashi, Y.; Chikada, S.; Adachi, T.; Sakanoi, T.

2007-12-01

Transient optical phenomena in the mesosphere and lower ionosphere called transient luminous events (TLEs) have been investigated extensively since the first discovery in 1989. In the lower ionosphere, elves are generated by the electromagnetic pulses (EMPs) radiated from the intense lightning current. On the ground-based observation, cameras can not always identify the occurrence of elves because elves emission is sometimes reduced significantly by the atmosphere and blocked by clouds. Therefore, it has been difficult to determine the threshold of intensity of EMPs necessary for initiation of elves. We simultaneously carried out optical and sferics measurements for TLEs and lightning discharges using a high altitude balloon launched at Sanriku Balloon Center on the night of August 25 / 26 in 2006. We fixed four CCD cameras on the gondola, each of which had horizontal FOV of ~100 degree. They cover 360 degree in horizontal direction and imaged the TLEs without atmospheric extinction nor blocking by clouds. The frame rate is 30 fps. We installed three dipole antennas at the gondola, which received the vertical and horizontal electric fields radiated from lightning discharges. The frequency range of the VLF receiver is 1-25 kHz. We also make use of VLF sferics data obtained by ground-based antennas located at Tohoku University in Sendai. We picked up six elves from the image data set obtained by the CCD cameras, and examined the maximum amplitudes of the vertical electric field for 22 lightning discharge events including the six elves events observed both at the balloon and at Sendai. It is found that the maximum amplitudes of the vertical electric field in the five elves events are much larger than those in the other lightning events. We estimate the intensity of the radiated electric field necessary for elves. About one elves event, we don't see intense vertical electric field in the balloon data.

First principles study of size and external electric field effects on the atomic and electronic properties of gallium nitride nanostructures

NASA Astrophysics Data System (ADS)

Yilmaz, Hulusi

A comprehensive density functional theory study of atomic and the electronic properties of wurtzite gallium nitride (GaN) nanostructures with different sizes and shapes is presented and the effect of external electric field on these properties is examined. We show that the atomic and electronic properties of [101¯0] facet single-crystal GaN nanotubes (quasi-1D), nanowires (1D) and nanolayers (2D) are mainly determined by the surface to volume ratio. The shape dependent quantum confinement and strain effects on the atomic and electronic properties of these GaN nanostructures are found to be negligible. Based on this similarity between the atomic and electronic properties of the small size GaN nanostructures, we calculated the atomic and electronic properties of the practical size (28.1 A wall thickness) single-crystal GaN nanotubes through computational much economical GaN nanoslabs (nanolayers). Our results show that, regardless of diameter, hydrogen saturated single-crystal GaN tubes with the wall thickness of 28.1 A are energetically stable and they have a noticeably larger band gap with respect to the band gap of bulk GaN. The band gap of unsaturated single-crystal GaN tubes, on the other hand, is always smaller than the band gap of the wurtzite bulk GaN. In a separate study, we show that a transverse electric field induces a homojunction across the diameter of initially semiconducting GaN single-crystal nanotubes and nanowires. The homojunction arises due to the decreased energy of the electronic states in the higher potential region with respect to the energy of those states in the lower potential region under the transverse electric field. Calculations on single-crystal GaN nanotubes and nanowires of different diameter and wall thickness show that the threshold electric field required for the semiconductor-homojunction induction increases with increasing wall thickness and decreases significantly with increasing diameter.

Immobilization thresholds of electrofishing relative to fish size

USGS Publications Warehouse

Dolan, C.R.; Miranda, L.E.

2003-01-01

Fish size and electrical waveforms have frequently been associated with variation in electrofishing effectiveness. Under controlled laboratory conditions, we measured the electrical power required by five electrical waveforms to immobilize eight fish species of diverse sizes and shapes. Fish size was indexed by total body length, surface area, volume, and weight; shape was indexed by the ratio of body length to body depth. Our objectives were to identify immobilization thresholds, elucidate the descriptors of fish size that were best associated with those immobilization thresholds, and determine whether the vulnerability of a species relative to other species remained constant across electrical treatments. The results confirmed that fish size is a key variable controlling the immobilization threshold and further suggested that the size descriptor best related to immobilization is fish volume. The peak power needed to immobilize fish decreased rapidly with increasing fish volume in small fish but decreased slowly for fish larger than 75-100 cm 3. Furthermore, when we controlled for size and shape, different waveforms did not favor particular species, possibly because of the overwhelming effect of body size. Many of the immobilization inconsistencies previously attributed to species might simply represent the effect of disparities in body size.

Effect of high-latitude ionospheric convection on Sun-aligned polar caps

NASA Technical Reports Server (NTRS)

Sojka, J. J.; Zhu, L.; Crain, D. J.; Schunk, R. W.

1994-01-01

A coupled magnetospheric-ionospheric (M-I) magnetohydrodynamic (MHD) model has been used to simulate the formation of Sun-aligned polar cap arcs for a variety of interplanetary magnetic field (IMF) dependent polar cap convection fields. The formation process involves launching an Alfven shear wave from the magnetosphere to the ionosphere where the ionospheric conductance can react self-consistently to changes in the upward currents. We assume that the initial Alfven shear wave is the result of solar wind-magnetosphere interactions. The simulations show how the E region density is affected by the changes in the electron precipitation that are associated with the upward currents. These changes in conductance lead to both a modified Alfven wave reflection at the ionosphere and the generation of secondary Alfven waves in the ionosphere. The ensuing bouncing of the Alfven waves between the ionosphere and magnetosphere is followed until an asymptotic solution is obtained. At the magnetosphere the Alfven waves reflect at a fixed boundary. The coupled M-I Sun-aligned polar cap arc model of Zhu et al.(1993a) is used to carry out the simulations. This study focuses on the dependence of the polar cap arc formation on the background (global) convection pattern. Since the polar cap arcs occur for northward and strong B(sub y) IMF conditions, a variety of background convection patterns can exist when the arcs are present. The study shows that polar cap arcs can be formed for all these convection patterns; however, the arc features are dramatically different for the different patterns. For weak sunward convection a relatively confined single pair of current sheets is associated with the imposed Alfven shear wave structure. However, when the electric field exceeds a threshold, the arc structure intensifies, and the conductance increases as does the local Joule heating rate. These increases are faster than a linear dependence on the background electric field strength. Furthermore, above the threshold, the single current sheet pair splits into multiple current sheet pairs. For the fixed initial ionospheric and magnetospheric conditions used in this study, the separation distance between the current pairs was found to be almost independent of the background electric field strength. For either three-cell or distorted two-cell background convection patterns the arc formation favored the positive B(sub y) case in the northern hemisphere.

Role of switching-on and -off effects in the vacuum instability

NASA Astrophysics Data System (ADS)

Adorno, T. C.; Ferreira, R.; Gavrilov, S. P.; Gitman, D. M.

2018-04-01

We find exact differential mean numbers of fermions and bosons created from the vacuum due to a composite electric field of special configuration. This configuration imitates a finite switching-on and -off regime and consists of fields that switch on exponentially from the infinitely remote past, remains constant during a certain interval T and switch off exponentially to the infinitely remote future. We show that calculations in the slowly varying field approximation are completely predictable in the framework of a locally constant field approximation. Beyond the slowly varying field approximation, we study effects of fast switching on and off in a number of cases when the size of the dimensionless parameter eET is either close or exceeds the threshold value that determines the transition from a regime sensitive to on-off parameters to the slowly varying regime for which these effects are secondary.

Power management system

DOEpatents

Algrain, Marcelo C.; Johnson, Kris W.; Akasam, Sivaprasad; Hoff, Brian D.

2007-10-02

A method of managing power resources for an electrical system of a vehicle may include identifying enabled power sources from among a plurality of power sources in electrical communication with the electrical system and calculating a threshold power value for the enabled power sources. A total power load placed on the electrical system by one or more power consumers may be measured. If the total power load exceeds the threshold power value, then a determination may be made as to whether one or more additional power sources is available from among the plurality of power sources. At least one of the one or more additional power sources may be enabled, if available.

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

Yoo, Hojin

The thesis presents studies of vacuum pair productions and its applications in early universe cosmology and high energy astrophysics. Vacuum often becomes unstable and spontaneously decays into pairs of particles in rapidly expanding universes or under strong external electromagnetic fields. Theoretically, spontaneous pair productions due to such non-trivial backgrounds of spacetimes or electromagnetic fields are well-understood. However, the effect of particle productions has not been observed so far because of experiemtal difficulties in obtaining large curvatures of space-times or strong electric fields. Although it may be impossible to observe the pair productions directly via laboratory experiments, there are still powerfulmore » sources of space-time curvatures or electric fields in cosmology and astrophysics, which result in observations. In Part I, we explore the inflationary models in early universe utilizing pair productions through gravity. We study observable signatures on the cosmic microwave background, such as isocurvature perturbations and non-Gaussianities, generated from the particle production of WIMPzillas and axions during or after inflation. In Part II, we investigate the electron-positron pair production in the magnetosphere of pulsars whose electromagnetic fields are expected to close to or even greater than the pair production threshold. In particular, we demonstrate that the pair production may be responsible for giant pulses from the Crab pulsar.« less

Time domain dielectric spectroscopy of nanosecond pulsed electric field induced changes in dielectric properties of pig whole blood.

PubMed

Zhuang, Jie; Kolb, Juergen F

2015-06-01

The dielectric spectra of fresh pig whole blood in the β-dispersion range after exposure to 300-nanosecond pulsed electric fields (nsPEFs) with amplitude higher than the supra-electroporation threshold for erythrocytes were recorded by time domain reflectometry dielectric spectroscopy. The implications of the dielectric parameters on the dynamics of post-pulse pore development were discussed in light of the Cole-Cole relaxation model. The temporal development of the Cole-Cole parameters indicates that nsPEFs induced significant poration and swelling of erythrocytes within the first 5 min. The results also show that the majority of erythrocytes could not fully recover from supra-electroporation up to 30 min. The findings of this study suggest that time domain dielectric spectroscopy is a promising label-free and real-time physiological measuring technique for nsPEF-blood related biomedical applications, capable of following the conformational and morphological changes of cells. Copyright © 2014 Elsevier B.V. All rights reserved.

Equilibrium configurations of the conducting liquid surface in a nonuniform electric field

NASA Astrophysics Data System (ADS)

Zubarev, N. M.; Zubareva, O. V.

2011-01-01

Possible equilibrium configurations of the free surface of a conducting liquid deformed by a nonuniform external electric field are investigated. The liquid rests on an electrode that has the shape of a dihedral angle formed by two intersecting equipotential half-planes (conducting wedge). It is assumed that the problem has plane symmetry: the surface is invariant under shift along the edge of the dihedral angle. A one-parametric family of exact solutions for the shape of the surface is found in which the opening angle of the region above the wedge serves as a parameter. The solutions are valid when the pressure difference between the inside and outside of the liquid is zero. For an arbitrary pressure difference, approximate solutions to the problem are constructed and it is demonstrated the approximation error is small. It is found that, when the potential difference exceeds a certain threshold value, equilibrium solutions are absent. In this case, the region occupied by the liquid disintegrates, the disintegration scenario depending on the opening angle.

The combined effects of transcutaneous electrical nerve stimulation (TENS) and stretching on muscle hardness and pressure pain threshold.

PubMed

Karasuno, Hiroshi; Ogihara, Hisayoshi; Morishita, Katsuyuki; Yokoi, Yuka; Fujiwara, Takayuki; Ogoma, Yoshiro; Abe, Koji

2016-04-01

[Purpose] This study aimed to clarify the immediate effects of a combined transcutaneous electrical nerve stimulation and stretching protocol. [Subjects] Fifteen healthy young males volunteered to participate in this study. The inclusion criterion was a straight leg raising range of motion of less than 70 degrees. [Methods] Subjects performed two protocols: 1) stretching (S group) of the medial hamstrings, and 2) tanscutaneous electrical nerve stimulation (100 Hz) with stretching (TS group). The TS group included a 20-minute electrical stimulation period followed by 10 minutes of stretching. The S group performed 10 minutes of stretching. Muscle hardness, pressure pain threshold, and straight leg raising range of motion were analyzed to evaluate the effects. The data were collected before transcutaneous electrical nerve stimulation (T1), before stretching (T2), immediately after stretching (T3), and 10 minutes after stretching (T4). [Results] Combined transcutaneous electrical nerve stimulation and stretching had significantly beneficial effects on muscle hardness, pressure pain threshold, and straight leg raising range of motion at T2, T3, and T4 compared with T1. [Conclusion] These results support the belief that transcutaneous electrical nerve stimulation combined with stretching is effective in reducing pain and decreasing muscle hardness, thus increasing range of motion.

Efficient charge-carrier extraction from Ag₂S quantum dots prepared by the SILAR method for utilization of multiple exciton generation.

PubMed

Zhang, Xiaoliang; Liu, Jianhua; Johansson, Erik M J

2015-01-28

The utilization of electron-hole pairs (EHPs) generated from multiple excitons in quantum dots (QDs) is of great interest toward efficient photovoltaic devices and other optoelectronic devices; however, extraction of charge carriers remains difficult. Herein, we extract photocharges from Ag2S QDs and investigate the dependence of the electric field on the extraction of charges from multiple exciton generation (MEG). Low toxic Ag2S QDs are directly grown on TiO2 mesoporous substrates by employing the successive ionic layer adsorption and reaction (SILAR) method. The contact between QDs is important for the initial charge separation after MEG and for the carrier transport, and the space between neighbor QDs decreases with more SILAR cycles, resulting in better charge extraction. At the optimal electric field for extraction of photocharges, the results suggest that the threshold energy (hνth) for MEG is 2.41Eg. The results reveal that Ag2S QD is a promising material for efficient extraction of charges from MEG and that QDs prepared by SILAR have an advantageous electrical contact facilitating charge separation and extraction.

Impact of nanosecond pulsed electric fields on primary hippocampal neurons

NASA Astrophysics Data System (ADS)

Roth, Caleb C.; Payne, Jason A.; Kuipers, Marjorie A.; Thompson, Gary L.; Wilmink, Gerald J.; Ibey, Bennett L.

2012-02-01

Cellular exposure to nanosecond pulsed electric fields (nsPEF) are believed to cause immediate creation of nanopores in the plasma membrane. These nanopores enable passage of small ions, but remain impermeable to larger molecules like propidium iodide. Previous work has shown that nanopores are stable for minutes after exposure, suggesting that formation of nanopores in excitable cells could lead to prolonged action potential inhibition. Previously, we measured the formation of nanopores in neuroblastoma cells by measuring the influx of extracellular calcium by preloading cells with Calcium Green-AM. In this work, we explored the impact of changing the width of a single nsPEF, at constant amplitude, on uptake of extracellular calcium ions by primary hippocampal neurons (PHN). Calcium Green was again used to measure the influx of extracellular calcium and FM1-43 was used to monitor changes in membrane conformation. The observed thresholds for nanopore formation in PHN by nsPEF were comparable to those measured in neuroblastoma. This work is the first study of nsPEF effects on PHN and strongly suggests that neurological inhibition by nanosecond electrical pulses is highly likely at doses well below irreversible damage.

Daily maternal separations during stress hyporesponsive period decrease the thresholds of panic-like behaviors to electrical stimulation of the dorsal periaqueductal gray of the adult rat.

PubMed

Borges-Aguiar, Ana Cristina; Schauffer, Luana Zanoni; de Kloet, Edo Ronald; Schenberg, Luiz Carlos

2018-05-15

The present study examined whether early life maternal separation (MS), a model of childhood separation anxiety, predisposes to panic at adulthood. For this purpose, male pups were submitted to 3-h daily maternal separations along postnatal (PN) days of either the 'stress hyporesponsive period' (SHRP) from PN4 to PN14 (MS11) or throughout lactation from PN2 to PN21 (MS20). Pups were further reunited to conscious (CM) or anesthetized (AM) mothers to assess the effect of mother-pup interaction upon reunion. Controls were subjected to brief handling (15 s) once a day throughout lactation (BH20). As adults (PN60), rats were tested for the thresholds to evoke panic-like behaviors upon electrical stimulation of dorsal periaqueductal gray matter and exposed to an elevated plus-maze, an open-field, a forced swim and a sucrose preference test. A factor analysis was also performed to gain insight into the meaning of behavioral tests. MS11-CM rather than MS20-CM rats showed enhanced panic responses and reductions in both swimming and sucrose preference. Panic facilitations were less intense in mother-neglected rats. Although MS did not affect anxiety, MS11-AM showed robust reductions of defecation in an open-field. Factor analysis singled out anxiety, hedonia, exploration, coping and gut activity. Although sucrose preference and coping loaded on separate factors, appetite (adult weight) correlated with active coping in both forced swim and open-field (central area exploration). Concluding, whereas 3h-daily maternal separations during SHRP increased rat's susceptibility to experimental panic attacks, separations throughout lactation had no effects on panic and enhanced active coping. Copyright © 2018 Elsevier B.V. All rights reserved.

Auditory cortical responses in patients with cochlear implants

PubMed Central

Burdo, S; Razza, S; Di Berardino, F; Tognola, G

2006-01-01

Summary Currently, the most commonly used electrophysiological tests for cochlear implant evaluation are Averaged Electrical Voltages (AEV), Electrical Advisory Brainstem Responses (EABR) and Neural Response Telemetry (NRT). The present paper focuses on the study of acoustic auditory cortical responses, or slow vertex responses, which are not widely used due to the difficulty in recording, especially in young children. Aims of this study were validation of slow vertex responses and their possible applications in monitoring postimplant results, particularly restoration of hearing and auditory maturation. In practice, the use of tone-bursts, also through hearing aids or cochlear implants, as in slow vertex responses, allows many more frequencies to be investigated and louder intensities to be reached than with other tests based on a click as stimulus. Study design focused on latencies of N1 and P2 slow vertex response peaks in cochlear implants. The study population comprised 45 implant recipients (aged 2 to 70 years), divided into 5 different homogeneous groups according to chronological age, age at onset of deafness, and age at implantation. For each subject, slow vertex responses and free-field auditory responses (PTAS) were recorded for tone-bursts at 500 and 2000 Hz before cochlear implant surgery (using hearing aid amplification) and during scheduled sessions at 3rd and 12th month after implant activation. Results showed that N1 and P2 latencies decreased in all groups starting from 3rd through 12th month after activation. Subjects implanted before school age or at least before age 8 yrs showed the widest latency changes. All subjects showed a reduction in the gap between subjective thresholds (obtained with free field auditory responses) and objective thresholds (obtained with slow vertex responses), obtained in presurgery stage and after cochlear implant. In conclusion, a natural evolution of neurophysiological cortical activities of the auditory pathway, over time, was found especially in young children with prelingual deafness and implanted in preschool age. Cochlear implantation appears to provide hearing restoration, demonstrated by the sharp reduction of the gap between subjective free field auditory responses and slow vertex responses threshold obtained with hearing aids vs. cochlear implant. PMID:16886849

Auditory Performance and Electrical Stimulation Measures in Cochlear Implant Recipients With Auditory Neuropathy Compared With Severe to Profound Sensorineural Hearing Loss.

PubMed

Attias, Joseph; Greenstein, Tally; Peled, Miriam; Ulanovski, David; Wohlgelernter, Jay; Raveh, Eyal

The aim of the study was to compare auditory and speech outcomes and electrical parameters on average 8 years after cochlear implantation between children with isolated auditory neuropathy (AN) and children with sensorineural hearing loss (SNHL). The study was conducted at a tertiary, university-affiliated pediatric medical center. The cohort included 16 patients with isolated AN with current age of 5 to 12.2 years who had been using a cochlear implant for at least 3.4 years and 16 control patients with SNHL matched for duration of deafness, age at implantation, type of implant, and unilateral/bilateral implant placement. All participants had had extensive auditory rehabilitation before and after implantation, including the use of conventional hearing aids. Most patients received Cochlear Nucleus devices, and the remainder either Med-El or Advanced Bionics devices. Unaided pure-tone audiograms were evaluated before and after implantation. Implantation outcomes were assessed by auditory and speech recognition tests in quiet and in noise. Data were also collected on the educational setting at 1 year after implantation and at school age. The electrical stimulation measures were evaluated only in the Cochlear Nucleus implant recipients in the two groups. Similar mapping and electrical measurement techniques were used in the two groups. Electrical thresholds, comfortable level, dynamic range, and objective neural response telemetry threshold were measured across the 22-electrode array in each patient. Main outcome measures were between-group differences in the following parameters: (1) Auditory and speech tests. (2) Residual hearing. (3) Electrical stimulation parameters. (4) Correlations of residual hearing at low frequencies with electrical thresholds at the basal, middle, and apical electrodes. The children with isolated AN performed equally well to the children with SNHL on auditory and speech recognition tests in both quiet and noise. More children in the AN group than the SNHL group were attending mainstream educational settings at school age, but the difference was not statistically significant. Significant between-group differences were noted in electrical measurements: the AN group was characterized by a lower current charge to reach subjective electrical thresholds, lower comfortable level and dynamic range, and lower telemetric neural response threshold. Based on pure-tone audiograms, the children with AN also had more residual hearing before and after implantation. Highly positive coefficients were found on correlation analysis between T levels across the basal and midcochlear electrodes and low-frequency acoustic thresholds. Prelingual children with isolated AN who fail to show expected oral and auditory progress after extensive rehabilitation with conventional hearing aids should be considered for cochlear implantation. Children with isolated AN had similar pattern as children with SNHL on auditory performance tests after cochlear implantation. The lower current charge required to evoke subjective and objective electrical thresholds in children with AN compared with children with SNHL may be attributed to the contribution to electrophonic hearing from the remaining neurons and hair cells. In addition, it is also possible that mechanical stimulation of the basilar membrane, as in acoustic stimulation, is added to the electrical stimulation of the cochlear implant.

40 CFR 98.451 - Reporting threshold.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 22 2012-07-01 2012-07-01 false Reporting threshold. 98.451 Section 98.451 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED... threshold. You must report GHG emissions under this subpart if your facility contains an electrical...

Field-Effect Transistors Based on Networks of Highly Aligned, Chemically Synthesized N = 7 Armchair Graphene Nanoribbons.

PubMed

Passi, Vikram; Gahoi, Amit; Senkovskiy, Boris V; Haberer, Danny; Fischer, Felix R; Grüneis, Alexander; Lemme, Max C

2018-03-28

We report on the experimental demonstration and electrical characterization of N = 7 armchair graphene nanoribbon (7-AGNR) field effect transistors. The back-gated transistors are fabricated from atomically precise and highly aligned 7-AGNRs, synthesized with a bottom-up approach. The large area transfer process holds the promise of scalable device fabrication with atomically precise nanoribbons. The channels of the FETs are approximately 30 times longer than the average nanoribbon length of 30 nm to 40 nm. The density of the GNRs is high, so that transport can be assumed well-above the percolation threshold. The long channel transistors exhibit a maximum I ON / I OFF current ratio of 87.5.

Electrical percolation threshold of cementitious composites possessing self-sensing functionality incorporating different carbon-based materials

NASA Astrophysics Data System (ADS)

Al-Dahawi, Ali; Haroon Sarwary, Mohammad; Öztürk, Oğuzhan; Yıldırım, Gürkan; Akın, Arife; Şahmaran, Mustafa; Lachemi, Mohamed

2016-10-01

An experimental study was carried out to understand the electrical percolation thresholds of different carbon-based nano- and micro-scale materials in cementitious composites. Multi-walled carbon nanotubes (CNTs), graphene nanoplatelets (GNPs) and carbon black (CB) were selected as the nano-scale materials, while 6 and 12 mm long carbon fibers (CF6 and CF12) were used as the micro-scale carbon-based materials. After determining the percolation thresholds of different electrical conductive materials, mechanical properties and piezoresistive properties of specimens produced with the abovementioned conductive materials at percolation threshold were investigated under uniaxial compressive loading. Results demonstrate that regardless of initial curing age, the percolation thresholds of CNT, GNP, CB and CFs in ECC mortar specimens were around 0.55%, 2.00%, 2.00% and 1.00%, respectively. Including different carbon-based conductive materials did not harm compressive strength results; on the contrary, it improved overall values. All cementitious composites produced with carbon-based materials, with the exception of the control mixtures, exhibited piezoresistive behavior under compression, which is crucial for sensing capability. It is believed that incorporating the sensing attribute into cementitious composites will enhance benefits for sustainable civil infrastructures.

Detection and Use of Load and Gage Output Repeats of Wind Tunnel Strain-Gage Balance Data

NASA Technical Reports Server (NTRS)

Ulbrich, N.

2017-01-01

Criteria are discussed that may be used for the detection of load and gage output repeats of wind tunnel strain-gage balance data. First, empirical thresholds are introduced that help determine if the loads or electrical outputs of a pair of balance calibration or check load data points match. A threshold of 0.01 percent of the load capacity is suggested for the identification of matching loads. Similarly, a threshold of 0.1 microV/V is recommended for the identification of matching electrical outputs. Two examples for the use of load and output repeats are discussed to illustrate benefits of the implementation of a repeat point detection algorithm in a balance data analysis software package. The first example uses the suggested load threshold to identify repeat data points that may be used to compute pure errors of the balance loads. This type of analysis may reveal hidden data quality issues that could potentially be avoided by making calibration process improvements. The second example uses the electrical output threshold for the identification of balance fouling. Data from the calibration of a six-component force balance is used to illustrate the calculation of the pure error of the balance loads.

Coupled-cavity surface-emitting lasers: spectral and polarization threshold characteristics and electrooptic switching.

PubMed

Panajotov, Krassimir P; Zujewski, Mateusz; Thienpont, Hugo

2010-12-20

We study spectral and polarization threshold characteristics of coupled-cavity Vertical-Surface-Emitting Lasers (CC-VCSEL) on the base of a simple matrix approach. We show that strong wavelength discrimination can be achieved in CC-VCSELs by slightly detuning the cavities. However, polarization discrimination is not provided by the coupled-cavity design. We also consider the case of reverse-biasing one of the cavities, i.e. using it as a modulator via linear and/or quadratic electrooptic effect. Such a CC-VCSEL can act as a voltage-controlled polarization or wavelength switching device that is decoupled from the laser design and can be optimized for high modulation speed. We also show that using QD stack instead of quantum wells in the top cavity would lead to significant reduction of the driving electrical field.

Biased-probe-induced water ion injection into amorphous polymers investigated by electric force microscopy

NASA Astrophysics Data System (ADS)

Knorr, Nikolaus; Rosselli, Silvia; Miteva, Tzenka; Nelles, Gabriele

2009-06-01

Although charging of insulators by atomic force microscopy (AFM) has found widespread interest, often with data storage or nanoxerography in mind, less attention has been paid to the charging mechanism and the nature of the charge. Here we present a systematic study on charging of amorphous polymer films by voltage pulses applied to conducting AFM probes. We find a quadratic space charge limited current law of Kelvin probe force microscopy and electrostatic force microscopy peak volumes in pulse height, offset by a threshold voltage, and a power law in pulse width of positive exponents smaller than one. We interpret the results by a charging mechanism of injection and surface near accumulation of aqueous ions stemming from field induced water adsorption, with threshold voltages linked to the water affinities of the polymers.

Circular-polarization-sensitive metamaterial based on triple-quantum-dot molecules.

PubMed

Kotetes, Panagiotis; Jin, Pei-Qing; Marthaler, Michael; Schön, Gerd

2014-12-05

We propose a new type of chiral metamaterial based on an ensemble of artificial molecules formed by three identical quantum dots in a triangular arrangement. A static magnetic field oriented perpendicular to the plane breaks mirror symmetry, rendering the molecules sensitive to the circular polarization of light. By varying the orientation and magnitude of the magnetic field one can control the polarization and frequency of the emission spectrum. We identify a threshold frequency Ω, above which we find strong birefringence. In addition, Kerr rotation and circular-polarized lasing action can be implemented. We investigate the single-molecule lasing properties for different energy-level arrangements and demonstrate the possibility of circular-polarization conversion. Finally, we analyze the effect of weak stray electric fields or deviations from the equilateral triangular geometry.

Bone-anchored Hearing Aids: correlation between pure-tone thresholds and outcome in three user groups.

PubMed

Pfiffner, Flurin; Kompis, Martin; Stieger, Christof

2009-10-01

To investigate correlations between preoperative hearing thresholds and postoperative aided thresholds and speech understanding of users of Bone-anchored Hearing Aids (BAHA). Such correlations may be useful to estimate the postoperative outcome with BAHA from preoperative data. Retrospective case review. Tertiary referral center. : Ninety-two adult unilaterally implanted BAHA users in 3 groups: (A) 24 subjects with a unilateral conductive hearing loss, (B) 38 subjects with a bilateral conductive hearing loss, and (C) 30 subjects with single-sided deafness. Preoperative air-conduction and bone-conduction thresholds and 3-month postoperative aided and unaided sound-field thresholds as well as speech understanding using German 2-digit numbers and monosyllabic words were measured and analyzed. Correlation between preoperative air-conduction and bone-conduction thresholds of the better and of the poorer ear and postoperative aided thresholds as well as correlations between gain in sound-field threshold and gain in speech understanding. Aided postoperative sound-field thresholds correlate best with BC threshold of the better ear (correlation coefficients, r2 = 0.237 to 0.419, p = 0.0006 to 0.0064, depending on the group of subjects). Improvements in sound-field threshold correspond to improvements in speech understanding. When estimating expected postoperative aided sound-field thresholds of BAHA users from preoperative hearing thresholds, the BC threshold of the better ear should be used. For the patient groups considered, speech understanding in quiet can be estimated from the improvement in sound-field thresholds.

Use of electric field sensors for recording respiration, heart rate, and stereotyped motor behaviors in the rodent home cage.

PubMed

Noble, Donald J; MacDowell, Camden J; McKinnon, Michael L; Neblett, Tamra I; Goolsby, William N; Hochman, Shawn

2017-02-01

Numerous environmental and genetic factors can contribute significantly to behavioral and cardiorespiratory variability observed experimentally. Affordable technologies that allow for noninvasive home cage capture of physio-behavioral variables should enhance understanding of inter-animal variability including after experimental interventions. We assessed whether EPIC electric field sensors (Plessey Semiconductors) embedded within or attached externally to a rodent's home cage could accurately record respiration, heart rate, and motor behaviors. Current systems for quantification of behavioral variables require expensive specialty equipment, while measures of respiratory and heart rate are often provided by surgically implanted or chronically affixed devices. Sensors accurately encoded imposed sinusoidal changes in electric field tested at frequencies ranging from 0.5-100Hz. Mini-metronome arm movements were easily detected, but response magnitude was highly distance dependent. Sensors accurately reported respiration during whole-body plethysmography. In anesthetized rodents, PVC tube-embedded sensors provided accurate mechanical detection of both respiratory and heart rate. Comparable success was seen in naturally behaving animals at rest or sleeping when sensors were attached externally. Video-verified motor behaviors (sniffing, grooming, chewing, and rearing) were detectable and largely separable by their characteristic voltage fluctuations. Larger movement-related events had comparably larger voltage dynamics that easily allowed for a broad approximation of overall motor activity. Spectrograms were used to quickly depict characteristic frequencies in long-lasting recordings, while filtering and thresholding software allowed for detection and quantification of movement-related physio-behavioral events. EPIC electric field sensors provide a means for affordable non-contact home cage detection of physio-behavioral variables. Copyright © 2016 Elsevier B.V. All rights reserved.

Miniaturized two-stack Blumlein pulser with a variable repetition-rate for non-thermal irreversible-electroporation experiments

NASA Astrophysics Data System (ADS)

Min, Sun-Hong; Kwon, Ohjoon; Sattorov, Matlabjon; Baek, In-Keun; Kim, Seontae; Jeong, Jin-Young; Hong, Dongpyo; Park, Seunghyuk; Park, Gun-Sik

2017-01-01

Non-thermal irreversible electroporation (NTIRE) to avoid thermal damage to cells during intense DC ns pulsed electric fields (nsPEFs) is a recent modality for medical applications. This mechanism, related to bioelectrical dynamics of the cell, is linked to the effect of a DC electric field and a threshold effect with an electrically stimulated membrane for the charge distribution in the cell. To create the NTIRE condition, the pulse width of the nsPEF should be shorter than the charging time constant of the membrane related to the cell radius, membrane capacitance, cytoplasm resistivity, and medium resistivity. It is necessary to design and fabricate a very intense nanosecond DC electric field pulser that is capable of producing voltages up to the level of 100 kV/cm with an artificial pulse width (˜ns) with controllable repetition rates. Many devices to generate intense DC nsPEF using various pulse-forming line technologies have been introduced thus far. However, the previous Blumlein pulse-generating devices are clearly inefficient due to the energy loss between the input voltage and the output voltage. An improved two-stage stacked Blumlein pulse-forming line can overcome this limitation and decrease the energy loss from a DC power supply. A metal oxide silicon field-effect transistor switch with a fast rise and fall time would enable a high repetition rate (max. 100 kHz) and good endurance against very high voltages (DC ˜ 30 kV). The load is designed to match the sample for exposure to cell suspensions consisting of a 200 Ω resistor matched with a Blumlein circuit and two electrodes without the characteristic RC time effect of the circuit (capacitance =0.174 pF).

Experimental study on the responsivity enhancement of Mn1.56Co0.96Ni0.48O4 detector under moderate bias field

NASA Astrophysics Data System (ADS)

Zhou, Wei; Hou, Yun; Gao, Yan Qing; Zhang, Leibo; Huang, Zhi Ming

2011-08-01

As a typical thermal sensitive material, Mn1.56Co0.96Ni0.48O4 (MCN) has achieved widely applications in uncooled bolometer. In this paper, we report that a large increase in electrical conductivity of MCN is obtained with moderate electric-field strengths (E~103V/cm) applied at room temperature (about 300K). Great enhancement in the responsivity is observed when operating with a proper electric bias field, which corresponds to a threshold voltage VTh. MCN bulk materials are prepared by using the sintering method. Micro MCN detector is fabricated by scribing the bulk material into pieces sized 200×100×10μm. The detector is clinged to an Al2O3 substrate with some electrical insulated epoxy glue which is mounted onto a Cu sink. The surrounding temperature is controlled precisely by a temperature controller with a precision of 1mK. Voltage-current characteristics at 270-330K are carefully examined. Different sweeping speeds of the bias-voltage are applied in different orders so as to find out a proper scanning rate, in which the electrical measurement is proceeded in a state of quasi-thermal equilibrium. According to quasi-thermal equilibrium and the time dependent nominal D.C. power, the temperature increase during the measurement is estimated. The conduction mechanism can be well explained with small polaron theory. Empirical equations are used to describe the thermal dynamic process in the pulsed mode, and the process is also simply simulated via numerical calculations. The experimental results and simulation works will be of some referential value to future studies in uncooled microbolometer made in transition metal oxides.

Comparison of electrically evoked cortical potential thresholds generated with subretinal or suprachoroidal placement of a microelectrode array in the rabbit

NASA Astrophysics Data System (ADS)

Yamauchi, Yasuyuki; Franco, Luisa M.; Jackson, Douglas J.; Naber, John F.; Ofer Ziv, R.; Rizzo, Joseph F., III; Kaplan, Henry J.; Enzmann, Volker

2005-03-01

The aim of the study was to directly compare the threshold electrical charge density of the retina (retinal threshold) in rabbits for the generation of electrical evoked potentials (EEP) by delivering electrical stimulation with a custom-made microelectrode array (MEA) implanted into either the subretinal or suprachoroidal space. Nine eyes of seven Dutch-belted rabbits were studied. The electroretinogram (ERG), visual evoked potentials (VEP) and EEP were recorded. Electrodes for the VEP and EEP were placed on the dura mater overlying the visual cortex. The EEP was recorded following electrical stimulation of the MEA placed either subretinally beneath the visual streak of the retina or in the suprachoroidal space in the rabbit eye. An ab externo approach was used for placement of the MEA. Liquid perfluorodecaline (PFCL; 0.4 ml) was placed within the vitreous cavity to flatten the neurosensory retina on the MEA after subretinal implantation. The retinal threshold for generation of an EEP was determined for each MEA placement by three consecutive measurements consisting of 100 computer-averaged recordings. Animals were sacrificed at the conclusion of the experiment and the eyes were enucleated for histological examination. The retinal threshold to generate an EEP was 9 ± 7 nC (0.023 ± 0.016 mC cm-2) within the subretinal space and 150 ± 122 nC (0.375 ± 0.306 mC cm-2) within the suprachoroidal space. Histology showed disruption of the outer retina with subretinal but not suprachoroidal placement. The retinal threshold to elicit an EEP is significantly lower with subretinal placement of the MEA compared to suprachoroidal placement (P < 0.05). The retinal threshold charge density with a subretinal MEA is well below the published charge limit of 1 mC cm-2, which is the level below which chronic stimulation of the retina is considered necessary to avoid tissue damage (Shannon 1992 IEEE Trans. Biomed. Eng. 39 424-6). Supported in part by The Charles D Kelman, MD Postdoctoral Scholar Award 2003 (YY); Boston VA Hospital (V523P-7278); Research to Prevent Blindness, New York City, NY and Kentucky Research Challenge Trust Fund (HJK).

40 CFR 98.301 - Reporting threshold.

Code of Federal Regulations, 2012 CFR

2012-07-01

... 40 Protection of Environment 22 2012-07-01 2012-07-01 false Reporting threshold. 98.301 Section 98.301 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED... threshold. (a) You must report GHG emissions from an electric power system if the total nameplate capacity...

The role of sensory input of the chorda tympani nerve and the number of fungiform papillae in burning mouth syndrome.

PubMed

Nasri-Heir, Cibele; Gomes, Julyana; Heir, Gary M; Ananthan, Sowmya; Benoliel, Rafael; Teich, Sorin; Eliav, Eli

2011-07-01

The aim of this study was to evaluate patients suffering from burning mouth syndrome (BMS) and control subjects by means of sensory testing and fungiform papillae count. The left and right anterior two-thirds of the tongue of of 25 BMS subjects and 20 healthy control subjects were evaluated for electric taste and electric detection threshold. The number of fungiform papillae/cm(2) was evaluated by using close-up digital photography. The electric taste/tingling detection threshold ratio was significantly higher in BMS compared with control subjects (P = .041). No difference was found between the number of fungiform papillae/cm(2) in the BMS compared with the control subjects (P = .277). Patients suffering from BMS for a prolonged period of time presented with a significantly elevated electric taste/tingling detection threshold ratio (P = .031). BMS may be a neurodegenerative process with chorda tympani nerve hypofunction potentially playing a role in the pathophysiology of this disorder. Copyright © 2011 Mosby, Inc. All rights reserved.

The effect of culture on pain sensitivity.

PubMed

Al-Harthy, M; Ohrbach, R; Michelotti, A; List, T

2016-02-01

Cross-cultural differences in pain sensitivity have been identified in pain-free subjects as well as in chronic pain patients. The aim was to assess the impact of culture on psychophysical measures using mechanical and electrical stimuli in patients with temporomandibular disorder (TMD) pain and pain-free matched controls in three cultures. This case-control study compared 122 female cases of chronic TMD pain (39 Saudis, 41 Swedes and 42 Italians) with equal numbers of age- and gender-matched TMD-free controls. Pressure pain threshold (PPT) and tolerance (PPTo) were measured over one hand and two masticatory muscles. Electrical perception threshold and electrical pain threshold (EPT) and tolerance (EPTo) were recorded between the thumb and index fingers. Italian females reported significantly lower PPT in the masseter muscle than other cultures (P < 0.001) and in the temporalis muscle than Saudis (P = 0.003). Swedes reported significantly higher PPT in the thenar muscle than other cultures (P = 0.017). Italians reported significantly lower PPTo in all muscles than Swedes (P ≤ 0.006) and in the masseter muscle than Saudis (P < 0.001). Italians reported significantly lower EPTo than other cultures (P = 0.01). Temporomandibular disorder cases, compared to TMD-free controls, reported lower PPT and PPTo in all the three muscles (P < 0.001). This study found cultural differences between groups in the PPT, PPTo and EPTo. Overall, Italian females reported the highest sensitivity to both mechanical and electrical stimulation, while Swedes reported the lowest sensitivity. Mechanical pain thresholds differed more across cultures than did electrical pain thresholds. Cultural factors may influence response to type of pain test. © 2015 John Wiley & Sons Ltd.

An Engineering Tool for the Prediction of Internal Dielectric Charging

NASA Astrophysics Data System (ADS)

Rodgers, D. J.; Ryden, K. A.; Wrenn, G. L.; Latham, P. M.; Sorensen, J.; Levy, L.

1998-11-01

A practical internal charging tool has been developed. It provides an easy-to-use means for satellite engineers to predict whether on-board dielectrics are vulnerable to electrostatic discharge in the outer radiation belt. The tool is designed to simulate irradiation of single-dielectric planar or cylindrical structures with or without shielding. Analytical equations are used to describe current deposition in the dielectric. This is fast and gives charging currents to sufficient accuracy given the uncertainties in other aspects of the problem - particularly material characteristics. Time-dependent internal electric fields are calculated, taking into account the effect on conductivity of electric field, dose rate and temperature. A worst-case model of electron fluxes in the outer belt has been created specifically for the internal charging problem and is built into the code. For output, the tool gives a YES or NO decision on the susceptibility of the structure to internal electrostatic breakdown and if necessary, calculates the required changes to bring the system below the breakdown threshold. A complementary programme of laboratory irradiations has been carried out to validate the tool. The results for Epoxy-fibreglass samples show that the code models electric field realistically for a wide variety of shields, dielectric thicknesses and electron spectra. Results for Teflon samples indicate that some further experimentation is required and the radiation-induced conductivity aspects of the code have not been validated.

Emptying Dirac valleys in bismuth using high magnetic fields

DOE PAGES

Zhu, Zengwei; Wang, Jinhua; Zuo, Huakun; ...

2017-05-19

The Fermi surface of elemental bismuth consists of three small rotationally equivalent electron pockets, offering a valley degree of freedom to charge carriers. A relatively small magnetic field can confine electrons to their lowest Landau level. This is the quantum limit attained in other dilute metals upon application of sufficiently strong magnetic field. Here in this paper we report on the observation of another threshold magnetic field never encountered before in any other solid. Above this field, B empty, one or two valleys become totally empty. Drying up a Fermi sea by magnetic field in the Brillouin zone leads tomore » a manyfold enhancement in electric conductance. We trace the origin of the large drop in magnetoresistance across B empty to transfer of carriers between valleys with highly anisotropic mobilities. The non-interacting picture of electrons with field-dependent mobility explains most results but the Coulomb interaction may play a role in shaping the fine details.« less

Crystalline ZrTiO{sub 4} gated p-metal–oxide–semiconductor field effect transistors with sub-nm equivalent oxide thickness featuring good electrical characteristics and reliability

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

Wu, Chao-Yi; Hsieh, Ching-Heng; Lee, Ching-Wei

2015-02-02

ZrTiO{sub 4} crystallized in orthorhombic (o-) phase was stacked with an amorphous Yb{sub 2}O{sub 3} interfacial layer as the gate dielectric for Si-based p-MOSFETs. With thermal annealing after gate electrode, the gate stack with equivalent oxide thickness (EOT) of 0.82 nm achieves high dielectric quality by showing a low interface trap density (D{sub it}) of 2.75 × 10{sup 11 }cm{sup −2}eV{sup −1} near the midgap and low oxide traps. Crystallization of ZrTiO{sub 4} and post metal annealing are also proven to introduce very limited amount of metal induced gap states or interfacial dipole. The p-MOSFETs exhibit good sub-threshold swing of 75 mV/dec which is ascribedmore » to the low D{sub it} value and small EOT. Owing to the Y{sub 2}O{sub 3} interfacial layer and smooth interface with Si substrate that, respectively, suppress phonon and surface roughness scattering, the p-MOSFETs also display high hole mobility of 49 cm{sup 2}/V-s at 1 MV/cm. In addition, I{sub on}/I{sub off} ratio larger than 10{sup 6} is also observed. From the reliability evaluation by negative bias temperature instability test, after stressing with an electric field of −10 MV/cm at 85 °C for 1000 s, satisfactory threshold voltage shift of 12 mV and sub-threshold swing degradation of 3% were obtained. With these promising characteristics, the Yb{sub 2}O{sub 3}/o-ZrTiO{sub 4} gate stack holds the great potential for next-generation electronics.« less

Role of extrinsic noise in the sensitivity of the rod pathway: rapid dark adaptation of nocturnal vision in humans.

PubMed

Reeves, Adam; Grayhem, Rebecca

2016-03-01

Rod-mediated 500 nm test spots were flashed in Maxwellian view at 5 deg eccentricity, both on steady 10.4 deg fields of intensities (I) from 0.00001 to 1.0 scotopic troland (sc td) and from 0.2 s to 1 s after extinguishing the field. On dim fields, thresholds of tiny (5') tests were proportional to √I (Rose-DeVries law), while thresholds after extinction fell within 0.6 s to the fully dark-adapted absolute threshold. Thresholds of large (1.3 deg) tests were proportional to I (Weber law) and extinction thresholds, to √I. rod thresholds are elevated by photon-driven noise from dim fields that disappears at field extinction; large spot thresholds are additionally elevated by neural light adaptation proportional to √I. At night, recovery from dimly lit fields is fast, not slow.

Low-voltage electric-double-layer paper transistors gated by microporous SiO2 processed at room temperature

NASA Astrophysics Data System (ADS)

Sun, Jia; Wan, Qing; Lu, Aixia; Jiang, Jie

2009-11-01

Battery drivable low-voltage SnO2-based paper thin-film transistors with a near-zero threshold voltage (Vth=0.06 V) gated by microporous SiO2 dielectric with electric-double-layer (EDL) effect are fabricated at room temperature. The operating voltage is found to be as low as 1.5 V due to the huge gate specific capacitance (1.34 μF/cm2 at 40 Hz) related to EDL formation. The subthreshold gate voltage swing and current on/off ratio is found to be 82 mV/decade and 2.0×105, respectively. The electron field-effect mobility is estimated to be 47.3 cm2/V s based on the measured gate specific capacitance at 40 Hz.

40 CFR 98.301 - Reporting threshold.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 21 2014-07-01 2014-07-01 false Reporting threshold. 98.301 Section 98.301 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Electrical Transmission and Distribution Equipment Use § 98.301 Reporting threshold. (a) You must report GHG...

40 CFR 98.301 - Reporting threshold.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 21 2011-07-01 2011-07-01 false Reporting threshold. 98.301 Section 98.301 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Electrical Transmission and Distribution Equipment Use § 98.301 Reporting threshold. (a) You must report GHG...

40 CFR 98.451 - Reporting threshold.

Code of Federal Regulations, 2011 CFR

2011-07-01

... 40 Protection of Environment 21 2011-07-01 2011-07-01 false Reporting threshold. 98.451 Section 98.451 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Electrical Equipment Manufacture or Refurbishment § 98.451 Reporting threshold. You must report GHG emissions unde...

40 CFR 98.451 - Reporting threshold.

Code of Federal Regulations, 2014 CFR

2014-07-01

... 40 Protection of Environment 21 2014-07-01 2014-07-01 false Reporting threshold. 98.451 Section 98.451 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Electrical Equipment Manufacture or Refurbishment § 98.451 Reporting threshold. You must report GHG emissions unde...

40 CFR 98.451 - Reporting threshold.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 22 2013-07-01 2013-07-01 false Reporting threshold. 98.451 Section 98.451 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Electrical Equipment Manufacture or Refurbishment § 98.451 Reporting threshold. You must report GHG emissions unde...

40 CFR 98.301 - Reporting threshold.

Code of Federal Regulations, 2013 CFR

2013-07-01

... 40 Protection of Environment 22 2013-07-01 2013-07-01 false Reporting threshold. 98.301 Section 98.301 Protection of Environment ENVIRONMENTAL PROTECTION AGENCY (CONTINUED) AIR PROGRAMS (CONTINUED) MANDATORY GREENHOUSE GAS REPORTING Electrical Transmission and Distribution Equipment Use § 98.301 Reporting threshold. (a) You must report GHG...

Nonlinear DC Conduction Behavior in Graphene Nanoplatelets/Epoxy Resin Composites

NASA Astrophysics Data System (ADS)

Yuan, Yang; Wang, Qingguo; Qu, Zhaoming

2018-01-01

Graphene nanoplatelets (GNPs)/Epoxy resin (ER) with a low percolation threshold were fabricated. Then the nonlinear DC conduction behavior of GNPs/ER composites was investigated, which indicates that dispersion, exfoliation level and conductivity of GNPs in specimens are closely related to the conduction of composites. Moreover, it could be seen that the modified graphene nanoplatelets made in this paper could be successfully used for increasing the electric conductivity of the epoxy resin, and the GNPs/ER composites with nonlinear conduction behavior have a good application prospects in the field of intelligent electromagnetic protection.

New design of a passive type RADFET reader for enhanced sensitivity

NASA Astrophysics Data System (ADS)

Lee, Dae-Hee

2016-07-01

We present a new design of a passive type RADFET reader with enhanced radiation sensitivity. Using a electostatic plate, we have applied a static electric field to the gate voltage, which impacts a positive biasing on the p-type MOSFET. The resultant effect shows that 1.8 times of radiation sensitivity increased when we measured the threshold voltage shift of the RADFET exposed to 30 krad irradiation. We discuss further about the characteristic changes of a RADFET according to the positive biasing on the gate voltage.

Pulsed operation of (Al,Ga,In)N blue laser diodes

NASA Astrophysics Data System (ADS)

Abare, Amber C.; Mack, Michael P.; Hansen, Mark W.; Sink, R. K.; Kozodoy, Peter; Keller, Sarah L.; Hu, Evelyn L.; Speck, James S.; Bowers, John E.; Mishra, Umesh K.; Coldren, Larry A.; DenBaars, Steven P.

1998-04-01

Room temperature (RT) pulsed operation of blue (420 nm) nitride based multi-quantum well (MQW) laser diodes grown on a-plane and c-plane sapphire substrates has been demonstrated. A combination of atmospheric and low pressure metal organic chemical vapor deposition (MOCVD) using a modified two-flow horizontal reactor was employed. The emission is strongly TE polarized and has a sharp transition in the far field pattern above threshold. Threshold current densities as low as 12.6 kA/cm2 were observed for 10 X 1200 micrometer lasers with uncoated reactive ion etched (RIE) facets on c-plane sapphire. Cleaved facet lasers were also demonstrated with similar performance on a-plane sapphire. Differential efficiencies as high as 7% and output powers up to 77 mW were observed. Laser diodes tested under pulsed conditions operated up to 6 hours at room temperature. Performance was limited by resistive heating during the electrical pulses. Lasing was achieved up to 95 degrees Celsius and up to a 150 ns pulse length (RT). Threshold current increased with temperature with a characteristic temperature, T0, of 125 K.

Growth of IZO/IGZO dual-active-layer for low-voltage-drive and high-mobility thin film transistors based on an ALD grown Al2O3 gate insulator

NASA Astrophysics Data System (ADS)

Ding, Xingwei; Zhang, Hao; Ding, He; Zhang, Jianhua; Huang, Chuanxin; Shi, Weimin; Li, Jun; Jiang, Xueyin; Zhang, Zhilin

2014-12-01

We successfully integrated the high-performance oxide thin film transistors with novel IZO/IGZO dual-active-layers. The results showed that dual-active-layer (IZO/IGZO) TFTs, compared with single active layer IGZO TFTs and IZO TFTs, exhibited the excellent performances; specifically, a high field effect mobility of 14.4 cm2/Vs, a suitable threshold voltage of 0.8 V, a high on/off ratio of more than 107, a steep sub-threshold swing of 0.13 V/dec, and a substantially small threshold voltage shift of 0.51 V after temperature stress from 293 K to 353 K. In order to understand the superior performance, the density-of-states (DOS) were investigated based on the temperature-dependent transfer curves. The superior electric properties were attributed to the smaller DOS and higher carrier concentration. The proposed IZO/IGZO-TFT in this paper can be used as driving devices in the next-generation flat panel displays.

Percolation Thresholds in Angular Grain media: Drude Directed Infiltration

NASA Astrophysics Data System (ADS)

Priour, Donald

Pores in many realistic systems are not well delineated channels, but are void spaces among grains impermeable to charge or fluid flow which comprise the medium. Sparse grain concentrations lead to permeable systems, while concentrations in excess of a critical density block bulk fluid flow. We calculate percolation thresholds in porous materials made up of randomly placed (and oriented) disks, tetrahedrons, and cubes. To determine if randomly generated finite system samples are permeable, we deploy virtual tracer particles which are scattered (e.g. specularly) by collisions with impenetrable angular grains. We hasten the rate of exploration (which would otherwise scale as ncoll1 / 2 where ncoll is the number of collisions with grains if the tracers followed linear trajectories) by considering the tracer particles to be charged in conjunction with a randomly directed uniform electric field. As in the Drude treatment, where a succession of many scattering events leads to a constant drift velocity, tracer displacements on average grow linearly in ncoll. By averaging over many disorder realizations for a variety of systems sizes, we calculate the percolation threshold and critical exponent which characterize the phase transition.

EHD Approach to Tornadic Thunderstorms and Methods of Their Destruction

NASA Astrophysics Data System (ADS)

Kikuchi, H.

2005-05-01

In many cases, tornadoes are accompanied or involved by lightning discharges and are thought to be com- posed of uncharged and charged components different from each other in terms of velocity, vorticity, heli- city, and appearance (shape and luminosity). Their visible dark portion may correspond to uncharged tor- nadoes, while luminous or bright part may involve charged tornadoes with return strokes. Usually, un- charged tornadoes have been considered to be ascending hot streams of thermohydrodynamic origin. This is the conventional theory of tornadoes, based on hydrodynamics (HD) or thermohydrodynamics (THD) but does not consider electrical effects that are really significant in tornadic thunderstorms..It has been shown, however, that a new electrohydrodynamics (EHD) established and developed over the last more than a decade is applicable to tornadic thunderstorms with lightning. This paper summarizes such an EHD approach and proposes the methods of tornado destruction based on EHD. Space charge and electric field configurations in tornadic thunderstorms are considered to be quadrupole-like, taking into account the cloud-charge images onto the ground. Accordingly, dynamics of particles and EHD flows in an electric quadrupole forming an electric cusp and mirror can straightly apply to those circumstances. When the gas pressure is below the breakdown threshold, there occur helical motion of particles, not only charged but also even uncharged, and/or vortex generation. While for gases whose pressure is beyond the breakdown threshold, the following basic processes succeed one after another. When the grain is uncharged, a dis- charge channel is formed towards each pole as a result of X-type reconnection. For a negatively or posi- tively charged grain, I-type reconnection occurs between the grain and positive or negative poles, respect- ively. For uncharged two grains, O-type reconnection between both grains could be involved in addition to X-type between each pole, while for oppositely charged two grains, F-type reconnection could be in- volved between grains in addition to I-type between each grain and a pole with opposite polarity. Thus one can say that the uncharged component of tornadic thunderstorms is composed of conventional ascending hot streams of thermohydrodynamic origin and particle flows of new EHD origin produced by a quadru- pole-like cloud-base, funnel-top charge distributions, while the charged component is a bunch of return strokes including charged flows due to dust-related electric reconnection and EHD vortices in large-scale generated by EHD helical turbulence where there may occur self-organization to coalescence of fluid vor- tex and electric displacement field lines at least in an initial stage of return stroke (rise time of some ms), since earth's magnetic field could be ignored. This also indicates that fluid vortex breakdown points also tend to merge electric cusps, X-type and O-type. Then the principle of dust-related electric reconnection could be replaced by dust cluster injection into electric cusps (X-type and O-type) in several ways just mentioned above. Thus a variety of such dust cluster injection could cause additional cloud-to-dust cluster discharges, expending electrostatic energy accumulated in thunderclouds considerably and destructing tornadoes consequently.

Evaluating Energy Conversion Efficiency

NASA Technical Reports Server (NTRS)

Byvik, C. E.; Smith, B. T.; Buoncristiani, A. M.

1983-01-01

Devices that convert solar radiation directly into storable chemical or electrical energy, have characteristic energy absorption spectrum; specifically, each of these devices has energy threshold. The conversion efficiency of generalized system that emcompasses all threshold devices is analyzed, resulting in family of curves for devices of various threshold energies operating at different temperatures.

Behavioral Stochastic Resonance

NASA Astrophysics Data System (ADS)

Freund, Jan A.; Schimansky-Geier, Lutz; Beisner, Beatrix; Neiman, Alexander; Russell, David F.; Yakusheva, Tatyana; Moss, Frank

2001-03-01

Zooplankton emit weak electric fields into the surrounding water that originate from their own muscular activities associated with swimming and feeding. Juvenile paddlefish prey upon single zooplankton by detecting and tracking these weak electric signatures. The passive electric sense in the fish is provided by an elaborate array of electroreceptors, Ampullae Lorenzini, spread over the surface of an elongated rostrum. We have previously shown that the fish use stochastic resonance to enhance prey capture near the detection threshold of their sensory system. But stochastic resonance requires an external source of electrical noise in order to function. The required noise can be provided by a swarm of plankton, for example Daphnia. Thus juvenile paddlefish can detect and attack single Daphnia as outliers in the vicinity of the swarm by making use of noise from the swarm itself. From the power spectral density of the noise plus the weak signal from a single Daphnia we calculate the signal-to-noise ratio and the Fisher information at the surface of the paddlefish's rostrum. The results predict a specific attack pattern for the paddlefish that appears to be experimentally testable.

Optimization and control of dynamic percolationin nanostructured silicon oils

NASA Astrophysics Data System (ADS)

Badard, Mathieu; Combessis, Anthony; Allais, Arnaud; Flandin, Lionel

2017-06-01

The addition of carbonaceous fillers in polymers allows the conception of composites with optimized electrical properties. The conductivity of such material depends of the fillers structuration in matrix, especially the presence of percolated network. The objective of this paper is to understand the main aggregation mechanisms of carbon nanotubes in different media. The structuration of these filler network is probed by the use of electrical and dielectrical measurements. The innovative part of our work lies in the use of liquid matrices, especially silicon oils, to overcome mechanical constraints present in polymers on the one hand and to simplify processing on the other hand. Our work has revealed a filler aggregation over time, well known as dynamic percolation. Conductivity has been modeled as a function of time and filler content from Kirkpatrick equation. The further use of an electrical field led to conductivity enhancement as well as a decrease in percolation threshold. Finally, a study of intrinsic parameters of matrix has shown a strong effect of viscosity and surface tension on nanotubes aggregation. Contribution to the topical issue "Electrical Engineering Symposium (SGE 2016)", edited by Adel Razek

Feature-based attention potentiates recovery of fine direction discrimination in cortically blind patients.

PubMed

Cavanaugh, Matthew R; Barbot, Antoine; Carrasco, Marisa; Huxlin, Krystel R

2017-12-10

Training chronic, cortically-blind (CB) patients on a coarse [left-right] direction discrimination and integration (CDDI) task recovers performance on this task at trained, blind field locations. However, fine direction difference (FDD) thresholds remain elevated at these locations, limiting the usefulness of recovered vision in daily life. Here, we asked if this FDD impairment can be overcome by training CB subjects with endogenous, feature-based attention (FBA) cues. Ten CB subjects were recruited and trained on CDDI and FDD with an FBA cue or FDD with a neutral cue. After completion of each training protocol, FDD thresholds were re-measured with both neutral and FBA cues at trained, blind-field locations and at corresponding, intact-field locations. In intact portions of the visual field, FDD thresholds were lower when tested with FBA than neutral cues. Training subjects in the blind field on the CDDI task improved FDD performance to the point that a threshold could be measured, but these locations remained impaired relative to the intact field. FDD training with neutral cues resulted in better blind field FDD thresholds than CDDI training, but thresholds remained impaired relative to intact field levels, regardless of testing cue condition. Importantly, training FDD in the blind field with FBA lowered FDD thresholds relative to CDDI training, and allowed the blind field to reach thresholds similar to the intact field, even when FBA trained subjects were tested with a neutral rather than FBA cue. Finally, FDD training appeared to also recover normal integration thresholds at trained, blind-field locations, providing an interesting double dissociation with respect to CDDI training. In summary, mechanisms governing FBA appear to function normally in both intact and impaired regions of the visual field following V1 damage. Our results mark the first time that FDD thresholds in CB fields have been seen to reach intact field levels of performance. Moreover, FBA can be leveraged during visual training to recover normal, fine direction discrimination and integration performance at trained, blind-field locations, potentiating visual recovery of more complex and precise aspects of motion perception in cortically-blinded fields. Copyright © 2017 Elsevier Ltd. All rights reserved.

Potentiated antibodies to mu-opiate receptors: effect on integrative activity of the brain.

PubMed

Geiko, V V; Vorob'eva, T M; Berchenko, O G; Epstein, O I

2003-01-01

The effect of homeopathically potentiated antibodies to mu-receptors (10(-100) wt %) on integrative activity of rat brain was studied using the models of self-stimulation of the lateral hypothalamus and convulsions produced by electric current. Electric current was delivered through electrodes implanted into the ventromedial hypothalamus. Single treatment with potentiated antibodies to mu-receptors increased the rate of self-stimulation and decreased the threshold of convulsive seizures. Administration of these antibodies for 7 days led to further activation of the positive reinforcement system and decrease in seizure thresholds. Distilled water did not change the rate of self-stimulation and seizure threshold.

Electrical percolation threshold of magnetostrictive inclusions in a piezoelectric matrix composite as a function of relative particle size

NASA Astrophysics Data System (ADS)

Barbero, Ever J.; Bedard, Antoine Joseph

2018-04-01

Magnetoelectric composites can be produced by embedding magnetostrictive particles in a piezoelectric matrix derived from a piezoelectric powder precursor. Ferrite magnetostrictive particles, if allowed to percolate, can short the potential difference generated in the piezoelectric phase. Modeling a magnetoelectric composite as an aggregate of bi-disperse hard shells, molecular dynamics was used to explore relationships among relative particle size, particle affinity, and electrical percolation with the goal of maximizing the percolation threshold. It is found that two factors raise the percolation threshold, namely the relative size of magnetostrictive to piezoelectric particles, and the affinity between the magnetostrictive and piezoelectric particles.

Gas breakdown driven by L band short-pulse high-power microwave

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

Yang Yiming; Yuan Chengwei; Qian Baoliang

2012-12-15

High power microwave (HPM) driven gas breakdown is a major factor in limiting the radiation and transmission of HPM. A method that HPM driven gas breakdown could be obtained by changing the aperture of horn antenna is studied in this paper. Changing the effective aperture of horn antenna can adjust the electric field in near field zone, leading to gas breakdown. With this method, measurements of air and SF{sub 6} breakdowns are carried out on a magnetically insulated transmission-line oscillators, which is capable of generating HPM with pulse duration of 30 ns, and frequency of 1.74 GHz. The typical breakdownmore » waveforms of air and SF{sub 6} are presented. Besides, the breakdown field strengths of the two gases are derived at different pressures. It is found that the effects of air and SF{sub 6} breakdown on the transmission of HPM are different: air breakdown mainly shortens the pulse width of HPM while SF{sub 6} breakdown mainly reduces the peak output power of HPM. The electric field threshold of SF{sub 6} is about 2.4 times larger than that of air. These differences suggest that gas properties have a great effect on the transmission characteristic of HPM in gases.« less

GaN HEMTs with p-GaN gate: field- and time-dependent degradation

NASA Astrophysics Data System (ADS)

Meneghesso, G.; Meneghini, M.; Rossetto, I.; Canato, E.; Bartholomeus, J.; De Santi, C.; Trivellin, N.; Zanoni, E.

2017-02-01

GaN-HEMTs with p-GaN gate have recently demonstrated to be excellent normally-off devices for application in power conversion systems, thanks to the high and robust threshold voltage (VTH>1 V), the high breakdown voltage, and the low dynamic Ron increase. For this reason, studying the stability and reliability of these devices under high stress conditions is of high importance. This paper reports on our most recent results on the field- and time-dependent degradation of GaN-HEMTs with p-GaN gate submitted to stress with positive gate bias. Based on combined step-stress experiments, constant voltage stress and electroluminescence testing we demonstrated that: (i) when submitted to high/positive gate stress, the transistors may show a negative threshold voltage shift, that is ascribed to the injection of holes from the gate metal towards the p-GaN/AlGaN interface; (ii) in a step-stress experiment, the analyzed commercial devices fail at gate voltages higher than 9-10 V, due to the extremely high electric field over the p-GaN/AlGaN stack; (iii) constant voltage stress tests indicate that the failure is also time-dependent and Weibull distributed. The several processes that can explain the time-dependent failure are discussed in the following.

Abnormal threshold voltage shift under hot carrier stress in Ti1-xNx/HfO2 p-channel metal-oxide-semiconductor field-effect transistors

NASA Astrophysics Data System (ADS)

Tsai, Jyun-Yu; Chang, Ting-Chang; Lo, Wen-Hung; Ho, Szu-Han; Chen, Ching-En; Chen, Hua-Mao; Tseng, Tseung-Yuen; Tai, Ya-Hsiang; Cheng, Osbert; Huang, Cheng-Tung

2013-09-01

This work investigates the channel hot carrier (CHC) effect in HfO2/Ti1-xNx p-channel metal oxide semiconductor field effect transistors (p-MOSFETs). Generally, the subthreshold swing (S.S.) should increase during CHC stress (CHCS), since interface states will be generated near the drain side under high electric field due to drain voltage (Vd). However, our experimental data indicate that S.S. has no evident change under CHCS, but threshold voltage (Vth) shifts positively. This result can be attributed to hot carrier injected into high-k dielectric near the drain side. Meanwhile, it is surprising that such Vth degradation is not observed in the saturation region during stress. Therefore, drain-induced-barrier-lowering (DIBL) as a result of CHC-induced electron trapping is proposed to explain the different Vth behaviors in the linear and saturation regions. Additionally, the influence of different nitrogen concentrations in HfO2/Ti1-xNx p-MOSFETs on CHCS is also investigated in this work. Since nitrogen diffuses to SiO2/Si interface induced pre-Nit occurring to degrades channel mobility during the annealing process, a device with more nitrogen shows slightly less impact ionization, leading to insignificant charge trapping-induced DIBL behavior.

Auditory-nerve single-neuron thresholds to electrical stimulation from scala tympani electrodes.

PubMed

Parkins, C W; Colombo, J

1987-12-31

Single auditory-nerve neuron thresholds were studied in sensory-deafened squirrel monkeys to determine the effects of electrical stimulus shape and frequency on single-neuron thresholds. Frequency was separated into its components, pulse width and pulse rate, which were analyzed separately. Square and sinusoidal pulse shapes were compared. There were no or questionably significant threshold differences in charge per phase between sinusoidal and square pulses of the same pulse width. There was a small (less than 0.5 dB) but significant threshold advantage for 200 microseconds/phase pulses delivered at low pulse rates (156 pps) compared to higher pulse rates (625 pps and 2500 pps). Pulse width was demonstrated to be the prime determinant of single-neuron threshold, resulting in strength-duration curves similar to other mammalian myelinated neurons, but with longer chronaxies. The most efficient electrical stimulus pulse width to use for cochlear implant stimulation was determined to be 100 microseconds/phase. This pulse width delivers the lowest charge/phase at threshold. The single-neuron strength-duration curves were compared to strength-duration curves of a computer model based on the specific anatomy of auditory-nerve neurons. The membrane capacitance and resulting chronaxie of the model can be varied by altering the length of the unmyelinated termination of the neuron, representing the unmyelinated portion of the neuron between the habenula perforata and the hair cell. This unmyelinated segment of the auditory-nerve neuron may be subject to aminoglycoside damage. Simulating a 10 micron unmyelinated termination for this model neuron produces a strength-duration curve that closely fits the single-neuron data obtained from aminoglycoside deafened animals. Both the model and the single-neuron strength-duration curves differ significantly from behavioral threshold data obtained from monkeys and humans with cochlear implants. This discrepancy can best be explained by the involvement of higher level neurologic processes in the behavioral responses. These findings suggest that the basic principles of neural membrane function must be considered in developing or analyzing electrical stimulation strategies for cochlear prostheses if the appropriate stimulation of frequency specific populations of auditory-nerve neurons is the objective.

Characteristics of edge breakdowns on Teflon samples

NASA Technical Reports Server (NTRS)

Yadlowsky, E. J.; Hazelton, R. C.; Churchill, R. J.

1980-01-01

The characteristics of electrical discharges induced on silverbacked Teflon samples irradiated by a monoenergetic electron beam have been studied under controlled laboratory conditions. Measurements of breakdown threshold voltages indicate a marked anisotropy in the electrical breakdown properties of Teflon: differences of up to 10 kV in breakdown threshold voltage are observed depending on the sample orientation. The material anisotropy can be utilized in spacecraft construction to reduce the magnitude of discharge currents.

Fabrication and Characteristics of High Mobility InSnZnO Thin Film Transistors.

PubMed

Choi, Pyungho; Lee, Junki; Park, Hyoungsun; Baek, Dohyun; Lee, Jaehyeong; Yi, Junsin; Kim, Sangsoo; Choi, Byoungdeog

2016-05-01

In this paper, we describe the fabrication of thin film transistors (TFTs) with amorphous indium-tin-zinc-oxide (ITZO) as the active material. A transparent ITZO channel layer was formed under an optimized oxygen partial pressure (OPP (%) = O2/(Ar + O2)) and subsequent annealing process. The electrical properties exhibited by this device include field-effect mobility (μ(eff)), sub-threshold swing (SS), and on/off current ratio (I(ON/OFF)) values of 28.97 cm2/V x s, 0.2 V/decade, and 2.64 x 10(7), respectively. The average transmittance values for each OPP condition in the visible range were greater than 80%. The positive gate bias stress resulted in a positive threshold voltage (V(th)) shift in the transfer curves and degraded the parameters μ(eff) and SS. These phenomena originated from electron trapping from the ITZO channel layer into the oxide/ITZO interface trap sites.

A magnetic-bottle multi-electron-ion coincidence spectrometer

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

Matsuda, Akitaka; Hishikawa, Akiyoshi; Department of Chemistry, Nagoya University, Furo-cho, Chikusa, Nagoya, Aichi 464-8602

2011-10-15

A novel multi-electron-ion coincidence spectrometer developed on the basis of a 1.5 m-long magnetic-bottle electron spectrometer is presented. Electrons are guided by an inhomogeneous magnetic field to a detector at the end of the flight tube, while a set of optics is used to extract counterpart ions to the same detector, by a pulsed inhomogeneous electric field. This setup allows ion detection with high mass resolution, without impairing the high collection efficiency for electrons. The performance of the coincidence spectrometer was tested with double ionization of carbon disulfide, CS{sub 2} {yields} CS{sub 2}{sup 2+} + e{sup -} + e{sup -},more » in ultrashort intense laser fields (2.8 x 10{sup 13} W/cm{sup 2}, 280 fs, 1030 nm) to clarify the electron correlation below the rescattering threshold.« less

CORRELATIONS IN LIGHT FROM A LASER AT THRESHOLD,

DTIC Science & Technology

Temporal correlations in the electromagnetic field radiated by a laser in the threshold region of oscillation (from one tenth of threshold intensity...to ten times threshold ) were measured by photoelectron counting techniques. The experimental results were compared with theoretical predictions based...shows that the intensity fluctuations at about one tenth threshold are nearly those of a Gaussian field and continuously approach those of a constant amplitude field as the intensity is increased. (Author)

Promising Electric Aircraft Drive Systems

NASA Technical Reports Server (NTRS)

Dudley, Michael R.

2010-01-01

An overview of electric aircraft propulsion technology performance thresholds for key power system components is presented. A weight comparison of electric drive systems with equivalent total delivered energy is made to help identify component performance requirements, and promising research and development opportunities.

Morphological and electro optic studies of polymer dispersed liquid crystal in reverse mode

NASA Astrophysics Data System (ADS)

Sharma, Vandna; Kumar, Pankaj; Chinky, Malik, Praveen; Raina, K. K.

2018-05-01

Present work deals with reverse mode polymer dispersed liquid crystals (PDLCs) sensitive to electric field. Contrary to the conventional PDLCs operate from opaque (OFF state) to transparent state (ON state) with the application of field, reverse mode PDLCs work in transparent to opaque state. Reverse mode PDLC composed of nematic LC and UV curable optical adhesive polymer were prepared by the polymerization induced phase separation. The polarizing optical microscope study shows the vertical alignment of LCs within droplets with initial dark state under cross polarizers and confirms preliminary natural transparent state. The electro optic (EO) results show that the reverse mode PDLC lowered the threshold and operating voltages significantly compared with reported values. The contrast ratio of the film was also studied.

Physical implication of transition voltage in organic nano-floating-gate nonvolatile memories

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

Wang, Shun; Gao, Xu, E-mail: wangsd@suda.edu.cn, E-mail: gaoxu@suda.edu.cn; Zhong, Ya-Nan

High-performance pentacene-based organic field-effect transistor nonvolatile memories, using polystyrene as a tunneling dielectric and Au nanoparticles as a nano-floating-gate, show parallelogram-like transfer characteristics with a featured transition point. The transition voltage at the transition point corresponds to a threshold electric field in the tunneling dielectric, over which stored electrons in the nano-floating-gate will start to leak out. The transition voltage can be modulated depending on the bias configuration and device structure. For p-type active layers, optimized transition voltage should be on the negative side of but close to the reading voltage, which can simultaneously achieve a high ON/OFF ratio andmore » good memory retention.« less

A Route for Polymer Nanocomposites with Engineered Electrical Conductivity and Percolation Threshold

PubMed Central

Kalaitzidou, Kyriaki; Fukushima, Hiroyuki; Drzal, Lawrence T.

2010-01-01

Polymer nanocomposites with engineered electrical properties can be made by tuning the fabrication method, processing conditions and filler’s geometric and physical properties. This work focuses on investigating the effect of filler’s geometry (aspect ratio and shape), intrinsic electrical conductivity, alignment and dispersion within the polymer, and polymer crystallinity, on the percolation threshold and electrical conductivity of polypropylene based nanocomposites. The conductive reinforcements used are exfoliated graphite nanoplatelets, carbon black, vapor grown carbon fibers and polyacrylonitrile carbon fibers. The composites are made using melt mixing followed by injection molding. A coating method is also employed to improve the nanofiller’s dispersion within the polymer and compression molding is used to alter the nanofiller’s alignment.

Electromagnetic exposure in a phantom in the near and far fields of wire and planar antennas

NASA Astrophysics Data System (ADS)

Mazady, Md. Anas Boksh

Due to the wide availability and usage of wireless devices and systems there have been and are concerns regarding their effects on the human body. Respective regulatory agencies have developed safety standards based on scientific research on electromagnetic (EM) exposure from wireless devices and antennas. The metric that quantifies the exposure level is called the Specific Absorption Rate (SAR). Wireless devices must satisfy the regulatory standards before being marketed. In the past, researchers have primarily focused on investigating the EM exposure from wireless devices that are used very near to the user's head or body (less than 25 mm). But as time progressed many more wireless devices have become ubiquitous (vehicular wireless devices, laptop PCMCIA cards, Bluetooth dongles, wireless LAN routers, cordless phone base stations, and pico base stations are to name a few) and are operated at distances greater than 25 mm yet smaller than 200 mm. Given the variations in operating frequency, distance, and antenna size and type it is challenging to develop an approach using which EM exposure from a wide variety of wireless devices can be evaluated. The problem becomes more involved owing to the difficulties in identifying the antenna zone boundaries, e.g. reactive near-field, radiating near-field, far-field etc. The focus of this thesis is to investigate a large class of low and highly directive antennas and evaluate the EM exposure from them into a large elliptical phantom. The objective is to be able to predict threshold power levels that meet the SAR limits imposed by the regulatory agencies. It was observed that among the low directivity antennas at close near-field distances, electrically small antennas induced distinguishably higher SAR than electrically larger antennas. But differences in SAR were small as the phantom moved into the far-fields of the antennas. SAR induced by highly directive antennas were higher when the phantom was in the far-field of the antennas and was facing the antenna frontal plane. The same was not true when the phantom was in the near-field of the antennas. Finally, by analyzing the simulation and measurement data threshold power formulas were developed for low directivity antennas using which power levels corresponding to the safe exposure limits independent of device type or geometry can be estimated.

Permeabilization of the nuclear envelope following nanosecond pulsed electric field exposure

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

Thompson, Gary L., E-mail: gary.l.thompson.3@gmail.com; Roth, Caleb C.; Kuipers, Marjorie A.

2016-01-29

Permeabilization of cell membranes occurs upon exposure to a threshold absorbed dose (AD) of nanosecond pulsed electric fields (nsPEF). The ultimate, physiological bioeffect of this exposure depends on the type of cultured cell and environment, indicating that cell-specific pathways and structures are stimulated. Here we investigate 10 and 600 ns duration PEF effects on Chinese hamster ovary (CHO) cell nuclei, where our hypothesis is that pulse disruption of the nuclear envelope membrane leads to observed cell death and decreased viability 24 h post-exposure. To observe short-term responses to nsPEF exposure, CHO cells have been stably transfected with two fluorescently-labeled proteins known tomore » be sequestered for cellular chromosomal function within the nucleus – histone-2b (H2B) and proliferating cell nuclear antigen (PCNA). H2B remains associated with chromatin after nsPEF exposure, whereas PCNA leaks out of nuclei permeabilized by a threshold AD of 10 and 600 ns PEF. A downturn in 24 h viability, measured by MTT assay, is observed at the number of pulses required to induce permeabilization of the nucleus. - Highlights: • The ability of nsPEF to damage nuclear structures within cells is investigated. • Leakage of proliferating nuclear antigen from nuclei is induced by nsPEF. • High doses of nsPEF disrupt cortical lamin and cause chromatin decompaction. • Histone H2B remains attached to chromatin following nsPEF exposure. • DNA does not leak out of nsPEF-permeabilized nuclei.« less

A statistical model describing combined irreversible electroporation and electroporation-induced blood-brain barrier disruption.

PubMed

Sharabi, Shirley; Kos, Bor; Last, David; Guez, David; Daniels, Dianne; Harnof, Sagi; Mardor, Yael; Miklavcic, Damijan

2016-03-01

Electroporation-based therapies such as electrochemotherapy (ECT) and irreversible electroporation (IRE) are emerging as promising tools for treatment of tumors. When applied to the brain, electroporation can also induce transient blood-brain-barrier (BBB) disruption in volumes extending beyond IRE, thus enabling efficient drug penetration. The main objective of this study was to develop a statistical model predicting cell death and BBB disruption induced by electroporation. This model can be used for individual treatment planning. Cell death and BBB disruption models were developed based on the Peleg-Fermi model in combination with numerical models of the electric field. The model calculates the electric field thresholds for cell kill and BBB disruption and describes the dependence on the number of treatment pulses. The model was validated using in vivo experimental data consisting of rats brains MRIs post electroporation treatments. Linear regression analysis confirmed that the model described the IRE and BBB disruption volumes as a function of treatment pulses number (r(2) = 0.79; p < 0.008, r(2) = 0.91; p < 0.001). The results presented a strong plateau effect as the pulse number increased. The ratio between complete cell death and no cell death thresholds was relatively narrow (between 0.88-0.91) even for small numbers of pulses and depended weakly on the number of pulses. For BBB disruption, the ratio increased with the number of pulses. BBB disruption radii were on average 67% ± 11% larger than IRE volumes. The statistical model can be used to describe the dependence of treatment-effects on the number of pulses independent of the experimental setup.

Targeted and controlled anticancer drug delivery and release with magnetoelectric nanoparticles

NASA Astrophysics Data System (ADS)

Rodzinski, Alexandra; Guduru, Rakesh; Liang, Ping; Hadjikhani, Ali; Stewart, Tiffanie; Stimphil, Emmanuel; Runowicz, Carolyn; Cote, Richard; Altman, Norman; Datar, Ram; Khizroev, Sakhrat

2016-02-01

It is a challenge to eradicate tumor cells while sparing normal cells. We used magnetoelectric nanoparticles (MENs) to control drug delivery and release. The physics is due to electric-field interactions (i) between MENs and a drug and (ii) between drug-loaded MENs and cells. MENs distinguish cancer cells from normal cells through the membrane’s electric properties; cancer cells have a significantly smaller threshold field to induce electroporation. In vitro and in vivo studies (nude mice with SKOV-3 xenografts) showed that (i) drug (paclitaxel (PTX)) could be attached to MENs (30-nm CoFe2O4@BaTiO3 nanostructures) through surface functionalization to avoid its premature release, (ii) drug-loaded MENs could be delivered into cancer cells via application of a d.c. field (~100 Oe), and (iii) the drug could be released off MENs on demand via application of an a.c. field (~50 Oe, 100 Hz). The cell lysate content was measured with scanning probe microscopy and spectrophotometry. MENs and control ferromagnetic and polymer nanoparticles conjugated with HER2-neu antibodies, all loaded with PTX were weekly administrated intravenously. Only the mice treated with PTX-loaded MENs (15/200 μg) in a field for three months were completely cured, as confirmed through infrared imaging and post-euthanasia histology studies via energy-dispersive spectroscopy and immunohistochemistry.

Comment on "Water-processed carbon nanotube/graphene hybrids with enhanced field emission properties" [AIP Advances 5, 097130 (2015)

NASA Astrophysics Data System (ADS)

Rani, Reena; Bhatia, Ravi

2018-03-01

In their research paper, M. Song et al. [AIP ADVANCES 5, 097130 (2015)] have claimed to have achieved enhanced field emission (FE) characteristics of carbon nanotubes (CNT)/graphene hybrids experimentally, exhibiting improved FE parameters e.g. turn-on electric field of 0.79 V/μm, threshold electric field of 1.05 V/μm, maximum emission current density (Jmax) of 5.76 mA/cm2, and field enhancement factor (β) of ˜1.3 × 104. The authors have emphasized on the surprisingly high value of β to be the basis of their claim of achieving superior FE performance which is further attributed to the optimized mass ratio CNT/ graphene, which is 5:1 in the present case. However, the claim based upon high value of β is misleading because it does not corroborate with the obtained Jmax parameter. Also, the obtained value of J is quite low in the mentioned study as compared to the reported values. For an instance, Sameera et al. [J. Appl. Phys. 111, 044307 (2012) & Appl. Phys. Lett. 102, 033102 (2013)] have reported FE properties of CNT composites and reduced graphene oxide with Jmax and β values of the order of ˜102 mA/cm2 and 6 × 103, respectively. Therefore, the conclusions drawn by M. Song et al. [AIP ADVANCES 5, 097130 (2015)] in their paper do no hold.

Carbon nanotube-based bioceramic grafts for electrotherapy of bone.

PubMed

Mata, D; Horovistiz, A L; Branco, I; Ferro, M; Ferreira, N M; Belmonte, M; Lopes, M A; Silva, R F; Oliveira, F J

2014-01-01

Bone complexity demands the engineering of new scaffolding solutions for its reconstructive surgery. Emerging bone grafts should offer not only mechanical support but also functional properties to explore innovative bone therapies. Following this, ceramic bone grafts of Glass/hydroxyapatite (HA) reinforced with conductive carbon nanotubes (CNTs) - CNT/Glass/HA - were prepared for bone electrotherapy purposes. Computer-aided 3D microstructural reconstructions and TEM analysis of CNT/Glass/HA composites provided details on the CNT 3D network and further correlation to their functional properties. CNTs are arranged as sub-micrometric sized ropes bridging homogenously distributed ellipsoid-shaped agglomerates. This arrangement yielded composites with a percolation threshold of pc=1.5vol.%. At 4.4vol.% of CNTs, thermal and electrical conductivities of 1.5W·m(-1)·K(-1) and 55S·m(-1), respectively, were obtained, matching relevant requisites in electrical stimulation protocols. While the former avoids bone damaging from Joule's heat generation, the latter might allow the confinement of external electrical fields through the conductive material if used for in vivo electrical stimulation. Moreover, the electrically conductive bone grafts have better mechanical properties than those of the natural cortical bone. Overall, these highly conductive materials with controlled size CNT agglomerates might accelerate bone bonding and maximize the delivery of electrical stimulation during electrotherapy practices. © 2013.

Composites of multi-walled carbon nanotubes with polypropylene and thermoplastic olefin blends prepared by melt compounding

NASA Astrophysics Data System (ADS)

Petrie, Kyle G.

Composites of multi-walled carbon nanotubes (MWCNTs) with polypropylene (PP) and thermoplastic olefins (TPOs) were prepared by melt compounding. Two non-covalent functionalization methods were employed to improve nanotube dispersion and the resulting composite properties are reported. The first functionalization approach involved partial coating of the surface of the nanotubes with a hyperbranched polyethylene (HBPE). MWCNT functionalization with HBPE was only moderately successful in breaking up the large aggregates that formed upon melt mixing with PP. In spite of the formation of large aggregates, the samples were conductive above a percolation threshold of 7.3 wt%. MWCNT functionalization did not disrupt the electrical conductivity of the nanotubes. The composite strength was improved with addition of nanotubes, but ductility was severely compromised because of the existence of aggregates. The second method involved PP matrix functionalization with aromatic moieties capable of pi-pi interaction with MWCNT sidewalls. Various microscopy techniques revealed the addition of only 25 wt% of PP-g-pyridine (Py) to the neat PP was capable of drastically reducing nanotube aggregate size and amount. Raman spectroscopy confirmed improved polymer/nanotube interaction with the PP-g-Py matrix. Electrical percolation threshold was obtained at a MWCNT loading of approximately 1.2 wt%. Electrical conductivity on the order of 10 -2 S/m was achieved, suggesting possible use in semi-conducting applications. Composite strength was improved upon addition of MWCNTs. The matrix functionalization with Py resulted in a significant improvement in composite ductility when filled with MWCNTs in comparison to its maleic anhydride (MA) counterpart. Preliminary investigations suggest that the use of alternating current (AC) electric fields may be effective in aligning nanotubes in PP to reduce the filler loading required for electrical percolation. Composites containing MWCNT within PP/ethylene-octene copolymer (EOC) blends were prepared. Microscopy revealed that MWCNTs localized preferentially in the EOC phase. This was explained by the tendency of the system to minimize interfacial energy when the MWCNTs reside in the thermodynamically preferential phase. A kinetic approach, which involved pre-mixing the MWCNTs with PP and adding the EOC phase subsequently was attempted to monitor the migration of MWCNTs. MWCNTs began to migrate after two minutes of melt mixing with the EOC. The PP-g-Py matrix functionalization appears to slightly delay the migration. A reduction in electrical percolation threshold to 0.5 wt% MWCNTs was achieved with a co-continuous blend morphology, consisting of a 50/50 by weight ratio of PP and EOC.

Linking physics with physiology in TMS: a sphere field model to determine the cortical stimulation site in TMS.

PubMed

Thielscher, Axel; Kammer, Thomas

2002-11-01

A fundamental problem of transcranial magnetic stimulation (TMS) is determining the site and size of the stimulated cortical area. In the motor system, the most common procedure for this is motor mapping. The obtained two-dimensional distribution of coil positions with associated muscle responses is used to calculate a center of gravity on the skull. However, even in motor mapping the exact stimulation site on the cortex is not known and only rough estimates of its size are possible. We report a new method which combines physiological measurements with a physical model used to predict the electric field induced by the TMS coil. In four subjects motor responses in a small hand muscle were mapped with 9-13 stimulation sites at the head perpendicular to the central sulcus in order to keep the induced current direction constant in a given cortical region of interest. Input-output functions from these head locations were used to determine stimulator intensities that elicit half-maximal muscle responses. Based on these stimulator intensities the field distribution on the individual cortical surface was calculated as rendered from anatomical MR data. The region on the cortical surface in which the different stimulation sites produced the same electric field strength (minimal variance, 4.2 +/- 0.8%.) was determined as the most likely stimulation site on the cortex. In all subjects, it was located at the lateral part of the hand knob in the motor cortex. Comparisons of model calculations with the solutions obtained in this manner reveal that the stimulated cortex area innervating the target muscle is substantially smaller than the size of the electric field induced by the coil. Our results help to resolve fundamental questions raised by motor mapping studies as well as motor threshold measurements.

A microfluidic flow-through device for high throughput electrical lysis of bacterial cells based on continuous dc voltage.

PubMed

Wang, Hsiang-Yu; Bhunia, Arun K; Lu, Chang

2006-12-15

Interest in electrical lysis of biological cells on a microfludic platform has increased because it allows for the rapid recovery of intracellular contents without introducing lytic agents. In this study we demonstrated a simple microfluidic flow-through device which lysed Escherichia coli cells under a continuous dc voltage. The E. coli cells had previously been modified to express green fluorescent protein (GFP). In our design, the cell lysis only happened in a defined section of a microfluidic channel due to the local field amplification by geometric modification. The geometric modification also effectively decreased the required voltage for lysis by several folds. We found that local field strength of 1000-1500 V/cm was required for nearly 100% cell death. This threshold field strength was considerably lower than the value reported in the literature, possibly due to the longer duration of the field [Lee, S.W., Tai, Y.C., 1999. Sens. Actuators A: Phys. 73, 74-79]. Cell lysis was detected by both plate count and fluorescence spectroscopy. The cell membrane was completely disintegrated in the lysis section of the microfluidic device, when the field strength was higher than 2000 V/cm. The devices were fabricated using low-cost soft lithography with channel widths considerably larger than the cell size to avoid clogging and ensure stable performance. Our tool will be ideal for high throughput processing of bacterial cells for chemical analysis of intracellular contents such as DNA and proteins. The application of continuous dc voltage greatly simplified the instrumentation compared to devices using electrical pulses for similar purposes. In principle, the same approach can also be applied for lysis of mammalian cells and electroporative transfection.

Electro-optical effects in porous PET films filled with liquid crystal: new possibilities for fiber optics and THZ applications.

PubMed

Chopik, A; Pasechnik, S; Semerenko, D; Shmeliova, D; Dubtsov, A; Srivastava, A K; Chigrinov, V

2014-03-15

The results of investigation of electro-optical properties of porous polyethylene terephthalate films filled with a nematic liquid crystal (5 CB) are presented. It is established that the optical response of the samples on the applied voltage drastically depends on the frequency range. At low frequencies of applied electrical field (ffc) electric field induces an overall change in the light intensity, which is typical for an electro-optical response of a liquid crystal (LC) layer in a conventional "sandwich"-like cell. The dependences of critical frequency fc, threshold voltages, and characteristic times on a pore diameter d were established. The peculiarities of electro-optical effects can be explained in the framework of the approach which connects the variations of light intensity with the corresponding changes of the effective refractive index n(eff) of a composite LC media. The unusual behavior of the electro-optical response at low frequencies is assigned to the orienting action of the specific shear flow typical for electrokinetic phenomena in polar liquids.

Avoiding neuromuscular stimulation in liver irreversible electroporation using radiofrequency electric fields

NASA Astrophysics Data System (ADS)

Castellví, Quim; Mercadal, Borja; Moll, Xavier; Fondevila, Dolors; Andaluz, Anna; Ivorra, Antoni

2018-02-01

Electroporation-based treatments typically consist of the application of high-voltage dc pulses. As an undesired side effect, these dc pulses cause electrical stimulation of excitable tissues such as motor nerves. The present in vivo study explores the use of bursts of sinusoidal voltage in a frequency range from 50 kHz to 2 MHz, to induce irreversible electroporation (IRE) whilst avoiding neuromuscular stimulation. A series of 100 dc pulses or sinusoidal bursts, both with an individual duration of 100 µs, were delivered to rabbit liver through thin needles in a monopolar electrode configuration, and thoracic movements were recorded with an accelerometer. Tissue samples were harvested three hours after treatment and later post-processed to determine the dimensions of the IRE lesions. Thermal damage due to Joule heating was ruled out via computer simulations. Sinusoidal bursts with a frequency equal to or above 100 kHz did not cause thoracic movements and induced lesions equivalent to those obtained with conventional dc pulses when the applied voltage amplitude was sufficiently high. IRE efficacy dropped with increasing frequency. For 100 kHz bursts, it was estimated that the electric field threshold for IRE is about 1.4 kV cm-1 whereas that of dc pulses is about 0.5 kV cm-1.

Two-Dimensional Quantum Model of a Nanotransistor

NASA Technical Reports Server (NTRS)

Govindan, T. R.; Biegel, B.; Svizhenko, A.; Anantram, M. P.

2009-01-01

A mathematical model, and software to implement the model, have been devised to enable numerical simulation of the transport of electric charge in, and the resulting electrical performance characteristics of, a nanotransistor [in particular, a metal oxide/semiconductor field-effect transistor (MOSFET) having a channel length of the order of tens of nanometers] in which the overall device geometry, including the doping profiles and the injection of charge from the source, gate, and drain contacts, are approximated as being two-dimensional. The model and software constitute a computational framework for quantitatively exploring such device-physics issues as those of source-drain and gate leakage currents, drain-induced barrier lowering, and threshold voltage shift due to quantization. The model and software can also be used as means of studying the accuracy of quantum corrections to other semiclassical models.

Human responses to electricity: A literature review

NASA Technical Reports Server (NTRS)

Turner, H. S.

1972-01-01

An extensive review of literature on research concerning biomedical sensors is presented for establishing standards for current limiting devices. The physiological and pathological responses of the human, when exposed to electricity are reported including the thresholds: for perception of electricity, pain by electric current, induction of muscular contraction by electric shock, and ventricular fibrillation. The passive electrical properties of cells and tissues are also reported.

Effect of contacts configuration and location on selective stimulation of cuff electrode.

PubMed

Taghipour-Farshi, Hamed; Frounchi, Javad; Ahmadiasl, Nasser; Shahabi, Parviz; Salekzamani, Yaghoub

2015-01-01

Cuff electrodes have been widely used chronically in different clinical applications. Advancements have been made in selective stimulation by using multi-contact cuff electrodes. Steering anodic current is a strategy to increase selectivity by reshaping and localizing electric fields. There are two configurations for contacts to be implemented in cuff, monopolar and tripolar. A cuff electrode with tripolar configuration can restrict the activation to a more localized region within a nerve trunk compared to a cuff with monopolar configuration and improve the selectivity. Anode contacts in tripolar configuration can be made in two structures, "ring" and "dot". In this study, the stimulation capabilities of these two structures were evaluated. The recruitment properties and the selectivity of stimulation were examined by measuring the electric potential produced by stimulation currents. The results of the present study indicated that using dot configuration, the current needed to stimulate fascicles in tripolar topologies would be reduced by 10%. It was also shown that stimulation threshold was increased by moving anode contacts inward the cuff. On the other hand, stimulation threshold was decreased by moving the anode contacts outward the cuff which would decrease selectivity, too. We conclude that dot configuration is a better choice for stimulation. Also, a cuff inward placement of 10% relative to the cuff length was near optimal.

Simulation of the Electrical Field in Equine Larynx to Optimize Functional Electrical Stimulation in Denervated Musculus Cricoarythenoideus Dorsalis

PubMed Central

Martinek, Johannes

2014-01-01

Distribution of the electrical field is very important to activate muscle and nerve cells properly. One therapeutic method to treat Recurrent Laryngeal Neuropathy (RLN) in horses can be performed by Functional Electrical Stimulation (FES). Current method to optimize the stimulation effect is to use implanted quadripolar electrodes to the musculus cricoarythenoideus dorsalis (CAD) and testing electrode configuration until best possible optimum is reached. For better understanding and finding of maximum possible activation of CAD a simulation model of the actual entire setting is currently in development. Therefore the geometric model is built from CT-data of a dissected larynx containing the quadripolar electrodes as well as fiducials for later data registration. The geometric model is the basis for a finite difference method containing of voxels with corresponding electrical conductivity of the different types of tissue due to threshold segmentation of the CT-data. Model validation can be done by the measurement of the 3D electrical potential distribution of a larynx positioned in an electrolytic tray. Finally, measured and calculated results have to be compared as well as further investigated. Preliminary results show, that changes of electrode as well as conductivity configuration leads to significant different voltage distributions and can be well presented by equipotential lines superimposed CT-slices – a Matlab graphical user interface visualizes the results in freely selectable slices of the 3D geometry. Voltage distribution along theoretically estimated fiber paths could be calculated as well as visualized. For further calculation of nerve or denervated muscle fiber activation and its optimization, real fiber paths have to be defined and referenced to the potential- and the CT-data. PMID:26913137

Airway epithelial wounds in rhesus monkey generate ionic currents that guide cell migration to promote healing

PubMed Central

Sun, Yao-Hui; Reid, Brian; Fontaine, Justin H.; Miller, Lisa A.; Hyde, Dallas M.; Mogilner, Alex

2011-01-01

Damage to the respiratory epithelium is one of the most critical steps to many life-threatening diseases, such as acute respiratory distress syndrome and chronic obstructive pulmonary disease. The mechanisms underlying repair of the damaged epithelium have not yet been fully elucidated. Here we provide experimental evidence suggesting a novel mechanism for wound repair: endogenous electric currents. It is known that the airway epithelium maintains a voltage difference referred to as the transepithelial potential. Using a noninvasive vibrating probe, we demonstrate that wounds in the epithelium of trachea from rhesus monkeys generate significant outward electric currents. A small slit wound produced an outward current (1.59 μA/cm2), which could be enhanced (nearly doubled) by the ion transport stimulator aminophylline. In addition, inhibiting cystic fibrosis transmembrane conductance regulator (CFTR) with CFTR(Inh)-172 significantly reduced wound currents (0.17 μA/cm2), implicating an important role of ion transporters in wound induced electric potentials. Time-lapse video microscopy showed that applied electric fields (EFs) induced robust directional migration of primary tracheobronchial epithelial cells from rhesus monkeys, towards the cathode, with a threshold of <23 mV/mm. Reversal of the field polarity induced cell migration towards the new cathode. We further demonstrate that application of an EF promoted wound healing in a monolayer wound healing assay. Our results suggest that endogenous electric currents at sites of tracheal epithelial injury may direct cell migration, which could benefit restitution of damaged airway mucosa. Manipulation of ion transport may lead to novel therapeutic approaches to repair damaged respiratory epithelium. PMID:21719726

Optical Emissions of Sprite Streamers in Weak Electric Fields

NASA Astrophysics Data System (ADS)

Liu, N.; Pasko, V. P.

2004-12-01

Sprites commonly consist of large numbers of needle-shaped filaments of ionization [e.g., Gerken and Inan, JASTP, 65, 567, 2003] and typically initiate at altitudes 70-75 km in a form of upward and downward propagating streamers [Stanley et al., GRL, 26, 3201, 1999; Stenbaek-Nielsen et al., GRL, 27, 3829, 2000; McHarg et al., JGR, 107, 1364, 2002; Moudry et al., JASTP, 65, 509, 2003]. The strong electric fields E exceeding the conventional breakdown threshold field Ek are needed for initiation of sprite streamers from single electron avalanches and recent modeling studies indicate that streamers propagating in fields E>Ek experience strong acceleration and expansion in good agreement with the above cited observations [Liu and Pasko, JGR, 109, A04301, 2004]. The initiated streamers are capable of propagating in fields substantially lower than Ek [Allen and Ghaffar, J. Phys. D: Appl. Phys., 28, 331, 1995] and it is expected that a significant part of sprite optical output comes from regions with EEk). Additionally, the values of electric fields inside of the streamer channel are always well below Ek and since the excitation coefficients for optical emissions are very sensitive to the driving electric field magnitude most of the optical luminosity of streamers in this case arises from streamer tips, indicating that observed streamer filaments in many cases may be produced by time averaging of optical luminosity coming from localized regions around streamer tips as streamers move through an instrument's field of view. We will discuss pressure dependent differences of optical emissions at different sprite altitudes, and important similarities between observed sprite streamers and recent time resolved (<1 ns) imaging of laboratory streamers in point-to-plane discharge geometry conducted at ground and near ground pressures [van Veldhuizen et al., IEEE Trans. Plasma Sci., 30, 162, 2002; Yi and Williams, J. Phys. D. Appl. Phys., 35, 205, 2002].

Microchip and wedge ion funnels and planar ion beam analyzers using same

DOEpatents

Shvartsburg, Alexandre A; Anderson, Gordon A; Smith, Richard D

2012-10-30

Electrodynamic ion funnels confine, guide, or focus ions in gases using the Dehmelt potential of oscillatory electric field. New funnel designs operating at or close to atmospheric gas pressure are described. Effective ion focusing at such pressures is enabled by fields of extreme amplitude and frequency, allowed in microscopic gaps that have much higher electrical breakdown thresholds in any gas than the macroscopic gaps of present funnels. The new microscopic-gap funnels are useful for interfacing atmospheric-pressure ionization sources to mass spectrometry (MS) and ion mobility separation (IMS) stages including differential IMS or FAIMS, as well as IMS and MS stages in various configurations. In particular, "wedge" funnels comprising two planar surfaces positioned at an angle and wedge funnel traps derived therefrom can compress ion beams in one dimension, producing narrow belt-shaped beams and laterally elongated cuboid packets. This beam profile reduces the ion density and thus space-charge effects, mitigating the adverse impact thereof on the resolving power, measurement accuracy, and dynamic range of MS and IMS analyzers, while a greater overlap with coplanar light or particle beams can benefit spectroscopic methods.

Electric bistability induced by incorporating self-assembled monolayers/aggregated clusters of azobenzene derivatives in pentacene-based thin-film transistors.

PubMed

Tseng, Chiao-Wei; Huang, Ding-Chi; Tao, Yu-Tai

2012-10-24

Composite films of pentacene and a series of azobenzene derivatives are prepared and used as the active channel material in top-contact, bottom-gate field-effect transistors. The transistors exhibit high field-effect mobility as well as large I-V hysteresis as a function of the gate bias history. The azobenzene moieties, incorporated either in the form of self-assembled monolayer or discrete multilayer clusters at the dielectric surface, result in electric bistability of the pentacene-based transistor either by photoexcitation or gate biasing. The direction of threshold voltage shifts, size of hysteresis, response time, and retention characteristics all strongly depend on the substituent on the benzene ring. The results show that introducing a monolayer of azobenzene moieties results in formation of charge carrier traps responsible for slower switching between the bistable states and longer retention time. With clusters of azobenzene moieties as the trap sites, the switching is faster but the retention is shorter. Detailed film structure analyses and correlation with the transistor/memory properties of these devices are provided.

Modeling of static electrical properties in organic field-effect transistors

NASA Astrophysics Data System (ADS)

Xu, Yong; Minari, Takeo; Tsukagoshi, Kazuhito; Gwoziecki, Romain; Coppard, Romain; Benwadih, Mohamed; Chroboczek, Jan; Balestra, Francis; Ghibaudo, Gerard

2011-07-01

A modeling of organic field-effect transistors' (OFETs') electrical characteristics is presented. This model is based on a one-dimensional (1-D) Poisson's equation solution that solves the potential profile in the organic semiconducting film. Most importantly, it demonstrates that, due to the common open-surface configuration used in organic transistors, the conduction occurs in the film volume below threshold. This is because the potential at the free surface is not fixed to zero but rather rises also with the gate bias. The tail of carrier concentration at the free surface is therefore significantly modulated by the gate bias, which partially explains the gate-voltage dependent contact resistance. At the same time in the so-called subthreshold region, we observe a clear charge trapping from the difference between C-V and I-V measurements; hence a traps study by numerical simulation is also performed. By combining the analytical modeling and the traps analysis, the questions on the C-V and I-V characteristics are answered. Finally, the combined results obtained with traps fit well the experimental data in both pentacene and bis(triisopropylsilylethynyl)-pentacene OFETs.

75 FR 14097 - Revision to Electric Reliability Organization Definition of Bulk Electric System

Federal Register 2010, 2011, 2012, 2013, 2014

2010-03-24

... Commission 18 CFR Part 40 [Docket No. RM09-18-000; 130 FERC ] 61,204] Revision to Electric Reliability... Reliability Organization (ERO) to revise its definition of the term ``bulk electric system'' to include all... compliance with mandatory Reliability Standards. The Commission believes that a 100 kV threshold for...

Energy Switching Threshold for Climatic Benefits

NASA Astrophysics Data System (ADS)

Zhang, X.; Cao, L.; Caldeira, K.

2013-12-01

Climate change is one of the great challenges facing humanity currently and in the future. Its most severe impacts may still be avoided if efforts are made to transform current energy systems (1). A transition from the global system of high Greenhouse Gas (GHG) emission electricity generation to low GHG emission energy technologies is required to mitigate climate change (2). Natural gas is increasingly seen as a choice for transitions to renewable sources. However, recent researches in energy and climate puzzled about the climate implications of relying more energy on natural gas. On one hand, a shift to natural gas is promoted as climate mitigation because it has lower carbon per unit energy than coal (3). On the other hand, the effect of switching to natural gas on nuclear-power and other renewable energies development may offset benefits from fuel-switching (4). Cheap natural gas is causing both coal plants and nuclear plants to close in the US. The objective of this study is to measure and evaluate the threshold of energy switching for climatic benefits. We hypothesized that the threshold ratio of energy switching for climatic benefits is related to GHGs emission factors of energy technologies, but the relation is not linear. A model was developed to study the fuel switching threshold for greenhouse gas emission reduction, and transition from coal and nuclear electricity generation to natural gas electricity generation was analyzed as a case study. The results showed that: (i) the threshold ratio of multi-energy switching for climatic benefits changes with GHGs emission factors of energy technologies. (ii)The mathematical relation between the threshold ratio of energy switching and GHGs emission factors of energies is a curved surface function. (iii) The analysis of energy switching threshold for climatic benefits can be used for energy and climate policy decision support.

Thermal Electron Contributions to Current-Driven Instabilities: SCIFER Observations in the 1400-km Cleft Ion Fountain and Their Implications to Thermal Ion Energization

NASA Technical Reports Server (NTRS)

Adrian, Mark L.; Pollock, C. J.; Moore, T. E.; Kintner, P. M.; Arnoldy, R. L.; Whitaker, Ann F. (Technical Monitor)

2001-01-01

SCIFER TECHS observations of the variations in the thermal electron distribution in the 1400-km altitude cleft are associated with periods of intense ion heating and field-aligned currents. Energization of the thermal ion plasma in the mid-altitude cleft occurs within density cavities accompanied by enhanced thermal electron temperatures, large field-aligned thermal electron plasma flows and broadband low-frequency electric fields. Variations in the thermal electron contribution to field-aligned current densities indicate small scale (approximately 100's m) filamentary structure embedded within the ion energization periods. TECHS observations of the field-aligned drift velocities and temperatures of the thermal electron distribution are presented to evaluate the critical velocity thresholds necessary for the generation of electrostatic ion cyclotron and ion acoustic instabilities. This analysis suggests that, during periods of thermal ion energization, sufficient drift exists in the thermal electron distribution to excite the electrostatic ion cyclotron instability. In addition, brief periods exist within the same interval where the drift of the thermal electron distribution is sufficient to marginally excite the ion acoustic instability. In addition, the presence an enhancement in Langmuir emission at the plasma frequency at the center of the ion energization region, accompanied by the emission's second-harmonic, and collocated with observations of high-frequency electric field solitary structures suggest the presence of electron beam driven decay of Langmuir waves to ion acoustic modes as an additional free energy source for ion energization.

Electrical modulus analysis on the Ni/CCTO/PVDF system near the percolation threshold

NASA Astrophysics Data System (ADS)

Yang, Wenhu; Yu, Shuhui; Sun, Rong; Ke, Shanming; Huang, Haitao; Du, Ruxu

2011-11-01

A type of Ni/CCTO/PVDF three-phase percolative composite was prepared, in which the filler content (volume fraction) of Ni and CCTO was set at 60 vol%. The dependence of permittivity, electrical modulus and ac conductivity on the concentration of Ni and CCTO fillers near the percolation threshold was investigated in detail. The permittivity of the composites dramatically increased as the Ni content approached 24 vol%. This unique physical mechanism was realized as the formation of conductive channels near the percolation threshold. Analysis on the electrical modulus showed that the conductive channels are governed by three relaxation processes induced by the fillers (Ni, CCTO) and PVDF matrix, which are the interfacial polarization derived from the interfaces between fillers (Ni, CCTO) and PVDF matrix, and the polarization of CCTO ceramic filler and PVDF matrix. The conductivity behaviour with various Ni loadings and temperature suggested that the transition from an insulating to a conducting state should be induced by charge tunnelling between Ni-Ni particles, Ni-CCTO fillers and Ni-PVDF matrix. These findings demonstrated that the tunnelling conduction in the composite can be attributed to the unique physical mechanism near the percolation threshold.

Effects of GABA receptor antagonists on thresholds of P23H rat retinal ganglion cells to electrical stimulation of the retina

NASA Astrophysics Data System (ADS)

Jensen, Ralph J.; Rizzo, Joseph F., III

2011-06-01

An electronic retinal prosthesis may provide useful vision for patients suffering from retinitis pigmentosa (RP). In animal models of RP, the amount of current needed to activate retinal ganglion cells (RGCs) is higher than in normal, healthy retinas. In this study, we sought to reduce the stimulation thresholds of RGCs in a degenerate rat model (P23H-line 1) by blocking GABA receptor mediated inhibition in the retina. We examined the effects of TPMPA, a GABAC receptor antagonist, and SR95531, a GABAA receptor antagonist, on the electrically evoked responses of RGCs to biphasic current pulses delivered to the subretinal surface through a 400 µm diameter electrode. Both TPMPA and SR95531 reduced the stimulation thresholds of ON-center RGCs on average by 15% and 20% respectively. Co-application of the two GABA receptor antagonists had the greatest effect, on average reducing stimulation thresholds by 32%. In addition, co-application of the two GABA receptor antagonists increased the magnitude of the electrically evoked responses on average three-fold. Neither TPMPA nor SR95531, applied alone or in combination, had consistent effects on the stimulation thresholds of OFF-center RGCs. We suggest that the effects of the GABA receptor antagonists on ON-center RGCs may be attributable to blockage of GABA receptors on the axon terminals of ON bipolar cells.

Calculations of key magnetospheric parameters using the isotropic and anisotropic SPSU global MHD code

NASA Astrophysics Data System (ADS)

Samsonov, Andrey; Gordeev, Evgeny; Sergeev, Victor

2017-04-01

As it was recently suggested (e.g., Gordeev et al., 2015), the global magnetospheric configuration can be characterized by a set of key parameters, such as the magnetopause distance at the subsolar point and on the terminator plane, the magnetic field in the magnetotail lobe and the plasma sheet thermal pressure, the cross polar cap electric potential drop and the total field-aligned current. For given solar wind conditions, the values of these parameters can be obtained from both empirical models and global MHD simulations. We validate the recently developed global MHD code SPSU-16 using the key magnetospheric parameters mentioned above. The code SPSU-16 can calculate both the isotropic and anisotropic MHD equations. In the anisotropic version, we use the modified double-adiabatic equations in which the T⊥/T∥ (the ratio of perpendicular to parallel thermal pressures) has been bounded from above by the mirror and ion-cyclotron thresholds and from below by the firehose threshold. The results of validation for the SPSU-16 code well agree with the previously published results of other global codes. Some key parameters coincide in the isotropic and anisotropic MHD simulations, but some are different.

Investigating the interaction of x-ray free electron laser radiation with grating structure.

PubMed

Gaudin, Jérôme; Ozkan, Cigdem; Chalupský, Jaromír; Bajt, Saša; Burian, Tomáš; Vyšín, Ludek; Coppola, Nicola; Farahani, Shafagh Dastjani; Chapman, Henry N; Galasso, Germano; Hájková, Vera; Harmand, Marion; Juha, Libor; Jurek, Marek; Loch, Rolf A; Möller, Stefan; Nagasono, Mitsuru; Störmer, Michael; Sinn, Harald; Saksl, Karel; Sobierajski, Ryszard; Schulz, Joachim; Sovak, Pavol; Toleikis, Sven; Tiedtke, Kai; Tschentscher, Thomas; Krzywinski, Jacek

2012-08-01

The interaction of free electron laser pulses with grating structure is investigated using 4.6±0.1 nm radiation at the FLASH facility in Hamburg. For fluences above 63.7±8.7 mJ/cm2, the interaction triggers a damage process starting at the edge of the grating structure as evidenced by optical and atomic force microscopy. Simulations based on solution of the Helmholtz equation demonstrate an enhancement of the electric field intensity distribution at the edge of the grating structure. A procedure is finally deduced to evaluate damage threshold.

Sauter-Schwinger pair creation dynamically assisted by a plane wave

NASA Astrophysics Data System (ADS)

Torgrimsson, Greger; Schneider, Christian; Schützhold, Ralf

2018-05-01

We study electron-positron pair creation by a strong and constant electric field superimposed with a weaker transversal plane wave which is incident perpendicularly (or under some angle). Comparing the fully nonperturbative approach based on the world-line instanton method with a perturbative expansion into powers of the strength of the weaker plane wave, we find good agreement—provided that the latter is carried out to sufficiently high orders. As usual for the dynamically assisted Sauter-Schwinger effect, the additional plane wave induces an exponential enhancement of the pair-creation probability if the combined Keldysh parameter exceeds a certain threshold.

Fast-response and scattering-free polymer network liquid crystals for infrared light modulators

NASA Astrophysics Data System (ADS)

Fan, Yun-Hsing; Lin, Yi-Hsin; Ren, Hongwen; Gauza, Sebastian; Wu, Shin-Tson

2004-02-01

A fast-response and scattering-free homogeneously aligned polymer network liquid crystal (PNLC) light modulator is demonstrated at λ=1.55 μm wavelength. Light scattering in the near-infrared region is suppressed by optimizing the polymer concentration such that the network domain sizes are smaller than the wavelength. The strong polymer network anchoring assists LC to relax back quickly as the electric field is removed. As a result, the PNLC response time is ˜250× faster than that of the E44 LC mixture except that the threshold voltage is increased by ˜25×.

Electrical detection of microwave assisted magnetization reversal by spin pumping

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

Rao, Siddharth; Subhra Mukherjee, Sankha; Elyasi, Mehrdad

2014-03-24

Microwave assisted magnetization reversal has been investigated in a bilayer system of Pt/ferromagnet by detecting a change in the polarity of the spin pumping signal. The reversal process is studied in two material systems, Pt/CoFeB and Pt/NiFe, for different aspect ratios. The onset of the switching behavior is indicated by a sharp transition in the spin pumping voltage. At a threshold value of the external field, the switching process changes from partial to full reversal with increasing microwave power. The proposed method provides a simple way to detect microwave assisted magnetization reversal.

Reorganization of the raccoon cuneate nucleus after peripheral denervation.

PubMed

Rasmusson, D D; Northgrave, S A

1997-12-01

The effects of peripheral nerve transection on the cuneate nucleus were studied in anesthetized raccoons using extracellular, single-unit recordings. The somatotopic organization of the cuneate nucleus first was examined in intact, control animals. The cuneate nucleus in the raccoon is organized with the digits represented in separate cell clusters. The dorsal cap region of the cuneate nucleus contains a representation of the claws and hairy skin of the digits. Within the representation of the glabrous skin, neurons with rapidly adapting properties tended to be segregated from those with slowly adapting properties. The representations of the distal and proximal pads on a digit also were segregated. Electrical stimulation of two adjacent digits provided a detailed description of the responses originating from the digit that contains the tactile receptive field (the on-focus digit) and from the adjacent (off-focus) digit. Stimulation of the on-focus digit produced a short latency excitation in all 99 neurons tested, with a mean of 10.5 ms. These responses had a low threshold (426 microA). Stimulation of an off-focus digit activated 65% of these neurons. These responses had a significantly longer latency (15.3 ms) than on-focus responses and the threshold was more than twice as large. Two to five months after amputation of digit 4, 97 cells were tested with stimulation of digits 3 and 5. A total of 44 were in the intact regions of the cuneate nucleus. They had small receptive fields on intact digits and their responses to electrical stimulation did not differ from the control neurons. The remaining 53 neurons were judged to be deafferented and in the fourth digit region on the basis of their location with respect to intact neurons. All but two of these cells had receptive fields that were much larger than normal, often including more than one digit and part of the palm. When compared with the off-focus control neurons, their responses to electrical stimulation had lower thresholds and an increased response probability and magnitude. The latencies of these cells did not decrease, however, and were the same as the off-focus control values. The enhanced responses of the deafferented neurons to adjacent digit stimulation indicate that there is a strengthening of synapses that were previously ineffective. The increased proportion of neurons that could be activated after amputation suggests that there is also a growth of new connections. This experiment demonstrates that reorganization in the adult somatotopic system does occur at the level of the dorsal column nuclei. As a consequence, many of the changes reported at the cortex and thalamus may be due to the changes occurring at this first synapse in the somatosensory pathway.

A review of the physics and response models for burnout of semiconductor devices

NASA Astrophysics Data System (ADS)

Orvis, W. J.; Khanaka, G. H.; Yee, J. H.

1984-12-01

Physical mechanisms that cause semiconductor devices to fail from electrical overstress--particularly, EMP-induced electrical stress--are described in light of the current literature and the authors' own research. A major concern is the cause and effects of second breakdown phenomena in p-n junction devices. Models of failure thresholds are evaluated for their inherent errors and for their ability to represent the relevant physics. Finally, the response models that relate electromagnetic stress parameters to appropriate failure-threshold parameters are discussed.

Organic field-effect transistor with octadecyltrichlorosilane (OTS) self-assembled monolayers on gate oxide: effect of OTS quality

NASA Astrophysics Data System (ADS)

Devynck, M.; Tardy, P.; Wantz, G.; Nicolas, Y.; Hirsch, L.

2011-12-01

The effect of OTS (octadecyltrichlorosilane) Self-Assembled Monolayer (SAM) grafted on SiO2 gate dielectric of pentacene-based OFETs (organic field-effect transistors) is investigated. A significant improvement of the charge mobility (μ), up to 0.74 cm2/V s, is reached thanks to OTS treatment. However, in spite of improved performances, several drawbacks, such as an increase in mobility dispersion, substantial hysteresis in IDS-VG characteristics and high threshold voltages (VT), are observed. Changing solvent and deposition method turns out to have no significant effect on the mobility dispersion. A more accurate approach on the evolution of the mobility and the threshold voltage dispersion with OTS storage time highlights the effect of the OTS solution aging. Even if no difference is evidenced in the surface energy and roughness of the OTS layer, electrical characteristics exhibit considerable deterioration with OTS solution storage time. Using an "aged" OTS solution, opened under air, kept under argon and distilled before use, results in an increase of the IDS-VG hysteresis as well as in VT and in mobility dispersion. In comparison, fresh-OTS-based OFETs present a very low hysteresis, a threshold voltage close to 0 and a much lower mobility dispersion. It is demonstrated that aged OTS solutions contain impurities that are not removed by distillation process, which leads to a less densely packed layer causing interfacial charge traps thus deteriorated performances.

Increased electrical nerve stimulation threshold of the sciatic nerve in patients with diabetic foot gangrene: a prospective parallel cohort study.

PubMed

Keyl, Cornelius; Held, Tanja; Albiez, Georg; Schmack, Astrid; Wiesenack, Christoph

2013-07-01

Peripheral neuropathy may affect nerve conduction in patients with diabetes mellitus. This study was designed to test the hypothesis that the electrical stimulation threshold for a motor response of the sciatic nerve is increased in patients suffering from diabetic foot gangrene compared to non-diabetic patients. Prospective non-randomised trial with two parallel groups. Two university-affiliated hospitals. Patients scheduled for surgical treatment of diabetic foot gangrene (n = 30) and non-diabetic patients (n = 30) displaying no risk factors for neuropathy undergoing orthopaedic foot or ankle surgery. The minimum current intensity required to elicit a typical motor response (dorsiflexion or eversion of the foot) at a pulse width of 0.1 ms and a stimulation frequency of 1 Hz when the needle tip was positioned under ultrasound control directly adjacent to the peroneal component of the sciatic nerve. The non-diabetic patients were younger [64 (SD 12) vs. 74 (SD 7) years] and predominantly female (23 vs. 8). The geometric mean of the motor stimulation threshold was 0.26 [95% confidence interval (95% CI) 0.24 to 0.28] mA in non-diabetic and 1.9 (95% CI 1.6 to 2.2) mA in diabetic patients. The geometric mean of the electrical stimulation threshold was significantly (P < 0.001) increased by a factor of 7.2 (95% CI 6.1 to 8.4) in diabetic compared to non-diabetic patients. The electrical stimulation threshold for a motor response of the sciatic nerve is increased by a factor of 7.2 in patients with diabetic foot gangrene, which might hamper nerve identification.

A comparison of the antinociceptive effects of xylazine, detomidine and romifidine on experimental pain in horses.

PubMed

Moens, Yves; Lanz, Francisca; Doherr, Marcus G; Schatzmann, Urs

2003-07-01

To study the analgesic potency of the alpha2-agonist romifidine in the horse using both an electrical current and a mechanical pressure model for nociceptive threshold testing. In addition, a comparison was made with doses of detomidine and xylazine that produce equivalent degrees of sedation. Randomized, placebo-controlled, blinded cross-over study. Six adult Swiss warmblood horses, one mare and five geldings, weighing from 530 to 650 kg and aged 6-15 years. Nociceptive thresholds were measured using an electrical stimulus applied to the coronary band and using a pneumatically operated pin pressing on the cannon bone. Measurements were made immediately before and every 15 minutes for 2 hours after IV injection of the test substances. Lifting of the foot indicated the test end point. The three alpha2-agonists caused a temporary increase in nociceptive thresholds with a maximal effect within 15 minutes and a return to baseline levels within 1 hour. Using electrical current testing nociceptive thresholds were significantly different from placebo (mean +/- SD) for detomidine at 15 minutes (from control 5.8 +/- 0.9 to 23.3 +/- 3.9 mA, p = 0.0066) and 30 minutes (from control 6.6 +/- 1.1 to 18.8 +/- 3.3 mA, p = 0.0091). The difference was significant for romifidine at 15 minutes only (from control 5.8 +/- 0.9 to 18.7 +/- 3.8 mA, p = 0.0066). With mechanical pressure testing nociceptive thresholds were significantly different from control for detomidine at 15 minutes (from 3.2 +/- 0.2 to 6.2 +/- 0.5 N, p = 0.00076) and 30 minutes (from 3.2 +/- 0.7 to 5.7 +/- 0.8 N, p = 0.0167). The difference was significant for xylazine at 15 minutes (from control 3.2 +/- 0.2 to 5.6 +/- 0.7 N, p = 0.0079). At 15 minutes the order of magnitude of the measured antinociceptive effect was significantly different between the two pain tests for both romifidine and detomidine, but not for xylazine. For romifidine, the increase of mean thresholds compared to placebo was 4.0 +/- 1.3 times placebo levels with the electrical current test compared to 1.3 +/- 0.3 times for the mechanical pressure test (p = 0.037). For detomidine, the increase of mean thresholds compared to placebo was 5.4 +/- 1.7 times control levels with the electrical current test compared to 2.0 +/- 0.2 times for the mechanical pressure test (p = 0.040). This represents a 2.7 (romifidine) and 3.4 times (detomidine) greater increase in thresholds using electrical current testing compared to the use of mechanical pressure testing. This study demonstrates the analgesic potential of alpha2-agonists in the horse for somatic pain and that they can have quantitatively different antinociceptive effects according to the antinociceptive test used.

Charge carrier mobility in a two-phase disordered organic system in the low-carrier concentration regime

NASA Astrophysics Data System (ADS)

Woellner, Cristiano F.; Li, Zi; Freire, José A.; Lu, Gang; Nguyen, Thuc-Quyen

2013-09-01

In this paper we use a three-dimensional Pauli master equation to investigate the charge carrier mobility of a two-phase system which can mimic donor-acceptor and amorphous-crystalline bulk heterojunctions. By taking the energetic disorder of each phase, their energy offset, and domain morphology into consideration, we show that the carrier mobility can have a completely different behavior when compared to a one-phase system. When the energy offset is equal to zero, the mobility is controlled by the more disordered phase. When the energy offset is nonzero, we show that the mobility electric field dependence switches from negative to positive at a threshold field proportional to the energy offset. Additionally, the influence of morphology, through the domain size and volume ratio parameters, on the transport is investigated and an approximate analytical expression for the zero field mobility is provided.

Unusual polarity-dependent patterns in a bent-core nematic liquid crystal under low-frequency ac field.

PubMed

Xiang, Ying; Zhou, Meng-jie; Xu, Ming-Ya; Salamon, Péter; Éber, Nándor; Buka, Ágnes

2015-04-01

Electric-field-induced patterns of diverse morphology have been observed over a wide frequency range in a recently synthesized bent-core nematic (BCN) liquid crystal. At low frequencies (up to ∼25 Hz), the BCN exhibited unusual polarity-dependent patterns. When the amplitude of the ac field was enhanced, these two time-asymmetrical patterns turned into time-symmetrical prewavylike stripes. At ac frequencies in the middle-frequency range (∼50-3000 Hz), zigzag patterns were detected whose obliqueness varied with the frequency. Finally, if the frequency was increased above 3 kHz, the zigzag pattern was replaced by another, prewavylike pattern, whose threshold voltage depended on the frequency; however, the wave vector did not. For a more complete characterization, material parameters such as elastic constants, dielectric permittivities, and the anisotropy of the diamagnetic susceptibility were also determined.

Increased susceptibility to cortical spreading depression in an animal model of medication-overuse headache

PubMed Central

Green, A Laine; Gu, Pengfei; De Felice, Milena; Dodick, David; Ossipov, Michael H; Porreca, Frank

2014-01-01

Objective The objective of this article is to evaluate electrically evoked thresholds for cortical spreading depression (CSD) and stress-induced activation of trigeminal afferents in a rat model of medication-overuse headache (MOH). Methods Sumatriptan or saline was delivered subcutaneously by osmotic minipump for six days to Sprague-Dawley rats. Two weeks after pump removal, animals were anesthetized and recording/stimulating electrodes implanted. The animals were pretreated with vehicle or topiramate followed by graded electrical stimulation within the visual cortex. CSD events were identified by decreased EEG amplitude and DC potential shift. Additional unanesthetized sumatriptan or saline-pretreated rats were exposed to bright light environmental stress and periorbital and hindpaw withdrawal thresholds were measured. Following CSD stimulation or environmental stress, immunohistochemical staining for Fos in the trigeminal nucleus caudalis (TNC) was performed. Results Sumatriptan pre-exposure significantly decreased electrical stimulation threshold to generate a CSD event. Topiramate normalized the decreased CSD threshold as well as stress-induced behavioral withdrawal thresholds in sumatriptan-treated rats compared to saline-treated animals. Moreover, CSD and environmental stress increased Fos expression in the TNC of sumatriptan-treated rats, and these effects were blocked by topiramate. Environmental stress did not elicit cutaneous allodynia or elevate TNC Fos expression in saline-treated rats. Conclusions A previous period of sumatriptan exposure produced long-lasting increased susceptibility to evoked CSD and environmental stress-induced activation of the TNC that was prevented by topiramate. Lowered CSD threshold, and enhanced consequences of CSD events (increased activation of TNC), may represent an underlying biological mechanism of MOH related to triptans. PMID:24335852

A Universal Threshold for the Assessment of Load and Output Residuals of Strain-Gage Balance Data

NASA Technical Reports Server (NTRS)

Ulbrich, N.; Volden, T.

2017-01-01

A new universal residual threshold for the detection of load and gage output residual outliers of wind tunnel strain{gage balance data was developed. The threshold works with both the Iterative and Non{Iterative Methods that are used in the aerospace testing community to analyze and process balance data. It also supports all known load and gage output formats that are traditionally used to describe balance data. The threshold's definition is based on an empirical electrical constant. First, the constant is used to construct a threshold for the assessment of gage output residuals. Then, the related threshold for the assessment of load residuals is obtained by multiplying the empirical electrical constant with the sum of the absolute values of all first partial derivatives of a given load component. The empirical constant equals 2.5 microV/V for the assessment of balance calibration or check load data residuals. A value of 0.5 microV/V is recommended for the evaluation of repeat point residuals because, by design, the calculation of these residuals removes errors that are associated with the regression analysis of the data itself. Data from a calibration of a six-component force balance is used to illustrate the application of the new threshold definitions to real{world balance calibration data.

Upper stimulation threshold for retinal ganglion cell activation.

PubMed

Meng, Kevin; Fellner, Andreas; Rattay, Frank; Ghezzi, Diego; Meffin, Hamish; Ibbotson, Michael R; Kameneva, Tatiana

2018-08-01

The existence of an upper threshold in electrically stimulated retinal ganglion cells (RGCs) is of interest because of its relevance to the development of visual prosthetic devices, which are designed to restore partial sight to blind patients. The upper threshold is defined as the stimulation level above which no action potentials (direct spikes) can be elicited in electrically stimulated retina. We collected and analyzed in vitro recordings from rat RGCs in response to extracellular biphasic (anodic-cathodic) pulse stimulation of varying amplitudes and pulse durations. Such responses were also simulated using a multicompartment model. We identified the individual cell variability in response to stimulation and the phenomenon known as upper threshold in all but one of the recorded cells (n  =  20/21). We found that the latencies of spike responses relative to stimulus amplitude had a characteristic U-shape. In silico, we showed that the upper threshold phenomenon was observed only in the soma. For all tested biphasic pulse durations, electrode positions, and pulse amplitudes above lower threshold, a propagating action potential was observed in the distal axon. For amplitudes above the somatic upper threshold, the axonal action potential back-propagated in the direction of the soma, but the soma's low level of hyperpolarization prevented action potential generation in the soma itself. An upper threshold observed in the soma does not prevent spike conductance in the axon.

Thresholds for activation of rabbit retinal ganglion cells with an ultrafine, extracellular microelectrode.

PubMed

Jensen, Ralph J; Rizzo, Joseph F; Ziv, Ofer R; Grumet, Andrew; Wyatt, John

2003-08-01

To determine electrical thresholds required for extracellular activation of retinal ganglion cells as part of a project to develop an epiretinal prosthesis. Retinal ganglion cells were recorded extracellularly in retinas isolated from adult New Zealand White rabbits. Electrical current pulses of 100- micro s duration were delivered to the inner surface of the retina from a 5- micro m long electrode. In about half of the cells, the point of lowest threshold was found by searching with anodal current pulses; in the other cells, cathodal current pulses were used. Threshold measurements were obtained near the cell bodies of 20 ganglion cells and near the axons of 19 ganglion cells. Both cathodal and anodal stimuli evoked a neural response in the ganglion cells that consisted of a single action potential of near-constant latency that persisted when retinal synaptic transmission was blocked with cadmium chloride. For cell bodies, but not axons, thresholds for both cathodal and anodal stimulation were dependent on the search method used to find the point of lowest threshold. With search and stimulation of matching polarity, cathodal stimuli evoked a ganglion cell response at lower currents (approximately one seventh to one tenth axonal threshold) than did anodal stimuli for both cell bodies and axons. With cathodal search and stimulation, cell body median thresholds were somewhat lower (approximately one half) than the axonal median thresholds. With anodal search and stimulation, cell body median thresholds were approximately the same as axonal median thresholds. The results suggest that cathodal stimulation should produce lower thresholds, more localized stimulation, and somewhat better selectivity for cell bodies over axons than would anodal stimulation.

Repeated noxious stimulation of the skin enhances cutaneous pain perception of migraine patients in-between attacks: clinical evidence for continuous sub-threshold increase in membrane excitability of central trigeminovascular neurons.

PubMed

Weissman-Fogel, Irit; Sprecher, Elliot; Granovsky, Yelena; Yarnitsky, David

2003-08-01

Recent clinical studies showed that acute migraine attacks are accompanied by increased periorbital and bodily skin sensitivity to touch, heat and cold. Parallel pre-clinical studies showed that the underlying mechanism is sensitization of primary nociceptors and central trigeminovascular neurons. The present study investigates the sensory state of neuronal pathways that mediate skin pain sensation in migraine patients in between attacks. The assessments of sensory perception included (a) mechanical and thermal pain thresholds of the periorbital area, electrical pain threshold of forearm skin, (b) pain scores to phasic supra-threshold stimuli in the same modalities and areas as above, and (c) temporal summation of pain induced by applying noxious tonic heat pain and brief trains of noxious mechanical and electrical pulses to the above skin areas. Thirty-four pain-free migraine patients and 28 age- and gender-matched controls were studied. Patients did not differ from controls in their pain thresholds for heat (44+/-2.6 vs. 44.6+/-1.9 degrees C), and electrical (4.8+/-1.6 vs. 4.3+/-1.6 mA) stimulation, and in their pain scores for supra-threshold phasic stimuli for all modalities. They did, however, differ in their pain threshold for mechanical stimulation, just by one von Frey filament (P=0.01) and in their pain scores of the temporal summation tests. Increased summation of pain was found in migraineurs for repeated mechanical stimuli (delta visual analog scale (VAS) +2.32+/-0.73 in patients vs. +0.16+/-0.83 in controls, P=0.05) and repeated electrical stimuli (delta VAS +3.83+/-1.91 vs -3.79+/-2.31, P=0.01). Increased summation corresponded with more severe clinical parameters of migraine and tended to depend on interval since last migraine attack. The absence of clinically or overt laboratory expressed allodynia suggests that pain pathways are not sensitized in the pain-free migraine patients. Nevertheless, the increased temporal summation, and the slight decrease in mechanical pain thresholds, suggest that central nociceptive neurons do express activation-dependent plasticity. These findings may point to an important pathophysiological change in membrane properties of nociceptive neurons of migraine patients; a change that may hold a key to more effective prophylactic treatment.

Low-loss resonance modes in a gain-assisted plasmonic multimer

NASA Astrophysics Data System (ADS)

Pan, Gui-Ming; Yang, Da-Jie; Zhou, Li; Hao, Zhong-Hua

2018-03-01

We theoretically study the properties of optical losses in a plasmonic multimer and find modes with lower radiative losses due to the cancellation of the dipole moment. High order plasmonic resonances, including electric quadrupole and magnetic dipole resonances, can be achieved by the reduction of symmetry in a multimer. Meanwhile, the dipole moment can be significantly reduced in these high order modes, and consequently, the radiative losses decrease efficiently. The low-loss modes can lead to a lower gain threshold in the gain-assisted nanosystem. In particular, compared with the electric dipolar mode in a single nanoshell, the gain threshold of the electric quadrupolar and magnetic dipolar modes in a multimer can drop by 57.66% and 59.22%, respectively. On the other hand, the gain threshold can reflect the extent of the optical losses of the plasmonic mode in a nanosystem. These findings may have potential applications in the design of a nanolaser, plasmon waveguide and photo-thermal device.

Exciton recombination in lasing contributing an opposite abrupt change of the electrical behavior near threshold between GaN- and GaAs- multi-quantum-well laser diodes

NASA Astrophysics Data System (ADS)

Feng, Liefeng; Wang, Shupeng; Li, Yang; Li, Ding; Wang, Cunda

2018-03-01

The opposite sudden change of electrical characteristics between narrow and wide bang-gap multi-quantum-well (MQW) laser diodes (LDs) in the threshold region (which is defined as a current region between two kinks of IdV/dI-I curve) shows an interesting phenomenon that the slope changes of IdV/dI-I or V j -I curve between two adjacent regions (‘below’ and ‘in’, or ‘in’ and ‘above’ threshold region) display an approximate e-exponential relationship with the wavelengths of LDs. After comparing the exciton binding energy in different MQW LDs, and analyzing the temperature dependence of V j -I and IdV/dI-I of GaN MQW LDs, we suggested that the fraction of exciton recombination into lasing is a reason causing the relationship of sudden changes of the electrical characteristics with wavelengths of LDs.

Multipoint Ignition of a Gas Mixture by a Microwave Subcritical Discharge with an Extended Streamer Structure

NASA Astrophysics Data System (ADS)

Aleksandrov, K. V.; Busleev, N. I.; Grachev, L. P.; Esakov, I. I.; Ravaev, A. A.

2018-02-01

The results of experimental studies on using an electrical discharge with an extended streamer structure in a quasioptical microwave beam in the multipoint ignition of a propane-air mixture have been reported. The pulsed microwave discharge was initiated at the interior surface of a quartz tube that was filled with the mentioned flammable mixture and introduced into a microwave beam with a subbreakdown initial field. Gas breakdown was initiated by an electromagnetic vibrator. The dependence of the type of discharge on the microwave field strength was examined, the lower concentration threshold of ignition of the propane-air mixture by the studied discharge was determined, and the dynamics of combustion of the flammable mixture with local and multipoint ignition were compared.

Monolithic integration of a vertical cavity surface emitting laser and a metal semiconductor field effect transistor

NASA Astrophysics Data System (ADS)

Yang, Y. J.; Dziura, T. G.; Bardin, T.; Wang, S. C.; Fernandez, R.; Liao, Andrew S. H.

1993-02-01

Monolithic integration of a vertical cavity surface emitting laser (VCSEL) and a metal semiconductor field effect transistor (MESFET) is reported for the first time. The epitaxial layers for both GaAs VCSELs and MESFETs are grown on an n-type GaAs substrate by molecular-beam epitaxy at the same time. The VCSELs with a 10-micron diam active region exhibit an average threshold current (Ith) of 6 mA and a continuous wave (CW) maximum power of 1.1 mW. The MESFETs with a 3-micron gate length have a transconductance of 50 mS/mm. The laser output is modulated by the gate voltage of the MESFETs and exhibits an optical/electrical conversion factor of 0.5 mW/V.

Effects of substrate on the femtosecond laser-induced damage properties of gold films

NASA Astrophysics Data System (ADS)

Huang, Haopeng; Wang, Leilei; Kong, Fanyu; Xia, Zhilin; Jin, Yunxia; Xu, Jiao; Chen, Junming; Cui, Yun; Shao, Jianda

2018-07-01

In this work, gold films on two different types of substrates were fabricated by electron beam (e-beam) evaporation, and the femtosecond laser-induced damage properties were evaluated. The first sample was gold film deposited on fused silica, whereas the second was gold deposited on photoresist. 1-on-1 damage tests were implemented by an 800 ± 30 nm laser with pulse duration of 30 fs. Different damage thresholds and morphologies were obtained for the two samples. The damage threshold of the gold film on fused silica was 0.64 J/cm2, with the typical damage morphology of thermal ablation and melting; the damage threshold of the gold film on photoresist was 0.30 J/cm2, with the typical damage morphology of blisters or peeling off. In order to better understand the impact of the substrate on the properties of the whole sample, the normalized electric field intensity, temperature, and thermal stress distributions were calculated. The adhesion between the gold film and substrate were measured and the experimental results well agreed with the theoretical analysis. The results indicate that gold films deposited onto grating-structured fused silica will have more powerful laser damage resistance performance.

The limits of the Bohm criterion in collisional plasmas

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

Valentini, H.-B.; Kaiser, D.

2015-05-15

The sheath formation within a low-pressure collisional plasma is analysed by means of a two-fluid model. The Bohm criterion takes into account the effects of the electric field and the inertia of the ions. Numerical results yield that these effects contribute to the space charge formation, only, if the collisionality is lower than a relatively small threshold. It follows that a lower and an upper limit of the drift speed of the ions exist where the effects treated by Bohm can form a sheath. This interval becomes narrower as the collisionality increases and vanishes at the mentioned threshold. Above themore » threshold, the sheath is mainly created by collisions and the ionisation. Under these conditions, the sheath formation cannot be described by means of Bohm like criteria. In a few references, a so-called upper limit of the Bohm criterion is stated for collisional plasmas where the momentum equation of the ions is taken into account, only. However, the present paper shows that this limit results in an unrealistically steep increase of the space charge density towards the wall, and, therefore, it yields no useful limit of the Bohm velocity.« less

Structural and electronic properties of copper-doped chalcogenide glasses

NASA Astrophysics Data System (ADS)

Guzman, David M.; Strachan, Alejandro

2017-10-01

Using ab initio molecular dynamics based on density functional theory, we study the atomic and electronic structure, and transport properties of copper-doped germanium-based chalcogenide glasses. These mixed ionic-electronic conductor materials exhibit resistance or threshold switching under external electric field depending on slight variations of chemical composition. Understanding the origin of the transport character is essential for the functionalization of glassy chalcogenides for nanoelectronics applications. To this end, we generated atomic structures for GeX3 and GeX6 (X = S, Se, Te) at different copper concentrations and characterized the atomic origin of electronic states responsible for transport and the tendency of copper clustering as a function of metal concentration. Our results show that copper dissolution energies explain the tendency of copper to agglomerate in telluride glasses, consistent with filamentary conduction. In contrast, copper is less prone to cluster in sulfides and selenides leading to hysteresisless threshold switching where the nature of transport is dominated by electronic midgap defects derived from polar chalcogen bonds and copper atoms. Simulated I -V curves show that at least 35% by weight of copper is required to achieve the current demands of threshold-based devices for memory applications.

Normal Threshold Size of Stimuli in Children Using a Game-Based Visual Field Test.

PubMed

Wang, Yanfang; Ali, Zaria; Subramani, Siddharth; Biswas, Susmito; Fenerty, Cecilia; Henson, David B; Aslam, Tariq

2017-06-01

The aim of this study was to demonstrate and explore the ability of novel game-based perimetry to establish normal visual field thresholds in children. One hundred and eighteen children (aged 8.0 ± 2.8 years old) with no history of visual field loss or significant medical history were recruited. Each child had one eye tested using a game-based visual field test 'Caspar's Castle' at four retinal locations 12.7° (N = 118) from fixation. Thresholds were established repeatedly using up/down staircase algorithms with stimuli of varying diameter (luminance 20 cd/m 2 , duration 200 ms, background luminance 10 cd/m 2 ). Relationships between threshold and age were determined along with measures of intra- and intersubject variability. The Game-based visual field test was able to establish threshold estimates in the full range of children tested. Threshold size reduced with increasing age in children. Intrasubject variability and intersubject variability were inversely related to age in children. Normal visual field thresholds were established for specific locations in children using a novel game-based visual field test. These could be used as a foundation for developing a game-based perimetry screening test for children.

Enhancement of Electrical Conductivity in Multicomponent Nanocomposites.

NASA Astrophysics Data System (ADS)

Ni, Xiaojuan; Hui, Chao; Su, Ninghai; Liu, Feng

To date, very limited theoretical or numerical analyses have been carried out to understand the electrical percolation properties in multicomponent nanocomposite systems. In this work, a disk-stick percolation model was developed to investigate the electrical percolation behavior of an electrically insulating matrix reinforced with one-dimensional (1D) and two-dimensional (2D) conductors via Monte Carlo simulation. The effective electrical conductivity was evaluated through Kirchhoff's current law by transforming it into an equivalent resistor network. The percolation threshold, equivalent resistance and conductivity were obtained from the distribution of nodal voltages by solving a system of linear equations with Gaussian elimination method. The effects of size, aspect ratio, relative concentration and contact patterns of 1D/2D inclusions on conductivity performance were examined. Our model is able to predict the electrical percolation threshold and evaluate the conductivity for hybrid systems with multiple components. The results suggest that carbon-based nanocomposites can have a high potential for applications where favorable electrical properties and low specific weight are required. We acknowledge the financial support from DOE-BES (No. DE-FG02-04ER46148).

Effect of Age and Severity of Facial Palsy on Taste Thresholds in Bell's Palsy Patients

PubMed Central

Park, Jung Min; Kim, Myung Gu; Jung, Junyang; Kim, Sung Su; Jung, A Ra; Kim, Sang Hoon

2017-01-01

Background and Objectives To investigate whether taste thresholds, as determined by electrogustometry (EGM) and chemical taste tests, differ by age and the severity of facial palsy in patients with Bell's palsy. Subjects and Methods This study included 29 patients diagnosed with Bell's palsy between January 2014 and May 2015 in our hospital. Patients were assorted into age groups and by severity of facial palsy, as determined by House-Brackmann Scale, and their taste thresholds were assessed by EGM and chemical taste tests. Results EGM showed that taste thresholds at four locations on the tongue and one location on the central soft palate, 1 cm from the palatine uvula, were significantly higher in Bell's palsy patients than in controls (p<0.05). In contrast, chemical taste tests showed no significant differences in taste thresholds between the two groups (p>0.05). The severity of facial palsy did not affect taste thresholds, as determined by both EGM and chemical taste tests (p>0.05). The overall mean electrical taste thresholds on EGM were higher in younger Bell's palsy patients than in healthy subjects, with the difference at the back-right area of the tongue differing significantly (p<0.05). In older individuals, however, no significant differences in taste thresholds were observed between Bell's palsy patients and healthy subjects (p>0.05). Conclusions Electrical taste thresholds were higher in Bell's palsy patients than in controls. These differences were observed in younger, but not in older, individuals. PMID:28417103

Sucrose acceptance and different forms of associative learning of the honey bee (apis mellifera L.) in the field and laboratory.

PubMed

Mujagic, Samir; Sarkander, Jana; Erber, Barbara; Erber, Joachim

2010-01-01

The experiments analyze different forms of learning and 24-h retention in the field and in the laboratory in bees that accept sucrose with either low (/=30% or >/=50%) concentrations. In the field we studied color learning at a food site and at the hive entrance. In the laboratory olfactory conditioning of the proboscis extension response (PER) was examined. In the color learning protocol at a feeder, bees with low sucrose acceptance thresholds (/=50%). Retention after 24 h is significantly different between the two groups of bees and the choice reactions converge. Bees with low and high acceptance thresholds in the field show no differences in the sucrose sensitivity PER tests in the laboratory. Acceptance thresholds in the field are thus a more sensitive behavioral measure than PER responsiveness in the laboratory. Bees with low acceptance thresholds show significantly better acquisition and 24-h retention in olfactory learning in the laboratory compared to bees with high thresholds. In the learning protocol at the hive entrance bees learn without sucrose reward that a color cue signals an open entrance. In this experiment, bees with high sucrose acceptance thresholds showed significantly better learning and reversal learning than bees with low thresholds. These results demonstrate that sucrose acceptance thresholds affect only those forms of learning in which sucrose serves as the reward. The results also show that foraging behavior in the field is a good predictor for learning behavior in the field and in the laboratory.

Avalanche buildup and propagation effects on photon-timing jitter in Si-SPAD with non-uniform electric field

NASA Astrophysics Data System (ADS)

Ingargiola, Antonino; Assanelli, Mattia; Gallivanoni, Andrea; Rech, Ivan; Ghioni, Massimo; Cova, Sergio

2009-05-01

Improving SPAD performances, such as dark count rate and quantum efficiency, without degrading the photontiming jitter is a challenging task that requires a clear understanding of the physical mechanisms involved. In this paper we investigate the contribution of the avalanche buildup statistics and the lateral avalanche propagation to the photon-timing jitter in silicon SPAD devices. Recent works on the buildup statistics focused on the uniform electric field case, however these results can not be applied to Si SPAD devices in which field profile is far from constant. We developed a 1-D Monte Carlo (MC) simulator using the real non-uniform field profiles derived from Secondary Ion Mass Spectroscopy (SIMS) measurements. Local and non-local models for impact ionization phenomena were considered. The obtained results, in particular the mean multiplication rate and jitter of the buildup filament, allowed us to simulate the statistical spread of the avalanche current on the device active area. We included space charge effects and a detailed lumped model for the external electronics and parasitics. We found that, in agreement with some experimental evidences, the avalanche buildup contribution to the total timing jitter is non-negligible in our devices. Moreover the lateral propagation gives an additional contribution that can explain the increasing trend of the photon-timing jitter with the comparator threshold.

Electrical conductivity of the Earth's mantle after one year of SWARM magnetic field measurements

NASA Astrophysics Data System (ADS)

Civet, François; Thebault, Erwan; Verhoeven, Olivier; Langlais, Benoit; Saturnino, Diana

2015-04-01

We present a global EM induction study using L1b Swarm satellite magnetic field measurements data down to a depth of 2000 km. Starting from raw measurements, we first derive a model for the main magnetic field, correct the data for a lithospheric field model, and further select the data to reduce the contributions of the ionospheric field. These computations allowed us to keep a full control on the data processes. We correct residual field from outliers and estimate the spherical harmonic coefficients of the transient field for periods between 2 and 256 days. We used full latitude range and all local times to keep a maximum amount of data. We perform a Bayesian inversion and construct a Markov chain during which model parameters are randomly updated at each iteration. We first consider regular layers of equal thickness and extra layers are added where conductivity contrast between successive layers exceed a threshold value. The mean and maximum likelihood of the electrical conductivity profile is then estimated from the probability density function. The obtained profile particularly shows a conductivity jump in the 600-700 km depth range, consistent with the olivine phase transition at 660 km depth. Our study is the first one to show such a conductivity increase in this depth range without any a priori informations on the internal strucutres. Assuming a pyrolitic mantle composition, this profile is interpreted in terms of temperature variations in the depth range where the probability density function is the narrowest. We finally obtained a temperature gradient in the lower mantle close to adiabatic.

Repetitively Pulsed Nonequilibrium Plasmas for Plasma-Assisted Combustion, Flow Control, and Molecular Lasers

NASA Astrophysics Data System (ADS)

Adamovich, Igor

2006-10-01

The paper presents results of three experiments using high voltage, short pulse duration, high repetition rate discharge plasmas. High electric field during the pulse (E/N˜500-1000 Td) allows efficient ionization and molecular dissociation. Between the pulses, additional energy can be coupled to the decaying plasma using a DC field set below the breakdown threshold. While the DC sustainer discharge adds 90-95% of all the power to the flow, it does not produce any additional ionization. The pulser and the sustainer discharges are fully overlapped in space. Low duty cycle of the pulsed ionizer, ˜1/1000, allows sustaining diffuse and uniform pulser-sustainer plasmas at high pressures and power loadings. The first experiment using the pulsed discharge is ignition of premixed hydrocarbon-air flows, which occurs at low pulsed discharge powers, ˜100 W, and very low plasma temperatures, 100-200^0 C. The second experiment is Lorentz force acceleration of low-temperature supersonic flows. The pulsed discharge was used to generate electrical conductivity in M=3 nitrogen and air flows, while the sustainer discharge produced transverse current in the presence of magnetic field of B=1.5 T. Retarding Lorentz force applied to the flow produced a static pressure increase of up to 15-20%, while accelerating force of the same magnitude resulted in static pressure rise of up to 7-8%, i.e. a factor of two smaller. The third experiment is singlet delta oxygen (SDO) generation in a high-pressure pulser-sustainer discharge. SDO yield was inferred from the integrated intensity of SDO infrared emission spectra calibrated using a blackbody source. The measured yield exceeds the laser threshold yield by about a factor of three, which makes possible achieving positive gain in the laser cavity. The highest gain measured so far is 0.03%/cm.

Assessment and mitigation of power quality problems for PUSPATI TRIGA Reactor (RTP)

NASA Astrophysics Data System (ADS)

Zakaria, Mohd Fazli; Ramachandaramurthy, Vigna K.

2017-01-01

An electrical power systems are exposed to different types of power quality disturbances. Investigation and monitoring of power quality are necessary to maintain accurate operation of sensitive equipment especially for nuclear installations. This paper will discuss the power quality problems observed at the electrical sources of PUSPATI TRIGA Reactor (RTP). Assessment of power quality requires the identification of any anomalous behavior on a power system, which adversely affects the normal operation of electrical or electronic equipment. A power quality assessment involves gathering data resources; analyzing the data (with reference to power quality standards) then, if problems exist, recommendation of mitigation techniques must be considered. Field power quality data is collected by power quality recorder and analyzed with reference to power quality standards. Normally the electrical power is supplied to the RTP via two sources in order to keep a good reliability where each of them is designed to carry the full load. The assessment of power quality during reactor operation was performed for both electrical sources. There were several disturbances such as voltage harmonics and flicker that exceeded the thresholds. To reduce these disturbances, mitigation techniques have been proposed, such as to install passive harmonic filters to reduce harmonic distortion, dynamic voltage restorer (DVR) to reduce voltage disturbances and isolate all sensitive and critical loads.

Unintended effects of electrofishing on nongame fishes

USGS Publications Warehouse

Miranda, Leandro E.; Kidwell, R. H.

2010-01-01

Most studies of injury associated with electrofishing have focused on game fishes, but few have given attention to cohabiting small nongame species. Under controlled laboratory conditions, we subjected small nongame cyprinids, ictalurids, and percids to a wide range of voltages and waveforms to examine potential harmful effects. Fish were treated with power levels distributed uniformly between the thresholds required to immobilize game fish and also were subjected multiple times to those thresholds to simulate the range of conditions that might exist in a heterogeneous electrical field formed during electrofishing in field situations. Across waveforms and species, the incidence of hemorrhages averaged 2% (range = 0–20%), the incidence of spinal injuries averaged 6% (range = 0–30%), and mortality averaged 16% (range = 0–90%). Continuous DC was generally less harmful than pulsed-DC waveforms; hemorrhages and spinal injuries tended to increase with high pulse frequencies, and mortalities tended to increase with low pulse frequencies. Ambiguities in the results were apparent, suggesting that some species may experience extensive harm, whereas others may not. Given the potential to harm numerically small populations and populations of imperiled species, we suggest (1) expanded efforts to overcome the power limitations that prevent effective use of continuous-DC electrofishing in many field situations and (2) pilot studies at geographic locations where numerically small populations of nongame species may be a concern.

Effect of oscillator strength and intermediate resonance on the performance of resonant phonon-based terahertz quantum cascade lasers

NASA Astrophysics Data System (ADS)

Fathololoumi, S.; Dupont, E.; Wasilewski, Z. R.; Chan, C. W. I.; Razavipour, S. G.; Laframboise, S. R.; Huang, Shengxi; Hu, Q.; Ban, D.; Liu, H. C.

2013-03-01

We experimentally investigated the effect of oscillator strength (radiative transition diagonality) on the performance of resonant phonon-based terahertz quantum cascade lasers that have been optimized using a simplified density matrix formalism. Our results show that the maximum lasing temperature (Tmax) is roughly independent of laser transition diagonality within the lasing frequency range of the devices under test (3.2-3.7 THz) when cavity loss is kept low. Furthermore, the threshold current can be lowered by employing more diagonal transition designs, which can effectively suppress parasitic leakage caused by intermediate resonance between the injection and the downstream extraction levels. Nevertheless, the current carrying capacity through the designed lasing channel in more diagonal designs may sacrifice even more, leading to electrical instability and, potentially, complete inhibition of the device's lasing operation. We propose a hypothesis based on electric-field domain formation and competition/switching of different current-carrying channels to explain observed electrical instability in devices with lower oscillator strengths. The study indicates that not only should designers maximize Tmax during device optimization but also they should always consider the risk of electrical instability in device operation.

Transport in a field aligned magnetized plasma/neutral gas boundary: the end of the plasma

NASA Astrophysics Data System (ADS)

Cooper, Christopher Michael

The objective of this dissertation is to characterize the physics of a boundary layer between a magnetized plasma and a neutral gas along the direction of a confining magnetic field. A series of experiments are performed at the Enormous Toroidal Plasma Device (ETPD) at UCLA to study this field aligned Neutral Boundary Layer (NBL) at the end of the plasma. A Lanthanum Hexaboride (LaB6) cathode and semi-transparent anode creates a magnetized, current-free helium plasma which terminates on a neutral helium gas without touching any walls. Probes are inserted into the plasma to measure the basic plasma parameters and study the transport in the NBL. The experiment is performed in the weakly ionized limit where the plasma density (ne) is much less than the neutral density (nn) such that ne/nn < 5%. The NBL is characterized by a field-aligned electric field which begins at the point where the plasma pressure equilibrates with the neutral gas pressure. Beyond the pressure equilibration point the electrons and ions lose their momentum by collisions with the neutral gas and come to rest. An electric field is established self consistently to maintain a current-free termination through equilibration of the different species' stopping rates in the neutral gas. The electric field resembles a collisional quasineutral sheath with a length 10 times the electron-ion collision length, 100 times the neutral collision length, and 10,000 times the Debye length. Collisions with the neutral gas dominate the losses in the system. The measured plasma density loss rates are above the classical cross-field current-free ambipolar rate, but below the anomalous Bohm diffusion rate. The electron temperature is below the ionization threshold of the gas, 2.2 eV in helium. The ions are in thermal equilibrium with the neutral gas. A generalized theory of plasma termination in a Neutral Boundary Layer is applied to this case using a two-fluid, current-free, weakly ionized transport model. The electron and ion momentum equations along the field are combined in a generalized Ohm's law which predicts the axial electric field required to maintain a current-free termination. The pressure balance criteria for termination and the predicted electric field are confirmed over a scaling of plasma parameters. The experiment and the model are relevant for studying NBLs in other systems, such as the atmospheric termination of the aurora or detached gaseous divertors. A steady state modified ambipolar system is measured in the ETPD NBL. The drift speeds associated with these currents are a small fraction of the plasma flow speeds and the problem is treated as a perturbation to the termination model. The current-free condition on the model is relaxed to explain the presence of the divergence free current.

Bloch oscillations in organic and inorganic polymers

NASA Astrophysics Data System (ADS)

Ribeiro, Luiz Antonio; Ferreira da Cunha, Wiliam; de Almeida Fonseca, Antonio Luciano; e Silva, Geraldo Magela

2017-04-01

The transport of polarons above the mobility threshold in organic and inorganic polymers is theoretically investigated in the framework of a one-dimensional tight-binding model that includes lattice relaxation. The computational approach is based on parameters for which the model Hamiltonian suitably describes different polymer lattices in the presence of external electric fields. Our findings show that, above critical field strengths, a dissociated polaron moves through the polymer lattice as a free electron performing Bloch oscillations. These critical electric fields are considerably smaller for inorganic lattices in comparison to organic polymers. Interestingly, for inorganic lattices, the free electron propagates preserving charge and spin densities' localization which is a characteristic of a static polaron. Moreover, in the turning points of the spatial Bloch oscillations, transient polaron levels are formed inside the band gap, thus generating a fully characterized polaron structure. For the organic case, on the other hand, no polaron signature is observed: neither in the shape of the distortion—those polaron profile signatures are absent—nor in the energy levels—as no such polaron levels are formed during the simulation. These results solve controversial aspects concerning Bloch oscillations recently reported in the literature and may enlighten the understanding about the charge transport mechanism in polymers above their mobility edge.

Dipolarization Fronts from Reconnection Onset

NASA Astrophysics Data System (ADS)

Sitnov, M. I.; Swisdak, M. M.; Merkin, V. G.; Buzulukova, N.; Moore, T. E.

2012-12-01

Dipolarization fronts observed in the magnetotail are often viewed as signatures of bursty magnetic reconnection. However, until recently spontaneous reconnection was considered to be fully prohibited in the magnetotail geometry because of the linear stability of the ion tearing mode. Recent theoretical studies showed that spontaneous reconnection could be possible in the magnetotail geometries with the accumulation of magnetic flux at the tailward end of the thin current sheet, a distinctive feature of the magnetotail prior to substorm onset. That result was confirmed by open-boundary full-particle simulations of 2D current sheet equilibria, where two magnetotails were separated by an equilibrium X-line and weak external electric field was imposed to nudge the system toward the instability threshold. To investigate the roles of the equilibrium X-line, driving electric field and other parameters in the reconnection onset process we performed a set of 2D PIC runs with different initial settings. The investigated parameter space includes the critical current sheet thickness, flux tube volume per unit magnetic flux and the north-south component of the magnetic field. Such an investigation is critically important for the implementation of kinetic reconnection onset criteria into global MHD codes. The results are compared with Geotail visualization of the magnetotail during substorms, as well as Cluster and THEMIS observations of dipolarization fronts.

Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching

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

Tartan, Chloe C., E-mail: chloe.tartan@eng.ox.ac.uk, E-mail: steve.elston@eng.ox.ac.uk; Salter, Patrick S.; Booth, Martin J.

2016-05-14

Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10–100 μs. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phasemore » of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.« less

Localised polymer networks in chiral nematic liquid crystals for high speed photonic switching

NASA Astrophysics Data System (ADS)

Tartan, Chloe C.; Salter, Patrick S.; Booth, Martin J.; Morris, Stephen M.; Elston, Steve J.

2016-05-01

Self-assembled periodic structures based upon chiral liquid crystalline materials have significant potential in the field of photonics ranging from fast-switching optoelectronic devices to low-threshold lasers. The flexoelectro-optic effect, which is observed in chiral nematic liquid crystals (LCs) when an electric field is applied perpendicular to the helical axis, has significant potential as it exhibits analogue switching in 10-100 μs. However, the major technological barrier that prohibits the commercial realisation of this electro-optic effect is the requirement of a uniform, in-plane alignment of the helix axis between glass substrates. Here, it is shown that periodic polymer structures engineered in the nematic phase of a chiral nematic LC device using direct laser writing can result in the spontaneous formation of the necessary uniform lying helix (ULH) state. Specifically, two-photon polymerization is used in conjunction with a spatial light modulator so as to correct for aberrations introduced by the bounding glass substrates enabling the polymer structures to be fabricated directly into the device. The ULH state appears to be stable in the absence of an externally applied electric field, and the optimum contrast between the bright and dark states is obtained using polymer structures that have periodicities of the order of the device thickness.

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

Elhadj, Selim; Yoo, Jae-hyuck; Negres, Raluca A.

The optical damage performance of electrically conductive gallium nitride (GaN) and indium tin oxide (ITO) films is addressed using large area, high power laser beam exposures at 1064 nm sub-bandgap wavelength. Analysis of the laser damage process assumes that onset of damage (threshold) is determined by the absorption and heating of a nanoscale region of a characteristic size reaching a critical temperature. We use this model to rationalize semi-quantitatively the pulse width scaling of the damage threshold from picosecond to nanosecond timescales, along with the pulse width dependence of the damage threshold probability derived by fitting large beam damage densitymore » data. Multi-shot exposures were used to address lifetime performance degradation described by an empirical expression based on the single exposure damage model. A damage threshold degradation of at least 50% was observed for both materials. Overall, the GaN films tested had 5-10 × higher optical damage thresholds than the ITO films tested for comparable transmission and electrical conductivity. This route to optically robust, large aperture transparent electrodes and power optoelectronics may thus involve use of next generation widegap semiconductors such as GaN.« less

Low-temperature solution-processed zinc oxide field effect transistor by blending zinc hydroxide and zinc oxide nanoparticle in aqueous solutions

NASA Astrophysics Data System (ADS)

Shin, Hyeonwoo; Kang, Chan-mo; Baek, Kyu-Ha; Kim, Jun Young; Do, Lee-Mi; Lee, Changhee

2018-05-01

We present a novel methods of fabricating low-temperature (180 °C), solution-processed zinc oxide (ZnO) transistors using a ZnO precursor that is blended with zinc hydroxide [Zn(OH)2] and zinc oxide hydrate (ZnO • H2O) in an ammonium solution. By using the proposed method, we successfully improved the electrical performance of the transistor in terms of the mobility (μ), on/off current ratio (I on/I off), sub-threshold swing (SS), and operational stability. Our new approach to forming a ZnO film was systematically compared with previously proposed methods. An atomic forced microscopic (AFM) image and an X-ray photoelectron spectroscopy (XPS) analysis showed that our method increases the ZnO crystallite size with less OH‑ impurities. Thus, we attribute the improved electrical performance to the better ZnO film formation using the blending methods.

Higher Order Bases in a 2D Hybrid BEM/FEM Formulation

NASA Technical Reports Server (NTRS)

Fink, Patrick W.; Wilton, Donald R.

2002-01-01

The advantages of using higher order, interpolatory basis functions are examined in the analysis of transverse electric (TE) plane wave scattering by homogeneous, dielectric cylinders. A boundary-element/finite-element (BEM/FEM) hybrid formulation is employed in which the interior dielectric region is modeled with the vector Helmholtz equation, and a radiation boundary condition is supplied by an Electric Field Integral Equation (EFIE). An efficient method of handling the singular self-term arising in the EFIE is presented. The iterative solution of the partially dense system of equations is obtained using the Quasi-Minimal Residual (QMR) algorithm with an Incomplete LU Threshold (ILUT) preconditioner. Numerical results are shown for the case of an incident wave impinging upon a square dielectric cylinder. The convergence of the solution is shown versus the number of unknowns as a function of the completeness order of the basis functions.

Molecular basis of ancestral vertebrate electroreception

PubMed Central

Bellono, Nicholas W.; Leitch, Duncan B.; Julius, David

2017-01-01

Elasmobranch fishes, including sharks, rays, and skates, use specialized electrosensory organs called Ampullae of Lorenzini to detect extremely small changes in environmental electric fields. Electrosensory cells within these ampullae are able to discriminate and respond to minute changes in environmental voltage gradients through an as-yet unknown mechanism. Here we show that the voltage-gated calcium channel CaV1.3 and big conductance calcium-activated potassium (BK) channel are preferentially expressed by electrosensory cells in little skate (Leucoraja erinacea) and functionally couple to mediate electrosensory cell membrane voltage oscillations, which are important in the detection of specific, weak electrical signals. Both channels exhibit unique properties compared with their mammalian orthologues to support electrosensory functions: structural adaptations in CaV1.3 mediate a low voltage threshold for activation, while alterations in BK support specifically tuned voltage oscillations. These findings reveal a molecular basis of electroreception and demonstrate how discrete evolutionary changes in ion channel structure facilitate sensory adaptation. PMID:28264196

A statistical model describing combined irreversible electroporation and electroporation-induced blood-brain barrier disruption

PubMed Central

Sharabi, Shirley; Kos, Bor; Last, David; Guez, David; Daniels, Dianne; Harnof, Sagi; Miklavcic, Damijan

2016-01-01

Background Electroporation-based therapies such as electrochemotherapy (ECT) and irreversible electroporation (IRE) are emerging as promising tools for treatment of tumors. When applied to the brain, electroporation can also induce transient blood-brain-barrier (BBB) disruption in volumes extending beyond IRE, thus enabling efficient drug penetration. The main objective of this study was to develop a statistical model predicting cell death and BBB disruption induced by electroporation. This model can be used for individual treatment planning. Material and methods Cell death and BBB disruption models were developed based on the Peleg-Fermi model in combination with numerical models of the electric field. The model calculates the electric field thresholds for cell kill and BBB disruption and describes the dependence on the number of treatment pulses. The model was validated using in vivo experimental data consisting of rats brains MRIs post electroporation treatments. Results Linear regression analysis confirmed that the model described the IRE and BBB disruption volumes as a function of treatment pulses number (r2 = 0.79; p < 0.008, r2 = 0.91; p < 0.001). The results presented a strong plateau effect as the pulse number increased. The ratio between complete cell death and no cell death thresholds was relatively narrow (between 0.88-0.91) even for small numbers of pulses and depended weakly on the number of pulses. For BBB disruption, the ratio increased with the number of pulses. BBB disruption radii were on average 67% ± 11% larger than IRE volumes. Conclusions The statistical model can be used to describe the dependence of treatment-effects on the number of pulses independent of the experimental setup. PMID:27069447

Room temperature-synthesized vertically aligned InSb nanowires: electrical transport and field emission characteristics

PubMed Central

2013-01-01

Vertically aligned single-crystal InSb nanowires were synthesized via the electrochemical method at room temperature. The characteristics of Fourier transform infrared spectrum revealed that in the syntheses of InSb nanowires, energy bandgap shifts towards the short wavelength with the occurrence of an electron accumulation layer. The current–voltage curve, based on the metal–semiconductor–metal model, showed a high electron carrier concentration of 2.0 × 1017 cm−3 and a high electron mobility of 446.42 cm2 V−1 s−1. Additionally, the high carrier concentration of the InSb semiconductor with the surface accumulation layer induced a downward band bending effect that reduces the electron tunneling barrier. Consequently, the InSb nanowires exhibit significant field emission properties with an extremely low turn-on field of 1.84 V μm−1 and an estimative threshold field of 3.36 V μm−1. PMID:23399075

Clinical evaluation of an inspiratory impedance threshold device during standard cardiopulmonary resuscitation in patients with out-of-hospital cardiac arrest.

PubMed

Aufderheide, Tom P; Pirrallo, Ronald G; Provo, Terry A; Lurie, Keith G

2005-04-01

To determine whether an impedance threshold device, designed to enhance circulation, would increase acute resuscitation rates for patients in cardiac arrest receiving conventional manual cardiopulmonary resuscitation. Prospective, randomized, double-blind, intention-to-treat. Out-of-hospital trial conducted in the Milwaukee, WI, emergency medical services system. Adults in cardiac arrest of presumed cardiac etiology. On arrival of advanced life support, patients were treated with standard cardiopulmonary resuscitation combined with either an active or a sham impedance threshold device. We measured safety and efficacy of the impedance threshold device; the primary end point was intensive care unit admission. Statistical analyses performed included the chi-square test and multivariate regression analysis. One hundred sixteen patients were treated with a sham impedance threshold device, and 114 patients were treated with an active impedance threshold device. Overall intensive care unit admission rates were 17% with the sham device vs. 25% in the active impedance threshold device (p = .13; odds ratio, 1.64; 95% confidence interval, 0.87, 3.10). Patients in the subgroup presenting with pulseless electrical activity had intensive care unit admission and 24-hr survival rates of 20% and 12% in sham (n = 25) vs. 52% and 30% in active impedance threshold device groups (n = 27) (p = .018, odds ratio, 4.31; 95% confidence interval, 1.28, 14.5, and p = .12, odds ratio, 3.09; 95% confidence interval, 0.74, 13.0, respectively). A post hoc analysis of patients with pulseless electrical activity at any time during the cardiac arrest revealed that intensive care unit and 24-hr survival rates were 20% and 11% in the sham (n = 56) vs. 41% and 27% in the active impedance threshold device groups (n = 49) (p = .018, odds ratio, 2.82; 95% confidence interval, 1.19, 6.67, and p = .037, odds ratio, 3.01; 95% confidence interval, 1.07, 8.96, respectively). There were no statistically significant differences in outcomes for patients presenting in ventricular fibrillation and asystole. Adverse event and complication rates were also similar. During this first clinical trial of the impedance threshold device during standard cardiopulmonary resuscitation, use of the new device more than doubled short-term survival rates in patients presenting with pulseless electrical activity. A larger clinical trial is underway to determine the potential longer term benefits of the impedance threshold device in cardiac arrest.

On Possible Arc Inception on Low Voltage Solar Array

NASA Technical Reports Server (NTRS)

Vayner, Boris

2015-01-01

Recent analysis of spacecraft failures during the period of 1990-2013 demonstrated clearly that electrostatic discharges caused more than 8 of all registered failures and anomalies, and comprised the most costly losses (25) for operating companies and agencies. The electrostatic discharges on spacecraft surfaces are the results of differential charging above some critical (threshold) voltages. The mechanisms of differential charging are well known, and various methods have been developed to prevent a generation of significant electric fields in areas of triple junctions. For example, low bus voltages in Low Earth Orbit plasma environment and slightly conducting layer over coverglass (ITO) in Geosynchronous Orbit surroundings are believed to be quite reliable measures to prevent discharges on respective surfaces. In most cases, the vulnerable elements of spacecraft (solar arrays, diode boards, etc.) go through comprehensive ground tests in vacuum chambers. However, tests articles contain the miniscule fragments of spacecraft components such as 10-30 solar cells of many thousands deployed on spacecraft in orbit. This is one reason why manufacturing defects may not be revealed in ground tests but expose themselves in arcing on array surface in space. The other reason for ineffectiveness of discharge preventive measures is aging of all materials in harsh orbital environments. The expected life time of modern spacecraft varies within the range of five-fifteen years, and thermal cycling, radiation damages, and mechanical stresses can result in surface erosion on conductive layers and microscopic cracks in coverglass sheets and adhesive films. These possible damages may cause significant increases in local electric field strengths and subsequent discharges. The primary discharges may or may not be detrimental to spacecraft operation, but they can produce the necessary conditions for sustained arcs initiation. Multiple measures were developed to prevent sustained discharges between adjacent strings, and many ground tests were performed to determine threshold parameters (voltage and current) for sustained arcs. And again, manufacturing defects and aging in space environments may result in considerable decrease of critical threshold parameters. This paper is devoted to the analysis of possible reasons behind arcing on spacecraft with low bus voltages.

On Possible Arc Inception on Low Voltage Solar Array

NASA Technical Reports Server (NTRS)

Vayner, Boris

2015-01-01

Recent analysis of spacecraft failures during the period of 1990-2013 demonstrated clearly that electrostatic discharges caused more than 8 percent of all registered failures and anomalies, and comprised the most costly losses (25 percent) for operating companies and agencies. The electrostatic discharges on spacecraft surfaces are the results of differential charging above some critical (threshold) voltages. The mechanisms of differential charging are well known, and various methods have been developed to prevent a generation of significant electric fields in areas of triple junctions. For example, low bus voltages in Low Earth Orbit plasma environment and slightly conducting layer over cover-glass (ITO) in Geosynchronous Orbit surroundings are believed to be quite reliable measures to prevent discharges on respective surfaces. In most cases, the vulnerable elements of spacecraft (solar arrays, diode boards, etc.) go through comprehensive ground tests in vacuum chambers. However, tests articles contain the miniscule fragments of spacecraft components such as 10-30 solar cells of many thousands deployed on spacecraft in orbit. This is one reason why manufacturing defects may not be revealed in ground tests but expose themselves in arcing on array surface in space. The other reason for ineffectiveness of discharge preventive measures is aging of all materials in harsh orbital environments. The expected life time of modern spacecraft varies within the range of five-fifteen years, and thermal cycling, radiation damages, and mechanical stresses can result in surface erosion on conductive layers and microscopic cracks in cover-glass sheets and adhesive films. These possible damages may cause significant increases in local electric field strengths and subsequent discharges. The primary discharges may or may not be detrimental to spacecraft operation, but they can produce the necessary conditions for sustained arcs initiation. Multiple measures were developed to prevent sustained discharges between adjacent strings, and many ground tests were performed to determine threshold parameters (voltage and current) for sustained arcs. And again, manufacturing defects and aging in space environments may result in considerable decrease of critical threshold parameters. This paper is devoted to the analysis of possible reasons behind arcing on spacecraft with low bus voltages.

Electrical leakage detection circuit

DOEpatents

Wild, Arthur

2006-09-05

A method is provided for detecting electrical leakage between a power supply and a frame of a vehicle or machine. The disclosed method includes coupling a first capacitor between a frame and a first terminal of a power supply for a predetermined period of time. The current flowing between the frame and the first capacitor is limited to a predetermined current limit. It is determined whether the voltage across the first capacitor exceeds a threshold voltage. A first output signal is provided when the voltage across the capacitor exceeds the threshold voltage.

Motor cortex stimulation: role of computer modeling.

PubMed

Manola, L; Holsheimer, J

2007-01-01

Motor cortex stimulation (MCS) is a promising clinical technique used to treat chronic, otherwise intractable pain. However, the mechanisms by which the neural elements that are stimulated during MCS induce pain relief are not understood. Neither is it known which of the main neural elements, i.e. cell bodies, dendrites or fibers are immediately excited by the electrical pulses in MCS. Moreover, it is not known what are the effects of MCS on fibers which are parallel or perpendicular to the cortical layers, below or away from the electrode. The therapy and its efficacy are less likely to be improved until it is better understood how it may work. In this chapter, we present our efforts to resolve this issue. Our computer model of MCS is introduced and some of its predictions are discussed. In particular, the influence of stimulus polarity and electrode position on the electrical field and excitation thresholds of different neural elements is addressed. Such predictions, supported with clinical evidence, should help to elucidate the immediate effects of an electrical stimulus applied over the motor cortex and may ultimately lead to optimizations of the therapy.

Formation of the lunar crust - An electrical source of heating

NASA Technical Reports Server (NTRS)

Sonett, C. P.; Colburn, D. S.; Schwartz, K.

1975-01-01

A model for formation of the lunar crust based on heating by electrical induction is explored, while adherence is maintained to certain constraints associated with existing models of the solar system. The heating mechanism is based on eddy current induction from disordered magnetic fields swept outwards by an intense (T Tauri-like) plasma flow from the sun. The electrical theory is an alternative to intense short-period accretion as a source of heat for the evolution of lunar maria and highlands, provided that long-lived radioactives are not swept to the surface from too large a melt volume during the initial thermal episode. This formation of the lunar highlands does not intrinsically require rapid accretion, nor on this basis is the time of formation of the planets generally restricted to a very short time. The threshold temperature for eddy current heating is attained by either a solar nebula at 300-400 C during formation of the moon or a very low energy long-period accumulation of the moon, both leading to melting in ten to the fifth to ten to the seventh power years.

Study protocol of hypoalgesic effects of low frequency and burst-modulated alternating currents on healthy individuals.

PubMed

Rampazo da Silva, Érika Patrícia; da Silva, Viviane Ribeiro; Bernardes, Anabelly Sato; Matuzawa, Fabio Massao; Liebano, Richard Eloin

2018-03-01

The aim of the study will be to compare different types of analgesic electrical currents in relation to the pressure pain threshold and sensory comfort in healthy individuals. A total of 100 individuals will be randomly assigned to four groups: transcutaneous electrical nerve stimulation, interferential current, Aussie current or placebo. The electrical stimulation will be administered with a strong level for 30 min and to the placebo group, the electrodes will be positioned while the equipment will remain switched off. The pressure pain threshold and sensory comfort will be measured with an algometer and the visual analogue scale, respectively. The level of significance will be p < 0.05. NCT01950728 (clinical trials).

Method and apparatus for controlling battery charging in a hybrid electric vehicle

DOEpatents

Phillips, Anthony Mark; Blankenship, John Richard; Bailey, Kathleen Ellen; Jankovic, Miroslava

2003-06-24

A starter/alternator system (24) for hybrid electric vehicle (10) having an internal combustion engine (12) and an energy storage device (34) has a controller (30) coupled to the starter/alternator (26). The controller (30) has a state of charge manager (40) that monitors the state of charge of the energy storage device. The controller has eight battery state-of-charge threshold values that determine the hybrid operating mode of the hybrid electric vehicle. The value of the battery state-of-charge relative to the threshold values is a factor in the determination of the hybrid mode, for example; regenerative braking, charging, battery bleed, boost. The starter/alternator may be operated as a generator or a motor, depending upon the mode.

Electrophysiological characterization of the rat trigeminal caudalis (Vc) neurons following intramuscular injection of capsaicin

PubMed Central

Chun, Yang H; Ro, Jin Y

2009-01-01

Extracellular single unit recording experiments were performed to examine response characteristics of wide dynamic range neurons in the Vc that receive masseter afferent input in Sprague Dawley rats. Capsaicin, or its vehicle, was directly administered into the masseter muscle and changes in resting discharge, responses to mechanical stimulation on the cutaneous receptive field and the electrical threshold for masseter nerve stimulation were assessed. Intramuscular capsaicin induced significant increase in the background discharge and mechanical hypersensitivity to the cutaneous stimulation and lowered the threshold masseter nerve stimulation evoked responses in the majority of neurons. The capsaicin-induced increase in evoked responses, but not the resting discharge, was partially attenuated when the muscle was pretreated with a mGluR antagonist. The present study suggests that injury or inflammation in the masseter muscle induce generalized hyperexcitability of central trigeminal neurons and that the blockade of peripherally localized mGluR5 can effectively attenuate muscular hypersensitivity. PMID:19818833

Wheel slip control with torque blending using linear and nonlinear model predictive control

NASA Astrophysics Data System (ADS)

Basrah, M. Sofian; Siampis, Efstathios; Velenis, Efstathios; Cao, Dongpu; Longo, Stefano

2017-11-01

Modern hybrid electric vehicles employ electric braking to recuperate energy during deceleration. However, currently anti-lock braking system (ABS) functionality is delivered solely by friction brakes. Hence regenerative braking is typically deactivated at a low deceleration threshold in case high slip develops at the wheels and ABS activation is required. If blending of friction and electric braking can be achieved during ABS events, there would be no need to impose conservative thresholds for deactivation of regenerative braking and the recuperation capacity of the vehicle would increase significantly. In addition, electric actuators are typically significantly faster responding and would deliver better control of wheel slip than friction brakes. In this work we present a control strategy for ABS on a fully electric vehicle with each wheel independently driven by an electric machine and friction brake independently applied at each wheel. In particular we develop linear and nonlinear model predictive control strategies for optimal performance and enforcement of critical control and state constraints. The capability for real-time implementation of these controllers is assessed and their performance is validated in high fidelity simulation.

Electrochemical activation and inhibition of neuromuscular systems through modulation of ion concentrations with ion-selective membranes

NASA Astrophysics Data System (ADS)

Song, Yong-Ak; Melik, Rohat; Rabie, Amr N.; Ibrahim, Ahmed M. S.; Moses, David; Tan, Ara; Han, Jongyoon; Lin, Samuel J.

2011-12-01

Conventional functional electrical stimulation aims to restore functional motor activity of patients with disabilities resulting from spinal cord injury or neurological disorders. However, intervention with functional electrical stimulation in neurological diseases lacks an effective implantable method that suppresses unwanted nerve signals. We have developed an electrochemical method to activate and inhibit a nerve by electrically modulating ion concentrations in situ along the nerve. Using ion-selective membranes to achieve different excitability states of the nerve, we observe either a reduction of the electrical threshold for stimulation by up to approximately 40%, or voluntary, reversible inhibition of nerve signal propagation. This low-threshold electrochemical stimulation method is applicable in current implantable neuroprosthetic devices, whereas the on-demand nerve-blocking mechanism could offer effective clinical intervention in disease states caused by uncontrolled nerve activation, such as epilepsy and chronic pain syndromes.

CNFET-based voltage rectifier circuit for biomedical implantable applications

NASA Astrophysics Data System (ADS)

Tu, Yonggen; Qian, Libo; Xia, Yinshui

2017-02-01

Carbon nanotube field effect transistor (CNFET) shows lower threshold voltage and smaller leakage current in comparison to its CMOS counterpart. In this paper, two kinds of CNFET-based rectifiers, full-wave rectifiers and voltage doubler rectifiers are presented for biomedical implantable applications. Based on the standard 32 nm CNFET model, the electrical performance of CNFET rectifiers is analyzed and compared. Simulation results show the voltage conversion efficiency (VCE) and power conversion efficiency (PCE) achieve 70.82% and 72.49% for CNFET full-wave rectifiers and 56.60% and 61.17% for CNFET voltage double rectifiers at typical 1.0 V input voltage excitation, which are higher than that of CMOS design. Moreover, considering the controllable property of CNFET threshold voltage, the effect of various design parameters on the electrical performance is investigated. It is observed that the VCE and PCE of CNFET rectifier increase with increasing CNT diameter and number of tubes. The proposed results would provide some guidelines for design and optimization of CNFET-based rectifier circuits. Project supported by the National Natural Science Foundation of China (Nos. 61131001, 61404077, 61571248), the Science and Technology Fund of Zhejiang Province (No. 2015C31090), the Natural Science Foundation of Ningbo (No. 2014A610147), State Key Laboratory of ASIC & System (No. 2015KF006) and the K. C. Wong Magna Fund in Ningbo University.

Assessment of deep tissue hyperalgesia in the groin - a method comparison of electrical vs. pressure stimulation.

PubMed

Aasvang, E K; Werner, M U; Kehlet, H

2014-09-01

Deep pain complaints are more frequent than cutaneous in post-surgical patients, and a prevalent finding in quantitative sensory testing studies. However, the preferred assessment method - pressure algometry - is indirect and tissue unspecific, hindering advances in treatment and preventive strategies. Thus, there is a need for development of methods with direct stimulation of suspected hyperalgesic tissues to identify the peripheral origin of nociceptive input. We compared the reliability of an ultrasound-guided needle stimulation protocol of electrical detection and pain thresholds to pressure algometry, by performing identical test-retest sequences 10 days apart, in deep tissues in the groin region. Electrical stimulation was performed by five up-and-down staircase series of single impulses of 0.04 ms duration, starting from 0 mA in increments of 0.2 mA until a threshold was reached and descending until sensation was lost. Method reliability was assessed by Bland-Altman plots, descriptive statistics, coefficients of variance and intraclass correlation coefficients. The electrical stimulation method was comparable to pressure algometry regarding 10 days test-retest repeatability, but with superior same-day reliability for electrical stimulation (P < 0.05). Between-subject variance rather than within-subject variance was the main source for test variation. There were no systematic differences in electrical thresholds across tissues and locations (P > 0.05). The presented tissue-specific direct deep tissue electrical stimulation technique has equal or superior reliability compared with the indirect tissue-unspecific stimulation by pressure algometry. This method may facilitate advances in mechanism based preventive and treatment strategies in acute and chronic post-surgical pain states. © 2014 The Acta Anaesthesiologica Scandinavica Foundation. Published by John Wiley & Sons Ltd.

Investigation of dielectric properties of polymer composites reinforced with carbon nanotubes in the frequency band of 0.01 Hz - 10 MHz

NASA Astrophysics Data System (ADS)

Goshev, A. A.; Eseev, M. K.; Kapustin, S. N.; Vinnik, L. N.; Volkov, A. S.

2016-08-01

The goal of this work is experimental study of dielectric properties of polymer nanocomposites reinforced with multiwalled carbon nanotubes (MWCNTs) in alternating electric field in low frequency band of 0.01 Hz - 10 MHz. We investigated the influence, functionalization degree, aspect ratio, concentration of carbon nanotubes (CNTs) on dielectric properties of polymer sample. We also studied the dependence of dielectric properties on the polymerization temperature. The dependence of CNTs agglomeration on sample polymerization temperature and temperature's influence on conductivity has been shown. We conducted model calculation of percolation threshold and figured out its dependence on CNTs aspect ratio.

The effect of subthreshold continuous electrical stimulation on the facial function of patients with Bell's palsy.

PubMed

Kim, Jin; Choi, Jae Young

2016-01-01

The drug regimen plus electrical stimulation was more effective in treating Bell's palsy than the conventional drug treatment alone. The effectiveness of such a sub-threshold, continuous, low frequency electrical stimulation suggests a new therapeutic approach to accelerate nerve regeneration and improve functional recovery after injury. The purpose of this study was to determine whether sub-threshold, continuous electrical stimulation at 20 Hz facilitates functional recovery of patients with Bell's palsy. The authors performed a prospective randomized study that included 60 patients with mild-to-moderate grade Bell's palsy (HB grade ≤4, SB grade ≥40), to evaluate the effect of developed electrical stimulation on the resolution of symptoms. Thirty patients were treated with prednisolone or/and acyclovir plus electrical stimulation within 7 days of the onset of symptoms. The other 30 patients were treated with only prednisolone or/and acyclovir as a control group. The overall rate of patient recovery among those treated with prednisolone or/and acyclovir plus electrical stimulation (96%) was significantly better (p < 0.05) than the rate among those treated with only prednisolone or/and acyclovir (88%).

LIDT test coupled with gamma radiation degraded optics

NASA Astrophysics Data System (ADS)

IOAN, M.-R.

2016-06-01

A laser can operate in regular but also in nuclear ionizing radiation environments. This paper presents the results of a real time measuring method used to detect the laser induced damage threshold (LIDT) in the optical surfaces/volumes of TEMPAX borosilicate glasses operating in high gamma rays fields. The laser damage quantification technique is applied by using of an automated station intended to measure the damage threshold of optical components, according to the International Standard ISO 21254. Single and multiple pulses laser damage thresholds were determined. For an optical material, life time when it is subjected to multiple pulses of high power laser radiation can be predicted. A few ns pulses shooting laser, operating in regular conditions, inflects damage to a target by its intense electrical component but also in a lower manner by local absorption of its transported thermal energy. When the beam is passing thru optical glass elements affected by ionizing radiation fields, the thermal component is starting to have a more important role, because of the increased thermal absorption in the material's volume caused by the radiation induced color centers. LIDT results on TEMPAX optical glass windows, with the contribution due to the gamma radiation effects (ionization mainly by Compton effect in this case), are presented. This contribution was highlighted and quantified. Energetic, temporal and spatial beam characterizations (according to ISO 11554 standards) and LIDT tests were performed using a high power Nd: YAG laser (1064 nm), before passing the beam through each irradiated glass sample (0 kGy, 1.3 kGy and 21.2 kGy).