Change Of Magnetic Flux Research Articles

A superconducting quantum interference device based read-out of a subattonewton force sensor operating at millikelvin temperatures

We present a scheme to measure the displacement of a nanomechanical resonator at cryogenic temperature. The technique is based on the use of a superconducting quantum interference device to detect the magnetic flux change induced by a magnetized particle attached on the end of the resonator. Unlike conventional interferometric techniques, our detection scheme does not involve direct power dissipation in the resonator, and therefore, is particularly suitable for ultralow temperature applications. We demonstrate its potential by cooling an ultrasoft silicon cantilever to a noise temperature of 25 mK, corresponding to a subattonewton thermal force noise of 0.5 aN/Hz.

Subsurface Velocity of Emerging and Decaying Active Regions

We study the temporal variation of subsurface flows of 828 active regions and 977 quiet regions. The horizontal flows cover a range of depths from the surface to about 16 Mm and are determined by analyzing Global Oscillation Network Group high-resolution Doppler data with ring-diagram analyses. The vertical velocity component is derived from the divergence of the measured horizontal flows using mass conservation. For comparison, we analyze Michelson Doppler Imager (MDI) Dynamics Run data covering 68 active regions common to both data sets. We determine the change in unsigned magnetic flux during the disk passage of each active region using MDI magnetograms binned to the ring-diagram grid. We then sort the data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. We find that emerging flux has a faster rotation than the ambient fluid and pushes it up, as indicated by enhanced vertical velocity and faster-than-average zonal flow. After active regions are formed, downflows are established within two days of emergence in shallow layers between about 4 and 10 Mm. Emerging flux in existing active regions shows a similar scenario, where the upflows at depths greater than about 10 Mm are enhanced and the already established downflows at shallower depths are weakened. When active regions decay, the corresponding flow pattern disappears as well; the zonal flow slows down to values comparable to that of quiet regions and the upflows become weaker at deeper layers. The residual meridional velocity is mainly poleward and shows no obvious variation. The magnitude of the residual velocity, defined as the sum of the squares of the residual velocity components, increases with increasing magnetic flux and decreases with decreasing flux.

Non-classical state effect on the persistent current in one-dimensional mesoscopic ring with electron-phonon interaction

Based on the efficacy of the phonon coherent state and with consideration of the non-classical effect of the squeezed state of phonon, the influence of the electron-magnon interaction and the electron-phonon interaction on the persistent current in one-dimensional mesoscopic ring is studied. Compared with the free ring, our study shows that in one-dimensional mesoscopic ring, the amplitude of the persistent current exponentially diminishes due to the electron-magnon interaction. For the normal state electron, the interaction of the electron-phonon causes the persistent current to weakendce to the Debye-Waller effect. However, taking the correlation between the hopping electron states and the one-phonon coherent states into the equation, the ground energy of the mesoscopic system is declined in a large scale. In result, the persistent current In is increased substantially. On the other hand, taking the behavior of the two-phonon coherent state into account, as the effect of the squeezed states of phonons maintains the phase coherence of electrons, so the Debye-Waller attenuation is weakened effectively. Especially, when the squeezed angle is larger, because of the non-adiabatic correlation between the squeezed-phonon states and the coherent states of phonon, it causes a significant decline in the ground state energy and a significant increase in the squeezed angle, thus persistent current has a even more significant increase. It should be pointed out, that the persistent current shows period oscillation as the external magnetic flux changes. Even the external magnetic flux Φem=0, still the persistent current of the intrinsic has I ~ n≠0. The system continuoues to support the equilibrium spin and charge flow, the external magnetic flux only plays the role of an adiabatic parameter.

A Critical Review of Neuroimaging Applications in Sports Concussion

While abnormalities related to concussion are typically not identified on traditional clinical neuroimaging (i.e., computed tomography [CT] or magnetic resonance imaging [MRI]), more sophisticated neuroimaging techniques have the potential to reveal the complex neurometabolic processes related to concussion and its recovery. Clinically, these techniques may one day provide useful information to guide clinicians in the management and treatment of sports concussion. This article critically reviews the current state of the literature regarding neuroimaging and sports concussion, identifies challenges in the application of these techniques, and identifies areas for future research.

A Hyper-Efficient Inverter Driven By Positive EMF in Combination With Transient Phenomenon

In these days, quite a many types of electrical device/unit use inverters as their key components. And, most of such inverters conventionally employ the Royer's circuit which is designed to use pulse current of rectangular form as input. On the other hand, the inverter prototype that the author has developed features the two points that 1) it employs pulse current of sharp spike form as input, and that 2) it takes advantage of transient phenomenon to be occurred simultaneously in the circuit for attaining a certain level improvement of the efficiency. Taking advantage of the above two features in combination; it becomes possible to develop a new type of inverter driven by positive EMF which gives outstanding efficiency. Now, consider what is “positive EMF”? It is electromotive force which is in the same direction as that of the input current. On the other hand, the so-called “back EMF” to be induced according to the well-known Faraday's law, is in the direction reverse to the input current. They are utterly different in nature. The value of the positive EMF to be induced in the coil depends on the rate of change of magnetic flux, where the second-order and even higher-order time derivatives of magnetic flux are involved.

Electromagnetic Interference’s Effect on the Performance of Electro-Hydraulic Control System

The performance of engineering machinery and equipments will be affected under the environment of unstable electromagnetic fields. In the magnetic field, with focusing on the proportional solenoid of a certain engineering machinery hydraulic proportional control system, the internal changes of characteristics in the magnetic field lead to the changes of force output characteristics through output changes in air gap magnetic flux, and the instantaneous output performance is affected by electromagnetic interference. The electromagnetic environment’s effect on the changes of electro-hydraulic control system is determined by implementation of the proportional solenoid electromagnetic interference. The result shows that the control performance of mechanical hydraulic control system becomes unstable, and the anti-electromagnetic interference capacity of electromagnetic sensitive element in the electro-hydraulic control system should be improved.

Magnetic Stress Sensitivity Analysis for Ferromagnetic Material

Based on counter magnetostriction effect the magnetization intensity and stress sensitivity was analyzed for ferromagnetic material. The stress sensitivity of magnetized material was discussed on basis of the law of minimum energy and movement of magnetic domain structure. In accordance with the effect of magnetization intensity from stress the applied stress can lead to movement of domain wall of magnetic domain in the demagnetizing state for ferromagnetic material when the net magnetic moment is equal to zero. Meanwhile easily magnetization axis can be established on known applied stress. Then when ferromagnetic material is forced by the applied stress the magnetization intensity can be changed obviously. It is happened so that magnetic flux is also changed simultaneously. The result shows that real-time strained condition of material can be judged on basis of testing change of magnetic flux. Furthermore the study theory of magnetic nondestructive testing of defect sensibility structure for long span steel structural is obtained through this analysis.

Gamma-Ray and High-Energy-Neutron Measurements on CORONAS-F during the Solar Flare of 28 October 2003

The solar flare of 28 October 2003 (X17.2/4B) was recorded by the SONG instrument onboard the CORONAS-F satellite. A description of the SONG instrument, its in-orbit operation and the principal data reduction methods used to derive the flare gamma-ray properties are presented. Appreciable gamma-ray emission was observed in the 0.2 – 300 MeV energy range. Several time intervals were identified which showed major changes in the intensity and spectral shape of the flare gamma-ray emission. The primary bremsstrahlung proves to be extended to 90 MeV and dominates during 11:02:11 – 11:03:50 UT time interval, i.e. at the beginning of the flare impulsive phase. Afterwards, the SONG response was consistent with detection of the pion-decay gamma emission. A sharp increase in the pion-decay-generated gamma-ray emission was observed at 11:03:51±2 s UT, implying a substantial change in the spectrum of accelerated ions, which testified the appearance of protons with energies of >300 MeV on the Sun. This emission lasted at least 8 – 9 min until the end of our measurements. The ion acceleration to high energies was also proved by the detection of neutrons with energies >500 MeV. It was found that the most efficient acceleration of high-energy protons coincides in time with the highest rate of the magnetic-flux change rate. The maximum gamma-ray flux at 100 MeV was 1.1×10−2 photons cm−2 s−1 MeV−1, exceeding all the fluxes that have ever been recorded.

Trend of photospheric magnetic helicity flux in active regions generating halo coronal mass ejections

[NASA ADS]

OBSERVATIONS OF CHROMOSPHERIC FLARE RE-BRIGHTENINGS

We investigate an active region that produced three C-class flares and one M-class flare within 2.5 hr. The morphology and location of the C-flares indicate that these events constitute a set of homologous flares. Radio observations indicate the occurrence of a downward-moving plasmoid during the impulsive phase of the M flare. We use TRACE 1700 A filtergrams and SOHO Michelson Doppler Imager magnetograms to examine the character of the UV brightenings; i.e., we search for re-brightenings of former flare areas both across the series of events and within one and the same event. We find that essentially the same footpoints re-brighten in each C flare. Based on the progression of both the derived magnetic flux change rate and the observed Radio Solar Telescope Network microwave emission, we speculate about a further re-brightening during the decay phase of the M flare as a further member of the series of homologous flares. We conclude that the postflare field is driven to repeated eruption by continuous, shear-increasing, horizontal, photospheric flows, as one end of the involved magnetic arcade is anchored in the penumbra of a large sunspot. The observed motion pattern of the UV kernels indicates that the arcade evolves during the series of events from a both highly sheared and heavily entangled state to a still sheared but more organized state.

Rapid changes of sunspot structure associated with solar eruptions

AbstractIn this paper we summarize the studies of flare-related changes of photospheric magnetic fields. When vector magnetograms are available, we always find an increase of transverse field at the polarity inversion line (PIL). We also discuss 1 minute cadence line-of-sight MDI magnetogram observations, which usually show prominent changes of magnetic flux contained in the flaring δ spot region. The observed limb-ward flux increases while disk-ward flux decreases rapidly and irreversibly after flares. These observations provides evidences, either direct or indirect, for the theory and prediction of Hudson, Fisher & Welsch (2008) that the photospheric magnetic fields would respond to coronal field restructuring and turn to a more horizontal state near the PIL after eruptions. From the white-light observations, we find that at flaring PIL, the structure becomes darker after an eruption, while the peripheral penumbrae decay. Using high-resolution Hinode data, we find evidence that only dark fibrils in the “uncombed” penumbral structure disappear while the bright grains evolve to G-band bright points after flares.

Miniature Explosively Driven High-Current Transverse-Shock-Wave Ferromagnetic Generators

Comprehensive studies of explosively driven ferromagnetic generators (FMGs) have been performed. It has been experimentally established that the initial magnetostatic energy stored in the magnetic element of the FMG (determined by the magnet's maximum energy product (BH)max and its volume), not the residual magnetic flux density Br, is the principal parameter that determines the output energy and the amplitude of the signals produced by the generator. Systematic studies were carried out with miniature high-current FMGs containing Nd2Fe14B high-energy hard ferromagnetic elements having a wide range of sizes. Utilization of transverse-shock demagnetization of Nd2Fe14B magnets (shock wave propagates across the magnetization vector \mmb M) instead of longitudinal-shock demagnetization dramatically changed the design of the FMGs and reduced the mass of the explosives used by two orders of magnitude in comparison with that used in longitudinal FMGs. Data for the initial magnetic flux and shock-induced magnetic flux change in Nd2 Fe14B magnets are presented. It was shown that FMGs with a volume of 25 cm3 are capable of producing pulsed currents with amplitudes of up to 4.4 kA and rise times of 23 μs in the seed coil of a magnetic flux compression generator.

OBSERVATIONAL EVIDENCE OF BACK REACTION ON THE SOLAR SURFACE ASSOCIATED WITH CORONAL MAGNETIC RESTRUCTURING IN SOLAR ERUPTIONS

Most models of solar eruptions assume that coronal field lines are anchored in the dense photosphere and thus the photospheric magnetic fields would not have rapid, irreversible changes associated with eruptions resulted from the coronal magnetic reconnection. Motivated by the recent work of Hudson, Fisher & Welsch (2008) on quantitatively evaluating the back reaction due to energy release from the coronal fields, in this Letter we synthesize our previous studies and present analysis of new events about flare-related changes of photospheric magnetic fields. For the 11 X-class flares where vector magnetograms are available, we always find an increase of transverse field at the polarity inversion line (PIL) although only 4 events had measurements with 1 minute temporal resolution. We also discuss 18 events with 1 minute cadence line-of-sight magnetogram observation, which all show prominent changes of magnetic flux contained in the flaring Delta spot region. Except in one case, the observed limb-ward flux increases while disk-ward flux decreases rapidly and irreversibly after flares. This observational evidence provides support, either directly or indirectly, for the theory and prediction of Hudson, Fisher & Welsch that the photospheric magnetic fields must respond to coronal field restructuring and turn to a more horizontal state near the PIL after eruptions.

Measurement of Minute Changes in Magnetic Flux Density by Means of a Novel GMR Needle Probe for Application in Hyperthermia Therapy

The accuracy of heat deposition, which is proportional to magnetic fluid weight density, appears to be a major factor in the quality of magnetic-fluid-based hyperthermia. An innovative giant magnetoresistance (GMR) needle probe is proposed as a means of estimating very-low-concentration magnetic fluid weight density in a low-invasive way. The method of estimation is based on the difference between magnetic flux densities inside and outside a magnetic-fluid-filled area in the body, given that the applied magnetic flux density is uniform. Since, for very-low magnetic fluid weight densities the percentage change in magnetic flux density is in the order of 1/100, it is important that the applied magnetic flux density be at least 1/10th more uniform. For this purpose a Lee-Whiting type coil was designed and fabricated, producing a 0.001% fluctuation from the center of the coil in approximately 35% of the outer coil spacing along the axial direction and 25% of the diameter of the coils in the radial direction. Concentrations as low as 0.03% weight density (a change in magnetic flux density in the order of nanotesla) were estimated by means of a GMR needle probe.

Nonlinear electromagnetic generators with polymeric materials for power harvesting from vibrations

The power consumption reduction of electronic devices has allowed supplying them through the harvesting and subsequent conversion of electrical energy that is present in different forms in the measurement environment. Mechanical energy from vibrations is the most common energy source. In the proposed nonlinear electromagnetic generators, the vibrations generate an oscillatory movement of a planar inductor placed in a constant magnetic field, thereby generating a voltage on the coil due to the change in magnetic flux. In the case of low-frequency vibrations, it is necessary to consider two conflicting demands: firstly, in the hypothesis of linearity, the resonant frequency reduction requires an increase in mass and softness of the spring, against the size reduction requires structural stiffening and an obvious reduction in mass. The generator considers a proposed nonlinear elastic behavior of the suspension on which the inductor is placed, improving the system efficiency than the linear case, and especially by introducing behaviors that are not intuitively predictable and potentially exploitable for the proposed purpose. A mathematical model is used to study the nonlinear behaviors; the model is referred to a mass-spring-damper system with harmonic force support. The retraction force is nonlinear by adding a cubic term, and damping is proportional to the speed with an electrical and mechanical component. The generators are built and tested using a specially designed experimental setup. The working frequencies of the generators are between 25–40 Hz. The experimental results are compared with results obtained by the mathematical model, getting a good match.

Thermodynamic functions of electron gas on the semiconductor nanotube surface in a magnetic field

Thermodynamic functions have been calculated in the effective mass approximation for degenerate and nondegenerate electron gases on the semiconductor cylindrical nanotube surface in a longitudinal magnetic field. The Laplace transform linking the density of states and the statistical sum has been used. The thermodynamic quantities of degenerate electron gas undergo the de Haas-van Alphen oscillations with the electron Fermi energy change and the Aharonov-Bohm oscillations with the magnetic flux change within the semiconductor tube cross section. The quantities related to nondegenerate gas oscillate only with the change of magnetic flux. A peak has been found in the nondegenerate gas heat capacity-temperature diagram. A limiting process to 2D electron gas on plane has been carried out.

HINODE OBSERVATIONS OF COHERENT LATERAL MOTION OF PENUMBRAL FILAMENTS DURING A X-CLASS FLARE

The X-3.4 class flare of 13 December 2006 was observed with a high cadence of 2 minutes at 0.2 arc-sec resolution by HINODE/SOT FG instrument. The flare ribbons could be seen in G-band images also. A careful analysis of these observations after proper registration of images show flare related changes in penumbral filaments of the associated sunspot, for the first time. The observations of sunspot deformation, decay of penumbral area and changes in magnetic flux during large flares have been reported earlier in the literature. In this Letter, we report lateral motion of the penumbral filaments in a sheared region of the delta-sunspot during the X-class flare. Such shifts have not been seen earlier. The lateral motion occurs in two phases, (i) motion before the flare ribbons move across the penumbral filaments and (ii) motion afterwards. The former motion is directed away from expanding flare ribbons and lasts for about four minutes. The latter motion is directed in the opposite direction and lasts for more than forty minutes. Further, we locate a patch in adjacent opposite polarity spot moving in opposite direction to the penumbral filaments. Together these patches represent conjugate foot-points on either side of the polarity inversion line (PIL), moving towards each other. This converging motion could be interpreted as shrinkage of field lines.

Solar source of energetic particles in interplanetary space during the 2006 December 13 event

An X3.4 solar flare and a fast halo coronal mass ejection (CME) occurred on 2006 December 13, accompanied by a high flux of energetic particles recorded both in near-Earth space and at ground level. Our purpose is to provide evidence of flare acceleration in a major solar energetic particle (SEP) event. We first present observations from ACE/EPAM, GOES, and the Apatity neutron monitor. It is found that the initial particle release time coincides with the flare emission and that the spectrum becomes softer and the anisotropy becomes weaker during particle injection, indicating that the acceleration source changes from a confined coronal site to a widespread interplanetary CME-driven shock. We then describe a comprehensive study of the associated flare active region. By use of imaging data from HINODE/SOT and SOHO/MDI magnetogram, we infer the flare magnetic reconnection rate in the form of the magnetic flux change rate. This correlates in time with the microwave emission, indicating a physical link between the flare magnetic reconnection and the acceleration of nonthermal particles. Combining radio spectrograph data from Huairou/NOAC, Culgoora/IPS, Learmonth/RSTN, and WAVES/WIND leads to a continuous and longlasting radio burst extending from a few GHz down to several kHz. Based on the photospheric vector magnetogram from Huairou/NOAC and the nonlinear force free field (NFFF) reconstruction method, we derive the 3D magnetic field configuration shortly after the eruption. Furthermore, we also compute coronal field lines extending to a few solar radii using a potential-field source-surface (PFSS) model. Both the so-called type III-l burst and the magnetic field configuration suggest that open-field lines extend from the flare active region into interplanetary space, allowing the accelerated and charged particles escape.

Emerging and Decaying Magnetic Flux and Subsurface Flows

We study the temporal variation of subsurface flows of 788 active regions and 978 quiet regions. The vertical-velocity component used in this study is derived from the divergence of the measured horizontal flows using mass conservation. The horizontal flows cover a range of depths from the surface to about 16 Mm and are determined by analyzing about five years of GONG high-resolution Doppler data with ring-diagram analysis. We determine the change in unsigned magnetic flux during the disk passage of each active region using MDI magnetograms binned to the ring-diagram grid. We then sort the data by their flux change from decaying to emerging flux and divide the data into five subsets of equal size. The average vertical flows of the emerging-flux subset are systematically shifted toward upflows compared to the grand average values of the complete data set, whereas the average flows of the decaying-flux subset show comparably more pronounced downflows especially near 8 Mm. For flux emergence, upflows become stronger with time with increasing flux at depths greater than about 10 Mm. At layers shallower than about 4 Mm, the flows might start to change from downflows to upflows, when flux emerges, and then back to downflows after the active regions are established. The flows in the layers between these two depth ranges show no response to the emerging flux. In the case of decaying flux, the flows change from strong upflows to downflows at depths greater than about 10 Mm, whereas the flows do not change systematically at other depths. A cross-correlation analysis shows that the flows in the near-surface and the deeper layers might change about one day before flux emerges. The flows associated with the quiet regions fluctuate with time but do not show any systematic variation.

Ensemble inversion of time‐dependent core flow models

Quasi‐geostrophic core flow models are built from two secular variation models spanning the periods 1960–2002 and 1997–2008. We rely on an ensemble method to account for the contributions of the unresolved small‐scale magnetic field interacting with core surface flows to the observed magnetic field changes. The different core flow members of the ensemble solution agree up to spherical harmonic degree ℓ ≃ 10, and this resolved component varies only weakly with regularization. Taking into account the finite correlation time of the small‐scale concealed magnetic field, we find that the time variations of the magnetic field occurring over short time scales, such as the geomagnetic jerks, can be accounted for by the resolved (large‐scale) part of the flow to a large extent. Residuals from our flow models are 30% smaller for recent epochs, after 1995. This result is attributed to an improvement in the quality of geomagnetic data. The magnetic field models show little frozen flux violation for the most recent epochs, within our estimate of the apparent magnetic flux changes at the core‐mantle boundary arising from spatial resolution errors. We associate the more important flux changes detected at earlier epochs with uncertainties in the field models at large harmonic degrees. Our core flow models show, at all epochs, an eccentric and planetary‐scale anticyclonic gyre circling around the cylindrical surface tangent to the inner core, at approximately 30 and 60 latitude under the Indian and Pacific oceans, respectively. They account well for the changes in core angular momentum for the most recent epochs.