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Letteratura scientifica selezionata sul tema "Low frequency currents interractions"

Autore: Grafiati
Pubblicato: 11 gennaio 2025

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Articoli di riviste sul tema "Low frequency currents interractions"

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Ward, Alex R., Warwick G. Oliver e Danielle Buccella. "Wrist Extensor Torque Production and Discomfort Associated With Low-Frequency and Burst-Modulated Kilohertz-Frequency Currents". Physical Therapy 86, n. 10 (1 ottobre 2006): 1360–67. http://dx.doi.org/10.2522/ptj.20050300.

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Abstract Background and Purpose. A randomized controlled trial to compare 2 forms of monophasic pulsed currents with 2 forms of burst-modulated, kilohertz-frequency alternating current (“Russian current” and “Aussie current”) was conducted to establish whether different amounts of wrist extensor torque were produced and whether discomfort varied with stimulus type. Subjects. The 32 subjects were adults who were healthy and were drawn from a population of staff and students at La Trobe University. Methods. Each subject received all 4 currents. Maximal electrically induced torque (MEIT) of the wrist extensors was measured for each stimulus type. Relative discomfort of stimulation also was assessed. Results. Russian current elicited lower mean torque than those elicited by Aussie current and monophasic pulsed currents. The Russian and Aussie currents elicited significantly less discomfort than the 2 monophasic pulsed currents. Discussion and Conclusion. When force production and relative discomfort were jointly used as the criteria, Aussie current was found to be more effective than either of the monophasic pulsed currents or Russian current stimulation.
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Margetis, Dionisios, e Nikos Savva. "Low-frequency currents induced in adjacent spherical cells". Journal of Mathematical Physics 47, n. 4 (aprile 2006): 042902. http://dx.doi.org/10.1063/1.2190333.

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Ehst, D. A. "Toroidal equilibrium with low-frequency wave-driven currents". Nuclear Fusion 25, n. 5 (1 maggio 1985): 629–32. http://dx.doi.org/10.1088/0029-5515/25/5/006.

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Elgar, Steve, e Britt Raubenheimer. "Field Evidence of Inverse Energy Cascades in the Surfzone". Journal of Physical Oceanography 50, n. 8 (1 agosto 2020): 2315–21. http://dx.doi.org/10.1175/jpo-d-19-0327.1.

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AbstractLow-frequency currents and eddies transport sediment, pathogens, larvae, and heat along the coast and between the shoreline and deeper water. Here, low-frequency currents (between 0.1 and 4.0 mHz) observed in shallow surfzone waters for 120 days during a wide range of wave conditions are compared with theories for generation by instabilities of alongshore currents, by ocean-wave-induced sea surface modulations, and by a nonlinear transfer of energy from breaking waves to low-frequency motions via a two-dimensional inverse energy cascade. For these data, the low-frequency currents are not strongly correlated with shear of the alongshore current, with the strength of the alongshore current, or with wave-group statistics. In contrast, on many occasions, the low-frequency currents are consistent with an inverse energy cascade from breaking waves. The energy of the low-frequency surfzone currents increases with the directional spread of the wave field, consistent with vorticity injection by short-crested breaking waves, and structure functions increase with spatial lags, consistent with a cascade of energy from few-meter-scale vortices to larger-scale motions. These results include the first field evidence for the inverse energy cascade in the surfzone and suggest that breaking waves and nonlinear energy transfers should be considered when estimating nearshore transport processes across and along the coast.
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Rumyantsev, Sergey L., Michael S. Shur, Michael E. Levinshtein, Pavel A. Ivanov, John W. Palmour, Mrinal K. Das e Brett A. Hull. "Low Frequency Noise in 4H-SiC MOSFETs". Materials Science Forum 615-617 (marzo 2009): 817–20. http://dx.doi.org/10.4028/www.scientific.net/msf.615-617.817.

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Low-frequency noise in 4H-SiC MOSFETs has been measured for the first time. At drain currents varying from deep subthreshold to strong inversion, the 1/f (flicker) noise dominated at frequencies 1 - 105 Hz. The dependence of relative spectral noise density, , on drain current Id (at a constant drain voltage Vd) differs qualitatively from that in Si MOSFETs. In Si MOSFETs, ~ 1/ in strong inversion, whereas tends to saturate in sub-threshold. In 4H-SiC MOSFETs under study, ~ 1/ over the whole range of currents from deep sub-threshold to strong inversion. Similar noise behavior is often observed in poly- or a-Si TFTs. The effective channel mobility in 4H-SiC MOSFETs, 3 - 7 cm2/Vs, is also as low as that in TFTs. Both noise behavior and transport properties of 4H-SiC MOSFETs are explained, analogously to TFTs, by a high density of localized states (bulk and interface) near the conduction band edge in the ion implanted p-well.
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Johnson, E. R. "Boundary Currents, Free Currents and Dissipation in the Low-Frequency Scattering of Shelf Waves". Journal of Physical Oceanography 19, n. 9 (settembre 1989): 1291–300. http://dx.doi.org/10.1175/1520-0485(1989)019<1291:bcfcad>2.0.co;2.

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Torres, Hector S., Patrice Klein, Jinbo Wang, Alexander Wineteer, Bo Qiu, Andrew F. Thompson, Lionel Renault et al. "Wind work at the air-sea interface: a modeling study in anticipation of future space missions". Geoscientific Model Development 15, n. 21 (7 novembre 2022): 8041–58. http://dx.doi.org/10.5194/gmd-15-8041-2022.

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Abstract. Wind work at the air-sea interface is the transfer of kinetic energy between the ocean and the atmosphere and, as such, is an important part of the ocean-atmosphere coupled system. Wind work is defined as the scalar product of ocean wind stress and surface current, with each of these two variables spanning, in this study, a broad range of spatial and temporal scales, from 10 km to more than 3000 km and hours to months. These characteristics emphasize wind work's multiscale nature. In the absence of appropriate global observations, our study makes use of a new global, coupled ocean-atmosphere simulation, with horizontal grid spacing of 2–5 km for the ocean and 7 km for the atmosphere, analyzed for 12 months. We develop a methodology, both in physical and spectral spaces, to diagnose three different components of wind work that force distinct classes of ocean motions, including high-frequency internal gravity waves, such as near-inertial oscillations, low-frequency currents such as those associated with eddies, and seasonally averaged currents, such as zonal tropical and equatorial jets. The total wind work, integrated globally, has a magnitude close to 5 TW, a value that matches recent estimates. Each of the first two components that force high-frequency and low-frequency currents, accounts for ∼ 28 % of the total wind work and the third one that forces seasonally averaged currents, ∼ 44 %. These three components, when integrated globally, weakly vary with seasons but their spatial distribution over the oceans has strong seasonal and latitudinal variations. In addition, the high-frequency component that forces internal gravity waves, is highly sensitive to the collocation in space and time (at scales of a few hours) of wind stresses and ocean currents. Furthermore, the low-frequency wind work component acts to dampen currents with a size smaller than 250 km and strengthen currents with larger sizes. This emphasizes the need to perform a full kinetic budget involving the wind work and nonlinear advection terms as small and larger-scale low-frequency currents interact through these nonlinear terms. The complex interplay of surface wind stresses and currents revealed by the numerical simulation motivates the need for winds and currents satellite missions to directly observe wind work.
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Wijesekera, H. W., W. J. Teague, D. W. Wang, E. Jarosz, T. G. Jensen, S. U. P. Jinadasa, H. J. S. Fernando e Z. R. Hallock. "Low-Frequency Currents from Deep Moorings in the Southern Bay of Bengal". Journal of Physical Oceanography 46, n. 10 (ottobre 2016): 3209–38. http://dx.doi.org/10.1175/jpo-d-16-0113.1.

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AbstractHigh-resolution currents and hydrographic fields were measured at six deep-water moorings in the southern Bay of Bengal (BoB) by the Naval Research Laboratory as part of an international effort focused on the dynamics of the Indian Ocean. Currents, temperature, and salinity were sampled over the upper 500 m for 20 months between December 2013 and August 2015. One of the major goals is to understand the space–time scales of the currents and physical processes that contribute to the exchange of water between the BoB and the Arabian Sea. The observations captured Southwest and Northeast Monsoon Currents, seasonally varying large eddies including a cyclonic eddy, the Sri Lanka dome (SLD), and an anticyclonic eddy southeast of the SLD. The observations further showed intraseasonal oscillations with periods of 30–70 days, near-inertial currents, and tides. Monthly averaged velocities commonly exceeded 50 cm s−1 near the surface, and extreme velocities exceeded 150 cm s−1 during the southwest monsoon. Tides were small and dominated by the M2 component with velocities of about 3 cm s−1. The average transport into the BoB over the measurement period was 2 Sv (1 Sv ≡ 106 m3 s−1) but likely exceeded 15 Sv during summer of 2014. This study suggests the water exchange away from coastal boundaries, in the interior of the BoB, may be largely influenced by the location and strength of the two eddies that modify the path of the Southwest Monsoon Current. In addition, there is a pathway below 200 m for transport of water into the BoB throughout the year.
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Shevchenko, I. V., P. S. Berloff, D. Guerrero-López e J. E. Roman. "On low-frequency variability of the midlatitude ocean gyres". Journal of Fluid Mechanics 795 (15 aprile 2016): 423–42. http://dx.doi.org/10.1017/jfm.2016.208.

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This paper studies the large-scale low-frequency variability of the wind-driven midlatitude ocean gyres and their western boundary currents, such as the Gulf Stream or Kuroshio, simulated with the eddy-resolving quasi-geostrophic model. We applied empirical orthogonal functions analysis to turbulent flow solutions and statistically extracted robust and significant large-scale decadal variability modes concentrated around the eastward jet extension of the western boundary currents. In order to interpret these statistical modes dynamically, we linearized the governing quasi-geostrophic equations around the time-mean circulation and solved for the corresponding full set of linear eigenmodes with their eigenfrequencies. We then projected the extracted decadal variability on the eigenmodes and found that this variability is a multimodal coherent pattern phenomenon rather than a single mode or a combination of several modes as in the flow regimes preceding developed turbulence.
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Laufer, Yocheved, e Michal Elboim. "Effect of Burst Frequency and Duration of Kilohertz-Frequency Alternating Currents and of Low-Frequency Pulsed Currents on Strength of Contraction, Muscle Fatigue, and Perceived Discomfort". Physical Therapy 88, n. 10 (1 ottobre 2008): 1167–76. http://dx.doi.org/10.2522/ptj.20080001.

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BackgroundLow-frequency pulsed currents (LPCs) and kilohertz-frequency alternating currents (KACs) are used clinically to augment muscle contractions. Treatment effectiveness may be enhanced by selecting stimulation parameters that evoke the strongest contractions with minimal discomfort and fatigue.ObjectiveThe objective of this study was to compare maximally induced strength (force-producing capacity) of contractions, muscle fatigue, and discomfort associated with an LPC and with 3 KACs differing in frequency and duration of burst modulation.DesignThis was a repeated-measures trial, with randomized order of current presentation.SettingThe study was conducted in the physical therapy laboratory at the University of Haifa.SubjectsTwenty-six volunteers without impairments, with a mean age of 27.4 years (SD=5.0, range=21–45), participated.InterventionAll currents were applied in separate sessions to the wrist extensors of each subject. Currents consisted of an LPC with a 50-Hz pulse frequency and 3 KACs with a 2.5-kHz carrier frequency, including the “Russian current” (RC) burst modulated at 50 Hz with 25 cycles per burst and 2 currents burst modulated at 20 or 50 Hz with 10 cycles per burst.MeasurementThe maximal electrically induced isometric force, the force integral of 21 electrically induced consecutive contractions, and the degree of discomfort were recorded.ResultsForce of contraction was not affected by type of current. The LPC was least fatiguing, and the RC was most fatiguing, with the 2 other KACs having an intermediate effect. Degree of discomfort was higher with the KAC modulated at 20 Hz.ConclusionsWhen comfort, strength, and fatigue are considered jointly, the LPC is advantageous. Electrically induced fatigue is affected by the number of cycles per second, rather than the number of bursts per second.
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Tesi sul tema "Low frequency currents interractions"

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Bella, Adrien. "Étude de l’impact des interactions entre ondes de marée interne et circulation basse fréquence sur le budget énergétique de la marée interne à l’aide d’une simulation numérique à haute résolution sur l’Atlantique Nord". Electronic Thesis or Diss., Université de Rennes (2023-....), 2024. http://www.theses.fr/2024URENS046.

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Dans cette thèse, le cycle de vie de la marée interne et sa perte de cohérence par ses interactions avec les courants sont étudiés dans l’Atlantique Nord à l’aide d’une simulation d’un océan réaliste à haute résolution. Une décomposition en mode verticaux est utilisée pour obtenir le budget d’énergie des différentes échelles de la marée interne. La dispersion topographique est dominante à l’échelle du bassin et aux niveaux des reliefs, tandis que les interactions entre la marée interne et la circulation basse fréquence signent au niveau du Gulf Stream, de son prolongement Nord Atlantique et dans le Nord du Bassin. Enfin, une décomposition en partie cohérente/incohérente est utilisée. Les causes de la perte de cohérence de la marée sur des échelles de un à trois mois sont l’advection de la marée interne par l’écoulement lentement variable et le cisaillement horizontal de ce dernier. Cette perte de cohérence se fait majoritairement sans changement d’échelle pour la marée
The life cycle of the internal tide and its loss of coherence due to its interactions with currents are studied over the North Atlantic basin using a high-resolution simulation of a realistic ocean. A vertical mode decomposition is used to obtain the energy budget of the different scales of the internal tide. Topographic scattering is dominant at the basin scale and around topographic features, while interactions between the internal tide and the low-frequency circulation are significant in the Gulf Stream, its North Atlantic extension and in the northern part of the basin. Finally, a coherent/incoherent decomposition is used. The causes of the internal tide loss of coherence on scales of one to three months are the advection of the internal tide by the slowly varying current and the horizontal shear of the latter. Most of this loss of coherence occurs without any change of scale for the internal tide
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Payne, Joseph Allen. "Spatial structure of very low frequency modulated ionospheric currents /". May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.

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Cole, Kelly Lynne. "Low-frequency variability of currents in the deepwater eastern Gulf of Mexico". [College Station, Tex. : Texas A&M University, 2008. http://hdl.handle.net/1969.1/ETD-TAMU-3030.

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Petersson, Marcus. "Beyond AMPA and NMDA: Slow synaptic mGlu/TRPC currents : Implications for dendritic integration". Licentiate thesis, KTH, Computational Biology, CB, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-24833.

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In order to understand how the brain functions, under normal as well as pathological conditions, it is important to study the mechanisms underlying information integration. Depending on the nature of an input arriving at a synapse, different strategies may be used by the neuron to integrate and respond to the input. Naturally, if a short train of high-frequency synaptic input arrives, it may be beneficial for the neuron to be equipped with a fast mechanism that is highly sensitive to inputs on a short time scale. If, on the contrary, inputs arriving with low frequency are to be processed, it may be necessary for the neuron to possess slow mechanisms of integration. For example, in certain working memory tasks (e. g. delay-match-to-sample), sensory inputs may arrive separated by silent intervals in the range of seconds, and the subject should respond if the current input is identical to the preceeding input. It has been suggested that single neurons, due to intrinsic mechanisms outlasting the duration of input, may be able to perform such calculations. In this work, I have studied a mechanism thought to be particularly important in supporting the integration of low-frequency synaptic inputs. It is mediated by a cascade of events that starts with activation of group I metabotropic glutamate receptors (mGlu1/5), and ends with a membrane depolarization caused by a current that is mediated by canonical transient receptor potential (TRPC) ion channels. This current, denoted ITRPC, is the focus of this thesis.

A specific objective of this thesis is to study the role of ITRPC in the integration of synaptic inputs arriving at a low frequency, < 10 Hz. Our hypothesis is that, in contrast to the well-studied, rapidly decaying AMPA and NMDA currents, ITRPC is well-suited for supporting temporal summation of such synaptic input. The reason for choosing this range of frequencies is that neurons often communicate with signals (spikes) around 8 Hz, as shown by single-unit recordings in behaving animals. This is true for several regions of the brain, including the entorhinal cortex (EC) which is known to play a key role in producing working memory function and enabling long-term memory formation in the hippocampus.

Although there is strong evidence suggesting that ITRPC is important for neuronal communication, I have not encountered a systematic study of how this current contributes to synaptic integration. Since it is difficult to directly measure the electrical activity in dendritic branches using experimental techniques, I use computational modeling for this purpose. I implemented the components necessary for studying ITRPC, including a detailed model of extrasynaptic glutamate concentration, mGlu1/5 dynamics and the TRPC channel itself. I tuned the model to replicate electrophysiological in vitro data from pyramidal neurons of the rodent EC, provided by our experimental collaborator. Since we were interested in the role of ITRPC in temporal summation, a specific aim was to study how its decay time constant (τdecay) is affected by synaptic stimulus parameters.

The hypothesis described above is supported by our simulation results, as we show that synaptic inputs arriving at frequencies as low as 3 - 4 Hz can be effectively summed. We also show that τdecay increases with increasing stimulus duration and frequency, and that it is linearly dependent on the maximal glutamate concentration. Under some circumstances it was problematic to directly measure τdecay, and we then used a pair-pulse paradigm to get an indirect estimate of τdecay.

I am not aware of any computational model work taking into account the synaptically evoked ITRPC current, prior to the current study, and believe that it is the first of its kind. We suggest that ITRPC is important for slow synaptic integration, not only in the EC, but in several cortical and subcortical regions that contain mGlu1/5 and TRPC subunits, such as the prefrontal cortex. I will argue that this is further supported by studies using pharmacological blockers as well as studies on genetically modified animals.


QC 20101005
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Škvarenina, Ľubomír. "Charakterizácia tenkovrstvových solárnych článkov a analýza mikroštruktúrnych defektov". Doctoral thesis, Vysoké učení technické v Brně. Fakulta elektrotechniky a komunikačních technologií, 2021. http://www.nusl.cz/ntk/nusl-447549.

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Thin-film solar cells based on an absorber layer of chalcogenide compounds (CIGS, CdTe) are today among the most promising photovoltaic technologies due to their long-term ability to gain a foothold in mass commercial production as an alternative to conventional Si solar cells. Despite this success, the physical origin of the defects present in the thin films are still insufficiently elucidated, especially in the compounds of the chalcopyrite family Cu(In_{1x},Ga_{x})(S_{y},Se_{1y})_{2}. The research focuses on the identification and analysis of microstructural defects responsible for the electrical instability of chalcopyrite-based thin-film solar cells with a typical heterostructure arrangement ZnO:Al/i-ZnO/CdS/Cu(In,Ga)Se_{2}/Mo. The non-uniform polycrystalline nature of semiconductor materials in this complex multilayer structure requires a comprehensive analysis of electro-optical, structural and compositional properties associated with the actual morphology at the macroscopic, microscopic or even nanoscopic level. The observed predominant ohmic or non-ohmic current conduction in the dark transport characteristics was also reflected in the slope deviations of the excessive noise fluctuations, which were in the spectral domain exclusively in the form of flicker noise with dependency S_{i} ~ f^{1}. Spatially resolved electroluminescence based on stimulated photon emission by charge carriers injecting into the depletion region, not only showed a significantly inhomogeneous distribution of intensity in planar heterojunction under forward bias, but also revealed light emitting local spots in reverse bias due to a trap-assisted radiative recombination through the high density of defect states. Microscopic examination of the defect-related light emitting spots revealed rather extensive defective complexes with many interruptions through the layers, especially at the heterojunction CdS/Cu(In,Ga)Se_{2} interface. Besides, the high leakage current via these defective complexes subsequently led to a considerable local overheating, which caused a clearly observable structural and morphological changes, such as deviations in absorber layer stoichiometry due to Cu–In–Ga–Se segregation, Cu-rich and Ga-rich grains formation with an occurrence of Se-poor or Cu_{x}Se_{y} secondary phases regions, material redeposition accompanied by evaporation of ZnO:Al/i-ZnO/CdS layers together with the formation of Se structures on the surface around the defects. Within the research, analytical modelling of transport characteristics was implemented with parameters extraction of individual transport mechanisms to understand the non-ohmic shunt behaviour due to leakage current. In addition to the proper current path along the main heterojunction, the proposed model contains parasitic current pathways as a consequence of recombination-dominated charge transport or current conduction facilitated by multi-step tunnelling via high density of mid-gap defect states in the depletion region, ohmic leakage current caused by pinholes or low-resistance paths along grain boundaries in Cu(In,Ga)Se_{2}, or space-charge limited current due to metals diffusion from the ZnO:Al layer and grid Ag contacts through disruptions in i-ZnO/CdS layers.
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Zelenke, Brian Christopher. "An empirical statistical model relating winds and ocean surface currents : implications for short-term current forecasts". Thesis, Connect to the title online, 2005. http://hdl.handle.net/1957/2166.

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Bruneau, Nicolas. "Modélisation morphodynamique des plages sableuses". Thesis, Bordeaux 1, 2009. http://www.theses.fr/2009BOR13765/document.

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Le long des littoraux sableux tels que la côte Aquitaine, les vagues et principalement les courants moyens induits par celles-ci jouent un rôle majeur dans l’évolution morphologique des plages. Que ce soit d’un point de vue socio-économique (aménagement des plages, protection de l’environnement) ou sécuritaire (noyade), comprendre la dynamique de tels environnements est devenu un réel enjeu scienti?que ces dernières années. Le développement d’une plateforme de modélisation morphodynamique opérationnelle a été menée au cours de cette thèse. Ce modèle est basé sur le couplage du modèle spectral de houle SWAN (Delft University of Technology) avec le modèle MARS 2DH (Ifremer), initialement conçu pour calculer les courants induits par la marée et les vents. Après avoir ajouté les phénomènes liés à la houle, un modèle sédimentaire a été développé pour estimer les évolutions morphodynamiques. La campagne de mesures Biscarrosse-PréECORS menée en juin 2007 sur la plage de Biscarrosse a permis de valider le modèle pour une large gamme d’état de mer. Le modèle a montré son e?cacité et sa robustesse pour décrire les courants et des circulations induites par les vagues au dessus de fortes hétérogénéités bathymétriques. Nous avons mis en évidence la forte modulation tidale des courants sagittaux qui sont intenses même pour de faibles conditions de vagues. La plateforme de modélisation morphodynamique a permis d’analyser la formation et le développement de morphologies tridimensionnelles rythmiques pour des systèmes simple et double barre. Pour les environnements à double barre comme la côte Aquitaine, l’intense couplage morphologique entre la barre externe et la barre interne a été étudié en réponse aux conditions de forçages. Nous avons mis en évidence l’in?uence de la marée sur la croissance des barres et révélé la corrélation existant entre croissance des barres et dissipation d’énergie des vagues sur les barres. Cette thèse a abouti au développement d’un modèle complet permettant d’appréhender la dynamique des environnements littoraux sableux
Along many sandy environments as the Aquitanian Coast, waves and wave-induced currents play a key role on the beach morphodynamics. Within a socio-economic (human interventions, natural environment protection) and touristic (human safety) framework, understand the complex dynamics of these systems is a real scienti?c challenge these last decades. The development of an operational morphodynamical modeling platform was performed during this PhD thesis. The modeling strategy consists in coupling the spectral wave model SWAN (Delft Univer- sity of Technology) with the non-linear shallow water model MARS 2DH (Ifremer). The MARS model was initially designed to compute tide- and wind-induced currents. Thus, the wave processes and a sed- imentary unit were implemented inside MARS to compute morphological evolutions of wave-dominated sandy beached. The Biscarrosse-PréECORS ?eld experiment carried out in June 2007 at Biscarrosse Beach was used to validate our modeling platform for a large range of o?shore wave conditions. Results have proved the e?ciency and the robustness of our model to calculate wave-induced currents and circulations over alongshore non-uniformities. The strong tidal modulation of currents and the intense rip currents for low-energy conditions were highlighted. The morphodynamical modeling platform was also used to analyze the generation and the development of rhythmic three-dimensional morphologies for one- and double-barred systems. For double-barred en- vironments, the intense morphological coupling between the inner and outer bar was studied in the response of wave and tide forcing. We have highlighted the in?uence of the tide on the bar growth and showed the correlation between the growth and the wave dissipation over the bar. This thesis has succeeded in the development of a complete model for understanding the dynamics of sandy coastal environments
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(9178664), Maria I. Muzquiz, e Ivette M. Muzquiz (9178658). "Reversible Nerve Conduction Block Using Low Frequency Alternating Currents". Thesis, 2020.

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Abstract (sommario):
This thesis describes a novel method to reversibly and safely block nerve conduction using a low frequency alternating current (LFAC) waveform at 1 Hz applied through a bipolar extrafascicular electrode. This work follows up on observations made on excised mammalian peripheral nerves and earthworm nerve cords. An in-situ electrophysiology setup was used to assess the LFAC
waveform on propagating action potentials (APs) within the cervical vagus nerve in anaesthetized Sprague-Dawley rats (n = 12). Two sets of bipolar cuff or hook electrodes were applied unilaterally to the cervical vagus nerve, which was crushed rostral to the electrodes to exclude reflex effects
on the animal. Pulse stimulation was applied to the rostral electrode, while the LFAC conditioning waveform was applied to the caudal electrode. The efferent volley, if unblocked, elicits acute bradycardia and hypotension. The degree of block of the vagal stimulation induced bradycardia
was used as a biomarker. Block was assessed by the ability to reduce the bradycardic drive by monitoring the heart rate (HR) and blood pressure (BP) during LFAC alone, LFAC with vagal stimulation, and vagal stimulation alone. LFAC applied via a hook electrode (n = 7) achieved 86.6 +/- 11% block at current levels 95 +/- 38 uAp (current to peak). When applied via a cuff electrode (n = 5) 85.3 +/- 4.60% block was achieved using current levels of 110 +/- 65 uAp. Furthermore, LFAC was explored on larger vagal afferent fibers in larger human sized nerve bundles projecting to effects mediated by a reflex. The effectiveness of LFAC was assessed in an in-situ electrophysiological setup on the left cervical vagus in anaesthetized domestic swine (n = 5). Two bipolar cuff electrodes were applied unilaterally to the cervical vagus nerve, which was crushed caudal to the electrodes to eliminate cardiac effects. A tripolar extrafascicular cuff electrode was placed most rostral on the nerve for recording of propagating APs induced by
electrical stimulation and blocked via the LFAC waveform.
Standard pulse stimulation was applied to the left cervical vagus to induce the Hering-Breuer reflex. If unblocked, the activation of the Hering-Breuer reflex would cause breathing to slow down and potentially cease. Block was quantified by the ability to reduce the effect of the Hering-Breuer
reflex by monitoring the breathing rate during LFAC alone, LFAC and vagal stimulation, and vagal stimulation alone. LFAC achieved 87.2 +/- 8.8% (n = 5) block at current levels of 0.8 +/- 0.3 mAp. Compound nerve action potentials (CNAP) were monitored directly. They show changes
in nerve activity during LFAC, which manifests itself as the slowing and amplitude reduction of components of the CNAPs. Since the waveform is balanced, all forward reactions are reversed, leading to a blocking method that is similar in nature to DC block without the potential issues of
toxic byproduct production. These results suggest that LFAC can achieve a high degree of nerve block in both small and large nerve bundles, resulting in the change in behavior of a biomarker, in-vivo in the mammalian nervous system at low amplitudes of electrical stimulation that are within the water window of the electrode.
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Muzquiz, Maria I. "Reversible Nerve Conduction Block Using Low Frequency Alternating Currents". Thesis, 2020. http://hdl.handle.net/1805/23576.

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Indiana University-Purdue University Indianapolis (IUPUI)
This thesis describes a novel method to reversibly and safely block nerve conduction using a low frequency alternating current (LFAC) waveform at 1 Hz applied through a bipolar extrafascicular electrode. This work follows up on observations made on excised mammalian peripheral nerves and earthworm nerve cords. An in-situ electrophysiology setup was used to assess the LFAC waveform on propagating action potentials (APs) within the cervical vagus nerve in anaesthetized Sprague-Dawley rats (n = 12). Two sets of bipolar cuff or hook electrodes were applied unilaterally to the cervical vagus nerve, which was crushed rostral to the electrodes to exclude reflex effects on the animal. Pulse stimulation was applied to the rostral electrode, while the LFAC conditioning waveform was applied to the caudal electrode. The efferent volley, if unblocked, elicits acute bradycardia and hypotension. The degree of block of the vagal stimulation induced bradycardia was used as a biomarker. Block was assessed by the ability to reduce the bradycardic drive by monitoring the heart rate (HR) and blood pressure (BP) during LFAC alone, LFAC with vagal stimulation, and vagal stimulation alone. LFAC applied via a hook electrode (n = 7) achieved 86.6 +/- 11% block at current levels 95 +/- 38 uAp (current to peak). When applied via a cuff electrode (n = 5) 85.3 +/- 4.60% block was achieved using current levels of 110+/-65 uAp. Furthermore, LFAC was explored on larger vagal afferent fibers in larger human sized nerve bundles projecting to effects mediated by a reflex. The effectiveness of LFAC was assessed in an in-situ electrophysiological setup on the left cervical vagus in anaesthetized domestic swine (n = 5). Two bipolar cuff electrodes were applied unilaterally to the cervical vagus nerve, which was crushed caudal to the electrodes to eliminate cardiac effects. A tripolar extrafascicular cuff electrode was placed most rostral on the nerve for recording of propagating APs induced by electrical stimulation and blocked via the LFAC waveform. Standard pulse stimulation was applied to the left cervical vagus to induce the Hering-Breuer reflex. If unblocked, the activation of the Hering-Breuer reflex would cause breathing to slow down and potentially cease. Block was quantified by the ability to reduce the effect of the Hering-Breuer reflex by monitoring the breathing rate during LFAC alone, LFAC and vagal stimulation, and vagal stimulation alone. LFAC achieved 87.2 +/- 8.8% (n = 5) block at current levels of 0.8 +/- 0.3 mAp. Compound nerve action potentials (CNAP) were monitored directly. They show changes in nerve activity during LFAC, which manifests itself as the slowing and amplitude reduction of components of the CNAPs. Since the waveform is balanced, all forward reactions are reversed, leading to a blocking method that is similar in nature to DC block without the potential issues of toxic byproduct production. These results suggest that LFAC can achieve a high degree of nerve block in both small and large nerve bundles, resulting in the change in behavior of a biomarker, in-vivo in the mammalian nervous system at low amplitudes of electrical stimulation that are within the water window of the electrode.
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Tsai, Yi-Lin, e 蔡依霖. "Low-frequency Variations of Currents in Spring and Autumn off Southwestern Taiwan". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/19156509568177909798.

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碩士
國立臺灣大學
海洋研究所
103
Flow patterns of the southern opening of Taiwan Strait were investigated by incorporated moored observations, wind speed measurement (from the weather station in Taiwan Strait) and sea-level measurements (from two nearby tide station), among them the moored current data include two sets of Recording Current Meters(RCMs) observations (from 1997 to 1998) and one set of ADCP data (from 2004 to 2013). Aside from these, trajectories of surface drifters and model results from the Luzon Strait Ocean Nowcast/Forecast System (LZSNFS), a data-assimilating, dynamical ocean model routinely operated by Naval Research Laboratory, USA, were used to display the simultaneous spatial structure of the flow field, which facilitates the interpretation of the significance of the variations of currents, from moored observations, associated to the larger scale flow pattern. All the time series data were pre-processed by low-passed filtration (the cut-off period of the filter used is 48 hours ), afterwards the orientation of the low-passed current data were projected to the principal and minor axes, in which the direction of the former is roughly in parallel to local isobaths. From the current data, five events could be identified, if an event is defined by the current reversal, i.e. as the direction of the low-passed current offshore Kaohsiung reverses from northwestward to southeastward within a few days. Model results from LZSNFS suggest this phenomenon is closely related to the process of the intrusion of Kuroshio from the Luzon Strait to the northeastern South China Sea (SCS), this process may induce an anti-cyclonic (clockwise) flow pattern offshore the southwest Taiwan. Statistics from the Empirical Orthogonal Function analysis (among low-pass filrated ADCP currents, sea-level and winds) and simultaneous results from LZSNFS suggest that, once an anti-cyclonic flow pattern moved into the observation region offshore southwest Taiwan, the costal sea-level near Kaohsiung descended and the low-frequency currents offshore Kaohsiung turned toward the southeast. This kind of current reversal events occurred frequently in both spring and autumn.
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Libri sul tema "Low frequency currents interractions"

1

Low frequency electromagnetic design. New York: M. Dekker, 1985.

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Appropriate electrode sites and electrical characteristics for TENS. Oxford University Press, 2014. http://dx.doi.org/10.1093/med/9780199673278.003.0004.

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The success of TENS treatment depends on the use of safe and appropriate TENS technique. Uncertainty about optimal TENS technique is due in part to the variety of possible electrode positions and electrical characteristics that can be chosen for treatment. Conventional TENS uses low-intensity, high-frequency currents to activate low-threshold afferent nerve fibres in the skin. AL-TENS uses high-intensity, low-frequency currents to generate non-painful phasic muscle contractions (twitching). The purpose of this chapter is to discuss the principles that underpin the use of safe and appropriate electrode sites and electrical characteristics during TENS. The chapter covers how to choose between conventional and AL-TENS, the appropriate electrode positioning for conventional TENS and AL-TENS including instances where AL-TENS may be more beneficial than conventional TENS, appropriate choice of electrical characteristics for stimulation, and biological, psychological, and social factors influencing response to TENS
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Capitoli di libri sul tema "Low frequency currents interractions"

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Ward, William W., e John C. Moulder. "Low Frequency, Pulsed Eddy Currents for Deep Penetration". In Review of Progress in Quantitative Nondestructive Evaluation, 291–98. Boston, MA: Springer US, 1998. http://dx.doi.org/10.1007/978-1-4615-5339-7_37.

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Grodnensky, I. M., D. Heitmann, K. von Klitzing e A. Yu Kamaev. "Low-Frequency Response and Dissipationless Edge Currents in the Integral QHE". In Springer Series in Solid-State Sciences, 135–38. Berlin, Heidelberg: Springer Berlin Heidelberg, 1992. http://dx.doi.org/10.1007/978-3-642-84408-9_20.

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Lin, Y., e L. C. Lee. "Generation of Region 1 and Mantle Field-Aligned Currents by the Secondary Rotational Discontinuity". In Solar Wind Sources of Magnetospheric Ultra-Low-Frequency Waves, 213–21. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm081p0213.

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Song, Yan, Robert L. Lysak e Naiguo Lin. "Control of the Generation of Field-Aligned Currents and Transverse ULF Waves by the Magnetic Helicity Input". In Solar Wind Sources of Magnetospheric Ultra-Low-Frequency Waves, 223–30. Washington, D. C.: American Geophysical Union, 2013. http://dx.doi.org/10.1029/gm081p0223.

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Davis, Richard J., e Donald T. Hayford. "Low Frequency Eddy Currents with Magnetic Saturation for In-Line Detection and Sizing of Stress Corrosion Cracks". In Review of Progress in Quantitative Nondestructive Evaluation, 323–30. Boston, MA: Springer US, 1995. http://dx.doi.org/10.1007/978-1-4615-1987-4_37.

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Wachtel, Howard. "Comparison of Endogenous Currents in and Around Cells with Those Induced by Exogenous Extremely Low Frequency Magnetic Fields". In Electromagnetic Fields, 99–107. Washington, DC: American Chemical Society, 1995. http://dx.doi.org/10.1021/ba-1995-0250.ch006.

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Garrett, Steven L. "One-Dimensional Propagation". In Understanding Acoustics, 453–512. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-44787-8_10.

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Abstract Having already invested in understanding both the equation of state and the hydrodynamic equations, only straightforward algebraic manipulations will be required to derive the wave equation, justify its solutions, calculate the speed of sound in fluids, and derive the expressions for acoustic intensity and the acoustic kinetic and potential energy densities of sound waves. The “machinery” developed to describe waves on strings will be sufficient to describe one-dimensional sound propagation in fluids, even though the waves on the string were transverse and the one-dimensional waves in fluids are longitudinal. These results are combined with the thermal and viscous penetration depths to calculate the frequencies and quality factors in standing wave resonators. The coupling of those resonators to loudspeakers will be examined. The introduction of reciprocal transducers that are linear, passive, and reversible will allow absolute calibration of transducers using only electrical measurements (i.e., currents and voltages) by the reciprocity method, if the acoustic impedance that couples the source and receiver is calculable. Reflection and transmission at junctions between multiple ducts and other networks will be calculated and applied to the design of filters. The behavior of waves propagating through horns will provide useful impedance matching but introduce a low-frequency cut-off.
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Metral, E., G. Rumolo e W. Herr. "Impedance and Collective Effects". In Particle Physics Reference Library, 105–81. Cham: Springer International Publishing, 2020. http://dx.doi.org/10.1007/978-3-030-34245-6_4.

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AbstractAs the beam intensity increases, the beam can no longer be considered as a collection of non-interacting single particles: in addition to the “single-particle phenomena”, “collective effects” become significant. At low intensity a beam of charged particles moves around an accelerator under the Lorentz force produced by the “external” electromagnetic fields (from the guiding and focusing magnets, RF cavities, etc.). However, the charged particles also interact with themselves (leading to space charge effects) and with their environment, inducing charges and currents in the surrounding structures, which create electromagnetic fields called wake fields. In the ultra-relativistic limit, causality dictates that there can be no electromagnetic field in front of the beam, which explains the term “wake”. It is often useful to examine the frequency content of the wake field (a time domain quantity) by performing a Fourier transformation on it. This leads to the concept of impedance (a frequency domain quantity), which is a complex function of frequency. The charged particles can also interact with other charged particles present in the accelerator (leading to two-stream effects, and in particular to electron cloud effects in positron/hadron machines) and with the counter-rotating beam in a collider (leading to beam–beam effects). As the beam intensity increases, all these “perturbations” should be properly quantified and the motion of the charged particles will eventually still be governed by the Lorentz force but using the total electromagnetic fields, which are the sum of the external and perturbation fields. Note that in some cases a perturbative treatment is not sufficient and the problem has to be solved self consistently. These perturbations can lead to both incoherent (i.e. of a single particle) and coherent (i.e. of the centre of mass) effects, in the longitudinal and in one or both transverse directions, leading to beam quality degradation or even partial or total beam losses. Fortunately, stabilising mechanisms exist, such as Landau damping, electronic feedback systems and linear coupling between the transverse planes (as in the case of a transverse coherent instability, one plane is usually more critical than the other).
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Singh, Jagmohan. "Low Frequency Currents". In Textbook of Electrotherapy, 69. Jaypee Brothers Medical Publishers (P) Ltd., 2005. http://dx.doi.org/10.5005/jp/books/10909_2.

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Singh, Jagmohan. "Low Frequency Currents". In Textbook of Electrotherapy, 75. Jaypee Brothers Medical Publishers (P) Ltd., 2012. http://dx.doi.org/10.5005/jp/books/11673_2.

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Atti di convegni sul tema "Low frequency currents interractions"

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Moglie, Franco, e Vincenzo Tassillo. "Low Frequency FDTD Technique for Evaluation of Currents Induced by a Power Line in a Biological Model of a Body". In 14th International Zurich Symposium and Technical Exposition on Electromagnetic Compatibility, 1–4. IEEE, 2001. https://doi.org/10.23919/emc.2001.10792066.

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Karlson, Samuel, Pauli Kehayias, Jennifer M. Schloss, Andrew C. Maccabe, David F. Phillips, Guoqing Wang, Paola Cappellaro e Danielle A. Braje. "Frequency-Tunable Current Imaging using a Quantum-Mixer Microscope Based on Nitrogen-Vacancy Centers in Diamond". In ISTFA 2024, 282–87. ASM International, 2024. http://dx.doi.org/10.31399/asm.cp.istfa2024p0282.

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Abstract Wide-field magnetic imagers using nitrogen-vacancy (NV) centers in diamond yield high-resolution images for various applications, including magnetic field imaging (MFI) of electronics. Despite the ongoing successes of this emerging technique for passively interrogating electronics components (including failure analysis troubleshooting), most of the focus has been on sensing DC and low-frequency currents, due to the technical challenges associated with measuring higher-frequency magnetic fields. Here, we overcome these existing challenges and adapt a recently developed technique for sensing MHz-frequency AC fields, a “quantum frequency mixing” approach. We demonstrate the instrument’s capabilities by imaging the current through a fabricated spiral test structure at various frequencies with a ~1 mm2 field of view. Finally, we discuss anticipated future applications in electronics interrogation and failure analysis for this imaging technique.
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Gao, Yuanfei, Tao Wang, Yixin Wang e Zhiliang Yuan. "Inter-pulse intensity correlation in gain-switched semiconductor laser for quantum key distribution". In CLEO: Fundamental Science, FM3K.3. Washington, D.C.: Optica Publishing Group, 2024. http://dx.doi.org/10.1364/cleo_fs.2024.fm3k.3.

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The transmitters in QKD usually employ a gain-switched semiconductor lasers (GSSL). Here, we investigated the intensity fluctuation and correlation between adjacent pulses. Strong intensity fluctuation and negative correlation were observed under low driving currents. Utilizing rate equations in our simulation, we confirmed the fluctuation resulted from an instability of GSSL at high repetition frequency. This work would be useful to test whether the transmitter is operating at optimal state.
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Li, Peng, Xiang-Wen Jiang, Qi-Jun Zhao e Guo-Qing Zhao. "Integrated Optimization Analyses on Aerodynamic/Stealth Characteristics of Helicopter Rotor Based on Surrogate Model". In Vertical Flight Society 70th Annual Forum & Technology Display, 1–13. The Vertical Flight Society, 2014. http://dx.doi.org/10.4050/f-0070-2014-9463.

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Based on Computational Fluid Dynamics (CFD) method, electromagnetic high-frequency method and surrogate model optimization techniques, an integration design method about aerodynamic/stealth has been established for helicopter rotor. The developed integration design method is composed of three modules: 1) integrated grids generation: the moving-embedded grids for CFD solver and the blade grids for Radar Cross Section (RCS) solver are generated by solving Poisson equations and folding approach. 2) aerodynamic/stealth solver: the aerodynamic characteristics are simulated by CFD method based upon Navier-Stokes(N-S) equations and Spalart-Allmaras(S-A) turbulence model, and the stealth characteristics are calculated by using a panel edge method combining the method of Physical Optics(PO), Equivalent Currents(MEC) and Quasi-Stationary (MQS), and 3) integrated optimization analysis: based upon the surrogate model optimization technique with Full Factorial Design (FFD) and Radial Basis Function (RBF), an integrated optimization analyses on aerodynamic/stealth characteristics of rotor are conducted. It has been demonstrated that CFD and RCS method are effective by comparing the calculated pressure distributions of UH-60A rotor and scattering distributions of cone with the experimental data. Then scattering characteristics of the rotor with different blade-tip swept and twist angles have been carried out. Considering the modulation of rotor, time-frequency domain grayscale with strong scattering regions of rotor have been given. Simultaneously, the effects of swept-tip and twist angles on the aerodynamic characteristic of rotor have been performed. Furthermore, by choosing suitable object function and constraint condition, the compromised design about swept and twist combinations of rotor with high aerodynamic performances and low scattering characteristics has been given at last.
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Schachinger, Philipp, Dennis Albert e Herwig Renner. "Low Frequency Currents Source Identification". In 2022 20th International Conference on Harmonics & Quality of Power (ICHQP). IEEE, 2022. http://dx.doi.org/10.1109/ichqp53011.2022.9808423.

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Du, Y., e Mingli Chen. "Low-frequency magnetic shielding against unbalanced currents". In 2015 7th Asia-Pacific Conference on Environmental Electromagnetics (CEEM). IEEE, 2015. http://dx.doi.org/10.1109/ceem.2015.7368690.

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Forest, C. B., M. Ono, Y. S. Hwang e D. S. Darrow. "Pressure Driven Currents in an ECH Heated, Low Aspect Ratio Torus". In Radio frequency power in plasmas. AIP, 1992. http://dx.doi.org/10.1063/1.41668.

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Janina, Rzasa. "Low-frequency components in the switch currents of Matrix Converter". In 2011 IEEE 20th International Symposium on Industrial Electronics (ISIE). IEEE, 2011. http://dx.doi.org/10.1109/isie.2011.5984178.

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Sergeev, Viacheslav, Ilya Frolov e Oleg Radaev. "Measurement of the LED electroluminescence 3dB frequency at low currents". In 2023 IX International Conference on Information Technology and Nanotechnology (ITNT). IEEE, 2023. http://dx.doi.org/10.1109/itnt57377.2023.10139230.

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Kherif, O., S. Robson, N. Harid, D. Thorpe e A. Haddad. "Considerations on Earthing Impedance Measurement using Low-magnitude Variable-frequency Currents". In 2022 36th International Conference on Lightning Protection (ICLP). IEEE, 2022. http://dx.doi.org/10.1109/iclp56858.2022.9942461.

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Rapporti di organizzazioni sul tema "Low frequency currents interractions"

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Kirby, James T. Modeling Beach Morphology Changes Coupled to Incident Wave Climate and Low Frequency Currents. Fort Belvoir, VA: Defense Technical Information Center, ottobre 2001. http://dx.doi.org/10.21236/ada405779.

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Kirby, James T. Modeling Beach Morphology Changes Coupled to Incident Wave Climate and Low Frequency Currents. Fort Belvoir, VA: Defense Technical Information Center, settembre 2000. http://dx.doi.org/10.21236/ada609993.

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Kirby, James T. Modeling Beach Morphology Changes Coupled to Incident Wave Climate and Low Frequency Currents. Fort Belvoir, VA: Defense Technical Information Center, settembre 1999. http://dx.doi.org/10.21236/ada629766.

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Kirby, James T. Modeling Beach Morphology Changes Coupled to Incident Wave Climate and Low Frequency Currents. Fort Belvoir, VA: Defense Technical Information Center, agosto 2001. http://dx.doi.org/10.21236/ada626143.

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Bruce e Fiore. L51629 Users Manual-Field Validation of the Low-Frequency Eddy Current Instrument-Software Listings. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), ottobre 1990. http://dx.doi.org/10.55274/r0010602.

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When an eddy current probe is placed near a conductive material, the alternating magnetic field from the probe causes electrical currents to flow in the material. These currents have associated with them their own magnetic field, which opposes the original magnetic field from the coil. The result is that the impedance of the probe is greatly reduced by the presence of the conducting material. If the conductor is also magnetic, as is normal steel, the situation is similar though slightly more complicated. Here, the impedance of the probe may be either increased or decreased depending on the permeability of the material and the frequency of the alternating field. Anything that affects the flow of current in the conductive material will also affect the impedance of the eddy current probe. For example, the electrical currents cannot flow through a crack but must flow around it. The alteration in the currents also changes the magnetic field produced by the currents and, consequently, the impedance of the probe. Normally, the impedance change caused by a defect is much smaller than that caused by the presence of the material in the first place, and measuring this small change requires a bridge circuit much like the balanced bridge used with strain gauges. The balanced bridge allows one to amplify the small changes in impedance caused by defects in the presence of the much larger change caused by the presence of the conductive and magnetic pipeline steel. The LFEC instrument is constructed using an� IBM-AT compatible portable computer. Inside the PAC-386 are two plug-in circuit cards that turn the PAC-386 into an eddy current instrument. The first, also commercially available, is a Spectrum DSP56000 digital signal processing card, while the second is a specially-built interface card for the eddy current probe. The PAC-386 is a standard MS-DOS machine and will operate most MS-DOS software. In the discussion below, it is assumed that the user is familiar with the MSDOS operating system.
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Hayford. L51566 Ultralow Frequency Eddy Current Instrument for the Detection and Sizing of Stress Corrosion Cracks. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), gennaio 1988. http://dx.doi.org/10.55274/r0010601.

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Eddy current testing has received only limited application to ferrous materials because the high permeability of the material in combination with the normally high frequency of the eddy current instrument results in a very small depth of penetration of the eddy currents into the material. The objectives of this research program were threefold. The first goal was to develop an eddy current instrument with frequencies low enough to penetrate pipeline steel. The second was to use the new instrument to develop techniques for locating stress corrosion cracks (SCC) on coated pipelines without requiring the removal of the coating. Our last goal was to develop methods of characterizing SCC; i.e. determining the lengths and depths of the defects.
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Unknown, Author. L51630 In-Line Detection and Sizing of Stress Corrosion Cracks Using EMAT Ultrasonics. Chantilly, Virginia: Pipeline Research Council International, Inc. (PRCI), aprile 1990. http://dx.doi.org/10.55274/r0010616.

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The development of stress corrosion cracks (SCC) in buried gas pipelineshas posed a serious threat to pipeline integrity for many years. It can be reliably detected by magnetic particle techniques in the field or by laboratory studies using low frequency eddy currents. It is also possible to find and measure the depths of the cracks from the ID by careful scanning with an ultra-sonic angle beam probe but the transducer must be manipulated by a skilled operator. All of these approaches are not very satisfactory for in-line inspections because they are not suitable for covering the total area of a pipeline and they are too labor intensive to be automated. In order to address this problem with new technology, the PRCI requested proposals for any technique that seemed to be practical and the Electromagnetic Acoustic Transducer (EMAT) was suggested as very promising because it has already demonstrated operation in the environment of the inside of a gas pipeline. Magnasonics, Inc., of Albuquerque, New Mexico, was chosen from many respondents to conduct an in-vestigation of the use of EMATs for overcoming the problems expected to arise from in-line operation and to incorporate the latest developments in ultrasonic inspection with EMATs. The objective of the program described in this report was twofold. First, to apply the most recent developments in EMAT technology to the problem of detecting and sizing stress corrosion cracks (SCC) in operating gas pipelines and second to exploit the ability of EMATs to generate and detect a wide variety of ultrasonic waves in the walls of a pipeline under operating conditions.
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Lafrancois, Toben, Mark Hove e Jay Glase. Zebra mussel (Dreissena polymorpha) distribution in Apostle Islands National Lakeshore: SCUBA-based search and removal efforts: 2019–2020. National Park Service, maggio 2022. http://dx.doi.org/10.36967/nrr-2293376.

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Invasive zebra mussels (Dreissena polymorpha) were first observed in situ at Apostle Islands National Lakeshore (APIS) in 2015. This report builds on 2018 SCUBA surveys and Environmental Protection Agency (EPA) veliger sampling to: 1) determine whether shoals on APIS borders act as sentinel sites to corroborate veliger drift hypotheses about invasion pathways, 2) evaluate ongoing hand-removal of zebra mussels from easily identified structures, and 3) continue efforts to assess native unionid mussel populations, particularly where zebra mussels are also present. Standard catch per unit effort survey methods by SCUBA teams were used to determine the distribution and relative abundance of zebra or quagga mussels (dreissenids) and native mussels (unionids). Zebra mussels were present at densities between 3 and 42 n/diver/hr (number of mussels per diver per hour), while native unionids were present at densities between 5 and 72 n/diver/hr. Shoal surveys (Eagle Island shoal, Sand Island shoal, York Island shoal, Bear Island shoal, Oak Island shoal, and Gull Island shoal) showed zebra mussels were more abundant on the west side of APIS and absent on the easternmost shoal (Gull Island), corroborating veliger work by the EPA that suggested drift from the Twin Ports of Duluth, Minnesota, and Superior, Wisconsin, is one pathway of invasion. Our results support the use of shallow shoals along the periphery of the park as sentinel sites gauging zebra mussel immigration and population dynamics. Zebra mussel densities in the central islands showed no obvious spatial pattern, and this survey cannot determine whether currents or human transport (or both) are invasion vectors. Given the mussels’ continued presence at heavily used mooring areas and docks where there are no zebra mussels on nearby natural features (e.g., Rocky Island dock, Stockton Island mooring areas), our findings are consistent with multiple invasion pathways (drift from the Twin Ports and anthropogenic sources at mooring areas). SCUBA search and removal of zebra mussels from docks was confirmed to be an effective method for significantly lowering the risk of zebra mussels reproducing and dispersing from these locations. We caution that this work is being done on what look like initial invasions at low densities. Repeated removal of zebra mussels by divers reduced numbers to zero at some sites after one year (South Twin docks, Stockton Island NPS docks, and the Ottawa wreck) or decreased numbers by an order of magnitude (Rocky Island docks). Dreissenid densities were more persistent on the Sevona wreck and longer-term work is required to evaluate removal versus recruitment (local and/or veliger drift). Given the size of the wreck, we have tracked detailed survey maps to guide future efforts. Zebra mussels were again observed attached to native mussels near Stockton Island and South Twin Island. Their continued presence on sensitive native species is of concern. Native unionid mussels were more widely distributed in the park than previously known, with new beds found near Oak and Basswood Islands. The work reported here will form the basis for continued efforts to determine the optimal frequency of zebra mussel removal for effective control, as well as evaluate impacts on native species.
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