Статті в журналах: "Currents fluctuations"

1

Nazarov, Yuli V. "Mesoscopic fluctuations of spin currents." New Journal of Physics 9, no. 9 (September 28, 2007): 352. http://dx.doi.org/10.1088/1367-2630/9/9/352.

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2

Deguchi, Ichiro, Mamoru Arita, and Takumi Yoshii. "FLUCTUATION OF RIP CURRENT MEASURED IN SHALLOW WATER REGION WITH SMALL TIDAL RANGE." Coastal Engineering Proceedings 1, no. 32 (January 25, 2011): 44. http://dx.doi.org/10.9753/icce.v32.currents.44.

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Disappearance and formation processes of rip channel are discussed based on the field measurements of wave height, current velocity, bottom topography and flow pattern of near-shore current. Sudden increase in wave height together with the change in the wave direction took place during a half day caused these phenomena and rip current rose and fell according to the transition of the bottom topography. Furthermore, flow pattern of rip current was not steady but transformed itself with low frequency fluctuations of the period of few minutes. It is found that such low frequency fluctuations are caused by the intrinsic fluctuations of the incident waves (grouping waves) through the numerical simulations.

3

Kim, Jae-Chang, and Sang-Shin Kwak. "Frequency-Domain Characteristics of Series DC Arcs in Photovoltaic Systems with Voltage-Source Inverters." Applied Sciences 10, no. 22 (November 13, 2020): 8042. http://dx.doi.org/10.3390/app10228042.

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In this study, the frequency characteristics of series DC arcs are analyzed according to the types of frequency fluctuations caused by inverters in photovoltaic (PV) systems. These frequency fluctuation types used in analysis include centralized frequency fluctuations by three-phase inverter, spread frequency fluctuations by three-phase inverter, and centralized frequency fluctuations by single-phase inverter. To collect arc current data, the frequency fluctuations are generated by inverters in the arc-generating circuit, designed by referring to UL1699B, and the arcs are generated by separating the arc rods of the arc generator. The frequency analysis of the arc current data, collected using an oscilloscope, is conducted using MATLAB. From the results of the frequency characteristics analysis, it is confirmed that the frequencies in the range from 5 to 40 kHz increase after arc generation regardless of the type of frequency fluctuation. In addition, the smaller the current, the greater the increase in frequencies between 5 and 40 kHz after arc generation. Further, in case of arc currents with centralized frequency fluctuations, for larger switching frequencies, the 5 to 40 kHz components increase to a greater extent after arcing.

4

González-Haro, Cristina, Aurélien Ponte, and Emmanuelle Autret. "Quantifying Tidal Fluctuations in Remote Sensing Infrared SST Observations." Remote Sensing 11, no. 19 (October 4, 2019): 2313. http://dx.doi.org/10.3390/rs11192313.

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The expected amplitude of fixed-point sea surface temperature (SST) fluctuations induced by barotropic and baroclinic tidal flows is estimated from tidal current atlases and SST observations. The fluctuations considered are the result of the advection of pre-existing SST fronts by tidal currents. They are thus confined to front locations and exhibit fine-scale spatial structures. The amplitude of these tidally induced SST fluctuations is proportional to the scalar product of SST frontal gradients and tidal currents. Regional and global estimations of these expected amplitudes are presented. We predict barotropic tidal motions produce SST fluctuations that may reach amplitudes of 0.3 K. Baroclinic (internal) tides produce SST fluctuations that may reach values that are weaker than 0.1 K. The amplitudes and the detectability of tidally induced fluctuations of SST are discussed in the light of expected SST fluctuations due to other geophysical processes and instrumental (pixel) noise. We conclude that actual observations of tidally induced SST fluctuations are a challenge with present-day observing systems.

5

Suo, Yuchen, Xinda Song, Zhendong Wu, Ziqi Yuan, Le Jia, and Tengyue Long. "Light-noise suppression method for the single-beam optically-pumped magnetometer arrays." Optics Express 31, no. 13 (June 9, 2023): 21280. http://dx.doi.org/10.1364/oe.489172.

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We propose a miniaturized single-beam optically pumped magnetometer (OPM) with a laser power differential structure, along with a dynamically-adjusted detection circuit. This design enables the suppression of optical fluctuation noise and the enhancement of magnetometer sensitivity. For a single-beam OPM, pump light fluctuation noise is a significant contributor to output noise. To address this, we propose an OPM with a laser differential structure that separates the pump light as a part of the reference signal before it enters the cell. The reference current and OPM output current are then subtracted to suppress the noise introduced by pump light fluctuations. To achieve optimal optical noise suppression, we implement balanced homodyne detection (BHD) with real-time current adjustment, which dynamically adjusts the reference ratio between the two currents according to their amplitude. Ultimately, we can reduce the noise introduced by pump light fluctuations by 47% of the original. The OPM with laser power differential achieves a sensitivity of 17.5 fT/Hz1/2, with the optical fluctuation equivalent noise at 13 fT/Hz1/2.

6

Wirth, Achim, and Bertrand Chapron. "Empirical evidence of a fluctuation theorem for the wind mechanical power input into the ocean." Nonlinear Processes in Geophysics 28, no. 3 (August 4, 2021): 371–78. http://dx.doi.org/10.5194/npg-28-371-2021.

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Abstract. Ocean dynamics is predominantly driven by the shear stress between the atmospheric winds and ocean currents. The mechanical power input to the ocean is fluctuating in space and time and the atmospheric wind sometimes decelerates the ocean currents. Building on 24 years of global satellite observations, the input of mechanical power to the ocean is analysed. A fluctuation theorem (FT) holds when the logarithm of the ratio between the occurrence of positive and negative events, of a certain magnitude of the power input, is a linear function of this magnitude and the averaging period. The flux of mechanical power to the ocean shows evidence of a FT for regions within the recirculation area of the subtropical gyre but not over extensions of western boundary currents. A FT puts a strong constraint on the temporal distribution of fluctuations of power input, connects variables obtained with different lengths of temporal averaging, guides the temporal down- and up-scaling and constrains the episodes of improbable events.

7

Petržílka, V., and B. Balescu. "Toroidal currents and radial transport driven by ponderomotive forces of fluctuations in a plasma." Journal of Plasma Physics 53, no. 3 (June 1995): 277–84. http://dx.doi.org/10.1017/s0022377800018201.

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Non-resonant ponderomotive force theory is applied to fluctuating electromagnetic fields in a plasma. Bootstrap-type relations between the radial transport velocity and the toroidal current driven by fluctuations are also discussed in the case of non-zero ponderomotive forces proportional to d/dr. A special case of fluctuating fields as measured in the SHEILA heliac is discussed.

8

Yoshioka, Hideo, and Hidetoshi Fukuyama. "Fluctuations of Josephson Currents and Persistent Currents in Mesoscopic Spin Glass Systems." Journal of the Physical Society of Japan 62, no. 2 (February 15, 1993): 612–23. http://dx.doi.org/10.1143/jpsj.62.612.

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9

Gargett, Ann E., and Dana K. Savidge. "Separation of Short Time Series of Currents into “Fluctuations,” “Tides,” and “Mean” Flow." Journal of Atmospheric and Oceanic Technology 33, no. 5 (May 2016): 1089–95. http://dx.doi.org/10.1175/jtech-d-15-0232.1.

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AbstractWith standard low-frequency velocity data from current meter moorings, pressure gradient–driven mean flow is determined by low-pass filtering, while tides are estimated by fitting tidal constituents, with accuracy and numbers of constituents determined by record length. With the advent of higher-frequency measurements from cabled coastal ocean observatories, current data also include supertidal variability (fluctuation) associated with a variety of turbulent and internal wave processes. To examine the relationships of such fluctuations to variability of the tides and/or potentially time-variable mean flows within which they are embedded, it is highly desirable to find a method whereby these flow components can be separated over relatively short periods of intensified event-scale forcing. A method is presented that first isolates “fluctuations” and then separates the remaining longer time-scale variability into “tides” and a remaining “mean,” without recourse to extraction of a fitted tide with the error inherent in such a fit over short data records.

10

Eckern, Ulrich, and Albert Schmid. "Stochastic fluctuations of persistent currents in mesoscopic rings." Annalen der Physik 505, no. 2 (1993): 180–200. http://dx.doi.org/10.1002/andp.19935050209.

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11

Kreeger, Lauren J., Arslaan Arshed, and Katrina M. MacLeod. "Intrinsic firing properties in the avian auditory brain stem allow both integration and encoding of temporally modulated noisy inputs in vitro." Journal of Neurophysiology 108, no. 10 (November 15, 2012): 2794–809. http://dx.doi.org/10.1152/jn.00092.2012.

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The intrinsic properties of tonically firing neurons in the cochlear nucleus contribute to representing average sound intensity by favoring synaptic integration across auditory nerve inputs, reducing phase locking to fine temporal acoustic structure and enhancing envelope locking. To determine whether tonically firing neurons of the avian cochlear nucleus angularis (NA) resemble ideal integrators, we investigated their firing responses to noisy current injections during whole cell patch-clamp recordings in brain slices. One subclass of neurons (36% of tonically firing neurons, mainly subtype tonic III) showed no significant changes in firing rate with noise fluctuations, acting like pure integrators. In contrast, many tonically firing neurons (>60%, mainly subtype tonic I or II) showed a robust sensitivity to noisy current fluctuations, increasing their firing rates with increased fluctuation amplitudes. For noise-sensitive tonic neurons, the firing rate vs. average current curves with noise had larger maximal firing rates, lower gains, and wider dynamic ranges compared with FI curves for current steps without noise. All NA neurons showed fluctuation-driven patterning of spikes with a high degree of temporal reliability and millisecond spike time precision. Single-spiking neurons in NA also responded to noisy currents with higher firing rates and reliable spike trains, although less precisely than nucleus magnocellularis neurons. Thus some NA neurons function as integrators by encoding average input levels over wide dynamic ranges regardless of current fluctuations, others detect the degree of coherence in the inputs, and most encode the temporal patterns contained in their inputs with a high degree of precision.

12

Busta, H. H. "Scaling of emission currents and of current fluctuations of gated silicon emitter ensembles." Journal of Vacuum Science & Technology B: Microelectronics and Nanometer Structures 12, no. 2 (March 1994): 689. http://dx.doi.org/10.1116/1.587371.

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13

Kijima, H., K. Nagata, A. Nishiyama, and H. Morita. "Receptor current fluctuation analysis in the labellar sugar receptor of the fleshfly." Journal of General Physiology 91, no. 1 (January 1, 1988): 29–47. http://dx.doi.org/10.1085/jgp.91.1.29.

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Fluctuations in the receptor current of the labellar sugar receptor of the fleshfly were analyzed. The receptor current was recorded extracellularly as a drop in potential between the tip and the base of the taste sensillum. After treatment with tetrodotoxin, the taste cells completely lost their impulses but retained their receptor currents, thus facilitating analysis of the receptor current without disturbance by impulses. The current fluctuation increased markedly when the sensillum was stimulated with effective sugars: maltose, sucrose, and fructose. The fluctuation increased in parallel with development of the receptor current, which indicates that it occurs as soon as the sugar reaches the apex of the sensory process. Analysis of fluctuations by computation of autocorrelation functions (ACFs) or power spectra (PS) revealed that: (a) the variance (mean square) of fluctuation vs. sugar concentration curve reached a maximum, in contrast to the monotonic increase shown by the receptor current; (b) the ACF was approximated by an exponential term, and its time constant differed according to the sugars used and their concentrations. The time constants for fructose and maltose decreased with increases in sugar concentration. At the concentrations of sugars evoking the same magnitude of receptor current, the time constant for fructose was the largest and that for maltose was the smallest. It was strongly suggested that transduction ion channels are present at the tip region of the sensory process of the sugar receptor cell and are operated directly by sugars.

14

Petrenko, Olexandr, Viktor Pererva, and Viktor Maslov. "Detection of the magnetic field parameters influence on discharge current fluctuations and optimal operation modes of the hall thruster." Eastern-European Journal of Enterprise Technologies 3, no. 5 (123) (June 30, 2023): 43–51. http://dx.doi.org/10.15587/1729-4061.2023.282059.

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The object of research reported in this work is the fluctuations of the discharge current in Hall thrusters. The presence of significant fluctuations in the discharge current in Hall thrusters causes a significant deterioration of the thruster parameters – thrust, specific impulse, and efficiency. The task addressed in the current work relates to determining the main factors that affect the conditions for the occurrence of discharge current fluctuations, finding ways to reduce them, and obtaining optimal values of the parameters of the Hall thruster. The review of literary sources revealed that the specified problem is typical and has not yet been solved. In order to solve this problem, studies of the ST-40M Hall thruster were carried out in order to determine the main factors that have the greatest influence on the occurrence of oscillations and means of reducing the oscillations of the discharge current. The result of the research determined that the fluctuations of the discharge current depend most significantly on the parameters of the magnetic field in the acceleration channel of the thruster. The parameters of the magnetic field are determined by the magnitude of the currents of the thruster electromagnet coils, and the nature of oscillations, amplitude, and frequency may differ significantly with a slight change in the coil currents. As a result of the study, it was found that for the values of the currents of the coils of the magnetic system of the thruster, for which the level of fluctuations of the discharge current is minimal, the average value of the discharge current of the thruster also takes a minimum value. The research made it possible to determine the optimal operating modes of the Hall thruster, which ensure, at a given level of specific power, the maximum values of thrust, specific impulse, and thruster efficiency. The conclusions from the study could be useful for most developers of electric propulsion systems based on Hall thrusters

15

Marchaudon, A., J. C. Cerisier, J. M. Bosqued, C. J. Owen, A. N. Fazakerley, and A. D. Lahiff. "On the structure of field-aligned currents in the mid-altitude cusp." Annales Geophysicae 24, no. 12 (December 21, 2006): 3391–401. http://dx.doi.org/10.5194/angeo-24-3391-2006.

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Abstract. We analyse two crossings of the polar cusp at mid-altitudes (≈4 RE) by Cluster in order to study the structure of field-aligned currents associated with the injection of magnetosheath plasma. The current density is deduced independently from magnetic field and from particle flux measurements. In both cases the data are carefully tested. Magnetic fluctuations are analysed by discriminating between those compatible with the plane current sheet hypothesis under which the current density can be calculated safely, and those resulting from filamentary current structures. At medium transverse scales (80 km), the structure of the currents is more often tube-like than sheet-like, and current sheets are not systematically elongated in the east-west direction. The total particle current is calculated from the electron and ion measurements. For electrons, the full energy range is taken into account, from above the photoelectron threshold up to 32 keV. Magnetosheath plasma injections are well correlated with pairs of field-aligned currents. In both cases, the parallel current is mainly carried by electrons while ions contribute for about 20%. In the plane current sheets, the ratio between magnetic and particle currents shows large variations between 0.4 and 1.1. These fluctuations can be explained by the convective motion of the current sheets.

16

Cho, B., T. Ishikawa, and C. Oshima. "Fluctuations of Field Emission Currents under Extreme High Vacuum." e-Journal of Surface Science and Nanotechnology 6 (2008): 64–67. http://dx.doi.org/10.1380/ejssnt.2008.64.

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17

Dereziński, Jan, Wojciech De Roeck, and Christian Maes. "Fluctuations of Quantum Currents and Unravelings of Master Equations." Journal of Statistical Physics 131, no. 2 (February 15, 2008): 341–56. http://dx.doi.org/10.1007/s10955-008-9500-8.

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18

Zverevich, Dmitry, and Alex Levchenko. "Transport signatures of plasmon fluctuations in electron hydrodynamics." Low Temperature Physics 49, no. 12 (December 1, 2023): 1376–84. http://dx.doi.org/10.1063/10.0022363.

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In two-dimensional electron systems, plasmons are gapless and long-lived collective excitations of propagating charge density oscillations. We study the fluctuation mechanism of plasmon-assisted transport in the regime of electron hydrodynamics. We consider pristine electron liquids where charge fluctuations are thermally induced by viscous stresses and intrinsic currents, while attenuation of plasmons is determined by the Maxwell mechanism of charge relaxation. It is shown that, while the contribution of plasmons to the shear viscosity and thermal conductivity of a Fermi liquid is small, plasmon resonances in the bilayer devices enhance the drag resistance. In systems without Galilean invariance, fluctuation-driven contributions to dissipative coefficients can be described only in terms of hydrodynamic quantities: intrinsic conductivity, viscosity, and plasmon dispersion relation.

19

Sui, J. L., and C. Y. Kao. "Roles of outward potassium currents in the action potentials of guinea pig ureteral myocytes." American Journal of Physiology-Cell Physiology 273, no. 3 (September 1, 1997): C962—C972. http://dx.doi.org/10.1152/ajpcell.1997.273.3.c962.

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Outward currents of freshly dissociated ureteral myocytes consist mainly of Ca(2+)-activated K+ current (IKCa) and a transient outward current (ITO). No delayed rectifier current was apparent. IKCa is small and nondecaying and fluctuates actively and irregularly. Blocking IKCa decreased resting membrane conductance and prolonged action potential plateaus, showing its roles in maintaining the resting potential and in repolarizing action potentials. It is also responsible for the membrane potential fluctuations on action potential plateaus. Neither 8-(diethylamino)octyl-3,4,5-trimethoxybenzoate hydrochloride nor caffeine reduced the fluctuations in the outward current or in the action potentials, indicating that internal Ca2+ storage contributes little to the fluctuations. ITO has fast activation and inactivation kinetics with inactivation time constants of approximately 15 and 150 ms, respectively. Its highly negative voltage-availability relationship (V0.5 = -70.5 mV) suggests a low availability (< 5%) at normal resting potentials. It has only trivial effects on action potentials.

20

Kuznetsov, A. I. "Influence of contact network voltage fluctuations on current transients in the electric locomotive power circuit." Herald of the Ural State University of Railway Transport, no. 2 (2022): 32–40. http://dx.doi.org/10.20291/2079-0392-2022-2-32-40.

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The statistics of electric arc transfers along the collector of traction electric motors of the 2ES6 electric locomotive for 2020 are given. It is noted that half of the failures are associated with a potential spark on the collector, which indicates increased armature currents in the electric locomotive power circuit. The given voltage curve of the contact network also indicates that the power circuit is subject to constant current fluctuations. In the model of the power circuit of the 2ES6 electric locomotive, the mechanical component of the drive has been modified. It takes into account the resistance to train movement on one of the difficult sections of the Sverdlovsk Sabik - Sarga railway, as well as the inertia of the rotating parts of the 2ES6 electric locomotive and four-axle freight gondolas. The effect of voltage fluctuations in the contact network on current transients at different values of the maximum excitation voltage has been modelled. It is established that with the increase in the excitation voltage, the amplitudes of the armature current and the excitation current decrease, the duration of exceeding the currents of their limit value decreases. With voltage fluctuations up to 200 V, the armature current and the excitation current in the power circuit of the 2ES6 electric locomotive are in the range of their limit values with the increased value of the maximum excitation voltage of 120 V. With voltage fluctuations of more than 200 V, it is advisable to use low pass input filters.

21

Doblin, Martina A., and Erik van Sebille. "Drift in ocean currents impacts intergenerational microbial exposure to temperature." Proceedings of the National Academy of Sciences 113, no. 20 (May 2, 2016): 5700–5705. http://dx.doi.org/10.1073/pnas.1521093113.

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Microbes are the foundation of marine ecosystems [Falkowski PG, Fenchel T, Delong EF (2008) Science 320(5879):1034–1039]. Until now, the analytical framework for understanding the implications of ocean warming on microbes has not considered thermal exposure during transport in dynamic seascapes, implying that our current view of change for these critical organisms may be inaccurate. Here we show that upper-ocean microbes experience along-trajectory temperature variability up to 10 °C greater than seasonal fluctuations estimated in a static frame, and that this variability depends strongly on location. These findings demonstrate that drift in ocean currents can increase the thermal exposure of microbes and suggests that microbial populations with broad thermal tolerance will survive transport to distant regions of the ocean and invade new habitats. Our findings also suggest that advection has the capacity to influence microbial community assemblies, such that regions with strong currents and large thermal fluctuations select for communities with greatest plasticity and evolvability, and communities with narrow thermal performance are found where ocean currents are weak or along-trajectory temperature variation is low. Given that fluctuating environments select for individual plasticity in microbial lineages, and that physiological plasticity of ancestors can predict the magnitude of evolutionary responses of subsequent generations to environmental change [Schaum CE, Collins S (2014) Proc Biol Soc 281(1793):20141486], our findings suggest that microbial populations in the sub-Antarctic (∼40°S), North Pacific, and North Atlantic will have the most capacity to adapt to contemporary ocean warming.

22

GONZALEZ-JUEZ, E., E. MEIBURG, and G. CONSTANTINESCU. "Gravity currents impinging on bottom-mounted square cylinders: flow fields and associated forces." Journal of Fluid Mechanics 631 (July 17, 2009): 65–102. http://dx.doi.org/10.1017/s0022112009006740.

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The unsteady drag and lift generated by the interaction of a gravity current with a bottom-mounted square cylinder are investigated by means of high-resolution Navier–Stokes simulations. Two-dimensional simulations for Reynolds numbers (Re) O(1000) and three-dimensional simulations for Re = O(10000) demonstrate that the drag coefficient increases exponentially towards a maximum as the current meets the cylinder, then undergoes strong fluctuations and eventually approaches a quasi-steady value. The simulation results show that the maximum drag coefficient can reach a value of 3, with the quasi-steady value being O(1), which should aid in selecting a design drag coefficient for submarine structures under the potential impact of gravity currents. The transient drag and lift fluctuations after impact are associated with the Kelvin–Helmholtz vortices in the mixing layer between the gravity current and the ambient fluid. As these vortices pass over the cylinder, they cause the convection of separated flow regions along the bottom wall towards the cylinder. In two-dimensional simulations at Re = O(10000), these flow structures are seen to be unrealistically coherent and to persist throughout the interaction, thus resulting in a noticeable overprediction of the drag and lift fluctuations. On the other hand, the impact of the current on the cylinder is seen to be very well captured by two-dimensional simulations at all Re values. Three-dimensional simulations lead to excellent agreement with available experimental data throughout the flow/structure interaction. They show that the spanwise variation of the drag is determined by the gravity current's lobe-and-cleft structure at impact and by an unsteady cellular flow structure similar to that found in constant-density flows at later times. A comparison between gravity-current flows and corresponding constant-density flows shows the hydrostatic drag component to be important for gravity currents.

23

Moskalets, Michael. "Auto- versus Cross-Correlation Noise in Periodically Driven Quantum Coherent Conductors." Entropy 23, no. 4 (March 25, 2021): 393. http://dx.doi.org/10.3390/e23040393.

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Expressing currents and their fluctuations at the terminals of a multi-probe conductor in terms of the wave functions of carriers injected into the Fermi sea provides new insight into the physics of electric currents. This approach helps us to identify two physically different contributions to shot noise. In the quantum coherent regime, when current is carried by non-overlapping wave packets, the product of current fluctuations in different leads, the cross-correlation noise, is determined solely by the duration of the wave packet. In contrast, the square of the current fluctuations in one lead, the autocorrelation noise, is additionally determined by the coherence of the wave packet, which is associated with the spread of the wave packet in energy. The two contributions can be addressed separately in the weak back-scattering regime, when the autocorrelation noise depends only on the coherence. Analysis of shot noise in terms of these contributions allows us, in particular, to predict that no individual traveling particles with a real wave function, such as Majorana fermions, can be created in the Fermi sea in a clean manner, that is, without accompanying electron–hole pairs.

24

RAO, C. V. K. PRASADA, J. SWAIN, P. V. HAREESH KUMAR, P. V. NAIR, V. N. PANCHALAI, and R. K. SHUKLA. "Underwater acoustic propagation experiments during ARMEX." MAUSAM 56, no. 1 (January 19, 2022): 281–86. http://dx.doi.org/10.54302/mausam.v56i1.905.

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Two-ship acoustic propagation experiments were conducted in deep waters of the Arabian Sea between 22-25 July and 7-8 August 2002 from onboard INS Sagardhwani and ORV Sagarkanya during ARMEX-I phase. The aim of this experiment was to understand the spatial (up to 30 km) and temporal (up to 24 hr) fluctuations of acoustic intensities within the surface duct. The acoustic transmissions were made from 15m depth at 2.4 KHz and 620 Hz frequencies from one ship and the signals were received at 15m and 40m depths on the second ship. The data were recorded for 10 min duration during each transmission and 30 sec averages were taken for computing acoustic intensities. Simultaneous oceanographic data on temperature (CTD and XBT), currents (ADCP) and waves (SBWR) were also recorded. Steady and homogeneous mixed layer depths of 50-60m offered an ideal environmental condition for surface duct propagation. The sea-state was moderate with significant wave height ranging from 1.5 to 2.3m. The surface and sub-surface currents in the upper 125m water column revealed the predominance of tides with change of current direction at 6 hr intervals. The current speeds were ~ 50 cm/s. The analysis of acoustic data highlighted the importance of temporal variations compared to spatial variations. Around 20 dB fluctuations in acoustic intensity were noticed for temporal variability where as only 7 dB fluctuation was observed for spatial variability.

25

Moss, G. W., and E. Moczydlowski. "Rectifying conductance substates in a large conductance Ca(2+)-activated K+ channel: evidence for a fluctuating barrier mechanism." Journal of General Physiology 107, no. 1 (January 1, 1996): 47–68. http://dx.doi.org/10.1085/jgp.107.1.47.

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In this study, we investigated the mechanism underlying the production of inwardly rectifying subconductance states induced in large conductance Ca(2+)-activated K+ channels (maxi K(Ca) channels) by the small, homologous proteins, bovine pancreatic trypsin inhibitor (BPTI) and dendrotoxin-I (DTX). Low-resolution bilayer recordings of BPTI-induced substates display excess noise that is well described by a beta-distribution characteristic of a filtered, two-state process. High-resolution patch recordings of maxi K(Ca) channels from vascular smooth muscle cells confirm that the BPTI-induced substate is actually comprised of rapid, voltage-dependent transitions between the open state and a nearly closed state. Patch recordings of DTX-induced substates also exhibit excess noise consistent with a similar two-state fluctuation process that occurs at rates faster than those measured for the BPTI-induced substate. The results indicate that these examples of ligand-induced substates originate by a fluctuating barrier mechanism that is similar to one class of models proposed by Dani, J.A., and J.A. Fox (1991. J. Theor. Biol. 153: 401-423) to explain subconductance behavior of ion channels. To assess the general impact of such rapid fluctuations on the practical measurement of unitary currents by amplitude histograms, we simulated single-channel records for a linear, three-state scheme of C (closed)-O(open)-S(substate). This simulation defines a range of transition rates relative to filter frequency where rapid fluctuations can lead to serious underestimation of actual unitary current levels. On the basis of these experiments and simulations, we conclude that fluctuating barrier processes and open channel noise may play an important physiological role in the modulation of ion permeation.

26

Mansouri, Nouha, Sihem Nasri, Abderezak Lashab, Josep M. Guerrero, and Adnen Cherif. "Innovative Grid-Connected Photovoltaic Systems Control Based on Complex-Vector-Filter." Energies 15, no. 18 (September 16, 2022): 6772. http://dx.doi.org/10.3390/en15186772.

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The research presented in this paper explains how the complex-vector-filter (CVF) method can help in minimizing the current harmonic of a grid-tied photovoltaic system. In fact, the harmonic-free positive sequence (HFPS) load current is used to produce referential sinusoidal currents. This control stabilizes the grid’s currents under unbalanced load currents, as well as mitigates undesirable harmonic load currents, while feeding clean active power to the grid. Thanks to the proposed controller, the performance, such as robustness, as well as the stability and dynamics of the CVF are more effective compared to the proportional-integral (PI) with phase-locked-loop (PLL) controller. Moreover, the CVF ensures robustness and stability during the synchronization between the photovoltaic (PV) generator and the utility grid system. The PI&PLL control presents higher active and reactive power fluctuations during synchronization. On the other hand, the CVF ensures the elimination of the reactive power fluctuations during synchronization. The performance of the proposed CVF is validated by simulation through MATLAB software. Under all conditions, the grid current, considering harmonics, is within the limits set by the IEEE-519 power quality standard, where a total harmonic distortion (THD) of 1.56% was achieved in the case of feeding a non-linear load.

27

Azouri, Assaf, Volker Roeber, and Douglas S. Luther. "THE RESPONSE OF HARBOR ENVIRONMENTS PROTECTED BY IRREGULAR FRINGING REEF SYSTEMS TO STRONG GRAVITY WAVE FORCING - A CASE STUDY." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 44. http://dx.doi.org/10.9753/icce.v36.currents.44.

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Three high-resolution, dispersive nearshore numerical models (BOSZ - Roeber & Cheung, 2012; FUNWAVE - Shi et al., 2012; XBeach - Roelvink et al., 2009) are compared and contrasted with observations from fringing- reef and harbor environments, in an attempt to test their ability to reproduce the wave transformation processes in a complex Hawaiian reef-system environment forced by highly energetic sea/swell wave conditions. Haleâ€™iwa Harbor, located on Oahuâ€™s North Shore (Figure 1), is a small boat harbor that faces serious operational problems resulting from water level fluctuations and currents during periods of strong swells. These oscillations are predominantly at infragravity periods (rather than swell periods), and, nearly every winter season, their amplitude levels are sufficiently large to trigger significant surges in the harbor. These surges can cause damage to harbor infrastructure and boats, and threaten the safety of mariners who attempt to enter or exit the harbor.

28

Vo, Van Tuan, Tan Van Vu, and Yoshihiko Hasegawa. "Unified thermodynamic–kinetic uncertainty relation." Journal of Physics A: Mathematical and Theoretical 55, no. 40 (September 29, 2022): 405004. http://dx.doi.org/10.1088/1751-8121/ac9099.

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Abstract Understanding current fluctuations is of fundamental importance and paves the way for the development of practical applications. According to the thermodynamic and kinetic uncertainty relations, the precision of currents can be constrained solely by the total entropy production or dynamical activity. In this study, we derive a tighter bound on the precision of currents in terms of both thermodynamic and kinetic quantities, demonstrating that these quantities jointly constrain current fluctuations. The thermodynamic and kinetic uncertainty relations become particular cases of our result in asymptotic limits. Intriguingly, the unified thermodynamic–kinetic uncertainty relation leads to a tighter classical speed limit, refining the time constraint on the system’s state transformation. The proposed framework can be extended to apply to state observables and systems with unidirectional transitions, thereby providing a constraint on the precision of the first-passage time.

29

NAKATA, KOUKI. "TEMPERATURE DEPENDENCE OF SPIN CURRENTS CARRIED BY JORDAN–WIGNER FERMIONS AND MAGNONS IN INSULATORS." International Journal of Modern Physics B 26, no. 01 (January 10, 2012): 1250011. http://dx.doi.org/10.1142/s0217979211102071.

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The temperature dependence of spin currents in insulators at the finite temperature near zero Kelvin is theoretically studied. The spin currents are carried by Jordan–Wigner fermions and magnons in one- and three-dimensional insulators. These spin currents are generated by the external magnetic field gradient along the quantization axis and also by the two-particle interaction gradient. In one-dimensional insulators, quantum fluctuations are strong and the spin current carried by Jordan–Wigner fermions shows the stronger dependence on temperatures than the one by magnons.

30

Moffatt, Luciano. "Estimation of Ion Channel Kinetics from Fluctuations of Macroscopic Currents." Biophysical Journal 93, no. 1 (July 2007): 74–91. http://dx.doi.org/10.1529/biophysj.106.101212.

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31

Schmid, Albert. "Persistent currents in mesoscopic rings by suppression of charge fluctuations." Physical Review Letters 66, no. 1 (January 7, 1991): 80–83. http://dx.doi.org/10.1103/physrevlett.66.80.

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32

Schmid, Albert. "Persistent Currents in Mesoscopic Rings by Suppression of Charge Fluctuations." Physical Review Letters 66, no. 10 (March 11, 1991): 1379. http://dx.doi.org/10.1103/physrevlett.66.1379.

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33

Motz, T., J. Ankerhold, and J. T. Stockburger. "Currents and fluctuations of quantum heat transport in harmonic chains." New Journal of Physics 19, no. 5 (May 16, 2017): 053013. http://dx.doi.org/10.1088/1367-2630/aa68bd.

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34

Ciliberto, S., R. Gomez-Solano, and A. Petrosyan. "Fluctuations, Linear Response, and Currents in Out-of-Equilibrium Systems." Annual Review of Condensed Matter Physics 4, no. 1 (April 2013): 235–61. http://dx.doi.org/10.1146/annurev-conmatphys-030212-184240.

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35

Surkov, V. V., and M. Hayakawa. "Natural electromagnetic ULF noise due to fluctuations of ionospheric currents." Journal of Geophysical Research: Space Physics 113, A11 (November 2008): n/a. http://dx.doi.org/10.1029/2008ja013196.

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36

Glavinović, M. I., P. Gooria, F. Aristizabal, and H. Taghirad. "Parametric spectral analysis of nonstationary fluctuations of excitatory synaptic currents." Biological Cybernetics 98, no. 2 (December 8, 2007): 145–69. http://dx.doi.org/10.1007/s00422-007-0200-2.

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37

Kozelov, B. V., I. V. Golovchanskaya, and O. V. Mingalev. "Inverse cascade in the structure of substorm aurora and non-linear dynamics of field-aligned current filaments." Annales Geophysicae 29, no. 8 (August 9, 2011): 1349–54. http://dx.doi.org/10.5194/angeo-29-1349-2011.

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Abstract. We investigate time evolution of scaling index αA that characterizes auroral luminosity fluctuations at the beginning of substorm expansion. With the use of UVI images from the Polar satellite, it is shown that αA typically varies from values less than unity to ~1.5, increasing with breakup progress. Similar scaling features were previously reported for fluctuations at smaller scales from all-sky TV observations. If this signature is interpreted in terms of non-linear interactions between scales, it means that the power of small-scale fluctuations is transferred with time to larger scales, a kind of the inverse cascade. Scaling behavior in the aurora during substorm activity is compared with that in the field-aligned currents simulated numerically in the model of non-linear interactions of Alfvénic coherent structures, according to the Chang et al. (2004) scenario. This scenario also suggests an inverse cascade, manifesting in clustering of small-scale field-aligned current filaments of the same polarity and formation of "coarse-grained" structures of field-aligned currents.

38

Sherstyukov, B. G., Yu P. Perevedentsev, and A. B. Sherstyukov. "ON THE RELATIONSHIP OF LONG-TERM FLUCTUATIONS IN AIR TEMPERATURE IN THE VOLGA FEDERAL DISTRICT WITH CYCLICAL SPACE IMPACTS ON THE EARTH." Bulletin of Udmurt University. Series Biology. Earth Sciences 30, no. 3 (October 29, 2020): 307–16. http://dx.doi.org/10.35634/2412-9518-2020-30-3-307-316.

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Based on observation data for 1891-2018, natural long-term fluctuations in the average annual air temperature in the Volga Federal District were studied after excluding the linear trend of anthropogenic climate warming. The method of asynchronous correlation analysis with lag from 0 to 70 years revealed a statistically significant relationship between long-term temperature fluctuations and the number of sunspots. The best positive relationship was found with a 65-year delay in temperature fluctuations relative to changes in solar activity. It is assumed that, with cyclical changes in solar activity, induced quasi-zonal electric currents arise in the World Ocean that can create changes in water temperature in the ocean depths, mainly in the area of the Antarctic Circumpolar Current. Cyclical temperature changes appear on the surface of the Southern Ocean with a delay of ~ 30 years. Then, through the system of currents of the Broker's global oceanic conveyor, temperature perturbations are transferred from the Southern Ocean to the North Atlantic and affect the air temperature in Europe with a delay of another 30-36 years.

39

ZHANG, YUQIANG, SHAOHONG CAI, and YUEWU HAN. "QUANTUM FLUCTUATIONS OF A DISSIPATIVE MESOSCOPIC CAPACITANCE–RESISTANCE–INDUCTANCE COUPLED CIRCUIT." Modern Physics Letters B 24, no. 11 (May 10, 2010): 1091–98. http://dx.doi.org/10.1142/s021798491002313x.

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Starting from Kirchhoff's equation for each mesoscopic coupled circuit, we investigated the quantum fluctuations of a dissipative mesoscopic capacitance–resistance–inductance coupled circuit using canonical transformation and unitary transformation. It is shown that the quantum fluctuations of charges and currents are not only related to the parameters of components in the self-circuit and coupled part, but also influenced by the parameters of other circuit. The uncertainty relations of the charges and currents are analyzed briefly.

40

Mestici, Simone, Fabio Giannattasio, Paola De De Michelis, Francesco Berrilli, and Giuseppe Consolini. "Scaling Properties of Magnetic Field Fluctuations in the High-Latitude Ionosphere." Remote Sensing 16, no. 11 (May 27, 2024): 1928. http://dx.doi.org/10.3390/rs16111928.

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Space plasma turbulence plays a relevant role in several plasma environments, such as solar wind and the Earth’s magnetosphere–ionosphere system, and is essential for describing their complex coupling. This interaction gives rise to various phenomena, including ionospheric irregularities and the amplification of magnetospheric and ionospheric currents. The structure and dynamics of these currents have relevant implications, for example, in studying ionospheric heating and the nature of electric and magnetic field fluctuations in the auroral and polar environments. In this study, we investigate the nature of small-scale fluctuations characterizing the ionospheric magnetic field in response to different geomagnetic conditions. We use high-resolution (50 Hz) magnetic data from the ESA’s Swarm mission, collected during a series of high-latitude crossings, to probe the scaling features of magnetic field fluctuations in auroral and polar cap regions at spatial scales still poorly explored. Our findings reveal that magnetic field fluctuations in field-aligned currents (FACs) and polar cap regions across both hemispheres are characterized by different scaling properties, suggesting a distinct driver of turbulence. Furthermore, we find that geomagnetic activity significantly influences the nature of energy dissipation in FAC regions, leading to more localized filamentary structures toward smaller scales.

41

Cao, Fuqiang, Quntao An, Jianqiu Zhang, Mengji Zhao, and Siwen Li. "Variable Weighting Coefficient of EMF-Based Enhanced Sliding Mode Observer for Sensorless PMSM Drives." Energies 15, no. 16 (August 18, 2022): 6001. http://dx.doi.org/10.3390/en15166001.

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In the field of permanent magnet synchronous motor (PMSM) control, the sliding mode observer (SMO)-based sensorless control is widely used; however, the actual control input of the current observation function is asymmetric. It can lead to different velocities of the estimated currents approaching to the actual currents and will make the current and back EMF fluctuations more severe, and result in more skewed angle and speed estimates, especially at a lower carrier ratio. In response to the above problems, this paper proposes a variable weighting coefficient of an EMF-based sliding mode observer (VWC-SMO). Unlike the traditional sliding mode observers, the weighted sliding mode switching variables and their bandpass-filtered values are used as the input of the current observer in the VWC-SMO. Thereby, the asymmetry of the control input in the current observation function can be well-suppressed, and almost the same approaching velocity on the two sides of the sliding surface can be obtained. Therefore, chattering near the sliding surface can also be suppressed. The method is verified on a motor controller experimental platform, and the comparative results shows that the VWC-SMO can reduce chattering of the observed currents and mitigate back EMFs fluctuations and improve the dynamic and steady-state performance.

42

Pattiaratchi, Charitha, and Sarath Wijeratne. "PROCESSES LEADING TO INFRA-GRAVITY PERIOD OSCILLATIONS AND CURRENTS IN PORTS AND MARINAS." Coastal Engineering Proceedings, no. 36 (December 30, 2018): 78. http://dx.doi.org/10.9753/icce.v36.currents.78.

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In this paper, we take the broad definition of tsunami (â€˜harbour waveâ€™) to describe oscillations in the infragravity (IG) periods (between 30 and 300s) in ports and marinas that often lead to interruption in harbour operations due to excessive vessel movements. The main processes that lead to these oscillations (also called seiches) are examined through the analysis of field measurements of water levels and currents from Western Australia. In a port or marina with lengths of the order of 500m and depths of the order of 10m, the natural oscillation periods are of the order of a few minutes. Changes in water levels in the coastal ocean adjacent to the port can setup oscillations within the port at its natural frequency. This results in water level fluctuations and strong horizontal currents within the port. If the incoming forcing is close to the natural frequency of oscillation resonance conditions may arise resulting in increased agitation inside the port. In addition if the harbour oscillation periods coincide with natural period of moored vessels, harbour operations can be severely interrupted due to strong vessel movements damaging to mooring lines and fenders.

43

Bułka, Bogdan R., and Jakub Łuczak. "Current Correlations in a Quantum Dot Ring: A Role of Quantum Interference." Entropy 21, no. 5 (May 24, 2019): 527. http://dx.doi.org/10.3390/e21050527.

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We present studies of the electron transport and circular currents induced by the bias voltage and the magnetic flux threading a ring of three quantum dots coupled with two electrodes. Quantum interference of electron waves passing through the states with opposite chirality plays a relevant role in transport, where one can observe Fano resonance with destructive interference. The quantum interference effect is quantitatively described by local bond currents and their correlation functions. Fluctuations of the transport current are characterized by the Lesovik formula for the shot noise, which is a composition of the bond current correlation functions. In the presence of circular currents, the cross-correlation of the bond currents can be very large, but it is negative and compensates for the large positive auto-correlation functions.

44

Garcia, O. E., E. Leer, H. L. Pécseli, and J. K. Trulsen. "Magnetic field-aligned plasma currents in gravitational fields." Annales Geophysicae 33, no. 3 (March 3, 2015): 257–66. http://dx.doi.org/10.5194/angeo-33-257-2015.

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Abstract. Analytical models are presented for currents along vertical magnetic field lines due to slow bulk electron motion in plasmas subject to a gravitational force. It is demonstrated that a general feature of this problem is a singularity in the plasma pressure force that develops at some finite altitude when a plasma that is initially in static equilibrium is set into slow motion. Classical fluid models thus do not allow general steady-state solutions for field-aligned currents. General solutions have to be non-stationary, varying on time scales of many periods of a plasma equivalent to the Brunt–Väisälä frequency. Except for very special choices of parameters, a steady-state solution exists only in an average sense. The conditions at large altitudes turn out to be extremely sensitive to even small changes in parameters at low altitudes. Low frequency fluctuations detected at large altitudes in the polar regions need not be caused by local low frequency instabilities, but merely reflect small fluctuations in conditions at low altitudes.

45

Lepidi, S., L. Cafarella, P. Francia, A. Meloni, P. Palangio, and J. J. Schott. "Low frequency geomagnetic field variations at Dome C (Antarctica)." Annales Geophysicae 21, no. 4 (April 30, 2003): 923–32. http://dx.doi.org/10.5194/angeo-21-923-2003.

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Abstract. We conduct an analysis of the geomagnetic field variations recorded at the new Antarctic station Dome C, located very close to the geomagnetic pole, which has been operating for approximately one month during the 1999–2000 campaign. We also perform a comparison with simultaneous measurements at the Italian Antarctic station Terra Nova Bay, in order to investigate the spatial extension of the phenomena observed at very high latitude. Our results show that between the two stations the daily variation is similar and the fluctuations with f ~ 1 mHz are coherent, provided that in both cases the comparison is made between geographically oriented components, suggesting that ionospheric currents related to the geographic position, more than field-aligned currents, are responsible for the lowest frequency variations; conversely, higher frequency (Pc5) fluctuations are substantially decoupled between the two stations. We also found that at Dome C the fluctuation power in the 0.55–6.7 mHz frequency band is well related with the solar wind speed during the whole day and that at Terra Nova Bay the correlation is also high, except around local geomagnetic noon, when the station approaches the polar cusp. These results indicate that the solar wind speed control of the geomagnetic field fluctuation power is very strict in the polar cap and less important close to the polar cusp.Key words. Magnetospheric physics (MHD waves and instabilities; Polar cap phenomena; Solar wind-magnetosphere interactions)

46

Oey, Lie-Yauw, Jia Wang, and M. A. Lee. "Fish Catch Is Related to the Fluctuations of a Western Boundary Current." Journal of Physical Oceanography 48, no. 3 (March 2018): 705–21. http://dx.doi.org/10.1175/jpo-d-17-0041.1.

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AbstractIn eastern boundary upwelling ecosystems, substantial variance of biological productivity (~50%) can often be related to physical forcing such as winds and ocean temperatures. Robust biophysical connections are less clear-cut in western boundary currents. Here the authors show that interannual variation of fish catch along the western boundary current of the North Pacific, the Kuroshio, significantly correlates (r = 0.67; p < 0.001) with the current’s off-slope (more fish) and on-slope (less fish) sideways shifts in the southern East China Sea. Remotely, transport fluctuations and fish catch are related to the oscillation of a wind stress-curl dipole in the tropical–subtropical gyre of the western North Pacific. Locally, the current’s sideways fluctuations are driven by transport fluctuations through a feedback process between along-isobath pressure gradients and vertical motions: upwelling (downwelling) during the off-slope (on slope) shift, which in turn significantly enhances (depresses) the chlorophyll-a (Chl-a) concentration in winter and early spring. The authors hypothesize that changes in the phytoplankton biomass as indicated by the Chl-a lead to changes in copepodites, the main food source of the fish larvae, and hence also to the observed variation in fish catch.

47

Morgulis, Andrey, and Konstantin Ilin. "Indirect Taxis on a Fluctuating Environment." Mathematics 8, no. 11 (November 17, 2020): 2052. http://dx.doi.org/10.3390/math8112052.

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In this article, we study a Patlak–Keller–Siegel (PKS) model of a community of two species placed in the inhomogeneous environment. We employ PKS law for modeling tactic movement due to interspecific taxis and in response to the environmental fluctuations. These fluctuations can arise for natural reasons, e.g., the terrain relief, the sea currents and the food resource distribution, and there are artificial ones. The main result in the article elucidates the effect of the small-scale environmental fluctuations on the large-scale pattern formation in PKS systems. This issue remains uncharted, although numerous studies have addressed the pattern formation while assuming an homogeneous environment. Meanwhile, exploring the role of the fluctuating environment is substantial in many respects, for instance, for predicting the side effects of human activity or for designing the control of biological systems. As well, it is necessary for understanding the roles played in the dynamics of trophic communities by the natural environmental inhomogeneities—those mentioned above, for example. We examined the small-scale environmental inhomogeneities in the spirit of Kapitza’s theory of the upside-down pendulum, but we used the homogenization instead of classical averaging. This approach is novel for the dynamics of PKS systems (though used commonly for other areas). Employing it has unveiled a novel mechanism of exerting the effect from the fluctuating environment on the pattern formation by the drift of species arising upon the homogenization of the fluctuations.

48

Divinsky, Boris V., and Sergey B. Kuklev. "Frequency spectra of horizontal current velocities on the northeastern shelf of the Black Sea." Hydrosphere Еcology (Экология гидросферы), no. 1(9) (November 2023): 18–25. http://dx.doi.org/10.33624/2587-9367-2023-1(9)-18-25.

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The paper presents a technique for restoring gaps in the original data, which made it possible to study the variability of fluctuations in the currents speed over significant time intervals. Analysis of the reconstructed continuous series of observations showed that high-frequency fluctuations in current speed predominate in the coastal zone, the possible source of which is the submesoscale eddies present here most of the time. On the continental slope, i.e. in the deep-water part of the sea, larger-scale processes dominate, associated with the dynamics of mesoscale eddies, meandering of the main Black Sea current, as well as global (on the scale of the entire sea) wind variability.

49

Crouzy, S. C., and F. J. Sigworth. "Fluctuations in ion channel gating currents. Analysis of nonstationary shot noise." Biophysical Journal 64, no. 1 (January 1993): 68–76. http://dx.doi.org/10.1016/s0006-3495(93)81341-9.

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50

Rogers, Neil C., James A. Wild, Emma F. Eastoe, Jesper W. Gjerloev, and Alan W. P. Thomson. "A global climatological model of extreme geomagnetic field fluctuations." Journal of Space Weather and Space Climate 10 (2020): 5. http://dx.doi.org/10.1051/swsc/2020008.

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This paper presents a multi-parameter global statistical model of extreme horizontal geomagnetic field fluctuations (dBH/dt), which are a useful input to models assessing the risk of geomagnetically induced currents in ground infrastructure. Generalised Pareto (GP) distributions were fitted to 1-min measurements of |dBH/dt| from 125 magnetometers (with an average of 28 years of data per site) and return levels (RL) predicted for return periods (RP) between 5 and 500 years. Analytical functions characterise the profiles of maximum-likelihood GP model parameters and the derived RLs as a function of corrected geomagnetic latitude, λ. A sharp peak in both the GP shape parameter and the RLs is observed at |λ| = 53° in both hemispheres, indicating a sharp equatorward limit of the auroral electrojet region. RLs also increase strongly in the dayside region poleward of the polar cusp (|λ| > 75°) for RPs > 100 years. We describe how the GP model may be further refined by modelling the probability of occurrences of |dBH/dt| exceeding the 99.97th percentile as a function of month, magnetic local time, and the direction of the field fluctuation, dBH, and demonstrate that these patterns of occurrence align closely to known patterns of auroral substorm onsets, ULF Pc5 wave activity, and (storm) sudden commencement impacts. Changes in the occurrence probability profiles with the interplanetary magnetic field (IMF) orientation reveal further details of the nature of the ionospheric currents driving extreme |dBH/dt| fluctuations, such as the changing location of the polar cusp and seasonal variations explained by the Russell-McPherron effect.

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