Articles de revues : « Drift current »

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Nakayama, Yoshihiro, Kay I. Ohshima et Yasushi Fukamachi. « Enhancement of Sea Ice Drift due to the Dynamical Interaction between Sea Ice and a Coastal Ocean ». Journal of Physical Oceanography 42, n^o 1 (1 janvier 2012) : 179–92. http://dx.doi.org/10.1175/jpo-d-11-018.1.

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Abstract Wind factor, the ratio of sea ice drift speed to surface wind speed, is a key factor for the dynamics of sea ice and is generally about 2%. In some coastal oceans, however, the wind factor tends to be larger near the coast. This study proposes the enhancement mechanism of the sea ice drift caused by the dynamical coupling between sea ice and a coastal ocean. In a coastal ocean covered with sea ice, wind-forced sea ice drift excites coastal trapped waves (shelf waves) and generates fluctuating ocean current. This ocean current can enhance sea ice drift when the current direction is the same as that of the wind-driven drift. The authors consider a simplified setting where spatially uniform oscillating wind drifts sea ice parallel to the coast. When a barotropic long shelf wave is assumed for the ocean response, sea ice drifts driven by wind and ocean are obtained analytically. The ratio of ocean-driven to wind-driven sea ice drifts is used for the evaluation of the oceanic contribution to the enhancement of sea ice drift. The enhancement is mostly determined by the characteristics of the shelf waves, and sea ice drift is significantly enhanced close to the coast with lower-frequency wind forcing. Comparison with the observation off the Sakhalin coast shows that the degree of enhancement of sea ice drift and its characteristic such that larger enhancement occurs near the coast are mostly consistent with our theoretical solution, suggesting that this mechanism is present in the real ocean.

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Mao, Yadan, et Malcolm L. Heron. « The Influence of Fetch on the Response of Surface Currents to Wind Studied by HF Ocean Surface Radar ». Journal of Physical Oceanography 38, n^o 5 (1 mai 2008) : 1107–21. http://dx.doi.org/10.1175/2007jpo3709.1.

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Abstract The momentum transfer from wind to sea generates surface currents through both the wind shear stress and the Stokes drift induced by waves. This paper addresses issues in the interpretation of HF radar measurements of surface currents and momentum transfer from air to sea. Surface current data over a 30-day period from HF ocean surface radar are used to study the response of surface currents to wind. Two periods of relatively constant wind are identified—one for the short-fetch condition and the other for the long-fetch condition. Results suggest that the ratio of surface current speed to wind speed is larger under the long-fetch condition, while the angle between the surface current vector and wind vector is larger under the short-fetch condition. Data analysis shows that the Stokes drift dominates the surface currents under the long-fetch condition when the sea state is more mature, while the Stokes drifts and Ekman-type currents play almost equally important roles in the total currents under the short-fetch condition. The ratios of Stokes drift to wind speed under these two fetch conditions are shown to agree well with results derived from the empirical wave growth function. These results suggest that fetch, and therefore sea state, significantly influences the total response of surface current to wind in both the magnitude and direction by variations in the significance of Stokes drift. Furthermore, this work provides observational evidence that surface currents measured by HF radar include Stokes drift. It demonstrates the potential of HF radar in addressing the issue of momentum transfer from air to sea under various environmental conditions.

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Imai, Yuki, Junichi Ninomiya et Nobuhito Mori. « IMPACT OF RANDOM WAVE SPECTRA ON STOKES DRIFT IN COASTAL CURRENT MODELING ». Coastal Engineering Proceedings, n^o 36 (30 décembre 2018) : 1. http://dx.doi.org/10.9753/icce.v36.currents.1.

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The wave-induced velocity, known commonly as Stokes drift, plays an important role on upper ocean current system. However, in general, the depth profile tends to be estimated using a regular wave approximation like calculation from significant wave height in order to simplify the modeling. Breivik et al. (2014) proposed an improved Stokes drift profile to considering random waves but discussed limited to deep water. This study proposes a novel treatment of Stokes drift on random waves to consider full directional spectra and the approximated treatment is introduced into coupled ocean-wave model to apply for the depth-limited region. To validate the proposed treatment, Stokes drift velocity derived from the treatment is theoretically and empirically compared with some derived from regular wave approximation. Finally coastal current simulation is performed for Kii channel of Japan focusing on Tanabe bay by the coupled model with two-way-nesting scheme.

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MUÑUZURI, A. P., V. PÉREZ-MUÑUZURI, M. GÓMEZ-GESTEIRA, V. I. KRINSKY et V. PÉREZ-VILLAR. « MECHANISM OF PARAMETRIC RESONANCE OF VORTICES IN EXCITABLE MEDIA ». International Journal of Bifurcation and Chaos 04, n^o 05 (octobre 1994) : 1245–56. http://dx.doi.org/10.1142/s0218127494000939.

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An alternating electric current induces a drift of spiral waves (vortices) in the Belousov-Zhabotinsky reaction. When the electric current frequency is twice the frequency of the vortex rotation, the vortex drifts with a velocity about 1/5 of the vortex drift in a constant electric current or 1/20 of the wave front velocity. The dependence of parametric resonance on the chirality of the vortex, excitability of the medium, phase shift between electric current and vortex rotation, frequency and amplitude of the alternating electric current is analyzed and used to control the direction and velocity of the drift. A kinematical model, based on the asymmetric effect of the current on the normal and tangential velocities of the vortex tip, is formulated and recovers the most important aspects of parametric resonance.

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Hara, Hideo, Tomoki Joichi, Shunsuke Abe et Shin Masuda. « Photo-induced DC drift in Mach-Zehnder modulators using lead lanthanum zirconate titanate thin films ». AIP Advances 12, n^o 12 (1 décembre 2022) : 125115. http://dx.doi.org/10.1063/5.0129414.

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We experimentally investigated the photo-induced direct current (DC) drift of a lead lanthanum zirconate titanate (PLZT) Mach-Zehnder modulator with large optical input power. We clarify the mechanism by which short-term and long-term DC drifts arise and discuss each case of DC drift. We reveal that short-term DC drift can be reduced by adjusting the buffer-layer resistivity of the PLZT modulator. We also found that the impurity level of the buffer layer affects long-term DC drift.

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Ahmad, Ali, et H. Saleem. « Current-driven electron drift solitons ». Physics Letters A 377, n^o 43 (décembre 2013) : 3128–30. http://dx.doi.org/10.1016/j.physleta.2013.07.061.

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Lee, Kwang-Ho, Tag-Gyeom Kim et Yong-Hwan Cho. « Influence of Tidal Current, Wind, and Wave in Hebei Spirit Oil Spill Modeling ». Journal of Marine Science and Engineering 8, n^o 2 (22 janvier 2020) : 69. http://dx.doi.org/10.3390/jmse8020069.

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The purpose of this study is to investigate the effects of three external forces (tidal current, wind, and waves) on the movement of oil spilled during the Hebei Spirit oil spill accident. The diffusion of the spilled oil was simulated by using a random walk (RW) model that tracks the movement caused by advection-diffusion assuming oil as particles. For oil simulation, the wind drift current generated by wind and tidal current fields were computed by using the environmental fluid dynamics code (EFDC) model. Next, the wave fields were simulated by using the simulating waves nearshore (SWAN) model, and the Stokes drift current fields were calculated by applying the equation proposed by Stokes. The computed tidal currents, wind drift currents, and Stokes drift currents were applied as input data to the RW model. Then, oil diffusion distribution for each external force component was investigated and compared with that obtained from satellite images. When the wind drift currents and Stokes drift currents caused by waves were considered, the diffusion distribution of the spilled oil showed good agreement with that obtained from the observation.

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Sakurai, Guilherme Yukio, Jessica Fernandes Lopes, Bruno Bogaz Zarpelão et Sylvio Barbon Junior. « Benchmarking Change Detector Algorithms from Different Concept Drift Perspectives ». Future Internet 15, n^o 5 (29 avril 2023) : 169. http://dx.doi.org/10.3390/fi15050169.

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The stream mining paradigm has become increasingly popular due to the vast number of algorithms and methodologies it provides to address the current challenges of Internet of Things (IoT) and modern machine learning systems. Change detection algorithms, which focus on identifying drifts in the data distribution during the operation of a machine learning solution, are a crucial aspect of this paradigm. However, selecting the best change detection method for different types of concept drift can be challenging. This work aimed to provide a benchmark for four drift detection algorithms (EDDM, DDM, HDDMW, and HDDMA) for abrupt, gradual, and incremental drift types. To shed light on the capacity and possible trade-offs involved in selecting a concept drift algorithm, we compare their detection capability, detection time, and detection delay. The experiments were carried out using synthetic datasets, where various attributes, such as stream size, the amount of drifts, and drift duration can be controlled and manipulated on our generator of synthetic stream. Our results show that HDDMW provides the best trade-off among all performance indicators, demonstrating superior consistency in detecting abrupt drifts, but has suboptimal time consumption and a limited ability to detect incremental drifts. However, it outperforms other algorithms in detection delay for both abrupt and gradual drifts with an efficient detection performance and detection time performance.

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Ghaffari, Peygham, et Jan Erik H. Weber. « Mass Transport in the Stokes Edge Wave for Constant Arbitrary Bottom Slope in a Rotating Ocean ». Journal of Physical Oceanography 44, n^o 4 (1 avril 2014) : 1161–74. http://dx.doi.org/10.1175/jpo-d-13-0171.1.

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Abstract The Lagrangian mass transport in the Stokes surface edge wave is obtained from the vertically integrated equations of momentum and mass in a viscous rotating ocean, correct to the second order in wave steepness. The analysis is valid for bottom slope angles β in the interval 0 < β ≤ π/2. Vertically averaged drift currents are obtained by dividing the fluxes by the local depth. The Lagrangian mean current is composed of a Stokes drift (inherent in the waves) plus a mean Eulerian drift current. The latter arises as a balance between the radiation stresses, the Coriolis force, and bottom friction. Analytical solutions for the mean Eulerian current are obtained in the form of exponential integrals. The relative importance of the Stokes drift to the Eulerian current in their contribution to the Lagrangian drift velocity is investigated in detail. For the given wavelength, the Eulerian current dominates for medium and large values of β, while for moderate and small β, the Stokes drift yields the main contribution to the Lagrangian drift. Because most natural beaches are characterized by moderate or small slopes, one may only calculate the Stokes drift in order to assess the mean drift of pollution and suspended material in the Stokes edge wave. The main future application of the results for large β appears to be for comparison with laboratory experiments in rotating tanks.

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Fukamachi, Yasushi, Kay I. Ohshima, Yuji Mukai, Genta Mizuta et Masaaki Wakatsuchi. « Sea-ice drift characteristics revealed by measurement of acoustic Doppler current profiler and ice-profiling sonar off Hokkaido in the Sea of Okhotsk ». Annals of Glaciology 52, n^o 57 (2011) : 1–8. http://dx.doi.org/10.3189/172756411795931507.

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AbstractIn the southwestern part of the Sea of Okhotsk off Hokkaido, sea-ice drift characteristics are investigated using the ice and water velocities obtained from a moored upward-looking acoustic Doppler current profiler (ADCP) during the winters of 1999–2001. Using hourly-mean values of these data along with the wind data measured at a nearby coastal station, the wind factor and turning angle of the relative velocity between the ice and water velocities with respect to the wind are calculated assuming free drift under various conditions. Since the simultaneous sea-ice draft data are also available from a moored ice-profiling sonar (IPS), we examine the dependence of drift characteristics on ice thickness for the first time. As ice thickness increases and wind decreases, the wind factor decreases and the turning angle increases, as predicted by the theory of free drift. This study clearly shows the utility of the moored ADCP measurement for studying sea-ice drift, especially with the simultaneous IPS measurement for ice thickness, which cannot be obtained by other methods.

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Muhammad Zaly Shah, Muhammad Zafran, Anazida Zainal, Taiseer Abdalla Elfadil Eisa, Hashim Albasheer et Fuad A. Ghaleb. « A Semisupervised Concept Drift Adaptation via Prototype-Based Manifold Regularization Approach with Knowledge Transfer ». Mathematics 11, n^o 2 (9 janvier 2023) : 355. http://dx.doi.org/10.3390/math11020355.

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Data stream mining deals with processing large amounts of data in nonstationary environments, where the relationship between the data and the labels often changes. Such dynamic relationships make it difficult to design a computationally efficient data stream processing algorithm that is also adaptable to the nonstationarity of the environment. To make the algorithm adaptable to the nonstationarity of the environment, concept drift detectors are attached to detect the changes in the environment by monitoring the error rates and adapting to the environment’s current state. Unfortunately, current approaches to adapt to environmental changes assume that the data stream is fully labeled. Assuming a fully labeled data stream is a flawed assumption as the labeling effort would be too impractical due to the rapid arrival and volume of the data. To address this issue, this study proposes to detect concept drift by anticipating a possible change in the true label in the high confidence prediction region. This study also proposes an ensemble-based concept drift adaptation approach that transfers reliable classifiers to the new concept. The significance of our proposed approach compared to the current baselines is that our approach does not use a performance measur as the drift signal or assume a change in data distribution when concept drift occurs. As a result, our proposed approach can detect concept drift when labeled data are scarce, even when the data distribution remains static. Based on the results, this proposed approach can detect concept drifts and fully supervised data stream mining approaches and performs well on mixed-severity concept drift datasets.

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Palli, Abdul Sattar, Jafreezal Jaafar, Heitor Murilo Gomes, Manzoor Ahmed Hashmani et Abdul Rehman Gilal. « An Experimental Analysis of Drift Detection Methods on Multi-Class Imbalanced Data Streams ». Applied Sciences 12, n^o 22 (17 novembre 2022) : 11688. http://dx.doi.org/10.3390/app122211688.

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The performance of machine learning models diminishes while predicting the Remaining Useful Life (RUL) of the equipment or fault prediction due to the issue of concept drift. This issue is aggravated when the problem setting comprises multi-class imbalanced data. The existing drift detection methods are designed to detect certain drifts in specific scenarios. For example, the drift detector designed for binary class data may not produce satisfactory results for applications that generate multi-class data. Similarly, the drift detection method designed for the detection of sudden drift may struggle with detecting incremental drift. Therefore, in this experimental investigation, we seek to investigate the performance of the existing drift detection methods on multi-class imbalanced data streams with different drift types. For this reason, this study simulated the streams with various forms of concept drift and the multi-class imbalance problem to test the existing drift detection methods. The findings of current study will aid in the selection of drift detection methods for use in developing solutions for real-time industrial applications that encounter similar issues. The results revealed that among the compared methods, DDM produced the best average F1 score. The results also indicate that the multi-class imbalance causes the false alarm rate to increase for most of the drift detection methods.

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Betti Beneventi, Giovanni, Massimo Ferro, Alessandro Calderoni et Paolo Fantini. « Physics-Based Statistical Modeling of PCM Current Drift Including Negative-Drift-Coefficients ». IEEE Electron Device Letters 34, n^o 7 (juillet 2013) : 879–81. http://dx.doi.org/10.1109/led.2013.2261892.

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Chernyshev, T. B., D. D. Krivoruchko et A. B. Skrylev. « Measurements of the Drift Current Oscillations in Thrusters with Closed Electron Drift ». Technical Physics 63, n^o 5 (mai 2018) : 689–94. http://dx.doi.org/10.1134/s1063784218050043.

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Byun, Sang-Shin, et Jin-Hee Yuk. « A Study on the Drift Characteristics of the Yellow Sea Using the Finite Element Model ». Journal of Korean Society of Coastal and Ocean Engineers 36, n^o 5 (31 octobre 2024) : 199–207. http://dx.doi.org/10.9765/kscoe.2024.36.5.199.

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This study investigates the drift characteristics of the Yellow Sea using a finite element model. A tidal model of the Yellow Sea was constructed, and its accuracy was verified by comparing the calculated tide levels and tidal current results with observed data. Six points with distinct tidal characteristics were selected across different areas of the Yellow Sea, and the drift paths due to tidal currents were analyzed. Additionally, the drift paths under the influence of increasing wind, in combination with tidal currents, were examined. At the point where a north-south reciprocating current occurs, the particle movement distance increases when a southwesterly wind blows, compared to the influence of the currents alone. On the other hand, at the point characterized by a counterclockwise elliptical current, the drift distance either increases or decreases depending on the location. The relationship between wind and water depth was analyzed, revealing that the shallower the water depth, the greater the wind's influence, leading to increased particle movement.

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Camerlenghi, Angelo, A. Crise, C. J. Pudsey, E. Accerboni, R. Laterza et M. Rebesco. « Ten-month observation of the bottom current regime across a sediment drift of the Pacific margin of the Antarctic Peninsula ». Antarctic Science 9, n^o 4 (décembre 1997) : 426–33. http://dx.doi.org/10.1017/s0954102097000552.

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We present two time series of bottom current and temperature collected 8 m above the seabed on either side of a large sediment drift located on the continental rise of the Pacific margin of the Antarctic Peninsula. The mean current speed is comparable (6.2 cm s−1 and 6.1 cm s−1 respectively), but the mean direction differs by about 121°. The direction of mean flow follows the bathymetric contour, and the maximum speed never exceeds 20 cm s−1 (below the typical benthic storm threshold). The potential temperature is remarkably stable (0.11 ± 0.01°C and 0.13 ± 0.02°C at the two sites). The cross-covariance indicates a significant peak at 20.2 days lag, slightly longer than the travel time of 18.7 days calculated between the two stations following the isobaths (98.4 km) and thus providing evidence for the topographic control on bottom water flow. The observed bottom water flow is consistent with deposition of Holocene hemipelagic sediments of the ‘drift maintenance’ stage. Indicators for palaeoceanographic conditions during glacial periods of the ‘drift maintenance’ stage and the older ‘drift growth’ stage are at present too scarce to understand fully how the past oceanographic conditions influenced the evolution of the drifts.

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Reolid, Jesús, Christian Betzler, Or M. Bialik et Nicolas Waldman. « Lenticular-bedding-like bioturbation and the onshore recognition of carbonate drifts (Oligocene, Cyprus) ». Journal of Sedimentary Research 90, n^o 12 (4 février 2020) : 1667–77. http://dx.doi.org/10.2110/jsr.2020.70.

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ABSTRACT The fine-grained carbonate deposits of the Oligocene to early Miocene of Cyprus are the most characteristic example of onshore outcropping carbonate drifts. These deposits were analyzed from a sedimentological and ichnological perspective, in order to determine the origin of the lenticular bedding characteristic of such deposits. The facies at the two study sections, Tsada and Petra Tou Romiou, consist of an alternation of thin, poorly cemented, intensely bioturbated marly limestone intervals and thick cemented wackestone intervals with abundant bioturbation and “lenticular bedding.” The ichnoassemblage, comprising Zoophycos, Thalassinoides, and Planolites is attributable to the Zoophycos Ichnofacies. The alternation of intervals with medium to well-preserved traces with completely biogenically homogenized facies reflects changes in substrate consistency related to changes in bottom-current velocity or to sedimentation. The presence of lenticular-bedding-like structures in the study deposits, traditionally considered diagnostic of bottom-current action in carbonate-drift outcrops, is shown to be exclusively the result of bioturbation. In the study sections, the “lenticular bedding” is the result of the coalescence of successive Zoophycos structures, which are readily preserved because they are constructed in the historical layer. It is proposed that the overlap of abundant isolated cone-shaped burrows of Zoophycos is the origin of the putative lenticular bedding recorded in the Oligocene fine-grained carbonate deposits of Cyprus, traditionally identified as drifts. Since this bedding is not related to currents in the study sections, the consideration of these carbonate deposits of Cyprus as drifts should be reevaluated. This has crucial implications for the recognition of carbonate drift outcrops elsewhere. Onshore carbonate drift outcrops wherein lenticular bedding is the main diagnostic criterion should be revisited and evaluated ichnologically.

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Denton, George H., James G. Bockheim, Scott C. Wilson, James E. Leide et Björn G. Andersen. « Late Quaternary Ice-Surface Fluctuations of Beardmore Glacier, Transantarctic Mountains ». Quaternary Research 31, n^o 2 (mars 1989) : 183–209. http://dx.doi.org/10.1016/0033-5894(89)90005-7.

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AbstractFormer longitudinal profiles of Beardmore Glacier, an outlet through the Transantarctic Mountains, constrain polar plateau elevations near the center of Antarctica and ice-shelf grouding in the southern Ross Embayment. Three gravel drift sheets of late Quaternary age occur alongside Beardmore Glacier. Plunket drift, the youngest, is parallel to and 7–30 m above the present ice surface. The upper limit of Beardmore drift, intermediate in age, is within 35–40 m of the present ice surface near the polar plateau but about 1100 m above the present ice surface near the glacier mouth. The upper limit of Meyer drift, the oldest, is parallel to and 30–50 m above Beardmore drift. From correlation with numerically dated drifts farther north, we assign an early Holocene age to Plunket drift, a late Wisconsin age to Beardmore drift, and an age of marine isotope Stage 6 to Meyer drift. By our age model, Beardmore Glacier was close to current elevations in its upper reaches and thickened considerably in its middle and lower reaches during the last two global glaciations represented by Beardmore and Meyer drifts. Most likely, grounded ice in the southern Ross Embayment caused such thickening of Beardmore Glacier almost to the polar plateau. A concomitant decline in precipitation is implied by ice-cap retreat on the nearby Dominion Range and is consistent with little change of upper Beardmore Glacier. Ice-shelf grounding most likely resulted from lowered sea level and/or basal melting. Lower than present precipitation was probably caused by colder air temperatures and more-distant open water. The Plunket profile records Holocene ice-surface lowering from increased surface ablation, decreased ice flow, or grounding-line recession.

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Bockheim, James G., Scott C. Wilson, George H. Denton, Björn G. Andersen et Minze Stuiver. « Late Quaternary Ice-Surface Fluctuations of Hatherton Glacier, Transantarctic Mountains ». Quaternary Research 31, n^o 2 (mars 1989) : 229–54. http://dx.doi.org/10.1016/0033-5894(89)90007-0.

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AbstractFormer longitudinal profiles of Hatherton Glacier, an outlet through the Transantarctic Mountains, constrain nearby polar plateau elevations and ice-shelf grounding in the southwestern Ross Embayment. Four gravel drift sheets of late Quaternary age beside Hatherton Glacier are, from youngest to oldest, Hatherton, Britannia I, Britannia II, and Danum. The Hatherton drift limit is uniformly 20 to 70 m above the present ice surface. The Britannia II drift limit is within 100 m of the present surface of uppermost Hatherton Glacier but is 450 m above middle Hatherton Glacier. Extrapolation of this profile downglacier indicates a surface elevation 1100 m above the present Ross Ice Shelf. The Britannia I drift limit is parallel to, but 50–100 m below, Britannia II drift. The Danum drift limit is parallel to, but 50–100 m above, the Britannia II profile. From correlation with drifts near McMurdo Sound and from local 14C dates, we assign an early Holocene age to Hatherton drift, a late Wisconsin age to Britannia drifts, and an age of marine isotope Stage 6 to Danum drift. By our age model, the upper reaches of Hatherton Glacier (and presumably the adjacent polar plateau) have not exceeded their current elevations by more than 100–150 m during the last two complete global glacial-interglacial cycles, whereas the middle and lower reaches of Hatherton Glacier have thickened considerably during the last two global glaciations (late Wisconsin and marine isotope Stage 6). The effect of ice-shelf grounding probably was the major control of these changes of Hatherton Glacier. Holocene ice-surface lowering probably represents the last pulse of grounding-line recession in the southwestern Ross Embayment.

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Chu, Cheng, W. Bard, R. Moore et Y. C. Lee. « Drift-Alfvén modes in high current pinches ». Physics of Fluids 28, n^o 4 (1985) : 1160. http://dx.doi.org/10.1063/1.865040.

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Itoh, Sanae-I., et Kimitaka Itoh. « Anomalous bootstrap current due to drift waves ». Physics Letters A 127, n^o 5 (février 1988) : 267–69. http://dx.doi.org/10.1016/0375-9601(88)90694-9.

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Gerrú, R., M. Wiesenberger, M. Held, A. H. Nielsen, V. Naulin, J. J. Rasmussen et H. Järleblad. « Conservation of currents in reduced full-F electromagnetic kinetic and fluid models ». Plasma Physics and Controlled Fusion 64, n^o 5 (22 mars 2022) : 054005. http://dx.doi.org/10.1088/1361-6587/ac55f6.

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Abstract In this paper, we present an analysis of the conservation of currents in a full-F electromagnetic gyro-kinetic model in the long-wavelength limit. This equation corresponds to what is usually called the ‘vorticity equation’, which is not strictly correct as it cannot be formulated as the curl of a velocity equation. In the paper, we will therefore use the term ‘current conservation equation’ instead. Our results are relevant to reduced plasma descriptions like gyro-kinetic, drift-kinetic, gyro-fluid and drift-fluid models for tokamaks and stellarators. The equation describes the change of the polarization charge density (often called ‘vorticity’) in terms of the polarization stress due to the E × B flow, external sources and three currents: the parallel current, the curvature current and a current related to the magnetic field fluctuations. We compare this equation with previous drift- and gyro-fluid equations and find general agreement, except in the vorticity source terms where previous drift-fluid models fail to capture the heating and density sources. We discuss the role of currents in the dynamics of diamagnetic and E × B flow shear. The possible connection between these currents with phenomena observed in experiments that influence the radial electric field in the edge of tokamak plasmas, like resonant magnetic perturbations, and different magnetic field configurations and shapes, is presented.

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Park, J., et H. Lühr. « Relation of zonal plasma drift and wind in the equatorial F region as derived from CHAMP observations ». Annales Geophysicae 31, n^o 6 (12 juin 2013) : 1035–44. http://dx.doi.org/10.5194/angeo-31-1035-2013.

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Abstract. In this paper we estimate zonal plasma drift in the equatorial ionospheric F region without counting on ion drift meters. From June 2001 to June 2004 zonal plasma drift velocity is estimated from electron, neutral, and magnetic field observations of Challenging Mini-satellite Payload (CHAMP) in the 09:00–20:00 LT sector. The estimated velocities are validated against ion drift measurements by the Republic of China Satellite-1/Ionospheric Plasma and Electrodynamics Instrument (ROCSAT-1/IPEI) during the same period. The correlation between the CHAMP (altitude ~ 400 km) estimates and ROCSAT-1 (altitude ~ 600 km) observations is reasonably high (R &approx; 0.8). The slope of the linear regression is close to unity. However, the maximum westward drift and the westward-to-eastward reversal occur earlier for CHAMP estimates than for ROCSAT-1 measurements. In the equatorial F region both zonal wind and plasma drift have the same direction. Both generate vertical currents but with opposite signs. The wind effect (F region wind dynamo) is generally larger in magnitude than the plasma drift effect (Pedersen current generated by vertical E field), thus determining the direction of the F region vertical current.

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Rabinovich, Alexander B., Georgy V. Shevchenko et Richard E. Thomson. « Sea Ice and Current Response to the Wind : A Vector Regressional Analysis Approach ». Journal of Atmospheric and Oceanic Technology 24, n^o 6 (juin 2007) : 1086–101. http://dx.doi.org/10.1175/jtech2015.1.

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The authors describe a two-dimensional (vector) regressional model for examining the anisotropic response of ice drift and ocean current velocity (“drift velocity”) to surface wind forcing. Illustration of the method is limited to sea ice response. The principal mathematical and physical properties of the model are outlined, together with estimates of the “response matrices” and the corresponding “response ellipses” (drift velocity response to a unity wind velocity forcing). For each direction, φ, of the wind vector the method describes a corresponding “wind factor” α(φ) (relative drift speed) and “turning angle” θ(φ) (the angle between the drift velocity and wind vector). The major ellipse axis corresponds to the direction of the “effective wind” (φ = φmax) and the minor axis to the direction of the “noneffective” wind. The eigenvectors of the response matrix define wind directions that are the same as the wind-induced drift velocity directions. Depending on the water depth and offshore distance, six analytical cases are possible, ranging from rectilinear response ellipses near the coast to purely circular response ellipses in the open ocean. The model is used to examine ice drift along the western shelf of Sakhalin Island (Sea of Okhotsk). Responses derived from the vector regression (four parameter) method are less constrained and therefore more representative of wind-induced surface motions than those derived using the traditional complex transfer function (two parameter) approach.

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Oppenheim, M. « Evidence and effects of a wave-driven nonlinear current in the equatorial electrojet ». Annales Geophysicae 15, n^o 7 (31 juillet 1997) : 899–907. http://dx.doi.org/10.1007/s00585-997-0899-z.

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Abstract. Ionospheric two-stream waves and gradient-drift waves nonlinearly drive a large-scale (D.C.) current in the E-region ionosphere. This current flows parallel to, and with a comparable magnitude to, the fundamental Pedersen current. Evidence for the existence and magnitude of wave-driven currents derives from a theoretical understanding of E-region waves, supported by a series of nonlinear 2D simulations of two-stream waves and by data collected by rocket instruments in the equatorial electrojet. Wave-driven currents will modify the large-scale dynamics of the equatorial electrojet during highly active periods. A simple model shows how a wave-driven current appreciably reduces the horizontally flowing electron current of the electrojet. This reduction may account for the observation that type-I radar echoes almost always have a Doppler velocity close to the acoustic speed, and also for the rocket observation that electrojet regions containing gradient-drift waves do not appear also to contain horizontally propagating two-stream waves. Additionally, a simple model of a gradient-drift instability shows that wave-driven currents can cause nonsinusoidal electric fields similar to those measured in situ.

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Browne, P. F. « Acceleration in the plasma focus and in astrophysics ». Laser and Particle Beams 6, n^o 3 (août 1988) : 409–20. http://dx.doi.org/10.1017/s0263034600005358.

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Both, in the laboratory (specifically the plasma focus) and in astrophysics, charges are accelerated in magnetically pinched current channels. The current channels are annular cylinders, defined by an electric double layer of thickness δrE and radius R due to radial polarization of the plasma. The electric field Er in the double layer and the azimuthal magnetic field Bϕ ensure drifts of charges in the axial direction, but ions do not take up the full drift velocity because their Larmor radius exceeds δrE. Magnetic pinching of the channel reduces the cross sectional area S, and an instability of drift velocity may denude a region of current channel. The inductively maintained current J then cannot be carried by free charges, even with relativistic drift velocity. A displacement current (S/4π) δEz/δt arises, Ez growing until all energy in Bϕ is transferred into Ez. During this transfer Bϕ decreases, so the pinch weakens, permitting discharge of accumulated space charge via a conduction current without reversal of J. Thereafter the cycle repeats quasi-periodically.In astrophysics acceleration occurs in a pinched magnetic vortex tube (MVT). The difference is that now Bϕ(r, +z) = −Bϕ(r, −z) due to winding of loops of field lines. Hence J reverses across mid-pinch, which implies accumulation of space charge of one sign at mid-pinch and of opposite sign at the ends of the pinch. Now there is reversal of J when the space charge relaxes.

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Jin, Jong W., et Yvan Bonnassieux. « Drift-Diffusion Analysis of Current Crowding Mechanism : Current-Dependent Series Resistance ». Journal of Display Technology 9, n^o 11 (novembre 2013) : 865–70. http://dx.doi.org/10.1109/jdt.2013.2247563.

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Fonseca, Nuno, et Fatemeh H. Dadmarzi. « A Wave Drift Force Model for Semi-Submersible Types of Floating Wind Turbines in Large Waves and Current ». Journal of Marine Science and Engineering 12, n^o 8 (14 août 2024) : 1389. http://dx.doi.org/10.3390/jmse12081389.

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The correct prediction of slowly varying wave drift loads is important for the mooring analysis of floating wind turbines (FWTs). However, present design analysis tools fail to correctly predict these loads in conditions with current and moderate and large waves. This paper presents a semi-empirical method to correct zero-current potential-flow quadratic transfer functions (QTFs) of horizontal wave drift loads in conditions with current and moderate and large waves. The method is applicable to column-stabilized types of substructures or semi-submersibles. In the first step, the potential-flow QTF is corrected for potential-flow wave–current effects by applying a heuristic method. Second, the generalized Exwave formula corrects for viscous drift effects. Viscous drift effects become important for moderate and large waves. Conditions with current in the same direction as the waves increase the viscous drift contribution further. The method is validated by comparing QTF predictions with empirical QTFs identified from model test data for the INO Windmoor semi. While potential-flow QTFs agree well with the empirical data for small seastates without current, they underestimate the wave drift loads for moderate and large seastates. Conditions with current increase the underestimation. The semi-empirical correction method significantly improves predictions.

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Palhares, Joao Henrique Quintino, Nikhil Garg, Yann Beilliard, Lorena Anghel, Fabien Alibart, Dominique Drouin et Philippe Galy. « Phase Change Memory Drift Compensation in Spiking Neural Networks Using a Non-Linear Current Scaling Strategy ». Journal of Low Power Electronics and Applications 14, n^o 4 (22 octobre 2024) : 50. http://dx.doi.org/10.3390/jlpea14040050.

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The non-ideality aspects of phase change memory (PCM) such as drift and resistance variability can pose significant obstacles in neuromorphic hardware implementations. A unique drift and variability compensation strategy is demonstrated and implemented in an FD-SOI SNN hardware unit composed of embedded phase change memories (ePCMs), current attenuators, and spiking neurons. The effect of drift and variability compensation on inference accuracy is tested on the MNIST dataset to show that our drift and variability mitigation strategy is effective in sustaining its accuracy over time. The variability is reduced by up to 5% while the drift coefficient is reduced by up to 57.8%. The drift is compensated and the SNN classification accuracy is sustained for up to 2 years with intrinsic control-free hardware that tracks the ePCM current over time and consumes less than 30 µW. The results are based on ePCM chip experimental data and pos-layout simulation of a test chip comprising the proposed circuit solution.

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Berthou, Maxime, Philippe Godignon, Pierre Brosselard, Dominique Tournier et José Millán. « Integration of Temperature and Current Sensors in 4H-SiC VDMOS ». Materials Science Forum 717-720 (mai 2012) : 1093–96. http://dx.doi.org/10.4028/www.scientific.net/msf.717-720.1093.

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Silicon Carbide VDMOS with integrated current and temperature sensors have been successfully fabricated without degradation of the chip forward or reverse characteristics due to the sensors. The temperature sensors show impedance correlated to the temperature, which permits to track the drift region’s temperature of the device. We have shown that the sensor current ratio can be influenced by the current spreading in the drift layer, especially when the channel resistance contribution is reduced. This aspect will be more critical on VDMOS with low channel resistance. Also, the sensor current ratio stability will be improved on devices with larger active area or thinner drift layer. Integration of such sensors will permit to monitor and protect innovative power electronic systems using SiC chips.

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Kim, Keunyong, Hong Thi My Tran, Kyu-Min Song, Yeong Baek Son, Young-Gyu Park, Joo-Hyung Ryu, Geun-Ho Kwak et Jun Myoung Choi. « Near-Surface Dispersion and Current Observations Using Dye, Drifters, and HF Radar in Coastal Waters ». Remote Sensing 16, n^o 11 (31 mai 2024) : 1985. http://dx.doi.org/10.3390/rs16111985.

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This study explores the near-surface dispersion mechanisms of contaminants in coastal waters, leveraging a comprehensive method that includes using dye and drifters as tracers, coupled with diverse observational platforms like drones, satellites, in situ sampling, and HF radar. The aim is to deepen our understanding of surface currents’ impact on contaminant dispersion, thereby improving predictive models for managing environmental incidents such as pollutant releases. Rhodamine WT dye, chosen for its significant fluorescent properties and detectability, along with drifter data, allowed us to investigate the dynamics of near-surface physical phenomena such as the Ekman current, Stokes drift, and wind-driven currents. Our research emphasizes the importance of integrating scalar tracers and Lagrangian markers in experimental designs, revealing differential dispersion behaviors due to near-surface vertical shear caused by the Ekman current and Stokes drift. During slow-current conditions, the elongation direction of the dye patch aligned well with the direction of a depth-averaged Ekman spiral, or Ekman transport. Analytical calculations of vertical shear, based on the Ekman current and Stokes drift, closely matched those derived from tracer observations. Over a 7 h experiment, the vertical diffusivity near the surface was first observed at the early stages of scalar mixing, with a value of 1.9×10−4 m2/s, and the horizontal eddy diffusivity of the dye patch and drifters reached the order of 1 m2/s at a 1000 m length scale. Particle tracking models demonstrate that while HF radar currents can effectively predict the trajectories of tracers near the surface, incorporating near-surface currents, including the Ekman current, Stokes drift, and windage, is essential for a more accurate prediction of the fate of surface floats.

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Zhou, Chihua, Xiaotong Lu, Benquan Lu, Yebing Wang et Hong Chang. « Demonstration of the Systematic Evaluation of an Optical Lattice Clock Using the Drift-Insensitive Self-Comparison Method ». Applied Sciences 11, n^o 3 (28 janvier 2021) : 1206. http://dx.doi.org/10.3390/app11031206.

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The self-comparison method is a powerful tool in the uncertainty evaluation of optical lattice clocks, but any drifts will cause a frequency offset between the two compared clock loops and thus lead to incorrect measurement result. We propose a drift-insensitive self-comparison method to remove this frequency offset by adjusting the clock detection sequence. We also experimentally demonstrate the validity of this method in a one-dimensional 87Sr optical lattice clock. As the clock laser frequency drift exists, the measured frequency difference between two identical clock loops is (240 ± 34) mHz using the traditional self-comparison method, while it is (−15 ± 16) mHz using the drift-insensitive self-comparison method, indicating that this frequency offset is cancelled within current measurement precision. We further use the drift-insensitive self-comparison technique to measure the collisional shift and the second-order Zeeman shift of our clock and the results show that the fractional collisional shift and the second-order Zeeman shift are 4.54(28) × 10−16 and 5.06(3) × 10−17, respectively.

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Li, Yong, Hui Li, Jian Wu, Xingbao Lv, Chengxun Yuan, Ce Li et Zhongxiang Zhou. « F-region drift current and magnetic perturbation distribution by the X-wave heating ionosphere ». Annales Geophysicae 41, n^o 2 (6 décembre 2023) : 541–49. http://dx.doi.org/10.5194/angeo-41-541-2023.

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Abstract. We present a theoretical and numerical study of the drift current and magnetic perturbation model in the ionosphere by incorporating the ohmic heating model and the magnetohydrodynamic (MHD) momentum equation. Based on these equations, the ionospheric electron temperature and drift current are investigated. The results indicate that the maximum change in electron temperature ΔTe is about 570 K, and the ratio is ΔTe/Te ∼ 48 %. The maximum drift current density is 8×10-10 A m−2, and its surface integral is 5.76 A. Diamagnetic drift current is the main form of current. The low collision frequency between charged particles and neutral particles has little effect on the current, and the collision frequency of electrons and ions is independent of the drift current. The current density profile is a flow ring. We present the effective conductivity as a function of the angle between the geomagnetic field and the radio wave; the model explains why the radiation efficiency was strongest when the X wave is heating along the magnetic dip angle, as reported in recent observations by Kotik et al. (2013). We calculate the magnetic field variation in the heating region based on the MHD theory: the results show that the maximum magnetic field perturbation in the heating area is 48 pT.

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Shevchenko, Georgy V., Alexander B. Rabinovich et Richard E. Thomson. « Sea-Ice Drift on the Northeastern Shelf of Sakhalin Island ». Journal of Physical Oceanography 34, n^o 11 (1 novembre 2004) : 2470–91. http://dx.doi.org/10.1175/jpo2632.1.

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Abstract Ice-drift velocity records from coastal radar stations, combined with data from moored current meters and coastal wind stations, are used to examine sea-ice motion off the northeastern coast of Sakhalin Island in the Sea of Okhotsk. Ice motion is shown to be governed primarily by diurnal tidal currents and wind-induced drift, which explain 92%–95% of the total ice-drift variance. Diurnal tidal motions predominate off the northern Sakhalin coast, accounting for 65%–80% of the variance, while low-frequency wind-induced motions prevail off the south-central coast, accounting for over 91% of the ice-drift variance. Maximum diurnal tidal ice-drift velocities range from 90–110 cm s−1 on the north coast to 10–15 cm s−1 on the south coast, in good agreement with the barotropic model of Kowalik and Polyakov. The presence of diurnal shelf waves accounts for the strong diurnal currents on the steeply sloping northern Sakhalin shelf, while the absence of such waves explains the weak diurnal currents on the more gently sloping south-central shelf. Using a vector regression model, the authors show that wind-induced ice-drift “response ellipses” (the current velocity response to a unity wind-velocity forcing) are consistent with a predominantly alongshore response to the wind, with wind-induced currents most pronounced off the south-central coast where water depths are relatively shallow. Time–frequency analysis of wind and ice-drift series reveals that, in winter, when sea ice is most extensive and internally cohesive, the ice response is almost entirely aligned with the alongshore component of the wind; in spring, when sea ice is broken and patchy, the ice responds to both the cross- and alongshore components of the wind.

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SHAIKHISLAMOV, I. F. « MHD analysis of the current-driven flute instability of a plasma ». Journal of Plasma Physics 68, n^o 1 (juillet 2002) : 59–73. http://dx.doi.org/10.1017/s0022377802001782.

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The lower-hybrid drift instability of a plasma driven by relative ion–electron motion is analyzed in the framework of the modified magnetohydrodynamic equations. The Hall contribution is expressed in terms that offer a simple physical interpretation of the process and allow a comprehensive study of various features and limits of instability. It is shown that in the chosen terms there are clear-cut ranges of magnetosonic drift, lower-hybrid drift, and kinetic versions of instability that have different properties. It is shown for the first time that the instability may have, besides a flute-like structure, a cell-like one as well. On the basis of the performed analysis, a new classification of the phenomenon is offered.

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Morgado, Tiago A., et Mário G. Silveirinha. « Active Graphene Plasmonics with a Drift-Current Bias ». ACS Photonics 8, n^o 4 (7 avril 2021) : 1129–36. http://dx.doi.org/10.1021/acsphotonics.0c01890.

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Gladd, N. T., et N. A. Krall. « Current-driven drift waves in reversed field pinches ». Physics of Fluids 29, n^o 5 (1986) : 1640. http://dx.doi.org/10.1063/1.865681.

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Yoon, P. H., et A. T. Y. Lui. « Drift instabilities in current sheets with guide field ». Physics of Plasmas 15, n^o 7 (juillet 2008) : 072101. http://dx.doi.org/10.1063/1.2938386.

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Bour, D. P., D. W. Treat, R. L. Thornton, R. S. Geels et D. F. Welch. « Drift leakage current in AlGaInP quantum-well lasers ». IEEE Journal of Quantum Electronics 29, n^o 5 (mai 1993) : 1337–43. http://dx.doi.org/10.1109/3.236147.

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Blanvillain, Sylvain, Alina Voda, Gildas Besancon et Gabriel Buche. « Subnanometer Positioning and Drift Compensation With Tunneling Current ». IEEE Transactions on Control Systems Technology 22, n^o 1 (janvier 2014) : 180–89. http://dx.doi.org/10.1109/tcst.2013.2248364.

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Smith, Stuart D. « Hindcasting iceberg drift using current profiles and winds ». Cold Regions Science and Technology 22, n^o 1 (novembre 1993) : 33–45. http://dx.doi.org/10.1016/0165-232x(93)90044-9.

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Stránský, M. « Comparison of drift current and MHD plasma models ». Czechoslovak Journal of Physics 54, S3 (mars 2004) : C143—C149. http://dx.doi.org/10.1007/bf03166393.

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Тандоев, А. Г., Т. Т. Мнацаканов et С. Н. Юрков. « Мощные диоды Шоттки с участком отрицательного дифференциального сопротивления на вольт-амперной характеристике ». Физика и техника полупроводников 55, n^o 1 (2021) : 75. http://dx.doi.org/10.21883/ftp.2021.01.50390.9521.

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It is shown that at high current densities the carrier transport in base layer of Schottky diodes in addition to commonly accepted diffusive and drift currents is defined by recently discovered diffusion stimulated by quasi-neutral drift (DSQD). The influence of this recently discovered component of current on current-voltage characteristics of Schottky diode has been investigated. It was shown that in case if the ratio of base width $W$ to ambipolar diffusive length $L$ is higher than 1 ($W/L>1$) a part with negative differential resistance appears on the current-voltage characteristics of Schottky diode. The results of analytical investigation are confirmed by numerical calculation using INVESTIGATION program.

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Ivanova, I. N., et O. N. Melnikova. « Drift flow on the water surface with a film of hydrophobic particles in a uniform and decelerating air flow ». Seriya 3 : Fizika, Astronomiya, n^o 4_2023 (20 septembre 2023) : 2340902–1. http://dx.doi.org/10.55959/msu0579-9392.78.2340902.

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The effect of a film of hydrophobic dust particles on the water surface on the development of a drift current under the influence of wind is studied. In a uniform air flow on a flat water surface, the drift current is caused by viscous forces and increases along the fetch. The formation of stationary waves on a drift current is found if the drift velocity is 𝑈𝑑𝑟> 0.23 m/s. In a decelerating air flow in the presence of wind waves, the total component of the drift velocity 𝑈𝑠𝑢𝑚 cyclically increases and drops to a viscous component when a steep wind wave breaks up into longer linear waves. As the particle settling time Ts increases, the maximum ratio 𝑈𝑤/𝑈𝑠𝑢𝑚 decreases from 0.6 for pure water to 0.3 for Ts = 4 days

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PHILLIPS, W. R. C., A. DAI et K. K. TJAN. « On Lagrangian drift in shallow-water waves on moderate shear ». Journal of Fluid Mechanics 660 (16 juillet 2010) : 221–39. http://dx.doi.org/10.1017/s0022112010002648.

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The Lagrangian drift in anO(ϵ) monochromatic wave field on a shear flow, whose characteristic velocity isO(ϵ) smaller than the phase velocity of the waves, is considered. It is found that although shear has only a minor influence on drift in deep-water waves, its influence becomes increasingly important as the depth decreases, to the point that it plays a significant role in shallow-water waves. Details of the shear flow likewise affect the drift. Because of this, two temporal cases common in coastal waters are studied, viz. stress-induced shear, as would arise were the boundary layer wind-driven, and a current-driven shear, as would arise from coastal currents. In the former, the magnitude of the drift (maximum minus minimum) in shallow-water waves is increased significantly above its counterpart, viz. the Stokes drift, in like waves in otherwise quiescent surroundings. In the latter, on the other hand, the magnitude decreases. However, while the drift at the free surface is always oriented in the direction of wave propagation in stress-driven shear, this is not always the case in current-driven shear, especially in long waves as the boundary layer grows to fill the layer. This latter finding is of particular interest vis-à-vis Langmuir circulations, which arise through an instability that requires differential drift and shear of the same sign. This means that while Langmuir circulations form near the surface and grow downwards (top down), perhaps to fill the layer, in stress-driven shear, their counterparts in current-driven flows grow from the sea floor upwards (bottom up) but can never fill the layer.

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Pudsey, Carol J., et Angelo Camerlenghi. « Glacial–interglacial deposition on a sediment drift on the Pacific margin of the Antarctic Peninsula ». Antarctic Science 10, n^o 3 (septembre 1998) : 286–308. http://dx.doi.org/10.1017/s0954102098000376.

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On the continental rise west of the Antarctic Peninsula there are nine large mounds interpreted as sediment drifts, separated by turbidity current channels. Drift 7 is 150 km long, 70 km wide and up to 700 m high and is asymmetric, with steep sides on the south-east (towards the continent) and south-west, and gentle slopes to north-west and north-east. Cores on the gentle sides of the drift show a cyclicity between brown, bioturbated, diatom-bearing mud with foraminifera and radiolarians, and grey, laminated, barren mud. Biostratigraphic evidence is consistent with a Late Quatermary age. Detailed lithostratigraphy and magnetic susceptibility data allow precise correlation over distances of tens of kilometres. On the basis of chemostratigraphy, the brown sediment is interpreted as interglacial (isotope stages 1 and 5) and the grey as glacial (stages 2–4 and 6). Sedimentation rates are 3.0–5.5 cm ka-1. Cores on the steep sides of the drift recovered a condensed section with thinner cycles and hiatuses. Fine grain size, very poor sorting and the absence of a mode in the silt size range indicate deposition from suspension with only weak current activity. There is little evidence for cyclic changes in bottom current strength. Supply of sediment to the benthic nepheloid layer was by entrainment of mud from turbidity currents, and by setting of pelagic material (biogenic grains, IRD, sediment suspended in meltwater plumes). Cyclic changes in sediment supply include more biogenic supply in interglacials with less sea ice cover, more terrigenous supply from turbidites in glacials with ice sheets grounded to the shelf edge, and changes in IRD content

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He, Ping, YunKai Ma et Hui Chen. « Temperature Drift Compensation of Eddy Current Sensor under High Temperature Environment ». E3S Web of Conferences 38 (2018) : 04005. http://dx.doi.org/10.1051/e3sconf/20183804005.

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Eddy current sensor is an sensor based on eddy current effect. In practical engineering applications, the ambient temperature of eddy current sensor may be up to 135 ℃. The temperature drift of eddy current sensor magnifies the error of displacement detection. In this paper, the main factors that cause temperature drift are analyzed in detail, and the results show that the compensation based on single parameter can not meet the demand of high-precision measurement. For this reason, this paper proposes an external compensation method which applies mathematical fitting to realize compensation for temperature drift. The experimental results show that the measurement accuracy of the external compensation method reaches 0.25% in the working temperature range, which greatly improves the measurement accuracy of eddy current sensor under high temperature.

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Barddal, Jean Paul, Heitor Murilo Gomes et Fabrício Enembreck. « Advances on Concept Drift Detection in Regression Tasks Using Social Networks Theory ». International Journal of Natural Computing Research 5, n^o 1 (janvier 2015) : 26–41. http://dx.doi.org/10.4018/ijncr.2015010102.

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Mining data streams is one of the main studies in machine learning area due to its application in many knowledge areas. One of the major challenges on mining data streams is concept drift, which requires the learner to discard the current concept and adapt to a new one. Ensemble-based drift detection algorithms have been used successfully to the classification task but usually maintain a fixed size ensemble of learners running the risk of needlessly spending processing time and memory. In this paper the authors present improvements to the Scale-free Network Regressor (SFNR), a dynamic ensemble-based method for regression that employs social networks theory. In order to detect concept drifts SFNR uses the Adaptive Window (ADWIN) algorithm. Results show improvements in accuracy, especially in concept drift situations and better performance compared to other state-of-the-art algorithms in both real and synthetic data.

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Lapenta, G., et J. U. Brackbill. « 3D reconnection due to oblique modes : a simulation of Harris current sheets ». Nonlinear Processes in Geophysics 7, n^o 3/4 (31 décembre 2000) : 151–58. http://dx.doi.org/10.5194/npg-7-151-2000.

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Abstract. Simulations in three dimensions of a Harris current sheet with mass ratio, mi/me = 180, and current sheet thickness, pi/L = 0.5, suggest the existence of a linearly unstable oblique mode, which is independent from either the drift-kink or the tearing instability. The new oblique mode causes reconnection independently from the tearing mode. During the initial linear stage, the system is unstable to the tearing mode and the drift kink mode, with growth rates that are accurately described by existing linear theories. How-ever, oblique modes are also linearly unstable, but with smaller growth rates than either the tearing or the drift-kink mode. The non-linear stage is first reached by the drift-kink mode, which alters the initial equilibrium and leads to a change in the growth rates of the tearing and oblique modes. In the non-linear stage, the resulting changes in magnetic topology are incompatible with a pure tearing mode. The oblique mode is shown to introduce a helical structure into the magnetic field lines.

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Bakerenkov, A. S., V. S. Pershenkov, A. V. Solomatin, V. V. Belyakov et V. V. Shurenkov. « Radiation Degradation Modeling of Bipolar Operational Amplifier Input Offset Voltage in LTSpice IV ». Applied Mechanics and Materials 565 (juin 2014) : 138–41. http://dx.doi.org/10.4028/www.scientific.net/amm.565.138.

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Integrated circuits are used in electronic equipment of spaceships. Therefore, they are impacted by ionizing radiation during space mission. It leads to electronic equipment failures. At present operational amplifiers are base elements of analog electronic devices. Radiation impact leads to degradation of operational amplifiers input stages. Input bias current increasing and input offset voltage drifts are the results of ionizing radiation expose of operational amplifiers. Therefore, space application electronic equipment fails after accumulation of limit dose. It isn’t difficult to estimate radiation degradation of input bias currents of bipolar operational amplifiers, but estimation of dose dependence of input offset voltage drift is more complex issue. Schematic modeling technique based on Gummel–Poon transistor model for estimation of input offset voltage drift produced by space radiation impact was experimentally verified for LM324 operational amplifier and presented in this work. Radiation sensitive parameters of Gummel–Poon model were determined using 2N2907 bipolar pnp transistor.

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