Effect of the Hartmann number on phase separation controlled by magnetic field for binary mixture system with large component ratio

NASA Astrophysics Data System (ADS)

Heping, Wang; Xiaoguang, Li; Duyang, Zang; Rui, Hu; Xingguo, Geng

2017-11-01

This paper presents an exploration for phase separation in a magnetic field using a coupled lattice Boltzmann method (LBM) with magnetohydrodynamics (MHD). The left vertical wall was kept at a constant magnetic field. Simulations were conducted by the strong magnetic field to enhance phase separation and increase the size of separated phases. The focus was on the effect of magnetic intensity by defining the Hartmann number (Ha) on the phase separation properties. The numerical investigation was carried out for different governing parameters, namely Ha and the component ratio of the mixed liquid. The effective morphological evolutions of phase separation in different magnetic fields were demonstrated. The patterns showed that the slant elliptical phases were created by increasing Ha, due to the formation and increase of magnetic torque and force. The dataset was rearranged for growth kinetics of magnetic phase separation in a plot by spherically averaged structure factor and the ratio of separated phases and total system. The results indicate that the increase in Ha can increase the average size of separated phases and accelerate the spinodal decomposition and domain growth stages. Specially for the larger component ratio of mixed phases, the separation degree was also significantly improved by increasing magnetic intensity. These numerical results provide guidance for setting the optimum condition for the phase separation induced by magnetic field.

Damping effects of magnetic fluids of various saturation magnetization (abstract)

NASA Astrophysics Data System (ADS)

Chagnon, Mark

1990-05-01

Magnetic fluids have been widely accepted for use in loudspeaker voice coil gaps as viscous dampers and liquid coolants. When applied properly to a voice coil in manufacturing of the loudspeaker, dramatic improvement in frequency response and power handling is observed. Over the past decade, a great deal of study has been given to the effects of damping as a function of fluid viscosity. It is known that the apparent viscosity of a magnetic fluid increases as a function of applied magnetic field, and that the viscosity versus field relationship approximate that of the magnetization versus applied field. At applied magnetic field strength sufficient to cause magnetic saturation of the fluid, no further increase in viscosity with increased magnetic field is observed. In order to provide a better understanding of the second order magnetoviscous damping effects in magnetic fluids used in voice coils and to provide a better loudspeaker design criterion using magnetic fluids, we have studied the effect on damping of several magnetic fluids of the same O field viscosity and of varying saturation magnetization. Magnetic fluids with saturation magnetization ranging from 50 to 450 G and 100 cps viscosity at O applied field were injected into the voice coil gap of a standard midrange loudspeaker. The frequency response over the entire dynamic range of the speaker was measured. The changes in frequency response versus fluid magnetization are reported.

Development of high-vacuum planar magnetron sputtering using an advanced magnetic field geometry

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

Ohno, Takahiro; Yagyu, Daisuke; Saito, Shigeru, E-mail: saito@ee.kagu.tus.ac.jp

2015-11-15

A permanent magnet in a new magnetic field geometry (namely, with the magnetization in the radial direction) was fabricated and used for high-vacuum planar magnetron sputtering using Penning discharge. Because of the development of this magnet, the discharge current and deposition rate were increased two to three times in comparison with the values attainable with a magnet in the conventional geometry. This improvement was because the available space for effective discharge of the energetic electrons for the ionization increased because the magnetic field distribution increased in both the axial and radial directions of discharge.

Control of the diocotron instability of a hollow electron beam with periodic dipole magnets

DOE PAGES

Jo, Y. H.; Kim, J. S.; Stancari, G.; ...

2017-12-28

A method to control the diocotron instability of a hollow electron beam with peri-odic dipole magnetic fields has been investigated by a two-dimensional particle-in-cell simulation. At first, relations between the diocotron instability and several physical parameters such as the electron number density, current and shape of the electron beam, and the solenoidal field strength are theoretically analyzed without periodic dipole magnetic fields. Then, we study the effects of the periodic dipole magnetic fields on the diocotron instability using the two-dimensional particle-in-cell simulation. In the simulation, we considered the periodic dipole magnetic field applied along the propagation direction of the beam,more » as a temporally varying magnetic field in the beam frame. Lastly, a stabilizing effect is observed when the oscillating frequency of the dipole magnetic field is optimally chosen, which increases with the increasing amplitude of the dipole magnetic field.« less

Tunable SERS signals of Rhodamine B molecules on Fe3O4@Au nanocomposite substrates controlled by magnetic field

NASA Astrophysics Data System (ADS)

Song, Hao; Fang, Rui Yang; Li, Ling

2018-02-01

In this work, we experimentally synthesized the Fe3O4@Au nanocomposites and used them as surface-enhanced Raman scattering (SERS) substrates. The Fe3O4@Au nanocomposites retained the metallic plasmon resonant effect and possessed the magnetic field controllable characteristics. The Raman spectra of Rhodamine B (RhB) probe molecules were studied under different external magnetic field. The magnitude of external magnetic field varied from 0 Gs to 700 Gs (1 Gs = 10-4 T) with intervals of 100 Gs. When the magnetic field magnitude increased, the Raman intensity of RhB probe molecules at 1356 cm-1 increased linearly. The slope of the linear fitting curves for the Raman intensity and area were 0.118/Gs and 3.700/Gs. The Raman enhancement could raise up to 7 times for RhB probe molecules when the magnetic field magnitude increased to 700 Gs. After removing the external magnetic field, the Raman peaks returned to its original intensity in several minutes. Under the external magnetic field, the Fe3O4@Au nanocomposites were concentrated, leading to the increase number of SERS "hot spots" and the surface Au density. The results show that the magnetic field controlled Fe3O4@Au nanocomposites can realize the enhanced and controllable SERS effect, which can be used in the reversible optical sensing and bio-medical applications.

Magnetic-field-induced DNA strand breaks in brain cells of the rat.

PubMed Central

Lai, Henry; Singh, Narendra P

2004-01-01

In previous research, we found that rats acutely (2 hr) exposed to a 60-Hz sinusoidal magnetic field at intensities of 0.1-0.5 millitesla (mT) showed increases in DNA single- and double-strand breaks in their brain cells. Further research showed that these effects could be blocked by pretreating the rats with the free radical scavengers melatonin and N-tert-butyl-alpha-phenylnitrone, suggesting the involvement of free radicals. In the present study, effects of magnetic field exposure on brain cell DNA in the rat were further investigated. Exposure to a 60-Hz magnetic field at 0.01 mT for 24 hr caused a significant increase in DNA single- and double-strand breaks. Prolonging the exposure to 48 hr caused a larger increase. This indicates that the effect is cumulative. In addition, treatment with Trolox (a vitamin E analog) or 7-nitroindazole (a nitric oxide synthase inhibitor) blocked magnetic-field-induced DNA strand breaks. These data further support a role of free radicals on the effects of magnetic fields. Treatment with the iron chelator deferiprone also blocked the effects of magnetic fields on brain cell DNA, suggesting the involvement of iron. Acute magnetic field exposure increased apoptosis and necrosis of brain cells in the rat. We hypothesize that exposure to a 60-Hz magnetic field initiates an iron-mediated process (e.g., the Fenton reaction) that increases free radical formation in brain cells, leading to DNA strand breaks and cell death. This hypothesis could have an important implication for the possible health effects associated with exposure to extremely low-frequency magnetic fields in the public and occupational environments. PMID:15121512

One-loop QCD thermodynamics in a strong homogeneous and static magnetic field

NASA Astrophysics Data System (ADS)

Rath, Shubhalaxmi; Patra, Binoy Krishna

2017-12-01

We have studied how the equation of state of thermal QCD with two light flavors is modified in a strong magnetic field. We calculate the thermodynamic observables of hot QCD matter up to one-loop, where the magnetic field affects mainly the quark contribution and the gluon part is largely unaffected except for the softening of the screening mass. We have first calculated the pressure of a thermal QCD medium in a strong magnetic field, where the pressure at fixed temperature increases with the magnetic field faster than the increase with the temperature at constant magnetic field. This can be understood from the dominant scale of thermal medium in the strong magnetic field, being the magnetic field, in the same way that the temperature dominates in a thermal medium in the absence of magnetic field. Thus although the presence of a strong magnetic field makes the pressure of hot QCD medium larger, the dependence of pressure on the temperature becomes less steep. Consistent with the above observations, the entropy density is found to decrease with the temperature in the presence of a strong magnetic field which is again consistent with the fact that the strong magnetic field restricts the dynamics of quarks to two dimensions, hence the phase space becomes squeezed resulting in the reduction of number of microstates. Moreover the energy density is seen to decrease and the speed of sound of thermal QCD medium increases in the presence of a strong magnetic field. These findings could have phenomenological implications in heavy ion collisions because the expansion dynamics of the medium produced in non-central ultra-relativistic heavy ion collisions is effectively controlled by both the energy density and the speed of sound.

Study of magnetic silk fibroin nanoparticles for massage-like transdermal drug delivery

PubMed Central

Chen, Ai-Zheng; Chen, Lin-Qing; Wang, Shi-Bin; Wang, Ya-Qiong; Zha, Jun-Zhe

2015-01-01

A synergistic approach by the combination of magnetic nanoparticles with an alternating magnetic field for transdermal drug delivery was investigated. Methotrexate-loaded silk fibroin magnetic nanoparticles were prepared using suspension-enhanced dispersion by supercritical CO2. The physiochemical properties of the magnetic nanoparticles were characterized. In vitro studies on drug permeation across skin were performed under different magnetic fields in comparison with passive diffusion. The permeation flux enhancement factor was found to increase under a stationary magnetic field, while an alternating magnetic field enhanced drug permeation more effectively; the combination of stationary and alternating magnetic fields, which has a massage-like effect on the skin, achieved the best result. The mechanistic studies using attenuated total reflection Fourier-transform infrared spectroscopy demonstrate that an alternating magnetic field can change the ordered structure of the stratum corneum lipid bilayers from the gel to the lipid-crystalline state, which can increase the fluidity of the stratum corneum lipids, thus enhancing skin penetration. Compared with the other groups, the fluorescence signal with a bigger area detected in deeper regions of the skin also reveals that the simulated massage could enhance the drug permeation across the skin by increasing the follicular transport. The combination of magnetic nanoparticles with stationary/alternating magnetic fields has potential for effective massage-like transdermal drug delivery. PMID:26229467

Spiraling contaminant electrons increase doses to surfaces outside the photon beam of an MRI-linac with a perpendicular magnetic field

NASA Astrophysics Data System (ADS)

Hackett, S. L.; van Asselen, B.; Wolthaus, J. W. H.; Bluemink, J. J.; Ishakoglu, K.; Kok, J.; Lagendijk, J. J. W.; Raaymakers, B. W.

2018-05-01

The transverse magnetic field of an MRI-linac sweeps contaminant electrons away from the radiation beam. Films oriented perpendicular to the magnetic field and 5 cm from the radiation beam edge show a projection of the divergent beam, indicating that contaminant electrons spiral along magnetic field lines and deposit dose on surfaces outside the primary beam perpendicular to the magnetic field. These spiraling contaminant electrons (SCE) could increase skin doses to protruding regions of the patient along the cranio-caudal axis. This study investigated doses from SCE for an MRI-linac comprising a 7 MV linac and a 1.5 T MRI scanner. Surface doses to films perpendicular to the magnetic field and 5 cm from the radiation beam edge showed increased dose within the projection of the primary beam, whereas films parallel to the magnetic field and 5 cm from the beam edge showed no region of increased dose. However, the dose from contaminant electrons is absorbed within a few millimeters. For large fields, the SCE dose is within the same order of magnitude as doses from scattered and leakage photons. Doses for both SCE and scattered photons decrease rapidly with decreasing beam size and increasing distance from the beam edge.

Magnetic-field-induced dose effects in MR-guided radiotherapy systems: dependence on the magnetic field strength.

PubMed

Raaijmakers, A J E; Raaymakers, B W; Lagendijk, J J W

2008-02-21

Several institutes are currently working on the development of a radiotherapy treatment system with online MR imaging (MRI) modality. The main difference between their designs is the magnetic field strength of the MRI system. While we have chosen a 1.5 Tesla (T) magnetic field strength, the Cross Cancer Institute in Edmonton will be using a 0.2 T MRI scanner and the company Viewray aims to use 0.3 T. The magnetic field strength will affect the severity of magnetic field dose effects, such as the electron return effect (ERE): considerable dose increase at tissue air boundaries due to returning electrons. This paper has investigated how the ERE dose increase depends on the magnetic field strength. Therefore, four situations where the ERE occurs have been simulated: ERE at the distal side of the beam, the lateral ERE, ERE in cylindrical air cavities and ERE in the lungs. The magnetic field comparison values were 0.2, 0.75, 1.5 and 3 T. Results show that, in general, magnetic field dose effects are reduced at lower magnetic field strengths. At the distal side, the ERE dose increase is largest for B = 0.75 T and depends on the irradiation field size for B = 0.2 T. The lateral ERE is strongest for B = 3 T but shows no effect for B = 0.2 T. Around cylindrical air cavities, dose inhomogeneities disappear if the radius of the cavity becomes small relative to the in-air radius of the secondary electron trajectories. At larger cavities (r > 1 cm), dose inhomogeneities exist for all magnetic field strengths. In water-lung-water phantoms, the ERE dose increase takes place at the water-lung transition and the dose decreases at the lung-water transition, but these effects are minimal for B = 0.2 T. These results will contribute to evaluating the trade-off between magnetic field dose effects and image quality of MR-guided radiotherapy systems.

Helicon double layer thruster operation in a low magnetic field mode

NASA Astrophysics Data System (ADS)

Harle, T.; Pottinger, S. J.; Lappas, V. J.

2013-02-01

Direct thrust measurements are made of a helicon double layer thruster operating in a low magnetic field mode. The relationship between the imposed axial magnetic field and generated thrust is investigated for a radio frequency input power range 200-500 W for propellant flow rates of 16.5 and 20 sccm (0.46 and 0.55 mg s-1) of argon. The measured thrust shows a strong dependence on the magnetic field strength, increasing by up to a factor of 5 compared with the minimum thrust level recorded. A peak thrust of 0.4-1.1 mN depending on thruster operating conditions is obtained. This increase is observed to take place over a small range of peak magnetic field strengths in the region of 70-110 G. The magnitude of the thrust and the corresponding magnitude of the magnetic field at which the peak thrust occurs is shown to increase with increasing input power for a given propellant flow rate. The ion current determined using a retarding field energy analyser and the electron number density found using a microwave resonator probe both correlate with the observed trend in thrust as a function of applied magnetic field.

Virtual special issue: Magnetic resonance at low fields

NASA Astrophysics Data System (ADS)

Blümich, Bernhard

2017-01-01

It appears to be a common understanding that low magnetic fields need to be avoided in magnetic resonance, as sensitivity and the frequency dispersion of the chemical shift increase with increasing field strength. But there many reasons to explore magnetic resonance at low fields. The instrumentation tends to be far less expensive than high-field equipment, magnets are smaller and lighter, internal gradients in heterogeneous media are smaller, conductive media and even metals become transparent at low frequencies to electromagnetic fields, and new physics and phenomena await to be discovered. On account of an increasing attention of the scientific community to magnetic resonance at low field, we have decided to launch JMR's Virtual Special Issue Series with this compilation about Low-Field Magnetic Resonance. This topic, for which we have chosen to focus on articles reporting measurements at fields lower than 2 T, is of widespread interest to our readership. We are therefore happy to offer to this constituency a selected outlook based on papers published during the last five years (volumes 214-270) in the pages of The Journal of Magnetic Resonance. A brief survey of the topics covered in this Virtual Special Issue follows.

Heat transfer enhancement of Fe3O4 ferrofluids in the presence of magnetic field

NASA Astrophysics Data System (ADS)

Fadaei, Farzad; Shahrokhi, Mohammad; Molaei Dehkordi, Asghar; Abbasi, Zeinab

2017-05-01

In this article, three-dimensional (3D) forced-convection heat transfer of magnetic nanofluids in a pipe subject to constant wall heat flux in the presence of single or double permanent magnet(s) or current-carrying wire has been investigated and compared. In this regard, laminar fluid flow and equilibrium magnetization for the ferrofluid were considered. In addition, variations of magnetic field in different media were taken into account and the assumption of having a linear relationship of magnetization with applied magnetic field intensity was also relaxed. Effects of magnetic field intensity, nanoparticle volume fraction, Reynolds number value, and the type of magnetic field source (i.e., a permanent magnet or current-carrying wire) on the forced-convection heat transfer of magnetic nanofluids were carefully investigated. It was found that by applying the magnetic field, the fluid mixing could be intensified that leads to an increase in the Nusselt number value along the pipe length. Moreover, the obtained simulation results indicate that applying the magnetic field induced by two permanent magnets with a magnetization of 3×105 (A/m) (for each one), the fully developed Nusselt number value can be increased by 196%.

SU-F-J-146: Experimental Validation of 6 MV Photon PDD in Parallel Magnetic Field Calculated by EGSnrc

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

Ghila, A; Steciw, S; Fallone, B

Purpose: Integrated linac-MR systems are uniquely suited for real time tumor tracking during radiation treatment. Understanding the magnetic field dose effects and incorporating them in treatment planning is paramount for linac-MR clinical implementation. We experimentally validated the EGSnrc dose calculations in the presence of a magnetic field parallel to the radiation beam travel. Methods: Two cylindrical bore electromagnets produced a 0.21 T magnetic field parallel to the central axis of a 6 MV photon beam. A parallel plate ion chamber was used to measure the PDD in a polystyrene phantom, placed inside the bore in two setups: phantom top surfacemore » coinciding with the magnet bore center (183 cm SSD), and with the magnet bore’s top surface (170 cm SSD). We measured the field of the magnet at several points and included the exact dimensions of the coils to generate a 3D magnetic field map in a finite element model. BEAMnrc and DOSXYZnrc simulated the PDD experiments in parallel magnetic field (i.e. 3D magnetic field included) and with no magnetic field. Results: With the phantom surface at the top of the electromagnet, the surface dose increased by 10% (compared to no-magnetic field), due to electrons being focused by the smaller fringe fields of the electromagnet. With the phantom surface at the bore center, the surface dose increased by 30% since extra 13 cm of air column was in relatively higher magnetic field (>0.13T) in the magnet bore. EGSnrc Monte Carlo code correctly calculated the radiation dose with and without the magnetic field, and all points passed the 2%, 2 mm Gamma criterion when the ion chamber’s entrance window and air cavity were included in the simulated phantom. Conclusion: A parallel magnetic field increases the surface and buildup dose during irradiation. The EGSnrc package can model these magnetic field dose effects accurately. Dr. Fallone is a co-founder and CEO of MagnetTx Oncology Solutions (under discussions to license Alberta bi-planar linac MR for commercialization).« less

Vector magnetic field changes associated with X-class flares

NASA Technical Reports Server (NTRS)

Wang, Haimin; Ewell, M. W., Jr.; Zirin, H.; Ai, Guoxiang

1994-01-01

We present high-resolution transverse and longitudinal magnetic field measurements bracketing five X-class solar flares. We show that the magnetic shear, defined as the angular difference between the measured field and calculated potential field, actually increases after all of these flares. In each case, the shear is shown to increase along a substantial portion of the magnetic neutral line. For two of the cases, we have excellent time resolution, on the order of several minutes, and we demonstrate that the shear increase is impulsive. We briefly discuss the theoretical implications of our results.

Magnetic field dependent measurement techniques of surface tension of magnetic fluid at an air interface

NASA Astrophysics Data System (ADS)

Nair, Nishant; Virpura, Hiral; Patel, Rajesh

2015-06-01

We describe here two measurement techniques to determine surface tension of magnetic fluid. (i) magneti c field dependent capillary rise method and (ii) Taylor wavelength method in which the distance between the consecutive stable spikes was measured and then surface tension was calculated. The surface tension measurements from both the methods are compared. It is observed that surface tension of magnetic fluid increases with increase in magnetic field due to field dependent structure formation in magnetic fluid at an air interface. We have also measured magnetic susceptibility and surface tension for different volume fractions. The measurement of magnetic susceptibility is carried out using Quincke's experimental techniques.

The effect of an exogenous magnetic field on neural coding in deep spiking neural networks.

PubMed

Guo, Lei; Zhang, Wei; Zhang, Jialei

2018-01-01

A ten-layer feed forward network is constructed in the presence of an exogenous alternating magnetic field. Specifically, our results indicate that for rate coding, the firing rate is significantly increased in the presence of an exogenous alternating magnetic field and particularly with increasing enhancement of the alternating magnetic field amplitude. For temporal coding, the interspike intervals of the spiking sequence are decreased and the distribution of the interspike intervals of the spiking sequence tends to be uniform in the presence of alternating magnetic field.

Maneuvering thermal conductivity of magnetic nanofluids by tunable magnetic fields

NASA Astrophysics Data System (ADS)

Patel, Jaykumar; Parekh, Kinnari; Upadhyay, R. V.

2015-06-01

We report an experimental investigation of magnetic field dependent thermal conductivity of a transformer oil base magnetic fluid as a function of volume fractions. In the absence of magnetic field, thermal conductivity increases linearly with an increase in volume fraction, and magnitude of thermal conductivity thus obtained is lower than that predicted by Maxwell's theory. This reveals the presence of clusters/oligomers in the system. On application of magnetic field, it exhibits a non-monotonous increase in thermal conductivity. The results are interpreted using the concept of a two-step homogenization method (which is based on differential effective medium theory). The results show a transformation of particle cluster configuration from long chain like prolate shape to the aggregated drop-like structure with increasing concentration as well as a magnetic field. The aggregated drop-like structure for concentrated system is supported by optical microscopic images. This shape change of clusters reduces thermal conductivity enhancement. Moreover, this structure formation is observed as a dynamic phenomenon, and at 226 mT field, the length of the structure extends with time, becomes maximum, and then reduces. This change results in the increase or decrease of thermal conductivity.

X-ray tube with magnetic electron steering

DOEpatents

Reed, Kim W.; Turman, Bobby N.; Kaye, Ronald J.; Schneider, Larry X.

2000-01-01

An X-ray tube uses a magnetic field to steer electrons. The magnetic field urges electrons toward the anode, increasing the proportion of electrons emitted from the cathode that reach desired portions of the anode and consequently contribute to X-ray production. The magnetic field also urges electrons reflected from the anode back to the anode, further increasing the efficiency of the tube.

Dynamics of magnetized plasma sheaths around a trench

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

Hatami, M. M., E-mail: m-hatami@kntu.ac.ir

2016-08-15

Considering a magnetized plasma sheath, the temporal evolution of the ion properties (the incident ion flux, the ion impact angle, and the incident ion dose) around a rectangular trench is studied numerically. Our results show that the ion flux along the bottom surface greatly reduces in the presence of magnetic field and its uniformity improves, but the magnetic field does not considerably affect the ion flux along the sidewall. In addition, the thickness of the plasma sheath increases by increasing the magnetic field while its conformality to the target surface reduces faster. Moreover, it is shown that any increase inmore » the magnitude (inclination angle) of the magnetic field causes a decrease (an increase) in the angle of incidence of ions on the bottom and sidewall surfaces. Furthermore, in the presence of magnetic field, the ions strike nearly normal to the surface of the bottom while they become less oblique along the sidewall surface. In addition, contrary to the corners of the trench, it is found that the magnetic field greatly affects the incident ion dose at the center of the trench surfaces. Also, it is shown that the incident ion dose along the sidewall is the highest near the center of the sidewall in both magnetized and magnetic-free cases. However, uniformity of the incident ion dose along the sidewall is better than that along the bottom in both magnetized and unmagnetized plasma sheath.« less

Magnetic field manipulation of spin current in a single-molecule magnet tunnel junction with two-electron Coulomb interaction

NASA Astrophysics Data System (ADS)

Zhang, Chao; Yao, Hui; Nie, Yi-Hang; Liang, Jiu-Qing; Niu, Peng-Bin

2018-04-01

In this work, we study the generation of spin-current in a single-molecule magnet (SMM) tunnel junction with Coulomb interaction of transport electrons and external magnetic field. In the absence of field the spin-up and -down currents are symmetric with respect to the initial polarizations of molecule. The existence of magnetic field breaks the time-reversal symmetry, which leads to unsymmetrical spin currents of parallel and antiparallel polarizations. Both the amplitude and polarization direction of spin current can be controlled by the applied magnetic field. Particularly when the magnetic field increases to a certain value the spin-current with antiparallel polarization is reversed along with the magnetization reversal of the SMM. The two-electron occupation indeed enhances the transport current compared with the single-electron process. However the increase of Coulomb interaction results in the suppression of spin-current amplitude at the electron-hole symmetry point. We propose a scheme to compensate the suppression with the magnetic field.

Magnetic fields and childhood cancer: an epidemiological investigation of the effects of high-voltage underground cables.

PubMed

Bunch, K J; Swanson, J; Vincent, T J; Murphy, M F G

2015-09-01

Epidemiological evidence of increased risks for childhood leukaemia from magnetic fields has implicated, as one source of such fields, high-voltage overhead lines. Magnetic fields are not the only factor that varies in their vicinity, complicating interpretation of any associations. Underground cables (UGCs), however, produce magnetic fields but have no other discernible effects in their vicinity. We report here the largest ever epidemiological study of high voltage UGCs, based on 52,525 cases occurring from 1962-2008, with matched birth controls. We calculated the distance of the mother's address at child's birth to the closest 275 or 400 kV ac or high-voltage dc UGC in England and Wales and the resulting magnetic fields. Few people are exposed to magnetic fields from UGCs limiting the statistical power. We found no indications of an association of risk with distance or of trend in risk with increasing magnetic field for leukaemia, and no convincing pattern of risks for any other cancer. Trend estimates for leukaemia as shown by the odds ratio (and 95% confidence interval) per unit increase in exposure were: reciprocal of distance 0.99 (0.95-1.03), magnetic field 1.01 (0.76-1.33). The absence of risk detected in relation to UGCs tends to add to the argument that any risks from overhead lines may not be caused by magnetic fields.

Canard and mixed mode oscillations in an excitable glow discharge plasma in the presence of inhomogeneous magnetic field

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

Shaw, Pankaj Kumar, E-mail: pankaj.shaw@saha.ac.in; Sekar Iyengar, A. N., E-mail: ansekar.iyengar@saha.ac.in; Nurujjaman, Md., E-mail: jaman-nonlinear@yahoo.co.in

2015-12-15

We report on the experimental observation of canard orbit and mixed mode oscillations (MMOs) in an excitable glow discharge plasma induced by an external magnetic field perturbation using a bar magnet. At a small value of magnetic field, small amplitude quasiperiodic oscillations were excited, and with the increase in the magnetic field, large amplitude oscillations were excited. Analyzing the experimental results, it seems that the magnetic field could be playing the role of noise for such nonlinear phenomena. It is observed that the noise level increases with the increase in magnetic field strength. The experimental results have also been corroboratedmore » by a numerical simulation using a FitzHugh-Nagumo like macroscopic model derived from the basic plasma equations and phenomenology, where the noise has been included to represent the internal plasma noise. This macroscopic model shows MMO in the vicinity of the canard point when an external noise is added.« less

Influences of magnetic field on the fractal morphology in copper electrodeposition

NASA Astrophysics Data System (ADS)

Sudibyo; How, M. B.; Aziz, N.

2018-01-01

Copper magneto-electrodeposition (MED) is used decrease roughening in the copper electrodeposition process. This technology plays a vital role in electrodeposition process to synthesize metal alloy, thin film, multilayer, nanowires, multilayer nanowires, dot array and nano contacts. The effects of magnetic fields on copper electrodeposition are investigated in terms of variations in the magnetic field strength and the electrolyte concentration. Based on the experimental results, the mere presence of magnetic field would result in a compact deposit. As the magnetic field strength is increased, the deposit grows denser. The increment in concentration also leads to the increase the deposited size. The SEM image analysis showed that the magnetic field has a significant effect on the surface morphology of electrodeposits.

Increasing the switching speed of liquid crystal devices with magnetic nanorods

NASA Astrophysics Data System (ADS)

Garbovskiy, Yu.; Baptist, J. R.; Thompson, J.; Hunter, T.; Lim, J. H.; Gi Min, Seong; Wiley, J. B.; Malkinski, L. M.; Glushchenko, A.; Celinski, Z.

2012-10-01

Liquid crystal (LC)/magnetic nanorods colloids were fabricated and tested using a magneto-optical setup. These thermotropic ferronematics do not show any signs of macroscopic aggregation, exhibit enhanced magnetic sensitivity, and faster time response in the simultaneous presence of crossed electric and magnetic fields. Magnetic nanorods increase an effective magnetic anisotropy of the colloid and decrease magnetic Freedericksz threshold. Applying a magnetic field along the direction perpendicular to the applied electric field leads to a decrease of the time OFF by a factor of 6 for pure liquid crystals, and by a factor of 9—for ferronematics.

The Effect of a Guide Field on the Structures of Magnetic Islands: 2D PIC Simulations

NASA Astrophysics Data System (ADS)

Huang, C.; Lu, Q.; Lu, S.; Wang, P.; Wang, S.

2014-12-01

Magnetic island plays an important role in magnetic reconnection. Using a series of 2D PIC simulations, we investigate the magnetic structures of a magnetic island formed during multiple X-line magnetic reconnection, considering the effects of the guide field in symmetric and asymmetric current sheets. In a symmetric current sheet, the current in the direction forms a tripolar structure inside a magnetic island during anti-parallel reconnection, which results in a quadrupole structure of the out-of-plane magnetic field. With the increase of the guide field, the symmetry of both the current system and out-of-plane magnetic field inside the magnetic island is distorted. When the guide field is sufficiently strong, the current forms a ring along the magnetic field lines inside magnetic island. At the same time, the current carried by the energetic electrons accelerated in the vicinity of the X lines forms another ring at the edge of the magnetic island. Such a dual-ring current system enhance the out-of-plane magnetic field inside the magnetic island with a dip in the center of the magnetic island. In an asymmetric current sheet, when there is no guide field, electrons flows toward the X lines along the separatrices from the side with a higher density, and are then directed away from the X lines along the separatrices to the side with a lower density. The formed current results in the enhancement of the out-of-plane magnetic field at one end of the magnetic island, and the attenuation at the other end. With the increase of the guide field, the structures of both the current system and the out-of-plane magnetic field are distorted.

The effect of a guide field on the structures of magnetic islands formed during multiple X line reconnections: Two-dimensional particle-in-cell simulations

NASA Astrophysics Data System (ADS)

Huang, Can; Lu, Quanming; Lu, San; Wang, Peiran; Wang, Shui

2014-02-01

A magnetic island plays an important role in magnetic reconnection. In this paper, using a series of two-dimensional particle-in-cell simulations, we investigate the magnetic structures of a magnetic island formed during multiple X line magnetic reconnections, considering the effects of the guide field in symmetric and asymmetric current sheets. In a symmetric current sheet, the current in the x direction forms a tripolar structure inside a magnetic island during antiparallel reconnection, which results in a quadrupole structure of the out-of-plane magnetic field. With the increase of the guide field, the symmetry of both the current system and out-of-plane magnetic field inside the magnetic island is distorted. When the guide field is sufficiently strong, the current forms a ring along the magnetic field lines inside a magnetic island. At the same time, the current carried by the energetic electrons accelerated in the vicinity of the X lines forms another ring at the edge of the magnetic island. Such a dual-ring current system enhances the out-of-plane magnetic field inside the magnetic island with a dip in the center of the magnetic island. In an asymmetric current sheet, when there is no guide field, electrons flow toward the X lines along the separatrices from the side with a higher density and are then directed away from the X lines along the separatrices to the side with a lower density. The formed current results in the enhancement of the out-of-plane magnetic field at one end of the magnetic island and the attenuation at the other end. With the increase of the guide field, the structures of both the current system and the out-of-plane magnetic field are distorted.

Varying self-inductance and energy storage in a sheared force-free arcade. [of coronal loops

NASA Technical Reports Server (NTRS)

Zuccarello, F.; Burm, H.; Kuperus, M.; Raadu, M.; Spicer, D. S.

1987-01-01

An electric circuit analogy is used to model the build-up and storage of magnetic energy in the coronal loops known to exist in the atmosphere of the sun. The present parameterization of magnetic energy storage in an electric circuit analog uses a bulk current I flowing in the circuit and a self-inductance L. Because the self-inductance is determined by the geometry of the magnetic configuration any change in its dimensions will change L. If L is increased, the amount of magnetic energy stored and the rate at which magnetic energy is stored are both increased. One way of increasing L is to shear the magnetic field lines and increase their effective geometrical length. Using the force-free field approximation for a magnetic arcade whose field lines are sheared by photospheric motions, it is demonstrated that the increase of magnetic energy is initially due to the increase of the current intensity I and later mainly due to the increase of the self-inductance.

Magneto-therapy of human joint cartilage.

PubMed

Wierzcholski, Krzysztof; Miszczak, Andrzej

2017-01-01

The topic of the present paper concerns the human joint cartilage therapy performed by the magnetic induction field. There is proved the thesis that the applied magnetic field for concrete cartilage illness should depend on the proper relative and concrete values of applied magnetic induction, intensity as well the time of treatment duration. Additionally, very important are frequencies and amplitudes of magnetic field as well as magnetic permeability of the synovial fluid. The research methods used in this paper include: magnetic induction field produced by a new Polish and German magneto electronic devices for the therapy of human joint cartilage diseases, stationary and movable magnetic applicators, magnetic bandage, ferrofluid injections, author's experience gained in Germany research institutes and practical results after measurements and information from patients. The results of this paper concern concrete parameters of time dependent electro-magnetic field administration during the joint cartilage therapy duration and additionally concern the corollaries which are implied from reading values gained on the magnetic induction devices. The main conclusions obtained in this paper are as follows: Time dependent magnetic induction field increases the dynamic viscosity of movable synovial fluid and decreases symptoms of cartilage illness for concrete intensity of magnetic field and concrete field line architecture. The ferrofluid therapy and phospholipids bilayer simultaneously with the administrated external electromagnetic field, increases the dynamic viscosity of movable synovial fluid.

Diffusion of magnetic field via turbulent reconnection

NASA Astrophysics Data System (ADS)

Santos de Lima, Reinaldo; Lazarian, Alexander; de Gouveia Dal Pino, Elisabete M.; Cho, Jungyeon

2010-05-01

The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our 3D MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e. without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our 3D simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the saturated final state of the simulations, supporting the notion that the reconnection-enabled diffusivity relaxes the magnetic field + gas system in the gravitational field to its minimal energy state. This effect is expected to play an important role in star formation, from its initial stages of concentrating interstellar gas to the final stages of the accretion to the forming protostar.

Static magnetic fields: A summary of biological interactions, potential health effects, and exposure guidelines

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

Tenforde, T.S.

1992-05-01

Interest in the mechanisms of interaction and the biological effects of static magnetic fields has increased significantly during the past two decades as a result of the growing number of applications of these fields in research, industry and medicine. A major stimulus for research on the bioeffects of static magnetic fields has been the effort to develop new technologies for energy production and storage that utilize intense magnetic fields (e.g., thermonuclear fusion reactors and superconducting magnet energy storage devices). Interest in the possible biological interactions and health effects of static magnetic fields has also been increased as a result ofmore » recent developments in magnetic levitation as a mode of public transportation. In addition, the rapid emergence of magnetic resonance imaging as a new clinical diagnostic procedure has, in recent years, provided a strong rationale for defining the possible biological effects of magnetic fields with high flux densities. In this review, the principal interaction mechanisms of static magnetic fields will be described, and a summary will be given of the present state of knowledge of the biological, environmental, and human health effects of these fields.« less

Increased accumulation of magnetic nanoparticles by magnetizable implant materials for the treatment of implant-associated complications

PubMed Central

2013-01-01

Background In orthopaedic surgery, accumulation of agents such as anti-infectives in the bone as target tissue is difficult. The use of magnetic nanoparticles (MNPs) as carriers principally enables their accumulation via an externally applied magnetic field. Magnetizable implants are principally able to increase the strength of an externally applied magnetic field to reach also deep-seated parts in the body. Therefore, the integration of bone-addressed therapeutics in MNPs and their accumulation at a magnetic orthopaedic implant could improve the treatment of implant related infections. In this study a martensitic steel platelet as implant placeholder was used to examine its accumulation and retention capacity of MNPs in an in vitro experimental set up considering different experimental frame conditions as magnet quantity and distance to each other, implant thickness and flow velocity. Results The magnetic field strength increased to approximately 112% when a martensitic stainless steel platelet was located between the magnet poles. Therewith a significantly higher amount of magnetic nanoparticles could be accumulated in the area of the platelet compared to the sole magnetic field. During flushing of the tube system mimicking the in vivo blood flow, the magnetized platelet was able to retain a higher amount of MNPs without an external magnetic field compared to the set up with no mounted platelet during flushing of the system. Generally, a higher flow velocity led to lower amounts of accumulated MNPs. A higher quantity of magnets and a lower distance between magnets led to a higher magnetic field strength. Albeit not significantly the magnetic field strength tended to increase with thicker platelets. Conclusion A martensitic steel platelet significantly improved the attachment of magnetic nanoparticles in an in vitro flow system and therewith indicates the potential of magnetic implant materials in orthopaedic surgery. The use of a remanent magnetic implant material could improve the efficiency of capturing MNPs especially when the external magnetic field is turned off thus facilitating and prolonging the effect. In this way higher drug levels in the target area might be attained resulting in lower inconveniences for the patient. PMID:24112871

Increased accumulation of magnetic nanoparticles by magnetizable implant materials for the treatment of implant-associated complications.

PubMed

Angrisani, Nina; Foth, Franziska; Kietzmann, Manfred; Schumacher, Stephan; Angrisani, Gian Luigi; Christel, Anne; Behrens, Peter; Reifenrath, Janin

2013-10-10

In orthopaedic surgery, accumulation of agents such as anti-infectives in the bone as target tissue is difficult. The use of magnetic nanoparticles (MNPs) as carriers principally enables their accumulation via an externally applied magnetic field. Magnetizable implants are principally able to increase the strength of an externally applied magnetic field to reach also deep-seated parts in the body. Therefore, the integration of bone-addressed therapeutics in MNPs and their accumulation at a magnetic orthopaedic implant could improve the treatment of implant related infections. In this study a martensitic steel platelet as implant placeholder was used to examine its accumulation and retention capacity of MNPs in an in vitro experimental set up considering different experimental frame conditions as magnet quantity and distance to each other, implant thickness and flow velocity. The magnetic field strength increased to approximately 112% when a martensitic stainless steel platelet was located between the magnet poles. Therewith a significantly higher amount of magnetic nanoparticles could be accumulated in the area of the platelet compared to the sole magnetic field. During flushing of the tube system mimicking the in vivo blood flow, the magnetized platelet was able to retain a higher amount of MNPs without an external magnetic field compared to the set up with no mounted platelet during flushing of the system. Generally, a higher flow velocity led to lower amounts of accumulated MNPs. A higher quantity of magnets and a lower distance between magnets led to a higher magnetic field strength. Albeit not significantly the magnetic field strength tended to increase with thicker platelets. A martensitic steel platelet significantly improved the attachment of magnetic nanoparticles in an in vitro flow system and therewith indicates the potential of magnetic implant materials in orthopaedic surgery. The use of a remanent magnetic implant material could improve the efficiency of capturing MNPs especially when the external magnetic field is turned off thus facilitating and prolonging the effect. In this way higher drug levels in the target area might be attained resulting in lower inconveniences for the patient.

DC corona discharge ozone production enhanced by magnetic field

NASA Astrophysics Data System (ADS)

Pekárek, S.

2010-01-01

We have studied the effect of a stationary magnetic field on the production of ozone from air at atmospheric pressure by a negative corona discharge in a cylindrical electrode configuration. We used a stainless steel hollow needle placed at the axis of the cylindrical discharge chamber as a cathode. The outer wall of the cylinder was used as an anode. The vector of magnetic induction was perpendicular to the vector of current density. We found that: (a) the magnetic field extends the current voltage range of the discharge; (b) for the discharge in the Trichel pulses regime and in the pulseless glow regime, the magnetic field has no substantial effect on the discharge voltage or on the concentration of ozone that is produced; (c) for the discharge in the filamentary streamer regime for a particular current, the magnetic field increases the discharge voltage and consequently an approximately 30% higher ozone concentration can be obtained; (d) the magnetic field does not substantially increase the maximum ozone production yield. A major advantage of using a magnetic field is that the increase in ozone concentration produced by the discharge can be obtained without additional energy requirements.

Twin-enhanced magnetic torque

NASA Astrophysics Data System (ADS)

Hobza, Anthony; García-Cervera, Carlos J.; Müllner, Peter

2018-07-01

Magnetic shape memory alloys experience magnetic-field-induced torque due to magnetocrystalline anisotropy and shape anisotropy. In a homogeneous magnetic field, torque results in bending of long samples. This study investigates the torque on a single crystal of Ni-Mn-Ga magnetic shape memory alloy constrained with respect to bending in an external magnetic field. The dependence of the torque on external magnetic field magnitude, strain, and twin boundary structure was studied experimentally and with computer simulations. With increasing magnetic field, the torque increased until it reached a maximum near 700 mT. Above 200 mT, the torque was not symmetric about the equilibrium orientation for a sample with one twin boundary. The torque on two specimen with equal strain but different twin boundary structures varied systematically with the spatial arrangement of crystallographic twins. Numerical simulations show that twin boundaries suppress the formation of 180° domains if the direction of easy magnetization between two twin boundaries is parallel to a free surface and the magnetic field is perpendicular to that surface. For a particular twin microstructure, the torque decreases with increasing strain by a factor of six due to the mutual compensation of magnetocrystalline and shape anisotropy. When free rotation is suppressed such as in transducers of magneto-mechanical actuators, magnetic-field-induced torque creates strong bending forces, which may cause friction and failure under cyclic loading.

Magnetic phase diagrams of CexLa1-xB6 in high magnetic fields

NASA Astrophysics Data System (ADS)

Akatsu, Mitsuhiro; Kazama, Nanako; Goto, Terutaka; Nemoto, Yuichi; Suzuki, Osamu; Kido, Giyuu; Kunii, Satoru

We have performed ultrasonic measurements under high magnetic fields up to 30 T by using the hybrid magnet at the National Institute for Materials Science to investigate the magnetic phase diagram for antiferroquadrupole (AFQ) phase II in CexLa1-xB6. With increasing Ce concentration x from x=0.50, the AFQ phase transition temperatures TQ indicate an almost linear increase in various fields. The large magnetic anisotropy of AFQ phase II, in which TQH∥[0 0 1] is much smaller than TQH∥[1 1 0] and TQH∥[1 1 1] in high magnetic fields, is revealed in x=0.75,0.60 as well as in x=0.50. These experimental results support the theoretical calculation based on the Γ5-type AFQ ordering and the magnetic field induced octupole Txyz.

Fluorescent lamp with static magnetic field generating means

DOEpatents

Moskowitz, Philip E.; Maya, Jakob

1987-01-01

A fluorescent lamp wherein magnetic field generating means (e.g., permanent magnets) are utilized to generate a static magnetic field across the respective electrode structures of the lamp such that maximum field strength is located at the electrode's filament. An increase in efficacy during operation has been observed.

Fluorescent lamp with static magnetic field generating means

DOEpatents

Moskowitz, P.E.; Maya, J.

1987-09-08

A fluorescent lamp wherein magnetic field generating means (e.g., permanent magnets) are utilized to generate a static magnetic field across the respective electrode structures of the lamp such that maximum field strength is located at the electrode's filament. An increase in efficacy during operation has been observed. 2 figs.

Heat Transfer Affected by Transverse Magnetic Field using 3D Modeling of Arc Plasma

NASA Astrophysics Data System (ADS)

Maeda, Yoshifumi; Tanaka, Tatsuro; Yamamoto, Shinji; Iwao, Toru

2016-10-01

Gas shielded metal arc welding is used to join the various metal because this is the high quality joining technology. Thus, this welding is used for a welding of large buildings such as bridges and LNG tanks. However, the welding defect caused by the heat transfer decrement may occur with increasing the wind velocity. This is because that the convection loss increases because the arc deflects to leeward side with increasing the wind velocity. In order to prevent from the arc deflection, it is used that the transverse magnetic field is applied to the arc. However, the arc deflection occurs with increasing the transverse magnetic field excessively. The energy balance of the arc is changed with increasing the convection loss caused by the arc deflection, and the heat transfer to the anode decreases. Therefore, the analysis including the arc and anode is necessary to elucidate the heat transfer to the anode. In this paper, the heat transfer affected by the transverse magnetic field using 3D modeling of the arc plasma is elucidated. The heat transfer to the anode is calculated by using the EMTF(electromagnetic thermal fluid) simulation with increasing the transverse magnetic field. As a result, the heat transfer decreased with increasing the transverse magnetic field.

Removal of hexavalent chromium from wastewater using PPy/Fe3O4 magnetic nanocomposite influenced by rotating magnetic field from two pole three-phase induction motor

NASA Astrophysics Data System (ADS)

Aigbe, U. O.; Ho, W. H.; Maity, A.; Khenfouch, M.; Srinivasu, V.

2018-03-01

The influence of varying rotating magnetic field using a 2-pole three-phase induction motor on the removal of hexavalent chromium ions from wastewater using polypyrrole magnetic nanocomposite was explored in this study. Hexavalent chromium removal in this study was observed to be pH dependent under the influence of rotating magnetic field, as the percentage removal of hexavalent chromium decreased with increase in pH. The percentage amount of hexavalent chromium ions removed from the aqueous solution increased as the rotating magnetic field intensity was increased from 8.96-12.15 mT in the anticlockwise direction and 10.10-13.38 mT in the clockwise direction with maximum removals of 73% and 81% observed.

Destabilizing effect of time-dependent oblique magnetic field on magnetic fluids streaming in porous media.

PubMed

El-Dib, Yusry O; Ghaly, Ahmed Y

2004-01-01

The present work studies Kelvin-Helmholtz waves propagating between two magnetic fluids. The system is composed of two semi-infinite magnetic fluids streaming throughout porous media. The system is influenced by an oblique magnetic field. The solution of the linearized equations of motion under the boundary conditions leads to deriving the Mathieu equation governing the interfacial displacement and having complex coefficients. The stability criteria are discussed theoretically and numerically, from which stability diagrams are obtained. Regions of stability and instability are identified for the magnetic fields versus the wavenumber. It is found that the increase of the fluid density ratio, the fluid velocity ratio, the upper viscosity, and the lower porous permeability play a stabilizing role in the stability behavior in the presence of an oscillating vertical magnetic field or in the presence of an oscillating tangential magnetic field. The increase of the fluid viscosity plays a stabilizing role and can be used to retard the destabilizing influence for the vertical magnetic field. Dual roles are observed for the fluid velocity in the stability criteria. It is found that the field frequency plays against the constant part for the magnetic field.

Diffusion of Magnetic Field and Removal of Magnetic Flux from Clouds Via Turbulent Reconnection

NASA Astrophysics Data System (ADS)

Santos-Lima, R.; Lazarian, A.; de Gouveia Dal Pino, E. M.; Cho, J.

2010-05-01

The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology via reconnection in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence reassures that the magnetic field behavior in computer simulations and turbulent astrophysical environments is similar, as far as magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our studies of magnetic field diffusion in turbulent medium reveal interesting new phenomena. First of all, our three-dimensional MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a de-correlation of the magnetic field and density, which corresponds well to the observations of the interstellar media. While earlier studies stressed the role of either ambipolar diffusion or time-dependent turbulent fluctuations for de-correlating magnetic field and density, we get the effect of permanent de-correlation with one fluid code, i.e., without invoking ambipolar diffusion. In addition, in the presence of gravity and turbulence, our three-dimensional simulations show the decrease of the magnetic flux-to-mass ratio as the gaseous density at the center of the gravitational potential increases. We observe this effect both in the situations when we start with equilibrium distributions of gas and magnetic field and when we follow the evolution of collapsing dynamically unstable configurations. Thus, the process of turbulent magnetic field removal should be applicable both to quasi-static subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and magnetic flux in the saturated final state of the simulations, supporting the notion that the reconnection-enabled diffusivity relaxes the magnetic field + gas system in the gravitational field to its minimal energy state. This effect is expected to play an important role in star formation, from its initial stages of concentrating interstellar gas to the final stages of the accretion to the forming protostar. In addition, we benchmark our codes by studying the heat transfer in magnetized compressible fluids and confirm the high rates of turbulent advection of heat obtained in an earlier study.

Magnetic field exposure stiffens regenerating plant protoplast cell walls.

PubMed

Haneda, Toshihiko; Fujimura, Yuu; Iino, Masaaki

2006-02-01

Single suspension-cultured plant cells (Catharanthus roseus) and their protoplasts were anchored to a glass plate and exposed to a magnetic field of 302 +/- 8 mT for several hours. Compression forces required to produce constant cell deformation were measured parallel to the magnetic field by means of a cantilever-type force sensor. Exposure of intact cells to the magnetic field did not result in any changes within experimental error, while exposure of regenerating protoplasts significantly increased the measured forces and stiffened regenerating protoplasts. The diameters of intact cells or regenerating protoplasts were not changed after exposure to the magnetic field. Measured forces for regenerating protoplasts with and without exposure to the magnetic field increased linearly with incubation time, with these forces being divided into components based on the elasticity of synthesized cell walls and cytoplasm. Cell wall synthesis was also measured using a cell wall-specific fluorescent dye, and no changes were noted after exposure to the magnetic field. Analysis suggested that exposure to the magnetic field roughly tripled the Young's modulus of the newly synthesized cell wall without any lag.

Magnetomechanical properties of composites and fibers made from thermoplastic elastomers (TPE) and carbonyl iron powder (CIP)

NASA Astrophysics Data System (ADS)

Schrödner, Mario; Pflug, Günther

2018-05-01

Magnetoactive elastomers (MAE) made from composites of five thermoplastic elastomers (TPE) of different stiffness with carbonyl iron powder (CIP) as magnetic component were investigated. The composites were produced by melt blending of the magnetic particles with the TPEs in a twin-screw extruder. The resulting materials were characterized by ac permeability testing, stress-strain measurements with and without external magnetic field and magnetically controlled bending of long cylindrical rods in a homogenous magnetic field. The magnetic field necessary for deflection of the rods decreases with decreasing modulus and increasing iron particle content. This effect can be used e.g. for magnetically controlled actuation. Some highly filled MAE show a magnetic field induced increase of Young's modulus. Filaments could be spun from some of the composites.

Flux flow induced microwave absorption in high temperature superconductor Bi 2-XPb XSr 2Ca N-1Cu NO 4+2N

NASA Astrophysics Data System (ADS)

Owens, F. J.

1990-12-01

Direct measurements of microwave absorption without use of rf H field modulation in granular composites of the 115 K superconductor Bi 2-XPb XSr 2Ca N-1Cu NO 4+2N as a function of magnetic field above 0.1 T reveal a continuing increase of absorption of microwave energy increasing magnetic field. The temperature and magnetic field dependence of the absorption are very different from the low magnetic field (<0.01 T) absorption arising from weak links in the material. The magnetic field and temperature dependence are consistent with the behavior of thermally activated flux flow resistance suggesting the absorption is due to flux creep.

Magnetic-flux pump

NASA Technical Reports Server (NTRS)

Hildebrandt, A. F.; Elleman, D. D.; Whitmore, F. C. (Inventor)

1966-01-01

A magnetic flux pump is described for increasing the intensity of a magnetic field by transferring flux from one location to the magnetic field. The device includes a pair of communicating cavities formed in a block of superconducting material, and a piston for displacing the trapped magnetic flux into the secondary cavity producing a field having an intense flux density.

FDTD simulation of radar cross section reduction by a collisional inhomogeneous magnetized plasma

NASA Astrophysics Data System (ADS)

Foroutan, V.; Azarmanesh, M. N.; Foroutan, G.

2018-02-01

The recursive convolution finite difference time domain method is addressed in the scattered field formulation and employed to investigate the bistatic radar cross-section (RCS) of a square conductive plate covered by a collisional inhomogeneous magnetized plasma. The RCS is calculated for two different configurations of the magnetic field, i.e., parallel and perpendicular to the plate. The results of numerical simulations show that, for a perpendicularly applied magnetic field, the backscattered RCS is significantly reduced when the magnetic field intensity coincides with the value corresponding to the electron cyclotron resonance. By increasing the collision frequency, the resonant absorption is suppressed, but due to enhanced wave penetration and bending, the reduction in the bistatic RCS is improved. At very high collision frequencies, the external magnetic field has no significant impact on the bistatic RCS reduction. Application of a parallel magnetic field has an adverse effect near the electron cyclotron resonance and results in a large and asymmetric RCS profile. But, the problem is resolved by increasing the magnetic field and/or the collision frequency. By choosing proper values of the collision frequency and the magnetic field intensity, a perpendicular magnetic field can be effectively used to reduce the bistatic RCS of a conductive plate.

Parametric study and optimization trends for the Von-Kármán-sodium dynamo experiment

NASA Astrophysics Data System (ADS)

Varela, J.

2018-05-01

We present magneto-hydrodynamic simulations of liquid sodium flow performed with the PLUTO compressible MHD code. We investigated the influence of the remanent magnetic field orientation and intensity, the impinging velocity field due to Ekman pumping as well as the impeller dimensions on the magnetic field collimation by helical flows in-between the impeller blades. For a simplified Cartesian geometry, we model the flow dynamics of a multi-blade impeller inspired by the Von-Kármán-Sodium experiment. This study shows that a remanent magnetic field oriented in the toroidal direction is the less efficient configuration to collimate the magnetic field, although if the radial or vertical components are not negligible, the collimation is significantly improved. As the intensity of the remanent magnetic field increases, the system magnetic energy becomes larger, but the magnetic field collimation efficiency remains the same, so the gain of magnetic energy is smaller as the remanent magnetic field intensity increases. The magnetic field collimation is modified if the impinging velocity field changes: the collimation is weaker if the impinging velocity increases from Γ = 0.8 to 0.9 and slightly larger if the impinging velocity decreases from Γ = 0.8 to 0.7. The analysis of the impeller dimensions points out that the most efficient configuration to collimate the magnetic field requires a ratio between the impeller blade height and the base longitude between 0.375 and 0.5. The largest enhancement of the hypothetical α2 dynamo loop, compared to the hypothetical Ω-α dynamo loop, is observed for the model that mimics the TM 73 impeller configuration rotating in the unscooping direction with a remanent magnetic field of 10-3 T orientated in the radial or vertical direction. The optimization trends obtained in the parametric analysis are also confirmed by simulations with a higher resolution and turbulence degree.

The effect of axial external magnetic field on tungsten inert gas welding of magnesium alloy

NASA Astrophysics Data System (ADS)

Li, Caixia; Zhang, Xiaofeng; Wang, Jing

2018-04-01

The influences of axial external magnetic field on the microstructure and mechanical property of the AZ31 magnesium (Mg) alloy joints were studied. The microstructure of Mg alloy joint consisted of the weld seam, heat affected zone and base metal zone. The average grain size of weld seam welded with magnetic field is 39 μm, which is 38% smaller than that of the joint welded with absence of magnetic field. And the microhardness of weld seam increases with the help of magnetic field treatment, owing to the coarse grain refinement. With coil current of 2.0A, the maximum mechanical property of joint increases 6.7% to 255 MPa over the specimen without magnetic field treatment. Furthermore, fracture location is near heat affected area and the fracture surface is characterized with ductile fracture.

The effects of high magnetic field on the morphology and microwave electromagnetic properties of MnO 2 powder

NASA Astrophysics Data System (ADS)

Zhang, Jia; Yuping, Duan; Shuqing, Li; Xiaogang, Li; Shunhua, Liu

2010-07-01

MnO 2 with a sea urchin-like ball chain shape was first synthesized in a high magnetic field via a simple chemical process, and a mechanism for the formation of this grain shape was discussed. The as-synthesized samples were characterized by XRD, SEM, TEM, and vector network analysis. The dielectric constant and the loss tangent clearly decreased under a magnetic field. The magnetic loss tangent and the imaginary part of the magnetic permeability increased substantially. Furthermore, the theoretically calculated values of reflection loss showed that the absorption peaks shifted to a higher frequency with increases in the magnetic field strength.

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

Beilis, I. I.

Experiments in the last decade showed that for cathode spots in a magnetic field that obliquely intercepts the cathode surface, the current per spot increased with the transverse component of the magnetic field and decreased with the normal component. The present work analyzes the nature of cathode spot splitting in an oblique magnetic field. A physical model for cathode spot current splitting was developed, which considered the relation between the plasma kinetic pressure, self-magnetic pressure, and applied magnetic pressure in a current carrying cathode plasma jet. The current per spot was calculated, and it was found to increase with themore » tangential component of the magnetic field and to decrease with the normal component, which agrees well with the experimental dependence.« less

Magnetic field effects on shear and normal stresses in magnetorheological finishing.

PubMed

Lambropoulos, John C; Miao, Chunlin; Jacobs, Stephen D

2010-09-13

We use a recent experimental technique to measure in situ shear and normal stresses during magnetorheological finishing (MRF) of a borosilicate glass over a range of magnetic fields. At low fields shear stresses increase with magnetic field, but become field-independent at higher magnetic fields. Micromechanical models of formation of magnetic particle chains suggest a complex behavior of magnetorheological (MR) fluids that combines fluid- and solid-like responses. We discuss the hypothesis that, at higher fields, slip occurs between magnetic particle chains and the immersed glass part, while the normal stress is governed by the MRF ribbon elasticity.

Driven acoustic oscillations within a vertical magnetic field

NASA Technical Reports Server (NTRS)

Hindman, Bradley W.; Zweibel, Ellen G.; Cally, P. S.

1995-01-01

The effects of a vertical magnetic field on p-mode frequencies, line widths, and eigenfunctions, are examined. A solar model, consisting of a neutrally stable polytropic interior matched to an isothermal chromosphere, is applied. The p-modes are produced by a spatially distributed driver. The atmosphere is threaded by a constant vertical magnetic field. The frequency shifts due to the vertical magnetic field are found to be much smaller than the shifts caused by horizontal fields of similar strength. A large vertical field of 2000 G produces shifts of several nHz. It is found that the frequency shifts decrease with increasing frequency and increase with field strength. The coupling of the acoustic fast mode to the escaping slow modes is inefficient. Constant vertical magnetic field models are therefore incapable of explaining the high level of absorption observed in sunspots and plage.

Magnetic particle capture for biomagnetic fluid flow in stenosed aortic bifurcation considering particle-fluid coupling

NASA Astrophysics Data System (ADS)

Bose, Sayan; Banerjee, Moloy

2015-07-01

Magnetic nanoparticles drug carriers continue to attract considerable interest for drug targeting in the treatment of cancer and other pathological conditions. Guiding magnetic iron oxide nanoparticles with the help of an external magnetic field to its target is the basic principle behind the Magnetic Drug Targeting (MDT). It is essential to couple the ferrohydrodynamic (FHD) and magnetohydrodynamic (MHD) principles when magnetic fields are applied to blood as a biomagnetic fluid. The present study is devoted to study on MDT technique by particle tracking in the presence of a non uniform magnetic field in a stenosed aortic bifurcation. The present numerical model of biomagnetic fluid dynamics (BFD) takes into accounts both magnetization and electrical conductivity of blood. The blood flow in the bifurcation is considered to be incompressible and Newtonian. An Eulerian-Lagrangian technique is adopted to resolve the hemodynamic flow and the motion of the magnetic particles in the flow using ANSYS FLUENT two way particle-fluid coupling. An implantable infinitely long cylindrical current carrying conductor is used to create the requisite magnetic field. Targeted transport of the magnetic particles in a partly occluded vessel differs distinctly from the same in a regular unblocked vessel. Results concerning the velocity and temperature field indicate that the presence of the magnetic field influences the flow field considerably and the disturbances increase as the magnetic field strength increases. The insert position is also varied to observe the variation in flow as well as temperature field. Parametric investigation is conducted and the influence of the particle size (dp), flow Reynolds number (Re) and external magnetic field strength (B0) on the "capture efficiency" (CE) is reported. The difference in CE is also studied for different particle loading condition. According to the results, the magnetic field increased the particle concentration in the target region. Analysis shows that there exists an optimum regime of operating parameters for which deposition of the drug carrying magnetic particles in a target zone on the partly occluded vessel wall can be maximized. The results provide useful design bases for in vitro set up for the investigation of MDT in stenosed blood vessels.

Improving Keyhole Stability by External Magnetic Field in Full Penetration Laser Welding

NASA Astrophysics Data System (ADS)

Li, Min; Xu, Jiajun; Huang, Yu; Rong, Youmin

2018-05-01

An external magnetic field was used to improve the keyhole stability in full penetration laser welding 316L steel. The increase of magnetic field strength gave rise to a shorter flying time of the spatter, a weaker size and brightness of the spatter, and a larger spreading area of vapor plume. This suggested that the dynamic behavior of the keyhole was stabilized by the external magnetic field. In addition, a stronger magnetic field could result in a more homogeneous distribution of laser energy, which increased the width of the weld zone, and the height of the bottom weld zone from 381 μm (0 mT) to 605 μm (50 mT). Dendrite and cellular crystal near the weld center disappeared, and grain size was refined. The external magnetic field was beneficial to the keyhole stability and improved the joint quality, because the weld pool was stirred by a Lorentz force resulting from the coupling effect of the magnetic field and inner thermocurrent.

Large-N solution of the Sp(N) Heisenberg quantum antiferromagnet on the anisotropic triangular lattice in a magnetic field.

NASA Astrophysics Data System (ADS)

Chung, Chung-Hou; Marston, Brad

2002-03-01

We study the Sp(N) generalization of the physical Sp(1) \\cong SU(2) Heisenberg antiferromagnet on the anisotropic triangular lattice( C. H. Chung, J. B. Marston and R. H. McKenzie, Journal of Physics: Condensed Matter 13), 5159 (2001). in a magnetic field. The model is relevant for describing recent experiments on the magnetic phases of the quasi-2D system Cs_2CuCl4 in a magnetic field(R. Coldea, D. A. Tennant, A. M. Tsvelik, and Z. Tylczynski, Phys. Rev. Lett. 86), 1335 (2001).. We solve the model in the large-N limit and study the effect of a magnetic field on the incommensurate magnetic order. Below a critical field the spins form a ``cone'' of polarization, in apparent agreement with neutron scattering experiments when the magnetic field is oriented perpendicular to the lattice. The incommensuration increases with increasing field strength. Above the critical field the spins are fully polarized. We have difficulty treating Dzyaloshinskii-Moriya interactions which are believed to be important for in-plane fields.

Electron cyclotron resonance heating by magnetic filter field in a negative hydrogen ion source.

PubMed

Kim, June Young; Cho, Won-Hwi; Dang, Jeong-Jeung; Chung, Kyoung-Jae; Hwang, Y S

2016-02-01

The influence of magnetic filter field on plasma properties in the heating region has been investigated in a planar-type inductively coupled radio-frequency (RF) H(-) ion source. Besides filtering high energy electrons near the extraction region, the magnetic filter field is clearly observed to increase the electron temperature in the heating region at low pressure discharge. With increasing the operating pressure, enhancement of electron temperature in the heating region is reduced. The possibility of electron cyclotron resonance (ECR) heating in the heating region due to stray magnetic field generated by a filter magnet located at the extraction region is examined. It is found that ECR heating by RF wave field in the discharge region, where the strength of an axial magnetic field is approximately ∼4.8 G, can effectively heat low energy electrons. Depletion of low energy electrons in the electron energy distribution function measured at the heating region supports the occurrence of ECR heating. The present study suggests that addition of axial magnetic field as small as several G by an external electromagnet or permanent magnets can greatly increase the generation of highly ro-vibrationally excited hydrogen molecules in the heating region, thus improving the performance of H(-) ion generation in volume-produced negative hydrogen ion sources.

Role of Magnetic Diffusion Induced by Turbulent Magnetic Reconnection for Star Formation

NASA Astrophysics Data System (ADS)

Lazarian, Alex; Santos de Lima, R.; de Gouveia Dal Pino, E.

2010-01-01

The diffusion of astrophysical magnetic fields in conducting fluids in the presence of turbulence depends on whether magnetic fields can change their topology or reconnect in highly conducting media. Recent progress in understanding fast magnetic reconnection in the presence of turbulence is reassuring that the magnetic field behavior in the computer simulations and turbulent astrophysical environments is similar, as far as the magnetic reconnection is concerned. This makes it meaningful to perform MHD simulations of turbulent flows in order to understand the diffusion of magnetic field in astrophysical environments. Our study of magnetic field diffusion reveals important propertie s of the process. First of all, our 3D MHD simulations initiated with anti-correlating magnetic field and gaseous density exhibit at later times a decorrelation of the magnetic field and density, which corresponds well to the observations of the interstellar media. In the presence of gravity, our 3D simulations show the decrease of the flux to mass ratio with density concentration when turbulence is present. We observe this effect both in the situations when we start with the equilibrium distributions of gas and magnetic field and when we start with collapsing dynamically unstable configurations. Thus the process of turbulent magnetic field removal should be applicable both to quasistatic subcritical molecular clouds and cores and violently collapsing supercritical entities. The increase of the gravitational potential as well as the magnetization of the gas increases the segregation of the mass and flux in the saturated final state of simulations, supporting the notion that turbulent diffusivity relaxes the magnetic field + gas system in the gravitational field to its minimal energy state. At the same time, turbulence of high level may get the system unbound making the flux to mass ratio more uniform through the simulation box.

Topology optimized permanent magnet systems

NASA Astrophysics Data System (ADS)

Bjørk, R.; Bahl, C. R. H.; Insinga, A. R.

2017-09-01

Topology optimization of permanent magnet systems consisting of permanent magnets, high permeability iron and air is presented. An implementation of topology optimization for magnetostatics is discussed and three examples are considered. The Halbach cylinder is topology optimized with iron and an increase of 15% in magnetic efficiency is shown. A topology optimized structure to concentrate a homogeneous field is shown to increase the magnitude of the field by 111%. Finally, a permanent magnet with alternating high and low field regions is topology optimized and a Λcool figure of merit of 0.472 is reached, which is an increase of 100% compared to a previous optimized design.

Nested Helmholtz coil design for producing homogeneous transient rotating magnetic fields

NASA Astrophysics Data System (ADS)

Podaru, George; Moore, John; Dani, Raj Kumar; Prakash, Punit; Chikan, Viktor

2015-03-01

Electromagnets that can produce strong rotating magnetic fields at kHz frequencies are potentially very useful to exert rotating force on magnetic nanoparticles as small as few nanometers in size. In this article, the construction of a pulsed high-voltage rotating electromagnet is demonstrated based on a nested Helmholtz coil design. The energy for the coils is provided by two high-voltage discharge capacitors. The triggered spark gaps used in the experiments show sufficient accuracy to achieve the high frequency rotating magnetic field. The measured strength of the rotating magnetic field is 200 mT. This magnetic field is scalable by increasing the number of turns on the coils, by reducing the dimensions of the coils and by increasing the discharge current/voltage of the capacitors.

Deconfinement phase transition in a magnetic field in 2 + 1 dimensions from holographic models

NASA Astrophysics Data System (ADS)

M. Rodrigues, Diego; Capossoli, Eduardo Folco; Boschi-Filho, Henrique

2018-05-01

Using two different models from holographic quantum chromodynamics (QCD) we study the deconfinement phase transition in 2 + 1 dimensions in the presence of a magnetic field. Working in 2 + 1 dimensions lead us to exact solutions on the magnetic field, in contrast with the case of 3 + 1 dimensions where the solutions on the magnetic field are perturbative. As our main result we predict a critical magnetic field Bc where the deconfinement critical temperature vanishes. For weak fields meaning B Bc we find that the critical temperature raises with growing field showing a magnetic catalysis (MC). These results for IMC and MC are in agreement with the literature.

Enhancement of Feedback Efficiency by Active Galactic Nucleus Outflows via the Magnetic Tension Force in the Inhomogeneous Interstellar Medium

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

Asahina, Yuta; Ohsuga, Ken; Nomura, Mariko, E-mail: asahina@cfca.jp

By performing three-dimensional magnetohydrodynamics simulations of subrelativistic jets and disk winds propagating into the magnetized inhomogeneous interstellar medium (ISM), we investigate the magnetic effects on the active galactic nucleus feedback. Our simulations reveal that the magnetic tension force promotes the acceleration of the dense gas clouds, since the magnetic field lines, which are initially straight, bend around the gas clouds. In the jet models, the velocity dispersion of the clouds increases with an increase in the initial magnetic fields. The increment of the kinetic energy of the clouds is proportional to the initial magnetic fields, implying that the magnetic tensionmore » force increases the energy conversion efficiency from the jet to the gas clouds. Through simulations of the mildly collimated disk wind and the funnel-shaped disk wind, we confirm that such an enhancement of the energy conversion efficiency via the magnetic fields appears even if the energy is injected via the disk winds. The enhancement of the acceleration of the dense part of the magnetized ISM via the magnetic tension force will occur wherever the magnetized inhomogeneous matter is blown away.« less

Nonlinear Right-Hand Polarized Wave in Plasma in the Electron Cyclotron Resonance Region

NASA Astrophysics Data System (ADS)

Krasovitskiy, V. B.; Turikov, V. A.

2018-05-01

The propagation of a nonlinear right-hand polarized wave along an external magnetic field in subcritical plasma in the electron cyclotron resonance region is studied using numerical simulations. It is shown that a small-amplitude plasma wave excited in low-density plasma is unstable against modulation instability with a modulation period equal to the wavelength of the excited wave. The modulation amplitude in this case increases with decreasing detuning from the resonance frequency. The simulations have shown that, for large-amplitude waves of the laser frequency range propagating in plasma in a superstrong magnetic field, the maximum amplitude of the excited longitudinal electric field increases with the increasing external magnetic field and can reach 30% of the initial amplitude of the electric field in the laser wave. In this case, the energy of plasma electrons begins to substantially increase already at magnetic fields significantly lower than the resonance value. The laser energy transferred to plasma electrons in a strong external magnetic field is found to increase severalfold compared to that in isotropic plasma. It is shown that this mechanism of laser radiation absorption depends only slightly on the electron temperature.

The swimming polarity of multicellular magnetotactic prokaryotes can change during an isolation process employing magnets: evidence of a relation between swimming polarity and magnetic moment intensity.

PubMed

de Melo, Roger Duarte; Acosta-Avalos, Daniel

2017-09-01

Magnetotactic microorganisms are characterized by swimming in the direction of an applied magnetic field. In nature, two types of swimming polarity have been observed: north-seeking microorganisms that swim in the same direction as the magnetic field, and south-seeking microorganisms that swim in the opposite direction. The present work studies the reversal in the swimming polarity of the multicellular magnetotactic prokaryote Candidatus Magnetoglobus multicellularis following an isolation process using high magnetic fields from magnets. The proportion of north- and south-seeking organisms was counted as a function of the magnetic field intensity used during the isolation of the organisms from sediment. It was observed that the proportion of north-seeking organisms increased when the magnetic field was increased. The magnetic moment for north- and south-seeking populations was estimated using the U-turn method. The average magnetic moment was higher for north- than south-seeking organisms. The results suggest that the reversal of swimming polarity must occur during the isolation process in the presence of high magnetic fields and magnetic field gradients. It is shown for the first time that the swimming polarity reversal depends on the magnetic moment intensity of multicellular magnetotactic prokaryotes, and new studies must be undertaken to understand the role of magnetic moment polarity and oxygen gradients in determination of swimming polarity.

Thermo-magnetic instabilities in Nb 3Sn superconducting accelerator magnets

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

Bordini, Bernardo

2006-09-01

The advance of High Energy Physics research using circulating accelerators strongly depends on increasing the magnetic bending field which accelerator magnets provide. To achieve high fields, the most powerful present-day accelerator magnets employ NbTi superconducting technology; however, with the start up of Large Hadron Collider (LHC) in 2007, NbTi magnets will have reached the maximum field allowed by the intrinsic properties of this superconductor. A further increase of the field strength necessarily requires a change in superconductor material; the best candidate is Nb 3Sn. Several laboratories in the US and Europe are currently working on developing Nb 3Sn accelerator magnets,more » and although these magnets have great potential, it is suspected that their performance may be fundamentally limited by conductor thermo-magnetic instabilities: an idea first proposed by the Fermilab High Field Magnet group early in 2003. This thesis presents a study of thermo-magnetic instability in high field Nb 3Sn accelerator magnets. In this chapter the following topics are described: the role of superconducting magnets in High Energy Physics; the main characteristics of superconductors for accelerator magnets; typical measurements of current capability in superconducting strands; the properties of Nb 3Sn; a description of the manufacturing process of Nb 3Sn strands; superconducting cables; a typical layout of superconducting accelerator magnets; the current state of the art of Nb 3Sn accelerator magnets; the High Field Magnet program at Fermilab; and the scope of the thesis.« less

Magnetic flux concentrations from dynamo-generated fields

NASA Astrophysics Data System (ADS)

Jabbari, S.; Brandenburg, A.; Losada, I. R.; Kleeorin, N.; Rogachevskii, I.

2014-08-01

Context. The mean-field theory of magnetized stellar convection gives rise to two distinct instabilities: the large-scale dynamo instability, operating in the bulk of the convection zone and a negative effective magnetic pressure instability (NEMPI) operating in the strongly stratified surface layers. The latter might be important in connection with magnetic spot formation. However, as follows from theoretical analysis, the growth rate of NEMPI is suppressed with increasing rotation rates. On the other hand, recent direct numerical simulations (DNS) have shown a subsequent increase in the growth rate. Aims: We examine quantitatively whether this increase in the growth rate of NEMPI can be explained by an α2 mean-field dynamo, and whether both NEMPI and the dynamo instability can operate at the same time. Methods: We use both DNS and mean-field simulations (MFS) to solve the underlying equations numerically either with or without an imposed horizontal field. We use the test-field method to compute relevant dynamo coefficients. Results: DNS show that magnetic flux concentrations are still possible up to rotation rates above which the large-scale dynamo effect produces mean magnetic fields. The resulting DNS growth rates are quantitatively reproduced with MFS. As expected for weak or vanishing rotation, the growth rate of NEMPI increases with increasing gravity, but there is a correction term for strong gravity and large turbulent magnetic diffusivity. Conclusions: Magnetic flux concentrations are still possible for rotation rates above which dynamo action takes over. For the solar rotation rate, the corresponding turbulent turnover time is about 5 h, with dynamo action commencing in the layers beneath.

Effect of magnetic field on the phase transition in a dusty plasma

NASA Astrophysics Data System (ADS)

Jaiswal, S.; Hall, T.; LeBlanc, S.; Mukherjee, R.; Thomas, E.

2017-11-01

The formation of a self-consistent crystalline structure is a well-known phenomenon in complex plasmas. In most experiments, the pressure and rf power are the main controlling parameters in determining the phase of the system. We have studied the effect of the externally applied magnetic field on the configuration of plasma crystals, suspended in the sheath of a radio-frequency discharge using the Magnetized Dusty Plasma Experiment device. Experiments are performed at a fixed pressure and rf power where a crystalline structure is formed within a confining ring. The magnetic field is then increased from 0 to 1.28 T. We report on the breakdown of the crystalline structure with the increasing magnetic field. The magnetic field affects the dynamics of the plasma particles and first leads to a rotation of the crystal. At a higher magnetic field, there is a radial variation (shear) in the angular velocity of the moving particles which we believe to lead to the melting of the crystal. This melting is confirmed by evaluating the variation of the pair correlation function as a function of magnetic field.

The effects of magnetic field in plume region on the performance of multi-cusped field thruster

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

Hu, Peng, E-mail: hupengemail@126.com; Liu, Hui, E-mail: thruster@126.com; Yu, Daren

2015-10-15

The performance characteristics of a Multi-cusped Field Thruster depending on the magnetic field in the plume region were investigated. Five magnetic field shielding rings were separately mounted near the exit of discharge channel to decrease the strength of magnetic field in the plume region in different levels, while the magnetic field in the upstream was well maintained. The test results show that the electron current increases with the decrease of magnetic field strength in the plume region, which gives rise to higher propellant utilization and lower current utilization. On the other hand, the stronger magnetic field in the plume regionmore » improves the performance at low voltages (high current mode) while lower magnetic field improves the performance at high voltages (low current mode). This work can provide some optimal design ideas of the magnetic strength in the plume region to improve the performance of thruster.« less

Performance improvement of magnetized coaxial plasma gun by magnetic circuit on a bias coil

NASA Astrophysics Data System (ADS)

Edo, Takahiro; Matsumoto, Tadafumi; Asai, Tomohiko; Kamino, Yasuhiro; Inomoto, Michiaki; Gota, Hiroshi

2016-10-01

A magnetized coaxial plasmoid accelerator has been utilized for compact torus (CT) injection to refuel into fusion reactor core plasma. Recently, CT injection experiments have been conducted on the C-2/C-2U facility at Tri Alpha Energy. In the series of experiments successful refueling, i.e. increased particle inventory of field-reversed configuration (FRC) plasma, has been observed. In order to improve the performance of CT injector and to refuel in the upgraded FRC device, called C-2W, with higher confinement magnetic field, magnetic circuit consisting of magnetic material onto a bias magnetic coil is currently being tested at Nihon University. Numerical work suggests that the optimized bias magnetic field distribution realizes the increased injection velocity because of higher conversion efficiency of Lorenz self force to kinetic energy. Details of the magnetic circuit design as well as results of the test experiment and field calculations will be presented and discussed.

Magnetically targeted delivery through cartilage

NASA Astrophysics Data System (ADS)

Jafari, Sahar; Mair, Lamar O.; Chowdhury, Sagar; Nacev, Alek; Hilaman, Ryan; Stepanov, Pavel; Baker-McKee, James; Ijanaten, Said; Koudelka, Christian; English, Bradley; Malik, Pulkit; Weinberg, Irving N.

2018-05-01

In this study, we have invented a method of delivering drugs deep into articular cartilage with shaped dynamic magnetic fields acting on small metallic magnetic nanoparticles with polyethylene glycol coating and average diameter of 30 nm. It was shown that transport of magnetic nanoparticles through the entire thickness of bovine articular cartilage can be controlled by a combined alternating magnetic field at 100 Hz frequency and static magnetic field of 0.8 tesla (T) generated by 1" dia. x 2" thick permanent magnet. Magnetic nanoparticles transport through bovine articular cartilage samples was investigated at various settings of magnetic field and time durations. Combined application of an alternating magnetic field and the static field gradient resulted in a nearly 50 times increase in magnetic nanoparticles transport in bovine articular cartilage tissue as compared with static field conditions. This method can be applied to locally deliver therapeutic-loaded magnetic nanoparticles deep into articular cartilage to prevent cartilage degeneration and promote cartilage repair in osteoarthritis.

Magnet pole tips

DOEpatents

Thorn, Craig E.; Chasman, Chellis; Baltz, Anthony J.

1984-04-24

An improved magnet which more easily provides a radially increasing magnetic field, as well as reduced fringe field and requires less power for a given field intensity. The subject invention comprises a pair of spaced, opposed magnetic poles which further comprise a pair of pole roots, each having a pole tip attached to its center. The pole tips define the gap between the magnetic poles and at least a portion of each pole tip is separated from its associated pole root. The separation begins at a predetermined distance from the center of the pole root and increases with increasing radial distance while being constant with azimuth within that portion. Magnets in accordance with the subject invention have been found to be particularly advantageous for use in large isochronous cyclotrons.

Magnet pole tips

DOEpatents

Thorn, C.E.; Chasman, C.; Baltz, A.J.

1981-11-19

An improved magnet more easily provides a radially increasing magnetic field, as well as reduced fringe field and requires less power for a given field intensity. The subject invention comprises a pair of spaced, opposed magnetic poles which further comprise a pair of pole roots, each having a pole tip attached to its center. The pole tips define the gap between the magnetic poles and at least a portion of each pole tip is separated from its associated pole root. The separation begins at a predetermined distance from the center of the pole root and increases with increasing radial distance while being constant with azimuth within that portion. Magnets in accordance with the subject invention have been found to be particularly advantageous for use in large isochronous cyclotrons.

The influence of a magnetic field on the heat transfer of a magnetic nanofluid in a sinusoidal channel

NASA Astrophysics Data System (ADS)

Valiallah Mousavi, S.; Barzegar Gerdroodbary, M.; Sheikholeslami, Mohsen; Ganji, D. D.

2016-09-01

In this study, two dimensional numerical simulations are performed to investigate the influence of the magnetic field on the nanofluid flow inside a sinusoidal channel. This work reveals the influence of variable magnetic field in the heat transfer of heat exchanger while the mixture is in a single phase. In this heat exchanger, the inner tube is sinusoidal and the outer tube is considered smooth. The magnetic field is applied orthogonal to the axis of the sinusoidal tube. In our study, the ferrofluid (water with 4 vol% nanoparticles (Fe3O4)) flows in a channel with sinusoidal bottom. The finite volume method with the SIMPLEC algorithm is used for handling the pressure-velocity coupling. The numerical results present validated data with experimentally measured data and show good agreement with measurement. The influence of different parameters, like the intensity of magnetic field and Reynolds number, on the heat transfer is investigated. According to the obtained results, the sinusoidal formation of the internal tube significantly increases the Nusselt number inside the channel. Our findings show that the magnetic field increases the probability of eddy formation inside the cavities and consequently enhances the heat transfer (more than 200%) in the vicinity of the magnetic field at low Reynolds number ( Re=50). In addition, the variation of the skin friction shows that the magnetic field increases the skin friction (more than 600%) inside the sinusoidal channel.

Electronic Properties of SiNTs Under External Electric and Magnetic Fields Using the Tight-Binding Method

NASA Astrophysics Data System (ADS)

Chegel, Raad; Behzad, Somayeh

2014-02-01

We investigated the electronic properties of silicon nanotubes (SiNTs) under external transverse electric fields and axial magnetic fields using the tight-binding approximation. It was found that, after switching on the electric and magnetic fields, band modifications such as distortion of degeneracy, change in energy dispersion and subband spacing, and bandgap size reduction occur. The bandgap of silicon gear-like nanotubes (Si g-NTs) decreases linearly with increasing electric field strength, but the bandgap for silicon hexagonal nanotubes (Si h-NTs) first increases and then decreases (metallic) or first remains constant and then decreases (semiconducting). Our results show that the bandgap of Si h-NTs is very sensitive to both electric and magnetic fields, unlike Si g-NTs, which are more sensitive to electric than magnetic fields.

Parallel magnetic field suppresses dissipation in superconducting nanostrips

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

Wang, Yong-Lei; Glatz, Andreas; Kimmel, Gregory J.

The motion of Abrikosov vortices in type-II superconductors results in a finite resistance in the presence of an applied electric current. Elimination or reduction of the resistance via immobilization of vortices is the "holy grail" of superconductivity research. Common wisdom dictates that an increase in the magnetic field escalates the loss of energy since the number of vortices increases. Here we show that this is no longer true if the magnetic field and the current are applied parallel to each other. Our experimental studies on the resistive behavior of a superconducting Mo0.79Ge0.21 nanostrip reveal the emergence of a dissipative statemore » with increasing magnetic field, followed by a pronounced resistance drop, signifying a reentrance to the superconducting state. Large-scale simulations of the 3D time-dependent Ginzburg-Landau model indicate that the intermediate resistive state is due to an unwinding of twisted vortices. When the magnetic field increases, this instability is suppressed due to a better accommodation of the vortex lattice to the pinning configuration. Our findings show that magnetic field and geometrical confinement can suppress the dissipation induced by vortex motion and thus radically improve the performance of superconducting materials.« less

NEAR-IR IMAGING POLARIMETRY TOWARD A BRIGHT-RIMMED CLOUD: MAGNETIC FIELD IN SFO 74

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

Kusune, Takayoshi; Sugitani, Koji; Miao, Jingqi

2015-01-01

We have made near-infrared (JHK {sub s}) imaging polarimetry of a bright-rimmed cloud (SFO 74). The polarization vector maps clearly show that the magnetic field in the layer just behind the bright rim is running along the rim, quite different from its ambient magnetic field. The direction of the magnetic field just behind the tip rim is almost perpendicular to that of the incident UV radiation, and the magnetic field configuration appears to be symmetric as a whole with respect to the cloud symmetry axis. We estimated the column and number densities in the two regions (just inside and farmore » inside the tip rim) and then derived the magnetic field strength, applying the Chandrasekhar-Fermi method. The estimated magnetic field strength just inside the tip rim, ∼90 μG, is stronger than that far inside, ∼30 μG. This suggests that the magnetic field strength just inside the tip rim is enhanced by the UV-radiation-induced shock. The shock increases the density within the top layer around the tip and thus increases the strength of the magnetic field. The magnetic pressure seems to be comparable to the turbulent one just inside the tip rim, implying a significant contribution of the magnetic field to the total internal pressure. The mass-to-flux ratio was estimated to be close to the critical value just inside the tip rim. We speculate that the flat-topped bright rim of SFO 74 could be formed by the magnetic field effect.« less

Effect of a weak transverse magnetic field on the microstructure in directionally solidified peritectic alloys

PubMed Central

Li, Xi; Lu, Zhenyuan; Fautrelle, Yves; Gagnoud, Annie; Moreau, Rene; Ren, Zhongming

2016-01-01

Effect of a weak transverse magnetic field on the microstructures in directionally solidified Fe-Ni and Pb-Bi peritectic alloys has been investigated experimentally. The results indicate that the magnetic field can induce the formation of banded and island-like structures and refine the primary phase in peritectic alloys. The above results are enhanced with increasing magnetic field. Furthermore, electron probe micro analyzer (EPMA) analysis reveals that the magnetic field increases the Ni solute content on one side and enhances the solid solubility in the primary phase in the Fe-Ni alloy. The thermoelectric (TE) power difference at the liquid/solid interface of the Pb-Bi peritectic alloy is measured in situ, and the results show that a TE power difference exists at the liquid/solid interface. 3 D numerical simulations for the TE magnetic convection in the liquid are performed, and the results show that a unidirectional TE magnetic convection forms in the liquid near the liquid/solid interface during directional solidification under a transverse magnetic field and that the amplitude of the TE magnetic convection at different scales is different. The TE magnetic convections on the macroscopic interface and the cell/dendrite scales are responsible for the modification of microstructures during directional solidification under a magnetic field. PMID:27886265

Thermoelectric efficiency enhanced in a quantum dot with polarization leads, spin-flip and external magnetic field

NASA Astrophysics Data System (ADS)

Yao, Hui; Niu, Peng-Bin; Zhang, Chao; Xu, Wei-Ping; Li, Zhi-Jian; Nie, Yi-Hang

2018-03-01

We theoretically study the thermoelectric transport properties in a quantum dot system with two ferromagnetic leads, the spin-flip scattering and the external magnetic field. The results show that the spin polarization of the leads strongly influences thermoelectric coefficients of the device. For the parallel configuration the peak of figure of merit increases with the increase of polarization strength and non-collinear configuration trends to destroy the improvement of figure of merit induced by lead polarization. While the modulation of the spin-flip scattering on the figure of merit is effective only in the absence of external magnetic field or small magnetic field. In terms of improving the thermoelectric efficiency, the external magnetic field plays a more important role than spin-flip scattering. The thermoelectric efficiency can be significantly enhanced by the magnetic field for a given spin-flip scattering strength.

Magnetic field sensing based on tilted fiber Bragg grating coated with nanoparticle magnetic fluid

NASA Astrophysics Data System (ADS)

Yang, Dexing; Du, Lei; Xu, Zengqi; Jiang, Yajun; Xu, Jian; Wang, Meirong; Bai, Yang; Wang, Haiyan

2014-02-01

A magnetic field sensor based on a tilted fiber Bragg grating (TFBG) coated with magnetic fluid is proposed and demonstrated experimentally. The sensing element is made by injecting the magnetic fluid into a capillary tube which contains a TFBG. The resonant wavelengths of the cladding modes of TFBG shift by varying the magnetic field which is perpendicular to the axis of TFBG. The results indicate that the resonant wavelength shifts of the cladding modes show a nonlinear dependence on the magnetic field. As the magnetic field increases to 32 mT, the largest resonant wavelength shift reaches to 106 pm. Moreover, this sensor shows good repeatability when it is used for magnetic field sensing.

Direct spectroscopic evidence for competition between thermal molecular agitation and magnetic field in a tetrameric protein in aqueous solution

NASA Astrophysics Data System (ADS)

Calabrò, Emanuele; Magazù, Salvatore

2018-05-01

Samples of a typical tetrameric protein, the hemoglobin, at the concentration of 150 mg/ml in bidistilled water solution, were exposed to a uniform magnetic field at 200 mT at different temperatures of 15∘C, 40∘C and 65∘C. Fourier Transform Infrared Spectroscopy was used to analyze the response of the secondary structure of the protein to both stress agents, heating and static magnetic field. The most relevant result which was observed was the significant increasing in intensity of the Amide I band after exposure to the uniform magnetic field at the room temperature of 15∘C. This result can be explained assuming that protein's α-helices aligned along the direction of the applied magnetic field due to their large dipole moment, inducing the alignment of the entire protein. Increasing of temperature up to 40∘C and 65∘C induced a significant reduction of the increasing in intensity of the Amide I band. This effect may be easily explained assuming that Brownian motion of the protein in water solution caused by thermal molecular agitation increased with increasing of temperature, contrasting the effect of the torque of the magnetic field applied to the protein in water solution.

Investigations on magnetic field induced optical transparency in magnetic nanofluids

NASA Astrophysics Data System (ADS)

Mohapatra, Dillip Kumar; Philip, John

2018-02-01

We study the magnetic field induced optical transparency and its origin in magnetic nanoemulsion of droplets of average size ∼200 nm containing superparamagnetic iron oxide nanoparticles. Beyond a certain volume fraction (Φ > 0.0021) of magnetic nanoemulsion and a critical magnetic field (Hc1), the transmitted light intensity increases drastically and reaches a maximum at another critical magnetic field (Hc2), beyond which the transmitted light intensity decreases and reaches a plateau. Interestingly, the transmitted light intensity at Hc2 is found to increase linearly with Φ and the critical magnetic fields Hc1 and Hc2 follow power law decay with Φ (i.e. Hc ∼ Φ-x), with exponents 0.48 and 0.27, respectively. The light intensity recovers to its initial value when the magnetic field is switched off, indicating the perfect reversibility of the field induced transparency process. The observed straight line scattered patterns above Hc2, on a screen placed perpendicular to the incident beam, confirms the formation of rod like anisotropic nanostructures perpendicular to the direction of light propagation. The magneto-optical measurements in the emulsion confirm that the observed field induced transparency in magnetic emulsions for Φ > 0.0021 is due to the optical birefringence caused by the rod like nanostructures. The reduced birefringence is found to be proportional to the square of the applied magnetic field. This finding offers several possibilities in using magnetic nanofluids in tunable optical devices.

Dynamics in the solar chromosphere as a function of the magnetic field topology

NASA Astrophysics Data System (ADS)

Karlsen, N.; Carlsson, M.

2002-06-01

We have looked at the coupling between the magnetic field and chromospheric dynamics. Observations with the SUMER spectrograph of the continuum radiation at 1319 Å have been correlated with simultaneous MDI magnetograms and dopplergrams in high resolution mode. We have used 7 different observing runs for our analysis, all from 1996. The absolute value of the magnetic field crossing the SUMER slit lies in the range 0-100 gauss. We observe a correlation between continuum intensity and magnetic field strength all the way to the sensitivity limit of MDI (about 2 G as 3σ in the mean value). Relative intensity fluctuations at frequencies corresponding to propagating acoustic waves (>4.5 mHz) have smaller amplitudes with increasing radiation temperature (or magnetic field strength). The absolute intensity fluctuations show an increase with increasing radiation temperature. These findings are consistent with a picture where a basic intensity level is set by a magnetic heating process even in the darkest internetwork areas with superimposed intensity variations caused by acoustic waves.

Effects of the magnetic field gradient on the wall power deposition of Hall thrusters

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Li, Peng; Zhang, Xu; Wei, Liqiu; Sun, Hezhi; Peng, Wuji; Yu, Daren

2017-04-01

The effect of the magnetic field gradient in the discharge channel of a Hall thruster on the ionization of the neutral gas and power deposition on the wall is studied through adopting the 2D-3V particle-in-cell (PIC) and Monte Carlo collisions (MCC) model. The research shows that by gradually increasing the magnetic field gradient while keeping the maximum magnetic intensity at the channel exit and the anode position unchanged, the ionization region moves towards the channel exit and then a second ionization region appears near the anode region. Meanwhile, power deposition on the walls decreases initially and then increases. To avoid power deposition on the walls produced by electrons and ions which are ionized in the second ionization region, the anode position is moved towards the channel exit as the magnetic field gradient is increased; when the anode position remains at the zero magnetic field position, power deposition on the walls decreases, which can effectively reduce the temperature and thermal load of the discharge channel.

Rotatable Small Permanent Magnet Array for Ultra-Low Field Nuclear Magnetic Resonance Instrumentation: A Concept Study.

PubMed

Vogel, Michael W; Giorni, Andrea; Vegh, Viktor; Pellicer-Guridi, Ruben; Reutens, David C

2016-01-01

We studied the feasibility of generating the variable magnetic fields required for ultra-low field nuclear magnetic resonance relaxometry with dynamically adjustable permanent magnets. Our motivation was to substitute traditional electromagnets by distributed permanent magnets, increasing system portability. The finite element method (COMSOL®) was employed for the numerical study of a small permanent magnet array to calculate achievable magnetic field strength, homogeneity, switching time and magnetic forces. A manually operated prototype was simulated and constructed to validate the numerical approach and to verify the generated magnetic field. A concentric small permanent magnet array can be used to generate strong sample pre-polarisation and variable measurement fields for ultra-low field relaxometry via simple prescribed magnet rotations. Using the array, it is possible to achieve a pre-polarisation field strength above 100 mT and variable measurement fields ranging from 20-50 μT with 200 ppm absolute field homogeneity within a field-of-view of 5 x 5 x 5 cubic centimetres. A dynamic small permanent magnet array can generate multiple highly homogeneous magnetic fields required in ultra-low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) instruments. This design can significantly reduce the volume and energy requirements of traditional systems based on electromagnets, improving portability considerably.

Technical Note: Enhancing the surface dose using a weak longitudinal magnetic field

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

Carlone, Marco, E-mail: marco.carlone@rmp.uhn.on.ca; Keller, Harald; Rezaee, Mohammad

2016-06-15

Purpose: The surface dose in radiotherapy is subject to the physical properties of the radiation beam and collimator. The purpose of this work is to investigate the manipulation of surface dose using magnetic fields produced with a resistive magnet. Better understanding of the feasibility and mechanisms of altered surface dose could have important clinical applications where the surface dose must be increased for therapeutic goals, or reduced to enhance the therapeutic benefit. Methods: A resistive magnet capable of generating a peak magnetic field up to 0.24 T was integrated with a cobalt treatment unit. The magnetic fringe field of themore » magnet was small due to the self-shielding built within the magnet. The magnetic field at the beam collimation jaws of the cobalt irradiator was less than 10 G. The surface dose and depth dose were measured for varying magnetic field strengths. Results: The resistive magnet was able to alter the dose in the buildup region of the {sup 60}Co depth dose significantly, and the magnitude of dose enhancement was directly related to the strength of the longitudinal magnetic field. Peak magnetic fields as low as 0.08 T were able to affect the surface dose. At a peak field of 0.24 T, the authors measured a surface dose enhancement of 2.8-fold. Conclusions: Surface dose enhancement using resistive magnets is feasible. Further experimental study is needed to understand the origin of the scattered electrons that contribute to the increase in surface dose.« less

Magnetic field effects on charge structure factors of gapped graphene structure

NASA Astrophysics Data System (ADS)

Rezania, Hamed; Tawoose, Nasrin

2018-02-01

We present the behaviors of dynamical and static charge susceptibilities of undoped gapped graphene using the Green's function approach in the context of tight binding model Hamiltonian. Specially, the effects of magnetic field on the plasmon modes of gapped graphene structure are investigated via calculating correlation function of charge density operators. Our results show the increase of magnetic field leads to disappear high frequency plasmon mode for gapped case. We also show that low frequency plasmon mode has not affected by increase of magnetic field and chemical potential. Finally the temperature dependence of static charge structure factor of gapp graphene structure is studied. The effects of both magnetic field and gap parameter on the static structure factor are discusses in details.

Effect of a High Magnetic Field on γ' Phase for Ni-Based Single Crystal Superalloy During Directional Solidification

NASA Astrophysics Data System (ADS)

Xuan, Weidong; Lan, Jian; Zhao, Dengke; Li, Chuanjun; Shang, Xingfu; Zhong, Yunbo; Li, Xi; Ren, Zhongming

2018-05-01

The effect of a high magnetic field on the γ' phase of Ni-based single crystal superalloy during directional solidification is investigated experimentally. The results clearly indicate that the magnetic field significantly reduces the γ' phase size. Further, the quenching experiment is carried out, and the results found that the length of mushy zone is obviously decreased under a high magnetic field. Based on both experimental results and nucleation mechanism, it is found that the decrease of γ' phase size should be attributed to the fact that a high magnetic field causes the increase of temperature gradient in front of solid/liquid interface and leads to the increase of undercooling of γ' phase.

On flow of electrically conducting fluids over a flat plate in the presence of a transverse magnetic field

NASA Technical Reports Server (NTRS)

Rossow, Vernon J

1958-01-01

The use of a magnetic field to control the motion of electrically conducting fluids is studied. The incompressible boundary-layer solutions are found for flow over a flat plate when the magnetic field is fixed relative to the plate or to the fluid. The equations are integrated numerically for the effect of the transverse magnetic field on the velocity and temperature profiles, and hence, the skin friction and rate of heat transfer. It is concluded that the skin friction and the heat-transfer rate are reduced when the transverse magnetic field is fixed relative to the plate and increased when fixed relative to the fluid. The total drag is increased in all of the areas.

New types of high field pinning centers and pinning centers for the peak effect

NASA Astrophysics Data System (ADS)

Gajda, Daniel; Zaleski, Andrzej; Morawski, Andrzej; Hossain, Md Shahriar A.

2017-08-01

In this article, we report the results of a study that shows the existence of pinning centers inside grains and between grains in NbTi wires. We accurately show the ranges of magnetic fields in which the individual pinning centers operate. The pinning centers inside grains are activated in high magnetic fields above 6 T. We show the range of magnetic fields in which individual defects, dislocations, precipitates inside grains and substitutions in the crystal lattice can operate. We show the existence of a new kind of high field pinning center, which operates in high magnetic fields from 8 to ˜9.5 T. We indicate that dislocations create pinning centers in the range of magnetic fields from 6 to 8 T. In addition, our measurements suggest that the peak effect (increased critical current density (J c) near the upper critical field (B c2)) could be attributed to martensitic (needle-shaped) α‧-Ti inclusions inside grains. These centers are very important because they work very effectively in magnetic fields above 9.5-10 T. We also show that the α-Ti precipitates (between grains) with a thickness similar to the coherence length create pinning centers which work very effectively in magnetic fields from 3 to 6 T. In magnetic fields below 3 T, they act very efficiently in grain boundaries. The measurements indicate that the pinning centers created by dislocations only can be tested by transport measurements. This indicates that dislocations do not increase the magnetic critical current density (J cm). Cold drawing improves pinning centers at grain boundaries and increases the dislocation density, and cold-drawing pinning centers are responsible for the peak effect.

Magnetism and high magnetic-field-induced stability of alloy carbides in Fe-based materials.

PubMed

Hou, T P; Wu, K M; Liu, W M; Peet, M J; Hulme-Smith, C N; Guo, L; Zhuang, L

2018-02-14

Understanding the nature of the magnetic-field-induced precipitation behaviors represents a major step forward towards unravelling the real nature of interesting phenomena in Fe-based alloys and especially towards solving the key materials problem for the development of fusion energy. Experimental results indicate that the applied high magnetic field effectively promotes the precipitation of M 23 C 6 carbides. We build an integrated method, which breaks through the limitations of zero temperature and zero external field, to concentrate on the dependence of the stability induced by the magnetic effect, excluding the thermal effect. We investigate the intimate relationship between the external field and the origins of various magnetics structural characteristics, which are derived from the interactions among the various Wyckoff sites of iron atoms, antiparallel spin of chromium and Fe-C bond distances. The high-magnetic-field-induced exchange coupling increases with the strength of the external field, which then causes an increase in the parallel magnetic moment. The stability of the alloy carbide M 23 C 6 is more dependent on external field effects than thermal effects, whereas that of M 2 C, M 3 C and M 7 C 3 is mainly determined by thermal effects.

A Dynamic Model of Mercury's Magnetospheric Magnetic Field

PubMed Central

Johnson, Catherine L.; Philpott, Lydia; Tsyganenko, Nikolai A.; Anderson, Brian J.

2017-01-01

Abstract Mercury's solar wind and interplanetary magnetic field environment is highly dynamic, and variations in these external conditions directly control the current systems and magnetic fields inside the planetary magnetosphere. We update our previous static model of Mercury's magnetic field by incorporating variations in the magnetospheric current systems, parameterized as functions of Mercury's heliocentric distance and magnetic activity. The new, dynamic model reproduces the location of the magnetopause current system as a function of systematic pressure variations encountered during Mercury's eccentric orbit, as well as the increase in the cross‐tail current intensity with increasing magnetic activity. Despite the enhancements in the external field parameterization, the residuals between the observed and modeled magnetic field inside the magnetosphere indicate that the dynamic model achieves only a modest overall improvement over the previous static model. The spatial distribution of the residuals in the magnetic field components shows substantial improvement of the model accuracy near the dayside magnetopause. Elsewhere, the large‐scale distribution of the residuals is similar to those of the static model. This result implies either that magnetic activity varies much faster than can be determined from the spacecraft's passage through the magnetosphere or that the residual fields are due to additional external current systems not represented in the model or both. Birkeland currents flowing along magnetic field lines between the magnetosphere and planetary high‐latitude regions have been identified as one such contribution. PMID:29263560

Effects of a high-gradient magnetic field on the migratory behavior of primary crystal silicon in hypereutectic Al–Si alloy

PubMed Central

Jin, Fangwei; Ren, Zhongming; Ren, Weili; Deng, Kang; Zhong, Yunbo; Yu, Jianbo

2008-01-01

The migration of primary Si grains during the solidification of Al–18 wt%Si alloy under a high-gradient magnetic field has been investigated experimentally. It was found that under a gradient magnetic field, the primary Si grains migrated toward one end of the specimen, forming a Si-rich layer, and the thickness of the Si-rich layer increased with increasing magnetic flux density. No movement of Si grains was apparent under a magnetic field below 2.3 T. For magnetic fields above 6.6 T, however, the thickness of the Si-rich layer was almost constant. It was shown that the static field also played a role in impeding the movement of the grains. The primary Si grains were refined in the Si layer, even though the primary silicon grains were very dense. The effect of the magnetic flux density on the migratory behavior is discussed. PMID:27877953

Pooled analysis of recent studies on magnetic fields and childhood leukaemia

PubMed Central

Kheifets, L; Ahlbom, A; Crespi, C M; Draper, G; Hagihara, J; Lowenthal, R M; Mezei, G; Oksuzyan, S; Schüz, J; Swanson, J; Tittarelli, A; Vinceti, M; Wunsch Filho, V

2010-01-01

Background: Previous pooled analyses have reported an association between magnetic fields and childhood leukaemia. We present a pooled analysis based on primary data from studies on residential magnetic fields and childhood leukaemia published after 2000. Methods: Seven studies with a total of 10 865 cases and 12 853 controls were included. The main analysis focused on 24-h magnetic field measurements or calculated fields in residences. Results: In the combined results, risk increased with increase in exposure, but the estimates were imprecise. The odds ratios for exposure categories of 0.1–0.2 μT, 0.2–0.3 μT and ⩾0.3 μT, compared with <0.1 μT, were 1.07 (95% CI 0.81–1.41), 1.16 (0.69–1.93) and 1.44 (0.88–2.36), respectively. Without the most influential study from Brazil, the odds ratios increased somewhat. An increasing trend was also suggested by a nonparametric analysis conducted using a generalised additive model. Conclusions: Our results are in line with previous pooled analyses showing an association between magnetic fields and childhood leukaemia. Overall, the association is weaker in the most recently conducted studies, but these studies are small and lack methodological improvements needed to resolve the apparent association. We conclude that recent studies on magnetic fields and childhood leukaemia do not alter the previous assessment that magnetic fields are possibly carcinogenic. PMID:20877339

Skin dose in longitudinal and transverse linac-MRIs using Monte Carlo and realistic 3D MRI field models.

PubMed

Keyvanloo, A; Burke, B; Warkentin, B; Tadic, T; Rathee, S; Kirkby, C; Santos, D M; Fallone, B G

2012-10-01

The magnetic fields of linac-MR systems modify the path of contaminant electrons in photon beams, which alters patient skin dose. To accurately quantify the magnitude of changes in skin dose, the authors use Monte Carlo calculations that incorporate realistic 3D magnetic field models of longitudinal and transverse linac-MR systems. Finite element method (FEM) is used to generate complete 3D magnetic field maps for 0.56 T longitudinal and transverse linac-MR magnet assemblies, as well as for representative 0.5 and 1.0 T Helmholtz MRI systems. EGSnrc simulations implementing these 3D magnetic fields are performed. The geometry for the BEAMnrc simulations incorporates the Varian 600C 6 MV linac, magnet poles, the yoke, and the magnetic shields of the linac-MRIs. Resulting phase-space files are used to calculate the central axis percent depth-doses in a water phantom and 2D skin dose distributions for 70 μm entrance and exit layers using DOSXYZnrc. For comparison, skin doses are also calculated in the absence of magnetic field, and using a 1D magnetic field with an unrealistically large fringe field. The effects of photon field size, air gap (longitudinal configuration), and angle of obliquity (transverse configuration) are also investigated. Realistic modeling of the 3D magnetic fields shows that fringe fields decay rapidly and have a very small magnitude at the linac head. As a result, longitudinal linac-MR systems mostly confine contaminant electrons that are generated in the air gap and have an insignificant effect on electrons produced further upstream. The increase in the skin dose for the longitudinal configuration compared to the zero B-field case varies from ∼1% to ∼14% for air gaps of 5-31 cm, respectively. (All dose changes are reported as a % of D(max).) The increase is also field-size dependent, ranging from ∼3% at 20 × 20 cm(2) to ∼11% at 5 × 5 cm(2). The small changes in skin dose are in contrast to significant increases that are calculated for the unrealistic 1D magnetic field. For the transverse configuration, the entrance skin dose is equal or smaller than that of the zero B-field case for perpendicular beams. For a 10 × 10 cm(2) oblique beam the transverse magnetic field decreases the entry skin dose for oblique angles less than ±20° and increases it by no more than 10% for larger angles up to ±45°. The exit skin dose is increased by 42% for a 10 × 10 cm(2) perpendicular beam, but appreciably drops and approaches the zero B-field case for large oblique angles of incidence. For longitudinal linac-MR systems only a small increase in the entrance skin dose is predicted, due to the rapid decay of the realistic magnetic fringe fields. For transverse linac-MR systems, changes to the entrance skin dose are small for most scenarios. For the same geometry, on the exit side a fairly large increase is observed for perpendicular beams, but significantly drops for large oblique angles of incidence. The observed effects on skin dose are not expected to limit the application of linac-MR systems in either the longitudinal or transverse configuration.

Operating a magnetic nozzle helicon thruster with strong magnetic field

NASA Astrophysics Data System (ADS)

Takahashi, Kazunori; Komuro, Atsushi; Ando, Akira

2016-03-01

A pulsed axial magnetic field up to ˜2.8 kG is applied to a 26-mm-inner-diameter helicon plasma thruster immersed in a vacuum chamber, and the thrust is measured using a pendulum target. The pendulum is located 30-cm-downstream of the thruster, and the thruster rf power and argon flow rate are fixed at 1 kW and 70 sccm (which gives a chamber pressure of 0.7 mTorr). The imparted thrust increases as the applied magnetic field is increased and saturates at a maximum value of ˜9.5 mN for magnetic field above ˜2 kG. At the maximum magnetic field, it is demonstrated that the normalized plasma density, and the ion flow energy in the magnetic nozzle, agree within ˜50% and of 10%, respectively, with a one-dimensional model that ignores radial losses from the nozzle. This magnetic nozzle model is combined with a simple global model of the thruster source that incorporates an artificially controlled factor α, to account for radial plasma losses to the walls, where α = 0 and 1 correspond to zero losses and no magnetic field, respectively. Comparison between the experiments and the model implies that the radial losses in the thruster source are experimentally reduced by the applied magnetic field to about 10% of that obtained from the no magnetic field model.

Increasing the magnetic-field capability of the magneto-inertial fusion electrical discharge system using an inductively coupled coil

NASA Astrophysics Data System (ADS)

Barnak, D. H.; Davies, J. R.; Fiksel, G.; Chang, P.-Y.; Zabir, E.; Betti, R.

2018-03-01

Magnetized high energy density physics (HEDP) is a very active and relatively unexplored field that has applications in inertial confinement fusion, astrophysical plasma science, and basic plasma physics. A self-contained device, the Magneto-Inertial Fusion Electrical Discharge System, MIFEDS [G. Fiksel et al., Rev. Sci. Instrum. 86, 016105 (2015)], was developed at the Laboratory for Laser Energetics to conduct magnetized HEDP experiments on both the OMEGA [T. R. Boehly et al., Opt. Commun. 133, 495-506 (1997)] and OMEGA EP [J. H. Kelly et al., J. Phys. IV France 133, 75 (2006) and L. J. Waxer et al., Opt. Photonics News 16, 30 (2005)] laser systems. Extremely high magnetic fields are a necessity for magnetized HEDP, and the need for stronger magnetic fields continues to drive the redevelopment of the MIFEDS device. It is proposed in this paper that a magnetic coil that is inductively coupled rather than directly connecting to the MIFEDS device can increase the overall strength of the magnetic field for HEDP experiments by increasing the efficiency of energy transfer while decreasing the effective magnetized volume. A brief explanation of the energy delivery of the MIFEDS device illustrates the benefit of inductive coupling and is compared to that of direct connection for varying coil size and geometry. A prototype was then constructed to demonstrate a 7-fold increase in energy delivery using inductive coupling.

Evidence for a Field-Induced Quantum Spin Liquid in α -RuCl3

NASA Astrophysics Data System (ADS)

Baek, S.-H.; Do, S.-H.; Choi, K.-Y.; Kwon, Y. S.; Wolter, A. U. B.; Nishimoto, S.; van den Brink, Jeroen; Büchner, B.

2017-07-01

We report a 35Cl nuclear magnetic resonance study in the honeycomb lattice α -RuCl3 , a material that has been suggested to potentially realize a Kitaev quantum spin liquid (QSL) ground state. Our results provide direct evidence that α -RuCl3 exhibits a magnetic-field-induced QSL. For fields larger than ˜10 T , a spin gap opens up while resonance lines remain sharp, evidencing that spins are quantum disordered and locally fluctuating. The spin gap increases linearly with an increasing magnetic field, reaching ˜50 K at 15 T, and is nearly isotropic with respect to the field direction. The unusual rapid increase of the spin gap with increasing field and its isotropic nature are incompatible with conventional magnetic ordering and, in particular, exclude that the ground state is a fully polarized ferromagnet. The presence of such a field-induced gapped QSL phase has indeed been predicted in the Kitaev model.

Effects of Magnetic Field on Biological Cells and Applications

NASA Astrophysics Data System (ADS)

Chen, Ching-Jen

2001-03-01

While there has been extensive research performed in the physics of magnetic fields and the physics and chemistry in life sciences, independent of each other, there has been a paucity of scientific research and development investigating the possible applications of magnetic fields in life sciences. The focus of this presentation is to present the stimulation mechanism by which magnetic fields affect (a) yeast cells (b) plant cells and (c) mammalian normal and cancer cells. Recently we have found that the Saccharomyces Cerevsa yeast growth increases by about 30to a 1 tesla field and the production of CO2 increases by about 30of yeast metabolism may be due to an increase in intercellular interaction and protein channel alignment, the introduction of an alteration in the DNA from the magnetic field exposure or a combination of these mechanisms. We also have found that the application of high magnetic fields (1 tesla and above) can have marked effects on the germination and growth of plants, especially corn, beans and peas. This finding has opened up the possibility of technology developments in botanical growth systems to accelerate seed germination and crop harvesting. Most recently we have investigated the application of high magnetic fields on leukemia, CaCoII and HEP G2 cancer cell lines. We found that when leukemia are exposed to a 12 tesla field for 2 hours has an increase in cell death by about 30that were not exposed to the magnetic field. Viability of CaCoII cells sandwiched between permanent magnets of maximum strength of 1.2 tesla was measured. A decrease in viable cells by 33unexposed cells. HSP 70 was measured for HEPG2 cells that were exposed to permanent magnetic field of 1.2 tesla for 40 minutes and for unexposed cells. It was found that the exposed cells produce 19 times more HSP70 compared to unexposed cells. Our results together with other investigators report suggest a strong evidence of a reduction in the cell growth rate for cancer cells when subjected to high magnetic field. Devices that utilize an applied steady magnetic filed in it operation such as devices for blood component separation and diagnostic sensors have been developed.

Analytical modeling of hyperthermia using magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Bensenane, Mohamed Nassim; Senoudi, Assia Rachida; Benmouna, Reda; Ould-Kaddour, Fouzia

2018-06-01

Hyperthermia using magnetic nanoparticles (MNPs) is one of many techniques to treat cancer causing minimal damage to healthy tissues. In the present work we give an analytical resolution of the bio-heat equation (based on Pennes model) providing the temperature rise as a function of the characteristics of the magnetic nanoparticles, the applied magnetic field and the biological properties of the tissue. The temperature inside the tumor was found to be very sensitive to the frequency f of alternating magnetic field, magnetic field amplitude H0 and volume fraction φ. This study optimizes the intensity of magnetic field to reach ideal hyperthermia conditions. When f varies between 50 and 150 KHz, temperature increases from 39 °C until 53 °C; when H0 is ranged from 5 - 15 kA/m, it increases from 39.5 °C until 49 °C, and when volume fraction φ of MNPs is ranged from 2 × 10-4 to 3 × 10-4 it increases from 44 °C until 48 °C.

Magnetic properties of NdFeB-coated rubberwood composites

NASA Astrophysics Data System (ADS)

Noodam, Jureeporn; Sirisathitkul, Chitnarong; Matan, Nirundorn; Rattanasakulthong, Watcharee; Jantaratana, Pongsakorn

2013-01-01

Magnetic properties of composites prepared by coating lacquer containing neodymium iron boron (Nd-Fe-B) powders on rubberwood were characterized by vibrating sample magnetometry (VSM), magnetic moment measurements, and attraction tests with an iron-core solenoid. The Nd-Fe-B powders were recycled from electronic wastes by the ball-milling technique. Varying the milling time from 20 to 300 min, the magnetic squareness and the coercive field of the Nd-Fe-B powders were at the minimum when the powders were milled for 130 min. It followed that the coercive field of the magnetic wood composites was increased with the milling time increasing from 130 to 300 min. For the magnetic wood composites using Nd-Fe-B obtained from the same milling time, the magnetic squareness and the coercive field were rather insensitive to the variation of Nd-Fe-B concentration in coating lacquer from 0.43 to 1.00 g/cm3. By contrast, the magnetization and magnetic moment were increased with the Nd-Fe-B concentration increasing. Furthermore, the electrical current in the solenoid required for the attraction of the magnetic wood composites was exponentially reduced with the increase in the amount of Nd-Fe-B used in the coating.

Effect of sample initial magnetic field on the metal magnetic memory NDT result

NASA Astrophysics Data System (ADS)

Moonesan, Mahdi; Kashefi, Mehrdad

2018-08-01

One of the major concerns regarding the use of Metal Magnetic Memory (MMM) technique is the complexity of residual magnetization effect on output signals. The present study investigates the influence of residual magnetic field on stress induced magnetization. To this end, various initial magnetic fields were induced on a low carbon steel sample, and for each level of residual magnetic field, the sample was subjected to a set of 4-point bending tests and, their corresponding MMM signals were collected from the surface of the bended sample using a tailored metal magnetic memory scanning device. Results showed a strong correlation between sample residual magnetic field and its corresponding level of stress induced magnetic field. It was observed that the sample magnetic field increases with applying the bending stress as long as the initial residual magnet field is low (i.e. <117 mG), but starts decreasing with higher levels of initial residual magnetic fields. Besides, effect of bending stress on the MMM output of a notched sample was investigated. The result, again, showed that MMM signals exhibit a drop at stress concentration zone when sample has high level of initial residual magnetic field.

Dielectrophoresis-magnetophoresis force driven magnetic nanoparticle movement in transformer oil based magnetic fluids.

PubMed

Lee, Jong-Chul; Lee, Sangyoup

2013-09-01

Magnetic fluid is a stable colloidal mixture contained magnetic nanoparticles coated with a surfactant. Recently, it was found that the fluid has properties to increase heat transfer and dielectric characteristics due to the added magnetic nanoparticles in transformer oils. The magnetic nanoparticles in the fluid experience an electrical force directed toward the place of maximum electric field strength when the electric field is applied. And when the external magnetic field is applied, the magnetic nanoparticles form long chains oriented along the direction of the field. The behaviors of magnetic nanoparticles in both the fields must play an important role in changing the heat transfer and dielectric characteristics of the fluids. In this study, we visualized the movement of magnetic nanoparticles influenced by both the fields applied in-situ. It was found that the magnetic nanoparticles travel in the region near the electrode by the electric field and form long chains along the field direction by the magnetic field. It can be inferred that the movement of magnetic nanoparticles appears by both the fields, and the breakdown voltage of transformer oil based magnetic fluids might be influenced according to the dispersion of magnetic nanoparticles.

Thermal Conductivity Measurement of Molten Cu-Co Alloy Using an Electromagnetic Levitator Superimposed with a Static Magnetic Field

NASA Astrophysics Data System (ADS)

Nakamura, Yuki; Takahashi, Ryuji; Shoji, Eita; Kubo, Masaki; Tsukada, Takao; Uchikoshi, Masahito; Fukuyama, Hiroyuki

2017-12-01

The thermal conductivity of molten Cu-Co alloy with different compositions around the liquidus line temperature was measured by the periodic laser-heating method using an electromagnetic levitator superimposed with a static magnetic field to suppress convection in a levitated droplet sample. During the measurement, a static magnetic field of 10 T was applied to the levitated droplet. To confirm that the strength of the static magnetic field was sufficient to suppress convection in the droplet, numerical simulations were performed for the flow and thermal fields in an electromagnetically levitated droplet under a static magnetic field, and moreover, for the periodic laser-heating method to determine the thermal conductivity. It was found that the thermal conductivity of molten Cu-Co alloy increased gradually with increasing Cu composition up to 80 at. pct, beyond which it increased markedly and reached that of pure Cu. In addition, it was found that the composition dependence of the thermal conductivity can be explainable by the Wiedemann-Franz law.

Propulsion and Levitation with a Large Electrodynamic Wheel

NASA Astrophysics Data System (ADS)

Gaul, Nathan; Lane, Hannah

We constructed an electrodynamic wheel using a motorized bicycle wheel with a radius of 12 inches and 36 one-inch cube magnets attached to the rim of the wheel. The radial magnetic field on the outside of the wheel was maximized by arranging the magnets into a series of Halbach arrays which amplify the field on one side of the array and reduce it on the other side. Rotating the wheel produces a rapidly oscillating magnetic field. When a conductive metal ``track'' is placed in this area of strong magnetic flux, eddy currents are produced in the track. These eddy currents create magnetic fields that interact with the magnetic fields from the electrodynamic wheel. The interaction of the magnetic fields produces lift and drag forces on the track which were measured with force gauges. Measurements were taken at a variety of wheel speeds, and the results were compared to the theoretical prediction that there should be a linear relationship between the lift and drag forces with increasing wheel speed. Partial levitation was achieved with the current electrodynamic wheel. In the future, the wheel will be upgraded to include 72 magnets rather than 36 magnets. This will double the frequency at which the magnetic field oscillates, increasing the magnetic flux. Electrodynamic wheels have applications to the transportation industry, since multiple electrodynamic wheels could be used on a vehicle to produce a lift and propulsion force over a conductive track.

Field-Induced Transitions in Anisotropic Kondo Lattice — Application to CeT2Al10 —

NASA Astrophysics Data System (ADS)

Kikuchi, Taku; Hoshino, Shintaro; Shibata, Naokazu; Kuramoto, Yoshio

2017-09-01

The magnetic properties of an anisotropic Kondo lattice are investigated under a magnetic field using dynamical mean field theory and the continuous-time quantum Monte Carlo method. The magnetic phase diagram is determined from the temperature dependence of both uniform and staggered magnetizations in magnetic fields. We find a spin-flop transition inside the antiferromagnetic (AF) phase, whose transition field increases with increasing Kondo coupling while the AF transition temperature decreases. These results cannot be described by a simple spin Hamiltonian and are consistent with the experimental results of the field-induced transition observed in CeT2Al10 (T = Ru, Os). The anisotropic susceptibilities of CeT2Al10 are reproduced in the whole temperature range by incorporating the effects of the crystalline electric field (CEF) in the anisotropic Kondo lattice. We also propose a possible explanation for the difference in anisotropies between the magnetic susceptibility and AF moments observed in experiments.

Enhanced superconductivity of fullerenes

DOEpatents

Washington, II, Aaron L.; Teprovich, Joseph A.; Zidan, Ragaiy

2017-06-20

Methods for enhancing characteristics of superconductive fullerenes and devices incorporating the fullerenes are disclosed. Enhancements can include increase in the critical transition temperature at a constant magnetic field; the existence of a superconducting hysteresis over a changing magnetic field; a decrease in the stabilizing magnetic field required for the onset of superconductivity; and/or an increase in the stability of superconductivity over a large magnetic field. The enhancements can be brought about by transmitting electromagnetic radiation to the superconductive fullerene such that the electromagnetic radiation impinges on the fullerene with an energy that is greater than the band gap of the fullerene.

Nonmonotonic and anisotropic magnetoresistance effect in antiferromagnet CaMn2Bi2

NASA Astrophysics Data System (ADS)

Kawaguchi, N.; Urata, T.; Hatano, T.; Iida, K.; Ikuta, H.

2018-04-01

We found a large and unique magnetoresistance (MR) effect for CaMn2Bi2 . When the magnetic field was applied along the crystallographic c axis at low temperatures, the resistivity increased with the magnetic field and the MR ratio reached several hundred percent, but then it decreased with further increasing the applied field. In addition, the angle dependence measurement revealed a strong anisotropy. This compound is an antiferromagnetic semiconductor with a narrow band gap, and Mn atoms form a corrugated honeycomb lattice. Therefore, a frustration among the magnetic moments is expected, and we propose that our observations can be understood by a nonmonotonic modulation of magnetic fluctuation under the magnetic field.

Investigation of effect of solenoid magnet on emittances of ion beam from laser ablation plasma

NASA Astrophysics Data System (ADS)

Ikeda, Shunsuke; Romanelli, Mark; Cinquegrani, David; Sekine, Megumi; Kumaki, Masafumi; Fuwa, Yasuhiro; Kanesue, Takeshi; Okamura, Masahiro; Horioka, Kazuhiko

2014-02-01

A magnetic field can increase an ion current of a laser ablation plasma and is expected to control the change of the plasma ion current. However, the magnetic field can also make some fluctuations of the plasma and the effect on the beam emittance and the emission surface is not clear. To investigate the effect of a magnetic field, we extracted the ion beams under three conditions where without magnetic field, with magnetic field, and without magnetic field with higher laser energy to measure the beam distribution in phase space. Then we compared the relations between the plasma ion current density into the extraction gap and the Twiss parameters with each condition. We observed the effect of the magnetic field on the emission surface.

Investigation of effect of solenoid magnet on emittances of ion beam from laser ablation plasma.

PubMed

Ikeda, Shunsuke; Romanelli, Mark; Cinquegrani, David; Sekine, Megumi; Kumaki, Masafumi; Fuwa, Yasuhiro; Kanesue, Takeshi; Okamura, Masahiro; Horioka, Kazuhiko

2014-02-01

A magnetic field can increase an ion current of a laser ablation plasma and is expected to control the change of the plasma ion current. However, the magnetic field can also make some fluctuations of the plasma and the effect on the beam emittance and the emission surface is not clear. To investigate the effect of a magnetic field, we extracted the ion beams under three conditions where without magnetic field, with magnetic field, and without magnetic field with higher laser energy to measure the beam distribution in phase space. Then we compared the relations between the plasma ion current density into the extraction gap and the Twiss parameters with each condition. We observed the effect of the magnetic field on the emission surface.

Interaction of neutrons with layered magnetic media in oscillating magnetic field

NASA Astrophysics Data System (ADS)

Nikitenko, Yu. V.; Ignatovich, V. K.; Radu, F.

2011-06-01

New experimental possibilities of investigating layered magnetic structures in oscillating magnetic fields are discussed. Spin-flip and nonspin-flip neutron reflection and transmission probabilities show a frequency dependency near the magnetic neutron resonance condition. This allows to increase the precision of the static magnetic depth profile measurements of the magnetized matter. Moreover, this opens new possibilities of measuring the induction of the oscillating field inside the matter and determining the magnetic susceptibility of the oscillating magnetic field. Refraction of neutrons as they pass through a magnetic prism in the presence of an oscillating magnetic field is also investigated. A non-polarized neutron beam splits into eight spatially separated neutron beams, whose intensity and polarization depend on the strength and frequency of the oscillating field. Also, it is shown that the oscillating magnetic permeability of an angstrom-thick layer can be measured with a neutron wave resonator.

Computational studies of suppression of microwave gas breakdown by crossed dc magnetic field using electron fluid model

NASA Astrophysics Data System (ADS)

Zhao, Pengcheng; Guo, Lixin; Shu, Panpan

2016-08-01

The gas breakdown induced by a square microwave pulse with a crossed dc magnetic field is investigated using the electron fluid model, in which the accurate electron energy distribution functions are adopted. Simulation results show that at low gas pressures the dc magnetic field of a few tenths of a tesla can prolong the breakdown formation time by reducing the mean electron energy. With the gas pressure increasing, the higher dc magnetic field is required to suppress the microwave breakdown. The electric field along the microwave propagation direction generated due to the motion of electrons obviously increases with the dc magnetic field, but it is much less than the incident electric field. The breakdown predictions of the electron fluid model agree very well with the particle-in-cell-Monte Carlo collision simulations as well as the scaling law for the microwave gas breakdown.

Computer simulation and experimental self-assembly of irradiated glycine amino acid under magnetic fields: Its possible significance in prebiotic chemistry.

PubMed

Heredia, Alejandro; Colín-García, María; Puig, Teresa Pi I; Alba-Aldave, Leticia; Meléndez, Adriana; Cruz-Castañeda, Jorge A; Basiuk, Vladimir A; Ramos-Bernal, Sergio; Mendoza, Alicia Negrón

2017-12-01

Ionizing radiation may have played a relevant role in chemical reactions for prebiotic biomolecule formation on ancient Earth. Environmental conditions such as the presence of water and magnetic fields were possibly relevant in the formation of organic compounds such as amino acids. ATR-FTIR, Raman, EPR and X-ray spectroscopies provide valuable information about molecular organization of different glycine polymorphs under static magnetic fields. γ-glycine polymorph formation increases in irradiated samples interacting with static magnetic fields. The increase in γ-glycine polymorph agrees with the computer simulations. The AM1 semi-empirical simulations show a change in the catalyst behavior and dipole moment values in α and γ-glycine interaction with the static magnetic field. The simulated crystal lattice energy in α-glycine is also affected by the free radicals under the magnetic field, which decreases its stability. Therefore, solid α and γ-glycine containing free radicals under static magnetic fields might have affected the prebiotic scenario on ancient Earth by causing the oligomerization of glycine in prebiotic reactions. Copyright © 2017 Elsevier B.V. All rights reserved.

Arc Voltage Between Deion Grid Affected by Division of Arc in Magnetic Driven Arc

NASA Astrophysics Data System (ADS)

Inuzuka, Yutaro; Yamato, Takashi; Yamamoto, Shinji; Iwao, Toru

2016-10-01

Magnetic driven arc has been applied to DC breaker and fault current limiters. However, it has not been researched, especially stagnation and re-strike of the arc. In this paper, the arc voltage between deion grid affected by division of arc in magnetic driven arc and arc behavior are measured by using the oscilloscope and HSVC (High Speed Video Camera). As a result, arc voltage increased because of division of the arc. The arc mean moving speed increases with increasing the external magnetic field. However, when the arc was not stalemate, the arc moving speed does not change so much. The arc re-strike time increases and stalemate time decreases with increasing the external magnetic field. Therefore, the anode spot moving speed increases 8 times because arc re-strike occurs easily with the external magnetic field. Thus, the erosion of electrodes decreases and the arc movement becomes the smooth. When the arc is divided, the arc voltage increased because of the electrode fall voltage. Therefore, the arc voltage increases with increasing the number of deion grid.

Magnetically tunable control of light reflection in an unusual optical protein of squid

NASA Astrophysics Data System (ADS)

Iwasaka, M.; Tagawa, K.; Kikuchi, Y.

2017-05-01

In this study, we focused on the magnetically tunable changes in the reflectivity of the protein reflectin, which is generated by squid and used to control their body surface color for camouflage in seawater. A cellular organelle called an iridosome was separated from the skin of the dorsal part of a squid (cuttlefish; Sepia esculenta), and the light reflection dynamics of iridosomes containing reflectin were measured with and without exposure to a magnetic field of 500 mT. The magnetic field induced both steady and transient increases of reflection by the iridosomes, suggesting that a reversible conformational change occurred inside the iridosomes when the magnetic field was switched on and off. The intensity of light scattering perpendicular to the direction of the magnetic field increased when the magnetic field was applied. This kind of behavior (Type I) occurred in the majority (60%) of the measured samples. Another kind of reflection change (Type II) was a transient increase in light reflection. It is speculated that the wave-shaped structure of the lipid membrane connected to reflectin proteins changed to enhance the light reflection of reflectin by altering the diamagnetic orientation of the lipid layer in the bent part of the membrane under the applied magnetic field. Overall, our results suggest that the mesoscale lipid layers changed their alignment diamagnetically and the length between iridescent layers was modified by the magnetic field, even though no obvious change in alignment occurred at the microscale.

Indoor Positioning System Using Magnetic Field Map Navigation and an Encoder System

PubMed Central

Kim, Han-Sol; Seo, Woojin; Baek, Kwang-Ryul

2017-01-01

In the indoor environment, variation of the magnetic field is caused by building structures, and magnetic field map navigation is based on this feature. In order to estimate position using this navigation, a three-axis magnetic field must be measured at every point to build a magnetic field map. After the magnetic field map is obtained, the position of the mobile robot can be estimated with a likelihood function whereby the measured magnetic field data and the magnetic field map are used. However, if only magnetic field map navigation is used, the estimated position can have large errors. In order to improve performance, we propose a particle filter system that integrates magnetic field map navigation and an encoder system. In this paper, multiple magnetic sensors and three magnetic field maps (a horizontal intensity map, a vertical intensity map, and a direction information map) are used to update the weights of particles. As a result, the proposed system estimates the position and orientation of a mobile robot more accurately than previous systems. Also, when the number of magnetic sensors increases, this paper shows that system performance improves. Finally, experiment results are shown from the proposed system that was implemented and evaluated. PMID:28327513

Indoor Positioning System Using Magnetic Field Map Navigation and an Encoder System.

PubMed

Kim, Han-Sol; Seo, Woojin; Baek, Kwang-Ryul

2017-03-22

In the indoor environment, variation of the magnetic field is caused by building structures, and magnetic field map navigation is based on this feature. In order to estimate position using this navigation, a three-axis magnetic field must be measured at every point to build a magnetic field map. After the magnetic field map is obtained, the position of the mobile robot can be estimated with a likelihood function whereby the measured magnetic field data and the magnetic field map are used. However, if only magnetic field map navigation is used, the estimated position can have large errors. In order to improve performance, we propose a particle filter system that integrates magnetic field map navigation and an encoder system. In this paper, multiple magnetic sensors and three magnetic field maps (a horizontal intensity map, a vertical intensity map, and a direction information map) are used to update the weights of particles. As a result, the proposed system estimates the position and orientation of a mobile robot more accurately than previous systems. Also, when the number of magnetic sensors increases, this paper shows that system performance improves. Finally, experiment results are shown from the proposed system that was implemented and evaluated.

Inversion in the magnetic field effect of benzilketyl:SDS radical pair at high fields

NASA Astrophysics Data System (ADS)

Misra, Ajay; Haldar, Mintu; Chowdhury, Mihir

1999-05-01

The effect of a high magnetic field (up to 13.3 T) on radical pairs generated by the hydrogen abstraction of the photoexcited benzil triplet from sodium dodecyl sulphate has been studied. It was found that both the radical pair lifetime and the free radical yield increase with an increase of field from 0 to 4 T. A further increase of field causes a decrease in both. This reversal of the magnetic field effect (MFE) above 4 T has been explained in terms of relaxation mechanism and competition between a number of rate processes. The effect of reducing the micelle size on the MFE inversion has been discussed.

The influences of solar wind pressure and interplanetary magnetic field on global magnetic field and outer radiation belt electrons

DOE PAGES

Yu, J.; Li, L. Y.; Cao, J. B.; ...

2016-07-28

Using the Van Allen Probe in situ measured magnetic field and electron data, we examine the solar wind dynamic pressure and interplanetary magnetic field (IMF) effects on global magnetic field and outer radiation belt relativistic electrons (≥1.8 MeV). The dynamic pressure enhancements (>2 nPa) cause the dayside magnetic field increase and the nightside magnetic field reduction, whereas the large southward IMFs (B z-IMF < –2nT) mainly lead to the decrease of the nightside magnetic field. In the dayside increased magnetic field region (magnetic local time (MLT) ~ 06:00–18:00, and L > 4), the pitch angles of relativistic electrons are mainlymore » pancake distributions with a flux peak around 90° (corresponding anisotropic index A > 0.1), and the higher-energy electrons have stronger pancake distributions (the larger A), suggesting that the compression-induced betatron accelerations enhance the dayside pancake distributions. However, in the nighttime decreased magnetic field region (MLT ~ 18:00–06:00, and L ≥ 5), the pitch angles of relativistic electrons become butterfly distributions with two flux peaks around 45° and 135° (A < 0). The spatial range of the nighttime butterfly distributions is almost independent of the relativistic electron energy, but it depends on the magnetic field day-night asymmetry and the interplanetary conditions. The dynamic pressure enhancements can make the nighttime butterfly distribution extend inward. The large southward IMFs can also lead to the azimuthal expansion of the nighttime butterfly distributions. As a result, these variations are consistent with the drift shell splitting and/or magnetopause shadowing effect.« less

The influences of solar wind pressure and interplanetary magnetic field on global magnetic field and outer radiation belt electrons

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

Yu, J.; Li, L. Y.; Cao, J. B.

Using the Van Allen Probe in situ measured magnetic field and electron data, we examine the solar wind dynamic pressure and interplanetary magnetic field (IMF) effects on global magnetic field and outer radiation belt relativistic electrons (≥1.8 MeV). The dynamic pressure enhancements (>2 nPa) cause the dayside magnetic field increase and the nightside magnetic field reduction, whereas the large southward IMFs (B z-IMF < –2nT) mainly lead to the decrease of the nightside magnetic field. In the dayside increased magnetic field region (magnetic local time (MLT) ~ 06:00–18:00, and L > 4), the pitch angles of relativistic electrons are mainlymore » pancake distributions with a flux peak around 90° (corresponding anisotropic index A > 0.1), and the higher-energy electrons have stronger pancake distributions (the larger A), suggesting that the compression-induced betatron accelerations enhance the dayside pancake distributions. However, in the nighttime decreased magnetic field region (MLT ~ 18:00–06:00, and L ≥ 5), the pitch angles of relativistic electrons become butterfly distributions with two flux peaks around 45° and 135° (A < 0). The spatial range of the nighttime butterfly distributions is almost independent of the relativistic electron energy, but it depends on the magnetic field day-night asymmetry and the interplanetary conditions. The dynamic pressure enhancements can make the nighttime butterfly distribution extend inward. The large southward IMFs can also lead to the azimuthal expansion of the nighttime butterfly distributions. As a result, these variations are consistent with the drift shell splitting and/or magnetopause shadowing effect.« less

Low pressure arc discharge lamp apparatus with magnetic field generating means

DOEpatents

Grossman, Mark W.; George, William A.; Maya, Jakob

1987-01-01

A low-pressure arc discharge apparatus having a magnetic field generating means for increasing the output of a discharge lamp is disclosed. The magnetic field generating means, which in one embodiment includes a plurality of permanent magnets, is disposed along the lamp for applying a constant transverse magnetic field over at least a portion of the positive discharge column produced in the arc discharge lamp operating at an ambient temperature greater than about 25.degree. C.

Magnetic Field Noise Changes Effect of Combined Magnetic Field on Gravitropic Reaction of Cress Roots.

NASA Astrophysics Data System (ADS)

Bogatina, Nina; Kordyum, Elizabeth; Sheykina, Nadezhda

The gravitropic reaction of cress roots in combined magnetic field was studied in details. It was shown that the negative roots gravitropism observed at the frequency of alternating component of combined magnetic field adjusted to the Ca ion cyclotron frequency could be observed only at Nayquist magnetic field noise level under 5 nT/Hz. While the magnetic noise level was increasing the negative gravitropism was disappearing. The inhibition of gravitropic reaction was observed in all cases. The effect was accompanied by the changes in the noise spectrum generated by cress roots.

Magnetic field therapy: a review.

PubMed

Markov, Marko S

2007-01-01

There is increasing interest in using permanent magnets for therapeutic purposes encouraged by basic science publications and clinical reports. Magnetotherapy provides a non invasive, safe, and easy method to directly treat the site of injury, the source of pain and inflammation, and other types of disease. The physiological bases for the use of magnetic fields for tissue repair as well as physical principles of dosimetry and application of various magnetic fields are subjects of this review. Analysis of the magnetic and electromagnetic stimulation is followed by a discussion of the advantage of magnetic field stimulation compared with electric current and electric field stimulation.

Numerical investigation on splitting of ferrofluid microdroplets in T-junctions using an asymmetric magnetic field with proposed correlation

NASA Astrophysics Data System (ADS)

Aboutalebi, Mohammad; Bijarchi, Mohamad Ali; Shafii, Mohammad Behshad; Kazemzadeh Hannani, Siamak

2018-02-01

The studies surrounding the concept of microdroplets have seen a dramatic increase in recent years. Microdroplets have applications in different fields such as chemical synthesis, biology, separation processes and micro-pumps. This study numerically investigates the effect of different parameters such as Capillary number, Length of droplets, and Magnetic Bond number on the splitting process of ferrofluid microdroplets in symmetric T-junctions using an asymmetric magnetic field. The use of said field that is applied asymmetrically to the T-junction center helps us control the splitting of ferrofluid microdroplets. During the process of numerical simulation, a magnetic field with various strengths from a dipole located at a constant distance from the center of the T-junction was applied. The main advantage of this design is its control over the splitting ratio of daughter droplets and reaching various microdroplet sizes in a T-junction by adjusting the magnetic field strength. The results showed that by increasing the strength of the magnetic field, the possibility of asymmetric splitting of microdroplets increases in a way that for high values of field strength, high splitting ratios can be reached. Also, by using the obtained results at various Magnetic Bond numbers and performing curve fitting, a correlation is derived that can be used to accurately predict the borderline between splitting and non-splitting zones of microdroplets flow in micro T-junctions.

Electromagnetic Gun With Commutated Coils

NASA Technical Reports Server (NTRS)

Elliott, David G.

1991-01-01

Proposed electromagnetic gun includes electromagnet coil, turns of which commutated in sequence along barrel. Electrical current fed to two armatures by brushes sliding on bus bars in barrel. Interaction between armature currents and magnetic field from coil produces force accelerating armature, which in turn, pushes on projectile. Commutation scheme chosen so magnetic field approximately coincides and moves with cylindrical region defined by armatures. Scheme has disadvantage of complexity, but in return, enables designer to increase driving magnetic field without increasing armature current. Attainable muzzle velocity increased substantially.

The Anomalous Magnetoresistance of Graphite at High Magnetic Fields,

DTIC Science & Technology

1983-05-01

magnetoresistance anomaly. In the present work, the unusual properties of this fine structure (which is periodic in magnetic field H ) is examined in more detail...structure associated with the magnetoresistance anomly is (AH/ H ) - 0.1 T/25 T or about 0.4 Z. Thus, for typical magnetic field sweep rates (10 T in 10...magnetoresistance above 12 T have been associated by lye at al.2 with a linear increase in carrier concentration with increasing H .1 The anomalous increase

Rotatable Small Permanent Magnet Array for Ultra-Low Field Nuclear Magnetic Resonance Instrumentation: A Concept Study

PubMed Central

Vegh, Viktor; Reutens, David C.

2016-01-01

Object We studied the feasibility of generating the variable magnetic fields required for ultra-low field nuclear magnetic resonance relaxometry with dynamically adjustable permanent magnets. Our motivation was to substitute traditional electromagnets by distributed permanent magnets, increasing system portability. Materials and Methods The finite element method (COMSOL®) was employed for the numerical study of a small permanent magnet array to calculate achievable magnetic field strength, homogeneity, switching time and magnetic forces. A manually operated prototype was simulated and constructed to validate the numerical approach and to verify the generated magnetic field. Results A concentric small permanent magnet array can be used to generate strong sample pre-polarisation and variable measurement fields for ultra-low field relaxometry via simple prescribed magnet rotations. Using the array, it is possible to achieve a pre-polarisation field strength above 100 mT and variable measurement fields ranging from 20–50 μT with 200 ppm absolute field homogeneity within a field-of-view of 5 x 5 x 5 cubic centimetres. Conclusions A dynamic small permanent magnet array can generate multiple highly homogeneous magnetic fields required in ultra-low field nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI) instruments. This design can significantly reduce the volume and energy requirements of traditional systems based on electromagnets, improving portability considerably. PMID:27271886

Enhancement of crystallinity and magnetization in Fe3O4 nanoferrites induced by a high synthesized magnetic field

NASA Astrophysics Data System (ADS)

Ma, Xinxiu; Zhang, Zhanxian; Chen, Shijie; Lei, Wei; Xu, Yan; Lin, Jia; Luo, Xiaojing; Liu, Yongsheng

2018-05-01

A one-step hydrothermal method in different dc magnetic fields was used to prepare the Fe3O4 nanoparticles. Under the magnetic field, the average particle size decreased from 72.9 to 41.6 nm, meanwhile, the particle crystallinity is greatly improved. The magnetic field enhances its saturation magnetization and coercivity. The high magnetic field induce another magnetic structure. At room temperature, these nanoparticles exhibit superparamagnetism whose critical size (D sp) is about 26 nm. The Verwey transition is observed in the vicinity of 120 K of Fe3O4 nanoparticles. The effective magnetic anisotropy decreases with the increase of the test temperature because of the H c decreased.

Evidence of Magnetic Inversion in Single Ni Nanoparticles

DOE PAGES

Jiang, W.; Gartland, P.; Davidović, D.

2016-11-08

Superparamagnetism is an unwanted property of small magnetic particles where the magnetization of the particle flips randomly in time, due to thermal noise. There has been an increased attention in the properties of superparamagnetic particles recently, because of their potential applications in high density storage and medicine. In electron transport through single nanometer scale magnetic particles, the current can also cause the magnetization to flip randomly in time, even at low temperature. Here we show experimental evidence that when the current is then reduced towards zero in the applied magnetic field, the magnetization can reliably freeze about a higher anisotropy-energymore » minimum, where it tends to be inverted with respect to the magnetic field direction. Specifically, we use spin-unpolarized tunneling spectroscopy of discrete levels in single Ni particles 2–4 nm in diameter at mK-temperature, and find that the the magnetic excitation energy at the onset of current decreases when the magnetic field increases, reaching near degeneracy at nonzero magnetic field. We discuss the potential for spintronic applications such as current induced magnetization switching without any spin-polarized leads.« less

Evidence of Magnetic Inversion in Single Ni Nanoparticles

PubMed Central

Jiang, W.; Gartland, P.; Davidović, D.

2016-01-01

Superparamagnetism is an unwanted property of small magnetic particles where the magnetization of the particle flips randomly in time, due to thermal noise. There has been an increased attention in the properties of superparamagnetic particles recently, because of their potential applications in high density storage and medicine. In electron transport through single nanometer scale magnetic particles, the current can also cause the magnetization to flip randomly in time, even at low temperature. Here we show experimental evidence that when the current is then reduced towards zero in the applied magnetic field, the magnetization can reliably freeze about a higher anisotropy-energy minimum, where it tends to be inverted with respect to the magnetic field direction. Specifically, we use spin-unpolarized tunneling spectroscopy of discrete levels in single Ni particles 2–4 nm in diameter at mK-temperature, and find that the the magnetic excitation energy at the onset of current decreases when the magnetic field increases, reaching near degeneracy at nonzero magnetic field. We discuss the potential for spintronic applications such as current induced magnetization switching without any spin-polarized leads. PMID:27824076

The influence of magnetic fields on the wake field and stopping power of an ion-beam pulse in plasmas

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

Zhao, Xiao-ying; Zhang, Ya-ling; Duan, Wen-shan

2015-09-15

We performed two-dimensional particle-in-cell simulations to investigate how a magnetic field affects the wake field and stopping power of an ion-beam pulse moving in plasmas. The corresponding density of plasma electrons is investigated. At a weak magnetic field, the wakes exhibit typical V-shaped cone structures. As the magnetic field strengthens, the wakes spread and lose their typical V-shaped structures. At a sufficiently strong magnetic field, the wakes exhibit conversed V-shaped structures. Additionally, strengthening the magnetic field reduces the stopping power in regions of low and high beam density. However, the influence of the magnetic field becomes complicated in regions ofmore » moderate beam density. The stopping power increases in a weak magnetic field, but it decreases in a strong magnetic field. At high beam density and moderate magnetic field, two low-density channels of plasma electrons appear on both sides of the incident beam pulse trajectory. This is because electrons near the beam pulses will be attracted and move along with the beam pulses, while other electrons nearby are restricted by the magnetic field and cannot fill the gap.« less

The effect of external magnetic field on the bremsstrahlung nonlinear absorption mechanism in the interaction of high intensity short laser pulse with collisional underdense plasma

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

Sedaghat, M.; Ettehadi-Abari, M.; Shokri, B., E-mail: b-shokri@sbu.ac.ir

2015-03-15

Laser absorption in the interaction between ultra-intense femtosecond laser and solid density plasma is studied theoretically here in the intensity range Iλ{sup 2}≃10{sup 14}−10{sup 16}Wcm{sup −2}μm{sup 2}. The collisional effect is found to be significant when the incident laser intensity is less than 10{sup 16}Wcm{sup −2}μm{sup 2}. In the current work, the propagation of a high frequency electromagnetic wave, for underdense collisional plasma in the presence of an external magnetic field is investigated. It is shown that, by considering the effect of the ponderomotive force in collisional magnetized plasmas, the increase of laser pulse intensity leads to steepening of themore » electron density profile and the electron bunches of plasma makes narrower. Moreover, it is found that the wavelength of electric and magnetic fields oscillations increases by increasing the external magnetic field and the density distribution of electrons also grows in comparison with the unmagnetized collisional plasma. Furthermore, the spatial damping rate of laser energy and the nonlinear bremsstrahlung absorption coefficient are obtained in the collisional regime of magnetized plasma. The other remarkable result is that by increasing the external magnetic field in this case, the absorption coefficient increases strongly.« less

Magnetic property in the ferromagnetic superconductor UGe2 at pressures above the ferromagnetic critical pressure

NASA Astrophysics Data System (ADS)

Tateiwa, Naoyuki; Haga, Yoshinori; Matsuda, Tatsuma D.; Yamamoto, Etsuji; Ōnuki, Yoshichika; Fisk, Zachary

2013-08-01

We have studied the high-pressure magnetic property in UGe2 where ferromagnetic superconductivity appears under high pressure. In this study, we focus on the magnetic property at pressures above the ferromagnetic critical pressure P c =1.6 GPa. The temperature and magnetic field dependences of the dc-magnetization have been measured under high pressures up to 5.1 GPa by using a ceramic anvil high pressure cell. At pressures above P c , the magnetic susceptibility x shows a broad maximum around T χmax and the magnetization at 2.0 K shows an abrupt increase (metamagnetic transition) at H c . With increasing pressure, the peak structure in x becomes broader, and the peak position T χmax moves to the higher temperature region. The metamagnetic field H c increases rapidly with increasing pressure. At pressures above 4.1 GPa, x shows a simple temperature dependence, and the magnetization increases linearly with increasing field. These phenomena in UGe2 resemble to those in the intermetallic compounds of 3 d transition metals such as Co(S1- x Se x ) and YCo2. We discuss the experimental results by using the phenomenological spin-fluctuation theory.

Reactive sintering process of ferromagnetic MnBi under high magnetic fields

NASA Astrophysics Data System (ADS)

Mitsui, Yoshifuru; Umetsu, Rie Y.; Takahashi, Kohki; Koyama, Keiichi

2018-05-01

The magnetic field effect on the reactive sintering process of MnBi was investigated. Magnetic-field-induced enhancement of the reaction was found to be exhibited at the initial stages. The coercivity field decreased with an increase in the in-field annealing time. The kinetics of the reaction were in good agreement with the diffusion-controlled reaction model. It is suggested that the decrease in activation energy at the initial stages of reaction increased the amount of formed MnBi phases, resulting in enhancement of the reaction Mn + Bi to MnBi phase by in-field reactive sintering.

Trapping and Injecting Single Domain Walls in Magnetic Wire by Local Fields

NASA Astrophysics Data System (ADS)

Vázquez, Manuel; Basheed, G. A.; Infante, Germán; Del Real, Rafael P.

2012-01-01

A single domain wall (DW) moves at linearly increasing velocity under an increasing homogeneous drive magnetic field. Present experiments show that the DW is braked and finally trapped at a given position when an additional antiparallel local magnetic field is applied. That position and its velocity are further controlled by suitable tuning of the local field. In turn, the parallel local field of small amplitude does not significantly affect the effective wall speed at long distance, although it generates tail-to-tail and head-to-head pairs of walls moving along opposite directions when that field is strong enough.

Effects of magnetic field strength in the discharge channel on the performance of a multi-cusped field thruster

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

Hu, Peng; Liu, Hui; Gao, Yuanyuan

The performance characteristics of a Multi-cusped Field Thruster depending on the magnetic field strength in the discharge channel were investigated. Four thrusters with different outer diameters of the magnet rings were designed to change the magnetic field strength in the discharge channel. It is found that increasing the magnetic field strength could restrain the radial cross-field electron current and decrease the radial width of main ionization region, which gives rise to the reduction of propellant utilization and thruster performance. The test results in different anode voltage conditions indicate that both the thrust and anode efficiency are higher for the weakermore » magnetic field in the discharge channel.« less

Spatial buckling analysis of current-carrying nanowires in the presence of a longitudinal magnetic field accounting for both surface and nonlocal effects

NASA Astrophysics Data System (ADS)

Foroutan, Shahin; Haghshenas, Amin; Hashemian, Mohammad; Eftekhari, S. Ali; Toghraie, Davood

2018-03-01

In this paper, three-dimensional buckling behavior of nanowires was investigated based on Eringen's Nonlocal Elasticity Theory. The electric current-carrying nanowires were affected by a longitudinal magnetic field based upon the Lorentz force. The nanowires (NWs) were modeled based on Timoshenko beam theory and the Gurtin-Murdoch's surface elasticity theory. Generalized Differential Quadrature (GDQ) method was used to solve the governing equations of the NWs. Two sets of boundary conditions namely simple-simple and clamped-clamped were applied and the obtained results were discussed. Results demonstrated the effect of electric current, magnetic field, small-scale parameter, slenderness ratio, and nanowires diameter on the critical compressive buckling load of nanowires. As a key result, increasing the small-scale parameter decreased the critical load. By the same token, increasing the electric current, magnetic field, and slenderness ratio resulted in a decrease in the critical load. As the slenderness ratio increased, the effect of nonlocal theory decreased. In contrast, by expanding the NWs diameter, the nonlocal effect increased. Moreover, in the present article, the critical values of the magnetic field of strength and slenderness ratio were revealed, and the roles of the magnetic field, slenderness ratio, and NWs diameter on higher buckling loads were discussed.

Plasma Properties of Microwave Produced Plasma in a Toroidal Device

NASA Astrophysics Data System (ADS)

Singh, Ajay; Edwards, W. F.; Held, Eric

2011-10-01

We have modified a small tokamak, STOR-1M, on loan from University of Saskatchewan, to operate as a low-temperature (~5 eV) toroidal plasma machine with externally induced toroidal magnetic fields ranging from zero to ~50 G. The plasma is produced using microwave discharges at relatively high pressures. Microwaves are produced by a kitchen microwave-oven magnetron operating at 2.45 GHz in continuous operating mode, resulting in pulses ~0.5 s in duration. Initial measurements of plasma formation in this device with and without applied magnetic fields are presented. Plasma density and temperature profiles have been measured using Langmuir probes and the magnetic field profile inside the plasma has been obtained using Hall probes. When the discharge is created with no applied toroidal magnetic field, the plasma does not fill the entire torus due to high background pressure. However, when a toroidal magnetic field is applied, the plasma flows along the applied field, filling the torus. Increasing the applied magnetic field seems to aid plasma formation - the peak density increases and the density gradient becomes steeper. Above a threshold magnetic field, the plasma develops low-frequency density oscillations due to probable excitation of flute modes in the plasma.

Pulsed Electromagnetic Field Assisted in vitro Electroporation: A Pilot Study

NASA Astrophysics Data System (ADS)

Novickij, Vitalij; Grainys, Audrius; Lastauskienė, Eglė; Kananavičiūtė, Rūta; Pamedytytė, Dovilė; Kalėdienė, Lilija; Novickij, Jurij; Miklavčič, Damijan

2016-09-01

Electroporation is a phenomenon occurring due to exposure of cells to Pulsed Electric Fields (PEF) which leads to increase of membrane permeability. Electroporation is used in medicine, biotechnology, and food processing. Recently, as an alternative to electroporation by PEF, Pulsed ElectroMagnetic Fields (PEMF) application causing similar biological effects was suggested. Since induced electric field in PEMF however is 2-3 magnitudes lower than in PEF electroporation, the membrane permeabilization mechanism remains hypothetical. We have designed pilot experiments where Saccharomyces cerevisiae and Candida lusitaniae cells were subjected to single 100-250 μs electrical pulse of 800 V with and without concomitant delivery of magnetic pulse (3, 6 and 9 T). As expected, after the PEF pulses only the number of Propidium Iodide (PI) fluorescent cells has increased, indicative of membrane permeabilization. We further show that single sub-millisecond magnetic field pulse did not cause detectable poration of yeast. Concomitant exposure of cells to pulsed electric (PEF) and magnetic field (PMF) however resulted in the increased number PI fluorescent cells and reduced viability. Our results show increased membrane permeability by PEF when combined with magnetic field pulse, which can explain electroporation at considerably lower electric field strengths induced by PEMF compared to classical electroporation.

Pulsed Electromagnetic Field Assisted in vitro Electroporation: A Pilot Study

PubMed Central

Novickij, Vitalij; Grainys, Audrius; Lastauskienė, Eglė; Kananavičiūtė, Rūta; Pamedytytė, Dovilė; Kalėdienė, Lilija; Novickij, Jurij; Miklavčič, Damijan

2016-01-01

Electroporation is a phenomenon occurring due to exposure of cells to Pulsed Electric Fields (PEF) which leads to increase of membrane permeability. Electroporation is used in medicine, biotechnology, and food processing. Recently, as an alternative to electroporation by PEF, Pulsed ElectroMagnetic Fields (PEMF) application causing similar biological effects was suggested. Since induced electric field in PEMF however is 2–3 magnitudes lower than in PEF electroporation, the membrane permeabilization mechanism remains hypothetical. We have designed pilot experiments where Saccharomyces cerevisiae and Candida lusitaniae cells were subjected to single 100–250 μs electrical pulse of 800 V with and without concomitant delivery of magnetic pulse (3, 6 and 9 T). As expected, after the PEF pulses only the number of Propidium Iodide (PI) fluorescent cells has increased, indicative of membrane permeabilization. We further show that single sub-millisecond magnetic field pulse did not cause detectable poration of yeast. Concomitant exposure of cells to pulsed electric (PEF) and magnetic field (PMF) however resulted in the increased number PI fluorescent cells and reduced viability. Our results show increased membrane permeability by PEF when combined with magnetic field pulse, which can explain electroporation at considerably lower electric field strengths induced by PEMF compared to classical electroporation. PMID:27634482

Operating a magnetic nozzle helicon thruster with strong magnetic field

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

Takahashi, Kazunori, E-mail: kazunori@ecei.tohoku.ac.jp; Komuro, Atsushi; Ando, Akira

A pulsed axial magnetic field up to ∼2.8 kG is applied to a 26-mm-inner-diameter helicon plasma thruster immersed in a vacuum chamber, and the thrust is measured using a pendulum target. The pendulum is located 30-cm-downstream of the thruster, and the thruster rf power and argon flow rate are fixed at 1 kW and 70 sccm (which gives a chamber pressure of 0.7 mTorr). The imparted thrust increases as the applied magnetic field is increased and saturates at a maximum value of ∼9.5 mN for magnetic field above ∼2 kG. At the maximum magnetic field, it is demonstrated that the normalized plasma density, and the ionmore » flow energy in the magnetic nozzle, agree within ∼50% and of 10%, respectively, with a one-dimensional model that ignores radial losses from the nozzle. This magnetic nozzle model is combined with a simple global model of the thruster source that incorporates an artificially controlled factor α, to account for radial plasma losses to the walls, where α = 0 and 1 correspond to zero losses and no magnetic field, respectively. Comparison between the experiments and the model implies that the radial losses in the thruster source are experimentally reduced by the applied magnetic field to about 10% of that obtained from the no magnetic field model.« less

Ultra-wide range field-dependent measurements of the relaxivity of Gd1−xEuxVO4 nanoparticle contrast agents using a mechanical sample-shuttling relaxometer

PubMed Central

Chou, Ching-Yu; Abdesselem, Mouna; Bouzigues, Cedric; Chu, Minglee; Guiga, Angelo; Huang, Tai-Huang; Ferrage, Fabien; Gacoin, Thierry; Alexandrou, Antigoni; Sakellariou, Dimitris

2017-01-01

The current trend for Magnetic Resonance Imaging points towards higher magnetic fields. Even though sensitivity and resolution are increased in stronger fields, T1 contrast is often reduced, and this represents a challenge for contrast agent design. Field-dependent measurements of relaxivity are thus important to characterize contrast agents. At present, the field-dependent curves of relaxivity are usually carried out in the field range of 0 T to 2 T, using fast field cycling relaxometers. Here, we employ a high-speed sample shuttling device to switch the magnetic fields experienced by the nuclei between virtually zero field, and the center of any commercial spectrometer. We apply this approach on rare-earth (mixed Gadolinium-Europium) vanadate nanoparticles, and obtain the dispersion curves from very low magnetic field up to 11.7 T. In contrast to the relaxivity profiles of Gd chelates, commonly used for clinical applications, which display a plateau and then a decrease for increasing magnetic fields, these nanoparticles provide maximum contrast enhancement for magnetic fields around 1–1.5 T. These field-dependent curves are fitted using the so-called Magnetic Particle (MP) model and the extracted parameters discussed as a function of particle size and composition. We finally comment on the new possibilities offered by this approach. PMID:28317892

The magnitude of the magnetic field near the surface of a high-T(sub c) superconductor with a trapped flux

NASA Technical Reports Server (NTRS)

Overcash, Dan R.

1991-01-01

In 1986, much excitement was caused by the discovery of a class of materials that conducted electricity with zero resistance at temperatures above the boiling temperature of liquid nitrogen. This excitement was checked by the difficulties of manufacturing ceramics and the usefulness of high temperature superconductors that were restricted by their becoming high resistive conductors at small current densities. A lack of pinning of the magnetic field flux caused the return of high resistance as the current was increased in these materials. A study of the magnetic field near the surface of a high temperature superconductor is the first step in the search for a means of pinning the flux lines and increasing their critical current densities. The author found that a comparison between the defects in the surface of the superconductor and the magnetic field showed only a change in the field near the notch and the edge. No correlation was found between the surface grain or structure and the oscillations in the magnetic field. The observed changes in the magnetic field show resonances which may give an indication of the non-flux pinning in these superconductors. A flux pinning mechanism will increase the critical current densities; therefore, other methods of determining this field should be tried. The author proposes using a flux gate magnetometer with a detector wound on a ferrite core to measure the magnitude and direction of the magnetic field.

Pressure dependence of resistivity and magnetic properties in a Mn1.9Cr0.1Sb alloy

NASA Astrophysics Data System (ADS)

Repaka, D. V. Maheswar; Sharma, Vinay; Chanda, Amit; Mahendiran, R.; Ramanujan, R. V.

2017-12-01

We report magnetic-field and hydrostatic pressure dependent electrical resistivity and magnetic properties of a Mn1.9Cr0.1Sb alloy. Upon cooling, the magnetization of Mn1.9Cr0.1Sb exhibits a first-order ferrimagnetic to antiferromagnetic transition at the exchange inversion temperature, TS = 261 K under a 0.1 T magnetic field. Our experimental results show that TS decreases with increasing magnetic field but increase with increasing hydrostatic pressure. The pressure induced transition is accompanied by a large positive baro-resistance of 30.5% for a hydrostatic pressure change of 0.69 GPa. These results show that the lattice parameters as well as the bond distance between Mn-Mn atoms play a crucial role in the magnetic and electronic transport properties of Mn1.9Cr0.1Sb. This sample also exhibits a large inverse magnetocaloric effect with a magnetic entropy change of ΔSm = +6.75 J/kg.K and negative magnetoresistance (44.5%) for a field change of 5 T at TS in ambient pressure which may be useful for magnetic cooling and spintronics applications.

Technical Note: A Monte Carlo study of magnetic-field-induced radiation dose effects in mice

PubMed Central

Liao, Zhongxing; Melancon, Adam D.; Guindani, Michele; Followill, David S.; Tailor, Ramesh C.; Hazle, John D.; Court, Laurence E.

2015-01-01

Purpose: Magnetic fields are known to alter radiation dose deposition. Before patients receive treatment using an MRI-linear accelerator (MRI-Linac), preclinical studies are needed to understand the biological consequences of magnetic-field-induced dose effects. In the present study, the authors sought to identify a beam energy and magnetic field strength combination suitable for preclinical murine experiments. Methods: Magnetic field dose effects were simulated in a mouse lung phantom using various beam energies (225 kVp, 350 kVp, 662 keV [Cs-137], 2 MV, and 1.25 MeV [Co-60]) and magnetic field strengths (0.75, 1.5, and 3 T). The resulting dose distributions were compared with those in a simulated human lung phantom irradiated with a 6 or 8 MV beam and orthogonal 1.5 T magnetic field. Results: In the human lung phantom, the authors observed a dose increase of 45% and 54% at the soft-tissue-to-lung interface and a dose decrease of 41% and 48% at the lung-to-soft-tissue interface for the 6 and 8 MV beams, respectively. In the mouse simulations, the magnetic fields had no measurable effect on the 225 or 350 kVp dose distribution. The dose increases with the Cs-137 beam for the 0.75, 1.5, and 3 T magnetic fields were 9%, 29%, and 42%, respectively. The dose decreases were 9%, 21%, and 37%. For the 2 MV beam, the dose increases were 16%, 33%, and 31% and the dose decreases were 9%, 19%, and 30%. For the Co-60 beam, the dose increases were 19%, 54%, and 44%, and the dose decreases were 19%, 42%, and 40%. Conclusions: The magnetic field dose effects in the mouse phantom using a Cs-137, 3 T combination or a Co-60, 1.5 or 3 T combination most closely resemble those in simulated human treatments with a 6 MV, 1.5 T MRI-Linac. The effects with a Co-60, 1.5 T combination most closely resemble those in simulated human treatments with an 8 MV, 1.5 T MRI-Linac. PMID:26328998

Construction of orthogonal synchronized bi-directional field to enhance heating efficiency of magnetic nanoparticles.

PubMed

Chen, Shih-Wei; Lai, Jr-Jie; Chiang, Chen-Li; Chen, Cheng-Lung

2012-06-01

Magnetic hyperthermia using magnetic nanoparticles (MNPs) has attracted considerable attention as one of the promising tumor therapy. The study has been developed under single magnetic field. Recently, we found that the immobile MNP may generate more heat under two synchronous ac magnetic fields than traditional single and circular polarized fields based on model simulation result. According to this finding we constructed an orthogonal synchronized bi-directional field (OSB field). The system contained two LC resonant inverters (L: inductor, C: capacitor) and both vertical and transverse ac magnetic fields were generated by two Helmholtz coils. To reduce the interference, the axis directional of two coils were arranged orthogonally. The experiments showed that the heating ability of aggregated MNPs is greatly enhanced under this newly designed OSB field without increasing the strength of magnetic field. The OSB field system provides a promising way for future clinical hyperthermia.

Construction of orthogonal synchronized bi-directional field to enhance heating efficiency of magnetic nanoparticles

NASA Astrophysics Data System (ADS)

Chen, Shih-Wei; Lai-Jie, Jr.; Chiang, Chen-Li; Chen, Cheng-Lung

2012-06-01

Magnetic hyperthermia using magnetic nanoparticles (MNPs) has attracted considerable attention as one of the promising tumor therapy. The study has been developed under single magnetic field. Recently, we found that the immobile MNP may generate more heat under two synchronous ac magnetic fields than traditional single and circular polarized fields based on model simulation result. According to this finding we constructed an orthogonal synchronized bi-directional field (OSB field). The system contained two LC resonant inverters (L: inductor, C: capacitor) and both vertical and transverse ac magnetic fields were generated by two Helmholtz coils. To reduce the interference, the axis directional of two coils were arranged orthogonally. The experiments showed that the heating ability of aggregated MNPs is greatly enhanced under this newly designed OSB field without increasing the strength of magnetic field. The OSB field system provides a promising way for future clinical hyperthermia.

Field dependence of the magnetic correlations of the frustrated magnet SrDy 2 O 4

DOE PAGES

Gauthier, N.; Fennell, A.; Prévost, B.; ...

2017-05-30

Tmore » he frustrated magnet SrDy 2 O 4 exhibits a field-induced phase with a magnetization plateau at 1 / 3 of the saturation value for magnetic fields applied along the b axis. We report here a neutron scattering study of the nature and symmetry of the magnetic order in this field-induced phase. Below ≈ 0.5 K, there are strong hysteretic effects, and the order is short- or long-ranged for zero-field and field cooling, respectively. We find that the long-range ordered magnetic structure within the zigzag chains is identical to that expected for the one-dimensional axial next-nearest neighbor Ising (ANNNI) model in longitudinal fields. he long-range ordered structure in field contrasts with the short-range order found at zero field, and is most likely reached through enhanced quantum fluctuations with increasing fields.« less

Field dependence of the magnetic correlations of the frustrated magnet SrDy2O4

NASA Astrophysics Data System (ADS)

Gauthier, N.; Fennell, A.; Prévost, B.; Désilets-Benoit, A.; Dabkowska, H. A.; Zaharko, O.; Frontzek, M.; Sibille, R.; Bianchi, A. D.; Kenzelmann, M.

2017-05-01

The frustrated magnet SrDy2O4 exhibits a field-induced phase with a magnetization plateau at 1 /3 of the saturation value for magnetic fields applied along the b axis. We report here a neutron scattering study of the nature and symmetry of the magnetic order in this field-induced phase. Below T ≈0.5 K, there are strong hysteretic effects, and the order is short- or long-ranged for zero-field and field cooling, respectively. We find that the long-range ordered magnetic structure within the zigzag chains is identical to that expected for the one-dimensional axial next-nearest neighbor Ising (ANNNI) model in longitudinal fields. The long-range ordered structure in field contrasts with the short-range order found at zero field, and is probably reached through enhanced quantum fluctuations with increasing fields.

Effect of electric field on the magnetic characteristics of a ferromagnetic nanosemiconductor

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

Kozhushner, M. A., E-mail: kozhushner@gmail.com; Lidskii, B. V.; Posvyanskii, V. S.

A theory is developed to describe the effect of an electric field on the magnetization of a thin ferromagnetic semiconductor plate. It is shown that the magnetic moment density is nonuniform under these conditions and that the total magnetic moment and its density depend on the electric field and the temperature. An electric field is found to increase the Curie temperature, and an inflection point is detected in the temperature dependence of the derivative of the total magnetic moment with respect to temperature.

Low pressure arc discharge lamp apparatus with magnetic field generating means

DOEpatents

Grossman, M.W.; George, W.A.; Maya, J.

1987-10-06

A low-pressure arc discharge apparatus having a magnetic field generating means for increasing the output of a discharge lamp is disclosed. The magnetic field generating means, which in one embodiment includes a plurality of permanent magnets, is disposed along the lamp for applying a constant transverse magnetic field over at least a portion of the positive discharge column produced in the arc discharge lamp operating at an ambient temperature greater than about 25 C. 3 figs.

Effect of axial magnetic field on a 2.45 GHz permanent magnet ECR ion source.

PubMed

Nakamura, T; Wada, H; Asaji, T; Furuse, M

2016-02-01

Herein, we conduct a fundamental study to improve the generation efficiency of a multi-charged ion source using argon. A magnetic field of our electron cyclotron resonance ion source is composed of a permanent magnet and a solenoid coil. Thereby, the axial magnetic field in the chamber can be tuned. Using the solenoid coil, we varied the magnetic field strength in the plasma chamber and measured the ion beam current extracted at the electrode. We observed an approximately three times increase in the Ar(4+) ion beam current when the magnetic field on the extractor-electrode side of the chamber was weakened. From our results, we can confirm that the multi-charged ion beam current changes depending on magnetic field intensity in the plasma chamber.

Radio frequency magnetic field effects on molecular dynamics and iron uptake in cage proteins.

PubMed

Céspedes, Oscar; Inomoto, Osamu; Kai, Shoichi; Nibu, Yoshinori; Yamaguchi, Toshio; Sakamoto, Nobuyoshi; Akune, Tadahiro; Inoue, Masayoshi; Kiss, Takanobu; Ueno, Shoogo

2010-05-01

The protein ferritin has a natural ferrihydrite nanoparticle that is superparamagnetic at room temperature. For native horse spleen ferritin, we measure the low field magnetic susceptibility of the nanoparticle as 2.2 x 10(-6) m(3) kg(-1) and its Néel relaxation time at about 10(-10) s. Superparamagnetic nanoparticles increase their internal energy when exposed to radio frequency magnetic fields due to the lag between magnetization and applied field. The energy is dissipated to the surrounding peptidic cage, altering the molecular dynamics and functioning of the protein. This leads to an increased population of low energy vibrational states under a magnetic field of 30 microT at 1 MHz, as measured via Raman spectroscopy. After 2 h of exposure, the proteins have a reduced iron intake rate of about 20%. Our results open a new path for the study of non-thermal bioeffects of radio frequency magnetic fields at the molecular scale.

Reducing blood viscosity with magnetic fields

NASA Astrophysics Data System (ADS)

Tao, R.; Huang, K.

2011-07-01

Blood viscosity is a major factor in heart disease. When blood viscosity increases, it damages blood vessels and increases the risk of heart attacks. Currently, the only method of treatment is to take drugs such as aspirin, which has, however, several unwanted side effects. Here we report our finding that blood viscosity can be reduced with magnetic fields of 1 T or above in the blood flow direction. One magnetic field pulse of 1.3 T lasting ˜1 min can reduce the blood viscosity by 20%-30%. After the exposure, in the absence of magnetic field, the blood viscosity slowly moves up, but takes a couple of hours to return to the original value. The process is repeatable. Reapplying the magnetic field reduces the blood viscosity again. By selecting the magnetic field strength and duration, we can keep the blood viscosity within the normal range. In addition, such viscosity reduction does not affect the red blood cells’ normal function. This technology has much potential for physical therapy.

Study of magnetic field expansion using a plasma generator for space radiation active protection

NASA Astrophysics Data System (ADS)

Jia, Xiang-Hong; Jia, Shao-Xia; Xu, Feng; Bai, Yan-Qiang; Wan, Jun; Liu, Hong-Tao; Jiang, Rui; Ma, Hong-Bo; Wang, Shou-Guo

2013-09-01

There are many active protecting methods including Electrostatic Fields, Confined Magnetic Field, Unconfined Magnetic Field and Plasma Shielding etc. for defending the high-energy solar particle events (SPE) and Galactic Cosmic Rays (GCR) in deep space exploration. The concept of using cold plasma to expand a magnetic field is the best one of all possible methods so far. The magnetic field expansion caused by plasma can improve its protective efficiency of space particles. One kind of plasma generator has been developed and installed into the cylindrical permanent magnet in the eccentric. A plasma stream is produced using a helical-shaped antenna driven by a radio-frequency (RF) power supply of 13.56 MHz, which exits from both sides of the magnet and makes the magnetic field expand on one side. The discharging belts phenomenon is similar to the Earth's radiation belt, but the mechanism has yet to be understood. A magnetic probe is used to measure the magnetic field expansion distributions, and the results indicate that the magnetic field intensity increases under higher increments of the discharge power.

Magnetic field amplification by the r-mode instability

NASA Astrophysics Data System (ADS)

Chugunov, A. I.; Friedman, J. L.; Lindblom, L.; Rezzolla, L.

2017-12-01

We discuss the magnetic field enhancement by unstable r-modes (driven by the gravitational radiation reaction force) in rotating stars. In the absence of a magnetic field, gravitational radiation exponentially increases the r-mode amplitude α, and accelerates differential rotation (secular motion of fluid elements). For a magnetized star, differential rotation enhances the magnetic field energy. Rezzolla et al (2000-2001) argued that if the magnetic energy grows faster than the gravitational radiation reaction force pumps energy into the r-modes, then the r-mode instability is suppressed. Chugunov (2015) demonstrated that without gravitational radiation, differential rotation can be treated as a degree of freedom decoupled from the r-modes and controlled by the back reaction of the magnetic field. In particular, the magnetic field windup does not damp r-modes. Here we discuss the effect of the back reaction of the magnetic field on differential rotation of unstable r-modes, and show that it limits the generated magnetic field and the magnetic energy growth rate preventing suppression of the r-mode instability by magnetic windup at low saturation amplitudes, α ≪ 1, predicted by current models.

Effect of external magnetic field on locking range of spintronic feedback nano oscillator

NASA Astrophysics Data System (ADS)

Singh, Hanuman; Konishi, K.; Bose, A.; Bhuktare, S.; Miwa, S.; Fukushima, A.; Yakushiji, K.; Yuasa, S.; Kubota, H.; Suzuki, Y.; Tulapurkar, A. A.

2018-05-01

In this work we have studied the effect of external applied magnetic field on the locking range of spintronic feedback nano oscillator. Injection locking of spintronic feedback nano oscillator at integer and fractional multiple of its auto oscillation frequency was demonstrated recently. Here we show that the locking range increases with increasing external magnetic field. We also show synchronization of spintronic feedback nano oscillator at integer (n=1,2,3) multiples of auto oscillation frequency and side band peaks at higher external magnetic field values. We have verified experimental results with macro-spin simulation using similar conditions as used for the experimental study.

The observation of resistivity change on the ultrasonic treated Fe-Cr ODS sinter alloy under magnetic field influence

NASA Astrophysics Data System (ADS)

Silalahi, Marzuki; Purwanto, Setyo; Mujamilah; Dimyati, Arbi

2018-03-01

About the observation of resistivity change on the ultrasonic treated Fe-Cr ODS sinter alloy under magnetic field influence. This paper reported about the observation of the resistivity change in the ultrasonic pre-treated Fe-Cr ODS sinter alloy under the influence of magnetic field at the Center for Science and Technology of Advanced Material, Nuclear Energy Agency of Indonesia. Fe-Cr ODS alloy were sinthesized by vacuum sintering of Fe- and Cr-powder dispersed Y2O3. However, before sintering the powder mixture was subjected to the irradiation process by ultrasonic for 50 hours at 20 kHz and then isostatic pressed up to 50.91 MPa to form a coin of 10 mm in diameter. LCR meassurement revealed the decreasing of resistivity about 3 times by increasing of applied magnetic field from 0 to 70 mT. In addition, VSM meassurement was performed on both as powder material and as sintered sample. The results showed increasing the magnetization with increasing magnetic field and the curve exhibits almost exact symmetry S-form with small hysterese indicating fast changing magnetization and demagnetization capability without energy loss. This opens strong speculations about the existence of magnetoresistant property of the material which is important for many application in field of sensors or electro magnetic valves.

Transverse spin relaxation and diffusion-constant measurements of spin-polarized 129Xe nuclei in the presence of a magnetic field gradient

PubMed Central

Liu, Xiaohu; Chen, Chang; Qu, Tianliang; Yang, Kaiyong; Luo, Hui

2016-01-01

The presence of a magnetic field gradient in a sample cell containing spin-polarized 129Xe atoms will cause an increased relaxation rate. We measured the transverse spin relaxation time of 129Xe verse the applied magnetic field gradient and the cell temperature. We then compared the different transverse spin relaxation behavior of dual isotopes of xenon (129Xe and 131Xe) due to magnetic field gradient in the same cell. The experiment results show the residual magnetic field gradient can be measured and compensated by applying a negative magnetic gradient in the sample cell. The transverse spin relaxation time of 129Xe could be increased 2–7 times longer when applying an appropriate magnetic field gradient. The experiment results can also be used to determine the diffusion constant of 129Xe in H2 and N2 to be 0.4 ± 0.26 cm2/sec and 0.12 ± 0.02 cm2/sec. The results are close with theoretical calculation. PMID:27049237

Taking the temperature of the interiors of magnetically heated nanoparticles.

PubMed

Dong, Juyao; Zink, Jeffrey I

2014-05-27

The temperature increase inside mesoporous silica nanoparticles induced by encapsulated smaller superparamagnetic nanocrystals in an oscillating magnetic field is measured using a crystalline optical nanothermometer. The detection mechanism is based on the temperature-dependent intensity ratio of two luminescence bands in the upconversion emission spectrum of NaYF4:Yb(3+), Er(3+). A facile stepwise phase transfer method is developed to construct a dual-core mesoporous silica nanoparticle that contains both a nanoheater and a nanothermometer in its interior. The magnetically induced heating inside the nanoparticles varies with different experimental conditions, including the magnetic field induction power, the exposure time to the magnetic field, and the magnetic nanocrystal size. The temperature increase of the immediate nanoenvironment around the magnetic nanocrystals is monitored continuously during the magnetic oscillating field exposure. The interior of the nanoparticles becomes much hotter than the macroscopic solution and cools to the temperature of the ambient fluid on a time scale of seconds after the magnetic field is turned off. This continuous absolute temperature detection method offers quantitative insight into the nanoenvironment around magnetic materials and opens a path for optimizing local temperature controls for physical and biomedical applications.

Unsteady magnetohydrodynamics micropolar fluid in boundary layer flow past a sphere influenced by magnetic fluid

NASA Astrophysics Data System (ADS)

Pratomo, Rizky Verdyanto; Widodo, Basuki; Adzkiya, Dieky

2017-12-01

Research about fluid flow was very interesting because have a lot of advantages and it can be applied in many aspects of life. The study on fluid flow which is now widely studied is on magnetohydrodynamic (MHD). Magnetohydrodynamic is a conductive and electrical in a magnetic field. This paper considers the effect of unsteady magnetic fields on the flow of magneto-hydrodynamic fluid on the boundary layer that flows past a sphere in micropolar fluid influenced by magnetic field. Our approach is as follows. First, we construct a mathematical model and then the system of equations obtained will be solved numerically using the Keller-Box scheme. Then the system is simulated to assess its effect on the fluid flow velocity profile and the profile of microrotation particles. The result of this research indicates, that when the magnetic parameters increase, then velocity profile increases. If material parameters increase, then velocity profile decreases and magnetic parameters increase for n = 0. For n = 0.5, if magnetic parameters increase, then microrotation profile decreases.

Wave propagation characteristics of a magnetic granular chain

NASA Astrophysics Data System (ADS)

Leng, Dingxin; Liu, Guijie; Sun, Lingyu; Wang, Xiaojie

2017-10-01

We investigate the wave propagation characteristics of a horizontal alignment of magnetic grains under a non-uniform magnetic field. The magnetic force of each grain is obtained using Maxwell's principle. The contact interaction of grains is based on Hertz potential. The effects of magnetic field strength on the dynamic responses of a granular chain under strong, intermediate, and weak amplitudes of incident impulses in comparison with static precompression force are studied. Different wave propagation modes induced by the magnetic field are observed. The applied field strength demonstrably reinforces the granular-position-dependent behaviors of decreasing amplitude and increasing wave propagation velocity. The magnetic field-induced features of a magnetic granular chain have potential applications in adaptive structures for shock attenuation.

Observation of the inductive to helicon mode transition in a weakly magnetized solenoidal inductive discharge

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

Lee, Min-Hyong; Chung, Chin-Wook

2008-10-13

A mode transition from an inductive mode to a helicon mode is observed in a solenoidal inductive discharge immersed in a weak dc magnetic field. The measured electron temperature and the plasma density at the reactor radial boundary show a sudden increase when the magnetic field strength reaches the critical value and the electron cyclotron frequency exceeds the rf driving frequency. These increases are due to the electron heating by the helicon wave. Such increases in the temperature and the density are not observed at the plasma center because the helicon wave cannot propagate to the center of the solenoidalmore » type reactor unless the magnetic field is very high. These results show that the transition of the discharge from the inductive to the helicon mode occurs at the critical magnetic field strength.« less

Controllable transition from positive space charge to negative space charge in an inverted cylindrical magnetron

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

Rane, R., E-mail: ramu@ipr.res.in; Ranjan, M.; Mukherjee, S.

2016-01-15

The combined effect of magnetic field (B), gas pressure (P), and the corresponding discharge voltage on the discharge properties of argon in inverted cylindrical magnetron has been investigated. In the experiment, anode is biased with continuous 10 ms sinusoidal half wave. It is observed that at a comparatively higher magnetic field (i.e., >200 gauss) and lower operating pressure (i.e., <1 × 10{sup −3} mbar), the discharge extinguishes and demands a high voltage to reignite. Discharge current increases with increase in magnetic field and starts reducing at sufficiently higher magnetic field for a particular discharge voltage due to restricted electron diffusion towards the anode.more » It is observed that B/P ratio plays an important role in sustaining the discharge and is constant for a discharge voltage. The discharge is transformed to negative space charge regime from positive space charge regime at certain B/P ratio and this ratio varies linearly with the discharge voltage. The space charge reversal is indicated by the radial profile of the floating potential and plasma potential in between two electrodes for different magnetic fields. At a particular higher magnetic field (beyond 100 gauss), the floating potential increases gradually with the radial distance from cathode, whereas it remains almost constant at lower magnetic field.« less

Static magnetic field reduced exogenous oligonucleotide uptake by spermatozoa using magnetic nanoparticle gene delivery system

NASA Astrophysics Data System (ADS)

Katebi, Samira; Esmaeili, Abolghasem; Ghaedi, Kamran

2016-03-01

Spermatozoa could introduce exogenous oligonucleotides of interest to the oocyte. The most important reason of low efficiency of sperm mediated gene transfer (SMGT) is low uptake of exogenous DNA by spermatozoa. The aim of this study was to evaluate the effects of static magnetic field on exogenous oligonucleotide uptake of spermatozoa using magnetofection method. Magnetic nanoparticles (MNPs) associated with the labeled oligonucleotides were used to increase the efficiency of exogenous oligonucleotide uptake by rooster spermatozoa. We used high-field/high-gradient magnet (NdFeB) to enhance and accelerate exogenous DNA sedimentation at the spermatozoa surface. Flow cytometry analysis was performed to measure viability and percentage of exogenous oligonucleotide uptake by sperm. Flow cytometry analysis showed a significant increase in exogenous oligonucleotide uptake by rooster spermatozoa (P<0.001) when spermatozoa were incubated in exogenous oligonucleotide solution and MNPs. However, by applying static magnetic field during magnetofection method, a significant decrease in exogenous oligonucleotide uptake was observed (P<0.05). Findings of this study showed that MNPs were effective to increase exogenous oligonucleotide uptake by rooster spermatozoa; however unlike others studies, static magnetic field, was not only ineffective to enhance exogenous oligonucleotide uptake by rooster spermatozoa but also led to reduction in efficiency of magnetic nanoparticles in gene transfer.

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.

High-Field Magnetization Study of R_{2} {Fe}_{17} {N}_{2} R 2 Fe 17 N 2 ( R = {Ho} R = Ho and Er) Nitrides

NASA Astrophysics Data System (ADS)

Tereshina, I. S.; Tereshina-Chitrova, E. A.; Pelevin, I. A.; Doerr, M.; Law, J. M.; Verbetski, V. N.; Salamova, A. A.

2018-03-01

The structure and magnetic properties of the nitrided compounds R2Fe_{17}N2 (R = Ho and Er) are studied. The type of crystal structure Th2Ni_{17} is preserved upon nitrogenation, and the relative unit cell volume Δ V{/}V increase exceeds 6%. Magnetic studies are performed in fields up to 60 T at 4.2 K on aligned powder samples. Field-induced spin-reorientation (SR) transitions are observed in the M( H) curves of R2Fe_{17}N2. Unlike the parent R2Fe_{17} compounds, where the magnetization increases in steps as the field grows stronger, R2Fe_{17}N2 demonstrate a gradual increase in magnetization. It is indicative of the change of the SR transition from first to the second type. Extrapolation of magnetization curves to the theoretical value of magnetization in the forced ferromagnetic state yields the coefficient of the inter-sublattice R-Fe exchange interaction. The inter-sublattice exchange is found to decrease upon nitrogenation.

Fabrication and viscoelastic characteristics of waste tire rubber based magnetorheological elastomer

NASA Astrophysics Data System (ADS)

Ubaidillah; Choi, H. J.; Mazlan, S. A.; Imaduddin, F.; Harjana

2016-11-01

In this study, waste tire rubber (WTR) was successfully converted into magnetorheological (MR) elastomer via high-pressure and high-temperature reclamation. The physical and rheological properties of WTR based MR elastomers were assessed for performance. The revulcanization process was at the absence of magnetic fields. Thus, the magnetizable particles were allowed to distribute randomly. To confirm the particle dispersion in the MR elastomer matrix, an observation by scanning electron microscopy was used. The magnetization saturation and other magnetic properties were obtained through vibrating sample magnetometer. Rheological properties including MR effect were examined under oscillatory loadings in the absence and presence of magnetic fields using rotational rheometer. The WTR based MR elastomer exhibited tunable intrinsic properties under presentation of magnetic fields. The storage and loss modulus, along with the loss factor, changed with increases in frequency and during magnetization. Interestingly, a Payne effect phenomenon was seen in all samples during dynamic swept strain testing. The Payne effect was significantly increased with incremental increases in the magnetic field. This phenomenon was interpreted as the process of formation-destruction-reformation undergone by the internal network chains in the MR elastomers.

The Uncertainty of Local Background Magnetic Field Orientation in Anisotropic Plasma Turbulence

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

Gerick, F.; Saur, J.; Papen, M. von, E-mail: felix.gerick@uni-koeln.de

In order to resolve and characterize anisotropy in turbulent plasma flows, a proper estimation of the background magnetic field is crucially important. Various approaches to calculating the background magnetic field, ranging from local to globally averaged fields, are commonly used in the analysis of turbulent data. We investigate how the uncertainty in the orientation of a scale-dependent background magnetic field influences the ability to resolve anisotropy. Therefore, we introduce a quantitative measure, the angle uncertainty, that characterizes the uncertainty of the orientation of the background magnetic field that turbulent structures are exposed to. The angle uncertainty can be used asmore » a condition to estimate the ability to resolve anisotropy with certain accuracy. We apply our description to resolve the spectral anisotropy in fast solar wind data. We show that, if the angle uncertainty grows too large, the power of the turbulent fluctuations is attributed to false local magnetic field angles, which may lead to an incorrect estimation of the spectral indices. In our results, an apparent robustness of the spectral anisotropy to false local magnetic field angles is observed, which can be explained by a stronger increase of power for lower frequencies when the scale of the local magnetic field is increased. The frequency-dependent angle uncertainty is a measure that can be applied to any turbulent system.« less

Spin dynamics of random Ising chain in coexisting transverse and longitudinal magnetic fields

NASA Astrophysics Data System (ADS)

Liu, Zhong-Qiang; Jiang, Su-Rong; Kong, Xiang-Mu; Xu, Yu-Liang

2017-05-01

The dynamics of the random Ising spin chain in coexisting transverse and longitudinal magnetic fields is studied by the recursion method. Both the spin autocorrelation function and its spectral density are investigated by numerical calculations. It is found that system's dynamical behaviors depend on the deviation σJ of the random exchange coupling between nearest-neighbor spins and the ratio rlt of the longitudinal and the transverse fields: (i) For rlt = 0, the system undergoes two crossovers from N independent spins precessing about the transverse magnetic field to a collective-mode behavior, and then to a central-peak behavior as σJ increases. (ii) For rlt ≠ 0, the system may exhibit a coexistence behavior of a collective-mode one and a central-peak one. When σJ is small (or large enough), system undergoes a crossover from a coexistence behavior (or a disordered behavior) to a central-peak behavior as rlt increases. (iii) Increasing σJ depresses effects of both the transverse and the longitudinal magnetic fields. (iv) Quantum random Ising chain in coexisting magnetic fields may exhibit under-damping and critical-damping characteristics simultaneously. These results indicate that changing the external magnetic fields may control and manipulate the dynamics of the random Ising chain.

Tunable magnetic vortex resonance in a potential well

NASA Astrophysics Data System (ADS)

Warnicke, P.; Wohlhüter, P.; Suszka, A. K.; Stevenson, S. E.; Heyderman, L. J.; Raabe, J.

2017-11-01

We use frequency-resolved x-ray microscopy to fully characterize the potential well of a magnetic vortex in a soft ferromagnetic permalloy square. The vortex core is excited with magnetic broadband pulses and simultaneously displaced with a static magnetic field. We observe a frequency increase (blueshift) in the gyrotropic mode of the vortex core with increasing bias field. Supported by micromagnetic simulations, we show that this frequency increase is accompanied by internal deformation of the vortex core. The ability to modify the inner structure of the vortex core provides a mechanism to control the dynamics of magnetic vortices.

A numerical simulation of the water vapor bubble rising in ferrofluid by volume of fluid model in the presence of a magnetic field

NASA Astrophysics Data System (ADS)

Shafiei Dizaji, A.; Mohammadpourfard, M.; Aminfar, H.

2018-03-01

Multiphase flow is one of the most complicated problems, considering the multiplicity of the related parameters, especially the external factors influences. Thus, despite the recent developments more investigations are still required. The effect of a uniform magnetic field on the hydrodynamics behavior of a two-phase flow with different magnetic permeability is presented in this article. A single water vapor bubble which is rising inside a channel filled with ferrofluid has been simulated numerically. To capture the phases interface, the Volume of Fluid (VOF) model, and to solve the governing equations, the finite volume method has been employed. Contrary to the prior anticipations, while the consisting fluids of the flow are dielectric, uniform magnetic field causes a force acting normal to the interface toward to the inside of the bubble. With respect to the applied magnetic field direction, the bubble deformation due to the magnetic force increases the bubble rising velocity. Moreover, the higher values of applied magnetic field strength and magnetic permeability ratio resulted in the further increase of the bubble rising velocity. Also it is indicated that the flow mixing and the heat transfer rate is increased by a bubble injection and applying a magnetic field. The obtained results have been concluded that the presented phenomenon with applying a magnetic field can be used to control the related characteristics of the multiphase flows. Compared to the previous studies, implementing the applicable cases using the common and actual materials and a significant reduction of the CPU time are the most remarkable advantages of the current study.

EBSD Study of the Influence of a High Magnetic Field on the Microstructure and Orientation of the Al-Si Eutectic During Directional Solidification

NASA Astrophysics Data System (ADS)

Li, Xi; Fautrelle, Yves; Gagnoud, Annie; Ren, Zhongming; Moreau, Rene

2016-06-01

The effect of a high magnetic field on the morphology of the Al-Si eutectic was investigated using EBSD technology. The results revealed that the application of the magnetic field modified the morphology of the Al-Si eutectic significantly. Indeed, the magnetic field destroyed the coupled growth of the Al-Si eutectic and caused the formation of the divorced α-Al and Si dendrites at low growth speeds (≤1 μm/s). The magnetic field was also found to refine the eutectic grains and reduce the eutectic spacing at the initial growth stage. Moreover, the magnetic field caused the occurrence of the columnar-to-equiaxed transition of the α-Al phase in the Al-Si eutectic. The abovementioned effects were enhanced as the magnetic field increased. This result should be attributed to the magnetic field restraining the interdiffusion of Si and Al atoms in liquid ahead of the liquid/solid interface and the thermoelectric magnetic force acting on the eutectic lamellae under the magnetic field.

Investigation of the interaction of ferromagnetic fluids with proteins by dynamic light scattering

NASA Astrophysics Data System (ADS)

Velichko, Elena; Nepomnyashchaya, Elina; Dudina, Alina; Pleshakov, Ivan; Aksenov, Evgenii

2018-04-01

In this article the interaction between ionically stabilized magnetic nanoparticles and blood serum albumin proteins in liquid medium are discussed. Some distributions of nanoparticles' agglomerate sizes in solutions of albumin molecules, magnetic nanoparticles and their mixtures both under the influence of magnetic field and free from it are presented. It is shown that magnetic nanoparticles interact with albumin molecules, forming agglomerates. It is also shown that at the influence of magnetic field sizes of agglomerates increase proportionally to the magnetic field density.

Simulation of double stage hall thruster with double-peaked magnetic field

NASA Astrophysics Data System (ADS)

Ding, Yongjie; Li, Peng; Sun, Hezhi; Wei, Liqiu; Xu, Yu; Peng, Wuji; Su, Hongbo; Li, Hong; Yu, Daren

2017-07-01

This study adopts double permanent magnetic rings and four permanent magnetic rings to form two symmetrical magnetic peaks and two asymmetrical magnetic peaks in the channel of a Hall thruster, and uses a 2D-3V PIC-MCC model to analyze the influence of magnetic strength on the discharge characteristic and performance of Hall thrusters with an intermediate electrode and double-peaked magnetic field. As opposed to the two symmetrical magnetic peaks formed by double permanent magnetic rings, increasing the magnetic peak value deep within the channel can cause propellant ionization to occur; with the increase in the magnetic peak deep in the channel, the propellant utilization, thrust, and anode efficiency of the thruster are significantly improved. Double-peaked magnetic field can realize separate control of ionization and acceleration in a Hall thruster, and provide technical means for further improving thruster performance. Contribution to the Topical Issue "Physics of Ion Beam Sources", edited by Holger Kersten and Horst Neumann.

Magnetic drug targeting through a realistic model of human tracheobronchial airways using computational fluid and particle dynamics.

PubMed

Pourmehran, Oveis; Gorji, Tahereh B; Gorji-Bandpy, Mofid

2016-10-01

Magnetic drug targeting (MDT) is a local drug delivery system which aims to concentrate a pharmacological agent at its site of action in order to minimize undesired side effects due to systemic distribution in the organism. Using magnetic drug particles under the influence of an external magnetic field, the drug particles are navigated toward the target region. Herein, computational fluid dynamics was used to simulate the air flow and magnetic particle deposition in a realistic human airway geometry obtained by CT scan images. Using discrete phase modeling and one-way coupling of particle-fluid phases, a Lagrangian approach for particle tracking in the presence of an external non-uniform magnetic field was applied. Polystyrene (PMS40) particles were utilized as the magnetic drug carrier. A parametric study was conducted, and the influence of particle diameter, magnetic source position, magnetic field strength and inhalation condition on the particle transport pattern and deposition efficiency (DE) was reported. Overall, the results show considerable promise of MDT in deposition enhancement at the target region (i.e., left lung). However, the positive effect of increasing particle size on DE enhancement was evident at smaller magnetic field strengths (Mn [Formula: see text] 1.5 T), whereas, at higher applied magnetic field strengths, increasing particle size has a inverse effect on DE. This implies that for efficient MTD in the human respiratory system, an optimal combination of magnetic drug career characteristics and magnetic field strength has to be achieved.

External magnetic field-induced selective biodistribution of magnetoliposomes in mice

NASA Astrophysics Data System (ADS)

García-Jimeno, Sonia; Escribano, Elvira; Queralt, Josep; Estelrich, Joan

2012-08-01

This study looked at the effect of an external magnet on the biodistribution of magnetoliposomes intravenously administrated in mice (8 mg iron/kg) with and without induced acute inflammation. Our results showed that due to enhanced vascular permeability, magnetoliposomes accumulated at the site of inflammation in the absence of an external magnetic field, but the amount of iron present increased under the effect of a magnet located at the inflammation zone. This increase was dependent on the time (20 or 60 min) of exposure of the external magnetic field. It was also observed that the presence of the magnet was associated with lower amounts of iron in the liver, spleen, and plasma than was found in mice in which a magnet had not been applied. The results of this study confirm that it is possible to target drugs encapsulated in magnetic particles by means of an external magnet.

Active magnetic force microscopy of Sr-ferrite magnet by stimulating magnetization under an AC magnetic field: Direct observation of reversible and irreversible magnetization processes

NASA Astrophysics Data System (ADS)

Cao, Yongze; Kumar, Pawan; Zhao, Yue; Yoshimura, Satoru; Saito, Hitoshi

2018-05-01

Understanding the dynamic magnetization process of magnetic materials is crucial to improving their fundamental properties and technological applications. Here, we propose active magnetic force microscopy for observing reversible and irreversible magnetization processes by stimulating magnetization with an AC magnetic field based on alternating magnetic force microscopy with a sensitive superparamagnetic tip. This approach simultaneously measures sample's DC and AC magnetic fields. We used this microscopy approach to an anisotropic Sr-ferrite (SrF) sintered magnet. This is a single domain type magnet where magnetization mainly changes via magnetic rotation. The proposed method can directly observe the reversible and irreversible magnetization processes of SrF and clearly reveal magnetic domain evolution of SrF (without stimulating magnetization—stimulating reversible magnetization—stimulating irreversible magnetization switching) by slowly increasing the amplitude of the external AC magnetic field. This microscopy approach can evaluate magnetic inhomogeneity and explain the local magnetic process within the permanent magnet.

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.

Effects of Dzyaloshinsky-Moriya interaction on magnetism in nanodisks from a self-consistent approach

NASA Astrophysics Data System (ADS)

Liu, Zhaosen; Ian, Hou

2016-01-01

We give a theoretical study on the magnetic properties of monolayer nanodisks with both Heisenberg exchange and Dzyaloshinsky-Moriya (DM) interactions. In particular, we survey the magnetic effects caused by anisotropy, external magnetic field, and disk size when DM interaction is present by means of a new quantum simulation method facilitated by a self-consistent algorithm based on mean field theory. This computational approach finds that uniaxial anisotropy and transversal magnetic field enhance the net magnetization as well as increase the transition temperature of the vortical phase while preserving the chiralities of the swirly magnetic structures, whereas when the strength of DM interaction is sufficiently strong for a given disk size, magnetic domains appear within the circularly bounded region, which vanish and give in to a single vortex when a transversal magnetic field is applied. The latter confirms the magnetic skyrmions induced by the magnetic field as observed in the experiments.

Mechanisms of anode power deposition in a low pressure free burning arc

NASA Technical Reports Server (NTRS)

Soulas, George C.; Myers, Roger M.

1994-01-01

Anode power deposition is a dominant power loss mechanism for arc jets and MPD thrusters. In this study, a free burning arc experiment was operated at pressures and current densities similar to those in arc jets and MPD thrusters in an attempt to identify the physics controlling this loss mechanism. Use of a free burning arc allowed for the isolation of independent variables controlling anode power deposition and provided a convenient and flexible way to cover a broad range of currents, anode surface pressures, and applied magnetic field strengths and orientations using an argon gas. Test results showed that anode power deposition decreased with increasing anode surface pressure up to 6.7 Pa (0.05 torr) and then became insensitive to pressure. Anode power increased with increasing arc current while the electron number density near the anode surface increased linearity. Anode power also increased with increasing applied magnetic field strength due to an increasing anode fall voltage. Applied magnetic field orientation had an effect only at high currents and low anode surface pressures, where anode power decreased when applied field lines intercepted the anode surface. The results demonstrated that anode power deposition was dominated by the current carrying electrons and that the anode fall voltage was the largest contributor. Furthermore, the results showed that anode power deposition can be reduced by operating at increased anode pressures, reduced arc currents, and applied magnetic field strengths and with magnetic field lines intercepting the anode.

Magnetic field control of microstructural development in melt-spun Pr2Co14 B

NASA Astrophysics Data System (ADS)

McGuire, Michael A.; Rios, Orlando; Conner, Ben S.; Carter, William G.; Huang, Mianliang; Sun, Kewei; Palasyuk, Olena; Jensen, Brandt; Zhou, Lin; Dennis, Kevin; Nlebedim, Ikenna C.; Kramer, Matthew J.

2017-05-01

In the processing of commercial rare earth permanent magnets, use of external magnetic fields is limited mainly to the alignment of anisotropic particles and the polarization of the finished magnets. Here we explore the effects of high magnetic fields on earlier stages of magnet synthesis, including the crystallization and chemical phase transformations that produce the 2:14:1 phase in the Pr-Co-B system. Pr2Co14 B alloys produced by melt-spinning were annealed in the presence of strong applied magnetic fields (H=90 kOe). The resulting materials were characterized by x-ray diffraction, electron microscopy, and magnetization measurements. We find that magnetic fields suppress the nucleation and growth of crystalline phases, resulting in significantly smaller particle sizes. In addition, magnetic fields applied during processing strongly affects chemical phase selection, suppressing the formation of Pr2Co14 B and α-Co in favor of Pr2Co17 . The results demonstrate that increased control over key microstructural properties is achievable by including a strong magnetic field as a processing parameter for rare-earth magnet materials.

Heating of cardiovascular stents in intense radiofrequency magnetic fields.

PubMed

Foster, K R; Goldberg, R; Bonsignore, C

1999-01-01

We consider the heating of a metal stent in an alternating magnetic field from an induction heating furnace. An approximate theoretical analysis is conducted to estimate the magnetic field strength needed to produce substantial temperature increases. Experiments of stent heating in industrial furnaces are reported, which confirm the model. The results show that magnetic fields inside inductance furnaces are capable of significantly heating stents. However, the fields fall off very quickly with distance and in most locations outside the heating coil, field levels are far too small to produce significant heating. The ANSI/IEEE C95.1-1992 limits for human exposure to alternating magnetic fields provide adequate protection against potential excessive heating of the stents.

Magnetically modified bioсells in constant magnetic field

NASA Astrophysics Data System (ADS)

Abramov, E. G.; Panina, L. K.; Kolikov, V. A.; Bogomolova, E. V.; Snetov, V. N.; Cherepkova, I. A.; Kiselev, A. A.

2017-02-01

Paper addresses the inverse problem in determining the area, where the external constant magnetic field captures the biological cells modified by the magnetic nanoparticles. Zero velocity isolines, in area where the modified cells are captured by the magnetic field were determined by numerical method for two locations of the magnet. The problem was solved taking into account the gravitational field, magnetic induction, density of medium, concentration and size of cells, and size and magnetization of nanoparticles attached to the cell. Increase in the number of the nanoparticles attached to the cell and decrease in the cell' size, enlarges the area, where the modified cells are captured and concentrated by the magnet. Solution is confirmed by the visible pattern formation of the modified cells Saccharomyces cerevisiae.

Optical fiber magnetic field sensors with TbDyFe magnetostrictive thin films as sensing materials.

PubMed

Yang, Minghong; Dai, Jixiang; Zhou, Ciming; Jiang, Desheng

2009-11-09

Different from usually-used bulk magnetostrictive materials, magnetostrictive TbDyFe thin films were firstly proposed as sensing materials for fiber-optic magnetic field sensing characterization. By magnetron sputtering process, TbDyFe thin films were deposited on etched side circle of a fiber Bragg Grating (FBG) as sensing element. There exists more than 45pm change of FBG wavelength when magnet field increase up to 50 mT. The response to magnetic field is reversible, and could be applicable for magnetic and current sensing.

Relationship between magnetic field strength and magnetic-resonance-related acoustic noise levels.

PubMed

Moelker, Adriaan; Wielopolski, Piotr A; Pattynama, Peter M T

2003-02-01

The need for better signal-to-noise ratios and resolution has pushed magnetic resonance imaging (MRI) towards high-field MR-scanners for which only little data on MR-related acoustic noise production have been published. The purpose of this study was to validate the theoretical relationship of sound pressure level (SPL) and static magnetic field strength. This is relevant for allowing adequate comparisons of acoustic data of MR systems at various magnetic field strengths. Acoustic data were acquired during various pulse sequences at field strengths of 0.5, 1.0, 1.5 and 2.0 Tesla using the same MRI unit by means of a Helicon rampable magnet. Continuous-equivalent, i.e. time-averaged, linear SPLs and 1/3-octave band frequencies were recorded. Ramping from 0.5 to 1.0 Tesla and from 1.0 to 2.0 Tesla resulted in an SPL increase of 5.7 and 5.2 dB(L), respectively, when averaged over the various pulse sequences. Most of the acoustic energy was in the 1-kHz frequency band, irrespective of magnetic field strength. The relation between field strength and SPL was slightly non-linear, i.e. a slightly less increase at higher field strengths, presumably caused by the elastic properties of the gradient coil encasings.

APPARATUS FOR THE DENSIFICATION AND ENERGIZATION OF CHARGED PARTICLES

DOEpatents

Post, R.F.; Coensgen, F.H.

1962-12-18

This patent relates to a device for materially increasing the energy and density of a plasma to produce conditions commensurate with the establishment and promotion of controlled thermonuclear reactions. To this end the device employs three successive stages of magnetic compression, each stage having magnetic mirrors to compress a plasma, the mirrors being moveable to transfer the plasma to successive stages for further compression. Accordingly, a plasma introduced to the first stage is increased in density and energy in stepwide fashion by virtue of the magnetic compression in the successive stages such that the plasma upon reaching the last stage is of extremely high energy and density commensurate the plasma particles undergoing thermonuclear reactions. The principal novelty of the device resides in the provision of a unidirectional magnetic field which increases in stepwise fashion in coaxially communicating compression chambers of progressively decreasing lengths and diameters. Pulsed magnetic fields are superimposed upon the undirectional field and are manipulated to establish resultant magnetic compression fields which increase in intensity and progressively move, with respect to time, through the compression chambers in the direction of the smallest one thereof. The resultant field in the last compression chamber is hence of relatively high intensity, and the density and energy of the plasma confined therein are correspondingly high. (AEC)

Analysis of high gradient magnetic field effects on distribution of nanoparticles injected into pulsatile blood stream

NASA Astrophysics Data System (ADS)

Reza Habibi, Mohammad; Ghassemi, Majid; Hossien Hamedi, Mohammad

2012-04-01

Magnetic nanoparticles are widely used in a wide range of applications including data storage materials, pharmaceutical industries as magnetic separation tools, anti-cancer drug carriers and micro valve applications. The purpose of the current study is to investigate the effect of a non-uniform magnetic field on bio-fluid (blood) with magnetic nanoparticles. The effect of particles as well as mass fraction on flow field and volume concentration is investigated. The governing non-linear differential equations, concentration and Navier-stokes are coupled with the magnetic field. To solve these equations, a finite volume based code is developed and utilized. A real pulsatile velocity is utilized as inlet boundary condition. This velocity is extracted from an actual experimental data. Three percent nanoparticles volume concentration, as drug carrier, is steadily injected in an unsteady, pulsatile and non-Newtonian flow. A power law model is considered for the blood viscosity. The results show that during the systole section of the heartbeat when the blood velocity increases, the magnetic nanoparticles near the magnetic source are washed away. This is due to the sudden increase of the hydrodynamic force, which overcomes the magnetic force. The probability of vein blockage increases when the blood velocity reduces during the diastole time. As nanoparticles velocity injection decreases (longer injection time) the wall shear stress (especially near the injection area) decreases and the retention time of the magnetic nanoparticles in the blood flow increases.

Conversion of magnetic field energy into kinetic energy in the solar wind

NASA Technical Reports Server (NTRS)

Whang, Y. C.

1972-01-01

The outflow of the solar magnetic field energy (the radial component of the Poynting vector) per steradian is inversely proportional to the solar wind velocity. It is a decreasing function of the heliocentric distance. When the magnetic field effect is included in the one-fluid model of the solar wind, the transformation of magnetic field energy into kinetic energy during the expansion process increases the solar wind velocity at 1 AU by 17 percent.

Numerical studies on the force characteristic of superconducting linear synchronous motor with HTS bulk magnet

NASA Astrophysics Data System (ADS)

Tang, Junjie; Li, Jing; Li, Xiang; Han, Le

2018-03-01

High temperature superconductor (HTS) bulks have significant potential use in linear motor application act as quasi-permanent magnet to replace traditional magnets. Force characteristic between HTS bulk magnet and traveling magnetic field was investigated with numerical simulation and experimental measurement in this paper. Influences of bulk height and number on the force characteristic were studied by the finite element model considering the nonlinear E-J relationship. Study was also made on addition of a back iron plate to the bulk magnet. Besides, force characteristic of bulk was compared with the permanent magnet results. The small initial decrease of the thrust could be explained by inside superconducting current redistribution. It was found that efficiency of linear motor did not increase by adding more bulk magnets. The bulk magnet will be remagnetized instead of erasing trapped field with the increase of the traveling magnetic field strength. The conclusions are helpful in prediction and design the linear motor with HTS bulk magnet.

Development of flexible Ni80Fe20 magnetic nano-thin films

NASA Astrophysics Data System (ADS)

Vopson, M. M.; Naylor, J.; Saengow, T.; Rogers, E. G.; Lepadatu, S.; Fetisov, Y. K.

2017-11-01

Flexible magnetic Ni80Fe20 thin films with excellent adhesion, mechanical and magnetic properties have been fabricated using magnetron plasma deposition. We demonstrate that flexible Ni80Fe20 thin films maintain their non-flexible magnetic properties when the films are over 60 nm thick. However, when their thickness is reduced, the flexible thin films display significant increase in their magnetic coercive field compared to identical films coated on a solid Silicon substrate. For a 15 nm flexible Ni80Fe20 film coated onto 110 μm Polyvinylidene fluoride polymer substrate, we achieved a remarkable 355% increase in the magnetic coercive field relative to the same film deposited onto a Si substrate. Experimental evidence, backed by micro-magnetic modelling, indicates that the increase in the coercive fields is related to the larger roughness texture of the flexible substrates. This effect essentially transforms soft Ni80Fe20 permalloy thin films into medium/hard magnetic films allowing not only mechanical flexibility of the structure, but also fine tuning of their magnetic properties.

Spatially and time resolved kinetics of indirect magnetoexcitons

NASA Astrophysics Data System (ADS)

Hasling, Matthew; Dorow, Chelsey; Calman, Erica; Butov, Leonid; Wilkes, Joe; Campman, Kenneth; Gossard, Arthur

The small exciton mass and binding energy give the opportunity to realize the high magnetic field regime for excitons in magnetic fields of few Tesla achievable in lab Long lifetimes of indirect exciton give the opportunity to study kinetics of magnetoexciton transport by time-resolved optical imaging of exciton emission. We present spatially and time resolved measurements showing the effect of increased magnetic field on transport of magnetoexcitons. We observe that increased magnetic field leads to slowing down of magnetoexciton transport. Supported by NSF Grant No. 1407277. J.W. was supported by the EPSRC (Grant EP/L022990/1). C.J.D. was supported by the NSF Graduate Research Fellowship Program under Grant No. DGE-1144086.

Surface structure of neutron stars with high magnetic fields

NASA Technical Reports Server (NTRS)

Fushiki, I.; Gudmundsson, E. H.; Pethick, C. J.

1989-01-01

The equation of state of cold dense matter in strong magnetic fields is calculated in the Thomas-Fermi and Thomas-Fermi-Dirac approximations. For use in the latter calculation, a new expression is derived for the exchange energy of the uniform electron gas in a strong magnetic field. Detailed calculations of the density profile in the surface region of a neutron star are described for a variety of equations of state, and these show that the surface density profile is strongly affected by the magnetic field, irrespective of whether or not matter in a magnetic field has a condensed state bound with respect to isolated atoms. It is also shown that, as a consequence of the field dependence of the screening potential, magnetic fields can significantly increase nuclear reaction rates.

Electromagnetism of Bacterial Growth

NASA Astrophysics Data System (ADS)

Ainiwaer, Ailiyasi

2011-10-01

There has been increasing concern from the public about personal health due to the significant rise in the daily use of electrical devices such as cell phones, radios, computers, GPS, video games and television. All of these devices create electromagnetic (EM) fields, which are simply magnetic and electric fields surrounding the appliances that simultaneously affect the human bio-system. Although these can affect the human system, obstacles can easily shield or weaken the electrical fields; however, magnetic fields cannot be weakened and can pass through walls, human bodies and most other objects. The present study was conducted to examine the possible effects of bacteria when exposed to magnetic fields. The results indicate that a strong causal relationship is not clear, since different magnetic fields affect the bacteria differently, with some causing an increase in bacterial cells, and others causing a decrease in the same cells. This phenomenon has yet to be explained, but the current study attempts to offer a mathematical explanation for this occurrence. The researchers added cultures to the magnetic fields to examine any effects to ion transportation. Researchers discovered ions such as potassium and sodium are affected by the magnetic field. A formula is presented in the analysis section to explain this effect.

Viscosity of two-dimensional strongly coupled dusty plasma modified by a perpendicular magnetic field

NASA Astrophysics Data System (ADS)

Feng, Yan; Lin, Wei; Murillo, M. S.

2017-11-01

Transport properties of two-dimensional (2D) strongly coupled dusty plasmas have been investigated in detail, but never for viscosity with a strong perpendicular magnetic field; here, we examine this scenario using Langevin dynamics simulations of 2D liquids with a binary Yukawa interparticle interaction. The shear viscosity η of 2D liquid dusty plasma is estimated from the simulation data using the Green-Kubo relation, which is the integration of the shear stress autocorrelation function. It is found that, when a perpendicular magnetic field is applied, the shear viscosity of 2D liquid dusty plasma is modified substantially. When the magnetic field is increased, its viscosity increases at low temperatures, while at high temperatures its viscosity diminishes. It is determined that these different variational trends of η arise from the different behaviors of the kinetic and potential parts of the shear stress under external magnetic fields.

Association between magnetic field fluctuations and energetic particle bursts in the earth's magnetotail

NASA Technical Reports Server (NTRS)

Lui, A. T. Y.; Krimigis, S. M.; Armstrong, T. P.

1982-01-01

The association between energetic protons (0.29-0.50 MeV) and simultaneous local fluctuations of magnetic field at 35 to 45 earth radii in the magnetotail is examined statistically with data from APL/JHU particle telescopes aboard IMP 7 and IMP 8. About four satellite years of 5.5 min averaged measurements are used in this study. In addition to confirming that the level of magnetic field fluctuations generally increases with the presence of energetic protons and their streaming anisotropy, it is found that increases in occurrence frequency of streaming of energetic protons are ordered far better by magnetic field fluctuations than by proximity to the neutral sheet. However, the presence of large magnetic field fluctuations (delta B greater than 5 nT or delta B/B greater than 50%) is neither a necessary nor a sufficient condition for the detection of large streaming in energetic protons.

Magnetic field affects enzymatic ATP synthesis.

PubMed

Buchachenko, Anatoly L; Kuznetsov, Dmitry A

2008-10-01

The rate of ATP synthesis by creatine kinase extracted from V. xanthia venom was shown to depend on the magnetic field. The yield of ATP produced by enzymes with 24Mg2+ and 26Mg2+ ions in catalytic sites increases by 7-8% at 55 mT and then decreases at 80 mT. For enzyme with 25Mg2+ ion in a catalytic site, the ATP yield increases by 50% and 70% in the fields 55 and 80 mT, respectively. In the Earth field the rate of ATP synthesis by enzyme, in which Mg2+ ion has magnetic nucleus 25Mg, is 2.5 times higher than that by enzymes, in which Mg2+ ion has nonmagnetic, spinless nuclei 24Mg or 26Mg. Both magnetic field effect and magnetic isotope effect demonstrate that the ATP synthesis is an ion-radical process, affected by Zeeman interaction and hyperfine coupling in the intermediate ion-radical pair.

Magnetic sponge prepared with an alkanedithiol-bridged network of nanomagnets.

PubMed

Ito, Yoshikazu; Miyazaki, Akira; Takai, Kazuyuki; Sivamurugan, Vajiravelu; Maeno, Takashi; Kadono, Takeshi; Kitano, Masaaki; Ogawa, Yoshihiro; Nakamura, Naotake; Hara, Michikazu; Valiyaveettil, Suresh; Enoki, Toshiaki

2011-08-03

The magnetic dipole-dipole interaction between nanomagnets having huge magnetic moments can have a strength comparable to that of the van der Waals interaction between them, and it can be manipulated by applying an external magnetic field of conventional strength. Therefore, the cooperation between the dipole-dipole interaction and the applied magnetic field allows the magnetic moments of nanomagnets to be aligned and organized in an ordered manner. In this work, a network of magnetic nanoparticles connected with flexible long-alkyl-chain linkers was designed to develop a "magnetic sponge" capable of absorbing and desorbing guest molecules with changes in the applied magnetic field. The magnetization of the sponge with long-alkyl-chain bridges (30 C atoms) exhibited a 500% increase after cooling in the presence of an applied field of 7 T relative to that in the absence of a magnetic field. Cooling in a magnetic field leads to anisotropic stretching in the sponge due to reorganization of the nanomagnets along the applied field, in contrast to the isotropic organization under zero-field conditions. Such magnetic-responsive organization and reorganization of the magnetic particle network significantly influences the gas absorption capacity of the nanopores inside the material. The absorption and desorption of guests in an applied magnetic field at low temperature can be regarded as a fascinating "breathing feature" of our magnetic sponge.

CHANGE OF MAGNETIC FIELD-GAS ALIGNMENT AT THE GRAVITY-DRIVEN ALFVÉNIC TRANSITION IN MOLECULAR CLOUDS: IMPLICATIONS FOR DUST POLARIZATION OBSERVATIONS

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

Chen, Che-Yu; King, Patrick K.; Li, Zhi-Yun

Diffuse striations in molecular clouds are preferentially aligned with local magnetic fields, whereas dense filaments tend to be perpendicular to them. When and why this transition occurs remain uncertain. To explore the physics behind this transition, we compute the histogram of relative orientation (HRO) between the density gradient and the magnetic field in three-dimensional magnetohydrodynamic (MHD) simulations of prestellar core formation in shock-compressed regions within giant molecular clouds. We find that, in the magnetically dominated (sub-Alfvénic) post-shock region, the gas structure is preferentially aligned with the local magnetic field. For overdense sub-regions with super-Alfvénic gas, their elongation becomes preferentially perpendicularmore » to the local magnetic field. The transition occurs when self-gravitating gas gains enough kinetic energy from the gravitational acceleration to overcome the magnetic support against the cross-field contraction, which results in a power-law increase of the field strength with density. Similar results can be drawn from HROs in projected two-dimensional maps with integrated column densities and synthetic polarized dust emission. We quantitatively analyze our simulated polarization properties, and interpret the reduced polarization fraction at high column densities as the result of increased distortion of magnetic field directions in trans- or super-Alfvénic gas. Furthermore, we introduce measures of the inclination and tangledness of the magnetic field along the line of sight as the controlling factors of the polarization fraction. Observations of the polarization fraction and angle dispersion can therefore be utilized in studying local magnetic field morphology in star-forming regions.« less

Electrical characterization of gold-DNA-gold structures in presence of an external magnetic field by means of I-V curve analysis.

PubMed

Khatir, Nadia Mahmoudi; Banihashemian, Seyedeh Maryam; Periasamy, Vengadesh; Ritikos, Richard; Abd Majid, Wan Haliza; Abdul Rahman, Saadah

2012-01-01

This work presents an experimental study of gold-DNA-gold structures in the presence and absence of external magnetic fields with strengths less than 1,200.00 mT. The DNA strands, extracted by standard method were used to fabricate a Metal-DNA-Metal (MDM) structure. Its electric behavior when subjected to a magnetic field was studied through its current-voltage (I-V) curve. Acquisition of the I-V curve demonstrated that DNA as a semiconductor exhibits diode behavior in the MDM structure. The current versus magnetic field strength followed a decreasing trend because of a diminished mobility in the presence of a low magnetic field. This made clear that an externally imposed magnetic field would boost resistance of the MDM structure up to 1,000.00 mT and for higher magnetic field strengths we can observe an increase in potential barrier in MDM junction. The magnetic sensitivity indicates the promise of using MDM structures as potential magnetic sensors.

Electrical Characterization of Gold-DNA-Gold Structures in Presence of an External Magnetic Field by Means of I–V Curve Analysis

PubMed Central

Khatir, Nadia Mahmoudi; Banihashemian, Seyedeh Maryam; Periasamy, Vengadesh; Ritikos, Richard; Majid, Wan Haliza Abd; Rahman, Saadah Abdul

2012-01-01

This work presents an experimental study of gold-DNA-gold structures in the presence and absence of external magnetic fields with strengths less than 1,200.00 mT. The DNA strands, extracted by standard method were used to fabricate a Metal-DNA-Metal (MDM) structure. Its electric behavior when subjected to a magnetic field was studied through its current-voltage (I–V) curve. Acquisition of the I–V curve demonstrated that DNA as a semiconductor exhibits diode behavior in the MDM structure. The current versus magnetic field strength followed a decreasing trend because of a diminished mobility in the presence of a low magnetic field. This made clear that an externally imposed magnetic field would boost resistance of the MDM structure up to 1,000.00 mT and for higher magnetic field strengths we can observe an increase in potential barrier in MDM junction. The magnetic sensitivity indicates the promise of using MDM structures as potential magnetic sensors. PMID:22737025

Controlling orientational order in block copolymers using low-intensity magnetic fields

PubMed Central

Choo, Youngwoo; Kawabata, Kohsuke; Kaufman, Gilad; Feng, Xunda; Di, Xiaojun; Rokhlenko, Yekaterina; Mahajan, Lalit H.; Ndaya, Dennis; Kasi, Rajeswari M.

2017-01-01

The interaction of fields with condensed matter during phase transitions produces a rich variety of physical phenomena. Self-assembly of liquid crystalline block copolymers (LC BCPs) in the presence of a magnetic field, for example, can result in highly oriented microstructures due to the LC BCP’s anisotropic magnetic susceptibility. We show that such oriented mesophases can be produced using low-intensity fields (<0.5 T) that are accessible using permanent magnets, in contrast to the high fields (>4 T) and superconducting magnets required to date. Low-intensity field alignment is enabled by the addition of labile mesogens that coassemble with the system’s nematic and smectic A mesophases. The alignment saturation field strength and alignment kinetics have pronounced dependences on the free mesogen concentration. Highly aligned states with orientation distribution coefficients close to unity were obtained at fields as small as 0.2 T. This remarkable field response originates in an enhancement of alignment kinetics due to a reduction in viscosity, and increased magnetostatic energy due to increases in grain size, in the presence of labile mesogens. These developments provide routes for controlling structural order in BCPs, including the possibility of producing nontrivial textures and patterns of alignment by locally screening fields using magnetic nanoparticles. PMID:29078379

Sequential magnetic switching in Fe/MgO(001) superlattices

NASA Astrophysics Data System (ADS)

Magnus, F.; Warnatz, T.; Palsson, G. K.; Devishvili, A.; Ukleev, V.; Palisaitis, J.; Persson, P. O. Å.; Hjörvarsson, B.

2018-05-01

Polarized neutron reflectometry is used to determine the sequence of magnetic switching in interlayer exchange coupled Fe/MgO(001) superlattices in an applied magnetic field. For 19.6 Å thick MgO layers we obtain a 90∘ periodic magnetic alignment between adjacent Fe layers at remanence. In an increasing applied field the top layer switches first followed by its second-nearest neighbor. For 16.4 Å MgO layers, a 180∘ periodic alignment is obtained at remanence and with increasing applied field the layer switching starts from the two outermost layers and proceeds inwards. This sequential tuneable switching opens up the possibility of designing three-dimensional magnetic structures with a predefined discrete switching sequence.

Magnetic resonance imaging without field cycling at less than earth's magnetic field

NASA Astrophysics Data System (ADS)

Lee, Seong-Joo; Shim, Jeong Hyun; Kim, Kiwoong; Yu, Kwon Kyu; Hwang, Seong-min

2015-03-01

A strong pre-polarization field, usually tenths of a milli-tesla in magnitude, is used to increase the signal-to-noise ratio in ordinary superconducting quantum interference device-based nuclear magnetic resonance/magnetic resonance imaging experiments. Here, we introduce an experimental approach using two techniques to remove the need for the pre-polarization field. A dynamic nuclear polarization (DNP) technique enables us to measure an enhanced resonance signal. In combination with a π / 2 pulse to avoid the Bloch-Siegert effect in a micro-tesla field, we obtained an enhanced magnetic resonance image by using DNP technique with a 34.5 μT static external magnetic field without field cycling. In this approach, the problems of eddy current and flux trapping in the superconducting pickup coil, both due to the strong pre-polarization field, become negligible.

Correlation between physical structure and magnetic anisotropy of a magnetic nanoparticle colloid.

PubMed

Dennis, C L; Jackson, A J; Borchers, J A; Gruettner, C; Ivkov, R

2018-05-25

We show the effects of a time-invariant magnetic field on the physical structure and magnetic properties of a colloid comprising 44 nm diameter magnetite magnetic nanoparticles, with a 24 nm dextran shell, in water. Structural ordering in this colloid parallel to the magnetic field occurs simultaneously with the onset of a colloidal uniaxial anisotropy. Further increases in the applied magnetic field cause the nanoparticles to order perpendicular to the field, producing unexpected colloidal unidirectional and trigonal anisotropies. This magnetic behavior is distinct from the cubic magnetocrystalline anisotropy of the magnetite and has its origins in the magnetic interactions among the mobile nanoparticles within the colloid. Specifically, these field-induced anisotropies and colloidal rearrangements result from the delicate balance between the magnetostatic and steric forces between magnetic nanoparticles. These magnetic and structural rearrangements are anticipated to influence applications that rely upon time-dependent relaxation of the magnetic colloids and fluid viscosity, such as magnetic hyperthermia and shock absorption.

Correlation between physical structure and magnetic anisotropy of a magnetic nanoparticle colloid

NASA Astrophysics Data System (ADS)

Dennis, C. L.; Jackson, A. J.; Borchers, J. A.; Gruettner, C.; Ivkov, R.

2018-05-01

We show the effects of a time-invariant magnetic field on the physical structure and magnetic properties of a colloid comprising 44 nm diameter magnetite magnetic nanoparticles, with a 24 nm dextran shell, in water. Structural ordering in this colloid parallel to the magnetic field occurs simultaneously with the onset of a colloidal uniaxial anisotropy. Further increases in the applied magnetic field cause the nanoparticles to order perpendicular to the field, producing unexpected colloidal unidirectional and trigonal anisotropies. This magnetic behavior is distinct from the cubic magnetocrystalline anisotropy of the magnetite and has its origins in the magnetic interactions among the mobile nanoparticles within the colloid. Specifically, these field-induced anisotropies and colloidal rearrangements result from the delicate balance between the magnetostatic and steric forces between magnetic nanoparticles. These magnetic and structural rearrangements are anticipated to influence applications that rely upon time-dependent relaxation of the magnetic colloids and fluid viscosity, such as magnetic hyperthermia and shock absorption.

Diffusion of external magnetic fields into the cone-in-shell target in the fast ignition

NASA Astrophysics Data System (ADS)

Sunahara, Atsushi; Morita, Hiroki; Johzaki, Tomoyuki; Nagatomo, Hideo; Fujioka, Shinsuke; Hassanein, Ahmed; Firex Project Team

2017-10-01

We simulated the diffusion of externally applied magnetic fields into cone-in-shell target in the fast ignition. Recently, in the fast ignition scheme, the externally magnetic fields up to kilo-Tesla is used to guide fast electrons to the high-dense imploded core. In order to study the profile of the magnetic field, we have developed 2D cylindrical Maxwell equation solver with Ohm's law, and carried out simulations of diffusion of externally applied magnetic fields into a cone-in-shell target. We estimated the conductivity of the cone and shell target based on the assumption of Saha-ionization equilibrium. Also, we calculated the temporal evolution of the target temperature heated by the eddy current driven by temporal variation of magnetic fields, based on the accurate equation of state. Both, the diffusion of magnetic field and the increase of target temperature interact with each other. We present our results of temporal evolution of the magnetic field and its diffusion into the cone and shell target.

A Brief Note on the Magnetowetting of Magnetic Nanofluids on AAO Surfaces

PubMed Central

Chien, Yu-Chin

2018-01-01

In magnetowetting, the material properties of liquid, surface morphology of solid, and applied external field are three major factors used to determine the wettability of a liquid droplet on a surface. For wetting measurements, an irregular or uneven surface could result in a significant experimental uncertainty. The periodic array with a hexagonal symmetry structure is an advantage of the anodic aluminum oxide (AAO) structure. This study presents the results of the wetting properties of magnetic nanofluid sessile droplets on surfaces of various AAO pore sizes under an applied external magnetic field. Stable, water-based magnetite nanofluids are prepared by combining the chemical co-precipitation with the sol-gel technique, and AAO surfaces are then generated by anodizing the aluminum sheet in the beginning. The influence of pore size and magnetic field gradient on the magnetowetting of magnetic nanofluids on AAO surfaces is then investigated by an optical test system. Experimental results show that increasing the processing voltage of AAO templates could result in enhanced non-wettability behavior; that is, the increase in AAO pore size could lead to the increase in contact angle. The contact angle could be reduced by the applied magnetic field gradient. In general, the magnetic field has a more significant effect at smaller AAO pore sizes. PMID:29461509

Magnetophoresis for enhancing transdermal drug delivery: Mechanistic studies and patch design

PubMed Central

Murthy, S. Narasimha; Sammeta, Srinivasa M.; Bower, C.

2017-01-01

Magnetophoresis is a method of enhancement of drug permeation across the biological barriers by application of magnetic field. The present study investigated the mechanistic aspects of magnetophoretic transdermal drug delivery and also assessed the feasibility of designing a magnetophoretic transdermal patch system for the delivery of lidocaine. In vitro drug permeation studies were carried out across the porcine epidermis at different magnetic field strengths. The magnetophoretic drug permeation “flux enhancement factor” was found to increase with the applied magnetic field strength. The mechanistic studies revealed that the magnetic field applied in this study did not modulate permeability of the stratum corneum barrier. The predominant mechanism responsible for magnetically mediated drug permeation enhancement was found to be “magnetokinesis”. The octanol/water partition coefficient of drugs was also found to increase when exposed to the magnetic field. A reservoir type transdermal patch system with a magnetic backing was designed for in vivo studies. The dermal bioavailability (AUC0–6 h) from the magnetophoretic patch system in vivo, in rats was significantly higher than the similarly designed nonmagnetic control patch. PMID:20728484

Magnetoviscous effect in ferrofluids diluted with sheep blood

NASA Astrophysics Data System (ADS)

Nowak, J.; Borin, D.; Haefner, S.; Richter, A.; Odenbach, S.

2017-11-01

Suspensions of magnetic nanoparticles in suitable carrier liquids, denoted as ferrofluids, are in the focus of current research in the biomedical area. Those fluids can be potentially used for the treatment of cancer by coupling chemotherapeutic agents and accumulating them in the diseased region with the help of external magnetic fields or by artificially local induced heating. Those applications rely on the help of external magnetic fields, which are well known to drastically influence the physical behaviour of ferrofluids. This study investigates the changing viscosity of a biocompatible ferrofluid in a flow situation close to the situation found in a biomedical application. For this purpose blood as diluting agent and thin capillaries have been utilised. The strong magnetoviscous effects found lead to the assumption of quite big changes of the microstructure due to the external magnetic fields, which was investigated and quantified using a microscopic setup. In the result an increases of the structure size as well as faster structure formation in the stronger magnetic fields were observed. Moreover, with increasing duration of the applied magnetic field the size of the structures increases too. The observed process of the structure formation is reversible.

Exposure to magnetic fields among electrical workers in relation to leukemia risk in Los Angeles County.

PubMed

London, S J; Bowman, J D; Sobel, E; Thomas, D C; Garabrant, D H; Pearce, N; Bernstein, L; Peters, J M

1994-07-01

To address the hypotheses that electrical workers are exposed to higher magnetic fields and are at higher risk of leukemia than nonelectrical workers, we performed a registry-based case-control study among men aged 20-64 years with known occupation who were diagnosed with cancer in Los Angeles County between 1972 and 1990. Controls were men with cancers other than those of the central nervous system or leukemia. Magnetic field measurements on workers in each electrical occupation and in a random sample of occupations presumed to be nonelectrical were used to estimate magnetic field exposures for each occupation. Among men in electrical occupations, 121 leukemias were diagnosed. With the exception of electrical engineers, magnetic field exposures were higher among workers in electrical occupations than in nonelectrical occupations. A weakly positive trend in leukemia risk across average occupational magnetic field exposure was observed (odds ratio [OR] per 10 milligauss increase in average magnetic field = 1.2, 95% confidence interval [CI] 1.0-1.5). A slightly stronger association was observed for chronic myloid leukemia, although only 28 cases occurred among electrical workers (OR 10 milligauss increase = 1.6, 95% CI = 1.2-2.0). The results were not materially altered by adjustment for exposure to several agents known or suspected to cause leukemia. Although not conclusive, these results are consistent with findings from studies based on job title alone that electrical workers may be at slightly increased risk of leukemia.

Field-dependent magnetization of BiFeO 3 in ultrathin La 0.7Sr 0.3MnO 3/BiFeO 3 superlattice

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

Fitzsimmons, Michael R.; Jia, Quanxi X.; Singh, Surendra

2015-12-02

We report the observation of field-induced magnetization of BiFeO 3 (BFO) in an ultrathin La 0.7Sr 0.3MnO 3 (LSMO)/BFO superlattice using polarized neutron reflectivity (PNR). The depth dependent structure and magnetic characterization of subnano layer thick (thickness ~ 0.7 nm each) LSMO/BFO hetrostructure is carried out using X-ray reflectivity and PNR techniques. Our PNR results indicate parallel alignment of magnetization as well as enhancement in magnetic moment across LSMO/BFO interfaces. The study showed an increase in average magnetization on increasing applied magnetic field at 10K. As a result, we observed a saturation magnetization of 110 ± 15 kA/m (~0.8 μmore » B/Fe) for ultrathin BFO layer (~2 unit cell) sandwiched between ultrathin LSMO layers (~ 2 unit cell).« less

Numerical investigation of the heat transfer of a ferrofluid inside a tube in the presence of a non-uniform magnetic field

NASA Astrophysics Data System (ADS)

Hariri, Saman; Mokhtari, Mojtaba; Gerdroodbary, M. Barzegar; Fallah, Keivan

2017-02-01

In this article, a three-dimensional numerical investigation is performed to study the effect of a magnetic field on a ferrofluid inside a tube. This study comprehensively analyzes the influence of a non-uniform magnetic field in the heat transfer of a tube while a ferrofluid (water with 0.86 vol% nanoparticles (Fe3O4) is let flow. The SIMPLEC algorithm is used for obtaining the flow and heat transfer inside the tube. The influence of various parameters, such as concentration of nanoparticles, intensity of the magnetic field, wire distance and Reynolds number, on the heat transfer is investigated. According to the obtained results, the presence of a non-uniform magnetic field significantly increases the Nusselt number (more than 300%) inside the tube. Also, the magnetic field induced by the parallel wire affects the average velocity of the ferrofluid and forms two strong eddies in the tube. Our findings show that the diffusion also raises as the concentration of the nanoparticle is increased.

Rates of change of the earth's magnetic field measured by recent analyses

NASA Technical Reports Server (NTRS)

Harrison, C. G. A.; Huang, Qilin

1990-01-01

Typical rates of change of the earth's magnetic field are presented as a function of the earth's spherical harmonics. Harmonics up to the eight degree are analyzed. With the increase in the degree of the harmonics an increase in the relative rate of change can be observed. For higher degrees, the rate of change can be predicted. This enables a differentiation between harmonics originating in the core and harmonics caused by crustal magnetization. The westward drift of the magnetic field depends on the longitudinal gradient of the field. In order to determine the longitudinal motions, harmonics up to degree 20 can be utilized. The average rate of secular acceleration increases with the degree of harmonics from 0.001 deg/sq yr for a dipole term to an average of 0.05 deg/sq yr for degree eight harmonics.

Improved convection compensating pulsed field gradient spin-echo and stimulated-echo methods.

PubMed

Sørland, G H; Seland, J G; Krane, J; Anthonsen, H W

2000-02-01

The need for convection compensating methods in NMR has been manifested through an increasing number of publications related to the subject over the past few years (J. Magn. Reson. 125, 372 (1997); 132, 13 (1998); 131, 126 (1998); 118, 50 (1996); 133, 379 (1998)). When performing measurements at elevated temperature, small convection currents may give rise to erroneous values of the diffusion coefficient. In work with high resolution NMR spectroscopy, the application of magnetic field gradients also introduces an eddy-current magnetic field which may result in errors in phase and baseline in the FFT-spectra. The eddy current field has been greatly suppressed by the application of bipolar magnetic field gradients. However, when introducing bipolar magnetic field gradients, the pulse sequence is lengthened significantly. This has recently been pointed out as a major drawback because of the loss of coherence and of NMR-signal due to transverse relaxation processes. Here we present modified convection compensating pulsed field gradient double spin echo and double stimulated echo sequences which suppress the eddy-current magnetic field without increasing the duration of the pulse sequences. Copyright 2000 Academic Press.

Granular cells in the presence of magnetic field

NASA Astrophysics Data System (ADS)

Jurčák, J.; Lemmerer, B.; van Noort, M.

2017-10-01

We present a statistical study of the dependencies of the shapes and sizes of the photospheric convective cells on the magnetic field properties. This analysis is based on a 2.5 hour long SST observations of active region NOAA 11768. We have blue continuum images taken with a cadence of 5.6 sec that are used for segmentation of individual granules and 270 maps of spectropolarimetric CRISP data allowing us to determine the properties of the magnetic field along with the line-of-sight velocities. The sizes and shapes of the granular cells are dependent on the the magnetic field strength, where the granules tend to be smaller in regions with stronger magnetic field. In the presence of highly inclined magnetic fields, the eccentricity of granules is high and we do not observe symmetric granules in these regions. The mean up-flow velocities in granules as well as the granules intensities decrease with increasing magnetic field strength.

Effect of magnetic fields on the r-modes of slowly rotating relativistic neutron stars

NASA Astrophysics Data System (ADS)

Chirenti, Cecilia; Skákala, Jozef

2013-11-01

We study here the r-modes in the Cowling approximation of a slowly rotating and magnetized neutron star with a poloidal magnetic field, where we neglect any deformations of the spherical symmetry of the star. We were able to quantify the influence of the magnetic field in both the oscillation frequency σr of the r-modes and the growth time tgw of the gravitational radiation emission. We conclude that magnetic fields of the order 1015G at the center of the star are necessary to produce any changes. Our results for σr show a decrease of up to ˜5% in the frequency with increasing magnetic field, with a B2 dependence for rotation rates Ω/ΩK≳0.07 and B4 for Ω/ΩK≲0.07. (These results should be trusted only within the slow rotation approximation, and we kept Ω/ΩK<0.3.) For tgw, we find that it is approximately 30% smaller than previous Newtonian results for nonmagnetized stars, which would mean a faster growth of the emission of gravitational radiation. The effect of the magnetic field in tgw causes a nonmonotonic effect that first slightly increases tgw and then decreases it further by another ˜5%. (The value of the magnetic field for which tgw starts to decrease depends on the rotational frequency, but it is generally around 1015G.) Future work should be dedicated to the study of the effect of viscosity in the presence of magnetic fields, in order to establish the magnetic correction to the instability window.

Numerical simulation of magnetic nanoparticles targeting in a bifurcation vessel

NASA Astrophysics Data System (ADS)

Larimi, M. M.; Ramiar, A.; Ranjbar, A. A.

2014-08-01

Guiding magnetic iron oxide nanoparticles with the help of an external magnetic field to its target is the principle behind the development of super paramagnetic iron oxide nanoparticles (SPIONs) as novel drug delivery vehicles. The present paper is devoted to study on MDT (Magnetic Drug Targeting) technique by particle tracking in the presence of magnetic field in a bifurcation vessel. The blood flow in bifurcation is considered incompressible, unsteady and Newtonian. The flow analysis applies the time dependent, two dimensional, incompressible Navier-Stokes equations for Newtonian fluids. The Lagrangian particle tracking is performed to estimate particle behavior under influence of imposed magnetic field gradients along the bifurcation. According to the results, the magnetic field increased the volume fraction of particle in target region, but in vessels with high Reynolds number, the efficiency of MDT technique is very low. Also the results showed that in the bifurcation vessels with lower angles, wall shear stress is higher and consequently the risk of the vessel wall rupture increases.

Effect of a gap opening on the conductance of graphene with magnetic barrier structures

NASA Astrophysics Data System (ADS)

Esmailpour, Mohammad

2018-04-01

In the present study Klein tunneling in a single-layer gapped graphene was investigated by transfer matrix method under normal magnetic field for one and two magnetic barriers. Calculations show that electron transmission through a magnetic barrier is deflected to positive angles and reduces as the magnitude of magnetic field and especially the energy gap increases. This reduction is even more significant in larger fields so that after reaching a specific value of energy gap, an effective confinement for fermions and suppression of Klein tunneling is reached particularly in normal incidence and the conductance becomes zero. Unlike one barrier, the process of tunneling through two magnetic barriers induces symmetric transmission probability versus the incident angle; even, for lower energy gaps, electron transmission probability increases which in turn reduces total conductance via proper changes in the value of the magnetic field and energy gap. In general, it is concluded that confining electrons in asymmetric transmission through one barrier is conducted better than two barriers.

Magnetic small-angle neutron scattering on bulk metallic glasses: A feasibility study for imaging displacement fields

NASA Astrophysics Data System (ADS)

Mettus, Denis; Deckarm, Michael; Leibner, Andreas; Birringer, Rainer; Stolpe, Moritz; Busch, Ralf; Honecker, Dirk; Kohlbrecher, Joachim; Hautle, Patrick; Niketic, Nemanja; Fernández, Jesús Rodríguez; Barquín, Luis Fernández; Michels, Andreas

2017-12-01

Magnetic-field-dependent small-angle neutron scattering (SANS) has been utilized to study the magnetic microstructure of bulk metallic glasses (BMGs). In particular, the magnetic scattering from soft magnetic Fe70Mo5Ni5P12.5B2.5C5 and hard magnetic (Nd60Fe30Al10) 92Ni8 alloys in the as-prepared, aged, and mechanically deformed state is compared. While the soft magnetic BMGs exhibit a large field-dependent SANS response with perturbations originating predominantly from spatially varying magnetic anisotropy fields, the SANS cross sections of the hard magnetic BMGs are only weakly dependent on the field, and their angular anisotropy indicates the presence of scattering contributions due to spatially dependent saturation magnetization. Moreover, we observe an unusual increase in the magnetization of the rare-earth-based alloy after deformation. Analysis of the SANS cross sections in terms of the correlation function of the spin misalignment reveals the existence of field-dependent anisotropic long-wavelength magnetization fluctuations on a scale of a few tens of nanometers. We also give a detailed account of how the SANS technique relates to unraveling displacement fields on a mesoscopic length scale in disordered magnetic materials.

The role of magnetic fields in cluster cooling flows

NASA Technical Reports Server (NTRS)

Soker, Noam; Sarazin, Craig L.

1990-01-01

An investigation is made of the dynamical effects of the intracluster magnetic field, whose radial inflow and shear can produce a dramatic increase in the field's strength while rendering it more radial, with cooling flows. It is found that field reconnection is the most likely dominant-loss mechanism, so that buoyancy effects are probably not important. Attention is given to the effect of the magnetic field on thermal instabilities. The most important observable effect of the magnetic field in cooling flows will probably be very strong Faraday rotation of the polarization of radio sources within or behind the cooling flow.

Magnetic flux conservation in an imploding plasma.

PubMed

García-Rubio, F; Sanz, J; Betti, R

2018-01-01

The theory of magnetic flux conservation is developed for a subsonic plasma implosion and used to describe the magnetic flux degradation in the MagLIF concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010)10.1063/1.3333505]. Depending on the initial magnetic Lewis and Péclet numbers and the electron Hall parameter, the implosion falls into either a superdiffusive regime in which the magnetization decreases or a magnetized regime in which the magnetization increases. Scaling laws for magnetic field, temperature, and magnetic flux losses in the hot spot of radius R are obtained for both regimes. The Nernst velocity convects the magnetic field outwards, pushing it against the liner and enhancing the magnetic field diffusion, thereby reducing the magnetic field compression and degrading the implosion performance. However, in the magnetized regime, the core of the hot spot becomes magnetically insulated and undergoes an ideal adiabatic compression (T∼R^{-4/3} compared to T∼R^{-2/3} without magnetic field), while the detrimental Nernst term is confined to the outer part of the hot spot. Its effect is drastically reduced, improving the magnetic flux conservation.

Magnetic flux conservation in an imploding plasma

NASA Astrophysics Data System (ADS)

García-Rubio, F.; Sanz, J.; Betti, R.

2018-01-01

The theory of magnetic flux conservation is developed for a subsonic plasma implosion and used to describe the magnetic flux degradation in the MagLIF concept [S. A. Slutz et al., Phys. Plasmas 17, 056303 (2010), 10.1063/1.3333505]. Depending on the initial magnetic Lewis and Péclet numbers and the electron Hall parameter, the implosion falls into either a superdiffusive regime in which the magnetization decreases or a magnetized regime in which the magnetization increases. Scaling laws for magnetic field, temperature, and magnetic flux losses in the hot spot of radius R are obtained for both regimes. The Nernst velocity convects the magnetic field outwards, pushing it against the liner and enhancing the magnetic field diffusion, thereby reducing the magnetic field compression and degrading the implosion performance. However, in the magnetized regime, the core of the hot spot becomes magnetically insulated and undergoes an ideal adiabatic compression (T ˜R-4 /3 compared to T ˜R-2 /3 without magnetic field), while the detrimental Nernst term is confined to the outer part of the hot spot. Its effect is drastically reduced, improving the magnetic flux conservation.

Influence of static and combined magnetic fields' noises on the adaptation of the gravitropic reaction of the cress and maize roots.

NASA Astrophysics Data System (ADS)

Bogatina, Nina; Sheykina, Nadiia

Dependencies of gravitropic reactions in the static magnetic field and at different frequencies of alternative component of the combined magnetic fields were investigated. These frequencies were equal to the cyclotron frequencies of Ca2+, Mg2+ ions and ions of auxin and abscisic acid. It was shown that the increasing of magnetic field noise assisted both to the observation of biological effects and to the acceleration of adaptation processes.

Mitigating stimulated scattering processes in gas-filled Hohlraums via external magnetic fields

NASA Astrophysics Data System (ADS)

Gong, Tao; Zheng, Jian; Li, Zhichao; Ding, Yongkun; Yang, Dong; Hu, Guangyue; Zhao, Bin

2015-09-01

A simple model, based on energy and pressure equilibrium, is proposed to deal with the effect of external magnetic fields on the plasma parameters inside the laser path, which shows that the electron temperature can be significantly enhanced as the intensity of the external magnetic fields increases. With the combination of this model and a 1D three-wave coupling code, the effect of external magnetic fields on the reflectivities of stimulated scattering processes is studied. The results indicate that a magnetic field with an intensity of tens of Tesla can decrease the reflectivities of stimulated scattering processes by several orders of magnitude.

Improvement of the limit torque for the torque limiter with magnetic rheological fluid

NASA Astrophysics Data System (ADS)

Umehara, Noritsugu; Kita, Shizuo

Robots are coming to support and help our life. The robots that work together with human need to avoid sever hitting and holding that force is more than the adequate and comfortable range. In order to keep the force to the safe level in the robot arms, t he limit torque should be controlled on the basis of the case the robot used. Magnetic rheological fluids were tried to be used for the clutch that transmission torque can be controlled continuously because MR fluids can be controlled its viscosity by magnetic field. However those clutch devices were too heavy and large to use for the robot arms. Therefore we tried to increase the sensitivity of magnetic field to viscosity of MR fluids. By applying rough surface for the mating surface, sensitivity of the magnetic field to the shearing torque increase drastically in the case of co-axial torque meter. On the other hand, the changing of the size of the orifice is effective to increase the sensitivity of the magnetic field on the flow resistance in the case of the orifice type equipment.

Magnetic structure and dispersion relation of the S = 1 2 quasi-one-dimensional Ising-like antiferromagnet BaCo 2 V 2 O 8 in a transverse magnetic field

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

Matsuda, M.; Onishi, H.; Okutani, A.

Here, BaCo 2V 2O 8 consists of Co chains in which a Co 2+ ion carries a fictitious spin 1/2 with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo 2V 2O 8 in a magnetic field perpendicular to the c axis which is the chain direction. With applying magnetic field along the a axis at 3.5 K, the antiferromagnetic order with the easy axis along the c axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the b axis.more » We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in the magnetic field is reproduced by the theoretical calculation based on the spin 1/2 XXZ antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.« less

Magnetic structure and dispersion relation of the S = 1 2 quasi-one-dimensional Ising-like antiferromagnet BaCo 2 V 2 O 8 in a transverse magnetic field

DOE PAGES

Matsuda, M.; Onishi, H.; Okutani, A.; ...

2017-07-25

Here, BaCo 2V 2O 8 consists of Co chains in which a Co 2+ ion carries a fictitious spin 1/2 with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo 2V 2O 8 in a magnetic field perpendicular to the c axis which is the chain direction. With applying magnetic field along the a axis at 3.5 K, the antiferromagnetic order with the easy axis along the c axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the b axis.more » We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in the magnetic field is reproduced by the theoretical calculation based on the spin 1/2 XXZ antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.« less

Magnetic structure and dispersion relation of the S =1/2 quasi-one-dimensional Ising-like antiferromagnet BaCo2V2O8 in a transverse magnetic field

NASA Astrophysics Data System (ADS)

Matsuda, M.; Onishi, H.; Okutani, A.; Ma, J.; Agrawal, H.; Hong, T.; Pajerowski, D. M.; Copley, J. R. D.; Okunishi, K.; Mori, M.; Kimura, S.; Hagiwara, M.

2017-07-01

BaCo2V2O8 consists of Co chains in which a Co2 + ion carries a fictitious spin 1/2 with Ising anisotropy. We performed elastic and inelastic neutron scattering experiments in BaCo2V2O8 in a magnetic field perpendicular to the c axis which is the chain direction. With applying magnetic field along the a axis at 3.5 K, the antiferromagnetic order with the easy axis along the c axis, observed in zero magnetic field, is completely suppressed at 8 T, while the magnetic field gradually induces an antiferromagnetic order with the spin component along the b axis. We also studied magnetic excitations as a function of transverse magnetic field. The lower boundary of the spinon excitations splits gradually with increasing magnetic field. The overall feature of the magnetic excitation spectra in the magnetic field is reproduced by the theoretical calculation based on the spin 1/2 X X Z antiferromagnetic chain model, which predicts that the dynamic magnetic structure factor of the spin component along the chain direction is enhanced and that along the field direction has clear incommensurate correlations.

Hot spot model of MagLIF implosions: Nernst term effect on magnetic flux losses

NASA Astrophysics Data System (ADS)

Garcia Rubio, Fernando; Sanz Recio, Javier; Betti, Riccardo

2016-10-01

An analytical model of a collisional plasma being compressed by a cylindrical liner is proposed and solved in a magnetized liner inertial fusion-like context. The implosion is assumed to be isobaric, and the magnetic diffusion is confined to a thin layer near the liner. Both unmagnetized and magnetized plasma cases are considered. The model reduces to a system of two partial differential equations for temperature and magnetic field. Special attention is given to the effect of the Nernst term on the evolution of the magnetic field. Scaling laws for temperature, magnetic field, hot spot mass increase and magnetic field losses are obtained. The temperature and magnetic field spatial profiles tend to a self-similar state. It is found that when the Nernst term is taken into account, the magnetic field is advected towards the liner, and the magnetic flux losses are independent of the magnetic Lewis number. Research supported by the Spanish Ministerio de Economía y Competitividad, Project No. ENE2014-54960R. Acknowledgements to the Laboratory of Laser Energetics (Rochester) for its hospitality.

Strain-assisted current-induced magnetization reversal in magnetic tunnel junctions: A micromagnetic study with phase-field microelasticity

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

Huang, H. B., E-mail: houbinghuang@gmail.com; Department of Physics, University of Science and Technology Beijing, Beijing 100083; Hu, J. M.

2014-09-22

Effect of substrate misfit strain on current-induced in-plane magnetization reversal in CoFeB-MgO based magnetic tunnel junctions is investigated by combining micromagnetic simulations with phase-field microelasticity theory. It is found that the critical current density for in-plane magnetization reversal decreases dramatically with an increasing substrate strain, since the effective elastic field can drag the magnetization to one of the four in-plane diagonal directions. A potential strain-assisted multilevel bit spin transfer magnetization switching device using substrate misfit strain is also proposed.

Minimizing magnetic fields for precision experiments

NASA Astrophysics Data System (ADS)

Altarev, I.; Fierlinger, P.; Lins, T.; Marino, M. G.; Nießen, B.; Petzoldt, G.; Reisner, M.; Stuiber, S.; Sturm, M.; Taggart Singh, J.; Taubenheim, B.; Rohrer, H. K.; Schläpfer, U.

2015-06-01

An increasing number of measurements in fundamental and applied physics rely on magnetically shielded environments with sub nano-Tesla residual magnetic fields. State of the art magnetically shielded rooms (MSRs) consist of up to seven layers of high permeability materials in combination with highly conductive shields. Proper magnetic equilibration is crucial to obtain such low magnetic fields with small gradients in any MSR. Here, we report on a scheme to magnetically equilibrate MSRs with a 10 times reduced duration of the magnetic equilibration sequence and a significantly lower magnetic field with improved homogeneity. For the search of the neutron's electric dipole moment, our finding corresponds to a 40% improvement of the statistical reach of the measurement. However, this versatile procedure can improve the performance of any MSR for any application.

Effect of single-particle magnetostriction on the shear modulus of compliant magnetoactive elastomers.

PubMed

Kalita, Viktor M; Snarskii, Andrei A; Shamonin, Mikhail; Zorinets, Denis

2017-03-01

The influence of an external magnetic field on the static shear strain and the effective shear modulus of a magnetoactive elastomer (MAE) is studied theoretically in the framework of a recently introduced approach to the single-particle magnetostriction mechanism [V. M. Kalita et al., Phys. Rev. E 93, 062503 (2016)10.1103/PhysRevE.93.062503]. The planar problem of magnetostriction in an MAE with magnetically soft inclusions in the form of a thin disk (platelet) having the magnetic anisotropy in the plane of this disk is solved analytically. An external magnetic field acts with torques on magnetic filler particles, creates mechanical stresses in the vicinity of inclusions, induces shear strain, and increases the effective shear modulus of these composite materials. It is shown that the largest effect of the magnetic field on the effective shear modulus should be expected in MAEs with soft elastomer matrices, where the shear modulus of the matrix is less than the magnetic anisotropy constant of inclusions. It is derived that the effective shear modulus is nonlinearly dependent on the external magnetic field and approaches the saturation value in magnetic fields exceeding the field of particle anisotropy. It is shown that model calculations of the effective shear modulus correspond to a phenomenological definition of effective elastic moduli and magnetoelastic coupling constants. The obtained theoretical results compare well with known experimental data. Determination of effective elastic coefficients in MAEs and their dependence on magnetic field is discussed. The concentration dependence of the effective shear modulus at higher filler concentrations has been estimated using the method of Padé approximants, which predicts that both the absolute and relative changes of the magnetic-field-dependent effective shear modulus will significantly increase with the growing concentration of filler particles.

Effect of single-particle magnetostriction on the shear modulus of compliant magnetoactive elastomers

NASA Astrophysics Data System (ADS)

Kalita, Viktor M.; Snarskii, Andrei A.; Shamonin, Mikhail; Zorinets, Denis

2017-03-01

The influence of an external magnetic field on the static shear strain and the effective shear modulus of a magnetoactive elastomer (MAE) is studied theoretically in the framework of a recently introduced approach to the single-particle magnetostriction mechanism [V. M. Kalita et al., Phys. Rev. E 93, 062503 (2016), 10.1103/PhysRevE.93.062503]. The planar problem of magnetostriction in an MAE with magnetically soft inclusions in the form of a thin disk (platelet) having the magnetic anisotropy in the plane of this disk is solved analytically. An external magnetic field acts with torques on magnetic filler particles, creates mechanical stresses in the vicinity of inclusions, induces shear strain, and increases the effective shear modulus of these composite materials. It is shown that the largest effect of the magnetic field on the effective shear modulus should be expected in MAEs with soft elastomer matrices, where the shear modulus of the matrix is less than the magnetic anisotropy constant of inclusions. It is derived that the effective shear modulus is nonlinearly dependent on the external magnetic field and approaches the saturation value in magnetic fields exceeding the field of particle anisotropy. It is shown that model calculations of the effective shear modulus correspond to a phenomenological definition of effective elastic moduli and magnetoelastic coupling constants. The obtained theoretical results compare well with known experimental data. Determination of effective elastic coefficients in MAEs and their dependence on magnetic field is discussed. The concentration dependence of the effective shear modulus at higher filler concentrations has been estimated using the method of Padé approximants, which predicts that both the absolute and relative changes of the magnetic-field-dependent effective shear modulus will significantly increase with the growing concentration of filler particles.

Rotating magnetic field induced oscillation of magnetic particles for in vivo mechanical destruction of malignant glioma.

PubMed

Cheng, Yu; Muroski, Megan E; Petit, Dorothée C M C; Mansell, Rhodri; Vemulkar, Tarun; Morshed, Ramin A; Han, Yu; Balyasnikova, Irina V; Horbinski, Craig M; Huang, Xinlei; Zhang, Lingjiao; Cowburn, Russell P; Lesniak, Maciej S

2016-02-10

Magnetic particles that can be precisely controlled under a magnetic field and transduce energy from the applied field open the way for innovative cancer treatment. Although these particles represent an area of active development for drug delivery and magnetic hyperthermia, the in vivo anti-tumor effect under a low-frequency magnetic field using magnetic particles has not yet been demonstrated. To-date, induced cancer cell death via the oscillation of nanoparticles under a low-frequency magnetic field has only been observed in vitro. In this report, we demonstrate the successful use of spin-vortex, disk-shaped permalloy magnetic particles in a low-frequency, rotating magnetic field for the in vitro and in vivo destruction of glioma cells. The internalized nanomagnets align themselves to the plane of the rotating magnetic field, creating a strong mechanical force which damages the cancer cell structure inducing programmed cell death. In vivo, the magnetic field treatment successfully reduces brain tumor size and increases the survival rate of mice bearing intracranial glioma xenografts, without adverse side effects. This study demonstrates a novel approach of controlling magnetic particles for treating malignant glioma that should be applicable to treat a wide range of cancers. Copyright © 2015 Elsevier B.V. All rights reserved.

Combined effects of complex magnetic fields and agmatine for contextual fear learning deficits in rats.

PubMed

McKay, B E; Persinger, M A

2003-04-18

Acute post-training exposures to weak intensity theta-burst stimulation (TBS) patterned complex magnetic fields attenuated the magnitude of conditioned fear learning for contextual stimuli. A similar learning impairment was evoked in a linear and dose-dependent manner by pre-conditioning injections of the polyamine agmatine. The present study examined the hypothesis that whole-body applications of the TBS complex magnetic field pattern when co-administered with systemic agmatine treatment may combine to evoke impairments in contextual fear learning. Within minutes of 4 mg/kg agmatine injections, male Wistar rats were fear conditioned to contextual stimuli and immediately exposed for 30 min to the TBS patterned complex magnetic field or to sham conditions. TBS patterned complex magnetic field treatment was found to linearly summate with the contextual fear learning impairment evoked by agmatine treatment alone. Furthermore, we report for sham-treated rats, but not rats exposed to the synthetic magnetic field pattern, that the magnitude of learned fear decreased and the amount of variability in learning increased, as the K-index (a measure of change in intensity of the time-varying ambient geomagnetic field) increased during the 3-hr intervals over which conditioning and testing sessions were conducted.

Generation of helical magnetic field in a viable scenario of inflationary magnetogenesis

NASA Astrophysics Data System (ADS)

Sharma, Ramkishor; Subramanian, Kandaswamy; Seshadri, T. R.

2018-04-01

We study the generation of helical magnetic fields in a model of inflationary magnetogenesis which is free from the strong coupling and backreaction problems. To generate helical magnetic fields, we add an f2F˜μ νFμ ν term to the Lagrangian of the Ratra model. The strong coupling and backreaction problems are avoided if we take a particular behavior of coupling function f , in which f increases during inflation and decreases postinflation to reheating. The generated magnetic field is fully helical and has a blue spectrum, d ρB/d ln k ∝k4. This spectrum is obtained when coupling function f ∝a2 during inflation. The scale of reheating in our model has to be lower than 4000 GeV to avoid backreaction postinflation. The generated magnetic field spectrum satisfies the γ -ray bound for all the possible scales of reheating. The comoving magnetic field strength and its correlation length are ˜4 ×10-11 G and 70 kpc respectively, if reheating takes place at 100 GeV. For reheating at the QCD scales of 150 MeV, the field strength increases to ˜ nano gauss, with coherence scale of 0.6 Mpc.

New measurements of photospheric magnetic fields in late-type stars and emerging trends

NASA Technical Reports Server (NTRS)

Saar, S. H.; Linsky, J. L.

1986-01-01

The magnetic fields of late-type stars are measured using the method of Saar et al. (1986). The method includes radiative transfer effects and compensation for line blending; the photospheric magnetic field parameters are derived by comparing observed and theoretical line profiles using an LTE code that includes line saturation and full Zeeman pattern. The preliminary mean active region magnetic field strengths (B) and surface area coverages for 20 stars are discussed. It is observed that there is a trend of increasing B towards the cooler dwarfs stars, and the linear correlation between B and the equipartition value of the magnetic field strength suggests that the photospheric gas pressure determines the photospheric magnetic field strengths. A tendency toward larger filling factors at larger stellar angular velocities is also detected.

Dramatic impact of the giant local magnetic fields on spin-dependent recombination processes in gadolinium based garnets

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

Romanov, N. G., E-mail: nikolai.romanov@mail.ioffe.ru; Tolmachev, D. O.; Gurin, A. S.

2015-06-29

A giant magnetic field effect on spin-dependent recombination of the radiation-induced defects has been found in cerium doped gadolinium based garnet crystals and ceramics, promising materials for scintillator applications. A sharp and strong increase in the afterglow intensity stimulated by external magnetic field and an evidence of the magnetic field memory have been discovered. The effect was ascribed to huge Gd-induced internal magnetic fields, which suppress the recombination, and cross-relaxation with Gd{sup 3+} ions leading to reorientation of the spins of the electron and hole centers. Thus, the spin system of radiation-induced defects in gadolinium garnet based scintillator materials wasmore » shown to accumulate significant energy which can be released in external magnetic fields.« less

MAGNETIC END CLOSURES FOR PLASMA CONFINING AND HEATING DEVICES

DOEpatents

Post, R.F.

1963-08-20

More effective magnetic closure field regions for various open-ended containment magnetic fields used in fusion reactor devices are provided by several spaced, coaxially-aligned solenoids utilized to produce a series of nodal field regions of uniform or, preferably, of incrementally increasing intensity separated by lower intensity regions outwardly from the ends of said containment zone. Plasma sources may also be provided to inject plasma into said lower intensity areas to increase plasma density therein. Plasma may then be transported, by plasma diffusion mechanisms provided by the nodal fields, into the containment field. With correlated plasma densities and nodal field spacings approximating the mean free partl cle collision path length in the zones between the nodal fields, optimum closure effectiveness is obtained. (AEC)

Magnetic field control of microstructural development in melt-spun Pr 2 Co 14 B

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

McGuire, Michael A.; Rios, Orlando; Conner, Ben S.

In the processing of commercial rare earth permanent magnets, use of external magnetic fields is limited mainly to the alignment of anisotropic particles and the polarization of the finished magnets. Here we explore the effects of high magnetic fields on earlier stages of magnet synthesis, including the crystallization and chemical phase transformations that produce the 2:14:1 phase in the Pr-Co-B system. Pr 2Co 14B alloys produced by melt-spinning were annealed in the presence of strong applied magnetic fields (H=90 kOe). The resulting materials were characterized by x-ray diffraction, electron microscopy, and magnetization measurements. We find that magnetic fields suppress themore » nucleation and growth of crystalline phases, resulting in significantly smaller particle sizes. In addition, magnetic fields applied during processing strongly affects chemical phase selection, suppressing the formation of Pr 2Co 14B and α-Co in favor of Pr 2Co 17. Here, the results demonstrate that increased control over key microstructural properties is achievable by including a strong magnetic field as a processing parameter for rare-earth magnet materials.« less

Magnetic field control of microstructural development in melt-spun Pr 2 Co 14 B

DOE PAGES

McGuire, Michael A.; Rios, Orlando; Conner, Ben S.; ...

2017-01-27

In the processing of commercial rare earth permanent magnets, use of external magnetic fields is limited mainly to the alignment of anisotropic particles and the polarization of the finished magnets. Here we explore the effects of high magnetic fields on earlier stages of magnet synthesis, including the crystallization and chemical phase transformations that produce the 2:14:1 phase in the Pr-Co-B system. Pr 2Co 14B alloys produced by melt-spinning were annealed in the presence of strong applied magnetic fields (H=90 kOe). The resulting materials were characterized by x-ray diffraction, electron microscopy, and magnetization measurements. We find that magnetic fields suppress themore » nucleation and growth of crystalline phases, resulting in significantly smaller particle sizes. In addition, magnetic fields applied during processing strongly affects chemical phase selection, suppressing the formation of Pr 2Co 14B and α-Co in favor of Pr 2Co 17. Here, the results demonstrate that increased control over key microstructural properties is achievable by including a strong magnetic field as a processing parameter for rare-earth magnet materials.« less

Zero field reversal probability in thermally assisted magnetization reversal

NASA Astrophysics Data System (ADS)

Prasetya, E. B.; Utari; Purnama, B.

2017-11-01

This paper discussed about zero field reversal probability in thermally assisted magnetization reversal (TAMR). Appearance of reversal probability in zero field investigated through micromagnetic simulation by solving stochastic Landau-Lifshitz-Gibert (LLG). The perpendicularly anisotropy magnetic dot of 50×50×20 nm3 is considered as single cell magnetic storage of magnetic random acces memory (MRAM). Thermally assisted magnetization reversal was performed by cooling writing process from near/almost Curie point to room temperature on 20 times runs for different randomly magnetized state. The results show that the probability reversal under zero magnetic field decreased with the increase of the energy barrier. The zero-field probability switching of 55% attained for energy barrier of 60 k B T and the reversal probability become zero noted at energy barrier of 2348 k B T. The higest zero-field switching probability of 55% attained for energy barrier of 60 k B T which corespond to magnetif field of 150 Oe for switching.

Magnetic properties of magnetic bilayer Kekulene structure: A Monte Carlo study

NASA Astrophysics Data System (ADS)

Jabar, A.; Masrour, R.

2018-06-01

In the present work, we have studied the magnetic properties of magnetic bilayer Kekulene structure with mixed spin-5/2 and spin-2 Ising model using Monte Carlo study. The magnetic phase diagrams of mixed spins Ising model have been given. The thermal total, partial magnetization and magnetic susceptibilities of the mixed spin-5/2 and spin-2 Ising model on a magnetic bilayer Kekulene structure are obtained. The transition temperature has been deduced. The effect of crystal field and exchange interactions on the this bilayers has been studied. The partial and total magnetic hysteresis cycles of the mixed spin-5/2 and spin-2 Ising model on a magnetic bilayer Kekulene structure have been given. The superparamagnetism behavior is observed in magnetic bilayer Kekulene structure. The magnetic coercive field decreases with increasing the exchange interactions between σ-σ and temperatures values and increases with increasing the absolute value of exchange interactions between σ-S. The multiple hysteresis behavior appears.

Evaluation of Occupational Exposure to Magnetic Fields and Motor Neuron Disease Mortality in a Population-Based Cohort

PubMed Central

Parlett, Lauren E.; Bowman, Joseph D.; van Wijngaarden, Edwin

2015-01-01

Objective Epidemiologic evidence for the association between electromagnetic fields and amyotrophic lateral sclerosis, the most common form of motor neuron disease (MND), has been inconclusive. We evaluated the association between electromagnetic fields and MND among workers in occupations potentially exposed to magnetic fields. Methods MND mortality (ICD-9 335.2) was examined in the National Longitudinal Mortality Study using multivariable proportional hazards models. Occupational exposure to magnetic fields was determined on the basis of a population-based job-exposure matrix. Age at entry, education, race, sex, and income were considered for inclusion as covariates. Results After adjusting for age, sex, and education, there were no increased risks of MND mortality in relation to potential magnetic field exposure, with hazard ratios around the null in all magnetic field exposure quartiles. Conclusions Our study does not provide evidence for an association between magnetic field exposure and MND mortality. PMID:22076040

A novel electron accelerator for MRI-Linac radiotherapy.

PubMed

Whelan, Brendan; Gierman, Stephen; Holloway, Lois; Schmerge, John; Keall, Paul; Fahrig, Rebecca

2016-03-01

MRI guided radiotherapy is a rapidly growing field; however, current electron accelerators are not designed to operate in the magnetic fringe fields of MRI scanners. As such, current MRI-Linac systems require magnetic shielding, which can degrade MR image quality and limit system flexibility. The purpose of this work was to develop and test a novel medical electron accelerator concept which is inherently robust to operation within magnetic fields for in-line MRI-Linac systems. Computational simulations were utilized to model the accelerator, including the thermionic emission process, the electromagnetic fields within the accelerating structure, and resulting particle trajectories through these fields. The spatial and energy characteristics of the electron beam were quantified at the accelerator target and compared to published data for conventional accelerators. The model was then coupled to the fields from a simulated 1 T superconducting magnet and solved for cathode to isocenter distances between 1.0 and 2.4 m; the impact on the electron beam was quantified. For the zero field solution, the average current at the target was 146.3 mA, with a median energy of 5.8 MeV (interquartile spread of 0.1 MeV), and a spot size diameter of 1.5 mm full-width-tenth-maximum. Such an electron beam is suitable for therapy, comparing favorably to published data for conventional systems. The simulated accelerator showed increased robustness to operation in in-line magnetic fields, with a maximum current loss of 3% compared to 85% for a conventional system in the same magnetic fields. Computational simulations suggest that replacing conventional DC electron sources with a RF based source could be used to develop medical electron accelerators which are robust to operation in in-line magnetic fields. This would enable the development of MRI-Linac systems with no magnetic shielding around the Linac and reduce the requirements for optimization of magnetic fringe field, simplify design of the high-field magnet, and increase system flexibility.

A novel electron accelerator for MRI-Linac radiotherapy

PubMed Central

Whelan, Brendan; Gierman, Stephen; Holloway, Lois; Schmerge, John; Keall, Paul; Fahrig, Rebecca

2016-01-01

Purpose: MRI guided radiotherapy is a rapidly growing field; however, current electron accelerators are not designed to operate in the magnetic fringe fields of MRI scanners. As such, current MRI-Linac systems require magnetic shielding, which can degrade MR image quality and limit system flexibility. The purpose of this work was to develop and test a novel medical electron accelerator concept which is inherently robust to operation within magnetic fields for in-line MRI-Linac systems. Methods: Computational simulations were utilized to model the accelerator, including the thermionic emission process, the electromagnetic fields within the accelerating structure, and resulting particle trajectories through these fields. The spatial and energy characteristics of the electron beam were quantified at the accelerator target and compared to published data for conventional accelerators. The model was then coupled to the fields from a simulated 1 T superconducting magnet and solved for cathode to isocenter distances between 1.0 and 2.4 m; the impact on the electron beam was quantified. Results: For the zero field solution, the average current at the target was 146.3 mA, with a median energy of 5.8 MeV (interquartile spread of 0.1 MeV), and a spot size diameter of 1.5 mm full-width-tenth-maximum. Such an electron beam is suitable for therapy, comparing favorably to published data for conventional systems. The simulated accelerator showed increased robustness to operation in in-line magnetic fields, with a maximum current loss of 3% compared to 85% for a conventional system in the same magnetic fields. Conclusions: Computational simulations suggest that replacing conventional DC electron sources with a RF based source could be used to develop medical electron accelerators which are robust to operation in in-line magnetic fields. This would enable the development of MRI-Linac systems with no magnetic shielding around the Linac and reduce the requirements for optimization of magnetic fringe field, simplify design of the high-field magnet, and increase system flexibility. PMID:26936713

Vector magnetic field evolution, energy storage, and associated photospheric velocity shear within a flare-productive active region

NASA Technical Reports Server (NTRS)

Krall, K. R.; Smith, J. B., Jr.; Hagyard, M. J.; West, E. A.; Cummings, N. P.

1982-01-01

Sheared photospheric velocity fields inferred from spot motions for April 5-7, 1980, are compared with both transverse magnetic field orientation changes and with the region's flare history. Rapid spot motions and high inferred velocity shear coincide with increased field alignment along the longitudinal neutral line and with increased flare activity, while a later decrease in velocity shear precedes a more relaxed magnetic configuration and decrease in flare activity. It is estimated that magnetic reconfiguration produced by the relative velocities of the spots could cause storage of about 10 to the 32nd erg/day, while flares occurring during this time expended no more than about 10 to the 31st erg/day.

Formation of space-charge bunches in a multivelocity-electron-beam-based microwave oscillator with a cathode unshielded from the magnetic field

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

Kalinin, Yu. A.; Starodubov, A. V.; Fokin, A. S., E-mail: alexander1989fokin@mail.ru

The influence of the magnitude and configuration of the magnetic field on the parameters of electron bunches formed in a multivelocity electron beam is analyzed. It is shown that the use of a cathode unshielded from the magnetic field and a nonuniform magnetic field increasing along the drift space enables the formation of compact electron bunches. The ratio between the current density in such bunches and the beam current density at the entrance to the drift space reaches 10{sup 6}, which results in a substantial broadening of the output microwave spectrum due to an increase in the amplitudes of themore » higher harmonics of the fundamental frequency.« less

Elliptical spreading characteristics of a liquid metal droplet impact on a glass surface under a horizontal magnetic field

NASA Astrophysics Data System (ADS)

Yang, Juan-Cheng; Qi, Tian-Yu; Han, Tian-Yang; Zhang, Jie; Ni, Ming-Jiu

2018-01-01

The spreading characteristics of a liquid GaInSn alloy droplet on a glass surface with the action of a horizontal magnetic field have been experimentally investigated in the present paper. With changing the impact velocity from 0.1 m/s to 1.2 m/s and increasing the magnetic field from 0 T to 1.6 T, we focus on studying the influence of the horizontal magnetic field on the spreading characteristics of a liquid metal droplet using the shadow-graph method. The elliptical spreading pattern of a liquid metal droplet induced by the horizontal magnetic field was discovered by experiments. By introducing a numerical method in getting the distribution of current lines and the Lorentz force inside the droplet, we give a detailed explanation on the mechanism of elliptical spreading. Furthermore, some quantitative results on a maximum spreading factor and time at moment of maximum spreading varied with the Hartmann number and Weber number are shown to give us a comprehensive understanding of the elliptical spreading. With the increasing of the magnetic field, the maximum spreading factor in the front view is reduced while that in the side view is increased, which reveals a larger deformation happened during the spreading process. While with the increasing of impact velocity, the spreading factor increased. Finally, we present a non-dimensional parameter to get scaling laws for the averaged maximum spreading factor and the aspect ratio of the maximum spreading factor; results show that the predict data can agree with experimental data in a certain degree.

Magneto-absorption effects in magnetic-field assisted laser ablation of silicon by UV nanosecond pulses

NASA Astrophysics Data System (ADS)

Farrokhi, H.; Gruzdev, V.; Zheng, H. Y.; Rawat, R. S.; Zhou, W.

2016-06-01

A constant magnetic field can significantly improve the quality and speed of ablation by nanosecond laser pulses. These improvements are usually attributed to the confinement of laser-produced plasma by the magnetic field and specific propagation effects in the magnetized plasma. Here we report a strong influence of constant axial magnetic field on the ablation of silicon by 20-ns laser pulses at wavelength 355 nm, which results in an increase of ablation depth by a factor of 1.3 to 69 depending on laser parameters and magnitude of the magnetic field. The traditional plasma effects do not explain this result, and magneto-absorption of silicon is proposed as one of the major mechanisms of the significant enhancement of ablation.

Changes in collection efficiency in nylon net filter media through magnetic alignment of elongated aerosol particles.

PubMed

Lam, Christopher O; Finlay, W H

2009-10-01

Fiber aerosols tend to align parallel to surrounding fluid streamlines in shear flows, making their filtration more difficult. However, previous research indicates that composite particles made from cromoglycic acid fibers coated with small nanoscaled magnetite particles can align with an applied magnetic field. The present research explored the effect of magnetically aligning these fibers to increase their filtration. Nylon net filters were challenged with the aerosol fibers, and efficiency tests were performed with and without a magnetic field applied perpendicular to the flow direction. We investigated the effects of varying face velocities, the amount of magnetite material on the aerosol particles, and magnetic field strengths. Findings from the experiments, matched by supporting single-fiber theories, showed significant efficiency increases at the low face velocity of 1.5 cm s(-1) at all magnetite compositions, with efficiencies more than doubling due to magnetic field alignment in certain cases. At a higher face velocity of 5.12 cm s(-1), filtration efficiencies were less affected by the magnetic field alignment being, at most, 43% higher for magnetite weight compositions up to 30%, while at a face velocity of 10.23 cm s(-1) alignment effects were insignificant. In most cases, efficiencies became independent of magnetic field strength above 50 mT, suggesting full alignment of the fibers. The present data suggest that fiber alignment in a magnetic field may warrant applications in the filtration and detection of fibers, such as asbestos.

A magnetic-dependent protein corona of tailor-made superparamagnetic iron oxides alters their biological behaviors

NASA Astrophysics Data System (ADS)

Liu, Ziyao; Zhan, Xiaohui; Yang, Minggang; Yang, Qi; Xu, Xianghui; Lan, Fang; Wu, Yao; Gu, Zhongwei

2016-03-01

In recent years, it is becoming increasingly evident that once nanoparticles come into contact with biological fluids, a protein corona surely forms and critically affects the biological behaviors of nanoparticles. Herein, we investigate whether the formation of protein corona on the surface of superparamagnetic iron oxides (SPIOs) is influenced by static magnetic field. Under static magnetic field, there is no obvious variation in the total amount of protein adsorption, but the proportion of adsorbed proteins significantly changes. Noticeably, certain proteins including apolipoproteins, complement system proteins and acute phase proteins, increase in the protein corona of SPIOs in the magnetic field. More importantly, the magnetic-dependent protein corona of SPIOs enhances the cellular uptake of SPIOs into the normal cell line (3T3 cells) and tumor cell line (HepG2 cells), due to increased adsorption of apolipoprotein. In addition, SPIOs with the magnetic-dependent protein corona cause high cytotoxicity to 3T3 cells and HepG2 cells. This work discloses that superparamagnetism as a key feature of SPIOs affects the composition of protein corona to a large extent, which further alters the biological behaviors of SPIOs.In recent years, it is becoming increasingly evident that once nanoparticles come into contact with biological fluids, a protein corona surely forms and critically affects the biological behaviors of nanoparticles. Herein, we investigate whether the formation of protein corona on the surface of superparamagnetic iron oxides (SPIOs) is influenced by static magnetic field. Under static magnetic field, there is no obvious variation in the total amount of protein adsorption, but the proportion of adsorbed proteins significantly changes. Noticeably, certain proteins including apolipoproteins, complement system proteins and acute phase proteins, increase in the protein corona of SPIOs in the magnetic field. More importantly, the magnetic-dependent protein corona of SPIOs enhances the cellular uptake of SPIOs into the normal cell line (3T3 cells) and tumor cell line (HepG2 cells), due to increased adsorption of apolipoprotein. In addition, SPIOs with the magnetic-dependent protein corona cause high cytotoxicity to 3T3 cells and HepG2 cells. This work discloses that superparamagnetism as a key feature of SPIOs affects the composition of protein corona to a large extent, which further alters the biological behaviors of SPIOs. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr08447d

Effect of orientational ordering of magnetic nanoemulsions immobilized in agar gel on magnetic hyperthermia

NASA Astrophysics Data System (ADS)

Lahiri, B. B.; Ranoo, Surojit; Philip, John

2018-04-01

Magnetic nanoemulsions of droplet size ∼200 nm, loaded with single domain superparamagnetic nanoparticles (MNP), are potential candidates for multimodal hyperthermia due to availability of large loading volume and enhanced permeation and retention (EPR) in the cancerous tissues. In such nanoemulsions, radio frequency alternating magnetic field induced heating occur at two entirely different length scales, viz. Neel-Brown relaxation of the dispersed MNP and Brownian relaxation of emulsion droplets. Here we study the effects of orientation ordering or texturing of droplets, immobilized in a tissue mimicking agar matrix, on the field induced heating efficiency. A higher specific absorption rate (maximum ∼73 ± 2 W/gFe) is observed for droplets orientated parallel to the direction of the alternating magnetic field because of the enhancement of effective uniaxial anisotropy energy density and increased effective relaxation time. For identical and non-interacting MNP oriented parallel to the external DC magnetic field, a threefold increase in the effective uniaxial anisotropy energy density and ∼20-30% increased specific absorption rate are observed as compared to those oriented perpendicular to the magnetic field. Magnetic force microscopy images showed that the spherical morphology of the droplets remains intact even after orientational ordering and average topographic height of the droplets are found to be ∼220 (±17) nm, which is in good agreement with the most probable size obtained from dynamic light scattering. The residual volume magnetization of the emulsion droplets is found to be 1.1 × 10-6 emu/cc, indicating the superparamagnetic nature of the droplets in tissue equivalent environment. The observed increase in heating efficiency of the immobilized and oriented emulsion droplets shows promising applications in multimodal hyperthermia therapy because of the requirement of lower dose of MNP and shorter treatment time.

The influence of convective blueshift on radial velocities of F, G, and K stars

NASA Astrophysics Data System (ADS)

Bauer, F. F.; Reiners, A.; Beeck, B.; Jeffers, S. V.

2018-02-01

Context. Apparent radial velocity (RV) signals induced by stellar surface features such as spots and plages can result in a false planet detection or hide the presence of an orbiting planet. Our ability to detect rocky exoplanets is currently limited by our understanding of such stellar signals. Aims: We model RV variations caused by active regions on the stellar surface of typical exoplanet-hosting stars of spectral type F, G, and K. We aim to understand how the stellar magnetic field strength, convective blueshift, and spot temperatures can influence RV signals caused by active regions. Methods: We use magneto-hydrodynamic (MHD) simulations for stars with spectral types F3V, a G2V, and a K5V. We quantify the impact of the magnetic field strength inside active regions on the RV measurement using the magnetic and non-magnetic FeI lines at 6165 Å and 6173 Å. We also quantify the impact of spot temperature and convective blueshift on the measured RV values. Results: Increasing the magnetic field strength increases the efficiency to suppress convection in active regions which results in an asymmetry between red- and blueshifted parts of the RV curves. A stronger suppression of convection also leads to an observed increase in RV amplitude for stronger magnetic fields. The MHD simulations predict convective motions to be faster in hotter stars. The suppression of faster convection leads to a stronger RV amplitude increase in hotter stars when the magnetic field is increased. While suppression of convection increases the asymmetry in RV curves,c a decreasing spot temperature counteracts this effect. When using observed temperatures for dark spots in our simulations we find that convective blueshift effects are negligible.

Study on the Ising Antiferromagnet in an External Magnetic Field

NASA Astrophysics Data System (ADS)

Kim, Seung-Yeon

2018-06-01

In an external magnetic field, the properties of an antiferromagnet are much less well understood than those of a ferromagnet are. An abnormal peak in the specific heat of matter at a low temperature, the so-called Schottky anomaly, is one of the most universal phenomena, and it is the most important concept in studying experimentally the low-energy structure of matter. We investigate the unknown properties of the Ising antiferromagnet in an external magnetic field B, in particular, the magnetic-field dependence of the Schottky anomaly of the Ising antiferromagnet systematically. We find three different kinds of Schottky anomalies for the Ising antiferromagnet. First, for B > B c , where B c is the critical magnetic field, both the maximum of the Schottky anomaly C s ( B) and the Schottky temperature T s ( B) increase as B increases. In particular, T s ( B) follows T s ( B) = 0.8336( B - B c ) only for B > B c . Second, for B < B c , both the maximum of the Schottky anomaly and the Schottky temperature decrease as B increases, in clear contrast to the increasing behaviors of the Schottky anomaly for B > B c . Third, at B = B c , the unusual Schottky anomaly appears due to the nonzero ground-state entropy, similar to real ice and spin glass. We expect that our results will play a vital role in measuring and understanding the properties of an antiferromagnet and related materials in an external magnetic field.

Effect of DC magnetic field on atmospheric pressure argon plasma jet

NASA Astrophysics Data System (ADS)

Safari, R.; Sohbatzadeh, F.

2015-05-01

In this work, external DC magnetic field effect on the atmospheric pressure plasma jet has been investigated, experimentally. The magnetic field has been produced using a Helmholtz coil configuration. It has been applied parallel and transverse to the jet flow. The strength of the DC magnetic field is 0-0.28 and 0-0.57 Tesla between the two coils in parallel and transverse applications, respectively. It has been shown that the plasma gas flow plays the main role in magneto-active collision-dominated plasma. The effect of plasma fluid velocity on the jet emission has been discussed, qualitatively. It has been observed that the external DC magnetic field has different trends in parallel and transverse applications. The measurements reveal that the plasma jet irradiance increases in parallel field, while it decreases in transverse field. The former has been attributed to increasing plasma number density and the latter to loss of plasma species that reduces the magneto-plasma jet irradiance and in turn shrinks plasma jet number density. As a result, the plasma fluid velocity is responsible for such trends though the magneto-active plasma remains isotropic.

Abnormal Magnetic Field Effects on Electrogenerated Chemiluminescence

NASA Astrophysics Data System (ADS)

Pan, Haiping; Shen, Yan; Wang, Hongfeng; He, Lei; Hu, Bin

2015-03-01

We report abnormal magnetic field effects on electrogenerated chemiluminescence (MFEECL) based on triplet emission from the Ru(bpy)3Cl2-TPrA electrochemical system: the appearance of MFEECL after magnetic field ceases. In early studies the normal MFEECL have been observed from electrochemical systems during the application of magnetic field. Here, the abnormal MFEECL suggest that the activated charge-transfer [Ru(bpy)33+ … TPrA•] complexes may become magnetized in magnetic field and experience a long magnetic relaxation after removing magnetic field. Our analysis indicates that the magnetic relaxation can gradually increase the density of charge-transfer complexes within reaction region due to decayed magnetic interactions, leading to a positive component in the abnormal MFEECL. On the other hand, the magnetic relaxation facilitates an inverse conversion from triplets to singlets within charge-transfer complexes. The inverse triplet --> singlet conversion reduces the density of triplet light-emitting states through charge-transfer complexes and gives rise to a negative component in the abnormal MFEECL. The combination of positive and negative components can essentially lead to a non-monotonic profile in the abnormal MFEECL after ceasing magnetic field. Nevertheless, our experimental studies may reveal un-usual magnetic behaviors with long magnetic relaxation from the activated charge-transfer [Ru(bpy)33+ … TPrA•] complexes in solution at room temperature.

An approach to improving the signal-to-optical-noise ratio of pulsed magnetic field photonic sensors

NASA Astrophysics Data System (ADS)

Wang, Jiang-ping; Li, Yu-quan

2008-12-01

During last years, interest in pulsed magnetic field sensors has widely increased. In fact, magnetic field measurement has a critical part in various scientific and technical areas. In order to research on pulsed magnetic field characteristic and corresponding measuring and defending means, a sensor with high immunity to electrical noise, high sensitivity, high accuracy and wide dynamic range is needed. The conventional magnetic field measurement system currently use active metallic probes which can disturb the measuring magnetic field and make sensor very sensitive to electromagnetic noise. Photonic magnetic field sensor exhibit great advantages with respect to the electronic ones: a very good galvanic insulation, high sensitivity and very wide bandwidth. Photonic sensing technology is fit for demand of a measure pulsed magnetic field. A type of pulsed magnetic field photonic sensor has been designed, analyzed, and tested. The cross polarization angle in photonic sensor effect on the signal-to-optical-noise ratio is theoretically analyzed in this paper. A novel approach for improving the signal-to-optical-noise ratio of pulsed magnetic field sensors was proposed. The experiments have proved that this approach is practical. The theoretical analysis and simulation results show that the signal-to-optical-noise ratio can potentially be considerably improved by setup suitable for the cross polarization angle.

Solar Dynamo Driven by Periodic Flow Oscillation

NASA Technical Reports Server (NTRS)

Mayr, Hans G.; Hartle, Richard E.; Einaudi, Franco (Technical Monitor)

2001-01-01

We have proposed that the periodicity of the solar magnetic cycle is determined by wave mean flow interactions analogous to those driving the Quasi Biennial Oscillation in the Earth's atmosphere. Upward propagating gravity waves would produce oscillating flows near the top of the radiation zone that in turn would drive a kinematic dynamo to generate the 22-year solar magnetic cycle. The dynamo we propose is built on a given time independent magnetic field B, which allows us to estimate the time dependent, oscillating components of the magnetic field, (Delta)B. The toroidal magnetic field (Delta)B(sub phi) is directly driven by zonal flow and is relatively large in the source region, (Delta)(sub phi)/B(sub Theta) much greater than 1. Consistent with observations, this field peaks at low latitudes and has opposite polarities in both hemispheres. The oscillating poloidal magnetic field component, (Delta)B(sub Theta), is driven by the meridional circulation, which is difficult to assess without a numerical model that properly accounts for the solar atmosphere dynamics. Scale-analysis suggests that (Delta)B(sub Theta) is small compared to B(sub Theta) in the dynamo region. Relative to B(sub Theta), however, the oscillating magnetic field perturbations are expected to be transported more rapidly upwards in the convection zone to the solar surface. As a result, (Delta)B(sub Theta) (and (Delta)B(sub phi)) should grow relative to B(sub Theta), so that the magnetic fields reverse at the surface as observed. Since the meridional and zonai flow oscillations are out of phase, the poloidal magnetic field peaks during times when the toroidal field reverses direction, which is observed. With the proposed wave driven flow oscillation, the magnitude of the oscillating poloidal magnetic field increases with the mean rotation rate of the fluid. This is consistent with the Bode-Blackett empirical scaling law, which reveals that in massive astrophysical bodies the magnetic moment tends to increase with the angular momentum of the fluid.

Magnetization Switching of a Co /Pt Multilayered Perpendicular Nanomagnet Assisted by a Microwave Field with Time-Varying Frequency

NASA Astrophysics Data System (ADS)

Suto, Hirofumi; Kanao, Taro; Nagasawa, Tazumi; Mizushima, Koichi; Sato, Rie

2018-05-01

Microwave-assisted magnetization switching (MAS) is attracting attention as a method for reversing nanomagnets with a high magnetic anisotropy by using a small-amplitude magnetic field. We experimentally study MAS of a perpendicularly magnetized nanomagnet by applying a microwave magnetic field with a time-varying frequency. Because the microwave field frequency can follow the nonlinear decrease of the resonance frequency, larger magnetization excitation than that in a constant-frequency microwave field is induced, which enhances the MAS effect. The switching field decreases almost linearly as the start value of the time-varying microwave field frequency increases, and it becomes smaller than the minimum switching field in a constant-frequency microwave field. To obtain this enhancement of the MAS effect, the end value of the time-varying microwave field frequency needs to be almost the same as or lower than the critical frequency for MAS in a constant-frequency microwave field. In addition, the frequency change typically needs to take 1 ns or longer to make the rate of change slow enough for the magnetization to follow the frequency change. This switching behavior is qualitatively explained by the theory based on the macrospin model.

Frequency and field dependent dynamic properties of CoFe{sub 2−x}Al{sub x}O{sub 4} ferrite nanoparticles

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

Kuanr, Bijoy K.; Department of Physics, University of Colorado, 1420 Austin Bluffs Parkway, Colorado Springs, CO 80918; Mishra, S.R., E-mail: srmishra@memphis.edu

2016-04-15

Highlights: “CoFe{sub 2−x} Al{sub x}O{sub 4} ferrite nanoparticles: Static and dynamic properties” • Grain size reduction with Al{sup 3+} content. • Reduction in Ms, Hc, with increasing Al{sup 3+} content. • Increase in resonance frequency with applied field. • Decrease in resonance field with increase in Al{sup 3+} content. • Decrease in Gilbert parameter with increase in Al{sup 3+} content. - Abstract: Aluminum doped CoFe{sub 2−x}Al{sub x}O{sub 4} (0 ≤ x ≤ 0.9) nanoparticles were synthesized via auto-combustion. Formation of single phase cubic spinel structure was confirmed by X-ray diffraction (XRD) analysis. XRD analysis suggests a linear decrease in latticemore » cell parameters and grain size (90–55 nm) with the increase in Al{sup 3+} content. The saturation magnetization of samples decrease with increasing Al{sup 3+} content due to magnetic dilution effect. A concomitant linear reduction in coercivity was also observed mainly due to decrease in magnetic anisotropy. Frequency and field dependent dynamic properties of nanoparticles were studied by ferromagnetic resonance (FMR) technique. The resonance frequency increases linearly with magnetic field for all nanoparticles. Magnetic field dependent experimental absorption data (S{sub 21} vs. frequency) were compared with effective medium theory considering an effective demagnetization field and was observed to be in good agreement with each other. High Al{sup 3+} content reduces the Gilbert damping parameter thus making CoFe{sub 2−x}Al{sub x}O{sub 4} as an attractive material for high frequency applications.« less

The slow collisional E×B ion drift characterized as the major instability mechanism of a poorly magnetized plasma column with an inward-directed radial electric field

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

Pierre, Thiéry

2016-04-15

The low-frequency instability of a cylindrical poorly magnetized plasma with an inward-directed radial electric field is studied changing the gas pressure and the ion cyclotron frequency. The unstable frequency always decreases when the gas pressure is increased indicating collisional effects. At a fixed pressure, the unstable frequency increases with the magnetic field when the B-field is low and decreases at larger magnetic field strength. We find that the transition between these two regimes is obtained when the ion cyclotron frequency equals the ion-neutrals collision frequency. This is in agreement with the theory of the slow-ion drift instability induced by themore » collisional slowing of the electric ion drift [A. Simon, Phys. Fluids 6, 382 (1963)].« less

The prospective opportunities offered by magnetic scaffolds for bone tissue engineering: a review

PubMed Central

ORTOLANI, ALESSANDRO; BIANCHI, MICHELE; MOSCA, MASSIMILIANO; CARAVELLI, SILVIO; FUIANO, MARIO; MARCACCI, MAURILIO; RUSSO, ALESSANDRO

2016-01-01

Magnetic scaffolds are becoming increasingly attractive in tissue engineering, due to their ability to enhance bone tissue formation by attracting soluble factors, such as growth factors, hormones and polypeptides, directly to the implantation site, as well as their potential to improve the fixation and stability of the implant. Moreover, there is increasing evidence that the synergistic effects of magnetic scaffolds and magnetic fields can promote bone repair and regeneration. In this manuscript we review the recent innovations in bone tissue engineering that exploit magnetic biomaterials combined with static magnetic fields to enhance bone cell adhesion and proliferation, and thus bone tissue growth. PMID:28217659

NMR spectroscopy up to 35.2T using a series-connected hybrid magnet.

PubMed

Gan, Zhehong; Hung, Ivan; Wang, Xiaoling; Paulino, Joana; Wu, Gang; Litvak, Ilya M; Gor'kov, Peter L; Brey, William W; Lendi, Pietro; Schiano, Jeffrey L; Bird, Mark D; Dixon, Iain R; Toth, Jack; Boebinger, Gregory S; Cross, Timothy A

2017-11-01

The National High Magnetic Field Laboratory has brought to field a Series-Connected Hybrid magnet for NMR spectroscopy. As a DC powered magnet it can be operated at fields up to 36.1T. The series connection between a superconducting outsert and a resistive insert dramatically minimizes the high frequency fluctuations of the magnetic field typically observed in purely resistive magnets. Current-density-grading among various resistive coils was used for improved field homogeneity. The 48mm magnet bore and 42mm outer diameter of the probes leaves limited space for conventional shims and consequently a combination of resistive and ferromagnetic shims are used. Field maps corrected for field instabilities were obtained and shimming achieved better than 1ppm homogeneity over a cylindrical volume of 1cm diameter and height. The magnetic field is regulated within 0.2ppm using an external 7 Li lock sample doped with paramagnetic MnCl 2 . The improved field homogeneity and field regulation using a modified AVANCE NEO console enables NMR spectroscopy at 1 H frequencies of 1.0, 1.2 and 1.5GHz. NMR at 1.5GHz reflects a 50% increase in field strength above the highest superconducting magnets currently available. Three NMR probes have been constructed each equipped with an external lock rf coil for field regulation. Initial NMR results obtained from the SCH magnet using these probes illustrate the very exciting potential of ultra-high magnetic fields. Copyright © 2017 Elsevier Inc. All rights reserved.

NMR spectroscopy up to 35.2 T using a series-connected hybrid magnet

NASA Astrophysics Data System (ADS)

Gan, Zhehong; Hung, Ivan; Wang, Xiaoling; Paulino, Joana; Wu, Gang; Litvak, Ilya M.; Gor'kov, Peter L.; Brey, William W.; Lendi, Pietro; Schiano, Jeffrey L.; Bird, Mark D.; Dixon, Iain R.; Toth, Jack; Boebinger, Gregory S.; Cross, Timothy A.

2017-11-01

The National High Magnetic Field Laboratory has brought to field a Series-Connected Hybrid magnet for NMR spectroscopy. As a DC powered magnet it can be operated at fields up to 36.1 T. The series connection between a superconducting outsert and a resistive insert dramatically minimizes the high frequency fluctuations of the magnetic field typically observed in purely resistive magnets. Current-density-grading among various resistive coils was used for improved field homogeneity. The 48 mm magnet bore and 42 mm outer diameter of the probes leaves limited space for conventional shims and consequently a combination of resistive and ferromagnetic shims are used. Field maps corrected for field instabilities were obtained and shimming achieved better than 1 ppm homogeneity over a cylindrical volume of 1 cm diameter and height. The magnetic field is regulated within 0.2 ppm using an external 7Li lock sample doped with paramagnetic MnCl2. The improved field homogeneity and field regulation using a modified AVANCE NEO console enables NMR spectroscopy at 1H frequencies of 1.0, 1.2 and 1.5 GHz. NMR at 1.5 GHz reflects a 50% increase in field strength above the highest superconducting magnets currently available. Three NMR probes have been constructed each equipped with an external lock rf coil for field regulation. Initial NMR results obtained from the SCH magnet using these probes illustrate the very exciting potential of ultra-high magnetic fields.

MAGNETIC BRAIDING AND PARALLEL ELECTRIC FIELDS

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

Wilmot-Smith, A. L.; Hornig, G.; Pontin, D. I.

2009-05-10

The braiding of the solar coronal magnetic field via photospheric motions-with subsequent relaxation and magnetic reconnection-is one of the most widely debated ideas of solar physics. We readdress the theory in light of developments in three-dimensional magnetic reconnection theory. It is known that the integrated parallel electric field along field lines is the key quantity determining the rate of reconnection, in contrast with the two-dimensional case where the electric field itself is the important quantity. We demonstrate that this difference becomes crucial for sufficiently complex magnetic field structures. A numerical method is used to relax a braided magnetic field towardmore » an ideal force-free equilibrium; the field is found to remain smooth throughout the relaxation, with only large-scale current structures. However, a highly filamentary integrated parallel current structure with extremely short length-scales is found in the field, with the associated gradients intensifying during the relaxation process. An analytical model is developed to show that, in a coronal situation, the length scales associated with the integrated parallel current structures will rapidly decrease with increasing complexity, or degree of braiding, of the magnetic field. Analysis shows the decrease in these length scales will, for any finite resistivity, eventually become inconsistent with the stability of the coronal field. Thus the inevitable consequence of the magnetic braiding process is a loss of equilibrium of the magnetic field, probably via magnetic reconnection events.« less

Tectonic implications of Mars crustal magnetism

PubMed Central

Connerney, J. E. P.; Acuña, M. H.; Ness, N. F.; Kletetschka, G.; Mitchell, D. L.; Lin, R. P.; Reme, H.

2005-01-01

Mars currently has no global magnetic field of internal origin but must have had one in the past, when the crust acquired intense magnetization, presumably by cooling in the presence of an Earth-like magnetic field (thermoremanent magnetization). A new map of the magnetic field of Mars, compiled by using measurements acquired at an ≈400-km mapping altitude by the Mars Global Surveyor spacecraft, is presented here. The increased spatial resolution and sensitivity of this map provide new insight into the origin and evolution of the Mars crust. Variations in the crustal magnetic field appear in association with major faults, some previously identified in imagery and topography (Cerberus Rupes and Valles Marineris). Two parallel great faults are identified in Terra Meridiani by offset magnetic field contours. They appear similar to transform faults that occur in oceanic crust on Earth, and support the notion that the Mars crust formed during an early era of plate tectonics. PMID:16217034

Coronal heating by stochastic magnetic pumping

NASA Technical Reports Server (NTRS)

Sturrock, P. A.; Uchida, Y.

1980-01-01

Recent observational data cast serious doubt on the widely held view that the Sun's corona is heated by traveling waves (acoustic or magnetohydrodynamic). It is proposed that the energy responsible for heating the corona is derived from the free energy of the coronal magnetic field derived from motion of the 'feet' of magnetic field lines in the photosphere. Stochastic motion of the feet of magnetic field lines leads, on the average, to a linear increase of magnetic free energy with time. This rate of energy input is calculated for a simple model of a single thin flux tube. The model appears to agree well with observational data if the magnetic flux originates in small regions of high magnetic field strength. On combining this energy input with estimates of energy loss by radiation and of energy redistribution by thermal conduction, we obtain scaling laws for density and temperature in terms of length and coronal magnetic field strength.

Tectonic implications of Mars crustal magnetism.

PubMed

Connerney, J E P; Acuña, M H; Ness, N F; Kletetschka, G; Mitchell, D L; Lin, R P; Reme, H

2005-10-18

Mars currently has no global magnetic field of internal origin but must have had one in the past, when the crust acquired intense magnetization, presumably by cooling in the presence of an Earth-like magnetic field (thermoremanent magnetization). A new map of the magnetic field of Mars, compiled by using measurements acquired at an approximately 400-km mapping altitude by the Mars Global Surveyor spacecraft, is presented here. The increased spatial resolution and sensitivity of this map provide new insight into the origin and evolution of the Mars crust. Variations in the crustal magnetic field appear in association with major faults, some previously identified in imagery and topography (Cerberus Rupes and Valles Marineris). Two parallel great faults are identified in Terra Meridiani by offset magnetic field contours. They appear similar to transform faults that occur in oceanic crust on Earth, and support the notion that the Mars crust formed during an early era of plate tectonics.

Magnetoresistances and magnetic entropy changes associated with negative lattice expansions in NaZn13-type compounds LaFeCoSi

NASA Astrophysics Data System (ADS)

Hu, Feng-Xia; Qian, Xiao-Ling; Wang, Guang-Jun; Sun, Ji-Rong; Shen, Bao-Gen; Cheng, Zhao-Hua; Gao, Ju

2005-11-01

Magnetoresistances and magnetic entropy changes in NaZn13-type compounds La(Fe1-xCox)11.9Si1.1 (x=0.04, 0.06 and 0.08) with Curie temperatures of 243 K, 274 K and 301 K, respectively, are studied. The ferromagnetic ordering is accompanied by a negative lattice expansion. Large magnetic entropy changes in a wide temperature range from ~230 K to ~320 K are achieved. Raising Co content increases the Curie temperature but weakens the magnetovolume effect, thereby causing a decrease in magnetic entropy change. These materials exhibit a metallic character below TC, whereas the electrical resistance decreases abruptly and then recovers the metal-like behaviour above TC. Application of a magnetic field retains the transitions via increasing the ferromagnetic ordering temperature. An isothermal increase in magnetic field leads to an increase in electrical resistance at temperatures near but above TC, which is a consequence of the field-induced metamagnetic transition from a paramagnetic state to a ferromagnetic state.

Magnetic field dependence of Griffith phase and magnetocaloric effect in Ca0.85Dy0.15MnO3

NASA Astrophysics Data System (ADS)

Nag, Ripan; Sarkar, Bidyut; Pal, Sudipta

2018-03-01

Temperature and Magnetic field dependent magnetization properties of electron doped polycrystalline sample Ca0.85Dy0.15MnO3 (CDMO) prepared by solid state reaction method have been studied. The sample undergoes ferromagnetic to paramagnetic phase transition at about 111k. From the study of magnetic properties in terms of Arrot plots it is observed that the phase transition is of 2nd order. The Griffith phase behavior of the sample is suppressed with the increase of the applied magnetic field strength H. We have estimated the magnetic entropy change from experimental magnetization and temperature data. For a magnetic field change of 8000 Oe, the maximum value of magnetic entropy change arrives at a value of 1.126 J-kg-1 k-1 in this magnetocaloric material.

Multilayered Magnetic Gelatin Membrane Scaffolds

PubMed Central

Samal, Sangram K.; Goranov, Vitaly; Dash, Mamoni; Russo, Alessandro; Shelyakova, Tatiana; Graziosi, Patrizio; Lungaro, Lisa; Riminucci, Alberto; Uhlarz, Marc; Bañobre-López, Manuel; Rivas, Jose; Herrmannsdörfer, Thomas; Rajadas, Jayakumar; De Smedt, Stefaan; Braeckmans, Kevin; Kaplan, David L.; Dediu, V. Alek

2016-01-01

A versatile approach for the design and fabrication of multilayer magnetic scaffolds with tunable magnetic gradients is described. Multilayer magnetic gelatin membrane scaffolds with intrinsic magnetic gradients were designed to encapsulate magnetized bioagents under an externally applied magnetic field for use in magnetic-field-assisted tissue engineering. The temperature of the individual membranes increased up to 43.7 °C under an applied oscillating magnetic field for 70 s by magnetic hyperthermia, enabling the possibility of inducing a thermal gradient inside the final 3D multilayer magnetic scaffolds. On the basis of finite element method simulations, magnetic gelatin membranes with different concentrations of magnetic nanoparticles were assembled into 3D multilayered scaffolds. A magnetic-gradient-controlled distribution of magnetically labeled stem cells was demonstrated in vitro. This magnetic biomaterial–magnetic cell strategy can be expanded to a number of different magnetic biomaterials for various tissue engineering applications. PMID:26451743

Multilayered Magnetic Gelatin Membrane Scaffolds.

PubMed

Samal, Sangram K; Goranov, Vitaly; Dash, Mamoni; Russo, Alessandro; Shelyakova, Tatiana; Graziosi, Patrizio; Lungaro, Lisa; Riminucci, Alberto; Uhlarz, Marc; Bañobre-López, Manuel; Rivas, Jose; Herrmannsdörfer, Thomas; Rajadas, Jayakumar; De Smedt, Stefaan; Braeckmans, Kevin; Kaplan, David L; Dediu, V Alek

2015-10-21

A versatile approach for the design and fabrication of multilayer magnetic scaffolds with tunable magnetic gradients is described. Multilayer magnetic gelatin membrane scaffolds with intrinsic magnetic gradients were designed to encapsulate magnetized bioagents under an externally applied magnetic field for use in magnetic-field-assisted tissue engineering. The temperature of the individual membranes increased up to 43.7 °C under an applied oscillating magnetic field for 70 s by magnetic hyperthermia, enabling the possibility of inducing a thermal gradient inside the final 3D multilayer magnetic scaffolds. On the basis of finite element method simulations, magnetic gelatin membranes with different concentrations of magnetic nanoparticles were assembled into 3D multilayered scaffolds. A magnetic-gradient-controlled distribution of magnetically labeled stem cells was demonstrated in vitro. This magnetic biomaterial-magnetic cell strategy can be expanded to a number of different magnetic biomaterials for various tissue engineering applications.

Design and investigations of the superconducting magnet system for the multipurpose superconducting electron cyclotron resonance ion source.

PubMed

Tinschert, K; Lang, R; Mäder, J; Rossbach, J; Spädtke, P; Komorowski, P; Meyer-Reumers, M; Krischel, D; Fischer, B; Ciavola, G; Gammino, S; Celona, L

2012-02-01

The production of intense beams of heavy ions with electron cyclotron resonance ion sources (ECRIS) is an important request at many accelerators. According to the ECR condition and considering semi-empirical scaling laws, it is essential to increase the microwave frequency together with the magnetic flux density of the ECRIS magnet system. A useful frequency of 28 GHz, therefore, requires magnetic flux densities above 2.2 T implying the use of superconducting magnets. A cooperation of European institutions initiated a project to build a multipurpose superconducting ECRIS (MS-ECRIS) in order to achieve an increase of the performances in the order of a factor of ten. After a first design of the superconducting magnet system for the MS-ECRIS, the respective cold testing of the built magnet system reveals a lack of mechanical performance due to the strong interaction of the magnetic field of the three solenoids with the sextupole field and the magnetization of the magnetic iron collar. Comprehensive structural analysis, magnetic field calculations, and calculations of the force pattern confirm thereafter these strong interactions, especially of the iron collar with the solenoidal fields. The investigations on the structural analysis as well as suggestions for a possible mechanical design solution are given.

Electron acceleration in a secondary magnetic island formed during magnetic reconnection with a guide field

NASA Astrophysics Data System (ADS)

Wang, Huanyu; Lu, Quanming; Huang, Can; Wang, Shui

2017-05-01

Secondary magnetic islands may be generated in the vicinity of an X line during magnetic reconnection. In this paper, by performing two-dimensional (2-D) particle-in-cell simulations, we investigate the role of a secondary magnetic island in electron acceleration during magnetic reconnection with a guide field. The electron motions are found to be adiabatic, and we analyze the contributions of the parallel electric field and Fermi and betatron mechanisms to electron acceleration in the secondary island during the evolution of magnetic reconnection. When the secondary island is formed, electrons are accelerated by the parallel electric field due to the existence of the reconnection electric field in the electron current sheet. Electrons can be accelerated by both the parallel electric field and Fermi mechanism when the secondary island begins to merge with the primary magnetic island, which is formed simultaneously with the appearance of X lines. With the increase in the guide field, the contributions of the Fermi mechanism to electron acceleration become less and less important. When the guide field is sufficiently large, the contribution of the Fermi mechanism is almost negligible.

Iron oxide nanoparticles for magnetically-guided and magnetically-responsive drug delivery.

PubMed

Estelrich, Joan; Escribano, Elvira; Queralt, Josep; Busquets, Maria Antònia

2015-04-10

In this review, we discuss the recent advances in and problems with the use of magnetically-guided and magnetically-responsive nanoparticles in drug delivery and magnetofection. In magnetically-guided nanoparticles, a constant external magnetic field is used to transport magnetic nanoparticles loaded with drugs to a specific site within the body or to increase the transfection capacity. Magnetofection is the delivery of nucleic acids under the influence of a magnetic field acting on nucleic acid vectors that are associated with magnetic nanoparticles. In magnetically-responsive nanoparticles, magnetic nanoparticles are encapsulated or embedded in a larger colloidal structure that carries a drug. In this last case, an alternating magnetic field can modify the structure of the colloid, thereby providing spatial and temporal control over drug release.

Iron Oxide Nanoparticles for Magnetically-Guided and Magnetically-Responsive Drug Delivery

PubMed Central

Estelrich, Joan; Escribano, Elvira; Queralt, Josep; Busquets, Maria Antònia

2015-01-01

In this review, we discuss the recent advances in and problems with the use of magnetically-guided and magnetically-responsive nanoparticles in drug delivery and magnetofection. In magnetically-guided nanoparticles, a constant external magnetic field is used to transport magnetic nanoparticles loaded with drugs to a specific site within the body or to increase the transfection capacity. Magnetofection is the delivery of nucleic acids under the influence of a magnetic field acting on nucleic acid vectors that are associated with magnetic nanoparticles. In magnetically-responsive nanoparticles, magnetic nanoparticles are encapsulated or embedded in a larger colloidal structure that carries a drug. In this last case, an alternating magnetic field can modify the structure of the colloid, thereby providing spatial and temporal control over drug release. PMID:25867479

Periodical plasma structures controlled by external magnetic field

NASA Astrophysics Data System (ADS)

Schweigert, I. V.; Keidar, M.

2017-11-01

The plasma of Hall thruster type in external magnetic field is studied in 2D3V kinetic simulations using PIC MCC method. The periodical structure with maxima of electron and ion densities is formed and becomes more pronounced with increase of magnetic field incidence angle in the plasma. These ridges of electron and ion densities are aligned with the magnetic field vector and shifted relative each other. This leads to formation of two-dimensional double-layers structure in cylindrical plasma chamber. Depending on Larmor radius and Debye length up to nineteen potential steps appear across the oblique magnetic field. The electrical current gathered on the wall is associated with the electron and ion density ridges.

Experimental study of effect of magnetic field on anode temperature distribution in an ATON-type Hall thruster

NASA Astrophysics Data System (ADS)

Liu, Jinwen; Li, Hong; Mao, Wei; Ding, Yongjie; Wei, Liqiu; Li, Jianzhi; Yu, Daren; Wang, Xiaogang

2018-05-01

The energy deposition caused by the absorption of electrons by the anode is an important cause of power loss in a Hall thruster. The resulting anode heating is dangerous, as it can potentially reduce the thruster lifetime. In this study, by considering the ring shape of the anode of an ATON-type Hall thruster, the effects of the magnetic field strength and gradient on the anode ring temperature distribution are studied via experimental measurement. The results show that the temperature distribution is not affected by changes in the magnetic field strength and that the position of the peak temperature is essentially unchanged; however, the overall temperature does not change monotonically with the increase of the magnetic field strength and is positively correlated with the change in the discharge current. Moreover, as the magnetic field gradient increases, the position of the peak temperature gradually moves toward the channel exit and the temperature tends to decrease as a whole, regardless of the discharge current magnitude; in any case, the position of the peak temperature corresponds exactly to the intersection of the magnetic field cusp with the anode ring. Further theoretical analysis shows that the electrons, coming from the ionization region, travel along two characteristic paths to reach the anode under the guidance of the cusped magnetic field configuration. The change of the magnetic field strength or gradient changes the transfer of momentum and energy of the electrons in these two paths, which is the main reason for the changes in the temperature and distribution. This study is instructive for matching the design of the ring-shaped anode and the cusp magnetic field of an ATON-type Hall thruster.

Optimization of magnetic field-assisted ultrasonication for the disintegration of waste activated sludge using Box-Behnken design with response surface methodology.

PubMed

Guan, Su; Deng, Feng; Huang, Si-Qi; Liu, Shu-Yang; Ai, Le-Xian; She, Pu-Ying

2017-09-01

This study investigated for the first time the feasibility of using a magnetic field for sludge disintegration. Approximately 41.01% disintegration degree (DD) was reached after 30min at 180mT magnetic field intensity upon separate magnetic field treatment. Protein and polysaccharide contents significantly increased. This test was optimized using a Box-Behnken design (BBD) with response surface methodology (RSM) to fit the multiple equation of the DD. The maximum DD was 43.75% and the protein and polysaccharide contents increased to 56.71 and 119.44mg/L, respectively, when the magnetic field strength was 119.69mT, reaction time was 30.49min, and pH was 9.82 in the optimization experiment. We then analyzed the effects of ultrasound alone. We are the first to combine magnetic field with ultrasound to disintegrate waste-activated sludge (WAS). The optimum effect was obtained with the application of ultrasound alone at 45kHz frequency, with a DD of about 58.09%. By contrast, 62.62% DD was reached in combined magnetic field and ultrasound treatment. This combined test was also optimized using BBD with RSM to fit the multiple equation of DD. The maximum DD of 64.59% was achieved when the magnetic field intensity was 197.87mT, ultrasonic frequency was 42.28kHz, reaction time was 33.96min, and pH was 8.90. These results were consistent with those of particle size and electron microscopy analyses. This research proved that a magnetic field can effectively disintegrate WAS and can be combined with other physical techniques such as ultrasound for optimal results. Copyright © 2017 Elsevier B.V. All rights reserved.

Origin and Evolution of Magnetic Field in PMS Stars: Influence of Rotation and Structural Changes

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

Emeriau-Viard, Constance; Brun, Allan Sacha, E-mail: constance.emeriau@cea.fr, E-mail: sacha.brun@cea.fr

During stellar evolution, especially in the pre-main-sequence phase, stellar structure and rotation evolve significantly, causing major changes in the dynamics and global flows of the star. We wish to assess the consequences of these changes on stellar dynamo, internal magnetic field topology, and activity level. To do so, we have performed a series of 3D HD and MHD simulations with the ASH code. We choose five different models characterized by the radius of their radiative zone following an evolutionary track computed by a 1D stellar evolution code. These models characterized stellar evolution from 1 to 50 Myr. By introducing amore » seed magnetic field in the fully convective model and spreading its evolved state through all four remaining cases, we observe systematic variations in the dynamical properties and magnetic field amplitude and topology of the models. The five MHD simulations develop a strong dynamo field that can reach an equipartition state between the kinetic and magnetic energies and even superequipartition levels in the faster-rotating cases. We find that the magnetic field amplitude increases as it evolves toward the zero-age main sequence. Moreover, the magnetic field topology becomes more complex, with a decreasing axisymmetric component and a nonaxisymmetric one becoming predominant. The dipolar components decrease as the rotation rate and the size of the radiative core increase. The magnetic fields possess a mixed poloidal-toroidal topology with no obvious dominant component. Moreover, the relaxation of the vestige dynamo magnetic field within the radiative core is found to satisfy MHD stability criteria. Hence, it does not experience a global reconfiguration but slowly relaxes by retaining its mixed stable poloidal-toroidal topology.« less

Rats avoid high magnetic fields: dependence on an intact vestibular system

PubMed Central

Houpt, Thomas A.; Cassell, Jennifer A.; Riccardi, Christina; DenBleyker, Megan D.; Hood, Alison; Smith, James C.

2009-01-01

Summary HOUPT, T.A., J.A. CASSELL, C. RICCARDI, M.D. DENBLEYKER, A. HOOD, AND J.C. SMITH. Rats avoid high magnetic fields: dependence on an intact vestibular system. PHYSIOL BEHAV 00(0)000-000, 2006. High strength static magnetic fields are thought to be benign and largely undetectable by mammals. As magnetic resonance imaging (MRI) machines increase in strength, however, potential aversive effects may become clinically relevant. Here we report that rats find entry into a 14.1 T magnet aversive, and that they can detect and avoid entry into the magnet at a point where the magnetic field is 2 T or lower. Rats were trained to climb a ladder through the bore of a 14.1 T superconducting magnet. After their first climb into 14.1 T, most rats refused to re-enter the magnet or climb past the 2 T field line. This result was confirmed in a resistive magnet in which the magnetic field was varied from 1 to 14 T. Detection and avoidance required the vestibular apparatus of the inner ear, because labyrinthectomized rats readily traversed the magnet. The inner ear is a novel site for magnetic field transduction in mammals, but perturbation of the vestibular apparatus would be consistent with human reports of vertigo and nausea around high strength MRI machines. PMID:17585969

Measurements of the magnetic-field-tuned conductivity of disordered two-dimensional Mo43Ge57 and InOx superconducting films: evidence for a universal minimum superfluid response.

PubMed

Misra, S; Urban, L; Kim, M; Sambandamurthy, G; Yazdani, A

2013-01-18

Our measurements of the low frequency ac conductivity in strongly disordered two-dimensional films near the magnetic-field-tuned superconductor-to-insulator transition show a sudden drop in the phase stiffness of superconducting order with either increased temperature or magnetic field. Surprisingly, for two different material systems, the abrupt drop in the superfluid density in a magnetic field has the same universal value as that expected for a Berezinskii-Kosterlitz-Thouless transition in a zero magnetic field. The characteristic temperature at which phase stiffness is suddenly lost can be tuned to zero at a critical magnetic field, following a power-law behavior with a critical exponent consistent with that obtained in previous dc transport studies on the dissipative side of the transition.

Conductance of graphene based normal-superconductor junction with double magnetic barriers

NASA Astrophysics Data System (ADS)

Abdollahipour, B.; Mohebalipour, A.; Maleki, M. A.

2018-05-01

We study conductance of a graphene based normal metal-superconductor junction with two magnetic barriers. The magnetic barriers are induced via two applied magnetic fields with the same magnitudes and opposite directions accompanied by an applied electrostatic potential. We solve Dirac-Bogoliubov-De-Gennes (DBdG) equation to calculate conductance of the junction. We find that applying the magnetic field leads to suppression of the Andreev reflection and conductance for all energies. On the other hand, we observe a crossover from oscillatory to tunneling behavior of the conductance as a function of the applied potential by increasing the magnetic field.

"CORKSCREW"-A DEVICE FOR CHANGING THE MAGNETIC MOMENT OF CHARGED PARTICLES IN A MAGNETIC FIELD

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

Wingerson, R.C.

1961-05-01

A helical, current-carrying magnetic field source (the "corkscrew") is described; it perturbs an axial uniform magnetic field B/sub 0/ such that the transverse energy components (ET) of selected particles moving along the sxis are increased or decreased monotonically. It is noted that, since the corkscrew has no over-all effect on B/sub 0/, the change in ET must result from a change in the particle's magnetic moment. The use of pairs of these devices in magnetic mirror machines to trap particles is suggested. (T.F.H.)

Dual-mode ferromagnetic resonance in an FeCoB/Ru/FeCoB synthetic antiferromagnet with uniaxial anisotropy

NASA Astrophysics Data System (ADS)

Wang, Cuiling; Zhang, Shouheng; Qiao, Shizhu; Du, Honglei; Liu, Xiaomin; Sun, Ruicong; Chu, Xian-Ming; Miao, Guo-Xing; Dai, Youyong; Kang, Shishou; Yan, Shishen; Li, Shandong

2018-05-01

Dual-mode ferromagnetic resonance is observed in FeCoB/Ru/FeCoB trilayer synthetic antiferromagnets with uniaxial in-plane magnetic anisotropy. The optical mode is present in the (0-108 Oe) magnetic field range, where the top and bottom layer magnetizations are aligned in opposite directions. The strong acoustic mode appears, when the magnetic field exceeds the 300 Oe value, which corresponds to the flop transition in the trilayer. Magnetic field and angular dependences of resonant frequencies are studied for both optical (low-field) and acoustic (high field) modes. The low-field mode is found to be anisotropic but insensitive to the magnetic field value. In contrast, the high field mode is quasi-isotropic, but its resonant frequency is tunable by the value of the magnetic field. The coexistence of two modes of ferromagnetic resonance as well as switching between them with the increase in the magnetic field originates from the difference in the sign of interlayer coupling energy at the parallel and antiparallel configurations of the synthetic antiferromagnet. The dual-mode resonance in the studied trilayer structures provides greater flexibility in the design and functionalization of micro-inductors in monolithic microwave integrated circuits.

Magnetic field dependence of the internal quality factor and noise performance of lumped-element kinetic inductance detectors

NASA Astrophysics Data System (ADS)

Flanigan, D.; Johnson, B. R.; Abitbol, M. H.; Bryan, S.; Cantor, R.; Day, P.; Jones, G.; Mauskopf, P.; McCarrick, H.; Miller, A.; Zmuidzinas, J.

2016-10-01

We present a technique for increasing the internal quality factor of kinetic inductance detectors (KIDs) by nulling ambient magnetic fields with a properly applied magnetic field. The KIDs used in this study are made from thin-film aluminum, they are mounted inside a light-tight package made from bulk aluminum, and they are operated near 150 mK. Since the thin-film aluminum has a slightly elevated critical temperature (Tc = 1.4 K), it therefore transitions before the package (Tc = 1.2 K), which also serves as a magnetic shield. On cooldown, ambient magnetic fields as small as approximately 30 µT can produce vortices in the thin-film aluminum as it transitions because the bulk aluminum package has not yet transitioned and therefore is not yet shielding. These vortices become trapped inside the aluminum package below 1.2 K and ultimately produce low internal quality factors in the thin-film superconducting resonators. We show that by controlling the strength of the magnetic field present when the thin film transitions, we can control the internal quality factor of the resonators. We also compare the noise performance with and without vortices present, and find no evidence for excess noise beyond the increase in amplifier noise, which is expected with increasing loss.

Effect of interdendritic thermoelectric magnetic convection on evolution of tertiary dendrite during directional solidification

NASA Astrophysics Data System (ADS)

Zhong, Hua; Li, Chuanjun; Ren, Zhongming; Rettenmayr, Markus; Zhong, Yunbo; Yu, Jianbo; Wang, Jiang

2016-04-01

The Al-4.5 wt%Cu alloy has been directionally solidified under a high static magnetic field up to 6 T. A novel α-Al dendrite morphology was presented when the <001> primary trunk aligned to the magnetic field and temperature gradient. It is observed that tertiary dendrites grew asymmetrically on secondary arms in the plane perpendicular to the primary trunk, and a pinwheel-like pattern formed. A numerical simulation was performed using finite-element code COMSOL software to investigate the thermoelectric magnetic convection (TEMC) induced by the external magnetic field. The results show that the velocity of the TEMC increases with the increasing of the magnetic field and reaches a maximum value near 6 T. Meanwhile, the magnitude of the TEMC on two sides of the secondary arm becomes unequal. Comparison of the experimental and numerical results reveals that the development of the pinwheel-like appearance is in accordance with the flow pattern of the TEMC. It is implies that the modification of the tertiary dendrite could be attributed to the TEMC generated on dendrite scale. This work also provides direct experimental evidence that a high magnetic field (>1 T) induces fluid flow in mushy zone.

Effects of magnetic impurities on upper critical fields in the high-T c superconductor La-doped CaFe2As2

NASA Astrophysics Data System (ADS)

Jung, Soon-Gil; Shin, Soohyeon; Jang, Harim; Mikheenko, Pavlo; Johansen, Tom H.; Park, Tuson

2017-08-01

We investigate the effects of magnetic impurities on the upper critical field (μ 0 H c2) in La-doped CaFe2As2 (LaCa122) single crystals. The magnetic field dependency of the superconducting transition temperature (T c) for LaCa122 is rapidly suppressed at low fields up to ˜1 kOe despite its large μ 0 H c2(0) value on the order of tens of Tesla, resulting in a large positive curvature of μ 0 H c2(T) near T c. The magnetization hysteresis (M-H) loop at temperatures above T c shows a ferromagnetic-like signal and the M(H) value rapidly increases with increasing magnetic field up to ˜1 kOe. Taken together with the linear suppression of T c with the magnetization in the normal state, these results suggest that the large upward curvature of μ 0 H c2(T) near T c in La-doped CaFe2As2 mainly originates from the suppression of superconductivity due to the presence of magnetic impurities.

TRAVELING WAVE PYROTRON

DOEpatents

Post, R.F.

1963-06-11

The invention relates to a pyrotron, i.e., magnetic mirror device, designed for continuous operation in producing a high-temperature fusion reaction plasma and for directly converting the plasma energy into electrical power. The device utilizes a system in which an axially symmetric magnetic field is produced and transports plasma through a first zone of progressively rising field intensity, a second reaction zone of slowly increasing intensity, and thenceforth through a third zone of progressively decreasing intensity wherein the plasma expands against the magnetic field thereby producing electrical current in magnetic field generating solenoids associated with said third zone. (AEC)

Magnetic field effect on the liquidus boundary of Bi-Mn binary system

NASA Astrophysics Data System (ADS)

Mitsui, Yoshifuru; Koyama, Keiichi; Oikawa, Katsunari; Watanabe, Kazuo

2014-10-01

The magnetic field effect (MFE) on liquidus boundary of Bi-Mn binary system was investigated by differential thermal analysis (DTA) and the computer coupling of phase diagram method (CALPHAD). The liquidus boundary for Bi-18at.%Mn and Bi-24at.%Mn rose clearly by the application of the magnetic fields. The MFE for liquidus boundary temperature Tliq changed from ΔTliq∝B2 to ΔTliq∝B because of the large increase of the peritectic temperature from BiMn and BiMn1.08 by the application of magnetic field.

Numerical simulation of a helical shape electric arc in the external axial magnetic field

NASA Astrophysics Data System (ADS)

Urusov, R. M.; Urusova, I. R.

2016-10-01

Within the frameworks of non-stationary three-dimensional mathematical model, in approximation of a partial local thermodynamic equilibrium, a numerical calculation was made of characteristics of DC electric arc burning in a cylindrical channel in the uniform external axial magnetic field. The method of numerical simulation of the arc of helical shape in a uniform external axial magnetic field was proposed. This method consists in that that in the computational algorithm, a "scheme" analog of fluctuations for electrons temperature is supplemented. The "scheme" analogue of fluctuations increases a weak numerical asymmetry of electrons temperature distribution, which occurs randomly in the course of computing. This asymmetry can be "picked up" by the external magnetic field that continues to increase up to a certain value, which is sufficient for the formation of helical structure of the arc column. In the absence of fluctuations in the computational algorithm, the arc column in the external axial magnetic field maintains cylindrical axial symmetry, and a helical form of the arc is not observed.

The effect of transverse wave vector and magnetic fields on resonant tunneling times in double-barrier structures

NASA Astrophysics Data System (ADS)

Wang, Hongmei; Zhang, Yafei; Xu, Huaizhe

2007-01-01

The effect of transverse wave vector and magnetic fields on resonant tunneling times in double-barrier structures, which is significant but has been frequently omitted in previous theoretical methods, has been reported in this paper. The analytical expressions of the longitudinal energies of quasibound levels (LEQBL) and the lifetimes of quasibound levels (LQBL) in symmetrical double-barrier (SDB) structures have been derived as a function of transverse wave vector and longitudinal magnetic fields perpendicular to interfaces. Based on our derived analytical expressions, the LEQBL and LQBL dependence upon transverse wave vector and longitudinal magnetic fields has been explored numerically for a SDB structure. Model calculations show that the LEQBL decrease monotonically and the LQBL shorten with increasing transverse wave vector, and each original LEQBL splits to a series of sub-LEQBL which shift nearly linearly toward the well bottom and the lifetimes of quasibound level series (LQBLS) shorten with increasing Landau-level indices and magnetic fields.

Reversible “triple-Q” elastic field structures in a chiral magnet

PubMed Central

Hu, Yangfan; Wang, Biao

2016-01-01

The analytical solution of the periodic elastic fields in chiral magnets caused by presence of periodically distributed eigenstrains is obtained. For the skyrmion phase, both the periodic displacement field and the stress field are composed of three “triple-Q” structures with different wave numbers. The periodic displacement field, obtained by combining the three “triple-Q” displacement structures, is found to have the same lattice vectors with the magnetic skyrmion lattice. We find that for increasing external magnetic field, one type of “triple-Q” displacement structure and stress structure undergo a “configurational reversal”, where the initial and the final field configuration share similar pattern but with opposite direction of all the field vectors. The solution obtained is of fundamental significance for understanding the emergent mechanical properties of skyrmions in chiral magnets. PMID:27457629

Electron beam therapy with coil-generated magnetic fields.

PubMed

Nardi, Eran; Barnea, Gideon; Ma, Chang-Ming

2004-06-01

This paper presents an initial study on the issues involved in the practical implementation of the use of transverse magnetic fields in electron beam therapy. By using such magnetic fields the dose delivered to the tumor region can increase significantly relative to that deposited to the healthy tissue. Initially we calculated the magnetic fields produced by the Helmholtz coil and modified Helmholtz coil configurations. These configurations, which can readily be used to generate high intensity magnetic fields, approximate the idealized magnetic fields studied in our previous publications. It was therefore of interest to perform a detailed study of the fields produced by these configurations. Electron beam dose distributions for 15 MeV electrons were calculated using the ACCEPTM code for a 3T transverse magnetic field produced by the modified Helmholtz configuration. The dose distribution was compared to those obtained with no magnetic field. The results were similar to those obtained in our previous work, where an idealized step function magnetic field was used and a 3T field was shown to be the optimal field strength. A simpler configuration was also studied in which a single external coil was used to generate the field. Electron dose distributions are also presented for a given geometry and given magnetic field strength using this configuration. The results indicate that this method is more difficult to apply to radiotherapy due to its lack of symmetry and its irregularity. For the various configurations dealt with here, a major problem is the need to shield the magnetic field in the beam propagation volume, a topic that must be studied in detail.

Childhood leukemia and magnetic fields in infant incubators.

PubMed

Söderberg, Karin C; Naumburg, Estelle; Anger, Gert; Cnattingius, Sven; Ekbom, Anders; Feychting, Maria

2002-01-01

In studies of magnetic field exposure and childhood leukemia, power lines and other electrical installations close to the children's homes constitute the most extensively studied source of exposure. We conducted a study to assess whether exposure to magnetic fields in infant incubators is associated with an increased leukemia risk. We identified all children with leukemia born in Sweden between 1973 and 1989 from the national Cancer Registry and selected at random one control per case, individually matched by sex and time of birth, from the study base. We retrieved information about treatment in infant incubators from medical records. We made measurements of the magnetic fields inside the incubators for each incubator model kept by the hospitals. Exposure assessment was based on measurements of the magnetic field level inside the incubator, as well as on the length of treatment. For acute lymphoblastic leukemia, the risk estimates were close to unity for all exposure definitions. For acute myeloid leukemia, we found a slightly elevated risk, but with wide confidence intervals and with no indication of dose response. Overall, our results give little evidence that exposure to magnetic fields inside infant incubators is associated with an increased risk of childhood leukemia.

Chiral phase transition of three flavor QCD with nonzero magnetic field using standard staggered fermions

NASA Astrophysics Data System (ADS)

Tomiya, Akio; Ding, Heng-Tong; Mukherjee, Swagato; Schmidt, Christian; Wang, Xiao-Dan

2018-03-01

Lattice simulations for (2+1)-flavor QCD with external magnetic field demon-strated that the quark mass is one of the important parameters responsible for the (inverse) magnetic catalysis. We discuss the dependences of chiral condensates and susceptibilities, the Polyakov loop on the magnetic field and quark mass in three degenerate flavor QCD. The lattice simulations are performed using standard staggered fermions and the plaquette action with spatial sizes Nσ = 16 and 24 and a fixed temporal size Nτ = 4. The value of the quark masses are chosen such that the system undergoes a first order chiral phase transition and crossover with zero magnetic field. We find that in light mass regime, the quark chiral condensate undergoes magnetic catalysis in the whole temperature region and the phase transition tend to become stronger as the magnetic field increases. In crossover regime, deconfinement transition temperature is shifted by the magnetic field when quark mass ma is less than 0:4. The lattice cutoff effects are also discussed.

Effect of magnetic field on the physical properties of water

NASA Astrophysics Data System (ADS)

Wang, Youkai; Wei, Huinan; Li, Zhuangwen

2018-03-01

In this study, the effect of magnetic field (MF) on the partial physical properties of water are reported, tap water (TW) and 4 types of magnetized water (MW) were measured in the same condition. It was found that the properties of TW were changed following the MF treatment, shown as the increase of evaporation amount, the decrease of specific heat and boiling point after magnetization, the changes depend on the magnetization effect. In addition, magnetic field strength (MFS) has a marked influence on the magnetization effect, the optimal magnetizing condition was determined as the MFS of 300 mT. The findings of this study offered a facile approach to improve cooling and power generation efficiency in industrial.

An Analytical Model for Non-Uniform Magnetic Field Effects on Two-Dimensional Laminar Jet Diffusion Flames

NASA Technical Reports Server (NTRS)

Calvert, M. E.; Baker, J.; Saito, K.; VanderWal, R. L.

2001-01-01

In 1846, Michael Faraday found that permanent magnets could cause candle flames to deform into equatorial disks. He believed that the change in flame shape was caused by the presence of charged particles within the flames interacting with the magnetic fields. Later researchers found that the interaction between the flame ions and the magnetic fields were much too small to cause the flame deflection. Through a force analysis, von Engel and Cozens showed that the change in the flame shape could be attributed to the diamagnetic flame gases in the paramagnetic atmosphere. Paramagnetism occurs in materials composed of atoms with permanent magnetic dipole moments. In the presence of magnetic field gradients, the atoms align with the magnetic field and are drawn into the direction of increasing magnetic field. Diamagnetism occurs when atoms have no net magnetic dipole moment. In the presence of magnetic gradient fields, diamagnetic substances are repelled towards areas of decreasing magnetism. Oxygen is an example of a paramagnetic substance. Nitrogen, carbon monoxide and dioxide, and most hydrocarbon fuels are examples of diamagnetic substances. In order to evaluate the usefulness of these magnets in altering flame behavior, a study has been undertaken to develop an analytical model to describe the change in the flame length of a laminar diffusion jet in the presence of a nonuniform magnetic field.

The effect of magnetic field on copper in various corrosive medium

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

Ang, L. Y.; Othman, N. K.; Jalar, A.

2014-09-03

The effect of applied magnetic field on the corrosion behaviour of copper within various corrosive medium is investigated. The copper coupon is immersed in 0.5 M HCl, 0.5 M NaCl and 0.5 M NaOH with or without applying up to 40 mT magnetic fields for 24 hours. The weight loss of copper coupon in HCl increased up to 96.56% with applied magnetic fields. However, in NaOH medium, only 33.33% more weight loss was observed and no difference were observed for coupons in NaCl when magnetic field is applied. This observation indicates that corrosion behaviour in HCl and NaOH is controlledmore » by mass transport that can be influenced by the induced magneto hydrodynamics effect when magnetic field is applied. There was no change in weight loss of copper in NaCl when magnetic field is applied because the corrosion mechanism of copper in NaCl is governed by electron charge transfer.« less

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

Zhang, Hongqi; Brandenburg, Axel; Sokoloff, D. D., E-mail: hzhang@bao.ac.cn

We adopt an isotropic representation of the Fourier-transformed two-point correlation tensor of the magnetic field to estimate the magnetic energy and helicity spectra as well as current helicity spectra of two individual active regions (NOAA 11158 and NOAA 11515) and the change of the spectral indices during their development as well as during the solar cycle. The departure of the spectral indices of magnetic energy and current helicity from 5/3 are analyzed, and it is found that it is lower than the spectral index of the magnetic energy spectrum. Furthermore, the fractional magnetic helicity tends to increase when the scale of themore » energy-carrying magnetic structures increases. The magnetic helicity of NOAA 11515 violates the expected hemispheric sign rule, which is interpreted as an effect of enhanced field strengths at scales larger than 30–60 Mm with opposite signs of helicity. This is consistent with the general cycle dependence, which shows that around the solar maximum the magnetic energy and helicity spectra are steeper, emphasizing the large-scale field.« less

Near room temperature magnetocaloric properties and the universal curve of MnCoGe1-xCux

NASA Astrophysics Data System (ADS)

Si, Xiaodong; Liu, Yongsheng; Lu, Xiaofei; Shen, Yulong; Wang, Wenli; Yu, Wenying; Zhou, Tao; Gao, Tian

2017-05-01

Intermetallic compounds based on MnCoGe have drawn attention due to the coupled magnetic and structural transformations and the large magnetocaloric entropy. Here, we provide a systematic comparison of experimental data under different magnetic fields with magnetic and the magnetocaloric properties. The ferromagnetic transition temperature (TC) increases from 353.4(6) K for x = 0.01 to 363.4(4) K for x = 0.04 with increasing nominal copper content. The maximum magnetic entropy change |ΔSM| in a magnetic field change of 5 T is found to be 18.3(2) J/(kg K) with a large relative cooling power (RCP) value of 292.5(4) J/kg for x = 0.01, revealing that the present system can provide an acceptable magnetocaloric effect at a cheaper price for magnetic refrigeration materials. Making attempt to contrast a master curve for the present system, we find the experimental values of magnetic field dependence of the magnetic entropy change are consistent with a phenomenological universal curve.

Fractional Matching Effect due to Pinning of the Vortex Lattice by an Array of Magnetic Dots

NASA Astrophysics Data System (ADS)

Stoll, O. M.; Montero, M. I.; Jönsson-Åkerman, B. J.; Schuller, Ivan K.

2001-03-01

We have investigated the pinning of magnetic flux quanta by rectangular arrays of nanoscaled magnetic dots. We measured the resistivity vs. magnetic field characteristics using a high magnetic field resolution of up to 0.1 G over the full field range ( 2 kG to 2 kG). By this we the appearance of minima at half and third integer values of the matching field. It is well known that a reconfiguration of the vortex lattice from a rectangular to a square type geometry occurs in rectangular arrays of magnetic dots when the magnetic field is increased over a threshold value H_r. If we lower the magnetic field after crossing H_r, we find that some of the minima at the full integer matching field are missing. This hysteretic behavior occurs only when Hr is exceeded before the subsequent decrease of the magnetic field. We present the experimental results and discuss preliminary models for the explanation of these observations. This work was supported by the grants NSF and DOE. Two of us acknowledge postdoctoral fellowships by the DAAD (Deutscher Akademischer Austauschdienst) (O.M.S.) and the Secretaria De Estado De Educacion Y Universidades (M.I.M.) respectively.

Magnetic-Field Density-Functional Theory (BDFT): Lessons from the Adiabatic Connection.

PubMed

Reimann, Sarah; Borgoo, Alex; Tellgren, Erik I; Teale, Andrew M; Helgaker, Trygve

2017-09-12

We study the effects of magnetic fields in the context of magnetic field density-functional theory (BDFT), where the energy is a functional of the electron density ρ and the magnetic field B. We show that this approach is a worthwhile alternative to current-density functional theory (CDFT) and may provide a viable route to the study of many magnetic phenomena using density-functional theory (DFT). The relationship between BDFT and CDFT is developed and clarified within the framework of the four-way correspondence of saddle functions and their convex and concave parents in convex analysis. By decomposing the energy into its Kohn-Sham components, we demonstrate that the magnetizability is mainly determined by those energy components that are related to the density. For existing density functional approximations, this implies that, for the magnetizability, improvements of the density will be more beneficial than introducing a magnetic-field dependence in the correlation functional. However, once a good charge density is achieved, we show that high accuracy is likely only obtainable by including magnetic-field dependence. We demonstrate that adiabatic-connection (AC) curves at different field strengths resemble one another closely provided each curve is calculated at the equilibrium geometry of that field strength. In contrast, if all AC curves are calculated at the equilibrium geometry of the field-free system, then the curves change strongly with increasing field strength due to the increasing importance of static correlation. This holds also for density functional approximations, for which we demonstrate that the main error encountered in the presence of a field is already present at zero field strength, indicating that density-functional approximations may be applied to systems in strong fields, without the need to treat additional static correlation.

Equatorial sandhoppers use body scans to detect the earth's magnetic field.

PubMed

Ugolini, A

2006-01-01

Adults of Talorchestia martensii were individually released in a confined environment, with and without the natural magnetic field, under the sun and in a dark room. The sandhoppers scanned the horizontal component of the magnetic field by left and right oscillations of the entire major body axis. The frequency of this behaviour increased in a zeroed magnetic field, as did the frequencies of other behavioural indicators that reflect the difficulty in identifying the ecologically efficient orientation direction (sea-land axis). Therefore, like head scans in birds, body scans seem to be used by equatorial sandhoppers to detect the magnetic symmetry plane.

Magnetic-field generation by pulsed irradiation of aluminium in air

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

Chumakov, A N; Chekan, P V

Magnetic-field generation arising under irradiation of an aluminium barrier in the air by a series of laser pulses is studied experimentally. It is found that the magnetic field increases nonlinearly from 10{sup -5} to 10{sup -3} T with increasing laser power density from 10{sup 7} to 10{sup 9} W cm{sup -2}, the degree of nonlinearity being different for single nanosecond pulses, for a series of such pulses with a repetition rate of 100 – 150 μs and for a combination of a millisecond laser pulse and a series of nanosecond laser pulses. The dependences of the magnetic-field induction on themore » power density of laser radiation in the above-mentioned regimes are established. (interaction of laser radiation with matter)« less

Wide Band Low Noise Love Wave Magnetic Field Sensor System.

PubMed

Kittmann, Anne; Durdaut, Phillip; Zabel, Sebastian; Reermann, Jens; Schmalz, Julius; Spetzler, Benjamin; Meyners, Dirk; Sun, Nian X; McCord, Jeffrey; Gerken, Martina; Schmidt, Gerhard; Höft, Michael; Knöchel, Reinhard; Faupel, Franz; Quandt, Eckhard

2018-01-10

We present a comprehensive study of a magnetic sensor system that benefits from a new technique to substantially increase the magnetoelastic coupling of surface acoustic waves (SAW). The device uses shear horizontal acoustic surface waves that are guided by a fused silica layer with an amorphous magnetostrictive FeCoSiB thin film on top. The velocity of these so-called Love waves follows the magnetoelastically-induced changes of the shear modulus according to the magnetic field present. The SAW sensor is operated in a delay line configuration at approximately 150 MHz and translates the magnetic field to a time delay and a related phase shift. The fundamentals of this sensor concept are motivated by magnetic and mechanical simulations. They are experimentally verified using customized low-noise readout electronics. With an extremely low magnetic noise level of ≈100 pT/[Formula: see text], a bandwidth of 50 kHz and a dynamic range of 120 dB, this magnetic field sensor system shows outstanding characteristics. A range of additional measures to further increase the sensitivity are investigated with simulations.

Magnetization reversal of in-plane uniaxial Co films and its dependence on epitaxial alignment

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

Idigoras, O., E-mail: o.idigoras@nanogune.eu; Suszka, A. K.; Berger, A.

2014-02-28

This work studies the influence of crystallographic alignment onto magnetization reversal in partially epitaxial Co films. A reproducible growth sequence was devised that allows for the continuous tuning of grain orientation disorder in Co films with uniaxial in-plane anisotropy by the controlled partial suppression of epitaxy. While all stable or meta-stable magnetization states occurring during a magnetic field cycle exhibit a uniform magnetization for fully epitaxial samples, non-uniform states appear for samples with sufficiently high grain orientation disorder. Simultaneously with the occurrence of stable domain states during the magnetization reversal, we observe a qualitative change of the applied field anglemore » dependence of the coercive field. Upon increasing the grain orientation disorder, we observe a disappearance of transient domain wall propagation as the dominating reversal process, which is characterized by an increase of the coercive field for applied field angles away from the easy axis for well-ordered epitaxial samples. Upon reaching a certain disorder threshold level, we also find an anomalous magnetization reversal, which is characterized by a non-monotonic behavior of the remanent magnetization and coercive field as a function of the applied field angle in the vicinity of the nominal hard axis. This anomaly is a collective reversal mode that is caused by disorder-induced frustration and it can be qualitatively and even quantitatively explained by means of a two Stoner-Wohlfarth particle model. Its predictions are furthermore corroborated by Kerr microscopy and by Brillouin light scattering measurements.« less

Stability analysis of a deterministic dose calculation for MRI-guided radiotherapy.

PubMed

Zelyak, O; Fallone, B G; St-Aubin, J

2017-12-14

Modern effort in radiotherapy to address the challenges of tumor localization and motion has led to the development of MRI guided radiotherapy technologies. Accurate dose calculations must properly account for the effects of the MRI magnetic fields. Previous work has investigated the accuracy of a deterministic linear Boltzmann transport equation (LBTE) solver that includes magnetic field, but not the stability of the iterative solution method. In this work, we perform a stability analysis of this deterministic algorithm including an investigation of the convergence rate dependencies on the magnetic field, material density, energy, and anisotropy expansion. The iterative convergence rate of the continuous and discretized LBTE including magnetic fields is determined by analyzing the spectral radius using Fourier analysis for the stationary source iteration (SI) scheme. The spectral radius is calculated when the magnetic field is included (1) as a part of the iteration source, and (2) inside the streaming-collision operator. The non-stationary Krylov subspace solver GMRES is also investigated as a potential method to accelerate the iterative convergence, and an angular parallel computing methodology is investigated as a method to enhance the efficiency of the calculation. SI is found to be unstable when the magnetic field is part of the iteration source, but unconditionally stable when the magnetic field is included in the streaming-collision operator. The discretized LBTE with magnetic fields using a space-angle upwind stabilized discontinuous finite element method (DFEM) was also found to be unconditionally stable, but the spectral radius rapidly reaches unity for very low-density media and increasing magnetic field strengths indicating arbitrarily slow convergence rates. However, GMRES is shown to significantly accelerate the DFEM convergence rate showing only a weak dependence on the magnetic field. In addition, the use of an angular parallel computing strategy is shown to potentially increase the efficiency of the dose calculation.

Stability analysis of a deterministic dose calculation for MRI-guided radiotherapy

NASA Astrophysics Data System (ADS)

Zelyak, O.; Fallone, B. G.; St-Aubin, J.

2018-01-01

Modern effort in radiotherapy to address the challenges of tumor localization and motion has led to the development of MRI guided radiotherapy technologies. Accurate dose calculations must properly account for the effects of the MRI magnetic fields. Previous work has investigated the accuracy of a deterministic linear Boltzmann transport equation (LBTE) solver that includes magnetic field, but not the stability of the iterative solution method. In this work, we perform a stability analysis of this deterministic algorithm including an investigation of the convergence rate dependencies on the magnetic field, material density, energy, and anisotropy expansion. The iterative convergence rate of the continuous and discretized LBTE including magnetic fields is determined by analyzing the spectral radius using Fourier analysis for the stationary source iteration (SI) scheme. The spectral radius is calculated when the magnetic field is included (1) as a part of the iteration source, and (2) inside the streaming-collision operator. The non-stationary Krylov subspace solver GMRES is also investigated as a potential method to accelerate the iterative convergence, and an angular parallel computing methodology is investigated as a method to enhance the efficiency of the calculation. SI is found to be unstable when the magnetic field is part of the iteration source, but unconditionally stable when the magnetic field is included in the streaming-collision operator. The discretized LBTE with magnetic fields using a space-angle upwind stabilized discontinuous finite element method (DFEM) was also found to be unconditionally stable, but the spectral radius rapidly reaches unity for very low-density media and increasing magnetic field strengths indicating arbitrarily slow convergence rates. However, GMRES is shown to significantly accelerate the DFEM convergence rate showing only a weak dependence on the magnetic field. In addition, the use of an angular parallel computing strategy is shown to potentially increase the efficiency of the dose calculation.

Corrigendum to "Stability analysis of a deterministic dose calculation for MRI-guided radiotherapy".

PubMed

Zelyak, Oleksandr; Fallone, B Gino; St-Aubin, Joel

2018-03-12

Modern effort in radiotherapy to address the challenges of tumor localization and motion has led to the development of MRI guided radiotherapy technologies. Accurate dose calculations must properly account for the effects of the MRI magnetic fields. Previous work has investigated the accuracy of a deterministic linear Boltzmann transport equation (LBTE) solver that includes magnetic field, but not the stability of the iterative solution method. In this work, we perform a stability analysis of this deterministic algorithm including an investigation of the convergence rate dependencies on the magnetic field, material density, energy, and anisotropy expansion. The iterative convergence rate of the continuous and discretized LBTE including magnetic fields is determined by analyzing the spectral radius using Fourier analysis for the stationary source iteration (SI) scheme. The spectral radius is calculated when the magnetic field is included (1) as a part of the iteration source, and (2) inside the streaming-collision operator. The non-stationary Krylov subspace solver GMRES is also investigated as a potential method to accelerate the iterative convergence, and an angular parallel computing methodology is investigated as a method to enhance the efficiency of the calculation. SI is found to be unstable when the magnetic field is part of the iteration source, but unconditionally stable when the magnetic field is included in the streaming-collision operator. The discretized LBTE with magnetic fields using a space-angle upwind stabilized discontinuous finite element method (DFEM) was also found to be unconditionally stable, but the spectral radius rapidly reaches unity for very low density media and increasing magnetic field strengths indicating arbitrarily slow convergence rates. However, GMRES is shown to significantly accelerate the DFEM convergence rate showing only a weak dependence on the magnetic field. In addition, the use of an angular parallel computing strategy is shown to potentially increase the efficiency of the dose calculation. © 2018 Institute of Physics and Engineering in Medicine.

Anisotropy and shape of hysteresis loop of frozen suspensions of iron oxide nanoparticles in water

NASA Astrophysics Data System (ADS)

Boekelheide, Zoe; Gruettner, Cordula; Dennis, Cindi

2014-03-01

Colloidal suspensions of nanoparticles in liquids have many uses in biomedical applications. We studied approximately 50 nm diameter iron oxide particles dispersed in H2O for magnetic nanoparticle hyperthermia cancer treatment. Interactions between nanoparticles have been indicated for increasing the heat output under application of an alternating magnetic field, as in hyperthermia. Interactions vary dynamically with an applied field as the nanoparticles reorient and rearrange within the liquid. Therefore, we studied the samples below the liquid freezing point in a range of magnetic field strengths to literally freeze in the effects of interactions. We found that the shape of the magnetic hysteresis loop is squarer (higher anisotropy) when the sample was cooled in a high field, and less square (lower anisotropy) when the sample was cooled in a low or zero field. The cause is most likely the formation of long chains of nanoparticles up to 500 μm, which we observe optically. This increase in anisotropy may indicate improved heating ability for these nanoparticles under an alternating magnetic field.

Fragmentation of a Filamentary Cloud Permeated by a Perpendicular Magnetic Field

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

Hanawa, Tomoyuki; Kudoh, Takahiro; Tomisaka, Kohji

We examine the linear stability of an isothermal filamentary cloud permeated by a perpendicular magnetic field. Our model cloud is assumed to be supported by gas pressure against self-gravity in the unperturbed state. For simplicity, the density distribution is assumed to be symmetric around the axis. Also for simplicity, the initial magnetic field is assumed to be uniform, and turbulence is not taken into account. The perturbation equation is formulated to be an eigenvalue problem. The growth rate is obtained as a function of the wavenumber for fragmentation along the axis and the magnetic field strength. The growth rate dependsmore » critically on the outer boundary. If the displacement vanishes in regions very far from the cloud axis (fixed boundary), cloud fragmentation is suppressed by a moderate magnetic field, which means the plasma beta is below 1.67 on the cloud axis. If the displacement is constant along the magnetic field in regions very far from the cloud, the cloud is unstable even when the magnetic field is infinitely strong. The cloud is deformed by circulation in the plane perpendicular to the magnetic field. The unstable mode is not likely to induce dynamical collapse, since it is excited even when the whole cloud is magnetically subcritical. For both boundary conditions, the magnetic field increases the wavelength of the most unstable mode. We find that the magnetic force suppresses compression perpendicular to the magnetic field especially in regions of low density.« less

Luminosity and cooling of highly magnetized white dwarfs: suppression of luminosity by strong magnetic fields

NASA Astrophysics Data System (ADS)

Bhattacharya, Mukul; Mukhopadhyay, Banibrata; Mukerjee, Subroto

2018-06-01

We investigate the luminosity and cooling of highly magnetized white dwarfs with electron-degenerate cores and non-degenerate surface layers where cooling occurs by diffusion of photons. We find the temperature and density profiles in the surface layers or envelope of white dwarfs by solving the magnetostatic equilibrium and photon diffusion equations in a Newtonian framework. We also obtain the properties of white dwarfs at the core-envelope interface, when the core is assumed to be practically isothermal. With the increase in magnetic field, the interface temperature increases whereas the interface radius decreases. For a given age of the white dwarf and for fixed interface radius or interface temperature, we find that the luminosity decreases significantly from about 10-6 to 10-9 L⊙ as the magnetic field strength increases from about 109 to 1012 G at the interface and hence the envelope. This is remarkable because it argues that magnetized white dwarfs are fainter and can be practically hidden in an observed Hertzsprung-Russell diagram. We also find the cooling rates corresponding to these luminosities. Interestingly, the decrease in temperature with time, for the fields under consideration, is not found to be appreciable.

Tripolar electric field Structure in guide field magnetic reconnection

NASA Astrophysics Data System (ADS)

Fu, Song; Huang, Shiyong; Zhou, Meng; Ni, Binbin; Deng, Xiaohua

2018-03-01

It has been shown that the guide field substantially modifies the structure of the reconnection layer. For instance, the Hall magnetic and electric fields are distorted in guide field reconnection compared to reconnection without guide fields (i.e., anti-parallel reconnection). In this paper, we performed 2.5-D electromagnetic full particle simulation to study the electric field structures in magnetic reconnection under different initial guide fields (Bg). Once the amplitude of a guide field exceeds 0.3 times the asymptotic magnetic field B0, the traditional bipolar Hall electric field is clearly replaced by a tripolar electric field, which consists of a newly emerged electric field and the bipolar Hall electric field. The newly emerged electric field is a convective electric field about one ion inertial length away from the neutral sheet. It arises from the disappearance of the Hall electric field due to the substantial modification of the magnetic field and electric current by the imposed guide field. The peak magnitude of this new electric field increases linearly with the increment of guide field strength. Possible applications of these results to space observations are also discussed.

Method for obtaining large levitation pressure in superconducting magnetic bearings

DOEpatents

Hull, John R.

1997-01-01

A method and apparatus for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap.

Method for obtaining large levitation pressure in superconducting magnetic bearings

DOEpatents

Hull, John R.

1996-01-01

A method and apparatus for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap.

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

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

Wang Haimin; Liu Chang, E-mail: haimin.wang@njit.ed, E-mail: chang.liu@njit.ed

2010-06-20

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

Dynamo action and magnetic activity during the pre-main sequence: Influence of rotation and structural changes

NASA Astrophysics Data System (ADS)

Emeriau-Viard, Constance; Brun, Allan Sacha

2017-10-01

During the PMS, structure and rotation rate of stars evolve significantly. We wish to assess the consequences of these drastic changes on stellar dynamo, internal magnetic field topology and activity level by mean of HPC simulations with the ASH code. To answer this question, we develop 3D MHD simulations that represent specific stages of stellar evolution along the PMS. We choose five different models characterized by the radius of their radiative zone following an evolutionary track, from 1 Myr to 50 Myr, computed by a 1D stellar evolution code. We introduce a seed magnetic field in the youngest model and then we spread it through all simulations. First of all, we study the consequences that the increase of rotation rate and the change of geometry of the convective zone have on the dynamo field that exists in the convective envelop. The magnetic energy increases, the topology of the magnetic field becomes more complex and the axisymmetric magnetic field becomes less predominant as the star ages. The computation of the fully convective MHD model shows that a strong dynamo develops with a ratio of magnetic to kinetic energy reaching equipartition and even super-equipartition states in the faster rotating cases. Magnetic fields resulting from our MHD simulations possess a mixed poloidal-toroidal topology with no obvious dominant component. We also study the relaxation of the vestige dynamo magnetic field within the radiative core and found that it satisfies stability criteria. Hence it does not experience a global reconfiguration and instead slowly relaxes by retaining its mixed poloidal-toroidal topology.

Effect of soft-iron impellers on the von Kármán-sodium dynamo.

PubMed

Xu, Mingtian

2014-01-01

The explanation for the observed axisymmetric magnetic field in the von Kármán-sodium (VKS) dynamo experiment is still an unresolved question. In this paper, the integral equation approach is extended to investigate the VKS dynamo action by taking into account the discontinuity of the magnetic permeability and electrical conductivity in the conducting region. When the relative magnetic permeability of the soft-iron impellers is set to 65, a steady toroidal field that is apparently axisymmetric is excited at the critical magnetic Reynolds number, Rmc≈27.23, which is close to the experimental result, Rmc≈30. Our results show that the critical magnetic Reynolds number declines as the relative magnetic permeability of the impellers increases. Furthermore, when the relative magnetic permeability is not greater than 37, an equatorial magnetic field with an azimuthal wave number m=1 is the dominant mode, otherwise a steady toroidal field with an azimuthal wave number m=0 predominates the magnetic field generated by the VKS dynamo action.

Energy dissipation in a finite volume of magnetic fluid

NASA Astrophysics Data System (ADS)

Bashtovoi, V.; Motsar, A.; Reks, A.

2017-06-01

This study is devoted to investigation of energy dissipation processes which happen in a magnetic fluid drop with compound magnet during its motion in cylindrical non magnetic container. The possibility of energy dissipation control by means of electromagnetic field is examined. It's found that a change of magnetic field of compound magnet can lead to both increase and decrease of oscillation decay time and relative damping factor can be varied in a range of ±35%.

Magnetization of InAs parabolic quantum dot: An exact diagonalization approach

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

Aswathy, K. M., E-mail: aswathykm20@gmail.com; Sanjeev Kumar, D.

2016-04-13

The magnetization of two electron InAs quantum dot has been studied as a function of magnetic field. The electron-electron interaction has been taken into account by using exact diagonalization method numerically. The magnetization at zero external magnetic field is zero and increases in the negative direction. There is also a paramagnetic peak where the energy levels cross from singlet state to triplet state. Finally, the magnetization falls again to even negative values and saturates.

Linear and nonlinear optical properties in an asymmetric double quantum well under intense laser field: Effects of applied electric and magnetic fields

NASA Astrophysics Data System (ADS)

Yesilgul, U.; Al, E. B.; Martínez-Orozco, J. C.; Restrepo, R. L.; Mora-Ramos, M. E.; Duque, C. A.; Ungan, F.; Kasapoglu, E.

2016-08-01

In the present study, the effects of electric and magnetic fields on the linear and third-order nonlinear optical absorption coefficients and relative change of the refractive index in asymmetric GaAs/GaAlAs double quantum wells under intense laser fields are theoretically investigated. The electric field is oriented along the growth direction of the heterostructure while the magnetic field is taken in-plane. The intense laser field is linear polarization along the growth direction. Our calculations are made using the effective-mass approximation and the compact density-matrix approach. Intense laser effects on the system are investigated with the use of the Floquet method with the consequent change in the confinement potential of heterostructures. Our results show that the increase of the electric and magnetic fields blue-shifts the peak positions of the total absorption coefficient and of the total refractive index while the increase of the intense laser field firstly blue-shifts the peak positions and later results in their red-shifting.

Study of magnetic domain evolution in an auxetic plane of Galfenol using Kerr microscopy

NASA Astrophysics Data System (ADS)

Raghunath, Ganesh; Flatau, Alison B.

2015-05-01

Galfenol (FexGa100-x), a magnetostrictive alloy (3/2λ 110-400 ppm) of Iron and Gallium exhibits an in-plane auxetic response in the ⟨110⟩ crystallographic direction. Negative Poisson's ratios have been observed in response to application of stress fields, where values of as low as -0.7 have been reported for compositions of greater than roughly 20% Ga [Zhang et al., J. Appl. Phys. 108(2), 023513 (2010)] and in response to application of magnetic fields, where values of as low as -2.5 have been reported to be expected for compositions of less than roughly 20% Ga [G. Raghunath and A. B. Flatau, IEEE Trans. Magn. (in press)]. Several models have been proposed to understand these two distinct phenomena. Galfenol samples with less than 20% Ga also exhibit an unusual response to an increasing magnetic field applied along the ⟨110⟩ direction. The longitudinal strain which increases initially with applied field experiences a dip (until ˜10 mT) before increasing again to reach saturation. The transverse strain increases and reaches a maximum value (at the same field of ˜10 mT) and then drops from the maximum by 5%-10% as magnetic saturation is approached [G. Raghunath and A. B. Flatau, IEEE Trans. Magn. (in press)].This work deals with discussing the evolution of magnetic domains in a 16 at. % Ga single crystal Galfenol sample when subjected to magnetic fields in the ⟨110⟩ direction in the (100) plane. The magnetic domains on the surface of mechanically polished Galfenol samples were imaged using Magneto-Optic Kerr Effect microscopy. Simultaneously, the strains along the longitudinal and transverse ⟨110⟩ directions were recorded using a bi-directional strain gauge rosette mounted on the unpolished bottom surface of the planar samples. The energy from the applied magnetic field is expected to grow the ⟨110⟩ oriented domains at the expense of domains oriented along all other directions. But since the plane has an easy ⟨100⟩ axis, we expect the domains to orient along the easy direction before saturating along the applied magnetic field direction. A correlation between the images recorded and the strains observed will be used to understand this shift of domains and bump in strain at low fields.

The effects of transverse magnetic field and local electronic interaction on thermoelectric properties of monolayer graphene

NASA Astrophysics Data System (ADS)

Rezania, Hamed; Azizi, Farshad

2018-02-01

We study the effects of a transverse magnetic field and electron doping on the thermoelectric properties of monolayer graphene in the context of Hubbard model at the antiferromagnetic sector. In particular, the temperature dependence of thermal conductivity and Seebeck coefficient has been investigated. Mean field approximation has been employed in order to obtain the electronic spectrum of the system in the presence of local electron-electron interaction. Our results show the peak in thermal conductivity moves to higher temperatures with increase of both chemical potential and Hubbard parameter. Moreover the increase of magnetic field leads to shift of peak in temperature dependence of thermal conductivity to higher temperatures. Finally the behavior of Seebeck coefficient in terms of temperature has been studied and the effects of magnetic field and Hubbard parameter on this coefficient have been investigated in details.

Effect of pressure and magnetic field on the electrical resistivity of TbB6

NASA Astrophysics Data System (ADS)

Sakai, Takeshi; Oomi, Gendo; Kunii, Satoru

2009-06-01

Electrical resistivity of a single crystal of TbB6 was studied under hydrostatic pressures up to 2.1 GPa and magnetic fields up to 9 T. The Néel temperature, rN, decreases linearly with increasing pressure: \\ddiff lnTN/\\ddiff P = 3.14×10-2 GPa-1 at zero external field. This pressure dependence of TN weakens as external fields increase. At ambient pressure, the magnetoresistance at 4.2 K is positive up to 4.8 T and becomes negative above 4.8 T. The positive magnetoresistance observed at ambient pressure is suppressed by applying pressure, which enhances the negative magnetoresistance. These results are interpreted in terms of the reduction of the scattering of conduction electrons, due to disordered magnetic moment being suppressed by derealization of 4f electrons at high pressure, and the magnetic field variation of the large transition probability between the ground state and the excited levels.

Flow of magnetic particles in blood with isothermal heating: A fractional model for two-phase flow

NASA Astrophysics Data System (ADS)

Ali, Farhad; Imtiaz, Anees; Khan, Ilyas; Sheikh, Nadeem Ahmad

2018-06-01

In the sixteenth century, medical specialists were of the conclusion that magnet can be utilized for the treatment or wipe out the illnesses from the body. On this basis, the research on magnet advances day by day for the treatment of different types of diseases in mankind. This study aims to investigate the effect of magnetic field and their applications in human body specifically in blood. Blood is a non-Newtonian fluid because its viscosity depends strongly on the fraction of volume occupied by red cells also called the hematocrit. Therefore, in this paper blood is considered as an example of non-Newtonian Casson fluid. The blood flow is considered in a vertical cylinder together with heat transfer due to mixed conviction caused by buoyancy force and the external pressure gradient. Effect of magnetic field on the velocities of blood and magnetic particles is also considered. The problem is modelled using the Caputo-Fabrizio derivative approach. The governing fractional partial differential equations are solved using Laplace and Hankel transformation techniques and exact solutions are obtained. Effects of different parameters such as Grashof number, Prandtl number, Casson fluid parameter and fractional parameters, and magnetic field are shown graphically. Both velocity profiles increase with the increase of Grashoff number and Casson fluid parameter and reduce with the increase of magnetic field.

Magnetic Flux Concentrations in Stratified Turbulent Plasma Due to Negative Effective Magnetic Pressure Instability

NASA Astrophysics Data System (ADS)

Jabbari, S.; Brandenburg, A.

2014-12-01

Recent studies have suggested a new mechanism that can be used to explain the formation of magnetic spots or bipolar regions in highly stratified turbulent plasmas. According to this model, a large-scale magnetic field suppresses the turbulent pressure, which leads to a negative contribution of turbulence to the effective magnetic pressure. Direct numerical simulations (DNS) have confirmed that the negative contribution is large enough so that the effective magnetic pressure becomes negative and leads to a large-scale instability, which we refer to as negative effective magnetic pressure Instability (NEMPI). NEMPI was used to explain the formation of active regions and sunspots on the solar surface. One step toward improving this model was to combine dynamo in- stability with NEMPI. The dynamo is known to be responsible for the solar large-scale magnetic field and to play a role in solar activity. In this context, we studied stratified turbulent plasmas in spherical geometry, where the background field was generated by alpha squared dynamo. For NEMPI to be excited, the initial magnetic field should be in a proper range, so we used quenching function for alpha. Using the Pencil Code and mean field simulations (MFS), we showed that in the presence of dynamo-generated magnetic fields, we deal with a coupled system, where both instabilities, dynamo and NEMPI, work together and lead to the formation of magnetic structures (Jabbari et al. 2013). We also studied a similar system in plane geometry in the presence of rotation and confirmed that for slow rotation NEMPI works, but as the Coriolis number increases, the rotation suppresses NEMPI. By increasing the Coriolis number even further, the combination of fast rotation and high stratification excites a dynamo, which leads again to a coupled system of dynamo and NEMPI (Jabbari et al. 2014). Another important finding concerning NEMPI is the case where the instability is excited by a vertical magnetic field (Brandenburg et al. 2013). When the field is vertical, the resulting magnetic flux concentrations lead to the magnetic spots and can be of equipartition field strength. DNS, MFS, and implicit large eddy simulations (ILES) confirm that in a proper parameter regime, vertical imposed fields lead to the formation of circular magnetic spots (Brandenburg et al. 2014).

The Role of Diffusivity Quenching in Flux-transport Dynamo Models

NASA Astrophysics Data System (ADS)

Guerrero, Gustavo; Dikpati, Mausumi; de Gouveia Dal Pino, Elisabete M.

2009-08-01

In the nonlinear phase of a dynamo process, the back-reaction of the magnetic field upon the turbulent motion results in a decrease of the turbulence level and therefore in a suppression of both the magnetic field amplification (the α-quenching effect) and the turbulent magnetic diffusivity (the η-quenching effect). While the former has been widely explored, the effects of η-quenching in the magnetic field evolution have rarely been considered. In this work, we investigate the role of the suppression of diffusivity in a flux-transport solar dynamo model that also includes a nonlinear α-quenching term. Our results indicate that, although for α-quenching the dependence of the magnetic field amplification with the quenching factor is nearly linear, the magnetic field response to η-quenching is nonlinear and spatially nonuniform. We have found that the magnetic field can be locally amplified in this case, forming long-lived structures whose maximum amplitude can be up to ~2.5 times larger at the tachocline and up to ~2 times larger at the center of the convection zone than in models without quenching. However, this amplification leads to unobservable effects and to a worse distribution of the magnetic field in the butterfly diagram. Since the dynamo cycle period increases when the efficiency of the quenching increases, we have also explored whether the η-quenching can cause a diffusion-dominated model to drift into an advection-dominated regime. We have found that models undergoing a large suppression in η produce a strong segregation of magnetic fields that may lead to unsteady dynamo-oscillations. On the other hand, an initially diffusion-dominated model undergoing a small suppression in η remains in the diffusion-dominated regime.

Genotoxic Effects of Superconducting Static Magnetic Fields (SMFs) on Wheat (Triticum aestivum) Pollen Mother Cells (PMCs)

NASA Astrophysics Data System (ADS)

Zhang, Pingping; Yin, Ruochun; Chen, Zhiyou; Wu, Lifang; Yu, Zengliang

2007-04-01

The effects of superconducting static magnetic fields (SMFs) on the pollen mother cells (PMCs) of wheat were investigated in order to evaluate the possible genotoxic effect of such non-ionizing radiation. The seeds of wheat were exposed to static magnetic fields with either different magnetic flux densities (0, 1, 3, 5 and 7 Tesla) for 5 h or different durations (1, 3 and 5 h) at a magnetic flux density of 7 Tesla. The seeds were germinated at 23oC after exposure and the seedlings were transplanted into the field. The PMCs from young wheat ears were taken and slides were made following the conventional method. The genotoxic effect was evaluated in terms of micronucleus (MN), chromosomal bridge, lagging chromosome and fragments in PMCs. Although the exposed groups of a low field intensity (below 5 Tesla) showed no statistically significant difference in the aberration frequency compared with the unexposed control groups and sham exposed groups, a significant increase in the chromosomal bridge, lagging chromosome, triple-polar segregation or micronucleus was observed at a field strength of 5 Tesla or 7 Tesla, respectively. The analysis of dose-effect relationships indicated that the increased frequency of meiotic abnormal cells correlated with the flux density of the magnetic field and duration, but no linear relationship was observed. Such statistically significant differences indicated a potential genotoxic effect of high static magnetic fields above 5 T.

Simulation of the small-scale magnetism in main-sequence stellar atmospheres

NASA Astrophysics Data System (ADS)

Salhab, R. G.; Steiner, O.; Berdyugina, S. V.; Freytag, B.; Rajaguru, S. P.; Steffen, M.

2018-06-01

Context. Observations of the Sun tell us that its granular and subgranular small-scale magnetism has significant consequences for global quantities such as the total solar irradiance or convective blueshift of spectral lines. Aims: In this paper, properties of the small-scale magnetism of four cool stellar atmospheres, including the Sun, are investigated, and in particular its effects on the radiative intensity and flux. Methods: We carried out three-dimensional radiation magnetohydrodynamic simulations with the CO5BOLD code in two different settings: with and without a magnetic field. These are thought to represent states of high and low small-scale magnetic activity of a stellar magnetic cycle. Results: We find that the presence of small-scale magnetism increases the bolometric intensity and flux in all investigated models. The surplus in radiative flux of the magnetic over the magnetic field-free atmosphere increases with increasing effective temperature, Teff, from 0.47% for spectral type K8V to 1.05% for the solar model, but decreases for higher effective temperatures than solar. The degree of evacuation of the magnetic flux concentrations monotonically increases with Teff as does their depression of the visible optical surface, that is the Wilson depression. Nevertheless, the strength of the field concentrations on this surface stays remarkably unchanged at ≈1560 G throughout the considered range of spectral types. With respect to the surrounding gas pressure, the field strength is close to (thermal) equipartition for the Sun and spectral type F5V but is clearly sub-equipartition for K2V and more so for K8V. The magnetic flux concentrations appear most conspicuous for model K2V owing to their high brightness contrast. Conclusions: For mean magnetic flux densities of approximately 50 G, we expect the small-scale magnetism of stars in the spectral range from F5V to K8V to produce a positive contribution to their bolometric luminosity. The modulation seems to be most effective for early G-type stars.

Total antioxidant capacity, total oxidant status and oxidative stress index in the men exposed to 1.5 T static magnetic field.

PubMed

Sirmatel, O; Sert, C; Sirmatel, F; Selek, S; Yokus, B

2007-06-01

The aim of this study was to investigate the effects of a high-strength magnetic field produced by a magnetic resonance imaging (MRI) apparatus on oxidative stress. The effects of a 1.5 T static magnetic field on the total antioxidant capacity (TAC), total oxidant status (TOS) and oxidative stress index (OSI) in male subjects were investigated. In this study, 33 male volunteers were exposed to a 1.5 T static magnetic field for a short time and the TAC, TOS and OSI of each subject were determined. Magnetic field exposure was provided using a magnetic resonance apparatus; radiofrequency was not applied. Blood samples were taken from subjects and TAC, TOS and OSI values were measured using the methods of Erel. TAC showed a significant increase in post-exposures compared to pre-exposures to the magnetic field (p < 0.05). OSI and TOS showed a significant decrease in post-exposures compared to pre-exposures to a 1.5 T magnetic field (for each of two, p < 0.01). The 1.5 T static magnetic field used in the MRI apparatus did not yield a negative effect; on the contrary, it produced the positive effect of decreasing oxidative stress in men following short-term exposure.

Behavior of moving plasma in solenoidal magnetic field in a laser ion source

NASA Astrophysics Data System (ADS)

Ikeda, S.; Takahashi, K.; Okamura, M.; Horioka, K.

2016-02-01

In a laser ion source, a solenoidal magnetic field is useful to guide the plasma and to control the extracted beam current. However, the behavior of the plasma drifting in the magnetic field has not been well understood. Therefore, to investigate the behavior, we measured the plasma ion current and the total charge within a single pulse in the solenoid by changing the distance from the entrance of the solenoid to a detector. We observed that the decrease of the total charge along the distance became smaller as the magnetic field became larger and then the charge became almost constant with a certain magnetic flux density. The results indicate that the transverse spreading speed of the plasma decreased with increasing the field and the plasma was confined transversely with the magnetic flux density. We found that the reason of the confinement was not magnetization of ions but an influence induced by electrons.

Behavior of moving plasma in solenoidal magnetic field in a laser ion source.

PubMed

Ikeda, S; Takahashi, K; Okamura, M; Horioka, K

2016-02-01

In a laser ion source, a solenoidal magnetic field is useful to guide the plasma and to control the extracted beam current. However, the behavior of the plasma drifting in the magnetic field has not been well understood. Therefore, to investigate the behavior, we measured the plasma ion current and the total charge within a single pulse in the solenoid by changing the distance from the entrance of the solenoid to a detector. We observed that the decrease of the total charge along the distance became smaller as the magnetic field became larger and then the charge became almost constant with a certain magnetic flux density. The results indicate that the transverse spreading speed of the plasma decreased with increasing the field and the plasma was confined transversely with the magnetic flux density. We found that the reason of the confinement was not magnetization of ions but an influence induced by electrons.

Laser pumping Cs atom magnetometer of theory research based on gradient tensor measuring

NASA Astrophysics Data System (ADS)

Yang, Zhang; Chong, Kang; Wang, Qingtao; Lei, Cheng; Zheng, Caiping

2011-02-01

At present, due to space exploration, military technology, geological exploration, magnetic navigation, medical diagnosis and biological magnetic fields study of the needs of research and development, the magnetometer is given strong driving force. In this paper, it will discuss the theoretical analysis and system design of laser pumping cesium magnetometer, cesium atomic energy level formed hyperfine structure with the I-J coupling, the hyperfine structure has been further split into Zeeman sublevels for the effects of magnetic field. To use laser pump and RF magnetic field make electrons transition in the hyperfine structure to produce the results of magneto-optical double resonance, and ultimately through the resonant frequency will be able to achieve accurate value of the external magnetic field. On this basis, we further have a discussion about magnetic gradient tensor measuring method. To a large extent, it increases the magnetic field measurement of information.

Magneto-optical properties of binar ferrocolloids

NASA Astrophysics Data System (ADS)

Pshenichnikov, A. F.; Lebedev, A. V.; Lakhtina, E. V.; Stepanov, G. V.

2018-03-01

In this work, a new method for increasing optical anisotropy of a ferrocolloid through introducing the coiled polymer molecules or elongated nanosized non-magnetic particles is realized. Since the dimensions of structural elements comprising such a binary colloidal solution are small compared to the wavelength, the ferrocolloid remains optically homogeneous. Type I binary ferrocolloids are obtained by introducing polybutadiene molecules into a magnetic fluid (magnetite + kerosene + oleic acid). In this case, an increase in the double refraction (DR) is due to the deformation and stretching of the polymer coils along the magnetic field. In weak fields, double amplification of the signal was detected for the concentration of polymer molecules of about 0.5 %. A further increase in the concentration of impurity molecules weakens DR due to a disturbance of the sedimentation stability of the solution and precipitation of colloidal particles. Type II binary solution is synthesized on the basis of a magnetic fluid and rod-shaped impurity nanoparticles of goethite ( αFeOOH). The transverse dimension of the impurity particles (10 ‑ 30 nm) was close to the average diameter of single-domain magnetite particles, and the longitudinal dimension was an order of magnitude larger. An increase in the DR occurs due to the orientation of long axes of impurity particles along the magnetic field caused by the difference in the ”demagnetizing” coefficients along and across the axis of the particle. The magnetic double refraction has been studied depending on the concentration of magnetite and impurity particles and the strength of the magnetic field. For the first time, an experimental substantiation of the multiple amplification of the DR signal by impurity particles was obtained. In the fields (up to 10 kA/m) and for the volume fraction of impurity particles of the order of one percent, the DR signal is amplified by more than an order of magnitude. In stronger fields, the signal gain, associated with the influence of impurity particles, reaches saturation and, with further increase in the field strength, remains practically unchanged, while the total anisotropy of the solution continues to increase due to the orientation of the magnetite particles.

Simulation of plasma double-layer structures

NASA Technical Reports Server (NTRS)

Borovsky, J. E.; Joyce, G.

1982-01-01

Electrostatic plasma double layers are numerically simulated by means of a magnetized 2 1/2 dimensional particle in cell method. The investigation of planar double layers indicates that these one dimensional potential structures are susceptible to periodic disruption by instabilities in the low potential plasmas. Only a slight increase in the double layer thickness with an increase in its obliqueness to the magnetic field is observed. Weak magnetization results in the double layer electric field alignment of accelerated particles and strong magnetization results in their magnetic field alignment. The numerical simulations of spatially periodic two dimensional double layers also exhibit cyclical instability. A morphological invariance in two dimensional double layers with respect to the degree of magnetization implies that the potential structures scale with Debye lengths rather than with gyroradii. Electron beam excited electrostatic electron cyclotron waves and (ion beam driven) solitary waves are present in the plasmas adjacent to the double layers.

The Magnetohydrodynamic Kelvin-Helmholtz Instability. III. The Role of Sheared Magnetic Field in Planar Flows

NASA Astrophysics Data System (ADS)

Jeong, Hyunju; Ryu, Dongsu; Jones, T. W.; Frank, Adam

2000-01-01

We have carried out simulations of the nonlinear evolution of the magnetohydrodynamic (MHD) Kelvin-Helmholtz (KH) instability for compressible fluids in 2.5 dimensions, extending our previous work by Frank et al. and Jones et al. In the present work we have simulated flows in the x-y plane in which a ``sheared'' magnetic field of uniform strength smoothly rotates across a thin velocity shear layer from the z-direction to the x-direction, aligned with the flow field. The sonic Mach number of the velocity transition is unity. Such flows containing a uniform field in the x-direction are linearly stable if the magnetic field strength is great enough that the Alfvénic Mach number MA=U0/cA<2. That limit does not apply directly to sheared magnetic fields, however, since the z-field component has almost no influence on the linear stability. Thus, if the magnetic shear layer is contained within the velocity shear layer, the KH instability may still grow, even when the field strength is quite large. So, here we consider a wide range of sheared field strengths covering Alfvénic Mach numbers, MA=142.9 to 2. We focus on dynamical evolution of fluid features, kinetic energy dissipation, and mixing of the fluid between the two layers, considering their dependence on magnetic field strength for this geometry. There are a number of differences from our earlier simulations with uniform magnetic fields in the x-y plane. For the latter, simpler case we found a clear sequence of behaviors with increasing field strength ranging from nearly hydrodynamic flows in which the instability evolves to an almost steady cat's eye vortex with enhanced dissipation, to flows in which the magnetic field disrupts the cat's eye once it forms, to, finally, flows that evolve very little before field-line stretching stabilizes the velocity shear layer. The introduction of magnetic shear can allow a cat's eye-like vortex to form, even when the field is stronger than the nominal linear instability limit given above. For strong fields that vortex is asymmetric with respect to the preliminary shear layer, however, so the subsequent dissipation is enhanced over the uniform field cases of comparable field strength. In fact, so long as the magnetic field achieves some level of dynamical importance during an eddy turnover time, the asymmetries introduced through the magnetic shear will increase flow complexity and, with that, dissipation and mixing. The degree of the fluid mixing between the two layers is strongly influenced by the magnetic field strength. Mixing of the fluid is most effective when the vortex is disrupted by magnetic tension during transient reconnection, through local chaotic behavior that follows.

Analysis of Mars magnetosphere structure near terminator using MAVEN measurements

NASA Astrophysics Data System (ADS)

Vaisberg, O. L.; Zelenyi, L. M.; Ermakov, V.; Shuvalov, S.; Dubinin, E.; Znobischev, A.; McFadden, J. P.; Halekas, J. S.; Connerney, J. E. P.

2017-12-01

Magnetosphere of Mars first observed on Mars-2, -3 and -5 in 1970th forms from solar wind magnetic flux tubes loaded by heavy planetary ions. These flux tubes decelerate on the dayside of Mars forming magnetic barrier forming an obstacle to the supersonic solar wind. Magnetic flux tubes pick-up planetary ions while drifting around the planet and form dynamic magnetosphere of Mars. Review of 100 MAVEN crossings of flank magnetic barrier and magnetosphere showed a variety of their properties. Magnetosphere is identified by domination of O+ and O2+ ions. The energy of these ions at the external boundary is close to the energy of ionosheath ions and decreases to the energy of ionospheric ions at the inner boundary. The number density of magnetospheric ions is close to the number density of ionosheath ions and increases by 2 orders of magnitude towards the inner boundary. From varying magnetic barrier/magnetosphere configurations and properties two types of were observed more frequently. First one has smooth profile of magnetic field and plasma characteristics with magnetic field increase starting in ionosheath and reaching maximal and nearly constant magnitude within magnetosphere. The number density and energy of protons are smoothly decreasing through ionosheath and magnetic barrier/magnetosphere. Pitch angles of planetary ions are close to 90°. Second barrier/magnetosphere structure is characterized by relatively sharp transition from ionosheath to magnetosphere. Magnetic field of barrier starts to increase far from magnetosphere and reaches maximum value at this boundary. The energy of the protons only slightly decreases in the magnetic barrier and may increase just before this boundary. Protons number density within magnetic barrier is smaller than in upstream flow but often increases just before magnetospheric boundary. Magnetic field magnitude drops within magnetosphere. The number densities of O+ and O2+ ions within magnetosphere strongly increase from upper boundary to inner boundary of magnetosphere. The magnetosphere in the second case is thinner than the magnetosphere in the first case. We discuss the influence of the upstream conditions and the dependence of the magnetosphere structure on MSE coordinates.

EFFECTS OF FIELD-LINE TOPOLOGY ON ENERGY PROPAGATION IN THE CORONA

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

Candelaresi, S.; Pontin, D. I.; Hornig, G.

We study the effect of photospheric footpoint motions on magnetic field structures containing magnetic nulls. The footpoint motions are prescribed on the photospheric boundary as a velocity field that entangles the magnetic field. We investigate the propagation of the injected energy, the conversion of energy, emergence of current layers, and other consequences of the nontrivial magnetic field topology in this situation. These boundary motions lead initially to an increase in magnetic and kinetic energy. Following this, the energy input from the photosphere is partially dissipated and partially transported out of the domain through the Poynting flux. The presence of separatrixmore » layers and magnetic null points fundamentally alters the propagation behavior of disturbances from the photosphere into the corona. Depending on the field-line topology close to the photosphere, the energy is either trapped or free to propagate into the corona.« less

Adiabatic and nonadiabatic responses of the radiation belt relativistic electrons to the external changes in solar wind dynamic pressure and interplanetary magnetic field

NASA Astrophysics Data System (ADS)

Li, L.

2013-12-01

By removing the influences of 'magnetopause shadowing' (r0>6.6RE) and geomagnetic activities, we investigated statistically the responses of magnetic field and relativistic (>0.5MeV) electrons at geosynchronous orbit to 201 interplanetary perturbations during 6 years from 2003 (solar maximum) to 2008 (solar minimum). The statistical results indicate that during geomagnetically quiet times (HSYM ≥-30nT, and AE<200nT), ~47.3% changes in the geosynchronous magnetic field and relativistic electron fluxes are caused by the combined actions of the enhancement of solar wind dynamic pressure (Pd) and the southward turning of interplanetary magnetic field (IMF) (ΔPd>0.4 nPa, and IMF Bz<0 nT), and only ~18.4% changes are due to single dynamic pressure increase (ΔPd >0.4 nPa, but IMF Bz>0 nT), and ~34.3% changes are due to single southward turning of IMF (IMF Bz<0 nT, but |ΔPd|<0.4 nPa). Although the responses of magnetic field and relativistic electrons to the southward turning of IMF are weaker than their responses to the dynamic pressure increase, the southward turning of IMF can cause the dawn-dusk asymmetric perturbations that the magnetic field and the relativistic electrons tend to increase on the dawnside (LT~00:00-12:00) but decrease on the duskside (LT~13:00-23:00). Furthermore, the variation of relativistic electron fluxes is adiabatically controlled by the magnitude and elevation angle changes of magnetic field during the single IMF southward turnings. However, the variation of relativistic electron fluxes is independent of the change in magnetic field in some compression regions during the enhancement of solar wind dynamic pressure (including the single pressure increases and the combined external perturbations), indicating that nonadiabatic dynamic processes of relativistic electrons occur there. Acknowledgments. This work is supported by NSFC (grants 41074119 and 40604018). Liuyuan Li is grateful to the staffs working for the data from GOES 8-12 satellites and OMNI database in CDAWeb.

On the condensation of exciton polaritons in microcavities induced by a magnetic field

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

Kochereshko, V. P., E-mail: Vladimir.Kochereshko@mail.ioffe.ru; Avdoshina, D. V.; Savvidis, P.

2016-11-15

The photoluminescence spectra of exciton polaritons in microcavities under conditions of three-dimensional quantization are studied as a factor of the density of the optical excitation and magnetic field. The behavior of the degree of circular polarization of the exciton luminescence in a magnetic field shows that, when the concentration of excitons increases, they condense at the lowest Zeeman sublevel.

Monolayer phosphorene under time-dependent magnetic field

NASA Astrophysics Data System (ADS)

Nascimento, J. P. G.; Aguiar, V.; Guedes, I.

2018-02-01

We obtain the exact wave function of a monolayer phosphorene under a low-intensity time-dependent magnetic field using the dynamical invariant method. We calculate the quantum-mechanical energy expectation value and the transition probability for a constant and an oscillatory magnetic field. For the former we observe that the Landau level energy varies linearly with the quantum numbers n and m and the magnetic field intensity B0. No transition takes place. For the latter, we observe that the energy oscillates in time, increasing linearly with the Landau level n and m and nonlinearly with the magnetic field. The (k , l) →(n , m) transitions take place only for l = m. We investigate the (0,0) →(n , 0) and (1 , l) and (2 , l) probability transitions.

Emergent kink stability of a magnetized plasma jet injected into a transverse background magnetic field

NASA Astrophysics Data System (ADS)

Zhang, Yue; Gilmore, Mark; Hsu, Scott C.; Fisher, Dustin M.; Lynn, Alan G.

2017-11-01

We report experimental results on the injection of a magnetized plasma jet into a transverse background magnetic field in the HelCat linear plasma device at the University of New Mexico [M. Gilmore et al., J. Plasma Phys. 81(1), 345810104 (2015)]. After the plasma jet leaves the plasma-gun muzzle, a tension force arising from an increasing curvature of the background magnetic field induces in the jet a sheared axial-flow gradient above the theoretical kink-stabilization threshold. We observe that this emergent sheared axial flow stabilizes the n = 1 kink mode in the jet, whereas a kink instability is observed in the jet when there is no background magnetic field present.

Magnetoreresistance of carbon nanotube-polypyrrole composite yarns

NASA Astrophysics Data System (ADS)

Ghanbari, R.; Ghorbani, S. R.; Arabi, H.; Foroughi, J.

2018-05-01

Three types of samples, carbon nanotube yarn and carbon nanotube-polypyrrole composite yarns had been investigated by measurement of the electrical conductivity as a function of temperature and magnetic field. The conductivity was well explained by 3D Mott variable range hopping (VRH) law at T < 100 K. Both positive and negative magnetoresistance (MR) were observed by increasing magnetic field. The MR data were analyzed based a theoretical model. A quadratic positive and negative MR was observed for three samples. It was found that the localization length decreases with applied magnetic field while the density of states increases. The increasing of the density of states induces increasing the number of available energy states for hopping. Thus the electron hopping probability increases in between sites with the shorter distance that results to small the average hopping length.

Numerical field evaluation of healthcare workers when bending towards high-field MRI magnets.

PubMed

Wang, H; Trakic, A; Liu, F; Crozier, S

2008-02-01

In MRI, healthcare workers may be exposed to strong static and dynamic magnetic fields outside of the imager. Body motion through the strong, non-uniform static magnetic field generated by the main superconducting magnet and exposure to gradient-pulsed magnetic fields can result in the induction of electric fields and current densities in the tissue. The interaction of these fields and occupational workers has attracted an increasing awareness. To protect occupational workers from overexposure, the member states of the European Union are required to incorporate the Physical Agents Directive (PAD) 2004/40/EC into their legislation. This study presents numerical evaluations of electric fields and current densities in anatomically equivalent male and female human models (healthcare workers) as they lean towards the bores of three superconducting magnet models (1.5, 4, and 7 T) and x-, y-, and z- gradient coils. The combined effect of the 1.5 T superconducting magnet and the three gradient coils on the body models is compared with the contributions of the magnet and gradient coils in separation. The simulation results indicate that it is possible to induce field quantities of physiological significance, especially when the MRI operator is bending close towards the main magnet and all three gradient coils are switched simultaneously. (c) 2008 Wiley-Liss, Inc.

Working Ni-Mn-Ga Single Crystals in a Magnetic Field Against a Spring Load

NASA Astrophysics Data System (ADS)

Lindquist, P. G.; Müllner, P.

2015-03-01

This research characterizes ferromagnetic shape memory elements for use as mechanical actuators. A single crystal of Ni-Mn-Ga was pre-strained in compression from 0 to 6 % and then the shape was recovered with a magnetic field perpendicular to the loading direction while working against a pair of springs. The magnetic field was raised from 0 to 0.64 MA/m and then reduced to zero field. Eight pairs of springs with combined spring constants ranging from 14.3 to 269.4 N/mm were used. When the magnetic field was on, the sample expanded against the springs due to magnetic field-induced strain. When the magnetic field was turned off, the springs compressed the sample back to the initial size before the next cycle. During each cycle, force and displacement were measured and the specific work was computed. Specific work increased with the applied magnetic field and the pre-strain, with a maximum of 14 kJ/m3 at 4.5 % pre-strain and 0.64 MA/m. This value is five times less than the values suggested in the literature which were inferred from stress-strain curves measured under various magnetic fields. The spring prescribes the load-displacement path of the magnetic shape memory element and controls the work output of the actuator.

Shear-induced inflation of coronal magnetic fields

NASA Technical Reports Server (NTRS)

Klimchuk, James A.

1989-01-01

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z)squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes.

Shear-induced inflation of coronal magnetic fields

NASA Technical Reports Server (NTRS)

Klimchuk, James A.

1990-01-01

Using numerical models of force-free magnetic fields, the shearing of footprints in arcade geometries leading to an inflation of the coronal magnetic field was examined. For each of the shear profiles considered, all of the field lines become elevated compared with the potential field. This includes cases where the shear is concentrated well away from the arcade axis, such that B(sub z), the component of field parallel to the axis, increases outward to produce an inward B(sub z) squared/8 pi magnetic pressure gradient force. These results contrast with an earlier claim, shown to be incorrect, that field lines can sometimes become depressed as a result of shear. It is conjectured that an inflation of the entire field will always result from the shearing of simple arcade configurations. These results have implications for prominence formation, the interplanetary magnetic flux, and possibly also coronal holes.

Global enhancement and structure formation of the magnetic field in spiral galaxies

NASA Astrophysics Data System (ADS)

Khoperskov, Sergey A.; Khrapov, Sergey S.

2018-01-01

In this paper we study numerically large-scale magnetic field evolution and its enhancement in gaseous disks of spiral galaxies. We consider a set of models with the various spiral pattern parameters and the initial magnetic field strength with taking into account gas self-gravity and cooling and heating processes. In agreement with previous studies we find out that galactic magnetic field is mostly aligned with gaseous structures, however small-scale gaseous structures (spurs and clumps) are more chaotic than the magnetic field structure. In spiral arms magnetic field often coexists with the gas distribution, in the inter-arm region we see filamentary magnetic field structure. These filaments connect several isolated gaseous clumps. Simulations reveal the presence of the small-scale irregularities of the magnetic field as well as the reversal of magnetic field at the outer edge of the large-scale spurs. We provide evidences that the magnetic field in the spiral arms has a stronger mean-field component, and there is a clear inverse correlation between gas density and plasma-beta parameter, compared to the rest of the disk with a more turbulent component of the field and an absence of correlation between gas density and plasma-beta. We show the mean field growth up to >3-10 μG in the cold gas during several rotation periods (>500-800 Myr), whereas ratio between azimuthal and radial field is equal to >4/1. We find an enhancement of random and ordered components of the magnetic field. Mean field strength increases by a factor of >1.5-2.5 for models with various spiral pattern parameters. Random magnetic field component can reach up to 25% from the total strength. By making an analysis of the time-dependent evolution of the radial Poynting flux, we point out that the magnetic field strength is enhanced more strongly at the galactic outskirts which is due to the radial transfer of magnetic energy by the spiral arms pushing the magnetic field outward. Our results also support the presence of sufficient conditions for the development of magnetorotational instability at distances >11 kpc after >300 Myr of evolution.

A proposed concept for the extraction of energy stored in magnetic or electric fields in space

NASA Technical Reports Server (NTRS)

Papailiou, D. D.

1976-01-01

It is known that enormous energy resources associated with electric, magnetic, gravitational, and other fields exist in space. It is also known that the major difficulty in 'tapping' this energy arises from the extremely low density level at which this energy exists. An analytical study has been made of a particular scheme that appears promising for an efficient utilization of some of these energy resources in propulsion. The principle involves the exchange of energy between a fluctuating magnetic field and a velocity field of electrically conducting fluid in turbulent motion located onboard a spacecraft. Under certain conditions the total energy of the turbulent flow field onboard the spacecraft can be increased and this increase appears in the form of Joulean heat. The utilization of the fluctuating part of the magnetic field, in the form of Joulean dissipation (because of its random character) does not introduce any drag on the spacecraft. The application appears promising for flights in the vicinity of Jupiter and other planets. The rate at which energy is gained by the conducting fluid is of the order of 100 watts when the rms value of the fluctuating magnetic field strength is about 1 gauss.

Magnetically tunable elasticity for magnetic hydrogels consisting of carrageenan and carbonyl iron particles.

PubMed

Mitsumata, Tetsu; Honda, Atomu; Kanazawa, Hiroki; Kawai, Mika

2012-10-11

A new class of magnetoelastic gel that demonstrates drastic and reversible changes in storage modulus without using strong magnetic fields was obtained. The magnetic gel consists of carrageenan and carbonyl iron particles. The magnetic gel with a volume fraction of magnetic particles of 0.30 exhibited a reversible increase by a factor of 1400 of the storage modulus upon a magnetic field of 500 mT, which is the highest value in the past for magnetorheological soft materials. It is considered that the giant magnetoelastic behavior is caused by both high dispersibility and high mobility of magnetic particles in the carrageenan gel. The off-field storage modulus of the magnetic gel at volume fractions below 0.30 obeyed the Krieger-Dougherty equation, indicating random dispersion of magnetic particles. At 500 mT, the storage modulus was higher than 4.0 MPa, which is equal to that of magnetic fluids, indicating that the magnetic particles move and form a chain structure by magnetic fields. Morphological study revealed the evidence that the magnetic particles embedded in the gel were aligned in the direction of magnetic fields, accompanied by stretching of the gel network. We conclude that the giant magnetoelastic phenomenon originates from the chain structure consisting of magnetic particles similar to magnetic fluids.

Dynamics of magnetic single domain particles embedded in a viscous liquid

NASA Astrophysics Data System (ADS)

Usadel, K. D.; Usadel, C.

2015-12-01

Kinetic equations for magnetic nano particles dispersed in a viscous liquid are developed and analyzed numerically. Depending on the amplitude of an applied oscillatory magnetic field, the particles orient their time averaged anisotropy axis perpendicular to the applied field for low magnetic field amplitudes and nearly parallel to the direction of the field for high amplitudes. The transition between these regions takes place in a narrow field interval. In the low field region, the magnetic moment is locked to some crystal axis and the energy absorption in an oscillatory driving field is dominated by viscous losses associated with particle rotation in the liquid. In the opposite limit, the magnetic moment rotates within the particle while its easy axis being nearly parallel to the external field direction oscillates. The kinetic equations are generalized to include thermal fluctuations. This leads to a significant increase of the power absorption in the low and intermediate field regions with a pronounced absorption peak as function of particle size. In the high field region, on the other hand, the inclusion of thermal fluctuations reduces the power absorption. The illustrative numerical calculations presented are performed for magnetic parameters typical for iron oxide.

Magnetic phase diagrams of erbium

NASA Astrophysics Data System (ADS)

Frazer, B. H.; Gebhardt, J. R.; Ali, N.

1999-04-01

The magnetic phase diagrams of erbium in the magnetic field-temperature plane have been constructed for applied magnetic fields along the a and b axes. For an a-axis applied field our H-T phase diagrams determined from magnetization and magnetoresistance data are in good agreement and consistent with that of Jehan et al. for temperatures below 50 K. A splitting of the basal plane Néel temperature (TN⊥) above 3.75 T introduces two new magnetic phases. Also a transition from a fan to a canted fan phase as suggested by Jehan et al. is observed in an increasing field below TC. Our phase diagram for a b-axis applied field constructed from magnetization data is very similar to the phase diagram of Watson and Ali using magnetoresistance measurements. However, the anomaly at 42 K reported by Watson and Ali is not observed in the present study. No splitting of the TN⊥ transition is observed in either work for a field applied along the b axis.

Progress with High-Field Superconducting Magnets for High-Energy Colliders

NASA Astrophysics Data System (ADS)

Apollinari, Giorgio; Prestemon, Soren; Zlobin, Alexander V.

2015-10-01

One of the possible next steps for high-energy physics research relies on a high-energy hadron or muon collider. The energy of a circular collider is limited by the strength of bending dipoles, and its maximum luminosity is determined by the strength of final focus quadrupoles. For this reason, the high-energy physics and accelerator communities have shown much interest in higher-field and higher-gradient superconducting accelerator magnets. The maximum field of NbTi magnets used in all present high-energy machines, including the LHC, is limited to ˜10 T at 1.9 K. Fields above 10 T became possible with the use of Nb3Sn superconductors. Nb3Sn accelerator magnets can provide operating fields up to ˜15 T and can significantly increase the coil temperature margin. Accelerator magnets with operating fields above 15 T require high-temperature superconductors. This review discusses the status and main results of Nb3Sn accelerator magnet research and development and work toward 20-T magnets.

Progress with high-field superconducting magnets for high-energy colliders

DOE PAGES

Apollinari, Giorgio; Prestemon, Soren; Zlobin, Alexander V.

2015-10-01

One of the possible next steps for high-energy physics research relies on a high-energy hadron or muon collider. The energy of a circular collider is limited by the strength of bending dipoles, and its maximum luminosity is determined by the strength of final focus quadrupoles. For this reason, the high-energy physics and accelerator communities have shown much interest in higher-field and higher-gradient superconducting accelerator magnets. The maximum field of NbTi magnets used in all present high-energy machines, including the LHC, is limited to ~10 T at 1.9 K. Fields above 10 T became possible with the use of Nbmore » $$_3$$Sn superconductors. Nb$$_3$$Sn accelerator magnets can provide operating fields up to ~15 T and can significantly increase the coil temperature margin. Accelerator magnets with operating fields above 15 T require high-temperature superconductors. Furthermore, this review discusses the status and main results of Nb$$_3$$Sn accelerator magnet research and development and work toward 20-T magnets.« less

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.

Method for obtaining large levitation pressure in superconducting magnetic bearings

DOEpatents

Hull, J.R.

1997-08-05

A method and apparatus are disclosed for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap. 4 figs.

Method for obtaining large levitation pressure in superconducting magnetic bearings

DOEpatents

Hull, J.R.

1996-10-08

A method and apparatus are disclosed for compressing magnetic flux to achieve high levitation pressures. Magnetic flux produced by a magnetic flux source travels through a gap between two high temperature superconducting material structures. The gap has a varying cross-sectional area to compress the magnetic flux, providing an increased magnetic field and correspondingly increased levitation force in the gap. 4 figs.

Minimising the Residual Field and Field Gradient in a Magnetically Shielded Room for an nEDM experiment at Los Alamos National Laboratory

NASA Astrophysics Data System (ADS)

Amarasinghe, Chamindu; LANL nEDM Collaboration

2017-09-01

The LANL neutron Electric Dipole Moment (nEDM) experiment is an effort to set a sensitivity limit of 3.2 × 10-27 e cm on the electric dipole moment of the neutron, an order of magnitude smaller than the current upper limit. This measurement uses Ramsey's method of oscillating magnetic fields. The magnetic field and field gradient have to be low enough to avoid the smearing of the Ramsey fringes and to increase the neutron dephasing time respectively. The experiment is enclosed in a two layer Mu-metal magnetically shielded room (MSR) to null any external magnetic fields from the environment. The MSR is degaussed to sufficiently reduce its residual magnetic field and field gradient. The MSR is designed for residual fields as low as 30 nT. The experiment further requires a field gradient of 1 nT/m or smaller. Here we report on the degaussing procedure and the resulting improvement in the shielding prowess of the MSR. Funded by an NSF Grant.

Relation between residential magnetic fields, light-at-night, and nocturnal urine melatonin levels in women: Volume 2 -- Magnetic field exposure analysis. Final report

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

Kaune, W.; Davis, S.; Stevens, R.

Scientists have postulated a link between exposure to magnetic fields and reduced blood melatonin levels. This EPRI study was designed to supplement a National Cancer Institute study (NCI-BC) of magnetic fields, light-at-night, and the risk of breast cancer. By expanding the exposure assessment of the NCI-BC and collecting data on urine melatonin levels, this project provides new insight into a possible magnetic field-melatonin link. It has been proposed that exposure to 60-Hz (power frequency) magnetic fields may increase the risk of breast cancer by suppressing the normal nocturnal rise in melatonin production in the pineal gland. It remains unknown whethermore » the human pineal gland is reproducibly responsive or sensitive to magnetic field exposure, and whether such exposures could alter elements of the endogenous hormonal environment in women that might be important in the etiology of breast cancer. The objective of this research was to investigate whether exposure to power-frequency magnetic fields and/or light-at-night is associated with levels of the primary urinary melatonin metabolite in women without a history of breast cancer.« less

Extremely low-frequency magnetic fields can impair spermatogenesis recovery after reversible testicular damage induced by heat.

PubMed

Tenorio, Bruno Mendes; Ferreira Filho, Moisés Bonifacio Alves; Jimenez, George Chaves; de Morais, Rosana Nogueira; Peixoto, Christina Alves; Nogueira, Romildo de Albuquerque; da Silva Junior, Valdemiro Amaro

2014-06-01

Male infertility is often related to reproductive age couples experiencing fertility-related issues. Men may have fertility problems associated with reversible testicular damage. Considering that men have been increasingly exposed to extremely low-frequency magnetic fields generated by the production, distribution and use of electricity, this study analyzed whether 60 Hz and 1 mT magnetic field exposure may impair spermatogenesis recovery after reversible testicular damage induced by heat shock using rats as an experimental model. Adult male rats were subjected to a single testicular heat shock (HS, 43 °C for 12 min) and then exposed to the magnetic field for 15, 30 and 60 d after HS. Magnetic field exposure during the spermatogenesis recovery induced changes in testis components volume, cell ultrastructure and histomorphometrical parameters. Control animals had a reestablished and active spermatogenesis at 60 d after heat shock, while animals exposed to magnetic field still showed extensive testicular degeneration. Magnetic field exposure did not change the plasma testosterone. In conclusion, extremely low-frequency magnetic field may be harmful to fertility recovery in males affected by reversible testicular damage.

The low magnetic field properties of superconducting bulk yttrium barium copper oxide - Sintered versus partially melted material

NASA Technical Reports Server (NTRS)

Hein, R. A.; Hojaji, H.; Barkatt, A.; Shafii, H.; Michael, K. A.; Thorpe, A. N.; Ware, M. F.; Alterescu, S.

1989-01-01

A comparison of the low magnetic field properties of sintered (990 C) and partially melted samples (1050 C) has been performed. Changes in the microstructure produced by recrystallization from the melt result in a significant increase in flux pinning at 77 K. Low-frequency (10-100 Hz), low-ac magnetic-field (0.01-9.0 Oe) ac susceptibility data show that gross changes in the loss component accompany the observed changes in microstructure. The effects of applied dc magnetic fields (10-220 Oe) on the ac responses of these microstructures have also been probed.

Copper Corrosion Under Non-uniform Magnetic Field in 0.5 M Hydrochloric Acid

NASA Astrophysics Data System (ADS)

Garcia-Ochoa, E.; Corvo, F.; Genesca, J.; Sosa, V.; Estupiñán, P.

2017-05-01

The influence of a magnetic field on the electrochemical reactions taking place at the surface of a copper electrode immersed in a 0.5 M HCl solution at room temperature has been studied. The symmetry axis of the magnetic field was lined up in the same direction of the ion flow to minimize the Lorentz forces. Measurements of potentiodynamic polarization curves, electrochemical impedance spectroscopy and electrochemical noise allow concluding that the magnetic field significantly affects the cathodic reactions, with corrosion rates increasing under the presence of oxygen in acid media and decreasing when oxygen is eliminated.

Effects of temperature on the ground state of a strongly-coupling magnetic polaron and mean phonon number in RbCl quantum pseudodot

NASA Astrophysics Data System (ADS)

Sun, Yong; Ding, Zhao-Hua; Xiao, Jing-Lin

2016-07-01

On the condition of strong electron-LO phonon coupling in a RbCl quantum pseudodot (QPD), the ground state energy and the mean number of phonons are calculated by using the Pekar variational method and quantum statistical theory. The variations of the ground state energy and the mean number with respect to the temperature and the cyclotron frequency of the magnetic field are studied in detail. We find that the absolute value of the ground state energy increases (decreases) with increasing temperature when the temperature is in the lower (higher) temperature region, and that the mean number increases with increasing temperature. The absolute value of the ground state energy is a decreasing function of the cyclotron frequency of the magnetic field whereas the mean number is an increasing function of it. We find two ways to tune the ground state energy and the mean number: controlling the temperature and controlling the cyclotron frequency of the magnetic field.

Urban runoff treatment using nano-sized iron oxide coated sand with and without magnetic field applying

PubMed Central

2013-01-01

Increase of impervious surfaces in urban area followed with increases in runoff volume and peak flow, leads to increase in urban storm water pollution. The polluted runoff has many adverse impacts on human life and environment. For that reason, the aim of this study was to investigate the efficiency of nano iron oxide coated sand with and without magnetic field in treatment of urban runoff. In present work, synthetic urban runoff was treated in continuous separate columns system which was filled with nano iron oxide coated sand with and without magnetic field. Several experimental parameters such as heavy metals, turbidity, pH, nitrate and phosphate were controlled for investigate of system efficiency. The prepared column materials were characterized with Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray analysis (EDXA) instruments. SEM and EDXA analyses proved that the sand has been coated with nano iron oxide (Fe3O4) successfully. The results of SEM and EDXA instruments well demonstrate the formation of nano iron oxide (Fe3O4) on sand particle. Removal efficiency without magnetic field for turbidity; Pb, Zn, Cd and PO4 were observed to be 90.8%, 73.3%, 75.8%, 85.6% and 67.5%, respectively. When magnetic field was applied, the removal efficiency for turbidity, Pb, Zn, Cd and PO4 was increased to 95.7%, 89.5%, 79.9%, 91.5% and 75.6% respectively. In addition, it was observed that coated sand and magnetic field was not able to remove NO3 ions. Statistical analyses of data indicated that there was a significant difference between removals of pollutants in two tested columns. Results of this study well demonstrate the efficiency of nanosized iron oxide-coated sand in treatment of urban runoff quality; upon 75% of pollutants could be removed. In addition, in the case of magnetic field system efficiency can be improved significantly. PMID:24360061

Magnetic losses of commercial REBCO coated conductors in the low frequency range

NASA Astrophysics Data System (ADS)

De Marzi, G.; Iannone, G.; Gambardella, U.

2018-05-01

We have investigated the frequency dependence of the magnetic losses of different 2 G commercial REBCO coated-conductor tapes in the low frequency range ∼1–10 mHz of applied magnetic field at 5 and 77 K. We explored high field range, well above the penetration field, with fields applied perpendicularly to the flat surface. We found that the in-field hysteresis losses increase with increasing frequencies in all the investigated high-temperature superconductor (HTS) tapes, following a power-law dependence. An electromagnetic 2D finite element method model, based on H-formulation, has also been implemented, in which the frequency dependence of the hysteretic loss is computed taking into account the measured power-law E(J) characteristic for the electric field, and the experimental J c(B). Experimental and numerical findings are in very good agreement, so an extrapolation to higher ramp rate values is possible, thus providing a useful basis for the assessment of the hysteresis losses in fusion and accelerator HTS magnets.

Numerical analysis of the effect of non-uniformity of the magnetic field produced by a solenoid on temperature distribution during magnetic hyperthermia

NASA Astrophysics Data System (ADS)

Tang, Yun-dong; Flesch, Rodolfo C. C.; Zhang, Cheng; Jin, Tao

2018-03-01

Magnetic hyperthermia ablates malignant cells by the heat produced by power dissipation of magnetic nanoparticles (MNPs) under an alternating magnetic field. Most of the works in literature consider a uniform magnetic field for solving numerical models to estimate the temperature field during a hyperthermia treatment, however this assumption is generally not true in real circumstances. This paper considers the magnetic field produced by a solenoid and analyzes its effects on the treatment temperature. To that end, a set of partial differential equations is numerically solved for a specific tumor model using the finite element method and the obtained results are analyzed to draw general conclusions. The magnetic field inside the solenoid is obtained by using Maxwell's theory, and the treatment temperature of the tumor model is determined by using Rosensweig's theory and Pennes bio-heat transfer equation. Simulation results demonstrate that the temperature field obtained using a solenoid model is similar to that obtained considering a uniform magnetic field if tumor is centered with respect to solenoid and if the physical characteristics of solenoid are properly defined based on tumor volume. As the distance of tumor from the solenoid center is increased, the effects of non-uniformity of magnetic field become more evident and the adoption of the proposed model is necessary to obtain accurate results.

Monte Carlo Study of Magnetic Properties of Mixed Spins in a Fullerene X 30 Y 30-Like Structure

NASA Astrophysics Data System (ADS)

Mhirech, A.; Aouini, S.; Alaoui-Ismaili, A.; Bahmad, L.

2018-03-01

In this work, inspiring form of the fullerene-C60 structures, we study the mixed X_{30} Y_{30} fullerene-like structure and investigate its magnetic properties. In a such a structure, the carbons are assumed to be replaced by magnetic atoms having spin moments σ = 1/2 and S = 1. Firstly, we elaborate the ground-state phase diagrams in different physical parameter planes. In a second stage, we investigate the exchange coupling interaction effects in the absence or presence of both external magnetic and crystal fields. Using the Monte Carlo method, we carried out a study of the system magnetic properties and the thermal behavior of such a system for the ferromagnetic case. It is found that the critical temperature increases when increasing the coupling exchange interactions. On the other hand, the coercive magnetic field increases also when increasing the coupling exchange interactions. However, this physical parameter decreases when increasing the reduced temperature.

Iron Oxide Nanocrystals for Magnetic Hyperthermia Applications

PubMed Central

Armijo, Leisha M.; Brandt, Yekaterina I.; Mathew, Dimple; Yadav, Surabhi; Maestas, Salomon; Rivera, Antonio C.; Cook, Nathaniel C.; Withers, Nathan J.; Smolyakov, Gennady A.; Adolphi, Natalie; Monson, Todd C.; Huber, Dale L.; Smyth, Hugh D. C.; Osiński, Marek

2012-01-01

Magnetic nanocrystals have been investigated extensively in the past several years for several potential applications, such as information technology, MRI contrast agents, and for drug conjugation and delivery. A specific property of interest in biomedicine is magnetic hyperthermia—an increase in temperature resulting from the thermal energy released by magnetic nanocrystals in an external alternating magnetic field. Iron oxide nanocrystals of various sizes and morphologies were synthesized and tested for specific losses (heating power) using frequencies of 111.1 kHz and 629.2 kHz, and corresponding magnetic field strengths of 9 and 25 mT. Polymorphous nanocrystals as well as spherical nanocrystals and nanowires in paramagnetic to ferromagnetic size range exhibited good heating power. A remarkable 30 °C temperature increase was observed in a nanowire sample at 111 kHz and magnetic field of 25 mT (19.6 kA/m), which is very close to the typical values of 100 kHz and 20 mT used in medical treatments. PMID:28348300

Effect of an external magnetic field on the mass attenuation coefficients of p-Si and n-Si

NASA Astrophysics Data System (ADS)

Yılmaz, D.; Önder, P.

2018-05-01

In this study, the mass attenuation coefficients of p-Si and n-Si semiconductor samples have been determined in an external magnetic field. The semiconductor samples were located to the external magnetic field of intensities 0.2 T, 0.4 T, 0.6 T and 0.8 T. The samples were bombarded by 59.5 keV, 80.1 keV, 121.8 keV and 244.7 keV gamma-rays emitted from Am241, Ba133 and Eu152 radioactive sources. The transmitted photons were detected by a CdTe detector. It was observed that the mass attenuation coefficients of p-Si and n-Si semiconductor samples decrease with increasing gamma-ray energy. Also, the mass attenuation coefficients of the samples increase with applying magnetic field intensity.

Magnetic Field Dependence of Excitations Near Spin-Orbital Quantum Criticality

NASA Astrophysics Data System (ADS)

Biffin, A.; Rüegg, Ch.; Embs, J.; Guidi, T.; Cheptiakov, D.; Loidl, A.; Tsurkan, V.; Coldea, R.

2017-02-01

The spinel FeSc2 S4 has been proposed to realize a near-critical spin-orbital singlet (SOS) state, where entangled spin and orbital moments fluctuate in a global singlet state on the verge of spin and orbital order. Here we report powder inelastic neutron scattering measurements that observe the full bandwidth of magnetic excitations and we find that spin-orbital triplon excitations of an SOS state can capture well key aspects of the spectrum in both zero and applied magnetic fields up to 8.5 T. The observed shift of low-energy spectral weight to higher energies upon increasing applied field is naturally explained by the entangled spin-orbital character of the magnetic states, a behavior that is in strong contrast to spin-only singlet ground state systems, where the spin gap decreases upon increasing applied field.

Magnetic filtration of phase separating ferrofluids: From basic concepts to microfluidic device

NASA Astrophysics Data System (ADS)

Kuzhir, P.; Magnet, C.; Ezzaier, H.; Zubarev, A.; Bossis, G.

2017-06-01

In this work, we briefly review magnetic separation of ferrofluids composed of large magnetic particles (60 nm of the average size) possessing an induced dipole moment. Such ferrofluids exhibit field-induced phase separation at relatively low particle concentrations (∼0.8 vol%) and magnetic fields (∼10 kA/m). Particle aggregates appearing during the phase separation are extracted from the suspending fluid by magnetic field gradients much easier than individual nanoparticles in the absence of phase separation. Nanoparticle capture by a single magnetized microbead and by multi-collector systems (packed bed of spheres and micro-pillar array) has been studied both experimentally and theoretically. Under flow and magnetic fields, the particle capture efficiency Λ decreases with an increasing Mason number for all considered geometries. This decrease may become stronger for aggregated magnetic particles (Λ ∝Ma-1.7) than for individual ones (Λ ∝Ma-1) if the shear fields are strong enough to provoke aggregate rupture. These results can be useful for development of new magneto-microfluidic immunoassays based on magnetic nanoparticles offering a much better sensitivity as compared to presently used magnetic microbeads.

Temperature behavior of the antiferromagnetic susceptibility of nanoferrihydrite from the measurements of the magnetization curves in fields of up to 250 kOe

NASA Astrophysics Data System (ADS)

Balaev, D. A.; Popkov, S. I.; Krasikov, A. A.; Balaev, A. D.; Dubrovskiy, A. A.; Stolyar, S. V.; Yaroslavtsev, R. N.; Ladygina, V. P.; Iskhakov, R. S.

2017-10-01

The cross-breeding problem of the temperature dependence of the antiferromagnetic susceptibility of ferrihydrite nanoparticles is considered. Iron ions Fe3+ in ferrihydrite are ordered antiferromagnetically; however, the existence of defects on the surface and in the bulk of nanoparticles induces a noncompensated magnetic moment that leads to a typical superparamagnetic behavior of ensemble of the nanoparticles with a characteristic blocking temperature. In an unblocked state, magnetization curves of such objects are described as a superposition of the Langevin function and the linear-in-field contribution of the antiferromagnetic "core" of the nanoparticles. According to many studies of the magnetization curves performed on ferrihydrite (and related ferritin) nanoparticles in fields to 60 kOe, dependence χAF( T) decreases as temperature increases, which was related before to the superantiferromagnetism effect. As the magnetic field range increases to 250 kOe, the values of χAF obtained from an analysis of the magnetization curves become lower in magnitude; however, the character of the temperature evolution of χAF is changed: now, dependence χAF( T) is an increasing function. The latter is typical for a system of AF particles with random orientation of the crystallographic axes. To correctly determine the antiferromagnetic susceptibility of AF nanoparticles (at least, ferrihydrite) and to search for effects related to the superantiferromagnetism effect, it is necessary to use in experiments the range of magnetic field significantly higher than that the standard value 60 kOe used in most experiments. The study of the temperature evolution of the magnetization curves shows that the observed crossover is due to the existence of small magnetic moments in the samples.

Effects of radio frequency magnetic fields on iron release from cage proteins.

PubMed

Céspedes, Oscar; Ueno, Shoogo

2009-07-01

Ferritin, the iron cage protein, contains a superparamagnetic ferrihydrite nanoparticle formed from the oxidation and absorption of Fe(2+) ions. This nanoparticle increases its internal energy when exposed to alternating magnetic fields due to magnetization lag. The energy is then dissipated to the surrounding proteic cage, affecting its functioning. In this article we show that the rates of iron chelation with ferrozine, an optical marker, are reduced by up to a factor of 3 in proteins previously exposed to radio frequency magnetic fields of 1 MHz and 30 microT for several hours. The effect is non-thermal and depends on the frequency-amplitude product of the magnetic field. (c) 2009 Wiley-Liss, Inc.

Enhanced ferromagnetic resonance linewidth of the free layer in perpendicular magnetic tunnel junctions

NASA Astrophysics Data System (ADS)

Gopman, D. B.; Dennis, C. L.; McMichael, R. D.; Hao, X.; Wang, Z.; Wang, X.; Gan, H.; Zhou, Y.; Zhang, J.; Huai, Y.

2017-05-01

We report the frequency dependence of the ferromagnetic resonance linewidth of the free layer in magnetic tunnel junctions with all perpendicular-to-the-plane magnetized layers. While the magnetic-field-swept linewidth nominally shows a linear growth with frequency in agreement with Gilbert damping, an additional frequency-dependent linewidth broadening occurs that shows a strong asymmetry between the absorption spectra for increasing and decreasing external magnetic field. Inhomogeneous magnetic fields produced during reversal of the reference and pinned layer complex is demonstrated to be at the origin of the symmetry breaking and the linewidth enhancement. Consequentially, this linewidth enhancement provides indirect information on the magnetic coercivity of the reference and pinned layers. These results have important implications for the characterization of perpendicular magnetized magnetic random access memory bit cells.

Launching of Jets and the Vertical Structure of Accretion Disks

NASA Astrophysics Data System (ADS)

Ogilvie, Gordon I.; Livio, Mario

2001-05-01

The launching of magnetohydrodynamic outflows from accretion disks is considered. We formulate a model for the local vertical structure of a thin disk threaded by a poloidal magnetic field of dipolar symmetry. The model consists of an optically thick disk matched to an isothermal atmosphere. The disk is supposed to be turbulent and possesses an effective viscosity and an effective magnetic diffusivity. In the atmosphere, if the magnetic field lines are inclined sufficiently to the vertical, a magnetocentrifugal outflow is driven and passes through a slow magnetosonic point close to the surface. We determine how the rate of mass loss varies with the strength and inclination of the magnetic field. In particular, we find that for disks in which the mean poloidal field is sufficiently strong to stabilize the disk against the magnetorotational instability, the mass-loss rate decreases extremely rapidly with increasing field strength and is maximal at an inclination angle of 40°-50°. For turbulent disks with weaker mean fields, the mass-loss rate increases monotonically with increasing strength and inclination of the field, but the solution branch terminates before achieving excessive mass-loss rates. Our results suggest that efficient jet launching occurs for a limited range of field strengths and a limited range of inclination angles in excess of 30°. In addition, we determine the direction and rate of radial migration of the poloidal magnetic flux and discuss whether configurations suitable for jet launching can be maintained against dissipation.

Numerical simulations of a sounding rocket in ionospheric plasma: Effects of magnetic field on the wake formation and rocket potential

NASA Astrophysics Data System (ADS)

Darian, D.; Marholm, S.; Paulsson, J. J. P.; Miyake, Y.; Usui, H.; Mortensen, M.; Miloch, W. J.

2017-09-01

The charging of a sounding rocket in subsonic and supersonic plasma flows with external magnetic field is studied with numerical particle-in-cell (PIC) simulations. A weakly magnetized plasma regime is considered that corresponds to the ionospheric F2 layer, with electrons being strongly magnetized, while the magnetization of ions is weak. It is demonstrated that the magnetic field orientation influences the floating potential of the rocket and that with increasing angle between the rocket axis and the magnetic field direction the rocket potential becomes less negative. External magnetic field gives rise to asymmetric wake downstream of the rocket. The simulated wake in the potential and density may extend as far as 30 electron Debye lengths; thus, it is important to account for these plasma perturbations when analyzing in situ measurements. A qualitative agreement between simulation results and the actual measurements with a sounding rocket is also shown.

Experimental study on copper cathode erosion rate and rotational velocity of magnetically driven arcs in a well-type cathode non-transferred plasma torch operating in air

NASA Astrophysics Data System (ADS)

Chau, S. W.; Hsu, K. L.; Lin, D. L.; Tzeng, C. C.

2007-04-01

The cathode erosion rate, arc root velocity and output power of a well-type cathode (WTC), non-transferred plasma torch operating in air are studied experimentally in this paper. An external solenoid to generate a magnetically driven arc and a circular swirler to produce a vortex flow structure are equipped in the studied torch system, which is designed to reduce the erosion rate at the cathode. A least square technique is applied to correlate the system parameters, i.e. current, axial magnetic field and mass flow rate, with the cathode erosion rate, arc root velocity and system power output. In the studied WTC torch system, the cathode erosion has a major thermal erosion component and a minor component due to the ion-bombardment effect. The cathode erosion increases with the increase of current due to the enhancement in both Joule heating and ion bombardment. The axial magnetic field can significantly reduce the cathode erosion by reducing the thermal loading of cathode materials at the arc root and improving the heat transfer to gas near the cathode. But, the rise in the mass flow rate leads to the deterioration of erosion, since the ion-bombardment effect prevails over the convective cooling at the cathode. The most dominant system parameter to influence the arc root velocity is the axial magnetic field, which is mainly contributed to the magnetic force driving the arc. The growth in current has a negative impact on increasing the arc root velocity, because the friction force acting at the spot due to a severe molten condition becomes the dominant component counteracting the magnetic force. The mass flow rate also suppresses the arc root velocity, as a result of which the arc root moves in the direction against that of the swirled working gas. All system parameters such as current, magnetic field and gas flow rate increase with the increase in the torch output power. The experimental evidences suggest that the axial magnetic field is the most important parameter to operate the straight-polarity WTC plasma torch at high output power with a limited cathode erosion rate. This emphasizes the importance of an external magnetic field on a WTC torch system for reducing the erosion at the cathode.

Magnetohydrodynamic simulations of hot jupiter upper atmospheres

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

Trammell, George B.; Li, Zhi-Yun; Arras, Phil, E-mail: gbt8f@virginia.edu, E-mail: zl4h@virginia.edu, E-mail: arras@virginia.edu

Two-dimensional simulations of hot Jupiter upper atmospheres including the planet's magnetic field are presented. The goal is to explore magnetic effects on the layer of the atmosphere that is ionized and heated by stellar EUV radiation, and the imprint of these effects on the Lyα transmission spectrum. The simulations are axisymmetric, isothermal, and include both rotation and azimuth-averaged stellar tides. Mass density is converted to atomic hydrogen density through the assumption of ionization equilibrium. The three-zone structure—polar dead zone (DZ), mid-latitude wind zone (WZ), and equatorial DZ—found in previous analytic calculations is confirmed. For a magnetic field comparable to thatmore » of Jupiter, the equatorial DZ, which is confined by the magnetic field and corotates with the planet, contributes at least half of the transit signal. For even stronger fields, the gas escaping in the mid-latitude WZ is found to have a smaller contribution to the transit depth than the equatorial DZ. Transmission spectra computed from the simulations are compared to Hubble Space Telescope Space Telescope Imaging Spectrograph and Advanced Camera for Surveys data for HD 209458b and HD 189733b, and the range of model parameters consistent with the data is found. The central result of this paper is that the transit depth increases strongly with magnetic field strength when the hydrogen ionization layer is magnetically dominated, for dipole magnetic field B {sub 0} ≳ 10 G. Hence transit depth is sensitive to magnetic field strength, in addition to standard quantities such as the ratio of thermal to gravitational binding energies. Another effect of the magnetic field is that the planet loses angular momentum orders of magnitude faster than in the non-magnetic case, because the magnetic field greatly increases the lever arm for wind braking of the planet's rotation. Spin-down timescales for magnetized models of HD 209458b that agree with the observed transit depth can be as short as ≅ 30 Myr, which is much shorter than the age of the system.« less

Structure and Dynamics of Current Sheets in 3D Magnetic Fields with the X-line

NASA Astrophysics Data System (ADS)

Frank, Anna G.; Bogdanov, S. Yu.; Bugrov, S. G.; Markov, V. S.; Dreiden, G. V.; Ostrovskaya, G. V.

2004-11-01

Experimental results are presented on the structure of current sheets formed in 3D magnetic fields with singular lines of the X-type. Two basic diagnostics were used with the device CS - 3D: two-exposure holographic interferometry and magnetic measurements. Formation of extended current sheets and plasma compression were observed in the presence of the longitudinal magnetic field component aligned with the X-line. Plasma density decreased and the sheet thickness increased with an increase of the longitudinal component. We succeeded to reveal formation of the sheets taking unusual shape, namely tilted and asymmetric sheets, in plasmas with the heavy ions. These current sheets were obviously different from the planar sheets formed in 2D magnetic fields, i.e. without longitudinal component. Analysis of typical plasma parameters made it evident that plasma dynamics and current sheet evolution should be treated on the base of the two-fluid approach. Specifically it is necessary to take into account the Hall currents in the plane perpendicular to the X-line, and the dynamic effects resulting from interaction of the Hall currents and the 3D magnetic field. Supported by RFBR, grant 03-02-17282, and ISTC, project 2098.

A versatile variable field module for Asylum Cypher scanning probe system

NASA Astrophysics Data System (ADS)

Liu, Hongxue; Comes, Ryan; Lu, Jiwei; Wolf, Stuart; Hodgson, Jim; Rutgers, Maarten

2013-03-01

Atomic force microscopy (AFM) has become one of the most widely used techniques for measuring and manipulating various characteristics of materials at the nanoscale. However, there are very limited option for the characterization of field dependence properties. In this work, we demonstrate a versatile variable field module (VFM) with magnetic field up to 1800 Oe for the Asylum Research Cypher system. The magnetic field is changed by adjusting the distance between a rare earth magnet and the AFM probe. A built-in Hall sensor makes it possible to perform in-situ measurements of the field. Rotating the magnet makes it possible to do angular field dependent measurements. The capability of the VFM system is demonstrated by degaussing a floppy disk media with increasing magnetic field. The written bits are erased at about 800 Oe. Angular dependence measurements clearly show the evolution of magnetic domain structures. A completely reversible magnetic force microscopy (MFM) phase contrast is observed when the magnetic field is rotated by 180°. Further demonstration of successful magnetic switching of CoFe2O4 pillars in CoFe2O4-BiFeO3 nanocomposites will be presented and field dependent MFM and piezoresponse force microscopy (PFM) will be discussed. The work at University of Virginia was supported by DARPA under contract no. HR-0011-10-1-0072.

Electro- and Magneto-Modulated Ion Transport through Graphene Oxide Membranes

PubMed Central

Sun, Pengzhan; Zheng, Feng; Wang, Kunlin; Zhong, Minlin; Wu, Dehai; Zhu, Hongwei

2014-01-01

The control of ion trans-membrane transport through graphene oxide (GO) membranes is achieved by electric and magnetic fields. Electric field can either increase or decrease the ion transport through GO membranes depending on its direction, and magnetic field can enhance the ion penetration monotonically. When electric field is applied across GO membrane, excellent control of ion fluidic flows can be done. With the magnetic field, the effective anchoring of ions is demonstrated but the modulation of the ion flowing directions does not occur. The mechanism of the electro- and magneto-modulated ion trans-membrane transport is investigated, indicating that the electric fields dominate the ion migration process while the magnetic fields tune the structure of nanocapillaries within GO membranes. Results also show that the ion selectivity of GO membranes can be tuned with the electric fields while the transport of ions can be enhanced synchronously with the magnetic fields. These excellent properties make GO membranes promising in areas such as field-induced mass transport control and membrane separation. PMID:25347969

Magnetorheological rotational flow with viscous dissipation

NASA Astrophysics Data System (ADS)

Ashrafi, Nariman

2017-11-01

Effects of a magnetic field and fluid nonlinearity are investigated for the rotational flow of the Carreau-type fluid while viscous dissipation is taken into account. The governing motion and energy balance equations are coupled, adding complexity to the already highly correlated set of differential equations. The numerical solution is obtained for the narrow-gap limit and steady-state base flow. Magnetic field effect on local entropy generation due to steady two-dimensional laminar forced convection flow was investigated. This study was focused on the entropy generation characteristics and its dependency on various dimensionless parameters. The effects of the Hartmann number, the Brinkman number, and the Deborah number on the stability of the flow were investigated. The introduction of the magnetic field induces a resistive force acting in the opposite direction of the flow, thus causing its deceleration. Moreover, the study shows that the presence of magnetic field tends to slow down the fluid motion. It, however, increases the fluid temperature. Moreover, the total entropy generation number decreases as the Hartmann number and fluid elasticity increase and increases with increasing Brinkman number.

Seismomagnetic effects from the long-awaited 28 September 2004 M 6.0 parkfield earthquake

USGS Publications Warehouse

Johnston, M.J.S.; Sasai, Y.; Egbert, G.D.; Mueller, R.J.

2006-01-01

Precise measurements of local magnetic fields have been obtained with a differentially connected array of seven synchronized proton magnetometers located along 60 km of the locked-to-creeping transition region of the San Andreas fault at Parkfield, California, since 1976. The M 6.0 Parkfield earthquake on 28 September 2004, occurred within this array and generated coseismic magnetic field changes of between 0.2 and 0.5 nT at five sites in the network. No preseismic magnetic field changes exceeding background noise levels are apparent in the magnetic data during the month, week, and days before the earthquake (or expected in light of the absence of measurable precursive deformation, seismicity, or pore pressure changes). Observations of electric and magnetic fields from 0.01 to 20 Hz are also made at one site near the end of the earthquake rupture and corrected for common-mode signals from the ionosphere/magnetosphere using a second site some 115 km to the northwest along the fault. These magnetic data show no indications of unusual noise before the earthquake in the ULF band (0.01-20 Hz) as suggested may have preceded the 1989 ML 7.1 Loma Prieta earthquake. Nor do we see electric field changes similar to those suggested to occur before earthquakes of this magnitude from data in Greece. Uniform and variable slip piezomagnetic models of the earthquake, derived from strain, displacement, and seismic data, generate magnetic field perturbations that are consistent with those observed by the magnetometer array. A higher rate of longer-term magnetic field change, consistent with increased loading in the region, is apparent since 1993. This accompanied an increased rate of secular shear strain observed on a two-color EDM network and a small network of borehole tensor strainmeters and increased seismicity dominated by three M 4.5-5 earthquakes roughly a year apart in 1992, 1993, and 1994. Models incorporating all of these data indicate increased slip at depth in the region, and this may have played a role in the final occurrence of the 28 September 2004 M 6.0 Parkfield earthquake. The absence of electric and magnetic field precursors for this, and other earthquakes with M 5-7.3 elsewhere in the San Andreas fault system, indicates useful prediction of damaging earthquakes seems unlikely using these electromagnetic data.

A new structure of superconducting magnetic system for 50 GHz operations (invited).

PubMed

Xie, D Z

2012-02-01

High field and high frequency have been leading the development of electron cyclotron resonance ion sources (ECRISs) in the past decade as demonstrated by the achieved great performance. The present superconducting magnet structures built with NbTi wires have reached an axial field of 3.5-4.0 T and a radial field of 2.0 T for operating frequency up to 28 GHz. Further increase of the magnetic field strength will require higher current superconductor, i.e., Nb(3)Sn wires. This paper will present the features of a new superconducting magnet structure and review of the existing structures. Using NbTi wires, the new magnet structure could be able to produce maximum fields of 7.0 T on axis and radial field of 3.7 T at a hexagonal plasma chamber wall for ECRIS operations up to 50 GHz. If this new magnet can be built with Nb(3)Sn wires, much higher fields can be expected.

Self-Generated Magnetic Fields in the Stagnation Phase of Indirect-Drive Implosions on the National Ignition Facility

NASA Astrophysics Data System (ADS)

Walsh, C. A.; Chittenden, J. P.; McGlinchey, K.; Niasse, N. P. L.; Appelbe, B. D.

2017-04-01

Three-dimensional extended-magnetohydrodynamic simulations of the stagnation phase of inertial confinement fusion implosion experiments at the National Ignition Facility are presented, showing self-generated magnetic fields over 104 T . Angular high mode-number perturbations develop large magnetic fields, but are localized to the cold, dense hot-spot surface, which is hard to magnetize. When low-mode perturbations are also present, the magnetic fields are injected into the hot core, reaching significant magnetizations, with peak local thermal conductivity reductions greater than 90%. However, Righi-Leduc heat transport effectively cools the hot spot and lowers the neutron spectra-inferred ion temperatures compared to the unmagnetized case. The Nernst effect qualitatively changes the results by demagnetizing the hot-spot core, while increasing magnetizations at the edge and near regions of large heat loss.

Self-Generated Magnetic Fields in the Stagnation Phase of Indirect-Drive Implosions on the National Ignition Facility.

PubMed

Walsh, C A; Chittenden, J P; McGlinchey, K; Niasse, N P L; Appelbe, B D

2017-04-14

Three-dimensional extended-magnetohydrodynamic simulations of the stagnation phase of inertial confinement fusion implosion experiments at the National Ignition Facility are presented, showing self-generated magnetic fields over 10^{4}  T. Angular high mode-number perturbations develop large magnetic fields, but are localized to the cold, dense hot-spot surface, which is hard to magnetize. When low-mode perturbations are also present, the magnetic fields are injected into the hot core, reaching significant magnetizations, with peak local thermal conductivity reductions greater than 90%. However, Righi-Leduc heat transport effectively cools the hot spot and lowers the neutron spectra-inferred ion temperatures compared to the unmagnetized case. The Nernst effect qualitatively changes the results by demagnetizing the hot-spot core, while increasing magnetizations at the edge and near regions of large heat loss.

Rules of Attraction

NASA Technical Reports Server (NTRS)

2004-01-01

This image composite shows two of the Mars Exploration Rover Opportunity's magnets, the 'capture' magnet (upper portion of left panel) and the 'filter' magnet (lower portion of left panel). Scientists use these tools to study the origins of martian dust in the atmosphere. The left panel was taken by the rover's panoramic camera. The four panels to the right, taken by the microscopic imager, show close-up views of the two magnets. The bull's-eye appearance of the capture magnet is a result of alternating magnetic fields, which are used to increase overall magnetic force. The filter magnet lacks these alternating fields and consequently produces a weaker magnetic force. This weaker force selectively attracts only strong magnetic particles.

Scientists were surprised by the large dark particles on the magnets because airborne particles are smaller in size. They theorize that these spots might be aggregates of small particles that clump together in a magnetic field.

Characteristics of the surface plasma wave in a self-gravitating magnetized dusty plasma slab

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

Lee, Myoung-Jae; Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr; Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 15588

2015-11-15

The dispersion properties of surface dust ion-acoustic waves in a self-gravitating magnetized dusty plasma slab are investigated. The dispersion relation is derived by using the low-frequency magnetized dusty dielectric function and the surface wave dispersion integral for the slab geometry. We find that the self-gravitating effect suppresses the frequency of surface dust ion-acoustic wave for the symmetric mode in the long wavelength regime, whereas it hardly changes the frequency for the anti-symmetric mode. As the slab thickness and the wave number increase, the surface wave frequency slowly decreases for the symmetric mode but increases significantly for the anti-symmetric mode. Themore » influence of external magnetic field is also investigated in the case of symmetric mode. We find that the strength of the magnetic field enhances the frequency of the symmetric-mode of the surface plasma wave. The increase of magnetic field reduces the self-gravitational effect and thus the self-gravitating collapse may be suppressed and the stability of dusty objects in space is enhanced.« less

The Influence of Magnetic Field on Electrokinetic Potential of Colloidal Particles

NASA Astrophysics Data System (ADS)

Koshoridze, S. I.; Levin, Yu. K.

2018-06-01

The influence of a magnetic field on the electrokinetic potential of colloidal particles in a water flow oversaturated with deposited salts is reported. For the first time, the ionic hydration and dielectric permittivity of water in the double electrical layer are taken into consideration. It is demonstrated that the magnetic field influence is increased with the decreasing dielectric permittivity of water but is decreased due to ionic hydration.

Size and diluted magnetic properties of diamond shaped graphene quantum dots: Monte Carlo study

NASA Astrophysics Data System (ADS)

Masrour, R.; Jabar, A.

2018-05-01

The magnetic properties of diamond shaped graphene quantum dots have been investigated by varying their sizes with the Monte Carlo simulation. The magnetizations and magnetic susceptibilities have been studied with dilutions x (magnetic atom), several sizes L (carbon atom) and exchange interaction J between the magnetic atoms. The all magnetic susceptibilities have been situated at the transitions temperatures of each parameters. The obtained values increase when increases the values of x, L and J. The effect of exchanges interactions and crystal field on the magnetization has been discussed. The magnetic hysteresis cycles for several dilutions x, sizes L, exchange interactions J and temperatures T. The magnetic coercive increases with increasing the exchange interactions and decreases when the temperatures values increasing.

Spin Biochemistry Modulates Reactive Oxygen Species (ROS) Production by Radio Frequency Magnetic Fields

PubMed Central

Usselman, Robert J.; Hill, Iain; Singel, David J.; Martino, Carlos F.

2014-01-01

The effects of weak magnetic fields on the biological production of reactive oxygen species (ROS) from intracellular superoxide (O2 •−) and extracellular hydrogen peroxide (H2O2) were investigated in vitro with rat pulmonary arterial smooth muscle cells (rPASMC). A decrease in O2 •− and an increase in H2O2 concentrations were observed in the presence of a 7 MHz radio frequency (RF) at 10 μTRMS and static 45 μT magnetic fields. We propose that O2 •− and H2O2 production in some metabolic processes occur through singlet-triplet modulation of semiquinone flavin (FADH•) enzymes and O2 •− spin-correlated radical pairs. Spin-radical pair products are modulated by the 7 MHz RF magnetic fields that presumably decouple flavin hyperfine interactions during spin coherence. RF flavin hyperfine decoupling results in an increase of H2O2 singlet state products, which creates cellular oxidative stress and acts as a secondary messenger that affects cellular proliferation. This study demonstrates the interplay between O2 •− and H2O2 production when influenced by RF magnetic fields and underscores the subtle effects of low-frequency magnetic fields on oxidative metabolism, ROS signaling, and cellular growth. PMID:24681944

SU-E-J-239: Influence of RF Coil Materials On Surface and Buildup Dose From a 6MV Photon Beam

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

Ghila, A; Fallone, B; Rathee, S

2015-06-15

Purpose: In order to perform real time tumour tracking using an integrated Linac-MR, images have to be acquired during irradiation. MRI uses RF coils in close proximity to the imaged volume. Given current RF coil designs this means that the high energy photons will be passing through the coil before reaching the patient. This study experimentally investigates the dose modifications that occur due to the presence of various RF coil materials in the treatment beam. Methods: Polycarbonate, copper or aluminum tape, and Teflon were used to emulate the base, conductor and cover respectively of a surface RF coil. These materialsmore » were placed at various distances from the surface of polystyrene or solid water phantoms which were irradiated in the presence of no magnetic field, a transverse 0.2T magnetic field, and a parallel 0.2T magnetic field. Percent depth doses were measured using ion chambers. Results: A significant increase in surface and buildup dose is observed. The surface dose is seen to decrease with an increasing separation between the emulated coil and the phantom surface, when no magnetic field is present. When a transverse magnetic field is applied the surface dose decreases faster with increasing separation, as some of the electrons created in the coil are curved away from the phantom’s surface. When a parallel field is present the surface dose stays approximately constant for small separations, only slightly decreasing for separations greater than 5cm, since the magnetic field focuses the electrons produced in the coil materials not allowing them to scatter. Conclusion: Irradiating a patient through an RF coil leads to an increase in the surface and buildup doses. Mitigating this increase is important for the successful clinical use of either a transverse or a parallel configuration Linac-MR unit. This project is partially supported by an operating grant from the Canadian Institute of Health Research (CIHR MOP 93752)« less

High-field magnets using high-critical-temperature superconducting thin films

DOEpatents

Mitlitsky, F.; Hoard, R.W.

1994-05-10

High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla are disclosed. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field. 4 figures.

High-field magnets using high-critical-temperature superconducting thin films

DOEpatents

Mitlitsky, Fred; Hoard, Ronald W.

1994-01-01

High-field magnets fabricated from high-critical-temperature superconducting ceramic (HTSC) thin films which can generate fields greater than 4 Tesla. The high-field magnets are made of stackable disk-shaped substrates coated with HTSC thin films, and involves maximizing the critical current density, superconducting film thickness, number of superconducting layers per substrate, substrate diameter, and number of substrates while minimizing substrate thickness. The HTSC thin films are deposited on one or both sides of the substrates in a spiral configuration with variable line widths to increase the field.

Hydrogen molecules and chains in a superstrong magnetic field

NASA Technical Reports Server (NTRS)

Lai, Dong; Salpeter, Edwin E.; Shapiro, Stuart L.

1992-01-01

The electronic structures of hydrogen polymolecules H(n) (n = 2,3,4,...) is studied in a superstrong magnetic field (B greater than about 10 exp 12 G) typically found on the surface of a neutron star. Simple analytical scaling relations for several limiting cases (e.g., large n, high B field) are derived. The binding energies of H(n) molecules are numerically calculated for various magnetic-field strengths. For a given magnetic-field strength, the binding energy per atom in the H(n) molecules is found to approach a constant value as n increases. For typical field strengths of interest, energy saturation is essentially achieved once n exceeds 3 to 4. Also considered is the structure of negative H ions in a high magnetic field. For B about 10 exp 12 G, the dissociation energy of an atom in a hydrogen chain and the ionization potential of H(-) are smaller than the ionization potential of neutral atomic hydrogen.

Modified dust ion-acoustic surface waves in a semi-bounded magnetized plasma containing the rotating dust grains

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

Lee, Myoung-Jae; Jung, Young-Dae, E-mail: ydjung@hanyang.ac.kr; Department of Applied Physics and Department of Bionanotechnology, Hanyang University, Ansan, Kyunggi-Do 15588

2016-05-15

The dispersion relation for modified dust ion-acoustic surface waves in the magnetized dusty plasma containing the rotating dust grains is derived, and the effects of magnetic field configuration on the resonant growth rate are investigated. We present the results that the resonant growth rates of the wave would increase with the ratio of ion plasma frequency to cyclotron frequency as well as with the increase of wave number for the case of perpendicular magnetic field configuration when the ion plasma frequency is greater than the dust rotation frequency. For the parallel magnetic field configuration, we find that the instability occursmore » only for some limited ranges of the wave number and the ratio of ion plasma frequency to cyclotron frequency. The resonant growth rate is found to decrease with the increase of the wave number. The influence of dust rotational frequency on the instability is also discussed.« less

Free-surface flow of liquid oxygen under non-uniform magnetic field

NASA Astrophysics Data System (ADS)

Bao, Shi-Ran; Zhang, Rui-Ping; Wang, Kai; Zhi, Xiao-Qin; Qiu, Li-Min

2017-01-01

The paramagnetic property of oxygen makes it possible to control the two-phase flow at cryogenic temperatures by non-uniform magnetic fields. The free-surface flow of vapor-liquid oxygen in a rectangular channel was numerically studied using the two-dimensional phase field method. The effects of magnetic flux density and inlet velocity on the interface deformation, flow pattern and pressure drop were systematically revealed. The liquid level near the high-magnetic channel center was lifted upward by the inhomogeneous magnetic field. The interface height difference increased almost linearly with the magnetic force. For all inlet velocities, pressure drop under 0.25 T was reduced by 7-9% due to the expanded local cross-sectional area, compared to that without magnetic field. This work demonstrates the effectiveness of employing non-uniform magnetic field to control the free-surface flow of liquid oxygen. This non-contact method may be used for promoting the interface renewal, reducing the flow resistance, and improving the flow uniformity in the cryogenic distillation column, which may provide a potential for enhancing the operating efficiency of cryogenic air separation.

A study on magneto-optic properties of CoxMg1-xFe2O4 nanoferrofluids

NASA Astrophysics Data System (ADS)

Karthick, R.; Ramachandran, K.; Srinivasan, R.

2018-04-01

Nanoparticles of CoxMg1-xFe2O4 (x = 0.1, 0.5, 0.9) were synthesized using chemical co-precipitation method. Characterization by X-ray diffraction technique confirmed the formation of cubic crystalline structure and the crystallite size of the samples obtained using Debye-Scherrer approximation were found to increase with increasing cobalt substitution. Surface morphology and the Chemical composition of the samples were visualized using scanning electron microscope (SEM) with energy dispersive analysis of X-rays (EDAX). Room temperature magnetic parameters of the nanoparticles by vibrating sample magnetometer (VSM) revealed the magnetic properties such as Saturation magnetization (Ms), Remanent magnetization (Mr) and Coercive field (Hc) found to increase with increasing cobalt substitution. Faraday rotation measurements on CoxMg1-xFe2O4 ferrofluids exhibited increase in rotation with cobalt substitution. Further, there is an increase in Faraday rotation with increasing magnetic field for all the samples.

Anisotropic Magnetic Nanostructures For Enhanced Hyperthermia

NASA Astrophysics Data System (ADS)

Torres, D.; Das, R.; Alonso, J.; Phan, M. H.; Srikanth, H.

Magnetic nanoparticles assisted hyperthermia is one of the most promising techniques for cancer treatment. By the use of magnetic nanoparticles in an external AC magnetic field, one can target a specific tumor location and deliver toxic doses of heat to the tumor area without damaging the surrounding healthy tissue. Magnetite is typically used in biomedical applications due to its biocompatibility, but the heating efficiency of the commonly used magnetite nanoparticles is not enough to obtain the best results in cancer treatment. Therefore, novel magnetic nanostructures are required in order to improve the heating efficiency. Recently, it has been proposed by different groups that it is possible to increase the heating efficiency of the nanoparticles by tuning their effective anisotropy. Considering this, we have synthesized high aspect ratio magnetic nanorods with increased effective anisotropy. A thorough structural and magnetic characterization has revealed high crystallinity and optimal magnetic properties of these nanorods. The hyperthermia response shows that by increasing the aspect ratio from 5 to 11, their heating efficiency is increased by 150%. In addition, we have observed that a good alignment of the nanorods with the magnetic field ensures the best heating results. Hence, these nanorods appear to be promising candidates for cancer treatment with magnetic hyperthermia.

Laser propagation and soliton generation in strongly magnetized plasmas

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

Feng, W.; Li, J. Q.; Kishimoto, Y.

The propagation characteristics of various laser modes with different polarization, as well as the soliton generation in strongly magnetized plasmas are studied numerically through one-dimensional (1D) particle-in-cell (PIC) simulations and analytically by solving the laser wave equation. PIC simulations show that the laser heating efficiency substantially depends on the magnetic field strength, the propagation modes of the laser pulse and their intensities. Generally, large amplitude laser can efficiently heat the plasma with strong magnetic field. Theoretical analyses on the linear propagation of the laser pulse in both under-dense and over-dense magnetized plasmas are well confirmed by the numerical observations. Mostmore » interestingly, it is found that a standing or moving soliton with frequency lower than the laser frequency is generated in certain magnetic field strength and laser intensity range, which can greatly enhance the laser heating efficiency. The range of magnetic field strength for the right-hand circularly polarized (RCP) soliton formation with high and low frequencies is identified by solving the soliton equations including the contribution of ion's motion and the finite temperature effects under the quasi-neutral approximation. In the limit of immobile ions, the RCP soliton tends to be peaked and stronger as the magnetic field increases, while the enhanced soliton becomes broader as the temperature increases. These findings in 1D model are well validated by 2D simulations.« less

Continuous Magnetic Refrigerators for Cooling in the 0.05 to 10 K Range

NASA Technical Reports Server (NTRS)

Shirron, Peter; DiPirro, Michael; Canavan, Edgar; Tuttle, James; Panek, John; Jackson, Michael; King, Todd; Numazawa, Takenori; Krebs, Carolyn (Technical Monitor)

2001-01-01

Low temperature refrigeration is an increasingly vital technology for NASA's Space Science program since most detectors being developed for x-ray, IR and sub-millimeter missions must be cooled to below 100 mK in order to meet the requirements for energy and spatial resolution. For space applications, magnetic refrigeration has an inherent advantage over alternative techniques because it does not depend on gravity. Adiabatic demagnetization refrigerators, or ADRs, are relatively simple, solid state devices. The basic elements are a magnetocaloric refrigerant (usually an encapsulated paramagnetic salt) located in the bore of a superconducting magnet, and a heat switch linking the salt to a heat sink. The alignment of magnetic spins with the magnetic field causes the refrigerant to warm as the magnetic field increases and cool as the field decreases. Thus the simple process of magnetizing the refrigerant to high field with the heat switch closed, then demagnetizing it with the heat switch open allows one to obtain temperatures well below 100 mK using a heat sink as warm as 4.2 K. The refrigerant can maintain a low temperature for a length of time depending on the applied and parasitic heat loads, its mass, and the initial magnetic field strength. Typically ADRs are designed for 12-24 hours of hold time, after which they must be warmed up and recycled.

Dynamical anisotropic response of black phosphorus under magnetic field

NASA Astrophysics Data System (ADS)

Liu, Xuefeng; Lu, Wei; Zhou, Xiaoying; Zhou, Yang; Zhang, Chenglong; Lai, Jiawei; Ge, Shaofeng; Sekhar, M. Chandra; Jia, Shuang; Chang, Kai; Sun, Dong

2018-04-01

Black phosphorus (BP) has emerged as a promising material candidate for next generation electronic and optoelectronic devices due to its high mobility, tunable band gap and highly anisotropic properties. In this work, polarization resolved ultrafast mid-infrared transient reflection spectroscopy measurements are performed to study the dynamical anisotropic optical properties of BP under magnetic fields up to 9 T. The relaxation dynamics of photoexcited carrier is found to be insensitive to the applied magnetic field due to the broadening of the Landau levels and large effective mass of carriers. While the anisotropic optical response of BP decreases with increasing magnetic field, its enhancement due to the excitation of hot carriers is similar to that without magnetic field. These experimental results can be well interpreted by the magneto-optical conductivity of the Landau levels of BP thin film, based on an effective k · p Hamiltonian and linear response theory. These findings suggest attractive possibilities of multi-dimensional control of anisotropic response (AR) of BP with light, electric and magnetic field, which further introduces BP to the fantastic magnetic field sensitive applications.

Gravitational dynamos and the low-frequency geomagnetic secular variation.

PubMed

Olson, P

2007-12-18

Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including nearly steady dipoles, chaotic nonreversing dipoles, and chaotic reversing dipoles. The time average dipole strength and dipolarity of the magnetic field decrease, whereas the dipole variability, average dipole tilt angle, and frequency of polarity reversals increase with Rayleigh number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power at frequencies corresponding to a few cycles per million years on Earth. Their external magnetic field structure, dipole statistics, low-frequency power spectra, and polarity reversal frequency are comparable to the geomagnetic field. The magnetic variability is driven by the Lorentz force and is characterized by an inverse correlation between dynamo magnetic and kinetic energy fluctuations. A constant energy dissipation theory accounts for this inverse energy correlation, which is shown to produce conditions favorable for dipole drift, polarity reversals, and excursions.

Gravitational dynamos and the low-frequency geomagnetic secular variation

PubMed Central

Olson, P.

2007-01-01

Self-sustaining numerical dynamos are used to infer the sources of low-frequency secular variation of the geomagnetic field. Gravitational dynamo models powered by compositional convection in an electrically conducting, rotating fluid shell exhibit several regimes of magnetic field behavior with an increasing Rayleigh number of the convection, including nearly steady dipoles, chaotic nonreversing dipoles, and chaotic reversing dipoles. The time average dipole strength and dipolarity of the magnetic field decrease, whereas the dipole variability, average dipole tilt angle, and frequency of polarity reversals increase with Rayleigh number. Chaotic gravitational dynamos have large-amplitude dipole secular variation with maximum power at frequencies corresponding to a few cycles per million years on Earth. Their external magnetic field structure, dipole statistics, low-frequency power spectra, and polarity reversal frequency are comparable to the geomagnetic field. The magnetic variability is driven by the Lorentz force and is characterized by an inverse correlation between dynamo magnetic and kinetic energy fluctuations. A constant energy dissipation theory accounts for this inverse energy correlation, which is shown to produce conditions favorable for dipole drift, polarity reversals, and excursions. PMID:18048345

Twisted magnetosphere with quadrupolar fields in the exterior of a neutron star

NASA Astrophysics Data System (ADS)

Kojima, Yasufumi

2018-04-01

The magnetar magnetosphere is gradually twisted by shearing from footpoint motion, and stored magnetic energy also increases at the same time. When a state exceeds a threshold, flares/outbursts manifest themselves as a result of a catastrophic transition. Axisymmetric static solutions for a relativistic force-free magnetosphere with dipole-quadrupole mixed fields at the surface have been calculated. The quadrupole component represents a kind of magnetic-field irregularity at a small scale. Locally twisted models are constructed by limiting current flow regions, where the small part originates from a dipole-quadrupole mixture. The energy along a sequence of equilibria increases and becomes sufficient to open the magnetic field in some models. In energetically metastable states, a magnetic flux rope is formed in the vicinity of the star. The excess energy may be ejected as a magnetar flare/outburst. The general relativistic gravity is sufficient to confine the flux rope and to store huge magnetic energy, and the mechanism is also discussed.

Development of High Interruption Capability Vacuum Circuit Breaker -Technology of Vacuum Arc Control-

NASA Astrophysics Data System (ADS)

Niwa, Yoshimitsu; Kaneko, Eiji

Vacuum circuit breakers (VCB) have been widely used for power distribution systems. Vacuum Interrupters, which are the current interruption unit, have been increased its interruption capability with the development of vacuum arc control technology by magnetic field. There are three major type electrodes: disk shaped electrodes, radial magnetic field electrodes, axial magnetic field (AMF) electrodes. In the disk shaped electrode, the vacuum arc between the electrodes is not controlled. In the AMF electrode, the vacuum arc is diffused and stabilized by an axial magnetic field, which is parallel to the arc current. In the last type of electrodes, the vacuum arc column is rotated by magnetic force generated by the current flowing in the electrodes. The interruption current and the voltage of one break VCB is increased to 100 kA, 144 kV respectively. This paper describes basic configurations and functions of VCB, vacuum arc control technology in vacuum interrupters, recent researches and applications of VCB.

Twisted magnetosphere with quadrupolar fields in the exterior of a neutron star

NASA Astrophysics Data System (ADS)

Kojima, Yasufumi

2018-07-01

The magnetar magnetosphere is gradually twisted by shearing from footpoint motion, and stored magnetic energy also increases at the same time. When a state exceeds a threshold, flares/outbursts manifest themselves as a result of a catastrophic transition. Axisymmetric static solutions for a relativistic force-free magnetosphere with dipole-quadrupole mixed fields at the surface have been calculated. The quadrupole component represents a kind of magnetic-field irregularity at a small scale. Locally twisted models are constructed by limiting current flow regions, where the small part originates from a dipole-quadrupole mixture. The energy along a sequence of equilibria increases and becomes sufficient to open the magnetic field in some models. In energetically metastable states, a magnetic flux rope is formed in the vicinity of the star. The excess energy may be ejected as a magnetar flare/outburst. The general relativistic gravity is sufficient to confine the flux rope and to store huge magnetic energy, and the mechanism is also discussed.

Dynamic blocked transfer stiffness method of characterizing the magnetic field and frequency dependent dynamic viscoelastic properties of MRE

NASA Astrophysics Data System (ADS)

Poojary, Umanath R.; Hegde, Sriharsha; Gangadharan, K. V.

2016-11-01

Magneto rheological elastomer (MRE) is a potential resilient element for the semi active vibration isolator. MRE based isolators adapt to different frequency of vibrations arising from the source to isolate the structure over wider frequency range. The performance of MRE isolator depends on the magnetic field and frequency dependent characteristics of MRE. Present study is focused on experimentally evaluating the dynamic stiffness and loss factor of MRE through dynamic blocked transfer stiffness method. The dynamic stiffness variations of MRE exhibit strong magnetic field and mild frequency dependency. Enhancements in dynamic stiffness saturate with the increase in magnetic field and the frequency. The inconsistent variations of loss factor with the magnetic field substantiate the inability of MRE to have independent control over its damping characteristics.

The influence of large-scale magnetic field in the structure of supercritical accretion flow with outflow

NASA Astrophysics Data System (ADS)

Ghasemnezhad, Maryam; Abbassi, Shahram

2017-08-01

We present the effects of ordered large-scale magnetic field on the structure of supercritical accretion flow in the presence of an outflow. In the cylindrical coordinates (r, φ, z), we write the 1.5-dimensional, steady-state (partial /partial t= 0) and axisymmetric (partial /partial \\varphi = 0) inflow-outflow equations by using self-similar solutions. Also, a model for radiation pressure supported accretion flow threaded by both toroidal and vertical components of magnetic field has been formulated. For studying the outflows, we adopt a radius-dependent mass accretion rate as \\dot{M}=\\dot{M}_{out}{(r/r_{out})^{s+1/2}} with s = 1/2. Also, by following the previous works, we have considered the interchange of mass, radial and angular momentum and the energy between inflow and outflow. We have found numerically that two components of magnetic field have the opposite effects on the thickness of the disc and similar effects on the radial and angular velocities of the flow. We have found that the existence of the toroidal component of magnetic field will lead to an increase in the radial and azimuthal velocities as well as the relative thickness of the disc. Moreover, in a magnetized flow, the thickness of the disc decreases with increase in the vertical component of magnetic field. The solutions indicated that the mass inflow rate and the specific energy of outflow strongly affect the advection parameter. We have shown that by increasing the two components of magnetic field, the temperature of the accretion flow decreases significantly. On the other hand, we have shown that the bolometric luminosity of the slim discs for high values of \\dot{m} (\\dot{m}>>1)\\dot{m} (\\dot{m}≫ 1) is not sensitive to mass accretion rate and is kept constant (L ≈ 10LE).

Electromagnetic field versus circuit weight training on bone mineral density in elderly women

PubMed Central

Elsisi, Hany Farid Eid Morsy; Mousa, Gihan Samir Mohamed; ELdesoky, Mohamed Taher Mahmoud

2015-01-01

Background and purpose Osteoporosis is a common skeletal disorder with costly complications and a global health problem and one of the leading causes of morbidity and mortality worldwide. Magnetic field therapy and physical activity have been proven as beneficial interventions for prevention and treatment of osteoporosis. The purpose of this study was to compare the response of bone mineral content and bone mineral density (BMD) in elderly women to either low-frequency low-intensity pulsed magnetic field (LFLIPMF) or circuit weight training (CWT) on short-run basis (after 12 weeks). Patients and methods Thirty elderly women, aged 60–70 years, were randomly assigned into two groups (magnetic field and CWT) (n=15 each group). The session was performed three times per week for magnetic field and CWT groups, for 12 weeks. BMD and bone mineral content of lumbar spine (L2–L4) and femoral neck, trochanter, and Ward’s triangle were evaluated before and after 12 weeks of treatment. Results Both magnetic field and CWT for 12 weeks in elderly women seem to yield beneficial and statistically significant increasing effect on BMD and bone mineral content (P<0.05). But magnetic field seems to have more beneficially and statistically significant effect than does CWT. Conclusion It is possible to conclude that LFLIPMF and CWT programs are effective modalities in increasing BMD but LFLIPMF is more effective in elderly women. PMID:25834412

Electromagnetic field versus circuit weight training on bone mineral density in elderly women.

PubMed

Elsisi, Hany Farid Eid Morsy; Mousa, Gihan Samir Mohamed; ELdesoky, Mohamed Taher Mahmoud

2015-01-01

Osteoporosis is a common skeletal disorder with costly complications and a global health problem and one of the leading causes of morbidity and mortality worldwide. Magnetic field therapy and physical activity have been proven as beneficial interventions for prevention and treatment of osteoporosis. The purpose of this study was to compare the response of bone mineral content and bone mineral density (BMD) in elderly women to either low-frequency low-intensity pulsed magnetic field (LFLIPMF) or circuit weight training (CWT) on short-run basis (after 12 weeks). Thirty elderly women, aged 60-70 years, were randomly assigned into two groups (magnetic field and CWT) (n=15 each group). The session was performed three times per week for magnetic field and CWT groups, for 12 weeks. BMD and bone mineral content of lumbar spine (L2-L4) and femoral neck, trochanter, and Ward's triangle were evaluated before and after 12 weeks of treatment. Both magnetic field and CWT for 12 weeks in elderly women seem to yield beneficial and statistically significant increasing effect on BMD and bone mineral content (P<0.05). But magnetic field seems to have more beneficially and statistically significant effect than does CWT. It is possible to conclude that LFLIPMF and CWT programs are effective modalities in increasing BMD but LFLIPMF is more effective in elderly women.

Effect of magnetic field annealing on soft magnetic properties of Co71Fe2Si14-xB9+xMn4 amorphous alloys with low permeability

NASA Astrophysics Data System (ADS)

Fan, Xingdu; Li, Meng; Zhang, Tao; Yuan, Chenchen; Shen, Baolong

2018-05-01

The effect of transverse magnetic field annealing (TFA) on soft magnetic properties of Co71Fe2Si14-xB9+xMn4 amorphous alloys was investigated with the aim of reducing effective permeability (μe). It was revealed that the increasing B content improved thermal stability, increased saturation magnetic flux density (Bs) of as-quenched alloys, while the samples exhibited a slightly larger coercivity (Hc) when the atom percentages of Si and B were similar. Permeability decreased dramatically after TFA. The decrease of permeability mainly depended on annealing temperature and magnetic field intensity. Besides, flat hysteresis loops were obtained after TFA, Lorentz micrograph observation revealed the TFA sample exhibited denser magnetic domain walls, which confirmed it was more difficult to be saturated. The Co71Fe2Si9B14Mn4 alloy was successful prepared with low μe of 3020, low Hc of 1.7 A/m and high resistance to DC bias 6 times that of as-quenched alloy at the DC field of 300 A/m.

Electric field control of magnetic properties in FeRh/PMN-PT heterostructures

NASA Astrophysics Data System (ADS)

Xie, Yali; Zhan, Qingfeng; Shang, Tian; Yang, Huali; Liu, Yiwei; Wang, Baomin; Li, Run-Wei

2018-05-01

We investigated electric control of magnetic properties in FeRh/PMN-PT heterostructures. An electric field of 1 kV/cm applied on the PMN-PT substrate could increase the coercivity of FeRh film from 60 to 161 Oe at 360 K where the FeRh antiferromagnetic to ferromagnetic phase transition occurs. The electric field dependent coercive field reveals a butterfly shape, indicating a strain-mediated magnetoelectric coupling across the FeRh/PMN-PT interface. However, the uniaxial magnetic anisotropy of FeRh is almost unchanged with the applied electric field on the PMN-PT substrate, which suggests the change of coercivity in FeRh films is mainly due to the shift of the magnetic transition temperature under the electric field.

Acute nonlymphocytic leukemia and residential exposure to power frequency magnetic fields

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

Severson, R.K.

1986-01-01

A population-based case-control study of adult acute nonlymphocytic leukemia (ANLL) and residential exposure to power frequency magnetic fields was conducted in King, Pierce and Snohomish Counties in Washington state. Of 164 cases who were diagnosed from January 1, 1981 through December 31, 1984, 114 were interviewed. Controls were selected from the study area on the basis of random digit dialing and frequency matched to the cases by age and sex. Analyses were undertaken to evaluate whether exposure to high levels of power frequency magnetic fields in the residence were associated with an increased risk of ANLL. Neither the directly measuredmore » magnetic fields nor the surrogate values based on the wiring configurations were associated with ANLL. Additional analyses suggested that persons with prior allergies were at decreased risk of acute myelocytic leukemia (AML). Also, persons with prior autoimmune diseases were at increased risk of AML. The increase in AML risk in rheumatoid arthritics was of borderline statistical significance. Finally, cigarette smoking was associated with an increased risk of AML. The risk of AML increased significantly with the number of years of cigarette smoking.« less

Optical Isolators With Transverse Magnets

NASA Technical Reports Server (NTRS)

Fan, Yuan X.; Byer, Robert L.

1991-01-01

New design for isolator includes zigzag, forward-and-backward-pass beam path and use of transverse rather than longitudinal magnetic field. Design choices produce isolator with as large an aperture as desired using low-Verdet-constant glass rather than more expensive crystals. Uses commercially available permanent magnets in Faraday rotator. More compact and less expensive. Designed to transmit rectangular beam. Square cross section of beam extended to rectangular shape by increasing one dimension of glass without having to increase magnetic field. Potentially useful in laser systems involving slab lasers and amplifiers. Has applications to study of very-high-power lasers for fusion research.

SU-E-T-145: Effects of Temporary Tachytherapy Inhibition Magnet On MOSFET Dose Measurements of Cardiovascular Implantable Electronic Devices (CIED) in Radiation Therapy Patients

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

P, Joshi; Salomons, G; Kerr, A

2014-06-01

Purpose: To determine the effects of temporary tachytherapy inhibition magnet on MOSFET dose measurements of cardiovascular implantable electronic devices (CIED) in radiation therapy patients. Methods: Infield and peripheral MOSFET dose measurements with 6MV photon beams were performed to evaluate dose to a CIED in the presence of a doughnut shaped temporary tachytherapy inhibition magnet. Infield measurements were done to quantify the effects of the magnetic field alone and shielding by the magnet. MOSFETs were placed inside a 20×20cm{sup 2} field at a depth of 3cm in the isocentre plane in the presence and absence of the magnet. Peripheral dose measurementsmore » were done to determine the impact of the magnet on dose to the CIED in a clinical setting. These measurements were performed at the centre, under the rim and half way between a 10×10cm{sup 2} field edge and the magnet with MOSFETS placed at the surface, 0.5cm and 1cm depths in the presence and absence of the magnet. Results: Infield measurements showed that effects of magnetic field on the MOSFET readings were within the 2% MOSFET dose measurement uncertainty; a 20% attenuation of dose under the magnet rim was observed. Peripheral dose measurements at the centre of the magnet show an 8% increase in surface dose and a 6% decrease in dose at 1cm depth. Dose under the magnet rim was reduced by approximately 68%, 45% and 25% for MOSFET placed at 0.0, 0.5 and 1.0cm bolus depths, respectively. Conclusions: The magnetic field has an insignificant effect on MOSFET dose measurements. Dose to the central region of CIED represented by centre of the magnet doughnut increases at the surface, and decreases at depths due to low energy scattering contributions from the magnet. Dose under the magnet rim, representing CIED edges, decreased significantly due to shielding.« less

Permanent superconducting magnets for space applications

NASA Technical Reports Server (NTRS)

Weinstein, Roy

1994-01-01

Work has been done to develop superconducting trapped field magnets (TFM's) and to apply them to a bumper-tether device for magnetic docking of spacecraft. The quality parameters for TFM's are J(c), the critical current of the superconductor, and d, the diameter of the superconducting tile. During this year we have doubled d, for production models, from 1 cm to 2 cm. This was done by means of seeding, an improved temperature profile in processing, and the addition of 1 percent Pt to the superconductor chemistry. Using these tiles we have set increasing records for the fields' permanent magnets. Magnets fabricated from old 1 cm tiles trapped 1.52 Tesla at 77K, 4.0T at 65K and 7.0T at 55K. The second of these fields broke a 17 year old record set at Stanford. The third field broke our own record. More recently using 2 cm tiles, we have trapped 2.3T at 77K, and 5.3T at 65K. We expect to trap lOT at 55K in this magnet in the near future. We have also achieved increases in J(c) using a method we developed for seeding U-235, and subsequently bombarding with neutrons. This method doubles J(c). We have not yet fabricated magnets from these tiles. During this year we have increased production yields from 15 percent to 95 percent. We have explored the properties of a magnetic bumper-tether for spacecraft. We have measured the bumper forces, and their dependence on time, distance, and the field of the ordinary ferromagnet (used together with a TFM). We have accounted for 85 percent of the collision energy, and its transformation to magnetic energy and heat energy. We have learned to control the relative bumper and tether forces by controlling TFM and ferromagnetic field strengths.

Effect of magnetic field on the phase transition in dusty plasma

NASA Astrophysics Data System (ADS)

Jaiswal, Surabhi; Thomas, Edward; Mukherjee, Rupak

2017-10-01

The formation of self-consistent crystalline structure is a well-known phenomenon in complex plasmas. In most experiments the pressure and rf power are the main controlling parameter in determining the phase of the system. We have studied the effect of externally applied magnetic field on the configuration of plasma crystals, suspended in the sheath of a radio-frequency discharge using the Magnetized Dusty Plasma Experiment (MDPX) device. Experiments are performed at a fixed pressure and rf power where a crystalline structure formed within the confining ring, but ramping the magnetic field up to 1.28 T. We report on the breakdown of the crystalline structure with increasing magnetic field. The magnetic field affects the dynamics of the plasma particles and first leads to a rotation of the crystal. At higher magnetic field, there is a radial variation (shear) in the angular velocity of the moving particles which we believe leads to the melting of the crystal. This melting is confirmed by evaluating the variation of the pair correlation function as a function of magnetic field. This work was supported by the US Dept. of Energy, DE - SC0010485.

Arc Deflection Length Affected by Transverse Rotating Magnetic Field with Lateral Gas

NASA Astrophysics Data System (ADS)

Shiino, Toru; Ishii, Yoko; Yamamoto, Shinji; Iwao, Toru; High Current Energy Laboratory (HiCEL) Team

2016-10-01

Gas metal arc welding using shielding gas is often used in the welding industry. However, the arc deflection affected by lateral gas is problem because of inappropriate heat transfer. Shielding gas is used in order to prevent the instability affected by the arc deflection. However, the shielding gas causes turbulence, then blowhole of weld defect occurs because the arc affected by the instability is contaminated by the air. Thus, the magnetic field is applied to the arc in order to stabilize the arc using low amount of shielding gas. The method of applying the transverse rotating magnetic field (RMF) to the arc is one of the methods to prevent the arc instability. The RMF drives the arc because of electromagnetic force. The driven arc is considered to be prevented to arc deflection of lateral gas because the arc is restrained by the magnetic field because of the driven arc. In addition, it is assume the RMF prevented to the arc deflection of lateral gas from the multiple directions. In this paper, the arc deflection length affected by the RMF with lateral gas was elucidated in order to know the effect of the RMF for arc stabilization. Specifically, the arc deflection length affected by the magnetic frequency and the magnetic flux density is measured by high speed video camera. As a result, the arc deflection length decreases with increasing magnetic frequency, and the arc deflection length increases with increasing the magnetic flux density.

Effects of plasmonic field due to gold nanoparticles and magnetic field on photocurrents of zinc porphyrin-viologen linked compound-gold nanoparticle composite films

NASA Astrophysics Data System (ADS)

Yonemura, Hiroaki; Niimi, Tomoki; Yamada, Sunao

2016-03-01

Composite films of zinc-porphyrin-viologen (ZnP-V2+) linked compound containing six methylene group [ZnP(6)V]-gold nanoparticles (AuNP) were fabricated by combining electrostatic layer-by-layer adsorption and the Langmuir-Blodgett method. The anodic photocurrents of the ZnP(6)V-AuNP composite films are higher than those of the ZnP(6)V films. The large photocurrents in ZnP(6)V-AuNP composite films are most likely attributable to the combination of localized surface plasmon resonance due to AuNP and photoinduced intramolecular electron transfer from excited state of ZnP to V2+. The photocurrents of the ZnP(6)V-AuNP composite films increase in the presence of magnetic field. The photocurrents increase with low magnetic fields (B ≤ 150 mT) and are almost constant under high magnetic fields (B ≥ 150 mT). Magnetic field effects (MFEs) were clearly observed for both ZnP(6)V-AuNP composite films and ZnP(6)V films. The MFEs can be explained by a radical pair mechanism.

A magneto-resistance and magnetisation study of TaAs2 semimetal

NASA Astrophysics Data System (ADS)

Harimohan, V.; Bharathi, A.; Rajaraman, R.; Sundar, C. S.

2018-04-01

Here we report on the magneto-transport and magnetization studies on single crystalline samples of TaAs2. The resistivity versus temperature of the single crystalline sample shows a metallic behavior with a large residual resistivity ratio. The TaAs2 crystal shows large magneto resistance at low temperature, reaching 91000% at 2.5K in a field of 15 T and the resistivity versus temperature shows an upturn at low temperature, when measured with increase in magnetic field. Resistivity and magnetization measurements as a function of magnetic field show characteristic Shubnikov de Haas and de Hass van Alphen oscillations, displaying anisotropy with respect to the crystalline direction. The effective mass and Dingle temperature were estimated from the analysis of the oscillation amplitude as a function of temperature and magnetic field. Negative magneto-resistance was not observed with current parallel to the magnetic field direction, suggesting that TaAs2 is not an archetypical Weyl metal.

Enhancements of magnetic properties and planar magnetoresistance by electric fields in γ-Fe{sub 2}O{sub 3}/MgO thin films

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

Cheng, Bin; Qin, Hongwei; Pei, Jinliang

2016-05-23

The treatment of perpendicular electric field upon γ-Fe{sub 2}O{sub 3}/MgO film at room temperature could adjust the magnetic properties (saturation magnetization, magnetic remanence, coercivity, and saturation magnetizing field) of the film. The enhancement of saturation magnetization after the treatment of electric field may be connected with the combined shift effects of Mg ions from MgO to γ-Fe{sub 2}O{sub 3} and O{sup 2−} ions from γ-Fe{sub 2}O{sub 3} to MgO. The negative magnetoresistance of the γ-Fe{sub 2}O{sub 3}/MgO film also enhances with the treatment of perpendicular electric field at room temperature, possibly due to the increasing of electron hopping rate betweenmore » Fe{sup 2+} and Fe{sup 3+}.« less

Superconducting magnet and fabrication method

NASA Technical Reports Server (NTRS)

Israelsson, Ulf E. (Inventor); Strayer, Donald M. (Inventor)

1994-01-01

A method of trapping a field in a block of superconductor material, includes providing (i) a block of material defining a bore, (ii) a high permeability core within the bore that defines a low reluctance path through the bore, (iii) a high permeability external structure on the exterior of the block of material that defines a low reluctance path between opposite ends of the core, and (iv) an electromagnet configured to apply a magnetic field around the high permeability core. The method proceeds by energizing the electromagnet to produce an applied magnetic field around the high permeability core, cooling the block of material sufficiently to render the block of material superconducting, de-energizing the electromagnet to result in a trapped magnetic field, and at least partially removing the low reluctance path defined by the core and the external structure in order to increase the magnetic flux density of the trapped magnetic field.

Charged particle transport in magnetic fields in EGSnrc.

PubMed

Malkov, V N; Rogers, D W O

2016-07-01

To accurately and efficiently implement charged particle transport in a magnetic field in EGSnrc and validate the code for the use in phantom and ion chamber simulations. The effect of the magnetic field on the particle motion and position is determined using one- and three-point numerical integrations of the Lorentz force on the charged particle and is added to the condensed history calculation performed by the EGSnrc PRESTA-II algorithm. The code is tested with a Fano test adapted for the presence of magnetic fields. The code is compatible with all EGSnrc based applications, including egs++. Ion chamber calculations are compared to experimental measurements and the effect of the code on the efficiency and timing is determined. Agreement with the Fano test's theoretical value is obtained at the 0.1% level for large step-sizes and in magnetic fields as strong as 5 T. The NE2571 dose calculations achieve agreement with the experiment within 0.5% up to 1 T beyond which deviations up to 1.2% are observed. Uniform air gaps of 0.5 and 1 mm and a misalignment of the incoming photon beam with the magnetic field are found to produce variations in the normalized dose on the order of 1%. These findings necessitate a clear definition of all experimental conditions to allow for accurate Monte Carlo simulations. It is found that ion chamber simulation times are increased by only 38%, and a 10 × 10 × 6 cm(3) water phantom with (3 mm)(3) voxels experiences a 48% increase in simulation time as compared to the default EGSnrc with no magnetic field. The incorporation of the effect of the magnetic fields in EGSnrc provides the capability to calculate high accuracy ion chamber and phantom doses for the use in MRI-radiation systems. Further, the effect of apparently insignificant experimental details is found to be accentuated by the presence of the magnetic field.

Magnetic hyperthermia properties of nanoparticles inside lysosomes using kinetic Monte Carlo simulations: Influence of key parameters and dipolar interactions, and evidence for strong spatial variation of heating power

NASA Astrophysics Data System (ADS)

Tan, R. P.; Carrey, J.; Respaud, M.

2014-12-01

Understanding the influence of dipolar interactions in magnetic hyperthermia experiments is of crucial importance for fine optimization of nanoparticle (NP) heating power. In this study we use a kinetic Monte Carlo algorithm to calculate hysteresis loops that correctly account for both time and temperature. This algorithm is shown to correctly reproduce the high-frequency hysteresis loop of both superparamagnetic and ferromagnetic NPs without any ad hoc or artificial parameters. The algorithm is easily parallelizable with a good speed-up behavior, which considerably decreases the calculation time on several processors and enables the study of assemblies of several thousands of NPs. The specific absorption rate (SAR) of magnetic NPs dispersed inside spherical lysosomes is studied as a function of several key parameters: volume concentration, applied magnetic field, lysosome size, NP diameter, and anisotropy. The influence of these parameters is illustrated and comprehensively explained. In summary, magnetic interactions increase the coercive field, saturation field, and hysteresis area of major loops. However, for small amplitude magnetic fields such as those used in magnetic hyperthermia, the heating power as a function of concentration can increase, decrease, or display a bell shape, depending on the relationship between the applied magnetic field and the coercive/saturation fields of the NPs. The hysteresis area is found to be well correlated with the parallel or antiparallel nature of the dipolar field acting on each particle. The heating power of a given NP is strongly influenced by a local concentration involving approximately 20 neighbors. Because this local concentration strongly decreases upon approaching the surface, the heating power increases or decreases in the vicinity of the lysosome membrane. The amplitude of variation reaches more than one order of magnitude in certain conditions. This transition occurs on a thickness corresponding to approximately 1.3 times the mean distance between two neighbors. The amplitude and sign of this variation is explained. Finally, implications of these various findings are discussed in the framework of magnetic hyperthermia optimization. It is concluded that feedback on two specific points from biology experiments is required for further advancement of the optimization of magnetic NPs for magnetic hyperthermia. The present simulations will be an advantageous tool to optimize magnetic NPs heating power and interpret experimental results.

Chirality-induced negative refraction in magnetized plasma

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

Guo, B.

2013-09-15

Characteristic equations in magnetized plasma with chirality are derived in simple formulations and the dispersion relations for propagation parallel and perpendicular to the external magnetic field are studied in detail. With the help of the dispersion relations of each eigenwave, the author explores chirality-induced negative refraction in magnetized plasma and investigates the effects of parameters (i.e., chirality degree, external magnetic field, etc.) on the negative refraction. The results show that the chirality is the necessary and only one factor which leads to negative refraction without manipulating electrical permittivity and magnetic permeability. Both increasing the degree of chirality and reducing themore » external magnetic field can result in greater range negative refraction. Parameter dependence of the effects is calculated and discussed.« less

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

ThMn12-type phases for magnets with low rare-earth content: Crystal-field analysis of the full magnetization process.

PubMed

Tereshina, I S; Kostyuchenko, N V; Tereshina-Chitrova, E A; Skourski, Y; Doerr, M; Pelevin, I A; Zvezdin, A K; Paukov, M; Havela, L; Drulis, H

2018-02-26

Rare-earth (R)-iron alloys are a backbone of permanent magnets. Recent increase in price of rare earths has pushed the industry to seek ways to reduce the R-content in the hard magnetic materials. For this reason strong magnets with the ThMn 12  type of structure came into focus. Functional properties of R(Fe,T) 12 (T-element stabilizes the structure) compounds or their interstitially modified derivatives, R(Fe,T) 12 -X (X is an atom of hydrogen or nitrogen) are determined by the crystal-electric-field (CEF) and exchange interaction (EI) parameters. We have calculated the parameters using high-field magnetization data. We choose the ferrimagnetic Tm-containing compounds, which are most sensitive to magnetic field and demonstrate that TmFe 11 Ti-H reaches the ferromagnetic state in the magnetic field of 52 T. Knowledge of exact CEF and EI parameters and their variation in the compounds modified by the interstitial atoms is a cornerstone of the quest for hard magnetic materials with low rare-earth content.

A high-damping magnetorheological elastomer with bi-directional magnetic-control modulus for potential application in seismology

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

Yu, Miao, E-mail: yumiao@cqu.edu.cn; Qi, Song; Fu, Jie

A high-damping magnetorheological elastomer (MRE) with bi-directional magnetic-control modulus is developed. This MRE was synthesized by filling NdFeB particles into polyurethane (PU)/ epoxy (EP) interpenetrating network (IPN) structure. The anisotropic samples were prepared in a permanent magnetic field and magnetized in an electromagnetic field of 1 T. Dynamic mechanical responses of the MRE to applied magnetic fields are investigated through magneto-rheometer, and morphology of MREs is observed via scanning electron microscope (SEM). Test result indicates that when the test field orientation is parallel to that of the sample's magnetization, the shear modulus of sample increases. On the other hand, when themore » orientation is opposite to that of the sample's magnetization, shear modulus decreases. In addition, this PU/EP IPN matrix based MRE has a high-damping property, with high loss factor and can be controlled by applying magnetic field. It is expected that the high damping property and the ability of bi-directional magnetic-control modulus of this MRE offer promising advantages in seismologic application.« less

Enhanced inductance in laminated multilayer magnetic planar inductor for sensitive magnetic field detection

NASA Astrophysics Data System (ADS)

Wang, Yao; Wen, Yumei; Song, Fapeng; Li, Ping; Yu, Shumin

2018-04-01

The authors reported laminated multilayer magnetic planar inductors for sensitive magnetic field detection, which consist of two serially connected sandwich planar inductors (i.e., FeCuNbSiB/micro planar coil/FeCuNbSiB/micro planar coil/FeCuNbSiB). When ac current is applied to coils, the greatly increased inductance by the incorporated high permeability magnetic material and enlarged mutual-inductance among coils significantly improve the sensor sensitivity to the dc magnetic field. The demagnetizing field is also found to affect the performance severely when the shape and the number of magnetic layers vary. The investigation indicates that the proposed laminate can provide an inductance ratio of 665% at the frequency of 1 kHz. By connecting the sensor with a capacitor, the sensor output with varying dc magnetic fields is obtained by tuning the resonant frequency shift. The study indicates that the proposed sensor can provide a sensitivity of about 3.57 kHz/Oe with a resolution of 28 nT between 2 Oe and 60 Oe, which outperforms most of the magnetic sensors with frequency shifting output.

Magnetic field sensor based on cascaded microfiber coupler with magnetic fluid

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

Mao, Lianmin; Su, Delong; Wang, Zhaofang

A kind of magnetic field sensor based on cascaded microfiber coupler with magnetic fluid is proposed and experimentally demonstrated. The magnetic fluid is utilized as the cladding of the fused regions of the cascaded microfiber coupler. As the interference valley wavelength of the sensing structure is sensitive to the ambient variation, considering the magnetic-field-dependent refractive index of magnetic fluid, the proposed structure is employed for magnetic field sensing. The effective coupling length for each coupling region of the as-fabricated cascaded microfiber coupler is 6031 μm. The achieved sensitivity is 125 pm/Oe, which is about three times larger than that of the previouslymore » similar structure based on the single microfiber coupler. Experimental results indicate that the sensing sensitivity can be easily improved by increasing the effective coupling length or cascading more microfiber couplers. The proposed magnetic field sensor is attractive due to its low cost, immunity to electromagnetic interference, as well as high sensitivity, which also has the potentials in other tunable all-fiber photonic devices, such as filter.« less

Field-aligned particle currents near an auroral arc.

NASA Technical Reports Server (NTRS)

Choy, L. W.; Arnoldy, R. L.; Potter, W.; Kintner, P.; Cahill, L. J., Jr.

1971-01-01

A Nike-Tomahawk rocket equipped to measure electric and magnetic fields and charged particles from a few eV to several hundred keV energy was flown into an auroral band on April 11, 1970. The purpose of this flight was to obtain evidence of the low-energy electrons and protons that constitute a field-aligned sheet current, and also to obtain the magnetic signature of such a current and the electric field in and near the auroral-arc electric current system. Particular attention was given to a sudden increase in the field-aligned current associated with a prior sudden increase in the electric field and a sudden change in the magnetic field, all occurring near the edge of a visual auroral arc. Data obtained are discussed and analyzed; they present an important contribution to the problem of mapping of atmospheric auroral phenomena to the magnetospheric equatorial plane.

Inflationary magneto-(non)genesis, increasing kinetic couplings, and the strong coupling problem

NASA Astrophysics Data System (ADS)

Bazrafshan Moghaddam, Hossein; McDonough, Evan; Namba, Ryo; Brandenberger, Robert H.

2018-05-01

We study the generation of magnetic fields during inflation making use of a coupling of the inflaton and moduli fields to electromagnetism via the photon kinetic term, and assuming that the coupling is an increasing function of time. We demonstrate that the strong coupling problem of inflationary magnetogenesis can be avoided by incorporating the destabilization of moduli fields after inflation. The magnetic field always dominates over the electric one, and thus the severe constraints on the latter from backreaction, which are the demanding obstacles in the case of a decreasing coupling function, do not apply to the current scenario. However, we show that this loophole to the strong coupling problem comes at a price: the normalization of the amplitude of magnetic fields is determined by this coupling term and is therefore suppressed by a large factor after the moduli destabilization completes. From this we conclude that there is no self-consistent and generic realization of primordial magnetogenesis producing scale-invariant fields in the case of an increasing kinetic coupling.

Magnetic suppression of turbulence and the star formation activity of molecular clouds

NASA Astrophysics Data System (ADS)

Zamora-Avilés, Manuel; Vázquez-Semadeni, Enrique; Körtgen, Bastian; Banerjee, Robi; Hartmann, Lee

2018-03-01

We present magnetohydrodynamic simulations aimed at studying the effect of the magnetic suppression of turbulence (generated through various instabilities during the formation of molecular clouds by converging) on the subsequent star formation (SF) activity. We study four magnetically supercritical models with magnetic field strengths B = 0, 1, 2, and 3 μG (corresponding to mass-to-flux ratios of ∞, 4.76, 2.38, and 1.59 times the critical value), with the magnetic field, initially being aligned with the flows. We find that, for increasing magnetic field strength, the clouds formed tend to be more massive, denser, less turbulent, and with higher SF activity. This causes the onset of SF activity in the non-magnetic or more weakly magnetized cases to be delayed by a few Myr in comparison to the more strongly magnetized cases. We attribute this behaviour to the suppression of the non-linear thin shell instability (NTSI) by the magnetic field, previously found by Heitsch and coworkers. This result is contrary to the standard notion that the magnetic field provides support to the clouds, thus reducing their star formation rate. However, our result is a completely non-linear one, and could not be foreseen from simple linear considerations.

Dependence of Perpendicular Viscosity on Magnetic Fluctuations in a Stochastic Topology

NASA Astrophysics Data System (ADS)

Fridström, R.; Chapman, B. E.; Almagri, A. F.; Frassinetti, L.; Brunsell, P. R.; Nishizawa, T.; Sarff, J. S.

2018-06-01

In a magnetically confined plasma with a stochastic magnetic field, the dependence of the perpendicular viscosity on the magnetic fluctuation amplitude is measured for the first time. With a controlled, ˜ tenfold variation in the fluctuation amplitude, the viscosity increases ˜100 -fold, exhibiting the same fluctuation-amplitude-squared dependence as the predicted rate of stochastic field line diffusion. The absolute value of the viscosity is well predicted by a model based on momentum transport in a stochastic field, the first in-depth test of this model.

Parametric scaling of neutral and ion excited state densities in an argon helicon source

NASA Astrophysics Data System (ADS)

McCarren, D.; Scime, E.

2016-04-01

We report measurements of the absolute density and temperature of ion and neutral excited states in an argon helicon source. The excited ion state density, which depends on ion density, electron density, and electron temperature, increases sharply with increasing magnetic field in the source. The neutral argon metastable density measurements are consistent with an increasing ionization fraction with increasing magnetic field strength. The ion temperature shows no evidence of increased heating with increasing magnetic field strength (which has only been observed in helicon sources operating at driving frequencies close to the lower hybrid frequency). The measurements were obtained through cavity ring down spectroscopy, a measurement technique that does not require the target excited state to be metastable or part of a fluorescence scheme; and is therefore applicable to any laser accessible atomic or ionic transition in a plasma.

Magnetic field cycling effect on the non-linear current-voltage characteristics and magnetic field induced negative differential resistance in α-Fe1.64Ga0.36O3 oxide

NASA Astrophysics Data System (ADS)

Bhowmik, R. N.; Vijayasri, G.

2015-06-01

We have studied current-voltage (I-V) characteristics of α-Fe1.64Ga0.36O3, a typical canted ferromagnetic semiconductor. The sample showed a transformation of the I-V curves from linear to non-linear character with the increase of bias voltage. The I-V curves showed irreversible features with hysteresis loop and bi-stable electronic states for up and down modes of voltage sweep. We report positive magnetoresistance and magnetic field induced negative differential resistance as the first time observed phenomena in metal doped hematite system. The magnitudes of critical voltage at which I-V curve showed peak and corresponding peak current are affected by magnetic field cycling. The shift of the peak voltage with magnetic field showed a step-wise jump between two discrete voltage levels with least gap (ΔVP) 0.345(± 0.001) V. The magnetic spin dependent electronic charge transport in this new class of magnetic semiconductor opens a wide scope for tuning large electroresistance (˜500-700%), magnetoresistance (70-135 %) and charge-spin dependent conductivity under suitable control of electric and magnetic fields. The electric and magnetic field controlled charge-spin transport is interesting for applications of the magnetic materials in spintronics, e.g., magnetic sensor, memory devices and digital switching.

The Role of Compressibility in Energy Release by Magnetic Reconnection

NASA Technical Reports Server (NTRS)

Birn, J.; Borovosky, J. E.; Hesse, M.

2012-01-01

Using resistive compressible magnetohydrodynamics, we investigate the energy release and transfer by magnetic reconnection in finite (closed or periodic) systems. The emphasis is on the magnitude of energy released and transferred to plasma heating in configurations that range from highly compressible to incompressible, based on the magnitude of the background beta (ratio of plasma pressure over magnetic pressure) and of a guide field in two-dimensional reconnection. As expected, the system becomes more incompressible, and the role of compressional heating diminishes, with increasing beta or increasing guide field. Nevertheless, compressional heating may dominate over Joule heating for values of the guide field of 2 or 3 (in relation to the reconnecting magnetic field component) and beta of 5-10. This result stems from the strong localization of the dissipation near the reconnection site, which is modeled based on particle simulation results. Imposing uniform resistivity, corresponding to a Lundquist number of 10(exp 3) to 10(exp 4), leads to significantly larger Ohmic heating. Increasing incompressibility greatly reduces the magnetic flux transfer and the amount of energy released, from approx. 10% of the energy associated with the reconnecting field component, for zero guide field and low beta, to approx. 0.2%-0.4% for large values of the guide field B(sub y0) > 5 or large beta. The results demonstrate the importance of taking into account plasma compressibility and localization of dissipation in investigations of heating by turbulent reconnection, possibly relevant for solar wind or coronal heating.

The Magnetic Response of the Solar Atmosphere to Umbral Flashes

NASA Astrophysics Data System (ADS)

Houston, S. J.; Jess, D. B.; Asensio Ramos, A.; Grant, S. D. T.; Beck, C.; Norton, A. A.; Krishna Prasad, S.

2018-06-01

Chromospheric observations of sunspot umbrae offer an exceptional view of magnetoacoustic shock phenomena and the impact they have on the surrounding magnetically dominated plasma. We employ simultaneous slit-based spectro-polarimetry and spectral imaging observations of the chromospheric He I 10830 Å and Ca II 8542 Å lines to examine fluctuations in the umbral magnetic field caused by the steepening of magnetoacoustic waves into umbral flashes. Following the application of modern inversion routines, we find evidence to support the scenario that umbral shock events cause expansion of the embedded magnetic field lines due to the increased adiabatic pressure. The large number statistics employed allow us to calculate the adiabatic index, γ = 1.12 ± 0.01, for chromospheric umbral locations. Examination of the vector magnetic field fluctuations perpendicular to the solar normal revealed changes up to ∼200 G at the locations of umbral flashes. Such transversal magnetic field fluctuations have not been described before. Through comparisons with nonlinear force-free field extrapolations, we find that the perturbations of the transverse field components are oriented in the same direction as the quiescent field geometries. This implies that magnetic field enhancements produced by umbral flashes are directed along the motion path of the developing shock, hence producing relatively small changes, up to a maximum of ∼8°, in the inclination and/or azimuthal directions of the magnetic field. Importantly, this work highlights that umbral flashes are able to modify the full vector magnetic field, with the detection of the weaker transverse magnetic field components made possible by high-resolution data combined with modern inversion routines.

An analysis on the magnetic fluid seal capacity

NASA Astrophysics Data System (ADS)

Meng, Zhao; Jibin, Zou; Jianhui, Hu

2006-08-01

The capacity of the magnetic fluid seal depends on the magnetic field and the saturation magnetization of the magnetic fluid. There are many factors that influence the magnetic field and the seal capacity of the magnetic fluid seal, such as the sealing gap, the shaft eccentricity, the shaft diameter, and the centrifugal force. In this paper, these factors are analyzed by numerical computations. When the material and structure are the same, the magnetic fluid seal capacity will reduce with the increasing of the sealing gap. When the shaft diameter is large the gravity should be considered. The centrifugal force has influence on the magnetic fluid seal capacity.

Marked rapid alterations in nocturnal pineal serotonin metabolism in mice and rats exposed to weak intermittent magnetic fields

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

Lerchl, A.; Nonaka, K.O.; Stokkan, K.A.

Adult AMES mice and male Sprague Dawley rats were exposed to an artificial magnetic field, generated by Helmholtz coils. 3.5 hours after the onset of darkness the coils were activated for one hour resulting in an inversion of the horizontal component of the earth's magnetic field. The coils were activated and deactivated at 5 min intervals during the 1 hour exposure period. In both mice and rats, the levels of serotonin in the pineal were markedly increased by the exposure. In rats, an increase of pineal 5-hydroxyindole acetic acid and a decrease of the activity of the pineal enzyme serotonin-N-acetyltransferasemore » also was observed. However, pineal and serum melatonin levels were not altered. The results indicate that the metabolism of serotonin in the pineal is quickly affected by the exposure of animals to a magnetic field.« less

Thermoelectric properties of an ultra-thin topological insulator.

PubMed

Islam, S K Firoz; Ghosh, T K

2014-04-23

Thermoelectric coefficients of an ultra-thin topological insulator are presented here. The hybridization between top and bottom surface states of a topological insulator plays a significant role. In the absence of a magnetic field, the thermopower increases and thermal conductivity decreases with an increase in the hybridization energy. In the presence of a magnetic field perpendicular to the ultra-thin topological insulator, thermoelectric coefficients exhibit quantum oscillations with inverse magnetic field, whose frequency is strongly modified by the Zeeman energy and whose phase factor is governed by the product of the Landé g-factor and the hybridization energy. In addition to the numerical results, the low-temperature approximate analytical results for the thermoelectric coefficients are also provided. It is also observed that for a given magnetic field these transport coefficients oscillate with hybridization energy, at a frequency that depends on the Landé g-factor.

Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li3 N

NASA Astrophysics Data System (ADS)

Fix, M.; Atkinson, J. H.; Canfield, P. C.; del Barco, E.; Jesche, A.

2018-04-01

The magnetic properties of dilute Li2 (Li1 -xFex )N with x ˜0.001 are dominated by the spin of single, isolated Fe atoms. Below T =10 K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla reveals exceptionally sharp tunneling resonances. Li2 (Li1 -xFex )N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.

Analysis of eddy current induced in track on medium-low speed maglev train

NASA Astrophysics Data System (ADS)

Li, Guanchun; Jia, Zhen; He, Guang; Li, Jie

2017-06-01

Electromagnetic levitation (EMS) maglev train relies on the attraction between the electromagnets and rails which are mounted on the train to achieve suspension. During the movement, the magnetic field generated by the electromagnet will induce the eddy current in the orbit and the eddy current will weaken the suspended magnetic field. Which leads to the attenuation of the levitation force, the increases of suspension current and the degradation the suspension performance. In this paper, the influence of eddy current on the air gap magnetic field is solved by theoretical analysis, and the correction coefficient of air gap magnetic field is fitted according to the finite element data. The levitation force and current are calculated by the modified formula, and the velocity curves of the levitation force and current are obtained. The results show that the eddy current effect increases the load power by 61.9% in the case of heavy loads.

Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li 3 N

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

Fix, M.; Atkinson, J. H.; Canfield, P. C.

Here, the magnetic properties of dilute Li 2(Li 1–xFe x)N with x~0.001 are dominated by the spin of single, isolated Fe atoms. Below T=10 K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla revealsmore » exceptionally sharp tunneling resonances. Li 2(Li 1–xFe x)N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.« less

Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li 3 N

DOE PAGES

Fix, M.; Atkinson, J. H.; Canfield, P. C.; ...

2018-04-04

Here, the magnetic properties of dilute Li 2(Li 1–xFe x)N with x~0.001 are dominated by the spin of single, isolated Fe atoms. Below T=10 K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla revealsmore » exceptionally sharp tunneling resonances. Li 2(Li 1–xFe x)N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.« less

Extreme Field Sensitivity of Magnetic Tunneling in Fe-Doped Li_{3}N.

PubMed

Fix, M; Atkinson, J H; Canfield, P C; Del Barco, E; Jesche, A

2018-04-06

The magnetic properties of dilute Li_{2}(Li_{1-x}Fe_{x})N with x∼0.001 are dominated by the spin of single, isolated Fe atoms. Below T=10  K the spin-relaxation times become temperature independent indicating a crossover from thermal excitations to the quantum tunneling regime. We report on a strong increase of the spin-flip probability in transverse magnetic fields that proves the resonant character of this tunneling process. Longitudinal fields, on the other hand, lift the ground-state degeneracy and destroy the tunneling condition. An increase of the relaxation time by 4 orders of magnitude in applied fields of only a few milliTesla reveals exceptionally sharp tunneling resonances. Li_{2}(Li_{1-x}Fe_{x})N represents a comparatively simple and clean model system that opens the possibility to study quantum tunneling of the magnetization at liquid helium temperatures.

Ground-state magnetic phase diagram of bow-tie graphene nanoflakes in external magnetic field

NASA Astrophysics Data System (ADS)

Szałowski, Karol

2013-12-01

The magnetic phase diagram of a ground state is studied theoretically for graphene nanoflakes of bow-tie shape and various sizes in external in-plane magnetic field. The tight-binding Hamiltonian supplemented with Hubbard term is used to model the electronic structure of the systems in question. The existence of the antiferromagnetic phase with magnetic moments localized at the sides of the bow-tie is found for low field and a field-induced spin-flip transition to ferromagnetic state is predicted to occur in charge-undoped structures. For small nanoflake doped with a single charge carrier, the low-field phase is ferrimagnetic and a metamagnetic transition to ferromagnetic ordering can be forced by the field. The critical field is found to decrease with increasing size of the nanoflake. The influence of diagonal and off-diagonal disorder on the mentioned magnetic properties is studied. The effect of off-diagonal disorder is found to be more important than that of diagonal disorder, leading to significantly widened distribution of critical fields for disordered population of nanoflakes.

Effect of intrinsic magnetic field decrease on the low- to middle-latitude upper atmosphere dynamics simulated by GAIA

NASA Astrophysics Data System (ADS)

Tao, C.; Jin, H.; Shinagawa, H.; Fujiwara, H.; Miyoshi, Y.

2017-12-01

The effects of decreasing the intrinsic magnetic field on the upper atmospheric dynamics at low to middle latitudes are investigated using the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA). GAIA incorporates a meteorological reanalysis data set at low altitudes (<30 km), which enables us to investigate the atmospheric response to various waves under dynamic and chemical interactions with the ionosphere. In this simulation experiment, we reduced the magnetic field strength to as low as 10% of the current value. The averaged neutral velocity, density, and temperature at low to middle latitudes at 300 km altitude show little change with the magnetic field variation, while the dynamo field, current density, and the ionospheric conductivities are modified significantly. The wind velocity and tidal wave amplitude in the thermosphere remain large owing to the small constraint on plasma motion for a small field. On the other hand, the superrotation feature at the dip equator is weakened by 20% for a 10% magnetic field because the increase in ion drag for the small magnetic field prevents the superrotation.

Effect of intrinsic magnetic field decrease on the low- to middle-latitude upper atmosphere dynamics simulated by GAIA

NASA Astrophysics Data System (ADS)

Tao, Chihiro; Jin, Hidekatsu; Shinagawa, Hiroyuki; Fujiwara, Hitoshi; Miyoshi, Yasunobu

2017-09-01

The effects of decreasing the intrinsic magnetic field on the upper atmospheric dynamics at low to middle latitudes are investigated using the Ground-to-topside model of Atmosphere and Ionosphere for Aeronomy (GAIA). GAIA incorporates a meteorological reanalysis data set at low altitudes (<30 km), which enables us to investigate the atmospheric response to various waves under dynamic and chemical interactions with the ionosphere. In this simulation experiment, we reduced the magnetic field strength to as low as 10% of the current value. The averaged neutral velocity, density, and temperature at low to middle latitudes at 300 km altitude show little change with the magnetic field variation, while the dynamo field, current density, and the ionospheric conductivities are modified significantly. The wind velocity and tidal wave amplitude in the thermosphere remain large owing to the small constraint on plasma motion for a small field. On the other hand, the superrotation feature at the dip equator is weakened by 20% for a 10% magnetic field because the increase in ion drag for the small magnetic field prevents the superrotation.

Effects of magnetic fields on dissolution of arthritis causing crystals

NASA Astrophysics Data System (ADS)

Takeuchi, Y.; Iwasaka, M.

2015-05-01

The number of gout patients has rapidly increased because of excess alcohol and salt intake. The agent responsible for gout is the monosodium urate (MSU) crystal. MSU crystals are found in blood and consist of uric acid and sodium. As a substitute for drug dosing or excessive water intake, physical stimulation by magnetic fields represents a new medical treatment for gout. In this study, we investigated the effects of a magnetic field on the dissolution of a MSU crystal suspension. The white MSU crystal suspension was dissolved in an alkaline solution. We measured the light transmission of the MSU crystal suspension by a transmitted light measuring system. The magnetic field was generated by a horizontal electromagnet (maximum field strength was 500 mT). The MSU crystal suspension that dissolved during the application of a magnetic field of 500 mT clearly had a higher dissolution rate when compared with the control sample. We postulate that the alkali solution promoted penetration upon diamagnetic rotation and this magnetic field orienting is because of the pronounced diamagnetic susceptibility anisotropy of the MSU crystal. The results indicate that magnetic fields represent an effective gout treatment approach.

Pressure-magnetic field induced phase transformation in Ni{sub 46}Mn{sub 41}In{sub 13} Heusler alloy

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

Rama Rao, N. V., E-mail: nvrrao@dmrl.drdo.in; Manivel Raja, M.; Pandian, S.

2014-12-14

The effect of hydrostatic pressure and magnetic field on the magnetic properties and phase transformation in Ni{sub 46}Mn{sub 41}In{sub 13} Heusler alloy was investigated. Pressure (P)-magnetic field (H)-temperature (T) phase diagram has been constructed from experimental results. In the P–T contour of the phase diagram, the slope of the austenite-martensite phase boundary line appears positive (dT/dP > 0), while it appears negative (dT/dH < 0) in the H–T contour. The results revealed that pressure and magnetic field have opposite effect on phase stabilization. The combined effect of pressure and magnetic field on martensitic transition has led to two important findings: (i) pressure dependent shiftmore » of austenite start temperature (A{sub s}) is higher when larger field is applied, and (ii) field dependent shift of A{sub s} is lowered when a higher pressure is applied. The pressure and magnetic field dependent shift observed in the martensitic transformation has been explained on the basis of thermodynamic calculations. Curie temperature of the phases was found to increase with pressure at a rate of 0.6 K/kbar.« less

DESTRUCTION OF NEUTRAL PARTICLES IN A DEVICE FOR PRODUCING A HIGH DENSITY PLASMA

DOEpatents

Simon, A.

1962-05-01

A method and apparatus are described for burning out neutral particles in an evacuated region and within a strong magnetic field. The method comprises injecting energetic molecular ions into the region perpendicular to the magnetic field and into the path of a dissociating, energetic arc discharge, the atomic ions formed in the dissociating process being trapped by the magnetic field, and then increasing the value of the trapped atomic ion current to such a value that the neutral particles are destroyed faster than they are formed, thereby causing a dense, energetic plasma to be built up and sustained by the magnetic field. (AEC)

Experimental and theoretical basis of agricultural plant immunostimulation with regard to pathogenic fungi by magnetic field and He-Ne laser irradiation

NASA Astrophysics Data System (ADS)

Belski, Alexey I.; Chivanov, Vadym D.

1996-09-01

Spring barley, winter wheat and maize seeds were subjected to the action of He-Ne laser irradiation having a low intensity in the visible region of the spectrum (628-640 nm) in conjunction with magnetic fields. The following results were obtained: laser irradiation with magnetic fields induced activation of the natural plant defence/immune systems gave the harvest crop level increased to about 50- 300 percent; a correlation was established between the rate of the fungal pathogens growth and the stimulation of plant immunity after the seeds had been treated with laser irradiation and magnetic field.

Making a Magnetorheological Fluid from Mining Tailings

NASA Astrophysics Data System (ADS)

Quitian, G.; Saldarriaga, W.; Rojas, N.

2017-12-01

We have obtained magnetite mining tailings and used it to fabricate a magnetorheological fluid (MRF). Mineralogical and morphological characteristics were determined using X-ray diffraction (XRD) and energy dispersive spectrometry (EDS), as well as size and geometry for the obtained magnetite. Finally, the fabricated MRF was rheologically characterized in a device attached to a rheometer. The application of a magnetic field of 0.12 Tesla can increase the viscosity of the MRF by more than 400 pct. A structural formation should occur within the fluid by a reordering of particles into magnetic columns, which are perpendicular to the flow direction. These structures give the fluid an increased viscosity. As the magnetic field increases, the structure formed is more resistant, resulting in an increased viscosity. One can appreciate that with a value equal to or less than 0.06 Tesla of applied magnetic field, many viscosity values associated with the work area of the oils can be achieved (0.025 and 0.34 Pa s).

Energy levels of a hydrogenic impurity in a parabolic quantum well with a magnetic field

NASA Astrophysics Data System (ADS)

Zang, J. X.; Rustgi, M. L.

1993-07-01

In this paper, we present a calculation of the energy levels of a hydrogenic impurity (or a hydrogenic atom) at the bottom of a one-dimensional parabolic quantum well with a magnetic field normal to the plane of the well. The finite-basis-set variational method is used to calculate the ground state and the excited states with major quantum number less than or equal to 3. The limit of small radial distance and the limit of great radial distance are considered to choose a set of proper basis functions. The results in the limit that the parabolic parameter α=0 are compared with the data of Rösner et al. [J. Phys. B 17, 29 (1984)]. The comparison shows that the present calculation is quite accurate. It is found that the energy levels increase with increasing parabolic parameter α and increase with increasing normalized magnetic-field strength γ except those levels with magnetic quantum number m<0 at small γ.

Lack of effects on key cellular parameters of MRC-5 human lung fibroblasts exposed to 370 mT static magnetic field

NASA Astrophysics Data System (ADS)

Romeo, Stefania; Sannino, Anna; Scarfì, Maria Rosaria; Massa, Rita; D'Angelo, Raffaele; Zeni, Olga

2016-01-01

The last decades have seen increased interest toward possible adverse effects arising from exposure to intense static magnetic fields. This concern is mainly due to the wider and wider applications of such fields in industry and clinical practice; among them, Magnetic Resonance Imaging (MRI) facilities are the main sources of exposure to static magnetic fields for both general public (patients) and workers. In recent investigations, exposures to static magnetic fields have been demonstrated to elicit, in different cell models, both permanent and transient modifications in cellular endpoints critical for the carcinogenesis process. The World Health Organization has therefore recommended in vitro investigations as important research need, to be carried out under strictly controlled exposure conditions. Here we report on the absence of effects on cell viability, reactive oxygen species levels and DNA integrity in MRC-5 human foetal lung fibroblasts exposed to 370 mT magnetic induction level, under different exposure regimens. Exposures have been performed by using an experimental apparatus designed and realized for operating with the static magnetic field generated by permanent magnets, and confined in a magnetic circuit, to allow cell cultures exposure in absence of confounding factors like heating or electric field components.

Enhancement in heat transfer of a ferrofluid in a differentially heated square cavity through the use of permanent magnets

NASA Astrophysics Data System (ADS)

Joubert, J. C.; Sharifpur, M.; Solomon, A. Brusly; Meyer, J. P.

2017-12-01

The natural convection heat transfer of a magnetic nanofluid in a differentially heated cavity is investigated with and without an applied external magnetic field. The effects of volume fraction, magnetic field configuration, and magnetic field strength are investigated. Spherical Fe2O3 nanoparticles with a diameter of 15-20 nm are used in the nanofluids. Volume fractions ranging between 0.05% and 0.3% are tested for the case with no magnetic field, while only a volume fraction of 0.1% was tested in an externally applied magnetic field. The experiments were conducted for a range of Rayleigh numbers in 1.7 × 108 < Ra < 4.2 × 108. The viscosity of the nanofluid was determined experimentally. An empirical correlation for the viscosity was determined, and the stability of various nanofluids was investigated. Using heat transfer data obtained from the cavity, the average heat transfer coefficient and average Nusselt number for the nanofluids are determined. It was found that a volume fraction of 0.1% showed a maximum increase of 5.63% to the Nu at the maximum Ra. For the magnetic field study, it was found that the best-performing magnetic field enhanced the heat transfer behaviour by an additional 2.81% in Nu at Ra = 3.8 × 108.

Lack of effects on key cellular parameters of MRC-5 human lung fibroblasts exposed to 370 mT static magnetic field

PubMed Central

Romeo, Stefania; Sannino, Anna; Scarfì, Maria Rosaria; Massa, Rita; d’Angelo, Raffaele; Zeni, Olga

2016-01-01

The last decades have seen increased interest toward possible adverse effects arising from exposure to intense static magnetic fields. This concern is mainly due to the wider and wider applications of such fields in industry and clinical practice; among them, Magnetic Resonance Imaging (MRI) facilities are the main sources of exposure to static magnetic fields for both general public (patients) and workers. In recent investigations, exposures to static magnetic fields have been demonstrated to elicit, in different cell models, both permanent and transient modifications in cellular endpoints critical for the carcinogenesis process. The World Health Organization has therefore recommended in vitro investigations as important research need, to be carried out under strictly controlled exposure conditions. Here we report on the absence of effects on cell viability, reactive oxygen species levels and DNA integrity in MRC-5 human foetal lung fibroblasts exposed to 370 mT magnetic induction level, under different exposure regimens. Exposures have been performed by using an experimental apparatus designed and realized for operating with the static magnetic field generated by permanent magnets, and confined in a magnetic circuit, to allow cell cultures exposure in absence of confounding factors like heating or electric field components. PMID:26762783

Tendency of a rotating electron plasma to approach the Brillouin limit

DOE PAGES

Gueroult, Renaud; Fruchtman, Amnon; Fisch, Nathaniel J.

2013-07-24

In this study, a neutral plasma is considered to be immersed in an axial magnetic field together with a radial electric field. If the electrons are magnetized, but the ions are not magnetized, then the electrons will rotate but the ions will not rotate, leading to current generation. The currents, in turn, weaken the axial magnetic field, leading to an increase in the rotation frequency of the slow Brillouin mode. This produces a positive feedback effect, further weakening the magnetic field. The operating point thus tends to drift towards the Brillouin limit, possibly finding stability only in proximity to themore » limit itself. An example of this effect might be the cylindrical Hall thruster configuration.« less

Monte Carlo study of magnetization reversal in the model of a hard/soft magnetic bilayer

NASA Astrophysics Data System (ADS)

Taaev, T. A.; Khizriev, K. Sh.; Murtazaev, A. K.

2017-06-01

Magnetization reversal in the model of a hard/soft magnetic bilayer under the action of an external magnetic field has been investigated by the Monte Carlo method. Calculations have been performed for three systems: (i) the model without a soft-magnetic layer (hard-magnetic layer), (ii) the model with a soft-magnetic layer of thickness 25 atomic layers (predominantly exchange-coupled system), and (iii) with 50 (weak exchange coupling) atomic layers. The effect of a soft-magnetic phase on the magnetization reversal of the magnetic bilayer and on the formation of a 1D spin spring in the magnetic bilayer has been demonstrated. An inf lection that has been detected on the arch of the hysteresis loop only for the system with weak exchange coupling is completely determined by the behavior of the soft layer in the external magnetic field. The critical fields of magnetization reversal decrease with increasing thickness of the soft phase.

Transmitted light relaxation and microstructure evolution of ferrofluids under gradient magnetic fields

NASA Astrophysics Data System (ADS)

Huang, Yan; Li, Decai; Li, Feng; Zhu, Quanshui; Xie, Yu

2015-03-01

Using light transmission experiments and optical microscope observations with a longitudinal gradient magnetic field configuration, the relationship between the behavior of the transmitted light relaxation and the microstructure evolution of ionic ferrofluids in the central region of an axisymmetric field is investigated. Under a low-gradient magnetic field, there are two types of relaxation process. When a field is applied, the transmitted light intensity decreases to a minimum within a time on the order of 101-102 s. It is then gradually restored, approaching its initial value within a time on the order of 102 s. This is type I relaxation, which corresponds to the formation of magnetic columns. After the transmission reaches this value, it either increases or decreases slowly, stabilizing within a time on the order of 103 s, according to the direction of the field gradient. This is a type II relaxation, which results from the shadowing effect, corresponding to the motion of the magnetic columns under the application of a gradient force. Under a magnetic field with a centripetal high-gradient (magnetic materials subjected to a force pointing toward the center of the axisymmetric field), the transmitted light intensity decreases monotonously and more slowly than that under a low-gradient field. Magnetic transport and separation resulted from magnetophoresis under high-gradient fields, changing the formation dynamics of the local columns and influencing the final state of the column system.

Small-scale anisotropic intermittency in magnetohydrodynamic turbulence at low magnetic Reynolds numbers.

PubMed

Okamoto, Naoya; Yoshimatsu, Katsunori; Schneider, Kai; Farge, Marie

2014-03-01

Small-scale anisotropic intermittency is examined in three-dimensional incompressible magnetohydrodynamic turbulence subjected to a uniformly imposed magnetic field. Orthonormal wavelet analyses are applied to direct numerical simulation data at moderate Reynolds number and for different interaction parameters. The magnetic Reynolds number is sufficiently low such that the quasistatic approximation can be applied. Scale-dependent statistical measures are introduced to quantify anisotropy in terms of the flow components, either parallel or perpendicular to the imposed magnetic field, and in terms of the different directions. Moreover, the flow intermittency is shown to increase with increasing values of the interaction parameter, which is reflected in strongly growing flatness values when the scale decreases. The scale-dependent anisotropy of energy is found to be independent of scale for all considered values of the interaction parameter. The strength of the imposed magnetic field does amplify the anisotropy of the flow.

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.

In-plane magnetic anisotropy and coercive field dependence upon thickness of CoFeB

NASA Astrophysics Data System (ADS)

Kipgen, Lalminthang; Fulara, Himanshu; Raju, M.; Chaudhary, Sujeet

2012-09-01

The structural and magnetic properties of as-grown 5-50 nm thin ion-beam sputter deposited transition metal-metalloid Co20Fe60B20 (CFB) films are reported in this communication. A broad peak observed at 2θ∼45° in the glancing angle X-ray diffraction pattern revealed the formation of very fine nano-sized grains embedded in majority amorphous CFB matrix. Although no magnetic field is applied during deposition, the longitudinal magneto-optic Kerr effect measurements performed at 300 K in these as-grown films clearly established the presence of in-plane uniaxial magnetic anisotropy (Ku). It is argued that this observed anisotropy is strain-induced. This is supported by the observed dependence of direction of Ku on the angle between applied magnetic field and crystallographic orientation of the underlying Si(100) substrate, and increase in the coercivity with the increase of the film thickness.

The role of guide field on magnetic reconnection during island coalescence

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

Stanier, Adam John; Daughton, William Scott; Simakov, Andrei Nikolaevich

A number of studies have considered how the rate of magnetic reconnection scales in large and weakly collisional systems by the modelling of long reconnecting current sheets. However, this set-up neglects both the formation of the current sheet and the coupling between the diffusion region and a larger system that supplies the magnetic flux. Recent studies of magnetic island merging, which naturally include these features, have found that ion kinetic physics is crucial to describe the reconnection rate and global evolution of such systems. In this paper, the effect of a guide field on reconnection during island merging is considered.more » In contrast to the earlier current sheet studies, we identify a limited range of guide fields for which the reconnection rate, outflow velocity, and pile-up magnetic field increase in magnitude as the guide field increases. The Hall-MHD fluid model is found to reproduce kinetic reconnection rates only for a sufficiently strong guide field, for which ion inertia breaks the frozen-in condition and the outflow becomes Alfvénic in the kinetic system. The merging of large islands occurs on a longer timescale in the zero guide field limit, which may in part be due to a mirror-like instability that occurs upstream of the reconnection region.« less

The role of guide field on magnetic reconnection during island coalescence

DOE PAGES

Stanier, Adam John; Daughton, William Scott; Simakov, Andrei Nikolaevich; ...

2017-02-01

A number of studies have considered how the rate of magnetic reconnection scales in large and weakly collisional systems by the modelling of long reconnecting current sheets. However, this set-up neglects both the formation of the current sheet and the coupling between the diffusion region and a larger system that supplies the magnetic flux. Recent studies of magnetic island merging, which naturally include these features, have found that ion kinetic physics is crucial to describe the reconnection rate and global evolution of such systems. In this paper, the effect of a guide field on reconnection during island merging is considered.more » In contrast to the earlier current sheet studies, we identify a limited range of guide fields for which the reconnection rate, outflow velocity, and pile-up magnetic field increase in magnitude as the guide field increases. The Hall-MHD fluid model is found to reproduce kinetic reconnection rates only for a sufficiently strong guide field, for which ion inertia breaks the frozen-in condition and the outflow becomes Alfvénic in the kinetic system. The merging of large islands occurs on a longer timescale in the zero guide field limit, which may in part be due to a mirror-like instability that occurs upstream of the reconnection region.« less

Design and experimental validation of Unilateral Linear Halbach magnet arrays for single-sided magnetic resonance.

PubMed

Bashyam, Ashvin; Li, Matthew; Cima, Michael J

2018-07-01

Single-sided NMR has the potential for broad utility and has found applications in healthcare, materials analysis, food quality assurance, and the oil and gas industry. These sensors require a remote, strong, uniform magnetic field to perform high sensitivity measurements. We demonstrate a new permanent magnet geometry, the Unilateral Linear Halbach, that combines design principles from "sweet-spot" and linear Halbach magnets to achieve this goal through more efficient use of magnetic flux. We perform sensitivity analysis using numerical simulations to produce a framework for Unilateral Linear Halbach design and assess tradeoffs between design parameters. Additionally, the use of hundreds of small, discrete magnets within the assembly allows for a tunable design, improved robustness to variability in magnetization strength, and increased safety during construction. Experimental validation using a prototype magnet shows close agreement with the simulated magnetic field. The Unilateral Linear Halbach magnet increases the sensitivity, portability, and versatility of single-sided NMR. Copyright © 2018 Elsevier Inc. All rights reserved.

Design and experimental validation of Unilateral Linear Halbach magnet arrays for single-sided magnetic resonance

NASA Astrophysics Data System (ADS)

Bashyam, Ashvin; Li, Matthew; Cima, Michael J.

2018-07-01

Single-sided NMR has the potential for broad utility and has found applications in healthcare, materials analysis, food quality assurance, and the oil and gas industry. These sensors require a remote, strong, uniform magnetic field to perform high sensitivity measurements. We demonstrate a new permanent magnet geometry, the Unilateral Linear Halbach, that combines design principles from "sweet-spot" and linear Halbach magnets to achieve this goal through more efficient use of magnetic flux. We perform sensitivity analysis using numerical simulations to produce a framework for Unilateral Linear Halbach design and assess tradeoffs between design parameters. Additionally, the use of hundreds of small, discrete magnets within the assembly allows for a tunable design, improved robustness to variability in magnetization strength, and increased safety during construction. Experimental validation using a prototype magnet shows close agreement with the simulated magnetic field. The Unilateral Linear Halbach magnet increases the sensitivity, portability, and versatility of single-sided NMR.

Simulation of an expanding plasma using the Boris algorithm

NASA Astrophysics Data System (ADS)

Neal, Luke; Aguirre, Evan; Steinberger, Thomas; Good, Timothy; Scime, Earl

2017-10-01

We present a Boris algorithm simulation in a cylindrical geometry of charged particle motion in a helicon plasma confined by a diverging magnetic field. Laboratory measurements of ion velocity distribution functions (ivdfs) provide evidence for acceleration of ions into the divergent field region in the center of the discharge. The increase in ion velocity is inconsistent with expectations for simple magnetic moment conservation given the magnetic field mirror ratio and is therefore attributed to the presence of a double layer in the literature. Using measured electric fields and ivdfs (at different radial locations across the entire plasma column) upstream and downstream of the divergent magnetic field region, we compare predictions for the downstream ivdfs to measurements. We also present predictions for the evolution of the electron velocity distribution function downstream of the divergent magnetic field. This work was supported by U.S. National Science Foundation Grant No. PHY-1360278.

Effects of low-frequency magnetic fields on embryonic development and pregnancy.

PubMed

Juutilainen, J

1991-06-01

Experimental and epidemiologic studies on the effects of low-frequency magnetic fields on pregnancy are reviewed. The literature suggests that these fields have adverse effects on chick embryo development. The interaction mechanism is not known. The results of experiments with mammals are inconsistent. There is more evidence of effects on mice than on rats, and the data suggest that fetal loss might be increased rather than malformations. Most of the epidemiologic studies related to pregnancy and low-frequency magnetic fields have concerned operators of a video display terminal (VDT). The results do not provide evidence for an association between adverse pregnancy outcome and use of a VDT. Other (stronger) sources of low-frequency magnetic fields have been addressed in only a few studies. It is not yet possible to conclude whether occupational or residential exposure to low-frequency magnetic fields affects human prenatal development. There is an apparent need for further investigation.

Quasiparticle Breakdown and Spin Hamiltonian of the Frustrated Quantum Pyrochlore Yb_{2}Ti_{2}O_{7} in a Magnetic Field.

PubMed

Thompson, J D; McClarty, P A; Prabhakaran, D; Cabrera, I; Guidi, T; Coldea, R

2017-08-04

The frustrated pyrochlore magnet Yb_{2}Ti_{2}O_{7} has the remarkable property that it orders magnetically but has no propagating magnons over wide regions of the Brillouin zone. Here we use inelastic neutron scattering to follow how the spectrum evolves in cubic-axis magnetic fields. At high fields we observe, in addition to dispersive magnons, a two-magnon continuum, which grows in intensity upon reducing the field and overlaps with the one-magnon states at intermediate fields leading to strong renormalization of the dispersion relations, and magnon decays. Using heat capacity measurements we find that the low- and high-field regions are smoothly connected with no sharp phase transition, with the spin gap increasing monotonically in field. Through fits to an extensive data set of dispersion relations combined with magnetization measurements, we reevaluate the spin Hamiltonian, finding dominant quantum exchange terms, which we propose are responsible for the anomalously strong fluctuations and quasiparticle breakdown effects observed at low fields.

Magnetization-induced second-harmonic generation in electrochemically synthesized magnetic films of ternary metal Prussian blue analogs

NASA Astrophysics Data System (ADS)

Ikeda, Katsuyoshi; Ohkoshi, Shin-ichi; Hashimoto, Kazuhito

2003-02-01

We observed magnetic field effects on transmitted second-harmonic generation (SHG) in electrochemically synthesized (FexIICr1-xII)1.5[CrIII(CN)6]ṡ7.5H2O magnetic films. These films showed a variety of temperature dependences for SH intensities below magnetic phase transition temperatures (TC). The SH intensity for x=0.25 increased monotonically with decreasing temperature and that for x=0.13 exhibited a minimum value around the magnetic compensation temperature under a zero magnetic field. These temperature dependences resembled those of the absolute value of magnetization, indicating that the magnetic strain of the films is responsible for the increase in SH below TC. In addition, the polarization of SH light was rotated by an applied external magnetic field. The observed SH rotation angle of 1.3° was much larger than the Faraday rotation angle of 0.079° at 388 nm. This SH rotation can be understood by the mechanism of magnetization-induced SHG caused by interaction between the electric polarization along the out-of-plane of film and spontaneous magnetization. The magnetic linear term [χijkLmagn(1)] contributed particularly to the SH rotation. The value of the magnetic linear tensor component relative to the crystallographic tensor component [|χyyyXmagn(1)|/|χzyycr], which induced the SH rotation, was 0.023 at 50 K under 10 kOe.

Detection and Analysis of the Magnetic Field Component of Electromagnetic Radiation Emission from Macroscopic Fracturing of Cement-Bound Granular Material

NASA Astrophysics Data System (ADS)

Maquiling, J. T.; Ceralde, P. I. B.

2016-12-01

Countries most prone to earthquake damage have been in pursuit of a possible earthquake precursor. This study aims to detect and measure the magnetic field component of the Electromagnetic Radiation (EMR) emitted by quasi-brittle materials that undergo macroscopic fracturing. Cement-Bound Granular Materials (CBGM) were prepared by mixing cement, sand and gravel in a beam mold. Additional aggregates in the form of saw dust were added to produce variable CBGM samples. A concrete beam holder was designed and fabricated such that induced cracks from impact loading would form at the center of the beam. Six Vernier software magnetic field sensors were used to detect the magnetic field (MF) component of the EMR emission. Initial calibration was done to minimize noise in the laboratory. The magnetic field sensors were set at a low amplification range (±6.4x10-3 T) setting with 0.0002 mT precision at 20-50 Hz. Sensor locations and orientations were specified and fixed throughout the experiment. The impact loading process was repeated until concrete failure. The time of drop was determined through the occurrence of peak sound levels (dB) induced by the collision noise using a sound level meter at fast time weighting. Magnetic field fluctuations manifesting near the occurrence of sound level impulses were recorded. Peak magnetic field values within ±200ms from the recorded time of impact were considered to be originating from the concrete fracture. Concrete samples consisting of cement, sand and gravel produced magnetic field emissions measuring 0.58-1.07 μT while the same concrete mixture added with dispersed fine sawdust released 0.55-1.28 μT. A more dispersed set of values of magnetic field emissions were observed for concrete with sawdust. Comparison between the average number of drops done before failure occurs between the two concrete mixtures also indicated that the addition of dispersed sawdust resulted to weaker CBGM samples. Upon increasing input energy from weight drop by 150%, magnetic field emissions from samples of the same concrete mixture showed significant increase with maximum magnitude of emission measured at 1.06 μT. A model of the magnetic field magnitudes with respect to sensor position was generated by non-linear data-fitting method using Microsoft Excel and SciLab.

Magnetocaloric effect: permanent magnet array for generation of high magnetic fields

NASA Astrophysics Data System (ADS)

Lee, Seong-Jae; Kenkel, John; Jiles, David

2002-03-01

The magnetocaloric effect (MCE), the heating or cooling of magnetic materials in a magnetic field, is unusually large in the Gd_5(Si_xGe_1-x)4 alloy system. Normally the maximum in the MCE occurs at the Curie temperature (Tc) because the spin entropy change is a maximum. By suitable selection of the composition of this alloy system the Curie temperature can be changed over the range 25 K for x = 0 to 340 K for x =1, and the composition range around x = 0.5 exhibits the largest magnetocaloric effect. In order to increase the amount of heat exchanged the change in applied magnetic field should be as large as possible, and in this research values above 1.5 Tesla are suggested. We have studied a permanent magnet array based on NdFeB, which with a remanent magnetization of only 1.2 Tesla can still generate a magnetic flux density, or magnetic induction B of 2-3 Tesla. In order to generate the high magnetic induction in the absence of a power supply, a modified hollow cylindrical permanent magnet array (HCPMA) has been designed to produce the required strength of magnetic field. Soft magnetic materials including permalloy (NiFe) were used for focusing the magnetic field in the central region. The magnitude of the magnetic flux density at the center was about 2 Tesla. The magnitude and homogeneity of the magnetic field for this design are comparable with the conventional C-shaped yoke and HCPMA. This can be easily adapted for a low power rotary system in which the magnetocaloric material can be exposed alternately to high and low magnetic fields so that it can accept and reject heat from its surroundings.

Magnetic anisotropies and rotational hysteresis in Ni81Fe19/Fe50Mn50 films: A study by torque magnetometry and anisotropic magnetoresistance

NASA Astrophysics Data System (ADS)

da Silva, O. E.; de Siqueira, J. V.; Kern, P. R.; Garcia, W. J. S.; Beck, F.; Rigue, J. N.; Carara, M.

2018-04-01

Exchange bias properties of NiFe/FeMn thin films have been investigated through X-ray diffraction, hysteresis loops, angular measurements of anisotropic magnetoresistance (AMR) and magnetic torque. As first predicted by Meiklejohn and Bean we found a decrease on the bias field as the NiFe layer thickness increases. However such reduction is not as strong as expected and it was attributed to the increase on the number of uncompensed antiferromagnetic spins resulting from the increase on the number of FeMn grains at the interface as the thickness of the NiFe layer is increased. The angular evolution of AMR and the magnetic torque were calculated and compared to the experimental ones using the minimization of the free magnetic energy and finding the magnetization equilibrium angle. The free energy, for each grain of the polycrystalline sample, is composed by the following terms: Zeeman, uniaxial, unidirectional and the rotatable energies. While from the AMR curves we obtain stable anisotropy fields independently on the measuring fields, from the torque curves we obtain increasing values of the uniaxial and rotatable fields, as the measuring field is increased. These results were attributed to the physical origin and sensitivity of the two different techniques. Magnetoresistance is mainly sensitive to the inner portion of the ferromagnetic layer, and the torque brings out information of the whole ferromagnetic layer including the interface of the layers. In this way, we believe that the increase in the uniaxial and rotatable values were due to an increase on the volume of the ferromagnetic layer, near the interfaces, which is made to rotate with the measuring field. Studying the rotational hysteresis by both techniques allows to separately obtain the contributions coming from the inner portion of ferromagnetic layer and from the interface.

Magnetization switching process in a torus nanoring with easy-plane surface anisotropy

NASA Astrophysics Data System (ADS)

Alzate-Cardona, J. D.; Sabogal-Suárez, D.; Restrepo-Parra, E.

2017-11-01

We have studied the effects of surface shape anisotropy in the magnetization behavior of a torus nanoring by means of Monte Carlo simulations. Stable states (vortex and reverse vortex states) and metastable states (onion and asymmetric onion states) were found in the torus nanoring. The probability of occurrence of the metastable states (stable states) tends to decrease (increase) as the amount of Monte Carlo steps per spin, temperature steps and negative values of the anisotropy constant increase. We evaluated under which conditions it is possible to switch the magnetic state of the torus nanoring from a vortex to a reverse vortex state by applying a circular magnetic field at certain temperature interval. The switching probability (from a vortex to a reverse vortex state) depends on the value of the current intensity, which generates the circular magnetic field, and the temperature interval where the magnetic field is applied. There is a linear relationship between the current intensity and the minimum temperature interval above which the vortex state can be switched.

Enhancement of the coercivity in Co-Ni layered double hydroxides by increasing basal spacing.

PubMed

Zhang, Cuijuan; Tsuboi, Tomoya; Namba, Hiroaki; Einaga, Yasuaki; Yamamoto, Takashi

2016-09-14

The magnetic properties of layered double hydroxides (LDH) containing transition metal ions can still develop, compared with layered metal hydroxide salts which exhibit structure-dependent magnetism. In this article, we report the preparation of a hybrid magnet composed of Co-Ni LDH and n-alkylsulfonate anions (Co-Ni-CnSO3 LDH). As Co-Ni LDH is anion-exchangeable, we can systematically control the interlayer spacing by intercalating n-alkylsulfonates with different carbon numbers. The magnetic properties were examined with temperature- and field-dependent magnetization measurements. As a result, we have revealed that the coercive field depends on the basal spacing. It is suggested that increasing the basal spacing varies the competition between the in-plane superexchange interactions and long-range out-of-plane dipolar interactions. Moreover, a jump in the coercive field at around 20 Å of the basal spacing is assumed to be the modification of the magnetic ordering in Co-Ni-CnSO3 LDH.