Journal articles: 'High frequency currents'

1

Mohsen, A. "High-frequency currents on conducting obstacles." Journal of Physics D: Applied Physics 24, no. 11 (November 14, 1991): 1901–5. http://dx.doi.org/10.1088/0022-3727/24/11/001.

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Bandelier, B., C. Daveau, A. Rais, and F. Rioux-Damidau. "Specific formulation for high frequency eddy-currents." IEEE Transactions on Magnetics 35, no. 3 (May 1999): 1171–74. http://dx.doi.org/10.1109/20.767157.

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Shay, Lynn K., Jorge Martinez-Pedraja, Thomas M. Cook, Brian K. Haus, and Robert H. Weisberg. "High-Frequency Radar Mapping of Surface Currents Using WERA." Journal of Atmospheric and Oceanic Technology 24, no. 3 (March 1, 2007): 484–503. http://dx.doi.org/10.1175/jtech1985.1.

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Abstract A dual-station high-frequency Wellen Radar (WERA), transmitting at 16.045 MHz, was deployed along the west Florida shelf in phased array mode during the summer of 2003. A 33-day, continuous time series of radial and vector surface current fields was acquired starting on 23 August ending 25 September 2003. Over a 30-min sample interval, WERA mapped coastal ocean currents over an ≈40 km × 80 km footprint with a 1.2-km horizontal resolution. A total of 1628 snapshots of the vector surface currents was acquired, with only 70 samples (4.3%) missing from the vector time series. Comparisons to subsurface measurements from two moored acoustic Doppler current profilers revealed RMS differences of 1 to 5 cm s−1 for both radial and Cartesian current components. Regression analyses indicated slopes close to unity with small biases between surface and subsurface measurements at 4-m depth in the east–west (u) and north–south (υ) components, respectively. Vector correlation coefficients were 0.9 with complex phases of −3° and 5° at EC4 (20-m isobath) and NA2 (25-m isobath) moorings, respectively. Complex surface circulation patterns were observed that included tidal and wind-driven currents over the west Florida shelf. Tidal current amplitudes were 4 to 5 cm s−1 for the diurnal and semidiurnal constituents. Vertical structure of these tidal currents indicated that the semidiurnal components were predominantly barotropic whereas diurnal tidal currents had more of a baroclinic component. Tidal currents were removed from the observed current time series and were compared to the 10-m adjusted winds at a surface mooring. Based on these time series comparisons, regression slopes were 0.02 to 0.03 in the east–west and north–south directions, respectively. During Tropical Storm Henri’s passage on 5 September 2003, cyclonically rotating surface winds forced surface velocities of more than 35 cm s−1 as Henri made landfall north of Tampa Bay, Florida. These results suggest that the WERA measured the surface velocity well under weak to tropical storm wind conditions.

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Buckingham, Steven D., and Andrew N. Spencer. "Role of High-Voltage Activated Potassium Currents in High-Frequency Neuronal Firing: Evidence From a Basal Metazoan." Journal of Neurophysiology 88, no. 2 (August 1, 2002): 861–68. http://dx.doi.org/10.1152/jn.2002.88.2.861.

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Certain neurons of vertebrates are specialized for high-frequency firing. Interestingly, high-frequency firing is also seen in central neurons in basal bilateral metazoans. Recently, the role of potassium currents with rightward-shifted activation curves in producing high-frequency firing has come under scrutiny. We apply intracellular recording, patch-clamp techniques, and compartmental modeling to examine the roles of rightward-shifted potassium currents in repetitive firing and shaping of action potentials in central neurons of the flatworm, Notoplana atomata ( Phylum Platyhelminthes). The kinetic properties of potassium and sodium currents were determined from patch-clamp experiments on dissociated brain cells. To predict the effects of changing the steady-state and kinetic properties of these potassium currents, these data were incorporated into a computer model of a 30-μm spherical cell with the levels of current adjusted to approximate the values recorded in voltage-clamp experiments. The model was able to support regenerative spikes at high frequencies in response to injected current. Current-clamp recordings of cultured cells and of neurons in situ also showed evidence of very-high-frequency firing. Adjusting the ratio of inactivating to non-inactivating potassium currents had little effect upon the firing pattern of the cell or its ability to fire at high frequencies, whereas the presence of the non-inactivating current was necessary for repetitive firing. Computer simulations suggested that the rightward shift in voltage sensitivity confers a raised firing threshold, while rapid channel kinetics underlie high frequency firing, and the large activation range enhances the coding range of the cell.

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Shay, L. K., T. M. Cook, H. Peters, A. J. Mariano, R. Weisberg, P. E. An, A. Soloviev, and M. Luther. "Very high-frequency radar mapping of surface currents." IEEE Journal of Oceanic Engineering 27, no. 2 (April 2002): 155–69. http://dx.doi.org/10.1109/joe.2002.1002470.

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Paduan, Jeffrey D., and Libe Washburn. "High-Frequency Radar Observations of Ocean Surface Currents." Annual Review of Marine Science 5, no. 1 (January 3, 2013): 115–36. http://dx.doi.org/10.1146/annurev-marine-121211-172315.

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Andronov, Ivan V., Daniel P. Bouche, and Marc Durufle. "High-Frequency Currents on a Strongly Elongated Spheroid." IEEE Transactions on Antennas and Propagation 65, no. 2 (February 2017): 794–804. http://dx.doi.org/10.1109/tap.2016.2633160.

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Bornhold, Brian D., Ping Ren, and David B. Prior. "High-frequency turbidity currents in British Columbia fjords." Geo-Marine Letters 14, no. 4 (December 1994): 238–43. http://dx.doi.org/10.1007/bf01274059.

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Czapp, Stanislaw, Krzysztof Dobrzynski, Jacek Klucznik, Zbigniew Lubosny, and Robert Kowalak. "Improving sensitivity of residual current transformers to high frequency earth fault currents." Archives of Electrical Engineering 66, no. 3 (September 1, 2017): 485–94. http://dx.doi.org/10.1515/aee-2017-0036.

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Abstract For protection against electric shock in low voltage systems residual current devices are commonly used. However, their proper operation can be interfered when high frequency earth fault current occurs. Serious hazard of electrocution exists then. In order to detect such a current, it is necessary to modify parameters of residual current devices, especially the operating point of their current transformer. The authors proposed the modification in the structure of residual current devices. This modification improves sensitivity of residual current devices when high frequency earth fault current occurs. The test of the modified residual current device proved that the authors’ proposition is appropriate.

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Barth, Alexander, Charles Troupin, Emma Reyes, Aida Alvera-Azcárate, Jean-Marie Beckers, and Joaquín Tintoré. "Variational interpolation of high-frequency radar surface currents using DIVAnd." Ocean Dynamics 71, no. 3 (January 23, 2021): 293–308. http://dx.doi.org/10.1007/s10236-020-01432-x.

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AbstractDIVAnd (Data-Interpolating Variational Analysis, in n-dimensions) is a tool to interpolate observations on a regular grid using the variational inverse method. We have extended DIVAnd to include additional dynamic constraints relevant to surface currents, including imposing a zero normal velocity at the coastline, imposing a low horizontal divergence of the surface currents, temporal coherence and simplified dynamics based on the Coriolis force, and the possibility of including a surface pressure gradient. The impact of these constraints is evaluated by cross-validation using the HF (high-frequency) radar surface current observations in the Ibiza Channel from the Balearic Islands Coastal Ocean Observing and Forecasting System (SOCIB). A small fraction of the radial current observations are set aside to validate the velocity reconstruction. The remaining radial currents from the two radar sites are combined to derive total surface currents using DIVAnd and then compared to the cross-validation dataset and to drifter observations. The benefit of the dynamic constraints is shown relative to a variational interpolation without these dynamical constraints. The best results were obtained using the Coriolis force and the surface pressure gradient as a constraint which are able to improve the reconstruction from the Open-boundary Modal Analysis, a quite commonly used method to interpolate HF radar observations, once multiple time instances are considered together.

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Slangen, T. M. H., B. R. F. Lustenhouwer, V. Cuk, and J. F. G. Cobben. "The Effects of High-Frequency Residual Currents on the Operation of Residual Current Devices." Renewable Energy and Power Quality Journal 19 (September 2021): 67–72. http://dx.doi.org/10.24084/repqj19.216.

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This research investigates the effects of high frequency currents between 50 Hz and 150 kHz on the operation of Residual Current Devices (RCDs). Nowadays, the increasing amount of large power-electronic switching devices can be a source of both harmonics (<2 kHz) and supraharmonics (2-150 kHz) currents injected to the grid. This can have several effects and possibly lead to unwanted tripping of RCDs, due to high earth-currents that can be emitted by the devices. The question is if supraharmonics can also lead to misoperation or fail-to-operate conditions for the RCDs, potentially leading to serious safety risks. A set-up is developed to introduce both 50 Hz and highfrequency leakage currents. First, the 50 Hz tripping-current of the RCDs is tested under nominal conditions. Secondly, the tripping current for non-nominal frequencies (between 50 Hz and 150 kHz) is determined to verify the possibility for false tripping. Lastly, the 50 Hz tripping current for the RCD is tested in the presence of a high-frequency current. The most important conclusion is that RCDs of type A and AC have an increased fundamental (50 Hz) tripping current when there are HFcomponents present. This potentially results in a safety risk.

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Idemen, M., and T. Şengör. "High-Frequency Surface Currents Induced on a Spherical Cap." SIAM Journal on Applied Mathematics 46, no. 1 (February 1986): 99–117. http://dx.doi.org/10.1137/0146009.

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13

Piot, Christophe, Stéphanie Lemaire, Bernard Albat, Jacques Seguin, Joël Nargeot, and Sylvain Richard. "High Frequency–Induced Upregulation of Human Cardiac Calcium Currents." Circulation 93, no. 1 (January 1996): 120–28. http://dx.doi.org/10.1161/01.cir.93.1.120.

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Minegishi, Shigeki, Koji Matsushima, Hitoshi Taira, and Akira Haga. "Propagation characteristics of high-frequency currents on ground wires." Electronics and Communications in Japan (Part I: Communications) 84, no. 1 (2000): 77–83. http://dx.doi.org/10.1002/1520-6424(200101)84:1<77::aid-ecja9>3.0.co;2-j.

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15

Jokela, Kari, Lauri Puranen, and Om P. Gandhi. "Radio Frequency Currents Induced in the Human Body for Medium-frequency/High-frequency Broadcast Antennas." Health Physics 66, no. 3 (March 1994): 237–44. http://dx.doi.org/10.1097/00004032-199403000-00001.

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16

Padilla, Enrique M., and Jose M. Alsina. "LABORATORY EXPERIMENTS OF BICHROMATIC WAVE GROUPS PROPAGATION ON A GENTLE SLOPE BEACH PROFILE AND ENERGY TRANSFER TO LOW AND HIGH FREQUENCY COMPONENTS." Coastal Engineering Proceedings, no. 35 (June 23, 2017): 6. http://dx.doi.org/10.9753/icce.v35.currents.6.

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This work presents a first analysis of experimental data studying the influence of the frequency bandwidth on the propagation of bichromatic wave groups over a constant 1:100 beach slope. The use of a large spatial cross-shore resolution and Bi-Spectral analysis techniques allows the identification of nonlinear energy transfers along the propagation of wave groups. During wave-group shoaling, nonlinear coupling between the primary wave frequencies results in a larger growth of superharmonics for narrow-banded wave conditions, increasing the skewness of the wave and leading to eventual instabilities and earlier high frequency (hf) wave breaking compared to the broad-banded wave condition. Regarding the growth of low frequency (lf) component, the data analysis has shown a larger growth of the incident bound long wave (IBLW) for broad-banded wave conditions. It is generally assumed that the transferred energy from the primary wave components to subharmonics does not affect the short wave energy budget. Here, the opposite is hypothesised, and a larger growth of the IBLW for broad-banded wave conditions is accompanied of a larger reduction of the primary wave components, a reduced growth of hf components and, consequently, a reduction in the growth of hf wave asymmetry during wave group shoaling. Conversely for narrow-banded wave conditions, a reduced IBLW growth is associated with a larger growth of hf wave asymmetry. After hf wave breaking, within the low frequency domain (lf), the IBLW decays slightly for narrow-banded conditions, consistent with a reduction in radiation stress forcing. This involves a nonlinear energy transfer from the wave group frequency back to hf components. The remaining lf energy, Outgoing Free Long Wave (OFLW), reflects back at the shoreline. However, for broad-banded wave conditions, strong dissipation and minimal reflection of lf components occurs close to the shoreline, which might be caused by lf wave breaking.

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Ibaceta, Raimundo, Rafael Almar, Jean-Pierre Lefebvre, Trinity Mensah-Senoo, and Wahab Sowah Layrea. "HIGH FREQUENCY MONITORING OF SWASH HYDRO-MORPHODYNAMICS ON A REFLECTIVE BEACH (GRAND POPO, BENIN): A NEW METHOD." Coastal Engineering Proceedings 1, no. 34 (October 28, 2014): 36. http://dx.doi.org/10.9753/icce.v34.currents.36.

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18

Cosoli, Simone, and Stuart de Vos. "Interoperability of Direction-Finding and Beam-Forming High-Frequency Radar Systems: An Example from the Australian High-Frequency Ocean Radar Network." Remote Sensing 11, no. 3 (February 1, 2019): 291. http://dx.doi.org/10.3390/rs11030291.

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Direction-finding SeaSonde (4.463 MHz; 5.2625 MHz) and phased-array WEllen RAdar WERA (9.33 MHz; 13.5 MHz) High-frequency radar (HFR) systems are routinely operated in Australia for scientific research, operational modeling, coastal monitoring, fisheries, and other applications. Coverage of WERA and SeaSonde HFRs in Western Australia overlap. Comparisons with subsurface currents show that both HFR types agree well with current meter records. Correlation (R), root-mean-squares differences (RMSDs), and mean bias (bias) for hourly-averaged radial currents range between R = (−0.03, 0.78), RMSD = (9.2, 30.3) cm/s, and bias = (−5.2, 5.2) cm/s for WERAs; and R = (0.1, 0.76), RMSD = (17.4, 33.6) cm/s, bias = (0.03, 0.36) cm/s for SeaSonde HFRs. Pointing errors (θ) are in the range θ = (1°, 21°) for SeaSonde HFRs, and θ = (3°, 8°) for WERA HFRs. For WERA HFR current components, comparison metrics are RU = (−0.12, 0.86), RMSDU = (12.3, 15.7) cm/s, biasU = (−5.1, −0.5) cm/s; and, RV = (0.61, 0.86), RMSDV = (15.4, 21.1) cm/s, and biasV = (−0.5, 9.6) cm/s for the zonal (u) and the meridional (v) components. Magnitude and phase angle for the vector correlation are ρ = (0.58, 0.86), φ = (−10°, 28°). Good match was found in a direct comparison of SeaSonde and WERA HFR currents in their overlap (ρ = (0.19, 0.59), φ = (−4°, +54°)). Comparison metrics at the mooring slightly decrease when SeaSonde HFR radials are combined with WERA HFR: scalar (vector) correlations for RU, V, (ρ) are in the range RU = (−0.20, 0.83), RV = (0.39, 0.79), ρ = (0.47, 0.72). When directly compared over the same grid, however, vectors from WERA HFR radials and vectors from merged SeaSonde–WERA show RU (RV) exceeding 0.9 (0.7) within the HFR grid. Despite the intrinsic differences between the two types of radars used here, findings show that different HFR genres can be successfully merged, thus increasing current mapping capability of the existing HFR networks, and minimising operational downtime, however at a likely cost of slightly decreased data quality.

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Chavanne, Cédric. "Do High-Frequency Radars Measure the Wave-Induced Stokes Drift?" Journal of Atmospheric and Oceanic Technology 35, no. 5 (May 2018): 1023–31. http://dx.doi.org/10.1175/jtech-d-17-0099.1.

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ABSTRACTHigh-frequency (HF) radars remotely measure ocean near-surface currents based on the Doppler shift of electromagnetic waves backscattered by surface gravity waves with half the electromagnetic wavelength, called Bragg waves. Since their phase velocity is affected not only by wave–current interactions with vertically sheared mean Eulerian currents but also by wave–wave interactions with all the other waves present at the sea surface, HF radars should measure a quantity related to the Stokes drift in addition to mean Eulerian currents. However, the literature is inconsistent—both theoretically and experimentally—on the specific expression and even on the existence of the Stokes drift contribution to the HF radar measurements. Three different expressions that have been proposed in the literature are reviewed and discussed in light of the relevant published experimental results: 1) the weighted depth-averaged Stokes drift, 2) the filtered surface Stokes drift, and 3) half of the surface Stokes drift. Effective measurement depths for these three expressions are derived for the Phillips wave spectrum. Recent experimental results tend to discard the second expression but are not inconsistent with the first and third expressions. The latter is physically appealing, since it is a quasi-Eulerian quantity that would be measured by a current meter at a fixed horizontal position but allowed to follow the free surface moving vertically up and down with the passage of the waves. A definitive answer will require further experimental investigations.

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Firdaus, R., E. L. Siadari, and F. Alfahmi. "Measurement and Analysis of Ocean Current using High- Frequency (HF) Radar Observation in the Bali Strait." IOP Conference Series: Earth and Environmental Science 893, no. 1 (November 1, 2021): 012053. http://dx.doi.org/10.1088/1755-1315/893/1/012053.

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Abstract High-Frequency (HF) Radar is an instrument using radio waves to measure ocean currents and waves remotely. This technology has many advantages, including has unprecedented spatial and temporal resolution, can operate in any weather condition, and is not dangerous for the environment. However, HF Radar's research is still limited in Indonesia. This research aimed to analyze the tidal and residual current in the Bali Strait in July 2020. Radial velocity from two HF Radar sites is combined to obtain the total currents. Current data from HF Radar were compared with Acoustic Doppler Current Profiler (ADCP) data to investigate its accuracy. Surface current data were analyzed using harmonic analysis to separate tidal and residual currents. Comparison between HF Radar and ADCP data are in good agreement for meridional current with a very high correlation of 0.813 and a small RMSE value of 0.22 m/s. Harmonic analysis shows that the dominant currents are tidal currents. The current direction was northward (southward) at flood (ebb), with maximum northward (southward) velocities are 2.17 m/s (2.97 m/s), respectively. The residual current has a random pattern, slightly faster northward than southward, and has similar spectral with the wind.

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Sperrevik, A. K., K. H. Christensen, and J. Röhrs. "Constraining energetic slope currents through assimilation of high-frequency radar observations." Ocean Science 11, no. 2 (March 11, 2015): 237–49. http://dx.doi.org/10.5194/os-11-237-2015.

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Abstract. Assimilation of high-frequency (HF) radar current observations and CTD hydrography is performed with the 4D-Var analysis scheme implemented in the Regional Ocean Modeling System (ROMS). We consider both an idealized case, with a baroclinic slope current in a periodic channel, and a realistic case for the coast of Vesterålen in northern Norway. In the realistic case, the results of the data assimilation are compared with independent data from acoustic profilers and surface drifters. Best results are obtained when background error correlation scales are small (10 km or less) and when the data assimilation window is short, i.e. about 1 day. Furthermore, we find that the impact of assimilating HF radar currents is generally larger than the impact of CTD hydrography. However, combining the HF radar currents with a few hydrographic profiles gives significantly better results, which demonstrates the importance of complementing surface observations with observations of the vertical structure of the ocean.

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Zika, T., I. C. Gebeshuber, F. Buschbeck, G. Preisinger, and M. Gröschl. "Surface analysis on rolling bearings after exposure to defined electric stress." Proceedings of the Institution of Mechanical Engineers, Part J: Journal of Engineering Tribology 223, no. 5 (March 18, 2009): 787–97. http://dx.doi.org/10.1243/13506501jet538.

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This article gives an overview about classical and frequency converter-induced spurious bearing currents in induction machines and discusses typical damage patterns caused by the current passage. To investigate on the electric damage mechanisms, test bearings are operated in a test rig and exposed to specific (classical low-frequency, and high-frequency) bearing currents. The induced damages to the surfaces are analysed visually and with the help of an atomic force microscope, and compared for the different electric regimes applied. Further, the electrically damaged bearing surfaces are characterized by standard roughness parameters. The surface structure observable on certain test bearings shows good correlation to the structure found with a bearing that had failed in the field under similar electric conditions. One of the investigated electric regimes applying high-frequency currents proved capable of generating fluting patterns - as found in real applications - on the test rig. The experiments also indicate that high-frequency bearing currents, although in total dissipating less energy, are more dangerous to a bearing than continuous current flow. The presented method gives a good starting point for further investigation on electric current damage in bearings, especially regarding high-frequency bearing currents, and on bearing/grease lifetime under specific electric regimes.

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Kawano, H., M. Ishikawa, H. Toda, T. Yokota, and Y. Yamagata. "Effect of high-frequency currents on interrupting performance of GCBs." IEEE Transactions on Power Delivery 9, no. 3 (July 1994): 1436–43. http://dx.doi.org/10.1109/61.311173.

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Zverev, E. A., V. Yu Skeeba, V. Vakhrushev, and D. V. Lobanov. "Grinding specifics of plasma coatings melted with high-frequency currents." IOP Conference Series: Materials Science and Engineering 843 (May 27, 2020): 012014. http://dx.doi.org/10.1088/1757-899x/843/1/012014.

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Koshuro, Vladimir, Marina Fomina, Aleksey Voyko, Igor Rodionov, Andrey Zakharevich, Aleksandr Skaptsov, and Aleksandr Fomin. "Surface morphology of zirconium after treatment with high-frequency currents." Composite Structures 202 (October 2018): 210–15. http://dx.doi.org/10.1016/j.compstruct.2018.01.055.

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Núñez, Manuel. "Generation of sheet currents by high frequency fast MHD waves." Physics Letters A 380, no. 29-30 (July 2016): 2288–93. http://dx.doi.org/10.1016/j.physleta.2016.05.010.

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Weng, Haixiao, Daryl G. Beetner, Richard E. DuBroff, and Jin Shi. "Estimation of High-Frequency Currents From Near-Field Scan Measurements." IEEE Transactions on Electromagnetic Compatibility 49, no. 4 (November 2007): 805–15. http://dx.doi.org/10.1109/temc.2007.908264.

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Urabe, Junichiro, Katsumi Fujii, Yasushi Matsumoto, and Akira Sugiura. "Measuring instrument for high-frequency currents flowing on power lines." Electronics and Communications in Japan (Part I: Communications) 88, no. 9 (2005): 27–37. http://dx.doi.org/10.1002/ecja.20191.

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Okayasu, Akio, Takenori Shimozono, Shinji Sato, Yoshimitsu Tajima, Haijiang Liu, Tomohiro Takagawa, and Hermann M. Fritz. "2011 TOHOKU TSUNAMI RUNUP AND DEVASTATING DAMAGES AROUND YAMADA BAY, IWATE: SURVEYS AND NUMERICAL SIMULATION." Coastal Engineering Proceedings 1, no. 33 (October 25, 2012): 4. http://dx.doi.org/10.9753/icce.v33.currents.4.

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Distributions of inundation and runup height for the 2011 off the Pacific coast of Tohoku Earthquake Tsunami were measured in and outside Yamada Bay located at the center of Iwate Prefecture, Japan. Numerical simulations were conducted to reproduce flow, inundation and runup height distributions. Surface elevation profiles recorded by the GPS wave gauges were used as the offshore boundary condition. In order to investigate characteristics of tsunami response to different geomorphological features, frequency separation was tried for the tsunami incident wave. It was found that the high frequency component was responsible for large tsunami height at narrow inlets and open bays, whereas the low frequency component had significant influence for inundation in closed bays.

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Seung, Young Ho, Jong Jin Park, Young-Yeon Kwon, Sung-Joon Kim, Hong-Sun Kim, and Yong-Chul Park. "Some High-Frequency Variability of Currents Obtained by "GeoDrifters" in the Tsushima Current Region." Ocean and Polar Research 39, no. 3 (September 30, 2017): 169–79. http://dx.doi.org/10.4217/opr.2017.39.3.169.

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Liu, Zhao, Wang, Huang, and Shi. "Compatibility Issues with Irregular Current Injection Islanding Detection Methods and a Solution." Energies 12, no. 8 (April 17, 2019): 1467. http://dx.doi.org/10.3390/en12081467.

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Islanding detection methods, based on injecting high-/low-frequency currents or negative sequence fundamental frequency currents and observing the resultant responses, are collectively referred to as irregular current injection methods in this paper. In multi-distributed generation (DG) operation, if there is no restriction to the phase of injected irregular currents, the currents at the same frequency may cancel each other out, and then their convergent current may be too small to cause a detectable response, for which reason islanding detection will be severely affected. Accordingly, this paper raises a compatibility issue, which requires the phase difference between any two injected irregular currents to be within a certain interval. In response to this issue, a solution is proposed. According to this solution, the terminal voltage of DG units is referenced to conduct irregular currents injection, and only certain high-frequency currents are used as injected currents. If this solution is adopted by as many manufacturers as possible, the effect and reliability of such methods will be greatly improved.

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Benda, Jan, and Andreas V. M. Herz. "A Universal Model for Spike-Frequency Adaptation." Neural Computation 15, no. 11 (November 1, 2003): 2523–64. http://dx.doi.org/10.1162/089976603322385063.

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Spike-frequency adaptation is a prominent feature of neural dynamics. Among other mechanisms, various ionic currents modulating spike generation cause this type of neural adaptation. Prominent examples are voltage-gated potassium currents (M-type currents), the interplay of calcium currents and intracellular calcium dynamics with calcium-gated potassium channels (AHP-type currents), and the slow recovery from inactivation of the fast sodium current. While recent modeling studies have focused on the effects of specific adaptation currents, we derive a universal model for the firing-frequency dynamics of an adapting neuron that is independent of the specific adaptation process and spike generator. The model is completely defined by the neuron's onset f-I curve, the steady-state f-I curve, and the time constant of adaptation. For a specific neuron, these parameters can be easily determined from electrophysiological measurements without any pharmacological manipulations. At the same time, the simplicity of the model allows one to analyze mathematically how adaptation influences signal processing on the single-neuron level. In particular, we elucidate the specific nature of high-pass filter properties caused by spike-frequency adaptation. The model is limited to firing frequencies higher than the reciprocal adaptation time constant and to moderate fluctuations of the adaptation and the input current. As an extension of the model, we introduce a framework for combining an arbitrary spike generator with a generalized adaptation current.

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Vahedi, Hani, Abdolreza Sheikholeslami, Mohammad Tavakoli Bina, and Mahmood Vahedi. "Review and Simulation of Fixed and Adaptive Hysteresis Current Control Considering Switching Losses and High-Frequency Harmonics." Advances in Power Electronics 2011 (June 28, 2011): 1–6. http://dx.doi.org/10.1155/2011/397872.

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Hysteresis Current Control (HCC) is widely used due to its simplicity in implementation, fast and accurate response. However, the main issue is its variable switching frequency which leads to extraswitching losses and injecting high-frequency harmonics into the system current. To solve this problem, adaptive hysteresis current control (AHCC) has been introduced which produces hysteresis bandwidth which instantaneously results in smoother and constant switching frequency. In this paper the instantaneous power theory is used to extract the harmonic components of system current. Then fixed-band hysteresis current control is explained. Because of fixed-band variable frequency disadvantages, the adaptive hysteresis current control is explained that leads to fixing the switching frequency and reducing the high-frequency components in source current waveform. Due to these advantages of AHCC, the switching frequency and switching losses will be diminished appropriately. Some simulations are done in MATLAB/Simulink. The Fourier Transform and THD results of source and load currents and the instantaneous switching frequency diagram are discussed to prove the efficiency of this method. The Fourier Transform and THD results of source and load currents are discussed to prove the validity of this method.

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Ehst, D. A. "Toroidal equilibrium with low-frequency wave-driven currents." Nuclear Fusion 25, no. 5 (May 1, 1985): 629–32. http://dx.doi.org/10.1088/0029-5515/25/5/006.

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35

Cienfuegos, Rodrigo, L. Duarte, L. Suarez, and P. A. Catalán. "NUMERICAL COMPUTATION OF INFRAGRAVITY WAVE DYNAMICS AND VELOCITY PROFILES USING A FULLY NONLINEAR BOUSSINESQ MODEL." Coastal Engineering Proceedings 1, no. 32 (January 29, 2011): 48. http://dx.doi.org/10.9753/icce.v32.currents.48.

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We present experimental and numerical analysis of nonlinear processes responsible for generating infragravity waves in the nearshore. We provide new experimental data on random wave propagation and associated velocity profiles in the shoaling and surf zones of a very mild slope beach. We analyze low frequency wave generation mechanisms and dynamics along the beach and examine in detail the ability of the fully nonlinear Boussinesq- type model SERR1D (Cienfuegos et al., 2010) to reproduce the complex dynamics of high frequency wave propagation and energy transfer mechanisms that enhance infragravity wave generation in the laboratory.

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Aliev, Yu M., V. Yu Bychenkov, M. S. Jovanović, and A. A. Frolov. "The kinetic theory of the nonlinear low-frequency response of a collisionless plasma to high-frequency electromagnetic radiation." Journal of Plasma Physics 48, no. 1 (August 1992): 167–76. http://dx.doi.org/10.1017/s0022377800016457.

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A kinetic theory of nonlinear currents, quasi-stationary electric and magnetic fields and the ponderomotive effect of high-frequency electromagnetic radiation on a collisionless plasma is developed. General expressions for nonlinear current densities, fields and ponderomotive forces that are applicable in a broad range of space-time scales, characteristie of low-frequency motion in plasma, are obtained. These expressions are compared with the results of previous papers.

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El-Shahat, Mohammed, Elsayed Tag Eldin, Nourhan A. Mohamed, Ahdab EL-Morshedy, and Mohamed E. Ibrahim. "Measurement of Power Frequency Current including Low- and High-Order Harmonics Using a Rogowski Coil." Sensors 22, no. 11 (June 1, 2022): 4220. http://dx.doi.org/10.3390/s22114220.

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The measurement of a power frequency current including low- and high-order harmonics is of great importance in calibration as well as in testing processes. Therefore, this paper presents the measurement of the power frequency current of light-emitting diode (LED) luminaires. LED luminaires were chosen as their input current includes both low- and high-order harmonics. The measurement process depends on reconstructing an LED luminaire current without using the coil parameters. Hence, the current reconstruction process is designed to be dependent on the measured characteristics of the Rogowski coil itself considering the frequency range at which the measurement process is required. An evaluation of the proposed measurement process was theoretically and experimentally carried out. A theoretical evaluation was carried out using MATALB SIMULINK software. However, the experimental evaluation was performed by building a Rogowski coil to measure the input currents of different LED luminaires having different power ratings of 300 W, 400 W, and 600 W. The currents measured using the Rogowski coil were compared with reference currents measured using a standard measurement technique. The obtained results show the efficacy of the proposed measurement method.

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Wang, Xiujuan, Zhihong Fu, Yao Wang, Wendong Wang, Wei Liu, and Junli Zhao. "A Wide-Frequency Constant-Amplitude Transmitting Circuit for Frequency Domain Electromagnetic Detection Transmitter." Electronics 8, no. 6 (June 6, 2019): 640. http://dx.doi.org/10.3390/electronics8060640.

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In this paper, a novel AC magnetic transmitter current source circuit is proposed for application of frequency domain electromagnetic method (FEM) prospecting. The proposed current source circuit is capable of generating high frequency and high constant amplitude currents, which are key technical problems for FEM. It is suitable for very wide frequencies. The main circuit of the proposed current source consists of a rising-edge enhancing unit, a constant current control unit, and a high voltage clamping unit. Large constant clamping voltage is applied during the rising edge and the falling edge of the alternating square current to obtain a high frequency and high linearity current source. On the current flat stage, the constant current unit provides the energy to the load to ensure the constant amplitude of the output current. Detailed operations of the proposed magnetic current source are given. Simulation and experimental results demonstrate that the proposed circuit achieves short reversal time, the linearity of the rising/falling edge, constant amplitude and low power loss. These are the desired characteristics of the ac square current source probing transmitter for the magnetic FEM applications.

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Fu, Pei-Hao, Qianqian Lv, Xiang-Long Yu, Jun-Feng Liu, and Jiansheng Wu. "The generation of switchable polarized currents in nodal ring semimetals using high-frequency periodic driving." Journal of Physics: Condensed Matter 34, no. 7 (November 23, 2021): 075401. http://dx.doi.org/10.1088/1361-648x/ac37db.

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Abstract A nodal ring semimetal (NRSM) can be driven to a spin-polarized NRSM or a spin-polarized Weyl semimetal (WSM) by a high-frequency electromagnetic field. We investigate the conditions in realizing these phases and propose a switchable spin-polarized currents generator based on periodically driven NRSMs. Both bulk and surface polarized currents are investigated. The polarization of bulk current is sensitive to the amplitude of the driving field and robust against the direction and polarization of the driving, the opaqueness of the lead–device interface and the misalignment between the nodal ring and the interface, which provides sufficient flexibility in manipulating the devices. Similar switchable polarized surface currents are also expected, which is contributed by the Fermi arc surface state associated with the WSM phases. The generation of polarized currents and the polarization switching effect offer opportunities to design periodic driving controlled topological spintronics devices based on NRSMs.

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40

NiehÃ¼ser, Sebastian, SÃ¶nke Dangendorf, Arne Arns, and JÃ¼rgen Jensen. "A NOVEL HIGH-RESOLUTION STORM SURGE FORECAST FOR THE GERMAN BIGHT." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 80. http://dx.doi.org/10.9753/icce.v36.currents.80.

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Storm surges are one of the most dangerous natural hazards in coastal areas and have the ability to cause great damages including fatalities. To be prepared when another storm surge hits the coast, reliable storm surge forecasts are indispensable. Storm surge warnings are routinely provided for selected tide gauge locations along a coastline through state-of-the-art forecast systems. In Germany, the Federal Maritime and Hydrographic Agency (BSH) (in cooperation with the German Weather Service (DWD)) have the responsibility for storm surge forecasts and warnings along the German North and Baltic Sea coastlines. The operational system in place for the North Sea consists of numerical weather forecast systems, a surge model and model output statistics. It provides accurate high frequency water level forecasts up to six days ahead at selected tide gauge sites (MÃ¼ller-Navarra and KnÃ¼pfer, 2010), but not for the coastline in between. Spatial forecasts are, however, currently not available for two reasons: first, the shallow coast with complex morphological structures leads to strong non-linearities between individual sites hampering simple interpolation schemes (Arns et al. 2015). Second, tidal predictions are limited to tide gauge locations, which do not fall dry during low tide, since the traditional estimation of tidal coefficients requires complete time series covering both low and high waters.

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Veremyev, V. I., V. M. Kutuzov, K. S. Plotnitskaya, V. V. Kovalenko, and V. A. Telegin. "HIGH-FREQUENCY RADAR FOR COASTAL AREAS MONITORING." Journal of the Russian Universities. Radioelectronics, no. 2 (April 24, 2019): 31–43. http://dx.doi.org/10.32603/1993-8985-2019-22-2-31-43.

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Introduction. The modern approach for ensuring marine activities of necessary quality related to the assessment of current information on the state of the ocean environment in Russia is clearly insufficient. The development of operational methods and instruments of observation, as well as the assessment of the state of the ocean and its forecast naturally determine such an approach. Therefore, the development of the concept, tools and methods of obtaining data is an urgent task of the operational Oceanography formation.Objective. The objective of the paper is to con-sider the concept of ocean surface monitoring using short-wave surface wave radar.Methods and materials. The paper presents a number of specific Oceanologic examples that require operational monitoring of the state of coastal waters of the oceans and individual regions. Also, it describes observational systems used in other countries. The paper pays special attention for the development of radar sensing of surface waters, carried out in our country occasionally. The resonant nature of the reflections gives the opportunity to obtain maps of high-precision measurements of surface currents and wave characteristics on the long-range area in real time. The paper notes difficulties of the experiments implementation and the results interpretation, shows the insistent issues for the establishment of the ocean surface operational monitoring, and gives the approaches for solvation of the existing problems. The paper formulates the main task of the world ocean parameters forecast for ensuring of the sea transport safety from natural and anthropogenic threats, as well as formulates the problems solution of effective nature management.Results. The paper shows that the optimal means of natural data acquisition is the creation of an observation network of coastal HF radars, which enables to assess surface currents and wave characteristics, as well as to solve the problem of monitoring. It is Important to develop an adequate coastal model and correlate its parameters with experimental data. The adaptive modeling and monitoring by modern technical means can overcome inadequacy of physical models to specific natural conditions can.Conclusion. By assimilation in hydrodynamic and wave models, these data become applicable in spatial mapping of hydrophysical inhomogeneities of the water layer, sound velocity, and underwater acoustic noise.

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Matthews, J. P., J. H. Simpson, and J. Brown. "Remote sensing of shelf sea currents using a high-frequency ocean surface current radar system." Journal of Geophysical Research 93, no. C3 (1988): 2303. http://dx.doi.org/10.1029/jc093ic03p02303.

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Jones, J. E., and A. M. Davies. "Influence of Wave-current Interaction, and High Frequency Forcing upon Storm Induced Currents and Elevations." Estuarine, Coastal and Shelf Science 53, no. 4 (October 2001): 397–413. http://dx.doi.org/10.1006/ecss.1999.0622.

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Lebedeva, Serafima V., N. P. Teplyuk, and V. S. Noveselov. "MODERN POSSIBILITIES OF HIGH FREQUENCY RADIO WAVE CURRENTS IN AESTHETIC MEDICINE." Russian Journal of Skin and Venereal Diseases 22, no. 5-6 (December 15, 2019): 192–98. http://dx.doi.org/10.17816/dv42958.

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The radio wave effect on biological tissues is of great interest to dermatologists, cosmetologists, and plastic surgeons. The modern information about radio wave therapy of involutional changes of face and neck skin is shown. A literature review of the physical aspects of the high-frequency current of the radio wave range is presented. The thermal and oscillation effects of radio frequency (RF) on biological tissues are shown, the mechanism of these effects at the cellular level is described. Primary targets of high-frequency currents exposure in the skin, their effect on the physicochemical properties of collagen and unicellular organisms are described. The mechanism of pulsed and continuous radio wave technologies and the possibility of their use in medical practice are described. Types of minimally invasive and non-invasive electrodes, when the choice of electrode diameter determines the therapy of specific clinical cases, are shown. The multifunctional minimally invasive RF device Innofill with needle and cannula active electrodes is presented. The technical characteristics and exposure modes of the device are considered. The features of the cannula electrode and the possibilities of its use in solving various dermatological and cosmetic problems are highlighted. A histological study of a combined technique of the Innofill radio wave method with the filler based on hyaluronic acid, was performed. A change in the amount of collagen and elastin fibers was noted. The distribution of the filler in the tissues was evaluated after the injection of the filler based on hyaluronic acid, after 30 and 60 seconds of RF exposure and after 30 seconds of RF exposure in a tunnel technique with the formation of a collagen channel. Histological material was stained with hematoxylin-eosin, Masson and Van Gieson trichrome. High efficiency, safety and prolonged effect of this exposure were described.

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Kuhnapfel, M., A. Stampa, R. Tabersky, and H. Tuczek. "Production of d.c. currents in a plasma by high frequency fields." Plasma Physics and Controlled Fusion 29, no. 10B (October 1, 1987): 1501–10. http://dx.doi.org/10.1088/0741-3335/29/10b/003.

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Prandle, D., and D. K. Ryder. "Measurement of surface currents in Liverpool Bay by high-frequency radar." Nature 315, no. 6015 (May 1985): 128–31. http://dx.doi.org/10.1038/315128a0.

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Göksu, Ç, and F. Güneş. "High frequency surface currents induced on a soft-hard cylindrical strip." IEE Proceedings A Science, Measurement and Technology 138, no. 2 (1991): 113. http://dx.doi.org/10.1049/ip-a-3.1991.0016.

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Fomin, A. A., M. A. Fomina, I. V. Rodionov, V. A. Koshuro, E. Yu Poshivalova, A. Yu Shchelkunov, A. A. Skaptsov, A. M. Zakharevich, and V. S. Atkin. "Superhard oxide coatings formed on titanium treated by high-frequency currents." Technical Physics Letters 41, no. 9 (September 2015): 909–11. http://dx.doi.org/10.1134/s1063785015090217.

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LOTFI, A. W., and F. C. LEE. "Two-dimensional eddy currents in foils for high-frequency power applications." International Journal of Electronics 75, no. 2 (August 1993): 349–59. http://dx.doi.org/10.1080/00207219308907114.

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Pazmany, Jozsef Gabor, Denes Fodor, and Bernard Bäker. "Simulation of Shield Current in Automotive High Voltage Systems." World Electric Vehicle Journal 12, no. 4 (November 3, 2021): 217. http://dx.doi.org/10.3390/wevj12040217.

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In automotive high voltage (HV) systems, the switching operation of a power electronic converter causes current and voltage ripple in the frequency range of [10 Hz–150 kHz]. Automotive system engineering provides requirements that define the behaviour of HV components in that frequency range. Shielded HV cables must stand induced current in the frequency range of the ripple. One of the relevant requirements is the maximal current stress of the shielding. Several individually shielded cables are used in automotive HV systems, and these shields influence differential mode disturbance currents, such as the ripple current from the traction inverter. In this work, we provide a model and an analysis of shielded cables integrated into an automotive HV system in relation to system-level design parameters. To fill the gaps of existing research, we focused on two questions: How do design parameters influence the shield current value in the frequency range of the current ripple in a vehicle, and how should a shield and connector system be designed with respect to shield currents over the life-time? We applied analytical and simulative solutions to these problems through a co-simulation approach on the architecture of a real vehicle. The presented approach extends existing research by integrating simulations and vehicle measurements to life-time prediction. Moreover, the proposed methods enable the replacement of the state-of-the-art constant 10 A requirement to a driver profile based predicted shield current requirement on individually shielded HV cables in battery electric vehicles (BEV).

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Journal articles on the topic 'High frequency currents'

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