Flux Oscillations Research Articles

The magnetization in the lattice of quantum rings with rashba spin-orbit interaction

The magnetic properties of the lattice formed by noninteracting semiconductor quantum rings in a longitudinal magnetic field are investigated. It was shown that when the value of the Rashba parameter ξ = 1.5, the magnetization varies from positive to negative with changes in the Aharonov–Bohm flux and amplitude oscillations decrease.

Possible anticorrelations between pulsation amplitudes and the disc growth of Be stars in giant-outbursting Be X-ray binaries

ABSTRACT The mechanism of X-ray outbursts in Be X-ray binaries remains a mystery, and understanding their circumstellar discs is crucial for a solution of the mass-transfer problem. In particular, it is important to identify the Be star activities (e.g. pulsations) that cause mass ejection and, hence, disc formation. Therefore, we investigated the relationship between optical flux oscillations and the infrared (IR) excess in a sample of five Be X-ray binaries. Applying the Lomb–Scargle technique to high-cadence optical light curves from the Transiting Exoplanet Survey Satellite (${\it TESS}$), we detected several significant oscillation modes in the 3–24 h period range for each source. We also measured the IR excess (a proxy for disc growth) of those five sources, using J-band light curves from Palomar Gattini-IR. In four of the five sources, we found anticorrelations between the IR excess and the amplitude of the main flux oscillation modes. This result is inconsistent with the conventional idea that non-radial pulsations drive mass ejections. We propose an alternative scenario where internal temperature variations in the Be star cause transitions between pulsation-active and mass-ejection-active states.

Evidence of a Strong 19.5 Hz Flux Oscillation in Swift BAT and Fermi GBM Gamma-Ray Data from GRB 211211A

The gamma-ray burst (GRB) GRB 211211A is believed to have occurred due to the merger of two neutron stars or a neutron star and a black hole, despite its duration of more than a minute. Subsequent analysis has revealed numerous interesting properties including the possible presence of a ∼22 Hz quasiperiodic oscillation (QPO) during precursor emission. Here we perform timing analysis of Fermi and Swift gamma-ray data on GRB 211211A and, although we do not find a strong QPO during the precursor, we do find an extremely significant 19.5 Hz flux oscillation, which has higher fractional amplitude at higher energies, in a ∼0.2 s segment beginning ∼1.6 s after the start of the burst. After presenting our analysis we discuss possible mechanisms for the oscillation.

Impact of the Sea Effect on Sudden Fog on the Western Coast of the Bohai Sea: A Case Study

The term “sea effect” generally refers to the process of air mass modification after cold air flows above a warm sea surface. Affected by the sea effect, small-scale and sudden fogs have occasionally been observed on the western coast of the Bohai Sea. A more in-depth study of this type of fog is crucial for ensuring the safety of maritime and aerial traffic routes in this region. This study investigated the formation mechanism of this specific type of fog on the morning of 17 October 2007, utilizing both meteorological stations and 255 m tower observations, combined with the results of the Weather Research and Forecasting model (WRF). It is demonstrated that Bohai Sea evaporation and the associated water vapor advection played crucial roles in the formation of fog along the west coast of the Bohai Sea. The cold return flow became more moist as it passed over the warm Bohai Sea, which was the primary contributor to triggering regional fog on the western coast. A moisture budget analysis revealed that water vapor from the Bohai Sea intruded into its western coast along an eastward trajectory, dominating the oscillations in the net moisture flux. The eastern water vapor flux significantly increased at 17:00 on the 16th (Local time, LST), reaching its peak at 21:00. Correspondingly, the fog water growth rate began to increase at 23:00 on the 16th, reaching its maximum at 03:00 on the 17th. A sensitivity experiment on evaporation further indicated that the Bohai sea effect played a decisive role in fog formation. With a tenfold reduction in evaporation from the Bohai Sea and subsequent significant weakening of water vapor advection, the simulated fog along the western coast of the Bohai Sea completely disappeared. Understanding the formation mechanism of this type of fog is beneficial for refining forecasting focal points, thereby enhancing forecast accuracy in a targeted manner.

Assessing the effects of pressure variations on combustion dynamics in vortex-tube flows

In our investigation, we scrutinize combustion stability in vortex-tube combustion at high operating pressures by examining stability limits, flame configurations, and pressure oscillations. Our examination deeply probes the intricacies of flow and flame behaviors in terms of aerodynamic, thermodynamic, and flamedynamic aspects to identify the fundamental reasons behind stability variances at different pressure levels. The findings indicate that combustion instability escalates with rising operating pressures, marked by increased variability in flame patterns and a monotonic upsurge in pressure oscillation amplitudes. Although aerodynamic and thermodynamic stabilities remain unaffected, the thermoacoustic stability is compromised at elevated pressures. This is evidenced by the strong link between the Rayleigh criterion and the amplitude of pressure fluctuations, with an increased “gain” in the flame transfer function as pressure mounts. The core of the observed thermoacoustic instability is traced back to heightened density variations and mean flow velocities at high pressures, leading to amplified momentum flux oscillations.

Solar radiation and lower gravitational effects on wave oscillations in heat transfer along magnetic-driven porous cone in the presence of Joule heating

Solar radiation is a very useful form of energy such as heat and current density in gas turbines, nuclear power plants and thermal energy storage. The fundamental source of heat for multiple reactions in the climate, oceans, and ecological system is solar radiation. The current radiative flow model has significant applications in nuclear power generation, radioactive reactor cooling mechanisms, heating boilers, recycling of underground radioactive materials, fabrication of glass-fiber material and thermal textiles. The significance of study to reduce excessive heating by using magnetized surface. The main goal of current research is to report the Joule heating effect on heat and magnetic flux along the magnetic-driven porous cone under solar radiations and lower gravitational region. The novelty of this work is to explore wave oscillations in heat and magnetic flux with solar radiations under lower gravitational region. The Joule heating is applied to control the thermal boundary layer along gravity-driven cone. The coupled mathematical model is changed into non-dimensional form for physical parameters. The steady and oscillatory parts are obtained by using Stokes conditions. For smooth programming in FORTRAN computing tool, the primitive variables are used. The efficient finite difference scheme is used to plot the numerical findings with Gaussian elimination technique. The impact of governing parameters involved in the problem on wave oscillations of magnetic flux and heat transmission are drafted physically and numerically. It is noted that the fluid velocity enhances with significant amplitude as lower gravity and solar radiation increases along porous cone. It is found that wave oscillations of heat and magnetic flux increases as magnetic Prandtl number enhances under lower gravitational region.

Speed control of a DFIG-based wind turbine using a new generation of ADRC

ABSTRACT This paper represents a new generation of adaptive disturbance rejection control (ADRC) which is more robust against disturbances than conventional ADRC. The non-derivability of the fal function employed in the traditional ADRC has negative impacts on its operation, so alternate functions will be used which are derivable at all segments. In this regard, odd hyperbolic and trigonometric functions were employed. The performance of the proposed structure was investigated to control the doubly fed induction generator (DFIG) speed. To enhance the efficiency of the suggested ADRC, fractional-order calculations and fuzzy logic were utilized simultaneously. The results in MATLAB platform indicate that: 1) With constant wind speed and changing reference speed, using new fal functions in fuzzy fractional-order ADRC (FFOADRC) has improved the performance compared to the PI regulator and FFOADRC with default fal function. 2) During wind speed variations and using new fal functions, the DFIG speed reaches the final steady amount as over damping, while this condition is critical damping when using FFOADRC with default fal function. 3) During network voltage reduction, using new FFOADRCs leads to fewer oscillations in the stator flux, DC-bus voltage, and DFIG speed, which shows their better performance than PI regulator and traditional ADRC.

Cosmic neutrino flux and spin flavor oscillations in intergalactic medium

The ultra high energy (UHE) cosmic neutrinos are expected to play a pivotal role in the disquisition of physics beyond the standard model of particle physics as well as serve as an ideal cosmic messengers. This epitomizes the selling point of several currently running or planned neutrino telescopes. The UHE cosmic neutrinos usually perambulate gargantuan scales in the extragalactic universe having a magnetic field. If neutrinos have a finite magnetic moment (μν) owing to quantum loop corrections, this may result in spin-flavor oscillations, which can affect the cosmic neutrino flux. Using the current limit and assuming neutrinos to be Dirac particles, we show that the flux of cosmic neutrinos will reduce by half if they traverse few Mpcs through the intergalactic magnetic field, in the range of μG to nG. Moreover, one can safely neglect the effect of μν if the current upper bound is improved by a few orders of magnitude even if the neutrinos travel through the size of the visible universe.

Study on the Density Wave Instability in Natural Circulation System under Rolling Conditions

In the ocean environment, the thermal fluid system installed on the ship moves with the waves. This unsteady transient motion imposes additional body forces on the liquid. Thereby, the thermohydraulic properties of the thermal fluid system are changed, especially for natural circulation systems with a low driving force. Flow instability related to system security is a common two-phase flow system phenomenon. It is an essential subject in the study of thermal-hydraulic characteristics. In this paper, the density wave instability in a low-pressure natural circulation system with several parallel heating channels in the circumstances of rolling motion is studied by PNCMC (Program for Natural Circulation under Motion Condition). PNCMC is a newly developed program by adding extra body force induced by ship motions in two-phase’s momentum equations. The mechanism of rolling motion and its impact on flow oscillation and unstable boundary power are investigated. The supercooled boiling caused by the higher surface heat flux firstly promotes the occurrence of density wave oscillations between parallel heating channels. When enough steam enters the riser, the system density wave oscillation occurs under the gravity pressure drop-flow rate-vapor fraction feedback. A more complicated compound oscillation is created by superimposing the interchannel oscillation and the system density wave oscillation. If the rolling motion has little change to the natural circulation flow, when density wave instability arises, the flux oscillation rule and the instability boundary power are basically consistent with the vertical conditions. When the rolling angle is large, the fairly large amplitude flow oscillation generated by rolling will prevent density wave instability from occurring and force the flow oscillation to obey the law of rolling effects.

Siberian Radioheliograph: sunspot oscillations in 3–6 GHz band

ABSTRACT We present the first observations of spatially resolved oscillation sources obtained with the Siberian Radioheliograph at 3–6 GHz. We have found significant flux oscillations with periods of about 3, 5, and 13 min emitted from AR12833. The 3-min periodicity dominates at higher frequencies. It was found that the apparent level of oscillations depends on the active region location on the disc, and scales down towards the limbs. The oscillations were studied in detail during 1 h interval on 2021 June 19. We found that sources of 3-min oscillations were located above the umbra and their emission is extraordinary polarized. The 5- and 13-min periods were manifested in emission at lower frequencies, down to 2.8 GHz. Sources with 5-min periodicity were located near the umbra/penumbra boundary and in the pore region. Positions of sources with 13-min oscillations were different at 3.1 and 4.7 GHz. We found consistency between spatial location of the oscillation sources in radio and ultraviolet at 171 and 304 Å. There is significant correlation of signals in two ranges. Time delays between microwave oscillations increase as the frequency decreases, which can be explained by upward propagation of periodic disturbances. The localization of oscillation sources is probably related to magnetic structures with different wave cut-off frequencies at different heights.

Dynamics of a single-phase natural circulation system under harmonic excitation.

A natural circulation system (NCS) has a broad application in the sector of thermal engineering, for example, in nuclear reactors due to its capability in transferring heat without any support of external power or a mechanical device. NCSs, although designed for steady operation, have been found to exhibit dynamical behavior, such as periodic oscillations, depending on the input heater power. The heater power, otherwise assumed to be steady, can be fluctuating in practice. The present study focuses on the dynamics of a single-phase square NCS, which exhibits periodic dynamics and is subjected to an external harmonic perturbation (chosen as the simplest form of fluctuation) over the steady heater power. The objective of the study is to study the dynamics of NCS under external (harmonic) disturbances using the framework of forced synchronization. Toward that, a 1D transient model of a square-shaped NCS is simulated with harmonically forced input power. The transition in the nature of synchronization between mass flux oscillations and the external forcing has been characterized by varying the frequency and amplitude of external perturbation independently. We find different nonlinear effects of the harmonic forcing, such as exhibition of quasiperiodic dynamics, frequency pulling/pushing, and frequency locking or forced synchronization. The aforementioned characterization techniques open up an avenue for detailed analysis of the more complex type of fluctuating input heat in real systems.

Energetic Electron and Proton Interactions with Pc5 Ultra Low Frequency (ULF) Waves during the Great Geomagnetic Storm of 15–16 July 2000

The dynamics of the outer zone radiation belt has received a lot of attention mainly due to the correlation between the occurrence of enhancing relativistic electron flux and spacecraft operation anomalies or even failures (e.g., Baker et al. 1994). Relativistic electron events are often observed during great storms associated with ultra low frequency (ULF) waves. For example, a large buildup of relativistic electrons was observed during the great storm of March 24, 1991 (e.g., Li et al. 1993; Hudson et al. 1995; Mann et al. 2013). However, the dominant processes which accelerate magnetospheric radiation belt electrons to MeV energies are not well understood. In this paper, we present observations of Pc5 ULF waves in the recovery phase of the Bastille day storm of July 16, 2000 and electron and proton flux simultaneously oscillating with the same frequencies as the waves. The mechanism for the observed electron and proton flux modulations is examined using groundbased and satellite observations. During this storm time, multiple packets of discrete frequency Pc5 ULF waves appeared associated with energetic particle flux oscillations. We model the drift paths of electrons and protons to determine if the particles drift through the ULF wave to understand why some particle fluxes are modulated by the ULF waves and others are not. We also analyze the flux oscillations of electrons and protons as a function of energy to determine if the particle modulations are caused by a ULF wave drift resonance or advection of a particle density gradient. We suggest that the energetic electron and proton modulations by Pc5 ULF waves provide further evidence in support of the important role that ULF waves play in outer radiation belt dyanamics during storm times.

Anomalous resonance between low-energy particles and electromagnetic plasma waves

Cyclotron resonance between plasma waves and charged particles is a fundamental and ubiquitous process in the plasma universe, during which the particle’s gyromotion has a constant phase in the wave field to enable a sustained energy exchange. In this classical picture, however, the particle’s angular velocity is determined only by the background magnetic field. Here, we show that the classical condition of cyclotron resonance fails to describe the observations of low-energy particles in resonance with large-amplitude waves, which highlights the roles of the wave field in nonlinearly modifying the resonant picture. The revised scenario of anomalous resonance is then validated by the agreement between test-particle simulations and ultrafast spacecraft measurements, which present in-phase and/or antiphase relationships between the wave magnetic field and ion flux oscillations at energy and pitch-angle ranges incompatible with the classical resonance condition. This revision could significantly affect the wave-particle energy exchange and wave evolution processes.

Sensitivity analysis in core diagnostics

In the CORTEX project, methods to simulate neutron flux oscillations were enhanced and machine-learning based tools to determine the causes of measured neutron flux oscillations were developed, using the results of simulations as training and validation data. For a selected combination of those methods and tools, several sensitivity analyses were performed to assess their robustness and trustworthiness. The neutron flux oscillations were simulated using the tool CORE SIM+. It calculates the three-dimensional field of the neutron flux oscillations, which can be used to determine the response of neutron detectors at given locations. For the sensitivity analysis, the neutron flux oscillations were assumed to be caused by the vibration of one fuel element. It was investigated how selected input parameters like the core loading pattern, the burn up of the fuel elements, the neutronic core data, the geometry details of the vibrating fuel element, the chosen detectors, and other noise source parameters like the amplitude of the fuel element vibrations, affect the simulated neutron flux oscillations. A three dimensional fully convolutional neural network had been developed and trained during the CORTEX project to determine the cause and location of perturbations causing given measurements of in-core detectors in pressurized water reactors. The robustness of this network was tested by applying it to the simulated detector readings created during the sensitivity analysis.

Magnetic Helicity Flux Oscillations in the Atmospheres of Flaring and Nonflaring Active Regions

Analyzing the evolution of magnetic helicity flux at different atmospheric heights is key for identifying its role in the dynamics of active regions (ARs). The three-dimensional (3D) magnetic field of both flaring and nonflaring ARs is constructed using potential field extrapolations, enabling the derivation of emergence, shearing, and total magnetic helicity components at a range of atmospheric heights. An analysis of temporal oscillations of the derived components shows that the largest significant period of the three helicity fluxes are common (within ±2 hr) from the photosphere up to at least 1 Mm for flaring ARs—being consistent with the presence of a coupled oscillatory behavior that is absent in the nonflaring ARs. We suggest that large, energetic solar eruptions may have been produced in ARs when the vertical and horizontal helicity flux components became a coupled oscillatory system in the low solar atmosphere.

Uncertainty analyses of neutron noise simulations in a Zero-Power reactor

A comprehensive uncertainty analysis methodology has been established for the modeling of stationary neutron flux oscillations induced by fuel rods vibration in a zero-power reactor. The methodology includes uncertainty propagation and sensitivity analysis. The target event is based on an actual experimental campaign at the CROCUS zero-power reactor and corresponds to the simultaneous oscillation of 18 metallic uranium fuel rods in the periphery of the core. Both the uncertainty propagation and the sensitivity analysis commonly use a large part of the entire analysis process, from the selection of uncertain parameters to the actual code simulations. Applying a random sampling-based approach, the input parameters are sampled N times from their distribution information and used as inputs for N noise simulations using CORE SIM +. The quantity of interest (QoI) is the amplitude of the Auto-Power Spectral Density at various detector locations, which is normalized by the amplitude of the Cross-Power Spectral Density of the reference detector. Their uncertainties are determined following the 4th order Wilks’ formula for two-sided limits. Through the determination of correlations among QoI at the installed detector locations, it is demonstrated that the neutron noise near the area of oscillating fuel rods (noise source) have different behavior compared to the neutron noise further away from the noise source. The following sensitivity analyses are carried out using multiple correlation coefficients within grouped parameters. As expected from the QoI correlations, the QoIs at two different locations (near and far from the noise source) are influenced by different input parameters. Near the noise source, the QoI uncertainty is driven by the uncertainties in the position of the noise source, while the uncertainties in the nuclear data for U-235 and U-238 are the leading contributors further away from the source. This paper provides general information on how to perform the uncertainty analyses for neutron noise simulations, as well as quantitative estimates of the computational uncertainty required for the validation of the computer programs under development for the simulation of neutron noise.

Assessment on R-410A saturated flow boiling heat transfer subject to periodic oscillating heat flux inside an annular duct

The objective of this study is concerned with assessing experimentally the heat transfer of time-dependent saturated flow boiling (TDSFB) for refrigerant R-410 A stemming from oscillations in the heat flux inside an annular duct with the gap of δ = 2 mm in order to improve the energy efficiency of heat exchanger system. The influences of operating parameters, such as mean applied heat flux q‾, heat flux oscillation amplitude Δq/q‾, mass flux of refrigerant G, oscillation period tp, and saturation temperature Tsat, on heat transfer characteristics of TDSFB are systematically explored. From the present experimental results, it is found that increasing mean applied heat flux enhances the average wall superheat and boiling heat transfer coefficient (BHTC, hr); while an increase in either Δq/q‾ or tp exerts very minor influence on the boiling curve and hr. As the q‾ oscillates in the triangular waveform, the wall temperature (Tw) varies in sinusoidal waves at the same frequency of q‾. At low, intermediate, and high q‾, three different flow patterns versus time are observed and named single-phase flow (SPF), intermittent boiling flow (IBF), and persistent boiling flow (PBF). The oscillation amplitudes of Tw and hr are increased with the increases of Δq/q‾. Enhancing either G or Tsat tends to result in a slight decrease in Tw, but an increase in hr. Moreover, the Tw does not fluctuate with the oscillation of lower q‾ under a shorter tp due to the tube thermal inertia, but oscillates significantly as the tp is raised. Finally, a correlation equation is presented to identify the bounds, distinguishing the three different flow patterns of R-410 A TDSFB subject to oscillatory heat flux inside horizontal annuli.

Oscillating modes of thermomagnetic avalanches in superconductors

Abstract In this work, the nature of the magnetic flux oscillations in superconductors was studied within the adiabatic approximation. It was shown that, under certain conditions, depending on the values of parameters of the system, oscillating modes of the magnetic flux may be observed.

Evaporative heat transfer of R410A flow in an annular duct under oscillatory wall heat flux

In this investigation, the evaporative heat transfer characteristics of R410A flow in a slender annular duct under an oscillatory heat flux are studied experimentally with emphasis on the influences of mean mass flux, heat flux, and oscillating amplitude and period of heat flux. The applied heat flux is varied in ranges of q = 5,000 to 15,000 W m−2 and the mean mass fluxes of 300 and 400 kg.(m−2s−1) are considered, respectively. The results reveal that increasing either oscillating amplitude or period of heat flux enhances the oscillation of surface temperature and evaporation heat transfer coefficient (HTC). The prevailing influence of heat flux oscillations on the evaporation heat transfer causes notable variations in the vapour quality and liquid film thickness. At a high level of vapour quality, the thickness of refrigerant liquid film on the hot surface is decreased, leading to the increase of the evaporation HTC. Furthermore, the oscillation in the wall temperature is slightly stronger as the period of heat flux oscillation boosts in the range of 120 s to 600 s. Based on the present measured data, some correlations are provided for the evaporation HTC of R410A as the function of the heat flux and vapour quality.

Statistics of Multi‐MeV Electron Drift‐Periodic Flux Oscillations Using Van Allen Probes Observations

AbstractMulti‐MeV electron drift‐periodic flux oscillations observed in Earth's radiation belts indicate radial transport and energization/de‐energization of these radiation belt core populations. Using multi‐year Van Allen Probes observations, a statistical analysis is conducted to understand the characteristics of this phenomenon. The results show that most of these flux oscillations result from resonant interactions with broadband ultralow frequency (ULF) waves and are indicators of ongoing radial diffusion. The occurrence frequency of flux oscillations is higher during high solar wind speed/dynamic pressure and geomagnetically active times; however, a large number of them were still observed under mild to moderate solar wind/geomagnetic conditions. The occurrence frequency is also highest (up to ∼30%) at low L‐shells () under various geomagnetic activity, suggesting the general presence of broadband ULF waves and radial diffusion at low L‐shells even during geomagnetically quiet times and showing the critical role of the electron phase space density radial gradient in forming drift‐periodic flux oscillations.