Coronal Loops: Observations and Modeling of Confined Plasma.

PubMed

Reale, Fabio

Coronal loops are the building blocks of the X-ray bright solar corona. They owe their brightness to the dense confined plasma, and this review focuses on loops mostly as structures confining plasma. After a brief historical overview, the review is divided into two separate but not independent parts: the first illustrates the observational framework, the second reviews the theoretical knowledge. Quiescent loops and their confined plasma are considered and, therefore, topics such as loop oscillations and flaring loops (except for non-solar ones, which provide information on stellar loops) are not specifically addressed here. The observational section discusses the classification, populations, and the morphology of coronal loops, its relationship with the magnetic field, and the loop stranded structure. The section continues with the thermal properties and diagnostics of the loop plasma, according to the classification into hot, warm, and cool loops. Then, temporal analyses of loops and the observations of plasma dynamics, hot and cool flows, and waves are illustrated. In the modeling section, some basics of loop physics are provided, supplying fundamental scaling laws and timescales, a useful tool for consultation. The concept of loop modeling is introduced and models are divided into those treating loops as monolithic and static, and those resolving loops into thin and dynamic strands. More specific discussions address modeling the loop fine structure and the plasma flowing along the loops. Special attention is devoted to the question of loop heating, with separate discussion of wave (AC) and impulsive (DC) heating. Large-scale models including atmosphere boxes and the magnetic field are also discussed. Finally, a brief discussion about stellar coronal loops is followed by highlights and open questions.

Plasmoids as magnetic flux ropes. [in geomagnetic tail

NASA Technical Reports Server (NTRS)

Moldwin, Mark B.; Hughes, W. J.

1991-01-01

A magnetic flux rope model is developed and used to determine whether the principal axis analysis (PAA) of magnetometer signatures from a single satellite pass is sufficient to obtain the magnetic topology of plasmoids. The model is also used to determine if plasmoid observations are best explained by the flux rope, closed loop, or large-amplitude wave picture. It was found that the principal axis directions is highly dependent on the satellite trajectory through the structure and, therefore, the PAA of magnetometer data from a single satellite pass is insufficient to differentiate between magnetic closed loop and flux rope models. Results also indicate that the flux rope model of plasmoid formation is well suited to unify the observations of various magnetic structures observed by ISEE 3.

The Magnetic Structure of H-Alpha Macrospicules in Solar Coronal Holes

NASA Technical Reports Server (NTRS)

Yamauchi, Y.; Moore, R. L.; Suess, S. T.; Wang, H.; Sakuri, T.

2003-01-01

Measurements by Ulysses in the high-speed polar solar wind have shown the wind to carry some fine-scale structures in which the magnetic field reverses direction by having a switchback fold in it. The lateral span of these magnetic switchbacks, translated to the Sun, is of the scale of the lanes and cells of the magnetic network in which the open magnetic flux of the polar coronal hole and polar solar wind are rooted. This suggests that the magnetic switchbacks might be formed from network-scale magnetic loops that erupt into the corona and then undergo reconnection with the open field. This possibility motivated us to undertake the study reported here of the structure of H-alpha macrospicules observed at the limb in polar coronal holes, to determine whether a significant fraction of these eruptions appear to be erupting loops. From a search of the polar-coronal holes in 6 days of image-processed full-disk H-alpha movies from Big Bear Solar Observatory, we found a total of 35 macrospicules. Nearly all of these (32) were of one or the other of two different forms: 15 were in the form of an erupting loop, and 17 were in the form of a single-column spiked jet. The erupting-loop macrospicules are appropriate for producing the magnetic switchbacks in the polar wind. The spiked-jet macrospicules show the appropriate structure and evolution to be driven by reconnection between network-scale closed field (a network bipole) and the open field rooted against the closed field. This evidence for reconnection in a large fraction of our macrospicules (1) suggests that many spicules may be generated by similar but smaller reconnection events, and (2) supports the view that coronal heating and solar wind acceleration in coronal holes and in quiet regions and corona are driven by explosive reconnection events in the magnetic network.

The Magnetic Structure of H-alpha Macrospicules in Solar Coronal Holes

NASA Technical Reports Server (NTRS)

Yamauchi, Y.; Moore, R. L.; Suess, S. T.; Wang, H.; Sakurai, T.

2004-01-01

Measurements by Ulysses in the high-speed polar solar wind have shown the wind to carry some fine-scale structures in which the magnetic field reverses direction by having a switchback fold in it. The lateral span of these magnetic switchbacks, translated back to the Sun, is of the scale of the lanes and cells of the magnetic network in which the open magnetic field of the polar coronal hole and polar solar wind are rooted. This suggests that the magnetic switchbacks might be formed from network-scale magnetic loops that erupt into the corona and then undergo reconnection with the open field. This possibility motivated us to undertake the study reported here of the structure of Ha macrospicules observed at the limb in polar coronal holes, to determine whether a significant fraction of these eruptions appear to be erupting loops. From a search of the polar coronal holes in 6 days of image- processed full-disk Ha movies from Big Bear Solar Observatory, we found a total of 35 macrospicules. Nearly all of these (32) were of one or the other of two different forms: 15 were in the form of an erupting loop, and 17 were in the form of a single column spiked jet. The erupting-loop macrospicules are appropriate for producing the magnetic switchbacks in the polar wind. The spiked-jet macrospicules show the appropriate structure and evolution to be driven by reconnection between network-scale closed field (a network bipole) and the open field rooted against the closed field. This evidence for reconnection in a large fraction of our macrospicules (1) suggests that many spicules may be generated by similar but smaller reconnection events and (2) supports the view that coronal heating and solar wind acceleration in coronal holes and in quiet regions are driven by explosive reconnection events in the magnetic network.

Three-Dimensional Structure and Evolution of Extreme-Ultraviolet Bright Points Observed by STEREO/SECCHI/EUVI

NASA Technical Reports Server (NTRS)

Kwon, Ryun Young; Chae, Jongchul; Davila, Joseph M.; Zhang, Jie; Moon, Yong-Jae; Poomvises, Watanachak; Jones, Shaela I.

2012-01-01

We unveil the three-dimensional structure of quiet-Sun EUV bright points and their temporal evolution by applying a triangulation method to time series of images taken by SECCHI/EUVI on board the STEREO twin spacecraft. For this study we examine the heights and lengths as the components of the three-dimensional structure of EUV bright points and their temporal evolutions. Among them we present three bright points which show three distinct changes in the height and length: decreasing, increasing, and steady. We show that the three distinct changes are consistent with the motions (converging, diverging, and shearing, respectively) of their photospheric magnetic flux concentrations. Both growth and shrinkage of the magnetic fluxes occur during their lifetimes and they are dominant in the initial and later phases, respectively. They are all multi-temperature loop systems which have hot loops (approx. 10(exp 6.2) K) overlying cooler ones (approx 10(exp 6.0) K) with cool legs (approx 10(exp 4.9) K) during their whole evolutionary histories. Our results imply that the multi-thermal loop system is a general character of EUV bright points. We conclude that EUV bright points are flaring loops formed by magnetic reconnection and their geometry may represent the reconnected magnetic field lines rather than the separator field lines.

Successive Two-sided Loop Jets Caused by Magnetic Reconnection between Two Adjacent Filamentary Threads

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tian, Zhanjun; Liu, Yu; Shen, Yuandeng

We present observational analysis of two successive two-sided loop jets observed by the ground-based New Vacuum Solar Telescope and the space-borne Solar Dynamics Observatory . The two successive two-sided loop jets manifested similar evolution processes and both were associated with the interaction of two small-scale adjacent filamentary threads, magnetic emerging, and cancellation processes at the jet’s source region. High temporal and high spatial resolution observations reveal that the two adjacent ends of the two filamentary threads are rooted in opposite magnetic polarities within the source region. The two threads approached each other, and then an obvious brightening patch is observedmore » at the interaction position. Subsequently, a pair of hot plasma ejections are observed heading in opposite directions along the paths of the two filamentary threads at a typical speed for two-sided loop jets of the order 150 km s{sup −1}. Close to the end of the second jet, we report the formation of a bright hot loop structure at the source region, which suggests the formation of new loops during the interaction. Based on the observational results, we propose that the observed two-sided loop jets are caused by magnetic reconnection between the two adjacent filamentary threads, largely different from the previous scenario that a two-sided loop jet is generated by magnetic reconnection between an emerging bipole and the overlying horizontal magnetic fields.« less

STEREOSCOPIC OBSERVATION OF SLIPPING RECONNECTION IN A DOUBLE CANDLE-FLAME-SHAPED SOLAR FLARE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gou, Tingyu; Liu, Rui; Wang, Yuming

2016-04-20

The 2011 January 28 M1.4 flare exhibits two side-by-side candle-flame-shaped flare loop systems underneath a larger cusp-shaped structure during the decay phase, as observed at the northwestern solar limb by the Solar Dynamics Observatory . The northern loop system brightens following the initiation of the flare within the southern loop system, but all three cusp-shaped structures are characterized by ∼10 MK temperatures, hotter than the arch-shaped loops underneath. The “Ahead” satellite of the Solar Terrestrial Relations Observatory provides a top view, in which the post-flare loops brighten sequentially, with one end fixed while the other apparently slipping eastward. By performingmore » stereoscopic reconstruction of the post-flare loops in EUV and mapping out magnetic connectivities, we found that the footpoints of the post-flare loops are slipping along the footprint of a hyperbolic flux tube (HFT) separating the two loop systems and that the reconstructed loops share similarity with the magnetic field lines that are traced starting from the same HFT footprint, where the field lines are relatively flexible. These results argue strongly in favor of slipping magnetic reconnection at the HFT. The slipping reconnection was likely triggered by the flare and manifested as propagative dimmings before the loop slippage is observed. It may contribute to the late-phase peak in Fe xvi 33.5 nm, which is even higher than its main-phase counterpart, and may also play a role in the density and temperature asymmetry observed in the northern loop system through heat conduction.« less

Impact of magnetic isolation on pointing system performance in the presence of structural flexibility

NASA Technical Reports Server (NTRS)

Seller, J.

1985-01-01

The inertial pointing stability of a gimbal pointing system (AGS) was compared with a magnetic pointing/gimbal followup system (ASPS), under certain conditions of system structural flexibility and disturbance inputs from the gimbal support structure. Separate 3 degree-of-freedom (3DOF) linear models based on NASTRAN modal flexibility data for the gimbal and support structures were generated for the ASPS configurations. Using the models inertial pointing control loops providing 6dB of gain margin and 45 deg of phase margin were defined for each configuration. The pointing loop bandwidth obtained for the ASPS is more than twice the level achieved for the AGS configuration. The AGS limit is attributed to the gimbal and support structure flexibility. As a result of the higher ASPS pointing loop bandwidth and the disturbance rejection provided by the magnetic isolation ASPS pointing performane is significantly better than that of the AGS system. The low frequency peak of the ASPS transfer function from base disturbance to payload angular motion is almost 60dB lower than AGS low frequency peak.

On build-up of magnetic energy in the solar atmosphere

NASA Technical Reports Server (NTRS)

Nakagawa, Y.; Steinolfson, R. S.; Wu, S. T.

1976-01-01

The dynamic response of the solar atmosphere is examined with the use of self-consistent numerical solutions to the complete set of nonlinear two-dimensional hydromagnetic equations. Of particular interest are the magnetic-energy buildup and the velocity field established by emerging flux at the base of an existing magnetic loop structure in a stationary atmosphere. For a plasma with a relatively low beta (0.03), the magnetic-energy buildup is approximately twice that of the kinetic energy, while the buildup in magnetic energy first exceeds but is eventually overtaken by the kinetic energy for a plasma with an intermediate beta (3). The increased magnetic flux causes the plasma to flow upward near the loop center and downward near the loop edges for the low-beta plasma. The plasma eventually flows downward throughout the lower portion of the loop carrying the magnetic field with it for the intermediate beta plasma. It is hypothesized that this latter case, and possibly the other case as well, may provide a reasonable simulation of the disappearance of prominences by flowing down into the chromosphere (a form of disparition brusque).

The effects of magnetic structure on the conduction cooling of flare loops

NASA Technical Reports Server (NTRS)

Van Hoven, G.

1979-01-01

A model of the sheared magnetic field in a coronal loop is used to evaluate the average cross-field suppression of axial thermal conduction. If the energy source is uniform in radius, this can lead to heat-flux reduction by a factor greater than three. When the source is annular, in a region of radius where the current density and shear are peaked, the effect can be significantly larger. In one extreme case, however, in which magnetic tearing provides the heating in a very narrow layer, the spatial resonance of the source excitation in a long loop leads to approximately axial conduction.

Structure and Dynamics of Coronal Plasma

NASA Technical Reports Server (NTRS)

Golub, Leon

1998-01-01

Brief summaries of the four published papers produced within the present performance period of NASA Grant NAGW-4081 are presented. The full text of the papers are appended to the report. The first paper titled "Coronal Structures Observed in X-rays and H-alpa Structures" was published in the Kofu Symposium proceedings. The study analyzes cool and hot behavior of two x-ray events, a small flare and a surge. It was found that a large H-alpha surge appears in x-rays as a very weak event, while a weak H-alpha feature corresponds to the brightest x-ray emission on the disk at the time of the observation. Calculations of the heating necessary to produce these signatures, and implications for the driving and heating mechanisms of flares vs. surges are presented. The second paper "Differential Magnetic Field Shear in an Active Region" has been published in The Astrophysical Journal. The study compared the three dimensional extrapolation of magnetic fields with the observed coronal structure in an active region. Based on the fit between observed coronal structure throughout the volume of the region and the calculated magnetic field configurations, the authors propose a differential magnetic field shear model for this active region. The decreasing field shear in the outer portions of the AR may indicate a continual relaxation of the magnetic field with time, corresponding to a net transport of helicity outward. The third paper "Difficulties in Observing Coronal Structure" has been published in the journal Solar Physics. This paper discusses the evidence that the temperature and density structure of the corona are far more complicated than had previously been thought. The discussion is based on five studies carried out by the group on coronal plasma properties, showing that any one x-ray instrument does see all of the plasma present in the corona, that hot and cool material may appear to be co-spatial at a given location in the corona, and that simple magnetic field extrapolations provide only a poor fit to the observed structure. The fourth paper "Analysis and Comparison of Loop Structures Imaged with NIXT and Yohkoh/SXT" has been published in Astronomy and Astrophysics. This paper analyzes and compares a variety of coronal loops, deriving loop pressure and emission measure from loop models. They are able to determine the volume filling factor in the corona, which is found to be in the range 0.001 to 0.01 for compact loops, and of order 1 for large structures. The small values suggest highly filamented structures, especially at lower temperatures.

Force-Free Magnetic Fields Calculated from Automated Tracing of Coronal Loops with AIA/SDO

NASA Astrophysics Data System (ADS)

Aschwanden, M. J.

2013-12-01

One of the most realistic magnetic field models of the solar corona is a nonlinear force-free field (NLFFF) solution. There exist about a dozen numeric codes that compute NLFFF solutions based on extrapolations of photospheric vector magnetograph data. However, since the photosphere and lower chromosphere is not force-free, a suitable correction has to be applied to the lower boundary condition. Despite of such "pre-processing" corrections, the resulting theoretical magnetic field lines deviate substantially from observed coronal loop geometries. - Here we developed an alternative method that fits an analytical NLFFF approximation to the observed geometry of coronal loops. The 2D coordinates of the geometry of coronal loop structures observed with AIA/SDO are traced with the "Oriented Coronal CUrved Loop Tracing" (OCCULT-2) code, an automated pattern recognition algorithm that has demonstrated the fidelity in loop tracing matching visual perception. A potential magnetic field solution is then derived from a line-of-sight magnetogram observed with HMI/SDO, and an analytical NLFFF approximation is then forward-fitted to the twisted geometry of coronal loops. We demonstrate the performance of this magnetic field modeling method for a number of solar active regions, before and after major flares observed with SDO. The difference of the NLFFF and the potential field energies allows us then to compute the free magnetic energy, which is an upper limit of the energy that is released during a solar flare.

Mass and energy supply of a cool coronal loop near its apex

NASA Astrophysics Data System (ADS)

Yan, Limei; Peter, Hardi; He, Jiansen; Xia, Lidong; Wang, Linghua

2018-03-01

Context. Different models for the heating of solar corona assume or predict different locations of the energy input: concentrated at the footpoints, at the apex, or uniformly distributed. The brightening of a loop could be due to the increase in electron density ne, the temperature T, or a mixture of both. Aim. We investigate possible reasons for the brightening of a cool loop at transition region temperatures through imaging and spectral observation. Methods: We observed a loop with the Interface Region Imaging Spectrograph (IRIS) and used the slit-jaw images together with spectra taken at a fixed slit position to study the evolution of plasma properties in and below the loop. We used spectra of Si IV, which forms at around 80 000 K in equilibrium, to identify plasma motions and derive electron densities from the ratio of inter-combination lines of O IV. Additional observations from the Solar Dynamics Observatory (SDO) were employed to study the response at coronal temperatures (Atmospheric Imaging Assembly, AIA) and to investigate the surface magnetic field below the loop (Helioseismic and Magnetic Imager, HMI). Results: The loop first appears at transition region temperatures and later also at coronal temperatures, indicating a heating of the plasma in the loop. The appearance of hot plasma in the loop coincides with a possible accelerating upflow seen in Si IV, with the Doppler velocity shifting continuously from -70 km s-1 to -265 km s-1. The 3D magnetic field lines extrapolated from the HMI magnetogram indicate possible magnetic reconnection between small-scale magnetic flux tubes below or near the loop apex. At the same time, an additional intensity enhancement near the loop apex is visible in the IRIS slit-jaw images at 1400 Å. These observations suggest that the loop is probably heated by the interaction between the loop and the upflows, which are accelerated by the magnetic reconnection between small-scale magnetic flux tubes at lower altitudes. Before and after the possible heating phase, the intensity changes in the optically thin (Si IV) and optical thick line (C II) are mainly contributed by the density variation without significant heating. Conclusions: We therefore provide evidence for the heating of an envelope loop that is affected by accelerating upflows, which are probably launched by magnetic reconnection between small-scale magnetic flux tubes underneath the envelope loop. This study emphasizes that in the complex upper atmosphere of the Sun, the dynamics of the 3D coupled magnetic field and flow field plays a key role in thermalizing 1D structures such as coronal loops. An animation associated to Fig. 1 is available at http://https://www.aanda.org

Reconnection on the Sun

NASA Astrophysics Data System (ADS)

Kohler, Susanna

2016-05-01

Because the Sun is so close, it makes an excellent laboratory to study processes we cant examinein distant stars. One openquestion is that of how solar magnetic fields rearrange themselves, producing the tremendous releases of energy we observe as solar flares and coronal mass ejections (CMEs).What is Magnetic Reconnection?Magnetic reconnection occurs when a magnetic field rearranges itself to move to a lower-energy state. As field lines of opposite polarity reconnect, magnetic energy is suddenly converted into thermal and kinetic energy.This processis believed to be behind the sudden releases of energy from the solar surface in the form of solar flares and CMEs. But there are many different models for how magnetic reconnection could occur in the magnetic field at the Suns surface, and we arent sure which one of these reconnection types is responsible for the events we see.Recently, however, several studies have been published presenting some of the first observational support of specific reconnection models. Taken together, these observations suggest that there are likely several different types of reconnection happening on the solar surface. Heres a closer look at two of these recent publications:A pre-eruption SDO image of a flaring region (b) looks remarkably similar to a 3D cartoon for typical breakout configuration (a). Click for a closer look! [Adapted from Chen et al. 2016]Study 1:Magnetic BreakoutLed by Yao Chen (Shandong University in China), a team of scientists has presented observations made by the Solar Dynamics Observatory (SDO) of a flare and CME event that appears to have been caused by magnetic breakout.In the magnetic breakout model, a series of loops in the Suns lower corona are confined by a surrounding larger loop structure called an arcade higher in the corona. As the lower loops push upward, reconnection occurs in the upper corona, removing the overlying, confining arcade. Without that extra confinement, the lower coronal loops expand upward, erupting from the solar surface.Snapshots from the SDO side view (left and center) and STEREO overhead view (right). The three rows show the time evolution of the double-loop structure after the initial flare. In the STEREO view, you can see the central footpoints of the loops slip to the left. [Gou et al. 2016]In the SDO observations presented by Chen and collaborators, the pre-flare/CME structures look remarkably like the structures predicted in the breakout model. Sequential heating of loops can be seen as the breakout reconnection starts, followed by anenormous flare and CME as the lower loops erupt outward.Study 2: Slipping ReconnectionA team of scientists from the University of Science and Technology of China, led by Tingyu Gou and Rui Liu, have presented the first stereoscopic observation of slipping reconnection in the Sun, made by the two-spacecraft Solar Terrestrial Relations Observatory (STEREO).In slipping reconnection, magnetic field lines continuously exchange connectivities with their neighbors, causing them to slip through plasma. Observations by STEREO of a flaring double-loop system revealed that the central footpoints the endpoints where the loops are anchored to the solar surface slipped sideways after a flare.The authors model of the double-loop structure at two different times, during which the central footpoint slips from point C to D. Projections onto the XY and YZ planes show STEREOs and SDOs views, respectively. [Gou et al. 2016]The authors reconstructed a 3D model of the loop system using the overhead observations from STEREO and a simultaneous side view from SDO. They speculate that the slipping reconnection was likely triggered by the initial solar flare.Double BonusCheck out the videos belowto watch these processes happen!This first video is from Chen et al. 2016, and shows the SDO view of coronal loops in three wavelengths. If you watch carefully, you can see the sequential brightening of loops signs of the breakout reconnection before the flare and CME.http://aasnova.org/wp-content/uploads/2016/05/breakout.mp4This second video is from Gou et al. 2016, and shows the SDO side view (left and center panels) and STEREO top view (right panel) of a flare and the slipping reconnection that occurred after. Keep your eye on the STEREO view between 0:02 and 0:04 to watch the central footpoint slide left.http://aasnova.org/wp-content/uploads/2016/05/slipping.mp4CitationYao Chen et al 2016 ApJ 820 L37. doi:10.3847/2041-8205/820/2/L37Tingyu Gou et al 2016 ApJ 821 L28. doi:10.3847/2041-8205/821/2/L28

Observable Signatures of Energy Release in Braided Coronal Loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pontin, D. I.; Janvier, M.; Tiwari, S. K.

We examine the turbulent relaxation of solar coronal loops containing non-trivial field line braiding. Such field line tangling in the corona has long been postulated in the context of coronal heating models. We focus on the observational signatures of energy release in such braided magnetic structures using MHD simulations and forward modeling tools. The aim is to answer the following question: if energy release occurs in a coronal loop containing braided magnetic flux, should we expect a clearly observable signature in emissions? We demonstrate that the presence of braided magnetic field lines does not guarantee a braided appearance to themore » observed intensities. Observed intensities may—but need not necessarily—reveal the underlying braided nature of the magnetic field, depending on the degree and pattern of the field line tangling within the loop. However, in all cases considered, the evolution of the braided loop is accompanied by localized heating regions as the loop relaxes. Factors that may influence the observational signatures are discussed. Recent high-resolution observations from Hi-C have claimed the first direct evidence of braided magnetic fields in the corona. Here we show that both the Hi-C data and some of our simulations give the appearance of braiding at a range of scales.« less

Characterisation of case depth in induction-hardened medium carbon steels based on magnetic minor hysteresis loop measurement technique

NASA Astrophysics Data System (ADS)

He, Cunfu; Yang, Meng; Liu, Xiucheng; Wang, Xueqian; Wu, Bin

2017-11-01

The magnetic hysteresis behaviours of ferromagnetic materials vary with the heat treatment-induced micro-structural changes. In the study, the minor hysteresis loop measurement technique was used to quantitatively characterise the case depth in two types of medium carbon steels. Firstly, high-frequency induction quenching was applied in rod samples to increase the volume fraction of hard martensite to the soft ferrite/pearlite (or sorbite) in the sample surface. In order to determine the effective and total case depth, a complementary error function was employed to fit the measured hardness-depth profiles of induction-hardened samples. The cluster of minor hysteresis loops together with the tangential magnetic field (TMF) were recorded from all the samples and the comparative study was conducted among three kinds of magnetic parameters, which were sensitive to the variation of case depth. Compared to the parameters extracted from an individual minor loop and the distortion factor of the TMF, the magnitude of three-order harmonic of TMF was more suitable to indicate the variation in case depth. Two new minor-loop coefficients were introduced by combining two magnetic parameters with cumulative statistics of the cluster of minor-loops. The experimental results showed that the two coefficients monotonically linearly varied with the case depth within the carefully selected magnetisation region.

Mini-filament Eruption as the Initiation of a Jet along Coronal Loops

NASA Astrophysics Data System (ADS)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan; Yang, Bo; Xu, Zhe; Xiang, Yongyuan

2016-10-01

Minifilament eruptions (MFEs) and coronal jets are different types of solar small-scale explosive events. We report an MFE observed at the New Vacuum Solar Telescope (NVST). As seen in the NVST Hα images, during the rising phase, the minifilament erupts outward orthogonally to its length, accompanied with a flare-like brightening at the bottom. Afterward, dark materials are found to possibly extend along the axis of the expanded filament body. The MFE is analogous to large filament eruptions. However, a simultaneous observation of the Solar Dynamics Observatory shows that a jet is initiated and flows out along nearby coronal loops during the rising phase of the MFE. Meanwhile, small hot loops, which connect the original eruptive site of the minifilament to the footpoints of the coronal loops, are formed successively. A differential emission measure analysis demonstrates that, on the top of the new small loops, a hot cusp structure exists. We conjecture that the magnetic fields of the MFE interact with magnetic fields of the coronal loops. This interaction is interpreted as magnetic reconnection that produces the jet and the small hot loops.

Symmetry transition via tetravalent impurity and investigations on magnetic properties of Li0.5Fe2.5O4

NASA Astrophysics Data System (ADS)

Kounsalye, Jitendra S.; Kharat, Prashant B.; Chavan, Apparao R.; Humbe, Ashok V.; Borade, R. M.; Jadhav, K. M.

2018-04-01

The present study, deals with the phase symmetry transformation of lithium ferrite after introducing tetravalent (Ti4+) impurity. The sol-gel auto combustion technique was adopted for the synthesis of nanoparticle samples with generic chemical formula Li0.5Fe2.5O4 and Li0.55Ti0.10Fe2.35O4. The synthesized nanoparticles were characterized by X-ray diffraction (XRD) technique for structural analysis. The XRD patterns show the single phase cubic structure without any impurity phase but the P4332 to Fd-3m transformation was observed after introducing Ti4+ impurity. The Nano size of the synthesized particles was confirmed by crystallite size ( 20nm) calculated using Debye-Scherrer's formula. The Fourier transform infrared spectroscopy (FTIR) studies shows shifting of band frequencies which reflect the structural changes after tetravalent substitutional impurities. The magnetic properties were studied through pulse field hysteresis loop (M-H loop) technique at room temperature, the M-H loops showdecrease in magnetic properties afternonmagnetic Ti4+ ion substitution. This is attributed to transition of inverse spinel structure of lithium ferrite to random spinel structure.

The Role of Magnetic Helicity in Structuring the Solar Corona

NASA Technical Reports Server (NTRS)

Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

2017-01-01

Two of the most widely observed and striking features of the Suns magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure filament channels is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result from a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.

Are Complex Magnetic Field Structures Responsible for the Confined X-class Flares in Super Active Region 12192?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhang, Jun; Li, Ting; Chen, Huadong, E-mail: zjun@nao.cas.cn, E-mail: hdchen@nao.cas.cn

From 2014 October 19 to 27, six X-class flares occurred in super active region (AR) 12192. They were all confined flares and were not followed by coronal mass ejections. To examine the structures of the four flares close to the solar disk center from October 22 to 26, we firstly employ composite triple-time images in each flare process to display the stratified structure of these flare loops. The loop structures of each flare in both the lower (171 Å) and higher (131 Å) temperature channels are complex, e.g., the flare loops rooting at flare ribbons are sheared or twisted (enwound)more » together, and the complex structures were not destroyed during the flares. For the first flare, although the flare loop system appears as a spindle shape, we can estimate its structures from observations, with lengths ranging from 130 to 300 Mm, heights from 65 to 150 Mm, widths at the middle part of the spindle from 40 to 100 Mm, and shear angles from 16° to 90°. Moreover, the flare ribbons display irregular movements, such as the left ribbon fragments of the flare on October 22 sweeping a small region repeatedly, and both ribbons of the flare on October 26 moved along the same direction instead of separating from each other. These irregular movements also imply that the corresponding flare loops are complex, e.g., several sets of flare loops are twisted together. Although previous studies have suggested that the background magnetic fields prevent confined flares from erupting,based on these observations, we suggest that complex flare loop structures may be responsible for these confined flares.« less

Large-scale flows, sheet plumes and strong magnetic fields in a rapidly rotating spherical dynamo

NASA Astrophysics Data System (ADS)

Takahashi, F.

2011-12-01

Mechanisms of magnetic field intensification by flows of an electrically conducting fluid in a rapidly rotating spherical shell is investigated. Bearing dynamos of the Eartn and planets in mind, the Ekman number is set at 10-5. A strong dipolar solution with magnetic energy 55 times larger than the kinetic energy of thermal convection is obtained. In a regime of small viscosity and inertia with the strong magnetic field, convection structure consists of a few large-scale retrograde flows in the azimuthal direction and sporadic thin sheet-like plumes. The magnetic field is amplified through stretching of magnetic lines, which occurs typically through three types of flow: the retrograde azimuthal flow near the outer boundary, the downwelling flow of the sheet plume, and the prograde azimuthal flow near the rim of the tangent cylinder induced by the downwelling flow. It is found that either structure of current loops or current sheets is accompanied in each flow structure. Current loops emerge as a result of stretching the magnetic lines along the magnetic field, wheres the current sheets are formed to counterbalance the Coriolis force. Convection structure and processes of magnetic field generation found in the present model are distinct from those in models at larger/smaller Ekman number.

Onset of multiferroicity in nickel and lithium co-substituted barium titanate ceramics

NASA Astrophysics Data System (ADS)

Alkathy, Mahmoud S.; James Raju, K. C.

2018-04-01

The structural, magnetic and ferroelectric properties of nickel and lithium co-substituted barium titanate were investigated in this work. Ba(1-x)LixNix/2TiO3 (x = 0, 0.02, 0.04 and 0.08) ceramics were synthesized via solid-state reaction with the assistance of microwave heating of the starting materials. The tetragonal structure has been observed in all samples, and it is confirmed by the Rietveld refinement study. The morphological study has been carried out by FE-SEM. Electron spin resonance (ESR) has been used to study the electron interaction and to verify the magnetism behavior of present samples. No resonance signal was observed in pure BaTiO3 samples. However, the resonance signal has appeared in the co-substituted samples. The result shows that the electron interactions are strongly affected by Ni2+ and Li+ concentrations. M-H loop was traced using VSM at room temperature. The results confirm that the sample with x = 0 shows an anti-ferromagnetic response. However, a ferromagnetic hysteresis loop arises with co-substitution. The emergence of M-H loops confirms the appearance of magnetic properties in Ni2+ and Li+ co-substituted BaTiO3 ceramics. The origin of magnetic behavior could be due to the carrier-mediated exchange interactions. Room temperature P-E hysteresis loop has been investigated at an applied electric field of 35 kV/cm and 33 Hz frequency. Measurements of room temperature ferroelectric and magnetic hysteresis loops indicate that the Ni2+ and Li+ co-substituted BaTiO3 ceramics show ferroelectricity and ferromagnetism simultaneously.

TRIGGER MECHANISM OF SOLAR SUBFLARES IN A BRAIDED CORONAL MAGNETIC STRUCTURE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiwari, Sanjiv K.; Alexander, Caroline E.; Winebarger, Amy R.

Fine-scale braiding of coronal magnetic loops by continuous footpoint motions may power coronal heating via nanoflares, which are spontaneous fine-scale bursts of internal reconnection. An initial nanoflare may trigger an avalanche of reconnection of the braids, making a microflare or larger subflare. In contrast to this internal triggering of subflares, we observe external triggering of subflares in a braided coronal magnetic field observed by the High-resolution Coronal Imager (Hi-C). We track the development of these subflares using 12 s cadence images acquired by SDO/AIA in 1600, 193, 94 Å, and registered magnetograms of SDO/HMI, over four hours centered on the Hi-Cmore » observing time. These data show numerous recurring small-scale brightenings in transition-region emission happening on polarity inversion lines where flux cancellation is occurring. We present in detail an example of an apparent burst of reconnection of two loops in the transition region under the braided coronal field which is appropriate for releasing a short reconnected loop downward and a longer reconnected loop upward. The short loop presumably submerges into the photosphere, participating in observed flux cancellation. A subflare in the overlying braided magnetic field is apparently triggered by the disturbance of the braided field by the reconnection-released upward loop. At least 10 subflares observed in this braided structure appear to be triggered this way. How common this external trigger mechanism for coronal subflares is in other active regions, and how important it is for coronal heating in general, remain to be seen.« less

Saturable inductor and transformer structures for magnetic pulse compression

DOEpatents

Birx, Daniel L.; Reginato, Louis L.

1990-01-01

Saturable inductor and transformer for magnetic compression of an electronic pulse, using a continuous electrical conductor looped several times around a tightly packed core of saturable inductor material.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xie, Haixia; Li, Bo; Huang, Zhenghua

How the solar corona is heated to high temperatures remains an unsolved mystery in solar physics. In the present study we analyze observations of 50 whole active region loops taken with the Extreme-ultraviolet Imaging Spectrometer on board the Hinode satellite. Eleven loops were classified as cool loops (<1 MK) and 39 as warm loops (1–2 MK). We study their plasma parameters, such as densities, temperatures, filling factors, nonthermal velocities, and Doppler velocities. We combine spectroscopic analysis with linear force-free magnetic field extrapolation to derive the 3D structure and positioning of the loops, their lengths and heights, and the magnetic fieldmore » strength along the loops. We use density-sensitive line pairs from Fe xii, Fe xiii, Si x, and Mg vii ions to obtain electron densities by taking special care of intensity background subtraction. The emission measure loci method is used to obtain the loop temperatures. We find that the loops are nearly isothermal along the line of sight. Their filling factors are between 8% and 89%. We also compare the observed parameters with the theoretical Rosner–Tucker–Vaiana (RTV) scaling law. We find that most of the loops are in an overpressure state relative to the RTV predictions. In a follow-up study, we will report a heating model of a parallel-cascade-based mechanism and will compare the model parameters with the loop plasma and structural parameters derived here.« less

Structure modulation of helix 69 from Escherichia coli 23S ribosomal RNA by pseudouridylations.

PubMed

Jiang, Jun; Aduri, Raviprasad; Chow, Christine S; SantaLucia, John

2014-04-01

Helix 69 (H69) is a 19-nt stem-loop region from the large subunit ribosomal RNA. Three pseudouridine (Ψ) modifications clustered in H69 are conserved across phylogeny and known to affect ribosome function. To explore the effects of Ψ on the conformations of Escherichia coli H69 in solution, nuclear magnetic resonance spectroscopy was used to reveal the structural differences between H69 with (ΨΨΨ) and without (UUU) Ψ modifications. Comparison of the two structures shows that H69 ΨΨΨ has the following unique features: (i) the loop region is closed by a Watson-Crick base pair between Ψ1911 and A1919, which is potentially reinforced by interactions involving Ψ1911N1H and (ii) Ψ modifications at loop residues 1915 and 1917 promote base stacking from Ψ1915 to A1918. In contrast, the H69 UUU loop region, which lacks Ψ modifications, is less organized. Structure modulation by Ψ leads to alteration in conformational behavior of the 5' half of the H69 loop region, observed as broadening of C1914 non-exchangeable base proton resonances in the H69 ΨΨΨ nuclear magnetic resonance spectra, and plays an important biological role in establishing the ribosomal intersubunit bridge B2a and mediating translational fidelity.

Adjustability of resonance frequency by external magnetic field and bias electric field of sandwich magnetoelectric PZT/NFO/PZT composites

NASA Astrophysics Data System (ADS)

Xu, Ling-Fang; Feng, Xing; Sun, Kang; Liang, Ze-Yu; Xu, Qian; Liang, Jia-Yu; Yang, Chang-Ping

2017-07-01

Sandwich magnetoelectric composites of PZT/NFO/PZT (PNP) have been prepared by laminating PZT5, NiFe2O4, and PZT5 ceramics in turn with polyvinyl alcohol (PVA) paste. A systematic study of structural, magnetic and ferroelectric properties is undertaken. Structural studies carried out by X-ray diffraction indicate formation of cubic perovskite phase of PZT5 ceramic and cubic spinel phase of NiFe2O4 ceramic. As increasing the content of PZT5 phase, ferroelectric loops and magnetic loops of PNP composites showed increasing remnant electric polarizations and decreasing remnant magnetic moments separately. Both external magnetic fields and bias voltages could regulate the basal radial resonance frequency of the composites, which should be originated with the transformation and coupling of the stress between the piezoelectric phase and magnetostrictive phase. Such magnetoelectric composite provides great opportunities for electrostatically tunable devices.

Exchange bias in multiferroic Ca3Mn2O7 effected by Dzyaloshinskii-Moriya interaction

NASA Astrophysics Data System (ADS)

Sahlot, Pooja; Jana, Anupam; Awasthi, A. M.

2018-04-01

Ruddlesden-Popper manganite Ca3Mn2O7 has been synthesized in single phase orthorhombic structure with Cmcm space group. Temperature dependent magnetization M(T) shows that Ca3Mn2O7 undergoes long range antiferromagnetic (AFM) transition below 123 K, with weak ferromagnetism (WFM) at lower temperatures. Field dependent magnetization M(H) confirms WFM character below ˜110 K in the AFM-base magnetic structure. Detailed analysis of the zero field cooled magnetic hysteresis loops reveals a measurable exchange bias (EB) effect in the sample. EB is attributed to the high anisotropy in the sample and the presence of Dzyaloshinskii-Moriya (D-M) interaction, responsible for the canted interfacial-spins that couple "FM-clusters" with the "AFM-matrix". Temperature dependence of horizontal shifts of the M(H) loops in terms of the coercive fields (Hc±) and vertical shifts in terms of the remnant magnetizations (Mr±) is presented.

Imaging a Magnetic-breakout Solar Eruption

NASA Astrophysics Data System (ADS)

Chen, Yao; Du, Guohui; Zhao, Di; Wu, Zhao; Liu, Wei; Wang, Bing; Ruan, Guiping; Feng, Shiwei; Song, Hongqiang

2016-04-01

The fundamental mechanism initiating coronal mass ejections (CMEs) remains controversial. One of the leading theories is magnetic breakout, in which magnetic reconnection occurring high in the corona removes the confinement on an energized low-corona structure from the overlying magnetic field, thus allowing it to erupt. Here, we report critical observational evidence of this elusive breakout reconnection in a multi-polar magnetic configuration that leads to a CME and an X-class, long-duration flare. Its occurrence is supported by the presence of pairs of heated cusp-shaped loops around an X-type null point and signatures of reconnection inflows. Other peculiar features new to the breakout picture include sequential loop brightening, coronal hard X-rays at energies up to ˜100 keV, and extended high-corona X-rays above the later restored multi-polar structure. These observations, from a novel perspective with clarity never achieved before, present crucial clues to understanding the initiation mechanism of solar eruptions.

Topological and trivial magnetic oscillations in nodal loop semimetals

NASA Astrophysics Data System (ADS)

Oroszlány, László; Dóra, Balázs; Cserti, József; Cortijo, Alberto

2018-05-01

Nodal loop semimetals are close descendants of Weyl semimetals and possess a topologically dressed band structure. We argue by combining the conventional theory of magnetic oscillation with topological arguments that nodal loop semimetals host coexisting topological and trivial magnetic oscillations. These originate from mapping the topological properties of the extremal Fermi surface cross sections onto the physics of two dimensional semi-Dirac systems, stemming from merging two massless Dirac cones. By tuning the chemical potential and the direction of magnetic field, a sharp transition is identified from purely trivial oscillations, arising from the Landau levels of a normal two dimensional (2D) electron gas, to a phase where oscillations of topological and trivial origin coexist, originating from 2D massless Dirac and semi-Dirac points, respectively. These could in principle be directly identified in current experiments.

An Assessment of Magnetic Conditions for Strong Coronal Heating in Solar Active Regions by Comparing Observed Loops with Computed Potential Field Lines

NASA Technical Reports Server (NTRS)

Gary, G. A.; Moore, R. L.; Porter, J. G.; Falconer, D. A.

1999-01-01

We report further results on the magnetic origins of coronal heating found from registering coronal images with photospheric vector magnetograms. For two complementary active regions, we use computed potential field lines to examine the global non-potentiality of bright extended coronal loops and the three-dimensional structure of the magnetic field at their feet, and assess the role of these magnetic conditions in the strong coronal heating in these loops. The two active regions are complementary, in that one is globally potential and the other is globally nonpotential, while each is predominantly bipolar, and each has an island of included polarity in its trailing polarity domain. We find the following: (1) The brightest main-arch loops of the globally potential active region are brighter than the brightest main- arch loops of the globally strongly nonpotential active region. (2) In each active region, only a few of the mainarch magnetic loops are strongly heated, and these are all rooted near the island. (3) The end of each main-arch bright loop apparently bifurcates above the island, so that it embraces the island and the magnetic null above the island. (4) At any one time, there are other main-arch magnetic loops that embrace the island in the same manner as do the bright loops but that are not selected for strong coronal heating. (5) There is continual microflaring in sheared core fields around the island, but the main-arch bright loops show little response to these microflares. From these observational and modeling results we draw the following conclusions: (1) The heating of the main-arch bright loops arises mainly from conditions at the island end of these loops and not from their global non-potentiality. (2) There is, at most, only a loose coupling between the coronal heating in the bright loops of the main arch and the coronal heating in the sheared core fields at their feet, although in both the heating is driven by conditions/events in and around the island. (3) The main-arch bright loops are likely to be heated via reconnection driven at the magnetic null over the island. The details of how and where (along the null line) the reconnection is driven determine which of the split-end loops are selected for strong heating. (4) The null does not appear to be directly involved in the heating of the sheared core fields or in the heating of an extended loop rooted in the island. Rather, these all appear to be heated by microflares in the sheared core field.

Feel the Burn: What accounts for spatial variations in coronal heating?

NASA Astrophysics Data System (ADS)

Atwood, Shane; Kankelborg, Charles C.

2016-05-01

The coronal volume is filled with magnetic field, yet only part of that volume has sufficient heating to exhibit hot x-ray loops. How does the Sun decide where the heat goes? Using XRT and AIA images and HMI magnetograms, we identify footpoints of hot coronal loops, and magnetically similar regions underlying relatively unheated corona. We then use IRIS rasters and sit-and-stare observations to compare the spatial, temporal, and spectral structure of these relatively ``heated’’ and ``unheated’’ regions. We seek a signature of upward propagating energy that could be associated with hot active region loops.

Flux trapping in multi-loop SQUIDs and its impact on SQUID-based absolute magnetometry

NASA Astrophysics Data System (ADS)

Schönau, T.; Zakosarenko, V.; Schmelz, M.; Anders, S.; Meyer, H.-G.; Stolz, R.

2018-07-01

The effect of flux trapping on the flux-voltage characteristics of multi-loop SQUID magnetometers was investigated by means of repeated cool-down cycles in a stepwise increased magnetic background field. For a SQUID with N parallel loops, N different flux offsets, each separated by {{{Φ }}}0/N, were observed even in zero magnetic field. These flux offsets further split into a so called fine structure, which can be explained by minor asymmetries in the SQUID design. The observed results are discussed with particular regard to their impact on the previously presented absolute SQUID cascade vector magnetometer.

Heating of the Solar Corona and its Loops

NASA Technical Reports Server (NTRS)

Klimchuk, James A.

2009-01-01

At several million degrees, the solar corona is more than two orders of magnitude hotter than the underlying solar surface. The reason for these extreme conditions has been a puzzle for decades and is considered one of the fundamental problems in astrophysics. Much of the coronal plasma is organized by the magnetic field into arch-like structures called loops. Recent observational and theoretical advances have led to great progress in understanding the nature of these loops. In particular, we now believe they are bundles of unresolved magnetic strands that are heated by storms of impulsive energy bursts called nanoflares. Turbulent convection at the solar surface shuffles the footpoints of the strands and causes them to become tangled. A nanoflare occurs when the magnetic stresses reach a critical threshold, probably by way of a mechanism called the secondary instability. I will describe our current state of knowledge concerning the corona, its loops, and how they are heated.

Feel the Burn, Part II: Quantifying and mapping spectral, spatial, and temporal structures of the transition region under hot and cold coronal regions

NASA Astrophysics Data System (ADS)

Atwood, Shane; Kankelborg, Charles C.

2017-08-01

The coronal volume is filled with magnetic field, yet only part of that volume has sufficient volume to exhibit hot X-ray loops. Using XRT and AIA images, we identify footpoints of hot coronal loops. We then use IRIS rasters to compare the spatial, temporal, and spectral structure of these relatively "heated" and "unheated" regions. We seek a signature of upward-propagating energy that could be associated with hot active region loops.

Neutral and charged scalar mesons, pseudoscalar mesons, and diquarks in magnetic fields

NASA Astrophysics Data System (ADS)

Liu, Hao; Wang, Xinyang; Yu, Lang; Huang, Mei

2018-04-01

We investigate both (pseudo)scalar mesons and diquarks in the presence of external magnetic field in the framework of the two-flavored Nambu-Jona-Lasinio (NJL) model, where mesons and diquarks are constructed by infinite sum of quark-loop chains by using random phase approximation. The polarization function of the quark-loop is calculated to the leading order of 1 /Nc expansion by taking the quark propagator in the Landau level representation. We systematically investigate the masses behaviors of scalar σ meson, neutral and charged pions as well as the scalar diquarks, with respect to the magnetic field strength at finite temperature and chemical potential. It is shown that the numerical results of both neutral and charged pions are consistent with the lattice QCD simulations. The mass of the charge neutral pion keeps almost a constant under the magnetic field, which is preserved by the remnant symmetry of QCD ×QED in the vacuum. The mass of the charge neutral scalar σ is around two times quark mass and increases with the magnetic field due to the magnetic catalysis effect, which is an typical example showing that the polarized internal quark structure cannot be neglected when we consider the meson properties under magnetic field. For the charged particles, the one quark-antiquark loop contribution to the charged π± increases essentially with the increase of magnetic fields due to the magnetic catalysis of the polarized quarks. However, the one quark-quark loop contribution to the scalar diquark mass is negative comparing with the point-particle result and the loop effect is small.

Hybrid Stars and Coronal Evolution

NASA Technical Reports Server (NTRS)

Mushotzky, Richard (Technical Monitor); Dupree, Andrea K.

2004-01-01

This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, TrA (K2 11-111). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars.

Imaging spectroscopy of type U and J solar radio bursts with LOFAR

NASA Astrophysics Data System (ADS)

Reid, Hamish A. S.; Kontar, Eduard P.

2017-10-01

Context. Radio U-bursts and J-bursts are signatures of electron beams propagating along magnetic loops confined to the corona. The more commonly observed type III radio bursts are signatures of electron beams propagating along magnetic loops that extend into interplanetary space. Given the prevalence of solar magnetic flux to be closed in the corona, why type III bursts are more frequently observed than U-bursts or J-bursts is an outstanding question. Aims: We use Low-Frequency Array (LOFAR) imaging spectroscopy between 30-80 MHz of low-frequency U-bursts and J-bursts, for the first time, to understand why electron beams travelling along coronal loops produce radio emission less often. Radio burst observations provide information not only about the exciting electron beams but also about the structure of large coronal loops with densities that are too low for standard extreme ultraviolet (EUV) or X-ray analysis. Methods: We analysed LOFAR images of a sequence of two J-bursts and one U-burst. The different radio source positions were used to model the spatial structure of the guiding magnetic flux tube and then deduce the energy range of the exciting electron beams without the assumption of a standard density model. We also estimated the electron density along the magnetic flux rope and compared it to coronal models. Results: The radio sources infer a magnetic loop that is 1 solar radius in altitude with the highest frequency sources starting around 0.6 solar radii. Electron velocities were found between 0.13 c and 0.24 c with the front of the electron beam travelling faster than the back of the electron beam. The velocities correspond to energy ranges within the beam from 0.7-11 keV to 0.7-43 keV. The density along the loop is higher than typical coronal density models and the density gradient is smaller. Conclusions: We found that a more restrictive range of accelerated beam and background plasma parameters can result in U-bursts or J-bursts, causing type III bursts to be more frequently observed. The large instability distances required before Langmuir waves are produced by some electron beams, and the small magnitude of the background density gradients makes closed loops less facilitative for radio emission than loops that extend into interplanetary space.

Comparative Examination of Plasmoid Ejection at Mercury, Earth, Jupiter, and Saturn

NASA Technical Reports Server (NTRS)

Slavin, James A.; Jackman, Caitriona M.; Vogt, Marissa F.

2011-01-01

The onset of magnetic reconnection in the near-tail of Earth, long known to herald the fast magnetospheric convection that leads to geomagnetic storms and substorms, is very closely associated with the formation and down-tail ejection of magnetic loops or flux ropes called plasmoids. Plasmoids form as a result of the fragmentation of preexisting cross-tail current sheet as a result of magnetic reconnection. Depending upon the number, location, and intensity of the individual reconnection X-lines and how they evolve, some of these loop-like or helical magnetic structures may also be carried sunward. At the inner edge of the tail they are expected to "re-reconnect' with the planetary magnetic field and dissipate. Plasmoid ejection has now been observed in the magnetotails of Mercury, Earth, Jupiter, and Saturn. These magnetic field and charged particle measurements have been taken by the MESSENGER, Voyager, Galileo, Cassini, and numerous Earth missions. Here we present a comparative examination of the structure and dynamics of plasmoids observed in the magnetotails of these 5 planets. The results are used to learn more about how these magnetic structures form and to assess similarities and differences in the nature of magnetotail reconnection at these planets.

THE ROLE OF MAGNETIC HELICITY IN STRUCTURING THE SOLAR CORONA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Knizhnik, K. J.; Antiochos, S. K.; DeVore, C. R.

Two of the most widely observed and striking features of the Sun's magnetic field are coronal loops, which are smooth and laminar, and prominences or filaments, which are strongly sheared. Loops are puzzling because they show little evidence of tangling or braiding, at least on the quiet Sun, despite the chaotic nature of the solar surface convection. Prominences are mysterious because the origin of their underlying magnetic structure—filament channels—is poorly understood at best. These two types of features would seem to be quite unrelated and wholly distinct. We argue that, on the contrary, they are inextricably linked and result frommore » a single process: the injection of magnetic helicity into the corona by photospheric motions and the subsequent evolution of this helicity by coronal reconnection. In this paper, we present numerical simulations of the response of a Parker (1972) corona to photospheric driving motions that have varying degrees of helicity preference. We obtain four main conclusions: (1) in agreement with the helicity condensation model of Antiochos (2013), the inverse cascade of helicity by magnetic reconnection in the corona results in the formation of filament channels localized about polarity inversion lines; (2) this same process removes most complex fine structure from the rest of the corona, resulting in smooth and laminar coronal loops; (3) the amount of remnant tangling in coronal loops is inversely dependent on the net helicity injected by the driving motions; and (4) the structure of the solar corona depends only on the helicity preference of the driving motions and not on their detailed time dependence. We discuss the implications of our results for high-resolution observations of the corona.« less

Automated Coronal Loop Identification using Digital Image Processing Techniques

NASA Astrophysics Data System (ADS)

Lee, J. K.; Gary, G. A.; Newman, T. S.

2003-05-01

The results of a Master's thesis study of computer algorithms for automatic extraction and identification (i.e., collectively, "detection") of optically-thin, 3-dimensional, (solar) coronal-loop center "lines" from extreme ultraviolet and X-ray 2-dimensional images will be presented. The center lines, which can be considered to be splines, are proxies of magnetic field lines. Detecting the loops is challenging because there are no unique shapes, the loop edges are often indistinct, and because photon and detector noise heavily influence the images. Three techniques for detecting the projected magnetic field lines have been considered and will be described in the presentation. The three techniques used are (i) linear feature recognition of local patterns (related to the inertia-tensor concept), (ii) parametric space inferences via the Hough transform, and (iii) topological adaptive contours (snakes) that constrain curvature and continuity. Since coronal loop topology is dominated by the magnetic field structure, a first-order magnetic field approximation using multiple dipoles provides a priori information that has also been incorporated into the detection process. Synthesized images have been generated to benchmark the suitability of the three techniques, and the performance of the three techniques on both synthesized and solar images will be presented and numerically evaluated in the presentation. The process of automatic detection of coronal loops is important in the reconstruction of the coronal magnetic field where the derived magnetic field lines provide a boundary condition for magnetic models ( cf. , Gary (2001, Solar Phys., 203, 71) and Wiegelmann & Neukirch (2002, Solar Phys., 208, 233)). . This work was supported by NASA's Office of Space Science - Solar and Heliospheric Physics Supporting Research and Technology Program.

Interparticle interactions effects on the magnetic order in surface of FeO4 nanoparticles.

PubMed

Lima, E; Vargas, J M; Rechenberg, H R; Zysler, R D

2008-11-01

We report interparticle interactions effects on the magnetic structure of the surface region in Fe3O4 nanoparticles. For that, we have studied a desirable system composed by Fe3O4 nanoparticles with (d) = 9.3 nm and a narrow size distribution. These particles present an interesting morphology constituted by a crystalline core and a broad (approximately 50% vol.) disordered superficial shell. Two samples were prepared with distinct concentrations of the particles: weakly-interacting particles dispersed in a polymer and strongly-dipolar-interacting particles in a powder sample. M(H, T) measurements clearly show that strong dipolar interparticle interaction modifies the magnetic structure of the structurally disordered superficial shell. Consequently, we have observed drastically distinct thermal behaviours of magnetization and susceptibility comparing weakly- and strongly-interacting samples for the temperature range 2 K < T < 300 K. We have also observed a temperature-field dependence of the hysteresis loops of the dispersed sample that is not observed in the hysteresis loops of the powder one.

Magnetic pinning in a superconducting film by a ferromagnetic layer with stripe domains

DOE Office of Scientific and Technical Information (OSTI.GOV)

Mancusi, D.; Di Giorgio, C.; Bobba, F.

2014-10-31

A magnetic study of superconductor/ferromagnet bilayers was performed by hysteresis loops and temperature-dependent magnetization measurements. The superconductor/ferromagnet bilayers consist of a Nb film deposited on a Py film with weak perpendicular magnetic anisotropy. By comparing the temperature-dependent magnetization data obtained on samples with different ferromagnetic layer thickness, a decrease of the magnetic pinning with increasing thickness of the ferromagnetic layer has been found. This is confirmed by the reduction of the Nb film critical current density at low fields extracted by using the magnetic irreversibility of the hysteresis loops. As the ferromagnetic layer exhibits a magnetic structure with stripe domains,more » whose width increases for increasing thickness as observed by magnetic force microscopy (MFM) measurements, we relate the reduction of the superconducting critical current in samples with thicker ferromagnetic layers to a weaker interaction between the vortices guided by the underlying magnetic template.« less

Analysis and Design of a Speed and Position System for Maglev Vehicles

PubMed Central

Dai, Chunhui; Dou, Fengshan; Song, Xianglei; Long, Zhiqiang

2012-01-01

This paper mainly researches one method of speed and location detection for maglev vehicles. As the maglev train doesn't have any physical contact with the rails, it has to use non-contact measuring methods. The technology based on the inductive loop-cable could fulfill the requirement by using an on-board antenna which could detect the alternating magnetic field produced by the loop-cable on rails. This paper introduces the structure of a speed and position system, and analyses the electromagnetic field produced by the loop-cable. The equivalent model of the loop-cable is given and the most suitable component of the magnetic flux density is selected. Then the paper also compares the alternating current (AC) resistance and the quality factor between two kinds of coils which the antenna is composed of. The effect of the rails to the signal receiving is also researched and then the structure of the coils is improved. Finally, considering the common-mode interference, 8-word coils are designed and analyzed. PMID:23012504

Analysis and design of a speed and position system for maglev vehicles.

PubMed

Dai, Chunhui; Dou, Fengshan; Song, Xianglei; Long, Zhiqiang

2012-01-01

This paper mainly researches one method of speed and location detection for maglev vehicles. As the maglev train doesn't have any physical contact with the rails, it has to use non-contact measuring methods. The technology based on the inductive loop-cable could fulfill the requirement by using an on-board antenna which could detect the alternating magnetic field produced by the loop-cable on rails. This paper introduces the structure of a speed and position system, and analyses the electromagnetic field produced by the loop-cable. The equivalent model of the loop-cable is given and the most suitable component of the magnetic flux density is selected. Then the paper also compares the alternating current (AC) resistance and the quality factor between two kinds of coils which the antenna is composed of. The effect of the rails to the signal receiving is also researched and then the structure of the coils is improved. Finally, considering the common-mode interference, 8-word coils are designed and analyzed.

Bursting reconnection of the two co-rotating current loops

NASA Astrophysics Data System (ADS)

Bulanov, Sergei; Sokolov, Igor; Sakai, Jun-Ichi

2000-10-01

Two parallel plasma filaments carrying electric current (current loops) are considered. The Ampere force induces the filaments' coalescence, which is accompanied by the reconnection of the poloidal magnetic field. Initially the loops rotate along the axii of symmetry. Each of the two loops would be in equilibrium in the absence of the other one. The dynamics of the reconnection is numerically simulated using high-resolution numerical scheme for low-resistive magneto-hydrodynamics. The results of numerical simulation are presented in the form of computer movies. The results show that the rotation strongly modifies the reconnection process, resulting in quasi-periodic (bursting) appearance and disappearance of a current sheet. Fast sliding motion of the plasma along the current sheet is a significant element of the complicated structure of reconnection (current-vortex sheet). The magnetic surfaces in the overal flow are strongly rippled by slow magnetosonic perturbations, so that the specific spiral structures form. This should result in the particle transport enhancement.

An investigation of coronal active region loop structures using AS&E rocket X-ray images

NASA Technical Reports Server (NTRS)

Webb, D. F.

1983-01-01

Simultaneous high spatial resolution observations at 6 cm in soft X-rays, in photospheric magnetograms, and in optical filtergrams were used to compare the most intense sources of centimetric emission in two active regions to coronal loops, sunspots, chromospheric structures, and photospheric magnetic fields. Results show that the majority of the bright microwave components are not associated with sunspots or X-ray emission. A nonthermal mechanism appears necessary to explain the brightest microwave components, discrete regions of continuous particle acceleration may be common in active regions. Studies of the plasma parameters of selected loops imply that the radio emission is consistent with gyro-resonance absorption at the third and fourth harmonic, at least from part of each loop. Results are presented for: (1) X-ray and microwave observations of active regions; (2) comparison of coronal holes observed in soft X-rays and Hel 10830 A spectrosheliograms; and (3) the reappearance of polar coronal holes and the evolution of the solar magnetic field.

Simultaneous Solar Maximum Mission (SMM) and very large array observations of solar active regions

NASA Technical Reports Server (NTRS)

Lang, K. R.

1986-01-01

The research deals mainly with Very Large Array and Solar Maximum Mission observations of the ubiquitous coronal loops that dominate the structure of the low corona. As illustrated, the observations of thermal cyclotron lines at microwave wavelengths provide a powerful new method of accurately specifying the coronal magnetic field strength. Processes are delineated that trigger solar eruptions from coronal loops, including preburst heating and the magnetic interaction of coronal loops. Evidence for coherent burst mechanisms is provided for both the Sun and nearby stars, while other observations suggest the presence of currents that may amplify the coronal magnetic field to unexpectedly high levels. The existence is reported of a new class of compact, variable moving sources in regions of apparently weak photospheric field.

SLIPPING MAGNETIC RECONNECTIONS WITH MULTIPLE FLARE RIBBONS DURING AN X-CLASS SOLAR FLARE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Ruisheng; Chen, Yao; Wang, Bing, E-mail: ruishengzheng@sdu.edu.cn

2016-06-01

With the observations of the Solar Dynamics Observatory , we present the slipping magnetic reconnections with multiple flare ribbons (FRs) during an X1.2 eruptive flare on 2014 January 7. A center negative polarity was surrounded by several positive ones, and three FRs appeared. The three FRs showed apparent slipping motions, and hook structures formed at their ends. Due to the moving footpoints of the erupting structures, one tight semi-circular hook disappeared after the slippage along its inner and outer edges, and coronal dimmings formed within the hook. The east hook also faded as a result of the magnetic reconnection betweenmore » the arcades of a remote filament and a hot loop that was impulsively heated by the under flare loops. Our results are accordant with the slipping magnetic reconnection regime in three-dimensional standard model for eruptive flares. We suggest that the complex structures of the flare are likely a consequence of the more complex flux distribution in the photosphere, and the eruption involves at least two magnetic reconnections.« less

Coronal loops and active region structure

NASA Technical Reports Server (NTRS)

Webb, D. F.; Zirin, H.

1981-01-01

Synoptic H-alpha Ca K, magnetograph and Skylab soft X-ray and EUV data were compared for the purpose of identifying the basic coronal magnetic structure of loops in a 'typical' active region and studying its evolution. A complex of activity in July 1973, especially McMath 12417, was emphasized. The principal results are: (1) most of the brightest loops connected the bright f plage to either the sunspot penumbra or to p satellite spots; no non-flaring X-ray loops end in umbrae; (2) short, bright loops had one or both ends in regions of emergent flux, strong field or high field gradients; (3) stable, strongly sheared loop arcades formed over filaments; (4) EFRs were always associated with compact X-ray arcades; and (5) loops connecting to other active regions had their bases in outlying plage of weak field strength in McM 417 where H-alpha fibrils marked the direction of the loops

Magnetic self-assembly for the synthesis of magnetically exchange coupled MnBi/Fe–Co composites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Xia; Hong, Yang-Ki, E-mail: ykhong@eng.ua.edu; Park, Jihoon

2015-11-15

Exchange coupled hard/soft MnBi/Fe–Co core/shell structured composites were synthesized using a magnetic self-assembly process. MnBi particles were prepared by arc-melting, and Fe–Co nanoparticles were synthesized by an oleic acid assisted chemical reduction method. Grinding a mixture of micron-sized MnBi and Fe–Co nanoparticles in hexane resulted in MnBi/Fe–Co core/shell structured composites. The MnBi/Fe–Co (95/5 wt%) composites showed smooth magnetic hysteresis loops, enhanced remanent magnetization, and positive values in the ΔM curve, indicating exchange coupling between MnBi and Fe–Co particles. - Graphical abstract: Both MnBi and Fe–Co particles were dispersed in hexane for grinding. Because of the oleic acid used during themore » Fe–Co nanoparticle synthesis, they could be well dispersed in hexane. During the grinding, the size of MnBi particles was decreased, hexane was evaporated, and the Fe–Co nanoparticles were concentrated in the solvent and magnetically attracted by MnBi particles, forming a core/shell structure. - Highlights: • Exchange coupled MnBi/Fe–Co composites are synthesized through magnetic selfassembly. • Magnetic exchange coupling is demonstrated by smooth magnetic hysteresis loops, enhanced remanent magnetization, and dominant positive peak in the ΔM curve. • The experimental results in magnetic properties are close to the theoretical calculation results.« less

Structure modulation of helix 69 from Escherichia coli 23S ribosomal RNA by pseudouridylations

PubMed Central

Jiang, Jun; Aduri, Raviprasad; Chow, Christine S.; SantaLucia, John

2014-01-01

Helix 69 (H69) is a 19-nt stem-loop region from the large subunit ribosomal RNA. Three pseudouridine (Ψ) modifications clustered in H69 are conserved across phylogeny and known to affect ribosome function. To explore the effects of Ψ on the conformations of Escherichia coli H69 in solution, nuclear magnetic resonance spectroscopy was used to reveal the structural differences between H69 with (ΨΨΨ) and without (UUU) Ψ modifications. Comparison of the two structures shows that H69 ΨΨΨ has the following unique features: (i) the loop region is closed by a Watson–Crick base pair between Ψ1911 and A1919, which is potentially reinforced by interactions involving Ψ1911N1H and (ii) Ψ modifications at loop residues 1915 and 1917 promote base stacking from Ψ1915 to A1918. In contrast, the H69 UUU loop region, which lacks Ψ modifications, is less organized. Structure modulation by Ψ leads to alteration in conformational behavior of the 5' half of the H69 loop region, observed as broadening of C1914 non-exchangeable base proton resonances in the H69 ΨΨΨ nuclear magnetic resonance spectra, and plays an important biological role in establishing the ribosomal intersubunit bridge B2a and mediating translational fidelity. PMID:24371282

Magnetic and thermodynamic properties of Ising model with borophene structure in a longitudinal magnetic field

NASA Astrophysics Data System (ADS)

Shi, Kaile; Jiang, Wei; Guo, Anbang; Wang, Kai; Wu, Chuang

2018-06-01

The magnetic and thermodynamic properties of borophene structure have been studied for the first time by Monte Carlo simulation. Two-dimensional borophene structure consisting of seven hexagonal B36 units is described by Ising model. Each B36 basic unit includes three benzene-like with spin-3/2. The general formula for the borophene structure is given. The numerical results of the magnetization, the magnetic susceptibility, the internal energy and the specific heat are studied with various parameters. The possibility to test the predicted magnetism in experiment are illustrated, for instance, the maximum on the magnetization curve. The multiple hysteresis loops and the magnetization plateaus are sensitive to the ferromagnetic or ferrimagnetic exchange coupling in borophene structure. The results show the borophene structure could have applications in spintronics, which deserves further studies in experiments.

MINI-FILAMENT ERUPTION AS THE INITIATION OF A JET ALONG CORONAL LOOPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hong, Junchao; Jiang, Yunchun; Yang, Jiayan

Minifilament eruptions (MFEs) and coronal jets are different types of solar small-scale explosive events. We report an MFE observed at the New Vacuum Solar Telescope (NVST). As seen in the NVST H α images, during the rising phase, the minifilament erupts outward orthogonally to its length, accompanied with a flare-like brightening at the bottom. Afterward, dark materials are found to possibly extend along the axis of the expanded filament body. The MFE is analogous to large filament eruptions. However, a simultaneous observation of the Solar Dynamics Observatory shows that a jet is initiated and flows out along nearby coronal loopsmore » during the rising phase of the MFE. Meanwhile, small hot loops, which connect the original eruptive site of the minifilament to the footpoints of the coronal loops, are formed successively. A differential emission measure analysis demonstrates that, on the top of the new small loops, a hot cusp structure exists. We conjecture that the magnetic fields of the MFE interact with magnetic fields of the coronal loops. This interaction is interpreted as magnetic reconnection that produces the jet and the small hot loops.« less

Automated Coronal Loop Identification Using Digital Image Processing Techniques

NASA Technical Reports Server (NTRS)

Lee, Jong K.; Gary, G. Allen; Newman, Timothy S.

2003-01-01

The results of a master thesis project on a study of computer algorithms for automatic identification of optical-thin, 3-dimensional solar coronal loop centers from extreme ultraviolet and X-ray 2-dimensional images will be presented. These center splines are proxies of associated magnetic field lines. The project is pattern recognition problems in which there are no unique shapes or edges and in which photon and detector noise heavily influence the images. The study explores extraction techniques using: (1) linear feature recognition of local patterns (related to the inertia-tensor concept), (2) parametric space via the Hough transform, and (3) topological adaptive contours (snakes) that constrains curvature and continuity as possible candidates for digital loop detection schemes. We have developed synthesized images for the coronal loops to test the various loop identification algorithms. Since the topology of these solar features is dominated by the magnetic field structure, a first-order magnetic field approximation using multiple dipoles provides a priori information in the identification process. Results from both synthesized and solar images will be presented.

Numerical Simulation of DC Coronal Heating

NASA Astrophysics Data System (ADS)

Dahlburg, Russell B.; Einaudi, G.; Taylor, Brian D.; Ugarte-Urra, Ignacio; Warren, Harry; Rappazzo, A. F.; Velli, Marco

2016-05-01

Recent research on observational signatures of turbulent heating of a coronal loop will be discussed. The evolution of the loop is is studied by means of numerical simulations of the fully compressible three-dimensional magnetohydrodynamic equations using the HYPERION code. HYPERION calculates the full energy cycle involving footpoint convection, magnetic reconnection, nonlinear thermal conduction and optically thin radiation. The footpoints of the loop magnetic field are convected by random photospheric motions. As a consequence the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is non-uniformly distributed so that only a fraction of thecoronal mass and volume gets heated at any time. Temperature and density are highly structured at scales which, in the solar corona, remain observationally unresolved: the plasma of the simulated loop is multi thermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. Typical simulated coronal loops are 50000 km length and have axial magnetic field intensities ranging from 0.01 to 0.04 Tesla. To connect these simulations to observations the computed number densities and temperatures are used to synthesize the intensities expected in emission lines typically observed with the Extreme ultraviolet Imaging Spectrometer (EIS) on Hinode. These intensities are then employed to compute differential emission measure distributions, which are found to be very similar to those derived from observations of solar active regions.

Observational Signatures of Coronal Heating

NASA Astrophysics Data System (ADS)

Dahlburg, R. B.; Einaudi, G.; Ugarte-Urra, I.; Warren, H. P.; Rappazzo, A. F.; Velli, M.; Taylor, B.

2016-12-01

Recent research on observational signatures of turbulent heating of a coronal loop will be discussed. The evolution of the loop is is studied by means of numericalsimulations of the fully compressible three-dimensionalmagnetohydrodynamic equations using the HYPERION code. HYPERION calculates the full energy cycle involving footpoint convection, magnetic reconnection,nonlinear thermal conduction and optically thin radiation.The footpoints of the loop magnetic field are convected by random photospheric motions. As a consequence the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is non-uniformly distributed so that only a fraction of thecoronal mass and volume gets heated at any time. Temperature and density are highly structured at scales which, in the solar corona, remain observationally unresolved: the plasma of the simulated loop is multi-thermal, where highly dynamical hotter and cooler plasma strands arescattered throughout the loop at sub-observational scales. Typical simulated coronal loops are 50000 km length and have axial magnetic field intensities ranging from 0.01 to 0.04 Tesla.To connect these simulations to observations the computed numberdensities and temperatures are used to synthesize the intensities expected inemission lines typically observed with the Extreme ultraviolet Imaging Spectrometer(EIS) on Hinode. These intensities are then employed to compute differentialemission measure distributions, which are found to be very similar to those derivedfrom observations of solar active regions.

Active Region Formation and Subsurface Structure

NASA Astrophysics Data System (ADS)

Stein, F.; Nordlund, Robert A.

2016-10-01

We present results from emerging magnetic flux simulations showing how several different active regions form and their very different subsurface structures. The simulations assumed an infinite sheet of uniform, untwisted, horizontal field advected into the computational domain by inflows at a depth of 20 Mm. Results from two different horizontal field strengths, 1 and 5 kG, will be presented. Convective up and down flows buckle the horizontal field into Omega and U loops. Upflows and magnetic buoyancy carry the field toward the surface, while fast downflows pin down the field. Small (granular) convective motions, near the surface, shred the emerging field into fine filaments that emerge as the observed "pepper and salt" pattern. The large (supergranular) motions, at depth, keep the overall loop structure intact, so that as the overall omega-loop emerges through the surface the opposite polarity fields counter-stream into large unipolar flux concentrations producing first pores which then coalesce into spots. These tend to be located over the supergranular downflow lanes near the bottom of the domain. The pores and spots exhibit a great variety of subsurface field structures - from monolithic but twisted bundles to intertwined separate spaghetti sturctures. We will show movies of the surface evolution of the field and emergent continuum intensity and of the subsurface evolution of the magnetic field lines.

A sandwich-like differential B-dot based on EACVD polycrystalline diamond slice

NASA Astrophysics Data System (ADS)

Xu, P.; Yu, Y.; Xu, L.; Zhou, H. Y.; Qiu, C. J.

2018-06-01

In this article, we present a method of mass production of a standardized high-performance differential B-dot magnetic probe together with the magnetic field measurement in a pulsed current device with the current up to hundreds of kilo-Amperes. A polycrystalline diamond slice produced in an Electron Assisted Chemical Vapor Deposition device is used as the base and insulating material to imprint two symmetric differential loops for the magnetic field measurement. The SP3 carbon bond in the cubic lattice structure of diamond is confirmed by Raman spectra. The thickness of this slice is 20 μm. A gold loop is imprinted onto each surface of the slice by using the photolithography technique. The inner diameter, width, and thickness of each loop are 0.8 mm, 50 μm, and 1 μm, respectively. It provides a way of measuring the pulsed magnetic field with a high spatial and temporal resolution, especially in limited space. This differential magnetic probe has demonstrated a very good common-mode rejection rate through the pulsed magnetic field measurement.

Nonlinear Force-free Coronal Magnetic Stereoscopy

NASA Astrophysics Data System (ADS)

Chifu, Iulia; Wiegelmann, Thomas; Inhester, Bernd

2017-03-01

Insights into the 3D structure of the solar coronal magnetic field have been obtained in the past by two completely different approaches. The first approach are nonlinear force-free field (NLFFF) extrapolations, which use photospheric vector magnetograms as boundary condition. The second approach uses stereoscopy of coronal magnetic loops observed in EUV coronal images from different vantage points. Both approaches have their strengths and weaknesses. Extrapolation methods are sensitive to noise and inconsistencies in the boundary data, and the accuracy of stereoscopy is affected by the ability of identifying the same structure in different images and by the separation angle between the view directions. As a consequence, for the same observational data, the 3D coronal magnetic fields computed with the two methods do not necessarily coincide. In an earlier work (Paper I) we extended our NLFFF optimization code by including stereoscopic constrains. The method was successfully tested with synthetic data, and within this work, we apply the newly developed code to a combined data set from SDO/HMI, SDO/AIA, and the two STEREO spacecraft. The extended method (called S-NLFFF) contains an additional term that monitors and minimizes the angle between the local magnetic field direction and the orientation of the 3D coronal loops reconstructed by stereoscopy. We find that when we prescribe the shape of the 3D stereoscopically reconstructed loops, the S-NLFFF method leads to a much better agreement between the modeled field and the stereoscopically reconstructed loops. We also find an appreciable decrease by a factor of two in the angle between the current and the magnetic field. This indicates the improved quality of the force-free solution obtained by S-NLFFF.

Coalescence of two current loops with a kink instability simulated by a three-dimensional electromagnetic particle code

NASA Technical Reports Server (NTRS)

Nishikawa, K.-I.; Sakai, J.-I.; Zhao, Jie; Neubert, T.; Buneman, Oscar

1994-01-01

We have studied the dynamics of a coalescence of current loops using three-dimensional electromagnetic (EM) particle simulation code. Our focus is the investigation of such kinetic processes as energy trasnfer, heating particles, and electromagnetic emissions associated with a current loop coalescence which cannot be studied by MHD simulations. First, the two loops undergo a pinching oscillation due to a pressure imbalance between the inside and outside of the current loop. During the pinching oscillation, a kinetic kink instability is excited and electrons in the loops are heated perpendicularly to an ambient magnetic field. Next, the two current loops collide and coalesce, while at the same time a helical structure grows further. Subsequently, the perturbed current, which is due to these helically bunched electrons, can drive a whistler instability. It should be noted in this case that the whistler wave is excited by the kinetic kink instability and not a beam instability. After the coalescence of two helical loops, tilting motions can be observed in the direction of left-hand rotation, and the helical structure will relax resulting in strong plasma heating mostly in the direction perpendicular to the ambient magnetic field. It is also shown that high-frequency electromagnetic waves can be emitted from the region where the two loops coalesce and propagate strongly in the direction of the electron drift velocity. These processes may be important in understanding heating mechansims for coronal loops as well as radio wave emission mechanisms from active regions of solar plasmas.

Supra Arcade Downflows with XRT Informed by Dipolarization Fronts with THEMIS

NASA Technical Reports Server (NTRS)

Kobelski, Adam; Savage, Sabrina Leah; Malaspina, David

2016-01-01

Magnetic reconnection can rapidly reconfigure the magnetic field of the corona, accelerating plasma through the site of reconnection. Ambiguities due to the nature of remote sensing have complicated the interpretation of observations of the inflowing and outflowing plasma in reconnecting regions. In particular, the interpretation of sunward moving density depletions above flare arcades (known as Supra Arcade Downflows - SADs) is still debated. Hinode/XRT has provided a wealth of observations for SADs and helped inform our current understanding of these structures. SADs have been interpreted as wakes behind newly reconnected and outflowing loops (Supra Arcade Downflowing Loops - SADLs). Models have shown the plausibility of this interpretation, though this interpretation has not yet been fully accepted. We present here observations of newly reconnected outflowing loops observed via in situ instruments in the magnetosphere. These observations, provided by five THEMIS spacecraft, show that around retracting loops (dipolarization fronts in this context) similar dynamic temperature and density structures are found as seen in SADs. We compare data from multiple SADs and dipolarization fronts to show that the observational signatures implied in the corona can be directly observed in similar plasma regimes in the magnetosphere, strongly favoring the interpretation of SADs as wakes behind retracting loops.

Study of a Solar X-Ray Telescope

NASA Technical Reports Server (NTRS)

Golub, Leon

1997-01-01

The highly structured nature of the outer solar atmosphere seems to be intimately linked to the presence, at the solar surface, of magnetic fields that have been generated inside the Sun and have emerged to the surface. The corona is brightest (and also hottest) at just those locations where the magnetic field has emerged from inside the Sun. Dynamo theory predicts that strong magnetic fields will be generated deep in the solar interior and that bundles or 'ropes' of magnetic flux will float to the surface. When this happens, a magnetically bipolar region will become visible, extending above the surface in a three-dimensional structure. The field lines penetrate through the surface, showing two magnetic poles, and also exhibit a three-dimensional structure above the surface. The structure created by the field emergence is rooted in the (relatively) cool photosphere and extends through the chromosphere and transition region to the corona. Thus, the magnetic field creates a region, called an active region, which contains portions at temperatures from less than 10(exp 4) K to greater than 10(exp 6) K, and is therefore visible at wavelengths from the infrared through x-rays. The locations where the magnetic field leaves and reenters the visible surface are called the 'footpoints' of the coronal structures associated with the magnetic field. The magnetic fields themselves are not directly visible. However, the hot coronal plasma is, for the most part, constrained to follow the direction of the magnetic field lines in the atmosphere. Now, 100 years after the discovery of x-rays by Wilhelm Roentgen in 1896, we can routinely make observations of the solar corona from outside the Earth's atmosphere in this region of the electromagnetic spectrum. As shown by comparing x-ray images with magnetograms, the bright corona over these bipolar magnetic regions consists of closed structures that seem to follow the orientation of the magnetic field. Although we can see down to the photosphere at x-ray wavelengths when observing the disk of the Sun, this part of the solar atmosphere emits so little that far from the peak of its Planck curve it appears dark in x-ray images. This impression of hot plasma following the magnetic field direction is further strengthened by quantitative studies that calculate coronal magnetic field strength and direction based on photospheric measurements and compare them with the observed brightness and location of the x-ray emitting structures. Such comparisons make it clear that, for the most part, the hot plasma conforms to the geometry of the magnetic field and that the coronal brightness is strongly linked to the strength of the magnetic fields which have erupted to the solar surface from the interior. It is also the case that the larger-scale, fainter corona, as well as coronal holes, are strongly influenced by the large-scale solar magnetic field. We may get a small hint of the reason that the coronal plasma outlines the direction of B by examining the thermal conductivity of a hot plasma in the presence of a magnetic field. This quantity has enormously different values in the directions parallel and perpendicular to the field for a coronal temperature of 10(exp 6) K, a particle density of 10(exp 9)/cu cm and a magnetic field strength of 100 G, the conductivity along the field is approximately 13 orders of magnitude greater than that perpendicular to the field. It is therefore not surprising that a parcel of plasma which is locally heated would conduct that heat preferentially in the direction of the field. We also note that the thermal conductivity parallel to the magnetic field increases with temperature T, while the perpendicular conductivity decreases. To the extent that the loop aspect ratio, i.e., the ratio of loop length to loop width, is determined by the thermal conductivity, we would expect that higher temperature loops are longer and thinner than cooler ones. However, if the loop width becomes smaller than the spatial resolution of the observing instrument, this effect will not be directly observable. For organizational purposes, we provide a listing of some scientific objectives for a Solar-B x-ray telescope, arranged in terms of identifiable features in the corona.

Investigation of the moving structures in a coronal bright point

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ning, Zongjun; Guo, Yang, E-mail: ningzongjun@pmo.ac.cn

2014-10-10

We have explored the moving structures in a coronal bright point (CBP) observed by the Solar Dynamic Observatory Atmospheric Imaging Assembly (AIA) on 2011 March 5. This CBP event has a lifetime of ∼20 minutes and is bright with a curved shape along a magnetic loop connecting a pair of negative and positive fields. AIA imaging observations show that a lot of bright structures are moving intermittently along the loop legs toward the two footpoints from the CBP brightness core. Such moving bright structures are clearly seen at AIA 304 Å. In order to analyze their features, the CBP ismore » cut along the motion direction with a curved slit which is wide enough to cover the bulk of the CBP. After integrating the flux along the slit width, we get the spacetime slices at nine AIA wavelengths. The oblique streaks starting from the edge of the CBP brightness core are identified as moving bright structures, especially on the derivative images of the brightness spacetime slices. They seem to originate from the same position near the loop top. We find that these oblique streaks are bi-directional, simultaneous, symmetrical, and periodic. The average speed is about 380 km s{sup –1}, and the period is typically between 80 and 100 s. Nonlinear force-free field extrapolation shows the possibility that magnetic reconnection takes place during the CBP, and our findings indicate that these moving bright structures could be the observational outflows after magnetic reconnection in the CBP.« less

Magnetic field role on the structure and optical response of photonic crystals based on ferrofluids containing Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

López, J., E-mail: javier.lopez@correounivalle.edu.co; González, Luz E.; Quiñonez, M. F.

2014-05-21

Ferrofluids based on magnetic Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} ferrite nanoparticles were prepared by co-precipitation method from aqueous salt solutions of Co (II), ZnSO{sub 4}, and Fe (III) in an alkaline medium. Ferrofluids placed in an external magnetic field show properties that make them interesting as magneto-controllable soft photonic crystals. Morphological and structural characterizations of the samples were obtained from Scanning Electron Microscopy and Transmission Electron Microscopy studies. Magnetic properties were investigated with the aid of a vibrating sample magnetometer at room temperature. Herein, the Co{sub 0.25}Zn{sub 0.75}Fe{sub 2}O{sub 4} samples showed superparamagnetic behavior, according to hysteresis loop results. Takingmore » in mind that the Co-Zn ferrite hysteresis loop is very small, our magnetic nanoparticles can be considered soft magnetic material with interesting technological applications. In addition, by using the plane-wave expansion method, we studied the photonic band structure of 2D photonic crystals made of ferrofluids with the same nanoparticles. Previous experimental results show that a magnetic field applied perpendicular to the ferrofluid plane agglomerates the magnetic nanoparticles in parallel rods to form a hexagonal 2D photonic crystal. We calculated the photonic band structure of photonic crystals by means of the effective refractive index of the magnetic fluid, basing the study on the Maxwell-Garnett theory, finding that the photonic band structure does not present any band gaps under the action of applied magnetic field strengths used in our experimental conditions.« less

Engineering the magnetic coupling and anisotropy at the molecule–magnetic surface interface in molecular spintronic devices

PubMed Central

Campbell, Victoria E.; Tonelli, Monica; Cimatti, Irene; Moussy, Jean-Baptiste; Tortech, Ludovic; Dappe, Yannick J.; Rivière, Eric; Guillot, Régis; Delprat, Sophie; Mattana, Richard; Seneor, Pierre; Ohresser, Philippe; Choueikani, Fadi; Otero, Edwige; Koprowiak, Florian; Chilkuri, Vijay Gopal; Suaud, Nicolas; Guihéry, Nathalie; Galtayries, Anouk; Miserque, Frederic; Arrio, Marie-Anne; Sainctavit, Philippe; Mallah, Talal

2016-01-01

A challenge in molecular spintronics is to control the magnetic coupling between magnetic molecules and magnetic electrodes to build efficient devices. Here we show that the nature of the magnetic ion of anchored metal complexes highly impacts the exchange coupling of the molecules with magnetic substrates. Surface anchoring alters the magnetic anisotropy of the cobalt(II)-containing complex (Co(Pyipa)2), and results in blocking of its magnetization due to the presence of a magnetic hysteresis loop. In contrast, no hysteresis loop is observed in the isostructural nickel(II)-containing complex (Ni(Pyipa)2). Through XMCD experiments and theoretical calculations we find that Co(Pyipa)2 is strongly ferromagnetically coupled to the surface, while Ni(Pyipa)2 is either not coupled or weakly antiferromagnetically coupled to the substrate. These results highlight the importance of the synergistic effect that the electronic structure of a metal ion and the organic ligands has on the exchange interaction and anisotropy occurring at the molecule–electrode interface. PMID:27929089

3D MHD MODELING OF TWISTED CORONAL LOOPS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reale, F.; Peres, G.; Orlando, S.

We perform MHD modeling of a single bright coronal loop to include the interaction with a non-uniform magnetic field. The field is stressed by random footpoint rotation in the central region and its energy is dissipated into heating by growing currents through anomalous magnetic diffusivity that switches on in the corona above a current density threshold. We model an entire single magnetic flux tube in the solar atmosphere extending from the high- β chromosphere to the low- β corona through the steep transition region. The magnetic field expands from the chromosphere to the corona. The maximum resolution is ∼30 km.more » We obtain an overall evolution typical of loop models and realistic loop emission in the EUV and X-ray bands. The plasma confined in the flux tube is heated to active region temperatures (∼3 MK) after ∼2/3 hr. Upflows from the chromosphere up to ∼100 km s{sup −1} fill the core of the flux tube to densities above 10{sup 9} cm{sup −3}. More heating is released in the low corona than the high corona and is finely structured both in space and time.« less

Driving morphological changes in magnetic nanoparticle structures through the application of acoustic waves and magnetic fields

NASA Astrophysics Data System (ADS)

Huang, Ann; Miansari, Morteza; Friend, James

The growing interest in acoustic manipulation of particles in micro to nanofluidics using surface acoustic waves (SAW), together with the many applications of magnetic nanoparticles-whether individual or in arrays-underpins our discovery of how these forces can be used to rapidly, easily, and irreversibly form 1D chains and 2D films. These films and chains are currently difficult to produce yet offer many advantages over individual nanoparticles in suspension. Making use of the scale of the structures formed, 10-9 to 10-5 m, and by taking a balance of the relevant external and interparticle forces, the underlying mechanisms responsible for the phenomena become apparent. For 1D chains, the magnetic field alone is sufficient, though applying an acoustic field drives a topology change from loosely connected chains to loops of 10 -100 particles. Adding the acoustic field drives a transition from these looped structures to dense 2D arrays via interparticle Bjerknes forces. Inter-particle drainage of the surrounding fluid leaves these structures intact after removal of the externally applied forces. Clear morphology transitions are present and depend on the relative amplitude of the incident Brownian, Bjerknes, and magnetic forces. UCSD: Frontiers of Innovation Scholars Program (U-1024).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zheng, Dezhi; Liu, Yixuan, E-mail: xuan61x@163.com; Guo, Zhanshe

A new maglev sensor is proposed to measure ultra-low frequency (ULF) vibration, which uses hybrid-magnet levitation structure with electromagnets and permanent magnets as the supporting component, rather than the conventional spring structure of magnetoelectric vibration sensor. Since the lower measurement limit needs to be reduced, the equivalent bearing stiffness coefficient and the equivalent damping coefficient are adjusted by the sensitivity unit structure of the sensor and the closed-loop control system, which realizes both the closed-loop control and the solving algorithms. A simple sensor experimental platform is then assembled based on a digital hardware system, and experimental results demonstrate that themore » lower measurement limit of the sensor is increased to 0.2 Hz under these experimental conditions, indicating promising results of the maglev sensor for ULF vibration measurements.« less

Theory and experiment research for ultra-low frequency maglev vibration sensor.

PubMed

Zheng, Dezhi; Liu, Yixuan; Guo, Zhanshe; Zhao, Xiaomeng; Fan, Shangchun

2015-10-01

A new maglev sensor is proposed to measure ultra-low frequency (ULF) vibration, which uses hybrid-magnet levitation structure with electromagnets and permanent magnets as the supporting component, rather than the conventional spring structure of magnetoelectric vibration sensor. Since the lower measurement limit needs to be reduced, the equivalent bearing stiffness coefficient and the equivalent damping coefficient are adjusted by the sensitivity unit structure of the sensor and the closed-loop control system, which realizes both the closed-loop control and the solving algorithms. A simple sensor experimental platform is then assembled based on a digital hardware system, and experimental results demonstrate that the lower measurement limit of the sensor is increased to 0.2 Hz under these experimental conditions, indicating promising results of the maglev sensor for ULF vibration measurements.

Theory and experiment research for ultra-low frequency maglev vibration sensor

NASA Astrophysics Data System (ADS)

Zheng, Dezhi; Liu, Yixuan; Guo, Zhanshe; Zhao, Xiaomeng; Fan, Shangchun

2015-10-01

A new maglev sensor is proposed to measure ultra-low frequency (ULF) vibration, which uses hybrid-magnet levitation structure with electromagnets and permanent magnets as the supporting component, rather than the conventional spring structure of magnetoelectric vibration sensor. Since the lower measurement limit needs to be reduced, the equivalent bearing stiffness coefficient and the equivalent damping coefficient are adjusted by the sensitivity unit structure of the sensor and the closed-loop control system, which realizes both the closed-loop control and the solving algorithms. A simple sensor experimental platform is then assembled based on a digital hardware system, and experimental results demonstrate that the lower measurement limit of the sensor is increased to 0.2 Hz under these experimental conditions, indicating promising results of the maglev sensor for ULF vibration measurements.

Magnetic Roots and the Driving of Extended Coronal Heating

NASA Technical Reports Server (NTRS)

Porter, Jason G.; Falconer, D. A.; Moore, Ronald L.; Harvey, Karen L.; Rabin, Douglas M.; Shimizu, T.

1998-01-01

We report results from a continuation of a previous study, in which we found large bright coronal loops within active regions and extending from active regions that have one end rooted near an island of included magnetic polarity that is a site of enhanced coronal heating and microflares. This suggested that magnetic activity such as microflaring results in enhanced heating in both the compact core field around the island and in the large loops extending from it. We might expect that the intensity variations due to enhanced heating in the compact and extended structures would be correlated. However, although some ex- tended loops do respond to the largest events taking place in the core fields near their feet, they do not show a clear response to most smaller individual events nor to the overall envelope of coronal heating activity in the core fields at their feet as determined from longer-term observations. Thus, while it is clear that the extended loops' heating is being driven from their ends at the magnetic islands, much of this heating is apparently by some form of footpoint activity that is not strongly coupled to the heating in the footpoint core fields. One possibility is that the remote heating in the extended loops is driven by reconnection at the magnetic null over the island, and that this reconnection is driven mainly by core-field activity that produces little coronal heating within the core field itself, perhaps in the manner of the numerical simulations by Karpen, Antiochos, and DeVore.

Automatic Event Detection in Search for Inter-Moss Loops in IRIS Si IV Slit-Jaw Images

NASA Technical Reports Server (NTRS)

Fayock, Brian; Winebarger, Amy R.; De Pontieu, Bart

2015-01-01

The high-resolution capabilities of the Interface Region Imaging Spectrometer (IRIS) mission have allowed the exploration of the finer details of the solar magnetic structure from the chromosphere to the lower corona that have previously been unresolved. Of particular interest to us are the relatively short-lived, low-lying magnetic loops that have foot points in neighboring moss regions. These inter-moss loops have also appeared in several AIA pass bands, which are generally associated with temperatures that are at least an order of magnitude higher than that of the Si IV emission seen in the 1400 angstrom pass band of IRIS. While the emission lines seen in these pass bands can be associated with a range of temperatures, the simultaneous appearance of these loops in IRIS 1400 and AIA 171, 193, and 211 suggest that they are not in ionization equilibrium. To study these structures in detail, we have developed a series of algorithms to automatically detect signal brightening or events on a pixel-by-pixel basis and group them together as structures for each of the above data sets. These algorithms have successfully picked out all activity fitting certain adjustable criteria. The resulting groups of events are then statistically analyzed to determine which characteristics can be used to distinguish the inter-moss loops from all other structures. While a few characteristic histograms reveal that manually selected inter-moss loops lie outside the norm, a combination of several characteristics will need to be used to determine the statistical likelihood that a group of events be categorized automatically as a loop of interest. The goal of this project is to be able to automatically pick out inter-moss loops from an entire data set and calculate the characteristics that have previously been determined manually, such as length, intensity, and lifetime. We will discuss the algorithms, preliminary results, and current progress of automatic characterization.

THE ROLE OF KELVIN–HELMHOLTZ INSTABILITY FOR PRODUCING LOOP-TOP HARD X-RAY SOURCES IN SOLAR FLARES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Fang, Xia; Yuan, Ding; Xia, Chun

We propose a model for the formation of loop-top hard X-ray (HXR) sources in solar flares through the inverse Compton mechanism, scattering the surrounding soft X-ray (SXR) photons to higher energy HXR photons. We simulate the consequences of a flare-driven energy deposit in the upper chromosphere in the impulsive phase of single loop flares. The consequent chromosphere evaporation flows from both footpoints reach speeds up to hundreds of kilometers per second, and we demonstrate how this triggers Kelvin–Helmholtz instability (KHI) in the loop top, under mildly asymmetric conditions, or more toward the loop flank for strongly asymmetric cases. The KHImore » vortices further fragment the magnetic topology into multiple magnetic islands and current sheets, and the hot plasma within leads to a bright loop-top SXR source region. We argue that the magnetohydrodynamic turbulence that appears at the loop apex could be an efficient accelerator of non-thermal particles, which the island structures can trap at the loop-top. These accelerated non-thermal particles can upscatter the surrounding thermal SXR photons emitted by the extremely hot evaporated plasma to HXR photons.« less

Exchange bias effect in L10-ordered FePt and FeCo-based bilayer structure: effect of increasing applied field

NASA Astrophysics Data System (ADS)

Singh, Sadhana; Kumar, Dileep; Bhagat, Babli; Choudhary, R. J.; Reddy, V. R.; Gupta, Ajay

2018-02-01

The applied magnetic field (H APP) dependence of the exchange bias (EB) is studied in an exchange-coupled thin-film bilayer composed of a hard ferromagnetic FePt layer in the proximity of a soft ferromagnetic FeCo layer. FePt/FeCo structure is deposited in an ultra-high vacuum chamber, where the FePt layer was first annealed at 823 K for 30 min and subsequently cooled to room temperature in the presence of an in-plane magnetic field, H MAX ~ 1.5 kOe to promote L10-ordered hard magnetic phase with magnetic moments aligned in one of the in-plane directions in the FePt layer. In-situ magneto-optical Kerr effect measurements during different stages of bilayer growth and detailed ex-situ superconducting quantum interference device-vibrating sample magnetometer measurements jointly revealed that due to the interplay between exchange coupling at the interface and dipolar energies of the saturated hard FePt layer, a hysteresis loop of FeCo layer shifts along the magnetic field axis. A clear dependence of EB field (H EB) on increasing maximum value of the H APP during the hysteresis loop measurement is understood in terms of the magnetic state of soft and hard magnetic layers, where EB increases with increasing H APP until the hard layer moment remains undisturbed in its remanence state. As soon as the field was sufficient to rotate the spins of the FePt layer, the loop became symmetric with respect to the field axis.

Coronal Structures in Cool Stars: XMM-NEWTON Hybrid Stars and Coronal Evolution

NASA Technical Reports Server (NTRS)

Dupree, Andrea K.; Mushotzky, Richard (Technical Monitor)

2003-01-01

This program addresses the evolution of stellar coronas by comparing a solar-like corona in the supergiant Beta Dra (G2 Ib-IIa) to the corona in the allegedly more evolved state of a hybrid star, alpha TrA (K2 II-III). Because the hybrid star has a massive wind, it appears likely that the corona will be cooler and less dense as the magnetic loop structures are no longer closed. By analogy with solar coronal holes, when the topology of the magnetic field is configured with open magnetic structures, both the coronal temperature and density are lower than in atmospheres dominated by closed loops. The hybrid stars assume a pivotal role in the definition of coronal evolution, atmospheric heating processes and mechanisms to drive winds of cool stars. We are attempting to determine if this model of coronal evolution is correct by using XMM-NEWTON RGS spectra for the 2 targets we were allocated through the Guest Observer program.

Structural, morphological and magnetic properties of pure and Ni-doped ZnO nanoparticles synthesized by sol-gel method

NASA Astrophysics Data System (ADS)

Undre, Pallavi G.; Birajdar, Shankar D.; Kathare, R. V.; Jadhav, K. M.

2018-05-01

In this work pure and Ni-doped ZnO nanoparticles have been prepared by sol-gel method. Influence of nickel doping on structural, morphological and magnetic properties of prepared nanoparticles was investigated by X-ray diffraction technique (XRD), Scanning electron microscopy (SEM) and Pulse field magnetic hysteresis loop. X-ray diffraction pattern shows the formation of a single phase with hexagonal wurtzite structure of both pure and Ni-doped ZnO nanoparticles. The lattice parameters `an' and `c' of Ni-doped ZnO is slightly less than that of pure ZnO nanoparticles. The crystalline size of prepared nanoparticles is found to be in 29 and 31 nm range. SEM technique used to examine the surface morphology of samples, SEM image confirms the nanocrystalline nature of present samples. From the pulse field hysteresis loop technique pure and Ni-doped ZnO nanoparticles show diamagnetic and ferromagnetic behavior at room temperature respectively.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chifu, Iulia; Wiegelmann, Thomas; Inhester, Bernd, E-mail: chifu@mps.mpg.de

Insights into the 3D structure of the solar coronal magnetic field have been obtained in the past by two completely different approaches. The first approach are nonlinear force-free field (NLFFF) extrapolations, which use photospheric vector magnetograms as boundary condition. The second approach uses stereoscopy of coronal magnetic loops observed in EUV coronal images from different vantage points. Both approaches have their strengths and weaknesses. Extrapolation methods are sensitive to noise and inconsistencies in the boundary data, and the accuracy of stereoscopy is affected by the ability of identifying the same structure in different images and by the separation angle betweenmore » the view directions. As a consequence, for the same observational data, the 3D coronal magnetic fields computed with the two methods do not necessarily coincide. In an earlier work (Paper I) we extended our NLFFF optimization code by including stereoscopic constrains. The method was successfully tested with synthetic data, and within this work, we apply the newly developed code to a combined data set from SDO /HMI, SDO /AIA, and the two STEREO spacecraft. The extended method (called S-NLFFF) contains an additional term that monitors and minimizes the angle between the local magnetic field direction and the orientation of the 3D coronal loops reconstructed by stereoscopy. We find that when we prescribe the shape of the 3D stereoscopically reconstructed loops, the S-NLFFF method leads to a much better agreement between the modeled field and the stereoscopically reconstructed loops. We also find an appreciable decrease by a factor of two in the angle between the current and the magnetic field. This indicates the improved quality of the force-free solution obtained by S-NLFFF.« less

Structural, vibrational and magnetic studies of Pb(Fe0.585Nb0.25W0.165)O3 multiferroic solid solution

NASA Astrophysics Data System (ADS)

Nagaraja, T.; Dadami, Sunanda T.; Matteppanvar, Shidaling; Shivaraja, I.; Rayaprol, Sudhindra; Angadi, Basavaraj

2018-04-01

In this paper, the complex structured A(B'B''B''')O3 perovskite Pb(Fe0.585Nb0.25W0.165)O3(PFNW) type multiferroic, was successfully synthesized in a single phase by a single step solid state reaction method and optimized synthesis parameters are calcination at 700 °C/2hr and sintering at 800 °C/3hr. The detailed room temperature (RT) structural, vibrational and temperature dependent magnetization were carried out through the X ray diffraction, Raman spectroscopy and vibrating sample magnetometer (VSM). Rietveld refinement was carried out on RT XRD data it confirms the cubic structure with Pm-3m space group, the obtained lattice parameters: a = b = c = 3.9948 Å, and α = β = γ = 90°. The RT Raman spectroscopy confirms the formation of cubic structure broad peak at 820 cm-1, related to the A1g mode. PFNW exhibits a cusp at around 255 K in the temperature dependent magnetic susceptibility corresponding to the Néel temperature (TN) and another peak around 10 K (Tsg) corresponding to spin-glass like transition. The M-H loops were measured at few selected temperatures above and below TN. The M-H loop at 5 K shows the well saturated loop with significant coercive field compared to 260 and 300K data, due to the existence of spin-glass ordering.

Study of the magnetic interaction in nanocrystalline Pr-Fe-Co-Nb-B permanent magnets

NASA Astrophysics Data System (ADS)

Dospial, M.; Plusa, D.; Ślusarek, B.

2012-03-01

The magnetic properties of an isotropic, epoxy resin bonded magnets made from Pr-Fe-Co-Nb-B powder were investigated. The magnetization reversal process and magnetic parameters were examined by measurements of the initial magnetization curve, major and minor hysteresis loops and sets of recoil curves. From the initial magnetization curve and the field dependencies of the reversible and irreversible magnetization components derived from the recoil loops it was found that the magnetization reversal process is the combination of the nucleation of reversed domains and pinning of domain walls at the grain boundaries and the reversible rotation of magnetization vector in single domain grains. The interactions between grains were studied by means of δM plots. The nonlinear behavior of δM curve approve that the short range intergrain exchange coupling interactions are dominant in a field up to the sample coercivity. The interaction domains and fine magnetic structure were revealed as the evidence of exchange coupling between soft α-Fe and hard magnetic Nd2Fe14B grains.

Micromagnetism in a planar system with a random magnetic anisotropy and two-dimensional magnetic correlations

NASA Astrophysics Data System (ADS)

Komogortsev, S. V.; Fel'k, V. A.; Iskhakov, R. S.; Shadrina, G. V.

2017-08-01

The hysteresis loops and the micromagnetic structure of a ferromagnetic nanolayer with a randomly oriented local easy magnetization axis and two-dimensional magnetization correlations are studied using a micromagnetic simulation. The properties and the micromagnetic structure of the nanolayer are determined by the competition between the anisotropy and exchange energies and by the dipole-dipole interaction energy. The magnetic microstructure can be described as an ensemble of stochastic magnetic domains and topological magnetization defects. Dipole-dipole interaction suppresses the formation of topological magnetization defects. The topological defects in the magnetic microstructure can cause a sharper change in the coercive force with the crystallite size than that predicted by the random magnetic anisotropy model.

Quasi-periodic Oscillations in Flares and Coronal Mass Ejections Associated with Magnetic Reconnection

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takahashi, Takuya; Shibata, Kazunari; Qiu, Jiong, E-mail: takahasi@kusastro.kyoto-u.ac.jp

We propose a mechanism for quasi-periodic oscillations of both coronal mass ejections (CMEs) and flare loops as related to magnetic reconnection in eruptive solar flares. We perform two-dimensional numerical MHD simulations of magnetic flux rope eruption, with three different values of the global Lundquist number. In the low Lundquist number run, no oscillatory behavior is found. In the moderate Lundquist number run, on the other hand, quasi-periodic oscillations are excited both at the bottom of the flux rope and at the flare loop top. In the high Lundquist number run, quasi-periodic oscillations are also excited; in the meanwhile, the dynamicsmore » become turbulent owing to the formation of multiple plasmoids in the reconnection current sheet. In high and moderate Lundquist number runs, thin reconnection jets collide with the flux rope bottom or flare loop top and dig them deeply. Steep oblique shocks are formed as termination shocks where reconnection jets are bent (rather than decelerated) in the horizontal direction, resulting in supersonic backflows. The structure becomes unstable, and quasi-periodic oscillations of supersonic backflows appear at locally confined high-beta regions at both the flux rope bottom and flare loop top. We compare the observational characteristics of quasi-periodic oscillations in erupting flux ropes, post-CME current sheets, flare ribbons, and light curves with corresponding dynamical structures found in our simulation.« less

Quasi-periodic Oscillations in Flares and Coronal Mass Ejections Associated with Magnetic Reconnection

NASA Astrophysics Data System (ADS)

Takahashi, Takuya; Qiu, Jiong; Shibata, Kazunari

2017-10-01

We propose a mechanism for quasi-periodic oscillations of both coronal mass ejections (CMEs) and flare loops as related to magnetic reconnection in eruptive solar flares. We perform two-dimensional numerical MHD simulations of magnetic flux rope eruption, with three different values of the global Lundquist number. In the low Lundquist number run, no oscillatory behavior is found. In the moderate Lundquist number run, on the other hand, quasi-periodic oscillations are excited both at the bottom of the flux rope and at the flare loop top. In the high Lundquist number run, quasi-periodic oscillations are also excited; in the meanwhile, the dynamics become turbulent owing to the formation of multiple plasmoids in the reconnection current sheet. In high and moderate Lundquist number runs, thin reconnection jets collide with the flux rope bottom or flare loop top and dig them deeply. Steep oblique shocks are formed as termination shocks where reconnection jets are bent (rather than decelerated) in the horizontal direction, resulting in supersonic backflows. The structure becomes unstable, and quasi-periodic oscillations of supersonic backflows appear at locally confined high-beta regions at both the flux rope bottom and flare loop top. We compare the observational characteristics of quasi-periodic oscillations in erupting flux ropes, post-CME current sheets, flare ribbons, and light curves with corresponding dynamical structures found in our simulation.

Structural, magnetic and electronic structure properties of Co doped ZnO nanoparticles

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Shalendra, E-mail: shailuphy@gmail.com; School of Materials Science and Engineering, Changwon National University, Changwon, Gyeongnam 641-773; Song, T.K., E-mail: tksong@changwon.ac.kr

Highlights: • XRD and HR-TEM results show the single phase nature of Co doped ZnO nanoparticles. • XMCD and dc magnetization results indicate the RT-FM in Co doped ZnO nanoparticles. • Co L{sub 3,2} NEXAFS spectra infer that Co ions are in 2+ valence state. • O K edge NEXAFS spectra show that O vacancy increases with Co doping in ZnO. - Abstract: We reported structural, magnetic and electronic structure studies of Co doped ZnO nanoparticles. Doping of Co ions in ZnO host matrix has been studied and confirmed using various methods; such as X-ray diffraction (XRD), field emission scanningmore » electron microscopy (FE-SEM), energy dispersed X-ray (EDX), high resolution transmission electron microscopy (HR-TEM), Fourier transform infrared spectroscopy (FT-IR), near edge X-ray absorption fine structure (NEXAFS) spectroscopy, magnetic hysteresis loop measurements and X-ray magnetic circular dichroism (XMCD). From the XRD and HR-TEM results, it is observed that Co doped ZnO nanoparticles have single phase nature with wurtzite structure and exclude the possibility of secondary phase formation. FE-SEM and TEM micrographs show that pure and Co doped nanoparticles are nearly spherical in shape. O K edge NEXAFS spectra indicate that O vacancies increase with Co doping. The Co L{sub 3,2} edge NEXAFS spectra revealed that Co ions are in 2+ valence state. DC magnetization hysteresis loops and XMCD results clearly showed the intrinsic origin of temperature ferromagnetism in Co doped ZnO nanoparticles.« less

Coronal magnetic structure and the latitude and longitude distribution of energetic particles, 1-5 AU

NASA Technical Reports Server (NTRS)

Roelof, E. C.; Mitchell, D. G.

1979-01-01

The relation of the coronal magnetic field structure to the distribution of approximately 1 MeV protons in interplanetary space between 1 and 5 AU is discussed. After ordering the interplanetary data by its estimated coronal emission source location in heliographic coordinates, the multispacecraft measured proton fluxes are compared with coronal magnetic field structure infrared as observed in soft X-ray photographs and potential field calculations. Evidence for the propagation and possible acceleration of solar flare protons on high magnetic loop structure in the corona is presented. Further, it is shown that corotating proton flux enhancements are associated with regions of low coronal X-ray emission (including coronal holes), usually in association with solar wind stream structure.

Numerical investigation of the relationship between magnetic stiffness and minor loop size in the HTS levitation system

NASA Astrophysics Data System (ADS)

Yang, Yong; Li, Chengshan

2017-10-01

The effect of minor loop size on the magnetic stiffness has not been paid attention to by most researchers in experimental and theoretical studies about the high temperature superconductor (HTS) magnetic levitation system. In this work, we numerically investigate the average magnetic stiffness obtained by the minor loop traverses Δz (or Δx) varying from 0.1 mm to 2 mm in zero field cooling and field cooling regimes, respectively. The approximate values of the magnetic stiffness with zero traverse are obtained using the method of linear extrapolation. Compared with the average magnetic stiffness gained by any minor loop traverse, these approximate values are Not always close to the average magnetic stiffness produced by the smallest size of minor loops. The relative deviation ranges of average magnetic stiffness gained by the usually minor loop traverse (1 or 2 mm) are presented by the ratios of approximate values to average stiffness for different moving processes and two typical cooling conditions. The results show that most of average magnetic stiffness are remarkably influenced by the sizes of minor loop, which indicates that the magnetic stiffness obtained by a single minor loop traverse Δ z or Δ x, for example, 1 or 2 mm, can be generally caused a large deviation.

Structural and multiferroic properties of Ba2+ doped BiFeO3 nanoparticles synthesized via sol-gel method

NASA Astrophysics Data System (ADS)

Shisode, M. V.; Kharat, Prashant B.; Bhoyar, Dhananjay N.; Vinayak, Vithal; Babrekar, M. K.; Jadhav, K. M.

2018-05-01

Ba2+ doped Bismuth ferrite nanoparticles having general formula Bi1-xBaxFeO3 (where, x = 0.00 and 0.20) were successfully synthesized by sol gel method, using nitrates as a starting material. Ethylene glycol was used as a solvent. The synthesized powder was sintered at 650°C for 4 hours to obtain pure phase BFO. Leaching with dilute nitric acid (HNO3) and distilled water (H2O) is done to remove the impurities. The structural, morphological, magnetic and ferroelectric properties were systematically investigated using standard characterization techniques like X-ray diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM) and room temperature magnetic behavior of the samples was studied using pulse field hysteresis loop tracer technique showing increase in saturation magnetizaion. P-E loop confirms the ferroelectric behavior of prepared nanoparticles. The coexistence of ferromagnetic and ferroelectric hysteresis loops in BFO and Bi0.8Ba0.2FeO3 nanoparticles samples at room temperature; it indicates that the samples are potential candidates for information storage and spintronics devices. The increase in magnetic properties may be important for practical application at room temperature.

Steady State Model for Solar Coronal Loops

NASA Astrophysics Data System (ADS)

Sugiyama, L.; Asgari-Targhi, M.

2017-12-01

Solar coronal loops on the surface of the sun provide background magnetic and plasma structures for the release of a significant amount of the sun's energy, through energetic solar flares and coronal mass ejections and more gradual processes. Understanding their steady states is the first step in understanding loop dynamics. A consistent MHD steady state model, for a curved magnetic flux rope that contains plasma, has been developed[1] for simple coronal loops with both ends anchored in the photosphere. Plasma pressure or current makes the loop unstable to expansion in major radius and must be balanced by external forces, such as the solar gravity. The MHD momentum equation has a well defined small parameter ordering in the loop inverse aspect ratio ɛ=a/Ro (minor/major radius). Different types of common coronal loops fall in different parameter regimes, determined by the relative values of the plasma beta β=po/(Bo2/2μo), the MHD gravity parameter Ĝ≡ga/vA2 (the gravitational acceleration g normalized to the minor radius a and shear Alfvén velocity vA), and ɛ. The largest possible gravity, Ĝ ɛ1β, corresponds to the largest loops because it reduces the plasma density at the top of the loop exponentially compared to its lower ends, reducing the downward gravitational force -ρĜ there. The thin loops that are ubiquitous in solar active regions have ``high'' beta, β ɛ1, for ɛ≃0.02, and fit the predicted model scalings. The thicker loops that can give rise to flares and CMEs have ``low'' beta, β ɛ2. Cool loops, such as solar filaments outside active regions, that have a central pressure lower than that of the surrounding corona would have the strongest stability against radial expansion. The model raises a number of questions about the connection of loops to the photosphere and the force-free nature of the magnetic field there. [1] L. Sugiyama, M. Asgari-Targhi, Phys. Plasmas 24, 022904 (2017).

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kitiashvili, I. N.; Mansour, N. N.; Wray, A. A.

Magnetic fields are usually observed in the quiet Sun as small-scale elements that cover the entire solar surface (the “salt-and-pepper” patterns in line-of-sight magnetograms). By using 3D radiative MHD numerical simulations, we find that these fields result from a local dynamo action in the top layers of the convection zone, where extremely weak “seed” magnetic fields (e.g., from a 10{sup −6} G) can locally grow above the mean equipartition field to a stronger than 2000 G field localized in magnetic structures. Our results reveal that the magnetic flux is predominantly generated in regions of small-scale helical downflows. We find thatmore » the local dynamo action takes place mostly in a shallow, about 500 km deep, subsurface layer, from which the generated field is transported into the deeper layers by convective downdrafts. We demonstrate that the observed dominance of vertical magnetic fields at the photosphere and horizontal fields above the photosphere can be explained by small-scale magnetic loops produced by the dynamo. Such small-scale loops play an important role in the structure and dynamics of the solar atmosphere and their detection in observations is critical for understanding the local dynamo action on the Sun.« less

Cool transition region loops observed by the Interface Region Imaging Spectrograph

NASA Astrophysics Data System (ADS)

Huang, Z.; Xia, L.; Li, B.; Madjarska, M. S.

2015-12-01

An important class of loops in the solar atmosphere, cool transition region loops, have received little attention mainly due to instrumental limitations. We analyze a cluster of these loops in the on-disk active region NOAA 11934 recorded in a Si IV 1402.8 Å spectral raster and 1400Å slit-jaw (SJ) images taken by the Interface Region Imaging Spectrograph. We divide these loops into three groups and study their dynamics, evolution and interaction.The first group comprises geometrically relatively stable loops, which are finely scaled with 382~626 km cross-sections. Siphon flows in these loops are suggested by the Doppler velocities gradually changing from -10 km/s (blue-shifts) in one end to 20 km/s (red-shifts) in the other. Nonthermal velocities from 15 to 25 km/s were determined. The obtained physical properties suggest that these loops are impulsively heated by magnetic reconnection occurring at the blue-shifted footpoints where magnetic cancellation with a rate of 1015 Mx/s is found. The released magnetic energy is redistributed by the siphon flows. The second group corresponds to two active footpoints rooted in mixed-magnetic-polarity regions. Magnetic reconnection in both footpoints is suggested by explosive-event line profiles with enhanced wings up to 200 km/s and magnetic cancellation with a rate of ~1015 Mx/s. In the third group, an interaction between two cool loop systems is observed. Mixed-magnetic polarities are seen in their conjunction area where explosive-event line profiles and magnetic cancellation with a rate of 3×1015 Mx/s are found. This is a clear indication that magnetic reconnection occurs between these two loop systems. Our observations suggest that the cool transition region loops are heated impulsively most likely by sequences of magnetic reconnection events.

Chromospheric counterparts of solar transition region unresolved fine structure loops

NASA Astrophysics Data System (ADS)

Pereira, Tiago M. D.; Rouppe van der Voort, Luc; Hansteen, Viggo H.; De Pontieu, Bart

2018-04-01

Low-lying loops have been discovered at the solar limb in transition region temperatures by the Interface Region Imaging Spectrograph (IRIS). They do not appear to reach coronal temperatures, and it has been suggested that they are the long-predicted unresolved fine structures (UFS). These loops are dynamic and believed to be visible during both heating and cooling phases. Making use of coordinated observations between IRIS and the Swedish 1-m Solar Telescope, we study how these loops impact the solar chromosphere. We show for the first time that there is indeed a chromospheric signal of these loops, seen mostly in the form of strong Doppler shifts and a conspicuous lack of chromospheric heating. In addition, we find that several instances have a inverse Y-shaped jet just above the loop, suggesting that magnetic reconnection is driving these events. Our observations add several puzzling details to the current knowledge of these newly discovered structures; this new information must be considered in theoretical models. Two movies associated to Fig. 1 are available at http://https://www.aanda.org

OBSERVATIONAL SIGNATURES OF CORONAL LOOP HEATING AND COOLING DRIVEN BY FOOTPOINT SHUFFLING

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dahlburg, R. B.; Taylor, B. D.; Einaudi, G.

The evolution of a coronal loop is studied by means of numerical simulations of the fully compressible three-dimensional magnetohydrodynamic equations using the HYPERION code. The footpoints of the loop magnetic field are advected by random motions. As a consequence, the magnetic field in the loop is energized and develops turbulent nonlinear dynamics characterized by the continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Dissipation is nonuniformly distributed so that only a fraction of the coronal mass and volume gets heated at any time. Temperature and density are highly structured at scalesmore » that, in the solar corona, remain observationally unresolved: the plasma of our simulated loop is multithermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. Numerical simulations of coronal loops of 50,000 km length and axial magnetic field intensities ranging from 0.01 to 0.04 T are presented. To connect these simulations to observations, we use the computed number densities and temperatures to synthesize the intensities expected in emission lines typically observed with the Extreme Ultraviolet Imaging Spectrometer on Hinode. These intensities are used to compute differential emission measure distributions using the Monte Carlo Markov Chain code, which are very similar to those derived from observations of solar active regions. We conclude that coronal heating is found to be strongly intermittent in space and time, with only small portions of the coronal loop being heated: in fact, at any given time, most of the corona is cooling down.« less

Enhanced magnetic hysteresis in Ni-Mn-Ga single crystal and its influence on magnetic shape memory effect

NASA Astrophysics Data System (ADS)

Heczko, O.; Drahokoupil, J.; Straka, L.

2015-05-01

Enhanced magnetic hysteresis due to boron doping in combination with magnetic shape memory effect in Ni-Mn-Ga single crystal results in new interesting functionality of magnetic shape memory (MSM) alloys such as mechanical demagnetization. In Ni50.0Mn28.5Ga21.5 single crystal, the boron doping increased magnetic coercivity from few Oe to 270 Oe while not affecting the transformation behavior and 10 M martensite structure. However, the magnetic field needed for MSM effect also increased in doped sample. The magnetic behavior is compared to undoped single crystal of similar composition. The evidence from the X-ray diffraction, magnetic domain structure, magnetization loops, and temperature evolution of the magnetic coercivity points out that the enhanced hysteresis is caused by stress-induced anisotropy.

ISEE 3 observations of low-energy proton bidirectional events and their relation to isolated interplanetary magnetic structures

NASA Technical Reports Server (NTRS)

Marsden, R. G.; Sanderson, T. R.; Tranquille, C.; Wenzel, K.-P.; Smith, E. J.

1987-01-01

The paper represents the results of a comprehensive survey of low-energy proton bidirectional anisotropies and associated transient magnetic structures as observed in the 35-1600 keV energy range on ISEE-3 during the last solar maximum. The majority of observed bidirectional flow (BDF) events (more than 70 percent) are associated with isolated magnetic structures which are postulated to be an interplanetary manifestation of coronal mass ejection (CME) events. The observed BDF events can be qualitatively grouped into five classes depending on the field signature of the related magnetic structure and the association (or lack of association) with an interplanetary shock. Concerning the topology of the CME-related magnetic structures, the observations are interpreted as being consistent with a detached bubble, comprising closed loops or tightly wound helices.

WHAT IS THE SOURCE OF QUIET SUN TRANSITION REGION EMISSION?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Schmit, D. J.; De Pontieu, Bart

Dating back to the first observations of the on-disk corona, there has been a qualitative link between the photosphere’s magnetic network and enhanced transition-temperature plasma emission. These observations led to the development of a general model that describes emission structures through the partitioning of the atmospheric volume with different magnetic loop geometries that exhibit different energetic equilibria. Does the internetwork produce transition-temperature emission? What fraction of network flux connects to the corona? How does quiet Sun emission compare with low-activity Sun-like stars? In this work, we revisit the canonical model of the quiet Sun, with high-resolution observations from the Interfacemore » Region Imaging Spectrograph ( IRIS ) and HMI in hand, to address those questions. We use over 900 deep exposures of Si iv 1393 Å from IRIS along with nearly simultaneous HMI magnetograms to quantify the correlation between transition-temperature emission structures and magnetic field concentrations through a number of novel statistics. Our observational results are coupled with analysis of the Bifrost MHD model and a large-scale potential field model. Our results paint a complex portrait of the quiet Sun. We measure an emission signature in the distant internetwork that cannot be attributed to network contribution. We find that the dimmest regions of emission are not linked to the local vertical magnetic field. Using the MHD simulation, we categorize the emission contribution from cool mid-altitude loops and high-altitude coronal loops and discuss the potential emission contribution of spicules. Our results provide new constraints on the coupled solar atmosphere so that we can build on our understanding of how dynamic thermal and magnetic structures generate the observed phenomena in the transition region.« less

Magnetization reversal process in (Sm, Dy, Gd) (Co, Fe, Cu, Zr)z magnets with different cellular structures

NASA Astrophysics Data System (ADS)

Liu, Lei; Liu, Zhuang; Zhang, Xin; Feng, Yanping; Wang, Chunxiao; Sun, Yingli; Lee, Don; Yan, Aru; Wu, Qiong

2017-05-01

Magnetization reversal mechanism is found to vary with cellular structures by a comparative study of the magnetization processes of three (Sm, Dy, Gd) (Co, Fe, Cu, Zr)z magnets with different cellular structures. Analysis of domain walls, initial magnetization curves and recoil loops indicates that the morphology of cellular structure has a significant effect on the magnetization process, besides the obvious connection to the difference of domain energy density between cell boundary phase (CBP) and main phase. The magnetization of Sample 2 (with a moderate cell size and uniformly continuous CBPs) behaves as a strong coherence domain-wall pinning effect to the domain wall and lead to a highest coercivity in the magnet. The magnetization of Sample 1 (with thin and discontinuous CBPs) shows an inconsistent pinning effect to the domain wall while that of Sample 3 (with thick and aggregate CBPs) exhibits a two-phase separation magnetization. Both the two cases lead to lower coercivities. A simplified model is given as well to describe the relationships among cellular structure and magnetization behavior.

Segmented surface coil resonator for in vivo EPR applications at 1.1GHz.

PubMed

Petryakov, Sergey; Samouilov, Alexandre; Chzhan-Roytenberg, Michael; Kesselring, Eric; Sun, Ziqi; Zweier, Jay L

2009-05-01

A four-loop segmented surface coil resonator (SSCR) with electronic frequency and coupling adjustments was constructed with 18mm aperture and loading capability suitable for in vivo Electron Paramagnetic Resonance (EPR) spectroscopy and imaging applications at L-band. Increased sample volume and loading capability were achieved by employing a multi-loop three-dimensional surface coil structure. Symmetrical design of the resonator with coupling to each loop resulted in high homogeneity of RF magnetic field. Parallel loops were coupled to the feeder cable via balancing circuitry containing varactor diodes for electronic coupling and tuning over a wide range of loading conditions. Manually adjusted high Q trimmer capacitors were used for initial tuning with subsequent tuning electronically controlled using varactor diodes. This design provides transparency and homogeneity of magnetic field modulation in the sample volume, while matching components are shielded to minimize interference with modulation and ambient RF fields. It can accommodate lossy samples up to 90% of its aperture with high homogeneity of RF and modulation magnetic fields and can function as a surface loop or a slice volume resonator. Along with an outer coaxial NMR surface coil, the SSCR enabled EPR/NMR co-imaging of paramagnetic probes in living rats to a depth of 20mm.

Segmented surface coil resonator for in vivo EPR applications at 1.1 GHz

PubMed Central

Petryakov, Sergey; Samouilov, Alexandre; Chzhan-Roytenberg, Michael; Kesselring, Eric; Sun, Ziqi; Zweier, Jay L.

2010-01-01

A four-loop segmented surface coil resonator (SSCR) with electronic frequency and coupling adjustments was constructed with 18 mm aperture and loading capability suitable for in vivo Electron Paramagnetic Resonance (EPR) spectroscopy and imaging applications at L-band. Increased sample volume and loading capability were achieved by employing a multi-loop three-dimensional surface coil structure. Symmetrical design of the resonator with coupling to each loop resulted in high homogeneity of RF magnetic field. Parallel loops were coupled to the feeder cable via balancing circuitry containing varactor diodes for electronic coupling and tuning over a wide range of loading conditions. Manually adjusted high Q trimmer capacitors were used for initial tuning with subsequent tuning electronically controlled using varactor diodes. This design provides transparency and homogeneity of magnetic field modulation in the sample volume, while matching components are shielded to minimize interference with modulation and ambient RF fields. It can accommodate lossy samples up to 90% of its aperture with high homogeneity of RF and modulation magnetic fields and can function as a surface loop or a slice volume resonator. Along with an outer coaxial NMR surface coil, the SSCR enabled EPR/NMR co-imaging of paramagnetic probes in living rats to a depth of 20 mm. PMID:19268615

Tuning the effective parameters in (Ta/Cu/[Ni/Co]x/Ta) multilayers with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Ayareh, Zohreh; Moradi, Mehrdad; Mahmoodi, Saman

2018-06-01

In this paper, we report perpendicular magnetic anisotropy (PMA) in a (Ta/Cu/[Ni/Co]x/Ta) multilayers structure. These typical structures usually include a multilayer of ferromagnetic and transition metal thin films. Usually, magnetic anisotropy is characterized by magnetization loops determined by magnetometer or magneto-optical Kerr effect (MOKE). The interface between ferromagnetic and metallic layers plays an important role in magnetic anisotropy evolution from out-of-plane to in-plane in (Ta/Cu/[Ni/Co]/Ta) structure. Obtained results from MOKE and magnetometry of these samples show that they have different easy axes due to change in thickness of Cu as spacer layer and difference in number of repetition of [Ni/Co] stacks.

NON-POTENTIAL FIELDS IN THE QUIET SUN NETWORK: EXTREME-ULTRAVIOLET AND MAGNETIC FOOTPOINT OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chesny, D. L.; Oluseyi, H. M.; Orange, N. B.

The quiet Sun (QS) magnetic network is known to contain dynamics which are indicative of non-potential fields. Non-potential magnetic fields forming ''S-shaped'' loop arcades can lead to the breakdown of static activity and have only been observed in high temperature X-ray coronal structures—some of which show eruptive behavior. Thus, analysis of this type of atmospheric structuring has been restricted to large-scale coronal fields. Here we provide the first identification of non-potential loop arcades exclusive to the QS supergranulation network. High-resolution Atmospheric Imaging Assembly data from the Solar Dynamics Observatory have allowed for the first observations of fine-scale ''S-shaped'' loop arcadesmore » spanning the network. We have investigated the magnetic footpoint flux evolution of these arcades from Heliospheric and Magnetic Imager data and find evidence of evolving footpoint flux imbalances accompanying the formation of these non-potential fields. The existence of such non-potentiality confirms that magnetic field dynamics leading to the build up of helicity exist at small scales. QS non-potentiality also suggests a self-similar formation process between the QS network and high temperature corona and the existence of self-organized criticality (SOC) in the form of loop-pair reconnection and helicity dissipation. We argue that this type of behavior could lead to eruptive forms of SOC as seen in active region (AR) and X-ray sigmoids if sufficient free magnetic energy is available. QS magnetic network dynamics may be considered as a coronal proxy at supergranular scales, and events confined to the network can even mimic those in coronal ARs.« less

General structure of fermion two-point function and its spectral representation in a hot magnetized medium

NASA Astrophysics Data System (ADS)

Das, Aritra; Bandyopadhyay, Aritra; Roy, Pradip K.; Mustafa, Munshi G.

2018-02-01

We have systematically constructed the general structure of the fermion self-energy and the effective quark propagator in the presence of a nontrivial background such as a hot magnetized medium. This is applicable to both QED and QCD. The hard thermal loop approximation has been used for the heat bath. We have also examined transformation properties of the effective fermion propagator under some of the discrete symmetries of the system. Using the effective fermion propagator we have analyzed the fermion dispersion spectra in a hot magnetized medium along with the spinor for each fermion mode obtained by solving the modified Dirac equation. The fermion spectra is found to reflect the discrete symmetries of the two-point functions. We note that for a chirally symmetric theory the degenerate left- and right-handed chiral modes in vacuum or in a heat bath get separated and become asymmetric in the presence of a magnetic field without disturbing the chiral invariance. The obtained general structure of the two-point functions is verified by computing the three-point function, which agrees with the existing results in one-loop order. Finally, we have computed explicitly the spectral representation of the two-point functions which would be very important to study the spectral properties of the hot magnetized medium corresponding to QED and QCD with background magnetic field.

Magnetic switch coupling to synchronize magnetic modulators

DOEpatents

Reed, K.W.; Kiekel, P.

1999-04-27

Apparatus for synchronizing the output pulses from a pair of magnetic switches is disclosed. An electrically conductive loop is provided between the pair of switches with the loop having windings about the core of each of the magnetic switches. The magnetic coupling created by the loop removes voltage and timing variations between the outputs of the two magnetic switches caused by any of a variety of factors. The only remaining variation is a very small fixed timing offset caused by the geometry and length of the loop itself. 13 figs.

Dynamical and Physical Properties of a Post-Coronal Mass Ejection Current Sheet

NASA Technical Reports Server (NTRS)

Ko, Yuan-Kuen; Raymond, John C.; Lin, Jun; Lawrence, Gareth; Li, Jing; Fludra, Andrzej

2003-01-01

In the eruptive process of the Kopp-Pneuman type, the closed magnetic field is stretched by the eruption so much that it is usually believed to be " open " to infinity. Formation of the current sheet in such a configuration makes it possible for the energy in the coronal magnetic field to quickly convert into thermal and kinetic energies and cause significant observational consequences, such as growing postflare/CME loop system in the corona, separating bright flare ribbons in the chromosphere, and fast ejections of the plasma and the magnetic flux. An eruption on 2002 January 8 provides us a good opportunity to look into these observational signatures of and place constraints on the theories of eruptions. The event started with the expansion of a magnetic arcade over an active region, developed into a coronal mass ejection (CME), and left some thin streamer-like structures with successively growing loop systems beneath them. The plasma outflow and the highly ionized states of the plasma inside these streamer-like structures, as well as the growing loops beneath them, lead us to conclude that these structures are associated with a magnetic reconnection site, namely, the current sheet, of this eruptive process. We combine the data from the Ultraviolet Coronagraph Spectrometer, Large Angle and Spectrometric Coronagraph Experiment, EUV Imaging Telescope, and Coronal Diagnostic Spectrometer on board the Solar and Heliospheric Observatory, as well is from the Mauna Loa Solar Observatory Mark IV K-coronameter, to investigate the morphological and dynamical properties of this event, as well as the physical properties of the current sheet. The velocity and acceleration of the CME reached up to 1800 km/s and 1 km/sq s, respectively. The acceleration is found to occur mainly at the lower corona (<2.76 Solar Radius). The post-CME loop systems showed behaviors of both postflare loops (upward motion with decreasing speed) and soft X-ray giant arches (upward motion with constant speed, or acceleration) according to the definition of Svestka. In the current sheet, the presence of highly ionized ions, such as Fe(+17) and Ca(+13), suggests temperature as high as (3-4) x 10(exp 6) K, and the plasma outflows have speeds ranging from 300 to 650 km/s. Absolute elemental abundances in the current sheet show a strong first ionization potential effect and have values similar to those found in the active region streamers. The magnetic field strength in the vicinity of the current sheet is found to be of the order of 1 G.

Effect of lanthanum substitution on structural and magnetic properties of nickel zinc ferrites

NASA Astrophysics Data System (ADS)

Šoka, Martin; Ušáková, Mariana; Dosoudil, Rastislav; Ušák, Elemír; Lokaj, Ján

2018-04-01

The purpose of the presented research is to investigate the effect of La3+ ions substitution for Fe3+ ions in Ni0.42Zn0.58LaxFe2-xO4 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.10) ferrite compositions prepared by the innovated glycine-nitrate process based on auto-combustion method. Structural and magnetic properties of examined samples were estimated by the analysis of X-ray spectra, EDAX spectrum, SEM micrographs, thermomagnetic characteristics, magnetic hysteresis loops and complex permeability spectra.

Antidot shape dependence of switching mechanism in permalloy samples

NASA Astrophysics Data System (ADS)

Yetiş, Hakan; Denizli, Haluk

2017-01-01

We study antidot shape dependence of the switching magnetization for various permalloy samples with square and triangular arrays of nanometer scale antidots. The remnant magnetization, squareness ratio, and coercive fields of the samples are extracted from the hysteresis loops which are obtained by solving the Landau-Lifshitz-Gilbert (LLG) equation numerically. We find several different magnetic spin configurations which reveal the existence of superdomain wall structures. Our results are discussed in terms of the local shape anisotropy, array geometry, and symmetry properties in order to explain the formation of inhomogeneous domain structures.

Observational Study of Particle Acceleration in the 2006 December 13 Flare

NASA Astrophysics Data System (ADS)

Minoshima, T.; Morimoto, T.; Kawate, T.; Imada, S.; Koshiishi, H.; Masuda, S.; Kubo, M.; Inoue, S.; Isobe, H.; Krucker, S.; Yokoyama, T.

2008-12-01

We study the particle acceleration in a flare on 2006 December 13, by using the Hinode, RHESSI, Nobeyama Radio Polarimeters (NoRP) and Nobeyama Radioheliograph (NoRH) observations. For technical reasons, both RHESSI and NoRH have a problem in imaging in this flare. Since we have succeeded in solving the problem, it is now possible to discuss the particle acceleration mechanism from an image analysis. This flare shows very long-lasting (1 hour) non-thermal emissions, consisting of many spikes. We focus on the second major spike at 02:29 UT, because the RHESSI image is available only in this period. The RHESSI 35-100 keV HXR image shows double sources located at the footpoints of the western soft X-ray (SXR) loop seen by the Hinode/XRT. The non-linear force-free (NLFF) modeling based on a magnetogram data by Inoue et al. shows the NLFF to potential magnetic transition of the loop, which would induce the electric field and then accelerate particles. Overlaying the HXR image on the photospheric three-dimensional magnetic field map taken by the Hinode Spectro-Polarimeter, we find that the HXR sources are located at the region where the horizontal magnetic fields invert. The NoRH 34 GHz microwave images show the loop structure connecting the HXR sources. The microwave peaks do not located at the top of the loop but between the loop top and the footpoints. The NoRP microwave spectrum shows the soft-hard-soft pattern in the period, same as the HXR spectrum (Ning 2008). From these observational results we suggest that the electrons were accelerated parallel to the magnetic field line near the magnetic separatrix.

Observations of loops and prominences

NASA Technical Reports Server (NTRS)

Strong, Keith T.

1994-01-01

We review recent observations by the Yohkoh-SXT (Soft X-ray Telescope) in collaboration with other spacecraft and ground-based observatories of coronal loops and prominences. These new results point to problems that SoHO will be able to address. With a unique combination of rapid-cadence digital imaging (greater than or equal to 32 s full-disk and greater than or equal to 2 s partial-frame images), high spatial resolution (greater than or equal to 2.5 arcsec pixels), high sensitivity (EM less than or equal to 10(exp 42) cm(exp -3)), a low-scatter mirror, and large dynamic range, SXT can observe a vast range of targets on the Sun. Over the first 21 months of Yohkoh operations SXT has taken over one million images of the corona and so is building up an invaluable long-term database on the large-scale corona and loop geometry. The most striking thing about the SXT images is the range of loop sizes and shapes. The active regions are a bright tangle of magnetic field lines, surrounded by a network of large-scale quiet-Sun loops stretching over distances in excess of 105 km. The cross-section of most loops seems to be constant. Loops displaying significant Gamma's are the exception, not the rule, implying the presence of widespread currents in the corona. All magnetic structures show changes. Time scales range from seconds to months. The question of how these structures are formed, become filled with hot plasma, and are maintained is still open. While we see the propagation of brightenings along the length of active-region loops and in X-ray jets with velocities of several hundred km/s, much higher velocities are seen in the quiet Sun. In XBP flares, for example, velocities of over 1000 km/s are common. Active-region loops seem to be in constant motion, moving slowly outward, carrying plasma with them. During flares, loops often produce localized brightenings at the base and later at the apex of the loop. Quiescent filaments and prominences have been observed regularly. Their coronal manifestation seems to be an extended arcade of loops overlying the filament. Reliable alignment of the ground-based data with the X-ray images make it possible to make a detailed intercomparison of the hot and cold plasma structures over extended periods. Hence we are able to follow the long-term evolution of these structures and see how they become destabilized and erupt.

EIGENMODES OF THREE-DIMENSIONAL MAGNETIC ARCADES IN THE SUN’S CORONA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hindman, Bradley W.; Jain, Rekha, E-mail: hindman@solarz.colorado.edu

We develop a model of coronal-loop oscillations that treats the observed bright loops as an integral part of a larger three-dimensional (3D) magnetic structure comprised of the entire magnetic arcade. We demonstrate that magnetic arcades within the solar corona can trap MHD fast waves in a 3D waveguide. This is accomplished through the construction of a cylindrically symmetric model of a magnetic arcade with a potential magnetic field. For a magnetically dominated plasma, we derive a governing equation for MHD fast waves and from this equation we show that the magnetic arcade forms a 3D waveguide if the Alfvén speedmore » increases monotonically beyond a fiducial radius. Both magnetic pressure and tension act as restoring forces, instead of just tension as is generally assumed in 1D models. Since magnetic pressure plays an important role, the eigenmodes involve propagation both parallel and transverse to the magnetic field. Using an analytic solution, we derive the specific eigenfrequencies and eigenfunctions for an arcade possessing a discontinuous density profile. The discontinuity separates a diffuse cylindrical cavity and an overlying shell of denser plasma that corresponds to the bright loops. We emphasize that all of the eigenfunctions have a discontinuous axial velocity at the density interface; hence, the interface can give rise to the Kelvin–Helmholtz instability. Further, we find that all modes have elliptical polarization with the degree of polarization changing with height. However, depending on the line of sight, only one polarization may be clearly visible.« less

FINE STRUCTURES AND OVERLYING LOOPS OF CONFINED SOLAR FLARES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shuhong; Zhang, Jun; Xiang, Yongyuan, E-mail: shuhongyang@nao.cas.cn

2014-10-01

Using the Hα observations from the New Vacuum Solar Telescope at the Fuxian Solar Observatory, we focus on the fine structures of three confined flares and the issue why all the three flares are confined instead of eruptive. All the three confined flares take place successively at the same location and have similar morphologies, so can be termed homologous confined flares. In the simultaneous images obtained by the Solar Dynamics Observatory, many large-scale coronal loops above the confined flares are clearly observed in multi-wavelengths. At the pre-flare stage, two dipoles emerge near the negative sunspot, and the dipolar patches aremore » connected by small loops appearing as arch-shaped Hα fibrils. There exists a reconnection between the small loops, and thus the Hα fibrils change their configuration. The reconnection also occurs between a set of emerging Hα fibrils and a set of pre-existing large loops, which are rooted in the negative sunspot, a nearby positive patch, and some remote positive faculae, forming a typical three-legged structure. During the flare processes, the overlying loops, some of which are tracked by activated dark materials, do not break out. These direct observations may illustrate the physical mechanism of confined flares, i.e., magnetic reconnection between the emerging loops and the pre-existing loops triggers flares and the overlying loops prevent the flares from being eruptive.« less

THE INSTABILITY AND NON-EXISTENCE OF MULTI-STRANDED LOOPS WHEN DRIVEN BY TRANSVERSE WAVES

DOE Office of Scientific and Technical Information (OSTI.GOV)

Magyar, N.; Van Doorsselaere, T., E-mail: norbert.magyar@wis.kuleuven.be

2016-06-01

In recent years, omni-present transverse waves have been observed in all layers of the solar atmosphere. Coronal loops are often modeled as a collection of individual strands in order to explain their thermal behavior and appearance. We perform three-dimensional (3D) ideal magnetohydrodynamics simulations to study the effect of a continuous small amplitude transverse footpoint driving on the internal structure of a coronal loop composed of strands. The output is also converted into synthetic images, corresponding to the AIA 171 and 193 Å passbands, using FoMo. We show that the multi-stranded loop ceases to exist in the traditional sense of themore » word, because the plasma is efficiently mixed perpendicularly to the magnetic field, with the Kelvin–Helmholtz instability acting as the main mechanism. The final product of our simulation is a mixed loop with density structures on a large range of scales, resembling a power-law. Thus, multi-stranded loops are unstable to driving by transverse waves, and this raises strong doubts on the usability and applicability of coronal loop models consisting of independent strands.« less

FAST CONTRACTION OF CORONAL LOOPS AT THE FLARE PEAK

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu Rui; Wang Haimin

On 2005 September 8, a coronal loop overlying the active region NOAA 10808 was observed in TRACE 171 A to contract at {approx}100 km s{sup -1} at the peak of an X5.4-2B flare at 21:05 UT. Prior to the fast contraction, the loop underwent a much slower contraction at {approx}6 km s{sup -1} for about 8 minutes, initiating during the flare preheating phase. The sudden switch to fast contraction is presumably corresponding to the onset of the impulsive phase. The contraction resulted in the oscillation of a group of loops located below, with the period of about 10 minutes. Meanwhile,more » the contracting loop exhibited a similar oscillatory pattern superimposed on the dominant downward motion. We suggest that the fast contraction reflects a suddenly reduced magnetic pressure underneath due either to (1) the eruption of magnetic structures located at lower altitudes or to (2) the rapid conversion of magnetic free energy in the flare core region. Electrons accelerated in the shrinking trap formed by the contracting loop can theoretically contribute to a late-phase hard X-ray burst, which is associated with Type IV radio emission. To complement the X5.4 flare which was probably confined, a similar event observed in SOHO/EIT 195 A on 2004 July 20 in an eruptive, M8.6 flare is briefly described, in which the contraction was followed by the expansion of the same loop leading up to a halo coronal mass ejection. These observations further substantiate the conjecture of coronal implosion and suggest coronal implosion as a new exciter mechanism for coronal loop oscillations.« less

Physics of magnetic flux ropes

NASA Astrophysics Data System (ADS)

Russell, C. T.; Priest, E. R.; Lee, L. C.

The present work encompasses papers on the structure, waves, and instabilities of magnetic flux ropes (MFRs), photospheric flux tubes (PFTs), the structure and heating of coronal loops, solar prominences, coronal mass ejections and magnetic clouds, flux ropes in planetary ionospheres, the magnetopause, magnetospheric field-aligned currents and flux tubes, and the magnetotail. Attention is given to the equilibrium of MFRs, resistive instability, magnetic reconnection and turbulence in current sheets, dynamical effects and energy transport in intense flux tubes, waves in solar PFTs, twisted flux ropes in the solar corona, an electrodynamical model of solar flares, filament cooling and condensation in a sheared magnetic field, the magnetopause, the generation of twisted MFRs during magnetic reconnection, ionospheric flux ropes above the South Pole, substorms and MFR structures, evidence for flux ropes in the earth magnetotail, and MFRs in 3D MHD simulations.

Development of the Vertical Electro Magnetic Profiling (VEMP) method

NASA Astrophysics Data System (ADS)

Miura, Yasuo; Osato, Kazumi; Takasugi, Shinji; Muraoka, Hirofumi; Yasukawa, Kasumi

1996-09-01

As a part of the "Deep-Seated Geothermal Resources Survey (DSGR)" project being undertaken by the New Energy and Industrial Technology Development Organization (NEDO), the "Vertical Electro Magnetic Profiling (VEMP)" method is being developed to accurately obtain deep resistivity structures. The VEMP method takes multi-frequency three-component magnetic field data in an open hole well using controlled source transmitters emitted at the surface (either loop or grounded-wire sources). Numerical simulations using EM3D have demonstrated that phase data of the VEMP method is not only very sensitive to the general resistivity structure, but will also indicate the presence of deeper anomalies. Forward modelling was used to determine the required transmitter moments for various grounded-wire and loop sources for a field test using the WD-1 well in the Kakkonda geothermal area. VEMP logging of the WD-1 well was carried out in May 1994 and the processed field data matches the computer simulations quite well.

OSCILLATION OF NEWLY FORMED LOOPS AFTER MAGNETIC RECONNECTION IN THE SOLAR CHROMOSPHERE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Shuhong; Xiang, Yongyuan, E-mail: shuhongyang@nao.cas.cn

With the high spatial and temporal resolution Hα images from the New Vacuum Solar Telescope, we focus on two groups of loops with an X-shaped configuration in the dynamic chromosphere. We find that the anti-directed loops approach each other and reconnect continually. The connectivity of the loops is changed and new loops are formed and stack together. The stacked loops are sharply bent, implying that they are greatly impacted by the magnetic tension force. When another reconnection process takes place, one new loop is formed and stacks with the previously formed ones. Meanwhile, the stacked loops retract suddenly and movemore » toward the balance position, performing an overshoot movement, which led to an oscillation with an average period of about 45 s. The oscillation of newly formed loops after magnetic reconnection in the chromosphere is observed for the first time. We suggest that the stability of the stacked loops is destroyed due to the attachment of the last new loop and then suddenly retract under the effect of magnetic tension. Because of the retraction, another lower loop is pushed outward and performs an oscillation with a period of about 25 s. The different oscillation periods may be due to their difference in three parameters, i.e., loop length, plasma density, and magnetic field strength.« less

Micromagnetic simulation of static magnetic properties and tuning of anisotropy strength in two dimensional square antidot elements

NASA Astrophysics Data System (ADS)

Dash, S.; Satish, S.; Parida, B.; Satapathy, S.; Ipsita, N. S.; Joshi, R. S.

2018-04-01

We demonstrate the tailoring of anisotropy in magnetic nano-wire element using finite element method based micromagnetic simulation. We calculate the magentostatic properties for the structure by simulating hysteresis for these nano wire elements. The angular variation of remanence for the structures of different dimensions is used as the depiction to establish fourfold magnetic anisotropy. The change of anisotropy strength, which is the ratio of squareness of hysteresis loop in hard axis to easy axis, is demonstrated in this study which is one of the most important parameters to utilize these nanowire elements in multi state magnetic memory application.

Two-dimensional magnetohydrodynamic model of emerging magnetic flux in the solar atmosphere

NASA Technical Reports Server (NTRS)

Shibata, K.; Tajima, T.; Steinolfson, R. S.; Matsumoto, R.

1989-01-01

The nonlinear undular mode of the magnetic buoyancy instability in an isolated horizontal magnetic flux embedded in a two-temperature layered atmosphere (solar corona-chromosphere/photosphere) is investigated using a two-dimensional magnetohydrodynamic code. The results show that the flux sheet with beta of about 1 is initially located at the bottom of the photosphere, and that the gas slides down the expanding loop as the instability develops, with the evacuated loop rising as a result of enhanced magnetic buoyancy. The expansion of the magnetic loop in the nonlinear regime displays self-similar behavior. The rise velocity of the magnetic loop in the high chromosphere (10-15 km/s) and the velocity of downflow noted along the loop (30-50 km/s) are consistent with observed values for arch filament systems.

Empirical scaling laws for coronal heating

NASA Technical Reports Server (NTRS)

Golub, L.

1983-01-01

The origins and uses of scaling laws in studies of stellar outer atmospheres are reviewed with particular emphasis on the properties of coronal loops. Some evidence is presented for a fundamental structuring of the solar corona and the thermodynamics of scaling laws are discussed. It is found that magnetic field-related scaling laws can be obtained by relating coronal pressure, temperature, and magnetic field strength. Available data validate this method. Some parameters of the theory, however, must be treated as adjustable, and it is considered necessary to examine data from other stars in order to determine the validity of the parameters. Using detailed observational data, the applicability of single loop models is examined.

Radio imaging of solar flares using the very large array - New insights into flare process

NASA Technical Reports Server (NTRS)

Kundu, M. R.; Schmahl, E. J.; Vlahos, L.; Velusamy, T.

1982-01-01

An interpretation of VLA observations of microwave bursts is presented in an attempt to distinguish between certain models of flares. The VLA observations provide information about the pre-flare magnetic field topology and the existence of mildly relativistic electrons accelerated during flares. Examples are shown of changes in magnetic field topology in the hour before flares. In one case, new bipolar loops appear to emerge, which is an essential component of the model developed by Heyvaerts et al. (1977). In another case, a quadrupole structure, suggestive of two juxtaposed bipolar loops, appears to trigger the flare. Because of the observed diversity of magnetic field topologies in microwave bursts, it is believed that the magnetic energy must be dissipated in more than one way. The VLA observations are clearly providing means for sorting out the diverse flare models.

Plateau on temperature dependence of magnetization of nanostructured rare earth titanates

NASA Astrophysics Data System (ADS)

Rinkevich, A. B.; Korolev, A. V.; Samoylovich, M. I.; Demokritov, S. O.; Perov, D. V.

2018-05-01

Magnetic properties of nanocomposite materials containing particles of rare earth titanates of R2Ti2O7 type, where R is a rare earth ion, including "spin ice" materials are investigated. The descending branches of hysteresis loop have been studied in detail in temperature range from 2 to 50 K. It has been shown that nanocomposites with Yb2Ti2O7, Dy2Ti2O7 and Er2Ti2O7 particles have one intersection point of the descending branches in some temperature range unlike many other nanocomposites. It is shown that magnetization has only weak temperature dependence near this point. It has been obtained that nanocomposites with Pr2Ti2O7 and Nd2Ti2O7 particles have no hysteresis loop. All above findings point out to unusual magnetic structures of the studied samples.

Computer Generated Snapshot of Our Sun's Magnetic Field

NASA Technical Reports Server (NTRS)

2003-01-01

These banana-shaped loops are part of a computer-generated snapshot of our sun's magnetic field. The solar magnetic-field lines loop through the sun's corona, break through the sun's surface, and cornect regions of magnetic activity, such as sunspots. This image --part of a magnetic-field study of the sun by NASA's Allen Gary -- shows the outer portion (skins) of interconnecting systems of hot (2 million degrees Kelvin) coronal loops within and between two active magnetic regions on opposite sides of the sun's equator. The diameter of these coronal loops at their foot points is approximately the same size as the Earth's radius (about 6,000 kilometers).

Temperature and Electron Density Diagnostics of a Candle-Flame Shaped Flare. Asymmetric Reconnection Evidence

NASA Astrophysics Data System (ADS)

Guidoni, Silvina E.; McKenzie, David E.; Longcope, Dana W.; Plowman, Joseph E.; Yoshimura, Keiji

2013-03-01

Candle-flame shaped flares are archetypical structures that represent indirect evidence of magnetic reconnection. For long-lived events, most of their observed features can be explained with the classic magnetic reconnection model of solar flares, the CSHKP model. A flare resembling 1992 Tsuneta's famous candle-flame flare occurred on January 28 2011; we present its temperature and electron density diagnostics. This flare was observed with Hinode/XRT, SDO/AIA, and STEREO (A)/EUVI, resulting in high resolution, broad temperature coverage, and stereoscopic views of this iconic structure. Our XRT filter-ratio temperature and density maps corroborate the general reconnection scenario. The high temperature images reveal a brightening that grows in size to form a tower-like structure at the top of the post-flare arcade, a feature that has been observed in other long duration events. This tower is a localized density increase, as shown by our XRT electron density maps. Despite the extensive work on the standard reconnection scenario, there is no complete agreement among models regarding the nature of this tower-like structure. The XRT maps also reveal that reconnected loops that are successively connected at their tops to this tower develop a density increase in one of their legs that can reach over 2 times the density value of the other leg, giving the appearance of ``half-loops''. Their density is nevertheless still lower than at the tower. These jumps in density last longer than several acoustic transit times along the loops. We use STEREO images to show that the half-loop brightening is not a line-of- sight projection effect of the type suggested by Forbes and Acton (1996). This would indicate that asymmetric reconnection took place between loops originally belonging to systems with different magnetic field strengths, densities, and temperatures. We hypothesize that the heat generated by reconnection's slow shocks is then transferred to each leg of the loop at different rates. Therefore, the increase in electron density due to chromospheric evaporation is different in each leg. Thermal pressure balance between the legs is prevented by shocked plasma at the top of the loops. We also present preliminary results comparing a new fast DEM method that uses SDO/AIA data with the XRT filter ratio method. Both methods complement each other, they agree at the overlap between their instruments' temperature response functions (3-12 MK) while the SDO/AIA method works well at lower temperatures and the XRT one at higher temperatures.

Multiple Plasma Ejections and Intermittent Nature of Magnetic Reconnection in Solar Chromospheric Anemone Jets

NASA Astrophysics Data System (ADS)

Singh, K. A. P.; Isobe, H.; Nishizuka, N.; Nishida, K.; Shibata, K.

2012-11-01

The recent discovery of chromospheric anemone jets with the Solar Optical Telescope (SOT) on board Hinode has shown an indirect evidence of magnetic reconnection in the solar chromosphere. However, the basic nature of magnetic reconnection in chromosphere is still unclear. We studied nine chromospheric anemone jets from SOT/Hinode using Ca II H filtergrams, and we found multiple bright, plasma ejections along the jets. In most cases, the major intensity enhancements (larger than 30% relative to the background intensity) of the loop correspond to the timing of the plasma ejections. The typical lifetime and size of the plasma ejecta are about 20-60 s and 0.3-1.5 Mm, respectively. The height-time plot of jet shows many sub-structures (or individual jets) and the typical lifetime of the individual jet is about one to five minutes. Before the onset of the jet activity, a loop appears in Ca II H and gradually increases in size, and after few minutes several jets are launched from the loop. Once the jet activity starts and several individual jets are launched, the loop starts shrinking with a speed of ~4 km s-1. In some events, a downward moving blob with a speed of ~35 km s-1 was observed, associated with the upward moving plasma along one of the legs of the loop hosting the jets. The upward moving plasma gradually developed into jets. Multiple plasma ejections in chromospheric anemone jet show the strongly time-dependent as well as intermittent nature of magnetic reconnection in the solar chromosphere.

Evidence for magnetic energy storage in coronal active regions

NASA Technical Reports Server (NTRS)

Krieger, A. S.; De Feiter, L. D.; Vaiana, G. S.

1976-01-01

Examination of X-ray images obtained by the S-054 X-ray spectrographic telescope on Skylab shows the presence of some atypical X-ray-emitting coronal structures in active regions which are not consistent with potential extrapolations of photospheric magnetic fields. Analysis of the observed temporal changes in the X-ray-emitting active-region structures demonstrates that the majority of these consist of brightness changes representing temperature (and perhaps density) variations of the material in the loops.

Meta-stable magnetic transitions and its field dependence in Co2.75Fe0.25O4 ferrite

NASA Astrophysics Data System (ADS)

Aswathi M., C.; Bhowmik, R. N.

2018-04-01

The Co2.75Fe0.25O4 ferrite has been prepared by chemical co-precipitation route. The as-prepared sample has been annealed at 500° C. X-ray diffraction pattern indicated cubic spinel structure in the sample. The sample showed ferrimagnetic nature with magnetic irreversibility and hysteresis loop. Magnetization data revealed high anisotropic nature and at least two prominent meta-stable magnetic transitions below the highest measurement temperature 350 K.

3D Studies of the Solar Corona and its Evolution with SOHO/EIT

NASA Astrophysics Data System (ADS)

Portier-Fozzani, F.

This thesis deals with 3D evolution of coronal structures based upon the ultraviolet telescope of SOHO : EIT. Anaglyphs and incertainties on a complete stereovision reconstruction are described. Stereoscopic methods for loop reconstruction were successfully made to find 3D parameters. With dynamical stereoscopy, physical conditions were derived for 30 loops of temperature around 1MK. A method which is able to derive twist variation were also built. Emerging loops were found highly twisted and they detwist as they grow. According to helicity conservation, this correspond to a transfert of twist into expansion. Long time twist evolution of magnetic flux tubes are followed in relation with flares as relaxation. Interaction between magnetic field lines were analysed. An example of reconnection between open and closed field line were observed. Other interactions were found with multi-wavelength observations : coronal holes borders (and thus CH) are better defined when an active region nearby is growing. Other imaging techniques were used to better take profit as possible of SOHO/EIT. A multiscale vision model (MVM) was applied with success to show small coronal structures evolutions hidden by the noise level.

Three-dimensional prominence-hosting magnetic configurations: Creating a helical magnetic flux rope

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xia, C.; Keppens, R.; Guo, Y.

2014-01-10

The magnetic configuration hosting prominences and their surrounding coronal structure is a key research topic in solar physics. Recent theoretical and observational studies strongly suggest that a helical magnetic flux rope is an essential ingredient to fulfill most of the theoretical and observational requirements for hosting prominences. To understand flux rope formation details and obtain magnetic configurations suitable for future prominence formation studies, we here report on three-dimensional isothermal magnetohydrodynamic simulations including finite gas pressure and gravity. Starting from a magnetohydrostatic corona with a linear force-free bipolar magnetic field, we follow its evolution when introducing vortex flows around the mainmore » polarities and converging flows toward the polarity inversion line near the bottom of the corona. The converging flows bring the feet of different loops together at the polarity inversion line, where magnetic reconnection and flux cancellation happen. Inflow and outflow signatures of the magnetic reconnection process are identified, and thereby the newly formed helical loops wind around preexisting ones so that a complete flux rope grows and ascends. When a macroscopic flux rope is formed, we switch off the driving flows and find that the system relaxes to a stable state containing a helical magnetic flux rope embedded in an overlying arcade structure. A major part of the formed flux rope is threaded by dipped field lines that can stably support prominence matter, while the total mass of the flux rope is in the order of 4-5× 10{sup 14} g.« less

Enhanced magnetic hysteresis in Ni-Mn-Ga single crystal and its influence on magnetic shape memory effect

DOE Office of Scientific and Technical Information (OSTI.GOV)

Heczko, O., E-mail: heczko@fzu.cz; Drahokoupil, J.; Straka, L.

2015-05-07

Enhanced magnetic hysteresis due to boron doping in combination with magnetic shape memory effect in Ni-Mn-Ga single crystal results in new interesting functionality of magnetic shape memory (MSM) alloys such as mechanical demagnetization. In Ni{sub 50.0}Mn{sub 28.5}Ga{sub 21.5} single crystal, the boron doping increased magnetic coercivity from few Oe to 270 Oe while not affecting the transformation behavior and 10 M martensite structure. However, the magnetic field needed for MSM effect also increased in doped sample. The magnetic behavior is compared to undoped single crystal of similar composition. The evidence from the X-ray diffraction, magnetic domain structure, magnetization loops, and temperature evolutionmore » of the magnetic coercivity points out that the enhanced hysteresis is caused by stress-induced anisotropy.« less

Space Science

NASA Image and Video Library

2003-01-01

These banana-shaped loops are part of a computer-generated snapshot of our sun's magnetic field. The solar magnetic-field lines loop through the sun's corona, break through the sun's surface, and cornect regions of magnetic activity, such as sunspots. This image --part of a magnetic-field study of the sun by NASA's Allen Gary -- shows the outer portion (skins) of interconnecting systems of hot (2 million degrees Kelvin) coronal loops within and between two active magnetic regions on opposite sides of the sun's equator. The diameter of these coronal loops at their foot points is approximately the same size as the Earth's radius (about 6,000 kilometers).

Slipping magnetic reconnection during an X-class solar flare observed by SDO/AIA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dudík, J.; Del Zanna, G.; Mason, H. E.

2014-04-01

We present SDO/AIA observations of an eruptive X-class flare of 2012 July 12, and compare its evolution with the predictions of a three-dimensional (3D) numerical simulation. We focus on the dynamics of flare loops that are seen to undergo slipping reconnection during the flare. In the Atmospheric Imaging Assembly (AIA) 131 Å observations, lower parts of 10 MK flare loops exhibit an apparent motion with velocities of several tens of km s{sup –1} along the developing flare ribbons. In the early stages of the flare, flare ribbons consist of compact, localized bright transition-region emission from the footpoints of the flaremore » loops. A differential emission measure analysis shows that the flare loops have temperatures up to the formation of Fe XXIV. A series of very long, S-shaped loops erupt, leading to a coronal mass ejection observed by STEREO. The observed dynamics are compared with the evolution of magnetic structures in the 'standard solar flare model in 3D.' This model matches the observations well, reproducing the apparently slipping flare loops, S-shaped erupting loops, and the evolution of flare ribbons. All of these processes are explained via 3D reconnection mechanisms resulting from the expansion of a torus-unstable flux rope. The AIA observations and the numerical model are complemented by radio observations showing a noise storm in the metric range. Dm-drifting pulsation structures occurring during the eruption indicate plasmoid ejection and enhancement of the reconnection rate. The bursty nature of radio emission shows that the slipping reconnection is still intermittent, although it is observed to persist for more than an hour.« less

Explaining observed red and blue-shifts using multi-stranded coronal loops

NASA Astrophysics Data System (ADS)

Regnier, S.; Walsh, R. W.; Pearson, J.

2012-03-01

Magnetic plasma loops have been termed the building blocks of the solar atmosphere. However, it must be recognised that if the range of loop structures we can observe do consist of many ''sub-resolution'' elements, then current one-dimensional hydrodynamic models are really only applicable to an individual plasma element or strand. Thus a loop should be viewed is an amalgamation of these strands. They could operate in thermal isolation from one another with a wide range of temperatures occurring across the structural elements. This scenario could occur when the energy release mechanism consists of localised, discrete bursts of energy that are due to small scale reconnection sites within the coronal magnetic field- the nanoflare coronal heating mechanism. These energy bursts occur in a time-dependent manner, distributed along the loop/strand length, giving a heating function that depends on space and time. An important observational discovery with the Hinode/EIS spectrometer is the existence of red and blue-shifts in coronal loops depending on the location of the footpoints (inner or outer parts of the active region), and the temperature of the emission line in which the Doppler shifts are measured. Based on the multi-stranded model developed by Sarkar and Walsh (2008, ApJ, 683, 516), we show that red and blue-shifts exist in different simulated Hinode/EIS passbands: cooler lines (OV-SiVII) being dominated by red-shifts, whilst hotter lines (FeXV-CaXVII) are a combination of both. The distribution of blue-shifts depends on the energy input and not so much on the heating location. Characteristic Doppler shifts generated fit well with observed values. We also simulate the Hinode/EIS rasters to closely compare our simulation with the observations. Even if not statistically significant, loops can have footpoints with opposite Doppler shifts.

Compensation behaviors and magnetic properties in a cylindrical ferrimagnetic nanotube with core-shell structure: A Monte Carlo study

NASA Astrophysics Data System (ADS)

Wang, Wei; Liu, Ying; Gao, Zhong-yue; Zhao, Xue-ru; Yang, Yi; Yang, Sen

2018-07-01

Compensation temperature Tcomp and transition temperature TC have significant applications for the experimental realization of magnetic nanotube structure in the field of thermal magnetic recording. In this work, we use the Monte Carlo simulation to investigate the phase diagrams, magnetizations, susceptibilities, internal energies, specific heats and hysteresis behaviors of a cylindrical ferrimagnetic nanotube with core-shell structure. The effects of the single-ion anisotropies (DC, DS) and the exchange couplings (Jint, JS) on the magnetic and thermodynamic properties of the system are examined. A number of characteristic behaviors are discovered in the thermal variations, depending on different physical parameters. In particular, the triple hysteresis loops behavior has been found for appropriate physical parameters. These findings are qualitatively in good agreement with related experimental and the other theoretical results.

UNRAVELLING THE COMPONENTS OF A MULTI-THERMAL CORONAL LOOP USING MAGNETOHYDRODYNAMIC SEISMOLOGY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Prasad, S. Krishna; Jess, D. B.; Klimchuk, J. A.

Coronal loops, constituting the basic building blocks of the active Sun, serve as primary targets to help understand the mechanisms responsible for maintaining multi-million Kelvin temperatures in the solar and stellar coronae. Despite significant advances in observations and theory, our knowledge on the fundamental properties of these structures is limited. Here, we present unprecedented observations of accelerating slow magnetoacoustic waves along a coronal loop that show differential propagation speeds in two distinct temperature channels, revealing the multi-stranded and multithermal nature of the loop. Utilizing the observed speeds and employing nonlinear force-free magnetic field extrapolations, we derive the actual temperature variationmore » along the loop in both channels, and thus are able to resolve two individual components of the multithermal loop for the first time. The obtained positive temperature gradients indicate uniform heating along the loop, rather than isolated footpoint heating.« less

Small-scale Magnetic Flux Emergence in the Quiet Sun

NASA Astrophysics Data System (ADS)

Moreno-Insertis, F.; Martinez-Sykora, J.; Hansteen, V. H.; Muñoz, D.

2018-06-01

Small bipolar magnetic features are observed to appear in the interior of individual granules in the quiet Sun, signaling the emergence of tiny magnetic loops from the solar interior. We study the origin of those features as part of the magnetoconvection process in the top layers of the convection zone. Two quiet-Sun magnetoconvection models, calculated with the radiation-magnetohydrodynamic (MHD) Bifrost code and with domain stretching from the top layers of the convection zone to the corona, are analyzed. Using 3D visualization as well as a posteriori spectral synthesis of Stokes parameters, we detect the repeated emergence of small magnetic elements in the interior of granules, as in the observations. Additionally, we identify the formation of organized horizontal magnetic sheets covering whole granules. Our approach is twofold, calculating statistical properties of the system, like joint probability density functions (JPDFs), and pursuing individual events via visualization tools. We conclude that the small magnetic loops surfacing within individual granules in the observations may originate from sites at or near the downflows in the granular and mesogranular levels, probably in the first 1 or 1.5 Mm below the surface. We also document the creation of granule-covering magnetic sheet-like structures through the sideways expansion of a small subphotospheric magnetic concentration picked up and pulled out of the interior by a nascent granule. The sheet-like structures that we found in the models may match the recent observations of Centeno et al.

On the nature of fast sausage waves in coronal loops

NASA Astrophysics Data System (ADS)

Bahari, Karam

2018-05-01

The effect of the parameters of coronal loops on the nature of fast sausage waves are investigated. To do this three models of the coronal loop considered, a simple loop model, a current-carrying loop model and a model with radially structured density called "Inner μ" profile. For all the models the Magnetohydrodynamic (MHD) equations solved analytically in the linear approximation and the restoring forces of oscillations obtained. The ratio of the magnetic tension force to the pressure gradient force obtained as a function of the distance from the axis of the loop. In the simple loop model for all values of the loop parameters the fast sausages wave have a mixed nature of Alfvénic and fast MHD waves, in the current-carrying loop model with thick annulus and low density contrast the fast sausage waves can be considered as purely Alfvénic wave in the core region of the loop, and in the "Inner μ" profile for each set of the parameters of the loop the wave can be considered as a purely Alfvénic wave in some regions of the loop.

GIANT CORONAL LOOPS DOMINATE THE QUIESCENT X-RAY EMISSION IN RAPIDLY ROTATING M STARS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cohen, O.; Yadav, R.; Garraffo, C.

2017-01-01

Observations indicate that magnetic fields in rapidly rotating stars are very strong, on both small and large scales. What is the nature of the resulting corona? Here we seek to shed some light on this question. We use the results of an anelastic dynamo simulation of a rapidly rotating fully convective M star to drive a physics-based model for the stellar corona. We find that due to the several kilo Gauss large-scale magnetic fields at high latitudes, the corona, and its X-ray emission are dominated by star-size large hot loops, while the smaller, underlying colder loops are not visible muchmore » in the X-ray. Based on this result, we propose that, in rapidly rotating stars, emission from such coronal structures dominates the quiescent, cooler but saturated X-ray emission.« less

Multiwavelength observations of a flux rope formation by series of magnetic reconnection in the chromosphere

NASA Astrophysics Data System (ADS)

Kumar, Pankaj; Yurchyshyn, Vasyl; Cho, Kyung-Suk; Wang, Haimin

2017-07-01

Using high-resolution observations from the 1.6 m New Solar Telescope (NST) operating at the Big Bear Solar Observatory (BBSO), we report direct evidence of merging and reconnection of cool Hα loops in the chromosphere during two homologous flares (B and C class) caused by a shear motion at the footpoints of two loops. The reconnection between these loops caused the formation of an unstable flux rope that showed counterclockwise rotation. The flux rope could not reach the height of torus instability and failed to form a coronal mass ejection. The HMI magnetograms revealed rotation of the negative and positive (N1/P2) polarity sunspots in the opposite directions, which increased the right- and left-handed twist in the magnetic structures rooted at N1/P2. Rapid photospheric flux cancellation (duration 20-30 min, rate ≈3.44 × 1020 Mx h-1) was observed during and even after the first B6.0 flare and continued until the end of the second C2.3 flare. The RHESSI X-ray sources were located at the site of the loop coalescence. To the best of our knowledge, such a clear interaction of chromospheric loops along with rapid flux cancellation has not been reported before. These high-resolution observations suggest the formation of a small flux rope by a series of magnetic reconnections within chromospheric loops that are associated with very rapid flux cancellation. Movies attached to Figs. 2, 7, 8, and 10 are available at http://www.aanda.org

Coronal Heating: Testing Models of Coronal Heating by Forward-Modeling the AIA Emission of the Ansample of Coronal Loops

NASA Astrophysics Data System (ADS)

Malanushenko, A. V.

2015-12-01

We present a systemic exploration of the properties of coronal heating, by forward-modeling the emission of the ensemble of 1D quasi-steady loops. This approximations were used in many theoretical models of the coronal heating. The latter is described in many such models in the form of power laws, relating heat flux through the photosphere or volumetric heating to the strength of the magnetic field and length of a given field line. We perform a large search in the parameter space of these power laws, amongst other variables, and compare the resulting emission of the active region to that observed by AIA. We use a recently developed magnetic field model which uses shapes of coronal loops to guide the magnetic model; the result closely resembles observed structures by design. We take advantage of this, by comparing, in individual sub-regions of the active region, the emission of the active region and its synthetic model. This study allows us to rule out many theoretical models and formulate predictions for the heating models to come.

Loop-loop interactions govern multiple steps in indole-3-glycerol phosphate synthase catalysis

PubMed Central

Zaccardi, Margot J; O'Rourke, Kathleen F; Yezdimer, Eric M; Loggia, Laura J; Woldt, Svenja; Boehr, David D

2014-01-01

Substrate binding, product release, and likely chemical catalysis in the tryptophan biosynthetic enzyme indole-3-glycerol phosphate synthase (IGPS) are dependent on the structural dynamics of the β1α1 active-site loop. Statistical coupling analysis and molecular dynamic simulations had previously indicated that covarying residues in the β1α1 and β2α2 loops, corresponding to Arg54 and Asn90, respectively, in the Sulfolobus sulfataricus enzyme (ssIGPS), are likely important for coordinating functional motions of these loops. To test this hypothesis, we characterized site mutants at these positions for changes in catalytic function, protein stability and structural dynamics for the thermophilic ssIGPS enzyme. Although there were only modest changes in the overall steady-state kinetic parameters, solvent viscosity and solvent deuterium kinetic isotope effects indicated that these amino acid substitutions change the identity of the rate-determining step across multiple temperatures. Surprisingly, the N90A substitution had a dramatic effect on the general acid/base catalysis of the dehydration step, as indicated by the loss of the descending limb in the pH rate profile, which we had previously assigned to Lys53 on the β1α1 loop. These changes in enzyme function are accompanied with a quenching of ps-ns and µs-ms timescale motions in the β1α1 loop as measured by nuclear magnetic resonance studies. Altogether, our studies provide structural, dynamic and functional rationales for the coevolution of residues on the β1α1 and β2α2 loops, and highlight the multiple roles that the β1α1 loop plays in IGPS catalysis. Thus, substitution of covarying residues in the active-site β1α1 and β2α2 loops of indole-3-glycerol phosphate synthase results in functional, structural, and dynamic changes, highlighting the multiple roles that the β1α1 loop plays in enzyme catalysis and the importance of regulating the structural dynamics of this loop through noncovalent interactions with nearby structural elements. PMID:24403092

Solution structure of a GAAA tetraloop receptor RNA.

PubMed Central

Butcher, S E; Dieckmann, T; Feigon, J

1997-01-01

The GAAA tetraloop receptor is an 11-nucleotide RNA sequence that participates in the tertiary folding of a variety of large catalytic RNAs by providing a specific binding site for GAAA tetraloops. Here we report the solution structure of the isolated tetraloop receptor as solved by multidimensional, heteronuclear magnetic resonance spectroscopy. The internal loop of the tetraloop receptor has three adenosines stacked in a cross-strand or zipper-like fashion. This arrangement produces a high degree of base stacking within the asymmetric internal loop without extrahelical bases or kinking the helix. Additional interactions within the internal loop include a U. U mismatch pair and a G.U wobble pair. A comparison with the crystal structure of the receptor RNA bound to its tetraloop shows that a conformational change has to occur upon tetraloop binding, which is in good agreement with previous biochemical data. A model for an alternative binding site within the receptor is proposed based on the NMR structure, phylogenetic data and previous crystallographic structures of tetraloop interactions. PMID:9405377

The pressure and energy balance of the cool corona over sunspots

NASA Technical Reports Server (NTRS)

Foukal, P. V.

1976-01-01

The 22 largest sunspots observed with the Skylab SO55 spectrometer are studied for a relation between their EUV radiation and their umbral size or magnetic classification. The ultimate goal is to determine why the coronal plasma is so cool over a sunspot and how this cool plasma manages to support itself against gravity. Based on the time behavior of the EUV emission, a steady-state model is developed for the pressure and energy balance of the cool coronal-plasma loops over the spots. Analysis of the temperature structure in a typical loop indicates that the loop is exceedingly well insulated from the outside corona, that its energy balance is determined purely by internal heating and cooling processes, and that a heat input of about 0.0001 erg/cu cm per sec is required along the full length of the loop. It is proposed that: (1) coronal material flows steadily across the field lines at the tops of the loops and falls downward along both sides under gravity; (2) the corona is heated by mechanical-energy transport across the very thin transition region immediately over network-cell interiors; and (3) strong magnetic fields tend to inhibit mechanical-energy dissipation in the corona.

Crystal structure and magnetic properties of Cr doped barium hexaferrite

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Supriya, Sweety; Pandey, Rabichandra; Pradhan, Lagen Kumar; Kar, Manoranjan

2018-04-01

The Cr3+ substituted BaFe12O19 has been synthesized by modified sol-gel method to tailor the magnetic anisotropy and coercivity for technological applications. Some basic studies have revealed that this substitution leads to unusual interactions among the magnetic sublattices of the M-type hexaferrite. In order to investigate these interactions, BaFe12-xCrxO19 (x = 0.0, 0.5, 1.0, 2.0, and 4.0) M-type hexaferrites were characterized by employing XRD (X-ray Diffractometer). It is confirmed that, all the samples are in nanocrystalline and single phase, no impurity has been detected within the XRD limit. The magnetic hysteresis (m-H) loops revealed the ferromagnetic nature of nanoparticles (NPs). The coercive field were increasing with the increasing Cr3+ content, but after the percolation limit it decreases. The magnetocrystalline anisotropy is increasing with the Cr3+ concentration in samples and high values of magnetocrystalline anisotropy revealed that all samples are hard magnetic materials. Magnetic hysteresis loops were analyzed using the Law of Approach to Saturation method.

Invariant structures of magnetic flux tubes

NASA Astrophysics Data System (ADS)

Solovev, A. A.

1982-04-01

The basic properties of a screened magnetic flux tube possessing a finite radius of curvature are discussed in order to complement the findings of Parker (1974, 1976) and improve their accuracy. Conditions of equilibrium, twisting equilibrium, and twisting oscillations are discussed, showing that a twisted magnetic loop or arch is capable of executing elastic oscillations about an equilibrium state. This property can in particular be used in the theory of solar flares. Invariant structures of a force-free magnetic tube are analyzed, showing that invariant structures of the field preserve their form when the geometrical parameters of the flux tube are changed. In a quasi-equilibrium transition of the tube from one state to another the length and pitch of the tube spiral change in proportion to the radius of its cross section.

Espisodic detachment of Martian crustal magnetic fields leading to bulk atmospheric plasma escape

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brain, D A; Baker, A H; Briggs, J

2009-06-02

We present an analysis of magnetic field and suprathermal electron measurements from the Mars Global Surveyor (MGS) spacecraft that reveals isolated magnetic structures filled with Martian atmospheric plasma located downstream from strong crustal magnetic fields with respect to the flowing solar wind. The structures are characterized by magnetic field enhancements and rotations characteristic of magnetic flux ropes, and characteristic ionospheric electron energy distributions with angular distributions distinct from surrounding regions. These observations indicate that significant amounts of atmosphere are intermittently being carried away from Mars by a bulk removal process: the top portions of crustal field loops are stretched throughmore » interaction with the solar wind and detach via magnetic reconnection. This process occurs frequently and may account for as much as 10% of the total present-day ion escape from Mars.« less

Magnetic and magneto-optical properties and domain structure of Co/Pd multilayers

NASA Technical Reports Server (NTRS)

Gadetsky, S.; Wu, Teho; Suzuki, T.; Mansuripur, M.

1993-01-01

The domain structure of Co/Pd(1.6/6.3 A)xN multilayers and its relation to the bulk magnetic properties of the samples were studied. The Co/Pd multilayers were deposited by rf and dc magnetron sputtering onto different substrates. It was found that magnetic and magnetooptical properties and domain structure of the multilayers were affected by total film thickness and substrate condition. Magnetization, coercivity, and anisotropy of the films decreased significantly as the film thickness dropped below 100 A. However, Kerr rotation angle had a maximum at the same thickness. The width of the domain structure increased with the decrease of the film thickness attaining the single domain state at N = 10. The initial curves in Co/Pd multilayers were found to depend on demagnetization process. The samples demagnetized by inplane field showed the largest difference between initial curves and the corresponding parts of the loops. Different domain structures were observed in the samples demagnetized by perpendicular and in-plane magnetic fields.

2D Magnetic Texture Analysis of Co-Cu Films

NASA Astrophysics Data System (ADS)

Bayirli, Mehmet; Karaagac, Oznur; Kockar, Hakan; Alper, Mursel

2017-05-01

The magnetic textures for the produced magnetic materials are important concepts in accordance with technical applications. Therefore, the aim of this article is to determine 2D magnetic textures of electrodeposited Co-Cu films by the measurement of hysteresis loops at the incremented angles. For that, Co-Cu films were deposited with different Co2+ in the electrolyte. In addition, the easy-axis orientation in the films from the squareness values of the angles, Mp(β) obtained by the hysteresis loops have been numerically studied using the Fourier series analysis. The differences observed in the magnetic easy-axis distributions were attributed to changes of the incorporation of Co in the films with the change of Co2+ in the electrolyte. The coefficients of Fourier series (A0 and A2n ) were also computed for 2D films. It is seen that a systematic and small decrease in A0 and an obvious decrease in A2n (n=1) were observed with increasing incorporated Co in the films. Results imply that interactions cause slightly demagnetization effect accordance with higher incorporation of Co in the films. Furthermore, the crystal structure of the Co-Cu films analysed by X-ray diffraction revealed that the films have dominantly face-centred cubic structure. Film contents analysed by energy-dispersive X-ray spectroscopy and film morphologies observed by scanning electron microscope also support the magnetic texture analysis results found by numerical computation.

Fast flux locked loop

DOEpatents

Ganther, Jr., Kenneth R.; Snapp, Lowell D.

2002-09-10

A flux locked loop for providing an electrical feedback signal, the flux locked loop employing radio-frequency components and technology to extend the flux modulation frequency and tracking loop bandwidth. The flux locked loop of the present invention has particularly useful application in read-out electronics for DC SQUID magnetic measurement systems, in which case the electrical signal output by the flux locked loop represents an unknown magnetic flux applied to the DC SQUID.

Structural and Functional Studies on the Marburg Virus GP2 Fusion Loop.

PubMed

Liu, Nina; Tao, Yisong; Brenowitz, Michael D; Girvin, Mark E; Lai, Jonathan R

2015-10-01

Marburg virus (MARV) and the ebolaviruses belong to the family Filoviridae (the members of which are filoviruses) that cause severe hemorrhagic fever. Infection requires fusion of the host and viral membranes, a process that occurs in the host cell endosomal compartment and is facilitated by the envelope glycoprotein fusion subunit, GP2. The N-terminal fusion loop (FL) of GP2 is a hydrophobic disulfide-bonded loop that is postulated to insert and disrupt the host endosomal membrane during fusion. Here, we describe the first structural and functional studies of a protein corresponding to the MARV GP2 FL. We found that this protein undergoes a pH-dependent conformational change, as monitored by circular dichroism and nuclear magnetic resonance. Furthermore, we report that, under low pH conditions, the MARV GP2 FL can induce content leakage from liposomes. The general aspects of this pH-dependent structure and lipid-perturbing behavior are consistent with previous reports on Ebola virus GP2 FL. However, nuclear magnetic resonance studies in lipid bicelles and mutational analysis indicate differences in structure exist between MARV and Ebola virus GP2 FL. These results provide new insight into the mechanism of MARV GP2-mediated cell entry. © The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America. All rights reserved. For Permissions, please e-mail: journals.permissions@oup.com.

Signatures Of Coronal Heating Driven By Footpoint Shuffling: Closed and Open Structures.

NASA Astrophysics Data System (ADS)

Velli, M. C. M.; Rappazzo, A. F.; Dahlburg, R. B.; Einaudi, G.; Ugarte-Urra, I.

2017-12-01

We have previously described the characteristic state of the confined coronal magnetic field as a special case of magnetically dominated magnetohydrodynamic (MHD) turbulence, where the free energy in the transverse magnetic field is continuously cascaded to small scales, even though the overall kinetic energy is small. This coronal turbulence problem is defined by the photospheric boundary conditions: here we discuss recent numerical simulations of the fully compressible 3D MHD equations using the HYPERION code. Loops are forced at their footpoints by random photospheric motions, energizing the field to a state with continuous formation and dissipation of field-aligned current sheets: energy is deposited at small scales where heating occurs. Only a fraction of the coronal mass and volume gets heated at any time. Temperature and density are highly structured at scales that, in the solar corona, remain observationally unresolved: the plasma of simulated loops is multithermal, where highly dynamical hotter and cooler plasma strands are scattered throughout the loop at sub-observational scales. We will also compare Reduced MHD simulations with fully compressible simulations and photospheric forcings with different time-scales compared to the Alfv'en transit time. Finally, we will discuss the differences between the closed field and open field (solar wind) turbulence heating problem, leading to observational consequences that may be amenable to Parker Solar Probe and Solar Orbiter.

Acceleration and Storage of Energetic Electrons in Magnetic Loops in the Course of Electric Current Oscillations

NASA Astrophysics Data System (ADS)

Zaitsev, V. V.; Stepanov, A. V.

2017-10-01

A mechanism of electron acceleration and storage of energetic particles in solar and stellar coronal magnetic loops, based on oscillations of the electric current, is considered. The magnetic loop is presented as an electric circuit with the electric current generated by convective motions in the photosphere. Eigenoscillations of the electric current in a loop induce an electric field directed along the loop axis. It is shown that the sudden reductions that occur in the course of type IV continuum and pulsating type III observed in various frequency bands (25 - 180 MHz, 110 - 600 MHz, 0.7 - 3.0 GHz) in solar flares provide evidence for acceleration and storage of the energetic electrons in coronal magnetic loops. We estimate the energization rate and the energy of accelerated electrons and present examples of the storage of energetic electrons in loops in the course of flares on the Sun or on ultracool stars. We also discuss the efficiency of the suggested mechanism as compared with the electron acceleration during the five-minute photospheric oscillations and with the acceleration driven by the magnetic Rayleigh-Taylor instability.

Fine flow structures in the transition region small-scale loops

NASA Astrophysics Data System (ADS)

Yan, L.; Peter, H.; He, J.; Wei, Y.

2016-12-01

The observation and model have suggested that the transition region EUV emission from the quiet sun region is contributed by very small scale loops which have not been resolved. Recently, the observation from IRIS has revealed that this kind of small scale loops. Based on the high resolution spectral and imaging observation from IRIS, much more detail work needs to be done to reveal the fine flow features in this kind of loop to help us understand the loop heating. Here, we present a detail statistical study of the spatial and temporal evolution of Si IV line profiles of small scale loops and report the spectral features: there is a transition from blue (red) wing enhancement dominant to red (blue) wing enhancement dominant along the cross-section of the loop, which is independent of time. This feature appears as the loop appear and disappear as the loop un-visible. This is probably the signature of helical flow along the loop. The result suggests that the brightening of this kind of loop is probably due to the current dissipation heating in the twisted magnetic field flux tube.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lagier, B.; Rousset, B.; Hoa, C.

Superconducting magnets used in tokamaks undergo periodic heat load caused by cycling plasma operations inducing AC losses, neutrons fluxes and eddy currents in magnet structures. In the cryogenic system of JT60-SA tokamak, the Auxiliary Cold Box (ACB) distributes helium from the refrigerator to the cryogenic users and in particular to the superconducting magnets. ACB comprises a saturated helium bath with immersed heat exchangers, extracting heat from independent cooling loops. The supercritical helium flow in each cooling loop is driven by a cold circulator. In order to safely operate the refrigerator during plasma pulses, the interface between the ACB and themore » refrigerator shall be as stable as possible, with well-balanced bath inlet and outlet mass flows during cycling operation. The solution presented in this paper relies on a combination of regulations to smooth pulsed heat loads and to keep a constant refrigeration power during all the cycle. Two smoothing strategies are presented, both regulating the outlet mass flow of the bath: the first one using the bath as a thermal buffer and the second one storing energy in the loop by varying the cold circulator speed. The bath outlet mass flow is also controlled by an immersed resistive heater which enables a constant evaporation rate in the bath when power coming from the loops is decreasing. The refrigeration power is controlled so that the compensating power remains within an acceptable margin. Experimental validation is achieved using the HELIOS facility. This facility running at CEA Grenoble since 2010 is a scaled down model of the ACB bath and Central Solenoid magnet cooling loop of the JT60-SA tokamak. Test results show performances and robustness of the regulations.« less

Decoupling capabilities of split-loop resonator structure for 7 Tesla MRI surface array coils

NASA Astrophysics Data System (ADS)

Hurshkainen, A.; Kurdjumov, S.; Simovski, C.; Glybovski, S.; Melchakova, I.; van den Berg, C. A. T.; Raaijmakers, A.; Belov, P.

2017-09-01

In this work we studied electromagnetic properties of one-dimentional periodic structures composed of split-loop res-onators (SLRs) and investigated their capabilities in decoupling of two dipole antennas for full-body magnetic resonance imaging (MRI). Two different finite structures comprising a single-SLR and a double-SLR constitutive elements were studied. Numerical simulations of the structures were performed to evaluate their decoupling capabilities. As it was demonstrated two dipole antennas equipped with either a single or a double-SLR structure exhibit high isolation even for an electrically short distance between the dipoles. Double-SLR structure while dramatically improving isolation of the dipoles keeps the field created by each of the decoupled dipoles comparable with one of a single dipole inside the target area.

Cool Transition Region Loops Observed by the Interface Region Imaging Spectrograph

NASA Astrophysics Data System (ADS)

Huang, Zhenghua; Xia, Lidong; Li, Bo; Madjarska, Maria S.

2015-09-01

We report on the first Interface Region Imaging Spectrograph (IRIS) study of cool transition region loops, a class of loops that has received little attention in the literature. A cluster of such loops was observed on the solar disk in active region NOAA11934, in the Si iv 1402.8 Å spectral raster and 1400 Å slit-jaw images. We divide the loops into three groups and study their dynamics. The first group comprises relatively stable loops, with 382-626 km cross-sections. Observed Doppler velocities are suggestive of siphon flows, gradually changing from -10 km s-1 at one end to 20 km s-1 at the other end of the loops. Nonthermal velocities of 15 ˜ 25 km s-1 were determined. Magnetic cancellation with a rate of 1015 Mx s-1 is found at the blueshifted footpoints. These physical properties suggest that these loops are impulsively heated by magnetic reconnection, and the siphon flows play an important role in the energy redistribution. The second group corresponds to two footpoints rooted in mixed-magnetic-polarity regions, where magnetic cancellation with a rate of 1015 Mx s-1 and explosive-event line profiles with enhanced wings of up to 200 km s-1 were observed. In the third group, interaction between two cool loop systems is observed. Evidence for magnetic reconnection between the two loop systems is reflected in the explosive-event line profiles and magnetic cancellation with a rate of 3× {10}15 Mx s-1 observed in the corresponding area. The IRIS has provided opportunity for in-depth investigations of cool transition region loops. Further numerical experiments are crucial for understanding their physics and their roles in the coronal heating processes.

Unmixing Magnetic Hysteresis Loops

NASA Astrophysics Data System (ADS)

Heslop, D.; Roberts, A. P.

2012-04-01

Magnetic hysteresis loops provide important information in rock and environmental magnetic studies. Natural samples often contain an assemblage of magnetic particles composed of components with different origins. Each component potentially carries important environmental information. Hysteresis loops, however, provide information concerning the bulk magnetic assemblage, which makes it difficult to isolate the specific contributions from different sources. For complex mineral assemblages an unmixing strategy with which to separate hysteresis loops into their component parts is therefore essential. Previous methods to unmix hysteresis data have aimed at separating individual loops into their constituent parts using libraries of type-curves thought to correspond to specific mineral types. We demonstrate an alternative approach, which rather than decomposing a single loop into monomineralic contributions, examines a collection of loops to determine their constituent source materials. These source materials may themselves be mineral mixtures, but they provide a genetically meaningful decomposition of a magnetic assemblage in terms of the processes that controlled its formation. We show how an empirically derived hysteresis mixing space can be created, without resorting to type-curves, based on the co-variation within a collection of measured loops. Physically realistic end-members, which respect the expected behaviour and symmetries of hysteresis loops, can then be extracted from the mixing space. These end-members allow the measured loops to be described as a combination of invariant parts that are assumed to represent the different sources in the mixing model. Particular attention is paid to model selection and estimating the complexity of the mixing model, specifically, how many end-members should be included. We demonstrate application of this approach using lake sediments from Butte Valley, northern California. Our method successfully separates the hysteresis loops into sources with a variety of terrigenous and authigenic origins.

Transequatorial loops interconnecting McMath regions 12472 and 12474

NASA Technical Reports Server (NTRS)

Svestka, Z.; Krieger, A. S.; Chase, R. C.; Howard, R.

1977-01-01

The paper reviews the life history of one transequatorial loop in a system observed in soft X-rays for at least 1.5 days and which interconnected a newly born active region with an old region. The birth of the selected loop is discussed along with properties of the interconnected active regions, sharpening and brightening of the loop, decay of the loop system, and physical relations between the interconnected regions. It is concluded that: (1) the loop was most probably born via reconnection of magnetic-field lines extending from the two active regions toward the equator, which occurred later than 33 hr after the younger region was born; (2) the fully developed interconnection was composed of several loops, all of which appeared to be rooted in a spotless magnetic hill of preceding northern polarity but were spread over two separate spotty regions of southern polarity in the magnetically complex new region; (3) the loop electron temperature increased from 2.1 million to 3.1 million K in one to three hours when the loop system brightened; and (4) the loops became twisted during the brightening, possibly due to their rise in the corona while remaining rooted in moving magnetic features in the younger region.

High-resolution imaging spectroscopy of two micro-pores and an arch filament system in a small emerging-flux region

NASA Astrophysics Data System (ADS)

González Manrique, S. J.; Bello González, N.; Denker, C.

2017-04-01

Context. Emerging flux regions mark the first stage in the accumulation of magnetic flux eventually leading to pores, sunspots, and (complex) active regions. These flux regions are highly dynamic, show a variety of fine structure, and in many cases live only for a short time (less than a day) before dissolving quickly into the ubiquitous quiet-Sun magnetic field. Aims: The purpose of this investigation is to characterize the temporal evolution of a minute emerging flux region, the associated photospheric and chromospheric flow fields, and the properties of the accompanying arch filament system. We aim to explore flux emergence and decay processes and investigate if they scale with structure size and magnetic flux contents. Methods: This study is based on imaging spectroscopy with the Göttingen Fabry-Pérot Interferometer at the Vacuum Tower Telescope, Observatorio del Teide, Tenerife, Spain on 2008 August 7. Photospheric horizontal proper motions were measured with Local correlation tracking using broadband images restored with multi-object multi-frame blind deconvolution. Cloud model (CM) inversions of line scans in the strong chromospheric absorption Hαλ656.28 nm line yielded CM parameters (Doppler velocity, Doppler width, optical thickness, and source function), which describe the cool plasma contained in the arch filament system. Results: The high-resolution observations cover the decay and convergence of two micro-pores with diameters of less than one arcsecond and provide decay rates for intensity and area. The photospheric horizontal flow speed is suppressed near the two micro-pores indicating that the magnetic field is already sufficiently strong to affect the convective energy transport. The micro-pores are accompanied by a small arch filament system as seen in Hα, where small-scale loops connect two regions with Hα line-core brightenings containing an emerging flux region with opposite polarities. The Doppler width, optical thickness, and source function reach the largest values near the Hα line-core brightenings. The chromospheric velocity of the cloud material is predominantly directed downwards near the footpoints of the loops with velocities of up to 12 km s-1, whereas loop tops show upward motions of about 3 km s-1. Some of the loops exhibit signs of twisting motions along the loop axis. Conclusions: Micro-pores are the smallest magnetic field concentrations leaving a photometric signature in the photosphere. In the observed case, they are accompanied by a miniature arch filament system indicative of newly emerging flux in the form of Ω-loops. Flux emergence and decay take place on a time-scale of about two days, whereas the photometric decay of the micro-pores is much more rapid (a few hours), which is consistent with the incipient submergence of Ω-loops. Considering lifetime and evolution timescales, impact on the surrounding photospheric proper motions, and flow speed of the chromospheric plasma at the loop tops and footpoints, the results are representative for the smallest emerging flux regions still recognizable as such.

Monte Carlo study of the magnetic properties in a bilayer dendrimer structure with non-magnetic layers

NASA Astrophysics Data System (ADS)

Jabar, A.; Masrour, R.

2017-12-01

In this paper, we study the Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions and magnetic layer effects on the bilayer transitions of a spin-5/2 Blume-Capel model formed by two magnetic blocs separated by a non-magnetic spacer of finite thickness. The thermalization process of magnetization for systems sizes has been given. We have shown that the magnetic order in the two magnetic blocs depend on the thickness of the magnetic layer. In the total magnetization profiles, the susceptibility peaks correspond to the reduced critical temperature. This critical temperature is displaced towards higher temperatures when increasing the number of magnetic layers. In addition, we have discussed and interpreted the behaviors of the magnetic hysteresis loops.

Open Loop Structure Low Cost Integrated Differential Inductive Micro Magnetic Volumetric Bio-Sensors

NASA Astrophysics Data System (ADS)

Khodadadi, Mohammad; Chang, Long; Litvinov, Dimitri

This investigation proposes a study, model, simulate and experiment innovative very low cost Magnetic induction biosensor for point of care diagnostics. The biosensor consists of 2 ``semi-loops'' in a micro fluidic channel, one as a sensor and one as a reference, the design takes advantage of microfabrication processes to produce more precise structures to improve sensitivity. Besides the attractively low cost, this biosensor has many advantages. Since the detector is basically a shaped wire, it is inherently robust and reliable. Typical errors in fabricating the wires will not affect its performance and it is sensing volumetric, unlike GMR-based sensors used in biosensor systems that boast single particle detection. Due to small dimensions the sensors do not need to be calibrated. This sensor also has a large range of detection since its sensitivity is proportional to the excitation frequency. Being able to sense Magnetic nano particles in the volume is an advantage in term of trapping MNPs and sensitivity and functionality. Basically, this new brilliant design, fill the gap between the fabricated sensors and hand wounded sensors.

Magnetic Properties and Magnetic Phase Diagrams of Trigonal DyNi3Ga9

NASA Astrophysics Data System (ADS)

Ninomiya, Hiroki; Matsumoto, Yuji; Nakamura, Shota; Kono, Yohei; Kittaka, Shunichiro; Sakakibara, Toshiro; Inoue, Katsuya; Ohara, Shigeo

2017-12-01

We report the crystal structure, magnetic properties, and magnetic phase diagrams of single crystalline DyNi3Ga9 studied using X-ray diffraction, electrical resistivity, specific heat, and magnetization measurements. DyNi3Ga9 crystallizes in the chiral structure with space group R32. The dysprosium ions, which are responsible for the magnetism in this compound, form a two-dimensional honeycomb structure on a (0001) plane. We show that DyNi3Ga9 exhibits successive phase transitions at TN = 10 K and T'N = 9 K. The former suggests quadrupolar ordering, and the latter is attributed to the antiferromagnetic order. It is considered that DyNi3Ga9 forms the canted-antiferromagnetic structure below T'N owing to a small hysteresis loop of the low-field magnetization curve. We observe the strong easy-plane anisotropy, and the multiple-metamagnetic transitions with magnetization-plateaus under the field applied along the honeycomb plane. For Hallel [2\\bar{1}\\bar{1}0], the plateau-region arises every 1/6 for saturation magnetization. The magnetic phase diagrams of DyNi3Ga9 are determined for the fields along principal-crystal axes.

Study of structural and magnetic characterization of polycrystalline Y0.5Ho0.5CrO3

NASA Astrophysics Data System (ADS)

Mall, Ashish Kumar; Garg, Ashish; Gupta, Rajeev

2018-05-01

A polycrystalline ceramic sample of Y0.5Ho0.5CrO3 was studied using powder X-ray diffraction, Raman spectroscopic and dc magnetometry measurement to understand the structural and magnetic properties. The Rietveld refinement of X-ray data suggests sample crystallized in Pnma orthorhombic structure without formation of any secondary phases confirming their phase-pure nature. However, Raman study shows a prominent effect of Ho doping in low wavenumber Raman active phonon modes. Further, M-T measurement shows magnetic phase transition (TN) at 141 K and a negative value of Curie-Weiss temperature suggesting an antiferromagnetic system. Subsequent, the appearance of the clear opening in the M-H loop below TN is an evidence of the appearance of a weak ferromagnetic component in the low- temperature regime while the magnetization increases linearly in the high magnetic field regime suggest antiferromagnetic component.

XMCD and TEM studies of as-cast and rapidly quenched Fe50Nd50 alloys

NASA Astrophysics Data System (ADS)

Menushenkov, V. P.; Menushenkov, A. P.; Shchetinin, I. V.; Wilhelm, F.; Ivanov, A. A.; Rudnev, I. A.; Ivanov, V. G.; Rogalev, A.; Savchenko, A. G.; Zhukov, D. G.; Rafalskiy, A. V.; Ketov, S. V.

2017-12-01

We present the XMCD analysis of as-cast and melt spun Fe50Nd50 samples performed at L2,3 -Nd and K-Fe absorption edges at 5 and 50 K in comparison with macroscopic data of XRD, TEM and magnetic properties measurements. In addition, we have measured the magnetic field dependence of XMCD signal for both types of the samples in magnetic fields up/down to 17 T. The obtained results pointed to the strong difference between structure and magnetic properties of the as-cast and melt spun Fe50Nd50 alloys for both macroscopic and local measurements. The element selective XMCD loops for melt spun alloy show almost identical value of the coercive force Hci for L 2-Nd and K-Fe edges and practically do not depend on temperature. XMCD loop at K-Fe edge is a sum of contributions of the Fe-based phases. The main Fe-rich phase has high Hci ≈ 2,4 T as a highly anisotropic phase. The absence of the K-Fe XMCD loop saturation in the field up to 17 T points to presence of the second Nd-rich Nd-Fe phase which is ferromagnetic at temperature lower than 50 K. In accordance to the TEM results these both phases may coexist as the mixture of nanocrystals which was formed as a result of decomposition of the amorphous-like matrix phase. The XMCD loop at L2 -Nd edge with Hci ≈ 1,9 T is the sum of contributions from two Nd-based phases: hard Fe-rich phase (Hci ≈ 2,4 T) and Nd-Fe matrix phase of medium hardness with Hci ≈ 1,3 T. The macroscopic loop showed the higher Hci compared to XMCD loops. Such discrepancy may be caused by the fact that XMCD signal is collected from a 5-10 mcm thick surface layer, which contains many defects that reduce anisotropy and coercivity.

STRUCTURAL, SURFACE MORPHOLOGICAL AND MAGNETIC STUDIES OF Zn1-xFexS (x=0.00-0.10) DILUTED MAGNETIC SEMICONDUCTORS GROWN BY CO-PRECIPITATION METHOD

NASA Astrophysics Data System (ADS)

Hassan, M.; Ghazanfar, M.; Arooj, N.; Riaz, S.; Hussain, S. Sajjad; Naseem, S.

We have fabricated Zn1-xFexS (x=0.00, 0.02, 0.04, 0.06, 0.08 and 0.10) diluted magnetic semiconductors using co-precipitation method. X-ray diffraction patterns depict that Zn1-xFexS appears as a dominant phase with cubic zinc blende structure and nanoscale crystallite size. In addition, a secondary phase of rhombohedral ZnS also appears; however, no additional phase arises that primarily belongs to Fe dopant. Using Debye-Scherrer relation, the crystallite size is found to be in the range of 20-27nm, which is in good agreement with the crystallite size calculated using the Williamson-Hall (WH) plot method. The appearance of secondary phase provoked to study the residual strain using Stokes-Wilson equation, which is nearly consistent to that observed using WH plot method. The surface morphology, revealed using scanning electron microscopy, depicts non-uniform surface structure with a variety of grains and void dimensions. Hysteresis loops measured for Zn1-xFexS at room temperature (RT) illustrate a paramagnetic behavior at higher fields; however, small ferromagnetic behavior is evident due to the small openings of the measured hysteresis loops around the origin. The measured RT ferromagnetism reveals the potential spintronic device applications of the studied diluted magnetic semiconductors.

Electrical and magnetic properties of nano-sized magnesium ferrite

NASA Astrophysics Data System (ADS)

T, Smitha; X, Sheena; J, Binu P.; Mohammed, E. M.

2015-02-01

Nano-sized magnesium ferrite was synthesized using sol-gel techniques. Structural characterization was done using X-ray diffractometer and Fourier Transform Infrared Spectrometer. Vibration Sample Magnetometer was used to record the magnetic measurements. XRD analysis reveals the prepared sample is single phasic without any impurity. Particle size calculation shows the average crystallite size of the sample is 19nm. FTIR analysis confirmed spinel structure of the prepared samples. Magnetic measurement study shows that the sample is ferromagnetic with high degree of isotropy. Hysterisis loop was traced at temperatures 100K and 300K. DC electrical resistivity measurements show semiconducting nature of the sample.

Design study of steady-state 30-tesla liquid-neon-cooled magnet

NASA Technical Reports Server (NTRS)

Prok, G. M.; Brown, G. V.

1976-01-01

A design for a 30-tesla, liquid-neon-cooled magnet was reported which is capable of continuous operation. Cooled by nonboiling, forced-convection heat transfer to liquid neon flowing at 2.8 cu m/min in a closed, pressurized heat-transfer loop and structurally supported by a tapered structural ribbon, the tape-wound coils with a high-purity-aluminum conductor will produce over 30 teslas for 1 minute at 850 kilowatts. The magnet will have an inside diameter of 7.5 centimeters and an outside diameter of 54 centimeters. The minimum current density at design field will be 15.7 kA/sq cm.

Design and simulation of permanent magnet synchronous motor control system

NASA Astrophysics Data System (ADS)

Li, Li; Liu, Yongqiu

2018-06-01

In recent years, with the development of power electronics, microelectronics, new motor control theory and rare earth permanent magnet materials, permanent magnet synchronous motors have been rapidly applied. Permanent magnet synchronous motors have the advantages of small size, low loss and high efficiency. Today, energy conservation and environmental protection are increasingly valued. It is very necessary to study them. Permanent magnet synchronous motor control system has a wide range of application prospects in the fields of electric vehicles, ships and other transportation. Using the simulation function of MATLAB/SIMULINK, a modular design structure was used to simulate the whole system model of speed loop adjustment, current PI modulation, SVPWM (Space Vector Pulse Width Module) wave generation and double closed loop. The results show that this control method has good robustness, and this method can improve the design efficiency and shorten the system design time. In this article, the analysis of the control principle of modern permanent magnet synchronous motor and the various processes of MATLAB simulation application will be analyzed in detail. The basic theory, basic method and application technology of the permanent magnet synchronous motor control system are systematically introduced.

Comparison between electric dipole and magnetic loop antennas for emitting whistler modes

NASA Astrophysics Data System (ADS)

Stenzel, R.; Urrutia, J. M.

2016-12-01

In a large uniform and unbounded laboratory plasma low frequency whistler modes are excited from an electric dipole and a magnetic loop. The excited waves are measured with a magnetic probe which resolves the three field components in 3D space and time. This yields the group velocity and energy density, from which one obtains the emitted power. The same rf generator is used for both antennas and the radiated power is measured under identical plasma conditions. The magnetic loop radiates 8000 times more power than the electric dipole. The reason is that the loop antenna carries a large conduction current while the electric dipole current is a much smaller displacement current through the sheath. The current, hence magnetic field excites whistlers, not the dipole electric field. Incidentally, a dipole antenna does not launch plane waves but m = 1 helicon modes. The findings suggest that active wave injections into the magnetosphere should be done with magnetic antennas. Two parallel dipoles connected at the free end could serve as an elongated loop.

METHODOLOGICAL NOTES: Integrating magnetism into semiconductor electronics

NASA Astrophysics Data System (ADS)

Zakharchenya, Boris P.; Korenev, Vladimir L.

2005-06-01

The view of a ferromagnetic-semiconducting hybrid structure as a single tunable system is presented. Based on an analysis of existing experiments it is shown that, contrary to a 'common sense', a nonmagnetic semiconductor is capable of playing an important role in controlling ferromagnetism. Magnetic properties of a hybrid (the hysteresis loop and the spatial orientation of magnetization) can be tuned both optically and electrically by utilizing semiconductor—making the hybrid an electronic-write-in and electronic-read-out elementary storage unit.

Loop heating by D.C. electric current and electromagnetic wave emissions simulated by 3-D EM particle zone

NASA Technical Reports Server (NTRS)

Sakai, J. I.; Zhao, J.; Nishikawa, K.-I.

1994-01-01

We have shown that a current-carrying plasma loop can be heated by magnetic pinch driven by the pressure imbalance between inside and outside the loop, using a 3-dimensional electromagnetic (EM) particle code. Both electrons and ions in the loop can be heated in the direction perpendicular to the ambient magnetic field, therefore the perpendicular temperature can be increased about 10 times compared with the parallel temperature. This temperature anisotropy produced by the magnetic pinch heating can induce a plasma instability, by which high-frequency electromagnetic waves can be excited. The plasma current which is enhanced by the magnetic pinch can also excite a kinetic kink instability, which can heat ions perpendicular to the magnetic field. The heating mechanism of ions as well as the electromagnetic emission could be important for an understanding of the coronal loop heating and the electromagnetic wave emissions from active coronal regions.

Effects of Coulomb collisions on cyclotron maser and plasma wave growth in magnetic loops

NASA Technical Reports Server (NTRS)

Hamilton, Russell J.; Petrosian, Vahe

1990-01-01

The evolution of nonthermal electrons accelerated in magnetic loops is determined by solving the kinetic equation, including magnetic field convergence and Coulomb collisions in order to determine the effects of these interactions on the induced cyclotron maser and plasma wave growth. It is found that the growth rates are larger and the possibility of cyclotron maser action is stronger for smaller loop column density, for larger magnetic field convergence, for a more isotropic injected electron pitch angle distribution, and for more impulsive acceleration. For modest values of the column density in the coronal portion of a flaring loop, the growth rates of instabilities are significantly reduced, and the reduction is much larger for the cyclotron modes than for the plasma wave modes. The rapid decrease in the growth rates with increasing loop column density suggests that, in flare loops when such phenomena occur, the densities are lower than commonly accepted.

Thermal and magnetic hysteresis associated with martensitic and magnetic phase transformations in Ni52Mn25In16Co7 Heusler alloy

NASA Astrophysics Data System (ADS)

Madiligama, A. S. B.; Ari-Gur, P.; Ren, Y.; Koledov, V. V.; Dilmieva, E. T.; Kamantsev, A. P.; Mashirov, A. V.; Shavrov, V. G.; Gonzalez-Legarreta, L.; Grande, B. H.

2017-11-01

Ni-Mn-In-Co Heusler alloys demonstrate promising magnetocaloric performance for use as refrigerants in magnetic cooling systems with the goal of replacing the lower efficiency, eco-adverse fluid-compression technology. The largest change in entropy occurs when the applied magnetic field causes a merged structural and magnetic transformation and the associated entropy changes of the two transformations works constructively. In this study, magnetic and crystalline phase transformations were each treated separately and the effects of the application of magnetic field on thermal hystereses associated with both structural and magnetic transformations of the Ni52Mn25In16Co7 were studied. From the analysis of synchrotron diffraction data and thermomagnetic measurements, it was revealed that the alloy undergoes both structural (from cubic austenite to a mixture of 7M &5M modulated martensite) and magnetic (ferromagnetic to a low-magnetization phase) phase transformations. Thermal hysteresis is associated with both transformations, and the variation of the thermal hystereses of the magnetic and structural transformations with applied magnetic field is significantly different. Because of the differences between the hystereses loops of the two transformations, they merge only upon heating under a certain magnetic field.

Coronal loop seismology using damping of standing kink oscillations by mode coupling

NASA Astrophysics Data System (ADS)

Pascoe, D. J.; Goddard, C. R.; Nisticò, G.; Anfinogentov, S.; Nakariakov, V. M.

2016-05-01

Context. Kink oscillations of solar coronal loops are frequently observed to be strongly damped. The damping can be explained by mode coupling on the condition that loops have a finite inhomogeneous layer between the higher density core and lower density background. The damping rate depends on the loop density contrast ratio and inhomogeneous layer width. Aims: The theoretical description for mode coupling of kink waves has been extended to include the initial Gaussian damping regime in addition to the exponential asymptotic state. Observation of these damping regimes would provide information about the structuring of the coronal loop and so provide a seismological tool. Methods: We consider three examples of standing kink oscillations observed by the Atmospheric Imaging Assembly (AIA) of the Solar Dynamics Observatory (SDO) for which the general damping profile (Gaussian and exponential regimes) can be fitted. Determining the Gaussian and exponential damping times allows us to perform seismological inversions for the loop density contrast ratio and the inhomogeneous layer width normalised to the loop radius. The layer width and loop minor radius are found separately by comparing the observed loop intensity profile with forward modelling based on our seismological results. Results: The seismological method which allows the density contrast ratio and inhomogeneous layer width to be simultaneously determined from the kink mode damping profile has been applied to observational data for the first time. This allows the internal and external Alfvén speeds to be calculated, and estimates for the magnetic field strength can be dramatically improved using the given plasma density. Conclusions: The kink mode damping rate can be used as a powerful diagnostic tool to determine the coronal loop density profile. This information can be used for further calculations such as the magnetic field strength or phase mixing rate.

Variable variance Preisach model for multilayers with perpendicular magnetic anisotropy

NASA Astrophysics Data System (ADS)

Franco, A. F.; Gonzalez-Fuentes, C.; Morales, R.; Ross, C. A.; Dumas, R.; Åkerman, J.; Garcia, C.

2016-08-01

We present a variable variance Preisach model that fully accounts for the different magnetization processes of a multilayer structure with perpendicular magnetic anisotropy by adjusting the evolution of the interaction variance as the magnetization changes. We successfully compare in a quantitative manner the results obtained with this model to experimental hysteresis loops of several [CoFeB/Pd ] n multilayers. The effect of the number of repetitions and the thicknesses of the CoFeB and Pd layers on the magnetization reversal of the multilayer structure is studied, and it is found that many of the observed phenomena can be attributed to an increase of the magnetostatic interactions and subsequent decrease of the size of the magnetic domains. Increasing the CoFeB thickness leads to the disappearance of the perpendicular anisotropy, and such a minimum thickness of the Pd layer is necessary to achieve an out-of-plane magnetization.

Temporal relationship between high-energy proton acceleration and magnetic field changes during solar flares

NASA Astrophysics Data System (ADS)

Kurt, Victoria; Yushkov, Boris

Understanding of the association of the magnetic field evolution in the corona and the temporal evolution of electromagnetic emissions produced by the accelerated particles during a solar flare can provide information about the nature of the energy-release process and its location. Recent high-spatial-resolution observations in HXR, UV and radio emissions allow one to study in detail a structure of two-ribbon flare site. According to these observations, the flare process can be divided into two different intervals with different temporal evolution of morphological structure: loop contraction during impulsive phase and subsequent loop expansion. On the other hand, the appearance of high-energy protons (with energy >300 MeV - an energy threshold of the pion production) in the solar atmosphere can be revealed from an emerging pion-decay component of high-energy gamma-ray emission. The present work is based on comparison of measurements of high-energy gamma-rays performed with the SONG detector onboard the CORONAS-F mission and reported observations of magnetic field evolution, such as HXR foot points (FP) separation and flare shear temporal behavior, or motion of UV/radio loops. We reliably identified the pion-decay component of gamma-ray emission in the course of five events attended with suitable spatial observations, namely, 2001 August 25, 2002 August 24, 2003 October 28, 2003 October 29, and 2005 January 20, and determined its onset time. We found that in these events the pion-decay emission occurred when the distance between conjugated foot-points of flare loops ceased to decrease and began to increase, i.e. changed from shrinkage to expansion. This result leads to the conclusion that the most efficient proton acceleration up to >300 MeV coincided in time with the radical reconfiguration of the magnetic field in the flare site. Earlier we found that the pion-decay emission onset in the 2003 October 28 flare was close to the time of maximum change rate of the magnetic flux calculated by Miklenic et al. (2009).

Coronal magnetic structures observing campaign. I - Simultaneous microwave and soft X-ray observations of active regions at the solar limb

NASA Astrophysics Data System (ADS)

Nitta, N.; White, S. M.; Kundu, M. R.; Gopalswamy, N.; Holman, G. D.; Brosius, J. W.; Schmelz, J. T.; Saba, J. L. R.; Strong, K. T.

1991-06-01

Using simultaneous microwave and soft X-ray measurements made with the Very Large Array (VLA) at 6 and 20 cm and the X-ray Polychromator (XRP) aboard the Solar Maximum Mission (SMM), we have studied two active regions near the solar limb. These observations were taken as part of the Coronal Magnetic Structures Observing Campaign (CoMStOC), a collaboration designed to study the magnetic field in the solar corona. The images in soft X-rays and at 20 cm wavelength are similar: both show peaks above the active regions and extended bridge of emission 200,000 km long connecting the two regions. The brightness temperature of the 20 cm emission is lower than that predicted from the X-ray emitting material, however; it can be attributed to free-free emission in cooler (<106 K) plasma not visible to XRP, with an optical depth ˜1. The 6 cm emission is concentrated at lower altitudes and in a ˜160,000 km long bundle of loops in the northern active region. Comparison of the 6 cm map with the potential magnetic field lines computed from photospheric magnetic fields (measured 2 days earlier) indicates that the 6 cm emission is associated with fields of less than ˜200 G. Such fields would be too weak to attribute the observed 6 cm emission to gyroresonance radiation. Analysis of the 6 cm loop bundle indicates that it is strongly asymmetric, with the magnetic field in the northern leg ˜2 times stronger than in the southern leg; the 6 cm emission most likely arises from a combination of hot ( ≥ 2 × 106 K) and cool plasmas, while the 20 cm emission becomes optically thick in the cooler (˜9 × 103 K) plasma. We estimate an Alfvén speed ˜7000 km s-1 and ratio of electron gyrofrequency to plasma frequency ˜1.0 in the northern leg of the 6 cm loop.

Magnetic suspension system for an Annular Momentum Control Device (AMCD)

NASA Technical Reports Server (NTRS)

1979-01-01

A technique to control a rim suspended in a magnetic field was developed. A complete system was developed, incorporating a support structure, magnetic actuators, a rim drive mechanism, an emergency fail-safe system, servo control system, and control electronics. Open loop and closed loop response of the system at zero speed and at 500 revolutions per minute (r/min) of the rim was obtained and analyzed. The rim was then dynamically balanced and a rim speed of 725 r/min was achieved. An analog simulation of the hardware was developed and tested with the actual control electronics connected to the analog computer. The system under development is stable at rim speeds below 700 r/min. Test results indicate that the rim under test is not rigid. The rim has a warp and a number of binding modes which prevented achievement of higher speeds. Further development efforts are required to achieve higher rim speeds.

Toward a Quantitative Comparison of Magnetic Field Extrapolations and Observed Coronal Loops

NASA Astrophysics Data System (ADS)

Warren, Harry P.; Crump, Nicholas A.; Ugarte-Urra, Ignacio; Sun, Xudong; Aschwanden, Markus J.; Wiegelmann, Thomas

2018-06-01

It is widely believed that loops observed in the solar atmosphere trace out magnetic field lines. However, the degree to which magnetic field extrapolations yield field lines that actually do follow loops has yet to be studied systematically. In this paper, we apply three different extrapolation techniques—a simple potential model, a nonlinear force-free (NLFF) model based on photospheric vector data, and an NLFF model based on forward fitting magnetic sources with vertical currents—to 15 active regions that span a wide range of magnetic conditions. We use a distance metric to assess how well each of these models is able to match field lines to the 12202 loops traced in coronal images. These distances are typically 1″–2″. We also compute the misalignment angle between each traced loop and the local magnetic field vector, and find values of 5°–12°. We find that the NLFF models generally outperform the potential extrapolation on these metrics, although the differences between the different extrapolations are relatively small. The methodology that we employ for this study suggests a number of ways that both the extrapolations and loop identification can be improved.

FORWARD MODELING OF STANDING KINK MODES IN CORONAL LOOPS. I. SYNTHETIC VIEWS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Ding; Doorsselaere, Tom Van, E-mail: DYuan2@uclan.ac.uk

2016-04-15

Kink magnetohydrodynamic (MHD) waves are frequently observed in various magnetic structures of the solar atmosphere. They may contribute significantly to coronal heating and could be used as a tool to diagnose the solar plasma. In this study, we synthesize the Fe ix λ171.073 Å emission of a coronal loop supporting a standing kink MHD mode. The kink MHD wave solution of a plasma cylinder is mapped into a semi-torus structure to simulate a curved coronal loop. We decompose the solution into a quasi-rigid kink motion and a quadrupole term, which dominate the plasma inside and outside of the flux tube, respectively.more » At the loop edges, the line of sight integrates relatively more ambient plasma, and the background emission becomes significant. The plasma motion associated with the quadrupole term causes spectral line broadening and emission suppression. The periodic intensity suppression will modulate the integrated intensity and the effective loop width, which both exhibit oscillatory variations at half of the kink period. The quadrupole term can be directly observed as a pendular motion at the front view.« less

Fusion basis for lattice gauge theory and loop quantum gravity

NASA Astrophysics Data System (ADS)

Delcamp, Clement; Dittrich, Bianca; Riello, Aldo

2017-02-01

We introduce a new basis for the gauge-invariant Hilbert space of lattice gauge theory and loop quantum gravity in (2 + 1) dimensions, the fusion basis. In doing so, we shift the focus from the original lattice (or spin-network) structure directly to that of the magnetic (curvature) and electric (torsion) excitations themselves. These excitations are classified by the irreducible representations of the Drinfel'd double of the gauge group, and can be readily "fused" together by studying the tensor product of such representations. We will also describe in detail the ribbon operators that create and measure these excitations and make the quasi-local structure of the observable algebra explicit. Since the fusion basis allows for both magnetic and electric excitations from the onset, it turns out to be a precious tool for studying the large scale structure and coarse-graining flow of lattice gauge theories and loop quantum gravity. This is in neat contrast with the widely used spin-network basis, in which it is much more complicated to account for electric excitations, i.e. for Gauß constraint violations, emerging at larger scales. Moreover, since the fusion basis comes equipped with a hierarchical structure, it readily provides the language to design states with sophisticated multi-scale structures. Another way to employ this hierarchical structure is to encode a notion of subsystems for lattice gauge theories and (2 + 1) gravity coupled to point particles. In a follow-up work, we have exploited this notion to provide a new definition of entanglement entropy for these theories.

Magnetic Properties and Phase Composition of Metamaterials Based on an Opal Matrix with 3 d-Transition Metal Particles

NASA Astrophysics Data System (ADS)

Rinkevich, A. B.; Korolev, A. V.; Samoilovich, M. I.; Perov, D. V.; Nemytova, O. V.

2018-02-01

The magnetic properties of metamaterials based on an opal matrix with transition-metal (iron, nickel, cobalt) particles have been studied. Magnetization curves and magnetic hysteresis loops have been measured and the dependences of real and imaginary parts of magnetization have been determined using the dynamic ac susceptibility measuring procedure. Structural studies of metamaterials have been performed. The saturation magnetization and coercive force of the studied metamaterials have been found to depend weakly on the temperature. The temperature dependence of magnetic susceptibility at a temperature above 30 K can be described adequately by Curie-Weiss law and, at lower temperature, deviates from the law.

STRUCTURE OF PROMINENCE LEGS: PLASMA AND MAGNETIC FIELD

DOE Office of Scientific and Technical Information (OSTI.GOV)

Levens, P. J.; Labrosse, N.; Schmieder, B.

We investigate the properties of a “solar tornado” observed on 2014 July 15, and aim to link the behavior of the plasma to the internal magnetic field structure of the associated prominence. We made multi-wavelength observations with high spatial resolution and high cadence using SDO/AIA, the Interface Region Imaging Spectrograph (IRIS) spectrograph, and the Hinode/Solar Optical Telescope (SOT) instrument. Along with spectropolarimetry provided by the Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires telescope we have coverage of both optically thick emission lines and magnetic field information. AIA reveals that the two legs of the prominence are stronglymore » absorbing structures which look like they are rotating, or oscillating in the plane of the sky. The two prominence legs, which are both very bright in Ca ii (SOT), are not visible in the IRIS Mg ii slit-jaw images. This is explained by the large optical thickness of the structures in Mg ii, which leads to reversed profiles, and hence to lower integrated intensities at these locations than in the surroundings. Using lines formed at temperatures lower than 1 MK, we measure relatively low Doppler shifts on the order of ±10 km s{sup −1} in the tornado-like structure. Between the two legs we see loops in Mg ii, with material flowing from one leg to the other, as well as counterstreaming. It is difficult to interpret our data as showing two rotating, vertical structures that are unrelated to the loops. This kind of “tornado” scenario does not fit with our observations. The magnetic field in the two legs of the prominence is found to be preferentially horizontal.« less

Structure of Prominence Legs: Plasma and Magnetic Field

NASA Astrophysics Data System (ADS)

Levens, P. J.; Schmieder, B.; Labrosse, N.; López Ariste, A.

2016-02-01

We investigate the properties of a “solar tornado” observed on 2014 July 15, and aim to link the behavior of the plasma to the internal magnetic field structure of the associated prominence. We made multi-wavelength observations with high spatial resolution and high cadence using SDO/AIA, the Interface Region Imaging Spectrograph (IRIS) spectrograph, and the Hinode/Solar Optical Telescope (SOT) instrument. Along with spectropolarimetry provided by the Télescope Héliographique pour l’Etude du Magnétisme et des Instabilités Solaires telescope we have coverage of both optically thick emission lines and magnetic field information. AIA reveals that the two legs of the prominence are strongly absorbing structures which look like they are rotating, or oscillating in the plane of the sky. The two prominence legs, which are both very bright in Ca II (SOT), are not visible in the IRIS Mg II slit-jaw images. This is explained by the large optical thickness of the structures in Mg II, which leads to reversed profiles, and hence to lower integrated intensities at these locations than in the surroundings. Using lines formed at temperatures lower than 1 MK, we measure relatively low Doppler shifts on the order of ±10 km s-1 in the tornado-like structure. Between the two legs we see loops in Mg II, with material flowing from one leg to the other, as well as counterstreaming. It is difficult to interpret our data as showing two rotating, vertical structures that are unrelated to the loops. This kind of “tornado” scenario does not fit with our observations. The magnetic field in the two legs of the prominence is found to be preferentially horizontal.

The Electromotive Force in Different Reference Frames

NASA Astrophysics Data System (ADS)

Adler, Charles L.

2018-05-01

The electromotive force (EMF) is the work per unit charge around a wire loop caused by a time-varying magnetic flux threading the loop. It is due to a force moving the charges around the loop. This is true whether the change in flux is due to the wire loop being stationary and the field changing in time, or the loop moving through a spatially varying field. In the first case, we say that the time-varying magnetic field induces an electric field that provides the force; in the second, we say that the force is due to the magnetic field acting on the charges in the moving loop. The theory of relativity states that both viewpoints must be equivalent, but it is sometimes difficult to harmonize them.

Quasi-periodic Counter-propagating Fast Magnetosonic Wave Trains from Neighboring Flares: SDO/AIA Observations and 3D MHD Modeling

NASA Astrophysics Data System (ADS)

Ofman, Leon; Liu, Wei

2018-06-01

Since their discovery by the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) in the extreme ultraviolet, rapid (phase speeds of ∼1000 km s‑1), quasi-periodic, fast-mode propagating (QFP) wave trains have been observed accompanying many solar flares. They typically propagate in funnel-like structures associated with the expanding magnetic field topology of the active regions (ARs). The waves provide information on the associated flare pulsations and the magnetic structure through coronal seismology (CS). The reported waves usually originate from a single localized source associated with the flare. Here we report the first detection of counter-propagating QFPs associated with two neighboring flares on 2013 May 22, apparently connected by large-scale, trans-equatorial coronal loops. We present the first results of a 3D MHD model of counter-propagating QFPs in an idealized bipolar AR. We investigate the excitation, propagation, nonlinearity, and interaction of the counter-propagating waves for a range of key model parameters, such as the properties of the sources and the background magnetic structure. In addition to QFPs, we also find evidence of trapped fast- (kink) and slow-mode waves associated with the event. We apply CS to determine the magnetic field strength in an oscillating loop during the event. Our model results are in qualitative agreement with the AIA-observed counter-propagating waves and used to identify the various MHD wave modes associated with the observed event, providing insights into their linear and nonlinear interactions. Our observations provide the first direct evidence of counter-propagating fast magnetosonic waves that can potentially lead to turbulent cascade and carry significant energy flux for coronal heating in low-corona magnetic structures.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Baker, D.; Van Driel-Gesztelyi, L.; Green, L. M.

Using spectra obtained by the EUV Imaging Spectrometer (EIS) instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359'' × 485''. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the age of the AR, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated atmore » AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line, where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope configuration.« less

Ni-rich precipitates in a lead bismuth eutectic loop

NASA Astrophysics Data System (ADS)

Kikuchi, K.; Saito, S.; Hamaguchi, D.; Tezuka, M.

2010-03-01

Solidified LBE was sampled from the specimens, electro-magnetic pump, filter, drain valve and oxygen sensor at the JAEA Lead Bismuth Loop-1 (JLBL-1) where the structural material was made of SS316. The concentration of Ni, Fe and Cr in LBE were analyzed by the Inductive Coupled Plasma atomic emission spectrometer. It was concluded that the solution of Ni into LBE was not saturated although the concentration of Fe and Cr almost achieved to the values in the literature. A needle-type structure appeared on the surface of solidified LBE inside the tube specimens. It was found to be Ni-rich precipitates by X-ray analyses (Field Emission Scanning Electron Microscope, FE-SEM). LBE samples collected from a circulating loop after discharging did not show the amount of impurities equivalent to the LBE bulk property.

Magnetic heat pumping

NASA Technical Reports Server (NTRS)

Brown, G. V. (Inventor)

1978-01-01

A ferromagnetic or ferrimagnetic element is used to control the temperature and applied magnetic field of the element to cause the state of the element as represented on a temperature-magnetic entropy diagram to repeatedly traverse a loop. The loop may have a first portion of concurrent substantially isothermal or constant temperature and increasing applied magnetic field, a second portion of lowering temperature and constant applied magnetic field, a third portion of isothermal and decreasing applied magnetic field, and a fourth portion of increasing temperature and constant applied magnetic field. Other loops may be four-sided, with two isotherms and two adiabats. Preferably, a regenerator is used to enhance desired cooling or heating effects, with varied magnetic fields, or varying temperatures including three-sided figures traversed by the representative point.

Simultaneous effect of crystal lattice and non magnetic substitution on magnetic properties of barium hexaferrite

NASA Astrophysics Data System (ADS)

Kumar, Sunil; Supriya, Sweety; Pradhan, Lagen Kumar; Pandey, Rabichandra; Kar, Manoranjan

2018-05-01

The aluminium doped barium hexaferrite BaFe12-xAlxO19 with x =0.0, 1.0, 2.0, 4.0 and 6.0 have been synthesized by the sol-gel method to modify the magnetic properties for technological applications. The crystal structure and phase purity of all the samples have been explored by employing the X-ray diffraction (XRD) technique. It confirms that the sample is nanocrystalline, hexagonal symmetry and all the intense peaks could be indexed to the P63/mmc space group. The obtained lattice parameters from the XRD analysis decrease with the increase in Al3+ content in the samples. The microstructural morphology and particle sizes of all samples were studied by using the Field Emission Scanning Electron Microscopy (FESEM-Hitachi-S4800) technique. The magnetic hysteresis (M-H) loops measurement has been carried out at room temperature by employing the vibrating sample magnetometer (VSM) over a field range of +20 kOe to -20 kOe. The magnetic hysteresis (M-H) loops revealed the ferromagnetic (hard magnetic materials) nature of the samples and, analyzed by using the Law of Approach to Saturation.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, K. A. P.; Nishida, K.; Shibata, K.

The recent discovery of chromospheric anemone jets with the Solar Optical Telescope (SOT) on board Hinode has shown an indirect evidence of magnetic reconnection in the solar chromosphere. However, the basic nature of magnetic reconnection in chromosphere is still unclear. We studied nine chromospheric anemone jets from SOT/Hinode using Ca II H filtergrams, and we found multiple bright, plasma ejections along the jets. In most cases, the major intensity enhancements (larger than 30% relative to the background intensity) of the loop correspond to the timing of the plasma ejections. The typical lifetime and size of the plasma ejecta are aboutmore » 20-60 s and 0.3-1.5 Mm, respectively. The height-time plot of jet shows many sub-structures (or individual jets) and the typical lifetime of the individual jet is about one to five minutes. Before the onset of the jet activity, a loop appears in Ca II H and gradually increases in size, and after few minutes several jets are launched from the loop. Once the jet activity starts and several individual jets are launched, the loop starts shrinking with a speed of {approx}4 km s{sup -1}. In some events, a downward moving blob with a speed of {approx}35 km s{sup -1} was observed, associated with the upward moving plasma along one of the legs of the loop hosting the jets. The upward moving plasma gradually developed into jets. Multiple plasma ejections in chromospheric anemone jet show the strongly time-dependent as well as intermittent nature of magnetic reconnection in the solar chromosphere.« less

Comparison of Two Coronal Magnetic Field Models to Reconstruct a Sigmoidal Solar Active Region with Coronal Loops

NASA Astrophysics Data System (ADS)

Duan, Aiying; Jiang, Chaowei; Hu, Qiang; Zhang, Huai; Gary, G. Allen; Wu, S. T.; Cao, Jinbin

2017-06-01

Magnetic field extrapolation is an important tool to study the three-dimensional (3D) solar coronal magnetic field, which is difficult to directly measure. Various analytic models and numerical codes exist, but their results often drastically differ. Thus, a critical comparison of the modeled magnetic field lines with the observed coronal loops is strongly required to establish the credibility of the model. Here we compare two different non-potential extrapolation codes, a nonlinear force-free field code (CESE-MHD-NLFFF) and a non-force-free field (NFFF) code, in modeling a solar active region (AR) that has a sigmoidal configuration just before a major flare erupted from the region. A 2D coronal-loop tracing and fitting method is employed to study the 3D misalignment angles between the extrapolated magnetic field lines and the EUV loops as imaged by SDO/AIA. It is found that the CESE-MHD-NLFFF code with preprocessed magnetogram performs the best, outputting a field that matches the coronal loops in the AR core imaged in AIA 94 Å with a misalignment angle of ˜10°. This suggests that the CESE-MHD-NLFFF code, even without using the information of the coronal loops in constraining the magnetic field, performs as good as some coronal-loop forward-fitting models. For the loops as imaged by AIA 171 Å in the outskirts of the AR, all the codes including the potential field give comparable results of the mean misalignment angle (˜30°). Thus, further improvement of the codes is needed for a better reconstruction of the long loops enveloping the core region.

Comparison of Two Coronal Magnetic Field Models to Reconstruct a Sigmoidal Solar Active Region with Coronal Loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Duan, Aiying; Zhang, Huai; Jiang, Chaowei

Magnetic field extrapolation is an important tool to study the three-dimensional (3D) solar coronal magnetic field, which is difficult to directly measure. Various analytic models and numerical codes exist, but their results often drastically differ. Thus, a critical comparison of the modeled magnetic field lines with the observed coronal loops is strongly required to establish the credibility of the model. Here we compare two different non-potential extrapolation codes, a nonlinear force-free field code (CESE–MHD–NLFFF) and a non-force-free field (NFFF) code, in modeling a solar active region (AR) that has a sigmoidal configuration just before a major flare erupted from themore » region. A 2D coronal-loop tracing and fitting method is employed to study the 3D misalignment angles between the extrapolated magnetic field lines and the EUV loops as imaged by SDO /AIA. It is found that the CESE–MHD–NLFFF code with preprocessed magnetogram performs the best, outputting a field that matches the coronal loops in the AR core imaged in AIA 94 Å with a misalignment angle of ∼10°. This suggests that the CESE–MHD–NLFFF code, even without using the information of the coronal loops in constraining the magnetic field, performs as good as some coronal-loop forward-fitting models. For the loops as imaged by AIA 171 Å in the outskirts of the AR, all the codes including the potential field give comparable results of the mean misalignment angle (∼30°). Thus, further improvement of the codes is needed for a better reconstruction of the long loops enveloping the core region.« less

Magnetic properties of ultrathin tetragonal Heusler D022-Mn3Ge perpendicular-magnetized films

NASA Astrophysics Data System (ADS)

Sugihara, A.; Suzuki, K. Z.; Miyazaki, T.; Mizukami, S.

2015-05-01

We investigated the crystal structure and magnetic properties of Manganese-germanium (Mn3Ge) films having the tetragonal D022 structure, with varied thicknesses (5-130 nm) prepared on chromium (Cr)-buffered single crystal MgO(001) substrates. A crystal lattice elongation in the in-plane direction, induced by the lattice mismatch between the D022-Mn3Ge and the Cr buffer layer, increased with decreasing thickness of the D022-Mn3Ge layer. The films exhibited clear magnetic hysteresis loops with a squareness ratio close to unity, and a step-like magnetization reversal even at a 5-nm thickness under an external field perpendicular to the film's plane. The uniaxial magnetic anisotropy constant of the films showed a reduction to less than 10 Merg/cm3 in the small thickness range (≤20 nm), likely due to the crystal lattice elongation in the in-plane direction.

Dynamic formation and magnetic support of loop or arcade prominences

NASA Technical Reports Server (NTRS)

Vanhoven, Gerard; Mok, Y.; Drake, J. F.

1992-01-01

The results of model dynamic simulations of the formation and support of a narrow prominence at the apex of a coronal magnetic loop or arcade are described. The condensation process proceeds via an initial radiative cooling and pressure drop, and a secondary siphon flow from the dense chromospheric ends. The antibuoyancy effect as the prominence forms causes a bending of a confining magnetic field, which propagates toward the semirigid ends of the magnetic loop. Thus, a wide magnetic 'hammock' or well (of a normal polarity Kippenhahn-Schlueter type) is formed, which supports the prominence at or near the field apex.

Structural, electrical, magnetic and magnetoelectric properties of composites

NASA Astrophysics Data System (ADS)

Rani, Renu; Juneja, J. K.; Singh, Sangeeta; Prakash, Chandra; Raina, K. K.

2013-11-01

The magnetoelectric (ME) composites with composition (y)Ni0.8Zn0.2Fe2O4+(1-y) Ba0.90Sr0.10Zr0.04Ti0.96O3 ((y)NZF+(1-y)BSZT) (where y=0.00-0.15 in wt%) were prepared by the conventional solid state reaction route. The existence of both phases was confirmed by the X-Ray diffraction technique and the lattice parameters for all samples were calculated. The dielectric properties such as dielectric constant and dielectric loss were measured as a function of temperature at different frequencies. P-E hysteresis loops and M-H hysteresis loops confirm the ferroelectric and ferrimagnetic nature of the composite samples. M-H loops for electrically poled and un-poled samples were compared to prove ME evidences. Variation of ME coefficient (α) with dc magnetic field was also studied for all composite samples. The maximum value of α (1.6 mV/cm Oe) was observed for y=0.10 at 750 Oe.

Dressed Wilson loops as dual condensates in response to magnetic and electric fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bruckmann, Falk; Endroedi, Gergely

2011-10-01

We introduce dressed Wilson loops as a novel confinement observable. It consists of closed planar loops of arbitrary geometry but fixed area, and its expectation values decay with the latter. The construction of dressed Wilson loops is based on chiral condensates in response to magnetic and electric fields, thus linking different physical concepts. We present results for generalized condensates and dressed Wilson loops on dynamical lattice configurations and confirm the agreement with conventional Wilson loops in the limit of large probe mass. We comment on the renormalization of dressed Wilson loops.

Hi-C Observations of an Active Region Corona, and Investigation of the Underlying Magnetic Structure

NASA Technical Reports Server (NTRS)

Tiwari, S. K.; Alexander, C. E.; Winebarger, A.; Moore, R. L.

2014-01-01

The solar corona is much hotter (>=10(exp 6) K) than its surface (approx 6000 K), puzzling astrophysicists for several decades. Active region (AR) corona is again hotter than the quiet Sun (QS) corona by a factor of 4-10. The most widely accepted mechanism that could heat the active region corona is the energy release by current dissipation via reconnection of braided magnetic field structure, first proposed by E. N. Parker three decades ago. The first observational evidence for this mechanism has only recently been presented by Cirtain et al. by using High-resolution Coronal Imager (Hi-C) observations of an AR corona at a spatial resolution of 0.2 arcsec, which is required to resolve the coronal loops, and was not available before the rocket flight of Hi-C in July 2012. The Hi-C project is led by NASA/MSFC. In the case of the QS, work done by convection/granulation on the inter-granular feet of the coronal field lines translates into the heat observed in the corona. In the case of the AR, as here, there could be flux emergence, cancellation/submergence, or shear flows generating large stress and tension in coronal field loops which is released as heat in the corona. We are currently investigating the changes taking place in photospheric feet of the magnetic field involved with brightenings in the Hi-C AR corona. For this purpose, we are also using SDO/AIA data of +/- 2 hours around the 5 minutes Hi-C flight. In the present talk, I will first summarize some of the results of the Hi-C observations and then present some results from our recent analysis on what photospheric processes feed the magnetic energy that dissipates into heat in coronal loops.

Co/Au multisegmented nanowires: a 3D array of magnetostatically coupled nanopillars

NASA Astrophysics Data System (ADS)

Bran, C.; Ivanov, Yu P.; Kosel, J.; Chubykalo-Fesenko, O.; Vazquez, M.

2017-03-01

Arrays of multisegmented Co/Au nanowires with designed segment lengths and diameters have been prepared by electrodeposition into aluminum oxide templates. The high quality of the Co/Au interface and the crystallographic structure of Co segments have determined by high-resolution transmission electron microscopy. Magnetic hysteresis loop measurements show larger coercivity and squareness of multisegmented nanowires as compared to single segment Co nanowires. The complementary micromagnetic simulations are in good agreement with the experimental results, confirming that the magnetic behavior is defined mainly by magnetostatic coupling between different segments. The proposed structure constitutes an innovative route towards a 3D array of synchronized magnetic nano-oscillators with large potential in nanoelectronics.

High-Temperature Magnetism as a Probe for Structural and Compositional Uniformity in Ligand-Capped Magnetite Nanoparticles

PubMed Central

2015-01-01

To investigate magnetostructural relationships in colloidal magnetite (Fe3O4) nanoparticles (NPs) at high temperature (300–900 K), we measured the temperature dependence of magnetization (M) of oleate-capped magnetite NPs ca. 20 nm in size. Magnetometry revealed an unusual irreversible high-temperature dependence of M for these NPs, with dip and loop features observed during heating–cooling cycles. Detailed characterizations of as-synthesized and annealed Fe3O4 NPs as well as reference ligand-free Fe3O4 NPs indicate that both types of features in M(T) are related to thermal decomposition of the capping ligands. The ligand decomposition upon the initial heating induces a reduction of Fe3+ to Fe2+ and the associated dip in M, leading to more structurally and compositionally uniform magnetite NPs. Having lost the protective ligands, the NPs continually sinter during subsequent heating cycles, resulting in divergent M curves featuring loops. The increase in M with sintering proceeds not only through elimination of a magnetically dead layer on the particle surface, as a result of a decrease in specific surface area with increasing size, but also through an uncommonly invoked effect resulting from a significant change in Fe3+/Fe2+ ratio with heat treatment. The interpretation of irreversible features in M(T) indicates that reversible M(T) behavior, conversely, can be expected only for ligand-free, structurally and compositionally uniform magnetite NPs, suggesting a general applicability of high-temperature M(T) measurements as an analytical method for probing the structure and composition of magnetic nanomaterials. PMID:25506407

Measuring the magnetic field of a trans-equatorial loop system using coronal seismology

NASA Astrophysics Data System (ADS)

Long, D. M.; Valori, G.; Pérez-Suárez, D.; Morton, R. J.; Vásquez, A. M.

2017-07-01

Context. EIT waves are freely-propagating global pulses in the low corona which are strongly associated with the initial evolution of coronal mass ejections (CMEs). They are thought to be large-amplitude, fast-mode magnetohydrodynamic waves initially driven by the rapid expansion of a CME in the low corona. Aims: An EIT wave was observed on 6 July 2012 to impact an adjacent trans-equatorial loop system which then exhibited a decaying oscillation as it returned to rest. Observations of the loop oscillations were used to estimate the magnetic field strength of the loop system by studying the decaying oscillation of the loop, measuring the propagation of ubiquitous transverse waves in the loop and extrapolating the magnetic field from observed magnetograms. Methods: Observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory (SDO/AIA) and the Coronal Multi-channel Polarimeter (CoMP) were used to study the event. An Empirical Mode Decomposition analysis was used to characterise the oscillation of the loop system in CoMP Doppler velocity and line width and in AIA intensity. Results: The loop system was shown to oscillate in the 2nd harmonic mode rather than at the fundamental frequency, with the seismological analysis returning an estimated magnetic field strength of ≈ 5.5 ± 1.5 G. This compares to the magnetic field strength estimates of ≈1-9 G and ≈3-9 G found using the measurements of transverse wave propagation and magnetic field extrapolation respectively. A movie associated to Figs. 1 and 2 is available at http://www.aanda.org

The Multi-Spectral Solar Telescope Array (MSSTA)

NASA Technical Reports Server (NTRS)

Walker, A. B. C., Jr.; Barbee, Troy W., Jr.; Hoover, Richard B.

1997-01-01

In 1987, our consortium pioneered the application of normal incidence multilayer X-ray optics to solar physics by obtaining the first high resolution narrow band, "thermally differentiated" images of the corona', using the emissions of the Fe IX/Fe X complex at ((lambda)lambda) approx. 171 A to 175 A, and He II Lyman (beta) at 256 A. Subsequently, we developed a rocket borne solar observatory, the Multi Spectral Solar Telescope Array (MSSTA) that pioneered multi-thermal imaging of the solar atmosphere, using high resolution narrow band X-ray, EUV and FUV optical systems. Analysis of MSSTA observations has resulted in four significant insights into the structure of the solar atmosphere: (1) the diameter of coronal loops is essentially constant along their length; (2) models of the thermal and density structure of polar plumes based on MSSTA observations have been shown to be consistent with the thesis that they are the source of high speed solar wind streams; (3) the magnetic structure of the footpoints of polar plumes is monopolar, and their thermal structure is consistent with the thesis that the chromosphere at their footpoints is heated by conduction from above; (4) coronal bright points are small loops, typically 3,500 - 20,000 km long (5 sec - 30 sec); their footpoints are located at the poles of bipolar magnetic structures that are are distinguished from other network elements by having a brighter Lyman a signature. Loop models derived for 26 bright points are consistent with the thesis that the chromosphere at their footpoints is heated by conduction from the corona.

Hybrid nodal loop metal: Unconventional magnetoresponse and material realization

NASA Astrophysics Data System (ADS)

Zhang, Xiaoming; Yu, Zhi-Ming; Lu, Yunhao; Sheng, Xian-Lei; Yang, Hui Ying; Yang, Shengyuan A.

2018-03-01

A nodal loop is formed by a band crossing along a one-dimensional closed manifold, with each point on the loop a linear nodal point in the transverse dimensions, and can be classified as type I or type II depending on the band dispersion. Here, we propose a class of nodal loops composed of both type-I and type-II points, which are hence termed as hybrid nodal loops. Based on first-principles calculations, we predict the realization of such loops in the existing electride material Ca2As . For a hybrid loop, the Fermi surface consists of coexisting electron and hole pockets that touch at isolated points for an extended range of Fermi energies, without the need for fine-tuning. This leads to unconventional magnetic responses, including the zero-field magnetic breakdown and the momentum-space Klein tunneling observable in the magnetic quantum oscillations, as well as the peculiar anisotropy in the cyclotron resonance.

Unresolved fine-scale structure in solar coronal loop-tops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Scullion, E.; Van der Voort, L. Rouppe; Wedemeyer, S.

2014-12-10

New and advanced space-based observing facilities continue to lower the resolution limit and detect solar coronal loops in greater detail. We continue to discover even finer substructures within coronal loop cross-sections, in order to understand the nature of the solar corona. Here, we push this lower limit further to search for the finest coronal loop substructures, through taking advantage of the resolving power of the Swedish 1 m Solar Telescope/CRisp Imaging Spectro-Polarimeter (CRISP), together with co-observations from the Solar Dynamics Observatory/Atmospheric Image Assembly (AIA). High-resolution imaging of the chromospheric Hα 656.28 nm spectral line core and wings can, under certainmore » circumstances, allow one to deduce the topology of the local magnetic environment of the solar atmosphere where its observed. Here, we study post-flare coronal loops, which become filled with evaporated chromosphere that rapidly condenses into chromospheric clumps of plasma (detectable in Hα) known as a coronal rain, to investigate their fine-scale structure. We identify, through analysis of three data sets, large-scale catastrophic cooling in coronal loop-tops and the existence of multi-thermal, multi-stranded substructures. Many cool strands even extend fully intact from loop-top to footpoint. We discover that coronal loop fine-scale strands can appear bunched with as many as eight parallel strands within an AIA coronal loop cross-section. The strand number density versus cross-sectional width distribution, as detected by CRISP within AIA-defined coronal loops, most likely peaks at well below 100 km, and currently, 69% of the substructure strands are statistically unresolved in AIA coronal loops.« less

Structural and magnetic properties of nanocrystalline NiFe2O4 thin film prepared by spray pyrolysis technique

NASA Astrophysics Data System (ADS)

Chavan, Apparao R.; Chilwar, R. R.; Shisode, M. V.; Hivrekar, Mahesh M.; Mande, V. K.; Jadhav, K. M.

2018-05-01

The nanocrystalline NiFe2O4 thin film has been prepared using a spray pyrolysis technique on glass substrate. The prepared thin film was characterized by using X-ray diffraction (XRD), Fourier transform Infrared spectroscopy (FTIR), and Field Emission-Scanning Electron Microscopy (FE-SEM) characterization techniques for the structural and microstructural analysis. The magnetic property was measured using vibrating sample magnetometer (VSM) at room temperature. X-ray diffraction studies show the formation of single phase spinel structure of the thin film. The octahedral and tetrahedral vibration in the sample was studied by Fourier transform infrared (FT-IR) spectra. Magnetic hysteresis loop was recorded for thin film at room temperature. At 15 kOe, saturation magnetization (Ms) was found to increase while coercivity (Hc) decreases with thickness of the NiFe2O4 thin film.

Magnetic properties of Zn1-xNixO

NASA Astrophysics Data System (ADS)

Mondal, A.; Giri, N.; Sarkar, S.; Ray, Ruma

2018-05-01

Ni doped ZnO (Zn1-xNixO for 0.01 ≤ x ≤ 0.11) have been prepared by chemical precipitation method. X-ray diffraction corroborates a hexagonal wurzite structure without any impurity phases upto 11% Ni doping. Morphology of the particles is investigated by FE-SEM which exhibits either rod or tube like structure depending on the dopant concentration. Magnetization of Zn1-xNixO for 0.03 ≤ x ≤ 0.11 measured at room temperature infers the paramagnetic behavior. Zero field cooled and field cooled magnetization for x = 0.11 follows Curie-Weiss behavior above 122 K with effective paramagnetic moment 3.9μB. The non-linear magnetic hysteresis loop at 2 K with a small coercivity (300 Oe) indicates signature of ferromagnetic ordering.

Difference in real-time magnetic image analysis of colonic looping patterns between males and females undergoing diagnostic colonoscopy.

PubMed

Lam, Jacob; Wilkinson, James; Brassett, Cecilia; Brown, Jonathan

2018-05-01

Background and study aim  Magnetic imaging technology is of proven benefit to trainees in colonoscopy, but few studies have examined its benefits in experienced hands. There is evidence that colonoscopy is more difficult in women. We set out to investigate (i) associations between the looping configurations in the proximal and distal colon and (ii) differences in the looping prevalence between the sexes. We have examined their significance in terms of segmental intubation times and position changes required for the completion of colonoscopy. Patients and methods  We analyzed 103 consecutive synchronized luminal and magnetic image videos of diagnostic colonoscopies with normal anatomy undertaken by a single experienced operator. Results  Deep transverse loops and sigmoid N-loops were more common in females. A deep transverse loop was more likely to be present if a sigmoid alpha-loop or N-loop had formed previously. Patients with sigmoid N-loops were turned more frequently from left lateral to supine before the sigmoid-descending junction was reached, but there was no statistical correlation between completion time and looping pattern. Conclusions  This study has reexamined the prevalence of the common looping patterns encountered during colonoscopy and has identified differences between the sexes. This finding may offer an explanation as to why colonoscopy has been shown to be more difficult in females. Although a deep transverse loop following a resolved sigmoid alpha-loop was the most commonly encountered pattern, no statistical correlation between completion time and looping pattern could be shown. It is the first study to examine segmental completion times using a magnetic imager in expert hands.

Three-Dimensional Steerable Magnetic Field (3DSMF)Sensor System for Classification of Buried Metal Targets

DTIC Science & Technology

2006-07-01

technical approach overview .............................................................................. 4 Figure 2 Magnetic field lines around a loop ...11 Figure 10 HMF (Bx) and loop (Bz) antenna comparison .............................................................. 12...Figure 26 Top view of one proposed receiver loop arrangement. ................................................ 25 Figure 27 Receiver response modeling

Three-Dimensional Steerable Magnetic Field (3DSMF) Sensor System for Classification of Buried Metal Targets

DTIC Science & Technology

2006-07-01

technical approach overview .............................................................................. 4 Figure 2 Magnetic field lines around a loop ...11 Figure 10 HMF (Bx) and loop (Bz) antenna comparison .............................................................. 12 Figure...26 Top view of one proposed receiver loop arrangement. ................................................ 25 Figure 27 Receiver response modeling

Dynamics of the Transition Corona

NASA Technical Reports Server (NTRS)

Masson, Sophie; McCauley, Patrick; Golub, Leon; Reeves, Katharine K.; DeLuca, Edward E.

2014-01-01

Magnetic reconnection between the open and closed magnetic fields in the corona is believed to play a crucial role in the corona/heliosphere coupling. At large scale, the exchange of open/closed connectivity is expected to occur in pseudo-streamer (PS) structures. However, there is neither clear observational evidence of how such coupling occurs in PSs, nor evidence for how the magnetic reconnection evolves. Using a newly developed technique, we enhance the off-limb magnetic fine structures observed with the Atmospheric Imaging Assembly and identify a PS-like feature located close to the northern coronal hole. We first identify that the magnetic topology associated with the observation is a PS, null-point (NP) related topology bounded by the open field. By comparing the magnetic field configuration with the extreme ultraviolet (EUV) emission regions, we determined that most of the magnetic flux associated with plasma emission are small loops below the PS basic NP and open field bounding the PS topology. In order to interpret the evolution of the PS, we referred to a three-dimensional MHD interchange reconnection modeling the exchange of connectivity between small closed loops and the open field. The observed PS fine structures follow the dynamics of the magnetic field before and after reconnecting at the NP obtained by the interchange model. Moreover, the pattern of the EUV plasma emission is the same as the shape of the expected plasma emission location derived from the simulation. These morphological and dynamical similarities between the PS observations and the results from the simulation strongly suggest that the evolution of the PS, and in particular the opening/closing of the field, occurs via interchange/slipping reconnection at the basic NP of the PS. Besides identifying the mechanism at work in the large-scale coupling between the open and closed fields, our results highlight that interchange reconnection in PSs is a gradual physical process that differs from the impulsive reconnection of the solar-jet model.

Nanoflares, Spicules, and Other Small-Scale Dynamic Phenomena on the Sun

NASA Technical Reports Server (NTRS)

Klimchuk, James

2010-01-01

There is abundant evidence of highly dynamic phenomena occurring on very small scales in the solar atmosphere. For example, the observed pr operties of many coronal loops can only be explained if the loops are bundles of unresolved strands that are heated impulsively by nanoflares. Type II spicules recently discovered by Hinode are an example of small-scale impulsive events occurring in the chromosphere. The exist ence of these and other small-scale phenomena is not surprising given the highly structured nature of the magnetic field that is revealed by photospheric observations. Dynamic phenomena also occur on much lar ger scales, including coronal jets, flares, and CMEs. It is tempting to suggest that these different phenomena are all closely related and represent a continuous distribution of sizes and energies. However, this is a dangerous over simplification in my opinion. While it is tru e that the phenomena all involve "magnetic reconnection" (the changin g of field line connectivity) in some form, how this occurs depends s trongly on the magnetic geometry. A nanoflare resulting from the interaction of tangled magnetic strands within a confined coronal loop is much different from a major flare occurring at the current sheet form ed when a CME rips open an active region. I will review the evidence for ubiquitous small-scale dynamic phenomena on the Sun and discuss wh y different phenomena are not all fundamentally the same.

Hysteresis in single and polycrystalline iron thin films: Major and minor loops, first order reversal curves, and Preisach modeling

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cao, Yue; Xu, Ke; Jiang, Weilin

Hysteretic behavior was studied in a series of Fe thin films, grown by molecular beam epitaxy, having different grain sizes and grown on different substrates. Major and minor loops and first order reversal curves (FORCs) were collected to investigate magnetization mechanisms and domain behavior under different magnetic histories. The minor loop coefficient and major loop coercivity increase with decreasing grain size due to higher defect concentration resisting domain wall movement. First order reversal curves allowed estimation of the contribution of irreversible and reversible susceptibilities and switching field distribution. The differences in shape of the major loops and first order reversalmore » curves are described using a classical Preisach model with distributions of hysterons of different switching fields, providing a powerful visualization tool to help understand the magnetization switching behavior of Fe films as manifested in various experimental magnetization measurements.« less

Hysteresis in single and polycrystalline iron thin films: Major and minor loops, first order reversal curves, and Preisach modeling

DOE PAGES

Cao, Yue; Xu, Ke; Jiang, Weilin; ...

2015-07-03

Hysteretic behavior was studied in a series of Fe thin films, grown by molecular beam epitaxy, having different grain sizes and grown on different substrates. Major and minor loops and first order reversal curves (FORCs) were collected to investigate magnetization mechanisms and domain behavior under different magnetic histories. The minor loop coefficient and major loop coercivity increase with decreasing grain size due to higher defect concentration resisting domain wall movement. First order reversal curves allowed estimation of the contribution of irreversible and reversible susceptibilities and switching field distribution. The differences in shape of the major loops and first order reversalmore » curves are described using a classical Preisach model with distributions of hysterons of different switching fields, providing a powerful visualization tool to help understand the magnetization switching behavior of Fe films as manifested in various experimental magnetization measurements.« less

Solar burst precursors and energy build-up at microwave wavelengths

NASA Technical Reports Server (NTRS)

Lang, Kenneth R.; Wilson, Robert F.

1986-01-01

We summarize high-resolution microwave observations (VLA) of heating and magnetic triggering in coronal loops. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interaction of two or more loops. Thermal cyclotron lines have been detected in coronal loops, suggesting the presence of hot current sheets that enhance emission from relatively thin layers of enhanced temperature and constant magnetic field. These current sheets may play a role in the excitation of solar bursts. A filament-associated source with a high brightness temperature and steep radiation spectrum occurs above a region of apparently weak photospheric field. This source might be attributed to currents that enhance coronal magnetic fields. Compact (phi=5 sec) transient sources with lifetimes of 30 to 60 minutes have also been detected in regions of apparently weak photospheric field. We conclude by comparing VLA observations of coronal loops with simultaneous SMM-XRP observations.

Solar burst precursors and energy build-up at microwave wavelengths

NASA Astrophysics Data System (ADS)

Lang, Kenneth R.; Wilson, Robert F.

We summarize high-resolution microwave observations (VLA) of heating and magnetic triggering in coronal loops. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interaction of two or more loops. Thermal cyclotron lines have been detected in coronal loops, suggesting the presence of hot current sheets that enhance emission from relatively thin layers of enhanced temperature and constant magnetic field. These current sheets may play a role in the excitation of solar bursts. A filament-associated source with a high brightness temperature and steep radiation spectrum occurs above a region of apparently weak photospheric field. This source might be attributed to currents that enhance coronal magnetic fields. Compact (phi=5 sec) transient sources with lifetimes of 30 to 60 minutes have also been detected in regions of apparently weak photospheric field. We conclude by comparing VLA observations of coronal loops with simultaneous SMM-XRP observations.

Brightness and magnetic evolution of solar coronal bright points

NASA Astrophysics Data System (ADS)

Ugarte-Urra, I.

2004-12-01

This thesis presents a study of the brightness and magnetic evolution of several Extreme ultraviolet (EUV) coronal bright points (hereafter BPs). BPs are loop-like features of enhanced emission in the coronal EUV and X-ray images of the Sun, that are associated to the interaction of opposite photospheric magnetic polarities with magnetic fluxes of ≈1018 - 1019 Mx. The study was carried out using several instruments on board the Solar and Heliospheric Observatory (SOHO): the Extreme Ultraviolet Imager (EIT), the Coronal Diagnostic Spectrometer (CDS) and the Michelson Doppler Imager (MDI), supported by the high resolution imaging from the Transition Region And Coronal Explorer (TRACE). The results confirm that, down to 1'' (i.e. ~715 km) resolution, BPs are made of small loops with lengths of ~6 Mm and cross-sections of ~2 Mm. The loops are very dynamic, evolving in time scales as short as 1 - 2 minutes. This is reflected in a highly variable EUV response with fluctuations highly correlated in spectral lines at transition region temperatures (in the range 3.2x10^4 - 3.5x10^5 K), but not always at coronal temperatures. A wavelet analysis of the intensity variations reveals, for the first time, the existence of quasi-periodic oscillations with periods ranging 400 -- 1000 s, in the range of periods characteristic of the chromospheric network. The link between BPs and network bright points is discussed, as well as the interpretation of the oscillations in terms of global acoustic modes of closed magnetic structures. A comparison of the magnetic flux evolution of the magnetic polarities to the EUV flux changes is also presented. Throughout their lifetime, the intrinsic EUV emission of BPs is found to be dependent on the total magnetic flux of the polarities. In short time scales, co-spatial and co-temporal TRACE and MDI images, reveal the signature of heating events that produce sudden EUV brightenings simultaneous to magnetic flux cancellations. This is interpreted in terms of magnetic reconnection events. Finally, a electron density study of six coronal bright points produces values of ~1.6x109 cm-3, closer to active region plasma than to quiet Sun. The analysis of a large coronal loop (half length of 72 Mm) introduces the discussion on the prospects of future plasma diagnostics of BPs with forthcoming solar missions like Solar-B.

Transverse Oscillations of Coronal Loops

NASA Astrophysics Data System (ADS)

Ruderman, Michael S.; Erdélyi, Robert

2009-12-01

On 14 July 1998 TRACE observed transverse oscillations of a coronal loop generated by an external disturbance most probably caused by a solar flare. These oscillations were interpreted as standing fast kink waves in a magnetic flux tube. Firstly, in this review we embark on the discussion of the theory of waves and oscillations in a homogeneous straight magnetic cylinder with the particular emphasis on fast kink waves. Next, we consider the effects of stratification, loop expansion, loop curvature, non-circular cross-section, loop shape and magnetic twist. An important property of observed transverse coronal loop oscillations is their fast damping. We briefly review the different mechanisms suggested for explaining the rapid damping phenomenon. After that we concentrate on damping due to resonant absorption. We describe the latest analytical results obtained with the use of thin transition layer approximation, and then compare these results with numerical findings obtained for arbitrary density variation inside the flux tube. Very often collective oscillations of an array of coronal magnetic loops are observed. It is natural to start studying this phenomenon from the system of two coronal loops. We describe very recent analytical and numerical results of studying collective oscillations of two parallel homogeneous coronal loops. The implication of the theoretical results for coronal seismology is briefly discussed. We describe the estimates of magnetic field magnitude obtained from the observed fundamental frequency of oscillations, and the estimates of the coronal scale height obtained using the simultaneous observations of the fundamental frequency and the frequency of the first overtone of kink oscillations. In the last part of the review we summarise the most outstanding and acute problems in the theory of the coronal loop transverse oscillations.

Replacing the Axial Ligand Tyrosine 75 or Its Hydrogen Bond Partner Histidine 83 Minimally Affects Hemin Acquisition by the Hemophore HasAp from Pseudomonas aeruginosa

PubMed Central

2015-01-01

Hemophores from Pseudomonas aeruginosa (HasAp), Serratia marcescens (HasAsm), and Yersinia pestis (HasAyp) bind hemin between two loops. One of the loops harbors conserved axial ligand Tyr75 (Y75 loop) in all three structures, whereas the second loop (H32 loop) contains axial ligand His32 in HasAp and HasAsm, but a noncoordinating Gln32 in HasAyp. Binding of hemin to the Y75 loop of HasAp or HasAsm causes a large rearrangement of the H32 loop that allows His32 coordination. The Q32 loop in apo-HasAyp is already in the closed conformation, such that binding of hemin to the conserved Y75 loop occurs with minimal structural rearrangement and without coordinative interaction with the Q32 loop. In this study, structural and spectroscopic investigations of the hemophore HasAp were conducted to probe (i) the role of the conserved Tyr75 loop in hemin binding and (ii) the proposed requirement of the His83–Tyr75 hydrogen bond to allow the coordination of hemin by Tyr75. High-resolution crystal structures of H83A holo-HasAp obtained at pH 6.5 (0.89 Å) and pH 5.4 (1.25 Å) show that Tyr75 remains coordinated to the heme iron, and that a water molecule can substitute for Nδ of His83 to interact with the Oη atom of Tyr75, likely stabilizing the Tyr75–Fe interaction. Nuclear magnetic resonance spectroscopy revealed that in apo-Y75A and apo-H83A HasAp, the Y75 loop is disordered, and that disorder propagates to nearby elements of secondary structure, suggesting that His83 Nδ–Tyr75 Oη interaction is important to the organization of the Y75 loop in apo-HasA. Kinetic analysis of hemin loading conducted via stopped-flow UV–vis and rapid-freeze-quench resonance Raman shows that both mutants load hemin with biphasic kinetic parameters that are not significantly dissimilar from those previously observed for wild-type HasAp. When the structural and kinetic data are taken together, a tentative model emerges, which suggests that HasA hemophores utilize hydrophobic, π–π stacking, and van der Waals interactions to load hemin efficiently, while axial ligation likely functions to slow hemin release, thus allowing the hemophore to meet the challenge of capturing hemin under inhospitable conditions and delivering it selectively to its cognate receptor. PMID:24625274

Coronal rain in magnetic bipolar weak fields

NASA Astrophysics Data System (ADS)

Xia, C.; Keppens, R.; Fang, X.

2017-07-01

Aims: We intend to investigate the underlying physics for the coronal rain phenomenon in a representative bipolar magnetic field, including the formation and the dynamics of coronal rain blobs. Methods: With the MPI-AMRVAC code, we performed three dimensional radiative magnetohydrodynamic (MHD) simulation with strong heating localized on footpoints of magnetic loops after a relaxation to quiet solar atmosphere. Results: Progressive cooling and in-situ condensation starts at the loop top due to radiative thermal instability. The first large-scale condensation on the loop top suffers Rayleigh-Taylor instability and becomes fragmented into smaller blobs. The blobs fall vertically dragging magnetic loops until they reach low-β regions and start to fall along the loops from loop top to loop footpoints. A statistic study of the coronal rain blobs finds that small blobs with masses of less than 1010 g dominate the population. When blobs fall to lower regions along the magnetic loops, they are stretched and develop a non-uniform velocity pattern with an anti-parallel shearing pattern seen to develop along the central axis of the blobs. Synthetic images of simulated coronal rain with Solar Dynamics Observatory Atmospheric Imaging Assembly well resemble real observations presenting dark falling clumps in hot channels and bright rain blobs in a cool channel. We also find density inhomogeneities during a coronal rain "shower", which reflects the observed multi-stranded nature of coronal rain. Movies associated to Figs. 3 and 7 are available at http://www.aanda.org

On Heating Large Bright Coronal Loops by Magnetic Microexplosions at their Feet

NASA Technical Reports Server (NTRS)

Moore, Ronald L; Falconer, D. A.; Porter, Jason G.

1999-01-01

In previous work, by registering Yohkoh SXT coronal X-ray images with MSFC vector magnetograms, we found that: (1) many of the larger bright coronal loops rooted at one or both ends in an active region are rooted around magnetic islands of included polarity, (2) the core field encasing the neutral line encircling the island is strongly sheared, and (3) this sheared core field is the seat of frequent microflares. This suggests that the coronal heating in these extended bright loops is driven by many small explosive releases of stored magnetic energy from the sheared core field at their feet, some of which magnetic microexplosions also produce the microflare heating in the core fields. In this paper, we show that this scenario is feasible in terms of the energy Abstract: required for the observed coronal heating and the magnetic energy available in the observed sheared core fields. In a representative active region, from the X-ray and vector field data, we estimate the coronal heating consumption by a selected typical large bright loop, the coronal heating consumption by a typical microflare at the foot of this loop, the frequency of microflares at the foot, and the available magnetic energy in the microflaring core field. We find that: (1) the rate of magnetic energy release to power the microflares at the foot (approx. 6 x 10(ext 25)erg/s) is enough to also power the coronal heating in the body of the extended loop (approx. 2 x l0(exp 25 erg/s), and (2) there is enough stored magnetic energy in the sheared core field to sustain the microflaring and extended loop heating for about a day, which is a typical time for buildup of neutral-line magnetic shear in an active region. This work was funded by the Solar Physics Branch of NASA's Office of Space Science through the SR&T Program and the SEC Guest Investigator Program.

ATM observations - X-ray results. [solar coronal structure from Skylab experiments

NASA Technical Reports Server (NTRS)

Vaiana, G. S.; Zombeck, M.; Krieger, A. S.; Timothy, A. F.

1976-01-01

Preliminary results of the solar X-ray observations from Skylab are reviewed which indicate a highly structured nature for the corona, with closed magnetic-loop structures over a wide range of size scales. A description of the S-054 experiments is provided, and values are given for the parameters - including size, density, and temperature - describing a variety of typical coronal features. The structure and evolution of active regions, coronal holes, and bright points are discussed.

A small-scale eruption leading to a blowout macrospicule jet in an on-disk coronal hole

DOE Office of Scientific and Technical Information (OSTI.GOV)

Adams, Mitzi; Sterling, Alphonse C.; Moore, Ronald L.

2014-03-01

We examine the three-dimensional magnetic structure and dynamics of a solar EUV-macrospicule jet that occurred on 2011 February 27 in an on-disk coronal hole. The observations are from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and the SDO Helioseismic and Magnetic Imager (HMI). The observations reveal that in this event, closed-field-carrying cool absorbing plasma, as in an erupting mini-filament, erupted and opened, forming a blowout jet. Contrary to some jet models, there was no substantial recently emerged, closed, bipolar-magnetic field in the base of the jet. Instead, over several hours, flux convergence and cancellation at the polarity inversionmore » line inside an evolved arcade in the base apparently destabilized the entire arcade, including its cool-plasma-carrying core field, to undergo a blowout eruption in the manner of many standard-sized, arcade-blowout eruptions that produce a flare and coronal mass ejection. Internal reconnection made bright 'flare' loops over the polarity inversion line inside the blowing-out arcade field, and external reconnection of the blowing-out arcade field with an ambient open field made longer and dimmer EUV loops on the outside of the blowing-out arcade. That the loops made by the external reconnection were much larger than the loops made by the internal reconnection makes this event a new variety of blowout jet, a variety not recognized in previous observations and models of blowout jets.« less

Double row loop-coil configuration for high-speed electrodynamic maglev suspension, guidance, propulsion and guideway directional switching

DOEpatents

He, Jianliang; Rote, Donald M.

1996-01-01

A stabilization and propulsion system comprising a series of loop-coils arranged in parallel rows wherein two rows combine to form one of two magnetic rails. Levitation and lateral stability are provided when the induced field in the magnetic rails interacts with the superconducting magnets mounted on the magnetic levitation vehicle. The loop-coils forming the magnetic rails have specified dimensions and a specified number of turns and by constructing differently these specifications, for one rail with respect to the other, the angle of tilt of the vehicle can be controlled during directional switching. Propulsion is provided by the interaction of a traveling magnetic wave associated with the coils forming the rails and the super conducting magnets on the vehicle.

Double row loop-coil configuration for high-speed electrodynamic maglev suspension, guidance, propulsion and guideway directional switching

DOEpatents

He, J.; Rote, D.M.

1996-05-21

A stabilization and propulsion system are disclosed comprising a series of loop-coils arranged in parallel rows wherein two rows combine to form one of two magnetic rails. Levitation and lateral stability are provided when the induced field in the magnetic rails interacts with the superconducting magnets mounted on the magnetic levitation vehicle. The loop-coils forming the magnetic rails have specified dimensions and a specified number of turns and by constructing differently these specifications, for one rail with respect to the other, the angle of tilt of the vehicle can be controlled during directional switching. Propulsion is provided by the interaction of a traveling magnetic wave associated with the coils forming the rails and the superconducting magnets on the vehicle. 12 figs.

Properties of dynamic magnetic loss of ferrite

NASA Astrophysics Data System (ADS)

Saotome, Hideo; Azuma, Keisuke; Kizuka, Hiroki; Tanaka, Takuma

2018-05-01

The B-H loop of ferrite becomes narrower with a decrease in the excitation frequency. However, even at frequencies lower than 1 kHz, the B-H loop exhibits a certain minimum width, which is referred to as the (DC) hysteresis loop, and its area corresponds to the hysteresis loss. The dynamic magnetic loss is obtained by subtracting the hysteresis loss from the B-H loop area measured at a frequency above 1-10 kHz. The temperature characteristics of the hysteresis and dynamic magnetic losses are determined to be experimentally different, which suggests that the mechanism for the generation of dynamic magnetic loss is not exactly the same as that for the hysteresis loss. The dynamic magnetic loss is expressed using the dynamic magnetic loss parameter, which is a function of B and its time derivative, dB/dt. The dynamic magnetic loss parameter is measured under excitation with a rectangular waveform voltage. A ferrite core of TDK PC47 was used and the maximum magnetic flux density Bm, was set to 350 mT. The measured dynamic magnetic loss parameter was experimentally verified to be one of the intrinsic characteristics of ferrite and was also validated for cases of excitation with sinusoidal waveform voltages.

Effects of the single-ion anisotropy on magnetic and thermodynamic properties of a ferrimagnetic mixed-spin (1, 3/2) cylindrical Ising nanowire

NASA Astrophysics Data System (ADS)

Wang, Wei; Bi, Jiang-lin; Liu, Rui-jia; Chen, Xu; Liu, Jin-ping

2016-10-01

Monte Carlo simulation has been performed in detail to study magnetic and thermodynamic properties of a ferrimagnetic mixed-spin (1, 3/2) cylindrical Ising nanowire with core-shell structure. The ground phase diagrams are obtained for different single-ion anisotropies. The system can display rich phase transitions such as the second- and first-order phase transitions, the tricritical points and the compensation points. Especially, emphasis has been given to the effects of the single-ion anisotropy and the temperate on the magnetization, the internal energy, the specific heat, the compensation points and hysteresis loops of the system as well as two sublattices. A number of characteristic phenomena such as such as various types of magnetization curves and triple, duadruple as well as quintuple hysteresis loops behaviors have been observed for certain physical parameters, originating from the competitions among the anisotropies, temperature and the longitudinal magnetic field. It is found that the single-ion anisotropy and the temperature strongly affect the coercivity and the remanence of the system. A satisfactory agreement can be achieved from comparisons between our results and previous theoretical and experimental works.

Magnetic Vortices in Nanodisks: What are the implications in macroscopic magnetic properties?

NASA Astrophysics Data System (ADS)

Gelvez Pedroza, Ciro Fernando; Patino, Edgar J.; Superconductivity; Nanodevices Laboratory Team

The study of nanodevices is of great importance nowadays. In particular nanodisks present extraordinary properties when varying their size, shape and materials. One of the most interesting ones has been the presence of magnetic vortices which are normally not present in continuous films or bulk materials. For that reason, these constitute of great interest in potential applications such as data storage, binary logic gates or nano-plasmonics. Although there are many high cost methods for fabrication we have chosen a low cost technique based on Colloidal Lithography. Using Polystyrene Nanoparticles (100nm) nanodisks of about 180 nm in diameter have been grown using Electron Beam evaporation. The fabrication technique requires a number of steps such as spin coating, oxygen plasma and Ion Beam Etching. The samples obtained with this method were Ti/Co/Nb nanodisks with various thickness of the Co layer. Micromagnetic simulations were carried out in OOMMF giving magnetic domain structure and hysteresis loops which were later compared with those obtained experimentally using Vibrating Sample Magnetometry. Simulation results suggest a critical thickness for the appearance of magnetic vortices, revealed by hysteresis loops with substantially lower coercive fields. Facultad de Ciencias,Vicerrectoria de Investigaciones - Universidad de los Andes.

Giant magnetoresistance in perpendicularly magnetized synthetic antiferromagnetic coupling with Ir spacer

NASA Astrophysics Data System (ADS)

Fukushima, A.; Taniguchi, T.; Sugihara, A.; Yakushiji, K.; Kubota, H.; Yuasa, S.

2018-05-01

Perpendicularly magnetized magnetic tunnel junction (p-MTJ) is a key element for developing high-density spin-transfer torque switching magnetoresistive random access memory. Recently, a large exchange coupling (IEC) in the synthetic antiferromagnetic reference layer with Ir interlayer was observed in p-MTJs. The evaluation of the IEC is, however, difficult due to the electrostatic breakdown of MTJs. This study demonstrates the evaluation of the IEC with Ir interlayer in giant magnetoresistive (GMR) nanopillar. We fabricated three kinds of perpendicularly magnetized GMR elements; bottom-free structures with Cu or Ir spacer, and top-free structure with Ir spacer. The magnetoresistance (RH) loops of all samples show sharp changes of the magnetoresistance at the magnetic fields over ±10 kOe, indicating the existence of the large IECs. In particular, a sharp change of the magnetoresistance at the field over ±20 kOe was found for the element with Cu of 2 nm thickness.

Modification of Co/Cu nanoferrites properties via Gd3+/Er3+doping

NASA Astrophysics Data System (ADS)

Ateia, Ebtesam E.; Soliman, Fatma S.

2017-05-01

Pure nanoparticles of the rare earth-substituted cobalt and copper ferrites with general formula Me Gd0.025 Er0.05 Fe1.925 O4 (Me = Co, Cu) were prepared by the chemical citrate method. X-ray diffraction, field emission scanning electron microscopy, BET analysis are utilized to study the effect of rare earth substitution and its impact on the physical properties of the investigated samples. Rare earth-doped cobalt shows type IV isotherm suggesting mesopore structure with its hysteresis loop. The estimated crystallite sizes are found in the range of 21.49 and 36.11 nm for the doped Co and Cu samples, respectively. The magnetic properties of rare earth-substituted cobalt and copper ferrites showed a definite hysteresis loop at room temperature. An increase in coercivity and a decrease in saturation magnetization were detected. This can be explained in view of weaker nature of the Re3+-Fe3+ interaction compared to Fe3+-Fe3+ interaction. Greater than 1.13-fold increase in coercivity (Hc = 2184 Oe) was observed in doped cobalt nanoferrite samples compared to copper (Hc = 1936 Oe). It was found that the decreasing in temperature leads to great improvement in the magnetic properties of the investigated samples. As the magnetic recording performance of the magnetic samples is improved for well-crystallized samples with nano-structural, the effect of rare earth substitution seems to be particularly valuable in this regard.

Impact of magnetic field strength and receiver coil in ocular MRI: a phantom and patient study.

PubMed

Erb-Eigner, K; Warmuth, C; Taupitz, M; Willerding, G; Bertelmann, E; Asbach, P

2013-09-01

Generally, high-resolution MRI of the eye is performed with small loop surface coils. The purpose of this phantom and patient study was to investigate the influence of magnetic field strength and receiver coils on image quality in ocular MRI. The eyeball and the complex geometry of the facial bone were simulated by a skull phantom with swine eyes. MR images were acquired with two small loop surface coils with diameters of 4 cm and 7 cm and with a multi-channel head coil at 1.5 and 3 Tesla, respectively. Furthermore, MRI of the eye was performed prospectively in 20 patients at 1.5 Tesla (7 cm loop surface coil) and 3 Tesla (head coil). These images were analysed qualitatively and quantitatively and statistical significance was tested using the Wilcoxon-signed-rank test (a p-value of less than 0.05 was considered to indicate statistical significance). The analysis of the phantom images yielded the highest mean signal-to-noise ratio (SNR) at 3 Tesla with the use of the 4 cm loop surface coil. In the phantom experiment as well as in the patient studies the SNR was higher at 1.5 Tesla by applying the 7 cm surface coil than at 3 Tesla by applying the head coil. Concerning the delineation of anatomic structures no statistically significant differences were found. Our results show that the influence of small loop surface coils on image quality (expressed in SNR) in ocular MRI is higher than the influence of the magnetic field strength. The similar visibility of detailed anatomy leads to the conclusion that the image quality of ocular MRI at 3 Tesla remains acceptable by applying the head coil as a receiver coil. © Georg Thieme Verlag KG Stuttgart · New York.

Unimodular gravity and the lepton anomalous magnetic moment at one-loop

DOE Office of Scientific and Technical Information (OSTI.GOV)

Martín, Carmelo P., E-mail: carmelop@fis.ucm.es

We work out the one-loop contribution to the lepton anomalous magnetic moment coming from Unimodular Gravity. We use Dimensional Regularization and Dimensional Reduction to carry out the computations. In either case, we find that Unimodular Gravity gives rise to the same one-loop correction as that of General Relativity.

Protein-mediated loops in supercoiled DNA create large topological domains

PubMed Central

Yan, Yan; Ding, Yue; Leng, Fenfei; Dunlap, David; Finzi, Laura

2018-01-01

Abstract Supercoiling can alter the form and base pairing of the double helix and directly impact protein binding. More indirectly, changes in protein binding and the stress of supercoiling also influence the thermodynamic stability of regulatory, protein-mediated loops and shift the equilibria of fundamental DNA/chromatin transactions. For example, supercoiling affects the hierarchical organization and function of chromatin in topologically associating domains (TADs) in both eukaryotes and bacteria. On the other hand, a protein-mediated loop in DNA can constrain supercoiling within a plectonemic structure. To characterize the extent of constrained supercoiling, 400 bp, lac repressor-secured loops were formed in extensively over- or under-wound DNA under gentle tension in a magnetic tweezer. The protein-mediated loops constrained variable amounts of supercoiling that often exceeded the maximum writhe expected for a 400 bp plectoneme. Loops with such high levels of supercoiling appear to be entangled with flanking domains. Thus, loop-mediating proteins operating on supercoiled substrates can establish topological domains that may coordinate gene regulation and other DNA transactions across spans in the genome that are larger than the separation between the binding sites. PMID:29538766

Plasma Composition in a Sigmoidal Anemone Active Region

NASA Astrophysics Data System (ADS)

Baker, D.; Brooks, D. H.; Démoulin, P.; van Driel-Gesztelyi, L.; Green, L. M.; Steed, K.; Carlyle, J.

2013-11-01

Using spectra obtained by the EUV Imaging Spectrometer (EIS) instrument onboard Hinode, we present a detailed spatially resolved abundance map of an active region (AR)-coronal hole (CH) complex that covers an area of 359'' × 485''. The abundance map provides first ionization potential (FIP) bias levels in various coronal structures within the large EIS field of view. Overall, FIP bias in the small, relatively young AR is 2-3. This modest FIP bias is a consequence of the age of the AR, its weak heating, and its partial reconnection with the surrounding CH. Plasma with a coronal composition is concentrated at AR loop footpoints, close to where fractionation is believed to take place in the chromosphere. In the AR, we found a moderate positive correlation of FIP bias with nonthermal velocity and magnetic flux density, both of which are also strongest at the AR loop footpoints. Pathways of slightly enhanced FIP bias are traced along some of the loops connecting opposite polarities within the AR. We interpret the traces of enhanced FIP bias along these loops to be the beginning of fractionated plasma mixing in the loops. Low FIP bias in a sigmoidal channel above the AR's main polarity inversion line, where ongoing flux cancellation is taking place, provides new evidence of a bald patch magnetic topology of a sigmoid/flux rope configuration.

Neutrino mass in flavor dependent gauged lepton model

NASA Astrophysics Data System (ADS)

Nomura, Takaaki; Okada, Hiroshi

2018-03-01

We study a neutrino model introducing an additional nontrivial gauged lepton symmetry where the neutrino masses are induced at two-loop level, while the first and second charged-leptons of the standard model are done at one-loop level. As a result of the model structure, we can predict one massless active neutrino, and there is a dark matter candidate. Then we discuss the neutrino mass matrix, muon anomalous magnetic moment, lepton flavor violations, oblique parameters, and relic density of dark matter, taking into account the experimental constraints.

CONFINEMENT OF HIGH TEMPERATURE PLASMA

DOEpatents

Koenig, H.R.

1963-05-01

The confinement of a high temperature plasma in a stellarator in which the magnetic confinement has tended to shift the plasma from the center of the curved, U-shaped end loops is described. Magnetic means are provided for counteracting this tendency of the plasma to be shifted away from the center of the end loops, and in one embodiment this magnetic means is a longitudinally extending magnetic field such as is provided by two sets of parallel conductors bent to follow the U-shaped curvature of the end loops and energized oppositely on the inside and outside of this curvature. (AEC)

Feasibility of self-structured current accessed bubble devices in spacecraft recording systems

NASA Technical Reports Server (NTRS)

Nelson, G. L.; Krahn, D. R.; Dean, R. H.; Paul, M. C.; Lo, D. S.; Amundsen, D. L.; Stein, G. A.

1985-01-01

The self-structured, current aperture approach to magnetic bubble memory is described. Key results include: (1) demonstration that self-structured bubbles (a lattice of strongly interacting bubbles) will slip by one another in a storage loop at spacings of 2.5 bubble diameters, (2) the ability of self-structured bubbles to move past international fabrication defects (missing apertures) in the propagation conductors (defeat tolerance), and (3) moving bubbles at mobility limited speeds. Milled barriers in the epitaxial garnet are discussed for containment of the bubble lattice. Experimental work on input/output tracks, storage loops, gates, generators, and magneto-resistive detectors for a prototype device are discussed. Potential final device architectures are described with modeling of power consumption, data rates, and access times. Appendices compare the self-structured bubble memory from the device and system perspectives with other non-volatile memory technologies.

Study of blood flow inside the stenosis vessel under the effect of solenoid magnetic field using ferrohydrodynamics principles

NASA Astrophysics Data System (ADS)

Badfar, Homayoun; Motlagh, Saber Yekani; Sharifi, Abbas

2017-10-01

In this paper, biomagnetic blood flow in the stenosis vessel under the effect of the solenoid magnetic field is studied using the ferrohydrodynamics (FHD) model. The parabolic profile is considered at an inlet of the axisymmetric stenosis vessel. Blood is modeled as electrically non-conducting, Newtonian and homogeneous fluid. Finite volume and the SIMPLE (Semi-Implicit Method for Pressure Linked Equations) algorithm are utilized to discretize governing equations. The investigation is studied at different magnetic numbers ( MnF=164, 328, 1640 and 3280) and the number of the coil loops (three, five and nine loops). Results indicate an increase in heat transfer, wall shear stress and energy loss (pressure drop) with an increment in the magnetic number (ratio of Kelvin force to dynamic pressure force), arising from the FHD, and the number of solenoid loops. Furthermore, the flow pattern is affected by the magnetic field, and the temperature of blood can be decreased up to 1.48 {}°C under the effect of the solenoid magnetic field with nine loops and reference magnetic field ( B0) of 2 tesla.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Calabrese, G.; Capineri, L., E-mail: lorenzo.capineri@unifi.it; Granato, M.

This paper describes the design of a system for the characterization of magnetic hysteresis behavior in soft ferrite magnetic cores. The proposed setup can test magnetic materials exciting them with controlled arbitrary magnetic field waveforms, including the capability of providing a DC bias, in a frequency bandwidth up to 500 kHz, with voltages up to 32 V peak-to-peak, and currents up to 10 A peak-to-peak. In order to have an accurate control of the magnetic field waveform, the system is based on a voltage controlled current source. The electronic design is described focusing on closed loop feedback stabilization and passivemore » components choice. The system has real-time hysteretic loop acquisition and visualization. The comparisons between measured hysteresis loops of sample magnetic materials and datasheet available ones are shown. Results showing frequency and thermal behavior of the hysteresis of a test sample prove the system capabilities. Moreover, the B-H loops obtained with a multiple waveforms excitation signal, including DC bias, are reported. The proposal is a low-cost and replicable solution for hysteresis characterization of magnetic materials used in power electronics.« less

Correlation between structural, electrical and magnetic properties of GdMnO3 bulk ceramics

NASA Astrophysics Data System (ADS)

Samantaray, S.; Mishra, D. K.; Pradhan, S. K.; Mishra, P.; Sekhar, B. R.; Behera, Debdhyan; Rout, P. P.; Das, S. K.; Sahu, D. R.; Roul, B. K.

2013-08-01

This paper reports the effect of sintering temperature on ferroelectric properties of GdMnO3 (GMO) bulk ceramics at room temperature prepared by the conventional solid state reaction route following slow step sintering schedule. Ferroelectric hysteresis loop as well as sharp dielectric anomaly in pure (99.999%) GMO sintered ceramics has been clearly observed. Samples sintered at 1350 °C become orthorhombic with Pbnm space group and showed frequency independent sharp dielectric anomalies at 373 K and a square type of novel ferroelectric hysteresis loop was observed at room temperature. Interestingly, dielectric anomalies and ferroelectric behavior were observed to be dependent upon sintering temperature of GdMnO3. Room temperature dielectric constant (ɛr) value at different frequencies is observed to be abnormally high. The magnetic field and temperature dependent magnetization show antiferromagnetic behavior at 40 K for both 1350 °C and 1700 °C sintered GMO. Present findings showed the possibility of application of GdMnO3 at room temperature as multifunctional materials.

Observations of simultaneous coronal loop shrinkage and expansion during the decay phase of a solar flare

NASA Astrophysics Data System (ADS)

Khan, J. I.; Fletcher, L.; Nitta, N. V.

2006-07-01

We report what we believe are the first direct and unambiguous observations of simultaneous coronal magnetic flux loop shrinkage and expansion during the decay phase of a solar flare. The retracting and expanding loops were observed nearly face-on (i.e., with the loop major axis approximately orthogonal to the line of sight) in emission in imaging data from the Yohkoh Soft X-ray Telescope (SXT). The retracting loop is observed to shrink with a speed of 118 ± 66 km s-1. The faint outward moving loop-like feature occurred ~200´´ above the shrinking loop during the time of the shrinking loop. We estimate the speed of the outward moving loop was ~129 ± 74 km s-1. We interpret the shrinking loop and simultaneous outward moving loop as direct evidence for reconnected magnetic field lines during a flare.

Structural and magnetic properties of the products of the transformation of ferrihydrite: Effect of cobalt dications

NASA Astrophysics Data System (ADS)

Camacho, K. I.; Pariona, N.; Martinez, A. I.; Baggio-Saitovitch, E.; Herrera-Trejo, M.; Perry, Dale L.

2017-05-01

The effect of cobalt dications on the transformation of 2-line ferrihydrite (2LF) has been studied. The products of the transformation reaction were characterized by X-ray diffraction, Mössbauer spectroscopy (MS), transmission electron microscopy (TEM), magnetometry, and first-order reversal curve (FORC) diagrams. It was found that the concentration of cobalt dications plays an important role on the structural and magnetic properties of the products; i.e., for low cobalt concentrations, cobalt-substituted hematite is formed, while higher concentrations promote the formation of cobalt-substituted magnetite. Structural results revealed that formation of other iron oxide polymorphs is avoided and residual 2LF is always present in the final products. In this way, hematite/2LF and magnetite/2LF nanocomposites were formed. For all the samples, magnetic measurements yielded non-saturated hysteresis loops at a maximum field of 12 kOe. For cobalt-substituted hematite/2LF samples, FORC diagrams revealed the presence of multiple single-domain (SD) components which generate interaction coupling between SD with low and high coercivity. Moreover, for cobalt-substituted magnetite/2LF samples, the FORC diagrams revealed the components of wasp-waist hysteresis loops which consist of mixtures of SD and superparamagnetic particles. One of the goals of the present study is the rigorous, experimental documentation of ferrihydrite/hematite mixtures as a function of reaction conditions for use as analytical standards research.

Structural and magnetic properties of hexagonal Cr1-δTe films grown on CdTe(001) by molecular beam epitaxy

NASA Astrophysics Data System (ADS)

Kanazawa, Ken; Yamawaki, Kazuma; Sekita, Naoya; Nishio, Yôtarô; Kuroda, Shinji; Mitome, Masanori; Bando, Yoshio

2015-04-01

We investigated the structural and magnetic properties of Cr1-δTe thin films grown on CdTe(001) layers by molecular beam epitaxy (MBE) with systematic variations of the ratio between Cr and Te fluxes and the substrate temperature Ts during the growth. Cr1-δTe of the hexagonal structure (hex-Cr1-δTe) was always formed irrespective of the growth conditions, but the growth orientation was different depending on the Cr/Te flux ratio and Ts. Hex-Cr1-δTe was grown in the [0001] axis in the range of small Cr/Te ratios and high Ts while it was also grown in the direction normal to the (1-102) plane at larger Cr/Te ratios or lower Ts. Hex-Cr1-δTe films grown in the both orientations show ferromagnetism, but they exhibit a clear contrast in the field dependence of perpendicular magnetization at 2 K; a square hysteretic loop in the film grown in the [0001] axis versus a round-shape loop in the film grown in the direction normal to the (1-102) plane. Moreover, the films grown in the [0001] axis at the smallest Cr/Te ratio show variations of ferromagnetic properties with Curie temperature (Tc) and the coercivity (Hc) varying according to the value of Ts.

CORE SATURATION BLOCKING OSCILLATOR

DOEpatents

Spinrad, R.J.

1961-10-17

A blocking oscillator which relies on core saturation regulation to control the output pulse width is described. In this arrangement an external magnetic loop is provided in which a saturable portion forms the core of a feedback transformer used with the thermionic or semi-conductor active element. A first stationary magnetic loop establishes a level of flux through the saturation portion of the loop. A second adjustable magnet moves the flux level to select a saturation point giving the desired output pulse width. (AEC)

Solar Tornadoes Triggered by Interaction between Filaments and EUV Jets

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Huadong; Zhang, Jun; Ma, Suli

We investigate the formations and evolutions of two successive solar tornadoes in/near AR 12297 during 2015 March 19–20. Recurrent EUV jets close to two filaments were detected along a large-scale coronal loop prior to the appearances of the tornadoes. Under the disturbances from the activities, the filaments continually ascended and finally interacted with the loops tracked by the jets. Subsequently, the structures of the filaments and the loop were merged together, probably via magnetic reconnections, and formed tornado-like structures with a long spiral arm. Our observations suggest that solar tornadoes can be triggered by the interaction between filaments and nearbymore » coronal jets, which has rarely been reported before. At the earlier development phase of the first tornado, about 30 small-scale sub-jets appeared in the tornado’s arm, accompanied by local EUV brightenings. They have an ejection direction approximately vertical to the axis of the arm and a typical maximum speed of ∼280 km s{sup −1}. During the ruinations of the two tornadoes, fast plasma outflows from the strong EUV brightenings inside tornadoes are observed, in company with the untangling or unwinding of the highly twisted tornado structures. These observational features indicate that self reconnections probably occurred between the tangled magnetic fields of the tornadoes and resulted in the rapid disintegrations and disappearances of the tornadoes. According to the reconnection theory, we also derive the field strength of the tornado core to be ∼8 G.« less

Solar Tornadoes Triggered by Interaction between Filaments and EUV Jets

NASA Astrophysics Data System (ADS)

Chen, Huadong; Zhang, Jun; Ma, Suli; Yan, Xiaoli; Xue, Jianchao

2017-05-01

We investigate the formations and evolutions of two successive solar tornadoes in/near AR 12297 during 2015 March 19-20. Recurrent EUV jets close to two filaments were detected along a large-scale coronal loop prior to the appearances of the tornadoes. Under the disturbances from the activities, the filaments continually ascended and finally interacted with the loops tracked by the jets. Subsequently, the structures of the filaments and the loop were merged together, probably via magnetic reconnections, and formed tornado-like structures with a long spiral arm. Our observations suggest that solar tornadoes can be triggered by the interaction between filaments and nearby coronal jets, which has rarely been reported before. At the earlier development phase of the first tornado, about 30 small-scale sub-jets appeared in the tornado’s arm, accompanied by local EUV brightenings. They have an ejection direction approximately vertical to the axis of the arm and a typical maximum speed of ˜280 km s-1. During the ruinations of the two tornadoes, fast plasma outflows from the strong EUV brightenings inside tornadoes are observed, in company with the untangling or unwinding of the highly twisted tornado structures. These observational features indicate that self reconnections probably occurred between the tangled magnetic fields of the tornadoes and resulted in the rapid disintegrations and disappearances of the tornadoes. According to the reconnection theory, we also derive the field strength of the tornado core to be ˜8 G.

FORWARD MODELING OF STANDING KINK MODES IN CORONAL LOOPS. II. APPLICATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yuan, Ding; Doorsselaere, Tom Van, E-mail: DYuan2@uclan.ac.uk

2016-04-15

Magnetohydrodynamic waves are believed to play a significant role in coronal heating, and could be used for remote diagnostics of solar plasma. Both the heating and diagnostic applications rely on a correct inversion (or backward modeling) of the observables into the thermal and magnetic structures of the plasma. However, due to the limited availability of observables, this is an ill-posed issue. Forward modeling is designed to establish a plausible mapping of plasma structuring into observables. In this study, we set up forward models of standing kink modes in coronal loops and simulate optically thin emissions in the extreme ultraviolet bandpasses,more » and then adjust plasma parameters and viewing angles to match three events of transverse loop oscillations observed by the Solar Dynamics Observatory/Atmospheric Imaging Assembly. We demonstrate that forward models could be effectively used to identify the oscillation overtone and polarization, to reproduce the general profile of oscillation amplitude and phase, and to predict multiple harmonic periodicities in the associated emission intensity and loop width variation.« less

Synthesis of flower-like BaTiO3/Fe3O4 hierarchically structured particles and their electrorheological and magnetic properties.

PubMed

Wang, Baoxiang; Yin, Yichao; Liu, Chenjie; Yu, Shoushan; Chen, Kezheng

2013-07-21

Flower-like BaTiO3/Fe3O4 hierarchically structured particles composed of nano-scale structures on micro-scale materials were synthesized by a simple solvothermal approach and characterized by the means of X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), magnetic testing and rotary viscometer. The influences on the morphology and structure of solvothermal times, type and amount of surfactant, EG : H2O ratio, etc. were studied. Magnetic testing results show that the samples have strong magnetism and they exhibit superparamagnetic behavior, as evidenced by no coercivity and the remanence at room temperature, due to their very small sizes, observed on the M-H loop. The saturation magnetization (M(s)) value can achieve 18.3 emu g(-1). The electrorheological (ER) effect was investigated using a suspension of the flower-like BaTiO3/Fe3O4 hierarchically structured particles dispersed in silicone oil. We can observe a slight shear-thinning behavior of shear viscosity at a low shear rate region even at zero applied electric field and a Newtonian fluid behavior at high shear rate regions.

Beam current sensor

DOEpatents

Kuchnir, M.; Mills, F.E.

1984-09-28

A current sensor for measuring the dc component of a beam of charged particles employs a superconducting pick-up loop probe, with twisted superconducting leads in combination with a Superconducting Quantum Interference Device (SQUID) detector. The pick-up probe is in the form of a single-turn loop, or a cylindrical toroid, through which the beam is directed and within which a first magnetic flux is excluded by the Meisner effect. The SQUID detector acts as a flux-to-voltage converter in providing a current to the pick-up loop so as to establish a second magnetic flux within the electrode which nulls out the first magnetic flux. A feedback voltage within the SQUID detector represents the beam current of the particles which transit the pick-up loop. Meisner effect currents prevent changes in the magnetic field within the toroidal pick-up loop and produce a current signal independent of the beam's cross-section and its position within the toroid, while the combination of superconducting elements provides current measurement sensitivities in the nano-ampere range.

Solar-burst precursors and energy buildup at microwave wavelengths

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lang, K.R.; Willson, R.F.

High-resolution microwave observations (VLA) of heating and magnetic triggering in coronal loops are summarized. Magnetic changes that precede solar eruptions on time scales of tens of minutes involve primarily emerging coronal loops and the interaction of two or more loops. Thermal cyclotron lines were detected in coronal loops, suggesting the presence of hot current sheets that enhance emission from relatively thin layers of enhanced temperature and constant magnetic field. These current sheets may play a role in the excitation of solar bursts. A filament-associated source with a high brightness temperature and steep radiation spectrum occurs above a region of apparentlymore » weak photospheric field. This source might be attributed to currents that enhance coronal magnetic fields. Compact (phi=5 sec) transient sources with lifetimes of 30 to 60 minutes were also detected in regions of apparently weak photospheric field. VLA observations of coronal loops are compared with simultaneous SMM-XRP observations in conclusion.« less

Beam current sensor

DOEpatents

Kuchnir, Moyses; Mills, Frederick E.

1987-01-01

A current sensor for measuring the DC component of a beam of charged particles employs a superconducting pick-up loop probe, with twisted superconducting leads in combination with a Superconducting Quantum Interference Device (SQUID) detector. The pick-up probe is in the form of a single-turn loop, or a cylindrical toroid, through which the beam is directed and within which a first magnetic flux is excluded by the Meisner effect. The SQUID detector acts as a flux-to-voltage converter in providing a current to the pick-up loop so as to establish a second magnetic flux within the electrode which nulls out the first magnetic flux. A feedback voltage within the SQUID detector represents the beam current of the particles which transit the pick-up loop. Meisner effect currents prevent changes in the magnetic field within the toroidal pick-up loop and produce a current signal independent of the beam's cross-section and its position within the toroid, while the combination of superconducting elements provides current measurement sensitivites in the nano-ampere range.

Suppression of Heating of Coronal Loops Rooted in Opposite Polarity Sunspot Umbrae

NASA Technical Reports Server (NTRS)

Tiwari, Sanjiv K.; Thalmann, Julia K.; Moore, Ronald L.; Panesar, Navdeep K.; Winebarger, Amy R.

2016-01-01

EUV observations of active region (AR) coronae reveal the presence of loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 Å images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-­polarity plage region. The AIA 94 Å images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the Heliosesmic Magnetic Imager (HMI) onboard SDO. The NLFFF model, validated by comparison of calculated model field lines with observed loops in AIA 193 and 94 Å, specifies the photospheric roots of the model field lines. Some model coronal magnetic field lines arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.

Kerr microscopy study of exchange-coupled FePt/Fe exchange spring magnets

NASA Astrophysics Data System (ADS)

Hussain, Zaineb; Kumar, Dileep; Reddy, V. Raghavendra; Gupta, Ajay

2017-05-01

Magnetization reversal and magnetic microstructure of top soft magnetic layer (Fe) in exchange spring coupled L10 FePt/Fe is studied using high resolution Kerr microscopy. With remnant state of the hard magnetic layer (L10 FePt) as initial condition, magnetization loops along with magnetic domains are recorded for the top soft magnetic layer (Fe) using Kerr microscopy. Considerable shifting of Fe layer hysteresis loop from center which is similar to exchange bias phenomena is observed. It is also observed that one can tune the magnitude of hysteresis shift by reaching the remanent state from different saturating fields (HSAT) and also by varying the angle between measuring field and HSAT. The hysteresis loops and magnetic domains of top soft Fe layer demonstrate unambiguously that soft magnetic layer at remanent state in such exchange coupled system is having unidirectional anisotropy. An analogy is drawn and the observations are explained in terms of established model of exchange bias phenomena framed for field-cooled ferromagnetic - antiferromagnetic bilayer systems.

Brightness and magnetic evolution of solar coronal bright points

NASA Astrophysics Data System (ADS)

Ugarte Urra, Ignacio

This thesis presents a study of the brightness and magnetic evolution of several Extreme ultraviolet (EUV) coronal bright points (hereafter BPs). The study was carried out using several instruments on board the Solar and Heliospheric Observatory, supported by the high resolution imaging from the Transition Region And Coronal Explorer. The results confirm that, down to 1" resolution, BPs are made of small loops with lengths of [approximate]6 Mm and cross-sections of ≈2 Mm. The loops are very dynamic, evolving in time scales as short as 1 - 2 minutes. This is reflected in a highly variable EUV response with fluctuations highly correlated in spectral lines at transition region temperatures, but not always at coronal temperatures. A wavelet analysis of the intensity variations reveals the existence of quasi-periodic oscillations with periods ranging 400--1000s, in the range of periods characteristic of the chromospheric network. The link between BPs and network bright points is discussed, as well as the interpretation of the oscillations in terms of global acoustic modes of closed magnetic structures. A comparison of the magnetic flux evolution of the magnetic polarities to the EUV flux changes is also presented. Throughout their lifetime, the intrinsic EUV emission of BPs is found to be dependent on the total magnetic flux of the polarities. In short time scales, co-spatial and co-temporal coronal images and magnetograms, reveal the signature of heating events that produce sudden EUV brightenings simultaneous to magnetic flux cancellations. This is interpreted in terms of magnetic reconnection events. Finally, a electron density study of six coronal bright points produces values of ≈1.6×10 9 cm -3 , closer to active region plasma than to quiet Sun. The analysis of a large coronal loop (half length of 72 Mm) introduces the discussion on the prospects of future plasma diagnostics of BPs with forthcoming solar missions.

Dynamics of quiescent prominences; Proceedings of the 117th Colloquium of IAU, Hvar, Yugoslavia, Sept. 25-29, 1989

NASA Technical Reports Server (NTRS)

Ruzdjak, Vladimir (Editor); Tandberg-Hanssen, Einar (Editor)

1990-01-01

Topics discussed include formation of a filament around a magnetic region, evolution of fine structures in a filament, the spatial distribution of prominence threads, high resolution analysis of quiescent prominences at NSO/Sacramento Peak Observatory, small-scale Doppler velocities in a quiescent prominence, Doppler velocity oscillations in quiescent prominences, oscillatory relaxation of an eruptive prominence, and matter flow velocities in an active region emission loop observed in H-alpha. Attention is also given to an automated procedure for measurement of prominence transverse velocities, the nonlinear evolution of magnetized filaments, thermal equilibrium of coronal loops and prominence formation, thermal instability in planar coronal strucutres, radiative transfer in cylindrical prominence threads, numerical simulation of a catastrophe model for prominence eruptions, and the law of evolution and destruction of solar prominences.

Electromagnetic Modeling of the Passive Stabilization Loop at EAST

NASA Astrophysics Data System (ADS)

Ji, Xiang; Song, Yuntao; Wu, Songtao; Wang, Zhibin; Shen, Guang; Liu, Xufeng; Cao, Lei; Zhou, Zibo; Peng, Xuebing; Wang, Chenghao

2012-09-01

A passive stabilization loop (PSL) has been designed and manufactured in order to enhance the control of vertical instability and accommodate the new stage for high-performance plasma at EAST. Eddy currents are induced by vertical displacement events (VDEs) and disruption, which can produce a magnetic field to control the vertical instability of the plasma in a short timescale. A finite element model is created and meshed using ANSYS software. Based on the simulation of plasma VDEs and disruption, the distribution and decay curve of the eddy currents on the PSL are obtained. The largest eddy current is 200 kA and the stress is 68 MPa at the outer current bridge, which is the weakest point of the PSL because of the eddy currents and the magnetic fields. The analysis results provide the supporting data for the structural design.

Magnetic Properties of Rapid Cooled FeCoB Based Alloys Produced by Injection Molding

NASA Astrophysics Data System (ADS)

Nabialek, M.; Jeż, B.; Jeż, K.; Pietrusiewicz, P.; Gruszka, K.; Błoch, K.; Gondro, J.; Rzącki, J.; Abdullah, M. M. A. B.; Sandu, A. V.; Szota, M.

2018-06-01

The paper presents the results of investigations of the structure and magnetic properties of massive rapid cooled Fe50-xCo20+xB20Cu1Nb9 alloys (where x = 0, 5). Massive alloys were made using the method of injecting a liquid alloy into a copper mold. Samples were obtained in the form of 0.5 mm thick plates. The structure of the obtained samples was examined using an X-ray diffractometer equipped with a CuKα lamp. The phase composition of the alloys formed was determined using the Match program. By using Sherrer’s dependence the grain sizes of the identified crystalline phases were estimated. Using the Faraday magnetic balance, the magnetization of samples as a function of temperature in the range from room temperature to 850K was measured. Magnetization of saturation and value of the coercive field for the prepared alloys were determined on the basis of magnetic hysteresis loop measurement using the LakeShore vibration magnetometer.

Detailed ADM-based Modeling of Shock Retreat and X-ray Emission of τ Sco

NASA Astrophysics Data System (ADS)

Fletcher, C. L.; Petit, V.; Cohen, D. H.; Townsend, R. H.; Wade, G. A.

2018-01-01

Leveraging the improvement of spectropolarimeters over the past few decades, surveys have found that about 10% of OB-type stars host strong (˜ kG) and mostly dipolar surface magnetic fields. One B-type star, τ Sco, has a more complex surface magnetic field than the general population of OB stars. Interestingly, its X-ray luminosity is an order of magnitude higher than predicted from analytical models of magnetized winds. Previous studies of τ Sco's magnetosphere have predicted that the region of closed field loops should be located close to the stellar surface. However, the lack of X-ray variability and the location of the shock-heated plasma measured from forbidden-to-intercombination X-ray line ratios suggest that the hot plasma, and hence the closed magnetic loops, extend considerably farther from the stellar surface, implying a significantly lower mass loss rate than initially assumed. We present an adaptation of the Analytic Dynamical Magnetosphere model, describing the magnetic confinement of the stellar wind, for an arbitrary field loop configuration. This model is used to predict the shock-heated plasma temperatures for individual field loops, which are then compared to high resolution grating spectra from the Chandra X-ray Observatory. This comparison shows that larger closed magnetic loops are needed.

Two component X-ray emission from RS CVn binaries

NASA Technical Reports Server (NTRS)

Swank, J. H.; White, N. E.; Holt, S. S.; Becker, R. H.

1980-01-01

A summary of results from the solid state spectrometer on the Einstein Observatory for 7 RS CVn binaries is presented. The spectra of all require two emission components, evidenced by line emission characteristic of plasma at 4 to 8 x 10 to the 6th power and bremsstrahlung characteristic of 20 to 100 x 10 to the 6th power K. The data are interpreted in terms of magnetic coronal loops similar to those seen on the Sun, although with different characteristic parameters. The emission regions could be defined by separate magnetic structures. For pressure less than approximately 10 dynes/sq cm the low temperature plasma would be confined within the stellar radii, while the high temperature plasma would, for the synchronous close binaries, fill the binary orbits. However, for loop pressures exceeding 100 dynes/sq cm, the high temperature components would also be confined to within the stellar radii, in loops covering only small fractions of the stellar surfaces. While the radio properties and the occurrence of X-ray flares suggest the larger emission regions, the observations of time variations leave the ambiguity unresolved.

Magnetic activity in the Galactic Centre region - fast downflows along rising magnetic loops

NASA Astrophysics Data System (ADS)

Kakiuchi, Kensuke; Suzuki, Takeru K.; Fukui, Yasuo; Torii, Kazufumi; Enokiya, Rei; Machida, Mami; Matsumoto, Ryoji

2018-06-01

We studied roles of the magnetic field on the gas dynamics in the Galactic bulge by a three-dimensional global magnetohydrodynamical simulation data, particularly focusing on vertical flows that are ubiquitously excited by magnetic activity. In local regions where the magnetic field is stronger, it is frequently seen that fast downflows slide along inclined magnetic field lines that are associated with buoyantly rising magnetic loops. The vertical velocity of these downflows reaches ˜100 km s-1 near the footpoint of the loops by the gravitational acceleration towards the Galactic plane. The two footpoints of rising magnetic loops are generally located at different radial locations and the field lines are deformed by the differential rotation. The angular momentum is transported along the field lines, and the radial force balance breaks down. As a result, a fast downflow is often observed only at the one footpoint located at the inner radial position. The fast downflow compresses the gas to form a dense region near the footpoint, which will be important in star formation afterwards. Furthermore, the horizontal components of the velocity are also fast near the footpoint because the downflow is accelerated along the magnetic sliding slope. As a result, the high-velocity flow creates various characteristic features in a simulated position-velocity diagram, depending on the viewing angle.

Vectorial magnetometry with the magneto-optic Kerr effect applied to Co/Cu/Co trilayer structures

NASA Astrophysics Data System (ADS)

Daboo, C.; Bland, J. A. C.; Hicken, R. J.; Ives, A. J. R.; Baird, M. J.; Walker, M. J.

1993-05-01

We describe an arrangement in which the magnetization components parallel and perpendicular to the applied field are both determined from longitudinal magneto-optic Kerr effect measurements. This arrangement differs from the usual procedures in that the same optical geometry is used but the magnet geometry altered. This leads to two magneto-optic signals which are directly comparable in magnitude thereby giving the in-plane magnetization vector directly. We show that it is of great value to study both in-plane magnetization vector components when studying coupled structures where significant anisotropies are also present. We discuss simulations which show that it is possible to accurately determine the coupling strength in such structures by examining the behavior of the component of magnetization perpendicular to the applied field in the vicinity of the hard in-plane anisotropy axis. We illustrate this technique by examining the magnetization and magnetic anisotropy behavior of ultrathin Co/Cu(111)/Co (dCu=20 Å and 27 Å) trilayer structures prepared by molecular beam epitaxy, in which coherent rotation of the magnetization vector is observed when the magnetic field B is applied along the hard in-plane anisotropy axis, with the magnitude of the magnetization vector constant and close to its bulk value. Results of micromagnetic calculations closely reproduce the observed parallel and perpendicular magnetization loops, and yield strong uniaxial magnetic anisotropies in both layers, while the interlayer coupling appears to be absent or negligible in comparison with the anisotropy strengths.

High frequency, high temperature specific core loss and dynamic B-H hysteresis loop characteristics of soft magnetic alloys

NASA Technical Reports Server (NTRS)

Wieserman, W. R.; Schwarze, G. E.; Niedra, J. M.

1990-01-01

Limited experimental data exists for the specific core loss and dynamic B-H loops for soft magnetic materials for the combined conditions of high frequency and high temperature. This experimental study investigates the specific core loss and dynamic B-H loop characteristics of Supermalloy and Metglas 2605SC over the frequency range of 1 to 50 kHz and temperature range of 23 to 300 C under sinusoidal voltage excitation. The experimental setup used to conduct the investigation is described. The effects of the maximum magnetic flux density, frequency, and temperature on the specific core loss and on the size and shape of the B-H loops are examined.

Magneto-optical Kerr effect of a Ni2.00Mn1.16Ga0.84 single crystal across austenite and intermartensite transitions

NASA Astrophysics Data System (ADS)

Fikáček, Jan; Heczko, Oleg; Kopecký, Vít; Kaštil, Jiří; Honolka, Jan

2018-04-01

We carried out magneto-optical Kerr effect (MOKE) and magnetization measurements on a single crystal of Ni2.00Mn1.16Ga0.84, which is a magnetic shape memory material with application potential for actuator devices or for energy recuperation. Up to the time of our study, there had been reports of MOKE measurements in polar geometry. Against earlier predictions, we show that surface magnetic states of the martensite and the austenite can be also probed efficiently via longitudinal MOKE. A single-variant magnetic state prepared at room temperature is characterized by square-shaped ferromagnetic hysteresis loops yielding coercive fields, which are key material properties for future applications. Temperature dependencies of Kerr rotation were found to be linearly proportional to magnetization for martensitic phases. After passing through an inter-martensitic structural transition below room temperature in zero magnetic field, the coercive fields are more than doubled in comparison with the room temperature values. Above room temperature where an austenite structure is formed, MOKE signals are dominated by quadratic contributions and the magnitude of Kerr rotation drops due to changes in the electronic and magnetic domains structure.

Equilibrium models of coronal loops that involve curvature and buoyancy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hindman, Bradley W.; Jain, Rekha, E-mail: hindman@solarz.colorado.edu

2013-12-01

We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to amore » detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.« less

EFFECT OF A SAUSAGE OSCILLATION ON RADIO ZEBRA-PATTERN STRUCTURES IN A SOLAR FLARE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yu, Sijie; Yan, Yihua; Nakariakov, V. M., E-mail: sjyu@nao.cas.cn

2016-07-20

Sausage modes that are axisymmetric fast magnetoacoustic oscillations of solar coronal loops are characterized by variation of the plasma density and magnetic field, and hence cause time variations of the electron plasma frequency and cyclotron frequency. The latter parameters determine the condition for the double plasma resonance (DPR), which is responsible for the appearance of zebra-pattern (ZP) structures in time spectra of solar type IV radio bursts. We perform numerical simulations of standing and propagating sausage oscillations in a coronal loop modeled as a straight, field-aligned plasma slab, and determine the time variation of the DPR layer locations. Instant valuesmore » of the plasma density and magnetic field at the DPR layers allowed us to construct skeletons of the time variation of ZP stripes in radio spectra. In the presence of a sausage oscillation, the ZP structures are shown to have characteristic wiggles with the time period prescribed by the sausage oscillation. Standing and propagating sausage oscillations are found to have different signatures in ZP patterns. We conclude that ZP wiggles can be used for the detection of short-period sausage oscillations and the exploitation of their seismological potential.« less

Prominence condensation and magnetic levitation in a coronal loop

NASA Technical Reports Server (NTRS)

Van Hoven, G.; Mok, Y.; Drake, J. F.

1992-01-01

The results of a model dynamic simulation of the formation and support of a narrow prominence at the apex of a coronal magnetic loop or arcade are described. The condensation process proceeds via an initial radiative cooling and pressure drop, and a secondary siphon flow from the dense chromospheric ends. The antibuoyancy effect as the prominence forms causes a bending of the confining magnetic field, which propagates toward the semirigid ends of the magnetic loop. Thus, a wide magnetic 'hammock' or well (of the normal-polarity Kippenhahn-Schlueter-type) is formed, which supports the prominence at or near the field apex. The simplicity of this 1.5-dimensional model, with its accompanying diagnostics, elucidates the various contributions to the nonlinear dynamics of prominence condensation and levitation.

Magnetic Field Configuration of Active Region NOAA 6555 at the Time of a Long Duration Flare on 23 March 1991: An Exception to Standard Flare Reconnection Model

NASA Technical Reports Server (NTRS)

Choudhary, Debi Prasad; Gary, Allen G.

1998-01-01

The high-resolution H(sub alpha) images observed during the decay phase of a long duration flare on 23 March 1991 are used to study the three-dimensional magnetic field configuration of the active region NOAA 6555. Whereas, all the large flares in NOAA 6555 occurred at the location of high magnetic shear and flux emergence, this long duration flare was observed in the region of low magnetic shear at the photosphere. The H(sub alpha) loop activity started soon after the maximum phase of the flare. There were few long loop at the initial phase of the activity. Some of these were sheared in the chromosphere at an angle of about 45 deg with the east-west axis. Gradually, increasing number of shorter loops, oriented along the east-west axis, started appearing. The chromospheric Dopplergrams show blue-shifts at the end points of the loops. By using different magnetic field models, we have extrapolated the photospheric magnetograms to the chromospheric heights. The magnetic field lines computed by using the potential field model correspond to most of the observed H(sub alpha) loops. The height of the H(sub alpha) loops were derived by comparing them with the computed field lines. From the temporal evolution of the H(sub alpha) loop activity, we derive the negative rate of appearance of H(sub alpha) features as a function of height. It is found that the field lines oriented along one of the neutral lines was sheared and low lying. The higher field lines were mostly potential. The paper also outlines a possible scenario for describing the post-flare stage of the observed long duration flare.

AQUILA Remotely Piloted Vehicle System Technology Demonstrator (RPV-STD) Program. Volume 2. System Evolution and Engineering Testing

DTIC Science & Technology

1979-04-01

crosshead of the piston assembly. Shock transients at this location cause demagnetization of the magnet . This is being alleviated by in- stallation of magnets ...substantial structure, such as bulk - heads with edge cape. Soond, the wire-out foam *or* for the wing could not be sufficiently precise to preven the used for...characterize the power potential, fuel consumption, weight, bulk , and adaptability to closed loop control of candidate carburetion systems to be employed with

Shock heating in numerical simulations of kink-unstable coronal loops

PubMed Central

Bareford, M. R.; Hood, A. W.

2015-01-01

An analysis of the importance of shock heating within coronal magnetic fields has hitherto been a neglected area of study. We present new results obtained from nonlinear magnetohydrodynamic simulations of straight coronal loops. This work shows how the energy released from the magnetic field, following an ideal instability, can be converted into thermal energy, thereby heating the solar corona. Fast dissipation of magnetic energy is necessary for coronal heating and this requirement is compatible with the time scales associated with ideal instabilities. Therefore, we choose an initial loop configuration that is susceptible to the fast-growing kink, an instability that is likely to be created by convectively driven vortices, occurring where the loop field intersects the photosphere (i.e. the loop footpoints). The large-scale deformation of the field caused by the kinking creates the conditions for the formation of strong current sheets and magnetic reconnection, which have previously been considered as sites of heating, under the assumption of an enhanced resistivity. However, our simulations indicate that slow mode shocks are the primary heating mechanism, since, as well as creating current sheets, magnetic reconnection also generates plasma flows that are faster than the slow magnetoacoustic wave speed. PMID:25897092

The Formation of Coronal Loops by Thermal Instability in Three Dimensions

NASA Technical Reports Server (NTRS)

Mok, Yung; Mikic, Zoran; Lionello, Roberto; Linker, Jon A.

2008-01-01

Plasma loops in solar active regions have been observed in EUV and soft X-rays for decades. Their formation mechanism and properties, however, are still not fully understood. Predictions by early models, based on 1D hydrostatic equilibria with uniform plasma heating, are not consistent with high-resolution measurements. In this Letter, we demonstrate, via 3D simulations, that a class of heating models can lead to the dynamic formation of plasma loops provided the plasma is heated sufficiently to match SXT soft X-ray measurements. We show that individual flux tubes in a 3D magnetic structure tend to stand out against their neighbors. The loops have large aspect ratios and nearly uniform cross sections in the corona, similar to those observed by EIT and TRACE. The coronal EUV emission from these thermally unstable solutions is roughly consistent with EIT measurements. The solution oscillates in time through a large-amplitude, nonlinear cycle, leading to repeated brightening and fading of the loops.

Exchange-coupling of hard and soft magnetic sublattices and magnetic anomalies in mixed spinel NiFe0.75Cr1.25O4 nanoparticles

NASA Astrophysics Data System (ADS)

Lyubutin, I. S.; Starchikov, S. S.; Baskakov, A. O.; Gervits, N. E.; Lin, Chun-Rong; Tseng, Yaw-Teng; Lee, Wen-Jen; Shih, Kun-Yauh

2018-04-01

A set of single-crystalline nanoparticles (NPs) of nickel-chromium ferrite NiFe0.75Cr1.25O4 with a cubic spinel structure were synthesized and investigated. The NPs size can be varied from about 5 to 50 nm by the final annealing of the precursor at different temperatures. The distribution of cations over the tetrahedral (A) and the octahedral [B] sites (Fe0.75 Ni0.25) [Ni0.75 Cr1.25] O4 was established from the magnetic and Mössbauer measurements. In large NPs, the magnetic structure at low temperatures is close to the collinear antiferromagnetic (AFM) structure of the Neel type; and the total magnetic moment Mtot of the ferrite coincides with the direction of the B-sublattice moment. Several size-dependent magnetic anomalies were revealed. Three types of magnetic ions present in the A- and B- sublattices cause the competition of AFM and FM exchange interactions resulting in the highly frustrated magnetic ordering and the occurrence of canted magnetic structure in the octahedral B-sublattice. The frustrated structure is very flexible and significantly subjected to temperature and applied field. It results in several magnetic anomalies observed, including the occurrence of magnetic compensation, abnormal behavior of ZFC and FC magnetization curves and hysteresis loops. It was shown that magnetic anomalies can be explained in terms of exchange coupling of "soft" and "hard" magnetic B- and A-sublattices. This effect in the (Fe0.75 Ni0.25) [Ni0.75Cr1.25] O4 NPs can be considered as an atomic-scale analog of a similar effect observed in two-phase exchange-coupled alloys developed for permanent magnets and for the perpendicular recoding media.

Influence of samarium substitution on the structural and magnetic properties of M-type hexagonal ferrites

NASA Astrophysics Data System (ADS)

Yasmin, Nazia; Mirza, Misbah; Muhammad, Safdar; Zahid, Maria; Ahmad, Mukhtar; Awan, M. S.; Muhammad, Altaf

2018-01-01

The M-type hexagonal ferrites with chemical formula SrFe12-xSmxO19 (x = 0, 0.01, 0.02, 0.03) were synthesized via sol-gel method. We studied the effects of substitution of rare earth on the structural and magnetic temperament of M-type hexaferrites. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) strategies are employed for the systematical examination of micrographs and structures of the samples. The magnetic particularities are studied by the use of vibrating sample magnetometery. The M-H loops are used to investigate the hard magnetic behavior of all the samples. The substantial value of coercivity (>1 kOe) for all the samples shows that the particular sample is permanent magnet and reveals the hard magnetic action. It is observed that values of saturation magnetization (Mr) and remanence (Ms) decline with increasing the rare earth ions substitution. This decrease may follow spin canting and the magnetic dilution, which results in dislocation of superexchange interactions. The improvement in Hc may be because of large anisotropy of magnetocrystalline, where ion anisotropy of Fe2+ ion on the 2a site probably overriding in all hexaferrites series. The synthesized composites were useful for applications in magnetic microwave absorbing materials.

Structural and magnetic study of La0.7Sr0.3MnO3 nanoparticles and AC magnetic heating characteristics for hyperthermia applications

NASA Astrophysics Data System (ADS)

Manh, D. H.; Phong, P. T.; Nam, P. H.; Tung, D. K.; Phuc, N. X.; Lee, In-Ja

We investigated structural and magnetic properties and alternating current magnetic heating characteristics of La0.7Sr0.3MnO3 nanoparticles with respect to the possible application for magnetic hyperthermia treatments. Using Rietveld Profile refinement of powder X-ray diffraction data, the hexagonal structure has been observed. The particle sizes varied from 20 to 50 nm as the annealing temperature increases from 700 to 900 °C. The hysteresis loop is not observed and the good fit of Langevin function with magnetization data reveals the superparamagnetic nature at room temperature for all samples. Characteristic magnetic parameters of the particles including saturation magnetization in the temperature range 10-300 K, an effective anisotropy constant and a magnetocrystalline anisotropy constant have been determined. The Specific Absorption Rate for 15 mg/mL sample concentration was measured in alternating magnetic fields of 50-80 Oe at a fixed frequency of 236 kHz. In addition, the intrinsic loss power (ILP) has been calculated from SAR values. It is believed that La0.7Sr0.3MnO3 nanoparticles with a high ILP will be useful for the in situ hyperthermia treatment of cancer.

Effects of aluminum substitution on the crystal structure and magnetic properties in Zn{sub 2}Y-type hexaferrites

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Wenfei; Yang, Jing, E-mail: jyang@ee.ecnu.edu.cn, E-mail: xdtang@sist.ecnu.edu.cn; Bai, Wei

2015-05-07

Crystal structure and magnetic properties of multiferroic Y-type hexaferrites Ba{sub 0.5}Sr{sub 1.5}Zn{sub 2}(Fe{sub 1−x}Al{sub x}){sub 12}O{sub 22} (x = 0, 0.04, 0.08, and 0.12) were investigated. The Z- and M-type impurity phases decrease with increasing Al content, and the pure phase samples can be obtained by modulating Al-doping. Lattice distortion exists in Al-doped samples due to the different radius of Al ion (0.535 Å) and Fe ion (0.645 Å). The microstructural morphologies show that the hexagonal shape grains can be observed in all the samples, and grain size decreases with increasing Al content. As for magnetic properties of Ba{sub 0.5}Sr{sub 1.5}Zn{sub 2}(Fe{sub 1−x}Al{sub x}){submore » 12}O{sub 22}, there exist rich thermal- and field-driven magnetic phase transitions. Temperature dependence of zero-field cooling magnetization curves from 5 K to 800 K exhibit three magnetic phase transitions involving conical spin phase, proper-screw spin phase, ferromagnetic phase, and paramagnetic phase, which can be found in all the samples. Furthermore, the phase-transition temperatures can be modulated by varying Al content. In addition, four kinds of typical hysteresis loops are observed in pure phase sample at different temperatures, which reveal different magnetization processes of above-motioned magnetic spin structures. Typically, triple hysteresis loops in low magnetic field range from 0 to 0.5 T can be observed at 5 K, which suggests low-field driven magnetic phase transitions from conical spin order to proper-screw spin order and further to ferrimagnetic spin order occur. Furthermore, the coercive field (H{sub C}) and the saturation magnetization (M{sub S}) enhance with increasing Al content from x = 0 to 0.08, and drop rapidly at x = 0.12, which could be attribute to that in initial Al-doped process the pitch of spin helix increases and therefore magnetization enhances, but conical spin phase eventually collapses in higher-concentration Al-doping.« less

Loop quantum corrected Einstein Yang-Mills black holes

NASA Astrophysics Data System (ADS)

Protter, Mason; DeBenedictis, Andrew

2018-05-01

In this paper, we study the homogeneous interiors of black holes possessing SU(2) Yang-Mills fields subject to corrections inspired by loop quantum gravity. The systems studied possess both magnetic and induced electric Yang-Mills fields. We consider the system of equations both with and without Wilson loop corrections to the Yang-Mills potential. The structure of the Yang-Mills Hamiltonian, along with the restriction to homogeneity, allows for an anomaly-free effective quantization. In particular, we study the bounce which replaces the classical singularity and the behavior of the Yang-Mills fields in the quantum corrected interior, which possesses topology R ×S2 . Beyond the bounce, the magnitude of the Yang-Mills electric field asymptotically grows monotonically. This results in an ever-expanding R sector even though the two-sphere volume is asymptotically constant. The results are similar with and without Wilson loop corrections on the Yang-Mills potential.

Surface and exchange-bias effects in compacted CaMnO3-δ nanoparticles

NASA Astrophysics Data System (ADS)

Markovich, V.; Fita, I.; Wisniewski, A.; Puzniak, R.; Mogilyansky, D.; Titelman, L.; Vradman, L.; Herskowitz, M.; Gorodetsky, G.

2008-02-01

Magnetic properties of compacted 50nm CaMnO3-δ (CMO) nanoparticles have been investigated. Measurements of ac-susceptibility exhibit upon cooling two magnetic transitions at Ttilde 270K accompanied by a small spontaneous magnetic moment and a para-antiferromagnetic (AFM) transition at TN˜120K , observed previously in bulk CMO. Asymmetric magnetization hysteresis loops observed in applied magnetic fields H≤90kOe are attributed to an exchange coupling between the antiferromagnetic core and the ferromagnetic (FM) shell of the CMO nanoparticles. This work provides the observation of exchange bias effect in manganite nanoparticles with inverted AFM-core-FM-shell structure, as compared to the typical FM-core-AFM-shell. Effects of surface and exchange anisotropy are also discussed.

Effect of Loop Geometry on TEM Response Over Layered Earth

NASA Astrophysics Data System (ADS)

Qi, Youzheng; Huang, Ling; Wu, Xin; Fang, Guangyou; Yu, Gang

2014-09-01

A large horizontal loop located on the ground or carried by an aircraft are the most common sources of the transient electromagnetic method. Although topographical factors or airplane outlines make the loop of arbitrary shape, magnetic sources are generally represented as a magnetic dipole or a circular loop, which may bring about significant errors in the calculated response. In this paper, we present a method for calculating the response of a loop of arbitrary shape (for which the description can be obtained by different methods, including GPS localization) in air or on the surface of a stratified earth. The principle of reciprocity is firstly used to exchange the functions of the transmitting loop and the dipole receiver, then the response of a vertical or a horizontal magnetic dipole is calculated beforehand, and finally the line integral of the second kind is employed to get the transient response. Analytical analysis and comparisons depict that our work got very good results in many situations. Synthetic and field examples are given in the end to show the effect of loop geometry and how our method improves the precision of the EM response.

The formation flare loops by magnetic reconnection and chromospheric ablation

NASA Technical Reports Server (NTRS)

Forbes, T. G.; Malherbe, J. M.; Priest, E. R.

1989-01-01

Noncoplanar compressible reconnection theory is combined here with simple scaling arguments for ablation and radiative cooling to predict average properties of hot and cool flare loops as a function of the coronal vector magnetic field. For a coronal field strength of 100 G, the temperature of the hot flare loops decreases from 1.2 x 10 to the 7th K to 4.0 x 10 to the 6th K as the component of the coronal magnetic field perpendicular to the plane of the loops increases from 0 percent to 86 percent of the total field. When the perpendicular component exceeds 86 percent of the total field or when the altitude of the reconnection site exceeds 10 to the 6th km, flare loops no longer occur. Shock-enhanced radiative cooling triggers the formation of cool H-alpha flare loops with predicted densities of roughly 10 to the 13th/cu cm, and a small gap of roughly 1000 km is predicted to exist between the footpoints of the cool flare loops and the inner edges of the flare ribbons.

Temperature evolution of a magnetic flux rope in a failed solar eruption

DOE Office of Scientific and Technical Information (OSTI.GOV)

Song, H. Q.; Chen, Y.; Li, B.

2014-03-20

In this paper, we report for the first time the detailed temperature evolution process of the magnetic flux rope in a failed solar eruption. Occurring on 2013 January 05, the flux rope was impulsively accelerated to a speed of ∼400 km s{sup –1} in the first minute, then decelerated and came to a complete stop in two minutes. The failed eruption resulted in a large-size high-lying (∼100 Mm above the surface), high-temperature 'fire ball' sitting in the corona for more than two hours. The time evolution of the thermal structure of the flux rope was revealed through the differential emissionmore » measure analysis technique, which produced temperature maps using observations of the Atmospheric Imaging Assembly on board the Solar Dynamic Observatory. The average temperature of the flux rope steadily increased from ∼5 MK to ∼10 MK during the first nine minutes of the evolution, which was much longer than the rise time (about three minutes) of the associated soft X-ray flare. We suggest that the flux rope is heated by the energy release of the continuing magnetic reconnection, different from the heating of the low-lying flare loops, which is mainly produced by the chromospheric plasma evaporation. The loop arcade overlying the flux rope was pushed up by ∼10 Mm during the attempted eruption. The pattern of the velocity variation of the loop arcade strongly suggests that the failure of the eruption was caused by the strapping effect of the overlying loop arcade.« less

Modulation in magnetic exchange interaction, core shell structure and Hopkinson's peak with chromium substitution into Ni0.75Co0.25Fe2O4 nano particles

NASA Astrophysics Data System (ADS)

Uday Bhasker, S.; Choudary, G. S. V. R. K.; Reddy, M. V. Ramana

2018-05-01

The ever growing applications and ever evolving challenges of magnetic nano particles has been motivating the researchers from various disciplines towards this area of magnetic nano particles. Cation substitutional effect on the magnetic structure of the nanoparticles forms a crucial aspect in their applications. Here the environmentally benign auto combustion method was employed to synthesize chromium substituted nickel cobalt ferrite (Ni0.75Co0.25Fe2-xCrxO4; x = 0, 0.10, 0.15) nano particles, from aqueous metal nitrate solutions. Chromium substitution has shown its effect on the structural, magnetic and electrical properties of Ni0.75Co0.25Fe2O4. Structural and phase analysis of the prepared samples show increased phase purity of ferrite sample with increasing Cr substitution. The TEM (Transmission Electron Microscope) image confirms the nano size of the particles, EDS (Energy dispersive X-ray Spectroscopy) has supported the stoichiometry of the prepared samples and FTIR (Fourier-transform infrared spectroscopic) analysis confirms the spinel structure and also suggests cation redistributions with chromium substitution. VSM (Vibrational Sample Magnetometer) is used to study the magnetic properties through magnetic hysteresis (M-H) loop and magnetic Hopkinson effect. All samples show hysteresis and show reduction in magnetic properties with increase in chromium content. The thermo magnetic study shows Hopkinson peak(s) in the magnetization vs. temperature (M-T) graph and also shows variation in the nature of Hopkinson peak with chromium substitution. Possible reasons for the changes in the nature of the peak are discussed.

Size-dependent magnetic properties of FeGaB/Al2O3 multilayer micro-islands

NASA Astrophysics Data System (ADS)

Wang, X.; Gao, Y.; Chen, H.; Chen, Y.; Liang, X.; Lin, W.; Sun, N. X.

2018-06-01

Recently, micrometer-size patterned magnetic materials have been widely used in MEMS devices. However, the self-demagnetizing action is significantly influencing the performance of the magnetic materials in many MEMS devices. Here, we report an experimental study on the magnetic properties of the patterned micro-scale FeGaB/Al2O3 multilayers. Ferromagnetic hysteresis loop, ferromagnetic resonance (FMR), permeability and domain behavior have been demonstrated by complementary techniques. Magnetic annealing was used to enhance the performance of magnetic multilayers. The comparisons among micro-islands with different sizes in the range of 200 μm ∼ 500 μm as well as full film show a marked influence of size-effect, the exchange coupling effect, and the different domain structures inside the islands.

Spatial structure and temporal development of a solar X-ray flare observed from Skylab on June 15, 1973

NASA Technical Reports Server (NTRS)

Pallavicini, R.; Vaiana, G. S.; Kahler, S. W.; Krieger, A. S.

1975-01-01

Morphological and quantitative analyses are presented of a 1B solar flare that was observed with high spatial and temporal resolution by the S-054 grazing-incidence X-ray telescope aboard Skylab. It is found that the flare had the configuration of a compact region with a characteristic size of the order of 30 arcsec at the intensity peak, the interior of the region appeared to be highly structured and to consist of temporally changing complex loop systems, brightening over an extended part of the active region preceded the flare onset, and the impulsive phase was marked by rapid brightening in the loop structures. The X-ray photographs also indicate that the X-ray emission was centered over the neutral line of the longitudinal magnetic field, loop systems formed at successively increasing heights during the decay phase, and different regions of the flare had distinctly different light curves. The flux profiles for the different regions are shown to suggest continued heating during the decay phase. It is concluded that flare models should be based on a multiplicity of volumes ordered in loops of successively larger scale lengths and heights rather than on a single point of energy release and deposition.

Portable battery-free charger for radiation dosimeters

DOEpatents

Manning, Frank W.

1984-01-01

This invention is a novel portable charger for dosimeters of the electrometer type. The charger does not require batteries or piezoelectric crystals and is of rugged construction. In a preferred embodiment, the charge includes a housing which carries means for mounting a dosimeter to be charged. The housing also includes contact means for impressing a charging voltage across the mounted dosimeter. Also, the housing carries a trigger for operating a charging system mounted in the housing. The charging system includes a magnetic loop including a permanent magnet for establishing a magnetic field through the loop. A segment of the loop is coupled to the trigger for movement thereby to positions opening and closing the loop. A coil inductively coupled with the loop generates coil-generated voltage pulses when the trigger is operated to open and close the loop. The charging system includes an electrical circuit for impressing voltage pulses from the coil across a capacitor for integrating the pulses and applying the resulting integrated voltage across the above-mentioned contact means for charging the dosimeter.

Structure and magnetic properties of the Nd9.5Fe84.5B6 alloy subjected to severe plastic deformation and annealing

NASA Astrophysics Data System (ADS)

Menushenkov, V. P.; Shchetinin, I. V.; Chernykh, S. V.; Savchenko, A. G.; Gorshenkov, M. V.; Zhukov, D. G.

2017-10-01

The effect of severe plastic deformation (SPD) by torsion and subsequent annealing on the structure and magnetic properties of the cast Nd9.5Fe84.5B6 alloy is studied. SPD by torsion is shown to lead to partial amorphization of the Nd2Fe14B phase and the precipitation of α-Fe; subsequent annealing results in the crystallization of the amorphous phase and the formation of a nanocomposite Nd2Fe14B/α-Fe structure. After SPD by torsion at 20 revolutions and annealing at 873 K, the (101) texture is formed; in this case, the coercive force is H c = 360 kA/m and the maximum energy product is ( BH) max = 166 kJ/m3. The residual magnetization and the squareness ratio of the hysteretic loop of the textured alloy decrease as the ambient temperature decreases.

Hysteresis losses and specific absorption rate measurements in magnetic nanoparticles for hyperthermia applications.

PubMed

Coïsson, Marco; Barrera, Gabriele; Celegato, Federica; Martino, Luca; Kane, Shashank N; Raghuvanshi, Saroj; Vinai, Franco; Tiberto, Paola

2017-06-01

Magnetic hysteresis loops areas and hyperthermia on magnetic nanoparticles have been studied with the aim of providing reliable and reproducible methods of measuring the specific absorption rate (SAR). The SAR of Fe 3 O 4 nanoparticles with two different mean sizes, and Ni 1-x Zn x Fe 2 O 4 ferrites with 0 ≤ x ≤ 0.8 has been measured with three approaches: static hysteresis loops areas, dynamic hysteresis loops areas and hyperthermia of a water solution. For dynamic loops and thermometric measurements, specific experimental setups have been developed, that operate at comparable frequencies (≈ 69kHz and ≈ 100kHz respectively) and rf magnetic field peak values (up to 100mT). The hyperthermia setup has been fully modelled to provide a direct measurement of the SAR of the magnetic nanoparticles by taking into account the heat exchange with the surrounding environment in non-adiabatic conditions and the parasitic heating of the water due to ionic currents. Dynamic hysteresis loops are shown to provide an accurate determination of the SAR except for superparamagnetic samples, where the boundary with a blocked regime could be crossed in dynamic conditions. Static hysteresis loops consistently underestimate the specific absorption rate but can be used to select the most promising samples. A means of reliably measure SAR of magnetic nanoparticles by different approaches for hyperthermia applications is presented and its validity discussed by comparing different methods. This work fits within the general subject of metrological traceability in medicine with a specific focus on magnetic hyperthermia. This article is part of a Special Issue entitled "Recent Advances in Bionanomaterials" Guest Editor: Dr. Marie-Louise Saboungi and Dr. Samuel D. Bader. Copyright © 2016 Elsevier B.V. All rights reserved.

A SOLAR TORNADO OBSERVED BY AIA/SDO: ROTATIONAL FLOW AND EVOLUTION OF MAGNETIC HELICITY IN A PROMINENCE AND CAVITY

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, Xing; Morgan, Huw; Leonard, Drew

During 2011 September 24, as observed by the Atmospheric Imaging Assembly instrument of the Solar Dynamic Observatory and ground-based H{alpha} telescopes, a prominence and associated cavity appeared above the southwest limb. On 2011 September 25 8:00 UT, material flows upward from the prominence core along a narrow loop-like structure, accompanied by a rise ({>=}50,000 km) of the prominence core and the loop. As the loop fades by 10:00, small blobs and streaks of varying brightness rotate around the top part of the prominence and cavity, mimicking a cyclone. The most intense and coherent rotation lasts for over three hours, withmore » emission in both hot ({approx}1 MK) and cold (hydrogen and helium) lines. We suggest that the cyclonic appearance and overall evolution of the structure can be interpreted in terms of the expansion of helical structures into the cavity, and the movement of plasma along helical structures which appears as a rotation when viewed along the helix axis. The coordinated movement of material between prominence and cavity suggests that they are structurally linked. Complexity is great due to the combined effect of these actions and the line-of-sight integration through the structure which contains tangled fields.« less

Rapid liquid phase sintered Mn doped BiFeO3 ceramics with enhanced polarization and weak magnetization

NASA Astrophysics Data System (ADS)

Kumar, Manoj; Yadav, K. L.

2007-12-01

Single-phase BiFe1-xMnxO3 multiferroic ceramics have been synthesized by rapid liquid phase sintering method to study the influence of Mn substitution on their crystal structure, dielectric, magnetic, and ferroelectric behaviors. From XRD analysis it is seen that Mn substitution does not affect the crystal structure of the BiFe1-xMnxO3 system. An enhancement in magnetization was observed for BiFe1-xMnxO3 ceramics. However, the ferooelectric hysteresis loops were not really saturated, we observed a spontaneous polarization of 10.23μC /cm2 under the applied field of 42kV/cm and remanent polarization of 3.99μC/cm2 for x =0.3 ceramic.

Hepatitis B virus nuclear export elements: RNA stem-loop α and β, key parts of the HBV post-transcriptional regulatory element.

PubMed

Lim, Chun Shen; Brown, Chris M

2016-09-01

Many viruses contain RNA elements that modulate splicing and/or promote nuclear export of their RNAs. The RNAs of the major human pathogen, hepatitis B virus (HBV) contain a large (~600 bases) composite cis-acting 'post-transcriptional regulatory element' (PRE). This element promotes expression from these naturally intronless transcripts. Indeed, the related woodchuck hepadnavirus PRE (WPRE) is used to enhance expression in gene therapy and other expression vectors. These PRE are likely to act through a combination of mechanisms, including promotion of RNA nuclear export. Functional components of both the HBV PRE and WPRE are 2 conserved RNA cis-acting stem-loop (SL) structures, SLα and SLβ. They are within the coding regions of polymerase (P) gene, and both P and X genes, respectively. Based on previous studies using mutagenesis and/or nuclear magnetic resonance (NMR), here we propose 2 covariance models for SLα and SLβ. The model for the 30-nucleotide SLα contains a G-bulge and a CNGG(U) apical loop of which the first and the fourth loop residues form a CG pair and the fifth loop residue is bulged out, as observed in the NMR structure. The model for the 23-nucleotide SLβ contains a 7-base-pair stem and a 9-nucleotide loop. Comparison of the models with other RNA structural elements, as well as similarity searches of human transcriptome and viral genomes demonstrate that SLα and SLβ are specific to HBV transcripts. However, they are well conserved among the hepadnaviruses of non-human primates, the woodchuck and ground squirrel.

Hepatitis B virus nuclear export elements: RNA stem-loop α and β, key parts of the HBV post-transcriptional regulatory element

PubMed Central

Lim, Chun Shen; Brown, Chris M.

2016-01-01

ABSTRACT Many viruses contain RNA elements that modulate splicing and/or promote nuclear export of their RNAs. The RNAs of the major human pathogen, hepatitis B virus (HBV) contain a large (~600 bases) composite cis-acting 'post-transcriptional regulatory element' (PRE). This element promotes expression from these naturally intronless transcripts. Indeed, the related woodchuck hepadnavirus PRE (WPRE) is used to enhance expression in gene therapy and other expression vectors. These PRE are likely to act through a combination of mechanisms, including promotion of RNA nuclear export. Functional components of both the HBV PRE and WPRE are 2 conserved RNA cis-acting stem-loop (SL) structures, SLα and SLβ. They are within the coding regions of polymerase (P) gene, and both P and X genes, respectively. Based on previous studies using mutagenesis and/or nuclear magnetic resonance (NMR), here we propose 2 covariance models for SLα and SLβ. The model for the 30-nucleotide SLα contains a G-bulge and a CNGG(U) apical loop of which the first and the fourth loop residues form a CG pair and the fifth loop residue is bulged out, as observed in the NMR structure. The model for the 23-nucleotide SLβ contains a 7-base-pair stem and a 9-nucleotide loop. Comparison of the models with other RNA structural elements, as well as similarity searches of human transcriptome and viral genomes demonstrate that SLα and SLβ are specific to HBV transcripts. However, they are well conserved among the hepadnaviruses of non-human primates, the woodchuck and ground squirrel. PMID:27031749

Investigation on demagnetization of Nd2Fe14B permanent magnets induced by irradiation

NASA Astrophysics Data System (ADS)

Li, Zhefu; Jia, Yanyan; Liu, Renduo; Xu, Yuhai; Wang, Guanghong; Xia, Xiaobin

2017-12-01

Nd2Fe14B is an important component of insertion devices, which are used in synchrotron radiation sources, and could be demagnetized by irradiation. In the present study, the Monte Carlo code FLUKA was used to analyze the irradiation field of Nd2Fe14B, and it was confirmed that the main demagnetization particle was neutron. Nd2Fe14B permanent magnet samples were irradiated by Ar ions at different doses to simulate neutron irradiation damage. The hysteresis loops were measured using a vibrating sample magnetometer, and the microstructure evolutions were characterized by transmission electron microscopy. Moreover, the relationship between them was discussed. The results indicate that the decrease in saturated magnetization is caused by the changes in microstructure. The evolution of single crystals into an amorphous structure is the reason for the demagnetization phenomenon of Nd2Fe14B permanent magnets when considering its microscopic structure.

Macroscopic Floquet topological crystalline steel and superconductor pump

NASA Astrophysics Data System (ADS)

Rossi, Anna M. E. B.; Bugase, Jonas; Fischer, Thomas M.

2017-08-01

The transport of a macroscopic steel sphere and a superconducting sphere on top of two-dimensional periodic magnetic patterns is studied experimentally and compared with the theory and with experiments on topological transport of magnetic colloids. Transport of the steel and superconducting sphere is achieved by moving an external permanent magnet on a closed loop around the two-dimensional crystal. The transport is topological, i.e., the spheres are transported by a primitive unit vector of the lattice when the external magnet loop winds around specific directions. We experimentally determine the set of directions the loops must enclose for nontrivial transport of the spheres into various directions. We show that the loops can be used to sort steel and superconducting spheres. We show that the topological transport is robust with respect to the scale of the system and therefore speculate on its down scalability to the molecular scale.

Research on hysteresis loop considering the prestress effect and electrical input dynamics for a giant magnetostrictive actuator

NASA Astrophysics Data System (ADS)

Zhu, Yuchuan; Yang, Xulei; Wereley, Norman M.

2016-08-01

In this paper, focusing on the application-oriented giant magnetostrictive material (GMM)-based electro-hydrostatic actuator, which features an applied magnetic field at high frequency and high amplitude, and concentrating on the static and dynamic characteristics of a giant magnetostrictive actuator (GMA) considering the prestress effect on the GMM rod and the electrical input dynamics involving the power amplifier and the inductive coil, a methodology for studying the static and dynamic characteristics of a GMA using the hysteresis loop as a tool is developed. A GMA that can display the preforce on the GMM rod in real-time is designed, and a magnetostrictive model dependent on the prestress on a GMM rod instead of the existing quadratic domain rotation model is proposed. Additionally, an electrical input dynamics model to excite GMA is developed according to the simplified circuit diagram, and the corresponding parameters are identified by the experimental data. A dynamic magnetization model with the eddy current effect is deduced according to the Jiles-Atherton model and the Maxwell equations. Next, all of the parameters, including the electrical input characteristics, the dynamic magnetization and the mechanical structure of GMA, are identified by the experimental data from the current response, magnetization response and displacement response, respectively. Finally, a comprehensive comparison between the model results and experimental data is performed, and the results show that the test data agree well with the presented model results. An analysis on the relation between the GMA displacement response and the parameters from the electrical input dynamics, magnetization dynamics and mechanical structural dynamics is performed.

Quasi-static evolution of coronal magnetic fields

NASA Technical Reports Server (NTRS)

Longcope, D. W.; Sudan, R. N.

1992-01-01

A formalism is developed to describe the purely quasi-static part of the evolution of a coronal loop driven by its footpoints. This is accomplished under assumptions of a long, thin loop. The quasi-static equations reveal the possibility for sudden 'loss of equilibrium' at which time the system evolves dynamically rather than quasi-statically. Such quasi-static crises produce high-frequency Alfven waves and, in conjunction with Alfven wave dissipation models, form a viable coronal heating mechanism. Furthermore, an approximate solution to the quasi-static equations by perturbation method verifies the development of small-scale spatial current structure.

Electron acceleration and radiation signatures in loop coronal transients

NASA Technical Reports Server (NTRS)

Vlahos, L.; Gergely, T. E.; Papadopoulos, K.

1982-01-01

It is proposed that in loop coronal transients an erupting loop moves away from the solar surface, with a velocity exceeding the local Alfven speed, pushing against the overlying magnetic fields and driving a shock in the front of the moving part of the loop. Lower hybrid waves are excited at the shock front and propagate radially toward the center of the loop with phase velocity along the magnetic field that exceeds the thermal velocity. The lower hybrid waves stochastically accelerate the tail of the electron distribution inside the loop. The manner in which the accelerated electrons are trapped in the moving loop are discussed, and their radiation signature is estimated. It is suggested that plasma radiation can explain the power observed in stationary and moving type IV bursts.

Circuitry, systems and methods for detecting magnetic fields

DOEpatents

Kotter, Dale K [Shelley, ID; Spencer, David F [Idaho Falls, ID; Roybal, Lyle G [Idaho Falls, ID; Rohrbaugh, David T [Idaho Falls, ID

2010-09-14

Circuitry for detecting magnetic fields includes a first magnetoresistive sensor and a second magnetoresistive sensor configured to form a gradiometer. The circuitry includes a digital signal processor and a first feedback loop coupled between the first magnetoresistive sensor and the digital signal processor. A second feedback loop which is discrete from the first feedback loop is coupled between the second magnetoresistive sensor and the digital signal processor.

Reconnection Outflows in the Extended Corona and Magnetotail

NASA Astrophysics Data System (ADS)

Savage, Sabrina; Kobelski, Adam

2017-08-01

Observational signatures of reconnection have been studied extensively in the lower corona for decades, successfully providing insight into energy release mechanisms in the region above post-flare arcade loops and below 1.5 solar radii. During large eruptive events, however, energy release continues to occur well beyond the presence of reconnection signatures at these low heights. Supra-arcade downflows (SADs) and downflowing loops (SADLs) are particularly useful measures of continual reconnection in the corona as they may indicate the presence and path of retracting post-reconnection loops. SADs and SADLs have been observed for days beyond the passage of corona mass ejections through the SOHO/LASCO field of view and for nearly a week after an eruption on 14 October 2014. The association of these features with magnetic reconnection increases the significance of understanding their genesis. SADs have been interpreted as wakes behind newly reconnected and outflowing loops (SADLs). Models have shown the plausibility of this interpretation, though this interpretation has not yet been fully accepted. We will present a preliminary study of complementary observations of magnetic reconnection detected via in situ instruments in the magnetosphere. These observations, provided by five THEMIS spacecraft, reveal similar structures and conditions to those related to SADs. We compare data from multiple SADs and dipolarization fronts to test the similarity between these plasma regimes, strongly favoring the interpretation of SADs as instabilities trailing retracting loops. We will also use these observations to strengthen the case for the development of an EUV wide-field coronal imager.

Switching dynamics of doped CoFeB trilayers and a comparison to the quasistatic approximation

NASA Astrophysics Data System (ADS)

Forrester, Michael; Kusmartsev, Feodor; Kovács, Endre

2013-05-01

The investigation of the switching times of the magnetization reversal of two interacting CoFeB nanomagnets, with dimensions small enough to maintain a single-domain structure, has been carried out. A quasistatic approximation is shown to give valid results and to compare well to the damped dynamical solutions of the Landau-Lifshitz-Gilbert equations. The characteristics of the switching are shown in the associated hysteresis loops and we build a complete phase diagram of the various parallel, antiparallel, and scissoring states of the magnetization in terms of the coupling energy between the nanomagnets, magnetic anisotropy, and the interaction with an applied magnetic field. The phase diagram summarizes the different kinds of hysteresis associated with the magnetization reversal phenomena. The switching fields and times are estimated and the vulnerabilities of the magnetic phases to thermally induced magnetic field variations are examined. The stability of the phases is a fine balance between intrinsic and extrinsic magnetism and we examine its precarious nature. Our work identifies the structures that have the most robust magnetization states and hence a design ethic for creating nanomagnetic heterostructures with outstanding magnetoresistance properties based upon the two magnetic elements.

Magnetic vortex chirality determination via local hysteresis loops measurements with magnetic force microscopy

PubMed Central

Coïsson, Marco; Barrera, Gabriele; Celegato, Federica; Manzin, Alessandra; Vinai, Franco; Tiberto, Paola

2016-01-01

Magnetic vortex chirality in patterned square dots has been investigated by means of a field-dependent magnetic force microscopy technique that allows to measure local hysteresis loops. The chirality affects the two loop branches independently, giving rise to curves that have different shapes and symmetries as a function of the details of the magnetisation reversal process in the square dot, that is studied both experimentally and through micromagnetic simulations. The tip-sample interaction is taken into account numerically, and exploited experimentally, to influence the side of the square where nucleation of the vortex preferably occurs, therefore providing a way to both measure and drive chirality with the present technique. PMID:27426442

Magnetic vortex chirality determination via local hysteresis loops measurements with magnetic force microscopy.

PubMed

Coïsson, Marco; Barrera, Gabriele; Celegato, Federica; Manzin, Alessandra; Vinai, Franco; Tiberto, Paola

2016-07-18

Magnetic vortex chirality in patterned square dots has been investigated by means of a field-dependent magnetic force microscopy technique that allows to measure local hysteresis loops. The chirality affects the two loop branches independently, giving rise to curves that have different shapes and symmetries as a function of the details of the magnetisation reversal process in the square dot, that is studied both experimentally and through micromagnetic simulations. The tip-sample interaction is taken into account numerically, and exploited experimentally, to influence the side of the square where nucleation of the vortex preferably occurs, therefore providing a way to both measure and drive chirality with the present technique.

Magnetic vortex chirality determination via local hysteresis loops measurements with magnetic force microscopy

NASA Astrophysics Data System (ADS)

Coïsson, Marco; Barrera, Gabriele; Celegato, Federica; Manzin, Alessandra; Vinai, Franco; Tiberto, Paola

2016-07-01

Magnetic vortex chirality in patterned square dots has been investigated by means of a field-dependent magnetic force microscopy technique that allows to measure local hysteresis loops. The chirality affects the two loop branches independently, giving rise to curves that have different shapes and symmetries as a function of the details of the magnetisation reversal process in the square dot, that is studied both experimentally and through micromagnetic simulations. The tip-sample interaction is taken into account numerically, and exploited experimentally, to influence the side of the square where nucleation of the vortex preferably occurs, therefore providing a way to both measure and drive chirality with the present technique.

Compact solar UV burst triggered in a magnetic field with a fan-spine topology

NASA Astrophysics Data System (ADS)

Chitta, L. P.; Peter, H.; Young, P. R.; Huang, Y.-M.

2017-09-01

Context. Solar ultraviolet (UV) bursts are small-scale features that exhibit intermittent brightenings that are thought to be due to magnetic reconnection. They are observed abundantly in the chromosphere and transition region, in particular in active regions. Aims: We investigate in detail a UV burst related to a magnetic feature that is advected by the moat flow from a sunspot towards a pore. The moving feature is parasitic in that its magnetic polarity is opposite to that of the spot and the pore. This comparably simple photospheric magnetic field distribution allows for an unambiguous interpretation of the magnetic geometry leading to the onset of the observed UV burst. Methods: We used UV spectroscopic and slit-jaw observations from the Interface Region Imaging Spectrograph (IRIS) to identify and study chromospheric and transition region spectral signatures of said UV burst. To investigate the magnetic topology surrounding the UV burst, we used a two-hour-long time sequence of simultaneous line-of-sight magnetograms from the Helioseismic and Magnetic Imager (HMI) and performed data-driven 3D magnetic field extrapolations by means of a magnetofrictional relaxation technique. We can connect UV burst signatures to the overlying extreme UV (EUV) coronal loops observed by the Atmospheric Imaging Assembly (AIA). Results: The UV burst shows a variety of extremely broad line profiles indicating plasma flows in excess of ±200 km s-1 at times. The whole structure is divided into two spatially distinct zones of predominantly up- and downflows. The magnetic field extrapolations show a persistent fan-spine magnetic topology at the UV burst. The associated 3D magnetic null point exists at a height of about 500 km above the photosphere and evolves co-spatially with the observed UV burst. The EUV emission at the footpoints of coronal loops is correlated with the evolution of the underlying UV burst. Conclusions: The magnetic field around the null point is sheared by photospheric motions, triggering magnetic reconnection that ultimately powers the observed UV burst and energises the overlying coronal loops. The location of the null point suggests that the burst is triggered low in the solar chromosphere. Movies associated to Figs. 2 and 4 are available at http://www.aanda.org

Neutral-Line Magnetic Shear and Enhanced Coronal Heating in Solar Active Regions

NASA Technical Reports Server (NTRS)

Falconer, D. A.; Moore, R. L.; Porter, J. G.; Gary, G. A.; Shimizu, T.

1997-01-01

By examining the magnetic structure at sites in the bright coronal interiors of active regions that are not flaring but exhibit persistent strong coronal heating, we establish some new characteristics of the magnetic origins of this heating. We have examined the magnetic structure of these sites in five active regions, each of which was well observed by both the Yohkoh SXT and the Marshall Space Flight Center Vector Magnetograph and showed strong shear in its magnetic field along part of at least one neutral line (polarity inversion). Thus, we can assess whether this form of nonpotential field structure in active regions is a characteristic of the enhanced coronal heating and vice versa. From 27 orbits' worth of Yohkoh SXT images of the five active regions, we have obtained a sample of 94 persistently bright coronal features (bright in all images from a given orbit), 40 long (greater than or approximately equals 20,000 km) neutral-line segments having strong magnetic shear throughout (shear angle greater than 45 deg), and 39 long neutral-line segments having weak magnetic shear throughout (shear angle less than 45 deg). From this sample, we find that: (1) all of our persistently bright coronal features are rooted in magnetic fields that are stronger than 150 G; (2) nearly all (95%) of these enhanced coronal features are rooted near neutral lines (closer than 10,000 km); (3) a great majority (80%) of the bright features are rooted near strong-shear portions of neutral lines; (4) a great majority (85%) of long strong-shear segments of neutral lines have persistently bright coronal features rooted near them; (5) a large minority (40%) of long weak-shear segments of neutral lines have persistently bright coronal features rooted near them; and (6) the brightness of a persistently bright Coronal feature often changes greatly over a few hours. From these results, we conclude that most persistent enhanced heating of coronal loops in active regions: (1) requires the presence of a polarity inversion in the magnetic field near at least one of the loop footpoints; (2) is greatly aided by the presence of strong shear in the core magnetic field along that neutral line; and (3) is controlled by some variable process that acts in this magnetic environment. We infer that this variable process is low-lying reconnection accompanying flux cancellation.

Electromagnetically Clean Solar Arrays

NASA Technical Reports Server (NTRS)

Stem, Theodore G.; Kenniston, Anthony E.

2008-01-01

The term 'electromagnetically clean solar array' ('EMCSA') refers to a panel that contains a planar array of solar photovoltaic cells and that, in comparison with a functionally equivalent solar-array panel of a type heretofore used on spacecraft, (1) exhibits less electromagnetic interferences to and from other nearby electrical and electronic equipment and (2) can be manufactured at lower cost. The reduction of electromagnetic interferences is effected through a combination of (1) electrically conductive, electrically grounded shielding and (2) reduction of areas of current loops (in order to reduce magnetic moments). The reduction of cost is effected by designing the array to be fabricated as a more nearly unitary structure, using fewer components and fewer process steps. Although EMCSAs were conceived primarily for use on spacecraft they are also potentially advantageous for terrestrial applications in which there are requirements to limit electromagnetic interference. In a conventional solar panel of the type meant to be supplanted by an EMCSA panel, the wiring is normally located on the back side, separated from the cells, thereby giving rise to current loops having significant areas and, consequently, significant magnetic moments. Current-loop geometries are chosen in an effort to balance opposing magnetic moments to limit far-0field magnetic interactions, but the relatively large distances separating current loops makes full cancellation of magnetic fields problematic. The panel is assembled from bare photovoltaic cells by means of multiple sensitive process steps that contribute significantly to cost, especially if electomagnetic cleanliness is desired. The steps include applying a cover glass and electrical-interconnect-cell (CIC) sub-assemble, connecting the CIC subassemblies into strings of series-connected cells, laying down and adhesively bonding the strings onto a panel structure that has been made in a separate multi-step process, and mounting the wiring on the back of the panel. Each step increases the potential for occurrence of latent defects, loss of process control, and attrition of components. An EMCSA panel includes an integral cover made from a transparent material. The silicone cover supplants the individual cover glasses on the cells and serves as an additional unitary structural support that offers the advantage, relative to glass, of the robust, forgiving nature of the silcone material. The cover contains pockets that hold the solar cells in place during the lamination process. The cover is coated with indium tin oxide to make its surface electrically conductive, so that it serves as a contiguous, electrically grounded shield over the entire panel surface. The cells are mounted in proximity to metallic printed wiring. The painted-wiring layer comprises metal-film traces on a sheet of Kapton (or equivalent) polyimide. The traces include contact pads on one side of the sheet for interconnecting the cells. Return leads are on the opposite side of the sheet, positioned to form the return currents substantially as mirror images of, and in proximity to, the cell sheet currents, thereby minimizing magnetic moments. The printed-wiring arrangement mimics the back-wiring arrangement of conventional solar arrays, but the current-loop areas and the resulting magnetic moments are much smaller because the return-current paths are much closer to the solar-cell sheet currents. The contact pads are prepared with solder fo electrical and mechanical bonding to the cells. The pocketed cover/shield, the solar cells, the printed-wiring layer, an electrical bonding agent, a mechanical-bonding agent, a composite structural front-side face sheet, an aluminum honeycomb core, and a composite back-side face sheet are all assembled, then contact pads are soldered to the cells and the agents are cured in a single lamination process.

Magnetic and Structural Properties of A-Site Ordered Chromium Spinel Sulfides: Alternating Antiferromagnetic and Ferromagnetic Interactions in the Breathing Pyrochlore Lattice

NASA Astrophysics Data System (ADS)

Okamoto, Yoshihiko; Mori, Masaki; Katayama, Naoyuki; Miyake, Atsushi; Tokunaga, Masashi; Matsuo, Akira; Kindo, Koichi; Takenaka, Koshi

2018-03-01

We report a comprehensive study on the magnetic and structural properties of the spinel sulfides LiInCr4S8, LiGaCr4S8, and CuInCr4S8, where Li+/Cu+ and Ga3+/In3+ ions form a zinc-blende-type order. On the basis of synchrotron X-ray diffraction and magnetization data obtained using polycrystalline samples, these three sulfides are suggested to be breathing pyrochlore magnets with alternating antiferromagnetic and ferromagnetic interactions on the small and large tetrahedra, respectively. The measured magnetization processes of the three sulfides up to 72 T are significantly different. The magnetization curves of LiInCr4S8 and CuInCr4S8 have large hysteresis loops with different shapes, while there is no hysteresis in that of LiGaCr4S8. Geometrical frustration of the small tetrahedron is likely to give rise to a wide variety of ground states, indicating the rich physics in these antiferromagnetic-ferromagnetic breathing pyrochlore magnets.

Magnetic field homogeneity of a conical coaxial coil pair.

PubMed

Salazar, F J; Nieves, F J; Bayón, A; Gascón, F

2017-09-01

An analytical study of the magnetic field created by a double-conical conducting sheet is presented. The analysis is based on the expansion of the magnetic field in terms of Legendre polynomials. It is demonstrated analytically that the angle of the conical surface that produces a nearly homogeneous magnetic field coincides with that of a pair of loops that fulfills the Helmholtz condition. From the results obtained, we propose an electric circuit formed by pairs of isolated conducting loops tightly wound around a pair of conical surfaces, calculating numerically the magnetic field produced by this system and its heterogeneity. An experimental setup of the proposed circuit was constructed and its magnetic field was measured. The results were compared with those obtained by numerical calculation, finding a good agreement. The numerical results demonstrate a significant improvement in homogeneity in the field of the proposed pair of conical coils compared with that achieved with a simple pair of Helmholtz loops or with a double solenoid. Moreover, a new design of a double pair of conical coils based on Braunbek's four loops is also proposed to achieve greater homogeneity. Regarding homogeneity, the rating of the analyzed configurations from best to worst is as follows: (1) double pair of conical coils, (2) pair of conical coils, (3) Braunbek's four loops, (4) Helmholtz pair, and (5) solenoid pair.

Magnetic field homogeneity of a conical coaxial coil pair

NASA Astrophysics Data System (ADS)

Salazar, F. J.; Nieves, F. J.; Bayón, A.; Gascón, F.

2017-09-01

An analytical study of the magnetic field created by a double-conical conducting sheet is presented. The analysis is based on the expansion of the magnetic field in terms of Legendre polynomials. It is demonstrated analytically that the angle of the conical surface that produces a nearly homogeneous magnetic field coincides with that of a pair of loops that fulfills the Helmholtz condition. From the results obtained, we propose an electric circuit formed by pairs of isolated conducting loops tightly wound around a pair of conical surfaces, calculating numerically the magnetic field produced by this system and its heterogeneity. An experimental setup of the proposed circuit was constructed and its magnetic field was measured. The results were compared with those obtained by numerical calculation, finding a good agreement. The numerical results demonstrate a significant improvement in homogeneity in the field of the proposed pair of conical coils compared with that achieved with a simple pair of Helmholtz loops or with a double solenoid. Moreover, a new design of a double pair of conical coils based on Braunbek's four loops is also proposed to achieve greater homogeneity. Regarding homogeneity, the rating of the analyzed configurations from best to worst is as follows: (1) double pair of conical coils, (2) pair of conical coils, (3) Braunbek's four loops, (4) Helmholtz pair, and (5) solenoid pair.

A Magnetic Reconnection Event in the Solar Atmosphere Driven by Relaxation of a Twisted Arch Filament System

NASA Astrophysics Data System (ADS)

Huang, Zhenghua; Mou, Chaozhou; Fu, Hui; Deng, Linhua; Li, Bo; Xia, Lidong

2018-02-01

We present high-resolution observations of a magnetic reconnection event in the solar atmosphere taken with the New Vacuum Solar Telescope, Atmospheric Imaging Assembly (AIA), and Helioseismic and Magnetic Imager (HMI). The reconnection event occurred between the threads of a twisted arch filament system (AFS) and coronal loops. Our observations reveal that the relaxation of the twisted AFS drives some of its threads to encounter the coronal loops, providing inflows of the reconnection. The reconnection is evidenced by flared X-shape features in the AIA images, a current-sheet-like feature apparently connecting post-reconnection loops in the Hα + 1 Å images, small-scale magnetic cancelation in the HMI magnetograms and flows with speeds of 40–80 km s‑1 along the coronal loops. The post-reconnection coronal loops seen in the AIA 94 Å passband appear to remain bright for a relatively long time, suggesting that they have been heated and/or filled up by dense plasmas previously stored in the AFS threads. Our observations suggest that the twisted magnetic system could release its free magnetic energy into the upper solar atmosphere through reconnection processes. While the plasma pressure in the reconnecting flux tubes are significantly different, the reconfiguration of field lines could result in transferring of mass among them and induce heating therein.

Magnetization reversal processes in bonded magnets made from a mixture of Nd-(Fe,Co)-B and strontium ferrite powders

NASA Astrophysics Data System (ADS)

Dospial, M.; Plusa, D.

2013-03-01

Isotropic epoxy-resin bonded magnets composed of different amounts of Magnequench MQP-B and strontium ferrite powders have been prepared using a compression molding technique. The magnetic parameters for magnets with different amounts of strontium ferrite and magnetization reversal processes have been studied by the measurement of the initial magnetization curves, the major hysteresis loops measured at a field up to 14 T and sets of recoil loops. The enhancement of μ0MR and μ0HC is observed in comparison with the calculated values. From the recoil loops the field dependences of the reversible, irreversible and total magnetization components and the differential susceptibilities were derived. From the dependence of the irreversible magnetization component versus an applied field it was deduced that the main mechanism of magnetization reversal process is the pinning of domain walls in MQP-B and strontium ferrite grains. The interactions between the magnetic particles and grains have been examined by the analysis of the δM plot. The δM behavior of magnets with ferrite has been interpreted as being composed of magnetizing exchange coupling and demagnetizing dipolar interactions.

Strain control of giant magnetic anisotropy in metallic perovskite SrCoO3-δ thin films.

PubMed

Hu, Songbai; Cazorla, Claudio; Xiang, Feixiang; Ma, Hongfei; Wang, Jianyuan; Wang, Jianbo; Wang, Xiaolin; Ulrich, Clemens; Chen, Lang; Seidel, Jan

2018-06-08

Magnetic materials with large magnetic anisotropy are essential for workaday applications such as permanent magnets and magnetic data storage. There is widespread interest in finding efficient ways of controlling magnetic anisotropy, among which strain control has proven to be a very powerful technique. Here we demonstrate strain-mediated magnetic anisotropy in SrCoO3-δ thin film, a perovskite oxide that is metallic and adopts a cubic structure at δ ≤ 0.25. We find that the easy-magnetization axis in SrCoO3-δ can be rotated by 90º upon application of moderate epitaxial strains ranging from -1.2% to +1.8%. The magnetic anisotropy in compressive SrCoO3-δ thin films is giant as shown by magnetic hysteresis loops rendering an anisotropy energy density of ~106 erg/cm3. The local variance of magnetic force microscopy (MFM) upon temperature and magnetic field reveals that the evolution of magnetic domains in SCO thin film is strongly dependent on the magnetic anisotropy.

Zr doping dependence of structural and magnetic properties of cobalt ferrite synthesized by sol-gel based Pechini method

NASA Astrophysics Data System (ADS)

Motavallian, Pourya; Abasht, Behzad; Abdollah-Pour, Hassan

2018-04-01

Nanocrystalline CoZrxFe2-xO4 (0 ≤ x ≤ 0.3 in a step of 0.05) powders were synthesized by Pechini sol-gel method. The dry gel was grinded and calcined at 700 °C in a static air atmosphere for 1 h. Some tests such as thermo gravimetric analysis (TGA) combined with differential analysis (DTA), fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and vibrating sample magnetometer (VSM) were carried out to investigate the thermal behaviour, structural bonds identification, crystallographic properties, morphology and magnetic properties of the obtained powders. X-ray diffraction revealed a single-phase cubic spinel structure for all samples, where the crystallite size decreases; the lattice parameter simultaneously increases with substitution of Zr. The results of FE-SEM showed that the particle size is in the 20-70 nm range. The magnetic properties such as saturation magnetization (Ms), remanent magnetization (Mr) and coercivity (Hc) were measured from the hysteresis loops. The greatest amount of saturation magnetization for CoZr0.05Fe1.95O4 sample was 67.9 emu·g-1.

Magnetism and 155Gd Mössbauer spectroscopy of GdAuMg

NASA Astrophysics Data System (ADS)

Łątka, Kazimierz; Kmieć, Roman; Pacyna, Andrzej W.; Fickenscher, Thomas; Hoffmann, Rolf-Dieter; Pöttgen, Rainer

2004-03-01

GdAuMg was synthesized by reaction of the elements in a sealed tantalum ampule in a high-frequency furnace. The structure was investigated by X-ray diffraction on both powders and single crystals: ZrNiAl type, P 6¯2m , a=756.3(1), c=412.71(7) pm, wR2=0.0285 for 308 F2 values, 14 variables. Geometrical motifs of the GdAuMg structure are gold centered tricapped trigonal prisms [Au1Mg 3Gd 6] and [Au2Mg 6Gd 3]. Together the gold and magnesium atoms form a three-dimensional [AuMg] network in which the gadolinium atoms fill distorted hexagonal channels. Bulk magnetic properties have been investigated by means of AC and DC magnetic susceptibility measurements and 155Gd Mössbauer spectroscopy was used to monitor the local electronic and magnetic structure. Two magnetic phase transitions were found. One transition, at T1= TN=81.1(1) K, is from a paramagnetic to an antiferromagnetic state of collinear character and the other at T2=19.0(1) from the antiferromagnetic to a kind of canted magnetic ordering characterized by a very narrow hysteresis loop.

Simultaneous Solar Maximum Mission and Very Large Array (VLA) observations of solar active regions

NASA Technical Reports Server (NTRS)

Lang, K. R.

1985-01-01

Simultaneous observations of solar active regions with the Solar Maximum Mission (SMM) Satellite and the Very Large Array (VLA) have been obtained and analyzed. Combined results enhance the scientific return for beyond that expeted from using either SMM or VLA alone. A total of two weeks of simultaneous SMM/VLA data were obtained. The multiple wavelength VLA observations were used to determine the temperature and magnetic structure at different heights within coronal loops. These data are compared with simultaneous SMM observations. Several papers on the subject are in progress. They include VLA observations of compact, transient sources in the transition region; simultaneous SMM/VLA observations of the coronal loops in one active region and the evolution of another one; and sampling of the coronal plasma using thermal cyclotron lines (magnetic field - VLA) and soft X ray spectral lines (electron density and electron temperaure-SMM).

Evidence of suppressed heating of coronal loops rooted in opposite polarity sunspot umbrae

NASA Astrophysics Data System (ADS)

Tiwari, Sanjiv K.; Thalmann, Julia K.; Winebarger, Amy R.; Panesar, Navdeep K.; Moore, Ronald

2015-04-01

Observations of active region (AR) coronae in different EUV wavelengths reveal the presence of various loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 A images we identify many clearly discernible coronal loops that connect opposite-polarity plage or a sunspot to a opposite-polarity plage region. The AIA 94 A images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the Heliosesmic Magnetic Imager (HMI) onboard SDO. After validation of the NLFFF model by comparison of calculated model field lines and observed loops in AIA 193 and 94 A, we specify the photospheric roots of the model field lines. The model field then shows the coronal magnetic loops that arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.From this result, we further hypothesize that the convective freedom at the feet of a coronal loop, together with the strength of the field in the body of the loop, determines the strength of the heating. In particular, we expect the hottest coronal loops to have one foot in an umbra and the other foot in opposite-polarity penumbra or plage (coronal moss), the areas of strong field in which convection is not as strongly suppressed as in umbrae. Many transient, outstandingly bright, loops in the AIA 94 A movie of the AR do have this expected rooting pattern.

Magnetic behavior control in niccolite structural metal formate frameworks [NH2(CH3)2][Fe(III)M(II)(HCOO)6] (M = Fe, Mn, and Co) by varying the divalent metal ions.

PubMed

Zhao, Jiong-Peng; Hu, Bo-Wen; Lloret, Francesc; Tao, Jun; Yang, Qian; Zhang, Xiao-Feng; Bu, Xian-He

2010-11-15

By changing template cation but introducing trivalent iron ions in the known niccolite structural metal formate frameworks, three complexes formulated [NH(2)(CH(3))(2)][Fe(III)M(II)(HCOO)(6)] (M = Fe for 1, Mn for 2, and Co for 3) were synthesized and magnetically characterized. The variation in the compositions of the complexes leads to three different complexes: mixed-valent complex 1, heterometallic but with the same spin state complex 2, and heterometallic heterospin complex 3. The magnetic behaviors are closely related to the divalent metal ions used. Complex 1 exhibits negative magnetization assigned as Néel N-Type ferrimagnet, with an asymmetric magnetization reversal in the hysteresis loop, and complex 2 is an antiferromagnet with small spin canting (α(canting) ≈ 0.06° and T(canting) = 35 K), while complex 3 is a ferrimagnet with T(N) = 32 K.

Formation of Large-scale Coronal Loops Interconnecting Two Active Regions through Gradual Magnetic Reconnection and an Associated Heating Process

NASA Astrophysics Data System (ADS)

Du, Guohui; Chen, Yao; Zhu, Chunming; Liu, Chang; Ge, Lili; Wang, Bing; Li, Chuanyang; Wang, Haimin

2018-06-01

Coronal loops interconnecting two active regions (ARs), called interconnecting loops (ILs), are prominent large-scale structures in the solar atmosphere. They carry a significant amount of magnetic flux and therefore are considered to be an important element of the solar dynamo process. Earlier observations showed that eruptions of ILs are an important source of CMEs. It is generally believed that ILs are formed through magnetic reconnection in the high corona (>150″–200″), and several scenarios have been proposed to explain their brightening in soft X-rays (SXRs). However, the detailed IL formation process has not been fully explored, and the associated energy release in the corona still remains unresolved. Here, we report the complete formation process of a set of ILs connecting two nearby ARs, with successive observations by STEREO-A on the far side of the Sun and by SDO and Hinode on the Earth side. We conclude that ILs are formed by gradual reconnection high in the corona, in line with earlier postulations. In addition, we show evidence that ILs brighten in SXRs and EUVs through heating at or close to the reconnection site in the corona (i.e., through the direct heating process of reconnection), a process that has been largely overlooked in earlier studies of ILs.

Additional hydrogen bonds and base-pair kinetics in the symmetrical AMP-DNA aptamer complex.

PubMed Central

Nonin-Lecomte, S; Lin, C H; Patel, D J

2001-01-01

The solution structure of an adenosine monophosphate (AMP)-DNA aptamer complex has been determined previously [Lin, C. H., and Patel, D. J. (1997) Chem. Biol. 4:817-832]. On a symmetrical aptamer complex containing the same binding loop, but with better resolved spectra, we have identified two additional hydrogen bond-mediated associations in the binding loop. One of these involves a rapidly exchanging G imino proton. The phosphate group of the AMP ligand was identified as the acceptor by comparison with other aptamer complexes. Imino proton exchange measurements also yielded the dissociation constants of the stem and binding loop base pairs. This study shows that nuclear magnetic resonance-based imino proton exchange is a good probe for detection of weak hydrogen-bond associations. PMID:11721004

Design and analysis of control system for VCSEL of atomic interference magnetometer

NASA Astrophysics Data System (ADS)

Zhang, Xiao-nan; Sun, Xiao-jie; Kou, Jun; Yang, Feng; Li, Jie; Ren, Zhang; Wei, Zong-kang

2016-11-01

Magnetic field detection is an important means of deep space environment exploration. Benefit from simple structure and low power consumption, atomic interference magnetometer become one of the most potential detector payloads. Vertical Cavity Surface Emitting Laser (VCSEL) is usually used as a light source in atomic interference magnetometer and its frequency stability directly affects the stability and sensitivity of magnetometer. In this paper, closed-loop control strategy of VCSEL was designed and analysis, the controller parameters were selected and the feedback error algorithm was optimized as well. According to the results of experiments that were performed on the hardware-in-the-loop simulation platform, the designed closed-loop control system is reasonable and it is able to effectively improve the laser frequency stability during the actual work of the magnetometer.

The Impact Induced Demagnetization Mechanism in NdFeB Permanent Magnets

NASA Astrophysics Data System (ADS)

Li, Yan-Feng; Zhu, Ming-Gang; Li, Wei; Zhou, Dong; Lu, Feng; Chen, Lang; Wu, Jun-Ying; Qi, Yan; Du, An

2013-09-01

Compression of unmagnetized Nd2Fe14B permanent magnets is executed by using shock waves with different pressures in a one-stage light gas gun system. The microstructure, crystal structure, and magnetic properties of the magnets are examined with scanning electronic microscopy, x-ray diffraction, hysteresis loop instruments, and a vibrating sample magnetometer, respectively. The NdFeB magnets display a demagnetization phenomenon after shock wave compression. The coercivity dropped from about 21.4 kOe to 3.2 kOe. The critical pressure of irreversible demagnetization of NdFeB magnets should be less than 4.92 GPa. The coercivity of the NdFeB magnets compressed by shock waves could be recovered after annealing at 900°C and 520°C for 2 h, sequentially. The chaotic orientation of Nd2Fe14B grains in the compressed magnets is the source of demagnetization.

Tunable Composite Metamaterials with Imbedded Coherently Controllable Atomic or Molecular Materials

DTIC Science & Technology

2010-10-07

using nanoporous alumina templates [G. Sauer, G. Brehm, and S. Schneider, “Highly ordered monocrystalline silver nanowire arrays” J. Appl...using stimulated Raman Scattering into the Stokes modes. Fig. 2: Left panel : A cross-sectional view of a typical unit cell of the plasmonic loop...Right panel : Magnetic response of an isolated loop inclusion illustrating the concentration of the magnetic field inside the loop at resonance, when

Minor loop dependence of the magnetic forces and stiffness in a PM-HTS levitation system

NASA Astrophysics Data System (ADS)

Yang, Yong; Li, Chengshan

2017-12-01

Based upon the method of current vector potential and the critical state model of Bean, the vertical and lateral forces with different sizes of minor loop are simulated in two typical cooling conditions when a rectangular permanent magnet (PM) above a cylindrical high temperature superconductor (HTS) moves vertically and horizontally. The different values of average magnetic stiffness are calculated by various sizes of minor loop changing from 0.1 to 2 mm. The magnetic stiffness with zero traverse is obtained by using the method of linear extrapolation. The simulation results show that the extreme values of forces decrease with increasing size of minor loop. The magnetic hysteresis of the force curves also becomes small as the size of minor loop increases. This means that the vertical and lateral forces are significantly influenced by the size of minor loop because the forces intensely depend on the moving history of the PM. The vertical stiffness at every vertical position when the PM vertically descends to 1 mm is larger than that as the PM vertically ascents to 30 mm. When the PM moves laterally, the lateral stiffness during the PM passing through any horizontal position in the first time almost equal to the value during the PM passing through the same position in the second time in zero-field cooling (ZFC), however, the lateral stiffness in field cooling (FC) and the cross stiffness in ZFC and FC are significantly affected by the moving history of the PM.

Simultaneous Solar Maximum Mission (SMM) and Very Large Array (VLA) observations of solar active regions

NASA Technical Reports Server (NTRS)

Willson, Robert F.

1991-01-01

Very Large Array observations at 20 cm wavelength can detect the hot coronal plasma previously observed at soft x ray wavelengths. Thermal cyclotron line emission was detected at the apex of coronal loops where the magnetic field strength is relatively constant. Detailed comparison of simultaneous Solar Maximum Mission (SMM) Satellite and VLA data indicate that physical parameters such as electron temperature, electron density, and magnetic field strength can be obtained, but that some coronal loops remain invisible in either spectral domain. The unprecedent spatial resolution of the VLA at 20 cm wavelength showed that the precursor, impulsive, and post-flare components of solar bursts originate in nearby, but separate loops or systems of loops.. In some cases preburst heating and magnetic changes are observed from loops tens of minutes prior to the impulsive phase. Comparisons with soft x ray images and spectra and with hard x ray data specify the magnetic field strength and emission mechanism of flaring coronal loops. At the longer 91 cm wavelength, the VLA detected extensive emission interpreted as a hot 10(exp 5) K interface between cool, dense H alpha filaments and the surrounding hotter, rarefield corona. Observations at 91 cm also provide evidence for time-correlated bursts in active regions on opposite sides of the solar equator; they are attributed to flare triggering by relativistic particles that move along large-scale, otherwise-invisible, magnetic conduits that link active regions in opposite hemispheres of the Sun.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yang, Bo; Jiang, Yunchun; Yang, Jiayan

Taking advantage of the high spatiotemporal resolution observations from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory, we present rare observations of the rapid formation of a filament caused by magnetic reconnection between two sets of dark threadlike structures. The two sets of dark threadlike structures belong to distinct flux systems with their adjacent ends anchored in an opposite-polarity magnetic field region, where the calculated photospheric velocity field shows that converging flows dominate there. Due to the converging flows, opposite-polarity magnetic flux converged and then canceled, leading to the formation ofmore » extreme ultraviolet (EUV) brightening that spread in opposite directions along the spine of the dark threadlike structures. Meanwhile, very weak remote brightening in the other terminals of the dark threadlike structures, as well as EUV loops, which rooted in the opposite-polarity magnetic field region, appeared. In addition, all of the AIA Fe line observations reveal that a flux rope was formed and underwent a rolling motion during the fadeaway of the EUV brightening. Soon after, as the EUV brightening disappeared, a filament that is very likely composed of two sets of intertwined dark threadlike structures was formed. Via differential emission measure (EM) analysis, it is found that both the EM and temperature of the plasma around the flux-canceling site increased during the brightening, implying that there, magnetic reconnection may occur to heat the plasma. These observations provide evidence that the filament is formed by magnetic reconnection associated with flux convergence and cancellation, and the magnetic structure of the filament is most likely a flux rope.« less

Coronal Seismology -- Achievements and Perspectives

NASA Astrophysics Data System (ADS)

Ruderman, Michael

Coronal seismology is a new and fast developing branch of the solar physics. The main idea of coronal seismology is the same as of any branches of seismology: to determine basic properties of a medium using properties of waves propagating in this medium. The waves and oscillations in the solar corona are routinely observed in the late space missions. In our brief review we concentrate only on one of the most spectacular type of oscillations observed in the solar corona - the transverse oscillations of coronal magnetic loops. These oscillations were first observed by TRACE on 14 July 1998. At present there are a few dozens of similar observations. Shortly after the first observation of the coronal loop transverse oscillations they were interpreted as kink oscillations of magnetic tubes with the ends frozen in the dense photospheric plasma. The frequency of the kink oscillation is proportional to the magnetic field magnitude and inversely proportional to the tube length times the square root of the plasma density. This fact was used to estimate the magnetic field magnitude in the coronal loops. In 2004 the first simultaneous observation of the fundamental mode and first overtone of the coronal loop transverse oscillation was reported. If we model a coronal loop as a homogeneous magnetic tube, then the ratio of the frequencies of the first overtone and the fundamental mode should be equal to 2. However, the ratio of the observed frequencies was smaller than 2. This is related to the density variation along the loop. If we assume that the corona is isothermal and prescribe the loop shape (usually it is assumed that it has the shape of half-circle), then, using the ratio of the two frequencies, we can determine the temperature of the coronal plasma. The first observation of transverse oscillations of the coronal loops showed that they were strongly damped. This phenomenon was confirmed by the subsequent observations. At present, the most reliable candidate for the explanation of the oscillation damping is resonant absorption. The damping due to resonant absorption is, broadly speaking, proportional to the inhomogeneity scale of the density in the loop in the transverse direction. This fact was used to estimate the density inhomogeneity scale from the observations. The first observation of the coronal loop transverse oscillations gave a strong boost to the theoretical study of this phenomenon. In the last ten years theorists sufficiently refined their models taking into account such loop properties as the density variation in the longitudinal and transverse directions, the twist of the magnetic field, the non-circular loop cross-section, the variation of the cross-section along the loop, and the loop curvature. Now, to obtain more accurate estimates of the coronal plasma parameters, we need the following from the observations: (i) Since the frequency of the loop oscillation depends on the plasma density, more accurate data on this quantity is required. (ii) Since the estimate of the coronal temperature strongly depends of the loop shape, an accurate three-dimensional picture of the loop is desirable. (iii) The fundamental frequency and first overtone of the loop oscillation are sufficiently affected by the variation of the loop cross-section. The observational data on this quantity is important for further progress of the coronal seismology.

Observational goals for Max '91 to identify the causative agent for impulsive bursts

NASA Technical Reports Server (NTRS)

Batchelor, D. A.

1989-01-01

Recent studies of impulsive hard x ray and microwave bursts suggest that a propagating causative agent with a characteristic velocity of the order of 1000 km/s is responsible for these bursts. The results of these studies are summarized and observable distinguishing characteristics of the various possible agents are highlighted, with emphasis on key observational goals for the Max '91 campaigns. The most likely causative agents suggested by the evidence are shocks, thermal conduction fronts, and propagating modes of magnetic reconnection in flare plasmas. With new instrumentation planned for Max '91, high spatial resolution observations of hard x ray sources have the potential to identify the agent by revealing detailed features of source spatial evolution. Observations with the Very Large Array and other radio imaging instruments are of great importance, as well as detailed modeling of coronal loop structures to place limits on their density and temperature profiles. With the combined hard x ray and microwave imaging observations, aided by loop model results, the simplest causative agent to rule out would be the propagating modes of magnetic reconnection. To fit the observational evidence, reconnection modes would need to travel at approximately the same velocity (the Alfven velocity) in different coronal structures that vary in length by a factor of 10(exp 3). Over such a vast range in loop lengths, it is difficult to believe that the Alfven velocity is constant. Thermal conduction fronts would be suggested by sources that expand along the direction of B and exhibit relatively little particle precipitation. Particle acceleration due to shocks could produce more diverse radially expanding source geometries with precipitation at loop footprints.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Antolin, P.; Verwichte, E., E-mail: patrick.antolin@astro.uio.no, E-mail: erwin.verwichte@warwick.ac.uk

The condensations composing coronal rain, falling down along loop-like structures observed in cool chromospheric lines such as H{alpha} and Ca II H, have long been a spectacular phenomenon of the solar corona. However, considered a peculiar sporadic phenomenon, it has not received much attention. This picture is rapidly changing due to recent high-resolution observations with instruments such as the Hinode/Solar Optical Telescope (SOT), CRISP of the Swedish 1-m Solar Telescope, and the Solar Dynamics Observatory. Furthermore, numerical simulations have shown that coronal rain is the loss of thermal equilibrium of loops linked to footpoint heating. This result has highlighted themore » importance that coronal rain can play in the field of coronal heating. In this work, we further stress the importance of coronal rain by showing the role it can play in the understanding of the coronal magnetic field topology. We analyze Hinode/SOT observations in the Ca II H line of a loop in which coronal rain puts in evidence in-phase transverse oscillations of multiple strand-like structures. The periods, amplitudes, transverse velocities, and phase velocities are calculated, allowing an estimation of the energy flux of the wave and the coronal magnetic field inside the loop through means of coronal seismology. We discuss the possible interpretations of the wave as either standing or propagating torsional Alfven or fast kink waves. An estimate of the plasma beta parameter of the condensations indicates a condition that may allow the often observed separation and elongation processes of the condensations. We also show that the wave pressure from the transverse wave can be responsible for the observed low downward acceleration of coronal rain.« less

ON THE ROLE OF REPETITIVE MAGNETIC RECONNECTIONS IN EVOLUTION OF MAGNETIC FLUX ROPES IN SOLAR CORONA

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kumar, Sanjay; Bhattacharyya, R.; Joshi, Bhuwan

Parker's magnetostatic theorem, extended to astrophysical magnetofluids with large magnetic Reynolds number, supports ceaseless regeneration of current sheets and, hence, spontaneous magnetic reconnections recurring in time. Consequently, a scenario is possible where the repeated reconnections provide an autonomous mechanism governing emergence of coherent structures in astrophysical magnetofluids. In this work, such a scenario is explored by performing numerical computations commensurate with the magnetostatic theorem. In particular, the computations explore the evolution of a flux rope governed by repeated reconnections in a magnetic geometry resembling bipolar loops of solar corona. The revealed morphology of the evolution process—including onset and ascent ofmore » the rope, reconnection locations, and the associated topology of the magnetic field lines—agrees with observations, and thus substantiates physical realizability of the advocated mechanism.« less

Magnetic field line reconnection experiments. V - Current disruptions and double layers

NASA Technical Reports Server (NTRS)

Stenzel, R. L.; Gekelman, W.; Wild, N.

1983-01-01

An investigation is conducted of the stability of a large laboratory plasma current sheet, which has been generated in the process of magnetic field line reconnection, with respect to local current increases. Magnetic flux variations in regions remote from the current sheet generate an inductive voltage in the current loop that drops off inside the plasma in the form of a potential double layer, leading to particle acceleration with velocities much larger than those expected from the steady state electric fields in the plasma. A model for the mechanism of the current disruptions is formulated in which the potential structure leads to ion expulsion, creating a localized density drop. The associated current drop in an inductive circuit drives the potential structure, providing feedback for the disruptive instability. Similarities to, and differences from, magnetospheric substorm phenomena are noted.

Superparamagnetic LaSrMnO3 nanoparticles for magnetic nanohyperthermia and their biocompatibility

NASA Astrophysics Data System (ADS)

Aneja, Mohit; Tovstolytkin, Alexandr; Singh Lotey, Gurmeet

2017-11-01

The nanohyperthermia investigation of superparamagnetic La0.77Sr0.23MnO3 nanoparticles synthesized by hydrothermal method has been carried out. The synthesized nanoparticles are found to be highly uniform in size and shape with average particle size 18 nm. Structural analysis confirms the pseudo-cubic perovskite crystal structure with space group of (R3c). The magnetization versus applied magnetic field (M-H) hysteresis loops measurements revealed the superparmagnetic nature of the synthesized nanoparticles. The induction heating of synthesized nanoparticles for their applications in nanohyperthermia has been studied. The in vitro cytotoxicity test of the synthesized superparamagnetic nanoparticles has been probed by evaluating the viability of HeLa (Human Negroid Cervix Epitheloid Carcinoma) cell lines. The mechanism responsible for nanohyperthermia heating of the synthesized nanoparticles has been discussed.

Top-quark loops and the muon anomalous magnetic moment

DOE PAGES

Czarnecki, Andrzej; Marciano, William J.

2017-12-07

The current status of electroweak radiative corrections to the muon anomalous magnetic moment is discussed. Asymptotic expansions for some important electroweak two-loop top quark triangle diagrams are illustrated and extended to higher order. Results are compared with the more general integral representation solution for generic fermion triangle loops coupled to pseudoscalar and scalar bosons of arbitrary mass. Furthermore, excellent agreement is found for a broader than expected range of mass parameters.

Origin of steps in magnetization loops of martensitic Ni-Mn-Ga films on MgO(001)

NASA Astrophysics Data System (ADS)

Laptev, Aleksej; Lebecki, Kristof; Welker, Gesa; Luo, Yuansu; Samwer, Konrad; Fonin, Mikhail

2016-09-01

We study the temperature dependent magnetization properties of (010)-oriented Ni-Mn-Ga epitaxial films on MgO(001) substrates. In the martensitic phase, we observe pronounced abrupt slope changes in the magnetization loops for all studied samples. Our experimental findings are discussed in conjunction with the micromagnetic simulations, revealing that the characteristic magnetization behavior is governed solely by the magnetization switching within the specific martensitic variant pattern, and no reorientation of twin variants is involved in the process. Our study emphasizes the important role of the magnetostatic interactions in the magnetization behavior of magnetic shape memory alloy thin films.

Dynamic mapping of brain and cognitive control of virtual gameplay (study by functional magnetic resonance imaging).

PubMed

Rezakova, M V; Mazhirina, K G; Pokrovskiy, M A; Savelov, A A; Savelova, O A; Shtark, M B

2013-04-01

Using functional magnetic resonance imaging technique, we performed online brain mapping of gamers, practiced to voluntary (cognitively) control their heart rate, the parameter that operated a competitive virtual gameplay in the adaptive feedback loop. With the default start picture, the regions of interest during the formation of optimal cognitive strategy were as follows: Brodmann areas 19, 37, 39 and 40, i.e. cerebellar structures (vermis, amygdala, pyramids, clivus). "Localization" concept of the contribution of the cerebellum to cognitive processes is discussed.

Formation, levitation, and stability of prominences in the magnetized solar atmosphere

NASA Technical Reports Server (NTRS)

Drake, J. F.; Mok, Y.; Van Hoven, G.

1993-01-01

The dynamic formation of prominences in the initial magnetothermal equilibrium and their stability to sideward displacements are investigated focusing on the structure of the 2D solar atmosphere in the presence of coronal arcades or loops. A model based on 2D magnetohydrodynamic equations takes into account gravity, compressible flows, heating, radiation, anisotropic thermal conduction, and coupling to a deep chromosphere. It is found that prominences in simple arcades characterized by magnetic field with significant curvature at the apex are unstable to a lateral displacement.

Smooth and rapid microwave synthesis of MIL-53(Fe) including superparamagnetic γ-Fe2O3 nanoparticles

NASA Astrophysics Data System (ADS)

Wengert, Simon; Albrecht, Joachim; Ruoss, Stephen; Stahl, Claudia; Schütz, Gisela; Schäfer, Ronald

2017-12-01

MIL-53(Fe) linked to superparamagnetic γ-Fe2O3 nanoparticles was created using time-efficient microwave synthesis. Intermediates as well as the final product have been characterized by Dynamic Light Scattering (DLS), Infrared Spectroscopy (FTIR) and Thermal Gravimetric Analysis (TGA). It is found that this route allows the production of Fe nanoparticles with typical sizes of about 80 nm that are embedded inside the metal-organic structures. Detailed magnetization measurements using SQUID magnetometry revealed a nearly reversible magnetization loop indicating essentially superparamagnetic behavior.

Macroscopic behavior and microscopic magnetic properties of nanocarbon

NASA Astrophysics Data System (ADS)

Lähderanta, E.; Ryzhov, V. A.; Lashkul, A. V.; Galimov, D. M.; Titkov, A. N.; Matveev, V. V.; Mokeev, M. V.; Kurbakov, A. I.; Lisunov, K. G.

2015-06-01

Here are presented investigations of powder and glass-like samples containing carbon nanoparticles, not intentionally doped and doped with Ag, Au and Co. The neutron diffraction study reveals an amorphous structure of the samples doped with Au and Co, as well as the magnetic scattering due to a long-range FM order in the Co-doped sample. The composition and molecular structure of the sample doped with Au is clarified with the NMR investigations. The temperature dependence of the magnetization, M (T), exhibits large irreversibility in low fields of B=1-7 mT. M (B) saturates already above 2 T at high temperatures, but deviates from the saturation behavior below 50 (150 K). Magnetic hysteresis is observed already at 300 K and exhibits a power-law temperature decay of the coercive field, Bc (T). The macroscopic behavior above is typical of an assembly of partially blocked magnetic nanoparticles. The values of the saturation magnetization, Ms, and the blocking temperature, Tb, are obtained as well. However, the hysteresis loop in the Co-doped sample differs from that in other samples, and the values of Bc and Ms are noticeably increased.

On the three-dimensional magnetic structure of the plasmoid created in the magnetotail at substorm onset

NASA Technical Reports Server (NTRS)

Hones, E. W., Jr.; Bame, S. J.; Birn, J.; Paschmann, G.; Russell, C. T.

1982-01-01

The magnetic field in the plasmoid which is created by the reconnection of magnetic field lines at a neutral line formed in the near-earth region of the plasma sheet at substorm onset, and which flows out of the magnetotail into the magnetosphere's wake, displays a strong positive or negative Y(SM) component that has been difficult to reconcile with the standard, two-dimensional reconnection geometry. It is shown that this deviation of the magnetic field is a manifestation of the newly-reconnected field line loop's draping toward the tail's central or midnight meridian, and that the draping is a consequence of the three-dimensional plasma flow associated with the reconnection process.

Phase controlled synthesis of (Mg, Ca, Ba)-ferrite magnetic nanoparticles with high uniformity

NASA Astrophysics Data System (ADS)

Wang, S. F.; Li, Q.; Zu, X. T.; Xiang, X.; Liu, W.; Li, S.

2016-12-01

(Mg, Ca, Ba)-ferrite magnetic nanoparticles were successfully synthesized through modifying the atomic ratio of polysaccharide and chelating agent at an optimal sintering temperature. In the process, the polysaccharide plays an important role in drastically shrinking the precursor during the gel drying process. In the metal-complex structure, M2+ ion active sites were coordinated by -OH of the water molecules except for EDTA anions. The MFe2O4 magnetic nanoparticles exhibited enhanced magnetic properties when compared with nano-MFe2O4 of similar particle size synthesized by other synthesis route reported in the literature. In particular, the sintering temperature improves the crystallinity and increases the hysteresis loop squareness ratio of (Mg, Ca, Ba)-ferrite nanoparticles significantly.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Li, X.; Guo, F.; Wang, X.

One-dimensional (1D) nanotubes of Nd{sub 0.1}Bi{sub 0.9}FeO{sub 3} (NBFO) with an inner diameter of ∼50 nm were synthesized via sol-gel based electrospinning without template assistant. The phases, morphologies, crystalline structures, and magnetic properties of these 1D nanostructures were characterized by means of X-ray diffraction, scanning electron microscopy, transmission electron microscopy and SQUID, respectively. It was found that the calcination condition plays a crucial role in determining the morphologies and the magnetic properties. Interestingly, these 1D NBFO nanotubes exhibit wasp-waisted magnetic hysteresis with a lower coercivity and larger saturation magnetization, which were prevalent in natural rocks and artificial composite materials. The originmore » of these wasp-waisted hysteresis loops was discussed.« less

Alfven-wave dissipation: A support mechanism for quiescent prominences

NASA Technical Reports Server (NTRS)

Jensen, Eberhart

1986-01-01

High resolution filtergrams or spectrograms of the main body of quiescent prominences often show a very vivid dynamical picture that cannot be reconciled with static models. Even if large differences exist between individual prominences in this respect, at least parts of the prominence are usually found to be in a 'choppy', turbulent state. Evidence for systematic flows are found in local regions in the prominence and also in the transition zone in the surroundings. These two regions are probably decoupled magnetically. Alfven waves are generally believed to be responsible for the heating in the upper chromosphere and corona (Hollweg 1986). Since evidence for the presence of Alfven-waves has also been found in the solar wind field, it is highly probable that such waves are generated in the convection zone of the sun and propagated outwards in the solar atmosphere wherever a proper magnetic field is present to carry the waves. The most basic magnetic formations in the solar atmosphere are simple loops. They occur all over the solar surface and cover a large range of magnetic field strengths. Loops with the strongest magnetic fields are found in active regions. It is to be expected that the Alfven-wave flux which is channelled into the loops from below, could show considerable variation both with heliocentric latitude, with time and locally between neighbouring loops. What happens when a magnetic loop is exposed to the appropriate Alfven-wave flux required to heat the upper solar atmosphere is examined.

Designing Hysteresis with Dipolar Chains

NASA Astrophysics Data System (ADS)

Concha, Andrés; Aguayo, David; Mellado, Paula

2018-04-01

Materials that have hysteretic response to an external field are essential in modern information storage and processing technologies. A myriad of magnetization curves of several natural and artificial materials have previously been measured and each has found a particular mechanism that accounts for it. However, a phenomenological model that captures all the hysteresis loops and at the same time provides a simple way to design the magnetic response of a material while remaining minimal is missing. Here, we propose and experimentally demonstrate an elementary method to engineer hysteresis loops in metamaterials built out of dipolar chains. We show that by tuning the interactions of the system and its geometry we can shape the hysteresis loop which allows for the design of the softness of a magnetic material at will. Additionally, this mechanism allows for the control of the number of loops aimed to realize multiple-valued logic technologies. Our findings pave the way for the rational design of hysteretical responses in a variety of physical systems such as dipolar cold atoms, ferroelectrics, or artificial magnetic lattices, among others.

Designing Hysteresis with Dipolar Chains.

PubMed

Concha, Andrés; Aguayo, David; Mellado, Paula

2018-04-13

Materials that have hysteretic response to an external field are essential in modern information storage and processing technologies. A myriad of magnetization curves of several natural and artificial materials have previously been measured and each has found a particular mechanism that accounts for it. However, a phenomenological model that captures all the hysteresis loops and at the same time provides a simple way to design the magnetic response of a material while remaining minimal is missing. Here, we propose and experimentally demonstrate an elementary method to engineer hysteresis loops in metamaterials built out of dipolar chains. We show that by tuning the interactions of the system and its geometry we can shape the hysteresis loop which allows for the design of the softness of a magnetic material at will. Additionally, this mechanism allows for the control of the number of loops aimed to realize multiple-valued logic technologies. Our findings pave the way for the rational design of hysteretical responses in a variety of physical systems such as dipolar cold atoms, ferroelectrics, or artificial magnetic lattices, among others.

DO THE LEGS OF MAGNETIC CLOUDS CONTAIN TWISTED FLUX-ROPE MAGNETIC FIELDS?

DOE Office of Scientific and Technical Information (OSTI.GOV)

Owens, M. J.

2016-02-20

Magnetic clouds (MCs) are a subset of interplanetary coronal mass ejections (ICMEs) characterized primarily by a smooth rotation in the magnetic field direction indicative of the presence of a magnetic flux rope. Energetic particle signatures suggest MC flux ropes remain magnetically connected to the Sun at both ends, leading to widely used model of global MC structure as an extended flux rope, with a loop-like axis stretching out from the Sun into the heliosphere and back to the Sun. The time of flight of energetic particles, however, suggests shorter magnetic field line lengths than such a continuous twisted flux ropemore » would produce. In this study, two simple models are compared with observed flux rope axis orientations of 196 MCs to show that the flux rope structure is confined to the MC leading edge. The MC “legs,” which magnetically connect the flux rope to the Sun, are not recognizable as MCs and thus are unlikely to contain twisted flux rope fields. Spacecraft encounters with these non-flux rope legs may provide an explanation for the frequent observation of non-MC ICMEs.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chitta, L. P.; Peter, H.; Solanki, S. K.

How and where are coronal loops rooted in the solar lower atmosphere? The details of the magnetic environment and its evolution at the footpoints of coronal loops are crucial to understanding the processes of mass and energy supply to the solar corona. To address the above question, we use high-resolution line-of-sight magnetic field data from the Imaging Magnetograph eXperiment instrument on the Sunrise balloon-borne observatory and coronal observations from the Atmospheric Imaging Assembly onboard the Solar Dynamics Observatory of an emerging active region. We find that the coronal loops are often rooted at the locations with minor small-scale but persistentmore » opposite-polarity magnetic elements very close to the larger dominant polarity. These opposite-polarity small-scale elements continually interact with the dominant polarity underlying the coronal loop through flux cancellation. At these locations we detect small inverse Y-shaped jets in chromospheric Ca ii H images obtained from the Sunrise Filter Imager during the flux cancellation. Our results indicate that magnetic flux cancellation and reconnection at the base of coronal loops due to mixed polarity fields might be a crucial feature for the supply of mass and energy into the corona.« less

Simple Analytic Expressions for the Magnetic Field of a Circular Current Loop

NASA Technical Reports Server (NTRS)

Simpson, James C.; Lane, John E.; Immer, Christopher D.; Youngquist, Robert C.

2001-01-01

Analytic expressions for the magnetic induction (magnetic flux density, B) of a simple planar circular current loop have been published in Cartesian and cylindrical coordinates [1,2], and are also known implicitly in spherical coordinates [3]. In this paper, we present explicit analytic expressions for B and its spatial derivatives in Cartesian, cylindrical, and spherical coordinates for a filamentary current loop. These results were obtained with extensive use of Mathematica "TM" and are exact throughout all space outside of the conductor. The field expressions reduce to the well-known limiting cases and satisfy V · B = 0 and V x B = 0 outside the conductor. These results are general and applicable to any model using filamentary circular current loops. Solenoids of arbitrary size may be easily modeled by approximating the total magnetic induction as the sum of those for the individual loops. The inclusion of the spatial derivatives expands their utility to magnetohydrodynamics where the derivatives are required. The equations can be coded into any high-level programming language. It is necessary to numerically evaluate complete elliptic integrals of the first and second kind, but this capability is now available with most programming packages.

Sweeping Arches and Loops [video

NASA Image and Video Library

2014-07-10

Two active regions with their intense magnetic fields produced towering arches and spiraling coils of solar loops above them (June 29 - July 1, 2014) as they rotated into view. When viewed in extreme ultraviolet light, magnetic field lines are revealed by charged particles that travel along them. These active regions appear as dark sunspots when viewed in filtered light. Note the small blast in the upper of the two major active regions, followed by more coils of loops as the region reorganizes itself. The still was taken on June 30 at 10:33 UT. Credit: NASA/Solar Dynamics Observatory Two active regions with their intense magnetic fields produced towering arches and spiraling coils of solar loops above them (June 29 - July 1, 2014) as they rotated into view. When viewed in extreme ultraviolet light, magnetic field lines are revealed by charged particles that travel along them. These active regions appear as dark sunspots when viewed in filtered light. Note the small blast in the upper of the two major active regions, followed by more coils of loops as the region reorganizes itself. The still was taken on June 30 at 10:33 UT. Credit: Solar Dynamics Observatory/NASA.

Electron cyclotron wave acceleration outside a flaring loop

NASA Technical Reports Server (NTRS)

Sprangle, P.; Vlahos, L.

1983-01-01

A model for the secondary acceleration of electrons outside a flaring loop is proposed. The results suggest that the narrow bandwidth radiation emitted by the unstable electron distribution inside a flaring loop can become the driver for secondary electron acceleration outside the loop. It is shown that a system of electrons gyrating about and streaming along an adiabatically spatially varying, static magnetic field can be efficiently accelerated to high energies by an electromagnetic wave propagating along and polarized transverse to the static magnetic field. The predictions from our model appear to be in general agreement with existing observations.

MHD Modelling of Coronal Loops: Injection of High-Speed Chromospheric Flows

NASA Technical Reports Server (NTRS)

Petralia, A.; Reale, F.; Orlando, S.; Klimchuk, J. A.

2014-01-01

Context. Observations reveal a correspondence between chromospheric type II spicules and bright upward-moving fronts in the corona observed in the extreme-ultraviolet (EUV) band. However, theoretical considerations suggest that these flows are probably not the main source of heating in coronal magnetic loops. Aims. We investigate the propagation of high-speed chromospheric flows into coronal magnetic flux tubes and the possible production of emission in the EUV band. Methods. We simulated the propagation of a dense 104 K chromospheric jet upward along a coronal loop by means of a 2D cylindrical MHD model that includes gravity, radiative losses, thermal conduction, and magnetic induction. The jet propagates in a complete atmosphere including the chromosphere and a tenuous cool (approximately 0.8 MK) corona, linked through a steep transition region. In our reference model, the jet initial speed is 70 km per second, its initial density is 10(exp 11) per cubic centimeter, and the ambient uniform magnetic field is 10 G. We also explored other values of jet speed and density in 1D and different magnetic field values in 2D, as well as the jet propagation in a hotter (approximately 1.5 MK) background loop. Results. While the initial speed of the jet does not allow it to reach the loop apex, a hot shock-front develops ahead of it and travels to the other extreme of the loop. The shock front compresses the coronal plasma and heats it to about 10(exp 6) K. As a result, a bright moving front becomes visible in the 171 Angstrom channel of the SDO/AIA mission. This result generally applies to all the other explored cases, except for the propagation in the hotter loop. Conclusions. For a cool, low-density initial coronal loop, the post-shock plasma ahead of upward chromospheric flows might explain at least part of the observed correspondence between type II spicules and EUV emission excess.

Using coronal seismology to estimate the magnetic field strength in a realistic coronal model

NASA Astrophysics Data System (ADS)

Chen, F.; Peter, H.

2015-09-01

Aims: Coronal seismology is used extensively to estimate properties of the corona, e.g. the coronal magnetic field strength is derived from oscillations observed in coronal loops. We present a three-dimensional coronal simulation, including a realistic energy balance in which we observe oscillations of a loop in synthesised coronal emission. We use these results to test the inversions based on coronal seismology. Methods: From the simulation of the corona above an active region, we synthesise extreme ultraviolet emission from the model corona. From this, we derive maps of line intensity and Doppler shift providing synthetic data in the same format as obtained from observations. We fit the (Doppler) oscillation of the loop in the same fashion as done for observations to derive the oscillation period and damping time. Results: The loop oscillation seen in our model is similar to imaging and spectroscopic observations of the Sun. The velocity disturbance of the kink oscillation shows an oscillation period of 52.5 s and a damping time of 125 s, which are both consistent with the ranges of periods and damping times found in observations. Using standard coronal seismology techniques, we find an average magnetic field strength of Bkink = 79 G for our loop in the simulation, while in the loop the field strength drops from roughly 300 G at the coronal base to 50 G at the apex. Using the data from our simulation, we can infer what the average magnetic field derived from coronal seismology actually means. It is close to the magnetic field strength in a constant cross-section flux tube, which would give the same wave travel time through the loop. Conclusions: Our model produced a realistic looking loop-dominated corona, and provides realistic information on the oscillation properties that can be used to calibrate and better understand the result from coronal seismology. A movie associated with Fig. 1 is available in electronic form at http://www.aanda.org

Development of closed loop roll control for magnetic balance systems

NASA Technical Reports Server (NTRS)

Covert, E. E.; Haldeman, C. W.; Ramohalli, G.; Way, P.

1982-01-01

This research was undertaken with the goal of demonstrating closed loop control of the roll degree of freedom on the NASA prototype magnetic suspension and balance system at the MIT Aerophysics Laboratory, thus, showing feasibility for a roll control system for any large magnetic balance system which might be built in the future. During the research under this grant, study was directed toward the several areas of torque generation, position sensing, model construction and control system design. These effects were then integrated to produce successful closed loop operation of the analogue roll control system. This experience indicated the desirability of microprocessor control for the angular degrees of freedom.

New Evidence that Magnetoconvection Drives Solar–Stellar Coronal Heating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.

2017-07-10

How magnetic energy is injected and released in the solar corona, keeping it heated to several million degrees, remains elusive. Coronal heating generally increases with increasing magnetic field strength. From a comparison of a nonlinear force-free model of the three-dimensional active region coronal field to observed extreme-ultraviolet loops, we find that (1) umbra-to-umbra coronal loops, despite being rooted in the strongest magnetic flux, are invisible, and (2) the brightest loops have one foot in an umbra or penumbra and the other foot in another sunspot’s penumbra or in unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra loops is new evidencemore » that magnetoconvection drives solar-stellar coronal heating: evidently, the strong umbral field at both ends quenches the magnetoconvection and hence the heating. Broadly, our results indicate that depending on the field strength in both feet, the photospheric feet of a coronal loop on any convective star can either engender or quench coronal heating in the loop’s body.« less

The origin of morphological asymmetries in bipolar active regions. [magnetic field in solar convective envelope

NASA Technical Reports Server (NTRS)

Fan, Y.; Fisher, G. H.; Deluca, E. E.

1993-01-01

A series of 3D numerical simulations was carried out to examine the dynamical evolution of emerging flux loops in the solar convective envelope. The innermost portions of the loops are anchored beneath the base of the convective zone by the subadiabatic temperature gradient of the underlying overshoot region. It is found that, as the emerging loops approach the photosphere, the magnetic field strength of the leading side of each rising loop is about twice as large as that of the following side at the same depth. The evacuation of plasma out of the leading side of the rising loop results in an enhanced magnetic field strength there compared with the following side. It is argued that this result provides a natural explanation for the fact that the preceding (leading) polarity tends to have a less organized and more fragmented appearance, and that the preceding spots tend to be larger in area and fewer in number, and have a longer lifetime than the following spots.

Xrt And Shinx Joint Flare Study: Ar 11024

NASA Astrophysics Data System (ADS)

Engell, Alexander; Sylwester, J.; Siarkowski, M.

2010-05-01

From 12:00 UT on July 3 through July 7, 2009 SphinX (Solar Photometer IN X-rays) observes 130 flares with active region (AR) 11024 being the only AR on disk. XRT (X-Ray Telescope) is able to observe 64 of these flare events. The combination of both instruments results in a flare study revealing (1) a relationship between flux emergence and flare rate, (2) that the presence of active region loops typically results in different flare morphologies (single and multiple loop flares) then when there is a lack of an active region loop environment where more cusp and point-like flares are observed, (3) cusp and point-like flares often originate from the same location, and (4) a distribution of flare temperatures corresponding to the different flare morphologies. The differences between the observed flare morphologies may occur as the result of the heated plasma through the flaring process being confined by the proximity of loop structures as for the single and multiple loop flares, while for cusp and point-like flares they occur in an early-phase environment that lack loop presence. The continuing flux emergence of AR 11024 likely provides different magnetic interactions and may be the source responsible for all of the flares.

Synthesis, characterization and magnetic properties of MFe2O4 (M=Co, Mg, Mn, Ni) nanoparticles using ricin oil as capping agent

NASA Astrophysics Data System (ADS)

Gherca, Daniel; Pui, Aurel; Cornei, Nicoleta; Cojocariu, Alina; Nica, Valentin; Caltun, Ovidiu

2012-11-01

We focused on obtaining MFe2O4 nanoparticles using ricin oil solution as surfactant and on their structural characterization and magnetic properties. The annealed samples at 500 °C in air for 6 h were analyzed for the crystal phase identification by powder X-ray diffraction using CuKα radiation. The particle size, the chemical composition and the morphology of the calcinated powders were characterized by scanning electron microscopy. All sintered samples contain only one phase, which has a cubic structure with crystallite sizes of 12-21 nm. From the infrared spectra of all samples were observed two strong bands around 600 and 400 cm-1, which correspond to the intrinsic lattice vibrations of octahedral and tetrahedral sites of the spinel structure, respectively, and characteristic vibration for capping agent. The magnetic properties of fine powders were investigated at room temperature by using a vibrating sample magnetometer. The room temperature M-H hysteresis loops show ferromagnetic behavior of the calcined samples, with specific saturation magnetization (Ms) values ranging between 11 and 53 emu/g.

Collider study on the loop-induced dark matter mediation

NASA Astrophysics Data System (ADS)

Tsai, Yuhsin

2016-06-01

Collider experiments are one of the most promising ways to constrain Dark Matter (DM) interactions. For DM couplings involving light mediators, especially for the loop-mediated interactions, a meaningful interpretation of the results requires to go beyond effective field theory. In this note we discuss the study of the magnetic dipole interacting DM, focusing on a model with anarchic dark flavor structure. By including the momentum-dependent form factors that mediate the coupling - given by the Dark Penguin - in collider processes, we study bounds from monophoton, diphoton, and non-pointing photon searches at the LHC. We also compare our results to constraints from the direct detection experiments.

Testing of the permanent magnet material Mn-Al-C for potential use in propulsion motors for electric vehicles

NASA Technical Reports Server (NTRS)

Abdelnour, Z.; Mildrun, H.; Strant, K.

1981-01-01

The development of Mn-Al-C permanent magnets is reviewed. The general properties of the material are discussed and put into perspective relative to alnicos and ferrites. The traction motor designer's demands of a permanent magnet for potential use in electric vehicle drives are reviewed. Tests determined magnetic design data and mechanical strength properties. Easy axis hysteresis and demagnetization curves, recoil loops and other minor loop fields were measured over a temperature range from -50 to 150 C. Hysteresis loops were also measured for three orthogonal directions (the one easy and two hard axes of magnetization). Extruded rods of three different diameters were tested. The nonuniformity of properties over the cross section of the 31 mm diameter rod was studied. Mechanical compressive and bending strength at room temperature was determined on individual samples from the 31 mm rod.

Surface effects and discontinuity behavior in nano-systems composed of Prussian blue analogues

NASA Astrophysics Data System (ADS)

Drissi, L. B.; Zriouel, S.; Bahmad, L.

2018-04-01

Magnetic properties and hysteresis loops of a nano-ferrimagnetic surface-bulk Prussian blue analogues (PBA) have been studied by means of Monte Carlo simulations. We have reported the effects of the magnetic and the crystal fields, as well as the intermediate and the bulk couplings, the temperature and the size on the phase diagram, the magnetization, the susceptibility, the hysteresis loops, the critical and the discontinuity temperatures of the model. The thermal dependence of the coercivity and the remanent magnetization are also discussed. This study shows a number of characteristic behaviors, such as the discontinuities in the magnetizations, the existence of Q- and N-types behaviors in the Néel classification nomenclature and the occurrence of single and triple hysteresis loops with high number of step-like plateaus. The obtained results make ferrimagnetic surface-bulk PBA useful for technological applications such as thermo-optical recording.

Study of nonlinear MHD equations governing the wave propagation in twisted coronal loops

NASA Technical Reports Server (NTRS)

Parhi, S.; DeBruyne, P.; Goossens, M.; Zhelyazkov, I.

1995-01-01

The solar corona, modelled by a low beta, resistive plasma slab, sustains MHD wave propagations due to shearing footpoint motions in the photosphere. By using a numerical algorithm the excitation and nonlinear development of MHD waves in twisted coronal loops are studied. The plasma responds to the footpoint motion by sausage waves if there is no twist. The twist in the magnetic field of the loop destroys initially developed sausage-like wave modes and they become kinks. The transition from sausage to kink modes is analyzed. The twist brings about mode degradation producing high harmonics and this generates more complex fine structures. This can be attributed to several local extrema in the perturbed velocity profiles. The Alfven wave produces remnants of the ideal 1/x singularity both for zero and non-zero twist and this pseudo-singularity becomes less pronounced for larger twist. The effect of nonlinearity is clearly observed by changing the amplitude of the driver by one order of magnitude. The magnetosonic waves also exhibit smoothed remnants of ideal logarithmic singularities when the frequency of the driver is correctly chosen. This pseudo-singularity for fast waves is absent when the coronal loop does not undergo any twist but becomes pronounced when twist is included. On the contrary, it is observed for slow waves even if there is no twist. Increasing the twist leads to a higher heating rate of the loop. The larger twist shifts somewhat uniformly distributed heating to layers inside the slab corresponding to peaks in the magnetic field strength.

SLIPPING MAGNETIC RECONNECTION, CHROMOSPHERIC EVAPORATION, IMPLOSION, AND PRECURSORS IN THE 2014 SEPTEMBER 10 X1.6-CLASS SOLAR FLARE

DOE Office of Scientific and Technical Information (OSTI.GOV)

Dudík, Jaroslav; Karlický, Marian; Dzifčáková, Elena

2016-05-20

We investigate the occurrence of slipping magnetic reconnection, chromospheric evaporation, and coronal loop dynamics in the 2014 September 10 X-class flare. Slipping reconnection is found to be present throughout the flare from its early phase. Flare loops are seen to slip in opposite directions toward both ends of the ribbons. Velocities of 20–40 km s{sup −1} are found within time windows where the slipping is well resolved. The warm coronal loops exhibit expanding and contracting motions that are interpreted as displacements due to the growing flux rope that subsequently erupts. This flux rope existed and erupted before the onset ofmore » apparent coronal implosion. This indicates that the energy release proceeds by slipping reconnection and not via coronal implosion. The slipping reconnection leads to changes in the geometry of the observed structures at the Interface Region Imaging Spectrograph slit position, from flare loop top to the footpoints in the ribbons. This results in variations of the observed velocities of chromospheric evaporation in the early flare phase. Finally, it is found that the precursor signatures, including localized EUV brightenings as well as nonthermal X-ray emission, are signatures of the flare itself, progressing from the early phase toward the impulsive phase, with the tether-cutting being provided by the slipping reconnection. The dynamics of both the flare and outlying coronal loops is found to be consistent with the predictions of the standard solar flare model in three dimensions.« less

Magnetization reversal in epitaxial exchange-biased IrMn/FeGa bilayers with anisotropy geometries controlled by oblique deposition

NASA Astrophysics Data System (ADS)

Zhang, Yao; Zhan, Qingfeng; Zuo, Zhenghu; Yang, Huali; Zhang, Xiaoshan; Dai, Guohong; Liu, Yiwei; Yu, Ying; Wang, Jun; Wang, Baomin; Li, Run-Wei

2015-05-01

We fabricated epitaxial exchange biased (EB) IrMn/FeGa bilayers by oblique deposition and systematically investigated their magnetization reversal. Two different configurations with the uniaxial magnetic anisotropy Ku parallel and perpendicular to the unidirectional anisotropy Ke b were obtained by controlling the orientation of the incident FeGa beam during deposition. A large ratio of Ku/Ke b was obtained by obliquely depositing the FeGa layer to achieve a large Ku while reducing the IrMn thickness to obtain a small Ke b. Besides the previously reported square loops, conventional asymmetrically shaped loops, and one-sided and two-sided two-step loops, unusual asymmetrically shaped loops with a three-step magnetic transition for the descending branch and a two-step transition for the ascending branch and biased three-step loops were observed at various field orientations in the films of both IrMn (tIrMn=1.5 to 20 nm)/FeGa (10 nm) with Ku⊥ Ke b and IrMn (tIrMn≤2 nm)/FeGa (10 nm) with Ku|| Ke b . Considering the geometries of anisotropies, a model based on domain wall nucleation and propagation was employed to quantitatively describe the angular dependent behaviors of IrMn/FeGa bilayers. The biased three-step magnetic switching was predicted to take place when | Ku|> ɛ90°+Ke b , where ɛ90° is the 90° domain wall nucleation energy, and the EB leads to the appearance of the unusual asymmetrically shaped hysteresis loops.

A matrix solution for the simulation of magnetic fields with ideal current loops

NASA Technical Reports Server (NTRS)

Stankiewicz, N.

1979-01-01

A matrix formulation is presented for describing axisymmetric magnetic field data with ideal current loops. A computer program written in APL is used to invert the matrix and hence to solve for the coil strengths which are used to represent the field data. Examples are given of the coil representation for (1) measured magnetic data, (2) refocusing fields, and (3) PPM focusing fields.

Dynamic contrast-enhanced breast MRI at 7 Tesla utilizing a single-loop coil: a feasibility trial.

PubMed

Umutlu, Lale; Maderwald, Stefan; Kraff, Oliver; Theysohn, Jens M; Kuemmel, Sherko; Hauth, Elke A; Forsting, Michael; Antoch, Gerald; Ladd, Mark E; Quick, Harald H; Lauenstein, Thomas C

2010-08-01

The aim of this study was to assess the feasibility of dynamic contrast-enhanced ultra-high-field breast imaging at 7 Tesla. A total of 15 subjects, including 5 patients with histologically proven breast cancer, were examined on a 7 Tesla whole-body magnetic resonance imaging system using a unilateral linearly polarized single-loop coil. Subjects were placed in prone position on a biopsy support system, with the coil placed directly below the region of interest. The examination protocol included the following sequences: 1) T2-weighted turbo spin echo sequence; 2) six dynamic T1-weighted spoiled gradient-echo sequences; and 3) subtraction imaging. Contrast-enhanced T1-weighted imaging at 7 Tesla could be obtained at high spatial resolution with short acquisition times, providing good image accuracy and a conclusively good delineation of small anatomical and pathological structures. T2-weighted imaging could be obtained with high spatial resolution at adequate acquisition times. Because of coil limitations, four high-field magnetic resonance examinations showed decreased diagnostic value. This first scientific approach of dynamic contrast-enhanced breast magnetic resonance imaging at 7 Tesla demonstrates the complexity of ultra-high-field breast magnetic resonance imaging and countenances the implementation of further advanced bilateral coil concepts to circumvent current limitations from the coil and ultra-high-field magnetic strength. 2010 AUR. Published by Elsevier Inc. All rights reserved.

Fast-sausage oscillations in coronal loops with smooth boundary

NASA Astrophysics Data System (ADS)

Lopin, I.; Nagorny, I.

2014-12-01

Aims: The effect of the transition layer (shell) in nonuniform coronal loops with a continuous radial density profile on the properties of fast-sausage modes are studied analytically and numerically. Methods: We modeled the coronal waveguide as a structured tube consisting of a cord and a transition region (shell) embedded within a magnetic uniform environment. The derived general dispersion relation was investigated analytically and numerically in the context of frequency, cut-off wave number, and the damping rate of fast-sausage oscillations for various values of loop parameters. Results: The frequency of the global fast-sausage mode in the loops with a diffuse (or smooth) boundary is determined mainly by the external Alfvén speed and longitudinal wave number. The damping rate of such a mode can be relatively low. The model of coronal loop with diffuse boundary can support a comparatively low-frequency, global fast-sausage mode of detectable quality without involving extremely low values of the density contrast. The effect of thin transition layer (corresponds to the loops with steep boundary) is negligible and produces small reductions of oscillation frequency and relative damping rate in comparison with the case of step-function density profile. Seismological application of obtained results gives the estimated Alfvén speed outside the flaring loop about 3.25 Mm/s.

Sequence Effect on the Formation of DNA Minidumbbells.

PubMed

Liu, Yuan; Lam, Sik Lok

2017-11-16

The DNA minidumbbell (MDB) is a recently identified non-B structure. The reported MDBs contain two TTTA, CCTG, or CTTG type II loops. At present, the knowledge and understanding of the sequence criteria for MDB formation are still limited. In this study, we performed a systematic high-resolution nuclear magnetic resonance (NMR) and native gel study to investigate the effect of sequence variations in tandem repeats on the formation of MDBs. Our NMR results reveal the importance of hydrogen bonds, base-base stacking, and hydrophobic interactions from each of the participating residues. We conclude that in the MDBs formed by tandem repeats, C-G loop-closing base pairs are more stabilizing than T-A loop-closing base pairs, and thymine residues in both the second and third loop positions are more stabilizing than cytosine residues. The results from this study enrich our knowledge on the sequence criteria for the formation of MDBs, paving a path for better exploring their potential roles in biological systems and DNA nanotechnology.

Does TRACE Resolve Isothermal Coronal Loops?

NASA Astrophysics Data System (ADS)

Weber, Mark A.; Schmelz, J.; Kashyap, V.; Roames, J.

2006-06-01

Historically, increasing resolution of solar data has revealed ever smaller length scales for both the thermodynamics and the magnetic structure of the corona. Furthermore, the dynamics there are governed by magnetohydrodynamic processes which are difficult to observe or model. Recent results in the literature suggest that some coronal loops with cross-sections near the resolution limits of the Transition Region and Coronal Explorer (pixel size = 0.5 arc-seconds, or approx. 360 km) are, in fact, isothermally homogeneous and thus may be identified as elementary loop strands. This poster presents some ongoing work that applies state-of-the-art estimation of differential emission measures in order to evaluate these claims for a sample of loops. We find that the data give no evidence to prefer the "isothermal" hypothesis over the "multithermal" hypothesis. The authors are supported by the following funds: contract SP02H820IR to the Lockheed-Martin Corp.; NSF grant ATM-0402729; NASA grant NNG05GE68G; and NASA contracts NAS8-39073 and NAS8-03060.

Spontaneous exchange bias formation driven by a structural phase transition in the antiferromagnetic material.

PubMed

Migliorini, A; Kuerbanjiang, B; Huminiuc, T; Kepaptsoglou, D; Muñoz, M; Cuñado, J L F; Camarero, J; Aroca, C; Vallejo-Fernández, G; Lazarov, V K; Prieto, J L

2018-01-01

Most of the magnetic devices in advanced electronics rely on the exchange bias effect, a magnetic interaction that couples a ferromagnetic and an antiferromagnetic material, resulting in a unidirectional displacement of the ferromagnetic hysteresis loop by an amount called the 'exchange bias field'. Setting and optimizing exchange bias involves cooling through the Néel temperature of the antiferromagnetic material in the presence of a magnetic field. Here we demonstrate an alternative process for the generation of exchange bias. In IrMn/FeCo bilayers, a structural phase transition in the IrMn layer develops at room temperature, exchange biasing the FeCo layer as it propagates. Once the process is completed, the IrMn layer contains very large single-crystal grains, with a large density of structural defects within each grain, which are promoted by the FeCo layer. The magnetic characterization indicates that these structural defects in the antiferromagnetic layer are behind the resulting large value of the exchange bias field and its good thermal stability. This mechanism for establishing the exchange bias in such a system can contribute towards the clarification of fundamental aspects of this exchange interaction.

Invisibility of Solar Active Region Umbra-to-Umbra Coronal Loops: New Evidence that Magnetoconvection Drives Solar-Stellar Coronal Heating

NASA Technical Reports Server (NTRS)

Tiwari, Sanjiv K.; Thalmann, Julia K.; Panesar, Navdeep K.; Moore, Ronald L.; Winebarger, Amy R.

2017-01-01

Coronal heating generally increases with increasing magnetic field strength: the EUV/X-ray corona in active regions is 10--100 times more luminous and 2--4 times hotter than that in quiet regions and coronal holes, which are heated to only about 1.5 MK, and have fields that are 10--100 times weaker than that in active regions. From a comparison of a nonlinear force-free model of the three-dimensional active region coronal field to observed extreme-ultraviolet loops, we find that (1) umbra-to-umbra coronal loops, despite being rooted in the strongest magnetic flux, are invisible, and (2) the brightest loops have one foot in an umbra or penumbra and the other foot in another sunspot's penumbra or in unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra loops is new evidence that magnetoconvection drives solar-stellar coronal heating: evidently, the strong umbral field at both ends quenches the magnetoconvection and hence the heating. Our results from EUV observations and nonlinear force-free modeling of coronal magnetic field imply that, for any coronal loop on the Sun or on any other convective star, as long as the field can be braided by convection in at least one loop foot, the stronger the field in the loop, the stronger the coronal heating.

Advanced MOKE magnetometry in wide-field Kerr-microscopy

NASA Astrophysics Data System (ADS)

Soldatov, I. V.; Schäfer, R.

2017-10-01

The measurement of MOKE (Magneto-Optical Kerr Effect) magnetization loops in a wide-field Kerr microscope offers the advantage that the relevant domain images along the loop can be readily recorded. As the microscope's objective lens is exposed to the magnetic field, the loops are usually strongly distorted by non-linear Faraday rotations of the polarized light that occur in the objective lens and that are superimposed to the MOKE signal. In this paper, an experimental method, based on a motorized analyzer, is introduced which allows to compensate the Faraday contributions, thus leading to pure MOKE loops. A wide field Kerr microscope, equipped with this technology, works well as a laser-based MOKE magnetometer, additionally offering domain images and thus providing the basis for loop interpretation.

Decoupling of a tight-fit transceiver phased array for human brain imaging at 9.4T: Loop overlapping rediscovered.

PubMed

Avdievich, Nikolai I; Giapitzakis, Ioannis-Angelos; Pfrommer, Andreas; Henning, Anke

2018-02-01

To improve the decoupling of a transceiver human head phased array at ultra-high fields (UHF, ≥ 7T) and to optimize its transmit (Tx) and receive (Rx) performance, a single-row eight-element (1 × 8) tight-fit transceiver overlapped loop array was developed and constructed. Overlapping the loops increases the RF field penetration depth but can compromise decoupling by generating substantial mutual resistance. Based on analytical modeling, we optimized the loop geometry and relative positioning to simultaneously minimize the resistive and inductive coupling and constructed a 9.4T eight-loop transceiver head phased array decoupled entirely by overlapping loops. We demonstrated that both the magnetic and electric coupling between adjacent loops is compensated at the same time by overlapping and nearly perfect decoupling (below -30 dB) can be obtained without additional decoupling strategies. Tx-efficiency and SNR of the overlapped array outperformed that of a common UHF gapped array of similar dimensions. Parallel Rx-performance was also not compromised due to overlapping the loops. As a proof of concept we developed and constructed a 9.4T (400 MHz) overlapped transceiver head array based on results of the analytical modeling. We demonstrated that at UHF overlapping loops not only provides excellent decoupling but also improves both Tx- and Rx-performance. Magn Reson Med 79:1200-1211, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Magnetic and Dielectric Investigations of Mn-Doped Ba Hexaferrite Nanoparticles by Hydrothermal Approach

NASA Astrophysics Data System (ADS)

Adeela, N.; Khan, U.; Iqbal, M.; Riaz, S.; Ali, H.; Maaz, K.; Naseem, S.

2016-11-01

A hydrothermal method followed by heat treatment was used to synthesize Mn-substituted Ba2Co2- x Mn x Fe12O22 nanoparticles with a nominal chemical composition of 0 ≤ x < 1 and step gap of 0.3. In this study, the effect of Mn substitution on Co2Y-type barium hexaferrite is investigated after employing x-ray diffraction for crystal structure, field emission scanning electron microscopy for morphology, energy dispersive analysis of x-ray spectroscopy for elemental composition, Fourier transform infrared spectroscopy to confirm bond modes, and vibrating sample magnetometry for magnetic measurements. It was found that the sample at x = 0.9 is of particular interest due to its large coercivity and anisotropy. Later on, for x = 0.9, temperature-dependent magnetic analyses including hysteresis loops, zero-field-cooled, and field-cooled at a particular field of 100 Oe were performed. The decreasing trend in saturation magnetization with increase in temperature was estimated. On the other hand, first an increase and then decrease in coercivity values were observed. These loops also revealed dependence of coercivity on magneto-crystalline anisotropy and average crystallite size of nanoparticles. Dielectric measurements at x = 0.9 make it suitable for high frequency applications.

Localization for robotic capsule looped by axially magnetized permanent-magnet ring based on hybrid strategy.

PubMed

Yang, Wanan; Li, Yan; Qin, Fengqing

2015-01-01

To actively maneuver a robotic capsule for interactive diagnosis in the gastrointestinal tract, visualizing accurate position and orientation of the capsule when it moves in the gastrointestinal tract is essential. A possible method that encloses the circuits, batteries, imaging device, etc into the capsule looped by an axially magnetized permanent-magnet ring is proposed. Based on expression of the axially magnetized permanent-magnet ring's magnetic fields, a localization and orientation model was established. An improved hybrid strategy that combines the advantages of particle-swarm optimization, clone algorithm, and the Levenberg-Marquardt algorithm was found to solve the model. Experiments showed that the hybrid strategy has good accuracy, convergence, and real time performance.

Doping effects on structural and magnetic properties of Heusler alloys Fe2Cr1-xCoxSi

NASA Astrophysics Data System (ADS)

Liu, Yifan; Ren, Lizhu; Zheng, Yuhong; He, Shikun; Liu, Yang; Yang, Ping; Yang, Hyunsoo; Teo, Kie Leong

2018-05-01

In this work, 30nm Fe2Cr1-xCoxSi (FCCS) magnetic films were deposited on Cr buffered MgO (100) substrates by sputtering. Fe2Cr0.5Co0.5Si exhibits the largest magnetization and optimal ordered L21 cubic structure at in-situ annealing temperature (Tia) of 450°C. The Co composition dependence of crystalline structures, surface morphology, defects, lattice distortions and their correlation with the magnetic properties are analyzed in detail. The Co-doped samples show in-plane M-H loops with magnetic squareness ratio of 1 and increasing anisotropy energy density with Co composition. Appropriate Co doping composition promotes L21 phase but higher Co composition converts L21 to B2 phase. Doping effect and lattice mismatch both are proved to increase the defect density. In addition, distortions of the FCCS lattice are found to be approximately linear with Co composition. The largest lattice distortion (c/a) is 0.969 for Fe2Cr0.25Co0.75Si and the smallest is 0.983 for Fe2CrSi. Our analyses suggest that these tetragonal distortions mainly induced by an elastic stress from Cr buffer account for the large in-plane anisotropy energy. This work paves the way for further tailoring the magnetic and structural properties of quaternary Heusler alloys.

Modeling of magnetic hystereses in soft MREs filled with NdFeB particles

NASA Astrophysics Data System (ADS)

Kalina, K. A.; Brummund, J.; Metsch, P.; Kästner, M.; Borin, D. Yu; Linke, J. M.; Odenbach, S.

2017-10-01

Herein, we investigate the structure-property relationships of soft magnetorheological elastomers (MREs) filled with remanently magnetizable particles. The study is motivated from experimental results which indicate a large difference between the magnetization loops of soft MREs filled with NdFeB particles and the loops of such particles embedded in a comparatively stiff matrix, e.g. an epoxy resin. We present a microscale model for MREs based on a general continuum formulation of the magnetomechanical boundary value problem which is valid for finite strains. In particular, we develop an energetically consistent constitutive model for the hysteretic magnetization behavior of the magnetically hard particles. The microstructure is discretized and the problem is solved numerically in terms of a coupled nonlinear finite element approach. Since the local magnetic and mechanical fields are resolved explicitly inside the heterogeneous microstructure of the MRE, our model also accounts for interactions of particles close to each other. In order to connect the microscopic fields to effective macroscopic quantities of the MRE, a suitable computational homogenization scheme is used. Based on this modeling approach, it is demonstrated that the observable macroscopic behavior of the considered MREs results from the rotation of the embedded particles. Furthermore, the performed numerical simulations indicate that the reversion of the sample’s magnetization occurs due to a combination of particle rotations and internal domain conversion processes. All of our simulation results obtained for such materials are in a good qualitative agreement with the experiments.

Preparation of Scandium-Doped, Textured, M-Type Barium Ferrite via a Wet Magnetizing Orientation Process

NASA Astrophysics Data System (ADS)

Wang, Yu; Liu, Yingli; Zhang, Huaiwu; Li, Jie; Gao, Liwen; Chen, Daming; Chen, Yong

2018-02-01

In this paper, a wet magnetizing orientation process was applied to synthesize c-axis-textured, M-type barium ferrite (BaFe12O19 or BaM), which is widely used to produce hard magnetic materials. To modify the magnetic properties of the BaM ferrite and make it suitable for certain operating frequencies, Sc3+ was substituted into Fe3+ sites of the BaM crystal structure. A BaSc x Fe12- x O19 ferrite with a typical relative density of ˜ 75% was successfully obtained. We used x-ray diffraction, scanning electronic microscopy, and a vibrating sample magnetometer to obtain phase information, detail of the microstructure, and magnetic properties of the BaSc x Fe12- x O19, respectively. The composition BaSc x Fe12- x O19 ( x = 0.1) featured a superior squareness ratio of ˜ 67% and a saturation magnetization ( M S) of ˜ 5300 Gauss in magnetic hysteresis loop measurements. These features match well with requirements for self-biased passive devices. Moreover, the site preference of Sc3+ in the hexagonal crystal structure was investigated.

The opposite induced magnetic moment in narrow zigzag graphene nanoribbons

NASA Astrophysics Data System (ADS)

Liu, Hong; Hu, Bian; Liu, Na

2016-11-01

Based on the analysis of band structure and edge states on zigzag graphene nanoribbons (ZGNRs), we can study theoretically the origination of two minimal quantum conductance. At the two energy points - 0.20 eV and 0.15 eV corresponding to the two dips of quantum conductance, the spin-polarized quantum conductance is about 45%. Furthermore, the two types of edge-localized carriers in the opposite transport directions along the two opposite edge sides form the quantum internal loop current, which can generate one big magnetic moment. At these two energy points - 0.17 eV and 0.15 eV the two induced magnetic moments are in opposite signals.

Influence of magnetic field structure on the conduction cooling of flare loops

NASA Technical Reports Server (NTRS)

Antiochos, S. K.; Sturrock, P. A.

1976-01-01

A simple model facilitates calculation of the influence of magnetic-field configuration on the conduction cooling rate of a hot post-flare coronal plasma. The magnetic field is taken to be that produced by a line dipole or point dipole at an arbitrary depth below the chromosphere. For the high temperatures (at least 10 million K) produced by flares, the plasma may remain static and isobaric. The influence of the field is such as to increase the heat flux (per unit area) into the chromosphere, but to decrease the total conduction cooling of the flare plasma. This leads to a significant enhancement of the total energy radiated by the flare plasma.

Energy and helicity of magnetic torus knots and braids

NASA Astrophysics Data System (ADS)

Oberti, Chiara; Ricca, Renzo L.

2018-02-01

By considering steady magnetic fields in the shape of torus knots and unknots in ideal magnetohydrodynamics, we compute some fundamental geometric and physical properties to provide estimates for magnetic energy and helicity. By making use of an appropriate parametrization, we show that knots with dominant toroidal coils that are a good model for solar coronal loops have negligible total torsion contribution to magnetic helicity while writhing number provides a good proxy. Hence, by the algebraic definition of writhe based on crossing numbers, we show that the estimated values of writhe based on image analysis provide reliable information for the exact values of helicity. We also show that magnetic energy is linearly related to helicity, and the effect of the confinement of magnetic field can be expressed in terms of geometric information. These results can find useful application in solar and plasma physics, where braided structures are often present.

Polyethylene glycol coated CoFe{sub 2}O{sub 4} nanoparticles: A potential spinel ferrite for biomedical applications

DOE Office of Scientific and Technical Information (OSTI.GOV)

Humbe, Ashok V.; Birajdar, Shankar D.; Jadhav, K. M., E-mail: drjadhavkm@gmail.com

2015-06-24

The structural and magnetic properties of the polyethylene glycol (PEG) coated cobalt spinel ferrite (CoFe{sub 2}O{sub 4}) nanoparticles have been reported in the present study. CoFe{sub 2}O{sub 4} nanoparticles were prepared by sol-gel auto-combustion method using citric acid + ethylene glycol as a fuel. The prepared powder of cobalt ferrite nanoparticles was annealed at 600°C for 6h and used for further study. The structural characterization of CoFe{sub 2}O{sub 4} nanoparticles were carried out by X-ray diffraction technique. The X-ray analysis confirmed the formation of single phase cubic spinel structure. The crystallite size, Lattice constant and X-ray density of the PEGmore » coated CoFe{sub 2}O{sub 4} nanoparticles were calculated by using XRD data. The presence of PEG on CoFe{sub 2}O{sub 4} nanoparticles and reduced agglomeration in the CoFe{sub 2}O{sub 4} nanoparticles were revealed by SEM studies. The magnetic properties were studied by pulse field hysteresis loop tracer technique at a room temperature. The magnetic parameters such as saturation magnetization, remanence magnetization, coercivity etc have been obtained. These magnetic parameters were get decreased by PEG coating.« less

Aspect-ratio dependence of magnetization reversal in cylindrical ferromagnetic nanowires

NASA Astrophysics Data System (ADS)

Sultan, Musaab S.; Atkinson, Del

2016-05-01

The magnetization reversal behavior in isolated cylindrical and square cross-section Ni81Fe19 nanowires was systematically studied as a function of nanowire cross-section dimensions from 10 up to 200 nm using micromagnetic simulations. This approach provides access to the switching field, remanence ratio and most significantly the magnetization structures during reversal, which allows the evolution of magnetization processes to be studied with scaling of the cross-sectional dimensions. The dimensional trends in reversal behavior for both square and circular cross-section were comparable throughout the range of dimensions studied. The thinnest nanowires showed simple square switching and 100% remanence. With increasing diameter the switching field reduces and above 40 nm the reversal behavior shows an increasing rotational component prior to sharp switching of the magnetization. The magnitude of the reversible component increases with increasing dimensions up to 150 nm, above which the magnetization reversal process is more complicated and the hysteresis loops are no longer bistable. The micromagnetic structures evolve from simple uniform parallel single domain states in the thinnest wires through the formation of vortex-like end states in thicker wires to complex multidomain structures during the reversal of the thickest wires. In the later cases the reversal is not simple curling-like behavior, although the angular switching field dependence was comparable with curling.

Magnetic-field-induced irreversible antiferromagnetic-ferromagnetic phase transition around room temperature in as-cast Sm-Co based SmCo7-xSix alloys

NASA Astrophysics Data System (ADS)

Feng, D. Y.; Zhao, L. Z.; Liu, Z. W.

2016-04-01

A magnetic-field-induced irreversible metamagnetic phase transition from antiferro- to ferromagnetism, which leads to an anomalous initial-magnetization curve lying outside the magnetic hysteresis loop, is reported in arc-melted SmCo7-xSix alloys. The transition temperatures are near room temperature, much higher than other compounds with similar initial curves. Detailed investigation shows that this phenomenon is dependent on temperature, magnetic field and Si content and shows some interesting characteristics. It is suggested that varying interactions between the Sm and Co layers in the crystal are responsible for the formation of a metastable AFM structure, which induces the anomalous phenomenon in as-cast alloys. The random occupation of 3g sites by Si and Co atoms also has an effect on this phenomenon.

A numerical study on flexoelectric bistable energy harvester

NASA Astrophysics Data System (ADS)

Kumar, Anuruddh; Sharma, Anshul; Vaish, Rahul; Kumar, Rajeev; Jain, Satish Chandra

2018-07-01

A flexoelectric energy harvesting can be a viable solution of energy source for low power devices and sensors due to its higher performance at nano/micro domain size. Numerical study has been performed on energy harvester based on flexoelectric phenomenon of dielectric materials. Cantilever type structure was opted here as it induces the polarization due to the breaking of lattice symmetry upon bending. Host layer of cantilever is made of barium strontium titanate (BST) as it has high flexoelectric coefficient, and electrodes are attached with the host layer to collect the charges. In this study, nonlinearity has been introduced using pair of magnets at the free end of the cantilever. Characteristics of the harvester performance (linear-non-linear) changes by varying the distance between magnets. Results revealed that the bistable energy harvester gives more operating frequency range when excitation is random as compared to the linear energy harvester. For the given dimension of the harvester, when magnets distance d = 6 mm, effective harvesting frequency ranges are 5-17.3 and 17.6-26 Hz as compared to linear harvester. Further, role of load resistance was investigated to understand the impact on the performance. Hysteresis loop between voltage and displacement significantly varies with the resistance. This hysteresis loop confirmed the backward coupling of flexoelectric layer, in which voltage affects the displacement due to actuation. Area under the hysteresis loop is maximum for optimum resistance value (20.4 kΩ) which confirms the maximum extraction of power during vibration.

Witnessing a Large-scale Slipping Magnetic Reconnection along a Dimming Channel during a Solar Flare

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jing, Ju; Lee, Jeongwoo; Xu, Yan

We report the intriguing large-scale dynamic phenomena associated with the M6.5 flare (SOL2015-06-22T18:23) in NOAA active region 12371, observed by RHESSI , Fermi , and the Atmospheric Image Assembly (AIA) and Magnetic Imager (HMI) on the Solar Dynamics Observatory ( SDO ). The most interesting feature of this event is a third ribbon (R3) arising in the decay phase, propagating along a dimming channel (seen in EUV passbands) toward a neighboring sunspot. The propagation of R3 occurs in the presence of hard X-ray footpoint emission and is broadly visible at temperatures from 0.6 MK to over 10 MK through themore » differential emission measure analysis. The coronal loops then undergo an apparent slipping motion following the same path of R3, after a ∼80 minute delay. To understand the underlying physics, we investigate the magnetic configuration and the thermal structure of the flaring region. Our results are in favor of a slipping-type reconnection followed by the thermodynamic evolution of coronal loops. In comparison with those previously reported slipping reconnection events, this one proceeds across a particularly long distance (∼60 Mm) over a long period of time (∼50 minutes) and shows two clearly distinguished phases: the propagation of the footpoint brightening driven by nonthermal particle injection and the apparent slippage of loops governed by plasma heating and subsequent cooling.« less

3D Realistic Modeling of the Interaction of Quiet-Sun Magnetic Fields with the Chromosphere

NASA Technical Reports Server (NTRS)

Kitiashvili, I. N.; Kosovichev, A. G.; Mansour, N. N.; Wray, A. A.

2017-01-01

High-resolution observations and 3D simulations suggest that a local dynamo operates near the surface and produces ubiquitous small-scale magnetic elements, thus contributing to the magnetic carpet in the photosphere and to the magnetic structure and dynamics of the solar atmosphere. It appears that the traditional mechanisms of chromospheric energy and mass transport by acoustic waves and shocks are likely to play a secondary role; instead, the primary drivers in the energetics and dynamics of the chromosphere and transition region are small-scale, previously unresolved, quiet-Sun magnetic fields. These fields appear as ubiquitous, rapidly changing (on the scale of a few seconds), tiny magnetic loops and magnetized vortex tubes. Questions then arise about their origin and dynamics in the chromosphere, their links to magnetic fields in the photosphere, and their role in the energy storage and exchange between subsurface layers and the chromosphere. In the talk we will present results of 3D radiative MHD simulations obtained with the StellarBox code and discuss the energetics and dynamical interlinks between the subphotospheric layers and low chromosphere, their effects on the structure of the chromosphere, and signatures of the fine-scale magnetic features in high-resolution spectro-polarimetric observations.

Microwave properties of Ni-based ferromagnetic inverse opals

NASA Astrophysics Data System (ADS)

Kostylev, M.; Stashkevich, A. A.; Roussigné, Y.; Grigoryeva, N. A.; Mistonov, A. A.; Menzel, D.; Sapoletova, N. A.; Napolskii, K. S.; Eliseev, A. A.; Lukashin, A. V.; Grigoriev, S. V.; Samarin, S. N.

2012-11-01

Investigations of microwave properties of Ni-based inverse ferromagnetic opal-like film with the [111] axis of the fcc structure along the normal direction to the film have been carried out in the 2-18 GHz frequency band. We observed multiple spin wave resonances for the magnetic field applied perpendicular to the film, i.e., along the [111] axis of this artificial crystal. For the field applied in the film plane, a broad band of microwave absorption is observed, which does not contain a fine structure. The field ranges of the responses observed are quite different for these two magnetization directions. This suggests a collective magnetic ground state or shape anisotropy and collective microwave dynamics for this foam-like material. This result is in agreement with SQUID measurements of hysteresis loops for the material. Two different models for this collective behavior are suggested that satisfactorily explain the major experimental results.

Theoretical properties of Omega-loops in the convective zone of the Sun. 1: Emerging bipolar magnetic regions

NASA Technical Reports Server (NTRS)

Parker, E. N.

1994-01-01

It is proposed that the observed 500 G intensity of the magnetic fields emerging through the surface of the Sun can be understood from the Bernoulli effect in the upwelling Omega-loops of magnetic field. It is also proposed that the inferred 10(exp 5) G azimuthal flux bundles below the base of the convective zone can be understood as a consequence of the large-scale buoyancy associated with the upwelling fluid in and around the rising Omega-loop. The process fits in naturally with the Babcock-Leighton form of the solar alpha-omega-dynamo. The emerging Omega-loop implies the coherence of the upwelling all the way from the bottom of the convective zone, enhancing the convective heat transport to account for the observed variation of the solar irradiance by about two parts in 10(exp 3).

Comparison of electric dipole and magnetic loop antennas for exciting whistler modes

DOE Office of Scientific and Technical Information (OSTI.GOV)

Stenzel, R. L.; Urrutia, J. M.

2016-08-15

The excitation of low frequency whistler modes from different antennas has been investigated experimentally in a large laboratory plasma. One antenna consists of a linear electric dipole oriented across the uniform ambient magnetic field B{sub 0}. The other antenna is an elongated loop with dipole moment parallel to B{sub 0}. Both antennas are driven by the same rf generator which produces a rf burst well below the electron cyclotron frequency. The antenna currents as well as the wave magnetic fields from each antenna are measured. Both the antenna currents and the wave fields of the loop antenna exceed that ofmore » the electric dipole by two orders of magnitude. The conclusion is that loop antennas are far superior to dipole antennas for exciting large amplitude whistler modes, a result important for active wave experiments in space plasmas.« less

Magnetoelastic Properties of Magnetic Thin Films Using the Magnetooptic Kerr Effect

NASA Astrophysics Data System (ADS)

Mayo, Elizabeth; Lederman, David

1998-03-01

The magnetoelastic properties of Co and Fe thin films were measured using the magnetooptic Kerr effect (MOKE). Films were grown via magnetron sputtering on thin mica substrates. Magnetization loops were measured using MOKE with the magnetic field along different in-plane directions. Subsequently, the samples were mounted on a cylindrical sample holder, which imposed a well-defined strain to the film. This caused the magnetization loops to change dramatically due to the magnetoelastic coefficient of the thin film materials. The effects of the surface roughness and film thickness will also be discussed.

Passive magnetic bearing for a motor-generator

DOEpatents

Post, Richard F [Walnut Creek, CA

2006-07-18

Conductive lap windings are interleaved with conventional loops in the stator of a motor-generator. The rotor provides magnetic induction lines that, when rotated, cut across the lap windings and the loops. When the rotor is laterally displaced from its equilibrium axis of rotation, its magnetic lines of induction induce a current in the interleaved lap windings. The induced current interacts with the magnetic lines of induction of the rotor in accordance with Lenz's law to generate a radial force that returns the rotor to its equilibrium axis of rotation.

The Structure and Dynamics of the Solar Corona and Inner Heliosphere

NASA Technical Reports Server (NTRS)

Mikic, Zoran

2002-01-01

This report covers technical progress during the second quarter of the first year of NASA Sun-Earth Connections Theory Program (SECTP) contract 'The Structure and Dynamics of the Solar Corona and Inner Heliosphere,' NAS5-99188, between NASA and Science Applications International Corporation. and covers the period November 16, 1999 to February 15, 2000. Under this contract SAIC and the University of California, Irvine (UCI) have conducted research into theoretical modeling of active regions, the solar corona, and the inner heliosphere, using the MHD (magnetohydrodynamic) model. The topics studied include: the effect of emerging flux on the stability of helmet streamers, coronal loops and streamers, the solar magnetic field, the solar wind, and open magnetic field lines.

Strong coercivity reduction and high initial permeability in NiCoP coated BaFe12O19-polystyrene bilayer composite

NASA Astrophysics Data System (ADS)

Hamad, Mahmoud A.; El-Sayed, Adly H.; Hemeda, O. M.; Tawfik, A.

2016-03-01

Soft-magnetic NiCoP coated hard-magnetic M-type ferrite BaFe12O19 (BaM)-polystyrene (PS) bilayer composite film was successfully synthesized. X-ray diffraction peaks exhibited no change in the structure of BaM after coating with PS. The NiCoP coated BaM-PS composite exhibited a wasp-waisted magnetic hysteretic loop with remarkable reduction in the coercivity, remanence and squareness with respect to BaM-PS, which is useful for the core of a magnetic switching device to control currents so large that they are unmanageable. Moreover, the initial permeability measurement exhibits initial permeability of around 100 000 and thermal stability up to 558 K, which is good for flux-amplifying components of smaller inductors.

Compositional dependence of magnetic anisotropy in chemically synthesized Co3- x Fe x O4 (0 ≤ x ≤ 2)

NASA Astrophysics Data System (ADS)

Hayashi, Kensuke; Yamada, Keisuke; Shima, Mutsuhiro

2018-01-01

Magnetic anisotropy of Co3- x Fe x O4 (CFO, 0 ≤ x ≤ 2) thin-film and powder samples prepared by a sol-gel method has been investigated as a function of Fe composition x. Structural analyses by X-ray diffraction show that CFO powder samples exhibit diffraction peaks associated with the spinel structure when x < 2, while CFO thin-film samples with thickness of 130-510 nm yield the peaks when 0 ≤ x ≤ 2. CFO thin-film samples are highly (111)-oriented with the Lotgering factor greater than 0.9 when 0.6 ≤ x ≤ 1.3. The magnetic anisotropy constant K 1 of CFO powder samples estimated from their room-temperature hysteresis loops yields a minimum when x = 0.9. Relatively large in-plane magnetic anisotropy (K eff = 5.7 × 105 erg/cm3) is observed for the CFO thin-film sample when x = 1.3. With increasing x, the magnetic easy axis of the spinel CFO changes from 〈111〉 to 〈100〉 when x = 0.9.

Helicity charging and eruption of magnetic flux from the Sun

NASA Technical Reports Server (NTRS)

Rust, David M.; Kumar, A.

1994-01-01

The ejection of helical toroidal fields from the solar atmosphere and their detection in interplanetary space are described. The discovery that solar magnetic fields are twisted and that they are segregated by hemisphere according to their chirality has important implications for the escape process. The roles played by erupting prominences, coronal mass ejections (CME's) and active region (AR) loops in expressing the escape of magnetic flux and helicity are discussed. Sporadic flux escape associated with filament eruptions accounts for less than one-tenth the flux loss. Azimuthal flux loss by CME's could account for more, but the major contributor to flux escape may be AR loop expansion. It is shown how the transfer of magnetic helicity from the sun's interior into emerged loops ('helicity charging') could be the effective driver of solar eruptions and of flux loss from the sun.

Structural and sequencing analysis of local target DNA recognition by MLV integrase.

PubMed

Aiyer, Sriram; Rossi, Paolo; Malani, Nirav; Schneider, William M; Chandar, Ashwin; Bushman, Frederic D; Montelione, Gaetano T; Roth, Monica J

2015-06-23

Target-site selection by retroviral integrase (IN) proteins profoundly affects viral pathogenesis. We describe the solution nuclear magnetic resonance structure of the Moloney murine leukemia virus IN (M-MLV) C-terminal domain (CTD) and a structural homology model of the catalytic core domain (CCD). In solution, the isolated MLV IN CTD adopts an SH3 domain fold flanked by a C-terminal unstructured tail. We generated a concordant MLV IN CCD structural model using SWISS-MODEL, MMM-tree and I-TASSER. Using the X-ray crystal structure of the prototype foamy virus IN target capture complex together with our MLV domain structures, residues within the CCD α2 helical region and the CTD β1-β2 loop were predicted to bind target DNA. The role of these residues was analyzed in vivo through point mutants and motif interchanges. Viable viruses with substitutions at the IN CCD α2 helical region and the CTD β1-β2 loop were tested for effects on integration target site selection. Next-generation sequencing and analysis of integration target sequences indicate that the CCD α2 helical region, in particular P187, interacts with the sequences distal to the scissile bonds whereas the CTD β1-β2 loop binds to residues proximal to it. These findings validate our structural model and disclose IN-DNA interactions relevant to target site selection. © The Author(s) 2015. Published by Oxford University Press on behalf of Nucleic Acids Research.

Magnetic antenna excitation of whistler modes. III. Group and phase velocities of wave packets

NASA Astrophysics Data System (ADS)

Urrutia, J. M.; Stenzel, R. L.

2015-07-01

The properties of whistler modes excited by single and multiple magnetic loop antennas have been investigated in a large laboratory plasma. A single loop excites a wavepacket, but an array of loops across the ambient magnetic field B0 excites approximate plane whistler modes. The single loop data are measured. The array patterns are obtained by linear superposition of experimental data shifted in space and time, which is valid in a uniform plasma and magnetic field for small amplitude waves. Phasing the array changes the angle of wave propagation. The antennas are excited by an rf tone burst whose propagating envelope and oscillations yield group and phase velocities. A single loop antenna with dipole moment across B0 excites wave packets whose topology resembles m = 1 helicon modes, but without radial boundaries. The phase surfaces are conical with propagation characteristics of Gendrin modes. The cones form near the antenna with comparable parallel and perpendicular phase velocities. A physical model for the wave excitation is given. When a wave burst is applied to a phased antenna array, the wave front propagates both along the array and into the plasma forming a "whistler wing" at the front. These laboratory observations may be relevant for excitation and detection of whistler modes in space plasmas.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Hahn, M.; Savin, D. W.

We have measured the energy and dissipation of Alfvénic waves in the quiet Sun. A magnetic field model was used to infer the location and orientation of the magnetic field lines along which the waves are expected to travel. The waves were measured using spectral lines to infer the wave amplitude. The waves cause a non-thermal broadening of the spectral lines, which can be expressed as a non-thermal velocity v {sub nt}. By combining the spectroscopic measurements with this magnetic field model, we were able to trace the variation of v {sub nt} along the magnetic field. At each footpointmore » of the quiet-Sun loops, we find that waves inject an energy flux in the range of 1.3-5.5 × 10{sup 5} erg cm{sup –2} s{sup –1}. At the minimum of this range, this amounts to more than 80% of the energy needed to heat the quiet Sun. We also find that these waves are dissipated over a region centered on the top of the loops. The position along the loop where the damping begins is strongly correlated with the length of the loop, implying that the damping mechanism depends on the global loop properties rather than on local collisional dissipation.« less

Subresolution Activity in Solar and Stellar Coronae from Magnetic Field Line Tangling

NASA Astrophysics Data System (ADS)

Rappazzo, A. F.; Dahlburg, R. B.; Einaudi, G.; Velli, M.

2018-05-01

The heating of coronal loops is investigated to understand the observational consequences in terms of the thermodynamics and radiative losses from the Sun as well as the magnetized coronae of stars with an outer convective envelope. The dynamics of the Parker coronal heating model are studied for different ratios of the photospheric forcing velocity timescale tp to the Alfvén crossing time along a loop tA. It is shown that for tp/tA ≳ 10-24 the heating rate and maximum temperature are largest and approximately independent of tp/tA, leading to a strong emission in X-rays and EUV. On the opposite decreasing tp/tA to smaller values leads to lower heating rates and plasma temperatures, and consequently fading high-energy radiative emission once tp/tA ≲ 1-3. The average volumetric loop heating rate is shown to scale as ℓ _p u_p B_0^2/4π L^2, where ℓp and up are respectively the convective granule length-scale and velocity, B0 is the intensity of the strong magnetic field threading the loop, and L the loop length. These findings support a recent hypothesis explaining ultracool dwarf observations of stars with similar magnetic field strength but radically different topologies displaying different radiative emission.

Nd: YAG laser irradiation effects on structural and magnetic properties of Ni1+xZrxFe2-2xO4 nanoparticles

NASA Astrophysics Data System (ADS)

Saraf, Tukaram S.; Kounsalye, Jitendra S.; Birajdar, Shankar D.; Shamkuwar, N. R.

2018-05-01

The effect of 112 mJ Nd: YAG laser irradiation on structural, morphological, infrared and magnetic properties of Ni1+xZrxFe2-2xO4 spinel ferrite nanoparticles has been systematically investigated in the present work. The sol-gel auto combustion synthesis method was successfully executed for the synthesis of the present system. All the samples were characterized by X-ray diffraction technique (XRD), scanning electron microscopy (SEM) and infrared spectroscopy (IR) technique. The magnetic properties of the present samples were measured by pulse field hysteresis loop technique. All the properties were measured for laser irradiated samples as well, to understand the effect of irradiation on the properties. The single-phase cubic spinel structure was confirmed by X-ray diffraction patterns of all samples and the disordered structure was observed for irradiated samples. The two principle absorption bands in IR spectra also confirm the formation of the spinel structure. Spherical and agglomerated morphology was observed for Zr4+ substituted nickel ferrite, whereas scratched morphology was observed for the irradiated samples. The grain size confirms the nanocrystalline nature, the crystallite size also evident the same. The magnetic parameters decreased after Zr4+ ion doping and strongly influenced by the irradiation.

Coupling Influences SMM Properties for Pure 4 f Systems.

PubMed

Zhang, Xuejing; Liu, Shuang; Vieru, Veacheslav; Xu, Na; Gao, Chen; Wang, Bing-Wu; Shi, Wei; Chibotaru, Liviu F; Gao, Song; Cheng, Peng; Powell, Annie K

2018-04-20

Increasing both the energy barrier for magnetization reversal and the coercive field of the hysteresis loop are significant challenges in the field of single-molecule magnets (SMMs). Coordination geometries of lanthanide ions and magnetic interactions between lanthanide ions are both important for guiding the magnetic behavior of SMMs. We report a high energy barrier of 657 K (457 cm -1 ) in a diamagnetic-ion-diluted lanthanide chain compound with a constrained bisphenoid symmetry (D 2d ); this energy barrier is substantially higher than the barrier of 567 K (394 cm -1 ) of the non-diluted chain compound with intrachain ferromagnetic interactions. Although intrachain magnetic interaction lowers the energy barrier for magnetization reversal, it can greatly enhance the coercive fields and zero-field remanence of the hysteresis loops, which is crucial for the rational design of high-performance SMMs. Factors related to the coordination sphere of the lanthanide center, which govern the high magnetic relaxation barriers through the second excited Kramer's doublets and the magnetic interactions that affect the hysteresis loops, were revealed through ab initio calculations. © 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.

Parameters of loop-controlled magnetic rheology drive for segmented large mirror

NASA Astrophysics Data System (ADS)

Deulin, Eugeni A.; Mikhailov, Valeri P.; Eliseev, Oleg N.; Sytchev, Victor V.

2000-07-01

The design, parameters and the amplitude-frequency analysis of the new magnetic rheology (MR) drive are presented. The combination of hydrostatic carrier, MR hydraulic loop control, elastic thin wall seal joined in a single unit ensures small positioning error nm and small time of response T

Damped transverse oscillations of interacting coronal loops

NASA Astrophysics Data System (ADS)

Soler, Roberto; Luna, Manuel

2015-10-01

Damped transverse oscillations of magnetic loops are routinely observed in the solar corona. This phenomenon is interpreted as standing kink magnetohydrodynamic waves, which are damped by resonant absorption owing to plasma inhomogeneity across the magnetic field. The periods and damping times of these oscillations can be used to probe the physical conditions of the coronal medium. Some observations suggest that interaction between neighboring oscillating loops in an active region may be important and can modify the properties of the oscillations. Here we theoretically investigate resonantly damped transverse oscillations of interacting nonuniform coronal loops. We provide a semi-analytic method, based on the T-matrix theory of scattering, to compute the frequencies and damping rates of collective oscillations of an arbitrary configuration of parallel cylindrical loops. The effect of resonant damping is included in the T-matrix scheme in the thin boundary approximation. Analytic and numerical results in the specific case of two interacting loops are given as an application.

New method of computing the contributions of graphs without lepton loops to the electron anomalous magnetic moment in QED

NASA Astrophysics Data System (ADS)

Volkov, Sergey

2017-11-01

This paper presents a new method of numerical computation of the mass-independent QED contributions to the electron anomalous magnetic moment which arise from Feynman graphs without closed electron loops. The method is based on a forestlike subtraction formula that removes all ultraviolet and infrared divergences in each Feynman graph before integration in Feynman-parametric space. The integration is performed by an importance sampling Monte-Carlo algorithm with the probability density function that is constructed for each Feynman graph individually. The method is fully automated at any order of the perturbation series. The results of applying the method to 2-loop, 3-loop, 4-loop Feynman graphs, and to some individual 5-loop graphs are presented, as well as the comparison of this method with other ones with respect to Monte Carlo convergence speed.

Synthesis, structural and magnetic behavior studies of Zn-Al substituted cobalt ferrite nanoparticles

NASA Astrophysics Data System (ADS)

Zare, Samad; Ati, Ali A.; Dabagh, Shadab; Rosnan, R. M.; Othaman, Zulkafli

2015-06-01

A series of nano-sized Zn-Al substituted cobalt ferrite Co(1-x)Zn(x)Fe2-xAlxO4 with 0.0 ⩽ x ⩽ 1.0 have been synthesized by chemical co-precipitation technique. The XRD spectra revealed the single phase spinel structure of Co(1-x)Zn(x)Fe2-xAlxO4 with average size of nanoparticles are estimated to be 17-30 nm. These are small enough to achieve the suitable signal to noise ratio, which is important in the high-density recording media. The FTIR spectra show the characteristic of two strong absorption bands at 560-600 cm-1 corresponds to the intrinsic stretching vibrations of the metal at the tetrahedral site and lowest band is observed at 370-410 cm-1 corresponds to octahedral site. The crystalline structures of nanoparticles composite were characterized by Field Emission Scanning Electron Microscopy (FE-SEM). The magnetic properties such as saturation magnetization, remanence magnetization, and coercivity were calculated from the hysteresis loops. Saturation magnetization were found to increase up to x = 0.4 while remanence magnetization and coercivity continuously decrease with increasing Zn-Al concentration. The stability in coercivity while increase in saturation magnetization confirms that the Co0.6Zn0.4Fe1.6Al0.4O4 ferrite sample is suitable for applications in high-density recording media.

Impact of structural symmetry on magnetization properties in SrCo0.95Mn0.05O3 prepared by sol-gel method

NASA Astrophysics Data System (ADS)

Kumar, Amit; Meenakshi, Mahto, Rabindra Nath

2018-04-01

We have investigated magnetization properties of the sol-gel prepared SrCo0.95Mn0.05O3 (SCMO) sample with respect to change in structural symmetry. The X-ray diffraction patterns show the crystal structure changes from nH-hexagonal, showing trigonal symmetry (SCMO1), to 2H-hexagonal phase (SCMO2). The trigonal crystal symmetry was obtained at lower annealing temperature (less than 1100 °C), however, the 2H-hexagonal symmetry was obtained at higher annealing temperature. The crystallite size calculated using Debye Scherer formula is found to be ˜ 46 nm and ˜ 33 nm for SCMO1 and SCMO2 samples respectively. The temperature dependence zero field cooled (MZFC) and field cooled (MFC) magnetization curves measured under the applied magnetic field of 500 Oe show magnetic reversibility for the SCMO1 sample. However, MZFC and MFC curves in hexagonal phase show magnetic irreversibility with onset temperature, Tirr ˜ 150 K, exhibits weak ferromagnetic ordering. The temperature variation of magnetization in paramagnetic region was analyzed by following Curie-Weiss law fitting. The χ-1(T) curve shows complete linear behavior with single slope for SCMO1 sample, whereas, the SCMO2 curve exhibit the linear behavior with two distinct slopes. Interestingly the sample in hexagonal phase shows small hysteresis loop at 2 K and 100 K respectively.

The thermal stability of magnetically exchange coupled MnBi/FeCo composites at electric motor working temperature

NASA Astrophysics Data System (ADS)

Cheng, Ye; Wang, Hongying; Li, Zhigang; Liu, Wanhui; Bao, Ilian

2018-04-01

The magnetically exchange coupled MnBi/FeCo composites were synthesized through a magnetic self-assembly process. The MnBi/FeCo composites were then hot pressed in a magnetic field to form magnets. The thermal stability of the magnets were tested by annealing at electric motor working temperature of 200 °C for 20, 40 and 60 h, respectively. It was found that after heating for 20 h, there was negligible change in its hysteresis loop. However, when the heating time was increased 40 and 60 h, the magnetic hysteresis loops presented two-phase magnetic behaviors, and the maximum energy products of the magnet were decreased. This research showed that the magnetically exchange coupled MnBi/FeCo composites had low thermal stability at electric motor working temperature.

Standing Kink modes in three-dimensional coronal loops

DOE Office of Scientific and Technical Information (OSTI.GOV)

Pascoe, D. J.; De Moortel, I., E-mail: dpascoe@mcs.st-andrews.ac.uk

2014-04-01

So far, the straight flux tube model proposed by Edwin and Roberts is the most commonly used tool in practical coronal seismology, in particular, to infer values of the (coronal) magnetic field from observed, standing kink mode oscillations. In this paper, we compare the period predicted by this basic model with three-dimensional (3D) numerical simulations of standing kink mode oscillations, as the period is a crucial parameter in the seismological inversion to determine the magnetic field. We perform numerical simulations of standing kink modes in both straight and curved 3D coronal loops and consider excitation by internal and external drivers.more » The period of oscillation for the displacement of dense coronal loops is determined by the loop length and the kink speed, in agreement with the estimate based on analytical theory for straight flux tubes. For curved coronal loops embedded in a magnetic arcade and excited by an external driver, a secondary mode with a period determined by the loop length and external Alfvén speed is also present. When a low number of oscillations is considered, these two periods can result in a single, non-resolved (broad) peak in the power spectrum, particularly for low values of the density contrast for which the two periods will be relatively similar. In that case (and for this particular geometry), the presence of this additional mode would lead to ambiguous seismological estimates of the magnetic field strength.« less

Temperature and field dependent magnetization studies on nano-crystalline ZnFe2O4 thin films

NASA Astrophysics Data System (ADS)

Sahu, B. N.; Suresh, K. G.; Venkataramani, N.; Prasad, Shiva; Krishnan, R.

2018-05-01

Single phase nano-crystalline zinc ferrite (ZnFe2O4) thin films were deposited on fused quartz substrate using the pulsed laser deposition technique. The films were deposited at different substrate temperatures. The field dependence of magnetization at 10 K shows hysteresis loops for all the samples. Temperature dependence of the field cooled (FC) and zero field cooled (ZFC) magnetization indicated irreversible behavior between the FC and ZFC data, and the irreversibility depends on the measuring magnetic field. The thermo-magnetic irreversibility in the magnetization data is correlated with the magnitude of the applied field and the coercivity (HC) obtained from the M-H loops.

Simulation of magnetic hysteresis loops and magnetic Barkhausen noise of α-iron containing nonmagnetic particles

DOE PAGES

Li, Yi; Xu, Ben; Hu, Shenyang; ...

2015-07-01

The magnetic hysteresis loops and Barkhausen noise of a single α-iron with nonmagnetic particles are simulated to investigate into the magnetic hardening due to Cu-rich precipitates in irradiated reactor pressure vessel (RPV) steels. Phase field method basing Landau-Lifshitz-Gilbert (LLG) equation is used for this simulation. The results show that the presence of the nonmagnetic particle could result in magnetic hardening by making the nucleation of reversed domains difficult. The coercive field is found to increase, while the intensity of Barkhausen noise voltage is decreased when the nonmagnetic particle is introduced. Simulations demonstrate the impact of nucleation field of reversed domainsmore » on the magnetization reversal behavior and the magnetic properties.« less

Rotor Position Sensorless Control and Its Parameter Sensitivity of Permanent Magnet Motor Based on Model Reference Adaptive System

NASA Astrophysics Data System (ADS)

Ohara, Masaki; Noguchi, Toshihiko

This paper describes a new method for a rotor position sensorless control of a surface permanent magnet synchronous motor based on a model reference adaptive system (MRAS). This method features the MRAS in a current control loop to estimate a rotor speed and position by using only current sensors. This method as well as almost all the conventional methods incorporates a mathematical model of the motor, which consists of parameters such as winding resistances, inductances, and an induced voltage constant. Hence, the important thing is to investigate how the deviation of these parameters affects the estimated rotor position. First, this paper proposes a structure of the sensorless control applied in the current control loop. Next, it proves the stability of the proposed method when motor parameters deviate from the nominal values, and derives the relationship between the estimated position and the deviation of the parameters in a steady state. Finally, some experimental results are presented to show performance and effectiveness of the proposed method.

Coronal Structure of a Flaring Region and Associated Coronal Mass Ejection

NASA Technical Reports Server (NTRS)

Kundu, Mukul R.; Manoharan, P. K.

2003-01-01

We report the multiwavelength investigations of an eruptive flare event that occurred on 2001 April 2 at about 11 UT. The manifestations associated with this flare event have been studied from the near-Sun region to about 0.5 AU. The H-alpha images from the Meudon Spectroheliograph reveal a fast spectacular eruption of plasmoids from the flare site to the west and a Moreton wave disturbance propagating toward the south, A bright, fast, wide coronal mass ejection (CME) associated with this eruptive event was imaged by SOHO/LASCO and the remote-sensing interplanetary scintillation technique. The timings and positions of the Type II radio bursts, H-alpha eruption, and CME onset as well as the magnetic field configuration suggest a release of energy at the null point. The results seem to support the "breakout" scenario proposed by Antiochos and coworkers, and they are also suggestive that the energy release is followed by magnetic reconnection between the low-lying loops near the separatrix and the loop system above them.

EFFECTS OF ALFVEN WAVES ON ELECTRON CYCLOTRON MASER EMISSION IN CORONAL LOOPS AND SOLAR TYPE I RADIO STORMS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zhao, G. Q.; Chen, L.; Wu, D. J.

Solar type I radio storms are long-lived radio emissions from the solar atmosphere. It is believed that these type I storms are produced by energetic electrons trapped within a closed magnetic structure and are characterized by a high ordinary (O) mode polarization. However, the microphysical nature of these emissions is still an open problem. Recently, Wu et al. found that Alfven waves (AWs) can significantly influence the basic physics of wave-particle interactions by modifying the resonant condition. Taking the effects of AWs into account, this work investigates electron cyclotron maser emission driven by power-law energetic electrons with a low-energy cutoffmore » distribution, which are trapped in coronal loops by closed solar magnetic fields. The results show that the emission is dominated by the O mode. It is proposed that this O mode emission may possibly be responsible for solar type I radio storms.« less

Velocity feedback control with a flywheel proof mass actuator

NASA Astrophysics Data System (ADS)

Kras, Aleksander; Gardonio, Paolo

2017-08-01

This paper presents four new proof mass actuators to be used in velocity feedback control systems for the control of vibrations of machines and flexible structures. A classical proof mass actuator is formed by a coil-magnet linear motor, with either the magnet or the armature-coil proof mass suspended on soft springs. This arrangement produces a net force effect at frequencies above the fundamental resonance frequency of the springs-proof mass system. Thus, it can be used to implement point velocity feedback loops, although the dynamic response and static deflection of the springs-proof mass system poses some stability and control performance limitations. The four proof mass actuators presented in this study include a flywheel element, which is used to augment the inertia effect of the suspended proof mass. The paper shows that the flywheel element modifies both the dynamic response and static deflection of the springs-proof mass system in such a way as the stability and control performance of velocity feedback loops using these actuators are significantly improved.

Antenna design for propagating spin wave spectroscopy in ferromagnetic thin films

NASA Astrophysics Data System (ADS)

Zhang, Yan; Yu, Ting; Chen, Ji-lei; Zhang, You-guang; Feng, Jian; Tu, Sa; Yu, Haiming

2018-03-01

In this paper, we investigate the characteristics of antenna for propagating-spin-wave-spectroscopy (PSWS) experiment in ferromagnetic thin films. Firstly, we simulate the amplitude and phase distribution of the high-frequency magnetic field around antenna by high frequency structure simulator (HFSS). And then k distribution of the antenna is obtained by fast Fourier transformation (FFT). Furthermore, three kinds of antenna designs, i.e. micro-strip line, coplanar waveguide (CPW), loop, are studied and compared. How the dimension parameter of antenna influence the corresponding high-frequency magnetic field amplitude and k distribution are investigated in details.

High-altitude closed magnetic loops at Mars observed by MAVEN

NASA Astrophysics Data System (ADS)

Xu, Shaosui; Mitchell, David; Luhmann, Janet; Ma, Yingjuan; Fang, Xiaohua; Harada, Yuki; Hara, Takuya; Brain, David; Webber, Tristan; Mazelle, Christian; DiBraccio, Gina A.

2017-10-01

With electron and magnetic field data obtained by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we have identified closed magnetic field lines, with both footpoints embedded in the dayside ionosphere, extending up to 6200 km altitude (2.8 $R_m$) into the Martian tail. This topology is deduced from photoelectrons produced in the dayside ionosphere being observed in both parallel and anti-parallel directions along the magnetic field line. At perpendicular pitch angles, cases with either solar wind electrons or photoelectrons have been found, indicative of different formation mechanisms of these closed loops. These large closed loops are predicted by MHD simulations. The case with field-aligned photoelectrons mixed with perpendicular solar wind electrons is likely to be associated with reconnection, while the case with photoelectrons in all directions are probably due to closed field lines being pulled back down tail. We have developed an automated algorithm for distinguishing photoelectrons from solar wind electrons in pitch angle resolved energy spectra. This allows us to systematically analyze the MAVEN database and map the spatial distribution and occurrence rate of these closed magnetic loops, ranging from a few percent to a few tens percent outside of the optical shadow and less than one percent within the wake. These observations can be used to investigate the general magnetic topology in the tail, which is relevant to ion escape, reconnection, and flux ropes.

Temperature dependent and applied field strength dependent magnetic study of cobalt nickel ferrite nano particles: Synthesized by an environmentally benign method

NASA Astrophysics Data System (ADS)

Sontu, Uday Bhasker; G, Narsinga Rao; Chou, F. C.; M, V. Ramana Reddy

2018-04-01

Spinel ferrites have come a long way in their versatile applications. The ever growing applications of these materials demand detailed study of material properties and environmental considerations in their synthesis. In this article, we report the effect of temperature and applied magnetic field strength on the magnetic behavior of the cobalt nickel ferrite nano powder samples. Basic structural properties of spinel ferrite nano particles, that are synthesized by an environmentally benign method of auto combustion, are characterized through XRD, TEM, RAMAN spectroscopy. Diffuse Reflectance Spectroscopy (DRS) is done to understand the nickel substitution effect on the optical properties of cobalt ferrite nano particles. Thermo magnetic studies using SQUID in the temperature range 5 K to 400 K and room temperature (300 K) VSM studies are performed on these samples. Fields of 0Oe (no applied field: ZF), 1 kOe (for ZFC and FC curves), 5 kOe (0.5 T), 50 kOe (5T) (for M-H loop study) are used to study the magnetic behavior of these nano particles. The XRD,TEM analysis suggest 40 nm crystallites that show changes in the cation distribution and phase changes in the spinel structure with nickel substitution. Raman micrographs support phase purity changes and cation redistributions with nickel substitution. Diffuse reflectance study on powder samples suggests two band gap values for nickel rich compounds. The Magnetic study of these sample nano particles show varied magnetic properties from that of hard magnetic, positive multi axial anisotropy and single-magnetic-domain structures at 5 K temperature to soft magnetic core shell like structures at 300 K temperature. Nickel substitution effect is non monotonous. Blocking temperature of all the samples is found to be higher than the values suggested in the literature.

EVIDENCE FOR COLLAPSING FIELDS IN THE CORONA AND PHOTOSPHERE DURING THE 2011 FEBRUARY 15 X2.2 FLARE: SDO/AIA AND HMI OBSERVATIONS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Gosain, S., E-mail: sgosain@nso.edu; Udaipur Solar Observatory, P.O. Box 198, Dewali, Udaipur, Rajasthan 313001

2012-04-10

We use high-resolution Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly observations to study the evolution of the coronal loops in a flaring solar active region, NOAA 11158. We identify three distinct phases of the coronal loop dynamics during this event: (1) slow-rise phase: slow rising motion of the loop-tops prior to the flare in response to the slow rise of the underlying flux rope; (2) collapse phase: sudden contraction of the loop-tops, with the lower loops collapsing earlier than the higher loops; and (3) oscillation phase: the loops exhibit global kink oscillations after the collapse phase at different periods, with themore » period decreasing with the decreasing height of the loops. The period of these loop oscillations is used to estimate the field strength in the coronal loops. Furthermore, we also use SDO/Helioseismic and Magnetic Imager (HMI) observations to study the photospheric changes close to the polarity inversion line (PIL). The longitudinal magnetograms show a stepwise permanent decrease in the magnetic flux after the flare over a coherent patch along the PIL. Furthermore, we examine the HMI Stokes I, Q, U, V profiles over this patch and find that the Stokes-V signal systematically decreases while the Stokes-Q and U signals increase after the flare. These observations suggest that close to the PIL the field configuration became more horizontal after the flare. We also use HMI vector magnetic field observations to quantify the changes in the field inclination angle and find an inward collapse of the field lines toward the PIL by {approx}10 Degree-Sign . These observations are consistent with the 'coronal implosion' scenario and its predictions about flare-related photospheric field changes.« less

Effect of crystallization annealing under loading on the magnetic properties and the structure of a soft magnetic FeSiNbCuB alloy doped with chromium

NASA Astrophysics Data System (ADS)

Ershov, N. V.; Fedorov, V. I.; Chernenkov, Yu. P.; Lukshina, V. A.; Shishkin, D. A.

2017-09-01

The changes of quasi-static magnetic hysteresis loops and X-ray diffraction patterns of the Fe73.5Si13.5B9Nb3Cu1 doped to 10 at % chromium instead of iron have been studied to elucidate the influence of the thermomechanical treatment consisting of annealing and cooling of the alloy under the tensile stress (tensile-stress annealing (TSA)) on the magnetic properties and the structure of these alloys. It is shown that the treatment results in the induction of the magnetic anisotropy of the hard axis type at which the magnetization reversal along the direction of applying the external stress during annealing is hampered. The energy of the induced magnetic anisotropy decreases as the chromium content increases. During TSA, the nanocrystal lattices are deformed, and the deformation is retained after cooling. The interplanar spacings increase along the extension direction and decrease in the transverse direction. The deformation anisotropy is observed for crystallographic directions. The anisotropic deformation of the bcc lattice of nanocrystals with high content of the ordered Fe3Si phase characterized by a negative magnetoelastic interaction is the cause of formation of the state with the transverse magnetic anisotropy of the hard axis type.

Diagonalizing controller for a superconducting six-axis accelerometer

NASA Astrophysics Data System (ADS)

Bachrach, B.; Canavan, E. R.; Levine, W. S.

A relatively simple MIMO (multiple input, multiple output) controller which converts an instrument with a nondiagonally dominant transfer function matrix into a strongly diagonally dominant device is developed. The instrument, which uses inductance bridges to sense the position of a magnetically levitated superconducting mass, has very lightly damped resonances and fairly strong cross coupling. By taking advantage of the particular structure of the instrument's transfer function matrix, it is possible to develop a relatively simple controller which achieves the desired decoupling. This controller consists of two parts. The first part cancels the nondiagonal terms of the open-loop transfer function matrix, while the second part is simply a set of SISO (single input, single output) controllers. The stability of the closed-loop system is studied using Rosenbrock's INA (inverse Nyguist array) technique, which produces a simple set of conditions guaranteeing stability. Simulation of the closed-loop system indicates that it should easily achieve its performance goals.

Testing of the permanent magnet material Mn-Al-C for potential use in propulsion motors for electric vehicles

NASA Technical Reports Server (NTRS)

Abdelnour, Z. A.; Mildrum, H. F.; Strnat, K. J.

1980-01-01

The development of Mn-Al-C permanent magnets is reviewed. The general properties of the material are discussed and put into perspective relative to alnicos and ferrites. The commercial material now available is described by the manufacturer's data. The traction motor designer's demands of a permanent magnet for potential use in electric vehicle drives are reviewed. From this, a list of the needed specific information is extracted. A plan for experimental work is made which would generate this information, or verify data supplied by the producer. The results of these measurements are presented in the form of tables and graphs. The tests determined magnetic design data and some mechanical strength properties. Easy axis hysteresis and demagnetization curves, recoil loops and other minor loop fields were measured over a temperature range from -50 C to +150 C. Hysteresis loops were also measured for three orthogonal directions (the easy and 2 hard axes of magnetization).

MRI surface-coil pair with strong inductive coupling.

PubMed

Mett, Richard R; Sidabras, Jason W; Hyde, James S

2016-12-01

A novel inductively coupled coil pair was used to obtain magnetic resonance phantom images. Rationale for using such a structure is described in R. R. Mett et al. [Rev. Sci. Instrum. 87, 084703 (2016)]. The original rationale was to increase the Q-value of a small diameter surface coil in order to achieve dominant loading by the sample. A significant improvement in the vector reception field (VRF) is also seen. The coil assembly consists of a 3-turn 10 mm tall meta-metallic self-resonant spiral (SRS) of inner diameter 10.4 mm and outer diameter 15.1 mm and a single-loop equalization coil of 25 mm diameter and 2 mm tall. The low-frequency parallel mode was used in which the rf currents on each coil produce magnetic fields that add constructively. The SRS coil assembly was fabricated and data were collected using a tissue-equivalent 30% polyacrylamide phantom. The large inductive coupling of the coils produces phase-coherency of the rf currents and magnetic fields. Finite-element simulations indicate that the VRF of the coil pair is about 4.4 times larger than for a single-loop coil of 15 mm diameter. The mutual coupling between coils influences the current ratio between the coils, which in turn influences the VRF and the signal-to-noise ratio (SNR). Data on a tissue-equivalent phantom at 9.4 T show a total SNR increase of 8.8 over the 15 mm loop averaged over a 25 mm depth and diameter. The experimental results are shown to be consistent with the magnetic resonance theory of the emf induced by spins in a coil, the theory of inductively coupled resonant circuits, and the superposition principle. The methods are general for magnetic resonance and other types of signal detection and can be used over a wide range of operating frequencies.

Utilisation of the magnetic sensor in a smartphone for facile magnetostatics experiment: magnetic field due to electrical current in straight and loop wires

NASA Astrophysics Data System (ADS)

Septianto, R. D.; Suhendra, D.; Iskandar, F.

2017-01-01

This paper reports on the result of a research into the utilisation of a smartphone for the study of magnetostatics on the basis of experiments. The use of such a device gives great measurement result and thus it can replace magnetic sensor tools that are relatively expensive. For the best experimental result, firstly the position of the magnetic sensor in the smartphone has to be considered by way of value mapping of a magnetic field due to permanent magnet. The magnetostatics experiment investigated in this research was the measurement of magnetic field due to electrical currents in two shapes of wire, straight and looped. The current flow, the distance between the observation point and the wire, and the diameter of the loop were the variable parameters investigated to test the smartphone’s capabilities as a measurement tool. To evaluate the experimental results, the measured data were compared with theoretical values that were calculated by using both an analytical and a numerical approach. According to the experiment results, the measured data had good agreement with the results from the analytical and the numerical approach. This means that the use of the magnetic sensor in a smartphone in physics experiments is viable, especially for magnetic field measurement.

Structural and Magnetic Response in Bimetallic Core/Shell Magnetic Nanoparticles

PubMed Central

Nairan, Adeela; Khan, Usman; Iqbal, Munawar; Khan, Maaz; Javed, Khalid; Riaz, Saira; Naseem, Shahzad; Han, Xiufeng

2016-01-01

Bimagnetic monodisperse CoFe2O4/Fe3O4 core/shell nanoparticles have been prepared by solution evaporation route. To demonstrate preferential coating of iron oxide onto the surface of ferrite nanoparticles X-ray diffraction (XRD), High resolution transmission electron microscope (HR-TEM) and Raman spectroscopy have been performed. XRD analysis using Rietveld refinement technique confirms single phase nanoparticles with average seed size of about 18 nm and thickness of shell is 3 nm, which corroborates with transmission electron microscopy (TEM) analysis. Low temperature magnetic hysteresis loops showed interesting behavior. We have observed large coercivity 15.8 kOe at T = 5 K, whereas maximum saturation magnetization (125 emu/g) is attained at T = 100 K for CoFe2O4/Fe3O4 core/shell nanoparticles. Saturation magnetization decreases due to structural distortions at the surface of shell below 100 K. Zero field cooled (ZFC) and Field cooled (FC) plots show that synthesized nanoparticles are ferromagnetic till room temperature and it has been noticed that core/shell sample possess high blocking temperature than Cobalt Ferrite. Results indicate that presence of iron oxide shell significantly increases magnetic parameters as compared to the simple cobalt ferrite. PMID:28335200

Rational Design of a Lanthanide-Based Complex Featuring Different Single-Molecule Magnets.

PubMed

Pointillart, F; Guizouarn, T; Lefeuvre, B; Golhen, S; Cador, O; Ouahab, L

2015-11-16

The rational synthesis of the 2-{1-methylpyridine-N-oxide-4,5-[4,5-bis(propylthio)tetrathiafulvalenyl]-1H-benzimidazol-2-yl}pyridine ligand (L) is described. It led to the tetranuclear complex [Dy4(tta)12(L)2] (Dy-Dy2-Dy) after coordination reaction with the precursor Dy(tta)3⋅2 H2O (tta(-) = 2-thenoyltrifluoroacetonate). The X-ray structure of Dy-Dy2-Dy can be described as two terminal mononuclear units bridged by a central antiferromagnetically coupled dinuclear complex. The terminal N2O6 and central O8 environments are described as distorted square antiprisms. The ac magnetism measurements revealed a strong out-of-phase signal of the magnetic susceptibility with two distinct sets of data. The high- and low-frequency components were attributed to the two terminal mononuclear single-molecule magnets (SMMs) and the central dinuclear SMM, respectively. A magnetic hysteresis loop was detected at very low temperature. From both structural and magnetic points of view, the tetranuclear SMM Dy-Dy2-Dy is a self-assembly of two known mononuclear SMMs bridged by a known dinuclear SMM. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Collider study on the loop-induced dark matter mediation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Tsai, Yuhsin, E-mail: yhtsai@umd.edu

2016-06-21

Collider experiments are one of the most promising ways to constrain Dark Matter (DM) interactions. For DM couplings involving light mediators, especially for the loop-mediated interactions, a meaningful interpretation of the results requires to go beyond effective field theory. In this note we discuss the study of the magnetic dipole interacting DM, focusing on a model with anarchic dark flavor structure. By including the momentum-dependent form factors that mediate the coupling – given by the Dark Penguin – in collider processes, we study bounds from monophoton, diphoton, and non-pointing photon searches at the LHC. We also compare our results tomore » constraints from the direct detection experiments.« less

Dynamic magnetic hysteresis properties of two-dimensional ferrimagnetic structures containing high-spin (S = 5/2) and low-spin (S = 1/2)

NASA Astrophysics Data System (ADS)

Batı, Mehmet; Ertaş, Mehmet

2017-09-01

The dynamic hysteresis behaviors of a containing high spin-5/2 and low spin-1/2 Ising ferrimagnetic system on a square lattice are studied by using the dynamic mean-field approximation. The influences of the temperature, the single-ion anisotropy and the frequency on dynamic hysteresis behaviors are investigated in detail. Somewhat characteristic behaviors are found, such as the presence of triple hysteresis loop for appropriate values of the crystal field or temperature. Besides, we observed that, hysteresis loop area and phase transition points are very sensitive to changes in frequency and thus have profound importance in device application.

Non-Potential Magnetic Fields and Magnetic Reconnection In Low Collisional Plasmas-Discovery of Solar EUV Mini-Sigmoids and Development of Novel In-Space Propulsion Systems

NASA Astrophysics Data System (ADS)

Chesny, David

Magnetic reconnection is the source of many of the most powerful explosions of astrophysical plasmas in the universe. Blazars, magnetars, stellar atmospheres, and planetary magnetic fields have all been shown to be primary sites of strong reconnection events. For studying the fundamental physics behind this process, the solar atmosphere is our most accessible laboratory setting. Magnetic reconnection resulting from non-potential fields leads to plasma heating and particle acceleration, often in the form of explosive activity, contributing to coronal heating and the solar wind. Large-scale non-potential (sigmoid) fields in the solar atmosphere are poorly understood due to their crowded neighborhoods. For the first time, small-scale, non-potential loop structures have been observed in quiet Sun EUV observations. Fourteen unique mini-sigmoid events and three diffuse non-potential loops have been discovered, suggesting a multi-scaled self-similarity in the sigmoid formation process. These events are on the order of 10 arcseconds in length and do not appear in X-ray emissions, where large-scale sigmoids are well documented. We have discovered the first evidence of sigmoidal structuring in EUV bright point phenomena, which are prolific events in the solar atmosphere. Observations of these mini-sigmoids suggest that they are being formed via tether-cutting reconnection, a process observed to occur at active region scales. Thus, tether-cutting is suggested to be ubiquitous throughout the solar atmosphere. These dynamics are shown to be a function of the free magnetic energy in the quiet Sun network. Recently, the reconnection process has been reproduced in Earth-based laboratory tokamaks. Easily achievable magnetic field configurations can induce reconnection and result in ion acceleration. Here, magnetic reconnection is utilized as the plasma acceleration mechanism for a theoretical propulsion system. The theory of torsional spine reconnection is shown to result in ion velocities of > 3000 km s-1 and thrusts on the order of 3-15 N. As current in-use ion propulsion technology can only achieve ˜ 30 km s-1, the proposed design can substantially increase thrust on a spacecraft and provide for fast manned interplanetary travel.

Non-Abelian Stokes theorem for the Wilson loop operator in an arbitrary representation and its implication to quark confinement

NASA Astrophysics Data System (ADS)

Matsudo, Ryutaro; Kondo, Kei-Ichi

2015-12-01

We give a gauge-independent definition of magnetic monopoles in the S U (N ) Yang-Mills theory through the Wilson loop operator. For this purpose, we give an explicit proof of the Diakonov-Petrov version of the non-Abelian Stokes theorem for the Wilson loop operator in an arbitrary representation of the S U (N ) gauge group to derive a new form for the non-Abelian Stokes theorem. The new form is used to extract the magnetic-monopole contribution to the Wilson loop operator in a gauge-invariant way, which enables us to discuss confinement of quarks in any representation from the viewpoint of the dual superconductor vacuum.

The Electromotive Force in Different Reference Frames

ERIC Educational Resources Information Center

Adler, Charles L.

2018-01-01

The electromotive force (EMF) is the work per unit charge around a wire loop caused by a time-varying magnetic flux threading the loop. It is due to a force moving the charges around the loop. This is true whether the change in flux is due to the wire loop being stationary and the field changing in time, or the loop moving through a spatially…

Suppression of heating of coronal loops rooted in opposite polarity sunspot umbrae

NASA Astrophysics Data System (ADS)

Tiwari, Sanjiv K.; Thalmann, Julia K.; Moore, Ronald L.; Panesar, Navdeep; Winebarger, Amy R.

2016-05-01

EUV observations of active region (AR) coronae reveal the presence of loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 A images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-polarity plage region. The AIA 94 A images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the HMI onboard SDO. After validation of the NLFFF model by comparison of calculated model field lines and observed loops in AIA 193 and 94, we specify the photospheric roots of the model field lines. The model field then shows the coronal magnetic loops that arch from the dim umbral areas of the opposite polarity sunspots. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.We hypothesize that the convective freedom at the feet of a coronal loop, together with the strength of the field in the body of the loop, determines the strength of the heating. In particular, we expect the hottest coronal loops to have one foot in an umbra and the other foot in opposite-polarity penumbra or plage (coronal moss), the areas of strong field in which convection is not as strongly suppressed as in umbra. Many transient, outstandingly bright, loops in the AIA 94 movie of the AR do have this expected rooting pattern. We will also present another example of AR in which we find a similar rooting pattern of coronal loops.

The Rocketdyne Multifunction Tester. Part 2: Operation of a Radial Magnetic Bearing as an Excitation Source

NASA Technical Reports Server (NTRS)

Hawkins, L. A.; Murphy, Brian T.; Lang, K. W.

1991-01-01

The operation of the magnetic bearing used as an excitation source in the Rocketdyne Multifunction Tester is described. The tester is scheduled for operation during the summer of 1990. The magnetic bearing can be used in two control modes: (1) open loop mode, in which the magnetic bearing operates as a force actuator; and (2) closed loop mode, in which the magnetic bearing provides shaft support. Either control mode can be used to excite the shaft; however, response of the shaft in the two control modes is different due to the alteration of the eigenvalues by closed loop mode operation. A rotordynamic model is developed to predict the frequency response of the tester due to excitation in either control mode. Closed loop mode excitation is shown to be similar to the excitation produced by a rotating eccentricity in a conventional bearing. Predicted frequency response of the tester in the two control modes is compared, and the maximum response is shown to be the same for the two control modes when synchronous unbalance loading is not considered. The analysis shows that the response of this tester is adequate for the extraction of rotordynamic stiffness, damping, and inertia coefficients over a wide range of test article stiffnesses.

Magnetic Bianchi type II string cosmological model in loop quantum cosmology

NASA Astrophysics Data System (ADS)

Rikhvitsky, Victor; Saha, Bijan; Visinescu, Mihai

2014-07-01

The loop quantum cosmology of the Bianchi type II string cosmological model in the presence of a homogeneous magnetic field is studied. We present the effective equations which provide modifications to the classical equations of motion due to quantum effects. The numerical simulations confirm that the big bang singularity is resolved by quantum gravity effects.

Stretched Loops

NASA Image and Video Library

2017-03-16

When an active region rotated over to the edge of the sun, it presented us with a nice profile view of its elongated loops stretching and swaying above it (Mar. 8-9, 2017). These loops are actually charged particles (made visible in extreme ultraviolet light) swirling along the magnetic field lines of the active region. The video covers about 30 hours of activity. Also of note is a darker twisting mass of plasma to the left of the active region being pulled and spun about by magnetic forces. Video is available at http://photojournal.jpl.nasa.gov/catalog/PIA21562

Microsoft C#.NET program and electromagnetic depth sounding for large loop source

NASA Astrophysics Data System (ADS)

Prabhakar Rao, K.; Ashok Babu, G.

2009-07-01

A program, in the C# (C Sharp) language with Microsoft.NET Framework, is developed to compute the normalized vertical magnetic field of a horizontal rectangular loop source placed on the surface of an n-layered earth. The field can be calculated either inside or outside the loop. Five C# classes with member functions in each class are, designed to compute the kernel, Hankel transform integral, coefficients for cubic spline interpolation between computed values and the normalized vertical magnetic field. The program computes the vertical magnetic field in the frequency domain using the integral expressions evaluated by a combination of straightforward numerical integration and the digital filter technique. The code utilizes different object-oriented programming (OOP) features. It finally computes the amplitude and phase of the normalized vertical magnetic field. The computed results are presented for geometric and parametric soundings. The code is developed in Microsoft.NET visual studio 2003 and uses various system class libraries.

Magnetic monopole versus vortex as gauge-invariant topological objects for quark confinement

NASA Astrophysics Data System (ADS)

Kondo, Kei-Ichi; Sasago, Takaaki; Shinohara, Toru; Shibata, Akihiro; Kato, Seikou

2017-12-01

First, we give a gauge-independent definition of chromomagnetic monopoles in SU(N) Yang-Mills theory which is derived through a non-Abelian Stokes theorem for the Wilson loop operator. Then we discuss how such magnetic monopoles can give a nontrivial contribution to the Wilson loop operator for understanding the area law of the Wilson loop average. Next, we discuss how the magnetic monopole condensation picture are compatible with the vortex condensation picture as another promising scenario for quark confinement. We analyze the profile function of the magnetic flux tube as the non-Abelian vortex solution of U(N) gauge-Higgs model, which is to be compared with numerical simulations of the SU(N) Yang-Mills theory on a lattice. This analysis gives an estimate of the string tension based on the vortex condensation picture, and possible interactions between two non-Abelian vortices.

Low-frequency (< 10 kHz) surface magnetic energy losses measured with polarized secondary electrons (abstract)

NASA Astrophysics Data System (ADS)

Woods, J.; O'Handley, R. C.

1990-05-01

The polarization of low-energy secondary electrons emitted from iron- and cobalt-based amorphous melt-spun ribbons is measured as a function of the applied in-plane magnetic field yielding surface hysteresis loops. The polarization is measured in real time up to a frequency of 10 kHz and hysteresis loops are displayed on an oscilloscope. The bulk losses are measured on the same samples in the same configuration with a secondary winding. The area of the loop (energy loss/cycle) is measured as a function of applied magnetic field switching rate for both the surface polarization and bulk magnetization measurements. The surface loss per cycle increases linearly with the switching rate and the bulk loss per cycle increases much more slowly with switching rate. This is the first discrimination of bulk and surface losses we are aware of.

Magnetic Memory from Site Isolated Dy(III) on Silica Materials

PubMed Central

2017-01-01

Achieving magnetic remanence at single isolated metal sites dispersed at the surface of a solid matrix has been envisioned as a key step toward information storage and processing in the smallest unit of matter. Here, we show that isolated Dy(III) sites distributed at the surface of silica nanoparticles, prepared with a simple and scalable two-step process, show magnetic remanence and display a hysteresis loop open at liquid 4He temperature, in contrast to the molecular precursor which does not display any magnetic memory. This singular behavior is achieved through the controlled grafting of a tailored Dy(III) siloxide complex on partially dehydroxylated silica nanoparticles followed by thermal annealing. This approach allows control of the density and the structure of isolated, “bare” Dy(III) sites bound to the silica surface. During the process, all organic fragments are removed, leaving the surface as the sole ligand, promoting magnetic remanence. PMID:28386602

Magnetic memory from site isolated Dy(III) on silica materials

DOE Office of Scientific and Technical Information (OSTI.GOV)

Allouche, Florian; Lapadula, Giuseppe; Siddiqi, Georges

Achieving magnetic remanence at single isolated metal sites dispersed at the surface of a solid matrix has been envisioned as a key step toward information storage and processing in the smallest unit of matter. Here, we show that isolated Dy(III) sites distributed at the surface of silica nanoparticles, prepared with a simple and scalable two-step process, show magnetic remanence and display a hysteresis loop open at liquid 4He temperature, in contrast to the molecular precursor which does not display any magnetic memory. This singular behavior is achieved through the controlled grafting of a tailored Dy(III) siloxide complex on partially dehydroxylatedmore » silica nanoparticles followed by thermal annealing. This approach allows control of the density and the structure of isolated, “bare” Dy(III) sites bound to the silica surface. Throughout the process, all organic fragments are removed, leaving the surface as the sole ligand, promoting magnetic remanence.« less

Magnetic memory from site isolated Dy(III) on silica materials

DOE PAGES

Allouche, Florian; Lapadula, Giuseppe; Siddiqi, Georges; ...

2017-02-22

Achieving magnetic remanence at single isolated metal sites dispersed at the surface of a solid matrix has been envisioned as a key step toward information storage and processing in the smallest unit of matter. Here, we show that isolated Dy(III) sites distributed at the surface of silica nanoparticles, prepared with a simple and scalable two-step process, show magnetic remanence and display a hysteresis loop open at liquid 4He temperature, in contrast to the molecular precursor which does not display any magnetic memory. This singular behavior is achieved through the controlled grafting of a tailored Dy(III) siloxide complex on partially dehydroxylatedmore » silica nanoparticles followed by thermal annealing. This approach allows control of the density and the structure of isolated, “bare” Dy(III) sites bound to the silica surface. Throughout the process, all organic fragments are removed, leaving the surface as the sole ligand, promoting magnetic remanence.« less

Electric, Magnetic, and Magnetoelectric Properties of Yttrium-Containing BaY0.025Ti0.9625O3-SrFe12O19 Composite

NASA Astrophysics Data System (ADS)

Rather, Mehraj ud Din; Samad, Rubiya; Want, Basharat

2018-03-01

The physical properties of BaY0.025Ti0.9625O3, SrFe12O19, and 0.90BaY0.025Ti0.9625O3-0.10 SrFe12O19 composite have been studied. The proposed composite was synthesized by solid-state reaction method from yttrium barium titanate processed by solid-state reaction and strontium hexaferrite obtained by a sol-gel process. Microstructural analysis revealed monophasic grains for yttrium barium titanate phase, while loosely packed biphasic structure was observed for the composite. Powder x-ray analysis showed that the individual phases retained their crystal structure in the composite, without formation of any new additional phase. Measurement of magnetic hysteresis loops at room temperature indicated that the magnetic parameters of the composite were diluted by the presence of the ferroelectric phase. The ferroelectric hysteresis of yttrium barium titanate confirmed the ferroelectric transition at 119°C. Meanwhile, the symmetrical ferroelectric loops observed at different fields established the ferroelectric nature of the composite. Improved dielectric properties and low dielectric losses were observed due to yttrium doping in the composite. The diffuseness of the ferroelectric transitions for the composite was confirmed by the Curie-Weiss law. Activation energy calculations revealed the charge-hopping conduction mechanism in the composite. Magnetodielectric studies confirmed that the overall magnetocapacitance in the composite exhibited combined effects of magnetoresistance and magnetoelectric coupling.

Strontium hexaferrite (SrFe12O19) based composites for hyperthermia applications

NASA Astrophysics Data System (ADS)

Rashid, Amin Ur; Southern, Paul; Darr, Jawwad A.; Awan, Saifullah; Manzoor, Sadia

2013-10-01

Mixed phase composites of SrFe12O19/MgFe2O4/ZrO2 were prepared via the citrate gel technique as potential candidate materials for magnetic hyperthermia. Structural and magnetic properties of the samples were studied using powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and a vibrating sample magnetometer. XRD and FE-SEM data confirm that magnesium ferrite and zirconium oxide phases increased with increasing Mg and Zr content in the precursors. Magnetization loops for the composites were measured at room temperature and showed significant variation of saturation magnetization, coercivity and remanence depending on the amount of the highly anisotropic Sr-hexaferrite phase. The sample with the highest Mg and Zr content had the lowest coercivity (80 Oe) and saturation magnetization (41 emu/g). The composite samples each were exposed to a 214 kHz alternating magnetic field of amplitude 22 Oe and a significant heating effect was observed in selected samples, which suggests potential for use in magnetic hyperthermia.

Multiple loop conformations of peptides predicted by molecular dynamics simulations are compatible with nuclear magnetic resonance.

PubMed

Carstens, Heiko; Renner, Christian; Milbradt, Alexander G; Moroder, Luis; Tavan, Paul

2005-03-29

The affinity and selectivity of protein-protein interactions can be fine-tuned by varying the size, flexibility, and amino acid composition of involved surface loops. As a model for such surface loops, we study the conformational landscape of an octapeptide, whose flexibility is chemically steered by a covalent ring closure integrating an azobenzene dye into and by a disulfide bridge additionally constraining the peptide backbone. Because the covalently integrated azobenzene dyes can be switched by light between a bent cis state and an elongated trans state, six cyclic peptide models of strongly different flexibilities are obtained. The conformational states of these peptide models are sampled by NMR and by unconstrained molecular dynamics (MD) simulations. Prototypical conformations and the free-energy landscapes in the high-dimensional space spanned by the phi/psi angles at the peptide backbone are obtained by clustering techniques from the MD trajectories. Multiple open-loop conformations are shown to be predicted by MD particularly in the very flexible cases and are shown to comply with the NMR data despite the fact that such open-loop conformations are missing in the refined NMR structures.

Radio-derived three-dimensional structure of a solar active region

NASA Astrophysics Data System (ADS)

Tun, Samuel D.

Solar active regions are the source of the most violent events observed on the Sun, some of which have a direct impact to modern civilization. Efforts to understand and predict such events require determination of the three-dimensional distributions of density, temperature, and magnetic fields above such active regions. This thesis presents the structure of the solar atmosphere above active region AR 10923, observed on 2006 Nov 10, as deduced from multi-wavelength studies including combined microwave observations from the Very Large Array (VLA) and the Owens Valley Solar Array (OVSA). The VLA observations provide excellent image quality at a few widely spaced frequencies while the OVSA data provide information at many intermediate frequencies to fill in the spectral coverage. In order to optimize the OVSA data for spectroscopic studies, the L1 method of self-calibration was implemented at this observatory, producing the best single frequency maps produced to date. Images at the 25 distinct, available frequencies are used to provide spatially resolved spectra along many lines of sight in the active region, from which microwave spectral diagnostics are obtained for deducing two-dimensional maps of temperature, magnetic field strength, and column density. The derived quantities are compared with multi-wavelength observations from SoHO and Hinode spacecraft, and with a standard potential magnetic field extrapolation. It is found that a two component temperature model is required to fit the data, in which a hot (> 2 MK) lower corona above the strong-field plage and sunspot regions (emitting via the gyroresonance process) is overlaid with somewhat cooler (˜ 1 MK) coronal loops that partially absorb the gyroresonance emission through the free-free (Bremsstrahlung) process. It is also found that the potential magnetic field extrapolation model can quantitatively account for the observed gyroresonance emission over most of the active region, but in a few areas a higher field strength is required. These areas of discrepancy are found to coincide with the foot points of hot X-ray loops over the sunspot's penumbra. The results and the extrapolation are used to explore the coronal configuration needed to explain the observations, from which it is found that the bulk of radio and X-ray free-free emission emanates from two loop systems, distinguished by the location of their loop foot points. The proposed stratification may explain the observed distribution of column emission measure and the differences in this quantity as obtained from X-rays or radio emission.

The magnetization process: Hysteresis

NASA Technical Reports Server (NTRS)

Balsamel, Richard

1990-01-01

The magnetization process, hysteresis (the difference in the path of magnetization for an increasing and decreasing magnetic field), hysteresis loops, and hard magnetic materials are discussed. The fabrication of classroom projects for demonstrating hysteresis and the hysteresis of common magnetic materials is described in detail.

Closed loop control of the induction heating process using miniature magnetic sensors

DOEpatents

Bentley, Anthony E.; Kelley, John Bruce; Zutavern, Fred J.

2003-05-20

A method and system for providing real-time, closed-loop control of the induction hardening process. A miniature magnetic sensor located near the outer surface of the workpiece measures changes in the surface magnetic field caused by changes in the magnetic properties of the workpiece as it heats up during induction heating (or cools down during quenching). A passive miniature magnetic sensor detects a distinct magnetic spike that appears when the saturation field, B.sub.sat, of the workpiece has been exceeded. This distinct magnetic spike disappears when the workpiece's surface temperature exceeds its Curie temperature, due to the sudden decrease in its magnetic permeability. Alternatively, an active magnetic sensor can measure changes in the resonance response of the monitor coil when the excitation coil is linearly swept over 0-10 MHz, due to changes in the magnetic permeability and electrical resistivity of the workpiece as its temperature increases (or decreases).

Microwave detector

DOEpatents

Meldner, H.W.; Cusson, R.Y.; Johnson, R.M.

1985-02-08

A microwave detector is provided for measuring the envelope shape of a microwave pulse comprised of high-frequency oscillations. A biased ferrite produces a magnetization field flux that links a B-dot loop. The magnetic field of the microwave pulse participates in the formation of the magnetization field flux. High-frequency insensitive means are provided for measuring electric voltage or current induced in the B-dot loop. The recorded output of the detector is proportional to the time derivative of the square of the envelope shape of the microwave pulse.

Static magnetism and thermal switching in randomly oriented L10 FePt thin films

NASA Astrophysics Data System (ADS)

Lisfi, A.; Pokharel, S.; Alqarni, A.; Akioya, O.; Morgan, W.; Wuttig, M.

2018-05-01

Static magnetism and thermally activated magnetic relaxation were investigated in granular FePt films (20 nm-200 nm thick) with random magnetic anisotropy through hysteresis loop, torque curve and magnetization time dependence measurements. While the magnetism of thicker film (200 nm thick) is dominated by a single switching of the ordered L10 phase, thinner film (20 nm) displays a double switching, which is indicative of the presence of the disordered cubic phase. The pronounced behavior of double switching in thinner film suggests that the film grain boundary is composed of soft cubic magnetic phase. The magnetic relaxation study reveals that magnetic viscosity S of the films is strongly dependent on the external applied field and exhibits a maximum value (12 kAm) around the switching field and a vanishing behavior at low (1 kOe) and large (12 kOe) fields. The activation volume of the thermal switching was found to be much smaller than the physical volume of the granular structure due to the incoherent rotation mode of the magnetization reversal mechanism, which is established to be domain wall nucleation.

Influence of magnetic field structure on the conduction cooling of flare loops

NASA Technical Reports Server (NTRS)

Antiochos, S. K.; Sturrock, P. A.

1976-01-01

A simple model facilitates calculation of the influence of magnetic field configuration on the conduction cooling rate of a hot post-flare coronal plasma. The magnetic field is taken to be that produced by a line dipole or point dipole at an arbitrary depth below the chromosphere. For the high temperatures (T greater than or equal to 10 to the 7th power K) produced by flares, the plasma may remain static and isobaric. The influence of the field is such as to increase the heat flux (per unit area) into the chromosphere, but to decrease the total conduction cooling of the flare plasma. This leads to a significant enhancement of the total energy radiated by the flare plasma.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Aparnadevi, N.; Department of Nuclear Physics, University of Madras, Guindy Campus, Chennai 600 025; Saravana Kumar, K.

Phase pure NdFeO{sub 3} has been achieved using high energy ball milling of oxide precursors with subsequent sintering. It is established that structural arrangement of NdFeO{sub 3} regulates the multifunctional feature of the material. Rietveld refinement of the room temperature X-ray diffraction pattern shows that the Fe-O-Fe bond angle significantly favors the super exchange interaction, which is predominantly antiferromagnetic in nature. Magnetization measurement illustrates antiferromagnetic behaviour with a weak ferromagnetic component caused by the canted nature of the Fe{sup 3+} spins at room temperature. Absorption bands in the visible ambit, apparent from the UV-Vis diffuse reflectance studies, is found duemore » to the crystal ligand field of octahedral oxygen environment of Fe{sup 3+} ions. The direct band gap is estimated to be 2.39 eV from the diffuse reflectance spectrum. The lossy natured ferroelectric loop having a maximum polarization of 0.23 μC/cm{sup 2} at room temperature is found to be driven by the non-collinear magnetic structure with reverse Dzyaloshinskii–Moriya effect. Magnetic field has influence on the dielectric constant as evident from the impedance spectroscopy, indicating the strong coupling between ferroelectric and the magnetic structure of NdFeO{sub 3}.« less

Xenon-ion irradiation of Co/Si bilayers: Magnetic and structural properties

NASA Astrophysics Data System (ADS)

Novaković, M.; Popović, M.; Zhang, K.; Čubrović, V.; Bibić, N.; Rakočević, Z.

2018-07-01

Evolution of the structure of cobalt-silicon films during Xe ions irradiation has been studied and the same is correlated with magnetic properties. The polycrystalline cobalt films were deposited by electron beam evaporation method to a thickness of 50 nm on crystalline silicon (c-Si) and silicon with pre-amorphized surface (a-Si). After deposition the layers were irradiated with 400 keV Xe ions to the fluences in the range of 2-30 × 1015 ions/cm2. Structural analysis was done by means of transmission electron microscopy, atomic force microscopy (AFM) and X-ray diffraction (XRD), while the magnetic properties were analyzed by using magneto-optical Kerr effect (MOKE) technique. For the both types of substrate the AFM and XRD results show that after Xe ions irradiation the layers become more rough and the grain size of the crystallites increases; the effects being more evidenced for all fluences for the layers deposited on pre-amorphized Si. The MOKE measurements provided the in-plane azimuthal angular dependence of the hysteresis loops and the change of magnetization with the structural parameters. Although the coercive field is influenced by the surface roughness, in the case of c-Si substrate we found it is much more determined by the size of the crystallites. Additionally, independently on the substrate used the magnetic anisotropy in the Co films disappeared as the Xe ion fluence increased, indicating that the changes of magnetization in both systems occur for similar reasons.

Coronal Jets in Closed Magnetic Regions on the Sun

NASA Astrophysics Data System (ADS)

Wyper, Peter Fraser; DeVore, C. R.

2015-04-01

Coronal jets are dynamic, collimated structures observed in solar EUV and X-ray emission. They appear predominantly in the open field of coronal holes, but are also observed in areas of closed field, especially active regions. A common feature of coronal jets is that they originate from the field above a parasitic polarity of opposite sign to the surrounding field. Some process - such as instability onset or flux emergence - induces explosive reconnection between the closed “anemone” field and the surrounding open field that generates the jet. The lesser number of coronal jets in closed-field regions suggests a possible stabilizing effect of the closed configuration with respect to coronal jet formation. If the scale of the jet region is small compared with the background loop length, as in for example type II spicules, the nearby magnetic field may be treated as locally open. As such, one would expect that if a stabilizing effect exists it becomes most apparent as the scale of the anemone region approaches that of the background coronal loops.To investigate if coronal jets are indeed suppressed along shorter coronal loops, we performed a number of simulations of jets driven by a rotation of the parasitic polarity (as in the previous open-jet calculations by Pariat et. al 2009, 2010, 2015) embedded in a large-scale closed bipolar field. The simulations were performed with the state of the art Adaptively Refined Magnetohydrodynamics Solver. We will report here how the magnetic configuration above the anemone region determines the nature of the jet, when it is triggered, and how much of the stored magnetic energy is released. We show that regions in which the background field and the parasitic polarity region are of comparable scale naturally suppress explosive energy release. We will also show how in the post-jet relaxation phase a combination of confined MHD waves and weak current layers are generated by the jet along the background coronal loops, both of which may have implications for coronal heating.This work was supported by an appointment to the NASA Postdoctoral Program (P.F.W.) and by NASA’s Living With a Star Targeted Research and Technology program (C.R.D.).

Article surveillance magnetic marker having an hysteresis loop with large Barkhausen discontinuities

DOEpatents

Humphrey, Floyd B.

1987-01-01

A marker for an electronic article surveillance system is disclosed comprising a body of magnetic material with retained stress and having a magnetic hysteresis loop with a large Barkhausen discontinuity such that, upon exposure of the marker to an external magnetic field whose field strength in the direction opposing the instantaneous magnetic polarization of the marker exceeds a predetermined threshold value, there results a regenerative reversal of the magnetic polarization of the marker. An electronic article surveillance system and a method utilizing the marker are also disclosed. Exciting the marker with a low frequency and low field strength, so long as the field strength exceeds the low threshold level for the marker, causes a regenerative reversal of magnetic polarity generating a harmonically rich pulse that is readily detected and easily distinguished.

Magnetic properties of a stainless steel irradiated with 6 MeV Xe ions

NASA Astrophysics Data System (ADS)

Xu, Chaoliang; Liu, Xiangbing; Qian, Wangjie; Li, Yuanfei

2017-11-01

Specimens of austenitic stainless steel were irradiated with 6 MeV Xe ions at room temperature to 2, 7, 15 and 25 dpa. The vibrating sample magnetometer (VSM), grazing incidence X-ray diffraction (GIXRD) and positron annihilation lifetime spectroscopy (PLS) were carried out to analysis the magnetic properties and microstructural variations. The magnetic hysteresis loops indicated that higher irradiation damage causes more significant magnetization phenomenon. The equivalent saturated magnetization Mes and coercive force Hc were obtained from magnetic hysteresis loops. It is indicated that the Mes increases with irradiation damage. While Hc increases first to 2 dpa and then decreases continuously with irradiation damage. The different contributions of irradiation defects and ferrite precipitates on Mes and Hc can explain these phenomena.

Oxygen vacancy induced room temperature ferromagnetism in (In1-xNix)2O3 thin films

NASA Astrophysics Data System (ADS)

Chakraborty, Deepannita; Kaleemulla, S.; Kuppan, M.; Rao, N. Madhusudhana; Krishnamoorthi, C.; Omkaram, I.; Reddy, D. Sreekantha; Rao, G. Venugopal

2018-05-01

Nickel doped indium oxide thin films (In1-xNix)2O3 at x = 0.00, 0.03, 0.05 and 0.07 were deposited onto glass substrates by electron beam evaporation technique. The deposited thin films were subjected to annealing in air at 250 °C, 350 °C and 450 °C for 2 h using high temperature furnace. A set of films were vacuum annealed at 450 °C to study the role of oxygen on magnetic properties of the (In1-xNix)2O3 thin films. The thin films were subjected to different characterization techniques to study their structural, chemical, surface, optical and magnetic properties. All the synthesized air annealed and vacuum annealed films exhibit body centered cubic structure without any secondary phases. No significant change in the diffraction peak position, either to lower or higher diffraction angles has been observed. The band gap of the films decreased from 3.73 eV to 3.63 eV with increase of annealing temperature from 250 °C to 450 °C, in the presence of air. From a slight decrease in strength of magnetization to a complete disappearance of hysteresis loop has been observed in pure In2O3 thin films with increasing the annealing temperature from 250 °C to 450 °C, in the presence of air. The (In1-xNix)2O3 thin films annealed under vacuum follow a trend of enhancement in the strength of magnetization to increase in temperature from 250 °C to 450 °C. The hysteresis loop does not disappear at 450 °C in (In1-xNix)2O3 thin films, as observed in the case of pure In2O3 thin films.

Significantly enhanced ferroelectricity and magnetic properties in (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3}-modified BiFeO{sub 3} ceramics

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, Juan; Liu, Xiao Qiang, E-mail: xqliu@zju.edu.cn, E-mail: xmchen59@zju.edu.cn; Chen, Xiang Ming, E-mail: xqliu@zju.edu.cn, E-mail: xmchen59@zju.edu.cn

2015-05-07

BiFeO{sub 3} multiferroic ceramics were modified by introducing (Sr{sub 0.5}Ca{sub 0.5})TiO{sub 3} to form solid solutions. The single phase structure was easy to be obtained in Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} (x = 0.2, 0.25, 0.3, and 0.4) solid solutions. Rietveld refinement of X-ray diffraction data revealed a transition from rhombohedral R3c (x = 0.2, 0.25, and 0.3) to orthorhombic Pnma (x = 0.4). Current density-field (J-E) characteristics indicated that the leakage current density was reduced by three orders of magnitude in Bi{sub 1−x}(Sr{sub 0.5}Ca{sub 0.5}){sub x}Fe{sub 1−x}Ti{sub x}O{sub 3} ceramics. Both the ferroelectricity and magnetic properties were significantly enhanced in the presentmore » solid solutions. P-E hysteresis loop measurements with dynamic leakage current compensation methods showed the significantly enhanced ferroelectric properties for x = 0.25 and 0.3 and the paraelectric behavior for x = 0.4. The best ferromagnetic characteristics were achieved in the composition of x = 0.25, where the saturated M-H loop was determined with M{sub r} = 34.8 emu/mol. The improvement of ferroelectricity was mainly due to the suppressed leakage current, and the enhanced magnetism originated from the partial substitution of Fe{sup 3+} by Ti{sup 4+}, which destroyed its previous spiral structure to allow the appearance of a macroscopic magnetization.« less

Ponderomotive Acceleration in Coronal Loops

NASA Astrophysics Data System (ADS)

Dahlburg, Russell B.; Laming, J. Martin; Taylor, Brian; Obenschain, Keith

2017-08-01

Ponderomotive acceleration has been asserted to be a cause of the First Ionization Potential (FIP) effect, the by now well known enhancement in abundance by a factor of 3-4 over photospheric values of elements in the solar corona with FIP less than about 10 eV. It is shown here by means of numerical simulations that ponderomotive acceleration occurs in solar coronal loops, with the appropriate magnitude and direction, as a ``byproduct'' of coronal heating. The numerical simulations are performed with the HYPERION code, which solves the fully compressible three-dimensional magnetohydrodynamic equations including nonlinear thermal conduction and optically thin radiation. Numerical simulations of a coronal loops with an axial magnetic field from 0.005 Teslas to 0.02 Teslas and lengths from 25000 km to 75000 km are presented. In the simulations the footpoints of the axial loop magnetic field are convected by random, large-scale motions. There is a continuous formation and dissipation of field-aligned current sheets which act to heat the loop. As a consequence of coronal magnetic reconnection, small scale, high speed jets form. The familiar vortex quadrupoles form at reconnection sites. Between the magnetic footpoints and the corona the reconnection flow merges with the boundary flow. It is in this region that the ponderomotive acceleration occurs. Mirroring the character of the coronal reconnection, the ponderomotive acceleration is also found to be intermittent.

New soft magnetic amorphous cobalt based alloys with high hysteresis loop linearity

NASA Astrophysics Data System (ADS)

Nosenko, V. K.; Maslov, V. V.; Kochkubey, A. P.; Kirilchuk, V. V.

2008-02-01

The new amorphous Co56÷59(Fe,Ni,Mn)21÷24(Si0.2B0.8)20-based metal alloys (AMA) with high saturation induction (BS>=1T) were developed. Toroidal tape wound magnetic cores made from these AMA after heat-magnetic treatment (HMT) in a reversal field are characterized by high hysteresis loop linearity, minimum effective magnetic permeability and its high field stability in combination with low coercivity Hc (1-3 A/m, 1 kHz). For the most prospecting alloy compositions the value of effective magnetic permeability decreases compared to known alloys up to 550 - 670 units and remains constant in the wide magnetic field range 1100 - 1300 A/m. Maximum remagnetization loop linearity is achieved after optimum HMT in high Ni containing AMAs, which are characterized by the record low squareness ratio values Ks=0.002-0.02 and Hc=1.0 A/m. Magnetic cores made from the new amorphous alloys can be used both in filter chokes of switch-mode power supply units and in matching mini-transformers of telecommunication systems; at that, high efficiency and accuracy of signal transmission including high frequency pulses are ensured under conditions of long-term influence of dc magnetic bias.

Sorting Rotating Micromachines by Variations in Their Magnetic Properties

NASA Astrophysics Data System (ADS)

Howell, Taylor A.; Osting, Braxton; Abbott, Jake J.

2018-05-01

We consider sorting for the broad class of micromachines (also known as microswimmers, microrobots, micropropellers, etc.) propelled by rotating magnetic fields. We present a control policy that capitalizes on the variation in magnetic properties between otherwise-homogeneous micromachines to enable the sorting of a select fraction of a group from the remainder and prescribe its net relative movement, using a uniform magnetic field that is applied equally to all micromachines. The method enables us to accomplish this sorting task using open-loop control, without relying on a structured environment or localization information of individual micromachines. With our method, the control time to perform the sort is invariant to the number of micromachines. The method is verified through simulations and scaled experiments. Finally, we include an extended discussion about the limitations of the method and address open questions related to its practical application.

Integrated CoPtP Permanent Magnets for MEMS Electromagnetic Energy Harvesting Applications

NASA Astrophysics Data System (ADS)

Mallick, Dhiman; Roy, Saibal

2016-10-01

This work reports the development of integrated Co rich CoPtP hard magnetic material for MEMS applications such as Electromagnetic Vibration Energy Harvesting. We report a new method of electrodeposition compared to the conventional DC plating, involving a combination of forward and reverse pulses for optimized deposition of Co rich CoPtP hard magnetic material. This results in significant improvements in the microstructure of the developed films as the pulse reverse plated films are smooth, stress free and uniform. Such improvements in the structural properties are reflected in the hard magnetic properties of the material as well. The intrinsic coercivities of the pulse reverse deposited film are more than 6 times higher for both in-plane and out-of-plane measurement directions and the squareness of the hysteresis loops also improve due to the similar reasons.

Hot spine loops and the nature of a late-phase solar flare

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sun, Xudong; Todd Hoeksema, J.; Liu, Yang

2013-12-01

The fan-spine magnetic topology is believed to be responsible for many curious features in solar explosive events. A spine field line links distinct flux domains, but direct observation of such a feature has been rare. Here we report a unique event observed by the Solar Dynamic Observatory where a set of hot coronal loops (over 10 MK) connected to a quasi-circular chromospheric ribbon at one end and a remote brightening at the other. Magnetic field extrapolation suggests that these loops are partly tracers of the evolving spine field line. Continuous slipping- and null-point-type reconnections were likely at work, energizing themore » loop plasma and transferring magnetic flux within and across the fan quasi-separatrix layer. We argue that the initial reconnection is of the 'breakout' type, which then transitioned to a more violent flare reconnection with an eruption from the fan dome. Significant magnetic field changes are expected and indeed ensued. This event also features an extreme-ultraviolet (EUV) late phase, i.e., a delayed secondary emission peak in warm EUV lines (about 2-7 MK). We show that this peak comes from the cooling of large post-reconnection loops beside and above the compact fan, a direct product of eruption in such topological settings. The long cooling time of the large arcades contributes to the long delay; additional heating may also be required. Our result demonstrates the critical nature of cross-scale magnetic coupling—topological change in a sub-system may lead to explosions on a much larger scale.« less

Evidence that the X-Ray Plasma in Microflares is in a Sequence of Subresolution Magnetic Tubes

NASA Technical Reports Server (NTRS)

Moore, Ronald L.; Falconer, D. A.; Porter, Jason G.

1998-01-01

We analyze the cooling of the X-ray emitting thermal plasma in microflares observed in active regions by the Yohkoh Soft X-ray Telescope. A typical microflare appears to be a transient brightening of an entire small magnetic loop, often having a diameter near the limit of resolution (approximately 2 x 10(exp 8) cm) (Shimizu 1995, PASJ, 47, 251). The X-ray plasma in the loop cools by emission of XUV radiation and by heat conduction to the cooler plasma at the feet of the loop. The cooling rate is determined by the plasma temperature and density and the loop length. The plasma density is determined from the observed X-ray brightness of the loop in combination with the temperature, the loop diameter, and the filling factor. The filling factor is the volume fraction of the loop occupied by the subset of magnetic tubes that is filled by the X-ray plasma and that contains practically all of the X-ray plasma present in the microflare loop. Taking typical values from the hundreds of microflares measured by Shimizu (1995) (X-ray brightness through the thin aluminum filter approximately 4 x 10(exp 3) DN/s/pixel, lifetime approximately 5 min, temperature approximately 6 x 10(exp 6) K, loop length approximately 10(exp 9) cm, loop diameter approximately 3 x 10(exp 8) cm), we find that for filling factors greater than approximately 1% (1) the cooling time is much shorter than the duration of the microflare, and (2) conductive cooling strongly dominates over radiative cooling. Because the cooling time is so short and because the conductive heat flux goes mainly into increasing the plasma density via chromospheric evaporation, we are compelled to conclude that (1) heating to X-ray temperatures continues through nearly the entire life of a microflare, (2) the heating keeps changing to different field lines, so that any one magnetic tube in the sequence of heated tubes emits X-rays only briefly in the life of the microflare, and (3) at any instant during the microflare the tubes filled with X-ray plasma occupy only a small fraction (less than approximately 10%) of the microflare loop. Hence, we expect that coronal X-ray images with spatial resolution 2-3 times better than from Yohkoh will show plenty of rapidly changing filamentary substructure in microflares.

The Twist Limit for Bipolar Active Regions

NASA Technical Reports Server (NTRS)

Moore, Ron; Falconer, David; Gary, Allen

2008-01-01

We present new evidence that further supports the standard idea that active regions are emerged magnetic-flux-rope omega loops. When the axial magnetic twist of a cylindrical flux rope exceeds a critical amount, the flux rope becomes unstable to kinking, and the excess axial twist is converted into writhe twist by the kinking. This suggests that, if active regions are emerged omega loops, then (1) no active region should have magnetic twist much above the limit set by kinking, (2) active regions having twist near the limit should often arise from kinked omega loops, and (3) since active regions having large delta sunspots are outstandingly twisted, these arise from kinked omega loops and should have twist near the limit for kinking. From each of 36 vector magnetograms of bipolar active regions, we have measured (1) the total flux of the vertical field above 100 G, (2) the area covered by this flux, and (3) the net electric current that arches over the polarity inversion line. These three quantities yield an estimate of the axial magnetic twist in a simple model cylindrical flux rope that corresponds to the top of the active region s hypothetical omega loop prior to emergence. In all 36 cases, the estimated twist is below the critical limit for kinking. The 11 most twisted active regions (1) have estimated twist within a factor of approx.3 of the limit, and (2) include all of our 6 active regions having large delta sunspots. Thus, our observed twist limit for bipolar active regions is in good accord with active regions being emerged omega loops.

Traveling wave tube and method of manufacture

NASA Technical Reports Server (NTRS)

Vancil, Bernard K. (Inventor)

2004-01-01

A traveling wave tube includes a glass or other insulating envelope having a plurality of substantially parallel glass rods supported therewithin which in turn support an electron gun, a collector and an intermediate slow wave structure. The slow wave structure itself provides electrostatic focussing of a central electron beam thereby eliminating the need for focussing magnetics and materially decreasing the cost of construction as well as enabling miniaturization. The slow wave structure advantageously includes cavities along the electron beam through which the r.f. energy is propagated, or a double, interleaved ring loop structure supported by dielectric fins within a ground plane cylinder disposed coaxially within the glass envelope.

Modification in structure, phase transition, and magnetic property of metallic gallium driven by atom-molecule interactions.

PubMed

Song, Le Xin; Chen, Jie; Zhu, Lin Hong; Xia, Juan; Yang, Jun

2011-09-05

The present work supports a novel paradigm in which the surface structure and stacking behavior of metallic gallium (Ga) were significantly influenced by the preparation process in the presence of organic small molecules (ethanol, acetone, dichloromethane, and diethyl ether). The extent of the effect strongly depends on the polarity of the molecules. Especially, a series of new atom-molecule aggregates consisting of metallic Ga and macrocyclic hosts (cyclodextrins, CDs) were prepared and characterized by various techniques. A comprehensive comparative analysis between free metallic Ga and the Ga samples obtained provides important and at present rare information on the modification in structure, phase transition, and magnetic property of Ga driven by atom-molecule interactions. First, there is a notable difference in microstructure and electronic structure between the different types of Ga samples. Second, differential scanning calorimetry analysis gives us a complete picture (such as the occurrence of a series of metastable phases of Ga in the presence of CDs) that has allowed us to consider that Ga atoms were protected by the shielding effect provided by the cavities of CDs. Third, the metallic Ga distributed in the aggregates exhibits very interesting magnetic property compared to free metallic Ga, such as the uniform zero-field-cooled and field-cooled magnetization processes, the enhanced responses in magnetization to temperature and applied field, and the fundamental change in shape of magnetic hysteresis loops. These significant changes in structural transformation and physical property of Ga provide a novel insight into the understanding of atom-molecule interactions between metallic atoms and organic molecules.

Magnetic Braids in Eruptions of a Spiral Structure in the Solar Atmosphere

NASA Astrophysics Data System (ADS)

Huang, Zhenghua; Xia, Lidong; Nelson, Chris J.; Liu, Jiajia; Wiegelmann, Thomas; Tian, Hui; Klimchuk, James A.; Chen, Yao; Li, Bo

2018-02-01

We report on high-resolution imaging and spectral observations of eruptions of a spiral structure in the transition region, which were taken with the Interface Region Imaging Spectrograph, and the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The eruption coincided with the appearance of two series of jets, with velocities comparable to the Alfvén speeds in their footpoints. Several pieces of evidence of magnetic braiding in the eruption are revealed, including localized bright knots, multiple well-separated jet threads, transition region explosive events, and the fact that all three of these are falling into the same locations within the eruptive structures. Through analysis of the extrapolated 3D magnetic field in the region, we found that the eruptive spiral structure corresponded well to locations of twisted magnetic flux tubes with varying curl values along their lengths. The eruption occurred where strong parallel currents, high squashing factors, and large twist numbers were obtained. The electron number density of the eruptive structure is found to be ∼3 × 1012 cm‑3, indicating that a significant amount of mass could be pumped into the corona by the jets. Following the eruption, the extrapolations revealed a set of seemingly relaxed loops, which were visible in the AIA 94 Å channel, indicating temperatures of around 6.3 MK. With these observations, we suggest that magnetic braiding could be part of the mechanisms explaining the formation of solar eruption and the mass and energy supplement to the corona.

Toroidal midplane neutral beam armor and plasma limiter

DOEpatents

Kugel, Henry W.; Hand Jr, Samuel W.; Ksayian, Haig

1986-02-04

For use in a tokamak fusion reactor having a midplane magnetic coil on the inner wall of an evacuated toriodal chamber within which a neutral beam heated, fusing plasma is magnetically confined, a neutral beam armor shield and plasma limiter is provided on the inner wall of the toroidal chamber to shield the midplane coil from neutral beam shine-thru and plasma deposition. The armor shield/plasma limiter forms a semicircular enclosure around the midplane coil with the outer surface of the armor shield/plasma limiter shaped to match, as closely as practical, the inner limiting magnetic flux surface of the toroidally confined, indented, bean-shaped plasma. The armor shield/plasma limiter includes a plurality of semicircular graphite plates each having a pair of coupled upper and lower sections with each plate positioned in intimate contact with an adjacent plate on each side thereof so as to form a closed, planar structure around the entire outer periphery of the circular midplane coil. The upper and lower plate sections are adapted for coupling to heat sensing thermocouples and to a circulating water conduit system for cooling the armor shield/plasma limiter.The inner center portion of each graphite plate is adapted to receive and enclose a section of a circular diagnostic magnetic flux loop so as to minimize the power from the plasma confinement chamber incident upon the flux loop.

Toroidal midplane neutral beam armor and plasma limiter

DOEpatents

Kugel, Henry W.; Hand, Jr, Samuel W.; Ksayian, Haig

1986-01-01

For use in a tokamak fusion reactor having a midplane magnetic coil on the inner wall of an evacuated toriodal chamber within which a neutral beam heated, fusing plasma is magnetically confined, a neutral beam armor shield and plasma limiter is provided on the inner wall of the toroidal chamber to shield the midplane coil from neutral beam shine-thru and plasma deposition. The armor shield/plasma limiter forms a semicircular enclosure around the midplane coil with the outer surface of the armor shield/plasma limiter shaped to match, as closely as practical, the inner limiting magnetic flux surface of the toroidally confined, indented, bean-shaped plasma. The armor shield/plasma limiter includes a plurality of semicircular graphite plates each having a pair of coupled upper and lower sections with each plate positioned in intimate contact with an adjacent plate on each side thereof so as to form a closed, planar structure around the entire outer periphery of the circular midplane coil. The upper and lower plate sections are adapted for coupling to heat sensing thermocouples and to a circulating water conduit system for cooling the armor shield/plasma limiter.The inner center portion of each graphite plate is adapted to receive and enclose a section of a circular diagnostic magnetic flux loop so as to minimize the power from the plasma confinement chamber incident upon the flux loop.

Giant Primeval Magnetic Dipoles

NASA Astrophysics Data System (ADS)

Thompson, Christopher

2017-07-01

Macroscopic magnetic dipoles are considered cosmic dark matter. Permanent magnetism in relativistic field structures can involve some form of superconductivity, one example being current-carrying string loops (“springs”) with vanishing net tension. We derive the cross-section for free classical dipoles to collide, finding it depends weakly on orientation when mutual precession is rapid. The collision rate of “spring” loops with tension { T }˜ {10}-8{c}4/G in galactic halos approaches the measured rate of fast radio bursts (FRBs) if the loops compose most of the dark matter. A large superconducting dipole (LSD) with mass ˜1020 g and size ˜1 mm will form a ˜100 km magnetosphere moving through interstellar plasma. Although hydromagnetic drag is generally weak, it is strong enough to capture some LSDs into long-lived rings orbiting supermassive black holes (SMBHs) that form by the direct collapse of massive gas clouds. Repeated collisions near young SMBHs could dominate the global collision rate, thereby broadening the dipole mass spectrum. Colliding LSDs produce tiny, hot electromagnetic explosions. The accompanying paper shows that these explosions couple effectively to propagating low-frequency electromagnetic modes, with output peaking at 0.01-1 THz. We describe several constraints on, and predictions of, LSDs as cosmic dark matter. The shock formed by an infalling LSD triggers self-sustained thermonuclear burning in a C/O (ONeMg) white dwarf (WD) of mass ≳1 M ⊙ (1.3 M ⊙). The spark is generally located off the center of the WD. The rate of LSD-induced explosions matches the observed rate of Type Ia supernovae.

Spacecraft momentum management procedures. [large space telescope

NASA Technical Reports Server (NTRS)

Chen, L. C.; Davenport, P. B.; Sturch, C. R.

1980-01-01

Techniques appropriate for implementation onboard the space telescope and other spacecraft to manage the accumulation of momentum in reaction wheel control systems using magnetic torquing coils are described. Generalized analytical equations are derived for momentum control laws that command the magnetic torquers. These control laws naturally fall into two main categories according to the methods used for updating the magnetic dipole command: closed loop, in which the update is based on current measurements to achieve a desired torque instantaneously, and open-loop, in which the update is based on predicted information to achieve a desired momentum at the end of a period of time. Physical interpretations of control laws in general and of the Space Telescope cross product and minimum energy control laws in particular are presented, and their merits and drawbacks are discussed. A technique for retaining the advantages of both the open-loop and the closed-loop control laws is introduced. Simulation results are presented to compare the performance of these control laws in the Space Telescope environment.

Low temperature nucleation of Griffiths Phase in Co doped LaMnO3 nanostructures

NASA Astrophysics Data System (ADS)

Adeela, N.; Khan, U.; Naz, S.; Iqbal, M.; Irfan, M.; Cheng, Y.

2017-11-01

We have reported magnetic properties of La1-xCoxMnO3 nanostructures synthesized by hydrothermal route. The crystal structure has been characterized by X-ray diffraction (XRD) technique, which shows rhombohedral perovskite structure at room temperature. Scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy (EDS) have been used to analyse morphology and chemical composition of prepared nanoparticles. Magnetic hysteresis loops of all the samples exhibit ferromagnetic behaviour at 10 K. Inverse susceptibility graphs as a function of temperature represent deviation from Curie Weiss law. The indication for short range ferromagnetic clusters well above Curie temperature is observed due to the Griffiths Phase (GP). It is proposed that the presence of GP arises from induced size effects of La and Co ions.

Structural, optical and magnetic behaviour of nanocrystalline Volborthite

DOE Office of Scientific and Technical Information (OSTI.GOV)

Arvind, Hemant K., E-mail: hemantarvind@gmail.com; Kumar, Sudhish, E-mail: skmlsu@gmail.com; Kalal, Sangeeta

2016-05-06

Nanocrystalline sample of Volborthite (Copper Pyrovanadate: Cu{sub 3}V{sub 2} (OH){sub 2}O{sub 7}.2H{sub 2}O) has been synthesized using wet chemical route and characterized by XRD, SEM, FTIR, UV-Vis-NIR spectroscopic and magnetization measurements. Room temperature X-ray diffraction analysis confirms the single phase monoclinic structure and nanocrystalline nature of Volborthite. The UV-Visible optical absorption spectrum displays two broad absorption peaks in the range of 200-350 nm and 400-1000 nm. The direct band gap is found to be E{sub g}= ∼2.74 eV. Bulk Volborthite was reported to be a natural frustrated antiferromagnet, however our nanocrystalline Volborthite display week ferromagnetic hysteresis loop with very small coercivity andmore » retentivity at room temperature.« less

Size-dependent magnetic anisotropy of PEG coated Fe3O4 nanoparticles; comparing two magnetization methods

NASA Astrophysics Data System (ADS)

Nayek, C.; Manna, K.; Imam, A. A.; Alqasrawi, A. Y.; Obaidat, I. M.

2018-02-01

Understanding the size dependent magnetic anisotropy of iron oxide nanoparticles is essential for the successful application of these nanoparticles in several technological and medical fields. PEG-coated iron oxide (Fe3O4) nanoparticles with core diameters of 12 nm, 15 nm, and 16 nm were synthesized by the usual co-precipitation method. The morphology and structure of the nanoparticles were investigated using transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), and X-ray diffraction (XRD). Magnetic measurements were conducted using a SQUID. The effective magnetic anisotropy was calculated using two methods from the magnetization measurements. In the first method the zero-field-cooled magnetization versus temperature measurements were used at several applied magnetic fields. In the second method we used the temperature-dependent coercivity curves obtained from the zero-field-cooled magnetization versus magnetic field hysteresis loops. The role of the applied magnetic field on the effective magnetic anisotropy, calculated form the zero-field-cooled magnetization versus temperature measurements, was revealed. The size dependence of the effective magnetic anisotropy constant Keff obtained by the two methods are compared and discussed.

High-Altitude Closed Magnetic Loops at Mars Observed by MAVEN

NASA Astrophysics Data System (ADS)

Xu, Shaosui; Mitchell, David; Luhmann, Janet; Ma, Yingjuan; Fang, Xiaohua; Harada, Yuki; Hara, Takuya; Brain, David; Weber, Tristan; Mazelle, Christian; DiBraccio, Gina A.

2017-11-01

With electron and magnetic field data obtained by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, we have identified closed magnetic field lines, with both foot points embedded in the dayside ionosphere, extending up to 6,200 km altitude into the Martian tail. This topology is deduced from photoelectrons produced in the dayside ionosphere being observed traveling both parallel and antiparallel to the magnetic field. At trapped-zone pitch angles (within a range centered on 90° where electrons magnetically reflect before interacting with the atmosphere), cases with either solar wind electrons or photoelectrons have been found, indicating different formation mechanisms for these closed loops. These large closed loops are present in MHD simulations. The case with field-aligned photoelectrons mixed with solar wind electrons having trapped-zone pitch angles is likely to be associated with reconnection, while the case with photoelectrons at all pitch angles is probably due to closed field lines being pulled tailward by the surrounding plasma flow. By utilizing an algorithm for distinguishing photoelectrons from solar wind electrons in pitch angle-resolved energy spectra, we systematically map the spatial distribution and occurrence rate of these closed magnetic loops over the region sampled by the MAVEN orbit. We find that the occurrence rate ranges from a few percent to a few tens of percent outside of the optical shadow and less than one percent within the shadow. These observations can be used to investigate the general magnetic topology in the tail, which is relevant to cold ion escape, reconnection, and flux ropes.

Coronal Heating and the Magnetic Field in Solar Active Regions

NASA Astrophysics Data System (ADS)

Falconer, D. A.; Tiwari, S. K.; Winebarger, A. R.; Moore, R. L.

2017-12-01

A strong dependence of active-region (AR) coronal heating on the magnetic field is demonstrated by the strong correlation of AR X-ray luminosity with AR total magnetic flux (Fisher et al 1998 ApJ). AR X-ray luminosity is also correlated with AR length of strong-shear neutral line in the photospheric magnetic field (Falconer 1997). These two whole-AR magnetic parameters are also correlated with each other. From 150 ARs observed within 30 heliocentric degrees from disk center by AIA and HMI on SDO, using AR luminosity measured from the hot component of the AIA 94 Å band (Warren et al 2012, ApJ) near the time of each of 3600 measured HMI vector magnetograms of these ARs and a wide selection of whole-AR magnetic parameters from each vector magnetogram after it was deprojected to disk center, we find: (1) The single magnetic parameter having the strongest correlation with AR 94-hot luminosity is the length of strong-field neutral line. (2) The two-parameter combination having the strongest still-stronger correlation with AR 94-hot luminosity is a combination of AR total magnetic flux and AR neutral-line length weighted by the vertical-field gradient across the neutral line. We interpret these results to be consistent with the results of both Fisher et al (1998) and Falconer (1997), and with the correlation of AR coronal loop heating with loop field strength recently found by Tiwari et al (2017, ApJ Letters). Our interpretation is that, in addition to depending strongly on coronal loop field strength, AR coronal heating has a strong secondary positive dependence on the rate of flux cancelation at neutral lines at coronal loop feet. This work was funded by the Living With a Star Science and Heliophysics Guest Investigators programs of NASA's Heliophysics Division.

Topological transformations of Hopf solitons in chiral ferromagnets and liquid crystals.

PubMed

Tai, Jung-Shen B; Ackerman, Paul J; Smalyukh, Ivan I

2018-01-30

Liquid crystals are widely known for their facile responses to external fields, which forms a basis of the modern information display technology. However, switching of molecular alignment field configurations typically involves topologically trivial structures, although singular line and point defects often appear as short-lived transient states. Here, we demonstrate electric and magnetic switching of nonsingular solitonic structures in chiral nematic and ferromagnetic liquid crystals. These topological soliton structures are characterized by Hopf indices, integers corresponding to the numbers of times that closed-loop-like spatial regions (dubbed "preimages") of two different single orientations of rod-like molecules or magnetization are linked with each other. We show that both dielectric and ferromagnetic response of the studied material systems allow for stabilizing a host of topological solitons with different Hopf indices. The field transformations during such switching are continuous when Hopf indices remain unchanged, even when involving transformations of preimages, but discontinuous otherwise.

Characterization of Magnetic Nanostructures Using Off-Axis Electron Holography

NASA Astrophysics Data System (ADS)

Zhang, Desai

This dissertation research has involved microscopic characterization of magnetic nanostructures using off-axis electron holography and Lorentz microscopy. The nanostructures investigated have included Co nanoparticles (NPs), Au/Fe/GaAs shell/core nanowires (NWs), carbon spirals with magnetic cores, magnetic nanopillars, Ni-Zn-Co spinel ferrite and CoFe/Pd multilayers. The studies have confirmed the capability of holography to describe the behavior of magnetic structures at the nanoscale. The phase changes caused by the fringing fields of chains consisting of Co NPs were measured and calculated. The difference between chains with different numbers of Co NPs followed the trend indicated by calculations. Holography studies of Au/Fe/GaAs NWs grown on (110) GaAs substrates with rotationally non-uniform coating confirmed that Fe was present in the shell and that the shell behaved as a bar magnet. No fringing field was observed from NWs with cylindrical coating grown on (111)B GaAs substrates. The most likely explanation is that magnetic fields are confined within the shells and form closed loops. The multiple-magnetic-domain structure of iron carbide cores in carbon spirals was imaged using phase maps of the fringing fields. The strength and range of this fringing field was insufficient for manipulating the carbon spirals with an external applied magnetic field. No magnetism was revealed for CoPd/Fe/CoPd magnetic nanopillars. Degaussing and MFM scans ruled out the possibility that saturated magnetization and sample preparation had degraded the anisotropy, and the magnetism, respectively. The results suggested that these nanopillars were not suitable as candidates for prototypical bit information storage devices. Observations of Ni-Zn-Co spinel ferrite thin films in plan-view geometry indicated a multigrain magnetic domain structure and the magnetic fields were oriented in-plane only with no preferred magnetization distribution. This domain structure helps explain this ferrite's high permeability at high resonance frequency, which is an unusual character. Perpendicular magnetic anisotropy (PMA) of CoFe/Pd multilayers was revealed using holography. Detailed microscopic characterization showed structural factors such as layer waviness and interdiffusion that could contribute to degradation of the PMA. However, these factors are overwhelmed by the dominant effect of the CoFe layer thickness, and can be ignored when considering magnetic domain structure.

Structure-based design of potent histatin analogues.

PubMed

Brewer, Dyanne; Lajoie, Gilles

2002-04-30

Conformational studies of human salivary peptide, histatin 3 (Hst3), were performed by nuclear magnetic resonance (NMR) and circular dichroism (CD) spectroscopy in a membrane-mimicking environment. The structural information that was obtained was used in the design of peptide analogues with improved antifungal activity. In the presence of increasing concentrations of L-alpha-dimyristoylphosphatidylcholine (L-alpha-DMPC) lipid vesicles, a dramatic increase in a minimum at 198 nm is observed in the CD spectra of Hst3. The NMR data of Hst3 in the presence of L-alpha-DMPC lipid vesicles reveal the proximity of residues Y(10) and S(20), indicating the existence of a more compact structure. Peptide analogues were designed on the basis of this observation, which incorporated a disulfide bond to stabilize an extended loop in this region of the sequence. One of these, peptide 4, was 100 times more potent than Hst5 against Saccharomyces cerevisiae cells. Conformational analysis of peptide 4 revealed a looped structure with charged residues protruding on the outside surface, while a combination of aromatic residues and histidines are packed into an internal core.

Rapid Damping of the Oscillations of Coronal Loops with an Azimuthal Magnetic Field

NASA Astrophysics Data System (ADS)

Mikhalyaev, B. B.

2005-06-01

We consider the MHD oscillations of an inhomogeneous coronal loop that consists of a dense cord surrounded by a shell. The magnetic field is longitudinal in the cord and has only an azimuthal component in the shell. The parameters of the loop are chosen to be such that there are no resonances; i.e., the resonance points are cut off. This choice is dictated by the formulated problem of considering the influence of the radiation of MHD waves into the surrounding space on the loop oscillations, thereby ruling out the possibility of resonant energy absorption. The wave radiation efficiency is high and allows low oscillation Q-factors, which are equal in order of magnitude to their observed values, to be obtained.

Research on the Dynamic Hysteresis Loop Model of the Residence Times Difference (RTD)-Fluxgate

PubMed Central

Wang, Yanzhang; Wu, Shujun; Zhou, Zhijian; Cheng, Defu; Pang, Na; Wan, Yunxia

2013-01-01

Based on the core hysteresis features, the RTD-fluxgate core, while working, is repeatedly saturated with excitation field. When the fluxgate simulates, the accurate characteristic model of the core may provide a precise simulation result. As the shape of the ideal hysteresis loop model is fixed, it cannot accurately reflect the actual dynamic changing rules of the hysteresis loop. In order to improve the fluxgate simulation accuracy, a dynamic hysteresis loop model containing the parameters which have actual physical meanings is proposed based on the changing rule of the permeability parameter when the fluxgate is working. Compared with the ideal hysteresis loop model, this model has considered the dynamic features of the hysteresis loop, which makes the simulation results closer to the actual output. In addition, other hysteresis loops of different magnetic materials can be explained utilizing the described model for an example of amorphous magnetic material in this manuscript. The model has been validated by the output response comparison between experiment results and fitting results using the model. PMID:24002230

PROPERTIES AND MODELING OF UNRESOLVED FINE STRUCTURE LOOPS OBSERVED IN THE SOLAR TRANSITION REGION BY IRIS

DOE Office of Scientific and Technical Information (OSTI.GOV)

Brooks, David H.; Reep, Jeffrey W.; Warren, Harry P.

Recent observations from the Interface Region Imaging Spectrograph ( IRIS ) have discovered a new class of numerous low-lying dynamic loop structures, and it has been argued that they are the long-postulated unresolved fine structures (UFSs) that dominate the emission of the solar transition region. In this letter, we combine IRIS measurements of the properties of a sample of 108 UFSs (intensities, lengths, widths, lifetimes) with one-dimensional non-equilibrium ionization simulations, using the HYDRAD hydrodynamic model to examine whether the UFSs are now truly spatially resolved in the sense of being individual structures rather than being composed of multiple magnetic threads.more » We find that a simulation of an impulsively heated single strand can reproduce most of the observed properties, suggesting that the UFSs may be resolved, and the distribution of UFS widths implies that they are structured on a spatial scale of 133 km on average. Spatial scales of a few hundred kilometers appear to be typical for a range of chromospheric and coronal structures, and we conjecture that this could be an important clue for understanding the coronal heating process.« less

A magneto-optic technique for studying magnetization reversal processes and anisotropies applied to Co/Cu/Co trilayer structures

NASA Astrophysics Data System (ADS)

Daboo, C.; Bland, J. A. C.; Hicken, R. J.; Ives, A. J. R.; Baird, M. J.; Walker, M. J.

1993-05-01

We report the magnetization reversal and magnetic anisotropy behavior of ultrathin Co/Cu(111)/Co (dCu=20 and 27 Å) trilayer structures prepared by MBE on a 500-Å Ge/GaAs(110) epilayer. We describe an arrangement in which the magnetization components parallel and perpendicular to the applied field are both determined from longitudinal MOKE measurements. For the samples examined, coherent rotation of the magnetization vector is observed when the magnetic field is applied along the hard in-plane anisotropy axis, with the magnitude of the magnetization vector constant and close to its bulk value. Results of micromagnetic calculations closely reproduce the observed parallel and perpendicular magnetization loops, and yield strong uniaxial magnetic anisotropies in both layers while the interlayer coupling appears to be absent or negligible in comparison with the anisotropy strengths. An absence of antiferromagnetic (AF) coupling has been observed previously [W. F. Egelhoff, Jr. and M. T. Kief, Phys. Rev. B 45, 7795 (1992)] in contrast to recent results, indicating that AF coupling [M. T. Johnson et al., Phys. Rev. Lett. 69, 969 (1992)] and GMR [D. Grieg et al., J. Magn. Magn. Mater. 110, L239 (1992)] can occur in Co/Cu(111)/Co structures grown by MBE, but these properties are sensitively dependent on growth conditions. The absence of coupling in our samples is attributed to the presence of a significant interface roughness induced by the Ge epilayer. The uniaxial anisotropies are assumed to arise from strain or defects induced in the film.

Coronal Heating, Weak MHD Turbulence, and Scaling Laws

NASA Technical Reports Server (NTRS)

Rappazzo, A. F.; Velli, M.; Einaudi, G.; Dahlburg, R. B.

2007-01-01

Long-time high-resolution simulations of the dynamics of a coronal loop in Cartesian geometry are carried out, within the framework of reduced magnetohydrodynamics (RMHD), to understand coronal heating driven by the motion of field lines anchored in the photosphere. We unambiguously identify MHD anisotropic turbulence as the physical mechanism responsible for the transport of energy from the large scales, where energy is injected by photospheric motions, to the small scales, where it is dissipated. As the loop parameters vary, different regimes of turbulence develop: strong turbulence is found for weak axial magnetic fields and long loops, leading to Kolmogorov-like spectra in the perpendicular direction, while weaker and weaker regimes (steeper spectral slopes of total energy) are found for strong axial magnetic fields and short loops. As a consequence we predict that the scaling of the heating rate with axial magnetic field intensity B, which depends on the spectral index of total energy for given loop parameters, must vary from B3/2 for weak fields to B2 for strong fields at a given aspect ratio. The predicted heating rate is within the lower range of observed active region and quiet-Sun coronal energy losses.

Narrow-band, slowly varying decimetric radiation from the dwarf M flare star YZ Canis Minoris

NASA Technical Reports Server (NTRS)

Lang, K. R.; Willson, R. F.

1986-01-01

Observations of slowly varying radiation from the dwarf M star YZ Canis Minoris with a maximum flux density of 20 mJy and narrow-band frequency structure at frequencies near 1465 MHz are presented. Possible explanations for this radiation are examined. Thermal gyroresonant radiation would require impossibly large coronal loops and magnetic field strengths. The narrow-band structure cannot be explained by continuum emission processes such as thermal bremsstrahlung, thermal gyroresonant radiation, or nonthermal gyrosynchrotron radiation. Coherent burst mechanisms seem to be required.

Room temperature exchange bias in multiferroic BiFeO3 nano- and microcrystals with antiferromagnetic core and two-dimensional diluted antiferromagnetic shell

NASA Astrophysics Data System (ADS)

Zhang, Chuang; Wang, Shou Yu; Liu, Wei Fang; Xu, Xun Ling; Li, Xiu; Zhang, Hong; Gao, Ju; Li, De Jun

2017-05-01

Exchange bias (EB) of multiferroics presents many potential opportunities for magnetic devices. However, instead of using low-temperature field cooling in the hysteresis loop measurement, which usually shows an effective approach to obtain obvious EB phenomenon, there are few room temperature EB. In this article, extensive studies on room temperature EB without field cooling were observed in BiFeO3 nano- and microcrystals. Moreover, with increasing size the hysteresis loops shift from horizontal negative exchange bias (NEB) to positive exchange bias (PEB). In order to explain the tunable EB behaviors with size dependence, a phenomenological qualitative model based on the framework of antiferromagnetic (AFM) core-two-dimensional diluted antiferromagnet in a field (2D-DAFF) shell structure was proposed. The training effect (TE) ascertained the validity of model and the presence of unstable magnetic structure using Binek's model. Experimental results show that the tunable EB effect can be explained by the competition of ferromagnetic (FM) exchange coupling and AFM exchange coupling interaction between AFM core and 2D-DAFF shell. Additionally, the local distortion of lattice fringes was observed in hexagonal-shaped BiFeO3 nanocrystals with well-dispersed behavior. The electrical conduction properties agreed well with the space charge-limited conduction mechanism.

Circuit Regulates Speed Of dc Motor

NASA Technical Reports Server (NTRS)

Weaver, Charles; Padden, Robin; Brown, Floyd A., Jr.

1990-01-01

Driving circuit regulates speed of small dc permanent-magnet motor in tape recorder. Two nested feedback loops maintain speed within 1 percent of constant value. Inner loop provides coarse regulation, while outer loop removes most of variation in speed that remains in the presence of regulation by the inner loop. Compares speed of motor with commanded speed and adjusts current supplied to motor accordingly.

On the heating mechanism of magnetic flux loops in the solar atmosphere

NASA Technical Reports Server (NTRS)

Song, M. T.; Wu, S. T.

1984-01-01

An investigation is conducted of physical heating mechanisms due to the ponderomotive forces exerted by turbulent waves along the solar atmosphere's curved magnetic flux loops. Results indicate that the temperature difference between the inside and outside of the flux loop can be classified into three parts, two of which represent the cooling or heating effect exerted by the ponderomotive force, while the third is the heating effect due to turbulent energy conversion from the localized plasma. This heating mechanism is used to illustrate solar atmospheric heating by means of an example that leads to the formulation of plages.

Influences of PZT addition on phase formation and magnetic properties of perovskite Pb(Fe0.5Nb0.5)O3-based ceramics

NASA Astrophysics Data System (ADS)

Amonpattaratkit, P.; Jantaratana, P.; Ananta, S.

2015-09-01

In this work, the investigation of phase formation, crystal structure, microstructure, microchemical composition and magnetic properties of perovskite (1-x)PFN-xPZT (x=0.1-0.5) multiferroic ceramics derived from a combination of perovskite stabilizer PZT and a wolframite-type FeNbO4 B-site precursor was carried out by using a combination of X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analyzer and vibrating sample magnetometer (VSM) techniques. The addition of PZT phase and its concentration have been found to have pronounced effects on the perovskite phase formation, densification, grain growth and magnetic properties of the sintered ceramics. XRD spectra from these ceramics reveal transformation of the (pseudo) cubic into the tetragonal perovskite structure. When increasing PZT content, the degree of perovskite phase formation and the tetragonality value of the ceramics increase gradually accompanied with the variation of cell volume, the M-H hysteresis loops, however, become narrower accompanied by the decrease of maximum magnetization (Mmax), remanent polarization (Mr), and coercive field (HC).

Effect of film thickness on soft magnetic behavior of Fe2CoSi Heusler alloy for spin transfer torque device applications

NASA Astrophysics Data System (ADS)

Asvini, V.; Saravanan, G.; Kalaiezhily, R. K.; Raja, M. Manivel; Ravichandran, K.

2018-04-01

Fe2CoSi based Heusler alloy thin films were deposited on Si (111) wafer (substrate) of varying thickness using ultra high vacuum DC magnetron sputtering. The structural behavior was observed and found to be hold the L21 structure. The deposited thin films were characterized magnetic properties using vibrating sample magnetometer; the result shows a very high saturated magnetization (Ms), lowest coercivity (Hc), high curie transition temperature (Tc) and low hysteresis loss. Thin film thickness of 75 nm Fe2CoSi sample maintained at substrate temperature 450°C shows the lowest coercivity (Hc=7 Oe). In general, Fe2CoSi Heusler alloys curie transition temperature is very high, due to strong exchange interaction between the Fe and Co atoms. The substrate temperature was kept constant at 450°C for varying thickness (e.g. 5, 20, 50, 75 and 100 nm) of thin film sample. The 75 nm thickness thin film sample shows well crystallanity and good magnetic properties, further squareness ratio in B-H loop increases with the increase in film thickness.